Image forming apparatus and fixing device for use with the same

BACKGROUND OF THE INVENTION

The present invention relates to an image forming apparatus, such as a printer, a facsimile machine or a copy machine, which is capable of forming a toner image on a recording medium, such as a paper sheet, by the electrophotography technique. More particularly, the invention relates to a fixing device for use with the image forming apparatus.

Generally, the image forming apparatus for forming a toner image on a recording medium by the electrophotography technique includes a photosensitive member to be driven to rotate, an exposure mechanism for forming an electrostatic latent image on the surface of the photosensitive member, a developing mechanism for developing the latent image into a toner image, a transfer mechanism for transferring the toner image onto a recording medium, and a fixing device for fusing and fixing the toner image on the recording medium in a manner that the recording medium having the toner image transferred thereto by the transfer mechanism is moved to pass therethrough.

The fixing device, usually, includes a first rotary member to be heated and a second rotary member pressed against the first rotary member. A recording medium having a toner image thereon is moved to pass through a press nip between the first and second rotary members. When passing through the press nip, the recording medium is compressed by those rotary members and heated, whereby the toner image is fused and permanently fixed onto the recording medium.

In the fixing device thus constructed, if a peripheral speed difference is present between the two rotary members, a toner image on the recording medium passing through the press nip (press contact portion) between the rotary members is blurred and the image is disturbed or disarranged. For this reason, the prior technique does not employ such a drive method as to drive and rotate both the rotary members, and instead, employs such a drive method that one of the rotary members is driven to rotate, while the other is rotated as a follower.

In a case where the rotary member to be heated consists of a roller, a long time is consumed for the initial heating of the roller. In connection with this, there is known a belt fixing device in which an endless belt is used for the rotary member to be heated, whereby the initial heating time is reduced.

FIG. 32

is a diagram showing an example of the belt fixing device (JP-A-9-138600).

The belt fixing device includes an endless heat-resistant belt endless heat-resistant belt

6

, rollers

7

a

and

7

b

for supporting the belt

6

on the inner side thereof, a roller

8

for heating the belt endless heat-resistant belt

6

, and an pressure application roller

9

in contact with the outer peripheral surface of the belt endless heat-resistant belt

6

. The pressure application roller

9

is driven by a motor M to rotate in the direction of an arrow “a”, while the belt

6

follows the pressure application roller

9

in rotation.

A recording medium having a toner image formed thereon is moved in the direction of an arrow “b” to pass through a press contact portion N between the belt

6

and the pressure application roller

9

. When passing the press contact portion N, the toner image is heated and fused, and permanently fixed on the recording medium.

FIG. 58

is a diagram showing another example of the belt fixing device (JP-A-8-334997).

In the belt fixing device, a fixing belt

1

extends around a fixing roller

2

driven to rotate and a heating roller

3

containg a heater. An pressure application roller

4

is pressed against the fixing roller

2

with the fixing belt

1

being interposed therebetween. A recording medium S having a toner image T formed thereon is moved in the direction of an arrow to pass through a pressure contact portion N therebetween, whereby the toner image T is fused and permanently affixed onto the recording medium S.

The heating roller

3

includes guide rings

3

a

as restricting portions which come in contact with the side ends

1

b

of the fixing belt

1

to restrict such a behavior of the fixing belt

1

as to move aside.

To prevent such a phenomenon that toner is transferred from the recording medium onto the surface of the fixing belt

1

(called offset phenomenon), the fixing device includes an oil coating roller

5

for coating the surface of the fixing belt

1

with release oil, such as silicone oil, as release agent.

The conventional belt fixing device shown in

FIG. 57

has the following problem. When a recording medium S that relatively easily slips, for example, a synthetic resin sheet, is supplied to the press contact portion N between the pressure application roller

9

to be driven to rotate and the belt

6

which follows the pressure application roller in rotation, a slip will occur between the pressure application roller

9

of the drive side and the recording medium and/or the recording medium and the belt

6

of the follower side because of the presence of the easily slidable recording medium. As a result, a peripheral speed of the belt

6

is different from that of the pressure application roller

9

. Further, a stable operation of the fixing device will be lost.

The conventional belt fixing device shown in

FIG. 58

has the following problem. When a recording medium S that relatively easily slips is supplied to the press contact portion N between the belt

1

to be driven and the pressure application roller

4

which follows the belt in rotation, and as a result, a slip will occur between the belt

1

of the drive side and the recording medium an/or the recording medium and the pressure application roller

4

of the follower side because of the presence of the easily slidable recording medium. As a result, a peripheral speed of the belt

1

is different from that of the pressure application roller

4

. Further, a stable operation of the fixing device will be lost.

Particularly in the belt fixing device shown in

FIG. 58

, the surface of the belt

1

is coated with release oil. Because of the coating of the release oil, the above slip is more likely to occur. The release oil that has been applied to the surface of the belt

1

gradually moves to the ends N′ of the press contact portion N to reduce a friction force acting between the a fixing roller

2

and the pressure application roller

4

at the ends N′. Further the release oil that will move the ends N′ of the press contact portion N also moves to between the belt

1

and the fixing roller

2

, to thereby reduce a friction force between the belt

1

and the fixing roller

2

. As a result, there is a fear that the fixing operation of the fixing device will be more instable.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to solve the above-mentioned problems of the conventional fixing devices for use with an image forming apparatus and to provide a fixing device which stably operates.

According to the present invention, there is provided a first image forming apparatus having a fixing device constructed such that the fixing device includes an endless belt to be heated and a rotary member to be in pressing contact with the endless belt, wherein one of the endless belt and the rotary member is driven to rotate while the other rotates in a follower fashion, and a recording medium having a toner image formed thereon is moved to pass through a part of a press contact portion in the fixing device, whereby the toner image is fused and fixed on the recording medium,

wherein a high grip portion is provided at a portion of the endless belt which is not pressed by the recording medium but pressed by the rotary member.

The present invention provides a second image forming apparatus having a fixing device constructed such that the fixing device includes an endless belt to be heated and a rotary member to be in pressing contact with the endless belt, wherein one of the endless belt and the rotary member is driven to rotate while the other rotates in a follower fashion, and a recording medium having a toner image formed thereon is moved to pass through a part of a press contact portion in the fixing device, whereby the toner image is fused and fixed on the recording medium, wherein a high grip portion is provided at a portion of the rotary member which is not pressed by the recording medium but pressed by the endless belt.

The invention provides a third image forming apparatus having a fixing device constructed such that the fixing device includes an endless belt to be heated, a rotary member which is in pressing contact with the endless belt and longer than the width of the endless belt, and a backup roller, longer than the width of the endless belt, for supporting the endless belt on the inner side thereof at a press nip between the endless belt and the rotary member, wherein one of the endless belt and the rotary member is driven to rotate while the other rotates in a follower fashion, and a recording medium having a toner image formed thereon is moved to pass through a press contact portion in the fixing device, whereby the toner image is fused and fixed on the recording medium,

wherein

a high grip portion is provided at a portion of the rotary member which is not pressed by the recording medium but pressed by the backup roller.

The invention provides a fourth image forming apparatus which corresponds to the third image forming apparatus specified such that a high grip portion, which will act on the backup roller, is provided on the rear side of a portion of the endless belt which is not pressed by the recording medium.

The invention provides a fifth image forming apparatus having a fixing device constructed such that the fixing device includes an endless belt to be heated, a rotary member which is in pressing contact with the endless belt and longer than the width of the endless belt, and a backup roller, longer than the width of the endless belt, for supporting the endless belt on the inner side thereof at a press nip between the endless belt and the rotary member, wherein one of the endless belt and the rotary member is driven to rotate while the other rotates in a follower fashion, and a recording medium having a toner image formed thereon is moved to pass through a press contact portion in the fixing device, whereby the toner image is fused and fixed on the recording medium,

wherein

a high grip portion is provided at a portion of the backup roller which is pressed by the rotary member.

The invention provides a sixth image forming apparatus which corresponds to the fifth image forming apparatus specified such that a high grip portion, which will act on the backup roller, is provided on the rear side of a portion of the endless belt which is not pressed by the recording medium.

The invention provides a seventh image forming apparatus having a fixing device constructed such that the fixing device includes an endless belt to be heated, a rotary member which is in pressing contact with the endless belt and longer than the width of the endless belt, and a backup roller, longer than the width of the endless belt, for supporting the endless belt on the inner side thereof at a press nip between the endless belt and the rotary member, wherein one of the endless belt and the rotary member is driven to rotate while the other rotates in a follower fashion, and a recording medium having a toner image formed thereon is moved to pass through a press contact portion in the fixing device, whereby the toner image is fused and fixed on the recording medium,

wherein

an oil coating mechanism is provided which applies release oil onto the surface of the endless belt, and an oil barrier is provided on the backup roller at a portion thereof between a contact portion of the backup roller where it is brought into contact with the endless belt and a portion of the backup roller where it is not brought into contact with the endless belt but is pressed by the rotary member.

The invention provides an eighth image forming apparatus which corresponds to the seventh image forming apparatus specified such that an oil barrier is further provided on the rotary member at a portion thereof between a contact portion of the rotary member where it is brought into contact with the endless belt and a portion of the rotary member where it is not brought into contact with the endless belt but is pressed by the backup roller.

The invention provides a ninth image forming apparatus which corresponds to the seventh image forming apparatus specified such that an oil barrier is provided at a portion of the backup roller which faces the side end of the endless belt.

The invention provides a 10th image forming apparatus which corresponds to the seventh image forming apparatus specified such that a high grip portion is provided at a portion of the rotary member which is not brought into contact with the endless belt but pressed by the backup roller.

The invention provides a 11th image forming apparatus which corresponds to the seventh image forming apparatus specified such that a high grip portion is provided at a portion of the backup roller which is not brought into contact with the endless belt but pressed by the rotary member.

The invention provides a 12th image forming apparatus having a fixing device constructed such that the fixing device includes a first rotary member to be heated and a second rotary member to be in pressing contact with the first rotary member, wherein one of the first and second rotary members is driven to rotate while the other rotates in a follower fashion, and a recording medium having a toner image formed thereon is moved to pass through a part of a press contact portion in the fixing device, whereby the toner image is fused and fixed on the recording medium, wherein a high grip portion is provided at a portion of one of the first and second rotary members which is not pressed by the recording medium but pressed by the other rotary members.

The invention provides a 13th image forming apparatus having a fixing device constructed such that the fixing device includes a first rotary member to be heated and a second rotary member to be in pressing contact with the first rotary member, wherein one of the first and second rotary members is driven to rotate while the other rotates in a follower fashion, and a recording medium having a toner image formed thereon is moved to pass through a part of a press contact portion in the fixing device, whereby the toner image is fused and fixed on the recording medium,

wherein

an oil coating mechanism for applying release oil onto a contact portion of at least one of the first and second rotary members where the one rotary member is brought into contact with the recording medium, is provided, and an oil barrier is provided at least between a contact portion of the rotary member to be coated with the release oil by the oil coating means and a portion of the rotary member where the rotary member is not in contact with the recording medium but is pressed by the other rotary member.

The invention provides a 14th image forming apparatus which corresponds to the 13th image forming apparatus specified such that an oil barrier is also provided between a contact portion of the other rotary member where the rotary member is brought into contact with the recording medium and a portion of the other rotary member where the other rotary member is not brought into contact with the recording medium but pressed by the one rotary member.

The invention provides a 15th image forming apparatus which corresponds to the 13th image forming apparatus specified such that a high grip portion is provided at a portion of one of the first and second rotary members which is not pressed by the recording medium but pressed by the other rotary member.

The invention provides a 16th image forming apparatus which corresponds to any of the first to 15th image forming apparatus, which is specified such that the image forming apparatus is capable of forming toner images on both sides of the recording medium.

The invention provides a 17th image forming apparatus which corresponds to any of the first to 15th image forming apparatus, which is specified such that the image forming apparatus is capable of forming a full color image by superimposing a plurality of different colors.

The invention provides a first belt fixing device which includes a fixing belt to be heated and a rotary member to be in pressing contact with the fixing belt, wherein one of the fixing belt and the rotary member is driven to rotate while the other rotates in a follower fashion, and a recording medium having a toner image formed thereon is moved to pass through a central part of a press contact portion in the fixing belt and the rotary member, whereby the toner image is fused and fixed on the recording medium,

wherein

the fixing belt is formed with a belt base as a mesh-like member of which the meshes each have a length shorter than a length of the press contact portion as measured in the circumferential direction, and a surface belt layer made of high release material, which is applied to at least the surface side of a central portion of the fixing base when viewed in the widthwise direction of the fixing base, wherein the fixing base includes exposing portions which are located on both sides of the fixing belt base.

The invention provides a second belt fixing device which corresponds to the first belt fixing device specified such that an oil coating mechanism for coating the surface of the fixing belt with release oil is provided, and of the threads forming the mesh-like member, those threads extending in the widthwise direction of the fixing belt are each formed with an aggregation of a plural number of very fine threads.

The invention provides a third belt fixing device which corresponds to the second belt fixing device specified such that the high release material has preferably a permeability to the release oil.

The invention provides a fourth belt fixing device which includes a fixing belt to be heated and a rotary member to be in pressing contact with the fixing belt, wherein one of the fixing belt and the rotary member is driven to rotate while the other rotates in a follower fashion, and a recording medium having a toner image formed thereon is moved to pass through a central part of a press contact portion in the fixing belt and the rotary member, whereby the toner image is fused and fixed on the recording medium,

wherein

a tape-like, high grip member is wound around each side end of the fixing belt and fastened thereto.

The invention provides a fifth belt fixing device which corresponds to the fourth belt fixing device specified such that a winding start end at which the winding of the tape-like, high grip member starts is not lapped on a winding terminating end at which the winding of the tape-like, high grip member terminates.

The invention provides a sixth belt fixing device which corresponds to the fourth belt fixing device specified such that the winding start end of the high grip member is confronted with the winding terminating end in a state that a gap slanted to the axial direction of the pressure application roller is interposed therebetween.

The invention provides a seventh belt fixing device which includes a fixing belt to be heated and a rotary member to be in pressing contact with the fixing belt, wherein one of the fixing belt and the rotary member is driven to rotate while the other rotates in a follower fashion, and a recording medium having a toner image formed thereon is moved to pass through a central part of a press contact portion in the fixing belt and the rotary member, whereby the toner image is fused and fixed on the recording medium,

wherein

high grip members are respectively provided around both side ends of the fixing belt, and each the high grip member is formed with an expandable endless belt having an inside diameter smaller than an outside diameter of each the side end of the fixing belt when the endless belt is in a free state.

The invention provides an eighth belt fixing device which includes a fixing belt to be heated and a rotary member to be in pressing contact with the fixing belt, wherein one of the fixing belt and the rotary member is driven to rotate while the other rotates in a follower fashion, and a recording medium having a toner image formed thereon is moved to pass through a central part of a press contact portion in the fixing belt and the rotary member, whereby the toner image is fused and fixed on the recording medium,

wherein

high grip members made of cloth are respectively provided around both side ends of the fixing belt.

The invention provides a ninth belt fixing device which includes a fixing belt which is to be heated and formed with an endless belt base and a surface belt layer layered over the belt base, and a rotary member to be in pressing contact with the fixing belt, wherein one of the fixing belt and the rotary member is driven to rotate while the other rotates in a follower fashion, and a recording medium having a toner image formed thereon is moved to pass through a central part of a press contact portion in the fixing belt and the rotary member, whereby the toner image is fused and fixed on the recording medium,

wherein

high grip members are respectively provided around both side ends of the fixing belt, and an outside diameter of each the high grip member is larger than that of the surface belt layer.

The invention provides a 10th belt fixing device which includes a fixing belt to be heated and a rotary member to be in pressing contact with the fixing belt, wherein one of the fixing belt and the rotary member is driven to rotate while the other rotates in a follower fashion, and a recording medium having a toner image formed thereon is moved to pass through a central part of a press contact portion in the fixing belt and the rotary member, whereby the toner image is fused and fixed on the recording medium,

wherein

high grip members are respectively provided around both side ends of the fixing belt, and each side edge of a high grip member is not linear in the circumferential direction.

The invention provides an 11th belt fixing device which includes a fixing belt to be heated and a rotary member to be in pressing contact with the fixing belt, wherein one of the fixing belt and the rotary member is driven to rotate while the other rotates in a follower fashion, and a recording medium having a toner image formed thereon is moved to pass through a central part of a press contact portion in the fixing belt and the rotary member, whereby the toner image is fused and fixed on the recording medium,

wherein

high grip members are respectively provided around both side ends of the fixing belt, and an uneven pattern on a surface of a high grip member is slanted with respect to the width direction.

The invention provides a 12th belt fixing device which corresponds to the 11th belt fixing device specified such that the uneven patterns on the surface of the high grip member are axially symmetry with respect to the center line as view in the width direction of the fixing belt.

The invention provides a 13th belt fixing device which includes a fixing belt to be heated, a rotary member to be in pressing contact with the fixing belt, and a restricting member which comes in contact with the side end of the fixing belt to restrict such a behavior of the fixing belt as to move aside, wherein one of the fixing belt and the rotary member is driven to rotate while the other rotates in a follower fashion, and a recording medium having a toner image formed thereon is moved to pass through a central part of a press contact portion in the fixing belt and the rotary member, whereby the toner image is fused and fixed on the recording medium,

wherein

high grip members are respectively fastened around both side ends of the fixing belt, and the high grip member comes in contact with the restricting member.

The invention provides a 14th belt fixing device which corresponds to the 13th belt fixing device specified such that a rigidity of the high grip member in the belt width direction is larger than that in the belt circumferential direction.

The invention provides a 15th belt fixing device which includes a fixing belt to be heated and a rotary member to be in pressing contact with the fixing belt, wherein one of the fixing belt and the rotary member is driven to rotate while. the other rotates in a follower fashion, and a recording medium having a toner image formed thereon is moved to pass through a central part of a press contact portion in the fixing belt and the rotary member, whereby the toner image is fused and fixed on the recording medium,

wherein

high grip members each having a thermal expansion coefficient substantially equal to that of the fixing belt are respectively fastened around both side ends of the fixing belt.

The invention provides a 16th belt fixing device which includes a fixing belt to be heated and a rotary member to be in pressing contact with the fixing belt, wherein one of the fixing belt and the rotary member is driven to rotate while the other rotates in a follower fashion, and a recording medium having a toner image formed thereon is moved to pass through a central part of a press contact portion in the fixing belt and the rotary member, whereby the toner image is fused and fixed on the recording medium,

wherein

high grip members are respectively fastened around both side ends of the fixing belt with a flexible adhesive layer being interposed therebetween.

The invention provides a 17th belt fixing device which includes a fixing belt to be heated, a rotary member to be in pressing contact with the fixing belt, and an oil coating mechanism for applying release oil to a surface of the fixing belt, wherein one of the fixing belt and the rotary member is driven to rotate while the other rotates in a follower fashion, and a recording medium having a toner image formed thereon is moved to pass through a central part of a press contact portion in the fixing belt and the rotary member, whereby the toner image is fused and fixed on the recording medium,

wherein

high grip members are respectively provided around both side ends of the fixing belt, and the high grip member has an oil absorption capability.

The invention provides a belt fixing device which corresponds to the 17th belt fixing device specified such that the high grip member allows the release oil to flow in the belt circumferential direction.

The invention provides a 19th belt fixing device which includes a fixing belt to be heated, a rotary member to be in pressing contact with the fixing belt, and an oil coating mechanism for applying release oil to a surface of the fixing belt, wherein one of the fixing belt and the rotary member is driven to rotate while the other rotates in a follower fashion, and a recording medium having a toner image formed thereon is moved to pass through a central part of a press contact portion in the fixing belt and the rotary member, whereby the toner image is fused and fixed on the recording medium,

wherein

high grip members are respectively provided around both side ends of the fixing belt, and the high grip member is made of a mixture of a high friction material and a material having an oil absorption capability.

The invention provides a 20th belt fixing device which corresponds to any of the 8th to 18th belt fixing devices, which is specified such that the high grip member is an expandable endless belt having an inside diameter smaller than an outside diameter of each side end of the fixing belt when the endless belt is in a free state.

The invention provides a 21st belt fixing device which corresponds to any of the 8th to 18th belt fixing devices, which is specified such that the high grip member is a tape-like member, and wound around and fastened to both side ends of the fixing belt.

The invention provides a 22nd belt fixing device which corresponds to the 21st belt fixing device specified such that a winding start end of the tape-like, high grip member is not lapped on a winding terminating end thereof.

The invention provides a 23rd belt fixing device which corresponds to the 21st belt fixing device specified such that the winding start end of the high grip member is confronted with the winding terminating end in a state that a gap slanted to the axial direction of the pressure application roller is interposed therebetween.

The invention provides a 24th belt fixing device which corresponds to the ninth to 18th belt fixing devices, which is specified such that the high grip member is cloth.

The invention provides a 25th belt fixing device which corresponds to any of the 4th to ninth, and 11th to 19th belt fixing devices, which is specified such that each side edge of the high grip member is not linear in the circumferential direction.

The invention provides a 26th belt fixing device which corresponds to any of the 4th to 8th, and 10th to 19th belt fixing devices, which is specified such that the fixing belt is formed with an endless belt base and a surface belt layer formed on a central portion of a surface of the belt base layer, and an outside diameter of the high grip member is larger than an outside diameter of the surface belt layer.

The invention provides a 27th belt fixing device which corresponds to any of the 4th to 19th belt fixing devices, which is specified such that the side ends of the high grip member are beveled.

The invention provides a 28th belt fixing device which corresponds to the 27th belt fixing device specified such that the beveled face is smoothed.

The invention provides a 29th belt fixing device which corresponds to any of the 4th to 14th, 17th and 18th belt fixing devices, which is specified such that the high grip member is made of a material having a thermal expansion coefficient substantially equal to that of the fixing belt.

The invention provides a 30th belt fixing device which corresponds to any of the 4th to 14th, 17th and 18th belt fixing devices, which is specified such that the high grip member is fastened with a flexible adhesive layer being interposed therebetween.

The invention provides a 31st belt fixing device which corresponds to any of the 21st to 16th belt fixing devices, which is specified such that an oil coating mechanism for coating the surface of the fixing belt with release oil is provided, and the high grip member has an oil absorbing capability.

The invention provides a 32nd belt fixing device which corresponds to the 31st belt fixing device specified such that the high grip member allows the release oil to flow in the belt circumferential direction.

The invention provides a 33rd belt fixing device which corresponds to the 31st belt fixing device specified such that the release oil applied by the oil coating mechanism is applied to only a press contact portion on the fixing belt with the recording medium.

The invention provides a 34th belt fixing device which corresponds to any of the 4th to 16th belt fixing devices, which is specified such that an oil coating mechanism for coating the surface of the fixing belt with release oil is provided, the high grip member is permeable to the release oil, and is fastened to each of both the side ends of the fixing belt with an adhesive layer capable of absorbing the oil.

The invention provides a belt fixing device which corresponds to the 34th belt fixing device specified such that the release oil applied by the oil coating mechanism is applied to only a press contact portion on the fixing belt with the recording medium.

The invention provides a 18th image forming apparatus which corresponds to the 1st to 10th, and 13th to 15th image forming apparatus, and the second belt fixing device, which are specified such that

second belt fixing device specified such that the release oil applied by the oil coating mechanism is applied to only a press contact portion on the fixing belt with the recording medium.

The invention provides a 36th belt fixing device which corresponds to any of the 17th to 19th belt fixing devices, which is specified such that the release oil applied by the oil coating mechanism is applied to only a press contact portion on the fixing belt with the recording medium.

The invention provides a 37th belt fixing device which corresponds to any of the first to 19th belt fixing devices, which is specified such that toner images may be fixed on both sides of the recording medium.

The invention provides a 38th belt fixing device which corresponds to any of the first to 19th belt fixing devices, which is specified such that a full color images formed by superimposing a plurality of different colors may be formed on the recording medium.

Operations and Effects

In the first image forming apparatus, a recording medium having a toner image formed thereon is moved to pass through a part of a press contact portion in the fixing device, whereby the toner image is fused and fixed on the recording medium. The fixing device includes an endless belt to be heated and a rotary member to be in pressing contact with the endless belt, wherein one of the endless belt and the rotary member is driven while the other rotates in a follower fashion.

In the belt fixing device, a high grip portion is provided at a portion of the endless belt which is not pressed by the recording medium but pressed by the rotary member. Therefore, when a recording medium, which relatively easily slips, is supplied to the part of the press contact portion between the endless belt and the rotary member, and as a result, when a slip will occur between the endless belt (or the rotary member) of the drive side and the recording medium and/or the recording medium and the rotary member (or the endless belt) of the follower side, the endless belt and the rotary member rotate at substantially equal peripheral speeds since the follower action of the endless belt (or the rotary member) of the follower side for the rotary member (or the endless belt) of the drive side is enhanced through the action of the high grip portion. Therefore, the slip is prevented (at least its occurrence is extremely infrequent). As a result, the fixing operation of the fixing device is stable. Accordingly, the toner image on the recording medium is little blurred, so that the resultant image is little disarranged.

In the second image forming apparatus, a recording medium having a toner image formed thereon is moved to pass through a part of a press contact portion in the fixing device, whereby the toner image is fused and fixed on the recording medium. The fixing device includes an endless belt to be heated and a rotary member to be in pressing contact with the endless belt, wherein one of the endless belt and the rotary member is driven while the other rotates in a follower fashion.

In the second image forming apparatus, a high grip portion is provided at a portion of the endless belt which is not pressed by the recording medium but pressed by the endless belt. Therefore, when a recording medium, which relatively easily slips, is supplied to the part of the press contact portion between the endless belt and the rotary member, and as a result, when a slip will occur between the endless belt (or the rotary member) of the drive side and the recording medium and/or the recording medium and the rotary member (or the endless belt) of the follower side, the endless belt and the rotary member rotate at substantially equal peripheral speeds since the follower action of the endless belt (or the rotary member) of the follower side for the rotary member (or the endless belt) of the drive side is enhanced through the action of the high grip portion. Therefore, the slip is prevented (at least its occurrence is extremely less frequent). As a result, the fixing operation of the fixing device is stable. Accordingly, the toner image on the recording medium is little blurred, so that the resultant image is little disarranged.

In third image forming apparatus, a recording medium having a toner image formed thereon is moved to pass through a press contact portion in the fixing device, whereby the toner image is fused and fixed on the recording medium. The fixing device includes an endless belt to be heated, a rotary member which is in pressing contact with the endless belt and longer than the width of the endless belt, and a backup roller, longer than the width of the endless belt, for supporting the endless belt on the inner side thereof at a press nip between the endless belt and the rotary member, wherein one of the endless belt and the rotary member is driven to rotate while the other rotates in a follower fashion.

In the belt fixing device, a high grip portion is provided at a portion of the rotary member which is not pressed by the recording medium but pressed by the backup roller. Therefore, when a recording medium, which relatively easily slips, is supplied to the press contact portion between the endless belt and the rotary member, and as a result, when a slip will occur between the endless belt (or the rotary member) of the drive side and the recording medium and/or the recording medium and the rotary member (or the endless belt) of the follower side, the endless belt and the rotary member rotate at substantially equal peripheral speeds since the follower action of the endless belt (or the rotary member) of the follower side for the rotary member (or the endless belt) of the drive side is enhanced through the action of the high grip portion.

This will be described in detail hereunder.

When the endless belt is driven, its drive force is transmitted to the rotary member which is pressed against the endless belt, and also is transmitted to the backup roller which follows the endless belt in rotation. Thus, the drive force from the endless belt is transmitted to the rotary member by way of two routes.

When the rotary member is driven, its drive force is transmitted to the endless belt pressed against the rotary member, and is also transmitted to the backup roller through the high grip portion. Also in this case, the drive force derived from the rotary member is transmitted tot he endless belt by way of two routes.

Accordingly, in a case where the rotary member is driven and also in a case where the endless belt is driven, the follower action of the rotary member (or the endless belt) of the follower side for the endless belt (or the rotary member) of the drive side is enhanced through the action of the high grip portion. Therefore, even when the recording medium, which relatively easily slips, is fed to the press contact portion, the endless belt and the rotary member rotate at substantially equal peripheral speeds.

The slip is prevented (at least its occurrence is extremely infrequent). As a result, the fixing operation of the fixing device is stable. Accordingly, the toner image on the recording medium is little blurred, so that the resultant image is little disarranged.

The fourth image forming apparatus corresponds to the third image forming apparatus specified such that a high grip portion, which will act on the backup roller, is provided on the rear side of a portion of the endless belt which is not pressed by the recording medium.

With the operation of the high grip portion, the follower action of the endless belt (or the rotary member) of the follower side for the rotary member (or the endless belt) of the drive side is further enhanced. As a result, the fixing device operates more stably. Accordingly, a chance of the blurring of the toner image on the recording medium is more lessened, and as a result, the resultant image is further improved in its quality.

In the fifth image forming apparatus, a recording medium having a toner image formed thereon is moved to pass through the press contact portion in the fixing device, whereby the toner image is fused and fixed on the recording medium. The fixing device includes an endless belt to be heated, a rotary member which is in pressing contact with the endless belt and longer than the width of the endless belt, and a backup roller, longer than the width of the endless belt, for supporting the endless belt on the inner side thereof at a press nip between the endless belt and the rotary member, wherein one of the endless belt and the rotary member is driven to rotate while the other rotates in a follower fashion.

In the belt fixing device, a high grip portion is provided at a portion of the backup roller which is pressed by the rotary member. Therefore, when a recording medium, which relatively easily slips, is supplied to the press contact portion between the endless belt and the rotary member, and as a result, when a slip will occur between the endless belt (or the rotary member) of the drive side and the recording medium and/or the recording medium and the rotary member (or the endless belt) of the follower side, the endless belt and the rotary member rotate at substantially equal peripheral speeds since the follower action of the endless belt (or the rotary member) of the follower side for the rotary member (or the endless belt) of the drive side is enhanced through the action of the high grip portion.

This will be described again detail hereunder for ease of understanding, while it was discussed in the operation description of the third image forming apparatus.

When the endless belt is driven, its drive force is transmitted to the rotary member which is pressed against the endless belt, and also is transmitted to the backup roller which follows the endless belt in rotation. When the rotary member is driven, its drive force is transmitted to the endless belt pressed against the rotary member, and is also transmitted to the backup roller through the high grip portion. Accordingly, in a case where the rotary member is driven and also in a case where the endless belt is driven, the follower action of the rotary member (or the endless belt) of the follower side for the endless belt (or the rotary member) of the drive side is enhanced through the action of the high grip portion. Therefore, even when the recording medium, which relatively easily slips, is fed to the press contact portion, the endless belt and the rotary member rotate at substantially equal peripheral speeds.

The slip is prevented (at least its occurrence is extremely infrequent). As a result, the fixing operation of the fixing device is stable. Accordingly, the toner image on the recording medium is little blurred, so that the resultant image is little disarranged.

The sixth image forming apparatus corresponds to the fifth image forming apparatus specified such that a high grip portion, which will act on the backup roller, is provided on the rear side of a portion of the endless belt which is not pressed by the recording medium.

Accordingly, the follower action of the rotary member (or the endless belt) of the follower side for the endless belt (or the rotary member) of the drive side is enhanced through the action of the high grip portion in the fifth image forming apparatus. Therefore, the slip is prevented (at least its occurrence is extremely infrequent). As a result, the fixing operation of the fixing device is stable. Accordingly, the toner image on the recording medium is little blurred, so that the resultant image is little disarranged.

In the seventh image forming apparatus, a recording medium having a toner image formed thereon is moved to pass through a press contact portion in the fixing device, whereby the toner image is fused and fixed on the recording medium. The fixing device includes an endless belt to be heated, a rotary member which is in pressing contact with the endless belt and longer than the width of the endless belt, and a backup roller, longer than the width of the endless belt, for supporting the endless belt on the inner side thereof at a press nip between the endless belt and the rotary member, wherein one of the endless belt and the rotary member is driven to rotate while the other rotates in a follower fashion. In the belt fixing device, an offset phenomenon is unlike to to occur since an oil coating mechanism for applying release oil onto the surface of the endless belt.

Further, an oil barrier is provided on the backup roller at a portion thereof between a contact portion (corresponding to each end N′ of a press contact portion N described in connection with

FIG. 58

) of the backup roller where it is brought into contact with the endless belt and a portion of the backup roller where it is not brought into contact with the endless belt but is pressed by the rotary member. Therefore, when the release oil having been applied to the surface of the endless belt will flow into the “portion of the backup roller where it is not brought into contact with the endless belt but is pressed by the rotary member”, its flow is blocked by the oil barrier (at least little flow is allowed.).

For this reason, a gripping force is sufficiently secured between the backup roller and the rotary member at the “portion of the backup roller where it is not brought into contact with the endless belt but is pressed by the rotary member”, so that the endless belt and the rotary member turn at substantially the equal peripheral speeds (The reason why the endless belt and the rotary member turn at substantially the equal peripheral speeds when a gripping force is sufficiently secured between the backup roller and the rotary member as stated in the operation description of the third image forming apparatus.).

In the seventh image forming apparatus, when a slip will occur between the rotary member of the drive side (or the endless belt) and the recording medium and/or the recording medium and the endless belt of the follower side (or the rotary member), the slip is prevented (at least its occurrence is extremely infrequent.) although such a construction is employed that the release oil is applied to the endless belt, and as a result, a stable fixing operation of the fixing device is performed. Accordingly, the toner on the recording medium is little blurred, and hence the resultant image is little disarranged.

The eighth image forming apparatus corresponds to the seventh image forming apparatus specified such that an oil barrier is further provided on the rotary member at a portion thereof between a contact portion of the rotary member where it is brought into contact with the endless belt and a portion of the rotary member where it is not brought into contact with the endless belt but is pressed by the backup roller. Therefore, when the release oil having been applied to the endless belt and transferred to the contact portion of the rotary member where it is brought into contact with the endless belt will flow into the “portion of the rotary member where it is not brought into contact with the endless belt but is pressed by the backup roller”, its flow is blocked by the oil barrier (at least little flow of it is allowed.).

Accordingly, a gripping force is more satisfactorily secured between the rotary member and the backup roller in the “portion of the rotary member where it is not brought into contact with the endless belt but is pressed by the backup roller”. As a result, a stable fixing operation of the fixing device is performed. Accordingly, the toner on the recording medium is little blurred, and hence the resultant image is little disarranged.

The ninth image forming apparatus corresponds to the seventh image forming apparatus specified such that an oil barrier is provided at a portion of the backup roller which faces the side end of the endless belt. Therefore, when the release oil having been applied to the surface of the endless belt will flow into between the endless belt and the backup roller, its flow is blocked by the oil barrier at the portion of the backup roller which faces the side end of the endless belt (at least little flow of it is allowed.).

Accordingly, a necessary friction force between the endless belt and the backup roller is secured, and the follower action of the endless belt and the rotary member is also enhanced. And the endless belt and the rotary member turn at substantially equal periphery speeds. (The reason why the endless belt and the backup roller turn at substantially the equal peripheral speeds when a gripping force is sufficiently secured between endless belt and the backup roller is as stated in the operation description of the third and fourth embodiments.).

Thus, in the ninth image forming apparatus, a more stable fixing operation of the fixing device is performed although the endless belt is coated with the release oil.

The 10th image forming apparatus corresponds to the seventh image forming apparatus specified such that a high grip portion is provided at a portion of the rotary member which is not brought into contact with the endless belt but pressed by the backup roller. With provision of the high grip portion, the follower action of the rotary member and the backup roller is further improved, and hence the follower action of the endless belt and the rotary member is also so done. This leads to a more stable fixing operation of the fixing device.

The 11th image forming apparatus corresponds to the seventh image forming apparatus specified such that a high grip portion is provided at a portion of the backup roller which is not brought into contact with the endless belt but pressed by the rotary member. Therefore, the follower action of the rotary member and the backup roller is further improved, and hence the follower action of the endless belt and the rotary member is also so done. This leads to a more stable fixing operation of the fixing device.

In the 12th image forming apparatus, a recording medium having a toner image formed thereon is moved to pass through a part of a press contact portion in the fixing device, whereby the toner image is fused and fixed on the recording medium. The fixing device includes a first rotary member to be heated and a second rotary member to be in pressing contact with the first rotary member, wherein one of the first and second rotary members is driven to rotate while the other rotates in a follower fashion.

In the belt fixing device, a high grip portion is provided at a portion of one of the first and second rotary members which is not pressed by the recording medium but pressed by the other rotary members. Therefore, when a recording medium, which relatively easily slips, is supplied to the part of the press contact portion between the two rotary members, and as a result, when a slip will occur between the heating roller as the rotary member of the drive side and the recording medium and/or the recording medium and the rotary member of the follower side, both the rotary members rotate at substantially equal peripheral speeds since the follower action of the rotary member of the follower side for the rotary member of the drive side is enhanced through the operation of the high grip portion. The slip is prevented (at least its occurrence is extremely infrequent). As a result, the fixing operation of the fixing device is stable. Accordingly, the toner image on the recording medium is little blurred, so that the resultant image is little disarranged.

In the 13th image forming apparatus, a recording medium having a toner image formed thereon is moved to pass through a part of a press contact portion in the fixing device, whereby the toner image is fused and fixed on the recording medium. The fixing device includes a first rotary member to be heated and a second rotary member to be in pressing contact with the first rotary member, wherein one of the first and second rotary members is driven to rotate while the other rotates in a follower fashion.

In the belt fixing device, an oil coating mechanism for applying release oil onto a contact portion of at least one of the first and second rotary members where the one rotary member is brought into contact with the recording medium, is provided. Therefore, an offset phenomenon is unlikely to occur.

Further, an oil barrier is provided at least between a contact portion of the rotary member to be coated with the release oil by the oil coating means and a portion of the rotary member where the rotary member is not in contact with the recording medium but is pressed by the other rotary member. The presence of the oil barrier prevents such a situation that the release oil having been applied to the heating roller

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flows from its contact portion with the recording medium to the “portion of the rotary member where the rotary member is not in contact with the recording medium but is pressed by the other rotary member” (at least its occurrence is extremely infrequent.).

For this reason, a gripping force is satisfactorily secured between both the rotary members at the “portion of the rotary member where the rotary member is not in contact with the recording medium but is pressed by the other rotary member”.

Accordingly, both the rotary members rotate at substantially equal peripheral speeds although such a construction is employed that the release oil is applied to the contact portion of one of the rotary members where it is brought into contact with the recording medium. Therefore, when a slip will occur between the rotary member of the drive side and the recording medium and/or the recording medium and the rotary member of the follower side, the slip is prevented (at least its occurrence is extremely infrequent). As a result, the fixing operation of the fixing device is stable. Accordingly, the toner image on the recording medium is little blurred, so that the resultant image is little disarranged.

To be more specific, in a case where no measure is taken in the construction where the release oil is applied to the contact portion of at least one of both the rotary members with the recording medium, the release oil that has been applied to the rotary member moves from its contact portion with the recording medium to the “portion of the rotary member where the rotary member is not in contact with the recording medium but is pressed by the other rotary member”, and a gripping force at the portion between both the rotary members is remarkably reduced. A slip will occur between the rotary member of the drive side and the recording medium and/or the recording medium and the rotary member of the follower side. A stable fixing operation of the fixing device will be lost. On the other hand, in the 13th image forming apparatus, presence of the oil barrier prevents such a situation that the release oil that has been applied to the rotary member moves from its contact portion with the recording medium to the “portion of the rotary member where the rotary member is not in contact with the recording medium but is pressed by the other rotary member” (at least a probability of occurrence of the situation is considerably reduced.). A gripping force is satisfactorily secured at the “portion of the rotary member where the rotary member is not in contact with the recording medium but is pressed by the other rotary member”. Therefore, the slip is prevented (at least its occurrence is extremely infrequent.) although such a construction is employed that the release oil is applied to the contact portion of one of the rotary members where it is brought into contact with the recording medium. As a result, a stable fixing operation of the fixing device is secured. Accordingly, the toner image on the recording medium is little blurred, so that the resultant image is little disarranged.

The 14th image forming apparatus corresponds to the 13th image forming apparatus specified such that an oil barrier is also provided between a contact portion of the other rotary member where the rotary member is brought into contact with the recording medium and a portion of the other rotary member where the other rotary member is not brought into contact with the recording medium but pressed by the one rotary member. The presence of the oil barrier prevents such a situation that the release oil, which was applied to the contact portion of the rotary member where it is brought into contact with the recording medium and moved to the contact portion of the other rotary member where it is brought into contact with the recording medium, moves to the “portion of the other rotary member where the other rotary member is not brought into contact with the recording medium but pressed by the one rotary member” (at least a probability of occurrence of such a situation is considerably reduced.).

Accordingly, a gripping force is satisfactorily secured at the “portion of the other rotary member where the other rotary member is not brought into contact with the recording medium but pressed by the one rotary member”. Therefore, a stable fixing operation of the fixing device is secured. Accordingly, there is less chance that the toner image on the recording medium is blurred, so that the resultant image is little disarranged.

The 15th image forming apparatus corresponds to the 13th image forming apparatus specified such that a high grip portion is provided at a portion of one of the first and second rotary members which is not pressed by the recording medium but pressed by the other rotary member. With presence of the high grip portion, a gripping force is more satisfactorily secured at the “portion of one of the first and second rotary members which is not pressed by the recording medium but pressed by the other rotary member”. As a result, a stable fixing operation of the fixing device is secured. Accordingly, there is less chance that the toner image on the recording medium is blurred, so that the resultant image is little disarranged.

The 16th image forming apparatus corresponds to any of the first to 15th image forming apparatuses, which is specified such that the image forming apparatus is capable of forming toner images on both sides of the recording medium. Therefore, there is a case that a recording medium having toner images formed on both sides thereof passes through the part of the press contact portion in the fixing device.

Sometimes the toner on the recording medium reduces the friction coefficient between the recording medium and the rotary member. And it interrupts the oil absorbing by the recording medium. Therefore, in a case where the toner images are formed on both sides of the recording medium, the recording medium is more likely to slip when comparing with a case where the toner image is formed on one side of the recording medium.

In this connection, in the 16th image forming apparatus, the oil barrier is provided between the contact portion of one of the belt and the rotary member which is not pressed by the recording medium but pressed by the other rotary member (or belt), or it is provided between the portion of the belt (or the rotary member) which is coated with the release oil by the oil coating mechanism, which the portion is brought into contact with the recording medium, and the contact portion which is not brought into contact with the recording medium but is pressed by the other rotary member (or the belt). Therefore, even when the toner images are formed on both sides of the recording medium, the slip does not occur (at least its occurrence is extremely infrequent). As a result, a stable fixing operation of the fixing device is secured.

Thus, the 16th image forming apparatus is capable of forming images suffering from no (at least little) image disarrangement on both sides of the recording medium.

The 17th image forming apparatus corresponds to any of the first to 15th image forming apparatuses, which is specified such that the image forming apparatus is capable of forming a full color image by superimposing a plurality of different colors. Therefore, there is a case that a recording medium having a full color image formed on at least one side thereof passes through the part of the press contact portion in the fixing device.

As described above, sometimes the toner on the recording medium reduces the friction coefficient between the recording medium and the rotary member, and it interrupts the oil absorbing by the recording medium. Therefore, in a case where the full color image by superimposing a plurality of different colors is formed on the recording medium, the recording medium is more likely to slip when comparing with a case where the toner image of monochromatic color is formed on the recording medium.

In this connection, in the 17th image forming apparatus, the oil barrier is provided between the contact portion of one of the belt and the rotary member which is not pressed by the recording medium but pressed by the other rotary member (or belt), or it is provided between the portion of the belt (or the rotary member) which is coated with the release oil by the oil coating mechanism, which the portion is brought into contact with the recording medium, and the contact portion which is not brought into contact with the recording medium but is pressed by the other rotary member (or the belt). Therefore, even when the full color image by superimposing a plurality of different colors is formed on the recording medium, the slip does not occur (at least its occurrence is extremely infrequent). As a result, a stable fixing operation of the fixing device is secured.

Thus, the 17th image forming apparatus is capable of forming images suffering from no (at least little) image disarrangement. When combined with the 16th image forming apparatus, it is capable of forming images suffering from no (at least little) image disarrangement on both sides of the recording medium.

In the first belt fixing device of the invention, a recording medium having a toner image formed thereon is moved to pass through a central part of a press contact portion in the fixing device, whereby the toner image is fused and fixed on the recording medium. The first belt fixing device includes a fixing belt to be heated and a rotary member to be in pressing contact with the fixing belt, wherein one of the fixing belt and the rotary member is driven to rotate while the other rotates in a follower fashion.

The fixing belt is formed with a belt base as a mesh-like member of which the meshes each have a length shorter than a length of the press contact portion as measured in the circumferential direction, and a surface belt layer made of high release material, which is applied to at least the surface side of a central portion of the fixing base when viewed in the widthwise direction of the fixing base, wherein the fixing base includes exposing portions which are located on both sides of the fixing belt base. Therefore, the surface belt layer forms a fixing surface for the toner image and the exposing portions form high grip portions, which act on the rotary member.

Accordingly, when a recording medium, which relatively easily slips, is supplied to the central part of the press contact portion between the fixing belt and the rotary member, and as a result, when a slip will occur between the fixing belt (rotary member) of the drive side and the recording medium and/or the recording medium and the rotary member (fixing belt) of the follower side, the fixing belt and the rotary member rotate at substantially equal peripheral speeds since the follower action of the rotary member (fixing belt) of the follower side for the fixing belt (rotary member) of the drive side is enhanced through the action of the high grip portions. Therefore, the slip is prevented (at least its occurrence is extremely less frequent). As a result, the fixing operation of the fixing device is stable. Accordingly, the toner image on the recording medium is little blurred, so that the resultant image is little disarranged.

Further, the high grip portion is formed by merely forming the exposing portions at both ends of the belt base itself. Therefore, the high grip portion of the belt fixing device is superior in strength to a high grip portion additionally provided on the belt base. In this respect, a reliability of the fixing device is improved. Further, the high grip portion of the belt fixing device may be manufactured more easily manufactured than a high grip portion additionally provided or formed on the belt base.

The second belt fixing device corresponds to the first belt fixing device specified such that an oil coating mechanism for coating the surface of the fixing belt with release oil is provided. Therefore, an offset phenomenon will infrequently occur.

As already stated, where the surface of the fixing belt is coated with the release oil, the oil will gradually move to the ends of the press contact portion between the fixing belt and the rotary member. In this connection, in the second fixing device, the fixing base is exposed at both ends of the press contact portion, and the belt base is made of cloth or a mesh-like member of which the threads extending in the widthwise direction are formed with threads each consisting of an aggregation of a plural number of very fine threads. The oil having reached each end of the press contact portion penetrates into the threads each consisting of an aggregation of a plural number of very fine threads of the cloth or the mesh-like member.

Accordingly, a little amount of the release oil is present on the surface of both ends of the belt base. As a result, a gripping force is satisfactorily secured at the both ends of the press contact portion. The slip is prevented (at least its occurrence is extremely infrequent.). A stable fixing operation of the fixing device is performed.

Thus, the second belt fixing device stably operates for fixing the toner image although it employs such a construction that the surface of the fixing belt is coated with the release oil.

The third belt fixing device corresponds to the second belt fixing device specified such that the high release material has preferably a permeability to the release oil. Because of this nature, the oil having being applied to the surface of the surface belt layer penetrates into the surface belt layer, and then to the threads each consisting of an aggregation of a plural number of very fine threads in the cloth or the mesh-like member, and retained in the cloth or the mesh-like member. The retained oil oozes, by its pressure, out of the cloth or the threads at the press contact portion, and further reaches the surface, or the fixing surface, of the surface belt layer to form an oil thin film on the fixing surface. As a result, the oil film is uniformized on the fixing surface, so that a quality of a toner image fixed thereon is improved.

The release oil having permeated into the ends of the belt base moves back to the central portion of the belt base through the cloth or the mesh-like member which forms the belt base. This reduces consumption of the release oil.

Accordingly, in a case where the fixing operation is not performed for a certain time, and the surplus oil will stay at a region near the press contact portion, the oil permeates into the surface belt layer, and to the threads each of an aggregation of a plural number of very fine threads in the cloth or the mesh-like member of the belt base, and is retained in the cloth or the mesh-like member. And a part of the retained release oil flows back to the central portion of the surface belt layer. Therefore, when the fixing operation is not performed for a certain time and then it is operated again, there is less chance that a first recording medium will be soiled by the surplus oil.

In the 4th belt fixing device,

(i) a recording medium having a toner image formed

thereon is moved to pass through a central part of a press contact portion between the fixing belt and the rotary member in a belt roller arrangement in which the fixing belt is heated and the rotary member is pressed against the fixing belt, and one of the fixing belt and the rotary member is driven to rotate while the other follows the one in rotation. As a result, the toner image is fused and permanently fixed on the recording medium.

The high grip tape is wound around each side end of the fixing belt and fastened thereto. As a result, high grip portions which act on the rotary member, are formed at both side ends of the fixing belt.

Therefore, when a recording medium, which relatively easily slips, is supplied to the central part of the press contact portion between the fixing belt and the rotary member, and as a result, when a slip will occur between the a fixing belt (rotary member) of the drive side and the recording medium and/or the recording medium and the rotary member (fixing belt) of the follower side, the fixing belt and the rotary member rotate at substantially equal peripheral speeds since the follower action of the rotary member (fixing belt) of the follower side for the fixing belt (rotary member) of the drive side is enhanced through the operation of the high grip portions. Therefore, the slip is prevented (at least its occurrence is extremely infrequent). As a result, the fixing operation of the fixing device is stable. Accordingly, the toner image on the recording medium S is little blurred, so that the resultant image is little disarranged.

(ii) Further, the high grip portions may be formed in

such a simple manner that the high grip tapes are wound around both the side ends of the fixing belt and are fastened to the side ends. Therefore, the manufacturing of the fixing belt is simpler than in the case where ring-like, high grip members are fit to both side ends of the belt or where the side ends themselves of the belt are worked to be high grip portions.

In the fifth belt fixing device based on the fourth fixing device, the winding start end

11

of the high grip tape is not lapped on the winding terminating end. Therefore, the following advantageous effects are produced.

If the winding start end

11

of the high grip tape is lapped on the winding terminating end, the lapping portion

31

is thick. Therefore, a speed of the turning fixing belt when the lapping portion is pressed on the rotary member will be different from that when the lapping portion is not pressed on the rotary member.

When the lapping portion is pressed against the rotary member, stress will concentrate at a portion of the rotary member where it is in contact with the lapping portion. As a result, an endurance of the rotary member will be reduced.

In this connection, in the 5th belt fixing device, the winding start end of the high grip portion is not lapped on the winding terminating end. Because of this, the speed of the turning belt fixing belt little varies. Additionally, little stress concentrates on the specific location of the rotary member, so that the endurance of the rotary member is little reduced.

In the sixth belt fixing device based on the fifth belt fixing device, the winding start end of the high grip member is confronted with the winding terminating end in a state that a gap slanted to the axial direction of the rotary member is interposed therebetween. Therefore, the follow advantageous effects are produced.

If the winding start end and the winding terminating end of the high grip member are not slanted (with respect to, for example, the axial direction of the rotary member), a traveling speed of the fixing belt when the gap between the winding start end and the winding terminating end is in contact with the rotary member will be different from that when it is not in contact with the rotary member. On the other hand, a probability of creating the above-mentioned speed difference of the fixing belt (or the rotary member) of the follower side is small in sixth belt fixing device since the winding start end of the high grip member is confronted with the winding terminating end in a state that the gap slanted to the axial direction of the rotary member is interposed therebetween.

The seventh fixing belt has the advantageous effects (i) of the 4th fixing device, and further the following advantageous effects.

In the 7th belt fixing device, the high grip portion is formed with an expandable endless belt having an inside diameter smaller than an outside diameter of each side end of the fixing belt when it is in a free state. Therefore, by the utilization of its expandability, the belt-like high grip member is expanded and fit to the side ends of the fixing belt to form a high grip portion well fit to and around the side ends of the fixing belt.

Where the high grip tape is wound around each side end of the fixing belt, there is a fear that high grip tape is easy to peel off the belt at its seam. In the fixing belt in this fixing device, such a fear is not present and the belt-like high grip member doubles as a reinforcing member for the side end of the fixing belt. In this respect, a reliability of the fixing belt is improved. As a result, the fixing belt may be thinned in structure. The fixing belt well follows an unevenness corresponding to the amounts of attached toner forming a toner image. This results in improvement of a fixing strength or a fixing uniformity. Further, a heat capacity of the fixing belt is small, so that it may be heated quickly.

The eighth fixing belt has the advantageous effects (i) of the fourth fixing device, and further the following advantageous effects.

Since the high grip portion is formed with the cloth a surface of the high grip portion is defined by a number of vertical and horizontal fine ridges of the threads (woven or knitted) running crosswise and lengthwise. The fine ridge crossing pattern spreads substantially uniformly over the surface.

A vibration and a speed variation, which are generated at both ends of the fixing belt by a drive force transmission, are extremely reduced, thereby ensuring a smooth drive force transmission.

Since the fine ridge crossing pattern are formed by the threads, each ridge is rounded in cross section. With this configuration of the ridges, the stress concentration is lessened, and hence the endurance of the rotary member will be increased.

Further, the high grip portion of this fixing device is superior to that formed with a rubber member of an uneven surface in the strength (particularly to shearing).

Accordingly, in the case of the high grip portion made of a film or a rubber member, for example, when a shearing force is applied to its edge, the edge first cracks, and then the crack rapidly propagates and the high grip portion is finally broken. In the case of the high grip portion made of the cloth, when the fiber at the edge of the cloth cracks to be broken, the breakage of the fiber does not propagates. That is, only one fiber at the edge is broken.

When the side edge of the belt is brought into contact with the inner surface of a flange (the guide ring) of the roller on which the fixing belt is put in order to restrict a zig-zag traveling of the fixing belt, a shearing force acting on the side edge of the belt is great in magnitude. In this fixing device, the high grip portions of cloth are provided on both side ends of the fixing belt. Therefore, the high grip portion is reluctant to its breakage and propagation of the breakage to the whole fixing belt

110

is also greatly impeded.

The high grip portions may be formed by merely fastening them on both side ends of the fixing belt. Therefore, the manufacturing of the fixing belt is simpler than in the case where the side ends themselves of the belt are worked to be high grip portions.

The ninth fixing belt has the advantageous effects (i) of the 4th fixing device, and further the following advantageous effects.

The outside diameter of the high grip member is larger than that of the surface belt layer. Therefore, at both the ends of the press contact portion between the fixing belt and the rotary member, the high grip members are pressed against the rotary member by a larger pressing force. Accordingly, a gripping force is satisfactorily secured between the fixing belt and the rotary member. And the slip is prevented with certainty (at least its occurrence is extremely infrequent.). As a result, a stable fixing operation of the fixing device is secured.

The 10th fixing belt has the advantageous effects (i) of the 4th fixing device, and further the following advantageous effects.

In this fixing device, each side edge of the high grip member is not linear in the circumferential direction, and therefore the following advantageous effects are produced.

If each side edge of the high grip member is linear in the circumferential direction, positions of the rotary member, which is to be in pressing contact with the fixing belt, at which it is pressed against the side edges of the high grip member are locally worn or deformed, to thereby possibly reduce the endurance of the rotary member.

In this connection, in this fixing device, each side edge of the high grip member is not linear in the circumferential direction. Because of this configuration, the local wearing or deformation of the rotary member are lessened. This results increase of the endurance of the rotary member.

The 11th fixing belt has the advantageous effects (i) of the 4th fixing device, and further the following advantageous effects.

The uneven pattern on the surface of the high grip member is slanted with respect to the width direction. This feature produces a called edge effect (edge effect in the rotational direction (power transmission direction)) by the uneven pattern at the press contact portion of it with the rotary member. As a result, the gripping force by the high grip portion is increased, and an uneven pattern on a surface of a high grip member is slanted with respect to the width direction. The slip is prevented (at least its occurrence is extremely infrequent), and a stable fixing operation of the fixing device is secured.

If the uneven pattern on the surface of the high grip member is not slanted with respect to the width direction (it is parallel to the axial direction of the rotary member), a vibration by the drive power transmission (vibration due to the uneven pattern) may increase. However, in this fixing device, such a vibration is remarkably reduced since the uneven pattern on the surface of the high grip member is slanted with respect to the width direction. Accordingly, a smooth drive power transmission is secured.

In the 12th belt fixing device based on the 28th belt fixing device, the uneven patterns on the surface of the high grip member are axially symmetry with respect to the center line as view in the width direction of the fixing belt. Therefore, thrust forces (acting in the belt width direction) caused by the inclination of the uneven pattern are cancelled, so that the fixing belt stably runs.

The 13th fixing belt has the advantageous effects (i) of the 4th fixing device, and further the following advantageous effects.

The side edges of the fixing belt is brought into contact with the restricting members, so that such a behavior of the traveling fixing belt as to move aside is restricted.

Since the side edges of the fixing belt is brought into contact with the restricting members, the following advantageous effects are produced additionally.

The high grip members are fastened to both side ends of the fixing belt, so that the both side ends of the fixing belt are reinforced. Further, the high grip member comes into contact with the restricting member. Therefore, the endurance of the fixing belt is increased although such a construction is employed that the side end of the fixing belt comes into contact with the restricting member.

Therefore, the fixing belt may be thinned in structure. The fixing belt well follows an unevenness corresponding to the amounts of attached toner forming a toner image. This results in improvement of a fixing strength or a fixing uniformity. Further, a heat capacity of the fixing belt is small, so that it may be heated quickly.

In the 14th fixing belt based on the 13th fixing device, a rigidity of the high grip member in the belt width direction is larger than that in the belt circumferential direction. Therefore, the following advantageous effects are produced.

Since the rigidity of the high grip member in the belt circumferential direction is relatively small, when the high grip member is fastened to the side end of the fixing belt, the high grip member is expanded, so that the fitting of the high grip member to the belt side end is easy. Further, the high grip member is well fit around the side end of the fixing belt. Since the rigidity of the high grip member in the belt width direction is relatively large, its buckling strength is increased when it is brought into contact with the restricting members. As a result, such a behavior of the traveling fixing belt as to move aside is restricted satisfactorily.

The 15th belt fixing device has the advantageous effects comparable with those (i) of the 4th fixing device.

In this belt fixing device, a thermal expansion coefficient of each high grip member is substantially equal to that of the fixing belt. Therefore, the belt fixing device will additionally produce the following advantageous effects.

In this type of the fixing device, when it is operated, the fixing belt is heated to high temperature (e.g., approximately 150° C. to 200° C.). If the thermal expansion coefficient of the high grip portion fastened to each side end of the fixing belt is greatly different from than that of the fixing belt, a stress is generated at both the fastening faces by the thermal expansion coefficient difference between the fixing belt and the high grip members fastened to the side ends thereof. As a result, the bent side ends are easy to be broken or the high grip portion is easy to strip off the belt.

In this connection, in the 15th fixing device, the thermal expansion coefficient of the high grip member is substantially equal to that of the fixing belt (viz., it is made of a material having a thermal expansion coefficient substantially equal to that of the fixing belt). Therefore, little or a little stress that is caused in both the fastening faces by the thermal expansion coefficient difference between them is present. As a result, the problem of damaging the side ends of the fixing belt and the stripping of the high grip portion is solved. Consequently, the fixing device is improved in its endurance.

The 16th belt fixing device will produce the advantageous effects comparable with those (i) of the fourth fixing device.

Further, in the 16th belt fixing device, a high grip member is fastened to the fixing belt with a flexible adhesive layer being interposed therebetween.

In this type of the fixing device, during its operation, the fixing belt is heated to be at high temperature (150° C. to 200° C., for example). If the adhesive layer which fastens the high grip member to each side end of the fixing belt is not flexible, a thermal expansion coefficient difference between the fixing belt and the high grip member will give rise to the following problem: the belt end is easy to be broken or the high grip member is easy to peel off the fixing belt.

In this connection, in the 16th fixing device of this embodiment, the adhesive layer which fastens the high grip member to each side end of the fixing belt is flexible, the thermal expansion coefficient difference between the fixing belt and the high grip member is soaked up by the adhesive layer. Therefore, there is no chance that the ends of the fixing belt are broken or the high grip member peels off the belt. As a result, the fixing belt is improved in its endurance.

The 17th belt fixing device produces advantageous effects comparable with those (i) by the 4th belt fixing device.

This belt fixing device includes an oil coating mechanism for applying release oil to the surface of the fixing belt. Therefore, an offset phenomenon is unlikely to occur.

The high grip portion is capable of absorbing the oil, and hence produces the following advantageous effects.

Where the surface of the fixing belt is coated with the release oil, the oil will gradually move to the ends of the press contact portion between the fixing belt and the rotary member. However, in the 17th fixing device, the oil having reached the ends of the press contact portion is absorbed by the high grip member since the high grip members are fastened around both the side ends of the fixing belt in the fixing device and the high grip members have oil absorbing capability.

Therefore, the amount of oil present on the surfaces of both the side ends of the fixing belt, viz., the surfaces of the cloth of the high grip members, is small. As a result, a gripping force is satisfactorily secured at both the ends of the press contact portion. The slip is prevented (at least its occurrence is extremely infrequent), and a stable fixing operation of the fixing device is secured.

Thus, the 17th fixing device of this embodiment is able to stably fix the toner image although the surface of the fixing belt is coated with the release oil.

In the 18th belt fixing device based on the 17th belt fixing device, the high grip member allows the oil to flow in the belt circumferential direction. Therefore, if the high grip member is saturated with the oil, the oil entering the high grip member is moved in the belt circumferential direction and excluded out of the press contact portion by the pressing force.

Therefore, if the high grip member is saturated with oil applied thereto. The amount of oil present on the surfaces of both the side ends of the fixing belt, is small at the press contact portion. As a result, a gripping force is satisfactorily secured at both the ends of the press contact portion. The slip is prevented (at least its occurrence is extremely infrequent), and a stable fixing operation of the fixing device is secured.

The 19th belt fixing device produces the advantageous effects comparable with those (i) by the fourth fixing device.

In the belt fixing device, an offset phenomenon is unlikely to occur since an oil coating mechanism for applying release oil onto the surface of the endless belt.

Since the high grip portion is made of a composite material of high friction material and material having an oil absorbing capability, the following advantageous effects are produced.

Where the surface of the fixing belt is coated with the release oil, the oil will gradually move to the ends of the press contact portion. However, in the 19th fixing device, the oil having reached the ends of the press contact portion is absorbed by the material having an oil absorbing capability since the high grip portion is made of a composite material of high friction material and material having an oil absorbing capability.

Therefore, the amount of oil present on the surfaces of the high grip portions where the high friction material are exposed, is small. As a result, a gripping force is satisfactorily secured at both the ends of the press contact portion. The slip is prevented (at least its occurrence is extremely infrequent), and a stable fixing operation of the fixing device is secured.

Thus, the 19th belt fixing device is able to stably fix the toner image although the surface of the fixing belt is coated with the release oil.

Further, since the high grip member is made of a composite material of high friction material and material having an oil absorbing capability, its strength is also increased.

In the 20th belt fixing device based on any of the 8th to 18th fixing devices, the high grip portion is formed with an expandable endless belt having an inside diameter smaller than an outside diameter of each side end of the fixing belt when it is in a free state. Therefore, by the utilization of its expandability, the belt-like high grip member is expanded and fit to the side ends of the fixing belt to form a high grip portion well fit to and around the side ends of the fixing belt.

Where the high grip tape is wound around each side end of the fixing belt, there is a fear that high grip tape is easy to peel off the belt at its seam. In the 20th fixing belt, such a fear is not present and the belt-like high grip member doubles as a reinforcing member for the side end of the fixing belt. In this respect, a reliability of the fixing belt is improved. As a result, the fixing belt may be thinned in structure. The fixing belt well follows an unevenness corresponding to the amounts of attached toner forming a toner image. This results in improvement of a fixing strength or a fixing uniformity. Further, a heat capacity of the fixing belt is small, so that it may be heated quickly.

In the 21st belt fixing device based on any of the 8th to 18th fixing devices, the high grip tape is wound around each side end of the fixing belt and fastened thereto. Therefore, the high grip portion is formed by merely forming the exposing portions at both ends of the belt base itself. Accordingly, a reliability of the fixing device is improved. Further, the high grip portion of the belt fixing device may be manufactured more easily manufactured than a high grip portion formed by fitting high grip members like endless belts to the side ends of the fixing belt and fixing them thereto or by working the side ends of the belt into high grip portions.

In the 22nd belt fixing device based on the 21st fixing device, the winding start end

11

of the high grip tape is not lapped on the winding terminating end. Therefore, the following advantageous effects produced are comparable with those by the 5th belt fixing device.

In the 23rd belt fixing device based on the 21st fixing device, the winding start end of the high grip member is confronted with the winding terminating end in a state that a gap slanted to the axial direction of the rotary member is interposed therebetween. Therefore, the follow advantageous effects produced are comparable with those by the 21st belt fixing device.

In the 24th belt fixing device based on any of the ninth to 18th belt fixing device, since the high grip portion is formed with the cloth a surface of the high grip portion is defined by a number of vertical and horizontal fine ridges of the threads (woven or knitted) running crosswise and lengthwise. The fine ridge crossing pattern spreads substantially uniformly over the surface.

Accordingly, a vibration and a speed variation, which are generated at both ends of the fixing belt by a drive force transmission, are extremely reduced, thereby ensuring a smooth drive force transmission.

Since the fine ridge crossing pattern are formed by the threads, each ridge is rounded in cross section. With this configuration of the ridges, the stress concentration is lessened, and hence the endurance of the rotary member is increased.

Further, the high grip portion of this fixing device is superior to that formed with a rubber member of an uneven surface in the strength (particularly to shearing).

In the case of the high grip portion made of a film or a rubber member, for example, when a shearing force is applied to its edge, the edge first cracks, and then the crack rapidly propagates and the high grip portion is finally broken. In the case of the high grip portion made of the cloth, when the fiber at the edge of the cloth cracks to be broken, the breakage of the fiber does not propagates. That is, only one fiber at the edge is broken.

When the side edge of the belt is brought into contact with the inner surface of a flange (the guide ring) of the roller on which the fixing belt is put in order to restrict a zig-zag traveling of the fixing belt, a shearing force acting on the side edge of the belt is great in magnitude. In this fixing device, the high grip portions of cloth are provided on both side ends of the fixing belt. Therefore, the high grip portion is reluctant to its breakage and propagation of the breakage to the whole fixing belt

110

is also greatly impeded.

In the 25th belt fixing device based on any of the 4th to 9th, and 11th to 19th belt fixing devices, each side edge of the high grip member is not linear in the circumferential direction, and therefore the following advantageous effects are produced.

If each side edge of the high grip member is linear in the circumferential direction, positions of the rotary member, which is to be in pressing contact with the fixing belt, at which it is pressed against the side edges of the high grip member are locally worn or deformed, to thereby possibly reduce the endurance of the rotary member.

In this connection, in the 25th belt fixing device, each side edge of the high grip member is not linear in the circumferential direction. Because of this configuration, the local wearing or deformation of the rotary member are lessened. This results increase of the endurance of the rotary member.

In the 26th belt fixing device based on any of the 4th to 9th, and 11th to 19th belt fixing devices, the fixing belt is formed with an endless belt base, and a surface belt layer which is applied to the surface side of a central portion of the fixing base when viewed in the widthwise direction of the fixing base, and an outside diameter of the high grip portion is larger than that of the surface belt layer. Therefore, the high grip portions are pressed against both ends of the press contact portion between the fixing belt and the rotary member by great pressing forces. Therefore, a gripping force between the fixing belt and the rotary member is increased, the slip is prevented more reliably (at least its occurrence is extremely less frequent). And a stable fixing operation of the fixing device is secured.

In the 27th belt fixing device based on any of the 9th to 19th belt fixing devices, each end of a high grip member as viewed in the width direction is beveled. Therefore, the stress concentration on the rotary member by the ends of the high grip member is lessened, and hence the endurance of the rotary member is further increased.

Accordingly, with the beveled end faces, the stress concentration on the rotary member by the ends of the high grip member is lessened, and hence the endurance of the rotary member is increased, although this embodiment has such a construction that the outside diameter of the high grip member is larger than that of the surface belt layer, and therefore, at the ends of the press contact portion between the fixing belt and the rotary member, the high grip members are pressed against the rotary member by a larger pressing force.

In the 28th belt fixing device based on the 27th belt fixing device, each beveled surface is smoothed. Accordingly, the endurance of the pressure application roller

120

is further increased.

In the 29th belt fixing device based on any of the 9th to 14th, 17th and 18th belt fixing devices, a thermal expansion coefficient of each high grip member is substantially equal to that of the fixing belt. Therefore, the belt fixing device will additionally produce the following advantageous effects.

As already described, in this type of the fixing device, when it is operated, the fixing belt is heated to high temperature (e.g., approximately 150° C. to 200° C.). If the thermal expansion coefficient of the high grip portion fastened to each side end of the fixing belt is greatly different from than that of the fixing belt, and if the adhesive layer is not flexible, a stress will be generated at both the fastening faces by the thermal expansion coefficient difference between the fixing belt and the high grip members fastened to the side ends thereof. As a result, the side ends are easy to be broken or the high grip portion is easy to strip off the belt.

In this connection, in the 29th belt fixing device, the thermal expansion coefficient of the high grip member is substantially equal to that of the fixing belt (viz., it is made of a material having a thermal expansion coefficient substantially equal to that of the fixing belt). Therefore, little or a little stress that is caused in both the fastening faces by the thermal expansion coefficient difference between them is present. As a result, the problem of damaging the side ends of the fixing belt and the stripping of the high grip portion is solved. Consequently, the endurance of the fixing device is increased.

In the 30th belt fixing device based on any of the 9th to 14th, 17th and 18th belt fixing devices, a high grip member is fastened to the fixing belt with a flexible adhesive layer being interposed therebetween. Therefore, the 30th belt fixing device will produces the advantageous effects comparable with those by the 16th belt fixing device.

In the 31st belt fixing device based on any of the 9th to 14th, 17th and 18th belt fixing devices, an oil coating mechanism for applying release oil to the surface of the fixing belt is provided. Therefore, an offset phenomenon is unlikely to occur.

As described above, where the surface of the fixing belt is coated with the release oil, the oil will gradually move to the ends of the press contact portion between the fixing belt and the rotary member. However, in the 31st fixing device, the oil having reached the ends of the press contact portion is absorbed by the high grip member since the high grip members are fastened around both the side ends of the fixing belt in the fixing device and the high grip members have oil absorbing capability.

Therefore, the amount of oil present on the surfaces of both the side ends of the fixing belt, viz., the surfaces of the cloth of the high grip members, is small. As a result, a gripping force is satisfactorily secured at both the ends of the press contact portion. The slip is prevented (at least its occurrence is extremely infrequent), and a stable fixing operation of the fixing device is secured.

Thus, the 31st fixing device of this embodiment is able to stably fix the toner image although the surface of the fixing belt is coated with the release oil.

In the 32nd belt fixing device based on the 31st belt fixing device, the high grip member allows the oil to flow in the belt circumferential direction. Therefore, if the high grip member is saturated with the oil, the oil entering the high grip member is moved in the belt circumferential direction and excluded out of the press contact portion by the pressing force.

Therefore, if the high grip member is saturated with oil applied thereto. The amount of oil present on the surfaces of both the side ends of the fixing belt, is small at the press contact portion. As a result, a gripping force is satisfactorily secured at both the ends of the press contact portion. The slip is prevented (at least its occurrence is extremely infrequent), and a stable fixing operation of the fixing device is secured.

In the 33rd belt fixing device based on the 31st belt fixing device, the release oil, which is applied by the oil coating mechanism, is applied to within only the contact portion of the fixing belt where it is brought into contact with the recording medium. Therefore, the applied oil is almost all absorbed by or transferred to the recording medium when the recording medium passes therethrough.

Accordingly, there is little chance that the release oil flows to the non-contact portions not in contact with the recording medium, i.e., the high grip portion. As a result, a more stable fixing operation of the fixing device is performed.

In the 34th belt fixing device based on the 4th to 16th belt fixing devices, an oil coating mechanism for applying release oil to the surface of the fixing belt is provided. Therefore, an offset phenomenon is unlikely to occur.

The high grip member is provided at both the side ends of the fixing belt, and is permeable to the oil, and is fastened to both the side ends of the fixing belt with an adhesive layer having an absorbing capability being interposed therebetween. Accordingly, the oil having entered the ends of the press contact portion is absorbed by the adhesive layer through the high grip members.

Therefore, the amount of oil present on the surfaces of both the side ends of the fixing belt, is small. As a result, a gripping force is satisfactorily secured at both the ends of the press contact portion. The slip is prevented (at least its occurrence is extremely infrequent), and a stable fixing operation of the fixing device is secured.

Thus, the 34th fixing device of this embodiment is able to stably fix the toner image although the surface of the fixing belt is coated with the release oil.

In the 35th belt fixing device based on the 34th belt fixing device, the release oil, which is applied by the oil coating mechanism, is applied to within only the contact portion of the fixing belt where it is brought into contact with the recording medium. Therefore, the applied oil is almost all absorbed by or transferred to the recording medium when the recording medium passes therethrough.

Accordingly, there is little chance that the release oil flows to the non-contact portions not in contact with the recording medium, i.e., the high grip portion. As a result, a more stable fixing operation of the fixing device is performed.

In the 18th image forming apparatus based on any of the 7th to 10th, and 13th to 15th image forming apparatuses, the release oil, which is applied by the oil coating mechanism, is applied to within only the contact portion of the fixing belt where it is brought into contact with the recording medium. Therefore, the applied oil is almost all absorbed by or transferred to the recording medium when the recording medium passes therethrough.

Accordingly, there is little chance that the release oil flows to the non-contact portions not in contact with the recording medium, i.e., (1) the contact portion between the rotary member and the backup roller in the non-contact portion not in contact with the fixing belt and (2) the nip between the endless belt and the backup roller. As a result, a more stable fixing operation of the fixing device is performed.

In the 36th belt fixing device based on any of the 17th to 29th belt fixing devices, the release oil, which is applied by the oil coating mechanism, is applied to within only the contact portion of the fixing belt where it is brought into contact with the recording medium. Therefore, the applied oil is almost all absorbed by or transferred to the recording medium when the recording medium passes therethrough.

Accordingly, there is little chance that the release oil flows to the non-contact portions not in contact with the recording medium, i.e., the high grip portion. As a result, a more stable fixing operation of the fixing device is performed.

The 37th belt fixing device, which is based on any of the first to 19th belt fixing devices, is capable of fixing toner images on both sides of the recording medium. Therefore, there is a case that a recording medium having toner images formed on both sides thereof passes through the press contact portion in the fixing device.

Sometimes the toner on the recording medium reduces the friction coefficient between the recording medium and the rotary member. And it interrupts the oil absorbing by the recording medium. Therefore, in a case where the toner images are formed on both sides of the recording medium, the recording medium is more likely to slip when comparing with a case where the toner image is formed on one side of the recording medium.

In this connection, in the 37th belt fixing device, the high grip portions are provided at both side ends of the fixing belt. Therefore, even when toner images are formed on both sides of the recording medium, the slip does not occur (at least its occurrence is extremely infrequent). As a result, a stable fixing operation of the fixing device is secured.

Thus, the 37the belt fixing device is capable of fixing toner images suffering from no (at least little) image disarrangement on both sides of the recording medium.

The 38th belt fixing device, which is based on any of the first to 19th belt fixing devices, is capable of fixing a full color image by superimposing a plurality of different colors. Therefore, there is a case that a recording medium having a full color image formed on at least one side thereof passes through the press contact portion in the fixing device.

As described above, sometimes the toner on the recording medium reduces the friction coefficient between the recording medium and the rotary member, and it interrupts the oil absorbing by the recording medium. Therefore, in a case where the full color image by superimposing a plurality of different colors is formed on the recording medium, the recording medium is more likely to slip when comparing with a case where the toner image of monochromatic color is formed on the recording medium.

In this connection, in the 38th belt fixing device, the high grip portions are provided at both side ends of the fixing belt. Therefore, even when the full color image by superimposing a plurality of different colors is formed on the recording medium, the slip does not occur (at least its occurrence is extremely infrequent). As a result, a stable fixing operation of the fixing device is secured.

Thus, the 38the belt fixing device is capable of fixing a full color image suffering from no (at least little) image disarrangement. When combined with the 37th belt fixing device, it is capable of fixing full color toner images no (at least little) suffering from image disarrangement on both sides of the recording medium.

The present invention further provides the following fixing devices:

(1) A fixing device comprising:

a first rotary member;

a second rotary member contacting the first rotary member and forming a nip in corporation with the first rotary member;

the first and second rotary members having mutually contacting surfaces that are maintained in contact with each other regardless of whether or not a sheet is passed through the nip;

at least one of first and second rotary members having a first surface and a second surface that is higher in at least one of frictional characteristic, oil absorbing characteristic, oil permeable characteristic and oil-flow permitting characteristic than the first surface and that forms at least a part of a corresponding one of the mutually contacting surfaces.

(2) A fixing device according to (1), wherein the first rotary member has the first and second surfaces.

(3) A fixing device according to claim (1), wherein the second rotary member has the first and second surfaces.

(4) A fixing device according to (1), wherein each of the second rotary member has the first and second surfaces.

(5) A fixing device comprising:

a laterally elongating rotary member;

an endless belt contacting the first rotary member and forming a nip in corporation with the first rotary member;

a backup member keeping the endless belt in contact with the first rotary member;

at least one of the first rotary member, the endless belt and the backup member having a first surface and a second surface that is higher in at least one of frictional characteristic, oil absorbing characteristic, oil permeable characteristic and oil-flow permitting characteristic than the first surface;

the first surface being laterally corresponding in location to a region of the nip wherein the region is contactable with a sheet passed through the nip;

the second surface being situated laterally outside the region, and maintained in contact with another one of the rotary member, the endless belt and the backup member.

(6) A fixing device of (5), wherein the rotary member has the first and second surfaces.

(7) A fixing device of (5), wherein the endless belt has the first and second surfaces.

(8) A fixing device of (5), wherein the backup member has the first and second surfaces.

(9) A fixing device of (5), wherein each of the rotary member and the endless belt has the first and second surfaces.

(10) A fixing device of (5), wherein each of the rotary member and the backup member has the first and second surfaces.

(11) A fixing device of (5), wherein each of the endless belt and the backup member has the first and second surfaces.

(12) A fixing device of (5), wherein each of the rotary member and the backup member has the first and second surfaces, and the endless belt has the first surface on each of opposite surfaces of the endless belt, and the second surface on each of the opposite surfaces of the endless belt.

(13) A fixing device of any one of (1) to (12), wherein the second surface is defined by a perforated surface having a large number of holes.

(14) A fixing device of any one of (1) to (12), wherein the second surface is defined by a mesh material.

(15) A fixing device of any one of (1) to (12), wherein the second surface is defined by a rubber having a large number of laterally elongating ribs.

(16) A fixing device of any one of (1) to (12), wherein the second surface is defined by a heat-resistant tape having a large number of laterally elongating ribs.

(17) A fixing device of any one of (1) to (12), wherein the second surface is defined by a silicone rubber sponge.

(18) A fixing device of any one of (1) to (12), wherein the second surface is defined by a combination of a large number of particles and adhesive.

(19) A fixing device of any one of (1) to (12), wherein the second surface is defined by a high friction material having protruded and recessed portions.

(20) A fixing device of any one of (1) to (12), wherein the second surface is defined by an expandable endless belt, and an inner circumferential length of the expandable endless belt is normally smaller than an outer circumferential length of the first surface before the expandable belt is installed in place to define the second surface.

(21) A fixing device of any one of (1) to (12), wherein the second surface is defined by a cloth.

(22) A fixing device of any one of (1) to (12), wherein the second surface is protruded relative to the first surface.

(23) A fixing device of any one of (1) to (12), wherein the second surface is defined by an open-cell porous material.

(24) A fixing device of any one of (1) to (12), wherein the second surface is defined by a synthetic-resin-made, heat-resistant sheet having a large number of cavities.

(25) A fixing device of any one of (1) to (12), wherein the second surface is defined by a synthetic-resin-made, heat-resistant sheet having a large number of through-holes.

(26) A fixing device of any one of (1) to (12), wherein the second surface has a beveled surface as a lateral boundary.

(27) A fixing device of any one of (1) to (12), wherein the second surface has a laterally offsetting edge.

(28) A fixing device of any one of (1) to (12), wherein the second surface has a varying, lateral length.

(29) A fixing device of any one of (1) to (12), wherein the second surface is defined by repeating patterns each slanted with respect to a lateral direction.

(30) A fixing device of any one of (1) to (12), wherein the second surface is defined by a member supported on a base, and the high grip member is laterally protruded beyond a lateral end of the base.

(31) A fixing device of any one of (1) to (12), wherein the second surface is defined by a member having a larger rigidity in a lateral direction than in a circumferential direction.

(32) A fixing device of any one of (1) to (12), wherein the second surface is defined by a member supported on a base, and the member is substantially equal in a thermal expansion coefficient to the base.

(33) A fixing device of any one of (1) to (12), wherein the second surface is defined by a combination of a high friction material and an oil absorbing material.

(34) A fixing device of any one of (1) to (4), further comprising:

an annular groove provided on at least one of the first and second rotary members, the annular groove being laterally situated between a region of the nip and the mutually contacting surfaces wherein the region is contactable with a sheet passed through the nip.

(35) A fixing device of any one of (5) to (12), further comprising:

an annular groove provided on at least one of the rotary member and the backup member, the annular groove being laterally situated between the region of the nip and mutually contacting surfaces of the rotary member and the backup member, wherein the mutually contacting surfaces are maintained in contact with each other regardless of whether or not a sheet is passed through the nip.

(36) A fixing device comprising:

a first rotary member;

a second rotary member contacting the first rotary member and forming a nip in corporation with the first rotary member;

the first and second rotary members having mutually contacting surfaces that are maintained in contact with each other regardless of whether or not a sheet is passed through the nip;

an annular groove provided on at least one of the first and second rotary members, the annular groove being laterally situated between a region of the nip and the mutually contacting surfaces wherein the region is contactable with a sheet passed through the nip.

(37) A fixing device comprising:

a laterally elongating rotary member;

an endless belt contacting the first rotary member and forming a nip in corporation with the first rotary member;

a backup member keeping the endless belt in contact with the first rotary member;

an annular groove provided on at least one of the rotary member and the backup member, the annular groove being laterally situated between a region of the nip and mutually contacting surfaces of the rotary member and the backup member, wherein the region is contactable with a sheet passed through the nip, and wherein the mutually contacting surfaces are maintained in contact with each other regardless of whether or not a sheet is passed through the nip.

The present disclosure relates to the subject matter contained in Japanese patent application Nos.:

1) Hei. 11-56215 (filed on Mar. 3, 1999);

2) Hei. 11-56216 (filed on Mar. 3, 1999);

3) Hei. 11-185083 (filed on Jun. 30, 1999);

4) Hei. 11-194761 (filed on Jul. 8, 1999);

5) Hei. 11-194762 (filed on Jul. 8, 1999);

6) Hei. 11-194763 (filed on Jul. 8, 1999);

7) Hei. 11-247031 (filed on Sep. 1, 1999);

8) Hei. 11-247030 (filed on Sep. 1, 1999);

9) Hei. 11-247034 (filed on Sep. 1, 1999);

10) Hei. 11-247033 (filed on Sep. 1, 1999);

11) Hei. 11-247037 (filed on Sep. 1, 1999); and

12) Hei. 11-247036 (filed on Sep. 1, 1999),

all of which are expressly incorporated herein by reference in their entireties.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1

is a view schematically showing a first embodiment of the present invention.

FIG. 2

is a view schematically showing a major portion of a fixing device

100

in the first embodiment.

FIG. 3

is a fragmentary view showing a major portion of the fixing device.

FIG. 4

is a diagram showing another example of a high grip portion

110

G; and

FIG. 4A

is a plan view showing the same and

FIG. 4B

is a cross sectional view taken on line b—b in FIG.

4

A.

FIGS.

5

A

1

and

5

A

2

show a first example of a high grip portion G; and FIG.

5

A

1

is a fragmentary perspective view showing the high grip portion and FIG.

5

A

2

is a fragmentary sectional view of the same. FIGS.

5

B

1

and

5

B

2

show a second example of the high grip portion G; and FIG.

5

B

1

is a fragmentary perspective view showing the high grip portion and FIG.

5

B

2

is a fragmentary sectional view of the same.

FIGS.

6

A

1

and

6

A

2

show a third example of the high grip portion G; and FIG.

6

A

1

is a fragmentary perspective view showing of the high grip portion G, FIG.

6

A

2

is a cross sectional view taken on line a

2

—a

2

, and FIG.

6

A

3

is a diagram for explaing an action of the high grip portion.

FIG. 6B

is a cross sectional view showing a fourth example of the high grip portion G (corresponding to the cross sectional view taken on line a

2

—a

2

in FIG.

6

A

1

).

FIG. 7

is a fragmentary side view showing a major portion of a fixing device

100

which is a third embodiment of the present invention.

FIG. 8

is a view showing a fixing device

100

which is a sixth embodiment of the present invention.

FIG. 9

is a fragmentary side view showing a major portion of the fixing device

100

.

FIG. 10

is a fragmentary, enlarged view showing an oil barrier B

2

.

FIG. 11

is a view showing a seventh embodiment of the present invention.

FIG. 12

is a diagram schematically showing a major portion of a fixing device

1001

.

FIG. 13

is a side view showing the right side portion in FIG.

12

.

FIG. 14

is a diagrammatic view schematically showing a major portion of a fixing device

1001

which is an eighth embodiment of the present invention.

FIG. 15

is a side view showing the right side portion in FIG.

14

.

FIG. 16

is a perspective view schematically showing a ninth embodiment of the present invention.

FIG. 17

shows an fixing belt

110

in the ninth embodiment;

FIG. 17A

is a perspective view showing the fixing belt, and

FIG. 17B

is an enlarged view showing a portion “b” in the FIG.

17

A.

FIG. 18A

is a side view showing the fixing belt

110

, and

FIG. 18B

is an enlarged view showing a portion “b” in the FIG.

18

A.

FIGS. 19A and 19B

are partially cutaway, perspective views showing exemplar structures of the ends

1122

d

of a mesh-like member.

FIGS. 20A and 20B

are explanatory diagrams useful in explaing the action of the mesh-like member.

FIGS. 21A and 21B

are explanatory diagrams useful in explaing the action of the mesh-like member.

FIG. 22

is a diagram showing a tenth embodiment of the present invention:

FIG. 22A

is a partial perspective view showing the fixing belt

110

(before it extends around the backup roller

130

and the heating roller

140

).

FIG. 22B

is a front view showing a tape-like, high grip member.

FIG. 23A

is a cross sectional view taken on line XXIIIa—XXIIIa in

FIG. 22

, and

FIG. 23B

is a cross sectional view showing a state that a winding start end G

11

of a high grip member is lapped on a winding terminating end G

21

.

FIG. 24

is a diagram showing a major portion of an eleventh embodiment of a belt fixing device according to the present invention:

FIG. 24A

is a partial front view showing a fixing belt

110

constructed according to the present invention; and

FIG. 24B

is a development of a tape-like, high grip member G.

FIG. 25

is a diagram showing a major portion of a twelfth embodiment of a belt fixing belt according to the present invention.

FIG. 25A

is an exploded, perspective view showing one end of a fixing belt

110

constructed according to the invention (corresponding to the cross sectional view taken on line XXIIIa—XXIIIa in FIG.

24

A);

FIG. 25B

is a side view showing the belt end;

FIG. 25C

is a perspective view of the belt end; and

FIG. 25D

is a side view showing the belt end.

FIG. 26A

diagrammatically shows a key portion of a thirteenth embodiment of a belt fixing device constructed according to the present invention, and is a cross sectional view showing a part of a fixing belt

110

(corresponding to the XXVIa—XXVIa cross section in FIG.

24

A).

FIGS. 26B and 26C

are enlarged views of a portion of the fixing belt;

FIG. 26A

shows a case where threads

1143

are made of single threads, and

FIG. 26B

shows a case where the threads

1143

are each made of an aggregation of a plural number of very fine threads.

FIG. 27

shows a modification of the fixing belt;

FIG. 27A

is a cross sectional view showing a part of the modification (corresponding to the XXVIa—XXVIa cross section in FIG.

24

A), and

FIG. 27B

is a cross sectional view showing a part of the modification in FIG.

27

A.

FIG. 28

shows a fourteenth embodiment of the present invention;

FIG. 28A

is an enlarged front view showing one end of a fixing belt

110

, and

FIG. 27B

is a cross sectional view taken on line b—b in FIG.

28

A.

FIG. 29

is a cross sectional view showing the ends N

2

of a press contact portion N of the fixing belt.

FIG. 30

is an enlarged cross sectional view showing one end of a fixing belt in a fifteenth embodiment of the present invention.

FIGS. 31A and 31B

show a key portion of a sixteenth embodiment of the present invention:

FIG. 31A

is a plan view showing a part of a fixing belt

110

; and

FIG. 31B

is a cross sectional view taken on line b—b in FIG.

31

A.

FIGS. 31C and 31D

show a key portion of a seventeenth embodiment of the present invention:

FIG. 31C

is a plan view showing a part of a fixing belt

110

; and

FIG. 31D

is a cross sectional view taken on line d—d in FIG.

31

C.

FIG. 32A

shows a key portion of an eighteenth embodiment of the present invention and is a cross sectional view showing one end of a fixing nip portion N, and

FIG. 32B

is a cross sectional view showing an instance for comparison.

FIG. 33

is a perspective view showing an instance of a beveled surface G

6

of a high grip portion G.

FIG. 34

is a perspective view showing a 19th embodiment of the present invention.

FIG. 35A

is an enlarged front view showing one end of a fixing belt

110

in a 20th embodiment of the present invention, and

FIG. 35B

is a cross sectional view taken on line b—b in FIG.

35

A.

FIG. 36

is a development of a high grip member G.

FIG. 37

is a front view showing one end of a modification of the fixing belt

110

.

FIG. 38

shows another modification of the fixing belt

110

;

FIG. 38A

is a front view showing a part of the fixing belt

110

, and

FIG. 38B

is a development of a high grip member G.

FIG. 39

is a cross sectional view showing the ends N

2

of the press contact portion N in the embodiment, useful in explaing the operation thereof.

FIG. 40

is a perspective view showing a key portion of a 21st embodiment of the present invention.

FIG. 41A

is a front view showing a part of a fixing belt

110

.

FIGS. 41B and 41C

are front views showing exemplary uneven patterns.

FIG. 42

diagrammatically shows one end of a fixing belt

110

employed in this embodiment;

FIG. 42A

is a front view showing a part of the belt, and

FIG. 42B

is a cross sectional view taken on line b—b in FIG.

42

A.

FIG. 43

is a diagram showing one end of a fixing belt

110

extending around the backup roller

130

and heating roller

140

in a 22nd embodiment of a belt fixing belt according to the present invention;

FIG. 43A

is a front view of the belt end.

FIG. 43B

is a longitudinal sectional view showing the same.

FIG. 44A

is an exploded, perspective view showing one end of the fixing belt

110

(before it is extended over the backup roller

130

and the heating roller

140

), and

FIG. 44B

is a perspective view showing the end thereof.

FIG. 45

a cross sectional view showing a part of the fixing belt

110

.

FIG. 46

shows a modification of the fixing belt:

FIG. 46A

is a perspective view showing a part of the fixing belt

110

(before it is extended over the backup roller

130

and the heating roller

140

); and

FIG. 46B

is a development of a high grip member G.

FIG. 47

shows one end of a modification of the fixing belt

110

:

FIG. 47A

is an enlarged, front view of the belt end; and

FIG. 47B

is a cross sectional view taken on line b—b in FIG.

47

A.

FIGS. 48A and 48B

show a modification of the fixing belt;

FIG. 48A

is a plan view showing a part of the fixing belt

110

, and

FIG. 48B

is a cross sectional view taken on line b—b in FIG.

48

A.

FIGS. 48C and 48D

show another modification of the fixing belt;

FIG. 48C

is a plan view showing a part of the fixing belt

110

, and

FIG. 48D

is a cross sectional view taken on line d—d in FIG.

48

C.

FIG. 49

is a diagram showing one end of a fixing belt

110

in a 23rd embodiment of the present invention:

FIG. 49A

is a front view of the belt end;

FIG. 49B

is a side view of the same; and

FIG. 49C

is a cross sectional view taken on line c—c in FIG.

49

B.

FIG. 50

is a cross sectional view showing the ends of a fixing nip (press contact portion) N in a key portion of a 24th embodiment of the present invention.

FIGS. 51A

to

51

D are cross sectional views showing the belt end in a 25th embodiment of the present invention, useful in explaining the operation of the embodiment.

FIGS. 52A

to

52

D are cross sectional views showing the belt end in a 26th embodiment of the present invention, useful in explaining the operation of the embodiment.

FIG. 53

is a diagrammatic view showing a major portion of a 26th embodiment of the present invention:

FIG. 53A

is a front view showing a part of a fixing belt

110

;

FIG. 53B

is a left side view of the same; and

FIG. 53C

is a traverse cross sectional view showing of the belt end.

FIG. 54

is a diagrammatic view showing a major portion of a 27th embodiment of the present invention:

FIGS. 54A and 54B

are front views showing a key portion when viewed from the oil coating roller

150

side.

FIG. 55

is an explanatory diagram showing another modification of the 27th embodiment (front view when viewed from the oil coating roller

150

side).

FIG. 56

is a cross sectional view showing a modification of the embodiment.

FIG. 57

is an explanatory diagram for explaing a conventional technique.

FIG. 58

is an explanatory diagram for explaing another conventional technique.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The preferred embodiments of the present invention will be described with reference to the accompanying drawings.

First Embodiment

FIG. 1

is a side view schematically showing an image forming apparatus which is a first embodiment of the present invention.

The image forming apparatus will first be described, and then a fixing device will be described in detail.

The image forming apparatus is designed to be capable of forming a monochromatic color image and a full color image by use of a development unit of four colors, Y (yellow), C(cyan), M (magenta) and K (black).

In

FIG. 1

, reference numeral

10

designates a photosensitive member unit, and its photosensitive member

11

is driven by an appropriate drive mechanism, not shown, to rotate in a direction of an arrow in the figure.

The photosensitive member

11

includes an electrically conductive substrate and a photosensitive layer formed over the surface of the conductive substrate.

A charging roller

12

as a charging mechanism, an exposure unit

20

as an exposing mechanism, a development unit

30

(Y, C, M and K) as a developing mechanism, an intermediate transfer unit

40

as a transfer mechanism, and a cleaning mechanism

13

are disposed along the circumference of the photosensitive member

11

in its rotation direction. The photosensitive member

11

, the charging roller

12

and the cleaning mechanism

13

are assembled into the photosensitive member unit

10

.

The charging roller

12

comes in contact with the outer peripheral surface of the photosensitive member

11

to uniformly charge the outer peripheral surface. The exposure unit

20

selectively radiates exposing light L

1

onto the uniformly charged outer peripheral surface of the photosensitive member

11

in accordance with desired image information, whereby an electrostatic latent image is formed on the photosensitive member

11

with the exposing light L

1

.

The development unit

30

applies toner to the electrostatic latent image to develop the latent image.

The development unit includes a yellow development sub-unit

30

Y, a cyan development sub-unit

30

C, a magenta development sub-unit

30

M, and a black development sub-unit

30

K. Those development sub-units

30

Y,

30

C,

30

M,

30

K are movable such that a development roller

31

of one of those development sub-units may selectively be brought into contact with the photosensitive member

11

. The development unit

30

thus arranged is capable of selectively applying each of color toner of yellow, cyan, magenta and black onto the surface of the photosensitive member

11

to develop the electrostatic latent image on the photosensitive member

11

and to form a toner image.

The toner image thus formed is transferred onto an intermediate transfer belt

46

, which forms an intermediate transfer member of the intermediate transfer unit

40

.

The cleaning mechanism

13

includes a cleaner blade for scraping off toner left on the outer peripheral surface of the photosensitive member

11

and a toner receiving portion for receiving the toner thus scraped off by the cleaner blade.

The intermediate transfer unit

40

includes a drive roller

41

, four roller followers

42

to

45

, and an endless intermediate transfer belt

46

as intermediate transfer member wound on those rollers.

A gear (not shown) fastened to an end of the drive roller

41

is in mesh with a drive gear (not shown) provided at an end of the photosensitive member

11

. Accordingly, the drive roller

41

is rotated at a peripheral speed substantially equal to that of the photosensitive member

11

, and it is circulated in a direction of an arrow in the figure at a peripheral speed substantially equal to that of the photosensitive member

11

.

The roller follower

45

is located at such a position between it and the drive roller

41

where the intermediate transfer belt

46

is pressed against the photosensitive member

11

by a tension of the intermediate transfer belt

46

itself. The pressing portion between the photosensitive member

11

and the intermediate transfer belt

46

forms a primary transfer portion T

1

.

An electrode roller, not shown, is provided in association with the drive roller

41

in a state that the intermediate transfer belt

46

intervenes therebetween. A primary transfer voltage is applied to the intermediate transfer belt

46

by way of the electrode roller.

The roller follower

42

is a tension roller, and urges the intermediate transfer belt

46

in its straing directions with the aid of urging mechanism (not shown).

The roller follower

43

is a backup roller forming a secondary transfer portion T

2

. A secondary transfer roller

48

as a secondary transfer mechanism is opposed to the backup roller

43

with respect to the intermediate transfer belt

46

. The secondary transfer roller

48

may be brought into contact with the intermediate transfer belt

46

and separated from the same, by a contact/separation mechanism (not shown). A secondary transfer voltage is applied to the secondary transfer roller

48

.

The roller follower

44

is a backup roller for a belt cleaner

49

. The belt cleaner

49

includes a cleaner blade

49

a

, which is brought into contact with the intermediate transfer belt

46

to scrape off toner left on the outer peripheral surface thereof, and a receiving portion

49

b

for receiving toner scraped off by the cleaner blade

49

a

. The belt cleaner

49

may be brought into contact with and separated from the intermediate transfer belt

46

by a contact/separation mechanism (not shown).

The intermediate transfer belt

46

consists of a multi-layer belt including a conductive layer and a resistive layer, which is formed on the conductive layer and is to be brought into pressing contact with the photosensitive member

11

. The conductive layer is formed on an insulating substrate made of synthetic resin. A primary transfer voltage is applied to the conductive layer by way of the electrode roller.

During a circulation of the intermediate transfer belt

46

, a toner image is transferred from the photosensitive member

11

onto the intermediate transfer belt

46

at the primary transfer portion T

1

. The toner image transferred onto the intermediate transfer belt

46

is transferred, at the secondary transfer portion T

2

, onto a sheet (recording medium) S, such as a sheet of paper, which is fed to between it and the secondary transfer roller

48

.

The electrode roller, the urging mechanism for the tension roller

42

, the secondary transfer roller

48

and the belt cleaner

49

are also assembled into the intermediate transfer unit

40

.

The recording medium S is fed to the secondary transfer a portion T

2

at a predetermined timing by a gate roller pair GRR, from a sheet supplying unit

50

a sheet supplying mechanism. Reference numeral

51

designates a paper supply cassette

51

which holds a stack of recording media S, and numeral

52

represents a pickup roller

52

.

A recording medium S to which a toner image has been transferred at the secondary transfer portion T

2

passes through a fixing device

100

as a fixing mechanism, and as a result, the toner image is fixed on the recording medium S.

As will subsequently be described in detail with reference to

FIG. 2

, the fixing device

100

includes an endless belt

110

to be heated and an pressure application roller

120

as a rotary member to be in pressing contact with the endless belt

110

. At a part (as viewed in the axial direction) of a press contact portion (or a nip) N between the endless belt

110

and the pressure application roller

120

, the belt and roller compress the recording medium S while at the same time heating the latter, whereby the toner image is fused and permanently fixed on the recording medium S.

After passing the fixing device

100

, the recording medium S is finally transported through a sheet discharge path

60

, and discharged to a sheet receiving portion

71

, which is formed on a case

70

of the apparatus body. The image forming apparatus includes an inverting/returning path

60

′ which inverts the recording medium S having passed through the fixing device

100

, and returns the inverted one to the secondary transfer portion T

2

. Specifically, a mechanism for transporting the recording medium S in the embodiment includes the sheet discharge path

60

and the inverting/returning path

60

′, and the sheet discharge path

60

forms a part of the inverting/returning path

60

′.

The inverting/returning path

60

′ includes a switch-back path

63

, and a return path

64

. The switch-back path

63

has two separate sheet discharge paths

61

and

62

, each of which is capable of transporting a recording medium S having passed through the fixing device

100

into the path per se, and transporting the recording medium S having been once transported therein to in the reverse direction. The return path

64

returns the recording medium S, which is reversely transported from the switch-back path

63

, to the secondary transfer portion T

2

, again. Accordingly, a recording medium S which is to be returned again to the secondary transfer portion T

2

by the inverting/returning path

60

′ will be returned to the secondary transfer portion T

2

in a state that the top and back surfaces or sides are inverted.

The image forming apparatus thus constructed is capable of forming a toner image on only the top surface (first surface) of the recording medium S and also both the top and back surfaces (first and second surfaces) of the same.

An operation of the overall image forming apparatus thus constructed will briefly be described.

(i) When a print command signal (image forming signal) that is transferred from a host computer or the like (personal computer or the like) to a control unit (not shown) of the image forming apparatus, the photosensitive member

11

, and the respective rollers

31

of the development unit

30

, and the intermediate transfer belt

46

are driven to turn.

(ii) The outer peripheral surface of the photosensitive member

11

is uniformly charged by the charging roller

12

.

(iii) The exposure unit

60

selectively exposes the uniformly charged outer peripheral surface of the photosensitive member in accordance with image information of a first color (for example, yellow), to thereby form an electrostatic latent image for yellow.

(iv) Only the development roller of the development sub-unit

30

Y of the first color (for example, yellow) is brought into contact with the photosensitive member

11

. The electrostatic latent image is developed and a toner image of the first color (for example, yellow) is formed on the photosensitive member

11

.

(v) A primary transfer voltage the polarity of which is Opposite to the charging polarity of the toner is applied to the intermediate transfer belt

46

. As a result, the toner image is transferred from the photosensitive member

11

to the intermediate transfer belt

46

at the primary transfer portion T

1

. At this time, the secondary transfer roller

48

and the belt cleaner

49

are separated from the intermediate transfer belt

46

.

(vi) Toner left on the photosensitive member

11

is removed by the cleaning mechanism

13

, and the charge of the photosensitive member

11

is then removed by charge removal light L

2

emitted from a charge removal mechanism

21

.

(vii) A sequence of operation steps (ii) to (vi) is repeated as required. Specifically, toner images of second to fourth colors are transferred and formed onto the intermediate transfer belt

46

in a superimposing manner in accordance with print command signals.

(viii) Just before or after the leading edge of a recording medium S, which is supplied at a predetermined timing from the sheet supplying unit

50

, reaches the secondary transfer portion T

2

(viz., at a timing that a toner image is transferred from the intermediate transfer belt

46

onto a desired location on the recording medium S), the secondary transfer roller

48

is pressed against the intermediate transfer belt

46

, while at the same time, a secondary transfer voltage is applied to the same, and the toner image (basically, a full color image formed by superimposing four color toner images) is transferred from the intermediate transfer belt

46

to the recording medium S. The belt cleaner

49

is brought into contact with the intermediate transfer belt

46

to remove toner still left on the intermediate transfer belt

46

after the secondary transfer.

(ix) The recording medium S passes through the fixing device

100

, so that the toner image is fixed thereon. Thereafter, the recording medium S is directed to a predetermined position (the sheet receiving portion

71

when the print mode is not the both-side print mode, and the switch-back path

63

and then the return path

64

when it is the both-side print mode).

To be more specific, when the image is formed on only the top side or surface (first surface) of the recording medium, the toner image is transferred onto the first surface of the recording medium S that is supplied from the sheet supplying unit

50

at the secondary transfer portion T

2

. After fixed by the fixing device

100

, it is discharged into the sheet receiving portion

71

by way of the sheet discharge path

61

or

62

. A path select mechanism (not shown) is provided at an entrance

60

A of those paths

61

and

62

. The path select mechanism selects the sheet discharge path (

61

or

62

) to which the recording medium S is to be transported.

When the image is formed on both sides (first and second sides or surfaces) of the recording medium, the toner image is transferred, at the secondary transfer portion T

2

, onto the first surface of the recording medium S which fed from the sheet supplying unit

50

. And it is fixed by the fixing device

100

. After the fixing, the recording medium enters the sheet discharge path

61

or

62

(switch-back path

63

), and transported in the reverse direction through the return path

64

, and transported back to the secondary transfer portion T

2

by means of the gate roller pair GRR at a predetermined timing, and the toner image is transferred also onto the second surface of the recording medium. Thereafter, the fixing device

100

fixes the toner image also onto the second surface, and the resultant recording medium is discharged onto the sheet receiving portion

71

by way of the sheet discharge path

61

or

62

.

The image forming apparatus of the present embodiment is constructed and operated as described above, and the fixing device

100

assembled therein to will now be described.

FIG. 2

is a view schematically showing a major portion of the fixing device

100

.

FIG. 3

is a side view showing a major portion of the fixing device.

As described above, the fixing device

100

includes the endless belt

110

to be heated and an pressure application roller

120

as a rotary member to be in pressing contact with the endless belt

110

. At a part N

1

(usually a central part as viewed in the axial direction) of a press contact portion N between the endless belt

110

and the pressure application roller

120

, the belt and roller compress a recording medium S traveling in a direction S

1

of an arrow while at the same time heating the latter, whereby the toner image is fused and permanently fixed on the recording medium S. The fixing device

100

further includes a backup roller

130

as a backup member for supporting the endless belt

110

on the inner side thereof at the press contact portion, and a heating roller

140

as a heating mechanism for heating the endless belt

110

. The endless belt

110

is suspended between the backup roller

130

and the heating roller

140

.

The drive roller for rotating the endless belt

110

and the respective rollers may be any of the rollers. In the embodiment, the pressure application roller

120

is used as the drive roller.

The pressure application roller

120

is driven to rotate in the direction (in the counterclockwise direction) of an arrow in

FIG. 2

by a drive mechanism, not shown, provided in the main body of the image forming apparatus, and the endless belt

110

, the backup roller

130

, and the heating roller

140

rotate in a follower manner. Specifically, the endless belt

110

follows in rotation the pressure application roller

120

by being pressure-contacted with the pressure application roller

120

. The endless belt

110

is wound on the backup roller

130

and the heating roller

140

, and the backup roller

130

and the heating roller

140

follow in rotation the endless belt

110

.

The endless belt

110

is formed with a belt base

110

a

(see

FIG. 4

) of a thin member of metal (such as nickel) and a surface belt layer

110

b

(for example, a silicone rubber layer), which exhibits good release characteristics for recording material and toner, formed over a surface of the belt base layer.

One of the features of the present embodiment resides in that a high grip portion

110

G is provided at a portion N

2

of the endless belt

110

which is not pressed by the recording medium S but pressed by the pressure application roller

120

(usually, the portion N

2

is provided at each of both side ends of the endless belt).

The high grip portion

110

G shown in

FIG. 3

is formed with a plurality of holes

112

equidistantly arrayed in a zig-zag fashion along each portion N

2

or each side end

10

c

of the endless belt

110

(when viewed from side, the high grip portion having the thus arranged holes is shaped like a ring.).

FIG. 4

is a view showing another instance of the high grip portion

110

G;

FIG. 4A

is a plan view showing a part of the high grip portion

110

G, and

FIG. 4B

is a cross sectional view taken on line b—b in FIG.

4

A.

A high grip portion

110

G′ shown in

FIG. 4

is constructed such that meshes

113

made of glass fiber are bonded, by adhesive

114

, to and along a side end

110

c

of the endless belt

110

at the portion N

2

thereof, more exactly, both surfaces of the belt base

110

a

of the endless belt at the portion N

2

.

The high grip portions

110

G are preferably provided on both the side ends of the endless belt

110

, although only one side end of the endless belt

110

is illustrated in

FIGS. 3 and 4

. In the present embodiment, the high grip portions

110

G are provided on both the side ends of the endless belt.

In

FIG. 2

, reference numeral

111

is a thermistor for sensing a temperature on a surface portion of the endless belt

110

where the belt is put on the backup roller

130

. The thermistor

111

is located upstream of a press contact portion N between it and the pressure application roller

120

.

The backup roller

130

is formed with a core member

131

of metal and a relatively thick, elastic layer

132

layered over the surface of the core member

131

. The backup roller

130

is supported by a shaft

131

a

of the core member

131

while being rotatable with respect to a side plate

101

of the frame of the fixing device

100

.

The heating roller

140

, shaped like a pipe, is made of a material having a good thermal conductivity (for example, aluminum). It contains a halogen lamp

141

as a heat source disposed therein. The heating roller

140

is capable of rapidly heating the endless belt

110

at a position where it is put on the endless belt

110

. In the embodiment, the heating roller

140

is constructed as a tension roller, and is urged in a straing direction of the endless belt

110

by an appropriate urging mechanism. In

FIG. 2

, reference numeral

143

represents a thermistor for sensing a temperature of the heating roller

140

.

The pressure application roller

120

is formed with a pipe-like core member

121

having a good thermal conductivity, a relatively thin, elastic layer

122

which is formed on the surface of the core member

121

and is harder than the elastic layer

132

of the backup roller

130

, and a surface belt layer

122

a

which is formed on a surface of the elastic layer

122

and well separable from the recording member and toner. A halogen lamp

123

as a heat source is disposed within the core member

121

.

The pressure application roller

120

is rotatably supported by a frame side plate

101

of the fixing device

100

, and it is rotated in the direction of an arrow (counterclockwise) in

FIG. 2

by means of a drive mechanism (not shown) provided on the main body of the image forming apparatus. The pressure application roller

120

is mounted immovable in the radial direction. It is pressed against the backup roller

130

by the utilization of elastic forces of the elastic layer

122

and the elastic layer

132

of the backup roller

130

, with the endless belt

110

being interposed therebetween. The elastic layer

132

of the backup roller

130

is thicker and softer than the elastic layer

122

of the pressure application roller

120

. Therefore, the fixing nip N is deflected toward the backup roller

130

. In

FIG. 2

, reference numeral

124

designates a thermistor for sensing a surface temperature of the pressure application roller

120

.

A frame

101

includes a guide

102

for guiding a recording medium S having a toner image formed (transferred) thereon at the secondary transfer portion T

2

(see

FIG. 1

) into a press contact portion (nip) N between the endless belt

110

and the pressure application roller

120

. A guide

104

and a sheet-discharge roller pair

103

are provided downstream of the press contact portion N. The guide

104

guides the recording medium S of which the toner image has been fixed to the sheet discharge path

60

. The respective thermistors are connected to the control unit (not shown). The control unit controls a value of current fed to each of the heat sources

123

and

141

in accordance with a temperature sensed by the related thermistor.

In the image forming apparatus of the present embodiment, a toner image is formed on a recording medium S. The recording medium S having the toner image formed thereon is moved to pass through the part N

1

of the press contact portion N in the fixing device

110

, whereby the toner image is fused and permanently fixed on the recording medium S. As state above, the fixing device

100

includes an endless belt

110

to be heated and an pressure application roller

120

as a rotary member to be in pressing contact with the endless belt

110

. Of the endless belt

110

and the pressure application roller

120

, the pressure application roller

120

is driven to rotate while the endless belt

110

follows the pressure application roller in its circulation.

Further, the high grip portion

110

G is provided at a portion N

2

of the endless belt

110

which is not pressed by the recording medium S but pressed by the pressure application roller

120

. Therefore, when a recording medium S, which relatively easily slips, is supplied to the part N

1

of the press contact portion N between the endless belt

110

and the pressure application roller

120

, and as a result, when a slip will occur between the pressure application roller

120

of the drive side (the endless belt

110

when the endless belt

110

is driven by the backup roller

130

; The same shall apply hereinafter.) and the recording medium S and/or the recording medium S and the endless belt

110

of the follower side (the pressure application roller

120

when the backup roller

130

drives the endless belt

110

; The same shall apply hereinafter.), the endless belt

110

and the pressure application roller

120

rotate at substantially equal peripheral speeds since the follower action of the endless belt

110

of the follower side for the pressure application roller

120

of the drive side is enhanced through the action of the high grip portion

110

G.

Therefore, the slip is prevented (at least its occurrence is extremely infrequent). As a result, the fixing operation of the fixing device is stable. Accordingly, the toner image on the recording medium S is little blurred, so that the resultant image is little disarranged.

The image forming apparatus is designed so as to be capable of forming toner images on both sides of the recording medium S. Therefore, there is a case that a recording medium S having toner images formed on both sides thereof passes through the part N

1

of the press contact portion N in the fixing device

100

.

The toner on the recording medium S sometimes reduces a frictional coefficient between the recording medium S and the belt. Therefore, in a case where the toner images are formed on both sides of the recording medium S, the recording medium is more likely to slip when comparing with a case where the toner image is formed on one side of the recording medium S.

In this connection, in the image forming apparatus of the embodiment, the high grip portion

110

G is provided on the endless belt

110

. Because of this, even when the toner images are formed on both sides of the recording medium S, the slip does not occur (at least its occurrence is extremely infrequent), and as a result, a fixing operation of the fixing device is stable.

Thus, the image forming apparatus of the embodiment can form images not disarranged (at least little disarranged) on both sides of the recording medium S.

The image forming apparatus is also designed to be capable of forming a full color image, which is formed by superimposing a plurality of different colors. Therefore, there is a case where a recording medium S having a full color image formed on at least one side thereof passes through the part N

1

of the press contact portion N in the fixing device

100

.

As described above, the toner on the recording medium S sometimes reduces a frictional coefficient between the recording medium S and the belt. Therefore, in a case where a full color image by superimposing a plurality of different colors is formed on the recording medium S, the recording medium is more likely to slip when comparing with a case where the monochromatic color image is formed on the recording medium S.

In connection with this, in the image forming apparatus of the embodiment, the high grip portion

110

G is provided on the endless belt

110

. Because of this, even when the full color image, which is formed by superimposing the plurality of different colors, is formed on the recording medium S, the slip does not occur (at least its occurrence is extremely infrequent), and as a result, a fixing operation of the fixing device is stable.

Thus, the image forming apparatus of the embodiment can form a full color image suffering from no (at least little) disarrangement of the image, and can form full color images, which suffering no (at least little) image disarrangement on both sides of the recording medium S.

The high grip portions

110

G are each provided at the portion of the endless belt which is not in pressing contact with the recording medium S. Therefore, the high grip portions

110

G do not have any adverse effect on the recording medium S and the image on the recording medium S.

Second Embodiment

A difference of a second embodiment of the present invention from the first embodiment resides in that as shown in

FIG. 3

, instead of providing a high grip portion

110

G on the endless belt

110

(or in addition to providing it on the endless belt), a high grip portion G is provided on a portion N

2

of the pressure application roller

120

which is not pressed by the recording medium S but pressed by the endless belt

110

. The remaing construction of the second embodiment is substantially the same as of the first embodiment. The high grip portions G are preferably provided on both the side ends of the pressure application roller

120

, although only one side end of the pressure application roller

120

is illustrated in FIG.

3

. In the present embodiment, the high grip portions G are provided on both the side ends of the pressure application roller.

The high grip portion

110

G may take a proper construction, and may take the following constructions, for example.

FIGS.

5

A

1

and

5

A

2

show a first example of the high grip portion

110

G. FIG.

5

A

1

is a perspective view showing a part of the first example, and FIG.

5

A

2

is a side view showing a part of the same.

In the first example, an endless rubber belt G

1

b

with a number of axially elongated, narrow strips (ribs) G

1

a

rectangular in cross section is secured to or formed integrally on a portion N

2

of the pressure application roller

120

which is not pressed by the recording medium S but pressed by the endless belt

110

. A height of each narrow strip G

1

a

is within a range of 100 μm to 500 μm.

FIGS.

5

B

1

and

5

B

2

show a second example of the high grip portion

110

G. FIG.

5

B

1

is a perspective view showing a part of the first example, and FIG.

5

B

2

is a side view showing a part of the same.

In the second example, a heat-resistance tape G

2

b

with a number of axially elongated, narrow strips (or ribs) G

2

a

semicircular in cross section or a wavy tape G

2

b

is bonded around a portion N

2

of the pressure application roller

120

which is not pressed by the recording medium S but pressed by the endless belt

110

. A height of each narrow strip G

2

a

is within a range of 100 μm to 500 μm, more preferably approximately 200 μm.

FIGS.

6

A

1

and

6

A

2

show a third example of the high grip portion

110

G. FIG.

6

A

1

is a perspective view showing a part of the first example, and FIG.

6

A

2

is a cross sectional view taken on line a

2

—a

2

in FIG.

6

A

1

.

A thick, band-like silicone rubber sponge G

3

a

is wound around and secured to a portion N

2

of the pressure application roller

120

which is not pressed by the recording medium S but pressed by the endless belt

110

or a thick, ring-like silicone rubber sponge G

3

a

is secured to the portion N

2

.

The silicone rubber sponge. G

3

a

, as shown in FIG.

6

A

3

, is compressed when the endless belt

110

and the pressure application roller

120

are pressed one against the other, to form a high grip portion G.

FIG. 6B

is a cross sectional view showing a fourth example of the high grip portion G (corresponds to the cross sectional view taken on line a

2

—a

2

in FIG.

6

A

1

).

The fourth example of the high grip portion G is formed by securing particles (e.g., glass beads) G

4

a

, by epoxy adhesive G

4

b

, onto a portion N

2

of the pressure application roller

120

which is not pressed by the recording medium S but pressed by the endless belt

110

. A preferable particle diameter of a particle G

4

a

is within a range of 200 μm to 500 μm.

Also in this embodiment of the image forming apparatus, as in the first embodiment, a toner image is formed on a recording medium S, the recording medium S having the toner image formed thereon passes through the part N

1

of the press contact portion N in the fixing device

100

, whereby the toner image is fused and fixed on the recording medium S.

The high grip portion G is provided at a portion N

2

of the pressure application roller

120

which is not pressed by the recording medium S but pressed by the endless belt

110

. Therefore, when a recording medium S, which relatively easily slips, is supplied to the part N

1

of the press contact portion between the endless belt

110

and the pressure application roller

120

, and as a result, when a slip will occur between the pressure application roller

120

of the drive side and the recording medium S and/or the recording medium S and the endless belt

110

of the follower side, the endless belt

110

and the pressure application roller

120

rotate at substantially equal peripheral speeds since the follower action of the endless belt

110

of the follower side for the pressure application roller

120

of the drive side is enhanced through the action of the high grip portion

110

G.

The slip is prevented (at least its occurrence is extremely infrequent). As a result, the fixing operation of the fixing device is stable. Accordingly, the toner image on the recording medium S is little blurred, so that the resultant image is little disarranged.

In the image forming apparatus of the embodiment, at least the high grip portion G is provided on the pressure application roller

120

. Because of this, even when the toner images are formed on both sides of the recording medium S or the full color image, which is formed by superimposing the plurality of different colors, is formed on the recording medium S, the slip does not occur (at least its occurrence is extremely infrequent), and as a result, a fixing operation of the fixing device is stable.

Thus, also in the image forming apparatus of the embodiment, it is possible to form a full color image suffering from no (at least little) image disarrangement, and to form full color images, which suffering no (at least little) image disarrangement, on both sides of the recording medium S.

The high grip portions G are each provided at the portion of the endless belt which is not in pressing contact with the recording medium S. Therefore, the high grip portions do not have any adverse effect on the recording medium S and the image on the recording medium S.

Third Embodiment

FIG. 7

is a side view schematically showing a major portion of a fixing device

100

in a third embodiment of an image forming apparatus according to the present invention. In the figure, like or equivalent portions are designated by like reference numerals used in the first embodiment.

A major feature of the third embodiment resides in that the pressure application roller

120

and the backup roller

130

are each wider than the endless belt

110

, and that a high grip portion G′ is formed at a portion N

3

of the pressure application roller

120

which is not pressed by the recording medium S but pressed by the backup roller

130

. A basic construction of the fixing device

100

and a construction of the image forming apparatus in the third embodiment are substantially the same as in the first embodiment. The high grip portions G′ are preferably provided on both the side ends of the pressure application roller

120

, although only one side end of the pressure application roller

120

is illustrated in FIG.

7

. In the present embodiment, the high grip portions G′ are provided on both the side ends of the pressure application roller.

The high grip portion G′ may take a proper construction, and may take, for example, any of the high grip portions described in connection with

FIGS. 5 and 6

.

Also in this embodiment of the image forming apparatus, as in the first embodiment, a toner image is formed on a recording medium S, the recording medium S having the toner image formed thereon passes through the press contact portion N (a part N

1

of the press contact portion N in this embodiment) in the fixing device

100

, whereby the toner image is fused and fixed on the recording medium S.

The high grip portion G′ is provided at a portion N

3

of the pressure application roller

120

which is not pressed by the recording medium S but pressed by the backup roller

130

. Therefore, when a recording medium S, which relatively easily slips, is supplied to the press contact portion N

1

between the endless belt

110

and the pressure application roller

120

, and as a result, when a slip will occur between the pressure application roller

120

of the drive side and the recording medium S and/or the recording medium S and the endless belt

110

of the follower side, the endless belt

110

and the pressure application roller

120

rotate at substantially equal peripheral speeds since the follower action of the endless belt

110

of the follower side for the pressure application roller

120

of the drive side is enhanced through the action of the high grip portion G′.

This will be described in detail hereunder.

When the pressure application roller

120

is driven, its drive force is transmitted to the endless belt

110

pressed against the pressure application roller

120

, and is also transmitted to the backup roller

130

through the high grip portion G′. Further, the drive force is transmitted from the backup roller

130

to the endless belt

110

at a position on the endless belt

110

where it is put on the backup roller

130

. That is, the drive force derived from the pressure application roller

120

is transmitted tot he endless belt

110

by way of two routes. When the endless belt

110

is driven (the endless belt

110

is driven by the backup roller

130

or the heating roller

140

), its drive force is transmitted to the pressure application roller

120

which is pressed against the endless belt

110

, and also is transmitted to the backup roller

130

which follows the endless belt

110

in rotation. And it is transmitted to the pressure application roller

120

through the high grip portion G′. Also in this case, the drive force from the endless belt

110

is transmitted to the pressure application roller

120

by way of two routes.

In a case where the pressure application roller

120

is driven and also in a case where the endless belt

110

is driven, the follower action of the endless belt

110

(pressure application roller

120

) of the follower side for the pressure application roller

120

(or the endless belt

110

) of the drive side is enhanced through the action of the high grip portion G′. Therefore, even when the recording medium S, which relatively easily slips, is fed to the press contact portion N, the endless belt

110

and the pressure application roller

120

rotate at substantially equal peripheral speeds.

The slip is prevented (at least its occurrence is extremely less frequent). As a result, the fixing operation of the fixing device is stable. Accordingly, the toner image on the recording medium S is little blurred, so that the resultant image is little disarranged.

In the image forming apparatus of the embodiment, the high grip portion G′ is provided on the pressure application roller

120

. Because of this, even when the toner images are formed on both sides of the recording medium S or the full color image, which is formed by superimposing the plurality of different colors, is formed on the recording medium S, the slip does not occur (at least its occurrence is extremely infrequent), and as a result, a fixing operation of the fixing device is stable.

Thus, also in the image forming apparatus of the embodiment, it is possible to form a full color image suffering from no (at least little) image disarrangement, which suffering no (at least little) image disarrangement, on both sides of the recording medium S.

The high grip portions G′ are each provided at the portion of the endless belt which is not in pressing contact with the recording medium S. Therefore, the high grip portions do not have any adverse effect on the recording medium S and the image on the recording medium S.

Fourth Embodiment

A difference of a fourth embodiment of the present invention from the third embodiment resides in that as shown in

FIG. 7

, instead of providing a high grip portion G′ on the pressure application roller

120

(or in addition to providing it on the endless belt), a high grip portion G″ is provided on a portion (N

3

) of the backup roller

130

which is pressed by the pressure application roller. The remaing construction of the fourth embodiment is substantially the same as of the third embodiment. The high grip portions G″ are preferably provided on both the side ends of the backup roller

130

, although only one side end of the backup roller

130

is illustrated in FIG.

7

. In this embodiment, the high grip portions G″ are provided on both the side ends of the backup roller.

The high grip portion G″ may take a proper construction, and may take, for example, any of the high grip portions described in connection with

FIGS. 5 and 6

.

The operation of and the advantageous effects produced by the image forming apparatus of this embodiment are similar to and comparable with those in the third embodiment.

Fifth Embodiment

A difference of a fifth embodiment of the present invention from the third or fourth embodiment resides in that, as shown in

FIG. 7

, the high grip portions G′ and/or G″ are provided on the pressure application roller

120

and/or the backup roller

130

, and that a high grip portion

110

G″, which acts on the backup roller

130

, is provided at the reverse side of a portion N

2

of the endless belt

110

which is not pressed by the recording medium S. The remaing construction of the fifth embodiment is substantially the same as of the third or fourth embodiment. Although only one side end of the endless belt

110

is illustrated in

FIG. 7

, the high grip portions

110

G″ are provided on both the side ends of the endless belt.

The high grip portion

110

G may take a proper construction, and may take, for example, any of the constructions of the high grip portion

110

G or

110

G′ which were described in connection with

FIGS. 3 and 4

.

The operation of and the advantageous effects produced by the image forming apparatus of this embodiment are similar to and comparable with those in the third embodiment.

Further, in the embodiment, power transmission between the endless belt

110

and the backup roller

130

is further improved since the high grip portion

110

G″, which acts on the backup roller

130

, is provided at the reverse side of a portion N

2

of the endless belt

110

which is not pressed by the recording medium S.

With the operation of the high grip portion G′ and/or G″, the follower action of the endless belt

110

(or the pressure application roller

120

) of the follower side for the pressure application roller

120

(or the endless belt

110

) of the drive side is further enhanced. As a result, the fixing device operates more stably. Accordingly, a chance of the blurring of the toner image on the recording medium S is more lessened, and as a result, the resultant image is further improved in its quality.

Sixth Embodiment

FIG. 8

is a view schematically showing a fixing device

100

in a sixth embodiment of an image forming apparatus according to the present invention.

FIG. 9

is a side view showing a major portion of the fixing device. In those figures, like or equivalent portions are designated by like reference numerals in the first embodiment.

This embodiment is different from the above-mentioned embodiments in that an oil roller

150

as oil coating mechanism for applying release oil onto the surface of the endless belt

110

, and that an oil barrier B is provided on the backup roller

130

at a portion thereof between a contact portion N of the backup roller where it is brought into contact with the endless belt

110

and a portion N

3

of the backup roller where it is not brought into contact with the endless belt

110

but is pressed by the pressure application roller

120

. The remaing construction of the embodiment is substantially the same as the above-mentioned embodiment.

The oil roller

150

includes a shaft

151

and a thick, oil holder layer

152

fastened around the shaft

151

. The oil holder layer

152

is made of porous material or fibrous material. The oil holder layer

152

is impregnated with release oil. In order to secure a uniform coating of oil, the surface of the oil holder layer

152

is coated with a thin film sheet having an oil permeability, such as a porous PTFE sheet

153

.

The oil roller

150

is pressed against the endless belt

110

by an appropriate urging mechanism (not shown), and it is rotated in a follower manner to apply release oil, such as silicone oil, onto the surface of the endless belt

110

. In

FIG. 8

, reference numeral

154

designates a cleaning member made of felt or the like, for cleaning the surface of the oil roller

150

. The cleaning member

154

is pressed against the surface of the oil roller

150

.

In this embodiment, as shown in

FIG. 9

, the oil roller

150

is shorter width than the endless belt

110

, and the release oil is applied to within only the press contact portion N

1

of the endless belt

110

where it is brought into contact with the recording medium S. The width of the press contact portion N

3

of the endless belt

110

, which is coated with the release oil by the oil roller

150

, is longer than the width of the maximum image forming area on the recording medium S.

The oil barrier B may appropriately be constructed. In the embodiment, it takes the form of a ring-like groove

135

formed around the backup roller

130

. A ring-like groove

125

, which is formed around the pressure application roller

120

, also constitutes the oil barrier B. The ring-like groove

125

forms an oil barrier provided between the press contact portion N of the pressure application roller

120

where it is pressed against the endless belt

110

and the portion N

3

of the pressure application roller

120

which is not brought into contact with the endless belt

110

but pressed by the backup roller

130

. An oil absorbing member (e.g., a ring-like member made of felt) is preferably provided within each of the ring-like grooves

135

and

125

in order to absorb the oil having flowed into the groove.

In the present embodiment, an oil barrier B

2

is provided at a portion of the backup roller

130

which faces the side end

110

c

of the endless belt

110

.

FIG. 10

is an enlarged cross sectional view showing the oil barrier B

2

.

The oil barrier B

2

includes a ring-like groove B

2

a

formed at a portion of the backup roller

130

which faces the side end

110

c

of the endless belt

110

, and an oil absorbing member B

2

b

(e.g., a ring-like member made of felt) located within the groove B

2

a

. The groove B

2

a

is also provided preferably at each of both side ends of the backup roller

130

.

The width of the oil barrier B

2

may be widened outside beyond the side end

110

c

of the endless belt

110

as indicated by a phantom line B

2

′ in FIG.

10

. In this case, the widened has a function equivalent to that of the oil barrier B, which is provided on the backup roller

130

at a portion thereof between the contact portion N of the backup roller where it is brought into contact with the endless belt

110

and the portion N

3

of the backup roller where it is not brought into contact with the endless belt

110

but is pressed by the pressure application roller

120

.

A high grip portion G′ and/or a high grip portion G″ are preferably provided at the press contact portion N

3

of at least one of the pressure application roller

120

and the backup roller

130

. In this embodiment, the high grip portion G′ (G

1

) shown in FIG.

5

A

1

is provided on the pressure application roller

120

, and the high grip portion G″ (G

2

) shown in FIG.

6

A

1

is provided on the backup roller

130

. In FIG.

9

. The high grip portions G′ and G″ are preferably provided on both the side ends of the rollers, although only one end of each of the rollers including the pressure application roller

120

is illustrated.

The image forming apparatus of the sixth embodiment of the invention operates in the following ways and produces the following useful effects.

(a) A toner image is formed on the recording medium S. The recording medium S having the toner image formed thereon passes through the press contact portion N of the fixing device

100

having the following construction. The toner image on the recording medium is fused and fixed on the recording medium S. The fixing device

100

includes the endless belt

110

to be heated, the pressure application roller

120

as a rotary member to be in pressing contact with the endless belt

110

, the width of the pressure application roller

120

being longer than that of the endless belt

110

, and the backup roller

130

for supporting the endless belt

110

on the inner side thereof at its press contact portion N, the width of the backup roller being longer than that of the endless belt

110

, wherein the pressure application roller

120

is driven and the endless belt

110

circulates in a follower fashion.

In the embodiment, an offset phenomenon is unlikely to occur since the oil roller

150

as the oil coating mechanism for applying the release oil onto the surface of the endless belt

110

is provided.

Further, it is noted that the oil barrier B is provided on the backup roller

130

at a portion thereof between a contact portion N of the backup roller where it is brought into contact with the endless belt

110

and a portion N

3

of the backup roller where it is not brought into contact with the endless belt

110

but is pressed by the pressure application roller

120

(N

3

: corresponds to the end N′ of the press contact portion N described in connection with FIG.

12

). When the release oil having been applied to the surface of the endless belt

110

will flow into the “portion N

3

of the backup roller where it is not brought into contact with the endless belt

110

but is pressed by the pressure application roller

120

”, its flow is blocked by the oil barrier B (at least its little flow into the portion is permitted.).

For this reason, a gripping force is sufficiently secured between the backup roller

130

and the pressure application roller

120

at the portion N

3

, so that the endless belt

110

and the pressure application roller

120

turn at substantially the equal peripheral speeds (The reason why the endless belt

110

and the pressure application roller

120

turn at substantially the equal peripheral speeds when a gripping force is sufficiently secured between the backup roller

130

and the pressure application roller

120

is as stated in the operation description of the third embodiment.).

In the image forming apparatus of this embodiment, when a slip will occur between the pressure application roller

120

of the drive side (or the endless belt

110

) and the recording medium S and/or the recording medium S and the endless belt

110

of the follower side (or the pressure application roller

120

), the slip is prevented (at least its occurrence is extremely infrequent.) although such a construction is employed that the release oil is applied to the endless belt

110

, and as a result, a stable fixing operation of the fixing device is performed. Accordingly, the toner on the recording medium is little blurred, and hence the resultant image is little disarranged.

(b) The oil barrier B is also provided between the press contact portion N of the pressure application roller

120

where it is pressed against the endless belt

110

and the portion N

3

of the pressure application roller

120

which is not brought into contact with the endless belt

110

but pressed by the backup roller

130

. The presence of the oil barrier B prevents such a situation that the release oil is applied to the endless belt

110

, and the oil that has been transferred to the contact portion N of the pressure application roller

120

where it is brought into contact with the endless belt

110

moves to the portion N

3

of the pressure application roller

120

(at least occurrence of such a situation is extremely infrequent.).

Accordingly, a gripping force is more sufficiently secured between the backup roller

130

and the pressure application roller

120

at the portion N

3

, so that a more stable fixing operation of the fixing device is performed. Accordingly, the toner on the recording medium is little blurred, and hence the resultant image is little disarranged. Accordingly, the toner image on the recording medium S is little blurred, so that the resultant image is little disarranged.

(c) The oil barrier B

2

is provided at a portion of the Backup roller

130

, which faces the side end

110

c

of the endless belt

110

. Therefore, if the release oil that has applied to the surface of the endless belt

110

will move from the side end

110

c

of the endless belt

110

to a nip T

3

between the endless belt

110

and the backup roller

130

, movement of the release oil to the nip is blocked by the oil barrier B

2

that is located at the portion of the backup roller, which faces the side end

110

c

of the endless belt

110

(at least the movement of the release oil to the nip is extremely impeded.).

Accordingly, a necessary friction force between the endless belt

110

and the backup roller

130

is secured, and hence a power transmission from the pressure application roller

120

to the backup roller

130

and then the endless belt

110

is also secured. Consequently, the follower action of the endless belt

110

and the pressure application roller

120

is also enhanced. And the endless belt

110

and the pressure application roller

120

turn at substantially equal periphery speeds.

Thus, in the image forming apparatus of this embodiment, a more stable fixing operation of the fixing device is performed although the endless belt

110

is coated with the release oil.

(d) The high grip portion G′ is provided at the portion N

3

of the pressure application roller

120

. Provision of the high grip portion G′ improves the follower action of the pressure application roller

120

and the backup roller

130

, and hence the follower action of the endless belt

110

and the pressure application roller

120

. As a result, a more stable fixing operation of the fixing device is performed.

(e) The high grip portion G′ is provided at the portion N

3

of the backup roller

130

. With provision of the high grip portion G″, the follower action of the pressure application roller

120

and the backup roller

130

is further improved, and hence the follower action of the endless belt

110

and the pressure application roller

120

is also so done. This leads to a more stable fixing operation of the fixing device.

(f) The release oil, which is applied by the oil roller

150

, is applied to within only the contact portion N

1

of the endless belt

110

where it is brought into contact with the recording medium S. Therefore, the applied oil is almost all absorbed by or transferred to the recording medium S when the recording medium S passes therethrough.

Accordingly, there is little chance that the release oil flows to the non-contact portions not in contact with the recording medium S, i.e., (1) the contact portion N

3

between the pressure application roller

120

and the backup roller

130

in the non-contact portion not in contact with the endless belt

110

and (2) the nip T

3

between the endless belt

110

and the backup roller

130

. As a result, a more stable fixing operation of the fixing device is performed.

(g) The image forming apparatus of this embodiment, like the first embodiment, is designed to be capable of forming toner images on both sides of the recording medium S. Therefore, sometimes, the recording medium S having toner images T on both sides thereof passes through a part N

1

of the press contact portion N in the fixing device

100

.

As described, there is a case that the toner on the recording medium S reduces the friction coefficient between the recording medium S and the rotary member. Therefore, in a case where the toner images T are formed on both sides of the recording medium S, the recording medium is more likely to slip when comparing with a case where the toner image is formed on one side of the recording medium.

In this connection, it is noted that the oil barrier B is provided on the backup roller

130

in the image forming apparatus of this embodiment. Therefore, the recording medium S is unlikely to slip even when toner images are formed on both sides of the recording medium S (at least a chance of its slipping is remarkably reduced.). As a result, a stable fixing operation of the fixing device is ensured.

Thus, the image forming apparatus of the embodiment can form images free from (at least with little) image disarrangement on both sides of the recording medium S.

(h) The image forming apparatus of the embodiment, like That of the first embodiment, is capable of forming a full color image formed by superimposing a plurality of different colors. Therefore, there is a case that a recording medium S having a full color image formed on at least one side thereof passes through the part N

1

of the press contact portion N in the fixing device

100

.

As described above, there is a case that the toner on the recording medium S reduces the friction coefficient between the recording medium S and the rotary member. Therefore, in a case where the full color image by superimposing a plurality of different colors is formed on the recording medium S, the recording medium S is more likely to slip when comparing with a case where the toner image of monochromatic color is formed on the recording medium.

In this connection, it is noted that the oil barrier B is provided on the backup roller

130

in the image forming apparatus of this embodiment. Therefore, the recording medium S is unlikely to slip even when a full color image by superimposing a plurality of different colors is formed on the recording medium S (at least a chance of its slipping is remarkably reduced.). As a result, a stable fixing operation of the fixing device is ensured.

Thus, the image forming apparatus of the embodiment can form a full color image free from (at least with little) image disarrangement on the recording medium S.

Seventh Embodiment

FIG. 11

is a side view schematically showing an image forming apparatus which is a seventh embodiment of the present invention.

The image forming apparatus of this embodiment is different from that of the first embodiment in that the fixing device

100

(

FIG. 1

) is substituted by a fixing device

1001

. The remaing construction of the seventh embodiment is substantially the same as of the first embodiment.

FIG. 12

is a diagram schematically showing a major portion of the fixing device

1001

, and

FIG. 13

is a diagram showing a right side of a portion of the fixing device shown in FIG.

12

.

The fixing device

1001

includes a heating roller (fixing roller)

1101

with a heat source as a first rotary member, and an pressure application roller

1201

as a second rotary member which is pressed against the heating roller

1101

. A recording medium S passes through a part N

1

(usually a central part as viewed in the axial direction) of a press contact portion N between the endless belt

110

and the pressure application roller

120

. When passing therethrough, it is compressed by the belt and roller while being heated, whereby the toner image is fused and permanently fixed on the recording medium S.

The heating roller

1101

is formed with a pipe-like core member

1111

having a good thermal conductivity, an elastic layer

1121

which is formed on the surface of the core member

1111

, and a surface belt layer

1121

a

which is formed on a surface of the elastic layer

1121

and well separable from the recording member and toner. A halogen lamp

1131

as a heat source is disposed within the core member

1111

.

The pressure application roller

1201

is formed with a pipe-like core member

1211

having a good thermal conductivity, an elastic layer

1221

which is formed on the surface of the core member

1211

, and a surface belt layer

1221

a

which is formed on a surface of the elastic layer

1221

and well separable from the recording member and toner.

The pressure application roller

1201

is pressed against the heating roller

1101

by an appropriate urging mechanism

1231

(see FIG.

1

), and rotates in a follower fashion. Reference numeral

1241

designates a shaft

1241

of the pressure application roller

1201

.

A frame

1011

is provided with a guide

1021

which guides a recording medium S with a toner image T formed transferred) thereon at a secondary transfer portion T

2

to a press contact portion (nip) N between the heating roller

1101

and the pressure application roller

1201

.

One of the features of the present embodiment resides in that a high grip portion G is provided at a portion N

2

of one of both the rotary members, i.e., the heating roller

1101

and the pressure application roller

1201

, which is not pressed by the recording medium S but pressed by the other rotary member.

In this embodiment, as shown in

FIG. 13

, the high grip portion G is provided at the side end of the pressure application roller

1201

. The high grip portion G may be provided on the heating roller

1101

or both the heating roller

1101

and the pressure application roller

1201

.

The high grip portion G is preferably provided on both the side ends of the rotary member, although only one side end of the rotary member is illustrated in FIG.

13

. In the present embodiment, the high grip portions G are provided on both the side ends of the rotary member.

The high grip portion G may take a proper construction, and may take, for example, any of the high grip portions described in connection with

FIGS. 5 and 6

.

The image forming apparatus of the seventh embodiment of the invention operates in the following ways and produces the following useful effects.

(a) A toner image T is formed on a recording medium S. The recording medium S having the toner image T passes through a part N

1

(see

FIG. 3

) of the press contact portion N in the fixing device

1001

. As already stated, the fixing device

1001

is formed with the heating roller

1101

as a first rotary member to be heated and the pressure application roller

1201

as a second rotary member to be pressed against the heating roller

1101

. Of those rollers, the heating roller

1101

is driven, and the pressure application roller

1201

follows the heating roller

1101

in rotation.

Further, in this embodiment, the high grip portion G is provided at the portion N

2

of at least one of both the rotary members, which is the pressure application roller

1201

in this embodiment, which is not pressed by the recording medium S but pressed by the other rotary member (heating roller

1101

). Therefore, when a recording medium S, which relatively easily slips, is supplied to the part N

1

of the press contact portion N between the two rotary members, and as a result, when a slip will occur between the heating roller

1101

as the rotary member of the drive side and the recording medium S and/or the recording medium S and the pressure application roller

1201

as the rotary member of the follower side, both the rotary members

1101

and

1201

rotate at substantially equal peripheral speeds since the follower action of the pressure application roller

1201

of the follower side for the heating roller

1101

as the rotary member of the drive side is enhanced through the action of the high grip portion G. The slip is prevented (at least its occurrence is extremely infrequent). As a result, the fixing operation of the fixing device is stable. Accordingly, the toner image on the recording medium S is little blurred, so that the resultant image is little disarranged.

The high grip portions G are each provided at the portion which is not in pressing contact with the recording medium S. Therefore, the high grip portions do not have any adverse effect on the recording medium S and the image on the recording medium S.

(b) The image forming apparatus is designed so as to be capable of forming toner images on both sides of the recording medium S. Therefore, there is a case that a recording medium S having toner images on both sides thereof passes through the part N

1

of the press contact portion N in the fixing device

1001

.

As described, there is a case that the toner on the recording medium S reduces the friction coefficient between the recording medium S and the rotary member. Therefore, in a case where the toner images T are formed on both sides of the recording medium S, the recording medium is more likely to slip when comparing with a case where the toner image is formed on one side of the recording medium.

In this connection, it is noted that the high grip portion G is provided at the portion N

2

of at least one of both the rotary members

1101

and

1201

, which is not pressed by the recording medium but pressed by the other rotary member. Therefore, the recording medium S is unlikely to slip even when toner images T are formed on both sides of the recording medium S (at least a chance of its slipping is remarkably reduced.). As a result, a stable fixing operation of the fixing device is ensured.

Thus, the image forming apparatus of this embodiment is capable of forming images suffering from no (at least little) image disarrangement on both sides of the recording medium S.

(c) The image forming apparatus of the embodiment is capable of forming a full color image formed by superimposing a plurality of different colors. Therefore, there is a case that a recording medium S having a full color image formed on at least one side thereof passes through the part N

1

of the press contact portion N in the fixing device

1001

.

As described above, there is a case that the toner on the recording medium S reduces the friction coefficient between the recording medium S and the rotary member. Therefore, in a case where the full color image by superimposing a plurality of different colors is formed on the recording medium S, the recording medium S is more likely to slip when comparing with a case where the toner image of monochromatic color is formed on the recording medium.

In this connection, it is noted that the high grip portion G is provided at the portion N

2

of at least one of both the rotary members

1101

and

1201

, which is not pressed by the recording medium but pressed by the other rotary member. Therefore, the recording medium S is unlikely to slip even when a full color image by superimposing a plurality of different colors is formed on the recording medium S (at least a chance of its slipping is remarkably reduced.). As a result, a stable fixing operation of the fixing device is ensured.

Thus, the image forming apparatus of this embodiment is capable of forming a full color image suffering from no (at least little) image disarrangement, and full color images suffering from no (at least little) image disarrangement on both sides of the recording medium S.

Eighth Embodiment

FIG. 14

is a diagram schematically showing a major portion of the fixing device

1001

in the eighth embodiment of the present invention, and

FIG. 15

is a diagram showing a right side of a portion of the fixing device shown in FIG.

14

.

In those figures, like or equivalent portions are designated by like reference numerals used in the seventh embodiment.

The eighth embodiment of the present invention is different from the seventh embodiment in that an oil roller

1301

as an oil coating mechanism is provided which applies release oil to a contact portion N

1

of the heating roller

1101

where it is brought into contact with the recording medium S, and an oil barrier B is provided between the contact portion N

1

of the heating roller

1101

as a rotary member to be coated with the release oil by the oil roller

1301

and a portion N

2

of it where it is not in contact with the recording medium S but is pressed by the pressure application roller

1201

as another rotary member. The remaing construction of the eighth embodiment is substantially the same as of the seventh embodiment.

In this embodiment, the contact portion N

1

of the heating roller where it is in contact with the recording medium S is separated from the oil barrier B by a distance A. However, the separation of the distance A is not essential in this embodiment. If required, the contact portion N

1

may be extended to a position near the oil barrier B, as indicated by N

1

′ in FIG.

15

.

The oil roller

1301

, as shown in

FIG. 14

, includes a shaft

1311

and a thick, oil holder layer

1321

fastened around the shaft

1311

. The oil holder layer

1321

is made of porous material or fibrous material. The oil holder layer

1321

is impregnated with release oil. In order to secure a uniform coating of oil, the surface of the oil holder layer

1321

is coated with a thin film sheet having an oil permeability, such as a porous PTFE sheet

1331

.

The oil roller

1301

is pressed against the heating roller

1101

by an appropriate urging mechanism (not shown), and it is rotated in a follower manner to apply release oil, such as silicone oil, onto the surface of the heating roller

1101

. In this embodiment, as shown in

FIG. 15

, the oil roller

1301

is shorter in width than the heating roller

1101

, and the release oil is applied to only the contact portion N

1

of the heating roller where it is brought into contact with the recording medium S. The width of the contact portion of it, which is coated with the release oil by the oil roller

1301

, is longer than the width of the maximum image forming area on the recording medium S.

The oil barrier B may appropriately be constructed. In the embodiment, it takes the form of a ring-like groove

1151

formed around the heating roller

1101

. A ring-like groove

1251

, which is formed around the pressure application roller

1201

, also constitutes the oil barrier B. An oil absorbing member (e.g., a ring-like member made of felt) is preferably provided within each of the ring-like grooves

1151

and

1251

in order to absorb the oil having flowed into the groove.

It is preferable that a high grip portion is provided at the portion N

2

of one of the rotary members

1101

and

1201

which is not brought into contact with the recording medium S but is pressed against the other rotary member. In this embodiment, a high grip portion G, which is similar to that (either of those shown in

FIGS. 5 and 6

) of the seventh embodiment, is provided on the pressure application roller

1201

. The high grip portion G is preferably provided on both the side ends of the rotary member, although only one side end of the rotary member is illustrated in FIG.

15

. In the present embodiment, the high grip portions G are provided on both the side ends of the rotary member.

The image forming apparatus of the eighth embodiment of the invention operates in the following ways and produces the following useful effects.

(d) A toner image T is formed on a recording medium S. The recording medium S having the toner image T passes through a part N

1

of the press contact portion N in the fixing device

1001

. As already stated, the fixing device

1001

is formed with the heating roller

1101

as a first rotary member to be heated and the pressure application roller

1201

as a second rotary member to be pressed against the heating roller

1101

. Of those rollers, the heating roller

1101

is driven, and the pressure application roller

1201

follows the heating roller

1101

in rotation.

The oil roller

1301

as the oil coating mechanism for applying the release oil is provided at the contact portion N

1

of the heating roller

1101

where it is brought into contact with the recording medium S. Therefore, an offset phenomenon is unlikely to occur.

The oil barrier B is provided between the contact portion N

1

of it where it is brought into contact with the recording medium S and a portion N

2

of it where it is not in contact with the recording medium S but is pressed by the pressure application roller

1201

. The presence of the oil barrier B prevents such a situation that the release oil having been applied to the heating roller

1101

flows its contact portion N

1

with the recording medium S to the portion N

2

(at least its occurrence is extremely infrequent.).

For this reason, a gripping force is satisfactorily secured between both the rotary members at the contact portion N

2

.

Accordingly, both the rotary members

1101

and

1201

rotate at substantially equal peripheral speeds although such a construction is employed that the release oil is applied to the contact portion N

1

of one (heating roller

1101

in this case) of the rotary members where it is brought into contact with the recording medium S. Therefore, when a slip will occur between the heating roller

1101

as the rotary member of the drive side and the recording medium S and/or the recording medium S and the pressure application roller

1201

as the rotary member of the follower side, the slip is prevented (at least its occurrence is extremely infrequent). As a result, the fixing operation of the fixing device is stable. Accordingly, the toner image on the recording medium S is little blurred, so that the resultant image is little disarranged.

To be more specific, in a case where no measure is taken in the construction where the release oil is applied to the contact portion N

1

of the heating roller

1101

where it is brought into contact with the recording medium S, the release oil that has been applied to the heating roller

1101

moves from its contact N

1

with the recording medium S to “its portion N

2

where is not brought into contact with the recording medium S but is pressed against the pressure application roller

1201

”. As a result, a gripping force at the portion N

2

between the rotary members

1101

and

1201

is remarkably reduced, and the peripheral speeds of the rotary members

1101

and

1201

become different. A slip will occur between the heating roller

1101

of the drive side and the recording medium S and/or the recording medium S and the pressure application roller

1201

of the follower side. As a result, a stable fixing operation of the fixing device is lost.

On the other hand, in the image forming apparatus of this embodiment, presence of the oil barrier B prevents such a situation that the release oil that has been applied to the heating roller

1101

moves from its contact portion N

1

with the recording medium S to “its portion N

2

where is not brought into contact with the recording medium S but is pressed against the pressure application roller

1201

” (at least a probability of occurrence of the situation is remarkably reduced.). A gripping force is satisfactorily secured at the contact portion N

2

between the rotary members

1101

and

1201

. Therefore, the slip is prevented (at least its occurrence is extremely infrequent.) although such a construction is employed that the release oil is applied to the contact portion N

1

of one (the heating roller

1101

in this case) of the rotary members where it is brought into contact with the recording medium S. As a result, a stable fixing operation of the fixing device is secured. Accordingly, the toner image on the recording medium S is little blurred, so that the resultant image is little disarranged.

(e) The oil barrier B is provided between the contact portion N

1

of the pressure application roller

1201

as the other rotary member it where it is brought into contact with the recording medium S and a portion N

2

of it where it is not in contact with the recording medium S but is pressed by the heating roller

1101

. The presence of the oil barrier B prevents such a situation that the release oil, which was applied to the contact portion N

1

of the heating roller

1101

where it is brought into contact with the recording medium S and moved to the contact portion N

1

of the pressure application roller

1201

where it is brought into contact with the recording medium S, moves to the contact portion N

2

of the pressure application roller

1201

(at least a probability of occurrence of the situation is considerably reduced.).

Accordingly, a gripping force is satisfactorily secured at the contact portion N

2

between the rotary members

1101

and

1201

. Therefore, a stable fixing operation of the fixing device is secured. Accordingly, there is less chance that the toner image on the recording medium S is blurred, so that the resultant image is little disarranged.

(f) The high grip portion G is provided at the portion N

2

of at least one (the pressure application roller

1201

in this case) of the rotary members

1101

and

1201

, which is not pressed by the recording medium S but pressed by the other rotary member. With presence of the high grip portion, a gripping force is more satisfactorily secured at the contact portion N

2

between the rotary members

1101

and

1201

. As a result, a stable fixing operation of the fixing device is secured. Accordingly, there is less chance that the toner image on the recording medium S is blurred, so that the resultant image is little disarranged.

(g) The release oil, which is applied by the oil coating mechanism

1301

, is applied to within only the contact portion N

1

of it where it is brought into contact with the recording medium S. Therefore, the applied oil is almost all absorbed by or transferred to the recording medium S when the recording medium S passes through the contact portion N

1

.

Accordingly, a chance of moving of the release oil to the press contact portion N

2

where the rotary members are pressed one upon the other and is not brought into contact with the recording medium S, is further lessened. Therefore, a gripping force is more satisfactorily secured at the contact portion N

2

between the rotary members

1101

and

1201

. As a result, a stable fixing operation of the fixing device is secured. Accordingly, there is less chance that the toner image on the recording medium S is blurred, so that the resultant image is little disarranged.

(h) The image forming apparatus, like that of the seventh embodiment, is capable of forming toner images on both sides of the recording medium S. Therefore, there is a case that a recording medium S having toner images formed on both sides thereof passes through the part N

1

of the press contact portion N in the fixing device

1001

.

As described above, sometimes the toner on the recording medium S reduces the friction coefficient between the recording medium S and the rotary member. Therefore, in a case where the toner images T are formed on both sides of the recording medium S, the recording medium is more likely to slip when comparing with a case where the toner image is formed on one side of the recording medium.

In this connection, in the image forming apparatus of this embodiment, the oil barrier B is provided at least between the contact portion N

1

of the rotary member

1101

that is coated with the release oil by the oil coating mechanism

1301

, which the portion is brought into contact with the recording medium S, and the contact portion N

2

which is not brought into contact with the recording medium S but is pressed by the other rotary member

1201

. Therefore, even when the toner images T are formed on both sides of the recording medium S, the slip does not occur (at least its occurrence is extremely infrequent). As a result, a stable fixing operation of the fixing device is secured.

Thus, the image forming apparatus of this embodiment is capable of forming images suffering from no (at least little) image disarrangement on both sides of the recording medium S.

(i) The image forming apparatus of the embodiment, like that of the seventh embodiment, is capable of forming a full color image formed by superimposing a plurality of different colors. Therefore, there is a case that a recording medium S having a full color image formed on at least one side thereof passes through the part N

1

of the press contact portion N in the fixing device

1001

.

As described above, there is a case that the toner on the recording medium S reduces the friction coefficient between the recording medium S and the rotary member. Therefore, in a case where the full color image by superimposing a plurality of different colors is formed on the recording medium S, the recording medium S is more likely to slip when comparing with a case where the toner image of monochromatic color is formed on the recording medium.

In this connection, the oil barrier B is provided at least between the contact portion N

1

of the rotary member

1101

that is coated with the release oil by the oil coating mechanism

1301

, which the portion is brought into contact with the recording medium S, and the contact portion N

2

which is not brought into contact with the recording medium S but is pressed by the other rotary member

1201

. Therefore, even when the full color image by superimposing a plurality of different colors is formed on the recording medium S, the slip does not occur (at least its occurrence is extremely infrequent). As a result, a stable fixing operation of the fixing device is secured.

Thus, the image forming apparatus of this embodiment is capable of forming images suffering from no (at least little) image disarrangement, and forming images suffering from no image (at least little) disarrangement on both sides of the recording medium S.

Ninth Embodiment

FIG. 16

is a perspective view showing a major portion of a 9th embodiment of a belt fixing device (or image forming apparatus) according to the present invention. A basic construction of this fixing device

100

is similar to that shown in FIG.

8

. Therefore, like or equivalent portions are designated by like reference numerals in FIG.

8

.

The fixing device

100

also includes an endless belt

110

to be heated and an pressure application roller

120

as a rotary member to be in pressing contact with the endless belt

110

. A recording medium S having a toner image (not shown) formed thereon is moved to pass, as indicated by an arrow S

1

, through a central part N

1

of a press contact portion N between the endless belt

110

and the pressure application roller

120

, whereby the toner image is fused and permanently fixed on the recording medium S.

The drive roller for rotating the endless belt

110

and the respective rollers may be any of other rollers than the oil roller

150

. In the embodiment, the pressure application roller

120

is used as the drive roller. The pressure application roller

120

is driven to rotate in the direction of an arrow (counterclockwise) in

FIG. 8

by a drive mechanism, not shown, and the backup roller

130

, the endless belt

110

, the heating roller

140

and the oil roller

150

rotate in a follower manner. Specifically, the endless belt

110

and the backup roller

130

are pressed against the pressure application roller

120

, and the endless belt

110

and the backup roller

130

follow in rotation the pressure application roller

120

. The endless belt

110

is wound on the heating roller

140

, and the heating roller

140

follows in rotation the endless belt

110

. The oil roller

150

is pressed against the endless belt

110

, and the oil roller

150

follows in rotation the endless belt

110

.

The heating roller

140

is provided with guide rings

145

as restricting members which come in contact with the side edges of the fixing belt

110

to restrict such a behavior of the traveling fixing belt

110

as to move aside.

A feature of this embodiment resides in a structure of the endless belt

110

, and hence the structure of the endless belt will be described.

FIG. 17

is a view showing the endless belt

110

;

FIG. 17A

is a perspective view schematically showing the endless belt; and

FIG. 17B

is an enlarged view showing a portion (b) in FIG.

17

A. The endless belt

110

illustrated in those figures is the one before it is extended around the backup roller

130

and the heating roller

140

.

The endless belt

110

is formed with a belt base

1122

as a heat-resistance, mesh-like member and a surface belt layer

1132

made of high parting or release material. The surface belt layer

1132

is applied to at least the surface side (the right side in

FIG. 4B

) of a central portion

1122

a

of the belt base

1122

when viewed in th e widthwise direction (horizontal direction in

FIG. 17

, or the axial direction of each roller). Exposing portions

1122

b

are formed on both sides of the belt base

1122

, respectively.

As shown in

FIG. 17B

, in the mesh-like member that constitutes the belt base

1122

, a length L

1

of each mesh

1122

c

as measured along the circumferential direction is shorter than a length L

2

of the press contact portion N as measured along the circumferential direction (see FIG.

20

A). If the length L

1

of the mesh

1122

c

is selected to be longer than the length L

2

of the press contact portion N, a gripping action of a grip portion, which is to be described later, will be unsatisfactory. Accordingly, a heat-resistance cloth may be used for the belt base

1122

.

The mesh-like member may be formed with threads

1142

made of alamide fiber, polyimide, glass fiber and the like. Of the threads

1142

forming the mesh-like member, those extending in the widthwise direction of the belt (horizontal direction in

FIG. 17

) are threads each consisting of an aggregation of a plural number of very fine threads (called multi-filaments, for example). In this embodiment, the just-mentioned threads

1142

a

and those

1142

b

extending in the circumferential direction of the belt are the threads each consisting of an aggregation of a plural number of very fine threads.

It is preferable that the ends

1122

d

of the mesh-like member are each reinforced by use of a structure as shown in

FIG. 19A

or

19

C.

In the structure shown in

FIG. 19A

, to reinforce the end

1122

d

of the mesh-like member, it is covered with synthetic resin

1152

by dipping process. In the structure shown in

FIG. 19B

, to reinforce the end

1122

d

of the mesh-like member, a single thread (called mono-filaments) as a reinforcing member is wound around or attached to the end

1122

d

of the mesh-like member, and then the resultant is covered with synthetic resin

1152

by dipping process.

The surface belt layer

1132

is formed in a manner that the central portion

1122

a

of the belt base

1122

as viewed in the widthwise direction is coated with high release material (material exhibiting good release characteristics for recording material and toner). In this embodiment, as shown in

FIG. 18B

, in the coating of the high release material, the high release layer is formed ranging up to the back side

1132

b

of the belt base

1122

as the mesh-like member. Filling the meshes

1122

c

(see

FIG. 17B

) of the belt base

1122

(the close meshes when the belt base

1122

is made of cloth) with the high release material to such an extent that the surface of the surface belt layer

1132

is smoothed, will do for the coating. Accordingly, in the coating, the belt base

1122

may be partially exposed on the back side

1132

b

thereof as indicated by a phantom line

1132

′ in

FIG. 18B

, for example. In a case where the belt base

1122

is made of cloth, the back side of the belt base

1122

is easy to be exposed.

A material having a permeability to the release oil (i.e., a material allowing the release oil to permeate therethrough) is preferable for the high release material. In this embodiment, such a material (as silicone rubber, fluorine rubber, fluorine plastic or the like) is used for the high release material.

The image forming apparatus of the sixth embodiment of the invention operates in the following ways and produces the following useful effects.

(a) A recording medium S having a toner image (not shown) formed thereon is moved to pass through a central part N

1

of a press contact portion N between the endless belt

110

and the pressure application roller

120

, whereby the toner image is fused and permanently fixed on the recording medium S. The endless belt

110

and the pressure application roller

120

are arranged such that one of them is driven while the other rotates following the one, and that the endless belt

110

is to be heated, and the pressure application roller

120

is pressed against the endless belt

110

.

The endless belt

110

is formed with a belt base

1122

as cloth or a mesh-like member of which the meshes

1122

c

each have a length shorter than a length L

2

of the press contact portion N as measured in the circumferential direction, and a surface belt layer

1132

made of high release material, which is applied to at least the surface side of a central portion

1122

a

of the belt base

1122

when viewed in the widthwise direction of the belt base, wherein the belt base

1122

includes exposing portions

1122

b

which are located at both side ends of the belt base

1122

. Therefore, the surface belt layer

1132

forms a fixing surface

1132

a

for the toner image and the exposing portions

1122

b

form high grip portions, which act on the pressure application roller

120

.

Accordingly, when a recording medium S, which relatively easily slips, is supplied to the central part N

1

of the press contact portion N between the endless belt

110

and the pressure application roller

120

, and as a result, when a slip will occur between the pressure application roller

120

of the drive side and the recording medium S and/or the recording medium S and the endless belt

110

of the follower side, the endless belt

110

and the pressure application roller

120

rotate at substantially equal peripheral speeds since the follower action of the endless belt

110

of the follower side for the pressure application roller

120

of the drive side is enhanced through the operation of the high grip portions, or the exposing portions

1122

b

. Therefore, the slip is prevented (at least its occurrence is extremely infrequent). As a result, the fixing operation of the fixing device is stable. Accordingly, the toner image on the recording medium S is little blurred, so that the resultant image is little disarranged.

It is noted that the high grip portion is formed by merely forming the exposing portions

1122

b

at both ends of the belt base

1122

itself. Therefore, the high grip portion of the embodiment is superior in strength to a high grip portion (not shown) additionally provided on the belt base

1122

. In this respect, a reliability of the fixing device is increased. Further, the high grip portion of the embodiment may be manufactured more easily manufactured than to a high grip portion (not shown) additionally provided or formed on the belt base

1122

.

(b) The oil coating mechanism

150

for coating the surface of the endless belt

110

with release oil is provided, so that an offset phenomenon is unlikely to occur.

As already stated, where the surface of the endless belt

110

is coated with the release oil, the oil will gradually move to the ends of the press contact portion N between the endless belt

110

and the pressure application roller

120

.

This will be described in detail with reference to

FIGS. 20 and 21

.

FIG. 20A

is a side view showing an operation of the fixing device including the endless belt.

FIG. 20B

is an enlarged view of a part of the fixing device.

FIG. 21A

is a front view showing the fixing device.

FIG. 21B

is an enlarged view of a part of the fixing device (corresponding to a cross sectional view taken on line XXIb—XXIb in FIG.

20

B).

In

FIGS. 21A and 21B

, a zone denoted as A is a paper-passing zone within which a recording medium S is brought into contact with the endless belt

110

and the pressure application roller

120

.

As shown in

FIG. 20B

, when the surface of the endless belt

110

, viz., the surface

1132

a

of the surface belt layer

1132

, is coated with release oil O, the release oil O comes in contact with the recording medium S within the zone A, so that it is absorbed by or transferred to the recording medium S. The release oil O located out of the zone A is not absorbed by and not transferred to the recording medium S. Therefore, as shown in

FIGS. 20 and 21

, it stays as surplus oil O

1

at both ends of the paper-passing zone A at a position before the press contact portion N between the endless belt

110

and the pressure application roller

120

(upstream) as viewed in the paper traveling direction. The surplus oil O

1

staying there moves to and reaches both ends N

2

along the press contact portion N to its both ends N

2

. The surplus oil that has reached both ends N

2

is denoted as

2

.

As already stated, if no measure is taken for such surplus oil O

2

, a gripping force between the fixing belt

110

and the pressure application roller

120

decreases and a slip will occur.

In this connection, in the fixing device of this embodiment, the belt base

1122

is exposed (

1122

b

) at both ends N

2

of the press contact portion N. Further, the belt base

1122

is made of cloth or a mesh-like member of which the threads

1142

a

extending in the widthwise direction are formed with threads each consisting of an aggregation of a plural number of very fine threads. The oil having reached each end N

2

of the press contact portion N penetrates into the threads

1142

a

each consisting of an aggregation of a plural number of very fine threads of the cloth or the mesh-like member (also to the threads

1142

b

in this embodiment).

Accordingly, a little amount of the release oil is present on the surface of both ends

1122

b

of the belt base

1122

. As a result, a gripping force is satisfactorily secured at the both ends N

1

of the press contact portion. The slip is prevented (at least its occurrence is extremely infrequent.). A stable fixing operation of the fixing device is performed.

Thus, the belt fixing device of this embodiment stably operates for fixing the toner image although it employs such a construction that the surface of the fixing belt

110

is coated with the release oil O.

(c) The high release material of the surface belt layer

1132

has a permeability to the release oil. Because of this nature, the oil O having being applied to the surface

1132

a

of the surface belt layer

1132

penetrates into the surface belt layer

1132

as indicated by arrows O

4

in

FIG. 20B

, and then to the threads

1142

a

and

1142

b

each consisting of an aggregation of a plural number of very fine threads in the cloth or the mesh-like member, and retained in the cloth or the mesh-like member. The retained oil O oozes, by its pressure, out of the cloth or the threads at the press contact portion N (in particular the central part N

1

) as indicated by arrows O

6

in FIG.

20

B and

FIGS. 21A and 21B

, and further reaches the surface

1132

a

, or the fixing surface, of the surface belt layer

1132

to form an oil thin film

07

(see

FIG. 20B

) on the fixing surface. As a result, the oil film is uniformized on the fixing surface, so that a toner image fixed thereon is improved in its quality.

The release oil O

8

having permeated into the ends

1122

b

of the belt base

1122

moves, as indicated by arrows O

9

, back to the central portion

1122

a

of the belt base

1122

through the widthwise-extending threads

1142

a

of the cloth or the mesh-like member which forms the belt base

1122

. This reduces consumption of the release oil. That is, the release oil is absorbed by the recording medium in the paper-passing zone A, i.e., the central portion

1122

a

. Therefore, an amount of the permeated oil in the zone is smaller than that at the ends thereof. As a result, the release oil moves back to the central portion of the belt base, from the ends thereof.

In a case where the fixing operation is not performed for a certain time, and the surplus oil will stay at a region near the press contact portion N, the oil permeates into the surface belt layer

1132

, and to the threads

1142

a

each of an aggregation of a plural number of very fine threads in the cloth or the mesh-like member of the belt base

1122

, and is retained in the cloth or the mesh-like member. And a part of the retained release oil flows back to the central portion of the surface belt layer. Therefore, when the fixing operation is not performed for a certain time and then it is operated again, there is less chance that a first recording medium will be soiled by the surplus oil.

10th Embodiment

A basic construction of a fixing device

100

which constitutes an eighth embodiment of the present invention is substantially the same as of the fixing device shown in

FIGS. 8 and 16

. Then, like or equivalent portions are designated by like reference numerals.

A feature of the present embodiment resides in a structure of an fixing belt

110

, and hence the structure of the fixing belt will be described.

FIG. 22A

is a partial perspective view showing the fixing belt

110

(before it extends around the backup roller

130

and the heating roller

140

).

FIG. 22B

is a front view showing a tape-like, high grip member.

FIG. 23A

is a cross sectional view taken on line XXIIIa—XXIIIa in FIG.

22

.

The fixing belt

110

, which is a heat-resistance belt, is formed with an fixing belt base

1123

and a surface belt layer

1133

which is applied to at least the surface side (the right side in

FIG. 4B

) of a central portion

1123

a

of the belt base

1123

when viewed in the widthwise direction (horizontal direction in

FIG. 16

, or the axial direction of each roller). Tape-like, high grip members G are wound around both side ends

1123

b

of the belt base

1123

, respectively.

The belt base

1123

is made of, for example, polyimide being conductive.

The surface belt layer

1133

is formed by coating the central portion

1123

a

of the belt base

1123

as viewed in the widthwise direction with high release material (which exhibits good release characteristics to a recording medium and toner, and is silicone rubber, for example).

The tape-like, high grip member (referred to as a high grip tape) G may be made of any of various materials which will be described later and may take any of various structures which will also be described later. The high grip tape G may also be a tape simply having a rugged surface (or a protruded or recessed surface) and made of high friction material, such as rubber.

In this embodiment, a high grip tape G as shown in

FIG. 22B

is wound around each side end

1123

b

of the belt base

1123

and fastened thereto by adhesive.

Also in this embodiment, the high grip tape is wound on each side end of the belt base such that, as shown in

FIGS. 22A and 23A

, a winding start end G

11

at which the winding of the high grip tape G starts is not lapped on a winding terminating end G

21

at which its winding terminates. Accordingly, a gap L is present between the winding start end G

11

and the winding terminating end G

21

. It is preferable that the gap L is as small as possible (at least it is shorter than a length (measured in the circumferential direction) of the press contact portion N between the fixing belt

110

and the pressure application roller

120

).

The high grip tape G may be wound on each side end of the belt base such that the winding start end G

11

laps on the winding terminating end G

21

., and the former is fastened to the latter, as shown in FIG.

23

B.

The fixing device

100

of this embodiment has the following advantageous effects.

(a) A recording medium S having a toner image formed thereon is moved to pass through a central part N

1

of a press contact portion N between the fixing belt

110

and the pressure application roller

120

in a belt roller arrangement in which the fixing belt

110

is heated and the pressure application roller

120

as a rotary member is pressed against the fixing belt

110

, and one of the fixing belt

110

and the pressure application roller

120

is driven to rotate while the other follows the one in rotation. As a result, the toner image is fused and permanently fixed on the recording medium S.

The high grip tape G is wound around each side end of the fixing belt and fastened thereto. As a result, high grip portions (G) which act on the pressure application roller

120

, are formed at both side ends of the fixing belt

110

.

Therefore, when a recording medium S, which relatively easily slips, is supplied to the central part N

1

of the press contact portion N between the fixing belt

110

and the pressure application roller

120

, and as a result, when a slip will occur between the pressure application roller

120

of the drive side and the recording medium S and/or the recording medium S and the fixing belt

110

of the follower side, the fixing belt

110

and the pressure application roller

120

rotate at substantially equal peripheral speeds since the follower action of the fixing belt

110

of the follower side for the pressure application roller

120

of the drive side is enhanced through the operation of the high grip portions G. Therefore, the slip is prevented (at least its occurrence is extremely infrequent). As a result, the fixing operation of the fixing device is stable. Accordingly, the toner image on the recording medium S is little blurred, so that the resultant image is little disarranged.

(b) Further, the high grip portions may be formed in such a simple manner that the high grip tapes G are wound around both the side ends of the fixing belt

110

and are fastened to the side ends. Therefore, the manufacturing of the fixing belt

110

(hence the fixing device) is simpler than in the case where ring-like, high grip members (not shown) are fit to both side ends of the belt

110

or where the side ends themselves of the belt are worked to be high grip portions.

(c) Further, the fixing device

100

of the embodiment has the following advantageous effects since the winding start end G

11

of the high grip tape G is not lapped on the winding terminating end G

21

.

As already stated in connection with

FIG. 23B

, when the winding start end G

11

of the high grip tape G is lapped on the winding terminating end G

21

, the lapping portion G

31

is thick. Therefore, a speed of the turning fixing belt

110

when the lapping portion G

31

is pressed on the pressure application roller

120

will be different from that when the lapping portion G

31

is not pressed on the pressure application roller

120

.

When the lapping portion G

31

is pressed against the pressure application roller

120

, stress will concentrate at a portion of the pressure application roller

120

where it is in contact with the lapping portion G

31

. As a result, an endurance of the pressure application roller

120

will be reduced.

In this connection, the winding start end G

11

of the high grip portion G is not lapped on the winding terminating end G

21

in the belt fixing device

100

of this embodiment. Because of this, the speed of the turning belt fixing belt

110

little varies. Additionally, little stress concentrates on the specific location of the pressure application roller

120

, so that the endurance of the pressure application roller

120

is little reduced.

(d) The oil coating mechanism

150

for coating the surface of the fixing belt

110

with release oil is provided, so that an offset phenomenon is unlikely to occur.

As already stated, where the surface of the fixing belt

110

is coated with the release oil, the oil will gradually move to the ends of the press contact portion N between the fixing belt

110

and the pressure application roller

120

. However, in this embodiment, the above-mentioned slip is unlikely to occur since the high grip tapes G are provided on both the side ends of the fixing belt

100

.

A width of the oil coating on the fixing belt by the oil roller

150

is preferably shorter than the width of the surface belt layer

1133

, or the paper-passing width (the width of the recording medium S).

11th Embodiment

FIG. 24

is a diagram showing a major portion of an 11th embodiment of a belt fixing device according to the present invention.

FIG. 24A

is a partial front view showing a fixing belt

110

constructed according to the present invention.

FIG. 24B

is a development of a tape-like, high grip member G. In

FIG. 24

, like or equivalent portions are designated by like reference numerals used in the 10th embodiment already described.

The 11th embodiment of the invention is different from the 10th embodiment in that the winding start end G

11

of the high grip member G is confronted with the winding terminating end G

21

in a state that a gap L slanted to the axial direction of the pressure application roller is interposed therebetween. The remaing structure of the 11th embodiment is substantially the same as of the 10th embodiment. Thus, the winding start end G

11

and the winding terminating end G

21

of the high grip member G are not in parallel to the axial direction of the pressure application roller

120

, and is also slanted to the circulating direction of the fixing belt

110

.

The present embodiment has the following operations and advantageous effects in addition to the corresponding ones of the 10th embodiment.

If the winding start end G

11

and the winding terminating end G

21

of the high grip member G are not slanted (with respect to, for example, the width direction of the fixing belt

110

or the axial direction of the pressure application roller

120

), a traveling speed of the fixing belt

110

when the gap L between the winding start end G

11

and the winding terminating end G

21

is in contact with the pressure application roller

120

will be different from that when it is not in contact with the pressure application roller

120

. If the gap L in the 10th embodiment is longer than the length of the press contact portion N between the fixing belt

110

and the pressure application roller

120

as viewed in the circumferential direction, a probability of creating the above-mentioned speed difference will increase.

On the other hand, a probability of creating the above-mentioned speed difference of the fixing belt

110

of the follower side is small in the 11th embodiment since the winding start end G

11

of the high grip member G is confronted with the winding terminating end G

21

in a state that the gap L slanted to the axial direction of the pressure application roller is interposed therebetween.

12th Embodiment

FIG. 25

is a diagram showing a major portion of a 12th embodiment of a fixing belt according to the present invention.

FIG. 25A

is an exploded, perspective view showing one end of a fixing belt

110

constructed according to the invention (before the fixing belt

110

extends around the backup roller

130

and the heating roller

140

).

FIG. 25B

is a side view showing the belt end.

FIG. 25C

is a perspective view of the belt end.

FIG. 25D

is a side view showing the belt end.

This embodiment is different from the 10th embodiment in that a high grip portion G is formed with an expandable member shaped like an endless belt (referred to as a belt-like high grip member). The belt-like high grip member has an inside diameter smaller than an outside diameter of each side end

1123

b

of the fixing belt when it is in a free state. As shown in

FIGS. 25A and 25B

, by the utilization of its expandability, the belt-like high grip member G is expanded to be somewhat larger than the outside diameter

1123

b

of the belt base

1123

, and is fit to each side end

1123

b

with an adhesive layer

1153

being interposed therebetween, and is fastened to each side end

1123

b

of the belt base

1123

by its expandability and by use of the adhesive layer

1153

.

The fixing belt

110

of this embodiment additionally produces the following advantageous effects.

As described above, the high grip portion G is formed with an expandable endless belt having an inside diameter smaller than an outside diameter of each side end

1123

b

of the fixing belt when it is in a free state. Therefore, by the utilization of its expandability, the belt-like high grip member is expanded and fit to the side ends

1123

b

of the fixing belt

110

to form a high grip portion G well fit to and around the side ends

1123

b

of the fixing belt

110

.

Where the tape-like high grip member, or the high grip tape, is wound around each side end of the fixing belt

110

, there is a fear that high grip tape is easy to peel off the belt at its seam (between the winding start and terminating ends). In the fixing belt in this embodiment, such a fear is not present and the belt-like high grip member doubles as a reinforcing member for the side end of the fixing belt. In this respect, a reliability of the fixing belt is increased. As a result, the fixing belt

110

may be thinned in structure. The fixing belt

110

well follows an unevenness corresponding to the amounts of attached toner forming a toner image. This results increase of a fixing strength or a fixing uniformity. Further, a heat capacity of the fixing belt

110

is small, so that it may be heated quickly.

The high grip portions may be formed in such a simple manner that the belt-like high grip members G are wound around both the side ends of the fixing belt

110

and are fastened to the side ends. Therefore, the manufacturing of the fixing belt

110

is simpler than in the case where the side ends themselves of the belt are worked to be high grip portions.

13th Embodiment

FIG. 26

is a diagram showing a key portion of a 13th embodiment of a belt fixing device constructed according to the present invention.

FIG. 26A

is a cross sectional view showing a part of a fixing belt

110

(before the fixing belt

110

extends around the backup roller

130

and the heating roller

140

, and corresponds to the XXVIa—XXVIa cross section in FIG.

24

A).

FIGS. 26B and 26C

are enlarged views of a portion of the fixing belt. In

FIG. 26

, like or equivalent portions are designated by like reference numerals used in the 10th to 12th embodiments already described.

A feature of the present embodiment resides in that high grip portions G are made of cloth.

The cloth G is formed by knitting or weaving threads

1143

a

and

1143

b

that run crosswise and lengthwise, and includes a mesh-like member with very fine meshes. Further, it may be unwoven fabric as shown in FIG.

27

.

The threads (weft and warp)

1143

may be formed with single threads (, e.g., called mono-filaments) as shown in

FIG. 26B

or threads each consisting of an aggregation of a plural number of very fine threads (called multi-filaments, for example). The threads

1143

may be made of any of alamide, polyimide, glass fiber, PET (polyethylene terephthalate) and the like.

Also when the threads

1143

are formed with single threads as shown in

FIG. 26B

, oil may be retained in empty spaces C

1

each between adjacent threads

1143

. Accordingly, the cloth G has an oil absorption. When each of the threads

1143

consists of an aggregation of a plural number of very fine threads as shown in

FIG. 26C

, the oil is absorbed by and retained in the innards of the threads

1143

themselves. Therefore, to increase the oil absorption, it is preferable to use the threads

1143

each consisting of an aggregation of a plural number of very fine threads. It is preferable that at least one of the weft

1143

a

and the warp

1143

b

is formed with the threads each consisting of an aggregation of a plural number of very fine threads.

The empty spaces C

1

extend vertically in

FIG. 26

, and are continuous in the belt circumferential direction (perpendicular to a paper surface in the drawing of FIG.

26

). Therefore, the cloth G is permeable to the oil, and allows the oil to flow in the belt circumferential direction.

The cloth G may be an unwoven fabric (e.g., alamide unwoven fabric) as shown in FIG.

27

. The unwoven fabric is also capable of absorbing the oil and is permeable to the oil, and allows the oil to flow in the belt circumferential direction.

In

FIGS. 26 and 27

, reference numeral

1153

is an adhesive layer (e.g., adhesive) for fastening the cloth G to the belt base

1123

.

The fixing device

100

of this embodiment operates in the following ways and produces the following advantageous effects.

Since the high grip portion is formed with the cloth G, a surface G

41

(see

FIG. 26

) of the high grip portion is defined by a number of vertical and horizontal fine ridges of the threads

1143

running crosswise and lengthwise. The fine ridge crossing pattern spreads substantially uniformly over the surface G

41

.

A vibration and a speed variation, which are generated at both ends of the fixing belt

110

by a drive force transmission, are extremely reduced, thereby ensuring a smooth drive force transmission.

Since the fine ridge crossing pattern are formed by the threads

1143

, each ridge is rounded in cross section. With this configuration of the ridges, the stress concentration is lessened, and hence the endurance of the pressure application roller

120

is increased.

Further, the high grip portion of this embodiment is superior to that formed with a rubber member of an uneven surface in the strength (particularly to shearing).

To be more specific, in the case of the high grip portion G made of a film or a rubber member, for example, when a shearing force is applied to its edge, the edge first cracks, and then the crack rapidly propagates and the high grip portion is finally broken. In the case of the high grip portion G made of the cloth, when the fiber (thread)

1143

at the edge of the cloth cracks to be broken, the breakage of the fiber does not propagates. That is, only one fiber at the edge is broken.

When the side edge of the belt is brought into contact with the inner surface (

145

a

) of a flange (the guide ring

145

of the heating roller

140

shown in

FIG. 16

) of the roller on which the fixing belt

110

is put in order to restrict a zig-zag traveling of the fixing belt

110

, a shearing force acting on the side edge of the belt is great in magnitude. In this fixing device, the high grip portions of cloth are provided on both side ends of the fixing belt. Therefore, the high grip portion G is unlikely to be broken and propagation of the breakage to the whole fixing belt

110

is also greatly impeded.

In this embodiment, an offset phenomenon is unlikely to occur since the oil coating mechanism

150

for applying the release oil onto the surface of the fixing belt

110

is provided.

As already stated, where the surface of the fixing belt

110

is coated with the release oil, the oil will gradually move to the ends N

2

of the press contact portion N between the fixing belt

110

and the pressure application roller

120

. However, in this embodiment, the oil having reached the ends N

2

of the press contact portion N is absorbed by the cloth G since the cloth G are fastened around both the side ends of the fixing belt

110

in the fixing device

100

and the cloth G has an oil absorbing capability.

Therefore, the amount of oil present on the surfaces of both the side ends of the fixing belt

110

, viz., the surfaces G

41

of the cloth G of the high grip portions G, is small. As a result, a gripping force is satisfactorily secured at the ends N

2

of the press contact portion N. The slip is prevented (at least its occurrence is extremely infrequent), and a stable fixing operation of the fixing device is secured.

Thus, the fixing device

100

of this embodiment is able to stably fix the toner image although the surface of the fixing belt

110

is coated with the release oil.

Such an effect is produced not only when the high grip member G is made of cloth but also when it is made of a material having an oil absorbing capability.

As recalled, the cloth G allows the oil to flow in the belt circumferential direction. Therefore, if the cloth G is saturated with the oil, the oil entering the cloth G is moved in the belt circumferential direction and excluded out of the ends N

2

of the press contact portion by the pressing force applied thereto.

Therefore, if the cloth G is saturated with the oil, the amount of oil present on the surfaces G

41

of the cloth G of the high grip portions G at both the side ends of the fixing belt

110

is small at the press contact portion. As a result, a gripping force is satisfactorily secured at the ends N

2

of the press contact portion N. The slip is prevented (at least its occurrence is extremely infrequent), and a stable fixing operation of the fixing device is secured.

This effect is produced not only when the high grip member G is made of cloth but also when it is made of a material allowing the oil to flow in the belt circumferential direction.

14th Embodiment

FIG. 28

is a diagram showing a 14th embodiment of a belt fixing device according to the present invention.

FIG. 28A

is a partial, enlarged front view showing one end of a fixing belt

110

.

FIG. 28B

is a cross sectional view taken on line b—b in FIG.

28

A.

In

FIG. 28

, like or equivalent portions are designated by like reference numerals used in the 10th to 13th embodiments already described.

A feature of this embodiment resides in that a high grip member G is fastened to the fixing belt with a flexible adhesive layer

1163

being interposed therebetween.

As shown in

FIG. 28B

, an outside diameter D

2

of the high grip member G is larger than that D

1

of the surface belt layer

1133

.

In the embodiment, the outside diameter D

2

of the high grip member G is set to be larger than that D

1

of the surface belt layer

1133

by selecting a thickness t

2

of each of the adhesive layer

1163

and the high grip member G to be larger than a thickness t

1

of the surface belt layer

1133

.

The high grip member G in this embodiment is made of cloth as described in the 13th embodiment (FIGS.

26

and

27

).

The adhesive layer

1163

is a flexible adhesive layer made of adhesive capable of absorbing the release oil (e.g., silicone adhesive).

The fixing device

100

of this embodiment produces the following advantageous effects.

As described above, the outside diameter D

2

of the high grip member G is larger than that D

1

of the surface belt layer

1133

. Therefore, at the ends N

2

of the press contact portion N between the fixing belt

110

and the pressure application roller

120

, the high grip members G are pressed against the pressure application roller

120

by a larger pressing force, as shown in FIG.

29

. Accordingly, a gripping force is satisfactorily secured between the fixing belt

110

and the pressure application roller

120

. And the slip is prevented with certainty (at least its occurrence is extremely infrequent.). As a result, a stable fixing Operation of the fixing device is secured.

The high grip member G is fastened to the fixing belt with the flexible adhesive layer

1163

being interposed therebetween. This feature yields the following advantageous effects.

In this type of the fixing device, during its operation, the fixing belt

110

is heated to be at high temperature (150° C. to 200° C., for example). If the adhesive layer which fastens the high grip member G to each side end of the fixing belt

110

is not flexible, a thermal expansion coefficient difference between the fixing belt

110

and the high grip member G will create the following problem: the belt end is easy to be broken or the high grip member G is easy to peel off the fixing belt.

In this connection, in the fixing device of this embodiment, the adhesive layer which fastens the high grip member G to each side end of the fixing belt

110

is flexible, the thermal expansion coefficient difference between the fixing belt

110

and the high grip member G is soaked up by the adhesive layer

1163

. Therefore, there is no chance that the ends of the fixing belt

110

are broken or the high grip member G peels off the belt. The result is increase of the endurance of the fixing belt

110

.

As already stated, where the surface of the fixing belt

110

is coated with the release oil, the oil will gradually move to the ends N

2

of the press contact portion N between the fixing belt

110

and the pressure application roller

120

. However, in this embodiment, the oil having reached the ends N

2

of the press contact portion N is absorbed by the high grip member G since the high grip members G are fastened around both the side ends of the fixing belt

110

in the fixing device

100

and the high grip members G have an oil absorbing capability.

Therefore, the amount of oil present on the surfaces of both the side ends of the fixing belt, viz., the surfaces G

41

of the cloth G of the high grip members, is small. As a result, a gripping force is satisfactorily secured at both the ends of the press contact portion. The slip is prevented (at least its occurrence is extremely infrequent), and a stable fixing operation of the fixing device is secured.

Thus, the fixing device

100

of this embodiment is able to stably fix the toner image although the surface of the fixing belt

110

is coated with the release oil.

As recalled, the high grip member G has an oil absorbing capability and allows the oil to flow in the belt circumferential direction. Therefore, if the cloth G is saturated with the oil, the oil entering the high grip member G is moved in the belt circumferential direction and excluded out of the ends N

2

of the press contact portion (in the vertical direction in

FIG. 28A

) by the pressing force applied thereto.

Therefore, if the high grip member G is saturated with the oil, the amount of oil present on the surfaces G

41

of both the side ends of the fixing belt

110

, is small at the press contact portion N

2

. As a result, a gripping force is satisfactorily secured at both the ends N

2

of the press contact portion. The slip is prevented (at least its occurrence is extremely infrequent), and a stable fixing operation of the fixing device is secured.

The high grip member G is permeable to the oil, and capable of absorbing the oil. Accordingly, the oil having entered the ends N

2

of the press contact portion N is absorbed by the adhesive layer

1163

through the high grip members G.

Therefore, the amount of oil present on the surfaces G

41

of both the side ends of the fixing belt

110

, is small. As a result, a gripping force is satisfactorily secured at both the ends of the press contact portion. The slip is prevented (at least its occurrence is extremely infrequent), and a stable fixing operation of the fixing device is secured.

15th Embodiment

FIG. 30

is an enlarged view showing one end of a fixing belt in a 15th embodiment of a belt fixing device according to the present invention. In the figure, like or equivalent portions are designated by like reference numerals used in the 10th to 15th embodiments already described.

This embodiment is different from those 10th to 14th embodiments in that the high grip member G is made of open-cell (or continuous-cell) porous material (e.g., silicone sponge). The remaing structure of this embodiment is substantially the same as of each of those embodiments. In the figure, an open-cell portion is denoted as C

3

.

The high grip member G made of the open-cell porous material is also capable of absorbing the release oil, allows the oil to flow in the belt circumferential direction, and is permeable to the oil, by the property of the open-cell portion G

3

.

Therefore, this embodiment also produces the advantageous effects comparable with those by the 14th embodiment (except the effects by the cloth used for the high grip member G).

16th Embodiment

FIGS. 31A and 31B

show a key portion of a 16th embodiment of the present invention:

FIG. 31A

is a plan view showing a part of a fixing belt

110

; and

FIG. 31B

is a cross sectional view taken on line b—b in FIG.

31

A. In the figure, like or equivalent portions are designated by like reference numerals used in the 10th to 14th embodiments already described.

This embodiment is different from the 10th to 14th embodiments in that a high grip member G is made of a heat-resistance sheet made of synthetic resin containg a number of empty spaces (or cavities) C

2

each extending in the direction orthogonal to the belt surface (vertical direction in FIG.

31

A), the lateral direction (horizontal direction in FIG.

31

A), and longitudinal direction (vertical direction in FIG.

31

A).

The heat-resistance sheet made of synthetic resin has also an uneven surface, and forms the high grip member G, and is also capable of absorbing the release oil, allows the oil to flow in the belt circumferential direction, and is permeable to the oil because of presence of the empty spaces C

2

.

Therefore, this embodiment also produces the advantageous effects comparable with those by the 14th embodiment (except the effects by the cloth used for the high grip member G).

17th Embodiment

FIGS. 31C and 31D

show a key portion of a 17th embodiment of the present invention:

FIG. 31C

is a plan view showing a part of a fixing belt

110

; and

FIG. 31D

is a cross sectional view taken on line d—d in FIG.

31

C. In the figure, like or equivalent portions are designated by like reference numerals used in the 10th to 14th embodiments already described.

This embodiment is different from the 10th to 14th embodiments in that a high grip member G is made of a heat-resistance sheet made of synthetic resin containg a number of perforations (or through-holes) C

4

. The remaing structure of this embodiment is substantially the same as of each of those embodiments.

The heat-resistance sheet made of synthetic resin has also an uneven surface, and forms the high grip member G, and is also capable of absorbing the release oil, and is permeable to the oil because of presence of the perforations C

4

.

Therefore, this embodiment also produces the advantageous effects comparable with those by the 14th embodiment (except the effects by the cloth used for the high grip member G and by the oil-flow permitting ability in the belt circumferential direction).

18th Embodiment

FIG. 32A

shows a key portion of an 18th embodiment of the present invention and is a cross sectional view showing one end of a fixing nip portion N. In the figure, like or equivalent portions are designated by like reference numerals used in the 10th to 14th embodiments already described.

This embodiment is different from the 10th to 14th embodiments in that each end of a high grip member G as viewed in the width direction (horizontal direction in

FIG. 32A

) is beveled (or chamfered) as indicated by G

6

. The remaing structure of this embodiment is substantially the same as of each of those embodiments.

When a high grip member G having a double layer structure of mesh members or high grip member G formed with cloth is beveled at each end, the beveled face G

6

is as shown in FIG.

33

.

In this embodiment, each end of a high grip member Gas viewed in the width direction is beveled (indicated by G

6

). With the beveled end faces, the stress concentration on the pressure application roller

120

by the ends (G

6

) of the high grip member G is lessened, and hence the endurance of the pressure application roller

120

is increased, although this embodiment has such a construction that the outside diameter of the high grip member G is larger than that of the surface belt layer

1133

, and therefore, at the ends N

2

of the press contact portion N between the fixing belt

110

and the pressure application roller

120

, the high grip members G are pressed against the pressure application roller

120

by a larger pressing force.

As shown in

FIG. 32B

, in the 10th to 17th embodiments, it is allowed that each end of a high grip member G as viewed in the width direction is not beveled. If not beveled, stress will concentrate on the pressure application roller

120

at its press contact portion with the ends G

5

of the high grip member. This leads to reduction of the endurance of the pressure application roller

120

. In this sense, that the ends of the high grip members are not beveled is not suggestible.

19th Embodiment

FIG. 34

is a perspective view showing a key portion of a 19th embodiment of the present invention. In the figure, like or equivalent portions are designated by like reference numerals used in the 18th embodiment.

A feature of this embodiment resides in that each beveled surface G

6

is smoothed.

The beveled surface G

6

may be smoothed in a manner that the beveled surface G

6

is coated with fluorine resin or silicone resin, or that each end surface

6

is heated and molten to be slanted.

This embodiment further increases the endurance of the pressure application roller

120

since the beveled surface G

6

is smoothed.

20th Embodiment

FIG. 35A

is an enlarged front view showing a part of a fixing belt

110

in a 20th embodiment of the present invention, and

FIG. 35B

is a cross sectional view taken on line b—b in FIG.

35

A.

FIG. 36

is a development of a high grip member G. In

FIGS. 35 and 36

, like or equivalent portions are designated by like reference numerals used in the 19th embodiment.

A feature of this embodiment resides in that each side edge G

5

of a high grip member G is not linear or is offset in the circumferential direction as shown in

FIGS. 35 and 36

. In other words, the side edge is not linear in the direction orthogonal to the belt width direction (horizontal direction in FIG.

35

). In this embodiment, both side edges G

5

are configured to be gently wavy when viewed from front or along the circumference of the fixing belt.

Also in this embodiment, the outside diameter D

2

of the high grip member G is larger than that D

1

of the surface belt layer

1133

, as shown in FIG.

35

B. In the embodiment, the outside diameter D

2

of the high grip member G is set to be larger than that D

1

of the surface belt layer

1133

by selecting a thickness t

2

of each of the adhesive layer

1163

and the high grip member G to be larger than a thickness t

1

of the surface belt layer

1133

.

This embodiment may be designed such that the high grip portion G is formed with an expandable member shaped like an endless belt. The belt-like high grip member has an inside diameter smaller than an outside diameter of each side end

1123

b

of the fixing belt when it is in a free state. By the utilization of its expandability, the belt-like high grip member G is expanded to be somewhat larger than the outside diameter

1123

b

of the belt base

1123

, and is fit to each side end

1123

b

with an adhesive layer

1163

being interposed therebetween, and is fastened to each side end

1123

b

of the belt base

1123

by its expandability and by use of the adhesive layer

1163

. Alternatively, a tape-like high grip member G is put around each side end of the fixing belt as shown in FIG.

37

.

FIG. 36

is a development of the high grip member G.

FIG. 38A

is a front view showing a part of a fixing belt

110

constructed such that the winding start end G

11

of the tape-like high grip member G is confronted with the winding terminating end G

21

in a state that a gap slanted to the axial direction of the pressure application roller is interposed therebetween.

FIG. 38B

is a development of the tape-like, high grip member G.

This embodiment in which each side edge of a high grip member is not linear in the circumferential direction produces the following advantageous effects.

If each side edge of the high grip member is linear in the circumferential direction (it is linear in the direction orthogonal to the belt width direction (horizontal direction in FIG.

35

), positions

126

(see

FIG. 39

) of the pressure application roller

120

, which is to be in pressing contact with the fixing belt

110

, at which it is pressed against the side edges G

5

of the high grip member G are locally worn or deformed, to thereby possibly reduce the endurance of the pressure application roller

120

.

In this connection, in this embodiment, each side edge of the high grip member is not linear in the circumferential direction. Because of this configuration, the local wearing or deformation of the pressure application roller

120

are lessened (those are broken up in the direction in which the side edge is wavy). This results increase of the endurance of the pressure application roller

120

.

The advantageous effects may be produced when the outside diameter D

2

of the high grip member G is not larger than that D

1

of the surface belt layer

1133

of the fixing belt

110

; however, the effects are marked when the outside diameter D

2

of the high grip member G is not larger than that D

1

of the surface belt layer

1133

. That is, where the outside diameter D

2

of the high grip member G is not larger than that D

1

of the surface belt layer

1133

of the fixing belt

110

, if no measure is taken, the local wearing or deformation at the positions

126

of the pressure application roller

120

at which it is pressed against the side edges G

5

of the high grip member G will be promoted. In this embodiment, however, each side edge of the high grip member is not linear in the circumferential direction, the local wearing or deformation of the pressure application roller

120

are lessened and hence the pressure application roller

120

is improved in its endurance.

21st Embodiment

FIG. 40

is a perspective view showing a key portion of a 21st embodiment of the present invention.

FIG. 41A

is a front view showing a part of a fixing belt

110

.

FIGS. 41B and 41C

are front views showing exemplary uneven patterns. In the figure, like or equivalent portions are designated by like reference numerals used in the 10th to 20th embodiments already described.

A feature of this embodiment resides in that an uneven pattern GP on a surface G

41

of a high grip member G is slanted with respect to the width direction. In

FIG. 41

, an angle of an inclination of the uneven pattern GP to the circumferential direction of the belt (vertical direction in

FIG. 41

) is denoted as θ. The inclination angle of the uneven pattern GP is preferably selected such that those uneven patterns are axially symmetry with respect to the center line CL as view in the width direction of the fixing belt

110

. In this embodiment, it is approximately 45°.

The high grip member G may be made of an appropriate material, e.g., rubber or synthetic resin. An appropriate pattern may be used for the uneven pattern GP on the surface of the high grip member. A lattice pattern is illustrated in

FIG. 41A. A

pattern shown in

FIG. 42B

consists of successions of elongated holes (or indentations) or elliptical (track-like) protrusions GP

1

. A pattern shown in

FIG. 42C

consists of successions of rectangular or diamond indentations (or holes) or protrusions GP

2

.

FIG. 42

diagrammatically shows one end of a fixing belt

110

employed in this embodiment.

FIG. 42A

is a front view showing a part of the belt.

FIG. 42B

is a cross sectional view taken on line b—b in FIG.

42

A.

In this embodiment, the high grip member G is made of cloth (involving a mesh-like member) formed by weaving or knitting threads

1143

a

and

1143

b

crossing each other, as shown in FIG.

42

.

This embodiment produces additional advantageous effects as described below.

The uneven pattern GP on the surface G

41

of the high grip member G is slanted with respect to the width direction. This feature produces a called wedge effect (wedge effect in the rotational direction (power transmission direction)) by the uneven pattern GP at the press contact portion N

2

(see

FIG. 40

) of it with the pressure application roller

120

. As a result, the gripping force by the high grip portion (G) is increased, and an uneven pattern GP on a surface G

41

of a high grip member G is slanted with respect to the width direction. The slip is prevented (at least its occurrence is extremely infrequent), and a stable fixing operation of the fixing device is secured.

If the uneven pattern on the surface of the high grip member is not slanted with respect to the width direction (it is parallel to the axial direction of the pressure application roller

120

, for example), a vibration by the drive power transmission (vibration due to the uneven pattern) may increase. However, in this embodiment, such a vibration is remarkably reduced since the uneven pattern GP on the surface G

41

of the high grip member G is slanted with respect to the width direction. Accordingly, a smooth drive power transmission is secured.

Further, the uneven patterns on the surface G

41

of the high grip member G are axially symmetry with respect to the center line CL as view in the width direction of the fixing belt

110

. Therefore, thrust forces (acting in the belt width direction) caused by the inclination of the uneven pattern GP are cancelled, so that the fixing belt

110

stably runs.

22nd Embodiment

FIG. 43

diagrammatically shows one end of a fixing belt

110

extending around the backup roller

130

and heating roller

140

in a 22nd embodiment of a belt fixing belt according to the present invention.

FIG. 43A

is a front view of the belt end.

FIG. 43B

is a longitudinal sectional view showing the same. In those figures, like or equivalent portions are designated by like reference numerals used in the 10th to 21th embodiments already described.

Feature of this embodiment reside in that as shown in

FIGS. 44B and 45

, a high grip member G is fastened to each side end

1123

c

of the belt base

1123

such that the outer end G

5

of the high grip member G is extended outward beyond the side end

1123

c

of the belt base

1123

, and that the outer end G

5

of the high grip member G is brought into contact with the inner face

145

a

of a guide ring

145

as a restricting mechanism.

FIGS. 44A and 44B

show an instance where the high grip member G is formed with an expandable member shaped like an endless belt, which has an inside diameter smaller than an outside diameter of each side end

1123

b

of the fixing belt when it is in a free state, and as shown in

FIG. 44A

, by the utilization of its expandability, the belt-like high grip member G is expanded to be somewhat larger than the outside diameter

1123

b

of the belt base

1123

, and is fit to each side end

1123

b

with an adhesive layer

1153

(not shown in

FIG. 44

) being interposed therebetween as shown in

FIG. 44B

, and is fastened to each side end

1123

b

of the belt base

1123

by its expandability and by use of the adhesive layer

1153

.

FIG. 45

a diagrammatically shows an instance in which the high grip member G is made of cloth.

FIG. 46

diagrammatically shows an instance in which a tape-like, high grip member G as shown in

FIG. 46B

is bonded to and around each of the side ends

1123

b

of the belt base

1123

by use of an adhesive layer

1163

as shown in FIG.

46

A.

FIG. 47

is a diagram showing an instance where a high grip member G is bonded to and around each of the side ends

1123

b

of the belt base by use of an adhesive layer

1163

having an oil absorbing capability (e.g., silicone adhesive layer).

FIGS. 48A and 48B

show an instance where a high grip member G is made of a heat-resistance sheet made of synthetic resin containg a number of empty spaces C

2

each extending in the direction orthogonal to the belt surface (vertical direction in FIG.

48

B), the lateral direction (horizontal direction in FIG.

48

A), and longitudinal direction (vertical direction in FIG.

48

A).

FIGS. 48C and 48D

show an instance where a high grip member G is made of a heat-resistance sheet made of synthetic resin containg a number of perforations C

4

.

This embodiment produces additional advantageous effects as described below.

The side edges G

5

of the fixing belt

110

is brought into contact with the restricting members

145

, so that such a behavior of the traveling fixing belt

110

as to move aside is restricted.

Since the side edges G

5

of the fixing belt

110

is brought into contact with the restricting members

145

, the following advantageous effects are produced additionally.

The high grip members G are fastened to both side ends of the fixing belt

110

, so that the both side ends of the fixing belt

110

are reinforced. Further, the high grip member G comes into contact with the restricting member

145

. Therefore, the endurance of the fixing belt

110

is increased although such a construction is employed that the side end of the fixing belt

110

comes into contact with the restricting member

145

.

Therefore, the fixing belt

110

may be thinned in structure. The fixing belt

110

well follows an unevenness corresponding to the amounts of attached toner forming a toner image. This results increase of a fixing strength or a fixing uniformity. Further, a heat capacity of the fixing belt

110

is small, so that it may be heated quickly.

When the side edge G

5

of the fixing belt

110

is brought into contact with the restricting members

145

to restrict a zig-zag traveling of the fixing belt

110

, a shearing force acting on the side edge of the belt is great in magnitude. If the high grip members G that are applied to both side ends of the fixing belt

110

are made of cloth, the high grip portion G is unlikely to be broken and propagation of the breakage to the whole fixing belt

110

is also greatly impeded.

23rd Embodiment

FIG. 49

is a perspective view showing one end of a fixing belt

110

which is a 23rd embodiment of the present invention.

FIG. 49A

is a front view of the belt end.

FIG. 49B

is a side view showing the same.

FIG. 49C

is a cross sectional view taken on line c—c in FIG.

49

B. In those figures, like or equivalent portions are designated by like reference numerals used in the 22nd embodiment already described.

This embodiment is different from the 22nd embodiment in that a rigidity of the high grip member G in the belt width direction (horizontal direction in

FIG. 49A

) is larger than that in the belt circumferential direction (vertical direction in FIG.

49

A). The remaing structure of this embodiment is substantially the same as of the 22nd embodiment.

In this embodiment, the high grip member G is made of cloth in which the weft

1143

a

is formed with single threads (, e.g., called mono-filaments), and the warp

1143

b

is formed of threads each consisting of an aggregation of a plural number of very fine threads (called multi-filaments, for example), whereby a rigidity of the high grip member G in the belt width direction is larger than that in the belt circumferential direction.

The advantageous effects produced by this embodiment are similar to those by the 22nd embodiment. Additionally, this embodiment produces the follow effects. That is, since a rigidity of the high grip member G in the belt width direction is larger than that in the belt circumferential direction, the following advantageous effects are obtained.

Since the rigidity of the high grip member G in the belt circumferential direction is relatively small, when the high grip member G is fastened to the side end of the fixing belt

110

, the high grip member G is expanded, so that the fitting of the high grip member G to the belt side end is easy. Further, the high grip member G is well fit around the side end of the fixing belt. Since the rigidity of the high grip member G in the belt width direction is relatively large, its buckling strength is increased when it is brought into contact with the restricting members

145

. As a result, such a behavior of the traveling fixing belt

110

as to move aside is restricted satisfactorily.

24th Embodiment

FIG. 50

is a cross sectional view showing one end of a press nip portion (press contact portion) N of a fixing belt which is a 24th embodiment of the present invention. In the figure, like or equivalent portions are designated by like reference numerals used in the 22nd embodiment already described.

This embodiment is different from the 22nd and 23rd embodiments in that an outside diameter D

2

of a high grip member G is larger than that D

1

of the surface belt layer

113

, and that the inner side edge G

6

of the high grip member G is beveled. The remaing construction of the second embodiment is substantially the same as of those embodiments.

In this embodiment, the outside diameter D

2

of the high grip member G is set to be larger than that D

1

of the surface belt layer

1133

by selecting a thickness t

2

of the high grip member G to be larger than a thickness t

1

of the surface belt layer

1133

.

This embodiment produces the following advantageous effects in addition to those by the 22nd and 23rd embodiments.

The outside diameter D

2

of the high grip member G is larger than that D

1

of the surface belt layer

1133

. Therefore, at both the ends N

2

of the press contact portion N between the fixing belt

110

and the pressure application roller

120

, the high grip members G are pressed against the pressure application roller

120

by a larger pressing force. Accordingly, a gripping force is satisfactorily secured between the fixing belt

110

and the pressure application roller

120

. And the slip is prevented with certainty (at least its occurrence is extremely infrequent.). As a result, a stable fixing operation of the fixing device is secured. Further, stress concentration on the pressure application roller

120

is lessened since the inner side edge G

6

of the high grip member G is beveled.

25th Embodiment

A feature of this embodiment resides in that in each of the 10th to 24th embodiments, the high grip member G is made of a material having a thermal expansion coefficient substantially equal to that of the belt base

1123

.

When the belt base

1123

is made of conductive polyimide, for example, the high grip member G is made of the polyimide.

That an adhesive layer

1153

in this embodiment is flexible is not essential. Use of adhesive of polyimide is preferable for the adhesive layer.

This embodiment has the following advantageous effects since a thermal expansion coefficient of the high grip member G is substantially equal to that of the fixing belt

110

.

As already stated, in this type of the fixing device, when it is operated, the fixing belt

110

is heated to high temperature (e.g., approximately 150° C. to 200° C.). If the thermal expansion coefficient of the high grip member G fastened to each side end of the fixing belt

110

is greatly different from than that of the fixing belt

110

, a stress is generated at both the fastening faces (

1153

) by the thermal expansion coefficient difference. As a result, the bent side ends are easy to be broken or the high grip member G is easy to strip off the belt.

In this connection, in this embodiment, the thermal expansion coefficient of the high grip member G is substantially equal to that of the fixing belt

110

(viz., it is made of a material having a thermal expansion coefficient substantially equal to that of the fixing belt

110

). Therefore, little or a little stress is caused by the thermal expansion coefficient difference. As a result, the problem of damaging the side ends of the fixing belt

110

and the stripping of the high grip member G is solved. Consequently, the endurance of the fixing device is increased.

This will be described in detail with reference to

FIGS. 51 and 52

.

FIGS. 51A

to

51

D are cross sectional views showing the belt end.

FIG. 51A

shows a structure state of the belts before the fixing device is operated (before the fixing belt

110

is heated).

FIGS. 51B

to

51

D show structure states of the fixing belt after the fixing device is operated (after the fixing belt

110

is heated).

FIG. 51B

shows a structure of this embodiment.

FIG. 51C

shows a structure state in a case where a thermal expansion coefficient of the high grip member G is larger than that of the fixing belt

110

(belt base

1123

).

FIG. 51D

shows a structure state in a case where a thermal expansion coefficient of the high grip member G is smaller than that of the fixing belt

110

.

FIGS. 52A

to

52

D are side views showing the belt end.

FIG. 52A

shows a structure state of the belts before the fixing device is operated (before the fixing belt

110

is heated).

FIGS. 52B

to

52

D show structure states of the fixing belt after the fixing device is operated (after the fixing belt

110

is heated).

FIG. 52B

shows a structure of this embodiment.

FIG. 52C

shows a structure state in a case where a thermal expansion coefficient of the high grip member G is larger than that of the fixing belt

110

(belt base

1123

).

FIG. 52D

shows a structure state in a case where a thermal expansion coefficient of the high grip member G is smaller than that of the fixing belt

110

.

As shown in

FIGS. 51C and 52C

, when a thermal expansion coefficient of the high grip member G is larger than that of the fixing belt

110

, a stress (ΔL

2

/L) is generated in each of the fastening portions (

1153

) of them by a thermal expansion coefficient difference ΔL

2

between those members. The belt ends are easy to be broken or as shown in

FIG. 52C

, the high grip member G is easy to peel off the belt. A peeling portion is denoted as G

5

.

As shown in

FIGS. 51D and 52D

, when a thermal expansion coefficient of the high grip member G is smaller than that of the fixing belt

110

, a stress (ΔL

3

/L) is generated in each of the fastening portions (

1153

) of them by a thermal expansion coefficient difference ΔL

23

between those members. The belt ends are easy to be broken. Also in this case, the high grip member G is easy to peel off the belt. When the high grip member G is a tape-like one, as shown in

FIG. 52D

, a gap C between the winding start end G

11

and the winding terminating end G

21

will increase.

In this connection, in the fixing device

100

of this embodiment, the thermal expansion coefficient of the high grip member G is substantially equal to that of the fixing belt

110

. As shown in

FIG. 51B

, those members are thermally expanded by approximately equal length ΔL

1

. Therefore, as shown in

FIGS. 51B and 52B

, little or a little stress is generated in the fastening portions of those members by the thermal expansion coefficient difference. The problems of damaging the side ends of the fixing belt

110

and the peeling of the high grip member G from the fixing belt

110

are solved successfully. Further, the problem of the increasing of the gap C is also solved.

26th Embodiment

FIG. 53

is a diagrammatic view showing a major portion of a 26th embodiment of the present invention:

FIG. 53A

is an enlarged, front view showing a part of a fixing belt

110

(before it is extended around the backup roller

130

and the heating roller

140

);

FIG. 53B

is a left side view of the same; and

FIG. 53C

is a traverse cross sectional view showing of the belt end. In

FIG. 53

, like or equivalent portions are designated by like reference numerals used in the 10th to 25th embodiment already described.

A feature of this embodiment resides in that the high grip member G is made of a composite material of high friction material G

114

and material

1164

having an oil absorbing capability. The high friction material G

114

may be particulate material (e.g., glass beads) for creating gripping force for the pressure application roller

120

. The material

1164

having an oil absorbing capability may be silicone rubber having an adhesive property. The particulate material is mixed into the silicone rubber. The side ends

1123

b

of the belt base

1123

are coated with the composite material to form high grip portions G. Accordingly, a tremendous number of particles of the high friction material G

114

appear on the surfaces G

41

of the high grip portions G thus formed.

In this embodiment, since the high grip portion G is made of a composite material of high friction material G

114

and material

1164

having an oil absorbing capability, the following advantageous effects are produced.

Where the surface of the fixing belt

110

is coated with the release oil, the oil will gradually move to the ends N

2

of the press contact portion N. However, in this embodiment, the high grip portion G is made of a composite material of high friction material G

114

and material

1164

having an oil absorbing capability. Therefore, the oil having reached the ends N

2

of the press contact portion N is absorbed by the material

1164

having the oil absorbing capability.

Accordingly, the amount of oil present on the surfaces G

41

of the high grip portions G where the high friction material G

114

are exposed, is small. As a result, a gripping force is satisfactorily secured at both the ends N

2

of the press contact portion. The slip is prevented (at least its occurrence is extremely infrequent), and a stable fixing operation of the fixing device is secured.

Thus, the fixing device

100

of this embodiment is able to stably fix the toner image although the surface of the fixing belt

110

is coated with the release oil.

Further, since the high grip member G is made of a composite material of high friction material G

114

and material

1164

having an oil absorbing capability, its strength is also increased. The and material

1164

has an oil absorbing capability. Thence, a strength of the high grip portion G is further increased.

27th Embodiment

A feature of this embodiment resides in that as shown in

FIG. 54B

, a length of the oil coating roller

150

is somewhat shorter than the width of the surface belt layer

1133

, whereby release oil is applied to only an image forming area.

In the 10th to 26th embodiments, as shown in

FIG. 54A

, a length of the oil coating roller

150

is somewhat longer than the width of the surface belt layer

1133

. Alternatively, it may be longer than the width of the surface belt layer

1133

but shorter than the width of the fixing belt

110

, as shown in FIG.

55

. When as shown in

FIG. 54A

, the length of the oil coating roller

150

is longer than the width of the fixing belt

110

, stress caused in the fixing belt

110

may be lessened.

Where the length of the oil coating roller

150

is somewhat shorter than the width of the surface belt layer

1133

to apply the release oil to only the image forming area, the oil is unlikely to flow to the end N

2

of the fixing contact portion N.

EXAMPLES

Specific examples of the embodiments will be described.

Fixing belt

110

In the 9th embodiment, the fixing belt

110

is a seam less belt. The belt base

1122

is a mesh-like member made of heat-resistance multi-filament (threads) of alamide fiber. A thickness of the belt base

1122

is bout 100 μm. Also in the case where it is made of cloth, its thickness is 100 μm.

A width of the belt base

1122

is 392 mm. Only its central portion is coated with silicone rubber so as to have a thickness of about 200 μm, whereby a surface belt layer

1132

is formed. Exposed portions

1122

b

of about 27 mm wide are formed on both sides of it.

An inside diameter of the belt base

1122

is about φ60 mm.

In each of other embodiments, the fixing belt

110

is a seam less belt. The belt base

1122

is an endless sheet made of conductive polyimide. A thickness of the belt base

1123

is bout 150 μm.

A width of the belt base

1122

is 392 mm. Only its central portion is coated with silicone rubber to be about 200 μm thick, whereby a surface belt layer

1133

is formed. Exposed portions

1122

b

of about 27 mm wide are formed on both sides of it.

An inside diameter of the belt base

1123

is about φ60 mm.

In the 14th, 20th and 21st embodiments, high grip members G are fastened to the exposing portions

1123

b

, respectively. A thickness of the high grip member G including the adhesive layer

1163

is about 300 μm.

Pressure Application Roller

120

A pipe portion

121

is extended from both ends of the pressure application roller. An elastic layer

122

of silicone rubber is layered around the outer circumferential surface of the pipe portion

121

made of iron (SUM

24

), about φ32 mm in outside diameter and φ22 mm inside diameter. The pipe portion includes a hollowed shaft

125

(see FIG.

16

). A surface layer

122

a

of fluorine plastics is further layered on the elastic layer

122

.

Rubber hardness of the elastic layer

122

is about JIS-A20°, and a thickness of it is about 1.5 mm.

The surface layer

122

a

is a fluorine latex film formed by applying fluorine latex coating there and heat-hardening it. Its thickness is about 60 μm.

About 230W at 100V is selected for the amount of heat generated by the halogen lamp

123

located in the hollowed portion.

An outside diameter of the pressure application roller

120

is about 35.2 mm.

The roller width (length in the axial direction) including the shaft portion

124

is about 444.3 mm.

Pressing load to the backup roller

130

is applied to the shaft portions

125

, about 60 Kg (totally 120 Kg) for each side. In this case, the backup roller

130

and the pressure application roller

120

are fixed at predetermined positions (shaft-shaft distance is fixed), and any special pressing means is not used. The pressure application roller

120

and the backup roller

130

are fixed to the frame

101

so that the shaft-shaft distance is smaller than the sum of the outside diameters of the rollers

120

and

130

, and both the rollers are compressed together. Then, the pressing load is generated. Load action points to the roller are coincident with the fixing points to the frame, and those are the positions of the bearings (not shown) of the shaft

124

.

A length L

2

of its press contact portion N with the fixing belt

110

is about 11 mm.

Backup roller

130

A solid roller of iron (SUM

24

) of about φ26 with a shaft portion

131

a

of about φ10 extended from both ends of the roller. An elastic layer

132

of silicone rubber is layered around the outer circumferential surface of the roller. A surface layer

132

a

of PFA (tetrafluoroethylene perfluoroalkoxy ethylene copolymer) is further layered on the elastic layer

132

.

An outside diameter of the backup roller

130

is about 38.5 mm, and the roller width except the shaft portion

131

a

is about 398 mm.

A thickness of the elastic layer

132

is about 6.25 mm. Rubber hardness is about JIS-A10°.

The surface layer

132

a

is a thermal shrinking PFA resin tube. Its thickness after coated is about 110 μm.

Heating Roller

140

The roller includes a shaft portion

144

of about φ20 extended from both sides thereof. The roller is an aluminum, pipe-like roller of about φ28 in outside diameter and about 3 mm in thickness.

The roller width except the shaft portion

144

is about 393 mm.

The heat generating means

141

, located within the hollow of the roller is a halogen lamp. About 695W at 100V is selected for the amount of heat generated by the halogen lamp.

Oil Coating Roller

150

An oil retaing layer

152

including an oil contained layer

152

a

and an oil supplying layer

152

b

and a surface layer

153

are layered, one on the other, on a shaft

151

made of iron (SUM

24

), about φ10 mm.

An outside diameter of the oil coating roller

150

is about 36 mm, the roller width exclusive of the shaft portion is about 338 to 392 mm, preferably a width wide enough to cover the paper-passing width, not reaching the high grip portions.

The oil-contained layer

152

a

is made of sponge, about 11 mm thick.

The oil supplying layer

152

b

is made of felt, about 2 mm thick.

The surface layer

153

is made of porous PTFE (tetrafluoroethylene ethylene copolymer) resin, about 120 μm.

The release oil is dimethyl silicone oil. Its viscosity (at 20°C.) is about 100 centistokes, and its total amount is about 140 g.

Contact load (pressing load) to the fixing belt

110

is within a range of about 0.5 to 2 Kg in total, preferably about 1 Kg.

A contact width (length in the belt traveling direction) between the oil coating roller

150

and the fixing belt

110

is about 3 mm.

While the present invention has been described by use of the preferred embodiments and examples, it should be understood that the invention is not limited to those described ones, but may variously be modified, altered and changed within the true spirits of the invention. For example, the present invention may also be implemented in the following ways:

(1) Those described embodiments may properly be combined (a construction of an embodiment is applied to another embodiment).

(2) In the first to sixth, 12th image forming apparatus, and the 18th, and the 21st to 33rd belt fixing devices, the oil coating mechanism is not essential.

(3) In the 21st to 23th, 26th to 27th, and 30th to 33rd belt fixing devices, the high grip portion G may be formed with a number of ridges G

7

extending in the width direction (perpendicular to a paper surface of the drawing of

FIG. 56

) may be formed on the surface of the rubber belt.

Number	Name	Date	Kind
4563073	Reynolds	Jan 1986	A
5267004	Mills	Nov 1993	A
5450183	O'Leary	Sep 1995	A
5546173	Hinotani et al.	Aug 1996	A
5666623	Yamada et al.	Sep 1997	A

Number	Date	Country
0375369	Jun 1990	EP
2234939	Feb 1991	GB
6-348156	Dec 1994	JP
9-204111	Aug 1997	JP
10-3227	Jan 1998	JP

Image forming apparatus and fixing device for use with the same

Information

Patent Number

Date Filed

Date Issued

Inventors

Original Assignees

Examiners

Agents

CPC

US Classifications

Field of Search

US

International Classifications

Abstract

Description

Claims

Priority Claims (12)

US Referenced Citations (5)

Foreign Referenced Citations (5)

Non-Patent Literature Citations (2)

Number	Date	Country
11-056215	Mar 1999	JP
11-056216	Mar 1999	JP
11-185083	Jun 1999	JP
11-194761	Jul 1999	JP
11-194762	Jul 1999	JP
11-194763	Jul 1999	JP
11-247030	Sep 1999	JP
11-247031	Sep 1999	JP
11-247033	Sep 1999	JP
11-247034	Sep 1999	JP
11-247036	Sep 1999	JP
11-247037	Sep 1999	JP

Entry
Patent Abstracts of Japan 10171291 A Jun. 26, 1998.
European Search Report.