Patent Grant
6947699
The present invention relates to an image heating apparatus preferable as a thermal heating apparatus for an image forming apparatus employing an electrophotographic, electrostatic recording method, or the like method. In particular, it relates to an image heating apparatus employing a flexible movable member, for example, a sleeve formed of film, as a member which contacts recording medium.
In an image forming apparatus employing an image processing means such as an electrophotographic recording means, an electrostatic recording means, a magnetic recording means, or the like, an unfixed image (toner image) is directly (direct method), or indirectly (transfer method), formed on a piece of recording medium (transfer sheet, electro-fax sheet, electrostatic recording sheet, OHP sheet, printing paper, formatted sheet, etc.) according to the image formation information, by the processing means. Then, the unfixed image is thermally fixed to the recording surface of the recording medium; it is turned into a permanent image. Among various types of fixing apparatuses, heat roller type fixing apparatuses have been widely used.
In recent years, from the standpoint of quick start and energy conservation, so-called film heating type fixing methods have been put to practical use. Further, fixing apparatuses employing an electromagnetic heating method have been proposed.
a) Film Heating method
Fixing apparatuses (fixing devices) employing the film heating method are proposed in Japanese Laid-open Patent Applications 63-313182, 2-157818, 4-44075, 4-204980, etc.
According to these applications, the fixing apparatus comprises a ceramic heater as a heating member, a pressure roller as a pressing member, a piece of heat resistant file (fixing film belt). The heat resistant film is sandwiched between the ceramic heater and pressure roller, forming a fixing nip. In operation, a recording medium bearing an unfixed toner image is fed into the fixing nip, between the fixing film and pressure roller, and conveyed through the fixing nip, along with the fixing film, being pressed upon the ceramic heater by the pressure roller. While the recording medium is conveyed through the fixing nip, the heat from the ceramic heater is given to the recording medium through the fixing film. As a result, the unfixed toner image is fixed to the surface of the recording medium.
With the employment of a combination of a ceramic heater with a low thermal capacity and a fixing film with a low thermal capacity, this film heating type fixing apparatus can be realized as an on-demand type fixing apparatus. More specifically, the temperature of a ceramic heater as a heat source has to be at the image fixing level only during the period in which an image is actually fixed. A film heating type fixing apparatus employing the combination of a ceramic heater with a low thermal capacity and a fixing film with a low thermal capacity enjoys a few advantages. For example, it is shorter in the time from the moment the power of an image forming apparatus is turned on to when the image forming apparatus becomes ready for an image forming process proper (being capable of quickly starting up), and uses a substantially smaller amount of power while it is on standby (being superior in terms of power conservation).
b) Film Heating Method based on Electromagnetic Induction
Japanese Laid-open Patent Application 7-114276 proposes a film heating type image heating apparatus, which comprises a fixing film and an electrically conductive member disposed close to the fixing film. In operation, eddy current is generated in the electrically conductive member to generate heat (Joule heat) in the film itself; in other words, heat is generated by electromagnetic induction. This film heating method based on electromagnetic induction makes it possible to place the heat generating portion of the fixing apparatus close to an object to be heated, being therefore superior to a film heating method employing a ceramic heater, in terms of thermal efficiency.
In a fixing apparatus employing a film heating type method inclusive of a film heating type method based on electromagnetic induction, an endless film in the form of a cylinder or the like is rotationally driven. As for the method for driving the endless fixing film, various methods are available. One of such methods is a pressure roller driving method. According to this method, a fixing film is sandwiched between a film guiding member (film supporting member), and a pressure roller. The film guiding member guides the fixing film by being placed in contact with the inward surface of the fixing film, In operation, the pressure roller is driven so that the fixing film is rotated by the rotation of the pressure roller. According to another method for driving the endless fixing film, an endless fixing film is suspended around a driving roller, a tension roller, a pressure roller, etc., and the pressure roller is rotated by the rotation of the fixing film.
The torque necessary to rotate a fixing film is affected by the friction between the fixing film and a film guiding member. Therefore, in order to reduce the friction between the fixing film and film guiding member, various measures are taken, for example, lubricant such as heat resistant grease is placed between the inward surface of the fixing film and the film guiding member. According to Japanese Laid-open Patent Application 5-27619 regarding a film heating method, lubricant (grease) is placed between a fixing film and a film guide to ensure that the fixing film easily slides on the film guide.
One of the problems of a conventional film heating type fixing apparatus is that a conventional film heating type fixing apparatus is likely to suffer from the so-called wraparound paper jam, that is, a problematic phenomenon that a recording medium wraps around the fixing film. This wraparound paper jam is likely to occur, in particular, while a full-color image, which is greater in the amount of toner on the recording medium, is fixed, and when an image is fixed to thin paper, or wet paper, which is relatively low in resiliency.
In order to prevent a wraparound paper jam, it is necessary to make it easier for a recording medium to separate from a fixing film after the passage of a recording medium through the fixing nip. One of the methods for making it easier for a recording medium to separate from a fixing film is to provide the downstream end, with respect to the film sliding portion of the film supporting member, of a film supporting member with a ridge which protrudes toward a pressure roller from the film sliding surface of the film supporting member. With the provision of this ridge, a recording medium is nudged in the direction in which the recording medium is to separate from the fixing film due to the curvature of the fixing film, assuring the separation of the recording medium from the fixing film.
However, the provision of a ridge such as the above described one resulted in the following problems. That is, the grease on the inward surface of the fixing film was scraped away by the ridge, collecting on the upstream side of the ridge, in terms of the direction in which the fixing film moves, and oozing from the lateral edges of the fixing film. Further, the loss or reduction of the grease from the inward surface of the fixing film resulted in the increase in the friction between the fixing film and film supporting member, which sometimes caused slip between the fixing film and pressure roller, or between the fixing film and recording medium. This slip sometimes resulted in a paper jam, image defects, etc. The increase in the friction between the fixing film and fixing film supporting member increased the torque necessary to drive the fixing device, putting the fixing apparatus driving motor out of synchronism. Further, the increase in the friction caused the fixing film to repeatedly stop and move with short intervals, generating the so-called “stick-and-slip noises”, which were more apparent when the fixing film and film supporting member were less-compatible in terms of friction.
The present invention was made in view of the above described problems, and its primary object is to provide an image heating apparatus in which an object to be heated is allowed to easily separate from the heating member, and which is low in the torque necessary to drive the image heating apparatus.
Another object of the present invention is to provide an image heating apparatus which enhances the effectiveness of the lubricant for reducing the torque necessary to drive the image heating apparatus.
Another object of the present invention is to provide an image heating apparatus comprising: flexible movable member; supporting member having a surface on which the movable member slides, and which supports the movable member; a pressing member kept pressed upon the supporting member to form a nipping portion, with the movable member sandwiched between the pressing member and supporting member; wherein the supporting member is provided with a ridge, which is disposed close to the fixing film sliding (supporting) portion of the surface of the supporting member, extending in the lengthwise direction of the supporting member, and which projects toward the pressing member from the fixing film sliding surface; and wherein the lengthwise end portions of the ridge do not protrude as high as the portion between the lengthwise end portions, from the film sliding surface of the supporting member, or are level with the fixing sliding surface of the supporting member.
Another object of the present invention is to provide an image heating apparatus comprising: a flexible movable member; a supporting member having a surface on which the movable member slides, and which supports the movable member; a pressing member kept pressed upon the supporting member to form a nipping portion, with the movable member sandwiched between the pressing member and supporting member; wherein the supporting member is provided with a ridge, which is disposed close to the fixing film sliding (supporting) portion of the surface of the supporting member, extending in the lengthwise direction of the supporting member, and which projects toward the pressing member from the fixing film sliding surface; and wherein the ridge has one or more slits.
These and other objects, features, and advantages of the present invention will become more apparent upon consideration of the following description of the preferred embodiments of the present invention, taken in conjunction with the accompanying drawings.
(1) Typical Image Forming Apparatus
This image forming apparatus has a photoconductive drum 101 as an latent image bearing member, which comprises a layer of organic photoconductor, amorphous silicon, or the like, and which is rotationally driven in the counterclockwise direction indicated by an arrow mark, at a predetermined conveyance speed (peripheral velocity). While the photoconductive drum 101 is rotated, it is uniformly charged by a charging apparatus 102 comprising a charging roller or the like, to predetermined polarity and potential level.
The charged surface of the photoconductive drum 101 is exposed to a beam L of laser light outputted in a scanning manner from an optical box (laser scanner) 110. More specifically, the peripheral surface of the photoconductive drum 101 is scanned by the laser beam 103 outputted from the optical box 110 while being modulated (turned on and off) with sequential electric signals in accordance with the image formation information regarding an intended image sent from an unshown image formation signal generating apparatus such as an image reading apparatus. As a result, an electrostatic latent image in accordance with the image formation information of the intended image is formed on the peripheral surface of the photoconductive drum 101. After being outputted from the optical box 110, the beam of laser light is deflected by a mirror 109 toward the peripheral surface of the photoconductive drum 101.
When forming a full-color image, four images corresponding to the four primary color components, into which a full-color image is separated, are consecutively formed. More specifically, first, the latent image corresponding to, for example, yellow color component, that is, one of the color components making up the intended full-color image, is formed, and this latent image is developed into a yellow toner image by a yellow component developing device 104y, that is, one of the four color component developing devices. The yellow toner image is transferred onto the peripheral surface of an intermediary transfer drum 105, in a primary transfer station T1, which is the interface between the photoconductive drum 101 and intermediary transfer drum 105 (or area in which two drums virtually contact each other). After the transfer of the toner image onto the peripheral surface of the photoconductive drum 101, the peripheral surface of the photoconductive drum 101 is cleared of residues, for example, transfer residue, by a cleaner 107; the peripheral surface of the photoconductive drum 101 is cleaned by the cleaner 107.
The above described image formation cycle comprising the charging process, exposing process, developing process, transfer process, and cleaning process is sequentially carried out for the second (for example, magenta), third (for example, cyan), and fourth (for example, black) color components of the intended full-color image, using the magenta developing device 104M, cyan developing device 104C, and black developing device 104Bk, respectively. As a result, the yellow, magenta, cyan, and black toner images are sequentially placed in layers on the peripheral surface of the intermediary transfer drum 105, synthetically realizing a color toner image which reflects the intended full-color image.
The intermediary transfer drum 105 comprises a metallic drum, an elastic intermediary layer, and a surface layer. The elastic layer covers the peripheral surface of the metallic drum, and its electrical resistance is in the mid range. The surface layer covers the intermediary layer, and its electrical resistance is in the high range. The intermediary transfer drum 105 is disposed so that its peripheral surface is placed in contact with, or close to, the peripheral surface of the photoconductive drum 101, and is rotationally driven in the clockwise direction indicated by an arrow mark, at the same peripheral velocity as the photoconductive drum 101. To the metallic drum of the intermediary transfer drum 105, a predetermined voltage is applied so that the toner image on the peripheral surface of the photoconductive drum 101 is transferred onto the peripheral surface of the intermediary transfer drum 105 by the difference (bias) in potential level between the photoconductive drum 101 and intermediary transfer drum 105.
The color toner images formed on the peripheral surface of the intermediary transfer drum 105 are conveyed to the secondary transfer station T2, which is the contact nip between the intermediary transfer drum 105 and a transfer roller 106, in which the color toner images are transferred onto the surface of a recording medium P delivered to the secondary transfer station T2 from an unshown sheet feeding station. More specifically, the transfer roller 106 gives to the recording medium P, from behind the recording medium P, such electrical charge that is opposite in polarity to the toner. As a result, the four color toner images making up the synthetic full-color image on the peripheral surface of the intermediary transfer drum 105 are transferred all at once onto the recording medium P as if they were rolled out onto the recording medium P.
After passing through the secondary transfer station T2, the recording medium P is separated from the peripheral surface of the intermediary transfer drum 105, and is introduced into a fixing apparatus (image heating apparatus) 100 as a fixing means, in which the unfixed toner images are thermally fixed to the recording medium P, becoming parts of a permanent full-color image. Thereafter, the recording medium P is discharged into an unshown delivery tray located outside the main assembly of the image forming apparatus.
After the transfer of the color toner images onto the recording medium P, the intermediary transfer drum 105 is cleared of residues such as toner particles, paper dust, etc., adhering to the peripheral surface of the intermediary transfer drum 105, by a cleaner 108; it is cleaned by the cleaner 108. Normally, the cleaner 108 is not kept in contact with the intermediary transfer drum 105; it is kept in contact with the intermediary transfer drum 105 only during the secondary transfer of the color toner images from the intermediary transfer drum 105 onto the recording medium P.
Normally, the transfer roller 106 also is not kept in contact with the intermediary transfer drum 105; it is kept in contact with the intermediary transfer drum 105, with the interposition of recording medium P, only during the secondary transfer of the color toner images from the intermediary transfer drum 105 onto the recording medium P.
The image forming apparatus in this embodiment is capable of carrying out: a monochromatic print mode, that is, a printing mode in which a monochromatic image such as a black-and-white image is formed; a two-side printing mode; and a multilayer printing mode.
The two-sided printing mode is carried out as follows. After coming out of the fixing apparatus 100, bearing a permanent image on one of its recording surfaces, the recording medium P is put through an unshown recirculatory conveyance mechanism, being thereby placed upside down. Then, the recording medium P is sent again to the secondary transfer station T2, in which an image is transferred onto the second recording surface of the transfer medium P. Then, the transfer medium P is sent for the second time into the fixing apparatus 100, in which the toner image on the second recording surface of the transfer medium P is fixed. Then, the recording medium P is outputted as a two-sided print.
The multilayer printing mode is carried out as follows. After coming out of the fixing apparatus 100, bearing a permanent image on one of its recording surfaces, the recording medium P is sent again to the secondary transfer station T2, without being placed upside down by being put through an unshown recirculatory conveyance mechanism. Then, in the secondary transfer station T2, another toner image is transferred onto the very surface of the transfer medium P, onto which an image has been already transferred during the first run. Then, the recording medium P is sent for the second time into the fixing apparatus 100, in which the second toner image is fixed. Then, the recording medium P is outputted as a multilayer print.
(2) General Structure of Fixing Apparatus 100
The fixing apparatus 100, as an embodiment of an image heating apparatus in accordance with the present invention, employs a cylindrical fixing film (fixing belt) in which heat can be generated by electromagnetic induction. Further, it employs a pressure roller driving method, and a heating method based on electromagnetic induction.
This apparatus 100 comprises: a cylindrical film guiding member 16 as a supporting member; a cylindrical fixing film 10a, as a flexible movable member (heating member), which is loosely fitted around the film guiding member 16, and in which heat can be generated by electromagnetic induction; and a pressure roller 30, as a pressing member, which is kept pressed upon the film guiding member 16, forming a nipping portion N between the pressure roller 30 and film guiding member 16, with the fixing film sandwiched between the pressure roller 30 and film guiding member 16.
The cylindrical film guiding member (film supporting member) 16 comprises the left and right halves 16a and 16b, which are virtually semicylindrical, and which are joined at their straight edges, forming a cylinder, or the cylindrical film guiding member 16. Referring to
The pressure roller 30 as a pressing member comprises: a metallic core 30a; a heat resistant elastic layer 30b, which covers the peripheral surface of the metallic core 30a; and a release layer 30c as the surface layer. The elastic layer 30b is in the form of a cylindrical roller, and is formed of a heat resistant substance such as silicone rubber, fluorinated rubber, or fluorinated resin. The axial line of the elastic layer 30b coincides with that of the metallic core 30a. As the material for the release layer 30c, one of such substances, as fluorinated resin, silicone resin, fluoro-silicone rubber, fluorinated rubber, silicone rubber, PFA, PTFE, FEP, etc., that is superior in release properties and heat resistance, can be selected. The pressure roller 30 is rotationally supported between the unshown side walls of the chassis of the apparatus 100, with the lengthwise end portions of the metallic core 30a being rotationally supported by the bearings attached to the side walls.
The film guiding member 16, around which the fixing film 10 is fitted, is above the pressure roller 30. Put through the hollow of the film guiding member 16 is a rigid stay 22 for pressure application. Between the lengthwise end portions of the rigid stay 22 and the spring seats 29a and 29b, a pair of pressure application springs 25a and 25b are disposed, one for one, in the compressed state, keeping thereby the rigid stay 22 pressed downward. Therefore, the bottom surface of the film guiding member 16, and the top surface of the pressure roller 30, are kept pressed on each other, with the interposition of the fixing film 10, forming a fixing nip N with a predetermined width in terms of the recording medium conveyance direction.
The pressure roller 30 is rotationally driven by a driving means M (
In order to reduce the friction between the bottom surface of the film guiding member 16 and the inward surface of the fixing film 10, the film guiding member 16 is provided with a slippery member 40, which is heat resistant and low in friction. The slippery member 40 is attached to the bottom surface of the film guiding member 16, covering the bottom surface of the film guiding member across the area corresponding to the fixing nip N. The slippery member 40 constitutes a part of the film guiding member 16, to which the slippery member 40 is attached. It is superior to the film guiding member 16, in terms of the slipperiness against the inward surface of the fixing film 10. As the material for the slippery member 40, polyimide resin, glass, alumina, glass coated alumina, etc., are desirable. The slippery member 40 in this embodiment comprises a substrate formed of alumina, and a layer of glass covering the substrate. As described above, the slippery member 40 may be considered to be a part of the fixing film supporting member. Instead of employing the slippery member 40, the bottom surface of the film guiding member 16 may be processed so that the bottom surface itself becomes satisfactorily slippery.
The slippery member 40 is in the form of a piece of narrow belt or tape, and its length and width are no less than the length and width of the fixing nip N, respectively. In this embodiment, it is fitted in the groove cut in the bottom surface of the film guiding member 16, in the lengthwise direction of the film guiding member 16, being thereby accurately positioned as well as securely held therein. It is desired that the slippery member 40 is attached with the use of a heat resistant glue.
Further, in order to reduce the friction between the fixing film 10 and slippery member 40, a lubricant G is placed between the slippery member 40 and the inward surface of the fixing film 10. In this embodiment, a fluorinated grease is used as the lubricant.
The structure of the portion of the film guiding member 16 next to the fixing film sliding portion, and the structure of the portion of the slippery member 40 next to the fixing film sliding portion, in the fixing nip N, will be described later in detail, in Section (5).
Referring again to
Referring to
With the provision of the above described structural arrangement, as the pressure roller 30 is rotationally driven, the fixing film 10 is rotated by the rotation of the pressure roller 30. Meanwhile, electrical power is supplied to the exciting coil 18 from an exciting circuit 27 (FIG. 4), generating a magnetic field, which induces electric current in the fixing film 10 as a heating member. As a result, heat is generated in the fixing film 10, heating the fixing nip N to a predetermined temperature. Once the temperature of the fixing nip N is raised to the predetermined level, control is executed so that the temperature of the fixing nip N is kept at this predetermined level. With the temperature of the fixing nip N kept at this level, a recording medium P bearing an unfixed toner image t is conveyed from the unshown image forming means to the fixing nip N, and is introduced between the fixing film 10 and pressure roller 30. Then, the recording medium P is conveyed through the fixing nip N, along with the fixing film 10, remaining nipped by the fixing film 10 and pressure roller 30, with the image bearing surface of the recording medium P being pressed against the outward surface of the fixing film 10.
After passing through the fixing nip N, the recording medium P separates from the outward surface of the fixing film 10, and is conveyed further to be discharged from the apparatus main assembly. After passing through the fixing nip N, the thermally fixed toner image on the recording medium P cools down, turning into a permanent image.
Since this embodiment of a thermal fixing apparatus 100 in accordance with the present invention uses a toner t containing ingredients which do not easily soften, it is not equipped with an oil application mechanism for offset prevention. However, a fixing apparatus employing a toner containing no ingredients which do not easily soften may be equipped with an oil application mechanism. Further, even a fixing apparatus which uses a toner containing ingredients which do not easily soften may be equipped an oil application mechanism, or a cooling mechanism for recording medium separation.
(3) Magnetic Field Generating Means
The magnetic cores 17a, 17b, and 17c are desired to be high in permeability. Therefore, the materials, such as ferrite, Permalloy, etc., used as a transformer core are preferable as the material for the magnetic cores 17a, 17b, and 17c. More preferably, such a ferrite that is low in loss even at a frequency of 100 kHz or more should be used.
The material for the exciting coil 18, which constitutes a magnetic field generating means, is a set of several pieces of fine copper wires, each of which is coated with electrically insulating substance. These copper wires are bundled and wound several times (twelve times in this embodiment) to form the exciting coil 18.
In consideration of the fact that the heat is generated in the fixing film 10, the substance with which the aforementioned copper wires are coated is desired to be heat resistant. For example, polyamide, polyimide, or the like, is recommendable. The insulating substance applied to the fine wires in this embodiment is polyimide, and is capable of remaining insulating up to 220° C.
The wire density of the exciting coil 18 may be increased by the application of external pressure.
Disposed between the magnetic field generating means 17a•17b•17c•18 and the rigid pressure application stay 22 is an insulating member 19. Not only is the material for the insulating member 19 desired to be superior in insulating properties, but also heat resistant. For example, phenol resin, fluorinated resin, polyimide resin, polyamide resin, polyamide-imide resin, polyether-ketone resin, polyester-sulfone resin, polyphenylene sulfide resin, PFA resin, PTFE resin, FEP resin, LCP resin, etc., are the recommendable choices.
The amount Q of the heat generated in the heat generation layer 1 is determined by the density of the magnetic flux C which passes through the heat generation layer 1, and shows such a distribution pattern that is represented by the graph in
The current supplied to the exciting coil 18 is controlled by an unshown temperature controlling system, inclusive of a temperature detecting means 26 (FIG. 1), so that the temperature of the fixing nip N remains at a predetermined level. The temperature detecting means 26 is a temperature sensor, for example, a thermistor, for detecting the temperature of the fixing film 10. In this embodiment, the temperature of the fixing nip N is controlled based on the temperature of the fixing film 10 measured with a thermistor.
(4) Fixing Film (Flexible Movable Member) 10
The fixing film 10 in this embodiment is a multilayer film comprising: the heat generation layer 1, a base layer, formed of metallic film, in which heat can be generated by electromagnetic induction; an elastic layer 2 layered on the outward surface of the heat generation layer 1; and a release layer 3 layered on the outward surface of the elastic layer 2.
For adhesion, a primer layer (unshown) may be added between the heat generation layer 1 and elastic layer 2, and between the elastic layer 2 and release layer 3.
The fixing film 10 is virtually cylindrical, and its heat generation layer 1 constitutes the most inward layer which contacts the slippery member 40, whereas the release layer 3 constitutes the most outward layer which contacts the pressure roller or recording medium (object to be heated).
As described above, as the alternating magnetic flux acts on the heat generation layer 1, eddy current is induced in the heat generation layer 1, generating heat in the heat generation layer 1. This heat is used to heat the recording medium P to thermally fix the toner image t while the recording medium P is passed through the fixing nip N.
a. Heat Generation Layer 1
As the material for the heat generation layer 1, a magnetic or nonmagnetic metal can be used. However, a magnetic metal, for example, nickel, iron, ferromagnetic stainless steel, nickel-cobalt alloy, Permalloy, etc., is preferable. In consideration of the fatigue resulting from the repetitive stress which occurs as the fixing film 10 is rotationally driven, the combination of nickel and a small amount of manganese may be used.
The thickness of the heat generation layer 1 is desired to be no less than the penetration depth σ [m] defined as follows, and no more than 200 μm, because when the thickness of the heat generation layer 1 in this range, the heat generation layer 1 efficiently absorbs electromagnetic waves, generating therefore a greater amount of heat.
σ=503×(ρ/fμ)1/2 (1)
The penetration depth a shows the depth from the surface of a given component, beyond which the strength of magnetic waves is less than 1/e. To state in reverse, virtually the entire energy of the electromagnetic waves will be absorbed by the time the electromagnetic waves reach this depth (see relationship between heat generation depth and electromagnetic wave strength, in FIG. 8).
It is preferred that the thickness of the heat generation layer 1 is in the range of 1-100 μm. If the thickness of the heat generation layer 1 is no more than the above range, the heat generation layer 1 fails to absorb all of the electromagnetic energy; it is inefficient. In comparison, if the thickness of the heat generation layer 1 is no less than the above range, the heat generation layer 1 is too rigid, being inferior in terms of flexibility. In other words, it is impractical to make the heat generation layer 1 thicker than the above range.
b. Elastic Layer 2
It is desired that the elastic layer 2 is formed of a heat resistant and highly heat conductive substance, for example, silicone rubber, fluorinated rubber, fluoro-silicone rubber, or the like.
In order to assure that an image is satisfactorily fixed, the thickness of the elastic layer 2 is desired to be in the range of 10-100 μm. In the case of a color image forming apparatus, its elastic layer 2 is desired to be in the range of 50-500 μm for the following reason. When making a color print, in particular, a photographic color print or the like, large solid areas of color are often formed across a recording medium P. In such a case, if the heating surface (or release layer 3) of the fixing film sometimes fails to perfectly conform to the surface irregularities of the recording medium P or toner layer t, the recording medium P and/or toner layer t is nonuniformly heated, resulting in the formation of a print nonuniform in glossiness; the areas to which more heat is transmitted become different in glossiness from the areas to which less heat is transmitted, the former being higher in glossiness than the latter. If the thickness of the elastic layer 2 is no more than the above range, the release layer 3 fails to perfectly conform to the surface irregularities of the recording medium P or toner layer t, resulting in the formation of an image nonuniform in glossiness. On the contrary, if the thickness of the elastic layer 2 is no less than the above range, the thermal resistance is too large to make it possible for a fixing apparatus to quickly start.
If the hardness of the elastic layer 2 is too high, the elastic layer 2 fails to perfectly conform to the irregularities of the recording medium P or toner layer t, resulting in the formation of an image nonuniform in glossiness. Thus, the hardness of the elastic layer 2 is desired to be no more than 60° (JIS-A), preferably, no more than 40° (JIS-A).
The thermal conductivity λ of the elastic layer 2 is desired to be in the range of 2.5×10−1−8.4×10−1 W/m·° C. If the thermal conductivity λ of the elastic layer 2 is no more than the above range, the thermal resistance is too large, delaying the temperature increase at the surface layer (release layer 3) of the fixing film 10. On the other hand, if the thermal conductivity A of the elastic layer 2 is no less than the above range, the elastic layer 2 is too hard, or is likely to be permanently deformed by compression. It is preferable that the thermal conductivity of the elastic layer 2 is in the range of 3.3×10−1−6.3×10−1 W/m·° C.
c. Release Layer 3
The release layer 3 is formed of such a material as fluorinated resin, silicone resin, fluorosilicone rubber, fluorinated rubber, silicone rubber, PFA, PTFE, FEP, etc., that is superior in releasing properties as well as heat resistance.
The thickness of the release layer 3 is desired to be in the range of 1-100 μm. An attempt to form a release layer 3, the thickness of which is no more than the above range, results in the formation of a release layer 3 which is nonuniform in thickness, being therefore inferior in releasing properties across some areas, and being not durable, which is a problem. On the other hand, if the thickness of the release layer 3 is no less than the above range, the release layer 3 is inferior in thermal conductivity. In particular, when a resinous substance is used as the material for the release layer 3, the release layer 3 is too hard, nullifying the effects of the elastic layer 3.
d. Thermal Insulation Layer 4
Referring to
The thickness of the thermal insulation layer 4 is desired to be in the range of 10-1,000 μm. If the thermal insulation layer 4 is no more than 10 μm, the thermal insulation layer 4 is not effective as a thermal insulation layer, and also falls short in durability. On the other hand, if the thickness of the thermal insulation layer 4 exceeds 1,000 μm, the distances from the magnetic cores 17a, 17b, and 17c, and exciting coil 18, to the heat generation layer 1 is too large; it is impossible for the magnetic flux to be absorbed by a sufficient amount by the heat generation layer 1.
The thermal insulation layer 4 prevents the heat generated in the heat generation layer 1, from being transmitted inward of the fixing film 10. Therefore, a fixing film 10 with the thermal insulation layer 4 is superior to a fixing film without the thermal insulation layer 4, in terms of the ratio of the heat supplied to the recording medium P, being therefore smaller in power consumption.
Further, the selection of a slippery substance as the material for the thermal insulation layer 4 makes it possible to reduce the friction between the slippery member 40 and fixing film 10.
(5) Structure of Adjacencies of Fixing Film Sliding Portion
The stair-like portion 50b, or the downstream stair-like portion of the film guiding member 16 with respect to the fixing film sliding portion S, in terms of the moving direction of the fixing film 10, contributes to the recording medium separation from the fixing film 10. The height h of the stair-like portion 50b from the outwardly facing surface of the slippery member 40 has only to be no less than 0.1 mm and no more than 1.0 mm. If the height h is no more than 0.1 mm, a recording medium does not always satisfactorily separate from the fixing film 10, resulting sometimes in the occurrence of the so-called wraparound paper jam in the fixing device. On the contrary, if the height h is no less than 1.0 mm, a recording medium becomes excessively curled as it is passed through the fixing nip N. Further, if the heat generation layer 1 of the fixing film 10 is formed of metallic substance as is the heat generation layer 1 in this embodiment, the greater the height h, the greater the stress to which the fixing film 10 is subjected as it is rotated, and therefore, the sooner the fixing film 10 is likely to break due to fatigue. Thus, it is preferred that the height h is no more than 0.5 mm. In this embodiment, the height h is 0.3 mm.
Referring to
In this embodiment, the downstream stair-like portion 50b (
Referring to
Further, rendering the inward surface of the fixing film 10 rougher increases the grease retention by the inward surface of the fixing film 10, contributing to the further reduction of the friction between the fixing film 10 and film guiding member 16. The roughness Ra of the inward surface of the fixing film 10 is desired to satisfy the following formula: 0.07≦Ra≦0.5 [μm]. Moreover, providing the inward surface of the fixing film 10 with ridges and valleys (grooves) parallel to the moving direction of the fixing film 10 prevents the amount by which the grease moves in the direction perpendicular to the moving direction of the fixing film 10, that is, in the lengthwise direction of the fixing film 10. In other words, providing the inward surface of the fixing film 10 with such grooves is a very effective counter measure against the oozing of the grease from the lateral edges of the fixing film 10.
In this embodiment, the aforementioned stair-like portion (or portions) of the film guiding member 16 for recording medium separation, which protrudes the predetermined distance from the fixing film sliding portion S, is structured so that the range across which it extends matches the range of the path of an image proper on a recording medium. Therefore, virtually the entirety of the grease on the fixing film 10 passes the fixing film sliding portion S by way of the ranges in which the ridge does not protrude as far as the predetermined distance, or a stair-like portion is not present. However, in order to make it easier for the grease to move from the upstream side of the stair-like portion to the downstream side of the stair-like portion, the stair-like portion proper may be provided with slits. If slits are to be formed after the formation of the film guiding member 16, the cost for the slit formation adds to the cost of a fixing apparatus. Even if the slits are formed as the integral parts of the film guiding member 16, it requires a higher degree of manufacture control for the formation of the stair-like portion of the film guiding member 16, adding to the cost of a fixing apparatus. In other words, as long as the cost problem can be managed, the stair-like portion may be provided with the above described slits.
Further, referring to
Referring to
This embodiment is similar in structure to Embodiments 1 and 2 (FIGS. 13 and 15), except that the various structural components in this embodiment are different in dimension, in terms of the lengthwise direction of the apparatus, from those in Embodiments 1 and 2, and satisfy the following conditions:
Lf, Ls>Lr>Ld
When the above conditions were satisfied, satisfactory results were obtained: grease was not expelled at the lateral edges of the fixing film 10, and the grease was efficiently circulated.
The condition: Lr>Ld, is required for the reason described before.
The condition: Ls>Lr, is required for the following reason.
When this condition was satisfied, not only was the grease recirculated within the range, which corresponds in position and length to the nip (pressure roller 30), but also it was circulated in the range outside the range corresponding in position and length to the nip (pressure roller 30). In other words, the body of grease expelled into the range outward of the lengthwise end of the pressure roller 30 was also recirculated. In other words, satisfying this condition is effective to prevent grease from oozing at the lateral edges of the fixing film 10.
Although the present invention is effective regardless of the relationship between Lf and Ls, Lf is preferred to be greater than Ls: Lf>Ls, for the following reason. That is, when the fixing film 10 is longer than the slippery member 40, the former does not contact the latter outside the range of the latter. Thus, even if grease is made to ooze at the lengthwise end of the slippery member 40, it is not made to ooze at the lateral edge of the fixing film 10.
Further, if the following condition is satisfied:
Lp>Ld>Lt
This embodiment is similar to Embodiment 1, except that the film guiding member 16 in this embodiment does not have the slippery member 40.
The film guiding member 16 in this embodiment is desired to be formed of a heat resistant substance, such as a heat resistant resin, for example, phenol, resins superior in heat resistance, for example, phenol resin, polyimide resin, polyamide resin, polyamide-imide resin, polyether-ketone resin, polyester-sulfone resin, polyphenylene sulfide resin, LCP resin, etc. Further, the material for the film guiding member 16 in this embodiment is desired to be superior in slipperiness. Therefore, fluorinated resin such as PFA resin, PTFE resin, and FEP resin, or a heat resistant resin containing a substance, such as fluorinated resin, superior in slipperiness, are recommendable as the material for the film guiding member 16 in this embodiment.
This embodiment does not employ the slippery member 40. Therefore, it is lower in cost.
Further, the elimination of the slippery member 40 makes it possible to form the stair-like portion 50b as an integral part of the film guiding member 16, making therefore it possible to drastically reduce manufacturing errors regarding the height h of the stair-like portion 50b, compared to the structural arrangement in Embodiment 1, in which the stair-like portion 50b is created by the combination of the slippery member 40 and film guiding member 16.
Needless to say, in terms of the structure for preventing grease from oozing at the lateral edges of the fixing film 10, and also for reducing the friction between the fixing film 10 and film guiding member 16, the downstream stair-like portion 50b in this embodiment is similar to the downstream stair-like portion 50b in Embodiment 1.
Otherwise, the structure of the fixing apparatus in this embodiment is the same as the fixing apparatus 100 in Embodiment 1, and therefore, will not be described to avoid the repetition of the same description.
Referring to
Otherwise, the structure of this fixing apparatus is the same as those of the fixing apparatuses 100 in Embodiments 1-5. Therefore, it will not be described to avoid the repetition of the same description.
This is an embodiment of an image heating apparatus in accordance with the present invention, in which the portion of the stair-like portion, corresponding in position to the image path, has a plurality of slits, through which grease is allowed to pass the stair-like portion.
Structure of Adjacencies of Fixing Film Sliding Portion
The stair-like portion 150b, which is on the downstream side with respect to the fixing film sliding portion S in terms of the moving direction of the fixing film 10 contributes to the recording medium separation from the fixing film 10. The height h of the top edge of the stair-like portion 150b from the outwardly facing surface of the slippery member 40 has only to be no less than 0.1 mm and no more than 1.0 mM. If this height h is no more than 0.1 mm, the stair-like portion 150b does not satisfactorily contribute to the recording medium separation, resulting sometimes in the occurrence of the so-called wraparound paper jam in the fixing device. On the contrary, if the height h is no less than 1.0 mm, a recording medium becomes excessively curled as it is passed through the fixing nip N. Further, if the heat generation layer 1 of the fixing film 10 is formed of metallic substance as is the heat generation layer 1 in this embodiment, the greater the height h, the greater the stress to which the fixing film 10 is subjected as it is rotated, and therefore, the sooner the fixing film 10 is likely to break due to fatigue. Thus, it is preferred that the height h is no more than 0.5 mm. In this embodiment, the height h is 0.3 Mm.
Referring to
Further, the grease which collects between the fixing film sliding portion S and the downstream stair-like portion 150b can be released downstream through the slits 60 as the fixing film 10 is moved. Therefore, even when grease viscosity is relatively high, for example, when the fixing device has not sufficiently warmed up, for example, immediately after the power of the main assembly is turned on, the friction between the fixing film 10 and stair-like portion 150b does not increase due to the grease collection between the fixing film sliding portion S and the downstream stair-like portion 150b.
The dimension (width) W of the slit 60 in terms of the direction perpendicular to the moving direction of the fixing film 10 is no less than 0.5 mm and no more than 5 mm. In this embodiment, the width W is the width of the slit 60 measured at half the depth d of the slit 60. If the width W is no more than 0.5 mm, it is difficult for grease to move through the slit 60, failing to successfully reduce the friction between the fixing film 10 and stair-like portion. On the other hand, if the width W is no less than 5 mm, the fixing film 10 is likely to crease along the slit 60; once a crease is formed, the pattern of the crease is transferred onto the image being fixed. Further, if a metallic substance is used as the material for the heat generation layer 1 of the fixing film 10 as in this embodiment, the heat generation layer 1, or metallic layer, is likely to be break due to fatigue as the fixing film 10 is bent (creased). In this embodiment, the width W of the slit 60 is 1.0 mm.
As seen from downstream in terms of the moving direction of the fixing film 10, the slits in this embodiment appear as shown in
Further, the slits 60 in this embodiment are the parts of the stair-like portion 150b (FIG. 20), which is on the downstream side with respect to the fixing film sliding portion S. However, they may be the parts of the stair-like portion 150a (FIG. 20), which is on the upstream side. In other words, according to this embodiment, the bodies of grease on the portions of the inward surface of the fixing film 10, corresponding in position to the slits 66, are not scraped away. Therefore, it is possible to efficiently send grease into the fixing film sliding portion S.
This embodiment is similar to the above described Embodiment 7, except that the height h′ of the stair-like portion 150a in this embodiment, which is on the upstream side with respect to the fixing film sliding portion S in terms of the moving direction of the fixing film 10, is less than that in Embodiment 7.
According to this embodiment, in order to reduce the amount by which grease collects in the space formed by the stair-like portion 150a, the outwardly facing surface of the slippery member 40, and fixing film 10, the height h′ of the upstream stair-like portion 150a is reduced. Therefore, when grease viscosity is relatively high, for example, immediately after the power source of the main assembly is turned on, when the fixing apparatus has not sufficiently warmed up, the friction between the fixing film 10 and stair-like portion 150a is not as high as that in Embodiment 7.
Otherwise, the structure of this fixing apparatus 100 is the same as that of the seventh embodiment of a fixing apparatus 100. Therefore, it will not be described to avoid repetition of the same description.
This embodiment is similar to the above described Embodiment 7, except that the film guiding member 160 in this embodiment does not have the slippery member 40.
The material for the film guiding member 160 in this embodiment is desired to be superior in heat resistance. For example, heat resistant resin, such as phenol resin, polyimide resin, polyamide resin, polyamide-imide resin, polyether-ketone resin, polyester-sulfone resin, polyphenylene sulfide resin, LCP resin, etc., are recommendable. Further, the material for the film guiding member 160 in this embodiment is desired to be superior in slipperiness. Therefore, fluorinated resin such as PFA resin, PTFE resin, and FEP resin, or heat resistant resins containing a slippery substance, such as fluorinated resin, are recommendable as the materials for the film guiding member 160 in this embodiment.
This embodiment does not employ the slippery member 40. Therefore, it is lower in cost.
Further, the elimination of the slippery member 40 makes it possible to form the stair-like portion 150b as an integral part of the film guiding member 160, making therefore it possible to drastically reduce manufacturing errors regarding the height h of the stair-like portion 150b, compare to the structural arrangement in Embodiment 7, in which the stair-like portion 150b is created by the combination of the slippery member 40 and film guiding member 160.
Further, the film guiding member 160 in this embodiment is provided with only the stair-like portion 150b, or the downstream stair-like portion which contributes to the recording medium separation; the portion of the film guiding member 160 in the upstream adjacencies of the fixing film sliding portion S is not provided with a stair-like portion. With the employment of such a structural arrangement, it does not occur that the grease on the inward surface of the fixing film 10 is scraped away by a stair-like portion, on the upstream side with respect to the fixing film sliding portion S. In other words, the employment of such a structural arrangement makes it possible to further reduce the friction between the fixing film 10 and film guiding member 160.
As will be expected, in order to reduce the friction between the fixing film 10 and film guiding member 160, the downstream stair-like portion 150b is provided with a plurality of slits 160 similar to those in Embodiment 7 (FIG. 22).
Otherwise, the structure of this embodiment of a fixing apparatus 100 in accordance with the present invention is the same as that of the seventh embodiment of a fixing apparatus 100. Therefore, it will not be described to avoid the repetition of the same description.
The selection of the structure of the fixing apparatus 100 as an image heating apparatus does not need to be limited to those of the seventh to ninth embodiments of the present invention, in which the pressure roller driving method was employed.
For example, referring to
On the inward side of the film guiding member 160, the combination of magnetic cores 17a, 17b, and 17c, and an exciting coil 18, is disposed as a magnetic field generating means.
The structures of the adjacencies of the fixing film sliding portion between the film guiding member 160 and fixing film 10 are similar to those in the seventh embodiment. That is, the film guiding member 160 has stair-like portions, and the stair-like portions have slits.
1) In the case of the fixing film 10 in which heat can be generated by electromagnetic induction, and which is used for a thermal fixing apparatus for a monochromatic image forming apparatus, or a single-pass pass multicolor image forming apparatus, the elastic layer 2 of the fixing film 10 may be eliminated. The material for the heat generation layer 1 may be a mixture of resin and metallic filler. Further, the fixing film 10 may be a mono-layer film formed of a single substance in which heat can be generated by electromagnetic induction.
2) The fixing film 10 does not need to be an endless rotatable member. For example, it may be a id long roll of web, which can be repeatedly rolled out at one end while being rolled up at the other end.
3) The pressing member 30 does not need to be in the form of a roller; it may be in a form other than a roller. For example, it may be in the form of a rotatable belt. Further, the pressing member 30 may be provided with a heat generating means, for example, a heating means based on electromagnetic induction, for supplying heat to a recording member from the pressing member 30 as well as the fixing film 10, to keep the temperature of the fixing nip N at a predetermined level.
4) The application of the present invention regarding an image heating apparatus is not limited to a thermal image fixing apparatus such as the above described embodiments of the present invention. The present invention can be applied to a wide range of means and apparatuses for thermally processing an object to be heated, for example, an image heating apparatus for improving the surface properties, such as glossiness, of an image, by heating the recording medium bearing the image, an image heating apparatus for temporarily fixing an image, etc.
While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth, and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2002/027970 | Feb 2002 | JP | national |
| 2002/087772 | Mar 2002 | JP | national |
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