Patent Grant
9405234
1. Field of the Invention
The present invention relates to image forming apparatuses that form images with electrophotography, such as copying machines, printers, fax machines, and multifunction machines.
2. Description of the Related Art
Some image forming apparatuses employing electrophotography such as copying machines or printers include an intermediate transfer belt as a transfer belt. An image forming apparatus including an intermediate transfer belt forms full-color images by performing a first transfer process and a second transfer process.
In the first transfer process, a toner image formed on the surface of the electrophotographic photoconductor is first-transferred to the intermediate transfer belt. The first transfer process is repeatedly performed on toner images of different colors, whereby the toner images of multiple colors are formed on the surface of the intermediate transfer belt. In the second transfer process, the toner images of multiple colors are collectively transferred to the surface of a transfer medium such as a paper sheet. The toner images that have been transferred to the transfer medium are subsequently fixed by a fixing unit, whereby a full-color image is obtained.
Examples usable as a transfer device of an image forming apparatus include transfer devices having, for example, a roller shape, a blade shape, or a brush shape. These transfer devices are contact members that come into contact with the inner peripheral surface of the intermediate transfer belt at a position at which the members are located opposite the corresponding photoconductors. Among the above-described transfer devices, a brush-shaped transfer device includes multiple conductive fiber threads and the individual fibers are independently capable of touching the inner peripheral surface of the intermediate transfer belt. The use of the brush-shaped transfer device thus reduces unevenness in contact-related properties that would result from the use of a roller-shaped or blade-shaped transfer device. Thus, the transfer device can more evenly come into contact with the inner peripheral surface of the intermediate transfer belt. The brush-shaped transfer device thus facilitates reduction of image defects that can occur during the first transfer process such as unevenness in density.
Japanese Patent Laid-Open No. 2011-248385 discloses an image forming apparatus that includes a brush-shaped transfer device as a transfer device. In the brush-shaped transfer device disclosed in Japanese Patent Laid-Open No. 2011-248385, multiple conductive fiber threads constituting a brush are supported by a metal holder made of stainless steel (holding member) using a double-sided adhesive tape. The metal holder is fixed and the conductive fiber threads constituting the transfer device come into contact with the back surface of the intermediate transfer belt using their elasticity.
In the above-described image forming apparatus, however, some of conductive fiber threads of the brush-shaped transfer device may be disposed so as to protrude upstream from a contact area, over which the intermediate transfer belt and the photoconductor drum come into contact with each other, in the direction in which the intermediate transfer belt moves. Conductive fiber threads disposed so as to protrude upstream from the contact area cause an electric field in a gap between the photoconductor drum and the surface of the intermediate transfer belt and the electric field causes discharging (pre-discharging). This discharging may cause a streak-like image defect.
On the other hand, if a conductive fiber thread receives force acting in the direction in which the intermediate transfer belt moves as a result of the conductive fiber rubbing against the intermediate transfer belt, the conductive fiber thread may come out of the holding member or may be displaced over the holding member.
The present invention provides an image forming apparatus in which multiple conductive fiber threads are brought into contact with a transfer belt, that minimizes the occurrence of streak-like image defects, and that is capable of preventing the conductive fiber threads from coming out of the holding member or being displaced over the holding member.
According to an aspect of the invention, an image forming apparatus includes an image carrying member that carries a toner image; a transfer belt that is endless and movable while being in contact with the image carrying member; and a transfer device that transfers the toner image from the image carrying member to the transfer belt, the transfer device including a fiber member including a plurality of conductive fiber threads and a holding member that holds the fiber member, the fiber member coming into contact with an inner peripheral surface of the transfer belt while being held by a holding surface of the holding member. The transfer device comes into contact with the transfer belt in such a manner that an upstream side of the fiber member in a movement direction of the transfer belt touches the transfer belt before a downstream side of the fiber member in the movement direction touches the transfer belt in an initial contact state in which the image carrying member is separated from the transfer belt and the fiber member starts touching the transfer belt. The holding surface is inclined with respect to an opposing portion of the inner peripheral surface of the transfer belt in such a manner that a distance between the holding surface and the opposing portion of the inner peripheral surface of the transfer belt increases from a downstream side to an upstream side in the movement direction of the transfer belt in a contact state in which the image carrying member and the transfer belt are in contact with each other and the transfer belt and the transfer device are in contact with each other.
Further features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings).
Hereinbelow, embodiments of the present invention are exemplarily described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative positions, or other properties of components described in the following embodiments should be appropriately changed depending on various conditions or the structure of the apparatus to which the present invention is applied. Unless otherwise specifically described, the embodiments are not meant to limit the scope of the invention to those described in the embodiments.
The image forming apparatus 1 is an apparatus of a tandem type employing an intermediate transfer method. Specifically, the image forming apparatus 1 obtains recorded images by sequentially first-transferring toner images of different colors, formed in accordance with image information decomposed into multiple color components, onto an intermediate transfer device so that the toner images are stacked one on top of another and then by collectively second-transferring the stacked toner images to a transfer medium.
The image forming apparatus 1 sequentially first-transfers toner images of different colors, formed in accordance with image information decomposed into multiple color components, onto an intermediate transfer belt 11, serving as an intermediate transfer device, so that the toner images are stacked one on top of another. Then, the image forming apparatus 1 collectively second-transfers the stacked toner images to a transfer medium P. Here, the intermediate transfer belt 11 is a transfer belt. The image forming apparatus 1 obtains a recorded image by fixing the toner images onto the transfer medium P. The image forming apparatus 1 includes first, second, third, and fourth stations SY, SM, SC, and SK, which are multiple image forming units. In this embodiment, the first to fourth stations SY to SK respectively form toner images of yellow (Y), magenta (M), cyan (C), and black (K).
In this embodiment, each of the first to fourth stations SY to SK have substantially the same configuration and perform substantially the same operations, except for the colors of toner used in each station. Thus, unless the stations are particularly required to be distinguished from one another, the alphabets Y, M, C, and K at the end of the reference symbols representing the colors for which the components are provided are omitted in the following description and a general description is provided, instead.
Each station S includes a photoconductor drum 2, which is a drum-shaped electrophotographic photoconductor, serving as an image carrying member. The photoconductor drum 2 is driven by a motor, not illustrated and serving as a driving unit, to rotate in a counter-clockwise direction in
In addition, an intermediate transfer belt 11, which is a movable endless belt and serves as a transfer belt, is disposed so as to face the photoconductor drums 2 of the respective stations S. The intermediate transfer belt 11 is made of a tube-shaped endless film and stretched by four rollers, which are stretching members including a driving roller 13, a second transfer opposing roller 12, and stretching rollers 14 and 28. The intermediate transfer belt 11 rotationally moves (rotates) in the direction of arrow d in
Multiple first transfer brushes 4, serving as brush-shaped transfer devices, are disposed inward of the inner peripheral surface (back surface) of the intermediate transfer belt 11 at positions at which the first transfer brushes 4 are located opposite the respective photoconductor drums 2 with the intermediate transfer belt 11 interposed therebetween. Specifically, as described below, the first transfer brushes 4 are pressed against the back surface of the intermediate transfer belt 11. As a result, each photoconductor drum 2 and the intermediate transfer belt 11 come into contact with each other and forms a first transfer portion B1, which is a contact area (in
At the time of image forming, the surface of the photoconductor drum 2 in rotation is uniformly charged by the charging roller 7. At this time, a predetermined charging voltage (charging bias) is applied to the charging roller 7 from a charging power source (not illustrated). A laser scanner 100 irradiates the surface of the charged photoconductor drum 2 with a laser beam L according to the image information. Thus, an electrostatic latent image is formed on the photoconductor drum 2.
The electrostatic latent image formed on the photoconductor drum 2 is developed (rendered visible) into a toner image by the developing unit 3. The developing unit 3 carries toner, serving as a developer, to a rotatable developer carrier, transports the toner to the position at which the toner faces the photoconductor drum 2 (development position), and feeds the toner to the surface of the photoconductor drum 2 in accordance with the electrostatic latent image formed on the photoconductor drum 2. At this time, a predetermined development voltage (development bias) is applied to the developer carrier from a development power source (not illustrated). In this embodiment, the developing unit 3 develops the electrostatic latent image on the photoconductor drum 2 using reversal development. Specifically, the developing unit 3 develops the electrostatic latent image by attaching toner charged in the same polarity as the polarity in which the photoconductor drum 2 is charged (negative polarity in the embodiment) to an image portion (exposure portion) on the photoconductor drum 2 that has been exposed to light after being charged and thus has a low absolute potential.
Each toner image formed on the photoconductor drum 2 in rotation is transferred (first-transferred) to the rotating intermediate transfer belt at the corresponding first transfer portion B1 with the operation of the corresponding first transfer brush 4. At this time, a voltage is applied to the first transfer brush 4 from the first transfer power source, serving as a voltage applying unit. This voltage is a first transfer voltage (first transfer bias), which is a direct current voltage having a polarity (positive polarity in this embodiment) opposite to the polarity in which toner forming the toner image is originally charged (negative polarity in this embodiment). In the first transfer process, toner remaining on the photoconductor drum 2 (remnant first transfer toner) without being transferred to the intermediate transfer belt 11 is removed by a drum cleaner.
To form, for example, a full-color image, the following process including charging, exposure to light, development, and first transfer is sequentially performed from the upstream side in the direction of movement of the surface of the intermediate transfer belt 11 in the first to fourth stations SY to SK. Thus, a multilayer toner image for a full-color image is formed on the intermediate transfer belt 11 as a result of toner images of four different colors, yellow, magenta, cyan, and black being transferred to the intermediate transfer belt 11 so as to be stacked one on top of another.
The toner image on the intermediate transfer belt 11 is transferred (second-transferred) onto a transfer medium P at the second transfer portion B2 by an operation of the second transfer roller 20. Specifically, one of transfer media P accommodated in a cassette is picked up by a feeding roller 31 and then fed to the second transfer portion B2 by a registration roller 33 at a predetermined timing. At substantially the same time, a second transfer voltage (second transfer bias), which is a direct current voltage having a polarity opposite to the polarity in which toner, forming a toner image, is originally charged, is applied to the second transfer roller 20 from a second transfer power source.
Toner remaining on the intermediate transfer belt (remnant second transfer toner) without being transferred to a transfer medium P in the second transfer process is transferred to the photoconductor drum 2 for recovery after being charged by the charging roller 19. The transfer medium P to which the toner image has been second-transferred is transported to a fixing unit 6. The fixing unit 6 heats and presses the transfer medium P while transporting the transfer medium P. The unfixed toner image on the transfer medium P is fixed onto the transfer medium P with heat and pressure. Then, the transfer medium P is transported by a conveying roller 34 to an outer receiving tray 10.
The fiber member 4a of each first transfer brush 4 according to the embodiment and the intermediate transfer belt 11 are capable of moving into contact with or away from each other.
In the contact state illustrated in
In the separated state illustrated in
Subsequently, the structure of the first transfer brushes 4Y, 4M, 4C, and 4K, serving as first transfer devices according to the embodiment, is described. Since the first transfer brushes 4Y, 4M, 4C, and 4K have the same structure, the symbols Y, M, C, and K are omitted in the following description.
In this embodiment, the width W of the first transfer brush 4 is 4 mm. The width of the first transfer brush 4 extends in the direction parallel to the direction in which the intermediate transfer belt 11 moves. The length L of the first transfer brush 4 is 230 mm. The length of the first transfer brush 4 extends in the direction perpendicular to the direction in which the intermediate transfer belt 6 moves.
In this embodiment, the width W of the first transfer brush 4 is 4 mm, whereby the contact area over which the first transfer brush 4 and the intermediate transfer belt 6 come into contact with each other can have a sufficiently large width.
Examples usable as the fiber member 4a of the first transfer brush 4 include a brush member of a pile textile type or an electrostatic flocking type. Pile textile is textile formed by interweaving pile yarns, serving as conductive fiber threads, into interstices in a ground fabric (corresponding to the board 4b) constituted by warp and weft. The pile textile is fixed to a support member by, for example, bonding using a bonding portion (double-sided adhesive tape 43 in the embodiment), so that the first transfer brush 4 serving as a brush member is obtained. Electrostatic flocking, on the other hand, is a method that utilizes electrostatic attracting force in a high-voltage electrostatic field for anchoring short fiber, serving as conductive fiber threads, on an unraised portion (corresponding to the board 4b) coated with an electroconductive adhesive in advance substantially perpendicularly to the unraised portion. The fiber member 4a can be also obtained with this method.
Examples usable as conductive fiber threads include synthetic fiber impregnated with an electroconductive agent. Specifically, conductive fiber threads made of material such as nylon or polyester containing scattered carbon powder are usable. Usable examples include conductive fiber threads having a single fiber fineness in the range of 2 to 15 dtex, a diameter in the range of 10 to 40 μm, and a dry strength in the range of 1 to 3 cN/dtex. Conductive fiber threads having a resistivity ρfiber in the range of 102 to 108 Ωcm are favorable in terms of the transfer efficiency.
The direction in which the fiber member 4a extends from the upper surface of the board 4b in the state where the fiber member 4a is not brought into contact with the intermediate transfer belt 11 is referred to as a direction of raising (the direction of up-pointing arrow in
In this embodiment, a brush member having the following specifications is used as the first transfer brush 4 having characteristic features:
Specifications of First Transfer Brush:
fiber member, pile textile made of conductive fiber threads;
material of conductive fiber threads, nylon fiber in which carbon powder is dispersed;
single fiber fineness of conductive fiber threads, 7 dtex;
diameter of conductive fiber threads, 28 μm;
dry strength of conductive fiber threads, 1.6 cN/dtex;
resistivity of conductive fiber threads, 106 Ωcm;
fiber length of conductive fiber threads, 2 mm; and
arrangement density, 10850 threads/cm2.
Referring now to
The holding arm 42 is rotatable around a rotation shaft 44. The rotation shaft 44 is located upstream from the first transfer brush 4 in the movement direction d of the intermediate transfer belt 11 and inward of the inner peripheral surface of the intermediate transfer belt 11. The direction in which the rotation shaft extends is substantially parallel to the direction in which the rotation axis of the photoconductor drum 2 extends (or substantially perpendicular to the movement direction d of the intermediate transfer belt 11). The rotation shaft 44 and the holding arm 42 that rotates around the rotation shaft 44 restricts the direction in which the first transfer brush 4 is movable and thus restricts the contact angle of the fiber member 4a with respect to the intermediate transfer belt 11. Since the rotation shaft 44 is located upstream from the contact area, over which the intermediate transfer belt 11 and the first transfer brush 4 come into contact with each other, in the direction in which the intermediate transfer belt 11 moves and inward of the inner peripheral surface of the intermediate transfer belt 10, the rotation shaft 44 can be rotated in such a direction as to reduce the pressure utilizing a force resulting from the contact between the intermediate transfer belt 11 and the first transfer brush 4. The rotation shaft 44 does not necessarily have to be located at this position and may be located, for example, outward of the outer peripheral surface of the intermediate transfer belt 10 with the use of an L-shaped holding member.
One feature of the embodiment is that, in the initial contact state, the fiber member 4a of the first transfer brush 4 comes into contact with the intermediate transfer belt 11 while being inclined toward the downstream side in the movement direction d of the intermediate transfer belt 11. Specifically, the upstream side of the fiber member 4a in the movement direction d touches the transfer belt 11 before the downstream side of the fiber member 4a touches the transfer belt 11. Specifically, condition A below is satisfied:
Condition A
In the initial contact state, an angle θa (fiber contact angle) formed between the movement direction d of the intermediate transfer belt 11 and the raising direction j satisfies 0<θa<90°; The raising direction j is defined as a direction of raising of conductive fiber threads extending perpendicularly to the holding surface 42a, where θa is defined as a fiber contact angle and θa=80° in
As described above, if the fiber member 4a is located so as to protrude upstream from the contact area (first transfer portion B1), over which the photoconductor drum 2 and the intermediate transfer belt 11 come into contact with each other, a transfer electric field is formed in a gap upstream from the contact area between the photoconductor drum 2 and the surface of the intermediate transfer belt 11. The transfer electric field formed upstream from the contact area causes pre-discharging and toner scattering. As a result, portions in which toner scattering occurs and portions in which toner scattering does not occur coexist in the longitudinal direction perpendicular to the movement direction of the intermediate transfer belt 11, causing a streak-like image defect. In the structure in which the brush-position changing unit 16 moves the first transfer brush 4 into contact with the intermediate transfer belt 11 as in the case of the embodiment, the upstream end of the fiber member 4a may bend so as to protrude toward the upstream side in the initial contact state.
The structure of the image forming apparatus according to the embodiment satisfies condition A, described above. Thus, in the process from the initial contact state to the contact state, the fiber member 4a bends so as to slide over the back surface of the intermediate transfer belt 11 toward the downstream side. Thus, the structure satisfying condition A prevents the upstream end of the fiber member 4a from protruding upstream from the contact area, over which the first transfer brush 4 and the photoconductor drum 2 come into contact with each other, in the initial contact state, minimizing the occurrence of streak-like image defects. In this embodiment, the first transfer brush 4 is brought into contact with the intermediate transfer belt 11 in the initial contact state while the intermediate transfer belt 11 is rotationally moved in the direction of arrow d. This structure enables the fiber member 4a to bend in the movement direction d of the intermediate transfer belt from the initial contact state upon receipt of force from the intermediate transfer belt 11, and thus can prevent the upstream end of the fiber member 4a from protruding.
Condition B
In the contact state, an angle θb (receiving surface contact angle) formed between the movement direction d of the intermediate transfer belt 11 and the normal k normal to the holding arm receiving surface satisfies 90<θb<180°, and θb=110° in the image forming apparatus according to the embodiment.
The portion enclosed with the dotted line in
Here, referring to
In the contact state, on the other hand, condition B is satisfied as illustrated in
Now, comparative example 2 is described.
In comparative example 2, the fiber member 4a of the first transfer brush 4 comes into contact with the intermediate transfer belt 11 in the initial contact state while being inclined toward the downstream side in the movement direction d of the intermediate transfer belt 11. Specifically, condition A is satisfied and the fiber contact angle θa is 70°. Thus, as in the case of the embodiment, this structure prevents the occurrence of streak-like image defects. In the contact state, on the other hand, as illustrated in
As described above, comparative example 1 does not satisfy condition A and thus causes streak-like image defects. Comparative example 2 does not satisfy condition B and thus the fiber member 4a of the first transfer brush 4 may come off the holding arm 42 or may be displaced over the holding arm 42.
The embodiment, on the other hand, satisfies condition A and condition B and thus can prevent streak-like image defects from occurring and prevent the fiber member 4a of the first transfer brush 4 from coming off or being displaced.
In the description of the structure of the first embodiment, the brush-position changing unit 16 moves the first transfer brushes 4 of all the stations into contact with or away from the intermediate transfer belt 11 and the first transfer brushes 4 that are moved into contact with or away from the intermediate transfer belt 11 satisfy condition A and condition B. In the second embodiment, on the other hand, the first transfer brush 4 of at least one station stays in the contact state without being moved into contact with or away from the intermediate transfer belt 11 by the brush-position changing unit 16. Other components of the image forming apparatus according to the second embodiment are the same as those of the image forming apparatus according to the first embodiment and thus are denoted by the same reference symbols.
The first transfer brush 4 of each color station has the same structure as that according to the first embodiment: the first transfer brush 4 of each color station satisfies condition A in the initial contact state and satisfies condition B in the contact state. Thus, the use of the first transfer brush 4 that is moved into contact with or away from the intermediate transfer belt 11 enables reduction of the occurrence of streak-like image defects while the fiber member 4a of the first transfer brush 4 can be prevented from coming off or being displaced.
On the other hand, the first transfer brush 4 corresponding to the black station stays in contact with the intermediate transfer belt 11 regardless of the states of the brushes 4 corresponding to the color stations, as illustrated in
The second embodiment does not satisfy condition B described in the first embodiment in the contact state. As will be described with reference to
The reason why the pressing forces are determined in this manner is as follows. In this embodiment, the brush-position changing unit 16 changes the first transfer brushes 4 of the color stations from the separated state to the contact state with respect to the intermediate transfer belt 11. The springs 41Y, 41M, and 41C exert a pressing force as high as 4 N in order to raise the corresponding first transfer brushes 4 against the tension of the intermediate transfer belt 11 stretched between the driving roller 13 and the second transfer opposing roller 12. In the black station, on the other hand, the first transfer brush 4 does not have to raise the intermediate transfer belt 11 and thus the spring 41K exerts a low pressing force of 2 N.
Thus, although condition B is not satisfied, the first transfer brush 4 receives from the intermediate transfer belt 11 a low frictional force toward the downstream side in the movement direction of the intermediate transfer belt 11 after the start of rotation of the intermediate transfer belt 11 in response to the start of the image forming operation. Thus, the first transfer brush 4 can be prevented from coming off the holding arm or being displaced over the holding arm without the occurrence of a force acting in such a direction as to press the first transfer brush 4 against the holding arm 42.
In the state illustrated in
When the frictional force temporarily increases as described above, a force acting in such a direction as to separate the first transfer brush 4 from the intermediate transfer belt 11 around the rotation shaft 44 acts on the holding arm 42 of the first transfer brush 4. Specifically, the state illustrated in
In the first embodiment and the second embodiment described above, an image forming apparatus including an intermediate transfer belt as a transfer belt has been described but the present invention is not limited to this image forming apparatus. Specifically, the same effects can be obtained from the use of a conveying belt, as a transfer belt, that transports a transfer medium to which a toner image is directly transferred from the photoconductor drum.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2014-099839, filed May 13, 2014, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2014-099839 | May 2014 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5649272 | Kwon | Jul 1997 | A |
| 5943526 | Kodama | Aug 1999 | A |
| 5966560 | Kodama | Oct 1999 | A |
| 20070014597 | Ishii | Jan 2007 | A1 |
| 20150117915 | Iida | Apr 2015 | A1 |
| Number | Date | Country |
|---|---|---|
| 0487046 | May 1992 | EP |
| 2743778 | Jun 2014 | EP |
| 2011-248385 | Dec 2011 | JP |
| 2014-077938 | May 2014 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20150331366 A1 | Nov 2015 | US |
