JP2015025847A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus having a conductive fiber as transfer means, configured to prevent reduction in contact performance between the conductive fiber and an intermediate transfer belt, to obtain desired transfer performance.SOLUTION: Transfer means includes a raised part 5a formed of a plurality of conductive fibers in contact with a transfer belt, a substrate part 5b which comes into contact with the raised part to support the raised part 5a, and a support member 11 for supporting the substrate part 5b with a support surface. The amount V of raised part 5a entering the transfer belt 6 is larger than flatness of the support member 11 in the support surface.

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, and a multi-function machine that forms an image by electrophotography.

  Conventionally, as an image forming apparatus such as a copying machine or a printer using an electrophotographic system, there is a system using an intermediate transfer belt. In an intermediate transfer belt type image forming apparatus, a full-color image is formed through a primary transfer process and a secondary transfer process.

  In the primary transfer step, the toner image formed on the surface of the electrophotographic photosensitive member is primarily transferred onto the intermediate transfer belt. By repeatedly performing the primary transfer process for a plurality of color toner images, a plurality of color toner images are formed on the surface of the intermediate transfer belt. In the secondary transfer process, toner images of a plurality of colors are collectively transferred onto the surface of a transfer material such as paper. The toner image transferred onto the transfer material is then fixed by fixing means. Thereby, a full color image is obtained.

  As a transfer unit of the image forming apparatus, a transfer member such as a roller, a blade, or a brush is used. These transfer members are contact members that contact the inner peripheral surface (back surface) of the intermediate transfer belt at a position facing the photoconductor. In particular, the brush-shaped transfer member is composed of a plurality of conductive fibers, and each of the fibers can contact the back surface of the intermediate transfer belt independently. Therefore, contact unevenness that occurs when a roller-like or blade-like transfer member is used is improved, and more uniform contact with the back surface of the intermediate transfer belt can be obtained. This makes it easy to suppress image defects such as density unevenness that occur in the primary transfer process.

  Patent Document 1 discloses an image forming apparatus including a brush-shaped transfer member as a transfer unit. In the brush-like transfer member of Patent Document 1, a plurality of conductive fibers constituting a brush are supported by a stainless steel metal holder via a double-sided tape. The metal holder is fixed, and the plurality of conductive fibers constituting the transfer member come into contact with the back surface of the intermediate transfer belt by the elasticity of the fibers themselves.

JP2011-248385A

  However, since the brush-shaped transfer member disclosed in Patent Document 1 has a metal holder that supports a plurality of conductive fibers fixed thereto, the shape of the intermediate transfer belt or the photosensitive drum that faces the intermediate transfer belt is fixed. It is necessary to follow the change only by the elasticity of the conductive fiber. For this reason, when the shape of the intermediate transfer belt or the photosensitive drum is largely changed, the contact property of the conductive fibers with respect to the intermediate transfer belt may be lowered, and it may be difficult to obtain desired transfer performance.

  Accordingly, the present invention provides an image forming apparatus that has a conductive fiber as a transfer unit, and that can suppress a decrease in the contact property of the conductive fiber with respect to the intermediate transfer belt and obtain desired transfer performance. The purpose is to do.

  In order to solve the above problems, the present invention provides an image carrier that carries a toner image, a transfer belt that can move in contact with the image carrier, and a position that faces the image carrier via the transfer belt. And a transfer unit configured to transfer a toner image from the image carrier to the transfer belt side. The transfer unit includes a raised portion made of a plurality of conductive fibers in contact with the transfer belt, and the raised An image forming apparatus comprising: a base member that contacts the portion and supports the raised portion; wherein the transfer unit includes a support member that supports the base portion on a support surface, and the support member is flexible. The amount of penetration of the raised portion into the transfer belt is greater than the flatness of the support surface.

  According to the present invention, the amount of intrusion of the raised portion of the transfer means into the intermediate transfer belt is made larger than the plane of the support member, thereby suppressing the decrease in the contact of the raised portion with the intermediate transfer belt and achieving desired transfer performance. It is possible to obtain.

1 is a schematic diagram illustrating an image forming apparatus according to a first embodiment. The perspective view of the transfer means of Embodiment 1. Sectional drawing explaining the support structure of the supporting member of Embodiment 1. Diagram for explaining the amount of intrusion of the transfer means The figure explaining the deformation | transformation of the supporting member regarding the longitudinal direction orthogonal to the moving direction of a transfer belt The figure explaining the contact state of the transfer member regarding the longitudinal direction orthogonal to the moving direction of a transfer belt Schematic for demonstrating the measuring method of the flatness of a supporting member The figure explaining the evaluation result of this embodiment FIG. 6 is a diagram illustrating the displacement amount of the transfer belt in the second embodiment. FIG. 5 is a diagram illustrating contact between the intermediate transfer belt and the primary transfer brush in Example 2. FIG. 6 is a diagram for explaining a method for measuring a displacement amount of a transfer belt in Embodiment 2.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in the following embodiments should be appropriately changed according to the configuration of the apparatus to which the present invention is applied and various conditions. Therefore, unless specifically stated otherwise, the scope of the present invention is not intended to be limited thereto.
(Embodiment 1)
1. 1 is a diagram showing a schematic cross section of an image forming apparatus according to the present invention. The image forming apparatus 100 according to the first embodiment is an electrophotographic full-color laser beam printer. The image forming apparatus 100 forms an image on a transfer material such as a recording sheet or an OHP sheet by an electrophotographic method in accordance with a signal sent from an external device such as a personal computer that is communicably connected to the image forming apparatus 100. be able to.

  The image forming apparatus 100 is of a tandem type using an intermediate transfer method. That is, the image forming apparatus 100 primarily superimposes each color toner image formed in accordance with the image information separated into a plurality of color components on the intermediate transfer member, and then transfers the image onto the transfer material. A recorded image is obtained by transfer.

  The image forming apparatus 100 according to the first embodiment includes first, second, third, and fourth stations Sa, Sb, Sc, and Sd as a plurality of image forming units. In the first embodiment, the first to fourth stations Sa to Sd are for forming toner images of respective colors of yellow (Y), magenta (M), cyan (C), and black (K). .

  There are many common parts in the configuration and operation of the stations Sa to Sd. Therefore, in the following, when it is not necessary to distinguish, subscripts a, b, c, and d for indicating an element provided for any color will be omitted.

  The image forming apparatus 100 includes a photosensitive drum 1 as an image carrier in the station S. The photosensitive drum 1 is rotationally driven in a direction indicated by an arrow R1 (counterclockwise) by a driving unit (not shown). The surface of the photosensitive drum 1 is uniformly charged by the charging roller 2. Next, the exposure device 3 irradiates the photosensitive drum 1 with laser light L according to the image information, and an electrostatic latent image is formed. When the surface of the photosensitive drum 1 further advances in the direction of the arrow R1 in the figure, the electrostatic latent image formed on the photosensitive drum 1 according to the image information is visualized as a toner image by the developing device 4. The developing device 4 develops the latent image on the photosensitive drum 1 by a reversal development method. That is, the developing device 4 develops a toner (negative polarity) charged with the same polarity as the charged polarity (negative polarity) of the photosensitive drum 1 on the uniformly charged image portion (exposure portion) on the photosensitive drum 1. I do.

  In the moving direction of the surface of the photosensitive drum 1 indicated by an arrow R1 in the figure, an intermediate transfer belt 6 that can be rotated and moved as an intermediate transfer member is disposed downstream of the developing position. The intermediate transfer belt 6 is a cylindrical and endless transfer belt that is stretched around three rollers of a driving roller 61, a secondary transfer counter roller 62, and a tension roller 63. The intermediate transfer belt 6 is moved in the direction indicated by the arrow R3 (clockwise) at substantially the same speed as that of the surface of the photosensitive drum 1 when the driving roller 61 is rotationally driven in the direction indicated by the arrow R2 (clockwise). To do.

  A transfer means 5 including a transfer member is disposed at a position facing the photosensitive drum 1 with the intermediate transfer belt 6 interposed therebetween. The primary transfer portion B1 is formed by the contact between the photosensitive drum 1 and the intermediate transfer belt 6. As the photosensitive drum 1 and the intermediate transfer belt 6 rotate, the toner image formed on the photosensitive drum 1 is primarily transferred to the intermediate transfer belt 6 by the action of the transfer means 5. (Primary transfer is performed on the intermediate transfer belt side.) At this time, a primary transfer power supply 50 applies a primary transfer voltage having a polarity (positive polarity) opposite to the charging polarity (negative polarity) of the toner to the transfer unit 5. The The diameter of the photosensitive drum 1 is 30 mm. Further, a primary transfer voltage of 0 to 1.0 kV can be applied to the transfer means 5 from the primary transfer power supply 50.

  Residual toner remaining on the photosensitive drum 1 without being transferred to the intermediate transfer belt 6 in the primary transfer process is cleaned by the photosensitive drum cleaner 7. The photosensitive drum cleaner 7 includes a cleaning blade 71 that is a plate-like elastic body that contacts the surface of the photosensitive drum 1. Further, the photosensitive drum cleaner 7 includes a toner container 72 that collects the toner removed from the surface of the photosensitive drum 1 by the cleaning blade 71.

  The charging, exposure, development, and primary transfer processes as described above are sequentially performed from the upstream side in the movement direction of the surface of the intermediate transfer belt 6 in each of the yellow, magenta, cyan, and black colors at the first to fourth stations Sa to Sd. Do about. As a result, a full-color image in which toner images of four colors of yellow, magenta, cyan, and black are superimposed on the intermediate transfer belt 6 is formed.

  A secondary transfer roller 8 is disposed at a position facing the secondary transfer counter roller 62 with the intermediate transfer belt 6 interposed therebetween. The secondary transfer roller 8 is pressed against the secondary transfer counter roller 62 via the intermediate transfer belt 6 to form a secondary transfer portion B2 where the intermediate transfer belt 6 and the secondary transfer roller 8 are in contact with each other.

  The toner image on the intermediate transfer belt 6 is secondarily transferred onto the transfer material P by the action of the secondary transfer roller 8. That is, in the transfer material supply unit 20, the transfer material P accommodated in the cassette 21 is sent out by the supply roller 22, and then the secondary transfer in which the intermediate transfer belt 6 and the secondary transfer roller 8 come into contact with each other by the registration roller 23. It is supplied to the part B2 at a predetermined timing. At substantially the same time, a secondary transfer voltage having a polarity (positive polarity) opposite to the normal charging polarity of the toner is applied to the secondary transfer roller 8 by the secondary transfer power supply 80.

  A cleaning blade 64 is disposed at a position facing the driving roller 61 with the intermediate transfer belt 6 interposed therebetween. The cleaning blade 64 comes into contact with the intermediate transfer belt 6 and collects transfer residual toner remaining on the intermediate transfer belt 6 without being transferred to the transfer material P in the secondary transfer process. The toner image transferred to the transfer material P is fixed by the fixing unit 90. Thereafter, the transfer material P is discharged to a transfer material stacking unit (not shown).

2. Intermediate transfer belt The intermediate transfer belt 6 was a polyimide resin film having a thickness of 60 μm and a volume resistivity adjusted to 10 ⁹ Ωcm by mixing a conductive agent. The intermediate transfer belt 6 is stretched around three axes of a drive roller 61, a secondary transfer counter roller 62, and a tension roller 63, and a tension of about 20 N is applied to the intermediate transfer belt 6 by the tension roller 63. Ribs 13 are provided at both ends of the intermediate transfer belt 6 to stabilize the conveyance of the intermediate transfer belt 6.

3. Secondary transfer roller As the secondary transfer roller 8, an elastic roller having a volume resistivity of 10 ⁷ to 10 ⁹ Ωcm and a hardness of 30 ° to 40 ° can be used. The secondary transfer roller 8 is pressed against the secondary transfer counter roller 62 via the intermediate transfer belt 6 with a total pressure of about 39.2N. Further, the secondary transfer roller 8 is driven to rotate as the intermediate transfer belt 6 rotates. Further, a secondary transfer voltage of 0 to 4.0 kV can be applied to the secondary transfer roller 8 from a secondary transfer power supply 80.

4). Configuration of Transfer Unit 5 FIG. 2 is a perspective view of the transfer unit 5. The transfer means of this embodiment includes a transfer member (5α, 5β) and a support member 11 that supports the transfer member. The transfer member includes a raised portion 5α made of a plurality of conductive fibers and a base portion 5β that supports the raised portion 5α. The support member 11 is a resin sheet 11 made of polyethylene terephthalate (PET) as a sheet-like member, and supports the transfer member on the support surface. The base material portion 5β is configured to be supported by the resin sheet 11 by being bonded to the resin sheet 11 with a double-sided tape. The plurality of conductive fibers constituting the raised portion 5α are raised in a direction perpendicular to the resin sheet 11 (normal direction). The raised portion 5α uses a pile fabric in which conductive fibers are densely arranged. In this embodiment, since the pile fabric is used as the transfer member (5α, 5β), the base material portion is the base fabric portion 5β.

  The dimension Wb of the raised portion 5α in the short direction (the direction parallel to the moving direction of the intermediate transfer belt) is Wb = 3 mm. Moreover, the dimension Wk of the short side direction of the base fabric part 5 (beta) is Wk = 5mm. The dimension L in the longitudinal direction of the base cloth portion 5β (the direction perpendicular to the moving direction of the intermediate transfer belt 6) is L = 250 mm. Of these, the raised portions 5α are provided in the region of K = 230 mm, and the portions where the raised portions 5α are not provided are equally provided with a width of 10 mm at both ends in the longitudinal direction. .

In the first embodiment, conductive nylon fibers in which carbon powder is dispersed are used as the conductive fibers that become the raised portions 5α. Specifically, the single yarn fineness is in the range of 2 to 15 dtex [dtex: indicates mass (unit of grams) per 10,000 meters of single fiber], the diameter is 10 to 40 μm, and the dry strength is within the range of 1 to 3 cN / dtex. Those are preferred. The fiber resistivity ρfiber is preferably in the range of 10 to 10 ⁸ Ωcm. The resistivity ρfiber is measured by the following method. A bundle of 50 fibers is brought into contact with a metal probe on the surface of the bundle with an interval of about 1 cm. Then, using a high resistance meter (Advantest R8340A) or the like, the resistance value Rfiber is measured under an applied voltage of 100 V, and the resistivity ρfiber is calculated by the following equation.
ρfiber = Rfiber × (fiber diameter / 2) ² × 3.14 × 50 ÷ 1.0
The direction in which the conductive fibers extend from the surface of the resin sheet 11 in the raised portion 5α in a non-contact state (a state where no pressure is applied to the fibers) is referred to as a raised direction.

  In the present embodiment, the fiber length d of the raised portion 5α is 1.4 mm. Here, the fiber length d is a length from the base fabric portion 5β in a non-contact state to the free end of the brush fiber. When the fiber length d of the raised portion 5α is 1.4 mm, the thickness h of the transfer means 5 including the resin sheet 11 in the non-contact state is 2.0 mm.

  The fiber material to be the raised portion 5α may be any material as long as conductivity is imparted, and is not limited to nylon fibers. Moreover, although the non-conductive polyester fiber is used for the fiber used as the base fabric part 5β of Embodiment 1, any fiber may be used as long as the raised part 5α can be woven. It is not limited.

  In addition, as the transfer means 5 in Embodiment 1, the thing of the following specification is used as what has a typical characteristic.

<Specifications of transfer member>
-Material type: Pile fabric-Material: Nylon fiber with carbon powder dispersed-Single yarn fineness: 7 dtex
・ Fiber diameter: 28μm
Dry strength: 1.6 cN / dtex
・ Resistivity: 10 ⁶ Ωcm
Array density: 10850 / cm ²
The resin sheet 11 has a thickness of 100 μm. The width in the longitudinal direction is 252 mm, and the width in the moving direction is 20 mm. The base fabric portion 5β is bonded on the resin sheet 11 with a gap of 1 mm at both ends in the longitudinal direction and 1 mm at the downstream end.

  In the present embodiment, the transfer member (5α, 5β) is supported by the resin sheet 11 having flexibility instead of the metal holder fixed as in Patent Document 1. With such a configuration, the transfer member can be brought into contact with the inner peripheral surface of the intermediate transfer belt 6 by using the elastic force of the resin sheet 11. The resin sheet 11 can be bent along the shape of the intermediate transfer belt 6 or the photosensitive drum 1 facing the intermediate transfer belt 6, and in addition to the elastic force of the conductive fibers, It is possible to bring the conductive fibers into contact with the intermediate transfer belt 6 by applying an elastic force. With this configuration, it is possible to further stabilize the contact of the transfer member (5α, 5β) with the intermediate transfer belt 6.

  FIG. 3 is a cross-sectional view for explaining the support structure of the resin sheet 11. Since the configuration is common to the primary transfer units of the stations Sa to Sd, the configuration of one station will be described as an example.

  The upstream end of the resin sheet 11 is bonded to a stainless steel metal plate (fixing member) 9 with a double-sided tape over the entire width in the moving direction 5 mm. In this example, as the double-sided tape 12 used for bonding the base fabric portion 5β, the resin sheet 11, and the metal plate 9, a non-woven fabric base material using an acrylic adhesive was used. Further, one end of the resin sheet 11 is held between the PC-ABS resin holder 10 and the metal plate 9, and is crimped by a convex portion provided on the holder 10. The other end of the resin sheet 11 is a free end.

  FIG. 4A is a schematic diagram illustrating a contact state of the transfer unit 5 with respect to the photosensitive drum 1 and the intermediate transfer belt 6. FIG. 4B will be described later. The raised portion 5α is in contact with the back surface of the intermediate transfer belt 6 at a position facing the photosensitive drum 1 on the intermediate transfer belt 6. The upstream end of the raised portion 5α is 1. from the intersection of the perpendicular drawn to the intermediate transfer belt 6 from the center of the photosensitive drum 1 and the intermediate transfer belt 6 (contact point between the photosensitive drum 1 and the intermediate transfer belt 6) to the upstream side. Located at 5 mm. The transfer members (5α, 5β) are biased toward the intermediate transfer belt 6 by a spring 51 that is a biasing member via the resin sheet 11. The biasing force F of the spring 51 is F = 4.9N, and the direction of F is a normal direction to the moving direction of the intermediate transfer belt.

  M1 in the drawing represents a primary transfer portion formed between the photosensitive drum 1 and the intermediate transfer belt 6. The intermediate transfer belt 6 linearly stretched by the driving roller 61 and the tension roller 63 is disposed so as to form a primary transfer portion having a width of 1 mm with the photosensitive drum 1 for each station. Such a flexible resin sheet 11 is exposed to a temperature rise in the image forming apparatus by repeated continuous printing operations or a high temperature environment, so that the resin sheet 11 is interposed between the resin sheet 11 and the metal plate 9. The resin sheet 11 may be deformed due to the difference in the linear expansion amount.

  FIG. 5 is a view for explaining the deformation of the resin sheet 11 in the longitudinal direction orthogonal to the moving direction of the intermediate transfer belt 5. As shown in FIG. 5, when the resin sheet 11 is deformed, the distance from the surface of the resin sheet 11 to the inner peripheral surface of the intermediate transfer belt 6 varies in the longitudinal direction. In this state, when the intrusion amount of the raised portion 5α into the intermediate transfer belt 6 is smaller than the deformation amount of the resin sheet 11, the raised portion 5α as the transfer member is intermediate in the longitudinal direction as shown in FIG. An area that cannot contact the transfer belt 6 is generated. As a result, a vertical stripe-like image defect may occur.

  Therefore, the present embodiment is characterized in that the amount of penetration V of the raised portion 5α into the intermediate transfer belt 6 is larger than the flatness J of the resin sheet 11. Here, the penetration amount V of the brush means the thickness h of the transfer unit 5 in a non-contact state (non-contact state) and the thickness (pressing force) of the transfer unit 5 in contact with the inner peripheral surface of the intermediate transfer belt 6. It means the difference from the time thickness Q). FIG. 4B is a schematic diagram for explaining the intrusion amount V. FIG. As shown in FIG. 4B, the raised portions 5α are in contact with the intermediate transfer belt 6 in a compressed state by the amount of penetration V.

Each measurement method will be described. First, the thickness h of the transfer means 5 in the non-contact state will be described. The transfer means 5 adhered on the resin sheet 11 is photographed from the side with an optical microscope, and the back surface of the resin sheet 11 (the non-sticking surface to which the base fabric portion 5β is not attached) is applied to the surface of the resin sheet 11. On the other hand, the distance to the tip of the fiber of the primary transfer brush 5 in the normal direction is the thickness h. Next, as the thickness of the transfer means 5 pressed against the back surface of the intermediate transfer belt 6 (pressed thickness Q), the primary transfer brush 5 when the primary transfer brush 5 is compressed with a force corresponding to the primary transfer pressure is used. The thickness was measured. The force urging the photosensitive drum 1 is F = 4.9N, the width in the transport direction of the primary transfer portion M1 is approximately 1 mm, and the longitudinal width of the raised portion 5α is 230 mm. Accordingly, the force corresponding to the primary transfer pressure in this embodiment is about 0.21 N / mm ² .
In the configuration of the present embodiment, the measured penetration amount V was 0.5 mm. In the configuration of the present embodiment, it is desirable to set the penetration amount V between 0.4 mm and 0.9 mm. In the case of the present embodiment, when the intrusion amount V is set to be larger than 0.9 mm, the upstream position of the raised end extends downstream to the vicinity of the contact point between the photosensitive drum 1 in the primary transfer portion M1 and the intermediate transfer belt 6. And the toner image may be scattered. On the other hand, as the flatness J of the resin sheet 11, the difference between the maximum value and the minimum value in the cross-sectional shape of the resin sheet 11 at the position corresponding to the primary transfer portion (M1) was taken. The primary transfer portion (M1) is a contact area where the photosensitive drum 1 and the intermediate transfer belt 6 are in contact with each other.

  A method for measuring the flatness J of the resin sheet 11 will be described with reference to FIG. FIG. 7 is a schematic view for explaining a method for measuring the flatness 7 of the resin sheet 11. As shown in FIG. 7A, the flatness J is measured by using a laser 14 displacement meter for the sheet shape at a position corresponding to the primary transfer portion (M1). As shown in FIG. 7B, the probe of the laser displacement meter 14 was scanned along the length of the brush member (Y direction in the figure), and the shape profile was measured over the entire length. As the laser displacement meter 14, LK-G35 manufactured by KEYENCE was used, and EZSM3E030-A manufactured by Oriental Motor was used to scan the displacement meter 14 longitudinally.

  As a result of measurement by this measurement method, the flatness J immediately after assembly was 0.1 mm in the combination of the resin sheet (polyethylene terephthalate) and the metal plate (SUS304).

  Therefore, in the present embodiment, since the penetration amount V (0.5 mm) is large with respect to the flatness J (0.1 mm), the raised portion 5α of the transfer member is reliably transferred over the longitudinal direction of the intermediate transfer belt 6. 6 can be contacted. FIG. 6 is a diagram illustrating the contact state of the transfer member in the longitudinal direction orthogonal to the moving direction of the intermediate transfer belt 5 in the present embodiment. If the intrusion amount V is larger than the flatness J as in this embodiment, the tip of the raised portion 5α is the inner peripheral surface of the intermediate transfer belt 6 even in the portion where the resin sheet 11 is recessed downward as shown in FIG. It is possible to make sure contact.

  In order to examine the effect of the transfer unit 5 of the present embodiment, evaluation was performed using the image forming apparatus of the first embodiment. As a comparative example, a transfer unit in which the fiber length d of the raised portion of the transfer unit 5 was changed was used. An image forming apparatus having the same basic configuration as the above image forming apparatus and having a different fiber length of the primary transfer brush was used. The fiber length d in each comparative example is as follows.

  As Comparative Example 1, an image forming apparatus having a brush fiber length d of 1.0 mm was used. As Comparative Example 2, an image forming apparatus having a brush fiber length d of 0.6 mm was used. A common resin sheet 11 is used, and the flatness J (0.1 mm) is common.

  As a paper passing experiment, CS-680 paper (Canon Marketing Japan, product name) was used as the recording material P, and the image ratio of each color of C (cyan), M (magenta), Y (yellow), and K (black) was 5%. 30,000 images were printed. The plain paper mode was used as the image forming mode, and the throughput was 18 sheets per minute. In the paper passing experiment, intermittent printing of two sheets was continuously performed in an environment of a temperature of 23 ° C. and a humidity of 50%.

  In addition, the evaluation image is sampled at the start of the paper passing experiment and every 3,000 images formed during the paper passing experiment, and the intrusion amount of the transfer means 5 and the flatness of the resin sheet 11 are measured. The difference between the penetration amount V and the flatness J was calculated. The following were output as evaluation images to be sampled. That is, a solid image (maximum density level image) and a halftone image (density 25%) are converted into C (cyan), M (magenta), Y (yellow), K (black), R (red), and B (blue), respectively. ) And G (green).

  The sampled evaluation images were ranked and evaluated from the viewpoint of image defects caused by uneven contact of the primary transfer brush 5 with the intermediate transfer belt 6 in the primary transfer portion (M1). As the criteria for ranking, ◯ indicates that almost no image defect occurs, and X indicates that image defect can be confirmed.

  An evaluation result is shown to Fig.8 (a) and FIG.8 (b). As shown in FIG. 8A, in the transfer unit 5 of the present embodiment, the resin sheet 11 is deformed with an increase in the number of sheets to be passed. The relationship was greater than the flatness J of the resin sheet 11. That is, the conductive fibers of the raised portions 5α are in contact with the back surface of the intermediate transfer belt 6 over the length, and are caused by uneven contact between the raised portions 5α and the back surface of the intermediate transfer belt 6 as shown in FIG. The defective image did not occur up to 30,000 sheets. On the other hand, in Comparative Example 1 and Comparative Example 2, when the number of sheets to be passed increases and the resin sheet 11 is deformed, the intrusion amount V is smaller than the flatness J of the resin sheet. A streak-like image defect occurred.

  As described above, in the image forming apparatus of the present embodiment, the transfer unit 5 employs the brush-shaped transfer member (5α, 5β), and the amount V of the transfer unit 5 entering the intermediate transfer belt 6 is determined as the support member of the transfer unit 5. It is set to be greater than 11 flatness. As a result, the conductive fibers constituting the raised portion 5α can be stably brought into contact with the inner peripheral surface of the intermediate transfer belt 6 to suppress the occurrence of image defects.

  Moreover, although demonstrated using the resin sheet 11 which has flexibility as a supporting member, the metal sheet (SUS film) which has flexibility similarly can also be used.

(Embodiment 2)
In the first embodiment, the configuration in which the intrusion amount V of the transfer unit 5 is larger than the flatness J of the support member 11 has been described. In contrast, the present embodiment is characterized in that the intrusion amount V of the transfer means 5 is larger than the sum of the flatness J and the displacement amount U of the intermediate belt. In the present embodiment, the transfer member (5α, 5β), the width in the short direction, and the fiber length d of the conductive fiber of the raised portion 5α are different from those in the first embodiment, but other configurations are the same as those in the first embodiment. Since it is the same as that of the image forming apparatus, description of the same part is omitted.

  The dimension Wb in the short direction of the raised portion 5α of the present embodiment is Wb = 5 mm. Moreover, the dimension Wk of the short side direction of the base fabric part 5 (beta) is Wk = 7mm. In accordance with this, the moving direction width of the resin sheet 11 is also extended to 22 mm. The installation position of the primary transfer brush 5 is aligned with that of the first embodiment at its upstream end. The fiber length d of the brush is d = 1.7 mm. When the fiber length d of the brush is d = 1.7 mm, the thickness h of the transfer means 5 including the resin sheet 11 in the non-contact state is 2.3 mm.

  By the way, when a thin film member such as the intermediate transfer belt 6 is stretched and tensioned by a plurality of shafts, there may be undulations with displacement of a mountain and valley due to uneven thickness in the longitudinal direction and uneven elasticity. . In this embodiment, the width of the transfer unit 5 in the short direction is increased to increase the area where the raised portion 5α of the transfer member on the downstream side of the primary transfer portion (M1) contacts the intermediate transfer belt 6. I am letting. With this configuration, it is possible to suppress an increase in the potential of the intermediate transfer belt 6 (to eliminate the charge of the intermediate transfer belt 6). However, when the intermediate transfer belt 6 is wavy, the following problems occur. In some cases, the raised portion 5α of the transfer member cannot uniformly contact the inner peripheral surface of the intermediate transfer belt 6 in a region where the photosensitive drum 1 on the downstream side of the primary transfer portion (M1) does not face. In particular, the contact between the raised portions 5α and the intermediate transfer belt 6 tends to become unstable between the concave portion generated as a result of the deformation of the resin sheet 11 and the crest-shaped corrugated portion of the intermediate transfer belt. In such a case, the potential of the intermediate transfer belt 6 cannot be properly eliminated, and an unintended discharge occurs, resulting in an image defect.

  Therefore, as a feature of the present embodiment, the amount of penetration V of the transfer means 5 into the inner peripheral surface of the intermediate transfer belt 6 is determined based on the flatness J of the resin sheet 11 as a support member and the pressing direction (thickness direction) of the intermediate transfer belt 6. Is set larger than the sum of the displacement amounts U. (The pressing direction is the direction in which the transfer unit 5 presses the intermediate transfer belt 6 and is the thickness direction of the intermediate transfer belt 6.) Here, the displacement U is the primary transfer portion (M1) of the intermediate transfer belt 6. The normal direction displacement of the surface to be formed is measured over the longitudinal direction. And the difference of the maximum value and the minimum value in the cross-sectional shape was taken. A specific measurement method will be described.

  In this embodiment, as shown in FIG. 10, the intermediate transfer belt 6 is stretched between two SUS metal shafts having a diameter of 30 mm and a force of 20 N is applied to the intermediate transfer belt 6. The position was measured by scanning the laser displacement meter 14 in the longitudinal direction (Y direction in the figure). The laser displacement meter 14 and the apparatus for scanning in the longitudinal direction are the same as those used in the first embodiment.

  In this embodiment, the penetration amount V was 0.7 mm, the flatness J immediately after assembly of the resin sheet 11 was 0.1 mm, and the displacement amount U of the intermediate transfer belt 6 was 0.3 mm. In this way, if the penetration amount V is larger than the sum of the flatness J and the displacement amount U of the intermediate belt, as shown in FIG. 9, the leading end of the raised portion 5α of the transfer means 5 extends in the longitudinal direction along the intermediate transfer belt. 6 can be brought into contact with the inner peripheral surface. Thereby, the conductive fibers can be stably brought into contact with the inner peripheral surface of the intermediate transfer belt, and in particular, it is possible to suppress the occurrence of image defects due to unintended discharge in a region where the photosensitive drum 1 is not opposed.

  In the first and second embodiments, the image forming apparatus including the intermediate transfer belt 5 as the transfer belt has been described. However, the configurations of the first and second embodiments can also be applied to an image forming apparatus including a conveyance belt that carries and conveys a transfer material as a transfer belt.

DESCRIPTION OF SYMBOLS 100 Image forming apparatus 1 Photoconductor drum 21 Intermediate transfer belt unit 6 Intermediate transfer belt 5 Transfer means 5a Brushed part 5b Base material part 11 Support member

Claims (9)

An image carrier for carrying a toner image;
A transfer belt movable in contact with the image carrier;
A transfer unit disposed at a position facing the image carrier via the transfer belt, and transferring a toner image from the image carrier to the transfer belt,
In the image forming apparatus, the transfer unit includes a raised portion made of a plurality of conductive fibers that are in contact with the transfer belt, and a base material portion that is in contact with the raised portion and supports the raised portion.
The transfer means includes a support member that supports the base portion with a support surface, and the support member has flexibility.
The image forming apparatus according to claim 1, wherein an amount of penetration of the raised portion into the transfer belt is greater than a flatness of the support surface.   The image forming apparatus according to claim 1, wherein the support member is a flexible sheet.   The image forming apparatus according to claim 1, wherein one end of the support member is fixed by a fixing member and the other end is a free end.   The image forming apparatus according to claim 1, further comprising an urging member that urges the support member toward the transfer belt.   5. The intrusion amount is a difference between a thickness of the transfer unit not in contact with the transfer belt and a thickness of the transfer unit in contact with the transfer belt. The image forming apparatus according to claim 1.   With respect to the moving direction of the transfer belt, a downstream end of a contact region between the raised portion and the transfer belt is located downstream of a downstream end of a contact region between the image carrier and the transfer belt. The image forming apparatus according to any one of claims 1 to 5.   Regarding the region between the raised portion and the downstream end of the contact region of the transfer belt and the downstream end of the contact region of the image carrier and the transfer belt, the intrusion amount depends on the flatness and the thickness direction of the transfer belt. The image forming apparatus according to claim 6, wherein the image forming apparatus is larger than a sum of the displacement amounts.   The image forming apparatus according to claim 1, wherein the transfer belt is an intermediate transfer belt to which a toner image is transferred from the image carrier. The image forming apparatus according to claim 1, wherein the transfer belt is a conveyance belt that carries and conveys a transfer material onto which a toner image is transferred from the image carrier.

Images