JP2011237664A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of ensuring that a belt moves stably in contact with a transferring member and the chattering of the transferring member and generation of abnormal sounds are suppressed, by suppressing an increase in frictions of the belt and the transferring member.SOLUTION: An image forming apparatus 100 comprises: a photoreceptor drum 1a which supports toner images; an intermediate transferring belt 80 which moves while contacting the photoreceptor drum 1a; and a primary transferring member 81a having a physical nip area part A in which protrusions 36a contacting a rear surface of an intermediate transferring belt 80 are formed with the intermediate transferring belt 80 contacting with the photoreceptor drum 1a, and a tension nip area part B in which protrusions 34a contacting the rear surface of the intermediate transferring belt 80 are formed with some space secured between the intermediate transferring belt 80 and the photoreceptor drum 1a. A first proportion of the protrusions 36a with respect to the physical nip area A and a second proportion of the protrusions 34a with respect to the tension nip area B are different from each other.

Description

  The present invention relates to an image forming apparatus that uses an electrophotographic recording system such as a laser printer, a copying machine, or a facsimile.

  Conventionally, in the process of an electrophotographic image forming apparatus, a toner image on a photosensitive drum is carried on an intermediate transfer belt or a recording material carrying belt by a transfer member to which an electric field having a polarity opposite to that of the toner is applied. There is a transfer process for electrostatically transferring the recording material. Hereinafter, the intermediate transfer belt and the recording material carrying belt may be collectively referred to as a belt. Further, as the transfer member, there is a contact transfer member such as a transfer roller which is connected to a high voltage power source and disposed at a position opposed to the photosensitive drum via a belt.

  When the transfer roller is used, the contact area (so-called transfer nip) between the belt and the transfer roller in the belt moving direction becomes non-uniform in the axial direction, that is, the longitudinal direction due to the influence of the deflection of the transfer roller. Therefore, the current required for the transfer process becomes non-uniform in the belt width direction orthogonal to the belt moving direction, and transfer failure may occur. Further, since the contact area in the belt moving direction is narrow, peeling discharge may occur at the peeling portion between the belt and the photosensitive drum, which may cause image defects. In order to solve this problem, the inventions described in Patent Documents 1 and 2 having characteristics of the transfer member have been proposed.

  The invention described in Patent Document 1 is an invention relating to an image forming apparatus using a conductive brush as a primary transfer electric field generating means of a primary transfer portion. Each fiber constituting the conductive brush is in contact with the intermediate transfer belt independently. According to the image forming apparatus described in Patent Document 1, the contact state of the contact area where the conductive brush contacts the intermediate transfer belt is uniform in the belt width direction orthogonal to the belt moving direction, and transfer defects are suppressed. The

  The invention described in Patent Document 2 is an invention relating to an image forming apparatus using a film as a secondary transfer electric field generating means of a secondary transfer portion. Specifically, this film rises steeply with respect to the contact portion with the back surface of the transfer material on the upstream side in the transfer material movement direction, and falls with a continuous curve from the contact portion on the downstream side in the transfer material movement direction. It has become the composition. According to such an image forming apparatus described in Patent Document 2, it is difficult for electric discharge to occur on the downstream side of the transfer portion, and it is possible to transfer the toner image to the transfer material with high fidelity and good reproducibility.

JP 05-127546 A Japanese Patent Laid-Open No. 09-120218

  However, when the conductive brush of Patent Document 1 and the film of Patent Document 2 are used facing the transfer member in contact with the rotating and moving belt, the belt is worn and scraped by the contact surface of the transfer member and the belt. Will increase the rotational torque. As a result, chattering of the transfer member in contact with the belt and high-frequency frictional noise (squeal) may occur, which may cause image defects such as transfer defects.

  In view of the above circumstances, the present invention can suppress an increase in friction between the belt and the transfer member, and the belt can move while stably contacting the transfer member, thereby suppressing chatter and abnormal noise on the transfer member. It is an object to provide a forming apparatus.

  In order to solve the above-described problems, an image forming apparatus according to the present invention includes an image carrier that carries a toner image, a belt that moves while contacting the image carrier, and a contact between the belt and the image carrier. A first contact region portion formed with a first contact portion that contacts the back surface of the belt in a state, and a first contact portion that contacts the back surface of the belt in a state where a space is secured between the belt and the image carrier. A transfer member having a second contact region portion formed with two contact portions, a first ratio of the first contact portion to the first contact region portion, and the second to the second contact region portion. The second ratio of the contact portions is different from each other.

  According to the present invention, an increase in friction between the belt and the transfer member can be suppressed, and the belt can be moved while being stably in contact with the transfer member, so that chatter and abnormal noise of the transfer member can be suppressed.

1 is a cross-sectional view illustrating a configuration of an image forming apparatus according to Embodiment 1 of the present invention. FIG. 4 is an enlarged cross-sectional view showing the configuration of a photosensitive drum and a primary transfer member. FIG. 3 is a cross-sectional view taken along line YY showing a configuration of a physical nip region in FIG. It is a perspective view etc. which show the structure of the primary transfer member which concerns on a prior art example. FIG. 10 is a perspective view illustrating a configuration of a primary transfer member according to Comparative Example 2. FIG. 10 is a perspective view illustrating a configuration of a primary transfer member included in an image forming apparatus according to a second embodiment. FIG. 10 is a perspective view illustrating a configuration of a primary transfer member included in an image forming apparatus according to Embodiment 3.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, since the dimensions, materials, shapes, relative positions, and the like of the components described in this embodiment are appropriately changed depending on the configuration of the apparatus to which the present invention is applied and various conditions, particularly specific descriptions are provided. Unless otherwise, the scope of the present invention is not limited to these.

  FIG. 1 is a cross-sectional view illustrating a configuration of an image forming apparatus 100 according to Embodiment 1 of the present invention. The image forming apparatus 100 is an image forming apparatus such as a color printer using an electrophotographic image forming process. As shown in FIG. 1, the image forming apparatus 100 includes an image forming apparatus main body (hereinafter simply referred to as “apparatus main body”) 100A. An image forming station 51 (51a, 51b, 51c, 51d), which is an “image forming unit” for forming an image, is provided inside the apparatus main body 100A. Each image forming station 51 (51a, 51b, 51c, 51d) forms different toner images. The image forming station 51 (51a, 51b, 51c, 51d) includes a photosensitive drum 1 (1a, 1b, 1c, 1d) that is an “image carrier” that carries a toner image.

  Here, the first image forming station 51a has a subscript a corresponding to yellow, and the second image forming station 51b has a subscript corresponding to magenta. The third image forming station 51c has a subscript corresponding to cyan, and the fourth image forming station 51d has a subscript corresponding to black.

  Process cartridges 9 (9a, 9b, 9c, 9d) corresponding to the respective colors are detachably attached to the image forming stations 51 (51a, 51b, 51c, 51d). Each process cartridge 9 (9a, 9b, 9c, 9d) has substantially the same structure. Each process cartridge 9 (9a, 9b, 9c, 9d) includes a photosensitive drum 1 (1a, 1b, 1c, 1d) as an “electrophotographic photosensitive member” that is an “image carrier”, and a charging roller as a charging means. 2 (2a, 2b, 2c, 2d). Each process cartridge 9 (9a, 9b, 9c, 9d) includes a developing unit 8 (8a, 8b, 8c, 8d) as a developing unit and a cleaning unit 3 (3a, 3b, 3c, 3d) as a cleaning unit. Have Each developing unit 8 (8a, 8b, 8c, 8d) has a developing sleeve 4 (4a, 4b, 4c, 4d) and a toner application blade 7 (7a, 7b, 7c, 7d), and toner (here, non-toner) Magnetic one-component developer) 5 (5a, 5b, 5c, 5d) is accommodated. Each charging roller 2 (2a, 2b, 2c, 2d) is connected to a charging bias power source 20 (20a, 20b, 20c, 20d) that is a voltage supply means to the charging roller 2 (2a, 2b, 2c, 2d). It is connected. Similarly, each developing sleeve 4 (4a, 4b, 4c, 4d) is also connected to a developing power source 21 (21a, 21b, 21c, 21d) which is a voltage supply means to the developing sleeve 4 (4a, 4b, 4c, 4d). It is connected.

  Further, in each image forming station, an optical unit 11 (11a, 11b, 11c, 11d) which is an “exposure unit” that irradiates the photosensitive drum 1 with laser light 12 (12a, 12b, 12c, 12d) corresponding to image information. ) Is provided.

  The image forming apparatus also includes an intermediate transfer belt 80 that is a “belt” that moves while contacting the photosensitive drum 1 (1a, 1b, 1c, 1d). The intermediate transfer belt 80 is formed in an endless shape. The intermediate transfer belt 80 is disposed so as to abut against all of the four photosensitive drums 1 (1a, 1b, 1c, 1d). The intermediate transfer belt 80 is supported by three rollers, ie, a secondary transfer counter roller 86, a driving roller 14, and a tension roller 15 as a stretching member, so that an appropriate tension is maintained. By driving the drive roller 14, the intermediate transfer belt 80 moves in the forward direction at substantially the same speed with respect to the photosensitive drum 1 (1a, 1b, 1c, 1d).

  Further, primary transfer members 81 (81a, 81b, 81c, 81d) are arranged at positions facing the respective photosensitive drums 1 (1a, 1b, 1c, 1d) via the intermediate transfer belt 80. Each primary transfer member 81 (81a to 81d) is connected to a primary transfer power source 84 (84a, 84b, 84c, 84d) that is a voltage supply means to the primary transfer member 81 (81a to 81d). Each primary transfer member 81 (81a to 81d) is applied with a voltage having a polarity opposite to that of the toner from each primary transfer power source 84 (84a, 84b, 84c, 84d). The intermediate transfer belt 80 moves between the photosensitive drum 1 (1a, 1b, 1c, 1d) and the primary transfer member 81 (81a, 81b, 81c, 81d). In each primary transfer region where the photosensitive drum 1 (1a to 1d) and the primary transfer member 81 (81a to 81d) face each other, one toner image is formed on each photosensitive drum 1 (1a to 1d). The next transfer member 81 sequentially transfers the images so as to overlap on the intermediate transfer belt 80.

Here, the intermediate transfer belt 80 is formed of PVDF having a thickness of 100 μm and a volume resistivity of 10 ¹⁰ Ωcm. Further, the drive roller 14 is made of an aluminum cored bar having a resistance of 10 ⁴ Ω dispersed with carbon as a conductive agent and an outer diameter of 25 mm covered with 1.0 mm thick EPDM rubber. The tension roller 15 is made of an aluminum metal rod having an outer diameter of 25 mm. Since the tension is 19.6 N on one side, 39.2 N is applied as a total pressure. The secondary transfer counter roller 86 is a roller having an outer diameter of 25 mm coated with EPDM rubber having a resistance of 10 ⁴ Ω and a wall thickness of 1.5 mm, in which carbon is dispersed in an aluminum core bar as a conductive agent. .

  Further, after the secondary transfer is completed, the transfer residual toner remaining on the intermediate transfer belt 80 and the recording material powder (paper dust) generated by the conveyance of the recording material P contact the intermediate transfer belt 80. The removed belt cleaning device 83 removes and recovers the belt from the surface. Here, an elastic cleaning blade made of urethane rubber or the like is disposed inside the belt cleaning device 83 which is a “belt cleaning unit”.

  Further, in the image forming apparatus 100, the secondary transfer counter roller 86 and the secondary transfer roller 82 face each other through the feed roller 17 and the intermediate transfer belt 80 that feed the recording material P one by one from each feed cassette 16. A registration roller pair 18 for conveying the recording material P is provided in the secondary transfer area. The secondary transfer roller 82 is connected to a secondary transfer power supply 85. The fixing unit 19 includes a fixing roller 19a and a pressure roller 19b, and fixes the toner image on the recording material P by applying heat and pressure to the toner image on the recording material P.

Here, as the secondary transfer roller 82, a nickel-plated steel bar having an outer diameter of 8 mm and an outer diameter of 18 mm covered with an NBR foam sponge body having a resistance value of 10 ⁸ Ω and a thickness of 5 mm are used. It has been. The secondary transfer roller 82 is brought into contact with the intermediate transfer belt 80 with a linear pressure of about 5 to 15 g / cm, and rotates at a substantially constant speed in the forward direction with respect to the moving direction of the intermediate transfer belt 80. Are arranged to be.

  Next, an image forming operation will be described. When the image forming operation starts, the photosensitive drums 1a to 1d, the intermediate transfer belt 80, and the like start to rotate in the arrow direction at a predetermined process speed. First, at the first image forming station, the photosensitive drum 1a is uniformly charged to the charging roller 2a to the negative polarity by the charging bias power source 20a. Subsequently, an electrostatic image is formed on the photosensitive drum 1a by the laser beam 12a irradiated from the optical unit 11a.

  The toner 5a inside the developing unit 8a is charged negatively by the toner application blade 7a and applied to the developing sleeve 4a. The developing sleeve 4a is supplied with a bias from a developing bias power source 21a. When the electrostatic image formed on the photosensitive drum 1a reaches the developing sleeve 4a, the electrostatic image is visualized by negative-polarity toner, and the first color (here, yellow) toner image is formed on the photosensitive drum 1a. Is formed.

  The toner image formed on the photosensitive drum 1a is primarily transferred onto the intermediate transfer belt 80 by the action of the primary transfer member 81a. After the primary transfer is completed, the toner remaining on the surface of the photosensitive drum 1a is cleaned by the cleaning unit 3a to prepare for the next image formation.

  The second to fourth image forming stations 51b, 51c, and 51d for magenta, cyan, and black are subjected to the same image forming process as the first image forming station 51a for yellow. That is, a toner image of each color is formed on each photosensitive drum, and the toner images of each color are transferred onto the intermediate transfer belt 80 so that a multiple image is formed on the intermediate transfer belt 80.

  On the other hand, in accordance with the image forming process described above, the recording material P stored in the feeding cassette 16 is fed one by one by the feeding roller 17 and conveyed to the registration roller pair 18. The recording material P is conveyed to a contact portion (secondary transfer region) formed by the intermediate transfer belt 80 and the secondary transfer roller 82 by the registration roller pair 18 in synchronization with the toner image on the intermediate transfer belt 80. . The four-color multiple toner images carried on the intermediate transfer belt 80 are collectively transferred onto the recording material P by the secondary transfer roller 82 to which a voltage having a polarity opposite to that of the toner is applied by the secondary transfer power source 85. Next transferred. After that, the toner image is fixed on the recording material P by applying heat and pressure to the toner image on the recording material P in the fixing unit 19. The recording material P on which the toner image is fixed is discharged to the outside of the apparatus main body 100A as an image formed product (print, copy).

  Further, the image forming apparatus 100 includes a controller 50 that controls driving of each internal device inside the apparatus main body 100A. Processes such as image formation are controlled by the control of the controller 50.

  FIG. 2A is an enlarged cross-sectional view showing the configuration of the photosensitive drum 1a and the primary transfer member 81a. Although only the configuration of the primary transfer member 81a of the first image forming station 51a is shown here, the primary transfer member 81b, the primary transfer member 81c, and the primary transfer member 81d are configured similarly. As shown in FIG. 2, the primary transfer member 81a, which is a “transfer member”, includes an elastic member 31a and a sheet member 32a.

  The sheet member 32a contacts the back surface of the intermediate transfer belt 80 in a state where the intermediate transfer belt 80 and the photosensitive drum 1a are in contact (the surface of the intermediate transfer belt 80 is in contact with the photosensitive drum 1a). 1st contact area | region part ". Further, the sheet member 32 a has a “second contact region portion” where the intermediate transfer belt 80 contacts the sheet member 32 a while ensuring a space with the photosensitive drum 1 a. The first contact region portion is a region where the intermediate transfer belt 80 is sandwiched between the sheet member 32 and the photosensitive drum 1a, and is a physical nip region portion A. The second contact area is an area where the intermediate transfer belt 80 contacts the photosensitive drum 1a with its own tension, that is, a tension nip area B. The tension nip area B is formed adjacent to the physical nip area A and extends downstream in the belt moving direction D. In the belt moving direction D, the tension nip area B is set longer than the physical nip area A. With such a configuration, charging of the surface of the intermediate transfer belt 80 is suppressed.

The reason why the tension nip region B is provided in this way is as follows. The intermediate transfer belt is a member that primarily transfers the toner image from the photosensitive drum and transfers the primarily transferred toner image onto the surface of the recording material. Since the intermediate transfer belt needs to form an electric field for the transfer, it cannot be made of an extremely low resistance material, and has a medium resistance or higher (volume resistivity of about 10 ⁷ Ω · cm or higher. ) Is generally made of a material having resistance. However, even if the resistance is medium resistance or higher, the surface is easy to be charged when a high resistance material is used, and even when the resistance is adjusted to medium resistance, the resistance changes greatly with respect to environmental fluctuations, and manufacturing variations are also large. There is a feature. Therefore, it has been difficult to prevent charging in all use environments. In particular, in a low humidity environment, the transfer performance deteriorates due to the surface of the intermediate transfer belt being charged up, and a special device for removing the charge from the intermediate transfer belt is necessary, which increases the size of the device. And there was a problem of incurring price increases. In order to solve these problems, a tension nip region B is provided for the physical nip region A. As a result, the surface of the intermediate transfer belt 80 can be effectively gradually electrified, and the occurrence of image defects can be suppressed while increasing the degree of freedom of the environment that can be handled.

  Further, as described above, the sheet member 32a is disposed between the intermediate transfer belt 80 and the elastic member 31a. The sheet member 32a is pressed against the back surface of the intermediate transfer belt 80 by the elastic member 31a and is in contact with the physical nip region A at a position facing the photosensitive drum 1a. The intermediate transfer belt 80 and the tension nip region B are in contact with each other at a position downstream of the belt moving direction D. However, with this configuration alone, the adsorption force acting between the tension nip region B and the intermediate transfer belt 80 is significantly increased, and it is difficult to suppress the increase in the rotational torque of the intermediate transfer belt 80. The configuration detailed in 2 (b) is provided.

  FIG. 2B is a perspective view showing the configuration of the uneven portion 53 and the uneven portion 54 provided on the surface of the primary transfer member 81a of FIG. As shown in FIG. 2B, the concave and convex portion 54 provided on the sheet member 32a of the primary transfer member 81a is provided with a large number of concave portions 33a and convex portions 34a (see FIG. 3B) adjacent to each other. It is what was done. Further, the uneven portion 53 is provided with a large number of concave portions 35a and convex portions 36a (see FIG. 3A) adjacent to each other. In FIG. 2A, the arrow indicates the belt moving direction D.

  The configuration of the primary transfer member 81a will be described in further detail below. The primary transfer member 81 a that is a “transfer member” has a physical nip region A in which a convex portion 36 a that is a “first contact portion” that contacts the photosensitive drum 1 a via the intermediate transfer belt 80 is formed. Further, the primary transfer member 81a has the following portions in a state where a space is secured between the intermediate transfer belt 80 and the photosensitive drum 1a. That is, the primary transfer member 81 a has a tension nip region B where a convex portion 34 a that is a “second contact portion” that contacts the back surface of the intermediate transfer belt 80 is formed.

  The physical nip region portion A is formed in a lattice shape in a plan view and is formed in a plurality of uneven shapes in a cross-sectional view. That is, the physical nip region A is a “first contact portion” as a “first convex portion” as a “first convex portion” (see FIG. 3A) and a “first” formed between the convex portions 36a. It has a recess 35a which is "1 recess". On the other hand, the tension nip region portion B is formed in a lattice shape in a plan view and is formed in a plurality of uneven shapes in a cross-sectional view. That is, the tension nip region portion B is formed between the convex portion 34a (see FIG. 3B) as the “second convex portion” which is the “second contact portion” and the “second contact portion”. It has a recess 33a which is "2 recesses".

  The first ratio of the convex portion 36a with respect to the physical nip region portion A and the second ratio of the convex portion 34a with respect to the tension nip region portion B are different from each other. That is, the second ratio is smaller than the first ratio. The first ratio is the ratio of the area of the tip of the convex portion 36a on the side of the intermediate transfer belt 80 to the area of the physical nip area A, and the second ratio is the area of the tension nip area B. The ratio of the area of the tip of the convex portion 34a on the intermediate transfer belt 80 side.

  The first ratio is the ratio of the contact area where the convex portion 36a contacts the intermediate transfer belt 80 with respect to the area of the physical nip area A, and the second ratio is the area of the tension nip area B. Suppose that the ratio of the contact area where the convex portion 34 a contacts the intermediate transfer belt 80 is assumed. Even in this case, it is considered that the same effect can be obtained.

  FIG. 3A is a cross-sectional view taken along line YY showing the configuration of the physical nip region A in FIG. FIG. 3B is a cross-sectional view along the line Y-Y showing the configuration of the tension nip region B in FIG. As shown in FIG. 3A, the uneven shape of the surface of the physical nip region A of the sheet member 32a is such that the top width D10 of the convex portion 36a and the bottom width (maximum width of the bottom portion) D20 of the concave portion 35a. Both are formed with a square of 50 μm. Further, the pitch E10 between the convex portions 36a and the pitch E20 between the concave portions 35a are both 100 μm. Further, the depth h0 of the recess 35a is 50 μm.

  As shown in FIG. 3B, the uneven shape on the surface of the tension nip region B of the sheet member 32a is a taper shape extending from the top of the convex portion 34a to the concave portion 33a. That is, the convex part 34a which is the “second convex part” includes a tapered part 34a1 sharpened toward the tip and a flat part 34a2 formed on the tip surface. Moreover, the width D1 of the top part of the convex part 34a is 10 μm, and the width D2 of the bottom part of the concave part 33a is 100 μm. The uneven shape on the surface of the tension nip region B of the sheet member 32a is a tapered shape in which the space between the top of each protrusion 34a and the bottom of each recess 33a extends from the top of the protrusion 34a toward the bottom of the recess 33a. It has become. Moreover, the pitch E1 between the adjacent convex parts 34a and the pitch E2 between the concave parts 33a are both 120 μm. Further, the depth h of the recess 33a is 50 μm. The depth h of the recess 33a is a vertical distance between the top of the projection 34a and the bottom of the recess 33a.

  The ratio of the contact area between the sheet member 32a and the intermediate transfer belt 80 in Example 1 is 75.0 in the physical nip region A when the surface of the sheet member 32a is 100% flat. % And 26.5% in the tension nip region B. The uneven portion 53 and the uneven portion 54 of the sheet member 32 a are disposed so as to be continuous with respect to the belt moving direction D of the intermediate transfer belt 80.

  Further, the dimension of the physical nip area A of the sheet member 32a in the belt movement direction D is 3 mm, and the dimension of the tension nip area B in the belt movement direction D is set to 5 mm. Then, in the belt moving direction D, the size of the bottom of the concave portion 35a formed between the convex portions 36a is set smaller than the size of the physical nip region A in the belt moving direction D.

  As the primary transfer member 81a, the elastic member 31a is a urethane foam sponge-like elastic body having a substantially rectangular parallelepiped shape with a thickness of 2 mm, a width of 5 mm, and a length of 230 mm. The hardness is 30 ° with Asker C 500 gf. Here, urethane foam is used for the elastic member 31a. However, the elastic member 31a is not limited to this, and a rubber material such as epichlorohydrin rubber, NBR, or EPDM may be used.

Further, as the primary transfer member 81a, the sheet member 32a has a volume resistivity of 10 ⁶ Ωcm when 100 V is applied, uses a polyamide (PA) resin having a thickness of 200 μm, disperses carbon in a conductive agent, and has an electric resistance value. Is set to 10 ⁸ Ω. Here, although a vinyl acetate sheet is used for the sheet member 32a, the present invention is not limited to this. For example, other materials such as a vinyl acetate sheet, polycarbonate (PC), PVDF, PET, polyimide (PI), and polyethylene (PE) may be used for the sheet member 32a.

  Further, in Example 1, as a method of forming the uneven portion 53 and the uneven portion 54 on the contact surface of the sheet member 32a, a mold roll (not shown) having an uneven shape formed on the surface by a photoetching method is used. A method of heating and pressing the surface of the member 32a was used. However, the above-described method for forming the uneven portion is not limited to this, and any other method may be used as long as the same uneven shape can be formed on the surface (contact surface with the belt) of the sheet member 32a. May be.

  The operational effects of the first embodiment will be described below. In the configuration in which the primary transfer bias is applied between the primary transfer member 81a and the intermediate transfer belt 80 as in the first embodiment, the primary transfer member 81a is in the middle of the force acting on the primary transfer member 81a. There is a vertical drag due to being pressed against the transfer belt 80. The force acting on the primary transfer member 81a includes an electrostatic attractive force (hereinafter referred to as an attracting force) between the primary transfer member 81a and the intermediate transfer belt 80 in addition to the above-described vertical drag.

  According to the study by the present inventors, when the surface of the primary transfer member 81a that is in contact with the intermediate transfer belt 80 is made uneven, the adsorption force is reduced, and consequently the increase in the rotational torque of the intermediate transfer belt 80 is suppressed. I know that This is due to the characteristic that the attractive force acting between the primary transfer member 81a and the intermediate transfer belt 80 increases or decreases in proportion to the contact area of each other.

  Further, in order to suppress abnormal discharge at the separation portion between the intermediate transfer belt 80 and the photosensitive drum 1a, the dimension in the belt movement direction D of the tension nip region B is set downstream of the belt movement direction D in which abnormal discharge occurs. Extend with. Then, as shown in FIG. 2, the size of the tension nip region B is larger than the size of the physical nip region A in the belt moving direction D, and due to the suction force between the tension nip region B and the intermediate transfer belt 80, The rotational torque of the intermediate transfer belt 80 increases.

  On the other hand, in the primary transfer member 81a and the intermediate transfer belt 80, when the ratio of the protrusions 34a in the tension nip area B is set smaller than the ratio of the protrusions 36a in the physical nip area A. It has been found that the following phenomenon occurs. That is, the intermediate transfer belt 80 and the photosensitive drum 1a are separated from each other without significantly increasing the suction force acting on the tension nip region B, and the convex portion 34a of the tension nip region B is used as the intermediate transfer belt 80. The neutralization effect on the surface can be exhibited, and peeling discharge can be suppressed.

  For example, when the negatively charged toner is transferred from the photosensitive drum 1a to the intermediate transfer belt 80 in the physical nip region A, the primary transfer member 81a charges the intermediate transfer belt 80 positively. In the tension nip region B, the negatively charged toner may perform the following operation depending on the potential difference between the photosensitive drum 1a and the intermediate transfer belt 80, although it is transferred to the intermediate transfer belt 80. . That is, the negatively charged toner moves to return to the photosensitive drum 1a or floats between the photosensitive drum 1a and the intermediate transfer belt 80.

  Here, as described above, the tension nip region portion B is provided in addition to the physical nip region portion A, so that the potential of the intermediate transfer belt 80 is temporarily determined and the toner moves along the surface of the intermediate transfer belt 80. The phenomenon of subtle movement is suppressed. However, when the ratio of the convex portion 34a to the tension nip region portion B described above is set smaller than the ratio of the convex portion 36a to the physical nip region portion A, the following effects can be obtained. That is, the convex portion 34a further functions as a slow current needle, and the phenomenon in which the toner moves delicately along the surface of the intermediate transfer belt 80 is further suppressed.

  Further, the convex portion 34a of the concave-convex portion 54 of the tension nip region portion B of the primary transfer member 81a (particularly, the convex portion 34a extending in the direction perpendicular to the belt moving direction D on the surface of the sheet member 32a) faces the tip. The following effects can be obtained by forming a tapered shape. That is, abnormal discharge due to a sudden difference between the concave portion 33a and the convex portion 34a can be prevented, and more stable transfer performance can be maintained. For example, if the concave portions 33a and the convex portions 34a have a U-shaped cross section (a U-shaped cross section) like the concave portions 35a and the convex portions 36a, the photosensitive drum 1a and the primary transfer member in the belt moving direction D. The potential difference between 81a will change abruptly. For this reason, the potential of the intermediate transfer belt 80 may change abruptly in the belt moving direction D. However, if the convex portion 34a has a tapered shape as shown in FIG. 3B, the potential difference between the photosensitive drum 1a and the primary transfer member 81a changes gradually in the belt moving direction D, and the belt In the moving direction D, the potential of the intermediate transfer belt 80 changes gradually. For this reason, the phenomenon that the toner moves along the surface of the intermediate transfer belt 80 is further suppressed.

  In order to examine the effect of the image forming apparatus 100 according to the first embodiment, the image forming apparatus 100 having a process speed of 50 mm / sec is used on the image at the initial stage and when 10 k sheets are passed along with the conventional example and the comparative example described below. Evaluation was made on transfer defects (dots and stripes) and peeling discharge traces.

FIG. 4A is a perspective view showing a configuration of a primary transfer member 581a according to a conventional example. As shown in FIG. 4, as the sheet member 532a, a sheet member having a smooth surface formed of a polyamide (PA) resin is used. The center line average roughness Ra of the surface of the sheet member 532a that is in contact with the intermediate transfer belt 80 is 0.2 to 0.3 μm, and is substantially smooth. Furthermore, the sheet member 532a of the conventional example is set so that carbon is dispersed in the conductive agent and the electric resistance value becomes 10 ⁸ Ω. In the belt moving direction D, the physical nip region A formed by the sheet member 532a and the intermediate transfer belt 80 has a dimension of 3 mm, and the tension nip region B has a dimension of 5 mm. The same elastic member 31a and intermediate transfer belt 80 used as conventional examples are used as in the first embodiment.

  FIG. 4B is a perspective view showing the configuration of the primary transfer member 181a according to Comparative Example 1. As shown in FIG. 4B, the concavo-convex portion 53 and the concavo-convex portion 154 provided on the sheet member 632a of the primary transfer member 181a have both the physical nip region A and the tension nip region B having the same shape. Is formed. The details of the shape of the uneven portion 53 and the uneven portion 154 are the same as those of the physical nip region portion A of the first embodiment, and thus description thereof is omitted. The dimension in the belt movement direction D of the physical nip area A of the sheet member 32a is 3 mm, and the dimension in the belt movement direction of the tension nip area B is set to 5 mm.

  FIG. 5A is a perspective view illustrating a configuration of a primary transfer member 281a according to Comparative Example 2. As shown in FIG. 5A, the uneven portion 253 provided on the sheet member 732a of the primary transfer member 281a has the same shape in both the physical nip region portion A and the tension nip region portion B. The uneven shape on the surface of the sheet member 732a is a square in which the width D1 between the tops of the convex portions 64a and the bottom width (maximum bottom width) D2 of the concave portions 63a are both 500 μm. The pitch E1 between the convex portions 64a and the pitch E2 between the concave portions 63a are both 600 μm. Further, the depth h of the recess 63a is 50 μm. The dimension in the belt moving direction D of the physical nip area A of the sheet member 732a is 3 mm, and the dimension in the belt moving direction of the tension nip area B is set to 5 mm. Thus, in the moving direction of the intermediate transfer belt 80, the maximum width of the bottom of the concave portion 63a between the convex portions 64a is set to be larger than the width of the physical nip region portion A between the intermediate transfer belt 80 and the sheet member 732a. Yes.

FIG. 5B is a table showing evaluation results using the primary transfer members according to Example 1, Conventional Example, Comparative Example 1, and Comparative Example 2. This evaluation was performed by paying attention to transfer unevenness in the belt width direction G, scattering on the intermediate transfer belt 80, and discharge traces in a 30% print halftone image. In addition, the paper passing durability test was performed with a 4024 basis weight of 75 g / m ² manufactured by Xerox, and the initial image and the image after passing 10k sheets were evaluated. In FIG. 5B, ◎ is very good, ◎ is good, Δ is slightly bad, and × is evaluation of poor and evaluation.

  In the configuration of Example 1, vertical stripes, transfer omission, and peeling discharge traces were good after passing 10k sheets from the beginning. In addition, through the above-described durability, there is no chatter or abnormal noise of the primary transfer member 81 due to an increase in the rotational torque of the intermediate transfer belt 80, and image defects such as transfer defects due to the above-described phenomenon occur. There was not.

  In the conventional example, an abnormal image was not seen at the time of the initial evaluation, but in the confirmation after passing 10k sheets, the occurrence of an abnormal image that seems to be caused by an increase in the rotational torque of the intermediate transfer belt 80, and the intermediate transfer belt No. 80 was also damaged.

  In Comparative Example 1, an abnormal image was not seen at the time of the initial evaluation, but an image of a slight wave that was thought to be caused by an increase in the rotational torque of the intermediate transfer belt 80 was generated in the confirmation after passing 50k sheets. However, the intermediate transfer belt 80 was not damaged.

  In Comparative Example 2, vertical streak-like transfer omission was observed on the 30% printed halftone image at the time of the initial evaluation, and an image that seemed to be entirely defective was observed. This is an image defect caused by an uneven portion having a width larger than the physical nip width.

  In the configuration of the image forming apparatus 100 according to the first exemplary embodiment, the surface of the primary transfer member 81a that is in contact with the intermediate transfer belt 80 has an uneven shape. Further, with respect to the physical nip region portion A and the tension nip region portion B, the ratio of the convex portion 34a in the tension nip region portion B is made smaller than the ratio of the convex portion 36a in the physical nip region portion A. In this case, it has been found that stable transfer performance can be maintained for a long time while greatly suppressing the above-described adsorption force and increase in the rotational torque of the intermediate transfer belt 80. This is because the electrostatic attraction force acting between the primary transfer member 81a and the intermediate transfer belt 80 is increased in proportion to the mutual contact area.

  Furthermore, since the tension nip region B slides at least in contact with the intermediate transfer belt 80, the potential of the peeling portion where the intermediate transfer belt 80 and the photosensitive drum 1a are peeled is determined, and peeling discharge can be suppressed. .

  FIG. 6A is a perspective view illustrating a configuration of a primary transfer member 481a provided in the image forming apparatus according to the second embodiment. 6B is a cross-sectional view taken along line YY in the tension nip region B of the sheet member 432a of FIG. Of the configuration of the primary transfer member 481a of the second embodiment, the same configurations and effects as those of the primary transfer member 81a of the first embodiment are denoted by the same reference numerals and description thereof is omitted as appropriate. Since the second embodiment can be applied to the same image forming apparatus as that of the first embodiment, the description of the image forming apparatus is omitted. The primary transfer member 481a of the second embodiment is different from the primary transfer member 81a of the first embodiment in that the shape of a sheet member 432a that is a “transfer member” is different from the primary transfer member 481a. The uneven portion 53 and the uneven portion 454 provided on the sheet member 432a of the primary transfer member 481a are provided with a large number of uneven portions 53 and a large number of uneven portions 454 provided adjacent to each other. The sheet member 432a has a concave portion 85a as a “planar portion” that is a “second concave portion” that is recessed from the convex portion 36a that is a “first convex portion”. Further, the sheet member 432a has a convex portion 86a as a “needle-like portion” which is a “second convex portion” formed in a needle shape on the surface of the concave portion 85a which is a “planar portion” (FIG. 6B). reference). The convex part 86a has a taper part 86a1, and the front-end | tip part 86a2 becomes a vertex (refer FIG.6 (b)). The arrow indicates the belt moving direction D. Further, since the convex portions 36a and the concave portions 35a of the concave and convex portion 53 of the physical nip region portion A of the sheet member 32a are the same as those described in the first embodiment, the description thereof is omitted.

  Further, the uneven portion 454 of the tension nip region B of the sheet member 32a has a plurality of conical convex portions 86a formed on a smooth concave portion 85a, and the radius of the bottom surface of the convex portion 86a is 25 μm. Further, the pitch E1 between the apexes of the adjacent convex portions 86a and the pitch E2 between the concave portions 85a are both 150 μm. The height L of the convex portion 86a is 50 μm. However, in the second embodiment, the conical convex portion 86a formed in the tension nip region B and the intermediate transfer belt 80 are not in contact at a single point. That is, the convex portion 86a contacts the intermediate transfer belt 80 and is elastically crushed, or the tip of the convex portion 86a is pressed by the intermediate transfer belt 80 and buried, resulting in a circular or conical shape with a small area. The nip portion is formed. Further, the apex of the convex portion 86a and the convex portion 36a of the physical nip region portion A are formed on the same plane on the sheet member 432a.

  Further, the ratio of the contact area where the sheet member 32a and the intermediate transfer belt 80 are in contact in Example 2 is 75 in the physical nip area A when the surface of the sheet member 32a is 100% when there is no unevenness. 0.0% and 5% or less in the tension nip region B.

  Further, the convex portions 36 a are arranged in a staggered pattern so as to be discontinuous with respect to the belt moving direction D of the intermediate transfer belt 80. The dimension of the physical nip area A of the sheet member 432a in the belt movement direction D is 3 mm, and the dimension of the tension nip area B in the belt movement direction D is set to 5 mm.

  Next, the function and effect of the second embodiment will be described. The inventors made the surface of the primary transfer member 481a in contact with the intermediate transfer belt 80 uneven. Further, regarding the physical nip area A and the tension nip area B that are in contact with each other between the primary transfer member 481a and the intermediate transfer belt 80, the ratio of the convex portion 86a in the tension nip area B is occupied in the physical nip area A. It was made smaller than the ratio of the convex part 36a. Further, by forming the convex portion 86a of the tension nip region B into a plurality of pointed needle shapes, the following effects can be obtained. That is, without reducing the size of the tension nip region B in the belt moving direction D, the suction force of the tension nip region B can be reduced, and the increase in the rotational torque of the intermediate transfer belt 80 can be further suppressed. .

  Further, by forming the concavo-convex portion 454 of the tension nip region B of the primary transfer member 81a into a sharp needle shape, it is possible to prevent the occurrence of abnormal discharge due to a sudden difference between the concave portion 85a and the convex portion 86a. At the same time, more stable transfer performance can be maintained. Since it acts as a needle-like electrode, the neutralization effect on the surface of the intermediate transfer belt 80 is greatly improved, and peeling discharge can be suppressed.

  FIG. 7A is a perspective view illustrating a configuration of a primary transfer member 581a provided in the image forming apparatus according to the third embodiment. FIG. 7B is a cross-sectional view taken along line YY in the tension nip region B of the sheet member 532a of FIG. Of the configuration of the primary transfer member 581a of Example 3, the same configurations and effects as those of the primary transfer member 481a of Example 2 are denoted by the same reference numerals and description thereof is omitted as appropriate. Since the third embodiment can be applied to the same image forming apparatus as that of the first embodiment, the description of the image forming apparatus is omitted. The primary transfer member 581a of the third embodiment is different from the primary transfer member 481a of the second embodiment in that the shape of a sheet member 532a that is a “transfer member” is different from the primary transfer member 581a. The uneven portion 53 and the uneven portion 554 provided on the sheet member 532a of the primary transfer member 581a are provided with a large number of uneven portions 53 and a large number of uneven portions 554 adjacent to each other. That is, the sheet member 532a has a concave portion 95a as a “planar portion” that is a “second concave portion” that is recessed from the convex portion 36a that is a “first convex portion”. Further, the sheet member 532a has a convex portion 96a as an “extended protrusion” that is a “second convex portion” that extends in the belt width direction G perpendicular to the belt moving direction L on the surface of the concave portion 95a. That is, the sheet member 532a has a linear convex part 96a and a linear concave part 95a. The convex part 96a has a taper part 96a1, and the front-end | tip part 96a2 becomes a vertex. The arrow indicates the belt moving direction D. Further, the convex portion 36a and the concave portion 35a of the concave and convex portion 53 of the physical nip region portion A of the sheet member 532a are the same as those described in the first embodiment, and thus the description thereof is omitted.

  Further, the uneven portion 554 of the tension nip region B of the sheet member 532a has a plurality of triangular pyramid-shaped convex portions 96a formed on a smooth concave portion 95a. The dimension of the bottom surface of the convex portion 96a in the YY direction is 25 μm. Further, the pitch E1 between the apexes of the adjacent convex portions 96a and the pitch E2 between the concave portions 95a are both 150 μm. The height L of the convex portion 96a is 50 μm. However, the triangular prism-shaped convex portion 96a formed in the tension nip region portion B in Example 3 and the intermediate transfer belt 80 are not in contact at a certain point, and a nip portion is formed on each surface. . Further, the apex of the convex portion 96a and the convex portion 36a of the physical nip region portion A are formed on the same plane on the sheet member 532a.

  Further, the convex portions 36 a are arranged in a staggered pattern so as to be discontinuous with respect to the belt moving direction D of the intermediate transfer belt 80. In the belt moving direction D, the physical nip region A formed by the sheet member 32a and the intermediate transfer belt 80 has a dimension of 3 mm, and the tension nip region B has a dimension of 5 mm.

[Other embodiments]
In the above-described embodiment, the primary transfer member 81a is exemplified as having the elastic member 31a and the sheet member 32a. However, the present invention is not limited to this. For example, the transfer member may be composed only of a sheet member.

  In the above-described embodiment, four image forming stations are used. However, the number of used stations is not limited, and may be set as necessary.

  In the above-described embodiment, the photosensitive drum 1a, the charging roller 2a acting on the photosensitive drum 1a, the developing unit 8a, and the cleaning unit 3a are integrally provided as the process cartridge 9a that is detachable from the apparatus main body 100A. A process cartridge is illustrated. However, the process cartridge is not limited to this. For example, in addition to the photosensitive drum, a process cartridge that integrally includes any one of the charging roller 2a, the developing unit 8a, and the cleaning unit 3a may be used.

  Further, in the above-described embodiment, the configuration in which the process cartridge 9a including the photosensitive drum 1a is detachable from the apparatus main body 100A is illustrated, but the present invention is not limited to this. For example, it may be an image forming apparatus in which each photosensitive drum or process means is incorporated, or an image forming apparatus in which each photosensitive drum or process means is detachable.

  In the above-described embodiments, the printer is exemplified as the image forming apparatus. However, the present invention is not limited to this, and other image forming apparatuses such as a copying machine and a facsimile machine, or a combination of these functions. Other image forming apparatuses such as multifunction peripherals may also be used. Further, the movable belt is not limited to the intermediate transfer belt 80, and a recording material carrier that carries and conveys a recording material is used, and each color toner is applied to the recording material carried on the recording material carrier. An image forming apparatus that sequentially superimposes and transfers images may be used. The same effect can be obtained by applying the present invention to these image forming apparatuses.

  According to the image forming apparatuses of the first and second embodiments and the other embodiments described above, an increase in friction between the intermediate transfer belt 80 and the primary transfer member 81a is suppressed, and the intermediate transfer belt 80 is stabilized to the primary transfer member 81a. And move while touching. As a result, the occurrence of chatter and abnormal noise on the primary transfer member 81a is suppressed. At the same time, the surface of the intermediate transfer belt 80 is effectively slowed down. As a result, even when the environment is bad, the occurrence of image defects is suppressed more than before.

1a to 1d Photosensitive drum (image carrier)
33a to 33d recess (second recess)
34a-34d Convex part (2nd convex part) (2nd contact part)
35a to 35d recess (first recess)
36a-36d Convex part (first convex part) (first contact part)
80 Intermediate transfer belt (belt)
81a to 81d Primary transfer member A Physical nip area (first contact area)
B Tension nip area (second contact area)

Claims (7)

An image carrier for carrying a toner image;
A belt that moves while contacting the image carrier;
There is a space between the belt and the image carrier, and a first contact region where a first contact portion is formed in contact with the back surface of the belt while the belt and the image carrier are in contact with each other. A transfer member having a second contact region portion formed with a second contact portion that contacts the back surface of the belt in a secured state,
An image forming apparatus, wherein a first ratio of the first contact portion to the first contact region portion and a second ratio of the second contact portion to the second contact region portion are different from each other.   The image forming apparatus according to claim 1, wherein the second ratio is smaller than the first ratio. The first ratio is a ratio of an area of a tip of the first contact portion on the belt side to an area of the first contact region portion,
The said 2nd ratio is a ratio of the area which the front end by the side of the said belt of the said 2nd contact part has with respect to the area of the said 2nd contact region part, The Claim 1 or Claim 2 characterized by the above-mentioned. The image forming apparatus described. The first ratio is a ratio of a contact area where the first contact portion contacts the belt with respect to an area of the first contact region portion,
The said 2nd ratio is a ratio of the contact area where the said 2nd contact part contacts the said belt with respect to the area of the said 2nd contact region part, The Claim 1 or Claim 2 characterized by the above-mentioned. Image forming apparatus. The first contact region portion is formed in a lattice shape in a plan view and is formed in a plurality of uneven shapes in a cross-sectional view, and the first convex portion that is the first contact portion, and the first convex portion Having a first recess formed therebetween,
The second contact region portion is formed in a lattice shape in a plan view and is formed in a plurality of uneven shapes in a cross-sectional view, and the second convex portion that is the second contact portion, and the second convex portion The image forming apparatus according to claim 1, further comprising a second concave portion formed therebetween. The second concave portion is a flat portion formed to be recessed from the first convex portion,
The image forming apparatus according to claim 5, wherein the second convex portion is a needle-like portion formed in a needle shape on the surface of the flat portion. The second concave portion is a flat portion formed to be recessed from the first convex portion,
The image forming apparatus according to claim 5, wherein the second convex part is an extending protrusion extending in a belt width direction orthogonal to a belt moving direction on a surface of the flat part.

Images