JP2013113854A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem in which: it has been difficult to suppress with a simple configuration the occurrence of a scattering phenomenon in which a toner image from an intermediate transfer belt moves to a position different from a predetermined position on a transfer material due to an electric field that occurs in the vicinity of a secondary transfer area.SOLUTION: An image forming apparatus includes a guide member 13 for regulating a direction of rotation of an intermediate transfer belt 10 while being in rubbing contact with the intermediate transfer belt 10 at a position facing a secondary transfer roller 20 with the intermediate transfer belt 10 interposed between the guide member 13 and the secondary transfer roller 20. The guide member 13 includes a low-resistance rubbing part and a high-resistance rubbing part that are in rubbing contact with the intermediate transfer belt 10. The high-resistance rubbing part is provided at least in the upstream side of the low-resistance rubbing part in the direction of rotation of the intermediate transfer belt 10 and thus the occurrence of scattering is suppressed to regulate an electric field in the vicinity of a secondary transfer area.

Description

  The present invention relates to an image forming apparatus such as a copying machine or a laser printer.

  In an electrophotographic color image forming apparatus, in order to print at high speed, each color image forming unit for forming yellow, magenta, cyan, and black images is independently provided. A configuration is known in which an image is transferred to an intermediate transfer member, and further, the image is transferred collectively from the intermediate transfer member to a transfer material.

  Patent Document 1 discloses an image forming apparatus that uses an endless intermediate transfer belt as an intermediate transfer member. A secondary transfer roller is used as the secondary transfer member, and one of the support rollers that supports the inner peripheral surface of the intermediate transfer belt is used as a counter roller of the secondary transfer roller. The secondary transfer roller is brought into pressure contact with the opposing roller via the intermediate transfer belt, and a secondary transfer region in which the secondary transfer roller and the intermediate transfer belt are in contact with each other is formed.

  A potential difference is generated between a secondary transfer roller to which a voltage is applied and a grounded counter roller with respect to the transfer material conveyed to the secondary transfer region, and the toner image on the intermediate transfer belt is electrostatically transferred. Transcript to.

JP 2004-29057 A

  However, an image forming apparatus that forms a secondary transfer region with an intermediate transfer belt, a secondary transfer roller, and a counter roller has the following problems.

  The action of the electric field generated between the secondary transfer roller and the counter roller extends not only to the secondary transfer region but also to its periphery. Since the electric field also acts in the nip entrance area located upstream of the secondary transfer area, the toner image on the intermediate transfer belt is transferred in the nip entrance area before the transfer material enters the secondary transfer area. In some cases, the material moved electrostatically. As a result, the toner image is transferred to a position different from a predetermined position (position to be originally transferred) of the transfer material, resulting in an image that is disturbed and scattered, and there is a problem that the image quality is deteriorated. Hereinafter, this phenomenon is referred to as scattering.

  An object of the present invention is to provide an image forming apparatus that can suppress scattering with a relatively simple configuration and can form a high-quality image.

In order to solve the above problems, the present invention has the following configuration.
An image carrier that carries a toner image, an endless intermediate transfer belt on which a toner image is primarily transferred from the image carrier, and a driving member that supports the inner peripheral surface of the intermediate transfer belt and rotates the intermediate transfer belt A support member that supports an inner peripheral surface of the intermediate transfer belt, and a secondary transfer member that contacts an outer surface of the intermediate transfer belt and forms a secondary transfer region with the intermediate transfer belt. In the image forming apparatus that secondarily transfers a toner image from the intermediate transfer belt to a recording material conveyed to a next transfer region, the support member is located at a position facing the secondary transfer member via the intermediate transfer belt. A guide member that regulates a rotation direction of the intermediate transfer belt while rubbing against the intermediate transfer belt, and the guide member includes a first resistance portion that rubs against the intermediate transfer belt, and a first resistance portion. Electrical A second resistance portion having a high resistance, and the second resistance portion is provided at least upstream of the first resistance portion in the rotation direction of the intermediate transfer belt. And

  According to the present invention, by restricting the electric field in the vicinity of the entrance of the secondary transfer region, it is possible to suppress the scattering with a relatively simple configuration and to provide an image forming apparatus capable of forming a high quality image. Objective.

1 is a schematic sectional view of an image forming apparatus according to an embodiment. Schematic cross-sectional view enlarging the vicinity of the secondary transfer region of the image forming apparatus of one embodiment Schematic cross-sectional view enlarging the vicinity of the secondary transfer region of the image forming apparatus of one embodiment (A) Schematic sectional view for explaining the electric field in the vicinity of the secondary transfer area when the counter roller is used as the counter member. (B) The electric field in the vicinity of the secondary transfer area when the guide member of one embodiment is used. Schematic cross section Schematic cross-sectional view enlarging the vicinity of the secondary transfer region of the image forming apparatus of one embodiment Schematic cross-sectional view enlarging the vicinity of the secondary transfer region of the image forming apparatus of one embodiment

Example 1
In the following, preferred embodiments of the present invention will be described in detail with reference to the drawings. However, the components described in this embodiment are merely examples, and are not intended to limit the scope of the present invention.

  FIG. 1 is a configuration diagram of a color image forming apparatus of an inline type (4-drum system). The image forming apparatus forms an image forming unit a that forms a yellow image, an image forming unit b that forms a magenta image, an image forming unit c that forms a cyan image, and a black image. The image forming unit d includes four image forming units. These four image forming units are arranged in a line at regular intervals.

  Since the configuration of each image forming unit is the same except for the color of the image to be formed, the image forming unit will be described using the image forming unit a.

  The image forming unit a includes a drum-shaped electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) 1a, a charging member 1b, a developing unit 4a, and a cleaning unit 5c. The image forming unit a of this embodiment is a process cartridge that integrates them and is detachable from the apparatus main body.

  The photosensitive drum 1a, which is an electrophotographic photosensitive member, is rotationally driven at a predetermined peripheral speed (process speed) in the arrow direction R1. The photosensitive drum 1a is uniformly charged to a predetermined polarity and potential by a charging roller 2a, which is a charging member, during this rotation process. In this embodiment, the photosensitive drum 1a is negatively charged by the charging roller 2a. Next, image exposure is performed by the exposure means 3a which is an exposure unit. Thereby, an electrostatic latent image corresponding to the yellow component image of the target color image is formed.

  Next, the electrostatic latent image is developed by the first developing unit (yellow developing device) 4a at the developing position and visualized as a yellow toner image. The yellow developer 4a contains yellow toner charged to a negative polarity, and is developed on the photosensitive drum 1a by a developing roller provided in the yellow developer 4a. The photosensitive drum 1a is an image carrier that carries a toner image.

  The yellow toner image on the photosensitive drum 1a is primarily transferred to the opposing intermediate transfer member. The intermediate transfer belt 10, which is an intermediate transfer body, is an endless belt, is supported by a plurality of support members, and has a photosensitive drum in an arrow direction R <b> 3 that moves in the same direction at a facing portion in contact with the photosensitive drum 1. 1 is rotated at the same peripheral speed as 1. A primary transfer member is provided at a position facing the photosensitive drum 1 a via the intermediate transfer belt 10. The yellow toner image formed on the photosensitive drum 1a is primarily transferred onto the intermediate transfer belt 10 in the process of passing through the primary transfer nip where the photosensitive drum 1a and the intermediate transfer belt 10 abut. At that time, a primary transfer voltage is applied from a primary transfer power supply 15a to a primary transfer roller 14a that is a primary transfer member that forms a primary transfer nip portion.

  The primary transfer residual toner remaining on the surface of the photosensitive drum 1a is cleaned and removed by the cleaning unit 5a.

  Similarly, in each of the image forming units (b) to (d), a second color magenta toner image, a third color cyan toner image, and a fourth color black toner image are formed and are formed on the intermediate transfer belt 10. The combined color image corresponding to the target color image is obtained by sequentially transferring the images. Respective exposure units 3b to 3d and primary transfer rollers 14b to 14d are provided in the image forming portions b to d, respectively.

The four color toner images on the intermediate transfer belt 10 are conveyed from the paper feeding means 50 in the process of passing through the secondary transfer region formed by the intermediate transfer belt 10 and the secondary transfer roller 20 as a secondary transfer member. Secondary transfer is performed on the surface of the transfer material P. At that time, a secondary transfer voltage is applied to the secondary transfer roller 20 from a secondary transfer power source 21. The secondary transfer roller 20 as a secondary transfer member has an outer diameter covered with a nickel-plated steel rod having an outer diameter of 8 mm and a foam sponge of NBR (nitrile rubber) adjusted to a resistance value of 10 ⁸ Ω · cm and a thickness of 5 mm. An 18 mm roller is used. The secondary transfer roller 20 is brought into contact with the outer peripheral surface of the intermediate transfer belt 10 with a pressurizing force of 50 N, and is driven to rotate with respect to the intermediate transfer belt 10.

  Thereafter, the transfer material P carrying the four-color toner images is introduced into the fixing device 30 where the four color toners are melted and mixed and fixed to the transfer material P by being heated and pressurized. Then, the transfer material P is discharged out of the apparatus.

  With the above operation, a full-color print image is formed on the transfer material P. Further, the secondary transfer residual toner remaining on the surface of the intermediate transfer belt 10 is cleaned and removed by the intermediate transfer belt cleaning unit 16.

Next, the intermediate transfer belt 10 and the plurality of support members 11, 12, and 13 that support the inner peripheral surface of the intermediate transfer belt 10 will be described. The intermediate transfer belt 10 and the support members 11, 12, and 13 are integrated as an intermediate transfer unit and can be attached to and detached from the apparatus main body. It is desirable that the intermediate transfer belt 10 has little charge remaining after transfer and does not require a static elimination mechanism. In this embodiment, it is preferable that the volume resistivity is made of a material of about 10 ⁸ to 10 ¹¹ Ω · cm because the residual charge after transfer is small and the neutralization mechanism can be made unnecessary. The intermediate transfer belt 10 of this embodiment is made of a material mainly composed of polyvinylidene fluoride (PVdF) having a thickness of 100 μm and a volume resistivity of 10 ⁹ Ω · cm. The intermediate transfer belt 10 may be made of other materials such as polyamide (PI), polyether ether ketone (PEEK).

  The support member 11 is a drive roller that is a drive member that supports the intermediate transfer belt 10 while driving it, and rotates in the arrow direction R2 to rotate and move the intermediate transfer belt 10 in the arrow direction R3. In this embodiment, as the support member 11, a roller in which an aluminum shaft having an outer diameter of 20 mm is coated with an elastic rubber (ethylene propylene rubber) having a thickness of 0.5 mm is used.

  The support member 12 is a tension roller that applies tension to the inner peripheral surface of the intermediate transfer belt 10 from the inner peripheral surface side toward the outer peripheral surface side. In this embodiment, a hollow aluminum shaft having an outer diameter of 20 mm is used as the support member 12. The support member 12 presses the intermediate transfer belt 10 with a total pressure of 39.2N by the spring 12h, and applies tension to the intermediate transfer belt 10.

  The support member 13 is a guide member that faces the secondary transfer roller 20 with the intermediate transfer belt 10 interposed therebetween. The guide member 13 regulates the rotation direction of the intermediate transfer belt 10 while sliding on the intermediate transfer belt 10 at a position facing the secondary transfer roller 20 via the intermediate transfer belt 10. The guide member 13 is not configured to rotate with the intermediate transfer belt 10 like other support members, but is configured to be fixed to the intermediate transfer unit. The configuration related to the guide member 13 will be described later.

  The intermediate transfer belt 10, the support members 11, 12, 13 and the primary transfer rollers 14a to 14d are integrated as an intermediate transfer unit. The driving roller 11, the tension roller 12, and the primary transfer rollers 14a to 14d, which are rollers, are supported by the respective bearings and are rotatable. On the other hand, the guide member 13 is fixed to a frame constituting the intermediate transfer unit.

  Below, the structure of the guide member 13 is demonstrated. The guide member 13 of this embodiment is a guide member that rubs against the intermediate transfer belt 10, and a portion having a different electric resistance in the moving direction of the intermediate transfer belt 10 on the rubbed surface of the guide member 13 with the intermediate transfer belt 10. It is characterized by having.

FIG. 2 is an enlarged schematic cross-sectional view of the vicinity of the secondary transfer region of the image forming apparatus according to the present exemplary embodiment.
The rubbing surface of the guide member 13 with the intermediate transfer belt 10 includes three secondary transfer regions N, a nip inlet region I upstream thereof, and a nip outlet region E downstream of the secondary transfer region N in the rotational direction of the intermediate transfer belt 10. Divided into areas.

  The guide member 13 includes a guide support member 13e, a low resistance rubbing portion 13g that is a first resistance portion, and a high resistance rubbing portion 13f that is a second resistance portion. A high resistance rubbing portion 13 f and a low resistance rubbing portion 13 g are provided on the rubbing surface on which the intermediate transfer belt 10 and the guide member 13 rub. Further, the high resistance rubbing portion 13f and the low resistance rubbing portion 13g are supported by the guide support member 13e. The high resistance rubbing portion 13f has higher electrical resistance than the low resistance rubbing portion 13g. In this embodiment, the surface of the guide support member 13e that comes into contact with the intermediate transfer belt 10 is configured to be a curved surface having a curvature radius of 12 mm.

  This curvature radius is preferably set in the range of 8 mm to 15 mm. If the radius of curvature is smaller than 8 mm, the curvature is too large, and there is a concern that a trace that is supported by the guide member 13 on the intermediate transfer belt 10, that is, so-called curl, occurs when left at a high temperature. When the toner image of the intermediate transfer belt 10 in which curling has occurred is transferred, an image defect occurs. On the other hand, when the radius of curvature is larger than 15 mm, the curvature is too small, and the separation performance of the transfer material P using the curvature separation is deteriorated, and a transfer material having no stiffness such as thin paper is wound around the intermediate transfer belt 10 to cause poor separation. There is. In addition, the size of the entire intermediate transfer unit becomes too large.

The guide support member 13e is preferably made of an insulating material having a volume resistivity of 10 ¹² Ω · cm or more. Since the guide support member 13e is not exposed on the rubbing surface with the intermediate transfer belt 10, any insulating member may be used as long as sufficient rigidity is obtained. As an example, the guide support member 13e of this embodiment is made of an insulating ABS resin. In order to increase the rigidity of the guide support member 13e, a reinforcing member made of a metal material or the like may be added.

The high resistance rubbing portion 13f is disposed upstream of the low resistance rubbing portion 13g in the rotational direction of the intermediate transfer belt 10. The high resistance rubbing portion 13f is provided at least upstream from the position of the most upstream end in the rotation direction (N1 in FIG. 2) of the secondary transfer region N where the secondary transfer roller 20 contacts the outer surface of the intermediate transfer belt 10. ing. In FIG. 2, the high-resistance rubbing portion 13f is provided in the nip portion entrance region I that is an upstream region from N1. The high-resistance rubbing part is desirably made of an insulating material having a volume resistivity of 10 ¹² Ω · cm or more. In this embodiment, an insulating ultrahigh molecular weight polyethylene sheet member having a thickness of 0.2 mm is used. Ultra-high molecular weight polyethylene is a polyethylene having a molecular weight increased to about 5 million, and is generally known as a material excellent in slipperiness and wear resistance.

  Any material other than ultra-high molecular weight polyethylene that does not hinder the rotation of the intermediate transfer belt 10 and has good slipperiness can be used as the high resistance rubbing portion 13f. Examples thereof include a fluororesin and a polyacetal resin.

On the other hand, the low resistance rubbing portion 13g is disposed at least between the position N1 at the most upstream side in the rotation direction of the secondary transfer area N and the position N2 at the most downstream side in the rotation direction of the secondary transfer area N. In FIG. 2, the surface that rubs against the intermediate transfer belt 10 on the downstream side of N1 is all the low resistance rubbing portion 13g. (E, which is an area downstream of N2 in FIG. 2, is hereinafter referred to as a nip exit area E.) The low-resistance rubbing portion 13g does not interfere with the rotation of the intermediate transfer belt 10 similarly to the high-resistance rubbing portion 13f. A material having good slipperiness can be employed. Further, since the low resistance rubbing portion 13g needs to function as a counter electrode in the secondary transfer region N, a material having a low electric resistance is preferable. Specifically, it is preferably composed of a material having a volume resistivity of 10 ⁸ Ω · cm or less. The low resistance rubbing portion 13g is electrically grounded by a conductor (not shown).

In this embodiment, a conductive ultra-high molecular weight polyethylene sheet member having a thickness of 0.2 mm in which carbon is dispersed as a conductive agent is used as the low resistance rubbing portion 13g. The electrical resistance of this conductive ultra-high molecular weight polyethylene sheet is 10 ⁷ Ω · cm or less in volume resistivity.

  In this embodiment, the other surface, which is the opposite surface (one surface) of the high-resistance rubbing portion 13f and the low-resistance rubbing portion 13g, is bonded and fixed to the surface of the guide support member 13e with an insulating double-sided tape. Has been.

  FIG. 3 is a schematic diagram illustrating a high resistance support portion 13h in which the guide support member 13e and the high resistance rubbing portion 13f of FIG. 2 are integrated. In the nip entrance region I of the guide member 13, the high resistance support portion 13h is in contact with the intermediate transfer belt 10, and in the secondary transfer region N and the nip exit region E, the low resistance rubbing portion 13g is in contact. The surface of the high resistance support portion 13h on which the low resistance rubbing portion 13g is disposed so that the rubbing surfaces of the secondary transfer region N and the nip outlet region E are the same height as the rubbing surface of the nip inlet region I. Is reduced according to the thickness so as not to cause a step. Since the high resistance support portion 13 h in FIG. 3 rubs against the intermediate transfer belt 10, it is preferable that the high resistance support portion 13 h be made of a material having good slipperiness with respect to the intermediate transfer belt 10. For example, you may comprise with an insulating polyacetal resin. The high resistance support portion 13h shown in FIG. 3 can reduce the number of components, and can suppress scattering with a low cost and simple configuration.

  The operation of the present embodiment will be described below. 4A is a schematic view of the vicinity of the secondary transfer region of the image forming apparatus using the conventional transfer counter roller 17, and FIG. 4B is an image forming apparatus using the guide member 13 of the present embodiment. It is the schematic of the secondary transfer area vicinity. An arrow F shown around the secondary transfer region N schematically shows electric lines of force corresponding to an electric field generated when a positive secondary transfer voltage is applied to the secondary transfer roller 20. is there.

4A, the transfer counter roller 17 is formed by coating an aluminum cored bar with an elastic rubber in which carbon as a conductive agent is dispersed, and having an outer diameter of 24 mm or less with a volume resistivity of 10 ⁶ Ω · cm or less. The rubber roller is used.

  As shown in FIG. 4A, in the space between the secondary transfer roller 20 and the intermediate transfer belt 10 in the nip entrance region I, an electric force line F directed from the secondary transfer roller 20 to the transfer counter roller 17 serving as a counter electrode. Exists. Therefore, the toner image on the intermediate transfer belt 10 may move from the intermediate transfer belt 10 toward the secondary transfer roller 20 before entering the secondary transfer region N. Therefore, in the configuration of FIG. 4A, there is a possibility that a scattering phenomenon occurs in which the toner image on the intermediate transfer belt 10 moves before entering the secondary transfer region N.

  On the other hand, as shown in FIG. 4B, the electric lines of force from the secondary transfer roller 20 to which a voltage has been applied are directed toward the low resistance rubbing portion 13g of the secondary transfer region N serving as a counter electrode. Therefore, in the nip entrance region I, the electric field is weakened by the absence of the low-resistance rubbing portion 13g serving as the counter electrode, and the electric lines of force F are relatively smaller than the configuration of the conventional example shown in FIG. Less. Therefore, in the nip entrance region I, the toner image on the intermediate transfer belt 10 becomes difficult to move to the recording material P, and the scattering phenomenon is improved.

  In this embodiment, the resistance change point X at which the high resistance rubbing portion 13f switches to the low resistance rubbing portion 13g in the moving direction (arrow direction R3) of the intermediate transfer belt 10 is the upstream end of the secondary transfer region N (FIG. 2). N1). The position of the resistance change point X may be slightly shifted upstream and downstream with respect to the upstream end of the secondary transfer region N. However, in order to suppress the occurrence of scattering, the resistance change point X is as small as possible. It is better to be located at the same position as the upstream end of the next transfer region N or at the downstream side.

  As described above, by using the guide member that rubs against the intermediate transfer belt 10, it is possible to locally change the arrangement and resistance value of the counter electrode. Thereby, the electric field in the vicinity of the secondary transfer region N can be regulated depending on the location.

  For the reasons described above, it is possible to suppress the occurrence of a toner image scattering phenomenon on the recording material P and provide a high-quality image.

(Example 2)
Next, another embodiment of the present invention will be described. The basic configuration of the image forming apparatus of this embodiment is the same as that of the first embodiment. Therefore, elements having the same functions or configurations as those of the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  The feature of this embodiment is that the high-resistance rubbing portion 13f is also provided in a region downstream of the upstream end N1 of the secondary transfer region N (in the secondary transfer region N) with respect to the configuration of the first embodiment. It is arranged.

  FIG. 5 is an enlarged view of the vicinity of the secondary transfer region for explaining the guide member 13 of the present embodiment. As shown in FIG. 5, the high-resistance rubbing portion 13 f is disposed so as to extend from the nip entrance region I to the upstream side in the secondary transfer region N. Therefore, the secondary transfer region N is divided into an upstream nip portion NU without a counter electrode and a downstream nip portion NL with a counter electrode. That is, the resistance change point X where the high resistance rubbing portion 13f switches to the low resistance rubbing portion 13g in the moving direction of the intermediate transfer belt 10 (arrow direction R3) is located in the secondary transfer region N. The toner image on the intermediate transfer belt 10 is substantially transferred at the downstream nip portion NL where the low resistance rubbing member 13g serving as a counter electrode is present.

  As described above, in the configuration of this embodiment, the electric field in the nip entrance region I can be further weakened, and the toner image on the intermediate transfer belt 10 and the recording material can be brought into contact before the toner image is transferred. Therefore, the flying of the toner to the recording material P is further effectively suppressed. Therefore, it is possible to provide a high-quality image with less scattering than in the first embodiment.

(Example 3)
Next, another embodiment of the present invention will be described. The basic configuration of the image forming apparatus of this embodiment is the same as that of the first embodiment. Therefore, elements having the same functions or configurations as those of the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  The feature of the present embodiment is that the contact surface of the guide member 13 that contacts the intermediate transfer belt 10 is a combination of a flat surface and curved surfaces with different curvatures, etc., compared to the configuration of the guide member 13 of the first embodiment shown in FIG. It is in the point that consists of.

  FIG. 6 is an enlarged schematic cross-sectional view of the vicinity of the secondary transfer region of the image forming apparatus of this embodiment.

  The rubbing surface of the guide member 13 with the intermediate transfer belt 10 is divided into a nip inlet upstream area IU, a nip inlet downstream area IL, a secondary transfer area N, a nip outlet upstream area EU, and a nip outlet downstream area EL.

  From the viewpoint of preventing image defects due to curling of the intermediate transfer belt 10, the rubbing surface of all regions of the guide member 13 is preferably configured by a curved surface or a substantially flat surface with a radius of curvature of 8 mm or more.

  In the nip inlet upstream area IU (first bent portion), the guide member 13 needs a function of changing the traveling angle of the intermediate transfer belt 10. In the present embodiment, the rubbing surface of the guide member 13 in the nip inlet upstream region IU is formed of a curved surface having a curvature radius of 10 mm. As described above, the guide member 13 can also integrally form the nip entrance upstream region IU that determines the curvature of the intermediate transfer belt 10. Unlike the roller shape, since the guide member 13 is a fixed member, its shape can also be freely selected.

  The guide member 13 suppresses the occurrence of curling on the intermediate transfer belt 10 by making the curvature radius of the nip entrance upstream region IU a large curved surface. For example, in the configuration of FIG. 4A, when the radius of curvature of the intermediate transfer belt 10 is increased, it is necessary to increase the diameter of the secondary transfer counter roller itself, which increases the size of the apparatus. In the configuration of this embodiment, since the secondary transfer belt 10 is bent (the nip inlet upstream area IU) may be a large curved surface, there is an effect of suppressing the enlargement of the apparatus.

  In the nip entrance downstream region IL, the guide member 13 needs to have a function of causing the intermediate transfer belt 10 to approach the recording material P and enter the secondary transfer region N. By bringing the intermediate transfer belt 10 and the recording material P close to each other, the movement distance when the toner on the intermediate transfer belt 10 moves to the recording material P upstream of the secondary transfer region N can be shortened. Misalignment is reduced and scattering can be suppressed.

  The rubbing surface of the guide member 13 in the recording material nip inlet downstream region IL is preferably formed of a substantially flat surface or a curved surface having a very large radius of curvature. In this case, the intermediate transfer belt 10 and the recording material P can be brought close to each other from a position away from the secondary transfer region N, which is advantageous for suppressing scattering. In the present embodiment, the nip inlet downstream region IL is configured by a substantially flat surface.

  In the nip inlet upstream region IU and the nip inlet downstream region IL described above, the high-resistance rubbing portion 13f is disposed in order to suppress scattering.

  In the secondary transfer region N, the guide member 13 needs to function as a counter member and a counter electrode of the secondary transfer roller 20. The substantial transfer of the toner image to the recording material P is performed in the secondary transfer region N. Therefore, in the secondary transfer region of the guide member 13, a low resistance rubbing portion 13g that functions as a counter electrode is disposed.

  The rubbing surface of the guide member 13 in the secondary transfer region N may have any shape as long as no image defect occurs due to winding of the intermediate transfer belt 10. In this embodiment, the rubbing surface of the guide member 13 in the secondary transfer region N is formed by a curved surface having a curvature radius of 15 mm.

  In the nip exit upstream region EU (second bent portion), the guide member 13 needs a function of separating the intermediate transfer belt 10 and the recording material P and a function of changing the traveling angle of the intermediate transfer belt 10. From the viewpoint of increasing the separation of the recording material P and reducing the size of the apparatus, it is preferable that the radius of curvature is small as long as no image defect occurs due to winding of the intermediate transfer belt 10. In the present embodiment, the rubbing surface of the guide member 13 in the nip outlet upstream region EU is constituted by a curved surface having a curvature radius of 10 mm. When comparing the curvature of the nip inlet upstream region IU where the secondary transfer belt 10 is bent and the nip outlet upstream region EU, the curvature of the nip inlet upstream region IU is larger than the curvature of the nip outlet upstream region EU.

  In the nip outlet downstream area EL, the guide member 13 has a function of securing an area for disposing the transfer belt cleaning member 16. On the other hand, from the viewpoint of securing a region for arranging the belt cleaning member 16, it is preferable that the plane or the radius of curvature is large.

  In this embodiment, the rubbing surface of the guide member 13 in the nip outlet downstream area EL is a flat surface. The nip outlet upstream area EU and the nip outlet downstream area EL are provided with the same low resistance rubbing portion 13g as the secondary transfer area N in order to prevent discharge or the like when the intermediate transfer belt 10 is separated from the guide member 13. Has been established.

  As described above, the transfer counter member is not a rotating body such as the transfer counter roller 17 as in the conventional image forming apparatus, but a guide member that rubs against the intermediate transfer belt 10, thereby disposing the counter electrode. In addition to the resistance value, the shape of the rubbing surface of the guide member can be locally changed.

  As a result, the electric field in the vicinity of the secondary transfer region N is restricted according to the location, curling of the secondary transfer belt 10 is suppressed, and the intermediate transfer belt 10 is moved in front of the secondary transfer region N. It can be moved close to the recording material P. Further, the recording material that has passed through the secondary transfer region N can be easily separated from the intermediate transfer belt 10. For the above reasons, it is possible to provide a high-quality image with less scattering.

DESCRIPTION OF SYMBOLS 10 Intermediate transfer body 11, 12 Support member 13 Guide member 13e Guide support member 13f High resistance rubbing part 13g Low resistance rubbing part 20 Secondary transfer member P Recording material

Claims (8)

An image carrier that carries a toner image, an endless intermediate transfer belt on which a toner image is primarily transferred from the image carrier, and a driving member that supports the inner peripheral surface of the intermediate transfer belt and rotates the intermediate transfer belt A support member that supports an inner peripheral surface of the intermediate transfer belt, and a secondary transfer member that contacts an outer surface of the intermediate transfer belt and forms a secondary transfer region with the intermediate transfer belt. In an image forming apparatus that secondarily transfers a toner image from the intermediate transfer belt to a recording material conveyed to a next transfer region,
The support member is a guide member that regulates the rotation direction of the intermediate transfer belt while sliding on the intermediate transfer belt at a position facing the secondary transfer member via the intermediate transfer belt, and the guide member is A first resistance portion that rubs against the intermediate transfer belt, and a second resistance portion having a higher electrical resistance than the first resistance portion, wherein the second resistance portion is at least the An image forming apparatus, wherein the image forming apparatus is provided upstream of the first resistance portion in the rotation direction of the intermediate transfer belt.   The image forming apparatus according to claim 1, wherein the guide member includes a guide support member that supports the first resistance portion and the second resistance portion.   The first resistance portion and the second resistance portion are characterized in that one surface is a rubbing surface rubbing against the intermediate transfer belt and the other surface is bonded to the guide support member. The image forming apparatus according to 2.   The image forming apparatus according to claim 1, wherein the second resistance portion also serves as a support portion that supports the first resistance portion.   The most upstream end of the first resistance portion is at least at the same position as the most upstream end of the secondary transfer region or a downstream position in the rotation direction of the intermediate transfer belt. The image forming apparatus according to any one of claims 1 to 4.   6. The image forming apparatus according to claim 1, wherein the first resistance portion is an ultrahigh molecular weight polyethylene imparted with electrical conductivity.   The image forming apparatus according to any one of claims 1 to 6, wherein the second resistance portion is an ultrahigh molecular weight polyethylene that does not impart conductivity.   The guide member includes a first bent portion that bends the intermediate transfer belt upstream of the secondary transfer region in the rotational direction of the intermediate transfer belt, and the intermediate transfer belt downstream of the secondary transfer region. The image forming apparatus according to claim 1, further comprising a second bent portion that bends.

Images