JP2008310060A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device, for obtaining further stable and satisfactory transfer performance with a simple structure. <P>SOLUTION: In the image forming device 100, a transfer member 5 includes an elastic member 51 and a sheet member 52 held between a belt body 7 and the elastic member 51 and surface-contacting with the belt body 7. In a moving direction of the belt body 7, a downstream-side end part of a contact area A between an image carrier 1 and the belt body 7 is located within a contact area B between the sheet member 51 and the belt body 7. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a laser beam printer and a copying machine having a step of transferring a toner image formed on an image carrier using an electrophotographic system or an electrostatic recording system onto a belt body or onto a transfer material carried on the belt body. The present invention relates to an image forming apparatus such as a facsimile apparatus.

  Conventionally, for example, in an image forming apparatus using an electrophotographic system, a toner image which is a developer image is formed on an electrophotographic photosensitive member (photosensitive member) as an image carrier. Then, an electric field having a polarity opposite to the normal charging polarity of the toner is applied to the transfer means, and the toner image carried on the photosensitive member is electrostatically applied to the surface of the transfer material or intermediate transfer belt carried on the transfer belt. A transfer step of transferring to is performed.

  For this reason, in an image forming apparatus including a movable belt body such as a transfer belt or an intermediate transfer belt, a voltage applying unit that applies a voltage necessary for the transfer process to the transfer unit is provided. As an example of this, there is a configuration in which a contact transfer member such as a transfer roller connected to a high voltage power source as a voltage applying unit is disposed as a transfer unit at a position facing the photoconductor (on the back side of the belt unit) across the belt unit. is there.

  However, in an image forming apparatus using a transfer roller, the contact area (so-called transfer nip) between the belt body and the transfer roller may be uneven in 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 longitudinal direction of the contact area between the belt body and the transfer roller, which may cause image defects such as transfer defects. In addition, since the transfer nip is narrow, peeling discharge occurs at the peeling portion between the belt member and the photosensitive member, which may cause image defects.

  As a countermeasure against the above problems, a configuration using a brush-like contact transfer member as a transfer unit has been proposed. In this case, since each fiber constituting the brush is in contact with the belt body independently, the contact state of the contact area with the belt body can be made uniform in the longitudinal direction, and the transfer failure as described above. It is advantageous to suppress the above (Patent Document 1).

Further, a configuration using a film as a transfer means has been proposed. More specifically, the film can be displaced between the film support and the photoconductor, and comes into contact with and separates from the transfer material depending on the presence or absence of electrostatic attraction force by supplying or not supplying voltage (patent) Reference 2).
JP 05-127546 A Japanese Patent Laid-Open No. 09-120218

  However, in the case of an image forming apparatus using a conventional brush as a transfer unit, when used for a long time, the tip of the brush is crushed and deformed, resulting in non-uniform contact with the belt body, resulting in poor transfer. There is.

  Specifically, each fiber constituting the brush falls by pressing the brush against the belt body. When used in such a state, the fibers of the brush are deformed with wrinkles in a fallen state. As a result, the contact between the brush and the belt body becomes non-uniform, and the transfer current value required for the transfer process becomes non-uniform, which may cause transfer failure.

  Further, when there is a downstream end (contact end) of the contact area between the belt body and the transfer member in the contact area between the belt body and the photosensitive member in the moving direction of the belt body, It has been found that problems may occur. That is, in the peeling portion of the belt member from the photosensitive member, a peeling discharge may occur due to a sudden change in potential, and the toner image on the belt member may be disturbed. In order to prevent this, it is desirable to provide a charge eliminating member, which may increase the size and cost of the apparatus.

  On the other hand, in an image forming apparatus using a conventional film as a transfer unit, there is no film backup member, and therefore transfer failure may occur due to undulation of the film.

  Specifically, when contacting the belt body only with the electrostatic attraction force of the film, the uniformity of the contact between the film and the belt body in the longitudinal direction may not be maintained due to the wave of the film. Therefore, a sufficient transfer current may not be ensured in a portion where the contact area is narrow or where the contact between the film and the belt body is insufficient. Therefore, a short streak-like transfer failure may occur due to insufficient transfer current.

  In addition, since the electrostatic adsorption of the film is positively used, the frictional force between the film and the belt body increases, and the load on the drive motor or the like may increase due to an increase in the driving torque of the belt body.

  Specifically, the frictional force actually acting between the belt body and the film is a force determined by the friction coefficient between the belt body and the film and an electrostatic adsorption force determined by the impedance between the film and the belt body. . For this reason, when the film is brought into and out of contact with the supply or non-supply of the transfer voltage, the electrostatic attraction force of the film is increased, which may increase the driving torque of the belt body.

  Note that the above-described problem is similarly caused when the belt body is an intermediate transfer belt or a transfer belt. When the belt body is an intermediate transfer belt, the toner image is transferred onto the intermediate transfer belt. When the belt body is a transfer belt, the toner image onto a transfer material such as paper carried on the transfer belt. The same phenomenon as described above may occur in the transfer process.

  Accordingly, an object of the present invention is to provide an image forming apparatus that can obtain more stable and better transfer performance with a simple configuration.

  The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention relates to an image carrier that carries a toner image, a belt member that is movable in contact with the image carrier, and the belt at a position facing the image carrier across the belt member. A transfer member disposed in contact with the body and transferring the toner image on the image carrier onto the belt body or a transfer material carried on the belt body; and a voltage for the transfer is applied to the transfer member. In the image forming apparatus including the voltage applying unit, the transfer member includes an elastic member, and a sheet member that is sandwiched between the belt body and the elastic member and contacts the belt body on the surface. In the moving direction of the belt member, the downstream end of the contact region between the image carrier and the belt member is located in the contact region between the sheet member and the belt member. Device.

  According to the present invention, it is possible to obtain more stable and better transfer performance with a simple configuration.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

Example 1
FIG. 1 shows a schematic sectional configuration of an embodiment of an image forming apparatus according to the present invention. The image forming apparatus 100 of this embodiment is a laser beam printer using an electrophotographic system. The image forming apparatus 100 according to the present exemplary embodiment temporarily superimposes the toner images of the respective colors formed according to the image information decomposed into the color components of yellow, magenta, cyan, and black onto the intermediate transfer member by primary transfer. An intermediate transfer method is used in which the image is later transferred to a transfer material. First, the overall configuration and operation of the image forming apparatus of this embodiment will be described.

  The image forming apparatus 100 includes four image forming units (stations) for forming toner images of yellow, magenta, cyan, and black as a plurality of image forming units, that is, first, second, and third. And fourth image forming portions Sa, Sb, Sc, and Sd. In this embodiment, the configuration and operation of each of the image forming units Sa to Sd have many portions that are substantially common except for the color of the toner image formed by each. Therefore, in the following description, if there is no particular need to distinguish, the subscripts a, b, c, and d given to the reference numerals are omitted to indicate that they are elements provided for any of the colors. I will explain it.

  The image forming unit S includes a drum-type photosensitive member as an image carrier, that is, a photosensitive drum 1. The photosensitive drum 1 is rotationally driven in a direction indicated by an arrow R1 (counterclockwise) by a driving unit (not shown). In this embodiment, the photosensitive drum 1 has an OPC (organic photoconductor) photosensitive layer. The image forming unit S includes, around the photosensitive drum 1, a charging roller 2 as a charging unit that charges the photosensitive drum 1, an exposure device 3 as an exposure unit, and a developing device 4 as a developing unit. Further, the image forming unit S includes a primary transfer member (transfer member) 5 as a primary transfer unit and a cleaning device 6 as a cleaning unit around the photosensitive drum 1.

  The cleaning device 6 includes a cleaning member such as a fur brush and a blade that scrapes and cleans the toner on the photosensitive drum 1, and a collected toner container that collects the toner removed from the photosensitive drum 1 by the cleaning member.

  In this embodiment, the developing device 4 develops the electrostatic image by a reversal development method. In other words, the developing device 4 applies the toner charged to a normal polarity (negative polarity in this embodiment) that is the same as the charging polarity of the photosensitive drum 1 on the photosensitive drum 1 whose charge has been attenuated by exposure after being charged. A toner image is formed on the photosensitive drum 1 by being attached to the portion (bright portion). In the present embodiment, the developing device 4 uses a non-magnetic one-component developer, that is, toner, as the developer. The developing device 4 carries toner on a developing roller 41 as a developer carrying member using a developer coating blade 42 as a developer regulating member, up to a portion (developing portion) facing the photosensitive drum 1. It is designed to be transported.

  The exposure apparatus 3 can be constituted by a laser scanner unit that scans laser light with a polygon mirror or an LED array. In this embodiment, the laser scanner unit is used. The exposure device 3 irradiates the photosensitive drum 1 with a scanning beam 18 modulated based on the image signal.

  In this embodiment, the photosensitive drum 1 and the charging roller 2, the developing device 4 and the cleaning device 6 as process means that act on the photosensitive drum 1 are integrally formed into a cartridge and stored in an image forming apparatus main body (apparatus main body). On the other hand, a removable process cartridge 19 is constructed. The process cartridge is an image forming apparatus in which an electrophotographic photosensitive member and at least one of a charging unit, a developing unit, and a cleaning unit that act on the electrophotographic photosensitive member are integrally formed into a cartridge. It can be attached to and detached from the main body.

  On the other hand, an intermediate transfer belt 7 composed of a movable endless belt body as an intermediate transfer body is disposed so as to contact all of the four photosensitive drums 1a to 1d. In the contact area (primary transfer nip, primary transfer portion) n1a to n1d between the intermediate transfer belt 7 and the photosensitive drums 1a to 1d, toner transfer (primary transfer) from the photosensitive drums 1a to 1d to the intermediate transfer belt 7 is performed. Transfer) is performed. The intermediate transfer belt 7 is supported by three rollers, that is, a secondary transfer counter roller 71, a driving roller 72, and a tension roller 73 as a stretching member, so that an appropriate tension is maintained. By driving the drive roller 72 to rotate, the intermediate transfer belt 7 moves in the forward direction at substantially the same speed with respect to the photosensitive drum 1 in each of the primary transfer portions n1a to n1d. That is, the intermediate transfer belt 7 rotates in the illustrated arrow R2 direction (clockwise).

  Primary transfer members 5a to 5d as primary transfer means corresponding to the respective photosensitive drums 1a to 1d are arranged at positions facing the respective photosensitive drums 1a to 1d with the intermediate transfer belt 7 interposed therebetween. As will be described in detail later, the primary transfer members 5a to 5d are disposed in contact with the surface (back surface) opposite to the surface that bears the toner image of the intermediate transfer belt 7.

  Further, at a position facing the secondary transfer counter roller 71 with the intermediate transfer belt 7 interposed therebetween, the secondary transfer roller 8 as a secondary transfer member as a secondary transfer unit is in contact with the intermediate transfer belt 7. Has been placed. The secondary transfer roller 8 contacts the surface of the intermediate transfer belt 7 that carries the toner image. In the contact area (secondary transfer nip, secondary transfer portion) n2 between the intermediate transfer belt 7 and the secondary transfer roller 8, the toner image is transferred (secondary transfer) from the intermediate transfer belt 7 to the transfer material P. .

  Further, the charging roller 2 is connected to a charging power source 14 which is a voltage application unit to the charging roller 2. The developing sleeve 41 of the developing device 4 is connected to a developing power source 15 that is a voltage application unit to the developing sleeve 41. The primary transfer member 5 is connected to a primary transfer power source 16 that is a means for applying a voltage to the primary transfer member 5. The secondary transfer roller 8 is connected to a secondary transfer power source 17 that is a voltage application unit to the secondary transfer roller 8.

  Next, the image forming operation will be described by taking full color image formation as an example. When the image forming operation starts, the photosensitive drums 1a to 1d, the intermediate transfer belt 6 and the like start to rotate in a predetermined direction at a predetermined process speed.

  The photosensitive drum 1 is uniformly charged to a predetermined polarity (negative polarity in this embodiment) by applying a charging bias voltage from the charging power supply 14 to the charging roller 2. Subsequently, an electrostatic image (latent image) according to the image information is formed on the charged photosensitive drum 1 by the scanning beam 18 from the exposure device 3. The electrostatic image formed on the photosensitive drum 1 reaches a portion (developing portion) facing the developing roller 41 of the developing device 4 as the photosensitive drum 1 rotates.

  The toner in the developing device 4 is charged to a normal charging polarity (negative polarity in this embodiment) by the developer applying blade 42 and applied onto the developing roller 41. Then, when a developing bias voltage is applied to the developing roller 41 from the developing power supply 15, the electrostatic image on the photosensitive drum 1 is visualized with negative toner, and a toner image is formed on the photosensitive drum 1.

  Next, the toner image formed on the photosensitive drum 1 is primarily transferred onto the intermediate transfer belt 7 in the primary transfer nip n1. At this time, a DC bias voltage having a polarity opposite to the normal charging polarity of the toner (positive polarity in this embodiment) is applied to the primary transfer member 5 from the primary transfer power source 16.

  After the primary transfer process, the toner remaining on the photosensitive drum 1 (primary transfer residual toner) is removed from the surface of the photosensitive drum 1 by the cleaning device 6 and collected.

  The above charging, exposure, development, and primary transfer processes are performed in the first to fourth image forming units Sa to Sd, so that the toner images of the respective colors are sequentially superimposed on the intermediate transfer belt 7. The image is transferred, and a multiple image is formed on the intermediate transfer belt 7. At this time, an electrostatic image obtained by exposure on each of the photosensitive drums 1a to 1d while delaying a writing signal from a controller (not shown) at a certain timing for each color according to the distance between the primary transfer positions of each color. Then, the electrostatic image is developed and primarily transferred.

  Thereafter, the transfer material P loaded on the transfer material cassette 11 is picked up by the transfer material supply roller 12 and conveyed to the registration roller 13 by a conveyance roller (not shown) in accordance with the formation of the electrostatic image by exposure. Is done. Then, the transfer material P is conveyed to the secondary transfer nip n2 by the registration roller 13 in synchronization with the toner image on the intermediate transfer belt 7. At this time, a DC bias voltage having a polarity opposite to the normal charging polarity of the toner (positive polarity in this embodiment) is applied to the secondary transfer roller 8 by a secondary transfer power source. As a result, the four-color multiple toner images carried on the intermediate transfer belt 7 are secondarily transferred onto the transfer material P collectively.

  After the secondary transfer process, toner remaining on the intermediate transfer belt 7 (secondary transfer residual toner) and paper dust generated by the transfer of the transfer material P are transferred by the belt cleaning means 74 to the intermediate transfer belt 7. Removed from the surface and recovered. In this embodiment, the belt cleaning unit 74 removes the deposits on the intermediate transfer belt 7 by an elastic cleaning blade formed of urethane rubber or the like as a cleaning member, which is disposed in contact with the intermediate transfer belt 7. Scrape.

  The transfer material P onto which the toner image has been transferred is conveyed to a fixing device 10 as a fixing unit, where the toner image on the transfer material P is melted, mixed, and fixed, and then a full-color image formed product (print, copy). Are discharged to the outside of the image forming apparatus 100.

  The image forming apparatus 100 can form a single-color or multi-color image by forming an image only in a desired single or plural (not all) image forming units S.

In this embodiment, the secondary transfer roller 8 is covered with a nickel-plated steel rod having a diameter of 8 mm and a foamed sponge of NBR (nitrile butadiene rubber) adjusted to have a resistance value of 10 ⁸ Ω and a thickness of 5 mm. An installed roller having a diameter of 18 mm was used. The secondary transfer roller 8 is brought into contact with the intermediate transfer belt 7 with a linear pressure of about 5 to 15 g / cm, and at a substantially constant speed in the forward direction with respect to the moving direction of the intermediate transfer belt 7. Arranged to rotate.

Further, as the material of the intermediate transfer belt 7, rubber such as EPDM (ethylene / propylene / diene), NBR, urethane, silicone rubber or the like can be suitably used. Alternatively, as the material of the intermediate transfer belt 7, the following resins can be suitably used. PI (polyimide), PA (polyamide), PC (polycarbonate), PVDF (polyvinylidene fluoride), ETFE (ethylene-tetrafluoroethylene copolymer), PET (polyethylene terephthalate), PC / PET, ETFE / PC, and the like. In this embodiment, as the intermediate transfer belt 7, an endless belt-like film made of PVDF having a thickness of 100 μm and a volume resistivity of 10 ¹⁰ Ωcm was used.

As the driving roller 72 as a stretching member of the intermediate transfer belt 7, an aluminum cored bar was coated with EPDM rubber having a resistance value of 10 ⁴ Ω dispersed with carbon as a conductive agent and a thickness of 1.0 mm. A roller with a diameter of 25 mm was used. As the tension roller 73 as a tension member of the intermediate transfer belt 7, an aluminum metal rod having a diameter of 25 mm was used. The tension applied to the intermediate transfer belt 7 by urging both longitudinal ends of the tension roller 73 was 19.6 N on one side and the total pressure 39.2 N. The secondary transfer counter roller 71 as a stretch member of the intermediate transfer belt 7 is an EPDM having a resistance value of 10 ⁴ Ω and a wall thickness of 1.5 mm obtained by dispersing carbon as a conductive agent on an aluminum cored bar. A roller covered with rubber and having a diameter of 25 mm was used.

[Primary transfer member]
Next, the primary transfer member 5 in the image forming apparatus 100 of this embodiment will be described in detail. In the present embodiment, the primary transfer member 5 has the same configuration in the first to fourth image forming portions Sa to Sd.

  As described above, in the image forming apparatus using the conventional brush as the primary transfer unit, the contact with the intermediate transfer belt may be non-uniform when used for a long time, which may cause a transfer failure.

  Further, in the moving direction of the intermediate transfer belt 7, the downstream end portion (contact end end) of the contact area between the intermediate transfer belt 7 and the primary transfer member 5 is in the contact area between the intermediate transfer belt 7 and the photosensitive drum 1. When there is, it was found that the following problems may occur. That is, at the peeling portion of the intermediate transfer belt 7 from the photosensitive drum 1, a peeling discharge may occur due to an abrupt potential change, and the toner image on the intermediate transfer belt 7 may be disturbed. In order to prevent this, it is desirable to provide a charge eliminating member, which may increase the size and cost of the apparatus.

  On the other hand, in an image forming apparatus using a conventional film as a transfer means, there is no film backup member, and therefore, a vertical streak-like transfer failure may occur due to the waviness of the film. In addition, since the electrostatic adsorption of the film is positively used, the frictional force between the film and the belt body increases, and the load on the drive motor or the like may increase due to an increase in the driving torque of the belt body.

  Therefore, the main purpose of this embodiment is to obtain more stable and better transfer performance with a simple configuration. One of the more detailed purposes of this embodiment is to maintain good transferability by maintaining uniform contact between the intermediate transfer belt 7 and the primary transfer member 5 with a simple configuration. In addition, another one of the more detailed purposes of this embodiment is to prevent the occurrence of peeling discharge between the photosensitive drum 1 and the intermediate transfer belt 7 without using a static eliminating member on the back surface of the intermediate transfer belt 7. It is to be.

A. Configuration FIG. 2 is a schematic exploded perspective view of the primary transfer member 5 of this embodiment. FIG. 3 is an enlarged view of the primary transfer portion N1 showing the positional relationship among the primary transfer member 5, the intermediate transfer belt 7, and the photosensitive drum 1 in this embodiment.

  In this embodiment, the primary transfer member 5 includes an elastic member 51 and a sheet member 52 that is sandwiched between the intermediate transfer belt 7 and the elastic member 51 and contacts the intermediate transfer belt 7 on the surface. In the moving direction of the intermediate transfer belt 7, the downstream end of the contact area A between the photosensitive drum 1 and the intermediate transfer belt 7 is located in the contact area B between the sheet member 52 and the intermediate transfer belt 7. That is, in the moving direction of the intermediate transfer belt 7, the downstream end of the contact area B between the sheet member 52 and the intermediate transfer belt 7 is above the downstream end of the contact area A between the photosensitive drum 1 and the intermediate transfer belt 7. Or it is located downstream (preferably downstream) from it.

  In this embodiment, the upstream end of the contact area A between the photosensitive drum 1 and the intermediate transfer belt 7 in the moving direction of the intermediate transfer belt 7 is the contact area B between the sheet member 52 and the intermediate transfer belt 7. Located inside (in the contact area). That is, in the moving direction of the intermediate transfer belt 7, the upstream end of the contact area B between the sheet member 52 and the intermediate transfer belt 7 is above the upstream end of the contact area A between the photosensitive drum 1 and the intermediate transfer belt 7. Alternatively, it is located upstream (typically upstream).

  Further, in this embodiment, the length of the contact region B between the sheet member 52 and the intermediate transfer belt 7 in the moving direction of the intermediate transfer belt 7 is equal to or longer than the length (width) D of the elastic member 51.

  More specifically, in this embodiment, the primary transfer member 5 includes an elastic member 51 and a sheet member 52, and the sheet member 52 is sandwiched between the intermediate transfer belt 7 and the elastic member 51. In this embodiment, the contact area B between the sheet member 52 and the intermediate transfer belt 7 is longer than the contact area A between the photosensitive drum 1 and the intermediate transfer belt 7 in the moving direction of the intermediate transfer belt 7, and the elastic member 51. The width D is greater than or equal to D.

  The elastic member 51 is formed as a substantially rectangular parallelepiped pad having a substantially rectangular cross section. The sheet member 52 is formed as a plate-like film that is sandwiched and supported between the elastic member 51 and the intermediate transfer belt 7.

More specifically, in this embodiment, the elastic member 51 of the primary transfer member 5 is a urethane foam sponge-like elastic body (foam sponge body), and has a thickness (t1) of 2 mm and a width ( w1: Corresponding to D) 5 mm and a longitudinal length (l1) of 230 mm. The width (w1) is the length in the direction along the moving direction of the intermediate transfer belt 7, and the longitudinal length (l1) is in a direction intersecting (substantially orthogonal in this embodiment) with the moving direction of the intermediate transfer belt 7. It is the length along. In this example, the hardness of the elastic member 51 was 30 ° in Asker C (500 gf). Further, in this example, the resistance value of the elastic member 51 was 1 × 10 ⁶ Ω when 500 V was applied.

  In this embodiment, urethane foam is used as the elastic member 51, but a rubber material such as epichlorohydrin rubber, NBR, or EPDM may be used. The hardness of the elastic member 51 is preferably 40 ° or less in Asker C (500 gf).

On the other hand, as the sheet member 52 of the primary transfer member 5, a sheet (film) made of vinyl acetate having a thickness (t2) of 50 μm and a longitudinal length (l2) of 232 mm was used. The volume resistivity of the sheet member 52 was 1 × 10 ⁶ Ωcm when 50 V was applied. The longitudinal length (l2) is a length in a direction along the longitudinal length (l1) of the elastic member 51.

  In this embodiment, a vinyl acetate sheet is used as the sheet member 52, but a sheet of PC, PVDF, PET, PI, PE (polyethylene), PA, or the like may be used.

  More specifically, in this embodiment, the contact area A between the photosensitive drum 1 and the intermediate transfer belt 7 in the moving direction of the intermediate transfer belt 7 is 3 mm, and the contact area B between the sheet member 52 and the intermediate transfer belt 7 is 6 mm. The width D of the elastic member 51 (corresponding to the above w1) was 5 mm. Further, in the moving direction of the intermediate transfer belt 7, the sheet member 52 comes into contact with the intermediate transfer belt 7 from the upstream end of the contact area A by 0.5 mm upstream (area E in FIG. 3). Further, in the moving direction of the intermediate transfer belt 7, the downstream end of the sheet member 52 is 3 mm downstream from the downstream end of the contact area A (area F in FIG. 3). The downstream end of the sheet member 52 is in contact with the intermediate transfer belt 7. A portion of a predetermined length at the end of the sheet member 52 on the upstream side in the moving direction of the intermediate transfer belt 7 is bent along the side surface of the elastic member 51.

  In this embodiment, the primary transfer power supply 16 is connected to the elastic member 51, and a voltage of 500 V is applied as a representative value during the image forming operation.

  Further, in this embodiment, the elastic member 51 is pressed (pressed) toward the photosensitive drum 1 (that is, toward the intermediate transfer belt 7) by a pressure spring (not shown) as an urging means. . Accordingly, the sheet member 52 is pressed toward the intermediate transfer belt 7 by the elastic member 51.

B. Action By configuring the primary transfer member 5 to include the elastic member 51 and the sheet member 52, the sheet member 52 can be pressed against the back surface of the intermediate transfer belt 7 by the elastic member 51. Accordingly, the sheet member 52 can be reliably brought into contact with the back surface of the intermediate transfer belt 7. Thereby, the slidability between the sheet member 52 and the intermediate transfer belt 7 is improved, and the primary transfer member 5 can be prevented from stick-slip. Then, an increase in driving torque of the intermediate transfer belt 7 can be suppressed. Further, since uniform contact between the sheet member 52 and the intermediate transfer belt 7 can be ensured, the vertical streak-like transfer caused by uneven contact in the longitudinal direction between the primary transfer member 5 and the intermediate transfer belt 7 is achieved. Defects can be prevented.

  The sheet member 52 contacts the intermediate transfer belt 7 inside the contact area A formed by the intermediate transfer belt 7 and the photosensitive drum 1, and the downstream end of the sheet member 52 is located inside the contact area A. not exist. Therefore, a gap such as a step due to the thickness of the sheet member 52 does not occur in the contact area A. Therefore, it is possible to prevent the occurrence of dot-like image omission (dot-like transfer omission) due to the toner being reversely charged in the contact area A and being unable to transfer due to discharge in the gap such as the gap.

  On the other hand, the contact area B between the sheet member 52 and the intermediate transfer belt 7 is made longer than the contact area A between the photosensitive drum 1 and the intermediate transfer belt 7 (forms the area F in FIG. 3). That is, in the moving direction of the intermediate transfer belt 7, at least the downstream end of the contact area A between the photosensitive drum 1 and the intermediate transfer belt 7 is positioned inside the contact area B between the sheet member 52 and the intermediate transfer belt 7. Like that. Thus, the sheet member 52 serves as a counter electrode at the downstream end (contact end point) C of the contact area A where the intermediate transfer belt 7 is peeled from the photosensitive drum 1. Accordingly, the potential of the peeling portion between the intermediate transfer belt 7 and the photosensitive drum 1 is determined, and peeling discharge can be suppressed. That is, image defects due to peeling discharge can be prevented without providing a neutralizing member that neutralizes the intermediate transfer belt 7.

  Further, since the contact area B between the sheet member 52 and the intermediate transfer belt 7 is longer than the contact area A between the photosensitive drum 1 and the intermediate transfer belt 7 and is equal to or larger than the width D of the elastic member 51, Since there is no direct contact with the transfer belt 7, sliding resistance can be suppressed. Then, an increase in driving torque of the intermediate transfer belt 7 can be suppressed.

  The above-described operation can be obtained in the same manner by configuring the primary transfer portions n1a to n1d in the first to fourth image forming portions Sa to Sd in the same manner.

C. Evaluation In order to examine the effect of this example, using an image forming apparatus 100 with a process speed of 100 mm / sec, together with the comparative example shown below, after the initial and 10k sheets passed, vertical streaks, dot transfer missing, and peeling discharge The trace was evaluated. In the image forming apparatus of the comparative example shown below, the primary transfer member 5 has the same configuration in the first to fourth image forming portions Sa to Sd.

(Comparative Example 1)
In Comparative Example 1, as shown in FIG. 4, the contact area B between the sheet member 52 and the intermediate transfer belt 7 is shorter than the contact area A between the photosensitive drum 1 and the intermediate transfer belt 7. The elastic member 51 of the primary transfer member 5 in Comparative Example 1 was the same as that in this example.

(Comparative Example 2)
In Comparative Example 2, as shown in FIG. 5, the primary transfer member 5 is composed of only the sheet member 52, and there is no elastic member 51. It is assumed that the sheet member 52 and the intermediate transfer belt 7 are brought into contact with only the electrostatic attraction force of the sheet member 52 only when a voltage is applied to the sheet member 52 by the primary transfer power supply 16. The sheet member 52 of the primary transfer member 5 in Comparative Example 2 was the same as that in this example.

(Comparative Example 3)
In Comparative Example 3, a brush-shaped primary transfer member 301 as shown in FIG. 6 was used. More specifically, the primary transfer member 301 of Comparative Example 3 is a brush made of polyamide having a resistance value of 1 × 10 ⁸ Ω, a pile length (t3) of 3 mm, and a width (w3) of 5 mm. The arrangement of the primary transfer member 301 in Comparative Example 3 was the same as that in Example 1.

(Evaluation results)
The evaluation results are shown in Table 1. Here, the evaluation was performed by paying attention to the vertical stripe-like transfer failure, the dot-like image missing (dot-like transfer missing), and the discharge trace in the 30% print halftone image. Further, the paper passing durability test was performed at 4024 basis weight 75 g / m ² manufactured by Xerox Co., Ltd., and an image after passing 10 k sheets was evaluated.

  In this example, from the initial stage until 10 k sheets were passed, all of the vertical stripes, the dot transfer missing, and the peeling discharge trace were good.

  In Comparative Example 1, the contact area B between the sheet member 52 and the intermediate transfer belt 7 is shorter than the contact area A between the photosensitive drum 1 and the intermediate transfer belt 7. Therefore, the sheet member 52 does not work as a counter electrode at the downstream end (contact end point) C of the contact area A where the intermediate transfer belt 7 is peeled from the photosensitive drum 1. Accordingly, peeling discharge occurred at the peeling portion between the intermediate transfer belt 7 and the photosensitive drum 1. Further, since the downstream end of the sheet member 52 is inside the contact area A formed by the intermediate transfer belt 7 and the photosensitive drum 1, a gap such as a step due to the thickness of the sheet member 52 is generated. Therefore, dot-like image omission occurred due to discharge in the gap such as the gap.

  In Comparative Example 2, the sheet member 52 is in contact with the intermediate transfer belt 7 only by the electrostatic attraction force of the sheet member 52. Therefore, a portion that cannot be brought into close contact with the back surface of the intermediate transfer belt 7 occurs due to the wave of the sheet member 52. Therefore, uniform contact between the sheet member 52 and the intermediate transfer belt 7 cannot be ensured, and vertical stripe-like transfer failure occurs.

  In Comparative Example 3, the initial state was satisfactory and good, but the tip of the brush was crushed after passing 10k sheets, and the longitudinal contact between the primary transfer member 301 and the intermediate transfer belt 7 was uneven. became. For this reason, the transfer unevenness in the longitudinal direction occurred after passing 10k sheets.

  As described above, according to the present embodiment, the slidability between the sheet member 52 and the intermediate transfer belt 7 is improved by configuring the primary transfer member 5 to include the elastic member 51 and the sheet member 52. To do. Further, uniform contact between the sheet member 52 and the intermediate transfer belt 7 can be secured, and vertical streak-like transfer failure due to contact unevenness in the longitudinal direction can be prevented.

  According to this embodiment, the sheet member 52 contacts the intermediate transfer belt 7 inside the contact area A formed by the intermediate transfer belt 7 and the photosensitive drum 1, and the sheet member is located inside the contact area A. There is no downstream end of 52. Therefore, it is possible to prevent occurrence of dot-like image omission due to discharge in a gap such as a gap due to the thickness of the sheet member 52.

  Further, according to this embodiment, the contact area B between the sheet member 52 and the intermediate transfer belt 7 is made longer than the contact area A between the photosensitive drum 1 and the intermediate transfer belt 7, so that the intermediate transfer belt 7 and the photosensitive drum are The potential of the peeling portion with 1 is fixed, and peeling discharge can be suppressed.

  Further, since the length of the contact region B between the sheet member 52 and the intermediate transfer belt 7 is equal to or greater than the width D of the elastic member 51, the elastic member 51 and the intermediate transfer belt 7 are not in direct contact with each other. Sliding resistance can be suppressed. Then, an increase in driving torque of the intermediate transfer belt 7 can be suppressed.

  As described above, according to the present exemplary embodiment, it is possible to maintain a uniform contact between the intermediate transfer belt 7 and the primary transfer member 5 with a simple configuration and to ensure good transferability. Further, according to the present embodiment, it is possible to prevent the occurrence of peeling discharge between the photosensitive drum 1 and the intermediate transfer belt 7 without using a neutralizing member on the back surface of the intermediate transfer belt 7. Accordingly, it is possible to prevent the toner image transferred to the intermediate transfer belt 7 from being disturbed with a simple configuration without increasing the size and cost of the apparatus. Therefore, according to this embodiment, it is possible to obtain more stable and better transfer performance with a simple configuration.

Example 2
Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the first embodiment. Accordingly, the same or corresponding elements as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

A. Configuration FIG. 7 is an enlarged view of the primary transfer portion N1 showing the positional relationship among the primary transfer member 5, the intermediate transfer belt 7, and the photosensitive drum 1 in this embodiment. In the present embodiment, the primary transfer member 5 has the same configuration in the first to fourth image forming portions Sa to Sd.

  In this embodiment, the upstream end of the contact area A between the photosensitive drum 1 and the intermediate transfer belt 7 in the moving direction of the intermediate transfer belt 7 is outside the contact area B between the sheet member 52 and the intermediate transfer belt 7 ( Located outside the contact area. That is, in the moving direction of the intermediate transfer belt 7, the upstream end of the contact area B between the sheet member 52 and the intermediate transfer belt 7 is above the upstream end of the contact area A between the photosensitive drum 1 and the intermediate transfer belt 7. Or it is located downstream (preferably downstream) from it.

  In this embodiment, the length of the contact area B between the sheet member 52 and the intermediate transfer belt 7 is less than the length (width) D of the elastic member 51 in the moving direction of the intermediate transfer belt 7.

  More specifically, in this embodiment, the primary transfer member 5 includes an elastic member 51 and a sheet member 52, and the sheet member 52 is sandwiched between the intermediate transfer belt 7 and the elastic member 51. In this embodiment, the contact area B between the sheet member 52 and the intermediate transfer belt 7 is longer than the contact area A between the photosensitive drum 1 and the intermediate transfer belt 7 in the moving direction of the intermediate transfer belt 7, and the elastic member 51. Less than width D.

  More specifically, in this embodiment, the contact area A between the photosensitive drum 1 and the intermediate transfer belt 7 in the moving direction of the intermediate transfer belt 7 is 3 mm, and the contact area B between the sheet member 52 and the intermediate transfer belt 7 is set. 4.5 mm, and the width D of the elastic member 51 was 5 mm. Further, in the moving direction of the intermediate transfer belt 7, the sheet member 52 comes into contact with the intermediate transfer belt 7 from 0.5 mm downstream side (region E in FIG. 7) from the upstream end of the contact region A. Further, in the moving direction of the intermediate transfer belt 7, the downstream end of the sheet member 52 is 2 mm downstream from the downstream end of the contact area A (area F in FIG. 7). The downstream end of the sheet member 52 is in contact with the intermediate transfer belt 7. A portion of a predetermined length at the end of the sheet member 52 on the upstream side in the moving direction of the intermediate transfer belt 7 is bent along the side surface of the elastic member 51.

  The resistance value, thickness, and material of the sheet member 52 used in the present embodiment are the same as those in the first embodiment.

  The primary transfer power supply 16 applies a voltage to the elastic member 51.

B. Action By configuring the primary transfer member 5 to include the elastic member 51 and the sheet member 52, the sheet member 52 can be pressed against the back surface of the intermediate transfer belt 7 by the elastic member 51. Therefore, the sheet member 52 can be reliably brought into contact with the back surface of the intermediate transfer belt 7. As a result, uniform contact between the sheet member 52 and the intermediate transfer belt 7 can be ensured, and vertical streak-like transfer caused by uneven contact in the longitudinal direction between the primary transfer member 5 and the intermediate transfer belt 7 can be ensured. Defects can be prevented.

  The sheet member 52 contacts the intermediate transfer belt 7 inside the contact area A formed by the intermediate transfer belt 7 and the photosensitive drum 1, and the downstream end of the sheet member 52 is located inside the contact area A. not exist. Therefore, a gap such as a step due to the thickness of the sheet member 52 does not occur in the contact area A. Therefore, it is possible to prevent the occurrence of dot-like image loss (point-like transfer loss) due to the toner being reversely charged due to discharge in the gaps such as the gaps and being unable to transfer.

  On the other hand, the contact area B between the sheet member 52 and the intermediate transfer belt 7 is made longer than the contact area A between the photosensitive drum 1 and the intermediate transfer belt 7 (forms the area F in FIG. 7). That is, in the moving direction of the intermediate transfer belt 7, at least the downstream end of the contact area A between the photosensitive drum 1 and the intermediate transfer belt 7 is positioned inside the contact area B between the sheet member 52 and the intermediate transfer belt 7. Like that. Thus, the sheet member 52 serves as a counter electrode at the downstream end (contact end point) C of the contact area A where the intermediate transfer belt 7 is peeled from the photosensitive drum 1. Accordingly, the potential of the peeling portion between the intermediate transfer belt 7 and the photosensitive drum 1 is determined, and peeling discharge can be suppressed. That is, image defects due to peeling discharge can be prevented without providing a neutralizing member that neutralizes the intermediate transfer belt 7.

  Further, by bringing the sheet member 52 into contact with the intermediate transfer belt 7 from the upstream end (contact start point) of the contact area A to the downstream (area E in FIG. 7), a voltage is applied to the primary transfer member 5. When applied, the influence of the transfer electric field formed between the photosensitive drum 1 and the primary transfer member 5 can be suppressed. That is, the transfer electric field acts in the contact area A between the intermediate transfer belt 7 and the photosensitive drum 1. As a result, the transfer electric field acts on the toner image on the photosensitive drum 1 before the contact area A, and the toner image is blurred by being transferred onto the intermediate transfer belt 7 before the contact area A. Defects (so-called scattering) can be suppressed.

  Further, the length of the contact region B between the sheet member 52 and the intermediate transfer belt 7 is made shorter than the width D of the elastic member 51, so that the sheet member 52 is elastic in the entire area in contact with the intermediate transfer belt 7. Pressed and supported. Since the sheet member 52 is sandwiched between the elastic member 51 and the intermediate transfer belt 7, the contact between the sheet member 52 and the intermediate transfer belt 7 becomes uniform. Therefore, the sheet member 52 is not pulled and stretched by the rotational force of the intermediate transfer belt 7, and the undulation of the sheet member 52 can be suppressed. Therefore, it is possible to prevent the toner image on the intermediate transfer belt 7 from being disturbed by the discharge in the gap between the sheet member 52 and the intermediate transfer belt 7. The corrugation of the sheet member 52 described above tends to worsen as the number of printed sheets increases, because the time for the sheet member 52 to be stretched and extended becomes longer. For this reason, the configuration of the present embodiment makes it possible to form a good image by maintaining a stable transfer performance for a longer period of time by making the contact state between the sheet member 52 and the intermediate transfer belt 7 uniform regardless of the number of prints. This is advantageous.

  As described above, according to the present embodiment, the primary transfer member 5 includes the elastic member 51 and the sheet member 52, thereby providing uniform contact between the sheet member 52 and the intermediate transfer belt 7. Can be secured. As a result, it is possible to prevent a vertical streak-like transfer failure caused by contact unevenness in the longitudinal direction.

  According to this embodiment, the sheet member 52 contacts the intermediate transfer belt 7 inside the contact area A formed by the intermediate transfer belt 7 and the photosensitive drum 1, and the sheet member is located inside the contact area A. There is no downstream end of 52. Therefore, it is possible to prevent occurrence of dot-like image omission due to discharge in a gap such as a gap due to the thickness of the sheet member 52.

  Further, according to this embodiment, the contact area B between the sheet member 52 and the intermediate transfer belt 7 is made longer than the contact area A between the photosensitive drum 1 and the intermediate transfer belt 7, so that the intermediate transfer belt 7 and the photosensitive drum are The potential of the peeling portion with 1 is fixed, and peeling discharge can be suppressed.

  Further, according to this embodiment, the sheet member 52 is brought into contact with the intermediate transfer belt 7 from the downstream side of the upstream end (contact start point) of the contact area A, thereby causing an image defect in which the toner image is blurred (so-called “so-called”). (Scattering) can be suppressed.

  Furthermore, according to the present embodiment, the length of the contact region B between the sheet member 52 and the intermediate transfer belt 7 is made shorter than the width D of the elastic member 51. Thereby, since the contact between the sheet member 52 and the intermediate transfer belt 7 can be made uniform throughout durability, stable transfer performance can be maintained throughout the durability.

Example 3
Next, still another embodiment of the present invention will be described. The image forming apparatus of this embodiment has a transfer belt as a transfer material carrier that carries and conveys a transfer material such as paper instead of the intermediate transfer belt in the first and second embodiments as a belt body. The configuration substantially the same as that described in the first and second embodiments is applied to the transfer unit of the image forming apparatus using the transfer belt.

[Entire configuration of image forming apparatus]
FIG. 8 shows a schematic cross-sectional configuration of the image forming apparatus 200 of the present embodiment. Note that the direct transfer type image forming apparatus 200 in this embodiment uses a transfer belt as a belt body, and the configuration and operation thereof are the same as those in Embodiment 1 except that the toner image is directly transferred from the image carrier to the transfer material. 2 is common to the image forming apparatus 100 of the intermediate transfer system in FIG. Accordingly, elements having the same or equivalent functions as those of the intermediate transfer type image forming apparatus 100 in Embodiments 1 and 2 shown in FIG.

  In the image forming apparatus 200 of the present embodiment, a transfer belt 207 configured by an endless belt body as a transfer material carrier is disposed so as to contact all of the four photosensitive drums 1a to 1d. In the contact areas (transfer nips, transfer portions) na to nd between the transfer belt 207 and the photosensitive drums 1 a to 1 d, the transfer of toner from the photosensitive drums 1 a to 1 d to the transfer material P carried on the transfer belt 207 is performed. Done.

  The transfer belt 207 is stretched between two rollers, a driving roller 271 that drives the transfer belt 207 and a tension roller 272 that applies tension to the transfer belt 207. The transfer belt 207 rotates in the direction indicated by an arrow R2 (counterclockwise). The transfer belt 207 carries the transfer material P and conveys the transfer material P to the transfer portions na to nd.

  Transfer members 5a to 5d as transfer means corresponding to the respective photosensitive drums 1a to 1d are arranged at positions facing the respective photosensitive drums 1a to 1d with the transfer belt 207 interposed therebetween. The transfer member 5 is connected to a transfer power supply 16 that is a means for applying a voltage to the transfer member 5.

  Next, the image forming operation will be described by taking full color image formation as an example. When the image forming operation starts, the photosensitive drums 1a to 1d, the transfer belt 207, and the like start to rotate in a predetermined direction at a predetermined process speed. Then, toner images are formed on the respective photosensitive drums 1a to 1d in the same manner as described in the first embodiment.

  On the other hand, the transfer material P loaded on the transfer material cassette 11 is picked up by the transfer material supply roller 12 and conveyed to the registration roller 13 by a conveyance roller (not shown). Then, the transfer material P is conveyed onto the transfer belt 207 by the registration roller 13 in synchronization with the toner image on the photosensitive drum 1a of the first image forming unit Sa.

  Next, the transfer material P is adsorbed and supported on the transfer belt 207 and conveyed to the transfer unit na of the first image forming unit Sa. First, in the transfer portion na of the first image forming portion Sa, the toner image on the photosensitive drum 1a is transferred onto the transfer material P carried on the transfer belt 207. At this time, a DC bias voltage having a polarity opposite to the normal charging polarity of the toner (positive polarity in this embodiment) is applied to the transfer member 5a.

  Then, in synchronization with the transfer material P being conveyed by the transfer belt 207, toner images are formed on the photosensitive drums 1b to 1d of the second to fourth image forming units Sb to Sd, and the toner images are formed. Are sequentially transferred to the transfer material P, and a multiple image is formed on the transfer material P.

  The transfer material P onto which the toner image has been transferred is separated from the transfer belt 207 and sent to the fixing device 10, where the toner image on the transfer material P is melted, mixed and fixed, and then a full-color image formed product (print, The image is discharged to the outside of the image forming apparatus 200 as a copy.

  Further, the toner remaining on the photosensitive drum 1 (transfer residual toner) after the transfer process is cleaned by the cleaning device 6.

[Transfer member]
In the image forming apparatus 200 of the present embodiment, the transfer material P carried on the transfer belt 207 moves following the transfer belt 207. Therefore, the contact area between the transfer material P and the photosensitive drum 1 in each transfer part n is substantially the same as the contact area between the transfer belt 207 and the photosensitive drum 1 in the transfer part n. Accordingly, the present invention can be applied to the transfer member 5 in the same manner as applied to the primary transfer member 5 in the first and second embodiments, and thereby the same effects as in the first and second embodiments. Can be obtained. That is, for the toner image formed on the transfer material P carried on the transfer belt 207 in each transfer portion n, the toner formed on the intermediate transfer belt 7 in each primary transfer portion n1 in the first and second embodiments. An effect similar to that obtained for the image can be obtained.

  As described above, the image forming apparatus 200 according to the present embodiment can have all the same features as those described in the first and second embodiments. Although not described in detail, the image forming apparatus 200 according to the present embodiment can achieve the following effects as in the first and second embodiments.

  By configuring the transfer member 5 to include the elastic member 51 and the sheet member 52, uniform contact between the sheet member 52 and the transfer belt 207 can be ensured. As a result, it is possible to prevent a vertical streak-like transfer failure due to contact unevenness in the longitudinal direction.

  Further, the sheet member 52 contacts the transfer belt 207 inside the contact area A formed by the transfer belt 207 and the photosensitive drum 1, and the downstream end portion of the sheet member 52 does not exist inside the contact area. Therefore, it is possible to prevent occurrence of dot-like image omission due to discharge in a gap such as a gap due to the thickness of the sheet member 52.

  Further, by making the contact area B between the sheet member 52 and the transfer belt 207 longer than the contact area A between the photosensitive drum 1 and the transfer belt 207, the potential of the peeling portion between the transfer material P and the photosensitive drum 1 is determined. Stripping discharge can be suppressed.

  In addition, the length of the contact region B between the sheet member 52 and the transfer belt 207 can be equal to or greater than the width D of the elastic member 51. In this case, since the elastic member 51 and the intermediate transfer belt 7 are not in direct contact, there is an advantage of suppressing sliding resistance.

  Further, the length of the contact region B between the sheet member 52 and the transfer belt 207 can be made shorter than the width D of the elastic member 51. In this case, there is an advantage that the contact between the sheet member 52 and the transfer belt 207 is made uniform through durability, and stable transfer performance is maintained through durability.

  The above-described effects can be obtained in the same manner by configuring the transfer portions na to nd in the first to fourth image forming portions Sa to Sd to have the same configuration.

1 is a schematic cross-sectional configuration diagram of an embodiment of an image forming apparatus according to the present invention. It is a schematic perspective view of an example of the primary transfer member constituted according to the present invention. FIG. 3 is an enlarged view of a primary transfer portion for explaining a positional relationship among a primary transfer member, a photosensitive drum, and an intermediate transfer belt configured according to the present invention. 6 is an enlarged view of a primary transfer portion for explaining a comparative example 1. FIG. 10 is an enlarged view of a primary transfer portion for explaining a comparative example 2. FIG. 10 is a schematic diagram for explaining a comparative example 3. FIG. It is an enlarged view of the primary transfer part for demonstrating the other example of the primary transfer member comprised according to this invention. FIG. 6 is a schematic cross-sectional configuration diagram of another embodiment of an image forming apparatus according to the present invention.

Explanation of symbols

1 Photosensitive drum 5 Primary transfer member (transfer member)
7 Intermediate transfer belt (belt body)
51 Elastic member 52 Sheet member 207 Transfer belt (belt body)

Claims (9)

An image carrier that carries a toner image, a belt body that is movable in contact with the image carrier, and is disposed in contact with the belt body at a position facing the image carrier across the belt body; An image having a transfer member for transferring a toner image on the image carrier to the belt member or a transfer material carried on the belt member, and a voltage applying unit for applying a voltage for the transfer to the transfer member. In the forming device,
The transfer member includes an elastic member, and a sheet member that is sandwiched between the belt body and the elastic member and contacts the belt body on a surface thereof, and the image bearing member in the moving direction of the belt body An image forming apparatus, wherein a downstream end portion of a contact area between the body and the belt body is located in a contact area between the sheet member and the belt body.   The upstream end of the contact region between the image carrier and the belt member in the moving direction of the belt member is located in the contact region between the sheet member and the belt member. Item 2. The image forming apparatus according to Item 1.   The upstream end of the contact region between the image carrier and the belt member in the moving direction of the belt member is located outside the contact region between the sheet member and the belt member. Item 2. The image forming apparatus according to Item 1.   The length of the contact region between the sheet member and the belt body in the moving direction of the belt body is equal to or longer than the length of the elastic member. The image forming apparatus described.   The length of the contact area between the sheet member and the belt body in the moving direction of the belt body is less than the length of the elastic member. The image forming apparatus described.   The image forming apparatus according to claim 1, wherein a downstream end portion of the sheet member is in contact with the belt body in a moving direction of the belt body.   The image forming apparatus according to claim 1, wherein the sheet member is pressed toward the belt body by the elastic member.   The image forming apparatus according to claim 1, wherein the elastic member has a substantially rectangular parallelepiped shape.   The image forming apparatus according to claim 1, wherein the elastic member is made of a foamed sponge body.

Images