JP2008310061A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of obtaining more stable and more excellent transfer performance with simple constitution. <P>SOLUTION: In the image forming apparatus 100, a transfer member 5 includes an elastic member 51 coming into surface-contact with a belt 7, and a sheet member 52 held between the belt 7 and the elastic member 51 and coming into surface-contact with the belt 7, and a contact area 53 between the transfer member 5 and the belt 7 includes a first area 53A where the belt 7 comes into contact with the sheet member 52 provided to cover over the elastic member 51, and a second area 53B where the belt 7 comes into contact with the elastic member 51 on a more downstream side in the moving direction of the belt 7 than the first area over a prescribed range to the downstream side from the end on the upstream side in the moving direction of the belt 7. <P>COPYRIGHT: (C)2009,JPO&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, a contact-type 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 (the back side of the belt unit) across the belt unit. There is a configuration.

  FIG. 11 shows an example of the configuration of the transfer means. This figure shows an example in which a transfer roller, which is a contact transfer member, is used as transfer means. A region A in the drawing is a region where the photosensitive member (photosensitive drum) 301 and the belt member 302 are in contact with each other, and the belt member 302 and the transfer member 303 are in contact with each other. Hereinafter, this area A is referred to as “physical nip”. A region B in the drawing is a region where the photosensitive member 301 and the belt member 302 are not in contact with each other and the belt member 302 and the transfer member 303 are in contact with each other on the upstream side in the moving direction of the belt member 302. Hereinafter, this region B is referred to as “upstream tension nip”. A region C in the drawing is a region where the photosensitive member 301 and the belt member 302 are not in contact with each other and the belt member 302 and the transfer member 303 are in contact with each other on the downstream side in the moving direction of the belt member 302. Hereinafter, this region C is referred to as a “downstream tension nip”. The definition of these areas A, B, and C is the same whether the belt body is an intermediate transfer belt or a transfer belt carrying a transfer material.

  However, in an image forming apparatus using a transfer roller, the physical nip A 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. Further, since the downstream tension nip C is narrow, a peeling discharge occurs at the peeling portion between the belt member and the photosensitive member, which may cause an image defect.

  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 the downstream tension nip C as shown in FIG. 11 cannot be disposed long, the following problems may occur. That is, in the separation portion of the belt member from the photosensitive member on the downstream side in the moving direction of the belt member, a peeling discharge may occur due to a sudden potential change, 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.

  In order to improve the transferability of the fixed transfer means, it is desirable to firmly press the transfer means against the photoconductor. Therefore, normally, the upstream tension nip B inevitably occurs on the upstream side of the belt body in the moving direction. As a result, the toner image on the photoconductor may be transferred before entering the physical nip A, which may cause image defects such as a scattering phenomenon.

  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, the film and the belt body are electrostatically attracted by the application of the transfer voltage, the frictional force between the film and the belt body is increased, the driving torque of the belt body is increased, and the load on the drive motor is increased. Sometimes.

  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, the transfer member is sandwiched between the belt member and the elastic member so as to be in contact with the belt member. And a contact region between the transfer member and the belt body is provided so as to cover the elastic member over a predetermined range from the upstream end in the moving direction of the belt body to the downstream side. Said sea A first region where the member and the belt body are in contact with each other, and a second region where the elastic member and the belt body on the downstream side in the moving direction of the belt body with respect to the first region are in contact with each other. An image forming apparatus including the image forming apparatus.

  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
[Entire configuration of image forming apparatus]
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. When the drive roller 72 is driven 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.

  In addition, when the downstream tension nip C as described above cannot be disposed long, a peeling discharge occurs due to a sudden change in potential at the peeling portion of the intermediate transfer belt 7 from the photosensitive drum 1, and the intermediate transfer belt 7 The toner image 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.

  In order to improve the transferability by using the fixed primary transfer unit, it is desirable to firmly press the primary transfer unit against the photosensitive drum 1, so that the intermediate transfer is usually performed as described above. An upstream tension nip B inevitably occurs on the upstream side of the belt 7 in the moving direction. As a result, the toner image on the photosensitive drum 1 may be transferred before entering the physical nip A, which may cause image defects such as a scattering phenomenon.

  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. Further, the film and the intermediate transfer belt 7 are electrostatically attracted by the application of the transfer voltage, the frictional force between the film and the intermediate transfer belt 7 is increased, the driving torque of the intermediate transfer belt 7 is increased, The load may increase.

  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 a uniform contact between the intermediate transfer belt 7 and the primary transfer member 5 with a simple configuration to ensure good transferability. Another more detailed object of this embodiment is to suppress an increase in driving torque of the intermediate transfer belt 7 by reducing a frictional force due to electrostatic adsorption. Another object of the present embodiment in more detail is to prevent scattering occurring on the upstream side of the intermediate transfer belt 7. Further, another one of the more detailed purposes of the present embodiment is 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. 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 in this embodiment.

  In the present embodiment, the primary transfer member 5 is sandwiched between the intermediate transfer belt 7 and the elastic member 51 and is in contact with the intermediate transfer belt 7 by the surface. Sheet member 52. The contact region 53 between the primary transfer member 5 and the intermediate transfer belt 7 is a first region 53A where the sheet member 52 and the intermediate transfer belt 7 are in contact with each other, and the elastic member 51 and the intermediate transfer belt 7 are in contact with each other. A second region 53B. Here, the sheet member 52 is provided so as to cover the elastic member 51 over a predetermined range from the upstream end in the moving direction of the intermediate transfer belt 7 to the downstream side. Further, the second area 53B is on the downstream side in the moving direction of the intermediate transfer belt 7 with respect to the first area 53A.

  In this embodiment, at least a part of the first area 53A is in the contact area between the photosensitive drum 1 and the intermediate transfer belt 7 in the moving direction of the intermediate transfer belt 7, that is, in the physical nip A. As will be described in detail later, the area of the first area 53A in 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 area of the contact area A. It is preferably 50% or less of the area.

  In this embodiment, the sheet member 52 covers at least a part of the side surface of the elastic member 51 that is located upstream in the moving direction of the intermediate transfer belt 7 and that intersects the moving direction of the intermediate transfer belt 7. To be provided.

  Further, in the present embodiment, the downstream tension nip C described above is preferably provided. That is, in the moving direction of the intermediate transfer belt 7, the downstream end of the contact region 53 between the primary transfer member 5 and the intermediate transfer belt 7 is the downstream end of the contact region A between the photosensitive drum 1 and the intermediate transfer belt 7. It is located on the part or on the downstream side (preferably on the downstream side). In other words, the downstream 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 in the contact area 53 between the primary transfer member 5 and the intermediate transfer belt 7. To position.

  In the present embodiment, typically, the above-described upstream tension nip B is provided. That is, in the moving direction of the intermediate transfer belt 7, the upstream end of the contact area 53 between the primary transfer member 5 and the intermediate transfer belt 7 is the upstream end of the contact area A between the photosensitive drum 1 and the intermediate transfer belt 7. Located on the part or upstream (typically upstream). In other words, 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 in the contact area 53 between the primary transfer member 5 and the intermediate transfer belt 7. To position. As will be described later, even with such a configuration, according to the present embodiment, the scattering phenomenon can be suppressed.

  More specifically, in this embodiment, the primary transfer member 5 includes a fixed elastic member 51 and a sheet member 52, and the sheet member 52 is interposed between the intermediate transfer belt 7 and the elastic member 51. It is pinched. The sheet member 52 is provided so as to cover only the upstream side of the elastic member 51 in the moving direction of the intermediate transfer belt 7. In this embodiment, the sheet member 52 enters the physical nip A that is a contact area between the intermediate transfer belt 7 and the photosensitive drum 1.

  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 formed of a foamed sponge-like elastic body (foamed sponge body) made of urethane and has a thickness (t1) of 2 mm and a width ( A substantially rectangular parallelepiped having w1) 5 mm and a longitudinal length (l1) 230 mm was used. 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).

  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, a film (sheet) made of silicone-based PTFE (polytetrafluoroethylene) having a thickness (t2) of 90 μm and a longitudinal length (l2) of 232 mm was used as the sheet member 52 of the primary transfer member 5. The sheet member 52 has a predetermined width (w2) so that the first region 53A and the second region 53B are formed. The longitudinal length (l2) is a length in a direction along the longitudinal length (l1) of the elastic member 51. In this embodiment, the sheet member 52 is electrically insulating.

  In this embodiment, the sheet member 52 is formed using a silicone-based PTFE film, but other resin sheets such as a Kapton (polyimide) H film and a polyester film may be used. However, the material constituting the sheet member 51 preferably contains at least fluorine, and a sheet made of a fluororesin such as PTFE can be suitably used.

As described above, in the present embodiment, the sheet member 52 is electrically insulating. As will be described in detail later, since the sheet member 52 is electrically insulated and has a significantly higher electric resistance than the elastic member 51, it is difficult for current to flow through the sheet member 52. . In a typical embodiment, a sheet having a volume resistivity of 1 × 10 ¹⁵ Ωcm or more can be used as the sheet member 52. The volume resistivity here refers to that measured by the following measuring method. That is, using Mitsubishi Chemical Corporation's Hiresta-UP (MCP-HT450), the measurement probe uses UR, the room temperature during measurement is set to 23 ° C., the room humidity is set to 50%, the applied voltage is 500 V, and the measurement time is 10 seconds. Volume resistivity measured under conditions.

  More specifically, in this embodiment, the physical nip A between the photosensitive drum 1 and the intermediate transfer belt 7 in the moving direction of the intermediate transfer belt 7 is 2.5 mm, and the intermediate between the primary transfer member 5 (especially the elastic member 51). The upstream tension nip B with the transfer belt 7 was 1 mm.

  Further, in the moving direction of the intermediate transfer belt 7, the width of the region where the photosensitive drum 1, the intermediate transfer belt 7, the sheet member 52, and the elastic member 51 overlap, that is, the region overlapping the physical nip A in the first region 53A. The width E of the inner sheet member 52 was set to 0.5 mm. Hereinafter, this width E is referred to as a sheet penetration amount E.

  In other words, in this embodiment, the sheet member 52 covers the elastic member 51 having an area corresponding to 20% of the area of the physical nip A in the area of the physical nip A in the moving direction of the intermediate transfer belt 7. It will be.

  Therefore, in this embodiment, the contact area (first area) 53A between the sheet member 52 and the intermediate transfer belt 7 in the moving direction of the intermediate transfer belt 7 is 1.5 mm.

  Further, the width w1 of the elastic member 51 in the moving direction of the intermediate transfer belt 7 is 5 mm as described above. The primary transfer power supply 16 is connected to the elastic member 51.

  Further, in this embodiment, the downstream tension nip C between the primary transfer member 5 (particularly the sheet member 52) and the intermediate transfer belt 7 in the moving direction of the intermediate transfer belt 7 is set to 1.5 mm.

  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. As a result, at least a part of the side surface of the elastic member 51 located on the upstream side in the moving direction of the intermediate transfer belt 7 along the direction intersecting the moving direction of the intermediate transfer belt 7, substantially all in the present embodiment, is the sheet member. 52. Thereby, the effect which suppresses generation | occurrence | production of the scattering mentioned later can be increased.

  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 The primary transfer member 5 includes an elastic member 51 and a sheet member 52. Accordingly, the elastic member 51 and the sheet member 52 can be pressed against the back surface of the intermediate transfer belt 7. Accordingly, the elastic member 51 and the sheet member 52 can be reliably brought into contact with the back surface of the intermediate transfer belt 7. Accordingly, the uniform contact between the elastic member 51 and the sheet member 52 and the intermediate transfer belt 7 can be ensured, and the vertical stripe caused by the contact unevenness in the longitudinal direction between the primary transfer member 5 and the intermediate transfer belt 7 can be ensured. Transfer failure can be prevented.

  On the other hand, by providing a downstream tension nip C that is a contact area between the elastic member 51 and the intermediate transfer belt 7, the elastic member 51 is connected to the downstream end portion of the physical nip A where the intermediate transfer belt 7 peels from the photosensitive drum 1 ( It serves as a counter electrode at the physical nip end point D. 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, according to the present embodiment, the sheet member 52 is formed of an insulating member (or a member having a volume resistivity of 1 × 10 ¹⁵ Ωcm or more). In this embodiment, the sheet member 52 penetrates into the physical nip A which is a contact area between the intermediate transfer belt 7 and the photosensitive drum 1, but only in an area corresponding to 20% of the area of the contact area A. Only invaded. For this reason, deterioration of transferability due to the sheet member 52 being insulative hardly appears. The sheet member 52 is shorter than the width of the elastic member 51 in the moving direction of the intermediate transfer belt 7. Therefore, even when a voltage is applied to the elastic member 51 from the primary transfer power supply 16, the charge amount of the sheet member 52 is small. Thereby, even when a transfer voltage is applied, the electrostatic adsorption force between the sheet member 52 and the intermediate transfer belt 7 is small, and the increase in the frictional force between the intermediate transfer belt 7, the sheet member 52, and the elastic member 51 is reduced. it can. Accordingly, an increase in driving torque of the intermediate transfer belt 7 can be suppressed.

  Further, on the upstream side in the moving direction of the intermediate transfer belt 7, the upstream tension nip B outside the contact area between the intermediate transfer belt 7 and the photosensitive drum 1 is covered with an insulating sheet member 52. Therefore, the transfer charge at the upstream tension nip B can also be blocked by shielding the transfer charge at the contact area between the sheet member 52 and the intermediate transfer belt 7, and an image defect due to toner scattering before the physical nip A. 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 the present embodiment, using the image forming apparatus 100 with a process speed of 100 mm / sec, together with the comparative example shown below, the initial streak, transferability, scattering, and peeling discharge after the initial and 10k sheets passed. The marks and driving torque (electrostatic adsorption) were 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 sheet member 52 enters the physical nip A that is a contact area between the photosensitive drum 1 and the intermediate transfer belt 7 as in this embodiment. In Comparative Example 1, the physical nip A was 2.5 mm, the upstream tension nip B was 1 mm, the downstream tension nip C was 1.5 mm, and the sheet penetration amount E was 1.25 mm. Accordingly, the contact area (first area) 53A between the sheet member 52 and the intermediate transfer belt 7 is 2.25 mm. That is, in Comparative Example 1, the sheet member 52 covers the elastic member 51 having an area corresponding to 50% of the area of the physical nip A in a region overlapping with the physical nip A. Other configurations of the sheet member 52 in the comparative example 1 are the same as those of the present embodiment. Further, the configuration of the elastic member 51 in Comparative Example 1 is the same as that of the present embodiment.

(Comparative Example 2)
In Comparative Example 2, as shown in FIG. 5, the sheet member 52 enters the physical nip A that is a contact area between the photosensitive drum 1 and the intermediate transfer belt 7 as in this embodiment. In Comparative Example 2, the physical nip A was 2.5 mm, the upstream tension nip B was 1 mm, the downstream tension nip C was 1.5 mm, and the sheet penetration amount E was 1.75 mm. Therefore, the contact area (first area) 53A between the sheet member 52 and the intermediate transfer belt 7 is 2.75 mm. That is, in Comparative Example 2, the sheet member 52 covers the elastic member 51 having an area corresponding to 70% of the area of the physical nip A in a region overlapping with the physical nip A. Other configurations of the sheet member 52 in the comparative example 2 are the same as those of the present embodiment. Further, the configuration of the elastic member 51 in Comparative Example 2 is the same as that of the present embodiment.

(Comparative Example 3)
In Comparative Example 3, as shown in FIG. 6, 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. In Comparative Example 3, the areas A, B, and C were set to A = 1 mm, B = 2.5 mm, and C = 1.5 mm, respectively. The sheet member 52 in Comparative Example 3 has a volume resistivity of 1 × 10 ⁶ Ωcm when 100 V is applied in order to obtain a transfer electric field. In addition, as the sheet member 52 in Comparative Example 3, a vinyl acetate sheet having a thickness of 50 μm was used.

(Comparative Example 4)
In Comparative Example 4, a brush-shaped primary transfer member 304 as shown in FIGS. 7 and 8 was used. More specifically, the primary transfer member 304 of Comparative Example 4 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. In Comparative Example 4, the arrangement of the primary transfer member 304, that is, the areas A, B, and C were the same as in this example.

(Evaluation results)
The evaluation results are shown in Table 1. Here, the evaluation was performed by paying attention to vertical streaks, transferability, scattered image defects on the intermediate transfer belt 7, image defects due to discharge traces in a 30% print halftone image, and whether or not there was an increase in driving torque. Further, the paper passing durability test was performed using 4024 basis weight 75 g / m ² manufactured by Xerox Co., Ltd., and an image after passing 10k sheets was evaluated.

  In this embodiment, sufficient transferability can be ensured from the beginning to after 10k sheets have passed, and none of vertical streaks of defective transfer, scattered image defects on the intermediate transfer belt 7 and peeling discharge traces have occurred. ,It was good. Further, the electrostatic attraction force between the sheet member 52 and the intermediate transfer belt 7 is substantially constant regardless of the increase in the voltage applied to the primary transfer member 5, and the intermediate transfer belt 7 and the primary transfer member 5 The frictional force of was able to be kept almost constant. As a result, an increase in driving torque of the intermediate transfer belt 7 could be suppressed.

  In Comparative Example 1, the sheet member 52 enters the physical nip A that is a contact area between the photosensitive drum 1 and the intermediate transfer belt 7. In the region overlapping with the physical nip A, the elastic member 51 having an area corresponding to 50% of the area of the physical nip A is covered with the sheet member 52. Therefore, a portion where the sheet member 52 shields the transfer charge in the physical nip A is generated, so that the transfer current is slightly insufficient, and transferability is slightly inferior to that of the present embodiment. However, this decrease in transferability is not a problem for practical use, and is generally good transferability. The vertical streak, which is a transfer defect, did not occur after the initial 10K paper feed. Further, since the sheet member 52 is an insulating sheet, it was possible to prevent charging. As a result, an increase in the driving torque of the intermediate transfer belt 7 could be suppressed for the same reason as described for the evaluation results of this example. That is, the comparative example 1 is an example of a transfer unit according to the present invention having almost the same capability as the present embodiment.

  In Comparative Example 2, the sheet member 52 has entered the physical nip A that is a contact area between the photosensitive drum 1 and the intermediate transfer belt 7. In the region overlapping with the physical nip A, the elastic member 51 having an area corresponding to 70% of the area of the physical nip A is covered with the sheet member 52. Therefore, a large portion where the sheet member 52 shields the transfer charge in the physical nip A causes a transfer current to be insufficient, and transferability is unacceptably worse than that of Comparative Example 1. The vertical streak, which is a transfer defect, did not occur after the initial 10K paper feed. Further, since the sheet member 52 is an insulating sheet, it was possible to prevent charging. As a result, for the same reason as described for the evaluation results of the present embodiment, it was possible to suppress an increase in the driving torque of the intermediate transfer belt 7 in general. However, since the length of the sheet member 52 is more than double that of the present embodiment, the driving torque is somewhat large, which shows an adverse effect.

  From the results of Comparative Example 1 and Comparative Example 2, when the elastic member 51 is covered with the sheet member 52 so as to exceed the area corresponding to 50% of the area of the physical nip A in the region overlapping the physical nip A, the transferability deteriorates. I understand that. Therefore, in order to ensure transferability, the area of the elastic member 51 covered with the sheet member 52 in the region overlapping the physical nip A is preferably set to an area corresponding to 50% or less of the area of the physical nip A. As described in the second embodiment, this area may be 0% of the area of the physical nip A, that is, the sheet member 52 may not be disposed in a region overlapping the physical nip A.

  In Comparative Example 3, 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. Further, since an electric field is applied to the upstream tension nip B on the upstream side in the moving direction of the intermediate transfer belt 7, scattering and image defects are clearly generated. Compared with the present embodiment, the length of the sheet member 52 of the sheet member 52 is very long and the resistance of the sheet member 52 is very low, so that the voltage applied to the primary transfer member 5 increases. Accordingly, the charge amount of the sheet member 52 is greatly increased. As a result, the electrostatic attraction force of the primary transfer member 5 to the intermediate transfer belt 7 is increased, and the driving torque of the intermediate transfer belt 7 is increased.

  In Comparative Example 4, an electric field acts on the contact area between the intermediate transfer belt 7 and the brush 304, which is the primary transfer member, on the upstream side in the movement direction of the intermediate transfer belt 7, so that scattering and image defects are clearly generated. This is because the brush as the primary transfer member 5 is strongly pressed against the photosensitive drum 1 in order to improve the transferability, and therefore the intermediate transfer belts 7 and 1 on the upstream side in the moving direction of the intermediate transfer belt 7 are inevitably. This is because a contact area with the brush 304 as the next transfer member is generated. In Comparative Example 4, the other evaluations were satisfactory in the initial stage with no problem, but were the same as in the present example. However, after passing the 10k sheets, the tip of the brush was crushed and the primary transfer member 304 The longitudinal contact with the intermediate transfer belt 7 became non-uniform. For this reason, the transfer unevenness in the longitudinal direction occurred after passing 10k sheets.

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

  Further, by providing the downstream tension nip C on the downstream side in the moving direction of the intermediate transfer belt 7, 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. The provision of the downstream tension nip C is very advantageous in that the above-described effect can be obtained. However, the downstream tension nip C may not be provided if desired, and in this case also, according to other features in the present embodiment. The effect can be obtained as well.

  Further, in the moving direction of the intermediate transfer belt 7, the sheet member 52 is shortened with respect to the width of the elastic member 51 in the contact area between the sheet member 52 and the intermediate transfer belt 7. Can be reduced (reduced). Thereby, an increase in frictional force between the intermediate transfer belt 7, the sheet member 52, and the elastic member 51 can be reduced, and an increase in driving torque of the intermediate transfer belt 7 can be suppressed.

  Further, an elastic member 51 in a region overlapping the upstream tension nip B is covered with an insulating sheet member 52 on the upstream side in the moving direction of the intermediate transfer belt 7. Thereby, the transfer charge in the upstream tension nip B can be shielded, and scattering and image defects can be suppressed.

  As described above, according to this 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, an increase in the driving torque of the intermediate transfer belt 7 can be suppressed by reducing the frictional force due to electrostatic adsorption. Further, according to the present embodiment, scattering that occurs on the upstream side of the intermediate transfer belt 7 can be prevented. 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. Therefore, in this embodiment, it is possible to obtain more stable and better transfer performance with a simple configuration without causing an increase in size and cost of the apparatus.

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. 9 is an enlarged view of the primary transfer portion n1 in the present 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 the present embodiment, the first area 53 A of the contact area 53 between the intermediate transfer belt 7 and the primary transfer member 5 is 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.

  More specifically, in this embodiment, the primary transfer member 5 includes a fixed elastic member 51 and a sheet member 52, and the sheet member 52 is interposed between the intermediate transfer belt 7 and the elastic member 51. It is pinched. The sheet member 52 is provided so as to cover only the upstream side of the elastic member 51 in the moving direction of the intermediate transfer belt 7. In this embodiment, the sheet member 52 does not enter the physical nip A that is a contact area between the intermediate transfer belt 7 and the photosensitive drum 1.

  More specifically, in this embodiment, the physical nip A between the photosensitive drum 1 and the intermediate transfer belt 7 in the moving direction of the intermediate transfer belt 7 is 2.5 mm, and the primary transfer member 5 (particularly the elastic member 51). The upstream tension nip B with the intermediate transfer belt 7 was 1 mm.

  In this embodiment, the contact area (first area) 34A between the sheet member 52 and the intermediate transfer belt 7 in the moving direction of the intermediate transfer belt 7 is set to 1 mm. Accordingly, the sheet member 52 does not enter the physical nip A of the intermediate transfer belt 7.

  Also in this embodiment, as in the first embodiment, the width w1 of the elastic member 52 in the moving direction of the intermediate transfer belt 7 is 5 mm. The primary transfer power supply 16 is connected to the elastic member 51.

  Further, in this embodiment, the downstream tension nip C between the primary transfer member 5 (particularly the sheet member 52) and the intermediate transfer belt 7 in the moving direction of the intermediate transfer belt 7 is set to 1.5 mm.

  In the present embodiment as well, as in the first embodiment, the portion of the end portion 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. Yes.

  Other settings such as resistance value, thickness, and material regarding the elastic member 51 and the sheet member 52 used in this embodiment are the same as those in the first embodiment.

B. Action According to this embodiment, the sheet member 52 is formed of an insulating member (or a member having a volume resistivity of 1 × 10 ¹⁵ Ωcm or more). In this embodiment, the sheet member 52 does not enter the physical nip A that is a contact area between the intermediate transfer belt 7 and the photosensitive drum 1, and the sheet member 52 is not moved in the moving direction of the intermediate transfer belt 7. It is much shorter than the width of the elastic member 51. Therefore, even when a voltage is applied to the elastic member 51 from the primary transfer power supply 16, the charge amount of the sheet member 52 is very small. Thereby, even when a transfer voltage is applied, the electrostatic adsorption force between the sheet member 52 and the intermediate transfer belt 7 is small, and the increase in the frictional force between the intermediate transfer belt 7, the sheet member 52, and the elastic member 51 is reduced. Can do. Accordingly, an increase in driving torque of the intermediate transfer belt 7 can be suppressed.

  In addition, also in this embodiment, the other actions described in Embodiment 1 can be obtained in the same manner.

  These effects 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 the present embodiment, using the image forming apparatus 100 with a process speed of 100 mm / sec, together with the comparative example shown below, the initial streak, transferability, scattering, and peeling discharge after the initial and 10k sheets passed. The marks and driving torque (electrostatic adsorption) were evaluated.

  In addition, the comparative example 1, the comparative example 2, the comparative example 3, and the comparative example 4 which were used in order to compare Example 1 and Example 1 were used for the comparison object. Therefore, the description of the configuration to be compared here is omitted.

(Evaluation results)
The evaluation results are shown in Table 2. Here, the same evaluation as that described in Example 1 was performed. Therefore, the description about the evaluation method, Example 1, and the evaluation results of Comparative Examples 1 to 4 is omitted.

  In this embodiment, sufficient transferability can be ensured from the beginning to after 10k sheets have passed, and none of vertical stripes of transfer failure, scattered image defects on the intermediate transfer belt 7, and peeling discharge traces have occurred. ,It was good. In addition, the electrostatic attraction force between the sheet member 52 and the intermediate transfer belt 7 is substantially constant regardless of the increase in the voltage applied to the primary transfer member 5, and the intermediate transfer belt 7 and the primary transfer member 5 The frictional force of was able to be kept almost constant. As a result, an increase in driving torque of the intermediate transfer belt 7 could be suppressed.

  As described above, according to the present invention, the same effects as those described in the first embodiment can be obtained. In particular, the sheet member 52 is a contact area between the photosensitive drum 1 and the intermediate transfer belt 7. Since it does not enter the physical nip A, the transferability can be further improved.

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. 10 shows a schematic cross-sectional configuration of the image forming apparatus 200 of this 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 caused by uneven contact between the transfer member 5 and the transfer belt 207 in the longitudinal direction.

  Further, by providing the downstream tension nip C on the downstream side in the moving direction of the transfer belt 207, the potential of the peeling portion between the transfer belt 207 and the photosensitive drum 1 is determined, and peeling discharge can be suppressed.

  Further, in the moving direction of the transfer belt 207, the contact area between the sheet member 52 and the transfer belt 207 is shortened with respect to the width of the elastic member 51, so that the electrostatic force between the sheet member 52 and the transfer belt 207 can be reduced. The adsorption force can be reduced (reduced). Accordingly, an increase in frictional force between the transfer belt 207, the sheet member 52, and the elastic member 51 can be reduced, and an increase in driving torque of the transfer belt 207 can be suppressed.

  Further, an insulating sheet member 52 is coated on the elastic member 51 in a region overlapping the upstream tension nip B on the upstream side in the moving direction of the transfer belt 207. Thereby, the transfer charge in the upstream tension nip B can be shielded, and scattering and image defects can be suppressed.

  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. It is an enlarged view of the primary transfer part for demonstrating an example of the primary transfer member comprised according to this 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. 10 is a schematic diagram for explaining a comparative example 4. FIG. 10 is a schematic diagram for explaining a comparative example 4. 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. It is a schematic cross-sectional block diagram of the transfer part using the conventional transfer roller.

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 (11)

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 that contacts the belt body by a surface; and a sheet member that is sandwiched between the belt body and the elastic member and contacts the belt body by a surface. The contact area between the belt member and the belt member is such that the sheet member provided so as to cover the elastic member over a predetermined range from the upstream end to the downstream side in the moving direction of the belt member is in contact with the belt member. An image forming apparatus, and a second area where the belt member comes into contact with the elastic member on the downstream side in the moving direction of the belt body relative to the first area. apparatus.   The image forming apparatus according to claim 1, wherein the sheet member is electrically insulating. The image forming apparatus according to claim 1, wherein the volume resistivity of the sheet member is 1 × 10 ¹⁵ Ωcm or more.   The at least part of said 1st area | region exists in the contact area | region of the said image carrier and the said belt body in the moving direction of the said belt body, The Claim 1 characterized by the above-mentioned. Image forming apparatus.   Of the first region, the area of the portion in the contact region between the image carrier and the belt member in the moving direction of the belt member is the area of the contact region between the image carrier and the belt member. The image forming apparatus according to claim 4, wherein the image forming apparatus is 50% or less.   The image forming apparatus according to claim 1, wherein the first area is outside a contact area between the image carrier and the belt body in a moving direction of the belt body. .   2. The downstream end of a contact area between the image carrier and the belt body in a moving direction of the belt body is located in a contact area between the transfer member and the belt body. The image forming apparatus according to any one of items 6 to 6.   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 a foamed sponge body.   The image forming apparatus according to claim 1, wherein the sheet member is formed of a fluororesin.

Images