JP2008310059A - 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 is composed of a substantially rectangular solid-shaped elastic member which surface-contacts with a belt body 7. In a moving direction of the belt body 7, an upstream-side end part B of a contact area between the transfer member 5 and the belt body 7 is located within a contact area A between an image carrier 1 and the belt body 7, and a downstream-side end part C of the contact area between the transfer member 5 and the belt body 7 is located out of the contact area A between the image carrier 1 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.

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).
JP-A-5-127546

  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 an upstream end (contact start end) of the contact area between the belt body and the transfer member outside 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, the toner image on the photoconductor is formed on the belt body before the contact area between the belt body and the photoconductor due to the influence of the transfer electric field formed between the photoconductor and the transfer member by the voltage applied to the transfer member. In some cases, the image quality is deteriorated such as scattering. This problem also occurs when the area where the surface of the transfer member that is not in contact with the belt body located upstream in the movement direction of the belt body is projected on the belt body is outside the contact area between the belt body and the photoconductor. It may occur as well.

  Furthermore, when the downstream end (contact end) of the contact area between the belt body and the transfer member is within 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.

  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 having voltage application means, the transfer member is an elastic member having a substantially rectangular parallelepiped shape that contacts the belt body on the surface, and the transfer member and the belt body in the moving direction of the belt body. An upstream end of the contact region is located in a contact region between the image carrier and the belt member, and a downstream end of the contact region between the transfer member and the belt member is the image carrier. And the contact of the belt body An image forming apparatus, characterized in that located outside.

  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, as the secondary transfer roller 8, a nickel-plated steel rod having a diameter of 8 mm is covered with a foam 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 ¹¹ 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.

  On the other hand, as a result of intensive studies, the present inventors have made the contact with the intermediate transfer belt 7 uniform over a long period of time by using the primary transfer member 5 that is in contact with the intermediate transfer belt 7 on the surface, thereby causing a transfer failure. Found to suppress.

  On the other hand, due to the arrangement of the primary transfer member, the present inventors cause scattering of the toner image in front of the contact area between the photosensitive drum 1 and the intermediate transfer belt 7 and disturbance of the toner image after the contact area. It has been found that this may occur.

  First, in the moving direction of the intermediate transfer belt 7, the upstream end portion (contact start end) of the contact area between the intermediate transfer belt 7 and the primary transfer member 5 outside 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. In other words, due to the influence of the transfer electric field formed between the photosensitive drum 1 and the primary transfer member 5 by the voltage applied to the primary transfer member 5, the photosensitive drum is exposed before the contact area between the intermediate transfer belt 7 and the photosensitive drum 1. The toner image on the drum 1 may be transferred onto the intermediate transfer belt 7. This may cause so-called image quality degradation such as scattering. This problem is that an area where the surface of the primary transfer member 5 that is not in contact with the intermediate transfer belt 7 located on the upstream side in the moving direction of the intermediate transfer belt 7 is projected onto the intermediate transfer belt 7 is exposed to the intermediate transfer belt 7 and the photosensitive member. It may occur in the same way even when it is outside the contact area with the drum 1.

  Further, in the moving direction of the intermediate transfer belt 7, the downstream end (contact 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.

  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 the present embodiment is to reduce the image quality by transferring the toner image on the photosensitive drum 1 in front of the contact area between the photosensitive drum 1 and the intermediate transfer belt 7 with a simple configuration. It is to suppress. In addition, another one of the more detailed purposes of this embodiment is to prevent the occurrence of peeling discharge without providing a neutralizing member on the back surface of the intermediate transfer belt 7, and to prevent the intermediate transfer belt 7 and the primary transfer member 5 from being generated. Is to ensure good transfer efficiency.

A. Configuration FIG. 2 is a schematic 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 is an elastic member that is in contact with the back surface of the intermediate transfer belt 7 and is fixed at a predetermined position as will be described in detail below. In this embodiment, in the moving direction of the intermediate transfer belt 7, the upstream end (contact) of the contact area between the primary transfer member 5 and the intermediate transfer belt 7 is in the contact area between the intermediate transfer belt 7 and the photosensitive drum 1. There is a starting end). Further, in the moving direction of the intermediate transfer belt 7, outside the contact area between the intermediate transfer belt 7 and the photosensitive drum 1, the downstream end (contact end) of the contact area between the primary transfer member 5 and the intermediate transfer belt 7. There is. The primary transfer member 5 is formed as a substantially rectangular parallelepiped pad having a substantially rectangular cross section.

  That is, in this embodiment, the primary transfer member 5 is a substantially rectangular parallelepiped elastic member that comes into contact with the intermediate transfer belt 7 on the surface. In the moving direction of the intermediate transfer belt 7, the upstream end of the contact area between the primary transfer member 5 and the intermediate transfer belt 7 is above the upstream end of the contact area between the photosensitive drum 1 and the intermediate transfer belt 7. Or it is located downstream (preferably downstream) from it. Further, the downstream end of the contact area between the primary transfer member 5 and the intermediate transfer belt 7 in the moving direction of the intermediate transfer belt 7 is the downstream end of the contact area 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).

More specifically, in this embodiment, 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 (w1) of 5 mm. A substantially rectangular parallelepiped having a longitudinal length (l1) of 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 resistance value of the primary transfer member 5 was 4 × 10 ⁷ Ω when 500 V was applied. In this example, the hardness of the primary transfer member 5 was 30 ° in Asker C (500 gf). The primary transfer member 5 preferably has a hardness of 40 ° or less in Asker C (500 gf).

  In FIG. 3, a contact area between the intermediate transfer belt 7 and the photosensitive drum 1 in the moving direction of the intermediate transfer belt 7 is denoted by A. Further, the upstream end (contact start end) of the contact area between the primary transfer member 5 and the intermediate transfer belt 7 in the moving direction of the intermediate transfer belt 7 is defined as B, the primary transfer member 5 and the intermediate transfer belt 7. Let C be the downstream end (contact end) of the contact area. And the positional relationship of these A, B, and C is as follows in a present Example as above-mentioned. In the moving direction of the intermediate transfer belt 7, the contact start end B between the intermediate transfer belt 7 and the primary transfer member 5 is inside the contact area A between the photosensitive drum 1 and the intermediate transfer belt 7 (that is, upstream of the contact area A). (Between the side end portion and the downstream end portion of the contact area A on the downstream side). Further, the contact end C between the intermediate transfer belt 7 and the primary transfer member 5 is outside the contact area A between the photosensitive drum 1 and the intermediate transfer belt 7 (that is, downstream from the downstream end of the contact area A). Is located.

  In this embodiment, the primary transfer power source 16 is connected to the primary transfer member 5 and a voltage of 500 V is applied as a representative value during the image forming operation.

  Further, in this embodiment, the primary transfer member 5 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 unit. Is done.

  Next, the position of a surface (non-contact surface) S2 that is not in contact with the intermediate transfer belt 7 of the primary transfer member 5 will be described with reference to FIG.

  In the drawing, the surface (contact surface) of the primary transfer member 5 that is in contact with the intermediate transfer belt 7 is S1, the surface that is not in contact with the intermediate transfer belt 7 (non-contact surface) S2, and the non-contact surface S2 is intermediate transfer. The area projected on the belt 7 is S3.

  In this embodiment, the primary transfer member 5 has a substantially rectangular parallelepiped shape, and is a contact surface S1 with respect to the intermediate transfer belt 7 and a surface that is not in contact with the intermediate transfer belt 7 located upstream in the movement direction of the intermediate transfer belt 7 ( Non-contact surface) S2 is connected substantially vertically. Therefore, as shown in FIG. 3, in the configuration of this embodiment, there is no region S <b> 3 in which the non-contact surface S <b> 2 is projected onto the intermediate transfer belt 7. However, as shown in FIG. 4, when there is such a region S3, the position of the region S3 is preferably set as follows.

  A region S3 in which a surface S2 that is not in contact with the intermediate transfer belt 7 located on the upstream side in the movement direction of the intermediate transfer belt 7 on the primary transfer member 5 is projected onto the intermediate transfer belt 7 is an area S3 in the movement direction of the intermediate transfer belt 7. The intermediate transfer belt 7 and the photosensitive drum 1 are located in the contact area A. That is, the region S3 is located on the upstream end of the contact region A between the photosensitive drum 1 and the intermediate transfer belt 7 or on the downstream side (preferably downstream) in the moving direction of the intermediate transfer belt 7. The region S3 is located upstream of the downstream end of the contact region A between the photosensitive drum 1 and the intermediate transfer belt 7 in the moving direction of the intermediate transfer belt 7.

  In the primary transfer member 5 of FIG. 4, the non-contact surface S2 facing the intermediate transfer belt 7 is inclined with respect to the contact surface S1.

B. Action By forming the primary transfer member 5 with an elastic body in surface contact with the back surface of the intermediate transfer belt 7, the followability of the surface of the primary transfer member 5 to the back surface of the intermediate transfer belt 7 is improved. As a result, uniform contact between the primary transfer member 5 and the intermediate transfer belt 7 can be ensured, and transfer defects caused by contact unevenness in the longitudinal direction between the primary transfer member 5 and the intermediate transfer belt 7 can be prevented. Can be prevented.

  Further, the contact start end B between the primary transfer member 5 and the intermediate transfer belt 7 is positioned inside the contact area A between the intermediate transfer belt 7 and the photosensitive drum 1, so that the photosensitive drum 1 in front of the contact area A is located. And the primary transfer member 5 can suppress the influence of the transfer electric field. That is, by setting the contact start end B to the above-described position, the intermediate transfer belt 7 and the photosensitive drum 1 are in contact with each other in a region where the primary transfer member 5 and the photosensitive drum 1 where the transfer electric field is generated are opposed to each other. ing. Therefore, the toner image on the photosensitive drum 1 is transferred onto the intermediate transfer belt 7 by the transfer electric field before the contact area A between the intermediate transfer belt 7 and the photosensitive drum 1. Blurred image defects (so-called scattering) can be suppressed.

  On the other hand, the contact transfer end C between the primary transfer member 5 and the intermediate transfer belt 7 is positioned outside the contact area A between the intermediate transfer belt 7 and the photosensitive drum 1, whereby the primary transfer member 5 is moved to the photosensitive drum 1. The intermediate transfer belt 7 serves as a counter electrode at the contact end point where the intermediate transfer belt 7 peels off. Therefore, peeling discharge can be suppressed, and image defects due to peeling discharge can be prevented without providing a neutralizing member for neutralizing the intermediate transfer belt 7.

  Further, when there is a region S3 on the intermediate transfer belt 7 where a surface S2 that is not in contact with the intermediate transfer belt 7 located on the upstream side in the movement direction of the intermediate transfer belt 7 is projected on the intermediate transfer belt 7, it is preferable. The area S3 is located inside the contact area A. Thereby, the influence of the transfer electric field formed between the photosensitive drum 1 and the non-contact surface S2 of the primary transfer member 5 in front of the contact area A can be suppressed. That is, in the region where the primary transfer member 5 and the photosensitive drum 1 where the transfer electric field is generated are opposed to each other, the intermediate transfer belt 7 and the photosensitive drum are also in the region S3 where the non-contact surface S2 of the primary transfer member 5 is projected. 1 is in contact. Therefore, the toner image on the photosensitive drum 1 is transferred onto the intermediate transfer belt 7 by the transfer electric field before the contact area A between the intermediate transfer belt 7 and the photosensitive drum 1. Blurred image defects (so-called scattering) 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, after the initial and 100k sheets passed, transfer unevenness in the longitudinal direction, transfer failure, scattering, The peel discharge 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. 5, the contact start end B between the intermediate transfer belt 7 and the primary transfer member 5 is located outside the contact area A between the photosensitive drum 1 and the intermediate transfer belt 7. . On the other hand, in Comparative Example 1, the contact end C between the intermediate transfer belt 7 and the primary transfer member 5 is located outside the contact area A between the photosensitive drum 1 and the intermediate transfer belt 7 as in this embodiment. ing. The primary transfer member 5 of Comparative Example 1 was the same as that of this example except for the arrangement (size).

(Comparative Example 2)
In Comparative Example 2, as shown in FIG. 6, the contact start end B 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 as in the present embodiment. Located inside. On the other hand, in Comparative Example 2, a contact end C between the intermediate transfer belt 7 and the primary transfer member 5 is located inside a contact area A between the photosensitive drum 1 and the intermediate transfer belt 7. The primary transfer member 5 of Comparative Example 2 was the same as that of this example except for the arrangement (size).

(Comparative Example 3)
In Comparative Example 3, a brush-shaped primary transfer member 301 as shown in FIG. 7 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 in this example.

(Comparative Example 4)
In Comparative Example 4, a blade-shaped primary transfer member 302 as shown in FIG. 8 was used. More specifically, the primary transfer member 302 of Comparative Example 4 is a blade made of urethane having a resistance value of 1 × 10 ⁸ Ω. In Comparative Example 4, the contact start end B between the intermediate transfer belt 7 and the primary transfer member 302 is located inside the contact area A between the photosensitive drum 1 and the intermediate transfer belt 7. On the other hand, in Comparative Example 4, the contact end C between the intermediate transfer belt 7 and the primary transfer member 302 is located inside the contact area A between the photosensitive drum 1 and the intermediate transfer belt 7. In Comparative Example 4, blade-shaped bending is used for contact between the intermediate transfer belt 7 and the primary transfer member 302. Therefore, in Comparative Example 4, there is a region S3 in which a surface S2 that is not in contact with the intermediate transfer belt 7 located on the upstream side in the movement direction of the intermediate transfer belt 7 on the primary transfer member 302 is projected onto the intermediate transfer belt 7. This region S3 is outside the contact region A between the intermediate transfer belt 7 and the photosensitive drum 1.

(Evaluation results)
The evaluation results are shown in Table 1. Here, the evaluation was performed by paying attention to uneven transfer in the longitudinal direction, scattering on the intermediate transfer belt 7, and discharge traces in a 30% printed halftone image. Further, the paper passing durability test was performed at 4024 basis weight of 75 g / m ² manufactured by Xerox, and an image after passing 100 k sheets was evaluated.

  In this example, all of scattering, transfer failure, and peeling discharge traces were good from the initial stage until 100 k sheets were passed.

  In Comparative Example 1, the contact start end B between the intermediate transfer belt 7 and the primary transfer member 5 is located outside the contact area A between the photosensitive drum 1 and the intermediate transfer belt 7. For this reason, the transfer electric field formed between the primary transfer member 5 and the photosensitive drum 1 scatters the toner image on the photosensitive drum 1 onto the intermediate transfer belt 7 before the contact area A.

  In Comparative Example 2, a contact end C between the intermediate transfer belt 7 and the primary transfer member 5 is located inside a contact area A between the photosensitive drum 1 and the intermediate transfer belt 7. Therefore, peeling discharge occurred at the end point of contact between the intermediate transfer belt 7 and the photosensitive drum 1, and a trace of discharge occurred in the halftone image.

  In Comparative Example 3, the initial state was satisfactory and satisfactory, but the tip of the brush was crushed after passing 100k sheets, so the longitudinal contact between the primary transfer member 301 and the intermediate transfer belt 7 became uneven. It was. For this reason, the uneven transfer in the longitudinal direction occurred after passing 100k sheets.

  In Comparative Example 4, a contact end C between the intermediate transfer belt 7 and the primary transfer member 302 is located inside a contact area A between the photosensitive drum 1 and the intermediate transfer belt 7. Therefore, peeling discharge occurred at the end point of contact between the intermediate transfer belt 7 and the photosensitive drum 1, and a trace of discharge occurred in the halftone image. In Comparative Example 4, the region S3 in which the non-contact surface S2 is projected onto the intermediate transfer belt 7 is outside the contact region A between the intermediate transfer belt 7 and the photosensitive drum 1. For this reason, the transfer electric field formed between the primary transfer member 5 and the photosensitive drum 1 scatters the toner image on the photosensitive drum 1 onto the intermediate transfer belt 7 before the contact area A.

  As described above, according to this embodiment, the primary transfer member 5 is an elastic member that is in contact with the back surface of the intermediate transfer belt 7 and fixed at a predetermined position. Therefore, through the durability, the contact between the intermediate transfer belt 7 and the primary transfer member 5 becomes uniform, and transfer unevenness in the longitudinal direction can be prevented.

  Further, according to this embodiment, the contact start end B between the primary transfer member 5 and the intermediate transfer belt 7 is located inside the contact area A between the intermediate transfer belt 7 and the photosensitive drum 1. Therefore, the influence of the transfer electric field generated when transferring the photosensitive drum 1 onto the intermediate transfer belt 7 formed between the photosensitive drum 1 and the primary transfer member 5 in front of the contact area A is suppressed. Can be prevented from being scattered.

  Further, according to this embodiment, the contact end end C between the primary transfer member 5 and the intermediate transfer belt 7 is located outside the contact area A between the intermediate transfer belt 7 and the photosensitive drum 1. Therefore, it is possible to suppress discharge generated between the primary transfer member 5 and the intermediate transfer belt 7 and prevent transfer failure. In addition, it is possible to prevent peeling discharge that occurs at the end point of contact between the intermediate transfer belt 7 and the photosensitive drum 1 without providing a charge eliminating member.

  Further, when there is a region S3 on the intermediate transfer belt 7 where a surface S2 that is not in contact with the intermediate transfer belt 7 located on the upstream side in the movement direction of the intermediate transfer belt 7 is projected on the intermediate transfer belt 7, it is preferable. The area S3 is located inside the contact area A. Thus, the transfer electric field formed between the primary transfer member 5 and the photosensitive drum 1 prevents the toner image on the photosensitive drum 1 from being transferred onto the intermediate transfer belt 7 before the contact area A. be able to.

  As described above, according to this embodiment, the toner image on the photosensitive drum 1 is prevented from being deteriorated by a simple configuration before the toner image is transferred in front of the contact area between the photosensitive drum 1 and the intermediate transfer belt 7. can do. Further, according to this embodiment, even if no neutralizing member is provided on the back surface of the intermediate transfer belt 7, the occurrence of peeling discharge can be prevented and the discharge between the intermediate transfer belt 7 and the primary transfer member 5 can be suppressed. Good transfer efficiency can be ensured. 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 The image forming apparatus 100 preferably includes the features described in the first embodiment and the features described below.

Referring to FIG. 9, let L be the length (contact width) 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. The length of the contact area between the primary transfer member 5 and the intermediate transfer belt 7 that overlaps the contact area A having the length L in the moving direction of the intermediate transfer belt 7 (that is, within the contact area A) ( The contact width is N. That is, the length N is a length of a region where all of the photosensitive drum 1, the intermediate transfer belt 7, and the primary transfer member 5 are in contact with each other in the moving direction of the intermediate transfer belt 7. At this time, the length L and the length N are as follows:
1 / 2L ≦ N
It is preferable to satisfy the relationship.

  More specifically, when the length L of the contact area A between the photosensitive drum 1 and the intermediate transfer belt 7 is 5 mm, all of the photosensitive drum 1, the intermediate transfer belt 7, and the primary transfer member 5 are in contact with each other. The length N of the existing region can be 2.5 mm or more.

B. The toner image formed on the photosensitive drum 1 is transferred onto the intermediate transfer belt 7 by a transfer bias voltage having a polarity opposite to the normal charging polarity of the toner supplied to the primary transfer member 5 from the primary transfer power supply 16. Is done. At this time, the actual primary transfer efficiency is determined by the current flowing from the primary transfer member 5 to the photosensitive drum 1. There are the following two types of current. First, I1 flows through a portion where the photosensitive drum 1, the intermediate transfer belt 7, and the primary transfer member 5 are all in contact (the portion of length N in FIG. 9). Second, I2 flows from the edge portion of the primary transfer member 5 through the intermediate transfer belt 7 and flows into a region where only the photosensitive drum 1 and the intermediate transfer belt 7 are in contact (portion N2 in FIG. 9). It is.

  The current I2 becomes inefficient with respect to the transfer bias due to the influence of surface resistance because the current conduction path in the intermediate transfer belt 7 becomes long. Accordingly, the length N of the region where all of the photosensitive drum 1, the intermediate transfer belt 7, and the primary transfer member 5 are in contact with the length L of the contact region A between the photosensitive drum 1 and the intermediate transfer belt 7. Is smaller, the influence of the current I2 becomes larger. Therefore, the transfer bias to be applied becomes large, and it becomes easy to generate a discharge in a region where all of the photosensitive drum 1, the intermediate transfer belt 7, and the primary transfer member 5 are in contact. Due to this discharge, the charge polarity of the toner in the region where all of the photosensitive drum 1, the intermediate transfer belt 7, and the primary transfer member 5 are in contact with each other may be reversed, leading to a decrease in transfer efficiency.

  That is, the length L of the contact area A between the photosensitive drum 1 and the intermediate transfer belt 7 and the length N of the area where all of the photosensitive drum 1, the intermediate transfer belt 7, and the primary transfer member 5 are in contact with each other. By satisfying the relationship of 1 / 2L ≦ N, it is possible to reduce the influence of the current I2. Thereby, it is possible to suppress discharge in a region where all of the photosensitive drum 1, the intermediate transfer belt 7, and the primary transfer member 5 are in contact.

As described above, the length L of the contact area A between the photosensitive drum 1 and the intermediate transfer belt 7 and the length of the area where all of the photosensitive drum 1, the intermediate transfer belt 7, and the primary transfer member 5 are in contact with each other. N is the following formula:
1 / 2L ≦ N ≦ L
It is preferable to satisfy the relationship. As a result, the current I <b> 2 flowing through the intermediate transfer belt 7 from the edge portion of the primary transfer member 5 and flowing in the region where only the photosensitive drum 1 and the intermediate transfer belt 7 are in contact can be reduced. Accordingly, it is possible to suppress discharge in a region where all of the photosensitive drum 1, the intermediate transfer belt 7, and the primary transfer member 5 are in contact with each other, thereby obtaining good transfer efficiency.

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 forming the transfer member 5 with an elastic body that is in surface contact with the back surface of the transfer belt 207, the followability of the front surface of the transfer member 5 to the back surface of the transfer belt 207 is improved. As a result, uniform contact between the transfer member 5 and the transfer belt 207 can be ensured, and transfer defects caused by uneven contact of the transfer member 5 with the transfer belt 207 in the longitudinal direction can be prevented.

  Further, since the contact start end B between the transfer member 5 and the transfer belt 207 is positioned inside the contact area A between the transfer belt 207 and the photosensitive drum 1, the toner image on the photosensitive drum 1 in front of the contact area A can be obtained. The influence of the transfer electric field generated when transferring onto the transfer material P can be suppressed. That is, by setting the contact start end B to the above-described position, the transfer material P and the photosensitive drum 1 are in contact with each other in a region where the transfer member 5 where the transfer electric field is generated and the photosensitive drum 1 face each other. Therefore, the toner image on the photosensitive drum 1 is transferred onto the transfer material P by the transfer electric field before the desired position on the transfer material P enters the contact area A between the transfer belt 207 and the photosensitive drum 1. Image defects (so-called scattering) in which the toner image on the transfer material P is blurred can be suppressed.

  On the other hand, when the contact end C of the transfer member 5 and the transfer belt 207 is located outside the contact area A between the transfer belt 207 and the photosensitive drum 1, the transfer member 5 peels off the transfer material P from the photosensitive drum 1. It acts as a counter electrode at the contact end point. Therefore, peeling discharge can be suppressed, and an image defect due to peeling discharge can be prevented without providing a charge removal member that removes the transfer material P.

  Further, when there is a region S3 on the transfer belt 207 where a surface S2 that is not in contact with the transfer belt 207 located upstream in the movement direction of the transfer belt 207 is projected on the transfer belt 207, the region S3 is preferably Be inside the contact area A. Thereby, the influence of the transfer electric field formed between the photosensitive drum 1 and the non-contact surface S2 of the transfer member 5 in front of the contact area A can be suppressed. That is, in the region where the transfer member 5 where the transfer electric field is generated and the photosensitive drum 1 face each other, the transfer material P carried on the transfer belt 207 and the photosensitive drum 1 are in contact also in the region S3. Therefore, the toner image on the photosensitive drum 1 is transferred onto the transfer material P by the transfer electric field before the desired position on the transfer material P enters the contact area A between the transfer belt 207 and the photosensitive drum 1. Image defects (so-called scattering) in which the toner image on the transfer material P is blurred 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.

  As described above, according to the present embodiment, not only can scattering be prevented, but also electric discharge generated between the transfer member 5 and the transfer material P can be prevented, and transfer can be performed without providing a charge removal member. It is possible to prevent peeling discharge that occurs at the end point of contact between the material P and the photosensitive drum 1. Accordingly, it is possible to prevent the toner image transferred to the transfer material P from being disturbed with a simple configuration without causing an increase in size and cost of the apparatus.

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. FIG. 4 is an enlarged view of a primary transfer portion for explaining a non-contact area between a primary transfer member and an intermediate transfer belt. 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. FIG. 9 is an enlarged view of a primary transfer portion for explaining a comparative example 4; 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 (image carrier)
5 Primary transfer member (transfer member)
7 Intermediate transfer belt (belt body)
207 Transfer belt (belt body)

Claims (5)

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 is an elastic member having a substantially rectangular parallelepiped shape that comes into contact with the belt body in a plane, and an upstream end portion of a contact area between the transfer member and the belt body in the moving direction of the belt body is the image. Located in the contact area between the carrier and the belt body, the downstream end of the contact area between the transfer member and the belt body is located outside the contact area between the image carrier and the belt body. An image forming apparatus.   The area of the transfer member projected on the belt body that is not in contact with the belt body located upstream of the belt body in the moving direction is the image carrier and the belt in the moving direction of the belt body. The image forming apparatus according to claim 1, wherein the image forming apparatus is located in the contact area with a body. The length L of the contact area between the image carrier and the belt body in the movement direction of the belt body, and the length in the movement direction of the belt body among the contact areas between the transfer member and the belt body. The length N of the region that overlaps the region of L is the following formula:
1 / 2L ≦ N
The image forming apparatus according to claim 1, wherein the relationship is satisfied.   The image forming apparatus according to claim 1, wherein the transfer member is pressed toward the belt body.   The image forming apparatus according to claim 1, wherein the elastic member is made of a foamed sponge body.

Images