JP2015102558A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent image defect to be caused when a substance on a belt body rear face is accumulated on transfer means.SOLUTION: Transfer means 7 includes a brush 71 which comes in contact with a belt body 6 to rub it, and brush holding means 72 which holds the brush 71. The brush 71 includes a plurality of brush members 712, 713 different in electric resistance. The electric resistance of the upstream brush member 712 arranged upstream in a rotation moving direction of the belt body 6 is higher than the electric resistance of the downstream brush member 713 arranged downstream. The upstream brush member 712 has electric resistance which is substantially the same as or higher than that of the belt body 6, and is arranged upstream of a contact area D between the belt body 6 and an image carrier 1. The downstream brush member 713 has electric resistance which is lower than that of the belt body 6, and is arranged in the contact area D between the belt body 6 and the image carrier 1.

Description

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

  Conventionally, an image forming apparatus such as a copying machine or a printer using an electrophotographic system has the following transfer process. The toner image carried on the photosensitive drum, which is the image carrier of the image forming apparatus, is applied to the transfer means by applying an electric field having a polarity opposite to the charged polarity of the toner to the transfer member or This is a transfer step of electrostatically transferring to the intermediate transfer belt. For this process, an image forming apparatus provided with a belt member such as a transfer material conveying belt or an intermediate transfer belt is provided with a voltage applying means for applying a voltage necessary for the transfer process to the transfer means. As a transfer unit of the image forming apparatus, a configuration including a transfer roller which is a rotary transfer member is used. Furthermore, a configuration including a transfer blade and a transfer brush, which are fixed transfer members, may be used. These transfer members are used in contact with the back surface of the belt body at a position facing the photosensitive drum. In particular, the transfer brush is composed of a group of conductive fibers, and each of the fibers can contact the back surface of the belt body independently. Therefore, the contact unevenness generated when the transfer roller and the transfer blade are used is improved, and a more uniform contact can be obtained with respect to the back surface of the belt body. As a result, image defects such as density unevenness generated in the transfer process are satisfactorily suppressed.

  Based on the background as described above, a transfer brush is used as the transfer member, and the contact surface between the transfer member and the belt body is adjusted to suppress contact unevenness. Thus, a configuration has been proposed in which the transfer electric field in the transfer portion is stabilized and the toner image is transferred to the transfer material or intermediate transfer belt with high fidelity and good reproducibility.

JP-A-4-345186

  However, the fixed-type transfer member including the transfer brush described above may rub against the back surface of the belt body by repeatedly performing image formation, and the transfer member and the belt body may be scraped. In addition, toner, paper powder, scraped powder of moving parts accompanying use, and the like easily enter the back side of the belt body. There is a problem that image defects occur due to the deposits on the back surface of the belt body staying on the transfer member.

  Accordingly, an object of the present invention is to provide an image forming apparatus capable of suppressing image defects caused by the deposits on the back surface of the belt body staying on the transfer means.

The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention provides an image carrier that carries a toner image;
A toner image is transferred from the image carrier, or a belt that conveys a transfer material to which the toner image is transferred;
Transfer means for transferring a toner image from the image carrier to the belt body;
In an image forming apparatus having
The transfer means includes a brush that contacts and rubs with the belt body, and a brush holding means that holds the brush,
The brush is composed of a plurality of brush members having different electric resistances,
The electrical resistance of the upstream brush member disposed on the upstream side in the rotational movement direction of the belt body is higher than the electrical resistance of the downstream brush member disposed on the downstream side,
The upstream brush member has an electrical resistance substantially equal to or higher than the electrical resistance of the belt body, and is disposed upstream of a contact area of the belt body and the image carrier. ,
The downstream brush member has an electric resistance lower than that of the belt body, and is disposed in a contact area between the belt body and the image carrier.

  According to the present invention, deposits on the back surface of the belt body can be removed by using transfer means having a plurality of brush members having different electric resistances on one brush holding means. Thereby, the image defect resulting from the deposit | attachment of a belt body back surface staying on a transfer means can be suppressed.

1 is a schematic cross-sectional view of an embodiment of an image forming apparatus according to the present invention. 2 is a schematic perspective view of a primary transfer brush according to Embodiment 1. FIG. 2 is a schematic cross-sectional view of a primary transfer portion in Embodiment 1. FIG. FIG. 6 is a diagram illustrating a relationship between the undulation of an intermediate transfer belt and a distance from a primary transfer nip. FIG. 4A is a schematic perspective view showing the undulation of the intermediate transfer belt, and FIG. 4B is a diagram showing the relationship between the undulation amount of the intermediate transfer belt and the distance to the upstream side in the transport direction. FIG. 6 is a schematic cross-sectional view of a primary transfer portion in Embodiment 2. 6 is a schematic perspective view illustrating an example of a brush member of a primary transfer brush according to Embodiment 2. FIG. FIG. 6 is a schematic cross-sectional view of a primary transfer portion in Embodiment 3. 6 is a schematic perspective view of a primary transfer brush of Example 3. FIG.

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

Example 1
1. 1 is a schematic cross-sectional view of an embodiment of an image forming apparatus 100 according to the present invention. The image forming apparatus 100 according to the present exemplary embodiment is an electrophotographic full color laser beam printer, and is of a tandem type using an intermediate transfer method. That is, the image forming apparatus 100 transfers each color toner image on the image carrier formed on the photosensitive drum, that is, on the photosensitive drum, on the belt-shaped intermediate transfer body, that is, the intermediate transfer belt. Superimpose sequentially and perform primary transfer. Thereafter, the toner images superimposed on the intermediate transfer belt are collectively transferred to the transfer material SH to obtain a recorded image.

  The image forming apparatus 100 includes first, second, third, and fourth image forming stations Sy, Sm, Sc, and Sk as a plurality of image forming units. In this embodiment, the first to fourth image forming stations Sy to Sk are for forming toner images of respective colors of yellow (Y), magenta (M), cyan (C), and black (K). It is.

  There are many common parts in the configuration and operation of the image forming stations Sy to Sk. Therefore, in the following, when it is not necessary to distinguish, subscripts y, m, c, k for indicating an element provided for one of the colors will be omitted.

  The image forming apparatus 100 includes in the image forming station S a photosensitive drum 1 that is a drum-shaped electrophotographic photosensitive member as an image carrier. Around the photosensitive drum 1, a charging roller 2, an exposure device 3, a developing device 4, and a photosensitive drum cleaner 5 are arranged. Under each image forming station S, an intermediate transfer belt 6 is disposed, and the image forming stations Sy, Sm, Sk are arranged at positions where the respective photosensitive drums 1y, 1m, 1c, 1k abut on the intermediate transfer belt 6 in a straight line. Sc and Sk are arranged. The distance between the image forming stations in the image forming apparatus 100 of this embodiment is 70 mm. The intermediate transfer belt 6 is stretched around a drive roller 61, a secondary transfer counter roller 62, and a tension roller 63. A primary transfer unit 7 is disposed at a position facing the photosensitive drum 1 with the intermediate transfer belt 6 interposed therebetween. A secondary transfer roller 8 serving as a secondary transfer unit is provided at a position opposite to the secondary transfer counter roller 62 across the intermediate transfer belt 6. Further, an intermediate transfer belt cleaning unit 9 is provided at a portion facing the driving roller 61 with the intermediate transfer belt 6 interposed therebetween. A cassette 10 which is a transfer material storage unit for storing the transfer material SH is provided below the image forming apparatus 100. A feeding roller 11, a registration roller pair 12, a secondary transfer roller 8, and a fixing device 13 are provided in the transfer movement direction of the transfer material SH.

  Next, image formation will be described together with details of the configuration of the image forming apparatus 100.

  When an image formation start signal is received from a host computer (not shown), the photosensitive drum 1 is rotationally driven in the direction of arrow R1 (counterclockwise) in the figure by a driving means (not shown). The surface of the photosensitive drum 1 is uniformly charged by the charging roller 2. Next, the exposure device 3 irradiates the photosensitive drum 1 with laser light L according to image information from a host computer (not shown), and an electrostatic latent image is formed on the surface of the photosensitive drum 1. When the photosensitive drum 1 further rotates and the electrostatic latent image on the surface of the photosensitive drum 1 advances in the direction of the arrow R1 in the figure, the electrostatic latent image formed on the photosensitive drum 1 according to the image information by the developing device 4 becomes a toner image. Is visualized as The developing device 4 develops the electrostatic latent image on the photosensitive drum 1 by a reversal developing method. That is, the developing device 4 attaches toner (negative polarity) charged to the same polarity as the charged polarity (negative polarity) of the photosensitive drum 1 to an exposure portion, that is, an electrostatic latent image, which is an image portion on the photosensitive drum 1. Develop and visualize as a toner image.

  In the moving direction of the surface of the photosensitive drum 1 indicated by an arrow R1 in the drawing, an intermediate transfer belt 6 that is a belt body as an endless belt-like intermediate transfer body is disposed downstream of the developing device 4.

  The intermediate transfer belt 6 is a cylindrical and endless belt-like film stretched around three rollers: a driving roller 61, a secondary transfer counter roller 62, and a tension roller 63. The intermediate transfer belt 6 rotates in the direction indicated by the arrow R2 (clockwise) in the drawing, so that the intermediate transfer belt 6 rotates in the direction indicated by the arrow R3 (clockwise) in the drawing at the substantially same speed as the moving speed of the surface of the photosensitive drum 1. Rotate.

  A primary transfer brush unit 7 serving as a primary transfer unit is disposed at a position facing the photosensitive drum 1 with the intermediate transfer belt 6 interposed therebetween. As is understood with reference to FIG. 3, the primary transfer brush unit 7 includes a primary transfer brush 71 and a primary transfer brush holding member 72 as primary transfer means.

  A primary transfer portion N1 is formed by the contact between the photosensitive drum 1 and the intermediate transfer belt 6. As the primary transfer process, the toner image formed on the photosensitive drum 1 as the photosensitive drum 1 and the intermediate transfer belt 6 rotate is primarily transferred to the outer peripheral surface of the intermediate transfer belt 6 on the belt body side by the action of the primary transfer brush 71. Is done. At this time, a primary transfer voltage is applied to the primary transfer brush 71 by a primary transfer power supply 70 with a polarity (positive polarity) opposite to the charging polarity (negative polarity) of the toner.

  Residual toner remaining on the photosensitive drum 1 without being transferred to the intermediate transfer belt 6 in the primary transfer process is cleaned by the photosensitive drum cleaner 5. The photosensitive drum cleaner 5 includes a cleaning blade 51 that is a plate-like elastic body that contacts the surface of the photosensitive drum 1. The photosensitive drum cleaner 5 includes a toner container 52 that collects the toner removed from the surface of the photosensitive drum 1 by the cleaning blade 51.

  The charging, exposure, development, and primary transfer processes as described above are sequentially performed from the upstream side in the movement direction of the surface of the intermediate transfer belt 6 at the first to fourth stations Sy to Sk, Y (yellow), M (magenta). , C (cyan) and K (black). As a result, a full-color toner image in which the four color toner images are superimposed on the intermediate transfer belt 6 is formed.

  A secondary transfer roller 8 is disposed at a position facing the secondary transfer counter roller 62 with the intermediate transfer belt 6 interposed therebetween. The secondary transfer roller 8 is pressed against the secondary transfer counter roller 62 via the intermediate transfer belt 6 to form a secondary transfer portion N2 where the intermediate transfer belt 6 and the secondary transfer roller 8 are in contact with each other.

  As a secondary transfer step, the toner image on the intermediate transfer belt 6 is secondarily transferred onto the transfer material SH by the action of the secondary transfer roller 8. That is, in the transfer material supply unit SHF, after the transfer material SH accommodated in the cassette 10 is sent out by the supply roller 11, the secondary transfer roller 8 is brought into contact with the intermediate transfer belt 6 and the secondary transfer roller 8 by the registration roller pair 12. The toner is supplied to the transfer portion N2 at a predetermined timing. At substantially the same time, a secondary transfer voltage having a polarity (positive polarity) opposite to the normal charging polarity of the toner is applied to the secondary transfer roller 8 by the secondary transfer power supply 80.

  An intermediate transfer belt cleaner 9 serving as an intermediate transfer belt cleaning unit is disposed at a position facing the driving roller 61 with the intermediate transfer belt 6 interposed therebetween. The cleaning blade 91 of the intermediate transfer belt cleaner 9 comes into contact with the intermediate transfer belt 6, collects secondary transfer residual toner remaining on the intermediate transfer belt 6 without being transferred to the transfer material SH in the secondary transfer step, and performing intermediate transfer. The belt 6 is cleaned.

  The image forming apparatus 100 according to the present exemplary embodiment is a printer for A4 size paper having a process speed of 116 mm / sec.

2. Intermediate transfer belt As the intermediate transfer belt 6, a polyimide resin film having a thickness of 60 μm and a volume resistivity adjusted to 10 ⁹ Ωcm by mixing a conductive agent can be used. The intermediate transfer belt 6 is stretched around three axes of a drive roller 61, a secondary transfer counter roller 62, and a tension roller 63, and a tension of about 20 N is applied to the intermediate transfer belt 6 by the tension roller 63.

  Further, an intermediate transfer belt cleaner 9 having a cleaning blade 91 that is a plate-like elastic body is provided on the surface of the intermediate transfer belt 6 as a cleaning member for removing attached toner. The toner removed from the surface of the intermediate transfer belt 6 by the cleaning blade 91 is collected in the toner container 92.

3. Secondary Transfer Roller As the secondary transfer roller 8, an elastic roller having a volume resistivity of 10 ⁷ to 10 ⁹ Ωcm and a hardness of 30 ° to 40 ° in Asker · C can be used. The secondary transfer roller 8 is pressed against the secondary transfer counter roller 62 via the intermediate transfer belt 6 with a total pressure of about 39.2N. Further, the secondary transfer roller 8 is driven to rotate as the intermediate transfer belt 6 rotates. Further, a secondary transfer voltage of 0 to 4.0 kV can be applied to the secondary transfer roller 8 from a secondary transfer power supply 80.

4). Primary Transfer Brush Unit Next, the primary transfer brush unit 7 of the primary transfer means, which is a characteristic part of the present invention, will be described with reference to FIGS.

  The primary transfer brush unit 7 includes a brush in which conductive fibers are densely arranged as the primary transfer brush 71. FIG. 2 is a perspective view showing an outline of the primary transfer brush 71 used in this embodiment. The primary transfer brush 71 is formed by forming pile rows 712 and 713 made of two kinds of conductive fibers having different resistances on a single base cloth 711. As the primary transfer brush 71, the resistance of the pile row 712 planted on the upstream side in the toner image transport direction R3 that is the rotational movement direction of the intermediate transfer belt 6 is higher than the resistance of the pile row 713 planted on the downstream side. Set.

  The role of each pile row 712, 713 will be described.

  The role of the high resistance pile row 712 installed on the upstream side in the rotational movement direction of the intermediate transfer belt 6 is to remove foreign matter that has entered the back surface of the intermediate transfer belt 6 such as scraped powder, toner, or paper dust generated in the image forming operation. Is to collect and recover. On the other hand, the role of the low resistance pile row 713 installed on the downstream side is to primarily transfer the toner image on the photosensitive drum 1 onto the surface of the intermediate transfer belt 6 in the primary transfer portion N1. By making the pile row 712 positioned upstream in the rotational movement direction of the intermediate transfer belt 6 high resistance, an unnecessary pre-transfer electric field is not formed, and good image formation can be performed.

  Details are described below.

5. Primary transfer brush member As described above, in this embodiment, the upstream brush member 712 and the downstream brush member 713 are formed on one base cloth 711 by two kinds of pile rows having different resistance values. The member 713 constitutes a primary transfer brush 71 that is adjacent and in contact therewith. As described above, the high resistance pile row 712 that is the upstream upstream brush member in the rotational movement direction of the intermediate transfer belt 6 is a pile row that plays a role of collecting and collecting foreign matter on the back surface of the intermediate transfer belt 6. Hereinafter, it is referred to as “cleaning pile row” 712. On the other hand, the low resistance pile row 713 which is a downstream brush member on the downstream side is a pile row having a role of primarily transferring the toner image on the photosensitive drum 1 to the surface of the intermediate transfer belt 6 in the primary transfer portion N1, and hence, “transfer” will be described below. It is referred to as “pile train” 713.

  For example, in the transfer brush configuration, when the resistance of the cleaning pile row 712 is as low as the resistance of the transfer pile row 713, an unnecessary pre-transfer electric field is generated between the intermediate transfer belt 6 and the photosensitive drum 1 immediately above the primary transfer nip D. Will form. In this case, when the foreign matter adhering to the back surface of the intermediate transfer belt 6 is captured by the function of the cleaning pile row 712 and stays at the interface between the intermediate transfer belt 6 and the transfer brush 71, the pre-transfer electric field is disturbed and the longitudinal length is not uniform. Image defects occur. Alternatively, when the cleaning pile row 712 is electrically floating or is an insulator, the intermediate transfer belt 6 is charged up due to the friction between the intermediate transfer belt 6 and the cleaning pile row 712. In this case, the potential of the intermediate transfer belt 6 becomes unstable due to repetition of image formation, and it becomes difficult to stably perform good image formation.

  However, when the primary transfer voltage is applied after setting the resistance of the cleaning pile row 712 higher than the resistance of the transfer pile row 713 as employed in the configuration of the present embodiment, it is favorable for the following reason. Image formation can be performed.

  Since the resistance of the cleaning pile row 712 located on the upstream side in the transport direction is high, the potential of the fiber tip of the cleaning pile row 712 is lower than the potential of the fiber tip of the transfer pile row 713 located on the downstream side. For this reason, under the primary transfer voltage applied for normal image formation, the cleaning pile row 712 is prevented from forming an unnecessary pre-transfer electric field. Therefore, even after the cleaning pile row 712 collects the foreign matter on the back surface of the intermediate transfer belt 6, a non-uniform pre-transfer electric field is not formed in the longitudinal direction, and image defects such as a dust image with longitudinal unevenness can be suppressed. . Here, in order to suppress formation of an unnecessary pre-transfer electric field by the cleaning pile row 712, it is desirable that the resistance value of the cleaning pile row 712 is substantially equal to or higher than the resistance value of the intermediate transfer belt 6.

  Note that the resistance value of the cleaning pile row 712 is about three orders of magnitude higher than the resistance value of the transfer pile row 713 and is about the same as the resistance value of the intermediate transfer belt 6, and is excessive in rubbing with the intermediate transfer belt 6. In a range that does not cause a significant charge-up. On the other hand, the resistance value of the transfer pile row 713 is preferably lower than the resistance value of the intermediate transfer belt 6 for the purpose of flowing a current from the back surface of the intermediate transfer belt 6 to the photosensitive drum 1.

  Details of the configuration of the primary transfer brush 71 of this embodiment will be described below.

  According to FIG. 2, the dimension W in the rotational movement direction of the intermediate transfer belt 6 of the base cloth 711 constituting the primary transfer brush 71 is W = 8 mm. In addition, a dimension L1 in the longitudinal direction, which is the rotation direction of the photosensitive drum 1, perpendicular to the rotational movement direction of the intermediate transfer belt 6 of the base fabric 711 is L1 = 250 mm. Among them, the dimension Wc + Wt in the rotational movement direction of the intermediate transfer belt 6 provided with the conductive fibers in the pile row is a region excluding 0.5 mm at both ends of the width W of the base fabric 711, and Wc + Wt = W− ( 0.5 × 2) = 7 mm. In the rotational movement direction of the intermediate transfer belt 6, Wc is the width of the upstream brush member 712 that is the cleaning pile row, and Wt is the width of the downstream brush member 713 that is the transfer pile row. In the longitudinal direction, which is the rotational axis direction of the photosensitive drum 1, portions (non-raised portions) where fibers are not provided are equally provided with a width of 10 mm at both ends of the base fabric 711. Accordingly, the width L2 of the raised portions in the longitudinal direction, which is the rotational axis direction of the photosensitive drum 1, of the upstream brush member 712 and the downstream brush member 713 which are pile rows on the base cloth 711 is L2 = L1− (10 × 2). = 230 mm.

  The breakdown of the two types of pile rows 712 and 713 in the direction of rotational movement of the intermediate transfer belt 6 in the flocked region of the conductive fibers is shown below. The cleaning pile row 712 has Wc = 3 mm (corresponding to 9 pile rows), and the transfer pile row 713 has Wt = 4 mm (corresponding to 12 pile rows). By setting the width of the cleaning pile row 712 to Wc = 3 mm, it is possible to form a contact surface having a width sufficient to capture foreign matter adhering to the back surface of the intermediate transfer belt 6 with the intermediate transfer belt 6. Further, by setting the width Pt of the transfer pile row 713 to 4 mm, a contact surface having a width sufficient to transfer the toner image on the photosensitive drum 1 to the surface of the intermediate transfer belt 6 with the intermediate transfer belt 6 is formed. be able to.

As the conductive fiber 5α forming the cleaning pile row 712 and the conductive fiber 5β forming the transfer pile row 713, there are materials made of nylon, polyester or the like in which carbon powder is dispersed. As the fibers used for the conductive fibers 5α and 5β, those having a single yarn fineness of 2 to 15 dtex, a diameter of 10 to 40 μm, and a dry strength of 1 to 3 cN / dtex can be used. The resistivity ρfiberα of the conductive fiber 5α is preferably in the range of 10 ⁸ to 10 ¹⁰ Ωcm, and the resistivity ρfiberβ of the conductive fiber 5β is preferably in the range of 10 to 10 ⁶ Ωcm. . The resistivity ρfiber is measured by the following method. That is, 50 fibers are made into one bundle, and a metal probe is brought into contact with the surface of the bundle with an interval of about 10 mm. Then, using a high resistance meter Advantest R8340A or the like, the resistance value Rfiber is measured under an applied voltage of 100 V, and the resistivity ρfiber is calculated by the following equation (1).

ρfiber = Rfiber × (fiber diameter / 2) ² × 3.14 × 50 (1)

The base fabric 711 in which the conductive fibers 5α and the conductive fibers 5β are planted is fixed to a stainless steel substrate 714, and the conductive fibers are raised in a direction perpendicular to the substrate (normal direction). The fiber length starting from the substrate of each fiber can be 3 to 5 mm, and the arrangement density on the substrate can be 5000 to 50000 pieces / cm ² .

  As the primary transfer brush 71 in this embodiment, a brush member having specifications shown in Table 1 below is used as having a typical characteristic.

  A pile fabric type can be used as the cleaning pile row 712 and the transfer pile row 713 on the base fabric of the brush member. The pile woven fabric is made by weaving pile yarns that become brush fibers into a gap between a base fabric 711 made of warp yarns and weft yarns. The primary transfer brush is bonded to the substrate 714 with a conductive adhesive or the like. 71 is obtained.

  The diameter of the photosensitive drum 1 is 20 mm. Further, a primary transfer voltage of 0 to 1.0 kV can be applied to the primary transfer brush 71 from the primary transfer power supply 70.

6). Arrangement of Primary Transfer Brush The arrangement configuration of the primary transfer brush 71 in this embodiment will be described.

  FIG. 3 is a diagram showing the positional relationship of the contact nip D, which is the contact area between each member in the primary transfer portion N1, the photosensitive drum 1 of the primary transfer portion, and the intermediate transfer belt 6. As shown in FIG. The seating surface on the primary transfer brush holding member 72 is located at a distance of 4 mm from the contact surface between the photosensitive drum 1 and the intermediate transfer belt 6, and the leading end of the conductive fiber of the primary transfer brush 71 is substantially on the back surface of the intermediate transfer belt 6. 1 mm intrudes and touches. The force F by which the conductive fibers of the primary transfer brush 71 press the photosensitive drum 1 via the intermediate transfer belt 6 due to its elasticity is 3N.

  The downstream end of the cleaning pile row 712, which is an upstream brush member planted upstream in the rotational movement direction of the intermediate transfer belt 6, is upstream of the contact nip D between the intermediate transfer belt 6 and the photosensitive drum 1. Installed. On the other hand, a transfer pile row 713 which is a downstream brush member installed on the downstream side in the rotational movement direction of the intermediate transfer belt 6 is installed at a position facing the photosensitive drum 1 across the intermediate transfer belt 6. Installed so that the upstream end C of the transfer pile row 713 is located 0.5 mm upstream from the upstream end E of the contact nip D formed from the photosensitive drum 1 and the intermediate transfer belt 6 in the rotational movement direction of the intermediate transfer belt 6. To do. This is because the primary transfer current is always stably applied regardless of variations in the rotational movement direction of the intermediate transfer belt 6 at the position of the transfer brush 71 with respect to the photosensitive drum 1.

  By the way, the intermediate transfer belt 6 which is a belt body suspended by a plurality of rotation shafts has a longitudinal direction due to uneven elasticity in the longitudinal direction which is the rotation axis direction of the photosensitive drum 1 of the belt body and the back of the belt body circumferential length. A wavy shape may occur. FIG. 4A is a schematic perspective view showing the undulation of the intermediate transfer belt 6. Here, as shown in FIG. 4A, a portion where the intermediate transfer belt 6 is convex toward the surface in the contact direction of the photosensitive drum 1 is defined as a convex portion. Further, a portion where the intermediate transfer belt 6 is convex toward the back surface in the contact direction of the primary transfer brush 71 is defined as a concave portion.

  FIG. 4B is a diagram showing the relationship of the wavy amount h of the intermediate transfer belt 6 with respect to the distance from the contact nip D of the primary transfer portion N1 to the upstream side in the rotational movement direction of the intermediate transfer belt 6. Here, the distance from the convex portion or concave portion of the intermediate transfer belt 6 to the belt surface without the undulation is indicated by the undulation amount h. As can be seen from FIG. 4B, the wavy amount h of the intermediate transfer belt 6 increases as the distance from the contact nip D of the primary transfer portion N1, that is, the position of the photosensitive drum shown in FIG.

  Therefore, when the upstream brush member 712, which is a cleaning pile row for the purpose of cleaning the back surface of the intermediate transfer belt 6, is installed in a region where the wavy amount h is large on the intermediate transfer belt 6, the following problems arise. It becomes. In order to bring the conductive fibers into contact with the entire longitudinal direction that is the rotational axis direction of the photosensitive drum 1 including the wavy convex portions of the intermediate transfer belt 6, a longer fiber length is required. In this case, not only may the cost increase due to an increase in the amount of conductive fibers used, but also the pressing force at the undulating recesses will be excessive, leading to scraping of the back surface of the intermediate transfer belt 6.

  However, in this embodiment, the primary transfer brush 71 is brought into contact with the contact nip D of the linear primary transfer portion N1 formed by the contact between the photosensitive drum 1 and the intermediate transfer belt 6. Accordingly, the cleaning pile row 712 formed on the upstream side in the conveying direction of the primary transfer brush 71 can be brought into contact with a portion where the undulation of the intermediate transfer belt 6 is small immediately above the contact nip D. As a result, even if the intermediate transfer belt 6 is wavy, it is possible to remove deposits on the back surface of the intermediate transfer belt 6 without unevenness in the longitudinal direction.

7). Confirmation of Effect In order to examine the effect of the image forming apparatus 100 of the present embodiment, evaluation was performed using an image forming apparatus having a process speed of 116 mm / sec.

  As a comparative example, an image forming apparatus having the same basic configuration as that of the image forming apparatus 100 described above and having the following configuration was used as the primary transfer unit 7. As Comparative Example 1, a primary transfer brush 71 having no cleaning pile row 712 upstream in the rotational movement direction of the intermediate transfer belt 6 was used. That is, the upstream end of the primary transfer brush 71 having the width W = 5 mm in the rotational movement direction of the intermediate transfer belt 6 and the flocked region width Wt = 4 mm of the conductive fiber 5β is upstream of the contact nip D of the primary transfer portion N1. An image forming apparatus installed so as to be located 0.5 mm upstream from the center was used. As Comparative Example 2, although the cleaning pile row 712 is provided upstream of the primary transfer brush 71 in the rotational movement direction of the intermediate transfer belt 6 as in the present embodiment, the resistance value of the cleaning pile row 712 is made equal to that of the transfer pile row 713. An image forming apparatus was used.

  As a long-term paper passing experiment, CS-680 paper (Canon Marketing Japan, trade name) is used as the transfer material SH, and the image ratio of each color of C (cyan), M (magenta), Y (yellow), and K (black) is 25. % 50,000 images were printed. The plain paper mode was used as the image forming mode, and the throughput was 18 sheets per minute.

  In addition, the evaluation images were sampled at the start of the long-term paper passing experiment and every 5,000 images formed during the long-term paper passing experiment. The following were output as evaluation images to be sampled. That is, a solid image, a halftone image, and a character thin line image, which are maximum density level images, are respectively C (cyan), M (magenta), Y (yellow), K (black), R (red), and B (blue). And G (green).

  The sampled evaluation images were ranked and evaluated from the viewpoint of image defects caused by the deposits on the back surface of the intermediate transfer belt 6. As the criteria for ranking, “◯” indicates that no image defect occurred, “Δ” indicates that the image can be confirmed slightly, and “x” indicates that the image can be confirmed. The atmosphere environment in which the experiment was performed is an NN environment having a temperature of 23 ° C. and a humidity of 50%.

  The evaluation results are shown in Table 2.

  In the image forming apparatus 100 of the present embodiment, image defects due to deposits on the back surface of the intermediate transfer belt 6 did not occur up to 50,000 sheets. Further, it was confirmed that scraping powder, toner, paper powder, and the like of the intermediate transfer belt 6 are held in the cleaning pile row 712 after the above durability test. On the other hand, in the image forming apparatus of Comparative Example 1, image defects due to foreign matter on the back surface of the intermediate transfer belt 6 did not occur up to 30,000 sheets, but occurred to a level that can be clearly confirmed from 35,000 sheets onwards. It was confirmed that the vertical streak-like image defect increased with the progress of the durability experiment. In the image forming apparatus of Comparative Example 2, the image defect due to the foreign matter in the back surface of the intermediate transfer belt 6 did not occur up to 35,000 sheets, but occurred to the extent that it can be slightly confirmed from 40,000 sheets or later. It was confirmed that it deteriorated as the durability experiment progressed.

  As described above, in the image forming apparatus 100 of this embodiment, pile rows 712 and 713 made of two types of conductive fibers having different resistances are formed on the primary transfer brush holding member 72 and one base cloth 711 as the primary transfer unit 7. The primary transfer brush 71 is used. Then, the resistance of the pile row 712 planted on the upstream side in the conveying direction is set higher than the resistance of the pile row 713 planted on the downstream side. As a result, it is possible to collect foreign matter existing in the back surface of the intermediate transfer belt 6 and suppress the occurrence of image defects. Needless to say, the present embodiment also has the same effect on foreign matter or the like attached to the back surface of the intermediate transfer belt 6 in the manufacturing process of the image forming apparatus 100.

Example 2
The image forming apparatus according to the present exemplary embodiment is the same as the image forming apparatus 100 according to the first exemplary embodiment in terms of the overall configuration. However, there is a new feature in the configuration of the primary transfer brush 71.

  In the first embodiment, the primary transfer means 7 is composed of the primary transfer brush holding member 72 and one brush member 71. In the present embodiment, the primary transfer means 7 is arranged between the primary transfer brush holding member 72 and each of them. It consists of two opened brush members 712a and 713a.

  FIG. 5 is a diagram showing a positional relationship between each member and the contact nip D in the primary transfer portion N1.

  The primary transfer brush unit 7 of the image forming apparatus 100 according to the present exemplary embodiment includes one primary transfer brush holding member 72 and two brush members 712a and 713a, and the two brush members 712a and 713a are installed in a state of being extremely close to each other. Is done. These two brush members 712a and 713a are composed of a cleaning brush member 712a disposed on the upstream side in the transport direction and a transfer brush member 713a disposed immediately downstream of the cleaning brush member 712a. As the two brush members 712a and 713a, pile rows 712 and 713 in which conductive fibers are densely arranged can be used as in the first embodiment. Here, the electrical resistance of the cleaning brush member 712a is set to be higher than the electrical resistance of the transfer brush member 713a.

  The role of each brush member 712a, 713a is demonstrated.

  The role of the high-resistance cleaning brush member 712a installed on the upstream side in the transport direction is to capture and collect foreign matters such as scraped powder, toner, and paper powder generated in the intermediate transfer belt 6. On the other hand, the role of the low-resistance transfer brush member 713a installed on the downstream side is to primarily transfer the toner image on the photosensitive drum 1 to the surface of the intermediate transfer belt 6 in the primary transfer portion N1. Specific contact configurations of the cleaning brush member 712a and the transfer brush member 713a, configurations of the brush members, and effects thereof will be described below.

1. FIG. 6 shows a schematic perspective view of a cleaning brush member 712a and a transfer brush member 713a used in this embodiment. In this embodiment, the dimension Wc of the cleaning brush member 712a in the rotational movement direction of the intermediate transfer belt 6 is Wc = 4 mm. Among them, the conductive fiber 5α is implanted with a width of 3 mm in the region excluding 0.5 mm upstream and downstream in the rotational movement direction of the intermediate transfer belt 6. By setting Wc = 4 mm, it is possible to form a contact surface having a width sufficient to capture the foreign matter adhering to the back surface of the intermediate transfer belt 6 with the intermediate transfer belt 6. In addition, the specifications such as the longitudinal dimension L1 which is the rotational axis direction of the photosensitive drum 1 of the brush member 712a and the longitudinal dimension L2 of the flocked region are the same as those in the first embodiment. Further, the conductive fiber is the same conductive fiber 5α as the cleaning pile row 712 in the first embodiment. On the other hand, the shape of the transfer brush member 713a is such that the dimension Wt in the rotational movement direction of the intermediate transfer belt 6 is Wt = 5 mm. Among them, the conductive fibers 5β are implanted with a width of 4 mm in the region excluding 0.5 mm upstream and downstream in the rotational movement direction of the intermediate transfer belt 6. By setting Wt = 5 mm, a contact surface having a width sufficient to transfer the toner image on the photosensitive drum 1 to the surface of the intermediate transfer belt 6 with the intermediate transfer belt 6 can be formed. In addition, the specifications such as the longitudinal dimension L1 which is the rotational axis direction of the photosensitive drum 1 of the brush member 713a, the longitudinal dimension L2 of the flocked region, and the like are the same as in the first embodiment. The conductive fiber is the same conductive fiber 5β as the transfer pile row 713 in the first embodiment.

  In addition, as the brush members 712a and 713a in the present embodiment, brush members having specifications shown in Table 3 below are used as having typical characteristics.

2. Arrangement of Brush Member The arrangement configuration of the cleaning brush member 712a and the transfer brush member 713a, which is characteristic in the image forming apparatus of this embodiment, will be described with reference to FIG.

  As a feature of the image forming apparatus 100 of the present embodiment, the two brush members, the cleaning brush member 712a and the transfer brush member 713a, are installed close to one primary transfer brush holding member 72 as a base. The downstream end of the cleaning brush member 712 a installed on the upstream side in the transport direction is installed closer to the upstream side than the contact nip D between the intermediate transfer belt 6 and the photosensitive drum 1. On the other hand, the transfer brush member 713a installed on the downstream side in the rotational movement direction of the intermediate transfer belt 6 is installed at a position facing the photosensitive drum 1 with the intermediate transfer belt 6 interposed therebetween. The upstream end J of the transfer brush member 713a is 0.5 mm upstream from the upstream end I in the rotational movement direction of the intermediate transfer belt 6 in the contact nip D of the primary transfer portion N1 formed from the photosensitive drum 1 and the intermediate transfer belt 6. Install so that it is located.

  As described above, the feature of the present invention is that the cleaning brush member 712a is stably brought into contact with an area where the waviness of the intermediate transfer belt 6 formed upstream of the contact nip D of the primary transfer portion N1 is small. The rear surface of the intermediate transfer belt 6 is cleaned. In the present embodiment, as described above, the two brush members 712a and 713a are arranged close to one primary transfer brush holding member 72. Accordingly, the cleaning brush member 712a installed on the upstream side in the rotational movement direction of the intermediate transfer belt 6 can be brought into contact with a portion where the undulation of the intermediate transfer belt 6 is small immediately above the contact nip D of the primary transfer portion N1. The cleaning brush member 712a is installed so that the distance from the downstream end K of the cleaning brush member 712a in the rotational movement direction of the intermediate transfer belt 6 to the upstream end J of the transfer brush member 713a is 3 mm.

  Further, as described in this embodiment, the following advantages can be obtained by separately providing the brush member 712a responsible for cleaning and the brush member 713a responsible for primary transfer.

  By repeating the image forming operation, the primary transfer brush 71 that rubs the intermediate transfer belt 6 that rotates is inclined in the rotational movement direction of the intermediate transfer belt 6. For this reason, when the pile rows 712 and 713 having different resistances are formed on one base cloth 711 as in the first embodiment, there is the following possibility. As the image forming operation is repeated, the pile row of the brush members 712 and 713 constituting the primary transfer brush 71 is rotated and moved by the friction with the intermediate transfer belt 6 as the intermediate transfer belt 6 rotates. Tilt in the direction. For this reason, the cleaning pile row 712 on the upstream side in the rotational movement direction of the intermediate transfer belt 6 enters the downstream transfer pile row 713 in a part of the longitudinal direction of the photosensitive drum 1 in the rotational axis direction. That is, there is a possibility that the high resistance pile row 712 enters the low resistance pile row 713 and disturbs the transfer electric field formed immediately upstream of the contact nip D of the primary transfer portion N1 due to the low resistance pile row.

  Similarly, the brush members 712a and 713a constituting the primary transfer brush 71 slidably rubbed with the rotating intermediate transfer belt 6 of the present embodiment are also moved in the rotational movement direction of the intermediate transfer belt 6 which is a rubbed material by repeating the image forming operation. Inclined.

  However, in this embodiment, the cleaning brush member 712a having the cleaning pile row 712 and the transfer brush member 713a having the transfer pile row 713 are separated, and a space having a clearance JK is provided therebetween. Therefore, it is possible to prevent the cleaning pile row 712 from immediately entering the transfer pile row 713 constituting the transfer brush member 713a even when a part of the cleaning brush member 712a is inclined downstream by repeating the image forming operation. Therefore, a good image can be obtained without disturbing the pre-transfer electric field formed by the transfer brush member 713a. In the configuration of this embodiment, the clearance between the downstream end of the cleaning brush member 712a in the rotational movement direction of the intermediate transfer belt 6 and the upstream end of the transfer brush member 713a is considered in consideration of the inclination of the cleaning brush member 712a due to long-term paper passing. The JK is desirably 2 mm or more. In consideration of the cleaning property of the back surface of the intermediate transfer belt 6, the downstream end K of the cleaning brush member 712 a in the rotational movement direction of the intermediate transfer belt 6 is within 4 mm upstream from the contact position between the photosensitive drum 1 and the intermediate transfer belt 6. It is desirable to be in the position.

3. Confirmation of Effect In order to confirm the effect of this example, the same evaluation as in Example 1 was performed. Evaluation conditions and the like are the same as those in Example 1.

  As a result of the evaluation, in the image forming apparatus 100 of the present embodiment, image defects due to deposits on the back surface of the intermediate transfer belt 6 did not occur up to 50,000 sheets. Further, the downstream end K of the cleaning brush member 712a after the long-term paper passing experiment was confirmed. The downstream end K of the cleaning brush member 712a is a part of the longitudinal direction that is the rotational axis direction of the photosensitive drum 1, and there is a portion that is inclined to the downstream side in the rotational movement direction of the intermediate transfer belt 6, but the transfer brush member 713a. Was not in contact with the upstream end J.

  From the above evaluation results, in this embodiment, as the primary transfer means 7, the cleaning brush member 712a and the transfer brush member 713a are arranged close to each other with the clearance JK provided on one primary transfer brush holding member 72. In addition, the resistance of the cleaning brush member 712a is set higher than the resistance of the transfer brush member 713a. Accordingly, it is possible to not only collect foreign matters existing on the back surface of the intermediate transfer belt 6 and suppress the occurrence of image defects, but also suppress the occurrence of image defects due to the fall of the pile of the cleaning brush member 712a.

Example 3
The image forming apparatus according to the present exemplary embodiment is the same as the image forming apparatus 100 according to the first exemplary embodiment in terms of the overall configuration. However, in Example 1, the primary transfer brush 71 was composed of pile rows 712 and 713 of two kinds of conductive fibers having different resistance values. On the other hand, the present embodiment is different in that the primary transfer brush 71 is composed of pile rows 712, 713, and 715 of three kinds of conductive fibers having different resistance values.

  FIG. 7 is a diagram showing the positional relationship between each member and the contact nip D in the primary transfer portion N1.

  The primary transfer brush unit 7 of the image forming apparatus 100 according to the present exemplary embodiment includes a primary transfer brush holding member 72 and a primary transfer brush 71 having three types of pile rows. These three pile rows are sandwiched between the two types of pile rows, a cleaning pile row 712 that is an upstream brush member arranged on the most upstream side in the conveying direction, a transfer pile row 713 that is a downstream brush member arranged on the most downstream side, and the above two types of pile rows. This is an intermediate pile row 715 that is an intermediate brush member that is arranged. The three pile rows are pile rows in which conductive fibers are densely arranged as in the first embodiment. The electrical resistance of the cleaning pile row 712 is set to be higher than that of the intermediate pile row 715, and the electrical resistance of the intermediate pile row 715 is set to be higher than that of the transfer pile row 713.

  The role of each pile row with different electrical resistance will be described.

  As in the first exemplary embodiment, the role of the high resistance cleaning pile row 712 disposed on the most upstream side in the rotational movement direction of the intermediate transfer belt 6 is to remove scraps of particles generated in the intermediate transfer belt 6, toner and paper. The purpose is to capture and collect foreign substances such as powder. On the other hand, the role of the low resistance transfer pile row 713 installed on the most downstream side is to primarily transfer the toner image on the photosensitive drum 1 onto the surface of the intermediate transfer belt 6 in the primary transfer portion N1. The intermediate pile row 715 located in the middle of them has the same role as the clearance JK between the cleaning brush member 712a and the transfer brush member 713a of the second embodiment. That is, the role of the clearance JK is to suppress the disturbance of the transfer electric field caused by the high resistance brush member 712 tilting and entering the low resistance brush member 713. Specific configurations of the cleaning pile row 712, the intermediate pile row 715, and the transfer pile row 713 and their effects will be described below.

1. Primary Transfer Brush Member FIG. 8 is a schematic perspective view of the primary transfer brush 71 used in this embodiment. In this embodiment, the dimension W of the primary transfer brush 71 in the rotational movement direction of the intermediate transfer belt 6 is W = 10 mm. Among them, the conductive fibers are provided in a region excluding both ends 0.5 mm in the rotational movement direction of the intermediate transfer belt 6.

  The breakdown of the three types of pile rows 712, 713, and 715 in the direction of rotational movement of the intermediate transfer belt 6 in the flocked region of conductive fibers is shown below.

  In the uppermost stream, as the cleaning pile row 712, the conductive fibers 5α are implanted with a width of Wc = 3 mm (corresponding to 9 pile rows). By setting Wc = 3 mm, it is possible to form a contact surface having a width sufficient to capture foreign matter adhering to the back surface of the intermediate transfer belt 6 with the intermediate transfer belt 6. Immediately downstream of the cleaning pile row 712, as an intermediate pile row 715, the conductive fibers 5γ are implanted with a width of Wm = 2 mm (corresponding to 6 pile rows). By setting Wm = 2 mm, it is possible to prevent the conductive fibers 5α of the cleaning pile row 712 from entering the transfer pile row 713 even when the cleaning pile row 712 is inclined downstream in the transport direction by repeating the image forming operation. be able to. On the most downstream side, as the transfer pile row 713, the conductive fibers 5β are implanted with a width of Wt = 4 mm (corresponding to 12 pile rows). By setting Wt = 4 mm, a contact surface with the intermediate transfer belt 6 having a width sufficient to transfer the toner image on the photosensitive drum 1 to the surface of the intermediate transfer belt 6 with the intermediate transfer belt 6 can be formed. it can. In addition, the specifications such as the longitudinal dimension L1 in the longitudinal direction which is the rotational axis direction of the photosensitive drum 1 of the brush member 712 and the longitudinal dimension L2 of the flocked region are the same as those in the first embodiment.

The conductive fibers 5α forming the cleaning pile row 712 and the conductive fibers 5β forming the transfer pile row 713 are the same as those in the first embodiment. The conductive fiber 5γ forming the intermediate pile row 715 is the same as the conductive fiber 5α and the conductive fiber 5β, and the resistivity ρfiberγ is preferably in the range of 10 ⁸ to 10 ⁹ Ωcm. It is.

  In addition, as each pile row | line | column 712, 713, 715 which is a brush member in a present Example, the pile row | line | column of the specification of following Table 4 is used as what has a typical characteristic.

2. Arrangement of Brush Member The arrangement of the primary transfer brush 71 of this embodiment will be described with reference to FIG.

  The primary transfer brush 71 is installed on a primary transfer brush holding member 72 that is a base. In the primary transfer brush 71, the upstream end P of the transfer pile row 713 installed on the most downstream side in the transport direction is upstream in the transport direction of the contact nip D of the primary transfer portion N1 formed from the photosensitive drum 1 and the intermediate transfer belt 6. Install so that it is located 0.5 mm upstream from the end Q.

  As described above, the feature of the present invention is that the intermediate position of the intermediate transfer belt 6 formed upstream of the contact portion D of the primary transfer nip is brought into contact with the region where the waviness of the intermediate transfer belt 6 is small so that the intermediate position can be stably achieved. The rear surface of the transfer belt 6 is cleaned. In this embodiment, since the cleaning pile row 712 and the transfer pile row 713 are formed on the same base cloth 711 as in the first embodiment, the cleaning pile row 712 is just above the contact nip D of the primary transfer portion N1. The intermediate transfer belt 6 can be brought into contact with a portion where the undulation is small. In addition, there is an advantage that the relative position of the cleaning pile row 712 and the transfer pile row 713 does not depend on the variation in the attachment position of the brush member. Due to this merit, the cleaning pile row 712 is brought into contact with the primary transfer portion N1 as compared with the second embodiment in which the high resistance brush member 712a as a cleaning brush member and the low resistance brush member 713a as a transfer brush member are separated. It can be installed near the nip D.

3. Confirmation of Effect In order to confirm the effect of this example, the same evaluation as in Example 1 was performed. Evaluation conditions and the like are the same as those in Example 1.

  As a result of the evaluation, in the image forming apparatus 100 of the present embodiment, image defects due to deposits on the back surface of the intermediate transfer belt 6 did not occur up to 50,000 sheets.

  From the above evaluation results, in this embodiment, as the primary transfer means 7, pile rows 712, 715, and 713 made of three types of conductive fibers having different resistances are provided on the primary transfer brush holding member 72 and one base cloth 711. Using the primary transfer brush 71 that has been flocked, the resistance of the pile row 712 that has been flocked upstream in the conveying direction is set to be higher than the resistance of the pile row 715 or 713 that has been flocked to the downstream side. As a result, it is possible to collect foreign matter existing in the back surface of the intermediate transfer belt 6 and suppress the occurrence of image defects.

  The image forming apparatus 100 in the above embodiment has been described as a configuration in which the toner image on the photosensitive drum 1 is directly transferred directly to the intermediate transfer belt 6 which is an intermediate transfer member of the belt, and then secondarily transferred to the transfer material SH. . However, the present invention is not limited to the case where the belt body as described above is an intermediate transfer belt. The present invention can also be applied to an image forming apparatus having a transfer material conveyance belt as a belt body that carries and conveys the transfer material SH, and can achieve the same effects. More specifically, it is as follows.

  In an image forming apparatus having a transfer material conveyance belt as a configuration, a toner image on a photosensitive drum that is indirectly in contact with the transfer material on the transfer material conveyance belt is transferred by a transfer unit. The transfer material conveyance belt carries the transfer material, and the back surface is in contact with the transfer means at the transfer portion which is a contact portion between the transfer material and the photosensitive drum. Similar to the above-described intermediate transfer belt, toner, paper powder, scraped powder of the same part due to use, and the like easily enter the back side of the transfer material conveyance belt. There is a problem that an image defect occurs due to the staying of these deposits on the transfer member. In order to solve this problem, by applying a transfer unit having the same configuration as that of the above-described embodiment, it is possible to suppress image defects by transferring while cleaning the deposit on the back surface.

1 Photosensitive drum (image carrier)
6 Intermediate transfer belt (belt body)
7 Primary transfer means (transfer means)
71 Brush 72 Primary transfer brush holding member (brush holding means)
711 Base cloth 712, 712a Upstream brush member 713, 713a Downstream brush member 715 Intermediate brush member SH Transfer material

Claims (10)

An image carrier for carrying a toner image;
A toner image is transferred from the image carrier, or a belt that conveys a transfer material to which the toner image is transferred;
Transfer means for transferring a toner image from the image carrier to the belt body;
In an image forming apparatus having
The transfer means includes a brush that contacts and rubs with the belt body, and a brush holding means that holds the brush,
The brush is composed of a plurality of brush members having different electric resistances,
The electrical resistance of the upstream brush member disposed on the upstream side in the rotational movement direction of the belt body is higher than the electrical resistance of the downstream brush member disposed on the downstream side,
The upstream brush member has an electrical resistance substantially equal to or higher than the electrical resistance of the belt body, and is disposed upstream of a contact area of the belt body and the image carrier. ,
The downstream brush member has an electrical resistance lower than that of the belt body, and is disposed in a contact area between the belt body and the image carrier.   The image forming apparatus according to claim 1, wherein the upstream brush member and the downstream brush member are configured by pile rows having different electric resistances formed on the same base cloth.   The upstream brush member and the downstream brush member are composed of pile rows having different electric resistances formed on different base fabrics, and are arranged in the brush holding means with a space in the rotational movement direction of the belt body. The image forming apparatus according to claim 1. The plurality of brush members including the upstream brush member and the downstream brush member are composed of pile rows having different electric resistances formed on the same base cloth,
On the same base cloth between the upstream brush member and the downstream brush member, there is an intermediate brush member composed of a pile row of electrical resistance different from that of the upstream brush member and the downstream brush member,
The intermediate brush member has an electric resistance substantially equal to or higher than an electric resistance of the belt body, and an electric resistance lower than that of the upstream brush member. Item 2. The image forming apparatus according to Item 1. An image carrier for carrying a toner image;
A toner image is transferred from the image carrier, or a belt that conveys a transfer material to which the toner image is transferred;
Transfer means for transferring a toner image from the image carrier to the belt body;
In an image forming apparatus having
The transfer means includes a brush that contacts and rubs with the belt body, and a brush holding means that holds the brush,
The brush is composed of a plurality of brush members having different electric resistances,
The electrical resistance of the upstream brush member disposed on the upstream side in the rotational movement direction of the belt body is higher than the electrical resistance of the downstream brush member disposed on the downstream side,
The image forming apparatus according to claim 1, wherein the upstream brush member is disposed upstream of a contact area between the image carrier and the belt body with respect to a rotational movement direction of the belt body.   The image forming apparatus according to claim 5, wherein the upstream brush member and the downstream brush member are adjacent to and in contact with each other.   The image forming apparatus according to claim 6, wherein the upstream brush member and the downstream brush member are implanted into one base cloth.   The said upstream brush member is provided with the electrical resistance substantially equivalent to the electrical resistance of the said belt body, or higher than the electrical resistance of the said belt body, The Claim 7 characterized by the above-mentioned. Image forming apparatus.   The image forming apparatus according to claim 5, wherein the downstream brush member has an electric resistance lower than an electric resistance of the belt body.   10. The image forming apparatus according to claim 5, wherein a voltage having the same magnitude is applied to the upstream brush member and the downstream brush member. 11.

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