JP6108749B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an electrophotographic or electrostatic recording type image forming apparatus, and more particularly to an image forming apparatus having a brush-like transfer means.

  2. Description of the Related Art Conventionally, as an image forming apparatus such as a copying machine or a printer using an electrophotographic system, there is an intermediate transfer system using an intermediate transfer belt. In an intermediate transfer belt type image forming apparatus, a full-color image is formed through a primary transfer process and a secondary transfer process. In the primary transfer step, the toner image formed on the surface of the photoconductor as the image carrier is transferred onto the intermediate transfer belt. This primary transfer process is repeatedly executed for a plurality of color toner images, whereby a plurality of color toner images are formed on the surface of the intermediate transfer belt. In the secondary transfer process, toner images of a plurality of colors formed on the surface of the intermediate transfer belt are collectively transferred onto the surface of a transfer material such as paper. The toner image transferred onto the surface of the transfer material is then fixed to the transfer material by a fixing unit. Thereby, a full color image is obtained.

  For example, as the primary transfer unit in the above-described intermediate transfer type image forming apparatus, a roller-type transfer unit, a blade-type transfer unit, a brush-type transfer unit, or the like is used. These transfer units are brought into contact with the back surface of the intermediate transfer belt at a position facing the photoconductor, and are used with a primary transfer voltage applied. Among the various transfer means described above, the brush-like transfer means is constituted by a group of conductive fibers, and each of the fibers can be in contact with the back surface of the intermediate transfer belt independently. Therefore, the contact unevenness that may occur when using a roller-shaped transfer unit or a blade-shaped transfer unit is improved, and more uniform contact with the back surface of the intermediate transfer belt can be obtained. As a result, image defects such as density unevenness that occur in the primary transfer step are satisfactorily suppressed.

  As a method of contacting the back surface of the belt with the brush-shaped transfer means, there is known a method in which the fibers are brought into contact with the back surface of the belt in a state where the fibers are tilted downstream in the belt moving direction (Patent Document 1). ). Thereby, it can suppress that a fiber falls down to the moving direction upstream and downstream of a belt at random, and can restrict a falling direction to a downstream. Therefore, abnormal discharge occurring on the upstream side of the transfer portion is suppressed, and image defects such as vertical stripes are suppressed satisfactorily.

JP 2001-134115 A

  For example, in the intermediate transfer type image forming apparatus as described above, the posture of the intermediate transfer belt in the primary transfer unit is generally such that the photoconductor from the surface side of the intermediate transfer belt stretched around a plurality of rollers. It is determined by intrusion. The brush-like transfer means abuts against such an intermediate transfer belt from the back side of the intermediate transfer belt.

  When the brush-like transfer unit is brought into contact with the back surface of the intermediate transfer belt, the brush-like transfer unit is formed between the intermediate transfer belt and the brush-like transfer unit when the mounting position of the brush-like transfer unit is deviated from a desired position. The nip (back nip) is also displaced from the target position.

  In particular, such a back surface nip position shift becomes prominent when the attachment position of the brush-like transfer unit is shifted along the normal direction of the intermediate transfer belt. For example, when the attachment position of the brush-like transfer means on the back surface of the intermediate transfer belt is closer to the back surface of the intermediate transfer belt than the desired position (the amount of intrusion increases), the pressure at the back surface nip increases and the fibers are in the middle. The transfer belt may fall greatly downstream in the moving direction. As a result, the position of the back surface nip moves to the downstream side in the moving direction of the intermediate transfer belt from the target position. On the other hand, if the attachment position of the brush-like transfer means with respect to the back surface of the intermediate transfer belt is further away from the back surface of the intermediate transfer belt than the desired position (the amount of intrusion decreases), the pressure at the back surface nip decreases, and the degree of fiber collapse Becomes smaller. As a result, the position of the back surface nip moves to the upstream side in the moving direction of the intermediate transfer belt from the target position.

  As described above, in the image forming apparatus using the brush-like transfer unit, the back surface nip may move greatly in the moving direction of the intermediate transfer belt on the downstream side depending on the mounting position of the transfer unit. If the back surface nip deviates greatly from the position facing the photoconductor, good primary transferability is impaired.

  Here, it is conceivable to manage and improve the dimensional tolerances and positioning accuracy of the component parts so that the mounting position of the brush-like transfer means in the image forming apparatus is always a desired position. However, it is not easy considering variations in manufacturing parts and assembling devices.

  Although the conventional problems have been described with an intermediate transfer type image forming apparatus as an example, a direct transfer type image in which a toner image is directly transferred from a photosensitive member onto a transfer material carried on a transfer material conveyance belt. In the forming apparatus, a similar problem may occur with respect to the transfer portion.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus in which the position of a nip formed between a belt and a brush-like transfer means can be prevented from shifting due to variations in component mounting positions and component dimensions. It is to be.

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, an endless belt that can move in contact with the image carrier, and a toner image that is transferred from the image carrier to the belt. Transfer means, wherein the transfer means includes a conductive fiber and a substrate for holding the fiber, and the fiber contacts the inner peripheral surface of the belt. An urging member that urges the belt toward the belt; and a guide member that regulates a moving direction of the transfer means. The contact portion where the image carrier and the belt are in contact with each other, the belt, and the transfer means. Only the transfer unit of the image carrier and the transfer unit is in contact with the belt on the downstream side of the first region with respect to the first region where the contact part is in contact with the moving direction of the belt. A second region and said Only the transfer unit of the image carrier and the transfer means upstream of the one region that is an image forming apparatus, wherein a third region in contact with the belt is formed.

  According to the present invention, it is possible to prevent the position of the nip formed between the belt and the brush-like transfer unit from being shifted due to variations in component mounting positions and component dimensions.

1 is a schematic cross-sectional view of an image forming apparatus according to an embodiment of the present invention. It is a typical perspective view of the primary transfer brush in one Example of this invention. FIG. 5 is a schematic cross-sectional view showing a positional relationship between each member of the primary transfer portion and a nip in an embodiment of the present invention. FIG. 3 is a schematic perspective view of one end portion in the longitudinal direction of the primary transfer brush for explaining the contact means of the primary transfer brush in one embodiment of the present invention. FIG. 6 is a schematic cross-sectional view for explaining the influence of variation in the direction along the moving direction of the intermediate transfer belt at the guide rail mounting position in an embodiment of the present invention. FIG. 6 is a schematic cross-sectional view for explaining the influence of the variation in the direction along the normal direction of the intermediate transfer belt at the guide rail mounting position in one embodiment of the present invention. It is typical sectional drawing which shows the positional relationship of each member and nip of the primary transfer part in one comparative example. It is typical sectional drawing for demonstrating the influence of the dispersion | variation in the attachment position of the primary transfer brush in one comparative example. It is typical sectional drawing which shows the positional relationship of each member and nip of the primary transfer part in the other Example of this invention. It is typical sectional drawing for demonstrating the influence of the dispersion | variation in the fiber length of the primary transfer brush in the other Example of this invention. It is typical sectional drawing which shows the positional relationship of each member and nip of the primary transfer part in another comparative example. It is typical sectional drawing for demonstrating the influence of the dispersion | variation in the fiber length of the primary transfer brush in another comparative example. It is typical sectional drawing which shows the positional relationship of each member and nip of the primary transfer part in the other Example of this invention. It is a typical perspective view of the primary transfer brush in the further another Example of this invention. It is typical sectional drawing which shows the positional relationship of each member of a primary transfer part and nip in the further another Example of this invention. FIG. 10 is a schematic cross-sectional view illustrating a configuration example of another image forming apparatus to which the present invention can be applied.

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

Example 1
1. First, the overall configuration and operation of an image forming apparatus according to an embodiment of the present invention will be described.

  FIG. 1 is a schematic cross-sectional view of a main part of the image forming apparatus 100 of the present embodiment. The image forming apparatus 100 according to the present exemplary embodiment is a tandem type full color laser beam printer that employs an intermediate transfer method and can form a full color image using an electrophotographic method.

  The image forming apparatus 100 primarily superimposes each color toner image formed according to the image information separated into a plurality of color components on the intermediate transfer belt 6 as an intermediate transfer member, and then primarily transfers the toner image onto the transfer material P. Secondary transfer at once. A recorded image is obtained by fixing the toner image on a transfer material. The image forming apparatus 100 includes first, second, third, and fourth stations Sa, Sb, Sc, and Sd as a plurality of image forming units. In the present embodiment, the first to fourth stations Sa to Sd form toner images of respective colors of yellow (Y), magenta (M), cyan (C), and black (K).

  In the present embodiment, the configurations and operations of the first to fourth stations Sa to Sd are substantially the same except that the color of the toner used is different. Therefore, in the following, when there is no need for distinction, a description will be given collectively with a, b, c, and d at the end of a symbol indicating an element provided for any color being omitted.

  The station S has a photosensitive drum 1 which is a photosensitive member as an image carrier. The photosensitive drum 1 is rotationally driven in the direction of arrow R1 (counterclockwise) in the figure by a motor (not shown) as a driving means. Around the photosensitive drum 1, the following units are provided in order along the rotation direction. First, the charging roller 2 is a roller-shaped charging member as charging means. Next, an exposure apparatus (laser scanner) 3 as an exposure unit. Next, there is a developing device 4 as a developing unit. Next, there is a primary transfer means 5 which is a primary transfer brush provided with a brush-shaped transfer member. Next, a drum cleaner 7 as a photosensitive member cleaning unit.

  Further, an intermediate transfer belt 6 that is an endless belt as an intermediate transfer member is disposed so as to face each photosensitive drum 1 of each station S. The intermediate transfer belt 6 is formed of a cylindrical and endless film, and is 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 (rotates) in the direction indicated by the arrow R3 (clockwise) in the figure by driving the drive roller 61 in the direction indicated by the arrow R2 (clockwise) in the figure. In this embodiment, the moving speed (peripheral speed) of the surface of the photosensitive drum 1 and the moving speed (peripheral speed) of the surface of the intermediate transfer belt 6 are substantially the same speed. On the inner peripheral surface (back surface) side of the intermediate transfer belt 6, each primary transfer unit 5 is disposed at a position facing each photosensitive drum 1 with the intermediate transfer belt 6 interposed therebetween. As will be described in detail later, the primary transfer unit 5 is pressed against the back surface of the intermediate transfer belt 6. Thus, the primary transfer portion B1 is formed by the contact between the photosensitive drum 1 and the intermediate transfer belt 6. On the outer peripheral surface (front surface) side of the intermediate transfer belt 6, a secondary transfer member, which is a roller-like transfer member, is disposed at a position facing the secondary transfer counter roller 62 across the intermediate transfer belt 6. A transfer roller 8 is disposed. The secondary transfer roller 8 is pressed against the secondary transfer counter roller 62 via the intermediate transfer belt 6. As a result, the intermediate transfer belt 6 and the secondary transfer roller 8 come into contact with each other to form the secondary transfer portion B2. A belt cleaner 65 serving as an intermediate transfer member cleaning unit is disposed at a position facing the driving roller 61 with the intermediate transfer belt 6 interposed therebetween.

  At the time of image formation, the surface of the rotating photosensitive drum 1 is uniformly charged by the charging roller 2. At this time, a predetermined charging voltage (charging bias) is applied to the charging roller 2 from a charging power source (not shown) as a charging voltage applying means. The surface of the charged photosensitive drum 1 is irradiated with laser light L according to the image information from the exposure device 3. As a result, an electrostatic latent image (electrostatic image) is formed on the photosensitive drum 1.

  The electrostatic latent image formed on the photosensitive drum 1 is developed (visualized) as a toner image by the developing device 4. The developing device 4 carries toner as a developer on a rotatable developer carrying member and conveys the toner to a portion facing the photosensitive drum 1 (development position). The developing device 4 performs photosensitivity according to the electrostatic latent image on the photosensitive drum 1. Toner is supplied onto the drum 1. At this time, a predetermined developing voltage (developing bias) is applied to the developer carrying member from a developing power source (not shown) as a developing voltage applying means. In this embodiment, the developing device 4 develops the electrostatic latent image on the photosensitive drum 1 by a reversal development method. That is, the developing device 4 is exposed to the charged polarity (negative polarity in this embodiment) of the photosensitive drum 1 on the image portion (exposure portion) on the photosensitive drum 1 that has been exposed after the charging process and the absolute value of the potential has decreased. The electrostatic latent image is developed by attaching toner charged to the same polarity.

  The toner image formed on the rotating photosensitive drum 1 is transferred (primary transfer) onto the rotating intermediate transfer belt 6 by the action of the primary transfer means 5 in the primary transfer portion B1. At this time, the primary transfer means 5 is supplied with a polarity opposite to the normal charging polarity (negative polarity in this embodiment) of the toner forming the toner image from the primary transfer power supply 50 as the primary transfer voltage application means. In this case, a primary transfer voltage (primary transfer bias) which is a DC voltage having a positive polarity is applied.

  Toner remaining on the photosensitive drum 1 without being transferred to the intermediate transfer belt 6 in the primary transfer step (primary transfer residual toner) is cleaned by a drum cleaner 7. The drum cleaner 7 includes a cleaning blade 71 that is a plate-like elastic body that comes into contact with the surface of the photosensitive drum 1, and a collected toner container 72. The cleaning blade 71 is a cleaning member for removing toner adhering to the surface of the photosensitive drum 1. The toner removed from the surface of the photosensitive drum 1 rotated by the cleaning blade 71 is collected in a collected toner container 72.

  For example, when a full-color image is formed, the charging, exposure, development, and primary transfer processes as described above are performed in order from the upstream side in the movement direction of the surface of the intermediate transfer belt 6 in order from the first to fourth stations Sa to Sd. Done in As a result, a multi-toner image for a full-color image is formed on the intermediate transfer belt 6 by transferring toner images of four colors of yellow, magenta, cyan, and black.

  The toner image on the intermediate transfer belt 6 is transferred (secondary transfer) onto the transfer material P by the action of the secondary transfer roller 8 in the secondary transfer portion B2. That is, in the transfer material supply unit 20, the transfer material P accommodated in the cassette 21 is fed by the supply roller 22 and then supplied to the secondary transfer unit B 2 by the registration roller 23 at a predetermined timing. At substantially the same time, the secondary transfer roller 8 receives a secondary transfer voltage from the secondary transfer power supply 80 as a secondary transfer voltage application unit, which is a DC voltage having a polarity opposite to the normal charging polarity of the toner forming the toner image. A voltage (secondary transfer bias) is applied.

  The toner remaining on the intermediate transfer belt 6 without being transferred to the transfer material P in the secondary transfer process (secondary transfer residual toner) is cleaned by the belt cleaner 65. The belt cleaner 65 includes a cleaning blade 64 that is a plate-like elastic body that comes into contact with the surface of the intermediate transfer belt 6, and a collected toner container 66. The cleaning blade 64 is a cleaning member for removing toner adhering to the surface of the intermediate transfer belt 6. The toner removed from the surface of the intermediate transfer belt 6 rotated by the cleaning blade 64 is collected in a collected toner container 66.

  The transfer material P onto which the toner image is secondarily transferred is conveyed to a fixing device 9 as a fixing unit. The fixing device 9 heats and pressurizes the transfer material P while conveying it. The unfixed toner image on the transfer material P is fixed on the transfer material P by heat and pressure. Thereafter, the transfer material P is conveyed outside the apparatus by a conveyance roller (not shown).

  Here, the image forming apparatus 100 of the present embodiment is a printer that supports image formation on an A4 size transfer material P having a process speed corresponding to the peripheral speed of the photosensitive drum 1 and the intermediate transfer belt 6 of 116 mm / s. is there. In this embodiment, the photosensitive drum 1 has a diameter of 20 mm.

In this embodiment, a polyimide resin film having a thickness of 60 μm and a volume resistivity adjusted to 10 ⁹ Ωcm by mixing a conductive agent was used as the intermediate transfer belt 6. 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 by the tension roller 63.

In this embodiment, an elastic roller having a volume resistivity of 10 ⁷ to 10 ⁹ Ωcm and a hardness of 30 ° to 40 ° is used as the secondary transfer roller 8. 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. The secondary transfer roller 8 is driven to rotate as the intermediate transfer belt 6 rotates. 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.

2. Primary Transfer Unit Next, the configuration of the primary transfer unit 5 will be described.

  FIG. 2 is a schematic perspective view showing the configuration of the primary transfer means 5. As the primary transfer means 5, a primary transfer brush 5 including a brush member in which brush fibers 51 formed of conductive fibers (conductive fibers) are densely arranged can be used.

  In this embodiment, the dimension W in the short direction of the primary transfer brush 5 is 4 mm. The short side direction of the primary transfer brush 5 is a direction in which the primary transfer brush 5 is arranged substantially perpendicular to the rotation axis direction of the photosensitive drum 1 (substantially parallel to the moving direction of the intermediate transfer belt 6). In this embodiment, the dimension L in the longitudinal direction of the primary transfer brush 5 is 250 mm. The longitudinal direction of the primary transfer brush 5 is a direction arranged substantially parallel to the rotational axis direction of the photosensitive drum 1 (a direction substantially perpendicular to the moving direction of the intermediate transfer belt 6). However, of the dimension L in the longitudinal direction of the primary transfer brush 5, the dimension K of the region (raised portion) 5A where the brush fibers 51 are provided is 230 mm. In addition, at both ends in the longitudinal direction of the primary transfer brush 5, regions (non-raised portions) 5 </ b> B, each having a dimension J of 10 mm, where the brush fibers 51 are not provided are provided substantially evenly.

  In this embodiment, by setting the dimension W in the short direction of the primary transfer brush 5 to 4 mm, a sufficiently wide nip (described later) can be formed between the primary transfer brush 5 and the intermediate transfer belt 6. . Further, by setting the dimension K of the raised portion 5A in the longitudinal direction of the primary transfer brush 5 to 230 mm, the primary transfer means can also serve as the primary transfer means for the width in the same direction of the A4 size transfer material P conveyed to the primary transfer portion B1. A sufficient width can be obtained.

  As the brush member of the primary transfer brush 5, a pile fabric type brush member or an electrostatic flocking type brush member can be preferably used.

  The pile woven fabric is formed by weaving pile yarns to be the brush fibers 51 into a gap between base fabrics composed of warp yarns and weft yarns. A brush member can be obtained by fixing it on the substrate 52 with a conductive adhesive or the like.

  Electrostatic flocking is a method in which short fibers that become brush fibers 51 are thrown substantially vertically onto a substrate 52 that has been previously coated with an adhesive, using electrostatic attraction in a high-voltage electrostatic field. A brush member is also obtained.

As the brush fiber 51, a conductive fiber (conductive fiber), in particular, a synthetic fiber containing a conductive agent can be preferably used. For example, a material made of nylon, polyester or the like in which carbon powder is dispersed can be preferably used. A single yarn having a 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 preferably used. The resistivity ρfiber of the brush fiber 51 is preferably in the range of 10 ² to 10 ⁸ Ωcm from the viewpoint of improving transfer efficiency.

The resistivity ρfiber is measured by the following method. A bundle of 50 fibers is made, and a metal probe is brought into contact with the surface of the bundle at an interval of about 1 cm. Then, using a high resistance meter Advantest R8340A (manufactured by Advantest Co., Ltd.) or the like, the resistance value Rfiber is measured with an applied voltage of 100 V, and the resistivity ρfiber is calculated by the following equation.
ρfiber = Rfiber × (fiber diameter / 2) ² × 3.14 × 50

  In this embodiment, the primary transfer brush 5 is configured by fixing a pile fabric formed of a base fabric and pile yarns to an upper surface 52A of a substantially uniformly flat substrate 52 made of stainless steel. In the present embodiment, the substrate 52 is a rectangular sheet metal having a dimension in the short side direction as W described above and a dimension in the longitudinal direction as L described above. In this embodiment, the brush fibers 51 formed of pile yarns of a pile fabric are raised in a direction (normal direction) substantially perpendicular to the upper surface 52A of the substrate 52.

The brush fibers 51 extend from the upper surface 52A of the substrate 52 in a state where they are not in contact with the intermediate transfer belt 6 (that is, when they are not deformed by being in contact with the intermediate transfer belt 6). The direction in which it is present is called the “raised direction”. The raising direction of the brush fibers 51 in this embodiment will be described later. The length (fiber length) starting from the substrate 52 of each brush fiber 51 can be set to 1 to 5 mm, for example. The arrangement density of the conductive wires 51 on the substrate 52 can be set to 5000 to 50000 lines / cm ² , for example.

  In the drawing, the base fabric constituting the pile fabric of the primary transfer brush 5 is not shown.

  In this embodiment, a brush member having the following specifications was used as the brush member of the primary transfer brush 5 having typical characteristics.

<Specifications of primary transfer brush>
-Material type: Pile fabric-Brush fiber material: Nylon fiber in which carbon powder is dispersed-Single yarn fineness of brush fiber: 7 dtex
・ Brush fiber diameter: 28 μm
-Dry strength of brush fibers: 1.6 cN / dtex
・ Brush fiber resistivity: 10 ⁶ Ωcm
・ Fiber length: 2mm
Array density: 10850 / cm ²

  The primary transfer brush 5 is brought into contact with the back surface of the intermediate transfer belt 6 at a position facing the photosensitive drum 1 through the intermediate transfer belt 6.

  A primary transfer voltage from 0 to 1.0 kV can be applied to the brush member of the primary transfer brush 5 from the primary transfer power supply 50.

3. Next, the configuration of the contact means of the primary transfer brush 5 will be described.

  Conventionally, when the primary transfer brush 5 is brought into contact with the back surface of the intermediate transfer belt 6, the primary transfer brush 5 is formed between the intermediate transfer belt 6 and the primary transfer brush 5 when the attachment position of the primary transfer brush 5 deviates from a desired position. There is a problem that the nip (back nip) is displaced from the target position. In particular, such a back surface nip position shift becomes significant when the attachment position of the primary transfer brush 5 is shifted along the normal direction of the intermediate transfer belt 6.

  One of the purposes of the present embodiment is to stably maintain the nip formed between the intermediate transfer belt 6 and the primary transfer brush 5 at a target position at all times regardless of variations in component mounting position and component dimensions. In other words, good primary transferability can be obtained.

  Therefore, in this embodiment, the image forming apparatus 100 includes an abutting unit 10 that abuts the primary transfer brush 5 against the intermediate transfer belt 6 (FIG. 3). The contact means 10 includes a biasing member for biasing the primary transfer brush 5 to the intermediate transfer belt 6 and a guide member for regulating the movable direction of the primary transfer brush 5. The urging member urges the primary transfer brush 5 to the intermediate transfer belt 6 so that the brush fibers 51 of the primary transfer brush 5 come into contact with the intermediate transfer belt 6. This will be described in more detail below.

  FIG. 3 is a schematic cross-sectional view showing the configuration of the contact means of the primary transfer brush 5. FIG. 4 is a schematic perspective view showing the configuration of the contact means of the primary transfer brush 5 at one end portion in the longitudinal direction of the primary transfer brush 5. In the present embodiment, the configurations of the primary transfer portions B1a to B1d of the stations Sa to Sd are the same.

  In the present embodiment, the primary transfer brush 5 can be moved by the abutting means 10 in a direction approaching and away from the back surface of the intermediate transfer belt 6. The contact means 10 includes a pedestal 11, a compression coil spring (hereinafter simply referred to as “spring”) 12 as an urging member, and a guide rail 13 as a guide member. In this embodiment, two sets of springs 12 and guide rails 13 are provided at both ends in the longitudinal direction of the primary transfer brush 5, respectively. The pedestal 11 is held movably. The configurations of the spring 2 and the guide rail 13 at both ends in the longitudinal direction of the primary transfer brush 5 are substantially the same.

  In the primary transfer brush 5, the bottom surface of the substrate 52 (the surface opposite to the upper surface 52 </ b> A on which the brush fibers 51 are raised) 52 </ b> B is fixed to the upper surface 11 </ b> A of the base 11 such as adhesion, welding, fastening, and engagement. Is held on the pedestal 11 by being fixed by or simply placed. In the present embodiment, the upper surface 11 </ b> A of the base 11 has substantially the same shape as the bottom surface 52 </ b> B of the substrate 52 of the primary transfer brush 5. The pedestal 11 is urged toward the back surface of the intermediate transfer belt 6 by a pressing force F by a spring 12 disposed between the pedestal 11 and the guide rail 13. As a result, the primary transfer brush 5 is brought into contact with the back surface of the intermediate transfer belt 6.

  In the primary transfer brush 5, both side portions 5 </ b> C and 5 </ b> C in the short direction of the primary transfer brush 5 in the non-raised portions 5 </ b> B and 5 </ b> B (FIG. 2) at both ends in the longitudinal direction of the substrate 52 are opposed to the guide rail 13. Guided by surfaces 13A, 13A. That is, the substrate 52 of the primary transfer brush 5 is sandwiched between the guide surfaces 13A and 13A of the guide rail 13 at the non-raised portions 5B and 5B at both ends in the longitudinal direction. Thereby, in this embodiment, the movable direction of the primary transfer brush 5 is regulated in the direction of arrow D in the figure. The spring 12 is disposed between the spring support surface 13B between the guide surfaces 13A and 13A and the bottom surface of the base 11 (the surface opposite to the upper surface 11A that supports the primary transfer brush 5) 11B. The direction in which the pressing force F by the spring 12 acts is also regulated in a direction substantially parallel to the arrow D direction in the figure. In this embodiment, the primary transfer brush 5 is urged toward the intermediate transfer belt 6, which is the sum of the pressing forces F acting on the primary transfer brush 5 by the springs 12 at both longitudinal ends of the primary transfer brush 5. The pressure is 1.96N.

  Here, in the present embodiment, the movable direction of the primary transfer brush 5 and the direction of the pressing force F indicated by an arrow D in the cross section substantially perpendicular to the rotational axis direction of the photosensitive drum 1 are the intermediate transfer belt. 6 is substantially parallel to the normal line direction (substantially perpendicular to the moving direction of the intermediate transfer belt 6). In this embodiment, the guide surfaces 13 </ b> A and 13 </ b> A as guide portions extend in a direction substantially parallel to the normal direction of the intermediate transfer belt 6, so that the regulation direction of the guide rail 13 is the normal direction of the intermediate transfer belt 6. And substantially parallel.

  Further, in a cross section substantially perpendicular to the rotational axis direction of the photosensitive drum 1, an angle (fiber inclination angle) θ formed by the brushed direction of the brush fibers 51 and the moving direction R3 of the intermediate transfer belt 6 is 70 ° ≦ θ ≦. It is 90 °.

  As a result, the primary transfer brush 5 is in a state where the brush fibers 51 are tilted (inclined) downstream along the moving direction of the intermediate transfer belt 6 with respect to the normal direction of the intermediate transfer belt 6. It contacts the back surface of the transfer belt 6.

  In this embodiment, the brush fibers 51 of the primary transfer brush 5 are raised substantially perpendicular to the upper surface 52A of the substrate 52. However, for example, when the primary transfer brush 5 is a pile woven fabric type, the pile yarn may spread as it moves away from the base fabric. Even in this case, each brush fiber 51 constituting the pile yarn only needs to satisfy the condition of the fiber inclination angle. In this embodiment, in order to obtain the above-described fiber inclination angle θ, an angle formed by the moving direction R3 of the intermediate transfer belt 6 and the upper surface 11A of the base 11 in a cross section substantially perpendicular to the rotation axis direction of the photosensitive drum 1. θb is set to 160 ° ≦ θb ≦ 180 °.

  In order to satisfactorily prevent the brush fiber 51 from falling to the upstream side in the moving direction of the intermediate transfer belt 6 and to satisfactorily suppress the abnormal discharge generated on the upstream side of the primary transfer portion B1, the brush fiber 51 is slightly inclined. In this state, the back surface of the intermediate transfer belt 6 may be contacted. However, if this inclination is excessively increased, the substrate 52 of the primary transfer brush 5 comes into contact with the back surface of the intermediate transfer belt 6 to cause scratches and the like, resulting in vertical stripes (in the direction along the moving direction of the intermediate transfer belt 6). May cause image defects.

  When examined using the primary transfer brush 5 of the present embodiment, when θ> 90 °, the brush fibers 51 fall to the upstream side in the moving direction of the intermediate transfer belt 6, and vertical stripes due to abnormal discharge occur. An image defect sometimes occurred.

  On the other hand, when θ <70 °, the substrate 52 of the primary transfer brush 5 comes into contact with the back surface of the intermediate transfer belt 6 and a vertical streak-like image defect may occur due to scratches.

  On the other hand, when 70 ° ≦ θ ≦ 90 °, there was no occurrence of vertical streak-like image defects due to abnormal discharge or scratches. In this embodiment, θ≈80 °.

4). Next, the nip arrangement in the primary transfer portion B1 will be described. FIG. 3 also shows the positional relationship between each member and the nip in the primary transfer portion B1.

  M1 in the drawing represents a nip (surface nip) formed between the photosensitive drum 1 and the intermediate transfer belt 6. In the present embodiment, the intermediate transfer belt 6 linearly stretched between the driving roller 61 and the tension roller 63 has a width in the moving direction of the intermediate transfer belt 6 between the photosensitive drum 1 for each station S. Forms a 1 mm surface nip M1.

  On the other hand, N1 in the figure represents a nip (back nip) formed between the intermediate transfer belt 6 and the primary transfer brush 5. Here, the back surface nip N <b> 1 is a contact end point (start point) from a contact start point (start point) between the primary transfer brush 5 composed of the plurality of brush fibers 51 and the back surface of the intermediate transfer belt 6 in the moving direction of the intermediate transfer belt 6. (End point). In the present embodiment, the brush fibers 51 of the primary transfer brush 5 are in a state where they are not in contact with the intermediate transfer belt 6 (that is, in a state where no pressure is applied to the brush fibers 51), the substrate 52 of the primary transfer brush 5. The upper surface 52A is raised substantially perpendicularly. However, when it is brought into contact with the back surface of the intermediate transfer belt 6 by the pressing force F, the brush fibers 51 are brought down. Since the primary transfer brush 5 is brought into contact with the back surface of the intermediate transfer belt 6 at an angle (fiber inclination angle θ), the inclination of the brush fibers 51 is large on the upstream side in the moving direction of the intermediate transfer belt 6 and on the downstream side. It gets smaller as you go. In this state, a restoring force is generated in the brush fiber 51 so as to return the brushed posture substantially perpendicular to the upper surface 52 A of the substrate 52 of the primary transfer brush 5, and this force causes the primary transfer brush 5 to move from the intermediate transfer belt 6. It becomes the force (reaction force) to push back in the direction away. Accordingly, the primary transfer brush 5 is stabilized at a position where the primary transfer brush 5 has entered the back surface of the intermediate transfer belt 6 to a position where the pressing force F and the reaction force are balanced. FIG. 3 shows a state in which the pressing force F and the reaction force are balanced. In this embodiment, the width of the back surface nip N1 in the moving direction of the intermediate transfer belt 6 is 3.6 mm.

  Next, the regions represented by s, t, and u in the drawing showing the positional relationship between each member and the nip in the primary transfer portion B1, which is important for obtaining good primary transfer properties, will be described.

In the drawing, s denotes a surface nip M1 where the photosensitive drum 1 and the intermediate transfer belt 6 are in contact with each other and a back surface nip N1 where the intermediate transfer belt 6 and the primary transfer brush 5 are in contact with each other in the moving direction of the intermediate transfer belt 6. It represents the first region that overlaps (overlap nip). The overlap nip s is a region where a transfer electric field is formed. If the overlap nip s is not formed, good primary transfer efficiency cannot be obtained. In this embodiment, the width of the overlap nip s in the moving direction of the intermediate transfer belt 6 is 1 mm.

T in the drawing represents a second region (tension nip) where only the primary transfer brush 5 contacts the intermediate transfer belt 6 on the downstream side of the overlap nip s in the moving direction of the intermediate transfer belt 6. That is, t in the drawing indicates that the back surface nip N1 where the intermediate transfer belt 6 and the primary transfer brush 5 are in contact with the front surface nip M1 where the photosensitive drum 1 and the intermediate transfer belt 6 are in contact with each other. This represents a region protruding to the downstream side in the movement direction. The tension nip t is applied by a transfer electric field formed in the overlap nip s, and excessive charge remaining on the intermediate transfer belt 6 even after passing through the overlap nip s flows back on the primary transfer brush 5 and returns. It is an area. The tension nip t is a region necessary for preventing the occurrence of image defects due to abnormal discharge caused by the excessive charge. In this embodiment, the width of the tension nip t in the moving direction of the intermediate transfer belt 6 is 2.5 mm.

In the drawing, u indicates the movement direction of the intermediate transfer belt 6 when the back surface nip N1 where the intermediate transfer belt 6 and the primary transfer brush 5 are in contact with the front surface nip M1 where the photosensitive drum 1 and the intermediate transfer belt 6 are in contact. A third region (extrusion nip) protruding to the upstream side is represented. That is, u in the drawing represents a region where only the primary transfer brush 5 contacts the intermediate transfer belt 6 on the upstream side of the overlap nip s in the movement direction of the intermediate transfer belt 6. When the protrusion nip u becomes large, a gap in which a transfer electric field is formed is formed between the photosensitive drum 1 and the intermediate transfer belt 6 on the upstream side in the movement direction of the intermediate transfer belt 6 in the primary transfer portion B1. For this reason, a phenomenon may occur in which the toner is transferred from the photosensitive drum 1 to the intermediate transfer belt 6 before entering the primary transfer portion B1, resulting in an image in which the toner is scattered (transfer scattering due to pre-transfer). In this embodiment, the width of the protruding nip u in the moving direction of the intermediate transfer belt 6 is 0.1 mm.

  In order to obtain good primary transferability, it is necessary to form both the overlap nip s and the tension nip t. It is also necessary that the protruding nip u is not large.

  In this embodiment, 1 mm is secured as the width of the overlap nip s in the moving direction of the intermediate transfer belt 6, and 2.5 mm is secured as the width of the tension nip t. Each member is arranged in the image forming apparatus 100 so that the width of the protruding nip u in the moving direction of the intermediate transfer belt 6 is 0.1 mm. Thereby, good primary transferability is obtained.

  As a result of studying the configuration of this embodiment, the width of the overlap nip s in the moving direction of the intermediate transfer belt 6 is 0.4 mm or more, the width of the tension nip t is 1 mm or more, and the width of the protruding nip u is 1 mm or less. As a result, it was confirmed that good primary transferability was obtained. If the width of the overlap nip s is too large, the toner image may be rubbed in the overlap nip s and the image may be distorted. For this reason, the width of the overlap nip s in the moving direction of the intermediate transfer belt 6 is normally 5 mm or less. On the other hand, if the width of the tension nip t is too large, the contact area between the intermediate transfer belt 6 and the primary transfer brush 5 increases, and the intermediate transfer belt 6 receives strong rubbing power from the primary transfer brush 5, so Running stability may deteriorate. From this, the width of the tension nip t is normally set to 10 mm or less. Further, the width of the protruding nip u in the moving direction of the intermediate transfer belt 6 may be 0 mm.

5. Influence of Member Attachment Position The attachment position of the guide rail 13 with respect to the photosensitive drum 1 and the intermediate transfer belt 6 may fluctuate due to the influence of component positioning variations during the assembly of the image forming apparatus 100. In the image forming apparatus 100 of the present embodiment, a direction along the moving direction of the intermediate transfer belt 6 (direction along the arrow x direction in the figure) and a direction along the normal direction of the intermediate transfer belt 6 (along the arrow z direction in the figure). In each direction) within a range of about ± 0.5 mm.

  FIG. 5 is a schematic cross-sectional view for explaining the influence of variations in the mounting position of the guide rail 13 in the direction along the moving direction of the intermediate transfer belt 6.

  FIG. 5A shows a state in which the mounting position of the guide rail 13 with respect to the back surface of the intermediate transfer belt 6 is deviated by δ along the moving direction of the intermediate transfer belt 6 with respect to the target position. Show. The back nip in this case is indicated as N1l.

  FIG. 5B shows a state where the mounting position of the guide rail 13 with respect to the back surface of the intermediate transfer belt 6 is a target position. The back nip in this case is indicated as N1.

  FIG. 5C shows a state in which the attachment position of the guide rail 13 to the back surface of the intermediate transfer belt 6 is shifted by δ along the moving direction of the intermediate transfer belt 6 with respect to the target position. Show. The back nip in this case is indicated as N1r.

  As shown in FIGS. 5A, 5 </ b> B, and 5 </ b> C, when the back surface nip N <b> 1 moves in the upstream / downstream direction of the intermediate transfer belt 6, the positions of the overlap nip s, the tension nip t, and the protrusion nip u are located. The width also changes.

  In this embodiment, even when the mounting position of the guide rail 13 fluctuates within the above range along the moving direction of the intermediate transfer belt 6, the above-described conditions for the nip arrangement for obtaining good primary transferability are satisfied. ing. That is, in this embodiment, each member is arranged in the image forming apparatus 100 so that a good primary transfer property can always be obtained even if the mounting position of the guide rail 13 varies along the moving direction of the intermediate transfer belt 6. Has been.

  On the other hand, FIG. 6 is a schematic cross-sectional view for explaining the influence of variations in the mounting position of the guide rail 13 in the direction along the normal direction of the intermediate transfer belt 6. In FIG. 6, the mounting position of the guide rail 13 in the direction along the moving direction of the intermediate transfer belt 6 is a target position (corresponding to FIG. 5B).

  FIG. 6A shows that the attachment position of the guide rail 13 to the back surface of the intermediate transfer belt 6 is δ in the direction away from the intermediate transfer belt 6 along the normal direction of the intermediate transfer belt 6 with respect to the target position. The state in the case of deviation is shown. The back nip in this case is indicated as N1d.

  FIG. 6B shows a state where the attachment position of the guide rail 13 with respect to the back surface of the intermediate transfer belt 6 is a target position. The back nip in this case is indicated as N1.

  FIG. 6C shows that the attachment position of the guide rail 13 with respect to the back surface of the intermediate transfer belt 6 is δ in the direction approaching the intermediate transfer belt 6 along the normal direction of the intermediate transfer belt 6 with the target position as a reference. The state in the case of deviation is shown. The back nip in this case is indicated as N1u.

  As shown in FIGS. 6A, 6 </ b> B, and 6 </ b> C, in this embodiment, even if the mounting position of the guide rail 13 varies in the above range along the normal direction of the intermediate transfer belt 6, The positions and widths of the nips N1d, N1, and N1u in the moving direction of the intermediate transfer belt 6 are substantially unchanged.

  In this embodiment, the pressing direction of the primary transfer brush 5 by the contact means 10 is substantially parallel to the normal line direction of the intermediate transfer belt 6 (the direction along the arrow z direction in the figure). Therefore, even if the mounting position of the guide rail 13 changes along the normal direction of the intermediate transfer belt 6, there is no influence because it becomes as follows. That is, the primary transfer brush 5 enters the back surface of the intermediate transfer belt 6 to a position where the pressing force F and the reaction force of the primary transfer brush 5 by the brush fibers 51 are balanced, and contacts the original position on the intermediate transfer belt 6. And stop. As a result, the nip position and width do not change significantly. Therefore, good primary transferability is maintained. As described above, the configuration of the contact means of this embodiment is very effective in suppressing the influence of the variation in the mounting position of the guide rail 13 in the direction along the normal direction of the intermediate transfer belt 6.

  Here, in order to obtain the above-described effect satisfactorily, it is preferable to use a spring that has a relatively small change in pressing force even if the operating length of the spring 12 changes. For example, the spring constant of the spring 12 is preferably 20 N / m to 2000 N / m, more preferably 100 N / m to 300 N / m. If the spring constant is larger than the above range, the effective pressure of the spring 12 changes greatly in the following cases, so that the change in the position and width of the nip may become slightly larger (Comparative Example described later). 1 is not preferable). That is, the above-described shift of the mounting position of the guide rail 13 with respect to the back surface of the intermediate transfer belt 6 occurs, and the working length of the spring 12 changes in a state where the primary transfer brush 5 is in contact with the back surface of the intermediate transfer belt 6. . On the other hand, if the spring constant is smaller than the above range, the length of the part of the spring 12 for realizing a predetermined primary transfer pressure is increased, which may lead to an increase in the size of the image forming apparatus 100.

  The direction of the pressing force F and the normal direction of the intermediate transfer belt 6 do not have to be completely parallel. Considering the degree of variation in the mounting position of the guide rail 13, the conditions may be set to be approximately parallel as appropriate. As a result of examination using the configuration of the present embodiment, if the direction of the pressing force F is set to an angle of 30 ° or less with respect to the normal direction of the intermediate transfer belt 6, the above-described effects can be obtained satisfactorily. It was confirmed.

<Comparative Example 1>
Here, the comparative example for showing the effect of a present Example is demonstrated. Note that the image forming apparatus of the comparative example (this comparative example and other comparative examples described later) has substantially the same configuration as the image forming apparatus of the embodiment according to the present invention, except for the differences particularly mentioned. . In the comparative example (this comparative example and other comparative examples described later), the elements having the same or equivalent functions and configurations as those of the image forming apparatus of the embodiment according to the present invention will be described with the same reference numerals.

  FIG. 7 is a schematic cross-sectional view showing the positional relationship between each member and the nip in the primary transfer portion B1 of the image forming apparatus 100 of Comparative Example 1.

  In Comparative Example 1, the primary transfer brush 5 is positioned and fixed to the frame of the image forming apparatus 100 with a screw or the like for each station S, and is brought into contact with the back surface of the intermediate transfer belt 6. .

  Also in Comparative Example 1, the angle (fiber inclination angle) θ formed by the raising direction of the brush fibers 51 and the moving direction R3 of the intermediate transfer belt 6 in a cross section substantially perpendicular to the rotational axis direction of the photosensitive drum 1 is 70 ° ≦ θ ≦ 90 °.

  FIG. 8 is a schematic cross-sectional view for explaining the influence of variations in the attachment position of the primary transfer brush 5 in the direction along the normal direction of the intermediate transfer belt 6 in Comparative Example 1. In FIG. 8, the attachment position of the primary transfer brush 5 in the direction along the moving direction of the intermediate transfer belt 6 is a target position.

  FIG. 8A shows that the attachment position of the primary transfer brush 5 with respect to the back surface of the intermediate transfer belt 6 is δ in a direction away from the intermediate transfer belt 6 along the normal direction of the intermediate transfer belt 6 with reference to the target position. The state when it has shifted by only is shown. The back nip in this case is indicated as N1d.

  FIG. 8B shows a state where the attachment position of the primary transfer brush 5 with respect to the back surface of the intermediate transfer belt 6 is a target position. The back nip in this case is indicated as N1.

  FIG. 8C shows that the attachment position of the primary transfer brush 5 with respect to the back surface of the intermediate transfer belt 6 is δ in a direction approaching the intermediate transfer belt 6 along the normal direction of the intermediate transfer belt 6 with the target position as a reference. The state when it has shifted by only is shown. The back nip in this case is indicated as N1u.

  The attachment position of the primary transfer brush 5 with respect to the photosensitive drum 1 and the intermediate transfer belt 6 may fluctuate due to the influence of variations in the positioning of components when the image forming apparatus 100 is assembled. In the image forming apparatus 100 of the comparative example 1, it fluctuates within a range of about ± 0.5 mm in the direction along the normal direction of the intermediate transfer belt 6 (direction along the arrow z direction in the figure).

  In the state shown in FIG. 8B, the width of the overlap nip s in the moving direction of the intermediate transfer belt 6 is 1 mm, and the width of the tension nip t is 2.5 mm. Each member is arranged in the image forming apparatus 100 so that the width of the protruding nip u in the moving direction of the intermediate transfer belt 6 is 0.1 mm. Thereby, good primary transferability is obtained.

  However, in the state of FIG. 8A, the back surface nip N1d moves to the upstream side in the movement direction of the intermediate transfer belt 6, and the back surface nip N1d greatly protrudes to the upstream side in the movement direction of the intermediate transfer belt 6 with respect to the front surface nip M1. At the same time, the overlap nip s has disappeared.

  In the state of FIG. 8C, the back surface nip N1u moves to the downstream side in the moving direction of the intermediate transfer belt 6, and the overlap nip s is an extremely narrow region.

  Therefore, good primary transferability cannot be obtained in either state of FIGS. 8A and 8C. That is, in the case of the state of FIG. 8A, vertical streak-like image defects may occur due to abnormal discharge that occurs on the upstream side in the movement direction of the intermediate transfer belt 6 of the primary transfer portion B1, and good transfer efficiency is obtained. The image density decreases. In the state of FIG. 8C, good primary transfer efficiency cannot be obtained, and the image density is lowered.

  As described above, in the case where variations in the mounting positions of the components, particularly variations in the direction along the normal direction of the intermediate transfer belt 6, can occur, the configuration of the present embodiment (press type) The configuration is more advantageous than the configuration of the first comparative example (fixed configuration). This is because, in this embodiment, variations in the position and width of the nip with respect to variations in the mounting positions of the components, particularly variations in the direction along the normal direction of the intermediate transfer belt 6, are suppressed.

  That is, the image forming apparatus 100 according to the present exemplary embodiment includes an image carrier 1 that carries a toner image, an endless belt 6 that can move in contact with the image carrier 1, and the image carrier 1 toward the belt 6. Transfer means 5 for transferring the toner image. The transfer unit 5 includes a fiber 51 having conductivity and a substrate 52 that holds the fiber 51, and the fiber 51 contacts the inner peripheral surface of the belt 6. In addition, the image forming apparatus 100 includes a biasing member 12 that biases the transfer unit 5 toward the belt 6 and a guide member 13 that regulates the moving direction of the transfer unit 5. Then, the transfer unit 5 biased by the biasing member 12 approaches the belt 6 at a position facing the image carrier 1 via the belt 6 while the movement direction is regulated by the guide member 13. It can move in the direction and away. In the present embodiment, the fiber 51 in a state of being urged by the urging member 12 is inclined downstream along the moving direction of the belt 6 with respect to the normal direction of the belt 6. In this embodiment, the regulation direction of the guide member 13 is substantially parallel to the normal direction of the belt 6. Preferably, an angle θ between the raising direction of the fibers 51 and the moving direction of the belt 6 in a state where the belt 51 is not deformed by being in contact with the belt 6 is 70 ° ≦ θ ≦ 90 °. Further, when the transfer unit 5 comes into contact with the belt 6, the next region is formed in the moving direction of the belt 6. One is a region s where the first contact portion M1 where the image carrier 1 and the belt 6 are in contact with each other and the second contact portion N1 where the belt 6 and the transfer means 5 are in contact with each other. The other one is a region t where only the transfer unit 5 of the image carrier 1 and the transfer unit 5 contacts the belt 6 on the downstream side of the overlapping region s.

  As described above, according to this embodiment, the random fall of the brush fibers 51 of the primary transfer brush 5 is suppressed, and the nip formed between the intermediate transfer belt 6 and the primary transfer brush 5 is the mounting position of the components. It is always placed at the target position regardless of variations. Accordingly, it is possible to stably obtain good primary transferability.

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

  In the present embodiment, the nip formed between the intermediate transfer belt 6 and the primary transfer brush 5 affects not only variations in the mounting position of components but also variations in component dimensions such as the fiber length of the primary transfer brush 5. It is not always kept at the target position.

  FIG. 9 is a schematic cross-sectional view showing the configuration of the contact means of the primary transfer brush 5 in this embodiment. In the present embodiment, the configurations of the primary transfer portions B1a to B1d of the stations Sa to Sd are the same.

  As shown in FIG. 9, the basic configuration and operation of the contact means 10 of the primary transfer brush 5 in this embodiment are the same as those in the first embodiment. However, in the present embodiment, the movable direction of the primary transfer brush 5 and the direction of the pressing force F indicated by the arrow D in the drawing in the cross section substantially perpendicular to the rotational axis direction of the photosensitive drum 1 are the brush fibers 51. It is substantially parallel to the raising direction. In the present embodiment, the guide surfaces 13 </ b> A and 13 </ b> A as the guide portions extend in a direction substantially parallel to the brushed direction of the brush fibers 51, so that the regulation direction of the guide rail 13 is substantially parallel to the brushed direction of the brush fibers 51. Has been.

  In the cross section substantially perpendicular to the rotational axis direction of the photosensitive drum 1, the angle (fiber inclination angle) θ formed by the brushed fiber 51 raising direction and the intermediate transfer belt 6 moving direction R3 is the same as in the first embodiment. 70 ° ≦ θ ≦ 90 °. In this embodiment, θ≈80 °. When θ is 90 °, the configuration is substantially the same as that of the first embodiment. This point will be described later.

  FIG. 10 is a schematic cross-sectional view for explaining the influence of variations in fiber length of the primary transfer brush 5.

  The brush-like transfer means is obtained as a member having a desired fiber length by appropriately cutting the tip of the fiber by shearing or the like in the manufacturing process.

  FIG. 10A shows a state where a primary transfer brush 5 having a desired fiber length (2 mm) is used. The back nip in this case is indicated as N1.

  FIG. 10B shows a state in which a primary transfer brush 5 having a fiber length shorter by about 0.6 mm than a desired fiber length (2 mm) is used. The back nip in this case is indicated as N1s.

  As shown in FIGS. 10A and 10B, the back surface nips N1 and N1s have substantially no change in the starting point (position) and width in the moving direction of the intermediate transfer belt 6.

  In the present embodiment, the direction in which the pressing force F acts is substantially parallel to the raising direction of the brush fiber 51. Therefore, even if the fiber length of the primary transfer brush 5 changes, the destination to which the primary transfer brush 5 is pressed remains at the position where the tip of the brush fiber 51 in the case of the desired fiber length contacts. As a result, there is no significant change in the position and width of the nip. Therefore, good primary transferability is maintained. As described above, the configuration of the contact means of this embodiment is very effective in suppressing the influence of changes in the component dimensions such as the change in the fiber length of the primary transfer brush 5. Here, the variations in the component dimensions include not only the variation in fiber length but also the size of any component that affects the dimension in the raised direction of the fibers in the components of the primary transfer section including the primary transfer means and the contact means. Even if there is variation, the same effect as described above can be obtained.

  In addition, the direction of the pressing force F and the raising direction of the brush fiber 51 do not need to be completely parallel. Considering the degree of variation in the component dimensions such as the fiber length of the primary transfer brush 5, the conditions may be set to be approximately parallel as appropriate. When the primary transfer brush 5 of this example was used for the study, the above-described effects can be obtained satisfactorily when the brushed direction of the brush fibers 51 is within an angle of 10 ° with respect to the direction of the pressing force F. It was confirmed that As described above, for example, when the primary transfer brush 5 is a pile woven fabric type, the pile yarn may spread as it moves away from the base fabric. Even in this case, it is only necessary to satisfy the above condition with respect to the raising direction of each brush fiber 51 constituting the pile yarn.

<Comparative example 2>
Here, the comparative example for showing the effect of a present Example is demonstrated.

  FIG. 11 is a schematic cross-sectional view showing the positional relationship between each member and the nip in the primary transfer portion B1 of the image forming apparatus 100 of Comparative Example 2.

  Also in Comparative Example 2, the contact means 10 includes a base 11 and two sets of springs 12 and guide rails 13 disposed at both ends in the longitudinal direction of the primary transfer brush 5. The pedestal 11 is urged toward the back surface of the intermediate transfer belt 6 by a pressing force G by a spring 12 disposed between the pedestal 11 and the guide rail 13. As a result, the primary transfer brush 5 is brought into contact with the back surface of the intermediate transfer belt 6. However, in Comparative Example 2, the guide rail 13 is configured so that the upper surface 52A of the substrate 52 and the bottom surface 11B of the base 11 are opposed to each other at the non-raised portions 5B and 5B at both ends in the longitudinal direction of the substrate 52 of the primary transfer brush 5. It is comprised so that it may be clamped by 13A and 13A. Thereby, in the comparative example 2, the movable direction of the primary transfer brush 5 is regulated in the direction of arrow E in the figure. The spring 12 is disposed between the spring support surface 13B between the guide surfaces 13A and 13A and the side surface 11C of the base 11 on the downstream side in the moving direction of the intermediate transfer belt 6. The direction in which the pressing force G by the spring 12 acts is also regulated in a direction substantially parallel to the arrow E direction in the figure. Also in Comparative Example 2, the primary transfer brush 5 is urged toward the intermediate transfer belt 6, which is the sum of the pressing forces G acting on the primary transfer brush 5 by the springs 12 at both longitudinal ends of the primary transfer brush 5. The total pressure is 1.96N.

  Here, in Comparative Example 2, for comparison, the movable direction of the primary transfer brush 5 and the direction of the pressing force G indicated by an arrow E in the drawing are in a cross section substantially perpendicular to the rotation axis direction of the photosensitive drum 1. Unlike the present embodiment, the brush fibers 51 are substantially perpendicular to the raising direction.

  In the cross section substantially perpendicular to the rotational axis direction of the photosensitive drum 1, the angle (fiber inclination angle) θ formed by the brushed fiber 51 raising direction and the intermediate transfer belt 6 moving direction R3 is the same as in the first embodiment. 70 ° ≦ θ ≦ 90 °.

  FIG. 12 is a schematic cross-sectional view for explaining the influence of variations in fiber length of the primary transfer brush 5 in Comparative Example 2.

  FIG. 12A shows a state where a primary transfer brush 5 having a desired fiber length (2 mm) is used. The back nip in this case is indicated as N1.

  FIG. 12B shows a state in which a primary transfer brush 5 having a fiber length shorter by about 0.6 mm than the desired fiber length (2 mm) is used. The back nip in this case is indicated as N1s.

  In the state of FIG. 12A, the width of the overlap nip s in the moving direction of the intermediate transfer belt 6 is 1 mm, and the width of the tension nip t is 2.5 mm. Each member is arranged in the image forming apparatus 100 so that the width of the protruding nip u in the moving direction of the intermediate transfer belt 6 is 0.1 mm. Thereby, good primary transferability is obtained.

  However, in the state of FIG. 12B, the back surface nip N1s moves to the upstream side in the moving direction of the intermediate transfer belt 6, the protruding nip u is formed large, and the tension nip t disappears.

  In Comparative Example 2, the movable direction of the primary transfer brush 5 is substantially perpendicular to the brushed direction of the brush fibers 51. For this reason, when the fiber length of the primary transfer brush 5 is shortened, the primary transfer brush 5 is largely pushed upstream in the moving direction of the intermediate transfer belt 6. As a result, a large change occurs in the position of the nip. Therefore, good primary transferability cannot be obtained.

  Thus, in the case where variations in the component dimensions such as the fiber length of the primary transfer brush 5 can occur, in order to ensure good primary transferability, the raising direction of the brush fibers 51 and the pressing force F as in this embodiment are used. A configuration in which the direction is substantially parallel is advantageous. That is, in the present embodiment, the regulation direction of the guide member 13 is substantially parallel to the raising direction of the fibers 51 in a state where the guide member 13 is not deformed by contacting the belt 6.

  As described above, according to this embodiment, the random fall of the brush fibers 51 of the primary transfer brush 5 is suppressed, and the nip formed between the intermediate transfer belt 6 and the primary transfer brush 5 is the primary transfer brush 5. Regardless of variations in component dimensions such as fiber length, the fiber is always placed at the target position. Accordingly, it is possible to stably obtain good primary transferability.

  By the way, as long as the fiber inclination angle θ is not far from 90 °, even if the mounting position of the guide rail 13 changes in the direction along the normal direction of the intermediate transfer belt 6, the intermediate transfer belt 6 and the primary transfer brush 5 The nip formed between the two is maintained near the target position. The case where the fiber inclination angle θ is not far from 90 ° is a case where the fiber inclination angle θ is within the range of 70 ° ≦ θ ≦ 90 °. This is because the direction of the pressing force F in this embodiment has a small angle with the normal direction of the intermediate transfer belt 6, and the effect described in the first embodiment can be obtained in the same manner. Therefore, in the configuration of the present embodiment, good primary transferability is ensured regardless of any variation in the mounting position of the components and variations in the component dimensions such as the fiber length. As described above, when θ is 90 °, the configuration is substantially the same as that of the first embodiment.

  As understood from the above, the direction of the pressing force F of the primary transfer brush 5 in the configuration of the present embodiment is an intermediate direction between the brushed direction of the brush fibers 51 and the normal direction of the intermediate transfer belt 6. be able to. The direction of the pressing force F can be determined as appropriate in consideration of the variation in the mounting position of components that can occur in the image forming apparatus 100 and the size relationship of variations in component dimensions such as fiber length. At this time, if the variation in the mounting position of the component is larger than the variation in the component dimensions such as the fiber length, the direction of the pressing force F may be set to a direction close to the normal direction of the intermediate transfer belt 6. Conversely, if the variation in component dimensions such as the fiber length is larger than the variation in the attachment position of the component, the direction of the pressing force F may be set to a direction close to the raising direction of the brush fiber 51.

  Further, the same effect as that of the present embodiment can be obtained by the configuration of the contact means of the primary transfer brush 5 as shown in FIG. That is, in the contact means 10 shown in FIG. 13, the primary transfer brush 5 is held by the pedestal 11 that can rotate around the rotation shaft 14. The rotation shaft 14 is disposed upstream of the primary transfer brush 5 in the movement direction of the intermediate transfer belt 6, and the rotation axis direction thereof is substantially parallel to the rotation axis direction of the photosensitive drum 1 (in the movement direction R 3 of the intermediate transfer belt 6). (Substantially perpendicular). The upper surface 52A of the substrate 52 of the primary transfer brush 5 and the upper surface 11A and the bottom surface 11B of the base 1 are substantially parallel. The spring 12 is held between the bottom surface 11 </ b> B of the base 11 and the spring receiver 15 and presses the primary transfer brush 5 toward the back surface of the intermediate transfer belt 6. In this case, the rotation shaft 14 and the pedestal 11 that rotates about this function as a guide member that regulates the movable direction of the primary transfer brush 5. Even in such a configuration, the direction of the pressing force F is substantially parallel to the raising direction of the brush fibers 51 (or an intermediate direction between the raising direction of the brush fibers 51 and the normal direction of the intermediate transfer belt 6). The effect of the present embodiment can be obtained in the same manner.

  In this way, by energizing the brush-like transfer means with respect to the back surface of the belt in a predetermined direction by a predetermined pressing force, the belt and the brush-shaped transfer device can be used regardless of variations in component mounting positions and component dimensions. The nip formed with the transfer means is maintained at the target position. Therefore, good primary transferability can be stably obtained.

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

  FIG. 14 is a schematic perspective view showing the configuration of the primary transfer brush 5 in the present embodiment. FIG. 15 is a schematic cross-sectional view showing the positional relationship between each member and the nip in the primary transfer portion B1. In the present embodiment, the configurations of the primary transfer portions B1a to B1d of the stations Sa to Sd are the same.

  As shown in FIGS. 14 and 15, the basic configuration and operation of the primary transfer brush 5 and the contact means 10 of the primary transfer brush 5 in this embodiment are the same as those in the first embodiment. However, in this embodiment, the brush fibers 51 of the primary transfer brush 5 are raised and inclined toward the downstream side in the moving direction of the intermediate transfer belt 6 with respect to the normal direction of the upper surface 52A of the substrate 52. . In a cross section substantially perpendicular to the rotation axis direction of the photosensitive drum 1, an angle formed by the normal direction of the upper surface 52 </ b> A of the substrate 52 of the primary transfer brush 5 and the raising direction of the brush fibers 51 is defined as a raising angle γ.

  In order to satisfactorily prevent the brush fibers 51 from falling to the upstream side in the moving direction of the intermediate transfer belt 6, the primary transfer brush 5 having no raising angle γ or a slight raising angle γ is used for the intermediate transfer belt 6. What is necessary is just to contact the back surface. Therefore, the raising angle γ can be set to γ ≧ 0 °.

  In the present embodiment, the movable direction of the primary transfer brush 5 and the direction of the pressing force F indicated by an arrow D in the cross section substantially perpendicular to the rotational axis direction of the photosensitive drum 1 are the same as those of the intermediate transfer belt 6. It is substantially parallel to the linear direction and is inclined at a raising angle γ from the raising direction of the brush fibers 51. The direction substantially parallel to the normal direction of the intermediate transfer belt 6 is a direction substantially perpendicular to the moving direction R3 of the intermediate transfer belt 6.

  Thereby, the brush fibers 51 of the primary transfer brush 5 come into contact with the back surface of the intermediate transfer belt 6 in a state where the brush fibers 51 are previously tilted to the downstream side in the moving direction of the intermediate transfer belt 6. Then, the contact further increases the degree of falling and stabilizes the posture.

  By the way, the primary transfer brush 5 in the present embodiment can be obtained by rolling a surface of a heated roller heated to a high temperature with a brush member that is originally raised in the manufacturing process. Therefore, when the primary transfer brush 5 having an extremely large raising angle is manufactured, a large amount of heat is applied to the surface of the member by the heat roller, and damage such as fiber tearing occurs. In order not to cause this damage, it is preferable to suppress the raising angle γ within the range of γ ≦ 20 °.

  As a result of examination using the configuration of this example, it was confirmed that good primary transferability can be secured by setting the raising angle γ to 0 ° ≦ γ ≦ 20 °.

  That is, in this embodiment, the fibers 51 of the transfer means 5 are raised with an inclination toward the downstream side along the moving direction of the belt 6 with respect to the normal direction of the substrate 52. In particular, preferably, an angle γ formed between the normal direction of the substrate 52 and the raising direction of the fibers 51 in a state in which the fiber 51 is not deformed by being in contact with the belt 6 is 0 ° ≦ γ ≦ 20 °. .

  As described above, for example, when the primary transfer brush 5 is a pile woven fabric type, the pile yarn may spread as it moves away from the base fabric. Even in this case, each brush fiber 51 constituting the pile yarn only needs to satisfy the condition of the raising angle.

  Here, in this embodiment, the primary transfer brush 5 is in the middle so that the surface formed by the tip of the brush fiber 51 tilted in advance at the raising angle γ contacts the back surface of the intermediate transfer belt 6 substantially in parallel. It is brought into contact with the back surface of the transfer belt 6. Therefore, the degree of tilting of the brush fibers 51 in the primary transfer brush 5 that contacts the back surface of the intermediate transfer belt 6 is uniformly distributed from the upstream side to the downstream side in the moving direction of the intermediate transfer belt 6. As a result, the portion where the brush fibers 51 come into contact with the back surface of the intermediate transfer belt 6 to form the transfer electric field also has a more uniform distribution in the back surface nip N1 as compared with the configurations of the first and second embodiments. It will have. That is, the contact uniformity with respect to the back surface of the intermediate transfer belt 6, which is a characteristic of the brush-like transfer unit, is further improved, and image defects such as density unevenness generated in the primary transfer process are more effectively suppressed. .

  As described above, according to the present embodiment, the same effects as those of the first embodiment can be obtained, and the primary transfer brush 5 in which the brush fibers 51 are raised at an inclined angle with respect to the substrate 52 can be used to perform the primary transfer process. Occurrence of image defects such as density unevenness that can be caused by the above is also suppressed more satisfactorily.

  In addition, using the primary transfer brush 5 in the present embodiment, a configuration in which the direction of the pressing force is substantially parallel to the raising direction of the primary transfer brush 5 can be employed as in the second embodiment. Thereby, even if the fiber length variation of the primary transfer brush 5 is large, the influence can be absorbed.

Other Embodiments Although the present invention has been described with reference to specific embodiments, the present invention is not limited to the above-described embodiments.

  In the above-described embodiments, the image forming apparatus is described as an intermediate transfer type image forming apparatus using an intermediate transfer belt. However, an image forming apparatus having another configuration is also conceivable as an image forming apparatus of a type in which the brush-shaped transfer unit is brought into contact with the image carrier via a belt-shaped member. For example, there is a direct transfer type image forming apparatus that sequentially directly transfers toner images on a plurality of photosensitive drums onto a transfer material conveyed on a transfer material conveyance belt. FIG. 16 is a schematic cross-sectional view of a main part of an example of a direct transfer type image forming apparatus. In FIG. 16, elements having the same or corresponding functions and configurations as those of the intermediate transfer type image forming apparatus shown in FIG. The direct transfer type image forming apparatus has a transfer conveyance belt 160 as a transfer material carrier instead of the intermediate transfer belt as an intermediate transfer body in the intermediate transfer type image forming apparatus. Then, the transfer material P is carried on the transfer material conveying belt 160 by the toner image formed on each photosensitive drum 1 of each station S by the action of the transfer brush 5 as the transfer means in each transfer portion B. The images are transferred in such a manner that they are sequentially superimposed on each other. Thereafter, the toner image is fixed on the transfer material P. As the configuration of each transfer unit and the contact unit thereof in such a direct transfer type image forming apparatus, the configuration of the primary transfer unit and the contact unit in each of the above embodiments can be equally applied. The same effect can be obtained.

1 Photosensitive drum (image carrier)
5 Primary transfer brush (brush-shaped transfer means)
6 Intermediate transfer belt (belt)
10 Contact means 11 Base 12 Spring (biasing member)
13 Guide rail (guide member)

Claims (14)

An image carrier that carries a toner image, an endless belt that can move in contact with the image carrier, and a transfer unit that transfers the toner image from the image carrier toward the belt, In the image forming apparatus, the transfer unit includes a fiber having conductivity and a substrate that holds the fiber, and the fiber contacts an inner peripheral surface of the belt.
An urging member that urges the transfer unit toward the belt; and a guide member that regulates a moving direction of the transfer unit ;
A first region where a contact portion where the image carrier and the belt are in contact with each other and a contact portion where the belt and the transfer unit are in contact with each other; and a downstream side of the first region with respect to the moving direction of the belt. A second area where only the transfer means contacts the belt on the side of the image carrier and the transfer means, and the transfer of the image carrier and the transfer means on the upstream side of the first area. An image forming apparatus characterized in that a third region in which only the means contacts the belt is formed . The transfer means urged by the urging member has a direction of approaching the belt at a position facing the image carrier via the belt in a state where the movement direction is regulated by the guide member; The image forming apparatus according to claim 1, wherein the image forming apparatus is movable in a direction away from the image forming apparatus. Before SL fibers, and regarding the normal direction of the belt, according to claim 1, characterized in that in contact with the inner peripheral surface of the belt in an inclined downstream along the moving direction of the belt or the image forming apparatus according to 2. Said transfer means, said by the guide member, the image forming apparatus according to any one of claims 1 to 3, characterized in that it is restricted to move in the normal direction and a direction substantially parallel to the belt. 2. The movement of the transfer unit is regulated by the guide member in a direction substantially parallel to a raising direction of the fibers in a state where the transfer unit is not deformed by contacting the belt. The image forming apparatus according to any one of claims 1 to 3 . The image forming apparatus according to claim 5, wherein the guide member includes a rotation shaft and a pedestal rotatable about the rotation shaft, and the substrate is held on the pedestal. The image forming apparatus according to claim 6, wherein the rotation shaft is disposed upstream of the transfer unit with respect to a moving direction of the belt and is positioned on an inner peripheral surface side of the belt. The fibers, with respect to a direction normal to the substrate, as claimed in any one of claims 1 to 7, characterized in that it is brushed inclined to the downstream side along the moving direction of the belt Image forming apparatus. An angle γ formed by a normal direction of the substrate and a raising direction of the fiber in a state where the fiber is not deformed by contact with the belt is 0 ° ≦ γ ≦ 20 °. The image forming apparatus according to claim 8 . The angle θ formed by the raising direction of the fiber and the moving direction of the belt in a state in which the fiber is not deformed by being in contact with the belt is 70 ° ≦ θ ≦ 90 °. Item 10. The image forming apparatus according to any one of Items 1 to 9 . The image forming apparatus according to claim 1, wherein a width of the second region is wider than a width of the first region with respect to a moving direction of the belt. The image forming apparatus according to claim 11, wherein a width of the third region is narrower than a width of the first region with respect to a moving direction of the belt. The belt, the image forming apparatus according to any one of claims 1 to 12 the toner image from said image bearing member, characterized in that an intermediate transfer belt is transferred. The belt, the image forming apparatus according to any one of claims 1 to 12, wherein the toner image from said image bearing member is a transfer material conveying belt for carrying and conveying the transfer material to be transferred .

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