JP2011022466A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus configured to prevent image failure resulting from wavy wrinkles of an intermediate transfer belt, even in a configuration where a secondary transfer roller is offset, in the upstream of a secondary transfer counter roller and a drive roller is located on the upstream side of a secondary transfer section. <P>SOLUTION: The image forming apparatus includes a stretching roller 36, located in the downstream of the drive roller 32 in the conveyance direction of the intermediate transfer belt 31 and stretching the intermediate transfer belt 31; and a transfer roller abutting on the intermediate transfer belt 31 on the upstream of the contact faces of the stretching roller 36 and the intermediate transfer belt 31 in the conveyance direction of the intermediate transfer belt 31, and forming a transfer nip 37, together with the stretching roller 36 with the intermediate transfer belt 31 between them. In the image forming apparatus, the stretching roller 36 has an inverted crown shape, in which its outside diameter is small in its lengthwise middle and increases toward both its ends. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image forming apparatus for transferring a toner image formed on an image carrier onto an intermediate transfer belt as an intermediate transfer member, and transferring and recording the toner image on a transfer material.

  2. Description of the Related Art Conventionally, there is an image forming apparatus in which a toner image formed on an image carrier is primarily transferred onto an intermediate transfer belt as an intermediate transfer member, and this toner image is secondarily transferred to a transfer material. The image forming apparatus having such a configuration includes a driving roller that drives the intermediate transfer belt, a tension roller that stretches the belt, and a secondary transfer roller that performs secondary transfer. In addition to these rollers, such an image forming apparatus includes a secondary transfer counter roller disposed opposite to the secondary transfer roller, and other stretching rollers. It is known to affect the image quality at the transfer portion.

  Under such circumstances, in Patent Document 1, as a method for preventing an image defect due to electric discharge generated when a transfer material enters the secondary transfer portion, the secondary transfer roller is subjected to the secondary transfer in the intermediate transfer belt moving direction. A method of offsetting upstream of the opposing roller is disclosed.

JP-A-9-90780

  In the configuration in which the secondary transfer roller is offset upstream of the secondary transfer counter roller as described above, there is no gap between the intermediate transfer belt and the transfer material, and image defects due to discharge can be prevented. However, if wavy wrinkles occur on the intermediate transfer belt near the secondary transfer section, the gap between the intermediate transfer belt and the transfer material is created due to the difference in the level of the generated wrinkles, resulting in wavy wrinkles on the intermediate transfer belt. This may cause streaky density unevenness.

  The wavy wrinkles of the intermediate transfer belt are particularly likely to occur when there is a drive roller upstream of the secondary transfer portion because the drive roller tends to push the intermediate transfer belt.

  Therefore, the present invention is caused by wavy wrinkles of the intermediate transfer belt even in a configuration in which the secondary transfer roller is offset upstream of the secondary transfer counter roller and the drive roller is upstream of the secondary transfer unit. An object of the present invention is to provide an image forming apparatus that suppresses image defects.

The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention
An intermediate transfer belt carrying a toner image;
A driving roller for conveying and driving the intermediate transfer belt;
A tension roller that stretches the intermediate transfer belt and is positioned downstream of the drive roller in the conveyance direction in the conveyance direction of the intermediate transfer belt;
In the conveyance direction of the intermediate transfer belt, the intermediate transfer belt contacts the intermediate transfer belt on the upstream side in the conveyance direction from the contact surface between the tension roller and the intermediate transfer belt, and the tension roller sandwiches the intermediate transfer belt. A transfer roller that forms a transfer nip,
In the image forming apparatus for transferring the toner image on the intermediate transfer belt to the transfer material at the transfer nip portion,
The tension roller is an image forming apparatus characterized in that the outer diameter is small at the central portion in the longitudinal direction, and has an inverted crown shape that is increased toward both ends.

  According to the present invention, even in a configuration in which the secondary transfer roller is offset to the upstream side in the transport direction from the secondary transfer counter roller, which is also a tension roller of the intermediate transfer belt, and the drive roller is upstream, Image defects due to the wavy wrinkles can be suppressed.

1 is a schematic configuration diagram of an embodiment of an image forming apparatus according to the present invention. It is a detail drawing explaining a secondary transfer part. FIG. 6 is a diagram for explaining wavy wrinkles generated on an intermediate transfer belt on the upstream side of conveyance in a secondary transfer nip portion. It is a schematic shape diagram of a secondary transfer counter roller.

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

  However, the materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified.

Example 1
<Overall configuration of image forming apparatus>
First, the overall configuration of the image forming apparatus will be described together with the image forming operation with reference to FIG. FIG. 1 is a schematic configuration diagram of an embodiment of an image forming apparatus according to the present invention.

  In this embodiment, the image forming apparatus 100 includes a process cartridge 1 (1a, 1b, 1c, 1d) that is detachable from the image forming apparatus main body 100A. These four process cartridges 1a, 1b, 1c, and 1d have the same structure, but images of toners of different colors, that is, yellow (Y), magenta (M), cyan (C), and black (Bk) are displayed. It differs in the point to form. The process cartridge 1 (1a, 1b, 1c, 1d) includes a developing unit 7 (7a, 7b, 7c, 7d) and an image carrier unit 8 (8a, 8b, 8c, 8d). Among these, the former developing unit 7 (7a, 7b, 7c, 7d) has a developing roller 4 (4a, 4b, 4c, 4d). The latter image carrier units 8 (8a, 8b, 8c, 8d) are drum-like photosensitive members (hereinafter referred to as “photosensitive drums”) 2 (2a, 2b, 2c, 2d) as image carriers. It has. Around the photosensitive drum 2, a charging roller 3 (3a, 3b, 3c, 3d) and a drum cleaning blade 5 (5a, 5b, 5c, 5d) are disposed. A toner container is attached.

  A scanner unit 6 is disposed below the process cartridge 1 (1a, 1b, 1c, 1d), and performs exposure based on the image signal to the photosensitive drum 2 (2a, 2b, 2c, 2d).

  The photosensitive drum 2 (2a, 2b, 2c, 2d) is charged to a predetermined negative potential by the charging roller 3 (3a, 3b, 3c, 3d), and then an electrostatic latent image is formed by the scanner unit 6, respectively. Is done. This electrostatic latent image is reversed and developed by the developing unit 7 (7a, 7b, 7c, 7d), and negative toner is attached to form Y, M, C, and Bk toner images, respectively.

  An intermediate transfer belt unit 30 provided with an intermediate transfer belt 31 as an intermediate transfer member is disposed above the process cartridge 1 (1a, 1b, 1c, 1d). In the intermediate transfer belt unit 30, the intermediate transfer belt 31 is stretched around stretching rollers such as a driving roller 32, a secondary transfer counter roller 36, and a tension roller 33, and the tension roller 33 applies tension in the arrow B direction. It is over. A primary transfer roller 34 (34a, 34b, 34c, 34d) is disposed inside the intermediate transfer belt 31 so as to face each photosensitive drum 2 (2a, 2b, 2c, 2d), and is not shown. A transfer bias is applied by a bias applying means.

  Here, each photosensitive drum 2 rotates in the direction of the arrow (clockwise), the intermediate transfer belt 31 is moved in the direction of arrow A, and a positive bias is applied to the primary transfer rollers 34a, 34b, 34c, and 34d. As a result, the toner images formed on the respective photosensitive drums 2a to 2d are sequentially transferred onto the intermediate transfer belt 31 sequentially from the toner images on the photosensitive drum 2a, and the secondary images in a state where the four color toner images are overlapped. It is conveyed to the transfer nip portion 37.

  The feeding / conveying device 20 includes a paper feeding roller 22 that feeds the transfer material P from the paper feeding cassette 21 that houses the transfer material P, and a transporting roller 24 that transports the fed transfer material P. . Then, the transfer material P conveyed from the feeding / conveying device 20 is conveyed substantially perpendicularly to the secondary transfer nip portion 37 by the registration roller pair 23.

  By applying a positive bias to the secondary transfer roller 35 at the secondary transfer nip portion 37, the four color toner images on the intermediate transfer belt 31 are secondarily transferred to the transported transfer material P.

  After transfer of the toner image, the transfer material P is conveyed to the fixing device 40 and heated and pressed by the fixing roller 42 and the pressure roller 41 to fix the toner image on the surface. The fixed transfer material P is discharged to a discharge tray 44 by a discharge roller pair 43.

  On the other hand, the toner remaining on the surface of the photosensitive drum 2 (2a, 2b, 2c, 2d) after the toner image transfer is removed by the cleaning blade 5 (5a, 5b, 5c, 5d). Further, the toner remaining on the intermediate transfer belt 31 after the secondary transfer to the transfer material P is removed by the cleaning blade 51 of the transfer belt cleaning device 50, and the removed toner passes through the waste toner conveyance path 52, It is collected in a waste toner collection container (not shown).

<Configuration of secondary transfer unit>
FIG. 2 shows the configuration of the secondary transfer portion of the image forming apparatus in this embodiment.

The intermediate transfer belt 31 has a volume resistivity adjusted to 10 ⁸ Ω · cm by dispersing carbon in polyimide resin, a thickness of 50 μm, and a width in a direction perpendicular to the moving direction is 346 mm.

  The driving roller 32 that conveys and drives the intermediate transfer belt 31 has an outer diameter of 30 mm, and employs an aluminum three-arrow tube that has both a light weight and rigidity for the roller cored bar 32a. On the roller surface layer 32b, a rubber layer having a high μ (friction coefficient) is wound over a width of 330 mm in the roller axial direction in order to drive the intermediate transfer belt 31 stably. The intermediate transfer belt 31 is conveyed in the direction of arrow A by the drive roller 32 at a process speed of 135 mm / s.

A secondary transfer roller 35 as a secondary transfer means is at a predetermined pressure via a secondary transfer counter roller 36 disposed downstream of the driving roller 32 in the transport direction of the intermediate transfer belt 31 and the intermediate transfer belt 31. The secondary transfer nip portion 37 is formed by contact. As the secondary transfer roller 35, a conductive firing roller having an outer diameter of 20 mm and an actual resistance of 10 ⁷ Ω · cm when 1 kV was applied was used. The shape of the secondary transfer roller 35 is a straight shape.

  Here, a normal line 35x extending perpendicularly to the intermediate transfer belt 31 from the center O1 of the secondary transfer roller 35, and a normal line 36x extending perpendicularly to the intermediate transfer belt 31 from the center O2 of the secondary transfer counter roller 36. Is offset by ΔE = 4 mm. That is, the normal line 35x is located upstream of the normal line 36x in the transport direction A of the intermediate transfer belt 31. That is, the secondary transfer roller 35 is arranged upstream of the secondary transfer counter roller 36 in the transport direction. With this arrangement, when the transfer material P enters the secondary transfer nip portion 37, the gap between the intermediate transfer belt 31 and the transfer material P is reduced to prevent image defects due to discharge. Can do.

  However, as described above, the secondary transfer roller 35 is caused by the intermediate transfer belt 31 even in the configuration in which the secondary transfer roller 35 is disposed on the upstream side in the transport direction from the contact surface between the intermediate transfer bell 31 and the secondary transfer counter roller 36. An image defect may occur.

  FIG. 3 is a view of the intermediate transfer belt 31 as seen from the secondary transfer roller 35 side (however, the secondary transfer roller 35 is not shown).

  As shown in FIG. 3, wavy wrinkles may occur on the intermediate transfer belt 31 on the upstream side in the transport direction of the secondary transfer nip portion 37. In this case, a gap between the intermediate transfer belt 31 and the transfer material P is generated due to the difference in level of the wrinkles, and streaky density unevenness due to the wavy wrinkles of the intermediate transfer belt 31 may occur.

  The wavy wrinkles on the upstream side of the secondary transfer nip portion 37 are likely to occur in an arrangement in which the drive roller 32 is located upstream of the secondary transfer nip portion 37 as in this embodiment. This is because the intermediate transfer belt 31 is liable to loosen with the secondary transfer counter roller 36 due to the pushing of the drive roller 32.

  Therefore, in this embodiment, a wavy wrinkle of the intermediate transfer belt 31 generated on the upstream side of the conveyance of the secondary transfer nip portion 37 is suppressed by attaching a reverse crown to the secondary transfer counter roller 36.

  FIG. 4 shows the shape of the secondary transfer counter roller 36. The secondary transfer counter roller 36 employs an aluminum three-pointer tube as the roller cored bar 36a in the same manner as the driving roller 32, and the roller surface layer 36b has a semiconductive rubber layer of 0 to stabilize the secondary transfer. It is wound with a thickness of 5 mm. The outer diameter shape of the secondary transfer counter roller 36 is such that the outer diameter d1 at the center is 22 mm, and the region of (L / 2) = 165 mm from the left and right ends 36c is represented by a quadratic function curve. The left and right symmetrical inverted crown shape. In other words, the secondary transfer counter roller 36, which is a tension roller of the intermediate transfer belt 31, has a reverse outer diameter that is small (d1) at the center in the longitudinal direction of the roller 36 and increases (d2) toward both ends. Crown shape.

  In this embodiment, an outer diameter difference Δd (= d2−d1) between the outer diameter d2 of the end portion 36c at 165 mm from the central portion and the outer diameter d1 of the central portion is defined as the reverse crown amount, and Δd = 10 The thing of 20 micrometers was used. The reason why the reverse crown amount Δd is set in this way will be described by the effects of the following embodiments.

<Effect of Example>
Table 1 shows the relationship between the reverse crown amount Δd of the secondary transfer counter roller 36 and the stripe-like density unevenness visually recognized on the transfer material P. Table 1 also shows the relationship with the low density at the center, which is a concern when the reverse transfer roller 36 is provided with a reverse crown. As the transfer material P, 75 g / mm LTR size paper was used, and streaky density unevenness was confirmed with a single-color halftone image, and the density density at the center was confirmed with a two-color solid image.

  As shown in Table 1, streaky density unevenness visually recognized on the transfer material P is improved by attaching a reverse crown to the secondary transfer counter roller 36 by Δd = 10 μm or more. This is because the reverse transfer roller 36 is attached with a reverse crown, so that the force is applied to the intermediate transfer belt 31 in the direction of being pulled in both directions, and is generated upstream of the secondary transfer nip portion 37 in the conveyance. This is because the wavy wrinkles of the intermediate transfer belt 31 are eliminated.

  On the other hand, the thin density at the central portion visually recognized on the transfer material P is deteriorated by applying a reverse crown to the secondary transfer counter roller 36 by Δd = 30 μm or more. This is because the pressure on the secondary transfer roller 35 and the secondary transfer counter roller 36 at the center is reduced by attaching the reverse crown to the secondary transfer counter roller 36.

  Therefore, as in the configuration of the present embodiment, the secondary transfer roller 35 is offset to the upstream side of the secondary transfer counter roller 36 and the drive roller 32 is upstream of the secondary transfer nip portion 37 in the transport direction. By adopting the following configuration, operational effects can be obtained. That is, by attaching a reverse crown to the secondary transfer counter roller 36 in a range of Δd = 10 to 20 μm, image defects caused by wavy wrinkles of the intermediate transfer belt 31 can be prevented without causing other image defects. It is possible to realize an image forming apparatus that can be used.

  In this embodiment, the reverse crown is Δd = 10 to 20 μm, but the reverse crown is the thickness of the intermediate transfer belt 31, the shape of the secondary transfer roller 35, and the length of the secondary transfer counter roller 36. However, the value is not limited to this value.

30 Intermediate Transfer Belt Unit 31 Intermediate Transfer Belt 32 Drive Roller 33 Tension Roller 34 Primary Transfer Roller 35 Stretch Roller (Secondary Transfer Roller)
36 Secondary transfer counter roller

Claims (2)

An intermediate transfer belt carrying a toner image;
A driving roller for conveying and driving the intermediate transfer belt;
A tension roller that stretches the intermediate transfer belt and is positioned downstream of the drive roller in the conveyance direction in the conveyance direction of the intermediate transfer belt;
In the conveyance direction of the intermediate transfer belt, the intermediate transfer belt contacts the intermediate transfer belt on the upstream side in the conveyance direction from the contact surface between the tension roller and the intermediate transfer belt, and the tension roller sandwiches the intermediate transfer belt. A transfer roller that forms a transfer nip,
In the image forming apparatus for transferring the toner image on the intermediate transfer belt to the transfer material at the transfer nip portion,
2. The image forming apparatus according to claim 1, wherein the tension roller has an inverted crown shape in which an outer diameter is small at a central portion in the longitudinal direction and is increased as it goes to both ends.   The image forming apparatus according to claim 1, wherein a surface of the tension roller is a rubber layer.

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