JP2008033191A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus equipped with a secondary counter roller that suppresses transfer defects due to differences in nip width between nip parts formed by the secondary counter roller at ends and a center part of the secondary counter roller although the secondary counter roller is kept in a straight shape. <P>SOLUTION: The image forming apparatus comprises the secondary counter roller 24 which rotates while wound with a belt-like image carrier 17, a secondary transfer roller 25 which rotates in the same direction as that of the secondary counter roller 24 and comes into contact with the secondary counter roller 24 across the image carrier 17, and resist roller 22 and 23 disposed in the region where the image carrier 17 and secondary transfer roller 25 comes into contact with each other upstream in the conveying direction of a transfer material so as to convey the transfer material 26, and transfers a toner image formed on an image carrier 17 to the transfer material 26 by applying a current or voltage from the secondary counter roller 24. The secondary counter roller 24 is formed of a crown-shaped rubber roller part 24b and a high-resistance coating material 24a formed thereupon and has a straight outward shape. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, and a printer, and more particularly to an image forming apparatus that transfers a toner image carried on a belt-like image carrier onto a transfer material using a transfer belt. .

In a color image forming apparatus, yellow, magenta, cyan, and black toner images are sequentially formed on a photosensitive drum, and these toner images are sequentially primary-transferred onto an intermediate transfer belt by a primary transfer roller. It is known that toner images of a plurality of colors are superimposed on a transfer belt, and then these intermediate transfer belt-like toner images are secondarily transferred collectively onto a transfer material such as paper by a secondary transfer roller. (For example, see Patent Documents 1 to 4).
In this image forming apparatus, the nip portion formed by the photosensitive member and the primary transfer roller, and the nip portion formed by the secondary transfer roller and the secondary counter roller are end portions of the primary transfer roller and the secondary transfer roller. It is formed by applying a load to.

FIG. 3 is a schematic view showing a nip portion formed by a conventional straight-shaped secondary opposing roller. In the color copying machine which is an image forming apparatus, when the secondary facing roller 24 has a straight shape, the nip portion formed by the secondary facing roller 24 shown in FIG. 3 has a nip width n2 at the center of the secondary facing roller 24. As a result, there is a difference in the nip width n1 at the end.
At the central portion and the end portion of the primary transfer portion and the secondary transfer portion, how to apply the load at the central portion is weakened, so that the nip width of the central portion is narrowed in the primary transfer portion and the secondary transfer portion. For this reason, there is a problem in that a transfer failure occurs because a transfer current is less likely to flow in the central portion where the nip width between the primary transfer portion and the secondary transfer portion is narrow.

In order to solve the above-described problem, Patent Document 1 discloses that the resistance value of the central portion of the feeding roller is lower than the resistance value of the end portion thereof, and Patent Document 2 discloses deformation of the roller due to thermal expansion. In view of this, it is disclosed to eliminate paper wrinkles.
Further, Patent Document 3 discloses that the shaft shaft is deformed, and Patent Document 4 discloses that the roller resistance is uniform, so that the roller resistance is made uniform.
In the above-described conventional technology, the difference between the nip widths of the central portion and the end portions of the primary transfer roller and the secondary transfer roller is further improved by making the primary transfer roller and the secondary transfer roller into a crown shape. There is also disclosed a technique for eliminating the transfer failure at the center portion.

Japanese Patent Application Laid-Open No. 07-036289 JP 09-152803 A JP 2002-14590 A JP-A-11-272097

However, the above-described crown-shaped transfer roller according to the prior art has a problem in that the pressing of the blade at the time of cleaning is not uniform in the axial direction of the roller, and a cleaning failure of the transfer roller occurs.
Further, in Patent Document 2, it is disclosed that silicon rubber and fluororubber latex are fired on the surface of a roller formed in a crown shape. However, as described above, this eliminates paper wrinkles. Even if this pressure roller is used for the purpose, the resistance value in the axial direction is not constant, and it is difficult to suppress transfer defects.
As described above, in an image forming apparatus that performs printing using a transfer roller, a transfer current flowing in the center of the transfer roller is reduced by the transfer roller pressing force being weakened in the center of the transfer roller. It is difficult to suppress image defects that occur in the central portion of the transfer roller by reducing the transfer current flowing into the portion.
In view of the above situation, the object of the present invention is to maintain the nip width between the end and the center of the secondary counter roller formed by the secondary counter roller while keeping the secondary counter roller in a straight shape. An object of the present invention is to provide an image forming apparatus including a secondary facing roller that suppresses transfer failure due to a difference.

In order to solve the above-mentioned problems, the invention according to claim 1 is characterized in that a belt-like image carrier is wound around a secondary counter roller that rotates and rotates in the same direction as the secondary counter roller, and the belt-like image is rotated. In order to transport the transfer material to a region where the belt-like image carrier and the secondary transfer roller are in contact with each other, a secondary transfer roller that is in contact with the secondary counter roller via the carrier, An image forming apparatus for transferring a toner image formed on the belt-shaped image carrier to the transfer material by applying a current or a voltage from the secondary counter roller. The secondary opposing roller is characterized in that the image forming apparatus is formed of a crown-like rubber roller portion and a high-resistance coating material applied on the rubber roller portion and has a straight appearance. To.
According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the secondary facing roller has a resistance value at a central portion lower than a resistance value at an end portion.

  According to the present invention, as described above, the secondary opposing roller is formed of a crown-shaped rubber roller portion and a high-resistance coating material applied thereon and has a straight appearance. Thus, the resistance value at the center can be made lower than the resistance value at the end. Therefore, the transfer failure at the central portion is suppressed, and the roller shape has a straight appearance, so that the cleaning blade can be uniformly pressed on the roller, and the cleaning failure can be suppressed.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram showing the overall configuration of a color copying machine to which the present invention is applied. Hereinafter, an embodiment of a color copying machine which is a color image forming apparatus to which the present invention is applied will be described. First, the configuration and operation of an image forming unit and a transfer unit, which are main parts of the color copying machine A, will be described with reference to FIG.
The image forming unit and the primary transfer unit include a charging device 10 (10a to 10d), an exposure device 11 (11a to 11d), a developing device 12 (12a to 12d), a static eliminating device 13 (13a to 13d), and a cleaner 14 ( 14a to 14d), a photoreceptor 15 (15a to 15d), a primary transfer roller 16 (16a to 16d), and an intermediate transfer belt 17 which is a belt-like image carrier.
The photoconductor 15 (15a to 15d) rotates in the direction of the arrow shown in the drawing. The intermediate transfer belt 17 is stretched by rollers 18 and 19 and is in contact with the photoreceptor 15 (15a to 15d).
Around the photosensitive member 15 (15a to 15d), the neutralization device 13 (13a to 13d) and the cleaner 14 described above with respect to the rotation direction of the photosensitive member 15 (15a to 15d) from the point of contact with the intermediate transfer belt 17. (14a-14d), charging device 10 (10a-10d), exposure device 11 (11a-11d), and developing device 12 (12a-12d) are arranged in this order.

  The primary transfer rollers 16 (16a to 16d) are arranged to be pressed from the back side of the area where the photoconductor 15 (15a to 15d) and the intermediate transfer belt 17 are in contact. In this embodiment, the roller that drives the intermediate transfer belt 17 is the intermediate transfer belt stretching roller 18, and the intermediate transfer belt 17 is moved in the direction of the arrow by the roller 18.

Next, an image forming method and a primary transfer method will be described. The photoreceptor 15 is charged by the charging device 10. Thereafter, an electrostatic latent image is generated on the charged photoconductor 15 by irradiating a laser beam from the exposure device 11 based on image data from a scanner and a PC (personal computer).
Thereafter, development is performed on the photoreceptor 15 with toner charged by the developing device 12. The toner image formed on the photoconductor 15 is transferred onto the intermediate transfer belt 17 by applying a transfer electric field with a constant current or a current or voltage controlled by a constant voltage to the primary transfer roller 16. .
After the toner image is transferred onto the intermediate transfer belt 17, the photoconductor 15 removes the residual charge remaining on the photoconductor 15 by the static eliminator 13 and removes the toner remaining on the photoconductor 15 by the cleaner 14. The process of returning to the charging device 10 is repeated.

In the embodiment of FIG. 1, image forming portions are arranged for four colors of cyan, magenta, yellow, and black, respectively, and a toner image formed on the photoconductor 15a is subjected to primary transfer onto the intermediate transfer belt 17. After the transfer, the intermediate transfer belt 17 moves to the photoconductor 15b and transfers the toner image formed by the photoconductor 15b onto the toner image transferred by the photoconductor 15a. Thereafter, the photoconductors 15c and 15d and the toner image are sequentially superposed and transferred.
The toner image transferred onto the intermediate transfer belt 17 is transferred by the registration rollers 22 and 23 at the secondary transfer portion formed by the secondary facing roller 24 and the secondary transfer roller 25 that hold the intermediate transfer belt 17. Transferred to the material 26.
In the secondary transfer portion described above, a current is applied to the secondary facing roller 24 and the transfer current flows into the secondary transfer roller 25, thereby transferring the toner image on the intermediate transfer belt 17 to the transfer material 26. Can do.
In the color copying machine which is the image forming apparatus described above, when the secondary facing roller 24 has a straight appearance, it is formed by the secondary facing roller 24 shown in FIG. 3 as described in the related art. In the nip portion, there is a difference between the nip width n2 at the center of the secondary facing roller 24 and the nip width n1 at the end. As a result, a transfer current is difficult to flow in the central portion where the nip width is narrow, which causes a transfer failure.

FIG. 2 is a schematic view showing an embodiment of the secondary opposing roller of the present invention. In the present invention, as shown in FIG. 2, a configuration is adopted in which a high-resistance coating material is applied onto the crown-shaped rubber roller 24 that constitutes the secondary facing roller. The rubber roller 24 includes a coating material 24a and a rubber roller portion 24b.
In this case, when the volume resistivity R1 of the coating material 24a, the layer thickness d of the coating material 24a, and the nip width are n, the resistance value R per unit length in the axial direction of the secondary opposing roller 24 is R = R1 × d / n
Therefore, in the present invention, when the thickness d1 of the coating material 24a at the end and the thickness at the center are d2, the resistance value R of the secondary facing roller 24 is R = R1 × d1 / n1 = R1 × d2. By determining d1 and d2 so as to be / n2, the resistance value of the secondary facing roller 24 can be made constant at the center portion and the end portion of the nip portion.
As a result, in the nip portion formed by the secondary facing roller 24, the same transfer current can be supplied to both the center portion and the end portion, so that transfer failure at the center portion can be suppressed.

1 is a schematic diagram showing the overall configuration of a color copying machine to which the present invention is applied. Schematic which shows embodiment of the secondary opposing roller of this invention. Schematic which shows the nip part formed of the conventional straight-shaped secondary opposing roller.

Explanation of symbols

10 (10a to 10d) charging device (charging device for each color of Y, M, C, K)
11 (11a to 11d) Exposure device (Y, M, C, K exposure devices for each color)
12 (12a to 12d) Developing device (Developing device for each color of Y, M, C, K)
13 (13a to 13d) Charger (Y, M, C, K colors)
14 (14a-14d) cleaner (cleaner for each color of Y, M, C, K)
15 (15a to 15d) Image carrier (photosensitive members for each color of Y, M, C, K)
16 (16a to 16d) primary transfer roller (primary transfer roller for each color of Y, M, C, K)
17 Belt-shaped image carrier (intermediate transfer belt)
18, 19 Intermediate transfer belt stretching roller 20, 21 Fixing roller 22, 23 Registration roller 24 Secondary opposing roller 24a Coating material 24b Rubber roller section 25 Secondary transfer roller 26 Transfer material

Claims (2)

A secondary opposing roller that rotates by winding a belt-like image carrier, and a secondary transfer that rotates in the same direction as the secondary opposing roller and is in contact with the secondary opposing roller via the belt-like image carrier. A roller, and a registration roller disposed upstream of the transfer material in the conveyance direction for conveying the transfer material to a region where the belt-shaped image carrier and the secondary transfer roller are in contact with each other. In the image forming apparatus for transferring the toner image formed on the belt-shaped image carrier to the transfer material by applying a current or a voltage,
The secondary opposing roller is formed of a crown-shaped rubber roller portion and a high-resistance coating material applied on the rubber roller portion, and has a straight appearance.   The image forming apparatus according to claim 1, wherein the secondary facing roller has a resistance value at a central portion lower than a resistance value at an end portion.

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