JP2012022245A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that uses both an intermediate transfer belt with an elastic layer and a secondary transfer roller with an elastic roller, and satisfies suppression of color shift, improvement in separability, and improvement in transferability.SOLUTION: A color printer of the present invention includes: an endless belt-like intermediate transfer belt 11 that has an elastic layer 11b is rotationally moved by being extended by a belt roller 42; a secondary transfer roller 41 disposed opposite to the belt roller 42 and used for transferring a toner image, formed on the intermediate transfer belt 11, to a recording member. The secondary transfer roller 41 includes a core metal 41a disposed in the center, an external layer 41c disposed on the outermost circumference, and an internal layer 41b disposed between the core metal 41a and the external layer 41c. The relation of hardness between the respective layers is as follows: the hardness of the internal layer>the hardness of the elastic layer>the hardness of the external layer.

Description

  The present invention relates to an electrophotographic image forming apparatus. More specifically, the present invention relates to an image forming apparatus having an elastic belt-like image carrier having an elastic layer.

  Conventionally, in an electrophotographic image forming apparatus, an endless belt-shaped image carrier is often used as an intermediate transfer belt in, for example, a tandem type color printer. Further, an elastic intermediate transfer belt having an elastic layer between the base material and the surface layer may be employed as the intermediate transfer belt.

  For example, Patent Document 1 discloses an image forming apparatus including an intermediate transfer belt having an elastic layer. According to this document, the intermediate transfer belt sandwiched between the driving roller for driving the intermediate transfer belt and the secondary transfer roller is recessed by elastic deformation of the elastic layer, so that the transfer material is easily separated. .

  In order to increase the transfer efficiency, a transfer roller having an elastic layer may be used (for example, see Patent Document 2). This document discloses a transfer roller in which an intermediate layer is provided between an outermost layer having a relatively high hardness and an elastic layer.

JP 2006-201470 A JP 2007-292844 A

  However, it has been found that when both the intermediate transfer belt having the elastic layer and the secondary transfer roller having the elastic layer are used to improve both the separation property and the transfer efficiency, another problem occurs. It was. For example, in an apparatus having a secondary transfer roller and a belt roller that are pressed against each other with an intermediate transfer belt interposed therebetween, the pressure contact state differs depending on the presence or absence of the transfer material in these nips or the thickness of the transfer material. Furthermore, the driving state of these rollers or the intermediate transfer belt differs depending on the pressure contact state. Therefore, there is a problem that the driving state of each member changes before and after the transfer material enters and exits.

  For example, when the secondary transfer roller and the belt roller are in pressure contact with each other by an elastic force such as a spring, the distance between the axes of both rollers changes when the transfer material enters and exits. Alternatively, in the case where the distance between the rollers is fixed, the rotational torque changes due to compression of the elastic layer. In these cases, the driving speed of the intermediate transfer belt differs before and after the transfer material enters and exits. Alternatively, the driving speed of the intermediate transfer belt changes at that moment. For this reason, if the primary transfer of one of the colors is being performed at that time, there is a risk of causing a color shift.

  The present invention has been made to solve the problems of the conventional image forming apparatus described above. In other words, the problem is that both an intermediate transfer belt having an elastic layer and a secondary transfer roller having an elastic layer are used together to suppress color misregistration, improve separation, and improve transferability. An object of the present invention is to provide an image forming apparatus that can satisfy the above requirements.

  The image forming apparatus of the present invention, which has been made for the purpose of solving this problem, has an elastic layer, is an endless belt, and is an intermediate transfer belt that is rotated around a plurality of belt rollers, and an intermediate transfer belt A toner image forming portion for forming a toner image thereon, and a transfer roller disposed opposite to one of the belt rollers and transferring the toner image formed on the intermediate transfer belt to the recording member by the toner image forming portion. In the image forming apparatus, the transfer roller has a cored bar disposed at the center, an outer layer disposed at the outermost periphery, and an inner layer disposed between the cored bar and the outer layer, and is elastic. The relationship between the hardness of the layer, the hardness of the outer layer, and the hardness of the inner layer is such that the hardness of the inner layer> the hardness of the elastic layer> the hardness of the outer layer.

According to the image forming apparatus of the present invention, an intermediate transfer belt having an elastic layer and a transfer roller having a layer structure of core metal + inner layer + outer layer, the order of hardness of each layer being the hardness of the inner layer > Hardness of elastic layer> Hardness of outer layer. That is, the outer layer of the transfer roller is formed of the softest elastic material. On the other hand, the inner layer of the transfer roller is the hardest of these three layers. Since the three layers have different hardnesses and are in this order, changes in the pressure contact state when the transfer material enters and exits are received step by step in the nip therebetween. Therefore, the intermediate transfer belt having the elastic layer and the secondary transfer roller having the elastic layer are used together, and all of the suppression of color misregistration, the improvement of the separation property, and the improvement of the transfer property can be satisfied.

Furthermore, in the present invention, it is desirable that the outer layer be formed of an elastic foam material, and the inner layer be formed of an elastic material.
If it is such, it is easy to form a transfer roller having the above-mentioned hardness.

Further, in the present invention, the shape of the nip formed at the contact point between the transfer roller and the intermediate transfer belt is a convex curved surface on the transfer roller side in the central portion with respect to the moving direction of the intermediate transfer belt. It is desirable that the intermediate transfer belt side is a convex curved surface at both ends located at.
If it is such, both transferability and separability can be ensured by the location in the nip.

  According to the image forming apparatus of the present invention, an intermediate transfer belt having an elastic layer and a secondary transfer roller having an elastic layer are used together, and any of suppression of color misregistration, improvement of separation, and improvement of transferability can be achieved. Can also be met.

1 is a schematic configuration diagram of an image forming apparatus according to the present embodiment. FIG. 3 is a cross-sectional view showing an intermediate transfer belt. It is sectional drawing which shows a secondary transfer roller. It is explanatory drawing which shows the shape of nip. It is explanatory drawing which shows the shape of the nip of a comparative example. It is explanatory drawing which shows the shape of the nip of a comparative example. It is explanatory drawing which shows the shape of the nip of a comparative example. It is explanatory drawing which shows the shape of the nip of a comparative example. It is explanatory drawing which shows the shape of the nip of a comparative example.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the best mode for embodying the present invention will be described in detail with reference to the accompanying drawings. In this embodiment, the present invention is applied to a tandem type electrophotographic color printer.

  The color printer 1 of the present embodiment is a so-called tandem image forming apparatus capable of forming a color image, as shown in FIG. In the middle of the figure, four color image forming portions are arranged along the intermediate transfer belt 11 in the order of yellow 10Y, magenta 10M, cyan 10C, and black 10K from left to right in the figure. In addition, a detachable paper feed cassette 13 is attached to the lower left portion of the color printer 1 in the drawing, and a manual feed unit 14 is attached to the lower right portion of the drawing.

  As shown in FIG. 1, the yellow image forming unit 10 </ b> Y includes a charging unit 22, a developing unit 24, a primary transfer unit 25, and a cleaner 26 with a photosensitive member 21 at the center. In the figure, only the yellow image forming unit 10Y is described with reference numerals, but the other colors have substantially the same configuration. The exposure unit 23 is provided below the image forming unit for each color, and is common to each color. Furthermore, hoppers 28Y, 28M, 28C, and 28K that store toner of each color are provided above the intermediate transfer belt 11 in the drawing. The black image forming unit and hopper are slightly larger than those of other colors.

  Further, on the right side in FIG. 1, paper transport paths 31 and 32 are provided. In the drawing, a sheet conveyance path 31 for conveying a sheet from bottom to top and a sheet conveyance path 32 for conveying a sheet from top to bottom in the figure are provided side by side. The paper transport path 32 is used when performing duplex printing. A plurality of conveyance rollers 33 are provided in the sheet conveyance paths 31 and 32, respectively. The color printer 1 according to the present embodiment is capable of conveying or stopping a sheet along the conveyance paths 31 and 32 as needed by controlling these conveyance rollers 33.

  As shown in FIG. 1, a secondary transfer unit 35 and a fixing unit 36 are disposed on the paper transport path 31. The fixing unit 36 includes a roller pair formed by two rollers (a heating roller 37 and a pressure roller 38) facing each other. The secondary transfer unit 35 has a secondary transfer roller 41. The intermediate transfer belt 11 is wound around a plurality of belt rollers 42 and 43, and the secondary transfer roller 41 is sandwiched between the intermediate transfer belt 11 and one of the belt rollers 42 is interposed therebetween. It is pressed using a spring. A control unit 40 for controlling each unit is also provided in the machine.

  The intermediate transfer belt 11 of this embodiment has a layer structure including an elastic material layer as shown in FIG. The lowermost layer in FIG. 2 is the innermost layer (the layer disposed on the inner peripheral side in FIG. 1), and has a base material layer 11a, an elastic layer 11b, and a surface layer 11c in order from the inner side to the outer side. is doing. In addition, you may have another layer other than these.

  The base material layer 11a is a layer having a thickness of about 50 to 200 μm formed of PET (polyethylene terephthalate) or PVdF (polyvinylidene fluoride). The elastic layer 11b is a layer made of an elastic material formed to a thickness of about 100 to 500 μm by an elastic material such as NBR (nitrile rubber), CR (chloroprene) rubber, urethane rubber or the like. Further, the surface layer 11c is a layer made of a resin material such as acrylic or ABS (acrylonitrile / butadiene / styrene copolymer synthetic resin), or a material obtained by applying a fluorine resin coating or oxidation treatment to the resin layer to further improve the releasability. And is formed to a thickness of about 0.1 to 5 μm.

  Further, as shown in FIG. 3, the secondary transfer roller 41 of the present embodiment has a cored bar 41a, an inner layer 41b, and an outer layer 41c. The cored bar 41a rotates the secondary transfer roller 41 by receiving a rotational driving force. The inner layer 41b is a layer formed of an elastic material. The outer layer 41c is a layer formed of a foam material obtained by foaming an elastic material. For example, NBR, CR rubber, urethane rubber, or the like can be used as the type of elastic material of the inner layer 41b or the outer layer 41c. The material types of the inner layer 41b and the outer layer 41c may be the same or different.

Here, in this embodiment, the hardness E11b of the elastic layer 11b of the intermediate transfer belt 11, the hardness E41b of the inner layer 41b of the secondary transfer roller 41, and the hardness E41c of the outer layer 41c are as follows. The material is selected.
E41b>E11b> E41c
That is, the inner layer 41b of the secondary transfer roller 41 is the hardest and the outer layer 41c of the secondary transfer roller 41 is the softest. The elastic layer 11b of the intermediate transfer belt 11 has an intermediate hardness.

  Since the hardness of the three layers has this relationship, the shape of the nip N at the press contact portion between the intermediate transfer belt 11 and the secondary transfer roller 41 is a wavy curved surface as shown in FIG. In the nip N, the softest outer layer 41c among the three layers is compressed most. However, in the vicinity of the center portion of the nip N, the outer layer 41c is greatly compressed, so that the outer layer 41c receives a repulsive force by the hardest inner layer 41b on the back side. Therefore, when the compression amount of the outer layer 41c is a certain level or more, the elastic layer 11b that is softer than the inner layer 41b is also compressed.

  As a result, the intermediate transfer belt 11, the secondary transfer roller 41, and the nip N are swelled in different directions at both ends Ne and the center Nf, as shown in FIG. At both ends Ne where the distance from the nip N to the inner layer 41b is large, only the outer layer 41c is compressed. For this reason, the intermediate transfer belt 11 side is convex at both ends Ne. On the other hand, in the central portion Nf where the distance from the nip N to the inner layer 41b is small, the intermediate transfer belt 11 is also compressed by the repulsive force of the inner layer 41b. In the central portion Nf, the secondary transfer roller 41 side is convex.

  Accordingly, the nip N is relatively flat as a whole, and the paper does not get tangled by passing through the nip N. Further, at the outlet P of the nip N, as shown in FIG. 4, the outer peripheral surface of the secondary transfer roller 41 is greatly curved, so that it is possible to separate the curvatures on both sides of the sheet. In this figure, a slight gap is provided between the intermediate transfer belt 11 and the secondary transfer roller 41, but this is to clearly show that both members are in this shape. It is. Except when paper or the like is caught in the nip N, no gap is generated between them.

  In this embodiment, since the nip N has such a shape, the transferability is high. Since the range in which the secondary transfer roller 41 side is convex in the nip N is limited, the pressure distribution becomes sharp. Therefore, the pressure applied at the center of the range is large. Further, since the intermediate transfer belt 11 is concave at the center of the nip N, the elastic layer 11b can follow the shape of the paper well even if the paper has a slightly concave portion. In particular, it can also be appropriately transferred to the recesses of uneven paper (for example, thick paper with a texture on the surface used for greeting cards).

  Furthermore, in this embodiment, the paper separation property is also excellent. The shape of the nip N has a relatively large curvature. Accordingly, curvature separation is performed near the exit of the nip N on both sides of the sheet. Particularly, in the vicinity of the exit P of the nip N, the intermediate transfer belt 11 side has a convex shape and has a relatively steep curve. Therefore, the sheet is peeled off by the elasticity of the sheet itself, and the sheet separation property is also good. .

  Furthermore, according to this embodiment, color misregistration is also suppressed. The compression amount corresponding to the thickness of the paper when entering and exiting the paper is distributed among the layers. Many portions are made by deformation of the outer layer 41c of the secondary transfer roller 41, which is the softest layer. This deformation mainly absorbs the shock of paper entry / escape. Further, the shock is absorbed in stages on both sides by the elastic layer 11b of the second softest intermediate transfer belt 11. Therefore, there is no influence that the rotational driving state of the belt roller 42 and the secondary transfer roller 41 changes. Thereby, the color shift is effectively suppressed.

  Next, the operation of each unit when a color image is formed by the color printer 1 will be described. A toner image is formed on each color photoconductor 21 at the same timing. That is, it is uniformly charged by the charging unit 22 and subsequently exposed by the exposure unit 23. As a result, an electrostatic latent image based on the image data of each color is formed on the surface of the photoconductor 21 of each color. Next, the developing unit 24 supplies toner to the electrostatic latent image, and a toner image is formed on the photoreceptor 21.

  The toner images respectively formed on the photosensitive members 21 of the respective colors are transferred onto the intermediate transfer belt 11 by the respective primary transfer portions 25 and are superimposed on each other. As a result, a color toner image is formed on the intermediate transfer belt 11. Note that the toner remaining on the photoconductor 21 even after passing through the primary transfer area is scraped off by the cleaner 26.

  On the other hand, sheets as recording members for image formation are pulled out one by one from the sheet feeding cassette 13 or the manual feed unit 14 to the sheet conveying path 31 as indicated by an arrow h in FIG. Then, the sheet is conveyed along the sheet conveyance path 31 toward the secondary transfer unit 35. The toner image superimposed on the intermediate transfer belt 11 is transferred to the conveyed paper in the secondary transfer unit 35.

  The sheet on which the toner image has been transferred is further conveyed upward to reach the fixing unit 36 where it is heated and pressurized. As a result, the toner is fixed on the paper. Then, the paper on which the image has been formed is discharged out of the machine. Further, the post-secondary transfer portion of the intermediate transfer belt 11 is further rotated in the direction of the arrow g in the drawing and reaches the belt cleaner 51. The intermediate transfer belt 11 from which the deposits on the surface have been removed by the belt cleaner 51 is further moved and used for the next image formation.

  The inventor confirmed the effect of this embodiment through experiments. For this purpose, an embodiment in which the material of the elastic layer 11b of the intermediate transfer belt 11, the inner layer 41b and the outer layer 41c of the secondary transfer roller 41 is appropriately selected, and the relationship of their hardnesses is the relationship of this embodiment is manufactured. did. Furthermore, five types of comparative examples were prepared in which the relationship between these hardnesses was different from the order of this embodiment. All of these comparative examples have the same layer configuration as that of this embodiment except for the order of hardness of each layer.

  In the examples, these layers were measured by an ASKER MD-1 type C manufactured by Kobunshi Keiki Co., Ltd., and had E11b = 48 °, E41b = 60 °, and E41c = 40 °. Therefore, the relationship of E41b> E11b> E41c is satisfied. Here, the elastic layer 11b of the intermediate transfer belt 11 is NBR, the inner layer 41b of the secondary transfer roller 41 is NBR, and the outer layer 41c is a foamed NBR.

  Each of Comparative Examples 1 to 5 is different in hardness from the examples. The order of hardness is as follows: Comparative Example 1 is E41b> E41c> E11b, Comparative Example 2 is E11b> E41b> E41c, Comparative Example 3 is E11b> E41c> E41b, Comparative Example 4 is E41c> E11b> E41b, Comparative Example 5 E41c> E41b> E11b. The material of the intermediate transfer belt 11 and the material of the secondary transfer roller 41 were appropriately selected so as to be a combination of these.

  In this experiment, three points were evaluated: transferability of uneven paper, paper separation, and color misregistration. In the evaluation of the transferability of the concavo-convex paper, a paper called “Rezac paper” (“Rezak” is a trade name) was used as an example of the concavo-convex paper to evaluate the transferability of the paper to the concave portion. The case where the transfer to the concave portion was good was marked with ◯, and the case where it was poor was marked with ×. In the evaluation of paper separation, double-sided printing was performed using a paper called “ST paper”, and the separation on the second side, which is particularly difficult to separate, was evaluated. Those that could be separated were marked with ○, and those that could not be separated were marked with ×. In the evaluation of color misregistration, visual evaluation was performed. The case where no color misregistration occurred and good image quality was obtained was marked with ◯, and when there was a color misalignment that could be judged visually, x was marked.

  The results of this experiment are shown in Table 1. Moreover, the shape of the nip part of each example was shown in FIGS. In the examples, good results were obtained in terms of transferability, separability, and color misregistration. In Comparative Example 1, the transferability was good, but the separation and color shift were not good. In Comparative Examples 2 and 3, there was no color shift, but neither transferability nor separation property was good. In Comparative Examples 4 and 5, both transferability and separation were satisfactory, but color misregistration occurred. Therefore, this experiment confirmed the effect of this embodiment.

  As described above in detail, according to the image forming apparatus of this embodiment, the hardness E11b of the elastic layer 11b of the intermediate transfer belt 11, the hardness E41b of the inner layer 41b of the secondary transfer roller 41, and the hardness E41c of the outer layer 41c are E41b. > E11b> E41c. Therefore, the shape of the nip N for secondary transfer is a curved surface having both irregularities. That is, there are a portion where the intermediate transfer belt 11 is convex and a portion where the secondary transfer roller 41 is convex. Thereby, it is possible to make both transferability and separability good according to each location. Furthermore, since the elastic layers on both sides can receive a shock when the paper enters and exits, color misregistration is suppressed. As a result, the intermediate transfer belt having the elastic layer and the secondary transfer roller having the elastic layer are used together to satisfy all of suppression of color misregistration, improvement of separation, and improvement of transferability.

In addition, this form is only a mere illustration and does not limit this invention at all. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof.
For example, in this embodiment, a tandem color printer is illustrated, but the present invention is not limited to this.

DESCRIPTION OF SYMBOLS 1 Color printer 10Y, 10M, 10C, 10K Image formation part 11 Intermediate transfer belt 11b Elastic layer 41 Secondary transfer roller 41a Core metal 41b Inner layer 41c Outer layer 42 Belt roller

Claims (3)

An intermediate transfer belt having an elastic layer and having an endless belt shape and being rotated around a plurality of belt rollers, a toner image forming portion for forming a toner image on the intermediate transfer belt, and the belt roller An image forming apparatus including a transfer roller disposed opposite to the toner image and configured to transfer a toner image formed on the intermediate transfer belt to the recording member by the toner image forming unit.
The transfer roller is
A cored bar arranged in the center;
An outer layer arranged on the outermost periphery;
An inner layer disposed between the cored bar and the outer layer;
The relationship between the hardness of the elastic layer, the hardness of the outer layer, and the hardness of the inner layer is
Hardness of inner layer> Hardness of elastic layer> Hardness of outer layer The image forming apparatus according to claim 1,
The outer layer is formed of an elastic foam material,
The image forming apparatus, wherein the inner layer is formed of an elastic material. The image forming apparatus according to claim 1, wherein:
The shape of the nip formed at the contact point between the transfer roller and the intermediate transfer belt is:
In the central portion with respect to the moving direction of the intermediate transfer belt, the transfer roller side is a convex curved surface,
An image forming apparatus, wherein the intermediate transfer belt side is a convex curved surface at both end portions located before and after the central portion.

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