JP2006259640A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of obtaining an image of high quality by suppressing local void phenomenons at low cost. <P>SOLUTION: In the image forming apparatus for sequentially performing primary transfer of images to a movable intermediate transfer belt 200 abutted on a plurality of image carriers on respective primary transfer portions and then collectively transferring toner images superposed and transferred to the intermediate transfer belt 200 to a transfer material on a secondary transfer portion; against a plane constituted of the image carrier 104 abutted on the uppermost portion in the traveling direction of the intermediate transfer belt 200, the image carrier 101 abutted with a belt contact nip midpoint on the lowermost portion, and the belt contact nip midpoint, the other image carriers 102, 103 and the belt contact NIP midpoints are offset to the belt side, the intermediate transfer belt 200 is wound around photoreceptors 202, 203, so that wide-range transfer nips can be formed without being pressed by the primary transfer rollers 206, 207 and the image can be transferred in an almost no-load state. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, and a printing machine, and more particularly, to a transfer technique of a multicolor image forming apparatus provided with a plurality of electrostatic latent image carriers and a plurality of developing devices.

A so-called tandem-type color output device using a plurality of photoconductors has the advantage that the number of output sheets per unit time is large and the production efficiency is high, but it is difficult to align the writing position for each color. There are two types of tandem color output devices: a type that directly transfers to the final transfer member, and a type that transfers to the final transfer member via an intermediate transfer member.

The direct transfer method is a method of transferring directly from an image carrier (photosensitive drum) to a final transfer member. The intermediate transfer method is a method in which the transfer member is not the final transfer member but is transferred to the final transfer member after being transferred to the intermediate transfer member. In this method using an intermediate transfer member (intermediate transfer method), since the material of the transfer member is constant when transferring from the image forming unit, the alignment of each color may be compared with the direct transfer method and there is less color misregistration. It has the feature that a high-quality color image can be obtained.
Further, in the one-drum system in which images are sequentially formed on a single photoconductor and color is superimposed on an intermediate transfer member, since there is one primary transfer, the cost is low and the apparatus can be downsized. However, there is a drawback that the number of output color images per unit time is small.

However, although the tandem intermediate transfer method can compensate for the color misregistration disadvantages of the tandem direct transfer method, there have been problems of cost reduction and downsizing of the apparatus as compared with the one-drum method. Further, the conventional intermediate transfer method has a problem in that a hollow image is generated due to toner aggregation at a local transfer pressure at the primary transfer portion.

In addition, when foamed sponge or silicon foam is used as the heat insulating member, the foamed layer is deformed by the applied pressure when left standing, and it takes time for the deformation to recover. There was also the possibility of causing problems such as noise.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus capable of obtaining a high-quality image at a low cost by suppressing a local hollowing phenomenon. And

As means for solving the above problems, the present invention has the following features.
In the image forming apparatus of the present invention, each toner image formed on at least three or more image carriers is placed on a movable intermediate transfer belt that comes into contact with the plurality of image carriers and each primary transfer portion. Each of the primary transfer portions sequentially performs primary transfer onto a plurality of image carriers via the intermediate transfer belt, and the toner images superimposed and transferred on the intermediate transfer belt are collectively transferred to a transfer material at the secondary transfer portion. In the image forming apparatus that performs secondary transfer, the image carrier that is in contact with the most upstream side in the running direction of the intermediate transfer belt, the image carrier that is in contact with the middle point of the belt contact nip and the most downstream side, and the belt contact nip The other image carrier and the belt contact nip midpoint are offset to the belt side with respect to the plane formed by the midpoint.
Further, the image forming apparatus of the present invention further includes a belt plane between the image carriers determined by the most upstream image carrier and an adjacent image carrier in the intermediate transfer belt traveling direction. A belt stretching roller disposed on the upstream side of the upstream image carrier is offset and intersects with the uppermost image carrier side with respect to the belt plane.
Further, the image forming apparatus of the present invention further includes a belt plane between the image carriers determined by an image carrier adjacent to the most downstream image carrier in the running direction of the intermediate transfer belt with respect to the belt plane between the image carriers. A belt stretching roller disposed on the downstream side of the downstream image carrier is offset and intersects with the belt surface on the most downstream image carrier side.

The image forming apparatus of the present invention is further characterized in that the distance between the axes of adjacent image carriers in the running direction of the intermediate transfer belt is the same.
The image forming apparatus according to claim 5 is the image forming apparatus according to any one of claims 1 to 4, wherein four image carriers are disposed on the intermediate transfer belt, and the belt is disposed in the belt running direction. On the other hand, the offset amounts of the two image carriers other than the image carrier in contact with the most upstream and the most downstream are the same.
The image forming apparatus of the present invention is further characterized in that at least one member for applying a potential via a belt does not exist facing the image carrier.

The image forming apparatus of the present invention is further characterized in that the volume resistance of the intermediate transfer belt is set to 10 ⁶ Ωcm or less.
The image forming apparatus of the present invention is further characterized in that the intermediate transfer belt is composed of multiple layers.
In the image forming apparatus of the present invention, the surface layer of the intermediate transfer belt contacting the image carrier is set to have a higher resistance than the back layer, and the volume resistance of the back layer of the belt is set to 10 ⁶ Ωcm or less. It is characterized by that.

As described above, according to the means for solving the above problems, the image forming apparatus of the present invention has the following effects.
According to the image forming apparatus of the present invention, since the primary transfer NIP is ensured without the pressurization by the primary transfer member, it is possible to suppress the two-color overlap and three-color overlap missing phenomenon.
According to the image forming apparatus of the present invention, since the primary transfer NIP is ensured even if there is no pressure applied by the primary transfer member, it is possible to suppress the void phenomenon in the case of a single color.
According to the image forming apparatus of the present invention, since the primary transfer NIP is ensured even if there is no pressurization by the primary transfer member, it is possible to suppress the void phenomenon during black.
According to the image forming apparatus of the present invention, it is possible to avoid the speed deviation due to the eccentricity of the drive roller, so that the color misregistration can be suppressed.
According to the image forming apparatus of the present invention, since the offset amount of the photosensitive member is made the same, the local void phenomenon can be suppressed.
According to the image forming apparatus of the present invention, since the primary transfer member can be deleted, the cost can be significantly reduced.
According to the image forming apparatus of the present invention, by adjusting the resistance of the intermediate transfer belt, transfer failure in primary transfer can be suppressed and a good color image can be obtained.
According to the image forming apparatus of the present invention, by forming the intermediate transfer belt in a multilayer structure, discharge at the secondary transfer portion in a low humidity environment can be suppressed, and toner scattering can be suppressed.
According to the image forming apparatus of the present invention, by adjusting the resistance of the multi-layer intermediate transfer belt, it is possible to suppress a transfer failure in the primary transfer and obtain a good color image.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the description, specific member names are used to facilitate understanding of the invention, but it should be clearly stated that the scope of the present invention is not limited thereby.

First, an example of a conventional image forming apparatus is shown in FIG. FIG. 1 shows the configuration of an intermediate transfer member serving as an image forming unit of an image forming apparatus. An image forming unit having four photosensitive members 101 to 104 is disposed, and a belt driving roller 111 and a stretching roller 112 are arranged. The intermediate transfer belt is stretched by the secondary transfer counter roller 109, and a predetermined voltage is applied to the primary transfer rollers 108 to 105 from the upstream side in the running direction of the intermediate transfer belt 100, whereby each color is transferred onto the intermediate transfer belt 100. A color image is formed by superimposing. The formed color image is transferred to a sheet 114 as a transfer material by applying a predetermined voltage to the secondary transfer roller 110, and is fixed (not shown) and output. The toner that cannot be transferred by the secondary transfer roller 110 and remains on the intermediate transfer belt is collected by the cleaner blade unit 113. Although not shown in the figure, a sheet feeding unit for storing recording paper is provided below the intermediate transfer member, and an image reading unit is provided above.

(First embodiment)
FIG. 2 is a diagram showing a first embodiment according to the present invention. An image forming unit having four photoconductors 201 to 204 is disposed, and the intermediate transfer belt 200 is stretched by the belt driving roller 211, the stretching roller 209, and the secondary transfer counter roller 212. First, each color is superimposed on the intermediate transfer belt 200 by applying a predetermined voltage to the primary transfer rollers 208 to 205 from the upstream side in the direction.
At this time, the photoconductors 202 and 203 are primary from the imaginary plane formed at the center of the contact nip formed by the photoconductor 201 and the intermediate transfer belt 200 and the center of the contact nip formed by the photoconductor 204 and the intermediate transfer belt 200. It was offset to the transfer rollers 205 and 208 side. In this embodiment, all the photoconductors are configured with φ30, and the photoconductors 202 and 203 are offset by 1.5 mm.

By making the offset, the intermediate transfer belt 200 inevitably wraps around the photoconductors 202 and 203, and a wide transfer NIP can be formed without applying pressure by the primary transfer rollers 206 and 207, and the primary transfer rollers 206 and 207 are almost free. It can be configured only with a function as a voltage application member in a loaded state.
In the present embodiment, the total primary transfer NIP load is reduced from the conventional 4N to 0.5N. The reduction of the primary transfer NIP load can drastically eliminate the omission phenomenon of vertical lines (lines in the paper passing direction) caused by toner aggregation in the NIP. As a result, in the present embodiment, the conventional general color superposition, which is the most upstream, is yellow, then magenta, then cyan, and finally black. It was possible to improve.

(Second Embodiment)
FIG. 3 is a diagram showing a second embodiment according to the present invention. Although the basic configuration of the second embodiment is the same as that of the first embodiment, the first embodiment is a technology that suppresses the hollow-out phenomenon when two colors and three colors are superimposed. No. 3 is an example in which an improvement is also made for the hollowing out phenomenon in the case of a single color. That is, in addition to the first embodiment of FIG. 2, the stretching roller 315 disposed on the upstream side of the most upstream photoconductor 304 with respect to the traveling direction of the intermediate transfer belt 300 is connected to the photoconductor 303 and the intermediate transfer belt. The center of the contact nip formed by the belt 300 and the imaginary plane formed by the center of the contact nip formed by the photosensitive member 304 and the intermediate transfer belt 300 were offset toward the photosensitive member 304 side.

By making the offset, the intermediate transfer belt 300 inevitably wraps around the photosensitive member 304, and a wide transfer NIP can be formed without pressure by the primary transfer roller 308. As a result, it can be configured with only functions. In the present embodiment, as in the first embodiment, the total load on the primary transfer nip is reduced from the conventional 4N to 0.5N. As a result, in the present embodiment, even when toner that is disadvantageous to the hollow out phenomenon comes in the order of yellow, then magenta, then cyan, and finally black, which is the conventional general color overlap, In the case of a single color image, it was possible to greatly improve the void phenomenon.

(Third embodiment)
FIG. 4 is a diagram showing a third embodiment according to the present invention. In the second embodiment, when the most upstream of the conventional toner is yellow, then magenta, then cyan, and finally black, even if a toner that is disadvantageous to the hollow out phenomenon comes, the improvement of the hollow out phenomenon when the color image is monochromatic. The third embodiment is an example of further improving the blackout phenomenon in the most downstream black as compared with the technique that achieves the above. That is, in addition to the second embodiment of FIG. 3, the tension roller 416 disposed on the downstream side of the most downstream photoreceptor 401 with respect to the traveling direction of the intermediate transfer belt 400 is replaced with the photoreceptor 402 and the intermediate transfer belt. The center of the contact nip formed by 400 and the center of the contact nip formed by the photoreceptor 401 and the intermediate transfer belt 400 are offset toward the photoreceptor 401 side.

By making the offset, the intermediate transfer belt 400 inevitably wraps around the photosensitive member 401, and a wide transfer NIP can be formed without pressure by the primary transfer roller 405. The primary transfer roller 405 is applied with a voltage in a substantially no-load state. It can be configured only by the function as a member. In this embodiment, like the second embodiment of FIG. 3, the total primary transfer NIP load is reduced from the conventional 4N to 0.5N. As a result, in this embodiment, in the order of the most common conventional color superposition, yellow, then magenta, then cyan, and finally black, the blackout phenomenon is greatly improved even for black images. I was able to.

In the conventional example, the pitch of each photoconductor is set to an integral multiple of the outer diameter of the driving roller 411 in order to prevent color misregistration. In this embodiment, since the photosensitive member axes are not on the same plane, the distance between the photosensitive member axes is set to be the same as an integral multiple of the outer diameter of the driving roller 411. Although the photosensitive member pitch is different, the color shift can be prevented without being affected by the eccentricity of the outer diameter of the driving roller 411 set to the same distance.

(Fourth embodiment)
FIG. 5 is a diagram showing a fourth embodiment according to the present invention. In the fourth embodiment, as shown in the first embodiment shown in FIG. 2, the photoconductors 202 and 203 are offset. When two colors are overlapped by making the offset amounts the same, for example, in the conventional example, In the order of yellow, magenta, then cyan, and finally black in the most upstream direction, it was possible to suppress local deterioration of the void phenomenon in the case of yellow and magenta color overlap and yellow and cyan color overlap. .

Further, in the conventional example, in order to secure the primary transfer NIP, the primary transfer pressure members 105 to 108 are provided, and a color image is secured by applying a voltage to the primary transfer rollers 105 to 108. According to the present embodiment, even if at least the primary transfer member facing the photoconductors 502 and 503 is omitted, the primary transfer NIP is secured, so that a color image can be displayed if there is a potential means for applying the primary transfer potential. Can be formed.

By combining the second embodiment and the third embodiment, the primary transfer member that faces the photoconductors 501 to 504 via the intermediate transfer belt 500 is omitted, and the conductive member 517 is placed on the secondary transfer counter roller 512. A color image could be formed on the intermediate transfer belt 500 by applying a primary transfer bias potential using. With the configuration of this embodiment, the primary transfer voltage application member (primary transfer roller) can be eliminated, and thus the cost of the image forming apparatus can be reduced.

In the embodiment shown in FIG. 5, a color image is formed on the intermediate transfer belt 500 by using the conductive member 517 to the secondary transfer counter roller 512 and applying the primary transfer bias potential. Since the bias is applied via the secondary transfer counter roller 512, if the belt volume resistance is high, a voltage difference is generated between the photoconductor 504 close to the secondary transfer counter roller 512 and the photoconductor 501 far from the secondary transfer counter roller 512, thereby improving the primary transfer property. A difference occurs and an appropriate color image cannot be obtained. As shown in Table 1, it can be seen that when the volume resistance exceeds 10 ⁶ Ωcm, transfer failure occurs. For this reason, an appropriate color image can be obtained by setting the volume resistance to 10 ⁶ Ωcm.

Next, in the fourth embodiment described above, since the resistance of the intermediate transfer belt 500 is low, it is disadvantageous against the toner scattering phenomenon caused by the discharge at the secondary transfer portion in a low humidity environment. That is, the intermediate transfer belt 500 has a two-layer structure, and the resistance of the surface that contacts the secondary transfer roller 510 is set higher than the resistance of the surface that contacts the secondary transfer counter roller 512. Could be suppressed. As a result, the scattering phenomenon in a low humidity environment was reduced.

Further, even in an intermediate transfer belt having a multi-layer structure, the resistance of the intermediate transfer belt 500 is low, which is disadvantageous against the toner scattering phenomenon caused by the discharge at the secondary transfer portion in a low humidity environment. As shown in FIG. 5, a color image is formed on the intermediate transfer belt by using a conductive member 517 for the secondary transfer counter roller 512 and applying a primary transfer bias potential, but the primary transfer bias is 2 Since the voltage is applied via the secondary transfer counter roller 512, if the belt volume resistance on the surface contacting the secondary transfer counter roller 512 is high, a voltage difference is generated between the photoconductor 504 close to the secondary transfer counter roller 512 and the photoconductor 501 far away. And a difference in primary transferability occurs, and an appropriate color image cannot be obtained. As shown in Table 2, it can be seen that when the volume resistance exceeds 10 ⁶ Ωcm, transfer failure occurs. For this reason, an appropriate color image can be obtained by setting the volume resistance to 10 ⁶ Ωcm.

FIG. 10 is a schematic configuration diagram illustrating an intermediate transfer member of a conventional image forming apparatus. FIG. 2 is a schematic configuration diagram illustrating an intermediate transfer member of the image forming apparatus according to the first embodiment. FIG. 10 is a schematic configuration diagram illustrating an intermediate transfer member of an image forming apparatus according to a second embodiment. FIG. 10 is a schematic configuration diagram illustrating an intermediate transfer member of an image forming apparatus according to a third embodiment. FIG. 10 is a schematic configuration diagram illustrating an intermediate transfer member of an image forming apparatus according to a fourth embodiment.

Explanation of symbols

100 Intermediate transfer belts 101 to 104 Photoconductors 105 to 108 Primary transfer roller 109 Secondary transfer opposite roller 110 Secondary transfer roller 111 Belt drive roller 112 Tension roller 113 Cleaner blade unit 200 Intermediate transfer belts 201 to 204 Photoconductors 205 to 205 208 Primary transfer roller 209 Tension roller 210 Secondary transfer roller 211 Belt drive roller 212 Secondary transfer counter roller 213 Cleaner blade unit 300 Intermediate transfer belts 301 to 204 Photoconductors 305 to 208 Primary transfer rollers 309 and 315 Tension rollers 310 Secondary transfer roller 311 Belt drive roller 312 Secondary transfer counter roller 313 Cleaner blade unit 400 Intermediate transfer belt 401-404 Photoconductor 405-408 Primary transfer roller 409, 415, 416 Stretching roller 410 Secondary transfer roller 411 Belt drive roller 412 Secondary transfer counter roller 413 Cleaner blade unit 500 Intermediate transfer belts 501 to 504 Photoconductor 509 Stretch roller 510 Secondary transfer roller 511 Belt drive roller 512 Secondary transfer counter roller 513 Cleaner blade Unit 517 conductive member

Claims (9)

Each toner image formed on at least three or more image carriers is transferred to each of the primary transfer units on a movable intermediate transfer belt that abuts the plurality of image carriers with each primary transfer unit. An image forming apparatus that sequentially performs primary transfer to a plurality of image carriers via the intermediate transfer belt, and then secondary-transfers the toner images superimposed and transferred on the intermediate transfer belt collectively onto a transfer material at a secondary transfer unit. In
With respect to a plane formed by the image carrier that contacts the most upstream with respect to the intermediate transfer belt traveling direction, the image carrier that contacts the belt contact nip midpoint and the most downstream, and the belt contact nip midpoint An image forming apparatus, wherein the other image carrier and the belt contact nip midpoint are offset to the belt side. It is arranged upstream of the most upstream image carrier with respect to the belt plane between the image carriers determined by the most upstream image carrier and the adjacent image carrier with respect to the intermediate transfer belt traveling direction. The image forming apparatus according to claim 1, wherein the belt stretching roller is offset and intersects with the uppermost image carrier side with respect to the belt plane. It is disposed on the downstream side of the most downstream image carrier with respect to the belt plane between the image carrier and the image carrier that is adjacent to the most downstream image carrier with respect to the traveling direction of the intermediate transfer belt. The image forming apparatus according to claim 1, wherein the belt stretching roller is offset and intersects with the belt plane toward the most downstream image carrier side. 4. The image forming apparatus according to claim 1, wherein the distance between the axes of adjacent image carriers in the running direction of the intermediate transfer belt is the same. 5.   Four image carriers are arranged on the intermediate transfer belt, and the offset amounts of the two image carriers other than the image carrier that abuts on the most upstream side and the most downstream side in the belt running direction are the same. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.   6. The apparatus according to claim 1, wherein at least one member for applying a potential via the belt is opposed to the image carrier that is in contact with the intermediate transfer belt. An image forming apparatus according to claim 1. The image forming apparatus according to claim 1, wherein a volume resistance of the intermediate transfer belt is set to 10 ⁶ Ωcm or less.   The image forming apparatus according to claim 1, wherein the intermediate transfer belt is formed of multiple layers. 9. The surface layer in contact with the image carrier of the intermediate transfer belt is set to have a higher resistance than the back layer, and the volume resistance of the back layer of the belt is set to 10 ⁶ Ωcm or less. Image forming apparatus.

Images