JP3700730B2 - Color image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electrophotographic color image forming apparatus used in printers, facsimiles, copiers, and the like. More specifically, the present invention relates to a toner image of each color formed on a belt-shaped image carrier, as an intermediate transfer medium or transfer drum. The present invention relates to a color image forming apparatus that forms a color image by superimposing colors.
[0002]
[Prior art]
In the conventional image forming apparatus, as disclosed in Japanese Patent Laid-Open No. 6-258890, the circumferential length of the photosensitive belt fitted on the driving roller is longer than the outer circumferential length of the driving roller. There is a technique in which an elastic member is elastically contacted to a position not in contact with the developing roller, the photosensitive belt is pressed against the driving roller, and the vicinity of the contacting position of the photosensitive belt with the developing roller is held loose. Proposed. Further, as disclosed in Japanese Patent Laid-Open No. 6-27859, the circumferential length of the photoreceptor belt fitted around the drive roller is formed longer than the circumference of the drive roller, and the charging roller and the transfer roller are provided as a photoreceptor. A technique has been proposed in which the pressure contact between the photosensitive belt and the driving roller is ensured by pressure contact with the belt, and further, the vibration of the photosensitive belt at the exposure portion is prevented.
[0003]
[Problems to be solved by the invention]
However, in the technique disclosed in Japanese Patent Application Laid-Open No. 6-258989, the elastic member that is elastically contacted with the photosensitive belt is configured to slide on the surface of the photosensitive belt. As described above, it is not possible to make an elastic contact with the image area near the center of the surface of the tourist body, and the elastic contact position is substantially limited to the vicinity of both ends of the photosensitive belt. Therefore, even in the region where the elastic member is elastically contacted and the photosensitive belt should be pressed against the drive roller, the central portion of the photosensitive belt whose slack portion has been pushed by the developing roller is separated from the drive roller, and exposure is performed. Since the position and the transfer position are shifted, stable exposure and transfer cannot be performed, and when colors are overlapped, a positional shift between colors occurs, and the color reproducibility of the color image is impaired.
[0004]
In the technique disclosed in Japanese Patent Application Laid-Open No. 6-27859, the exposure unit is located on the downstream side of the photosensitive belt from the charging unit, that is, on the side close to the developing unit. And vibration cannot be suppressed by the charging roller, and stable exposure cannot be performed. Furthermore, the force with which the photosensitive belt is pushed up by the developing device cannot be cut off simply by being pressed by the charging roller or the transfer roller, and a part of the slack on the developing device side of the photosensitive belt is below the charging roller or the transfer roller. May cause small slack between the charging roller and the cleaner, or between the transfer roller and the cleaner, and the distance from the charging position on the photosensitive belt to the transfer position may change. The color reproducibility of the color image is impaired, and the image quality is deteriorated.
[0005]
The present invention has been made in view of the above-described conventional problems. The object of the present invention is to use a belt-like image carrier as a single support roller having an outer diameter smaller than the inner diameter of the image carrier. In a color image forming apparatus using a structure that supports and drives, the exposure position on the image carrier is stabilized, and further, the position and length of the image carrier from the exposure part to the transfer part are stabilized precisely. Accordingly, it is an object of the present invention to provide a color image forming apparatus excellent in color reproducibility, which performs high-precision color superposition and minimizes positional deviation between colors.
[0006]
[Means for Solving the Problems]
In order to solve the above problems, a color image forming apparatus of the present invention includes a belt-shaped image carrier and a support roller that has an outer diameter smaller than the inner diameter of the image carrier and supports and drives the image carrier. Charging means for charging the image carrier, exposure means for forming an electrostatic latent image on the image carrier in accordance with image formation information, and a pressing roller for pressing the image carrier toward the support roller The electrostatic latent image on the image carrier is successively visualized with a plurality of color toners in proximity to or in contact with a slack portion of the image carrier caused by the difference between the inner diameter of the image carrier and the outer diameter of the support roller. A color image forming apparatus comprising: a plurality of developing means for converting; a transfer means for sequentially transferring the developed toner image onto a transfer medium; and a cleaning means for cleaning the surface of the image carrier after the transfer. Roller peripheral speed Was a faster speed than the moving speed of the image bearing member, the support as said cleaning means from said transfer means in the rotation direction of the support roller, the image bearing member to said charging means and said presser roller is brought into close contact with the support rollers Then, charging by the charging unit and formation of an electrostatic latent image by the exposure unit are performed on the image carrier at the portion supported in close contact .
[0007]
Further, the pressing roller is configured such that the outer diameter dimension on the shaft end side is larger than the outer diameter dimension on the shaft center side.
[0008]
Further, the pressing roller is made of a material having a resistance value of 10 ⁸ Ωcm or more.
[0009]
Further, the moving speed of the transfer medium is slower than the moving speed of the image carrier.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the drawings.
[0011]
FIG. 1 is a cross-sectional view of an essential part showing an embodiment of a color image forming apparatus of the present invention.
[0012]
In the figure, reference numeral 10 denotes an image carrier formed in a belt shape, and this image carrier 10 is a flexible organic photoreceptor in which a charge generation layer and a charge transport layer are formed in this order on a nickel electroformed tube. It is. The image carrier 10 is a primary transfer unit that is disposed with an intermediate transfer medium 30 interposed between the image carrier 10 and a support roller 11 that drives the image carrier 10 and rotates in the direction of arrow A. The primary transfer roller 31 is caused by the pressing force of the transfer roller 31, the first cleaning unit 25, the charging roller 21 serving as a charging unit, and the pressing roller 23 for pressing the image carrier 10 toward the support roller 11. From the first cleaning means 25 and the charging means 21 to the pressing roller 23 so as to be in close contact with each other. In particular, the pressure contact force by the first cleaning unit is maximized, and the driving force transmitted to the image carrier 10 is configured to be the maximum that is applied from the support roller 11 at the pressure contact portion of the first cleaning unit 25. is there. At this time, the friction coefficient between the cleaning blade 25 a provided in the first cleaning unit and the surface of the image carrier 10 is set to be smaller than the friction coefficient between the back surface of the image carrier 10 and the surface of the support roller 11. It is.
[0013]
The image carrier 10 is sequentially developed by a plurality of developing means, and its configuration and operation are as follows.
[0014]
The length of the image carrier 10 in the rotational direction is set larger than the outer peripheral length of the support roller 11. The image carrier 10 is rotationally driven in the direction of arrow B by the support roller 11 rotating in the direction of arrow A, so that the image carrier 10 is separated from the support roller 11 in the section from the pressing roller 23 to the primary transfer roller 31 in the rotational direction. It moves along an arc-shaped locus defined by the elastic force of the image carrier 10. In a section away from the support roller 11, toner is developed on the image portion of the image carrier 10 by a plurality of developing means, and the electrostatic latent image is visualized. The plurality of developing units include a yellow developing unit 241 having a yellow developing roller 241a for developing yellow toner, a magenta developing unit 242 having a magenta developing roller 242a for developing magenta toner, and developing cyan toner. A cyan developing unit 243 having a cyan developing roller 243a and a black developing unit 244 having a black developing roller 244a for developing black toner. Each developing unit is selectively operated according to image color data. The electrostatic latent image on the image carrier 10 is developed for each color.
[0015]
The developing units 241 to 244 are detachably positioned in a housing (not shown), and further moved in the directions of arrows G, H, I, and J, so that the positions of the developing rollers 241a to 244a are changed to image positions. In the section where the carrier 10 is separated from the support roller 11, it is possible to select whether it is close to, in contact with, or separated from the image carrier 10. In the drawing, the developing device 241 is in a state in which the developing roller 241a is close to or in contact with the image carrier 10, and the developing devices 242, 243, and 244 are separated from the image carrier 10 by the developing rollers 242a, 243a, and 244a, respectively. It shows that it is in a state. Therefore, FIG. 1 shows a state in which only development with yellow toner is possible.
[0016]
A toner image of each color is sequentially formed on the image carrier 10 supported and moved in this manner by an electrophotographic process such as charging, exposure, development, and transfer.
[0017]
In the figure, a charging roller 21 is a portion where the image carrier 10 is supported so as to be in close contact with the support roller 11, and is disposed so as to face the support roller 11 and make contact with light pressure across the image carrier 10. Then, the image carrier 10 is driven to rotate. By applying a predetermined DC charging bias to the charging roller 21, the surface of the image carrier 10 can be uniformly charged to a predetermined charging potential sequentially.
[0018]
Next, the charged image carrier 10 is a portion where the image carrier 10 is supported so as to be in close contact with the support roller 11, and is image-exposed with a laser beam 22 irradiated from an exposure unit (not shown). An electrostatic latent image is formed on 10.
[0019]
Subsequently, the image carrier 10 on which the electrostatic latent image is formed passes through a pressing roller 23 disposed opposite to the support roller 11 and moves in the direction of arrow B of the image carrier 10, and a plurality of developing units. Among them, the toner is developed on the image portion by one developing device 241 that is selected based on the color data of the image and is close to or in contact with the image, and the electrostatic latent image is visualized. The plurality of developing units sequentially move the respective developing units toward or in contact with the image carrier 10 based on the color data of the image, and develop the electrostatic latent image on the image carrier 10 one color at a time.
[0020]
Subsequently, the toner image formed with the toner of a predetermined color is transferred from the image carrier 10 to the intermediate transfer medium 30 by the primary transfer roller 31 which is a transfer unit. The primary transfer roller 31 is disposed to face the support roller 11 with the intermediate transfer medium 30 and the image carrier 10 interposed therebetween.
[0021]
After the primary transfer, the untransferred toner remaining on the image carrier 10 is sent to the first cleaning unit 25, scraped off by the cleaning blade 25a, and discharged into the internal space of the cleaning unit 25. The cleaning blade 25a is pressed against the support roller 11 with the image carrier 10 interposed therebetween, and the rotational driving force from the support roller 11 to the image carrier 10 by the frictional force between the image carrier 10 and the support roller 11 generated by this pressure contact force. Communicate most of the.
[0022]
Thereafter, the toner image of the next color formed by charging, exposing, and developing again is transferred from the image carrier 10 to the intermediate transfer medium 30 by the primary transfer roller 31, and is overlaid on the intermediate transfer medium 30. Is done. Here, the intermediate transfer medium 30 is stretched between the drive roller 32, the first driven roller 33, and the second driven roller 34, and has a primary transfer roller 31 therein, and rotates in the direction of arrow C. It is driven by the driving roller 32, is given tension by the first driven roller 33, and moves in the direction of arrow D. In addition, it is possible to form a color image by performing the same color superposition without using the intermediate transfer medium 31 and using a transfer drum holding a recording material or a paper conveying belt. In this case, the transfer drum or paper The moving speed of the transfer belt at the transfer unit is set slower than the moving speed of the image carrier 10.
[0023]
The image forming operation for each color is started by an index signal generated every rotation of the intermediate transfer medium 30 to prevent a color shift due to a periodic positional shift of the intermediate transfer medium.
[0024]
A color toner image formed by repeating such an operation for a predetermined color is separated from the leading edge of the image by the secondary transfer roller 41 urged toward the second driven roller 34 by performing the separating operation in the direction of the arrow L. Are collectively transferred to the recording medium 40 conveyed in accordance with
[0025]
On the other hand, the residual toner remaining on the intermediate transfer medium 30 after the secondary transfer is transferred to the second cleaning unit 35, scraped off by the second cleaning blade 35a, and discharged into the internal space of the second cleaning unit 35. Is done. The second cleaning unit 35 moves in the direction of arrow M toward the intermediate transfer medium 30 and performs cleaning in response to the operation of transferring the toner image to the recording medium 40. It is held at a position separated from the other.
[0026]
On the other hand, according to the secondary transfer of the color toner image, the recording medium 40 is fed toward the secondary transfer roller 41 along the recording medium conveyance path 42 by a paper feeding unit (not shown) and a paper conveyance unit (not shown). The color toner images on the intermediate transfer medium 30 are secondarily transferred onto the recording medium 40 at once. Further, the recording medium 40 is conveyed to a fixing unit (not shown) along the recording medium conveyance path 42, and after the toner image is heated and fixed, it is discharged to a paper discharge tray (not shown).
[0027]
In this manner, a color toner image composed of a plurality of colors of toner is fixed on the recording medium 40, and a series of color image forming operations is completed. Further, when forming color images continuously, the same image forming process is repeated, and when forming a monochromatic image, only the image forming process for one color is performed.
[0028]
The support roller 11 and the drive roller 32 may be a metal sleeve or the like fitted with a flange, and the outer peripheral surface may be roughened or the outer peripheral surface may be coated with a resin.
[0029]
Here, unlike the average moving speed of the image carrier 10, the outer periphery of the pressing roller 23 rotates while maintaining a slightly higher peripheral speed. As a result, the image carrier 10 is pressed against the support roller 11 by the pressing roller 23 and is simultaneously tensioned in the moving direction, so that it is released from the surface of the supporting roller in the section from the first cleaning means 25 to the pressing roller 23. It adheres without gaps and moves at a stable speed. Therefore, the timing of exposure by the laser beam 22 is not affected by the unstable behavior of the image carrier 10, and the color reproducibility is minimized by minimizing the positional shift between colors when the colors are superimposed. There is an effect that a color image can be obtained.
[0030]
At this time, the friction coefficient between the pressing roller 23 and the surface of the image carrier 10 is set to be smaller than the friction coefficient between the back surface of the image carrier 10 and the surface of the support roller 11. Accordingly, the image carrier 10 moves at a stable speed depending only on the speed of the support roller 11 regardless of the speed of the pressing roller 23.
[0031]
The slightly faster speed mentioned here is specifically the circumference of the outer periphery of the pressing roller 23 with respect to the average moving speed of the image carrier 10 when the radius of the support roller 11 is r1 (mm) and the deflection is a1 (mm). It is preferable to set the speed ratio so that the speed ratio is higher in a range exceeding 1 + a1 / r1 and less than 1.05. Further, the speed ratio is increased in a range exceeding 1 + a1 / r1 + 0.001 and less than 1.025. Is good. If the speed ratio does not exceed 1 + a1 / r1, it cannot be said that the peripheral speed of the pressing roller 23 is always high with respect to the moving speed of the image carrier 10, and a sufficient effect cannot be obtained. Adverse effects such as wear and heat generated by
[0032]
If the speed ratio is faster than 1 + a1 / r1 + 0.001 and less than 1.025, a more stable and good effect can be obtained. Further, the shape of the pressing roller 23 may be a shape that presses only the portion outside the image area near both ends of the image carrier 10, or a shape that presses over the entire width of the image carrier 10. In the case of pressing only the outer portion of the image area near both ends, the pressing roller 23 is configured so that the outer diameter of the shaft end side is larger than that of the shaft center side. Therefore, a force to spread the image carrier 10 outwardly acts, and the central portion in the moving direction of the image carrier 10 is partially separated from the support roller 11 and swells. Can be prevented. The shape in which the outer diameter of the pressing roller 23 on the shaft end side is larger than that of the shaft center side is also effective when pressing over the entire width. Further, when pressing over the entire width, it is preferable to use a roller material having a high resistance of 10 ⁸ Ωcm or more or an insulating material.
[0033]
Further, the belt-like intermediate transfer medium 30 that is rotationally driven by the drive roller 32 moves at a slightly different speed from the moving speed of the image carrier 10, and the primary transfer roller 31 rotates following the intermediate transfer medium 30. . As a result, the image carrier 10 is pressed against the support roller 11 by the primary transfer roller 31 and is simultaneously tensioned by the intermediate transfer medium 30 in the direction opposite to the moving direction, so that the primary transfer roller 31 from the first cleaning unit 25. In the section up to, it adheres without gap from the surface of the support roller 11 and moves at a stable speed. At this time, since the driving force applied to the image carrier 10 at the pressing roller 23 is smaller than the driving force applied by the pressure contact portion of the first cleaning means 25, the moving speed of the image carrier 10 is the speed of the support roller 11. Follow the rotation speed.
[0034]
Here, the slightly slower speed means specifically that the radius of the support roller 11 is r1 (mm), the deflection is a1 (mm), the radius of the driving roller 32 that drives the intermediate transfer medium 30 is r2, and the deflection is a2. Is set so that the speed ratio of the average moving speed of the intermediate transfer medium 30 to the average moving speed of the image carrier 10 exceeds 0.95 and is less than 1-a1 / r1-a2 / r2. Further, it is preferable to slow the speed ratio within a range exceeding 0.975 and less than 1-a1 / r1-a2 / r2-0.001. When the speed ratio exceeds 1-a1 / r1-a2 / r2, it cannot be said that the moving speed of the intermediate transfer medium 30 is always slower than the moving speed of the image carrier 10, and a sufficient effect cannot be obtained. On the other hand, when it is 0.95 or less, adverse effects such as image distortion during transfer become conspicuous. If the speed ratio exceeds 0.975 and is less than 1-a1 / r1-a2 / r2-0.001, a more stable and good effect can be obtained.
[0035]
Further, since the entire circumferential length of the image carrier 10 is constant, the effect of the pressing roller 23 and the effect of the primary transfer roller 31 and the intermediate transfer medium 30 cause the primary transfer by the primary transfer roller 31 from the exposure by the laser light 22. Until then, the circumferential length of the image carrier 10 does not vary, and the image carrier 10 always moves in a stable state. For this reason, the vibration or shape change of the image carrier 10 due to the separation operation of a plurality of developing means or the change of the contact position with the developing device for each color with respect to the section separated from the support roller 11 of the image carrier 10, The exposure and primary transfer processes are not affected, and image jitter and misregistration do not occur. Furthermore, high-precision color superposition is possible, and there is an effect that an image of excellent image quality with good color reproducibility can be obtained.
[0036]
At the same time, the movement of the image carrier 10 in the section away from the support roller 11 is also stable, so that the proximity accuracy of each developing device or the pressure contact state and the pressure nip are stabilized, the density unevenness of the image can be reduced, and the image quality improves. There is an effect of doing.
[0037]
As described above, according to the above-described embodiment, a color image without color misregistration can be formed on an intermediate transfer medium using a belt-shaped image carrier. It is desirable to provide a flange and a guide for preventing meandering. The same applies to the intermediate transfer medium, and a drum-shaped intermediate transfer medium may also be used.
[0038]
Therefore, according to the above embodiment, a color image forming apparatus using a configuration in which a belt-like image carrier is mainly supported and driven by a single support roller having an outer diameter smaller than the inner diameter of the image carrier. In this case, the exposure position on the image carrier is stabilized, and further, the position and length of the image carrier from the exposure part to the transfer part are precisely stabilized, so that high-precision color overlay is performed. It is possible to provide a color image forming apparatus excellent in color reproducibility with minimal positional deviation.
[0039]
【The invention's effect】
As described above, according to the present invention, color image formation using a configuration in which a belt-like image carrier is mainly supported and driven by a single support roller having an outer diameter smaller than the inner diameter of the image carrier. In the device, the exposure position on the image carrier is stabilized, and furthermore, the position and length of the image carrier from the exposure part to the transfer part are stabilized precisely, so that high-precision color overlap is performed. Therefore, it is possible to provide a color image forming apparatus with excellent color reproducibility with minimal positional deviation.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of an essential part showing an embodiment of a color image forming apparatus of the present invention.
[Explanation of symbols]
10 Image carrier 11 Support roller 21 Charging roller 22 Laser light 23 Pressing roller 241 Yellow developing unit 242 Magenta developing unit 243 Cyan developing unit 244 Black developing unit 241a Yellow developing roller 242a Magenta developing roller 243a Cyan developing roller 244a Black developing roller 25 One cleaning means 25a First cleaning blade 30 Intermediate transfer medium 31 Support roller 32 Drive roller 33 First driven roller 34 Second driven roller 35 Second cleaning means 35a Second cleaning blade 40 Recording medium 41 Secondary transfer roller 42 Recording medium conveyance Route

Claims (4)

A belt-shaped image carrier;
A support roller having an outer diameter smaller than the inner diameter of the image carrier and supporting and driving the image carrier;
Charging means for charging the image carrier;
Exposure means for forming an electrostatic latent image on the image carrier according to image formation information;
A pressing roller that presses the image carrier toward the support roller;
The electrostatic latent image on the image carrier is successively visualized with a plurality of color toners in proximity to or in contact with the slack portion of the image carrier resulting from the difference between the inner diameter of the image carrier and the outer diameter of the support roller. A plurality of developing means,
Transfer means for sequentially transferring the developed toner image onto a transfer medium;
A color image forming apparatus having cleaning means for cleaning the surface of the image carrier after the transfer, wherein a peripheral speed of the outer periphery of the pressing roller is set to a speed faster than a moving speed of the image carrier, and the rotation direction of the support roller The image carrier is supported from the transfer unit to the cleaning unit, the charging unit, and the pressure roller so as to be in close contact with the support roller, and is supported on the image carrier at the portion that is supported to be in close contact. A color image forming apparatus, wherein charging by the charging unit and formation of an electrostatic latent image by the exposure unit are performed .   The color image forming apparatus according to claim 1, wherein the pressing roller is configured such that an outer diameter dimension on a shaft end side is larger than an outer diameter dimension on a shaft center side. The color image forming apparatus according to claim 1, wherein the pressing roller is made of a material having a resistance value of 10 ⁸ Ωcm or more.   4. The color image forming apparatus according to claim 1, wherein a moving speed of the transfer medium is slower than a moving speed of the image carrier.

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