JP2001175057A - Color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable even a color image forming device whose image forming frequency is increased in comparison with a monochromatic machine to be used for a long term. SOLUTION: A photoreceptor drum 1 is provided with an electrifying roller 9 electrifying the drum 1 while rotating in accordance with the drum 1 in a direction shown by an arrow B on a condition that it is always made to press- contact with the drum 1. Then, a roller cleaning member 22 is arranged in a contact state so as to clean the surface of the roller 9. Even when toner left on the surface of the drum 1 is moved to the surface of the roller 9, it is eliminated by the cleaning member 22. Then, when the direction of the grinding marks of the surface of the roller 9 is set so that they are brought into contact with the cleaning member 22 in a forward direction, the sliding resistance thereof does not become large to such an extent that the rotational irregularity of the roller 9 is caused. Thus, color slippage caused by jitter is prevented from occurring.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus such as a color copying machine, a color printer, and a color facsimile apparatus for forming a color image by charging an image carrier by a charging roller.

[0002]

2. Description of the Related Art For example, in a color image forming apparatus such as a color copying machine or a color printer, a photosensitive member which is an image carrier,
An image forming unit in which a developing device, a charging device, and the like are housed in an integrated case to reduce the size of the entire image forming apparatus is increasing.

In this type of image forming unit, an image is color-separated into three or four colors, images corresponding to the respective colors are sequentially formed on a photosensitive member, and the images are sequentially superimposed on an intermediate transfer member. To form an image of one page. Therefore, the number of times of image formation is larger than that in the case of the monochrome machine, and the amount of ozone generated for forming one page image is three times or four times that in the case of the monochrome machine. Therefore, in the case of such a color image forming apparatus, a roller-charging type charging device (for example, JP-A-6-102737, JP-A-6-308806, JP-A-6-308806) which generates less ozone during charging. -244
435) is environmentally advantageous.

[0004]

However, in the case of such a roller charging type contact type charging device, since the charging roller is in contact with the surface of the photoreceptor, an image is formed on the photoreceptor. In some cases, the residual toner remaining after the transfer is easily transferred to the surface of the charging roller. In the case of a color image forming apparatus, since the number of image formations is equal to the number of color separations to form a one-page image as described above, the contamination of the charging roller is three to three times smaller than in a monochrome machine.
Sometimes it was quadrupled. Therefore, there has been a problem that the life of the color image forming unit is reduced to 1/3 to 1/4 in the case of long-term use as compared with the case of a monochrome machine.

The present invention has been made in view of the above-mentioned problems, and is intended to endure long-term use even in a color image forming apparatus in which the number of times of image formation is larger than in a monochrome machine. The purpose is to do. It is another object of the present invention to prevent color misregistration caused by occurrence of jitter.

[0006]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a rotating image carrier and a charging device for charging the image carrier while being driven and rotated while being constantly pressed against the image carrier. And a latent image corresponding to each color separated into three or four colors sequentially formed on the charged surface of the image carrier charged by the charging roller with the corresponding charging roller is developed with a toner of a corresponding color. In a color image forming apparatus including a developing device, a cleaning member for cleaning the surface of the charging roller is provided.

[0007] The charging roller has a surface having a predetermined surface roughness with directionality on the polishing surface, and the direction of the polishing surface is brought into contact with the cleaning member in a forward direction. It is good to It is effective to set the predetermined surface roughness of the charging roller to 5 μm or more and 40 μm or less. The cleaning member may be a sponge.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing an image forming unit of a color image forming apparatus according to an embodiment of the present invention.
FIG. 3 is a side view showing a charging roller provided in the color image forming apparatus.

In this color image forming apparatus, as shown in FIG. 1, a photosensitive drum 1 which is an image carrier and rotates in a direction indicated by an arrow A, and an image bearing member B which is constantly pressed against the photosensitive drum 1 as indicated by an arrow B
And a charging device 2 having a charging roller 9 for charging the photosensitive drum 1 while rotating in the direction. A roller cleaning member 22 for cleaning the surface of the charging roller 9 is provided in contact therewith.

Further, this color image forming apparatus is capable of coping with three colors (or four colors) which are sequentially formed on the charged surface of the photosensitive drum 1 charged by the charging roller 9. Developing devices 4, 5, and 6 for developing latent images to be developed with toners of colors corresponding to the latent images, respectively. The developing devices 4, 5, and 6 are supplied with toners of respective colors from a toner supply device (not shown) through toner supply ports.

Around the photosensitive drum 1, a charging roller 9 is provided.
An exposure device 3 for irradiating a laser beam L on the photosensitive drum 1 charged uniformly with the laser beam L to form an electrostatic latent image thereon is provided. An intermediate transfer belt 8 for transferring the three color toner images developed by the developing devices 4, 5, and 6 in a superimposed state is provided downstream of the developing device 4 in the rotation direction of the photosensitive drum 1. Three rollers 13, 14
And 15 are provided.

On the right side of the intermediate transfer belt 8 in FIG. 1, there is provided a transfer roller 12 for transferring a color image superimposed on the intermediate transfer belt 8 onto transfer paper.
On the downstream side of the intermediate transfer belt 8 in the rotation direction of the photosensitive drum 1, there is provided a cleaning device 10 for removing residual toner on the photosensitive drum 1, and further downstream of the cleaning device 10.
The static elimination lamps 11 for eliminating the residual charges are arranged.

In this color image forming apparatus, when the image forming operation is started, the photosensitive drum 1 rotates in the direction of arrow A.
Then, the surface of the photosensitive drum 1 is discharged by the discharge lamp 11, and the surface potential is averaged to a reference potential of 0 to -150V. Next, the surface of the photosensitive drum 1 is charged by the charging roller 9, and the surface potential is -1000V.
Before and after.

The charged surface is irradiated with a laser beam L corresponding to the image of the first color from the exposure device 3, and the laser beam L
The surface potential of the portion (image portion) irradiated with is 0 to -200
V and a latent image is formed. Then, when the photosensitive drum 1 reaches the developing position of the corresponding color among the developing devices 4, 5, and 6 by rotating the photosensitive drum 1 in the direction of arrow A, the first color toner adheres there. It becomes a toner image.

When the toner image moves to a position in contact with the intermediate transfer belt 8 by rotation of the photosensitive drum 1, the toner image of the first color is temporarily transferred to the intermediate transfer belt 8 and held. The cleaning device 10 removes residual toner from the portion of the photosensitive drum 1 on which the toner image has been transferred, and the charge is removed by a charge removing lamp 11.
The surface potential is averaged to a reference potential of 0 to -150 V and completely initialized.

Next, the image formation of the second color is started, the surface of the photosensitive drum 1 rotating in the direction of arrow A is charged again by the charging roller 9, and the surface potential becomes about -1000V. The charged surface is irradiated with laser light L corresponding to the image of the second color from the exposure device 3, and the surface potential of the portion (image portion) irradiated with the laser light L becomes 0 to −200 V to form a latent image. Is formed. When the photosensitive drum 1 rotates in the direction of arrow A, the latent image is developed.
Reaches the developing position of the corresponding color, the toner of the second color is then attached to form a toner image.

When the toner image moves to a position in contact with the intermediate transfer belt 8 by the rotation of the photosensitive drum 1, the second color toner image is held on the intermediate transfer belt 8 so as to overlap the first color image. Then, the portion of the photosensitive drum 1 where the toner image has been transferred again is the cleaning device 1.
0, the residual toner is removed, and
, The surface potential is averaged to a reference potential of 0 to -150 V, and is initialized again. Thereafter, the third color image is formed in the same manner, and the third color toner image is superimposed on the intermediate transfer belt 8 with the first and second color images, and held as a three-color superimposed color image.

On the other hand, transfer paper is fed from a paper feed unit (not shown), and the transfer paper is transferred at an accurate timing when the leading edge of the image on the leading edge of the paper coincides with the leading edge of the color image on the intermediate transfer belt 8. The transfer roller 12 transfers the three-color superimposed color image on the intermediate transfer belt 8 to transfer paper. Then, the transfer paper is sent to a fixing unit (not shown), where heat and pressure are applied to fuse the toner, and then the paper is discharged to a paper discharge tray or the like.

Next, the charging device 2 shown in FIG. 1 will be described. As shown in FIG. 2, the charging roller 9 of the charging device 2 has a small hygroscopic property on the outer periphery except for both ends of the metal core 7,
A conductive rubber 16 having a stable resistance value is formed by molding (a surface layer may be further formed outside the conductive rubber 16), and the surface of the conductive rubber 16 is formed on the photosensitive drum 1 (FIG. 1). The surface of the photoreceptor drum 1 is uniformly charged by applying a high voltage to the cored bar 7 by being constantly brought into pressure contact with the surface of the photoreceptor drum 1.

The roller cleaning member 22 described above is constantly pressed against the surface of the charging roller 9 as shown in FIG.
Is a foam such as a sponge (or may be a brush or the like), which is attached to the cleaning pad holding member 23 with an adhesive such as a double-sided tape.

In this image forming apparatus, since the charging roller 9 is a normal contact type charging device 2 which is always in pressure contact with the photosensitive drum 1, the minute toner adhering to the surface of the photosensitive drum 1 is charged. When the surface of the charging roller 9 is transferred and becomes dirty, charging unevenness easily occurs. However, when the charging roller 9 rotates, the roller cleaning member 22 rubs the surface of the charging roller 9. 9 can be removed by the roller cleaning member 22, so that charging unevenness can be prevented.

The conductive rubber 16 of the charging roller 9 is molded as a rubber roller on the outer periphery of the core bar 7 excluding both ends as described above. There are many molding methods. The final step generally involves grinding and polishing steps. Then, by the grinding and polishing steps, the roller surface of the conductive rubber 16 is shaved to obtain desired straightness and surface roughness.

By the grinding and polishing steps, the charging roller 9
In addition to the desired straightness and surface roughness of the roller surface of the portion of the conductive rubber 16 described above, the surface thereof is as shown in FIGS. 4 (exaggerated for convenience of explanation) and FIG. , A predetermined surface roughness on which a directional pattern called a polished eye 25 is formed.

In the charging device 2, the rotating direction of the charging roller 9 is adjusted so that the direction of the polished surface of the charging device 2 is brought into contact with the roller cleaning member 22 in the forward direction as shown in FIG. The direction is the arrow B direction. In addition,
When the charging roller 9 is rotated in the direction opposite to the arrow B, the contact of the polished eyes 25 with the roller cleaning member 22 is as follows.
We call it a contrarian contact. Further, the shape of the surface roughness as seen in the conventional charging roller shown in FIG. 6 is a case where there is no directionality (no polishing grain).

As described above, in the color image forming apparatus according to this embodiment, the direction of the polished line 25 on the surface of the conductive rubber 16 of the charging roller 9 is adjusted by the roller cleaning member 22.
, The sliding resistance between the conductive rubber 16 of the charging roller 9 and the roller cleaning member 22 does not become large enough to cause uneven rotation of the charging roller 9. It is possible to prevent color shift due to jitter which occurs when the sliding resistance is large.

Further, in this color image forming apparatus, since the charging roller 9 is always in contact with the surface of the photosensitive drum 1, the residual toner on the surface of the charging roller 9 from the photosensitive drum 1 side. However, the surface of the charging roller 9 is always fixed to the roller cleaning member 22.
Therefore, even in a color image forming apparatus in which the number of times of image formation is larger than that in a monochrome machine, uneven charging can be prevented and a long life can be maintained.

Next, in order to confirm the effects of the present invention,
Experimental results performed using the color image forming apparatus having the configuration shown in FIG. 1 will be described with reference to FIGS.
The surface of the conductive rubber portion of the charging roller used in the experiment was roughened by a sandblast method in which sand for cutting was blown by pressurized air, and the surface roughness was averaged by 10 points.
(Rz) of 1 μm to 50 μm was used. Each of the charging rollers having a different surface roughness was sequentially assembled into an image forming apparatus, and a print test was performed.

The evaluation of the test results includes evaluation of color misregistration due to jitter and color unevenness of a halftone image on an image after 20,000 sheets have been printed (image density is reduced to facilitate evaluation). Were evaluated by sensory evaluation in five steps. In the sensory evaluation, rank 1 was the worst, rank 5 was the best, and rank 4 or higher was regarded as a pass level.

FIG. 7 shows the evaluation of color misregistration due to the jitter.
FIG. 8 shows the evaluation of the color unevenness of the halftone image after printing 20,000 sheets. In order to confirm the effect, in the experiment, FIG.
A similar confirmation test was also performed on a conductive rubber having no directional polished surface as in the conventional charging roller shown in FIG.

As can be seen from the experimental results shown in FIG. 7, a conventional charging roller having a 10-point average roughness (Rz) of 20 μm or more formed a jitter image and was rejected. However, as in the case of the charging roller according to the present invention, in which a directional polished line is formed on the conductive rubber portion and the polished line is brought into contact with the roller cleaning member in the normal direction, the 10-point average roughness is obtained. With respect to those having a thickness (Rz) in the range of 1 μm to 40 μm, no jitter was generated and the level was sufficient for use as a color image forming apparatus (evaluation of acceptance).

The results of the evaluation of halftone color unevenness after printing 20,000 sheets in FIG. 8 show that the one using the charging roller according to the present invention has a 10-point average roughness Rz of 1 μm to 3 μm. Since the micro-vibration of the roller cleaning member was extremely small, the halftone color unevenness progressed due to the contamination of the charging roller, resulting in a poor evaluation. However, when the 10-point average roughness Rz is 5 μm or more, the micro-vibration of the roller cleaning member is sufficiently large, and the vibration makes it difficult for the dirt to adhere to the surface of the charging roller. The accompanying halftone color unevenness has been eliminated.

Here, on the diagram of FIG. 8, an experimental result of the charging roller according to the present invention described with reference to FIG. (Indicated by the line marked with a triangle) are superimposed as shown in FIG. According to this result, when the direction of the polished portion of the conductive rubber portion of the charging roller is brought into contact with the roller cleaning member in the forward direction as in this color image forming apparatus, the surface roughness of the polished portion is reduced. When the average roughness Rz is in the range of 5 μm or more and 40 μm or less, it is possible to prevent the occurrence of a jitter image and the occurrence of halftone color unevenness, thereby obtaining a good color image.

[0033]

As described above, according to the present invention, the following effects can be obtained. According to the color image forming apparatus of the first aspect, since the surface of the charging roller is cleaned by the cleaning member, the charging roller is constantly pressed against the image carrier, and furthermore, compared with a monochrome machine, to form a color image. Even if the number of image formation is large, residual toner and the like transferred from the image carrier after the image is transferred to the surface of the charging roller is immediately cleaned, so that the surface of the charging roller can always be kept clean. Therefore, it is possible to prevent uneven charging due to contamination of the surface of the charging roller and also prevent fusion of the toner, thereby extending the life.

According to the color image forming apparatus of the second aspect,
The surface of the charging roller is polished to have directionality, and the polished surface is brought into contact with the cleaning member in the forward direction, so that toner is prevented from fusing and a long life is achieved. The occurrence of color shift can also be prevented.

According to the color image forming apparatus of the third aspect,
Since the surface roughness of the charging roller is 5 μm or more and 40 μm or less, the minute vibration of the cleaning member during rotation of the charging roller becomes a vibration that makes it difficult for dirt to adhere to the surface of the charging roller. It becomes difficult.
As a result, it is possible to prevent the occurrence of halftone color unevenness due to the contamination of the charging roller, thereby improving the image quality.

According to the color image forming apparatus of the fourth aspect,
Since the cleaning member is a sponge, even if the cleaning member is always in pressure contact with the surface of the charging roller, a minute vibration is generated when the charging roller rotates, so that dirt on the surface of the charging roller can be removed. Good cleaning properties can be maintained over a long period of time.

[Brief description of the drawings]

FIG. 1 is a configuration diagram illustrating an image forming unit of a color image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a side view showing a charging roller of the color image forming apparatus.

FIG. 3 is a schematic view showing the charging roller and a roller cleaning member for cleaning the surface of the charging roller.

FIG. 4 is a schematic view exaggerating the polished line for explaining how the charging roller rotates so that the polished line comes into contact with the roller cleaning member in a forward direction.

FIG. 5 is an explanatory diagram for explaining contact in the normal direction and reverse direction of the polishing line.

FIG. 6 is an explanatory diagram for explaining a case where a surface does not have a directional polishing line.

FIG. 7 is a diagram showing an experimental result of color misregistration due to jitter performed to confirm the effect of the present invention.

FIG. 8 is a diagram showing the results of an experiment performed to confirm color unevenness of a halftone image after printing 20,000 sheets.

[Explanation of symbols]

 1: photosensitive drum (image carrier) 4, 5, 6: developing device 9: charging roller 22: roller cleaning member 25: polishing eye

Claims (4)

[Claims] A rotating image carrier, a charging roller for charging the image carrier while being driven and rotated while constantly pressed against the image carrier, and the image charged by the charging roller. A developing device for developing a latent image corresponding to each of the three colors or four colors sequentially formed on the charging surface of the carrier with toner of a corresponding color. A color image forming apparatus comprising a cleaning member for cleaning a surface of a roller. 2. The charging roller according to claim 1, wherein a surface of the charging roller has a predetermined surface roughness having a direction of a polished eye, and the direction of the polished eye is adjusted to a contact with the cleaning member in a forward direction. The color image forming apparatus according to claim 1, wherein 3. The charging roller has a predetermined surface roughness of 5 μm.
3. The color image forming apparatus according to claim 2, wherein the thickness is not less than m and not more than 40 [mu] m. 4. The color image forming apparatus according to claim 1, wherein said cleaning member is a sponge.