JP2000267400A - Color image forming equipment - Google Patents

Abstract

(57) [Problem] To quickly collect toner adhered to the surface of a charging roller so that the toner does not fuse to the surface of the charging roller. SOLUTION: A cleaning pad 22 is provided on a surface of a charging roller 2 so as to be always in contact with the surface of the charging roller 2 for cleaning by sliding contact with the surface of the charging roller 2. The cleaning pad 22 is formed of, for example, a sponge. When the charging roller 2 is rotating during image formation, a portion of the cleaning pad 22 in contact with the surface of the charging roller 2 repeats minute contact with and separation from the charging roller 2.
Accordingly, the cleaning pad 22 removes minute foreign matters such as toner and paper dust adhered to the surface of the charging roller 2, so that charging unevenness that occurs when the charging roller 2 becomes dirty can be prevented.

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 copying machine, a printer, a facsimile, etc., provided with a cleaning member for charging a photosensitive member with a charging roller and cleaning the surface of the charging roller.

[0002]

2. Description of the Related Art In a color image forming apparatus such as a color copying machine or a color printer, a photoreceptor, a developing device, a charging device, and the like are housed in a case to form an integrated color image forming unit. More and more. In this type of color image forming apparatus, an image per page is separated into three or four colors to form an image, and the images are sequentially superimposed to form a one-page image.

[0003] Therefore, in such a color image forming apparatus, the number of times of charging is three or four times (for color separation) larger than that of a monochrome image forming apparatus, and the amount of ozone generated during charging is accordingly reduced. More. Therefore, in such a color image forming apparatus, a contact-type charging device that performs charging by bringing a charging member such as a charging roller into contact with a photoreceptor is advantageous because the amount of generated ozone is small from an environmental point of view. .

However, in such a contact-type charging device, for example, charging is performed in a state where the charging roller is in contact with the surface of the photoreceptor, so that the toner remaining on the surface of the photoreceptor is transferred to the charging roller side. Was easy to get dirty. When the toner adheres to the charging roller, charging failure occurs, which is troublesome.

[0005] Therefore, in the case of such a contact type charging device, for example, as described in JP-A-7-244435, a cleaning roller formed of a metal roller is brought into contact with the charging roller, The toner adhered to the charging roller is collected by a cleaning roller, and the collected toner is collected in a toner collection box. Some image forming apparatuses using a contact-type charging device press a cleaning member against a charging roller at the end of one job.

[0006]

However, as described above, the color image forming apparatus continuously forms images of three or four colors as described above, and sequentially superimposes the images to form one color image. Therefore, the image forming time required to form one image is three to four times or more as long as that of a monochrome image forming apparatus. Sometimes it was more than four times. Therefore, the life of the color imaging unit that houses the charging roller in the case is
There is a problem that the life of the monochrome machine is reduced to 1/3 to 1/4.

Further, in the case where the toner adhered to the charging roller is collected by a metal cleaning roller which is in contact with the charging roller, there is no problem with the toner scraped off from the charging roller. There is a problem that the toner is rubbed against the surface of the charging roller by the roller, so that it may be difficult to remove the toner.

Further, in the case of a color image forming apparatus in which a cleaning member is pressed against a charging roller at the end of one job, the image forming time required for forming an image of one job is three to four times longer than that of a monochrome machine. Therefore, even if one image is formed, one image is formed at the end of image formation.
In some cases, the color toner adheres (fuses) to the surface of the charging roller due to the friction with the photosensitive drum and the heat of the charging current, making it difficult to remove the toner.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above problems, and has as its object to quickly collect toner adhered to the surface of a charging roller so that the toner does not fuse to the surface of the charging roller. And

[0010]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a rotatable photoreceptor and a rotatable photoreceptor which is constantly pressed against the surface of the photoreceptor while the voltage is increased while being driven by the rotation of the photoreceptor. A charging roller that charges the surface of the photoreceptor by being applied, a cleaning member that cleans the surface of the charging roller by sliding on the surface of the charging roller, and a developing device that uses toner of three or four colors. In the color image forming apparatus provided with, the cleaning member, at least when the charging roller during image formation is rotating, such that a portion in contact with the surface of the charging roller repeats minute contact and separation with the charging roller. It was done. And the surface roughness of the charging roller is
The thickness is preferably 5 μm or more and 30 μm or less. Also, the cleaning member may be a sponge.

[0011]

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. This color image forming apparatus is driven around a drum-shaped photoconductor (image carrier) 1 rotatable in the direction of arrow A while being in contact with the surface of the photoconductor 1 and following the rotation of the photoconductor 1. While a voltage is applied from a power supply (not shown), a charging roller 2 charges the surface of the photoconductor 1 uniformly, and an electrostatic latent image is formed by irradiating the photoconductor 1 with a laser beam L. And an exposure device 3 for performing the operation. Further, there are provided developing devices 4, 5, and 6 corresponding to each color, which visualizes the electrostatic latent image to form a toner image, and an intermediate transfer belt 8 which holds the toner images of the respective colors so as to overlap each other. .

Further, a transfer roller 9 for transferring the toner image on the rotating intermediate transfer belt 8 which is stretched between a plurality of rollers and collectively transferring the toner image onto transfer paper, and a transfer roller 9 for transferring the toner image to the intermediate transfer belt 8.
A cleaning device 10 for removing residual toner remaining on the photoreceptor 1 after transfer to the photoreceptor 1 and a charge removing lamp 11 for removing charge remaining on the photoreceptor 1 are also provided. Then, toner corresponding to each color is supplied to the developing devices 4, 5, and 6 from a supply port by a toner supply device (not shown).

In this color image forming apparatus, when the image forming operation is started, the photosensitive member 1 starts rotating in the direction of arrow A.
Then, the surface of the photoconductor 1 is neutralized by static elimination light emitted from the static elimination lamp 11, and the surface potential of the portion is reduced to 0.
It is averaged to a reference potential of -150V. Next, the photosensitive member 1 is charged by applying a voltage to the charging roller 2 which is driven and rotated while being in contact with the surface of the photosensitive member 1, and the surface potential of the photosensitive member 1 becomes about -1000V.

The charged surface of the photoreceptor 1 is irradiated with a laser beam L corresponding to the first color image from the exposure device 3, and the surface potential of a portion which becomes an image by the irradiation of the laser beam L becomes zero. It becomes -200V. Then, the first color toner is attached to the exposed portion by the developing device 4 to form a toner image. Thus, the photosensitive member 1
The first color toner image formed on the photosensitive member 1 is indicated by arrow A.
When it is moved to a position facing the intermediate transfer belt 8, the image is temporarily transferred to and held on the intermediate transfer belt 8.

Photoconductor 1 after transfer of the toner image
Is the cleaning blade 12 of the cleaning device 10
Removes the residual toner and cleans it.
The surface of the photoconductor 1 is neutralized by the neutralization lamp 11 and is completely initialized. Subsequently, the image forming operation for the second color is started, and the surface potential of the photoconductor 1 averaged to the reference potential of 0 to -150 V becomes about -1000 V.

Then, the surface of the photoreceptor 1 is irradiated with a laser beam L corresponding to the image of the second color by the exposure device 3, and the surface potential of the portion irradiated with the laser beam L is 0 to 0.
-200V. Then, the toner of the second color is attached to the exposed portion by the developing device 5 to form a toner image.

The second color toner image is moved to a position facing the intermediate transfer belt 8 by rotating the photosensitive member 1 in the direction indicated by the arrow A, and is transferred to the intermediate transfer belt 8 there. Is superimposed and held. Then, the photoconductor 1 after the transfer of the toner image
Then, the residual toner is scraped off again by the cleaning blade 12 of the cleaning device 10 to be cleaned, and the surface of the photoconductor 1 is discharged by the discharge lamp 11 to be completely initialized.

Hereinafter, the third color image is formed in the same manner using the developing device 6, and a three-color superposed toner image is formed on the intermediate transfer belt 8. In the case of a four-color superposed color image forming apparatus, a four-color superposed toner image is similarly formed on the intermediate transfer belt.

On the other hand, a transfer paper is fed from a paper feed unit (not shown), and the transfer paper is superposed by a pair of registration rollers (not shown) so that the leading end of the transfer paper is formed on the intermediate transfer belt 8 by three-color superposition. The toner image is conveyed at a timing coincident with the leading end of the toner image, and a three-color superimposed toner image is transferred onto the paper by the transfer roller 9.

Then, the transfer paper is conveyed to a fixing unit, where the toner image is melted and fixed by applying heat and pressure, and then discharged as a color copy to a discharge tray or the like. Then, the residual toner remaining on the photoconductor 1 is scraped off by the cleaning blade 12 of the cleaning device 10, and then the surface of the photoconductor 1 is discharged by the discharge lamp 11. Thereafter, this image forming process is repeated.

Next, the charging device will be described in detail.
The charging roller 2 is formed by forming a conductive rubber 21b having a small hygroscopic property and a stable resistance value on the outer periphery except for both ends of the metallic core 21a (so that a surface layer is further formed outside the conductive rubber 21b). The surface of the conductive rubber 21b is always in pressure contact with the surface of the photoreceptor 1 so that the surface of the photoreceptor 1 can be driven and rotated by applying a high voltage to the core metal 21a. Charges uniformly.

On the surface of the charging roller 2, a cleaning pad 22, which is a cleaning member for cleaning by sliding on the surface of the charging roller 2, is provided so as to be always in contact therewith.
Is formed of a foam such as a sponge, and is adhered to the cleaning pad holding member 23 with an adhesive such as a double-sided tape. Although the cleaning pad 22 will be described in detail later, at least when the charging roller 2 is rotating during image formation,
The portion in contact with the surface of the charging roller 2 repeats minute contact with and separation from the charging roller 2.

Accordingly, the charging roller 2 keeps in contact with the surface of the photoreceptor 1 and is driven to rotate, so that foreign matters such as fine toner and paper powder are transferred from the photoreceptor 1 side. However, since the cleaning pad 22 cleans the surface and removes foreign matters such as minute toner and paper dust adhered to the surface, it is possible to prevent charging unevenness that occurs when the charging roller 2 becomes dirty. it can.

The conductive roller 21b of the charging roller 2 is formed by rubber molding, and is ground and polished in the final step after the molding to obtain desired straightness and predetermined surface roughness. In this embodiment, the surface roughness of the charging roller 2 after processing is 5 μm or more and 30 μm or less. The grounds for setting the surface roughness of the charging roller 2 to 5 μm or more and 30 μm or less will be described later with reference to experimental results.

By the way, in this color image forming apparatus,
When the charging roller 2 is rotating, the portion of the cleaning pad 22 that is in contact with the charging roller 2 repeats minute contact with and separation from the charging roller 2. It is to improve. That is, when the cleaning pad 22 comes into contact with the charging roller 2, an impact force is applied to the foreign matter adhering to or about to adhere to the charging roller 2, and the foreign matter falls from the surface of the charging roller 2. It will be easier.

However, if the cleaning pad is in constant contact with the charging roller, and the portion of the cleaning pad that contacts the charging roller does not repeat minute contact and separation due to micro-vibration, the above-described impact force is not generated. In addition, foreign substances such as toner are less likely to fall off the charging roller.
Therefore, particularly in the case of a color image forming apparatus using a color toner having a low glass transition point, the color toner easily adheres to the charging roller and is easily melted.

As described above, once the color toner melts on the surface of the charging roller, the toner cannot be removed without wiping with an organic solvent. When the charging operation is performed while the toner is melted on the surface of the charging roller, the portion where the toner is melted has an increased resistance, so that the discharge is hindered, so that charging cannot be performed. For this reason, the image becomes a streak of the circumference of the charging roller and appears in the image, so that the image quality is significantly reduced.

In particular, in the case of a color image, since halftone is mainly used, slight unevenness of the charged potential in units of 10 V has a great effect on image quality. However, in the color image forming apparatus according to this embodiment, as described above, when the charging roller 2 is rotating, the portion of the cleaning pad 22 in contact with the charging roller 2 repeats minute contact and separation with the charging roller 2. Therefore, the above-described problem does not occur.

Next, a mechanism by which foreign matters such as toner and paper dust adhering to the surface of the charging roller 2 can be removed by the color image forming apparatus according to the present invention will be described with reference to FIG.
This will be described with reference to FIGS. FIG. 2 to FIG. 5 are enlarged explanatory views showing contact portions between the charging roller 2 and the cleaning pad 22, respectively. In these figures, the charging roller 2 is shown linearly for convenience.

The cleaning pad 22 adheres to the surface of the charging roller 2 by the contacting / separating operation even if the cleaning pad 22 keeps contacting and separating from the charging roller 2 even if the cleaning pad 22 is always minute due to minute vibration without standing still. Since the impact force can be continuously applied to the foreign matter 25 such as the toner, the fusion of the toner can be prevented. This minute contacting / separating operation of the cleaning pad 22 is generally called chatter.

The operation of contacting and separating the cleaning pad 22 called chatter will be described below. In FIG. 2, the cleaning pad 22 is stationary, but the charging roller 2 is moving in the direction of arrow B. In addition, foreign matter 25 such as toner exists between adjacent ridges 2 a on the surface of the charging roller 2.

In this state, the charging roller 2 rotates in the direction of arrow B (moves rightward in FIG. 2), so that the protrusion 22a on the surface of the cleaning pad 22 moves in the direction of arrow B. And is deformed in the direction of arrow C as shown in FIG. And the convex part 22a
When the deformation proceeds to a certain point, the charging roller 2 tries to return to the original position shown in FIG.

When the projection 22a returns to its original position and collides with the foreign matter 25 such as toner as shown in FIG. 4, a large impact force is applied to the foreign matter 25 from the projection 22a. Since it acts in the direction indicated by arrow E, the foreign matter 25 is repelled from the surface of the charging roller 2 and separates from the surface of the charging roller 2 as shown in FIG.

If the surface of the charging roller 2 is in a completely homogeneous state (a smooth state without the peak 2a), the cleaning pad 22 moves in the rotation direction of the charging roller 2 in FIG. As shown in (2), the convex portion 22a is deformed, and in the dynamic state, the convex portion 22a comes to rest in the deformed state.

In this state, as is often seen in the cleaning blade 12 (see FIG. 1) of the cleaning device 10 for cleaning the surface of the photosensitive member 1, the tip of the cleaning blade 12 comes into contact with and separates from the photosensitive member 1 by minute deformation. Does not occur, the cleaning blade 12 does not generate an impact force on foreign substances such as toner. Further, since the foreign matter is rotated by generating a rotating force on the foreign matter, the foreign matter is thereby rotated.
(For convenience, the photosensitive member 1 is shown in a linear shape.) As shown in FIG.
Will slip through.

However, in this color image forming apparatus, the surface roughness of the charging roller 2 is set to 5 μm or more and 30 μm or less, and
Is formed of a sponge having appropriate elasticity and resistance to permanent distortion, so that the cleaning pad 2 is rotated while the charging roller 2 is rotating, as described with reference to FIGS.
The fine protrusions 22a on the surface of the surface 2 do not stand still with respect to the charging roller 2, but repeatedly contact and separate (chatter) with the charging roller 2 even if they are very small. Therefore, it is possible to always apply an impact force to the foreign matter 25 such as the toner adhered to the surface of the charging roller 2 so that the toner in the foreign matter 25 does not fuse to the surface of the charging roller 2.

【Example】

Next, a description will be given of an experimental result which is a basis for setting the surface roughness of the charging roller 2 to 5 μm or more and 30 μm or less. In the experiment, the surface of the charging roller was polished, and the surface roughness was adjusted to 10 μm average roughness (RZ) of 1 μm to 5 μm.
Several types having a thickness of 0 μm were prepared and used, and a 20,000-sheet print test was performed on each of them.

The evaluation was carried out by five-stage visual sensory evaluation of halftone color unevenness due to contamination of the charging roller after the print test of 20,000 sheets and jitter of the halftone image. In the evaluation, rank 1 was the worst, and rank 5
Was the best, and those having a rank of 4 or more were judged as acceptable.
In FIG. 9, a mark “推移” indicates a change in rank of halftone color unevenness due to uneven charge potential, and a mark “×” indicates a change in jitter rank.

According to the results of this experiment, in the case of a charging roller having a surface roughness of 1 μm to 3 μm in terms of 10-point average roughness (Rz), the micro vibration of the cleaning pad (cleaning member) is small, Halftone color unevenness due to stains progressed, but the 10-point average roughness (Rz) was 5 μm.
In the charging roller described above, the cleaning roller was sufficiently vibrated by the minute vibration, so that the charging roller was hardly stained, and halftone color unevenness due to the stain was not generated on the charging roller.

On the other hand, the surface roughness of the jitter image is 10%.
In the case of the charging roller having a point average roughness (RZ) of 1 μm to 30 μm, it was not observed, but in the case of the charging roller having a 10 point average roughness (RZ) of 35 μm or more, the fine vibration of the cleaning pad became excessive, A wavy jitter image was generated in the halftone image. When the charging roller had a 10-point average roughness (RZ) of 35 μm or more, the cleaning pad vibrated too much and generated noise. From the above experimental results, the surface roughness of the charging roller 2 is 5 μm or more and 30 μm or more.
It is preferable to set the following.

[0041]

As described above, according to the present invention, even in a color image forming apparatus using a color toner having a low glass transition point, when the charging roller is rotating as in image formation. Since the cleaning member repeatedly contacts and separates minutely from the surface of the charging roller, the toner is prevented from fusing to the surface of the charging roller.
Deterioration of image quality can be prevented.

When the surface roughness of the charging roller is set to 5 μm or more and 30 μm or less, vibration caused by contact and separation of the cleaning member with respect to the surface of the charging roller can be optimized, and a jitter image can be generated. As a result, good image quality can be obtained. further,
If the cleaning member is made of a sponge, it is an inexpensive material but has appropriate elasticity and has permanent distortion resistance.
The cleaning property of the charging roller surface can be relatively easily secured.

[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 an enlarged view showing a state in which a charging roller relatively moves with respect to a cleaning pad with a foreign substance adhered to the surface thereof.

FIG. 3 is an enlarged view showing a state in which a projection on the surface of the cleaning pad is hooked on a mountain of the charging roller and deformed by the relative movement of the charging roller with respect to the cleaning pad.

FIG. 4 is an enlarged view showing a state in which the convex portion collides with a foreign matter on the charging roller when returning from the peak of the charging roller to its original position.

FIG. 5 is an enlarged view showing a state in which the foreign matter is repelled from the surface of the charging roller by a projection on the surface of the cleaning pad and is separated.

FIG. 6 is an enlarged view showing a state in which a foreign object has entered between the cleaning blade and the photoconductor when the tip of the cleaning blade does not move toward and away from the photoconductor.

FIG. 7 is an enlarged view showing a state in which a foreign substance has entered while rotating between the protrusion of the cleaning blade and the photosensitive member after the state of FIG. 6;

FIG. 8 is an enlarged view showing a state in which foreign matter has passed through a convex portion of the cleaning blade after the state of FIG. 7;

FIG. 9 is a diagram showing the relationship between the surface roughness of a charging roller, halftone color unevenness, and the rank of a jitter image.

[Explanation of symbols]

 1: photosensitive member 2: charging roller 4, 5, 6: developing device 22: cleaning pad (cleaning member)

Claims (3)

[Claims] 1. A rotatable photoreceptor, and a charging roller for charging the surface of the photoreceptor by applying a voltage while being constantly pressed against the surface of the photoreceptor while rotating following the rotation of the photoreceptor. And a cleaning member that cleans the surface of the charging roller by slidingly contacting the surface of the charging roller, and a developing device that uses three or four color toners. A color image forming apparatus, wherein at least a portion of the charging roller which is in contact with the surface of the charging roller during image formation is repeatedly contacted with and separated from the charging roller when the charging roller is rotating. 2. The color image forming apparatus according to claim 1, wherein the charging roller has a surface roughness of 5 μm or more and 30 μm or less. 3. The color image forming apparatus according to claim 1, wherein the cleaning member is a sponge.