JPH11143183A - Electrifying device for image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable stable electrification even when a roller cleaning member is always made in press contact with an electrifying roller. SOLUTION: In order to reduce the size of a device, even when the roller cleaning member 22 is always made in press contact with the charging roller 9, by defining a surface roughness on the surface butting to the roller cleaning member 22 of the charging roller 9 as >=5 μm and <=30 μm in ten points mean roughness, the roller cleaning member 22 is appropriately finely vibrated at the rotary time of the charging roller 9, therefore depositions can be hardly stuck on the surface of the charging roller 9. Therefore, the jittery image can be prevented from the occurrence, since the stable charge is made possible by restraining variance of the charge potential.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging roller for charging a photoreceptor while rotating following the rotation of the photoreceptor in a state of being constantly pressed against the surface of the photoreceptor, and a charging roller for constantly pressing the surface of the charging roller. And a roller cleaning member for cleaning the surface of the charging roller in a state.

[0002]

2. Description of the Related Art For example, in an image forming apparatus such as a copying machine or a facsimile, a photosensitive member, a developing device, a charging device and the like are housed in a case to form an image forming unit, thereby reducing the size of the entire image forming device. In many cases, the size is reduced. In an image forming unit of this type, a charging device of a roller charging type for bringing a roller-shaped charging member into contact with a photoconductor is often used. In such a roller charging type charging device, the surface of the photoconductor is uniformly charged by applying a voltage to the charging roller in a state where the charging roller is pressed against the photoconductor.

In such a charging device in which the charging roller is pressed against the photosensitive member, the toner remaining on the photosensitive member after the toner image is transferred onto the transfer paper easily adheres to the charging roller.
For example, a roller cleaning member made of a sponge or the like is brought into contact with the surface of the charging roller so as to bite in an appropriate amount, and when the charging roller rotates, the surface of the roller cleaning member rubs, so that toner adhered to the surface can be Other adhering substances (foreign substances) such as paper dust are removed (for example, see Japanese Patent Application Laid-Open No. 2-272594).

Incidentally, such a roller cleaning member is capable of coming into contact with and separating from the surface of the charging roller.
There is a type that is always in pressure contact with the surface of the charging roller (normal contact). In order to reduce the size of the apparatus as a whole, it is advantageous to adopt a normal contact type in which the roller cleaning member is not brought into contact with or separated from the surface of the charging roller because the mechanism can be simplified and reduced in size.

[0005]

However, in such a normal contact type charging device in which such a roller cleaning member always presses against the charging roller, if the charging roller is driven to rotate (co-rotate) with the photoreceptor, If the charging roller vibrates due to the friction load applied from the roller cleaning member to the charging roller during the operation of the photoconductor, the vibration is applied to the photoconductor and the photoconductor vibrates. Until now, it has been considered that the charged potential is varied and an image in which streaks appear on the image, that is, a so-called jitter image tends to occur.

Accordingly, many charging devices using a charging roller have a mechanism that enables the roller cleaning member to be brought into contact with and separated from the surface of the charging roller. As a result, the configuration becomes complicated, and it is difficult to reduce the size of the entire apparatus.

The present invention has been made in view of the above-mentioned problems, and even if a roller charging member of a type in which a roller cleaning member is always in pressure contact with a charging roller is employed for miniaturization of the device. It is another object of the present invention to prevent a charging roller from vibrating during an image forming operation, thereby causing a variation in charging potential and preventing a jitter image from being formed.

[0008]

In order to achieve the above object, the present invention provides a charging roller for charging a photoreceptor while rotating following the rotation of the photoreceptor while constantly pressing the surface of the photoreceptor, And a roller cleaning member for cleaning the surface of the charging roller in a state of being constantly pressed against the surface of the charging roller, wherein the surface roughness of the surface of the charging roller in contact with the roller cleaning member is provided. Is 10 μm or less in average roughness at 10 points. And the 10-point average roughness is 5
It is effective if the thickness is not less than μm and not more than 30 μm.

The friction coefficient between the charging roller and the roller cleaning member as described above may be set to 1.0 or less. In this case, it is effective if the friction coefficient between the charging roller and the roller cleaning member is set to 0.5 or more and 1.0 or less.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram showing an image forming unit of an image forming apparatus provided with a charging device according to the present invention. In this image forming apparatus, a voltage is applied from a power supply (not shown) around a drum-shaped photoconductor (image carrier) 1 in a state of being in contact with the surface of the photoconductor 1, thereby causing the surface of the photoconductor 1 to be charged. A charging device 2 having a charging roller 9 for charging such electric charges, an exposure device 3 for forming an electrostatic latent image by irradiating the photosensitive member 1 with a laser beam L, and a visualization of the electrostatic latent image. And a developing device 4 for converting the toner image into a toner image.

A developing device 4 is provided around the photosensitive member 1.
Belt 5 for transferring the toner image formed by the method on a transfer sheet, and photoreceptor 1 after transferring the toner image to the transfer sheet
Cleaning device 6 for removing residual toner remaining on top
In addition, a charge removing lamp 7 for removing charges remaining on the photoconductor 1 is also provided. Then, toner is supplied to the developing device 4 from a supply port by a toner supply device (not shown).

Next, an image forming operation of the image forming unit of the image forming apparatus will be described. In this image forming apparatus, when the image forming operation is started, the photoconductor 1 starts rotating in the direction of arrow A. Then, the surface of the photoreceptor 1 is neutralized by static elimination light emitted from the static elimination lamp 7, and the surface potential of the portion is averaged to a reference potential of 0 to -150V. Next, by applying a voltage to the charging roller 9, the photoconductor 1 is charged, and the surface potential of the photoconductor 1 becomes about -1000V.

The charged surface of the photoreceptor 1 is irradiated with a laser beam L from the exposure device 3 and the surface potential of an image forming portion when the laser beam L is irradiated is 0 to -200 V.
Becomes Therefore, the toner on the developing sleeve 10 of the developing device 4 adheres to the portion where the image is formed. In this way, the toner image formed on the photoconductor 1 is moved toward the transfer position where the photoconductor 1 and the transfer belt 5 are in contact with each other as the photoconductor 1 rotates in the direction of arrow A. .

On the other hand, transfer paper is fed from a paper feed unit (not shown), and the transfer paper is aligned by a pair of registration rollers 8 so that the leading end of the transfer paper coincides with the leading end of the toner image formed on the photoreceptor 1. And the toner image on the photoconductor 1 is transferred onto the paper surface. 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 to a discharge tray or the like. Then, the remaining toner remaining on the photoreceptor 1 is removed by the cleaning blade 11 of the cleaning device 6.
After that, the surface of the photoconductor 1 is discharged by the discharge lamp 7. Thereafter, this image forming process is repeated.

Next, the charging device 2 will be described. As shown in FIG. 2, the charging roller 9 of the charging device 2 is formed by forming a conductive rubber 13 having a small hygroscopic property and a stable resistance value on the outer periphery except for both ends of a metal core 12. (A surface layer may be further formed on the outside), and the surface of the conductive rubber 13 is always in pressure contact with the surface of the photoreceptor 1 (FIG. 1) so that it can be driven and rotated. The surface of the photoreceptor 1 is uniformly charged by applying a high voltage to the photosensitive member 1.

As shown in FIG. 3, a roller cleaning member 22 is always in pressure contact with the surface of the charging roller 9, and the roller cleaning member 22 is, for example, a foam such as sponge or a brush. Are attached to the cleaning pad holding member 23 with an adhesive such as a double-sided tape. The charging roller 9 has a surface roughness (RZ) of 10
The point average roughness is, for example, 30 μm or less.

In this image forming apparatus, since the charging roller 9 is a normal-type charging device in which the charging roller 9 is constantly pressed against the photosensitive member 1, minute toner adhering to the surface of the photosensitive member 1 is removed from the surface of the charging roller 9. When the charging roller 9 rotates, the roller cleaning member 22 rubs against the surface of the charging roller 9. Since the adhered matter such as the adhered toner can be removed by the roller cleaning member 22, uneven charging can be prevented.

As described above, the roller cleaning member for cleaning the surface of the charging roller includes one that comes into contact with and separates from the charging roller and one that is always in contact with the charging roller. When the roller cleaning member comes into contact with or separates from the charging roller, the roller cleaning member also gives an impact to the attached matter adhered to the surface of the charging roller when the roller cleaning member comes into contact with the charging roller. ,
The impact makes it easier for the deposits to fall off the surface of the charging roller.

However, in the case of the normal contact type in which the roller cleaning member is always in contact with the surface of the charging roller, not only the above-mentioned roller cleaning member does not contact the charging roller from a distant position, but also, for example, In the medium to long term after printing 5,000 sheets or more, the contact surface between the charging roller and the roller cleaning member is smooth due to abrasion or the like. Will not be added. Therefore, the adhered matter adhered to the surface of the charging roller hardly falls off therefrom.

On the contrary, if the deposits on the charging roller particularly have a glass transition point, the deposits are generated by friction heat generated when the roller cleaning member rubs the surface of the charging roller. Will promote fusion to the surface of the charging roller. In such a case, in the case of a negative-positive image, the portion where the deposits on the charging roller are fused is impaired in the charging function, so that charging cannot be performed. Therefore, black streaks appear on the image at the pitch of the circumference of the charging roller, and the image quality is significantly reduced.

This is similar to the fact that when the dust on the clothes is just dropped, it can be easily dropped by hitting the dust portion, but it becomes difficult to remove the dust by gentle rubbing. However, even if the roller cleaning member is always in contact with such a charging roller, if the roller cleaning member performs an appropriate minute vibration, the surface of the charging roller is caused by the minute vibration. Deposits (foreign matter and the like) adhered to the surface can be dropped therefrom.

Hereinafter, the mechanism will be described with reference to FIGS. FIGS. 4 to 7 are explanatory views showing step by step the state in which the adhered matter adhered to the surface of the charging roller falls off due to the micro-vibration of the roller cleaning member. And a charging roller is disposed in FIG.

Even when the roller cleaning member 22 is in constant contact with the surface of the charging roller 9, if the roller cleaning member 22 repeats minute vibrations without standing still, It is possible to apply an impact force to the attached matter 25 attached to the charging roller 9, so that the attached matter 25 can be prevented from fusing to the charging roller 9.

As described above, the roller cleaning member 22
Is generally called chattering by repeating minute vibrations, and this chattering is very effective in dropping the attached matter 25 from the charging roller 9. . The mechanism by which the deposit 25 falls off the surface of the charging roller 9 due to the chattering phenomenon of the roller cleaning member 22 will be described.

Now, as shown in FIG. 4, when the charging roller 9 is enlarged, many irregularities are present on the surface thereof,
It is assumed that the attached matter (foreign matter) 25 is located between a and 9b. On the other hand, when the roller cleaning member 22 is also enlarged, a large number of irregularities formed by the convex portions 22a, 22b and the like are present on the surface thereof, and the convex portions 22a and 22b are in contact with the surface of the charging roller 9 at the illustrated positions. Suppose. Also, the peak 9c of the charging roller 9 bites into a part of the projection 22b of the roller cleaning member 22, and the left side of the projection 22b in FIG. 4 enters between the peaks 9b and 9c of the charging roller 9. I do.

In this state, when the charging roller 9 is moved in the direction indicated by the arrow B by the rotation of the photosensitive member 1 (see FIG. 1), the projection 22b of the roller cleaning member 22 is moved by the movement of the charging roller 9 as shown in FIG. As shown in FIG. Then, as shown by a virtual line in FIG. 6, when the charging roller 9 moves in the arrow B direction to a position where the convex portion 22b is separated from the peak 9b of the charging roller 9, the convex portion 22b is held by the roller cleaning member 22 itself. The elastic force returns to the direction indicated by the arrow E as indicated by the solid line in FIG.

At this time, as shown in FIG.
7A and 9B, the portion is further enlarged, and as shown in FIG. 7, the protrusion 25b of the roller cleaning member 22 displaced in the direction of arrow E causes the protrusion 25b to move away from the arrow. The object is flipped in the direction indicated by G.
As a result, the deposit 25 is removed from the surface of the charging roller 9.

As described above, when the charging roller 9 relatively moves with respect to the roller cleaning member 22, the minute protrusions 22 formed on the surface of the roller cleaning member 22.
Due to the slight vibration of the surface of the roller cleaning member 22 caused by the displacement of a, 22b, etc., the deposit 25 attached to the surface of the charging roller 9 can be removed.

Therefore, if this minute vibration is generated on the roller cleaning member 22, even if the roller cleaning member 22 is constantly in contact with the surface of the charging roller 9, it adheres to the surface of the charging roller 9. The attached matter 25 is removed, and the attached matter 25 is transferred to the charging roller 9.
Can be prevented from being fused.

Next, the problem that the surface roughness of the surface of the charging roller 9 in contact with the roller cleaning member 22 is too small (approximately smooth) will be described with reference to FIGS.
0 will be described. As shown in FIG. 8, when the surface roughness of the surface of the charging roller 9 is extremely small and almost flat, the roller cleaning member 22 which is always in contact with the charging roller 9 has its surface portion charged. The roller 9 is pulled in the same direction by the movement in the direction of arrow B, and comes into contact with the surface of the charging roller 9 in a substantially stationary state while being pulled and displaced.

In this case, since the surface of the charging roller 9 is too smooth, the roller cleaning member 22 does not generate a minute vibration as in the case described with reference to FIGS. Therefore, no force is applied to the attached matter 25 attached to the surface of the charging roller 9 to apply an impact to the attached matter 25 to drop the attached matter 25. Therefore, it is possible to remove the attached matter 25 from the surface of the charging roller 9. Can not.

Further, at this time, as shown in FIG. 8, if there is a deposit 25 between the protrusions 22a and 22b of the roller cleaning member 22, the deposit 25 moves in the direction of arrow B of the charging roller 9. 9, while rotating in the direction of the arrow, enters the lower side of the convex portion 22b as shown in FIG. 9 and passes through the convex portion 22b as shown in FIG. Is difficult to remove from the surface of the charging roller 9. Therefore, even if the surface roughness of the surface of the charging roller 9 in contact with the roller cleaning member 22 is too small, inconvenience occurs.

[0033]

EXAMPLE The surface of a charging roller was roughened by sandblasting in which sand for cutting was blown with pressurized air, and the surface of the charging roller was made to have a 10-point average roughness (RZ) of 1 μm to 50 μm. Each charging roller having a different surface roughness is sequentially assembled into an image forming apparatus, and each of the charging rollers has a surface roughness of 300.
A print test of 00 sheets was performed. The evaluation of the test results was conducted by a sensory evaluation based on a five-point evaluation of the background stain on the image after printing 30,000 sheets and the occurrence of jitter in the halftone image (the image density was reduced to facilitate evaluation). Performed in In the sensory evaluation of the occurrence of jitter, rank 1 was the worst, rank 5 was the best, and rank 4 or higher was regarded as a pass level.

FIG. 11 is a diagram showing the results of the sensory evaluation of the background stain and generation of jitter. As is apparent from the evaluation results, in the case of the charging roller formed with a surface roughness of 1 μm to 3 μm with a 10-point average roughness (Rz), since the micro-vibration of the roller cleaning member is very small, In this case, the deposits (foreign matter and the like) attached to the surface of the charging roller cannot be dropped therefrom. Therefore, dirt accumulates on the surface of the charging roller, and background dirt is generated on the image.

However, the 10-point average roughness (Rz) is 5
In the case of μm or more, the micro-vibration of the roller cleaning member became sufficiently large, and the micro-vibration caused the adhering substances that had adhered to the surface of the charging roller to fall off therefrom. Has become.
Therefore, the background dirt does not occur. In the case of a charging roller having a surface roughness of 10 μm to 30 μm with a 10-point average roughness (Rz), no jitter image was observed (rank 4 or more), but the 10-point average roughness was 35 μm or more. In this case, the fine vibration of the roller cleaning member becomes excessive, and a wavy jitter image is generated in the halftone image (fail).

Further, when the ten-point average roughness was 45 μm or more, the roller cleaning member vibrated too much and generated noise. From the above results, the surface roughness of the surface of the charging roller in contact with the roller cleaning member was 10
When the point average roughness is 5 μm or more and 30 μm or less, the evaluation ranks of the background stain and the jitter both become 4 or more.

FIG. 12 shows various charging rollers having different friction coefficients between the charging roller and the roller cleaning member by varying the surface roughness of the charging roller to provide a friction coefficient of 0.2 to 1.5. FIG. 9 is a diagram showing the results of sensory evaluation of background stains and occurrence of jitter on an image after the charging rollers are sequentially assembled to the image forming apparatus and each of 30,000 sheets has been printed.

As in the case of the diagram shown in FIG. 11, the background dirt on the image and the state of occurrence of jitter in the halftone image are both evaluated by sensory evaluation in five stages, and rank 1 is the worst. , Rank 5 best, rank 4
The above was regarded as a pass level. As is apparent from the results shown in FIG. 12, when the friction coefficient was 0.2 to 0.4, the micro-vibration of the roller cleaning member was extremely small, so that dirt was deposited on the surface of the charging roller.

However, when the friction coefficient is 0.5 or more, the micro-vibration of the roller cleaning member is sufficiently large, and the vibration causes the adhering substances adhering to the surface of the charging roller to fall off from the roller cleaning member. The surface is less likely to get dirty. Therefore, the background dirt does not occur. No jitter image was observed when the coefficient of friction was 0.2 to 1.0 (rank 4 or higher). However, when the coefficient of friction was 1.1 or higher, the micro-vibration of the roller cleaning member was excessive, and A wavy jitter image was generated in the tone image (fail). From the above results, the coefficient of friction between the charging roller and the roller cleaning member was 0.5 or more and 1.0 or more.
In the following case, the evaluation ranks of the background dirt and the jitter both become 4 or more.

[0040]

As described above, according to the charging device of the image forming apparatus according to the present invention, even if the roller cleaning member is always pressed against the charging roller, an appropriate minute vibration is generated in the roller cleaning member. Therefore, it is possible to reduce the size of the apparatus and to make it difficult for the deposits to adhere to the surface of the charging roller. Therefore, generation of a jitter image can be prevented.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating an image forming unit of an image forming apparatus including a charging device according to the present invention.

FIG. 2 is a side view showing a charging roller of a charging device provided in an image forming unit of the image forming apparatus.

FIG. 3 is a side view showing a state in which a roller cleaning member is provided in a state of being constantly pressed against the surface of the charging roller.

FIG. 4 is an enlarged schematic view similarly showing a contact portion between the charging roller and a roller cleaning member.

5 is a schematic diagram similar to FIG. 4, showing a state in which the charging roller has moved in the direction of arrow B from the state of FIG. 4;

6 is a schematic diagram similar to FIG. 4, showing a state in which the charging roller has further moved in the direction of arrow B from the state of FIG. 5;

FIG. 7 is a schematic diagram in which a part of FIG. 6 is further enlarged.

FIG. 8 is an enlarged schematic view showing a state in which a roller cleaning member is in contact with a charging roller formed in a state in which the surface is almost smooth.

9 is a schematic diagram similar to FIG. 8, showing a state in which the charging roller has moved in the direction of arrow B from the state of FIG. 8;

FIG. 10 is a schematic diagram similar to FIG. 8, showing a state in which the charging roller has further moved in the direction of the arrow from the state of FIG. 9;

FIG. 11 is a diagram showing the results of sensory evaluation of background stains and occurrence of jitter on an image after printing 30,000 sheets using each charging roller having a different surface roughness.

FIG. 12 shows an image after printing 30,000 sheets using various charging rollers when the surface roughness of the charging roller is changed to make the friction coefficient between the charging roller and the roller cleaning member different. FIG. 4 is a diagram showing a result of judging the occurrence of background soil and jitter by sensory evaluation.

[Explanation of symbols]

 1: Photoreceptor 2: Charging device 9: Charging roller 22: Roller cleaning member

Claims (4)

[Claims] 1. A charging roller for charging a photosensitive member while being driven by the rotation of the photosensitive member in a state of being constantly pressed against the surface of the photosensitive member, and a charging roller in a state of being constantly pressed against the surface of the charging roller. A charging device for an image forming apparatus, comprising: a roller cleaning member for cleaning a surface of a roller, wherein a surface roughness of a surface of the charging roller in contact with the roller cleaning member is 30 μm or less in 10-point average roughness. Charging device of the image forming apparatus. 2. A surface roughness of a surface of the charging roller in contact with the roller cleaning member is 10 μm average roughness of 5 μm.
2. The charging device for an image forming apparatus according to claim 1, wherein the thickness is not less than 30 [mu] m. 3. A charging roller for charging the photosensitive member while being driven by the rotation of the photosensitive member in a state of being constantly pressed against the surface of the photosensitive member, and the charging roller in a state of being constantly pressed against the surface of the charging roller. A charging device for an image forming apparatus, comprising: a roller cleaning member for cleaning a surface of a roller, wherein a friction coefficient between the charging roller and the roller cleaning member is set to 1.0 or less. apparatus. 4. The charging device for an image forming apparatus according to claim 3, wherein a friction coefficient between said charging roller and said roller cleaning member is set to 0.5 or more and 1.0 or less.