JPH11295964A - Electrifying roller and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To hardly allow the occurrence of filming of a toner and the deposition of an oligomer of a low mol.wt. on a roller surface by applying a semiconductor resin of a prescribed thickness on the outer peripheral surface of a semiconductive rubber roller thicker on one end side and thinner toward the other end side. SOLUTION: The semiconductor resin of a thickness 10 to 20 μm is applied on the outer peripheral surface of the semiconductive rubber roller so as to be thicker on one end side and thinner toward the other end side. The electrifying roller 3 consists of the semiconductive urethane rubber roller 13 formed by coating the outer peripheral surface with a semiconductive urethane resin 12, disposing a conductive shaft 14 as a fulcrum shaft integrally, for example, concentrically with the urethane rubber roller 13 and adhering the same by a conductive adhesive 15. The thickness of the urethane resin 12 is made thicker on the one end 14a side of the shaft 14 having a gear and thinner toward the other end 14b side. The electrifying roller 3 is formed by applying the urethane resin 12 on the outer periphery of the urethane rubber roller 13 by a dipping method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electrophotographic printer,
The present invention relates to an image forming apparatus used for a copying machine or the like, and more particularly to a charging roller.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus used in an electrophotographic printer, a copying machine, etc., a uniform charge is charged on a surface of a photosensitive drum by a charging device, and an electrostatic device is charged on the surface of the charged photosensitive drum by an exposure device. A latent image is formed, toner is supplied to the electrostatic latent image from a developing device to develop the electrostatic latent image, and the developed toner image is transferred to a printing medium by a transfer device. Also,
The residual toner remaining on the surface of the photosensitive drum is evenly dispersed by a cleaning device, returned to the photosensitive drum little by little, and collected by a developing device.

The charging device has a charging roller pressed against the surface of the photosensitive drum, and applies a predetermined voltage to a support shaft of the charging roller.

The charging roller is formed by integrally forming a semiconductive rubber roller on a conductive shaft. The charging roller has a gear meshed with a drum driving gear for rotating a photosensitive drum on one end side of the conductive shaft. It rotates with a constant peripheral speed ratio with the drum.

When the image forming apparatus constructed as described above repeats the printing operation, the toner that has entered the pressure contact portion between the charging roller and the photosensitive drum is crushed by friction, and the roller surface of the charging roller is damaged. Attachment starts (hereinafter referred to as toner filming phenomenon). At first, an image defect occurs in a halftone, and a toner adhesion phenomenon (toner stain phenomenon) gradually occurs even on a printing background portion.

[0006] When the photosensitive drum rotates, the gear of the charging roller generates a repulsive force on the drum driving gear, so that the filming phenomenon of the toner occurs on the other end without the gear rather than on the one end with the gear. Cheap.

On the roller surface of the charging roller to which the crushed toner adheres, the friction with the photosensitive drum further increases, and the toner crushes at an accelerated rate, thereby forming an insulating layer by the toner. .

Therefore, the urging force of the urging member for urging the support shaft at the other end of the charging roller is determined by the urging force of the urging member for urging the support shaft at the one end. Adjustment is made so that the charging roller is pressed against the photosensitive drum with an equal urging force, so that the surface potential of the photosensitive drum is charged to a constant potential.

[0009]

In the conventional image forming apparatus, when the printing operation is repeated, for example, an urging member for urging the support shaft at the other end of the charging roller is required. Power
Even if the urging force of the urging member that urges the shaft part on one end side having the gear is weakened, the charging roller is applied to the photosensitive drum by the swing of the gear with respect to the conductive shaft, the play between the gears, and the like. There was a problem that it was not possible to make uniform pressure contact, and a toner insulating layer was formed on the charging roller, resulting in poor printing.

When the charging roller is left under a high temperature and a high humidity for a long time, the oligomer having a low molecular weight in the semiconductive urethane rubber roller precipitates on the surface of the roller, and the photosensitive drum and the photosensitive drum come into contact with each other. Reacts chemically with the photosensitive layer of the photosensitive drum at the contact area of
The photosensitive layer is denatured, and the photosensitive layer is deformed (dented) by a contact portion of the charging roller and toner inserted between the charging roller and the photosensitive drum, and the photosensitive layer is exposed to light. There is also a problem that the recess formed in the contact portion with the drum is not charged, and the toner is constantly developed.

According to the present invention, the toner filming phenomenon does not easily occur, and even if the toner is left under high temperature and high humidity for a long time, low molecular weight oligomers in the semiconductive urethane rubber roller precipitate on the roller surface. An object of the present invention is to provide a charging roller which is difficult to perform and an image forming apparatus using the charging roller.

[0012]

In order to achieve the above object, a charging roller according to the present invention comprises applying a semiconductive resin having a thickness of 10 .mu.m to 20 .mu.m on an outer peripheral surface of a semiconductive rubber roller. The rubber roller is provided so as to be thicker at one end and thinner toward the other end.

[0013]

Embodiments of the present invention will be described with reference to the drawings. Elements common to the drawings are denoted by the same reference numerals. First Embodiment FIG. 8 is a schematic diagram showing a schematic structure of an image forming apparatus. An image forming apparatus 1 used in an electrophotographic printer has a charging roller 3, an optical head 4, a developing roller 5, a transfer roller 7, and a cleaning roller 9 arranged around a photosensitive drum 2. The photosensitive drum 2 and each roller are rotatably supported by a frame (not shown), and rotate in the direction of an arrow during printing.

A constant negative potential is charged on the surface of the photosensitive drum 2 by the charging roller 3 and is exposed by the optical head 4 to form an electrostatic latent image having a potential of almost 0V.
The electrostatic latent image is developed by a negatively charged toner 6 supplied to a developing roller 5. The toner image is transferred to the positively charged print medium 8 by the transfer roller 7, but remains on the surface of the photosensitive drum 2 as a partial residual toner, and is uniformly dispersed by the cleaning roller 9. The toner is returned to the photosensitive drum 2 by a small amount while being collected and collected by the developing roller 5.

FIG. 1 is a sectional view of a charging roller according to the first embodiment, and FIG. 2 is a front view of the charging roller and the photosensitive drum shown in FIG. The charging roller 3 is pressed against the photosensitive drum 2 by urging the bearings 10a and 10b provided on the support shaft with urging members, for example, compression coil springs 11a and 11b.

The charging roller 3 has a semiconductive urethane rubber roller 13 (hereinafter referred to as a urethane rubber roller) whose outer peripheral surface is covered with a semiconductive urethane resin 12 (hereinafter referred to as a urethane resin 12).
A conductive shaft 1 as a support shaft.
4 (hereinafter referred to as shaft 14) is a urethane rubber roller 1
3, a shaft 14 is provided concentrically with a urethane rubber roller 13 and bonded with a conductive adhesive 15.
At one end 14a of the shaft 14, a gear 16 shown in FIG.
Is provided with a D-cut portion 17 for fixing.

The gear 16 meshes with a drum drive gear 18 for rotating the photosensitive drum 2, has a constant peripheral speed ratio, and rotates the charging roller 3 faster than the photosensitive drum 2. The charging roller 3 generates a pressing force G against a bearing 10a provided on the other end 14b of the shaft 14 by a repulsive force F generated at a meshing portion of the gear 16.

Accordingly, during rotation, the tension of the compression coil spring 11a is made weaker than the tension of the compression coil spring 11b so that the roller surface of the charging roller 3 is uniformly pressed against the roller surface of the photosensitive drum 2. It is.

However, since the gear 16 oscillates with respect to the shaft 14 and there is play between the gears 16 and 18, even if the tension of the compression coil spring 11a is made weaker than the tension of the compression coil spring 11b, the printing operation is not performed. During the repetition, the toner 6 attached to the surface of the charging roller 3 is removed from the charging roller 3 and the photosensitive drum 2.
, Causing a filming phenomenon of the toner. The toner filming phenomenon is caused by the pressing force G
This is more likely to occur on the other end 14b side where the action is effected, and is more likely to occur as the urethane resin 12 is thicker.

FIG. 3 is a diagram showing the relationship between the thickness of the urethane resin and the number of printed sheets where the filming phenomenon occurs. The vertical axis indicates the number of prints (thousands) when the filming phenomenon occurs, the horizontal axis indicates the thickness (μm) of the urethane resin 12, and the dot positions indicate the number of prints and the urethane when the filming phenomenon occurs. The relationship between the thickness of the resin and the thickness of the urethane resin 1 is shown.
It can be seen that the filming phenomenon occurs with a smaller number of prints as the thickness of No. 2 increases.

FIG. 3 shows a room temperature (20 ± 3) ° C., humidity (5
It is an experiment result in an environment of 0 ± 5)%.

FIG. 4 is a diagram showing the relationship between the thickness of the urethane resin and the fusing force. The vertical axis indicates the fusion force (gf), and the horizontal axis indicates the thickness (μm) of the urethane resin 12. The fusing force is temperature 80
It is an experimental result when left for 24 hours in an environment of 80 ° C. and 80% humidity. The fusing force means that the charging roller 3 and the photosensitive drum 2 are fused when drum contamination occurs, so that the charging roller 3 is required to be separated from the photosensitive drum 2 by using a tension gauge. This is a value obtained by measuring the force. A high fusion force means that the amount of drum contamination is large and black streaks are likely to occur.

As can be seen from FIG. 4, the urethane resin 12
The smaller the thickness of the roller, the greater the fusion force. In particular, when the thickness of the urethane resin 12 is 12.5 (μm) or less, the fusion force sharply increases.
It is understood that the thickness should be set to 2.5 (μm) or more.

Therefore, from FIGS. 3 and 4, in order to cope with the filming phenomenon of the toner and the contamination of the drum, the width of the thickness of the urethane resin 12 is set to 12.5 (μm) to 16.5 (μm).
It turns out that it is good to do.

According to the first embodiment, the thickness of the semiconductive urethane resin covering the outer peripheral surface of the semiconductive urethane rubber roller is set to 12.5 (μm) to 16.5 (μm). As a result, the toner filming phenomenon is less likely to occur, the number of printed sheets can be increased, and the semiconductive urethane rubber rubber can be used even when left under high temperature and high humidity for a long time.
Low molecular oligomers in the roller hardly precipitate on the roller surface, and the life of the charged roller can be extended.

Second Embodiment FIG. 5 is a sectional view of a charging roller according to a second embodiment. The difference from the charging roller according to the first embodiment is that the thickness of the urethane resin 12 is thicker at one end 14a of the shaft 14 having the gear 16 and becomes thinner toward the other end 14b. It is. In the charging roller 3 according to the second embodiment, the urethane resin 12 is applied to the outer periphery of the urethane rubber roller 13 by a dipping method.

FIG. 6 is a schematic view showing a step of applying a urethane resin by a dipping method. In the dipping method, as shown in FIG. 1A, a urethane rubber roller 13 on which the urethane resin 12 is not applied is removed from the urethane resin 12.
Then, the urethane resin 12 is applied by throwing it up at a constant speed as shown in FIG.

At this time, the D-cut portion 1 to which the gear 16 is fixed
The other end 1a of the shaft 14 provided with the shaft 7 is fixed with a chuck 22 and immersed in the urethane resin 12.
4b so that the urethane resin 12 is not coated.
Put 3 on.

As shown in FIG. 2B, the end surface 13a of the urethane rubber roller 13 is located above the liquid surface of the urethane resin 12 so that the urethane resin 12 is not applied to one end 14a of the shaft 14. To do. Shaft 1
When the urethane resin 12 is applied up to 4, a leak current is generated between the urethane resin 12 and the shaft 14 during printing, and the charging roller 3 becomes poorly charged.

When the urethane rubber roller 13 is pulled up, the thickness of the urethane resin 12 increases at one end 14a of the shaft 14 and decreases toward the other end 14b due to a dripping phenomenon.

According to the second embodiment, the semiconductive urethane resin is applied so that the thickness of the semiconductive urethane resin is thicker on one end side and thinner toward the other end side.
The charging roller can be evenly pressed against the photosensitive drum as compared with the first embodiment, even if there is a runout of the gear with respect to the shaft, play between the gears, or the like.

Third Embodiment FIG. 7 is a sectional view of a charging roller according to a third embodiment . The difference from the charging roller 3 according to the second embodiment is that a urethane rubber roller is used. Chamfer 1 on the end face 13a of the la 13
3b.

By providing the chamfer 13b on the end surface 13a of the urethane rubber roller 13, when the urethane rubber roller 13 is charged into the tank 21 filled with the liquid of the urethane resin 12, the liquid level of the urethane resin 12 is reduced. Is soaked that it is located on the chamfer 13b. As a result, the urethane resin 12
Can be prevented from being applied to the shaft 14. The chamfer length L is set to 2.5 so that the liquid surface of the urethane resin 12 is always located at the chamfer 13b even when a general coating device is used.
mm or more is desirable.

According to the third embodiment, the semiconductive urethane rubber roller is filled with the liquid of the semiconductive urethane resin by chamfering the end face of the semiconductive urethane rubber roller. When immersed in the immersed tank, the urethane resin can be easily positioned at a position where the urethane resin is not applied to one end of the conductive shaft.

In the first to third embodiments, the semiconductive urethane resin is applied to the outer peripheral surface of the semiconductive urethane rubber roller. A semiconductive nylon resin may be applied to the outer peripheral surface. In this case, the thickness of the semiconductive nylon resin is set to 10 μm to 20 μm.

[0036]

Since the present invention is configured as described above, it has the following effects. By providing a semiconductive resin on the outer peripheral surface of the semiconductive rubber roller so as to be thicker at one end of the semiconductive rubber roller and thinner toward the other end, the photosensitive drum is rotated at one end. The gear has a gear that meshes with the gear, and when it is pressed against the photosensitive drum and rotated together with the photosensitive drum, even if the gear oscillates with respect to the conductive shaft, play between gears, etc., the charging roller is evenly applied to the photosensitive drum. And the filming phenomenon of the toner hardly occurs, and the number of printed sheets can be increased.

Further, since a semiconductive resin having a thickness of 10 μm to 20 μm is applied to the outer peripheral surface of the semiconductive rubber roller, even if the semiconductive rubber roller is left under a high temperature and a high humidity for a long time, the low level of the semiconductive roller is maintained. It becomes difficult for molecular oligomers to precipitate on the roller surface,
The life of the charging roller can be extended.

[Brief description of the drawings]

FIG. 1 is a sectional view of a charging roller according to a first embodiment.

FIG. 2 is a front view of a charging roller and a photosensitive drum shown in FIG.

FIG. 3 is a diagram showing the relationship between the thickness of a urethane resin and the number of printed sheets where a filming phenomenon occurs.

FIG. 4 is a relationship diagram between the thickness of the urethane resin and the fusing force.

FIG. 5 is a sectional view of a charging roller according to a second embodiment.

FIG. 6 is a schematic view showing a urethane resin coating step by a dipping method.

FIG. 7 is a sectional view of a charging roller according to a third embodiment.

FIG. 8 is a schematic diagram illustrating a schematic structure of an image forming apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Photosensitive drum 3 Charging roller 12 Semiconductive urethane resin 13 Semiconductive urethane rubber roller 14 Conductive shaft

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Masayuki Suzuki 4-11-11 Shibaura, Minato-ku, Tokyo Inside Oki Data Corporation

Claims (4)

[Claims] 1. A charging roller in which a semiconductive rubber roller is integrally formed concentrically with a conductive shaft, wherein a thickness of the semiconductive rubber roller is 10 μm to 20 μm on an outer peripheral surface of the semiconductive rubber roller.
A charging roller comprising a semi-conductive rubber roller coated with a thickness of .mu.m and having a thickness increasing at one end of the semi-conductive rubber roller and decreasing toward the other end. 2. The charging roller according to claim 1, wherein said semiconductive resin is a semiconductive urethane resin, and has a thickness of 12.5 μm to 16.5 μm. 3. The charging device according to claim 1, wherein a chamfered portion having a chamfered length of 2.5 mm or more is provided on an end face of the semiconductive rubber roller, and the length of the chamfered portion is 2.5 mm or more. Roller. 4. An image forming apparatus having a gear meshing with a gear for rotating a photosensitive drum at one end of a charging roller, wherein the charging roller is pressed against the photosensitive drum and rotates together with the photosensitive drum. An image forming apparatus using the charging roller according to claim 1 as a roller.