JP2002062715A - Electrostatic charging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrostatic charging apparatus which can be simply constituted and does not generate sounds caused by electrostatic vibration, even if DC voltage with overlapped AC is applied. SOLUTION: This electrostatic charging apparatus has an elastic tube 31, provided with photoconductivity and at least two pieces of rollers 32 and 33 pressing the tube 31 to a photoreceptor 16. Preferably, the tube 31 has a volume resistance ratio of between 103 to 109 Ω/cm, a hardness of >=50A degree and a maximum surface roughness of <=15 μm. A conductive member 43 having a U-shaped cross section may be used, instead of two rollers 32 and 33.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device for applying a charge to a photosensitive member of an electrophotographic apparatus.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 4, in order to apply a charge to a photoreceptor 1 with a uniform charge distribution prior to exposure, a half of a conductive core material 3 made of metal or the like is concentrically arranged. A charging roller 2 provided with a conductive elastic layer 4 is used. A DC voltage is applied between the photoreceptor 1 and the core material 3 of the charging roller 2 by a power source 6, and the surface of the elastic layer 4 of the charging roller 2 is negatively charged, for example. It is applied to the photoconductor 1 from the charging roller 2 at a contact portion 5 of the charging roller 2. In order for the transfer of the electric charge to be easily performed in the contact portion 5, the contact portion 5 has an appropriate pressing force in the direction of the photoconductor 1 so that the core member 3 has a constant width (nip width) L in the circumferential direction. Is pressed. In this prior art, in order to press the charging roller 2 against the photoreceptor 1, the bearing of the charging roller 2 must be configured so as to be able to move toward and away from the charging roller 1, and the configuration is complicated. There is a problem.

In order to stabilize the charging potential, an AC component is superimposed on a DC voltage by a power supply 7. When the DC component and the AC component are superposed in this way, the photoconductor 1 vibrates, and the vibration of the photoconductor 1 also vibrates the charging roller 2, thereby generating noise. In the prior art, in order to reduce noise, a heavy object is packed inside the photoconductor 1 to change the natural frequency. In such a configuration, the configuration is obviously complicated, and a large power is required for driving the photoconductor 1.

[0004] In another prior art, the elastic layer 4 is made of foam to reduce the aforementioned noise. In the configuration using a foam for the elastic layer 4, it is difficult to adjust the pressing force applied to the core material 3, and a new resistance adjusting layer must be provided on the surface of the elastic layer 4 to adjust its conductivity.

FIG. 5 is a cross-sectional view of a portion of another prior art charging device. An endless charging belt 9 is pressed against the photoconductor 1 by a roller 8.

FIG. 6 is a cross-sectional view of a portion of another prior art charging device. The photoconductor 1 includes rollers 10 and 11
The endless charging belt 12 stretched therebetween is brought into contact. In each of the prior arts shown in FIGS. 5 and 6 as well, the configuration for obtaining an appropriate nip width L becomes complicated,
In addition, a configuration for preventing generation of noise when AC is superimposed becomes complicated.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to make sure that the surface of a photoreceptor is charged by making contact with a desired appropriate nip width in the circumferential direction of a rotating body, and to reduce noise when superimposed on an AC component. An object of the present invention is to provide a charging device capable of suppressing generation with a simple configuration.

[0008]

According to the present invention, there is provided a charging device for charging a surface of a photoreceptor upstream of an exposure area of the photoreceptor, comprising: an elastic tube having at least an outer surface having semiconductivity; A pressing means for contacting at least two points along the circumferential direction of the tube and pressing the outer circumferential surface of the tube against the surface of the photoreceptor along the circumferential direction by the elasticity of the tube. is there.

The charging device according to the present invention comprises a tube, which is an elastic endless belt having conductivity, and pressing means for pressing the tube against the surface of the photoreceptor at least at two places from the inner surface by the elasticity of the tube. including. In the present invention, since the tube is used, the nip width L can be easily adjusted, and since the light-weight tube comes in contact with the photoconductor, the photoconductor vibrates by superimposing an alternating current on a direct-current voltage. Even if the tube vibrates, almost no noise is generated by the vibration of the tube.

Further, according to the present invention, the volume resistivity of the tube is 1 unit.
0 ³ to 10 ⁹ Ω · cm.

When the volume resistivity of the tube is less than 10 ³ Ω · cm, when the photosensitive member is damaged, current leaks from the wound,
The photoconductor surface cannot be charged uniformly. On the other hand, if it exceeds 10 ⁹ Ω · cm, a sufficient current does not flow, and a necessary charge cannot be applied to the photoconductor.

Further, according to the present invention, the hardness of the tube is JIS
-A hardness is 50 degrees or more.

The elastic tube has a hardness of Japanese Industrial Standard JIS
If the -A hardness is less than 50 degrees (hereinafter abbreviated as 50 degrees), the self-shape of the tube is not sufficiently maintained, and the inner peripheral surface of the tube has a hardness of 2 degrees.
The required nip width cannot be maintained if the photosensitive member is pressed at the location. The upper limit of the hardness of the elastic tube is not particularly limited, but may be about 100 A or less for the tube.

Further, the present invention is characterized in that the maximum surface roughness of the tube is 15 μm or less.

If the maximum surface roughness of the tube is more than 15 μm, a portion of the nip width that comes into contact with the photoreceptor and a portion that does not come into contact are formed, resulting in uneven charging of the photoreceptor.

Further, the present invention is characterized in that the pressing means has a plurality of rollers, at least one of the rollers is a conductive roller, and a voltage is applied to the conductive roller.

The pressing means is not particularly limited, but the pressing means according to the present invention comprises a plurality of rollers, preferably two rollers, at least one of which is conductive such as metal. A voltage is applied via a roller to charge the tube surface.

Further, the present invention is characterized in that the pressing means comprises a conductive member having a U-shaped cross section, and a voltage is applied to the conductive member.

The pressing means according to the present invention comprises a conductive member having a U-shaped cross section, and resiliently presses the tube against the photoreceptor at two points at the tip of the U-shaped cross section. A voltage is applied via the conductive member.

[0020]

FIG. 1 is an enlarged sectional view showing the vicinity of a charging device 15 according to an embodiment of the present invention, and FIG. 2 is a sectional view showing the vicinity of a photosensitive member 16 of an electrophotographic apparatus using the charging device 15. FIG. The charging device 15 includes a photoconductor 16 having a cylindrical shape.
Before the exposure, it functions to pre-charge the surface with a uniform charge amount. The photoconductor 16 is driven to rotate in the direction of arrow 17. A charging device 15 is provided upstream of the exposure area 18 of the photoconductor 16, and the photoconductor 16 is uniformly charged with, for example, a negative charge by the charging device 15 on the surface. In the exposure area 18, an image is exposed by the laser beam from the exposure unit 19, and an electrostatic latent image is formed in which the negative charge on the exposed portion is neutralized.

The electrostatic latent image on the photoreceptor 16 is
Is developed by the positively charged toner supplied from the developing roller 22.

In the transfer area 23, the developed image is transferred to a recording medium 25 such as paper supplied between the photoconductor 16 and the transfer roller 24. The transfer is performed by moving the toner on the photoreceptor 16 via the recording medium 25 such as paper in the direction of the transfer roller 24 to which a voltage having a polarity opposite to that of the toner is applied. The toner image transferred onto the recording medium 25 is fixed on the recording medium 25 by the fixing device 26.

After the surface of the photoconductor 16 has passed the transfer region 23, the surface of the photoconductor 16 comes into contact with the cleaning blade 27, and the remaining toner is scraped off and removed. , Charging device 1 again
5 allows a negative charge to be uniformly applied prior to exposure.

The charging device 15 includes an elastic tube 31 and 2
It is configured to include the rollers 32 and 33 of the book. The tube 31 has, for example, a thickness t = 0.5 mm, has a thin film shape, and is formed as an endless belt. Rollers 32 and 33 inserted into the tube 31 at intervals in the circumferential direction of the photoconductor 16 are attached to the photoconductor 16 of the tube 31.
Of the photosensitive member 16 over the nip width L.
In the circumferential direction of the elastic member to make a surface contact. These rollers 32 and 33 may have the same configuration, for example, and may be configured so that they can be adjusted by approaching and separating from the photoconductor 16, and only one of the rollers 32 and 33 may be adjusted. It may be adjusted so that it can be displaced toward and away from the photoconductor 16.

These rollers 32 and 33 are connected to the photosensitive member 16.
From the distances d1 and d2 exceeding the thickness of the tube 31 (t <d1 and t <d2). d1 = d
It may be 2. The rollers 32 and 33 may be provided so as to be rotatable around the axis thereof, or may be provided fixed so as not to rotate. Rollers 32, 33
The nip width L can be easily adjusted with a relatively simple configuration by adjusting at least one of the distances d1 and d2 toward and away from the photoconductor 16.

In the experiment of the present inventor, the tube 31
The volume resistivity was adjusted to 10 ⁷ Ω · cm by mixing chloroprene rubber as a main component and conductive carbon. The chloroprene rubber has a hardness of 70A and is extruded by an extrusion method.
For example, the outer surface was formed so as to have an outer diameter of 12 mmφ and a thickness t of 0.5 mm, and to have a maximum surface roughness of 15 μm or less. The two rollers 32 and 33 are made of stainless steel having an outer diameter of 4 mmφ, and the surface of the photoconductor 21 and the roller 3
The distance between the tubes 2 and 33 was 1 mm, and the tube 31 was set on two rollers as shown in FIG. Elastic tube 1
Due to the elasticity of 2, a region having a uniform nip width L, for example, 3 mm, in surface contact can be formed between the photoconductor 21 and the tube 12. When the photoconductor 16 is rotated in the direction of arrow 17, the photoconductor 16 is rotated in the direction of arrow 34 by the frictional force between the outer surface of the tube 31 and the surface of the photoconductor 16. At this time, the inner surface of the tube 31 and the rollers 32 and 33 come into frictional contact, and the rollers 32 and 33 rotatably supported rotate by the rotation of the photoreceptor 16 and, therefore, together with the rotation of the tube 31. One roller 33 has a tube 1
2 is negatively charged, for example, -1500
A DC voltage of V is applied by a DC power supply 35. Further, an AC voltage may be applied and superimposed by the AC power supply 36. The inner surface of the photoconductor 16 opposite to the charging device 15 is grounded.

In the configuration in which the AC voltage is superimposed by the AC power supply 36, the photosensitive member 16 and the tube 31 vibrate, but the tube 31 is in the form of a thin film. , So that the rollers 32 and 33 do not vibrate. It was confirmed by the experiment of the present inventor that no noise was generated by this.

FIG. 3 is a sectional view of a charging device 41 according to another embodiment of the present invention. Elastic tube 42 of this embodiment
Is similar to the tube 31 of the above-described embodiment, but has an inner surface coated with a fluororesin thin film. The conductive member 43 having a U-shaped cross section perpendicular to the rotation axis of the photoconductor 16 is formed by bending a stainless steel plate, and includes a leg 44 on the upstream side in the rotation direction 17,
It includes a downstream leg 45 and a connecting portion 46 connecting these legs 44 and 45 at a position away from the photoconductor 16. End portions 47, 48 of the legs 44, 45 on the photoconductor 16 side.
Are arranged at intervals in the circumferential direction of the photoconductor 16, and the distances d3 and d4 between the photoconductor 16 and the photoconductor 16 are selected to be greater than the thickness t of the tube 42 (t <d3 and t <d4).
d3 = d4 may be satisfied. The conductive member 43 is provided so as to be adjustable by being displaced toward and away from the photoconductor 16. The intervals d3 and d4 correspond to the nip width L at which the tube 42 and the photoconductor 16 resiliently contact.

With the rotation of the photosensitive member 16 in the direction of arrow 17, the tube 42 rotates in the direction of arrow 49. At this time, the inner peripheral surface of the tube 42 is connected to the end 4 of the conductive member 18.
7, 48 slides. As shown in FIG.
2, a DC power supply 35 may be connected, and an AC power supply 36 may be connected.

In another embodiment of the present invention, three or more rollers may be inserted into the tube 31 of the charging device 15 shown in FIG. 1 to support the tube 31. In the third charging device 41, the conductive member 43 inserted into the tube 42 is provided with not only a pair of legs 44 and 45 but also a large number of legs so as to support the tube 42. You may.

[0031]

As described above, according to the present invention, an elastic tube and a pressing means for pressing the tube against the photoreceptor at least at two places from the inner surface of the charging device are used, so that a fixed nip is provided with a simple structure. The width can be obtained, and the generation of noise can be prevented even when a voltage in which an alternating current is superimposed is applied to the pressing means or the like.

[Brief description of the drawings]

FIG. 1 is a simplified cross-sectional view of a charging device 15 according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view around a photoconductor 16 of an electrophotographic apparatus using the charging device 15 shown in FIG.

FIG. 3 is a cross-sectional view of a charging device 41 according to another embodiment of the present invention.

FIG. 4 is a cross-sectional view of a conventional charging roller 2.

FIG. 5 is a sectional view of a part of another conventional charging device.

FIG. 6 is a cross-sectional view of a part of still another conventional charging device.

[Explanation of symbols]

 15, 41 Charging device 16 Photoreceptor 31, 42 Tube 32, 33 Roller 35 DC power supply 36 AC power supply 43 Conductive member 44, 45 Leg L nip width

Claims (6)

[Claims] 1. A charging device for charging a surface of a photoreceptor upstream of an exposure area of the photoreceptor, comprising: an elastic tube having at least an outer surface having semiconductivity; and an inner surface of the tube extending along a circumferential direction of the tube. And a pressing means for pressing the outer circumferential surface of the tube against the surface of the photoreceptor along the circumferential direction by the elasticity of the tube. 2. The tube has a volume resistivity of 10 ³ to 10 ⁹ Ω.
2. The charging device according to claim 1, wherein the value is cm. 3. 3. The hardness of the tube is 5 in JIS-A hardness.
The charging device according to claim 1, wherein the charging device is at 0 ° or more. 4. The charging device according to claim 1, wherein the maximum surface roughness of the tube is 15 μm or less. 5. The pressing device according to claim 1, wherein the pressing means has a plurality of rollers, at least one of the rollers is a conductive roller, and a voltage is applied to the conductive roller. The charging device according to one of the above. 6. The charging device according to claim 1, wherein the pressing means comprises a conductive member having a U-shaped cross section, and a voltage is applied to the conductive member. apparatus.