JPH04309974A - Contact electrostatic charging device - Google Patents

Abstract

PURPOSE:To prevent a charge from flowing in a pin hole from the peripheral part of a part opposed to the pin hole on an abutting member when the pin hole is caused on the surface of a photosensitive body and to prevent the fault of an image such as the omission of the image in a wide range. CONSTITUTION:A conductive member 6 positioned on the outer peripheral part of an electrostatic charging roller, which exists on the abutting member, has insulating property and a columnar conductive filler 7 is carried. Both ends of the filler 7 are exposed to the upper and the lower surfaces of the member 6. Therefore, the member 6 has conductivity only in the thickness direction and voltage is impressed on the surface of the photosensitive body from a DC power source connected to the electrostatic charging roller through the filler 7. Then, the charge does not flow in the pin hole from other than the filler 7 opposed to the pin hole.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a charging device that supplies a predetermined surface potential to a photoreceptor in an image forming apparatus using electrophotography such as a laser printer, and more particularly to a contact member that directly contacts the surface of the photoreceptor. The present invention relates to a contact charging device that applies a DC voltage to a photoreceptor.

0002

2. Description of the Related Art There is a charging device for applying a predetermined charging potential to the surface of a photoreceptor in an image forming apparatus using electrophotography, which uses corona discharge using a single wire electrode. However, in corona discharge, the charging efficiency on the surface of the photoreceptor is low, and a voltage that is extremely large compared to the charging potential must be applied to the wire electrode, resulting in the problem of increasing the size and cost of the power supply device. Further, this corona discharge generates ozone, which poses a problem of image deterioration and adverse effects on the human body.

[0003] Therefore, Japanese Patent Application Laid-Open No. 64-73364,
JP-A-64-73365 and JP-A-64-733
As disclosed in Japanese Patent No. 67 and the like, a contact charging device has been proposed in which a DC voltage is applied to a photoreceptor from a contact member that directly contacts the surface of the photoreceptor. By applying voltage directly to the surface of the photoreceptor from the contact member in this way, it is possible to improve charging efficiency, reduce costs by downsizing the power supply device, and eliminate the generation of ozone due to air discharge. deterioration and adverse effects on the human body can be prevented.

0004

[Problems to be Solved by the Invention] However, in the contact charging device described above, since a contact member such as a blade is in direct contact with the surface of the photoreceptor, pinholes are formed in the insulating layer on the surface of the photoreceptor due to deterioration over time. In this case, charges flow into the pinhole not only from the part facing the pinhole in the contact member but also from the surrounding area, and a relatively wide area around the pinhole on the surface of the photoreceptor becomes uncharged. There was a problem in that no image was formed in this area, leading to image deterioration.

That is, as shown in FIG. 4, when there is no pinhole in the OPC layer 21a of the photosensitive drum 21, negative charges and corresponding positive charges are lined up above and below the OPC layer 21a, but 5, when a pinhole 22 is formed in the OPC layer 21a, charges flow into the conductive base 21b of the photoreceptor drum 21 from the periphery of the portion of the contact member 11 that faces the pinhole 22. death,
In the OPC layer 21a, no charge exists in a relatively wide range around the pinhole 21, and the developer cannot be adsorbed in this range. It is known that the range in which this image cannot be formed is the range from the edge of the pinhole that is approximately equal to the thickness p of the base 21b.
There was a problem in that image omission occurred in a considerably wider range than the diameter of the pinhole 22 formed in a, and image deterioration due to the pinhole became noticeable.

[0006] An object of the present invention is to prevent, when a pinhole is formed on the surface of a photoreceptor, an uncharged state from occurring in a relatively wide area around the photoreceptor, and to prevent an uncharged state from occurring in a relatively wide area around the pinhole. It is an object of the present invention to provide a contact charging device that does not cause image deterioration such as image omission.

[0007]

[Means for Solving the Problems] A contact charging device of the present invention applies a DC voltage to a photoreceptor from a contact member that contacts the surface of the photoreceptor, the contact member comprising:
It is characterized by being formed of an anisotropic conductor having conductivity in the thickness direction and insulation in the direction perpendicular to the thickness direction.

[0008]

In the present invention, the contact member that contacts the photoreceptor surface has conductivity only in the thickness direction, and is insulated in the direction perpendicular to this, that is, in the plane direction of the photoreceptor surface. Therefore, even if a pinhole occurs on the surface of the photoreceptor,
No current flows from the part of the contact member that does not face the pinhole to the part that faces the pinhole.
Charge does not flow in from the periphery of the portion facing the pinhole.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic diagram showing the structure of a contact charging device according to an embodiment of the present invention. The photosensitive drum 3 is rotatably supported inside the image forming apparatus by a rotating shaft 4. As shown in FIG. The photosensitive drum 3 is generally made of a base made of a conductive material such as aluminum, and an insulating layer such as an OPC layer is formed on the circumferential surface of the base. This base body is grounded via a rotating shaft 4.

A charging roller 1 is in contact with a portion of the circumferential surface of the photoreceptor 3 over almost the entire axial direction. This charging roller 1 is rotatably supported inside the image forming apparatus via a rotating shaft 2 parallel to a rotating shaft 4 of a photosensitive drum 3. The outer peripheral surface of the charging roller 1 is covered with an elastic material such as silicone rubber or polyurethane rubber, and the outer peripheral surface of the charging roller 1 is covered with an elastic material such as silicone rubber or polyurethane rubber.
Elastic deformation occurs within a predetermined range due to contact with the material. The charging roller 1 has a metal core as a base, and a voltage is applied from a DC power source 5 to the core.

FIG. 2 is an enlarged perspective view showing the upper part of the charging roller. The conductive member 6 of the charging roller 1 uses a carrier such as insulating silicone rubber or polyurethane rubber as a support, and a conductive filler 7 such as conductive rubber, conductive resin, carbon fiber, metal wire, or metallized resin. They are supported at equal intervals. The conductive filler 7 has its longitudinal direction aligned with the thickness direction of the conductive member 6, and both ends of the conductive filler 7 are exposed on the upper and lower surfaces of the conductive member 6. As a result, in the charging roller 1, the conductive member 6 has conductivity only in its thickness direction, and exhibits insulation in a direction perpendicular to this direction. Further, the inner end of the conductive filler 7 contacts the core metal of the charging roller 1 , and the outer end contacts the circumferential surface of the photoreceptor drum 3 .

[0012] The material of the conductive member 6 has a hardness of 40
In order to prevent uneven charging due to the distribution of the conductive filler 7 on the surface of the photoreceptor drum 3,
A relative speed difference should be given between the peripheral speed Vd of the photoreceptor drum 3 and the peripheral speed Vr of the charging roller 1 so that the peripheral surface of the charging roller 1 slides on the peripheral surface of the photoreceptor drum 3.

Further, the value of the contact range (so-called nip width) L between the charging roller 1 and the photosensitive drum 3 is L·V.
The calculation result of r/Vd must be equal to or greater than the pitch P of the conductive fillers 7, and preferably about 4 to 10 times the pitch P of the conductive fillers 7.

When a DC voltage is directly applied to the photoreceptor drum 3 using the charging roller 1 constructed as described above, a pinhole 8 is formed in the OPC layer 3a of the photoreceptor drum 3 as shown in FIG. If this occurs, the conductive member 6 of the charging roller 1
In this case, charges flow only from the portion facing the pinhole 8, and charges in the peripheral portions do not flow into the pinhole 8. Therefore, even if a pinhole 8 is formed on the surface of the photoreceptor drum 3, image loss will not occur in an area exceeding the diameter of the pinhole, and the image formation state can be maintained in good condition. .

By configuring the conductive member 6 of the charging roller 1 into two layers, and using a nonlinear resistance material with the inner layer as a low-resistance layer, the inflow of current at the pinhole portion can be further suppressed. be able to. Further, the abutting member is not limited to the charging roller 1, and the present invention can be similarly implemented using a blade or the like.

[0016]

Effects of the Invention According to the present invention, it is possible to suppress the charge from flowing into the pinhole from the periphery of the portion facing the pinhole in the abutting member, and the surface of the photoreceptor can be This has the advantage of preventing an uncharged state over a large area, preventing image dropout, etc. over a wide area, and improving the image formation state.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the configuration of a contact charging device that is an embodiment of the present invention.

FIG. 2 is an enlarged perspective view of a conductive member of a charging roller constituting the contact charging device.

FIG. 3 is a schematic diagram showing the charging state of a photoreceptor in the contact charging device.

FIG. 4 is a schematic diagram showing the charging state of a pinhole-free photoreceptor in a general contact charging device.

FIG. 5 is a schematic diagram showing the charging state of a photoreceptor with pinholes in a conventional contact charging device.

[Explanation of symbols]

1-Charging roller (contact member) 3,21-Photoreceptor drum 8,22-pinhole 11-Abutting member

Claims (1)

[Claims] 1. A contact charging device that applies a DC voltage to the photoreceptor from a contact member that contacts the surface of the photoreceptor, wherein the contact member is electrically conductive in the thickness direction and insulating in the direction perpendicular to the thickness direction. A contact charging device characterized in that it is formed of an anisotropic conductor having the following characteristics.