JPH052313A - Electrifying device - Google Patents

Abstract

PURPOSE:To obtain images with uniform electrification and to decrease the dependence of the environment of the picture while hardly receiving the influence of the pinholes of a latent image holding member and to facilitate the process for production. CONSTITUTION:The electrifying member of the electrifying device which electrifies the latent image holding member by bringing the electrifying member into contact with the image holding member consists of a supporting member and a surface member and the surface member consisting of a shrink tube made of a conductive fluororesin.

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 an electrophotographic apparatus. In particular, the present invention relates to a contact charging device used for charging a latent image holding member and its manufacture.

[0002]

2. Description of the Related Art Conventionally, as a charging device for a latent image holding member used in an electrophotographic apparatus such as a plain paper copying machine, a laser printer, an LED printer or a liquid crystal printer, a corona discharge device is generally used and widely used. It is being appreciated. However, the corona discharge device has the following problems.

1) A high-voltage power supply is required to generate a discharge, which requires about 4 KV or more. Therefore, the cost of the power source increases, a high-voltage cable is required for wiring, etc., and an electrical high-voltage insulating material must be used, which further increases the cost. 2) Generation of ozone is unavoidable due to air discharge. Due to environmental problems in recent years, the generation of ozone, which is unfavorable to the human body, must be avoided as much as possible. 3) Charging tends to be non-uniform. That is, in order to cause a discharge phenomenon, a wire and a shield case are generally placed around the wire and a high voltage is applied between them. It deposits and the discharge becomes unstable. Therefore, charging of the latent image holding member becomes non-uniform and unevenness occurs on the image.

In particular, during negative corona discharge, this product stains the wire, making the discharge extremely unstable. Therefore, regular wire cleaning is indispensable and maintenance is troublesome. Therefore, in order to improve the drawbacks of these corona discharge devices, it has been proposed to use a contact charging device and make it a compact charging device that generates less ozone with a low voltage power source. (See, for example, JP-A-63-149669).

[0005]

However, when such a contact charging device is used, it is difficult to obtain uniform charging. That is, if the electric resistance of the charging member is too low, uneven charging of the latent image holding member occurs, resulting in image defects that cause image unevenness in the black portion during normal development and fog in the white portion during reversal development. On the other hand, if the electric resistance is too high, poor charging occurs and the image bearing member is not sufficiently charged.

Further, since the charging member directly contacts the latent image holding member, if the latent image holding member has a defect such as a pinhole, a current leaks from the charging member and the latent image holding member is unevenly charged. However, an image defect occurs. At this time, the charging member itself is also damaged by the leak current. Further, since the charging member comes into contact with the latent image holding member, there is also a problem that a change in the electric resistance due to an environmental change of the charging member affects the charging property of the latent image holding member and deteriorates the image quality. ..

[0007]

The inventors of the present invention have conducted various studies to solve these problems, and as a result, by using a specific charging member, uniform charging is assured and defects such as pinholes are eliminated. The present invention has been achieved by knowing that a contact charging device that is less likely to cause image defects even with a latent image holding member and has little environmental dependence can be obtained.

That is, the gist of the present invention is an apparatus for charging a charging member by contacting it with a latent image holding member, wherein the charging member comprises a support member and a surface member, and the surface member is a conductive fluororesin shrink tube. The charging device is characterized by comprising

The present invention will be described in detail below. The charging member may have any shape such as a brush shape, a blade shape, or a roller shape as long as it contacts the latent image holding member, but a roller shape is preferable for use. When the charging device is in the form of a roller, it is usually composed of a core material and a charging member that covers the core material. As the charging member, a conductive or semiconductive elastic body having a relatively low hardness is preferable because it is necessary to closely contact with the latent image holding member, and for example, conductive particles such as carbon or other semiconductive particles are used for the rubber material. Conductive rubber or the like containing is used.

As a method for controlling the electric conductivity of the charging member, there is known a method of changing the amount of conductive particles contained in the charging member, but the hardness and the conductivity are contradictory and balanced. Is difficult. In order to solve this problem, the charging member is divided into a support member and a surface member, and the support member has an appropriate hardness to maintain the adhesion to the latent image holding member and the like, and the surface member provides an optimum electric resistance for image quality. A charging member whose functions are separated so as to hold it is used. Further, by providing the surface member having an appropriate insulating property, it is possible to suppress the current leakage from the charging member with respect to the pinhole defect of the latent image holding member.

By adopting the function-separated type as described above, it becomes possible to select the electric resistance of the surface member independently of the supporting member, which increases the degree of freedom in design, and the charging uniformity and pinhole resistance can be freely set. In addition, the fluororesin itself has low hygroscopicity, so the surface electric resistance change due to environmental conditions is extremely small, and uniform charging independent of environmental conditions can be achieved, resulting in a good image. Can be achieved.

The charging device of the present invention will be described below with reference to FIG. Reference numeral 1 is a core material that supports the charging member. Both ends of this core material are held by a bearing (not shown) supported by a suitable pressure applying device, for example, a metal spring, for bringing the charging member into contact with the latent image holding member 4. A bias potential is then applied using the core bearing or other electrical contact means. Any material having conductivity can be used as the material of the core material, and a metal is usually used in many cases. Examples of metals include iron, copper, brass, stainless steel, aluminum and the like. Besides, a conductive organic material, for example, a resin molded product in which carbon or the like is kneaded can be used.

In FIG. 1, 2 is a roller-shaped support member,
It rotates in close contact with the latent image holding member via the surface member 3.
The driving force for the rotation may be applied from the outside, or may be freely rotated by the contact frictional force with the latent image holding member. As the material of the support member, any material having conductivity or semiconductivity may be used. Normally, a rubber material which is an elastic body having a relatively low surface hardness because it is necessary to closely contact the latent image holding member through the surface member 3, such as NBR, EPDM, silicon, neoprene, or a natural rubber material and these rubbers. A conductive rubber in which conductive particles such as carbon or other semiconductive particles are kneaded is used.

Of course, a material other than an elastic body such as rubber may be used as long as it has a well-precision surface so that good adhesion can be maintained. The resistivity of the support member is 10 ² −
10 ¹⁵ Ωcm is good, preferably 10 ⁴ -10 ¹² Ωc
m, and more preferably 10 ⁶ -10 ¹⁰ Ωcm.

Reference numeral 3 in FIG. 1 denotes a surface member. In the present invention, the surface member is formed by coating the support member with the conductive fluororesin shrink tube and then heat molding. The conductive fluororesin shrink tube has a resin composition of tetrafluoroethylene resin, tetrafluoroethylene-6-fluoropropylene copolymer resin, tetrafluoroethylene-perfluoroalkoxyethylene copolymer resin, trifluorochloroethylene resin, Carbon particles or surface-treated carbon particles, titania particles, alumina particles, magnesia particles, oxidation as conductive particles in fluororesins such as tetrafluoroethylene-ethylene copolymer resin, vinylidene fluoride resin, vinyl fluoride resin Metal oxide particles such as tin and indium oxide, other semiconductor particles and the like are dispersed and contained and molded into a tube shape. The content of these conductive particles is 1-50% with respect to the fluororesin, preferably 3-30.
%, And more preferably 5-15%.

The resistance of the surface member is 10³-10¹⁴
Ωcm is good, preferably 10^Five-10 ¹²Ωcm is good
More preferably 10⁷-10^TenΩcm is good. table
As the film thickness of the surface member, it is durable due to abrasion as the charging member.
It is better to be thick considering the sex, but if it is too thick a latent image
Since the holding member has a poor charging ability, it is usually 0.01μ.
-1000μ, preferably 0.1-500μ, more preferably
0.5 μ-100 μ is preferable.

As a method of manufacturing the surface member, the surface member is conventionally formed on the support member by a dipping method, a spray method, a vacuum deposition method, a plasma coating method or the like, but these methods have complicated manufacturing steps. However, in the present invention, the function-separated charging roller can be easily manufactured by covering the support member with the conductive fluororesin shrink tube and heating it, so that the process can be shortened.

Reference numeral 4 in FIG. 1 denotes a latent image holding member. The latent image holding member may be an inorganic photoreceptor such as A-Se, ZnO, CdS, or A-Si and an organic photoreceptor, and may have any shape such as a drum shape or a sheet shape. In order to charge such a latent image holding member, only a DC voltage may be applied to the charging member, that is, the core material, or an AC current may be added to the DC voltage. Any alternating voltage may be used as long as it is a voltage that changes periodically.

The range of voltage is 100 in the case of DC voltage.
Suitable is -4000 volts, preferably 300-3000 volts, more preferably 400-2000 volts. The peak-to-peak voltage is 100-
4000 volts, preferably 300-3000 volts,
More preferably, 400-2000 volts is suitable.

[0020]

EXAMPLES The present invention will now be described in more detail with reference to examples. Example 1. As the supporting member 2 using the charging device shown in FIG. 1, the core material is a stainless steel rod having a diameter of 6 mm, and the conductive EPDM is used.
12 mm diameter roller using rubber (10 ⁴ Ωcm),
The surface member 3 is covered with a conductive fluororesin shrink tube (10 ⁸ Ωcm) having a film thickness of 50 μm, and then 150 ° C.
And heated to prepare a charging member.

A commercially available printer (NEC Corporation)
Manufactured by PR406LM), the charging member is brought into contact with the latent image holding member, and DC 1200 V is applied to the core material as a power source bias, and the humidity is 6 ° C at 25 ° C.
As a result of evaluating the image in an environment of 5%, a good image without fog was obtained. Further, as a result of evaluating the images under the environment of 5 ° C. and 25% humidity and under the environment of 35 ° C. and 85% humidity, good images without fog were obtained. Further, no image defect on a black band which would occur when electric charges leaked to the pinhole of the latent image holding member did not occur.

Example 2. 10 as conductive EPDM rubber
^A charging device was obtained in the same manner as in Example 1 except that a material having a resistivity of ⁸ Ωcm was used. Then, instead of the corona charger of a commercially available printer (PR406LM manufactured by NEC Corporation), this charging member is brought into contact with the latent image holding member, and 1200 V DC is applied to the core material as a power source bias,
As a result of evaluating the image in an environment of 25 ° C. and 65% humidity, a good image free from fog was obtained. 5 ° C humidity 25
%, And an image evaluated in an environment of 35 ° C. and 85% humidity, a good image free from fog was obtained. Further, no image defect on a black band which would occur when electric charges leaked to the pinhole of the latent image holding member did not occur.

Comparative Example 1. A 6 mm diameter stainless steel rod was used as the core material, a conductive EPDM rubber (10 ⁴ Ωcm) was used as the supporting member 2, a 12 mm diameter roller, and a charging member without the surface member 3 was prepared. Then, instead of the corona charger of a commercially available printer (PR406LM manufactured by NEC Corporation), this charging member was brought into contact with the latent image holding member, and 1200 V DC was applied to the core material as a power supply bias, As a result of evaluating the image under the environment of the temperature and humidity of 65%, there was a lot of fog and a good image could not be obtained. Further, as a result of evaluating the image in an environment of 5 ° C. and 25% humidity, only an image with severe fog was obtained. In addition, an image defect on a black band which occurs when electric charge leaks to the pinhole of the latent image holding member also occurs.

Comparative Example 2. A 6 mm diameter stainless steel rod was used as the core material, a conductive EPDM rubber (10 ⁸ Ωcm) was used as the supporting member 2, a 12 mm diameter roller, and a charging member without the surface member 3 was prepared. Then, instead of the corona charger of a commercially available printer (PR406LM manufactured by NEC Corporation), this charging member was brought into contact with the latent image holding member, and 1200 V DC was applied to the core material as a power supply bias, As a result of evaluating the image under the environment of the temperature and humidity of 65%, a lot of fog was not obtained and a good image could not be obtained. Further, as a result of evaluating the image in an environment of 5 ° C. and 25% humidity, only an image with severe fog was obtained. In addition, an image defect on a black band which occurs when electric charge leaks to the pinhole of the latent image holding member also occurs.

[0025]

As described above, according to the present invention, by using the specific surface member as the charging member, the charging is uniform, the influence of the pinhole defect of the latent image holding member is less likely to occur, and the image quality is less dependent on the environment. Enables a contact charging device that is easy to manufacture

[Brief description of drawings]

FIG. 1 shows a sectional explanatory view of a charging device according to an embodiment of the present invention. 1 core material 2 support member 3 surface member 4 latent image holding member

FIG. 2 is a cross-sectional explanatory view of a charging device of a comparative example. 1 core material 2 support member 4 latent image holding member

Claims (1)

Claim: What is claimed is: 1. A charging device for charging a charging member by bringing the charging member into contact with a latent image holding member, wherein the charging member comprises a support member and a surface member, and the surface member is a conductive fluororesin. A charging device comprising a shrink tube.