JPH09265228A - Electrifying member and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent production of transverse stripes on a transferred image due to scratches on the surface of a photoreceptor. SOLUTION: In the electrifying member 1 having an elastic layer 102 and a surface layer 103 which covers the surface of the elastic layer, the surface layer 103 is produced by dispersing a hydrophobic silica and a low structure type acetylene black which can be easily dispersed in an alcohol in a copolymer nylon resin which is soluble with an alcohol. In the surface layer 103, the amt. of the acetylene black dispersed is larger in the area near the elastic layer 102, while the amt. of silica dispersed increases with the distance from the elastic layer 102. This layer 103 is formed by repeatedly applying solns. of different blending ratios of the acetylene black and the silica to the copolymer nylon resin in several times.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used, for example, in electrophotographic copying machines, PPCs, laser printers, facsimiles, etc., for uniform charging of a charge carrying medium or for transferring a visible image to an image carrier. The present invention relates to a charging member of a contact charging device.

[0002]

2. Description of the Related Art In an electrophotographic copying machine, a corona discharger has been widely used as a means for uniformly charging a photoreceptor. Since the corona discharger is not in contact with the photoconductor, it is less affected by the type of the photoconductor and the usage environment, and the photoconductor can be uniformly charged to a predetermined potential. However, there is a problem that the device is complicated and that ozone generated by the discharge deteriorates the photoconductor and peripheral members. In addition, the suppression of ozone generation as an environmental problem has been a market demand.

A contact roller charger has been introduced here. However, charging unevenness is likely to occur, and it is necessary to apply a superimposed voltage of DC (direct current) and AC (alternating current) in order to make it uniform. . As a result of a detailed examination of the cause of uneven charging when only a DC voltage is applied, it is found that the elastic layer is a dispersion layer of rubber and carbon,
By replacing this with a medium resistance epichlorohydrin rubber, it was made possible to eliminate electrical non-uniformity and eliminate charging unevenness that occurs when only a DC voltage is applied.

As an example of this, a roller charging device disclosed in Japanese Patent Laid-Open No. 7-49602 has a DC charging roller.
In a roller charging device that applies only a voltage to uniformly charge the surface of a photosensitive member, the charging roller is made of epichlorohydrin rubber, and the roller hardness of the charging roller is 42 (JIS.
Or more (according to A type hardness tester). Further, Japanese Patent Laid-Open No.
205180 proposes a charging member having a surface layer containing N-alkoxymethylated nylon.

[0005]

However, the medium resistance (1
As a practical problem of a charging roller composed of an epichlorohydrin rubber elastic layer (having a thickness of 0 ⁷ to 10 ⁹ Ω · cm) (thickness 1 to 5 mm), the roller surface is easily soiled, and the charging potential fluctuates greatly due to environmental fluctuations. Therefore, a surface layer of a non-adhesive resin covering the surface of the elastic layer is required.
In the method disclosed in Japanese Patent Application Laid-Open No. 1-205180, the N-alkoxymethylated nylon surface layer has excellent non-adhesiveness and environmental characteristics, but the film strength is weak and durability as a charging roller is a problem. is there. Japanese Patent Laid-Open No. 7-4960
The charging member disclosed in Japanese Patent Publication No. 2 is a polyamide resin (film thickness 5
Although a fluororesin-based surface layer containing 4% of carbon, which has a large humidity dependency, is used as the surface layer, the dispersibility of the carbon and the fluororesin is poor and the charging uniformity is poor.

A charging roller provided with a surface layer made of acetylene black having a low structure which is easily dispersible in methanol and a copolymerized nylon resin soluble in methanol on the surface of the elastic layer of epichlorohydrin has (1) a photoreceptor and It is characterized by good non-adhesiveness with toner, (2) small humidity dependence, and (3) good charge uniformity. However, if too much conductive carbon is added to the surface layer in order to reduce fluctuations in charging potential due to environmental fluctuations,
If the surface resistance of the charging roller becomes too low and there are defects such as scratches on the surface of the photoconductor that are contact-charged, charge leakage will occur, and the charges will not be limited to only the scratches on the photoconductor surface, but will be charged in horizontal stripes. There was a new problem that the impossible part expanded.

The present invention aims to remedy this type of problem.

[0008]

[Means for Solving the Problems]

(1) The charging member having two layers of the elastic layer and the surface layer covering the surface of the present invention comprises a copolymerized nylon resin soluble in alcohol, acetylene black having a low structure easily dispersible in alcohol and hydrophobicity. It is characterized by having a surface layer in which silica is dispersed.

(2) The charging member having two layers of the elastic layer and the surface layer covering the surface of the present invention has a structure in which acetylene black and hydrophobic silica are dispersed in copolymerized nylon resin, and silica is closer to the elastic layer. It is characterized in that it has a surface layer having a larger amount of acetylene black dispersed therein, and a larger amount of silica dispersed than acetylene black farther from the elastic layer.

(3) In the present invention, the surface of the elastic layer is formed by coating the copolymerized nylon resin with a solution having a different blending ratio of acetylene black and silica a plurality of times so that the surface layer is formed.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION

[0012]

【Example】

Example 1 FIG. 1 shows a charging roller 1 according to an example of the present invention. The charging roller 1 has a thickness of 3 on a core metal 101 of φ8 mm (diameter 8 mm).
mm epichlorohydrin rubber elastic layer 102 is formed,
The surface layer 103 is formed on the surface of the elastic layer 102. The electric resistance of the elastic layer 102 is 1.2 × 10 ⁸ Ω.
cm, rubber hardness 42 (JISA), average surface roughness Rz =
It is 5.5 μm.

On the peripheral surface of the elastic layer 102, the coating liquid A is applied by spraying, and the surface layer 10 having a thickness of 10 μm after drying is applied.
3 was formed. The charging roller 1 of this Example 1 is referred to as Sample 1: Coating liquid A: Copolymerized nylon resin (Daiamide T171, Daicel-Schuls) 100 (weight, the same applies hereinafter) Acetylene black (HS-100 Denka) 10 Hydrophobic Silica 10 Methanol 1200 dispersed for 20 minutes with a Homongenizer.

As a comparative sample, a coating liquid B prepared by removing silica from the coating liquid A was prepared and spray-coated to form a surface layer having a thickness of 10 μm after drying. The charging roller thus obtained (Comparative Example 1) is referred to as Comparative Sample 1.

-Example 2-On the peripheral surface of the elastic layer 102 prepared in Example 1, the following Table 1
The coating liquid and the coating liquid shown in (1) were successively applied by spraying to form a surface layer 103 having a thickness after drying of 10 μm. The charging roller 1 of this Example 2 is referred to as Sample 2.

[0016]

[Table 1]

Both the coating solution and the coating solution were dispersed in a Hommonizer for 20 minutes.

FIG. 2 shows an experimental apparatus for evaluating the charging characteristics of the charging roller 1. 1 is a charging roller to be evaluated, 101 is a core metal of the charging roller 1, and 2 is the charging roller 1.
A power source for applying a DC voltage Va to the core bar 101, 3 is a photoconductor drum, 5 is a discharge lamp, and 4 is an electrometer for measuring the charging potential Vs of the surface of the photoconductor drum 3.

FIG. 3 shows a roller charging type image forming apparatus using the charging roller 1. In FIG. 3, the photoconductor on the surface of the photoconductor drum 3 is uniformly charged by the charging roller 1.
Image light 6 is projected onto the charged surface by an exposing unit (not shown), and an electrostatic latent image is formed on the photosensitive member. The electrostatic latent image is visualized by the developing device 7 and becomes a toner image. This toner image is transferred onto the recording paper 9 by the transfer belt 8. The recording paper 9 onto which the toner image has been transferred is sent to a fixing device (not shown), where the toner image is heated and pressed and fixed to the recording paper 9. The recording paper exiting the fixing device is discharged to the outside of the apparatus. After the transfer, the surface of the photoconductor is cleaned by the drum cleaner 10 and discharged by the discharge lamp 5.

In order to test the characteristics of the charging roller 1 of the present invention, a photosensitive drum having two defects (scratches) on the photosensitive surface was used as the photosensitive drum 3, and the charging roller 1 was used. Image formation was performed.

Charging characteristics of the above-mentioned charging roller 1 in three environments (temperature and humidity) of Sample 1 (Example 1), Sample 2 (Example 2) and Comparative Sample 1 (Comparative Example 1) (see FIG. 2). Table 2 shows the image characteristics (using the image forming apparatus of FIG. 3) and the image characteristics (using the image forming apparatus of FIG. 3).

[0022]

[Table 2]

According to the above-mentioned image forming experiment, the charging roller according to the present invention (Samples 1 and 2) has a charging position with respect to environmental characteristics as compared with the charging roller before improvement (Comparative Sample 1)
Except for a slightly low charge level at low temperature and low humidity, non-adhesiveness and cleaning property, while maintaining the charge uniformity to the same level or higher, there was no problem in generating an abnormal image of the drum pitch due to a photoreceptor defect. It turned out that this problem has been greatly improved.

[0024]

The material for the surface layer of the charging member of the present invention, acetylene black having a low structure which is easily dispersible in methanol and the copolymerized nylon resin which is soluble in methanol, have extremely good dispersibility and are electrically uniform. It is effective for forming a smooth surface layer, and since the nylon resin has a good film forming property, the non-adhesiveness of the roller surface to OPC and toner is also improved. However, acetylene black has a higher purity (more carbon content) than carbon black, and has a low hydrogen content, and therefore has good conductivity (small electrical resistance). Therefore,
Although the electrical resistance changes greatly with a small amount of addition to the resin component, silica is added as a filler to the surface layer of the charging member of the present invention in order to mitigate this change. This silica was extremely effective in adjusting the electric resistance.

In the surface layer of the charging member of the present invention, the closer it is to the surface of the charging member, the larger the amount of dispersion of silica having high resistance and the smaller the amount of dispersion of acetylene black having good conductivity. The surface resistance is suppressed to a high level, and even if the surface of the photoconductor that is contact-charged is scratched, there is no leakage of charge or an abnormal image is generated. Since the surface layer is divided into a plurality of times with solutions having different blending ratios of acetylene black and silica and overcoated, a desired electric resistance distribution in the thickness direction of the surface layer can be stably obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the configuration of a charging roller 1 according to a first embodiment of the present invention.

FIG. 2 is a transverse cross-sectional view showing a schematic configuration of an experimental apparatus for evaluating the charging characteristics of the charging roller 1.

FIG. 3 is a cross-sectional view schematically showing the configuration of a roller charging type image forming apparatus.

[Explanation of symbols]

1: charging roller 101: core metal 102: elastic layer 2: power supply 3: photoconductor drum 4: electrometer 5: static elimination lamp 6: image exposure 7: developing device 8: transfer belt 9: recording paper 10: drum greener

Claims (3)

[Claims] 1. A charging member having two layers, an elastic layer and a surface layer covering the surface of the elastic layer, wherein an alcohol-soluble copolymerized nylon resin is used, and an easily dispersible acetylene black having a low structure in alcohol and hydrophobic silica are used. A charging member having a dispersed surface layer. 2. In a charging member having two layers of an elastic layer and a surface layer covering the surface thereof, acetylene black and hydrophobic silica are dispersed in a copolymerized nylon resin, and acetylene black is dispersed more than silica in a region closer to the elastic layer. A charging member comprising a surface layer having a large amount of silica and a greater amount of silica dispersed than acetylene black at a distance from the elastic layer. 3. A charging member, characterized in that a surface layer is formed by coating the surface of the elastic layer with a solution of acetylene black and silica having different blending ratios to the copolymerized nylon resin in multiple times. Production method.