JPS6270879A - Developing sleeve - Google Patents

Abstract

PURPOSE:To faithfully reproduce an image having a good gradation characteristic by forming a conductive high-polymer material layer on the surface of a developing sleeve made of a metal and specifying surface electric resistance. CONSTITUTION:The surface 2 of the metallic sleeve 2 made of aluminum, stainless steel, etc. is roughened to 5-1,000mum, more preferably 50-500mum average roughness and the coating layer consisting of the conductive high-polymer material is formed on the surface. The electric resistance of the surface is made 1X10<-4>-1X10<1>OMEGAcm (volumetric resistance value). For example, PE or PP is used for the high-polymer material and carbon black is added thereto in order to provide electrical conductivity thereto.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Object of the Invention [Field of Industrial Application] The present invention relates to a developing sleeve for an electrophotographic image forming apparatus for electrostatic printing, electrostatic printing, or the like.

[Conventional technology]

2. Description of the Related Art In image forming apparatuses such as electronic copying machines, it is necessary to faithfully reproduce a copied image of a document.

In order to improve the reproducibility of the copied image, the reproducibility of the copy density with respect to the original density, that is, the gradation reproducibility (hereinafter referred to as γ characteristic) is a major factor.

Figure 4 is a gamma characteristic diagram showing the relationship between original density and copy density. In Figure 6, for example, when copying an original with thin text written on a white background, the gamma characteristic is set to curve A. In other words, if the density of the text is not much different from the background density D1 of the original, such as D2, the steep gradient of the γ characteristic is used to add the text to the copy image. can be clearly copied.

However, when copying an original with delicate contrast such as a photograph, for example, an original with a density value between density D2 and density D3, the original density of curve A is D2 and D3.
A copy image that faithfully reproduces the original density cannot be obtained with a gentle slope characteristic between the two.
It is desirable to set the γ characteristic to be similar to the γ characteristic (γ=1) of . In fact, by setting the γ characteristic shown by curve B, faithful copies can be obtained even for originals with delicate contrast, such as photographs.

Therefore, in the copying process, the copy density is adjusted.One way is to adjust the exposure amount of the exposure lamp according to the brightness and darkness of the original, and to adjust the potential of the electrostatic latent image according to the darkness of the original. Another method is to change the amount of toner attached to the electrostatic latent image Vs by adjusting the developing bias voltage in accordance with the brightness and darkness. Both methods are indirect methods in which the surface potential or developing bias voltage is varied in order to adjust the copy density by varying the amount of toner attached to the electrostatic latent image vS. With the γ characteristics shown, it is difficult to faithfully reproduce originals with delicate contrast.

Therefore, as a method for directly adjusting the copy density, in a developing device using a developing sleeve, the developing sleeve is used to control the amount of toner flying from the developing sleeve to the photoreceptor between -D4 and A method is known in which the electrical resistance of the sleeve surface is increased in order to reduce the lines of electric force per unit area generated by the electric field due to the latent image potential between the sleeve and the photoreceptor.

[Problem that the invention seeks to solve]

However, it is difficult to delicately control the electrical resistance of the sleeve surface. For example, when the surface of the developing sleeve is entirely made of metal, the electrical resistance of the surface is generally io = ~1O-5 (0 cm) in terms of volume resistivity. ), and the amount of flying toner increases in accordance with the generated electric lines of force, and as a result, the copy density becomes as shown by curve A. On the other hand, when the surface resistance of the metal sleeve is increased by thermal spraying, carburizing, nitriding, etc., the copy density is extremely reduced as shown by curve E.

Even with such a direct method, it is difficult to subtly adjust the electrical surface resistance of the developing sleeve to provide gradation like the curve C for γ=1 or the approximate curve B.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a developing sleeve having a γ characteristic close to curve C using a novel and simple method.

Summary: Structure of the Invention [Means for Solving the Problems] The first invention is a developing sleeve of an image forming apparatus, in which the surface of the metal sleeve is covered with a conductive polymer material,
The electrical resistance of its surface is lX10=~ IX 10'Ωc
+s (volume resistance conversion value).

A second invention is the above-mentioned invention, and further the surface of the metal developing sleeve has an average surface roughness Rz of 5 to 1000 g.
It is characterized by having a rough surface of m, and coating the rough surface with a conductive polymer material.

[For production]

By making the electrical resistance of the sleeve surface larger than that of a metal sleeve, the concentration of electric lines of force caused by the electric field between the photoreceptor and the developing sleeve can be prevented, and an appropriate amount of toner can be applied to the photoreceptor. An image with good gradation as shown by curve B in the figure can be formed.

The second invention further improves the adhesion between the metal sleeve and the conductive polymer material, making it possible to maintain the properties of the sleeve for a long time.

〔Example〕

FIG. 1 shows a cross-sectional view of an embodiment of the present invention, where l is a magnet and 2 is a metal sleeve made of aluminum or stainless steel, etc., which is loosely fitted to the magnet and rotates. A coating layer of conductive polymer material 3 is formed on the metal sleeve 2, and the electrical resistance of the surface is determined as lX10=~IX
101Ωca+ (volume resistance value).

The polymer material used is, for example, polyethylene or polypropylene, to which carbon black is added to impart electrical conductivity. The electrical surface resistance is adjusted by the blending ratio of the polymer material and carbon black, but the amount of carbon blank added is 1
0 to 45 parts is suitable, preferably 20 to 40 parts.

These two types of materials are kneaded and melted at 120 to 250°C to form carbon plastic, which is then fused to a metal sleeve. The appropriate coating thickness at this time is 0.1 to 3.0 tax. Further, the resistance can be easily lowered by grafting the carbon plastic material to 10<-2> to 10<3>[Omega]cm or less within the claimed range. FIG. 2 shows the relationship between the amount of added carbon blank and the electrical resistance value of the conductive polymer material.

In the above configuration, if the normally processed metal sleeve surface is coated with a conductive polymer material, the adhesion between the two becomes a problem, and the long rotation of the sleeve may result in insufficient contact at the T: adhesion interface. There is a risk that the interfacial resistance between both materials will increase.

Therefore, the second invention, as shown in the third figure, makes the surface 2a of the metal sleeve 2 a rough surface with an average roughness Rz of 5 to 11000p, preferably 50 to 500Bm, and the above-mentioned conductive polymer material layer is applied to the surface. 3 was formed.

The resistance in the examples of the present invention is expressed as a surface resistance value (0 cm) in terms of 1 volume resistance, the metal resistance is based on the chemical handbook, and the four-probe method was used for material measurement. The four-probe method is like placing four wooden needles in contact with the object to be measured, two of them measuring the current, and the other two measuring the voltage, and the resistance is calculated by dividing the voltage by the current. be.

C. As described in detail of the invention, by forming a conductive polymer material layer on the surface of the metal developing sleeve and appropriately selecting the surface electrical resistance, the γ characteristic can be changed to extremely gradation close to γ-1. The result is a sleeve that can faithfully reproduce images with subtle contrast, such as those found in good photographs.

Moreover, the second invention can increase the adhesion strength between the metal sleeve and the conductive polymer material layer, thereby improving the durability of the invention having the above effects.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of the developing sleeve of the present invention, FIG. 2 is a curve diagram of electrical resistance with respect to the blending ratio of the conductive polymer material of the present invention, and FIG. 3 is a cross-sectional view of the sleeve of the second invention. FIG. 4 is a γ characteristic curve diagram showing the relationship between original density and copy density. 1... Magnet, 2... Metal sleeve, 3... Conductive polymer material layer, 2a... Rough surface of metal sleeve 2. Figure 1 Figure 3 Figure 4 Original 1μ

Claims (2)

[Claims] (1) In the developing sleeve of an image forming apparatus, the surface of the metal sleeve is covered with a conductive polymer material, and the electrical resistance of the surface is 1 x 10^-^4 to 1 x 10^ in terms of volume resistance.
A developing sleeve characterized by having a resistance of 1 Ωcm. (2) In the developing sleeve of an image forming apparatus, the surface of the metal developing sleeve has an average surface roughness Rz of 5 to 1000 μm.
The rough surface is coated with a conductive polymer material, and the electrical resistance of the surface is 1 × 10^-^4~ in terms of volume resistance.
A developing sleeve characterized by having a resistance of 1×10^1 ΩCm or less.