JPS62157045A - Photosensitive drum for electrophotographic copying machine - Google Patents

Abstract

PURPOSE:To form a photosensitive layer having uniform quality and to obtain an image which is free from a drop-out, etc. by specifying the range of the thickness of an elastic material layer and/or the surface roughness of a layer for supporting the photosensitive layer thereby considerably decreasing the uneven contact between a photosensitive drum and developing roller. CONSTITUTION:The thickness of the elastic material layer is specified to >=6mm and/or the surface roughness of the layer for supporting the photosensitive layer is specified to a 0.2-2mum range. The photosensitive drum has the construction consisting in attaching the elastic material layer 3 around a shaft 2 consisting of a rigid body, forming the layer 4 for supporting the photosensitive layer around the elastic material layer 3 and further providing the photosensitive layer 5 around said layer. The shaft 2 is freely rotatably attached to the body of a copying machine. The layer 4 which is molded to a sleeve shape is fitted onto the layer 3 so as not to be shifted and moved in the ordinary use condition. These layers are positioned concentrically with the shaft 2. The photosensitive layer 5 is provided by coating, etc. of inorg. or org. photoconductors such as OPC, selenium, zinc oxide and amorphous materials.

Description

Detailed Description of the Invention [Technical Field] The present invention relates to a photoreceptor drum for electrophotography, and more specifically, a photoreceptor layer, an elastically deformable photoreceptor support layer supporting the photoreceptor layer, and a photoreceptor drum supporting the photoreceptor layer. The present invention relates to a photoreceptor drum in an electrophotographic copying machine having a supporting layer of elastic material.

[Prior Art] A photosensitive drum usually has a rigid support and a photosensitive layer supported by the support. The photosensitive drum is rotatably incorporated into the main body of the copying machine, and during a copying operation, an electrostatic latent image is formed on the surface/photosensitive layer, and the electrostatic latent image is made visible by a developer. However, if the photosensitive drum is made of such a rigid body, not only will it not be possible to obtain a high-quality image, but there will also be drawbacks such as damage to the photosensitive layer.

In other words, if there is a slight distortion on the circumferential surface of the photoreceptor drum, or if the outer diameter of the drum is not even slightly accurate, there will be a large gap between the photoreceptor drum and the developing roller holding extremely thin toner during development. A gap may be created, or conversely, the two may be pressed together with excessive force and the photosensitive layer may be damaged. This tendency is even more remarkable when development is performed using a developing roller whose surface is made of a rigid body. However, even if the photosensitive drum itself does not have the above-mentioned distortions, such inconveniences will be recognized if the developing roller itself has such distortions.

However, it is actually extremely difficult to manufacture photoreceptor drums and developing rollers with high precision so as to eliminate surface distortions and variations in outer diameter.

As a means to resolve these inconveniences, it has been considered to use a photoreceptor belt instead of the photoreceptor drum, and to bend this belt somewhat to contact the developing roller. At least two rollers are required to support the copying machine, which complicates the structure and increases the size of the copying machine.

However, recently, a photosensitive drum whose surface can be elastically deformed solves the above-mentioned inconveniences and manufacturing difficulties, as disclosed in Japanese Patent Application Laid-open No. 59-192260 and No. 59-192.
This method has been proposed in publications such as No. 278 and Japanese Unexamined Patent Publication No. 59-192279. By using this, it is possible to maintain good images for a fairly long period of time.

On the other hand, it is desired to form a more homogeneous photosensitive layer in order to further improve image quality.

[Objective] The present invention further achieves the above-mentioned "photoreceptor drum whose surface can be elastically deformed" by improving it, and by producing a photoreceptor drum having a homogeneous photoreceptor layer. The present invention provides a photosensitive drum for a desirable electrophotographic copying machine.

[Structure] The present invention provides a photosensitive drum for an electrophotographic copying machine in which a surface photosensitive layer, an elastically deformable photosensitive layer support layer, and an elastic material layer are sequentially laminated, and the elastic material layer has a thickness of 6 m. or more, and/or the surface roughness of the photosensitive layer support layer is 0.2μ
It is characterized in that it ranges from m to 2 μm.

By the way, the inventors of the present invention published Japanese Patent Publication No. 59-19226 on Sagi.
When we investigated the photosensitive drum equipped with a photosensitive layer, an elastically deformable photosensitive layer support layer, and an elastic material layer, as proposed in publications such as No. It was confirmed that even if the hardness of the tobacco layer was small, the necessary amount of elastic deformation could be obtained, and that if the surface roughness of the photosensitive layer support layer was at a certain value, even better quality images could be obtained. The present invention was completed based on this knowledge.

The present invention will be explained in more detail below with reference to the drawings. FIG. 1 shows a photosensitive drum (latent image carrier) 1 according to the present invention.
A typical example is shown in which an elastic material layer 3 is attached around a shaft 2 made of a rigid body, a photosensitive layer support layer 4 is formed around the elastic material layer 3, and a photosensitive layer 5 is further formed around the elastic material layer 3.
It has a structure with

The shaft 2 is rotatably attached to the main body of the copying machine. Further, the photosensitive layer support layer 4, which is shaped like a sleeve, is fitted onto the outer circumferential surface of the elastic material layer 3 so that it will not come off or move during normal use. Each of these layers is located concentrically with respect to the axis 2. The photosensitive layer 5 formed on the outer peripheral surface of the photosensitive layer support layer 4 is coated with an inorganic or organic photoconductive material such as OPC, selenium, zinc oxide, or an amorphous material, as in conventional photosensitive drums. . Note that between the photosensitive layer support layer 4 and the photosensitive layer 5, if necessary, for the purpose of suppressing the decrease in sensitivity of the photosensitive layer M5,
For example, an intermediate layer of a conductive material having a specific volume resistivity of 10 9 Ω■ or less may be provided.

Examples of such photoreceptors include an aluminum material for the shaft 2;
For example, the elastic material layer 3 is a chloroprene rubber sponge, the photosensitive layer support layer 4 is a nickel sleeve (t=50 μm), and the photosensitive layer 5 is a functionally separated organic photosensitive material. As the elastic material layer 3, urethane foam or a rubber material with low hardness can also be used. Further, as the photosensitive layer support layer 4, a conductive resin film, a metal vapor-deposited resin film, or the like can be used.

Here, contact development using this photoreceptor will be explained based on FIG. 2. First, the toner 8 is regulated to one or two layers or less on the developer carrier (here, a developing roller is used) 6 by the thinning blade 7 and charged. The developing roller 6 comes into contact with the photoreceptor 1 under a certain pressure, and dents the photoreceptor 1. A developing nip is formed in this recessed portion. Before the photoreceptor 1 enters the developing nip, it undergoes a charging-exposure process to form an electrostatic latent image on it, and as it passes through the developing area (developing nip), the charged toner is transferred to the latent image. Attraction is developed depending on the pattern. The reason why the number of toner layers on the developing roller 6 is limited to one or two layers or less is to prevent the charge amount of the toner from decreasing.Generally, when there are multiple layers of toner, the charge amount of the toner decreases and causes problems such as fogging. Cause.

After the development, a transfer process begins, in which the toner on the photoreceptor 1 is transferred onto the transfer paper 9. The transfer paper 9 then enters a fixing process, and the toner on the transfer paper 9 is fixed and output. In FIG. 2, 10 is a charging charger, 11 is an optical system, 12 is a transfer charger, and 13 is a cleaning blade.

As can be understood from the fact that a dent is formed in the photoreceptor by the contact development described above (this dent is also formed by the pressure from the cleaning blade 13), in the photoreceptor of the present invention, the elastic material layer 3 is Preferably, it is made of non-foamed rubber or a suitable foam.

However, in this case, when external pressure is applied to the elastic material layer 3,
As seen in Figure 2, the hardness is such that external pressure is absorbed in that part or in its vicinity, and the force is not easily transmitted to other elastic material layer parts, but also that a predetermined amount of elastic deformation can be obtained. It is desirable to select a material that has the property that the elastic material M3 can return to its original cylindrical shape when removed, and that will not permanently deform even if external pressure is applied to the elastic material layer 3 for a long time. Practically, the appropriate hardness is about 5 to 50 degrees as measured by a JIS C type rubber hardness tester. Typical examples of such materials include non-foamed rubber and a polyurethane foam (hardness: 20 degrees on the JIS C type rubber hardness tester) manufactured by ROGER 5CORPORATION in the United States under the trade name MICRO CELL RUBBER.

In addition, it is desirable that the elastic material layer 3 in the present invention has a thickness of 6 m or more. In Figure 3, the pressing force is constant, the hardness of the material of the elastic material layer 3 is the same, and the thickness is 1).
It shows the amount of deformation when changing . As can be seen from FIG. 3, when the thickness of the elastic material layer 3 becomes less than a certain value, the deformation area becomes smaller even if the material is the same hard material. In other words,
Even if a material has the characteristics of low hardness and large deformation, it cannot take advantage of its characteristics. Therefore, t
The value varies depending on the hardness of the material, but rubber hardness JISA
When the angle is 15°, it is about 12 mm, and when it is 50°, it is about 61 um.

FIG. 4 shows the relationship between the pressing force and the amount of deformation in a certain material. It is known that the amount of saturated deformation (χ) increases as the thickness increases for materials of equal hardness. Further, if the thickness is small (for example, 2 mm), it may not be possible to obtain the necessary amount of deformation (for example, 0.5 mm) within the elastic deformation region, no matter how small the hardness is. For these reasons as well, the thickness of the elastic material layer 3 is 6 mm or more, preferably 12 mm or more.

On the other hand, as can be inferred from the previous explanations based on FIG. In order to achieve this, the amount of deformation of the metal sleeve alone, which is the photosensitive layer support layer 4, under this pressing force must be greater than the amount of deformation of the elastic material layer 3 in the state where the axis is present. In other words, the metal sleeve 4 seems to be softer.

The metal sleeve 4 is made of, for example, nickel, stainless steel, aluminum, etc. Nickel and stainless steel have relatively high yield strength and longitudinal elastic modulus, so when the photosensitive layer support vJ4 is manufactured from these materials, the It is desirable to set the thickness to 100 μm or less. If this thickness is set larger than 100 μm, it will become difficult to deform the photosensitive layer support layer 4 unless the external pressure applied to the photosensitive drum 1 is increased, and there will be limited room for selection of the material for the elastic material layer 3. As a result, the photosensitive drum The drum becomes susceptible to undesirable deformation. In addition, when the photosensitive layer support layer 4 is made of aluminum, the yield strength and modulus of longitudinal elasticity of aluminum are smaller than those of nickel or stainless steel, so it is preferable to make the thickness slightly thicker, and according to an experiment, the thickness is 200 μm.
It has been found that it is advantageous to set it to less than m.

Electroforming is the most effective method for obtaining such a thin sleeve.

Electroforming is a method of creating objects of a certain shape by depositing metal (electrodeposition) on a mold that is an electrode using electrolysis. Since the intention here is to produce a thin metal sleeve 4, it is advantageous to use a metallic cylinder as the mold.

The surface roughness of the metal sleeve (photosensitive layer support layer) 4 is 0.2~
It is necessary to keep the thickness within the range of 2 μm. This is due to the following reasons. That is, the metal sleeve 4 is intended to have a photosensitive layer 5 formed on its surface, and in FIG. As shown in the figure showing an example, the surface roughness of the metal sleeve causes thickness unevenness in the photosensitive layer 5, which has thin portions and thick portions. The surface of the photosensitive layer 5 is charged to form an electrostatic latent image, and the surface potential and amount of surface charge at this time depend on the capacitance of the photosensitive layer, that is, the thickness of the photosensitive layer. Normally, the surface potential is kept constant during the charging process, so the amount of surface charge on the photosensitive layer differs between thinner and thicker areas. If we describe the above using the equation of a gondenser, the capacitance is inversely proportional to the layer thickness as shown in the blank below, and the amount of surface charge is Q = CV
V: Surface potential Since V = conot, it becomes cc-, which is also inversely proportional to the layer thickness. In other words, the uneven thickness of the photosensitive layer 5 causes the uneven amount of surface charge. Next, after exposure, charge generation and propagation occur in the photosensitive layer, which neutralizes the surface charge and lowers the surface potential.If the potential of the exposed area of a certain layer thickness is set to an appropriate value, the amount of exposure will inevitably be determined.

Therefore, since the amount of charge generated is determined by the amount of exposure, any more surface charge on the photosensitive layer remains as a residual charge. That is, unevenness in the amount of surface charge due to unevenness in the thickness of the photosensitive layer 5 remains as a residual charge even after exposure, and appears in an electrostatic latent image that is a pattern on the order of one surface pattern.

Then, when the development process begins, development is carried out using a development electric field generated by the potential difference between the surface potential and the development bias applied to the development electrode, so the unevenness of the latent image due to unevenness in thickness is developed, and the output is It also appears in . The permissible level of such thickness unevenness is considered to be up to about 2 μm.

FIG. 6 shows the obtained potential after exposure with respect to the layer thickness of the photosensitive layer 5. Here, the photosensitive layer (relative permittivity is 3)
Based on a thickness of about 25μm, surface potential when charged is -800V
The potential after exposure is set to 150V.

In this case, if the exposed area is the white part of the background of the image output, as the thickness of the photosensitive layer becomes thinner, the potential increases, making it easier for the developer to adhere, which appears as dirt on the background.

Normally, a development bias is applied to prevent the background from being developed, but if the bias is too high, the reproducibility of low contrast deteriorates, the overall density decreases, and the image quality deteriorates. do. The same can be said for methods of increasing the amount of light and increasing the thickness of the photosensitive layer. Therefore, the post-exposure potential must be at a somewhat low level and its variations must be kept to a minimum, and this also leads to the regulation that the surface roughness of the photosensitive layer support layer 4 is 2 μm at most.

When an image is actually taken with the photoconductor tram 1 whose surface has been roughened by about 3 μm to form the photoconductor layer 5, there is background dirt on the background, and even after exposure, the black solid areas and halftone areas, which have a high potential, have surface roughness. Density unevenness is seen because potential unevenness occurs due to this.

The surface roughness of the photosensitive layer support layer 4 is also 0.2 μm or more. This is because it is difficult to achieve a surface roughness of less than 0.2 μm in the electroforming process, but this surface roughness is also necessary to ensure that the photosensitive layer 5 is well adhered and supported on the surface of the photosensitive layer support layer 4. is effective.

As described above, in the photosensitive drum of the present invention, the thickness of the elastic material layer 3 and the surface roughness of the photosensitive layer support layer 4 have the above-mentioned specific values, but even if they are satisfied separately, they cannot be satisfied at the same time. You may do so.

[Effects] According to the present invention, uneven contact between the photoreceptor drum and the developing roller can be significantly reduced, and a homogeneous photosensitive layer can be formed, so that an image with uniform density and no white spots etc. can be obtained. become.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a typical example of the photosensitive drum according to the present invention, FIG. 2 is a diagram for explaining the state of contact development, and FIG. 3 is a diagram showing the relationship between the thickness of the elastic material layer and the amount of deformation. FIG. 4 is a graph showing the relationship between the pressing force and the amount of deformation in the elastic material layer. FIG. 5 is a graph showing the relationship between the pressing force and the amount of deformation in the elastic material layer. FIG. 5 shows the state where a photosensitive layer consisting of two layers is provided on the photosensitive layer support layer 6 is a graph showing the surface potential after exposure with respect to the layer thickness of the photosensitive layer. 1... Photosensitive drum 2... Shaft 3... Elastic material layer 4... Photosensitive layer support layer 5...
photosensitive layer

Claims (1)

[Claims] 1. A surface photosensitive layer, an elastically deformable photosensitive layer support layer,
In the photosensitive drum in which elastic material layers are sequentially laminated, the thickness of the elastic material layer is 6 mm or more, and/or the surface roughness of the photosensitive layer support layer is in the range of 0.2 μm to 2 μm. Features of photosensitive drums in electrophotographic copying machines. 2. The photosensitive drum according to claim 1, wherein the elastic material layer is made of a foamed material or a non-foamed material. 3. The photosensitive drum according to claim 1, wherein the photosensitive layer support layer is made of nickel or aluminum.