JPS62138856A - Electrophotographic sensitive body improved in surface hardness - Google Patents

Abstract

PURPOSE:To obtain an electrophotographic sensitive body superior in sensitivity and surface hardness by forming on a substrate a photoconductive layer formed by mixing a burned or nonburned zinc oxide powder specified in bulk density with an insulating resin. CONSTITUTION:The photoconductive layer is prepared by using the burned or nonburned zinc oxide power having a bulk density of 0.3-0.6g/cm<3>, preferably, 0.33-0.4g/cm<3>, and it is prepared by compressing the zinc oxide powder used so far for forming the photoconductive layer of the electrophotographic sensitive body with an optional compressor to 0.3-0.6g/cm<3>, or buring the compressed power at a temperature of 200-600 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an electrophotographic photoreceptor, and more particularly to an electrophotographic photoreceptor having a photoconductive layer with excellent surface hardness.

[Prior Art] A photoreceptor conventionally used in electrophotography consists of a light guide with a thickness of approximately Log made mainly of zinc oxide powder and an insulating resin on a support such as electrically conductive treated paper or plastic film. ' is formed by providing layers.

The zinc oxide powder forming the photoconductive layer is a powder having a particle size of 1 liter or less, usually 0.2 to 0.5 liters, and silicone resin, acrylic resin, alkyd resin, etc. are used as the insulating resin. ing.

To form a photoconductive layer, zinc oxide powder is dispersed in an organic solvent solution of an insulating resin so that the weight ratio of zinc oxide powder to insulating resin is about 4 to 7:1. It is manufactured by coating a dispersion onto a support.

[Problems to be Solved by the Invention] When a zinc oxide photoreceptor is used for printing, for example, in offset printing, it is required to have the durability to print at least 3000 sheets, preferably 5000 sheets or more. However, the photoreceptor coated with the conventional zinc oxide photoconductive layer as described above is easily abraded because the surface hardness of the photoconductive layer is not sufficient, which causes background stains and blurred images during plate-making printing. ing. There are various possible causes for this, but one of them is that the insulating resin, which is the binder in the photoconductive layer that formed the image on the photoreceptor, is worn away and detached or peeled off as the print turns green, and the zinc oxide powder The zinc oxide itself may fall off, making the image unclear, or zinc oxide may be exposed.
This is because the developer or toner adheres here and stains the printed screen.

Therefore, as a means to improve the surface hardness of the photoconductive layer, it is possible to use a hard resin such as polyester resin as the insulating resin, but this method may cause a decrease in the photosensitivity of the photoconductive layer, or This is not preferred because the flexibility of the photoconductive layer becomes poor and the photoconductive layer tends to crack and cause unevenness.

Moreover, when making the conventional zinc oxide powder-insulating resin dispersion for making the photoconductive layer, when the zinc oxide powder is dispersed in the insulating resin solution, the zinc oxide powder does not behave as a single powder particle but aggregates. This forms aggregates, which remain intact even when 1 g of the dispersion is applied to a support and dried. Since these aggregates have minute cavities within them, they have a relatively weak cohesive force. Therefore, when the photoreceptor is used for printing, the photoconductive layer is affected by the frictional force of the zinc oxide aggregates as well as the wear of the insulating resin. This causes the above-mentioned defects to occur due to destruction, falling off, or caving in.

The present invention aims to overcome the drawbacks of the conventional photoreceptor having a photoconductive layer using zinc oxide powder and an insulating resin, and to provide an electrophotographic photoreceptor with excellent surface hardness.

[Problems to be Solved by the Invention] The structure of the electrophotographic photoreceptor according to the present invention is such that the electrophotographic photoreceptor has a photoconductive layer made of zinc oxide and an insulating resin on a support. As zinc, 0.3
The gist is a photoreceptor for electrophotography that has excellent performance for offset printing and is made of fired and/or unfired zinc oxide having a bulk density of 3 g/cta or more and less than 0.6 g/ays 3. It is something.

[Function] The calcined zinc oxide used in the present invention is as described above.
The powder has a bulk density of 0.3 g/c+s3 or more and less than 0.8 g/cra3, preferably 0.33 to 0.5 g/c3, more preferably 0.33 to 0.4 g/am3. .

Such zinc oxide powder can be produced as follows. That is, zinc oxide powder has been conventionally used to form the photoconductive layer of electrophotographic photoreceptors.

It can be produced by compressing it using any compressor so that the bulk density is 0.3 g/cm3 or more and less than 0.8 g/c++3, or this compressed powder can be
It can also be made by firing at 600°C.

Any compressor such as a hermetic screw compressor can be used for the above compression. When compressing zinc oxide powder, it is preferable to use a screw compressor with a pitch width of 3 to 15 cm, preferably 5 to locm.A pitch width smaller than 3 cm requires a large amount of power and has a bulk density of 0.
If the pitch width exceeds 8 g/cm3, the photosensitivity of the photoconductive layer decreases, which is undesirable. If the pitch width exceeds 15 cm, the surface hardness of the photoconductive layer becomes insufficient, which is not preferred.

Alternatively, a similar objective can be achieved by using a continuous deaerator to provide the bulk density described above.

The compressed zinc oxide powder can be used as it is to produce a photoreceptor with excellent sensitivity and hardness, but this compressed product is further heated at 200 to 600°C, more preferably at 200 to 400°C.
The performance can be further improved by firing it. 200
Even at temperatures above 600°C, a slight increase in sensitivity is observed compared to unfired powder, but the hardness of the photoreceptor is not sufficient, and when the temperature exceeds 600°C,
The 412 potential of the photoconductive layer decreases, resulting in a decrease in image density. Also, firing is done in rotary kiln, tunnel kiln,
This can be carried out in a commonly used firing furnace such as a Matsufuru furnace.

When the above-mentioned zinc oxide powder according to the present invention or its fired product is used, a photoconductive layer with excellent surface hardness can be formed, unlike when using the above-mentioned conventional zinc oxide powder.

The zinc oxide powder and/or its fired product produced by the method of the present invention is dispersed in an organic solvent solution of an insulating resin by a conventionally known method, coated on a known support, and dried. It can be used as a photoreceptor for electrophotography.

[Example 1] Zinc oxide powder with a particle size of 0.2 to 1.5 mm for ordinary electrophotography was processed using a closed screw pressure 1II machine (pitch width 10 cm).
3 pitches at 5cm, 5 pitches at 5cm) once, twice, 3 times.
The powder was compressed twice and then four times to obtain zinc oxide powder having a bulk density as shown in Table 1. Among these, zinc oxide powder having a bulk density of 0.34 g/cm3 was heated at 200°C, 300°C, 400°C, and 500°C.
C. and 600.degree. C. for 1 hour, respectively, to obtain baked zinc oxide powder.

A zinc oxide dispersion having the following formulation was prepared using each of the zinc oxide powders obtained in Section L.

Zinc oxide powder 35.0g Acrylic resin LR-637 (manufactured by Mitsubishi Rayon Co., Ltd., product name 5) 17.5g Bromphe/-Siblue 1% methanol solution 0.5cc Toluene 2 Disperse each component in 80cc using a ball mill for 4 hours. liquid was produced. The back side is coated with a polymeric conductive agent (ECR-77 manufactured by Dow Chemical Company).
) The above dispersion was applied to the surface of the paper that had been conductively treated in step 1.
After drying at 00°C for 5 minutes, a zinc-soluble photosensitive paper was prepared. The coating amount was 22 g/2 (solid content).

As a comparative example, a zinc oxide photosensitive paper was similarly prepared using 35.0 g of ordinary photoconductive zinc oxide powder instead of the zinc oxide powder used in the above dispersion. Paint! a The amount is the same <22
g/m2 (solid content).

The properties of these photosensitive papers were as shown in Tables 1 and 2.

(Left below) Example 2 1: The zinc oxide powder fired at 400"C for 1 hour from the above example was used in combination with ordinary photoconductive zinc oxide powder in the formulation shown in Table 3 to produce zinc oxide. I made photosensitive paper.The coating amount was 22
g/m2 (solid content).

The properties of these photosensitive papers are also shown in Table 3.

(Margins below) 4-2 As is clear from the data in Tables 1 and 2, the photosensitive paper made using the fired zinc oxide powder of the present invention has the following properties:
As shown in the comparative example, which is a conventional example, not only the sensitivity and the hardness of the photosensitive layer are improved compared to those using ordinary photoconductive powder, but also the fact that the fired powder is mixed with ordinary photoconductive powder. The sensitivity and hardness of the photosensitive layer can also be further improved by using the photosensitive layer. For this reason, these are excellent as photoreceptors for electrophotography such as original plates for offset printing and original plates for transfer.

[Effects of the Invention] The present invention is constructed as described above, and by mixing fired or unfired zinc oxide powder with a specified bulk density with an insulating resin to form a photoconductive layer on a support. An electrophotographic photoreceptor with excellent sensitivity and surface hardness could be obtained.

Claims (2)

[Claims] (1) In an electrophotographic photoreceptor in which a photoconductive layer made of zinc oxide and an insulating resin is provided on a support, the zinc oxide has a bulk of 0.3 g/cm^3 or more and less than 0.6 g/cm^3. A photoreceptor for electrophotography, characterized in that it is mainly composed of zinc oxide powder having density. (2) 10% by weight of zinc oxide powder contained in the photoconductive layer
Claim 1: The above is fired after compression.
The electrophotographic photoreceptor described in .