JPS6211860A - Preparation of electrophotographic zinc oxide particles - Google Patents

Abstract

PURPOSE:To prevent agglomeration of zinc oxide particles in an insulating resin solution by pulverizing their compressed blocks obtained by compressing the zinc oxide powder with a pressure of 20-150kg/cm<2>, and burning the obtained particles of <=2.0mm diameter at a temperature of 200-600 deg.C. CONSTITUTION:The zinc oxide powder is compressed with a pressure of 20-150kg/cm<2>, pulverizing the compressed product to <=2.0mm particle diameter, and burning the obtained particles at a temperature of 200-600 deg.C to obtain the intended electrophotographic zinc powder. To compress the zinc oxide powder, an optional compressor, such as a hydraulic press used for molding mozaic tiles, can be used, and the compressed blocks may be pulverized by an optional method, and the intended particles can be obtained by passing the pulverized product through a sieving step. To burn the compressed blocks, a rotary kiln can be used, and particle density is, generally, 0.6-1.5g/cm<3>, and preferably, 0.7-1.2g/cm<3>.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved method for producing zinc oxide particles for use in electrophotographic photoreceptors.

Zinc oxide photoreceptors conventionally used in electrophotography consist of a photoconductive layer with a thickness of about 1 OJL mainly composed of zinc oxide powder and an insulating resin on a support such as paper or plastic film that has been subjected to conductive treatment. It is made by applying.

The zinc oxide powder conventionally used to form the photoconductive layer is IIi, hereinafter more generally 0.2 to 0.
．． It is a powder with a particle size of 5 mm, and silicone resin, acrylic resin, alkyd resin, etc. are used as the insulating resin.

To form the 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 approximately 4 to 7:l, and this dispersion is It is manufactured by coating a support with:

When printing using a zinc oxide photoreceptor for offset printing or as a transfer plate, the number of printed sheets is at least 300.
However, the conventional zinc oxide photoreceptor coated with a photoconductive layer as described above does not have sufficient surface hardness. Easy to wear, dirt on the background during printing,
This causes the image to become unclear. There are various possible causes for this, but one of them is that the insulating resin, which is the binder of the photoconductive layer that formed the latent or developed image on the zinc oxide photoreceptor-1, is worn out during repeated printing or transfer. This is because the zinc chloride powder may detach or peel off, and the zinc chloride powder itself may fall off, making the image unclear, or the zinc chloride may be exposed, and the developer or toner may adhere to it, staining the printed screen. .

For this reason, one possible method for improving the surface hardness of the photoconductive layer is to use a hard resin, such as polyester resin, as the insulating resin, but this method may result in a decrease in the photosensitivity of the photoconductive layer. Otherwise, the flexibility of the photoconductive layer becomes poor, and the photoconductive layer is likely to crack and cause unevenness, which is undesirable.

When making a conventional zinc oxide powder-insulating resin dispersion for making a photoconductive layer, when zinc oxide powder is dispersed in an insulating resin solution, the zinc oxide powder does not behave as a single powder particle but aggregates. The dispersion liquid forms aggregates, and these aggregates remain as they are even when the dispersion is applied to a support and dried. This aggregate has a relatively weak cohesive force and has minute cavities within it, so when the photoreceptor is used for printing, the zinc oxide compressed body is destroyed by frictional force and falls off when the insulating resin is worn. Or it may cave in, causing the above-mentioned drawbacks.

The present invention has been made in view of the drawbacks mentioned above, and its purpose is to eliminate the drawbacks of the conventional photoreceptor having a photoconductive layer using zinc oxide powder and an insulating resin, and to reduce the surface hardness. An object of the present invention is to provide a method for producing zinc oxide particles that can provide an excellent photoreceptor.

The present invention uses zinc oxide powder at a rate of 20 to 150 Kg/cm2.
The present invention provides a method for producing zinc oxide particles for electrophotography, which comprises firing particles having a particle size of 2.0 or less obtained by compressing the compressed body at a pressure of 2.0 to 600.

As the zinc oxide powder used in the present invention, a hardened lead-resistant powder that has been conventionally used for forming photoconductive layers for electrophotography can be used.

Any compressor, such as a hydraulic press for forming mosaic tile substrates, can be used to compress the zinc oxide powder to form a compressed body. When compressing zinc oxide powder, 20 kg/
cm2-150 Kg/cm2, preferably 40
It is better to adopt a pressure between Kg/Cm2 and 100Kg/Cm2, and at a pressure lower than 20 Kg/cm2,
Subsequently, the bonding force of the particles obtained by crushing the compressed body is not sufficient, and the particles may be further crushed in the baking process, and the surface hardness of the photoconductive layer formed using the particles may not be sufficient. Undesirable.

Moreover, if the pressure exceeds 150 Kg/cm2, the photosensitivity of the photoconductive layer may be lowered, which is not preferable.

Also, if it is too large, it will take a lot of effort to crush the compressed body.
In addition, it is not practical to make the compressor unnecessarily large in terms of its performance.

According to the present invention, the zinc oxide compressed body obtained by compression as described above is crushed. Crushing can be achieved by passing the compressed body through a rear process of crushing it by any method,
As the sieving means, a rotating sieve, a single plane sieve, etc. can be used, but a vibrating sieve is more preferable. Alternatively, the zinc oxide particles can be compressed and crushed at the same time by introducing the zinc oxide powder into two rolls of two rolls adjusted to apply the above-mentioned pressure and compressing the powder.

If necessary, the zinc oxide particles obtained by crushing are sieved to remove coarse particles, and the particle size is 2.0 mm or less, preferably 0.3 mm.
The particle size is 1.0 mm to 1.0 mm.

In the present invention, the particles are heated at a temperature of 200 to 600°C, preferably 200 to 4.0°C. By firing at 00° C., the sensitivity and hardness of the photoreceptor component are increased. 20
Sensitivity is improved compared to unfired particles even below 0°C, but the hardness of the photoreceptor is not sufficient, and below 600°C, it takes time to disperse the zinc oxide particles and the insulating resin, and the electrification level increases. This causes a decrease in image density, resulting in a decrease in image density.

Further, for firing, a commonly used firing furnace such as a rotary kiln, tunnel kiln, Matsufuru furnace, etc. can be used. These particles are generally 0.6-1.5 g/
am3 preferably has a bulk density of 0.7-1.2 g/cm''.

If the particle size of the fired particles exceeds 2.0 mm, it will take a long time to disperse when producing a dispersion of zinc oxide particles, which is not preferable. There is no strict regulation on the lower limit of particle size. The produced zinc oxide particles preferably have a hardness of 2.0 to 10.0 g, particularly 3.0 to 6.0 g, as measured by the following method.

It has been found that within this range, the surface hardness of the photoreceptor made using the zinc oxide particles according to the present invention is good and the wear resistance can be improved. The hardness was measured as follows. That is, the diameter is 0.84 mm (20 meshes)
Take ~1.7 mm (10 mesh) particles, compress the particles using a spring-type weighing machine with a planet (reading limit) set to 0.5 g, and calculate the displayed weight when the particles collapse as hardness. It was displayed as follows.

When the calcined zinc oxide particles having the above-mentioned particle size produced according to the present invention are used, a photoconductive layer with excellent surface hardness can be formed, unlike the case where the conventional zinc oxide powder described above is used.

The zinc oxide particles produced by the method of the present invention are dispersed in an organic solvent solution of an insulating resin by a conventionally known method, applied to a known support, and dried to form an electrophotographic photoreceptor. be able to.

The present invention will be explained below with reference to Examples and Reference Examples.

Example Zinc oxide powder with a particle size of 0.2 to 0.5p for ordinary electrophotography was heated at 80 K using a hydraulic press for mosaic tile substrates.
g/cm2, and the formed compressed body was then crushed and sieved using a vibrating sieve to obtain 500 g of zinc oxide particles with a particle size of 1 mm or less. These zinc oxide particles were heated at 200°C.
1 at 300°C, 400'0°, 500°C and 600°C, respectively.
It was fired for a period of time to obtain fired zinc oxide particles.

Reference Example Using each of the calcined zinc oxide particles prepared in the above examples, a zinc oxide dispersion having the following formulation was prepared.

Calcined zinc oxide particles 35.0 g Acrylic resin LR-637 (manufactured by Mitsubishi Rayon Co., Ltd., trade name) 17.5 g Bromophenol blue 1% methanol solution 0.5 cc Toluene 80 cc The above components were dispersed in a ball mill for 4 hours to prepare a dispersion liquid. Manufactured. The back side is coated with a polymer conductive agent (ECR-7 manufactured by Dow Chemical Company).
Applying the above dispersion to the surface of the paper treated with conductivity in 7),
It was dried at 100° C. for 5 minutes to produce zinc oxide photosensitive paper. The coating amount was 22 g/.2 (solid content).

As a comparative example, instead of the calcined zinc oxide particles used in the above dispersion, 35.0 g of ordinary photoconductive zinc oxide powder and zinc oxide particles that were not calcined (crushed and sieved after pressure wj molding) were used. Zinc oxide photosensitive paper was similarly made using The coating amount was also 22 g/m2 (solid content).

The properties of these photosensitive papers were as follows.

(Margin below) As is clear from the data in the table above, the photosensitive paper made using the calcined zinc oxide particles made by the method of the present invention has a normal photoconductivity as shown in the comparative example, which is a conventional example. Compared to powder and unfired particles, the sensitivity and hardness of the photosensitive layer are improved. For this reason, these are excellent as photoreceptors for electrophotography such as original plates for offset printing and original plates for transfer.

Claims (3)

[Claims] (1) Particles with a particle size of 2.0 mm or less obtained by compressing zinc oxide powder at a pressure of 20 to 150 kg/cm^2 and crushing the compressed body are fired at 200 to 600°C. A method for producing zinc oxide particles for electrophotography. (2) Zinc oxide particles of at least 0.6 g/cm^3
The manufacturing method according to claim 1, having a bulk density of . (3) The manufacturing method according to claim 1 or 2, wherein the zinc oxide particles have a hardness that can be crushed under a load of 2.0 to 10.0 g.