JPH0353624B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a laminated electrophotographic photoreceptor, and particularly to a positively charged organic photoconductive photoreceptor.

Organic photoconductive materials such as polyvinylcarbazole, anthracene, oxadiazole, etc.
Since the sensitivity is lower than that of inorganic photoconductive materials such as zinc oxide and cadmium sulfide, several sensitization methods have been devised, but an effective method is to use a charge generation layer that generates charge carriers upon exposure to light. , in combination with a charge transport layer that has the ability to transport the generated charge carriers.

A laminated electrophotographic photoreceptor made by such a method includes, for example, a conductive support such as an aluminum vapor-deposited film, a β-type steel phthalocyanine pigment, a styrene-butadiene resin dispersion layer, and an oxadiazole dissolved in a polyester resin. A device in which charge transport layers are laminated is known. Similar to a general single-layer photoreceptor, such a laminated photoreceptor can form an image using the Carlson process, which has basic steps of charging, imagewise exposure, and development.

Laminated photoreceptors may have a structure in which a charge generation layer is laminated on a charge transport layer, or vice versa, and the present invention is directed to the production of photoreceptors with particularly high sensitivity in the former structure. The main purpose is to provide a method.

Conventionally, photoreceptors having a structure in which a charge generation layer is formed on a charge transport layer tend to have poor sensitivity because the injection of charge carriers from the charge generation layer to the transport layer decreases, but in the present invention, the charge carriers are As a result of various experiments regarding the injection properties of pigments, we have found that in order to improve the dispersibility of the pigment in the charge generation layer and to improve the wettability of the charge generation layer to the charge transport layer, we have used a specific surfactant when dispersing the pigment. It was found that adding .

That is, the electrophotographic photoreceptor according to the present invention is a laminated electrophotographic photoreceptor having a charge transport layer and a charge generation layer on a substrate in this order, in which the charge generation layer contains an organic photoconductive pigment and a polyoxyethylene-polyoxy Propylene condensate, linear alcohol ethoxylate, nonylphenol ethoxylate, octylphenol ethoxylate, polynuclear phenol ethoxylate, higher alcohol sulfate,
Dispersing in a binder resin together with a nonionic surfactant selected from the group consisting of higher alcohol ether sulfate, aromatic phosphate ester, aliphatic phosphate ester, polyoxyethylene glycol oleate, and polyoxyethylene glycol stearate. It is characterized by being formed by.

In the present invention, by adding a specific surfactant, great effects can be obtained in improving the dispersibility of pigments, improving the stability of coating liquids, preventing re-aggregation of pigments, and improving coating properties. Furthermore, by improving the "wetting" of the charge generation layer, the injection property of charge carriers is improved, and the sensitivity of the photoreceptor is improved.

To explain the present invention in more detail, first, the substrate is made of metal, paper, plastic, etc. into a predetermined shape, and is used after being subjected to conductive treatment and subbing treatment as required.

A charge transport layer is applied on top of this. The charge transport layer generally contains a polycyclic aromatic compound such as anthracene, birene, phenanthrene, coronene, etc., or indole, carbazole, oxazole, isoxazole, thiazole, imidazole, birazole, oxadiazole, etc. in the main chain or side chain. If necessary, an electron-donating charge transporting substance such as a compound having a nitrogen-containing cyclic compound may be added to polyester, polystyrene, polyvinyl acetate, polyvinyl chloride, polyarylate, polycarbonate, polysalvon, polyacrylic ester, etc. It is applied as a solution along with at least one resin.

Mixing ratio of resin to charge transport material is 20-200
It is about % by weight. The solvent may be any solvent as long as it dissolves both, and generally includes ketones such as methyl ethyl ketone and acetone, esters such as ethyl acetate and butyl acetate, aromatic hydrocarbons such as toluene and xylene, monochlorobenzene and dichlorobenzene. Chlorinated hydrocarbons such as chlorobenzene and chlorotoluene are used. The thickness of the charge transport layer is approximately 5 to 25 microns.

Next, a charge generation layer is formed using, for example, an azo pigment such as Sudan Red or Diane Blue, a quinone pigment such as Algol Yellow or Pinon Quinone, or an indigo pigment.
A charge-generating pigment such as an indigo pigment such as thioindigo, a phthalocyanine pigment such as copper phthalocyanine, a bisbenzimidazole pigment, or a quinacridine pigment is first dispersed together with a binder resin. The resin may be the same as that used in the charge transport layer, or may also be a resin such as polyvinyl acetal, polyvinyl butyral, polyvinylpyridine, polyamide, polyurethane, methylcellulose, or phenolic resin. The ratio of resin to pigment is 20 to 500% by weight, particularly 50 to 400% by weight, and methods such as a ball mill, vibratory ball mill, attritor, sand mill, and homogenizer are used for dispersion.

A surfactant, which is a feature of the present invention, is added during dispersion. There are nonionic, cationic, anionic, and amphoteric types of surfactants, but nonionic surfactants are preferred in consideration of electrical properties. Nonionic surfactants used in the present invention include polyoxyethylene-polyoxypropylene condensates, linear alcohol ethoxylates, nonylphenol ethoxylates, octylphenol ethoxylates, polynuclear phenol ethoxylates, higher alcohol sulfates, higher Mention may be made of alcohol ether sulfates, aromatic phosphates, aliphatic phosphates, polyoxyethylene glycol oleate and polyoxyethylene glycol stearate. Its amount is from 0.1 to 10% by weight, based on the pigment.

It is necessary to select a solvent that has good pigment dispersibility and dissolves the binder resin. The solvent may be the same as the solvent for the charge transport layer, or may be one that dissolves it; however, in such a case, if the charge generation layer is coated on the charge transport layer, the charge transport layer may be eluted. If this occurs, the characteristics will deteriorate significantly. Therefore, it is important to apply the agent in a manner that prevents it from eluting, and spray application is suitable for this purpose.

When spraying, the type of gun, air pressure, amount of application, spray distance, etc. are set appropriately. Film thickness is 0.1~
The thickness is 1μ, and if it is thin, the sensitivity will be low, and if it is thick, the charging potential will decrease.

The electrophotographic photoreceptor according to the present invention, which has a charge generation layer formed by dispersing a pigment together with a surfactant, has improved dispersibility of the pigment, so it has very good coating properties and is free from spots and repellents. There are almost no defects. Improvement in sensitivity was observed due to improved "wetting" to the charge transport layer. In addition, the coating liquid can be stored for a long period of time due to reduced pigment sedimentation and aggregation.

Example 1 An aluminum cylinder of 80φ×300mm was coated with casein to form a base with a thickness of 5 μm. next, 1 part of a pyrazoline compound represented by the structural formula (parts by weight, the same applies hereinafter) and 1 part of a polyarylate resin (trade name: U-100, manufactured by Unitika) were dissolved in 7 parts of monochlorobenzene, and the solution was applied onto the above substrate by a dipping method. It was coated and dried at 100° C. for 1 hour to form a charge transport layer with a thickness of 14 μm.

On the other hand, 10 parts of a pigment purified by heating β-type copper phthalocyanine pigment in water, ethanol, and methyl ethyl ketone (MEK) in sequence, 12 parts of polyester resin (trade name: Vylon 200, manufactured by Toyobo Co., Ltd.), and primary linear chain Alcohol ethoxylate surfactant (product name: Adecatol LO-5, manufactured by Asahi Denka) 0.1
A mixed solution containing 100 parts of cyclohexanone was subjected to dispersion treatment for 2 hours using a sand mill apparatus. This solution was diluted by adding 120 parts of MEK, and sprayed onto the charge transport layer. The spray application conditions were as follows: Using a Binks spray gun, air pressure was 1.5 kg/cm ² , distance between gun and substrate was 3 cm, and coating amount was 8 ml/min. While rotating the substrate, the gun was moved in the longitudinal direction of the substrate. I sprayed it. The mixture was thoroughly dried at 80°C to form a charge generation layer, and an electrophotographic photoreceptor was obtained.

The surface of this photoreceptor is charged with a +6.2KV corona charger.
It was charged to 560V, and then used in an electrophotographic copying machine that consists of image exposure, dry toner development, toner transfer to paper, and fur brush cleaning processing. The sensitivity was defined as the exposure intensity at which the potential was halved, and the sensitivity was 6.5 lux·sec. The copy image was good.

In order to investigate the stability of the coating solution for the charge generation layer, a photoreceptor manufactured using the same process 30 days after dispersion showed the same characteristics, and there were no abnormalities in the coating solution.

For comparison, we measured a photoreceptor in which a charge generation layer was formed by dispersing pigments without adding a surfactant, and found that the sensitivity was slightly lower at 6.8 lux·sec. In order to obtain this, it was necessary to give a rather strong exposure. When a photoreceptor was produced in the same manner 30 days after dispersion, the sensitivity was as low as 7.6 lux·sec, and when the dispersion was carefully examined, pigment precipitation was observed.

Example 2 The same procedure as in Example 1 was performed up to the charge transport layer.

Next, 1 part of the following disazo pigment disclosed in JP-A-55-82160, 3 parts polystyrene resin (product name: HF77, manufactured by Mitsubishi Monsanto), nonylphenol ethoxylate surfactant (product name: NP-695, manufactured by Asahi Denka)
A mixed solution consisting of 0.02 parts of toluene and 15 parts of toluene was dispersed for 1 hour in a vibrating ball mill using 1φ glass beads. This dispersion was spray coated in the same manner as in Example 1.

When measuring the characteristics of this photoreceptor, the potential is 540V
The sensitivity was 5.2 lux·sec, and good copy images were obtained.

Example 3 Even if 0.02 part of an aliphatic phosphate ester surfactant (trade name: ADEKA COL PS-331E, manufactured by Asahi Denka) was used instead of the surfactant used in Example 2,
A similar photoreceptor could be obtained.

Claims (1)

[Claims] 1. In a laminated electrophotographic photoreceptor having a charge transport layer and a charge generation layer on a substrate in this order, the charge generation layer contains an organic photoconductive pigment and a polyoxyethylene-
Polyoxypropylene condensate, linear alcohol ethoxylate, nonylphenol ethoxylate, octylphenol ethoxylate, polynuclear phenol ethoxylate, higher alcohol sulfate, higher alcohol ether sulfate,
aromatic phosphate ester, aliphatic phosphate ester,
An electrophotographic photoreceptor characterized in that it is formed by dispersing in a binder resin together with a nonionic surfactant selected from the group consisting of polyoxyethylene glycol oleate and polyoxyethylene glycol stearate.