JPH0549232B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Field of Application) The present invention relates to an electrophotographic photoreceptor, which is used in an electrophotographic system known as the Carlson process, and is formed by providing a photoconductive layer and a surface layer on a support. (Prior art) Conventionally used electrophotographic photoreceptors include Se, Se-Te alloys, Se-As, etc. as photosensitive layers on conductive substrates.
Typical examples include those formed by vapor-depositing an alloy or the like, or those coated with an organic photoconductor such as polyvinylcarbazole or 2,4,7-trinitrofluorenone. However, when using these photoconductors repeatedly, they are easily damaged by peeling off the transfer paper or cleaning residual toner, and the photoconductor layer is also prone to wear, so the photoconductor may be used at a relatively early stage before its characteristics deteriorate. I had to replace it. In order to improve this point, it is known to provide a surface layer on the surface of the photoreceptor. One of the surface layers is an insulating layer made of a material with relatively high electrical insulation. This insulating layer has the advantage of being able to be made thick and having high mechanical strength. However, in order to use such a photoreceptor repeatedly, it is necessary to
A special latent image forming process is required, such as secondary charging → reverse polarity secondary charging → image exposure or primary charging → secondary charging simultaneous image exposure → uniform exposure, etc. Each copying process requires two or more charging processes, which complicates the apparatus, resulting in unstable characteristics and increased costs. There is also a protective layer as a surface layer that does not require the above-mentioned special latent image forming process and can use the so-called Carlson process of charging→image exposure. This protective layer needs to have low insulation to prevent charge from accumulating on or inside the protective layer. The method that has been used so far is to add quaternary ammonium salts etc. to the protective layer, but the conductivity of these materials generally fluctuates widely due to moisture absorption, and the protective layer deteriorates when dry. As the conductivity decreases and charge accumulates,
Fog occurs on the image, and when the temperature is high, the conductivity increases more than necessary, causing charge to move in the lateral direction, causing blur in the image. Furthermore, in order to use the conventional protective layer in the Carlson process, it must be relatively thin, with a film thickness of several microns or less, which is difficult to satisfy in terms of mechanical strength, and requires low insulation. The protective layer is colored by the substances added for
This had an undesirable effect on the spectral sensitivity of the photoreceptor. Attempts to obtain a protective layer by adjusting the conductivity by dispersing conductive powder in a binder resin are known, for example, from Japanese Patent Laid-Open No. 53-3338 and No. 53-44028. (Problems to be Solved by the Invention) However, when carbon or metal is dispersed as a conductive powder, light absorption is strong, and it is difficult to increase conductivity while maintaining transparency. Furthermore, when particles such as zinc oxide or titanium oxide that do not absorb visible light are dispersed, even though they do not absorb light, the light that passes through the film is strongly dispersed due to the non-uniformity of the refractive index, causing turbidity. In addition to this, the conductivity is not sufficient. On the other hand, when a fairly large amount of tin oxide or other metal oxide fine powder is incorporated into a resin to improve conductivity, there is a drawback that permeability is impaired. The present invention has been made in view of the above-mentioned problems in the conventional technology. Therefore, the present invention relates to an electrophotographic photoreceptor having an improved surface layer used in the Carlson process, particularly a surface layer having excellent light transmittance, and which exhibits less charge accumulation even when used repeatedly. The object of the present invention is to provide an electrophotographic photoreceptor that operates stably even under environmental conditions that vary from low humidity to high temperature. (Means and effects for solving the problems) The above object of the present invention is to provide an electrophotographic photoreceptor having a photoconductive layer and a surface layer on a support, in which the binder resin of the surface layer is reduced. This is achieved by dispersing fine tin oxide powder. In the present invention, the reduction-treated fine tin oxide powder to be dispersed in the binder resin is obtained by, for example, hydrolyzing tin chloride to obtain tin hydroxide, which is then washed and then treated with a reducing gas such as hydrogen gas. It can be obtained by introducing it and firing it at a high temperature. The reduced tin oxide in the present invention has a resistance value of about 10 ⁸ Ω・cm before reduction, but by reducing it with hydrogen gas, it has a resistance value of 10 ³ to ^{10 6} Ω・cm. It has become a resistance value. Reduction processing is 350 to 700
This can be carried out by heating at a temperature of 1 to 10 hours. If the heating time is too long, it becomes metallic tin, which is undesirable because it tends to be colored. According to X-ray analysis, no metallic tin was observed in the reduced tin oxide of the present invention, and the color of the powder was closer to white than that of the powder that had not undergone reduction treatment. are doing. The reduced tin oxide fine powder in the present invention may contain one or more of P, Ge, and LiF as impurities. As a result, the resistance value of the reduced tin oxide fine powder further decreases and becomes nearly white. These impurities are generated during the manufacturing process of reduced tin oxide fine powder, for example,
By adding phosphorus chloride, germanium chloride, and lithium fluoride to the raw materials, they can be included in the reduced tin oxide. It is not clear in what state these impurities are contained in the reduced tin oxide, but for example, the reduced tin oxide and impurity oxide may be in a fused state or in a solid solution. It is assumed that These impurities are contained in the reduced tin oxide.
It is contained in a range of 0.001 to 30%, preferably 0.01 to 5%. In the present invention, the reduced tin oxide fine powder used has a BET surface area of about 50 to 60 m ² /g and a particle size of 0.3 μm or less, preferably 0.2 μm or less. The binder resin that can be used for the surface layer in the present invention is preferably one that is transparent to visible light and has excellent electrical insulation, mechanical strength, and adhesive properties, such as polyester resin, polycarbonate resin,
Examples include polyurethane resin, epoxy resin, acrylic resin, vinyl chloride-vinyl acetate copolymer, silicone resin, alkyd resin, polyvinyl chloride resin, cyclized butadiene rubber, and fluorine resin. Furthermore, when solvent resistance of the surface layer is required, it is desirable to use a curable resin. The composition ratio of the binder resin and the reduced tin oxide powder in the surface layer varies depending on the combination of materials, but it has a specific resistance value of 10 ¹¹ to ^{10 13} Ωcm, which is a desirable value for a protective layer. Usually, the reduced tin oxide fine powder is used in an amount of 5 to 100 parts by weight based on 100 parts by weight of the binder resin. In the present invention, the thickness of the surface layer is suitably in the range of 1 to 30 μm. However, since the generation of charge carriers by light takes place in the photoconductive layer, the surface layer must be substantially transparent to the wavelength range of light to which the photoconductive layer is sensitive. As the support in the electrophotographic photoreceptor of the present invention, known supports can be used. For example, conductive supports such as aluminum, stainless steel, etc.
and insulating supports made of synthetic resins such as polyethylene terephthalate and polycarbonate. When using an insulating support, it is desirable to conduct a conductive treatment on the surface on which the photoconductive layer is provided. Various known photoconductive layers can be used as the photoconductive layer in the electrophotographic photoreceptor of the present invention, and can also be used in photoconductors that have low mechanical strength and cannot be used in ordinary electrophotographic systems. for example,
Se, Se-Te alloy, Se-As alloy, Se-Sb alloy,
Vapor deposited film such as Se-Bi alloy, organic photoconductor layer such as polyvinylcarbazole-2,4,7-trinitrofluorenone, a-Si photoreceptor layer, ZnO, CdS
A photosensitive layer having an inorganic photoconductor dispersed in a binder resin, or a laminated layer of a charge generation layer and a charge transport layer can be used. In the electrophotographic photoreceptor of the present invention, an intermediate layer may be provided between the surface layer and the photoconductive layer, if necessary, in order to improve adhesion or charge retention. The intermediate layer must have a higher resistance than the surface layer, which is at least a low insulating layer.
In addition to the role of the charge injection blocking layer, the intermediate layer can also function as an adhesive layer between the photoconductive layer and the surface layer. Materials suitable for the intermediate layer include those whose main component is a polymer compound or those whose main component is an inorganic compound. Examples of polymeric compounds include epoxy resins, polyester resins, polyamide resins, polyurethane resins, nitrified cotton, vinylidene chloride resins, silicone resins, fluorine resins, etc. Examples of inorganic compounds include:
Examples include zirconium oxide, silica, Se, S, As ₂ O ₃ and the like. The intermediate layer can be configured in any way, e.g.
It is formed by painting, and its thickness is arbitrarily set, but preferably 3 μm or less, particularly 1 μm or less. The electrophotographic photoreceptor of the present invention is basically different from a photoreceptor known as a conventional laminated photoreceptor in which a photoconductive layer is provided on a conductive support and an insulating layer is provided thereon. different. That is, in the electrophotographic photoreceptor of the present invention, a charge pattern is formed between the conductive surface layer/photoconductive layer interface and the conductive support. In contrast, in conventional photoreceptors having an insulating layer on the surface, the charge pattern is formed between the insulating layer surface and the conductive support. Furthermore, in the surface layer of the present invention, electrical charges must be injected from the surface to the interface between the surface layer and the photoconductive layer, but in a laminated photoreceptor in which an insulating layer is present, the charges must remain on the surface. Furthermore, it must have a thinner film thickness than the photoconductive layer so that a sufficient potential difference is generated between the bright and dark areas, and therefore the function of the layer and the properties of the interface must be In this case, something different from what is required in the present invention is required. (Example) Next, the present invention will be explained by referring to an example. Example 1 80 parts by weight of polyurethane resin (Rethane 4000 manufactured by Kansai Paint Co., Ltd.) and tin oxide were mixed in a hydrogen gas atmosphere to approx.
50 parts by weight of reduced tin oxide fine powder (10 ⁶ Ω cm) obtained by heating at a temperature of 600°C for about 2 hours and 100 parts by weight of a mixed solvent of cellosolve acetate and xylene were placed in a glass ball mill. Get in,
Mixed and dispersed for 50 hours. A coating liquid was obtained by mixing 20 parts by weight of a curing agent into this dispersion. On the other hand, a photosensitive layer was formed by vapor depositing As ₂ Se ₃ to a thickness of 60 μm on an aluminum pipe, and on top of that, a 0.2 μm thick layer of zirconium oxide was formed by heating a zirconium oxide-butyl alcohol mixed system. A charge retention layer was provided. The above coating liquid was applied onto this charge retention layer and cured to form a surface layer with a thickness of 7 μm to obtain an electrophotographic photoreceptor. When an image was formed using this electrophotographic photoreceptor, a good copy image was obtained. Comparative example Reduction-treated tin oxide fine powder in Example 1
An electrophotographic photoreceptor having a surface layer with a thickness of 7 μm was obtained in the same manner as in Example 1, except that 50 parts by weight of the tin oxide fine powder (10 ⁸ Ω cm) which had not been reduced was used. . Example 2 Reduction-treated tin oxide fine powder in Example 1
An electrophotographic photoreceptor was obtained in the same manner as in Example 1 except that 50 parts by weight was changed to 40 parts by weight. When an image was formed using this electrophotographic photoreceptor, a good copy image was obtained. Example 3 Reduction-treated tin oxide fine powder in Example 1
A reduced tin oxide fine powder (10 ³ Ω・An electrophotographic photoreceptor was obtained in the same manner as in Example 1 except that the amount was changed to 50 parts by weight (cm). When an image was formed using this electrophotographic photoreceptor, a good copy image was obtained. Example 4 Reduction-treated tin oxide fine powder in Example 1
A reduced tin oxide fine powder (10 ³ Ω・An electrophotographic photoreceptor was obtained in the same manner as in Example 1 except that the amount was changed to 40 parts by weight (cm). When an image was formed using this electrophotographic photoreceptor, a good copy image was obtained. Example 5 Reduction-treated tin oxide fine powder in Example 1
A reduced tin oxide fine powder (10 ³ Ω・Example 1 except that the film thickness of the surface layer was changed from 0.2 μm to 10 μm in place of 40 parts by weight (cm).
An electrophotographic photoreceptor was obtained in the same manner as above. When an image was formed using this electrophotographic photoreceptor, a good copy image was obtained. The electrophotographic photoreceptors of Examples 1 to 5 and Comparative Example were installed in an FX4370 copying machine (manufactured by Fuji Xerox Co., Ltd.), and the residual potential at the 500th cycle was measured, and the following results were obtained.

【table】

[Table] From the above results, the electrophotographic photoreceptor of the present invention has
The conductive powder content can be lowered than that of the comparative example (Examples 2 and 4), and the residual potential is significantly lower when the conductive powder content is the same as that of the comparative example (Examples 1 and 4). 3) I can understand things. In addition, when the conductive powder content is lowered,
It was found that even if the film thickness was significantly increased, the residual potential and relative sensitivity were not significantly inferior to those of the comparative example (Example 5). (Effects of the Invention) In the electrophotographic photoreceptor of the present invention, since the reduced tin oxide fine powder is used in the surface layer as described above, compared to the conventional one using unreduced tin oxide fine powder. with low metal oxide content,
It has the excellent effect of increasing the conductivity of the surface layer and having a low residual potential. Therefore, according to the present invention, not only is it possible to obtain an electrophotographic photoreceptor having a surface layer having a desirable volume resistivity value as a protective layer, but also it is possible to obtain an electrophotographic photoreceptor having a surface layer having a desirable volume resistivity as a protective layer. An electrophotographic photoreceptor having a surface layer with excellent transparency can be obtained. Furthermore, the electrophotographic photoreceptor of the present invention has the following advantages compared to conventionally known ones. That is, (1) a latent image can be formed without using any special process; (2) There is almost no accumulation or increase in residual charge even after repeated use. (3) Not easily affected by temperature and humidity. (4) The thickness of the surface layer can be made relatively thick. (5) It does not substantially affect the photosensitivity of the photoconductive layer.

Claims (1)

[Scope of Claims] 1. An electrophotographic photoreceptor having a photoconductive layer and a surface layer on a support, characterized in that the surface layer is formed by dispersing reduced tin oxide fine powder in a binder resin. An electrophotographic photoreceptor. 2. The electrophotographic photoreceptor according to claim 1, wherein the reduced tin oxide fine powder contains one or more of P, Ge, or LiF as impurities.