JPH0243175B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an electrophotographic photoreceptor having an undercoat layer. An electrophotographic photoreceptor basically consists of a substrate and a photosensitive layer. However, improvements in adhesion between the substrate and photosensitive layer, improvement in coating properties of the photosensitive layer, protection of the substrate, covering defects on the substrate, protection against electrical breakdown of the photosensitive layer, improvement of charge injection from the substrate to the photosensitive layer, etc. Therefore, it is effective to provide an undercoat layer between the substrate and the photosensitive layer. Conventionally known materials for the undercoat layer include polyvinyl alcohol, polyvinyl methyl ether, poly-N-vinylimidazole, ethyl cellulose, methyl cellulose, ethylene-acrylic acid copolymer, casein, gelatin, and polyamide. The first characteristic required of the undercoat layer is electrical characteristics. Since it is used in an electrophotographic photoreceptor, it is important not to affect the electrophotographic properties, and for this purpose it is necessary to have low electrical resistance. When the electrical resistance is high, a charged potential is applied to the undercoat layer, and fogging occurs in the image as a so-called residual potential. Furthermore, it is necessary that the electrical resistance is unaffected by changes in the external environment, in particular by changes in atmospheric humidity. For example, if the electrical resistance increases due to low humidity, fogging will occur. Such characteristics are required for the undercoat layer,
In the case of only a single resin layer, it has been difficult to obtain good results in the past. Therefore, the thickness of the resin layer is made very thin, or conductive powder (nickel, metal powder such as copper, silver, etc.) is dispersed in the resin as necessary. However, reducing the thickness of the resin layer has the disadvantage that its performance as an undercoat layer is insufficient.On the other hand, in the undercoat layer in which metal powder is dispersed, the metal particles are rough, so the undercoat layer The problem was that the surface properties of the material were reduced. An object of the present invention is to provide an electrophotographic photoreceptor that eliminates the above-mentioned drawbacks. Another object of the present invention is to provide an electrophotographic photoreceptor having an undercoat layer that can substantially eliminate defects in a rough substrate. Another object of the present invention is to provide an electrophotographic photoreceptor having a smooth surface between a rough substrate and a photoreceptor layer, and an undercoat layer that can be formed thickly. The present invention uses tin oxide (SnO ₂ ) powder and titanium oxide (TiO ₂ ) powder to create an undercoat layer that has good dispersibility of the powder in the resin and has a smooth surface. It is characterized by the fact that it forms. Tin oxide powder has a sufficiently low resistance that it is possible to form an undercoat layer by dispersing it alone, but its dispersibility is poor, and if it is used as a coating, there will be problems with the smoothness of the coating. The resistance when made into a membrane is 10 ⁵ ~
It is approximately 10 ⁸ Ωcm, which is a sufficiently low value for an undercoat layer. At this time, tin oxide is added to the resin 1 in the undercoat layer.
0.1 to 10 parts by weight, preferably 0.5 to 10 parts by weight
It is suitable that it is dispersed and contained in an amount of 5 parts by weight. On the other hand, titanium oxide is a white pigment called titanium white, and its resistance when formed into a paint film is around 10 ¹¹ to 10 ¹³ Ωcm, which is lower than that of an insulating material, so even when mixed with tin oxide, it should be used in a large amount. Although it can be mixed, titanium oxide is generally mixed with resin 1 in the undercoat layer.
It is suitable to disperse and contain it in an amount of 0.1 to 10 parts by weight, preferably 0.5 to 5 parts by weight. In addition, titanium oxide has extremely fine particles of less than 1 μm, and has great hiding power, so it has a great ability to smooth surfaces. Therefore, by using a mixture of titanium oxide and tin oxide, the resistance can be lowered to 10 ¹² Ωcm or less, which is required for the undercoat layer, and a smooth surface can be obtained. The mixing ratio (weight) of titanium oxide and tin oxide is 10:1 to 1:1.
degree is preferred. Further, titanium oxide may be of rutile type or anatase type, or a mixture thereof. The resin used for dispersing titanium oxide and tin oxide is
Any thermoplastic resin such as polyester resin, acrylic resin, vinyl acetate resin, vinyl chloride-vinyl acetate copolymer resin, or thermosetting resin such as alkyd resin, melamine resin, urethane resin, epoxy resin, silicone resin, phenolic resin, etc. well,
It is selected in consideration of adhesion to the substrate, pigment dispersibility, etc. Among these, thermosetting resins are more preferred in terms of solvent resistance. Further, the coating liquid used when forming the undercoat layer can contain various organic solvents. The organic solvent used varies depending on the type of resin, but generally alcohols such as methanol, ethanol, and isopropanol, ketones such as acetone, methyl ethyl ketone, and cyclohexanone, N,N-dimethylformamide, N,N Amides such as dimethylacetamide, sulfoxides such as dimethyl sulfoxide, ethers such as tetrahydrofuran, dioxane, and ethylene glycol monomethyl ether, esters such as methyl acetate and ethyl acetate, chloroform, methylene chloride, dichloroethylene, carbon tetrachloride, Resin group halogenated hydrocarbons such as trichloroethylene, aromatics such as benzene, toluene, xylene, ligroin, monochlorobenzene, dichlorobenzene, etc. can be used. Coating can be carried out using coating methods such as dip coating, spray coating, spinner coating, bead coating, Meyer bar coating, blade coating, roller coating, and curtain coating. Furthermore, a resin layer containing no conductive powder may be provided between the undercoat layer containing tin oxide powder and titanium oxide powder and the photosensitive layer. In particular, when the photosensitive layer is of a functionally separated type consisting of a charge generation layer and a charge transport layer, the thickness of the charge generation layer is generally extremely thin, which improves coating properties, prevents penetration, improves drying properties, and improves electrophotography. It is very effective to provide a resin layer containing no conductive powder on the undercoat layer to improve properties. As such a resin layer, the conventional undercoat layer resin material described above can be used. At this time, since the desired performance as an undercoat layer is substantially taken care of by the undercoat layer containing dispersed titanium oxide and tin oxide, the resin layer thereon may be a thin layer. The thickness of the undercoat layer of the present invention is 1 to 20 μm, especially 2 μm.
The film thickness is preferably about 15 μm, and the resin layer thereon is formed to a thickness of 0.1 μm to 5 μm, preferably about 0.2 μm to 1 μm. If the film thickness is too thin, the desired effect cannot be obtained, and if the film is too thick, the resistance will be high and residual potential will be accumulated. To explain the electrophotographic photoreceptor of the present invention in more detail, first, the substrate may be a metal such as aluminum, horizontal copper, or stainless steel, or a polymeric material such as polyethylene terephthalate, polybutylene terephthalate, phenolic resin, polypropylene, nylon, or polystyrene, or a hard material. It is used by molding paper or other materials into a cylindrical shape, or by making it into a film or foil.
In the case of an insulator, it is necessary to conduct a conductive treatment, which includes methods such as impregnation with a conductive substance, lamination with metal foil, and metal vapor deposition. The photosensitive layer is
Dye-sensitized zinc oxide, selenium powder, amorphous silicon powder, polyvinyl carbazole, phthalocyanine pigment, oxadiazole pigment, etc. are coated together with a binder resin as required. Furthermore, when using organic photoconductive materials, an effective method for improving properties is to combine a charge generation layer that generates charge carriers upon exposure to light and a charge transport layer that has the ability to move the generated charge carriers. There is also. The charge generation layer is made of azo pigments such as Sudan Red, Diane Blue, and Jenas Green B; quinone pigments such as Algol Yellow, Pyrene Quinone, and Indanthrene Brilliant Violet RRP;
Indigo pigments such as quinocyanine pigments, perylene pigments, indigo and thioindigo, bisbenzimidazole pigments such as India First Orange Toner, phthalocyanine pigments such as copper phthalocyanine, quinacridone pigments, and charge generating substances such as pyrylium dyes, polyester, polystyrene, Polyvinyl acetate, acrylic, polyvinyl butyral, polyvinylpyrrolidone, methylcellulose,
It is formed by being dispersed in a binder resin such as hydroxypropyl methylcellulose or cellulose esters. Further, it can also be formed by vapor deposition or the like. The thickness of the charge generation layer is approximately 0.05 to 0.2 μm. In addition, the charge transport layer may contain polycyclic aromatic compounds such as anthracene, pyrene, phenanthrene, coronene, etc., or indole, carbazole, oxazole, isoxazole, thiazole, imidazole, pyrazole, oxadiazole, pyrazoline, thiadiazole, etc. in the main chain or side chain. It is formed by dissolving a hole-transporting substance such as a compound having a nitrogen-containing cyclic compound such as triazole or a hydrazone compound in a resin that has film-forming properties. This is because the charge transporting substance generally has a low molecular weight and has poor film-forming properties by itself. Examples of such resins include polycarbonate, polyarylate, polystyrene, polymethacrylic acid esters, styrene-methyl methacrylate copolymer, polyester, styrene-acrylonitrile polymer, polysulfone, and the like. The thickness of the charge transport layer is 5-20μ
That's about it. The undercoat layer used in the present invention has titanium oxide powder and tin oxide powder dispersed in the resin, so it has a smooth surface, has a large hiding power of the base, has low electrical resistance, and has a low film thickness. Coupled with the ability to increase the thickness, even defective substrates can be adequately covered. Hereinafter, the present invention will be explained according to examples. Example 1 and Comparative Examples 1 and 2 Titanium oxide powder (manufactured by Sakai Chemical Co., Ltd.) Part T (part by weight,
(same below), tin oxide powder (manufactured by Mitsubishi Metals Co., Ltd.) S part,
16 parts of one-component epoxy resin (trade name: U33, manufactured by Amicon Japan) (solid content concentration 50%) and 30 parts of toluene were dispersed in a ball mill for 6 hours. The ratio of T and S is shown in the table below.

[Table] Each dispersion was applied to a 50μ thick aluminum sheet using a wire bar to form a 10μ thick undercoat layer, which was heated and cured at 150°C for 30 minutes. This sheet can be used at room temperature (25℃, 60%RH) and low humidity (15℃,
The volume electrical resistivity was measured in an environment of 10% RH). In addition, the surface roughness of the formed coating film was measured. The results are summarized in Table 2.

[Table] As shown above, sample B, which is made only of titanium oxide, has a fine surface roughness, but the resistance increases significantly at low humidity.
Further, although sample C containing only tin oxide had a low resistance, its surface roughness was rough. Next, each sample was coated on an 80φ x 300mm aluminum cylinder by a dipping method and cured by heating to form a 10μ thick undercoat layer. Next, zinc oxide powder for electrophotography (manufactured by Hakusui Chemical)
50 parts, 0.2 parts of Rose Bergal (product name: N164, manufactured by Dainippon Ink Co., Ltd.), 0.5 parts of methanol, n-
It was added to a solution consisting of 50 parts of heptane and dispersed for 20 minutes using a homogenizer. This was taken out by suction filtration and thoroughly dried at 80°C to obtain dye-sensitized zinc oxide. Acrylic resin (product name: Acrybase CMZ-20, manufactured by Fujikura Kasei, solid content 40%) with 30 parts of this zinc oxide
12 parts and 45 parts of toluene were added, and the mixture was dispersed in a ball mill for 4 hours. The dispersion was coated on the undercoat layer to form a 22 μm thick photosensitive layer, and thoroughly dried at 80°C. Then on top of this, add a weight average molecular weight of about 12
10,000, an acrylic resin emulsion (trade name: Aron HD-11, manufactured by Toagosei Kagaku Co., Ltd.) with a glass transition temperature of 90℃ was diluted with water to a viscosity of 15 cp, coated on the photosensitive layer, dried with hot air at 70℃, Creates a thick protective layer. This photosensitive drum is charged with -5.5KV, exposed to image, developed with dry toner, transferred to plain paper, and then transferred to a thickness of 1.
mm, hardness 70° urethane rubber blade at an angle of 30°,
It was used in a copying machine where the blade is cleaned by pressing at a pressure of 4 gw/cm. When copying images, the photosensitive drum using Sample A produced good quality images in all environments, but the photosensitive drum using Sample B showed fogging in low humidity, and the photosensitive drum using Sample C showed good quality. With the photosensitive drum used, fine spots were seen throughout the image. In addition, when a photoreceptor was prepared by coating the photosensitive layer directly onto the substrate without forming an undercoat layer, when an entire black image was taken, numerous white spots were generated and the image was not a normal image. As described above, the image of the undercoat layer of the present invention was the best. Example 2 10 parts of titanium oxide powder (manufactured by Titan Kogyo Co., Ltd.), 7 parts of tin oxide powder (manufactured by Mitsubishi Metals Co., Ltd.), acrylic resin (trade name: Acrydik A405, Dainippon Ink Co., Ltd.)
(manufactured by Dainippon Ink Co., Ltd.), 4 parts of melamine resin (trade name: Super Betsucomin L121, manufactured by Dainippon Ink Co., Ltd.), and 20 parts of toluene were dispersed in a ball mill for 6 hours. This dispersion was applied to an 80φ x 300mm aluminum cylinder and cured at 150℃ for 30 minutes.
A 10μ thick undercoat layer was formed. On top of this, polyamide resin (product name: Amilan
A 4% methanol solution (CM8000, manufactured by Toray Industries, Inc.) was applied to form a 0.6μ thick resin layer. Next, add 10 parts of the disazo pigment with the following structural formula. Cellulose acetate butyrate resin (product name: CAB-381;
(manufactured by Eastman Chemical) and 60 parts of cyclohexanone were dispersed for 20 hours using a sand mill device using 1φ glass beads. Add 100 parts of methyl ethyl ketone to this dispersion, soak it on the undercoat layer, heat dry at 100°C for 10 minutes, and get 0.1 g/m ^{3 .}
A charge generation layer was formed with a coating amount of . Next, add 10 parts of a hydrazone compound having the following structural formula. and 12 parts of styrene-methyl methacrylate copolymer resin (trade name: MS-200, manufactured by Steel Chemical Co., Ltd.) were dissolved in 70 parts of toluene, and the solution was coated on the charge generation layer.
It was dried at ℃ for 60 minutes to form a charge transport layer with a thickness of 16μ. When the electrophotographic photoreceptor produced in this manner was installed in a copying machine, good quality copy images were obtained. Comparative Examples 3 to 9 16 parts of the metal oxide shown in Table 3, 16 parts of one-component epoxy resin (product name: U33, manufactured by Amicon Japan) (solid content concentration 50% by weight), and 30 parts of toluene were mixed using a ball mill. Dispersed for 6 hours.

[Table] After applying each of the obtained dispersions onto a 50μ thick aluminum sheet using a Mayer bar, the mixture was heated at 150°C.
was heated for 30 minutes to cure and form an undercoat layer with a thickness of 10 μm. For these sheets, normal temperature and humidity (25℃, 60℃
%RH) and in a low temperature and low humidity environment (15°C, 10%RH). In addition, the surface roughness of the formed coating film was measured. The results are shown in Table 4.

【table】

[Table] As shown above, samples D, E, G, H, and I had a large resistance at low humidity, and samples F and G had a large surface roughness. The sample using Sample J had a small increase in resistance at low humidity and also had a small surface roughness. Next, in the same manner as in Example 1, each sample was coated as an undercoat layer on an aluminum cylinder, and a photosensitive layer and a protective layer were provided on the undercoat layer to obtain seven types of photoreceptors. These photoreceptors were evaluated in the same manner as in Example 1, but fogging was observed in the photoreceptors using Samples D, E, G, and H at low humidity, and fogging was observed in the photoreceptors using Samples F, I, and J. In the case of the photoreceptor, fine spots were seen throughout the image.

Claims (1)

[Claims] 1. An electrophotographic photoreceptor having an undercoat layer and a photosensitive layer on a substrate, wherein the undercoat layer is a resin layer in which titanium oxide powder and tin oxide powder are dispersed.