JPH0217105B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an electrophotographic photoreceptor, particularly an electrophotographic photoreceptor containing zinc oxide as a photoconductive substance. Conventionally, photoconductive materials such as amorphous selenium alloys, zinc oxide, cadmium sulfide, and organic photoconductors (OPCs) have been used in electrophotographic photoreceptors.
Among these, photoreceptors using zinc oxide have the following advantages: the raw material and photoreceptor are non-toxic, they are inexpensive, they can be manufactured using traditional coating technology, they can be easily made into large areas, and their image quality is good. It has a number of features, including the ability to control color sensitivity. Furthermore, in recent years, the reactivity and contamination of chemical substances to living organisms and the environment have become a problem, and photoreceptors are no exception to this. Among the photoreceptors currently in practical use, only zinc oxide has been confirmed to be non-polluting, including its raw materials, and from this point of view, zinc oxide photoreceptors have recently been actively reevaluated. Now, the problems with conventional zinc oxide photoreceptors include the following. 1) The repeat durability is 500 to 2,500 sheets, which is short compared to other photoreceptors. 2) Difficulty in compatibility with the blade cleaning mechanism. 3) There is an induction effect during photodischarge, and the photosensitivity is slow. 4) Photoresponsiveness in positive charging mode is slow, and residual potential increases significantly with repeated use. In view of the above circumstances, the present applicant has aimed to provide a zinc oxide photoreceptor that has improved repeated durability, has high photoresponsiveness to both positive and negative polarities, and is also compatible with a blade cleaning mechanism. After extensive research, it was discovered that the above object can be achieved by simultaneously containing a specific binder polymer and a low-molecular organic compound having a specific structure together with zinc oxide in the photoconductive layer.The present invention has been made. I have come to the conclusion. That is, the object of the present invention described above is to deposit zinc oxide, general formula () on a conductive support. [However, in the formula, R ₁ and R ₃ may be the same or different and represent a hydrogen atom, an alkyl group, an alkenyl group, an aryl group, or an aralkyl group, and R ₂ and R ₄ are the same or different and The heterocyclic group often represents a phenyl group or a naphthyl group containing at least one nitrogen atom, which groups may be substituted with an alkyl group, an alkenyl group, an alkoxy group or a halogen, and in addition at least one of these groups. is an electron-donating group

[Formula] (However, R ₅ and R ₆ may be the same or different and represent a substituted or unsubstituted alkyl group, phenyl group, aryl group, or aralkyl group, and may form a heterocycle with the nitrogen atom. azine compounds and polycarbonates and/or polycarbonates of the general formula This was achieved by an electrophotographic photoreceptor comprising a photoconductive dispersion layer containing a thermoplastic aromatic polyarylate (where n is an integer from 20 to 200). The present invention will be explained in detail below. The applicant has conducted a detailed study on using various polymers with film-forming ability as a matrix and using a composition in which a low-molecular-weight organic compound is uniformly dispersed in molecular form as a binder for a zinc oxide photoreceptor. As a result, a composition in which a polycarbonate and/or a polyarylate represented by the above general formula () is used as a polymer matrix, and an azine compound represented by the above general formula () is uniformly dispersed in molecular form, is used as zinc oxide. It has been discovered that when a photoreceptor is prepared using a binder for zinc oxide, practical electrophotographic properties are maintained even when the blending ratio of binder to zinc oxide is 100% by weight or more. This finding was not foreseen in conventional electrophotographic photoreceptor technology, that is, photoreceptor technology that has a photoconductive layer in which zinc oxide powder is dispersed in a paint resin binder such as acrylic resin or silicone resin. . In conventional zinc oxide photoreceptors, the blending ratio of binder to zinc oxide is limited to a certain range. For example, if the blending ratio of the binder to zinc oxide is 10% by weight, sufficient charging ability will not be obtained and the repeated durability will be significantly reduced. On the other hand, if this blending ratio exceeds 50% by weight, the mechanical, electrical and chemical durability during repeated use will improve, but the photoresponsiveness will drop significantly. The residual potential increases with repeated use. For this reason, in conventional zinc oxide photoreceptors, the ratio of binder to zinc oxide is approximately 10
It was limited to a range of ~50% by weight. In the present invention, the azine compound used by dispersing molecules of polycarbonate and/or polyarylate as a polymer matrix, which will be described later, is represented by the general formula (). Symmetrical and asymmetric azines represented by the general formula () are, for example, Houben-Weyl, Methoden ber
Organischen Chemib, 4th edition, 10/2 volumes, 89~
111 pages, Georg Thieme Verlag Publishing, 1967
Related compounds can be synthesized by commonly known methods such as those described in 1996. Among the compounds represented by the general formula (), specific examples suitable for the electrophotographic photoreceptor of the present invention are listed below. The zinc oxide used in the present invention may be any of the known zinc oxides conventionally used in electrophotographic photoreceptors. In addition, zinc oxide, which has conventionally been considered undesirable as a photoreceptor, can also be applied to the present invention. For example, zinc oxide with a specific surface area of 2 m ² /g or less, a specific surface area of about 8
Zinc oxide having a particle size of m ² /g or more or acicular zinc oxide is suitable for the present invention. In particular, the present invention is characterized in that the electrophotographic properties of the photoreceptor are further improved by selecting zinc oxides having different properties. For example, by using zinc oxide having a specific surface area of about 8 m ² /g or more or acicular zinc oxide, the photoresponsiveness and repeatability in the positive charging mode are further improved. On the other hand, zinc oxide having a specific surface area of about 2 m ² /g or less, preferably doped with metal atoms selected from the group consisting of lithium, sodium, ^potassium , and copper. By using this, the photoresponsiveness and repetition characteristics in the negative charging mode are further improved. In the present invention, it is desirable that zinc oxide be dye-sensitized. Suitable dye sensitizers include fluorescein, dichlorofluorescein, dibromofluorescein, diiodofluorescein, tetrachlorfluorescein, tetrabromofluorescein, tetraiodofluorescein, tetrachlortetrabromofluorescein, tetrachlortetraiodofluorescein, tetrabromtetraiodo Xanthene dyes such as fluorescein, bromophenol blue, tetrabromophenol blue, tetrabromophenol blue,
Phenolsulfophthalein dyes such as tetraiodophenol blue, bromthymol blue, bromcresol purple, bromcresol green, thiazine dyes such as methylene blue, triphenylmethane dyes such as crystal violet and malachite green, acridine yellow, acridine Acridine dyes such as orange, which are conventionally used in zinc oxide photoreceptors, can be used as they are. Although the amount of these dye sensitizers added varies depending on the specific surface area of zinc oxide, it is generally appropriate to use them in an amount in the range of 0.01 to 10 parts by weight per 100 parts by weight of zinc oxide. Conventionally known techniques can be used to sensitize zinc oxide using a dye sensitizer. For example, 1) a method in which a dye sensitizer solution and zinc oxide are mixed, the dye sensitizer is adsorbed onto the surface of the zinc oxide, and then the solution containing the unadsorbed dye sensitizer is removed. 2) After mixing the dye sensitizer and zinc oxide and adsorbing the dye sensitizer on the surface of the zinc oxide, the binder solution is mixed without removing the solution containing the unadsorbed dye sensitizer. A method of preparing a charge generation layer coating solution by adding 3)
A method of simultaneously adding a dye sensitizer solution, zinc oxide and a binder solution and mixing and dispersing them is also effective. The dye sensitizer is dissolved in a suitable solvent, and a coating solution in which zinc oxide is added to this dye solution is sufficiently mixed and dispersed in a ball mill etc. to adsorb the dye sensitizer on the surface of the zinc oxide. The solution containing the dye sensitizer is removed and the dyed zinc oxide cake is dried to produce zinc oxide powder previously dyed with the dye sensitizer (hereinafter abbreviated as yarn-dyed zinc oxide powder).
The method for preparing is a suitable dye sensitization method for the present invention. As a method for removing the solution containing the unadsorbed dye sensitizer, filtration, heat drying, freeze drying, spray drying, or the technique disclosed in Japanese Patent Publication No. 39819/1986 are all effective. The polycarbonate used as a matrix component of the binder in the electrophotographic photoreceptor of the present invention is a polyester having a carbonate type structure in its structural unit, and is produced by a transesterification method, a phosgene method, a self-polycondensation reaction, etc. Polymers having the following repeating units are particularly useful. Here, R represents an unsubstituted phenylene group, a halogen-substituted phenylene group, or an alkyl-substituted phenylene group, and R ₁ and R ₂ are each a hydrogen atom, a substituted or unsubstituted alkyl group, or a substituted or unsubstituted aryl group. represents a group. Further R ₁ and
R ₂ may be cyclized with each other to form a saturated or unsaturated hydrocarbon ring having 3 to 19 carbon atoms.
Specific examples suitable for the present invention are listed below. B1 Poly(4.4′-dioxydiphenyl carbonate) B2 Poly(4.4′-dioxydiphenylmethane carbonate) B3 Poly(4.4′-dioxydiphenyl-1.1-ethane carbonate) B4 Poly(4.4′-dioxydiphenyl methane carbonate) enyl-1.2-ethane carbonate) B5 Poly(4.4′-dioxydiphenyl-2.2-propane carbonate) B6 Poly(4.4′-dioxydiphenyl-1.1-butane polycarbonate) B7 Poly(4.4′-dioxydiphenyl-2.2-propane carbonate) 2.2-butane polycarbonate) B8 Poly(4.4'-dioxydiphenyl-1.1-isobutane polycarbonate) B9 Poly(4.4'-dioxydiphenyl-1.1-cyclohexane polycarbonate) B10 Poly(4.4'-dioxy-2.2'-dimethyl diphenyl) enyl-2,2-propane carbonate) The thermoplastic aromatic polyarylate used together with or in place of the polycarbonate in the electrophotographic photoreceptor of the present invention is represented by the general formula () as described above. (However, n is an integer from 20 to 200.) This polymer can be used, for example, with 2.2-bis(4-hydroxyphenyl)propane or bis(4-hydroxyphenyl)methane and phthalic acid such as phthalic acid, isophthalic acid, and terephthalic acid. Perform interfacial condensation polymerization with acid chloride of acids in the presence of alkali, or 2.2-bis(4-hydroxyphenyl)propane or 2.2-bis(4-hydroxyphenyl)propane.
It can be easily obtained by known synthesis methods such as melt polymerization of -bis(4-hydroxyphenyl)methane and esters of phthalic acids. Preferred polyarylates for the present invention are as shown below. B11 Poly-2.2-propane bis(4-phenyl isophthalic acid-terephthalic acid coester) B12 Poly-2.2-propane bis(4-phenyl terephthalic acid ester) B13 Poly-2.2-propane bis(3.5-dichloro-4-phenyl isophthalic acid-terephthalic acid coester) B14 Poly-methanebis(4-phenylisophthalic acid-terephthalic acid coester) The blending ratio of the azine compound represented by the general formula () to zinc oxide is 5 parts by weight or more per 100 parts by weight of zinc oxide. is required, preferably 20 parts by weight or more. The blending ratio of polycarbonate and/or thermoplastic aromatic polyarylate to zinc oxide is 5 to 100 parts by weight of zinc oxide.
It is used in an amount of 400 parts by weight, but from the viewpoint of the mechanical strength and repeated durability of the photoreceptor, it is preferably 50 parts by weight or more. Further, when a mixture of polycarbonate and thermoplastic aromatic polyarylate is used as a binder in the photoconductive layer, it can be used in any mixing ratio. The electrophotographic photoreceptor of the present invention is preferably prepared by ball milling a mixture consisting of dye-sensitized zinc oxide powder, an azine compound represented by the general formula (), polycarbonate and/or the above-mentioned thermoplastic aromatic polyarylate, and a dispersion solvent. Uniformly mixed and dispersed using a dispersing machine such as an attritor, sand mill, Keday mill, three-roll mill, etc., this photoconductive layer coating liquid can be applied to blade coating, reverse coating, rod coating, gravure coating, knife coating, Coating on a conductive support using a coating method such as a spray coating method,
Created by drying. The appropriate thickness of the photoconductive layer is 5 to 100 μm, preferably 10 to 100 μm.
It is 50μm. Dispersion solvents used for preparing the photoconductive layer coating solution include aromatic hydrocarbons such as benzene, toluene, and xylene, methylene chloride, chloroform, 1.1-dichloroethane, 1.2-dichloroethane, 1.1.2-trichloroethane, and 1.1.2.2- Examples include halogenated hydrocarbons such as tetrachloroethane and chlorobenzene, and cyclic ethers such as tetrahydrofuran and 1,4-dioxane. In preparing the photoconductive layer coating liquid, it is desirable to dissolve the azine compound represented by the general formula () and the polycarbonate and/or thermoplastic aromatic polyarylate in a dispersion solvent in advance. Conductive supports suitable for the present invention include metals such as aluminum, nickel, chromium, and palladium, and oxides such as tin oxide and indium oxide, on paper, plastic film, glass, etc., by vapor deposition, ion plating, or sputtering. It is possible to use materials such as those made by laminating metal foil such as aluminum with paper or plastic film, carbon-containing paper, paper or plastic film treated with an organic or inorganic conductive treatment agent, etc. Further, regarding its shape, it may be sheet-like, cylinder-like, or other shapes. In the present invention, an intermediate layer can be provided between the conductive support and the photoconductive layer. This intermediate layer prevents the injection of free carriers from the conductive support into the photoconductive layer and acts as an adhesive layer to hold the photoconductive layer integrally adhesively attached to the conductive support. Furthermore, it also has a buffering effect to prevent dielectric breakdown of the photoconductive layer due to corona discharge overcurrent during corona charging. Materials for this intermediate layer include aqueous polymers such as gelatin, casein, starch, polyvinyl alcohol, polyvinylpyrrolidone, carboxymethyl cellulose, hydroxypropyl cellulose, water-soluble polyvinyl butyral, polyacrylic acid, polyethyleneimine, polyethylene glycol, and polypropylene glycol. Substances can be used. The thickness of the middle layer is
A range of 0.5 to 10 μm is suitable. The electrophotographic photoreceptor of the present invention has the above structure and has the following features compared to conventional zinc oxide photoreceptors. 1 A composition containing an azine compound () in a molecularly dispersed state in polycarbonate and/or thermoplastic polyarylate is used as a binder for zinc oxide, and has practical charging ability and photoresponsiveness for both positive and negative polarities. In particular, since the induction period during photodischarge disappears, the photoresponsiveness is significantly improved. 2. A composition containing an azine compound () in a molecularly dispersed state in polycarbonate and/or thermoplastic polyarylate is used as a binder for zinc oxide, and even if the blending ratio of the binder to zinc oxide is sufficiently high, Retains practical electrophotographic properties. Therefore, the repeated durability is significantly improved, and the surface smoothness and mechanical strength of the surface are excellent, so that it can be adapted to a blade cleaning mechanism. Therefore, the electrophotographic photoreceptor of the present invention can be applied to a PPC type electrophotographic copying machine, and in particular can be applied to any electrophotographic copying machine using the Carlson type without being limited to charging polarity. It is also suitable as a photosensitive medium for PPC microfilm readers that produce copies from negative and positive microfilms. EXAMPLES Next, the present invention will be described in more detail with reference to Examples, but the embodiments of the present invention are not limited thereby. Note that the specific surface area of the zinc oxide powder used in the following examples was previously measured. A specific surface area automatic analyzer (SS-2200 manufactured by Shimadzu Micromeritechs) was used for specific surface area measurement. The degassing conditions for the sample were 250 to 300°C for 30 minutes. Example 1 Preparation of yarn-dyed zinc oxide 0.4 parts by weight of tetrachlortetraiodofluorescein is dissolved in 100 parts by weight of tetrahydrofuran. Next, 100% of zinc oxide Sazetx 2000 (manufactured by Sakai Chemical Industry Co., Ltd., specific surface area: 39 m ² /g) was added to this dye sensitizer solution.
Add parts by weight and disperse and mix for 3 hours using a porcelain ball mill. Transfer the resulting coating liquid to a beaker and stir while maintaining the coating liquid temperature at 80°C to completely evaporate the tetrahydrofuran. Thus, a zinc oxide powder dyed with tetrachlortetraiodofluorescein was prepared. Preparation and evaluation of photoreceptor Water-soluble polyvinyl butyral (Eslec W201,
A 10% aqueous solution (manufactured by Sekisui Chemical Co., Ltd.) was applied using the blade coating method, and dried at 110°C for 1 minute to determine the thickness.
Provide an intermediate layer of 1 μm. On the other hand, 10 parts by weight of polycarbonate resin (Panlite L-1225 manufactured by Teijin Kasei Ltd.) was dissolved in 100 parts by weight of 1,2-dichloroethane,
Thereafter, 10 parts by weight of the exemplary compound represented by CA-2 is added and completely dissolved. Next, 10 parts by weight of the yarn-dyed zinc oxide is added to this solution, and the mixture is dispersed in a porcelain ball mill for 10 hours. The resulting coating solution is applied onto the above-mentioned intermediate layer by a blade coating method and dried at 110°C for 10 minutes. The thickness of the photoconductive layer formed was 28 μm. The electrophotographic properties of the thus obtained electrophotographic photoreceptor were evaluated using an electrostatic copying paper tester (Model SP-428, manufactured by Kawaguchi Denki Seisakusho Co., Ltd.). Attach the sample to the test equipment, corona discharge voltage ±6kV, scanning speed
Charged at 250mm/sec, the potential Vo immediately after charging
Measure [V]. After dark decaying for 5 seconds (potential V ₅ [V]), the surface potential was irradiated with tungsten light with a color temperature of 2854 K° and an illuminance of 2 lux.
The exposure amount required to attenuate to V ₅ /2 [V], that is, the half-decreased exposure amount E1/2 [lux seconds] is defined as the photosensitivity,
20 [lux seconds] The potential after irradiation is the residual potential V _R
It was recorded as [V]. Table 1 shows the results of repeated measurements 1000 times.

[Table] As is clear from the above results, the electrophotographic photoreceptor of the present invention exhibits excellent electrophotographic properties. Example 2 In place of exemplified compound CA-2 in Example 1,
Electrophotographic photoreceptors 2-1 to 2-5 of this example were prepared using the compounds listed in Table 2 and according to the procedure of Example 1. The resulting photoreceptor was evaluated according to the procedure of Example 1. The results are shown in Table 2.

[Table] As is clear from the above results, all the electrophotographic photoreceptors of this example exhibited excellent electrophotographic properties. Example 3 In Example 1, thermoplastic aromatic polyarylate U100 (manufactured by Unitika Co., Ltd., structural formula B11) or polycarbonate L-
Electrophotographic photoreceptors 3-1 and 3-2 of this example were prepared using a mixture of equal weights of 1225 and polyarylate U100 according to the procedure of Example 1, and the characteristics of the photoreceptors were evaluated. The results are shown in Table 3.

[Table] As is clear from the above results, all the electrophotographic photoreceptors of this example exhibited excellent electrophotographic properties. Example 4 The procedure of Example 1 was repeated except that the zinc oxide in Example 1 was replaced with fine zinc white (manufactured by Sakai Chemical Industry Co., Ltd., specific surface area: 9.64 m ² /g) and the amount of dye sensitizer added was 1.0 parts by weight. Yarn-dyed zinc oxide powder and an electrophotographic photoreceptor were prepared according to the procedure, and the characteristics of the photoreceptor were evaluated. The results are shown in Table 4.

[Table] As is clear from the above results, in the electrophotographic photoreceptor of this example, the photoresponsivity and repeatability in the positive charging mode were significantly improved. Example 5 Preparation of zinc oxide powder doped with lithium 100 parts by weight of zinc oxide (Sazetsu 2000, Sakai Chemical Industry Co., Ltd. Co., Ltd.)
and disperse the mixture in a ball mill for 2 hours. Transfer the resulting paste to a beaker and boil for 110 minutes.
Stir while heating at ℃ to sufficiently evaporate water and obtain a zinc oxide cake. This cake was placed in a Matsufuru furnace and heated at 600°C for 5 hours while flowing dry air at a flow rate of 100 ml/min. After the treatment, the zinc oxide is cooled and ground gently for 30 minutes using an Ishikawa grinder to form a lithium-doped product with a specific surface area value of 1.7.
m ² /g of zinc oxide powder was obtained. Preparation of photoreceptor and evaluation of photoreceptor properties Pre-dyed zinc oxide was prepared according to the procedure of Example 1, except that the above lithium-doped zinc oxide was used and the amount of dye sensitizer added was changed to 0.2 parts by weight. A photoreceptor was prepared and its electrophotographic properties were evaluated. The results are shown in Table 5.

[Table] As is clear from the above results, in the electrophotographic photoreceptor of this example, the photoresponsivity and repeatability in the negative charging mode were significantly improved. Example 6 In photoreceptor sample 2-2 of Example 2, the support was replaced with an aluminum cylinder, the dipping method was used as the coating method, and the drying time after coating the photoconductive layer was 140
Two electrophotographic photoreceptor drums of this example were prepared according to the procedure of Example 2, except that the heating time was 10 minutes at ℃. This drum is loaded into a PPC copying machine that has a blade cleaning mechanism and can select charge polarity, and the initial surface potential due to positive charging is set to +500V.Charging - Image exposure - Two-component dry development - Ordinary transfer - A.C.
A running test was conducted by repeating the process of static elimination and blade cleaning. Result 10000
No changes in sensitivity or image quality were observed up to cycling. Next, the drum was replaced, the surface potential was set to -500V using a negative charging process, and a running test was performed using the same procedure as above. As a result, no change in sensitivity or image quality was observed up to 10,000 cycles. Comparative Example 1 Compound represented by the following formula in place of exemplified compound CA-2 in Example 1 An electrophotographic photoreceptor of this comparative example was prepared in the same manner as in Example 1 except that the electrophotographic photoreceptor was used, and its electrophotographic properties were evaluated. The results are shown in Table 6.

[Table] As is clear from the above results, a sufficient charging potential could not be obtained with the electrophotographic photoreceptor of this comparative example. Comparative Example 2 The procedure of Example 1 was followed except that vinyl chloride-vinyl acetate-maleic anhydride copolymer (VMCA, manufactured by Union Carbide Company, USA) was used instead of polycarbonate in Example 1. An electrophotographic photoreceptor was prepared and its electrophotographic properties were evaluated. The results are shown in Table 7.

[Table] As is clear from the above results, the electrophotographic photoreceptor of this comparative example did not have sufficient photoresponsiveness.

Claims (1)

[Claims] 1 Zinc oxide on a conductive support, general formula () [However, in the formula, R ₁ and R ₃ may be the same or different and represent a hydrogen atom, an alkyl group, an alkenyl group, an aryl group, or an aralkyl group, and R ₂ and R ₄ are the same or different and Heterocyclic groups often containing at least one nitrogen atom,
It represents a phenyl group or a naphthyl group, and these groups may be substituted with an alkyl group, an alkenyl group, an alkoxy group, or a halogen, and furthermore, at least one of these groups is an electron-donating group [Formula] (However, R ₅ and R ₆ may be the same or different from each other and represent a substituted or unsubstituted alkyl group, phenyl group, aryl group or aralkyl group,
may form a heterocycle with the nitrogen atom, or may be part of a fused heterocyclic ring system)
] and polycarbonate and/or general formula () An electrophotographic photoreceptor comprising a photoconductive dispersion layer containing a thermoplastic aromatic polyarylate (where n is an integer from 20 to 200).