JPH0429061B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a positively charged electrophotographic photoreceptor having a protective layer on its surface. (Prior art) In electrophotographic photoreceptors that use photoconductive substances as photosensitive materials, inorganic photoconductive substances such as selenium, zinc oxide, titanium oxide, and cadmium sulfide have conventionally been used as the main photoconductive substances. It has been used in However, many of these are generally highly toxic and there are problems with how to dispose of them. On the other hand, photosensitive materials that use organic photoconductive compounds are generally less toxic than those that use inorganic photoconductive substances, and also have superior transparency, flexibility, lightness, surface smoothness, price, etc. Since it is advantageous in terms of, it has been widely studied and put into practical use in recent years. Among them, composite photoreceptors that separate the functions of charge generation and transport have been rapidly increasing in recent years because they can significantly improve sensitivity, which was a major drawback of conventional photoreceptors using organic photoconductive compounds. progress is being made. When these composite photoreceptors are applied to an electrophotographic device using the Carlson method, an electrostatic latent image is first formed on the surface of the photoreceptor, and then developed with a developer commonly called a toner that is charged with opposite signs. The toner image can be transferred and fixed to another substrate, such as paper, to obtain a copy. (Problems to be Solved by the Invention) Conventional electrophotographic photoreceptors using organic photoconductive compounds generally have a charge generation layer and a hole transfer type charge transport layer laminated in sequence on a conductive layer. , the surface of the photoreceptor is negatively charged. When negatively charged by corona discharge, more ozone is generated than when positively charged, and charging tends to be uneven.
In this regard, if possible, a photoreceptor that functions with a positive charge,
That is, a positively charged electrophotographic photoreceptor is desirable. Furthermore, in the electrophotographic apparatus described above, it is necessary to remove (clean) the toner remaining on the surface of the photoreceptor using a brush or blade, and by repeating the steps of development, transfer, and cleaning, the photoreceptor is cleaned. The problem is that the surface is worn and damaged, resulting in blurred transferred images and a significantly shortened photoreceptor life. Therefore, the photoreceptor needs to have strong durability. As described above, the demand for electrophotographic photoreceptors that can be used with positive charging and have high durability has been rapidly increasing in recent years. Positive charging type electrophotographic photoreceptors include (1) a photoreceptor in which a charge-generating layer and a charge-transporting layer containing an electron-accepting charge-transporting substance are sequentially laminated on a conductive layer, and (2) an electron-donating photoreceptor on a conductive layer. (3) A photosensitive layer consisting of a single layer of a charge-generating material or a mixture of a charge-generating material and a charge-transporting material on a conductive layer. Although there are photoreceptors equipped with a photoreceptor (in this case exhibiting both positive and negative chargeability), the durability of these photoreceptors is not yet sufficient at present. Therefore, it is considered to provide a protective layer on the surface in order to improve durability. However, when thermoplastic resin is used as in conventional protective layers, the effect of improving wear resistance is not sufficient, and when thermosetting resin is used, high temperature and long curing reactions are required when forming the protective layer. During this time, the underlying photosensitive layer will undergo thermal deterioration, resulting in a decline in electrophotographic properties.Furthermore, if the thickness of the protective layer is increased even slightly to improve wear resistance, the electrophotographic properties may deteriorate.
In particular, there is a need for the development of a protective layer for positively charged electrophotographic photoreceptors that has high abrasion resistance and does not impair electrophotographic properties, since it tends to cause an increase in residual potential and a decrease in sensitivity. Therefore, it is an object of the present invention to provide a positively charged electrophotographic photoreceptor that satisfies the above requirements and has excellent electrophotographic properties and durability. (Means for Solving the Problems) The present invention provides an electrophotographic photoreceptor that can function with positive charging, on the surface of which (a) the number average molecular weight is 1500 or less, and the number of formaldehyde bound per melamine nucleus is 2; -4 butyl etherified melamine/formaldehyde resin having 1 to 2 methylol groups, (b) polyvinyl acetal resin, and (c) cured film of electron-accepting carboxylic acid compound and/or electron-accepting polycarboxylic acid anhydride. The present invention relates to a positively charged electrophotographic photoreceptor having a protective layer containing. The positively charged electrophotographic photoreceptor according to the present invention is formed by sequentially laminating a photoconductive layer and the above-mentioned protective layer on a conductive layer. The conductive layer of the present invention is a conductive material such as a conductive treated paper or plastic film, a plastic film laminated with a metal foil such as aluminum, a metal plate or a metal drum made of a conductive metal such as aluminum. The photoconductive layer of the present invention can itself function with positive charge, and even if it functions as a single layer, it is composed of a layer mainly having a charge generation function and a layer mainly having a charge transport function. A functionally separated composite photoconductive layer may also be used. Below, aspects of the photoconductive layer of the present invention will be explained. (1) An example of the photoconductive layer of the present invention includes a charge-generating layer containing an organic pigment that generates a charge and a charge-transporting layer containing an electron-accepting charge-transporting substance.
It is laminated on top of a conductive layer. Organic pigments that generate charges and are included in the charge generation layer include azoxybenzene, disazo, trisazo, benzimidazole, polycyclic quinoline, indigoid, quinacridone, phthalocyanine, perylene, and methine. Pigments known to generate charges such as can be used. These pigments are described, for example, in JP-A-47-37453, JP-A-47-37544, JP-A-47
−18543, JP-A No. 18544, JP-A-48-
No. 43942, JP-A-48-70538, JP-A-49-1231
No., JP-A-49-105536, JP-A-50-75214,
It is disclosed in Japanese Patent Application Laid-Open No. 50-92738.
In particular, τ, which is described in Japanese Patent Application Laid-Open No. 58-182640 and European Patent Application Publication No.
τ′, η, and η′ type metal-free phthalocyanines have high sensitivity even to long wavelengths, and are also effective as electrophotographic photoreceptors for printers equipped with diode lasers. In addition to these, any organic pigment that generates charge carriers upon irradiation with light can be used. Further, additives such as a binder, a plasticizer, a fluidity imparting agent, a pinhole suppressing agent, etc., which are commonly used in electrophotographic photoreceptors, may be used in the charge generation layer, if necessary. Examples of the binder include silicone resin, polyamide resin, polyurethane resin, polyester resin, epoxy resin, polyketone resin, polycarbonate resin, polystyrene resin, polymethyl methacrylate resin, and polyacrylamide resin. Also, heat and/or
Alternatively, a photocurable resin can also be used. In any case, there is no particular restriction as long as the resin is electrically insulating and can form a film under normal conditions. In the charge generation layer,
The binder is used in an amount of 300% by weight or less based on the organic pigment. If it exceeds 300% by weight, electrophotographic properties will deteriorate. Examples of the plasticizer include halogenated paraffin, dimethylnaphthalene, and dibutyl phthalate. As fluidity imparting agents, Modaflow (manufactured by Monsanto Chemical Company), Acronal 4F
(manufactured by BASF Corporation), and examples of pinhole suppressants include benzoin and dimethyl phthalate. Each of these is preferably used in an amount of 5% by weight or less based on the organic pigment. The electron-accepting charge-transporting substance used in the charge-transporting layer has an electron-transporting function, and specifically includes fluorene, fluorenone, 2,7
-dinitro-9-fluorenone, 2,4,7-
Trinitro-9-fluorenone, 4H-indeno(1,2,6)thiophen-4-one, 3,
7-dinitro-dibenzothiophene-5-oxide, tetrachlorophthalic anhydride, 2,5-
Dichloro-1,4-benzoquinone, 2,6-dichloro-1,4-benzoquinone, 2,3,5,
6-tetrachloro-1,4-benzoquinone, anthraquinone, 2-chloroanthraquinone,
1,8-dichloroanthraquinone, 1,5-dichloroanthraquinone, 1,2,5,8-tetrahydroxyanthraquinone, 2-methylanthraquinone, 1,4-naphthoquinone, 2,3-
Dichloro-1,4-naphthoquinone, 2,3,5
-Trichlor-1,4-naphthoquinone, 2,3
-dichloro-5-bromo-1,4-naphthoquinone, 2-nitro-3-methyl-1,4-naphthoquinone, 2,3-dibrom-5-methyl-1,
Electron-accepting compounds such as 4-naphthoquinone, 2,3-dibrom-5-ethyl-1,4-naphthoquinone, tetracyanoethylene, trinitrobenzene, tetracyanoquinodimethane, and derivatives thereof. The charge transport layer also contains the same binder as the charge generation layer.
A plasticizer, fluidity imparting agent, pinhole inhibitor, etc. can be used as necessary. Among these, the binder is preferably 400% by weight or less based on the charge transporting substance so as not to deteriorate the electrophotographic properties.
For low-molecular charge-transporting substances, the amount is preferably 50% by weight or more in view of film properties. The amount of other additives is preferably 5% by weight or less based on the charge transporting substance. In this embodiment of the photoconductive layer, a charge transport layer containing an electron-donating charge transport material may be deposited immediately below the charge generating layer. Here, the electron-donating charge-transporting substance has a hole-transporting function, and specifically includes a polymer compound such as poly-N-vinylcarbazole, polyvinylpyrene, polyvinylpyrazoline, etc.
Carbazole, 3-phenylcarbazole, 2
-phenylindole, oxadiazole, 1
-Phenyl-3-(4-diethylaminostyryl)-5-(4-diethylaminophenyl)pyrazoline, hydrazone, 2-phenyl-4-(4
-diethylaminophenyl)-5-phenyloxazole, triphenylamine, imidazole, and other electron-donating compounds such as derivatives thereof. This charge transport layer includes
Additives such as the above-mentioned binder and plasticizer, fluidity imparting agent, pinhole inhibitor, etc. can be used in the same manner as in the case of the charge transport layer containing the above-mentioned electron-accepting charge-transporting substance. However, if the electron-donating charge-transporting substance is a polymeric compound, the binder may not be used. (2) In another example of the photoconductive layer of the present invention, a charge transport layer containing an electron-donating charge transport substance and a charge generation layer containing an organic pigment that generates charges are sequentially laminated on a conductive layer. This is what I did. Here, the electron-donating charge-transporting substance, the charge-transporting layer containing the same, the organic pigment that generates a charge, and the charge-generating layer containing the same are the same as in item (1) above. (3) Still another example of the photoconductive layer of the present invention consists of a single layer or a stack of layers containing an organic pigment that generates charge. Moreover, the layer is
It may also contain a charge transporting substance. Here, the organic pigment that generates a charge and additives such as a binder, a plasticizer, a fluidity imparting agent, and a pinhole inhibitor that may be contained in a layer containing the organic pigment are as described above.
The same materials as can be used for the charge generation layer in (1) can be used. Further, as the charge transporting substance, the electron donating charge transporting substance and/or the electron accepting charge transporting substance described in item (1) above can be used. In this example, the photoconductive layer preferably contains a binder in an amount of 100 to 900% by weight, especially 200 to 900% by weight of the charge-generating organic pigment when the organic pigment is not used together with a charge-transporting substance. Preferably, 400% by weight is used. At this time, if the amount of the binder is too large, the sensitivity of the photoreceptor tends to decrease, and if it is too small, the charging property tends to decrease. Further, in this example, when the photoconductive layer contains both an organic pigment that generates a charge and a charge transporting substance, the amount of the binder used is preferably 450% by weight or less based on the charge transporting substance; Especially 300% by weight
The following are preferred. If there is too much binder, the sensitivity of the photoreceptor tends to decrease. In addition, when the charge transport substance is a low-molecular compound, the amount of the binder used is preferably 80% by weight or more, especially
100% by weight or more is preferable. At this time, if the amount of binder is too small, the photoconductive layer will not be able to maintain sufficient strength, and the charging property will tend to decrease. Even when the charge transport substance is a polymeric compound, from the viewpoint of chargeability, it is preferable to use the binder in an amount of 80% by weight or more, particularly preferably 100% by weight or more, based on the compound. The organic pigment that generates a charge should be used in an amount of 0.1 to 20% of the total amount of the charge transport substance and binder.
Preferably, it is used in an amount of 0.5 to 5% by weight, particularly preferably 0.5 to 5% by weight. If the amount is too small, the sensitivity of the photoreceptor tends to decrease, and if it is too large, the charging property tends to decrease. Further, other additives are preferably used in the photoconductive layer in an amount ranging from 0 to 5% by weight. In the case of the photoconductive layer (1) and (2), the thickness of each of these layers is preferably 0.001 to 10 μm, especially the charge generation layer.
0.2-5 μm is preferred. The charge transport layer preferably has a thickness of 5 to 50 μm, particularly preferably 8 to 20 μm. If the thickness of the charge generation layer is less than 0.001 μm, the sensitivity tends to be poor, and if it exceeds 10 μm, the residual potential tends to increase. Also, the thickness of the charge transport layer
If the thickness is less than 5 μm, the charging property tends to be poor. If it exceeds 50 μm, sensitivity tends to decrease. The thickness of the photoconductive layer of the photoreceptor (3) is preferably 5 to 50 μm, particularly preferably 8 to 20 μm. If it is less than 5 μm, the charging property tends to be poor, and if it exceeds 50 μm, the sensitivity tends to decrease. Next, the method of forming each layer will be described. In the case of photoconductive layers (1) and (2), the charge generation layer can be formed by vacuum deposition if only an organic pigment is used;
Binders and optional additives such as acetone, methyl ethyl ketone, tetrahydrofuran, toluene,
It can also be formed by uniformly dissolving or dispersing in a solvent such as xylene, methylene chloride, trichloroethane, etc., then coating and drying. When forming a charge transport layer, the charge transport material, binder, additives, etc. are uniformly dissolved in the same solvent as for the charge generation layer, and then the layer is coated and dried. can do. In the case of the photoconductive layer (3), the charge-generating material and, if necessary, the charge-transporting substance, binder, additives, etc., are uniformly dissolved or dispersed in the same solvent as in the case of the charge-generating layer. After that, it can be applied and dried. Photoreceptors of the present invention may have a thin adhesive or barrier layer immediately above the conductive layer. Next, the protective layer will be explained. The protective layer of the present invention is mainly formed by a cured film of a specific butyl etherified melamine/formaldehyde resin, polyvinyl acetal resin, and an electron-accepting carboxylic acid compound and/or an electron-accepting polycarboxylic acid anhydride. This cured film can be obtained by curing a coating film containing these by heating. The number average molecular weight of the butyl etherified melamine/formaldehyde resin used in the present invention is
1500 or less, and if the number average molecular weight exceeds 1500, the reactivity decreases. The resin also has 2 to 4 bound formaldehydes per melamine core. 4
When the number exceeds 2, the reactivity decreases, and when the number is less than 2, the storage stability of the resin deteriorates and the cured coating film becomes brittle. Furthermore, the resin has 1 to 2 methylol groups per melamine nucleus. If the number of methylol groups exceeds 2, the storage stability of the resin will be poor and the cured coating will become brittle. Moreover, if it is less than one, the reactivity is poor. Such butyl etherified melamine/formaldehyde resin can be produced by dissolving melamine in butanol and dropping formaldehyde thereto to perform an addition reaction and butyl etherification reaction, or by dissolving melamine and formaldehyde in butanol and adding this solution. It can be produced by a method of heating and performing an addition reaction and a butyl etherification reaction. In these methods, the reaction is preferably carried out under acidic conditions, preferably at pH 3 to 6, by adding an acidic catalyst such as nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, p-toluenesulfonic acid, etc., and the reaction temperature is the reflux temperature of butanol, preferably is preferably about 90-100°C. In the present invention, 4 to 5 moles of butanol and 3 to 5 moles of formaldehyde are used per mole of melamine.
Preferably, 7 mol is used to carry out the reaction. The butyl etherified melamine/formaldehyde resin used in the protective layer of the present invention can be cured at a lower temperature than conventional melamine resins, so it does not cause thermal deterioration of the electrophotographic photoreceptor before forming the protective layer, and has excellent abrasion resistance. A highly durable protective layer can be formed. The polyvinyl acetal resin in the present invention is
Preferably, the number average molecular weight is 5000 to 250000,
It has a repeating unit of the following formula - or -. vinyl acetal group (However, R is hydrogen or an alkyl group such as a methyl group) Vinyl alcohol group vinyl acetate group The repeating units of formula ~ are 70% by weight or more of vinyl acetal group, 4 to 25% by weight of vinyl alcohol group, and 26% by weight of vinyl acetate group.
Preferably, less than % by weight of the resin is used. Among these, the ratio of the vinyl alcohol group is particularly important, and if it is less than 4% by weight, the curing reaction when forming a protective layer by heat curing in combination with the butyl etherified melamine formaldehyde resin will be slow, and the wear resistance of the protective layer will be reduced. Sex is also likely to deteriorate. Moreover, if it exceeds 25% by weight, the protective layer tends to become brittle. To describe an example of a method for producing polyvinyl acetal resin, first, vinyl acetate monomer is polymerized to synthesize polyvinyl acetate. Polyvinyl alcohol is produced by saponifying polyvinyl acetate. On this occasion,
Some vinyl acetate groups remain. Next, a polyvinyl acetal resin can be produced by adding an aldehyde such as butyraldehyde or formaldehyde to perform acetalization. To form the protective layer of the present invention, the butyl etherified melamine/formaldehyde resin and the polyvinyl acetal resin are used in a weight ratio of 95/95/
A ratio of 5 to 30/70 is preferred, and a ratio of 80/20 to 50/50 is particularly optimal. If the ratio is outside this range, the wear resistance tends to decrease. Even the cured film made of the specific butyl etherified melamine/formaldehyde resin and polyvinyl acetal resin described above has excellent abrasion resistance and cures under relatively low temperature and short curing conditions compared to conventionally known protective layers. It is possible to prevent deterioration of electrophotographic properties due to thermal deterioration of the photoconductive layer occurring therein. However, the present invention further adds the following features by using an electron-accepting carboxylic acid compound and/or an electron-accepting polycarboxylic acid anhydride. (1) Since the electron-accepting carboxylic acid compound and/or the electron-accepting polycarboxylic acid anhydride accelerate the curing reaction, the curing reaction can be completed at a lower temperature and in a shorter time. As a result, deterioration in the electrophotographic properties of the photoreceptor due to thermal deterioration of the photoconductive layer due to heating during the curing reaction can be significantly reduced. (2) Since the curing reaction is accelerated as described above, the wear resistance of the protective layer is further improved, and the life of the photoreceptor can be extended. (3) Since the above carboxylic acid and acid anhydride are electron-accepting, this property is introduced into the protective layer. As a result, electrons can be efficiently injected into the protective layer, and a decrease in sensitivity and an increase in residual potential after light irradiation can be extremely minimized. Therefore, the protective layer can be made thicker, and the life of the photoreceptor can be extended. The electron-accepting carboxylic acid compound is a compound having one or more carboxyl groups and exhibiting electron-accepting properties, and has an electron-withdrawing group such as a nitro group, a nitrile group, or a carbonyl group in the compound. You can leave it there. Specifically, butyric acid, valeric acid,
Heptanoic acid, acrylic acid, methacrylic acid, tiglic acid, succinic acid, adipic acid, glutaric acid, sebacic acid, undecanniic acid, maleic acid, glutaconic acid, propane-1,2,3-tricarboxylic acid,
Butane-1,1,4-tricarboxylic acid, pentane-1,3,3,5-tetracarboxylic acid, quinobic acid, phenylpropionic acid, phenyl acetic acid, benzoic acid, phthalic acid, isophthalic acid, terephthalic acid,
trimellitic acid, hemimellitic acid, trimesic acid, merofanic acid, pyromellitic acid, cinnamic acid,
Cinnamylidenic acid, benzyl acrylic acid, α-phenylcrotonic acid, benzalpropionic acid, biphenyl-2-carboxylic acid, diphenic acid, α-naphthoic acid, β-naphthoic acid, naphthalene-1,2-
dicarboxylic acid, naphthalic acid, naphthalene-1,
4,5-tricarboxylic acid, naphthalene-1,4,
5,8-tetracarboxylic acid, anthracene-1-
Carboxylic acid, anthracene-1,9-dicarboxylic acid, anthracene-2,3-dicarboxylic acid, phenanthrene-1-carboxylic acid, phenanthrene-
9-carboxylic acid, dibenzothiophene-1-carboxylic acid, thianaphthene-2,3-dicarboxylic acid,
perylene-3,4,9,10-tetracarboxylic acid,
3-nitroheptanoic acid, 2-nitroadipic acid,
4-nitrobenzoic acid, 2,3-dinitrobenzoic acid, 2,4,6-trinitrobenzoic acid, 3-nitrophthalic acid, 4,6-dinitroisophthalic acid,
2,6-dinitroterephthalic acid, 4-cyanobenzoic acid, 4,6-dicyanoisophthalic acid, benzophenone-2,2'-dicarboxylic acid, benzophenone-2,4,2',4'-tetracarboxylic acid, 4- Nitro-2-naphthoic acid, 8-nitro-1-naphthoic acid, anthrone-9-carboxylic acid, 2-nitro-
Anthracene-1-carboxylic acid, 2-carboxy-1,4-benzoquinone, p-benzoquinoylacetic acid, 5-carboxy-1,4-naphthoquinone, 2
Examples include -nitro-5-carboxy-1,4-naphthoquinone, 1-carboxy-anthraquinone, and 2-carboxy-4,7-dinitrofluorenone. The electron-accepting polycarboxylic acid anhydride is an acid anhydride of one of the electron-accepting carboxylic acid compounds having two or more carboxyl groups,
Specifically, succinic anhydride, glutaric anhydride, maleic anhydride, phthalic anhydride, trimellitic anhydride, pyromellitic anhydride, naphthalic anhydride, naphthalene-1,4,5-tricarboxylic acid Examples include anhydride, naphthalene-1,4,5,8-tetracarboxylic anhydride, anthracene-2,3-dicarboxylic anhydride, and 3-nitrophthalic anhydride. One or more types of the electron-accepting carboxylic acid compound and the electron-donating polycarboxylic acid anhydride are used, and the amount used is 0.1 based on the total amount of the butyl etherified melamine formaldehyde resin and the polyvinyl acetal resin. -40% by weight is preferred, particularly 1-20% by weight. If the amount used is too small, it will be difficult to exhibit the above-mentioned characteristics, and if it is too large, the moisture resistance of the protective layer will tend to decrease. The protective layer of the present invention includes (1) in the description of the photoconductive layer.
The additives described in the above may be included as appropriate. The thickness of the protective layer of the present invention is preferably 0.01 to 10 μm, particularly preferably 0.1 to 5 μm. If it is less than 0.01μm, the effect as a protective layer tends to be small;
If the value exceeds 100%, there is a tendency for the sensitivity to decrease and the residual potential to increase. To form the protective layer, the above-mentioned butyl etherified melamine/formaldehyde resin, polyvinyl acetal resin, and electron-accepting carboxylic acid compound and/or electron-accepting polycarboxylic acid anhydride,
Further, in some cases, additives may be uniformly dissolved in a solvent, and then applied onto the photoconductive layer and dried by heating. Preferably, the heating is carried out to a temperature of 90 to 140°C. When copying or printing using the electrophotographic photoreceptor according to the present invention, the surface is positively charged and exposed in the same manner as before, and then developed to form an image on a transfer material such as plain paper. All you have to do is transfer it and fix it. (Example) Next, the present invention will be described in detail based on Examples, but the present invention is not limited thereto. Each material used in the examples below is listed below. Abbreviations are shown in parentheses. (1) Organic pigment that generates charge τ-type metal-free phthalocyanine (τ-H ₂ PC) (2) Charge-transporting substance Γ Electron-accepting compound 2,3,5-trichloro-1,4-naphthoquinone Γ Electron-donating Compound 2-(p-dimethylamino)phenyl-4-
(p-dimethylamino)phenyl-5-(o-chlorophenyl)-1,3-oxazole (oxz) (3) Binder Γ Silicone varnish: KR-255 [Shin-Etsu Chemical Co., Ltd. product name] Γ Silicone Varnish: Tosgard T510 [Product name of Toshiba Silicone Co., Ltd.] Γ Polyester resin: Vylon 200 [Product name of Toyobo Co., Ltd.] (4) Material for protective layer (A) Butyl etherified melamine formaldehyde resin (BMF) (BMF- Synthesis of 1) In a flask equipped with a stirrer, a reflux condenser, and a thermometer, 126 g of melamine, 444 g of n-butanol, and
Add 0.2 g of 61% nitric acid aqueous solution and raise the temperature to 100°C, then add 169 g of paraformaldehyde at equal intervals in 6 portions over 30 minutes, then react at reflux temperature for 30 minutes, remove moisture, and heat. Solvent removal was carried out so that the residue was 50%. The resulting resin solution had a viscosity of B according to Gardner (25°C). (Synthesis of BMF-2) Using the same equipment as for the synthesis of BMF-1, 126 g of melamine, 444 g of n-butanol, and 61% nitric acid aqueous solution were prepared.
0.2 g of paraformaldehyde and 169 g of paraformaldehyde were mixed and charged, the temperature was raised to 100°C, and the mixture was reacted for 30 minutes. Thereafter, reflux dehydration was performed for 30 minutes to remove water and the solvent was removed so that the heating residue was 50%. The viscosity of the resulting resin solution was Gardner (25
It was C at ℃). (Synthesis of BMF-3) Using the same apparatus as in the synthesis of BMF-1, 217.5 g of paraformaldehyde, 444 g of n-butanol, and 126 g of melamine were weighed out, and an addition reaction was carried out at 90 to 100°C for 30 minutes. Thereafter, the mixture was cooled to 40 to 45°C, 0.1 g of phthalic acid was added, and reflux dehydration and dissolution were performed under acidic conditions. After this, the heating residue was adjusted to 50%. The viscosity at this time is (Gardner/25
℃）B. Table 1 below shows the number of formaldehyde bound, the number of buter ether groups, the number of methylol groups, and the number average molecular weight per melamine nucleus of BMF-1, BMF-2, and BMF-3. However, the number of bound formaldehyde is determined by measuring the amount of unreacted formaldehyde using the sodium sulfite method. The methylol group was determined from the above number of butyl ether groups and the NMR spectrum. Further, the number average molecular weight was determined by gel permeation chromatography using a standard polystyrene calibration curve.

【table】

【table】 (B) Polyvinyl acetal resin Γ Polyvinyl butyral resin (A1): Denka Butyral #3000-1 [Denki Kagaku Kogyo Co., Ltd.] Γ Polyvinyl formal resin (A2): Denka formal #20 [Denki Kagaku Kogyo Co., Ltd.] (Characteristics of each resin are shown in Table 2)

[Table] (C) Carboxylic acids and acid anhydrides Γ Pyromellitic anhydride Γ 3-nitrophthalic acid Γ Naphthalene-1,4,5,8-tetracarboxylic acid Comparative example 1 τ-H ₂ Pc 2.0g, silicone varnish ( KR−
255) and 94 g of tetrahydrofuran were kneaded for 8 hours using a ball mill (3-inch pot mill manufactured by Nihon Kagaku Togyo Co., Ltd.). The resulting pigment dispersion was applied onto an aluminum plate (thickness: 0.1 mm) using an applicator and dried at 90° C. for 1 hour to form a charge generation layer with a thickness of about 1.0 μm. Next, 4 g of 2,3,5-trichloro-1,4-naphthoquinone, 2008 g of Vylon, and 88 g of a mixed solvent of dichloromethane/dichloroethane = 1/1 were completely dissolved. The obtained solution was applied onto the charge generation layer using an applicator and heated at 90°C for 1 hour.
A charge transport layer of 15 μm was formed by drying for hours. Comparative Example 2 10 g of oxz and 10 g of Vylon 200 were mixed in 80 g of tetrahydrofuran and completely dissolved. The obtained solution was applied onto an aluminum plate using an applicator and dried at 90° C. for 1 hour to form a charge transport layer of 15 μm. Next, 2.0 g of τ-H ₂ PC, 6.7 g of silicone varnish (Tosgard T510), and 94 g of a mixed solvent of toluene/isopropanol = 4/6 (weight ratio) were kneaded for 15 hours using a ball mill to obtain a pigment dispersion. was applied onto the charge transport layer using an applicator and dried at 110° C. for 15 minutes to form a charge generation layer with a thickness of about 1.0 μm. Comparative example 3 τ−H ₂ PC0.6g, ozz5.0g, Byron 20014.4
g and 80 g of tetrahydrofuran were kneaded for 10 hours using a ball mill. The obtained dispersion was applied onto an aluminum plate using an applicator and heated at 100°C.
After drying for 15 hours, a single-layer electrophotographic photoreceptor with a thickness of 15 μm was produced. Comparative Examples 4 to 5 On a photoconductor produced in the same manner as Comparative Example 1
A solution consisting of 40 g (solid content: 20 g) of BMF-3 and 60 g of isopropanol was applied using an applicator. Table 3 shows the drying conditions and film thickness of the protective layer. Comparative Examples 6-7 On the photoconductor produced in the same manner as Comparative Example 2
A solution consisting of 30 g (solid content: 15 g) of BMF-3, 5 g of polyvinyl butyral resin, and 65 g of isopropanol was applied using an applicator. Table 3 shows the drying conditions and film thickness of the protective layer. Comparative Examples 8 to 9 A solution consisting of 40 g (solid content: 20 g) of BMF-1 and 60 g of isopropanol was applied onto a photoreceptor prepared in the same manner as in Comparative Example 3 using an applicator. Table 3 shows the drying conditions and film thickness of the protective layer. Comparative Examples 10-11 30 g of BMF-1 (15 g in solid content), 5 g of polyvinyl butyral resin, and 65 g of isopropanol were placed on a photoreceptor prepared in the same manner as in Comparative Example 2.
A solution consisting of was applied using an applicator.
Table 3 shows the drying conditions and film thickness of the protective layer. Examples 1 to 9 A protective layer solution having the composition ratio shown in Table 3 (using a mixed solvent of tetrahydrofuran/isopropanol = 1/1) was applied onto the photoreceptor prepared in the same manner as Comparative Examples 1 to 3 using an applicator. Coated.
Table 3 shows the drying conditions and film thickness of the protective layer. The electrophotographic properties of the obtained electrophotographic photoreceptor were measured using an electrostatic recording paper tester (SP-428 manufactured by Kawaguchi Electric). The results are shown in Table 4. The initial potential V _p (V) in the table indicates the charging potential when a positive 5 kV corona is discharged for 10 seconds in dynamic measurement, and the dark decay V _k indicates the charge potential after 30 seconds in the dark.
Indicates the potential retention rate when left for seconds, E ₅₀ , E ₇₅
is irradiated with 10 lux of white light and the potential is 50%, respectively.
The light amount value required to reduce by 75% (l _x

Claims (1)

[Claims] 1. In an electrophotographic photoreceptor that can function with positive charging, the surface thereof has (a) a number average molecular weight of 1500 or less, a number of formaldehyde bound to 2 to 4 and a number of methylol groups per melamine nucleus; (b) a polyvinyl acetal resin; and (c) a protective layer containing a cured film of an electron-accepting carboxylic acid compound and/or an electron-accepting polycarboxylic acid anhydride. A positively charged electrophotographic photoreceptor. 2. An electrophotographic photoreceptor capable of functioning with positive charging is provided with a charge transport layer containing an electron-donating charge transport substance, a charge generation layer containing an organic pigment that generates a charge, and a protective layer on a conductive layer. The positively charged electrophotographic photoreceptor according to claim 1, which is a laminated material. 3. An electrophotographic photoreceptor capable of functioning with positive charging is provided with a charge generation layer containing an organic pigment that generates a charge, a charge transport layer containing an electron-accepting charge transporting substance, and a protective layer on a conductive layer. The positively charged electrophotographic photoreceptor according to claim 1, which is a laminated material. 4. The electrophotographic photoreceptor capable of functioning with positive charging is one in which a photoconductive layer containing an organic pigment that generates a charge and a protective layer are sequentially laminated on a conductive layer. Positively charged electrophotographic photoreceptor. 5. The positively charged electrophotographic photoreceptor according to claim 4, wherein the photoconductive layer contains an organic pigment that generates a charge and a charge transporting substance.