JPH0431580B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to an electrophotographic photoreceptor that has excellent durability and provides good images even under high humidity. (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 in how to dispose of them. On the other hand, the use of organic photoconductive compounds is generally less toxic than the use of inorganic photoconductive substances, and is also advantageous in terms of transparency, flexibility, lightness, cost, etc. It has been widely studied 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 a toner image is created using a developer, generally called a toner, charged with opposite signs. can be transferred and fixed onto another substrate, such as paper, to obtain a copy. At this time, it is necessary to remove (clean) the slight amount of toner remaining on the surface of the photoreceptor using a brush, blade, or the like. By repeating this process of development, transfer, and cleaning, the surface of the photoreceptor is worn and damaged, resulting in blurred transferred images.
In some cases, the charge transport layer or charge generation layer may peel off, resulting in a significantly shortened life of the photoreceptor. Due to these problems, photoreceptors are required to have strong durability. Therefore, in order to improve the durability,
It has been proposed to provide a protective layer on the surface, as disclosed in Japanese Patent Application Laid-open No. 76928 and Japanese Patent Application Laid-Open No. 17732/1984. (Problems to be solved by the invention) However, when a thermoplastic resin is used as in the conventional protective layer, the abrasion resistance effect is not sufficient, and when a thermosetting resin is used, when forming the protective layer, high temperature,
Because of the long time required, the materials in the underlying charge generation layer and charge transport layer deteriorate due to heat during that time, resulting in a decline in electrophotographic properties.Furthermore, in order to improve wear resistance, the thickness of the protective layer must be increased. Because it needs to be thick, it tends to increase the residual potential and decrease the sensitivity in electrophotographic characteristics.Also, the protective layer, as typified by urethane resin, has high hygroscopicity, so it can cause blurring of the image under high humidity. There is a drawback that image defects such as running and disappearance are likely to occur, and there is a desire to develop a protective layer that has high abrasion resistance and good moisture resistance without impairing electrophotographic properties. Therefore, an object of the present invention is to provide an electrophotographic photoreceptor that satisfies the above requirements and has excellent electrophotographic properties, durability, and moisture resistance. (Means for Solving the Problems) The present invention solves the above problems by providing a specific protective layer. That is, the present invention provides an electrophotographic photoreceptor in which a charge generation layer containing an organic pigment that generates a charge, a charge transport layer containing an electron donating charge transporting substance, and a protective layer are sequentially laminated on a conductive layer. , the protective layer is (a) a butyl etherified melamine/formaldehyde resin having a number average molecular weight of 1500 or less, 2 to 4 formaldehyde bonds and 1 to 2 methylol groups per melamine nucleus; (b) A protective layer containing a cured film containing an alkyl etherified benzoguanamine formaldehyde resin having a number average molecular weight of 400 to 2000 and (c) an electron-donating carboxylic acid compound and/or an electron-donating polycarboxylic acid anhydride as components. This invention relates to an electrophotographic photoreceptor. The materials used in the electrophotographic photoreceptor of the present invention will be described in detail below. First, in the present invention, the conductive layer is a conductive material such as paper or plastic film subjected to conductivity treatment, a plastic film laminated with metal foil such as aluminum, a metal plate, a metal drum, or the like. 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. It is possible to use pigments known to generate electric charge upon irradiation with light such as . These pigments are, for example,
No. 47-37453, JP-A-47-37544, JP-A-47-
No. 18543, JP-A-47-18544, JP-A-48-43942
No., JP-A-48-70538, JP-A-49-1231, JP-A-49-105536, JP-A-50-75214, JP-A-Sho.
It is disclosed in Publication No. 50-92738 and the like. In particular, the τ, τ', η, and η' type metal-free phthalocyanines described in JP-A-58-182640 and European Patent Application Publication No. 92255 have high sensitivity up to long wavelengths, and are suitable for use with diode lasers. It is also effective as an electrophotographic photoreceptor for installed printers. 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 inhibitor, and the like, which are commonly used in electrophotographic photoreceptors, can 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. Heat and/or photocurable resins 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. Examples of fluidity imparting agents include Modaflow (manufactured by Monsanto Chemical Company) and Acronal 4F (manufactured by Basf Company), and examples of pinhole inhibitors include:
Examples 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-donating charge-transporting substance used in the charge-transporting layer (electron-donating charge-transporting layer) has a function of transporting positive charge carriers (holes), and specifically, carbazole, 3-fluoride, etc. enylcarbazole, 2-phenylindole, 2-phenylnaphthalene, oxadiazole, oxatriazole, 1-phenyl-3-(4-diethylaminostyryl)-5-(4-diethylaminophenyl)pyrazoline, 2-phenyl- Low molecular weight compounds such as 4-(4-diethylaminophenyl)-5-phenyloxazole, triphenylamine, imidazole, poly-N-vinylcarbazole, halogenated poly-N-vinylcarbazole, polyvinylpyrene, polyvinylindoquinoxaline , polyvinylbenzothiophene, polyvinylanthracene,
Examples include polymer compounds such as polyvinyl acridine and polyvinyl pyrazoline, and derivatives thereof. The same binder, plasticizer, fluidity imparting agent, pinhole inhibitor, etc. as in the charge generation layer can be used in the charge transport layer 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, and when using a low-molecular compound, it is preferably 50% by weight or more based on the film properties. is preferred. The amount of other additives is preferably 5% by weight or less based on the charge transporting substance. In the present invention, immediately below the charge generation layer,
Electron-accepting charge transport layers may be laminated. This is a layer containing an electron-accepting charge-transporting material.
The electron-accepting charge-transporting substance has a charge-transporting function, and specifically includes fluorene, fluorenone, 2,7-dinitro-9-fluorenone, 2,4,7-trinitro-9-fluorenone, 4H-indeno(1,2,6)thiophene-
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,
Electrons such as 3-dibromo-5-methyl-1,4-naphthoquinone, 2,3-dibromo-5-ethyl-1,4-naphthoquinone, tetracyanoethylene, trinitrobenzene, tetracyanoquinodimethane, etc. and derivatives thereof. It is a receptive compound. The same binder, plasticizer, fluidity imparting agent, pinhole inhibitor, etc. as in the charge generation layer can be used in this charge transport layer, if 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, and 50% by weight or less for the low-molecular charge-transporting substance due to film properties.
The above is preferable. The amount of other additives is preferably 5% by weight or less based on the charge transporting substance. Next, the protective layer will be explained. The protective layer of the present invention is mainly formed of a cured film of a specific butyl etherified melamine/formaldehyde resin, polyvinyl acetal resin, and an electron-donating carboxylic acid compound and/or an electron-donating 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. The composition is 4 to 5 moles of butanol and 3 moles of formaldehyde to 1 mole of melamine.
Preferably, ~7 mol is used. 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 during the formation of the protective layer, and has excellent abrasion resistance. A highly protective layer can be formed. On the other hand, the alkyl etherified benzoguanamine formaldehyde resin, which is another component of the protective layer, has a number average molecular weight of 400 to 2000, preferably 800 to 2000.
1500 resin is used. When the number average molecular weight is less than 400, the cured coating film becomes brittle, and when it exceeds 2000, the reactivity decreases. Further, all of the methylol groups of the benzoguanamine resin may be alkyl etherified, but some of them may remain as methylol groups. In this case, the alkyl group includes methyl group, ethyl group, propyl group, isopropyl group,
Examples include butyl group and isobutyl group. Such alkyl etherified benzoguanamine/formaldehyde resin is produced by dissolving benzoguanamine in an alcohol such as methanol, ethanol, propanol, isopropanol, butanol, isobutanol, etc., and adding formaldehyde dropwise thereto to perform the addition reaction and alkyl etherification. Alternatively, it can be produced by dissolving benzoguanamine and formaldehyde in alcohol and heating this solution to perform an addition reaction and an alkyl etherification reaction. In these methods, the reaction is carried out using nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, p
- It can be produced in the same manner as the above-mentioned butyl etherified melamine/formaldehyde resin by adding an acidic catalyst such as toluenesulfonic acid. The cured film of the alkyl etherified benzoguanamine/formaldehyde resin alone used in the protective layer of the present invention has the characteristics of being hard, strong, and having low water absorption. Therefore, by combining the above-mentioned butyl etherified melamine/formaldehyde resin and alkyl etherified benzoguanamine/formaldehyde resin, the features of both are added, and a strong film with fast thermosetting and good moisture resistance can be obtained. To form the protective layer according to the present invention, the above-mentioned butyl etherified melamine/formaldehyde resin and alkyl etherified benzoguanamine/formaldehyde resin are used in a weight ratio of 90/10 to 20/
It is preferable to mix it so that it is 80, especially 75/2
A ratio of 5 to 40/60 is optimal. If this weight ratio is too large, moisture resistance will be reduced, and if this weight ratio is too small, thermosetting properties will be poor. Even with the cured film made of the specific butyl etherified melamine/formaldehyde resin and alkyl etherified benzoguanamine/formaldehyde resin described above, compared to conventionally known protective layers, it has better wear resistance due to the curing conditions at relatively low temperatures and short times. It has excellent moisture resistance and can prevent deterioration of electrophotographic properties due to thermal deterioration of the photoreceptor that occurs during curing. However, the present invention further adds the following features by using an electron-donating carboxylic acid compound and/or an electron-donating polycarboxylic acid anhydride. (1) Since the electron-donating carboxylic acid compound and/or the electron-donating 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 electrophotographic properties due to thermal deterioration of the photoreceptor 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-mentioned carboxylic acids and acid anhydrides are electron-donating, this property is introduced into the protective layer. As a result, holes are 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-donating carboxylic acid compound includes an electron-donating group such as an amino group, a hydroxyl group, a halogen,
Compounds having one or more aromatic rings substituted with one or more alkoxyl groups, alkyl groups, etc. and a carboxyl group, and compounds having an electron-donating skeleton and a carboxyl group; the former include 4-
aminobenzoic acid, 4-dimethylaminobenzoic acid,
3,4-bis(dimethylamino)benzoic acid, 3,
4,5-tris(dimethylamino)phthalic acid, salicylic acid, 4-chloro-salicylic acid, 3,4-dibromobenzoic acid, 3,4-dimethoxybenzoic acid,
3,4,5-trimethoxybenzoic acid, 2,4,5
-trimethoxybenzoic acid, 3,4,5-trimethoxyphenylacetic acid, diphenylamine-2-carboxylic acid, 2,5-pyridinedicarboxylic acid, 3,
4,5-trimethoxyphthalic acid, 3-ethyl-
4,5-dimethoxybenzoic acid, 3,4-dimethoxy-5-chlorophenylpropionic acid, 4-t-
Butyl-5-methoxybenzoic acid, 1-carboxy-2,3-dimethylaminonaphthalene, 1,8-
Examples include dicarboxy-2,3,4-trimethoxynaphthalene, 2-carboxy-3,6,7-trimethoxyanthracene, and 2-carboxy-3,6-bis(dimethylamino)anthracene. The latter include oxazole, oxydiazole,
Pyrazoline, stilbene hydrazone, pyrrole,
There are substituents with one or more carboxyl groups of electron-donating compounds such as imidazole, carbazole, indole, etc. and their derivatives, specifically 2-(2-carboxy-4-diethylamino).
Phenyl-1,3-oxazole, 1,-(4-carboxy)phenyl-3-(4-diethylaminostyryl)-5-(4-diethylamino)phenylpyrazoline, α-phenyl-4'-N,N' -dicarboxyphenylaminostilbene, N-methyl-
N-carboxyphenylhydrazono-3-methylidene-9-ethylcarbazole, pyrrole-2-
There are carboxylic acids, etc. The electron-donating polycarboxylic acid anhydride is an acid anhydride of one of the electron-donating carboxylic acid compounds having two or more carboxyl groups,
Specifically, 3,4,5-tris(dimethylamino)phthalic anhydride, 3,4,5-trimexyphthalic anhydride, 1,8-dicarboxy-2,3,
Examples include acid anhydride of 4-trimethoxynaphthalene. One or more of the electron-donating carboxylic acid compounds and electron-donating polycarboxylic anhydrides are used, and the amount used is based on the total amount of the butyl etherified melamine formaldehyde resin and the alkyl etherified benzoguanamine formaldehyde resin. It is preferably 0.1 to 40% by weight, particularly 1 to 20% by weight. If the amount used is too small, it will be difficult to exhibit the above-mentioned features, and if it is too large, the moisture resistance of the protective layer will tend to decrease. The protective layer in the present invention may further contain additives such as a fluidity imparting agent and a pinhole inhibitor that may be used in the charge generation layer and the charge transport layer. The electrophotographic photoreceptor according to the present invention has a structure in which a charge generation layer, a charge transport layer, and a protective layer are sequentially laminated on a conductive layer. In this electrophotographic photoreceptor, the thickness of the charge generation layer is preferably 0.001 to 10 μm, particularly preferably 0.2 to 5 μm. If the charge generation layer is less than 0.001 μm, the electrophotographic properties (especially sensitivity) tend to be poor, and if it exceeds 10 μm, the residual potential tends to increase. The thickness of the charge transport layer is preferably 5 to 50 μm, particularly preferably 8 to 20 μm. If it is less than 5 μm, the initial potential tends to be low, and if it exceeds 50 μm, the sensitivity tends to decrease. The thickness of the protective layer is preferably 0.01 to 10 μm, especially
0.1-5 μm is preferable. If it is less than 0.01 μm, it will have little effect as a protective layer, and its durability will tend to deteriorate.
If it exceeds 10 μm, the sensitivity tends to be poor and the residual potential tends to increase. When only an organic pigment is used as a method for forming the charge generation layer, vacuum deposition can be used. ,
It can also be formed by uniformly dissolving or dispersing in a solvent such as trichloroethane, then coating and drying. When forming a charge transport layer, a charge transporting substance, a binder, and optionally an additive may be uniformly dissolved in the same solvent as in the case of the charge generation layer, and then it can be formed by coating and drying. . When forming the protective layer of the present invention, the above-mentioned butyl etherified melamine/formaldehyde resin, alkyl etherified benzoguanamine/
It can be formed by uniformly dissolving formaldehyde resin, electron-donating carboxylic acid compound and/or electron-donating polycarboxylic acid anhydride, and other additives as necessary in a solvent, and then coating and curing by heating. . At this time, the heating temperature is preferably 90 to 140°C. The electrophotographic photoreceptor of the present invention may further have a charge transport layer containing an electron-accepting charge transport material, a thin adhesive layer, or a barrier layer immediately above the conductive layer. When copying or printing using the electrophotographic photoreceptor of the present invention, the surface is negatively charged and exposed in the same manner as before, and then developed to transfer an image onto 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 explained in detail based on an example.
The present invention is not limited to this. 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 2-(p-dimethylamino)phenyl-4-
(p-dimethylamino)phenyl-5-(o-chlorophenyl)-1,3-oxazole (OXZ) (3) Binder (A) Binder for charge generation layer Silicone varnish: KR-255 [Shin-Etsu Chemical Co., Ltd. )Product name] (B) Binder for charge transport layer Polyester resin: Vylon 200 [Product name of Toyobo Co., Ltd.] (4) Material for protective layer (A) Butyl etherified melamine formaldehyde resin (BMF) (BMF-1 Synthesis) 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℃, 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. The number of formaldehyde bound, the number of butyl ether groups, the number of methylol groups, and the number average molecular weight per melamine nucleus of BMF-1, BMF-2, and BMF-3 are shown in Table 1 below. However, the number of bound formaldehyde is determined by measuring the amount of unreacted formaldehyde using the charged amount and the sodium sulfite method, and the number of butyl ether groups is determined by measuring the amount of butanol charged and unreacted butanol by gas chromatography using sec-butyl alcohol as an internal standard solution. 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) Alkyl etherified benzoguanamine formaldehyde resin (BBF) Using the same equipment as in the synthesis of BMF-1, 112 g of paraformaldehyde, 222 g of n-butanol and 187 g of benzoguanamine were added to a flask, and 90 g of benzoguanamine was added.
The addition reaction was carried out for 1 h at °C, and then using sulfuric acid
After adjusting the pH to 5, the mixture was heated again and dehydrated under reflux for 2 hours, and then desolubilized. After this, the heating residue
Adjusted to 50%. The viscosity at this time is Gardner (25°C) L, and the number average molecular weight is 1,
It was 300. (C) Electron-donating carboxylic acid compound or electron-donating polycarboxylic acid anhydride 〇 3,4,5-trimethoxyphenylacetic acid 〇 3,4-bis(dimethylamino)phthalic anhydride 〇 Pyrrole-2-carboxylic acid Comparative Example 1 2.0 g of τ-H ₂ Pc, 4.0 g of silicone varnish, 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 obtained pigment dispersion was applied onto an aluminum plate (thickness: 0.1 mm) using an applicator and heated at 100℃ for 15 minutes.
It was dried for a minute to form a charge generation layer with a thickness of 1.0 μm. Next, 5 g of OXZ and 15 g of Vylon 200 were mixed with 140 g of tetrahydrofuran and completely dissolved. The obtained solution was applied onto the charge generation layer using an applicator and dried at 90°C for 20 minutes to form a charge transport layer of 15 μm. Comparative Examples 2 to 3 A charge generation layer and a charge transport layer were formed in the same manner as in Comparative Example 1, and then 3.40 g of BMF (solid content) was added.
A solution consisting of 20g) and 60g of isopropanol was applied using an applicator. Table 2 shows the drying conditions and film thickness of the protective layer. Comparative Examples 4 to 5 A charge generation layer and a charge transport layer were formed in the same manner as in Comparative Example 1, and 3.32 g of BMF (solid content) was added.
A solution consisting of 16g), 8g BBF (4g solids) and 60g isopropanol was applied using an applicator. Table 2 shows the drying conditions and film thickness of the protective layer.
Comparative Examples 6 to 7 A charge generation layer and a charge transport layer were formed in the same manner as in Comparative Example 1, and then BMF-1.40g (solid content: 20g)
A solution consisting of 60 g of isopropanol and 60 g of isopropanol was applied using an applicator and heated at 110° C. for 1 hour to form a protective layer with a thickness of 1 to 3 μm. Comparative Examples 8 to 9 A charge generation layer and a charge transport layer were formed in the same manner as in Comparative Example 1, and 1.32 g of BMF (solid content) was added.
A solution consisting of 16 g), 4 g of polyvinyl butyral resin, and 64 g of isopropanol was applied using an applicator. Table 2 shows the drying conditions and film thickness of the protective layer.
Shown below. Examples 1 to 8 A charge generation layer and a charge transport layer were formed in the same manner as in Comparative Example 1, and a protective layer solution having the composition ratio shown in Table 2 (tetrahydrofuran/isopropanol=
(using a mixed solvent of 1/1 [weight ratio]) was applied using an applicator. Table 2 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 3. In addition, the initial potentials Vo and V in the table indicate the charging potential when a negative 5KV corona was discharged for 10 seconds in dynamic measurement, and the dark decay _VK indicates the charge potential after discharging a negative 5KV corona for 10 seconds.
It shows the potential retention rate when left for 30 seconds, and E ₅₀ and E ₇₅ are the light amount values (xs) required for the potential to decrease by 50% and 75%, respectively, when irradiated with 10ux white light.
Show. Residual potential V _R indicates the surface potential after irradiation with 10 ux white light for 30 seconds. In addition, using a friction tester (manufactured by Suga Test Instruments),
The surface of the electrophotographic photoreceptor was rubbed with gauze, and the abrasion resistance was evaluated by the number of times the surface was rubbed until the abrasion scratches on the surface passed through the protective layer and reached the layer below. Furthermore, comparative example 1
In the case of , the number of sliding movements until fiber traces of the gauze could be visually confirmed was measured. The results are shown in Table 3. The water absorption rate of the protective layer is 91 at 25℃ for the protective layer only film.
It was exposed to an atmosphere of %RH for 48 hours, and the water absorption rate was determined from the increase in weight. In addition, an image evaluation machine was used to evaluate the image quality under high humidity and a continuous printing test to evaluate the printing life until image deterioration. The results are also shown in Table 3.

[Table] * Values for each material indicate parts by weight of solid content.

【table】

[Table] The photoreceptor of Comparative Example 1 has excellent electrophotographic properties, but has poor wear resistance because it does not have a protective layer.
200 times, which is extremely low. Furthermore, when melamine resin (BMF-3) outside the scope of the present invention is used as the protective layer material (Comparative Examples 2 and 3), the curing temperature is low (110°C).
However, due to insufficient curing, there was no effect of improving wear resistance (Comparative Example 2), and as a result of increasing the curing temperature to a high temperature (160°C), increasing the curing time to 3 hours, and increasing the film thickness to 3 μm, the resistance was improved. Abrasion resistance was slightly improved (Comparative Example 3). However, the electrophotographic properties deteriorate, i.e., E ₅₀ ,
The increase in E ₇₅ and _VR was significant, and as a result, background staining occurred from the beginning, making image evaluation impossible. When a protective layer consisting of a melamine resin (BMF-3) outside the scope of the present invention and a benzoguanamine resin (BBF) within the scope of the present invention was formed on the photoreceptor of Comparative Example 1 (Comparative Examples 4 and 5) , low-temperature curing results in insufficient curing and low wear resistance (Comparative Example 4),
When the abrasion resistance was increased by increasing the film thickness and maintaining the film at high temperature for a long period of time, the electrophotographic properties deteriorated significantly and background staining occurred on the image (Comparative Example 5), as in Comparative Example 3. However, the water absorption of the protective layer was reduced compared to Comparative Examples 2 and 3, which did not contain the benzoguanamine resin within the scope of the present invention. Melamine resin within the scope of the present invention (BMF-1)
When formed alone as a protective layer (Comparative Example 6,
7), it was sufficiently cured even at a low temperature for a short time, and the abrasion resistance and associated printing life were greatly improved (Comparative Example 6). Even when compared with the photoreceptor of Comparative Example 1 in which no protective layer was formed, no deterioration in electrophotographic properties was observed.
However, the water absorption rate of the protective layer was high, and image defects occurred under high humidity conditions. Furthermore, when the thickness of the protective layer was increased to 3 μm in order to improve the printing life, the electrophotographic properties were still deteriorated and background stains occurred in the image (Comparative Example 7). Melamine resin (BMF-
When 1) and benzoguanamine resin (BBF) are used together in the protective layer (Comparative Examples 8 and 9), the wear resistance is the same as in Comparative Examples 6 and 7, but the water absorption rate of the protective layer decreases and the No image defects occurred even under humid conditions (Comparative Example 8). However, when the thickness of the protective layer was increased in order to further improve the printing life, the electrophotographic properties deteriorated and background staining occurred (Comparative Example 9). However, in the photoreceptors of Examples 1 to 8 according to the present invention in which a third component of carboxylic acid or acid anhydride was added to the protective layer, the protective layer could be formed at a lower temperature and in a shorter time than in the comparative example. While maintaining almost the same electrophotographic properties as the photoreceptor without a protective layer (1), the abrasion resistance has been significantly improved, and the printing life has been greatly improved (to improve the printing life, the protective layer has been added). No deterioration in electrophotographic properties was observed even when the film thickness was increased). Furthermore, since the water absorption rate of the protective layer was low, even under high humidity conditions, no image defects occurred and good images could be obtained. (Effects of the Invention) A cured film containing a specific butyl etherified melamine/formaldehyde resin, alkyl etherified benzoguanamine/formaldehyde resin, and an electron-donating carboxylic acid or its acid anhydride as components on the surface of the electrophotographic photoreceptor according to the present invention. An electrophotographic photoreceptor having a protective layer containing the above is an electrophotographic photoreceptor having excellent electrophotographic properties and excellent environmental resistance and durability.

Claims (1)

[Scope of Claims] 1. An electrophotographic photoreceptor in which a charge generation layer containing an organic pigment that generates a charge, a charge transport layer containing an electron donating charge transport substance, and a protective layer are sequentially laminated on a conductive layer. , the protective layer is (a) a butyl etherified melamine/formaldehyde resin having a number average molecular weight of 1500 or less, 2 to 4 formaldehyde bonds and 1 to 2 methylol groups per melamine nucleus, (b ) an alkyl etherified benzoguanamine formaldehyde resin having a number average molecular weight of 400 to 2000; and (c) a protective layer containing a cured film containing as a component an electron-donating carboxylic acid compound and/or an electron-donating polycarboxylic acid anhydride. An electrophotographic photoreceptor.