JPH0431579B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a positively charged 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 advantageous in terms of transparency, flexibility, light weight, cost, etc. Therefore, it has been widely researched in recent years and is being put into practical use. 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. Electrophotographic photoreceptors using conventional organic photoconductive compounds generally have a charge generation layer and a hole transfer type charge transport layer sequentially laminated on a conductive layer, so that the surface of the photoreceptor is negatively charged. use. When negatively charged by corona discharge, more ozone is generated than when positively charged, and charging tends to be uneven.
In this respect, if possible, a photoreceptor that can function with positive charging,
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. (Problems to be solved by the invention) However, when a thermoplastic resin is used as in the conventional protective layer, the effect of improving wear resistance is not sufficient, and when a thermosetting resin is used, the protective layer is Sometimes, a high-temperature, long-term curing reaction is required, which can cause thermal deterioration of the underlying photosensitive layer and reduce electrophotographic properties.Furthermore, in order to improve abrasion resistance, the thickness of the protective layer must be made even slightly thicker. This tends to lead to a decrease in electrophotographic properties, especially an increase in residual potential and a decrease in sensitivity.Also, the protective layer, as typified by urethane resin, has high hygroscopicity, resulting in blurring, blurring, and disappearance of images under high humidity. It has the disadvantage that image defects are likely to occur. Thus, it is desired to develop a protective layer for positively charged electrophotographic photoreceptors that has high abrasion resistance and good moisture resistance without impairing electrophotographic properties. 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, durability, and moisture resistance. (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) alkyl etherified benzoguanamine formaldehyde resin having a number average molecular weight of 400 to 2000, and (c) electron-accepting carboxylic acid compound and/or The present invention relates to a positively charged electrophotographic photoreceptor having a protective layer containing a cured film containing an electron-accepting polycarboxylic anhydride as a component. 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 paper or plastic film subjected to conductivity treatment, a plastic film laminated with metal foil such as aluminum, or a metal plate or metal drum made of 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-based, disazo-based, trisazo-based, benzimidazole-based, polycyclic quinoline-based, indigoid-based, quinacridone-based, phthalocyanine-based, perylene-based, methine-based. 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-47-18544, 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 suppressor, and the like, which are commonly used in electrophotographic photoreceptors, can be used in the charge generation layer as 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), etc., and examples of pinhole suppressants include benzoin, dimethyl phthalate, and the like. 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 generation 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-ethyl-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, pophole 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 generating layer containing an electron donating charge transporting material may be laminated immediately below said 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, and pinhole inhibitor 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 the 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 preferred. 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 is
If it 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, alkyl etherified benzoguanamine/formaldehyde resin, and an electron-accepting carboxylic acid compound and/or an electron-accepting polycarboxylic acid anhydride. However, 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, chlorine, 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 before forming the protective layer, and has excellent abrasion resistance. A highly durable 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.
~1500 resins are used. Number average molecular weight is 400
If it is less than 2,000, the cured coating film becomes brittle, and if it exceeds 2,000, the reactivity decreases. Further, all of the methylol groups of the benzoguanamine resin may be alkyl etherified, but some may remain as methylol groups. In this case, the alkyl group is
Examples include methyl group, ethyl group, propyl group, isopropyl group, butyl group, and isobutyl group. Such alkyl etherified benzoguanamine/formaldehyde resin can be produced by dissolving benzoguanamine in an alcohol such as methanol, propanol, isopropanol, butanol, isobutanol, etc., and adding formaldehyde thereto to perform an 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 can be carried out by adding an acidic catalyst such as nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, p-toluenesulfonic acid, etc., and producing the resin in the same manner as for the butyl etherified melamine/formaldehyde resin described above. 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, the specific butyl etherified melamine formaldehyde resin and alkyl etherified benzoguanamine
When formaldehyde resins are combined, 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 of 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 90/10 to the latter.
It is preferable to mix 20/80, especially
A ratio of 75/25 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 photoconductive layer that occurs during curing. 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, the deterioration of 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 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-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, undecanedioic 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, piphenyl-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 of the electron-accepting carboxylic acid compounds and electron-donating polycarboxylic anhydrides are used, and the amount used is equal to 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 preferred is 1 to 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, alkyl etherified benzoguanamine/formaldehyde resin, electron-accepting carboxylic acid compound and/or electron-accepting polycarboxylic acid anhydride, and optionally additives are added in acetone. , tetrahydrofuran, methanol, isopropanol, or the like, and then coated on 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 of the present invention, the surface is positively 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 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 〇 Electron-accepting compound 2,3,5-trichloro-1,4-naphthoquinone 〇 Electron-donating Compound 2-(p-dimethylamino)phenyl-4-
(p-dimethylamino)phenyl-5-(o-chlorophenyl)-1,3-oxazole (OXZ) (3) Binder 〇 Silicone varnish: KR-255 [Shin-Etsu Chemical Co., Ltd. product name] 〇 Silicone varnish: Tosgard T510 [Product name of Toshiba Silicone Co., Ltd.] 〇 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) In a flask equipped with a stirrer, reflux condenser, and 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℃, 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 in 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] (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 was adjusted to 50%. The viscosity at this time was L according to Gardner (25°C), and the number average molecular weight determined in the same manner as the butyl etherified melamine formaldehyde resin was 1300. (C) Carboxylic acids and acid anhydrides 〇 Pyromellitic anhydride 〇 3-nitrophthalic acid 〇 Naphthalene-1,4,5,8-tetracarboxylic acid Comparative example 1 τ-H ₂ Pc2.0g, silicone varnish (KR-255 )
4.0 g 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 1.0 μm. Next, 4 g of 2,3,5-trichloro-1,4-naphthoquinone, 8 g of Vylon 200, 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 with 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, OXZ5.0g, Byron 200 14.4
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 2 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 of BMF-3 (15 g in solid content), 10 g of BBF (5 g in solid content), and 60 g of isopropanol was applied using an applicator. Table 2 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 2 shows the drying conditions and film thickness of the protective layer.
Shown below. Comparative Examples 10-11 30 g of BMF-1 (15 g in solid content) and 10 g of BBF were placed on the photoreceptor prepared in the same manner as Comparative Example 2.
A solution consisting of (5 g in solid content) and 60 g of isopropanol was applied using an applicator. Table 2 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 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), and the results are shown in Table 3. The initial potentials Vo and V in the table indicate the charging potential when a positive 5KV corona is discharged for 10 seconds in dynamic measurement, and the dark decay _VK indicates the charge potential when a positive 5KV corona is discharged for 10 seconds.
Indicates the potential retention rate when left for 30 seconds, E ₅₀ ,
E ₇₅ is irradiated with 10ux white light and the potential is 50
%, shows the light amount value (xs) required to reduce by 75%. The residual potential V _R and V indicate the surface potential after irradiation with 10 ux white light for 30 seconds. In addition, a friction tester (manufactured by Suga Test Instruments) is used to slide gauze over the surface of the electrophotographic photoreceptor, and the wear resistance is measured by the number of times the surface is slid until the abrasion scratches on the surface pass through the protective layer and reach the layer below. was evaluated. In addition, Comparative Examples 1 to 3
In the case of the photoreceptor, the number of times it was slid 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 25℃ for the protective layer only.
It was exposed to an atmosphere of 91% 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 conditions and a continuous printing test, and the printing life until the image quality deteriorated was evaluated. The results are also shown in Table 3.

【table】

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

【table】

[Table] The photoreceptors of Comparative Examples 1 to 3 function with positive charging, and the photoreceptors of Comparative Examples 2 and 3 in particular have excellent electrophotographic properties, but their wear resistance is poor because they are not provided with a protective layer. It is extremely poor and has a short printing life of less than 200 times.
Furthermore, when melamine resin (BMF-3) outside the scope of the present invention was used alone as a protective layer material on the surface of the photoreceptor of Comparative Example 1 (Comparative Examples 4 and 5), the thermosetting property was poor and the low temperature (110 ℃) and short drying conditions (1 hour), there is no effect of improving wear resistance due to insufficient curing (Comparative Example 4). Set the curing temperature to high temperature (160℃),
The curing time was increased to 3 hours, and the thickness of the protective layer was increased.
When the thickness was increased to 3 μm (Comparative Example 5), the wear resistance was slightly improved. However, the electrophotographic properties deteriorated significantly, that is, the E ₅₀ , E ₇₅ , and _VR increased significantly, and when this photoreceptor was evaluated using an image evaluation machine, the background stain was significant, making it impossible to evaluate the printing life. In addition, the water absorption rate of the protective layer was high and image defects such as a decrease in image density and white spots occurred under high humidity conditions. 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 2 (Comparative Examples 6 and 7) , low-temperature curing results in insufficient curing and low wear resistance (Comparative Example 6),
When the abrasion resistance was increased by increasing the film thickness at high temperatures for a long period of time, as in Comparative Example 5, the electrophotographic properties deteriorated significantly and background staining occurred on the image (Comparative Example 7). However, the water absorption of the protective layer was reduced compared to Comparative Examples 4 and 5, which did not contain the benzoguanamine resin within the scope of the present invention. When a melamine resin (BMF-1) within the range of the present invention was formed alone as a protective layer on the surface of the photoreceptor of Comparative Example 3 (Comparative Examples 8 and 9), it was sufficiently cured even at low temperatures for a short time, and had good wear resistance. The durability and the associated printing life were greatly improved (Comparative Example 8). Even when compared with the photoreceptor of Comparative Example 3 in which no protective layer was formed, the electrophotographic properties were less degraded. 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 9). When melamine resin (BMF-1) and benzoguanamine resin (BBF) within the scope of the present invention were used together as a protective layer on the surface of the photoreceptor of Comparative Example 2 (Comparative Examples 10 and 11), Comparative Examples 8 and 9 Compared to , the abrasion resistance was the same, but the water absorption rate of the protective layer was lower, and no image defects occurred even in images under high humidity (Comparative Example 10). However, if the thickness of the protective layer is increased to further improve the printing life, the electrophotographic properties will deteriorate.
Staining of the skin occurred (Comparative Example 11). However, in the photoreceptors of Examples 1 to 9 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, and While maintaining almost the same electrophotographic properties as the photoreceptor without protective layers 1 to 3, the abrasion resistance has been significantly improved, and the printing life has been greatly improved. Even if the thickness was increased to 3 μm, no deterioration in electrophotographic properties was observed). 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. (Effect of the invention) A specific butyl etherified melamine/formaldehyde resin, alkyl etherified benzoguanamine/formaldehyde resin, and an electron-accepting carboxylic acid or its acid anhydride are used on the surface of the electrophotographic photoreceptor that can function with positive charging according to the present invention. An electrophotographic photoreceptor having a protective layer containing a cured film containing as a component has excellent electrophotographic properties and is excellent in environmental resistance and durability.

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) an alkyl etherified benzoguanamine/formaldehyde resin having a number average molecular weight of 400 to 2000; and (c) an electron-accepting carboxylic acid compound and/or an electron-accepting polycarboxylic acid anhydride. A positively charged electrophotographic photoreceptor comprising a protective layer containing a cured film containing a compound as a component. 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 product. 3. An electrophotographic photoreceptor capable of functioning with positive charging has 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 stacked one after another on a conductive layer. A positively charged electrophotographic photoreceptor according to claim 1, which is a positively charged electrophotographic photoreceptor. 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.