JPH0245183B2 - SEITAIDENGATADENSHISHASHINKANKOTAI - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a positively charged electrophotographic photoreceptor having excellent electrophotographic properties and durability. (Prior Art) In an electrophotographic photoreceptor that uses a photoconductive substance as a photosensitive material, conventionally, as the conductive substance,
Inorganic photoconductive materials such as selenium, zinc oxide, titanium oxide, and cadmium sulfide have been mainly used. However, many of these are generally highly toxic;
There are also problems with the method of disposal. 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 respect, an electrophotographic photoreceptor that can be used with positive charging is desirable. On the other hand, a single-layer electrophotographic photoreceptor made of 2,4,7-trinitrofluorenone and polyvinylcarbazole can be used even if it is positively charged;
4,7-trinitrofluorenone has toxicity problems and is difficult to use in the future. Further, a single-layer type electrophotographic photoreceptor made of an organic pigment that generates a charge without any toxicity problem and a charge transport material having a charge transport function can be used even when positively charged, but the sensitivity is low. For these reasons, there is a strong desire to develop a positively charged electrophotographic photoreceptor that is free from safety problems and has excellent electrophotographic properties. On the other hand, in the electrophotographic apparatus described above, it is usually necessary to remove (clean) a small amount of toner remaining on the surface of the photoreceptor using a brush, blade, or the like. By repeating this cleaning process, the surface of the photoreceptor is worn and damaged, resulting in blurred transferred images and, in some cases, peeling of the charge transport layer and charge generation layer. The life of the photoreceptor will be significantly shortened. Due to these problems, photoreceptors are required to have strong durability. In order to improve durability, it has been proposed to provide a protective layer on the surface as disclosed in JP-A-52-76928 and JP-A-54-17732, but the conventional protective layer However, the abrasion resistance effect is not sufficient and the electrophotographic properties tend to increase the residual potential and decrease the sensitivity. desired. 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 characteristics and durability. (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 transport layer, a charge generation layer containing an organic pigment that generates a charge, and a protective layer are sequentially laminated on a conductive layer, and the protective layer has a number average molecular weight of 1500 or less. The present invention relates to a positively charged electrophotographic photoreceptor containing a butyl etherified melamine/formaldehyde resin in which the number of bound formaldehydes per melamine nucleus is 2 to 4 and the number of methylols is 1 to 2. The materials used in the electrophotographic photoreceptor of the present invention will be described in detail below. First, in the present invention, a conductive layer is a conductive-treated paper or plastic film, a plastic film laminated with metal foil such as aluminum,
It is a conductor such as a metal plate. The charge transporting substance that is the main component of the charge transport layer includes polymer compounds such as poly-N-vinylcarbazole, polyvinylpyrene, polyvinylbenzothiophene, and polyvinylpyrazoline, carbazole, 3-phenylcarbazole, and 2-phenylcarbazole. enylindole, oxadiazole, 1-phenyl-3
-(4-diethylaminostyryl)-5-(4-
Low molecular weight compounds such as (diethylaminophenyl) pyrazoline, hydrazone, 2-phenyl-4-(4-diethylaminophenyl)-5-phenyloxazole, triphenylamine, and imidazole, and electron-donating compounds such as derivatives thereof. . In addition, examples of organic pigments that generate charges included in the charge generation layer include azoxybenzene-based pigments,
Any pigment known to generate an electric charge can be used, such as disazo-based, trisazo-based, benzimidazole-based, polycyclic quinone-based, indigoid-based, quinacridone-based, perylene-based, and methine-based pigments. These pigments are, for example, disclosed in Japanese Patent Application Laid-open No.
No. 37544, JP-A-47-18543, JP-A-47-18544
No., JP-A-48-43942, JP-A-48-70538, JP-A-49-1231, JP-A-49-105536, JP-A-50
-75214, JP-A-50-92738, etc. In particular, the τ, τ', η, and η' type metal-free phthalocyanines described in Japanese Patent Application Laid-Open No. 182640/1982 and European Patent Application Publication No. 92255 have high sensitivity to long wavelengths and can be used as diode lasers. It is also effective as an electrophotographic photoreceptor for installed printers. Additionally, additives such as binders, plasticizers, flowability agents, pinhole inhibitors, etc., which are commonly used in electrophotographic photoreceptors, can be added to the charge transport layer and the charge generation layer as necessary. . As a binder,
Examples include silicone resin, polyamide resin, polyurethane resin, polyester resin, epoxy resin, polyketone resin, polycarbonate resin, polystyrene resin, polymethyl methacrylate resin, and polyacrylamide resin. Furthermore, thermosetting resins and photocuring resins that are crosslinked by heat and/or light can also be used. In any case, there are no particular limitations as long as the resin is insulative and can form a film under normal conditions, and the resin can be cured by heat and/or light to form a film. Examples of the plasticizer include halogenated paraffin, dimethylnaphthalene, dibutyl phthalate, and the like. As the fluidity imparting agent, Modaflow (manufactured by Monsanto Chemical Company),
Examples include Acronal 4F (manufactured by Basf), and pinhole inhibitors include benzoin, dimethyl phthalate, and the like. These may be selected and used as appropriate, and the amount thereof may be determined as appropriate. If the charge transporting substance is a polymer compound in the charge transport layer, a binder may not be used, but the binder may be used in an amount of 400% by weight or less based on the polymer compound. It's okay. The amount of binder is 400
If the amount exceeds % by weight, the electrophotographic properties will deteriorate. In addition, when the charge transport substance is a low molecular compound, the binder is added to the low molecular compound at a
Use 400% by weight. When the binder content is less than 30% by weight, it tends to be difficult to form a charge transport layer, and when it exceeds 400% by weight, the electrophotographic properties tend to deteriorate. Further, additives such as plasticizers are appropriately used in an amount of 5% by weight or less based on the charge transporting substance. The binder can be used in the charge generating layer in an amount up to 400% by weight based on the charge generating material.
If the amount of binder exceeds 400% by weight, the electrophotographic properties will deteriorate. The above-mentioned additives such as plasticizers are appropriately used in an amount of 5% by weight or less based on the total amount of organic pigments. Next, the cured film of butyl etherified melamine/formaldehyde resin forming the protective layer will be described in detail. The cured film is obtained by curing a coating film of butyl etherified melamine/formaldehyde resin. The number average molecular weight of the butyl etherified melamine formaldehyde resin used in the present invention is 1500 or less, and when the number average molecular weight exceeds 1500, the reactivity decreases. The resin also has 2 to 4 bound formaldehydes per melamine core. When the number exceeds 4, the reactivity decreases, and when the number is less than 2, safety deteriorates. 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 if it is less than 1, the reactivity will be poor. Butyl etherified melamine with this structure
Formaldehyde resin has the characteristics of curing at a lower temperature and forming a hard film than normal melamine resin, and is suitable as a material for the protective layer of electrophotographic photoreceptors using organic materials that are not very heat resistant. . The butyl etherified melamine/formaldehyde resin used in the present invention 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, It can be produced by heating this solution to carry out 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 about 90-100℃
It is preferable that In the present invention, it is preferred to carry out the reaction using 4 to 5 moles of butanol and 3 to 7 moles of formaldehyde per mole of melamine. In order to cure the above-mentioned butyl etherified melamine formaldehyde resin, a method is adopted in which the resin is heated in the presence or absence of a curing catalyst, and a method in which a resin that can be cured by reacting with the resin is used in combination. Ru. Examples of the curing catalyst include acids such as hydrochloric acid, phosphoric acid, and p-toluenesulfonic acid, and the amount thereof added is preferably 1% by weight or less based on the butyl etherified melamine/formaldehyde resin. Examples of resins that can be cured by reacting with butyl etherified melamine/formaldehyde resins include acrylic resins, alkyd resins, and alkyd-modified acrylic resins, and the hydroxyl value of these resins is 15 to 200.
It is preferable that If the hydroxyl value is less than 15, the curability of the resin will be poor, and if it exceeds 200, the water resistance of the protective layer will be poor. Butyl etherified melamine
The formaldehyde resin and the resin that can be cured by reacting with the resin have a weight ratio of the former/latter of 5/95 to 5/95.
Mix so that the ratio is 100/0. If the butyl etherified melamine/formaldehyde resin is less than 5% by weight, the durability as a protective layer decreases. The protective layer can contain appropriately selected various additives used in the charge transport layer and the charge generation layer, and the amount of the additives can also be determined as appropriate. The electrophotographic photoreceptor of the present invention has a charge transport layer, a charge generation layer, and a protective layer formed in this order on a conductive layer. This electrophotographic photoreceptor is manufactured by applying a uniform positive charge to its surface by corona discharge in advance, and then irradiating it with light. Among the carriers generated in the upper charge generation layer, electrons pass through the organic pigment to the surface. Neutralizing the positive charges, holes are injected from the charge generation layer into the charge transport layer and reach the conductive layer through the charge transport material, especially the electron donating compound. The thickness of the charge transport layer is 5 to 50 μm, preferably 8 μm.
~20 μm. A thickness of less than 5 μm results in a low initial potential, and a thickness greater than 50 μm results in a decrease in sensitivity.
In addition, the charge generation layer has a thickness of 0.001 to 10 μm, preferably
Make it 0.2-5 μm thick. If it is less than 0.001 μm, it will be difficult to form a charge generation layer uniformly, and if the thickness is less than 10 μm,
If it exceeds 20%, the electrophotographic properties tend to deteriorate. The thickness of the protective layer is 0.01~10μm, preferably 0.1~
It is 5μm. If it is less than 0.01μm, it will have little effect as a protective layer and have poor durability, and if it exceeds 5μm,
Sensitivity is poor and residual potential tends to increase. When manufacturing the electrophotographic photoreceptor of the present invention, first, in order to form a charge transport layer, necessary components are mixed with a ketone solvent such as acetone and methyl ethyl ketone, an ether solvent such as tetrahydrofuran,
After uniformly dissolving it in an aromatic solvent such as toluene or xylene, a halogenated hydrocarbon solvent such as methylene chloride or carbon tetrachloride, or an alcohol solvent such as methanol, ethanol or propanol, it is applied onto the conductive layer, dry. Next, in order to form a charge generation layer, necessary components are dispersed in an organic solvent, coated on the charge transport layer, and dried, as in the case of forming the charge transport layer. after that,
Furthermore, in order to form a protective layer, the necessary components are dissolved in an organic solvent, coated on the charge generation layer, and dried, as in the case of forming the charge transport layer. The electrophotographic photoreceptor of the present invention may further have a thin adhesive layer or barrier layer immediately above the conductive layer. When copying is performed using the electrophotographic photoreceptor of the present invention, the surface is charged and exposed in the same manner as before, and then developed and the image is transferred onto plain paper.
It just needs to take root. (Function) The butyl etherified melamine/formaldehyde resin used for the protective layer in the present invention cures at a lower temperature than ordinary melamine resins and forms a hard film. The formed film protects the electrophotographic photoreceptor and significantly improves its durability without impairing the electrophotographic properties of the electrophotographic photoreceptor. The electrophotographic photoreceptor of the present invention having such a protective layer can be used with positive charging, has high sensitivity, and has excellent durability. (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) Charge transport substance 2-(p-diethylaminophenyl)-4-
(p-dimethylaminophenyl)-5-(o-
(chlorophenyl)-1,3-oxazole (OXZ) (2) Organic pigment that generates charge τ-type metal-free phthalocyanine (H ₂ PC) (3) Binder Polyester resin: Vylon 200 [Toyobo Co., Ltd. trade name] Butyral Resin: Eslex BM-S [Sekisui Chemical Co., Ltd. product name] (4) Butyl etherified melamine formaldehyde resin (BMF) (Synthesis of BMF-1) In a flask equipped with a stirrer, reflux condenser, and thermometer. Melamine 126g, n-butanol 444g 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 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, 61% nitric acid aqueous solution
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 obtained resin is Gardner (25℃)
So it was C. 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 and BMF-2 are shown in Table 1 below. However, the number of bound formaldehyde is determined by measuring the amount of unreacted formaldehyde using the sodium sulfite method, and the number of butyl ether groups is determined by measuring the amount of butanol charged and 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] Comparative Example 10 g of OXZ and 10 g of Byron 200 were completely dissolved in 80 g of tetrahydrofuran. This solution was applied onto an aluminum plate (conductive layer) using an applicator and dried at 90°C for 20 minutes to form a charge transport layer with a thickness of 15 μm. Next, H ₂ PC 2.0g, Esrex BM-S 2.0g
A mixed solution of 80 g of methanol and 80 g of methanol was kneaded for 8 hours using a ball mill (3-inch pot mill manufactured by Nippon Kagaku Tou Co., Ltd.). The resulting dispersion was applied onto the charge transport layer using an applicator and dried at 100°C for 1 hour to form a charge generation layer with a thickness of about 1 μm, forming an electrophotographic photoreceptor without a protective layer. Created. Examples 1 to 4 A charge transport layer and a charge generation layer were formed on a conductive layer in the same manner as in the above comparative example. Next, add BMF-1 or BMF-2 to isopropanol until the solid content is 5.
The resulting solution was applied to the above charge generation layer using an applicator and cured by heating at 120°C for 1 hour to form a protective layer with a thickness shown in Table 2. An electrophotographic photoreceptor having layers was obtained. The electrophotographic properties of the obtained electrophotographic photoreceptor were measured using an electrostatic recording tester (SP-428 manufactured by Kawaguchi Electric), and the results are shown in Table 2. In addition, the initial potential V ₀ (V) in the table indicates the charging potential when a positive 5KV corona is discharged for 10 seconds in dynamic measurement, and the dark decay (Vk) indicates the charging potential when the corona is discharged for 10 seconds in a dark place. It shows the potential decay rate, and the half-reduction exposure amount (E50) shows the light amount value until the potential is halved when irradiated with 10 lx white light. In addition, the spectral sensitivity of 800nm (S800) uses a halogen lamp as a light source and passes through a monochromator.
Irradiate monochromatic light of 800 nm, find the time t (s) required for the potential to be halved after irradiation, multiply this by the energy of the irradiated light (mW/m ² ), and take the reciprocal. This is what I was looking for. Furthermore, using a friction tester (manufactured by Suga Test Instruments),
The surface of the electrophotographic photoreceptor was rubbed with gauze, and the number of times that fiber traces of the gauze were visually confirmed on the surface of the photoreceptor is shown in Table 2 as abrasion resistance.

[Table] (Effects of the invention) The electrophotographic photoreceptor according to the present invention, which has a cured film of butyl etherified melamine/formadehyde resin on its surface as a protective layer, exhibits excellent electrophotographic properties, good dark decay, and high sensitivity. It is. especially,
Due to its high spectral sensitivity at 800 nm, it is equipped with a diode laser with an oscillation wavelength in the near-infrared region.
It is also applicable to LBP. Further, the abrasion resistance of the electrophotographic photoreceptor of the present invention is extremely high. In this way, the electrophotographic photoreceptor of the present invention is
This is a positively charged electrophotographic photoreceptor with high electrophotographic properties and durability.

Claims (1)

[Scope of Claims] 1. An electrophotographic photoreceptor in which a charge transport layer, a charge generation layer containing an organic pigment that generates charges, and a protective layer are sequentially laminated on a conductive layer, wherein the protective layer has a number average molecular weight of 1500. A positively charged electrophotographic photoreceptor comprising a cured film of a butyl etherified melamine/formaldehyde resin having the following properties and the number of bound formaldehydes per melamine nucleus is 2 to 4 and the number of methylols is 1 to 2. 2. The positively charged electrophotographic photoreceptor according to claim 1, wherein the charge transport layer contains an electron donating compound as a charge transporting substance. 3. The positively charged electrophotographic photoreceptor according to claim 1 or 2, wherein the organic pigment that generates a charge is at least one of τ, τ', η, and η' type metal-free phthalocyanines.