JPS61210361A - Positively electrifiable type electrophotographic sensitive body - Google Patents

Abstract

PURPOSE:To obtain a positively electrifiable electrophotographic sensitive body good in electrophotographic characteristics and image quality, high in abrasion resistance, and long in printing resistance life by using a specified binder for an electrostatic charge generating layer. CONSTITUTION:A charge transfer layer contg. a charge transfer material of an electron donor, and the charge generating layer contg. an org. pigment producing charge, such as one of tau, tau', eta, and eta'-type metal-free phthalocyanines, and a hardened product of a polyvinyl-acetal resin and a butyl-etherified melamine-formaldehyde resin in a weight ratio of 95:5-30:70, having a number average mol.wt. of <=1,500, a bonded formaldehyde number of 2-4 and a methylol number of 1-2 per mol of melamine are laminated on a conductive substrate in succession.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a positively charged electrophotographic photoreceptor with excellent image quality and a long printing life.

(Prior Art) In an electrophotographic photoreceptor that uses a photoconductive substance as a photosensitive material, conventional photoconductive substances are used as photoconductive substances.

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 and there are problems with how to dispose of them.

On the other hand, photosensitive materials using organic photoconductive compounds are generally less toxic than those using inorganic photoconductive substances, and also have transparency, flexibility, lightness, surface smoothness, price, etc. Since it is advantageous in this respect, 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 developed in recent years because they can greatly improve the sensitivity, which was a major drawback of conventional photoreceptors using organic photoconductive compounds. Rapid progress is being made.

When these composite photoreceptors are applied to an electrophotographic device using the Carlnon method, an electrostatic latent image is first formed on the surface of the photoreceptor, and then developed with a developer generally called a toner that is charged with opposite signs. The toner image can be transferred to another substrate 1, such as paper, and then a copy can be obtained.

(Problems to be Solved by the Invention) Electrophotographic photoreceptors using conventional organic photoconductive compounds generally have a charge generation layer and a hole transfer type charge transport/it sequentially laminated on a conductive layer. Therefore, the surface of the photoreceptor is charged negatively for convenience. When negatively charged by corona discharge, more ozone is generated than when positively charged, and charging tends to be uneven.

In this respect, it is desirable to use an electrophotographic photoreceptor that can be positively charged.

On the other hand, a single-layer electrophotographic photoreceptor made of 2,4,7-)linitrofluorenone and polyvinylcarbazole can be used even if it is positively charged, but 2,4,7-linitrofluorenone has toxicity problems. There is.

It will be difficult to use it 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 photographic properties.

Therefore, one object of the present invention is to provide a positively charged electrophotographic photoreceptor with excellent electrophotographic properties without using toxic substances.
tOne purpose.

Further, the positively charged ffi electrophotographic photoreceptor of the present invention provides an electrophotographic photoreceptor in which a charge transport layer and a charge generation layer are successively laminated on a conductive layer, but the present inventors have According to the study, if the charge generation layer is non-uniform,
In particular, uneven dispersion of pigments causes many image defects.

■If you dry the charge generation layer at high temperatures for a long time.

The material used for the photoreceptor deteriorates due to heat, resulting in a significant drop in electrophotographic properties, and as a result, background stains occur on the image.■The thin charge generation layer is a surface layer. It is known that in order to improve the printing life, it is necessary to use a binder with high wear resistance in the charge generation layer.

Therefore, the main object of the present invention is to provide a positively charged electrophotographic photoreceptor that has good electrophotographic characteristics and image quality, has high wear resistance, and has a long printing life.

(Means for Solving the Problems) The present invention achieves the above objects by using specific butyl etherified melamine formaldehyde resins and polyvinyl acetal resins as binders for the charge generation layer.

That is, the present invention provides an electron-donating compound 15 on the conductive layer (A).
00 or less, and the number of formaldehydes bound per one melamine nucleus is 2 to 4, and it relates to a methylol electrophotographic photoreceptor.

Materials used in the positive charge plate electrophotographic photoreceptor according to the present invention will be described in detail below.

First, in the present invention, the conductive layer is a conductive material such as conductively treated paper, conductively treated plastic, a plastic film laminated with metal foil such as aluminum, a metal plate, or a metal drum.

The charge transporting substance which is the main component of the charge transporting layer includes polymer compounds such as poly-N-vinylcarbazole, polyvinylpyrene, polyvinylbenzothiophene, and polyvinylpyrazoline, and carbazole.

3-phenylcarbazole, 2-phenylindole,
Oxadiazole, l-722-3-(4-diethylaminosteryl)-5-(4-diethylaminophenyl]pyrazoline, hydrazone.

2-phenyl-4-(4-diethylamino7enyl)-
There are electron-donating compounds such as low molecular weight compounds such as 5-phenyloxazole, triphenylamine, and imidazole, and derivatives thereof, and these are selected with due consideration to safety.

Further, additives such as a binder, a plasticizer, a fluidity imparting agent, and a pinhole suppressing agent, which are commonly used in electrophotographic photoreceptors, can be added to the charge transport layer as necessary. Silicone resin is used as a binder.

Polyamide resin, polyurethane resin, polyester resin, epoxy resin, polyketone resin, polycarbonate resin, polystyrene resin, polymethyl methacrylate resin,
Examples include polyacrylamide resin. Furthermore, thermosetting resins and photocuring resins that are crosslinked by heat and/or light can also be used. In any case, there is no particular restriction as long as the resin is insulating and forms a film under normal conditions, or the resin is cured by heat and/or light to form a film. Halogenated paraffins are used as plasticizers.

Examples include dimethylnaphthalene and dibutyl phthalate. Examples of the fluidity imparting agent include Modaflow (manufactured by Monsanto Chemical Company) and Acronal 4F (manufactured by Pass 7 Company), and examples of the pinhole suppressor include benzoin and dimethyl heptatalate. These may be selected and used as appropriate, and the amount thereof may be determined as appropriate.

In the charge transport layer, when the charge transport substance is a polymer compound, a binder may not be used, but the binder may be used in an amount of tl-400% by weight or less based on the polymer compound. May be used. When the amount of binder exceeds 40,000 weight, the electrophotographic properties deteriorate. Further, when the charge transporting substance is a low molecular weight compound, it is used in an amount of 30 to 400 times the binder ti low molecular weight compound. The binder is 3
If the amount is less than 0% by weight, it tends to be difficult to form a charge transport layer (II), and if it exceeds 400% by weight, the electrophotographic properties tend to deteriorate. In addition, additives such as plasticizers,
It is suitably used in an amount of 5% by weight or less based on the charge transporting substance.

Examples of organic pigments that generate charges contained 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,
Pigments known to generate charges, such as methine-based pigments, can be used.

These pigments are disclosed in, for example, JP-A No. 47-37453;
JP-A-47-37544, JP-A-47-18543, JP-A-47-18544 1% JP-A-48-43942
No. 0% Kai No. 48-70538.

These are disclosed in JP-A-49-1231 1%, JP-A-49-105536, JP-A-50-75214, and JP-A-50-92738. Especially JP-A-58-18264
τ, τ', v and η' type gold metal phthalocyanine described in Publication No. 0 and European Patent Application Publication No. 92255, which has high sensitivity to long wavelengths and is suitable for printers equipped with diode lasers. It is also effective as an electrophotographic photoreceptor. In addition to these, any organic pigment that generates charge carriers upon irradiation with light can be used.

The charge generating layer of the present invention can be obtained by uniformly dissolving or dispersing these organic pigments in specific butyl etherified melamine formaldehyde resins and polyvinyl acetal resins, and curing the film by heating.

Butyl etherified melamine used in the present invention
The formaldehyde resin has a number average molecular weight of 1,500 or less, and a number average molecular weight of more than 1,500 lowers its reactivity. The resin has 2 to 4 bound formaldehydes per melamine core. If it exceeds 4, the 9 reactivity will decrease, and if it is less than 2, the storage stability of the resin will deteriorate,
The cured coating becomes brittle. Further, the resin has one melamine nucleus or one to two methylol groups.

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 heating the solution. It can be produced by a method of carrying out an addition reaction and a butyl etherification reaction. In these methods the reaction is nitric acid.

It is preferable to add an acidic catalyst such as hydrochloric acid, sulfuric acid, phosphoric acid, or p-toluenesulfonic acid, and carry out the reaction under acidic conditions, preferably at pH 3 to 6.1 The reaction temperature is the reflux temperature of butanol, preferably about 90 to 100°C. 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.

The reason for specifying the butyl etherified melamine/formaldehyde resin used in the charge generation layer of the present invention is that by using such a resin, it can be cured at a lower temperature than conventional melamine resins, and when forming the charge generation layer, it can be cured at a lower temperature. This is because the electrophotographic photoreceptor is not thermally degraded, so that a charge generation layer that maintains good electrophotographic properties and has high wear resistance can be formed. Since it has a good effect on the dispersibility of organic pigments, a charge generation layer can be formed uniformly, and the quality of the resulting image is also extremely high.

Next, the polyvinyl acetal resin used in combination with this butyl etherified melamine/formaldehyde resin will be explained. By combining the polyvinyl acetal resin of the present invention, the uniform dispersibility of the organic pigment is further improved, and a charge generation layer having excellent abrasion resistance after curing can be formed.

The polyvinyl acetal resin according to the second aspect of the present invention is as follows.

Those having a number average molecular weight of s, o o o to 250,000 are preferable, and have repeating units of the following formulas 1-11 or 4.

(However, R is hydrogen or an alkyl group such as a methyl group) ■, vinyl alcohol group ■, vinyl acetate group In the repeating unit of formula 1-Ill, the vinyl acetal group is 70% by weight or more, and the vinyl alcohol group is 4% by weight.
-25% by weight and 0-26% by weight of vinyl acetate groups are used. In particular, if the ratio of the vinyl alcohol group is less than 4 weight xi, the curing reaction when forming the charge generation layer by heat curing in combination with the above-mentioned butyl etherified melamine formaldehyde resin will be slow, and the charge generation layer will be It also has poor wear resistance. Moreover, if it exceeds 25% by weight, the uniform dispersion of the pigment tends to decrease and the charge generation layer tends to become brittle. An example of a method for producing polyvinyl acetal resin is to first polymerize vinyl acetate hetamine to synthesize polyvinyl acetate.

Polyvinyl alcohol is produced by saponifying polyvinyl acetate. At this time, some vinyl acetate groups remain. Next, an aldehyde such as butyraldehyde or formaldehyde is added to perform acetalization, thereby making it possible to completely produce a polyvinyl acetal resin.

As the binder for the charge generating layer of the present invention, a butyl etherified melamine formaldehyde resin and a polyvinyl acetal resin can be used in a weight ratio of 95=5 to 30 n/0.

In particular, a ratio of 80:20 to 50:50 is optimal. If the ratio is outside these ranges, the dispersibility of the pigment in the charge generation layer is poor, resulting in a decrease in image quality and also in the abrasion resistance of the charge generation layer.

The ratio of organic pigment and binder (butyl etherified melamine/formaldehyde resin and mixture of hypoly and nyl acetal resin) in the charge generation layer is 80:20 to 20 by weight.
: Can be used within the range of 80. 60 to Il#:
A ratio of 40 to 40:60 is optimal. 8 organic pigments
If it exceeds 0 weight, the organic pigment in the charge generation layer will not be uniformly dispersed, resulting in poor image quality and poor abrasion resistance. Additionally, the binders lumaldehyde resin and polyvinyl acetal resin are cured. As the curing catalyst used at this time, hydrochloric acid, phosphoric acid, p-toluenesulfonic acid, etc. are used in an amount of 5% by weight or less. The charge generation layer of the present invention may further contain additives used in the charge transport layer, such as a fluidity imparting agent, a pinhole suppressor, and a pinhole suppressor.

The electrophotographic photoreceptor of the present invention has a structure in which a charge transport layer and a charge generation layer are sequentially laminated on a conductive layer.

The thickness of the charge transport layer is 5 to 50 μm, preferably 8 to 20 μm.
It is μm. When the thickness is less than 5 μm, the charging property decreases.

If it exceeds 50 μm, sensitivity decreases.

The thickness of the charge generation layer is 0.01 to 10 μm, preferably 0.01 to 10 μm.
．． It is 2 to 5 μm. If it is less than 0.01 μm, it will be difficult to uniformly form a charge generation layer, and if it exceeds 10 μm, the electrophotographic properties will deteriorate.

When forming a charge transport layer, charge transport materials, binders and additives may be used such as acetone, methyl ethyl ketone, tetrahydrofuran, toluene, methanol, ethanol, xylene, methylene chloride, etc.

L, 2-) Uniformly in a solvent such as IJ dichlorothane?
It can be formed by coating and drying after it is dissolved.

When forming a charge generation layer, after uniformly dispersing or dissolving an organic pigment, a certain percentage of butyl etherified melamine/formaldehyde resin, polyvinyl acetal resin, a curing catalyst, and other additives as necessary in an organic solvent. , can be applied, dried and formed. The drying temperature at this time is preferably 100 to 140°C.

The electrophotographic photoreceptor of the present invention may have a thin contact layer immediately above the conductive layer, a barrier layer, and a protective layer on the surface.

When copying is performed using the electrophotographic photoreceptor of the present invention, the surface may be charged and exposed in the same manner as in the prior art, developed, and the image transferred onto plain paper for further printing.

(Function) By using specific butyl etherified melamine formaldehyde resin and polyvinyl acetal resin as a binder in the charge generation layer in the second aspect of the present invention, the dispersibility of the pigment is improved, and the coating film appearance is also good and the printing quality is high. You can get the image.

In addition, it is possible to form a strong charge generation layer by curing at low temperatures.
It is possible to obtain an electrophotographic photoreceptor that does not deteriorate due to heat during the formation of the charge generation layer, maintains good electrophotographic properties, and has good abrasion resistance, that is, has a long printing life.

Furthermore, since the electrophotographic photoreceptor of the present invention is positively charged, it generates less ozone during corona charging during one use, and can be applied to a printing system with less environmental pollution.

(Examples) 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) Charge transporting substance 2-(p-dimethylamino)phenyl-4-(p-dimethylamino)phenyl-3-(0-chlorophenyl)
-1,3-Oxazole (OXZ) (2) Organic pigment τ-type metal-free 7-talocyanine (τ-)hPc) that generates electric charge (3)
Binder Binder polyester resin for charge transport layer: Pylon 200 [Toyobo ■Product name] (Bl Binder for charge generation layer (1) Acrylic resin: Elbasai) 2045 (
DuPont product name] (II) Polyvinyl acetal resin 0 Polyvinyl butyral resin (Al): Denkapterra Luna 3000-1 [Denka Kagaku Kogyo ■] O Polyvinyl formal resin (A2): Denka Formal Luna 20 [Denka Kagaku Kogyo ■] (Characteristics of each resin are shown in Table 1) (iil Butyl etherified melamine formaldehyde resin (BMF') (Synthesis of BMF-1) 126 g of melamine, n-butanol in a flask equipped with a stirrer, reflux condenser, and thermometer. 4449 and 0.29% of a 61% nitric acid aqueous solution were added and the temperature was raised to 100°C, then paraformaldehyde 1699 was added at equal intervals in 6 portions for 30 minutes, and then reacted at reflux temperature for 30 minutes to remove water. However, I was disappointed in Canada.

(Synthesis of BMF-2) Melamine 126 was synthesized using the same equipment as BMF-1.
9. n-butanol 4449.61% nitric acid aqueous solution 0.2
9 and 169 g of paraformaldehyde were mixed and charged, the temperature was raised to 100° C., and the mixture was reacted for 30 minutes. After that, reflux dehydration was performed for 30 minutes.

-C at the donor (25°C).

(Synthesis of BMF-3) Using the same apparatus as in the synthesis of BMF-1, 217.5 g of paraformaldehyde, 4449 n-butanol, and 126 g of melamine were weighed out, and an addition reaction was performed at 90 to 100° C. for 30 minutes. Thereafter, the mixture was cooled to 40 to 45°C, 0.19% of phthalic acid was added, and reflux dehydration and dissolution were performed under acidic conditions. After this, adjustments were made so that the amount remaining after heating was 50 inches.

The viscosity at this time was B in Gardner (25°C).

Melamine core 1 of BMF-1, BMF-2 and BMF-3
Table 2 shows the number of formaldehyde bonds, the number of butyl ether groups, the number of methylol groups, and the number average molecular weight per unit.

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 from the amount of butanol charged and unreacted butanol by gas chromatography using 5ee-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.

Comparative Example 1 Oxz 59 and polyester resin 159 were mixed in 140 g of tetrahydrofuran and completely dissolved. The obtained solution was applied to an aluminum plate (thickness 0) using an applicator.
．． 1 mm) and dried at 90'i: for 1 hour to form a 15 μm charge transport layer.

Next, r H2POZOg, 7 acrylic resin 109 g, tetrahydrofuran 83 g, and ingropanol 13 g were mixed using a ball mill (Nippon Kagaku Togyo R3 size pot mill).
Kneaded for hours. The resulting pigment 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 having a thickness of about 1.0 μm.

Comparative Examples 2 to 3 2.0 g of τ-H5PC, 34.0 g of BMF (solid content: zo g), and 94 g of methyl alcohol were kneaded for 8 hours using a ball mill. The obtained pigment separation liquid was applied onto a charge transport layer prepared in the same manner as in Comparative Example 1 using an applicator to form a charge generation layer having a thickness of about 1.0 μm. Table 3 shows the drying conditions for the charge generation layer.

Comparative example 4 τ-H2PC 2.0 g, BMF -32.49 (solid content 1.29), polyvinyl butyral resin 0.8
g and 94.59 g of methyl alcohol were kneaded for 8 hours using a ball mill. The resulting pigment dispersion was prepared in the same manner as in Comparative Example 1. It was applied onto the charge transport layer using an applicator and dried at 160° C. for 3 hours to form a charge generation layer with a thickness of about 1.0 μm.

Examples 1 to 5 r HzPC2.0g, a mixed binder of nophthylnitered melamine/formaldehyde resin and polyvinyl acetal resin in the composition ratio shown in Table 3 was mixed with a solid content of '2.0g. ．． Og
Then, methyl alcohol was added so that the total solid content was 4% by weight, and the mixture was kneaded for 8 hours using a ball mill. However, only in the case of Example 3, a mixed bath medium containing methyl alcohol and tetrahydrofuran in a ratio of 50:50 was used. The resulting pigment dispersion was applied using an applicator onto a charge transport layer prepared in the same manner as in Comparative Example 1 to form a charge generation layer having a thickness of about 0.5 to 10 μm. Table 3 shows the drying conditions for the charge generation layer.

The electrophotographic properties of the obtained electrophotographic photoreceptor were measured using an electrostatic recording paper tester (5P-428 manufactured by Kawaguchi Denki), and the results are shown in Table 3.

The initial potential V (1 (V)) in the table indicates the electrical potential when a positive 5KV corona is discharged for 10 seconds in dynamic measurement, and the dark decay (V, ) indicates the potential when left in a dark place for 30 seconds. Indicates the attenuation rate and half-exposure (Eso
) shows the light amount value until the 10 lux white light is irradiated and the value becomes half. The residual potential VR indicates the surface potential after irradiation with 10 lux white light for 30 seconds. Furthermore, using a friction tester (manufactured by Suga Test Instruments), 1 was slid on the surface of the child photoreceptor with gauze.

Wear resistance was evaluated by the number of times the surface was slid until the wear scratches passed through the charge generation layer and reached the charge transport layer.

In addition, pieces of the obtained electrophotographic photoreceptor were
Attach it to a L aluminum tube and use an image evaluation machine (positive charging type, regular development method) to check for poor dispersion of the organic pigment in the charge generation layer, white spots on solid black areas due to non-uniformity, density unevenness, background stains, etc. The image quality was evaluated. The results are shown in Table 3.

In Comparative Example 1, a charge generation layer could be formed by drying at low temperature, but the image quality was poor because the pigment in the charge generation layer was poorly dispersed and nonuniform. Comparative Examples 2 and 3 are cases where a melamine resin outside the scope of the melamine resin specified in the present invention was used as a binder for the charge generation layer, but the pigment dispersibility was still low and the image quality was correspondingly poor. There is. Furthermore, when the drying temperature of the charge generation layer was lowered (Comparative Example 2), the abrasion resistance of K was poor because the melamine resin was insufficiently cured. On the other hand, when drying at high temperature for a long time (Comparative Example 3), the abrasion resistance improves.

Due to thermal deterioration of other materials of the photoreceptor, deterioration of electrophotographic properties, particularly an increase in half-decreased exposure and residual potential, was observed, and as a result, new background stains appeared in the image. Comparative Example 4 is a case where a melamine resin outside the scope of the melamine resin specified in the present invention and a specified polyvinyl acetal resin were used as the binder of the charge generation layer, but the dispersibility was improved compared to Comparative Examples 1 to 3. As a result, image defects such as density unevenness and white spots in solid black areas are reduced. However, since drying of the charge generation layer requires a high temperature and a long time, as in Comparative Example 3, the half-reduced exposure amount and the residual potential increase significantly, resulting in an image with a lot of background stains.

On the other hand, the photoreceptors of Examples 1 to 5 according to the present invention were:
Good images without image defects can be obtained because the pigment in the charge generation layer is uniformly dispersed, and the electrophotographic properties are improved because the charge generation layer can be dried at low temperatures and in a short time. It will be done. It is also understood that since the abrasion resistance is high, a photoconductor with a long printing life can be obtained.

Further, the electrophotographic photoreceptors of Comparative Examples 1 to 4 and Examples 1 to 8 were subjected to a continuous printing test using an image evaluation machine, and the printing life until the image quality deteriorated was evaluated. As a result, there was a correlation between the above-described wear resistance and printing life, and the electrophotographic photosensitive plates shown in the comparative examples generally had a printing life of 500 sheets or less. On the other hand, in the electrophotographic photosensitive plates shown in Examples, no deterioration in image quality was observed even after continuous testing of 15,000 sheets, and it was confirmed that the printing life was limited.

(Effects of the Invention) The electrophotographic photoreceptor of the present invention has a charge generation layer using a specific butyl etherified melamine/formaldehyde resin and polyvinyl acetal resin as a binder, and is laminated on a hole transfer type charge transport layer. It is characterized by having forgery.

As a result, by using a specific binder in the charge generation layer, 1) the dispersibility of the pigment is significantly improved, and 2) the charge generation layer can be formed with low knitting and short drying time, so there is no thermal deterioration of the material. Excellent images without image defects can be obtained because of the good electrophotographic properties. Furthermore, since the abrasion resistance is high, a photoreceptor with a long printing life can be obtained.

Furthermore, since the charge generation layer is laminated on the charge transport layer, it can be used as a positively charged photoreceptor, so it has the advantage of generating less ozone during corona charging and can be applied to printing systems with less environmental pollution. have.

1゛-yo-121゛

Claims (1)

[Scope of Claims] 1. A charge transport layer (B) containing a charge transport substance made of an electron donating compound on the conductive layer (A), an organic pigment that generates a charge, and a number average molecular weight of 1500 or less. , the number of bound formaldehydes per melamine nucleus is 2 to 4.
A positively charged electrophotographic photoreceptor comprising a charge generating layer (C) containing a cured product of a butyl etherified melamine/formaldehyde resin having 1 to 2 methylol groups and a cured polyvinyl acetal resin. 2. 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.