JPS63261269A - Positive chargeable electrophotographic sensitive body - Google Patents

Abstract

PURPOSE:To enhance electrophotographic characteristics and durability of a photosensitive body by forming a protective layer containing an electric charge generating organic pigment. CONSTITUTION:The photosensitive body is formed by successively laminating on a conductive substrate a charge transfer layer containing an electron receptive charge transfer material, a charge generating layer containing an organic pigment (a), preferably such as one or more of tau, tau', eta' and eta-type metal-free phthalocyanines, and the protective layer (A) containing the organic pigment (b), such as a desired pigment containing said phthalocyanine, dispersed into an insulating resin (c), preferably such as a butylated melamine.formaldehyde resin (a) having a number average molecular weight of <=1,500, a bonded formaldehyde number of 2-4 and a methylol number of 1 or 2 per one melamine ring.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a positively charged electrophotographic photoreceptor having excellent electrophotographic properties and durability.

(Prior Art) Conventionally, photoconductive substances are used as photoconductive substances in electrophotographic photoreceptors that utilize photoconductive substances as photosensitive materials.

Inorganic photoconductors 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 in 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 are also transparent, flexible, and lightweight.

It is advantageous in terms of surface smoothness, price, etc.

In recent years, it has been widely researched 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. We are finally making great progress. Such composite photoreceptors are disclosed in, for example, U.S. Pat. No. 3,837,851 and U.S. Pat. No. 3,871,882.

When these composite photoreceptors are applied to an electrophotographic device using the Carlson method,! First, an electrostatic latent image is formed on the surface of the photoreceptor, and then it is developed with a developer, generally called toner, which is charged with the opposite sign.The toner image is transferred and fixed onto another substrate, such as paper, to make a copy. Obtainable.

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 negative charging is performed by corona discharge, more ozone is generated than in the case of positive charging, and charging tends to be uneven. In this respect, it is desirable to use a photoreceptor that can function with positive charging, that is, a positively charged electrophotographic photoreceptor. As a positively charged electrophotographic photoreceptor, there is a photoreceptor in which a charge transport layer containing an electron-donating charge transporting substance and a charge generation layer are sequentially laminated on a conductive layer. Generally, the thickness of the image forming surface layer, that is, the charge generation layer, of this photoreceptor is very thin, about 1 μm at most. However, in the electrophotographic apparatus described above, the toner remaining on the surface of the window photoreceptor after development and transfer is removed using a brush or blade pressed against the surface of the photoreceptor, so if the photoreceptor is used repeatedly, Body surfaces gradually become worn and damaged. Therefore, the above-described positively charged photoreceptor in which the charge generation layer, which is the image forming surface layer, has a thickness of at most 1 μm has a drawback that it is extremely poor in durability and becomes unusable soon.

One possible way to improve this drawback is to provide a protective layer on the charge generation layer. It has been known for a long time to provide a protective layer in order to improve the durability of a photoreceptor.
41F Publication No. 38-20697, U.S. Patent No. 2,8
No. 60,048, No. 2.894708, No. 2
, 901,348 and JP-A-51-78331, protective layers made of polystyrene, poly-n-butyl methacrylate, polyamide, polyester, polyurethane, polycarbonate, polyvinyl formal, cellulose acetate, etc. are proposed. . Also, JP-A-5
Publication No. 0-137740, Publication No. 51-15441,
No. 51-15442, No. 51-54441, No. 51-66834, No. 52-76928, No. 54-35728, No. 54-143644
The application of a crosslinkable protective layer is also proposed in the above publication as a method of improving wear resistance.

(Problems to be Solved by the Invention) However, as the protective layer made of an insulating resin as proposed above, as the film thickness increases, the sensitivity tends to decrease and the residual potential increases. It is not possible to increase the thickness of the photoreceptor, and it is not possible to provide sufficient durability to the photoreceptor. Therefore, it is desired to develop a protective layer that does not impair electrophotographic properties even when the film thickness is increased.

The present invention has developed a protective layer that meets the above requirements.

An object of the present invention is to provide a positively charged electrophotographic photoreceptor having excellent electrophotographic properties and durability.

(Means for Solving the Problems) 5. The present invention provides 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 present invention relates to a positively charged electrophotographic photoreceptor in which the protective layer contains an organic pigment that generates a charge in a sequentially laminated electrophotographic photoreceptor.

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

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, 1-phenyl-3-(4-diethylaminostyryl)-5-(4-diethylaminophenyl)pyrazoline, hydrazone.

2-phenyl-4-(4-diethylaminophenyl)-
Examples include low-molecular compounds such as 5-phenyloxazole, triphenylamine, and imidazole, and electron-donating compounds such as derivatives thereof.

Further, additives such as a binder, a plasticizer, a fluidity imparting agent, a pinhole suppressor, etc., which are commonly used in photographic photoreceptors, can be added to the charge transport layer, if 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 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. Halogenated paraffins are used as plasticizers.

Examples include dimethylnaphthalene and dibutyl phthalate. Examples of the fluidity imparting agent include Modaflow (manufactured by Monsando Chemical Co.) and Acronal 4F (manufactured by Pasuf Co., Ltd.), and examples of the pinhole suppressor include benzoin, dimethyl phthalate, and the like. These may be selected and used as appropriate, and the amount thereof may be determined as appropriate.

In the charge transport layer, if the charge transport substance is a polymer compound, no binder may be used, but the binder may be used in an amount of 400% by weight or less based on the polymer compound. You may. When the amount of binder exceeds 400% by weight, the electrophotographic properties deteriorate. Further, when the charge transport substance is a low molecular weight compound, the binder is used in an amount of 30 to 400% by weight based on the low molecular weight compound. 30% binder by weight
When p is less than 400% by weight, it tends to be difficult to form a charge transport layer, and when it exceeds 400% by weight, electrophotographic properties tend to deteriorate. Further, additives such as plasticizers are appropriately used in the amount of 5 i'- or less with respect to the charge transporting substance.

The thickness of the charge transport layer is preferably 5 to 50 μm.

Particularly preferred is 8 to 20 μm. The thickness of the charge transport layer is 5μ
If it is less than 50 μm, the charging property tends to be poor, and if it exceeds 50 μm, the sensitivity tends to decrease.

When forming a charge transport layer, the necessary ingredients are a ketone solvent such as acetone and methyl ethyl ketone.

Ether solvents such as tetrahydrofuran, aromatic solvents such as toluene and xylene, and methylene chloride.

After uniformly dissolving in a halogenated hydrocarbon solvent such as carbon tetrachloride, or an alcohol solvent such as methanol, ethanol, propatool, etc., it is applied onto the conductive layer and dried.

Photoreceptors of the present invention may have a thin adhesive or barrier layer immediately above the conductive layer.

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 charge, such as methine-based pigments, can be used.

These pigments are 9, for example, 1%,
JP-A-47-37544, JP-A-47-18543, JP-A-47-18544, 4? Kaisho 48-4394
No. 2, JP-A-48-70538, JP-A-49-123
No. 1, JP-A-49-105536.

It is disclosed in Japanese Patent Application Laid-Open No. 50-75214, 9% Publication No. 50-92738, etc. Especially JP-A-58-18264
τ, τ', η and η' type metal-free 7 described in Publication No. 0 and European Patent Application Publication No. 92,255
It has commercial sensitivity up to long wavelengths of talocyanine, and is also effective as an electrophotographic photoreceptor for printers equipped with diode lasers. In addition to these, any organic pigment that generates a stain carrier upon irradiation with light can be used.

The same binder, plasticizer, fluidity imparting agent, pinhole inhibitor, etc. as in the charge transport layer can be used in the charge generation layer as necessary.

Among these, 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 deteriorate. The amount of other additives is preferably 5% by weight or less based on the organic pigment.

The thickness of the charge generation layer is preferably 0.005 to 3 μm,
Particularly preferred is 0.01 to 1 μm. If the thickness of the charge generation layer is less than 0.005 μm, the sensitivity tends to be poor;
If the value exceeds 100%, the residual potential tends to increase.

When only an organic pigment is used as a method for forming the charge generation layer, vacuum deposition can be used. It can also be formed by uniformly dissolving or dispersing the charge transport layer in a solvent such as ethanol, xylene, methylene chloride, trichloroethane, etc., and then coating it on the charge transport layer and drying it.

Now let's talk about the protective layer.

The protective layer of the present invention is characterized in that it contains an organic pigment that generates stains when irradiated with light. For a protective layer.

When the above-mentioned organic pigment is contained, the resistance of the protective layer is lowered during exposure, so that the increase in residual potential can be made smaller than when the protective layer is made of only an insulating resin.

Therefore, it is possible to provide a thicker protective layer than in the past, and a photoreceptor with excellent durability can be obtained.

As the organic pigment that generates a charge contained in the protective layer, any organic pigment that generates a stain upon irradiation with light may be used, as mentioned above as the organic pigment that generates a charge contained in the charge generation layer. can.

The resin used for the protective layer is not particularly limited as long as it is insulating and forms a film, such as conventional insulating resins and binders for charge transport layers, but the resin has a number average molecular weight of 1
500 or less, and the number of formaldehydes bound to each melamine nucleus is 2 to 4 and the number of methylol groups is 1 to 2,
It is particularly preferred because it hardens at low temperatures and has excellent wear resistance. When the number average molecular weight exceeds 1500, the 1 reactivity tends to decrease. Also, if the number of bound formaldehydes per melamine nucleus is less than 2.

The storage stability of the resin is poor, the cured film tends to become brittle, and if there are more than 4, the reactivity tends to decrease. Furthermore, the number of methylol groups per melamine nucleus is 1.
If the number is less than 9, the reactivity tends to be poor; if it exceeds 2, the storage stability of the resin tends to be poor and the cured film tends to be brittle.

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, I)-) luenesulfonic acid, and carry out the reaction under acidic conditions, preferably at pH 3 to 6.9 The reaction temperature is the reflux temperature of butanol, preferably about 90 to Preferably, the temperature is 10°C. In the present invention, 4 to 5 butanol per mole of melamine is used.
Preferably, the reaction is carried out using 3 to 7 mol of formaldehyde.

The ratio of organic pigment (3) and resin (B) in the protective layer is A/
The weight ratio of B is preferably within the range of 0.5799.5 to 20480, and preferably within the range of 9% to 1/99 to 10/90.

When the amount of organic pigment exceeds 20% by weight, sensitivity decreases and abrasion resistance also deteriorates. Furthermore, when the resin content exceeds 99.5% by weight, the residual potential increases.

The protective layer of the present invention may further contain additives such as plasticizers, fluidizers, pinhole inhibitors, etc. similar to those in the charge transport layer.

The thickness of the Fa # is preferably 0.01 to 10 μm.

Particularly preferred is 0.1 to 5 μm. Protective layer thickness is 0.0
If it is less than 1 μm, the wear resistance tends to be poor, and if it exceeds 10 μm, the residual potential tends to increase.

The protective layer can be formed by uniformly dissolving or dispersing the organic pigment, resin and optional additives in a solvent, then coating the mixture on the charge generating layer and drying.

When copying or printing using the electrophotographic photoreceptor according to the present invention, the surface is positively charged, exposed, and developed in the same way as in the past, and then transferred onto a transfer material such as plain paper. All you have to do is transfer the image and fix it.

(Example) Next, the present invention will be explained in detail based on examples.

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-(0-chlorophenyl)
-1,3-oxazole (OXZ) (2) Organic pigment that generates charge +11 τ-type metal-free phthalocyanine (τ-H2PC)
(11) α-type gold-free maple phthalocyanine (α-H2Pc) (
3) Binder Binder Polyester resin for charge transport layer: Vylon 200 [Toyobo ■Product name] (B) Butyral resin binder for charge generation layer: Nisrex BM-8 [Tanezu Chemical Industry ■Product name] ( 4) Resin for protective layer (1) Silicone resin: KP-80 [Shin-Etsu Chemical ■Product name] (Solid content: 25 cm) (11) Butyl etherified melamine formaldehyde resin (BMF) (Synthesis of BMF-1) Stirrer melamine 1269.0 in a flask equipped with a reflux condenser and a thermometer. Add 0.2 g of n-butanol 4449 and 61 dinitric 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, and then react at reflux temperature for 30 minutes. Moisture was removed and the solvent was removed so that the heating residue was 50%. The viscosity of the obtained resin solution was determined by Gardner (25°C
) was 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 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 unreacted formaldehyde using the amount of butanol and gas chromatography using 5ec-butyl alcohol as an internal standard solution. The methylol group was determined from the 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 1 Characteristics of butyl etherified melamine/formaldehyde resin Comparative Example 1 0XZ89 and polyester resin 129 were mixed with tetrahydroylene 809 and completely dissolved. Apply the obtained solution to a sia aluminum plate (thickness: 0.1 mm) using an applicator.
mm) and dried at 90°C for 20 minutes to give a
A charge transport layer of .mu.m was formed. Next, τ-H2PC1,6
9w Butyral resin Z49 and methanol 809 were mixed using a ball mill (3-inch bot mill made by Nippon Kagaku Tou Co., Ltd.).
Kneaded for hours.

The resulting dispersion was applied onto the charge transport layer using an applicator, and dried at 100°C for 1 hour to form a layer with a thickness of about 1 μm.
A charge generation layer was formed to produce an electrophotographic photoreceptor without a protective layer.

Comparative example 2 on a photoreceptor produced in the same manner as Comparative Example 1.

A solution containing silicone resin 409 and methanol 609 was applied using an applicator and dried at 100° C. for 2 hours to form a protective layer with a thickness of 1 μm.

Comparative examples 3-4 on a photoreceptor produced in the same manner as Comparative Example 1.

A solution consisting of BMF-1409 (20 g solids) and Inbanol 609 was applied using an applicator. Table 2 shows the drying conditions and film thickness of the protective layer.

Examples 1 to 5 Comparison of 9 dispersions obtained by kneading in a ball mill for 8 hours and having the composition ratio shown in Table 2 (methanol was used as the solvent in Example 1.2, and isopropanol was used in other cases) Example 1
It was coated with an applicator onto a photoconductor prepared in the same manner as above, and the protective layer was formed by heating and drying. Table 2 shows the drying conditions and film thickness of the protective layer.

The electrophotographic properties of the obtained electrophotographic photoreceptor are tested using an electrostatic recording paper tester! (5P-428 manufactured by Kawaguchi Electric).

The results are shown in Table 3.

In addition, the initial potential Vo (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 potential retention rate when left in the dark for 30 seconds. ETIO* E75 is 101
It shows the light amount value (/X-5) required for the electric potential to drop by 50 and 75 inches, respectively, by irradiating white light of uχ. Residual potential V
R(V) indicates the surface potential after irradiation with 10 lux white light for 30 seconds.

In addition, using a friction tester (manufactured by Suga Teirinki), the surface of the electrophotographic photoreceptor was rubbed with gauze, and the wear resistance was measured by the number of times the surface was slid until the abrasion scratches on the surface passed through the protective layer and reached the layer below. The gender was evaluated. In the case of the photoreceptors of Comparative Examples 1 to 3, the number of times of sliding was measured until fiber traces of the gauze were visually confirmed.

The results are shown in Table 4.

Although the photoreceptor of Comparative Example 1 functions with positive charging and has excellent electrophotographic properties, it has extremely poor abrasion resistance of 200 cycles or less because it is not provided with a protective layer.

Silicone resin (KP-8
0) When a retention layer consisting of a single layer is formed (Comparative Example 2),
Although the abrasion resistance is improved, the photographic properties are greatly reduced.

When a protective layer consisting solely of melamine resin (BMF-1) within the scope of the present invention was formed on the surface of the photoreceptor of Comparative Example 1 (Comparative Example 3.4), it was sufficiently cured even at low temperatures and for a short time, and had good resistance. The wear resistance is greatly improved, and the electrophotographic properties are less deteriorated (Comparative Example 3). However, when the thickness of the protective layer was increased to 3 μm in order to further improve the abrasion resistance, the photographic characteristics of the stain deteriorated (Comparative Example 4).

However, the photoreceptors of Examples 1 to 5 according to the present invention had better abrasion resistance than Comparative Example 1, and the electrophotographic properties were not significantly degraded. especially.

In Example 9 of the present invention, the deterioration in electrophotographic properties due to the thickening of the protective layer, which was observed in Comparative Example 4, was significantly suppressed.

Margins below (Effects of the Invention) The electrophotographic photoreceptor of the present invention is a positively charged electrophotographic photoreceptor with excellent electrophotographic properties and durability, and is characterized by containing an organic pigment that generates a charge in the protective layer. be.

Claims (1)

[Claims] 1. An electrophotographic photoreceptor in which 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 are sequentially laminated on a conductive layer. , a positively charged electrophotographic photoreceptor in which the protective layer contains an organic pigment that generates a charge; 2. The charge-generating organic pigment contained in the charge-generating layer is τ
, τ', η, and η' type metal-free phthalocyanine. 3. The resin contained in the protective layer is a butyl etherified melamine/formaldehyde resin having a number average molecular weight of 1500 or less, the number of bound formaldehydes per melamine nucleus is 2 to 4, and the number of methylol groups is 1 to 2. A positively charged electrophotographic photoreceptor according to claim 1 or 2.