JPH1130871A - Method for producing pigment dispersion for electrophotographic photoreceptor - Google Patents

Abstract

(57) Abstract: Provided is a method for easily preparing a pigment dispersion for forming a charge generation layer of an electrophotographic photoreceptor. SOLUTION: The pigment is dispersed to a particle diameter of 250 μm or less by dry dispersion, then slurried with an organic solvent, wet-dispersed, and dispersed to a particle diameter of 0.5 μm or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a pigment dispersion for producing a coating type electrophotographic photoreceptor. According to the present invention, the production of a pigment dispersion is significantly facilitated.

[0002]

2. Description of the Related Art As is well known, an electrophotographic photosensitive member has a structure in which a photosensitive layer is formed on a conductive substrate. Conventionally, this photosensitive layer has been formed of an inorganic substance such as selenium, cadmium sulfide, and zinc oxide. In recent years, electrophotographic photoreceptors having an organic photosensitive layer using an organic photoconductive substance instead of the inorganic photosensitive layer formed of these inorganic substances have been widely used. Since the organic photosensitive layer can be formed by coating, there is an advantage that the productivity is good and the performance can be easily controlled by selecting an organic photoconductive substance to be used.
In particular, the development of a function-separated photosensitive layer in which a charge generation layer composed of an organic photoconductive pigment and a charge transport layer composed of a photoconductive polymer, etc., have been developed, greatly expanding the range of material choices, and improving sensitivity and durability. Etc. were also significantly improved.

In the electrophotographic photoreceptor provided with the function-separated type photosensitive layer, it is important to uniformly generate a large number of carriers in the charge generation layer and to efficiently inject the generated carriers into the charge transport layer. The quality of the characteristics of the electrophotographic photosensitive member largely depends on the charge generation layer. It is generally considered that the more uniform and smooth the charge generation layer, the better the characteristics of the electrophotographic photoreceptor.

Conventionally, a pigment dispersion for forming a charge generation layer is produced by wet-dispersing an organic pigment in an organic solvent for a long period of time using a ball mill, sand grind mill, planetary mill, roll mill, or the like. It is common. The thickness of the charge generation layer is usually from 0.1 to several μm, and the pigment has an average particle diameter of 0.5 μm or less, preferably an average particle diameter of 0.5 μm.
Disperse to 1-0.35 μm.

[0005]

However, it is considerably difficult to disperse the organic pigment to the above-mentioned particle size by wet dispersion in an organic solvent. When coarse particles are contained in the pigment dispersion, the charge generation layer formed using the same has non-uniform film thickness and electric characteristics.Therefore, the pigment dispersion contains no coarse particles and is as uniform as possible. Must be distributed. The present invention provides a method for producing such a pigment dispersion.

[0006]

According to the present invention, the pigment for an electrophotographic photosensitive member is dispersed to a particle size of 250 μm or less by dry dispersion, and then the average particle size is 0.5 μm or less by wet dispersion in an organic solvent. , A pigment dispersion suitable for an electrophotographic photoreceptor can be easily produced.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION As a pigment used in the production of a pigment dispersion in the present invention, any organic pigment which has been conventionally proposed to be used for this purpose can be used. Such pigments include, for example, azo pigments, phthalocyanine pigments, anthrone pigments, quinacridone pigments, cyanine pigments, pyrylium pigments, thiapyrylium pigments, indigo pigments, polycyclic quinone pigments, squaric acid And the like.

In the present invention, these pigments are dispersed to a particle size of 250 μm or less by dry dispersion. Dispersion can be performed using various devices, but is usually performed using a ball mill, a sand grind mill, or the like. Beads or balls of glass, alumina, zirconia, stainless steel, ceramics and the like are used as a dispersion medium to be charged into these dispersing apparatuses. In short, any material can be used as long as the dispersion medium does not become powdered during the dispersion treatment and can be easily separated after the dispersion treatment. Dispersion is performed until the particle size of the pigment becomes 250 μm or less, preferably 200 μm or less. However, since it is not efficient to disperse to a small particle size by dry dispersion, almost all of the dry dispersion passes through a sieve having an opening of 250 μm and a sieve having an opening of 149 μm passes through a sieve of 20 to 50%.
Is preferably dispersed to such an extent as to pass through.

The pigment dispersed to a predetermined particle size by dry dispersion is then slurried with an organic solvent and subjected to wet dispersion. Examples of the organic solvent include alcohols such as methanol, ethanol, and propanol; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; (halo) aromatic hydrocarbons such as benzene, toluene, xylene, and chlorobenzene; dioxane; Ethers such as tetrahydrofuran and the like, dimethylformamide, acetonitrile and the like are used. A resin that acts as a binder for the pigment in the photosensitive layer may be added to the slurry. Examples of such a resin include polyester, polyvinyl acetate, poly (meth) acrylate, polycarbonate, polyvinyl acetoacetal, polyvinyl butyral, polyvinyl propional, phenoxy resin, epoxy resin, polyurethane, cellulose ester, and cellulose ether. Can be

The wet dispersion is preferably performed by a dispersion apparatus using a spherical medium such as a ball mill, a sand grind mill, and an attritor. As in the case of the dry dispersion, beads, balls, and the like of glass, alumina, zirconia, stainless steel, ceramics, and the like are used as the spherical medium. The spherical medium is usually used in a volume ratio of 0.5 to 5 times the pigment dispersion. The particle size of the spherical medium is 0.4-0.8 mm, in particular 0.
It is preferably from 4 to 0.6 mm. Generally, a spherical medium having a small particle size tends to give a uniform dispersion in a short time. The wet dispersion is performed until the average particle size of the pigment becomes 0.5 μm or less. It is preferable to disperse the particles until the average particle diameter becomes 0.1 to 0.35 μm.

[0011] The pigment dispersion thus produced is
If desired, a binder or various auxiliaries are added to form a coating solution, which is used for forming a photosensitive layer. Usually, it is used for forming a charge generation layer of a function-separated type photoreceptor, but it can also be used for forming a dispersion type photoreceptor by adding a charge transport material. The concentration of the organic pigment in the coating solution is usually 0.1 to 10% by weight, and the ratio of the binder to the organic pigment is 5 to 500 parts by weight of the organic pigment per 100 parts by weight of the binder. The charge transport material is
It is used in an amount of 5 to 500 parts by weight per 100 parts by weight of the binder.

The coating solution can be applied to the substrate by a dip coating method, a spray coating method or any other conventional method. After the application, it is preferable to first dry at room temperature to evaporate most of the solvent, and then heat and dry to completely remove the solvent. For example, drying is performed at 30 to 200 ° C. for about 5 minutes to 2 hours. The thickness of the charge generation layer is usually 0.1.
1 to 10 μm, and the thickness of the charge transport layer is 5 to 60 μm.
It is. In the case of a dispersion type photoreceptor, the thickness is preferably 5 to 60 μm.

As the charge transporting material for the charge transporting layer, electron withdrawing substances such as trinitrofluorenone and tetracyanoquinodimethane, carbazole, indole,
Heterocyclic compounds such as imidazole, oxazole, pyrazole, oxadiazole, pyrazoline, thiadiazole, aniline derivatives, stilbene derivatives, hydrazone derivatives, aromatic amine derivatives, or polymers having a group consisting of these compounds in the main chain or side chain Various substances proposed for this purpose, such as an electron donating substance such as, for example, can be used. When a binder is used in combination with the charge transporting material, those exemplified as those used in the charge generation layer can be used.

Aluminum is mainly used as the conductive substrate, but other metal materials such as stainless steel and nickel, and aluminum, copper, palladium, tin oxide,
An insulating material such as a polyester film, paper, or glass provided with a conductive layer such as indium oxide can also be used. A barrier layer is usually provided between the photosensitive layer and these substrates. In the case of an aluminum substrate, it is usually formed by anodizing to form an alumite layer on the surface or by coating a polymer layer on the surface. For example, polyvinyl alcohol, casein, polyvinylpyrrolidone, polyacrylic acid, celluloses, gelatin, starch, polyimide, polyurethane, polyamide and the like are used. In the case other than the aluminum substrate, a solution containing these polymers is usually applied to form a barrier layer. The thickness of the barrier layer is usually 0.1 to 20 μm, and 0.1 to 1 μm.
0 μm is preferred.

[0015]

EXAMPLES The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Example 1 An azo pigment having the structure of the formula (1) was dry-dispersed for 2 hours using a ball mill using ceramic balls as a dispersion medium, and then sieved with a 250 μm mesh sieve to obtain a sifted product. did.

[0017]

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To 1 part by weight of the sieved product, 15 parts by weight of 1,2-dimethoxyethane was added to form a slurry. This slurry was charged into a sand mill and subjected to a dispersion treatment for 6 hours using glass beads having an average particle diameter of 0.7 mm as a dispersion medium. The glass beads were used so as to have the same volume as the slurry. In the obtained pigment dispersion, 1% of polyvinyl butyral resin was added.
The 2-dimethoxyethane solution was mixed so that the polyvinyl butyral resin was 0.5 part by weight with respect to 1 part by weight of the azo pigment, to obtain a coating liquid for a charge generation layer.

The coating solution obtained above was applied to the aluminum surface of a substrate obtained by evaporating aluminum on a polyester film using a bar coater so that the dry film thickness was 0.4 μm. On this charge generation layer, a coating solution for a charge transport layer was applied by a film applicator so that the dry film thickness became 17 μm. Table 1 shows the appearance and half-life exposure of the electrophotographic photoreceptor thus manufactured. The half-exposure amount was measured using an electrostatic copying paper tester (Kawaguchi Electric Works, E
PA-8100). The coating solution for the charge transport layer includes a hydrazone compound 56 of the formula (2).
A solution obtained by dissolving 14 parts by weight of the hydrazone compound of the formula (3), 1.5 parts by weight of the dicyano compound of the formula (4), and 100 parts by weight of a polycarbonate resin in 1,000 parts by weight of 1,4-dioxane was used.

[0020]

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Example 2 Dry dispersion and wet dispersion were carried out in the same manner as in Example 1 except that the azo pigment of the formula (5) was used instead of the azo pigment of the formula (1). A pigment dispersion was obtained. An electrophotographic photoreceptor was manufactured in exactly the same manner as in Example 1 except that this pigment dispersion was used. The results are shown in Table 1.

[0022]

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Example 3 Dry dispersion and wet dispersion were carried out in the same manner as in Example 1 except that oxytitanium phthalocyanine of the formula (6) was used instead of the azo pigment of the formula (1). Thus, a pigment dispersion was obtained. An electrophotographic photoreceptor was manufactured in exactly the same manner as in Example 1 except that this pigment dispersion was used. The results are shown in Table 1.

[0024]

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Comparative Examples 1 to 3 Pigment dispersions were prepared in exactly the same manner as in Examples 1 to 3, except that the dry dispersion was omitted and the wet dispersion was performed for a long time. An electrophotographic photoreceptor was manufactured in exactly the same manner as in Examples 1 to 3, except that this pigment dispersion was used. Table-Results
It is shown in FIG.

[0026]

[Table 1] * 1 Measured using a particle size distribution analyzer, CAPA-500, manufactured by Horiba, Ltd.

Claims (3)

[Claims] 1. An electron, wherein a pigment for an electrophotographic photosensitive member is dispersed to a particle diameter of 250 μm or less by dry dispersion, and then dispersed to an average particle diameter of 0.5 μm or less by wet dispersion in an organic solvent. A method for producing a pigment dispersion for a photoreceptor. 2. The method for producing a pigment dispersion for an electrophotographic photosensitive member according to claim 1, wherein the wet dispersion is performed using a spherical medium as a dispersion medium. 3. Due to the dry dispersion, almost the whole amount passes through a sieve having an aperture of 250 μm and a sieve having an aperture of 149 μm passes through a sieve having a diameter of 149 μm.
3. The method for producing a pigment dispersion for an electrophotographic photosensitive member according to claim 1, wherein the dispersion is subjected to wet dispersion after dispersing until about 50% has passed.