JP2802511B2 - Method for producing pigment dispersion for electrophotographic photoreceptor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a dispersion of organic photoconductor pigment particles used in the production of an electrophotographic photoreceptor.

[Conventional technology]

An electrophotographic photosensitive member has a basic structure in which a photosensitive layer is formed on a conductive substrate. As a photoconductive substance for forming the photosensitive layer, one using selenium has conventionally been generally used, and cadmium sulfide, zinc oxide and the like are also known as other inorganic photoconductive substances.

However, in recent years, attempts have been made to improve the film forming property by using an organic photoconductive substance, and to increase the productivity by producing by coating. Examples of the organic photoconductive material include poly-N-vinylcarbazole and 2,5
-Bis (P-diethylaminophenyl) -1,3,4-oxadiazole and the like are known.

The particle size of the organic photoconductor particles as the charge generating material when using this organic photoconductive substance greatly affects the electrophotographic characteristics. That is, if the average particle size is large, the thickness of the charge generation layer cannot be reduced, and it takes time to move carriers in the charge generation layer, resulting in low sensitivity. Therefore, conventionally, an organic photoconductive substance is put into a solvent or a solvent in which a binder resin is dissolved, and wet dispersion is performed by a media type disperser such as a sand grinder or a ball mill.

[Problems to be solved by the invention]

However, achieving dispersion using a media type disperser has many problems as follows.

(1) In the case of wet dispersion using a liquid, if a medium is used, the target particles can be atomized, but the medium itself is worn, the dispersion is contaminated, and the electrophotographic characteristics are degraded.

(2) Since the photoconductive material comes into contact with the medium during the dispersing process and receives an impact, the photoconductive material is damaged, and the electrophotographic characteristics are degraded.

(3) Each time dispersion is performed, the medium needs to be washed, and workability is poor.

(4) The dispersion may remain between the media, resulting in poor liquid recovery, and the previous dispersion remaining in the next dispersion operation, deteriorating the liquid properties.

(5) If the micronization and dispersion are performed simultaneously, a long dispersion time is required to obtain the desired particle size.

Therefore, a main object of the present invention is to provide a method for producing a dispersion for an electrophotographic photoreceptor which solves the above-mentioned problems all at once, and in particular, improves electrophotographic characteristics.

[Means for solving the problem]

The above problem is solved by dispersing the organic photoconductive pigment in a solvent or a solvent in which a binder resin is dissolved, atomizing the organic photoconductive pigment in a dry state to an average particle diameter of 5 μm or less in advance using a gas evaporation method, and dispersing the organic photoconductive pigment. It can be solved by wet dispersion without using media.

[Action]

The present inventors have previously prepared an organic photoconductive material having an average particle size of 5 μm.
It has been discovered that, if the particles are atomized, the organic photoconductive material can be sufficiently and uniformly dispersed by using a weak external force such as stirring without using a strong media type disperser.

Therefore, as can be easily estimated, the above (1) to (1) to
All problems of (5) can be solved.

Further, in the present invention, when the organic photoconductive pigment is preliminarily atomized to an average particle diameter of 5 μm or less in a dry state, a gas evaporation method is used. Therefore, as described below, advantages such as an increase in productivity are provided.

[Specific configuration of the invention]

 Hereinafter, the present invention will be described in more detail.

In the present invention, when dispersing an organic photoconductive substance in a solvent or a solvent in which a binder resin is dissolved, the organic photoconductive substance is atomized in advance to an average particle diameter of 5 μm or less in a dry state, and wet dispersed without using a dispersion medium. I do.

The average particle diameter referred to herein is a median diameter (==) that vertically divides the cumulative passage distribution curve D or the cumulative residual distribution curve R into two.
D ₅₀ ). At the time of the measurement, for example, a centrifugal particle size distribution analyzer “CAPA = 500” manufactured by Horiba Ltd. can be used.

The lower limit of the average particle size is desirably 0.01 μm, and still more preferably, the average particle size range is 0.05 to 1.0 μm.
m, especially 0.05 to 0.5 μm.

Fine particles of the organic photoconductive material having such an average particle size,
It is obtained by performing atomization treatment in a dry state. Examples of the dry pulverization method include mechanical pulverization methods such as ball mill, vibration mill, attritor, hammer mill, turbo mill, jet mill, ong mill, sand mill, pearl mill, CF mill, dynamic mill, zegomil, and colloid mill;
Physical methods such as gas evaporation method, sputtering method, vacuum evaporation method on fluidized oil surface, and hybrid plasma method; precipitation method, hydrolysis method, spray method, redox method, freeze drying method, laser synthesis method, spark discharge And any other method such as a chemical production method such as a chemical method.

The finely divided organic photoconductive material is wet-dispersed in a solvent or a solvent in which a binder resin is dissolved without using a medium.

As the wet dispersion method without using the medium, any method such as an impeller stirring method, a jet stirring method, a shake stirring method, and an ultrasonic dispersion method can be used. The dispersion time can be set as appropriate according to the desired dispersibility.

Since there is no liquid in the dry pulverization by the media type pulverizer, the organic photoconductive pigment substance adheres to and forms a film on the surface of the medium, causing a cushioning effect of the organic substance, and the medium itself is hardly worn, and contaminants are not generated. Absent. Furthermore, pulverization by a jet mill or a grinding mill (for example, an ong mill) originally has very little contamination. As long as the obtained fine particles are wet-dispersed by a stirring method or the like as a post-process, the pigment dispersion by the contamination is performed. Liquid contamination is negligible.

Further, the gas evaporation method as a means for atomization is an effective means.

In the gas evaporation method, various substances are heated, evaporated, and sublimated in an inert gas atmosphere introduced into a vacuum vessel, and the resulting vapor molecules are gradually cooled while colliding with the inert gas molecules. Are aggregated to form ultrafine particles, and the ultrafine particles are collected. In particular, since many organic photoconductive materials have sublimability, atomization by such a gas evaporation method is extremely effective. BACKGROUND ART Conventionally, in order to remove impurities in an organic photoconductive material raw material, sublimation purification is performed in a vacuum, and then dispersion is often performed. However, the sublimation purification in vacuum and the evaporation in gas method are operations that only differ in the vacuum atmosphere, so that the evaporation method in gas has a sufficient purification effect and also has the effect of atomization, so that it can be obtained. A pigment dispersion for an electrophotographic photoreceptor can be produced simply by stirring and dispersing the fine particles for about 1 hour. This is a surprisingly simple task compared to the conventional method that took tens of hours, and the productivity was greatly improved. I do.

 Representative examples of organic pigments having sublimability are as follows.

(1) Azo pigments such as monoazo pigments, polyazo pigments, metal complex salt azo pigments, pyrazolone azo pigments, stilbene azo pigments, and thiazole azo pigments.

(2) Perylene pigments such as perylene anhydride and perylene imide.

(3) Anthraquinone-based or polycyclic quinone-based pigments such as anthraquinone derivatives, anthantrone derivatives, dibenzavirenequinone derivatives, pyranthrone derivatives, biolanthrone derivatives, and isobiolanthrone derivatives.

(4) Indigo pigments such as indigo derivatives and thioindigo derivatives.

(5) Phthalocyanine pigments such as metal phthalocyanine and non-metal phthalocyanine.

(6) Perinone pigments such as bisbenzimidazole derivatives.

(7) Quinacridone pigments.

(8) Cyanine and merocyanine pigments.

(9) Quinoline pigments.

Specific examples of these pigments are disclosed in, for example, JP-A-49-48334, JP-A-49-128334, JP-A-50-75042, JP-A-47-18544.

However, such a gas evaporation method is also just one means of micronization, and it is possible to easily disperse without using a media type dispersing machine as long as atomization is performed, for example, only by stirring. This is the basic idea.

Further, for example, when the organic photoconductive material itself is fine particles, it can be easily dispersed without using a media type disperser by selecting an appropriate solvent and a binder (binder resin),
Surprisingly good characteristics (for example, electrophotographic characteristics) can be obtained without liquid contamination due to media contamination and material damage due to collision with the media.

As described above, the organic photoconductive substance is dispersed on a dispersion medium and a binder resin by a disperser, and then coated on a conductive substrate.

The photoconductor finally obtained by employing the present invention is a single-layer photoconductor in which organic photoconductor particles (pigment) are dispersed in a charge transporting material as a charge generating material on a conductive substrate. And a function-separated type photoconductor in which a charge generation material layer is formed on a conductive substrate and a charge transport material layer is formed thereon.

In any case, the organic photoconductor particles according to the present invention used as the charge generating material include azo pigments, particularly disazo pigments, anthranthrone pigments, berylen pigments, phthalocyanine pigments, quinacridone pigments, and cyanine pigments. Pigments, bilylium pigments, thiopyrylium pigments, indigo pigments, squaric acid pigments, polycyclic quinone pigments and the like can be used.

As a dispersion medium of the pigment, methanol, ethanol,
Alcohol solvents such as isopropyl alcohol, ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone, aromatic solvents such as benzene, toluene, xylene and chlorobenzene, DM
Various solvents such as F and DMAC can be used.

As the binder resin, polyvinyl butyral, formal resin, polyamide resin, polyurethane resin, cellulose resin, polyester resin, polysulfone resin, polycarbonate resin, acrylic resin, styrene resin and the like are used.

In the case of constituting a function-separated type photoreceptor, the charge generation layer can be formed by applying the above-mentioned dispersion liquid directly on a conductive substrate or on an adhesive layer interposed therebetween, and a charge transport layer is formed on the charge generation layer. Is formed by coating. The charge generation layer may be coated on the charge transport layer.
It is desirable that the thickness of the charge generation layer be 5 μm or less, preferably 0.01 to 1 μm. Most of the incident light is absorbed by the charge generation layer to generate a large amount of charge, and the generated charge carriers need to be injected into the charge transport layer without being deactivated by recombination or trapping. Thickness is preferred.

Coating can be performed using a coating method such as a dip coating method, a spray coating method, a spinner coating method, a bead coating method, a Meyer bar coating method, a blade coating method, a roller coating method, and a curtain coating method.
Drying is preferably performed by touch drying at room temperature and then heating and drying. The heating and drying can be performed at a temperature of 30 to 200 ° C. for a time in a range of 5 minutes to 2 hours, at rest or under blowing.

The charge transport layer is electrically connected to the above-described charge generation layer, and has a function of receiving charge carriers injected from the charge generation layer in the presence of an electric field and transporting these charge carriers to the surface. ing. At this time, the charge transport layer may be stacked on the charge generation layer as described above, or may be stacked thereunder. However, the charge transport layer is desirably laminated on the charge generation layer.

It is preferable that the material for transporting charge carriers in the electric transport layer (hereinafter, simply referred to as charge transport material) is substantially insensitive to the wavelength range of the electromagnetic wave to which the above-described charge generation layer is sensitive. The term “electromagnetic wave” used here means γ-ray, X-ray,
The broad definition of "light" includes ultraviolet, visible, near infrared, infrared, far infrared and the like. When the light-sensitive wavelength region of the charge transport layer coincides with or overlaps that of the charge generation layer, the charge carriers generated by both of them capture each other, resulting in a decrease in sensitivity.

As the electric transport material, any known materials can be used, and examples thereof include a hydrazone derivative, a pyrazoline derivative, a triphenylamine derivative, and polyvinyl carbazole.

In addition to these organic charge transport materials, selenium, selenium
Inorganic materials such as tellurium, amorphous silicon, and cadmium sulfide can also be used.

These electric transport materials can be used alone or in combination of two or more.

When the charge transporting material does not have a film-forming property, a film can be formed by selecting an appropriate binder. Resins that can be used as the binder include, for example, insulating resins such as acrylic resins, polyarylates, polyesters, polycarbonates, polystyrenes, acrylonitrile-styrene copolymers, acrylonitrile-butadiene copolymers, polyvinyl butyral, polyvinyl formal, polysulfone polyacrylamide, polyamide, and chlorinated rubber. Resin, or poly-N-vinyl carbazole,
Organic photoconductive polymers such as polyvinyl anthracene and polyvinyl pyrene can be exemplified.

As a substrate having conductivity, a substrate having conductivity itself, for example, aluminum, aluminum platinum, copper,
Zinc, stainless steel, vanadium, molybdenum, chromium,
Titanium, nil, indium, gold and platinum can be used, and in addition, aluminum, aluminum alloy,
Plastics (for example, polyethylene, polypropylene, and the like) having a layer in which indium sulfide, tin oxide, indium oxide-tin oxide alloy, and the like are formed by a vacuum deposition method.
Polyvinyl chloride, polyethylene terephthalate, acrylic resin, polyfluoroethylene, etc.), conductive particles (for example, carbon black, silver particles, etc.) coated with a suitable binder on plastic, and conductive particles on plastic or paper It can be used for an impregnated substrate or a plastic having a conductive polymer.

An undercoat layer having a barrier function and an adhesive function may be provided between the conductive layer and the photosensitive layer.

〔Example〕

Hereinafter, comparative examples are shown together with examples of the present invention to clarify the effects of the present invention.

(Example 1) As an organic photoconductive material, 4,10-dibromoanthranthrone (needle-shaped particles having a short axis of several μm and a long axis of several hundred μm) was dry-ground with a ball mill for 24 hours, and was observed to be about 0.2 μm by TEM observation. Fine particles were obtained. Next, dispersion was attempted according to the following formulation.

4,10-dibromoanthranthrone 3 parts by weight Polycarbonate 1.5 parts by weight 1,2-dichloroethane 125 parts by weight At the time of dispersion, impeller stirring was carried out at a peripheral speed of 1.3 m / sec.
Dispersed by performing time.

Example 2 Fine particles of about 0.1 μm were obtained by atomizing an organic photoconductive substance by a gas evaporation method over 0.5 hours. The conditions were as follows: He gas was introduced into a vacuum vessel, and sublimation was performed at 350 ° C. under 0.1 Torr. Others were the same as Example 1.

(Example 3) The same organic photoconductive substance as in Example 1 was atomized using an attritor for 0.5 hour to obtain fine particles of about 0.2 µm, and ultrasonic dispersion was performed for 0.5 hour with the formulation of Example 1. .

(Example 4) Disazo organic pigments (aggregated coarse particles having a primary particle diameter of about 1 μm) represented by the following formula (I) were micronized to about 0.2 μm over 0.5 hour using an attritor, and then the following formulation was used. Below, dispersion was achieved by performing impeller stirring at a peripheral speed of 12.6 m / sec for 2 hours.

<Formulation> Substance represented by formula (I) 2 parts by weight PMMA 1 part by weight MEK 250 parts by weight (Example 5) Using the same organic photoconductive substance as in Example 4, using a vibrating ball mill to micronize to about 0.3 μm in 0.5 hours, and using the same prescription as in Example 4, without inserting media,
0.25 by paint conditioner (Red Devil)
Time shaking dispersed.

(Comparative Example 1) A treatment was performed under the same conditions as in Example 1 except that the raw material was not atomized and dispersion was performed by a sand mill using a medium over 24 hours.

(Comparative Example 2) The same procedure as in Example 4 was performed except that the raw material was not atomized and dispersion was performed for 48 hours using an attritor using a medium.

<Results> For each of the above examples, the physical properties of the obtained fine particles, the liquid recovery rate due to the dispersion, and the characteristics when used as an electrophotographic photosensitive member were examined. The results shown in Table 1 were obtained. The electrophotographic photoreceptor was prepared by sequentially applying an undercoat layer, a charge generation layer having organic photoconductive pigment particles, and a charge transport layer on an aluminum-evaporated PET base.

The meanings of the items in Table 1 are as follows.

According to the above results, according to the present invention, each item is significantly improved in comparison with the conventional example.

〔The invention's effect〕

As described above, according to the present invention, the following effects are provided.

(1) Since no media is used, there is no contamination of the dispersion due to abrasion of the media itself, and the electrophotographic characteristics are improved.

(2) The photoconductive material is not damaged by the impact of the photoconductive material coming into contact with the medium during the dispersion process, and the electrophotographic characteristics are improved.

(3) Since it is not necessary to wash the medium every time the dispersion is performed, the workability is simplified.

(4) In contrast to the case where the dispersion liquid remains between the media and the liquid recovery rate is poor, and the previous acid separation liquid remains and deteriorates the physical properties of the liquid in the next dispersion operation, the use of a medium is difficult. As a result, the liquid recovery rate is greatly increased.

(5) In addition to separately performing micronization and dispersion, the processing time for obtaining a desired particle size in dry pulverization is extremely short, and if micronization is performed in advance, wet dispersion can be easily performed in a short time. Therefore, the overall processing time can be greatly reduced.

[Brief description of the drawings]

 FIG. 1 is an explanatory diagram of dark decay.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Akira Nishiwaki 1 Konica Sakuracho, Hino-shi, Tokyo Inside Konica Corporation (56) References JP-A-61-278857 (JP, A) JP-A-61-170746 ( JP, A) JP-A-59-184353 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G03G 5/00-5/16

Claims (3)

(57) [Claims] When the organic photoconductive pigment is dispersed in a solvent or a solvent in which a binder resin is dissolved, the organic photoconductive pigment is previously atomized in a dry state so as to have an average particle size of 5 μm or less by a gas evaporation method, A method for producing a pigment dispersion for an electrophotographic photoreceptor, comprising performing wet dispersion without using a dispersion medium. 2. The method according to claim 1, wherein the wet dispersion method is selected from the group consisting of an impeller stirring method, a jet stirring method, a shake stirring method and an ultrasonic dispersion method. 3. The method according to claim 1, wherein an organic photoconductive pigment having a sublimation property is used as a material evaporated in the gas evaporation method.