JP5109034B2 - Method for producing pigment dispersion for producing electrophotographic photoreceptor and electrophotographic photoreceptor using this dispersion - Google Patents

Description

The present invention relates to an electrophotographic photoreceptor, and more particularly to a method for producing a pigment dispersion for producing an electrophotographic photoreceptor excellent in coatability and an electrophotographic photoreceptor using the dispersion.

  An electrophotographic photosensitive member having a photosensitive layer mainly composed of an organic photoconductive material such as an organic charge generating material or an organic charge transport material is relatively easy to manufacture, inexpensive, and easy to handle. In addition, since it has many advantages such as excellent thermal stability, it is now the mainstream of electrophotographic photoreceptors and is produced in large quantities. These electrophotographic photoreceptors are used in copying machines, laser printers, and the like.

  Among electrophotographic photoreceptors using organic photoconductive substances, function-separated photoreceptors in which the charge generation function and the charge transport function are shared by different substances have become the mainstream and are widely used. The feature of the function-separated type photoconductor is that materials suitable for each function can be selected from a wide range, and a lot of research has been advanced since a photoconductor having an arbitrary performance can be easily manufactured.

  Among these, various substances such as phthalocyanine pigments, squalium dyes, azo pigments, perylene pigments have been studied as substances responsible for the charge generation function, and among them, azo pigments can have various molecular structures and are high It has been widely researched because of its expectation of charge generation efficiency, and its practical application is also progressing. In addition, since phthalocyanine pigments can be expected to have high-sensitivity characteristics with respect to near-infrared light, they have been put into practical use as photoconductor materials for laser printers.

  As a method for producing an electrophotographic photosensitive member using an organic photoconductive substance, means for immersing a conductive support in a coating solution containing an organic photoconductive substance or the like is often employed. In the case of a function-separated photoreceptor in which a charge generation layer and a charge transport layer are laminated, a charge generation material forming coating liquid (pigment dispersion) obtained by dispersing a charge generation material pigment in an organic solvent in which a binder is dissolved, It is produced by applying a coating solution for forming a charge transport layer obtained by dissolving a charge transport material and a binder in an organic solvent in this order or in the reverse order. The dispersion described here is to make a pigment or the like into a fine particle in a solvent to make it a suspended state without a precipitate, and the dispersion stability over time is a uniform fine particle size and stable in a solvent for a long time. It means that it is stored in.

  When the dispersibility of pigments and the like is deteriorated, the coated surface becomes rough, and the electrophotographic photosensitive member causes image failures such as pinholes and density unevenness. Also, the dispersion particles settle out over time and the concentration of the dispersion is not uniform, resulting in unevenness in image density between the photoreceptors obtained by applying the same coating liquid or between parts of the same photoreceptor, This also leads to a decrease in productivity, such as increasing the viscosity of the dispersion and causing fluctuations in the coating amount.

  In order to obtain a good pigment dispersion, a part of the molecular structure of the pigment is changed or a pigment having a different structure is mixed to control the aggregation state, or a solvent soluble resin is used on the pigment surface. There are methods of adsorption. However, with these methods, the electrophotographic properties of the original pigment, that is, sensitivity and repetitive characteristics, are changed, and the initial objective as a photoreceptor has not been achieved in the basic performance of the pigment.

Various attempts have been made so far to improve such problems. For example, a method of using a specific organic solvent as a dispersion solvent (for example, see Patent Document 1), a binder
A method of dissolving and dispersing in a solvent after heat treatment (for example, see Patent Document 2) and a method of using a coating solution for forming a charge generation layer having a specific surface tension (for example, see Patent Document 3) have already been reported. Has been. However, even if these are used, the above-mentioned pigment dispersibility cannot be improved.

Japanese Patent Laid-Open No. 7-140678 JP-A-9-304950 JP-A-9-281724

  The object of the present invention is to produce a pigment dispersion for producing an electrophotographic photosensitive member having good dispersibility and stability over time, and excellent coating properties, and using this dispersion, an electrophotography having high sensitivity and excellent repetitive characteristics. It is to provide a photoreceptor.

As a result of researches to achieve the above-mentioned object, the present inventors have dispersed a pigment for a charge generating material in an organic solvent in which at least one binder is dissolved, and advancing contact angle θa with respect to the suspension plate by the Wilhelmy method and By producing a dispersion that satisfies the relationship of the following formula (I) when the receding contact angle θr is measured, a pigment dispersion for producing an electrophotographic photosensitive member having extremely good dispersibility and coatability can be obtained. The headline, the present invention has been reached.
0 ° <θa−θr <5 ° (I)

According to the present invention, there are provided a method for producing a pigment dispersion for producing an electrophotographic photoreceptor having good dispersibility and stability over time, and excellent coatability, and an electrophotographic photoreceptor having high sensitivity and excellent repeatability. Can do.

  Hereinafter, each component of the present invention will be described in detail.

  Examples of the charge generating material pigment used in the present invention include monoazo pigments, polyazo pigments, metal complex azo pigments, pyrazolone azo pigments, stilbene pigments, thiazole azo pigments, and other azo pigments, perylene acid anhydrides and perylenes. Perylene pigments typified by acid imides, anthraquinone derivatives, anthanitron derivatives, dibenzpyrenequinone derivatives, pyranthrone derivatives, violanthrone derivatives and anthraquinone or polycyclic quinone pigments typified by isoviolanthrone derivatives, Examples thereof include phthalocyanine pigments represented by metal phthalocyanine, metal naphthalocyanine, metal-free phthalocyanine, metal-free naphthalocyanine and the like. Of these, bisazo pigments are preferred because pigment dispersions having particularly good coating properties can be obtained. Further, among the bisazo pigments, the pigment represented by the following general formula (1) is particularly preferable because it gives an electrophotographic photoreceptor excellent in sensitivity, repeatability and image characteristics.

  In general formula (1), A1 is hydrogen, an alkyl group which may have a substituent, an aryl group, or a heterocyclic group, m and n are 0 or 1, X is hydrogen, a methyl group, cyano Group, halogen, and Cp1 represents a coupler residue.

  Specific examples of the bisazo pigment represented by the general formula (1) according to the present invention are illustrated below, but are not limited thereto.

As the binder (binder resin) used in the present invention, acetal resin, butyral resin, vinyl chloride copolymer resin, silicon resin, phenoxy resin, phenol resin, epoxy resin, polycarbonate, polyarylate, polyester, polyether polyol, Polyamide, polyimide, urethane resin, acrylic resin and the like can be mentioned. Among these, it is preferable to use an acetal resin or a butyral resin because the pigment dispersion exhibits high dispersibility and coating properties are improved. These resins can be used alone or in admixture of two or more.

  In the pigment dispersion, the binder is used in the range of 10 to 500 parts by weight, preferably 50 to 150 parts by weight, with respect to 100 parts by weight of the charge generating material pigment. If the resin ratio is too high, the charge generation efficiency of the electrophotographic photosensitive member is lowered, and if the resin ratio is too low, there may be a problem in film formability.

  Examples of the organic solvent used for dispersing the pigment for the charge generating material in the present invention include alcohol solvents such as methanol, ethanol, isopropyl alcohol, ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, ethyl formate, acetic acid. Ester solvents such as ethyl and n-butyl acetate, ether solvents such as diethyl ether, 1,2-dimethoxyethane, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, anisole, N, N-dimethylformamide, Amide solvents such as N, N-dimethylacetamide, N-methyl-2-pyrrolidone, dichloromethane, chloroform, bromoform, methyl iodide, dichloroethane, trichloroethane, trichloroethylene, chlorobenzene, o-dichloroben Halogenated hydrocarbon solvents such as benzene, fluorobenzene, bromobenzene, iodobenzene, α-chloronaphthalene, n-pentane, n-hexane, n-octane, 1,5-hexadiene, cyclohexane, methylcyclohexane, cyclohexadiene, Examples thereof include hydrocarbon solvents such as benzene, toluene, o-xylene, m-xylene, p-xylene, ethylbenzene, cumene and the like. Among these, it is preferable to use a ketone solvent because the pigment dispersion exhibits high dispersibility and coating properties are also improved. These organic solvents can be used alone or in admixture of two or more.

  The apparatus used for dispersing the pigment for the charge generating material is a disperser using a dispersion medium such as a ball mill, a paint conditioner, a vertical bead mill, a horizontal bead mill, an attritor or the like. As the material of the dispersion medium, soda glass, low alkali glass, and yttria-containing zirconia are preferable, and beads having a diameter of several mm are used.

  In the present invention, as a method for applying the pigment dispersion, known methods such as spin coating, blade coating, knife coating, reverse roll coating, rod bar coating, spray coating and the like are used. In particular, when applying to a drum, a dip coating method or the like is used.

  In the present invention, it is preferable to filter with a filter at least once during the period from the production of the pigment dispersion to the application. Examples of the filter medium include polyethylene, polypropylene, polyester, cellulose acetate, polyethersulfone, tetrafluoroethylene resin, acrylic resin, glass fiber, stainless steel, cotton, activated carbon, and the like. By applying the pigment dispersion filtered through a filter, aggregated pigment particles and the like are easily removed, and pinholes and density unevenness do not occur on the coated surface. As a result, when an image is formed by an electrophotographic process, an electrophotographic photosensitive member free from image failures such as white spots, black spots, and density unevenness can be obtained.

In the present invention, in order to evaluate the dispersibility and coating property of the pigment dispersion, the advancing contact angle θa and the receding contact angle θr with respect to the suspension plate are measured using the Wilhelmy plate method. When the suspension plate (mass m) suspended from the load detector is immersed and pulled up at a constant speed, the load F applied to the load detector is represented by the following formula (II).
F = mg + Pγcos θ−Fb (II)
Here, g is the gravitational acceleration, P is the suspension plate perimeter, γ is the surface tension of the dispersion, θ is the contact angle, and Fb is the buoyancy. When the bottom surface of the suspension plate is equal to the liquid level, Fb = 0, and when the zero point adjustment of the load detector is performed with the suspension plate attached, the equation (II) is expressed by the following equation (III) Indicated by
F = Pγcos θ (III)
From formula (III), the advancing contact angle θa obtained in the process of sinking the suspension plate in the dispersion and the receding contact angle θr obtained in the process of lifting the suspension plate can be obtained. The measurement principle of the Wilhelmy plate method is described in, for example, “Surface and Interfacial Aspect of Biomedical Polymers, Vol. D. Andrade et al (Plenum Press, New York, 1985).

  When θa and θr of an organic solvent or a solution obtained by dissolving a binder in an organic solvent are measured, θa and θr are almost equal. On the other hand, when θa and θr of the pigment dispersion are measured, θa and θr are often not equal and show hysteresis. In the pigment dispersion, the fine particles may aggregate, and if the aggregates are easily generated, the fine particles are likely to settle with time. In addition, a pigment dispersion liquid in which fine particles tend to aggregate is likely to cause a large change in the aggregation state during the dip coating process, and as a result, θa and θr have significantly different values. A pigment dispersion with good dispersibility is a dispersion in which the agglomeration rate of fine particles is slow and aggregates are difficult to form, and a uniform dispersion state is maintained in the dip coating process, so the difference between θa and θr is small. . In short, it can be said that the smaller the value of θa−θr, the more excellent the dispersion stability.

  A pigment dispersion having a value of θa−θr of 5 or more has uneven density and pinholes on the coated surface. Therefore, when the obtained electrophotographic photosensitive member is mounted on a copying machine or the like to form an image, the density unevenness is formed. Such image failures are seen. On the other hand, since the pigment dispersion satisfying the relationship of the above formula (I) does not show sedimentation of fine particles over time and gives a uniform coated surface without unevenness in density, pinholes, etc., the obtained electrophotographic photosensitive member is Even if the image is formed by attaching it to a copying machine or the like, no image failure is observed.

  The electrophotographic photosensitive member of the present invention is a laminate type photosensitive member in which a charge generating layer comprising a charge generating material and a binder, and a charge transporting layer comprising a charge transporting material and a binder are provided on a conductive support. Also, if necessary, an undercoat layer (blocking layer) for controlling injection of charges from the charge generation layer to the conductive support is provided between the conductive support and the charge generation layer. An overcoat layer can also be provided in order to improve the durability.

  As the conductive support according to the present invention, various types can be used including those employed in known electrophotographic photoreceptors. Specifically, for example, gold, silver, platinum, titanium, aluminum, copper, zinc, iron, drums or sheets of conductive metal oxides, sheets, belts, laminates of these thin films, vapor depositions, etc. It is done.

  In addition, a conductive material such as metal powder, metal oxide, carbon black, carbon fiber, copper iodide, charge transfer complex, inorganic salt, or ion conductive polymer electrolyte is coated with an appropriate binder and embedded in the polymer matrix. Drums, sheets, belts, etc. composed of plastics, ceramics, paper, etc. that have been subjected to conductive treatment, and drums, sheets, belts, etc., made of plastics, ceramics, papers, etc. that contain such conductive substances and become conductive Etc.

  In the present invention, when an undercoat layer is provided between the conductive support and the charge generation layer, the undercoat layer is composed of a binder alone or a mixture of a binder and an inorganic pigment. Examples of the binder include polyamide resin, epoxy resin, urethane resin, and the like. Examples of the inorganic pigment include titanium oxide, zinc oxide, and zirconium oxide. The thickness of the undercoat layer is determined according to the degree of surfaceization of the conductive support and the electrophotographic characteristics at low temperature and low humidity, but is used at 0.1 to 30 μm.

  The charge transport material used in the present invention includes a hole transfer material and an electron transfer material. Examples of the hole transfer material include oxadiazoles disclosed in Japanese Patent Publication No. 34-5466, triphenylmethanes disclosed in Japanese Patent Publication No. 45-555, and Japanese Patent Publication No. 52-4188. Pyrazolines disclosed in Japanese Patent Publication No. 55-42380, hydrazones disclosed in Japanese Patent Publication No. 55-42380, oxadiazoles disclosed in Japanese Patent Publication No. 56-123544, etc., Japanese Patent Publication No. 58-32372 And trisylamines disclosed in JP-A-58-198043, and the like. On the other hand, examples of the electron transfer substance include chloranil, tetracyanoethylene, tetracyanoquinodimethane, 2,4,7-trinitro-9-fluorenone, 2,4,5,7-tetranitro-9-fluorenone, 2,4 , 5,7-tetranitroxanthone, 2,4,8-trinitrothioxanthone, 1,3,7-trinitrodibenzothiophene, 1,3,7-trinitrodibenzothiophene-5,5-dioxide, etc. . These charge transport materials can be used alone or in combination of two or more.

  Among these charge transport materials, hydrazones and stilbenes are preferable because they have high charge (hole) mobility and provide an excellent electrophotographic photoreceptor. Among the hydrazones, JP-A-1-1-100555, JP-A-2690541, JP-A-2-511163, JP-A-2-96767, JP-A-2-183260, JP-A-2-184856. The hydrazone compounds described in JP-A-2-184858, JP-A-2-184859, JP-B-5-16025, JP-A-2951469 and JP-A-7-140686 are particularly preferred. Among the stilbenes, those described in Japanese Patent No. 2659561, Japanese Patent Laid-Open No. 2-184857, Japanese Patent No. 2812729, Japanese Patent No. 2866187, Japanese Patent No. 3130154, Japanese Patent No. 3193757, Japanese Patent No. 3323757, Japanese Patent No. 3592455, Japanese Patent No. 3587941 Stilbene compounds are particularly preferred.

  Further, as a sensitizer that further increases the sensitizing effect, a certain kind of electron-withdrawing compound can be added. Examples of the electron-withdrawing compound include quinones such as 2,3-dichloro-1,4-naphthoquinone, 1-nitroanthraquinone, 1-chloro-5-nitroanthraquinone, 2-chloroanthraquinone, and phenanthrenequinone, 4-nitro Aldehydes such as benzaldehyde, ketones such as 9-benzoylanthracene, indandione, 3,5-dinitrobenzophenone, or 3,3 ', 5,5'-tetranitrobenzophenone, phthalic anhydride, 4-chloronaphthalic anhydride Acid anhydrides such as terephthalalmalononitrile, 9-anthrylmethylidenemalononitrile, 4-nitrobenzalmalononitrile, or cyano compounds such as 4- (p-nitrobenzoyloxy) benzalmalononitrile, 3-benzalphthalide , 3- (α-cyano- - Nitorobenzaru) phthalide, or 3- (alpha-cyano -p- Nitorobenzaru) -4,5,6,7 can be mentioned phthalides such as tetrachloro phthalide like.

  As binders used for the charge transport layer, polystyrene, acrylic resin represented by polymethyl methacrylate, polycarbonate having a skeleton represented by bisphenol A and Z, polyarylate, polyester, polyphenylene ether, polyether sulfone, polyamide, Polyimide or the like can be used. These binders can be used alone or in combination of two or more.

  These binders contained in the charge transport layer are preferably 0.1 to 2000 parts by weight, and more preferably 1 to 500 parts by weight with respect to 100 parts by weight of the charge transport material. If the ratio of the binder is too high, the sensitivity is lowered, and if the ratio of the binder is too low, the repetition characteristics may be deteriorated or the coating film may be lost.

  The electrophotographic photoreceptor of the present invention is charged with an antioxidant such as 2,6-di-tert-butyl-p-cresol and DL-α-tocopherol in order to prevent deterioration of the organic compound of the constituent material due to oxidation. It is preferable to add to the transport layer. By adding these antioxidants, an electrophotographic photoreceptor excellent in repetitive characteristics can be obtained.

  EXAMPLES Next, although an Example demonstrates this invention still in detail, this invention is not limited to these at all.

  1 part by weight of butyral resin (manufactured by Sekisui Chemical Co., Ltd .; BL-S) is dissolved in 200 parts by weight of methyl isobutyl ketone, and 10 parts by weight of a bisazo pigment represented by the exemplified compound (2) is added to this solution. Dispersion was carried out for 4 hours together with glass beads having a diameter of 1 mm by a paint conditioner apparatus made by the manufacturer. 4 parts by mass of butyral resin (manufactured by Sekisui Chemical; BL-S) and 5 parts by mass of polyether polyol (manufactured by Asahi Denka Kogyo; BPX-11) were dissolved in 300 parts by mass of methyl isobutyl ketone. The obtained solution was added and further dispersed for 30 minutes by a paint conditioner device to prepare a pigment dispersion. The advancing contact angle θa and receding contact angle θr of the pigment dispersion with respect to the suspension plate were measured using a dynamic contact angle measuring device (Orientic; DCA-100). The suspension plate used for the measurement is an aluminum plate having a smooth surface, a length of 50 mm, a width of 20 mm, a thickness of 1 mm, and a peripheral length of 42 mm. The pulling speed at the time of measurement was 20 mm / min. The measurement results are shown in Table 1.

  The pigment dispersion was applied on a metal aluminum thin plate (JIS standard # 1050) with a dip coating apparatus and dried to form a charge generation layer having a thickness of about 0.2 μm. The results of observing the coating properties of the pigment dispersion are shown in Table 2. Table 2 shows the results of observation of the state of sedimentation of the dispersed particles after the pigment dispersion was allowed to stand for 1 week.

  Next, 100 parts by mass of the stilbene compound represented by the exemplified compound (12), 100 parts by mass of polycarbonate (manufactured by Mitsubishi Gas Chemical; Z-400), and 1 part by mass of DL-α-tocopherol (manufactured by Riken Vitamin; E1000) were added to tetrahydrofuran. Dissolved in 2000 parts by mass, this solution was applied onto the charge generation layer with a dip coating apparatus and dried to form a charge transport layer having a dry film thickness of 25 μm, thereby obtaining an electrophotographic photoreceptor.

The electrophotographic photoreceptor thus prepared is stored overnight in a dark place at room temperature, and then attached to a drum-shaped aluminum base tube and mounted on a commercially available office copying machine to form an image. I investigated. The state of the obtained copy image is given in Table 2. Furthermore, using an electrostatic recording test apparatus (manufactured by Kawaguchi Electric Manufacturing Co., Ltd .; EPA-8200), the electrophotographic photosensitive member is charged with a charged voltage of -5.0 kV, and then irradiated with 2 lux tungsten light, thereby electrophotographic photosensitive member. The half-exposure amount E _{1/2 of} was measured. The results are shown in Table 3.

  Next, the electrophotographic photosensitive member is attached to an aluminum drum tube, and using a drum photosensitive evaluation device (Gentec; Cynthia 90), a process speed of 190 mm / second and a charging voltage of −7.0 kV are satisfied. Then, charging and discharging were repeated 10,000 times, and the charging potential and residual potential of the electrophotographic photosensitive member were measured before and after that. These results are shown in Table 3.

  2 parts by weight of butyral resin (manufactured by Sekisui Chemical Co., Ltd .; BL-S) is dissolved in 200 parts by weight of methyl isobutyl ketone, and 10 parts by weight of a bisazo pigment represented by exemplary compound (2) is added to this solution. Dispersion was carried out for 6 hours together with glass beads having a diameter of 1 mm using a paint conditioner device made by the manufacturer. 3 parts by mass of butyral resin (manufactured by Sekisui Chemical; BL-S) and 5 parts by mass of polyether polyol (manufactured by Asahi Denka Kogyo; BPX-11) were dissolved in 300 parts by mass of methyl isobutyl ketone. The obtained solution was added and further dispersed for 30 minutes by a paint conditioner device to prepare a pigment dispersion. The advancing contact angle θa and receding contact angle θr of the pigment dispersion with respect to the suspension plate were measured in the same manner as in Example 1. The measurement results are shown in Table 1. Next, coating properties and dispersed particle sedimentation were observed using the pigment dispersion in the same manner as in Example 1, and an electrophotographic photoreceptor was prepared and evaluated in the same manner as in Example 1. The results are shown in Tables 2 and 3.

2 parts by weight of butyral resin (manufactured by Sekisui Chemical Co., Ltd .; BL-S) and 1 part by weight of polyether polyol (manufactured by Asahi Denka Kogyo; BPX-11) are dissolved in 200 parts by mass of methyl isobutyl ketone. 10 parts by mass of the bisazo pigment shown in 2) was added and dispersed for 5 hours together with glass beads having a diameter of 1 mm by a paint conditioner manufactured by Red Devil. In the obtained pigment dispersion, 3 parts by mass of butyral resin (manufactured by Sekisui Chemical; BL-S) and 4 parts by mass of polyether polyol (manufactured by Asahi Denka Kogyo; BPX-11) were dissolved in 300 parts by mass of methyl isobutyl ketone. The obtained solution was added and further dispersed for 1 hour by a paint conditioner device to prepare a pigment dispersion. The advancing contact angle θa and receding contact angle θr of the pigment dispersion with respect to the suspension plate were measured in the same manner as in Example 1. The measurement results are shown in Table 1. Next, coating properties and dispersed particle sedimentation were observed using the pigment dispersion in the same manner as in Example 1, and an electrophotographic photoreceptor was prepared and evaluated in the same manner as in Example 1. The results are shown in Tables 2 and 3.

[Comparative Example 1]
1 part by weight of a butyral resin (manufactured by Sekisui Chemical; BL-S) and 4 parts by weight of a polyether polyol (manufactured by Asahi Denka Kogyo; BPX-11) are dissolved in 200 parts by weight of methyl isobutyl ketone. 10 parts by mass of the bisazo pigment represented by 2) was added and dispersed with a glass bead having a diameter of 1 mm for 2 hours by a paint conditioner device manufactured by Red Devil. 4 parts by mass of butyral resin (manufactured by Sekisui Chemical; BL-S) and 1 part by mass of polyether polyol (manufactured by Asahi Denka Kogyo; BPX-11) were dissolved in 300 parts by mass of methyl isobutyl ketone. The obtained solution was added, and further dispersed for 10 minutes by a paint conditioner device to prepare a pigment dispersion. The advancing contact angle θa and receding contact angle θr of the pigment dispersion with respect to the suspension plate were measured in the same manner as in Example 1. The measurement results are shown in Table 1. Next, coating properties and dispersed particle sedimentation were observed using the pigment dispersion in the same manner as in Example 1, and an electrophotographic photoreceptor was prepared and evaluated in the same manner as in Example 1. The results are shown in Tables 2 and 3.

[Comparative Example 2]
1 part by weight of a butyral resin (manufactured by Sekisui Chemical Co., Ltd .; BL-S) and 5 parts by weight of a polyether polyol (manufactured by Asahi Denka Kogyo; BPX-11) are dissolved in 350 parts by weight of methyl isobutyl ketone. 10 parts by mass of the bisazo pigment shown in 2) was added and dispersed for 1 hour together with glass beads having a diameter of 1 mm by a paint conditioner device manufactured by Red Devil. A solution obtained by dissolving 4 parts by mass of butyral resin (manufactured by Sekisui Chemical Co., Ltd .; BL-S) in 150 parts by mass of methyl isobutyl ketone was added to the obtained pigment dispersion, and further dispersed for 10 minutes by a paint conditioner device. A pigment dispersion was prepared. The advancing contact angle θa and receding contact angle θr of the pigment dispersion with respect to the suspension plate were measured in the same manner as in Example 1. The measurement results are shown in Table 1. Next, coating properties and dispersed particle sedimentation were observed using the pigment dispersion in the same manner as in Example 1, and an electrophotographic photoreceptor was prepared and evaluated in the same manner as in Example 1. The results are shown in Tables 2 and 3.

[Comparative Example 3]
2 parts by mass of butyral resin (manufactured by Sekisui Chemical; BL-S) and 2 parts by mass of polyether polyol (manufactured by Asahi Denka Kogyo; BPX-11) are dissolved in 250 parts by mass of methyl isobutyl ketone, and the exemplified compound ( 10 parts by mass of the bisazo pigment represented by 2) was added and dispersed with glass beads having a diameter of 1 mm for 20 minutes by a paint conditioner manufactured by Red Devil. 3 parts by mass of butyral resin (manufactured by Sekisui Chemical Co., Ltd .; BL-S) and 3 parts by mass of polyether polyol (manufactured by Asahi Denka Kogyo; BPX-11) were dissolved in 250 parts by mass of methyl isobutyl ketone in the resulting pigment dispersion. The obtained solution was added and further dispersed for 2 minutes by a paint conditioner device to prepare a pigment dispersion. The advancing contact angle θa and receding contact angle θr of the pigment dispersion with respect to the suspension plate were measured in the same manner as in Example 1. The measurement results are shown in Table 1. Next, coating properties and dispersed particle sedimentation were observed using the pigment dispersion in the same manner as in Example 1, and an electrophotographic photoreceptor was prepared and evaluated in the same manner as in Example 1. The results are shown in Tables 2 and 3.

5 parts by mass of alcohol-soluble nylon (manufactured by Nagase ChemteX; Toresin EF-30T) is dissolved in 100 parts by weight of methanol, and 5 parts by mass of titanium oxide (Ishihara Sangyo; TTO-55N) is mixed. It was dispersed for 5 hours together with zirconia beads having a diameter of 1 mm by a conditioner device. The titanium oxide dispersion thus obtained was applied onto a metal aluminum thin plate (JIS standard # 1050) with a dip coating apparatus and dried to form an undercoat layer having a thickness of 0.5 μm.

  5 parts by weight of a butyral resin (manufactured by Sekisui Chemical Co., Ltd .; BM-S) is dissolved in 2000 parts by weight of methyl isobutyl ketone, and 120 parts by weight of a bisazo pigment represented by exemplary compound (6) is added to this solution. Dispersion was carried out for 4 hours together with glass beads having a diameter of 1 mm by a paint conditioner apparatus made by the manufacturer. A solution obtained by dissolving 75 parts by mass of butyral resin (manufactured by Sekisui Chemical Co., Ltd .; BM-S) in 5000 parts by mass of methyl isobutyl ketone was added to the obtained pigment dispersion, and further dispersed for 30 minutes by a paint conditioner device. A pigment dispersion was prepared. The advancing contact angle θa and receding contact angle θr of the pigment dispersion with respect to the suspension plate were evaluated in the same manner as in Example 1. Table 4 shows the measurement results.

  The pigment dispersion was applied onto the undercoat layer with a dip coating apparatus and dried to form a charge generation layer having a thickness of about 0.2 μm. The results of observing the coating properties of the pigment dispersion are shown in Table 5. Table 5 shows the results of observation of the state of sedimentation of the dispersed particles after the pigment dispersion was left for 1 week.

  Next, 100 parts by mass of the hydrazone compound represented by the exemplified compound (13), 100 parts by mass of polycarbonate (manufactured by Mitsubishi Gas Chemical; Z-200), and 1 part by mass of DL-α-tocopherol (manufactured by Riken Vitamin; E1000) were added to tetrahydrofuran. Dissolved in 2000 parts by mass, this solution was applied onto the charge generation layer with a dip coating apparatus and dried to form a charge transport layer having a dry film thickness of 20 μm.

The electrophotographic photoreceptor thus prepared was stored overnight in a dark place at room temperature, and then evaluated in the same manner as in Example 1. The results are shown in Tables 5 and 6.

Reference example 1
A pigment dispersion and an electrophotographic photosensitive member were prepared in the same manner as in Example 4 except that the bisazo pigment represented by the exemplary compound (14) was used instead of the bisazo pigment represented by the exemplary compound (6). Similar evaluations were made. The results are shown in Tables 5 and 6.

Reference example 2
The same pigment as in Example 4, except that metal-free phthalocyanine (manufactured by Dainippon Ink & Chemicals, Inc .; 8120BS) was used instead of the bisazo pigment represented by the exemplary compound (6), and 1,3-dioxolane was used instead of methyl isobutyl ketone A dispersion and an electrophotographic photosensitive member were prepared and evaluated in the same manner as in Example 4. The results are shown in Tables 5 and 6.

[Comparative Examples 4 to 6]
A pigment dispersion and an electrophotographic photosensitive member were prepared in the same manner as in Example 4 except that ethyl acetate, butyl acetate, and toluene were used in place of methyl isobutyl ketone, and the same evaluation as in Example 4 was performed. The results are shown in Tables 5 and 6.

The pigment dispersion satisfying the relationship of the above formula (I) of the present invention is excellent in dispersibility, stability over time, and coatability. By using the dispersion, an electrophotographic photoreceptor having high sensitivity and high durability can be obtained. It is done.

  The electrophotographic photosensitive member of the present invention can be used for a copying machine, a printer and the like. In particular, since the electrophotographic photosensitive member of the present invention has high sensitivity, high durability, and high resolution, it can be applied to a printer using a semiconductor laser having a short oscillation wavelength as an exposure light source.

Claims (2)

Dispersion of pigment for producing an electrophotographic photosensitive member, in which at least one selected from bisazo pigments represented by the following general formula (1) is dispersed as a pigment for a charge generating material in an organic solvent in which at least one binder is dissolved. In the method for producing a liquid, when the advancing contact angle θa and the receding contact angle θr with respect to the suspension plate of the dispersion liquid are measured by the Wilhelmy method, it includes a process control for confirming that the relationship of the following formula (I) is satisfied. A method for producing a pigment dispersion for producing an electrophotographic photosensitive member.
0 ° <θa−θr <5 ° (I)

(In General Formula (1), A1 is hydrogen, an alkyl group which may have a substituent, an aryl group, or a heterocyclic group, m and n are 0 or 1, X is hydrogen, a methyl group, A cyano group and halogen, and Cp1 represents a coupler residue.) 2. The method for producing a pigment dispersion for producing an electrophotographic photosensitive member according to claim 1 , wherein the organic solvent is at least one selected from ketone solvents.