An electrophotographic photoconductor and a method for preparing the same

Abstract: The electrophotographic photoconductor of the present invention includes a conductive substrate and a photosensitive layer containing perylene pigment as a charge generating material formed on the conductive substrate. The X-ray diffraction peak of the perylene pigment exhibits its peak when the value of 2ϑ is 14°(±0.3°), and the half-width of the peak when the value of 2ϑ is 14° (±0.3°) is 0.5 or more. This electrophotographic photoconductor has excellent qualities of low residual potential and stabilized quality.

Description: The present invention relates to an electrophotographic photoconductor for use in an image-forming apparatus such as an electro-static copying machine or a laser printer, said electrophotographic photoconductor comprising a specific perylene pigment as a charge generating material, and to a method for preparing the same. A coating solution for a photoconductor is prepared by dissolving binding resin in a solvent and then mixing a charge generating material, a charge transport material, etc., therein. This coating solution is applied onto a conductive substrate in lamination or monolayer, and then dried to prepare a photoconductor. The photoconductor obtained by the use of the coating solution has the advantages of high capability of forming a film and high productivity because it can be produced in a coating process. The photoconductor has further advantages in that the selection of pigment, etc., may freely control the photosensitive property, etc. Accordingly, the photoconductor has been studied in many respects. As a charge generating material present in the aforesaid coating solution, a perylene pigment may be used. This perylene pigment can be obtained usually by reacting perylene tetracarboxylic acid anhydride with an amine compound. An electrophotographic organic photoconductor using perylene pigment thus synthesized requires properties such as sufficient sensitivity and repeatability to be a photoconductor. Properties such as the purity, the type of crystal, and the particle size of the pigment have been studied as factors which control the properties of the photoconductor. These properties of the pigment affect not only the aforesaid properties of the photoconductor but also the stability of preserving a coating solution, so the crude pigment after being synthesized requires various treatments immediately. PA of Japan of JP-A-61-87158, Vol.10, No.260 (P-494) (2316), september 5, 1986 discloses a perylene dye having an average particle diameter of 50-100nm. The dye is obtained by treating a known perylene type dye with an organic solvent or dissolving the dye in a strong solvent, and precipitating in a nonsolvent. The applicant of the present invention has filed an application relating to a monolayer positively charged photoconductor having excellent repeatability and aging property utilizing perylene pigment as a charge generating material in Japanese Laid-Open Patent Publication No. 63-85750. In this publication, the perylene pigment is prepared in the following manner. The synthesized perylene pigment is dissolved in sulfuric acid, after which the sulfuric acid solution is dropped into ice water to prepare α type perylene pigment. Thereafter, the resulting dispersion is washed with water to prepare a crude material. To the crude material is added nitrobenzene or dichloromethane to prepare β type perylene pigment. Then, the resulting β type perylene pigment solution is treated in a ball mill to prepare α and β type perylene pigment. Thereafter, methanol is added to the resulting mixture which is then filtered, and then the filtered substance is dried and classified to obtain perylene pigment having a particle size in the range of 0.05 µm to 0.1 µm. However, when a coating solution for a photoconductor is prepared by the use of the perylene pigment obtained by the above method as a charge generating material, the particle size of the perylene pigment increases due to the crystal growth in the coating solution. As a result, when copying using the resulting photoconductor, there is a problem in that the surface potential (residual potential) of the photoconductor increases after exposure, this occurring markedly in the case of a monolayer photoconductor. The electrophotographic photoconductor of this invention, which overcomes the above-discussed and numerous other disadvantages and deficiencies of the prior art, is as claimed in claim 1. In a preferred embodiment, the perylene pigment is represented by the following formula: In a further preferred embodiment, the perylene pigment has a pH in the range of 6.3 to 7.7. A method for preparing an electrophotographic photoconductor including a conductive substrate and a photosensitive layer containing perylene pigment as a charge generating material formed on the conductive substrate, is as claimed in claim 6. Thus, the invention described herein makes possible the objectives of : (1) providing an electrophotographic photoconductor with excellent low residual potential by preventing the particle size of perylene pigment in a coating solution from being increased; (2) providing a stabilized electrophotographic photoconductor of high quality because there is no large decrease in the quality of the coating solution during storage thereof; (3) providing an electrophotographic photoconductor with high productivity by imparting longer life to the coating solution; and (4) providing a method for preparing an electrophotographic photoconductor having the aforesaid properties. In the description which follows, reference will be made to the accompanying drawings, wherein: Figures 1 and 2 are graphs showing the X-ray diffraction peak of a perylene pigment of the present invention. Figures 3 and 4 are graphs showing the X-ray diffraction peak of the perylene pigment of a Comparative Example. The electrophotographic photoconductor of the present invention can be prepared in the following manner. Binding resin, the aforesaid perylene pigment as a charge generating material, solvent, etc., are mixed to prepare a coating solution. The resulting coating solution is applied onto a conductive substrate, and then dried to form a photosensitive layer. The above photosensitive layer can be classified into the following two kinds. One is a monolayer form having a charge generating material, a charge transport material, and binding resin. The other kind is a lamination form having a charge generating layer containing a charge generating material, and a charge transport layer containing a charge transport material. An electrophotographic photoconductor having a monolayer photosensitive layer may be obtained by forming a monolayer containing perylene pigment as a charge generating material, a charge transport material, binding resin, etc., on the conductive substrate. On the other hand, an electrophotographic photoconductor having a lamination of photosensitive layers may be obtained in the following manner. A charge generating layer containing perylene pigment is formed on the conductive substrate. Then, a charge transport layer containing a charge transport material is formed on the charge generating layer. Alternatively, the build-up sequence to form the charge generating layer on the charge transport layer may be reversed. The electrophotographic photoconductor of the present invention can be applicable to any of the aforesaid types thereof. The coating solution used to form a photosensitive layer can be prepared by mixing a charge generating material, a charge transport material, and binding resin in a known process, for example, a process using a roll mill, ball mill, attriter, a paint shaker, an ultrasonic dispersing apparatus, etc. In a laminated electrophotographic photoconductor, a charge generating material and binding resin for constituting a charge generating layer may be used in various ratios. The preferable amount of the charge generating material to be used is in the range of 5 to 500 parts by weight per 100 parts by weight of binding resin, and is more preferably in the range of 10 to 250 parts by weight. The charge generating layer preferably has a thickness in the range of 0.01 to 5 µm, and more preferably in the range of 0.1 to 3 µm. A charge transport material and binding resin for constituting a charge transport layer may be used in various ratios. In order to easily transport the charge generated in the charge generating layer by irradiation with light, it is preferable that the charge transport material be used in an amount in the range of 10 to 500 parts by weight per 100 parts by weight of binding resin, and more preferably in an amount in the range of 25 to 200 parts by weight. It is preferable that the charge transport layer have a thickness in the range of 2 to 100 µm, and more preferably in the range of 5 to 30 µm. In a monolayer electrophotographic photoconductor, a charge generating material may preferably be used in an amount in the range of 2 to 20 parts by weight per 100 parts by weight of binding resin, and more preferably in an amount in the range of 3 to 15 parts by weight. A charge transport material may preferably be used in an amount in the range of 40 to 200 parts by weight per 100 parts by weight of binding resin, and more preferably in an amount in the range of 50 to 100 parts by weight. The thickness of the photosensitive layer may preferably be in the range of 10 to 50 µm, and more preferably in the range of 15 to 25 µm. Perylene pigment having an X-ray diffraction peak when the value of 2 is 14°, the half-width of the aforesaid peak when the value of 2 is 14° being 0.5 or more, is used in the present invention. The "half-width" prescribed in the present invention represents the width of the peak at half height (c) of the peak (B) from a base line (A) in Figure 1. The half-width when the value of 2 is 14° is about 0.8° in Figure 1. Other than the peak when the value of 2 is 14°, the X-ray diffraction peak generally exhibits other peaks mainly when the value of 2 is 5°, 10°, 19°, 21.5°, 23.2°, 24.4°, 25.8°, and 28.2° (each value may have an extra width of ±0.3°). The perylene pigment having such an X-ray diffraction peak has a type crystal structure, high efficiency of generating charge, and excellent charge transport property. Perylene pigment having a structure represented by the following formula (I) is used in the present invention. with R 1 and R 2 independently representing alkylaryl group or a phenyl group. Particularly preferred is a perylene pigment having a structure represented by the following formula (II); A perylene pigment for use in the present invention can be prepared, for example, in the following manner. Generally, perylene pigment can be obtained by reacting perylene tetracarboxylic acid anhydride with a compound having an amino group. Since the synthesized perylene pigment contains unreacted substance, i.e., an amine compound such as 3,5-xylidine, and a catalyst such as zinc chloride, it may be purified according to a conventional process. Examples of this purification process include water cleaning, acid cleaning, and alkali cleaning, by using respectively water, an acid aqueous solution, and an alkali aqueous solution. These processes may be utilized in a combination of two or more kinds thereof. Particularly, it is preferable that acid cleaning be utilized together with alkali cleaning, after which water cleaning is conducted. An amine compound such as xylidine remaining in the pigment can be neutralized by the acid cleaning, and zinc chloride, etc., can be decomposed and removed by the alkali cleaning. In the present invention, pigment may be used, the pH of which is in the range of 6.3 to 7.7 after cleaning with washing. The use of pigment having a pH of less than 6.3 adversely affects other materials such as binding resin, thereby lowering the aging property of the resulting photoconductor. On the other hand, when a pigment having a pH of more than 7.7 is used, an alkali component such as xylidine remains in the pigment, which traps carriers generated in a photosensitive layer, thereby lowering the sensitivity of the photoconductor. A pigment preferably having a pH in the aforesaid range is used to prepare a coating solution. The resulting coating solution is applied and dried to form a photosensitive layer, thereby obtaining a photoconductor with high quality. Accordingly, a purification degree may be prescribed which is such that the pH of the pigment to be used is included within the aforesaid range which is at attained simply by the necessary purification processes. This eliminates the time and labor required for unnecessary processes. As stated above, synthesized (and purified) perylene pigment and solvent such as xylene are put into a dispersing apparatus. Then, the pigment is mechanically crushed and further ground by means of a dispersing apparatus such as a ball mill. Thereafter, the ground material is filtered, and to the filtered material is added solvent such as methanol. Then, the mixture is washed, filtered, and heat-treated to obtain perylene pigment for use in the present invention. In a coating solution for a photoconductor utilizing the perylene pigment thus prepared, the condition of the crystals and cohesion of the charge generating material hardly changed during storage thereof. This may be attributable to the following fact. The perylene pigment synthesized in the above manner is treated with an organic solvent, and then subjected to a grinding process to form a crystal lattice defect in the pigment. Therefore, in the coating solution for a photoconductor, the crystal growth of the pigment is prevented and the increasing in size and the cohesion of particles of the perylene pigment are inhibited. Consequently, even when a photoconductor is prepared by the use of a coating solution which has been left for a predetermined time, the quality of the photoconductor does not significantly decrease. When the half-width of the peak of the X-ray diffraction peak of the perylene pigment, when the value of 2 is 14° is less than 0.5, in a coating solution for a photoconductor prepared by the use of this perylene pigment as a charge generating material, there is enhanced increase in size of particles of the pigment due to the crystal growth during storage thereof. Accordingly, a photoconductor prepared by the use of this coating solution disadvantageously shows high surface potential after exposure. The perylene pigment of the present invention has a particle size in the range of 0.01 µm to 0.05 µm. When the particle size of the perylene pigment is less than 0.01 µm, or more than 0.05 pm, the charge generating efficiency becomes low, thereby lowering the sensitivity of the resulting photoconductor. The aforesaid perylene pigment may be used independently, or in combination with other charge generating materials. Examples of other charge generating materials include selenium, selenium-tellurium, amorphous silicon, pyrylium salts, anthanthrone pigments, phthalocyanine pigments, indigo pigments, triphenylmethane pigments, indanthrene pigments, toluidine pigments, pyrazoline pigments, azo pigments, quinacridone pigments, etc. As the aforesaid charge transport material, conventional charge transport materials can be used. Examples of the charge transport material include nitrogen-containing cyclic compounds such as oxadiazole compounds including 2,5-di(4-methylaminophenyl)-1,3,4-oxadiazole, styryl compounds such as 9-(4-diethylaminostyryl)anthracene, carbazole compounds such as polyvinylcarbazole, pyrazoline compound such as 1-phenyl-3-(p-dimethylaminophenyl)pyrazole, hydrazone compounds, triphenylamine compounds, indole compounds, oxazole compounds, isooxazole compounds, thiazole compounds, thiadiazole compounds, imidazole compounds, pyrazole compounds, and triazole compounds; and condensed polycyclic compounds. These charge transport materials can be used independently or in combinations of two or more thereof. As the aforesaid binding resin, various kinds of conventional resin can be used. Examples of this binding resin include various kinds of polymer such as styrene polymers, styrene-butadiene copolymers, styrene-acrylonitrile copolymers, styrene-maleic acid copolymers, acrylic polymers, styrene-acrylic copolymers, ethylene-vinyl acetate copolymers, polyvinyl chloride, vinyl chloride-vinyl acetate copolymers, polyesters, alkyd resins, polyamides, polyurethanes, acrylic modified urethane resins, epoxy resins, polycarbonates, polyacrylates, polysulfones, diallylphthalate resins, silicone resins, ketone resins, polyvinyl butyral resins, polyether resins, phenol resins. Photo-cure resin such as epoxy acrylate. resins can also be used. Further examples of the binding resin may include photoconductive polymer such as poly-N-vinylcarbazole. The aforesaid solvent can be selected from conventional solvents, the choice depending, inter alia, on the kind of the binding resin used. Examples of solvents include alcohols such as methanol, ethanol, propanol, isopropanol, butanol; aliphatic hydrocarbons such as n-hexane, octane, and cyclohexane; aromatic hydrocarbons such as benzene, toluene, and xylene; halogenated hydrocarbons such as dichloromethane, dichloroethane, carbon tetrachloride, and chlorobenzene; ethers such as dimethyl ether, diethyl ether, tetrahydrofuran, ethyleneglycoldimethylether, and ethyleneglycoldiethylether; ketones such as acetone, ethylketone, and cyclohexanone; and esters such as ethyl acetate and methyl acetate. These materials may be used independently or in combination of two or more kinds thereof. In order to improve the dispersing property, the coating property, etc., of the charge transport material and the charge generating material, a photosensitive solution may further contain surfactant, leveling agent, etc. Examples of the aforesaid conductive substrates include simple metal and alloy substrates such as aluminium, copper, tin, platinum, silver, vanadium, molybdenum, chromium cadmium, titanium, nickel, palladium, indium, stainless steel, and brass; plastic materials vacuum-evaporated or laminated with the aforesaid metal; and glass coated with aluminium iodide, tin oxide, indium oxide. The conductive substrate may have any form, being, for example, sheet-like or drum-like in form. The substrate itself has conductivity, or the surface of the substrate has conductivity. A preferable substrate has sufficient mechanical strength as such for the intended use. Examples The present invention will now be explained in detail by reference to examples. Preparation of an electrophotographic photoconductor Example 1 One hundred parts by weight of N,N-di(3,5-dimethylphenyl)perylene-3,4,9,10-tetracarboxylic acid diimide (PV Fast Red B, manufactured by Hoechst Co.) and 2,000 parts by weight of xylene as a solvent are put into a paint shaker to be crushed with zirconia beads for 1 hour, after which the mixture was ground in a ball mill for 3 days. Then, the mixture was filtered, 1,000 parts by weight of methanol were added, and then the mixture obtained was filtered. This filtering step was repeated for three times, after which heat treatment was conducted to obtain perylene pigment. The measurement of the X-ray diffraction peak of the perylene pigment thus obtained showed that the half-width of the peak when the value of 2 was 14° was 0.6. One part by weight of this perylene pigment and 40 parts by weight of tetrahydrofuran were stirred and mixed for 1 minute by means of an ultrasonic dispersing apparatus. To the mixture were added 100 parts by weight of 10% solution of polyvinylcarbazole (manufactured by ANAN KORYO CO., TSUBICOL 210) in tetrahydrofuran as a charge transport material, which was subjected to secondary dispersion for 2 minutes by means of the ultrasonic dispersing apparatus to prepare a coating solution for a monolayer photosensitive layer. The resulting coating solution was applied onto an aluminium foil by means of a wire bar (#28), and subjected to hot-air drying at 100°C for 1 hour to form a monolayer photosensitive layer with a thickness of about 10 µm, thereby completing an electrophotographic photoconductor. Example 2 Perylene pigment was obtained in the same manner as in Example 1, except that the number of days during which grinding continued in a ball mill was 5 days. The X-ray diffraction peak of the perylene pigment thus obtained was measured and found to be as shown in Figure 1, indicating that the half-width of the peak when the value of 2 was 14° was 0.8. A monolayer electrophotographic photoconductor was prepared in the same manner as in Example 1, except that this perylene pigment was used. Example 3 Perylene pigment was obtained in the same manner as in Example 1, except that the number of days during which grinding continued in a ball mill was 7 days. The measurement of the X-ray diffraction peak of the perylene pigment thus obtained showed that the half-width of the peak when the value of 2 was 14° was 1.0. A monolayer electrophotographic photoconductor was prepared in the same manner as in Example 1, except that this perylene pigment was used. Example 4 Perylene pigment was obtained in the same manner as in Example 1, except that the number of days during which grinding continued in a ball mill was 10 days. The X-ray diffraction peak of the perylene pigment thus obtained was measured and found to be as shown in Figure 2, indicating that the half-width of the peak when the value of 2 was 14° was 1.5. A monolayer electrophotographic photoconductor was prepared in the same manner as in Example 1, except that this perylene pigment was used. Comparative Example 1 Perylene pigment was obtained in the same manner as in Example 1, except that the grinding process in a ball mill was not conducted. The X-ray diffraction peak of the perylene pigment thus obtained was measured and found to be as shown in Figure 3, indicating that the half-width of the peak when the value of 2 was 14° was 0.2. A monolayer electrophotographic photoconductor was prepared in the same manner as in Example 1, except that this perylene pigment was used. Comparative Example 2 Perylene pigment was obtained in the same manner as in Example 1, except that the number of days during which grinding continued in a ball mill was 1 day. The measurement of the X-ray diffraction peak of the perylene pigment thus obtained showed that the half-width of the peak when the value of 2 was 14° was 0.4. A monolayer electrophotographic photoconductor was prepared in the same manner as in Example 1, except that this perylene pigment was used. Comparative Example 3 One part by weight of N,N-di(3,5-dimethylphenyl)perylene-3,4,9,10-tetracarboxylic acid diimide (PV Fast Red B, manufactured by Hoechst Co.) was dissolved in 20 parts by weight of concentrated sulfuric acid, to which was added a large amount of water prior to effecting crystallization. Then, the solution was filtered. The resulting filtered substance was washed with water, and then twice with methanol to obtain β type perylene pigment having an X-ray diffraction peak as shown in Figure 4. A monolayer electrophotographic photoconductor was prepared in the same manner as in Example 1, except that 1 part by weight of this perylene pigment was used. Example 5 One part by weight of perylene pigment (the half-width when the value of 2 is 14° is 0.6) obtained in the same manner as in Example 1 as a charge generating material, 1 part by weight of vinyl chloride-vinyl acetate as binding resin, and 60 parts by weight of tetrahydrofuran were used to prepare a dispersion by means of an ultrasonic dispersing apparatus. Then, the resulting dispersion was applied onto an aluminium plate, and dried at 100°C for 30 minutes to form a charge generating layer with a thickness of 0.5 µm. Next, 0.7 parts by weight of N,N-di(3-tolyl)-N,N'di(4-tolyl)-1,3-phenylenediamine as a charge transport material, 1 part by weight of polycarbonate as binding resin, and 50 parts by weight of benzene were used to prepare a dispersion. Then, the resulting dispersion was applied onto the charge generating layer to form a charge transport layer with a thickness of 20 µm, thereby completing a laminated electrophotographic photoconductor. Comparative Example 4 A laminated electrophotographic photoconductor was prepared in the same manner as in Example 5, except that 1 part by weight of the perylene pigment as that used in Comparative Example 2 (the half-width when the value of 2 is 14° is 0.4) was used as a charge generating material. The evaluation of the electrophotographic photoconductor The electrophotographic photoconductors thus obtained were each installed in an electrostatic process copying test device (manufactured by KAWAGUCHI ELECTRIC CO., Model-8100). Then, the monolayer photoconductor was positively charged by applied voltage + 5.5 KV, and the laminated photoconductor was negatively charged by applied voltage - 5.5 KV. The characteristics of the photoconductor were measured under the conditions set out below. The results are shown in Table 1. Exposure time: 10 seconds Light for use in exposure: White light Luminous intensity: 10 lux Dark attenuation after being charged: 2 seconds In Table 1, V 1 (V) denotes the initial surface potential (V) of the photoconductor when charged by application of voltage under the above conditions. E 1 1/2 (lux·sec) denotes the half-value exposure calculated from the exposure time required for the surface potential to decrease to 1/2 of the initial surface potential V 1 (V). The value of V 1 r.P.(V) in Table is obtained as residual potential by measuring the surface potential of the photoconductor which has been left for 5 seconds after exposure. As for a monolayer photoconductor, first, a coating solution for a photoconductor was prepared. Then, the resulting coating solution was kept for 10 days, and then applied onto an aluminium foil to prepare an electrophotographic photoconductor. This photoconductor was also evaluated under the same condition as described above. The results are shown in Table 2. As for this photoconductor obtained by the use of the coating solution which had been kept for 10 days, the initial surface potential, the half-value exposure, and the residual potential are denoted by V 2 (V), E 2 1/2(lux·sec), and V 2 r.p., respectively. As apparent from Tables 1 and 2, the photoconductor using perylene pigment having a half-width when the value of 2 is 14° of 0.5 or more had high sensitivity and low residual potential. On the other hand, the photoconductor using perylene pigment having a half-width when the value of 2 is 14° of less than 0.5 had inferior sensitivity and high residual potential. The coating solution for a photoconductor using perylene pigment having a half-width when the value of 2 is 14° of 0.5 or more did not significantly decrease in quality during storage thereof, thereby not affecting the properties of the photoconductor. On the other hand, the coating solution for a photoconductor using perylene pigment having a half-width when the value of 2 is 14° of less than 0.5 decreased in quality during storage thereof, thereby affecting the properties of the photoconductor. The photoconductor using perylene pigment having a β type crystal structure was inferior in all properties such as sensitivity, residual potential, and and storage properties of the coating solution. V 1 (V) V 1 r.p.(V) E 1 1/2(lux.sec) Example 1 680 46 16.1 Example 2 670 45 16.2 Example 3 670 35 15.7 Example 4 680 35 14.8 Comparative Example 1 680 88 23.7 Comparative Example 2 670 70 19.8 Comparative Example 3 670 90 24.2 Example 5 -715 -58 15.6 Comparative Example 4 -710 -80 21.8 V 2 (V) V 2 r.p.(V) E 2 1/2(lux.sec) Example 1 670 50 17.2 Example 2 680 47 16.7 Example 3 690 40 16.2 Example 4 680 35 15.1 Comparative Example 1 650 105 33.1 Comparative Example 2 640 90 23.7 Comparative Example 3 680 120 32.3

Claims: An electrophotographic photoconductor comprising a conductive substrate and a photosensitive layer containing α-type perylene pigment as a charge generating material formed on said conductive substrate, characterized in that the X-ray diffraction peak of said α-type perylene pigment exhibits its peak when the value of 2Θ is 14° (± 0.3°), and the half-width of said peak when the value of 2Θ is 14° (±0.3°) is 0.5° or more, in that said α-type perylene pigment has a particle size in the range of 0.01 to 0.05µm, and in that said α-type perylene pigment is represented by the general formula: with, in the formula, R 1 and R 2 being independently an alkyl aryl group or a phenyl group. An electrophotographic photoconductor according to claim 1, wherein said α-type perylene pigment has been obtained by grinding an α-type perylene pigment the X-ray diffraction peak of which exhibits its peak when the value of 2Θ is 14° (±0.3°), the half-width of said peak when 2Θ is 14° (±0.3°) being less than 0.5°. An electrophotographic photoconductor according to claim 1 or 2, wherein said α-type perylene pigment is represented by the formula: An electrophotographic photoconductor according to any preceding claim, wherein said X-ray diffraction peak further exhibits its peak when the value of 2Θ is 5°, 10°, 19°, 21.5°, 23.2°, 24.4°, 25.8°, and 28.2° (each value may have an extra width of ±0.3°). An electrophotographic photoconductor according to any preceding claim, wherein the pH of said α-type perylene pigment is in the range of 6.3 to 7.7. A method for preparing an electrophotographic photoconductor including a conductive substrate and a photosensitive layer containing the α-type perylene pigment represented by the general formula: with R 1 and R 2 being independently an alkyl aryl group or a phenyl group as a charge generating material formed on said conductive substrate, which method is characterized in that it comprises the steps of: preparing said α-type perylene pigment the X-ray diffraction peak of which exhibits its peak when the value of 2Θ is 14° (±0.3°), the half-width of said peak when the value of 2Θ is 14° (±0.3°) being 0.5° or more, said α-type perylene pigment having a particle size in the range of 0.01 to 0.05 µm, by grinding α-type perylene pigment the X-ray diffraction peak of which exhibits its peak when the value of 2Θ is 14° (±0.30), the half-width of the peak when the value of 2Θ is 14° (±0.3°) being less than 0.5°, preparing a coating solution for a photoconductor containing the obtained α-type perylene pigment; and contacting the conductive substrate with said coating solution and drying the coating solution then present on the conductive substrate. A method for preparing an electrophotographic photoconductor according to claim 6, wherein grinding of the α-type perylene pigment is conducted according to a wet method.

Inventors: MAEDA TATSUO, MIYAMOTO EIICHI, MUTO NARIAKI, MAEDA, TATSUO, MIYAMOTO, EIICHI, MUTO, NARIAKI
Applicants: MITA INDUSTRIAL CO LTD, MITA INDUSTRIAL CO., LTD.
Application year: 1991
Main classification: G03G5
IPC codes: G03G5