Patent Publication Number: US-5292604-A

Title: Phthalocyanine crystal of mixed pigments and electrophotographic photoreceptor using the same

Description:
FILED OF THE INVENTION 
     This invention relates to a novel crystal of mixed pigments of oxytitanium phthalocyanine and a halogenated gallium phthalocyanine or a halogenated indium phthalocyanine and an electrophotographic photoreceptor containing the same as a charge generating material. 
     BACKGROUND OF THE INVENTION 
     Known charge generating materials having sensitivity in the near infrared region which can be used in electrophotographic photoreceptors include squarylium pigments, bisazo pigments, and phthalocyanine pigments. Of these materials, oxytitanium phthalocyanine has recently been attracting particular attention because of its high sensitivity, and various species thereof having different crystal forms have hitherto been proposed for use as a charge generating material of electrophotographic photoreceptors. For example, the α-crystal form is disclosed in JP-A-61-217050; the β-crystal form in JP-A-59-49544; the C-crystal form in JP-A-62-256865; the D-crystal form in JP-A-62-67094; the Y-crystal form in JP-A-64-17066; the γ-crystal form in JP-A-1-299874; and the ω-crystal form in JP-A-2-99969, respectively (the term &#34;JP-A&#34; as used herein means an &#34;unexamined published Japanese patent application&#34;). Further, the D-, Y-, and γ-crystals forms are known to have an X-ray diffraction peak at a Bragg angle (2θ±0.2) of around 27.2°. 
     On the other hand, gallium phthalocyanine (see JP-A-1-221459) and indium phthalocyanine (see JP-A-60-59355 and JP-A-61-124951) were also reported to be effective as a charge generating material for electrophotographic photoreceptors. 
     Additionally, JP-A-1-142658, JP-A-1-221461, JP-A-2-70763, JP-A-2-170166, JP-A-2-272067, and JP-A-2-280169 proposed use of a crystal of mixed pigments or mere mixture of oxytitanium phthalocyanine and other phthalocyanine as a charge generating material. 
     However, a crystal of mixed pigments of oxytitanium phthalocyanine and a halogenated gallium phthalocyanine or a halogenated indium phthalocyanine has not yet been reported. 
     While the above-described known oxytitanium phthalocyanine species and crystals of mixed pigments thereof are useful as a charge generating material, they are still unsatisfactory. For example, the oxytitanium phthalocyanine having the maximum diffraction peak at a Bragg angle (2θ±0.2°) of 27.3°, disclosed in JP-A-62-67094 supra, exhibits very high sensitivity but is still insufficient in stability on repeated use, crystal form stability in a coating composition, and dispersibility in a coating composition. In order to settle these problems, it has been proposed to mix oxytitanium phthalocyanine with a small amount of a substituted phthalocyanine as described, e.g., in JP-A-3-9962, JP-B-55-27583,  and JP-B-54-44684 (the term &#34;JP-B&#34; as used herein means an &#34;examined Japanese patent publication&#34;). In this case, however, since a substituted phthalocyanine is markedly different from unsubstituted phthalocyanine in crystal form, mixing them gives rise to another problem, such as reduction in electrophotographic characteristics. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of the present invention is to provide a crystal of mixed pigments containing oxytitanium phthalocyanine which is suitable for producing an electrophotographic photoreceptor having excellent stability on repeated use and excellent environmental stability. 
     Another object of the present invention is to provide an electrophotographic photoreceptor excellent in stability on repeated use and stability to environment. 
     The inventors have conducted extensive investigations on crystal forms of various phthalocyanine complexes with the purpose of developing an electrophotographic photoreceptor excellent in electrophotographic characteristics and productivity. As a result, they found a wonderful similarity in crystal form between a halogenated gallium phthalocyanine or a halogenated indium phthalocyanine and oxytitanium phthalocyanine. Based on this finding, they have reached the fact that the similarity in crystal form makes it possible to form a crystal of mixed pigments between the former and the latter while controlling the crystal form of the crystal of mixed pigments by selecting a mixing ratio. It has also been confirmed that such a novel crystal of mixed pigments is excellent in crystal form stability, dispersibility, and sensitivity and therefore quite suited for use in electrophotographic photoreceptors. 
     The phthalocyanine crystal of mixed pigments according to the present invention is a crystal of mixed pigments of oxytitanium phthalocyanine and a halogenated gallium phthalocyanine or a halogenated indium phthalocyanine. 
    
    
     BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS 
     FIG. 1 is a powder X-ray diffraction pattern of an oxytitanium phthalocyanine crystal. 
     FIG. 2 is a powder X-ray diffraction pattern of a chlorogallium phthalocyanine crystal. 
     FIG. 3 is a powder X-ray diffraction pattern of a chloroindium phthalocyanine crystal. 
     FIGS. 4 to 11 are powder X-ray diffraction patterns of the oxytitanium phthalocyanine-chlorogallium phthalocyanine crystals obtained in Examples 1, 2, 3, 7, 10, 11, 12, and 14, respectively. 
     FIGS. 12 to 19 are powder X-ray diffractions pattern of the oxytitanium phthalocyanine-chloroindium phthalocyanine crystals obtained in Examples 17, 18, 19, 20, 23, 25, 26, and 30, respectively. 
     FIGS. 20 and 21 are powder X-ray diffraction patterns of the oxytitanium phthalocyanine crystals of Comparative Examples 1 and 2, respectively. 
     FIG. 22 is a powder X-ray diffraction pattern of the chlorogallium phthalocyanine crystal obtained in Comparative Example 3. 
     FIGS. 23 and 24 are powder X-ray diffraction patterns of the oxytitanium phthalocyanine crystals obtained in Comparative Examples 4 and 8, respectively. 
     FIGS. 25 to 27 are powder X-ray diffraction patterns of the chlorogallium phthalocyanine crystals obtained in Comparative Examples 10, 11, and 14, respectively. 
     FIGS. 28 and 29 are powder X-ray diffraction patterns of the chloroindium phthalocyanine crystals obtained in Comparative Examples 17 and 18, respectively. 
     FIG. 30 is a powder X-ray diffraction pattern of the oxytitanium phthalocyanine crystal obtained in Comparative Example 22. 
     FIG. 31 is an infrared absorption spectrum of the oxytitaniumphthalocyanine-chlorogalliumphthalocyanine crystal obtained in Example 10. 
     FIG. 32 is a thermogram of the oxytitanium phthalocyanine-chlorogallium phthalocyanine crystal obtained in Example 10. 
     FIG. 33 is an infrared absorption spectrum of the oxytitanium phthalocyanine crystal obtained in Comparative Example 8. 
     FIG. 34 is a thermogram of the oxytitanium phthalocyanine crystal obtained in Comparative Example 8. 
     FIG. 35 is an infrared absorption spectrum of the oxytitanium phthalocyanine crystal obtained in Comparative Example 17. 
     FIG. 36 is a thermogram of the oxytitanium phthalocyanine crystal obtained in Comparative Example 17. 
     FIG. 37 is an infrared absorption spectrum of a chlorogallium phthalocyanine crystal. 
     FIG. 38 is a powder X-ray diffraction pattern of the oxytitaniumphthalocyanine-chlorogalliumphthalocyanine crystal obtained in Example 33. 
     FIGS. 39 and 40 each schematically illustrate the layer structure of the electrophotographic photoreceptor of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The crystal of mixed pigments of oxytitanium phthalocyanine and a halogenated gallium phthalocyanine according to the present invention (hereinafter referred to as phthalocyanine mixed crystal) preferably includes those having the maximum X-ray diffraction peak at a Bragg angle (2θ±0.2°) of 27.2°. 
     More preferred oxytitanium phthalocyanine-halogenated gallium phthalocyanine crystals include the following species. 
     (a) Crystal having strong peaks at Bragg angles of 8.9° and 27.0°. 
     (b) Crystals having strong peaks at Bragg angles of 9.3°, 10.6°, 13.3°, 15.1°, and 26.3°. 
     (c) Crystals having strong peaks at Bragg angles of 7.4°, 11.1°, 17.9°, 20.1°, 26.6°, and 29.2°. 
     (d) Crystals having strong peaks at Bragg angles of 7.5°, 16.7°, 22.1°, 24.7°, 25.6°, and 28.6°. 
     (e) Crystals having strong peaks at bragg angles of 7.6°, 16.7°, 22.5°, 24.2°, 25.3°, and 28.6°. 
     The crystal of mixed pigments of oxytitanium phthalocyanine and a halogenated indium phthalocyanine according to the present invention preferably includes the crystals of mixed pigments of oxytitanium phthalocyanine and chloroindium phthalocyanine. Specific examples of preferred oxytitanium phthalocyanine-halogenated indium phthalocyanine crystals include the following species. 
     (f) Crystals having strong peaks at Bragg angles of 7.6°, 16.4°, 22.4°, 25.5°, and 28.6°. 
     (g) Crystals having strong peaks at Bragg angles of 7.6°, 10.6°, 15.2°, 26.3°, and 28.7°. 
     (h) Crystals having strong peaks at Bragg angles of 7.5°, 11.1°, 18.1°, 20.3°, 26.7°, and 29.2°. 
     (i) Crystals having strong peaks at Bragg angles of 9.4°, 15.2°, 26.4°, and 27.4°. 
     (j) Crystal having strong peaks at Bragg angles of 7.4°, 16.6°, 25.3°, and 28.2°. 
     (k) Crystals having strong peaks at Bragg angles of 7.3°, 16.7°, 25.3°, and 27.8°. 
     The phthalocyanine crystal of mixed pigments of the present invention can be prepared by using oxytitanium phthalocyanine and a halogenated gallium phthalocyanine or a halogenated indium phthalocyanine. 
     Oxytitanium phthalocyanine may be synthesized by known processes, such as a process comprising reacting phthalonitrile and titanium tetrachloride in an appropriate organic solvent, followed by hydrolysis, and a process comprising reacting diiminoisoindoline and a titanium tetraalkoxide in an appropriate organic solvent. 
     A halogenated gallium phthalocyanine or a halogenated indium phthalocyanine may be synthesized by known processes, such as a process comprising reacting a trihalogenated gallium or a trihalogenated indium with phthalonitrile or diiminoisoindoline in an appropriate organic solvent. 
     In the preparation of the phthalocyanine crystal of mixed pigments of the present invention, oxytitanium phthalocyanine and a halogenated gallium or indium phthalocyanine are mixed at an appropriate ratio, and the mixture is ground by dry grinding or milling (e.g., salt milling) in a ball mill, a sand mill, a kneader, a mortar, etc. until the X-ray diffraction spectrum of the ground mixture reveals no clear peak. Alternatively, each of the starting phthalocyanine compounds is separately ground to become non-crystalline and then mixed together to prepare the crystal of mixed pigments. Then, the resulting crystal of mixed pigments is treated with an organic solvent. Examples of useful organic solvents include halogenated hydrocarbons, e.g., methylene chloride and chloroform; aromatic hydrocarbons, e.g., toluene, benzene, and chlorobenzene; alcohols, e.g., methanol and ethanol; ketones, e.g., acetone and methyl ethyl ketone; acetic esters, e.g., ethyl acetate and butyl acetate; aliphatic hydrocarbons, e.g., hexane and octane; ethers e.g., diethyl ether, dioxane, and tetrahydrofuran; and mixtures of these organic solvents, or mixtures of these organic solvents and water. The amount of the solvent to be used and the solvent treating time are not particularly limited. 
     It is also effective that the starting phthalocyanine compounds are treated with a solvent, such as dimethylformamide (DMF), N-methylpyrrolidone (NMP), tetrahydrofuran (THF), methylene chloride, or sulfolane prior to the grinding step. It is also effective that the solvent treatment of the mixture be conducted while milling in a ball mill, a sand mill, etc. 
     The crystal of mixed pigments of the present invention preferably forms a solid solution of pigments. Further, it is more preferred that the crystal of mixed pigments is treated with a solvent so as to have a definite X-ray diffraction peak at a Bragg angle. 
     The phthalocyanine crystal of mixed pigments of the present invention is useful as a charge generating material for electrophotography and provides an electrophotographic photoreceptor excellent in stability on repeated use and environmental stability. 
     Illustrative examples of the structure of the photoreceptor using the phthalocyanine crystal of mixed pigments of the present invention are explained below by referring to FIGS. 39 and 40. 
     FIGS. 39-(a) through (d) show photoreceptors having a laminate structure. The photoreceptor shown in FIG. 39-(a) is composed of conductive substrate 1 having thereon charge generating layer 2 and charge transporting layer 3 in this order. The photoreceptor shown in FIG. 39-(b) is composed of conductive substrate 1 having thereon charge transporting layer 3 and charge generating layer 2 in this order. The photoreceptors shown in FIGS. 39-(c) and (d) additionally have subbing layer 4 on conductive substrate 1. FIGS. 40-(a) and (b) show photoreceptors having a single layer structure, in which photoconductive layer 5 is provided on conductive substrate 1 with or without subbing layer 4. 
     Where a photoreceptor has a laminate structure as shown in FIG. 39, the charge generating layer comprises the phthalocyanine crystal of mixed pigments of the present invention and a binder resin. The binder resin to be used is selected from a wide range of insulating resins or organic photoconductive polymers, e.g., poly-N-vinyl carbazole, polyvinyl anthracene, and polyvinyl pyrene. Examples of suitable binder resins are insulating resins, such as polyvinyl butyral, polyarylates (e.g., a polycondensate of bisphenol A and phthalic acid), polycarbonates, polyesters, phenoxy resins, vinyl chloride-vinyl acetate copolymers, polyvinyl acetate, acrylic resins, polyacrylamide, polyamides, polyvinyl pyridine, cellulose resins, urethane resins, epoxy resins, casein, polyvinyl alcohol, and polyvinyl pyrrolidone. 
     The charge generating layer is formed by coating on a conductive substrate a coating composition prepared by dispersing the phthalocyanine crystal of mixed pigments of the present invention in a solution of the binder resin dissolved in an organic solvent. A compounding ratio of the phthalocyanine crystal of mixed pigments to the binder resin ranges from 40:1 to 1:10, and preferably from 10:1 to 1:4, by weight. If the ratio of the phthalocyanine crystal of mixed pigments is too high, the stability of the coating composition would be reduced. If it is too low, the sensitivity of the charge generating layer would be reduced. 
     The solvents to be used in the coating composition are preferably selected from those incapable of dissolving the lower layer, i.e., the layer provided right under the charge generating layer. Examples of suitable organic solvents include alcohols, e.g., methanol, ethanol, and isopropanol; ketones, e.g., acetone, methyl ethyl ketone, and cyclohexanone; amides, e.g., N,N-dimethylformamide and N,N-dimethylacetamide; dimethyl sulfoxides; ethers, e.g., tetrahydrofuran, dioxane, and ethylene glycol monomethyl ether; esters, e.g., methyl acetate and ethyl acetate; halogenated aliphatic hydrocarbons, e.g., chloroform, methylene chloride, dichloroethylene, carbon tetrachloride, and trichloroethylene; and aromatic hydrocarbons, e.g., benzene, toluene, xylene, ligroin, monochlorobenzene, and dichlorobenzene. 
     The coating composition for a charge generating layer can be coated by any known coating technique, such as dip coating, spray coating, spinner coating, bead coating, wire bar coating, blade coating, roller coating, and curtain coating. Drying after coating is preferably carried out first by drying in high temperatures to the touch and then heat-drying. Heat-drying may be performed at a temperature of from 50° to 200° C. for a period of from 5 minutes to 2 hours in still air or in an air flow. The charge generating layer usually has a thickness of from about 0.05 to 5 μm. 
     The charge transporting layer of the laminate structure comprises a charge transporting material and a binder resin. Any of known charge transporting materials including polycyclic aromatic compounds, e.g., anthracene, pyrene, and phenanthrene; compounds having a nitrogen-containing heterocyclic ring, e.g., indole, carbazole, and imidazole; pyrazoline compounds, hydrazone compounds, triphenylmethane compounds, triphenylamine compounds, enamine compounds, and stilbene compounds, may be employed. 
     Also included in usable charge transporting materials are photoconductive polymers, such as poly-N-vinyl carbazole, halogenated poly-N-vinyl carbazole, polyvinyl anthracene, poly-N-vinylphenyl anthracene, polyvinyl pyrene, polyvinyl acridine, polyvinyl acenaphthylene, polyglycidyl carbazole, pyreneformaldehyde resins, and ethyl carbazole-formaldehyde resins. These photoconductive polymers may be used alone for formation of a charge transporting layer without the aid of a binder resin. 
     The same binder resins as used in the charge generating layer can be used in the charge transporting layer. 
     The charge transporting layer can be formed by coating a substrate with a coating composition comprising the above-described charge transporting material, a binder resin, and an organic solvent incapable of dissolving the lower layer. The solvent and the coating technique to be used are the same as described for the formation of the charge generating layer. A compounding ratio of the charge transporting material to the binder resin usually ranges from 5:1 to 1:5 by weight. The charge transporting layer usually has a thickness of from about 5 to 50 μm. 
     Where a photoreceptor has a single layer structure as shown in FIG. 40, the photosensitive layer is a photoconductive layer comprising a binder resin having dispersed therein a charge transporting material and the phthalocyanine crystal of mixed pigments according to the present invention. A compounding ratio of the charge transporting material to the binder resin preferably ranges from 1:20 to 5:1 by weight, and a compounding ratio of the phthalocyanine crystal of mixed pigments to the charge transporting material preferably ranges from about 1:10 to 10:1 by weight. The charge transporting material and binder resin to be used are the same as described above. Formation of the photoconductive layer can be effected in the same manner as described above. 
     Any of conventional conductive substrates known for electrophotographic photoreceptors can be used in the present invention. 
     If desired, a subbing layer may be provided on the conductive substrate. The subbing layer is effective for inhibiting injection of unnecessary charges from the conductive substrate thereby serving to enhance chargeability of the photosensitive layer. It also functions to increase adhesion between the photosensitive layer and the conductive substrate. 
     Materials constituting the subbing layer include polyvinyl alcohol, polyvinyl pyrrolidone, polyvinyl pyridine, cellulose ethers, cellulose esters, polyamides, polyurethanes, casein, gelatin, polyglutamic acid, starch, starch acetate, amino starch, polyacrylic acid, polyacrylamide, zirconium chelate compounds, zirconium alkoxide compounds, organozirconium compounds, titanyl chelate compounds, titanyl alkoxide compounds, organotitanium compounds, and silane coupling agents. The subbing layer usually has a thickness of from about 0.05 to 2 μm. 
     The present invention is now illustrated by way of Synthesis Examples, Examples, and Comparative Examples, but it should be understood that the present invention is not deemed to be limited thereto. All the percents and parts are given by weight unless otherwise indicated. All the mixing ratios of solvents in mixed solvents are given by volume. 
     For obtaining X-ray diffraction pattern, X-ray diffractometry was conducted by measuring the intensity of Bragg angle (28) to the characteristic X-rays (wavelength 1.541 Å) of CuKα with the following measurement conditions: 
     
         ______________________________________                                    
X-ray diffractometer:                                                     
                  RAD-RC manufactured by                                  
                  Rigaku K.K.                                             
X-ray tube output:                                                        
                  18 KW                                                   
Target:           Cu (1.54050 Å)                                      
Voltage:          40.0 KV                                                 
Current:          300.0 mA                                                
Start angle:      5.00 deg                                                
Stop angle:       40.00 deg                                               
Step angle:       0.020 deg                                               
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     SYNTHESIS EXAMPLE 1 
     Thirty parts of 1,3-diiminoisoindoline and 17 parts of titanium tetrabutoxide were added to 200 parts of 1-chloronaphthalene, and the mixture was allowed to react at 190° C. for 5 hours in a nitrogen stream. The reaction mixture was filtered, and the filter cake was washed successively with aqueous ammonia, water, and acetone to obtain 40 parts of oxytitanium phthalocyanine. The powder X-ray diffraction pattern of the resulting oxytitanium phthalocyanine crystal is shown in FIG. 1. 
     SYNTHESIS EXAMPLE 2 
     Thirty parts of 1,3-diiminoisoindoline and 9.1 parts of gallium trichloride were added to 230 parts of quinoline, and the mixture was allowed to react at 200° C. for 3 hours in a nitrogen stream. The reaction mixture was filtered, and the filter cake was washed successively with acetone and methanol and dried to obtain 28 parts of chlorogallium phthalocyanine. The powder X-ray diffraction pattern of the resulting chlorogallium phthalocyanine crystal is shown in FIG. 2. 
     SYNTHESIS EXAMPLE 3 
     Thirty parts of 1,3-diiminoisoindoline and 12.3 parts of indium trichloride were added to 230 parts of quinoline, and the mixture was allowed to react at 200° C. for 5 hours in a nitrogen stream. The reaction mixture was filtered, and the filter cake was washed successively with acetone and methanol and dried to obtain 16.2 parts of chloroindium phthalocyanine. The powder X-ray diffraction pattern of the resulting chloroindium phthalocyanine crystal is shown in FIG. 3. 
     EXAMPLE 1 
     Nine parts of the oxytitanium phthalocyanine crystal obtained in Synthesis Example 1 and 1 part of the chlorogallium phthalocyanine crystal obtained in Synthesis Example 2 were ground in an automatic mortar (&#34;LABO-MILL UT-21&#34; manufactured by Yamato Kagaku) for 10 hours. The powder X-ray diffraction pattern of the resulting powder is shown in FIG. 4. 
     EXAMPLE 2 
     Five parts of the oxytitanium phthalocyanine crystal obtained in Synthesis Example 1 and 5 parts of the chlorogallium phthalocyanine crystal obtained in Synthesis Example 2 were ground in an automatic mortar &#34;LABO-MILL UT-21&#34; for 10 hours. The powder X-ray diffraction pattern of the resulting powder is shown in FIG. 5. 
     EXAMPLE 3 
     In a 100 parts-volume glass container were put 0.5 part of the crystal of mixed pigments obtained in Example 1 and 15 parts of methylene chloride together with 30 g of glass beads (diameter: 1 mm), and the crystal was subjected to milling at 150 rpm for 24 hours. The crystals were collected by filtration and dried to obtain 0.4 part of an oxytitanium phthalocyanine-chlorogallium phthalocyanine crystal of the present invention. The powder X-ray diffraction pattern of the resulting crystal of mixed pigments is shown in FIG. 6. 
     EXAMPLES 4 TO 16 
     The crystal of mixed pigments obtained in Examples 1 or 2 were treated with the solvent shown in Table 1 below in the same manner as in Example 3. The Figure No. of the powder X-ray diffraction pattern of the resulting crystal of mixed pigments is shown in Table 1. 
     
                       TABLE 1                                                     
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        Crystal                   X-ray                                   
Example of Mixed                  Diffraction                             
No.     Pigments   Solvent        Pattern                                 
______________________________________                                    
4       Example 1  monochlorobenzene                                      
                                  the same as                             
                                  FIG. 6                                  
5       &#34;          THF            the same as                             
                                  FIG. 6                                  
6       &#34;          methyl ethyl ketone                                    
                                  the same as                             
                                  FIG. 6                                  
7       &#34;          ethylene glycol                                        
                                  FIG. 7                                  
8       &#34;          DMF            the same as                             
                                  FIG. 6                                  
9       &#34;          water/monochloro-                                      
                                  the same as                             
                   benzene = 1/14 FIG. 6                                  
10      Example 2  methylene chloride                                     
                                  FIG. 8                                  
11      &#34;          monochlorobenzene                                      
                                  FIG. 9                                  
12      &#34;          THF            FIG. 10                                 
13      &#34;          methyl ethyl ketone                                    
                                  the same as                             
                                  FIG. 10                                 
14      &#34;          ethylene glycol                                        
                                  FIG. 11                                 
15      &#34;          DMF            the same as                             
                                  FIG. 10                                 
16      &#34;          water/monochloro-                                      
                                  the same as                             
                   benzene = 1/14 FIG. 9                                  
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     EXAMPLE 17 
     Nine parts of the oxytitanium phthalocyanine crystal obtained in Synthesis Example 1 and 1 part of the chloroindium phthalocyanine crystal obtained in Synthesis Example 3 were ground in an automatic mortar &#34;LABO-MILL UT-21&#34; for 10 hours. The powder X-ray diffraction pattern of the resulting powder is shown in FIG. 12. 
     EXAMPLE 18 
     Five parts of the oxytitanium phthalocyanine crystal obtained in Synthesis Example 1 and 5 parts of the chloroindium phthalocyanine crystal obtained in Synthesis Example 3 were ground in an automatic mortar &#34;LABO-MILL UT-21&#34; for 10 hours. The powder X-ray diffraction pattern of the resulting powder is shown in FIG. 13. 
     EXAMPLE 19 
     In a 100 parts-volume glass container were put 0.5 part of the crystal of mixed pigments obtained in Example 17 and 15 parts of methylene chloride together with 30 g of glass beads (diameter: 1 mm), and the crystal was subjected to milling at 150 rpm for 24 hours. The crystals were collected by filtration and dried to obtain 0.4 part of an oxytitanium phthalocyanine-chloroindium phthalocyanine crystal of pigments. The powder X-ray diffraction pattern of the resulting crystal of mixed pigments is shown in FIG. 14. 
     EXAMPLES 20 TO 32 
     The crystal of mixed pigments obtained in Examples 17 or 18 was treated with the solvent shown in Table 2 below in the same manner as in Example 3. The Figure No. of the powder X-ray diffraction pattern of the resulting crystal of mixed pigments is shown in Table 2. 
     
                       TABLE 2                                                     
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        Crystal                   X-ray                                   
Example of Mixed                  Diffraction                             
No.     Pigments   Solvent        Pattern                                 
______________________________________                                    
20      Example 17 monochlorobenzene                                      
                                  FIG. 15                                 
21      &#34;          THF            the same as                             
                                  FIG. 14                                 
22      &#34;          methyl ethyl ketone                                    
                                  the same as                             
                                  FIG. 14                                 
23      &#34;          ethylene glycol                                        
                                  FIG. 16                                 
24      &#34;          DMF            the same as                             
                                  FIG. 14                                 
25      &#34;          water/monochloro-                                      
                                  FIG. 17                                 
                   benzene = 1/14                                         
26      Example 18 methylene chloride                                     
                                  FIG. 18                                 
27      &#34;          monochlorobenzene                                      
                                  FIG. 18                                 
28      &#34;          THF            the same as                             
                                  FIG. 18                                 
29      &#34;          methyl ethyl ketone                                    
                                  the same as                             
                                  FIG. 18                                 
30      &#34;          ethylene glycol                                        
                                  FIG. 19                                 
31      &#34;          DMF            the same as                             
                                  FIG. 18                                 
32      &#34;          water/monochloro-                                      
                                  the same as                             
                   benzene = 1/14 FIG. 18                                 
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     COMPARATIVE EXAMPLE 1 
     Ten parts of the oxytitanium phthalocyanine crystal obtained in Synthesis Example 1 were subjected to milling in the same manner as in Example 1, instead of 9 parts of the oxytitanium phthalocyanine crystal and 1 part of the chlorogallium phthalocyanine crystal. The powder X-ray diffraction pattern of the resulting powder is shown in FIG. 20. 
     COMPARATIVE EXAMPLE 2 
     The same procedure as in Comparative Example 1 was repeated, except for decreasing the milling time to 1 hour. The powder X-ray diffraction pattern of the resulting powder is shown in FIG. 21. 
     COMPARATIVE EXAMPLE 3 
     Ten parts of the chlorogallium phthalocyanine crystal obtained in Synthesis Example 2 were subjected to milling in the same manner as in Example 1, instead of 9 parts of the oxytitanium phthalocyanine crystal and 1 part of the chlorogallium phthalocyanine crystal. The powder X-ray diffraction pattern of the resulting powder is shown in FIG. 22. 
     COMPARATIVE EXAMPLES 4 TO 16 
     The ground crystal obtained in Comparative Examples 1, 2, or 3 was treated with the solvent shown in Table 3 below in the same manner as in Example 3. The Figure No. of the powder X-ray diffraction pattern of the resulting crystal is shown in Table 3. 
     
                       TABLE 3                                                     
______________________________________                                    
Compara.                                                                  
        Crystal                   X-ray                                   
Example of Mixed                  Diffraction                             
No.     Pigments   Solvent        Pattern                                 
______________________________________                                    
4       Compara.   methylene chloride                                     
                                  FIG. 23                                 
        Example 1                                                         
5       Compara.   methyl ethyl ketone                                    
                                  the same as                             
        Example 1                 FIG. 23                                 
6       Compara.   ethylene glycol                                        
                                  FIG. 7                                  
        Example 1                                                         
7       Compara.   DMF            the same as                             
        Example 1                 FIG. 23                                 
8       Compara.   water/monochloro-                                      
                                  FIG. 24                                 
        Example 1  benzene = 1/14                                         
9       Compara.   methylene chloride                                     
                                  the same as                             
        Example 2                 FIG. 6                                  
10      Compara.     &#34;            FIG. 25                                 
        Example 3                                                         
11      Compara.   monochlorobenzene                                      
                                  FIG. 26                                 
        Example 3                                                         
12      Compara.   THF            the same as                             
        Example 3                 FIG. 26                                 
13      Compara.   methyl ethyl ketone                                    
                                  the same as                             
        Example 3                 FIG. 26                                 
14      Compara.   ethylene glycol                                        
                                  FIG. 27                                 
        Example 3                                                         
15      Compara.   DMF            the same as                             
        Example 3                 FIG. 26                                 
16      Compara.   water/monochloro-                                      
                                  the same as                             
        Example 3  benzene = 1/14 FIG. 26                                 
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     COMPARATIVE EXAMPLE 17 
     Ten parts of the chloroindium phthalocyanine crystal obtained in Synthesis Example 3 were subjected to milling in the same manner as in Example 1, instead of 9 parts of the oxytitanium phthalocyanine crystal and 1 part of the chlorogallium phthalocyanine crystal. The powder X-ray diffraction pattern of the resulting powder is shown in FIG. 28. 
     COMPARATIVE EXAMPLES 18 TO 21 
     The ground crystal obtained in Comparative Example 17 was treated with the solvent shown in Table 4 below in the same manner as in Example 19. The Figure No. of the powder X-ray diffraction pattern of the resulting crystal is shown in Table 4. 
     
                       TABLE 4                                                     
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Compara.                   X-ray Diffraction                              
Example No. Solvent Used   Pattern                                        
______________________________________                                    
18          methylene chloride                                            
                           FIG. 29                                        
19          THF            the same as                                    
                           FIG. 29                                        
20          ethylene glycol                                               
                           the same as                                    
                           FIG. 29                                        
21          DMF            the same as                                    
                           FIG. 29                                        
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     COMPARATIVE EXAMPLE 22 
     In 750 parts of α-chloronaphthalene was added 97.5 parts of o-phthalonitrile. After the mixture was thoroughly stirred in a nitrogen stream, 22 parts of titanium tetrachloride was added thereto dropwise. The temperature was gradually elevated up to 200° C., at which the mixture was allowed to react for 3 hours. After completion of the reaction, the reaction mixture was allowed to cool to 100° C., and the precipitated crystal was collected by filtration, washed with 200 parts of α-chloronaphthalene previously heated to 100° C. and then successively with 300 parts of α-chloronaphthalene and 300 parts of methanol. The crystal was dispersed in 800 parts of methanol and stirred at reflux for 1 hour. The crystal was filtered and dispersed in 700 parts of distilled water, followed by stirring at 60° C. for 1 hour. The washing with water was repeated 10 times. The final filtrate had a pH of 6.0. The resulting wet cake was freeze-dried to obtain 70 parts of an oxytitanium phthalocyanine crystal. The powder X-ray diffraction pattern of the resulting crystal is shown in FIG. 30. 
     The phthalocyanine crystal of mixed pigments according to the present invention was compared with the conventional crystal forms. The infrared absorption spectrum and the thermogram of the phthalocyanine crystal of mixed pigments obtained in Example 10 are shown in FIGS. 31 and 32, respectively. The infrared absorption spectrum and the thermogram of the oxytitanium phthalocyanine crystal obtained in Comparative Example 8 are shown in FIGS. 33 and 34, respectively. The infrared absorption spectrum and the thermogram of the oxytitanium phthalocyanine crystal obtained in Comparative Example 17 are shown in FIGS. 35 and 36, respectively. The infrared absorption spectrum of the chlorogallium phthalocyanine crystal obtained in Synthesis Example 2 is shown in FIG. 37. It is apparent from these figures that the phthalocyanine crystal of mixed pigments according to the present invention differs from any of the conventionally known phthalocyanine crystal forms. 
     EXAMPLE 33 
     A mixture of 0.25 part of the amorphous oxytitanium phthalocyanine crystal obtained in Comparative Example 1 and 0.25 part of the crystal of mixed pigments obtained in Example 11 was subjected to a solvent treatment in the same manner as in Example 3. The powder X-ray diffraction pattern of the resulting crystal of mixed pigments is shown in FIG. 38. 
     EXAMPLE 34 
     A coating composition comprising 10 parts of an organozirconium compound (&#34;ORGATICS ZC540&#34; produced by Matsumoto Seiyaku K. K.), 2 parts of a silane coupling agent (&#34;A1110&#34; produced by Nippon Unicar K. K.), 30 parts of isopropyl alcohol, and 30 parts of n-butanol was coated on an aluminum-plated substrate by dip coating and dried at 150° C. for 5 minutes to form a 0.1 μm thick subbing layer. 
     A mixture of 0.1 part of the oxytitanium phthalocyanine-chlorogallium phthalocyanine crystal obtained in Example 3, 0.1 part of polyvinyl butyral (&#34;S-Lec BM-S&#34; produced by Sekisui Chemical Co., Ltd.), and 10 parts of cyclohexanone was dispersed in a paint shaker together with glass beads for 1 hour to prepare a coating composition. The resulting coating composition was coated on the subbing layer by dip coating and dried at 100° C. for 5 minutes to form a 0.2 μm thick charge generating layer. 
     In 8 parts of monochlorobenzene were dissolved 1 part of a compound of formula (1) shown below and 1 part of poly(4,4-cyclohexylidenediphenylene carbonate) of formula (2) shown below, and the resulting coating composition was coated on the charge generating layer by dip coating and dried at 120° C. for 1 hour to form a 15 μm thick charge transporting layer. ##STR1## 
     EXAMPLE 35 TO 41 
     An electrophotographic photoreceptor was produced in the same manner as in Example 34, except for replacing the oxytitaniumphthalocyanine-chlorogalliumphthalocyanine crystal with the charge generating material shown in Table 5 below. 
     COMPARATIVE EXAMPLES 23 TO 28 
     An electrophotographic photoreceptor was produced in the same manner as in Example 34, except for replacing the oxytitaniumphthalocyanine-chlorogalliumphthalocyanine crystal with the charge generating material shown in Table 5. 
     EXAMPLE 42 
     An electrophotographic photoreceptor was produced in the same manner as in Example 34, except for replacing the oxytitaniumphthalocyanine-chlorogalliumphthalocyanine crystal with 0.1 part of the mixed crystal obtained in Example 19. 
     EXAMPLES 43 TO 47 
     An electrophotographic photoreceptor was produced in the same manner as in Example 34, except for replacing the oxytitaniumphthalocyanine-chlorogalliumphthalocyanine crystal with the charge generating material shown in Table 5. 
     COMPARATIVE EXAMPLES 29 TO 31 
     An electrophotographic photoreceptor was produced in the same manner as in Example 34, except for replacing the oxytitaniumphthalocyanine-chlorogalliumphthalocyanine crystal with the charge generating material shown in Table 5. 
     Electrophotographic characteristics of each of the electrophotographic photoreceptors prepared in Examples 34 to 46 and Comparative Examples 23 to 31 were evaluated by making the following measurements with a flat plate scanner under a normal temperature and normal humidity condition (20° C., 40% RH). The results obtained are shown in Table 5. 
     1) Initial Surface Potential 
     The photoreceptor was charged to -6.0 kV by a corona discharge, and the surface potential after 1 second (V DDP ) was measured. 
     2) Light Decay Rate 
     The negatively charged photoreceptor was exposed to monochromatic light (780 nm) isolated through a band transmission filter to determine a decay rate of the potential (dV/dE). 
     Residual Potential 
     The negatively charged photoreceptor was exposed to white light of 50 erg/cm 2  for 0.5 second, and the residual surface potential (V RP ) was measured. 
     4) Durability 
     The above-described charging and exposure were repeated 1000 times, and V DDP  and V RP  were measured to obtain a difference from those in the initial stage (ΔV DDP , ΔV RP ). 
     
                       TABLE 5                                                     
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            Initial Electrophoto-                                         
            graphic Characteristics                                       
Charge                dV/dE         Durability                            
Example Generating                                                        
                  V.sub.DDP                                               
                          (Vcm.sup.2 /                                    
                                 V.sub.RP                                 
                                      .sup.Δ V.sub.DDP              
                                            .sup.Δ V.sub.RP         
No.     Material  (V)     erg)   (V)  (V)   (V)                           
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Example 34                                                                
        Example 3 -500    77     -12  20     5                            
Example 35                                                                
        Example 7 -480    73     -15  30    12                            
Example 36                                                                
        Example 8 -480    107    -10  15     3                            
Example 37                                                                
        Example 10                                                        
                  -490    105    -10  10     3                            
Example 38                                                                
        Example 12                                                        
                  -520    80     -15  10    11                            
Example 39                                                                
        Example 14                                                        
                  -450    72     -15  15    13                            
Example 40                                                                
        Example 15                                                        
                  -520    81     -12  13    11                            
Example 41                                                                
        Example 16                                                        
                  -550    75     -13  20     7                            
Example 42                                                                
        Example 19                                                        
                  -480    70     -10  15     5                            
Example 43                                                                
        Example 20                                                        
                  -500    75     -10  20     5                            
Example 44                                                                
        Example 23                                                        
                  -450    60     -20  30    12                            
Example 45                                                                
        Example 25                                                        
                  -500    120    -10  10     5                            
Example 46                                                                
        Example 26                                                        
                  -490    85     -15  20    11                            
Example 47                                                                
        Example 30                                                        
                  -450    95     -15  25    10                            
Compara.                                                                  
        Compara.  -450    34     -30  50    20                            
Example 23                                                                
        Example 6                                                         
Compara.                                                                  
        Compara.  -500    70     -11  10     5                            
Example 24                                                                
        Example 7                                                         
Compara.                                                                  
        Compara.  -520    63     -13  30     7                            
Example 25                                                                
        Example 9                                                         
Compara.                                                                  
        Compara.  -520    62     -15  25    15                            
Example 26                                                                
        Example 10                                                        
Compara.                                                                  
        Compara.  -470    50     -18  30    20                            
Example 27                                                                
        Example 14                                                        
Compara.                                                                  
        Compara.  -500    58     -20  30    20                            
Example 28                                                                
        Example 16                                                        
Compara.                                                                  
        Compara.  -480    65     -11  20     7                            
Example 29                                                                
        Example 4                                                         
Compara.                                                                  
        Compara.  -520    60     -30  50    15                            
Example 30                                                                
        Example 19                                                        
Compara.                                                                  
        Compara.  -430    80     -20  40    10                            
Example 31                                                                
        Example 21                                                        
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     The phthalocyanine crystal of mixed pigments according to the present invention, of oxytitanium phthalocyanine and a halogenated gallium phthalocyanine or a halogenated indium phthalocyanine in a novel crystal form, serves as an excellent charge generating material to provide a highly reliable electrophotographic photoreceptor having high sensitivity, excellent stability on repeated use, and excellent environmental stability. 
     While the invention has been described in detail and with reference to specific examples thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.