Titanylphthalocyanine crystals, methods for preparing the same, and electrophotographic photoreceptors using such crystals

Abstract: A titanyloxyphthalocyanine crystal to be used as a charge-generation material has a maximum diffraction intensity observed at Bragg angle (2) of 9.6° ± 0.2° and clear peaks of diffraction intensity observed at 7.22° ± 0.2°, 9.60° ± 0.2°, 11.60° ± 0.2°, 13.40° ± 0.2°, 14.88° ± 0.2°, 18.34° ± 0.2°, 23.62° ± 0.2°, 24.14° ± 0.2°, and 27.32° ± 0.2°, respectively, in a X-ray diffraction spectrum obtained by performing a X-ray diffraction method using CuKα as a source of radiation. In addition, an electrophotographic photoreceptor has the titanyloxyphthalocyanine crystal as a charge-generation material.

Description: The present invention relates to a novel titanyl _phthalocyanine crystal, a method for preparing such crystal, and an electrophotographic photoreceptor that comprises the titanyl phthalocyanine crystal as a charge-generation material. After inventing a principal theory of the process of electrophotography by C.F. Carlson in 1937, the electrophotographic technologies have been dramatically developed and applied in the devices for processing information, such as digital photocopying machines, laser printers, light-emitting diode printers, and facsimile machines. The electrophotography is an image-forming method that depends on a skillful combination of photoconductive characteristics and electrostatic phenomena of the electrophotographic photoreceptor(C. F. Carlson, U.S. Patent No. 2297691, 1942). That is, the electrophotography is characterized by the process comprising the steps of: charging a surface of the electrophotographic photoreceptor by subjecting to corona discharge in darkness; producing an electrostatic latent image including characters, pictures, and the like in an original by exposing the charged surface of the photoreceptor to light; visualizing (i.e., developing) the electrostatic latent image by using a toner (i.e., colored and charged particles) that adheres to the charged surface of the photoreceptor for transforming the latent image into a real image; and transferring the developed toner image to the surface of a substrate (e.g., a sheet of paper) and fixing the image thereon. Then the photoreceptor is discharged and cleaned of any excess toner using coronas, lamps or the like for recycling the photoreceptor. In accordance with the above electrophotography, it is possible to digitize an original image of a document by scanning and exposing a surface of the photoreceptor to light emitted from a light source such as a semiconductor laser or a light-emitting diode (LED). Therefore, an input image information can be recorded by converting an output of the data-processing device into a plurality of dots of light, and scanning and exposing the surface of the photoreceptor by using these dots. As the information-processing has been advanced and sped up in recent years, the data-processing devices (such as laser printing machines and digital copying machines which perform the high-qualified image formation at a predetermined high printing speed) have been sprung into wide use. Especially, in the case of using the semiconductor laser as a source of exposure light in the above information-processing device, it is not only possible to provide a comparatively small and cheap device, but it is also possible to provide the device having a high reliability and a high image quality. Thus the photoreceptor has been investigated and developed so as to have an excellent sensitivity against the light emitted from the semiconductor laser to be used as the above light source. Currently, by the way, the wavelength of the light generated by the semiconductor laser in practical use has been limited to the range of comparatively long wavelengths of near infrared rays (i.e., about 700∼800 nm). Consequently, it has been required that the photoreceptor to be applied in a device that uses a semiconductor laser as an exposure light source should be of a high sensitivity against the above wavelengths. In addition, it has been also required that such photoreceptor should have the properties of being stable in repeat use and in various environmental conditions. That is, the needs for preventing changes in electrical characteristics of the photoreceptor, the qualities of output images, the generation of memory, and the like are constantly increased in repeat use. For the above requests, therefore, charge-generation materials have been studied and developed. In general, the following materials are known as the charge-generation materials: polyazo pigments, phthalocyanine pigments, azulenium base pigments, pyrylium pigments, and naphthoquinone pigments. However, the naphthoquinone pigments are of no practical use because of their insufficient photosensitivity. In case of the azulenium base pigments and the pyrylium pigments, their chemical constructions are unstable under a strong light such as a laser beam. The phthalocyanine pigment, on the other hand, have the following advantages compared with the others. That is, (1) the phthalocyanine pigments are chemically and physically stable and in general used as color pigments of e.g. color inks and coating compounds; (2) the phthalocyacine pigments can easily be prepared; (3) the phthalocyanine pigments have the ability of absorbing light at the wavelengths of extending up to the long wavelengths of the near infrared ; and (4) the light absorption wavelengths and photo-conductivities of the phthalocyanine pigments are depended on the type of their central atom, crystal form, and preparation method, so that big variations in these characteristics of the phthalocyanine can be obtained. From the above point of view, therefore, the phthalocyanine pigments can be provided as a preferable charge generation material of an electrophotographic photoreceptor. The following pigment compounds have been studied for finding an appropriate type of the phthalocyanine pigment to be used as the charge generation material. For example, ε-type copper phthalocyanines, X-type nonmetal phthalocyanines, τ-type nonmetal phthalocyanines, chloroaluminium phthalocyanine, chloroindium phthalocyanine, chlorogallium phthalocyanine, chlorogermanium phthalocyanine, vanadyl phthalocyanine, and titanyl phthalocyanine have been studied. Among these pigments, the titanyl phthalocyanine has attracted a great deal of public attention because of the following reasons. That is, the nonmetal phthalocyanines and the divalent metallic phthalocyanines do not have sufficient photosensitivity against the laser beam at the wavelengths of the near infrared region. In addition, the trivalent and quadrant metallic phthalocyanines have disadvantages that their electric characteristics are changed in accordance with the progress of hydrolysis in which their chemical compounds are gradually decomposed by the reaction with water in the atmosphere. However, the quadrant metallic phthalocyanines having the metal connected with an oxygen atom show stable electric characteristics. Especially in recent years, therefore, titanyl phthalocyanine has been energetically studied for providing it as a charge-generation material and disclosed in the documents, for example Japanese Patent Application Publication No. 49-4338 that discloses titanyl phthalocyanine as an example of a metal phthalocyanine to be used as a photoconductive material of a resin-dispersed photoreceptor in the type of having a photosensitive layer formed as a single layer (hereinafter, it will be referred as a mono-type photoreceptor). By the way, a laminate-type photoreceptor having a photosensitive layer formed as a laminate of functionally distinguishable layers (a charge generation layer and a charge transport layer) shows excellent electrophotographic properties compared with that of the mono-type photoreceptor. Accordingly, the above described titanyl phthalocyanine have been investigated as a material to be applied in a charge-generation layer of the laminate-type photoreceptor as described below. In the documents of Japanese Patent Application Laying-open Nos. 59-49544 and 59-166959, deposit films of titanyl phthalocyanine to be used as charge generation layers are disclosed. However, the deposition for preparing a charge generation layer is not appropriate for the mass production because it requires large investment in plant and equipment, such as a vacuum deposition system, and results in costly production of electrophotographic photoreceptors. For the industrial production, therefore, it is preferable to make a charge generation layer by a coating method comprising the steps of dispersing and dissolving both a charge generation material and a binder in a solvent to prepare a coating solution and applying the obtained solution on a surface of a substrate to form the charge generation layer. However, the photoreceptor having the charge-generation layer provided as a film formed by the coating method is not advantageous to the one obtained by the deposition method with respect to their electric characteristics, image-characteristics, and the changes in the characteristics by repeat use. Comparing with the photoreceptor obtained by the deposition method, the photoreceptor obtained by the coating method shows a low charge retentivity, a high residual potential, and an almost 40 percent lower spectral sensitivity (e.g., one of the examples is described in an official gazette of Japanese Patent Application Laying-open No. 59-49544). About the cause, the charge-generation material does not work uniformly and effectively in the coated charge-generation Layer being formed unevenly by an effect of settling out or aggregating the charge-generation material as a result of the unstable dispersion of the charge-generation material being dispersed in the solvent. Besides, the trapping of charge carriers and the dropping of photo sensitivity are observed at the portion where the content of the charge generation material is lowered. During the repeat use of the photoreceptor, the photo-sensitivities are changed and image ghost and memory phenomena are generated. In addition, another portion where in the charge generation material is comparatively concentrated may be responsible for the image noise because of the difference in electric properties between the portion where in the charge generation material is comparatively concentrated and its surroundings. Accordingly, these phthalocyanines must be furnished with many required characteristics not only their electrical characteristics but also their dispersion stabilities and the like, for using them as charge-generation materials in the coating method for preparing a photoreceptor. Thus, the phthalocyanines must have excellent electrical characteristics, such as an excellent photosensitivity, an excellent static electrification, and a small residual potential, and also must be stable in darkness without causing gradual deterioration to an inferior state. It is further required that the photoreceptor has a cycle stability, i.e., keeping its electrical characteristics stable during and after the period of using the photoreceptor repeatedly. Furthermore, the charge-generation material has to keep a dispersion stability without causing any troubles, such as coagulation, sedimentation, and crystal growth, in a coating solution for a long time. It has been known that the electrical characteristics of phthalocyanines depend largely on their coordinated metal species. Also, the phthalocyanines show different properties of e.g. static electrification, dark attenuation and photosensitivity, not only in accordance with the type of coordinated metal but also with their crystal form (Sawada, M, Japanese Journal of "DYES and CHEMICALS", vol. 24, No. 6, 1979). Further, it has been known that the dispersion stability of a phthalocyanine pigment, on the other hand, depends on the particle size, the particle form, and the surface ξ-potential (Kumano, I. Denshi Shasin Gakkai-shi, pages 111-120, No. 2, vol. 2, 1984). In this case, the particle form and the quantum surface potential are also affected by various kinds of crystal forms (i.e., habit) depending on the extent of the growth of the crystallographically equivalent surfaces. Therefore, it is very important to develop a crystal particle having a habit suitable for providing excellent electrical characteristics and an excellent dispersion stability. Conventionally, it has been possible to develop phthalocyanine crystals having crystal forms for providing good electrical characteristics but not with habits suitable for providing dispersion stabilities. In the case of the same materials having different habits, by the way, it is possible to distinguish between the two by means of the external forms of their crystals. However, they can be distinguished more precisely by making a comparison between their patterns of X-ray diffraction spectra to be obtained e.g. by performing a X-ray powder method. That is, the process includes the steps of obtaining a X-ray diffraction spectrum of each crystal sample and making a comparison between their diffraction intensities with respect to each angle of diffraction. As listed in Table 1 below, the titanylphthalocyanine crystals are classified into several structure types in accordance with their X-ray diffraction spectra, and also their lattice constants are determined by means of the structure analysis. Crystal type Lattice constant Reference α Phase II JP61-217050 JP61-239348 JP62-134651 I Phase I JP62-67094 II JP62-67094 A Phase I JP63-364, JP63-366 B Phase II JP63-364, JP63-366 C JP63-364, JP63-366 m C JP63-198067 amorphous JP1-123868 Figs. 1 to 4 are X-ray diffraction spectra of titanyl phthalocyanine crystals in the types of I, II, α, and amorphous, respectively. That is, Fig. 1 is an X-ray diffraction spectrum of titanyl phthalocyanine crystal (type I) described in Japanese Patent Application Laying-open No.62-67094; Fig. 2 is an X-ray diffraction spectrum of titanyl phthalocyanine crystal (type II) described in Japanese Patent Application Laying-open No. 62-67094; Fig. 3 is an X-ray diffraction spectrum of titanyl phthalocyanine crystal (type α) described in Japanese Patent Application Laying-open No.62-134651; and Fig. 4 is an X-ray diffraction spectrum of amorphous titanyl phthalocyanine crystal. Regarding the above lattice constants listed in Table 1, phase II type crystals are grouped in triclinic crystals, while phase 1 and C type crystals are grouped in monoclinic crystals. The above clarification is also explained in Journal of Imaging Science and Technology, 605-609, vol. 37, No. 6, 1993. Furthermore, there is another way for classifying titanyl phthalocyanine crystals in accordance with Bragg angles and intensities in their X-ray diffraction spectra. That is, they are classified into the following four groups. (1) Titanyl phthalocyanine crystals classified in a first group are thermodynamically stable and can be obtained immediately after their syntheses. The X-ray diffraction spectrum of each crystal is characterized by having the maximum intensity of diffraction at the Bragg angle (2) of 26.3° (±0.2°). (2) Titanyl phthalocyanine crystals classified in a second group are such as crystals in the type of II as disclosed in Japanese Patent Application Laying-open No. 62-67094. The X-ray diffraction spectrum of each crystal is characterized by having the maximum intensity of diffraction at a Bragg angle (2) of 27.3° (±0.2°). (3) Titanyl phthalocyanine crystals classified in a third group are such as crystals in the type of a as disclosed in Japanese Patent Application Laying-open No. 61-217050. The X-ray diffraction spectrum of each crystal is characterized by having the maximum intensity of diffraction at a Bragg angle (2) of 7.5° (±0.2°). (4) Titanyl phthalocyanine crystals classified in a fourth group are such as crystals disclosed in Japanese Patent Application Laying-open No. 5-320167. The X-ray diffraction spectrum of each crystal is characterized by having the peak intensities of diffraction at Bragg angles (2) of 9°, 5°, 14.1°, 17.8°, 27.1°, and 29.0° and the maximum intensity of diffraction at a Bragg angle (2) of 9.5°(±0.2°). US-A-5190839 and US-A-5114815 disclose titanyl phthalocyanine crystals, having X-ray diffraction spectra, wherein the peak intensities at a Bragg angle (2) of 9.6° and 27.3° are either almost equal of the peak intensity observed at a Bragg angle (2) of 9.6° is smaller than that at a Bragg angle (29) of 27.3° However, the titanyl phthalocyanines of the above groups have some disadvantages in practical use. That is, for example, the photoreceptor comprising one of them does not show a sufficient photo sensitivity against a beam of laser, a sufficient charging ability, a sufficient potential stability under the condition of recycling use; and a potential stability under the changes in use conditions. In addition, there is another disadvantage of an insufficient dispersion stability when the above typed titanyl phthalocyanine crystals are used as a charge generation material to be dispersed in a solvent to prepare a coating solution. For that reason, in the case of forming charge generation layers by using the coating solution immediately after the dispersion or after passing times, the changes in electrophotographic characteristics of the resultant photoreceptors can be observed in spite of using the same coating condition. In this case, furthermore, there are other troubles such as an image noise to be caused by aggregated particles. As a result, it is very difficult to obtain an electrophotographic photoreceptor which is of good quality and of excellent characteristics in industrial and economical terms. In general, by the way, a charge transport material preferable for a certain charge generation material is not always good for other charge generation materials. In addition, a charge generation material preferable for a certain charge transport material is not always good for other charge transport materials. That is, it means that there is an appropriate combination between them. Thus an inappropriate combination between them leads to several problems in practical use, such as insufficient sensitivities, low static electrification, and unstable electrical characteristics in repeat use of the photoreceptor. As described above, the above combination is a matter of great importance to the photoreceptor. However, there is no definite theory concerned about the combination. Therefore the appropriate combination of the above materials has been investigated by way of experiment. It means that the appropriate combination of the charge generation material and the charge transport material have been hardly found. In the case of the laminate-type photoreceptor, furthermore, there is an under-coating layer mainly consisting of a resin between the conductive layer and the photosensitive layer for preventing the injection of charge carriers from the conductive substrate. The reasons of applying the under-coating layer on the substrate is for forming a good photosensitive layer without causing unevenness thereof. That is, the under-coating layer covers defects of substrate's surface, such as an irregular shape, impurities and roughness thereof. The resin to be used for the under-coating layer can for example be selected from the group of solvent-soluble polyamide, polyvinyl alcohol, polyvinyl butyral and casein. It is possible to prevent the injection of charge carriers by processing the resin into a thin film of under 0.5 µm in thickness. In general, however, the under-coating layer should be formed as a film of over 0.5 µm in thickness for covering-a surface of the conductive substrate and forming a photoconductive layer without unevenness. As the case may be, the under-coating layer should be formed as a film of over 1µm in thickness, for example in accordance with the conditions of processing the substrate and the conditions of impurities on the substrate's surface. However, if the resin layer is prepared as a thick film made of the above resin such as polyvinyl alcohol, polyvinyl butyral, and casein, it shows large electrical resistivity and high residual potential of the photoreceptor. In this case, furthermore, there is another problem of the big change in electrical properties of the photoreceptor under the condition of low temperature and low humidity or the condition of high temperature and high humidity because of the following reasons. That is, water-absorption properties of the resin layer is comparatively large and thus the water content thereof is largely changed in accordance with the surrounding conditions. In addition, the electrical conductivity of the resin layer depends on the movement of H + ions and OH - ions to be generated by dissociating water molecules in the resin (i.e., ionic conductivity). Currently, various materials have been proposed as an appropriate material to be used as an under-coating layer having low electric resistivity whether the layer is thick or not. For example, Japanese Patent Laying-open No. 2-193152, Japanese Patent Laying-open No. 3-288157, and Japanese Patent Laying-open No. 4-31870 disclose the specific resin structures of solvent-soluble polyamide resins. Japanese Patent Laying-open No. 3-145652, Japanese Patent Laying-open No. 3-81788, and Japanese Patent Laying-open No. 2-281262 disclose the mixtures of polyamide resin with other resins in expectation of reducing the effects of environmental changes by adjusting the electric resistance. However, these materials cannot avoid the effects of thermal and humidal conditions because their compositions mainly include polyamide resin. Therefore the first object of the present invention is to provide a novel titanyl phthalocyanine crystal having the electrical characteristics appropriate to electrophotography and showing an excellent dispersion stability and a sufficient sensitivity against the wavelengths of the near infrared rays (i.e., about 700∼800 nm)such as a semiconductor laser beam. The second object of the present invention is to provide a method for preparing the novel titanyl phthalocyanine crystal. The third object of the present invention is to provide an electrophotographic photoreceptor using the novel titanyloxyphthalocyanine crystal as a charge generation material, having excellent electrical characteristics; a sufficient sensitivity against the wavelengths of near infrared ray, such as a semiconductor laser beam; the ability of forming an image without any defects in quality, such as image noise and unevenness of image concentration; and a sufficient durability to last of tens of thousands of cycles of the image formation to keep the stable electric characteristics and the stable image quality (i.e., cycle stability). According to a first aspect, the present invention provides a titanyl phthalocyanine crystalto be used as a charge generation material of an electrophotographic photoreceptor, wherein the titanylphthalocyanine is represented by general formula (I) wherein X 1 , X 2 , X 3 and X 4 stand for Cl or Br and each of n, m, l and k is an integer from 0 to 4, and wherein the titanyl phthalocyanine crystal has a maximum diffraction intensity observed at Bragg angle (2) of 9.6° ± 0.2° and clear peaks of diffraction intensity observed at 7.22° ± 0.2°, 9.60° ± 0.2°, 11.60° ± 0.2°, 13.40° ± 0.2°, 14.88° ± 0.2°, 18.34° ± 0.2°, 23.62° ± 0.2°, 24.14° ± 0.2°, and 27.32° ± 0.2°, respectively, in a X-ray diffraction spectrum obtained by performing a X-ray diffraction method using CuKα as a source of radiation and having a lattice constant of: with an allowable error of ± 1%. In a second aspect of the present invention, there is provided an electrophotographic photoreceptor comprising a conductive substrate and a photosensitive layer including a charge generation material and a charge transport material, wherein the charge generation material is the above described titanyl phthalocyanine crystal. Herein, the photosensitive layer may be composed of a charge generation layer including the charge generation material and a charge transport layer including the charge transport layer, wherein the charge transport material works appropriately in combination with the above titanyl phthalocyanine. The charge transport material may be a hydrazone compound. The hydrazone compound may be represented by the formula [II]: wherein R 1 , R 2 , R 3 , and R 4 are groups selected from an alkyl group, an aralkyl group, and an aryl group, respectively, which may be substituted; and R 5 is an atom or a group selected from a hydrogen atom, a halogen atom, an alkyl group, and an alkoxy group, and R 1 and R 2 may be bound together to form a ring, and also R 1 or R 2 may be bound with R 5 to form a ring. The charge transport material may be a distyryl compound. The distyryl compound may be represented by the formula [III] wherein R 1 , R 2 , R 3 , and R 4 are groups selected from an alkyl group and an aryl group, respectively, which may be substituted; R 5 is an atom or a group selected from a hydrogen atom, a halogen atom, an alkyl group, and an alkoxy group, and Ar is an aryl group or an aromatic heterocyclic group. An under-coating layer may be formed between the conductive substrate and the photosensitive layer. The under-coating layer is responsible for coating the charge generation layer mainly comprising the above titanyloxyphthalocyanine on a substrate without causing non uniform appearance of the resultant layer and for keeping the electrical resistance almost stable under the changes in surroundings. The under-coating layer may be a hardened film mainly comprising melamine resin, aromatic carboxylic acid and/or aromatic carboxylic anhydride, and iodine being fixed thereon. In a third aspect of the present invention, there is provided a method for preparing the above titanyl phthalocyanine to be used as a charge generation material of an electrophotographic receptor, comprising the steps of: dispersing a predetermined amount of amorphous titanyl phthalocyanine in an aqueous solution in which ionic substances are dissolved, under mechanical force at a temperature of less than 50°C, to obtain a mixture characterized by comprising fine dispersions; adding a non-aqueous organic solvent to said mixture to shift a dispersion of titanyl phthalocyanine from an aqueous phase to a non-aqueous organic solvent phase so as to remove water; and removing said non-aqueous organic solvent phase to obtain a pellet of said titanyl phthalocyanine crystal. The above and other objects, effects, features, and advantages of the present invention will become apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings. Fig. 1 is a pattern of an X-ray diffraction spectrum of titanyl phthalocyanine crystals (I-type) disclosed in Japanese Patent Application Laying-open No. 62-67094; Fig. 2 is a pattern of an X-ray diffraction spectrum of titanyl phthalocyanine crystals (II-type) disclosed in Japanese Patent Application Laying-open No. 62-67094; Fig. 3 is a pattern of an X-ray diffraction spectrum of titanyl phthalocyanine crystals (α-type)disclosed in Japanese Patent Application Laying-open No. 62-134651; Fig. 4 is a pattern of an X-ray diffraction spectrum of titanyl phthalocyanine crystals (amorphous type); Fig. 5 is a pattern of an X-ray diffraction spectrum of titanyl phthalocyanine crystals in accordance with the present invention; Fig. 6 shows a pattern of a X-ray diffraction spectrum of titanyl phthalocyanine crystals in accordance with the present invention (A), a pattern of an X-ray diffraction spectrum of I-type titanyl phthalocyanine crystals (C), and a pattern of an X-ray diffraction spectrum of α-type titanyl phthalocyanine crystals (B); and Fig. 7 is a schematic cross-sectional view of one of the preferred embodiments of the electrophotographic photoreceptor in accordance with the present invention. Fig. 5 shows a X-ray diffraction spectrum of titanyl phthalocyanine crystals in accordance with the present invention. As shown in the figure, the titanyl phthalocyanine crystals have the maximum diffraction intensity observed at Bragg angle (2) of 9.6° ± 0.2° and clear peaks of diffraction intensity observed at 7.22° ± 0.2°, 9.60° ± 0.2°, 11.60° ± 0.2°, 13.40° ± 0.2°, 14.88° ± 0.2°, 18.34° ± 0.2°, 23.62° ± 0.2°, 24.14° ± 0.2°, and 27.32° ± 0.2°, respectively, in a X-ray diffraction spectrum obtained by performing a X-ray diffraction method using CuKα as a source of radiation. This spectrum pattern has something in common with the X-ray diffraction spectrum pattern of titanyl phthalocyanine crystals (corresponding to the fourth group described above) disclosed in the official gazette of Japanese Patent Application Laying-open No. 5-320167. However, they are not coincide with each other even if we give careful consideration to their permitted errors (2 ± 0.2°). Consequently, the titanyl phthalocyanine crystal of the present invention must be a novel one. Furthermore, a result of the structural analysis using X-ray indicates that the titanyl phthalocyanine crystal of the present invention is classified as a triclinic crystal having a lattice constant of: a = 16.3058 Å, b = 23.078 Å, c = 8.7155 Å, α = 101.352°, β = 23.078°, and γ = 117.530°, with an allowable error of ± 1%. This kind of the lattice constant is completely different from that of the conventional titanyl phthalocyanine crystals. The structure of the titanyl phthalocyanine in accordance with the present invention is represented by the general formula (I) below. wherein X 1 , X 2 , X 3 , and X 4 stand for Cl or Br, and each of n, m, l, and k is an integer from 0 to 4. The titanyl phthalocyanine crystal of the present invention can be prepared by the method as described below. To begin with, a titanium compound is reacted with o-phthalodinitryl, amino-imino-isoindorenin, or alkoxy-imino-isoindorenin in an inactive solvent having a high-melting point, such as α-chloronaphthalene. The reaction is performed at the temperature of 160 °C to 300°C, preferably in general 160°C to 260°C. The titanium compound can be selected from the group of titanium halides such as titanium tetrachloride, titanium tetrachloride, and titanium tetrabromide. Especially, titanium tetrachloride is preferably used in terms of cost-effectiveness. When the titanium halide, such as titanium tetrachloride (TiCl 4 ), is used as a reaction agent, however, the reaction can be progressed in accordance with the following formula. 160°C-300°C Second step: PcTiCl 2 → (hydrolysis) → PcTi=O The above process will be explained in more detail for the case of using titanium halide as a titanium compound. For the process, the above inert solvent with a high boiling point can e.g. be selected from dichlorobenzene, trichlorobenzene, α-chloronaphthalene, diphenyl ether, α-methyl naphtalene, methoxy naphtalene, diphenylethane, ethyleneglcyol alkylether and quinoline. In general, a reaction temperature is in the range of 160°C to 300°C, preferably 180°C to 250°C. After the reaction, dichlorotitanium phthalocyanine thus obtained is separated by means of filtration and then washed with the same solvent to remove impurities generated by the reaction and unreacted raw materials. It is preferable to treat the obtained dichlorotitanium phthalocyanine with one of the solvents selected from alcohols including, for example, methanol, ethanol, and isopropyl alcohol, ethers including, for example tetrahydrofuran and dioxane; amides including, for example, dimethylformamide and N-methyl-2-pyrrolidone; and electron donor solvents, such as sulfolane, dimethyl sufoxide, morpholine, and pyridine. Next, the dichlorotitanium phthalocyanine is hydrolyzed by a heat treatment in an aqueous solution, resulting in titanyl phthalocyanine. It is preferable to perform further purification in order to obtain the titanyl phthalocyanine in high purity. The purification can be performed by one of the conventional methods, for example, a cleaning method, a re-crystallization method, an extraction method such as Soxhlet method, and a thermal suspension. It is also possible to purify the titanyl phthalocyanine e.g. by means of sublimation. It is noted that the above purification is not limited to one of the above methods, it is also possible to use other methods for eliminating unreacted raw materials, reaction by-products, and impurities. The titanyl phthalocyanine is dispersed or solved in concentrated sulfuric acid at a temperature of less than 5°C. Then the mixture is poured into a large amount of water being cooled to less than room temperature. Precipitated titanyl phthalocyanine is filtrated and washed by an excess amount of water so as to become neutral. After washing, the titanyl phthalocyanine is dried. The obtained titanyl phthalocyanine is subjected to the X-ray diffraction analysis and its resultant X-ray diffraction spectrum is like that of the amorphous material of a small degree of crystallization without showing any clear peak of diffraction. Furthermore, the titanyl phthalocyanine is dispersed and microparticlized in an aqueous solution containing dissolved ionic materials at a temperature of less than 50°C, preferably less than 30°C, in the presence of mechanical force, such as deformation force, shear force, and impulsive force. Then a nonaqueous organic solvent is added into the mixture and subjected to the mechanical force to shift the titanyl phthalocyanine dispersed in the aqueous phase to the nonaqueous phase so as to remove water. The resultant titanyl phthalocyanine in the form of paste is washed by a hydrophilic solvent, such as methanol and acetone, for dissolving the above organic solvent. Finally, the resultant titanyl phthalocyanine is washed by water to remove ionic materials and then dried to obtain the crystallized titanyl phthalocyanine of the present invention. The resultant crystals can be easily dispersed in an aqueous solution and show excellent electrophotographic properties. By the way, the above ionic materials to be used are those which can be solved in water to become ions and provide the water an electrical conductivity. Therefore, the materials can be selected from inorganic or organic materials. For example, the inorganic materials are sodium chloride, sodium silicate or potassium chloride, while the organic materials are carboxylic acid compounds or quaternized amine compounds. However, it is preferable to use the inorganic material e.g. in consideration of cost effectiveness and simple purification. Furthermore, the above nonaqueous organic solvent can be selected from the compounds of straight-chain aliphatic hydrocarbons, branched-chain aliphatic hydrocarbons, cyclic hydrocarbons, and aromatic hydrocarbons. These compounds may have substituent groups, such as nitrile and halogen. The device to be used for applying the above mechanical force can be selected from the conventional mills or mixing devices, such as attriter, ball mill, high-speed mixer, banbary mixer, spec mixer, roller mill, three rollers, nanomizer, stamping mill, planet mill, vibrating mill, and kneader. In addition, a dispersion medium can be optionally used for applying the above mechanical force, which can, for example, be selected from glass beads, steel beads, zirconia bead, aluminum beans, zirconia balls and flint stones. The titanyl phthalocyanine crystal in accordance with the present invention has a spectrum of light absorption as shown in Fig. 6. In this figure, the curve A indicates a spectrum of titanyl phthalocyanine crystal in accordance with the present invention, the curve B indicates a spectrum of α-type titanyl phthalocyanine as a comparative example, and the curve C indicates a spectrum of I-type titanyl phthalocyanine as another comparative example. Comparing with the I-type titanyl phthalocyanine (C), as shown in the figure, the titanyl phthalocyanine of the present invention (A) shows excellent properties of light-absorption at the wavelengths of ultra-violet ray region to near infrared ray region. The present titanyl phthalocyanine crystal (A) is also superior to the α-type crystal (B) and shows excellent properties of light absorption at the wavelengths of up to 820 nm or more. Therefore, it is possible to obtain an electrophotographic photoreceptor appropriate to absorb light at the wavelengths of the near-infrared (e.g., a semiconductor laser beam). Besides, the titanyl phthalocyanine crystals have an excellent dispersion stability because they are very stable in a coating solution for preparing a charge-generation layer and hardly aggregate or precipitate therein. Therefore an electrophotographic photoreceptor can be prepared without causing microscopic non-uniformity of layers to be caused by inhomogeneous dispersion of charge-generation materials or the presence of aggregated large-sized charge-generation materials. Furthermore, the coating solution is stable with time, so that there is no need to change the coating solution with time to obtain a layer having a stable quality. Therefore, the process for preparing the electrophotographic photoreceptor becomes more simple. In addition, it is noted that the resultant photoreceptor provides an image without generating noise and unevenness. Accordingly, the electrophotographic photoreceptor has excellent properties of static electrification and photosensitivity, and also these characteristics can be stable in repeat use. Fig. 7 is a preferred embodiment of the electrophotographic photoreceptor in accordance with the present invention. The electrophotographic photoreceptor 1 is of the type having functionally distinguishable layers. That is, an under-coating layer 3 is formed on an electroconductive substrate 2 and then a charge generation layer 5 and a charge transport layer 6 are stacked on the under-coating layer 3 in that order to form a photosensitive layer 4. However, the present invention is not limited to the type of having functionally distinguishable layers but can also be conducted with the type having a single layer that performs both steps of generating and transporting charges. In the present invention, the electroconductive substrate 2 is in the form of a metallic drum or sheet made of aluminum, vanadium, nickel, copper, zinc, palladium, indium, tin, platinum, stainless steel, chromium, brass, or other metals; a sheet of plastic material on which one of the above metals is deposited or laminated; or a plastic drum or a sheet of plastic material made of a dispersion of electroconductive material in an electroconductive or non-conductive plastic material. However, it is not limited to the above materials but it is also possible to use other materials to be charged. Also, it is not limited to the above forms but it is also possible to prepare the substrate 2 for example in the shape of a plate, sheet, or cylinder. The under-coating layer used in the present invention is preferably provided as a hardened film which is basically composed of melamine resin and aromatic carboxylic acid and/or aromatic carboxylic acid anhydride, and iodine being fixed in the selected mixture. The melamine resin used in the present invention may be prepared by the following process. First of all, a methylol compound is obtained by reacting melamine with formaldehyde and then butyl etherified by reacting with alcohol. The aromatic carboxylic acid, aromatic carboxylic acid anhydride, are terephthalic acid, isophthalic acid, phthalic anhydride, trimellitic acid, pyromellitic acid, pyromellitic anhydride, naphtalene caryboxylic acid, benzoic acid, and their ammonium salt and sulfate. The total amount of the aromatic carboxylic acid to be mixed with the melamine resin is in the range of 5 to 100 parts by weight with respect to 100 parts by weight of melamine resin. If the amount of the aromatic carboxylic acid is lower than 5 parts by weight, the hardness of the membrane is lowered, and membrane disorders, such as swelling and melting, occur when the charge generation layer is applied. If the amount of the aromatic carboxylic acid is in the range of over 100 parts by weight, the pot stability of the coating solution is lowered. For the purpose of preventing a tan of the coating membrane, the under-coating layer may be further comprised of a filler to prevent a moire of the image to be caused by light reflected to the substrate. The filler can be selected from several compounds such as titanium oxide, aluminum oxide, kaolin, talc, and silicon oxide. It is preferable to use the above described hardened film as an under-coating layer to be applied in the present invention. However, it is not limited to that film but a film selected from: a film made of a metal oxide such as alumite; a film made of a film-forming polymer resin, for example one selected from polyamides such as nylon 6, nylon 66, nylon 11, nylon 610, copolymerized nylon, and alkoxymethylated nylon, or selected from casein, polyvinyl alcohol, ethylene acrylate copolymer, gelatin, and polyvinyl butyral; and a resin film with dispersed conductive-, semiconductive-, or dielectric particles made of metal oxide such as zinc oxide or titanium oxide, aluminum oxide, silicon nitride, silicon carbide or carbon black; can also be used. Accordingly, the electrophotographic photoreceptor of the present invention, which comprises a hardened film as an under-coating layer prepared in the presence of iodine, is superior to the conventional one that uses an under-coating layer prepared by solidifying a melamine resin by mixing with an amino resin and an aromatic carboxylic acid and/or an aromatic carboxylic anhydride, or an aromatic carboxylic acid without presence of iodine. That is, the under-coating layer proposed in the present invention can be applied thickly on a substrate so as to sufficiently cover the substrate for uniformly applying a charge generation layer thereon. In this case, the photoconductor thus obtained keeps its excellent electrophotographic properties under various environmental conditions whether the under-coating layer is formed as the extremely thick one (e.g., 10-20 µm in thickness) or not. Thus the electric properties of the under-coating layer can be hardly affected at all. That is, the charge potential and photo sensitivity do not fall, and also the residual potential does not rise after using the photoreceptor repeatedly. In addition, many inhomogeneous, shape-defective, rough, and impure regions formed on the surface of the photoconductive substrate can be covered with the under-coating layer so that the photosensitive layer can be formed so as to reduce the membrane defects and make it uniform throughout. In the case of the photoreceptor of the functionally deviated layer type in which the photosensitive layer is formed by laminating the charge transport layer on the charge generation layer, the charge generation layer can be easily formed as a thin film which is uniform throughout. Consequently, the photoreceptor for constantly providing images having excellent image qualities can be obtained, and also it is very rare to provide poor images with defects. It has been known that an addition product formed by reacting nylon-6 with a large amount of iodine (i.e., 80-100%) acts as an electroconductive material having an extremely low resistance thereof (J. of Mat. Sci., 21. 604-610, 1986). Furthermore, polyvinyl alcohol, polytetrahydrofuran, and polyacrylonitrile can be reacted with iodine to form addition products having electroconductivity. As described above, however, the hardened film solidified by adding iodine to the mixture of melamine resin and aromatic carboxylic acid and/or aromatic carboxylic anhydride, or aromatic carboxylic acid shows good conductivity by adding a small amount of iodine thereto. In addition, the conductivity of the hardened film is almost kept at a constant under the various environmental conditions. Consequently, the above hardened film works effectively when it is applied as an under-coating layer of the photoreceptor with a charge-generation layer comprising the novel titanyl phthalocyanine. The charge generation layer 5 is formed by applying a coating solution on a surface of the under-coating layer formed on the substrate. The coating solution is prepared by dispersing and dissolving a charge generation material and a binding agent in a solvent. The titanyl phthalocyanine crystal of the present invention can be used as the charge generation material. However, according to the present invention it is also possible to use other charge generating materials in combination with the titanyl phthalocyanine. That is, the material can e.g. be selected from non-metal phthalocyanines in various crystal forms; various metal phthalocyanines in which a central metal of the phthalocyanine skeleton is for example iron, cobalt, nickel, aluminum, silicon, copper, titanium, vanadium, indium, gallium, germanium or magnesium; bis- and tri-azo compounds; anthraquinone compounds; perylene compounds; perinone compounds; azulenium chloride compounds; squarilium (squaleum) chloride compounds; and pyrropyrrole compounds. The binding agent to be preferably used in the present invention is selected from the group of hydrophobic high-molecular polymers or co-polymers that form high electrical insulating films. To put it more concretely, the binder is for example made of at least one selected from the group of phenol resins, polyester resins, vinyl acetate compounds, polycarbonate resins, polypeptide resins, cellulose resins, polyvinyl pyrolidone, polyethylene oxide, polyvinyl chloride resins, polyvinylidene chloride resins, polystyrene resins, polyvinyl acetate, styrene-butadiene copolymers, vinylidene chloride - acrylonitrile copolymers, vinyl chloride - vinyl acetate copolymers, vinyl chloride - vinyl acetate - maleic anhydride copolymers, silicon - alkyd resins, phenol - formaldehyde resins, styrene-alkyd resins, polyvinyl alcohol, acrylic copolymer resins, methacryl copolymer resins, silicone resins, methacrylonitrile copolymer resins, polyvinyl butyral, polyvinylidene chloride resins, and mixtures of these compounds. In general, the thickness of the charge generation layer is in the range of 0.01 µm to 5 µm. The charge transport layer 6 is formed as a layer comprising a material with the ability of transporting charge carriers. For the material, a hydrazone compound or a distyryl compound can be used. A preferable hydrazone compound is indicated by the general formula (II) below. wherein R 1 , R 2 , R 3 , and R 4 are groups selected from an alkyl group, an aralkyl group, and an aryl group, respectively, which may be substituted; and R 5 is an atom or a group selected from a hydrogen atom, a halogen atom, an alkyl group, and an alkoxy group. In the formula (II), R 1 and R 2 , may be bound together to form a ring, and also R 1 or R 2 , may be bound with R 5 to form a ring. A preferable distyryl compound is indicated by the general formula (III) below. wherein R 1 , R 2 , R 3 , and R 4 are groups selected from an alkyl group and an aryl group, respectively, which may be substituted; R 5 is an atom or a group selected from a hydrogen atom, a halogen atom, an alkyl group, and an alkoxy group, and Ar is an aryl group or an aromatic heterocyclic group. Furthermore, the following general formulae (II-1) to (II-18) are concrete examples of the above hydrazone compound, while (III-1) to (III-96) are concrete examples of the above distyryl compound. However, the material responsible for transporting charge carriers is not limited to one of the above compounds, but other materials which have been known in the art, for example hydrazone compounds described in the documents such as the specification of European Patent Application No. 13172, pyrazoline compounds described in Japanese Patent Application Laying-open No. 49-105536, oxadiazole compounds described in Japanese Patent Application Laying-open No. 54-112637 and US Patent No. 318944, styryl compounds referenced in Japanese Patent Application Laying-open No. 50-3173, arylamine compounds described in US Patent No. 3567450, Japanese Patent Application Publication No. 49-35702, German Patent No. 1110518, US Patent No. 3180703, US Patent No. 3240597, US Patent No. 3658520, US Patent No. 4232103, US Patent No. 4175961, US Patent No. 4012376, Japanese Patent Application Laying-open No. 55-144250, Japanese Patent Application Laying-open No. 56-119132, and Japanese Patent Application Publication No. 39-27577, oxazole compounds described in US Patent No. 3543546, pyrazoline and pyrazolone compounds described in US Patent 3180729 and Japanese Patent Application Laying-open No. 49-105536, polyarylalkane compounds described in US Patent NO. 3615402, US Patent NO. 3820989, US Patent No. 3542544, Japanese Patent Application Publication No. 45-555, and Japanese Patent Application Publication No. 51-10983, polyvinylcarbazole compounds and their derivatives described in Japanese Patent Application Publication No. 34-10966, polymers of N-acrylamide methylcarbazole described in Japanese Patent Application Laying-open 50-85337, 6-vinylindro-(2,3-6)-quinoxaline polymers described in Japanese Patent Application Laying-open 50-93432, vinyl polymers described in Japanese Patent Application Publication No. 43-18674 and Japanese Patent Application Publication No. 43-19192, triphenylmethane polymers described in Japanese Patent Application Laying-open No. 56-90883 and Japanese Patent Application Laying-open No. 56-161550, styrene copolymers described in Japanese Patent Application Publication No. 43-19193, polyindene, polyacenaphthene, copolymers of styrene with acenaphthylene, and formaldehyde condensation resin described in Japanese Patent Application Publication No. 56-13940; can also be used. If these charge-carrier transport materials have film-forming ability, they can be used in the form of an aqueous solution and can be applied an a substrate to prepare a charge transport layer. In case a low molecular weight compound is used which does not have film-forming ability, however, it may be dissolved in an aqueous solution with a resin having film-forming ability. In general the thickness of charge transport layer is preferably in the range of 5 µm to 40 µm. The above photosensitive layer 4 may be optionally comprised of an electron acceptor for the purpose of increasing the photosensitivity and preventing the decrease in residual potential, and preventing the electrophotographic characteristics from change in repeat use. The material to be used as an electron acceptor can for example be selected from succinic anhydride, maleic anhydride, dibromsuccinic anhydride, phthalic anhydride, 3-nitrophtalic anhydride, 4-nitrophtalic anhydride, pyromellitic anhydride, pyromellitic acid, trimellitic acid, trimellitic anhydride, phthalimide, 4-nitrophthalimide, tetracyanoethylene, tetracyanoquinodimethane, chloranil, bromanil and o-nitrobenzoic acid, which are characterized by their good electron affinities. In the above photosensitive layer 4, furthermore, at least one of deterioration-preventing agents, such as anti-oxidizing agents and light-stabilizing agents, may be included for improving the stabilities thereof to harmful light and to environmental conditions. The material to be used for attaining that purpose may for example, be selected from chromanol derivatives, such as tocopherol and their etherified compounds or esterified compounds, polyarylalkane compounds, hydroquinone derivatives and their mono-etherified compounds or di-esterified compounds, benzophenone derivatives, benzotriazole derivatives, thioetherified compounds, phenylene diamine derivatives, phosphonate, phosphite, phenol compounds, hindered phenol compound, straight-chain amine compounds, cyclic amine compounds and hindered amine compounds. Each layer of the photoreceptor of the present invention can be formed by using a well-known device such as a dip coater, spray coater, wire-bar coater, applicator, doctor blade, roller coater, curtain coater, and bead coater. Preferable embodiments of the present invention will now be described in detail. However, the present invention is not to be restricted to these embodiments. In the embodiments, "parts" denotes "parts by weight" and "%" denotes "weight %". First of all, the process for preparing titanyl phthalocyanine of the present invention will be explained. <Example 1(1)> Synthesis Example 1 of titanyl phthalocyanine Titanyl phthalocyanine in accordance with the present invention was prepared by the following process. At first, amorphous titanyl phthalocyanine was prepared as follows. 128 parts of phthalodinitrile were placed in a four-necked flask (2 l in volume) attached to a stirring device and a cooling device. Then 1000 parts of quinoline were added therein. After that, 47.5 parts of titanium were dropped into the flask and then the flask was heated up to 200°C ± 10°C to start a reaction. After the reaction at 200°C ± 10°C for 8 hours, the flask was cooled and its contents was filtrated at a temperature of 130°C and washed with 500 parts of quinoline heated to 130°C. Further, the filter cake was washed with N-methyl-2-pyrolidone heated to 130°C until the filter cake became transparent. Then the filter cake was washed with ethanol and water in that order until the solvent was removed from the wet cake. The obtained wet cake was dispersed into 1000 parts of 3% sodium hydroxide and then heated for 4 hours. Then it was filtrated and washed to obtain a neutral filter cake. The filter cake was further washed with methanol and acetone. Then the purification step of washing the filter cake with an alkali-acid-methanol-acetone system was repeated several times until the filter cake after washing with methanol and acetone became colorless and transparent. Consequently, the total yield of the product was 101.2 parts. The purity of the obtained titanyl phthalocyanine was analyzed by a field desorption mass spectrometry (FDMS). The resultant spectrum showed a single peak at the molecular weight of 576, corresponding to that of the purified titanyl phthalocyanine. The titanyl phthalocyanine was further analysed by X-ray diffraction The resultant spectrum is almost the same as the one shown in Fig. 1. It means that the crystal form of the product corresponded to that of the type I described in Japanese Patent Application Laying-open No. 62-67094. Crystal transformation Example 1 of titanyl phthalocyanine Then 50 parts of the titanyl phthalocyanine were gradually added to 750 parts of concentrated ammonium sulfate cooled to less than -10°C. For keeping the temperature at least below -5°C, the ammonium sulfate was stirred and cooled. The mixture was further stirred for 2 hours and then purged into ice-water (0°), resulting in the precipitation of a blue material. The blue material was washed and filtrated, and then dispersed in 500 parts of a 2% sodium hydroxide aqueous solution. The mixture was heated and then washed with water until the filter cake became neutral, perfectly. Then the filter cake was dried to obtain titanyl phthalocyanine as a product. Consequently, the total yield of product was 47 parts. The titanyl phthalocyanine was further analysed by X-ray diffraction. The resultant spectrum was almost the same as the one shown in Fig. 4 in which any peak of diffraction intensity was not observed, so that the product was amorphous. <Example 1(2)> Preparation of titanyl phthalocyanine crystals of the present invention A mixture of 40 parts of the amorphous titanylphthalocyanine obtained by the above steps, 100 parts of sodium chloride, and 400 parts of water was introduced into a sand mill filled with zirconia beads. The mixture was dispersed and granulated at a room temperature for 3 hours. Then 200 parts of dichlorotoluene was added in the sand mill. The sand mill was driven in succession. During the movement of the sand mill, titanyl phthalocyanine was gradually shifted from the water phase to an oil layer phase. Water being separated was removed during the period of performing the movement of the sand mill for dispersion and granulation for 3 hours. Then the content was taken out from the sand mill and then dichlorotoluene was distilled by means of steam distillation. After the distillation, the remaining titanyl phthalocyanine was filtrated with water and then dried. The resultant titanyl phthalocyanine was subjected to a X-ray diffraction method using CuKα as a source of radiation, resulting in a X-ray diffraction spectrum which is the same as the one shown in Fig. 5. In the figure, the maximum diffraction intensity was observed at a Bragg angle (2) of 9.6° ± 0.2° and peaks of diffraction intensity were observed at Bragg angles (2) of 7.22° ± 0.2°, 9.60° ± 0.2°, 11.60° ± 0.2°, 13.40° ± 0.2°, 14.88° ± 0.2°, 18.34° ± 0.2°, 23.62° ± 0.2°, 24.14° ± 0.2°, and 27.32° ± 0.2°, respectively. Thus the titanyl phthalocyanine crystal of the present invention was obtained. Furthermore, a result of the structural analysis using X-ray indicates that the obtained titanyl phthalocyanine crystal had a lattice constant of: with an allowable error of ± 1%. <Example 2> A mixture of 40 parts of the amorphous titanyl phthalocyanine obtained by crystal transformation Example 1, 100 parts of sodium chloride, and 400 parts of water was introduced into the same sand mill as that of Example 1 for dispersing and granulating at a room temperature for 3 hours. Then the content of the sand mill was transferred into a twin-screw kneader. In addition, 20 parts of α-dichloronaphthalene were added thereto, following that the kneader was driven. During the period of driving the kneader, titanyl phthalocyanine was gradually shifted from the water phase to the oil layer phase. Water being separated was removed during the period of performing the movement of the sand mill for dispersion and granulation for 3 hours. Then the content was taken out from the kneader and then α-dichloronaphthalene was distilled by means of steam distillation. After the distillation, the remaining titanyl phthalocyanine was filtrated with water and then dried. The resultant titanyl phthalocyanine showed the same X-ray diffraction spectrum as that of the one shown in Fig. 5. Thus the titanyl phthalocyanine crystals of the present invention were obtained. <Example 3> A mixture of 40 parts of the amorphous titanyl phthalocyanine obtained by crystal transformation example 1, 100 parts of sodium chloride, and 400 parts of water were introduced into a ball mill filled with zirconia balls for dispersing and granulating at a room temperature for 3 hours. Then 200 parts of dichlorotoluene were added in the ball mill. The ball mill was driven in succession. During the movement, titanyl phthalocyanine was gradually shifted from the water phase to the oil layer phase. Water being separated was removed during the period of performing the movement of the sand will for dispersion and granulation for 8 hours. Then the content was taken out from the and then remaining dichlorotoluene was distilled by means of steam distillation. After the distillation, the remaining titanyl phthalocyanine was filtrated with water and then dried. The resultant titanyl phthalocyanine showed the same X-ray diffraction spectrum as that of the first embodiment shown in Fig. 5. Thus the titanyl phthalocyanine crystals of the present invention were obtained. <Comparative example 1> In this comparative example, titanyl phthalocyanine was crystallized in accordance with the method disclosed in Japanese Patent Application Laying-open No. 2-131243. That is, 5 g of titanyl phthalocyanine was stirred in 100 g of 90 % sulfuric acid at 3°C to 5°C for 2 hours and then the obtained mixture was filtrated. After the filtration, the sulfuric acid solution was dropped into 3 l of water to precipitate a bulk of crystals. The obtained crystals were washed with deionized water. The washing was repeated until the filter cable became neutral, Thus, a wet cake was obtained. Successively, o-dichlorobenzene was added to the wet cake as a dispersion medium and then the mixture was milled by a sand grinder at room temperature. The dispersion medium was removed from the sand grinder. There after the content thereof was washed with acetone and methanol to obtain a bulk of distinct blue crystals. The X-ray diffraction spectrum of the resultant titanyl phthalocyanine crystals was characterized by the maximum peak of diffraction intensity at a Bragg angle (2) of 27.3°. In the range of 6° to 8°, the maximum peak of diffraction intensity was observed at a Bragg angle (2) of 6.8°. Consequently, the product was of the same crystal form as that of the crystals disclosed in Japanese Patent Application Laying-open No. 2-131243. <Comparative example 2> In this comparative example, α-titanyl phthalocyanine was prepared by the method disclosed in Japanese Patent Application Laying-open No.62-134651. That is, a mixture of 40 g of phthalodinitrile, 18 g of titanium tetrachloride, and 500 cm 3 of chloronaphthalene were stirred at a temperature of 240°C to 250°C for 3 hours in nitrogenous atmosphere to completely react with each other. The mixture was filtered after the reaction, and as a result dichlorotitanium phthalocyanine was obtained. The obtained dichlorotitanium phthalocyamine was mixed with 300 cm 3 of a concentrated ammonium solution to obtain a mixture. Then the mixture was heat-refluxed for 1 hour and subjected to purification by using a Soxhlet extractor. Consequently, titanyl phthalocyanine was obtained by drying the purified product. The resultant titanyl phthalocyanine was confirmed as α-type crystals having an X-ray diffraction spectrum which is the same as the one shown in Fig. 3. [Dispersion stability of coating solutions for charge generation layers, external appearance of the charge generation layers, and photoreceptor images] The titanyl phthalocyanine samples obtained by Example 1 and Comparative examples 1 and 2 were used in the process of forming photoreceptors, respectively. For each titanyl phthalocyanine, a coating solution for preparing a charge generations layer was prepared. The coating solution was left alone for observing the change in dispersion conditions just after the preparation and after 3-weeks . Also, the external appearance of the charge generation layer applied by a dip-coating method was observed. Furthermore, the image of each photoreceptor prepared by using the charge generation layer coating solution just after the preparation and after standing for 3-weeks was estimated. 2 parts of titanyloxyphthalocyanine obtained by the above examples and comparative examples were dispersed with a resin solution in a ball mill for 6 hours. In this case, the resin solution was prepared by dissolving vinyl chloride - vinyl acetate copolymer resin (Trade name:VMCH manufactured by Union Carbide Co., LTD.) in 97 parts of tetrahydrofuran. Consequently, coating solutions No. 1 to No. 4 for preparing charge-generation layers were obtained as listed in Table 2 below. Coating solution No. Charge-generating material (Crystal form or maximum Bragg angle) 1 Example 1(2) (novel type) 2 Synthesis, Example 1 (I-type) 3 Comparative example 2 (α-type) 4 Comparative example 1 (27.3°) The dispersion state of each of these coating solutions was observed just after the preparation and after standing for 3 weeks. Then, a coating solution was applied onto the outer peripheral surface of an aluminum cylinder (30 mm in outer diameter) by using a wire-bar coater. In this case, the coating solution was prepared by dissolving 10 parts of copolymer nylon (6,66,610 nylon, trade name "ALAMIN CM8000" manufactured by Toray Co., LTD.) with 190 parts of ethanol in a ball mill by stirring them for 3 hours. The solution applied to the cylinder was dried at 100°C for 1 hour. Thus, an under-coating layer of 0.5 µm thickness was formed. Each of the above coating solutions for the charge generation layers just after the preparation and after standing for 3-weeks was applied onto the under-coating layer to form a charge generation layer. The applied solution was dried at 100°C for 2 hours. The resultant charge generation layer had a thichness of 0.3 µm and its external appearance was visually observed. Furthermore, another coating solution was prepared by dissolving a charge transport material by dissolving 10 parts of 1-phenyl-1, 2, 3, 4-tetrahydroquinoline-6-carboaldehyde-1',1'-diphenylhydrazone and 10 parts of a polycarbonate resin (bis-phenol A-type polycarbonate, trade name "PANLITE" manufactured by Teijin Kasei Co., LTD.) in 100 parts of methylene chloride. The prepared coating solution was applied on each charge-generation layer described above and then dried to form a charge transport layer of 15 µm thickness. Consequently, photoreceptors, which correspond to the coating solutions Nos. 1-4, respectively, were obtained. The resultant photoreceptors were subjected to the test of forming an image by using a commercially-obtainable semiconductor laser beam printer to estimate their electrophotographic characteristics. The results were listed in Table 3. (1) Initial dispersion state of the coating solutions for applying a charge generation layer Photo- recep. NO. Coating Sol. No. Dispersion Appearance Image quality 1 1 - - - 2 2 - - - 3 3 - - - 4 4 - - - In the table, "-" means that the materials were homogeneously dispersed in the coating solution, good external appearance of the coating solution was obtained, or good image quality was attained by using the photoreceptor (2) Dispersion state of the coating solutions for applying a charge generation layer after resting for 3 weeks. Photo-recep. NO. Coating Sol. No. Dispersion Appearance Image quality 1 1 - - - 2 2 + + + 3 3 + + + 4 4 ++ ++ ++ In the table, "-" means that the materials were homogeneously dispersed in the coating solution, good external appearance of the coating solution was obtained, or good image quality was attained by using the photoreceptor; "+" means that a partial precipitation or a partial agglutination was observed in the coating solution, or an image having many black dot noises was obtained by using the photoreceptor; and "++" means that a lot of precipitations or a lot of agglutination with uneveness was observed in the coating solution, or an image having many black dot noises with uneveness was obtained by using the photoreceptor. As shown in the table, the coating solution in accordance with the present invention did not cause agglutination and precipitation even after standing for 3 weeks. Whether the time proceeds or not, consequently, the excellent charge generation layers were obtained without changing the coating conditions. The resultant charge generation layers did not have any troubles of agglutination and unevenness of the coated surface. As a result, an image obtained by the photoreceptor comprising the above charge generation layers according to the invention did not show any defects to be caused by the agglutination and unevenness of the coated surface of the charge generation layer. Furthermore, the photoreceptor did not cause a memory phenomenon. [Photoreceptor preparation and evaluation of characteristics] Plate-type photoreceptors were prepared for the evaluation of their electrical characteristics. These plate-type photoreceptors were prepared by using different titanyl phthalocyanines described previously as their charge generation materials; different charge transport materials to be combined with the above charge generation materials; and different under-coating layers, respectively. <Example 4> First of all, a coating solution was prepared by the steps of adding 10 parts of copolymerized nylon (trade name "AMILAN CM8000" manufactured by Toray Co., LTD.) and 190 parts of ethanol into a ball mill and stirring them for 3 hours to mix and dissolve. The obtained coating solution was applied on to an aluminum base plate by means of a wire-bar coater and then dried at 100 °C for 1 hour; thus, an under-coating layer of 0.5 µm thickness was formed. Then the above coating solution of No. 1 for a charge generation layer was applied and dried at 100°C for 2 hours; thus, a charge generation layer of 0.3 µm thickness was formed. Next, another coating solution for preparing a charge transport layer, which was prepared by dissolving 10 parts of 1-phenyl-1, 2, 3, 4-tetrahydroquinoline-6-carboaldehyde-1', 1'-diphenylhydrazone and 10 parts of polycarbonate resin (trade name "VMCH" manufactured by Union Carbide Co., LTD.) in 100 parts of methylene chloride, was applied on the charge generation layer and then it was dried to form a charge transport layer. Thus, the photoreceptor of Example 4 was obtained. The electrical characteristics of the photoreceptor were evaluated by using an electrostatic recording paper testing device (trade name "SP-428" manufactured by Kawaguchi Denki Seisakusho). A surface of the photoreceptor was charged by a corona discharge of a corotron system in darkness. In this case, a discharge voltage was regulated so as to charge the photoreceptor's surface at a charged potential Vo of -600V. Then the corona discharge was switched off and the photoreceptor was illuminated by light with a wavelength of 780 nm after placing in darkness for 5 seconds. The wavelength of the light was determined so as to correspond to an oscillation wavelength of 760 nm to 800 nm of semiconductor laser to be used in a general laser printer. In addition, the light was monochromatic one generated from a 500W xenon lamp as a light source through monochrometer. Photosensitivities of the photoreceptor was estimated by means of an exposure energy E 1/2 (µJ/cm 2 ) at the time of a half decay of the surface potential. Furthermore, the residual potential VR5 was measured after 5 minutes passed from the end of illumination. Next, the discharge voltage was further regulated so as to be kept at a constant level. The steps of charging and exposing the photoreceptor were repeated continuously 10,000 times and then V o , E 1/2 , and V R5 were measured and fatigue characteristics of the photoreceptor have been estimated. The results are listed in Table 4 below. <Comparative Examples 3, 4, and 5> The above steps were repeated to prepare the photoreceptors of Comparative examples 3, 4, and 5, excepting that the above coating solutions of Nos. 2, 3, and 4 in Table 2 for charge generation layers were used, respectively. The resulting photoreceptors were subjected to the above tests to estimate their photo-sensitivities. The results are listed in Table 4 below. Electrophotographic characteristics of the photoreceptors before and after repeating the cycle 10,000 times Photoreceptor Coating Solution State V o (-V) V R5 (-V) E 1/12 (µJ/cm 2 ) Example No. 1 Before 600 5 0.09 After 602 6 0.10 Comparative Examples 3 No. 2 Before 603 20 0.42 After 625 30 0.50 4 No. 3 Before 605 12 0.31 After 610 22 0.32 5 No. 4 Before 601 7 0.16 After 570 15 0.19 As shown in Table 4, the photoreceptor of Example 4 using the titanyl phthalocyanine crystal of Example 1 had the highest sensitivity compared with others and had good fatigue characteristics. Therefore, the titanyl phthalocyanine of the present invention attains superiority over others when used in a charge-generation layer. <Example 5> An under-coating layer was applied on a base plate in the same way as that of Example 4. On the under-coating layer, a coating solution for preparing charge generation layer was applied and dried at 100°C for 2 hours; thus, a charge generation layer of 0.3 µm in thickness was formed. The above coating solution was preparating the charge generation layer was prepared by dispersing 2 parts of the titanyl phthalocyanine obtained by the method of example 1 and a resin solution where a vinyl chloride - vinyl acetate copolymer resin (trade name "VMCH" manufactured by Union Carbide Co., LTD) was dissolved in 97 parts of tetrahydrofuran in a ball mill for 6 hours Furthermore, another coating solution, which was prepared by dissolving 10 parts of hydrazone compound (II-5) and 10 parts of a polycarbonate resin (trade name "PANLITE" manufactured by Teijin Kasei Co., LTD) in 100 parts of methylene chloride, was applied on the above charge generation layer and dried to obtain a charge transport layer . The resultant charge transport layer had a thickness of 15 µm. As a result, a photoreceptor was formed. <Example 6> A photoreceptor was prepared in the same way as that of Example 5 except that a different hydrazone compound was used. This means that in this example hydrazone compound (II-9) was used as a charge transporting material instead of the hydrazone compound (II-5). <Example 7> A photoreceptor was prepared in the same way as that of Example 5 except that a different hydrazone compound was used. That means that in this example hydrazone compound (II-15) was used as a charge transporting material instead of the hydrazone compound (II-5). <Comparative example 6> A photoreceptor was prepared in the same way as that of example 5 except that a different charge generation material was used. This means that in this example the titanyl phthalocyanine of Comparative example 1 was used as a charge generation material instead of that of example 5. <Comparative example 7> A photoreceptor was prepared in the same way as that of example 5 except that a different charge generation material was used. That means that in this example the titanyl phthalocyanine of Comparative example 1 was used as a charge generation material instead of that of example 5. <Comparative example 8> A photoreceptor was prepared in the same way as that of example 5 except that a different charge generation material was used. That means that in this example the titanyl phthalocyanine of Comparative example 2 was used as a charge generation material instead of that of example 5. <Comparative example 9> A photoreceptor was prepared in the same way as that of example 5 except that a different hydrazone compound was used. That means that in this example compound (H-1) having the following structure was used as a charge transporting material instead of the hydrazone compound (II-5). The photoreceptors of Examples 5 to 7 and Comparative examples 6 to 9 were subjected to the same test as that of Example 4 for estimating the electrical characteristics of each photoreceptor. The results are listed in Table 5. Electrophotographic characteristics of the photoreceptors before and after repeating the cycle Photoreceptor State V o (-V) V R5 (-V) E 1/2 (µJ/cm 2 ) Example 5 Before 600 5 0.09 After 602 6 0.10 6 Before 601 8 0.10 After 602 10 0.12 7 Before 600 5 0.12 After 601 7 0.12 Comparative Example 6 Before 602 20 0.42 After 625 30 0.50 7 Before 601 7 0.12 After 570 15 0.16 8 Before 605 12 0.31 After 610 22 0.32 9 Before 601 6 0.10 After 620 25 0.28 From the data in Table 5, it is evident that the photoreceptor having the combination of the titanyl phthalocyanine crystal of the present invention and the hydrazone compound according to formula (II) attains superiority over others. <Example 8> A photoreceptor was prepared by forming an under-coating layer and a charge generation layer on a base plate in the same way as in Example 5. However the charge transport layer was different. That means that in this example a charge transport layer was formed by the steps of preparing a coating solution by dissolving 10 parts of distyryl compound (III-2) as a charge transport material and 10 parts of polycarbonate resin in 100 parts of methylene chloride; applying the coating solution on a surface of the charge generation layer; and drying the applied coating solution. The resultant charge transport layer had a thickness of 15 µm. Consequently, a photoreceptor was obtained. <Example 9> A photoreceptor was prepared in the same way as that of Example 8, except that distyryl compound (III-19) as a charge transport material was used instead of the distyryl compound (III-2). <Example 10> A photoreceptor was prepared in the same way as that of Example 8, except that distyryl compound (III-50) as a charge transport material was used instead of the distyryl compound (III-2). <Example 11> A photoreceptor was prepared in the same way as that of Example 8, except that distyryl compound (III-74) as a charge transport material was used instead of the distyryl compound (III-2). <Example 12> A photoreceptor was prepared in the same way as that of Example 8, except that distyryl compound (III-92) as a charge transport material was used instead of the distyryl compound (III-2). <Comparative example 10> A photoreceptor was prepared in the same way as that of Example 8 except that a different charge generation material was used. That means that in this example the I-type titanyl phthalocyanine obtained in Synthesis Example 1 was used as a charge generation material instead of the crystalline titanyl phthalocyanine obtained in Example 1 (2). <Comparative example 11> A photoreceptor was prepared in the same way as that of Example 8 except that a different charge generation material was used. That means that in this example the titanyl phthalocyanine of Comparative example 1 was used as a charge generation material instead of that of Example 1(2). <Comparative example 12> A photoreceptor was prepared in the same way as that of Example 8 except that a different charge generation material was used. That means that in this example the titanyl phthalocyanine of Comparative Example 2 was used as a charge generation material instead of that of Example 1(2). <Comparative example 13> A photoreceptor was prepared in the same way as that of Example 8 except that a different charge transport material was used. That means that in this example 1-phenyl-3-(p-diethylaminostyryl)-5-(p-diethylaminophenyl)-2-p-pyrazoline (ASPP) was used as a charge transport material instead of distyryl compound (III-2). <Comparative example 14> A photoreceptor was prepared in the same way as that of Example 8 except that a different charge transport material was used. That means that in this example p-diethylaminobenzaldehyde-diphenylhydrazone (ABPH) was used as a charge transport material instead of distyryl compound (III-2). The electrical characteristics of each photoreceptor use estimated by using an electrostatic charging testing device EPA-8100 manufactured by Kawaguchi Denki Seisakusho. A surface of the photoreceptor of Example 5 was charged by a corona discharge of a corotron system in darkness. In this case, a discharge voltage was regulated so as to charge the photoreceptor's surface at a charged potential V o of -600V. Then the corona discharge was switched off and the photoreceptor was illuminated by light with a wavelength of 780 nm after placing in darkness for 5 seconds. The wavelength of the light was controlled so as to correspond to an oscillation wavelength of 700 nm to 800 nm of a semiconductor laser to be used in a general laser printer. In addition, the light was monochromatic light generated from a 100W halogen lamp as a light source through an optical filter and illuminated the photoreceptor's surface at 0.7 µW/cm 2 . The photosensitivity of each photoreceptor was estimated by means of an exposure energy E 1/2 (µJ/cm 2 ) at the time of a half decay of the surface potential. Furthermore, the residual potential VR5 was measured after 5 minutes had passed after the end of illumination. Next, the discharge voltage was further regulated so as to be kept at a constant level. The steps of charging and exposing the photoreceptor were repeated continuously for 10,000 times and then V o , E 1/2 , and V R5 were measured and fatigue characteristics of the photoreceptor are estimated. The results are listed in Table 6 below. Electrophotographic characteristics of the photoreceptors before and after repeating the cycle Photoreceptor State V o (-V) V R5 (-V) E 1/2 (µJ/cm 2 ) Examples 8 Before 600 8 0.12 After 610 18 0.14 9 Before 601 10 0.14 After 605 20 0.14 10 Before 601 9 0.12 After 603 16 0.15 11 Before 600 7 0.11 After 603 11 0.13 12 Before 602 11 0.11 After 611 15 0.12 Comparative Examples 10 Before 600 22 0.52 After 625 65 0.70 11 Before 603 7 0.12 After 567 32 0.17 12 Before 605 12 0.31 After 610 28 0.35 13 Before 601 9 0.35 After 610 55 0.38 14 Before 601 12 0.25 After 605 75 0.32 From the data in Table 6, it is evident that the photoreceptor having the combination of the titanyl phthalocyanine crystal of the present invention and the distyryl compound according to formula (III) attains superiority over others. <Example 13 and Comparative Example 15> An aluminum cylinder of 30 mm in outer diameter, 28 mm in inner diameter, 260.3 mm in length, and 1.0 µm in surface roughness indicated by the maximum height (R max ) was used as a conductive substrate. An under-coating composition was applied on an outer peripheral surface of the aluminum cylinder to form an under-coating layer. The under coating composition was selected from one of the following materials of A to D. A. melamine resin (n-butylated melamin resin, trade name "Uban 20HS" manufactured by Mitsui Toatsu Co., LTD) B. acids (aromatic carboxylic acid, aromatic carboxylic acid compound) B1 phthalic acid B2 ammonium benzoate C. adipic acid D. iodine One of the above materials A to D and a solvent prepared by mixing dichloromethane with methanol (1:1) were used for preparing the under-coating layer coating solution having the composition shown in Table 7. The coating solution was dip-coated on the conductive substrate and dried at 120°C for 1 hour to form an under-coating layer of 15 µm in thickness. Under-coating solution No. Composition of under-coating layer (parts by weight) Melamine Acid Iodine 1 A (100) B1 (20) (6) 2 A (100) B1 (20) (6) 3 A (100) C (20) (6) 4 A (100) B1 (20) (0) Furthermore, a charge generation layer and a charge transporting layer were formed on each of the above under-coating layers. That is, a coating solution was prepared by dispersing 2 parts of one of the titanyl phthalocyanines prepared in Examples 1 and 2 and Comparative examples 1 and 2 and a resin solution where a vinyl chloride - vinyl acetate copolymer resin (trafe name "VMCH." manufactured by Union Carbide, Co., LTD) was dissolved in 97 parts of tetrahydrofuran in a ball mill for 6 hours. Then the coating solution was applied onto the under-coating layer and dried at 100 °C for 2 hours to form a charge generation layer of 0.3 µm in thickness. After forming the charge generation layer, the charge transport layer was formed thereon. That is, a coating solution, which was prepared by dissolving 10 parts of N, N-diethylaminobenzaldehyde diphenylhydrazone and 10 parts of polycarbonate (trade name "PANLITE" manufactured by Teijin Kasei Co., LTD.) in 100 parts of methylene chloride, was applied onto the charge generation layer and dried. The resultant charge transport layer had a thickness of 20 µm. Then these steps were repeated with respect to each of the above under-coating layer, thus obtaining 15 different photoreceptors as shown in Table 8 below. Photoreceptor Coating solution for under-coating layer Charge-generation material Example 13-1 No. 1 Example 1(2) Example 13-2 No. 2 Example 1(2) Example 13-3 No. 3 Example 1(2) Example 13-4 No. 4 Example 1(2) Example 13-5 No. 1 Example 2 Example 13-6 No. 2 Example 2 Example 13-7 No. 3 Example 2 Example 13-8 No. 4 Example 2 Comp. 15-1 No. 1 Comp. 1 Comp. 15-2 No. 2 Comp. 1 Comp. 15-3 No. 3 Comp. 1 Comp. 15-4 No. 4 Comp. 1 Comp. 15-5 No. 1 Comp. 2 Comp. 15-6 No. 2 Comp. 2 Comp. 15-7 No. 3 Comp. 2 In the table, "Comp." means "Comparative example". In the table, "Comp." means "Comparative example". Electrical characteristics of the photoreceptors thus obtained were evaluated by means of a photoreceptor-process testing machine. The photoreceptor was installed on the testing machine and rotated at the peripheral Velocity of 78.5 mm/s. During the rotation, a surface of the photoreceptor was charged by a corotron system in darkness. In this case, a discharge voltage was regulated so as to charge the photoreceptor's surface at a charged potential V o of -600V. Then the potential retention rate V k5 (%) was estimated by measuring a potential after leaving the photoreceptor in darkness for 5 minutes. Then the photoreceptor was illuminated by light having the wavelength of 780 nm and a luminous flux density of 2 µW/cm 2 .Blight potential V I was defined as a potential measured after the irradiation for 0.2 seconds. The process comprising one cycle of charging and exposure was repeated 10,000 times and the characteristic changes were observed before and after 10,000 repetitions. The results are shown in Table 9. Before After Photoreceptor V o (-V) V K5 (%) V I (-V) V o (-V) V K5 (%) V I (-V) Example 13-1 600 95 60 602 94 62 Example 13-2 603 96 70 625 96 72 Example 13-3 605 94 71 610 90 120 Example 13-4 604 93 100 570 93 180 Example 13-5 610 96 55 610 95 58 Example 13-6 602 95 62 609 95 64 Example 13-7 611 93 73 620 91 110 Example 13-8 610 93 110 630 93 170 Comp. 15-1 603 94 89 611 93 105 Comp. 15-2 605 96 94 610 94 102 Comp. 15-3 607 95 95 613 92 97 Comp. 15-4 600 93 120 648 93 198 Comp. 15-5 603 92 180 630 92 195 Comp. 15-6 601 93 188 625 91 190 Comp. 15-7 602 94 220 655 94 250 In the table, "Comp." means "Comparative example". As shown in Table 9, the photoreceptor comprising an under-coating layer that does not contain iodine has a high residual potential and insufficient electrophotographic characteristics in repeated use. In addition, the photoreceptor comprising an under-coating layer that contains iodine and further contains an aliphatic carboxylic acid instead of an aromatic carboxylic acid has a high bright potential V i and insufficient electrophotographic characteristics in repeated use. Furthermore, the photoreceptor comprising an under-coating layer that contains iodine and further contains an aromatic carboxylic acid or its chloride has a high residual potential and insufficient electrophotographic characterisitics in repeated use when the titanyl phthalocyanine of Comparative example 2 is contained. Further, the residual potential of the photoreceptor using the titanyl phthalocyanine of Comparative example 1 is increased in repeated use. Furthermore, the changes in electrical characteristics of the photoreceptor were observed under the circumstances of: HH: high temperature and humidity (35 °C, 85% RH) ; or LL: low temperature and humidity (10 °C, 50% RH). The results thus obtained are listed in Table 10. LL HH Photoreceptor V O (-V) V K5 (%) V I (-V) V o (-V) V K5 (%) V I (-V) Example 13-1 600 94 60 603 94 44 Example 13-2 603 95 70 627 96 62 Example 13-3 605 94 71 612 90 66 Example 13-4 601 93 100 588 93 107 Example 13-5 610 96 55 613 95 55 Example 13-6 602 95 62 614 95 61 Example 13-7 611 91 88 622 91 77 Example 13-8 610 91 110 620 93 107 Comp. 15-1 633 91 89 621 93 77 Comp. 15-2 650 921 94 613 94 88 Comp. 15-3 640 92 95 615 92 98 Comp. 15-4 635 93 120 648 93 198 Comp. 15-5 633 93 180 637 90 195 Comp. 15-6 640 94 188 622 81 190 Comp. 15-7 637 93 220 650 80 250 In the table, "Comp." means "Comparative example". The photoreceptor thus obtained was placed in the laser-beam printer "Laser Jet 111 (trademark, manufactured by Hewlett Packerd Co., LTD.). Image qualities were measured by counting the number of black dots having a diameter of 0.2 mm or more produced on the square with sides of 90 mm an the surface of the photoreceptor. The measurements were performed under the circumstances of: HH: high temperature and humidity (35 °C, 85% RH) ; NN: room temperature and humidity (10 °C, 50% RH); or LL: low temperature and humidity (10 °C, 50% RH). The results thus obtained were listed in Table 11. In the table, each symbol indicates a number of the black dots: "-" means N < 5; "+" means 5 ≤ N < 20; "++" means 20 ≤ N < 50; and "+++" means 50 ≤ N. The number of black dots Photoreceptor LL NN HH Example 13-1 - - + Example 13-2 - - + Example 13-3 + + ++ Example 13-4 low conc. + ++ Example 13-5 - - + Example 13-6 - - + Example 13-7 + + ++(uneven) Example 13-8 low conc. + ++ Comp. 15-1 + + ++ Comp. 15-2 + + ++ Comp. 15-3 + +(uneven) ++(uneven) Comp. 15-4 low conc. low conc. + Comp. 15-5 low conc. + fogging Comp. 15-6 low conc. + fogging Comp. 15-7 low conc. low conc. memory In the table, "Comp." means "Comparative example".

Claims: A titanyl phthalocyanine crystal to be used as a charge generation material of an electrophotographic photoreceptor, wherein the titanyl phthalocyanine is represented by general formula (I) wherein X 1 , X 2 , X 3 and X 4 stand for Cl or Br and each of n, m, l and k is an integer from 0 to 4, and wherein the titanyl phthalocyanine crystal has a maximum diffraction intensity observed at Bragg angle (2) of 9.6° ± 0.2° and clear peaks of diffraction intensity observed at 7.22° ± 0.2°, 9.60° ± 0.2°, 11.60° ± 0.2°, 13.40° ± 0.2°, 14.88° ± 0.2°, 18.34° ± 0.2°, 23.62° ± 0.2°, 24.14° ± 0.2° and 27.32° ± 0.2°, respectively, in a X-ray diffraction spectrum obtained by performing a X-ray diffraction method using CuKα as a source of radiation, and having a lattice constant of: with an allowable error of ± 1%. An electrophotographic photoreceptor characterized by comprising a conductive substrate and a photosensitive layer including a charge transport material and the titanyl phthalocyanine crystal according to claim 1 as a charge generation material. The electrophotographic photoreceptor as claimed in claim 2, characterized in that said photosensitive layer is composed of a charge generation layer including said charge generation material and a charge transport layer including said charge transport material. The electrophotographic photoreceptor as claimed in claim 2, characterized in that said charge transport material is a hydrazone compound. The electrophotographic photoreceptor as claimed in claim 4, characterized in that said hydrazone compound is represented by the formula [II]: wherein R 1 , R 2 , R 3 , and R 4 are groups selected from an alkyl group, an aralkyl group, and an aryl group, respectively, which may be substituted; and R 5 is an atom or a group selected from a hydrogen atom, a halogen atom, an alkyl group, and an alkoxy group, and R 1 and R 2 may be bound together to form a ring, and also R 1 or R 2 may be bound with R 5 to form a ring. The electrophotographic photoreceptor as claimed in claim 2, characterized in that said charge transport material is a distyryl compound. The electrophotographic photoreceptor as claimed in claim 6, characterized in that said disytryl compound is represented by the formula [III] wherein R 1 , R 2 , R 3 , and R 4 are groups selected from an alkyl group and an aryl group, respectively, which may be substituted; R 5 is an atom or a group selected from a hydrogen atom, a halogen atom, an alkyl group, and an alkoxy group, and Ar is an aryl group or an aromatic heterocyclic group. The electrophotographic photoreceptor as claimed in claim 2, characterized in that an under-coating layer is formed between said conductive substrate and said photosensitive layer. The electrophotographic photoreceptor as claimed in claim 8, characterized in that said under-coating layer is a hardened film mainly comprising melamine resin, aromatic carboxylic acid and/or aromatic carboxylic anhydride, and iodine being fixed thereon. A method for preparing a titanyl phthalocyanine crystal according to claim 1, comprising the steps of : dispersing a predetermined amount of amorphous titanyl phthalocyanine in an aqueous solution in which ionic substances are dissolved, under mechanical force at a temperature of less than 50°C, to obtain a mixture characterized by comprising fine dispersions; adding a non-aqueous organic solvent to said mixture to shift a dispersion of titanyl phthalocyanine from an aqueous phase to a non-aqueous organic solvent phase so as to remove water; and removing said non-aqueous organic solvent phase to obtain a pellet of said titanyl phthalocyanine crystal according to claim 1.

Inventors: EGOTA KAZUMI, ITOHI NAOKI, OHKURA KENICHI, SHINICHI TAMURA, TEI YOUICHI, EGOTA, KAZUMI, ITOHI, NAOKI, OHKURA, KENICHI, SHINICHI, TAMURA, TEI, YOUICHI, Egota, Kazumi, c/o Fuji Electric Co., Ltd., Itohi, Naoki, c/o Fuji Electric Co., Ltd., Ohkura, Kenichi, c/o Fuji Electric Co., Ltd., Shinichi, Tamura, c/o Fuji Electric Co., Ltd., Tei, Youichi, c/o FUJI ELECTRIC CO., LTD.
Applicants: FUJI ELECTRIC CO LTD, FUJI ELECTRIC CO., LTD.
Application year: 1995
Main classification: G03G5
IPC codes: G03G5, C09B67, C07D487