Electrophotosensitive material

Abstract: An electrophotosensitive material of the present invention is formed by providing a photosensitive layer containing a bis-azo pigment expressed in formula (1): wherein A¹, A², R¹ and n are as defined, as a charge generating material, and a diamine compound expressed in formula (2): wherein R², R³, R⁴, R⁵, R⁶ and R⁷ p and q k, l, m and o are as defined, as a charge-trasferring material, on a conductive substrate. As a charge generating material, a perylene pigment, anthanthrone pigment, X-type metal-free phthalocyanine pigment, imidazoleperylene pigment or perylene bis-azo pigment are preferable used together with the bis-azo pigment. Thus, photosensitive material is excellent in sensitivity and durability.

Description: The present invention relates to an electrophotosensitive material for use in an image forming apparatus making use of an electrophotographic method, such as electrostatic copying machine and laser beam printer. An electrophotographic method such as Carlson process comprises a step of uniformly charging the surface of an electrophotosensitive material by corona discharge, a light exposure step of exposing the charged surface of the electrophotosensitive material to form an electrostatic latent image on the surface, a developing step of contacting a developing agent with the formed electrostatic latent image to make the electrostatic latent image into a toner image with the toner contained in the developing agent, a transfer step of transferring the toner image onto paper, a fixing step of fixing the transferred toner image, and a cleaning step of cleaning the toner remaining on the surface on the electrophotosensitive material after the transfer step. Recently, in the electrophotosensitive material, instead of those mainly composed of inorganic photoconductive materials such as selenium and cadmium sulfide which are toxic and are hard to handle, various so-called organic photosensitive materials using less toxic organic photoconductive compounds have been proposed. Such organic photosensitive materials are excellent in processability, are easy to manufacture, and provide a large degree of freedom of function design. Such organic photosensitive materials are often composed of photosensitive layers of function separation type generally comprising a charge generating material for generating an electric charge by irradiation with light, and a charge transferring material for conveying the generated charge. The Patent Abstracts of Japan, Vol. 14, No. 8 (P-987) (3951), January 10, 1990 concerning JP-A-1-257959 discloses an electrophotographic body composed of a bis-azo pigment as the charge generating material. A charge transferring layer comprises two different types of benzidine derivatives. As the charge generating material used in another electrophotosensitive material, a specific bis-azo pigment is disclosed in the U.S.Patents 5,041,349 and 4,999,269. This bis-azo compound is expressed in the following Formula (1): where A 1 and A 2 are same or different, coupler residues, R 1 denotes a hydrogen atom, an alkyl group, an aryl group or a heterocyclic group, and the alkyl group, the aryl group and the heterocyclic group may have a substituent, and n is 0 or 1. This bis-azo pigment (1) is stable when exposed to heat and light, possesses a high charge generation efficiency, and is high in sensitivity and excellent in repeatability. To prepare an organic photosensitive material of function separation type using charge generating material and charge transferring material, it is necessary to select materials superior in matching and materials which satisfy all electrophotographic properties including the sensitivity, potential retaining performance, potential stability, and residual potential. For example, even if the charge generating material sufficiently generates an electric charge, satisfactory electrophotograhic properties are not obtained unless combined with a charge transferring material capable of injecting and conveying the charge efficiently. According to the preceding U.S. patents, by combining the bis-azo pigment expressed in Formula (1) with various charge transferring materials (carrier moving substances), it is found that photosensitive materials stable in heat and light are obtained. However, the charge generating materials disclosed in the U.S. patents are, as compared with the ordinary charge generating materials such as phthalocyanine or perylene pigment, fluorene type bis-azo pigment (Japanese Unexamined Patent Publication JP-A-57-96345), or oxadiazole type azo pigment possessing a coupler having perinone skeleton (Japanese Unexamined Patent Publication JP-A-59-229564), easier to oxidize and deteriorate in ozone, nitrogen oxide NOx and light in the copying machine, and the photosensitive material characteristics are easily lowered. The oxidation and deterioration of such bis-azo pigment (1) may be considered to be due to decomposition of the azo group by adsorption of ozone on the azo group. Such oxidation and deterioration will be promoted when the bis-azo compound (1) is used in combination with the charge transferring material which is an electron donor compound. It is considered because the electron donor compound is oriented on the azo group when the basicity of the electron donor compound is strong, and the electron density in the azo group is intensified so as to be vulnerable to the attacks of ozone or nitrogen oxides. Therefore, it was hitherto impossible to obtain a photosensitive material possessing a high sensitivity and an excellent repeatability without sacrificing the superior characteristics of the bis-azo pigment (1). Yet, although matching of charge generating material and charge transferring material is satisfactory, if there is a problem in the properties of the binding resin for composing the photosensitive layer by coupling these materials, a photosensitive material comprehensively excellent in electrophotographic properties cannot be obtained. For example, if the strength of the photosensitive layer is not enough or if the adhesion of the photosensitive layer to the base is not sufficient, the surface may be flawed or the photosensitive material may be peeled off due to physical impact received from the cleaning blade pressed to the photosensitive material surface in the image forming apparatus, a felt preventive the toner splash, a charging roller, a transfer roller and other members, or paper contacting with the surface of the photosensitive material at the time of image formation. Therefore, despite excellent sensitivity, a spotless excellent image is not obtained, and despite excellent repeatability, sufficient durability is not obtained. As the binding resin, various high polymers disclosed in the foregoing U.S. patents, such as polystyrene, (meth)acrylic ester, polycarbonate, polyester, butyral resin, and epoxy resin, are generally used. In the Japanese Unexamined Patent Publication JP-A-57-4051, polycarbonate is disclosed as a material excellent in film forming capability and capable of forming a tough photosensitive layer superior in resistance to abrasion. However, the polycarbonate does not adhere well to the conductive substrate or base layer, and hence a certain pretreatment is needed prior to layer forming in order to improve the adhesion, which leads to problems in productivity and cost. In the Japanese Unexamined Patent Publications JP-A-61-132954 and JP-A-2-236555, derivatives of polycarbonate having silicon introduced in the main chain are used as the binding resin, but these derivatives, same as the ordinary polycarbonate, are not sufficient in adhesion. In order to eliminate the defects of the polycarbonate and improve the adhesion of the photosensitive layer, the Japanese Unexamined Patent Publication JP-A-59-71057 discloses a blend of polycarbonate, and the Japanese Unexamined Patent Publication JP-A-62-212660 discloses a blend of polyester or polyallylate. In these polymers, however, the main chain is stiff, and the ester bond responsible for adhesion does not act sufficiently on the base such as the conductive substrate. Hence, it is necessary to add a large content to enhance the adhesion, which may lead to lowering of sensitivity of the photosensitive material as the polar group (the electron aspirating group) in the molecule works as a carrier trap, or promotion of photo-oxidation deterioration of the charge generating material and charge transferring material in the high electric field. In particular, the bis-azo pigment (1) is a molecule not having planeness like the conventional phthalocyanine or perylene pigment, and is high in dissolution in solvent. The rate of dispersion of one molecule each in the photosensitive layer is relatively high, and hence it is more vulnerable to photo-oxidation deterioration as compared with conventional pigments dispersed in the photosensitive layer as fine particles composed of multiple molecules. Accordingly, the polyester-carbonate or the like cannot be blended in a large quantity, and the adhesion of the photosensitive layer cannot be enhanced sufficiently. It was therefore impossible to obtain a photosensitive material possessing high sensitivity and repeatability without sacrificing the excellent characteristics of the bis-azo pigment (1). It is a main object of the invention to present an improved electrophotosensitive material high in sensitivity and excellent in durability, by using the bis-azo pigment expressed in Formula (1) as the charge generating material. It is further object of the invention to present an improved electrophotosensitive material having a photosensitive layer containing the bis-azo pigment expressed in Formula (1) and possessing a high strength and adhesion. According to the present invention, an electrophotosensitive material is provided as defined in claim 1. The electrophotosensitive material is formed as a photosensitive layer containing the bis-azo pigment expressed in Formula (1) as the charge generating material and a diamine compound expressed in Formula (2): (where R 2 , R 3 , R 4 , R 5 , R 6 , R 7 are same or different, an alkyl groups, an alkoxy groups, a halogen atoms, an aryl groups, a nitro groups, a cyano groups, or an alkylamino groups, p and q are integers of 0 to 3, and k,l, m, and o are integers of 0 to 2) as the charge transferring material. It is disposed on a conductive substrate and exhibits high sensitivity and high repeatability, without sacrificing the excellent characteristics of the bis-azo pigment (1). That is by combining the above specific charge generating material with the charge transferring material, it becomes stable against oxidation and deterioration by ozone, nitrogen oxides and light, so that the sensitivity and repeatability (durability) may be outstandingly improved as compared with the conventional electrophotosensitive material. The action by the combination of the charge generating material and charge transferring material in the invention as defined in claim 1 is not fully clarified, but the suppressing action on the oxidation and deterioration induced by ozone, nitrogen oxides or the like may be estimated as follows. The diamine compound (2) used as the charge transferring material is advanced in the non-localization of electrons, and the coordination into the azo group of the bis-azo pigment (1) is impeded by the stereo obstacle by enclosure of nitrogen atoms with phenyl groups, and hence the electron density of the azo group is not increased, so that it is estimated to be less vulnerable to attacks of ozone or the like. In addition, the bis-azo pigment (1) possesses a high charge generating efficiency and a high sensitivity. The diamine compound (2) is closely related with the bis-azo pigment (1) in ionization potential, and also being excellent in light fastness and durability and the mobility less dependent on the electric field intensity. Accordingly, these characteristics are not decreased, and an optimum combination is realized, so that the high performance of the electrophotosensitive material may be expressed. The ionization potential of the bis-azo pigment (1) is 5.7 to 5.9 eV, and the diamine compound (2) is 5.4 to 5.7 eV (as measured by model AC-1 of Riken Kiki Co.), and therefore in the combination their difference may be within about 0.3 eV, such that the barrier on the hole injection from the bis-azo pigment (1) is easy, and the repeatability is improved. By contrast, if the difference of ionization potential of the two is too large, the hole injection from the pigment to the diamine compound (2) in the charging state (dark state) is very easy, so that the charging capability may be lowered. In addition to the bis-azo pigment (1), other pigments and diamine compound (2) as defined in claim 1, it is preferred to include a hydrazone compound expressed in Formula (3): (where R 8 is an alkyl group or an aryl group which may possess a substituent, R 9 and R 10 are the same or different, alkyl groups, alkoxy groups, halogen atoms, aryl groups, nitro groups, cyano groups, or alkylamino groups), a fluorene compound expressed in Formula (4): (where R 11 and R 12 are the same or different, hydrogen atoms, halogen atoms, alkoxy groups or alkyl groups, R 17 and R 18 are the same or different, hydrogen atoms, alkyl groups or halogen atoms), and a diphenoquinone derivative expressed in Formula (5): (where R 13 , R 14 , R 15 and R 16 are the same or different, alkyl groups, alkoxyl groups, aryl groups or aralkyl groups). That is, the diamine compound (2) is dependent on temperature, and it tends to lower in sensitivity when the temperature rises, but the hydrazone compound expressed in Formula (3) is effective for improving the temperature dependence of the diamine compound (2). This is because the hydrazone compound (3) is low in mobility but small in temperature dependence, and also does not act as a trap in charge transferring as the ionization potential is close to the value of the diamine compound (2). On the other hand, the hydrazone compound (3) is likely to isomerize optically to deteriorate, and as the optical excitation quenching agent of the hydrazone compound (3), the fluorene compound expressed by Formula (4) is added. The fluorene compound (4) also acts as a charge transferring material. The diphenoquinone derivative expressed in Formula (5) acts to decrease the electrons accumulated in the photosensitive layer and improve the repeatability. However, if the diphenoquinone derivative (5) is added more than a specific content, it hardly contributes to the charge transferring. To the contrary, it forms a trap of charge by interaction with the fluorene compound (4) having the ionization potential of 6 eV or more, thereby lowering the sensitivity. In other embodiment of the invention, it is preferred to use the same diphenoquinone derivative as in Formula (5). That is, in this embodiment, different from the foregoing embodiment, the diphenoquinone derivative expressed in Formula (5) is used alone. However, the diphenoquinone derivative (5) must be added more than in the foregoing embodiment. This diphenoquinone derivative (5) possesses the ultraviolet ray shielding effect having the absorption near 450 nm. On the other hand, the bis-azo pigment (1) can be used for PPC (using the light source with visible rays such as halogen fluorescent lamp), but when compared with other pigments such as phthalocyanine and perylene carboxylic diimide, the light fastness (photo-oxidation ozone property, toughness) is weak, and decomposition is promoted by ultraviolet light, and accordingly by adding the diphenoquinone derivative (5), it is more effective for stabilization of the photosensitive material, that is, resistance to photo-oxidation deterioration and improvement of repeatability by decrease of trap. When used in a high speed copying machine with the printing speed of 40 to 50 sheets/min, a photosensitive material is exposed to severe environments of use, such as ozone and nitrogen oxides produced in the machine. Also, a greater quantity of light is required, and therefore a further improvement of durability against ozone and nitrogen oxides is demanded. It is therefore preferred to add at least one type selected from stabilizing agents I to IX in the following combinations. Stabilizing agent I A combination of an amine antioxidant which is a polyester oligomer, expressed in Formula (6): where Y 1 and Y 2 are the same or different, alkylene groups, R 20 R 21 , R 22 , R 23 are the same or different, hydrogen atoms or alkyl groups, R 24 is a hydrogen atom, an aralkyl group or an aryl group, and r is an integer of 3 to 40, and a phenolic antioxidant expressed in Formula (7-a) or (7-b): where either one or both of R 25 and R 26 are tert-butyl groups, tert-amyl groups, or α, α-dimethylbenzylphenyl groups, and when one is tert-butyl group, tert-amyl group or a, a-dimethylbenzylphenyl group, the other is a hydrogen atom or an alkyl group, and R 27 is a hydrogen atom, an alkyl group or a halogen atom. Stabilizing agent II A combination of the amine antioxidant which is the polyester oligomer expressed in Formula (6), and a benzotriazole ultraviolet ray absorber of Formula (9): where R 34 , R 35 , R 36 , R 37 and R 38 are the same or different, hydrogen atoms, halogen atoms, hydroxyl groups, alkyl groups, aralkyl groups or alkoxy groups, and the alkyl groups, aralkyl groups and alkoxy groups may possess substituents. Stabilizing agent III A combination of the amine antioxidant which is the polyester oligomer expressed in Formula (6), and an amine antioxidant expressed in Formula (8-b): where R 45 , R 46 , R 47 , R 48 and R 49 are the same or different, hydrogen atoms or alkyl groups. Stabilizing agent IV A combination of the amine antioxidant which is the polyester oligomer expressed in Formula (6), a spiro type amine antioxidant expressed in Formula (8-a): where Z 1 , Z 2 and Z 3 are hydrogen atoms or monovalent organic groups, R 28 , R 29 , R 30 and R 31 are the same or different, hydrogen atoms or alkyl groups, R 32 and R 33 are the same or different, hydrogen atoms, alkyl groups, halogen atoms or hydroxyl groups, and the benzotriazole ultraviolet ray absorbent expressed in Formula (9). Stabilizing agent V A combination of the amine antioxidant which is the polyester oligomer expressed in Formula (6), the spiro type amine antioxidant expressed in Formula (8-a), and a phenol antioxidant expressed in Formula (7-e): where R 41 and R 42 are the same or different, hydrogen atoms, alkyl groups, cyclohexyl groups or dimethylbenzylphenol groups, E is a group: (where R 56 is a hydrogen atom or alkyl group), and Y 6 is an alkylene group, an alkylenecarbonyloxyalkyl group, or an alkyleneoxycarboxyalkyl group. Stabilizing agent VI A combination of the amine antioxidant which is the polyester oligomer expressed in Formula (6), the spiro type amine antioxidant expressed in Formula (8-a), and a phenol antioxidant expressed in Formula (7-d): where R 41 and R 42 are the same as above, Y 4 is an alkylene group, and Y 5 is an alkylene group or an alkylene glycol residue. Stabilizing agent VII A combination of the amine antioxidant which is the polyester oligomer expressed in Formula (6), the spiro type amine antioxidant expressed in Formula (8-a), and a phenol antioxidant expressed in Formula (7-c): where R 41 and R 42 are the same as above, and Y 3 is an alkylene group. Stabilizing agent VIII A combination of the amine antioxidant which is the polyester oligomer expressed in Formula (6), the spiro type amine antioxidant expressed in Formula (8-a), and a piperidine antioxidant expressed in Formula (10): where R 50 and R 51 are the same or different, hydrogen atoms, alkyl groups, cyclohexyl groups or dimethyl benzyl phenyl groups, R 52 , R 53 , R 54 and R 55 are the same or different, hydrogen atoms or alkyl groups, and Y 7 , Y 8 and Y 9 are the same or different, alkylene groups. Stabilizing agent IX A combination of the amine antioxidant which is the polyester oligomer expressed in Formula (6), the spiro type amine antioxidant expressed in Formula (8-a), and the phenol antioxidant expressed in either Formula (7-a) or (7-b). In the combination of stabilizing agent IV, meanwhile, the phenol antioxidant expressed in Formula (7-e) or the phenol antioxidant expressed in Formula (7-d) may be further combined. These stabilizing agents are intended to provide resistance to oxidation deterioration caused by ozone, nitrogen oxides and light. Since the amine antioxidant (3) is of oligomer type and has a relatively high molecular weight, bleeding (oozing) on the surface of the photosensitive material is suppressed. The other compounds such as phenol antioxidants (7-a), (7-b), spiro type amine antioxidant (8-a), and benzotriazole ultraviolet absorber (9) are low in molecular weight, and are characterized by smooth bleeding on the surface. Therefore, by combining these antioxidants, the antioxidants such as the phenol antioxidants (7-a), (7-b) and the ultraviolet absorber are much dispersed on the surface of the photosensitive layer, while the amine antioxidant (3) is dispersed inside. Therefore if the surface of the photosensitive layer is worn out and peeled off by long use, the antioxidation effect is not spoiled. At the same time, since the amine antioxidant (3) is an oligomer having an ester bond, it is excellent in adhesion for forming the photosensitive layer. The preferred binding resin includes polycarbonate and polyester possessing repetitive units expressed in Formula (50): where either one of A 3 and A 4 is a bivalent group containing at least an aromatic ring in the main chain, and the other is a bivalent group not containing aromatic ring in the main chain. By combining the above specific charge generating material, charge transferring material and binding resin, it is possible to form a photosensitive layer that is stable against oxidation and deterioration by ozone, nitrogen oxides and light, excellent in adhesion to the base such as conductive substrate, and is tough, so that the sensitivity and repeatability (durability) may be outstandingly improved as compared with the conventional electrophotosensitive material. The action by the combination of the charge generating material, charge transferring material and binding resin in the invention is not fully clarified, but the suppressing action on the oxidation and deterioration induced by ozone, nitrogen oxides or the like may be estimated as follows. The diamine compound (2) used as the charge transferring material is advanced in the non-localization of electrons, and the coordination of the bis-azo pigment (1) into the azo group is impeded by the stereo hindrance by enclosure of nitrogen atoms with phenyl groups. Hence the electron density of the azo group is not increased, so that it is estimated to be less vulnerable to attacks of the acid (acceptor) group of the polyester (50) or ozone. Also, due to the suppressing action on oxidation and deterioration induced by ozone and nitrogen oxide, it is possible to lower the amount of the polyester (50) as compared with the conventional material. In addition, the bis-azo pigment (1) possesses a high charge generating efficiency and a high sensitivity, and the diamine compound (2) is closely related with the bis-azo pigment (1) in ionization potential, and also being excellent in light fastness and durability and the mobility less dependent on the electric field intensity. These characteristics are not decreased, and an optimum combination is realized, so that the high performance of the electrophotosensitive material is obtained. In addition, the polyester (50) is flexible in the main chain as compared with the conventional material, and the ester bond portion contributing to the adhesion acts sufficiently on the base, so that the adhesion of the photosensitive layer may be enhanced by adding at a small amount. Hence, without lowering the sensitivity of the photosensitive material or promoting the photo-oxidation deterioration of the azo group of the bis-azo pigment (1), the adhesion of the photosensitive layer made of polycarbonate having a tough property may be enhanced. The electrophotosensitive material of the invention is characterized by disposing, on a conductive substrate, a photosensitive layer containing the bis-azo pigment expressed in Formula (1) and at least one further pigment as defined in claim 1. One such material is a perylene pigment expressed in Formula (51): where R 70 , R 71 , R 72 and R 73 are the same or different, hydrogen atoms, alkyl groups, alkoxyl groups or aryl groups, as charge generating materials. By using the perylene pigment expressed in Formula (51) in the mixture of the bis-azo pigment expressed in Formula (1), a gelation (coagulation) phenomenon which is generated during preservation of the coating liquid for the photosensitive layer which is in a single dispersion state is effectively prevented, and therefore the stability of the coating liquid is improved. It is assumed that the gelation phenomenon is generated by associating the bis-azo pigments to each other by hydrogen bonds. On the contrary, when mixing the bis-azo pigment (1) with the perylene pigment (51), the association mentioned above is prevented in view of the molecular structures, thereby improving the stability of coating liquid. Also, the combination of the bis-azo pigment (1) and the perylene pigment (51) results in remarkably lowering the residual potential and remarkable improvements of the repeatability. Therefore an electrophotosensitive material excellent in sensitive property and durability is obtained. Instead of the perylene pigment or together with perylene pigment, at least one type selected from the group consisting of anthanthrone pigment, X-type metal-free phthalocyanine pigment, imidazole perylene pigment, and a perylene bis-azo pigment is used. The alkyl group used in the invention may include, for example, methyl group, ethyl group, propyl group, isopropyl group, butyl group, t-butyl group, pentyl group, hexyl group, and other alkyl group having 1 to 6 carbon atoms. Examples of aryl group include, among others, phenyl group, o-terphenyl group, naphthyl group, anthryl group, and phenanthryl group. Examples of heterocyclic groups include thienyl group, pyrrolyl group, pyrrolinidyl group, oxazolyl group, iso-oxazolyl group, thiazolyl group, isothiazolyl group, imidazolyl group, 2H-imidazolyl group, pyrazolyl group, triazolyl group, tetrazolyl group, pyranyl group, pyridyl group, piperidyl group, piperidino group, 3-morphorinyl group, morphorino group, and thiazolyl group. Also, a heterocyclic group condensed with an aromatic ring may be used. The substituents that may substitute for the above groups include, for example, halogen atom, amino group, hydroxyl group, carboxyl group that may be esterified, cyano group, alkyl group with 1 to 6 carbon atoms, alkoxy group with 1 to 6 carbon atoms, and alkenyl group with 2 to 6 carbon atoms that may possess an aryl group. The coupler residues expressed in A 1 and A 2 may include, for example, the groups expressed in Formulae (a) to (g). In these formulae, R 60 denotes carbamoyl group, sulfamoyl group, allophanoyl group, oxamoyl group, anthraniloyl group, carbazoyl group, glycyl group, hidantoyl group, phthalamoyl group, and succinamoyl group. These groups may possess halogen atom, phenyl group that may possess substituent, naphthyl group that may possess substituent,and other substituents such as nitro group, cyano group, alkyl group, alkenyl group, carbonyl group, and carboxyl group. R 61 represents an atomic group necessary for forming an aromatic ring, polycyclic hydrocarbon or heterocyclic ring by condensing with a benzene ring possessing R 60 and hydroxyl group, and these rings may possess the same substituents as mentioned above. R 62 denotes an oxygen atom, a sulfur atom, or an imino group. R 63 denotes a divalent cyclic hydrocarbon group or a divalent aromatic hydrocarbon group, and these groups may possess the same substituents as mentioned above. R 64 denotes an alkyl group, an aralkyl group, an aryl group or a heterocyclic group, and these groups may possess the same substituents as mentioned above. R 65 denotes a divalent cyclic hydrocarbon group, a divalent aromatic hydrocarbon group or an atomic group necessary for forming a heterocyclic ring together with the portion expressed in formula (h): in the above formula (e), and the formed ring may possess the same substituents as mentioned above. R 66 represents hydrogen atom, alkyl group, amino group, carbamoyl group, sulfamoyl group,allophanoyl group, carboxyl group, ester of carboxyl group, aryl group, or cyano group, and the groups except for the hydrogen atom may possess the same substituents as mentioned above. R 67 denotes an alkyl group or an aryl group, and these groups may possess the same substituents as mentioned above. In R 61 , meanwhile, as the atomic group necessary for forming an aromatic ring by condensing with the benzene ring possessing R 60 and hydroxyl group, for example, methylene group, ethylene group, propylene group, butylene group, and other alkylene groups may be listed. Examples of the aromatic ring formed by condensation of R 61 with the benzene ring possessing R 60 and hydroxyl group include naphthalene ring, anthracene ring, phenanthrene ring, pyrene ring, chrysene ring, and naphthasene ring. In R 61 , examples of the atomic group necessary for forming the polycyclic hydrocarbon by condensing with the benzene ring possessing R 60 and hydroxyl group include methylene group, ethylene group, propylene group, butylene group,and other alkylene group with 1 to 4 carbon atoms. In R 61 , the polycyclic hydrocarbon formed by condensing with the benzene ring possessing R 60 and hydroxyl group may be, for example, carbazole ring, benzocarbazole ring and dibenzofurane ring. In R 61 , the atomic group necessary for forming the heterocyclic ring by condensing with the benzene ring possessing R 60 and hydroxyl group may be, for example, benzofuranyl group, benzothiophenyl group, indolyl group, 1H-indolyl group, benzoxazolyl group, benzothiazolyl group, 1H-indadolyl group, benzoimidazolyl group, chromenyl group, chromanyl group, isochromanyl group, quinolinyl group, isoquinolinyl group, cinnolinyl group, phthalazinyl group, quinazolinyl group, quinoxalinyl group, dibenzofuranyl group, carbazolyl group, xanthenyl group, acridinyl group, phenantridinyl group, phenadinyl group, phenoxadinyl group, and thiantrenyl group. Examples of the aromatic heterocyclic group formed by condensation of R 61 with the benzene ring possessing R 60 and hydroxyl group include thienyl group, furyl group, pyrrolyl group, oxazolyl group, iso-oxazolyl group, thiazolyl group, isothiazolyl group, imidazolyl group, pyrazolyl group, trazolyl group, tetrazolyl group, pyridyl group, and thiazolyl group. Moreover, heterocyclic groups condensed with other aromatic rings (for example, benzofuranyl group, benzoimidazolyl group, benzoxazolyl group, benzothiazolyl group, and quinolinyl group) may be also used. In R 63 and R 65 , as examples of the divalent cyclic hydrocarbon gorup, ethylene group, propylene group, and butylene group may be listed, and examples of divalent aromatic hydrocarbon gorup include phenylene group, naphthylene group, and phenantrilene group. In R 64 , as the heterocyclic group, for example, pyridyl group, pyradyl group, thienyl group, pyranyl group, indolyl group and others may be used. In R 65 , the atomic group necessary for forming the heterocyclic ring together with the portion expressed in Formula (h) is, for example, phenylene group, naphthylene group, phenantrilene group, ethylene group, propylene group, and butylene group. Examples of the aromatic heterocyclic ring formed by R 65 and the portion expressed in Formula (h) include benzimidazole, benzo[f]benzimdazole, dibenzo [e,g]benzimidazole, and benzopyrimidine. These rings may possess the same substituents as mentioned above. In R 66 , as the ester of carboxyl group, methylester, ethylester, propylester, and butylester are known among others. Practical examples of the coupler residues A 1 , A 2 expressed in Formulae (a) to (g) include the following groups. Practical examples of the bis-azo compound (1) include the compounds expressed in Formulae (B1) to (B10) below. In the electrophotosensitive material of the present invention providing, on the conductive substrate, the photosensitive layer containing the bis-azo pigment of Formula (1) and the diamine compound of Formula (2), it is preferred that the bis-azo pigment (1) is used in the form of fine particles having a particle diameter of -0.5 µ m or less. Specifically, the bis-azo pigment (1) is added to a coating liquid for the photosensitive layer, after finely pulverizing to the particle diameter of 0.5 µ m or less. The bis-azo pigment acts as a n-type pigment to have a electron-transfer capacity. Therefore, by containing the finely pulverized bis-azo pigment, the distance of the pigments from each other is shortened, thereby to increase the photoconductivity. As a result, the initial sensitivity, repeatability and image quality are improved, and image defects such as fogs are decreased. Besides, it is preferred that the bis-azo pigment of Formula (1) used in the combination with the diamine compound of Formula (2) being the charage transferring material is preferably used in the mixture of 2 types thereof or more. As a result, a gelation (coagulation) phenomenon which is generated during preservation of the coating liquid for the photosensitive layer which is in a single dispersion state is effectively prevented, and therefore the stability of the coating liquid is improved. It is assumed that the gelation phenomenon mentioned above is generated by, for example, associating the bis-azo pigments to each other with hydrogen bonds. On the contrary, when mixing 2 types or more of the bis-azo pigment which are similar structures to each other, the association mentioned above is prevented in view of the molecular structures, thereby improving the stability of coating liquid. Also, the combination of 2 types or more of the bis-azo pigments similar to each other in electron state results in improvements of the charge stability and the sensitive stability in the time of printing, without lowering the initial sensitivity. In the diamine compound expressed in Formula (2), as the alkyl group and the aryl group corresponding to R 2 through R 7 in the formula, for example, the same group as shown in Formula (1) may be used. Examples of the halogen atom include chlorine, iodine, bromine and fluorine. Examples of the alkoxyl group include methoxy group, ethoxy group, isopropoxy group, butoxy group, t-butoxy group, and hexyloxy group. Examples of the alkylamino group include methylamino group, dimethylamino group, ethylamino group, diethylamino group, propylamino group, isopropylamino group, butylamino group, isobutylamino group, t-butylamino group, pentylamino group, and hexylamino group. Practical compounds of the diamine compound expressed in Formula (2) include, for example, those shown in Nos. Al to A15 in Table 1. In the table, for example, " 3-CH 3 " means that the methyl group is bonded at the 3-position of the phenyl group, and "3,5-CH 3 " means that the methyl group is bonded at the 3- and 5-positions of the phenyl group. The diamine compound (2) can be synthesized in various methods, and, for example, it may be manufactured by simultaneously or sequentially reacting the compound expressed in Formula (40) with the compounds expressed in Formulae (41) to (44). where R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , k, l, m, n, o, p and q are the same as defined above, and X denotes a halogen atom. The reaction between the compound expressed in Formula (40) and the compounds expressed in Formulae (41) through (44) is performed usually in an organic solvent. As the organic solvent, any solvent may be used herein so far as not to affect the reaction adversely, and examples of such organic solvent include nitrobenzene, dichlorobenzene, quinoline, N,N-dimethylformamide, N-methylpyrrolidone, and dimethylsulfoxide. The reaction proceeds usually at a temperature of 150 to 250 °C in the presence of copper powder, copper oxide, copper halide, or other catalysts, or sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, or other basic substance. The compound expressed in Formula (2) possessing a symmetrical structure can be prepared by controlling the substitution positions of the substituents R 2 , R 3 , R 4 , and R 5 . For example, the compound expressed in Formula (46) is obtained by the reaction of the compound expressed in Formula (45) with the compounds expressed in Formulae (41) and (43), and by hydrolyzing the compound expressed in Formula (46) to conduct deacylation, the compound expressed in Formula (47) is obtained, and it is reacted with the compounds expressed in Formulae (42) and (44), thereby manufacturing the object compound. where R 8 and R 9 denote alkyl groups, and R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , k, l, m, n, o, p and q are the same as defined above. The reaction between the compound expressed in Formula (45) and the compounds expressed in Formulae (41), (43) is performed the same as the reaction between the compound expressed in Formula (40) and the compounds expressed in Formulae (41), (42), (43) and (44). The deacylation by hydrolysis of the compound expressed in Formula (46) is carried out in the conventional manner in the presence of a basic catalyst. The reaction between the compound expressed in Formula (47) and the compounds expressed in Formulae (42) and (44) is performed the same as the reaction between the compound expressed in Formula (40) and the compounds expressed in Formulae (41), (42), (43), (44). After termination of the reaction, the reaction mixture is concentrated, and may be easily separated and refined by the conventional means, such as recrystallization, solvent extraction and column chromatography. Practical compounds of the hydrazone compounds expressed in Formula (3) include N-propyl-3-carbazolyl aldehyde N,N-diphenyl hydrazone, N-butyl-3-carbazolyl aldehyde N,N-diphenyl hydrazone, N-isobutyl-3-carbazolyl aldehyde N,N-diphenyl hydrazone, N-tert-butyl-3-carbazolyl aldehyde N,N-diphenyl hydrazone, N-pentyl-3-carbazolyl aldehyde N,N-diphenyl hydrazone, and N-hexyl-3-carbazolyl aldehyde N,N-diphenyl hydrazone, among others, and more specifically those shown in Formulae (C1) to (C12) may be used. This hydrazone compound (3) may be added approximately at a rate of 10 to 200 parts by weight to 100 parts by weight of the diamine compound (2). Practical compounds of the fluorene compound expressed in Formula (4) include, for example, the compounds expressed in Nos. (D1) to (D11) in Table 2 below. This fluorene compound (4) may be added at a rate of about 5 to 100 parts by weight to 100 parts by weight of the hydrazone compound (3). Practical compounds of diphenoquinone derivative expressed in Formula (5) may include, for example, those expressed in Formulae (E1) to (E7) below. The diphenoquinone derivative (5) is, when combined with the hydrazone compound (3) and fluorene compound (4), added at a rate of 2 to 50 parts by weight to 100 parts by weight of the fluorene compound (4), and if exceeding this range, traps are formed by interaction with the fluorene compound (4) having the ionization potential of 6 eV or more, which may lead to lowering of sensitivity. On the other hand, when the diphenoquinone derivative (5) is used alone, it must be added more than in the case of combined use, and usually it is added at a rate of 10 parts by weight or more, preferably 15 to 100 parts by weight to 100 parts of the diamine compound (2). The reducing potential of the diphenoquinone derivative contained in the photosensitive layer is desired to be in a range of -0.5 to -1.2 V. As a result, the stability to light is improved, and the lowering tendency of surface potential in repetitive exposure may be notably suppressed, and it may be preferably applied particularly to the single layer-type organic photosensitive material. The reducing potential refers to the value determined in the following measuring method. Reducing potential measuring method As the measuring solvent, 0.1 mole of electrolyte (tert-butyl ammonium perchlorate), 0.1 mole of measuring objective material (each acceptor), and 1 liter of solvent (dichloromethane) were blended, and measured by the cyclic voltammetry of three-electrode type [glassy carbon electrode as working electrode, platinum electrode as counter electrode, and silver-silver nitrate electrode (0.1 mole/liter AgNO 3 -acetonitrile solution) as reference electrode]. The diphenoquinone derivative possessing such reducing potential acts to effectively suppress lowering of the surface potential in exposure repetition only by adding at a small amount in the photosensitive layer, but generally it is preferred to add the diphenoquinone derivative at a rate of 0.1 to 10 parts by weight, more preferably 0.25 to 1 part by weight to 1 part by weight of the charge generating material. The action of the diphenoquinone derivative possessing a specific reducing potential is as follows. First, using the bis-azo pigment (1) as the charge generating material, it is combined with the charge transferring material, so that an excellent sensitivity (charge generating capability) is exhibited, while the residual potential is at a low level. When the diphenoquinone derivative is contained in the photosensitive layer containing this bis-azo pigment (1), lowering of surface potential in exposure repetition may be notably suppressed without spoiling the excellent sensitivity of the bis-azo pigment (1). That is, the photosensitive layer containing the bis-azo pigment (1) is, characteristically, high in sensitivity with the half-life light exposure (E 1/2 ) of 1.23 lux-sec., and relatively low in the residual potential at 68 V, but after repeating 1,000 times of exposure, as compared with the surface potential after the first exposure, the surface potential may be lowered by as much as -315 V. By contrast, when the diphenoquinone derivative is blended in the photosensitive layer, it is possible to suppress the lowering of the surface potential after 1,000 times of exposure to -120 V or less, while maintaining the excellent sensitivity and low residual potential by the bis-azo pigment (1). It is important that the reducing potential of the diphenoquinone derivative is in a range of -0.5 to -1.2 V, and when the reducing potential is lower than -1.2 V or higher than -0.5 V, it is difficult to suppress the lowering of the surface potential after 1,000 exposures. Generally, the tendency of lowering of the surface potential of the photosensitive layer by repetitions of exposure is recognized, for example in the positively charged photosensitive layer, to be due to residue of the electrons of the opposite charging polarity in the photosensitive layer, especially by trapping in the pigment, and deterioration of the photosensitive material constituent material by attack of active gas due to activation by repetitive exposure or further by corona discharge. On the other hand, the specific diphenoquinone derivative used in the invention acts effective as the an electron acceptor to eliminate the trapped electrons in the photosensitive layer and also as a quencher for the photosensitive layer illuminated with light, thereby suppressing the lowering of the surface potential in repetitive exposures. The diphenoquinone derivative to be used possesses a quinone-type oxygen atom excellent in electron acceptability at both ends of the molecular chain, and is structurally characterized by possessing a double bond in the conjugate relation over the entire molecular chain. As a result, it is easy to move electrons within the structure and easy to exchange electrons, which is regarded to be related with the excellent results above. In addition, the fact that the reducing potential is within a specific range seems to contribute to ease of exchange of electrons. The diphenoquinone derivative possessing such reducing potential is, specifically, ones that R 13 , R 14 , R 15 and R 16 in Formula (5) are the same and different, an alkyl group, alkoxyl group or aryl group, two of the groups out of R 13 , R 14 , R 15 and R 16 possess a greater number of carbon atoms than the other two groups, and the reducing potential is within the specified range mentioned above. When the group having the greater number of carbon atoms is an alkyl group having 4 or more carbon atoms, the other group is desired to be an methyl group. When the group with the greater number of carbon atoms is an aryl group; the other group is desired to be an alkyl group with 4 or less carbon atoms. Such diphenoquinone derivative is excellent in solubility to the solvent as compared with the unreplaced material, and it is easy to blend into the photosensitive layer. On the photosensitive layer, it is desired to add, as a stabilizer, the amine antioxidant which is a polyester oligomer expressed in Formula (6), and at least one phenol antioxidant selected from those expressed in Formulae (7-a), (7-b), (7-c), (7-d) and (7-e). In Formulae (7-c), (7-d), and (7-e), as the alkylene group, for example, methylene group, ethylene group, propylene group, tetramethylene group, pentamethylene group, and hexamethylene group may be used. As the alkylene glycol residue in Formula (7-d), for example in the form of -Y 5 -Y 5 -, triethylene glycol residue, tripropylene glycol residue, tetraethylene glycol residue, and pentaethylene glycol residue may be used, among others. As the alkylene carbonyl oxyalkyl group of Formula (7-e), for example, methylene carbonyl oxymethyl group, ethylene carbonyl oxypropyl group, butylene carbonyl oxymethyl group, hexamethylene carbonyl oxymethyl group, methylene carbonyl oxypropyl group, and pentamethylene carbonyl oxyhexyl group may be used. As the alkylene oxycarbonyl alkyl group of Formula (7-e), examples include methylene oxycarbonyl methyl group, ethylene oxycarbonyl propyl group, butylene oxycarbonyl methyl group, hexamethylene oxycarbonyl methyl group, methylene oxycarbonyl propyl group, and pentamethylene oxycarbonyl hexyl group. These stabilizers are commonly intended to provide with oxidation deterioration resistance to ozone, nitrogen oxide and light. At this time, since the amine antioxidant (6) is of oligomer type and is relatively high in molecular weight, and hence bleeding on the surface of the photosensitive layer is suppressed, while the phenol antioxidants (7-a) to (7-e) are relatively low in molecular weight, and are hence easy to bleed on the surface. Therefore, by combining the both antioxidants, the phenol antioxidants (7-a) to (7-e) are much dispersed on the surface of the photosensitive layer, while the amine antioxidant (6) is much dispersed inside, and therefore if the photosensitive layer surface is worn out after long use, the antioxidation effect is not sacrificed. Moreover, since the amine antioxidant (6) is an oligomer, it is excellent in adhesion for forming the photosensitive layer. The combination of such oligomer type amine antioxidant (6) and the phenol antioxidants (7-a) to (7-e) is desired to be used in the composition of photosensitive layer relating to the combination of, in particular, bis-azo pigment (1), diamine compound (2), hydrazone compound (3), fluorene compound (4),and diphenoquinone derivative (5). Practical compounds of the oligomer type amine antioxidant (6) include, for example, the compounds expressed in Formulae (F1) to (F6) below. The content of the oligomer type amine antioxidant (6) may be usually about 0.5 to 20 parts by weight of 100 parts by weight of the binding resin. Practical compounds of the phenol antioxidants (7-a) , (7-b) include the compounds shown in Formulae (G1) to (G6). Practical compounds of the other phenol antioxidants (7-c) to (7-e) include the compounds expressed in Formulae (G7) to (G30) below. The amounts of the phenol antioxidants (7-a) to (7-e) to be added may be usually about 1 to 30 parts by weight of 100 parts by weight of the binding resin. As other stabilizers, an amine antioxidant expressed in Formula (6), an amine antioxidant expressed in Formula (8-a) or (8-b), and a benzotriazole ultraviolet absorber expressed in Formula (9) may be added to the photosensitive layer. Examples of the aralkyl group include benzyl group, benzhydril group, trityl group and phenetyl group, among others. The action of the oligomer type amine antioxidant (6) and the amine antioxidant (8-a) or (8-b) is same as above. Specifically, the amine antioxidant (8-a) or (8-b) of relatively low molecular weight bleeds and exists much on the surface of the photosensitive layer, while the oligomer type amine antioxidant (6) of relatively high molecular weight is widely present inside of the photosensitive layer, and exhibits the antioxidation effect for a longer period. On the other hand, by the benzotriazole ultraviolet absorber expressed in Formula (9) , the photo-oxidation deterioration of the bis-azo pigment (1) is prevented. This combination is effective particularly for the combination of the bis-azo pigment (1), diamine compound (2) and diphenoquinone derivative (5) mentioned above. That is, in the photosensitive layer composition comprising the combination of the bis-azo pigment (1), diamine compound (2) , hydrazone compound (3), fluorene compound (4), and diphenoquinone derivative (5), the fluorene compound (4) absorbs the light of up to 550 nm, and works to prevent photo-oxidation deterioration of the bis-azo pigment (1), and it is not required to add ultraviolet absorbent, but in the photosensitive layer composition without fluorene compound (4), it is necessary to add an ultraviolet absorber. Of course, the additive of this compound may be also added to the above photosensitive layer composition with fluorene compound (4). The amount of the oligomer type amine antioxidant (6) in this combination is enough at about 0.5 to 20 parts by weight to 100 parts by weight of the binding resin. As practical compounds of the amine antioxidant (8-a), for example, the following compounds expressed in Formulae (H1) to (H6) are employed. As practical compounds of amine antioxidant (8-b), for example, the following compounds expressed in Formulae (H7) to (H13) are employed. The amount of the amine antioxidant (8-a) or (8-b) to be added may be about 0.5 to 20 parts by weight to 100 parts by weight of the binding resin. Practical compounds of benzotriazole ultraviolet absorber (9) include the following examples expressed in Formulae (I1) to (I7). The ultraviolet absorber (9) may be added by about 1 to 4 parts by weight to 100 parts by weight of the binding resin. Besides, as the substitutes for the phenol antioxidants (7-c) to (7-e) and amine antioxidants (8-a), (8-b), the piperidine antioxidant expressed in Formula (10) may be used. That is, this piperidine antioxidant (10) possesses the functions of both amine and phenol, and also has a proper molecular weight, whereby it can be used as a substitute for the phenol antioxidants (7-c) to (7-e) and amine antioxidants (8-a), (8-b). Practical compounds of the piperidine antioxidant of Formula (10) may include the examples of compounds expressed in Formulae (J1) to (J8) below. Below are explained the stabilizing agents I to IX which are preferred combinations of the stabilizer in the invention. The stabilizing agent I is composed of polyester type amine antioxidant (6) and phenol antioxidant (7-a) or (7-b). The content of each component may be the same as defined above. The stabilizing agent II is composed of polyester type amine antioxidant (6) and benzotriazole ultraviolet absorbent (9). The content of each component may be the same as defined above. To enhance the stabilizing effect furthermore, at least one of the following stabilizers may be also added. (1) Phenol antioxidant of Formula (4-a) or (4-b) (2) Phenol antioxidant of Formula (7-c) (3) Phenol antioxidant of Formula (7-d) (4) Phenol antioxidant of Formula (7-e) (5) Piperidine antioxidant of Formula (10) The stabilizing agent III is composed of polyester type amine antioxidant (6) and amine antioxidant (8-b). The content of each component may be the same as defined above. The stabilizing agent IV is composed of polyester type amine antioxidant (6), spiro type amine antioxidant (8-a), and benzotriazole ultraviolet absorber (9). The content of each component may be the same as defined above. The stabilizing agent V is composed of polyester type amine antioxidant (6), spiro type amine antioxidant (8-a), and phenol antioxidant (7-e). The content of each component may be the same as defined above. The stabilizing agent VI is composed of polyester type amine antioxidant (6), spiro type amine antioxidant (8-a), and phenol antioxidant (7-d). The content of each component may be the same as defined above. The stabilizing agent VII is composed of polyester type amine antioxidant (6), spiro type amine antioxidant (8-a), and phenol antioxidant (7-c). The content of each component may be the same as defined above. The stabilizing agent VIII is composed of polyester type amine antioxidant (6), spiro type amine antioxidant (8-a), and piperidine antioxidant (10). The content of each component may be the same as defined above. The stabilizing agent IX is composed of polyester type amine antioxidant (6), spiro type amine antioxidant (8-a), and phenol antioxidants (7-a) and (7-b). The content of each component may be the same as defined above. Other stabilizing agents usable in the invention include the following compounds. These stabilizing agents may be used either alone or in combination with the above stabilizing agents. where R 90 , R 91 , R 92 , R 93 , R 95 , and R 96 denote the same or different, hydrogen atoms, alkyl groups, alkoxy groups, or aryl groups, and Y 10 is an alkylene group. where R 41 , R 42 , and Y 3 are the same as defined above, and R 97 denotes alkyl group, alkenyl group or aryl group. where R 99 , R 100 and R 101 are the same or different, hydrogen atoms, alkyl groups, alkoxy groups or aryl groups, and Y 11 denotes an alkylene group. Examples of the alkenyl group include vinyl group, allyl group, 2-butenyl group, 1-methylallyl group, 2-pentenyl group,and 2-hexenyl group. Examples of the alkyl group, alkoxy group, aryl group and alkylene group are the same as mentioned above. The photosensitive material of the invention may be applied to the photosensitive layer of either single layer-type or multilayer-type. However, the effect by the combination of the charge generating material and charge transferring material is expressed more manifestly in the single layer-type photosensitive layer having the both materials contained in the same layer, in particular. Preferably the electrophotosensitive material is formed as a single layer-type photosensitive layer. To obtain the photosensitive material of single layer type, the photosensitive layer containing the bis-azo pigment (1) as charge generating material, diamine compound (2) as charge transferring material, and binding resin and the like is formed on the conductive substrate by coating or other application means. To obtain the photosensitive material of multilayer-type, the bis-azo pigment (1) alone is evaporated on the conductive substrate to form a charge generating layer, or a charge generating layer containing the bis-azo pigment (1) and binding resin is formed on by coating or other application means, and a charge transferring layer containing the diamine compound (2) and binding resin is formed on this charge generating layer. To the contrary, first the charge transferring layer may be formed on the conductive substrate, then the charge generation layer may be formed. As the charge generating material, aside from the bis-azo pigment (1), other charge generating materials are used as defined in claim 1. In particular, it is effective for extending the sensitivity range of the electrophotosensitive material so as to possess the absorption wavelength region in a desired region. Other charge generating materials include selenium, selenium-tellurium, selenium-arsenic, amorphous silicon, pyririum salt, other azo pigment than defined in Formula (1), perylene pigment, ansanthrone pigment, phthalocyanine pigment, naphthalocyanine pigment, indigo pigment, triphenylmethane pigment, threne pigment, toluidine pigment, pyrazoline pigment, quinacridone pigment, and dithioketopyrolopyrol pigment. In particular, when the perylene pigment expressed in Formula (51) is combined with the bis-azo pigment (1), the residual potential may be notably lowered, while the repeatability is markedly improved, and therefore an electrophotosensitive material excellent in sensitivity characteristic and durability may be obtained. As the alkyl group, alkoxyl group and aryl group in such perylene pigment (51), the same compounds as specified above may be used. As the perylene pigment (51), for example, the following compounds may be used. Together with perylene pigment or instead of perylene pigment, at least one type selected from the group consisting of ansanthrone pigment, X type metal-free phthalocyanine pigment, imidazole perylene pigment, and perylene bis-azo pigment is used. As the ansanthrone pigment, for example, the compound expressed in Formula (52): (where X denotes a halogen atom) is preferably used, and a practical example of the ansanthrone pigment may be a dibromoansanthrone where X is a bromine atom. When the ansanthrone pigment is used together with the bis-azo pigment (1), in particular, the repeatability is improved, and an electrophotosensitive material excellent in durability is obtained. The X-type metal-free phthalocyanine pigment is, when combined with the bis-azo pigment (1), particularly improved in the repeatability, and an electrophotosensitive material excellent in durability is obtained. As the imidazole perylene pigment, for example, the compound expressed in Formula (53): (where R 86 and R 87 are the same or different, hydrogen atoms, alkyl groups, alkoxy groups, or aryl groups) may be used preferably. Practical examples of the ansanthrone pigment include the compounds where R 86 and R 87 are both hydrogen atoms. When the imidazole perylene pigment is used together with the bis-azo pigment (1), the repeatability is particularly improved, and an electrophotosensitive material excellent in durability may be obtained. An example of perylene bis-azo pigment is a compound expressed in Formula (54): (where A denotes a coupler residue exhibited above). When this perylene bis-azo pigment is combined with the bis-azo pigment expressed in Formula (1), the repeatability is particularly improved, and an electrophotosensitive material excellent in durability may be obtained. The photosensitive material of the invention is composed of a photosensitive layer containing, as the charge generating material, one or two or more types of bis-azo pigment expressed in Formula (1), and at least one pigment selected from the group consisting of perylene pigment, ansanthrone pigment, X-type metal-free phthalocyanine pigment, imidazole perylene pigment, and perylene bis-azo pigment. Other pigments to be used in combination with the bis-azo pigment expressed in Formula (1) may be used either alone or in combination of two or more types. The blending rate of the bis-azo pigment expressed in Formula (1) and other pigments is not specifically defined, but it is preferred to blend the bis-azo pigment and other pigments so that the rate of the bis-azo pigment in the total quantity of the charge generating material may be in a range of 10 to 80 % by weight. If the rate of the bis-azo pigment in the total quantity of the charge generating material is less than 10 % by weight, the desired sensitivity is not obtained. If exceeding 80 % by weight, to the contrary, the effect of using the other pigments is insufficient, the residual potential is high, and the change of the surface potential by repeated charging and exposure increases. The diamine compound (2) which is a charge transferring material may be used either alone or in combination with other known charge transferring materials. Examples of known charge transferring materials include various electron-attracting compounds and electron-donating compounds. Electron-attracting compounds include, for example, diphenoquinone derivatives such as 2,6-dimethyl-2,6-di-tert-dibutyldiphenoquinone, malonitrile, thiopyrane compound, tetracyanoethylene, 2,4,8-trinitrothioxanthone, fluorene compounds such as 3,4,5-tetranitro-9-fluorene, dinitrobenzene, dinitroanthracene, dinitroacridine, nitroanthraquinone, dinitroanthraquinone, succinic anhydride, maleic anhydride, and dibromo maleic anhydride. Electron-donating compounds include, for example, oxadiazole compounds such as 2,5-di(4-methylaminophenyl)-1,3,4-oxadiazole, styryl compounds such as 9-(4-diethylaminostyryl) anthracene, carbazole compounds such as polyvinyl carbazole, pyrazoline compounds such as 1-phenyl-3-(p-dimethylaminophenol) pyrazoline, hydrazone compounds other than specified in Formula (3), triphenylamine compound, indole compound, oxazole compound, iso-oxazole compound, thiazole compound, thiadiazole compound, imidazole compound, pyrazole compound, triazole compound, other nitrogen-containing cyclic compounds, and condensation polycyclic compounds. These charge transferring materials are used either alone or in a mixture of two or more types. Incidentally, when the charge transferring material having a film forming property such as polyvinyl carbazole is used, the binding resin is not always required. As the binding resin, various resins may be used, for example, a thermoplastic resin such as styrene polymer, styrene-butadiene copolymer, styrene-acrylonitrile copolymer, styrene-maleic acid copolymer, acrylic copolymer, styrene-acrylic acid copolymer, polyethylene, ethylene-vinyl acetate copolymer, chlorinated polyethylene, polyvinyl chloride, polypropylene, vinyl chloride-vinyl acetate copolymer, polyester alkyd resin, polyamide, polyurethane, polycarbonate, polyallylate, polysulfone, diallyl phthalate resin, ketone resin, polyvinyl butyral resin, polyether resin, polyester resin; a crosslinking thermosetting resin such as silicone resin, epoxy resin, phenol resin, urea resin, melamine resin; and a photosetting resin such as epoxy acrylate, urethaneacrylate. These binding resins may be used alone or in a mixture of two or more types. The combination of the polycarbonate and polyester possessing repetitive unit shown in Formula (50) is preferably used as the binding resin. In the polyester possessing repetitive units expressed in Formula (50), it is necessary that either group A 3 or A 4 contains an aromatic ring in the main chain in the formula, and the other should not contain an aromatic ring in the main chain. If both groups A 3 and A 4 contain aromatic rings, the main chain becomes stiff, and therefore the effect of improvement of adhesion by the carbonyl group is sacrificed. On the other hand, when both groups A 3 and A 4 are free from aromatic ring, compatibility with the polycarbonate is spoiled, and a homogeneous photosensitive layer is not obtained. When the divalent group not containing aromatic ring in the main chain contains an aliphatic group, this aliphatic group is preferred to be a saturated aliphatic group not containing double bond or triple bond in its main chain. If the aliphatic group contains double bond or triple bond in the main chain, the stiffness of the main chain is somewhat increased, and the effect of improvement of adhesion by the carbonyl group may be decreased. At the end of the main chain of Formula (50), an -OH group or a -COOH group is attached, and the acid value indicating the quantity of the -COOH group is desired to be 2 (KOH mg/g) or less. If the acid value is far more than 2, although the adhesion of the photosensitive layer to the conductive substrate is improved, a complex is formed with the diamine compound (2) which is an electron-donating compound, and the resistance of the photosensitive layer is lowered, which may lead to lowering of the charging capability. The -COOH group may work as an ion trap for the cation radical to block the charge transferring, which may cause a drop in sensitivity. The molecular weight of the polyester possessing the repetitive unit expressed in Formula (50) is not particularly specified, but the number-average molecular weight is preferred to be 10000 to 50000, or the glass transition temperature Tg to be 15°C or more. If the number-average molecular weight is less than 10000, the glass transition temperature Tg is lowered, and if the glass transition temperature Tg becomes less than 15°C , the film strength of the photosensitive layer may be lowered. On the other hand, if the number-average molecular weight is far greater than 50000, the -OH groups and -COOH groups at the molecular ends decrease, and the adhesion is lowered. Such polyester is obtained by reaction between the acid component expressed in Formula (50a) and the diol component expressed in Formula (50b). HOOC―A 3 ―COOH HO―A 4 ―OH Examples of the acid component include the compounds expressed in Formulae (55) to (59). Examples of the diol component include the compounds expressed in Formulae (60) to (66). These acid components and diol components are used in proper combinations so that either one of the groups A 3 and A 4 in Formula (50) may contain an aromatic ring in the main chain, and the other may not. Two or more types of acid components and diol components expressed above may be mixed. Of the acid components and diol components which are raw materials of polyester, the rate of those containing aromatic ring in the main chain is not particularly defined, but is preferred to be somewhere between 40 and 80 mole%. Practical compounds of the polyester possessing the repetitive unit expressed in Formula (50) include, for example, the compounds (M1) to (M5) shown in Table 8 below. In the table, "(58)u=2" in the column of acid component means a succinic acid in which u in Formula (58) is 2, "(58)u=4" is an adipic acid in which u is 4, and " (58)u=7" represents an azelaic acid in which u is 7. In the column of diol component, "(60)v=2" represents an ethylene glycol in which v in Formula (60) is 2. Of the polycarbonate and specific polyester used as the preferred binding resins, the content of polyester is desired to be 0.5 to 50 % by weight. If the content of polyester is less than 0.5 % by weight, the adhesion of the photosensitive layer may not be improved sufficiently. On the other hand, if the content exceeds 50 % by weight by far, as mentioned above, the polar group in the polyester molecule acts as a carrier trap to lower the sensitivity of the photosensitive material, or promote photo-oxidation deterioration of the charge generating material and charge transferring material in a high electric field. Besides, as the content of the polycarbonate is decreased, the strength is lowered, and, as a result, a tough photosensitive layer excellent in resistance to abrasion may not be obtained. As the polycarbonate used together with the specific polyester as the binding resin, various known compounds may be used, and at least one of the compounds possessing repetitive units expressed in Formulae (67), (68) and (69) is preferably used: where R 74 and R 75 are the same or different, hydrogen atoms, aliphatic groups, or aromatic groups, and the aliphatic groups and aromatic groups may possess substituents, and R 74 and R 75 may be mutually bonded to form a ring; R 76 , R 77 , R 78 , R 79 , R 80 , R 81 , R 82 and R 83 may be the same or different, hydrogen atoms, halogen atoms, aliphatic groups or aromatic groups, and the aliphatic groups and aromatic groups may possess substituents; R 84 and R 85 denote hydrogen atoms, halogen atoms, alkyl groups or aryl groups, and the alkyl groups and aryl groups may possess substituents; and s and t represent the numerals as defined below: 0. 2 ≦ s s + t ≦ 0. 8 In the above formulae, aliphatic groups include alkyl group and alkoxy group as stated above, and aromatic groups include aryl group, benzyl group and other aralkyl group as stated above. These groups may possess substituents as stated above. Preferred compounds of polycarbonate expressed in Formula (67) include, for example, the following compounds possessing repetitive units in (L1) to (L3). Practical compounds of polycarbonate expressed in Formula (68) include, for example, the following compound possessing a repetitive unit in (L4). where s and t are s / s + t = 0. 5. Preferred compounds of polycarbonate expressed in Formula (69) include, for example, the following compounds possessing repetitive units in (L5) to (L7). Each photosensitive layer of single layer-type and multilayer-type may contain additives, such as a sensitizer, other fluorene compounds than expressed in Formula (4), an antioxidant, ultraviolet absorber, other deterioration preventive agents and plasticizers. To enhance the sensitivity of the charge generating layer, the charge generating material may be combined with known sensitizers, for example, terphenyl, halonaphthoquinone and acenaphthylene. In the multilayer-type photosensitive material, the charge generating material and binding resin for composing the charge generating layer may be blended at various ratios. It is preferred to add 5 to 1000 parts by weight of the charge generating material, more preferably 30 to 500 parts by weight to 100 parts by weight of the binding resin. The charge transferring material and binding resin for composing the charge transferring layer may be blended at various ratios so far as not to impede the transfer of charge or not to crystallize. In order that the charge generated in the charge generating layer may be easily transferred by irradiation with light, it is desired to add the charge transferring material by 10 to 500 parts by weight , or more preferably 25 to 200 parts by weight to 100 parts by weight of the binding resin. The thickness of the photosensitive layer of the multilayer-type is preferably about 0.01 to 5 µm in the charge generating layer, more preferably 0.1 to 3 µm, and 2 to 100 µm in the charge transferring layer, preferably 5 to 50 µm. In the photosensitive layer of single layer type, the charge generating material should be present at 0.1 to 50 parts by weight, more preferably 0.5 to 30 parts by weight to 100 parts by weight of the binding resin, and the charge transferring material is present at 20 to 500 parts by weight, preferably 30 to 200 parts by weight. The thickness of the photosensitive layer of single layer type should be 5 to 100 µm, or more preferably 10 to 50 µm. In the single layer-type photosensitive material, between the conductive substrate and the photosensitive layer, and in the multilayer-type photosensitive material, between the conductive substrate and charge generating layer, between the conductive substrate and charge transferring layer, or between the charge generating layer and charge transferring layer, a barrier layer may be formed in a range so as not to impede the characteristic of the photosensitive material. On the surface of the photosensitive material, a protective layer may be formed. As the conductive substrate on which the layers are formed, various materials possessing electric conductivity may be used, for example, aluminum, copper, tin, platinum, silver, vanadium, molybdenum, chromium, cadmium, titanium, nickel, palladium, indium, stainless steel, brass, other metals alone, or metal evaporated or laminated plastics, and glass coated with aluminum iodide, tin oxide, indium oxide, and the like. The conductive substrate may be either sheet or drum, and the substrate itself may be conductive, or the surface of the substrate may be conductive. The conductive substrate is desired to have a sufficient mechanical strength in use. When forming each layer by a coating method, the charge generating material, the charge transferring material, the binding resin, and others exemplified above are dispersed and mixed, together with proper solvents, by known methods, such as roll mill, ball mill, attriter, paint shaker and ultrasonic dispersing device, and a coating solution is prepared, which is applied and dried by known methods. Solvents for preparing a coating liquid include various organic solvents, for example, other alcohols such as methanol, ethanol, isopropanol, butanol; aliphatic hydrocarbons such as n-hexane, octane, cyclohexane; aromatic hydrocarbons such as benzene, toluene, xylene; halogenated hydrocarbons such as dichloromethane, dichloroethane, carbon tetrachloride, chlorobenzene; other ethers such as dimethyl ether, diethylether, tetrahydrofurane, ethyleneglycol dimethylether, diethyleneglycol dimethylether; ketones such as acetone, methylethylketone, cyclohexanone; esters such as ethyl acetate, methyl acetate, dimethyl formaldehyde, dimethyl formamide and dimethyl sulfoxide, and others. These solvents may be used either alone or in a mixture of two or more types. To enhance the dispersion of the charge transferring material and charge generating material, and smoothness of the surface of the photosensitive layer, surfactants, leveling agents and others may be also used. Thus, according to the invention, the diamine compound expressed in Formula (2) and other pigments are selected as the charge transferring material, and it is combined with the bis-azo pigment expressed in Formula (1) as the charge generating material, so that an organic photosensitive material possessing extremely excellent electrophotographic characteristics not known before may be obtained. Preferably, by adding the hydrazone compound (3), fluorene compound (4) and diphenoquinone derivative (5) ,or by adding the diphenoquinone derivative (5) alone, an organic photosensitive material further enhanced in sensitivity and repeatability may be obtained. EXAMPLES The following description will illustrate in more detail the present invention with reference to Examples thereof and Comparative Examples. The following tests were conducted on the electrophotosensitive material of each Example and Comparative Example. Electrical properties The surface of each electrophotosensitive material prepared in each Example and Comparative Example was charged at about ± 800 V. Under this condition, after the surface potential (V) was measured, the half-life light exposure was measured by using light having a wave length of 550 nm which is the most necessary in electrophotosensitive material for PPC. Specifically, light having a wave length of 550 nm which was isolated from a xenon lamp with use of a spectroscope was exposed at an intensity of 0.1 mW/cm 2 and an exposure time of 1 second, thereby to measure the half-life light exposure (µ /cm 2 ). On the other hand, the surface potential at a time just 0.5 seconds from the exposure was measured as a potential after light exposure (V). Repeat properties After repeating a copy 50,000 times with an electrostatic copying machine (DC-1670M manufactured by Mita Kogyo Co., Ltd.), the surface potential, the half-life light exposure and the potential after light exposure were measured. Example 1 (single layer-type photosensitive material) Together with the predetermined amounts of tetrahydrofuran, 3 parts by weight of the bis-azo pigment expressed by formula (B10) mentioned above, 5 parts by weight of the perylene pigment expressed by formula (P1) mentioned above, both which are charge generating materials, 50 parts by weight of the diamine compound expressed by formula (A9) mentioned above, 50 parts by weight of the hydrazone compound expressed by formula (C2) mentioned above, both which are charge transferring materials and 100 parts by weight of polycarbonate resin which is a binding resin are mixed and dispersed for 2 minutes by an ultrasonic dispersing device to prepare a coating solution for single-layer type photosensitive layer. The bis-azo pigment and the perylene pigment used were previously pulverized by a ball-mill. The coating solution was applied to the surface of an aluminum sheet served as a conductive substrate by use of a bar-coat method using a wire bar, so that a layer having a thickness of 25 to 30 µ m was prepared, and allowed to dry at 110 °C for 30 minutes. Thus, a sheet-type electrophotosensitive material having a single layer-type photosensitive layer was prepared. Also, the coating solution was applied to the surface of an aluminum roll (outer diameter: 78 mm, length: 350 mm) served as a conductive substrate by use of a bar-coat method, so that a layer having a thickness of 25 to 30 µm was prepared, and allowed to dry at 110 °C for 30 minutes. Thus, a drum-type electrophotosensitive material having a single layer-type photosensitive layer was prepared. Examples 2 to 4 and Comparative Examples 1 to 2 A sheet-type electrophotosensitive material and a drum-type electrophotosensitive material, both of which have single layer-type photosensitive layers were prepared in the same manner as for Example 1, except that the bis-azo pigment expressed by formula (B10) and the perylene pigment expressed by formula (P1) were mixed at a ratio shown in Table 9. Example No. Amounts (parts by weight) Bis-azo pigment Perylene pigment 1 3 5 2 4 4 3 5 3 4 6 2 Comp. Ex. 1 8 0 Comp. Ex. 2 6 0 The following tests were conducted on the electrophotosensitive materials of Examples 1 to 4 and Comparative Examples 1 to 2, and these properties were evaluated. Measurement of Initial Surface Potential With the surface of each sheet-type electrophotosensitive material charged at about +800 V by adjusting a pouring current value with an electrostatic test copier (EPA-8100 manufactured by Kawaguchi Electric Ltd.), the initial surface potential V s.p.(V) was measured. Measurement of Residual Potential I The sheet-type electrophotosensitive material maintaining a charged condition in measurement of the above initial surface potential was exposed at the condition that exposure intensity is 10 lux with the use of a white color-halogen lamp which is the light source for exposure, and the surface potential at a time of 0.3 seconds from initiation of exposure was measured as residual potential V 1 r.p. (V). Measurement of Residual potential II After removing charge from the sheet-type electrophotosensitive material, which maintained a charged condition in measurement of the above initial surface potential, with the use of a white color-fluorescent lamp at exposure intensity of 100 lux and charge removing time of 1.0 second, the surface potential was measured as residual potential V 2 r.p. (V). Durability Test After measuring an initial surface potential V 1s.p. (V) of the drum-type electrophotosensitive material prepared in each Example and Comparative Example in the same manner as for mentioned above, each photosensitive material was set in an electrostatic copying machine (DC-1657 manufactured by Mita Kogyo Co., Ltd.). After a process of charge-exposure-removal of charge was repeated 1,000 times, surface potential V 2 s.p. (V) was measured again. Thus, change amountsΔ V s.p. (v) of the surface potential were caluculated by the following formula to evaluate the durability of each electrophotosensitive material. Δ V s.p. = V 2 s.p. - V 1 s.p. These results are shown in Table 10. Example No. V s.p. (V) V1 r.p. (V) V2 r.p. (V) ΔV s.p. (V) Ex. 1 795 215 35 - 55 2 805 211 40 - 55 3 800 213 45 - 55 4 795 210 55 - 60 Comparative Ex. 1 805 205 80 - 70 2 800 215 90 - 70 From the results shown in Table 10, it was found that the electrophotosensitive materials of Examples 1 to 4 had higher sensitivity than those of Comparative Examples 1 and 2 wherein the bis-azo pigment was solely used, since when adjusted in almost the same surface potential (about 800 V), the electrophotosensitive materials of the Examples had nearly the same residual potential after exposure as those of the Comparative Examples, but showed the remarkably low residual potential after removing charge. Further, it was found that the electrophotosensitive materials of the Examples were excellent in durability in view of the low change amounts of the surface potential after repeating exposure. Example 5 A sheet-type electrophotosensitive material and a drum-type electrophotosensitive material, each of which has a single layer type photosensitive layer, were prepared in the same manner as for Examples 1 to 4, except that 4 parts by weight of a bis-azo pigment expressed in the following formula (B11) were used instead of the bis-azo pigment expressed in (B10). Example 6 A sheet-type electrophotosensitive material and a drum-type electrophotosensitive material, each of which has a single layer type photosensitive layer, were prepared in the same manner as for Examples 2 to 4, except that 4 parts by weight of a bis-azo pigment expressed in the following formula (B12) were used instead of the bis-azo pigment expressed in (B10). Example 7 A sheet-type electrophotosensitive material and a drum-type electrophotosensitive material, each of which has a single layer type photosensitive layer, were prepared in the same manner as for Examples 1, except that 3 parts by weight of a bis-azo pigment expressed in the following formula (B13) were used instead of the bis-azo pigment expressed in (B10). Example 8 A sheet-type electrophotosensitive material and a drum-type electrophotosensitive material, each of which has a single layer type photosensitive layer, were prepared in the same manner as for Examples 1, except that among the charge generating materials, the amounts of the bis-azo pigment expressed in (B10) to be mixed were set in 6 parts by weight, and 1 part by weight of the perylene pigment expressed in the formula (P2) mentioned above was used instead of 5 parts by weight of the perylene pigment expressed in the formula (P1) . Example 9 A sheet-type electrophotosensitive material and a drum-type electrophotosensitive material, each of which has a single layer type photosensitive layer, were prepared in the same manner as for Examples 8, except that 1 part by weight of the perylene pigment expressed in the formula (P3) mentioned above was used instead of the perylene pigment expressed in the formula (P2) . Concerning the electrophotosensitive material of each Example, measurements of both initial surface potential and residual potential II and the durability test were conducted in the same manner as mentioned above to evaluate the properties. Results are shown in Table 11. Example No. V s.p. (V) V1 r.p. (V) V2 r.p. (V) ΔV s.p. (V) Ex. 5 795 210 45 - 55 6 795 215 45 - 50 7 810 220 50 - 45 8 800 175 70 - 50 9 810 195 80 - 55 From the results shown in Table 11, it was found that the electrophotosensitive materials of Examples 5 to 9 had higher sensitivity than those of Comparative Examples 1 and 2 wherein the bis-azo pigment was solely used, since when adjusted in almost the same surface potential (about 800 V), the electrophotosensitive materials of the Examples had nearly the same residual potential after exposure as those of the Comparative Examples, but showed the remarkably low residual potential after removing charge. Further, it was found that the electrophotosensitive materials of the Examples were excellent in durability in view of the low change amounts of the surface potential after repeating exposure. Especially, it was found that Examples 8 and 9 were excellent in durability, since the change amounts of the surface potential after repeating exposure was low. Further, it was expected that the sensitivity of each of the Examples 8 and 9 was increased, if increasing the amounts of the perylene pigment to be contained to the same amounts as in Examples 5 to 7, since Examples 8 and 9 had low residual potential after removing charge and high sensitivity in spite of lower amounts of perylene than Examples 5 to 7. Example 10 A sheet-type electrophotosensitive material and a drum-type electrophotosensitive material, each of which has a single layer type photosensitive layer, were prepared in the same manner as for Examples 1, except that among the charge generating materials, the amounts of the bis-azo pigment expressed in (B10) to be mixed were set in 6 parts by weight, and 1 part by weight of a dibromoanthanthrone having bromine atom as X in the above general formula (52) was used instead of 5 parts by weight of the perylene pigment expressed in the formula (P1). Example 11 A sheet-type electrophotosensitive material and a drum-type electrophotosensitive material, each of which has a single layer type photosensitive layer, were prepared is the same manner as for Examples 10, except that 1 part by weight of a X-type metal-free phthalocyanine was used instead of the dibromoanthanthrone. Example 12 A sheet-type electrophotosensitive material and a drum-type electrophotosensitive material, each of which has a single layer type photosensitive layer, were prepared in the same manner as for Examples 10, except that 1 part by weight of an imidazoleperylene having hydrogen atoms as R 6 and R 7 in the general formula (4) was used instead of the dibromoanthanthrone. Example 13 A sheet-type electrophotosensitive material and a drum-type electrophotosensitive material, each of which has a single layer type photosensitive layer, were prepared in the same manner as for Examples 10, except that 1 part by weight of a perylene bis-azo pigment expressed in the following formula was used instead of the dibromoanthanthrone. Concerning the electrophotosensitive material of each Example, measurements of both initial surface potential and residual potential II and the durability test were conducted in the same manner as mentioned above. Results are shown in Table 12 together with results of Comparative Example 2. Example No. V s.p. (V) V2 r.p. (V) ΔV s.p. (V) Ex. 10 795 80 - 50 11 805 75 - 50 12 795 80 - 55 13 810 80 - 50 Comparative Ex. 2 800 90 - 70 From the results shown in Table 12, it was found that the electrophotosensitive materials of Examples 10 to 13 had higher sensitivity than those of Comparative Example 2. wherein the bis-azo pigment was solely used, since when adjusted in almost the same surface potential (about 800 V), the electrophotosensitive materials of the Examples had the remarkably low residual potential after removing charge. Further, it was found that the electrophotosensitive materials of the Examples were excellent in durability, since the change amounts of the surface potential after repeating exposure was low. Example 14 (single-layer photosensitive material) Together with a predetermined tetrahydrofuran, as the charge generating materials, 5 parts by weight of bis-azo pigment expressed in the formula (B10) and 3 parts by weight of perylene pigment expressed in the formula (P1); as the charge transferring materials, 90 parts by weight of diamine compound expressed in the formula (A9) and 18 parts by weight of diphenoquinone derivative expressed in the formula (E1); as the stabilizers, 1.5 parts by weight of oligomer-type amine antioxidant (molecular weight of not less than 3,000) expressed in the formula (F3), 2 parts by weight of amine antioxidant expressed in the formula (H4) and 10 parts by weight of benzotriazole UV absorber expressed in the formula (I3); and 100 parts by weight of polycarbonate resin as the binding resin were mixed, and a coating liquid for single layer-type photosensitive layer was prepared in the same manner as for Example 37. By using the coating liquid thus obtained, sheet-type and drum-type electrophotsensitive materials, each of which had a a single layer-type photsensitive layer having a thickness of 25 to 30 µm were prepared in the same manner as for Example 1. Example 15 (single-layer photosensitive material) Sheet-type and drum-type electrophotsensitive materials, each of which had a single layer-type photsensitive layer were respectively prepared in the same manner as for Example 14, except that N,N,N',N'-tetrakis(3-methylphenyl) -1.3-diaminobenzene was used as the charge transferring material instead of diamine compound expressed in the formula (A9) at the same amount as diamine compound. Example 16 (single-layer photosensitive material) Sheet-type and drum-type electrophotsensitive materials, each of which had a single layer-type photsensitive layer were respectively prepared in the same manner as for Example 14, except that 60 parts by weight of diamine compound expressed in the formula (A9) and 30 parts by weight of N,N,N',N'-tetrakis(3-methylphenyl)-1,3-diaminobenzene were used as the charge transferring materials instead of diamine compound expressed in the formula (A9). Example 17 (single-layer photosensitive material) Sheet-type and drum-type electrophotsensitive materials, each of which had a single layer-type photsensitive layer were respectively prepared in the same manner as for Example 14, except that 90 parts by weight of diamine compound expressed in the formula (A9), 10 parts by weight of hydrazone compound expressed in the formula (C2) and 2 parts by weight of fluorene compound expressed in the formula (D1) were used instead of diamine compound expressed in the formula (A9). Example 18 (single-layer photosensitive material) Sheet-type and drum-type electrophotsensitive materials, each of which had a single layer-type photsensitive layer were respectively prepared in the same manner as for Example 14, except that 12 parts by weight of diphenoquinone derivative expressed in the formula (E7) was used instead of 18 parts by weight of diphenoquinone derivative expressed in the formula (E1) . Example 19 (single-layer photosensitive material) Sheet-type and drum-type electrophotsensitive materials, each of which had a single layer-type photsensitive layer were respectively prepared in the same manner as for Example 14, except that 10 parts by weight of diphenoquinone derivative expressed in the formula (E1) and 5 parts by weight of diphenoquinone derivative expressed in the formula (E7) were used instead of 18 parts by weight of diphenoquinone derivative expressed in the formula (E1) . Example 20 (single-layer photosensitive material) Sheet-type and drum-type electrophotsensitive materials, each of which had a single layer-type photsensitive layer were respectively prepared in the same manner as for Example 14, except that a compound expressed in formula (Q1): was used as the stabilizer instead of oligomer-type amine antioxidant expressed in the formula (F3) at the same amount as oligomer-type amine antioxidant. Example 21 (single-layer photosensitive material) Sheet-type and drum-type electrophotsensitive materials, each of which had a single layer-type photsensitive layer were respectively prepared in the same manner as for Example 14, except that 3 parts by weight of piperidine antioxidant expressed in formula (J4) was used instead of 1.5 parts by weight of oligomer-type amine antioxidant expressed in the formula (F3) at the same amount as oligomer-type amine antioxidant. Example 22 (single-layer photosensitive material) Sheet-type and drum-type electrophotsensitive materials, each of which had a single layer-type photsensitive layer were respectively prepared in the same manner as for Example 14, except that 1.5 parts by weight of oligomer-type amine antioxidant expressed in the formula (F3) and 1 parts by weight of piperidine antioxidant expressed in formula (J4) were used instead of 1.5 parts by weight of oligomer-type amine antioxidant expressed in the formula (F3). Example 23 (single-layer photosensitive material) Sheet-type and drum-type electrophotsensitive materials, each of which had a single layer-type photsensitive layer were respectively prepared in the same manner as for Example 14, except that 85 parts by weight of diamine compound expressed in the formula (A9), 5 parts by weight of N,N,N',N'-tetrakis(3-methylphenyl)-1.3-diaminobenzene and 10 parts by weight of diphenoquinone expressed in formula (E7) were used instead of 90 parts by weight of diamine compound expressed in the formula (A9) and 18 parts by weight of the diphenoquinone derivative of Formula (El). Example 24 (single-layer photosensitive material) Sheet-type and drum-type electrophotsensitive materials, each of which had a single layer-type photsensitive layer were respectively prepared in the same manner as for Example 14, except that 1.5 parts by weight of oligomer-type amine antioxidant expressed in the formula (F3) and 10 parts by weight of a compound expressed in formula (Q2): was used as the stabilizer instead of 1.5 parts by weight of oligomer-type amine antioxidant expressed in the formula (F3). Example 25 (single-layer photosensitive material) Sheet-type and drum-type electrophotsensitive materials, each of which had a single layer-type photsensitive layer were respectively prepared in the same manner as for Example 14, except that 1.5 parts by weight of oligomer-type amine antioxidant expressed in the formula (F3) and 0.5 parts by weight of a compound expressed in formula (Q1) were used instead of 1.5 parts by weight of oligomer-type amine antioxidant expressed in the formula (F3). Example 26 (single-layer photosensitive material) Sheet-type and drum-type electrophotsensitive materials, each of which had a single layer-type photsensitive layer were respectively prepared in the same manner as for Example 14, except that 1.5 parts by weight of oligomer-type amine antioxidant expressed in the formula (F3) and 5 parts by weight of tribenzylamine [N(CH 2 -C 6 H 5 ) 3 ] were used as the stabilizer instead of 1.5 parts by weight of oligomer-type amine antioxidant expressed in the formula (F3). Example 27 (single-layer photosensitive material) Sheet-type and drum-type electrophotsensitive materials, each of which had a single layer-type photsensitive layer were respectively prepared in the same manner as for Example 14, except that diamine compound expressed in the formula (A3) was used instead of diamine compound expressed in the formula (A9). An initial surface potential, a potential after light exposure and a half-life light exposure were measured on the photsensitive material of each Example 14 to 27 in the same manner as for Examples 1 to 13, and a durability test was conducted in the same manner as for Example 1 to calculate a change amount Δ V s.p. of the surface potential. These test results are shown in Table 13. Example No. Initial Vs.p. (V) Potential after light exposure (V) E 1/2 (µJ/cm 2 ) Δ Vs.p. after repeating 1,000 copies (V) Ex. 14 + 805 + 55 0.55 - 5 15 + 800 + 60 0.61 + 25 16 + 795 + 57 0.54 ± 0 17 + 805 + 52 0.51 + 5 18 + 810 + 54 0.50 - 5 19 + 795 + 54 0.56 - 10 20 + 805 + 60 0.57 - 5 21 + 805 + 62 0.56 - 10 22 + 810 + 67 0.62 + 5 23 + 795 + 58 0.54 - 5 24 + 815 + 68 0.69 ± 0 25 + 800 + 65 0.62 + 5 26 + 795 + 70 0.68 - 10 27 + 805 + 55 0.57 - 15 Example 28 to 34 (single-layer photosensitive material) Together with dichloromethan, 6 parts by weight of the bis-azo pigment (using 2 types with the mixture ratio of 1:1) which is a charge generating material, 60 parts by weight of the diamine compound which is a charge transferring material), 40 parts by weight of the hydrazone compound, 25 parts by weight of the fluorene compound, 10 parts by weight of the diphenoquinone derivative, 150 parts by weight of the bisphenol Z type polycarbonate, as stabilizers, 10 parts by weight of the oligomer type amine antioxidant and 20 parts by weight of UV absorber were mixed and dispersed for 2 minutes by an ultrasonic dispersing device to prepare a coating liquids for single-layer type photosensitive layer. The coating liquids were applied to the surfaces of an aluminum cyrinders by dipping, and allowed to dry at 80 °C for 120 minutes to form single layer-type photosensitive layers having thicknesses of 30 µ m. Thus, single layer-type electrophotosensitive materials being positive type were prepared. Each material used are shown in Table 14 with the compound number in practical examples mentioned above. Stability of coating liquid After preserving the coating liquid prepared in each of Examples 28 to 34 for 2 weeks, single layer-type electrophotosensitive material being positive type was prepared by the same manner as mentioned above. Concerning the electrophotosensitive material prepared in each Example, tests for the electrical property and the repetitive property were conducted by the same manner as above to evaluate the properties. Test results are shown in Tables 15 and 16. After 50,000 continuous copies Coating liquid at Initiation Example No. Vs.p (V) Potential after light exposure (V) E 1/2 (µJ/cm 2 ) 28 757 72 1.08 29 772 75 1.16 30 753 75 1.13 31 763 80 1.20 32 769 73 1.01 33 772 64 0.82 34 759 62 0.79

Claims: An electrophotosensitive material comprising a conductive substrate and a photosensitive layer provided on said conductive substrate, characterized in that said photosensitive layer contains, as charge generating materials, a bis-azo pigment expressed in formula (1): wherein A 1 and A 2 denote the same or different coupler residual groups; R 1 denotes a hydrogen atom, an alkyl group, an aryl group or a heterocyclic group, and the alkyl group, the aryl group or the heterocyclic group may have a substituent; n is 0 or 1, at least one material selected from the group consisting of a perylene pigment, an anthanthrone pigment, an X-type metal-free phthalocyanine, an imidazoleperylene pigment and a perylene bis-azo pigment; and as charge transferring materials a diamine compound in formula (2); wherein R 2 , R 3 , R 4 , R 5 , R 6 and R 7 are the same or different, and are alkyl groups, alkoxyl groups, halogen atoms, aryl groups, nitro groups, cyano groups or alkylamino groups; p and q are the same or different, and are integers in the range of 0 to 3; and k, l, m and o are the same or different, and are integers in the range of 0 to 2. An electrophotosensitive material according to Claim 1, wherein said photosensitive layer further includes: a hydrazone compound expressed in formula (3); wherein R 8 denotes an alkyl group, or an aryl group which may have a substituent; R 9 and R 10 are the same or different, and are alkyl groups, alkoxyl groups, halogen atoms, aryl groups, nitro groups, cyano groups or alkylamino groups, a fluorene compound expressed in formula (4): wherein R 11 and R 12 are the same or different, and are hydrogen atoms, alkyl groups, halogen atoms, alkoxyl groups or alkylamino groups; R 17 and R 18 are the same or different, and are hydrogen atoms, alkyl groups or halogen atoms, and a diphenoquinone derivative expressed in formula (5): wherein R 13 , R 14 , R 15 and R 16 are the same or different, and are alkyl groups, alkoxyl groups, aryl groups or aralkyl groups. An electrophotosensitive material according to Claim 1, wherein said photosensitive layer contains a diphenoquinone derivative expressed in the formula (5). An electrophotosensitive material according to Claim 1, wherein the photosensitive layer is a single layer.

Inventors: HANATANI YASUYUKI, IWASAKI HIROAKI, MIYAMOTO EIICHI, MUTO NARIAKI, OKI TSUNEO, SAKAI HIROAKI, SUMIDA KEISUKE, HANATANI, YASUYUKI, IWASAKI, HIROAKI, MIYAMOTO, EIICHI, MUTO, NARIAKI, OKI, TSUNEO, SAKAI, HIROAKI, SUMIDA, KEISUKE, HANATANI, YASUYUKI, C/O MITA INDUSTRIAL CO., LTD., Iwasaki, Hiroaki, c/o Mita Industrial Co., Ltd., MIYAMOTO, EIICHI, C/O MITA INDUSTRIAL CO., LTD., MUTO, NARIAKI, C/O MITA INDUSTRIAL CO., LTD., OKI, TSUNEO, C/O MITA INDUSTRIAL CO., LTD., SAKAI, HIROAKI, C/O MITA INDUSTRIAL CO., LTD., SUMIDA, KEISUKE, C/O MITA INDUSTRIAL CO., LTD.
Applicants: MITA INDUSTRIAL CO LTD, MITA INDUSTRIAL CO. LTD.
Application year: 1993
Main classification: G03G5
IPC codes: G03G5