Organic photosensitive material for electrophotography

Abstract: A photosensitive material is disclosed having a photosensitive layer which comprises a diphenoquinone derivative of the following general formula (1); wherein R₁, R₂, R₃ and R₄ are each independently selected from alkyl groups, alkoxy groups, aryl groups and aralkyl groups, provided that at least one of R₁, R₂, R₃ and R₄ is an aryl group or an aralkyl group, and at least two of the remaining R₁, R₂, R₃ and R₄ are independently selected from alkyl groups and alkoxy groups. The organic photosensitive material has excellent sensitivity and residual potential and is useful in electrophotography.

Description: The present invention relates to an organic photosensitive material for electrophotography used for copying machines, laser printers and the like. More specifically, the invention relates to an organic phctosensitive material for electrophotography containing a particular diphenoquinone derivative and having excellent sensitivity and residual potential. (Description of Prior Art) A source of light having a wavelength of longer than 700 nm is usually used for photosensitive materials for electrophotography that employs a digital optical system. As photosensitive materials that are sensitive in this wavelength region, there have been known organic photosensitive materials (OPCs), amorphous silicon (a-Si) and some selenium photosensitive materials. From the overall standpoint such as sensitivity and cost, however, OPCs are used in many cases. Many organic photosensitive materials are those of the so-called function separated type, i.e., the laminated layer type in which a charge-generating layer (CGL) and a charge-transporting layer (CTL) are laminated one upon the other. However, there have also been known organic photosensitive materials of the single layer type in which a charge-generating agent is dispersed in the medium of the charge-transporting agent. The charge-transporting agents for the photosensitive material of this kind must have a high carrier mobility. However, the charge-transporting agents having high carrier mobility are in almost all cases are of the positive hole-transporting type. Therefore, those put into practical use are limited to those organic photosensitive materials of the negatively charged type. However, the organic photosensitive materials of the negatively charged type which utilize negatively charged corona discharge generate large amounts of ozone. This leads to such problems as pollution of the environment and deterioration of the photosensitive material. In order to prevent these problems, special systems are needed such as a particular electrifying system for preventing generation of ozone, a system for decomposing ozone that is formed, and a system for exhausting ozone in the apparatus. This causes the electrophotographic process and the apparatus used to become complex. Moreover, a laminated layer type photosensitive material needs the photosensitive layer to be coated twice. Otherwise the photosensitive layer has an interface between the charge-generating layer and the charge-transporting layer which develops interference fringes which is a problem from the optical point of view. Among a few examples of the charge-transporting agents having electron-transporting ability, Japanese Laid-Open Patent Publication No. 1-206349 proposes a compound having a diphenoquinone structure as a charge-transporting agent for electrophotography. Electrophotographic organic photosensitive materials comprising a diphenoquinone derivative as electron transporting agent have also been disclosed in EP-A-0,506,387. Other types of photosensitive material have been disclosed in for example EP-A-506,387, EP-A-337,307, EP-A-504,794, EP-A-392,805, JP-A-1/253753 and JP-A-1/179160. These disclose a variety of positive hole-transporting agents. It has been said that the diphenoquinone derivatives exhibit good transporting ability but exhibit poor sensitivity when they are used for high-speed copying machines and are, hence, not yet satisfactory from the practical point of view. SUMMARY OF THE INVENTION The present inventors have discovered that among a variety of diphenoquinone derivatives, the diphenoquinone derivatives having substituents at particular positions exhibit markedly excellent sensitivity compared with the diphenoquinone derivatives that have heretofore been known as electron-transporting agents. The present invention therefore seeks to provide a photo-sensitive material for electrophotography which contains a particular diphenoquinone derivative as an electron-transporting agent, which can be positively charged in an image-forming apparatus, and which enables copying speed to be increased. According to the present invention, there is provided a single layer photosensitive material comprising an electron-transporting agent, a hole-transporting agent and a charge generating agent dispersed in a binder resin, which electron-transporting agent is a diphenoquinone derivative of formula (1); wherein R 1 , R 2 , R 3 and R 4 are each independently selected from alkyl groups, alkoxy groups, aryl groups and aralkyl groups, provided that at least three of R 1 , R 2 , R 3 and R 4 are different, at least one of R 1 , R 2 , R 3 and R 4 is an aryl group or an aralkyl group, and at least two of the remaining R 1 , R 2 , R 3 and R 4 are independently selected from alkyl groups and alkoxy groups; wherein the diphenoquinone derivative of formula (1) is present in an amount from 10 to 100 parts by weight, the hole-transporting agent is present in an amount from 10 to 100 parts by weight and the charge generating agent is present in an amount from 1 to 20 parts by weight per 100 parts by weight of the binder resin and the diphenoquinone derivative of formula (1) provides 20 to 80 % by weight of the charge-transporting material. According to the invention, there is further provided a laminated photosensitive material comprising a charge-generating layer and a charge-transporting layer, wherein the charge-transporting layer comprises resin binder and a diphenoquinone derivative of formula (1); wherein R 1 , R 2 , R 3 and R 4 are each independently selected from alkyl groups, alkoxy groups, aryl groups and aralkyl groups, provided that at least three of R 1 , R 2 , R 3 and R 4 are different, at least one of R 1 , R 2 , R 3 and R 4 is an aryl group or an aralkyl group, and at least two of the remaining R 1 , R 2 , R 3 and R 4 are independently selected from alkyl groups and alkoxy groups; and the diphenoquinone derivative is present in an amount from 10 to 100 parts by weight per 100 parts by weight of a binder resin in the charge-transporting layer. It is desired that in the above general formula (1), at least one of R 1 , R 2 , R 3 and R 4 is a branched chain alkyl group with 3 to 9 carbon atoms. The most preferred example is a diphenoquinone derivative of the tri-substituted type having three kinds of substituents represented by the general formula (1) wherein R 1 is a tertiary alkyl group with 4 to 9 carbon atoms, R 3 is a phenyl group or a benzyl group, R 2 and R 4 are primary or secondary alkyl groups or alkoxy groups. particular examples of the compounds of formula (1) which may be used in the invention are: 3,5-diisopropyl-3'-t-butyl-5'-phenyl-4,4'-diphenoquinone; 3,5-diisopropyl-3'-(α,α,γ,γ-tetramethylbutyl)-5'-phenyl-4,4'-diphenoquinone; 3,5-di-sec-butyl-3'-t-butyl-5'-phenyl-4,4'-diphenoquinone; 3,5-dimethoxy-3'-(α,α,γ,γ-tetramethylbutyl)-5'-phenyl-4,-4'-diphenoquinone; and 3,5-dimethyl-3'-sec-butyl-5'-cumyl-4,4'-diphenoquinone. As the positive hole-transporting agents, the following compounds can be advantageously used: A compound represented by the following general formula (2): wherein R 5 , R 6 , R 7 , R 8 , R 9 and R 10 are alkyl groups, alkoxy groups, halogen atoms, aryl groups, nitro groups, cyano groups or alkylamino groups independently of each other, p and q are integers of 0 to 4, and k, l, m and o are integers of 0 to 5; a compound represented by the following general formula (3); wherein R 11 , R 12 , R 13 and R 14 are hydrogen atoms, alkyl groups or alkoxy groups, and n and h are integers of 1 to 3; a compound represented by the following general formula (4); wherein R 15 and R 17 are alkyl groups, alkoxy groups or halogen atoms, g and i are integers of 0 to 4, R 16 is a hydrogen atom, an alkyl group which may have a substituent, an aralkyl group, an aryl group, or a heterocyclic group, Ar 1 and Ar 2 are alkyl groups, aralkyl groups, aryl groups or heterocyclic groups which may have substituents but Ar 1 and Ar 2 may be coupled together to form a ring except when Ar 1 and Ar 2 are hydrogen atoms simultaneously, and Ar 3 and Ar 4 are alkyl groups, aralkyl groups, aryl groups or heterocyclic rings which may have substituents but Ar 3 and Ar 4 may be coupled together to form a ring; a compound of the following general formula (5); wherein R 18 and R 19 are alkyl groups or alkoxy groups, and j and r are integers of 0 to 3; a compound represented by the following general formula (6); wherein R 20 is an alkyl group or an alkoxy group, Ar 5 , Ar 6 , Ar 7 and Ar 8 are hydrogen atoms, alkyl groups, alkoxy groups, aralkyl groups or aryl groups which may have a substituent, and s is an integer of 1 to 2, and t is an integer of 0 to 2; a compound represented by the following general formula (7); wherein R 21 and R 22 are alkyl groups or alkoxy groups, u is an integer of 0 to 2, and Ar 9 and Ar 10 are aryl groups which may have a substituent; a compound represented by the following general formula (8); wherein R 23 is an alkyl group or an aryl group; a compound represented by the following general formula (9); wherein R 24 , R 25 , R 26 and R 27 are alkyl groups or alkoxy groups, and v and w are integers of 0 to 3; a compound of the following general formula (10); wherein R 28 is an alkyl group or an aryl group, R 29 and R 30 are alkyl groups or alkoxy groups independently from each other, and x is an integer of 0 to 3; and a compound represented by the following general formula (11); wherein R 31 and R 32 are alkyl groups or alkoxy groups, and y and z are integers of 0 to 3. The present invention is based on a discovery that a diphenoquinone derivative having structure represented by the above general formula (1) exhibits markedly improved sensitivity and residual potential while maintaining charging property and repetitive property which are nearly equivalent to those of the diphenoquinone derivatives that have been known as electron-transporting agents. As a diphenoquinone derivative that easily dissolves in solvent, exhibits good compatibility to binder resin and has the most excellent electron-transporting property, there has been known a 3,5-dimethyl-3',5'-ditertbutyl-4,4'-diphenoquinone (DMDB) of the following formula (a), Among diphenoquinone derivatives, DMDB has high charging property and excellent sensitivity, but needs be improved for its sensitivity when it is used for high-speed copying machines, and is not hence still satisfactory from a practical point of view. When a diphenoquinone derivative of the structure represented by the above general formula (1) is used in accordance with the present invention, on the other hand, it becomes possible to markedly improve the sensitivity and residual potential while maintaining the electrifying property and repetitive property at the same levels as those of the DMDB (see Examples appearing later). The fact that the diphenoquinone derivative used in the present invention exhibits the above-mentioned improvements was found as phenomena through extensive experiments. It is presumed that the derivative has low symmetry and, hence, permits less association or aggregation in the photosensitive layer. This enables, therefore, the diphenoquinone molecules to be effectively distributed in the same volume which is advantageous for the electrons to be hopping-conducted. The diphenoquinone derivative of the present invention should be used in combination with positive hole-transporting agents and, particularly, in combination with those positive hole-transporting agents of the general formulas (2) to (11). In general, even when charge-transporting materials having high charge-transporting abilities are used in combination together, good electrophotographic properties are not necessarily obtained. In a system in which the positive hole-transporting material and the electron-transporting material exist together as the charge-transporting material, attention must be given to the formation of a charge-moving complex. That is, when a charge-moving complex is formed, positive holes and electrons are bonded together again, and the movement of the electric charge decreases as a whole. Moreover, when the energy gap between HOMO of the positive hole-transporting material and LUMO of the electron-transporting material is in agreement with the wavelength energy of the main exposure light and of the light for removing electricity, the light is absorbed by the charge-moving complex and the charge-generating efficiency decreases drastically. The present invention has selected a compound represented by the above general formula (1) as a particular electron-transporting material and compounds represented by the above general formulas (2) to (11) as particular positive hole-transporting materials, in order to improve sensitivity, repetitive property and residual potential as will be comprehended from the comparison of Examples with Comparative Examples appearing later. Inconvenience such as fogging does not take place even without increasing the output of the exposure lamp that is fitted as a standard lamp to the copying machine, contributing to extending the life of the exposure lamp and decreasing the consumption of electric power. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT (Electron-transporting agent) As used herein, an alkyl group may be straight or branched and may, for example, be a C 1 -C 9 , e.g. a C 1 -C 6 , or a C 1 -C 4 alkyl group. Examples include a primary alkyl group having up to 9 carbon atoms such as a methyl group, an ethyl group, an n-propyl group, an n-butyl group, an n-pentyl group, an n-hexyl group or a 2-ethylhexyl group; a secondary alkyl group with 3 to 9 carbon atoms, e.g. a C 3 -C 6 secondary alkyl group such as an isopropyl group or a sec-butyl group; or an alkyl group with 4 to 9 carbon atoms, e.g. a C 4 -C 8 tertiary alkyl group such as a tert-butyl group, an α,α,γ,γ-tetramethylbutyl group, and the like. An alkoxy group may be straight or branched and may be, for example, a C 1 -C 9 , e.g. a C 1 -C 6 , or a C 1- C 4 alkoxy group, such as a methoxy group, an ethoxy group, a propoxy group, a butoxy group, a t-butoxy group, a hexyloxy group, and a 2-ethylhexyloxy group. Among them, the methoxy group and ethoxy group are favorably used. An aryl group may be a phenyl group, an o-terphenyl group, a naphthyl group, a tolyl group, an ethylphenyl group, an anthryl group, and a phenanthryl group. Among them, an aryl group with 6 to 16 carbon atoms, e.g. C 6 -C 12 , is preferably used. Examples of the aralkyl group include those having 7 to 11 carbon atoms such as a benzyl group, a phenethyl group, and a cumyl group. Examples of optional substituents for any of the above groups include a halogen atom, an amino group, a hydroxyl group, a carboxyl group which may be esterified, a cyano group, an alkyl group, such as a C 1 -C 6 alkyl group and an alkenyl group with 2 to 6 carbon atoms that may have an aryl group. In the present invention, a diphenoquinone derivative is preferably used having three kinds of substituents which are different from each other and are represented by the following formulas (12), (13) and (14); wherein R 1 ' is an alkyl group or an alkoxy group, R 2 ' is a secondary or tertiary alkyl group, R 3 ' is an aryl group or an aralkyl group, and wherein R 1 ' and R 2 ' are different from each other. The diphenoquinone derivatives represented by the above general formulas (12), (13) and (14) can be synthesized by a variety of widely known methods. For example, the diphenoquinone derivative represented by the general formula (12) can be synthesized by bringing a bi-substituted phenol represented by the following formula (i) wherein R 1 ' is as defined in the above formula (12), and a bi-substituted phenol represented by the following formula (ii) wherein R 2 ' and R 3 ' are as defined in the above formula (12), into contact with molecular oxygen in a polar solvent in the presence of a copper salt-tertiary amine complex catalyst. Furthermore, the diphenoquinone derivative represented by the general formula (13) can be synthesized in the same manner as above but using bi-substituted phenols represented by the following formulas (iii) and (iv) instead of using those of the above formulas (i) and (ii), wherein R 1 ', R 2 ' and R 3 ' are as defined in the above formula (13). Further, the diphenoquinone derivative represented by the above general formula (14) can be synthesized in the same manner as described above but using bi-substituted phenols represented by the following formulas (v) and (vi) instead of using those of the above formulas (i) and (ii), wherein R 1 ', R 2 ' and R 3 ' are as defined in the above formula (14). The diphenoquinone derivatives represented by the above general formulas (12), (13) and (14) may be used alone or being mixed together. (Positive hole-transporting agent) Any positive hole-transporting agents can be used such as nitrogen-containing cyclic compounds, e.g., an oxadiazole compound, a styryl-type compound, a carbazole-type compound, an organic polysilane-type compound, a pyrazoline-type compound, a hydrazone-type compound, a triphenylamine-type compound, an indole-type compound, an oxazole-type compound, an isooxazole-type compound, a thiazole-type compound, a thiadiazole-type compound, an imidazole-type compound, a pyrazole-type compound, and a triazole-type compound, as well as those of the condensed polycyclic compounds having ionization potentials of from 5.3 eV to 5.6 eV [as measured by using a photoelectron analyzer (AC-1, produced by Riken Keiki Co.) in an open atmosphere]. Though there is no particular limitation, suitable examples of the positive hole-transporting agent include: a 1,1-bis(p-diethylaminophenyl)-4,4 diphenyl-1,3-butadiene (IP = 5.32 eV, drift mobility = 7.5 x 10 -6 cm 2 /V·sec); an N,N'-bis(o,p-dimethylphenyl)-N,N'-diphenylbenzidine (IP = 5.43 eV, drift mobility = 2.8 x 10 -5 cm 2 /V·sec) ; a 3,3'-dimethyl-N,N,N',N'-tetrakis-4-methylphenyl(1,1'-biphenyl)-4,4'-diamine(IP = 5.56 eV, drift mobility = 5.1 x 10 -5 cm 2 /V·sec); an N-ethyl-3-carbozolylaldehyde-N,N'-diphenylhydrazone (IP = 5.53 eV, drift mobility = 3.2 x 10 -5 cm 2 /V·sec);and a 4-[N,N-bis(p-toluyl)amino]- β-phenylstilbene (IP =5.53 eV, drift mobility = 3.5 x 10 -5 cm 2 /V·sec). Concrete examples of the compound represented by the general formula (2) include those of Nos. A1 to A15 in Table B. In Table B, symbol "3-CH 3 " indicates that a methyl group is bonded to the third position of the phenyl group, and "3,5-CH 3 " indicates that methyl groups are bonded to the third position and fifth position of the phenyl group. The compound (2) can be synthesized by a variety of methods and can be synthesized by, for example, reacting a compound represented by the following general formula (15) with compounds represented by the general formulas (16) to (19) either simultaneously or successively. wherein R 5 , R 6 , R 7 , R 8 , R 9 and R 10 are alkyl groups, alkoxy groups, halogen atoms, aryl groups, nitro groups, cyano groups or alkylamino groups independently of each other, p and q are integers of 0 to 4, k, l, m and o are integers of 0 to 5, and X is a halogen atom. Among the positive hole-transporting agents of the general formulas (2) to (11) preferably used for the present invention, the alkyl groups, alkoxy groups and aryl groups corresponding to R 5 , R 6 , R 7 , R 8 , R 9 and R 10 are those defined in the aforementioned general formula (1). Examples of the halogen atom include chlorine, iodine, bromine and fluorine. The alkylamino group may be straight or branched and may, for example, be a C 1 -C 9 alkylamino group, for example a C 1 -C 6 alkylamino group, such as a methylamino group, a dimethylamino group, an ethylamino group, a diethylamino group, a propylamino group, an isopropylamino group, a butylamino group, an isobutylamino group, a t-butylamino group, a pentylamino group and a hexylamino group. The reaction of the compound represented by the general formula (15) with the compounds represented by the general formulas (16) to (19) is usually carried in an organic solvent. Any solvent can be used provided it does not adversely affect the reaction, such as organic solvents, e.g., a nitrobenzene, a dichlorobenzene, a quinoline, an N,N-dimethylformamide, an N-methylpyrrolidone and a dimethylsulfoxide. The reaction is usually carried out in the presence of a catalyst such as a copper powder, copper oxide or copper halide, or a basic substance such as sodium hydroxide or potassium hydrogencarbonate at a temperature of 150 to 250°C. After the reaction, the reaction mixture is condensed, recrystallized, extracted with a solvent, and is easily isolated and purified through a customary means such as column chromatography. In the positive hole-transporting material of the general formula (3), the alkyl groups and alkoxy groups corresponding to R 11 , R 12 , R 13 and R 14 are those as defined in the above general formula (1). In the compound of the general formula (4), the alkyl groups, alkoxy groups and halogen atoms corresponding to R 15 and R 17 may be those defined in the general formula (2), and the alkyl groups and aryl groups corresponding to R 16 may be those defined in the general formula (1). Examples of the aralkyl groups include a benzyl group, a benzhydryl group, a trityl group and a phenethyl group. Examples of the heterocyclic ring group include a thienyl group, a pyrrolyl group, a pyrrolidinyl group, an oxazolyl group, an isooxazolyl group, a thiazolyl group, an isothiazolyl group, an imidazolyl group, a 2H-imidazolyl group, a pyrazolyl group, a triazolyl group, a tetrazolyl group, a pyranyl group, a pyridyl group, a piperidyl group, a piperidino group, a 3-morpholinyl group, a morpholino group and a thiazolyl group. The alkyl group, aryl group, aralkyl group and heterocyclic ring group may have a substituent, respectively. Examples of the substituent include a nalogen atom, an alkyl group, an alkoxy group, cyano group and the like. The alkyl groups, aryl groups, aralkyl groups, heterocyclic groups corresponding to Ar 1 , Ar 2 , Ar 3 and Ar 4 and substituents which may be possessed by them may be those as defined by R 16 above. Examples of the ring formed by Ar 1 and Ar 2 which are bonded to the neighboring carbons may be a fluorenyl group and a xanthenyl group. Examples of the ring formed by Ar 3 and Ar 4 which are bonded to the neighboring bons may be an indolyl group, a 1H-indazolyl group, a benzimidazolyl group, a benztriazolyl group, and a carbazolyl group. Examples of the compound represented by the general formula (4) include the following in addition to those described later. The compounds of the formula (4) can be synthesized by a variety of known methods. In the compound represented by the general formula (5), the alkyl groups or alkoxy groups corresponding to R 18 and R 19 are those defined by the above general formula (1). This compound is synthesized by a method known per se. In the positive hole-transporting material represented by the above general formula (6), the alkyl group and alkoxy group corresponding to R 20 may be those defined in the general formula (1). The alkyl groups, alkoxy groups, and aryl groups corresponding to Ar 5 to Ar 8 are those defined in the general formula (i). Examples of the aralkyl group include a benzyl group, a benzhydryl group, a trityl group and a phenethyl group. This compound is synthesized by a method which is known per se. In the positive hole-transporting material represented by the above general formula (7), the alkyl group and alkoxy group corresponding to R 21 and R 22 or the aryl groups corresponding to Ar 9 and Ar 10 are those defined by the above general formula (1). Examples of the substituent include a halogen atom, an alkyl group, an alkoxy group and a cyano group. The compound (7) is synthesized by a method known per se. In the positive hole-transporting material represented by the above general formula (8), the alkyl group and aryl group corresponding to R 23 are those as defined in the above general formula (1). The compound (8) is synthesized by a method known per se. In the positive hole-transporting material represented by the above general formula (9), the alkyl groups and alkoxy groups corresponding to R 24 , R 25 , R 26 and R 27 are those defined by the above general formula (1). The compound (9) is synthesized by a method known per se. In the positive hole-transporting material represented by the above general formula (10), the alkyl groups and aryl groups corresponding to R 28 and the alkyl groups and alkoxy groups corresponding to R 29 and R 30 are those as defined in the above general formula (1). This compound is synthesized by a method known per se. In the positive hole-transporting material represented by the above general formula (11), the alkyl groups and alkoxy groups corresponding to R 31 and R 32 are those as defined by the above general formula (1). This compound is synthesized by a method which is known per se. The compounds represented by the above general formulas (1) and (2) to (11) which are the charge-transporting materials can be used in combination with any other widely known charge-transporting materials. As the widely known charge-transporting materials, there can be used a variety of electron-attracting compounds and electron-donating compounds. Examples of the electron-attracting compound include diphenoquinone derivatives such as a 2,6-dimethyl-2',6'-ditert-dibutyldiphenoquinone and the like, a malononitrile, a thiopyrane-type compound, a tetracyanoethylene, a 2,4,8-trinitrothioxyxanthone, 3,4,5,7-tetranitro-9-fluorenone, a dinitrobenzene, a dinitroanthracene,a dinitroacridine, a nitroanthraquinone, a dinitroanthraquinone, a succinic anhydride, a maleic anhydride, and dibromomaleic anhydride. Examples of the electron-donating compound include an oxadiazole-type compound such as a 2,5-di(4-methylaminophenyl) and a 1,3,4-oxadiazole, a styryl-type compound such as a 9-(4-diethylaminostyryl) anthracene, a carbazole-type compound such as a polyvinyl carbazole, a pyrazoline-type compound such as a 1-phenyl-3-(p-dimethylaminophenyl) pyrazoline, nitrogen-containing cyclic compounds such as a hydrazone-type compound, a triphenylaminoe-type compound, an indole-type compound, an oxazole-type compound, an isooxazole-type compound, a thiazole-type compound, a thiadiazole-type compound, an imidazole-type compound, a pyrazole-type compound and a triazole-type compound, as well as condensed polycyclic compounds. The charge-transporting materials are used in one kind or being mixed in two or more kinds. The binder resin needs not be necessarily used when there is used a charge-transporting material having film-forming property such as polyvinyl carbazole or the like. (Charge-generating material) Any widely known charge-generating material can be used such as selenium, selenium-tellurium, selenium-arsenic, amorphous silicon, a pyrilium salt, an azo-type pigment, a perylene-type pigment, an anthanthrone-type pigment, a phthalocyanine-type pigment, an indigo-type pigment, a triphenylmethane-type pigment, a threne-type pigment, a toluidine-type pigment, a pyrazoline-type pigment, a quinacridone-type pigment and a pyrrolopyrrole-type pigment. Preferred examples include a metal-free phthalocyanine, a copper phthalocyanine, an oxotitanyl phthalocyanine and the like, and those materials which exhibit ionization potentials of from 5.3 eV to 5.6 eV [as measured by a photoelectron analyzer (AC-1, produced by Riken Keiki Co.) in an open air] are preferred. Particularly preferred examples are as follows: X-type metal-free phthalocyanine (IP = 5.38 eV) β-type metal-free phthalocyanine (IP = 5.32 eV) Oxotitanyl phthalocyanine (IP = 5.32 eV) 1,4-dithioketo-3,6-diphenyl-pyrrolo-(3,4-C) pyrrolopyrrole (IP = 5.46 eV) N,N-bis(3',5'-dimethylphenyl)perylene-3,4,9,10-tetracarboxyldiimide (IP= 5.60 eV) (Binder resin) A variety of binder resins can be used. Examples include thermoplastic resins such as a styrene-type polymer, a styrene-butadiene copolymer, a styrene-acrylonitrile copolymer, a styrene-maleic acid copolymer, an acrylic copolymer, a styrene-acrylic acid copolymer, a polyethylene, an ethylene-vinyl acetate copolymer, a chlorinated polyethylene, a polyvinyl chloride, a polypropylene, a vinyl chloride-vinyl acetate copolymer, a polyesteralkyd resin, a polyamide, a polyurethane, a polycarbonate, a polyacrylate, a polysulfone, a diaryl phthalate resin, a ketone resin, a polyvinyl butylal resin, a polyether resin, and a polyester resin, as well as a silicone resin, an epoxy resin, a phenol resin, a urea resin, a melamine resin and other crosslinking thermosetting resins, and photocuring resins such as an epoxy acrylate, an urethane-acrylate and the like. The binder resins can be used in one kind or in two or more kinds being mixed together. (Electrically conducting substrate) A variety of materials having electrically conducting property can be used as an electrically conducting substrate for forming the photosensitive layer, such as simple metals, e.g., aluminum, copper, tin, platinum, silver, vanadium, molybdenum, chromium, cadmium, titanium, nickel, palladium, indium, a stainless steel and a brass, as well as a plastic material on which the above metals are vaporized or laminated, and a glass coated with aluminum iodide, tin oxide, indium oxide or the like. The electrically conducting substrate may be either in the form of a sheet or a drum provided the surface itself has electrically conducting property or the surface of the substrate has electrically conducting property. It is desired that the electrically conducting substrate exhibits sufficiently large mechanical strength when it is being used. (Additive) The organic photosensitive layer may contain deterioration-preventing agents such as a sensitizer, a fluorene-type compound, an antioxidant and an ultraviolet-ray absorbing agent, as well as a plasticizer. Preferred examples of the antioxidant are as follows: It was found that the durability of the photosensitive layer can be strikingly improved without adversely affecting the electrophotographic properties if the above steric hindrance phenol-type antioxidant is blended in an amount of from 0.1 to 50% by weight per the whole solid content. In order to improve the sensitivity of the charge-generating layer, furthermore, a known sensitizer such as terphenyl, halonaphthoquinones or acenaphthylene may be used together with the charge-generating material. (Constitution of the photosensitive material) The photosensitive material of the present invention can be adapted to the photosensitive layer of either the single layer type or the laminated layer type. However, the electron-transporting agent represented by the above general formula (1) exhibits its effects distinguishedly particularly in the single layer type photosensitive layer in which the charge-generating agent, positive-hole transporting agent and electron-transporting agent are contained in the same layer. It can therefore be said that the resent invention is better adapted to the photosensitive material for electrophotography having a photosensitive layer of the single layer type. In order to obtain a photosensitive material of the single layer type, the photosensitive layer containing a charge-generating material, a compound of the above general formula (1) which is an electron-transporting material and, as required, compounds represented by the above formulas (2) to (11) which are positive hole-transporting materials, and a binder resin, should be formed on the electrically conducting substrate by such means as coating or the like. That is, a charge image in the single layer system is formed based on the principle in that electrons are injected into the electron-transporting material when a charge (positive holes, electrons) is generated in the charge-generating material due to exposure, positive holes are injected into the positive-hole transporting material, and the thus injected charge (positive holes, electrons) is exchanged in the transporting materials without being trapped and is finally transported to the surface of the photosensitive layer or to the surface of the electrically conducting substrate. That is, in the above-mentioned photosensitive material of the single layer type, trapping of the electric charge is suppressed contributing to improving sensitivity and further enabling the photosensitive material to be electrified into both polarities to find a wide range of applications. Moreover, the photosensitive material of the single layer type does not require the photosensitive layer to be applied twice, and contributes to increasing productivity. The photosensitive material of the laminated layer type can be obtained by forming a charge-generating layer containing a charge-generating material on the electrically conducting substrate by such means as vaporization or coating, and by forming on the charge-generating layer a charge-transporting layer which contains a compound represented by the general formula (1) which is an electron-transporting material, compounds represented by the above general formulas (2) to (11) which are positive hole-transporting materials, and a binder resin. Contrary to the above, it is also allowable to form a charge-transporting layer on the electrically conducting substrate and then form a charge-generating layer thereon. The above-mentioned photosensitive material of the laminated layer type can be charged into both polarities to find a wide range of applications. It is further allowable to form a positive hole-transporting layer containing a binder resin and compounds represented by the general formulas (2) to (11) which are the positive hole-transporting materials on the electrically conducting substrate, form a charge-generating layer containing the charge-generating material on the positive hole-transporting layer by such means as vaporization or coating, and form an electron-transporting layer containing a binder resin and a compound represented by the general formula (1) which is the electron-transporting material on the charge-generating layer. The photosensitive material of the above-mentioned laminated layer type is of the positively charged type. Contrary to the above, it is allowable to form the electron-transporting layer on the electrically conducting substrate and then form the charge-generating layer and the positive hole-transporting layer. The photosensitive material of the above-mentioned laminated layer type is of the negatively charged type. It is further allowable to provide a protection layer on the organic photosensitive layer and to provide an intermediate layer between the organic photosensitive layer and the electrically conducting substrate. When formed in a single layer, the organic photosensitive layer should have a thickness of from 10 to 50 µm and, more preferably, from 15 to 30 µm. It is desired that the charge-generating material is contained in an amount of from 1 to 20 parts by weight and, more preferably, from 1 to 10 parts by weight per 100 parts by weight of the binder resin in the organic photosensitive layer. When the content of the charge-generating material is smaller than 1 part by weight, the obtained photosensitive material exhibits small charge-generating ability. When the content of the charge-generating material is greater than 20 parts by weight, on the other hand, the obtained photosensitive material may lose abrasion resistance. It is desired that the electron-transporting material represented by the above general formula (1) is contained in an amount of from 10 to 100 parts by weight and, more preferably, from 20 to 70 parts by weight per 100 parts by weight of the binder resin in the organic photosensitive layer. When the content of the electron-transporting material is smaller than 10 parts by weight, the obtained photosensitive material exhibits poor sensitivity and repetitive property. When the content of the electron-transporting material is greater than 100 parts by weight, on the other hand, the obtained photosensitive material may lose abrasion resistance. It is desired that the positive hole-transporting materials represented by the above general formulas (2) to (11) are contained in amounts of from 10 to 100 parts by weight and, more preferably, from 20 to 70 parts by weight per 100 parts by weight of the binder resin in the organic photosensitive layer. When the content of the positive hole-transporting materials is smaller than 10 parts by weight, the obtained photosensitive material loses sensitivity. When the content of the positive hole-transporting materials becomes greater than 100 parts by weight, on the other hand, the obtained photosensitive material may lose abrasion resistance. It is desired that the electron-transporting material represented by the above general formula (1) is contained in an amount of from 20 to 80% by weight and, particularly, in an amount of 30 to 70% by weight in the charge-transporting material. When the content of the electron-transporting material in the charge-transporting material is smaller than 20 % by weight, the obtained photosensitive material exhibits poor sensitivity and repetitive property. When the content of the electron-transporting material is greater than 80% by weight, on the other hand, the obtained photosensitive material exhibits poor sensitivity. When the organic photosensitive layer comprises the charge-generating layer and the charge-transporting layer, the charge-generating layer should have a thickness of from 0.1 to 5 µm and, more preferably, from 0.5 to 2 µm. The charge-transporting layer should have a thickness of from 10 to 50 µm and, more preferably, from 15 to 30 µm. It is desired that the charge-generating material is contained in an amount of from 50 to 500 parts by weight and, more preferably, from 100 to 300 parts by weight per 100 parts by weight of the binder resin in the charge-generating layer. When the content of the charge-generating material is smaller than 50 parts by weight, the obtained photosensitive material exhibits small charge-generating ability. When the content of the charge-generating material is greater than 500 parts by weight, on the other hand, the obtained photosensitive material may lose mechanical strength. It is desired that the electron-transporting material represented by the above general formula (1) is contained in an amount of from 10 to 100 parts by weight and, more preferably, from 20 to 70 parts by weight per 100 parts by weight of the binder resin in the charge-transporting layer. When the content of the electron-transporting material is smaller than 10 parts by weight, the obtained photosensitive material loses sensitivity and repetitive property. When the content of the electron-transporting material is greater than 100 parts by weight, on the other hand, the obtained photosensitive material may lose abrasion resistance. It is desired that the positive hole-transporting materials represented by the above general formulas (2) to (11) are contained in amounts of from 10 to 100 parts by weight and, more preferably, from 20 to 70 parts by weight per 100 parts by weight of the binder resin in the charge-transporting layer. When the content of the positive hole-transporting materials is smaller than 10 parts by weight, the obtained photosensitive material loses sensitivity. When the content of the positive hole-transporting materials is greater than 100 parts by weight, on the other hand, the obtained photosensitive material may lose abrasion resistance. It is desired that the electron-transporting material represented by the above general formula (1) is contained in an amount of from 20 to 80% by weight and, particularly, from 30 to 70% by weight in the charge-transporting material. When the content of the electron-transporting material is smaller than 20% by weight in the charge-transporting material, the obtained photosensitive material loses sensitivity and repetitive property. When the content of the electron-transporting material is greater than 80% by weight, on the other hand, the obtained photosensitive material loses sensitivity. (Preparation of photosensitive material) When the above-mentioned layers are to be formed by the method of coating, the above-mentioned charge-generating material, charge-transporting material, binder resin and the like are dispersed and mixed together by a conventional method, such as by using a roll mill, a ball mill, an attritor, a paint shaker or an ultrasonic wave dispersing device to prepare a coating solution which is then applied and dried in a customary manner. A variety of organic solvents can be used for preparing a coating solution. Examples include alcohols such as methanol, ethanol, isopropanol, butanol and the like; aliphatic hydrocarbons such as n-hexane, octane, cyclohexane and the like; aromatic hydrocarbons such as benzene, toluene and xylene; halogenated hydrocarbons such as dichloromethane, dichloroethane, carbon tetrachloride, chlorobenzene and the like; ethers such as dimethyl ether, diethyl ether, tetrahydrofurane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether and the like; ketones such as acetone, methyl ethyl ketone, cyclohexanone and the like; esters such as ethyl acetate, methyl acetate and the like; and dimethylformaldehyde, dimethylformamide, dimethyl sulfoxide and the like. These solvents can be used in a single kind or in two or more kinds being mixed together. It is further allowable to use a surfactant and a ievelling agent in order to improve dispersion property of the charge-transporting material and the charge-generating material and to improve smoothness on the surface of the photosensitive layer. The invention will now be described in detail by way of Working Examples and Comparative Examples. Synthesis 1. Synthesis of a 3,5-diisopropyl-3'-t-butyl-5'-phenyl-4,4-diphenoquinone. 7.8 Grams of a 2,6-diisopropylphenol, 9.94 g of a 2-t-butyl-6-phenylphenol, 0.18 g of a cuprous chloride, 0.414 g of a tetramethylethylene diamine, and 100 millilters of methanol were fed into a 500-milliliter separable flask equipped with an oxygen gas introduction pipe, a waste gas exhaust pipe and a stirrer. The reaction was carried out with vigorous stirring while feeding a pure oxygen gas into the gas phase in the flask. After the reaction, the precipitated crystals were separated by filtration, bashed with water and dried. The crystals were then isolated using a column chromatography filled with silica gel to obtain an object material represented by the following general formula (c). The amount of the object material was 4.9 g (yield, 27%). Synthesis 2. Synthesis of a 3,5-diisopropyl-3'-(α,α,γ,γ-tetramethylbutyl)-5'-phenyl-4,4,-diphenoquinone. The reaction was carried out in the same manner as in the above Synthesis 1 with the exception of using a 2,6-diisopropylphenol and a 2-(α,α,γ,γ-tetramethylbutyl)-6-phenylphenol as bi-substituted phenols which are starting materials, in order to obtain an object material represented by the following general formula (d). The amount of the object material was 6.4 g (yield, 32%). Synthesis 3. Synthesis of a 3,5-di(secondary butyl)-3'-t-butyl-5'-phenyl-4,4'-diphenoquinone. The reaction was carried out in the same manner as in Synthesis 1 with the exception of using a 2,6-di(secondary butyl) phenol and a 2-t-butyl-6-phenylphenol as bi-substituted phenols which are starting materials, in order to obtain an object material represented by the following general formula (b), Synthesis 4. Synthesis of a 3,5-dimethoxy-3'-(α,α,γ,γ-tetramethylbutyl)-5'-phenyl-4,4'-diphenoquinone. The reaction was carried out in the same manner as in Synthesis 1 with the exception of using a 2,6-dimethoxy-phenol and a 2-phenyl-6-(α,α,γ,γ-tetramethylbutyl)-phenol as bi-substituted phenols which are starting materials, in order to obtain an object material represented by the following general formula (e), Synthesis 5. Synthesis of a 3,5-dimethyl-3'-(secondary butyl)-5'-(α-dimethyl-benzyl) 4,4'-diphenoquinone. The reaction was carried out in the same manner as in Synthesis 1 with the exception of using a 2,6-dimethyl-phenol and a 2-(α-dimethyl-benzyl)-6-(secondary butyl)-phenol as bi-substituted phenols which are starting materials, in order to obtain an object material represented by the following general formula (f), Single layer type photosensitive material for electrophotography. Examples 1 to 36 and Comparative Examples 1 to 8: 5 Parts by weight of a charge-generating agent, 40 parts by weight of an electron-transporting agent, 40 parts by weight of a positive hole-transporting agent, 100 parts by weight of a polycarbonate which is a binder, and a predetermined amount of dichloromethane which is a solvent were mixed and dispersed in a ball mill to prepare a coating solution for the single layer type photosensitive layer. The coating solution was applied onto an aluminum foil using a wire bar, and was dried with the hot air heated at 100 °C for 60 minutes to obtain a single layer type photosensitive material for electrophotography having a thickness of 15 to 20 µm. As the charge-generating agent, the following compounds I and II were used. I: X-type metal-free phthalocyanine (IP = 5.38 eV) II: Oxotitanyl phthalocyanine (IP = 5.32 eV) As the positive hole-transporting agent, the compounds of the following general formulas (A) to (E) were used : As the electron-transporting agent, the compounds of the aforementioned formulas (a) to (f) were used as concretely shown in Table 2. Laminated layer type photosensitive material for electrophotography. Examples 37 to 57 and Comparative Examples 9 to 13: 100 Parts by weight of a charge-generating agent, 100 parts by weight of a butyral resin as a binding agent and a predetermined amount of tetrahydrofurane as a solvent were mixed and dispersed in a ball mill to prepare a coating solution for the charge-generating layer. The coating solution was applied onto an aluminum foil using a wire bar and was dried with the hot air heated at 100 °C for 60 minutes to form a charge-generating layer having a thickness of 1 to 2 µm. Then, 40 parts by weight of an electron-transporting agent, 40 parts by weight of a positive hole-transporting agent, 100 parts by weight of polycarbonate as a binding agent and a predetermined amount of toluene as a solvent were mixed and dispersed in a ball mill to prepare a coating solution for the charge-transporting layer. The coating solution was applied onto the above charge-generating layer by using a wire bar and was dried with the hot air heated at 100 °C for 60 minutes to obtaina laminated layer type photosensitive material for electrophotography having a thickness of 15 to 20 µm. The charge-generating agent, positive hole-transporting agent,and electron-transporting agent used were the same as those used for the above-mentioned single layer type photosensitive material for electrophotography as concretely shown in Table 3. The photosensitive materials for electrophotography of the above Examples and Comparative Examples were tested as described below to evaluate their properties. (Electric property) By using an electrostatic copy tester (EPA-8100 manufactured by Kawaguchi Denki Co.), voltages of ±7 KV were applied to the surfaces of the sheet-like photosensitive materials for electrophotography prepared in Examples and Comparative Examples to charge the surfaces thereof into positive or negative potential in order to measure the initial surface potential V1 (V). Thereafter, the surfaces were irradiated with light from an incandescent halogen lamp that is a source of light for exposure for 6 seconds to measure the half exposure amount (µJ/cm2). Further, after three seconds have passed from the start of the exposure, the surface potential was found as the initial residual potential V2 (V). (Repetitive property) The photosensitive materials for electrophotography obtained in the aforementioned Examples and Comparative Examples were stuck to an aluminum cylinder using an adhesive tape and were fitted onto an electrostatic copying machine DC-1656 (manufactured by Mita Kogyo Co.). After the copying operation was repeated 1000 times, the surface potential V1' (V) before exposure and the potential V2' (V) after exposure were measured in the same manner as above, and the differences from the initial surface potential and the initial residual potential were calculated by using the following relations. Δ V1 =|V1'| - | V1| Δ V2 = |V2'| - |V2| The results were as shown in Tables 2 and 3. As will be obvious from Table 2, the single layer type photosensitive materials for electrophotography of Examples 1 to 36 could be charged into both positive and negative polarities, exhibited excellent sensitivity, residual potential and repetitive property, and exhibited particularly excellent sensitivity. On the other hand, the positively electrified single layer type photosensitive materials of Comparative Examples 1 to 4 ehxibited sensitivity, residual potential and repetitive property that were inferior to those of Examples 1 to 15 and 19 to 33. The negatively electrified single layer type photosensitive materials of Comparative Examples 5 to 8 exhibited sensitivity, residual potential and repetitive property that were inferior to those of Examples 16 to 18 and 34 to 36. As will be obvious from Table 3, the laminated layer type photosensitive materials of the present invention of Examples 37 to 57 exhibited excellent sensitivity, residual potential and repetitive property. On the other hand, the positively electrified laminated layer type photosensitive materials of Comparative Examples 9 to 11 exhibited sensitivity, residual potential and repetitive property that were inferior to those of Examples 37 to 51. The negatively charged laminated layer type hotosensitive material of Comparative Example 12 exhibited sensitivity, residual potential and retitive property that were inferior to those of Example 52. Furthermore, the positively charged laminated layer type photosensitive material without containing positive hole-transporting agent of Comparative Example 13 exhibited sensitivity, residual potential and repetitive property that were Inferior to those of Examples 53 to 57. Examples 58 to 66 and Comparative Example 14: 5 Parts by weight of a charge-generating material, 40 parts by weight of an electron-transporting material, 40 parts by weight of a positive hole-transporting material, 100 parts by weight of a polycarbonate resin as a binder resin, and a predetermined amount of dichloromethane as a solvent were mixed and dispersed in a ball mill to prepare a coating solution for the single layer type photosensitive material. The coating solution was applied onto an aluminum sheet using a wire bar and was dried with the hot air heated at 100 °C for 60 minutes to obtain a photosensitive material for electrophotography having a single layer type photosensitive layer which is i5 to 50 µm in thickness. As the charge-generating material, the following compound (I) was used: I: X-type metal-free phthalocyanine (IP = 5.38 eV) As the positive hole-transporting agent, the compounds of the following general formulas (1C) to (1E) were used: As the electron-transporting material, the compounds of the above-mentioned formulas (a) to (d) were used as concretely shown in Table 4. The photosensitive materials for electrophotography of the above Examples and Comparative Examples were tested for their electric properties and repetitive properties in the same manner as in Example 1 to evaluate their properties. The results were as shown in Table 4. It will be understood from Table 4 that the photosensitive materials of Examples 58 to 66 are superior to the photosensitive material of Comparative Example 14 in regard to potential after exposure, half exposure amount and repetitive property. Examples 67 to 84 and Comparative Example 15: 5 Parts by weight of a charge-generating material, 10 parts by weight of an electron-transporting material, 40 parts by weight of a positive hole-transporting material, 100 parts by weight of a polycarbonate resin as a binder resin, and a predetermined amount of dichloromethane as a solvent were mixed and dispersed in a ball mill to prepare a coating solution for the single layer type photosensitive material. The coating solution was applied onto an aluminum sheet using a wire bar and was dried with the hot air heated at 100 °C for 60 minutes to obtain a photosensitive material for electrophotography having a single layer type photosensitive layer which is 15 to 50 µm in thickness. As the charge-generating material, the following compound (I) was used: I: X-type metal-free phthalocyanine (IP = 5.38 eV) As the positive hole-transporting agent, the compounds of the following general formulas (2C) to (2H) were used: As the electron-transporting material, the compounds of the above-mentioned formulas (a) to (d) were used as concretely shown in Table 5. The photosensitive materials for electrophotography of the above Examples and Comparative Examples were tested for their electric properties and repetitive properties in the same manner as in Example 1 to evaluate their properties. The results were as shown in Table 5. As will be obvious from Table 5, the photosensitive materials for electrophotography of the present invention of Examples 67 to 84 exhibit potential after exposure, half exposure amount and repetitive property which are superior to those of the photosensitive materials of Comparative Example 15, and offer high performance from the electrophotographic point of view. Examples 85 to 102 and Comparative Example 16: 5 Parts by weight of a charge-generating material, 40 parts by weight of an electron-transporting material, 40 parts by weight of a positive hole-transporting material, 100 parts by weight of a polycarbonate resin as a binder resin, and a predetermined amount of dichloromethane as a solvent were mixed and dispersed in a ball mill to prepare a coating solution for the single layer type photosensitive material. The coating solution was applied onto an aluminum sheet using a wire bar and was dried with the hot air heated at 100 °C for 60 minutes to obtain a photosensitive material for electrophotography having a single layer type photosensitive layer which is 15 to 50 µm in thickness. As the charge-generating material, the following compound (I) was used: I: X-type metal-free phthalocyanine (IP = 5.38 eV) As the positive hole-transporting agent, the compounds of the following general formulas (3C) to (3H) were used: As the electron-transporting material, the compounds of the above-mentioned formulas (a) to (d) were used as concretely shown in Table 6. The photosensitive materials for electrophotography of the above Examples and Comparative Examples were tested for their electric properties and repetitive properties in the same manner as in Example 1 to evaluate their properties. The results were as shown in Table 6. As will be obvious from Table 6, the photosensitive materials for electrophotography of the present invention of Examples 85 to 102 exhibit potential after exposure, half exposure amount and repetitive property which are superior to those of the photosensitive materials of Comparative Example 16, and offer high performance from the electrophotographic point of view. Examples 103 to 111 and Comparative Example 17: 5 Parts by weight of a charge-generating material, 40 parts by weight of an electron-transporting material, 40 parts by weight of a positive hole-transporting material, 100 parts by weight of a polycarbonate resin as a binder resin, and a predetermined amount of dichloromethane as a solvent were mixed and dispersed in a ball mill to prepare a coating solution for the single layer type photosensitive material. The coating solution was applied onto an aluminum sheet using a wire bar and was dried with the hot air heated at 100 °C for 60 minutes to obtain a photosensitive material for electrophotography having a single layer type photosensitive layer which is 15 to 50 µm in thickness. As the charge-generating material, the following compound (I) was used: I: X-type metal-free phthalocyanine (IP = 5.38 eV) As the positive hole-transporting agent, the compounds of the following general formulas and (4C) to (4E) were used: As the electron-transporting material, the compounds of the above-mentioned formulas (a) to (d) were used as concretely shown in Table 7. The photosensitive materials for electrophotography of the above Examples and Comparative Examples were tested for their electric properties and repetitive properties in the same manner as in Example 1 to evaluate their properties. The results were as shown in Table 7. As will be obvious from Table 7, the photosensitive materials for electrophotography of the present invention of Examples 103 to 111 exhibit potential after exposure, half exposure amount and repetitive property which are superior to those of the photosensitive materials of Comparative Example 17, and offer high performance from the electrophotographic point of view. Examples 112 to 138 and Comparative Example 18: 5 Parts by weight of a charge-generating material, 10 parts by weight of an electron-transporting material, 40 parts by weight of a positive hole-transporting material, 100 parts by weight of a polycarbonate resin as a binder resin, and a predetermined amount of dichloromethane as a solvent were mixed and dispersed in a ball mill to prepare a coating solution for the single layer type photosensitive material. The coating solution was applied onto an aluminum sheet using a wire bar and was dried with the hot air heated at 100 °C for 60 minutes to obtain a photosensitive material for electrophotography having a single layer type photosensitive layer which is 15 to 50 µm in thickness. As the charge-generating material, the following compound (I) was used: I: X-type metal-free phthalocyanine (IP = 5.38 eV) As the positive hole-transporting agent, the compounds of the following general formulas (5C) to (5K) were used: As the electron-transporting material, the compounds of the above-mentioned formulas (a) to (d) were used as concretely shown in Table 8. The photosensitive materials for electrophotography of the above Examples and Comparative Examples were tested for their electric properties and repetitive properties in the same manner as in Example 1 to evaluate their properties. The results were as shown in Tables 8, 9 and 10. As will be obvious from Tables 8, 9 and 10, the photosensitive materials for electrophotography of the present invention of Examples 112 to 138 exhibit potential after exposure, half exposure amount and repetitive property which are superior to those of the photosensitive materials of Comparative Example 18, and offer high performance from the electrophotographic point of view. Examples 139 to 147 and Comparative Example 19: 5 Parts by weight of a charge-generating material, 40 parts by weight of an electron-transporting material, 40 parts by weight of a positive hole-transporting material, 100 parts by weight of a polycarbonate resin as a binder resin, and a predetermined amount of dichloromethane as a solvent were mixed and dispersed in a ball mill to prepare a coating solution for the single layer type photosensitive material. The coating solution was applied onto an aluminum sheet using a wire bar and was dried with the hot air heated at 100 °C for 60 minutes to obtain a photosensitive material for electrophotography having a single layer type photosensitive layer which is 15 to 50 µm in thickness. As the charge-generating material, the following compounds (I) and (II) were used: I: X-type metal-free phthalocyanine (IP = 5.38 eV) As the positive hole-transporting agent, the compounds of the following general formulas (6C) to (6E) were used: As the electron-transporting material, the compounds of the above-mentioned formulas (a) to (d) were used as concretely shown in Table 11. The photosensitive materials for electrophotography of the above Examples and Comparative Examples were tested for their electric properties and repetitive properties in the same manner as in Example 1 to evaluate their properties. The results were as shown in Table 11. As will be obvious from Table 11, the photosensitive materials for electrophotography of the present invention of Examples 139 to 147 exhibit potential after exposure, half exposure amount and repetitive property which are superior to those of the photosensitive materials of Comparative Example 19, and offer high performance from the electrophotographic point of view. Examples 148 to 156 and Comparative Example 20: 5 Parts by weight of a charge-generating material, 40 parts by weight of an electron-transporting material, 40 parts by weight of a positive hole-transporting material, 100 parts by weight of a polycarbonate resin as a binder resin, and a predetermined amount of dichloromethane as a solvent were mixed and dispersed in a hall mill to prepare a coating solution for the single layer type photosensitive material. The coating solution was applied onto an aluminum sheet using a wire bar and was dried with the hot air heated at 100 °C for 60 minutes to obtain a photosensitive material for electrophotography having a single layer type photosensitive layer which is 15 to 50 µm in thickness. As the charge-generating material, the following compound (I) was used: I: X-type metal-free phthalocyanine (IP = 5.38 eV) As the positive hole-transporting agent, the compounds of the following general formulas (7C) to (7E) were used: As the electron-transporting material, the compounds of the above-mentioned formulas (a) to (d) were used as concretely shown in Table 12. The photosensitive materials for electrophotography of the above Examples and Comparative Examples were tested for their electric properties and repetitive properties in the same manner as in Example 1 to evaluate their properties. As will be obvious from Table 12, the photosensitive materials for electrophotography of the present invention of Examples 148 to 156 exhibit potential after exposure, half exposure amount and repetitive property which are superior to those of the photosensitive materials of Comparative Example 20, and offer high performance from the electrophotographic point of view. Examples 157 to 165 and Comparative Example 21: 5 Parts by weight of a charge-generating material, 40 parts by weight of an electron-transporting material, 40 parts by weight of a positive hole-transporting material, 100 parts by weight of a polycarbonate resin as a binder resin, and a predetermined amount of dichloromethane as a solvent were mixed and dispersed in a ball mill to prepare a coating solution for the single layer type photosensitive material. The coating solution was applied onto an aluminum sheet using a wire bar and was dried with the hot air heated at 100 °C for 60 minutes to obtain a photosensitive material for electrophotography having a single layer type photosensitive layer which is 15 to 50 µm in thickness. As the charge-generating material, the following compound (I) was used: I: X-type metal-free phthalocyanine (IP = 5.38 eV) As the positive hole-transporting agent, the compounds of the following general formulas (8C) to (8E) were used: As the electron-transporting material, the compounds of the above-mentioned formulas (a) to (d) were used as concretely shown in Table 13. The photosensitive materials for electrophotography of the above Examples and Comparative Examples were tested for their electric properties and repetitive properties in the same manner as in Example 1 to evaluate their properties. The results were as shown in Table 13. As will be obvious from Table 13, the photosensitive materials for electrophotography of the present invention of Examples 157 to 165 exhibit potential after exposure, half exposure amount and repetitive property which are superior to those of the photosensitive materials of Comparative Example 21, and offer high performance from the electrophotographic point of view. Examples 166 to 174 and Comparative Example 22: 5 Parts by weight of a charge-generating material, 40 parts by weight of an electron-transporting material, 40 parts by weight of a positive hole-transporting material, 100 parts by weight of a polycarbonate resin as a binder resin, and a predetermined amount of dichloromethane as a solvent were mixed and dispersed in a ball mill to prepare a coating solution for the single layer type photosensitive material. The coating solution was applied onto an aluminum sheet using a wire bar and was dried with the hot air heated at 100 °C for 60 minutes to obtain a photosensitive material for electrophotography having a single layer type photosensitive layer which is 15 to 50 µm in thickness. As the charge-generating material, the following compound (I) was used: I: X-type metal-free phthalocyanine (IP = 5.38 eV) As the positive hole-transporting agent, the compounds of the following general formulas (9C) to (9E) were used: As the electron-transporting material, the compounds of the above-mentioned formulas (a) to (d) were used as concretely shown in Table 14. The photosensitive materials for electrophotography of the above Examples and Comparative Examples were tested for their electric properties and repetitive properties in the same manner as in Example 1 to evaluate their properties. The results were as shown in Table 14. As will be obvious from Table 14, the photosensitive materials for electrophotography of the present invention of Examples 166 to 174 exhibit potential after exposure, half exposure amount and repetitive property which are superior to those of the photosensitive materials of Comparative Example 22, and offer high performance from the electrophotographic point of view.

Claims: A single layer photosensitive material comprising an electron-transporting agent, a hole-transporting agent and a charge generating agent dispersed in a binder resin, which electron-transporting agent is a diphenoquinone derivative of formula (1); wherein R 1 , R 2 , R 3 and R 4 are each independently selected from alkyl groups, alkoxy groups, aryl groups and aralkyl groups, provided that at least three of R 1 , R 2 , R 3 and R 4 are different, at least one of R 1 , R 2 , R 3 and R 4 is an aryl group or an aralkyl group, and at least two of the remaining R 1 , R 2 , R 3 and R 4 are independently selected from alkyl groups and alkoxy groups; wherein the diphenoquinone derivative of formula (1) is present in an amount from 10 to 100 parts by weight, the hole-transporting agent is present in an amount from 10 to 100 parts by weight and the charge generating agent is present in an amount from 1 to 20 parts by weight per 100 parts by weight of the binder resin and the diphenoquinone derivative of formula (1) provides 20 to 80 % by weight of the charge-transporting material. A material according to claim 1, wherein the diphenoquinone derivative of formula (1) provides 30 to 7C % by weight of the charge-transporting material. A laminated photosensitive material comprising a charge-generating layer and a charge-transporting layer, wherein the charge-transporting layer comprises resin binder and a diphenoquinone derivative of formula (1); wherein R 1 , R 2 , R 3 and R 4 are each independently selected from alkyl groups, alkoxy groups, aryl groups and aralkyl groups, provided that at least three of R 1 , R 2 , R 3 and R 4 are different, at least one of R 1 , R 2 , R 3 and R 4 is an aryl group or an aralkyl group, and at least two of the remaining R 1 , R 2 , R 3 and R 4 are independently selected from alkyl groups and alkoxy groups; and the diphenoquinone derivative is present in an amount from 10 to 100 parts by weight per 100 parts by weight of a binder resin in the charge-transporting layer. A material according to claim 3 wherein the charge-transporting layer further comprises a hole-transporting agent. A material according to claim 4, wherein the hole-transporting agent is present in an amount from 10 to 100 parts by weight per 100 parts by weight of the binder resin in the charge-transporting layer. A material according to claim 5, wherein the diphenoquinone derivative of formula (1) provides 20 to 80 % by weight of the charge-transport material. A material according to claim 4, 5 or 6, in which the charge-generating layer comprises a charge-generating agent in an amount from 50 to 500 parts by weight per 100 parts by weight of the binder resin in the charge-generating layer. A material according to any one of the preceding claims, wherein in formula (1) at least one of R 1 , R 2 , R 3 and R 4 is a branched chain alkyl group with 3 to 9 carbon atoms. A material according to any one of the preceding claims, wherein in formula (1) R 1 is a tertiary alkyl group with 4 to 9 carbon atoms, R 3 is a phenyl group or a benzyl group, and each of R 2 and R 4 is, independently, a primary or secondary alkyl group or an alkoxy group. A material according to any one of the preceding claims, wherein the diphenoquinone derivative of formula (1) is selected from: 3,5-diisopropyl-3'-t-butyl-5'-phenyl-4,4'-diphenoquinone; 3,5-diisopropyl-3'-(α,α,γ,γ-tetramethylbutyl)-5'-phenyl-4,4'-diphenoquinone; 3,5-di-sec-butyl-3'-t-butyl-5'-phenyl-4,4'-diphenoquinone; 3,5-dimethoxy-3'-(α,α,γ,γ-tetramethylbutyl)-5'-phenyl-4,-4'-diphenoquinone; and 3,5-dimethyl-3'-sec-butyl-5'-cumyl-4,4'-diphenoquinone. A material according to any one of the preceding claims, which comprises, as hole-transporting agent, a compound of the following general formula (2) ; wherein R 5 , R 6 , R 7 , R 8 , R 9 and R 10 are each independently selected from alkyl groups, alkoxy groups, halogen atoms, aryl groups, nitro groups, cyano groups and alkylamino groups, each of p and q is, independently, an integer of 0 to 4, and each of k, l, m and o is, independently, an integer of 0 to 5. A material according to any one of claims 1 to 10 which comprises, as hole-transporting agent, a compound of the following general formula (3); wherein R 11 , R 12 , R 13 and R 14 , are each independently selected from hydrogen atoms, alkyl groups and alkoxy groups, and each of n and h is, independently, an integer of 1 to 3. A material according to any one of claims 1 to 10 which comprises as hole-transporting agent, a compound of the following general formula (4); wherein each R 15 and R 17 is, independently, selected from alkyl groups, alkoxy groups and halogen atoms, each of g and i is, independently, an integer of 0 to 4, R 16 is hydrogen, an optionally substituted alkyl group, an aralkyl group, an aryl group, or a heterocyclic group, each of Ar 1 and Ar 2 is, independently, selected from alkyl groups, aralkyl groups, aryl groups and heterocyclic groups, all of which are optionally substituted, or Ar 1 and Ar 2 may form together with the carbon atom to which they are attached, a ring structure, and each of Ar 3 and Ar 4 is independently selected from alkyl groups, aralkyl groups, aryl groups and heterocyclic rings, all of which are optionally substituted, or Ar 3 and Ar 4 form, together with the nitrogen atom to which they are attached, a ring structure. A material according to any one of claims 1 to 10 which comprises, as hole-transporting agent, a compound of the following general formula (5); wherein each of R 18 and R 19 is selected from alkyl groups and alkoxy groups, and each of j and r is, independently, an integer of 0 to 3. A material according to any one of claims 1 to 10 which comprises, as hole-transporting agent, a compoun of the following general formula (6); wherein R 20 is an alkyl group or an alkoxy group, each of Ar 5 , Ar 6 , Ar 7 and Ar 8 is independently selected from hydrogen atoms, alkyl groups, alkoxy groups, aralkyl groups and aryl groups, all of which may be optionally substituted, s is 1 or 2, and t is 0, 1 or 2. A material according to any one of claims 1 to 10 which comprises, as hole-transporting agent, a compound of the following general formula (7); wherein each of R 21 and R 22 is, independently, an alkyl group or an alkoxy group, u is 0, 1 or 2, and each of Ar 9 and Ar 10 is, independently, an optionally substituted aryl group. A material according to any one of claims 1 to 10 which comprises, as hole-transporting agent, a compound of the following general formula (8); wherein R 23 is an alkyl group or an aryl group. A material according to any one of claims 1 to 10, which comprises, as hole-transporting agent, a compound of the following general formula (9); wherein each of R 24 , R 25 , R 26 and R 27 is independently selected from alkyl groups and alkoxy groups, and each of v and w is, independently, 0 or an integer of 1 to 3. A material according to any one of claims 1 to 10 which comprises, as hole-transporting agent, a compound of the following general formula (10); wherein R 28 is an alkyl group or an aryl group, R 29 and R 30 is independently selected from alkyl groups and alkoxy groups, and x is 0 or an integer of 1 to 3. A material according to any one of claims 1 to wherein the positive hole-transporting agent, is a compound of the following general formula (11); wherein each of R 31 and R 32 is independently selected from alkyl groups and alkoxy groups, and each of y and z is, independently, 0 or an integer of 1 to 3.

Inventors: FUKAMI TOSHIYUKI, KATSUKAWA MASATO, NAKAMORI HIDEO, TANAKA MASASHI, FUKAMI, TOSHIYUKI, KATSUKAWA, MASATO, NAKAMORI, HIDEO, TANAKA, MASASHI
Applicants: MITA INDUSTRIAL CO LTD, MITA INDUSTRIAL CO., LTD.
Application year: 1993
Main classification: G03G5
IPC codes: C07C211, C07C50, C07C217, C07D209, C07C46, G03G5, C07C251