Abstract:
Disazo compounds as well as the compositions an electrophotographic light-sensitive materials utilizing them are disclosed. The disazo compounds are represented by the general formula (I): ##STR1## wherein the substituents within the general formula (I) are defined within the specification. By utilizing the specifically disclosed disazo compounds the electrophotographic light-sensitive material has high sensitivity and high durability.

Description:
FIELD OF THE INVENTION 
     The present invention relates to novel disazo compounds, photoconductive compositions containing these disazo compounds, and electrophotographic light-sensitive materials comprising an electrophotographic light-sensitive layer containing these disazo compounds. 
     BACKGROUND OF THE INVENTION 
     A photoconductive process for electrophotographic light-sensitive materials consists of (1) a step of generating electric charges by exposing to light, and (2) a step of transporting the electric charges. 
     An example of a substance for conducting steps (1) and (2) in the same substance in a selenium light-sensitive plate. A combination of amorphous selenium and poly-N-vinylcarbazole can be used to conduct step (1) and (2) separately. By carrying out steps (1) and (2) with different substances respectively the substances used in the electrophotographic light-sensitive materials can be selected from a wide range and, consequently, electrophotographic characteristics of the electrophotographic light-sensitive materials, such as sensitivity or acceptable electric potential, etc. are improved. Further, substances suitable for producing the electrophotographic light-sensitive coating layer can be selected from a wide range. 
     Photoconductive substances in the electrophotographic light-sensitive materials now used for the electrophotographic process include selenium, cadmium sulfide and zinc oxide, etc. 
     In the electrophotographic process, as be disclosed in U.S. Pat. No. 2,297,691 by Carlson, a photoconductive material comprising a base coated with a substance which is insulating in the dark, the electric resistance of which varies according to an exposure applied during imagewise exposing to light, is used. This photoconductive material is generally charged first to give uniform surface electric charges in the dark after carrying out dark adaptation for a suitable time. This material is then imagewise exposed to light by a light pattern which has the effect of reducing surface electric charges according to relative energy included in various parts of the light pattern. The residual surface electric charges or latent images formed on the surface of the photoconductive material layer (electrophotographic light-sensitive layer) are brought into contact with a suitable electroscopic indication material, namely, a toner to obtain visible images. 
     The toner is contained in an insulating solution or a dry carrier. The toner will adhere to the surface of the electrophotographic light-sensitive layer according to the electric charge pattern. The adhered indication material can be fixed by a known means such as heat, pressure or solvent vapor, etc. Further, the latent images can be transferred to the second base (for example, paper or film, etc.). Likewise, the latent images can be transferred to the second base where they are developed. The electrophotographic process is one of such image forming processes. 
     In such an electrophotographic process, the basic characteristics required for the electrophotographic light-sensitive materials include: (1) the electrophotographic light-sensitive material can be changed in a suitable electric potential in the dark, (2) there is a low level of leakage of electric charges in the dark is at a low level, and (3) electric charges can be quickly discharged by light irradiation. 
     The above described inorganic substances used hitherto have many advantages but also have various disadvantages. For example, selenium widely used at the present sufficiently satisfies the above described requirements (1)-(3). However selenium is not desirable because production thereof requires maintaining difficult conditions which increase production cost, i.e., it is difficult to process it to make a long sheet because it has substantially no flexibility, and it is necessary to handle it with care because due to its sensitivity to thermal or mechanical impacts. Cadmium sulfide and zinc oxide are used as electrophotographic light-sensitive materials by dispersing in a resin binder, but they can not be repeatedly used, because they have mechanical disadvantages such as in smoothness, hardness, tensile strength or friction resistance, etc. 
     In the recent years, in order to remove the disadvantages of these inorganic substances, electrophotographic light-sensitive materials using various organic substances have been proposed and some of them have been put to practical use. Examples of such material include an electrophotographic light-sensitive material composed of poly-N-vinylcarbazole and 2,4,7-trinitrofluorenon-9-one (U.S. Pat. No. 3,484,237), an electrophotographic light-sensitive material in which poly-N-vinylcarbazole is sensitized with pyrylium salt type dyes (U.S. Pat. No. 3,617,268), an electrophotographic light-sensitive material containing an organic pigment as a main component (U.S. Pat. No. 3,898,084) and an electrophotographic light-sensitive material containing an eutectoid complex composed of a dye and a resin as the main component (U.S. Pat. Nos. 3,732,180 and 3,684,502), etc. 
     In these organic electrophotographic light-sensitive materials, the mechanical characteristics and flexibility of the above described inorganic electrophotographic light-sensitive material can be improved to certain extent. However, the material still do not sufficiently satisfy requirements for the electrophotographic light-sensitive material because they generally have a low light-sensitivity and are not suitable for repeated use. 
     SUMMARY OF THE INVENTION 
     As a result of earnest studies to eliminate disadvantages in the above described prior electrophotographic light-sensitive materials, the present inventors have found that electrophotographic light-sensitive materials containing novel disazo compounds have high sensitivity and high durability sufficient to put in practical use. 
     The present invention relates to novel disazo compounds (disazo pigments) represented by the following general formula, photoconductive compositions containing the same, and electrophotographic light-sensitive materials having an electrophotographic light-sensitive layer containing the same. 
     Namely, the present invention relates to 
     (1) Disazo compounds represented by the following general formula (I): ##STR2## wherein L 1  and L 2  each represents a hydrogen atom, a halogen atom (for example, a chlorine atom, a bromine atom, an iodine atom or a fluorine atom), a cyano group or a methylthio group, but L 1  and L 2  do not represent hydrogen atoms together, though they may represent identical or different groups, and A represents ##STR3## wherein X represents a group necessary to form an aromatic ring such as a naphthalene ring or an anthracene ring or a heterocyclic ring such as an iodole ring, a carbazole ring, a benzocarbazole ring or a dibenzofuran ring (which may be substituted or nonsubstituted) or condensing with the benzene ring in the above described formula to which a hydroxyl group and Y are attached, Y represents ##STR4## R 1  represents an alkyl group, a phenyl group or a substituted alkyl or phenyl group, R 2  represents a hydrogen atom, a lower alkyl group, a carbamoyl group, a carboxyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, or a substituted or nonsubstituted amino group, R 3  and R 5  each represents an alkyl group, an aromatic group such as a phenyl group, a naphthyl group or an anthryl group, etc., a heteroaromatic group such as a dibenzofuranyl group, a carbazolyl group, a benzocarbazolyl group or an indolyl group, etc., or a substituted group of the alkyl, aromatic or heteroaromatic group, and R 4  represents a hydrogen atom, an alkyl group, a phenyl group or a substituted alkyl or phenyl group, 
     (2) photoconductive compositions containing disazo compounds represented by the above described general formula (I), and 
     (3) electrophotographic light-sensitive materials having an electrophotographic light-sensitive layer containing disazo compounds represented by the above described general formula (I). 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The FIGURE is an infrared ray absorption spectrum (KBr method) of the disazo compound (1E) of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Disazo compounds represented by the general formula (I) are illustrated in greater detail. 
     L 1  and L 2  are preferably halogen atoms, a cyano group or a methylthio group and are more preferably halogen atoms, such as a chlorine atom or a bromine atom. 
     X is a group capable of forming an aromatic ring such as a naphthalene ring or an anthracene ring, etc. or a heterocyclic ring such as an indole ring, a carbazole ring, a benzocarbazole ring or a dibenzofuran ring, etc. by condensing with the benzene ring to which the hydroxyl group and Y are attached. 
     When X is an aromatic ring or heterocyclic ring having substituents, examples of substituents are halogen atoms (for example, fluorine atom, chlorine atom and bromine atom, etc.), lower alkyl groups and, preferably, lower alkyl groups having 1 to 8 carbon atoms (for example, methyl group, ethyl group, propyl group, butyl group, isopropyl group and isobutyl group, etc.). The number of substituents is 1 or 2. When there are two substituents, they may be identical or different from each other. 
     R 1  is an alkyl group, preferably having 1 to 12 carbon atoms or a phenyl group. 
     When R 1  is a nonsubstituted alkyl group, examples of R 1  include methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, isopropyl group, isobutyl group, isoamyl group, isohexyl group, neopentyl group and tert-butyl group, etc. 
     When R 1  is a substituted alkyl group, examples of substituents include hydroxyl group, alkoxy groups having 1 to 12 carbon atoms, cyano group, amino group, alkylamino groups having 1 to 12 carbon atoms, dialkylamino groups having two alkyl groups having 1 to 12 carbon atoms, halogen atoms and aryl groups having 6 to 15 carbon atoms. Examples of the substituted alkyl group include hydroxyalkyl groups (for example, hydroxymethyl group, 2-hydroxyethyl group, 3-hydroxypropyl group and 2-hydroxypropyl group, etc.), alkoxyalkyl groups (for example, methoxymethyl group, 2-methoxyethyl group, 3-methoxypropyl group, ethoxymethyl group and 2-ethoxyethyl group, etc.), cyanoalkyl groups (for example, cyanomethyl group and 2-cyanoethyl group, etc.), aminoalkyl groups (for example, aminomethyl group, 2-aminoethyl group and 3-aminopropyl group, etc.), (alkylamino)alkyl groups (for example, (methylamino)methyl group, 2-(methylamino)ethyl group and (ethylamino)methyl group, etc.), (dialkylamino)alkyl groups (for example, (dimethylamino)methyl group and 2-(dimethylamino)ethyl group, etc.), halogenoalkyl groups (for example, fluoromethyl group, chloromethyl group and bromomethyl group, etc.) and aralkyl groups (for example, benzyl group and phenetyl group, etc.). 
     When R 1  is a substituted phenyl group, examples of substituents include hydroxyl group, alkoxy groups having 1 to 12 carbon atoms, cyano group, amino group, alkylamino groups having 1 to 12 carbon atoms, dialkylamino groups having two alkyl groups having 1 to 12 carbon atoms, halogen atoms, alkyl groups having 1 to 6 carbon atoms and nitro group. Examples of the substituted phenyl group include hydroxyphenyl groups, alkoxyphenyl groups (for example, methoxyphenyl group and ethoxyphenyl group, etc.), cyanophenyl groups, aminophenyl groups, (alkylamino)phenyl groups (for example, (methylamino)phenyl group and (ethylamino)phenyl group, etc.), (dialkylamino)phenyl groups (for example, dimethylamino phenyl group, etc.), halogenophenyl groups (for example, fluorophenyl group, chlorophenyl group and bromophenyl group, etc.), alkylphenyl groups (for example, tolyl group, ethylphenyl group, cumenyl group, xylyl group and mesityl group, etc.), nitrophenyl groups, and groups having two or three of the above described substituents (which may be identical or different from one another) (position of the substituents and relation of the position between each of them are arbitrary). 
     It is preferred that R 2  is a hydrogen atom, a lower alkyl group having 1 to 6 carbon atoms, a carbamoyl group, a carboxyl group, an alkoxycarbonyl group having an alkoxy group having 1 to 12 carbon atoms, an aryloxycarbonyl group having an aryloxy group having 6 to 20 carbon atoms, or a substituted or nonsubstituted amino group. 
     When R 2  is a substituted amino group, examples thereof include methylamino group, ethylamino group, propylamino group, phenylamino group, tolylamino group, benzylamino group, phenetylamino group, dimethylamino group, diethylamino group and diphenylamino group, etc. 
     When R2 is a lower alkyl group, examples thereof include methyl group, ethyl group, propyl group, butyl group, isopropyl group and isobutyl group, etc. 
     When R 2  is an alkoxycarbonyl group, examples thereof include methoxycarbonyl group, ethoxycarbonyl group, propoxycarbonyl group, butoxycarbonyl group, isopropoxycarbonyl group and benzyloxycarbonyl group, etc. 
     When R 2  is an aryloxycarbonyl group, examples thereof include phenoxycarbonyl group and tolyloxycarbonyl group, etc. 
     It is preferred that R 3  and R 5  each is an alkyl group having 1 to 20 carbon atoms, an aromatic group such as a phenyl group or a naphthyl group, etc., a heteroaromatic group containing an oxygen atom, a nitrogen atom or a sulfur atom, etc. such as a dibenzofuranyl group, a carbazolyl group or a benzocarbazolyl group, etc., or a substituted group of them. 
     When R 3  and R 5  are each a substituted or nonsubstituted alkyl group, examples thereof include the same groups as the above described substituted or nonsubstituted alkyl groups in R 1 . 
     When R 3  and R 5  are each a substituted aromatic group such as a substituted phenyl group or a substituted naphthyl group, etc. or a substituted heteroaromatic group containing hetero atoms such as a substituted dibenzofuranyl group or a substituted carbazolyl group, examples of substituents include hydroxyl group, cyano group, nitro group, halogen atoms (for example, fluorine atom, chlorine atom and bromine atom, iodine atom, etc.), alkyl groups having 1 to 12 carbon atoms (for example, methyl group, ethyl group, propyl group and isopropyl group, etc.), alkoxy groups having 1 to 12 carbon atoms (for example, methoxy group, ethoxy group, propoxy group, butoxy group, pentyloxy group, isopropoxy group, isobutoxy group, isoamyloxy group, tert-butoxy group and neopentyloxy group, etc.), amino group, alkylamino groups having 1 to 12 carbon atoms (for example, methylamino group, ethylamino group and propylamino group, etc.), dialkylamino groups having 1 to 12 carbon atoms (for example, dimethylamino groups, diethylamino group and N-methyl-N-ethylamino group, etc.), arylamino groups having 6 to 12 carbon atoms (for example, phenyl amino group and tolylamino group, etc.), diarylamino groups having two aryl groups having 6 to 15 carbon atoms (for example, diphenylamino group, etc.), carboxyl group, alkali metal carboxylate groups (examples of alkali metal (cation): Na + , K +  and Li + , etc.), alkali metal sulfonate groups (examples of alkali metal (cation): Na + , K + , Li + , etc.), alkylcarbonyl groups (for example, acetyl group, propionyl group and benzylcarbonyl group, etc.), arylcarbonyl groups having an aryl group having 6 to 12 carbon atoms (for example, benzoyl group, toluoyl group, etc.) alkylthio groups having 1 to 12 carbon atoms (for example, methylthio group and ethylthio group, etc.) and arylthio groups having 1 to 12 carbon atoms (for example, phenylthio group and tolylthio group, etc.). The number of the substituents is 1 to 3. When there is a plurality of substituents, they may be identical or different from one another and have a suitable combination. Further, the position of the substituents is arbitrary. 
     R 4  may be a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, a phenyl group or a substituted group thereof. 
     When R 4  is a substituted or nonsubstituted alkyl or phenyl group, examples thereof include the same groups as those of the above described substituted or nonsubstituted alkyl or phenyl group in R 3  and R 5 . 
     As A which is derived from couplers, ##STR5## is preferred, because a photoconductive composition or electrophotographic light-sensitive layer having a high light sensitivity is obtained and the disazo compounds can be produced at a low cost because the raw materials are easily available. 
     Further, as X, a group forming a naphthalene ring, a carbazole ring or a dibenzofuran ring is preferred. 
     As Y, ##STR6## is preferred. 
     In the following, examples of the compounds of the present invention are described. ##STR7## 
     The novel disazo compounds of the present invention can be produced by a known process. Namely, they can be easily produced by a process which comprises diazotizing 2,5-substituted-1,4-bis-(aminostyryl)benzene to isolate as a tetrazonium salt and thereafter carrying out a coupling reaction with a compound corresponding to the above described each pigment (for example, a naphthol AS type coupler) in a suitable organic solvent such as N,N-dimethylformamide in the presence of an alkali. 
     The disazo compounds of the present invention can be used as disazo pigments. 
     For example, the above described disazo compound (1E) can be produced according to Synthesis Example 1. 
     SYNTHESIS EXAMPLE 1 
     3.86 g of 2,5-dichloro-1,4-bis-(aminostyryl)benzene was added to diluted hydrochloric acid prepared from 5 ml of concentrated hydrochloric acid and 5 ml of water, and the mixture was well stirred on a water bath at 60° C. for about 30 minutes. The resulting mixture was then cooled to 0° C., and a solution prepared by dissolving 1.5 g of sodium nitrite in 30 ml of water was added dropwise thereto at 0° C. over about 30 minutes. Then, the mixture was stirred at the same temperature for 1 hour, and the formed tetrazonium chloride was filtered out. The tetrazonium salt was dissolved in water, and the resulting solution was mixed with the filtrate. To the mixed solution, 6 ml of 42% borofluoric acid was added, and the separated crystals were filtered out. After the crystals were washed with a small amount of cold water, they were dried to obtain 4.7 g (yield: 84%) of redish orange crystals of tetrazonium floroborate. 
     2 g of the resulting tetrazonium salt and 1.92 g of 2-hydroxy-3-naphthoic acid anilide as a coupler were dissolved in 150 ml of N,N-dimethylformamide. After a solution composed of 4 mg of sodium acetate and 30 ml of water was added dropwise at a temperature of 0° C. over about 20 minutes to the resulting solution, the mixture was stirred at a room temperature for about 2 hours. Thereafter, the formed precipitates were filtered out and washed with 300 ml of water. Then, they were washed with stirring in 100 ml of N,N-dimethylformamide. Thereafter, they were washed with ethanol and dried to obtain 2.97 g (yield: 88%) of a disazo pigment: Compound (1E). 
     Decomposition point: above 300° C. 
     Elementary analysis: As C 56  H 38  O 4  N 6  Cl 2  : Calculation value: C 72.33% H 4.12% N 9.04% Cl 7.63%. Found value: C 72.88% H 3.89% N 9.39% Cl 7.43%. 
     IR absorption spectrum (KBr tablet): Amide: 1570 cm -1 . 
     Visible ray absorption spectrum: Absorption maximum wavelength: 648 nm (in dichloromethane solution). 
     SYNTHESIS EXAMPLES 2-10 
     Disazo compounds (2E), (3E), (4E), (5E), (11E), (13E), (15E), (25E) and (26E) were synthesized by the same process as in Synthesis Example 1, except that compounds described in Table 1 were used as couplers. The decomposition point, elementary analysis values, IR absorption spectrum and visible ray absorption spectrum of each disazo compound are shown in Table 1. 
     
         __________________________________________________________________________                                        IR absorption                 Disazo compound                          Elementary analysis value                                        spectrumSynthesis             (Decomposition                            Calcination                                  Found νc = 0 cm.sup.-1ExampleCoupler          point)     value (%)                                  value (%)                                        (KBr method)                                                λmax:nm__________________________________________________________________________ ##STR8##        (2E)(above 300° C.)                          CHNCl                            72.724.428.777.40                                  72.684.738.517.67                                        1670    649(In                                                dichloroethane)3 ##STR9##        (3E)(above 300° C.)                          CHNCl                            70.374.288.497.16                                  70.304.548.457.42                                        1665    646(In                                                dichloroethane)4 ##STR10##       (4E)(above 300° C.)                          CHNCl                            67.35 3.63 8.4114.20                                  67.33 3.31 8.7314.22                                        1670    574(In                                                dichloroethane)5 ##STR11##       (5E)(above 300° C.)                          CHNCl                            70.88 3.7011.44 3.15                                  70.90 3.5611.69 3.46                                        1670    529(In                                                dichloroethane)6 ##STR12##       (11E)(above 300° C.)                          CHNCl                            67.85 3.93 8.1813.81                                  68.18 3.67 8.3413.71                                        1670    539(In                                                dichloroethane)7 ##STR13##       (13E)(above 300° C.)                          CHNCl                            73.104.708.527.19                                  73.174.598.567.07                                        1670    656(In                                                dichloroethane)8 ##STR14##       (15E)(above 300° C.)                          CHNCl                            70.374.288.497.16                                  70.404.458.767.14                                        1670    631(In                                                dichloroethane)9 ##STR15##       (25E)(above 300° C.)                          CHNCl                            74.634.118.166.88                                  74.544.178.066.73                                        1675    645(In                                                dichloroethane)10 ##STR16##       (26E)(above 300° C.)                          CHNCl                            74.634.118.166.88                                  74.514.238.136.77                                        1680    656(In                                                dichloroethane)__________________________________________________________________________ 
    
     An infrared absorption spectrum (KBr method) of the disazo compound (1E) is shown in the FIGURE. 
     Other disazo compounds can be synthesized according to the above described Synthesis Example by changing the coupler. 
     The electrophotographic light-sensitive materials of the present invention have an electrophotographic light-sensitive layer containing one or more disazo compounds represented by the above described general formula. Various types of electrophotographic light-sensitive material have been known, and the electrophotographic light-sensitive materials of the present invention can be applied to any type of light-sensitive material. However, they generally have the following types of electrophotographic light-sensitive construction. 
     (1) An electrophotographic light-sensitive layer in which disazo compounds are dispersed in a binder or a charge transporting medium is provided on an electrically conductive base. 
     (2) A charge transporting generation layer containing the disazo compounds as a main component is provided on an electrically conductive base, and a charge carrier transporting medium layer is provided on the above described layer. 
     The disazo compounds of the present invention act as photoconductive substances, which produce charge carriers in a very high efficiency when light is absorbed. Although the produced charges can be transported through the disazo compounds as a medium, it is more effective to transport through a charge transporting compound as a medium. 
     In order to produce electrophotographic light-sensitive materials of the type (1), fine particles of the disazo compounds are dispersed in a solution of a binder or a solution prepared by dissolving a charge carrier transporting compound and a binder, and the resulting dispersion is applied to an electrically conductive base and dried. The electrophotographic light-sensitive layer in this case is preferred to have a thickness of 3 to 30μ, preferably 5 to 20μ. 
     In order to produce electrophotographic light-sensitive materials of the type (2), the disazo compounds are applied to an electrically conductive base by vacuum evaporation or by applying a solution prepared by dissolving the disazo compounds in a suitable solvent such as amine, etc. or by applying a dispersion propared by dispersing fine particles of the disazo compounds in a suitable solvent or, if necessary, a solvent containing a binder and drying, and, thereafter, a solution containing a charge transporting compound and a binder is applied to the resulting layer and dried. The disazo compound layer which is a charge generating layer in this case is preferred to have a thickness of 4μ or less, preferably, 2μ or less, and the charge transporting layer is preferred to have a thickness of 3 to 30μ, more preferably 5 to 20μ. 
     The disazo compounds used for the light-sensitive materials of the types (1) and (2) are prepared by grinding by means of a dispersing machine such as a ball mill, a sand mill or a vibration mill so as to have a particle size of 5μ or less, preferably 2μ or less. 
     If the amount of the disazo compounds used in the electrophotographic light-sensitive materials of the type (1) is too small, the sensitivity is inferior, and, if it is too large, the electrically charging property deteriorates or the strength of the electrophotographic light-sensitive layer becomes weak. Accordingly, the weight amount of the disazo compounds in the electrophotographic light-sensitive layer is preferred to be in a range of 0.01 to 2 times, preferably 0.05 to 1 times the weight of the binder. The weight amount of the charge transporting compound which is added as occasion demands is preferred to be in a range of 0.1 to 2 times, preferably 0.3 to 1.3 times the weight of the binder. Further, when using the charge transporting compound which can be used as a binder, the disazo compounds are preferably used in a weight amount of 0.01 to 0.5 times the weight of the binder. 
     Further, in the electrophotographic light-sensitive materials of the type (2), when a disazo compound containing layer which is a charge generating layer is formed by coating, it is preferred that the weight amount of the disazo compounds is 0.2 time the weight or more of the binder resin. If the weight amount is less than 0.2 time the weight sufficient sensitivity can not be obtained. The weight amount of the charge transporting compound in the charge transporting medium is preferably in a range of 0.2 to 2 times, more preferably 0.3 to 1.3 times the weight of the binder. When using a high molecular charge transporting compound which can be used itself as a binder, it is possible to such a compound use without using another binder. 
     When producing the electrophotographic light-sensitive materials of the present invention, additives such as a plasticizer or a sensitizer, etc. may be used together with the binder. 
     The electrically conductive base used in the electrophotographic light-sensitive materials of the present invention may be metal plates such as aluminium, copper or zinc plates, etc., plastic sheets such as polyester sheets, etc., plastic films to which an electrically conductive material such as aluminium, indium oxide or SnO 2 , etc. is applied by vacuum evaporation or by applying a dispersion thereof, and papers which are treated so as to have an electrically conductive property. 
     Useful binders include condensation type resins such as polyamide, polyurethane, polyester, epoxy resin, polyketone or polycarbonate, etc., and vinyl polymers such as polyvinylketone, polystyrene, poly-N-vinylcarbazole, and polyacrylamide all of which are resins which are electrically insulating and have an adhesive property. 
     Useful plasticizers include biphenyl, chlorinated biphenyl, o-terphenyl, p-terphenyl, dibutyl phthalate, dimethyl glycol phthalate, dioctyl phthalate, triphenyl phosphate, methylnaphthalene, benzophenone, chlorinated paraffin, polypropylene, polystyrene, dilaurylthio-di-propionate, 3,5-dinitrosalicylic acid and various fluorohydrocarbons. 
     In addition, silicone oil, etc. may be added in order to improve surface properties of the electrophotographic light-sensitive materials. 
     Useful sensitizers include chloranil, tetracyanoethylene, Methyl Violet, Rhodamine B, cyanine dyes, merocyanine dyes, pyrylium dyes and thiapyrylium dyes, etc. 
     Compounds which transport charge carriers are classified generally into two kinds one of which is a compound which transports electrons and the other of which is a compound which transports positive holes. In the electrophotographic light-sensitive materials of the present invention, both of them can be used. Compound which transports electrons include compounds having electron attractive groups, examples of which include 2,4,7-trinitro-9-fluorenone, 2,4,5,7-tetranitro-9-fluorenone, 9-dicyanomethylene-2,4,7-trinitrofluoreneon, 9-dicyanomethylene-2,4,5,7-tetranitrofluorenone, tetranitrocarbazole chloranil, 2,3-dichloro-5,6-dicyanobenzoquinone, 2,4,7-trinitro-9,10-phenanthrenequinone, tetrachlorophthalic acid anhydride, tetracyanoethylene and tetracyanoquinodimethane, etc. 
     Compounds which transfers positive holes include compounds having electron donative groups. 
     Examples of high polymers include 
     (1) Polyvinylcarbazole and derivatives thereof described in Japanese Patent Publication 10966/59, 
     (2) Vinyl polymers described in U.S. Pat. Nos. 3,232,755 and 3,162,532, such as polyvinylpyrene, polyvinylanthracene, poly-2-vinyl-4-(4&#39;-dimethylaminophenyl)-5-phenyl-oxazole or poly-3-vinyl-N-ethylcarbazole, etc., 
     (3) Polymers described in U.S. Pat. No. 3,169,060, such as polyacenaphthylene, polyindene or acenaphthylenestyrene copolymer, etc., 
     (4) Condensation resins as described in U.S. Pat. Nos. 3,842,038 and 3,881,922, such as pyrene-formaldehyde resin, bromopyrene-formaldehyde resin or ethylcarbazoleformaldehyde resin, etc., and 
     (5) Triphenylmethane polymers described in Japanese Patent Applications (OPI) 90833/81 and 161550/81. 
     Further, examples of low molecular compounds include 
     (6) Triazole derivatives described in U.S. Pat. No. 3,112,197, etc., 
     (7) Oxadiazole derivatives described in U.S. Pat. No. 3,189,447, etc., 
     (8) Imidazole derivatives described in Japanese Patent Publication No. 16096/62, etc., 
     (9) Polyarylalkane derivatives described in U.S. Pat. Nos. 3,615,402, 3,820,898, 3,542,544, 3,542,547, 3,963,799 and 4,127,412, Japanese Patent Application (OPI) Nos. 17105/80 and 4148/81, and Japanese Patent Application (OPI) Nos. 108667/80, 156953/80 and 36656/81, etc., 
     (10) Pyrazoline derivatives and pyrazolone derivatives described in U.S. Pat. Nos. 3,180,729, 3,837,851 and 4,278,746, and Japanese Patent Application (OPI) Nos. 88064/80, 88065/80, 51086/80, 80051/81, 88141/81, 45545/82, 112637/79 and 74546/80, etc., 
     (11) Phenylenediamine derivatives described in U.S. Pat. No. 3,615,404, Japanese Patent Publication No. 10105/76, Japanese Patent Application (OPI) Nos. 83435/79, 110836/79 and 119925/79, and Japanese Patent Publication Nos. 3712/71 and 28336/72, etc. 
     (12) Arylamine derivatives described in U.S. Pat. No. 3,567,450, Japanese Patent Publication No. 35702/74, German Patent (DAS) No. 1110518, U.S. Pat. Nos. 3,180,703, 3,240,597, 3,658,520, 4,232,103, 4,175,961 and 4,012,376, Japanese Patent Application (OPI) Nos. 144250/80 and 119132/81, Japanese Patent Publication No. 27577/64, and Japanese Patent Application (OPI) No. 22437/81. 
     (13) Amino substituted chalcone derivatives described in U.S. Pat. No. 3,526,501, 
     (14) N,N-Bicarbazyl derivatives described in U.S. Pat. No. 3,542,546, etc., 
     (15) Oxazole derivatives described in U.S. Pat. No. 3,257,203, 
     (16) Styrylanthracene derivatives described in Japanese Patent Application (OPI) No. 46234/81, etc., 
     (17) Fluorenone derivatives described in U.S. Pat. No. 4,245,021, etc., and 
     (18) Hydrazole derivatives described in U.S. Pat. No. 3,717,462, Japanese Patent Application (OPI) Nos. 59143/79 (corresponding to U.S. Pat. No. 4,150,987), 52063/80, 52064/80, 46760/80 and 58495/80, Japanese Patent Application Nos. 33832/81 and 85495/80, and 64244/82 and Japanese Patent Application (OPI) No. 64244/82, etc. 
     In the present invention, the compounds which transport charges are not limited to the above described compounds (1)-(18), since any of the known charge transporting compounds can be used. 
     It is possible to use, if desired, two or more of these charge transporting materials together. 
     Further, in the light-sensitive materials obtained as described above, it is possible to provide, if necessary, an adhesive layer or a barrier layer between the electrically conductive base and the light-sensitive layer. Materials used for these layers include polyamide and nitrocellulose and aluminium oxide. These layers are preferred to have a thickness of 1 μm or less. 
     The electrophotographic light-sensitive materials of the present invention have been described in detail in the above, and are generally characterized by having high sensitivity and excellent durability. 
     The electrophotographic light-sensitive materials of the present invention can be applied not only to electrophotographic copying machines but also in the field of light-sensitive materials for printers in which laser or Braun tubes are used as a light source. 
     The photoconductive compositions containing the disazo compounds of the present invention can be used as a photoconductive layer in video camera tubes and as a photoconductive layer in the known solid camera elements which have a light receiving layer (photoconductive layer) provided on the whole face of a semiconductor circuit arranged one- or two-dimensionally so as to carry out signal transfer or scanning. Further, they can be used as a photoconductive layer in solar cells, as described in A. K. Ghosh, Tom Feng, J. Appl. Phys. 49 (12) 5982 (1978). 
     Further, as described in Japanese Patent Publication No. 17162/62, Japanese Patent Application (OPI) Nos. 19063/80 and 161250/80 and Japanese Patent Application No. 33579/81, after the disazo compounds of the present invention are dispersed in a solution of alkali soluble resin such as phenol resin, etc. together with the above described charge transporting compound such as oxadiazole derivatives or hydrazone derivatives, etc., and applied to an electrically conductive base such as aluminium, etc. and dried, the resulting material is subjected to imagewise exposing to light, toner development and etching with an aqueous alkaline solution, by which not only printing plates having a high resolving power, a high durability and a high sensitivity are obtained, but also print circuits can be produced. 
     In the following, the present invention is illustrated in greater detail with reference to examples, but the present invention is not limited to them. In the examples, the term &#34;part&#34; means &#34;part by weight&#34;. 
     EXAMPLE 1 
     1 part of disazo compound (1E), 5 parts of 4,4&#39;-bis-(diethylamino)-2,2&#39;-dimethyltriphenylmethane and 5 parts of polycarbonate of bisphenol A were added to 95 parts of dichloromethane. The mixture was ground and blended by means of a ball mill. The resulting coating solution was applied to an electrically conductive transparent base (wherein an indium oxide membrane is provided by vacuum evaporation on the surface of a polyethylene terephthalate film (having a thickness of 100 μm; surface resistivity: 10 3  Ω) by means of a wire wound rod and dried to prepare an electrophotographic light-sensitive material having a monolayer type electrophotographic light-sensitive layer having a thickness of about 8 μm. 
     This electrophotographic light-sensitive material was electrified in +400 V by corona discharging at +5 KV by means of a testing apparatus for electrostatic copying paper (Type SP-428, produced by Kawaguchi Denki Co.) and, thereafter, it was exposed to light by a tungsten lamp having a color temperature of 3000° K. so as to have a surface illuminance of 4 luxes. When the half-decay exposure amount E 50  (Lux. sec) was determined by measuring the time necessary to reduce the surface electric potential to half of the initial surface electric potential, it was 10.2 (Lux. second). After two steps of electrifying and exposing to light were repeated 3000 times, the value E 50  hardly changed. 
     EXAMPLE 2-81 
     Electrophotographic light-sensitive materials having a monolayer construction were produced by the same manner as in Example 1, except that disazo compounds (1A), (2A), (3A), (4A), (5A), (11A), (13A), (48A), (53A), (61A), (1B), (2B), (3B), (4B), (5B), (25B), (26B), (49B), (54B), (62B), (1C), (3C), (4C), (5C), (11C), (13C), (25C), (48C), (55C), (C), (1D), (2D), (4D), (5D), (13D), (18D), (26D), (49D), (56D), (64D), (2E), (3E), (4E), (5E), (11E), (13E), (15E), (25E), (26E), (48E), (57E), (65E), (1F), (3F), (5F), (11F), (13F), (26F), (29F), (45F), (53F), (61F), (2G), (3G), (4G), (5G), (11G), (13G), (48G), (54G), (62G), (1H), (3H), (5H), (8H), (23H), (25H), (47H), (57H) and (63H) were used instead of the disazo compound (1E). When the half-decay exposure amount was measured by positively electrifying by the same manner as in Example 1, values shown in Table 2 were obtained. 
     
                       TABLE 2______________________________________Ex-                      Ex-am-  Disazo    E.sub.50  am-  Disazo  E.sub.50ple  compound  (lux · sec)                    ple  compound                                 (lux · sec)______________________________________2    (1A)      10.5      42   (2E)    22.13    (2A)      6.0       43   (3E)    14.34    (3A)      7.0       44   (4E)    5.95    (4A)      18.4      45   (5E)    40.46    (5A)      8.9       46   (11E)   3.87    (11A)     8.7       47   (13E)   34.78    (13A)     5.6       48   (15E)   39.59    (48A)     40.6      49   (25E)   20.210   (53A)     18.5      50   (26E)   21.311   (61A)     59.0      51   (48E)   7.512   (1B)      11.7      52   (57E)   94.013   (2B)      6.6       53   (65E)   40.614   (3B)      6.7       54   (1F)    27.815   (4B)      7.0       55   (3F)    6.616   (5B)      29.0      56   (5F)    25.617   (25B)     55.3      57   (11F)   38.118   (26B)     4.3       58   (13F)   21.719   (49B)     62.0      59   (26F)   7.720   (54B)     30.8      60   (29F)   27.721   (62B)     84.0      61   (45F)   20.922   (1C)      9.1       62   (53F)   37.023   (3C)      14.5      63   (61F)   71.224   (4C)      5.6       64   (2G)    4.325   (5C)      11.4      65   (3G)    6.626   (11C)     19.5      66   (4G)    6.327   (13C)     6.3       67   (5G)    6.028   (25C)     8.1       68   (11G)   6.629   (48C)     9.1       69   (13G)   9.130   (55C)     53.0      70   (48G)   6.531   (63C)     42.9      71   (54G)   32.832   (1D)      16.4      72   (62G)   33.233   (2D)      8.9       73   (1H)    4.334   (4D)      44.5      74   (3H)    12.035   (5D)      15.0      75   (5H)    7.736   (13D)     7.4       76   (8H)    8.737   (18D)     9.8       77   (23H)   17.338   (26D)     54.6      76   (25H)   43.539   (49D)     28.9      79   (47H)   7.240   (56D)     40.8      80   (57H)   64.841   (64D)     74.5      81   (63H)   70.5______________________________________ 
    
     EXAMPLE 82 
     5 g of the disazo compound (1A) was dispersed in a solution prepared by dissolving 2 g of polyvinyl butyral resin (degree of butyral: 63% by mol) in 100 ml of ethanol by processing in a ball mill for 20 minutes. Thereafter, the dispersion was applied to an electrically conductive base (wherein an aluminium membrane formed by vacuum evaporation was provided on the surface of a polyethylene terephthalate film having 100 μm; surface electric resistivity: 10 3  Ω) by means of a wire wound rod and dried to form a charge generating layer having a thickness of 1 μm. 
     A solution prepared by dissolving 2 parts of p-(diphenylamino)benzaldehyde N&#39;-methyl-N&#39;-phenylhydrazone ##STR17## and 4 parts of polycarbonate of bisphenol A in 60 parts of dichloromethane was then applied to the resulting charge generating layer by means of a wire wound rod and dried to form a charge transporting layer having a thickness of 8 μm, by which an electrophotographic light-sensitive material having an electrophotographic light-sensitive layer consisting of two layers was produced. 
     After the light-sensitive material was electrified in -400 V by corona discharging at -5 KV, the half-decay exposure amount was measured. E 50  was 12.4 (lux.second). 
     EXAMPLES 83-146 
     Electrophotographic light-sensitive materials having two layer construction were produced by the same manner as in Example 82, except that disazo compounds (2A), (3A), (5A), (7A), (12A), (43A), (54A), (62A), (1B), (2B), (15B), (17B), (27B), (45B), (56B), (61B), (2C), (4C), (6C), (10C), (37C), (48C), (55C), (64C), (1D), (4D), (5D), (8D), (25D), (46D), (57D), (63D), (1E), (2E), (7E), (16E), (29E), (47E), (53E), (65E), (2F), (3F), (9F), (12F), (38F), (49F), (58F), (66F), (1G), (4G), (18G), (19G), (39G), (48G), (60G), (61G), (2H), (4H), (6 H), (7H), (18H), (49H), (56H) and (63H) were used instead of the disazo compound (1A), respectively, and E 50  was measured. Results are shown in Table 3. 
     
                       TABLE 3______________________________________ Ex-                      Ex-am-   Disazo    E.sub.50  am-  Disazo  E.sub.50ple   compound  (lux · sec)                     ple  compound                                  (lux · sec)______________________________________83    (2A)      15.5      115  (1E)    4.584    (3A)      41.0      116  (2E)    10.885    (5A)      27.3      117  (7E)    8.686    (7A)      6.6       118  (16E)   34.187    (12A)     15.2      119  (29E)   47.188    (43A)     6.1       120  (47E)   14.389    (54A)     15.7      121  (53E)   61.490    (62A)     45.7      122  (65E)   47.391    (1B)      29.2      123  (2F)    9.792    (2B)      8.5       124  (3F)    5.493    (15B)     8.7       125  (9F)    9.694    (17B)     9.8       126  (12F)   34.095    (27B)     38.1      127  (38F)   27.796    (45B)     6.8       128  (49F)   7.497    (56B)     46.0      129  (58F)   31.198    (61B)     44.3      130  (66F)   23.499    (2C)      5.1       131  (1G)    5.0100   (4C)      9.5       132  (4G)    31.3101   (6C)      22.0      133  (18G)   7.9102   (10C)     7.2       134  (19G)   49.1103   (37C)     5.1       135  (39G)   4.9104   (48C)     6.3       136  (48G)   4.8105   (55C)     9.1       137  (60G)   4.2106   (64C)     30.1      138  (61G)   20.2107   (1D)      29.8      139  (2H)    7.2108   (4D)      11.4      140  (4H)    27.3109   (5D)      7.4       141  (6H)    8.1110   (8D)      4.5       142  (7H)    5.4111   (25D)     6.5       143  (18H)   18.8112   (46D)     8.4       144  (49H)   7.3113   (57D)     8.7       145  (56H)   40.0114   (63D)     46.7      146  (63H)   17.6______________________________________ 
    
     EXAMPLE 147 
     A charge transporting layer having a thickness of 12 m was formed on a charge generating layer having a thickness of 1 m by the same manner as in Example 82, except that 4 parts of 2,4,7-trinitro-9-fluorenone were used in the charge transporting layer instead of p-(diphenylamino)benzaldehyde N&#39;-methyl-N&#39;-phenylhydrazone. 
     The resulting electrophotographic light-sensitive material was charged in +60 OV by corona discharging at +5 KV. When E 50  was measure, it was 18.2 (lux.sec). 
     EXAMPLE 148-179 
     Electrophotographic light-sensitive materials having two layer construction were produced by the same manner as in Example 82, except that disazo compounds (2A), (50A), (57A), (62A), (10B), (46B), (55B), (63B), (15C), (51C), (54C), (61C), (7D), (43D), (56D), (64D), (14E), (52E), (59E), (66E), (11F), (48F), (60F), (65F), (5G), (48G), (53G), (61G), (11H), (48H), (55H), and (62H) were used instead of the disazo compound (1A), respectively, and E 50  was measured. 
     Results are shown in Table 4 
     
                       TABLE 4______________________________________         Disazo    E.sub.50Example       compound  (lux · sec)______________________________________148           (2A)      46.7149           (50A)     45.2150           (57A)     10.8151           (62A)     34.1152           (10B)     4.7153           (46B)     14.3154           (55B)     37.4155           (63B)     17.9156           (15C)     24.5157           (51C)     9.6158           (54C)     34.0159           (61C)     27.7160           (7D)      7.4161           (43D)     31.1162           (56D)     23.4163           (64D)     31.1164           (14E)     7.9165           (52E)     49.1166           (59E)     49.8167           (66E)     48.2168           (11F)     41.5169           (48F)     20.2170           (60F)     27.8171           (65F)     27.9172           (5G)      8.2173           (48G)     18.8174           (53G)     38.7175           (61G)     40.0176           (1H)      7.7177           (48H)     9.6178           (55H)     40.0179           (62H)     24.7______________________________________ 
    
     EXAMPLE 180 
     1 Part of disazo compound (1A) and 1 part of polycarbonate of bisphenol A were added to 25 parts of dichloromethane, and the mixture was ground and blended in a ball mill. The resulting coating solution was applied to an electrically conductive transparent base wherein an indium oxide membrane formed by vacuum evaporation was provided on the surface of a polyethylene terephthalate film having 100 μm; surface resistivity: 10 3  Ω) by means of a wire wound rod, and dried to obtain an electrophotographic light-sensitive material having a monolayer type electrophotographic light-sensitive layer having a thickness of about 9 μm. 
     After the resulting electrophotographic light-sensitive material was charged in +450 V by corona discharging at +5 KV, E 50  was measured. It was 22.6 (lux.sec). 
     EXAMPLES 181-212 
     Monolayer type electrophotographic light-sensitive materials were produced by the same manner as in Example 180, except that the disazo compounds (3A), (51A), (56A), (61A), (12B), (45B), (54B), (62B), (18C), (48C), (58C), (63C), (17D), (44D), (53D), (63D), (21E), (46E) (55E), (62E), (24F), (44F), (57F), (64F), (19G), (51G), (54G), (61G), (13H), (45H), (59H) and (64H) were used instead of the disazo compound (1A), respectively, and E 50  was measured. Results are shown in Table 5. 
     
                       TABLE 5______________________________________         Disazo    E.sub.50Example       compound  (lux · sec)______________________________________181           (3A)      4.6182           (51A)     28.5183           (56A)     49.7184           (61A)     83.0185           (12B)     14.2186           (45B)     20.8187           (54B)     52.1188           (62B)     30.6189           (18C)     5.4190           (48C)     8.3191           (58C)     15.1192           (63C)     35.9193           (17D)     48.4194           (44D)     7.5195           (53D)     37.9196           (63D)     59.1197           (21E)     13.6198           (46E)     9.3199           (55E)     19.9200           (62E)     36.4201           (24F)     5.9202           (44F)     12.4203           (57F)     26.3204           (64F)     26.8205           (19G)     32.8206           (51G)     43.7207           (54G)     54.6208           (61G)     59.3209           (13H)     19.8210           (45H)     12.8211           (59H)     12.4212           (64H)     50.0______________________________________ 
    
     EXAMPLE 213 
     1 Part of disazo pigment (1E), 1 part of p-(diphenylamino)benzaldehyde N&#39;-methyl-N&#39;-phenylhydrazone used in Example 82 and 6 parts of m-cresol-formaldehyde resin were added to 30 parts of ethylene glycol monomethyl ether, and the mixture was ground and blended in a ball mill. The resulting coating solution was applied to an aluminium plate having a thickness of about 0.25 mm which was dressed by sanding and subjecting it to anodic oxidation and sealing treatment, by means of a wire round rod, and dried at 90° C. for 10 minutes and 50° C. for 1 day to produce a sample having a thickness of about 6 μm. 
     This sample was then subjected to corona discharging in the dark so as to have a surface electric potential of 500 V and it was exposed to a negative image by tungsten light (300 luxes.second). When reversal development was carried out using Mitsubishi Diafax Master-LOM-ED toner (produced by Mitsubishi Paper Mills, Ltd.), a very sharp positive image could be obtained on the printing original plate. This printing original plate was immersed in a solution prepared by diluting an etching solution DP-1 (aqueous solution of sodium silicate, produced by Fuji Photo Film Co.) 10 times, for 1 minute to remove the light-sensitive layer of the parts where the toner did not adhere (nonimage parts) by dissolution. As a result, the pigment in the nonimage parts could be easily removed together with the binder to produce a printing plate having a sharp image. 
     While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes ad modifications can be made therein without departing from the spirit and scope thereof.