Abstract:
The present invention provides electrophotographic sensitive materials having a high sensitivity as well as a high flexibility which comprise a conductive support and a photosensitive layer formed thereon, said photosensitive layer containing one disazo pigment, as an effective ingredient, which is selected from the group consisting of disazo pigments expressed by the following general formulas I, II, III, and IV, ##STR1##

Description:
BACKGROUND OF THE INVENTION 
     (a) Field of the Invention 
     The present invention relates to electrophotographic sensitive materials, in particular novel sensitive materials which comprise a photosensitive layer containing a disazo pigment as an effective ingredient. 
     (b) Description of the Prior Art 
     As the electrophotographic sensitive material prepared by forming a photosensitive layer containing some azo pigment as an effective ingredient on a conductive support, one prepared by employing monoazo pigment (cf. Japanese Patent Publication No. 16474/1969), one prepared by employed benzidine-type disazo pigment (cf. U.S. Pat. No. 3,898,048 and U.S. Pat. No. 4,052,210), etc. are well known. These azo pigments are admittedly useful materials as an effective ingredient of the photosensitive layer as stated above, but when various requirements for photosensitive materials are taken into account from the viewpoint of the electrophotographic process, there has in fact not yet been obtained such a material as will sufficiently meet these requirements. Therefore, it is a matter of more importance to provide a wide variety of pigments, not limited to azo pigments, so as to afford a wide range of selection of pigments acting as an effective ingredient, thereby rendering it possible to provide a photosensitive material apposite to any specific process. In other words, it is desirable for the electrophotographic process that the variety of the pigments workable as an effective ingredient of photosensitive materials is as wide as possible. 
     SUMMARY OF THE INVENTION 
     A primary object of the present invention is to provide electrophotographic sensitive materials containing novel disazo pigments workable as an effective ingredient for a variety of electrophotographic processes. 
     A secondary object of the present invention is to provide electrophotographic sensitive materials which afford a wide range of selection of pigments workable as an effective ingredient. 
     Another object of the present invention is to provide electrophotographic sensitive materials having a high sensitivity as well as high flexibility and which contain the aforesaid disazo pigment. 
     In other words, the present invention provides electrophotographic sensitive materials characterized by having a photosensitive layer containing a disazo pigment, as an effective ingredient, which is selected from the group consisting of disazo pigments expressed by the following general formulas I, II, III, and IV, ##STR2## [wherein A is selected from the group consisting of ##STR3## is selected from the group consisting of aromatic rings such as benzene ring, naphthalene ring, etc., hetero rings such as indole ring, carbazole ring, benzofuran ring, etc. and their substituents, Ar 1  is selected from the group consisting of aromatic rings such as benzene ring, naphthalene ring, etc., hetero rings such as dibenzofuran, etc. and their substituents, Ar 2  and Ar 3  are selected from the group consisting of aromatic rings such as benzene ring, naphthalene ring, etc. and their substituents, R 1  and R 3  are selected from the group consisting of hydrogen, lower alkyl radical or phenyl radical and their substituents and R 2  is selected from the group consisting of lower alkyl radical, carboxyl radical and their esters)]. 
     Hereinafter are shown concrete examples of the compounds expressed by the foregoing general formula I by means of structural formula. ##STR4## The portion ##STR5## being common to Compounds No. 2A-66A, is omitted and is expressed as --Y 1  -- in short hereinafter. ##STR6## 
     The disazo pigments expressed by the general formula I can be easily prepared through the process comprising first diazotizing the starting material 2,7-diaminofluoren-9-one which is readily available commercially or in accordance with conventional methods to precipitate tetrazonium salt and thereafter effecting coupling reaction of this tetrazonium salt with a coupler, such as Naphthol AS, corresponding to the aforedescribed various pigments within an appropriate organic solvent such as N,N-dimethyl formamide in the presence of alkali. For instance, the process of preparing the pigment No. 1A is as described in the following. Further, other disazo pigments can also be prepared by applying the same process excepting for changing the material used. 
     PREPARATION EXAMPLE 
     5.5 g of 2,7-diaminofluoren-9-one is added to a dilute hydrochloric acid consisting of 46 ml of concentrated hydrochloric acid and 46 ml of water, and same is well stirred at 60° C. for about 30 minutes. Next, this mixture is cooled to about 0° C., and a solution obtained by dissolving 3.8 g of sodium nitrite in 6 ml of water is added dropwise to said mixture at a temperature of 0°-5° C. for about 30 minutes. Then, the same is stirred at the same temperature for about 30 minutes, a small amount of unreacted matter is filtered, the filtrate is poured in 40 ml of 42% borofluoric acid, the so separated crystals are removed by filtration, washed with water and dried to obtain 7.4 g (yield 70%) of cream-colored crystals of bisdiazonium-bistetrafluoroborate. Next, the thus obtained 2 g of bisdiazonium salt and 2.9 g of 2-hydroxy-3-phenylcarbamoyl naphthalene as a coupler are dissolved in 425 ml of cooled -N,N-dimethylformamide, a solution consisting of 4.1 g of sodium acetate and 60 ml of water is added dropwise thereto at a temperature of 4°-8° C. for 1 hour, and the same is stirred at room temperature for about 3 hours. Thereafter, precipitates are removed by filtration, washed 3 times with 300 ml of water, and further washed 7 times with 300 ml of N,N-dimethylformamide. Still residual N,N-dimethylformamide is washed away with acetone, and thus obtained golden-colored crystals are dried at 70° C. under reduced pressure of 2 mmHg to obtain 3 g (the yield 80%) of disazo pigment No. 1A. The melting point is over 300° C. 
     
         ______________________________________Elementary analysis (as C.sub.47 H.sub.30 N.sub.6 O.sub.5)      Calculated value                     Observed value______________________________________C (%)      74.39          74.01H (%)       3.99           4.06N (%)      11.08          11.39______________________________________IR Absorption Spectrum (KBr tablet)1675 cm.sup.-1        (Secondary amide)1720 cm.sup.-1        (Carbonyl)______________________________________ 
    
     Hereinafter will be shown concrete examples of compounds represented by the general formula II. 
     
         __________________________________________________________________________                                     Compound                                     No.__________________________________________________________________________ ##STR7##                                 1B__________________________________________________________________________ 
    
      The portion ##STR8## being common to Compounds No. 2B-66B, is omitted and represented as --Y 2  -- in short hereinafter. ##STR9## 
     The disazo pigments expressed by the general formula II can be easily prepared through the aforesaid process for preparing the disazo pigments expressed by the general formula I excepting the use of 3,7-diaminodibenzothiophene as the starting material. For instance, the process of preparing the pigment No. 1B is as described in the following. Further, other disazo pigments expressed by the general formula II can also be prepared in accordance with this preparation example excepting for changing the material used. 
     Preparation Example 
     4.3 g of 3,7-diaminodibenzothiophene is added to a dilute hydrochloric acid consisting of 36 ml of concentrated hydrochloric acid and 36 ml of water, and same is well stirred at 60° C. for about 30 minutes. Next, this mixture is cooled to 0° C., and a solution obtained by dissolving 2.9 g of sodium nitrite in 10 ml of water is added dropwise to said mixture at a temperature of 0°-5° C. for about 30 minutes. Then, the same is stirred at the same temperature for about 30 minutes, a small amount of unreacted matter is filtrated, the filtrate is poured in 40 ml of 42% borofluoric acid, separated crystals are removed by filtration, washed with water and dried to obtain 80 g (the yield 98%) of yellow-colored crystals of bisdiazonium-distetrafluoroborate. The decomposition point is about 140° C. Next, the thus obtained 8.0 g of bisdiazonium salt and 11.6 g of 2-hydroxy-3 -phenylcarbamoyl naphthalene as a coupler are dissolved in 1.5 l of cooled N-N-dimethylformamide, a solution consisting of 16.4 g of sodium acetate and 160 ml of water is added dropwise thereto at a temperature of 4°-8° C. for 1 hour, and the same is stirred at room temperature for about 3 hours. Thereafter, precipitates are removed by filtration, washed 3 times with 500 ml of water, and further washed 8 times with 500 ml of N,N-dimethylformamide. Still residual N-N-dimethylformamide is washed away with acetone, and thus obtained pale and dark crystals are dried at 70° C. under reduced pressure of 2 mmHg to obtain 13.0 g (the yield 86%) of disazo pigment No. 1B. The melting point is over 300° C. 
     
         ______________________________________Elementary analysis results (as C.sub.46 H.sub.30 N.sub.8 O.sub.4 S)      Calculated value                     Observed value______________________________________C (%)      72.42          72.05H (%)       3.96           3.79N (%)      11.02          10.85______________________________________IR Absorption Spectrum (KBr tablet)1680.sup.-1  (Secondary amide)______________________________________ 
    
     Hereinafter will be shown concrete examples of compounds expressed by the general formula III. 
     
         __________________________________________________________________________                                 Compound                                 No.__________________________________________________________________________ ##STR10##                            1C__________________________________________________________________________ 
    
     The portion ##STR11## being common to Compounds No. 2C-66C, is omitted and represented as --Y 3  -- in short hereinafter. ##STR12## 
     The portion ##STR13## being common to Compounds No. 68C-132C, is omitted and represented as --Z-- in short hereinafter. ##STR14## 
     The disazo pigments expressed by the general formula III can be easily prepared through the aforesaid process for preparing the disazo pigments expressed by the general formula I excepting the use of diamino derivatives of the corresponding stilbene as the starting material. For instance, the process of preparing the aforesaid pigment No. 1C is as described in the following. Further, other disazo pigments expressed by the general formula III can also be prepared in accordance with this preparation example excepting for changing the material used. 
     Preparation Example 1.5 g of 2,2&#39;-diaminostilbene is added to a dilute hydrochloric acid consisting of 12.6 ml of concentrated hydrochloric acid and 12.6 ml of water, and same is well stirred at 60° C. for about 30 minutes. Next, time mixture is cooled to about 0° C., and a solution obtained by dissolving 1.1 g of sodium nitrite in 1.7 ml of water is added dropwise to said mixture at a temperature of -1˜0° C. for about 30 minutes. Then, the same is stirred at the same temperature for about 30 minutes, a small amount of unreacted matter is filtrated, the filtrate is poured in 11 ml of 42% borofluoric acid, the so separated crystals are removed by filtration, washed with water and dried to obtain 2.4 g (the yield 83%) of yellow-colored crystals of bisdiazonium-bistetrafluoroborate. The decomposition point is about 130° C. 
     Next, the thus obtained 2.0 g of bisdiazonium salt and 2.9 g of 2-hydroxy-3-phenylcarbamoylnaphthalene as a coupler are dissolved in 425 ml of cooled N,N-dimethylformamide, a solution consisting of 4.1 g of sodium acetate and 60 ml of water is added dropwise thereto at a temperature of 4°-8° C. for 1 hour, and then the same is stirred at room temperature for about 3 hours. Thereafter, precipitates are removed by filtration, washed 3 times with 300 ml of water, and further washed 8 times with 300 ml of N,N-dimethylformamide. Still residual N,N-dimethylformamide is washed away with acetone, and thus obtained pale and dark crystals are dried at 70° C. under reduced pressure of 2 mmHg to obtain 3.0 g (the yield 79%) of disazo pigment No. 1C. The melting point is over 300° C. 
     
         ______________________________________Elementary analysis (as C.sub.48 H.sub.34 N.sub.6 O.sub.4)    Calculated value               Observed value______________________________________C (%)      75.97        75.53H (%)      4.52         4.32N (%)      11.08        10.80IR Absorption Spectrum (KBr tablet)1680 cm.sup.-1        (Secondary amide)______________________________________ 
    
     Hereinafter will be shown concrete examples of compounds expressed by the general formula IV. ##STR15## The portion ##STR16## being common to Compounds No. 2D-66D, is omitted and represented as --Y 4  -- in short hereinafter. ##STR17## 
     The disazo pigments expressed by the general formula IV can be easily prepared through the aforesaid process for preparing the disazo pigment expressed by the general formula I excepting the use of 3,7-diaminodibenzothiophene-5,5-dioxide as the starting material. For instance, the process of preparing the aforesaid pigment No. 1D is as described in the following. Further, other disazo pigments expressed by the general formula IV can also be prepared in accordance with this preparation example expecting for changing the material used. 
     Preparation Example 
     1.3 g of 3,7-diaminodibenzothiophene-5,5-dioxide is added to a dilute hydrochloric acid consisting of 9 ml of concentrated hydrochloric acid and 9 ml of water, and same is well stirred at 80° C. for about 30 minutes. Next, this mixture is cooled to about 0° C., and a solution obtained by dissolving 0.8 g of sodium nitrite in 1 ml of water is added dropwise to said mixture at a temperature of 0°-5° C. for about 30 minutes. Then, the same is stirred at the same temperature for about 30 minutes, a small amount of unreacted matter is filtrated, the filtrate is poured in 10 ml of 42% borofluoric acid, the so separated crystals are removed by filtration, washed with water and dried to obtain 2.2 g (the yield 99%) of yellow-colored crystals of bisdiazoniumbistetrafluoroborate. The decomposition point is about 140° C. Next, the thus obtained 2.2 g of bisdiazonium salt and 2.9 g of 2-hydroxy-3-phenylcarbamoylnaphthalene as a coupler are dissolved in 425 ml of cooled N,N-dimethylformamide, a solution consisting of 4.1 g of sodium acetate and 60 ml of water is added dropwise thereto at a temperature of 4°-8° C. for 1 hour, and then the same is stirred at room temperature for about 3 hours. Thereafter, precipitates are removed by filtration, washed 3 times with 300 ml of water, and further washed 8 times with 300 ml of N,N-dimethylformamide. Still residual N,N-dimethylformamide is washed away with acetone, and thus obtained pale and dark crystals are dried at 70° C. under reduced pressure of 2 mmHg to obtain 3.2 g (the yield 30%) of disazo pigment No. 1D. The melting point is over 300° C. 
     
         ______________________________________Elementary analysis results (as C.sub.46 H.sub.30 N.sub.6 O.sub.6 S)   Calculated value                 Observed value______________________________________C (%)     69.51           68.95H (%)      3.80            3.79N (%)     10.57           10.85IR Absorption Spectrum (KBr tablet)1680 cm.sup.-1 (Secondary amide)______________________________________ 
    
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 through FIG. 4 illustrate, respectively, enlarged cross-sectional views of photosensitive materials according to the present invention. 
    
    
     Among the reference numerals in the drawings, 1 denotes a conductive support, 2, 2&#39;, and 2&#34;&#39; denote respectively a photosensitive layer, 3 denotes a binder, 4 denotes a disazo compound, 5 denotes a charge-transfer medium, 6 denotes a charge-carrier generating layer, and 7 denotes a charge-transfer medium layer. 
     The photosensitive materials according to the present invention contain the above mentioned disazo pigments represented by the general formulas I, II, III and IV and can assume such structures as illustrated in FIGS. 1-4 according to the way of application of these pigments. The photosensitive material illustrated in FIG. 1 is one prepared by forming a disazo pigment 4 (which serves herein as a photoconductive substance)-resinous binder 3 type photosensitive layer 2 on a conductive support 1. The photosensitive material illustrated in FIG. 2 is one prepared by forming a disazo pigment 4 (which serves herein as a charge-carrier generating substance)-charge transfer medium (which is a mixture of charge-transfer substance and a resinous binder) 5 type photosensitive layer 2&#39; on a conductive support 1. And the photosensitive materials illustrated in FIGS. 3-4 are modifications of the photosensitive material illustrated in FIG. 2 and the photosensitive layers 2&#34; and 2&#34;&#39; are each composed of a charge-carrier generating layer 6 consisting essentially of the disazo pigment 4 and a charge-transfer medium layer 7. The respective ingredients of these photosensitive materials are supposed to assume such function and mechanism as mentioned hereinafter. 
     First, in the photosensitive material of FIG. 1, the disazo pigment acts as a photoconductive substance, and generation and transfer of the charge-carrier necessary for light decay is performed through the pigment particles. In the case of the photosensitive material of FIG. 2, the charge-transfer susbstance forms a charge-transfer medium together with the binder (plus a plasticizer as occasion demands), while the disazo pigment acts as a charge-carrier generating substance. This charge-transfer medium has no charge-carrier generating ability as disazo pigments do, but it has an ability to accept and transfer the charge-carrier generated by disazo pigments. That is, in the case of the photosensitive material of FIG. 2, generation of the charge-carrier necessary for light decay is performed by the disazo pigment, while transfer of the charge-carrier is performed mainly by the charge-transfer medium. An additional essential condition required for the charge-transfer medium on this occasion is that the scope of absorption wavelength of the charge-transfer medium should not fall on mainly the scope of absorption wavelength of the visible region of the disazo pigment. The reason for this is that it is necessary to transmit the light to the surface of the disazo pigment in order to generate the charge carrier efficiently in the said pigment. This, however, is not applicable to the case of, for instance, a photosensitive material which is sensitive only to a specific wavelength. Therefore, it will do if the absorption wavelengths of both the charge-transfer medium and the disazo pigment do not completely overlap each other. Next, in the case of the photosensitive material of FIG. 3, the light after passing through the charge-transfer medium layer reaches to the photosensitive layer 2&#34; which acts as a charge-carrier generating layer, whereby generation of the charge-carrier is performed by the disazo pigment present in the portion, while the charge-transfer medium layer accepts the charge-carrier poured therein and transfers. The mechanism of this photosensitive material that generation of the charge-carrier required for light decay is performed by the disazo pigment and transfer of the charge-carrier is performed by the charge-transfer medium is the same as in the case of the photosensitive material illustrated in FIG. 2. The disazo pigment herein is likewise a charge-carrier generating substance. In this regard it is to be noted that the operation mechanism of the charge-transfer medium and charge-carrier generating layer in the photosensitive material of FIG. 4 is the same as in the case of the photosensitive material of FIG. 3. 
     In order to prepare the photosensitive material of FIG. 1, it suffices to coat a conductive support with a dispersion obtained by dispersing fine particles of a disazo pigment in a binder solution and then dry. In order to prepare the photosensitive material of FIG. 2, it suffices the disperse fine particles of a disazo pigment in a solution dissolved a charge-transfer substance and a binder therein, coat a conductive support with the resulting dispersion and then dry. And the photosensitive material of FIG. 3 can be obtained either by depositing a disazo pigment on a conductive support through vacuum evaporation or through the procedure comprising dispersing fine particles of a disazo pigment in an appropriate solvent dissolved a binder therein as occasion demands, coating the resulting dispersion on a conductive support and then drying and if further required, subjecting the thus formed photosensitive layer to the surface finishing, for instance, such as puff-grinding or the like or adjust the thickness of the coating film, thereafter coating thereon a solution containing a charge-transfer substance and a binder and drying. In this regard it is to be noted that in the case of the photosensitive material of FIG. 4 it can be obtained according to the procedure of preparing the photosensitive material of FIG. 3 wherein the order of forming the layers is reversed. In any case, the disazo pigment for use in the present invention is employed upon being pulverized into a particle size of less than 5μ, preferably less than 2μ, by means of a ball-mill or the like. Coating is effected using the conventional means such as doctor blade, wire bar, etc. The thickness of the photosensitive layers illustrated in FIGS. 1 and 2 is about 3-50μ, preferably 5-20μ. In the case of the photosensitive materials illustrated in FIGS. 3 and 4 the thickness of the charge-carrier generating layer is less than 5μ, preferably less than 2μ, and the thickness of the charge-transfer medium layer is about 3-50μ, preferably 5-20μ. In the case of the photosensitive material illustrated in FIG. 1, the proper amount of the disazo pigment contained in the photosensitive layer is 30-70% by weight, preferably about 50% by weight based on the weight of the photosensitive layer. (As above-described, in the case of the photosensitive material of FIG. 1 the disazo pigment acts as a photoconductive substance, and generation and transfer of the charge carrier required for light decay are performed through the pigment particles. Therefore, it is desirable that the contact between the pigment particles should be continuous from the photosensitive layer surface to the support. In view of this, it is desirable that the ratio of the disazo pigment to the photosensitive layer is as high as possible, but when taking both the strength and the sensitivity of the photosensitive layer into consideration, preferably it is about 50% by weight.) In the case of the photosensitive material illustrated in FIG. 2, the proper amount of the disazo pigment contained in the photosensitive layer is 1-50% by weight, preferably less than 20% by weight, and the proper amount of the charge-transfer substance therein is 10-95% by weight, preferably 30-90% by weight. And in the case of the photosensitive materials illustrated in FIGS. 3-4 the amount of the charge-transfer substance contained in the charge-transfer medium layer is 10-95% by weight, preferably 30-90% by weight as in the case of the photosensitive layer of the photosensitive material illustrated in FIG. 2. Further, in preparing all the photosensitive materials illustrated in FIGS. 1-4 it is possible to employ some plasticizer in combination with the binder. 
     In the photosensitive materials of the present invention there can be employed, as the conductive support, a plate or foil of a metal such as aluminum, etc., a plastic film deposited thereon a metal such as aluminum, etc. through vacuum evaporation, or a paper processed for conductivity. As binders suitably employed in the present invention, there are enumerated such condensation resins such as polyamide, polyurethane, polyester, epoxide resin, polyketone, polycarbonate, etc., vinyl polymers such as polyvinyl ketone, polystyrene, poly-N-vinyl carbazole, polyacrylamide, etc., and the like, but in spite of this, resins which are insulating and adhesive are all employable. As available plasticizers there can be enumerated halogenated paraffin, polyvinyl chloride, dimethyl naphthalene, dibutyl phthalate, etc. And as available charge-transfer substances there can be enumerated, as high molecular substances, vinyl polymers such as poly-N-vinyl carbazole, halogenated poly-N-vinyl carbazole, polyvinyl pyrene, polyvinyl indroquinoxaline, polyvinyl dibenzothiophene, polyvinyl anthracene, polyvinyl acridine, etc. and condensation resins such as pyrene-formaldehyde resin, bromopyrene-formaldehyde resin, ethyl carbazole-formaldehyde resin, chloroethyl carbazole-formaldehyde resin, etc., and as low molecular substances (monomers), fluorenone, 2-nitro-9-fluorenone, 2,7-dinitro-9-fluorenone, 2,4,7-trinitro-9-fluorenone, 2,4,5,7-tetranitro-9-fluorenone, 4H-indeno[1,2-b]thiophen-4-one, 2-nitro-4H-indeno[1,2-b]thiophen-4-one, 2,6,8-trinitro-4H-indeno[1,2-b]thiophen-4-one, 8H-indeno[2,1-b]thiophen-8-one, 2intro-8H-indeno[2,1-b]thiophen-8-one, 2-bromo-6,8-dinitro-4H-indeno[1,2-b]thiophene, 6,8-dinitro-4H-indeno[1,2-b]thiophene, 2-nitrodibenzothiophene, 2,8-dinitrodibenzothiophene, 3-nitrodibenzothiophene-5-oxide, 3,7-dinitrodibenzothiophene-5-oxide, 1,3,7-trinitrodibenzothiophene-5,5-dioxide, 3-nitro-dibenzothiophene-5,5-dioxide, 3,7-dinitro-dibenzothiophene-5,5-dioxide, 4-dicyanomethylene-4H-indeno[1,2-b]thiophene, 6,8-dinitro-4-dicyanomethylene-4H-indeno[1,2-b]thiophene, 1,3,7,9-tetranitrobenzo[c]cinnoline-5-oxide, 2,4,10-trinitrobenzo[c]cinnoline-6-oxide, 2,4,8-trinitrobenzo[c]cinnoline-6-oxide, 2,4,8-trinitrothioxanthone, 2,4,7-trinitro-9,10-phenanthrene-guinone, 1,4-naphthoquinone-benzo[a]anthracene-7,12-dione, 2,4,7-trinitro-9-dicyanomethylene fluorene, tetrachlorophthalic anhydride, 1-bromopyrene, 1-methylpyrene, 1-ethylpyrene, 1-acetylpyrene, carbazole, N-ethylcarbazole, N-β-chloroethylcarbazole, N-β-hydroxyethyl carbazole, 2-phenyl indole, 2-phenylnaphthalene, 2,5-bis(4-diethylaminophenyl)-1,3,4-oxadiazole, 2,5-bis(4-diethylaminophenyl)-1,3,4-triazole, 1-phenyl-3-(4-diethylaminostyryl)-5-(4-diethylaminophenyl)pyrazoline, 2-phenyl-4-(4-diethylaminophenyl)-5-phenyloxazole, triphenyl amine, tris(4-diethylaminophenyl)methane, 3,6-bis(dibenzylamino)-9-ethyl carbazole, etc. These charge-transfer substances are employed either singly or in a combination of two or more of them. 
     Further, in every photosensitive material thus prepared an adhesive layer or a barrier layer can be disposed in between the conductive support and the photosensitive layer as occasion demands. The material suitably used in the formation of aforesaid layers includes polyamide, nitrocellulose, aluminum oxide, etc. and preferably the thickness of the layers is less than 1μ. 
     Reproduction using the photosensitive material according to the present invention can be achieved through the procedure comprising electrifying the photosensitive layer side of the photosensitive material, exposing and then developing, and if necessary, transferring onto an ordinary paper or the like. 
     The photosensitive materials according to the present invention have excellent advantages in that they are generally of high sensitivity and rich in flexibility. 
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     EXAMPLE 1 1 part by weight of polyester resin (namely, Polyester Adhesive 49000, the manufacture of Du Pont Inc.), 1 part by weight of the disazo compound No. 1A and 26 parts by weight of tetrahydrofuran were pulverized and mixed together within a ball-mill, and the resulting dispersion was coated, by means of a doctor blade, on a polyester film deposited with aluminum through vacuum evaporation and was dried at a temperature of 100° C. for 10 minutes, whereby there was obtained a photosensitive material having a 7μ-thick photosensitive layer and a structure illustrated in FIG. 1. 
     Subsequently, after charging positive electricity on the photosensitive layer of this photosensitive material by applying +6KV corona discharge for 20 seconds by means of a commercial electrostatic copying paper testing apparatus, the photosensitive material was left alone in the dark for 20 seconds, and the surface potential Vpo(volt) at the time was measured. Next, light was applied to the photosensitive layer by means of a tungsten lamp so as to attain the illumination of 20 luxes on the surface thereof, and the time (unit: second) required for reducing said surface potential Vpo to half was sought, whereby the amount of exposure E1/2 (lux·sec.) was obtained. The result was as follows: 
     
         Vpo=590 V, E1/2=15 lux·sec. 
    
     EXAMPLE 2 THROUGH 10 
     Varieties of photosensitive materials were prepared by applying the same procedure as in Example 1 save for employing the respective disazo compounds referred to by number in the following Table-1 in place of the disazo compound No. 1A used in Example 1. When these photosensitive materials were subsequently subjected to the same measurement of Vpo and E1/2 as in Example 1, the result was as shown in Table-1, respectively. 
     
                       TABLE 1______________________________________     DisazoExample   compound    Vpo        El/2No.       No.         (volt)     (lux . sec.)______________________________________2          4A         630         83         17A         800         54         18A         700        155         32A         710        196         37A         725        307         49A         680        218         58A         695        259         62A         710        2510        65A         800        30______________________________________ 
    
     EXAMPLE 11 
     10 parts by weight of polyester resin (the same as that in Example 1), 10 parts by weight of 2,4,7-trinitro-9-fluorenone, 2 parts by weight of disazo compound No. 1A and 198 parts by weight of tetrahydrofuran were pulverized and mixed together within a ball-mill, and the resulting dispersion was coated, by means of a doctor blade, on a polyester film deposited with aluminum through vacuum evaporation and was dried at a temperature of 100° C. for 10 minutes, whereby there was obtained a photosensitive material having a 10μ-thick photosensitive layer and a structure illustrated in FIG. 2. Subsequently, measurement of Vpo and E1/2 of this photosensitive material was conducted through the same procedure as in Example 1 save for applying -6KV corona discharge instead of +6KV corona discharge employed in Example 1. The result was as follows: 
     
         Vpo=450 V, E1/2=10 lux·sec. 
    
     EXAMPLES 12 THROUGH 20 
     Varieties of photosensitive materials having a structure illustrated in FIG. 2 were prepared by applying the same procedure as in Example 11 save for employing the respective disazo compounds referred to by number in the following Table-2 in place of the disazo compound No. 1A used in Example 11. When these photosensitive materials were subsequently subjected to the same measurement of Vpo and E1/2 as in Example 11, the result was as shown in Table-2, respectively. 
     
                       TABLE 2______________________________________     DisazoExample   compound    Vpo        El/2No.       No.         (volt)     (lux . sec.)______________________________________12         3A         480        1013         5A         520        1514        11A         450        2015        23A         500        1516        25A         500        1517        35A         450        1018        38A         480        2019        41A         600        2020        60A         750        25______________________________________ 
    
     EXAMPLE 21 
     10 parts by weight of polyester resin (the same as that in Example 1), 10 parts by weight of 2,5-bis(4-diethylaminophenyl)-1,3,4-oxadiazole, 2 parts by weight of the disazo compound No. 1A and 198 parts by weight of tetrahydrofuran were pulverized and mixed together within a ball-mill, and the resulting dispersion was coated, by means of a doctor blade, on a polyester film deposited with aluminum through vacuum evaporation and was dried at a temperature of 120° C. for 10 minutes, whereby there was prepared a photosensitive material having a 10μ-thick photosensitive layer and a structure illustrated in FIG. 2. When this photosensitive material was subsequently subjected to the same measurement as in Example 1, the result was as follows: 
     
         Vpo=830 V, E1/2=10 lux·sec. 
    
     EXAMPLES 22 THROUGH 30 
     Varieties of photosensitive materials having a structure illustrated in FIG. 2 were prepared by applying the same procedure as in Example 21 save for employing the respective disazo compounds referred to by number in the following Table-3 in place of the disazo compound No. 1A used in Example 21. When these photosensitive materials were subsequently subjected to the same measurement of Vpo and E1/2 as in Example 1, the result was as shown in the following Table-3, respectively. 
     
                       TABLE 3______________________________________     DisazoExample   compound    Vpo        El/2No.       No.         (volt)     (lux . sec.)______________________________________22         2A         900        1523         9A         850        1824        13A         880        1625        28A         800         926        33A         900        1527        45A         820        1728        47A         930        1029        52A         950        1530        66A         910        20______________________________________ 
    
     EXAMPLE 31 
     200 parts by weight of poly-N-vinyl carbazole, 33 parts by weight of 2,4,7-trinitro-9-fluorenone, 20 parts by weight of polyester resin (the same as that in Example 1) and 20 parts by weight of the disazo compound No. 1A as added to 1780 parts by weight of tetrahydrofuran were pulverized and mixed together within a ball-mill, and the resulting dispersion was coated, by means of a doctor blade, on a polyester film deposited with aluminum through vacuum evaporation and was dried at a temperature of 100° C. for 10 minutes and at a temperature of 120° C. for 5 minutes in succession, whereby there was obtained a photosensitive material having a 13 μ-thick photosensitive layer and a structure illustrated in FIG. 2. When this photosensitive material was subjected to the same measurement as in Example 1, the result was as follows: 
     
         Vpo=1,035 V, E1/2=5 lux.sec. 
    
     EXAMPLES 32 through 40 
     Varieties of photosensitive materials having a structure illustrated in FIG. 2 were prepared by applying the same procedure as in Example 31 save for employing the respective disazo compound referred to by number in the following Table-4 in place of the disazo compound No. 1A used in Example 31. When these photosensitive materials were subsequently subjected to the same measurement of Vpo and E1/2 as in Example 1, the result was as shown in the following Table-4, respectively. 
     
                       TABLE 4______________________________________     DisazoExample   compound    Vpo        El/2No.       No.         (volt)     (lux . sec.)______________________________________32         9A         1035       633        10A         1040       734        17A         1100       735        29A         1100       836        40A         1150       537        42A         1200       1538        51A         1280       1039        63A         1430       1940        64A         1500       15______________________________________ 
    
     EXAMPLE 41 
     2 parts by weight of the disazo compound No. 1A and 98 parts by weight of tetrahydrofuran were pulverized and mixed together within a ball-mill, and the resulting dispersion was coated, by means of a doctor blade, on a polyester film deposited with aluminum through vacuum evaporation and was subjected to natural drying, whereby there was formed a 1 μ-thick charge-carrier generating layer. Meanwhile, another dispersion was prepared by mixing 2 parts by weight of 2,4,7-trinitro-9-fluorenone, 2 parts by weight of polycarbonate (namely, Panlite L, the manufacture of TEIJIN Co., Ltd.) and 46 parts by weight of tetrahydrofuran together, and this dispersion was coated on the foregoing charge-carrier generating layer by means of a doctor blade and then dried at a temperature of 100° C. for 10 minutes to form a 10 μ-thick charge-transfer medium layer, whereby there was obtained a photosensitive material having a structure illustrated in FIG. 3. When the thus obtained photosensitive material was subjected to the same measurement as in Example 1, the result was as follows: 
     
         Vpo=850 V, E1/2=15 lux·sec. 
    
     EXAMPLES 42 through 50 
     Varieties of photosensitive materials having a structure illustrated in FIG. 3 were prepared by applying the same procedure as in Example 41 save for employing the respective disazo compounds referred to by number in the following Table-5 in place of the disazo compound No. 1A used in Example 41. When these photosensitive materials were subjected to the same measurement of Vpo and E1/2 as in Example 1, the result was as shown in Table-5, respectively. 
     
                       TABLE 5______________________________________     DisazoExample   compound    Vpo        El/2No.       No.         (volt)     (lux . sec.)______________________________________42         8A         850         943        15A         880        1044        21A         880        1045        30A         870         846        33A         870         947        43A         855        1048        53A         865        1049        55A         880        1550        61A         880        15______________________________________ 
    
     EXAMPLE 51 
     2 parts by weight of the disazo compound No. 1A and 98 parts by weight of tetrahydrofuran were pulverized and mixed together within a ball-mill, and the resulting dispersion was coated, by means of a doctor blade, on a polyester film deposited with aluminum through vacuum evaporation and was subjected to natural drying, whereby there was formed a 1 μ-thick charge-carrier generating layer. Meanwhile, another dispersion was prepared by mixing 2 parts by weight of 2,5-bis(4-diethylaminophenyl)-1,3,4-oxadiazole, 2 parts by weight of polycarbonate (the same as that in Example 41) and 46 parts by weight of tetrahydrofuran together, and this dispersion was coated on the foregoing charge-carrier generating layer by means of a doctor blade and then dried at a temperature of 120° C. for 10 minutes to form a 10 μ-thick charge-transfer medium layer, whereby there was obtained a laminate-type photosensitive material illustrated in FIG. 3. When the thus obtained photosensitive material was subjected to the same measurement of Vpo and E1/2 as in Example 1 save for applying -6 KV corona discharge instead of +6 KV corona discharge, the result was as follows: 
     
         Vpo=1,000 V, E1/2=8 lux·sec. 
    
     EXAMPLE 52 through 60 
     Varieties of photosensitive materials having the same structure as that of Example 51 were prepared by employing the respective disazo compound referred to by number in the following Table-6 in place of the disazo compound No. 1A used in Example 51. When these photosensitive materials were subjected to the same measurement of Vpo and E1/2 as in Example 1, the result was as shown in Table-6, respectively. 
     
                       TABLE 6______________________________________     DisazoExample   compound    Vpo        El/2No.       No.         (volt)     (lux . sec.)______________________________________52         6A         1000       553        14A         950        854        19A         980        555        22A         990        756        27A         990        957        36A         1020       1058        44A         990        1259        48A         1000       1560        53A         1100       20______________________________________ 
    
     EXAMPLE 61 
     1 part by weight of polyester resin (namely, Polyester Adhesive 49000, the manufacture of Du Pont Inc.), 1 part by weight of the disazo compound No. 1B and 26 parts by weight of tetrahydrofuran were pulverized and mixed together within a ball-mill, and the resulting dispersion was coated, by means of a doctor blade, on a polyester film deposited with aluminum through vacuum evaporation and was dried at a temperature of 100° C. for 10 minutes, whereby there was obtained a photosensitive material having a 7 μ-thick photosensitive layer and a structure illustrated in FIG. 1. 
     Subsequently, after charging positive electricity on the photosensitive layer of this photosensitive material by applying +6 KV corona discharge for 20 seconds by means of a commercial electrostatic copying paper testing apparatus, the photosensitive material was left alone in the dark for 20 seconds, and the surface potential Vpo(volt) at that time was measured. Next, light was applied to the photosensitive layer by means of a tungsten lamp so as to attain the illumination of 20 luxes on the surface thereof, and the time (unit: second) required for reducing said surface potential Vpo to half was sought, whereby the amount of exposure E1/2 (lux·sec.) was obtained. The result was as follows: 
     
         Vpo=500 V, E1/2=12 lux·sec. 
    
     EXAMPLES 62 through 70 
     Varieties of photosensitive materials were prepared by applying the same procedure as in Example 61 save for employing the respective disazo compounds referred to by number in the following Table-7 in place of the disazo compound No. 1B used in Example 61. When these photosensitive materials were subsequently subjected to the same measurement of Vpo and E1/2 as in Example 61, the result was as shown in Table-7, respectively. 
     
                       TABLE 7______________________________________     DisazoExample   compound    Vpo        E1/2No.       No.         (volt)     (lux . sec.)______________________________________62         4B         620        1063        17B         600        1264        18B         680        1065        32B         620        1566        37B         630        2067        49B         690        1968        58B         680        2569        62B         680        2570        65B         690        30______________________________________ 
    
     EXAMPLE 71 
     10 parts by weight of polyester resin (the same as that in Example 61), 10 parts by weight of 2,4,7-trinitro-9-fluorenone, 2 parts by weight of disazo compound No. 1B and 198 parts by weight of tetrahydrofuran were pulverized and mixed together within a ball-mill, and the resulting dispersion was coated, by means of a doctor blade, on a polyester film deposited with aluminum through vacuum evaporation and was dried at a temperature of 100° C. for 10 minutes, whereby there was obtained a photosensitive material having a 10 μ-thick photosensitive layer and a structure illustrated in FIG. 2. Subsequently, measurement of Vpo and E1/2 of this photosensitive material was conducted through the same procedure as in Example 61 save for applying -6 KV corona discharge instead of +6 KV corona discharge employed in Example 61. The result was as follows: 
     
         Vpo=520 V, E1/2=9 lux·sec. 
    
     EXAMPLES 72 through 80 
     Varieties of photosensitive materials having a structure illustrated in FIG. 2 were prepared by applying the same procedure as in Example 71 save for employing the respective disazo compounds referred to by number in the following Table-8 in place of the disazo compound No. 1B used in Example 71. When these photosensitive materials were subsequently subjected to the same measurement of Vpo and E1/2 as in Example 61, the result was as shown in Table-8, respectively. 
     
                       TABLE 8______________________________________     DisazoExample   compound    Vpo        El/2No.       No.         (volt)     (lux . sec.)______________________________________72         3B         480        1073         5B         . 500      1074        11B         480        1275        23B         500         976        25B         500        1577        35B         490        1578        38B         520        1579        41B         500        2080        60B         580        18______________________________________ 
    
     EXAMPLE 81 
     10 parts by weight of polyester resin (the same as that in Example 61), 10 parts by weight of 2,5-bis(4-diethylaminophenyl)-1,3,4-oxadiazole, 2 parts by weight of the disazo compound No. 1B and 198 parts by weight of tetrahydrofuran were pulverized and mixed together within a ball-mill, and the resulting dispersion was coated, by means of a doctor blade, on a polyester film deposited with aluminum through vacuum evaporation and was dried at a temperature of 120° C. for 10 minutes, whereby there was prepared a photosensitive material having a 10 μ-thick photosensitive layer and a structure illustrated in FIG. 2. When this photosensitive material was subsequently subjected to the same measurement as in Example 61, the result was as follows: 
     
         Vpo=790 V, E1/2=5 lux·sec. 
    
     EXAMPLES 82 through 90 
     Varieties of photosensitive materials having a structure illustrated in FIG. 2 were prepared by applying the same procedure as in Example 81 save for employing the respective disazo compounds referred to by number in the following Table-9 in place of the disazo compound No. 1B used in Example 81. When these photosensitive materials were subsequently subjected to the same measurement of Vpo and E1/2 as in Example 61, the result was as shown in the following Table-9, respectively. 
     
                       TABLE 9______________________________________     DisazoExample   compound    Vpo        El/2No.       No.         (volt)     (lux . sec.)______________________________________82         2B         950        1083         9B         920        1284        13B         900        1085        28B         920        1586        33B         900        1387        45B         920        1988        47B         990        1989        52B         1000       2090        66B         950        25______________________________________ 
    
     EXAMPLE 91 
     200 parts by weight of poly-N-vinyl carbazole, 33 parts by weight of 2,4,7-trinitro-9-fluorenone, 20 parts by weight of polyester resin (the same as that in Example 61) and 20 parts by weight of the disazo compound No. 1B is added to 1780 parts by weight of tetrahydrofuran were pulverized and mixed together within a ball-mill, and the resulting dispersion was coated, by means of a doctor blade, on a polyester film deposited with aluminum through vacuum evaporation and was dried at a temperature of 100° C. for 10 minutes and at a temperature of 120° C. for 5 minutes in succession, whereby there was obtained a photosensitive material having a 13 μ-thick photosensitive layer and a structure illustrated in FIG. 2. When this photosensitive material was subjected to the same measurement as in Example 61, the result was as follows: 
     
         Vpo=1,020 V, E1/2=3 lux·sec. 
    
     EXAMPLES 92 through 100 
     Varieties of photosensitive materials having a structure illustrated in FIG. 2 were prepared by applying the same procedure as in Example 91 save for employing the respective disazo compound referred to by number in the following Table-10 in place of the disazo compound No. 1B used in Example 91. When these photosensitive materials were subsequently subjected to the same measurement of Vpo and E1/2 as in Example 61, the result was as shown in the following Table-10, respectively. 
     
                       TABLE 10______________________________________     DisazoExample   compound    Vpo        El/2No.       No.         (volt)     (lux . sec.)______________________________________92         9B         1020       593        10B         1000       394        17B         1120       595        29B         1100       596        40B          980       897        42B         1000       1098        51B         1100       1299        63B         1000       15100       64B         1100       20______________________________________ 
    
     Example 101 
     2 parts by weight of the disazo compound No. 1B and 98 parts by weight of tetrahydrofuran were pulverized and mixed together within a ball-mill, and the resulting dispersion was coated, by means of a doctor blade, on a polyester film deposited with aluminum through vacuum evaporation and was subjected to natural drying, whereby there was formed a 1 μ-thick charge-carrier generating layer. Meanwhile, another dispersion was prepared by mixing 2 parts by weight of 2,4,7-trinitro-9-fluorenone, 2 parts by weight of polycarbonate (namely, Panlite L, the manufacture of TEIJIN Co. Ltd.) and 46 parts by weight of tetrahydrofuran together, and this dispersion was coated on the foregoing charge-carrier generating layer by means of a doctor blade and then dried at a temperature of 100° C. for 10 minutes to form a 10 μ-thick charge-transfer medium layer, whereby there was obtained a photosensitive material having a structure illustrated in FIG. 3. When the thus obtained photosensitive material was subjected to the same measurement as in Example 61, the result was as follows: 
     
         Vpo=900 V, E1/2=15 lux.sec. 
    
     EXAMPLES 102 THROUGH 110 
     Varieties of photosensitive materials having a structure illustrated in FIG. 3 were prepared by applying the same procedure as in Example 101 save for employing the respective disazo compounds referred to by number in the following Table-11 in place of the disazo compound No. 1B used in Example 101. When these photosensitive materials were subjected to the same measurement of Vpo and E1/2 as in Example 61, the result was as shown in Table-11, respectively. 
     
                       TABLE 11______________________________________     DisazoExample   compound    Vpo        El/2No.       No.         (volt)     (lux . sec.)______________________________________102        8B         800        10103       15B         820        10104       21B         870        12105       30B         900        15106       33B         910        18107       43B         880        20108       53B         900        15109       55B         920        20110       61B         900        20______________________________________ 
    
     EXAMPLE 111 
     2 parts by weight of the disazo compound No. 1B and 98 parts by weight of tetrahydrofuran were pulverized and mixed together within a ball-mill, and the resulting dispersion was coated, by means of a doctor blade, on a polyester film deposited with aluminum through vacuum evaporation and was subjected to natural drying, whereby there was formed a 1 μ-thick charge-carrier generating layer. Meanwhile, another dispersion was prepared by mixing 2 parts by weight of 2,5-bis(4-diethylaminophenyl)-1,3,4-oxadiazole, 2 parts by weight of polycarbonate (the same as that in Example 101) and 46 parts by weight of tetrahydrofuran together, and this dispersion was coated on the foregoing charge-carrier generating layer by means of a doctor blade and then dried at a temperature of 120° C. for 10 minutes to form a 10 μ-thick charge-transfer medium layer, whereby there was obtained a laminate-type photosensitive material illustrated in FIG. 3. When the thus obtained photosensitive material was subjected to the same measurement of Vpo and E1/2 as in Example 61 save for applying -6 KV corona discharge instead of +6 KV corona discharge, the result was as follows: 
     
         Vpo=1,020 V, E1/2=10 lux.sec. 
    
     EXAMPLES 112 THROUGH 120 
     Varieties of photosensitive materials having the same structure as that of Example 111 were prepared by employing the respective disazo compound referred to by number in the following Table-12 in place of the disazo compound No. 1B used in Example 111. When these photosensitive materials were subjected to the same measurement of Vpo and E1/2 as in Example 61, the result was as shown in Table-12, respectively. 
     
                       TABLE 12______________________________________     DisazoExample   compound    Vpo        El/2No.       No.         (volt)     (lux . sec.)______________________________________112        6B         1000       9113       14B          990       10114       19B          980       8115       22B         1000       12116       27B         1020       15117       36B         1030       10118       44B         1000       9119       48B         1100       20120       53B         1200       25______________________________________ 
    
     EXAMPLE 121 
     1 part by weight of polyester resin (namely, Polyester Adhesive 49000, the manufacture of Du Pont Inc.), 1 part by weight of the disazo compound No. 1C and 26 parts by weight of tetrahydrofuran were pulverized and mixed together within a ball-mill, and the resulting dispersion was coated, by means of a doctor blade, on a polyester film deposited with aluminum through vacuum evaporation and was dried at a temperature of 100° C. for 10 minutes, whereby there was obtained a photosensitive material having a 7 μ-thick photosensitive layer and a structure illustrated in FIG. 1. 
     Subsequently, after charging positive electricity on the photosensitive layer of this photosensitive material by applying +6 KV corona discharge for 20 seconds by means of a commercial electrostatic copying paper testing apparatus, the photosensitive material was left alone in the dark for 20 seconds, and the surface potential Vpo (volt) at that time was measured. Next, light was applied to the photosensitive layer by means of a tungsten lamp so as to attain the illumination of 20 luxes on the surface thereof, and the time (unit: second) required for reducing said surface potential Vpo to half was sought, whereby the amount of exposure E1/2 (lux.sec.) was obtained. The result was as follows: 
     
         Vpo=700 V, E1/2=10 lux.sec. 
    
     EXAMPLES 122 THROUGH 130. 
     Varieties of photosensitive materials were prepared by applying the same procedure as in Example 121 save for employing the respective disazo compounds referred to by number in the following Table-13 in place of the disazo compound No. 1C used in Example 121. When these photosensitive materials were subsequently subjected to the same measurement of Vpo and E1/2 as in Example 121, the result was as shown in Table-13, respectively. 
     
                       TABLE 13______________________________________     DisazoExample   compound    Vpo        El/2No.       No.         (volt)     (lux . sec.)______________________________________122        3C         720        10123        5C         700         8124       18C         680        10125       30C         700        12126       44C         800        15127       49C         890        10128       55C         800        20129       67C         800        10130       93C         790         5______________________________________ 
    
     EXAMPLE 131 
     10 parts by weight of polyester resin (the same as that in Example 121), 10 parts by weight of 2,4,7-trinitro-9-fluorenone, 2 parts by weight of disazo compound No. 1C and 198 parts by weight of tetrahydrofuran were pulverized and mixed together within a ball-mill, and the resulting dispersion was coated, by means of a doctor blade, on a polyester film deposited with aluminum through vacuum evaporation and was dried at a temperature of 100° C. for 10 minutes, whereby there was obtained a photosensitive material having a 10 μ-thick photosensitive layer and a structure illustrated in FIG. 2. Subsequently, measurement of Vpo and E1/2 of this photosensitive material was conducted through the same procedure as in Example 121 save for applying -6 KV corona discharge instead of +6 KV corona discharge employed in Example 121. The result was as follows: 
     
         Vpo=430 V, E1/2=12 lux.sec. 
    
     EXAMPLES 132 THROUGH 140 
     Varieties of photosensitive materials having a structure illustrated in FIG. 2 were prepared by applying the same procedure as in Example 131 save for employing the respective disazo compounds referred to by number in the following Table-14 in place of the disazo compound No. 1C used in Example 131. When these photosensitive materials were subsequently subjected to the same measurement of Vpo and E1/2 as in Example 121, the result was as shown in Table-14, respectively. 
     
                       TABLE 14______________________________________     DisazoExample   compound    Vpo        El/2No.       No.         (volt)     (lux . sec.)______________________________________132        3C         450        12133        5C         480        13134       12C         490        12135       25C         520        15136       27C         450        10137       48C         440        11138       69C         450        10139       71C         440        10140       110C        440        20______________________________________ 
    
     EXAMPLE 141 
     10 parts by weight of polyester resin (the same as that in Example 121), 10 parts by weight of 2,5-bis(4-diethylaminophenyl)-1,3,4-oxadiazole, 2 parts by weight of the disazo compound No. 1C and 198 parts by weight of tetrahydrofuran were pulverized and mixed together within a ball-mill, and the resulting dispersion was coated, by means of a doctor blade, on a polyester film deposited with aluminum through vacuum evaporation and was dried at a temperature of 120° C. for 10 minutes, whereby there was prepared a photosensitive material having a 10 μ-thick photosensitive layer and a structure illustrated in FIG. 2. When this photosensitive material was subsequently subjected to the same measurement as in Example 121, the result was as follows: 
     
         Vpo=820 V, E1/2=8 lux.sec. 
    
     EXAMPLES 142 THROUGH 150 
     Varieties of photosensitive materials having a structure illustrated in FIG. 2 were prepared by applying the same procedure as in Example 141 save for employing the respective disazo compounds referred to by number in the following Table-15 in place of the disazo compound No. 1C used in Example 141. When these photosensitive materials were subsequently subjected to the same measurement of Vpo and E1/2 as in Example 121, the result was as shown in the following Table-15, respectively. 
     
                       TABLE 15______________________________________     DisazoExample   compound    Vpo        El/2No.       No.         (volt)     (lux . sec.)______________________________________142       17C         800        5143       27C         800        9144       56C         790        35145       62C         800        30146       67C         820        10147       71C         820        10148       83C         800        8149       101C        810        10150       126C        830        20______________________________________ 
    
     EXAMPLE 151 
     200 parts by weight of poly-N-vinyl carbazole, 33 parts by weight of 2,4,7-trinitro-9-fluorenone, 20 parts by weight of polyester resin (the same as that in Example 121) and 20 parts by weight of the disazo compound No. 1C as added to 1780 parts by weight of tetrahydrofuran were pulverized and mixed together within a ball-mill, and the resulting dispersion was coated, by means of a doctor blade, on a polyester film deposited with aluminum through vacuum evaporation and was dried at a temperature of 100° C. for 10 minutes and at a temperature of 120° C. for 5 minutes in succession, whereby there was obtained a photosensitive material having a 13 μ-thick photosensitive layer and a structure illustrated in FIG. 2. When this photosensitive material was subjected to the same measurement as in Example 121, the result was as follows: 
     
         Vpo=1,000 V, E1/2=5 lux.sec. 
    
     EXAMPLES 152 THROUGH 160 
     Varieties of photosensitive materials having a structure illustrated in FIG. 2 were prepared by applying the same procedure as in Example 151 save for employing the respective disazo compound referred to by number in the following Table-16 in place of the disazo compound No. 1C used in Example 151. When these photosensitive materials were subsequently subjected to the same measurement of Vpo and E1/2 as in Example 121, the result was as shown in the following Table-16, respectively. 
     
                       TABLE 16______________________________________     DisazoExample   compound    Vpo        El/2No.       No.         (volt)     (lux . sec.)______________________________________152        3C         1100       5153        5C         1100       3154       19C         1000       8155       55C          900       15156       67C          980       5157       91C         1020       3158       110C        1040       8159       123C        1080       18160       127C        1200       25______________________________________ 
    
     EXAMPLE 161 
     2 parts by weight of the disazo compound No. 1C and 98 parts by weight of tetrahydrofuran were pulverized and mixed together within a ball-mill, and the resulting dispersion was coated, by means of a doctor blade, on a polyester film deposited with aluminum through vacuum evaporation and was subjected to natural drying, whereby there was formed a 1 μ-thick charge-carrier generating layer. Meanwhile, another dispersion was prepared by mixing 2 parts by weight of 2,4,7-trinitro-9-fluorenone, 2 parts by weight of polycarbonate (namely, Panlite L, the manufacture of TEIJIN Co., Ltd.) and 46 parts by weight of tetrahydrofuran together, and this dispersion was coated on the foregoing charge-carrier generating layer by means of a doctor blade and then dried at a temperature of 100° C. for 10 minutes to form a 10 μ-thick charge-transfer medium layer, whereby there was obtained a photosensitive material having a structure illustrated in FIG. 3. When the thus obtained photosensitive material was subjected to the same measurement as in Example 121, the result was as follows: 
     
         Vpo=920 V, E1/2=15 lux.sec. 
    
     EXAMPLES 162 THROUGH 170 
     Varieties of photosensitive materials having a structure illustrated in FIG. 3 were prepared by applying the same procedure as in Example 161 save for employing the respective disazo compounds referred to by number in the following Table-17 in place of the disazo compound No. 1C used in Example 161. When these photosensitive materials were subjected to the same measurement of Vpo and E1/2 as in Example 121, the result was as shown in Table-17, respectively. 
     
                       TABLE 17______________________________________     DisazoExample   compound    Vpo        El/2No.       No.         (volt)     (lux . sec.)______________________________________162        3C         980        15163        5C         920        12164       19C         900        10165       55C         950        20166       67C         930        10167       91C         990         8168       110C        990        10169       123C        920        19170       127C        1000       30______________________________________ 
    
     EXAMPLE 171 
     2 parts by weight of the disazo compound 1C and 98 parts by weight of tetrahydrofuran were pulverized and mixed together within a ball-mill, and the resulting dispersion was coated, by means of a doctor blade, on a polyester film deposited with aluminum through vacuum evaporation and was subjected to natural drying, whereby there was formed a 1 μ-thick charge-carrier generating layer. Meanwhile, another dispersion was prepared by mixing 2 parts by weight of 2,5-bis(4-diethylaminophenyl)-1,3,4-oxadiazole, 2 parts by weight of polycarbonate (the same as that in Example 151) and 46 parts by weight of tetrahydrofuran together, and this dispersion was coated on the foregoing charge-carrier generating layer by means of a doctor blade and then dried at a temperature of 120° C. for 10 minutes to form a 10 μ-thick charge-transfer medium layer, whereby there was obtained a laminate-type photosensitive material illustrated in FIG. 3. When the thus obtained photosensitive material was subjected to the same measurement of Vpo and E1/2 as in Example 121 save for applying -6 KV corona discharge instead of +6 KV corona discharge, the result was as follows: 
     
         Vpo=990 V, E1/2 =8 lux.sec. 
    
     EXAMPLES 172 THROUGH 180 
     Varieties of photosensitive materials having the same structure as that of Example 171 were prepared by employing the respective disazo compound referred to by number in the following Table-18  in place of the disazo compound No. 1C used in Example 171. When these photosensitive materials were subjected to the same measurement of Vpo and E1/2 as in Example 121, the result was as shown in Table-18, respectively. 
     
                       TABLE 18______________________________________     DisazoExample   compound    Vpo        El/2No.       No.         (volt)     (lux . sec.)______________________________________172        3C         900        10173        5C         890        10174       19C         910        12175       55C         910        25176       67C         900        12177       91C         880        18178       110C        870        15179       123C        890        20180       127C        900        35______________________________________ 
    
     EXAMPLE 181 
     1 parts by weight of polyester resin (namely, Polyester Adhesive 49000, the manufacture of Du Pont Inc.), 1 part by weight of the disazo compound 1D and 26 parts by weight of tetrahydrofuran were pulverized and mixed together within a ball-mill, and the resulting dispersion was coated, by means of a doctor blade, on a polyester film deposited with aluminum through vacuum evaporation and was dried at a temperature of 100° C. for 10 minutes, whereby there was obtained a photosensitive material having a 7 μ-thick photosensitive layer and a structure illustrated in FIG. 1. 
     Subsequently, after charging positive electricity on the photosensitive layer of this photosensitive materials by applying +6 KV corona discharge for 20 seconds by means of a commercial electrostatic copying paper testing apparatus, the photosensitive material was left alone in the dark for 20 seconds, and the surface potential Vpo(volt) at that time was measured. Next, light was applied to the photosensitive layer by means of a tungsten lamp so as to attain the illumination of 20 luxes on the surface thereof, and the time (unit: second) required for reducing said surface potential Vpo to half was sought, whereby the amount of exposure E1/2 (lux.sec.) was obtained. The result was as follows: 
     
         Vpo=500 V, E1/2 =15 lux.sec. 
    
     EXAMPLES 182 THROUGH 190 
     Varieties of photosensitive materials were prepared by applying the same procedure as in Example 181 save for employing the respective disazo compounds referred to by number in the following Table-19 in place of the disazo compound No. 1D used in Example 181. When these photosensitive materials were subsequently subjected to the same measurement of Vpo and E1/2 as in Example 181, the result was as shown in Table-19, respectively. 
     
                       TABLE 19______________________________________     DisazoExample   compound    Vpo        El/2No.       No.         (volt)     (lux . sec.)______________________________________182        4D         620        10183       17D         620        10184       18D         700        12185       32D         710        14186       37D         700        25187       49D         690        30188       58D         690        30189       62D         700        20190       65D         800        35______________________________________ 
    
     EXAMPLE 191 
     10 parts by weight of polyester resin (the same as that in Example 181), 10 parts by weight of 2,4,7-trinitro-9-fluorenone, 2 parts by weight of disazo compound No. 1D and 198 parts by weight of tetrahydrofuran were pulverized and mixed together within a ball-mill, and the resulting dispersion was coated, by means of a doctor blade, on a polyester film deposited with aluminum through vacuum evaporation and was dried at a temperature of 100° C. for 10 minutes, whereby there was obtained a photosensitive material having a 10 μ-thick photosensitive layer and a structure illustrated in FIG. 2. Subsequently, measurement of Vpo and E1/2 of this photosensitive material was conducted through the same procedure as in Example 181 save for applying -6 KV corona discharge instead of +6 KV corona discharge employed in Example 15. The result was as follows: 
     
         Vpo=500 V, E1/2 =8 lux.sec. 
    
     EXAMPLES 192 THROUGH 200 
     Varieties of photosensitive materials having a structure illustrated in FIG. 2 were prepared by applying the same procedure as in Example 191 save for employing the respective disazo compounds referred to by number in the following Table-20 in place of the disazo compound No. 1D used in Example 181. When these photosensitive materials were subsequently subjected to the same measurement of Vpo and E1/2 as in Example 181, the result was as shown in Table-20, respectively. 
     
                       TABLE 20______________________________________     DisazoExample   compound    Vpo        El/2No.       No.         (volt)     (lux . sec.)______________________________________192        3D         490         8193        5D         480         5194       11D         500         9195       23D         500        15196       25D         480        18197       35D         520        20198       38D         500        20199       41D         490        18200       60D         630        18______________________________________ 
    
     EXAMPLE 201 
     10 parts by weight of polyester resin (the same as that in Example 181), 10 parts by weight of 2,5-bis(4-diethylaminophenyl)-1,3,4-oxadiazole, 2 parts by weight of the disazo compound No. 1D and 198 parts by weight of tetrahydrofuran were pulverized and mixed together within a ball-mill, and the resulting dispersion was coated, by means of a doctor blade, on a polyester film deposited with aluminum through vacuum evaporation and was dried at a temperature of 120° C. for 10 minutes, whereby there was prepared a photosensitive material having a 10 μ-thick photosensitive layer and a structure illustrated in FIG. 2. When this photosensitive material was subsequently subjected to the same measurement as in Example 181, the result was as follows: 
     
         Vpo=800 V, E1/2 =6 lux.sec. 
    
     EXAMPLES 202 THROUGH 210 
     Varieties of photosensitive materials having a structure illustrated in FIG. 2 were prepared by applying the same procedure PG,129 as in Example 201 save for employing the respective disazo compounds referred to by number in the following Table-21 in place of the disazo compound No. 1D used in Example 201. When these photosensitive materials were subsequently subjected to the same measurement of Vpo and E1/2 as in Example 181, the result was as shown in the following Table-21, respectively. 
     
                       TABLE 21______________________________________     DisazoExample   compound    Vpo        El/2No.       No.         (volt)     (lux . sec.)______________________________________202        2D         950        10203        9D         900        12204       13D         920         8205       28D         930        15206       33D         890        16207       45D         900        19208       47D         900        20209       52D         890        21210       66D         950        25______________________________________ 
    
     EXAMPLE 211 
     200 parts by weight of poly-N-vinyl carbazole, 33 parts by weight of 2,4,7-trinitro-9-fluorenone, 20 parts by weight of polyester resin (the same as that in Example 181) and 20 parts by weight of the disazo compound No. 1D as added to 1780 parts by weight of tetrahydrofuran were pulverized and mixed together within a ball-mill, and the resulting dispersion was coated, by means of a doctor blade, on a polyester film deposited with aluminum through vacuum evaporation and was dried at a temperature of 100° C. for 10 minutes and at a temperature of 120° C. for 5 minutes in succession, whereby there was obtained a photosensitive material having a 13 μ-thick photosensitive layer and a structure illustrated in FIG. 2. When this photosensitive material was subjected to the same measurement as in Example 181, the result was as follows: 
     
         Vpo=1,000 V, E1/2 =3 lux.sec. 
    
     EXAMPLES 212 THROUGH 220 
     Varieties of photosensitive materials having a structure illustrated in FIG. 2 were prepared by applying the same procedure as in Example 211 save for employing the respective disazo compounds referred to by number in the following Table-22 in place of the disazo compound No. 1D used in Example 211. When these photosensitive materials were subsequently subjected to the same measurement of Vpo and E1/2 as in Example 181, the result was as shown in the following Table-22, respectively. 
     
                       TABLE 22______________________________________     DisazoExample   compound    Vpo        El/2No.       No.         (volt)     (lux . sec.)______________________________________212        9D         1020       5213       10D         1000       3214       17D         1120       8215       29D         1000       6216       40D          995       10217       42D         1150       8218       51D         1200       12219       63D         1200       15220       64D         1210       15______________________________________ 
    
     EXAMPLE 221 
     2 parts by weight of the disazo compound No. 1D and 98 parts by weight of tetrahydrofuran were pulverized and mixed together within a ball-mill, and the resulting dispersion was coated, by means of a doctor blade, on a polyester film deposited with aluminum through vacuum evaporation and was subjected to natural drying, whereby there was formed a 1 μ-thick charge-carrier generating layer. Meanwhile, another dispersion was prepared by mixing 2 parts by weight of 2,4,7-trinitro-9-fluorenone, 2 parts by weight of polycarbonate (namely, Panlite L, the manufacture of TEIJIN Co. Ltd.) and 46 parts by weight of tetrahydrofuran together, and this dispersion was coated on the foregoing charge-carrier generating layer by means of a doctor blade and then dried at a temperature of 100° C. for 10 minutes to form a 10 μ-thick charge-transfer medium layer, whereby there was obtained a photosensitive material having a structure illustrated in FIG. 3. When the thus obtained photosensitive material was subjected to the same measurement as in Example 181, the result was as follows: 
     
         Vpo=800 V, E1/2 =15 lux.sec. 
    
     EXAMPLES 222 THROUGH 230 
     Varieties of photosensitive materials having a structure illustrated in FIG. 3 were prepared by applying the same procedure as in Example 221 save for employing the respective disazo compounds referred to by number in the following Table-23 in place of the disazo compound No. 1D used in Example 221. When these photosensitive materials were subjected to the same measurement of Vpo and E1/2 as in Example 181, the result was as shown in Table-23, respectively. 
     
                       TABLE 23______________________________________     DisazoExample   compound    Vpo        El/2No.       No.         (volt)     (lux . sec.)______________________________________222        8D         850        9223       15D         800        10224       21D         870        8225       30D         880        15226       33D         890        20227       43D         900        10228       53D         865        10229       55D         880        18230       61D         900        25______________________________________ 
    
     EXAMPLE 231 
     2 parts by weight of the disazo compound No. 1D and 98 parts by weight of tetrahydrofuran were pulverized and mixed together within a ball-mill, and the resulting dispersion was coated, by means of a doctor blade, on a polyester film deposited with aluminum through vacuum evaporation and was subjected to natural drying, whereby there was formed a 1 μ-thick charge-carrier generating layer. Meanwhile, another dispersion was prepared by mixing 2 parts by weight of 2,5-bis(4-diethylaminophenyl)-1,3,4-oxadiazole, 2 parts by weight of polycarbonate (the same as that in Example 221) and 46 parts by weight of tetrahydrofuran together, and this dispersion was coated on the foregoing charge-carrier generating layer by means of a doctor blade and then dried at a temperature of 120° C. for 10 minutes to form a 10 μ-thick charge-transfer medium layer, whereby there was obtained a laminate-type photosensitive material illustrated in FIG. 3. When the thus obtained photosensitive material was subjected to the same measurement of Vpo and E1/2 as in Example 181 save for applying -6 KV corona discharge instead of +6 KV corona discharge, the result was as follows: 
     
         Vpo=1,000 V, E1/2 =8 lux.sec. 
    
     EXAMPLES 232 THROUGH 240 
     Varieties of photosensitive materials having the same structure as that of Example 231 were prepared by employing the respective disazo compound referred to by number in the following Table-24 in place of the disazo compound No. 1D used in Example 231. When these photosensitive materials were subjected to the same measurement of Vpo and E1/2 as in Example 181, the result was as shown in Table-24, respectively. 
     
                       TABLE 24______________________________________     DisazoExample   compound    Vpo        El/2No.       No.         (volt)     (lux . sec.)______________________________________232        6D         1000       8233       14D          990       8234       19D          980       10235       22D          990       8236       27D         1000       10237       36D          990       15238       44D         1000       8239       48D         1020       19240       53D         1100       25______________________________________