Electrophotographic Sensitive Materials Containing a Disazo Pigment

(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.

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.sub.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.sub.2 and Ar.sub.3 are selected from the group consisting of aromatic rings such as benzene ring, naphthalene ring, etc. and their substituents, R.sub.1 and R.sub.3 are selected from the group consisting of hydrogen, lower alkyl radical or phenyl radical and their substituents and R.sub.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.sub.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.

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.degree. C. for about 30 minutes. Next, this mixture is cooled to about 0.degree. 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.degree.-5.degree. 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.degree.-8.degree. 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.degree. 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.degree. C.

Hereinafter will be shown concrete examples of compounds represented by the general formula II.

The portion ##STR8## being common to Compounds No. 2B-66B, is omitted and represented as --Y.sub.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.

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.degree. C. for about 30 minutes. Next, this mixture is cooled to 0.degree. 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.degree.-5.degree. 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.degree. 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.degree.-8.degree. 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.degree. 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.degree. C.

Hereinafter will be shown concrete examples of compounds expressed by the general formula III.

The portion ##STR11## being common to Compounds No. 2C-66C, is omitted and represented as --Y.sub.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.

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.degree.-8.degree. 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.degree. 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.degree. C.

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.sub.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.

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.degree. C. for about 30 minutes. Next, this mixture is cooled to about 0.degree. 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.degree.-5.degree. 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.degree. 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.degree.-8.degree. 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.degree. 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.degree. C.

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', and 2"' 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' 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" and 2"' 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" 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 5.mu., preferably less than 2.mu., 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 3-50.mu., preferably 5-20.mu.. In the case of the photosensitive materials illustrated in FIGS. 3 and 4 the thickness of the charge-carrier generating layer is less than 5.mu., preferably less than 2.mu., and the thickness of the charge-transfer medium layer is about 3-50.mu., preferably 5-20.mu.. 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-.beta.-chloroethylcarbazole, N-.beta.-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 1.mu..

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.

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.multidot.sec.) was obtained. The result was as follows:

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.

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.degree. C. for 10 minutes, whereby there was obtained a photosensitive material having a 10.mu.-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:

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.

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.degree. C. for 10 minutes, whereby there was prepared a photosensitive material having a 10.mu.-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:

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.

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.degree. C. for 10 minutes and at a temperature of 120.degree. C. for 5 minutes in succession, whereby there was obtained a photosensitive material having a 13 .mu.-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:

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.

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 .mu.-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.degree. C. for 10 minutes to form a 10 .mu.-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:

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.

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 .mu.-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.degree. C. for 10 minutes to form a 10 .mu.-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:

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.

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.degree. C. for 10 minutes, whereby there was obtained a photosensitive material having a 7 .mu.-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.multidot.sec.) was obtained. The result was as follows:

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.

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.degree. C. for 10 minutes, whereby there was obtained a photosensitive material having a 10 .mu.-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:

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.

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.degree. C. for 10 minutes, whereby there was prepared a photosensitive material having a 10 .mu.-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:

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.

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.degree. C. for 10 minutes and at a temperature of 120.degree. C. for 5 minutes in succession, whereby there was obtained a photosensitive material having a 13 .mu.-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:

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.

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 .mu.-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.degree. C. for 10 minutes to form a 10 .mu.-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:

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.

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 .mu.-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.degree. C. for 10 minutes to form a 10 .mu.-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:

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.

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.degree. C. for 10 minutes, whereby there was obtained a photosensitive material having a 7 .mu.-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:

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.

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.degree. C. for 10 minutes, whereby there was obtained a photosensitive material having a 10 .mu.-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:

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.

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.degree. C. for 10 minutes, whereby there was prepared a photosensitive material having a 10 .mu.-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:

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.

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.degree. C. for 10 minutes and at a temperature of 120.degree. C. for 5 minutes in succession, whereby there was obtained a photosensitive material having a 13 .mu.-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:

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.

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 .mu.-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.degree. C. for 10 minutes to form a 10 .mu.-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:

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.

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 .mu.-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.degree. C. for 10 minutes to form a 10 .mu.-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:

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.

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.degree. C. for 10 minutes, whereby there was obtained a photosensitive material having a 7 .mu.-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:

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.

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.degree. C. for 10 minutes, whereby there was obtained a photosensitive material having a 10 .mu.-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:

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.

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.degree. C. for 10 minutes, whereby there was prepared a photosensitive material having a 10 .mu.-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:

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.

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.degree. C. for 10 minutes and at a temperature of 120.degree. C. for 5 minutes in succession, whereby there was obtained a photosensitive material having a 13 .mu.-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:

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.

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 .mu.-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.degree. C. for 10 minutes to form a 10 .mu.-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:

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.

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 .mu.-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.degree. C. for 10 minutes to form a 10 .mu.-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:

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.