Heat Treatment Of An Electrophotographic Photosensitive Member

Abstract

An electrophotographic photosensitive material comprising mainly an organic photoconductive material of low molecular weight and a high polymer resin which is subjected to heat treatment or atmosphere treatment, and if desired, stimulus treatment to improve the electrophotographic properties.

Description

This invention relates to a novel organic photosensitive member and, in particular, to a photosensitive member suitable for electrophotography comprising a photosensitive film mainly composed of an organic compund of low molecular weight and a high polymer binder resin said photosensitive film being subjected to a treatment for controlling the crystalline state of the film.

Heretofore, various organic photoconductive materials have been known, for example, condensed polynuclear aromatic compunds such as anthracene, phrene, and perylene, heterocyclic compunds such as triphenyl-pyrazoline derivatives, acylhydrazone derivatives, and high polymer compunds such as poly-N-vinylcarbazole. However, photosensitivity of organic photoconductive materials is so low that organic photoconductive materials are generally not suitable for electrophotographic photosensitive materials. There have been recently found organic compounds, the photosensitivity of which is as high as that of inorganic substances such as zinc oxide and selenium. As representative examples of such highly photosensitive organic materials, there may be mentioned brominated poly-N-vinylcarbazole in Japanese Pat. publication No. 25230/1967, poly-3,6-duodo-9-vinylcarbazole in Japanese Pat. publication No. 7592/1968, poly-N-vinyl-3-aminocarbazole in Japanese Pat. publication No. 9639/1967, and polyvinylanthracene in Japanese Pat. publication No. 2629/1968. However, these organic photoconductive materials are prepared through particular and complicated synthetic processes so that these materials are not preferable from economical and practical points of view.

Organic photoconductive materials are usually used as an electrophotographic photosensitive material, and the material may be used, as it is, without mixing with other components, or it may be used by mixing it with a binder in a form of dispersion system or solid solution state.

In such a photosensitive layer, with the lapse of time, coarse crystals form spontaneously, and the coarse crystals continue to grow depending on the outer conditions to form coarse crystals in a wide distribution of particle size. Therefore, not only is the transparency lowered, transparency being an important advantage of organic photoconductive materials, but also the mechanical strength of the photosensitive layer and the photosensitivity is substantially deteriorated.

The present inventors have studied the crystallization phenomenon which reduces the practicability of organic photoconductive materials, and found that excellent photosensitive materials can be obtained by controlling the crystallization state of organic photoconductive materials of low molecular weight. This invention solves various disadvantages of conventional organic photoconductive materials such as low photosensitivity, poor economy, and coarse crystals.

An object of this invention is to provide a photosensitive member comprising an organic photoconductive material of low molecular weight which has photosensitivity, stability and resolving power as high as those of the conventional zinc oxide or selenium.

Another object of this invention is to provide a photosensitive member having good photosensitivity, physical properties and a dot pattern effect corresponding to the shape or resolving power required for the photosensitive member.

A further object of this invention is to provide a photosensitive member having excellent photosensitivity, resolving power, stability, physical properties and a dot pattern effect which can be easily produced by a simple method of manufacturing.

Still another object of this invention is to provide a photosensitive member obtained by applying a treatment for controlling the crystal state to a photosensitive film containing an organic photoconductive material of low molecular weight and a high polymer binder resin.

Further objects and advantages of this invention will be apparent from the following description.

According to the treatment for controlling the crystalline state, the crystalline state formed after subjection to the treatment for controlling the crystalline state has a higher photoconductivity than the original crystalline state.

The treatment for controlling the crystalline state and the photoconductivity thus sensitized depend on crystalline states before and after the treatment. This will be understood by the following explanation. Heretofore, various efforts have been made to prevent crystallization in an organic photosensitive film by, for example, adding crystallization inhibitors such as a plasticizer, polymerization inhibitor, and a softening agent since spontaneous crystallization in an organic photosensitive film deteriorates various useful properties thereof. However, crystallization of the organic photoconductive material is due to the inherent property of the material itself so that it is very difficult to find a useful and practical means for preventing the crystallization. Therefore, the deterioration of photoconductivity and physical properties caused by crystallization has not yet been removed. In general, crystallization does not uniformly occur over the whole surface of the material, but initially occurs at a point where crystallization easily occurs (hereinafter called "specific point") and then the crystals thus formed grow and result in the crystallization phenomenon which deteriorates photosensitive film. Under natural conditions, crystallization proceeds starting from the specific point previously formed when the film has been produced. Such specific points are not uniformly distributed and are distributed at low density so that coarse crystals form locally. As a result, the film thus produced is in a state similar to that containing impurities, i.e. the coarse crystals, are not uniform distributed. In other words, a portion where the impurity exists is different from the surroundings in points of photoconductivity, and therefore, fog and irregular charging occur. Further, the physical property at that portion of impurities is different from the surroundings and therefore, the refractive index is different and devitrification occurs and further the mechanical strength is lowered.

According to this invention, the above-mentioned crystallization is positively utilized, and a treatment for controlling the crystalline state is applied so as to sensitize the photoconductivity while keeping the mechanical strength unchanged without causing deterioration of various properties of the photosensitive film.

In a photosensitive film composed of an organic photoconductive material of low molecular weight dispersed in a high polymer binder resin in a form of solid solution, under material conditions the organic photoconductive material of low molecular weight crystallizes to form coarse crystals in the binder resin, but, by applying a treatment for controlling crystalline the state, microcrystals of the organic photoconductive material uniformly form in the binder resin at a high density, and this state shows high photoconductivity. The treatment for controlling the crystalline state imparts external energy to the photosensitive film and produces specific points on the whole film by the stimulus without depending only upon the preliminarily present specific points. Further, the treatment for controlling the crystalline state enables molecules of the organic photoconductive material of low molecular weight to move easily for the purpose of facilitating the formation of microcrystals. More particularly, the treatment is carried out by plasticizing the binder resin by applying heat or solvent so as to facilitate the molecular arrangement for crystallization of the organic photoconductive material of low molecular weight. Even if the stimulus by external energy is absent, the increased mobility of molecules often results in controlling the crystalline state. The photosensitive film thus subjected to the treatment for controlling the crystalline state has clearly sensitized photoconductivity. In a sense, this system is similar to a system wherein cadmium sulfide powders a known excellent photoconductive material are dispersed in a binder resin, but the cadmium sulfide powders are dispersed in an insulating binder resin for the purpose of retaining the insulation property at a dark place and therefore, the purpose is different from the present invention.

The theoretical mechanism of the effect obtained by the treatment for controlling crystalline state is not yet clear, but is considered to be as follows. The conventional formation of coarse crystals of organic photoconductive materials under natural conditions results in nonuniform crystals, wide distribution of particle size, and lowered physical property, photosensitivity and resolving power, while the crystalline state obtained after treatment for controlling crystalline state is uniform with a narrow distribution of crystal size. Therefore, high photosensitivity and high resolving power of the photosensitive member according to this invention predominantly depend on the uniformity of crystal state and narrow distribution of crystal size.

The photosensitive member of this invention is generally obtained by coating an organic photoconductive material of low molecular weight together with a high polymer resin on a support base, if desired, drying, hardening, and then applying a treatment for controlling crystalline state. The treatment for controlling crystalline state may be effected by various methods. The representative methods are heat treatment and atmosphere treatment. These two treatments may be applied singly or in combination for controlling crystalline state.

A standard of treatment for controlling crystalline state may be shown by a graph of temperature-crystal formation velocity and temperature-crystal growing velocity illustrating the relation between temperature and change of crystalline state.

The attached drawing illustrates a graph of temperature-crystal formation velocity and temperature-crystal growing velocity.

In the graph, the ordinate is velocity and the abscissa is temperature. With respect to the curves 1, 2, and 3, the ordinate is crystal formation velocity, crystal growing velocity and melting velocity, respectively. The symbol Tm denotes melting temperature. This graph gives various indications referring to the control of crystalline state. When the treatment for controlling crystalline state is effected at a relatively low temperature for long time, the crystal formation velocity exceeds the crystal growing velocity so that microcrystals are formed. On the contrary, when the treatment is effected at high temperature, relatively large crystals are obtained. At an intermediate temperature, particularly, a temperature between that at the peak of crystal formation velocity and that at the peak of crystal growth velocity, various crystalline states may be controlled depending on the temperature. It should be noted here that the treatment temperature should be kept below the melting temperature.

In addition, referring to heat treatment, it is necessary to adjust appropriately heat treating conditions depending on kinds of organic photoconductive materials of low molecular weight. According to the experimental results, stability of an organic photoconductive material of low molecular weight becomes high with increase in symmetry, regularity and polarity of molecular structure of the organic photoconductive material of low molecular weight. Therefore, the optimal heat treating conditions may range widely.

When the heat treatment is effected at a temperature near the second order transition temperature Tg ) glass transition temperature) of the binder resin, the crystallization is effectively accelerated. In general, when heat treatment is carried out at a temperature higher than the melting point of the photosensitive film, the photosensitive film becomes amorphous. In view of the foregoing the Tg and the melting point have a great effect on treatment for controlling crystalline state. Therefore, the heat treating conditions should be appropriately selected depending upon the organic photoconductive material, binder resin, plasticizer, amount thereof and the like.

Heat treatment is usually conducted by a direct heating means a furnace, high frequency wave heating and infrared ray heating, but secondary heating methods such as ion irradiation or electron ray irradiation may be employed and further, if desired, cooling may be employed.

Another treatment for controlling crystallization state is atmosphere treatment. The crystalline state resulting from atmosphere treatment is, to some extent, similar to the relation between temperature and crystalline state in heat treatment, but there are uncertain factors and it is not always possible to determine clearly crystallization state common to that in heat treatment.

As an example of atmosphere treatment, there is "solvent atmosphere treatment". Control of the crystalline state by the solvent atmosphere treatment is similar to that of heat treatment. Referring to the drawing again, the abscissa is concentration of solvent (the solvent being capable of softening the photosensitive film) present above the coating surface as atmosphere, as shown in the parentheses. The control of crystalline state by using concentration of vapor is sufficiently effective. According to the practical procedure, a solution containing an organic photoconductive material of low molecular weight and a high polymer binder resin is made into a coating film and then a solvent vapor of a certain concentration is kept in contact with the coating film for a certain period to control the crystalline state. In this case, the crystalline state is considerably affected by the thickness of coating layer. When the coating layer is thick, for example, over 25 .mu., evaporation of the solvent present in the coating layer is so slow that a relatively large amount of solvent remains in the coating layer for a considerably long time, and thereby, as shown in the attached graph, the crystal growing velocity exceeds the crystal formation velocity and relatively large crystals are formed from the initial stage of crystallization. On the contrary, when the coating layer is thin, a tendency opposite thereto appears.

The solvent atmosphere treatment lowers Tg of photosensitive film and thereby facilitates crystallization.

The treatment in an antioxidizing atmosphere such as a reducing atmosphere and an inert gas atmosphere prevents oxidation, particularly, in case of high temperature treatment. As the antioxidizing atmosphere, various gases such as nitrogen, hydrogen and rare gas may be used.

These treatments for controlling crystalline state should be applied taking into consideration the shape and inherent property of the organic photoconductive material to be treated, and in addition, resolving the power requested. It is particularly important to control the crystal size so as to obtain high photosensitivity and high resolving power. With respect to the relation among crystal size, crystal orientation and resolving power of the photosensitive film, the crystal size and crystal orientation should be appropriately selected so as to obtain resolving power required.

When the photosensitive member employs a paper as the support and a resolving power of about 10 lines per mm. is desired, the crystal size of about 20 particles per mm. (0.05 mm. in size) is suitable. The control range of crystal size is 0.1 to 100 .mu. and a crystal particle of above 1 .mu. can be observed by a microscope. Further, referring to the thickness of the layer of the photosensitive film and degree of crystallization, a thick layer results in easy crystallization and formation of coarse crystals. If there exist coarse crystals in the initial stage of film formation, it is preferable to return the crystalline state once to an amorphous state and then apply the treatment again producing microcrystalline state.

According to another aspect of this invention, a stimulus treatment such as external mechanical, physical and chemical stimulus treatments may be employed in combination with the above mentioned treatment for controlling crystalline state to obtain a photosensitive member.

As the stimulus, there may be mentioned mechanical stimulus such as contact, pressure contact, needle pressure, and friction, physical stimulus such as various radiation irradiation, and ion or electron ray irradiation, and chemical stimulus such as etching oxidation and reduction.

The stimulus treatment not only facilitates the formation of specific points, but also, on the contrary, suppresses the crystallization. The effect of stimulus treatment is so wide as mentioned above depending on the treatment conditions. The action of stimulus treatment may be explained as follows. In general, crystallization starts from the surface of the photosensitive film. The stimulus by the stimulus treatment is given to the film surface to yield specific points on a part of the surface the whole surface. An example of such a specific point is that capable of being a crystal nucleus from which crystallization starts, and only the neighborhood of the specific points is subjected to the treatment for controlling crystalline state and thus when the treatment is applied locally, a photosensitive member having dot pattern effect. This treatment for producing a dot pattern effect may be conducted by one of the above-mentioned stimulus treatments, that is, a pressure contact treatment. By appropriately selecting a heat treatment or atmosphere treatment to be combined, control of crystal size of amorphous or crystalline photosensitive film and control of crystal orientation can be more effectively conducted to produce a photosensitive member excellent in photosensitivity, resolving power, and stability. The dot pattern effect may be obtained by applying locally and partly heat treatment or atmosphere treatment.

The heat treatment and atmosphere treatment, and in addition, the stimulus treatment according to this invention can give a photosensitivity of several to about 10 times that of a photosensitive member not subjected to the treatment for controlling crystalline state. Furthermore, resolving power and stability of photosensitive members are increased by controlling the crystal size and crystal orientation. Mechanical, physical or chemical stimulus can give excellent dot pattern effect and improve the properties.

These effects such as sensitization, resolving power, dot pattern effect and improvement of properties can be easily obtained by simply applying heat treatment, atmosphere treatment, and if desired, additionally a stimulus treatment at a step in the formation of the photosensitive film. Therefore, it is commercially valuable. Furthermore, the electrophotographic photosensitive member according to this invention has various desireable properties requested to conventional organic photosensitive materials, such as high reliability, high stability, simple handling and high photosensitivity.

Compositions used for this invention are as shown below.

A As organic photoconductive materials of low molecular weight, there may be mentioned the following compounds:

1. As compounds having heterocyclic ring, and aromatic ring, there are, for example, 2,5-bis-(4'-aminophenyl-1')-1,3,4-oxadiazoles, such as 2,5-bis-(4'-aminophenyl-1')-1,3,4-oxadiazole, 2,5-bis-(4'-monoalkylaminophenyl-1')-1,3,4-oxadiazole, 2,5-bis-(4'-dialkylaminophenyl-1')-1,3,4-oxadiazole and 2,5 bis-(4'-acylaminophenyl-1')-1,3,4-oxadiazole; diphenylene hydrazones of aliphatic, aromatic or heterocyclic aldehydes or ketones as disclosed in Japanese Pat. publication No. 4298/1964, such as acetaldehyde-diphenylene hydrazone, benzaldehyde-diphenylene hydrazone, o- or p- chlorobenzaldehyde-diphenylene hydrazone, 2,4-dichloro benzaldehyde-diphenylene hydrazone, p-dimethylaminocinnamic aldehyde-diphenylene hydrazone, 2-pyridine aldehyde-diphenylene hydrazone, p-dimethylamino benzaldehyde-diphenylene hydrazone, benzaldehyde-3-chloro-diphenylene hydrazone, benzaldehydro-3-bromo-diphenylene hydrazone, p-dimethylaminobenzal-3-chloro-diphenylene hydrazone, p-dimethylaminobenzal-3-bromo-diphenylene hydrazone, benzaldehyde-3,6-dichloro -diphenylene hydrazone, benzaldehyde-3,6-dibromo -diphenylene hydrazone, benzaldehyde-3-chloro-6-bromo -diphenylene hydrazone, p-aminodimethylbenzaldehyde -3,6-dichloro diphenylene hydrazone, p-aminodimethyl benzaldehyde -3,6-dibromo diphenylene hydrazone and p-aminodimethyl-benzaldehyde-3-chloro-6-bromo diphenylene hydrazone; 1,3,5-triphenyl pyrazoline, 5-aminothiazole derivatives, 4,1,2-triazole derivatives, imidazolone derivatives, oxazole derivatives, imidazole derivatives, pyrazoline derivatives, imidazolidine derivatives, polyphenylene thiazole derivatives, and 1,6-methoxyphenazine derivatives.

2. As compounds having a condensed ring, there may be given, for example, various derivatives of benzthiazole, benzimidazole, benzoazole, aminoacridine and quinoxaline.

3. As compounds having double bond, there may be given, for example, acylhydrazone derivatives and 1,1,6,6-tetraphenyl hexatriene.

4. As compounds having amino or nitrile group, there may be given, for example, aminated biphenyls, allylideneazines, N,N,N',N'-tetrabenzl -p-phenylene diamine, triphenylamine and p-dimethylaminostyryl ketone.

5. As condensation products, there may be given, for example, condensation products of aldehyde and aromatic amine and reaction products of aromatic amine and aromatic halide.

6. As condensed polymer, there may be given, for example, intermediate condensation products of carboxylic acid halide and triphenylamine.

B. As high polymer binder resins, there may be mentioned, for example, polystyrene resin, polyvinyl chloride resin, phenolic resin, polyvinylacetate resin, polyvinylacetal resin, epoxy resin, xylene resin, alkyd resin, polycarbonate resin, polymethylmethacrylate resin, and polyvinylbutyral resin.

C. As plasticizers, there may be mentioned, for example, dioctylphthalate, tricresyl phosphate, diphenyl chloride, methylnaphthalene, p-terphenyl and diphenyl.

D. As solvents, there may be mentioned, for example, benzene, chlorobenzene, toluene, acetone, methanol, ethanol, ethyl acetate, methylethyl ketone, trichloroethylene, carbon tetrachloride, methylcellusolve, tetrahydrofuran, dioxane and dimethylformaldehyde.

The organic photoconductive material of low molecular weight used in this invention is that of molecular weight of about 100 to 2000, preferred with 250 to 1000.

Preferable materials having high photosensitivity are 2,5-bis-(4'-aminophenyl)-1,3,4-oxadiazole, diphenylene-hydrazones, 1,3,5-triphenylpyrazoline, N,N,N',N' -tetrabenzyl-p-phenylenediamine, p-dimethylaminophenyl styryl ketone, and triphenylamine.

The amount of binder resin is not critical. It is preferably from 30 to 50 percent by weight based on amount of the organic photoconductive material of low molecular weight. For the purpose of improving further the property of film, a plasticizer may be added in an amount of 5 to 80 percent by weight on the basis of the amount of the organic photoconductive material of low molecular weight.

As the coating method, there may be used conventional methods such as, for example, rotary coating, wire-bar coating, flow coating, and air-knife coating, and the thickness of coating may be adjusted to several .mu. to several tens .mu. depending on the purpose.

As the support, there may be used a metal plate such as aluminum, copper, zinc, and silver plates, a solvent proof paper, aluminum laminate paper, synthetic resin film containing surfactant, and glass, paper and synthetic resin film having a metal, metal oxide or metal halide deposited on the surface by, for example, vapor deposition. In general, any material may be used which has surface resistivity less than that of the photoconductive layer, i.e. less than 10.sup.8 .OMEGA., preferably less than 10.sup.5 .OMEGA., may be used.

Conventional electrophotographic processes may be applied to the electrophotographic photosensitive member to form electrophotographic images. For example, the electrophotographic photosensitive member according to this invention is passed several times under a corona discharging device of + 6 KV. in a dark place to accumulate positive charge to become 150-600 V. An appropriate light source, for example, tungsten lamp, is used for projecting light through a positive pattern to the photosensitive member and the charge at the exposed portion is ventrallized. Then, a negative toner is is applied by magnet brush method, cascade method, or furbrush method to produce positive images. This images may be fixed by heating or passing through an appropriate solvent vapor atmosphere. Further, a liquid developer may be used. The polarity of charge by corona discharging may be either positive or negative.

The following examples are given for illustrating the present invention, but should not be construed as a restriction of the present invention.

EXAMPLE 1

2,5-Bis-[4'-n-propylaminophenyl-(1)]- 1,3,4-oxadiazole (m.p. 98.degree.C) 1.0 g. Maleic acid resin (Bechacite 1111, trade name, supplied by Japan Reichhold Co.) (Second order transition temperature 60.degree. - 65.degree.C) 1.0 g. Methylene chloride 20 ml. Methylene Blue 10 mg.

The above components were mixed to form a homogeneous solution, applied uniformly to a one-sided art paper (80 .mu. in thickness) to a thickness of 5 .mu., and dried naturally to form a photosensitive coating, followed by heat treatment at 90.degree.C for 30 minutes. The photosensitive coating thus heat treated was given a positive charge of about 400 V. by a corona charging device of +6KV, exposed to a high pressure mercury lamp, and soaked in a commercially available negative liquid developer to produce a clear visible image.

The exposure time of the photosensitive coating thus heat treated and oriented was about 1/5 that in a case where the heat treatment was not applied.

EXAMPLE 2

p-Dimethylaminobenzaldehyde diphenylene hydrazone* (m.p. 175.degree. - 7.degree.C) 1.0 g. Alkyd resin (Bechosol - 786, trade name, supplied by Japan Reichhold Co.) 2 g. Cobalt naphthenate 0.02 g. Methylene chloride 20 ml.

The above components were mixed to form a homogeneous solution, applied to a baryta paper (80 .mu. thick) undercoated on both sides to a thickness of about 5 .mu., and heat treated at 140.degree.C for 60 minutes in a room flushed with nitrogen gas. The resulting photosensitive coating gave a clear visible image by following the electrophotographic procedure in Example 1. The photosensitivity was increased to about four times.

When benzaldehyde diphenylene hydrazone was used in place of p-dimethylaminobenzaldehyde diphenylene hydrazone, a similar result was obtained.

EXAMPLE 3

p-Diethylaminobenzylidene-nicotinic acid hydrazide (m.p. 153.degree. - 154.degree.C) 1.0 g. Xylene resin (Nikanol S-101, trade name, available from Nippon Gas Chemical) 1 g. Methyl cellosolve 30 ml.

The mixture of the above components was treated in a procedure similar to Example 1, to form a photosensitive coating. The thus obtained coating was subjected to heat treatment at 80.degree.C for 30 minutes. The thus produced coating was treated and developed in a manner similar to Example 1 to produce a clear visible image. The photosensitivity was increased to about four times by the heat treatment.

EXAMPLE 4

1,3,5-Triphenylpyrazoline (m.p. 139.degree.C) 1.0 g. Acrylnitrile-styrene copolymer (second order transition temperature, 72.degree. - 75.degree.C) 1 g. Diphenyl chloride (Kanechlor No. 400, trade name, commercially available from Kanegafuchi Chemical) 0.5 g. Methylene chloride 20 ml.

The photosensitive preparation mixture of the above components was applied uniformly to an aluminum foil (30 .mu. in thickness) to form a coating of about 10 .mu. thick.

The coating thus obtained was in a complete amorphous solid solution state. This coating was subjected to heat treatment at 70.degree.C for 30 minutes to produce a photosensitive member having a coating containing microcrystallites.

The photosensitive member thus obtained was subjected to the lightening of 200 lux of surface intensity of illumination by tungsten lamp, with negative charge for 1.5 seconds to produce a contrast of 200 V. compared with the untreated member which needed an exposure of 10 seconds for the production of the same contrast. The photosensitivity was increased to 6.5 times.

In this Example, the effect on the photosensitivity was observed by a variation of the periods of the heat treatments. The heat treatment at 70.degree.C for 10 minutes resulted in that the photosensitive coating slightly clouded and the crystal growth was observed, but the change of the sensitivity cannot be measured. The heat treatment at 70.degree.C for 20 minutes resulted in that the photosensitive coating clouded considerably, and the photosensitivity was increased to about two times. The heat treatment at 70.degree.C for 30 minutes resulted in that the photosensitive coating changed throughout opaque, and the photosensitivity was increased as above mentioned to 6.5 times that of the untreated coating.

In addition, the heat treatment at 70.degree.C for 50 minutes resulted in that the photosensitive coating did not change in its appearance, but the photosensitivity was increased to about four times that of the untreated coating. Such effect was somewhat smaller than that of the former treatment.

EXAMPLE 5

The photosensitive member produced in Example 4 was placed in a saturated vapor of methylene chloride for 60 minutes as an atmosphere treatment to give a photosensitive member which was microcrystallized. As the result of determination similar to Example 4, the photosensitivity was increased to five times.

EXAMPLE 6

The photosensitive coating having the same components as Example 4 was subjected to heat treatment at 125.degree.C for 20 minutes to produce a coating in solid solution state. This coating was subjected to heat treatment at 70.degree.C for 30 minutes similarly to Example 4 to gain an increase of about 4 times in the photosensitivity. In comparison with Examples 4 and 5, the coating thus obtained retains a considerable amount of residual charge upon decay by light after charging. Therefore, the performance of this coating as an electrophotographic photosensitive coating was less advantageous. The growth of microcrystallites was investigated by a microscope of 500 magnifications resulting in that there was observed more amount of amorphous area on the surface of the coating subjected to heat treatment at 125.degree.C for 20 minutes, than that on the coating obtained in Example 4.

EXAMPLE 7

To the coating of the photosensitive member of Example 4 was pressed a metal wire network of 150 mesh, and then heat treatment was applied thereto at 70.degree.C for 15 minutes. The thus treated coating was investigated by a microscope of 500 magnifications with the result that the growth of crystallite was partially caused from a part contacted with the metal wire network as a crystal nucleus. To the thus obtained coating was applied a light at 200 lux for 2 seconds to form an image. There was obtained a clear visible image having a dot pattern effect. This was advantageous in the production of a half tone image.

EXAMPLE 8

The preparation mixture in Example 4 was applied to an aluminum foil (30 microns in thickness) to form a coating of about 50 microns in thickness, which was then changed to containing coarse crystals as a result of evaporation of the solvent used. Thus obtained coating was excellent in photosensitivity, but poor in image quality. The coating was then subjected to heat treatment in a room saturated by nitrogen gas at 150.degree.C for 20 minutes with the result that the coating changed into a solid solution (amorphous) state, and the image quality was increased, but the photosensitivity was reduced.

Furthermore, this coating was subjected to heat treatment at 70.degree.C for 30 minutes resulting in the growth of microcrystallite and satisfactory image quality and photosensitivity.

EXAMPLE 9

The photosensitive preparation mixture as used in Example 4 was applied to an aluminum film of about 30 micron in thickness to form a coating of about 70 micron in thickness. The thus obtained coating was subjected to heat treatment at 70.degree.C for 30 minutes to produce a photosensitive coating containing microcrystallite. To the surface of the photosensitive layer a polyester film of about 25 micron in thickness was adhered completely by using epoxy resin bonding agent to produce a photosensitive member of three layered structure. The photosensitive member thus obtained was subjected to charging of positive charge by a corona discharger of +6 KV, uniformly on the surface of the polyester film of the photosensitive member contemporaneously with whole surface exposure by a tungsten lamp. Then, to the surface of the polyester film, the original image was projected by a tungsten lamp of about 1000 lux, contemporaneously with the application of charging by negative corona discharger of -6 KV. Then, tungsten lamp of 100 W was applied thereto for about 2 seconds to produce an electrostatic image corresponding to a contrast pattern of the original image. This latent image was developed by magnet brush method to produce an excellent visible image.

EXAMPLE 10

Benzaldehyde-3,6-dichloro- diphenylene hydrazone* 1.0 gr. ##SPC1## (m.p. 165.degree.C) 2,4,7-Trinitrofluorenone 5 mg. Diphenylamine Blue 20 mg. ##SPC2## Cumarone-indene resin 1.5 gr. (second order transition temperature; 60.degree.-65.degree.C) Methyl ethyl ketone 5 ml. (*This compound can be prepared by a process which comprises treating 3,6-dichlorocarbazole, m.p., 201.degree.C, in glacial acetic acid with sodium nitrite to provide 3,6-dichloro-9-nitroso carbazole, m.p., 110.degree.C, reducing the resulting compound in ether by zinc dust and hydrochloric acid, and immediately condensing the product with benzaldehyde.)

The preparation mixture of the above components was applied to a polyester film undercoated with a conductive polymer, and dried at 50.degree.C for 3 minutes to form a photosensitive coating. The thus obtained coating was determined as amorphous by X-ray diffraction spectrum of the collected sample from the coating. The thus obtained film was kept in an oven at 80.degree.C for the period indicated in the Table below, and then cooled. There is shown the transmittivity and appropriate exposure of thus treated films in the Table below. The appropriate exposure was based upon exposure to tungsten lamp by a positive charge and electrophoresis development.

Table

transmittivity appropriate Sample No. the period ratio exposure (minutes) % lux.sec 1 5 80 150 2 10 73 125 3 30 50 300 untreated 0 85 1000

The transmittivity was measured by a white light, and calculated by assuming the transmittivity of the used film base as 100 percent.

The photosensitivity was increased in Samples 1 and 2 but reduced in Sample 3. The crystalline pattern was observed in the X-ray diffraction spectrum of Sample 3. This result teaches that the increase of a photosensitivity needs a proper degree of crystal growth, or an increase of amount of microcrystallites.

In the replacement of benzaldehyde-3,6-dichloro diphenyl hydrazone of this Example, by benzaldehyde-3-bromodiphenyl hydrazone (I), benzaldehyde-3-chloro-diphenylene hydrazone (II), p-dimethylaminobenzaldehyde-3,6-dichlorodiphenylene hydrazone (III), dimethylamino-3,6-dibromo diphenylene hydrazone (IV) and p-dimethylamino-3-chlorodiphenylene hydrazone (V), the procedures of this Example were repeated to result in the appropriate exposure indicated in the Table below for the compounds (I) - (V) by the heat treatment for 10 minutes.

Table

Compound I II III IV V Appropriate exposure 190 230 115 125 170 lux. sec.

EXAMPLE 11

N,N,N',N'-Tetrabenzyl-p-phenylene diamine 1.0 gr. Polyvinyl butylal resin (commercially available under the trade name S-lec BLS by Sekisui Chemical) 1.0 gr. Crystal violet 10 mg. Chloroform 10 ml.

The above components were mixed homogeneously and the mixture was applied uniformly to a one-sided art paper of 80 micron in thickness to form a coating of about 5 micron, thick and dried naturally to form a photosensitive coating. Thus obtained coating was subjected to heat treatment at 95.degree.C for 20 minutes. The thus treated photosensitive paper was charged to about 350 V of positive charge by a corona discharger of 5 KV in charge voltage, then exposed at 250 lux. sec. by tungsten lamp of 100 W, and developed in a liquid developer to produce a visible image. For the similar photosensitive paper which was not subjected to the above heat treatment, the exposure of about 1,000 lux.sec. was necessary to produce a clear visible image by the similar electrophotographic duplication process.

EXAMPLE 12

p-Dimethylaminophenylstyryl ketone 1.0 gr. Polystyrene resin (commercially available under the trade name "Piccolastic D-100" by ESSO) 1 gr. Methylene blue 10 mg. Methyl ethyl ketone 10 ml.

The preparation solution of the above components was applied uniformly to an aluminum foil plate to a thickness of about 5 micron, and dried by hot air blow at 50.degree.C for 5 minutes to form a photosensitive coating. The thus obtained photosensitive plate was subjected to heat treatment at 80.degree.C for 30 minutes. This plate was subjected to an electrophotographic duplication process similar to Example 11. The exposure of about 200 lux.sec. was necessary to produce a clear visible image.

EXAMPLE 13

Triphenylamine 1.0 gr. Acrylonitrile styrene copolymer resin (commercially available under the trade name "Estylene AS-61NT" by Yahata Chemical) 1.0 gr. Malachite Green 10 mg. Benzene 20 ml.

The preparation solution of the above components was applied to a polyethyleneterephthalate film (90 .mu. thick) to the surface of which electroconductivity was imparted by coating the film surface with a solution composed of 4 gr. of cuprous iodide and 150 ml. of acetonitrile to which 30 ml. of a 5 percent solution of polyvinyl formal was added, to form a photoconductive coating, then which was dried naturally. The thus obtained photosensitive film was subjected to heat treatment at 70.degree.C, for 30 minutes. To the thus treated film, an electrophotographic duplication process was applied. The exposure of about 250 lux.sec. was necessary to produce a clear visible image. For the similar photosensitive film which was not subjected to the above heat treatment, the exposure of 1200 lux.sec. was necessary to produce a clear visible image.

Claims

What is claimed is:

1. An electrophotographic photosensitive member which comprises a photosensitive film comprising an organic photoconductive material of molecular weight ranging from 100 to 2,000 and selected from the group consisting of diphenylene hydrazones, 2,5-bis-(4'-aminophenyl)-1,3,4-oxadiazoles, 2,5-bis-(4'-substituted aminophenyl)-1,3,4-oxadiazoles wherein the substituent is a monoalkyl, dialkyl or acyl group, 1,3,5triphenylpyrazolines, p-dimethyl-aminostyrylketones, N,N,N',N'-tetrabenzyl-p-phenylenediamine and triphenylamines and a high polymer binder resin, said photosensitive film being heated at a temperature not lower than the second order transition temperature and lower than the melting point of the high polymer binder resin for a period sufficiently long to convert said organic photoconductive material to a uniform crystalline state.

2. An electrophotographic photosensitive member according to claim 1 in which the antioxidizing atmosphere is an inert gas.

3. An photosensitive photosenstive member which comprises a photosensitive film comprising an organic photoconductive material of molecular weight ranging from 100 to 2,000 and selected from the group consisting of diphenylene hydrazones, 2,5-bis(4'-aminophenylene), -1,3,4-oxadiazoles wherein the substituent is a monoalkyl, dialkyl or acyl group, 1,3,5 triphenylpyrazolines, p-dimethyl-aminostyrylketones, N,N,N',N'-tetrabenzyl-p-phenylenediamine and triphenylamines and a high polymer binder resin, said photosensitive film being heated at a temperature not lower than the second order transition temperature for a period sufficiently long to convert the film to an amorphous state, said photosensitive film then being softened with a solvent vapor capable of softening the photosensitive film.

4. An electrophotographic photosensitive member which comprises a photosensitive film comprising an organic photoconductive material of molecular weight ranging from 100 to 2,000 selected from the group consisting of diphenylene hydrazones, 2,5-bis-(4'-aminophenyl)-1,3,4-oxadiazoles, 2,5-bis-(4'-substituted aminophenyl)-1,3,4-oxadiazoles wherein the substituent is a monoalkyl, dialkyl or acyl group, 1,3,5-triphenylpyrazolines, p-dimethyl-aminostyrylketones, N,N,N',N'-tetrabenzyl-p-phenylenediamine and triphenylamines and a high polymer binder resin, said photoconductive film being heated at a temperature not lower than the melting point of the high polymer binder resin, for a period sufficient to convert said photoconductor to a uniform crystalline state the surface of said film being stimulated by applying pressure thereto so as to yield specific points on the surface resulting in a dot pattern effect.

5. An electrophotographic photosensitive member which comprises a photosensitive film comprising a diphenylene hydrazone and a high polymer binder resin, said photosensitive film being heated at a temperature not lower than the second order transition temperature and lower than the melting point of the high polymer binder resin for a period sufficient to convert said photoconductor to a uniform crystalline state.

6. An electrophotographic photosensitive member according to claim 5 in which the diphenylene hydrazones are aliphatic aldehyde diphenylene hydrazones.

7. An electrophotographic photosensitive member according to claim 5 in which the diphenylene hydrazones are aromatic aldehyde diphenylene hydrazones.

8. An electrophotographic photosensitive member according to claim 5 in which the diphenylene hydrazones are heterocyclic aldehyde diphenylene hydrazones.

9. An electrophotographic photosensitive member according to claim 7 in which the aromatic aldehyde diphenylene hydrazone is a member selected from the group consisting of benzaldehyde diphenylene hydrazone and p-dimethylaminobenzaldehyde diphenylene hydrazone.

10. An electrophotographic photosensitive member according to claim 6 in which the aliphatic aldehyde diphenylene hydrazone is a halogen substituted aliphatic aldehyde diphenylene hydrazone.

11. An electrophotographic photosensitive member according to claim 7 in which the aromatic aldehyde diphenylene hydrazone is a halogen substituted aromatic aldehyde diphenylene hydrazone.

12. An electrophotographic photosensitive member according to claim 8 in which the heterocyclic aldehyde diphenylene hydrazone is a halogen substituted heterocyclic aldehyde diphenylene hydrazone.

13. An electrophotographic photosensitive member according to claim 11 in which the halogen substituted aromatic aldehyde diphenylene hydrazone is a member selected from the group consisting of benzaldehyde-3-halogen substituted diphenylene hydrazone, p-dimethylaminobenzaldehyde-3-halogen substituted diphenylene hydrazone, benzaldehyde-3,6-dihalogen substituted diphenylene hydrazone, and p-dimethylamino-benzaldehyde-3,6-dihalogen substituted diphenylene hydrazone.

14. An electrophotographic photosensitive member according to claim 13 in which the benzaldehyde-3-halogen substituted diphenylene hydrazone is a member selected from the group consisting of benzaldehyde-3-chlorodiphenylene hydrazone and benzaldehyde-3-bromodiphenylene hydrazone.

15. An electrophotographic photosensitive member according to claim 13 in which the p-dimethylaminobenzaldehyde-3-halogen substituted diphenylene hydrazone is a member selected from the group consisting of p-dimethylaminobenzaldehyde-3-chlorodiphenylene hydrazone and p-dimethylaminobenzaldehyde-3-bromodiphenylene hydrazone.

16. An electrophotographic photosensitive member according to claim 13 in which the benzaldehyde-3,6-dihalogen substituted diphenylene hydrazone is a member selected from the group consisting of benzaldehyde-3,6-dichloro diphenylene hydrazone, benzaldehyde-3,6-dibromodiphenylene hydrazone and benzaldehyde-3-chloro-6-bromo-diphenylene hydrazone.

17. An electrophotographic photosensitive member according to claim 13 in which the p-dimethylaminobenzaldehyde-3,6-dihalogen substituted diphenylene hydrazone is a member selected from the group consisting of p-dimethylaminobenzaldehyde-3,6-dichlorodiphenylene hydrazone, p-dimethylaminobenzaldehyde-3,6-dibromodiphenylene hydrazone and p-dimethylaminobenzaldehyde-3-chloro-6-bromo-diphenylene hydrazone.