Electrophotographic photosensitive member

Abstract: An electrophotographic photosensitive member comprising an electroconductive support and a photosensitive layer on said electroconductive support, said photosensitive layer containing a compound represented by the formula (4) wherein R 4-1 is a thiophene ring group having a nitro group; each of R 4-2 and R 4-3 is a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted aromatic ring group, a nitro group, a cyano group, -(CH=CH) f -NO 2 , -(CH=CH) g -R 4-4 or and at least either of R 4-2 and R 4-3 is -(CH=CH) f -NO 2 , -(CH=CH) g -R 4-4 or each of R 4-4 and R 4-5 is an aromatic ring group having a nitro group or a heterocyclic ring group having a nitro group; and R 4-6 is a substituted or unsubstituted alkyl group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted aromatic ring group, or a substituted or unsubstituted heterocyclic ring group; and each of f and g is an integer of 1 or 2; h is an integer of 0 or 1; each of R 4-5 and R 4-6 may be bonded to form a ring directly or with the interposition of a saturated hydrocarbon, an unsaturated hydrocarbon, an oxygen atom or a sulfur atom.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to an electrophotographic photosensitive member having improved electrophotographic characteristics, and more specifically it relates to an electrophotographic photosensitive member having a photosensitive layer containing a compound with a specific structure. Related Background Art An organic electrophotographic photosensitive member containing an organic photoconductive compound as the main component has many advantages, and for example, it is free from drawbacks of an inorganic photosensitive member regarding film-forming properties, plasticity and manufacturing cost. Therefore, in recent years, much attention is paid to the organic electrophotographic photosensitive member, and many techniques concerning the same have been suggested and some of them have been put into practice. As such an organic photosensitive member, there has been suggested an electrophotographic photosensitive member mainly comprising a photoconductive polymer typified by poly(N-vinylcarbazole) or a charge transfer complex made from a Lewis acid such as 2,4,7-trinitro-9-fluorenone. This kind of organic photoconductive polymer is more excellent in lightweight properties and film-forming properties as compared with an inorganic photoconductive polymer, but the former is inferior to the latter in sensitivity, durability, stability to environmental change. For this reason, the organic photoconductive polymer is not always satisfactory. Afterward, the electrophotographic photosensitive member of a separate-function type, which comprises different substances each bearing a charge-generating function or a charge-transporting function, has brought about improvements in sensitivity and durability which has been disadvantages of conventional organic photosensitive members. Such a separate-function type of photosensitive member is advantageous because the substances for the charge-generating substance and the charge-transporting substance can be selected respectively from a wide range of substances, which allows easier production of the electrophotographic photosensitive member having a desired properties. As the charge-generating substance, there have been known azo pigments, polycyclic quinone pigments, cyanine dyes, squaric acid dyes and pyrylium salt dyes. Above all, the azo pigments are preferable because of strong light resistance, high charge-generating ability and the relatively easy synthesis of materials and the like, and many kinds thereof have been suggested and put into practice. Examples of the known charge-transporting substance include pyrazolines in Japanese Patent Publication No. 52-4188, hydrazones in Japanese Patent Publication No. 55-42380 and Japanese Patent Application Laid-open No. 55-52063, triphenylamines in Japanese Patent Publication No. 58-32372 and Japanese Patent Application Laid-open No. 61-132955, and stilbenes in Japanese Patent Application Laid-open Nos. 54-151955 and 58-198043. The charge-transporting substance can be classified into hole-transporting type and electron-transporting type, but the above-mentioned charge-transporting substances and most of charge-transporting substances used in the organic electrophotographic photosensitive members which have been put into practice so far are of the hole-transporting type. In many cases of the photosensitive members each comprising the charge-transporting substance with hole-transporting ability, each photosensitive member has a conductive support, a charge-generating layer and a charge-transporting layer in this order, and in this case, the polarity of the charge which moves to the photosensitive member is negative. When the polarity of the charge is negative, ozone generates at the time of charging and causes the photosensitive member to be chemically modified inconveniently. Thus, this kind of photosensitive member is inferior to inorganic photosensitive members such as a-Se and a-Si in durability disadvantageously. As measures against the deterioration of the photosensitive member with ozone generated at the time of charging, there have been suggested an electrophotographic photosensitive member having a conductive support, a charge-transporting layer and a charge-generating layer in this order, and an electrophotographic photosensitive member in which a protective layer is disposed on a photosensitive layer, for example, in Japanese Patent Application Laid-open Nos. 61-75355 and 54-58445. However, in the electrophotographic photosensitive member having such a layer constitution, the relatively thin charge-generating layer is used as an upper layer, and when the member is repeatedly used, the surface of the photosensitive member is severely damaged by abrasion. In the photosensitive member provided with the protective layer for the purpose of solving this problem, this protective layer is an insulating layer, and therefore when the protective layer is repeatedly used, its potential is not stable, so that stable characteristics of the member cannot be maintained. In view of the foregoing, it is expected to invent an organic electrophotographic photosensitive member which has a conductive support, a charge-generating layer and a charge-transporting layer in this order and which can be used in a condition that a positive pole is charged. However, in order to realize this expectation, a charge-transporting substance having electron-transporting ability is required. Suggested examples of the charge-transporting substance having the electron-transporting ability include 2,4,7-trinitro-9-fluorenone (TNF), dicyanomethylenefluorene carboxylate in Japanese Patent Application Laid-open No. 61-148159, anthraquinodimethane in Japanese Patent Application Laid-open Nos. 63-70257, 63-72664 and 63-104061, 1,4-naphthoquinone in Japanese Patent Application Laid-open No. 63-85749, and diphenyldicyanoethylene in Japanese Patent Application Laid-open Nos. 63-174993. Japanese Patent Application Laid-Open No. Hei 2-97953 suggests an electrophotographic photosensitive member having a charge-generating layer comprising a positive hole-transporting charge-generating material and a small amount of dicyanovinyl compound having a specific constitution. However, to fill the present demand of a high-quality image, an electrophotographic photosensitive member has been investigated which can sufficiently meet requirements such as sensitivity, potential properties, cost and the compatibility of the charge-transporting substance with an organic solvent or a binder. SUMMARY OF THE INVENTION An object of the present invention is to provide an electrophotographic photosensitive member having a photosensitive layer containing a charge-transporting substance with a novel structure. Another object of the present invention is to provide an electrophotographic photosensitive member which has a high sensitivity and which can maintain stable and excellent electrophotographic characteristics, even when repeatedly used. The present invention is directed to an electrophotographic photosensitive member comprising an electroconductive support and a photosensitive layer on the electroconductive support, and the photosensitive layer contains a compound represented by the formula (4) wherein R 4-1 is a thiophene ring group having a nitro group; each of R 4-2 and R 4-3 is a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted aromatic ring group, a nitro group, a cyano group, -(CH=CH) f -NO 2 , -(CH=CH) g -R 4-4 or and at least either of R 4-2 and R 4-3 is -(CH=CH) g -R 4-4 or -(CH=CH) h -CH=C-R 4-6 ; each of R 4-4 and R 4-5 is an aromatic ring group having a nitro group or a heterocyclic ring group having a nitro group; and R 4-6 is a substituted or unsubstituted alkyl group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted aromatic ring group, or a substituted or unsubstituted heterocyclic ring group; and each of f and g is an integer of 1 or 2; h is an integer of 0 or 1; each of R 4-5 and R 4-6 may be bonded to form a ring directly or with the interposition of a saturated hydrocarbon, an unsaturated hydrocarbon, an oxygen atom or a sulfur atom. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 illustrates an outline of the constitution of an electrophotographic photosensitive apparatus employing an electrophotographic photosensitive member of the present invention. Fig. 2 illustrates an example of the block diagram of a facsimile device employing the electrophotographic photosensitive member of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An electrophotographic photosensitive member of the present invention has a photosensitive layer containing a compound represented by the formula (4). The reduction potentials can be measured in the following procedure. (Measurement of Reduction Potentials) A saturated calomel electrode is selected as a reference electrode, and a 0.1 N-(n-Bu) 4 N + + ClO 4 - acetonitrile solution is used. A potential at a working electrode is swept by a potential sweeper, and a peak position on the resultant current-potential curve is regarded as a value of reduction potential. Specifically, a sample is dissolved in the electrolyte of the 0.1 N-(n-Bu) 4 N + + ClO 4 - acetonitrile solution so as to be a concentration of about 5-10 mmol%. Afterward, voltage is applied to this sample solution and is then changed linearly from a higher potential (0 V) to a lower potential (-1.5 V), and at this time, current changes are measured to obtain a current-voltage curve. The value of a potential at the peak (the maximum potential) of current values on this current-voltage curve is regarded as the reduction potential in the present invention. In the compounds which can be used in the present invention, examples of the halogen atom include a fluorine atom, a chlorine atom and a bromine atom; examples of the alkyl group include methyl, ethyl, propyl and butyl groups; examples of the aralkyl group include benzyl, phenethyl and naphthylmethyl groups; examples of the aromatic ring group include phenyl and naphthyl groups; and examples of the heterocyclic ring group include thienyl, pyridyl and furil groups. Furthermore, examples of the substituents which the above-mentioned compounds may have include alkyl groups such as methyl and ethyl groups, halogen atoms such as fluorine and chlorine atoms, a cyano group and a nitro group. The Compounds represented by Formula (4) are specifically exemplified below, but they are not limited thereto. Referring to a way of showing specific compounds, a basic constitution common to those specific compounds is first indicated and then they are defined by specifying variable portions in the basic constitution. Basic constitution Compound 4-(1) R 4-1 : R 4-2 : -CH = CH-NO 2 R 4-3 : -H Compound 4-(2) R 4-1 : ditto R 4-2 : (CH = CH NO 2 R 4-3 : -H Compound 4-(3) R 4-1 : ditto R 4-2 : -CH=CH-NO 2 R 4-3 : -Cℓ Compound 4-(4) R 4-1 : ditto R 4-2 : R 4-3 : -H Compound 4-(5) R 4-1 : ditto R 4-2 : R 4-3 : -H Compound 4-(6) R 4-1 : ditto R 4-2 : R 4-3 : -H Compound 4-(7) R 4-1 : ditto R 4-2 : R 4-3 : -H Compound 4-(8) R 4-1 : ditto R 4-2 : R 4-3 : -H Compound 4-(9) R 4-1 : ditto R 4-2 : R 4-3 : -H Compouns 4-(10) R 4-1 : ditto R 4-2 : R 4-3 : -H Compound 4-(11) R 4-1 : ditto R 4-2 : R 4-3 : -H Compound 4-(12) R 4-1 : ditto R 4-2 : R 4-3 : -H Compound 4-(13 ) R 4-1 : ditto R 4-2 : R 4-3 : -H Compound 4-(14) R 4-1 : ditto R 4-2 : R 4-3 : -H Compound 4-(15) R 4-1 : ditto R 4-2 : R 4-3 : -H Compound 4-(16) R 4-1 : ditto R 4-2 : -CH=CH-NO 2 R 4-3 : -CH 3 Compound 4-(17) R 4-1 : ditto R 4-2 : -(CH = CH) 2 -NO 2 R 4-3 : -C 4 H 9 (t) Compound 4-(18) R 4-1 : ditto R 4-2 : R 4-3 : Compound 4-(19) R 4-1 : ditto R 4-2 : R 4-3 : -Br Compound 4-(20) R 4-1 : ditto R 4-2 : -CH=CH-NO 2 R 4-3 : -CN Compound 4-(21) R 4-1 : ditto R 4-2 : R 4-3 : Compound 4-(22) R 4-1 : ditto R 4-2 : R 4-3 : -CH=CH-NO 2 Compound 4-(23) R 4-1 : R 4-2 : -CH=CH-NO 2 R 4-3 : -H Compound 4-(24) R 4-1 : ditto R 4-2 : R 4-3 : -H Compound 4-(25) R 4-1 : ditto R 4-2 : R 4-3 : -H Compound 4-(26) R 4-1 : ditto R 4-2 : (CH=CH NO 2 R 4-3 : -NO 2 Compound 4-(27) R 4-1 : ditto R 4-2 : R 4-3 : -CH=CH-NO 2 Compound 4-(28) R 4-1 : ditto R 4-2 : -CH=CH-NO 2 R 4-3 : -CH=CH-NO 2 Compound 2-(29) R 4-1 : R 4-2 : R 4-3 : -NO 2 Compound 4-(30) R 4-1 : ditto R 4-2 : -CH=CH-NO 2 R 4-3 : -H Compound 4-(31) R 4-1 : ditto R 4-2 : -CH=CH-NO 2 R 4-3 : Compound 4-(32) R 4-1 : ditto R 4-2 : -CH=CH-NO 2 R 4-3 : Compound 4-(33) R 4-1 : ditto R 4-2 : R 4-3 : -CN Compound 4-(34) R 4-1 : R 4-2 : -CH=CH-NO 2 R 4-3 : Compound 4-(35) R 4-1 : ditto R 4-2 : -CH=CH-NO 2 R 4-3 : Compound 4-(36) R 4-1 : ditto R 4-2 : -CH=CH-NO 2 R 4-3 : Compound 4-(37) R 4-1 : ditto R 4-2 : R 4-3 : Compound 4-(38) R 4-1 : ditto R 4-2 : R 4-3 : Compound 4-(39) R 4-1 : ditto R 4-2 : R 4-3 : -H Next, synthesis examples of the compounds which can be used in the present invention will be described. Synthesis Example 1 [Synthesis of Compound Example 4-(17)] 0.63 g (11.7 mmols) of sodium methylate was added to 15 ml of DMF, and a solution of 2.8 g (10.2 mmols) of diethyl o-nitrobenzylphosphate and 15 ml of DMF were slowly added dropwise thereto at 20-25°C. After completion of the addition, the solution was stirred for 15 minutes as it was, and a solution of 1.5 g (6.4 mmols) of and 10 ml of DMF were then slowly added dropwise thereto at 25°C or less. After completion of the addition, the solution was stirred for 15 minutes as it was, and it was further heated and stirred at 50-60°C for 2 hours on an oil bath. After standing for cooling, the solution was poured into 300 ml of methanol, and the precipitated crystals were then collected by filtration. The resultant crude crystals were further washed with methanol and then recrystallized several times from a mixed solvent of toluene and ethyl acetate, thereby obtaining 1.6 g of the desired compound. Its yield was 71%. The other compounds can also be synthesized in similar manners, but these synthesis methods are not restrictive. The electrophotographic photosensitive member of the present invention comprises an electroconductive support and a photosensitive layer laid on the electroconductive support. Constitutional examples of the photosensitive layer include the following types (1), (2), (3) and (4). Each constitution of these types will be shown with the expression of a lower layer/an upper layer. (1) Layer containing a charge-generating substance/layer containing a charge transporting substance, (2) layer containing a charge-transporting substance/layer containing a charge-generating substance, (3) layer containing a charge-generating substance and a charge transporting substance, and (4) layer containing a charge-generating substance/layer containing a charge-generating substance and a charge transporting substance. The usable compounds in the present invention which can be typified by the above-mentioned compounds have high ability for enhancing the mobility of positive holes. In the type (1) of photosensitive layer, the compounds are preferably employed for positive charges; in the type (2), the compounds are preferably employed for negative charges; and in the types (3) and (4), the compounds can be employed either for positive charges or for negative charges. Naturally, the constitution of the electrophotographic photosensitive member of the present invention is not limited to the above-mentioned fundamental constitutions. The particularly preferable type of the photosensitive layers of the present invention is the above-mentioned type (1), and thus this type will be described in more detail. In the present invention, any charge-generating substance can be used, so long as it has charge-generating ability. Examples of the charge-generating substance are as follows. (1) Azo pigments such as monoazo, bisazo and trisazo, (2) phthalocyanine pigments such as metal phthalocyanine and non-metal phthalocyanine, (3) indigo pigments such as indigo and thioindigo, (4) perylene pigments such as perylenic anhydride and perylenic imide, (5) polycyclic quinone pigments such as anthraquinone and pyrenequinone, (6) squarilium dyes, (7) pyrylium salts and thiopyrylium salts, (8) triphenylmethane dyes, and (9) inorganic substances such as selenium and amorphous silicon. Such a charge-generating substance may be used singly or in combination of two or more thereof. A layer containing the charge-generating substance, that is, a charge-generating layer can be formed by dispersing the charge-generating substance in a suitable binder, and then applying the resultant dispersion on an electroconductive support. The charge-generating layer can also be obtained by forming a thin film on an electroconductive support by a dry method such as vapor deposition, sputtering, CVD and the like. The above-mentioned binder may be selected from a great variety of binder resins, and examples of the binder resins include polycarbonates, polyesters, polyarylates, butyral resins, polystyrenes, polyvinylacetals, diallyl phthalate resins, acrylic resins, methacrylic resins, vinyl acetate resins, phenolic resins, silicon resins, polysulfones, styrene-butadiene copolymers, alkid resins, epoxy resins, urea resins and vinyl chloride-vinyl acetate copolymers. However, the above-mentioned binder is not limited thereto. These resins may be used singly or in combination of two or more thereof. The resin is contained in the charge-generating layer preferably in an amount of not more than 80% by weight, more preferably not more than 40% by weight based on the total layer weight. The film thickness of the charge-generating layer is preferably not more than 5 µm, more preferably in the range of from 0.01 to 2 µm. The charge-generating layer may further contain a sensitizing agent. The layer containing the charge-transporting substance, that is, a charge-transporting layer can be formed by combining the compound which can be used in the present invention with a suitable binder resin. In this case, the compounds regarding the present invention can be used singly or in combination of two or more thereof, and another charge-transporting substance may further be used in combination. Examples of the binder resin for the charge-transporting layer include photoconductive polymers such as polyvinylcarbazoles and polyvinylanthracenes in addition to the above-mentioned substances used as the binder for the charge-generating layer. The blend ratio of the compound which can be used in the present invention to the binder resin is such that the amount of the fluorene is from 10 to 500 parts by weight with respect to 100 parts by weight of the binder. The thickness of the charge-transporting layer is preferably in the range of from 5 to 40 µm, more preferably from 10 to 30 µm. The charge-transporting layer can additionally contain an antioxidant, an ultraviolet absorbing agent or a plasticizer, if necessary. In the case where the photosensitive layer has the constitution type (3) mentioned above, that is, in the case of the single layer, this layer is formed by dispersing or dissolved the above-mentioned charge-generating substance and the compound which can be used in the present invention in the above-mentioned suitable binder to prepare a coating liquid, applying the coating liquid on a support, and then drying the same. The thickness of the layer is preferably in the range of from 5 to 40 µm, more preferably from 10 to 30 µm. In the present invention, a layer havinga barrier function and an adhesive function, i.e., the so-called subbing layer can be provided between the electroconductive support and the photosensitive layer. Examples of the material for the subbing layer include polyvinyl alcohol, polyethylene oxide, ethyl cellulose, methyl cellulose, casein, polyamide, glue and gelatin. The subbing layer can be formed by dissolving the above-mentioned material in a suitable solvent, and then applying the resultant solution on an electroconductive support. The thickness of the subbing layer is preferably 5 µm or less, more preferably in the range of from 0.2 to 3.0 µm. Furthermore, in the present invention, for protecting the photosensitive layer from various external mechanical and electrical forces, a resin layer or another resin layer containing an electroconductive substance dispersed therein may be provided on the photosensitive layer. The above-mentioned various layers can be formed on the electroconductive support by coating technique such as immersion coating, spray coating, spinner coating, roller coating, Meyer-bar coating or blade coating by the use of a suitable solvent. Examples of the electroconductive support in the present invention include the following types. (1) A metal such as aluminum, an aluminum alloy, stainless steel or copper in a plate shape or a drum shape. (2) A non-electroconductive support such as a glass, a resin or a paper, or an electroconductive support mentioned in the previous item (1) on which a metal such as aluminum, palladium, rhodium, gold or platinum is vapor-deposited or laminated in the form of a coating film. (3) A non-electroconductive support such as a glass, a resin or a paper, or an electroconductive support mentioned in the previous item (1) on which an electroconductive polymer, or an electroconductive compound such as tin oxide or indium oxide is vapor-deposited or applied. The electrophotographic photosensitive member of the present invention is useful not only for electrophotographic copying machines but also for a variety of application fields of electrophotography such as facsimiles, leaser printers, CRT printers and electrophotographic engraving systems. Fig. 1 shows a schematic embodiment of a usual transfer type electrophotographic apparatus employing the electrophotographic photosensitive member of the present invention. In Fig. 1, a drum type photosensitive member 1 serves as an image carrier and is rotated around an axis 1a in an arrow direction at a predetermined peripheral speed. The photosensitive member 1 is uniformly charged with positive or negative predetermined potential on the peripheral surface thereof by an electrostatic charging means 2 during the rotation thereof, and an exposure part 3 of the member 1 is then exposed to image-exposure light L (e.g., slit exposure, laser beam-scanning exposure or the like) by an image-exposure means (not shown), whereby an electrostatic latent image corresponding to the exposed image is sequentially formed on the peripheral surface of the photosensitive member 1. The electrostatic latent image is developed with a toner by a developing means 4, and the toner-developed image is sequentially transferred by a transfer means 5 onto the surface of a transfer material P which is fed from a paper feeder (not shown) between the photosensitive member 1 and the transfer means 5 synchronizing with the rotation of the photosensitive member 1. The transfer material P which has received the transferred image is separated from the surface of the photosensitive member, introduced into an image fixing means 8 to fix the image, and then discharged from the copying machine as a copy. After the transfer of the image, the surface of the photosensitive member 1 is cleaned with a cleaning means 6 to remove the residual untransferred toner, and the member 1 is then subjected to an electrostatic charge eliminating treatment by an exposure means 7 so as to be repeatedly used for image formation. As the uniformly charging means for the photosensitive member 1, a corona charging apparatus is usually widely used. Furthermore, also as the transfer means 5, the corona charging apparatus is usually widely used. The electrophotographic apparatus can comprise an integral apparatus unit consisting of some of constitutional members such as the above-mentioned photosensitive member, developing means, cleaning means and the like, and this unit may be adapted to be detachable from the main apparatus. For example, at least one of the electrostatic charging means, the developing means and the cleaning means can be combined with the photosensitive member to form a unit which can be optionally detached from the main apparatus with the aid of a guiding means such as rails extending from the main apparatus. In this case, the apparatus unit may be associated with the electrostatic charging means and/or the developing means. In the case where the electrophotographic apparatus is used as a copying machine or a printer, the optical image exposure light L is projected onto the photosensitive member as the reflected light or transmitted light from an original copy, or alternatively the signalized information is read out from an original copy by a sensor and then followed by scanning with a leaser beam, driving an LED array, or driving a liquid crystal shutter array in accordance with the signal, and the exposure light is projected onto the photosensitive member. In the case where the electrophotographic apparatus is used as a printer of a facsimile device, the optical image exposure light L functions as an exposure for printing the received data. Fig. 2 is a block diagram of one example in this case. A controller 11 controls an image reading part 10 and a printer 19. The whole of the controller 11 is controlled by a CPU 17. The readout data from the image reading part is transmitted through a transmitting circuit 13 to the partner communication station. The data received from the partner communication station is transmitted through a receiving circuit 12 to a printer 19. The predetermined amount of the image data is stored in an image memory. A printer controller 18 controls the printer 19. Numeral 14 denotes a telephone set. The image received through the circuit 15 (the image information from a remote terminal connected through the circuit) is demodulated by the receiving circuit 12, treated to decode the image information in the CPU 17, and then successively stored in an image memory 16. When at least one page of the image has been stored in the image memory 16, the image is recorded in such a manner that the CPU 17 reads out the one page of the image information from the image memory 16, and then sends out the decoded one page of the information to the printer controller 18. On receiving the one page of the information from the CPU 17, this printer controller 18 controls the printer 19 to record the image information. Incidentally, the CPU 17 receives the following page of the information, while the recording is conducted by the printer 19. The receiving and recording of the images are carried out in the above-mentioned manner. Example 1 4 g of oxytitaniumphthalocyanine obtained in accordance with a preparation example disclosed in Japanese Patent Application Laid-open No. 61-239248 (USP 4,728,592) was dispersed in a solution obtained by dissolving 2 g of a polybutyral resin (butyralization degree 70 mol%, weight average molecular weight 80,000) in 95 ml of cyclohexanone for 10 hours by means of a sand mill, thereby preparing a coating liquid. This coating liquid, after diluted, was applied onto an aluminum sheet by a Meyer bar so that the thickness of a dry layer might be 0.2 µm, to form a charge-generating layer. Next, 5 g of Compound Example 4-(4) which was a charge-transporting substance and 6 g of a polycarbonate resin (weight average molecular weight 50,000) were dissolved in 40 g of a mixture of monochlorobenzene, and the resultant solution was applied onto the above-mentioned charge-generating layer by the Meyer bar to form a charge-transporting layer having a dry thickness of 19 µm, whereby an electrophotographic photosensitive member was prepared. The charging characteristics of the thus prepared electrophotographic photosensitive member were evaluated by subjecting this member to corona discharge under +6 KV in accordance with a static mode by the use of an electrostatic copying-paper tester (model EPA-8100, made by Kawaguchi Denki K.K.), allowing it to stand in the dark for 1 hour, and then exposing it to the light having an illuminance of 20 lux. As the charging characteristics, there were measured a surface potential (V 0 ), a potential (V 1 ) after dark decay by standing for 1 second in the dark, an exposure (E 1/2 ) necessary to decay V 1 to 1/2, and a potential after irradiation of a light volume of 100 Lux.sec, i.e., a remaining potential (V R ). Furthermore, for the purpose of evaluating the durability of the previously prepared electrophotographic photosensitive member, this member was attached onto the photosensitive drum of a copying machine (a remodeled type of NP-6650, made by Canon K.K.), and 2,000 sheets were copied by the machine. In this case, a light-portion potential (V L ) and a dark-portion potential (V D ) were measured for the copies at an early stage and the copies after 2,000 sheets were copied. Here, V D and V L at the early stage were set so as to be +650 V and +150 V, respectively. The results are shown in Table 1. Examples 2 to 10 and Comparative Examples 1 to 2 The same procedure as in Example 1 was effected except that Compound Example 4-(4) of a charge-transporting substance was replaced with each of Compound Examples 4-(3), 4-(8), 4-(9), 4-(13), 4-(18), 4-(21), 4-(27), 4-(29) and 4-(37), to prepare electrophotographic photosensitive members, and these members were then evaluated. For comparison, the same procedure as in the above-mentioned examples was effected except that the following comparative compounds were used as charge-transporting materials, thereby obtaining electrophotographic photosensitive members, and these members were then evaluated. The results are shown in Table 2. Comparative Compound Example 4-(1) Comparative Compound Example 4-(2) Example 11 An aluminum sheet was coated by a Meyer bar with a solution which was prepared by dissolving 5 g of an N-methoxymethylated nylon 6 resin (weight average molecular weight 100,000) and 5 g of an alcohol-soluble copolymerized nylon resin (weight average molecular weight 80,000) in 100 g of methanol, whereby a subbing layer having a dry thickness of 1 µm was formed on the aluminum sheet. Next, 1 g of a charge-generating substance represented by the formula 0,7 g of a polyvinylbutyral resin (butyralization degree 70%, and weight average molecular weight 150,000) and 50 g of dioxane were dispersed for 20 hours by means of a ball mill dispersing device. The resultant dispersion, after diluted, was applied onto the above-mentioned subbing layer by blade coating to form a charge-generating layer having a dry thickness of 0,4 µm thereon. Next, 10 g of Compound Example 4-(18) which was a charge-transporting substance and 10 g of a polymethyl methacrylate resin (weight average molecular weight 100,000) were dissolved in 100 g of monochlorobenzene, and the resultant solution was applied onto the previously formed charge-generating layer by blade coating to form a charge-transporting layer having a dry layer thickness of 16 µm thereon. The thus prepared photosensitive member was then subjected to corona discharge under +6 KV, and at this time, a surface potential (V 0 ) was measured. Furthermore, this photosensitive member was allowed to stand in the dark for 1 second, and after the dark decay, a surface potential (V 1 ) was measured. Sensitivity was evaluated by measuring an exposure (E 1/2 ) necessary to decay V 1 to 1/2. Further, for remaining potential, a potential where a laser light volume of 100 µJ/cm 2 was projected was measured. A light source which was used in this case was a ternary semiconductor laser comprising gallium, aluminum and arsenic (output 5 mW; oscillation wave length 780 nm). Next, the above-mentioned photosensitive member was set on a remodeled type of NP-9330 made by Canon K.K. which was a reversal development system digital copying machine equipped with the same semiconductor laser as mentioned above, and an actual image forming test was carried out. Setting was made so that a surface potential after primary charging might be +600 V and so that a surface potential after image exposure might be +100 V (exposure 3.2 µJ/cm 2 ), and letters and images were visually evaluated at an early stage of the copying and after 5,000 sheets were copied. The results are shown in Table 3. Example 12 7 g of oxytitaniumphthalocyanine obtained in accordance with a preparation example disclosed in Japanese Patent Application Laid-open No. 62-67094 (USP 4,664,997) was added to a solution prepared by dissolving 4 g of a polyvinylbenzal resin (benzalation degree 78 mol%, weight average molecular weight 100,000) in 100 g of cyclohexanone, and they were then dispersed in a ball mill for 20 hours. The resultant dispersion, after diluted, was applied onto an aluminum sheet by a Meyer bar, followed by drying at 90°C for 30 minutes, whereby a charge-generating layer having a thickness of 0.20 µm was formed thereon. Next, 5 g of Compound Example 4-(29) which was a charge-transporting substance and 5 g of a bisphenol Z type polycarbonate resin (weight average molecular weight 100,000) were dissolved in 80 g of monochlorobenzene, and the resultant solution was then applied onto the previously formed charge-generating layer by the Meyer bar, followed by drying at 140°C for 1 hour, thereby forming a charge-transporting layer having a thickness of 20 µm. The thus prepared photosensitive member was evaluated in the same manner as in Example 11. The results are shown in Table 4. Example 13 An aluminum substrate was coated with a 5% methanol solution of an alcohol-soluble copolymerized nylon resin (weight average molecular weight 50,000), so that a subbing layer having a dry thickness of 0.5 µm was formed thereon. Next, 5 g of a pigment represented by the formula was dispersed in 50 ml of tetrahydrofuran by means of a sand mill. Afterward, 5 g of Compound Example 4-(26) which was a charge-transporting substance and 7 g of a polycarbonate resin (weight average molecular weight 50,000) were dissolved in 50 g of a chlorobenzene (70 parts by weight)/dichloromethane (30 parts by weight) solution, and the solution was then added to the previously prepared dispersion, followed by further dispersing for 25 hours by the sand mill. The dispersion was applied onto the previously formed subbing layer by a Meyer bar and dried so that a dry thickness might be 18 µm. The thus prepared photosensitive member was evaluated in the same manner as in Example 1. The results are shown in Table 5. Example Compound Example V 0 (+V) V 1 (+V) E 1/2 (lux·sec) V R (+V) 13 4-(26) 700 690 3.8 65 Example 14 5 g of Compound Example 4-(33) which was a charge-transporting substance and 5 g of a polycarbonate resin (weight average molecular weight 80,000) were dissolved in 70 g of chlorobenzene, and the resultant solution was applied onto an aluminum sheet by a Meyer bar to form a charge-transporting layer having a dry thickness of 15 µm. Next, 2 g of a disazo pigment represented by the formula was dispersed in 50 ml of a solution prepared by dissolving 1.5 g of a polyvinylbutyral resin (butyralization degree 80 mol%) in 50 ml of cyclohexanone for 50 hours by means of a sand mill to obtain a coating liquid. This coating liquid, after diluted, was applied onto the above-mentioned charge-transporting layer by the Meyer bar so that the dry thickness of a charge-generating layer might be 0.3 µm, whereby the charge-generating layer was formed. The charging characteristics of the thus prepared electrophotographic photosensitive member were evaluated in the same manner as in Example 1, except that the corona charging was carried out unter -5kV. The results are shown in Table 6. Example Compound Example V 0 (+V) V 1 (+V) E 1/2 (lux·sec) V R (+V) 14 4-(33) -700 -680 3.2 -40

Claims: An electrophotographic photosensitive member comprising an electroconductive support and a photosensitive layer on said electroconductive support, said photosensitive layer containing a charge-transporting substance with electron-transporting ability, said charge-transporting substance being represented bv the formula (4) wherein R 4-1 is a thiophene ring group having a nitro group; each of R 4-2 and R 4-3 is a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted aralkyl group, or a substituted or unsubstituted aromatic ring group, a nitro group, a cyano group, - (CH=CH) f -NO 2 , -(CH=CH) g -R 4-4 or and at least either of R 4-2 and R 4-3 is -(CH=CH) f -NO 2 , -(CH=CH) g -R 4-4 or each of R 4-4 and R 4-5 is an aromatic ring group having a nitro group or a heterocyclic ring group having the nitro group; and R 4-6 is a substituted or unsubstituted alkyl group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted aromatic ring group, or a substituted or unsubstituted heterocyclic ring group; and each of f and g is an integer of 1 or 2; h is an integer of 0 or 1; each of R 4-5 and R 4-6 may be bonded to form a ring directly or with the interposition of a saturated hydrocarbon, an unsaturated hydrocarbon, an oxygen atom or a sulfur atom. The electrophotographic photosensitive member according to claim 1, wherein said photosensitive layer has a charge-generating layer containing a charge-generating substance and a charge-transporting layer containing a charge transporting substance. The electrophotographic photosensitive member according to claim 2 having said electroconductive support, said charge-generating layer and said charge-transporting layer in this order. The electrophotographic photosensitive member according to claim 2 having said electroconductive support, said charge-transporting layer and said charge-generating layer in this order. The electrophotographic photosensitive member according to claim 1, wherein said photosensitive layer is a single layer. The electrophotographic photosensitive member according to claim 1, having a subbing layer between said electroconductive support and said photosensitive layer. The electrophotographic photosensitive member according to claim 1 having said electroconductive support, said photosensitive layer and a protective layer in this order. An electrophotographic apparatus comprising an electrophotographic photosensitive member according to anyone of claims 1 to 7, an electrostatic latent image-forming means, a means for developing the formed electrostatic latent image, and a means for transferring the developed image to a transfer material.

Inventors: KIKUCHI TOSHIHIRO, MARUYAMA AKIO, NAGAHARA SHIN, OHTANI NORIKO, SAKAKIBARA TEIGO, TANAKA HISAMI, TANAKA TAKAKAZU, KIKUCHI, TOSHIHIRO, C/O CANON KABUSHIKI KAISHA, MARUYAMA, AKIO, C/O CANON KABUSHIKI KAISHA, NAGAHARA, SHIN, C/O CANON KABUSHIKI KAISHA, OHTANI, NORIKO, C/O CANON KABUSHIKI KAISHA, SAKAKIBARA, TEIGO, C/O CANON KABUSHIKI KAISHA, TANAKA, HISAMI, C/O CANON KABUSHIKI KAISHA, TANAKA, TAKAKAZU, C/O CANON KABUSHIKI KAISHA
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1991
Main classification: G03G5
IPC codes: G03G5