Electrophotosensitive material and image forming method using the same

Abstract: The material comprises a photosensitive layer containing a m-phenylenediamine compound represented by the general formula (1): wherein R 1A and R 1B are the same or different and indicate an alkyl group; and R 1C , R 1D , R 1E and R 1F are the same or different and indicate a hydrogen atom or an alkyl group, which has high sensitivity and issuperior in stability to strong light, durability and heat resistance, and an image forming method capable of realizing more higher speed and more larger energy saving than the prior art.

Description: BACKGROUND OF THE INVENTION The present invention relates to electrophotosensitive materials which are used in image forming apparatus utilizing a so-called electrophotographic process, such as electrostatic copying machines, plain paper facsimiles, laser printers and the like, and to image forming methods using the same. Recently, there have been used widely so-called organic photoconductors (OPCs) including photoconductors comprising a single-layer type photosensitive layer obtained by dispersing an electric charge generating material capable of generating electric charges (holes and electrons) by light irradiation and an electric charge transferring material capable of transferring the generated electric charge in a single layer made of a binding resin, and photoconductors comprising a multi-layer type photosensitive layer obtained by laminating an electric charge transferring layer containing an electric charge transferring material and an electric charge generating layer containing an electric charge generating material, as the above electrophotosensitive material. Such organic photoconductors have advantages such as easier production than inorganic photoconductors using a deposited film made of an inorganic semiconductor material, selection of photosensitive materials (e.g. electric charge generating material, electric charge transferring material, binding resin, etc.) and high rate of freedom with functional design. Examples of the electric charge transferring material include hole transferring materials having excellent transferring capability of holes and electron transferring materials having excellent transferring capability of electrons. As the hole transferring materials, various organic compounds such as carbazole compounds, oxadiazole compounds, pyrazoline compounds, phenylenediamine compounds, benzidine compounds and the like are known. Among them, an m-phenylenediamine compound represented by the general formula (2): wherein R 2A , R 2B , R 2C and R 2D are the same or different and indicate a hydrogen atom, an alkyl group, an alkoxy group or aryl group has widely been used, particularly, because of its excellent characteristics as described below. The m-phenylenediamine compound (2) has the following advantages. The transferring capability of holes is excellent because of large drift mobility, which indicates the transferring capability of holes, and a residual potential is liable to be drawn at low electric fields because dependence of the drift mobility on field intensity is small. Furthermore, the m-phenylenediamine compound is superior in compatibility with binding resins constituting the electric charge transferring layer and also has resistance to some extent to ultraviolet light. However, a photoconductor using the m-phenylenediamine compound (2) had a problem that unrestorable damage is caused by exposing to a fluorescent lamp for interior illumination or strong light such as sunlight coming into a room through a window in the state where the body of an image forming device is opened for a long time in case of maintenance, or by exposing to strong light described above in the high-temperature state in case of operation even for a short time when the body is opened because a paper jam occurs during the operation of the device. The reason for this is considered to be as follows. A photo-deterioration reaction occurs by exposing to strong light described above, specifically a cylization between the central benzene ring and another phenyl group, thereby changing the m-phenylenediamine compound (2) into impurities as a trap to transfer of holes. The density of electrons of the m-phenylenediamine compound (2) is thus biased against the benzene ring in the molecular centre and the compound has such a molecular structure that the carbon at the 5-position of above benzene ring is likely to be attacked by an oxidizing substance such as oxygen in case of light excitation because of its configuration. Therefore, it is considered that the above cyclization reaction can occur by drawing electrons from the carbon atom at the 5-position of the benzene ring. Further, since the melting point of the m-phenylenediamine compound (2) is generally low, a photosensitive layer obtained by using the compound has a low glass transition temperature and is insufficient in durability and heat resistance. Particularly, when a device stops in the high-temperature state in the course of operation and is allowed to stand for a long time, an impression due to a cleaning blade appears as a striped concave portion on the surface of the photosensitive layer, which can cause image defects. Therefore, in order to solve these problems, m-phenylenediamine compounds, and an electrophotosensitive material using the same, have been suggested wherein the durability to strong light exposure is improved by substituting a group such as an alkyl group on the 5-position of the central benzene ring as shown in the general formula (3) below (Japanese Examined Patent Publication No. 9579/1996). wherein R 3A , R 3B , R 3C and R 3D are the same or different and indicate an alkyl group, an alkoxy group, a halogen atom, an amino group or a N-substituted amino group; A, B, C and D are the same or different and indicate an integer of 0 to 5; and R 3E indicates an alkyl group, an alkoxy group, an amino group, an allyl group or an aryl group. Since such an m-phenylenediamine compound (3) has characteristics particular to a conventional m-phenylendiamine compound (2) described above and has high durability to strong light exposure, it is expected that the performance of the organic electrophotosensitive material can be better than the prior art. Further, a compound wherein an aryl group such as a phenyl group is substituted as the above group R 3E has a particularly high melting point and, therefore, it is expected that the durability and heat resistance can be improved by raising the glass transition temperature of the photosensitive layer. However, in order to satisfy increasing requirements such as realization of more higher speed and much larger energy saving in image-forming devices, the sensitivity of an electrophotosensitive material using a conventional hole transferring material including the above m-phenylenediamine compound (3) is already becoming insufficient. Therefore, it is required to develop a novel hole-transferring material capable of forming an electrophotosensitive material having a higher sensitivity. SUMMARY OF THE INVENTION The present inventors have studied intensively to improve the molecular structure, particularly the kind and position of substituents, of the above m-phenylenediamine compound (3). As a result, the invention provides an electrophotosensitive material comprising a photosensitive layer containing an m-phenylenediamine compound represented by the following general formula (1), preferably as a hole transferring material: wherein R 1A and R 1B are the same or different and indicate an alkyl group; and R 1C , R 1D , and R 1F are the same or different and indicate a hydrogen atom or an alkyl group, which is substantially included in the scope of the general formula (3) but is not specifically disclosed in the above publication of the prior application (Japanese Examined Patent Publication No. 9579/1996). Thus, the sensitivity of the electrophotosensitive material can be remarkably improved while maintaining the characteristics of the m-phenylenediamine compound (3) such as stability to strong light, durability and heat resistance and, therefore, an electrophotosensitive material having a sufficient sensitivity can be obtained even if it is used in an image forming-device capable of realizing high speed and energy saving, wherein light exposure to the photosensitive material is not more than 0.54 mW/cm 2 and the exposure time is not more than 25 ms, for example. The electrophotosensitive material of the present invention comprises a photosensitive layer containing a m-phenylenediamine compound represented by the above general formula (1). Further, an image forming method of the present invention, which comprises the steps of uniformly charging the surface of an electrophotosensitive material of the present invention and exposing the light under conditions of light exposure of not more than 0.54 mW/cm 2 and an exposure time of not more than 25 ms to form an electrostatic latent image on the surface. Electrophotosensitive materials according to the present invention can provide a photosensitive layer not only having particularly high sensitivity and being able to cope sufficiently with requirements such as realization of higher speed and larger energy saving in image-forming devices, but also having good stability to strong light, durability and heat resistance. The electrophotosensitive materials of the invention can also provide an image-forming method capable of realizing higher speed and larger energy saving. BRIEF DESCRIPTION OF THE DRAWING Fig. 1 is perspective view showing one embodiment of a method of measuring the light exposure to an electrophotosensitive material. DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in detail hereinafter. The electrophotosensitive material of the present invention is characterized by providing a photosensitive layer containing the above m-phenylenediamine compound (1), for example on a conductive substrate. The m-phenylenediamine compound (1) is different from the previous compound (3) in that the substituent to be substituted on the 5-position of the central benzene ring is limited to a phenyl group and, at the same time, the substitution position of both groups R 1A and R 1B is limited to the 4-position of two phenyl groups combined with the above central benzene ring through a nitrogen atom. The compound (1) thus limited is substantially included in the scope of the previous compound (3), however, the above publication of the prior application does not disclose specifically such a compound (1). For example, in the table in page 3-4 of the publication of the prior application, there are described some compounds wherein the substituent R 3E (R 5 in the publication) is a phenyl group substituted on the 5-position of the central benzene ring but the publication does not describe the substitution positions of the other substituents R 3A to R 3D (R 1 to R 4 in the publication). In the first to fourth Synthesis Examples corresponding to the Examples of the publication of the prior application as well as the Comparative Example, the substitution position of all substituents R 3A to R 3D is specified as the 3-position of the phenyl group. Consequently, it is assumed that the substitution position of all substituents R 3A to R 3D in the respective compounds in the above table is specified as the 3-position. Therefore, the m-phenylenediamine compound (1) used in the present invention is not disclosed specifically in the publication of the prior application. The alkyl groups corresponding to the groups R 1A to R 1F in the general formula (1) include, for example, alkyl groups having 1 to 6 carbon atoms, such as methyl, ethyl, normal propyl, isopropyl, normal butyl, isobutyl, sec-butyl, tert-butyl, pentyl, hexyl or the like. An alkyl group having 1 to 4 carbon atoms, particularly three kinds of alkyl groups such as methyl, isopropyl and normal butyl, may be preferably used. A specific formula of m-phenylenediamine compounds (1) includes, for example, compounds (1-1) to (1-11) wherein each kind and each substitution position of the groups R 1A to R 1F in the formula (1) are as shown in Table 1, but is not limited thereto. Compound No. R 1A R 1B R 1C R 1D R 1E R 1F 1-1 Me Me H H H H 1-2 Me Me 3-Me H H 3-Me 1-3 Me Me 4-Me 3-Me 3-Me 4-Me 1-4 Me Me 3-Me 3-Me 3-Me 3-Me 1-5 Me Me 4-iPr H H 4-iPr 1-6 Me Me 4-iPr 3-Me 3-Me 4-iPr 1-7 iPr iPr H H H H 1-8 Me Me 4-nBu H H 4-nBu 1-9 Me Me 4-nBu 3-Me 3-Me 4-nBu 1-10 nBu nBu 3-Me H H 3-Me 1-11 nBu nBu H H H H In the above table, abbreviations in each column of R 1A and R 1B mean the following substituents. Me: methyl iPr: isopropyl nBu: normal butyl In the above table, abbreviations in each column of R 1C to R 1F mean the following substituents. H: hydrogen atom 3-Me: methyl substituted on the 3-position of phenyl group 4-Me: methyl substituted on the 4-position of phenyl group 4-iPr: isopropyl substituted on the 4-position of phenyl group 4-nBu: normal butyl substituted on the 4-position of phenyl group Each position at which R 1C to R 2F are substituted on the phenyl group is a position represented by each small numeral in the following general formula (1). The specific structure of each compound shown in Table 1 will be shown below. Among the above m-phenylenediamine compounds (1), compounds wherein the groups R 1A and R 1B are respectively an alkyl group having 1 to 4 carbon atoms, the groups R 1C and R 1F are respectively an alkyl group having 1 to 4 carbon atoms substituted at the 3- or 4-position of a phenyl group and the groups R 1D and R 1E are respectively a hydrogen atom, particularly a compound wherein the alkyl groups corresponding to the groups R 1A , R 1B , R 1C and R 1F respectively are methyl, isopropyl or normal butyl, is particularly superior in the above-described characteristics as is apparent from the results of the Examples described hereinafter and, therefore, it is preferably used in the present invention. The compounds satisfying these conditions include, for example, compounds (1-2), (1-5), (1-8) and (1-10) As the photosensitive layer containing the above m-phenylenediamine compound (1), any construction of so-called single-layer type and multi-layer type photosensitive layers may be employed. The single-layer type photosensitive layer is characterized by the m-phenylenediamine compound (1) being contained as the hole transferring material in a binding resin, together with an electric charge generating material. Such a single-layer type photosensitive layer is capable of coping with any of positive and negative charging using a single construction, and has simple layer construction and is superior in productivity. The single-layer type photosensitive layer can contain an organic electron transferring material having an excellent electron transferring capabilityin addition to the above respective components. Such a photosensitive layer does not cause an interaction between the m-phenylenediamine compound (1) and electron transferring material and, therefore, the sensitivity is much higher. That is, even if both transferring materials are contained in the same layer in a high concentration at which transfer of holes and electrons occurs efficiently, an electric charge transfer complex, which does not contribute to transfer of holes and electrons in the layer, is not formed. Therefore, the m-phenylenediamine compound (1) as the hole transferring material can efficiently transfer holes, whereas, the electron transferring material can efficiently transfer electrons. As a result, the residual potential of the electrophotosensitive material is drastically lowered and the sensitivity is improved. On the other hand, the multi-layer type photosensitive layer comprises an electric charge generating layer containing an electric charge generating material and an electric charge transferring layer containing an electric charge transferring material on a conductive substrate. The order of forming both layers may be optional. However, the film thickness of the electric charge generating layer is usually thinner than that of the electric charge transferring layer. Therefore, for protecting the electric charge generating layer, the electric charge generating layer is preferably formed on the conductive substrate and the electric charge transferring layer is formed thereon. Depending on the order of forming the electric charge generating layer and electric charge transferring layer and kind of the electric charge transferring material (hole transferring material or electron transferring material) used in the electric charge transferring layer, it is decided whether the multi-layer type photosensitive layer becomes a positive or negative charging type. For example, when the m-phenylenediamine compound (1), which is the hole transferring material, is used as the electric charge transferring material of the electric charge transferring layer in the multi-layer type photosensitive layer obtained by forming the electric charge generating layer on the conductive substrate and forming the electric charge transferring layer thereon, the resulting photosensitive layer becomes a negative charging type. In this case, when the electron transferring material is contained in the electric charge generating layer, the sensitivity is further improved. When the electron transferring material is used as the electric charge transferring material of the electric charge transferring layer in the multi-layer type photosensitive layer with the above layer construction, the resulting photosensitive layer becomes a positive charging type. In this case, the m-phenylenediamine compound (1) as the holetransferring material may be contained in the electric charge generating layer. The electric charge generating material, electron transferring material, hole transferring material and binding resin used in the electrophotosensitive material of the present invention are as follows. Electric charge generating material Examples of the electric charge generating material include compounds represented by the following general formulas (CG1) to (CG12) : (CGI) Metal-free phthalocyanine (CG2) Oxotitanyl phthalocyanine (CG3) Perylene pigments wherein R g1 and R g2 are the same or different and represent a substituted or non-substituted alkyl group having 18 or less carbon atoms, a cycloalkyl group, an aryl group, an alkanoyl group or an aralkyl group; (CG4) Bisazo pigments Cp 1 -N=N-Q-N=N-Cp 2 wherein Cp 1 and Cp 2 are the same or different and represent a coupler residue; and Q represents a group represented by the following formulas (Q-1) to (Q-8): (wherein R g3 represents a hydrogen atom, an alkyl group, an aryl group or a heterocyclic group, and the alkyl group, aryl group or heterocyclic group may have a substituent; and ω represents 0 or 1); (wherein R g4 and R g5 are the same or different and represent a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, a halogen atom, an alkoxy group, an aryl group or an aralkyl group); (wherein R g6 represents a hydrogen atom, an ethyl group, a chloroethyl group or a hydroxyethyl group); or (wherein R g7 , R g8 and R g9 are the same or different and represent a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, a halogen atom, an alkoxy group, an aryl group or an aralkyl group) ; (CG5) Dithioketopyrrolopyrrole pigments wherein R g10 and R g11 are the same or different and represent a hydrogen atom, an alkyl group, an alkoxy group or a halogen atom; and R g12 and R g13 are the same or different and represent a hydrogen atom, an alkyl group or an aryl group; (CG6) Metal-free naphthalocyanine pigments wherein R g14 , R g15 , R g16 and R g17 are the same or different and represent a hydrogen atom, an alkoxy group or a halogen atom; (CG7) Metal naphthalocyanine pigments wherein R g18 , R g19 , R g20 and R g21 are the same or different and represent a hydrogen atom, an alkyl group, an alkoxy group or a halogen atom; and M represents Ti or V; (CG8) Squaline pigments wherein R g22 and R g23 are the same or different and represent a hydrogen atom, an alkyl group, an alkoxy group or a halogen atom; (CG9) Trisazo pigments wherein Cp 3 , Cp 4 and Cp 5 are the same or different and represent a coupler residue; (CG10) Indigo pigments wherein R g24 and R g25 are the same or different and represent a hydrogen atom, an alkyl group or an aryl group; and Z is an oxygen atom or a sulfur atom; (CG11) Azulenium pigments wherein R g26 and R g27 are the same or different and represent a hydrogen atom, an alkyl group or an aryl group; and (CG12) Cyanine pigments wherein R g28 and R g29 are the same or different and represent a hydrogen atom, an alkyl group, an alkoxy group or a halogen atom; and R g30 and R g31 are the same or different and represent a hydrogen atom, an alkyl group or an aryl group. In the above electric charge generating material, examples of the alkyl group include the same groups as those described above. Examples of the alkyl group include substituted or non-substituted alkyl groups having 18 or less carbon atoms, such as octyl, nonyl, decyl, dodecyl, tridecyl, pentadecyl, octadecyl, etc., in addition to the above alkyl groups having 1 to 6 carbon atoms. Examples of the cycloalkyl group include groups having 3 to 8 carbon atoms, such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, and cyclooctyl. Examples of the alkoxy group include groups having 1 to 6 carbon atoms, such as methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy, s-butoxy, t-butoxy, pentyloxy, and hexyloxy. Examples of the aryl group include groups such as phenyl, tolyl, xylyl, naphthyl, anthryl, phenanthryl, fluorenyl, biphenylyl, and o-terphenyl. Examples of the aralkyl group include groups such as benzyl, benzyhydryl, trityl, and phenethyl. Examples of the alkanoyl group include groups such as formyl, acetyl, propionyl, butyryl, pentanoyl, and hexanoyl. Examples of the heterocyclic group include thienyl, furyl, pyrrolyl, pyrrolidinyl, oxazolyl, isooxazolyl, thiazolyl, isothiazolyl, imidazolyl, 2H-imidazolyl, pyrazolyl, triazolyl, tetrazolyl, pyranyl, pyridyl, piperidyl, piperidino, 3-morpholinyl, morpholino, and thiazolyl. In addition, it may be a heterocyclic group condensed with an aromatic ring. Examples of the substituent which may be substituted on the groups include halogen atoms, amino groups, hydroxyl groups, optionally esterified carboxyl groups, cyano groups, alkyl groups having 1 to 6 carbon atoms, alkoxy groups having 1 to 6 carbon atoms, alkenyl groups having 2 to 6 carbon atoms which may have an aryl group, etc. Examples of the halogen atom include fluorine, chlorine, bromine and iodine. Examples of the coupler residue represented by Cp 1 , Cp 2 , Cp 3 , Cp 4 and Cp 5 include the groups shown in the following formulas (Cp-1) to (Cp-11). In the respective formulas, R g32 is a carbamoyl group, a sulfamoyl group, an allophanoyl group, oxamoyl group, anthranyloyl group, carbazoyl group, glycyl group, hydantoyl group, phthalamoyl group or a succinamoyl group. These groups may have one or more substituents such as halogen atoms, substituted or unsubstituted phenyl groups, substituted or unsubstituted naphthyl groups, nitro groups, cyano groups, alkyl groups, alkenyl groups, carbonyl groups, and carboxyl groups. R g33 is an atomic group which is required to form an aromatic ring, a polycyclic hydrocarbon or a heterocycle by condensing with a benzene ring. These rings may have one or more substituents as those described above. R g34 is an oxygen atom, a sulfur atom or an imino group. R g35 is a divalent chain hydrocarbon or aromatic hydrocarbon group. These groups may have one or more substituents as those described above. R g36 is an alkyl group, an aralkyl group, an aryl group or a heterocyclic group. These groups may have one or more substituents as those described above. R g37 is an atomic group which is required to form a heterocycle, together with a divalent chain hydrocarbon or aromatic hydrocarbon group, or two nitrogen atoms in the above formulas (Cp-7) to (Cp-10). These rings may have one or more substituents as those described above. R g38 is a hydrogen atom, an alkyl group, an amino group, a carbamoyl group, a sulfamoyl group, an allophanoyl group, a carboxyl group, an alkoxycarbonyl group, an aryl group or a cyano group. The groups other than the hydrogen atom may have one or more substituents as those described above. R g39 is an alkyl group or an aryl group. These groups may have one or more substituents as those described above. Examples of the alkenyl group include alkenyl groups having 2 to 6 carbon atoms, such as vinyl, allyl, 2-butenyl, 3-butenyl, 1-methylallyl, 2-pentenyl, 2-hexenyl and the like. In the above R g33 , examples of the atomic group which is required to form an aromatic ring by condensing with a benzene ring include alkylene groups having 1 to 4 carbon atoms, such as methylene, ethylene, trimethylene, and tetramethylene. Examples of the aromatic ring to be formed by condensing the above R g33 with a benzene ring include naphthalene ring, anthracene ring, phenanthrene ring, pyrene ring, chrysene ring, and naphthacene ring. In the above R g33 , examples of the atomic group which is required to form a polycyclic hydrocarbon by condensing with a benzene ring include the above alkylene groups having 1 to 4 carbon atoms, or carbazole ring, benzocarbazole ring, and dibenzofuran ring. In the above R g33 , examples of the atomic group which is required to form a heterocycle by condensing with a benzene ring include benzofuranyl, benzothiophenyl, indolyl, 1H-indolyl, benzoxazolyl, benzothiazolyl, 1H-indadolyl, benzoimidazolyl, chromenyl, chromanyl, isochromanyl, quinolinyl, isoquinolinyl, cinnolinyl, phthalazinyl, quinazolinyl, quinoxalinyl, dibenzofuranyl, carbazolyl, xanthenyl, acridinyl, phenanthridinyl, phenazinyl, phenoxazinyl, and thianthrenyl. Examples of the aromatic heterocyclic group to be formed by condensing the above R g33 and the benzene ring include thienyl, furyl, pyrrolyl, oxazolyl, isoxazolyl, thiazolyl, isothiazolyl, imidazolyl, pyrazolyl, triazolyl, tetrazolyl, and pyridyl. In addition, it may also be a heterocyclic group condensed with other aromatic rings (e.g. benzofuranyl, benzoimidazolyl, benzoxazolyl, benzothiazolyl, quinolyl, etc.). In the above R g35 and R g37 , examples of the divalent chain hydrocarbon include ethylene, trimethylene, and tetramethylene. Examples of the divalent aromatic hydrocarbon include phenylene, naphthylene, and phenanthrylene. In the above R g36 , examples of the heterocyclic group include pyridyl, pyrazyl, thienyl, pyranyl, and indolyl. In the above R g37 , examples of the atomic group which is required to form a heterocycle, together with two nitrogen atoms, include phenylene, naphthylene, phenanthrylene, ethylene, trimethylene, and tetramethylene. Examples of the aromatic heterocyclic group to be formed by the above R g37 and two nitrogen atoms include benzoimidazole, benzo[f]benzoimidazole, dibenzo[e,g]benzoimidazole, and benzopyrimidine. These groups may respectively have the same group as that described above. In the above R g38 , examples of the alkoxycarbonyl group include methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, and butoxycarbonyl. In the present invention, there can be used powders of inorganic photoconductive materials such as selenium, selenium-tellurium, selenium-arsenic, cadmium sulfide, amorphous silicon, etc. and electric charge generating materials, which have hitherto been known, such as pyrilium salts, anthanthrone pigments, triphenylmethane pigments, threne pigments, toluidine pigments, pyrazoline pigments, quinacridone pigments, etc., in addition to the above electric charge generating materials. The above electric charge generating materials can be used alone or in combination thereof to present an absorption wavelength within a desired range. Among the above electric charge generating materials, a photosensitive material having sensitivity at the wavelength range of 700 nm or more is required in digital-optical image forming apparatus such as laser beam printers, facsimiles which used a semiconductor laser light source, etc. Therefore, phthalocyanine pigments such as metal-free phthalocyanine represented by the above formula (CG1), oxotitanyl phthalocyanine represented by the formula (CG2), etc. are preferably used. The crystal form of the above phthalocyanine pigments is not specifically limited, and various phthalocyanine pigments having different crystal form can be used. In analogue optical image forming apparatus such as electrostatic copying machines using a white light source such as a halogen lamp, etc., a photosensitive material having sensitivity at the visible range is required. Therefore, for example, the perylene pigment represented by the above general formula (CG3) and bisazo pigment represented by the general formula (CG4) are suitably used. Electron transferring material Examples of the electron transferring material include compounds represented by the following general formulas (ET1) to (ET17) : (ET1) wherein R e1 , R e2 , R e3 , R e4 and R e5 are the same or different and represent a hydrogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryl group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted phenoxy group, or a halogen atom; (ET2) wherein R e6 represents an alkyl group; R e7 represents a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryl group, a substituted or unsubstituted aralkyl group, a halogen atom or a halogenated alkyl group; and γ represents any one of integers 0 to 5; provided that each R e7 may be different when γ is 2 or more; (ET3) wherein R e8 and R e9 may be the same or different and represent an alkyl group: δ represents an integer of 1 to 4; and ε represents an integer of 0 to 4; provided that each R e8 and R e9 may be different when δ and ε are 2 or more; (ET4) wherein R e10 represents an alkyl group, an aryl group, an aralkyl group, an alkoxy group, a halogenated alkyl group or a halogen atom; ζ represents any one of integers 0 to 4; and η represents any one of integers 0 to 5; provided that each R e10 may be different when η is 2 or more; (ET5) wherein R e11 represents an alkyl group; and a represents any one of integers 1 to 4; provided that each R e11 may be different when σ is 2 or more; (ET6) wherein R e12 and R e13 are the same or different and represent a hydrogen atom, a halogen atom, an alkyl group, an aryl group, an aralkyloxycarbonyl group, an alkoxy group, a hydroxyl group, a nitro group or a cyano group; and X represents an oxygen atom, a =N-CN group or a =C(CN) 2 group; (ET7) wherein R e14 represents a hydrogen atom, a halogen atom, an alkyl group, or a substituted or unsubstituted phenyl group; R e15 represents a halogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted phenyl group, an alkoxycarbonyl group, a N-alkylcarbamoyl group, a cyano group or a nitro group; and λ represents any one of integers 0 to 3; provided that each R e15 may be different when λ is 2 or more; (ET8) wherein  represents an integer of 1 to 2; (ET9) wherein R e16 and R e17 are the same or different and represent a halogen atom, a substituted or unsubstituted alkyl group, a cyano group, a nitro group or an alkoxycarbonyl group; and ν and ξ respectively represent any one of integers 0 to 3; provided each R e16 and R e17 may be different when either of ν or ξ is 2 or more; (ET10) wherein R e18 and R e19 are the same or different and represent a phenyl group, a polycyclic aromatic group or a heterocyclic group, and these groups may each be substituted or unsubstituted; (ET11) wherein R e20 represents an amino group, a dialkylamino group, an alkoxy group, an alkyl group or a phenyl group; and π represents an integer of 1 or 2; provided that each R e20 may be different when π is 2; (ET12) wherein R e21 represents a hydrogen atom, an alkyl group, an aryl group, an alkoxy group or an aralkyl group; (ET13) wherein R e22 represents a halogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted phenyl group, an alkoxycarbonyl group, a N-alkylcarbamoyl group, a cyano group or a nitro group; and µ represents any one of integers 0 to 3; provided that each Re22 may be different when µ is 2 or more; (ET14) wherein R e23 represents a substituted or unsubstituted alkyl group, or a substituted or unsubstituted aryl group; and R e24 represents a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group, or a group: -O-R e24a (R e24a represents a substituted or unsubstituted alkyl group, or a substituted or unsubstituted aryl group); (ET15) wherein R e25 , R e26 , R e27 , R e28 , R e29 , R e30 and R e31 are the same or different and represent an alkyl group, aryl group, aralkyl group, alkoxy group, a halogen atom or a halogenated alkyl group; and x and  are the same or different and represent any one of integer 0 to 4; (ET16) wherein R e32 and R e33 are the same or different and represent an alkyl group, an aryl group, an alkoxy group, a halogen atom or a halogenated alkyl group; τ and  are the same or different and represent any one of integers 0 to 4; and (ET17) wherein R e34 , R e35 , R e36 and R e37 are the same or different and represent a hydrogen atom, an alkyl group, an alkoyl group, an aryl group, an aralkyl group, a cycroalkyl group or an amino group; and two of the groups R e34 , R e35 , R e36 and R e37 are the same group not hydrogen atom. In the above electron transferring materials, examples of the halogenated alkyl group include those of which alkyl portions are various alkyl groups having 1 to 6 carbon atoms, such as chloromethyl, bromomethyl, fluoromethyl, iodomethyl, 2-chloroethyl, 1-fluoroethyl, 3-chloropropyl, 2-bromopropyl, 1-chloropropyl, 2-chloro-1-methylethyl, 1-bromo-1-methylethyl, 4-iodobutyl, 3-fluorobutyl, 3-chloro-2-methylpropyl, 2-iodo-2-methylpropyl, 1-fluoro-2-methylpropyl, 2-chloro-1,1-dimethylethyl, 2-bromo-1,1-dimethylethyl, 5-bromopentyl, and 4-chlorohexyl. Examples of the polycyclic aromatic group include naphthyl, penanthryl and anthryl. Examples of the alkyl group, heterocyclic group, cycloalkyl group, alkoxycarbonyl group and halogen atom include the same groups as those described above. Examples of the aralkyloxycarbonyl group include those of which aralkyl portions are various aralkyl groups described above. Examples of the N-alkylcarbamoyl group include those of which alkyl portions are various alkyl groups described above. Examples of the dialkylamino group include those of which alkyl portions are various alkyl groups described above. Two alkyl groups substituted on the amino may be the same or different. Examples of the substituent, which may be substituted on the groups described above, include halogen atom, amino group, hydroxyl group, optionally esterified carboxyl group, cyano group, alkyl group having 1 to 6 carbon atoms, alkoxy group having 1 to 6 carbon atoms, and alkenyl having 2 to 6 carbon atoms which may have an aryl group. The substitution position(s) of the substituents(s) are not specifically limited. Furthermore, there can be used electron transferring materials, with the above-described electron transferring materials (ET1) to (ET17), or in place of them, which have hitherto been known, such as benzoquinone compounds, malononitrile, thiopyran compounds, tetracyanoethylene, 2,4,8-trinitrothioxanthone, dinitrobenzene, dinitroanthracene, dinitroacridine, nitroanthraquinone, dinitroanthraquinone, succinic anhydride, maleic anhydride, dibromomaleic anhydride, etc., in addition to those described above. Hole transferring material In the present invention, other hole transferring materials, which have hitherto been known, may be contained in the photosensitive layer, in addition to the above m-phenylenediamine compound (1) as a hole transferring material. Examples thereof include compounds represented by the following general formulas (HT1) to (HT13): (HT1) wherein R h1 , R h2 , R h3 , R h4 , R h5 and R h6 are the same or different and represent a halogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, or a substituted or unsubstituted aryl group; a and b are the same or different and represent anyone of integers 0 to 4; and c, d, e and f are the same or different and represent any one of integers 0 to 5; provided that each R h1 , R h2 , R h3 , R h4 , R h5 and R h6 may be different when a, b, c, d, e or f is 2 or more; (HT2) For example, the phenylenediamine compounds include the above m-phenylenediamine compounds (2) and (3), p-phenylenediamine compound and the like except m-phenylenediamine compound (1). (HT3) wherein R h12 , R h13 , R h14 and R h15 are the same or different and represent a halogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, or a substituted or unsubstituted aryl group; R h16 is a halogen atom, a cyano group, a nitro group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, or a substituted or unsubstituted aryl group; m, n, o and p are the same or different and represent any one of integers 0 to 5; and q is any one of integers 1 to 6; provided that each R h12 , R h13 , R h14 , R h15 and R h16 may be different when m, n, o, p or q is 2 or more; (HT4) wherein R h17 , R h18 , R h19 and R h20 are the same or different and represent a halogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, or a substituted or unsubstituted aryl group; r, s, t and u are the same or different and represent any one of integers 0 to 5; provided that each R h17 , R h18 , R h19 and R h20 may be different when r, s, t or u is 2 or more; (HT5) wherein R h21 and R h22 are the same or different and represent a hydrogen atom, a halogen atom, an alkyl group or an alkoxy group; and R h23 , R h24 , R h25 and R h26 may be same or different and represent a hydrogen atom, an alkyl group or an aryl group; (HT6) wherein R h27 , R h28 and R h29 are the same or different and represent a hydrogen atom, a halogen atom, an alkyl group or an alkoxy group; (HT7) wherein R h30 , R h31 , R h32 and R h33 may be the same or different and represent a hydrogen atom, a halogen atom, an alkyl group or an alkoxy group; (HT8) wherein R h34 , R h35 , R h36 , R h37 and R h38 may be the same or different and represent a hydrogen atom, a halogen atom, an alkyl group or an alkoxy group; (HT9) wherein R h39 represents a hydrogen atom or an alkyl group; and R h40 , R h41 and R h42 may be the same or different and represent a hydrogen atom, a halogen atom, an alkyl group or an alkoxy group; (HT10) wherein R h43 , R h44 and R h45 may be the same or different and represent a hydrogen atom, a halogen atom, an alkyl group or an alkoxy group; (HT11) wherein R h46 and R h47 are the same or different and represent a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group, or a substituted or unsubstituted alkoxy group; and R h48 and R h49 are the same or different and represent a hydrogen atom, a substituted or unsubstituted alkyl group, or a substituted or unsubstituted aryl group; (HT12) wherein R h50 , R h51 , R h52 , R h53 , R h54 and R h55 are the same or different and represent a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, or a substituted or unsubstituted aryl group; a represents any one of integers 1 to 10; v, w, x, y, z and β are the same or different and represent any one of integers of 0 to 2; provided that each R h50 , R h51 , R h52 , R h53 , R h54 and R h55 may be different when either of v, w, x, y, z or β is 2; and (HT13) wherein R h56 , R h57 , R h58 and R h59 may be the same or different and represent a hydrogen atom, a halogen atom, an alkyl group or an alkoxy group; and Φ represent any one of groups (Φ-1), (Φ-2) or (Φ-3) respectively represented by the formulas. In the hole transferring material as described above, examples of the alkyl group, alkoxy group and halogen atoms include the same groups as those described above. Examples of the substituents which may be substituted on the groups include halogen atom, amino group, hydroxyl group, optionally esterified carboxyl group, cyano group, alkyl groups having 1 to 6 carbon atoms, alkoxy groups having 1 to 6 carbon atoms, alkenyl groups having 2 to 6 carbon atoms which may have an aryl group, etc. In addition, the substitution positions (s) of the substituents(s) are not specifically limited. Furthermore, there can be used hole transferring materials, with the above-described hole transferring materials (HT1) to (HT13), or in place of them, which have hitherto been known, that is, nitrogen-containing cyclic compounds and condensed polycyclic compounds, e.g. oxadiazole compounds such as 2,5-di(4-methylaminophenyl)-1,3,4- oxadiazole, etc.; styryl compounds such as 9-(4- diethylaminostyryl)anthracene, etc.; carbazole compounds such as polyvinyl carbazole, etc.; organopolysilane compounds; pyrazoline compounds such as 1-phenyl-3-(p- dimethylaminophenyl)pyrazoline, etc.; hydrazone compounds; triphenylamine compounds; indole compounds; oxazole compounds; isoxazole compounds; thiazole compounds; thiadiazole compounds; imidazole compounds; pyrazole compounds; and triazole compounds. In the present invention, these hole transferring materials may be used alone or in combination thereof. When using the hole transferring material having film forming properties, such as poly(vinylcarbazole), etc., a binding resin is not required necessarily. Binding resin As the binding resin for dispersing the above respective components, there can be used various resins which have hitherto been used in the photosensitive layer, and examples thereof include thermoplastic resins such as styrene- butadiene copolymer, styrene-acrylonitrile copolymer, styrene- maleic acid copolymer, acrylic copolymer, styrene-acrylic acid copolymer, polyethylene, ethylene-vinyl acetate copolymer, chlorinated polyethylene, polyvinyl chloride, polypropylene, ionomer, vinyl chloride-vinyl acetate copolymer, polyester, alkyd resin, polyamide, polyurethane, polycarbonate, polyarylate, polysulfon, diaryl phthalate resin, ketone resin, polyvinylbutyral resin, polyether resin, polyester resin, etc.; crosslinking thermosetting resins such as silicone resin, epoxy resin, phenol resin, urea resin, melamine resin, etc.; and photosetting resins such as epoxy acrylate, urethane acrylate, etc. In addition, various additives which have hitherto been known, such as deterioration inhibitors (e.g. antioxidants, radical scavengers, singlet quenchers, ultraviolet absorbers, etc.), softeners, plasticizers, surface modifiers, bulking agents, thickening agents, dispersion stabilizers, wax, acceptors, donors, etc. can be formulated in the photosensitive layer without injury to the electrophotographic characteristics. In order to improve the sensitivity of the photosensitive layer, known sensitizers such as terphenyl, halonaphthoquinones, acenaphthylene, etc. may be used in combination with the electric charge generating material. A method of producing the electrophotosensitive material of the present invention will be described hereinafter. In a method of producing a single-layer type electrophotosensitive material, an electric charge generating material, a hole transferring material, a binding resin and an electron transferring material may be dissolved or dispersed in a suitable solvent, and the resulting coating solution is applied on a conductive substrate using means such as application, followed by drying. In the single-layer type photosensitive material, the electric charge generating material may be formulated in an amount of 0.1 to 50 parts by weight, preferably 0.5 to 30 parts by weight, based on 100 parts by weight of the binding resin. The electron transferring material may be formulated in an amount of 5 to 100 parts by weight, preferably 10 to 80 parts by weight, based on 100 parts by weight of the binding resin. In addition, the hole transferring material may be formulated in an amount of 5 to 500 parts by weight, preferably 25 to 200 parts by weight, based on 100 parts by weight of the binding resin. In a case that the electron transferring material is used with the hole transferring material, it is suitable that the total amount of the hole transferring material and electron transferring material is 10 to 500 parts by weight, preferably 30 to 200 parts by weight, based on 100 parts by weight of the binding resin. When other electron transferring material which has a predetermined redox potential is contained, the amount of the other electron transferring material is suitably 0.1 to 40 parts by weight, preferably 0.5 to 20 parts by weight, based on 100 parts by weight of the binding resin. The thickness of the single-layer type photosensitive material is preferably 5 to 100 µm, more preferably 10 to 50 µm. In a method of producing a multi-layer type electrophotosensitive material, an electric charge generating layer containing an electric charge generating material may be formed on a conductive substrate using means such as deposition, application, etc., and then a coating solution containing an electron transferring material and a binding resin is applied on the electric charge generating layer using means such as application, followed by drying, to form an electric charge transferring layer. In the multi-layer photosensitive material, the electric charge generating material and binding resin which constitute the electric charge generating layer may be used in various proportions. It is suitable that the electric charge generating material is formulated in the amount of 5 to 1,000 parts by weight, preferably 30 to 500 parts by weight, based on 100 parts by weight of the binding resin. When a hole transferring material is contained in the electric charge generating layer, it is suitable that the hole trasferring material is formulated in the amount of 10 to 500 parts by weight, preferably 50 to 200 parts by weight, based on 100 parts by weight of the binding resin. The electron transferring material and binding resin, which constitute the electric charge transferring layer, can be used in various proportions within such a range as not to prevent the transfer of electrons and to prevent the crystallization. It is suitable that the electron transferring material is used in the amount of 10 to 500 parts by weight, preferably 25 to 100 parts by weight, based on 100 parts by weight of the binding resin so as to easily transfer electrons generated by light irradiation in the electric charge generating layer. When the other electron trasferring material which has a predetermined redox potential is contained, the amount of the other electron transferring material is suitably 0.1 to 40 parts by weight, preferably 0.5 to 20 parts by weight based on 100 parts by weight of the binding resin. Regarding the thickness of the multi-layer type photosensitive layer, the thickness of the electric charge generating layer is suitably about 0.01 to 5 µm, preferably about 0.1 to 3 µm, and that of the electric charge transferring layer is suitably 2 to 100 µm, preferably about 5 to 50 µm. A barrier layer may be formed, in such a range as not to injure the characteristics of the photosensitive material, between the conductive substrate and photosensitive layer in the single-layer type photosensitive material, or between the conductive substrate and electric charge generating layer or between the conductive substrate layer and electric charge transferring layer in the multi-layer type photosensitive material. Further, a protective layer may be formed on the surface of the photosensitive layer. As the conductive substrate which may be used in the electrophotosensitive material of the present invention, various materials having the conductivity can be used, and examples thereof include single metals such as iron aluminum, copper, tin, platinum, silver, vanadium, molybdenum, chromium, cadmium, titanium, nickel, palladium, indium, stainless steel, brass, etc.; plastic materials which are vapor-deposited or laminated with the above metal; glass materials coated with aluminum iodide, tin oxide, indium oxide, etc. The conductive substrate may be made in the form of a sheet or a drum to the construction of image-forming apparatus. The substrate itself may have a conductivity or only the surface of the substrate may have a conductivity. It is preferred that the conductive substrate has sufficient mechanical strength when used. The photosensitive layer may be produced by applying a dispersing (coating) solution, obtained by dissolving or dispersing a resin composition containing the above respective components in a suitable solvent, on a conductive substrate, followed by drying. That is, the above electric charge generating material, electric charge transferring material and binding resin may be dispersed and mixed with a suitable solvent by a known method, for example, using a roll mill, a ball mill, an atriter, a paint shaker, a supersonic dispenser, etc. to prepare a dispersion, which is applied by a known means and then allowed to dry. As the solvent for preparing the dispersing solution, there can be used various organic solvents, and examples thereof include alcohols such as methanol, ethanol, isopropanol, butanol, etc.; aliphatic hydrocarbons such as n- hexane, octane, cyclohexane, etc.; aromatic hydrocarbons such as benzene, toluene, xylene, etc.; halogenated hydrocarbons such as dichloromethane, dichloroethane, chloroform, carbon tetrachloride, chlorobenzene, etc.; ethers such as dimethyl ether, diethyl ether, tetrahydrofuran, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, etc.; ketones such as acetone, methyl ethyl ketone, cyclohexanone, etc.; esters such as ethyl acetate, methyl acetate, etc.; dimethylformaldehyde, dimethylformamide, dimethyl sulfoxide, etc. These solvents may be used alone or in combination thereof. In order to improve a dispersibility of the electric charge transferring material and electric charge generating material as well as a smoothness of the surface of the photosensitive layer, there may be used surfactants, leveling agents, etc. The image forming method of the present invention will be described hereinafter. The image forming method of the present invention comprises the steps of uniformly charging the surface of the above electrophotosensitive material of the present invention, and exposing to light under the conditions of light exposure of not more than 0.54 mW/cm 2 and an exposure time of not more than 25 ms to form an electrostatic latent image on the surface, as described previously. The electrostatic latent image formed on the surface of the electrophotosensitive material is realised according to general method to form a toner image, transferred on the surface of a material for transfer such as paper and then fixed on the above transfer material, for example by means of heating or pressurizing. The electrophotosensitive material on which the toner image has been transferred is used for the subsequent image formation, usually after removing the residual toner on the surface using a cleaning blade. According to such an image forming method of the present invention, since the electrophotosensitive material of the present invention can have high sensitivity, even such as has never been accomplished, as described above, it becomes possible to form a good image having a sufficient image concentration even under the exposure conditions capable of realizing higher speed and energy saving wherein the exposure dose is not more than 0.54 mW/cm 2 and the exposure time is not more than 25 ms. The light exposure may be determined as follows in the practical image forming device. For example, as shown in Fig. 1, exposure is performed in the state where a light receiving portion of a light detector 3 [e.g. Optical Block TQ82021, manufactured by Advantest Co., Ltd.] is located at the position of the center of an electrophotosensitive material 1 in a width direction out of the portion (indicated by a two-dot chain line in the drawing) to be exposed to light from a light source 2 on the surface of the electrophotosensitive material 1, that is, the position of a perpendicular (indicated by a one-dot chain line in the drawing) from the light source 2 on the electrophotosensitive material 1, and then the measured value is analyzed by using a analyzer 4 [e.g. Optical Power Meter TQ8215, manufactured by Advantest Co., Ltd.], thereby to obtain a light exposure. The exposure time is determined from an exposure width in the circumferential direction of the surface of the electrophotosensitive material 1 due to the light source 2, and a rotational rate of said electrophotosensitive material 1. As described in detail hereinabove, the present invention can exert a specific working effect capable of providing an electrophotosensitive material which has a photosensitive layer not only having particularly high sensitivity and being able to sufficiently cope with the requirements such as realization of much higher speed and much larger energy saving of the image forming device, but also having excellent stability to strong light, durability and heat resistance, and an image forming method using the same, capable of realizing much higher speed and much larger energy saving. EXAMPLES The following Examples further illustrate the present invention in detail. Electrophotosensitive material for analogue light source (single-layer type) Example 1 5 Parts by weight of a bisazo pigment represented by the formula (CG4-1): as the electric charge generating material, 100 parts by weight of a m-phenylenediamine compound represented by the formula (1-1): as the hole transferring material and 100 parts by weight of poly(4,4'-cyclohexylidenediphenyl)carbonate as the binding resin were mixed and dispersed, together with a predetermined amount of tetrahydrofuran, by using an ultrasonic dispersion mixer to prepare a coating solution for single-layer type photosensitive layer. Then, this coating solution was applied on an aluminum tube having an outer diameter of 78 mm and a length of 340 mm as the conductive substrate by using a dip coating method, followed by hot-air drying in a dark place at 100°C for 30 minutes to obtain a drum type electrophotosensitive material for analogue light source, which has a single-layer type photosensitive layer of 24 µm in film thickness. Example 2 According to the same manner as that described in Example 1 except for using 100 parts by weight of a m-phenylenediamine compound represented by the formula (1-2): as the hole transferring material, a drum type electrophotosensitive material for analogue light source, which has a single-layer type photosensitive layer, was produced. Example 3 According to the same manner as that described in Example 1 except for using 100 parts by weight of a m-phenylenediamine compound represented by the formula (1-3): as the hole transferring material, a drum type electrophotosensitive material for analogue light source, which has a single-layer type photosensitive layer, was produced. Example 4 According to the same manner as that described in Example 1 except for using 100 parts by weight of a m-phenylenediamine compound represented by the formula (1-4): as the hole transferring material, a drum type electrophotosensitive material for analogue light source, which has a single-layer type photosensitive layer, was produced. Example 5 According to the same manner as that described in Example 1 except for using 100 parts by weight of a m-phenylenediamine compound represented by the formula (1-5): as the hole transferring material, a drum type electrophotosensitive material for analogue light source, which has a single-layer type photosensitive layer, was produced. Example 6 According to the same manner as that described in Example 1 except for using 100 parts by weight of a m-phenylenediamine compound represented by the formula (1-6): as the hole transferring material, a drum type electrophotosensitive material for analogue light source, which has a single-layer type photosensitive layer, was produced. Example 7 According to the same manner as that described in Example 1 except for using 100 parts by weight of a m-phenylenediamine compound represented by the formula (1-7): as the hole transferring material, a drum type electrophotosensitive material for analogue light source, which has a single-layer type photosensitive layer, was produced. Example 8 According to the same manner as that described in Example 1 except for using 100 parts by weight of a m-phenylenediamine compound represented by the formula (1-8): as the hole transferring material, a drum type electrophotosensitive material for analogue light source, which has a single-layer type photosensitive layer, was produced. Example 9 According to the same manner as that described in Example 1 except for using 100 parts by weight of a m-phenylenediamine compound represented by the formula (1-9): as the hole transferring material, a drum type electrophotosensitive material for analogue light source, which has a single-layer type photosensitive layer, was produced. Example 10 According to the same manner as that described in Example 1 except for using 100 parts by weight of a m-phenylenediamine compound represented by the formula (1-10): as the hole transferring material, a drum type electrophotosensitive material for analogue light source, which has a single-layer type photosensitive layer, was produced. Example 11 According to the same manner as that described in Example 1 except for using 100 parts by weight of a m-phenylenediamine compound represented by the formula (1-11): as the hole transferring material, a drum type electrophotosensitive material for analogue light source, which has a single-layer type photosensitive layer, was produced. Comparative Example 1 According to the same manner as that described in Example 1 except for using 100 parts by weight of a m-phenylenediamine compound represented by the formula (3-1): which belongs to the compound of the fourth Synthesis Example of the publication of the prior application among the conventional m-phenylenediamine compound (3) as the hole transferring material, a drum type electrophotosensitive material for analogue light source, which has a single-layer type photosensitive layer, was produced. Comparative Example 2 According to the same manner as that described in Example 1 except for using 100 parts by weight of a m-phenylenediamine compound represented by the formula (4): wherein the outer phenyl group is substitute with a methoxy group which is a substituent other than a hydrogen atom and an alkyl group defined in the present invention, as the hole transferring material, a drum type electrophotosensitive material for analogue light source, which has a single-layer type photosensitive layer, was produced. Comparative Example 3 According to the same manner as that described in Example 1 except for using 100 parts by weight of a m-phenylenediamine compound represented by the formula (2-1): which belongs to the conventional m-phenylenediamine compound (2) as the hole transferring material, a drum type electrophotosensitive material for analogue light source, which has a single-layer type photosensitive layer, was produced. Comparative Example 4 According to the same manner as that described in Example 1 except for using 100 parts by weight of a m-phenylenediamine compound represented by the formula (2-2): which belongs to the conventional m-phenylenediamine compound (2) as the hole transferring material, a drum type electrophotosensitive material for analogue light source, which has a single-layer type photosensitive layer, was produced. Comparative Example 5 According to the same manner as that described in Example 1 except for using 100 parts by weight of a m-phenylenediamine compound represented by the formula (2-3): which belongs to the conventional m-phenylenediamine compound (2) as the hole transferring material, a drum type electrophotosensitive material for analogue light source, which has a single-layer type photosensitive layer, was produced. Comparative Example 6 According to the same manner as that described in Example 1 except for using 100 parts by weight of a m-phenylenediamine compound represented by the formula (5): wherein a chlorine atom which is a group other than that defined in the publication of the prior application is substituted on the 5-position of the central benzene ring, as the hole transferring material, a drum type electrophotosensitive material for analogue light source, which has a single-layer type photosensitive layer, was produced. The electrophotosensitive materials of the above respective Examples and Comparative Examples were subjected to the following respective tests, and their characteristics were evaluated. Photosensitivity test I Using a drum sensitivity tester (GENTEC SINSIA 30 M) manufactured by GENTEC Co., a voltage was applied to the electrophotosensitive material of the respective Examples and Comparative Examples to charge the surface at +800 V. Then, the above electrophotosensitive material in the charged state was exposed (exposure time: 25 msec) by irradiating white light (light exposure: 0.54 mW/cm 2 ) from a halogen lamp which is a light source of the above mentioned test machine on the surface. Then, a surface potential at the time at which 0.15 seconds has passed since the beginning of exposure was measured as a residual potential Vrp1 (V). The above exposure condition corresponds to an exposure condition in a high-speed image forming device wherein an image forming speed is 40 copies per minute as double as that of a current model. The lower the residual potential becomes, the higher the sensitivity of the electrophotosensitive material. High-temperature light resistance test Under the environmental conditions of 50 °C, white light with 4,000 lux from a white fluorescent lamp was irradiated on the electrophotosensitive materials of the respective Examples and Comparative Examples for 20 minutes. After the electrophotosensitive materials were allowed to stand in a dark place for 30 minutes, thereby cooling to a normal temperature, the residual potential was measured again under the same conditions by using the same drum sensitivity tester as that described above. Then, a difference ΔVrp1 between the residual potentials before and after light irradiation was determined and the stability at high temperature to strong light, that is, high-temperature light resistance was evaluated. The smaller the difference ΔVrp1 becomes, the better the high-temperature light resistance of the electrophotosensitive material. Measurement of glass transition temperature Each photosensitive layer of the electrophotosensitive materials of the respective Examples and Comparative Examples was peeled off in the form of a film (about 5 mg), put in an aluminum pan and then sealed to obtain a sample. With respect to this sample, the glass transition temperature [Tig (extrapolated glass transition initiation temperature °C), JIS K7121] of the photosensitive layer was measured under the conditions (atmospheric gas: air, heating rate: 20 °C/min.) using a differential scanning calorimeter (DSC) device [DSC8230D, manufactured by Rigaku Denki Co., Ltd.]. High-temperature durability test The coating solution for single-layer type photosensitive layer prepared in the respective Examples and Comparative Examples was applied on an aluminum tube having an outer diameter of 30 mm and a length of 346 mm as the conductive substrate by using a dip coating method, followed by hot-air drying in a dark place at 100 °C for 30 minutes to obtain a drum type electrophotosensitive material for analogue light source, which has a single-layer type photosensitive layer of 24 µm in film thickness, used for high-temperature durability test. Then, each electrophotosensitive material was mounted in a drum unit for an electrostatic copying machine [DC-2355, manufactured by Mita Industries Co., Ltd.] and was stored in an oven at 50 °C for a week in the state where a cleaning blade is always contacted with the surface. The linear pressure in case of pressing the cleaning blade was 30 N/cm 2 . Then, this drum unit was mounted in the above electrostatic copying machine and copying of a gray scale image was performed. The formed image was visually observed and evaluated by the following criteria. bad: High-temperature durability is poor because an black stripe is appeared on the formed image, that is an impression due to a cleaning blade appeared as a stripe which was caused by concave portion on the surface of the photosensitive layer. good: High-temperature durability is good because no black stripe is observed on the formed image, that is, any deformation due to pressing of a cleaning blade did not occur. The above results are shown in Table 2. Compound No. Vrp1 (V) Δrp1 (V) Tig (°C) High-temperature durability Ex. 1 1-1 230 +5 72.4 Good Ex. 2 1-2 230 +5 71.0 Good Ex. 3 1-3 219 +18 73.6 Good Ex. 4 1-4 224 +12 70.5 Good Ex. 5 1-5 204 +16 71.0 Good Ex. 6 1-6 220 +15 73.6 Good Ex. 7 1-7 236 +15 71.5 Good Ex. 8 1-8 201 +10 70.0 Good Ex. 9 1-9 216 +15 70.6 Good Ex. 10 1-10 220 +8 70.0 Good Ex. 11 1-11 226 +13 71.0 Good Com.Ex.1 3-1 269 +13 71.0 Good Com.Ex.2 4 265 +12 73.0 Good Com.Ex.3 2-1 250 +68 62.0 Bad Com.Ex.4 2-2 248 - - - Com.Ex.5 2-3 222 - - - Com.Ex.6 5 250 +49 61.0 Bad As is apparent from Table 2, both of an electrophotosensitive material using the compound of the formula (3-1) belonging to the conventional m-phenylenediamine compounds (3) as the hole transferring material of Comparative Example 1 and an electrophotosensitive material using the compound of the formula (4) of Comparative Example 2, which is similar to a m-phenylenediamine compound (1) in the present invention but is different in kind of substituents have the same results as those of the respective Examples of the present invention with respect to the stability to strong light, durability and heat resistance, however, the initial sensitivity is insufficient. An electrophotosensitive material using the compound of the formula (2-1) belonging to the conventional m-phenylenediamine compounds (2) as the hole transferring material of Comparative Example 3 and an electrophotosensitive material using the compound of the formula (5) corresponding to a compound obtained by substituting a chlorine atom on the 5-position of the central benzene ring of the compound of the formula (2-1) of Comparative Example 6 showed low initial sensitivity and, furthermore, the stability to strong light, durability and heat resistance were insufficient. An electrophotosensitive material using the compound of the formula (2-2) of Comparative Example 4 showed low initial sensitivity. Furthermore, since the compound was slightly crystallized in the photosensitive layer, we abandoned other tests. Regarding the electrophotosensitive material using the compound of the formula (2-3) of Comparative Example 5, the initial sensitivity was improved but the compound was crystallized in the photosensitive layer. Therefore, we abandoned other tests. On the other hand, it has been found that electrophotosensitive materials using a m-phenylenediamine compound of the formula (1) of Examples 1 to 11 of the present invention have high initial sensitivity and are superior in stability to strong light, durability and heat resistance. It has been confirmed that even the electrophotosensitive material of Example 7 wherein the initial sensitivity is the lowest, that is, the initial residual potential Vrp1 is the highest, the residual potential Vrp1 is 33 V lower than that of the electrophotosensitive material of Comparative Example 1 which corresponds to the construction of the prior art and the sensitivity is very high. That is, the difference in residual potential is close to an increase in residual potential in case that a continuous image formation (1,000,000 copies close to the life of the electrophotosensitive material) is performed using an electrophotosensitive material of Example 7. As is apparent from this fact, the electrophotosensitive material of the present invention has higher sensitivity than that of the prior art. As a result of a comparison between the electrophotosensitive materials of the above respective Examples, it has been confirmed that electrophotosensitive materials using compounds wherein the groups R 1A and R 1B are respectively an alkyl group having 1 to 4 carbon atoms, the groups R 1C and R 1F are respectively an alkyl group having 1 to 4 carbon atoms substitute on the 3- or 4-position of a phenyl group and the groups R 1D and R 1E are respectively a hydrogen atom among the m-phenylenediamine compound (1), particularly compounds of the formulas (1-2), (1-5), (1-8) and (1-10) wherein the alkyl group corresponding to the groups R 1A , R 1B , R 1C and R 1F is methyl, isopropyl or normal butyl group of Examples 2, 5, 8 and 10 are generally superior in initial sensitivity, stability to strong light, durability and heat resistance. Photosensitivity test II Using the above-described drum sensitivity tester (GENTEC SINSIA 30 M) manufactured by GENTEC Co., a voltage was applied to each of the electrophotosensitive materials of Example 2 and Comparative Example 1 among the respective Examples and Comparative Examples to charge the surface at +800 V. Then, the above electrophotosensitive material with the charged state was exposed (exposure time: 25 msec) by irradiating white light (light exposure: 0.92 mW/cm 2 ) from a halogen lamp as an exposure light source of the above tester on the surface. Then, the surface potential at the time at which 0.15 seconds has passed since the beginning of exposure was measured as a residual potential Vrp2 (V). The above exposure condition corresponds to an exposure condition in an image forming speed wherein the image forming rate is 20 copies per minute of a current model. The lower the residual potential Vrp2 becomes, the higher the sensitivity of the electrophotosensitive material. The above results are shown in Table 3, together with the results of the above-described photosensitivity test I. Vrp1 (V) Vrp2 (V) Ex.2 230 99 Com.Ex.1 269 100 As is apparent from Table 3, a clear difference in sensitivity between the electrophotosensitive material of Example 2 of the present invention and a conventional electrophotosensitive material of Comparative Example 1 is not recognized in case of an image forming rate closer to that of a current model, however, a difference in sensitivity appears with an increase of the image forming speed, that is, high sensitivity is attained. Consequently, it has been confirmed that the electrophotosensitive material of the present invention has sufficient sensitivity even if it is used in an image forming device capable of realizing higher speed and energy saving wherein the exposure dose is not more than 0.54 mW/cm 2 and the exposure time is not more than 25 msec.

Claims: An electrophotosensitive material comprising a photosensitive layer containing an m-phenylenediamine compound represented by the general formula (1): wherein R 1A and R 1B are the same or different and indicate an alkyl group; R 1C , R 1D , R 1E and R 1F are the same or different and indicate a hydrogen atom or an alkyl group. An electrophotosensitive material according to claim 1, wherein the groups R 1A and 1B in the general formula (1) are respectively an alkyl group having 1 to 4 carbon atoms, the groups R 1C and R 1F are respectively an alkyl group having 1 to 4 carbon atoms substituted on the 3- or 4-position of a phenyl group, and the groups R 1D and R 1E are respectively a hydrogen atom. An electrophotosensitive material according to claim 2, wherein the alkyl group corresponding to each of the groups R 1A , R 1B , R 1C and R 1F is methyl, isopropyl or normal butyl. An electrophotosensitive material according to claim 3, wherein the m-phenylenediamine compound contained in the photosensitive layer is a compound represented by the formula (1-2) : An electrophotosensitive material according to claim 3, wherein the m-phenylenediamine compound contained in the photosensitive layer is a compound represented by the formula (1-5): An electrophotosensitive material according to claim 3, wherein the m-phenylenediamine compound contained in the photosensitive layer is a compound represented by the formula (1-8): An electrophotosensitive material according to claim 3, wherein the m-phenylenediamine compound contained in the photosensitive layer is a compound represented by the formula (1-10): Use of an electrophotosensitive material according to any preceding claim, in an image-forming device wherein the light exposure to the electrophotosensitive material is not more than 0.54 mW/cm 2 and the exposure time is not more than 25 ms. An image-forming method, which comprises the steps of uniformly charging the surface of an electrophotosensitive material comprising a photosensitive layer containing a m-phenylenediamine compound represented by the general formula (1) : wherein R 1A and R 1B are the same or different and indicate an alkyl group; and R 1C , R 1D , R 1E and R 1F are the same or different and represent a hydrogen atom or an alkyl group, and exposing to light under conditions of light exposure of not more than 0.54 mW/cm 2 and an exposure time of not more than 25 ms to form an electrostatic latent image on the surface. An image-forming method according to claim 9, further comprising the steps of developing the electrostatic latent image formed on the surface of the electrophotosensitive material with a developer comprising a toner, thereby realising the electrostatic latent image to form a toner image, transferring the toner image on the surface of a transfer material, and fixing the toner image.

Inventors: IWASAKI HIROAKI, MATSUMOTO SHYUNICHI, SAITOH SAKAE, UCHIDA MAKI, WATANABE YUKIMASA, IWASAKI, HIROAKI, MATSUMOTO, SHYUNICHI, SAITOH, SAKAE, UCHIDA, MAKI, WATANABE, YUKIMASA, Iwasaki, Hiroaki, c/o Mita Industrial Co., Ltd., Matsumoto, Shyunichi, c/o Mita Industrial Co.,Ltd., Saitoh, Sakae, c/o Mita Industrial Co., Ltd., Uchida, Maki, c/o Mita Industrial Co., Ltd., Watanabe, Yukimasa, c/o Mita Industrial Co., Ltd.
Applicants: KYOCERA MITA CORP, KYOCERA MITA CORPORATION
Application year: 1998
Main classification: G03G5
IPC codes: G03G5, G03G15