The present invention is to provide a charge transport substance having high resistance to stress within electrophotographic processes, an electrophotographic photoreceptor which has excellent high-speed responsiveness, shows a sufficient residual potential, and has high resistance to stress within electrophotographic processes, an electrophotographic cartridge, and an image-forming apparatus. The invention provides a charge transport substance having a specific structure. The invention further provides an electrophotographic photoreceptor including a photosensitive layer which contains the charge transport substance having a specific structure, an electrophotographic cartridge, and an image-forming apparatus, equipped with this electrophotographic photoreceptor.

An electrophotographic photoreceptor includes a conductive substrate; and a photosensitive layer arranged on the conductive substrate and containing, as a charge generating material, any one material selected from the group consisting of titanyl phthalocyanines, metal-free phthalocyanines, chlorogallium phthalocyanines and hydroxygallium phthalocyanines; and, as an electron transporting material, a naphthalene tetracarboxylic acid diimide compound represented by Formula (1) below, where R.sup.1 and R.sup.2 each represent a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an alkylene group, an alkoxy group, an alkyl ester group, a phenyl group optionally having a substituent, a naphthyl group optionally having a substituent, or a halogen element; and R.sup.1 and R.sup.2 are optionally the same or different:

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The photoreceptor realizes a stable print density even in a low-temperature environment by suppressing a reduction in print density that is caused by potential fluctuation of the photoreceptor in the low-temperature environment.

An electrophotographic photoreceptor includes a conductive support and a single-layer photosensitive layer. The conductive support has an outer peripheral surface with a maximum surface roughness height (Rmax) of about 4.0 m or less, and the outer peripheral surface has a recess with a depth-to-aperture size ratio (depth/aperture size) of about 0.03 or more and about 0.12 or less. The single-layer photosensitive layer is disposed on the conductive support and has a thickness of about 20 m or more and a modulus of elasticity of about 4.5 GPa or more.

A photoreceptor for electrophotography and an electrophotography device having the same reduces wear loss of the photoreceptor surface and stably obtaining a favorable image for long time. The photoreceptor for electrophotography includes a conductive substrate and a charge transport layer provided on the conductive substrate. The charge transport layer contains a charge transport material, a resin binder, and an inorganic oxide filler surface-treated with a silane coupling agent. A difference (SPa) in a dipole-dipole force component that is a Hansen solubility parameter between the charge transport material and the silane coupling agent satisfies a relationship SPa<1.0. A difference (SPb) in a London dispersion force component that is a Hansen solubility parameter between the resin binder and the silane coupling agent satisfies a relationship SPb<2.5.

A positively chargeable single-layer electrophotographic photosensitive member is used as an image bearing member in an image forming apparatus including a charging section configured to be in contact with the image bearing member to apply a voltage thereto. The positively chargeable single-layer electrophotographic photosensitive member includes a conductive substrate and a photosensitive layer. The photosensitive layer contains at least a charge generating material, a hole transport material, an electron transport material, and a binder resin. The hole transport material contains a triarylamine derivative represented by the following general formula (I). In general formula (I), R.sub.1, R.sub.2, m and n have the same meaning as R.sub.1, R.sub.2, m, and n defined in the description. ##STR00001##

A polyarylate resin is represented by general formula (1) shown below. In general formula (1), R.sup.1 represents a hydrogen atom or methyl group. R.sup.2 and R.sup.3 each represent a hydrogen atom or an alkyl group having a carbon number of at least 1 and no greater than 4. R.sup.2 and R.sup.3 are not the same as one another. When R.sup.1 represents a hydrogen atom, R.sup.2 and R.sup.3 are not bonded to one another. When R.sup.1 represents a methyl group, R.sup.2 and R.sup.3 are optionally bonded to one another to form a ring. r and s each represent a number greater than or equal to 0 and less than or equal to 49. t and u each represent a number greater than or equal to 1 and less than or equal to 50. r+s+t+u=100. r+t=s+u.

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A polyarylate resin includes at least one type of repeating unit represented by a general formula (1), at least one type of repeating unit represented by a general formula (2), and a terminal group represented by a general formula (3). R.sup.1, R.sup.2, R.sup.3, and R.sup.4 each represent, independently of one another, a hydrogen atom or a methyl group. R.sup.5 and R.sup.6 each represent, independently of each other, a hydrogen atom or a C.sub.1-4 alkyl group. R.sup.5 and R.sup.6 may bond together to represent a C.sub.5-7 cycloalkylidene group. X.sup.1 represents a divalent group represented by a chemical formula (2A), (2B), (2C), or (2D) with the proviso that when only one type of repeating unit represented by the general formula (2) is included, X.sup.1 does not represent a divalent group represented by the chemical formula (2D). R.sup.f represents a chain aliphatic group having at least one fluoro group.

##STR00001##

An electrophotographic photoreceptor includes a conductive substrate and a photosensitive layer disposed so as to overlie the conductive substrate and containing a first charge-transporting material having two triphenylamine skeletons and a charge mobility of approximately 410.sup.6 cm.sup.2/Vs or more and at least one second charge-transporting material selected from the group consisting of a charge-transporting material having one triphenylamine skeleton and a charge mobility of approximately 510.sup.5 cm.sup.2/Vs or more, a charge-transporting material having two triphenylamine skeletons and being different from the first charge-transporting material, and a charge-transporting material having three triphenylamine skeletons, wherein the second charge-transporting material content is approximately from 0.2 weight % to 1.0 weight % relative to the total charge-transporting material content.

An electrophotographic photosensitive member includes a conductive substrate and a photosensitive layer. The photosensitive layer contains at least a charge generating material, a charge transport material, and a binder resin. The binder resin includes a polyarylate resin. The polyarylate resin is represented by general formula (1) shown below. In general formula (1), X represents a divalent group represented by chemical formula (1-1), (1-2), (1-3), or (1-4) shown below. ##STR00001##

Provided is a photoreceptor for electrophotography, having high sensitivity and high-speed response performance, and which prevents accumulation of residual potential even when used repeatedly. Also, provided are a photoreceptor cartridge and an image forming apparatus, each employing the photoreceptor.