DE68913100T2 - Photoreceptor. - Google Patents

Description

BACKGROUND OF THE INVENTION

The present invention relates to a photoreceptor, e.g. a photoreceptor usable in electrophotography.

In electrophotographic copying using the Carlson process, an electrically charged layer is applied to the surface of a photoreceptor. After exposure to form a latent electrostatic image, the latter is developed using a toner. The visible image formed is transferred to a receiving sheet, e.g. paper, and fixed there. The toner is then removed from the photoreceptor surface and any residual charges are neutralized to completely erase the electrostatic image and prepare the photoreceptor for another cycle. In this way, the photoconductor can be used cyclically over a long period of time.

For successful electrophotographic work, the photoreceptor must meet various requirements, not only in terms of electrophotographic properties, e.g. good chargeability and sensitivity plus low dark decay, but also in terms of physical properties, e.g. long service life and high resistance to wear and moisture during cyclic use, as well as resistance to environmental conditions, e.g. to ozone generated during corona discharge and to UV radiation emitted during exposure.

Electrophotographic photoreceptors commonly used in the relevant field are inorganic products with a photosensitive layer based on inorganic photoconductors such as selenium, zinc oxide and cadmium sulfide. In recent years, the use of various organic photoconductors as an effective component of photosensitive layers in electrophotographic photoreceptors has been the subject of active research and development attempts. For example, an organic photoreceptor with a photosensitive layer containing poly-N-vinylcarbazole and 2,477-trinitro-9-fluorenone has been disclosed in JP-B-50-10496 (the term "JP-B" stands for "Examined Japanese Patent Publication"). However, this photoreceptor still leaves something to be desired in terms of sensitivity and durability. In order to overcome these problems, attempts have been made to develop an organic photoreceptor with high sensitivity and durability by constructing the photosensitive layer from two different substances, namely a compound responsible for generating charge and a compound capable of transporting charge. Such electrophotographic photoreceptors with function separation provide a wide scope for the selection of suitable substances with the respective desired functions, so that photoreceptors with the desired properties can be provided without difficulty.

The advantage of the organic electrophotographic photoreceptors described above is that their photosensitive layer can be produced using coating techniques, so that it can not only be produced inexpensively without the risk of environmental pollution, but also in a wide variety of forms including sheet or film form. On the other hand, conventional organic electrophotographic photoreceptors have the following disadvantages which require a solution.

(1) The photosensitive layer consists of a low molecular weight organic compound dispersed in a high molecular weight organic binder, so that the mechanical strength of the layer is not high enough to protect the photoreceptor surface against damage or abrasion by the developing blade or some other phenomena occurring during cyclic use of the photoreceptor.

(2) The photoreceptor is principally of the negatively chargeable type (see JP-A-60-247647, the term "JP-A" stands for "unexamined published Japanese patent application") and consists of a substrate having a thin carrier generation layer thereon and a comparatively thick carrier transport layer thereon. When used as the negatively chargeable type, the photoreceptor has a high carrier (hole) mobility and allows the use of hole transporting substances. This is clearly advantageous in terms of photosensitivity. In contrast, the currently available electron transporting substances hardly have the desired properties or are not suitable for practical use due to their potentially carcinogenic or teratogenic nature.

A problem with the negatively chargeable photoreceptor is that a negative corona charge, in a highly undesirable manner, releases a larger volume of ozone into the working atmosphere during negative charging with a charging device than in the case of a positive corona charge. This consequently impairs the working conditions. This either leads to an adsorption of ion species on the surface of the photoreceptor or to a deterioration of the material on its surface. The resulting drop in potential during cyclic use leads to a variety of undesirable phenomena, such as increased residual potential, reduced sensitivity and impaired image quality. Furthermore, the service life of the photoreceptor is shortened.

(3) Electrophotographic copying machines are operated under a wide variety of conditions for long periods of time, and often under hot and humid conditions. Therefore, a photoreceptor with high environmental resistance suitable for practical use must be developed.

From US-A-4 637 971 a photoreceptor with a polycarbonate resin of one of the following formulas (I) and (II) is known. This publication describes a photoreceptor with good chargeability, reusability and durability while avoiding the disadvantages of toner film accumulation and the like. However, the photoreceptor does not have good resistance to environmental factors such as ozone, heat and humidity.

From JP-A-60 12551 a photoreceptor is known whose charge transport layer consists of two or more layer components and in which the weight ratio of charge transport material/binder in a layer component that is closer to the electrically conductive layer carrier is higher than the weight ratio of charge transport material/binder in a layer component that is further away from the layer carrier. The photoreceptor described in this publication is intended to solve the problem of providing improved durability. However, the photoreceptor does not have acceptable performance. in hot and humid environments.

SUMMARY OF THE INVENTION

The present invention is therefore based on the object of providing a photoreceptor with high mechanical strength, high charge potential and good sensitivity properties, in which the residual potential does not increase significantly and which has a high resistance to environmental influences, including hot and humid conditions.

The present invention relates to a photoreceptor with an electrically conductive carrier, a charge carrier generation layer formed thereon and a charge carrier transport layer overlying the charge carrier generation layer and containing a charge carrier transport material and a binder, wherein the charge carrier transport layer comprises at least two layer components, so that the weight ratio of charge carrier transport material/binder in a continuous layer closer to the electrically conductive layer carrier is higher than the weight ratio of the charge carrier transport material in a layer component further away from the electrically conductive layer carrier, and a polycarbonate with, as the main recurring unit, a structural unit of the following general formula (I) and/or a structural unit of the following general formula (II):

where:

R¹ and R² each represent a hydrogen atom, a substituted or unsubstituted aliphatic group, a substituted or unsubstituted carbocyclic group or a substituted or unsubstituted aromatic group, where at least one of R¹ and R² represents a "bulky" group, and

R³, R⁴, R⁵, R⁶, R⁷, R⁴, R⁸, R⁴ and R¹⁰ each represents a hydrogen atom, a halogen atom, a substituted or unsubstituted aliphatic group or a substituted or unsubstituted carbocyclic group;

wherein R³, R⁴, R⁵, R⁶, R⁷, R⁴, R⁸, R⁴, and R¹⁰ each have the meaning given and Z represents an atomic group required to form a substituted or unsubstituted carbon ring or a substituted or unsubstituted heterocyclic ring.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 - 4 are partial sections through variously constructed electrophotographic photoreceptors according to the invention and

Fig. 5 shows a tabular summary of the electrophotographic properties of the photoreceptor samples prepared in Examples 1 - 8 and Comparative Examples 1 - 6.

One of the main features of the photoreceptor according to the invention is that the charge carrier transport layer is divided into two or more layer components with different concentrations of charge carrier transport material. A layer component which is closer to the electrically conductive layer support has a higher concentration of charge carrier transport material, so that the photocarriers generated in the charge carrier generation layer are effectively injected into the charge carrier transport layer. On the other hand, a layer component which is further away from the electrically conductive layer support has a lower concentration of charge transport material, so that a corresponding increase in the mechanical strength of the carrier transport layer can be achieved due to the reduced use of charge carrier transport material with a low molecular weight.

Another important feature of the present invention is that a polycarbonate having a structural unit of the general formula (I) and/or the general formula (II) as the main recurring unit is incorporated as a binder in a layer component of the bearing carrier transport layer arranged furthest from the electrically conductive layer carrier. Polycarbonates having a structural unit corresponding to the general formula (I) and/or the general formula (II) as the main recurring unit have high mechanical strength, good scratch and wear resistance, a long service life and the desired charging properties. In particular, such polycarbonates have a hard surface despite acceptable slip properties. In addition, they have a high degree of transparency and insulating ability and are highly miscible with the carrier transport material. In the polycarbonate, the radicals R¹ and R², at least one of which is "bulky", are bonded to the central atom of the bisphenol A unit and it is around the relevant A ring is formed around the carbon atom so that R¹ and/or R² or Z effectively prevent the molecular chain of the polycarbonate from being oriented in a certain direction. As a result, the polycarbonate does not crystallize with bleeding on the surface of the formed photosensitive layer. Deterioration of properties, loss of yield due to abnormal projections and defective image due to toner filming or premature gelation of the coating solution can thus be prevented.

Furthermore, the polycarbonates of the general formula (I) and the general formula (II) are ozone-impermeable and therefore reduce the risk of impairment of the charge carrier transport material. This advantage is particularly pronounced in the photoreceptor according to the invention, since a layer component of the charge carrier transport layer that is further away from the electrically conductive layer carrier has a lower concentration of charge transport material.

The charge transport layer can be composed of two or three or more layer components. If it consists of three or more layer components, the content of the charge carrier transport material is highest in the layer component closest to the electrically conductive layer carrier, while the relevant concentration decreases towards the outer surface of the charge carrier transport layer.

For illustration purposes, four basic embodiments of the photoreceptor according to the invention are shown schematically in Figs. 1 - 4.

The photoreceptor shown in Fig. 1 contains an electrically conductive layer carrier 1, a charge carrier generation layer 2 resting on the latter and a charge carrier transport layer 3 located on the latter and made up of layer components 3A and 3B. The electrically conductive layer carrier 1 of the photoreceptor shown in Fig. 2 consists of a flexible substrate 1A with an electrically conductive layer 1B located thereon. In the photoreceptor according to Fig. 3, the charge carrier generation layer 2 is overlaid by the charge transport layer 3 made up of layer components 3A, 3B and 3C. The photoreceptor shown in Fig. 4 corresponds to that shown in Fig. 1, but with the exception that an intermediate layer or adhesive or primer layer 6 is provided between the charge carrier generation layer 2 and the electrically conductive layer carrier 1.

The weight ratio of charge carrier transport material to binder in a layer component furthest away from the electrically conductive layer support (hereinafter referred to as "outermost layer component of the charge carrier transport layer") (layer 3B in the examples of Figs. 1, 2 and 4 and layer 3C in the example according to Fig. 3) is preferably not more than 70 wt. %, preferably 5 to 70 wt. %. If the weight ratio of charge carrier transport material to binder is set to a value within the specified range, the strength of the charge transport layer can be increased without impairing its ability to transport charge carriers.

The weight ratio of charge carrier transport material/binder in a layer component closest to the electrically conductive layer carrier (layer 3A in the examples according to Fig. 1 - 4) is expediently at least 30 wt.%, preferably 30 - 300 wt.%. If the weight ratio of charge carrier transport material/binder is set to a value within this range, a larger amount of photocarriers can be injected from the charge carrier generation layer into the charge carrier transport layer. It should be noted that the proportion of the charge transport material in this layer component can be increased up to 300 wt.%. This is possible for two reasons: first, the charge carrier transport layer consists of two or more layer components, and second, the layer component located farthest from the electrically conductive layer carrier has increased strength.

The weight ratio of charge carrier transport material/binder in a layer component arranged furthest away from the electrically conductive layer carrier preferably differs from the weight ratio of charge carrier transport material/binder in a layer component arranged closest to the electrically conductive layer carrier by at least 1.0% by weight.

The binder in each of the layer components of the charge carrier transport layer can consist of a polycarbonate of the general formula (I) and/or the general formula (II). In this way, a further improvement in the strength of the charge carrier transport layer can be achieved.

In the following, the materials from which the photoreceptor according to the invention is made and their formulations are explained in more detail. First of all, the polycarbonate with a structural unit corresponding to the general formula (I) and/or the general formula (II) as the main recurring unit is to be discussed. Due to the "bulkiness" of R¹ and R² in formula (I) or due to the effect of the ring formed by Z in formula (II), crystallization of the polycarbonate can be prevented and the resulting and already known advantages. In this connection, it should be noted that R¹ and R² in formula (I) should preferably be different from each other.

For the polycarbonate of formula (I), it is essential that at least one of the radicals R¹ and R² consists of a bulky group, preferably one with at least 3 carbon atoms, in order to ensure such steric hindrance that the molecular chain cannot orient itself.

The following are examples of such a "bulky" group:

wherein R¹¹ represents a hydrogen atom, an alkyl group, e.g. methyl, or an alkyl ester group of the formula (CH₂)m COOR with R being an alkyl group and m ≥ 1;

(3) an alkyl group of the formula CmH2m+1 (m ≥ 4); and

(4) an alkyl ester group of the formula -(CH₂)m COOR¹², where R¹² is an alkyl group and m ≥ 2.

If one of the radicals R¹ and R² represents a bulky group, the other may consist of a hydrogen atom or an alkyl group, e.g. methyl.

In the general formulas (I) and (II), R³ - R¹⁰ can represent not only a hydrogen atom, but also a halogen atom such as Cl, Br or F, an alkyl group such as methyl, and a carbocyclic group, e.g. cyclohexyl.

In the polycarbonate of the general formula (II), Z can represent an atomic group forming a 5- or 6-membered carbon ring or heterocyclic ring, e.g. a cyclohexyl group or a cyclopentyl group. These groups can be partially substituted by acetyl, acetylamino or other groups.

Illustrative examples of structural units corresponding to the general formulas (I) and (II) are:

Polycarbonates usable in the invention have as their main recurring unit a structural unit of the general formula (I) and/or a structural unit of the general formula (II). The main recurring unit may consist of a single structural unit of the general formula (I) or the general formula (II) (for example, the structural unit (I-2) as the only recurring unit) or of two or more structural units of the general formula (I) and/or the general formula (II) in co-condensed form. If necessary, a recurring unit of the general formula (I) and/or the general formula (II) may be co-condensed with minor amounts of other recurring units to provide improved physical, chemical and electrical properties. The cocondensate polycarbonates obtained also fall within the scope of the present invention, provided they are not detrimental to the intended objective. Specific examples of cocondensate polycarbonates are polycarbonates obtained by cocondensing 4,4'-dihydroxyphenyl-1,1-cyclohexane with a minor amount of bisphenol A or by polycondensing 4,4'-dihydroxyphenyl-1,1-cyclohexane and an aromatic dicarboxylic acid, such as terephthalic or isophthalic acid.

Further examples of polycarbonates which can be used according to the invention correspond to the following general formulas (Ia) and (IIa):

wherein R¹, R², R³, R⁴, R⁵, R⁴, R⁵, R⁴, R⁵, R⁴, R⁵9 and R¹⁴ each represent have the meaning given in formulas (I) and (II) and n = 10 - 5000, preferably 50 - 2000;

wherein R³, R⁴, R⁵, R⁶, R⁻, R⁴, R⁴, R⁹⁰, Z and n have the same meaning as in the general formulas (I) and (II).

A polycarbonate with a structural unit of the general formula (II) as the main recurring unit is preferred because it leads to a more effective solution to the problem of the invention. Particularly advantageous structural units are the units identified by the formulas (II-2), (II-4) and (II-9) with a cyclohexane ring bonded to the central carbon atom of the bisphenol A part. The structural unit (II-2) is particularly preferred.

The charge carrier transport material to be accommodated in the charge carrier transport layer is described below.

Examples of charge carrier transport materials are carbazole derivatives of the following general formula (III) and hydrazone compounds of the following general formulas (IV) - (VI):

where:

R¹³ is a substituted or unsubstituted aryl group;

R¹⁴ represents a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group, an alkoxy group, an amino group, a hydroxyl group or a substituted amino group and

R¹⁵ represents a substituted or unsubstituted aryl group or a substituted or unsubstituted heterocyclic group.

where:

R¹⁶ and R¹⁶ each represent a hydrogen atom or a halogen atom

R¹⁹8 and R¹⁹9 each represent a substituted or unsubstituted aryl group and

Ar¹ is a substituted or unsubstituted arylene group.

where:

R²⁰ represents a substituted or unsubstituted aryl group or a substituted or unsubstituted heterocyclic group;

R²¹ represents a hydrogen atom, a substituted or unsubstituted alkyl group or a substituted or unsubstituted aryl group;

Q is a hydrogen atom, a halogen atom, an alkyl group, a substituted amino group, an alkoxy group or a cyano group and

p is an integer, namely 0 or 1.

where:

R²² is a substituted or unsubstituted aryl group or a substituted or unsubstituted heterocyclic group;

R²³ is a hydrogen atom, a substituted or unsubstituted alkyl group or a substituted or unsubstituted aryl group;

X'₂ represents a hydrogen atom, a halogen atom, an alkyl group, a substituted amino group, an alkoxy group or a cyano group and

q is an integer, namely 0 or 1.

According to the invention, charge carrier transport materials of the following general formulas (VII) - (IX) can also be used.

where:

l is an integer, namely 0 or 1;

R²⁴, R²⁵ and R²⁶ each represent a substituted or unsubstituted aryl group;

R²⁷ and R²⁸ each represent a hydrogen atom, an alkyl group having 1-4 carbon atoms, a substituted or unsubstituted aryl or aralkyl group, provided that R²⁷ and R²⁸ do not simultaneously represent a hydrogen atom and, when l = 0, R²⁸ does not represent a hydrogen atom.

where:

R²⁹9 and R³⁹0 represent a substituted or unsubstituted alkyl or phenyl group, wherein the substituent consists of an alkyl, alkoxy or phenyl group;

R³¹ is a substituted or unsubstituted phenyl, naphthyl, anthryl, fluorenyl or heterocyclic group, wherein the substituent consists of an alkyl or alkoxy group, a halogen atom and a hydroxyl or phenyl group;

R31' is a hydrogen atom, a substituted or unsubstituted alkyl or phenyl group and

R³², R³³, R³⁴ and R³⁵ each represent a hydrogen atom, a halogen atom, an alkyl group, an alkoxy group or an alkylamino group

where:

Ar² and Ar³ each represent a substituted or unsubstituted phenyl group, wherein the substituent consists of a halogen atom or an alkyl, nitro or alkoxy group, and

Ar⁴ represents a substituted or unsubstituted phenyl, naphthyl, anthryl, fluorenyl or heterocyclic group, wherein the substituent consists of an alkyl or alkoxy group, a halogen atom or a hydroxyl, aryloxy, aryl, amino, nitro, piperidino, morpholino, naphthyl, anthryl or substituted amino group, provided that the last-mentioned substituted amino group has as a substituent an acyl, alkyl, aryl or aralkyl group.

According to the invention, hydrazone compounds of the following general formula (X) can also be used:

where:

D is a substituted or unsubstituted phenyl group or a substituted or unsubstituted carbazolyl group, for example one of the formulas

R³⁶ and R³⁷ each represent a substituted or unsubstituted alkyl group, a substituted or unsubstituted aralkyl group or a substituted or unsubstituted aryl group (examples of alkyl groups are methyl, ethyl, propyl and butyl groups, examples of aralkyl groups are benzyl and phenethyl groups, examples of aryl groups are phenyl, α-naphthyl and β-naphthyl groups, examples of substituents are a halogen atom, an alkyl group, an alkoxy group or a substituted amino group such as a dimethylamino, diethylamino, dipropylamino or dibenzylamino group);

R³⁹8;, R³⁹9; and R⁹4;⁹5 each represent a radical corresponding to R³⁹6; and R³⁹7; and

R⁴, R⁴¹, R⁴², R⁴³, R⁴⁴ and R⁴⁴ each represent an alkyl group, an alkoxy group, a halogen atom and the like.

The described charge carrier transport materials can be synthesized by known methods. One of these methods consists in carrying out a dehydrating condensation between an α, β-unsaturated ketone and phenylhydrazine in the presence of an acid catalyst.

The charge carrier generating layer (CGL) of a photoreceptor according to the invention contains a charge carrier generating material (CGM). Polycyclic quinone pigments of the following general formulas (XI), (XII) and (XIII) are suitable as CGM.

In the individual formulas, X represents a halogen atom, a nitro group, a cyano group, an acyl group or a carboxyl group, n represents an integer from 0 to 4 and m represents an integer from 0 to 6.

These polycyclic quinone pigments can be synthesized using known methods.

Further examples of suitable charge carrier generating materials are bisazo compounds of the following general formula (XIV):

where:

Ar⁵ and Ar⁶ each represents a substituted or unsubstituted carbocyclic aromatic group or a substituted or unsubstituted heterocyclic aromatic group;

R⁴⁷ and R⁴⁷ each represent an electron-withdrawing group or a hydrogen atom (at least one of R⁴⁷ and R⁴⁷ represents -CN, a halogen atom such as -Cl, or an electron-withdrawing group such as -NO₂) and

where:

X is a hydroxyl group,

or -NHSO₂-R�sup5;²

with R⁵⁰ and R⁵¹ each being a hydrogen atom or a substituted or unsubstituted alkyl group and R⁵² being a substituted or unsubstituted alkyl group or a substituted or unsubstituted aryl group;

Y represents a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group, an alkoxy group, a carboxyl group, a sulfo group, a substituted or unsubstituted carbamoyl group or a substituted or unsubstituted sulfamoyl group (wherein Y may represent different groups in the case that m represents 2 or more):

Z is the atom grouping required to form a substituted or unsubstituted carbocyclic aromatic ring or a substituted or unsubstituted heterocyclic aromatic ring:

R⁴⁹ represents a hydrogen atom, a substituted or unsubstituted amino group, a substituted or unsubstituted carbamoyl group, a carboxyl group or an ester of the same;

A' is a substituted or unsubstituted aryl group;

n is an integer, namely 1 or 2 and

m is an integer from 0 - 4.

Of the bisazo compounds of formula (XIV), those of the following general formula (XIVa) are preferred:

wherein Ar⁵, Ar⁶ and A have the meaning given in formula (XIV).

Particular preference is given to those compounds in which Ar⁵ and Ar⁶ in formula (XIVa) each represent a substituted or unsubstituted phenyl group having an alkyl group, e.g. methyl or ethyl group, an alkoxy group, e.g. methoxy or ethoxy group, a halogen atom, e.g. chlorine or bromine, a hydroxyl group or a cyano group as a substituent.

Bisazo compounds of the following general formula (XV) are also suitable as charge carrier generating materials:

with A equal to a group of formulas:

where:

Z is the atom grouping required to form a substituted or unsubstituted aromatic carbon ring or a substituted or unsubstituted aromatic heterocyclic ring;

Y represents a hydrogen atom, a hydroxyl group, a carboxyl group, an ester group thereof, a sulfo group, a substituted or unsubstituted carbamoyl group or a substituted or unsubstituted sulfamoyl group;

R⁵³ represents a hydrogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted amino group, a substituted or unsubstituted carbamoyl group, a carboxyl group, an ester group thereof or a cyano group;

Ar7 is a substituted or unsubstituted aryl group; and

R⁵⁴ represents a substituted or unsubstituted alkyl group, a substituted or unsubstituted aralkyl group or a substituted or unsubstituted aryl group.

Of the bisazo compounds of formula (XV), bisazo compounds belonging to the fluorenylidene group of the following general formula (XVa) is particularly effective:

where:

R⁵⁵ and R⁵⁶ each represent an alkyl group, an alkoxy group or an aryl group;

R⁵⁷, R⁵⁷, R⁵⁷, R⁷, R⁷¹ and R⁷² each represent a hydrogen atom, a halogen atom, an alkyl group, an alkoxy group, an amino group, a hydroxyl group or an aryl group; and

A" is a substituted or unsubstituted aryl group.

The bisazo compounds of formula (XVa), whose intramolecular carbazole group is likely to make a sensitization contribution, are able to ensure high sensitivity, especially in the longer wavelength range. The combination with the intramolecular carbamoyl unit provides an effective coupler with acceptable sensitivity properties over a wide wavelength range. When used, an effective photoreceptor can be produced for use with a semiconductor laser.

Bisazo compounds of the following general formula (XVI) are also suitable as charge carrier generation materials.

where:

X¹ and X² each represent a halogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a nitro group, a cyano group, a hydroxyl group or a substituted or unsubstituted amino group, provided that at least one of the radicals X¹ and X² represents a halogen atom;

p and q are each an integer, namely 0, 1 or 2, whereby p and q cannot be 0 at the same time, and in the case that p = 2, X¹ can stand for the same or different groups, and in the case that q = 2, X² can stand for the same or different groups, and

A is a group of the following general formula (XVII):

in which Ar8 represents an aromatic carbocyclic or heterocyclic group having at least one fluorinated hydrocarbon group; Z represents a group of non-metallic atoms required to form a substituted or unsubstituted aromatic carbon ring or a substituted or unsubstituted aromatic hetero ring, and m and n each represent an integer, namely 0, 1 or 2, with the proviso that m and n must not be 0 at the same time.

Examples of the halogen atom represented by X¹ and X² in formula (XVI) are chlorine, bromine, fluorine and iodine atoms. At least one of the radicals X¹ and X² has a halogen atom. The alkyl group represented by X¹ and X² preferably consists of a substituted or unsubstituted alkyl group having 1 - 4 carbon atoms, e.g. Methyl, ethyl, β-cyanoethyl, isopropyl, trifluoromethyl and tert-butyl group. The alkoxy group represented by X¹ and X² preferably consists of a substituted or unsubstituted alkoxy group having 1-4 carbon atoms, e.g. a methoxy, ethoxy, β-chloroethyl or sec-butoxy group. The substituted or unsubstituted amino groups represented by X¹ and X² include those substituted by an alkyl group, an aryl group, preferably phenyl group, and the like, e.g. N-methylamino, N-ethylamino, N,N-dimethylamino, N,N-diethylamino, N-phenylamino and N,N-diphenylamino, and those substituted by an acyl group, e.g. acetylamino and p-chlorobenzoylamino.

In formula (XVI), p and q are each 0, 1 or 2, where p and q cannot be 0 at the same time. The preferred case is that p = 1 and q = 0 or that p = 1 and q = 1. If p or q = 2, X¹ and X² can be the same or different.

In formula (XVI), A stands for the following general formula (XVII):

wherein Ar⁸ represents an aromatic carbocyclic or heterocyclic group having at least one fluorinated hydrocarbon group. The fluorinated hydrocarbon group preferably contains 1-4 carbon atoms and consists, for example, of trifluoromethyl, pentafluoroethyl, tetrafluoroethyl, heptafluoropropyl and the like. Trifluoromethyl is preferred. Examples of aromatic carbocyclic groups are phenyl, naphthyl and anthryl, preferably Phenyl. Examples of aromatic heterocyclic groups are carbazolyl and dibenzofuryl. These aromatic carbocyclic and heterocyclic groups can also contain substituents other than fluorinated hydrocarbon groups. Such optionally present substituents are a substituted or unsubstituted alkyl group with 1 - 4 carbon atoms, e.g. methyl, ethyl, isopropyl, tert-butyl or trifluoromethyl, a substituted or unsubstituted aralkyl group, e.g. benzyl or phenethyl, a halogen atom, e.g. chlorine, bromine, fluorine or iodine, a substituted or unsubstituted alkoxy group with 1 - 4 carbon atoms, e.g. methoxy, ethoxy, isopropoxy, tert-butoxy or 2-chloroethoxy, a hydroxyl group, a substituted or unsubstituted aryloxy group, e.g. p-chlorophenoxy or 1-naphthoxy, an acyloxy group, e.g. acetyloxy or p-cyanobenzoyloxy, a carboxyl group or an ester group thereof, e.g. ethoxycarbonyl or m-bromophenoxycarbonyl, a carbamoyl group, e.g. aminocarbonyl, tert-butylaminocarbonyl or anilinocarbonyl, an acyl group, e.g. acetyl or o-nitrobenzoyl, a sulfo group or a sulfamoyl group, e.g. aminosulfonyl, tert-butylaminosulfonyl or p-tolylaminosulfonyl, an amino group or an acylamino group, e.g. acetylamino or benzoylamino, a sulfonamido group, e.g. methanesulfonamido or p-toluenesulfonamido, a cyano group or a nitro group. Of these substituents, the following are preferred: a substituted or unsubstituted alkyl group having 1 - 4 carbon atoms, e.g. methyl, ethyl, isopropyl, tert-butyl or trifluoromethyl, a halogen atom such as chlorine, bromine, fluorine or iodine, a substituted or unsubstituted alkoxy group having 1 - 4 carbon atoms, e.g. methoxy, ethoxy, tert-butoxy or 2-chloroethoxy, a nitro group or a cyano group.

In formula (XVII), Z represents the group required to form a substituted or unsubstituted aromatic hydrocarbon or heterocyclic ring. This may be, for example, the atomic groups required to form a substituted or unsubstituted benzene ring, a substituted or unsubstituted naphthalene ring, a substituted or unsubstituted indole ring, a substituted or unsubstituted carbazole ring and the like. The atomic groups required to form these rings may contain substituents, e.g. those listed in connection with Ar⁸. Preferred examples thereof are a halogen atom, e.g. chlorine, bromine, fluorine or iodine, a sulfo group or a sulfamoyl group, e.g. aminosulfonyl, p-tolylaminosulfonyl and the like.

Of the bisazo compounds that can be represented by the formula (XVI), those of the following general formulae (XVIII), (XIX), (XX) and (XXI) are preferred:

In the formulas:

X1a, X1b, X2a and X2b each represent a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a nitro group, a cyano group, a hydroxyl group or a substituted or unsubstituted amino group, where at least one of the radicals X1a, X1b, X2a and X2b represents a halogen atom and where X1a and X1b or X2a and X2b can be the same or different. Ar' has the same meaning as Ar⁸ in formula (XVI). Y has the same meaning as the substituent on Z in formula (XVI).

The bisazo compounds of the general formula (XVI) can be prepared without difficulty by conventional known methods.

Synthesis example (preparation of compound XVI-71 of the formula below)

2,7-Diamino-4-bromo-9-fluorenone (2.89 g, 0.01 mol) was dispersed in 10 mL of HCl and 20 mL of water. To the dispersion, while cooling to 5°C or below, a solution of 1.40 g (0.02 mol) of sodium nitrite in 5 mL of water was added dropwise. After continuous stirring at the indicated temperature for 1 h, the insoluble material was filtered off and the filtrate was treated with a solution of 4.6 g of ammonium hexafluorophosphate in 50 mL of water. The precipitated tetrazonium salt was filtered off and dissolved in 100 mL of N,N-dimethylformamide (DMF). While cooling to 5°C or below, a solution of 6.62 g (0.02 mol) of 2-hydroxy-3-naphthoic acid-3'-trifluoromethylanilide in 200 ml of DMF is added dropwise.

A solution of 6 g (0.04 mol) of triethanolamine in 30 ml of DMF is then added dropwise while continuously cooling to 5ºC or below. The mixture is incubated at 5ºC or stirred for 1 h and then for a further 4 h at room temperature. After the reaction was complete, the crystals obtained were filtered off, washed successively with DMF and water and finally dried to give 8.71 g of the final product. This had the following elemental analysis data:

calculated: C = 60.5%; H = 2.77%; N = 8.63%

found: C = 60.1%; H = 2.95%; N = 8.72%.

Other compounds can be synthesized using similar measures. First, appropriate amino compounds are used to produce diazonium compounds. These are then reacted with 2-hydroxy-3-naphthoic acid-substituted anilide or 2-hydroxy-3-(substituted phenylcarbamoyl)benzo[a]-substituted or unsubstituted carbazole.

The electrically conductive layer carrier to be used according to the invention can consist of a foil made of metal, e.g. aluminum, nickel, copper, zinc, palladium, silver, indium, tin, platinum, gold, stainless steel, brass and the like. The electrically conductive layer carrier can also be provided by applying an electrically conductive layer to an insulating base, e.g. made of paper, plastic films and other flexible materials having sufficient strength (to withstand bending, pulling or other stresses). The electrically conductive layer can be formed by a variety of methods including laminating a metal foil and vapor deposition of a metal in a vacuum.

The charge carrier generation layer may consist of a charge carrier generation material (CGM) alone or a combination thereof with a suitable resin binder. Optionally, a charge carrier transport material of high Charge carrier mobility with specific or non-specific polarity can be incorporated. Specific methods for forming the charge carrier generation layer are, for example, vacuum deposition of a CGM on the previously described electrically conductive layer support and application or dip coating of a CGM in the form of a solution or dispersion in a suitable solvent either alone or together with a suitable resin binder and drying the coating. In the latter method, a resin binder or a charge carrier transport material can also be used. In this case, the ratio of charge carrier generation material/resin binder/charge carrier transport material is 1/(0 - 100)/(0 - 500), preferably 1/(1 - 10)/(0 - 50) on a weight basis.

Layer components of the charge carrier transport layer can be prepared as follows: dissolving or dispersing a charge carrier transport material and a resin binder in a solvent, applying the solution or dispersion to the charge carrier generation layer or other layer components of the charge carrier transport layer and drying the applied layers.

An intermediate layer or an adhesive or primer layer can be prepared by applying and drying a solution of a resin binder dissolved in a solvent. Examples of solvents or dispersants that can be used are n-butylamine, diethylamine, ethylenediamine, isopropanolamine, monoethanolamine, triethanolamine, triethylenediamine, N,N-dimethylformamide, acetone, methyl ethyl ketone, cyclohexanone, benzene, toluene, xylene, chloroform, 1,2-dichloroethane, dichloromethane, tetrahydrofuran, dioxane, methanol, ethanol, isopropanol, ethyl acetate, butyl acetate and dimethyl sulfoxide.

In addition to polycarbonates having a structural unit of the general formula (I) and/or the general formula (II) as the main recurring unit, the following resins can be used either alone or in admixture as binders: polycarbonates other than those described above, polyesters, methacrylic resins, acrylic resins, polyvinyl chloride, polyvinylidene chloride, polystyrene, polyvinyl acetate, melamine resins, polyurethanes, styrene/acrylate copolymers, styrene/butadiene copolymer, vinylidene chloride/acrylonitrile copolymer, vinyl chloride/vinyl acetate copolymer, vinyl chloride/vinyl acetate/maleic anhydride copolymer, silicone resins, silicone/alkyd resins, phenolic resins, styrene/alkyd resins, poly-N-vinylcarbazole and polyvinyl butyral.

Other suitable resins are transparent resins having a volume resistivity of at least 108Ω cm, preferably at least 1010Ω cm, preferably at least 1013Ω cm. Resins which cure when exposed to light or heat can also be used as binders. Examples of such photo- or thermosetting resins are thermosetting acrylic resins, epoxy resins, urethane resins, urea resins, polyester resins, alkyd resins, melamine resins and photo-curable cinnamic acid ester resins, as well as copolymerized and condensed resins thereof. All other photo- and thermosetting resins which are usually used in electrophotographic recording materials can also be used according to the invention. To improve the handling properties and physical properties (eg preventing cracking and making flexible), the protective layer can contain less than 50% by weight of a thermoplastic resin if necessary. Common thermoplastic resins include polypropylene, acrylic resins, methacrylic resins, vinyl chloride resins, vinyl acetate resins, epoxy resins, polycarbonate resins, copolymerized resins thereof, high molecular weight organic semiconductors such as poly-N-vinylcarbazole, and any other thermoplastic resins commonly used in electrophotographic recording materials.

Resin binders to be used in an intermediate layer or an adhesion or primer layer can be selected from metal oxides such as aluminum oxide and indium oxide and high molecular materials such as acrylic resins, methacrylic resins, vinyl chloride resin, vinyl acetate resin, epoxy resins, polyurethane resins, phenolic resins, polyester resins, alkyd resins, polycarbonate resins, silicone resins, melamine resins, vinyl chloride/vinyl acetate copolymer resin and vinyl chloride/vinyl acetate/maleic anhydride copolymer resin.

In the photoreceptors shown in Figs. 1-4, the layer components 3A, 3B and 3C of the charge carrier transport layer 3 can contain the same or different resin binders. For example, with a view to improving photosensitivity, the uppermost or outermost layer component 3B or 3C can contain a polycarbonate according to the invention and the lowermost or closest layer component to the electrically conductive layer support can contain a polycarbonate of the bisphenol A type. If desired, the layer component 3A (or 3B) which is adjacent to the outermost layer component 3B (or 3C) and closer to the electrically conductive layer support can be designed in such a way that it contains a resin binder which is hardly soluble in the solvent used to apply the outermost layer component. This offers the advantage that not only diffusion of the charge carrier transport material into the lowest layer component 3A, but also swelling of this layer is prevented.

The layer component 3B or 3C, which is further away from the electrically conductive layer carrier, can be than the bottom layer component 3A. For example, the layer component 3A can be applied by dip coating, the layer component 3B or 3C by spray coating. In this way, dissolution or swelling of the bottom layer component 3A can be prevented.

The lowermost layer component 3A expediently has a thickness of 5 - 50 µm, preferably 5 - 30 µm. The outermost layer component 3B or 3C expediently has a thickness of 0.1 - 30 µm, preferably 0.5 - 10 µm.

The charge carrier generation layer expediently has a thickness of 0.01 - 10 µm, preferably 0.1 - 5 µm.

The photosensitive layer may contain a high molecular weight semiconductor incorporated therein. Although a variety of high molecular weight semiconductors can be used, poly-N-vinylcarbazole and its derivatives are preferred because of their high degree of hardening. Poly-N-vinylcarbazole derivatives are those in which all or part of the carbazole rings in the repeating units contain a variety of substituents, e.g. an alkyl group, a nitro group, an amino group, a hydroxyl group or a halogen atom.

The photosensitive layer may contain at least one electron acceptor for a variety of purposes, e.g. to improve sensitivity, to reduce residual potential and to minimize fatigue during cyclic use of the photoreceptor. Examples of electron acceptors usable in the photoreceptor according to the invention are succinic anhydride, maleic anhydride, dibromomaleic anhydride, phthalic anhydride, tetrachlorophthalic anhydride, tetrabromophthalic anhydride, 3-nitrophthalic anhydride, 4-nitrophthalic anhydride, Pyromellitic anhydride, mellitic anhydride, tetracyanoethylene, tetracyanoquinodimethane, o-dinitrobenzene, m-dinitrobenzene, m-dinitrobenzene, 1,3,5-trinitrobenzene, p-nitrobenzonitrile, picryl chloride, quinone chlorimide, chloranyl, bromanyl, 2-methylnaphthoquinone, dichlorodicyano-p-benzoquinone, anthraquinone, dinitroanthraquinone, trinitrofluorenone, 9-fluorenylidene-(dicyanomethylenemalonodinitrile), polynitro-9-fluorenylidene-(dicyanomethylenemalonodinitrile), picric acid, o-nitrobenzoic acid, p-nitrobenzoic acid, 3,5-dinitrobenzoic acid, pentafluorobenzoic acid, 5-nitrosalicylic acid, 3,5-dinitrosalicylic acid, phthalic acid, Mellitic acid and other compounds with a high degree of electron affinity. These electron acceptors can be used alone or in mixtures. Of these examples, fluorenone compounds, quinone compounds and benzene derivatives with electron-withdrawing substituents such as Cl, CN and NO₂ can be used with particular advantage.

Silicone oil and fluorine-containing surfactants can be incorporated into the photoreceptor of the present invention as surface modifiers. Ammonium compounds can be incorporated therein as durability improvers. Furthermore, ultraviolet (UV) absorbents can also be incorporated. Preferred examples are benzoic acid, stilbene compounds and their derivatives, and nitrogen-containing compounds such as triazole compounds, imidazole compounds, triazine compounds, coumarin compounds, oxadiazole compounds, thiazole compounds and their derivatives.

An antioxidant can be incorporated in the charge carrier transport layer, the charge carrier generation layer and the photosensitive layer. This not only helps to minimize the adverse effects of the ozone generated during charging, but also to prevent the increase in the residual potential or decrease in the charge potential, which may occur during cyclic use of the photoreceptor. Examples of antioxidants are hindered phenol, hindered amines, p-phenylenediamine, arylalkanes, hydroquinone, spirochromans, spiroindanone and their derivatives, organic sulfur compounds and organic phosphorus compounds.

The following examples are intended to further illustrate the invention without limiting it.

Manufacturing of electrophotographic photoreceptors:

Electrophotographic photoreceptor samples are explained below:

EXAMPLE 1

A 100 µm thick electroconductive support made of aluminum-vaporized polyethylene terephthalate was coated with an intermediate layer of about 0.1 µm thick made of a vinyl chloride/vinyl acetate/maleic anhydride copolymer ("ES-lac MF-10" from Sekisui Chemical Co., Ltd.). In the next step, 4 g of a polycyclic quinone pigment having the structural formula XI-3 given later was pulverized in a ball mill for 24 hours. The resulting particles were mixed with a solution of 2 g of a bisphenol A type polycarbonate ("Panlite L-1250" from Teijin Ltd.) in 130 ml of 1,2-dichloroethane. The mixture was then stirred for a further 24 hours to form a dispersion. The dispersion was then coated and dried onto the previously formed intermediate layer using a coating knife, whereby a charge carrier generation layer (CGL) of approximately 0.5 µm thick was obtained.

In the next step, 8 g of a styryl compound (charge carrier transport material) of the type given later Structural formula VIII-35 and 10 g of a polycarbonate ("Panlite L-1250") were dissolved in 100 ml of 1,2-dichloroethane. The resulting solution was coated onto the charge carrier generation layer by means of an air knife and dried at 80°C for 1 hour to obtain a charge carrier transport layer component 18 µm thick, arranged closest to the electrically conductive support layer. In this layer component, the weight ratio of charge carrier transport material to resin binder was 80 wt.%.

In the next step, 6 g of a styryl compound represented by the structural formula VIII-35 and 10 g of a polycarbonate (viscosity average molecular weight: about 30,000) composed of repeating units represented by the structural formula II-2 were dissolved in 100 ml of monochlorobenzene. The resulting solution was coated onto the layer component of the charge carrier transport layer closest to the electrically conductive support by means of an air knife, thereby obtaining the outer layer component of the charge carrier transport layer having a thickness of 4 µm. In this outer layer component, the weight ratio of the charge carrier transport material to the resin binder was 60 wt%. Since the solubility of the polycarbonate "Panlite L-1250" in monochlorobenzene was lower than that of the polycarbonate made of repeating units of the structural formula II-2, the layer component of the charge carrier transport layer arranged closest to the electrically conductive layer carrier did not readily dissolve when the outer layer component was applied.

EXAMPLE 1A

An electrophotographic photoreceptor was prepared in accordance with Example 1, except that the amount of charge carrier transport material in the layer component closest to the electrically conductive layer support was the charge carrier transport layer was changed from 8 g to 20 g (200%).

EXAMPLE 2

An intermediate layer and a charge carrier generation layer were produced in accordance with Example 1. The layer component of the charge carrier transport layer arranged closest to the electrically conductive layer carrier was produced in accordance with Example 1, but with a layer thickness of 19 µm.

In the next step, the outer layer component of the charge carrier transport layer was produced according to Example 1, but the amount of charge carrier transport material and the layer thickness were changed to 4 g and 3 μm, respectively.

COMPARISON EXAMPLE 1

According to Example 1, an intermediate layer and a charge carrier generation layer were prepared.

In the next step, 8 g of a charge transport material of the structural formula VIII-35 and 10 g of a polycarbonate "Panlite L-1250" were dissolved in 100 ml of 1,2-dichloroethane. The resulting solution was coated on the charge generation layer to form a single-layer charge transport layer with a thickness of 22 µm.

COMPARISON EXAMPLE 1A

Another comparative photoreceptor was produced according to the following measures. In the first step, an intermediate layer and a charge carrier generation layer were produced according to Example 1. In the next step, the layer component of the Charge carrier transport layer and the outer layer component of the charge carrier transport layer were produced, but the content of the charge carrier transport material in the layer component of the charge carrier transport layer arranged closest to the electrically conductive layer carrier and the thickness of this layer component were changed to 4 g and 19 µm, respectively, and the content of the charge carrier transport material in the outer layer component and the thickness of the outer layer component were changed to 8 g and 3 µm, respectively.

COMPARISON EXAMPLE 1B

Another comparative photoreceptor was prepared in accordance with Example 1, but using the bisphenol A type polycarbonate "Panlite L-1250" as the resin binder in the outer layer component of the charge carrier transport layer.

EXAMPLE 3

An intermediate layer and a charge generation layer were prepared in the same manner as in Example 1 but using a fluorenone compound represented by the structural formula XVI-71 given later as a charge carrier generation material.

Then, 10 g of a polycarbonate having repeating units represented by the general structural formula II-2 and 10 g of a carrier transport material represented by the structural formula VIII-38 given later were dissolved in 100 ml of monochlorobenzene. The resulting solution was coated on the carrier generation layer to form a layer component of the carrier transport layer closest to the conductive support and having a thickness of 15 µm.

In the manner described, but with a reduction in the A coating solution for the outer layer component was prepared by reducing the amount of charge carrier transport material to 7 g. This solution was applied by spray coating to the layer component of the charge carrier transport layer closest to the electrically conductive layer support to form the outer layer component in a thickness of 5 µm.

EXAMPLE 4

An electrophotographic photoreceptor was prepared in the same manner as in Example 3 except that the thickness of the layer component of the charge transport layer closest to the electrically conductive support, the content of the charge transport material in the outer layer component and the thickness thereof were changed to 17 µm, 5 µm and 3 µm, respectively.

EXAMPLE 5

An electrophotographic photoreceptor was prepared in the same manner as in Example 3, except that the thickness of the layer component of the charge transport layer closest to the electrically conductive support, the content of the charge transport material in the outer layer component, and the thickness thereof were changed to 18 µm, 3 µm, and 2 µm, respectively.

COMPARISON EXAMPLE 3

According to Example 3, an intermediate layer and a charge carrier generation layer were prepared.

In the next step, a coating solution of the same composition as the solution for forming the layer component of the charge carrier transport layer closest to the electrically conductive layer carrier according to Example 3 (with 10 g of the charge carrier transport material) was applied to the charge carrier generation layer by means of an air knife to obtain a 20 µm thick single-layer charge carrier transport layer.

COMPARISON EXAMPLE 4

Another comparative electrophotographic photoreceptor was prepared in the same manner as in Comparative Example 3 except that the content of the charge transport material in the charge transport layer was changed to 3 g.

EXAMPLE 6

An intermediate layer was prepared according to Example 1.

In the next step, a carrier generation layer was prepared in the same way as in Example 1, but containing a bisazo compound of the structural formula XIV-5 given later as the carrier generation material and a polyester resin "Vylon-200" from Toyobo Co., Ltd. as the resin binder.

Then, 10 g of a charge carrier transport material with the following structural formula X-2 and 10 g of poly-N-vinylcarbazole "Ruvican M-170" from BASF A.G. were dissolved in 100 ml of tetrahydrofuran (THF). The resulting solution was applied to the charge carrier generation layer using an air knife to produce a 18 μm thick layer component of the charge carrier transport layer that was closest to the electrically conductive layer carrier.

Then, 6 g of a charge carrier transport material of the structural formula X-2 and 10 g of a polycarbonate made up of structural units of the formula II-2 were dissolved in 100 ml of 1,2-dichloroethane. The resulting solution was applied to the layer component closest to the electrically conductive layer support, wherein the outer layer component was obtained in a thickness of 4 µm.

EXAMPLE 7

An electrophotographic photoreceptor was prepared in the same manner as in Example 6 except that the thickness of the layer component of the charge transport layer closest to the electrically conductive support, the thickness of the outer layer component, and the weight ratio of the charge transport material/resin binder in the outer layer component were changed to 19 µm, 3 µm, and 40%, respectively.

COMPARISON EXAMPLE 6

An intermediate layer and a charge carrier generation layer were prepared in accordance with Example 6. In the next step, a coating solution having the same composition as the coating solution for forming the layer component of the charge carrier transport layer closest to the electrically conductive layer carrier according to Example 6 was prepared and applied to the charge carrier generation layer by means of an air knife, whereby a 22 µm thick single-layer charge carrier transport layer was obtained.

EXAMPLE 8

According to Example 1, an intermediate layer and a charge carrier generation layer were prepared.

In the next step, 8 g of a pyrazoline compound of the structural formula VII-22 given later and 10 g of a polycarbonate "Panlite L-1250" were dissolved in 100 ml of 1,2-dichloroethane. The resulting solution was used to form a 18 µm thick layer component of the charge carrier transport layer closest to the electrically conductive layer carrier. applied to the charge carrier generation layer.

Thereafter, 6 g of a pyrazoline compound of the structural formula VII-22 and 10 g of a polycarbonate composed of structural units of the formula II-5 were dissolved in 100 ml of monochlorobenzene. The resulting solution was coated onto the layer component of the charge carrier transport layer closest to the electrically conductive layer support using an air knife to form a 4 µm thick outer layer component. Structural formulas:

Evaluation of photoreceptor properties:

The electrophotographic photoreceptor samples according to Examples 1 to 8 and Comparative Examples 1 to 6 were installed in an adapted copying machine U-Bix 1550 MR manufactured by Konica Corp., and a copying test was carried out for 5 x 10⁴ cycles. At the same time, measurements were made of the black paper potential VB and the white paper potential VW. After making 5 x 10⁴ copies, it was checked whether the thickness of the photoreceptor had decreased due to wear and whether scratches appeared on the image surface. The values of VB and VW measured before copying and after making 5 x 10⁴ copies, as well as changes in the respective values (Δ VB and Δ VW ) are shown in Fig. 5.

The term "black paper potential" means the surface potential developed on a photoreceptor used in the cyclic copy test described when using a black paper original with a reflection density of 1.3. The term "white paper potential" means the surface potential developed on the same photoreceptor when using a white paper original.

The results in Fig. 5 show that the photoreceptor samples of Examples 1-8 had high abrasion and scratch resistance and acceptable values of both black paper and white paper potentials and allowed the production of a large number of image copies of consistent quality with minimal changes in the values of black paper and white paper potentials.

Claims (30)

1. A photoreceptor comprising an electrically conductive support, a charge carrier generation layer formed thereon, and a charge carrier transport layer overlying the charge carrier generation layer and containing a charge carrier transport material and a binder, the charge carrier transport layer comprising at least two layers constituting the same such that the weight ratio of the charge carrier transport material to the binder in a continuous layer closer to the electrically conductive base is higher than the weight ratio of the charge carrier transport material in a constituting layer further away from the electrically conductive support, and a polycarbonate having as the main repeating unit a structural unit represented by the formula (I) or a structural unit represented by the formula (II) in the binder in the outermost constituting layer of the charge carrier transport layer: wherein R¹ and R² each represent a hydrogen atom, an optionally substituted aliphatic group, an optionally substituted aromatic group; R³, R⁴, R⁵, R⁶, R⁷, R⁴, R⁸, R⁴ and R¹⁰ each represent a hydrogen atom, a halogen atom, an optionally substituted aliphatic group, an optionally substituted carbocyclic group; wherein Z represents the group of atoms necessary to form an optionally substituted carbon ring or an optionally substituted heterocyclic ring; and at least one of R¹ and R² belongs to the groups (1) to (4) listed below, wherein R¹¹ is a hydrogen atom, an alkyl group or an alkyl ester group represented by -(CH₂)nCOOR, wherein R is an alkyl group, and m ≥ 1; (3) is an alkyl group represented by -CmH2m+1, where m ≥ 4; and (4) is an alkyl ester group represented by -(CH2)mCOOR¹² wherein R¹² is an alkyl group and m ≥ 2. 2. Photoreceptor according to claim 1, characterized in that the ratio of the charge carrier transport material to the binder in a constitutive layer closest to the electrically conductive support is higher than the weight ratio of the charge carrier transport material to the binder in the outermost constitutive layer of the charge carrier transport layer, the difference between the two weight ratios being at least 20%. 3. Photoreceptor according to claim 2, characterized in that the weight ratio of the charge carrier transport material to the binder is in a constituent layer closest to the electrically conductive carrier is higher than the weight ratio of the charge carrier transport material to the binder in the outermost constituent layer of the charge carrier transport layer, the difference between the two weight ratios being in the range between 20% and 140%. 4. Photoreceptor according to claim 1, characterized in that the charge carrier transport layer contains a polycarbonate having at least the structural unit represented by formula (II) as the main repeating unit. 5. Photoreceptor according to claim 1, characterized in that the outermost constituent layer of the charge carrier transport layer comprises the charge carrier transport material in an amount of not more than 70% by weight of the binder in the outermost constituent layer of the charge carrier transport layer. 6. Photoreceptor according to claim 5, characterized in that the outermost constituent layer of the charge transport layer comprises the charge transport material in an amount of between 5% to 70% by weight of the binder in the outermost constituent layer of the charge transport layer. 7. Photoreceptor according to claim 1, characterized in that the constituent layer of the charge carrier transport layer closest to the electrically conductive carrier comprises the charge carrier transport material in an amount of more than 30% by weight of the binder in the constituent layer of the charge carrier transport layer closest to the electrically conductive carrier. 8. Photoreceptor according to claim 7, characterized in that the constituent layer of the charge carrier transport layer closest to the electrically conductive carrier contains the charge carrier transport material in an amount of between 30% by weight and 300% by weight of the binder in the constituent layer of the charge carrier transport layer closest to the electrically conductive carrier. charge carrier transport layer. 9. Photoreceptor according to claim 1, characterized in that R¹ and R² in the general formula (I) represent different groups. 10. Photoreceptor according to claim 1, characterized in that at least one of R¹ and R² in the general formula (I) represents a bulky group having at least 3 carbon atoms. 11. Photoreceptor according to claim 1, characterized in that the groups R³ to R¹⁰ in the general formulas (I) and (II) each represent a hydrogen atom, a halogen atom, a methyl group or a cyclohexyl group. 12. Photoreceptor according to claim 1, characterized in that Z in the general formula (II) forms a 5- or 6-membered carbon ring or heterocyclic ring. 13. Photoreceptor according to claim 1, characterized in that the number of repetitions of the structural unit represented by the general formula (I) or (II) is between 10 and 5000. 14. Photoreceptor according to claim 13, characterized in that the number of repetitions of the structural unit represented by the general formula (I) or (II) is between 50 and 2000. 15. Photoreceptor according to claim 1, characterized in that the polycarbonate has at least one structural unit represented by the general formula (II). 16. Photoreceptor according to claim 12, characterized in that the groups R³ to R¹⁰ in the general formula (II) each represent a hydrogen atom and Z represents the group of atoms necessary to form a cyclohexylidene ring. 17. Photoreceptor according to claim 1, characterized in that the charge carrier transport material is at least one of the compounds represented by the following general formulas (III) to (X): (wherein R¹³ represents an optionally substituted aryl group; R¹⁴ represents a hydrogen atom, a halogen atom, an optionally substituted alkyl group, an alkoxy group, an amino group, a hydroxyl group or a substituted amino group; and R¹⁵ represents an optionally substituted aryl group or an optionally substituted heterocyclic group); (wherein R¹⁶ and R¹⁷ each represent a hydrogen atom or a halogen atom; R¹⁸ and R¹⁹ each represent an optionally substituted alkyl group; and Ar¹ represents an optionally substituted arylene group); (wherein R²⁰ represents an optionally substituted aryl group or an optionally substituted heterocyclic group; R²¹ represents a hydrogen atom, an optionally substituted alkyl group or an optionally substituted aryl group; Q represents a hydrogen atom, a halogen atom, an alkyl group, a substituted amino group, an alkoxy group or a cyano group; and p is an integer of 0 or 1); (wherein R²² represents an optionally substituted aryl group or an optionally substituted heterocyclic group; R²³ represents a hydrogen atom, an optionally substituted alkyl group or an optionally substituted aryl group; X'₂ represents a hydrogen atom, a halogen atom, an alkyl group, a substituted amino group, an alkoxy group or a cyano group; and q is an integer of 0 or 1); (wherein l is an integer having the value 0 or 1; R²⁴, R²⁵ and R²⁶ each represent an optionally substituted aryl group; R²⁷ and R²⁸ each represent a hydrogen atom, an alkyl group having 1-4 carbon atoms, an optionally substituted aryl or aralkyl group, with the proviso that R²⁷ and R²⁸ do not simultaneously represent a hydrogen atom, and that for l = 0 R²⁸ does not represent a hydrogen atom); (wherein R²⁹9 and R³⁹0 each represent an optionally substituted alkyl or phenyl group, wherein the substituent is an alkyl, alkoxy or phenyl group; R³¹ represents an optionally substituted phenyl, naphthyl, anthryl, fluorenyl group or a heterocyclic group, wherein the substituent is an alkyl group, an alkoxy group, a halogen atom, a hydroxyl group or a phenyl group; R³¹' represents a hydrogen atom, an optionally substituted alkyl or phenyl group; and R³², R³³, R³⁴ and R³⁵ each represent a hydrogen atom, a halogen atom, an alkyl group, an alkoxy group or an alkylamino group); (wherein Ar² and Ar³ each represent an optionally substituted phenyl group, the substituent being a halogen atom, an alkyl group, a nitro group or an alkoxy group; and Ar⁴ represents an optionally substituted phenyl, naphthyl, anthryl, fluorenyl group or heterocyclic group, the substituent being an alkyl group, an alkoxy group, a halogen atom, a hydroxyl group, an aryloxy group, an aryl group, an amino group, a nitro group, a piperidino group, a morpholino group, a naphthyl group, an anthryl group or a substituted amino group, the substituent being an acyl, an alkyl, an aryl or an aralkyl group; where D is an optionally substituted phenyl group or an optionally substituted carbazolyl group or one of the groups: wherein R³⁶, R³⁷, R³⁸, R³⁸ and R⁴⁵ each represent an optionally substituted alkyl group, an optionally substituted aralkyl group or an optionally substituted aryl group; and R⁴⁴, R⁴⁹, R⁴⁲, R⁴⁳, R⁴⁴ and R⁴⁵ each represent an alkyl group, an alkoxy group or a halogen atom. 18. A photoreceptor according to claim 1, wherein the charge carrier generation material contained in said charge carrier generation layer is a polycyclic quinone pigment or a bisazo pigment. 19. A photoreceptor according to claim 16, wherein said polycyclic quinone pigment is an anthanthrone pigment represented by the following general formula (XI): where X represents a halogen atom, a nitro group, a cyano group, an acyl group or a carboxyl group; n is an integer between 0 and 4; and m is an integer between 0 and 6. 20. A photoreceptor according to claim 16, wherein said bisazo pigment is a fluorenylidene pigment represented by the following general formula (XVa): wherein R⁵⁵ and R⁵⁶ each represent an alkyl group, an alkoxy group or an aryl group; R⁵⁷, R⁵⁶, R⁵⁷, R⁶¹ and R⁶² each represent a hydrogen atom, a halogen atom, an alkyl group, an alkoxy group, an amino group, a hydroxyl group or an aryl group; and A" represents an optionally substituted aryl group. 21. A photoreceptor according to claim 16, wherein said bisazo pigment is a fluorenone pigment represented by the following general formula (XVI): wherein X¹ and X² each represent a halogen atom, an optionally substituted alkyl group, an optionally substituted alkoxy group, a nitro group, a cyano group, a hydroxyl group or an optionally substituted amino group, with the proviso that at least one of X¹ and X² is a halogen atom; p and q each represent an integer having the values 0, 1 or 2, with the proviso that p and g are not simultaneously zero, and for p = 2 X¹ can represent the same or different groups, and that for q = 2 X² can represent the same or different groups; and A represents a group represented by the following general formula (XVII): (wherein Ar⁸ represents an aromatic carbocyclic or heterocyclic group having at least one fluorinated hydrocarbon group; Z represents the group for forming an optionally substituted aromatic carbon ring or an optionally substituted aromatic heterocyclic ring); m and n each represent an integer having the values 0, 1 or 2, with the proviso that m and n are not simultaneously zero. 22. Photoreceptor according to claim 1, in which a constitutive layer of the charge transport layer closer to the electrically conductive support and adjacent to the outermost constitutive layer of said charge transport layer contains a polycarbonate of the bisphenol A type as a binder. 23. A photoreceptor according to claim 1, wherein the binder resin contained in a constituent layer of said charge transport layer closer to the electrically conductive support and adjacent to the outermost constituent layer of said charge transport layer is hardly soluble in the solvent used in coating said outermost constituent layer. 24. A photoreceptor according to claim 1, in which a constituent layer of said charge transport layer closest to the electrically conductive support is formed by dip coating and a constituent layer of said charge transport layer adjacent to said constituent layer and remote from the electrically conductive support is formed by spray coating. 25. A photoreceptor according to claim 1, in which a constituent layer of said charge transport layer closest to the conductive support has a thickness of 5 - 50 µm. 26. A photoreceptor according to claim 1, in which a constituent layer of said charge transport layer closest to the electrically conductive support has a thickness of 5 - 30 µm. 27. A photoreceptor according to claim 1, wherein the outermost constituent layer of said charge transport layer has a thickness of 0.1 - 30 µm. 28. A photoreceptor according to claim 1, wherein the outermost constituent layer of said Charge carrier transport layer has a thickness of 0.5 - 10 μm. 29. A photoreceptor according to claim 1, wherein said carrier generation layer has a thickness of 0.01 - 10 µm. 30. A photoreceptor according to claim 1, wherein said charge carrier generation layer has a thickness of 1-5 µm.