JPS6278559A - electrophotographic photoreceptor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an electrophotographic photoreceptor, and in particular to an electrophotographic photoreceptor having a photosensitive layer with improved characteristics by containing a specific disazo pigment and a polycarbonate (Z) resin. Regarding photographic photoreceptors.

[Prior Art] Conventional electrophotographic photoreceptors include those using inorganic photoconductive materials such as selenium, cadmium sulfide, zinc oxide, and amorphous silicon, and those using photoconductive materials such as poly-N-vinylcarbazole and polyvinylanthracene. There are known photoconductive materials using various low-molecular organic photoconductive substances such as polymers or diethylaminobenzaldehyde-N,N-diphenylhydrazone, and those in which organic pigments are dispersed. Among these, the organic pigments used in electrophotographic photoreceptors include Sudan Red,
Azo pigments such as Guianpuru, disazo pigments, quinone pigments such as algol yellow and pyrenequinone, quinocyanine pigments, perylene pigments, indigo pigments such as indigo and thioindigo, bisbenzimidazole pigments such as India First Orange toner, and phthalocyanine pigments such as copper phthalocyanine. , quinacridone pigments, and the like.

Although some photoreceptors having these pigments dispersed therein have been put to practical use, they are not fully satisfactory in terms of sensitivity.

This is because pigments require a binder to form a film, and this binder inhibits the movement of charges.

Therefore, when using Face Nene 4, it is essential to use a binder that is optimal for the pigment.

On the other hand, in the case of a functionally separated photosensitive layer in which the photosensitive layer is divided into a charge generation layer that generates charges by light and a charge transport layer that transports the charges, a pigment is used in the charge generation layer. In this case, not only the binder of the charge generation layer but also the binder of the charge transport layer becomes a factor in determining the sensitivity.

In other words, the key to high sensitivity is to efficiently inject the charges generated in the charge generation layer into the charge transport layer, but if the combination of the pigment in the charge generation layer and the binder in the charge transport layer is poor, the interface between the two layers This creates an injection barrier and reduces injection efficiency. Therefore, it is essential to select a binder for the charge transport layer that is optimal for the pigment even in the functional type 2I photosensitive layer.

[Problems to be Solved by the Invention] In view of the above-mentioned conventional techniques, the present invention solves the following problems by combining a pigment contained in a photosensitive layer and a binder resin.
The purpose is to provide an electrophotographic photoreceptor with higher sensitivity.

Still another object is to provide an electrophotographic photoreceptor with excellent production stability.

[Means and effects for solving the problems] The present invention uses at least one disazo pigment represented by the general formula (1) below as a pigment, and polycarbonate z represented by the general formula (2) below as a binder. The above object is achieved by combining the resin with the resin.

That is, the present invention relates to an electrophotographic photoreceptor having a photosensitive layer containing at least one disazo pigment represented by the following general formula (1) and a polycarbonate Z resin represented by the following general formula (2). configured.

General formula % Formula % In the formula, A represents a Cambler residue having phenolic OHQti, R1, R1', R2 and R2' are a hydrogen atom, a halogen atom or an alkyl group which may have a substituent,
Indicates a group selected from an alkoxy group and an aralkyl group.

In the formula, n represents the average degree of polymerization and is in the range of 50 to 5,000.

According to the present invention, the disazo pigment represented by the general formula (1) has higher sensitivity and less deterioration due to light irradiation than other organic pigments, and is highly durable.

Furthermore, by combining with the polycarbonate Z resin represented by the general formula (2), a highly durable photosensitive layer with high sensitivity and little mechanical surface deterioration is formed.

R, , R1', R2 and R in the above general formula (1)
In the group indicated by 2°, specific examples of the halogen atom include fluorine atom, chlorine atom, bromine atom, iodine atom, etc., and specific examples of the alkyl group include groups such as methyl, ethyl, propyl, butyl, and alkoxy groups. Specific examples of the group include methoxy, ethoxy, propoxy, butoxy, and specific examples of the aralkyl group include benzyl, phenethyl, naphthylmethyl, and the like.

Furthermore, examples of the substituents that the furkyl group, alkoxy group and aralkyl group may have include alkyl groups such as methyl, ethyl and propyl, and alkoxy groups such as methoxy, ethoxy and boxy.

Examples include halogen atoms such as fluorine atom, chlorine atom, bromine atom, and iodine atom, and substituted amino groups such as nitro group, cyano group, dimethylamino, dibenzylamino, and diphenylamino.

Further, the coupler residue having a phenolic OH group represented by 8 in the above general formula (1) is selected from groups represented by the following general formulas (3) to (9).

In the general formula, X is a naphthalene ring condensed with a benzene ring, an anthracene ring, a carbazole ring, benzcarhezole I
Residues necessary to form a polycyclic aromatic ring or a heterocycle selected from F, dibenzofuran ring, benzonaphthofuran ring, and diphenylene sulfide ring, among which naphthalene ring, anthracene ring, benzcarbazole ring, and carbazole ring are More preferably, R3 and R4 are hydrogen atoms,
Alkyl groups and aralkyl groups that may have substituents.

a group selected from an aryl group and a heterocyclic group, or R3,
It shows a cyclic amino group formed with the nitrogen atom to which R4 is bonded, and specific examples of the alkyl group include methyl, ethyl,
Examples of the aralkyl group include benzyl, phenethyl, and naphthylmethyl; specific examples of the aryl group include phenyl, diphenyl, naphthyl, and anthryl. .

HeteoJJ groups include carbazole, dibenzofuran,
benzimidacilone, benzthiazole, thiazole,
Examples include groups such as pyridine.

Examples of the substituents that the above alkyl groups, aralkyl groups, aryl groups and heterocyclic groups may have include alkyl groups such as methyl, ethyl and propyl, methoxy, ethoxy,
Flukoxy group such as propoxy, fluorine atom, chlorine atom,
Examples include halogen atoms such as a bromine atom and an iodine atom, a nitro group, a cyano group, and substituted amino groups such as dimethylamino, dibenzylamino, and diphenylamino.

General Formula R9 General Formula R6 R5 and R6 in General Formulas (4) and (5) represent a group selected from an alkyl group, an aralkyl group, and an aryl group that may have a substituent.

Specific examples of the above R5 and R6 include the above general formula (3)
The same examples as R3 and R4 in .

H1 General Formula In the general formulas (6) and (7), Y represents a divalent group of aromatic hydrocarbon or a divalent group of hetero atom containing a nitrogen atom in the ring.

The divalent groups of the aromatic hydrocarbons mentioned above include divalent groups of monocyclic aromatic hydrocarbons such as 0-phenylene, 0-naphthylene, perinaphthylene, l,2-antrylene, 8.10
- Divalent groups of polycyclic aromatic hydrocarbons such as phenanthrylene are mentioned, and examples of heterocyclic divalent groups containing a nitrogen atom in the ring include 3,4-pyrazolediyl, 2,3
-pyridinediyl, 4,5-pyrimidinediyl, 6,7
-Imidazolediyl, 5.8-benzimidazolediyl, 6.7-chiralindiyl, and other 5- or 6-membered heterocyclic rings and divalent groups.

In the formula, R7 and R8 are a hydrogen atom, an alkyl group that may have a substituent, an aralkyl group, an aryl group, a heterocyclic ring, (separated from each other), (or a carbon atom to which R, y, and Rr are bonded. This 5- or 6-membered ring may have a fused aromatic ring, and Z is a naphthalene ring fused with a benzene ring;
anthracene ring.

Indicates a residue necessary to form a polycyclic aromatic ring or a heterocycle selected from a carbazole ring, a benzcarbazole ring, a dibenzofuran ring, a benzonaphthofuran ring, and a diphenylene sulfide ring.

Specific examples of the above alkyl groups include methyl, ethyl, propyl, butyl, etc. Specific examples of the aralkyl group include benzyl, phenethyl, naphthylmethyl, etc. Specific examples of the aryl group include phenyl, naphthyl, anthryl,
Examples of heterocyclic groups include groups such as pyrenyl, pyridyl, chenyl, furyl, carbazoyl, etc. Furthermore, substituents that the above groups may have include fluorine atom, chlorine atom, etc. , halogen atoms such as bromine atom and iodine atom, alkyl groups such as methyl, ethyl, propyl and butyl, alkoxy groups such as methoxy, ethoxy, propoxy and butoxy, nitro group, cyano group, dimethylamino, diethylamino, dipropylamino, Dibenzylamino, diphenylamino, morpholino, piperidino,
Examples include substituted amino groups such as pyrrolidino. Above R7
Specific examples of groups that form a 5- or 6-membered ring together with the bonded carbon atom of ゜R8, and this 5- or 6-membered ring may have a condensed aromatic ring include cyclopentylidene, Examples include groups such as cyclohexylidene and 3-xanthenylidene.

In the formula, R9 and Rlo are a hydrogen atom, a group selected from an alkyl group, an aralkyl group, an aryl group, and a heterocyclic group which may have a substituent, or a 5- or 6-membered group together with the carbon atom to which R9 and R1° are bonded. Indicates the residues that form the members,
This 5- or 6-membered ring may have a fused aromatic ring, and Z is a naphthalene ring or anthracene ring fused with a benzene ring.

Represents a residue necessary to form a polycyclic aromatic ring or a heterocycle selected from a carhezole ring, a benzcarbazole ring, a dibenzofuran ring, a benzonaphthofuran ring, and a diphenylene sulfide ring.

Specific examples of the alkyl group in the above group include methyl, ethyl,
Groups such as propyl and butyl; specific examples of aralkyl groups include benzyl, phenethyl, and naphthylmethyl; specific examples of aryl groups include phenyl, diphenyl, naphthyl, anthryl, and pyrenyl; specific examples of heterocyclic groups. Examples include groups such as pyridyl, chenyl, furyl, and carbazoyl, and examples of substituents that the above groups may have include halogen atoms such as fluorine atom, chlorine atom, bromine atom, and iodine atom, methyl, ethyl, Alkyl groups such as propyl, butyl, alkoxy groups such as methoxy, ethoxy, propoxy, butoxy, nitro groups, cyano groups, dimethylamino, diethylamino, dipropylamino, dibenzylamino, diphenylamino, morpholino, piperidino, pyrrolidino, etc. Examples include substituted amino groups.

A specific example of a group that forms a 5- or 6-membered ring together with the bonded carbon atoms of R9 and R10, and this 5- or 6-membered ring may have a fused aromatic ring is cyclopentyl. Examples include groups such as lydene, cyclohexylidene, and 9-merenylidene.

Specific examples of the disazo pigment represented by the general formula (1) are shown below.

Exemplary Compounds of O9 In addition to these exemplary pigments, there are many disazo pigments included in the general formula (1).

The polycarbonate Z resin represented by the general formula (2) has (a) good transparency, (b) high electrical insulation and withstand voltage, and (e) a hard surface with appropriate lubricity. ,
It has characteristics such as being resistant to mechanical wear, and (d) has excellent stability when dissolved in a solvent.

Ordinary polycarbonate resin, i.e., bisphenol A type polycarbonate resin, has a high polymer crystallinity, so it easily gels when dissolved.
It has the disadvantage that it becomes unusable after about two days, and is very different in this respect.

By combining the specific disazo pigment of the present invention with polycarbonate Z resin, the extent to which a barrier layer is formed at the interface between the pigment particles and the resin to prevent charge movement during light irradiation is much greater than when combining with other than polycarbonate Z resin. The benzene ring and cyclohexyl group of the polycarbonate Z resin structure facilitate charge transfer,
It seems to improve sensitivity.

The form of the electrophotographic photoreceptor according to the present invention includes (a) a photosensitive layer in which a disazo pigment represented by general formula (1) (hereinafter referred to as "disazo pigment") is dispersed in a polycarbonate Z resin; (b) A photosensitive layer in which a disazo pigment is dispersed in polycarbonate resin A and a charge transport substance (electron donating compound and/or electron accepting compound).

(C) Disazo pigment with binder resin (polycarbonate z
(d) a functionally separated photosensitive layer in which a charge transport layer containing a polycarbonate Z resin and a charge transport substance is laminated on a charge generation layer containing carbon atoms dispersed in a resin or other resin; (d) a charge transport layer; Examples include a functionally separated photosensitive layer in which a charge generation layer containing a disazo pigment and a polycarbonate Z resin is laminated on top of the layer.

Examples of electron-donating compounds include polycyclic aromatic compounds such as anthracene, helene, phenanthrene, and coronene in the main chain or side chain, or indole, carbazole, ogisazole, inoxazole, thiazole, imidazole, pyrazole,
Examples include compounds having nitrogen-containing heterocycles such as oxadiazole, pyrazoline, thiadiazole, and triazole, hydrazone compounds, and aromatic amino compounds.

Examples of electron-accepting compounds include aliphatic cyclic compounds, aromatic compounds, and heterotopic compounds having electron-accepting substituents such as nitro, nitrone, and cyano groups, such as tetracyanoethylene, trinitrobenzene, dinitroacetophenone, trinitroanisole, tetranitronaphthalene, terephthalonitrile, inphthalonitrile,
Examples include benzoyl cyanide, quinoline cyanide, cyanopyridine, nitroanthracene, dinitrofluorenone, trinitrofluorenone, tetranitrofluorenone, and tetracyanopyrene.

Electron-accepting compounds are generally not preferred due to their carcinogenicity and other harmful properties.

When an electron donating compound is used, the above-mentioned form (C) is used for negative charging, and the form (d) is used for positive charging.

The charge transport layer contains a charge transport substance and a resin in a ratio of 5=1 to 1:2 (
The film thickness is approximately 5 to 20 liters.

In addition to polycarbonate Z, the binder resin for the disazo pigment in the form (C) above includes polyester, polyvinylbenzal, polyvinyl butyral, polyvinylpyrrolidone, and methylcellulose.

Polyacrylic esters, cellulose esters, etc. are used as appropriate.

Dispersion can be carried out by a conventional method such as a ball mill, roll mill, sand mill, or colloid mill after the pigment is mixed into the resin solution.

The thickness of the charge generation layer is 0.01 to IJL, preferably 0.01 to IJL.
05 to 0.5 islands.

When formed over a charge transport layer, it is thicker and has a thickness of 0.
The ratio of pigment to resin is about 5:1 to 1:2.

[Effects of the Invention] In the electrophotographic photoreceptor of the present invention, the photosensitive layer containing a specific disazo pigment and polycarbonate Z resin has high sensitivity and low residual potential, and also has a low bright area potential when rerecording charging and exposure. It is stable without rising, and since the polycarbonate Z resin is present on the surface, the surface has a high altitude and has excellent lubricity, so it is less prone to scratches and improves mechanical durability. can.

Furthermore, since the polycarbonate Z resin solution has good storage stability, it can improve productivity and contribute to quality stabilization.

[Examples] Examples 1 to 6 An aluminum cylinder with a wall thickness of 0.5 mm and a size of 60φ×260 mm was prepared as a base.

Next, copolymerized nylon (product name CM8000, manufactured by Toshi ■)
Part 4 and Type 8 nylon (trade name Rafcamide 500)
3. 4 parts (manufactured by Dainippon Ink Chemical ■), 50 parts of methanol,
The solution was dissolved in 50 parts of n-butanol and applied by dip coating onto the above substrate to form a polyamide undercoat layer having a thickness of 0.6 mm.

Next, 10 parts of the disazo pigment recovered from the exemplary disazo pigment of general formula (1) and 1 part of polyvinyl butyral (trade name: Kosuretsuku BM-2, Building Block Chemical ■! 1J)
0 part was dispersed with 120 parts of cyclohexanone in a sand mill for 10 hours to dissolve 30 parts of methyl ethyl ketone.
A 0.15 μl thick charge generation layer was formed by coating the undercoat layer on top of the undercoat layer.

Next, prepare 10 parts of polycarbonate Z resin (manufactured by Mitsubishi Gas Chemical) with a weight average molecular weight of 120,000, and add 8 parts of monochlorobenzene together with 10 parts of a hydrazone compound having the following structural formula.
Dissolved in 0 parts. Coat this on the charge generation layer and
A charge transport layer having a thickness of 6 μm was formed.

Exemplary disazo pigments (1), (9), (14) of the above selections
, (16), (22), and (30), Examples 1-
6 electrophotographic photoreceptor.

The electrophotographic photoreceptor thus prepared was heated at -5,6K.
V corona charging, image exposure, dry toner development, toner transfer to plain paper, urethane rubber blade (70° altitude, 5 kg w/cm2 pressure, 20° angle to photoconductor)
), and the electrophotographic properties were evaluated.

When measuring the potential, the dark potential (V)) was -700V and 10
The potential (v) when exposed to light of lux/second was as shown in Table 1.

Comparative Examples 1 to 4 Electrophotographic photoreceptors were prepared in the same manner as in Example 1, except that the following organic pigments A to D were used in place of the disazo pigment in Example 1. Examples 1 to 4).

The measurement results of electrophotographic properties are shown in Table 1.

Organic pigment A βff1ffl phthalocyanine (unmanufactured by Dainippon Ink, but it is a face pigment produced by heating water, ethanol, and methyl ethyl ketone in sequence) 1st surface Photoreceptor Exemplary pigment V After 1000 cycles 1000
Image Example 1 of (-V) after (-V) (1) +40 150
Good Example 2 (9) 140 150
Good tt 3 (14) 15
0 180 Good // 4
(1G) 150 180
Good // 5 (22)
150 180 Good //
I ((30) 155 185
Good occurrence tt 3 C170200F! i Fog Occurrence As described above, the electrophotographic photoreceptor of the example had higher sensitivity than the comparative example, and moreover, clear images without fog were obtained.

Example 7 An electrophotographic photoreceptor was prepared in the same manner as in Example 1, except that the above-mentioned exemplary pigment (4) was used in place of the disazo pigment in Example 1.

Comparative Examples 5 to 8 Electrophotographic photoreceptors were produced in the same manner as in Example 7, except that the following resins were used in place of the polycarbonate Z resin used in forming the charge transport layer in Example 7.

Using these electrophotographic photoreceptors, an electrophotographic copying machine having the same process as in Example 1 (however, the exposure amount was 7.2
The evaluation was made by lux.seconds). The evaluation is initial V
F, B, and Vl) and VL after running for 10,000 sheets were further compared by looking at the 10,000th sheet image. The results are shown in Table 2.

Table 2 Initial stage 1 After the cutting edge V'o (-V) VL (-V) Vp (-V) VL
(-V) Example 7 700 135 985 1
80 Comparative Example 5 [i, 90 150 1315
190/l 13 Ga4 15
0 625 190// 7 83
5 85 520 to.

10,000th image example? Good Comparative Example 5 Thin fog/! 6 Slight fogging tt 7 Low image density tt 9 jf3 Gagging due to scratches As described above, in terms of durability after 10,000 cycles, the embodiments of the present invention using polycarbonate Z resin have excellent sensitivity, potential stability, and image quality. proved to be superior in terms of

Comparative Example 9 Polycarbonate A resin (trade name Panlite L-1250, manufactured by Teijin Chemicals) was used in place of the polycarbonate Z resin used in forming the charge transport layer in Example 7, and the other conditions were the same as in Example 7. When an electrophotographic photoreceptor was prepared using the method, the characteristics as an electrophotographic photoreceptor varied from 0 to 10 V, which was about the experimental error, and there was no significant difference.

However, the viscosity of the resin solution of polycarbonate A resin and hydrazone compound increased 3 to 4 times after 24 hours, and it gelled and lost fluidity after 48 hours, whereas in the case of polycarbonate Z resin, There was no change at all even after 48 hours, and the solution was extremely excellent in terms of stability.

Example 8 Polyvinyl carhachizole (weight average molecular weight 60,000)
10 parts and 2 parts of m-terphenyl to 8 parts of monochlorobenzene
0 parts and 20 parts of methylene chloride.

This was applied by dip coating onto the undercoat layer formed in the same manner as in Example 1 to provide a charge transport layer with a thickness of 18 μm.

Next, 10 parts of the disazo pigment of the exemplary pigment (6) was added to polycarbonate Z resin (manufactured by Kijin Kasei Co., Ltd., weight average molecular weight 5).
The mixture was added to 250 parts of an 8% cyclohexanone solution (100%) and dispersed for 10 hours using a sand mill. This dispersion was spray coated onto the charge transport layer while rotating the drum. In this way, a charge generation layer having a thickness of 3 μl was formed.

This electrophotographic photoreceptor was attached to the same electrophotographic copying machine as in Example 1 and evaluated. However, corona charge is +5.2K
It was set to V.

As a result, the Vv was 700V, and the VV was 140V when exposed for 7.5 lux seconds, and a good image could be obtained, and the same results as in Example 7 could be obtained.

On the other hand, even when electrophotographic photoreceptors were produced using different resins in the same manner as in Comparative Examples 5 to 8, the results were still similar to those in Comparative Examples 5 to 8.

Example 9 An electrophotographic photoreceptor was produced in the same manner as in Example except that the disazo pigment of Example 1 was replaced by the disazo pigment of Exemplary Pigment (2).

A corona discharge of 15 KV was applied to the electrophotographic photoreceptor thus prepared. The surface potential at this time was measured (initial potential V
o).

Furthermore, the surface potential (dark decay VK) of this electrophotographic photoreceptor was measured after it was left in a dark place for 5 seconds.

Sensitivity was evaluated by measuring the exposure m (El/2 gJ/am2) required to attenuate the potential Vg to 1/2 after dark decay.

At this time, the light source was a gallium/aluminum/arsenic three-element semiconductor laser (output 5 mW, oscillation wavelength 778 nm).
) was used.

The results were as follows.

Vo knee 680V, Vk: 98%, El/2
: 0.9pLJ/am2 Next, a laser beam printer (a reversal development type electrophotographic printer equipped with the same semiconductor laser as above) (
(Product name: LBP-CX, Canon Stock System), replace the above electrophotographic π photoreceptor with the LBP-CX photoreceptor, and set it.
The zero conditions under which the actual image forming test was conducted are as follows.

-Surface potential knee 700V after next charging.

Surface potential knee after image exposure 150V (exposure amount 2J/cm
2), Transfer potential: +700V, Developer polarity: Negative polarity, Process speed: 50mm/see.

Development conditions (development bias) knee 450V, image exposure scanning method: image scan, - exposure before next charging: red full exposure at 50 lux·sec Image formation was performed by line scanning a laser beam in accordance with character signals and image signals.

As a result of copying 10,000 copies, clear images with no fogging were obtained.

On the other hand, images of electrophotographic photoreceptors produced using different resins in the same manner as Comparative Examples 5 to 8 had low image densities and fog, and good images could not be obtained.

Claims (5)

[Claims] (1) An electrophotographic photoreceptor comprising a photosensitive layer containing at least one disazo pigment represented by the following general formula (1) and a polycarbonate Z resin represented by the following general formula (2). General formula▲There are mathematical formulas, chemical formulas, tables, etc.▼(1) In the formula, A represents a coupler residue having a phenolic OH group, and R_1, R_1', R_2, and R_2' are hydrogen atoms, halogen atoms, or substituents. represents a group selected from an alkyl group, an alkoxy group, and an aralkyl group that may have . General formula ▲ There are numerical formulas, chemical formulas, tables, etc. ▼ (2) In the formula, n indicates the average degree of polymerization and is in the range of 50 to 5000. (2) A in general formula (1) is represented by the following general formula (3) to (
9) The electrophotographic photoreceptor according to claim 1, wherein the electrophotographic photoreceptor is selected from coupler residues having a phenolic OH group represented by 9). General formula ▲ Numerical formula, chemical formula, table, etc. ▼ (3) In the formula, Indicates the residues necessary to form a polycyclic aromatic ring or heterocycle selected from sulfide rings, R_3 and R_4
represents a hydrogen atom, a group selected from an alkyl group which may have a substituent, an aralkyl group, an aryl group, and a heterocyclic group, or a cyclic amino group formed together with the nitrogen atom to which R_3 and R_4 are bonded. General formula ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ (4) General formula ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ (5) R_5 and R_6 in general formulas (4) and (5) have substituents. represents a group selected from an optional alkyl group, an aralkyl group, and an aryl group. General formula ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ (6) General formula ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ (7) Y in general formulas (6) and (7) is a divalent aromatic hydrocarbon or a heterocyclic divalent group containing a nitrogen atom in the ring. General formula ▲ Numerical formula, chemical formula, table, etc. ▼ (8) In the formula, R_7 and R_8 are a hydrogen atom, a group selected from an alkyl group that may have a substituent, an aralkyl group, an aryl group, and a heterocyclic group, or a residue that forms a 5- or 6-membered ring together with the carbon atoms to which R_7 and R_8 are bonded; this 5- or 6-membered ring may have a fused aromatic ring; Z is fused to a benzene ring; Residues necessary to form a polycyclic aromatic ring or heterocycle selected from naphthalene ring, anthracene ring, carbazole ring, benzcarbazole ring, dibenzofuran ring, benzonaphthofuran ring, and diphenylene sulfide ring. General formula ▲ Numerical formula, chemical formula, table, etc. ▼ (9) In the formula, R_9 and R_1_0 are a hydrogen atom, a group selected from an alkyl group that may have a substituent, an aralkyl group, an aryl group, and a heterocyclic group, Alternatively, it represents a residue that forms a 5- or 6-membered ring with the carbon atom to which R_9 or R_1_0 is bonded, and this 5- or 6-membered ring may have a fused aromatic ring, and Z is fused with a benzene ring. Residues necessary to form a polycyclic aromatic ring or heterocycle selected from naphthalene ring, anthracene ring, carbazole ring, benzcarbazole ring, dibenzofuran ring, benzonaphthofuran ring, and diphenylene sulfide ring. (3) The photosensitive layer comprises a disazo pigment of the general formula (1) as a charge generating material dispersed in a charge transporting material and a polycarbonate Z resin of the general formula (2). The electrophotographic photoreceptor according to item 2. (4) The photosensitive layer is a laminate of a charge generation layer containing a disazo pigment of general formula (1), a charge transport material, and a charge transport layer containing a polycarbonate Z resin of general formula (2). The electrophotographic photoreceptor according to item 1 or 2. (5) The photosensitive layer is a charge-generating layer containing a disazo pigment of general formula (1) and a polycarbonate Z resin of general formula (2) laminated on a charge transport layer. The electrophotographic photoreceptor according to item 2.