JPH0772253B2 - Azo compound and electrophotographic photoreceptor using the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to an azo compound suitable as a charge generating material in an electrophotographic photoreceptor and an electrophotographic photoreceptor using the same.

<Problems to be Solved by Conventional Techniques and Inventions> In recent years, as electrophotographic photoreceptors for image forming apparatuses such as copying machines, organic photoreceptors having excellent processability and economical efficiency and having a large degree of freedom in functional design have been widely used. It is used.

The Carlson process is widely used to form a copied image using an electrophotographic photosensitive member. The Carlson process includes a charging step of uniformly charging a photoconductor by corona discharge, an exposure step of exposing a document image on the charged photoconductor to form an electrostatic latent image corresponding to the document image,
Developing the electrostatic latent image with a developer containing toner to form a toner image, transferring the toner image to a substrate such as paper, and fixing the toner image transferred to the substrate It includes a fixing step and a cleaning step of removing the toner remaining on the photoconductor after the transfer step. In order to form a high quality image in this Carlson process, it is required that the electrophotographic photosensitive member has excellent charging characteristics and photosensitive characteristics and that the residual potential after exposure is low.

Conventionally, inorganic photoconductors such as selenium and cadmium sulfide have been known as electrophotographic photosensitive materials, but they have the drawbacks of toxicity and high production cost.

Therefore, so-called organic electrophotographic photoreceptors using various organic substances in place of these inorganic substances have been proposed. Such an organic electrophotographic photoreceptor usually has a photosensitive layer composed of a charge generating material that generates a charge upon exposure and a charge transporting material that has a function of transporting the generated charge.

In order to satisfy various conditions desired for such an organic electrophotographic photoreceptor, it is necessary to appropriately select these charge generating material and charge transporting material. Among these, as the charge generating material, organic photoconductive polymers such as polyvinylcarbazole, low molecular weight organic photoconductors such as hydrazone compounds, phthalocyanine compounds, perylene compounds, quinacridone compounds, ansanthrone compounds, azo compounds Many compounds have been proposed. For example, as azo compounds, those disclosed in JP-A-47-37543 are known.

However, the above-mentioned conventional charge generation materials often have a narrow photosensitive wavelength region or have strong absorption in the near infrared region,
It does not have a photosensitive wavelength characteristic over the entire visible light region.
Therefore, the electrophotographic photosensitive member using the above conventional charge generating material has a problem that it is difficult to faithfully reproduce a color original depending on the absorption wavelength characteristic of the photosensitive member, and the sensitivity is not sufficient as a whole. .

In particular, the conventional azo-based compound as a charge generation material changes the photosensitivity of the photoconductor after repeated use over a long period of time.
Due to the drawbacks that the durability is not sufficient and the sensitivity is lowered, few of them have been put into practical use.

The present invention has been made in view of the above problems, and uses an azo compound having excellent photosensitivity and stable sensitivity to light even when repeatedly used for a long period of time, and the same. An object is to provide an electrophotographic photoreceptor.

<Means and Actions for Solving the Problems> The azo compound of the present invention has the general formula [I]: (In the formula, R ¹ and R ² are the same or different and are a hydrogen atom,
An alkyl group, an alkenyl group, a hydroxyl group, an alkoxy group, a carboxy group, an alkoxycarbonyl group, an acyl group, an aryl group, a halogen atom or a cyano group, and A represents formulas (a) to (g): [In the formula, R ³ is a hydroxyl group, (In the formula, R ⁹ and R ¹⁰ are the same or different and each represents a hydrogen atom or an alkyl group.) Or group: —NHSO ₂ R ¹¹ (In the formula, R ¹¹ is a hydrogen atom, an alkyl group, an alkenyl group or an aryl group. R ⁴ represents a hydrogen atom, a halogen atom, an alkyl group, an alkoxy group, a carboxyl group, an alkoxycarbamoyl group, a carbamoyl group, a sulfamoyl group or an aryl group, and the alkyl group, the alkoxy group, the carbamoyl group and The sulfamoyl group may have a substituent.

R ⁵ represents an atomic group necessary for forming an aromatic ring, an aliphatic ring or a heterocycle by being condensed with the benzene ring having R ³ and R ⁴ , and these rings may have a substituent. Good.

R ⁶ is a hydrogen atom, amino group, N-substituted amino, alkyl group,
It represents an alkenyl group, a hydroxy group, a carbamoyl group, a carboxyl group or an alkoxycarbonyl group, and the alkyl group and alkenyl group may have a substituent.

R ⁷ represents a hydrogen atom, an alkyl group or an aryl group,
The alkyl group and aryl group may have a substituent.

R ⁸ represents a phenylene group or a naphthylene group, and these groups may have a substituent. ] The coupler residue represented by either of these is shown, and Z shows an oxygen atom or a sulfur atom. ) Is represented by.

An electrophotographic photoreceptor is obtained by providing a photosensitive layer containing the azo compound of the present invention on a conductive substrate.

Since the electrophotographic photosensitive member of the present invention contains the above-mentioned azo compound in the photosensitive layer, it has high sensitivity in the visible light region, particularly in the visible region of 450 to 600 nm, and the reduction of the surface potential due to repeated use is prevented. Further, it has stable sensitivity to long-time exposure and exposure at high temperature, and has excellent light stability.

The reason why the azo compound of the present invention has such high durability and stable sensitivity is considered as follows. That is, the azo compound of the present invention has the formula of the above-mentioned JP-A-47-37543: [In the formula, A'indicates a Kuppler residue. It is presumed that the π-conjugation spreads over the entire central structure compared to the azo compound represented by, and thus planarization of the molecular structure is further promoted and intermolecular interaction due to overlapping between molecules becomes stronger. It

Further, in the above-mentioned coupler residue A, examples of the substituent which may be substituted on the alkyl group and the alkoxy group represented by R ⁴ include a halogen atom, a phenyl group, a naphthyl group, a nitro group and a cyano group. can give. Also,
Examples of the substituent that may be substituted on the carbamoyl group and the sulfamoyl group represented by R ⁴ include, for example, a halogen atom,
Phenyl group, naphthyl group, alkyl group, alkenyl group,
Examples thereof include carbonyl group and carboxyl group. A group represented by R ⁵ , an alkyl group and an alkenyl group represented by R ⁶ , an alkyl group and an aryl group represented by R ⁷ , and
Examples of the substituent which may be substituted on the group represented by R ⁸ include the same substituents as described above.

Examples of the alkyl group include methyl, ethyl, propyl,
Examples thereof include alkyl groups having 1 to 6 carbon atoms such as isopropyl, butyl, isobutyl, tert-butyl, pentyl and hexyl.

Examples of the alkenyl group include vinyl, allyl,
2-butenyl, 3-butenyl, 1-methylallyl, 2-
Examples thereof include alkenyl groups having 2 to 6 carbon atoms such as pentenyl and 2-hexenyl.

Examples of the halogen atom include fluorine, chlorine, bromine and iodine.

Examples of the alkoxy group include methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, te.
C1-C6 alkoxy groups such as rt-butoxy, pentyloxy, hexyloxy and the like can be mentioned.

Examples of the alkoxycarbonyl group include methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, isopropoxycarbonyl, butoxycarbonyl,
Isobutoxycarbonyl, pentyloxycarbonyl,
Examples thereof include lower alkoxycarbonyl groups having 1 to 6 carbon atoms in the alkoxy moiety such as hexyloxycarbonyl.

Further, in R ⁵ , the atomic group that is condensed with the benzene ring having R ³ and R ⁴ to form an aliphatic ring is an alkylene having 1 to 4 carbon atoms such as a methylene group, an ethylene group, a propylene group, a butylene group or the like. The group is raised.

The heterocycle formed by condensation of R ⁵ and the benzene ring having R ³ and R ⁴ includes benzofuranyl, benzothiophenyl, indolyl, 1H-indolyl, benzoxazolyl, benzothiazolyl, 1H-isodazolyl, benzimidazolyl. , Chromenyl, chromanyl, isochromanyl, quinolinyl, isoquinolinyl, cinnolinyl, phthalazinyl, quinazolinyl, quinoxalinyl, dibenzofuranyl, carbazolyl, xanthenyl, acridinyl,
Examples include phenanthridinyl, phenazinyl, phenaxazinyl, thianthrenyl and the like.

Further, examples of the compound of the present invention represented by the above general formula [I] include compounds shown in Table 1.

The azo compound of the present invention can be synthesized by various methods.

For example, as shown in the following reaction formula, it can be easily produced by diazotizing a diamine to form a tetrazonium salt, and then coupling this to a predetermined coupler in an organic solvent. Reaction formula: (Wherein R ¹ , R ² , A and Z are the same as above, X is Cl ⁻ , B
Anions such as r ⁻ , NO ₃ ⁻ , and BF ₂ ⁻ . ) The diazotization is carried out at low temperature (usually -10 by stirring sodium nitrite or nitrous acid in an acidic aqueous solution of diamine (1)).
Natrazonium salt (2) crystallized by adding hydrogen borofluoride, hydrogen halide, sulfuric acid, etc.
To get

In the coupling reaction, a predetermined amount of coupler (3) is added to the tetrazonium salt (2) in an organic solvent such as N, N-dimethylformamide or dimethylsulfoxide to cause a reaction.

The compound of the present invention can be used alone or in combination of two or more kinds. It can also be used in combination with other conventionally known charge generating materials. Examples of the charge generating material include selenium, selenium-tellurium, amorphous silicon, pyrylium salts, conventionally known disazo compounds, ansanthrone compounds, phthalocyanine compounds, indigo compounds, triphenylmethane compounds, and slene compounds. Examples thereof include compounds, toluidine compounds, pyrazoline compounds, perylene compounds, quinacridone compounds and the like.

Further, the compound of the present invention can be applied to any of so-called single-layer type and multi-layer type electrophotographic photoreceptors.

In order to obtain a single-layer type electrophotographic photoreceptor, a photosensitive layer containing the azo compound of the present invention which is a charge generating material, a charge transporting material and a binder resin is formed on a conductive substrate by means of coating or the like. do it. In order to obtain a laminated electrophotographic photoreceptor, a charge generation layer containing the azo compound is formed on a conductive substrate by means such as vapor deposition or coating, and a charge generation layer is formed on the charge generation layer. A charge transport layer containing a transport material and a binder resin may be formed. Alternatively, the charge transport layer may be formed on the conductive base material, and then the charge generation layer containing the charge generation material may be formed by means such as coating.

As the charge-transporting material, a conventionally known material can be used. For example, oxadiazole compounds such as 2,5-di (4-dimethylaminophenyl) -1,3,4-oxadiazole, 9 Styryl compounds such as-(4-diethylaminostyryl) anthracene, carbazole compounds such as polyvinylcarbazole, 1-phenyl-3- (p
-Pyrazoline compounds such as dimethylaminophenyl) birazoline, indole compounds, oxazole compounds, isoxazole compounds, thiazole compounds,
Examples thereof include nitrogen-containing cyclic compounds such as thiadiazole-based compounds, imidazole-based compounds, pyrazole-based compounds and triazole-based compounds, condensed polycyclic compounds, hydrazone-based compounds and the like. These charge transport materials may be used alone or in combination of two or more. In addition, polyvinylcarbazole, etc.
When using a charge transporting material having film forming properties, the binder resin is not always necessary.

Further, various resins can be used as the binder resin in the photosensitive layer, the charge generation layer and the charge transport layer.
Styrene polymers, acrylic polymers, styrene-acrylic copolymers, polyethylene, ethylene-vinyl acetate copolymers, olefin polymers such as chlorinated polyethylene, polypropylene and ionomers, polyvinyl chloride, vinyl chloride-acetic acid Vinyl copolymer, polyester, alkyd resin, polyamide, polyurethane, epoxy resin,
Polycarbonate, polyarylate, polysulfone, diallyl phthalate resin, silicone resin, ketone resin,
Examples include various polymers such as polyvinyl butyral resin, polyether resin, phenol resin, and photocurable resins such as urethane acrylate and epoxy acrylate.
These binder resins may be used alone or in combination of two or more.

A solvent is used when the charge generation layer and the charge transport layer are formed by the coating means. As the solvent, various organic solvents can be used. Alcohols such as methanol, ethanol, isopropanol and butanol, aliphatic hydrocarbons such as n-hexane, octane and cyclohexane, aromatic carbonization such as benzene, toluene and xylene. Halogenated hydrocarbons such as hydrogen, dichloromethane, dichloroethane, carbon tetrachloride and chlorobenzene, dimethyl ether, diethyl ether, tetrahydrofuran, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether and other ethers, acetone, methyl ethyl ketone, cyclohexanone and other ketones , Various solvents such as ethyl acetate, esters such as methyl acetate, dimethylformamide, dimethyl sulfoxide, etc. Mixed and used in.

In order to improve the sensitivity of the charge generation layer, for example,
Conventionally known sensitizers such as terphenyl, halonaphthoquinones, and acenaphthylene may be used together with the charge generating material. Furthermore, in order to improve the dispersibility and coatability of the charge generating material, a surfactant, a leveling agent, etc. may be used in combination.

As the conductive substrate, various materials having conductivity can be used, for example, aluminum, copper, tin, platinum, gold,
Metal element such as silver, vanadium, molybdenum, chromium, cadmium, titanium, nickel, palladium, indium, stainless steel, brass, or plastic material in which the above metal is deposited or laminated, aluminum iodide, tin oxide, indium oxide, etc. Illustrated are, for example, the formed glass. The conductive base material may be sheet-shaped or drum-shaped, and the base material itself has conductivity, or the surface of the base material has conductivity and has sufficient mechanical strength when used. Those are preferable.

The charge of the laminated type can be used in various proportions of the charge generating material and the binder resin in the charge generating layer, but the charge generating material is 5 to 500 parts by weight with respect to 100 parts by weight of the binder resin.
Particularly, it is preferable to use 10 to 250 parts by weight.

The charge generation layer may have an appropriate film thickness, but it is preferably formed to a thickness of 0.01 to 5 μm, particularly 0.1 to 3 μm.

The charge transporting material and the binder resin in the laminated charge transporting layer can be used in various ratios within the range where the charge transport is not hindered, but the charge generated in the charge generating layer by light irradiation is easily transported. As much as possible, 10 to 500 parts by weight, particularly 25 to 200 parts by weight, of the charge transport material is preferable with respect to 100 parts by weight of the binder resin.

The charge transport layer has a thickness of 2 to 100 μm, particularly 5 to 30 μm.
It is preferable that the film is formed to a film thickness of about the same.

In order to form the charge generation layer and the charge transport layer by a coating means, the charge generation material and the binder resin are prepared by a conventionally known method, for example, a roll mill, a ball mill, an attritor,
It may be adjusted by using a paint shaker or an ultrasonic disperser, and applied and dried by a conventionally known application means.
As described above, the charge generation layer may be formed by depositing the charge generation material.

In order to obtain a single-layer type electrophotographic photoreceptor, a photosensitive layer containing the compound of the present invention as a charge generating material, a charge transporting material, and a binder resin is formed into a charge generating layer or a charge transporting layer. It may be formed on the conductive substrate by a method similar to the case.

The addition amount of the charge transport material in the single-layer type photosensitive layer is 40 to 200 parts by weight, preferably 50 to 200 parts by weight with respect to 100 parts by weight of the binder resin.
Suitably 100 parts by weight.

Further, the amount of the charge generating material added to the single-layer type photosensitive layer is appropriately 2 to 20 parts by weight, preferably 3 to 15 parts by weight, based on 100 parts by weight of the binder.

Further, the thickness of the single-layer type photosensitive layer is 10 to 50 μm, especially 15 to
It is preferably about 25 μm. Further, in the case of a single-layer type electrophotographic photoreceptor, between the base material and the photosensitive layer, and in the case of a laminated type electrophotographic photoreceptor, the conductive base material and the charge generation layer or A barrier layer may be formed between the charge-transporting layer and between the charge-generating layer and the charge-transporting layer as long as the characteristics of the photoreceptor are not impaired, and a protective layer is formed on the surface of the photoreceptor. May be.

<Example> Hereinafter, the azo compound of the present invention and the electrophotographic photoreceptor using the same will be described in more detail based on Examples and Comparative Examples.

Example 1 In 75 ml of 10% hydrochloric acid, the following formula (A): 9.07 g (0.023 mol) of the diamine-based compound represented by was added and stirred while cooling with an ice-water bath, and the liquid temperature was kept at -1 ° C. Next, 3.54 g (0.051 mol) of sodium nitrite is added to 10 ml of water.
What was melt | dissolved in was dripped over 30 minutes, with the liquid temperature kept at -2 to 1 degreeC, and after stirring for 1 hour, it left to cool. Then, 20 ml of 42% hydrogen borofluoride was added to this, the generated crystals were filtered, washed with ethanol and dried,
10.19 g of tetrazonium difluoroborate was obtained (yield
74.8%).

Then, the obtained tetrazonium difluoroborate 1.
18 g (0.002 mol) and the following formula (B): 1.06 g (0.004 mol) of the coupler represented by is dissolved in 100 ml of N, N-dimethylformamide, to which sodium acetate is added.
What dissolved 0.35 g (0.0043 mol) in 5 ml of water was 17-21 ° C.
It was added dropwise over a period of 5 minutes while being kept at. Then, after stirring for 3 hours, the formed precipitate was filtered and washed with 200 ml of N, N-dimethylformamide 5 times. Then, it was washed twice with water and dried under reduced pressure to obtain 1.48 g of a disazo pigment (yield: 78.5
%) Was obtained.

Elemental analysis was performed on the obtained disazo pigment, and it was confirmed that this compound was represented by the following formula (C).

Elemental analysis value: Calculated value (%) as C ₅₈ H ₃₉ N ₆ O ₆ C: 76.42 H: 4.49 N: 8.91 Actual value (%) C: 76.53 H: 4.58 N: 8.82 Example 2 p-cresol was used as a coupler. An azo compound was obtained in the same manner as in Example 1 except that the azo compound was used.

Elemental analysis value: Calculated value (%) as C ₄₀ H ₃₂ N ₄ O ₄ C: 75.93 H: 5.10 N: 8.86 Measured value (%) C: 76.06 H: 4.97 N: 8.94 Example 3 4-hydroxyindoline as a coupler An azo compound was obtained in the same manner as in Example 1 except that was used.

Elemental analysis value: Calculated value (%) as C ₄₂ H ₃₄ N ₆ O ₄ C: 73.45 H: 4.99 N: 12.24 Measured value (%) C: 73.20 H: 5.11 N: 12.43 Example 4 N-methylaniline as a coupler Except using
An azo compound was obtained in the same manner as in Example 1.

Elemental analysis value: Calculated value (%) as C ₄₀ H ₃₄ N ₆ O ₂ C: 77.40 H: 5.52 N: 13.54 Actual value (%) C: 77.66 H: 5.42 N: 13.75 Example 5 1-methyl-as a coupler An azo compound was obtained in the same manner as in Example 1 except that 5-hydroxypyrazole was used.

Elemental analysis value: Calculated value (%) as C ₃₄ H ₂₈ N ₈ O ₄ C: 66.66 H: 4.61 N: 18.29 Measured value (%) C: 66.80 H: 4.49 N: 18.38 Example 6 Formula (B1): An azo compound was obtained in the same manner as in Example 1 except that the compound represented by

Elemental analysis value: Calculated value (%) as C ₅₂ H ₃₄ N ₆ O ₈ C: 71.72 H: 3.94 N: 9.65 Measured value (%) C: 71.96 H: 4.08 N: 9.41 Example 7 Formula (B2): An azo compound was obtained in the same manner as in Example 1 except that the compound represented by

Elemental analysis value: Calculated value (%) as C ₆₂ H ₃₆ N ₆ O ₆ C: 77.49 H: 3.78 N: 8.74 Measured value (%) C: 77.63 H: 3.95 N: 8.52 Example 8 In the above formula (A) Instead of the compound represented, the following formula (A
3): An azo compound was obtained in the same manner as in Example 1 except that the compound represented by

Elemental analysis: Calculated as C ₄₀ H ₃₂ N ₄ O ₂ S ₂ (%) C: 72.26 H: 4.85 N: 8.43 Measured value (%) C: 72.44 H: 4.62 N: 8.56 Preparation of electrophotographic photoreceptor Preparation of Layer Type Electrophotographic Photoreceptor 8 parts by weight of the azo compound obtained in Examples 1 to 8 as a charge generating material and 3,3'-dimethyl-N, N, N ', N'- as a charge transport material. Tetraxy-4-methylphenyl (1,
100 parts by weight of 1'-biphenyl) -4,4'-diamine, 100 parts by weight of poly- (4,4'-cyclohexylidenediphenyl) carbonate (polycarbonate Z200 manufactured by Mitsubishi Gas Chemical Co., Inc.) as a binder resin and a predetermined amount. Tetrahydrofuran was mixed and dispersed by an ultrasonic disperser to prepare a single layer type photosensitive layer coating liquid. After this coating liquid was applied onto an aluminum tube, it was heated and dried at 100 ° C. for 30 minutes in a dark place to prepare a drum type electrophotographic photoreceptor having a single-layer type photosensitive layer having a thickness of 24 μm.

Preparation of Laminated Electrophotographic Photosensitive Material Polyvinyl butyral (manufactured by Sekisui Chemical Co., Ltd. as a binder resin,
Brand name S-REC BL1) 100 parts by weight, and 100 parts by weight of the azo compound obtained in Examples 1 to 8 as a charge generating material,
Charge a predetermined amount of tetrahydrofuran and a ball mill,
A charge generation layer coating solution is prepared by stirring and mixing for 24 hours, and the prepared solution is applied onto an aluminum tube by a dipping method,
Film thickness by drying in hot air at 110 ℃ for 30 minutes and curing
A 0.5 μm charge generation layer was formed.

Next, 100 parts by weight of a polycarbonate resin (trade name: Iupilon, manufactured by Mitsubishi Gas Chemical Co., Inc.) as a binder resin and 3,3′-dimethyl-N, N, N ′, N′-tetrakis-4-methyl as a charge transport material. Phenyl (1,1'-phenyl) -4,4'-
100 parts by weight of diamine and a predetermined amount of toluene were mixed by stirring with a homomixer to prepare a charge transport layer coating liquid. This coating solution is applied to the surface of the charge generation layer by a dipping method,
A charge transport layer having a thickness of about 20 μm was formed by drying with hot air at 90 ° C. for 30 minutes to prepare a laminated electrophotographic photoreceptor.

Comparative Example Instead of the azo compound represented by the above formula (A), the following formula (D): Single-layer type and multi-layer type electrophotographic photoconductors were prepared in the same manner as in Example except that chlorodian blue represented by

Evaluation of electrophotographic photoconductor Measurement of initial surface potential V _SP Each of the above single-layer type electrophotographic photoconductors was loaded into an electrostatic copying tester (Gentec Cynthia 30M manufactured by Gentec Co., Ltd.), and its surface was positive or negative. Then, the surface potential V _SP (V) of each photoconductor was measured.

Measurement of half-exposure amount E _1/2 and residual potential _rP Each electrophotographic photosensitive member in the above charged state was exposed at an exposure intensity of 10 lux using a halogen lamp which is an exposure light source of the above electrostatic copying test apparatus, and the surface potential was measured. The half-exposure amount E _1/2 (lux · sec) was calculated by obtaining the time until V _SP (V) becomes 1/2.

The surface potential after 0.15 seconds has elapsed from the start of the exposure is _defined as the residual potential V _rP (V).

Table 2 shows the measurement results of the above electrophotographic characteristics.

As shown in Table 1, both the single-layer type and the multi-layer type photoreceptors using the azo compound of the present invention as a charge generating material have a very small residual potential V _rP as compared with Comparative Examples, and It can be seen that the stability against is excellent. Further, it can be seen that the half-exposure amount E _1/2 is also small, it has stable high sensitivity, it has excellent repeatability, and it is suitable as a charge generation material.

<Effects of the Invention> As described above, the azo-based compound of the present invention has high sensitivity in the visible light region and excellent photostability because the π-conjugation is spread over the entire central structure. Moreover, it is easy to manufacture.

Further, by using this azo compound, an electrophotographic photoreceptor having high sensitivity, excellent light stability and excellent repeating characteristics can be produced at high productivity and at low cost.

Claims (2)

[Claims] 1. The following general formula (I): (In the formula, R ¹ and R ² are the same or different and are a hydrogen atom,
An alkyl group, an alkenyl group, a hydroxyl group, an alkoxy group, a carboxy group, an alkoxycarbonyl group, an acyl group, an aryl group, a halogen atom or a cyano group, and A represents formulas (a) to (g): [In the formula, R ³ is a hydroxyl group, (In the formula, R ⁹ and R ¹⁰ are the same or different and each represents a hydrogen atom or an alkyl group.) Or group: —NHSO ₂ R ¹¹ (In the formula, R ¹¹ is a hydrogen atom, an alkyl group, an alkenyl group or an aryl group. R ⁴ represents a hydrogen atom, a halogen atom, an alkyl group, an alkoxy group, a carboxyl group, an alkoxycarbamoyl group, a carbamoyl group, a sulfamoyl group or an aryl group, and the alkyl group, the alkoxy group, the carbamoyl group and The sulfamoyl group may have a substituent. R ⁵ represents an atomic group necessary for forming an aromatic ring, an aliphatic ring or a heterocycle by being condensed with the benzene ring having R ³ and R ⁴ , and these rings may have a substituent. Good. R ⁶ represents a hydrogen atom, an amino group, an N-substituted amino group, an alkyl group, an alkenyl group, a hydroxy group, a carbamoyl group, a carboxyl group or an alkoxycarbonyl group, and the alkyl group and the alkenyl group each have a substituent. Good. R ⁷ represents a hydrogen atom, an alkyl group or an aryl group, and the alkyl group and the aryl group may have a substituent. R ⁸ represents a phenylene group or a naphthylene group, and these groups may have a substituent. ] The coupler residue represented by either of these is shown, and Z shows an oxygen atom or a sulfur atom. ) An azo compound represented by. 2. An electrophotographic photoreceptor comprising a conductive layer and a photosensitive layer containing the azo compound according to claim 1 provided on the conductive substrate.