JPH0260172B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an electrophotographic photoreceptor, and more specifically,
The present invention relates to an improved electrophotographic photoreceptor containing an azo pigment having excellent dispersibility with suppressed crystal growth, stability over time, and excellent electrophotographic properties. More specifically, when obtaining an azo pigment, a coupler represented by the general formula () and 2-hydroxy-3-naphthoic acid are reacted with a bisdiazonium salt represented by the general formula () to suppress crystal growth. The present invention relates to an electrophotographic photoreceptor having a photosensitive layer containing an azo pigment obtained as described above. K0626 (In the general formula (), R ¹ and R ² are hydrogen, halogen,
These include nitro, furyl group, alkyl group which may have a substituent, and phenyl group which may have a substituent. Furthermore, R ¹ and R ² may form a ring,
This ring may have substituents such as halogen, nitro, alkyl, alkoxy, and alkylthio groups. ) Y N ₂ -A-N ₂ Y...() (In the general formula (), A is a C atom and is a divalent residue bonded to the N atom forming an azo, Y is an anionic functional group ) Conventionally, electrophotographic photoreceptors having a photosensitive layer containing an inorganic photoconductor such as selenium, zinc oxide, or cadmium sulfide as a main component have been widely known. However, these are not necessarily satisfactory in terms of sensitivity, thermal stability, moisture resistance, durability, etc., and in particular, selenium and cadmium sulfide are toxic, so there are restrictions in production and handling. On the other hand, electrophotographic photoreceptors having a photosensitive layer containing an organic photoconductive compound as a main component are relatively easy to manufacture, inexpensive, easy to handle, and are generally more heat sensitive than selenium photoreceptors. It has many advantages such as excellent stability, and has attracted a lot of attention in recent years. Poly-N-vinylcarbazole is well known as such an organic photoconductive compound, and charge transfer complexes formed from poly-N-vinylcarbazole and Lewis acids such as 2,4,7-trinitro-9-fluorenone are mainly used. Electrophotographic photoreceptors having a photosensitive layer as a component are not necessarily satisfactory in terms of sensitivity and durability. On the other hand, in laminated or dispersed function-separated photoreceptors, in which the carrier generation function and the carrier movement function are assigned to separate substances, each material has a wide range of selection, and the charging characteristics, sensitivity, durability, etc. It has the advantage that an electrophotographic photoreceptor having arbitrary electrophotographic properties can be produced relatively easily. As described above, the present invention relates to a functionally separated photoreceptor in which the carrier generation function and the carrier movement function are assigned to separate substances, and an azo pigment with suppressed crystal growth is used as the compound having the carrier generation function. There is a particular thing. Conventional azo pigments that can be used as carrier generating substances generally do not have very good dispersing ability, and therefore have problems with the storage stability of the dispersion liquid, the uniformity of the coated surface, etc., and are not easy to handle. Therefore, various dispersion stabilizers (for example, sorbitan fatty acid ester, alkylimidazoline, polyacrylic acid partial fatty acid ester) are used to improve the stability of the dispersion liquid.

[Formula] (R: alkyl), calcium salt of alkylbenzenesulfonate, etc.) may be considered, but the addition of these dispersion stabilizers inevitably deteriorates the carrier generation efficiency of the azo pigment, and is therefore not very preferable. Also, n-
Although there is a method of using a strong basic solvent such as butylamine or ethylenediamine as a solvent, it is difficult to say that it is practical considering the toxicity of these solvents. In view of the above, the present inventors have conducted various studies and have arrived at the present invention. That is, it has been discovered that an azo pigment having a carrier-generating function can be produced in a manner that suppresses crystal growth from the viewpoint of synthesis, and a photoreceptor coating liquid can be obtained that has excellent dispersibility and has no problems in storage stability or coating properties. Further, the photoreceptor using the azo pigment of the present invention was an excellent photoreceptor with no problems in electrophotography. The azo pigment with improved dispersibility in this way is N-(2-thiazolyl), which is a coupler component represented by the general formula below.
-2-Hydroxy-3-naphthoic acid amide derivative (hereinafter abbreviated as HSA) and 2 shown by the following structural formula.
-Hydroxy-3-naphthoic acid (hereinafter abbreviated as HNA) is simultaneously dissolved in a suitable solvent such as dimethylformamide or dimethyl sulfoxide, an alkaline catalyst (e.g. caustic soda, amines, pyridine) is added, and at the same time a bisdiazonium salt is dissolved. Obtained by a method of reaction. K0628 Next, the ratio of HSA and HNA can be added in any ratio. However, generally
If the proportion of HNA increases, electrophotographic properties will be adversely affected, and if the proportion of HNA decreases, dispersibility will be adversely affected. Therefore, the ratio of HSA and HNA that improves dispersibility while maintaining good electrophotographic properties may be within a molar ratio of 100:1 to 100:30. In the present invention, by using the azo pigment with suppressed crystal growth obtained by each of the above methods as a photoconductive substance constituting the photosensitive layer of an electrophotographic photoreceptor, the azo pigment of the present invention can be used as an excellent carrier. By utilizing only the carrier generating ability and using it as a carrier generating material for a so-called functionally separated electrophotographic photoreceptor, in which carrier generation and transport are performed using separate substances, the film has excellent physical properties and dispersion properties, and has excellent charge retention properties. It has excellent electrophotographic properties such as power, sensitivity, and residual potential, and exhibits stable characteristics with little fatigue deterioration even after repeated use, and the above properties do not change even when exposed to heat or light. It is possible to create an electrophotographic photoreceptor. The shape of the azo pigment according to the present invention was investigated by X-ray diffraction, mass spectrum, IR, reflection spectrum, etc., and the following symmetrical type:
It is reasonable to think that it is a mixture of asymmetric disazo pigments. K0629 K0630 K0631 (R ¹ , R ² , and A in each of the above general formulas have the same meanings as in the above general formulas () and ().) These three types of compounds are intricately entangled in the pigment fine particles, It is thought that this suppresses pigment crystal growth, resulting in favorable properties. Naphthol AS, naphthol AS instead of HNA
−SR, naphthol AS−MX, naphthol AS−
It is also possible to suppress crystal growth in the same way by reacting KN and its homologs together with HSA.
The dispersibility was not much better than that of HNA, and the properties of electrophotographic photoreceptors using it were also not good. On the other hand, the bisdiazonium salt of the general formula () is preferably an aromatic bisdiazonium salt, and among these, the following 4,4'-biphenylene bisdiazonium salt is particularly preferable. K0632 K0633 K0634 K0635 K0636 K0637 (Y is an anionic functional group.) Next, a method for synthesizing a representative example of the azo pigment of the present invention will be described. Synthesis Examples In the synthesis examples, parts indicate parts by weight. Synthesis Example 1 13.04 parts of 3,3'-dichloro-4,4'-biphenylenediamine dihydrochloride was dispersed in a mixture of 24 parts of concentrated hydrochloric acid and 40 parts of water, and 5.52 parts of sodium nitrite was added thereto.
A solution of 20 parts of ammonium hexafluoride phosphate dissolved in 200 parts of water was added dropwise under ice-cooling, and stirred for 1 hour while cooling.
The precipitate was separated by filtration, washed with water, and dried to obtain 19.27 parts of the stabilized bisdiazonium salt shown below (yield: 85
%). K0638 Next, as a coupler component, 7.30 parts of N-(2-thiazolyl)-2-hydroxy-3-naphthoic acid amide K0639 and 0.56 parts of 2-hydroxy-3-naphthoic acid K0640 were added to N,N- containing 8.96 parts of triethanolamine. A Kappler solution with a molar ratio of HSA to HNA of 100:11 was prepared by dissolving it in 1200 parts of dimethylformamide (hereinafter abbreviated as DMF), and this was cooled to 0 to 5°C in an ice-water bath, and the above-mentioned mixture was added thereto. A solution of 8.50 parts of stabilized bisdiazonium salt dissolved in 100 parts of DMF was added dropwise, and the resulting blue-purple suspension was heated at 10°C.
The mixture was kept at a temperature below and stirred for 4 hours. The generated precipitate was filtered, and the residue was washed with 1000 parts of DMF and 2000 parts of water, and then dried under reduced pressure to obtain 11.27 parts of an azo pigment. Synthesis Examples 2-39 Aromatic diamine dihydrochloride and
Using HSAs and HSA pairs shown in Table 1
Pigments of Synthesis Examples 2 to 39 were synthesized in the same manner as Synthesis Example 1 except that the HNA molar ratio was used.

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[Table] The photosensitive layer of the electrophotographic photoreceptor of the present invention is usually of the type exemplified below. A photosensitive layer comprising a disazo pigment.A photosensitive layer comprising a disazo pigment dispersed in a binder.A photosensitive layer comprising a disazo pigment dispersed in a well-known charge transfer substance.The photosensitive layer of ~ above serves as a charge generation layer, and a well-known charge transfer substance is added to the photosensitive layer. Photosensitive layer laminated with a charge transfer layer comprising a photosensitive layer The disazo pigment of the present invention generates charge carriers with extremely high efficiency when it absorbs light. The generated carrier can be transferred using a disazo pigment as a medium, but it is preferable to use a known charge transfer material as a medium. From this point of view, photosensitive layers in the form of and are particularly preferred. Charge transfer substances are generally classified into two types: electron transfer substances and hole transfer substances, and both can be used in the photosensitive layer of the photoreceptor of the present invention, and mixtures of substances having the same type of function, Alternatively, a mixture of materials having different functions can also be used. Substances that transfer electrons include electron-withdrawing compounds that have electron-absorbing groups such as nitro groups, cyano groups, and ester groups, such as 2,4,7-trinitrofluorenone, 2,4 , nitrated fluorenone such as 5,7-tetranitrofluorenone,
Alternatively, compounds such as tetracyanoquinodimethane, tetracyanoethylene, 2,4,5,7-tetranitroxanthone, 2,4,8-trinitrothioxanthone, or polymerized products of these electron-absorbing compounds, etc. can give. Further, as the hole transfer medium, there are electron-donating organic photoconductive compounds, such as the following. K0661 K0662 K0663 K0664 K0665 K0666 K0667 K0668 K0669 K0670 K0671 K0672 K0673 K0674 K0675 K0676 K0677 K0678 K0679 K0680 K0681 K0682 K0683 K0684 K068 5 K0686 K0687 K0688 K0689 K0690 K0691 K0692 K0693 K0694 K0695 K0696 K0697 K0698 K0699 K0700 K0701 K0702 K0703 K0704 K0705 K0706 K0707 K0708 K0709 K071 0 K0711 K0712 K0713 K0714 K0715 K0716 K0717 K0718 K0719 K0720 K0721 K0722 K0723 K0724 K0725 K0726 K0727 K0728 K0729 K0730 K0731 K0732 K0733 K0734 K073 5 K0736 K0737 K0738 K0739 K0740 K0741 K0742 K0743 K0744 K0745 K0746 K0747 K0748 K0749 etc. Other polymeric compounds that can be used include poly-N-vinylcarbazole, halogenated poly-N-vinylcarbazole, polyvinylpyrene, polyvinylanthracene, polyvinylacridine, polyglycidylcarbazole, polyvinylacenaphthylene, and ethylcarbazole-formaldehyde resin. . The carrier transfer substances are not limited to those described herein, and when used, one type or a mixture of two or more types of carrier transfer substances can be used. The electrophotographic photoreceptor of the present invention can be manufactured by a conventional method. For example, an electrophotographic photoreceptor having the above-mentioned type of photosensitive layer is prepared by coating and drying a coating solution obtained by dissolving or dispersing the azo pigment according to the present invention in a suitable medium on a conductive support, and then drying the azo pigment in a suitable medium. It can be manufactured by forming a photosensitive layer with a thickness of μm to several tens of μm. As a medium for preparing the coating solution, a basic solvent that dissolves bisazo compounds such as n-butylamine and ethylenediamine, or tetrahydrofuran,
Ethers such as 1,4-dioxane; Ketones such as methyl ethyl ketone and cyclohexanone; Aromatic hydrocarbons such as toluene and xylene; Aprotic polarity such as N,N-dimethylformamide, acetonitrile, N-methylpyrrolidone, and dimethyl sulfoxide Solvents; alcohols such as methanol, ethanol, and isopropanol; esters such as ethyl acetate, methyl acetate, and methyl cellosolve acetate; and media for dispersing azo compounds such as chlorinated hydrocarbons such as dichloroethane and chloroform. When using a medium for dispersing azo pigments,
It is necessary to micronize the azo pigment to a particle size of 5 μm or less, preferably 3 μm or less, optimally 1 μm or less. Furthermore, as the conductive support on which the photosensitive layer is formed, any of those employed in well-known electrophotographic photoreceptors can be used. Specifically, examples include metal drum sheets made of aluminum, copper, etc., and laminates and vapor deposits of these metal foils. Furthermore, metal powder, carbon black, copper iodide,
Examples include plastic film, plastic drum paper, etc., which are coated with a conductive substance such as a polymer electrolyte together with a suitable binder to conductivity treatment. Also included are plastic sheets and drums that contain conductive substances such as metal powder, carbon black, and carbon fibers to make them conductive. An electrophotographic photoreceptor having the above type of photosensitive layer can be produced by dissolving a binder in a coating liquid used for forming the above type of photosensitive layer. In this case, the medium of the coating liquid is preferably one that dissolves the binder. Binders include polymers and copolymers of vinyl compounds such as styrene, vinyl acetate, acrylic esters, and methacrylic esters, phenoxy resins, polysulfones, acrylate resins, polycarbonates, polyesters, cellulose esters, cellulose ethers, urethane resins, and epoxy resins. , various polymers such as acrylic polyol resins. The amount of binder used is usually
It is in the range of 0.1 to 5 times the weight. In addition, when forming this type of photosensitive layer, fine particles of disazo pigment are added to the binder.
For example, it is preferable to exist in the form of fine particles with a particle size of 3 μm or less, particularly 1 μm or less. Similarly, an electrophotographic photoreceptor having the above-mentioned type of photosensitive layer can be manufactured by dissolving a charge transfer medium in the coating liquid used to form the above-mentioned type of photosensitive layer. As the charge transfer medium, any of those exemplified above can be used. In addition to charge transfer media that can themselves be used as binders, such as polyvinylcarbazole and polyglycidylcarbazole, it is preferable to use other binders as binders. As the binder, any of those exemplified above can be used. In this case, the amount of the binder used is usually 5 to 10 μm times the weight of the azo pigment, and the amount of the charge transfer medium used is usually 0.2 to 1.5 times the weight of the binder, preferably 0.3 to 1.2 times the weight of the binder.
The range is twice the weight. In the case of a charge transport medium which itself can be used as a binder, it is usually used 5 to 10 times the weight of the azo pigment. In this type of photosensitive layer, as in the above-mentioned type of photosensitive layer, it is preferable that the disazo pigment is present in the charge transport medium and the binder in the form of fine particles. If a coating solution obtained by dissolving a charge transfer medium in a suitable medium is applied onto the photosensitive layer of the above type ~ and dried to form a charge transfer layer, an electrophotographic photosensitive layer having the above type of photosensitive layer can be obtained. body can be manufactured. In this case, the photosensitive layer of the type described above plays the role of a charge generation layer. The charge transfer layer does not necessarily need to be provided above the charge generation layer, but may be provided between the charge generation layer and the conductive support. However, the former is preferable in terms of durability. The charge transfer layer is formed in the same manner as the photosensitive layer described above. That is, the coating liquid for forming the photosensitive layer described above except the azo pigment may be used as the coating liquid. Typically the charge generating layer is between 5 and 50 micrometers thick. Of course, the photosensitive layer of the electrophotographic photoreceptor of the present invention may contain a known sensitizer. Suitable sensitizers include Lewis acids that form charge transfer complexes with organic photoconductive materials and dye dyes. Examples of Lewis acids include chloranil, 2,3-dichloro-1,4-naphthoquinone,
Quinones such as 2-methylanthraquinone, 1-nitroanthraquinone, 1-chloro-5-nitroanthraquinone, 2-chloroanthraquinone, phenanthrenequinone, aldehydes such as 4-nitrobenzaldehyde, 9-benzoylanthracene, indanedione , 3,5-dinitrobenzophenone, ketones such as 3,3',5,5'-tetranitrobenzophenone, acid anhydrides such as phthalic anhydride, 4-chlornaphthalic anhydride, tetracyanoethylene, Terephthal malonitrile, 4-
Cyano compounds such as nitrobenzalmalonenitrile, 3-benzalphthalide, 3-(α-cyano-
Examples include electron-withdrawing compounds such as p-nitrobenzal) phthalide and 3-(α-cyano-p-nitrobenzal) phthalide. Examples of dyes include triphenylthane dyes such as methyl violet, brilliant green, and crystal violet, thiazine dyes such as methylene blue, quinone dyes such as quinizarin, cyanine dyes, pyrylium salts, thiapyrylium salts, and benzopyrylium salts. It will be done. In addition to these, inorganic photoconductive fine particles such as selenium and selenium-arsenic alloys, and organic photoconductive pigments such as copper phthalocyanine pigments and perylene pigments may also be contained. Further, the photosensitive layer of the electrophotographic photoreceptor of the present invention may contain a known plasticizer in order to improve film formability, flexibility, and mechanical strength. Examples of the plasticizer include aromatic compounds such as phthalic esters, phosphoric esters, epoxy compounds, chlorinated paraffins, chlorinated fatty acid esters, and metalnaphthalenes. Moreover, it goes without saying that an adhesive layer, an intermediate layer, and a transparent insulating layer may be included as necessary. The photoreceptor using the azo pigment of the present invention has high sensitivity and good color sensitivity, and when used repeatedly, there is little change in sensitivity and chargeability, and there is little optical fatigue, and it is extremely durable. . Furthermore, the photoreceptor of the present invention can be widely used in electrophotographic applications such as photoreceptors for printers using lasers, cathode ray tubes (CRTs), and light emitting diodes (LEDs) as light sources, in addition to electrophotographic copying machines. Next, the present invention will be explained in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist thereof. Example 1 A vinyl chloride:vinyl acetate:maleic anhydride copolymer (Eslec MF, manufactured by Sekisui Chemical Co., Ltd.) was placed on a conductive support consisting of a polyester film laminated with aluminum foil (Alpet 85 manufactured by Daido Chemical Co., Ltd., aluminum film thickness 10 μm). -10) to form an intermediate layer with a thickness of 0.05 μm consisting of Pigment 2 of Synthesis Example 1.
g and polyarylate resin (Unitika U-100)
Add 2g to 100ml of 1,2-dichloroethane,
An azo compound dispersion obtained by dispersing it in a paint conditioner for about 1 hour is applied onto the intermediate layer to a dry film thickness of 0.5 μm to form a carrier generation layer, and then a carrier generation layer is formed. 5 g of the transfer substance N,N-dibenzylaminobenzaldehyde-1,1-diphenylhydrazone was mixed with 7 g of polyarylate resin in 1,2-dichloroethane.
The electrophotographic photoreceptor of the present invention was prepared by coating and drying a solution dissolved in 50 ml so that the film thickness after drying was 12 μm to form a carrier transfer layer. After storing this photoreceptor in a dark place at a room temperature of 30°C for one week, this electrophotographic photoreceptor was attached to an electrostatic paper tester "SP-428" (manufactured by Kawaguchi Denki Seisakusho), and the following characteristic tests were conducted. . That is, a voltage of -6KV is applied to the charger to charge the photosensitive layer by corona discharge for 5 seconds, and the potential at that time is V ₀ (-V), and then the illuminance on the surface of the photosensitive layer is
The exposure amount E1/2 (lux·sec) required to attenuate the surface potential of the photosensitive layer to 1/2 by irradiating it with light from a halogen lamp under a condition of 30 lux was determined. Also
Surface potential after exposure with an exposure amount of 30 lux/second,
That is, the residual potential _E50 (-V) was determined. Similar measurements
I did it 500 times. In addition, a tungsten lamp is used as a light source to eliminate residual potential.
Further exposure was performed for 0.3 seconds at 300 lux to completely reduce the residual potential to 0. The results are shown in Table 1.

[Table] Examples 2 to 6 As carrier generating substances, Synthesis Example 2,
Example 1 except that pigments 3, 7, 11, and 16 were used.
A total of five types of electrophotographic photoreceptors were prepared in the same manner as above, and similar characteristic tests were conducted on each of them. The results were as shown in Table 2.

[Table] Reference Examples 1 to 6 The pigments used in Examples 1 to 6 were synthesized in the same manner except that 2-hydroxy-3-naphthoic acid was not used. A generation layer was formed. The carrier generation layers of Examples 1 to 6 were homogeneous coating films, but the carrier generation layers of Reference Examples 1 to 6 were
A large amount of coarse pigment was generated, which is considered to be due to poor dispersibility. Example 7 A synthesis example in which a 0.04 μm thick intermediate layer made of vinyl chloride:vinyl acetate (87:13) copolymer (manufactured by Union Carbide Co., Ltd., VYHH) was formed on the surface of an aluminum drum with a diameter of 80 nm. 4 g of pigment No. 36 was added to 400 ml of 1,2-dichloroethane and dispersed for about 3 hours using a paint conditioner. The resulting dispersion was applied onto the intermediate layer so that the film thickness after drying was 0.5 μm. It was dried to form a carrier generation layer. On this carrier generating layer, 10 g of a carrier transfer substance N,N-diethylaminobenzaldehyde-1-phenyl-1-allylhydrazone represented by the structural formula K0750 was added together with 12 g of polycarbonate resin (Teijin Panlite L-1250) and 1,2- A solution dissolved in 100 ml of dichloroethane was applied and dried to a film thickness of 15 μm after drying to form a carrier transfer layer, thereby producing a drum-type electrophotographic photoreceptor according to the present invention. When this electrophotographic photoreceptor was installed in a modified commercially available cartridge-type electrophotographic copying machine and a copied image was formed, a clear visible image with high contrast and faithful to the original was obtained. 1000 copies again
Although the process was repeated several times, a visible image equivalent to that of the first time was obtained until the end. Examples 8 to 11 A 0.05 μm thick intermediate layer made of vinyl chloride:vinyl acetate copolymer (Kanebirakku L-CP manufactured by Kaneka Co., Ltd.) was formed on a conductive support made of a polyester film on which aluminum was vapor-deposited, and synthesis was carried out. Example 6,
A solution of pigments Nos. 12, 15, and 32 dissolved in n-butyleamine was applied onto the intermediate layer to form a carrier generating layer having a thickness of 0.1 μm. Then, 1-diethylaminophenyl-3 is applied on this carrier generating layer.
- A solution of 5 g of phenyl-5-styryl pyrazonone and 5 g of polyester resin (Vylon-200 manufactured by Toyobo) dissolved in 40 ml of 1,2-dichloroethane,
A carrier transfer layer was formed by coating and drying so that the film thickness after drying was 14 μm, thereby producing an electrophotographic photoreceptor of the present invention. Example 12 Styrene on Al plate with grained surface oxidation:
Methyl methacrylate: Methacrylic acid copolymer (acid value 185), the pigment of Synthesis Example 2 and diethylamino-benzaldehyde-N-phenyl-N-4-ethylbenzylhydrazone were blended in a weight ratio of 1.5:0.2:1.0. A dispersion solution prepared by dissolving (resin component, hydrazone compound) and dispersing (azo pigment) in dioxane was applied and dried to prepare a single layer type photoreceptor with a film thickness of 6 μm. The photoreceptor thus prepared was subjected to an electrophotographic property test using the electrostatic paper tester described above. The applied voltage was +6KV V ₀ =420 (+V), and E1/2 = 5.8 (lux·sec). In addition, this photoreceptor is visualized with a developer (toner), and then an alkaline processing solution (for example, 3% triethanolamine, 10% ammonium carbonate, and 20% polyethylene glycol with an average molecular weight of 190 to 210) is applied.
When treated with , toner-free areas are easily eluted,
Next, by washing with water containing sodium silicate, a printing original plate could be easily prepared. When offset printing is performed using this original plate, approximately
It was found that it could withstand printing of 100,000 sheets. The optimum exposure amount (light source: halogen lamp) for obtaining a visible toner image was 50 lux and 1.5 seconds. In addition, when creating a printing original plate, it was performed by direct plate making without using a base material.

Claims (1)

[Claims] 1. A coupler component represented by the general formula () and 2-hydroxy-3-naphthoic acid are simultaneously reacted with a bisdiazonium salt represented by the general formula () on a conductive support. An electrophotographic photoreceptor comprising a photosensitive layer containing the obtained azo pigment. K0624 (In formula (), R ¹ and R ² are hydrogen, halogen, nitro, furyl, alkyl or phenyl group that may have a substituent, and R ¹ and R ² may form a ring. ) Y N ₂ -A-N ₂ Y ... () (In the general formula (), A is a C atom and is a divalent residue bonded to the N atom forming an azo, Y is an anionic functional group 2. Claim No. 2, which contains an azo pigment in which the molar ratio of the coupler component represented by the general formula () to 2-hydroxy-3-naphthoic acid is from 100:1 to 100:30. The electrophotographic photoreceptor according to item 1. 3. The electrophotographic photoreceptor according to claim 1, wherein the photosensitive layer contains a carrier transfer substance and a carrier generation substance, and the carrier generation substance is the azo pigment. 4. The electrophotographic photoreceptor according to claim 1, wherein the bisdiazonium salt represented by the general formula () is a biphenylene bisdiazonium salt represented by the following structural formula. K0625 (In the formula, X may be the same or different and is a halogen, nitro, methyl, ethyl, methoxy, or ethoxy group, Y is an anionic functional group, and n represents an integer from 0 to 2.)