JP2881182B2 - Electrophotographic photoreceptor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to an electrophotographic photoreceptor, and particularly to an electrophotographic photoreceptor which does not increase in residual potential even when used repeatedly for a long period of time and has excellent charge stability. It relates to a photoreceptor.

[Conventional technology]

Conventionally known photoconductive materials for electrophotographic photoreceptors include inorganic substances such as selenium, cadmium sulfide, and zinc oxide. However, these inorganic substances are not necessarily satisfactory in characteristics such as photosensitivity, thermal stability, and durability and manufacturing conditions required for an electrophotographic photosensitive member. For example, selenium is easily crystallized due to heat, dirt, and the like, and its characteristics are easily degraded. Also, manufacturing cost, impact resistance,
There are drawbacks, such as toxicity and care in handling. Photoconductors using cadmium sulfide are inferior in moisture resistance and durability,
There are also problems such as toxicity. Zinc oxide also has the drawback of poor moisture resistance and durability.

In contrast to electrophotographic photoreceptors that use these inorganic photoconductive materials, photoreceptors that use organic photoconductive materials are actively researched because of their light weight, ease of film formation, manufacturing costs, and the wide range of variations as organic compounds. Development is taking place. For example, at the beginning, polyvinyl carbazole described in JP-B-50-10496 and 2,4,7-trinitro-
Photoreceptor containing 9-fluorenone, JP-B-48-25658
A photoconductor sensitized with polyvinylpyrazole with a pyrylium salt dye or a photoconductor containing a eutectic complex as a main component has been proposed. However, these photoconductors are not sufficient in sensitivity and durability. Therefore, in recent years, a function-separated type photoreceptor in which a charge generation layer and a charge transport layer are separated has been proposed, and a photoreceptor combining chlordian blue and a hydrazone compound described in JP-B-55-42380,
As a charge generating substance, a bisazo compound is disclosed in
JP-A-133445, JP-A-54-21728, JP-A-54-22834, and as the charge transporting substance, JP-A-5
8-198043 Japanese Patent Application Laid-Open No. 58-199352 and the like are known. However, these functionally separated photoconductors are not particularly satisfactory in durability,
In recent years, with increasing demand for durability, securing charging stability has become a problem that cannot be ignored. That is, when the chargeability is reduced, the image density of a copy is reduced in a copying machine, and in the case of a laser printer using a reversal development method, the image quality is reduced such as generation of background stain. In order to solve these problems, it has been proposed to provide an intermediate layer between the conductive substrate and the photosensitive layer. However, when a high resistance material having a high barrier property is used for stabilizing the chargeability of the intermediate layer, the chargeability is improved, but the photosensitivity is reduced and the residual potential is increased. If a material with a relatively low resistance that does not increase the residual potential is used,
The charging stability becomes insufficient.

On the other hand, when the photoconductor is actually used in a copying machine, the photoconductor is exposed to ozone generated from a corona charger. From the viewpoint that this ozone oxidizes the charge transporting substance and the like in the photosensitive layer and causes a decrease in sensitivity, an increase in residual potential, or a decrease in charge potential, JP-A-57-122444 and JP-A-61-122444 disclose such ozone. Proposal of adding an antioxidant to a photosensitive layer as disclosed in JP-A-156052, and providing a gas barrier resin layer on a charge transport layer as disclosed in JP-A-63-135955. Has been made. However, even with the measures described above, a satisfactory photoreceptor has not been obtained in that there is a complication such as an increase in residual potential and a decrease in sensitivity, and the improvement in durability is still insufficient.

[Problems to be solved by the invention]

The present invention solves the above-mentioned conventional problems. Specifically, the present invention is excellent in ozone resistance, excellent in charging stability even when used repeatedly, and does not increase the residual potential. It is an object of the present invention to provide an electrophotographic photoreceptor that gives a good image free from contamination.

[Means for solving the problem]

According to the present invention, in an electrophotographic photosensitive member having a photosensitive layer containing at least a charge generating substance and a charge transporting substance on a conductive substrate, the photosensitive layer has the following general formula (I) or (II) An electrophotographic photoreceptor characterized by containing a compound represented by the formula:

(Wherein, R _{1 to} R ₄ each represent a hydrogen atom, a halogen atom, a hydroxy group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted Represents an alkoxy group, a substituted or unsubstituted aryloxy group, a substituted amino group, an imino group, a heterocyclic group, a substituted or unsubstituted alkylthio group, or an arylthio group, a sulfoxide group, a sulfonyl group, an acyl group, or an azo group. (Wherein, R _{1 to} R ₈ each represent a hydrogen atom, a halogen atom, a hydroxy group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted Alkoxy group, substituted or unsubstituted aryloxy group, substituted amino group, imino group, heterocyclic group, substituted or unsubstituted alkylthio group, or arylthio group, sulfoxide group, sulfonyl group, acyl group, azo group, carboxyl group or carbonyl The electrophotographic photoreceptor according to the present invention contains at least one compound represented by the general formula (I) or (II) in the photosensitive layer, so that it can be favorably used by repeated use. It shows charge stability and does not increase residual potential, and therefore has a long life without image density reduction and background contamination, It is highly reliable.

Specific examples of the compound represented by formula (I) or (II) that can be used in the present invention are shown below, but the present invention is not limited thereto.

[Specific Examples of Compound of General Formula (I)]

[Specific examples of compound of general formula (II)] In the present invention, the above-mentioned general formula (I) or general formula (II)
The reason why a photosensitive member having excellent durability can be obtained by including at least one of the compounds represented by the formula (I) in the photosensitive layer is not clear, but the compatibility with the constituent material of the photosensitive layer, particularly the binder resin, is not clear. It does not have any adverse effects such as reacting with other photosensitive layer constituent materials, does not act as a trap for charge carriers, has an excellent ability to react quickly with radical substances and prevent the generation of traps, etc. No.

Further, in the present invention, a phosphorus-based compound or a sulfur-based compound is mentioned as a secondary deterioration inhibitor from the viewpoint of further improving the storage stability and heat resistance with respect to the above-mentioned compound. preferable.

Specific examples of the phosphorus compound include tris (nonylphenyl) phosphite, tris (p-tert-octylphenyl) phosphite, tris [2,4,6-tris (α-phenylethyl)] phosphite, tris ( p-2-butenylphenyl) phosphite, bis (p-nonylphenyl) cyclohexylphosphite, tris (2,4-di-t
ert-butylphenyl) phosphite, di (2,4-di-te
(rt-butylphenyl) pentaerythritol diphosphite, distearylpentaerythritol diphosphite, 4,4'-isopropylidene-diphenolalkyl phosphite, tetratridecyl-4,4'-butylidene-bis (3-methyl- 6-tert-butylphenol) diphosphite, tetrakis (2,4-di-tert-butylphenyl) -4,4'-biphenylenediphosphite, 2,6-
Di-tert-butyl-4-methylphenyl phenyl pentaerythritol diphosphite, 2,6-di-tert-
Butyl-4-methylphenyl methyl pentaerythritol diphosphite, 2,6-di-tert-butyl-4-
Ethylphenyl stearyl pentaerythritol diphosphite, di (2,6-di-tert-butyl-4-methylphenyl) pentaerythritol diphosphite,
6-di-tert-amyl-4-methylphenyl phenyl pentaerythritol diphosphite, 2,2-methylenebis (4,6-di-tert-butylphenyl) octyl phosphite and the like. These can be used in combination.

As the charge generating substance that can be used in the electrophotographic photoreceptor of the present invention, any of inorganic substances and organic substances can be used as long as they absorb light to generate charge carriers.

Examples of the inorganic substance include amorphous selenium, trigonal selenium, selenium-arsenic alloy, selenium-tellurium alloy, cadmium sulfide, zinc oxide, amorphous silicon, and the like.

Examples of the organic substance include phthalocyanine pigments such as metal phthalocyanine and metal-free phthalocyanine, azulhenium salt pigments, methine squaric acid pigments, azo pigments having a carbazole skeleton, azo pigments having a triphenylamine skeleton, azo pigments having a diphenylamine skeleton Azo pigments having a dibenzothiophene skeleton, pigments having an oxadiazole skeleton, azo pigments having a fluorenone skeleton, azo pigments having a bisstillene skeleton, azo pigments having a distyryl oxadiazole skeleton, azo pigments having a distyryl carbazole skeleton Pigments, perylene pigments, anthraquinone or polycyclic quinone pigments, quinone imine pigments, diphenylmethane and triphenylmethane pigments, benzoquinone and naphthoquinone pigments, cyanine and azomethine Pigments, indigoid pigments, bisbenzimidazole pigments.

Examples of the charge transport material that can be used in the present invention include:
Poly-N-vinylcarbazole and its derivatives, poly-r-carbazolylethylglutamate and its derivatives, pyrene-formaldehyde condensate and its derivatives, polyvinylpyrene, polyvinylphenanthrene, oxazole derivatives, oxadiazole derivatives, imidazole derivatives, Phenylamine derivative, 9- (p-diethylaminostyryl) anthracene-1,1-bis-
Examples include electron-donating substances such as (4-dibenzylaminophenyl) propane, styrylanthracene, styrylpyrazoline, phenylhydrazones, α-phenylstilbene derivatives, and particularly, aromatic amine compounds represented by the following general formula. Use is preferred.

(Wherein, R ₁ and R ₂ represent an aromatic ring group or a heterocyclic aromatic group selected from a substituted or unsubstituted phenyl group, a naphthyl group, and a polyphenyl group, and R ₃ represents a substituted or unsubstituted group. The following are specific examples of the aromatic amine compound represented by the above general formula, but the present invention is not limited to these.

The photosensitive layer of the electrophotographic photoreceptor of the present invention is a charge generating substance,
A single-layer type or a function-separated type can be used by combining charge transport materials.

In the case of a single-layer structure, a photosensitive layer in which a charge generating substance and a charge transporting substance are dispersed in a binder is provided on a conductive substrate.

In the case of the function separation type, a charge generation layer containing a charge generation substance and a binder is formed on a substrate, and a charge transport layer containing a charge transport substance and a binder is formed thereon. In such a case, the charge generation layer and the charge transport layer may be stacked in reverse order. In the case of the function separation type, a charge transport material may be contained in the charge generation layer. In particular, in the case of the positive charging configuration, the sensitivity becomes good.

Further, an intermediate layer may be provided between the photosensitive layer and the substrate in order to improve the adhesive property and the charge blocking property. Further, a protective layer may be provided on the photosensitive layer in order to improve mechanical durability such as abrasion resistance. Examples of the binder used when forming the charge generation layer, the charge transport layer and the dispersion type photosensitive layer include polycarbonate (bisphenol A type, bisphenol Z type), polyester, methacrylic resin, acrylic resin, polyethylene, vinyl chloride, vinyl acetate, polystyrene, Phenolic resin, epoxy resin, polyurethane,
Vinylidene chloride, alkyd resin, silicone resin, polyvinyl carbazole, polyvinyl butyral, polyvinyl formal, polyarylate, polyacrylamide,
Polyamide, phenoxy resin and the like are used. These binders can be used alone or as a mixture of two or more.

When a photoreceptor is prepared using the above-described layer constitution and substance, there are preferable ranges for the film thickness and the ratio of the substance.

In the case of the negative charge type (lamination of the substrate / charge generation layer / charge transport layer), the ratio of the binder to the charge generation substance in the charge generation layer is preferably 0 to 400% by weight, and the film thickness is preferably 0.1 to 5 μm. In the charge transport layer, the ratio of the charge transport material to the binder is preferably 20 to 200% by weight, and the film thickness is preferably 5 to 50 μm.

In the case of the positive charge type (lamination of the substrate / charge transport layer / charge generation layer), in the charge transport layer, the ratio of the charge transport substance to the binder is 20 to 200% by weight, and the film thickness is 5 to 50 μm. Is preferred. The charge generation layer preferably contains a charge generation material in an amount of 10 to 500% by weight based on the binder.
Further, it is preferable that the charge generation layer contains a charge transporting substance. By including the charge transporting substance, it is effective in suppressing the residual potential and improving the sensitivity. In this case, the charge transporting material is preferably contained in an amount of 20 to 200% by weight based on the binder.

 The thickness is preferably 0.1 to 10 μm.

In the case of a single layer type, the ratio of the charge transporting substance and the charge generating substance to the binder is preferably 50 to 150% by weight and 10 to 50% by weight, respectively, and the film thickness is preferably 5 to 50 μm. .

The amount of the compound represented by the general formula (I) or (II) in the present invention may be 0.01 to 0.01 relative to the charge transporting material in the case of the function-separated type and when added to the charge transporting layer. Preferably it is ~ 5.0% by weight. When added to the charge generation layer, the content is preferably 0.1 to 20.0% by weight based on the charge generation substance. In the case of a single layer type, it is preferable to add 0.01 to 10.0% by weight to the charge transporting substance.

When the amount of the compound is less than the lower limit, the effect of increasing the durability cannot be obtained by addition, and when the amount is more than the upper limit, adverse effects such as a decrease in sensitivity are caused.

When the compound represented by the general formula (I) or the general formula (II) is a function-separated type photoreceptor, a charge generation layer, a charge transport layer,
It may be added to any layer. This is considered to be due to the fact that diffusion into other layers is actively performed by the coating liquid dispersion medium or the solvent during coating of the photosensitive layer.

The intermediate layer provided as necessary generally comprises a resin as a main component. However, considering that these resins are coated with a photosensitive layer with a solvent, the resin has a solvent resistance to a general organic solvent. It is desirable that the resin is high in resin. Examples of such a resin include water-soluble resins such as polyvinyl alcohol, casein and sodium polyacrylate, alcohol-soluble resins such as copolymerized nylon and methoxymethylated nylon, polyurethane, melamine resin, phenol resin, alkyd-melamine resin, and epoxy resin. Curable resins that form a three-dimensional network structure, such as resins, are exemplified.

In addition, titanium oxide, silica, alumina, zirconium oxide, etc.
Fine powder pigments of metal oxides, such as tin oxide and indium oxide, may be added.

The charge generation layer, the solvent or dispersion medium used in forming the charge transport layer, N, N'-dimethylformamide, acetone, methyl ethyl ketone, cyclohexanone, benzene, toluene, xylene, chloroform, 1,2-dichloroethane, Examples thereof include dichloromethane, monochlorobenzene, tetrahydrofuran, dioxane, methanol, ethanol, isopropanol, ethyl acetate, butyl acetate, and dimethyl sulfoxide.

As a method for forming the photosensitive layer, a method of dipping the substrate in a coating solution for the charge generation layer and the charge transport layer, a method of spraying the coating solution on the substrate, and the like are used.

As the substrate used in the electrophotographic photoreceptor of the present invention,
Aluminum, brass, stainless steel, nickel and other metal drums and sheets, polyethylene terephthalate, polypropylene, nylon, paper, etc.
A sheet-like or cylindrical substrate such as plastic or paper which has been subjected to a conductive treatment by depositing a metal such as nickel or applying a conductive substance such as titanium oxide, tin oxide or carbon black together with a suitable binder can be used.

〔effect〕

Since the electrophotographic photoreceptor of the present invention has the above-mentioned constitution, the photoreceptor characteristics such as chargeability are not deteriorated even by repeated use for a long period of time.

〔Example〕

 Hereinafter, the present invention will be described in detail with reference to examples.

Example 1 15 parts by weight of an alkyd resin [Beccosol 1307-60-EL (manufactured by Dainippon Ink and Chemicals)] and 10 parts by weight of melamine resin [Super Becamine G-821-60 (manufactured by Dainippon Ink and Chemicals)] Was dissolved in 150 parts by weight of methyl ethyl ketone, and 90 parts by weight of titanium oxide powder (Taipec CR-EL (manufactured by Ishihara Sangyo Co., Ltd.)) was added thereto and dispersed by a ball mill for 12 hours to prepare a coating solution for an intermediate layer.

This was applied to an aluminum plate having a thickness of 0.2 mm [A1080 (manufactured by Sumitomo Light Metal Co., Ltd.)] and dried at 130 ° C. for 20 minutes to form an intermediate layer having a thickness of 2 μm.

Next, a polyvinyl butyral resin [S-LEC BL-S
(Sekisui Chemical Co., Ltd.)] 4 parts by weight of cyclohexanone 15
0 parts by weight, which is represented by the following structural formula [a], 10 parts by weight of the trisazo pigment was added, and the mixture was dispersed in a ball mill for 48 hours. Further, 210 parts by weight of cyclohexanone was added and dispersed for 3 hours. This was taken out into a container and diluted with cyclohexanone so that the solid content was 1.5% by weight. The thus-obtained charge-generating layer coating solution is applied on the intermediate layer,
After drying at 130 ° C. for 20 minutes, a charge generation layer having a thickness of 0.2 μm was formed.

Next, a polycarbonate resin [Panlite K-1300
(Manufactured by Teijin Chemicals Limited)] 10 parts by weight, silicone oil [KF-50
(Shin-Etsu Chemical Co., Ltd.)] 0.002 parts by weight of methylene chloride 83
Parts by weight, and 7 parts by weight of the charge transport material represented by the structural formula [b]. 0.035 parts by weight of the compound of Exemplified Compound No. (I) -4 was added,
The solution was dissolved to prepare a charge transport layer coating solution. This was applied on the charge generation layer and dried at 100 ° C. for 20 minutes to form a charge transport layer having a thickness of 20 μm.

As described above, the electrophotographic photosensitive member of Example 1 was prepared.

Examples 2,3,4,5,6 In Example 1, instead of Exemplified Compound No. (I) -4, Exemplified Compound No. (I) -7 and No. (I) -1 respectively.
Example 2 was repeated in the same manner as in Example 1 except that the compounds No. (II) -1, No. (II) -7, and No. (II) -9 were used.
3,4,5,6 electrophotographic photoreceptors were prepared.

Comparative Example 1 An electrophotographic photosensitive member of Comparative Example 1 was prepared in the same manner as in Example 1, except that the compound of Exemplified Compound No. (I) -4 was not added.

Comparative Examples 2 to 4 Comparative Examples were performed in the same manner as in Example 1 except that 0.07 parts by weight of Comparative Compounds 1, 2, and 3 shown below were added in place of the compound of Exemplified Compound No. (I) -4. 2 to 4 electrophotographic photosensitive members were prepared.

Was prepared in the same manner as in Example 1 except that 0.07 parts by weight of was added to prepare electrophotographic photosensitive members of Comparative Examples 2, 3, and 4.

Example 7 3 parts by weight of an alcohol-soluble polyamide [CM-8000 (manufactured by Toray Industries, Inc.)] was heated and dissolved in 100 parts by weight of a mixed solvent of MeOH / n-BuOH = 8/2 to prepare a coating liquid for an intermediate layer. This is the thickness
It was applied to a 0.2 mm aluminum plate [A1080 (manufactured by Sumitomo Light Metal Co., Ltd.)] and dried at 120 ° C. for 10 minutes to form a 0.2 μm thick intermediate layer.

Next, 2 parts by weight of polyvinyl butyral (Eslec BL-S (manufactured by Sekisui Chemical Co., Ltd.)) was dissolved in 125 parts by weight of 1,2-dichloroethane, and prepared in the same manner as described in JP-B-49-4338. One part by weight of the X-type metal-free phthalocyanine thus obtained was added, and ultrasonic dispersion was performed using an ultrasonic dispersion machine. The thus-obtained charge-generating layer coating solution was applied onto the intermediate layer by a dip coating method, and dried at 100 ° C. for 10 minutes to a thickness of 0.5 μm.
Was formed.

Next, a charge transport layer coating solution was prepared in the same manner as in Example 1, applied on the charge generation layer, and dried at 100 ° C. for 20 minutes to form a charge transport layer having a thickness of 20 μm. A photoreceptor was made.

Examples 8, 9, 10, 11, 12 In Example 7, instead of Exemplified Compound No. (I) -4, Exemplified Compound No. (I) -7 and No. (I)-, respectively.
The electrophotographic photoreceptors of Examples 8, 9, 10, 11, and 12 were prepared in the same manner as in Example 7 except that the compounds of (12), (II) -1, (II) -7, and (II) -9 were used. Created.

Comparative Example 5 An electrophotographic photosensitive member of Comparative Example 5 was prepared in the same manner as in Example 7, except that the compound of Exemplified Compound No. (I) -4 was not added.

Comparative Examples 6 to 8 In the same manner as in Example 7, except that 0.07 part by weight of Comparative Compounds 1, 2, 3, described above was added in place of the compound of Exemplified Compound No. (I) -4, Electrophotographic photoreceptors of Comparative Examples 6 to 8 were prepared.

The electrostatic characteristics of the electrophotographic photosensitive member obtained as described above were measured by a dynamic method using SP-428 (manufactured by Kawaguchi Electric Works). First, after charging for 20 seconds at an applied voltage of −6 KV, exposure was performed for 30 seconds with a dark decay for 20 seconds and a surface illuminance of 6 lux.

The charging potential is the surface potential V ₂ (−V) 2 seconds after charging, and the sensitivity is the exposure amount E _1/10 (lux · sec) required for the surface potential to change from −800 V to −80 V after exposure. The potential was measured as the surface potential 30 seconds after exposure. After that, after 5 hours of irradiation with 5 lux of tungsten light having a color temperature of 2856 K and repeated charging fatigue at −6 KV for 3 hours, V ₂ (−V) and E were again obtained in the same manner as before.
_1/10 (lux · sec) and V ₃₀ (−V) were measured. Table 1 shows the measurement results.

Example 13 An intermediate layer was formed on an aluminum plate in the same manner as in Example 1, and the coating solution for the charge transport layer described in Example 1 was applied on the intermediate layer by a dip coating method and dried to a film thickness of 20 μm.
Was formed.

Next, 10 parts by weight of a polycarbonate resin (Panlite L-1250, manufactured by Teijin Chemicals Ltd.) was dissolved in a mixed solvent of 75 parts by weight of 1,2-dichloroethane and 75 parts by weight of 1,1,2-trichloroethane, and the above-mentioned structure was dissolved therein. 3 parts by weight of the trisazo pigment of the formula [a] was added, and the mixture was dispersed in a ball mill for 48 hours. Further, 7 parts by weight of the charge transporting substance represented by the structural formula [b], 150 parts by weight of 1,2-dichloroethane, and 150 parts by weight of 1,1,2-trichloroethane were added to this dispersion, and dispersed and dissolved in a ball mill for 24 hours. Then, a coating solution for a charge generation layer was prepared. This was spray-coated on the charge transporting layer and dried to provide a charge generating layer having a thickness of 3 μm, thereby preparing an electrophotographic photosensitive member.

Examples 14, 15, 16, 17 In Example 13, the compound of Example Compound No. (I) -4 contained in the charge transporting layer was replaced with No. (I) -12,
Example except that compounds of (II) -1 and (II) -19 were used
In the same manner as in Example 13, the electrophotographic photosensitive members of Examples 14, 15, 16 and 17 were produced.

Comparative Example 9 An electrophotographic photosensitive member of Comparative Example 9 was prepared in the same manner as in Example 13, except that the compound of Exemplified Compound No. (I) -4 contained in the charge transporting layer was omitted.

Comparative Examples 10 and 11 Same as Example 13 except that 0.07 parts by weight of Comparative Compounds 1 and 3 were added in place of the compound of Exemplified Compound No. (I) -4 contained in the charge transporting layer. Thus, electrophotographic photoreceptors of Comparative Examples 10 and 11 were prepared.

The electrostatic characteristics of Examples 13, 14, 15, 16, and 17 and Comparative Examples 9, 10, and 11 obtained as described above were obtained by setting the applied voltage of charging to +6 KV.
The evaluation was performed in the same manner as in the evaluation of the electrophotographic photosensitive member of Example 1, except that the evaluation of the potential was made positive.

 Table 2 shows the evaluation results.

Claims (1)

(57) [Claims] 1. An electrophotographic photosensitive member having a photosensitive layer containing at least a charge-generating substance and a charge-transporting substance on a conductive substrate, wherein the photosensitive layer has the following general formula (I) or (II): An electrophotographic photoreceptor comprising at least one of the compounds shown below. (Wherein, R _{1 to} R ₄ each represent a hydrogen atom, a halogen atom, a hydroxy group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted Represents an alkoxy group, a substituted or unsubstituted aryloxy group, a substituted amino group, an imino group, a heterocyclic group, a substituted or unsubstituted alkylthio group, or an arylthio group, a sulfoxide group, a sulfonyl group, an acyl group, or an azo group. (Wherein, R _{1 to} R ₈ each represent a hydrogen atom, a halogen atom, a hydroxy group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted Alkoxy group, substituted or unsubstituted aryloxy group, substituted amino group, imino group, heterocyclic group, substituted or unsubstituted alkylthio group, or arylthio group, sulfoxide group, sulfonyl group, acyl group, azo group, carboxyl group or carbonyl Represents a group.)