JPH06105360B2 - Electrophotographic photoreceptor - Google Patents

Description

The present invention relates to an electrophotographic photoreceptor, and more particularly to a novel electrophotographic photoreceptor having a photosensitive layer containing an organic photoconductive compound as a main component.

[Prior art]

Conventionally, as an electrophotographic photoreceptor, an inorganic photoreceptor having a photosensitive layer containing an inorganic photoconductive compound such as selenium, zinc oxide, cadmium sulfide and silicon as a main component has been widely used. However, these are not always satisfactory in terms of sensitivity, thermal stability, moisture resistance, durability and the like. For example, when selenium crystallizes, the characteristics as an electrophotographic photosensitive member deteriorate, and therefore it is difficult to manufacture, and selenium crystallizes due to heat, fingerprints, etc., and the performance as an electrophotographic photosensitive member deteriorates. In addition, cadmium sulfide and zinc oxide have problems in moisture resistance and durability.

In order to overcome the drawbacks of these inorganic photoconductors, research and development of organic photoconductors having a photosensitive layer containing various organic photoconductive compounds as main components have been actively conducted in recent years.

For example, Japanese Examined Patent Publication (Kokoku) No. 50-10496 describes an organic photoreceptor comprising a photosensitive layer containing poly-N-vinylcarbazole and 2,4,7-trinitro-9-fluorenone. However, this photoreceptor is not always satisfactory in sensitivity and durability.

In order to improve such a defect, attempts have been made to develop a high-performance organic photoconductor in which the carrier generation function and the carrier transport function are shared by different substances. Such a so-called function-separated type photoreceptor has been extensively researched because each material can be selected from a wide range and a photoreceptor having arbitrary performance can be prepared relatively easily.

As a result, various azo compounds have been developed and put into practical use as carrier generating substances. On the other hand, as for carrier transport materials, see, for example, JP-A-51-94829 and JP-A-52-72231.
No. 53, No. 53-27033, No. 55-52063, No. 58-65440, No. 58
-A wide variety of substances have been proposed as disclosed in No. 198425.

[Problems to be solved by the invention]

Some electrophotographic photoreceptors using the carrier transporting material as described above have relatively excellent electrophotographic performance, but have poor durability against light, ozone, or electrical load, and have poor performance after repeated use. Since it is stable and causes deterioration, etc., it does not sufficiently satisfy practical requirements, and it is desired to develop a carrier-transporting substance having an excellent carrier-transporting function and exhibiting stable performance for long-term use. Was there.

Further, in recent years, the demand for mounting an organic photoconductor on an electrophotographic copying machine capable of copying at higher speed has been increasing more and more, and development of a photoconductor having higher sensitivity and higher durability has been desired.

The present invention has been made to solve these problems and provide a photoreceptor having extremely high sensitivity and high durability.

[Means for solving problems]

The above-mentioned problem is that a photosensitive layer comprising a conductive support and a layer containing at least one hydrazone compound represented by the following general formula [I] or general formula [II] as a carrier transporting substance is provided. It has been solved by an electrophotographic photoreceptor having.

General formula [I] General formula (II) In the formula, Ar ₁ , Ar ₂ , Ar ₃ , Ar ₄ , Ar ₅ and Ar ₆ represent a substituted or unsubstituted arylene group, preferably a substituted or unsubstituted phenyl group or a substituted or unsubstituted naphthyl group. , R ₁ , R ₂ , R ₃ , R ₄ ,
R ₅ , R ₆ , R ₇ , R ₈ , R ₉ , R ₁₀ , R ₁₁ , R ₁₂ , R ₁₃ , R ₁₄ , R ₁₅ , R ₁₆ , R ₁₇ ,
R ₁₈ , R ₁₉ , R ₂₀ , R ₂₁ , R ₂₂ , R ₂₃ , R ₂₄ , R ₂₅ , R ₂₆ , R ₂₇ , R ₂₈ , R ₂₉ , R
₃₀ , R ₃₁ , R ₃₂ , R ₃₃ , R ₃₄ , R ₃₅ , R ₃₆ , R ₃₇ , R ₃₈ , R ₃₉ are hydrogen atoms,
Represents a halogen atom, an alkyl group, and an alkoxy group. Here, the alkyl group and the alkoxy group may have a substituent. That is, in the present invention, the carrier transporting ability of the compound represented by the general formula [I] is utilized, and the carrier transporting of a so-called function-separated electrophotographic photosensitive member is performed in which the carrier generation and the carrier transport are performed by separate substances. When used as a substance, it has excellent coating physical properties, excellent electrophotographic properties such as charge retention, sensitivity, residual potential, and little fatigue deterioration even after repeated use, and also with respect to heat, ozone, or light. It is possible to produce an electrophotographic photosensitive member that can exhibit stable characteristics.

Further, the carrier transporting material used in the present invention can be used alone or in combination of two or more kinds from the compounds represented by the above general formula [I] or general formula [II]. May be used in combination.

Specific examples of the carrier transporting material represented by the general formula [I] or the general formula [II] effective in the present invention include those having the following structural formulas. The substance is not limited.

Exemplified compound [I] Exemplified compound [II] The carrier transport material is easily synthesized by a known synthesis method. For example, JP-A-57-64244 and 57-67940
The method described in the issue is referred to.

Synthesis Example (Synthesis of Exemplified Compound (I-1)) 22.2 g (0.15 mol) of the hydrazine ( 1 ) and 16.5 g (0.05 mol) of the aldehyde ( 2 ) were dissolved in 500 ml of ethanol, 10 ml of acetic acid was added, and the mixture was heated under reflux for 5 hours. The crystals that were left standing to cool were collected by filtration, washed with ethanol, and then recrystallized from a mixed solvent of ethanol and methyl ethyl ketone.

Yield 30.3 g (84.2%) It was confirmed that the target compound was synthesized by observing a molecular ion peak of 719 in the FD-mass spectrum.

Next, as the carrier generating material suitable for the present invention, azo pigments are preferable, but generally, both inorganic pigments and organic pigments are used as long as they absorb visible light to infrared light and generate free carriers. be able to. For example, in addition to inorganic pigments such as amorphous selenium, trigonal selenium, selenium-arsenic alloy, selenium-tellurium alloy, and cadmium sulfide, organic pigments represented by the following representative examples may be used.

(1) Monoazo pigment, bisazo pigment, trisazo pigment,
Azo pigments such as metal complex salt azo pigments (2) Perylene-based pigments such as perylene anhydride, perylene imide (3) Anthraquinone derivatives, anthanthrone derivatives, dibenzpyrenequinone derivatives, pyranthrone derivatives, violanthrone derivatives and isoviolanthrone Derivatives and other polycyclic quinone pigments (4) Indigoid pigments such as indigo derivatives and thioindigo derivatives (5) Phthalocyanine pigments such as metal phthalocyanines and metal-free phthalocyanines (6) Diphenylmethane pigments, triphenylmethane pigments, xanthene pigments and acridine pigments (7) Aquinone pigment such as azine pigment, oxazine pigment and thiazine pigment (8) Methine pigment such as cyanine pigment and azomethine pigment (9) Quinoline pigment (10) Benzoquine And naphthoquinone-based pigments (11) naphthalimide-based pigments (12) perinone-based pigments such as bisbenzimidazole derivatives The carrier-transporting substances used in the present invention have no ability to form a film by themselves, and therefore are combined with various binders. To form a photosensitive layer.

As the binder used in the carrier generation layer and the carrier transport layer, any binder can be used, but it is preferable to use a hydrophobic electrically insulating film-forming polymer. Examples of such high molecular weight polymers include, but are not limited to, the followings.

(1) Polycarbonate (2) Polyester (3) Methacrylic resin (4) Acrylic resin (5) Polyvinyl chloride (6) Polyvinylidene chloride (7) Polystyrene (8) Polyvinyl acetate (9) Styrene copolymer resin (for example, styrene -Butadiene copolymer, styrene-methyl methacrylate copolymer, etc.) (10) Acrylonitrile-based copolymer resin (for example, vinylidene chloride-acrylonitrile copolymer, etc.) (11) Vinyl chloride-vinyl acetate copolymer (12) Vinyl chloride-vinyl acetate-maleic anhydride copolymer (13) Silicon resin (14) Silicon-alkyd resin (15) Phenolic resin (for example, phenol-formaldehyde resin, cresol-formaldehyde resin,
Etc.) (16) Styrene-alkyd resin (17) Poly-N-vinylcarbazole (18) Polyvinyl butyral (19) Polyvinyl formal (20) Polyhydroxystyrene These binders may be used alone or as a mixture of two or more kinds. Can be used.

As shown in FIGS. 1 and 2, the photoreceptor of the present invention comprises a carrier generating layer 2 containing a carrier generating substance as a main component and a compound of the present invention as a main component of a carrier transporting substance on a conductive support 1. A photosensitive layer 4 composed of a laminate with the carrier transport layer 3 contained therein is provided. As shown in FIGS. 3 and 4, the photosensitive layer 4 may be provided via an intermediate layer 5 provided on the conductive support 1. In this way, when the photosensitive layer 4 has a two-layer structure, an electrophotographic photosensitive member having the best electrophotographic characteristics can be obtained. Further, in the present invention, as shown in FIGS. 5 and 6, the photosensitive layer 4 formed by dispersing the fine particle carrier generating substance 7 in the layer 6 containing the carrier transporting substance as a main component is used as the conductive support. It may be provided directly on the intermediate layer 1 or via the intermediate layer 5.

Further, a protective layer 8 may be provided on the photosensitive layer 4 if necessary.

Here, when the photosensitive layer 4 has a two-layer structure, which of the carrier generation layer 2 and the carrier transport layer 3 is the upper layer is determined depending on whether the charging polarity is positive or negative. That is, when the negative charge type photosensitive layer is used, the carrier transport layer 3
Is an upper layer, because the carrier-transporting substance in the carrier-transporting layer 3 is a substance having a high hole-transporting ability.

In addition, the carrier generation layer 2 constituting the photosensitive layer 4 having a two-layer structure
Can be formed by the following method directly on the conductive support 1 or the carrier transport layer 3, or on the intermediate layer such as an adhesive layer or a barrier layer, if necessary.

(1) Vacuum evaporation method (2) Method of applying a solution in which a carrier generating substance is dissolved in an appropriate solvent (3) The carrier generating substance is made into fine particles in a dispersion medium by a ball mill, a sand grinder or the like, and if necessary,
A method of applying a dispersion obtained by mixing and dispersing with a binder.

The thickness of the carrier generating layer 2 thus formed is
The thickness is preferably 0.01 μm to 5 μm, more preferably 0.05 μm to 3 μm.

The thickness of the carrier transport layer 3 may be changed as necessary, but is usually preferably 5 μm to 30 μm. The composition ratio in the carrier transporting layer 3 is preferably 0.8 to 10 parts by weight of the binder with respect to 1 part by weight of the carrier transporting substance of the present invention, but the photosensitive layer 4 in which the fine particle carrier generating substance is dispersed. Carrier-forming substance 1
It is preferable to use the binder in an amount of 5 parts by weight or less based on parts by weight.

Further, when the carrier generation layer is constituted as a dispersion type with a binder, it is preferable to use the binder in an amount of 5 parts by weight or less with respect to 1 part by weight of the carrier generating substance.

The layer structure of the photoreceptor of the present invention includes a layered structure and a single layer structure as described above, and any one of a carrier transport layer serving as a surface layer, a carrier generation layer, a single layer photosensitive layer or a protective layer, or a plurality of layers. The layer may contain one or more electron-accepting substances for the purpose of improving sensitivity, residual potential or reducing fatigue during repeated use.

The intermediate layer functions as an adhesive layer or a barrier layer, and in addition to the binder resin, polyvinyl alcohol, ethyl cellulose, carboxymethyl cellulose, casein, etc. are used.

As the electroconductive support 1 used in the construction of the electrophotographic photosensitive member of the present invention, the following are mainly used, but not limited thereto.

(1) Aluminum plates, metal plates such as stainless plates, and drum-shaped ones.

(2) A thin metal layer of aluminum, palladium, gold or the like provided on a support such as paper or a plastic film by laminating or vapor deposition.

(3) A layer of a conductive compound such as a conductive polymer, indium oxide or tin oxide is applied or vapor-deposited on a support such as paper or a plastic film.

The formation of constituent layers such as the carrier transport layer and the carrier generation layer according to the present invention includes vacuum deposition, sputtering, and CVD.
A vapor phase deposition method such as or a coating method such as dipping, spraying, blade, or roll method may be used.

The photoconductor of the present invention has the above-mentioned structure and is excellent in charging property, sensitivity property, and image forming property, as will be apparent from the examples described later. In particular, even when it is subjected to a repetitive transfer type electrophotographic method, it has little fatigue deterioration and excellent durability.

(Examples) Examples of the present invention will be specifically described below, but the embodiments of the present invention are not limited thereto.

Example 1 A vinyl chloride-vinyl acetate-maleic anhydride copolymer "S-REC MF-10" (manufactured by Sekisui Chemical Co., Ltd.) was formed on a conductive support obtained by vapor-depositing aluminum on a polyester film.
An intermediate layer having a thickness of 0.1 μm.

On top of that, 1 part by weight of dibromoanthanthrone "Monolight Red 2Y" (manufactured by ICI) represented by the following structural formula and 0.5 part by weight of polycarbonate resin "Panlite L-1250" (manufactured by Teijin Kasei) A carrier generating layer was formed by mixing 100 parts by weight of 2-dichloroethane and dispersing with a ball mill for 24 hours so that the film thickness after drying was 1 μm.

In addition, the exemplary compound (I-1) as a carrier transport substance
4.0 parts by weight and polycarbonate resin “Panlite L-125
0 "10 parts by weight and 80 parts by weight of 1,2-dichloroethane are dissolved in the solution so that the film thickness after drying is 16 μm to form a carrier transporting layer to form the electrophotographic photoreceptor of the present invention. did.

About this electrophotographic photoreceptor Electrostatic copying paper test equipment "SP-4
28 ”(manufactured by Kawaguchi Denki Seisakusho) was used to measure electrophotographic characteristics by a dynamic method.

That is, the surface potential V _A when the surface of the photosensitive layer of the photosensitive member was charged with a charging voltage of −6 kV for 5 seconds, and then the illuminance of the tungsten lamp light on the surface of the photosensitive member was 3.5 lux · sec. The exposure dose (sensitivity) required to attenuate the surface potential from −600 V to −100 V by irradiation, ▲ E ⁶⁰⁰ ₁₀₀ ▼, and the surface potential (residual potential) V _R after irradiation with an exposure dose of 35 lux · sec, respectively. I asked.

The same measurement was repeated 100 times. The result is first
As shown in the table

Comparative Example (1) A comparative photoconductor was prepared in the same manner as in Example 1 except that the hydrazone derivative represented by the following structural formula was used as the carrier-transporting substance, and the same measurement was performed.

The results are as shown in Table 1.

As is clear from the above results, the electrophotographic photosensitive member of the present invention of Example 1 is significantly superior to the photosensitive member of Comparative Example (1) in sensitivity, residual potential characteristics and stability of repetition.

Examples 2 to 10 Exemplified compounds (I-2) and (I-
6), (I-8), (I-10), (I-14), (II-2),
An electrophotographic photoreceptor of the present invention was prepared in the same manner as in Example 1 except that (II-5), (II-8) and (II-14) were used. These electrophotographic photosensitive members were measured in the same manner as in Example 1. The results are shown in Table 2.

Example 11 1 part by weight of a bisazo pigment represented by the following structural formula as a carrier-generating substance and a polymethylmethacrylate resin "Dynar BR-80" (Mitsubishi Rayon) on a conductive support formed by laminating an aluminum foil on a polyester film. 0.5 parts by weight) and a liquid dispersed for 4 hours by a sand grinder were applied so that the film thickness after drying would be 0.4 μm to form a carrier generation layer.

Next, exemplary compound (I-3) as a carrier transporting substance 4.
0 parts by weight and polycarbonate resin "Panlite K-1300"
(Manufactured by Teijin Kasei) 10 parts by weight and 1,2-dichloroethane 100
A solution dissolved in parts by weight was applied so as to have a film thickness after drying of 15 μm to form a carrier transport layer, thereby preparing an electrophotographic photoreceptor of the present invention.

When this electrophotographic photosensitive member was measured in the same manner as in Example 1, the results shown in Table 3 were obtained.

Comparative Example (2) A comparative photoconductor (2) was prepared in the same manner as in Example 11 except that the hydrazone derivative represented by the following structural formula was used as the carrier-transporting substance. When this comparative photoconductor was measured in the same manner as in Example 1, the results shown in Table 3 were obtained.

As is clear from the above results, the electrophotographic photosensitive member of the present invention of Example 11 is remarkably excellent in sensitivity, residual potential and stability of repetition as compared with the comparative photosensitive member.

Example 12 Vinyl chloride-vinyl acetate-maleic anhydride copolymer "S-REC MF-10" having a thickness of 0.1 .mu.m on a conductive support obtained by vapor-depositing aluminum on a polyester film.
Was provided.

1 part by weight of a bisazo pigment represented by the following structural formula as a carrier-generating substance and 0.5 part by weight of a polycarbonate resin "Panlite K-1300" (manufactured by Teijin Kasei Co., Ltd.) were added to 100 parts by weight of tetrahydrofuran and dispersed by a ball mill for 24 hours. The obtained liquid was applied so that the film thickness after drying would be 0.4 μm to form a carrier generation layer.

Next, an exemplary compound (II
-9) 4.0 parts by weight of polycarbonate resin "Panlite K-1"
A liquid obtained by dissolving 10 parts by weight of "300" in 100 parts by weight of tetrahydrofuran was applied so that the film thickness after drying would be 17 μm to prepare an electrophotographic photoreceptor of the present invention.

When this electrophotographic photosensitive member was measured in the same manner as in Example 1, the results shown in Table 4 were obtained.

Example 13 An electrophotographic photoreceptor of the present invention was prepared in the same manner as in Example 12, except that the bisazo pigment represented by the structural formula below was used as the carrier-generating substance.

When this electrophotographic photosensitive member was measured in the same manner as in Example 1, the results shown in Table 4 were obtained.

Example 14 Vinyl chloride-vinyl acetate-maleic anhydride copolymer "S-REC MF-1" was placed on a cylindrical aluminum drum having a diameter of 80 mm.
A 0.1 μm thick intermediate layer of 0 ”was applied by dipping.

Dibromoanth Anthron "Monolight Red on it
1 part by weight of 2Y and polycarbonate resin "Panlite L-12"
1 part by weight of 50 "was mixed with 100 parts by weight of 1,2-dichloroethane, and the solution dispersed by a ball mill for 24 hours was applied by a dipping method to form a carrier generation layer having a film thickness of 1 μm.

Furthermore, an exemplary compound (I-
1) 7.5 parts by weight and polycarbonate resin "Z-200" (manufactured by Mitsubishi Gas Chemical Company) represented by the following structural formula A solution of 10 parts by weight and 80 parts by weight of 1,2-dichloroethane was applied by the same dipping method to form a carrier transporting layer having a film thickness of 17 μm to prepare an electrophotographic photoreceptor of the present invention.

This electrophotographic photoconductor is an electrophotographic copying machine "U-Bix 1550MR"
When the image was copied onto the original, a copy image that was true to the original image, high in contrast, and excellent in gradation was obtained. Even if this was repeated 50,000 times, a copied image similar to the initial one was obtained.

Comparative Example (3) A comparative photoconductor (3) was prepared in the same manner as in Example 14 except that the hydrazone derivative represented by the following structural formula was used as the carrier-transporting substance.

When an image was copied on this comparative photoconductor in the same manner as in Example 14, a good copy image was obtained in the initial stage as in Example 14, but fogging gradually became noticeable from around 15,000 copies and 20,000 copies were made. Then, only images with a lot of fog and lowered contrast were obtained.

Example 15 A vinyl chloride-vinyl acetate-maleic anhydride copolymer "ESREC MF-10" having a thickness of 0.1 on a conductive support obtained by laminating an aluminum foil on a polyester film.
An intermediate layer of μm was provided.

Next, an exemplary compound (II
-13) 4.0 parts by weight of polycarbonate resin "Panlite L-
A solution prepared by dissolving 10 parts by weight of 1250 "in 80 parts by weight of 1,2-dichloroethane was applied so that the film thickness after drying would be 15 µm to form a carrier transport layer.

Furthermore, a carrier generating substance 1 represented by the following structural formula
Examples of the compound (II-1
3) 1.5 parts by weight of polycarbonate resin "Panlite L-12"
50 '' 2 parts by weight was added to 100 parts by weight of 1,2-dichloroethane, and the solution dispersed by a ball mill was applied for 24 hours, and the film thickness after drying was 3
An electrophotographic photoreceptor of the present invention was prepared by providing a carrier generation layer having a thickness of μm.

This electrophotographic photosensitive member was measured in the same manner as in Example 1 except that the charged voltage was changed to +6 kV, and the results shown in Table 5 were obtained.

Comparative Example (4) A comparative photoconductor was prepared in the same manner as in Example 15 except that the hydrazone derivative represented by the following structural formula was used as the carrier transport material.

When this comparative photoreceptor was measured in the same manner as in Example 15, the results shown in Table 5 were obtained.

As is clear from the above results, the electrophotographic photosensitive member of the present invention has extremely excellent characteristics in sensitivity and stability of repetition as compared with the comparative photosensitive member.

Example 16 A 0.1 μm-thick intermediate layer made of a vinyl chloride-vinyl acetate-maleic anhydride copolymer “S-REC MF-10” was provided on a polyester film on which aluminum was vapor-deposited.

1,2-dichloroethane 100 was added with 1.0 part by weight of a bisazo pigment represented by the following structural formula as a carrier-generating substance and 0.5 part by weight of a polycarbonate resin "Panlite L-1250".
In addition to the parts by weight, a liquid dispersed by a ball mill for 24 hours was applied so that the film thickness after drying would be 0.3 μm to form a carrier generation layer.

Furthermore, as an example of the carrier transport substance, the exemplified compound (II-1
5) 4.0 parts by weight of polycarbonate resin "Panlite K-13"
A solution of 100 parts by weight of "00" dissolved in 100 parts by weight of 1,2-dichloroethane was applied so that the film thickness after drying was 16 μm to form a carrier transport layer, and an electrophotographic photoreceptor of the present invention was prepared. .

When this electrophotographic photosensitive member was measured in the same manner as in Example 1, the results shown in Table 6 were obtained.

Example 17 1 part by weight of a carrier-generating substance represented by the following structural formula and a polyester resin "Vylon 200" were formed on a polyester film on which aluminum was vapor deposited. (Manufactured by Toyobo Co., Ltd.) 0.5 part by weight and 1,2-dichloroethane 10
In addition to 0 parts by weight, a liquid dispersed by a ball mill for 24 hours was applied to form a carrier generation layer having a thickness of 0.5 μm.

Furthermore, an exemplary compound (I-
4) 4.0 parts by weight and the following structural formula The present invention was prepared by applying a solution prepared by dissolving 3.5 parts by weight of a hydrazone derivative (A) and 10 parts by weight of a polycarbonate resin “Panlite K-1300” in 100 parts by weight of 1,2-dichloroethane to form a carrier transport layer having a thickness of 15 μm. An electrophotographic photoconductor of was prepared.

When this electrophotographic photosensitive member was measured in the same manner as in Example 1, the results shown in Table 7 were obtained.

Comparative Example (5) A comparative photoconductor (5) was prepared in the same manner as in Example 17, except that 7.5 parts by weight of the hydrazone derivative (A) used in Example 17 was used as the carrier-transporting substance.

When this comparative photoconductor was measured in the same manner as in Example 1, the results shown in Table 7 were obtained.

As is clear from the above results, the electrophotographic photosensitive member of the present invention is remarkably superior to the comparative photosensitive member in sensitivity, residual potential characteristics and repeating stability.

[Brief description of drawings]

1 to 6 are cross-sectional views showing examples of the mechanical constitution of the photoconductor of the present invention. 1 ... Conductive support 2 ... Carrier generation layer 3 ... Carrier transport layer 4 ... Photosensitive layer 5 ... Intermediate layer 6 ... Layer containing carrier transport material 7 ... Carrier generation material

Claims (1)

[Claims] 1. An electrophotographic photoreceptor comprising a conductive support and a photosensitive layer containing at least one hydrazone compound represented by the following general formula [I] or general formula [II]. General formula [I] General formula (II) [Wherein Ar ₁ , Ar ₂ , Ar ₃ , Ar ₄ , Ar ₅ and Ar ₆ represent a substituted or unsubstituted arylene group, and R ₁ , R ₂ , R ₃ , R ₄ , R ₅ and R ₆ , R ₇ ,, R ₈ , R ₉ , R ₁₀ , R
₁₁ , R ₁₂ , R ₁₃ , R ₁₄ , R ₁₅ , R ₁₆ , R ₁₇ , R ₁₈ , R ₁₉ , R ₂₀ , R ₂₁ , R ₂₂ ,
R ₂₃ , R ₂₄ , R ₂₅ , R ₂₆ , R ₂₇ , R ₂₈ , R ₂₉ , R ₃₀ , R ₃₁ , R ₃₂ , R ₃₃ , R ₃₄ , R
₃₅ , R ₃₆ , R ₃₇ , R ₃₈ and R ₃₉ represent a hydrogen atom, a halogen atom, an alkyl group and an alkoxy group. Here, the alkyl group and the alkoxy group may have a substituent. ]