JP2610502B2 - Electrophotographic photoreceptor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an electrophotographic photoreceptor, and more particularly, to an electrophotographic photoreceptor having a low-molecular organic photoconductor that provides improved electrophotographic properties.

[Prior Art] Conventionally, various organic photoconductive polymers such as polyvinyl carbazole have been proposed as photoconductive materials used in an electrophotographic photoreceptor. However, these polymers are compared with inorganic photoconductive materials. Despite being excellent in film-forming properties and lightness, it has been difficult to put it to practical use until now because sufficient film-forming properties have not yet been obtained, and sensitivity and durability have been high. And inferior to inorganic photoconductive materials in stability due to environmental changes.

Further, hydrazone compounds described in U.S. Pat.No. 4,150,087, etc., triarylpyrazolin compounds described in U.S. Pat.No. 3,838,781, etc., JP-A-51-94828, JP-A-51-94829. For example, low-molecular organic photoconductive materials such as a 9-styrylanthracene compound described in US Pat. Such a low molecular organic photoconductive material,
By properly selecting the binder to be used, the drawback of the film forming property which has been a problem in the field of the organic photoconductive polymer can be solved, but it cannot be said to be sufficient in terms of sensitivity.

For these reasons, a laminated structure in which the photosensitive layer is functionally separated into a charge generation layer and a charge transport layer has recently been proposed. The electrophotographic photoreceptor having this laminated structure as a photosensitive layer can be improved in terms of sensitivity to visible light, charge retention, surface strength, and the like.

Such an electrophotographic photoreceptor is disclosed, for example, in US Pat.
Nos. 851 and 3871882.

However, a conventional electrophotographic photoreceptor using a low-molecular organic photoconductor for the charge transport layer is not always sufficient in sensitivity and characteristics, and when repeatedly charged and exposed, a light portion potential and a dark portion potential are obtained. There is a point that the fluctuations of the data need to be greatly improved.

[Problems to be Solved by the Invention] An object of the present invention is to provide a novel organic photoconductor, and to provide an electrophotographic photoreceptor which has solved the above-mentioned disadvantages or disadvantages.

[Means for Solving the Problems and Action] The present invention provides an electrophotographic photosensitive member having a photosensitive layer laminated on a conductive support, wherein the photosensitive layer contains a compound represented by the following general formula. It is composed of a photoreceptor.

General formula In the formula, Ar ₁ and Ar ₂ represent an aryl group or a heterocyclic group which may have a substituent, and at least one of Ar ₁ and Ar ₂ is (Wherein, R ₂ and R ₃ represent a hydrogen atom, an alkyl group which may have a substituent, an aryl group, an aralkyl group or a heterocyclic group, and R ₂ and R ₃ are a 5- to 7-membered ring together with a nitrogen atom. R ₁ represents a hydrogen atom, an alkyl group, an alkoxy group, a halogen atom, a cyano group, an acyl group or a trifluoromethyl group.

However, only Ar ₁ When Ar ₁ is a phenyl group, and at the position para to the central benzene ring in the above general formula Never have.

Specifically, in Ar ₁ and Ar _2, the aryl group of benzene, naphthalene, groups such as anthracene, as the heterocyclic group, pyrrole, oxazole, pyridine, quinoline, include groups such as carbazole, also, R ₁ In the alkyl group, methyl, ethyl, propyl and the like, aralkyl group as benzyl, phenethyl and the like, alkoxy group as methoxy, ethoxy and the like, halogen atom as fluorine atom, chlorine atom,
Groups such as a bromine atom and acyl groups include groups such as acetyl and butyryl.

Further, as a substituent of the above group, for example, a fluorine atom, a chlorine atom, a halogen atom such as a bromine atom, methyl,
Examples include an alkyl group such as ethyl and propyl; an alkoxy group such as methoxy and ethoxy; an aryl group such as benzene, naphthalene and anthracene; and a heterocyclic group such as pyrrole, pyridine and carbazole.

In R ₂ and R ₃ , an alkyl group is a group such as methyl, ethyl, or propyl; an aryl group is a group such as benzene, naphthalene or anthracene; an aralkyl group is a group such as benzyl or phenethyl; or a heterocyclic group. Represents a group such as pyrrole, oxazole, pyridine, quinoline or carbazole, and examples of the 5- to 7-membered ring include an acridine ring and a carbazole ring.

Examples of the substituent which the group may have include an alkyl group such as methyl, ethyl and propyl; an aryl group such as benzene, naphthalene and anthracene; a heterocyclic group such as pyrrole, pyridine and carbazole; and an aralkyl such as benzyl and phenethyl. Examples include a group, an alkoxy group such as methoxy and ethoxy, and a halogen atom such as fluorine, chlorine and bromine, and the above group may have a substituent.

However, in the present invention, only Ar ₁ is When Ar ₁ is a phenyl group, and at the para position with respect to the central benzene ring in the above general formula Never have.

Hereinafter, typical examples of the compound represented by the general formula will be listed.

Synthesis Example (Synthesis of Compound Example (8)) Obtained by nitrating o-tert-phenyl by a known method and then reducing it. 4.00 g (15.30 mmol) in anhydrous tetrahydrofuran 50 ml
And 3.70 g (92.20 mmol) of oily sodium hydride (60% content) were added slowly with stirring at room temperature. After the addition was completed, the mixture was further stirred at room temperature for 15 minutes, and then 19.71 g (138.81 mmol) of methyl iodide was slowly added dropwise.
Heating and stirring were performed for 3 hours. After completion of the reaction, the reaction mixture was poured into water, and the precipitated crystals were washed with methanol and further purified by recrystallization to obtain 3.60 g of the desired compound.

Elemental analysis Calculated value (%) Actual measured value (%) C 83.50 83.40 H 7.65 7.70 N 8.85 8.82 Compounds other than the synthesis examples are generally synthesized in the same manner.

In a preferred embodiment of the present invention, a compound represented by the above general formula is used as a charge transporting material of an electrophotographic photosensitive member in which a photosensitive layer is functionally separated into a charge generating layer and a charge transporting layer.

The charge transport layer in the invention is preferably formed by applying and drying a solution in which the compound represented by the general formula and the binder are dissolved in an applicable solvent.

Examples of the binder used here include polyarylate, polysulfone, polyamide, acrylic resin, acrylonitrile resin, methacrylic resin, vinyl chloride resin, vinyl acetate resin, phenolic resin, epoxy resin, polyester, alkyd resin, polycarbonate, polyurethane or copolyester. Polymers such as styrene-butadiene copolymer, styrene-acrylonitrile copolymer, styrene-maleic acid copolymer and the like can be mentioned.

In addition to such insulating polymers, organic photoconductive polymers such as polyvinyl carbazole, polyvinyl anthracene, and polyvinyl pyrene can be used.

The mixing ratio of the binder and the charge transport material of the present invention is as follows:
It is preferable that the charge transporting material is 10 to 500 parts by weight per 100 parts by weight of the binder.

The charge transport layer is electrically connected to the charge generation layer described below, and has a function of receiving charge carriers injected from the charge generation layer in the presence of an electric field and transporting these charge carriers to the surface. doing. In this case, the charge transport layer may be laminated on the charge generation layer, or may be laminated thereunder. However, the charge transport layer is preferably laminated on the charge generation layer.

Since the charge transport layer has a limit for transporting charge carriers, it cannot be made thicker than necessary.
Generally, it is 5 to 40 μm, but a preferable range is 10 to 30 μm.
μm.

The organic solvent used for forming such a charge transport layer preferably varies depending on the type of the binder used, or is selected from those which do not dissolve the charge generation layer or the undercoat layer described below. Specific organic solvents include methanol, ethanol, alcohols such as isopropanol, acetone, methyl ethyl ketone, ketones such as cyclohexane, N, N-dimethylformamide, amides such as N, N-dimethylacetamide, dimethyl sulfoxide and the like. Sulfoxides, tetrahydrofuran, dioxane, ethers such as ethylene glycol monomethyl ether, methyl acetate, esters such as ethyl acetate,
Aliphatic halogenated hydrocarbons such as methylene chloride, dichloroethylene, carbon tetrachloride, and trichloroethylene, or aromatic compounds such as benzene, toluene, xylene, chlorobenzene, and dichlorobenzene can be used.

The coating can be performed using a coating method such as a dip coating method, a spray coating method, a spinner coating method, a heat coating method, a Meyer bar coating method, a blade coating method, a roller coating method, and a curtain coating method. Drying is preferably performed by touch drying at room temperature and then heating and drying. In general, the heating and drying is preferably performed at a temperature of 30 to 200 ° C. for 5 minutes to 2 hours while still or under blowing.

The charge transport layer according to the invention may contain various additives. For example, diphenyl, m-ter-phenyl, plasticizers such as dibutyl phthalate, silicone oils, graft-type silicone polymers, surface lubricants such as various fluorocarbons, dicyanovinyl compounds, potential stabilizers such as carbazole derivatives, β-carotene, Examples include an antioxidant such as a Ni complex and 1,4-diazabicyclo [2,2,2] octane.

The charge generation layer in the present invention, selenium, selenium-tellurium, inorganic charge generation substances such as amorphous silicones, pyrylium dyes, thiapyrylium dyes, azurenium dyes, thiocyanine dyes, cation dyes such as quinocyanine dyes, squarylium salts Dyes, phthalocyanine pigments, anthantrone pigments, dibenzopyrene quinone pigments, polycyclic quinone pigments such as pyranthrone pigments, indigo pigments, quinacridone pigments, and organic charge generating substances such as azo pigments. The materials can be used alone or in combination and used as a vapor deposition layer or a coating layer.

Among the above-mentioned charge generating substances, azo pigments are particularly diversified. Representative examples of azo pigments having particularly high effects are described below.

As a general formula of the azo pigment, the central skeleton is represented by A,
The coupler moiety is shown as Cp, where n is 1 or 2, and specific examples are given.

AN = N−Cp) _{n As} a specific example of A, As a specific example of Cp, And the like.

The central skeleton A and the coupler Cp form a pigment serving as a charge generating substance when properly combined.

The charge generation layer can be formed by dispersing the above-described charge generation material in a suitable binder and applying this to a support, or can be formed by forming a deposition film with a vacuum deposition device. .

The binder can be selected from a wide range of insulating resins,
Further, it can be selected from organic photoconductive polymers such as poly-N-vinylcarbazole, polyvinylanthracene and polyvinylpyrene.

Preferably, polyvinyl butyral, polyarylate (polycondensate of bisphenol A and phthalic acid, etc.), polycarbonate, polyester, phenoxy resin, polyvinyl acetate, acrylic resin, polyacrylamide, polyamide, polyvinyl pyridine, cellulose resin, urethane resin, epoxy Resins, casein, polyvinyl alcohol, polyvinyl pyrrolidone, and the like can be used.

The amount of the resin contained in the charge generation layer is suitably 80% by weight or less, preferably 40% by weight or less.

Examples of the organic solvent used for coating include alcohols such as methanol, ethanol, and isopropanol; ketones such as acetone, methyl ethyl ketone and cyclohexanone; amides such as N, N-dimethylformamide and N, N-dimethylacetamide; Sulfoxides such as sulfoxide, tetrahydrofuran, dioxane,
Ethers such as ethylene glycol monomethyl ether; esters such as methyl acetate and ethyl acetate; aliphatic halogenated hydrocarbons such as chloroform, methylene chloride, dichloroethylene, carbon tetrachloride, and trichloroethylene; or benzene, toluene, xylene, and monochlor Aromatic compounds such as benzene and dichlorobenzene can be used.

The coating can be performed by using a coating method such as an immersion coating method, a spray coating method, a spinner coating method, a bead coating method, a Meyer bar coating method, a blade coating method, a roller coating method, and a curtain coating method.

Drying is preferably performed by touch drying at room temperature and then heating and drying. In general, the heating and drying is preferably performed at a temperature of 30 to 200 ° C. for 5 minutes to 2 hours while still or under blowing.

The charge generation layer contains as much of the organic photoconductor as possible to obtain sufficient absorbance, and a thin film layer, for example, for injecting the carrier into the charge transport layer within the life of the generated charge carrier, for example, 5 μm or less, preferably 0.01 to 1
It is desirable to form a thin film layer having a thickness of μm.

The photosensitive layer having such a laminated structure of the charge generation layer and the charge transport layer is provided on a support having a conductive layer.
As a support having a conductive layer, a support having conductivity itself, for example, aluminum, an aluminum alloy,
Copper, zinc, stainless steel, vanadium, molybdenum, chromium, titanium, nickel, indium, gold, platinum and the like can be used.In addition, aluminum, aluminum alloy, indium oxide, tin oxide, indium oxide-tin oxide alloy, etc. Plastic having a layer formed by a vapor deposition method (eg, polyethylene, polypropylene, polyvinyl chloride, polyethylene terephthalate, acrylic resin, polyethylene), and conductive particles (eg, aluminum powder, titanium oxide, tin oxide,
A support in which zinc oxide, carbon black, silver particles, etc.) are coated on a plastic or the conductive support with an appropriate binder, a support in which conductive particles are impregnated in plastic or paper, or a plastic having a conductive polymer, etc. Can be used.

An undercoat layer having a barrier function and an adhesive function can be provided between the conductive support and the photosensitive layer.

The undercoat layer is formed of casein, polyvinyl alcohol, nitrocellulose, ethylene-acrylic acid copolymer, polyamide (nylon 6, nylon 66, nylon 610, copolymer nylon, alkoxymethylated nylon, etc.), polyurethane, gelatin, aluminum oxide, etc. it can.

The thickness of the undercoat layer is 0.1 to 5 μm, preferably 0.5 to 3 μm.
Is appropriate.

In the case of using a photoconductor in which a conductive support, a charge generation layer, and a charge transport layer are laminated in this order, the charge transport compound in the present invention has a hole transport property, and therefore, it is necessary to negatively charge the surface of the charge transport layer. When exposed after charging, in the exposed area, holes generated in the charge generation layer are injected into the charge transport layer, and then reach the surface to neutralize negative charges, attenuate the surface potential, and cause a gap between the exposed area and the unexposed area. Causes an electrostatic contrast.

 At the time of development, it is necessary to use a positively charged toner.

In another embodiment of the present invention, the above-mentioned azo pigments or U.S. Patent Nos. 3,554,745, 3,567,438 and 3,567,438.
Increasing the number of photoconductive pigments and dyes such as pyrylium dyes, thiapyrylium dyes, selenapyrylium dyes, benzopyrylium dyes, benzothiapyrylium dyes, naphthopyrylium dyes, and naphthiapyrylium dyes disclosed in 3586500 and the like. It can also be used as a sensitizer.

In another specific example, a eutectic complex of a pyrylium dye disclosed in US Pat. No. 3,684,502 or the like and an electrically insulating polymer having an alkylidene diarylene moiety can be used as a sensitizer. This eutectic complex is, for example, 4-
[4-bis (2-chloroethyl) aminophenyl] -2,
6-Diphenylthiapyrylium perchlorate and poly (4,4'-isopropylidenediphenylene carbonate) are converted into halogenated hydrocarbon solvents such as dichloromethane, chloroform, carbon tetrachloride, 1,1-dichloroethane, 1,2- Dichloroethane, 1,1,2-trichloroethane,
After dissolving in chlorobenzene, bromobenzene, 1,2-dichlorobenzene, etc., add a non-polar solvent, such as hexane, octane, decane, 2,2,4-trimethylbenzene, ligroin, etc. Obtained as a crystalline complex.

The electrophotographic photoreceptor in this specific example includes styrene-
Butadiene copolymer, silicone resin, vinyl resin,
Vinylidene chloride-acrylonitrile copolymer, styrene-acrylonitrile copolymer, vinyl acetate-
Vinyl chloride copolymer, polyvinyl butyral, polymethyl methacrylate, polyesters, cellulose esters and the like can be contained as a binder.

The electrophotographic photoreceptor of the present invention can be widely used not only for electrophotographic copying machines but also for electrophotographic applications such as laser beam printers, CRT printers, and electrophotographic plate making systems.

The electrophotographic photoreceptor of the present invention is advantageous in that it has high sensitivity and has small fluctuations in the bright portion potential and the dark portion potential upon repeated charging and exposure.

Example 1 Example 5 5 g of disazo pigment represented by the following structural formula was added to 2 g of butyral resin (butyralization degree: 63 mol%) and 100 m of cyclohexanone.
The mixture was dispersed in a sand mill together with the liquid dissolved in l for 24 hours to prepare a coating liquid.

This coating solution was applied on an aluminum sheet with a Meyer bar so that the dry film thickness was 0.2 μm, to form a charge generation layer.

Next, 10 g of Compound Example (9) and 10 g of polycarbonate (average molecular weight: 20,000) were dissolved in 70 g of chlorobenzene as a charge transporting substance, and this solution was applied on the previous charge generating layer with a Meyer bar, and then dried. A charge transport layer having a thickness of 20 μm was formed, and an electrophotographic photosensitive member was prepared.

The electrophotographic photoreceptor thus prepared was corona-charged at −5 KV in a static manner using an electrostatic copying paper tester Model-SP-428 manufactured by Kawaguchi Electric Co., Ltd., and was held for 1 second in a dark place. And the charging characteristics were examined.

As the charging characteristics, the surface potential (V ₀₎ and the exposure required to attenuate one second dark decay is potential when was the (V ₁₎ to 1/2 (E1 /
2) was measured.

Further, in order to measure the fluctuations in the dark place potential and the light portion potential when repeatedly used, the electrophotographic photosensitive member created in this example was mounted on a photosensitive drum cylinder of a PPC copier NP-3525 manufactured by Canon Inc. 5,000 copies were made with the same machine, and the variations in the dark potential (V _D ) and the light potential (V _L ) at the initial stage and after copying 5,000 copies were measured.

Incidentally, the initial V _D and V _L were set respectively -700 V, so that the -200 V. The results are shown.

As is clear from the above results, when the charge transport material specified in the present invention is used, it has a good sensitivity and a small fluctuation in potential during durability.

Example 2-14 In this example, compound examples (1), (3), and (3) were used in place of charge transport compound example (9) used in example 1.
(6), (7), (8), (10), (11), (16),
(17), (18), (21), (22) and (24)
An electrophotographic photoreceptor was prepared in the same manner as in Example 1 except that a pigment having the following structural formula was used as a charge generating substance.

The electrophotographic characteristics of each electrophotographic photosensitive member were measured by the same method as in Example 1. The results are shown.

Example 15 Aqueous ammonia solution of casein (11.2 g of casein, 1 g of 28% aqueous ammonia, 222 ml of water) on an aluminum cylinder
Was applied by a blade coating method to form an undercoat layer having a dry film thickness of 1 μm.

Next, 10 g of a charge generating substance represented by the following structural formula, 5 g of butyral resin (butyralization degree: 63 mol%) and 200 g of cyclohexanone were dispersed by a ball mill disperser for 48 hours. This dispersion was applied on the previously formed undercoat layer by a blade coating method to form a charge generation layer having a dry film thickness of 0.15 μm.

Next, 10 g of Compound Example (15) and 10 g of polymethyl methacrylate (average molecular weight: 50,000) were dissolved in chlorobenzene, and applied on the previously formed charge generating layer by a blade coating method. A transport layer was formed.

A corona discharge of -5 KV was applied to the electrophotographic photosensitive member thus produced. The surface potential at this time was measured (initial potential
V ₀ ). Further, the surface potential of this photoconductor after leaving it in a dark place for 1 second was measured.

Sensitivity, exposure required to attenuate the potential V ₁ of the after dark decay to 1/2 (E1 / 2, the micro-Joules / cm ²⁾ was evaluated by measuring.

At this time, a ternary semiconductor laser of gallium / aluminum / arsenic (output: 5 mw, oscillation wavelength: 780 nm) was used as a light source. The results are shown.

V ₀ : −730V v ₁ : −720V E1 / 2: 2.3 microjoules / cm ² Next, a laser printer (Canon Inc., LBP, a reversal developing type electrophotographic printer equipped with a semiconductor laser as described above) -CX), the above photoreceptor was set in place of the LBP-CX photoreceptor, and an actual image forming test was performed.

Conditions were as follows: surface potential after primary charging: -700 V, surface potential after image exposure: -150 V (exposure amount: 2.0 microjoules / c)
m ² ), transfer potential: +700 V, developer polarity: negative polarity, process speed: 50 mm / sec, development condition (development bias): -4
50 V, image exposure scan method: image scan, exposure before primary charging: red light exposure of 50 lux, sec. The image was formed by performing a line scan using a laser beam in accordance with a character signal and an image signal. Good prints were obtained for both characters and images. Further, when 3,000 images were continuously printed, stable and good prints were obtained from the initial to 3,000 sheets.

Example 16 4- (4-dimethylaminophenyl) -2,6-diphenylthiapyrylium perchlorate (3 g) and compound example (19)
5g to polyester (Polyester Adhesive 4900)
The mixture was mixed with 100 ml of a toluene (50 parts by weight) -dioxane (50 parts by weight) solution of 0, Dubon Co., Ltd.) and dispersed in a ball mill for 6 hours. This dispersion was applied on an aluminum sheet using a Meyer bar so that the film thickness after drying was 15 μm.

The electrophotographic characteristics of the electrophotographic photoreceptor thus prepared were measured in the same manner as in Example 1. The results are shown.

V ₀ : −710V V ₁ : −700V E1 / 2: 3.9lux, sec Initial V _D : −700V V _L : −200V After 5,000 sheets endurance V _D : −690V V _L : −225V Example 17 4- 3 g of (4-dimethylaminophenyl) -2,6-diphenylthiapyrylium perchlorate and poly (4,4'-
After sufficiently dissolving 3 g of isopropylidene diphenylene carbonate) in 200 ml of dichloromethane, 100 ml of toluene was added to precipitate an amorphous complex. After the precipitate was separated by filtration, dichloromethane was added to redissolve it, and then 100 ml of n-hexane was added to the solution to obtain a precipitate of a eutectic complex.

5 g of this eutectic complex was added to 95 ml of a methanol solution containing 2 g of polyvinyl butyral, and dispersed by a ball mill disperser for 6 hours. This dispersion was applied on an aluminum plate having a casein layer with a Meyer bar so that the film thickness after drying was 0.4 μm to form a charge generation layer.

Next, a charge transport layer coating layer was formed in exactly the same manner as in Example 1 except that Compound Example (26) was used on the charge generation layer.

The electrophotographic characteristics of the electrophotographic photoreceptor thus prepared were measured in the same manner as in Example 1. The results are shown.

V ₀ : −720V V ₁ : −710V E1 / 2: 3.7lux, sec Initial V _D : −700V V _L : −200V After 5,000 sheets endurance V _D : −670V V _L : −205V Example 18 Aluminum plate Aqueous ammonia solution of casein (described above) was applied thereon with a Meyer bar to form an undercoat layer having a dry film thickness of 1 μm. On this, the charge transport layer and the charge generation layer of Example 10 were sequentially laminated, and an electrophotographic photosensitive member was prepared in exactly the same manner as in Example 10 except that the layer configuration was different. Was measured. However, the charging polarity was +. The results are shown.

V ₀ : +725 V V ₁ : +700 V E1 / 2: 4.0 lux, sec Example 19 A 5% methanol solution of soluble nylon (6-66-610-12 quaternary nylon copolymer) was applied on an aluminum plate and dried. An undercoat layer having a thickness of 0.5 μm was formed.

Next, 5 g of a pigment having the following structural formula was added to 95 ml of tetrahydrofuran.
The mixture was dispersed in a sand mill for 20 hours.

Next, a solution prepared by dissolving 5 g of Compound Example (27) and 10 g of bisphenol Z-type polycarbonate (viscosity average molecular weight 30,000) in 30 ml of chlorobenzene was added to the previously prepared dispersion, and the mixture was further dispersed by a sand mill for 2 hours. This dispersion was applied on a previously formed undercoat layer using a Meyer bar so that the film thickness after drying was 20 μm, and dried.

The electrophotographic characteristics of the electrophotographic photoreceptor thus prepared were measured in the same manner as in Example 1. The results are shown.

V ₀ : −715 V V ₁ : −695 V E1 / 2: 4.2 lux, sec [Effect of the Invention] The electrophotographic photoreceptor containing the specific compound of the present invention as a charge transport material has high sensitivity and is repeatedly charged. An electrophotographic photoreceptor having excellent durability with small fluctuations in a light portion potential and a dark portion potential during continuous image formation by exposure.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Masakazu Matsumoto 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (56) References JP-A-1-280763 (JP, A) JP-A Sho50 −19441 (JP, A)

Claims (1)

(57) [Claims] 1. An electrophotographic photosensitive member having a photosensitive layer laminated on a conductive support, wherein the photosensitive layer contains a compound represented by the following general formula. General formula In the formula, Ar ₁ and Ar ₂ represent an aryl group or a heterocyclic group which may have a substituent, and at least one of Ar ₁ and Ar ₂ is (Wherein, R ₂ and R ₃ represent a hydrogen atom, an alkyl group which may have a substituent, an aryl group, an aralkyl group or a heterocyclic group, and R ₂ and R ₃ are a 5- to 7-membered ring together with a nitrogen atom. R ₁ represents a hydrogen atom, an alkyl group, an alkoxy group, a halogen atom, a cyano group, an acyl group or a trifluoromethyl group. However, only Ar ₁ When Ar ₁ is a phenyl group, and at the position para to the central benzene ring in the above general formula Never have.