JPH0619581B2 - Electrophotographic photoreceptor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to an electrophotographic photoreceptor, more specifically, in a photoconductive layer formed on a conductive support. ，
By containing a novel hydrazone compound, an electrophotographic photoreceptor having excellent photosensitivity and durability is provided.

(Prior Art) The electrophotographic method is already disclosed by Carlson in US Pat. No. 2.297.69.
As clarified in No. 1, this photographic method is a skillful combination of electrostatic phenomenon and photoconductive phenomenon. The surface of a photoconductive photoconductor is uniformly charged by corona discharge in a dark place. This is one of the image forming methods in which a photoconductive image is converted into an electrostatic latent image by utilizing photoconductivity, and colored charged powder (toner) is attached to the electrostatic latent image to form a visible image.

The basic electrical and opto-electrical characteristics required for the photoreceptor in such electrophotography are that it can be charged to an appropriate potential in a dark place, that this potential can be maintained for an appropriate time, and that it can be rapidly irradiated by light irradiation. It can be said that the charge can be dissipated.

In such a photoreceptor, conventionally, amorphous selenium,
Inorganic photoconductive materials such as cadmium sulfide and zinc oxide have been widely used. Although these inorganic materials satisfy the above conditions, they also have some drawbacks. For example, cadmium sulfide and zinc oxide are used as a photoconductor by dispersing them in a resin as a binder, but they have mechanical defects such as smoothness, flexibility, hardness, tensile strength, and abrasion resistance, so they are used as they are. Cannot withstand repeated use. Furthermore, in cadmium sulfide, it is necessary to consider hygiene issues.

In addition, in the case of amorphous selenium, the manufacturing method must be vapor deposition, which not only makes the manufacturing cost expensive, but also has no flexibility and is difficult to process into a belt shape.
Since it is sensitive to the toxicity of selenium and to heat and mechanical shock, it has a drawback that it requires careful handling.

In recent years, in order to eliminate the drawbacks of these inorganic photoreceptors,
Research on organic photoconductors is proceeding, and in organic photoconductors,
Various organic photoreceptors have been proposed and some have been put to practical use because they have many advantages such as ease of film formation, ease of production, light weight, flexibility, and multimodification of spectral sensitivity.

For example, poly-N-vinylcarbazole and 2,4,7-
A photoconductor comprising trinitrofluoren-9-one (U.S. Pat. No. 3.484.237), poly-N-vinylcarbazole sensitized with a pyrylium salt dye (Japanese Patent Publication No. Sho 48).
No. 25658), and a photoreceptor containing a eutectic complex composed of a dye and a resin as a main component (JP-A 47-10735).

Further, an electrophotographic photosensitive member has been proposed in which a substance that generates a charge by light (called a charge generating substance) and a substance that can transport the generated charge (called a charge transporting substance) are combined. . For example, U.S. Pat. No. 3.791.82
No. 6 discloses a photoconductor having a charge transport layer provided on a charge generation layer, and US Pat. No. 3,764.3.315 discloses a photoconductor layer having a charge transport substance dispersed in the charge transport substance. Is described. By making the functions of charge generation and charge transport of this kind by different substances, that is, by combining the charge generation substance and the charge transport substance, the characteristics become better, and a useful photoreceptor is provided. To be done.

So far, many useful charge generating substances have been known in this type of photoconductor. On the other hand, although various substances have been proposed as charge transport substances, it is difficult to say that they are always satisfactory. An excellent charge-transporting substance is, as a basic property, capable of holding a sufficient electric potential when charged, and allowing light of an effective wavelength such that a charge is generated from the charge-generating substance to sufficiently penetrate into the charge-generating substance. In addition, it has the ability to quickly transport the charges generated by the charge generating substance. Also,
The properties required for practical use, either alone or dissolved in a binder, can form a uniform film, the temperature, the ozone generated during humidity and corona discharge, in harsh environmental conditions due to NO _X, etc. , It is necessary not to cause deterioration or change of electrostatic characteristics. Heretofore, as a charge transport material of this kind, polyphenyl compounds such as triphenyl have been classified according to their chemical structural formulas, and US Pat. No. 3,717,462.
No. 4,150.987, JP-A-55-520.
64, hydrazone compounds, U.S. Pat. No. 3,820,989, diarylalkane compounds, U.S. Pat. No. 3,189,477, 2, 5-bis (P-diethylaminophenyl) -1,3,4-oxadiazole, the pyrazoline compounds described in U.S. Pat. No. 3.837.851, etc. have been proposed in recent years and are relatively excellent. It is a charge transport material. However, even with these charge-transporting substances, it cannot be said that all of the above conditions are satisfied.

(Problems to be Solved by the Invention) The present invention provides an electrophotographic photoreceptor having excellent sensitivity, repeatability, durability and the like.

[Structure of Invention]

(Means for Solving the Problem) As a result of intensive studies, the present inventors have found that a hydrazone compound having a specific structure is a truly useful charge-transporting substance for an electrophotographic photosensitive member. The inventors have found that an electrophotographic photosensitive member using a charge transport material has excellent properties and completed the present invention.

That is, the present invention provides an electrophotographic photosensitive member having excellent properties by using a hydrazone derivative having a novel structure.

An object of the present invention is to provide an electrophotographic photosensitive member having high sensitivity and low residual potential by containing a novel charge transporting substance. Another object of the present invention is charging exposure,
When used as a photoreceptor for repetitive transfer type electrophotography, in which development and transfer processes are repeated, there is little fatigue deterioration due to repeated use, and in various severe environments under low temperature, high temperature and high humidity. , To provide an electrophotographic photoreceptor having excellent durability and environmental characteristics that maintain stable characteristics.

The object of the present invention is to provide an electrophotographic photoreceptor having a photosensitive layer containing a charge generating substance and a charge transporting substance on a conductive support, wherein the charge generating substance is ε-type copper phthalocyanine,
Alternatively, it is a phthalocyanine composition obtained by dissolving copper phthalocyanine and phthalocyanine having a nitro group in concentrated sulfuric acid and then precipitating with water, wherein at least one hydrazone compound represented by the following general formula (I) is used as a charge transport material. It is achieved by the inclusion.

General formula (I) (In the formula, X is an oxygen atom, a sulfur atom or an imino group which may have a substituent.

R ₁ and R ₂ are each independently an alkyl group, an aralkyl group, an aryl group or a heterocyclic residue. R ₁ and R ₂ may form a heterocyclic residue; R ₃ and R ₄ are each independently a hydrogen atom, an alkyl group, an aralkyl group, an alkoxy group or a halogen atom. Further, R ₁ and R ₃ , or R ₂ and R ₄ may form an aliphatic heterocycle. However, when R ₁ and R ₂ are both alkyl groups or R ₁ and R ₂ form a heterocyclic residue, R ₃
Except when both R ₄ and R ₄ are hydrogen atoms.

R ₅ is an alkyl group, an aralkyl group, an aryl group or a heterocyclic residue.

R ₆ and R ₇ are each independently a hydrogen atom, a halogen atom, an alkyl group, an alkoxy group, an aryl group, an amino group or an alkylamino group. R ₆ and R ₇ may form a naphthalene ring.

n is an integer of 0 or 1. ) Further, the substituents will be described in detail.
Of R ₁ , R ₂ , R ₃ , R ₄ , R ₅ , R ₆ , and R ₇ , an alkyl group is methyl, ethyl, a linear or branched propyl group, a butyl group, a pentyl group, or hexyl. Groups, substituents such as stearyl groups; aralkyl groups are substituents such as benzyl, phenethyl, cinnamyl, naphthylmethyl, benzhydryl groups; aryl groups include phenyl, naphthyl, and anthryl groups. Substituents such as; methoxy groups, ethoxy groups, butoxy groups, hexyloxy groups, benzyloxy groups and the like; heterocyclic residues are pyridyl groups, thiazolyl groups, benzoxazolyl groups substituents such as (but piperidino group as the case of forming a heterocyclic ring in R ₁ and R _2, substituents such as morpholino group); and alkyl group, an ethylamino group, Jiechiruami Group shown, substituents such as dibutylamino group, respectively.

The hydrazone compound of the present invention represented by the general formula [I] can be produced, for example, by the following method.

One method is the general formula [II] (Wherein, R ₅ , R ₆ and R ₇ are the same as those in the general formula [I]) and the hydrazine represented by the general formula [II]
This is a method of reacting an aldehyde represented by I] in an organic solvent.

General formula (III) (Wherein R ₁ , R ₂ , R ₃ and R ₄ are the same as those in the general formula [I]) As the solvent, non-reactive organic solvents can be widely used, but alcohols such as methanol and ethanol are preferable. Alternatively, dimethylformamide, dioxane and the like can be used alone or in combination.

In another method, the general formula [IV] (Wherein R ₆ and R ₇ are the same as in the general formula [I]) The hydrazine represented by the general formula [I] or its mineral acid salt is reacted with the aldehyde compound represented by the general formula [III] in a solvent, and then the general formula R _5- Z [V] (wherein Z represents a negative group such as a halogen atom) is reacted in a solvent, preferably under basic conditions, to obtain the hydrazone compound of the present invention. be able to.

Although a non-reactive solvent can be widely used as the solvent, preferably, a protic solvent such as water or alcohol, or an aprotic polar solvent such as dimethyl sulfoxide or dimethylformamide, ketones such as acetone or methyl ethyl ketone, Aromatic hydrocarbons such as benzene, toluene and xylene, ethers such as tetrahydrofuran and dioxane, chlorinated hydrocarbons such as dichloromethane and 1,2-dichloroethane, or amines such as pyridine and triethylamine are used alone or in combination. be able to. As the base, sodium hydroxide, potassium hydroxide, potassium carbonate, sodium methylate, sodium hydride or the like is used.

Typical examples of the hydrazone compound used in the present invention obtained by such a synthetic method are listed below.

[Hydrazone compound]

These compounds can be used alone or in combination of two or more.

The photoconductor of the present invention contains the hydrazone compound as described above, and photoconductors having various characteristics can be obtained depending on the application of these hydrazone compounds. For example, a hydrazone compound as a charge transport material in the present invention is provided on a conductive supporting substrate in the same layer as the charge generating material,
The structure is usually called a single-layer type photoreceptor, or two layers of a first layer mainly containing a charge generating substance and a second layer mainly containing a charge transporting substance are laminated on a conductive supporting substrate. It can be used in a structure generally called a laminated type photoreceptor. The selection of these constitutions is appropriately selected depending on the polarity of the photoreceptor. Also,
The charge generating substance used in the present invention is a phthalocyanine composition obtained by dissolving ε-type copper phthalocyanine or copper phthalocyanine and a phthalocyanine having a nitro group in concentrated sulfuric acid and then precipitating with water.

Since the hydrazone compound in the present invention does not have a film-forming ability by itself, a binder resin is used to form it as a photosensitive layer. Further, as for the charge generating substance, it is not possible to form a film by itself except for a polymer resin such as polyvinyl carbazole, so a binder may be used if necessary.

The binder preferably used in the present invention is a film-forming high molecular polymer or copolymer having high electric insulation. Such high molecular weight polymers and copolymers,
The binder preferably used in the present invention is phenol resin, polyester resin, vinyl acetate resin, polycarbonate resin, polypeptide resin, cellulosic resin, polyurethane resin, polyvinylpyrrolidone, polyethylene oxide, polyvinyl chloride resin, starch, polyvinyl alcohol, Examples thereof include acrylic copolymer resin, methacrylic copolymer resin, silicone resin, polyacrylonitrile copolymer resin, polyacrylamide, polyvinyl butyral, polyvinyl carbazole, and polyvinylidene chloride resin. These polymer binders may be used alone or in combination of two or more, but the binder usable in the present invention is not limited to these. Further, the photoreceptor of the present invention is provided with a charge generating layer containing a charge generating substance as a main component on an electrically conductive support through an intermediate layer, if necessary, and a charge transporting substance as a main component is adjacent to the layer. A laminated structure in which a charge transport material is provided may be used. Further, in the case of such a laminated structure, which of the charge generation layer and the charge transport layer is to be the upper layer is determined depending on whether the charging property is positive or negative. In general, when negatively charged, it is advantageous in terms of characteristics that the charge transport layer is an upper layer. When the photoreceptor of the present invention has a laminated structure composed of a charge generation layer and a charge transport layer, which are separate layers, the charge generation layer may be provided directly on the conductive support or, if necessary, as an adhesive layer or a barrier. Vacuum deposition on top of an intermediate layer such as a layer, or a solution of a charge generating substance dissolved in a suitable solvent, or
The charge-generating substance can be provided by a method such as making the charge-generating substance finer in a dispersion solvent by a ball mill, an attritor, etc., and coating a dispersion obtained by mixing and dispersing with a polymer binder, if necessary. The polymer binder used at this time may be the same as that used in the charge transport layer.

Further, it may be a single photosensitive layer comprising the hydrazone compound according to the present invention and a binder.

The charge transport material is preferably 10 to 300 parts by weight per 100 parts by weight of the binder. However, the present invention is not limited to this range. In addition, the thickness of this photosensitive layer depends on the required photosensitivity and durability, and
It is determined by the mixing ratio of the charge generating substance and the charge transporting substance to the binder.
The thickness of the photosensitive layer on the supporting conductive substrate is 50 microns or less,
From the viewpoint of flexibility of the coating, preferably about 7 to 30 μm is suitable.

Further, the photosensitive layer can be coated with a layer serving as a protective layer, if necessary.

The support used for the electrophotographic photosensitive member of the present invention may be any one as long as it has conductivity, and any type of conventionally used conductive layer may be used. Specifically, metals such as aluminum, copper, stainless steel, and brass, plastics obtained by vapor deposition or lamination of aluminum, indium oxide, tin oxide, or the like or conductive particles such as carbon black, tin particles, plastics in which aluminum particles are dispersed are used. Can be mentioned. The shape may be a sheet shape, a cylinder shape, or any other shape. When the electrophotographic photoreceptor according to the present invention is used, the light source is usually a halogen lamp or the like, and when the charge generating substance is phthalocyanine, the sensitivity is 750 nm or more, and therefore gallium-aluminum-arsenic is used. Laser light such as a semiconductor laser (oscillation wavelength 780 nm) can also be used.

Next, the present invention will be described more specifically with reference to synthesis examples and examples, but the present invention is not limited to the following examples. Hereinafter, in the examples, "parts" in the examples means parts by weight.

Synthesis Example 1 A synthesis example of the compound (1) of the present invention is shown.

After adding 77 parts of phosphorus oxychloride to 40 parts of dimethylformamide at 15 to 20 ° C., 54 parts of N, N-dibenzylaniline is added at the same temperature and stirred at 50 to 55 ° C. for 4 hours. After the reaction solution is cooled, it is poured into 2500 parts of ice water.
Then, the mixture is neutralized with sodium hydroxide to pH 9-10, cooled, filtered, washed with water and dried to obtain 54 parts of an aldehyde having the following structure.

Then, 150 parts of ethanol, 30 parts of the above aldehyde, 18 parts of hydrazine having the following structure, and acetic acid as a catalyst were used. Add 3 parts and stir at 70-80 ° C for 2 hours. The reaction solution is cooled and the precipitated crystals are filtered and washed with water. Then, after reslurrying this crystal in ammonia-alkaline water,
Filtration, washing with water and drying give 43 parts of compound (1).
Recrystallization from acetonitrile gives 41 parts of pure product, mp 185-186 ° C.

Synthesis Example 2 A synthesis example of the compound (2) of the present invention is shown.

After adding 77 parts of phosphorus oxychloride to 50 parts of dimethylformamide at 15 to 20 ° C, add 33 parts of N, N-dianisylaniline at the same temperature and stir at 60 to 70 ° C for 3 hours. After the reaction solution is cooled, it is poured into 2500 parts of ice water.
Then, it is neutralized with sodium hydroxide, cooled to pH 9-10, filtered, washed with water and dried to obtain 32 parts of an aldehyde having the following structure.

Then, in 50 parts of ethanol, 18 parts of the above aldehyde, 9 parts of hydrazine having the following structure, and p- as a catalyst were used.
Toluenesulfonic acid Add 1 part and stir at 70-80 ° C for 2 hours. Hydrazone having the following structure after cooling, filtering and drying 22 parts are obtained.

Then, 2.4 parts of sodium hydroxide is added to 50 parts of dimethylformamide at 15 to 20 ° C., and then 20 parts of the hydrazone is added at the same temperature. Then, 7 parts of butyl bromide is added dropwise at 20 to 25 ° C. After stirring at the same temperature for 3 hours, it is poured into 1000 parts of ice water, filtered, washed with water and dried to obtain 22 parts of compound (3).

Synthesis Example 3 A synthesis example of the compound (8) of the present invention is shown.

By using 44 parts of m- (N, N-dibutylamino) -toluene in place of 54 parts of N, N-dibenzylaniline in Synthesis Example [1], 45 parts of aldehyde having the following structure is obtained.

Then, to 150 parts of ethanol are added 25 parts of the above aldehyde, 18 parts of hydrazine having the following structure, and 3 parts of acetic acid as a catalyst, and the mixture is stirred at 70 to 80 ° C. for 2 hours.

The reaction solution is cooled and the precipitated crystals are filtered and washed with water. Then, the crystals are reslurried in aqueous ammonia, filtered, washed with water and dried to obtain 40 parts of the compound (8). Recrystallized from acetonitrile, melting point 118-121
35 parts of pure product at 0 ° C. are obtained. m- (N, N-dibenzylamino) -toluene instead of m- (N, N-dibenzylamino) -toluene was reacted in the same manner to obtain 151 to 15
Compound (3) with a melting point of 3 ° C. is obtained.

Example 1 40 parts of copper phthalocyanine and 0.5 part of tetranitro copper phthalocyanine are dissolved in 500 parts of 98% concentrated sulfuric acid with sufficient stirring. The dissolved liquid is poured into 5000 parts of water to deposit a composition of copper phthalocyanine and tetranitrocopper phthalocyanine, filtered, washed with water, and dried under reduced pressure at 120 ° C.

Next, 1 part of this composition, 2.5 parts of compound (1), acrylic polyol (Takelac A-7 manufactured by Takeda Pharmaceutical Co., Ltd.)
02) 3.6 parts, epoxy resin (Shell Chemical Co., Epon 1007) 0.5 part, methyl ethyl ketone 1.2 parts and cellosolve acetate 1.2 parts were kneaded for 48 hours in a magnetic ball mill. A photoconductive composition is obtained.

Next, this photoconductive composition was roll-coated on aluminum of a laminated film of an aluminum foil having a thickness of 5 microns and a polyester film having a thickness of 75 microns to a dry film thickness of 8 microns, and uniformly heated to 110 ° C. It was placed in the oven for 1 hour to prepare an electrophotographic photoreceptor.
Corona discharge is applied to the sample thus obtained at a charging speed of +5.7 KV, corona gap 10 mm, and 10 m / min, and 10 seconds after the discharge is stopped, it is exposed with a 2854 K tungsten light source at an illuminance of 10 Lux. At this time, the sensitivity was defined as the irradiation amount of light required to reduce the potential immediately before exposure by 50%. The sample measured in this way has a maximum surface charge of 640 V, a dark decay rate of 17%, a sensitivity of 1.2 Lux.sec,
The residual potential was 20 V, which was a value sufficient for practical use in terms of both charging property and sensitivity, and during charging exposure, no induction was observed in the surface potential decay, and the J curve light decay curve was shown. Also, this photoconductor is 10,000 times positively charged by a copying machine.
Although the copies were taken in succession, the obtained image was excellent in gradation, and even if a normal photo was used as a document for copying, a beautiful image was obtained in terms of the detailed intermediate color density.
There was no change in sensitivity, and although the photoconductor had scratches, a clear image with no scratches on the copied image was obtained.

Examples 2 to 4 In Example 1, the compounds (6), (11) and (12) were used in place of the compound (1), and the same tests as in Example 1 were carried out. Both chargeability and sensitivity are sufficient for practical use, and no induction is observed in surface potential decay during charging exposure.
Furthermore, the repeatability was also good.

Example 5 40 parts of copper phthalocyanine and 1.5 parts of dinitrometal-free phthalocyanine are dissolved in 100 parts of 98% concentrated sulfuric acid with sufficient stirring. The dissolved liquid is poured into 1000 parts of water to precipitate a phthalocyanine composition, which is then filtered and washed with water,
Dry under reduced pressure at 120 ° C. 1 part of this composition, 3 parts of compound (3) and 4 parts of a polycarbonate resin (Panlite L-1250, Teijin Limited) were dispersed in a ball mill together with 10 parts of tetrahydrofuran, and this solution was sprayed to a thickness of 10 μm. After coating on aluminum cylinder, dry,
The electrophotographic photoreceptor was used. The electrophotographic characteristics of the sample thus obtained were measured in the same manner as in Example 1. The sample measured in this way has a maximum surface charge of 600
V, sensitivity is 1.1 Lux.sec, shows J curve without induction in its light decay curve, and 100 even in the repeated actual copying test by positive charging by a copying machine.
With 00 copies, a clear image was obtained with excellent gradation even in the initial and final images, with no change in sensitivity.

Example 6 1 part of ε-type copper phthalocyanine, 2 parts of compound (8),
Triphenylmethane (0.8 parts), acrylic resin (4 parts), and cellosolve acetate (20 parts) were dispersed in a ball mill, and a sample was measured in the same manner as in Example 1. The obtained light decay curve is a J curve without induction, the maximum surface potential at this time is 590 V, and the dark decay rate is 10
%, The sensitivity was 1.7 Lux.sec, and the residual potential was 15 V. Further, the same result as in Example 1 was obtained in the actual copying test.

Example 7 From 10 parts of copper phthalocyanine obtained in Example 1, 36 parts of acrylic polyol (Takelac A-702), 5 parts of epoxy resin (manufactured by Shell Chemical Co.) and 50 parts of methyl ethyl ketone: cellosolve acetate (1: 1). The resulting composition is kneaded in a ball mill for 24 hours to prepare a photoconductive paint, and the paint is applied to an aluminum support in an amount of about 1
The charge generation layer was formed by coating so as to have a thickness of μ.

Next, polycarbonate resin (Panlite L-125
0) 10 parts and polyester resin (manufactured by Goodyear) 3 parts were mixed with tetrahydrofuran and toluene solvent 100 parts. The solvent weight ratio is 9: 1. Compound (2) 9
Parts were added along with 0.02 parts of silicone oil. Apply this solution on the charge generation layer to a thickness of about 15μ
And dried to form a charge transport layer, and a laminated photoreceptor was obtained.

The surface potential of this photoconductor was -810V when it was charged with a corona of -6.5KV for 0.2 seconds, and the sensitivity was 1.2Lux.se.
It was c, which was an extremely high-sensitivity photoconductor.

Examples 8 to 9 In Example 7, instead of the compound (2), the compound (1
0) and (14) were used and tested in the same manner as in Example 7, and as in Example 7, both chargeability and sensitivity were values sufficient for practical use, and during charging exposure, the induction in surface potential decay was Not seen, and the repeatability was also good.

〔The invention's effect〕

The present invention has the above-mentioned configuration, and when using it,
High sensitivity for positive and negative charging,
There is little deterioration of the photoreceptor due to repeated use, and in practical use, it has excellent characteristics such as charge holding power from low temperature to high temperature, from low humidity to high humidity, environmental resistance in sensitivity change, and durability.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Michisatsu Hikosaka 2-33-1 Kyobashi, Chuo-ku, Tokyo Toyo Inki Manufacturing Co., Ltd. 56) References JP-A-60-63538 (JP, A)

Claims (1)

[Claims] 1. An electrophotographic photoreceptor having a photosensitive layer containing a charge generating substance and a charge transporting substance on a conductive support, wherein the charge generating substance is ε-type copper phthalocyanine, or
A phthalocyanine composition obtained by dissolving copper phthalocyanine and phthalocyanine having a nitro group in concentrated sulfuric acid and then precipitating with water, wherein the charge transport substance is at least one compound represented by the following general formula (I): Characteristic electrophotographic photoreceptor. General formula (I) (In the formula, X is an oxygen atom, a sulfur atom or an imino group which may have a substituent. R ₁ and R ₂ are each independently an alkyl group, an aralkyl group,
It is an aryl group or a heterocyclic residue. R ₁ and R ₂ may form a heterocyclic residue; R ₃ and R ₄ are each independently a hydrogen atom, an alkyl group, an aralkyl group, an alkoxy group or a halogen atom. Further, R ₁ and R ₃ , or R ₂ and R ₄ may form an aliphatic heterocycle. However, when R ₁ and R ₂ are both alkyl groups or R ₁ and R ₂ form a heterocyclic residue, the case where both R ₃ and R ₄ are hydrogen atoms is excluded. R ₅ is an alkyl group, an aralkyl group, an aryl group or a heterocyclic residue. R ₆ and R ₇ are each independently a hydrogen atom, a halogen atom, an alkyl group, an alkoxy group, an aryl group, an amino group or an alkylamino group. R ₆ and R ₇ may form a naphthalene ring. n is an integer of 0 or 1. )