JPH0567231B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to an electrophotographic photoreceptor, and particularly to a positively charging photoreceptor. [Prior Art] Conventionally, for example, as an electrophotographic photoreceptor, a photoreceptor having a photosensitive layer containing an inorganic photoconductive substance such as selenium, zinc oxide, or cadmium sulfide has been widely used. On the other hand, the use of various organic photoconductive substances as materials for photosensitive layers of electrophotographic photoreceptors has been actively developed and researched in recent years. For example, in Japanese Patent Publication No. 50-10496, poly-N
- describes an organic photoreceptor having a photosensitive layer containing vinylcarbazole and 2,4,7,-trinitro-9-fluorenone. However, this photoreceptor is not necessarily satisfactory in sensitivity and durability. In order to improve these drawbacks, attempts have been made to develop organic photoreceptors with high sensitivity and durability by assigning the charge generation function and charge transport function to different substances in the photosensitive layer. ing. In such so-called function-distributed electrophotographic sensitive materials, substances that exhibit each function can be selected from a wide range of materials, so it is relatively easy to create electrophotographic sensitive materials with arbitrary characteristics. It is possible to create a Many substances have been proposed as charge-generating substances that are effective for such functionally separated electrophotographic photoreceptors. Examples of using inorganic substances include, for example, as described in Japanese Patent Publication No. 16198/1983,
There is amorphous selenium, which is combined with organic charge transport materials. In addition, many electrophotographic photoreceptors using organic dyes or organic pigments as charge-generating substances have been proposed.
For example, those having a photosensitive layer containing a bisazo compound are disclosed in JP-A-47-37543 and JP-A-55-22834.
No. 54-79632, No. 56-116040, and other publications. By the way, the conventional photoreceptor using the organic photoconductive substance is usually used for negative charging. The reason for this is that when negative charging is used, the mobility of holes among the charges is large, which is advantageous in terms of photosensitivity and the like. However, it has been found that using such negative charging causes the following problems. That is, there is a problem in that ozone is likely to be generated in the atmosphere during negative charging by the charger, worsening the environmental conditions. Still another problem is that positive polarity toner is required for development of negatively charged photoreceptors, but positive polarity toner is difficult to manufacture in view of the triboelectric charging sequence with respect to ferromagnetic charged particles. Therefore, it has been proposed to use a positively charged photosensitive couple using an organic photoconductive material, for example,
When a photoreceptor is formed by laminating a charge transport layer on a charge generation layer, a material having a high electron transport ability, such as trinitrofluorenone, is used in the charge transport layer in order to efficiently cancel the positive charge on the surface of the photoreceptor. However, the substance is carcinogenic and is extremely unsuitable from a pollution standpoint. Furthermore, as a positive charging photoreceptor, the U.S. Patent No.
No. 3,615,414 discloses a material containing a thiapyrylium salt (charge generating substance) so as to form a eutectic complex with polycarbonate (binder resin). However, with this known photoreceptor,
The disadvantage is that the memory phenomenon is large and ghosts are likely to occur. U.S. Patent No. 3,357,989 also discloses a photoreceptor containing phthalocyanine, but the characteristics of phthalocyanine change depending on the crystal type, and the crystal type must be strictly controlled. It has disadvantages, has a large memory phenomenon, and has low short wavelength sensitivity, making it unsuitable for copying machines that use visible light including the short wavelengths as a light source. As described above, various attempts have been made to obtain photoreceptors for positive charging, but all of them have many problems that need to be improved in terms of photosensitivity, memory, pollution, etc. Therefore, a charge generation layer containing a charge generation substance that generates holes and electrons when irradiated with light is added as an upper layer (surface layer).
It is conceivable that a photoreceptor having a photosensitive layer having a laminated structure with a charge transporting layer containing a charge transporting substance having a hole transporting function as a lower layer may be used for positive charging. Furthermore, it is considered that a photoreceptor having a single-layered photosensitive layer containing the charge generating substance and the charge transporting substance can also be used for positive charging. In addition, in such a photoreceptor that is used for positive charging, if a charge generating substance having, for example, an electron-withdrawing group is used in the structure, the movement of electrons to cancel the positive charge on the surface of the photoreceptor will be accelerated. , it is thought that high sensitivity characteristics can be obtained. However, since all of the positive charging photoreceptors have a layer containing a charge-generating substance formed as a surface layer, the charge-generating substance is sensitive to external effects such as light irradiation, corona discharge, humidity, and especially mechanical friction. Since they are present near the surface layer, electrophotographic performance deteriorates during the storage of the photoreceptor and during the image formation process, leading to a decrease in image quality. In a negative charging photoreceptor having a conventional charge transport layer as a surface layer, the effects of the various functions described above are extremely small; rather, the charge transport layer has the effect of protecting the underlying charge generation layer. On the other hand, in the case of a positively charging photoreceptor, the surface layer containing a charge-generating substance is subject to mechanical abrasion and damage due to external effects, especially development and cleaning, resulting in image defects such as white spots and streaks. In addition, deterioration of electrophotographic performance such as surface potential, sensitivity, memory, residual potential, etc. will occur. Therefore, it is conceivable to provide a thin protective layer made of an insulating and transparent resin to reinforce the layer containing the charge-generating substance, but the protective layer blocks the charges generated during light irradiation, resulting in photoconductivity. The problem is that the information is lost. Further, it is possible to increase the wear resistance and scratch resistance of the charge generation layer by increasing the thickness of the charge generation layer serving as the surface layer, but there is a problem that the increase in the thickness causes a decrease in sensitivity. [Object of the Invention] Therefore, the object of the present invention is to provide an electronic photoconductor that is suitably configured for positive charging using an organic photoconductive substance, has excellent scratch resistance, high sensitivity, and durability, and has excellent resistance to ozone oxidation. The purpose of the present invention is to provide a photographic photoreceptor. [Structure and Effects of the Invention] In an electrophotographic photoreceptor in which a charge transport layer and a charge generation layer, or a charge transport layer, a charge generation layer and a protective layer are sequentially laminated on a conductive support, charge transport is carried out in the charge generation layer. Achieved by a positive charging electrophotographic photoreceptor containing a substance and at least one of the compounds represented by the following general formula [], [], or [] in the outermost layer. be done. General formula []

[Formula] In the formula, R represents an alkyl group, an alkenyl group, a cycloalkyl group, an aryl group or a heterocyclic group,
R ₁ , R ₂ and R ₃ are each a hydrogen atom, a halogen atom, an alkyl group, a cycloalkyl group, an alkoxy group, an alkylthio group, an aryl group, an aryloxy group, an arylthio group, an acyl group, an acylamino group, a diacylamino group, Represents an acyloxy group, an alkylamino group, a sulfonamide group, or an alkoxycarbonyl group. Further, R and R ₁ may be cyclized with each other to form a chroman ring, and this chroman ring may have a substituent. R ₄ , R ₅ , R ₆ , R ₇ , R ₈ and R ₉ are each a hydrogen atom, a halogen atom, an alkyl group, an alkoxy group,
It represents an alkylthio group, an alkenyl group, an alkenoxy group, an aryl group, an aryloxy group, an N-substituted amino group, or a heterocyclic group, but R ₄ , R ₅ , R ₆ and R ₇ are never hydrogen atoms at the same time. Further, R ₆ and R ₉ may be cyclized with each other to form a carbocycle, and the carbocycle may be substituted with an alkyl group. General formula []

[Formula] In the formula, R, R ₁ , R ₂ and R ₃ are the above general formula []
Each has the same meaning as R, R ₁ , R ₂ and R ₃ in . Furthermore, R and R ₁ may be cyclized with each other to form a coumaran ring, and this coumaran ring may have a substituent. R ₄ , R ₅ , R ₆ and R ₇ also have the same meaning as R ₄ , R ₅ , R ₆ and R ₇ in general formula [], but R ₄ and R ₅ are never hydrogen atoms at the same time. . General formula []

[Chemical formula] In the formula, R ₁ to R ₉ are R ₁ in the above general formula []
〜R ₉ and R ₁ ′〜R ₉ ′ are synonymous with R 1 〜R ₉ , respectively.
R ₉ and synonymous with each other, but R ₄ , R ₅ , R ₆ ,
R ₇ , R ₄ ′, R ₅ ′, R ₆ ′ and R ₇ ′ are never hydrogen atoms at the same time. X is an alkylene group whose carbon chain is -O-, -S-, -
Represents an alkylene group, phenylene group, cycloalkylene group, or divalent heterocyclic group which may be bonded via NH- or _-SO2- . Note that the effects of the present invention are more effectively exhibited when the thickness of the charge generation layer is 2 to 7 μm. As described in the conventional technology, positively charging photoreceptors using organic photoconductive substances lack scratch resistance and lack durability because the charge generation layer (hereinafter sometimes abbreviated as CGL) is the surface layer. In order to improve
It is necessary to increase the CGL film thickness. however,
Increasing the film thickness causes a decrease in sensitivity. One way to suppress this decrease in sensitivity is to add a charge transport material (hereinafter sometimes abbreviated as CTM) to CGL, but this CTM is a charge generating material (hereinafter referred to as CGM).
Since it has a structure that is more susceptible to ozone oxidation than the photoreceptor (sometimes abbreviated as ), it is easily deteriorated by ozone and the durability of the photoreceptor is impaired. As a result of intensive studies on improving ozone deterioration resistance, the present inventors discovered that the surface layer of a positive charging photoreceptor
The present inventors have discovered that the above deterioration can be significantly reduced by incorporating the compound of the present invention into CGL, leading to the present invention. Although the details of its effects are unknown, ozone
It is believed that the compound of the present invention acts on the compound of the present invention before CTM in CGL deteriorates and protects CTM by guarding against further ozone oxidation. Since the compound of the present invention prevents ozone deterioration of CTM by its own oxidation, CGL can be used as needed.
In a photoreceptor with a protective layer (hereinafter sometimes abbreviated as OCL) provided thereon, it is of course added to OCL, but it may also be added to CGL, and a charge transport layer (hereinafter sometimes abbreviated as OCL) mainly composed of CTM is added. (hereinafter sometimes abbreviated as CTL) may also be added. The present invention will be described in more detail below. The compounds of the present invention represented by the general formulas [], [] and [] have a chroman group having an alkoxy, alkenoxy, cycloalkyloxy or heterocyclic group at the 6-position, and an alkoxy, alkenoxy, cycloalkyloxy or heterocyclic group at the 5-position. It includes coumarans having a heterocyclic oxy group and the bis form of the above chroman. In the general formulas [] and [], R is a substituted or unsubstituted alkyl group or cycloalkyl group, R ₁ , R ₂ and R ₃ are hydrogen atoms, alkyl groups or cycloalkyl groups, and R ₄ to _{R 9} are hydrogen Preferred are compounds in which an atom, a halogen atom, an alkyl group or a cycloalkyl group, and R and R ₁ are an atomic group necessary for cyclization with each other to form a chroman ring, and R ₈ and R ₉ are cyclized with each other to form a carbocycle. . In addition, in the general formula [], R ₁ , R ₁ ′, R ₄ , R ₄ ′,
R ₈ , R ₈ ′, R ₉ and R ₉ ′ are alkyl groups R ₂ , R ₂ ′,
R ₃ , R ₃ ′, R ₅ , R ₅ ′, R ₆ , R ₆ ′, R ₇ and R ₇ ′ are hydrogen atoms and X is an alkylene group or the carbon chain of the alkylene group is bonded via -SO ₂ - Particularly preferred are compounds having an alkylene group. Typical specific examples of compounds preferably used in the present invention are shown below, but the invention is not limited thereto.

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[Table] These compounds are disclosed in U.S. Pat.
By reacting 6-hydroxychroman and 5-hydroxychroman obtained by the method described in No. 20977 etc. with a halide, sulfuric ester or vinyl compound in the presence of an alkali, which is a general alkylation method, or Patent No. 1938672,
Journal of the American Chemical
Society (J.Am.Chem.Soc.), vol. 66, 1523
~5 pages, Journal of the Chemical Society (J.Chem.Soc.), 1850~2 pages (1958)
It can be synthesized by bonding a phenol having an ether bond at the p-position according to the method described in the same journal, pp. 3350-78 (1959). When used in CGL, the amount of the compound of the present invention added is 0.1 to 100% by weight, preferably 1 to 50% by weight, particularly preferably 5% by weight, based on CTM in CGL.
~25% by weight. In addition, when used in OCL, 0.1 to 100
% by weight, preferably from 1 to 50% by weight. Next, the structure of the photoreceptor of the present invention will be explained with reference to the drawings. For example, as shown in FIG. 1, the photoreceptor has a support 1 (a conductive support or a sheet with a conductive layer provided thereon) and a charge transport layer 2 containing CTM and, if necessary, a binder resin, as a lower layer. year,
A photosensitive layer 4 having a laminated structure consisting of CGM, CTM and a charge generating layer 3 containing a binder resin as an upper layer, as shown in FIG. 2, has a protective layer on top of the photosensitive layer shown in FIG. (OCL) 4, and as shown in FIG. 3, a single-layer photosensitive layer 4 containing CGM, CTM, and binder resin as necessary is provided on a support. , an OCL may be provided on the photosensitive layer having a single layer structure as shown in FIG. 3, or an intermediate layer may be provided between the support and the photosensitive layer. Next, as the charge generating substance suitable for the present invention, any inorganic pigment or organic pigment can be used as long as it absorbs visible light and generates free charges. In addition to inorganic pigments such as , selenium-arsenic alloy, selenium-tellurium alloy, cadmium sulfide, cadmium selenide, cadmium selenide sulfide, mercury sulfide, lead oxide, and lead sulfide, organic pigments such as the following representative examples are used. May be used. (1) Azo pigments such as monoazo pigments, polyazo pigments, metal complex azo pigments, pyrazolone azo pigments, stilbene azo and thiazole azo pigments. (2) Perylene pigments such as perylene anhydride and perylene imide. (3) Anthraquinone or polycyclic quinone pigments such as anthraquinone derivatives, anthanthrone derivatives, dibenzpyrenequinone derivatives, pyrantrone derivatives, violanthrone derivatives, and isoviolanthrone derivatives (4) Indigoid pigments such as indigo derivatives and thioindigo derivatives (5) Phthalocyanine pigments such as metal phthalocyanine and metal-free phthalocyanine (6) Carbonium pigments such as diphenylmethane pigment, triphenylmethane pigment, xanthene pigment and acridine pigment (7) Quinone imine such as azine pigment, oxazine pigment and thiazine pigment Cyanine pigments and azomethine pigments (9) Quinoline pigments (10) Nitro pigments (11) Nitroso pigments (12) Benzoquinone and naphthoquinone pigments (13) Naphthalimide pigments (14) ) Perinone pigments such as bisbenzimidazole derivatives Various azo pigments with electron-withdrawing groups are used because of their good electrophotographic properties such as sensitivity, memory phenomenon, and residual potential, but polycyclic quinones are preferred due to their ozone resistance. pigments are most preferred. Although the details are unknown, this is probably because the azo group is susceptible to ozone oxidation and the electrophotographic properties deteriorate, whereas polycyclic quinones are inert to ozone. As the azo pigment used in the present invention,
For example, there are compounds shown in the following exemplified compound groups [] to [].

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[Table] Furthermore, the following exemplified compound groups [] to [] consisting of polycyclic quinone pigments can be most preferably used as CGM.

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[Table] Next, there are no particular limitations on charge transport substances that can be used in the present invention, but examples include oxazole derivatives, oxadiazole derivatives, thiazole derivatives, thiadiazole derivatives, triazole derivatives, imidazole derivatives, imidazolone derivatives,
Imidazolidine derivatives, bisimidazolidine derivatives, styryl compounds, hydrazone compounds, pyrazoline derivatives, oxazolone derivatives, benzothiazole derivatives, benzimidazole derivatives, quinazoline derivatives, benzofuran derivatives, acridine derivatives, phenazine derivatives, aminostilbene derivatives, poly-N-vinyl Carbazole, poly-1-
It may be vinylpyrene, poly-9-vinylanthracene, etc. However, it is preferable to use a CTM that has an excellent ability to transport holes generated during light irradiation to the support side and is suitable for combination with the carrier generating substance. Examples of such CTM include the following exemplified compound group [] or [ ] is used.

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[Table] In addition, the following exemplified compound groups [XI] ~
Hydrazone compounds represented by [ ] can also be used.

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[Table] In addition, pyrazoline compounds shown in the following exemplified compounds [] can also be used as CTMs.

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[Table] In addition, the following exemplified compound group as CTM []
Amine derivatives represented by can also be used.

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〔Example〕

The present invention will be explained below with reference to Examples, but the embodiments of the present invention are not limited thereby. Example 1 A conductive support made of polyester film laminated with aluminum foil was coated with a layer of vinyl chloride-vinyl acetate-maleic anhydride copolymer (Eslec MF-10, manufactured by Sekisui Chemical Co., Ltd.).
An intermediate layer of 0.1 μm was formed. Next, polycarbonate resin (Panlite L-
1250, manufactured by Teijin Chemicals)/CTM (-75) = 100/75
A 1,2-dichloroethane solution containing 16.5% by weight of
A charge transport layer having a thickness of m was formed. Next, in a ball mill in 1,2-dichloroethane, 24 CTM (-75) is added to Panlite L-1250 in the liquid that is crushed for 24 hours and then dispersed for 24 hours.
75% by weight for and 10% by weight for CTM
Exemplified Compound (2) was added. A dispersion prepared by adding monochlorobenzene to this solution so that the ratio of 1,2-dichlorobenzene/monochlorobenzene was 7/3 (volume ratio) was spray applied onto the CTL,
A charge generation layer having a thickness of 5 μm was formed by drying, and a photoreceptor according to the present invention having a photosensitive layer having a laminated structure was obtained. Comparative Example 1 A comparative photoreceptor was obtained in exactly the same manner as in Example 1 except that Exemplary Compound (2) was omitted. Example 2 A photoreceptor was obtained in exactly the same manner as in Example 1 except that Exemplified Compound (10) was used in place of Exemplified Compound (2). Example 3 On the photosensitive layer (same as the photoreceptor of Comparative Example 1) except for Exemplified Compound (2) of Example 1, thermosetting acrylic
A coating solution prepared by dissolving 1.55 parts by weight of melamine-epoxy (1:1:1) resin and 0.155 parts by weight of exemplified compound (2) in a mixed solvent of monochlorobenzene/1,1,2-trichloroethane was spray applied and dried. A photoreceptor having a protective layer with a thickness of 1 μm was obtained. Example 4 On the photosensitive layer excluding exemplified compound (2) of Example 1,
Primer PH91 for silicone hard coat (manufactured by Toshiba Silicone Co., Ltd.) is spray applied to a thickness of 0.1 μm, and on top of that, silicone hard coat Tosguard 510 (manufactured by Toshiba Silicone Co., Ltd.) and exemplified compound (2) are applied to the resin in an amount of 100 parts by weight. A solution containing 10 parts by weight of the solution was spray-coated and dried to form a 1 μm thick protective layer to obtain a photoreceptor. Example 5 An intermediate layer with a thickness of about 0.1 μm made of vinyl chloride-vinyl acetate-maleic anhydride copolymer (Eslec MF-10, supra) was formed on a conductive support made of polyester film laminated with aluminum foil. was formed. Next, 8% by weight of butyral resin (Eslec BX-1, manufactured by Sekisui Chemical Co., Ltd.) was used as a CTL coating liquid.
A coating solution obtained by dissolving 6 wt.
Next, apply 0.2 g of CGM (-7) to a paint conditioner (Paint Conditioner, manufactured by Red Devil).
Grind for 30 minutes, and add polycarbonate resin (Panlite L-1250, mentioned above) to this in a mixed solvent of 1,2-dichloroethane/1,1,2-trichloroethane.
Add 8.3g of a solution dissolved at 0.5% by weight and disperse for 3 minutes, then add 3.3% by weight, 2.6% by weight and 0.26% by weight of polycarbonate resin, CTM (-75) and Exemplary Compound (2), respectively. A solution obtained by dissolving in a mixed solvent of 1,2-dichloroethane/1,1,2/trichloroethane so that
19.1 g was added and dispersed for an additional 30 minutes. (The thus obtained dispersion was spray coated on the CTL and dried to form a charge generation layer with a thickness of 5 μm,
A photoreceptor having a photosensitive layer having a laminated structure was obtained. Comparative Example 2 A comparative photoreceptor was obtained in exactly the same manner as in Example 5 except that Exemplary Compound (2) was omitted. Example 6 A photoreceptor was obtained in exactly the same manner as in Example 5 except that Exemplified Compound (10) was used in place of Exemplified Compound (2). Example 7 A protective layer containing the same exemplified compound (2) as in Example 3 was installed on the photosensitive layer (same as the photoreceptor of Comparative Example 2) except for the exemplified compound (2) in Example 5, A photoreceptor was obtained. Example 8 On the photosensitive layer excluding exemplified compound (2) of Example 5,
A protective layer containing the same exemplified compound (2) as in Example 4 was provided to obtain a photoreceptor. The ozone resistance of the photoreceptor sample obtained as described above was evaluated using the following ozone fatigue tester. That is, an electrostatic tester (SP-428 manufactured by Kawaguchi Electric Seisakusho)
type) to the ozone generator (Japan Ozone Co., Ltd.)
An apparatus equipped with an ozone monitor (Model EG-2001 manufactured by Ebara Jitsugyo Co., Ltd.) was used. Attach the photoreceptor at an ozone concentration of 90ppm,
After applying a voltage of +6 KV and charging the photosensitive layer by corona discharge for 5 seconds, leave it for 5 seconds (the potential at this time is the initial potential V ₀ ), and then the illuminance on the surface of the photosensitive layer becomes 14 lux. This process was repeated 100 times by irradiating it with light from a tungsten lamp. When the potential after 100 irradiations is V _I , V _I /V _I0 ×
Ozone resistance was expressed as 100 (%). V _I /V _I0 is 100
This indicates the degree of potential drop after repetition, and the larger the value, the better. Also, without introducing ozone, the initial potential can be increased to +
Exposure required to attenuate from 600V to +100V
E ⁶⁰⁰ ₁₀₀ (lux seconds) was also measured. The smaller the number, the higher the sensitivity. These results are shown in the attached table.

[Table] From the attached table, the photoreceptors of the present invention all have excellent ozone resistance and electrophotographic properties, while
It can be seen that the comparative photoreceptor suffered from significant ozone deterioration and had poor electrophotographic characteristics.

[Brief explanation of the drawing]

1 to 3 are cross-sectional views of the positively charging photoreceptor of the present invention. DESCRIPTION OF SYMBOLS 1...Support, 2...Charge transport layer, 3...Charge generation layer, 4...Photosensitive layer, 5...Charge transport material (CTM), 6...Charge generation material (CGM), 7...
protective layer.

Claims (1)

[Scope of Claims] 1. An electrophotographic photoreceptor in which a charge transport layer and a charge generation layer, or a charge transport layer, a charge generation layer, and a protective layer are sequentially laminated on a conductive support, in which a charge transport substance is contained in the charge generation layer. 1. An electrophotographic photoreceptor for positive charging, characterized in that the outermost layer contains at least one compound represented by the following general formula [], [], or []. General formula [] [Formula] [wherein R represents an alkyl group, an alkenyl group, a cycloalkyl group, an aryl group or a heterocyclic group,
R ₁ , R ₂ and R ₃ are each a hydrogen atom, a halogen atom, an alkyl group, a cycloalkyl group, an alkoxy group, an alkylthio group, an aryl group, an aryloxy group, an arylthio group, an acyl group, an acylamino group, a diacylamino group, Represents an acyloxy group, an alkylamino group, a sulfonamide group, or an alkoxycarbonyl group. Further, R and R ₁ may be cyclized with each other to form a chroman ring, and this chroman ring may have a substituent. _R4 , _R5 , _R6 ,
R ₇ , R ₈ and R ₉ each represent a hydrogen atom, a halogen atom, an alkyl group, an alkoxy group, an alkylthio group, an alkenyl group, an alkenoxy group, an aryl group, an aryloxy group, an N-substituted amino group or a heterocyclic group However, R ₄ , R ₅ , R ₆ and R ₇ are never hydrogen atoms at the same time. Further, R ₆ and R ₉ may be cyclized with each other to form a carbocycle, and the carbocycle may be substituted with an alkyl group. ] General formula [ ] [In the formula, R, R ₁ , R ₂ and R ₃ are the above general formula [ ]
Each has the same meaning as R, R ₁ , R ₂ and R ₃ in . Furthermore, R and R ₁ may be cyclized with each other to form a Claman ring, and this Claman ring may have a substituent. R ₄ , R ₅ , R ₆ and R ₇ are also synonymous with R ₄ , R ₅ , R ₆ and R ₇ in the general formula [], but
R ₄ and R ₅ are never hydrogen atoms at the same time. ] General formula [ ] [In the formula, R ₁ to _{R 9} are R ₁ in the above general formula [ ]
~ _R9 , respectively, and _R1 ~ _R9 are synonymous with _R1 ~ _R9.
are synonymous with R ₄ , R ₅ , R ₆ , R ₇ ,
R ₄ , R ₅ , R ₆ and R ₇ are never hydrogen atoms at the same time. X is an alkylene group whose carbon chain is -O-,
Represents an alkylene group, phenylene group, cycloalkylene group or divalent heterocyclic group which may be bonded via -S-, -NH- or _-SO2- . ]