JPH08262751A - Composition for electric charge transferring layer and electrophotographic photoreceptor using same - Google Patents

Abstract

PURPOSE: To unnecessitate a halogen-contg. solvent from the viewpoint of the protection of environment, to form a printed image having high image quality and to ensure rapid optical responsiveness by incorporating polyester resin having specified repeating structural units and an electric charge transferring material. CONSTITUTION: This compsn. contains polyester resin having repeating structural units represented by the formula and an electric charge transferring material. In the formula, each of R<1> and R<2> is a divalent org. group and each of R<3> -R<6> is H or 1-4C alkyl. The wt. average mol.wt. Mw (expressed in terms of polystyrene) of the polyester resin measured by gel permeation chromatography is preferably 20,000-900,000, especially preferably 50,000-300,000. In the case of <20,000, the frictional resistance of the electric charge transferring material is liable to decrease. In the case of >900,000, it becomes difficult to form a film in a uniform thickness. Any of various known electric charge transferring materials such as fluorene and fluorenone may be used as the electric charge transferring material.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a composition for a charge transport layer and an electrophotographic photoreceptor using the composition.

[0002]

2. Description of the Related Art An electrophotographic photosensitive member using an organic photoconductive compound has been widely researched recently because it is advantageous in flexibility, lightness, surface smoothness and cost. Among them, a function-separated electrophotographic photoreceptor provided with a charge generation layer that generates charge carriers by light absorption and a charge transport layer that transports the generated charge carriers by an electric field has conventionally used an organic photoconductive compound. Since the photoresponsiveness, sensitivity, etc., which are the major drawbacks of electrophotographic photoreceptors, can be greatly improved, recent rapid progress is being made.

These function-separated type organic electrophotographic photoreceptors are used by being mounted on an electrophotographic apparatus (printer, copying machine, etc.) by the Carlson method.

However, recently, due to the high image quality of a printed image obtained by an electrophotographic apparatus such as a copying machine or a laser beam printer and the increase in printing speed due to the downsizing of the electrophotographic apparatus, the electrophotographic photosensitive member has a great advantage. There is an increasing demand for higher image quality of printed images and faster photoresponse.

Conventionally, as the binder resin for the charge transport layer of the electrophotographic photosensitive member, the following formula is used in view of transparency and mechanical strength.

[Chemical 4] Bisphenol A having a repeating structural unit represented by
Type polycarbonate resins are the most commonly used.

The composition for charge transport layer comprises a charge transport material,
It is prepared by uniformly dissolving or dispersing a bisphenol A type polycarbonate resin which is a binder resin and additives such as a plasticizer, a fluidity imparting agent and a pinhole control agent, which are used as necessary, in a solvent.

However, since the bisphenol A type polycarbonate resin is inferior in solubility, halogen type solvents (methylene chloride, 1,2-dichloromethane, 1,1,2-trichloroethane, etc.), a mixture of halogen type solvents or a halogen type solvent. And a non-halogen solvent.

In order to obtain high-speed photoresponsiveness, the charge transporting substance in the composition for charge transporting layer is increased.

In the composition for the charge transporting layer containing the increased amount of the charge transporting substance, the charge transporting substance and the bisphenol A type polycarbonate resin are uniformly dissolved in a solution state, but this is dried and the solvent is removed. In the formed solid-state charge transport layer, the charge-transporting substance and the bisphenol A type polycarbonate resin are phase-separated, and the coating film tends to be non-uniform in terms of morphology and composition. When the electrophotographic photosensitive member is formed using the layer composition, image defects such as fogging, black spots, and white spots occur from the initial stage of use,
It is not possible to obtain an electrophotographic photosensitive member that satisfies high-speed photoresponsiveness and high image quality. Further, during repeated use, the developer (toner) may adhere to the surface of the charge transport layer, causing a so-called filming phenomenon, which may be one of the causes of streak-like defects in the image. On the other hand, the movement to protect the global environment has intensified,
The abolition of CFCs that destroy the ozone layer and the regulation of halogen-based solvents that contaminate groundwater have been tightened.

[0010]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems of the prior art, does not require a halogen-based solvent from the standpoint of environmental protection, improves the quality of printed images, and has a fast photoresponsiveness. The present invention provides a composition for a charge transport layer capable of producing an excellent electrophotographic photoreceptor and an electrophotographic photoreceptor using the same.

[0011]

The present invention has achieved the above object by using a polyester resin having a specific repeating structural unit in a composition for a charge transport layer.

That is, the present invention has the general formula (I)

Embedded image [In the formula, R ¹ and R ² each independently represent a divalent organic group,
R ³ , R ⁴ , R ⁵ and R ⁶ each independently represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms] and a charge transporting layer containing a polyester resin having a repeating structural unit and a charge transporting substance. The present invention relates to a composition for use and an electrophotographic photosensitive member having a charge transport layer using the composition.

The present invention will be described in detail below. The molecular weight of the polyester resin having the repeating structural unit represented by the general formula (I) in the present invention is 20,000 to 900,000 in terms of polystyrene-converted weight average molecular weight Mw measured by gel permeation chromatography. It is preferable and it is more preferable that it is 50,000 to 300,000. If this molecular weight is less than 50,000, the abrasion resistance of the charge transport layer tends to be reduced, and if it exceeds 900,000, it tends to be difficult to form a uniform film thickness. Examples of the polyester resin having the repeating structural unit represented by the general formula (I) include O-PET (trade name, manufactured by Kanebo Co., Ltd.).

Examples of the divalent organic groups R ¹ and R ² in the general formula (I) include methylene group, ethylene group, propylene group, butylene group, pentylene group and hexylene group. From the viewpoints of easiness of synthesis, solubility, etc., an ethylene group is preferable. Examples of R ³ , R ⁴ , R ⁵ and R ⁶ which are alkyl groups having 1 to 4 carbon atoms include, for example:
Examples thereof include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group and a tert-butyl group.

The polyester resin having a repeating unit represented by the general formula (I) is easy to synthesize, soluble,
From the viewpoint of electrophotographic characteristics, general formula (II)

[Chemical 6] [In the formula, R ¹ , R ² , R ³ , R ⁴ , R ⁵ and R ⁶ have the same meanings as in formula (I), and R ⁷ , R ⁸ and R ⁹ are each independently a divalent organic group. Represents a group, and m and n have m / n of 1 to
It is a positive integer selected so as to be 10].

Examples of the divalent organic groups R ⁷ , R ⁸ and R ⁹ in the general formula (II) include, for example,

[Chemical 7] [In the formula, r is an integer of 1 to 6] and the like, and among these, from the viewpoint of availability, mechanical properties, and the like,

Embedded image Is preferred. As the polyester resin having the repeating unit represented by the general formula (II), the polyester resin having the general formula (III) is most easily available.

[Chemical 9] [Wherein, m and n are positive integers selected so that m / n is from 1 to 10] and are preferably polyester resins having a repeating structural unit.

The general formula (II) and the general formula (II
The copolymer composition ratio (m / n) in I) needs to be selected to be 1 to 10, preferably 2 to 9. If the copolymer composition ratio (m / n) is less than 1, the resin becomes rigid and difficult to dissolve in the solvent, and if it exceeds 10, the resin becomes rigid and difficult to dissolve in the solvent.

The charge transporting substance in the present invention includes
Various known compounds can be used, for example, fluorene, fluorenone, 2,7-dinitro-9-fluorenone, 4
H-indeno (1,2,6) thiophen-4-one,
3,7-Dinitro-dibenzothiophene-5-oxide, 1-bromopyrene, 2-phenylpyrene, carbazole, 3-phenylcarbazole, 2-phenylindole, 2-phenylnaphthalene, oxazole, oxadiazole, oxatriazole, triphenyl Amine, imidazole, chrysene, tetraphene, aclidene, various hydrazones, styryl compounds, poly-N-vinylcarbazole, halogenated poly-N-vinylcarbazole, 1-phenyl-3- (4-diethylaminostyryl) -5- ( 4-diethylaminophenyl) pyrazoline, polyvinylpyrene, 2-phenyl-4- (4-diethylaminophenyl) -5-phenyloxazole, polyvinyl indoloquinoxaline, 1,1-bis (p-diethylaminophenyl) 4,4-diphenyl-1,3
-Butadiene, polyvinyl benzothiophene, polyvinyl anthracene, polyvinyl acridine, benzidine,
Examples thereof include polyvinyl pyrazoline and derivatives thereof.

The charge transport layer composition of the present invention usually contains
Although a solvent is included, it is preferable to use a non-halogen solvent capable of dissolving the polyester resin having the repeating structural unit represented by the general formula (I) as such a solvent from the viewpoint of environmental protection. The boiling point temperature of the solvent used is preferably 35 to 170 ° C., and 40 to 1
More preferably, it is 55 ° C. If the boiling point temperature of this solvent is less than 35 ° C., unevenness in the thickness of the coating film may occur when dip coating is performed, and the characteristics of the obtained photoreceptor tend to vary depending on the position. If it exceeds, the thickness unevenness of the coating film tends to occur when the dip coating is performed, and the characteristics tend to vary depending on the position of the obtained photoreceptor.

Examples of the solvent include non-halogen solvents such as tetrahydrofuran, methyl ethyl ketone, benzene, toluene and xylene. These are used alone or in combination of two or more. The blending amount of these solvents is 300 to 900 with respect to 100 parts by weight of the total amount of the charge transporting substance and the polyester resin having the repeating structural unit represented by the general formula (I).
It is preferably used in the range of parts by weight. If the amount is less than 300 parts by weight, the viscosity of the composition is too high, and it tends to be difficult to form a uniform coating film.
If the amount is more than parts by weight, the viscosity of the composition tends to be too low and the film thickness of the coating film tends to be too thin.

The compounding amount of the polyester resin having the repeating structural unit represented by the general formula (I) in the composition for charge transporting layer of the present invention is as follows.
It is preferably used in the range of 50 to 450 parts by weight with respect to 0 parts by weight. If the amount is less than 50 parts by weight,
The coating properties tend to be inferior, and if it exceeds 450 parts by weight,
The electrophotographic properties tend to deteriorate.

Further, the charge transport layer composition of the present invention may contain known additives such as a plasticizer, a fluidity imparting agent and a pinhole controlling agent, if necessary. It is preferable to use each of these additives in an amount of 5 parts by weight or less based on 100 parts by weight of the charge transporting substance.

Next, a method for manufacturing the electrophotographic photosensitive member will be described. The electrophotographic photosensitive member is obtained by forming an undercoat layer on a conductive substrate, if necessary, and then forming a charge generation layer and a charge transport layer. Here, as the conductive substrate, a metal (aluminum, iron, copper, nickel, etc.), a conductive paper or plastic film, a sheet and a seamless belt, a plastic film laminated with a metal foil (aluminum, etc.), a sheet and a seamless film are used. belt,
Examples thereof include a film sheet of a metal plate, a seamless belt, and a conductor such as a metal drum.

The undercoat layer used as necessary on the above-mentioned conductive substrate is, for example, titanium oxide, aluminum oxide, zirconia, titanic acid, zirconic acid, lanthanum lead, titanium black, silica, titanic acid. Fine particles of lead and barium titanate, polyamide resin, phenol resin, casein, melamine resin, benzoguanamine resin,
Polyurethane resin, epoxy resin, cellulose, polyvinyl butyral resin and the like are mentioned, and these are used alone or in combination of two or more kinds. Among them, when the fine particles are used, the resin is adsorbed on the fine particles and a smooth film can be obtained, and therefore it is preferable to use the fine particles and the resin together.

As a method for forming the undercoat layer, a solution obtained by dispersing and dissolving the fine particles and / or resin in a solvent is applied onto a conductive substrate by dip coating method, spray coating method, roll coating method, applicator coating method, It can be formed by coating using a coating method such as a wire bar coating method and drying.

Examples of the solvent used at this time include acetone, methyl ethyl ketone, methyl isobutyl ketone, tetrahydrofuran, toluene, ethyl acetate, toluene, xylene, cellosolve, methanol, isopropyl alcohol, isobutyl alcohol, n-butyl alcohol and the like. The thickness of the undercoat layer is 0.01 to
20.0 μm is preferable, and 0.1 to 3.0 μm
More preferably, it is m. This thickness is 0.01μ
When it is less than m, it tends to be difficult to uniformly form the undercoat layer, and when it exceeds 20.0 μm, electrophotographic properties tend to be deteriorated. After forming the undercoat layer as described above, the charge generation layer and the charge transport layer can be sequentially laminated on the layer to form the undercoat layer.

In the present invention, as the photoconductive substance used in the charge generation layer, azoxybenzene type, disazo type, trisazo type, benzimidazole type, polycyclic quinoline type, indigoid type, quinacridone type, phthalocyanine type, Known organic pigments such as naphthalocyanine-based, pyrrolopyrrole-based, perylene-based, and methine-based organic pigments that generate an electric charge when irradiated with light are included.

When the charge generating layer is formed using only the photoconductive substance, a vacuum deposition method or the like is used, and
When the charge generation layer is formed using the photoconductive substance and other components, the photoconductive substance, the binder and the plasticizer, the curing catalyst, the fluidity imparting agent, the pinhole control agent, etc. are required. The additive used according to the above is uniformly dissolved in a solvent such as acetone, methyl ethyl ketone, methyl isobutyl ketin, tetrahydrofuran, ethyl acetate, cellosolve, methanol, isopropyl alcohol, isobutyl alcohol, n-butyl alcohol, and a mixed solvent thereof. Alternatively, a dispersed charge generation layer-forming coating liquid is prepared, and the coating liquid is applied onto the undercoat layer by a coating method such as a dip coating method, a spray coating method, a roll coating method, an applicator coating method, or a wire bar coating method. It can be formed by coating and drying.

As the binder, for example, silicone resin, polyamide resin, polyurethane resin, polyester resin, epoxy resin, polyketone resin, polycarbonate resin, polystyrene resin, polymethacrylate resin,
Polyacrylamide resin, polybutadiene resin, polyisoprene resin, melamine resin, benzoguanamine resin,
Polychloroprene resin, polyacrylonitrile resin, ethyl cellulose resin, nitrocellulose resin, urea resin, phenol resin, phenoxy resin, polyvinyl butyral resin, formal resin, vinyl acetate resin, vinyl acetate / vinyl chloride copolymer, polyester carbonate resin, etc. To be Further, a heat and / or light curable resin can also be used. In any case, there is no particular limitation as long as it is an electrically insulating resin that can form a film in a normal state.

As described above, when the charge generating layer is formed using the photoconductive substance and other components, the binder resin content in the charge generating layer is 100 wt% of the photoconductive substance. 5 to 200 parts by weight relative to parts,
More preferably, it is 10 to 100 parts by weight. If the amount is less than 5 parts by weight, the film of the charge generation layer tends to be non-uniform and the image quality tends to be poor, and if it exceeds 200 parts by weight, the sensitivity tends to decrease and the residual potential tends to increase.

Examples of the plasticizer include halogenated paraffin, dimethyl naphthalene, dibutyl phthalate and the like. Examples of the curing catalyst include sulfonic acid systems such as methanesulfonic acid, dodecylbenzenesulfonic acid, and dinonylnaphthalenedisulfonic acid. Also,
Examples of the fluidity-imparting agent include Modaflow (manufactured by Monsanto Chemical Co., Ltd.) and Acronal 4F (manufactured by Basuf Co.). Furthermore, examples of the pinhole control agent include benzoin and dimethyl phthalate. Each of these is preferably used in an amount of 5 parts by weight or less based on the photoconductive substance.

The thickness of the charge generation layer is 0.01 to 2.0 μm.
The thickness is preferably m, and more preferably 0.1 to 0.8 μm. If this thickness is less than 0.01 μm, it tends to be difficult to uniformly form the charge generation layer, and if it exceeds 2.0 μm, the electrophotographic characteristics tend to deteriorate. After forming the charge generation layer as described above, the composition for the charge transport layer produced as described above is further applied onto this layer by dip coating, spray coating, roll coating, applicator coating. It can be formed by coating using a coating method such as a wire bar coating method and drying. The thickness of the charge transport layer is preferably 5 to 50 μm, more preferably 8 to 35 μm. If this thickness is less than 5 μm, the potential tends to be low in the initial stage, and if it exceeds 50 μm, the electrophotographic characteristics tend to deteriorate.

In the electrophotographic photoreceptor of the present invention, a protective layer can be further formed on the charge transport layer from the viewpoint of abrasion resistance. The thickness of the protective layer is preferably 0.01 to 10 μm, more preferably 0.1 to 3 μm. If the film thickness is less than 0.01 μm, the protective layer is not effective and the durability tends to be poor, and if it exceeds 10 μm, the sensitivity tends to decrease and the residual potential tends to increase.

When printing is performed using the electrophotographic photosensitive member of the present invention, it is possible to transfer the image onto plain paper and fix it by developing it after charging and exposing as in the conventional case. .

[0035]

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

The materials used in the following examples are listed below. The abbreviations are shown in parentheses. (A) Photoconductive substance that generates electric charge τ type metal-free phthalocyanine (τ-H ₂ Pc) (manufactured by Toyo Ink Industry Co., Ltd.) (b) Charge transporting substance

[Chemical 10] 1,1-bis (P-diethylaminophenyl) -4,4
-Diphenyl-1,3-butadiene (PBD) (manufactured by Takasago International Corporation) (A) For undercoat layer MX1970 (MX1970), solid content 100% by weight
(Manufactured by Nippon Rilsan Co., Ltd.) Melan 2000 (ML2000) (butylated melamine resin having a bound formaldehyde number of 4.0 and a methylol group number of 1.0), solid content 50% by weight (manufactured by Hitachi Chemical Co., Ltd.) (B) Brominated phenoxy resin for charge generation layer YPB-43 (YPB-43), solid content 40% by weight (Toto Kasei Co., Ltd.)

(C) For charge transport layer Polycarbonate resin having the following repeating structural unit

[Chemical 11] Lexan 141-111 (L141), solid content 100% by weight (manufactured by General Electric Company), polyester resin having the following repeating structural unit

[Chemical 12] O-PET (O-PET), m / n = 7/3, solid content 1
00 wt% (Kanebo Co., Ltd.) Polycarbonate resin having the following repeating structural unit

[Chemical 13] TS-2050 (TS-2050), solid content 100% by weight (manufactured by Teijin Chemicals Ltd.)

Example 1 70 g of MX1970, 140 g of ML2000 and 4.2 g of trimellitic acid were mixed with 3600 of methyl ethyl ketone.
completely dissolved in g, and this solution was applied onto an aluminum drum (outer diameter 120 mm, length 486 mm, thickness 4 mm) by a dip coating method and dried at 120 ° C. for 30 minutes to give a film thickness of 0.3 μm. To form an undercoat layer. Next, τ-H ₂ Pc
100 g, 200 g of YPB-43 and 3700 g of tetrahydrofuran were dispersed for 80 hours using an ultrasonic disperser, and the resulting charge generation layer coating liquid was applied onto the undercoat layer by a dip coating method, It was dried at 140 ° C. for 30 minutes to form a charge generation layer having a thickness of 0.3 μm. Then P
BD 140 g and O-PET 260 g are dissolved in tetrahydrofuran 2400 g, and this solution is applied onto the charge generation layer by a dip coating method and dried at 100 ° C. for 30 minutes to form a charge transport layer having a thickness of 18 μm. Then, an electrophotographic photosensitive member (1) was formed.

The photoresponsiveness and image quality (initial and after 100 KP printing) of the obtained electrophotographic photosensitive member (1) were evaluated by the following methods, and the results are shown in Table 1. Light response: Light attenuation measurement (Midaya Denki Co., Cynthia 30)
When corona charging is performed so that the surface potential becomes −700 V and light of wavelength 780 nm is irradiated for 20 ms, V
_The time (millisecond) required for ₀ to become -350V was measured. Image quality: Using an image evaluation machine (negative charging, reversal development method),
Fogging, black spots, white spots, and filming were visually confirmed at the initial stage and after 100 KP printing. The surface potential is -70.
The bias potential was 0 V and -600 V. In addition, the image density of a black background can be measured by the Macbeth reflection densitometer (A division of koll
mergen Corporation).

Comparative Example 1 In the same manner as in Example 1, after forming an undercoat layer and a charge generation layer, PBD 140 g and L141 260 g were formed.
Was dissolved in 2400 g of tetrahydrofuran, and a charge transport layer having a film thickness of 17 μm was formed in the same manner as in Example 1 to form an electrophotographic photoreceptor (2). Photoresponsiveness and image quality of the obtained electrophotographic photosensitive member (2) (initial and after printing 100 KP)
Was evaluated in the same manner as in Example 1, and the results are shown in Table 1.

Comparative Example 2 After forming an undercoat layer and a charge generation layer in the same manner as in Example 1, 140 g of PBD and TS-20502 were formed.
60 g of tetrahydrofuran was dissolved in 2400 g of tetrahydrofuran, and a charge transport layer having a film thickness of 16 μm was formed in the same manner as in Example 1 to form an electrophotographic photosensitive member (3). Photoresponsiveness and image quality of the obtained electrophotographic photosensitive member (3) (initial and 100 KP
(After printing) was evaluated in the same manner as in Example 1, and the results are shown in Table 1.
It was shown to.

[0042]

[Table 1]

From Table 1, the electrophotographic photosensitive member of Example 1 is
It has a good photoresponsiveness, there is no fog, black spots, and white spots in the initial image quality as well as the image quality after 100KP printing, and there are no black stripe defects due to toner filming on the surface of the charge transport layer. The concentration was also good. Further, the electrophotographic photosensitive member of Comparative Example 1 had good photoresponsiveness and good image density, but in the initial image quality, a large amount of fog, black spots, and white spots occurred, and the charge transport layer surface Since black streak defects due to toner filming also occurred, evaluation after 100 KP printing was not performed. In addition, the electrophotographic photosensitive member of Comparative Example 2 has a good photoresponsiveness and a good image density, and has no fog, black spots, or white spots in the initial image quality, and the toner on the surface of the charge transport layer. Although there were no black streak defects due to filming, black streak defects due to filming occurred in the image quality after 100 KP printing.

[0044]

The composition for the charge transport layer according to claim 1 comprises:
A mixed state of a charge transporting substance and a polyester resin as a binder in a charge transporting layer formed by using this can be made extremely uniform, and an electrophotographic photoreceptor having the charge transporting layer can be used as a high speed printer. When it is mounted on and is used for continuous printing, it produces excellent image quality without fog, black spots, white spots, and filming. The composition for a charge transport layer according to claim 2 exhibits the effect of the composition for a charge transport layer according to claim 1, and is further excellent in easiness of synthesis, solubility and electrophotographic characteristics. The composition for a charge transport layer according to claim 3 is the composition according to claim 2.
The effect of the composition for a charge transport layer described above is exhibited, and the availability and mechanical properties are excellent. The composition for a charge transport layer according to claim 4 has the effects of the composition for a charge transport layer according to claims 1, 2 and 3, and is also excellent in environmental protection. The electrophotographic photoreceptor according to claim 5 can be applied extremely advantageously to a printer that requires high-speed response, high image quality, and a high number of printed sheets.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Susumu Kaneko 4-13-1, Higashimachi, Hitachi City, Ibaraki Prefecture Hitachi Chemical Co., Ltd. Yamazaki Plant (72) Inventor Yasuo Katsutani 4-chome, Higashimachi, Ibaraki Prefecture No. 1 Hitachi Chemical Co., Ltd. Yamazaki Factory

Claims (5)

[Claims] 1. A compound of the general formula (I) [In the formula, R ¹ and R ² each independently represent a divalent organic group,
R ³ , R ⁴ , R ⁵ and R ⁶ each independently represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms] and a charge transporting layer containing a polyester resin having a repeating structural unit and a charge transporting substance. Composition. 2. A polyester resin having a repeating unit represented by the general formula (I) is represented by the general formula (II): [In the formula, R ¹ , R ² , R ³ , R ⁴ , R ⁵ and R ⁶ have the same meanings as in formula (I), and R ⁷ , R ⁸ and R ⁹ are each independently a divalent organic group. Represents a group, and m and n have m / n of 1 to
It is a positive integer selected so as to be 10.] The composition for a charge transport layer according to claim 1, which is a polyester resin having a repeating structural unit represented by the formula: 3. A polyester resin having a repeating unit represented by the general formula (II) is represented by the general formula (III): A polyester resin having a repeating structural unit represented by the formula: wherein m and n are positive integers selected so that m / n is 1 to 10. Composition. 4. The composition for a charge transport layer according to claim 2, further comprising a non-halogen solvent capable of dissolving the polyester resin. 5. An electrophotographic photoreceptor having a charge transport layer, which comprises the composition for a charge transport layer according to claim 2, 3 or 4.