JPH10282699A - Electrophotographic photoreceptor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the electrophotographic photoreceptor usable for copying machines and printers in a positively charged state and high in sensitivity and superior in electric characteristics by incorporating at least one of a specified thiophene derivative and a charge transfer material in a photosensitive layer. SOLUTION: This electrophotographic photoreceptor is provided on the conductive substrate with the photosensitive layer containing at least one kind of the thiophene derivative represented by formula I in which each of R<1> -R<6> and R<9> is an H atom or an alkyl or alkoxy group; each of R<7> and R<8> is cyano or alkoxycarbonyl group; and each of alkyl and alkoxy groups of R<1> -R<9> is, preferably, a 1-8C group, and the thiophene derivative can be synthesized by the usual method, thus permitting the obtained electrophotographic photoreceptor to be usable in a positive charged state and high in sensitivity and superior in electric characteristics.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic photoreceptor, and more particularly to an electrophotographic photoreceptor related to an improvement in an electric charge transport material used in a photosensitive layer.

[0002]

2. Description of the Related Art Conventionally, an inorganic photoconductive material such as selenium or a selenium alloy has been used as a photosensitive layer of an electrophotographic photosensitive member.
One in which an inorganic photoconductive substance such as zinc oxide or cadmium sulfide is dispersed in a resin binder has been used.
However, in recent years, application to electrophotographic photoconductors using an organic photoconductive substance has been advanced, and sensitivity, durability, and the like have been improved and commercialized.

A photoreceptor is required to have a function of retaining a surface charge in a dark place, a function of receiving light to generate a charge, and a function of receiving light and transporting a charge. A layer separates the functions into a so-called single-layer type photoreceptor that combines these functions, a layer that mainly contributes to charge generation, and a layer that contributes to charge transport when receiving surface light in the dark and receiving light. There is a so-called laminated type photoconductor in which layers are laminated. For image formation by electrophotography using these photoconductors,
For example, the Carlson method is applied. Image formation by this method is performed by charging the photoconductor in a dark place by corona discharge,
Forming an electrostatic latent image such as a character or a picture of a document on the charged photoreceptor surface, developing the formed electrostatic latent image with toner,
The developed toner image is fixed on a support such as paper, and the photoreceptor after transfer of the toner image is subjected to charge elimination, removal of residual toner, light charge elimination, and the like, and then reused.

[0004] Practically used organic photoreceptors have advantages such as flexibility, film forming property, low cost, and safety as compared with inorganic photoreceptors. Improvements are underway. Most of the organic photoreceptors are laminated photoreceptors in which functions are separated into a charge generation layer and a charge transport layer. In general, a laminated organic photoreceptor is obtained by sequentially forming a charge generation layer composed of a charge generation substance such as a pigment and a dye, and a charge transport layer composed of a charge transport substance such as hydrazone and triphenylamine on a conductive support. Due to the nature of the electron-transporting charge transporting substance, it becomes a hole-transfer type and has sensitivity when the surface of the photoreceptor is negatively charged. However, in the case of negative charging, the corona discharge used during charging is more unstable than in the case of positive charging, and ozone and nitrogen oxides are generated and are likely to be physically and chemically deteriorated by being adsorbed on the photoreceptor surface. Is worse. From such a point, as a photosensitive member, a positive charging type photosensitive member having a greater degree of freedom in use conditions is more widely applied and advantageous than a negative charging type photosensitive member.

Therefore, various photoconductors for use in positive charging have been proposed. For example, a method in which a charge generating substance and a charge transporting substance are simultaneously dispersed in a resin binder and used as a single photosensitive layer has been proposed and partially put into practical use.
However, the sensitivity is not sufficient for application to a high-speed machine, and further improvement is required in terms of repetition characteristics and the like.
Further, in order to obtain a function-separated type laminated structure for the purpose of increasing the sensitivity, a method of forming a photoreceptor by laminating a charge generating layer on a charge transporting layer, and using the photoreceptor with positive charge may be considered. But,
In this method, since the charge generation layer is formed on the surface, there is a problem in stability during repeated use due to corona discharge, light irradiation, mechanical abrasion, and the like. In this case, it has been proposed to further provide a protective layer on the charge generation layer. However, this method has a problem that although mechanical wear is improved, electrical characteristics such as sensitivity are reduced.

Further, there has been proposed a method of forming a photoreceptor by laminating a charge transport layer on a charge generation layer. As the charge transport substance, 2,4,7-trinitro-9-fluorene and the like are known, but this substance is carcinogenic and has a safety problem. In addition, cyano compounds and quinone compounds are disclosed in JP-A-50-131941, JP-A-6-594.
No. 83, Japanese Patent Application Laid-Open No. 6-123986, and the like, but it is the actual situation that a compound having an electron transporting ability sufficient for practical use has not been obtained.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and has been developed by using a new organic material which has never been used as a charge transport material in the photosensitive layer. It is an object of the present invention to provide an electrophotographic photoreceptor for a copying machine and a printer, which can be used with positive charge and has high sensitivity and excellent electric characteristics.

[0008]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have found that by including at least one specific thiophene derivative as a charge transport material in a photosensitive layer of an electrophotographic photosensitive member. The inventors have found that the above object can be achieved, and have completed the present invention.

That is, the electrophotographic photoreceptor of the present invention comprises:
The photosensitive layer formed on the conductive substrate has the following general formula (I),(Where R ¹, R², R³, R⁴, R⁵, R⁶And R ⁹
Is a hydrogen atom, an alkyl group or an alkoxy group,
⁷And R⁸Is a cyano group or an alkoxycarbonyl group, respectively.
Represents a radical. )
At least one kind is included as a charge transport material
Things.

Further, another electrophotographic photoreceptor of the present invention comprises:
The photosensitive layer formed on the conductive substrate has the following general formula (II), (Wherein, R ¹² , R ¹³ , R ¹⁴ , R ¹⁵ , R ¹⁶ and R ¹⁷ each represent a hydrogen atom, an alkyl group or an alkoxy group, and R ¹⁰ and R ¹¹ each represent a cyano group or an alkoxycarbonyl group. ), Which contains at least one of the thiophene derivatives as a charge transport material.

The alkyl and alkoxy groups in R ^{1 to} R ⁹ in the above formula (I) preferably have 1 to 8 carbon atoms.

Further, the alkyl group and the alkoxy group represented by R ^{12 to} R ¹⁷ in the above formula (II) preferably have 1 to 8 carbon atoms.

Heretofore, no example of an electrophotographic photosensitive member using a thiophene derivative represented by the above general formula (I) or (II) for a photosensitive layer has been known. The present inventors have intensively studied various organic materials in order to achieve the above-mentioned object, and as a result of conducting numerous experiments on these thiophene derivatives, the technical elucidation thereof has not yet been sufficiently completed. It has been found that the use of a thiophene derivative having a specific skeleton represented by the general formula (I) or (II) as a charge transporting substance is extremely effective in improving electrophotographic properties, and a high charge that can be used in positive charging. An electrophotographic photoreceptor having excellent sensitivity and electrical characteristics has been obtained.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The above general formula used in the present invention
The thiophene derivatives represented by (I) and (II) can be synthesized by a usual method. That is, the general formula
The compound represented by (I) is an aldehyde represented by the following structural formula (III), a compound represented by the following structural formula (IV), and the compound represented by the general formula (II) has the following structure An aldehyde represented by the formula (V) and a compound represented by the following structural formula (VI) are subjected to a dehydration condensation reaction in a suitable organic solvent such as benzene or toluene in the presence of an alkali. Can be easily synthesized.

[0015] Specific examples of the thiophene derivatives represented by the general formulas (I) and (II) thus obtained are as follows.

[0016]

[0017]

The photoreceptor of the present invention contains the above-mentioned thiophene derivative in the photosensitive layer. Depending on how these thiophene derivatives are applied to the photosensitive layer, as shown in FIG. 1 or FIG. Can be used.

FIGS. 1 and 2 are conceptual cross-sectional views of an electrophotographic photosensitive member as an example of the present invention, wherein 1 is a conductive substrate, 2 and 5 are photosensitive layers, and 3 is a charge generating layer. Reference numeral 4 denotes a charge transport layer, and reference numeral 6 denotes a coating layer.

FIG. 1 shows a photosensitive layer 2 in which a charge generating substance and a thiophene derivative as a charge transporting substance are dispersed in a resin binder (binder) on a conductive substrate 1. 1 shows an electrophotographic photoconductor provided with a coating layer 6, which is generally referred to as a single-layer photoconductor.

FIG. 2 shows that a photosensitive layer 5 composed of a laminate of a charge generation layer 3 mainly composed of a charge generation substance and a charge transport layer 4 containing a thiophene derivative as a charge transport substance is provided on a conductive substrate 1. 1 shows a photoconductor for electrophotography, which is generally referred to as a laminated photoconductor.

The photoreceptor shown in FIG. 1 can be manufactured by dispersing a charge generating substance in a solution in which a charge transporting substance and a resin binder are dissolved, and applying this dispersion on a conductive substrate. If necessary, a coating layer can be applied and formed.

In the photoreceptor shown in FIG. 2, a charge-generating substance is vacuum-deposited on a conductive substrate, or a dispersion obtained by dispersing particles of the charge-generating substance in a solvent or a resin binder is applied and dried. And a solution in which a charge transport material and a resin binder are dissolved is applied thereon and dried.

The conductive substrate 1 serves as an electrode of the photoreceptor and serves as a support for the other layers, and may be cylindrical, plate-like or film-like. , A metal such as nickel, or a material obtained by performing a conductive treatment on glass, resin, or the like can be used.

The charge generation layer 3 is formed by applying a material in which particles of a charge generation substance are dispersed in a resin binder as described above, or is formed by a method such as vacuum deposition, and receives light to generate charges. Occur. In addition, it is important that the charge generation efficiency is high, and at the same time, the injectability of the generated charges into the charge transport layer 4 is important. As the charge generating substance, metal-free phthalocyanine, phthalocyanine compounds such as titanyl phthalocyanine, various azo, quinone, indigo, cyanine, squarylium, azulhenium, pigments or dyes such as pyrylium compounds, and selenium or selenium compounds are used. A suitable substance can be selected according to the light wavelength region of the exposure light source used for the formation. Since the charge generation layer only needs to have a charge generation function, its thickness is determined by the light absorption coefficient of the charge generation substance, and is generally 5 μm or less, preferably 2 μm or less. The charge generation layer may be mainly composed of a charge generation substance, to which a charge transport substance or the like is added. As the resin binder, polycarbonate, polyester, polyamide, polyurethane, vinyl chloride, phenoxy resin, polyvinyl butyral, diallyl phthalate resin, and polymers and copolymers of methacrylic acid esters can be used in appropriate combination.

The charge transport layer 4 is a coating film in which a thiophene derivative represented by the general formula (I) or (II) is dispersed as a charge transport material in a resin binder. In a dark place, the photosensitive layer serves as an insulator layer. And has the function of transporting the charge injected from the charge generation layer during photoreception. The thickness of such a charge transport layer is preferably from 10 to 40 μm. Polymers and copolymers of polycarbonate, polyester, polystyrene, and methacrylate can be used as the resin binder. In order to prevent ozone deterioration and the like which may hinder the use of the obtained photoreceptor, the charge transport layer 4 may be made of amine, phenol, sulfur, phosphite, phosphorus, etc. It is also possible to contain an antioxidant.

The layer 6 has a function of receiving and holding the charge of corona discharge in a dark place, and has a function of transmitting light sensitive to the photosensitive layer. In addition, in the multilayer 6,
At the time of exposure, it is necessary to transmit light to reach the photosensitive layer and to inject generated charges to neutralize and eliminate surface charges. As the coating material, an organic insulating film forming material such as polyester and polyamide can be used. In addition, these organic materials can be used in combination with an inorganic material such as glass resin and SiO ₂ , and further, a material such as a metal or a metal oxide that reduces electric resistance. As described above, it is desirable that the coating material is as transparent as possible in the wavelength region where the light absorption of the charge generating substance is maximum.

Although the thickness of the coating layer itself depends on the composition of the coating layer, it can be arbitrarily set within a range that does not cause adverse effects such as an increase in residual potential when used repeatedly and continuously.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below more specifically based on embodiments. Example 1 x-type metal-free phthalocyanine (hereinafter abbreviated as H ₂ Pc) 1
0 parts by weight and 100 parts by weight of a thiophene derivative represented by the structural formula (I-1) are mixed with 100 parts by weight of a polyester resin (trade name: Byron 200, manufactured by Toyobo Co., Ltd.) and a tetrahydrofuran solvent by a mixer for 3 hours. A coating solution was prepared by kneading, and the conductive substrate was an outer diameter of 30 mm and a length of 2
It was applied on a 60 mm aluminum drum and a photoreceptor was manufactured so that the film thickness after drying was 10 μm.

Example 2 Titanyl phthalocyanine (hereinafter abbreviated as TiOPc) 7
0 parts by weight and a vinyl chloride copolymer (trade name: MR-11)
0, manufactured by Nippon Zeon Co., Ltd.) and 30 parts by weight together with methylene chloride by a mixer for 3 hours to prepare a coating solution.
A film thickness of about 1 μm on an aluminum support as a conductive substrate
m to form a charge generating layer.
Next, the thiophene derivative 1 represented by the structural formula (I-3)
00 parts by weight and a polycarbonate resin (trade name: PCZ
-200, manufactured by Mitsubishi Gas Chemical Co., Ltd.) and 100 parts by weight of silicone oil were mixed with methylene chloride, and the resulting mixture was coated on the charge generating layer to a thickness of about 10 μm.
m to form a charge transport layer.

Example 3 In Example 2, the following structural formula was used instead of TiOPc. Using a thiophene derivative represented by the structural formula (I-8) in place of the structural formula (I-3) as a charge transport material, and otherwise using the same method as in Example 2, A photoreceptor was produced.

Example 4 In Example 2, the following structural formula was used instead of metal-free phthalocyanine: A charge generation layer was formed in the same manner as in Example 2 using the bisazo pigment represented by Next, 100 parts by weight of a thiophene derivative represented by the structural formula (II-2) as a charge transporting substance, 100 parts by weight of a polycarbonate resin (trade name: BP-PC, manufactured by Idemitsu Kosan Co., Ltd.), and silicone oil 0 .
1 part by weight was mixed with methylene chloride, and the resulting mixture was applied onto the charge generation layer so as to have a film thickness of about 10 μm to form a charge transport layer.

Example 5 In Example 4, the compound represented by the structural formula (II-
The thiophene derivative shown in 4) was used, and others were used in Example 4.
A photoreceptor was produced in the same manner as described above.

Example 6 In Example 4, the compound represented by the structural formula (II-
The thiophene derivative shown in 5) was used, and the others were used in Example 4.
A photoreceptor was produced in the same manner as described above.

Example 7 In Example 4, the compound represented by the structural formula (II-
The thiophene derivative shown in 6) was used, and the others were used in Example 4.
A photoreceptor was produced in the same manner as described above. Was.

Example 8 In place of the bisazo pigment in Example 4, the following structural formula was used: A charge generation layer was formed in the same manner as in Example 4 using the bisazo pigment represented by Next, 100 parts by weight of a furan derivative thiophene derivative represented by the structural formula (II-8) as a charge transporting material and a polycarbonate resin (trade name: BP-P
C, 100 parts by weight of Idemitsu Kosan Co., Ltd.) and 0.1 part by weight of silicone oil are mixed with methylene chloride, and the resulting mixture is adjusted to a thickness of about 10 μm on the charge generation layer. It was applied to form a charge transport layer. And a photoconductor was prepared in the same manner as in Example 4 except for using the above.

The electrophotographic characteristics of the photoreceptor thus obtained were measured. Vs (V) is the initial surface potential when the surface of the photoreceptor is positively charged by performing a corona discharge of +4.5 kV in a dark place. The surface potential Vd (V) is measured, and subsequently, the time (sec) until the surface of the photoreceptor is irradiated with white light having an illuminance of 100 lux to reduce Vd to half is obtained, and the sensitivity E _1/2 (lux · s) is obtained. And In addition, illuminance 10
The surface potential at the time of irradiating 0-lux white light for 10 seconds was defined as residual potential Vr (V). In Examples 1, 2 and 3, since high sensitivity with long wavelength light can be expected, the electrophotographic characteristics when monochromatic light with a wavelength of 780 nm was used were also measured. That is, measurement is performed in the same manner as described above up to Vd, and then monochromatic light (78 μm) of 1 μW is used instead of white light.
0 nm) to determine the amount of half-attenuated exposure (μJ / cm ² ), and the residual potential Vr (V) when this light was irradiated to the surface of the photoreceptor for 10 seconds was measured. The measurement results are shown in Table 1 below.

[0038]

[Table 1]

[0039]

According to the present invention, by using a thiophene derivative represented by the above general formula (I) or (II) as a charge transporting substance on a conductive substrate, it has high sensitivity and excellent electric characteristics in positive charging. Photoreceptor can be obtained. In this case, a suitable substance can be selected as the charge generating substance according to the type of the exposure light source. A photoreceptor can be obtained. Further, if necessary, a coating layer may be provided on the surface to improve the durability.

[Brief description of the drawings]

FIG. 1 is a conceptual cross-sectional view showing a single-layer type photoconductor as an example of the present invention.

FIG. 2 is a conceptual sectional view showing a positively-charged laminated photoconductor as another example of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 conductive substrate 2 photosensitive layer 3 charge generation layer 4 charge transport layer 5 photosensitive layer 6 coating layer

Claims (2)

[Claims] 1. A photosensitive layer formed on a conductive substrate comprises:
General formula (I),(Where R ¹, R², R³, R⁴, R⁵, R⁶And R ⁹
Is a hydrogen atom, an alkyl group or an alkoxy group,
⁷And R⁸Is a cyano group or an alkoxycarbonyl group, respectively.
Represents a radical. )
At least one kind is included as a charge transport material
Photoconductor for electrophotography. 2. The photosensitive layer formed on a conductive substrate has the following general formula (II): (Wherein, R ¹² , R ¹³ , R ¹⁴ , R ¹⁵ , R ¹⁶ and R ¹⁷ each represent a hydrogen atom, an alkyl group or an alkoxy group, and R ¹⁰ and R ¹¹ each represent a cyano group or an alkoxycarbonyl group. An electrophotographic photoconductor comprising at least one of the thiophene derivatives represented by the formula (1) as a charge transporting substance.