JPH09218523A - Electrophotographic photoreceptor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photoreceptor less liable to the increase of residual potential even after repeated use by using a halogenated hydrocarbon solvent as the solvent of a coating soln. for an electric charge transferring layer. SOLUTION: A halogenated hydrocarbon solvent is used as the solvent of a coating soln. for forming an electric charge transferring layer in a process for producing a laminate type photoreceptor so that the concn. distribution of an electric charge transferring material in an electric charge transferring layer is made proper and the injection of electric charges from an electric charge generating layer into the electric charge transferring layer and the transfer of electric charges are smoothly carried out. The halogenated hydrocarbon solvent is, e.g. aliphatic, alicyclic or arom. hydrocarbon such as dichloromethane, dichloroethane or monochlorobenzene. A coating layer formed by coating with the resultant coating soln. is dried by heating at >=125 deg.C, preferably >=135 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic photosensitive member used in a device such as a copying machine, a printer and a facsimile, which is formed by using a charge generating material and a charge transporting material having different ionization potentials. And a laminated electrophotographic photosensitive member.

[0002]

2. Description of the Related Art In recent years, photosensitive materials used for electrophotographic photosensitive members have been changed from inorganic materials to organic materials in view of environmental stability and cost. The layer structure of this electrophotographic photosensitive member includes a laminated type photosensitive member in which the photosensitive layer is functionally separated into a charge generating layer having a charge generating function and a charge transporting layer having a charge transporting function. A single-layer type photoconductor having a single charge transport function is known, but relatively many organic photoconductors have a laminated type layer structure because of their characteristics.

In the multi-layer type electrophotographic photoconductor, since different kinds of materials and thin films are formed in a multi-layer structure, in addition to the charge generating function and the charge transporting function which are the photoconductive functions of the photoconductor, the charge generating layer. A charge injection function is required at the interface between the charge transport layer and the charge transport layer. In general, the conditions for this charge injection are ideal that the conduction band levels of the charge generation layer and the charge transport layer are the same when the charge is an electron, and on the other hand, when the charge is a hole. Ideally, the valence band levels of the charge generation layer and the charge transport layer match. Taking these as vacuum level standards, the conduction band corresponds to the electron affinity, and the valence band corresponds to the ionization potential. The ionization potential is the energy required to dissociate one electron from an atom or molecule in the ground state to infinity and dissociate it into one cation and a free electron.

If this energy level is 0.5 eV or more apart between the charge generating material and the charge transporting material, a charge injection barrier exists, and the charge smoothly flows from the charge generating layer to the charge transporting layer. It is not injected and accumulates at the interface between the charge generation layer and the charge transport layer to form space charges. As a result, there has been a problem that the residual potential is increased during repeated use.

Japanese Unexamined Patent Publication (Kokai) No. 62-31861 proposes to use a halogen-based solvent as a solvent for a coating liquid when forming a photosensitive layer of an electrophotographic photoreceptor. Since the combination of the ionization potentials of the charge generating material and the charge transporting material of the photoconductor has not been studied, it has a problem that the residual potential increases during repeated use.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances in the prior art, and has been made to solve the problems. That is, the object of the present invention is to repeat when the charge generation material and the charge transport material used in the charge generation layer and the charge transport layer of the electrophotographic photoreceptor have ionization potential values of 0.5 eV or more, respectively. Another object of the present invention is to provide an electrophotographic photoreceptor in which the increase in residual potential is small even when used.

[0007]

The electrophotographic photosensitive member of the present invention comprises a charge generating layer and a charge transporting layer, which are formed by using a charge generating material and a charge transporting material having ionization potential values separated by 0.5 eV or more, respectively. In a laminated electrophotographic photoreceptor, a halogenated hydrocarbon solvent is used as a solvent for the coating liquid for the charge transport layer.

[0008]

Embodiments of the present invention will be described below in detail. The present invention relates to an ionization potential value of a charge generating material and a charge transporting material used in a laminated type photoreceptor formed by functionally separating a charge generating layer having a charge generating material and a charge transporting layer having a charge transporting material. When there is a difference of 0.5 eV or more from the ionization potential value of, the charge transport layer is formed by a specific method to prevent an increase in residual potential due to the formation of a charge injection barrier during repeated use. And to obtain an electrophotographic photoreceptor having excellent electrical characteristics.

In the electrophotographic photosensitive member, the charge transport material in the charge transport layer seems to be uniformly dispersed due to molecular dispersion, but in reality, it is non-uniformly dispersed. This phenomenon can be confirmed by, for example, a method of dying the charge transport material in the charge transport layer and observing it with an electron microscope, or quantitatively, judging from the peak intensity ratio by IR / ATR measurement. can do. In the photoconductor in which the charge transport material in the charge transport layer is non-uniformly dispersed, the charge is not transported smoothly and space charges are formed, resulting in an increase in residual potential after repeated use. Will cause it.

It is considered that the concentration of the charge transport material in the charge transport layer is closely related to the charge injection at the interface between the charge generation layer and the charge transport layer. This charge injection process is
Assuming hopping transfer between different molecules, the charge injection depends on the intermolecular distance, and if the charge number of the charge transport material is too small, the charge will not be injected. Therefore, as described above, the charges are accumulated at the interface between the charge generation layer and the charge transport layer to form space charges, and the residual potential increases during repeated use. Since the same phenomenon is considered to occur in the charge transport layer, it is necessary to sufficiently consider the concentration distribution of the charge transport material in the charge transport layer.

According to the present invention, the concentration distribution of the charge transport material in the charge transport layer is optimized so that the charge injection from the charge generation layer to the charge transport layer and the transfer of the charge in the charge transport layer are smoothly performed. Therefore, a halogenated hydrocarbon-based solvent is used as a solvent for the coating solution for forming the charge transport layer in the step of producing the laminated photoreceptor. Examples of the halogenated hydrocarbon solvent used in the present invention include aliphatic halogenated hydrocarbons, aliphatic cyclic halogenated hydrocarbons and aromatic halogenated hydrocarbons, and specifically, dichloromethane , Dichloroethane, monochlorobenzene, etc., or a mixed solvent using two or more thereof.

Further, it is preferable to coat the coating liquid for forming the charge transport layer and then heat and dry the coating layer. The heating temperature is preferably 125 ° C. or higher, and more preferably 135 ° C. or higher. The electrophotographic photosensitive member manufactured in this manner can keep the residual potential low even after repeated use.

In the present invention, the conductive support, binder resin, photosensitive material and other additives used in the production of the laminated electrophotographic photoreceptor are appropriately selected from conventionally known ones before use. can do.

[0014]

The present invention will be described below in detail with reference to examples. Example 1 A 30 mmφ aluminum pipe was used as a cylindrical conductive support, and a butyl alcohol solution of polyvinyl butyral resin mixed with a zirconium compound was applied thereon by a dip coating method and dried to a film thickness of about 1 μm. To form an undercoat layer. Next, an X-type metal-free phthalocyanine pigment (ionization potential value = 4.98 eV) 1.2
A solution in which 5 g and 1.25 g of polyvinyl butyral resin were dispersed so that the solid content concentration in cyclohexanone 97.5 ml was 2.5% by weight was dip-coated on the undercoat layer of the support, It was dried at 100 ° C. for 10 minutes using an oven dryer to form a charge generation layer having a film thickness of 0.25 μm. Next, 11.25 g of N, N-bis (3,4-dimethylphenyl) biphenyl-4-amine (ionization potential value = 5.52 eV) and 11.25 g of a polycarbonate resin were mixed with 77.5 g of monochlorobenzene to give a solid. A solution dispersed to have a partial concentration of 22.5% by weight is dip-coated on the charge generation layer, and dried at 135 ° C. for 40 minutes using an oven dryer to give a film thickness of 24 μm. An electrophotographic photosensitive member was produced by forming the charge transport layer of.

Example 2 In the same manner as in Example 1, a charge generation layer was formed on a cylindrical conductive support. Next, as the charge transport layer, N,
N-bis (3,4-dimethylphenyl) biphenyl-4
-Amine 11.25 g and polycarbonate resin 11.2
5 g and a solution of 77.5 g of dichloromethane dispersed such that the solid content concentration becomes 22.5% by weight are dip-coated on the charge generation layer, and the solution is dried using an oven drier.
An electrophotographic photosensitive member was prepared by drying at 35 ° C. for 40 minutes to form a charge transport layer composed of a coating film having a film thickness of 24 μm.

Example 3 In the same manner as in Example 1, a charge generating layer was formed on a cylindrical conductive support. Next, as the charge transport layer, N,
N-bis (3,4-dimethylphenyl) biphenyl-4
-Amine 11.25 g and polycarbonate resin 11.2
5 g was mixed with 77.5 g of a mixed solvent of monochlorobenzene and dichloromethane (weight ratio 2: 1) to obtain a solid content concentration of 2
A solution dispersed so as to have a concentration of 2.5% by weight is applied onto the charge generation layer by dip coating, and the solution is dried using an oven drier.
An electrophotographic photosensitive member was prepared by drying at 5 ° C. for 40 minutes to form a charge transport layer composed of a coating film having a film thickness of 24 μm.

Comparative Example 1 In the same manner as in Example 1, a charge generation layer was formed on a cylindrical conductive support. Next, as the charge transport layer, N,
N-bis (3,4-dimethylphenyl) biphenyl-4
-Amine 11.25 g and polycarbonate resin 11.2
A solution in which 5 g and 77.5 g of tetrahydrofuran are dispersed so that the solid content concentration is 22.5% by weight is dip-coated on the charge generation layer, and the solution is dried using an oven drier.
An electrophotographic photosensitive member was produced by performing drying at 35 ° C. for 40 minutes to form a charge transport layer composed of a coating film having a film thickness of 24 μm.

Comparative Example 2 In the same manner as in Example 1, a charge generating layer was formed on a cylindrical conductive support. Next, as the charge transport layer, N,
N-bis (3,4-dimethylphenyl) biphenyl-4
-Amine 11.25 g and polycarbonate resin 11.2
A solution prepared by dispersing 5 g of the above in a mixed solvent of 77.5 g of a mixed solvent of monochlorobenzene and tetrahydrofuran (weight ratio 1: 3) to a solid content concentration of 22.5% by weight was immersed in the charge generation layer. Apply 1 using oven dryer
An electrophotographic photosensitive member was produced by performing drying at 35 ° C. for 40 minutes to form a charge transport layer composed of a coating film having a film thickness of 24 μm.

With respect to the electrophotographic photoreceptors produced in Examples 1 to 3 and Comparative Examples 1 and 2, the electrical characteristics of the photoreceptors were evaluated by the following methods. [Electrical Characteristics of Photoreceptor] The electrical characteristics of the electrophotographic photoreceptor are as follows: a device having a means for rotating a cylindrical photoreceptor at a constant speed, a means for charging, a means for exposing, and a means for measuring surface potential. It was measured using. As a measurement sample,
The photoconductor was charged by a scorotron set to VGRID = 500V, and the potential after exposure to 100 mJ / m2 was measured as the residual potential by using light with a halogen lamp light passing through an interference filter and having a wavelength of 660 nm. It was used to evaluate the stability of the photoconductor. In the above method, the residual potential was measured at the 10th cycle and the 200th cycle. Table 1 shows the results.

[0020]

[Table 1] In the table, MCB is monochlorobenzene, DCM is dichloromethane, and THF is tetrahydrofuran.

According to Table 1, in Examples 1 to 3, since only the solvent composed of halogenated hydrocarbon was used as the solvent of the coating liquid for forming the charge transport layer, the residual potential was 10 cycles. The amount of change between the eye and the 200th cycle is small and stable at 3 to 4V. On the other hand, in Comparative Examples 1 and 2, since tetrahydrofuran or a mixed solvent of monochlorobenzene and tetrahydrofuran was used as the solvent, the residual potential was significantly changed to 20 to 22 V between both cycles. , Indicates a problem with stability. Therefore, it is apparent that the electrophotographic photosensitive member of the present invention is greatly suppressed in the amount of increase in residual potential after repeated use.

[0022]

According to the present invention, even if the charge generation material and the charge transport material have an ionization potential value of 0.5 eV or more, a specific solvent is used as a solvent for the coating solution for forming the charge transport layer. It is intended to provide an excellent laminated electrophotographic photosensitive member which has an extremely small increase in residual potential after repeated use.

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Claims (1)

[Claims] 1. An electrophotographic photosensitive member comprising a charge generation layer and a charge transport layer, which are formed by using a charge generation material and a charge transport material having ionization potential values separated by 0.5 eV or more, respectively. An electrophotographic photoreceptor comprising a halogenated hydrocarbon solvent as a solvent for the coating liquid.