JPH0217018B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a laminated electrophotographic photoreceptor characterized in that a layer of an acceptor organic substance and a layer of a donor polymer substance are laminated on a conductive support. BACKGROUND ART Conventionally, electrophotographic photoreceptors of the type in which a charge generation layer and a charge transport layer are laminated on a conductive support are known. However, with this type of laminated photoreceptor, sufficient sensitivity has not yet been obtained, and when the photoreceptor is repeatedly charged and exposed immediately after being exposed to strong light, the bright area potential and the dark area potential are different. The drawback was that the potential fluctuation was large. OBJECT OF THE INVENTION An object of the present invention is to provide an electrophotographic photoreceptor that eliminates the above-mentioned drawbacks. Structure and Effects of the Invention The photoreceptor of the present invention has a layer consisting of an acceptor organic substance and a donor polymer substance on a conductive support, thereby forming a charge transfer complex at the interface between the two layers. It is characterized by forming a thin layer and using it as a charge generation layer. In this specification, the term "acceptor organic substance" refers to either an acceptor low-molecular substance, an acceptor low-molecular substance molecularly dispersed in a polymer matrix, or an acceptor polymer substance. The reason why the sensitivity of laminated photoreceptors, in which the photosensitive layer is functionally separated into a charge generation layer and a charge transport layer, is not improved is that there are many carrier traps generated by exposure to light in the charge generation material. Possible reasons include that the holes and electrons thus generated cannot move efficiently, and that carriers are not efficiently injected from the charge generation layer to the charge transport layer. At the same time, the aforementioned inefficiency of carrier movement has an important effect on fluctuations in bright area potential and dark area potential when repeatedly charging and exposing the photoreceptor immediately after irradiating it with strong exposure light. The present inventors formed a thin layer of a charge transfer complex at the interface between the acceptor substance layer and the donor substance layer through the interaction of the two substances, and used this thin layer as a charge generation layer. Holes and electrons generated during exposure move efficiently through the donor material layer and acceptor material layer, respectively, without being trapped within this thin layer, resulting in high sensitivity and the ability to irradiate the photoreceptor with intense light at the same time. It has been found that it is possible to reduce fluctuations in bright area potential and dark area potential when repeated charging and exposure are performed immediately after. In this specification, the term "charge transfer complex" refers to an organic molecule complex DA consisting of an electron donor D and an electron acceptor A.
The stabilizing energy is obtained by some movement of electrons from D to A in
Whether or not a charge transfer complex has been formed can be easily confirmed by whether a spectroscopic charge transfer absorption band is observed. Generally speaking, in terms of material selection, the ionization potential I _p of D is small, and the electron affinity _E A of A is small.
It can be said that it is better to find a compound with a large D is a donor-like polymeric substance, A is an acceptor-like low-molecular substance,
It refers to either an acceptor-type low-molecular substance dispersed in a polymer matrix or an acceptor-type polymer substance. The materials used to create the laminated electrophotographic photoreceptor of the present invention include, for example, 1,3,5-tricyanobenzene, m-dinitrobenzene, 1,2,4, 5-tetracyanobenzene, tetrachlorophthalic anhydride, maleic anhydride, 2,4,6-trinitrotoluene, 1,3,5-trinitrobenzene, p-
Benzoquinone, pyromellitic anhydride, chloro-
p-benzoquinone, 1,2-dicarboxy-1,
2-dicyanoethylene, 2,3-dichloro-p-
Benzoquinone, 2,5-dichloro-p-benzoquinone, 2,6-dichloro-p-benzoquinone,
2,4,7-trinitro-9-fluorenone, trichloro-p-benzoquinone, p-iodoanil, p-bromanyl, p-chloranil, o-chloranil, o-bromanyl, tetracyano-p-benzoquinone, tetracyano-p-quinodimethane,
2,3-dicyano-p-benzoquinone, 2,6-
Dinitro-p-benzoquinone, tetracyanoethylene, 2,3-dichloro-5,6-dicyano-p
-benzoquinone and the like. Furthermore, these acceptor-based low-molecular substances may be used by being molecularly dispersed in a polymer matrix, and the blending polymers used in this case include, for example, polyarylate resins, polysulfone resins, polyamide resins, acrylic resins, acrylonitrile resin,
Methacrylic resins, vinyl chloride resins, vinyl acetate resins, phenolic resins, epoxy resins, polyester resins, alkyd resins, polycarbonates, polyurethanes, or copolymer resins containing two or more repeating units of these resins, such as styrene-butadiene copolymers, Examples include styrene-acrylonitrile copolymer and styrene-maleic acid copolymer. Further, examples of the acceptor polymer substance include polyvinyl butyral, maleic acid resin, ketone resin, cellulose ester, etc., and these may be used alone or in combination of two or more. On the other hand, examples of donor polymers include polystyrene, polymethylstyrene, polydimethylaminostyrene, polyvinylcarbazole, polycarbasylethyl vinyl ether, poly-2-vinylpyridine, poly-4-vinylpyridine, poly-
Examples include 2-methyl-5-vinylpyridine, polynaphthylmethylglutamate, polyvinylnaphthalene, polyvinylanthracene, polyvinylpyrene, polyvinylphenylanthracene, and polyacenaphthalene. FIG. 1 of the accompanying drawings shows a sectional view of a laminated photoreceptor of the present invention coated on the surface of a conductive layer 1. In this example, a layer 2 made of an acceptor organic substance is electrically connected to a layer 4 made of a donor polymer substance, and a charge transfer complex is formed at an interface 3 between these layers. At this time, by performing exposure in the presence of negative corona charging, holes and electrons of the charge carriers generated at the interface 3 are efficiently injected into the layer 4 and the layer 2, respectively. FIG. 2 shows another example of the laminated photoreceptor of the present invention. In this example, layer 4 and layer 2 are stacked in a reversed manner compared to FIG. 1, and are used for positive corona charging. A photosensitive layer having such a laminated structure of a donor layer and an acceptor layer is provided on a substrate having a conductive layer. As the substrate having a conductive layer, materials that are themselves conductive can be used, such as aluminum, aluminum alloy, copper, zinc, stainless steel, vanadium, molybdenum, chromium, titanium, nickel, indium, gold, and platinum. In addition, plastics (e.g., polyethylene, polypropylene, polyvinyl chloride, polyethylene terephthalate, (acrylic resin, polyethylene fluoride, etc.)
A substrate in which conductive particles (e.g., carbon black, silver particles, etc.) are coated on plastic together with a suitable binder, a substrate in which plastic or paper is impregnated with conductive particles, a plastic containing a conductive polymer, etc. can be used. . A subbing layer having barrier and adhesive functions can also be provided between the conductive layer and the photosensitive layer. The subbing layer is made of casein, polyvinyl alcohol, nitrocellulose, ethylene-acrylic acid copolymer, polyamide (nylon 6, nylon 66, nylon
610, copolymerized nylon, alkoxymethylated nylon, etc.), polyurethane, gelatin, aluminum oxide, etc. The thickness of the undercoat layer is 0.1 micron to 5 micron.
Preferably, 0.5 micron to 3 micron is appropriate. The organic solvents used when forming the undercoat layer, donor layer, acceptor layer, etc. as described above are as follows:
Alcohols such as methanol, ethanol, isopropanol, ketones such as acetone, methyl ethyl ketone, cyclohexanone, N,N-
Amides such as dimethylformamide and N,N-dimethylacetamide, sulfoxides such as dimethyl sulfoxide, ethers such as tetrahydrofuran, dioxane, and ethylene glycol monomethyl ether, esters such as methyl acetate and ethyl acetate, chloroform, methylene chloride, and Examples include aliphatic halogenated hydrocarbons such as chloroethylene, carbon tetrachloride, and trichloroethylene, and aromatics such as benzene, toluene, xylene, ligroin, monochlorobenzene, and dichlorobenzene. Naturally, the organic solvents used to form each type vary depending on the type of substance used, and when forming an undercoat layer, the solvent used for the donor layer or acceptor layer may be used to form the undercoat layer. It is preferable to select from those that do not dissolve. What is particularly ingenious about the laminated photoreceptor of the present invention is the method of forming a charge transfer complex as thin as possible at the interface between the donor and acceptor layers. In other words, by efficiently forming a thin layer of charge transfer complex at the interface between the donor layer and acceptor layer, the sensitivity is increased and at the same time, the sensitivity is improved when the photoreceptor is repeatedly charged and exposed immediately after being exposed to strong light. This has succeeded in improving the characteristics of potential changes. Specifically, a first layer of donor or acceptor coating is first formed on the conductive layer by the coating method described below, dried, and then a second layer is formed.
If the first layer is a donor layer, an acceptor substance is used as the layer, and if the first layer is an acceptor layer, the donor substance is dissolved in a solvent and laminated. However, it is necessary to select a solvent for the second layer that also dissolves the substance used for the first layer. Then, the moment the second layer is applied, a color change can be observed at the interface between the first layer and the second layer, and a thin layer of the charge transfer complex is immediately formed. In addition, in order to confirm that a charge transfer complex is formed due to the interaction between a donor substance and an acceptor organic substance as described above, a coating film is formed using a coating liquid containing a mixture of both substances. , it is sufficient to confirm that characteristic strong absorption based on charge transfer appears in the visible light region of the absorption spectrum.
At this time, depending on the selection of the donor polymeric material and the acceptor organic material, a sufficiently strong charge transfer absorption band may not appear in the visible light region, and the sensitivity when stacking such materials may be lower than expected. However, it wasn't good. Coating can be carried out using coating methods such as dip coating, spray coating, spinner coating, bead coating, Meyer bar coating, blade coating, roller coating, and curtain coating. For drying, it is preferable to dry to the touch at room temperature and then heat dry. Heat drying at a temperature of 30℃ to 200℃ for 5 minutes to 2
It can be carried out stationary or under blown air for a period of time within a range of hours. The electrophotographic photoreceptor of the present invention can be used not only for electrophotographic copying machines, but also for laser printers,
It can also be widely used in electrophotographic applications such as CRT printers and electrophotographic plate making systems. According to the present invention, it is possible to provide a highly sensitive electrophotographic photoreceptor, and the variation in bright area potential and dark area potential when repeatedly charging and exposing the photoreceptor immediately after irradiating it with strong light is reduced. It has the advantage of being small. Hereinafter, the present invention will be explained according to examples. Example 1 Polycarbonate (trade name Teijin Panlite L-1250 manufactured by Teijin Ltd.) 3 g 2,4,7-trinitro-9-fluorenone
3 g was dissolved in 30 c.c. of tetrahydrofuran. This coating solution was applied onto an aluminum sheet using a Mayer bar to give a dry film thickness of 8 microns to form an acceptor layer. Next, dissolve 3 g of poly-N-vinylcarbazole (trade name Lubican M-170) in 30 cc. An electrophotographic photoreceptor having a photosensitive layer having a two-layer structure was prepared by coating the photoreceptor so that it had a thickness of 8 microns, and was designated as Sample 1. On the other hand, as a comparative sample, a functionally separated photoreceptor having a charge generation layer and a charge transfer layer laminated in this order on a conductive support was prepared as follows. That is, the following disazo pigment (1) is placed in a 50 c.c. glass bottle.
4.1 g of the solution was taken, 18.1 g of cyclohexanone and 20 ml of glass beads were added thereto, and the mixture was dispersed using a red devil for 4 hours. To this dispersion, 4.4 g of a 9.1% by weight solution of polyvinyl butyral (trade name: BM-2, manufactured by Sekisui Chemical Co., Ltd.) in a 1:1 weight ratio of methyl ethyl ketone: cyclohexanone was added as a binder, and the mixture was further dispersed for 2 hours using a red devil. did. This dispersion was coated onto an aluminum sheet using a Mayer bar so that the dry film thickness was 0.2 microns to form a charge generation layer. Next, monochlorobenzene was prepared by mixing hydrazone of the following structural formula (2) with styrene-acrylic resin (product name: MS-200 manufactured by Nippon Steel Chemical Co., Ltd.) as a binder at a weight ratio of 1:1. 20% by weight
A charge transport layer was formed by applying the solution onto the charge generation layer using a Mayer bar to a dry film thickness of 12 microns. Comparative sample 1 was prepared in this way. The electrophotographic photoreceptor produced in this way was tested using an electrostatic copying paper tester Model SP-428 manufactured by Kawaguchi Electric Co., Ltd.
The sample was corona-charged using a dynamic method, held in a dark place for 1 second, and then exposed to light for 4 seconds at an illuminance of 5 lux to examine the charging characteristics. As for charging characteristics, the surface potential and the exposure amount (E1/6) required to attenuate the potential _V1 to 1/6 when dark decayed for 1 second were measured. Furthermore, 1
The sample measured as described above was irradiated with a 600 lux fluorescent lamp for 3 minutes, then left in the dark for 1 minute, and then exposed to charged light again. The potential difference △V ₁ from the first time of V ₁ is representative. shall be allowed to do so. The larger the value of ΔV ₁ is, the greater the fluctuations in the bright and dark potentials will be during repeated use. Next, the measurement results for the above photoreceptor will be shown.

[Table] From the above results, it can be seen that Sample 1, which has the layer structure of conductive support-acceptor layer-donor layer, has high sensitivity and small potential fluctuation when intense exposure is applied. On the other hand, it can be seen that Comparative Sample 1, which has a layer structure of conductive support-charge generation layer-charge transport layer, has poor characteristics. This result indicates that there are many traps in the charge generation layer, and the carriers generated by light irradiation cannot move efficiently. Example 2 An aluminum sheet was heated to 180°C on a hot plate, and 1 g of 2,4,7-trinitro-9-fluorenone in a crystalline state was placed on the aluminum sheet.
was taken and melted. Immediately thereafter, it was applied to a constant film thickness using a wire bar heated to 180°C, and then removed from the hot plate and left to cool rapidly at room temperature to obtain a transparent amorphous film with a thickness of 1 μm. Further, a poly-N-vinylcarbazole film having a thickness of 8 microns was laminated thereon in the same manner as in Example 1 to prepare Sample 2, and the charging characteristics were examined and the following results were obtained.

[Table] Example 3 A 2% methanol solution of polyamide (product name: Toray Industries, Inc. CM-8000/Teikoku Kagaku Co., Ltd. Torezin = 1/1 weight ratio) was placed on an aluminum sheet in a 50 c.c. glass bottle. An undercoat layer was formed by coating with a Mayer bar to a dry film thickness of 0.5 microns. Next, 3 g of polystyrene (product name: Dialex HF55, manufactured by Mitsubishi Monsanto Corporation) was dissolved in 27 g (10% by weight) of monochlorobenzene to prepare a coating solution, and a dry film thickness of 8.5 g was coated on top of the previous subbing layer with a Meyer bar. It was coated to a micron thickness. Next, 3 g of polycarbonate (trade name: Teijin Panlite L-1250, manufactured by Teijin Ltd.) and 3 g of maleic anhydride were dissolved in 30 c.c. of tetrahydrofuran. This coating solution was applied onto the polystyrene layer using a Mayer bar so that the dry film thickness was 8 microns. Sample 3 is the three-layer laminated photoreceptor fabricated as described above.
The charging characteristics were investigated in the same manner as in Example 1. However, the charging polarity at this time was as follows. The results are shown in the table below.

【table】 [Brief explanation of drawings]

1 and 2 are cross-sectional views of an example of the electrophotographic photoreceptor of the present invention. DESCRIPTION OF SYMBOLS 1... Conductive substrate, 2... Acceptor layer, 3... Charge transfer complex layer, 4... Donor layer.

Claims (1)

[Claims] 1 Lamination characterized by providing a layer made of an acceptor organic substance and a layer made of a donor polymer substance on a conductive support, thereby forming a thin layer of a charge transfer complex at the interface of both layers. type electrophotographic photoreceptor.