Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Radiation-sensitive composition or product
Reexamination Certificate
2001-03-15
2002-09-03
Goodrow, John (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Radiation-sensitive composition or product
C430S129000
Reexamination Certificate
active
06444385
ABSTRACT:
BACKGROUND OF THE INVENTION
Present invention relates to an electrophotosensitive material used in image forming apparatuses such as laser beam printer, electrostatic copying machine, plain paper facsimile, and combined machine with functions of them. The present invention also relates to a method of producing the electrophotosensitive material.
Recently, an organic photosensitive material comprising an electric charge generating material capable of generating electric charges by irradiation with light, an electric charge transferring material capable of transferring generated electric charges, and a binder resin has widely been used as the electrophotosensitive material. The organic photosensitive material is easily produced as compared with a conventional inorganic photosensitive material using an inorganic semiconductor material. Also the organic photosensitive material has advantages such as wide range of choice of materials such as electric charge generating material, electric charge transferring material and binder resin, and high functional design freedom.
The organic photosensitive material includes:
a photosensitive material comprising a single-layer type photosensitive layer wherein an electric charge generating material and an electric charge transferring material are dispersed in the same single layer made of a binder resin, and
a photosensitive material comprising a multi-layer type photosensitive layer wherein an electric charge generating layer containing an electric charge generating material and an electric charge transferring layer containing an electric charge transferring material are mutually laminated. The single-layer type photosensitive layer is formed by applying a coating solution, which is prepared by dispersing the respective components constituting the layer in a dispersion medium (organic solvent is exclusively used), on a conductive substrate, followed by drying-up. The multi-layer type photosensitive layer is formed by applying a coating solution for electric charge generating layer and a coating solution for electric charge transferring layer on a conductive substrate in this order or reverse order, followed by drying-up.
The electric charge generating material used in the photosensitive material includes various pigments according to the wavelength range at which the photosensitive material has the sensitivity. As the pigment for photosensitive material, which is sensitive to infrared to near infrared light such as semiconductor laser, infrared LED or the like, a phthalocyanine pigment is used. The phthalocyanine pigment includes metal-free phthalocyanine, titanyl phthalocyanine and the like, which differ in chemical structure.
The dispersibility of the pigment in the coating solution exerts a large influence on sensitivity characteristics of the photosensitive material. Therefore, various studies about a dispersion medium, which is capable of satisfactorily dispersing a pigment and a binder resin therein and also exhibits good stability after dispersion, have been made.
As the dispersion medium, a halogenated organic solvent has widely been used as a medium having excellent dispersibility of the pigment. However, use of the halogenated organic solvent tends to be avoided because of consideration to rise in environmental consciousness. Therefore, it has been required to secure the same dispersibility as that of the halogenated dispersion medium using a non-halogen dispersion medium.
As the non-halogen dispersion medium, for example, cyclohexanone, acetic esters, propanol, cellosolves and tetrahydrofuran are generally used. Also there is a report that alcohol is preferably used as the dispersion medium in case of &agr;-type titanyl phthalocyanine (Japanese Laid-open Patent Publication JP 08-160643 A).
Japanese Laid-open Patent Publication JP 03-033859 A suggests use of at least one selected from the group consisting of branched ester, branched alcohol and branched ketone as the dispersion medium capable of satisfactorily dispersing Y-type titanyl phthalocyanine, and polyvinyl butyral and/or silicone resin.
Japanese Laid-open Patent Publication JP 06-337525 A suggests use of an organic solvent having a hydroxyl group and an ether group in a molecule (so-called cellosolves) as the dispersion medium capable of satisfactorily dispersing a phthalocyanine pigment such as &agr;-type titanyl phthalocyanine, and polyvinyl butyral.
The present inventors have studied and found that a conventional coating solution using a phthalocyanine pigment in combination with a binder resin and the dispersion medium described in the respective prior arts described above has the following problems.
(i) It tends to cause precipitation or separation of a pigment immediately after preparation of the coating solution because the dispersibility of the pigment is still insufficient.
(ii) It is liable to cause precipitation or separation of a pigment during the storage of the coating solution for a long period of time because the dispersion stability of the pigment is insufficient, even if the dispersibility of the pigment is comparatively good.
(iii) Regarding an electrophotosensitive material comprising a layer containing a binder resin and a pigment (hereinafter, referred to as a “pigment dipersion layer”), which is formed by applying and drying the coating solution having the problem (i) or (ii), the sensitivity is drastically lowered. As used herein, the “pigment dispersion layer” includes a single-layer type photosensitive layer itself, and an electric charge generating layer among a multi-layer type photosensitive layer.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a novel electrophotosensitive material which is free from lowering of the sensitivity and is superior in sensitivity characteristics.
Another object of the present invention is to provide a method of producing such an electrophotosensitive material.
The present inventors has studied intensively about the cause for lowering of the sensitivity of the photosensitive material as a result of formation of the pigment dispersion layer from the coating solution having the problem (i) or (ii) using a conventional dispersion medium, as described in (iii), and found the following fact.
The phthalocyanine pigment generally has strong agglomeration properties. Therefore, when the phthalocyanine pigment is used in combination with a conventional dispersion medium having poor dispersibility of the pigment, the pigment agglomerates to form agglomerates within a very short time until a pigment dispersion layer is formed by applying and drying the coating solution. Regarding the pigment dispersion layer thus formed, a large number of agglomerates of the pigment are formed in the layer. In such a pigment dispersion layer, the concentration of the pigment at the portion other than the agglomerates is drastically decreased as compared with the case where the pigment is uniformly dispersed in the layer. Therefore, the sensitivity at the portion is drastically lowered, thus lowering the sensitivity of the whole photosensitive material.
In some case, the degree of the lowering of the sensitivity at the portion other than the agglomerates is not large enough to impair the practicality because of less agglomeration of the pigment. In this case, however, there arises a new problem that image defects such as black spots and fogging are liable to be caused by lowering of charge at the agglomerate portion.
Therefore, the present inventors have studied about the cause for lowering of the dispersibility of the pigment and the dispersion stability of the coating solution in the coating solution using a conventional dispersion medium. As a result, they have found that the surface condition of particles of the pigment has a close relation with these characteristics.
In a dispersion medium, a binder resin is adsorbed on the surface of pigment particles and the pigment particles are stably dispersed in the dispersion medium by swelling of the binder resin with the dispersion medium. Therefore, when the amount of th
Azuma Jun
Ihara Mitsuo
Imanaka Yukikatsu
Kuboshima Daisuke
Nakatsu Hiromi
Goodrow John
Kyocera Mita Corporation
Smith Gambrell & Russell
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