Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Process of making radiation-sensitive product
Reexamination Certificate
1995-06-07
2001-11-27
Dote, Janis L. (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Process of making radiation-sensitive product
C430S127000
Reexamination Certificate
active
06322945
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a process for producing an electrophotographic photoreceptor that has a light-sensitive layer coated on an electroconductive base. More particularly, the invention relates to a process by which electrophotographic photoreceptors of high quality can be manufactured for a long term without experiencing variations in their characteristics. The invention also relates to the electrophotographic photoreceptor that is produced by that process.
Various inorganic and organic photoconductive materials are known to be useful in electrophotographic photoreceptors. Organic photoconductive materials as applied to electrophotography have several advantages such as high film transparency, good film forming property, flexibility and low cost.
With a view to improving the sensitivity and durability of photoreceptors that use organic photo-conductive materials, a double-layer type has been proposed that has the light-sensitive layer divided functionally into a charge generation layer and a charge transport layer. In a typical case, the charge generation layer is formed by first preparing a coating solution that has a charge generation material dissolved in a suitable solvent together with a binder resin and any necessary additives, then applying the solution to a conductive base and finally drying the applied coat. Similarly, the charge transport layer is formed by first preparing a coating solution that has a charge transport material dissolved in a suitable solvent together with a binder resin and any necessary additives, then applying the solution to the already formed charge generation layer, and finally drying the applied coat. If necessary for improving the adhesion of the applied coat and the charge retaining ability, a subbing layer may sometimes be applied and dried between the base and the light-sensitive layer. The respective coating solutions used in this particular case are typically prepared in separate steps and supplied individually to the application and drying steps.
The subbing layer, the charge generation and the charge transport layer can be applied by various coating methods including blade coating, wire bar coating, spray coating, dip coating, bead coating, curtain coating, air knife coating, rod coating, applicator coating, web coating and gravure coating. The applied coatings of subbing layer, charge generation layer and charge transport layer can be dried by various known techniques including the blasting of hot air as produced by heating atmospheric air and exposure to electromagnetic waves such as infrared rays and electron beams.
The above-stated process for the manufacture of electrophotographic photoreceptors has involved the problem that variations in the quality of coating solutions occur in the step of their preparation to affect the characteristics of the photoreceptor as the final product. In other words, preparing coating solutions from the same materials by the same processing method will in no way assure consistency in the quality of the coating solutions and this has made it difficult to manufacture electrophotographic photoreceptors having consistent characteristics.
Furthermore, using production equipment that employed devices for applying the coating solutions and drying the applied coatings in accordance with the steps described above, the present inventors produced a lot of electrophotographic photoreceptors on a continuous basis for a prolonged term and conducted close studies on the characteristics of those photoreceptors. As it turned out, even in a one-day production, some photoreceptors had high photosensitivity while others had low sensitivity. When the production continued for several days, variations occurred on different days of coating application. Significant variations are also frequent in a one-year production. These variations affected the performance of the electrophotographic photoreceptors as the final product, making it impossible to manufacture photoreceptors having consistent characteristics. Thus, the adverse effects of the variations on the quality of the final product have been a great concern to the manufacturers of photoreceptors.
The present invention has been accomplished under these circumstances and has as an object providing a process by which electrophotographic photoreceptors having consistent characteristics can be manufactured continuously for a long period of time.
SUMMARY OF THE INVENTION
To attain this object, the present inventors conducted intensive studies and have finally found that the variations in the characteristics of electrophotographic photoreceptors that occur within a day, between days and even between seasons when those photoreceptors are manufactured for a prolonged continuous period are due to the entrance of very small amounts of aerial impurity gases into the solution preparing compartments or the coating compartments or the drying units. Further analyses have shown that while several kinds of pollutants exist in very small quantities in atmospheric air, the changes in the concentrations of photochemical oxidants are very closely related to the variations in the characteristics of electrophotographic photoreceptors.
The term “photochemical oxidants” as used herein means ozone, peroxyacetyl nitrate (PAN) and any other oxidative substances that are formed by photochemical reactions which, excepting nitrogen dioxide, will release iodine from a neutral solution of potassium iodide; nearly 90% of these photochemical oxidants are occupied by ozone. The concentration of aerial ozone varies complexly due not only to the photochemical reactions but also to the fall of stratospherical ozone on the ground and the phenomenon of discharges in air.
The present inventors found that by suppressing the variation in the concentration of oxidants in ambient air during the process of preparing coating solutions or applying them or drying the applied coatings and by preferably holding the maximum concentration of oxidants to no more than specified values, electrophotographic photoreceptors of consistent characteristics could be manufactured even on an industrial scale involving prolonged continuous production. The present invention has been accomplished on the basis of this finding.
In the general aspect to the present invention, a process for producing an electrophotographic photoreceptor includes a step of coating a light-sensitive layer on an electroconductive base, a step of removing part or all of oxidants present from an air atmosphere by an oxidants removing unit, a step of dealing with a coating solution for forming the light-sensitive layer in the air atmosphere from which concentration of oxidants is suppressed by the step of removing part or all of oxidants present, and a step of suppressing variation in the concentration of oxidants in the air atmosphere, wherein the step of dealing with the coating solution for the light-sensitive layer includes at least one of the steps of preparing the coating solution for forming the light-sensitive layer, applying the light-sensitive layer and drying an applied coating.
Preferably, the maximum concentration of oxidants in the air atmosphere is suppressed to 80 ppb and below when preparing the coating solution, or suppressed to 50 ppb and below when applying or drying the light-sensitive layer, or both.
The present invention has been described below in detail.
When preparing coating solutions in a step of the process for producing an electrophotographic photoreceptor, the starting materials for each coating solution are taken out of their storage sites, weighted, dispersed or dissolved and subjected to any other necessary processing operations. If oxidants enter the compartments where the coating solutions are being prepared, the oxidants contact the respective coating solutions and will either react with their components or will be adsorbed on the coating solutions, thereby affecting adversely the characteristics of the coating solutions being prepared.
The base to which the coating solutions have been appl
Aoki Kazuaki
Hashimoto Kiyoshi
Hongo Kazuya
Inakage Satoru
Nakabayashi Wataru
Dote Janis L.
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Fuji Xerox Co. LTD
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