Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Radiation-sensitive composition or product
Reexamination Certificate
2000-11-07
2002-05-28
Goodrow, John (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Radiation-sensitive composition or product
C430S059600
Reexamination Certificate
active
06395440
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an electrophotographic photoreceptor excellent in charge-transporting property and mechanical properties, and a process cartridge and an electrophotographic apparatus using the same.
DESCRIPTION OF THE RELATED ART
In recent years, an electrophotographic technology has played a central part in an image output field of copiers, printers and facsimiles because of advantages that high printing qualities can be obtained at high speed. As a structural material of an electrophotographic photoreceptor which is the heart of the electrophotographic technology, inorganic photoconductive materials such as selenium, a selenium-tellurium alloy and a selenium-arsenic alloy have been widely used from the beginning. Meanwhile, the study and the development of an electrophotographic photoreceptor using organic photoconductive materials which are superior to these inorganic photoreceptors in costs, productivity and disposability have been increasingly conducted, and they have currently exceeded the inorganic photoreceptors. Especially, selection of the materials can be more freely conducted by introduction of functional separation designing that charge generation and charge transport being basic steps of photoconduction are conducted by separate materials, and the remarkable improvement of performance has been achieved on the basis of the diversity provided by organic materials. At present, a functional separation laminated organic photoreceptor in which a thin-film charge-generating layer having a charge-generating function and a thick-film charge transport layer having a charge transport function, a chargeability and mechanical strengths are laminated on an electroconductive substrate has been mainly used as an electrophotographic photoreceptor.
Most of the organic charge-transporting materials are hole-transporting materials such as triphenylamine derivatives and hydrazone derivatives, and electron-transporting materials having performance of practical level are rare. Because of this restriction of materials and the structure made of the electroconductive support, the charge-generating layer and the charge transport layer, the organic photoreceptor has generally such a restriction of an driving polarity that it is driven only by negative charging.
With respect to the driving polarity, there are desirable polarities according to a sub-system and a total system used. In order to use the organic photoreceptors more widely and efficiently, the development of negative charging-type, positive charging-type and further bipolar charging-type photoreceptors has been in demand.
For example, when a wire discharge-type charging unit such as an inexpensive scorotron is used as a charging sub-system, there is a problem that harmful gases such as ozone and nitrogen oxides are generated in the discharge. It is known that amounts of the harmful gases generated are smaller by one figure in the positive charging than in the negative charging with the same charging unit. Thus, a positive charging-type photoreceptor has been demanded in a less costly and/or small-sized electrophotographic apparatus in which a filter for removing harmful gases cannot be mounted.
On the other hand, with respect to the requirement of the high image quality, it is advisable to conduct discharge area development using a negative charging-type photoreceptor in using the existing developer. At this time, to cope with the removal of harmful gases, it is required to use a filter of activated carbon or to use a charging unit of a contact charging system in which amounts of harmful gases are reduced.
Further, when the discharge area development system is employed to conduct transfer electrostatically, the charging polarity in transfer is reverse to the charging polarity in latent image formation. Since the charging in transfer is conducted in theory through a transfer material such as paper or a film for primary transfer, a photoreceptor is not directly charged. However, the photoreceptor is actually charged with polarity which is reverse to that in latent image formation between the transfer material and the next transfer material. In this case, the charging with reverse polarity in the transfer cannot be optically extinguished in the photoreceptor which is actuated only with monopolarity. Accordingly, a problem sometimes occurs that in some ability of the charging unit, the history thereof appears in the next copy or print. This problem is basically solved by using a bipolar charging-type photoreceptor having a hole-transporting property and an electron-transporting property.
Meanwhile, the functional separation laminated organic photoreceptor has the following defects owing to the laminated structure, and the development of a photoreceptor capable of conquering these defects has been in demand.
With respect to the first defect owing to the laminated structure, there are problems that since two or more layers have to be formed in comparison with the single-layer photoreceptor, the productivity is decreased and the costs are increased.
With respect to the second defect owing to the laminated structure, when a dip coating method is used which is a film-forming method generally employed because of high mass productivity, care must be taken not to attack a lower layer in coating an upper layer and a resistance to an upper layer coating solvent is required for a lower layer material, and there are problems accompanied by the same.
That is, a charge-generating layer which is generally a lower layer is made of a pigment as a charge-generating material and a binder resin having a film-forming property. A material which is not attacked by a coating solvent of a charge transport layer as an upper layer has to be selected as the binder resin. Generally, the charge-transporting material has a relatively low polarity. A solvent having a relatively low polarity, such as toluene, chlorobenzene, tetrahydrofuran, dioxane or dichloromethane is used as the coating solvent. Accordingly, as the binder resin of the charge-generating layer, a thermoplastic resin having a high polarity, such as an acetal-modified vinyl alcohol resin or a vinyl chloride-vinyl acetate-maleic anhydride copolymer resin having a low solubility in the solvents is employed.
It has been; however, known that a charge-transporting property is decreased in resins having a high polarity. Further, the resins having the high polarity are sometimes problematic in that they have a high moisture absorption and cause change in photoelectric characteristics accompanied by high environmental change. Further, since these thermoplastic resins having the high polarity are not completely insoluble, somewhat roughening is unavoidable in coating an upper layer, which sometimes results in the change in photoelectric characteristics and non-uniformity of the image. Thus, the improvement has been demanded in the application to an electrophotographic apparatus requiring a high image quality of full color.
In order to avoid this problem, the use of a thermosetting resin as a binder resin of a charge-generating layer has been proposed. However, there are a pot life problem that a curing reaction proceeds in a coating solution over the course of time to cause thickening and gelation and a problem that an uncured site remains in film formation and it has an adverse effect on photoelectric characteristics. Thus, the very problem remains substantially unresolved. Further, the charge-generating material such as a pigment cannot completely be insoluble in the coating solvent of the charge transport layer. Consequently, the contamination of a coating bath of the charge transport layer proceeds owing to elution of the charge-generating material with the increase in number of coatings of the photoreceptor, which induces the restriction of the pot life of the coating solution.
With respect to the third defect caused by the laminated structure, when a coherent light of a laser is used as an exposure light source, there arises a problem that a defective image of a s
Hoshizaki Taketoshi
Iijima Masakazu
Iwasaki Masahiro
Sakaguchi Yasuo
Tambo Fumiaki
Fuji 'Xerox Co., Ltd.
Goodrow John
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