Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Radiation-sensitive composition or product
Reexamination Certificate
2000-12-19
2002-11-19
Chapman, Mark (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Radiation-sensitive composition or product
Reexamination Certificate
active
06482560
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrophotographic photoreceptor.
More particularly, it relates to an electrophotographic photoreceptor excellent in abrasion resistance, surface slip characteristics, and the like, and having good electric response characteristics.
2. Description of the Related Art
An electrophotographic technology has found widespread applications not only in the field of a copying machine, but also in the field of various printers in recent years because it can provide an image of immediacy and high quality.
As for the photoreceptor which is the core of the electrophotographic technology, there have been developed photoreceptors using, as the photoconductive materials, conventional inorganic photoconductors such as selenium, arsenic-selenium alloy, cadmium sulfide, and zinc oxide, and in recent years, organic photoconductive materials having advantages of entailing no pollution, ensuring easy film-forming, being easy to manufacture, and the like.
As the organic photoreceptors, there are known a so-called dispersion type photoreceptor obtained by dispersing a photoconductive fine powder in a binder rein, and a lamination type photoreceptor obtained by laminating a charge generation layer and a charge transport layer. The lamination type photoreceptor has a high possibility of ranking as a dominant photoreceptor because a high sensitivity photoreceptor can be provided by using a charge generation material and a charge transport material each having a high efficiency in combination, a high safety photoreceptor can be obtained because of its wide material selection range, and it is relatively advantageous in terms of cost due to its high productivity of coating. Therefore, it has been vigorously developed and has gone into actual use.
The electrophotographic photoreceptor is repeatedly used in an electrophotographic process, i.e., in cycles of charging, exposure, development, transfer, cleaning, chargeremoval, and the like, during which it is subjected to various stresses to be deteriorated. Such deterioration include chemical or electrical deterioration due to the following facts. That is, strongly oxidizing ozone or NO
x
arisen from, for example, a corona charger commonly used as a charger causes a chemical damage to a photosensitive layer, carriers (current) generated upon image exposure passes through the inside of the photosensitive layer, a photosensitive composition is decomposed by charge-removed light, or light from the outside. Further, as other deterioration than such deterioration, there is mechanical deterioration of abrasion or occurrence of flaws on the surface of the photosensitive layer, or peeling off of a film due to rubbing with a cleaning blade, a magnetic brush, or the like, contact with a developing agent or paper, and the like. Especially, such damage occurring on the photosensitive layer surface tends to become evident on the copied image. Accordingly, it directly damages the image quality and hence it is largely responsible for restricting the life of the photoreceptor. Namely, the enhancement of the electrical and chemical durability as well as the enhancement of the mechanical strength are essential conditions for developing a long-life photoreceptor.
In general, it is a charge transport layer that receives such a load in the case of the lamination type photoreceptor. The charge transport layer generally comprises a binder resin and a charge transport material. It is the binder resin that substantially determines the strength. However, since the amount of the charge transport material to be doped is considerably large, a sufficient mechanical strength has not yet been achieved.
Further, there has been a demand for a material adaptable to a higher-speed electrophotographic process to meet a growing need for a higher-speed printing. In this case, the photoreceptor is required not only to have a high sensitivity and a long life, but also to have good response characteristics so as to reduce the length of time between exposure and development thereof. It is known that, although the response characteristics are controlled by the charge transport layer, especially the charge transport material, it is also largely changed by the binder resin.
As conventional binder resins of the charge transport layer, there have been used thermoplastic resins and various thermosetting resins, including vinyl polymers such as polymethyl methacrylate, polystyrene, and polyvinyl chloride, and copolymers thereof, polycarbonate, polyester, polysulfone, phenoxy, epoxy, and silicone resins. The polycarbonate resin has a relatively excellent performance out of a large number of the binder resins, and hence various carbonate resins have been developed and have gone into actual use so far. For example, JP-A-50-98332 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) discloses bisphenol P type polycarbonates, JP-A-59-71057 discloses bisphenol Z type polycarbonates, JP-A-59-184251 discloses copolymer type polycarbonates of bisphenol P and bisphenol A, and JP-A-5-21478 discloses a polycarbonate copolymer including a structure of bis(4-hydroxyphenyl)ketone type, as binder resins, respectively. However, in actuality, since the conventional organic photoreceptors have drawbacks that the surface is worn and the flaws on the surface occurs due to loads applied in use, such as development with toner, friction with paper, and abrasion by the cleaning member (blade), they have only the restricted printing performances in actual use.
On the other hand, in JP-A-56-135844, there is disclosed the technology of the electrophotographic photoreceptor using a polyarylate resin of the following structure as a binder, commercially available under the trade name “U-polymer”. In the publication, it is shown that the electrophotographic photoreceptor thus disclosed is particularly excellent in sensitivity as compared with the one using polycarbonate.
Further, in JP-A-10-288845, it is disclosed that use of a polyarylate using a bisphenol component of a specific structure as the binder resin improves the solution stability in manufacturing the photoreceptor. In JP-A-10-288846, it is shown that the electrophotographic photoreceptor using the polyarylate resin having a specific kinematic viscosity range is excellent in the mechanical strength, especially the abrasion resistance.
However, when currently available polycarbonate resins are used for the electrophotographic process, in many cases, they are still unsatisfactory in the abrasion resistance, the scratching resistance, the response characteristics, the adhesion with a substrate, and the like.
Further, with a commercially available polyarylate resin “U-polymer”, there can be observed some improvement in the abrasion resistance and the sensitivity. However, the stability of the coating solution is inferior, and hence it is impossible to coat the solution for manufacturing a photoreceptor.
Still further, although the solubility/solution stability, the mechanical strength, and the like are improved by using the polyarylate resin of a specific structure, the electric characteristics, especially the response characteristics have been unsatisfactory because of a recent growing demand for a higher-speed printing. Therefore, the amount of the charge transport material to be used is required to be increased for overcoming these deficiencies. However, if the content of the charge transport material in the photosensitive layer is increased, the mechanical strength is reduced. Accordingly, there has been a problem that the mechanical characteristics typical of the polyarylate resin cannot be manifested.
Therefore, in actuality, there has been a demand for a binder resin which ensures an excellent mechanical strength, is easy to dissolve in a non-halogen solvent, and excellent in the solution stability, and excellent in the response characteristics.
SUMMARY OF THE INVENTION
Under such circumstances, the present inventors have conducted a close study o
Fujii Akiteru
Kato Satoshi
Kumano Yuuta
Mitsumori Teruyuki
Nozomi Mamoru
Chapman Mark
Mitsubishi Chemical Corporation
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