Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Radiation-sensitive composition or product
Reexamination Certificate
2000-08-25
2001-05-01
Martin, Roland (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Radiation-sensitive composition or product
C430S076000, C430S083000, C430S134000
Reexamination Certificate
active
06225016
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a photoconductor for electrophotography, hereinafter referred to simply as a “photoconductor”, used in electrophotographic apparatuses such as printers, copying machines and facsimiles. More specifically, the present invention relates to a photoconductor that includes a photosensitive film containing a specific bisazo compound as a charge generation agent.
Conventional photoconductors include an electrically conductive substrate and a photosensitive film on the electrically conductive substrate. It is necessary for the photosensitive film to retain surface charges in the dark, to generate charges in response to the received light, and to transport charges in response to the received light. The so-called single-layer-type photoconductor includes a mono-layered photosensitive film that exhibits all the above described functions. The so-called laminate-type photoconductor includes a photosensitive laminate film including a charge generation layer that contributes mainly to charge generation and a charge transport layer that contributes to surface charge retention in the dark and to charge transport under light exposure.
The photoconductive materials for the photoconductor includes inorganic photoconductive materials such as selenium, selenium alloys, zinc oxide, and cadmium sulfide. The selenium film or the selenium alloy film is formed by vacuum deposition. Small grains of zinc oxide or cadmium sulfide are dispersed into an organic solvent, in that a resin binder is dissolved, and the organic solvent is used as a coating liquid. The photoconductive materials for the photoconductor also includes organic photoconductive materials such as poly-N-vinylcarbazole, poly(vinyl anthracene), phthalocyanine compounds and bisazo compounds. The poly-N-vinylcarbazole solution or the poly(vinyl anthracene) solution is used as a coating liquid. A film of a phthalocyanine compound or a film of a bisazo compound is formed by vacuum deposition. Optionally, small grains of a phthalocyanine compound or a bisazo compound are dispersed into an organic solvent, in that a resin binder is dissolved, and the organic solvent is used as a coating liquid.
When a bisazo compound is used as a charge generation agent to form a single-layer-type photoconductor or a laminate-type photoconductor, usually small grains of the bisazo compound are dispersed into an organic solvent, into which an appropriate resin binder is dissolved. Visual defects and image nonuniformity are caused when the bisazo compound grains are not so small enough as to be dispersed uniformly. Various investigations have been conducted on the influences of the kinds and the amounts of the impurities on the grain size and the dispersibility of the bisazo compound.
Among many bisazo compounds, a bisazo compound described by a structural formula (I) (hereinafter referred to as “DCPB”)
is used as a charge generation agent that provides the photoconductors with preferable electrical properties such as high sensitivity and a low residual potential (cf Japanese Unexamined Laid Open Patent Application No. S63-305362).
DCPB is synthesized by the method disclosed in Japanese Unexamined Laid Open Patent Application No. H01-282268. In many cases, DCPB is synthesized using a compound described by a structural formula (II) (hereinafter referred to as “PB”).
As described above, it has been known to those skilled in the art that DCPB is a preferable charge generation agent. As a consequence, various investigations have been conducted on synthesis of DCPB and its purification. However, it has not yet been clarified that there exists a certain material that relates closely to the preferable grain diameter of DCPB and its preferable dispersibility which are favorable to obtain a uniform and even coating film of DCPB.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the invention to provide a photoconductor, including a photosensitive film, that overcomes the foregoing problems.
It is a further object of the present invention to provide a photoconductor, including a photosensitive film, that contains small-grained and uniformly dispersed DCPB as a charge generation agent.
It is another object of the invention to provide a photoconductor, containing DCPB uniformly in the photosensitive film, that does not cause any visual defect nor image nonuniformity, that might otherwise be caused by nonuniform distribution of DCPB in the photosensitive film.
It is still another object of the invention to provide a method of manufacturing such an excellent photoconductor.
Briefly stated, the present invention provides a photoconductor for electrophotography which includes a photosensitive film containing a bisazo charge generation agent described by structural formula (I)
and from 100 nmol to 40 mmol, preferably from 500 nmol to 20 mmol, of a compound described by a structural formula (II)
with respect to 1 mol of the bisazo charge generation agent. Such a photoconductor for electrophotography minimizes visual defects and image nonuniformity.
According to an aspect of the invention, there is provided a photoconductor for electrophotography including an electrically conductive substrate; and a photosensitive film on the electrically conductive substrate; the photosensitive film containing a bisazo charge generation agent described by the structural formula (I) and from about 100 nmol to about 40 mmol of the compound described by the structural formula (II) with respect to 1 mol of the bisazo charge generation agent.
Preferably, the photosensitive film contains from about 500 nmol to about 20 nmol of the compound described by the structural formula (II) with respect to 1 mol of the bisazo charge generation agent.
PB is used very often as a raw material for synthesizing DCPB. PB is yielded also as a byproduct of DCPB synthesis and remains as an impurity in synthesized DCPB. As a result of extensive and intensive investigations conducted to obviate the foregoing problems, the inventors of the present invention have found that limiting the PB content in DCPB within the foregoing specific range reduces the grain diameter of DCPB, disperses DCPB uniformly in the photosensitive film, and prevents visual defects and image nonuniformity due to nonuniform distribution of DCPB in the photosensitive film from forming.
The mechanisms for reducing the DCPB grain diameter and for improving the dispersibility of DCPB by limiting the PB content in DCPB within a certain range have not yet been clarified. However, while not limiting to any one theory, it is considered, when the PB content exceeds 40 mmol, the DCPB small grains coagulate with each other to elongate the grain diameters thereof and to impair the dispersibility thereof, since PB contained in DCPB weakens the electric repulsion between the DCPB small crystals. It is also considered, when the PB content is less than 100 nmol, that the DCPB small grains also coagulate with each other to elongate the grain diameters thereof and to impair the dispersibility thereof, since DCPB is so pure that crystallization of DCPB is prompted.
PB is removed easily from DCPB by purification, since PB is dissolved easily in organic solvents such as acetonitrile and N,N-dimethylformamide. Therefore, the PB content is adjusted easily by sufficiently purifying synthesized DCPB with any of the organic solvents described above and, then, by adding a necessary amount of PB to purified DCPB. Alternatively, PB remaining after synthesizing DCPB or by-product PB may be utilized.
According to another aspect of the invention, there is provided a method of manufacturing a photoconductor for electrophotography, including an electrically conductive substrate and a photosensitive film on the electrically conductive substrate, the method including the steps of: preparing a coating liquid containing a bisazo charge generation agent described by the structural formula (I) and from about 100 nmol to about 40 mmol of a compound described by the structural formula (II) with respect to 1 mol of the bisazo ch
Nakamura Yoichi
Sasaki Teruo
Fuji Electric Imaging Device Co. Ltd.
Martin Roland
Morrison Law Firm
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