Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Radiation-sensitive composition or product
Reexamination Certificate
2001-07-24
2002-12-03
Goodrow, John (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Radiation-sensitive composition or product
C430S066000, C430S067000
Reexamination Certificate
active
06489071
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an electrophotosensitive material.
BACKGROUND OF THE INVENTION
As an electrophotosensitive material for use in image forming apparatuses such as electrostatic copiers, laser beam printers, plain paper facsimiles and the like, a so-called organic electrophotosensitive material is widespread which comprises a combination of the following components:
a charge generating material for generating an electric charge (positive hole and electron) when exposed to light;
a charge transport material for transporting the generated electric charge; and
a binder resin.
The charge transport materials fall into two broad categories which include a positive-hole transport material for transporting positive holes of the electric charge, and an electron transport material for transporting electrons.
The organic electrophotosensitive material has an advantage over an inorganic electrophotosensitive material employing an inorganic semiconductor material in that the organic electrophotosensitive material is fabricated more easily at less production costs than the latter.
In addition, the organic electrophotosensitive material also has a merit of greater freedom of function design by virtue of a wide variety of options for materials including charge generating materials, charge transport materials, binder resins and the like.
The organic electrophotosensitive material is constructed by forming a single-layer or multi-layer photosensitive layer over a conductive substrate.
The single-layer photosensitive layer is formed by dispersing a charge generating material and a charge transport material (a positive-hole transport material and/or an electron transport material) in a binder resin.
The multi-layer photosensitive layer is formed by forming a lamination of the charge generating layer containing the charge generating material and the charge transport layer containing the charge transport material (the positive-hole transport material or the electron transport material).
Despite the aforementioned various merits, the organic electrophotosensitive material is susceptible to scratches, mars and the like in an actual use environment, thus suffering a smaller durability than the inorganic electrophotosensitive material.
With an aim at increasing the durability of the organic electrophotosensitive material by solving the above problem, study has been made on an approach to overlay a surface protective layer on an outermost layer.
The widely used surface protective layer is exemplified by an organic layer which is preferable in the light of adhesion to and affinity with the organic photosensitive layer, integrity as a lamination, and consistency in the film forming process. A usable surface protective layer includes, for example, a layer of binder resin, and a layer of binder resin having conductive particles, such as of metal oxides, dispersed therein.
However, the electrophotosensitive material employing such an organic layer as the surface protective layer suffers the drawbacks of an increased residual potential and a lowered chargeability when repeatedly used for image forming processes, and of significant variations in the photosensitivity characteristics due to environmental changes (temperature, humidity and the like).
In this connection, more recent years have seen investigations made on the use of an inorganic layer as the surface protective layer, the inorganic layer comprising an inorganic material such as metallic elements, carbon and inorganic compounds containing any of these elements, and having high hardness and wear resistance. The inorganic surface protective layer may be laid over the organic photosensitive layer by, for example, the vapor deposition methods such as sputtering, plasma CVD, photo CVD or the like.
The inorganic surface protective layer is employed for the purposes of protecting the organic photosensitive layer and overcoming the above problem. Specifically, the electrophotosensitive material with the inorganic surface protective layer laid over the organic photosensitive layer has functions associated with the characteristics of the individual layers thereof, the organic photosensitive layer involved in the generation and transport of the electric charge, the surface protective layer responsible for ensuring the good durability and environmental resistance.
As compared with the organic surface protective layer, however, the inorganic surface protective layer has a lower ability to achieve a sufficient adhesion to the organic photosensitive layer. Even if adjustments for the deposition process or the deposition conditions may provide the inorganic layer with a sufficient initial adhesion to the organic layer, the inorganic layer is prone to suffer cracks or delamination due to various stresses imposed thereon under the actual use environment or during the long-term storage thereof.
In the combination of the organic photosensitive layer and the inorganic surface protective layer, which are formed of different materials, there are not attained as good adhering relation, affinity and integrity as in the combination of the organic layers or of the inorganic layers. That is, the organic layer and the inorganic layer are often merely combined with each other through a very small binding strength.
Accordingly, when subjected to mechanical stresses such as of contact pressure from a cleaning blade of the image forming apparatus, or thermal stresses due to repeated cycles of heating during the operation of the apparatus and cooling during the nonoperation thereof, or temperature changes during storage, the electrophotosensitive material will suffer cracks in the inorganic surface protective layer or delamination of the surface protective layer from the organic photosensitive layer as a result of increased differences between the hardnesses, flexibilities, expansion/shrinkage properties or the like of these layers.
In the present conditions, therefore, the conventional inorganic surface protective layer is yet to be put to practical use because it has not achieved a sufficient effect to increase the durability of the organic photosensitive layer.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an organic electrophotosensitive material comprising an inorganic surface protective layer less prone to suffer cracks or delamination and excellent in physical stability, thereby achieving a greater durability as compared with the prior-art products.
For achieving the above object, the inventors have analyzed and investigated the film forming process for the inorganic surface protective layer.
As a result, the inventors have discovered that a condition of the surface protective layer initially deposited on the outermost part of the organic photosensitive layer has a significant influence on the physical stability of the surface protective layer subsequently deposited.
At an initial stage of the film formation, the inorganic material forming the surface protective layer is somehow combined with a part of the material of the organic photosensitive layer that is exposed at the outermost part thereof, thereby forming a nucleus for film growth. A film of the inorganic material grows about the resultant nucleus and thus, the surface protective layer is formed. In the surface protective layer thus formed, the nucleus portion functions as a binding point with the organic photosensitive layer, ensuring the good adhesion between these layers.
Therefore, the magnitude of binding strength between the organic photosensitive layer and the inorganic material at individual binding points as well as the per-area number of binding points namely the density of the binding points at an interface between the organic photosensitive layer and the surface protective layer give significant influences on the adhesion of the surface protective layer to the organic photosensitive layer and the physical stability of the surface protective layer.
Specifically, with increase in the binding strength between the organic photosensitive layer and the inorgani
Fukunaga Hideaki
Inagaki Yoshio
Miyamoto Eiichi
Goodrow John
Kyocera Mita Corporation
Smith Gambrell & Russell
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