Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Radiation-sensitive composition or product
Reexamination Certificate
2001-12-12
2003-06-03
Chapman, Mark A. (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
06573017
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a single-layer type electrophotosensitive material, which is used in image forming apparatuses such as electrophotographic copying machine, facsimile and laser beam printer. More particularly, the present invention relates to a single-layer type electrophotosensitive material, which is less likely to cause wear of a photosensitive layer due to a blade cleaning means that recovers a residual toner and is therefore superior in wear resistance, and also does not cause defects such as image fog and black belt due to reduction of a surface potential and lowering of the sensitivity even when exposed to ozone generated in a charging, transferring or separating means in the image forming apparatus and is therefore superior in ozone resistance.
In an image forming apparatus based on a Carlson process, an image has conventionally been formed by uniformly charging the surface of an electrophotosensitive material, exposing the surface of the electrophotosensitive material to light to form an electrostatic latent image, developing the electrostatic latent image to form a toner image, transferring the toner image onto a transfer material (e.g. paper) and fixing the toner image. After transferring, the electrophotosensitive material is repeatedly used for a long period after cleaning of the residual toner and destaticization.
It is, therefore, necessary that electrophotosensitive material is not only superior in initial electric characteristics such as initial charge characteristics and initial sensitivity characteristics, but also in repeated electric characteristics such as charge stability and sensitivity stability so as to endure periodic duty for a long term.
The electrophotosensitive material is classified roughly into an inorganic photosensitive material using an inorganic material such as selenium in a photosensitive layer, and an organic photosensitive material using an organic material in a photosensitive layer. Among these photosensitive materials, the organic photosensitive material has widely been studied because it is easily produced as compared with the inorganic photosensitive material and has a wide range of choice of photosensitive materials such as electric charge transferring material, electric charge generating material and binder resin as well as high functional design freedom.
The organic photosensitive material is classified roughly into a so-called multi-layer type photosensitive material having a structure of an electric charge generating layer containing an electric charge generating material and an electric charge transferring layer containing an electric charge transferring material, which are mutually laminated, and a single-layer type photosensitive material wherein an electric charge generating material and an electric charge transferring material are dispersed in the same photosensitive layer. Among these organic photosensitive materials, it is a multi-layer type photosensitive material, which has a monopoly position in the wide market. The multi-layer type photosensitive material is exclusively a negative charging type photosensitive material comprising a conductive substrate, and an electric charge generating layer and an electric charge transferring layer formed in order on the conductive substrate.
The single-layer type photosensitive material has become of major interest recently because of its advantages described below. That is, the single-layer type photosensitive material is superior in productivity because of its simple layer construction and can inhibit the occurrence of layer defects of the photosensitive layer, and can also improve optical characteristics because of less interface between layers. Furthermore, one photosensitive material can be used as both of positive and negative charge type photosensitive materials by using, as the electric charge transferring material, an electron transferring material and a hole transferring material in combination.
In the image forming apparatus based on the Carlson process, to which an organic photosensitive material is mounted, in case a charging means, a transferring means or a separating means is composed of a charger system, the photosensitive material is exposed to ozone generated by corona discharge. Since ozone is a gas having a very strong oxidizing action, the strong oxidizing action is exerted on the photosensitive material. The strong oxidizing action is exerted on constituent substances of the photosensitive layer (e.g. electric charge generating material and electric charge transferring material) in a binder resin, which forms a photosensitive layer of the organic photosensitive material, thereby causing problems such as lowering of the charge capability of the photosensitive material and lowering of the sensitivity, and thus the repeated electric characteristics become worse.
When using the organic photosensitive material having lowered charge capability as it is, the surface potential is reduced, thereby to cause image defects such as image fog, black belt, densification of gray images and thickening of image letters.
In an image forming apparatus based on a Carlson process, an image is formed by uniformly charging the surface of an electrophotosensitive material, exposing the surface of the electrophotosensitive material to light to form an electrostatic latent image, developing the electrostatic latent image to form a toner image, transferring the toner image onto a transfer material (e.g. paper) and fixing the toner image. After transferring, the electrophotosensitive material is repeatedly used for a long period after cleaning of the residual toner and destaticization.
It is, therefore, necessary that electrophotosensitive material is not only superior in initial electric characteristics such as initial charge characteristics and initial sensitivity characteristics, but also in repeated electric characteristics such as charge stability and sensitivity stability so as to endure periodic duty for a long term.
In order to achieve excellent repeated electric characteristics, it is essential to use an organic photosensitive material, which is less likely to cause wear of a photosensitive layer due to a blade cleaning means that recovers a residual toner and is therefore superior in “wear resistance”, and also does not cause reduction of a surface potential and lowering of the sensitivity even when exposed to ozone generated in a charging, transferring or separating means in the image forming apparatus and is therefore superior in “ozone resistance”.
Influence of Wear Resistance
The developed toner is transferred to a transfer material such as paper in the transfer process. However, the toner is not transferred completely (100%) and is partially remained on the photosensitive material. If the residual toner is not removed, it is made impossible to obtain a high-quality image, which is free from contamination in the repeated processes. Therefore, it is required to clean the residual toner. In the cleaning process, a fur brush, a magnetic brush or a blade is typically used. In view of the cleaning accuracy and rationalization of apparatus construction, it is general to select a blade cleaning wherein cleaning is performed by contacting a blade-shaped resin plate directly with a photosensitive material.
Although the blade cleaning has high accuracy, it increases a mechanical load on the photosensitive material, thereby causing problems such as increase in wear amount of the photosensitive layer, reduction in surface potential, lowering of the sensitivity, and thus the repeated electric characteristics become worse.
Influence of Ozone Resistance
In case a charging means, a transferring means or a separating means is composed of a charger system, the photosensitive material is exposed to ozone generated by corona discharge. Since ozone is a gas having a very strong oxidizing action, the strong oxidizing action is exerted on the photosensitive material. The strong oxidizing action is exerted on constituent substances of the photosensitive
Azuma Jun
Honma Hisakazu
Miyamoto Eiichi
Uchida Maki
Watanabe Yukimasa
Chapman Mark A.
Kyocera Mita Corporation
Smith , Gambrell & Russell, LLP
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