Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Radiation-sensitive composition or product
Reexamination Certificate
2001-03-29
2003-03-11
Dote, Janis L. (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Radiation-sensitive composition or product
C430S067000, C430S069000, C399S159000
Reexamination Certificate
active
06531253
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrophotographic photosensitive member and an electrophotographic apparatus using such a member and, more particularly, to an electrophotographic photosensitive member and an electrophotographic apparatus which are not susceptible, or not readily susceptible, to unevenness in image density even when there arises uneven abrasion (non-uniform wearing).
2. Related Background Art
In an electrophotographic apparatus, such as a copying machine, a facsimile or a printer, the peripheral surface of a photosensitive member, on which a photoconductive layer is formed, is uniformly charged by charging means such as corona charging, roller charging, fur brush charging or magnetic brush charging; then an electrostatic latent image is formed on the peripheral surface of the photosensitive member by exposure of a copied image of an copying object with laser or LED light according to a reflected light or modulated signal; a toner image is formed by adhering a toner to the photosensitive member; and the toner image is transferred to a sheet of copying paper or the like to form a copied image.
After a copied image is formed in the electrophotographic apparatus in this manner, there remains on the peripheral surface of the photosensitive member a part of the toner, and the residual toner needs to be removed. Usually, the residual toner is removed by a cleaning step using a cleaning blade, a fur brush, a magnetic brush or the like.
In recent years, from the viewpoint of consideration for environment, there have been proposed and introduced to the market electrophotographic apparatuses in which the cleaning device is dispensed with to reduce or eliminate a waste toner. They include what is disclosed in the Japanese Patent Application Laid-Open No. 6-118741, in which a direct charger, such as a brush charger, also serves the cleaning purpose, and what is disclosed in the U.S. Pat. No. 6,128,456, in which a developer also takes charge of cleaning, but both involve a step in which the toner and the surface of the photosensitive member are worn to remove the toner.
However, the need for high level of picture quality of printed images in recent years has led to the use of a toner smaller in average grain size than what was previously used or a toner with a lower melting point that is compatible with energy conservation, and there has been occurred the phenomenon that such a toner will be fusion bonded to a surface of a photosensitive member. In a toner removing process for removing the toner at an initial stage of fusion bonding, there is a case where the increase of load imposed on the cleaning step generates uneven abrasion of a surface layer of a photosensitive member or where an unevenly located charging member remains in contact with a surface layer of a photosensitive member to generate uneven abrasion of the surface layer.
Thus, there has been a problem that irradiation with an image exposure light in such a condition will generate interference due to unevenness in the thickness of a surface layer, which in turn will give rise to a difference in quantity of light incident on a photoconductive layer to generate belt-like unevenness in a halftone image. Moreover, along with the increasing digitization of electrophotographic apparatuses in recent years, latent image formation with a light source mainly emitting a light of a single wavelength is becoming the main stream, which results in frequent occurrence of interference, thereby aggravating the problem.
With a view to solving this problem, as disclosed in the Japanese Patent Publication No. 5-49108 and U.S. Pat. No. 4,795,691, there are proposed methods to prevent the halftone image unevenness caused by unevenness in the quantity of incident light attributable to uneven abrasion of a surface layer by providing an intermediate layer between a photoconductive layer and a surface layer of a photosensitive member with a photosensitive layer of amorphous Si or by continuously varying the composition of the interface to thereby reduce or eliminate reflection at the interface.
Whereas recently introduced digital copying machines and printers use such a photosensitive member, they are often inadequate for preventing unevenness in halftone images arising from unevenness in film thickness of fine pitches, ranging from tens of &mgr;m to a few mm attributable to the aforementioned cleaner or contact charger. On the other hand, the configuration to continuously vary the interface composition to effect control so as to restrain interface reflection at that part, requires strict control of the manufacturing conditions to achieve steady production by reducing fluctuations in characteristics within and between individual photosensitive members and, moreover, involves such a delicate aspect that, where the composition of a photosensitive member has changed, the optimal continuous interface is determined by a balance of various characteristics.
Further, Japanese Patent Application Laid-Open No. 11-2996 proposes to polish a photosensitive member to regulate the surface roughness Rz to a predetermined value. However, no attention is paid to the occurrence or prevention of halftone image unevenness arising from unevenness in film thickness of fine pitches, ranging from tens of &mgr;m to a few mm attributable to a cleaner or contact charger.
Along with the increasing digitization of electrophotographic apparatuses in recent years, latent image formation with a light source mainly emitting a light of a single wavelength, such as a laser or an LED array, is becoming the main stream, but at the same time the speed of copying, i.e. the number of revolution of the photosensitive member, keeps on increasing along with the advancement of electric circuit elements. As a result, by merely relying on the method of reducing or eliminating reflection at the interface by provision of an intermediate layer between the photoconductive layer and the surface layer of a photosensitive member or continuously varying the composition of the interface, there arises a difference in the quantity of exposure light incident on the photoconductive layer, due to interference by the single wavelength light due to uneven abrasion of the surface layer, thereby sometimes generating a belt-like density difference in the printed image.
Further, the new addition of a step of previously roughing the surface of the conductive substrate will increase the production cost. Machining the substrate with such a roughness as to generate no density difference may pose a new problem of lowering in the image sharpness.
The present inventors have conducted extensive studies and found that the effect of preventing the belt-like (or linear) unevenness in a halftone image due to uneven abrasion of the surface layer is not determined merely by the control of the interface composition or the substrate roughness, but also greatly depends on the microscopic surface roughness (more specifically in the order of a few nm to tens of nm) peculiar to the surface of the a-Si (amorphous silicon) photosensitive member.
SUMMARY OF THE INVENTION
An object of the present invention, completed on the basis of the above described findings, is to provide a photosensitive member and an image forming apparatus that successfully ensure formation of a satisfactory image by preventing fusion bonding of a toner during cleaning.
According to the present invention, there is provided an electrophotographic photosensitive member formed by successively stacking on a conductive substrate a photoconductive layer comprising amorphous Si and a surface protective layer comprised of an amorphous material, wherein the minimum value (hereinafter referred to as Min) and the maximum value (hereinafter referred to as Max) of the reflectance (%) of the photosensitive member within the wavelength range of 600 nm to 700 nm satisfy the relation of 0≦(Max−Min)/(Max+Min)≦0.20, and a center line average roughness Ra
1
of the interface on the surface side of
Ehara Toshiyuki
Karaki Tetsuya
Kawada Masaya
Kawamura Kunimasa
Ohwaki Hironori
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