Incremental printing of symbolic information – Electric marking apparatus or processes – Electrostatic
Reexamination Certificate
1999-12-21
2001-09-04
Pendegrass, Joan (Department: 2852)
Incremental printing of symbolic information
Electric marking apparatus or processes
Electrostatic
C347S133000, C430S031000
Reexamination Certificate
active
06285385
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrophotographic method and an electrophotographic apparatus, and more particularly to an electrophotographic method and an electrophotographic apparatus suitable for a digital electrophotographic method employing a laser beam printer, a digital copying apparatus or the like and an electrophotographic apparatus therefor.
2. Related Background Art
Electrophotographic apparatus such as laser beam printer or copying apparatus is recently attracting attention of the market because of various features such as high image quality and high printout speed. Also outputs of photographs are rapidly increasing in addition to those of characters, thereby increasing the demand for higher image quality of the electrophotographic apparatus. The photosensitive members employed in such electrophotographic apparatus can be classified into organic type photographic members and inorganic type photographic members.
Organic materials as photoconductive materials employed in the electrophotographic photosensitive members have been actively developed in recent years. Particularly, the function-separated photosensitive member composed of a charge generating layer and a charge transporting layer mutually stacked is already commercialized and is adopted, for example, in the copying apparatus and the laser beam printers.
These photosensitive members have generally been evaluated on the durability. The durability can be divided into physical durability relating to the electrophotographic process such as sensitivity, retentive potential, charging ability, faint image and the mechanical durability such as abrasion or scratch on the surface of the photosensitive member resulting from friction, both being important factors determining the service life of the photosensitive member. Among these, it is already known that the defect on the electrophotographic physical durability, particularly the faint image, results from degradation of the charge transporting substance contained in the surface layer of the photosensitive member, by active substances such as ozone or NO
x
generated from the corona charger. It is also known that the defect on the mechanical durability is caused by physical contact and friction of paper, cleaning member such as blade or roller, or toner with the photosensitive layer. In order to improve the electrophotographic physical durability, it is important to employ a charge transporting substance which is not easily degraded by the active substance such as ozone or NO
x
, and, for this purpose, there is already known to use the charge transporting substance of a high oxidation potential. Also, for improving the mechanical durability, it is important to increase the surface lubricating property to thereby reduce the friction in order to withstand the abrasion by the paper or cleaning member, and to improve the releasing property of the surface in order to prevent filming-melting-adhesion of the toner, and, for this purpose it is already known to mix a lubricant such as fluorinated resin power, fluorinated graphite or polyolefin resin power in the surface layer. However, when the abrasion is significantly lowered, the hygroscopic substances generated by the active substances such as ozone or NO
x
are deposited on the surface of the photosensitive member, thereby reducing the surface resistance to induce the lateral movement of the surface charge and result in the faint image (smeared image). Also, since certain abrasion is necessary because of the above-mentioned reason, the potential characteristics such as sensitivity or charging ability inevitably vary in a prolonged period, and the change in the surfacial topography resulting from the abrasion induces light scattering, thereby degrading the image quality.
On the other hand, an example of the inorganic materials employed for the photosensitive member is amorphous silicon (hereinafter, referred to as “a-Si”). In the electrophotographic photosensitive member, the photoconductive material constituting the photosensitive layer is required (1) to have a high sensitivity, a high S/N ratio [photocurrent (Ip)/dark current (Id)] and an absorption spectrum matching the spectral characteristics of the irradiating electromagnetic wave; (2) to have a fast light response and a desired dark resistance; and (3) to be harmless to the human body at the use. The above-mentioned ecological safety at the use is particularly important in case of the photosensitive member to be incorporated into the image forming apparatus for use as an office equipment.
A material meeting these requirements is hydrogenated amorphous silicon (hereinafter, referred to as “a-Si:H”), and application of a-Si:H for the photosensitive member in the image forming apparatus is disclosed, for example, in U.S. Pat. No. 4,265,991. In comparison with the aforementioned organic type photosensitive members, the a-Si:H photosensitive member is provided with various advantages such as (1) very high linearity in the photosensitive characteristics, (2) uniformity in material structure and absence of light scattering, and (3) a high dielectric constant and a strong electric field effect, and is particularly suitable in realizing the high image quality.
Also, U.S. Pat. No. 5,382,487 discloses a photosensitive member, for use in the image forming apparatus, composed of a conductive substrate and a photoconductive layer consisting of a-Si containing halogen atoms (X) as a constituent (hereinafter, referred to as “a-Si:H”). The above-mentioned patent teaches that a heat-resistant photoconductive layer having satisfactory electrical and optical characteristics for use in the photosensitive member for the image forming apparatus can be obtained by adding 1 to 40 atomic % of halogen atoms to a-Si.
Also, in order to improve the electrical, optical and photoconductive characteristics such as dark resistance, photosensitivity and optical response and the environmental characteristics such as moisture resistance in the photoconductive member having a photoconductive layer composed of a deposited a-Si layer, Japanese Patent Application Laid-Open No. 57-115556 discloses a technology of forming a surface layer composed of a non-photoconductive amorphous material containing silicon atoms and carbon atoms on a photoconductive layer composed of an amorphous material containing silicon atoms as a matrix.
Furthermore, Japanese Patent Application Laid-Open No. 60-67951 discloses a technology of stacking a translucent insulating overcoat layer containing amorphous silicon, carbon, oxygen and fluorine on a photosensitive member, and U.S. Pat. No. 4,788,120 discloses a technology of employing in the surface layer an amorphous material containing silicon atoms, carbon atoms and 41 to 70 atomic % of hydrogen atoms as constituents.
Furthermore, Japanese Patent Application Laid-Open No. 57-158650 discloses that a photosensitive member of a high sensitivity and a high resistance for use in the image forming apparatus is obtained by employing a photoconductive layer having a-Si:H containing 10 to 40 atomic % of hydrogen and a ratio of 0.2 to 1.7 in the absorption coefficients of the infrared absorption peaks of 2100 cm
−1
and 2000 cm
−1
.
On the other hand, Japanese Patent Application Laid-Open No. 60-95551 discloses a technology, for improving the image quality of the amorphous silicon photosensitive member, of executing the image forming steps of charging, exposure and development and transfer while maintaining the temperature in the vicinity of the surface of the photosensitive member at 30° C. to 40° C., thereby preventing the decrease in the surface resistance caused by the moisture absorption on the surface of the photosensitive member and the image smear (high humidity smear) resulting therefrom.
These technologies have improved the electrical, optical and photoconductive characteristics of the photosensitive member for the image forming apparatus and the environmental characteristics thereof, thereby re
Ehara Toshiyuki
Karaki Tetsuya
Kawamura Kunimasa
Owaki Hironori
Yamazaki Koji
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Pendegrass Joan
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