Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2002-03-27
2004-02-03
Dote, Janis L. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S066000, C430S067000, C430S125320
Reexamination Certificate
active
06686109
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrophotographic apparatus in which the surface of a photosensitive member (or an image bearing member) is charged, image information is written on the charged surface by visible light, line scanning laser light or the like to be made into toner images, and the toner images are transferred to a transfer material, thereby carrying out image formation, and the photosensitive member surface after the transfer process is cleaned with a cleaning means. More specifically, the present invention is directed to such as printers, copying machines, facsimile machines, etc. using an amorphous silicon drum (the “amorphous silicon is hereinafter referred to as a-Si).
2. Related Art
Electrophotographic apparatus based on the so-called Charlson's process have been well-known in which each of the process means for conducting exposure, development, transfer, cleaning (residual toner removal), decharging and charging is arranged on the periphery of a photosensitive drum and image formation is carried out through a predetermined electrophotographic process.
In cleaning devices, particularly, a cleaning blade made of a belt-like elastic material such as urethane rubber is often used. Such a cleaning blade is excellent for removing toner remaining on a photosensitive member and widely used in electrophotographic apparatus whose speeds range from high to low.
In recent years, among the photosensitive drums used in electrophotographic apparatus, some use an a-Si photosensitive drum for the purpose of improving durability and making maintenance free. For the a-Si photosensitive drum, it is suggested that amorphous silicon carbide (hereinafter referred to as a-SiC) or amorphous carbon (hereinafter referred to as a-C) may be used as a surface protective layer. Since such a surface protective layer is much harder than the surfaces of organic photosensitive drums, with respect to cleaning with the above-mentioned cleaning blade, it is almost abrasion free and exhibits high durability, so that it is very useful in high speed electrophotography.
In recent digital electrophotographic processes, a photosensitive member is uniformly charged, then latent images are formed on the photosensitive member by laser or LED array, and the latent images on the photosensitive member are developed with a developer by a developing means. The developing method includes a reverse developing method in which portions where latent images are formed by laser, etc. are developed with a developer and a normal developing method in which portions where latent images are not formed are developed with a developer.
In analog electrophotographic processes, reflected light from an original on a stand is used as a latent image forming means, hence a normal development method is used.
With the digital electrophotographic process, both the reverse and normal developing methods may easily be applied, but taking account of the light emission intensity or lifetime of a laser or LED array, it is advantageous to shorten the length of time the light is emitted by the laser or LED array emits light as much as possible, hence the reverse developing method is more useful than the normal developing method.
In addition, Although, even in digital electrophotographic apparatus, its copying speed was heretofore 30 to 40 sheets (A4-sized, widthwise) per minute, with the increased speed of current electrophotographic apparatus, electrophotographic apparatus having a copying speed of 60 sheets (A4-sized, widthwise) or more per minute has appeared. As a result, the moving speed of the photosensitive member surface needs to be about 260 mm/second or more.
For cleaning such a surface moving at a high speed, a cleaning method is suited in which the developer remaining on the electrophotographic apparatus is cleaned with a cleaning blade so provided as to come into contact with the photosensitive member surface. However, it was found that in the reverse developing method, when cleaning the surface moving at a high speed, a new problem occurred.
In the reverse developing method, the charge polarity of the photosensitive member is the same as that of the developer. In the process using the photosensitive member and developer having the same polarity, when cleaning the developer from the photosensitive member surface moving at a high speed, a phenomenon occurs giving, at the time the developer is stripped off the photosensitive member, a charge opposite to the polarity of the developer to the photosensitive member surface (static discharge phenomenon).
The discharge amount is very slight, but the size of the developer is as small as a few microns and the resistance of the developer is high, hence the static discharge concentrates at a minute area on the photosensitive member surface, thus such a discharge amount is sufficient to destroy the charge retaining ability of the surface protective layer of the photosensitive member.
As a result, the photosensitive member deteriorates in its ability to retain the charge with the same polarity as the photosensitive member and results in image defects. Such a discharge phenomenon (hereinafter referred to as sripping discharge) may occur more frequently as the developer stripping speed is higher, i.e., the surface moving speed is faster, and as the developer to be cleaned is greater.
SUMMARY OF THE INVENTION
The object of the present invention is to provide an electrophotographic process and an electrophotographic apparatus which prevent image defects caused by stripping discharge due to high speed operation from occurring and have high durability.
Specifically, the present invention provides an electrophotographic process which comprises the step of:
pre-exposing a photosensitive member comprising a conductive substrate, and a photoconductive layer formed of a non-single crystal material containing silicon and a surface protective layer overlaid on the substrate,
charging the photosensitive member,
forming a latent image on the photosensitive member,
developing the latent image by reverse development, and
cleaning the photosensitive member surface with a cleaning blade so provided as to come into contact with the photosensitive member,
wherein a surface moving speed of the photosensitive member PS (mm/second) is 320 mm/second or more, and
where a film thickness and a specific resistance of the surface protective layer are represented respectively by Ds (&mgr;m) and Rs (ohm.m), the following conditions are satisfied:
1.0×10
9
≦Rs≦
1.0×10
13
Ds≦−0.136
Ln
(
Rs
)+(−0.004
×PS
)
in which Ln represents a natural logarithm) wherein, when on completion of 1,000,000-sheet copies of a sequence of solid black images having a latent image density of 100%, a dark portion potential of the photosensitive member is measured by a potential measuring method using a voltage direct-application method, the following conditions are satisfied:
(
Vd
0
−Vd
1)/
Vd
0≦0.30
where Vd0 is a potential at an initial stage and Vd1 is a potential on completion of 1,000,000-sheet copies.
In addition, the present invention also provides an electrophotographic apparatus using the above electrophotographic process.
REFERENCES:
patent: 5729800 (1998-03-01), Ohba et al.
patent: 2002/0051920 (2002-05-01), Owaki et al.
patent: 0777164 (1997-06-01), None
patent: 0825493 (1998-02-01), None
patent: 0913733 (1999-05-01), None
patent: 957413 (1999-11-01), None
Karaki Tetsuya
Katagiri Hiroyuki
Matsuoka Hideaki
Segi Yoshio
Canon Kabushiki Kaisha
Dote Janis L.
Fitzpatrick ,Cella, Harper & Scinto
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