Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2001-02-02
2003-09-16
Rodee, Christopher (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S069000, C430S120400, C399S350000
Reexamination Certificate
active
06620570
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrophotographic method used for the image-forming apparatuses such as copiers, laser printers and plain paper facsimiles. More specifically, the invention relates to an electrophotographic method capable of executing an image-forming processing at a high speed.
2. Description of the Prior Art
In an image-forming apparatus utilizing an electrophotographic method as represented by a copier, a rotary photosensitive material drum is subjected to an image-forming processing which includes main electric charging, exposure to image-bearing light, developing, transfer, cleaning and removal of electric charge, in order to form an image.
A variety types of drum-like photosensitive materials have been used for the image-forming process based on the electrophotographic method. In recent years, in particular, there has been widely used an organic photosensitive material having an organic photosensitive layer formed on an electrically conducting blank tube. That is, the organic photosensitive material has a great advantage in that an organic photosensitive layer can be easily formed by a coating method at a decreased cost. Many organic photosensitive materials can be used for forming the organic photosensitive layer. By using a less harmful compound, the user is allowed to dispose of the photosensitive material when it is out of service life, offering a so-called maintenance-free advantage.
The above organic photosensitive materials can be grouped into single-layer organic photosensitive materials in which a photosensitive layer is a single layer containing an electric charge-generating agent and an electric charge-transporting agent, and function-separated laminated organic photosensitive materials in which the photosensitive layer includes an electric charge-generating layer containing an electric charge-generating agent and an electric charge-transporting layer containing an electric charge-transporting agent.
In modern high-speed digital image-forming apparatuses employing the above image-forming process that works at high speeds in a digital manner, however, various problems are occurring being caused by a high-speed rotation of the photosensitive material drum and due to the use of a semiconductor laser as a source of light for exposure to image-bearing light.
For example, when the function-separated laminated organic photosensitive material is exposed to image-bearing light by using a semiconductor laser as a source of light, interference fringes (Moire fringes) easily occur being affected by the surface of the electrically conducting blank tube which is the photosensitive layer-forming surface. In order to prevent the occurrence of interference fringes, a method has been known to set the surface roughness of the electrically conducting blank tube to lie within a predetermined range leaving, however, a problem that results from the high-speed rotation of the photosensitive material drum. That is, in the image-forming process, a cleaning blade is brought into pressed contact with the surface of the photosensitive material drum in order to remove the toner remaining on the surface of the photosensitive material drum. With the cleaning blade being brought into pressed contact with the surface of the photosensitive material drum, however, the electric charge-transporting layer on the surface of the photosensitive material drum is worn out to deteriorate the image properties to a conspicuous degree.
In the single-layer organic photosensitive material, on the other hand, light in the step of exposure to light is almost all absorbed by the surface of the photosensitive layer or near the surface thereof, and the interference fringes develop very little and the wear of the photosensitive layer is not much of a problem. That is, in the single-layer organic photosensitive material, the thickness of the photosensitive layer is considerably larger than that of the electric charge-transporting layer in the function-separated laminated photosensitive material. Therefore, wear of the photosensitive layer does not much affect the image properties. Thus, the single-layer organic photosensitive material is suited for the digital image-forming process of a high speed. Even by using the above organic photosensitive material, however, limitation is imposed on the processing speed for favorably forming images for extended periods of time. For example, when the image-forming process is conducted by rotating the photosensitive material drum at a peripheral speed of not smaller than 400 mm/sec, the photosensitive material drum is quickly accelerated up to a predetermined peripheral speed at the start of image formation, and a strong static frictional force acts on the tip of the cleaning blade that comes in contact with the surface of the photosensitive layer. Even in a steady state where the photosensitive material drum is rotating at a constant peripheral speed, a strong centrifugal force acts due to a high rotational speed, and a large dynamic frictional force acts on the tip of the cleaning blade. As a result, the tip of the blade is burred (the blade edge is finely cut and is burred) and, in an extreme case, the tip of the blade is turned up, causing the cleaning to become defective and making it difficult to favorably form the images within short periods of time.
Thus, no means has yet been proposed for avoiding defective cleaning of when the image-forming process is conducted at a high speed.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an electrophotographic method which is capable of effectively preventing the defective cleaning at the time when an image-forming process is conducted by using a single-layer organic photosensitive material drum and by rotating the photosensitive material drum at a peripheral speed of not smaller than 400 mm/sec.
Another object of the present invention is to provide an electrophotographic method capable of favorably forming images without interference fringes even when a digital image-forming process is executed at a high speed by effecting the exposure to image-bearing light by using a semiconductor laser as a source of light.
According to the present invention, there is provided an electrophotographic method for forming image by subjecting a rotary photosensitive material drum to an image-forming process which includes main electric charging, exposure to image-bearing light, developing, transfer, cleaning and removal of electric charge, wherein:
said image-forming process is conducted by rotating the photosensitive material drum at a speed of not lower than a peripheral speed of 400 mm/sec;
said photosensitive material drum is a single-layer organic photosensitive material drum having a single organic photosensitive layer of a thickness of not smaller than 25 &mgr;m formed on an electrically conducting blank tube having a surface roughness Ra as defined in JIS-B-0601) of not larger than 0.6 &mgr;m; and
the cleaning is effected by using a cleaning blade that is brought into pressed contact with the surface of the photosensitive material drum.
JIS-B-0601 describes a surface roughness Ra determined by the following Formula (I)
Ra=
1
/L∫
0
L
|f
(
x
)|
dx
Formula (I)
In particular, an arithmetic average roughness (Ra)
L
is taken along a standard length (L) obtained at random from a surface to be measured. The standard length is then taken along a roughness curve well known to those of ordinary skill in the art and as shown in FIG.
3
. The length is given in the direction of the removed portion and an Y-axis established in the direction of lengthwise magnification, wherein the roughness curve is expressed as y=f(x).
In the present invention, a distinguished feature resides in the image-forming process by using the single-layer organic photosensitive material drum having a single organic photosensitive layer of a thickness of not smaller than 25 &mgr;m formed on the electrically conducting blan
Kashiwagi Nobuyuki
Kimoto Keizo
Shiomi Hiroshi
Kyocera-Mita Corporation
Rodee Christopher
Sherman & Shalloway
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