Roll or roller – Concentric layered annulus – Specific composition
Reexamination Certificate
1999-01-20
2001-02-20
Hughes, S. Thomas (Department: 3726)
Roll or roller
Concentric layered annulus
Specific composition
C399S176000, C492S018000
Reexamination Certificate
active
06190295
ABSTRACT:
This application is based on Japanese Patent Application No. 10-41512 filed Feb. 24, 1998, the content of which is incorporated hereinto by reference.
CROSS REFERENCE TO RELATED APPLICATION
Not Applicable
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a charging roll for use in an image forming apparatus such as an electrophotographic copying machine, laser beam printer, or the like.
2. Discussion of the Related Art
There is known a charging roll which is installed in an image forming apparatus such as an electrophotographic copying machine or printer, such that the charging roll is held in rolling contact with a photosensitive drum for charging the circumferential surface of the photosensitive drum. More specifically described, such a charging roll is used in a so-called “roll charging” method which is one of the known methods for charging a photosensitive drum on which an electrostatic latent image is formed. In the roll charging method, the charging roll to which a charging voltage is applied is held in pressing contact with the outer circumferential surface of the photosensitive drum. The charging roll and the photosensitive drum are rotated together so that the outer circumferential surface of the photosensitive drum is evenly charged by the charging roll before the surface is locally imagewise exposed to optical image signals.
In general, the charging roll includes an electrically conductive center shaft (metal core) and an electrically conductive rubber layer which has a low hardness and is formed of a rubber layer. The rubber layer consists of either a solid elastic body whose hardness is reduced by adding a large amount of softener, or a foamed body. The electrically conductive rubber layer is formed on the outer circumferential surface of the center shaft with a suitable thickness. On the outer circumferential surface of the conductive rubber layer, there are laminated a resistance adjusting layer and a protective layer in this order. An electrode layer is interposed, as needed, between the conductive rubber layer and the resistance adjusting layer.
In the charging roll constructed as described above, there has been employed the resistance adjusting layer which is formed of a rubber composition prepared by mixing a suitable rubber material with an ion- conductive material such as quaternary ammonium salt, so as to give the rubber composition a desired volume resistivity. However, the resistance adjusting layer containing the ionconductive material tends to suffer from a variation of its characteristics due to a change of the operating environment of the charging roll. To solve this problem, it is considered to form the resistance adjusting layer by using a rubber composition which includes electron-conductive particles such as carbon black particles as a conductive material.
However, the use of the charging roll whose resistance adjusting layer contains the electron-conductive particles deteriorates a quality of a reproduced or printed image, when the surface of the photosensitive drum has flaws such as pinholes, or any scratched, warred or otherwise damaged or defective portions. Namely, the reproduced image undesirably includes printing defects (e.g., pinhole defect) corresponding to the defective portions even when the surface defects of the photosensitive drum are not so considerably serious. For instance, an image area corresponding to a pinhole and its vicinity tends to be blurred.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a charging roll which is capable of preventing occurrence of printing defects due to defective portions of the outer circumferential surface of a photosensitive drum used with the charging roll.
The above object may be achieved according to a principle of the present invention which provides a charging roll comprising: a center shaft; an electrically conductive rubber layer formed on an outer circumferential surface of the center shaft and having a relatively low hardness; a resistance adjusting layer formed radially outwardly of the conductive rubber layer; and a protective layer formed radially outwardly of the resistance adjusting layer. The resistance adjusting layer is formed of a rubber composition prepared by mixing a rubber material with particles of an electron-conductive material and particles of an electrically insulating material. The rubber composition comprises 10-50 parts by weight of the electrically insulating material per 100 parts by weight of the electron-conductive particles.
In the charging roll constructed according to the present invention, the resistance adjusting layer contains the predetermined amount of the elastically insulating particles as well as the electron-conductive particles, such that the electrically insulating particles and the electron-conductive particles are dispersed in the rubber material. This charging roll effectively prevents occurrence of the printing defects due to pinholes or other defective portions of the sur ace of the photosensitive drum.
According to one preferred form of the present invention, the electrically conductive rubber layer consists of a foamed body which is formed by foaming a foamable electrically conductive rubber composition.
According to another preferred form of the present invention, the electrically conductive rubber layer consists of a solid elastic body, and the charging roll further comprises an electrode layer interposed between the electrically conductive rubber layer and the resistance adjusting layer.
According to a further preferred form of the present invention, the rubber composition of the resistance adjusting layer comprises 30-100 parts by weight of the electron-conductive material per 100 parts by weight of the rubber material, so that the resistance adjusting layer has a desired electric conductivity (resistance value).
According to a still further preferred form of the present invention, the resistance adjusting layer has a thickness within a range of 100-300 &mgr;m.
According to a yet further preferred form of the present invention, the resistance adjusting layer has a volume resistivity within a range of 1×10
5
-×10
11
&OHgr;·cm.
REFERENCES:
patent: 4062812 (1977-12-01), Safford et al.
patent: 5312662 (1994-05-01), Ohta
patent: 5359395 (1994-10-01), Shimura et al.
patent: 5567494 (1996-10-01), Ageishi et al.
patent: 5604031 (1997-02-01), Yamamoto et al.
patent: 5822658 (1998-10-01), Tanka et al.
patent: 5851657 (1998-12-01), Yasuno et al.
patent: 0 308 185 (1989-03-01), None
patent: 0 329 366 (1989-08-01), None
patent: 0 417 801 (1991-03-01), None
patent: 797 128 A2 (1997-09-01), None
patent: 867 782 A2 (1998-09-01), None
patent: 2-311868 (1990-12-01), None
patent: 2-311867 (1990-12-01), None
patent: 05 088 509 (1993-04-01), None
patent: 5-88509 (1993-04-01), None
patent: 07 140 760 (1995-06-01), None
patent: 8-286470 (1996-11-01), None
patent: 10 186 799 (1998-07-01), None
patent: 10 319 678 (1998-12-01), None
Kawano Atsuhiro
Tsuchiya Kenichi
Burr & Brown
Butler Marc W.
Hughes S. Thomas
Tokai Rubber Industries Ltd.
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