Electrophotography – Image formation – Charging
Reexamination Certificate
1999-08-12
2001-07-10
Chapman, Mark (Department: 1753)
Electrophotography
Image formation
Charging
C361S225000, C428S323000
Reexamination Certificate
active
06259875
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention concerns a charging member for charging a material to be charged such as a light sensitive material for use in electrophotography and electrostatic recording processes in image forming apparatus such as electrophotographic copying machines and printers. More specifically, it relates to a charging member to be pressed on the surface of a material to be charged such as a light sensitive material and a dielectric material for uniformly charging the surface of the material to be charged, and a charging device.
2. Description of the Related Art
In electrophotographic apparatus, uniform charging is conducted to the surface of a material to be charged such as a light sensitive material and a dielectric material. A method of conducting charging by corona generated by applying a high voltage to metal wires has been adopted as a charging treatment means. However, the corona charging method involves a drawback that corona-induced products such as ozone and nitrogen oxide (NOx) formed upon charging denature the surface of the light sensitive material to deteriorate the light sensitive material or cause image blurring, and that the contamination of the wires gives an undesired effect on the image quality, leading to whitening and streaking.
In addition to the non-contact method described above, there is a contact method of conducting charging by bringing a charging member into contact with a material to be charged. The contact type charging method has an advantage that a voltage to be applied to the charging member is generally low and the amount of ozone formed is extremely small. However, it has a drawback that a toner or an external toner additive passing through a cleaning blade deposits or fuses on the charging member to cause image defects due to failed charging caused by contamination.
As a technique for improving such drawbacks, the technique disclosed in Japanese Patent Unexamined Publication 7-134467 has been known for instance.
The publication discloses a charging member in which a lubricant is contained in a surface layer formed on the surface of an elastic layer. The technique has a contamination-preventing effect due to the reduction of dynamic friction coefficient in an initial stage.
However, the technique has a problem that a hard material such as the external toner additive thrusts into the surface of the charging member during continuous use, which triggers adhesion of the toner. The surface layer of the charging member is made of a less wearing material including the technique and is formed to a thickness of about 10 &mgr;m in the related art.
Therefore, the surface layer of the charging member is also contaminated during long time use, resulting in charging failure.
SUMMARY OF THE INVENTION
In view of the above, the object of the present invention is to prevent deterioration of the charging performance of a charging member caused by contamination of the surface layer of the charging member, to maintain stable and satisfactory uniform charging property and image quality for a long period of time.
Another object of the present invention is to positively abrade the surface layer of the charging member contaminated by a toner to always keep the surface clean thereby maintaining stable and satisfactory uniform charging property and image quality for a long period of time.
The present invention achieved for overcoming the foregoing problems is to be explained next, in which each constituent of the present invention is depicted by a reference numeral for the constituent surrounded by parentheses corresponding to the reference numeral in example to be described later for facilitating correspondence with the constitution in the examples. The reason for explaining the present invention corresponding to the reference numerals of the examples is for better understanding of the present invention, and not for limiting the scope of the present invention only to that of the examples.
The foregoing object can be attained in accordance with the present invention by a charging member pressed to the surface of the material to be charged for charging the material to be charged, having the following conditions:
a conductive core;
a conductive elastic layer formed on the surface of the conductive core; and
a wearing surface layer to be used also as a resistance controlling layer formed on the surface of the conductive elastic layer for controlling the resistance value between the surface of the conductive core material and the surface of the charging member, and comprising of a surface layer-forming resin and a resistance controlling conductive filler for developing conductivity by electron conduction and having a specific wearing amount of 5.0×10
−4
(mm
3
/N·km) or more.
In the present invention, the specific wearing amount (unit slide distance, a wearing amount per unit load) is a value measured by a wearing test method for plastics according to JIS K 7218.
The following materials can be used as the surface layer-forming resin for forming the wearing surface layer to be used also as the resistance controlling layer and the resistance controlling conductive filler for developing conductivity by electron conduction described above.
For the surface layer-forming resin: urethane, nylon, acryl, epoxy, phenol, polyester, polyethylene, polyamide, polyimide and polyvinyl butyral resin may be used. Urethane and nylon resin are preferred.
For the resistance controlling conductive filler: carbon black, graphite, metal oxides (for example, tin oxide, titanium oxide, zinc oxide and nickel oxide), different atom doped metal oxides (antimony-doped tin oxide) and metals may be used. Carbon black having pH of 4.0 or less, and tin oxide are preferred.
For the conductive elastic layer: rubber in which the fine powder (carbon black, metal oxide and metal) is dispersed; and silicone, urethane, styrene butadiene, NBR and epichlorohydrin rubber may be used. Silicone and urethane rubber are preferred.
The charging member of the invention having the constitution described above is pressed onto the surface of the material to be charged to thereby charge the material to be charged.
The conductive elastic layer is formed on the surface of the conductive core, and the wearing surface layer to be used also as the resistance controlling layer is formed on the surface of the conductive elastic layer. The wearing surface layer to be used also as the resistance controlling layer has the surface layer-forming resin and the resistance controlling conductive filler for developing conductivity by electron conduction, and controls the resistance value between the conducive core and the surface of the charging member. Since the wearing surface layer to be used also as the resistance controlling layer has a specific wearing amount of 5.0×10
−4
(mm
3
/N·km) or more, it tends to be worn easily. Since the contamination formed on the wearing surface layer to be used as the resistance controlling layer can be removed by the wearing of the surface, stable charging property can be obtained for a long period of time.
The charging device in accordance with the present invention comprises: a charging member having a surface layer to be pressed on the surface to be charged for charging the material to be charged; a cleaner for cleaning the surface of the wearing surface layer to be used also as a resistance controlling layer.
In the charging device of the present invention, the surface layer of the charging member is pressed on the surface of the material to be charged. The charging member charges the material to be charged. The cleaner cleans the surface. Accordingly, since the surface of the charging member is hardly contaminated, stable charging property can be obtained for a long period of time.
The wearing surface layer is used also as a resistance controlling layer having a specific wearing amount of 5.0×10
−2
(mm
3
/N·km) or less.
If the specific wearing amount is more than 5.0×10
−2
(mm
3
/N·km), the amoun
Kataoka Hiroyuki
Miura Hiroyuki
Takayama Hiroshi
Chapman Mark
Fuji 'Xerox Co., Ltd.
Oliff & Berridg,e PLC
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