Electrophotography – Image formation – Charging
Patent
1997-05-05
1999-02-09
Lee, S.
Electrophotography
Image formation
Charging
361225, G03G 1502
Patent
active
058706577
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a charging apparatus for uniformly charging an image bearing member, namely, a photoconductor.
BACKGROUND ART
In a copying machine using an electrophotographic system, and an image formation apparatus such as a laser printer, a corona discharger is in general use for charging an image bearing member, that is, a photoconductor, for performing image transfer, for separating copy paper, or for quenching charges of the photoconductor, since uniform charging can be performed by the corona charger.
However, since a high voltage as high as 4000 to 8000 V is applied to the corona discharger, a large amount of ozone (O.sub.3) is generated by the corona discharger when discharging is carried out. Effects of ozone on living body system are described in detail in an article entitled "Troubles caused by corona discharging and techniques for preventing the troubles" (Electrophotography 30.3/1991) by Yasuyuki Tabata. Nitrogen oxides (Nox) which are generated at the same time as the generation of ozone are also considered to work as factors by which the quality of produced images is degraded and the life of the photoconductor is shortened, since such nitrogen oxides are deposited on the surface of the photoconductor or penetrate into the photoconductor.
In particular, nitrogen oxides (Nox=NO, NO.sub.2, NO.sub.3, . . . ) react with water in air to produce nitric acid (HNO.sub.3) which is deposited not only on the photoconductor, but also on and around the charging apparatus itself, and corrodes metallic materials used in the charging apparatus. As a result, the characteristics of the photoconductor are caused to deteriorate (refer to Japanese Laid-Open Patent Applications 61-12358, 62-7065 and 2-79069). Therefore, as countermeasures for controlling the generation of corona products from the corona discharger, many proposals have been reported, such as locally providing an ozone absorbing material on a shield wall for the discharger, providing an ozone decomposing material in vicinity with the photoconductor, and heating the discharger. However, currently such proposals cannot always sufficiently cope with the above-mentioned problems, since those proposals have problems with respect to the continuity of the effect, the cost, or the capability of completely nullifying ozone products. Under such circumstances, in recent years, there have been made studies as to how to make practically usable contact charging methods (such as roller charging method and brush charging method) which are considered to be methods with an extremely small amount of generation of ozone, and such a method has already actually been put to practical use in some copying machines.
FIG. 17 shows an outline of a conventional corona charger. In the figure, reference number 1 indicates a photoconductor; 50, a shield case; 51, a charge wire; and 52, a grid. Contact charging apparatus are shown in FIG. 18 to FIG. 20. FIG. 18 shows a brush contact charging apparatus. In the figure, reference numeral 53 indicates an electroconductive brush. FIG. 19 shows a blade contact charging apparatus. In the figure, reference numeral 54 indicates a core material, and 55 indicates an electroconductive unwoven cloth. Furthermore, FIG. 20 shows a roller contact charging apparatus. In the figure, reference numeral 56 indicates a resistor layer, and 57 indicates a surface protective layer. In the charging apparatus shown in FIG. 18 and FIG. 19, there are generally used electroconductive fibers which are carbonized to such a degree that the resistance thereof is, for instance, in the range of about 10.sup.3 to 10.sup.6 .OMEGA.; and in the charging apparatus shown in FIG. 20, there is generally used an electroconductive rubber roller with the resistance thereof being adjusted to about 10.sup.5 .OMEGA..multidot.cm by uniformly dispersing carbon powder in the rubber.
The corona discharger generates ozone in an amount of about 1 to 10 ppm, and nitrogen oxides (Nox) such as NO.sub.2 and NO.sub.3 in an amount of about 0.05 to 0.5 ppm
Ikuno Hiroshi
Kojima Narihito
Nagame Hiroshi
Lee S.
Ricoh & Company, Ltd.
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