Electrophotography – Image formation – Charging
Reexamination Certificate
2002-03-15
2003-11-11
Chen, Sophia S. (Department: 2852)
Electrophotography
Image formation
Charging
C361S221000, C361S225000, C399S168000, C399S313000
Reexamination Certificate
active
06647231
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrically conductive member capable of being used in an electrophotographic apparatus running on an electrophotographic process, such as a copy machine, a printer, a facsimile device and the like, and an image forming apparatus equipped with the electrically conductive member.
2. Description of the Related Art
As electrophotographic processes, many have been known as described in Japanese Patent Application Publication (JP-B) No. 42-23910. In general, an electrographic process includes plural steps of: electrically forming, by various means, a latent image on the surface of a photosensitive member (latent image bearing member) made from a photoconductive material; forming a toner image by developing the formed latent image with a toner; thereafter transferring the toner image on the surface of the photosensitive member, by way of an intermediate transfer member or directly, onto the surface of a transfer substrate such as paper or the like; and fixing the transferred image by heating, applying pressure, conducting hot-press, or using a solvent vapor or the like, to obtain a fixed image. The toner remaining on the surface of the photosensitive member, when required, is cleaned by means of various methods to be recycled in the above plural steps.
In an image forming apparatus for forming an image using the electrophotographic process, there have been typically adopted a contact charge type or a contact transfer type with very small generation of ozone. In such types, preferably used is a member in the shape of a roller excellent in wear-resistance and in transportability of a transfer substrate in a transfer section.
As the member in the shape of a roller, used generally is a semiconductive roller with a structure that a semiconductive elastic layer having a resistance value in the range of 1×10
5
to 1×10
12
&OHgr; adjusted by addition of carbon, an ion conductive agent or the like is formed on a core metal made of stainless steel (SUS), iron or the like. Such a semiconductive roller has an elastic layer and the elastic layer is pressed to the photosensitive member or the intermediate transfer member, which is an image bearing member, to enable a nip to be formed with certainty.
In the semiconductive roller, various components are included in rubber of the elastic layer: such as residuals of a reaction initiator added in synthesis for a base polymer, a by-product accompanying the synthesis, a low molecular component of the base polymer, and a vulcanizer, softner and plasticizer added in molding of a rubber roller. If the semiconductive roller is left for a long time in press contact with a photosensitive member or an intermediate transfer member, a phenomenon occurs with ease that the components in the roller seep out on the surface of the elastic layer, which is a so-called bleeding. Most of the seeping-out components are easy to react with the photosensitive member or the intermediate transfer member, leading a problem that the components attach onto the surfaces of the photosensitive member or the intermediate transfer member to denature physical properties of the surfaces thereof via chemical reactions.
Furthermore, an elastic layer of a semiconductor roller is adjusted on its surface resistance by mechanically mixing and dispersing carbon, a metal oxide or an ion conductive agent into a rubber material and in a case where an ion conductive agent is adopted, the elastic layer not only receives a change in physical properties thereof in an environment at high temperature and high humidity, but also precipitates the ion conductive agent out on the surface thereof, thereby having resulted in a problem of a local change in surface electrical resistance value thereof. Moreover, if the semiconductive roller is left in press contact with a photosensitive member or an intermediate transfer member, there has been a case where a problem arises that the precipitated ion conductive agent contaminates the photosensitive member and the intermediate member.
In order to solve the problems, an idea comes to mind that coating is applied on the surface of an elastic layer of a semiconductive roller with a material serving as a barrier layer for preventing a component contained in the elastic layer from seeping out or precipitating on the surface thereof, whereas by the coating, the semiconductive roller is of a plural layer structure, which again produces a problem of a high cost due to increases in material cost and complexity of fabrication process.
Recently, on the other hand, in an image forming apparatus running on an electrophotographic process has come to be desired for quietness. A charging roller, one kind of semiconductive roller, produces a so-called charging sound therefrom, which is an unpleasant, offensive sound, when a high frequency AC bias is superimposed on a DC bias and reduction in such a charging sound has remained a great technical problem.
As one of methods to reduce the charging sound, a method has been proposed in which a weight is put into the interior of a photosensitive member in contact with the charging roller to prevent high frequency vibrations caused by the charging roller from propagating. However, in this method, a necessity arises for a new process that a member serving as a weight is fixed in place inside of the photosensitive member, for example a adhesion process, inevitably leading to cost-up. Moreover, as an alternative for reduction in charging sound, a method has been adopted in which a foamed layer is provided on a charging roller to absorb the vibrations. However, in this method, the material of the foamed layer is rubber and thus inevitably disables a photosensitive member in contact therewith. That is, an adverse influence therefrom as described above cannot be avoided.
Moreover, in an image forming apparatus running on an electrographic process, a long life of a photosensitive member has been desired for reduction in unit price of prints and photocopies (in other words, referred to as reduction in running cost). The surface of a charging roller in contact with a photosensitive member is, however, scraped with ease by discharge produced in a tiny gap between the photosensitive member and the charging roller, or in other words by a so-called etching phenomenon, in a case where a high frequency AC bias is superimposed on a DC bias; thereby, having lead to a problem of no realization of a long life photosensitive member.
A proposal has been made on a method that only DC bias is applied to a charging roller, in other words a so-called DC charging, as a method of reducing the charging sound and the etching phenomenon. In order to charge the charging roller in a uniform manner with such a DC charging, requirements arise for more of resistivity uniformity and a higher level surface smoothness of the charging roller as compared with requirements thus far. However, a charging roller has components contained in an elastic layer that bleeds with ease as described above and in addition, toner, paper powder and the like are attached onto the surface thereof with ease due to a conductivity thereof; therefore, the charging roller has had a problem of virtually no possibility of retaining resistance uniformity and surface smoothness with no achievement of fundamental solution of the problem.
A proposal has been made on another method for reduction in charging sound and etching phenomenon of a photosensitive member that is a new charging technique for the surface of an image bearing member, which is called injection charging, and adopted in part of apparatuses on the market. Since such a technique enables an applied DC bias to be a potential on the surface of a photosensitive member as is, no requirement arises for application of an AC bias theoretically.
The injection charging technique is, however, a technique requiring a combination of a member of a structure in which magnetic powder is held on the outer peripheral surface of a metal sleeve by the action o
Chen Sophia S.
Fuji 'Xerox Co., Ltd.
Oliff & Berridg,e PLC
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