Electrophotography – Image formation – Charging
Reexamination Certificate
2002-07-10
2004-10-26
Braun, Fred L. (Department: 2852)
Electrophotography
Image formation
Charging
C399S279000, C399S313000, C399S357000
Reexamination Certificate
active
06810225
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a conductive member used for a charging unit, a development unit, a transfer unit, and a cleaning unit, which are used for electrophotographic apparatus or an electrostatic recording process, and an electrophotographic apparatus including a charging unit, a development unit, a transfer unit, and a cleaning unit, each of which uses the conductive member.
An electrophotographic apparatus or an electrostatic recording apparatus, such as a copying machine, a facsimile, or a printer is operated in accordance with a printing method, which includes a charging step of uniformly charging the surface of a photosensitive body, an electrostatic latent image forming step of projecting an image from an optical system to the photosensitive body, to erase charges in a portion irradiated with light, thereby forming an electrostatic latent image, a development step of sticking toner on the latent image, to form a toner image, and a transfer step of transferring the toner image to a recording medium such as a paper sheet.
In this printing process, the initial step of charging a photosensitive body has been generally performed by using a corona discharging method. The corona discharging method, however, is undesirable from the viewpoints of safety and maintenance of the apparatus because the corona discharging method needs the supply of a high voltage such as 6 to 10 kV. The corona discharging method also presents an environmental problem because a hazardous substance such as ozone or NOx occurs during discharge of corona.
To solve the above problems, various attempts have been made to develop a new charging method capable of performing charging at a voltage lower than that required for the corona discharging method and suppressing occurrence of a hazardous substance such as ozone. For example, a contact type charging method shown in
FIG. 3
has been proposed as an alternative to the corona charging method. Referring to
FIG. 3
, a roller-shaped charging member (charging roller)
14
, to which a voltage has been applied from a power source
16
, is brought into contact with a body
15
to be charged such as a photosensitive body at a specific pressure, to thereby charge the body
15
to be charged.
With respect to the development step, as a development method of supplying a non-magnetic one-component developer to a photosensitive drum or the like on which a latent image has been formed, to stick the developer to the latent image on the photosensitive drum, thereby visualizing the latent image, a pressure development method has been known, for example, from U.S. Pat. Nos. 3,152,012 and 3,731,146. This pressure development method can eliminate the need of use of any magnetic material, and is thereby advantageous in simplifying the structure of the apparatus and easily reducing the size of the apparatus, and further easily realizing development using a plurality of kinds of colored toner.
Referring to
FIG. 2
, the pressure development method is performed by bringing a development roller
6
, on which toner (non-magnetic one-component developer) has been supported, into contact with a latent image support
5
such as a photosensitive drum on which an electrostatic latent image has been formed, to stick the toner to the latent image on the latent image support
5
, thereby developing the latent image. Accordingly, the development roller
6
must be rotated while certainly holding the state that the development roller
6
is brought into close-contact with the latent image support
5
such as a photosensitive drum, and therefore, the development roller
6
is required to be made from a conductive elastic body.
A transfer unit, used in the transfer step, for transferring a toner image, which has been developed with toner for visualization, from a latent image support to a transfer medium such as a paper sheet, has been generally configured to transfer a toner image to a transfer medium by charging the transfer medium with the use of a corona charger. The corona discharge, however, has the above-described problems associated with occurrence of ozone and the need of a high voltage power source. To solve such problems, there has been known a transfer unit shown in
FIG. 2
, wherein a transfer medium
8
is charged by using a bias roller (transfer roller)
9
made from a conductive rubber. In this method, to enhance the transfer efficiency and obtain a uniform transfer image, it is required to set a specific nip width between the transfer roller
9
and a photosensitive drum
5
and reduce a pressure applied between the roller and the drum, and to meet such a requirement, a very soft conductive rubber must be used as the material forming the transfer roller
9
. It is to be noted that, as shown in
FIG. 2
, the toner image transferred to the transfer medium
8
is heated by a fixing unit
13
to be thus fixed to the transfer medium
8
.
After transfer of a toner image, toner remaining on a photosensitive drum is removed by a cleaning unit. Such a cleaning unit has been generally configured to scrape toner by an edge of a blade made from a urethane rubber or the like pressed on a photosensitive body. The use of the blade, however, has a problem that since a large frictional force occurs against a photosensitive body, a drive force becomes large, the photosensitive drum is liable to be damaged by the edge of the blade, and in the worst case, the cleaning operation becomes impossible because of damage of the rubber blade. To solve such a problem, a cleaning unit
12
using a cleaning roller
11
to which a voltage is applicable (see
FIG. 2
) has been proposed, wherein residual toner is directly removed from the surface of the photosensitive drum
5
by the cleaning roller
11
. Alternatively, a cleaner-less method has been proposed, in which toner is forcibly charged and then recovered by a development roller or the like. In the case of adopting the cleaning method using the cleaning unit
12
, the cleaning roller
11
constituting the cleaning unit
12
also requires the same characteristics as those required for the transfer roller.
The above-described charging roller, development roller, transfer roller, or cleaning roller has been configured as a conductive member obtained by forming a resin layer on the surface of an elastic layer such as a rubber material or a urethane form. The formation of the resin layer is for ensuring a surface smoothness, adjusting a surface resistance, and improving a charging characteristic. The resin layer is typically formed by coating the elastic layer with a solution of a resin selected from an acrylic resin, a urethane resin, nylon, a polyethylene resin, an epoxy resin, a polyester resin, a polyether resin, a polystyrene resin, a phenol resin, an ABS resin, a polyamide resin, and a urethane modified acrylic resin by a dipping method or a spraying method.
The above-described conventional conductive member, however, has the following problems:
Initial Fog/Fog after Repeated Printing
In the recent electrophotographic field, there have been strong demands to enhance the image quality, lower the cost (lower the voltage or reduce the size of a member), increase the operational speed, and improve the durability, and to meet such demands, attempts have been made to improve electrophotographic apparatuses. These apparatuses thus improved to meet the above-described demands, however, may often cause a problem associated with initial image defects (such as initial fog) and image defects after repeated printing (such as fog after repeated printing) due to the effect of a conductive member used for a charging roller, a development roller, a transfer roller, or a cleaning roller. The reason why the image defects such as fog occur due to the effect of the conductive member, however, has not been basically revealed, and at the present time, any countermeasure capable of sufficiently solving such a problem has not been proposed yet.
Adhesiveness to Photosensitive Body (OPC)
A conductive member used for a charging roller, a deve
Kitano Hajime
Yakushiji Gaku
Braun Fred L.
Bridgestone Corporation
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