Electrophotography – Image formation – Transfer
Reexamination Certificate
1999-02-12
2001-01-09
Braun, Fred L. (Department: 2852)
Electrophotography
Image formation
Transfer
C399S308000, C399S313000
Reexamination Certificate
active
06173148
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus including a transfer device, and more particularly relates to an image forming apparatus which enhances a transfer of an image with the transfer device.
2. Discussion of the Background
An image forming apparatus (e.g., a copier, facsimile, printer or similar image forming apparatus) is known to use a transfer system capable of transferring an image to a recording medium, e.g. a paper sheet, or which utilizes an intermediate transfer system. Such transfer systems have a transfer device, which contacts an image carrier, for transferring a toner image from the image carrier to the recording medium by applying a transfer bias voltage.
However, when utilizing such a transfer system it is possible that the transfer bias voltage may be improperly discharged (e.g., a leakage may occur) if the transfer device or the image carrier has pinholes, defects, or the like. Further, it is possible that the recording medium may be improperly transferred or an image forming may be improperly operated because of noise generated from the improper discharge.
Preventing such an improper discharge has been addressed. For example, Japanese Laid-Open Patent Publication No. 7-13440 discloses a transfer device having a transfer belt and plural electrodes for applying a transfer bias to the transfer belt. Japanese Laid-Open Patent Publication No. 8-152789 discloses a transfer device having a transfer belt and a transfer bias electrode that has at least a two-layer structure in order to prevent an improper discharge from the transfer belt to an image carrier. Japanese Laid-Open Patent Publication No. 9-73239 discloses a relation between a maximum applied voltage to an electrode and a shortest distance between a surface of the electrode and an image carrier in order to prevent an improper discharge from the transfer belt to the image carrier.
However, each of the solutions disclosed in the above-noted publications can only provide a limited solution to preventing the improper discharge. This is particularly the case since in recent years high-speed image forming apparatuses are starting to use a transfer system. In such high-speed image forming apparatuses, the amount of discharge for a unit area to be deposited on the transfer belt may be required to be increased if a process speed, including a moving speed of a transfer belt for forming a toner image, increases due to speeding up of the image forming operation, and as an applied voltage to the transfer belt increases. Thus, in such high-speed image forming apparatuses it becomes more likely that a transfer bias voltage may be improperly discharged (e.g., a leakage may occur). The solutions noted in the above background art may be inadequate to prevent an improper discharge under such conditions.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a novel transfer device which provides a stable image transferring under various conditions, including a high speed operation.
The present invention achieves these and other objects by providing an image forming apparatus which includes an image carrier configured to carry a visible image. A transfer support element is configured to contact the image carrier. A transfer member is configured to apply a transfer bias to the transfer support element. This transfer member is in contact with an inner layer of the transport support element. Further, the transfer member has a medium inherent volume resistance which is less than an inherent volume resistance of the inner layer of the transport support element.
As a further feature in the present invention which can achieve the above-noted and other objects, a plurality of transfer members may be configured to apply the transfer bias to the transfer support element. In this situation, a selected transfer member located at a nearest position to a transfer nip portion will have the highest inherent volume resistance of the plurality of transfer members.
As a further feature in the present invention, if the plurality of transfer members are utilized, an electrical resistance of a current flowing path between the nearest of the plurality of transfer members to the transfer nip portion may be less than the electric resistance of any current flowing path between the other plurality of transfer members and the transfer nip portion.
As a further feature in the present invention, when a plurality of transfer members are utilized, a contact pressure between a transfer member located nearest to the transfer nip portion and the transfer support element may be less than a contact pressure between any of the other of the plurality of transfer members and the transfer support element.
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Japanese Patent Abstract No. 5-127546, date May 25, 1993; Title: Image Forming Device.
Japanese Patent Abstract No. 7-013440, date Jan. 17, 1995; Title: Transfer Belt Device.
Japanese Patent Abstract No. 8-152789, date Jun. 11, 1996; Title: Belt Transfer Device.
Japanese Patent Abstract No. 9-073239, date Mar. 18, 1997; Title: Transfer Separating Device.
Japanese Patent Abstract No. 10-055092, date Feb. 24, 1998; Title: Image Forming Device.
Japanese Patent Abstract No. 10-186878 date Jul. 14, 1998; Title Image Forming Device.
Kaneko Chiemi
Matsuda Itaru
Tanoue Ryou
Braun Fred L.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ricoh & Company, Ltd.
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