Electrophotography – Image formation – Transfer
Reexamination Certificate
2001-08-31
2003-05-27
Brase, Sandra (Department: 2852)
Electrophotography
Image formation
Transfer
Reexamination Certificate
active
06571079
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image recording section in which a toner image is transferred onto a print medium, and more particularly to an image recording apparatus that incorporates a plurality of image forming sections for color printing.
2. Description of the Related Art
A conventional color electrophotographic printer incorporates a plurality of image forming sections that are in cartridge form and form images of corresponding colors. A cartridge configuration is advantageous in that a cartridge of a specific toner color can be replaced at any time.
A tandem type electrophotographic printer is a type in which image forming sections of the respective colors are aligned in a direction of travel of a print medium. As the print medium passes the respective image forming sections in sequence, toner images of corresponding colors are transferred onto the print medium in order.
Each image forming section incorporates a photoconductive drum on which a toner image is developed. There is provided a transfer roller in pressure contact with the photoconductive drum. The toner image on the photoconductive drum is charged negatively. The transfer roller receives a positive high voltage. Thus, when the print medium passes a transfer point defined between the photoconductive drum and the transfer roller, the toner image formed on the photoconductive drum is attracted to the print medium.
A problem with the aforementioned tandem type electrophotographic printer is that when the leading end of the print medium approaches each of image forming sections downstream of the first image forming section, the toner particles on the downstream photoconductive drum are pulled to the print medium. This phenomenon is referred to as “migration.” The higher the printing duty is, the more of toner is pulled to the print medium. This is because when toner is deposited over a large area on the photoconductive drum (i.e., high printing duty), the toner particles are attracted less strongly to the surface of the photoconductive drum. Thus, when the printing duty is high, a larger amount of toner will be pulled to the print medium.
It can be presumed that migration occurs because the print medium becomes positively charged and attracts the negatively charged toner particles on the photoconductive drum when the print medium approaches the transfer point of a downstream image forming section. Another reason for migration may be that charge accumulates gradually on a high resistance material such as plastic films (e.g., insulation film
12
) during printing, resulting in non-uniform charging of the print medium.
SUMMARY OF THE INVENTION
An image-recording apparatus has a plurality of image-forming sections. Each image-forming section has a transfer point where a corresponding toner image is transferred from a photoconductive drum onto a print medium when the print medium passes through the transfer point. Each of the image-forming sections includes a surface that opposes the print medium; and an electrically conductive member provided on the surface.
The surface is downstream of the photoconductive drum with respect to a direction of travel of the print medium.
The surface and print medium are spaced apart by a distance in the range of 1 to 3 mm and the electrically conductive member has a sheet resistance value of 15 k&OHgr;/□ to 10 M&OHgr;/□.
The electrically conductive member is an electrically conductive film to which a high concentration of carbon black is contained.
The electrically conductive member is grounded.
The electrically conductive member is a metal and is grounded through an electrical resistor.
Another image-recording apparatus has a plurality of image-forming sections. Each image-forming section has a transfer point where a corresponding toner image is transferred from a photoconductive drum onto a print medium when the print medium passes through the transfer point. Each of the image-forming sections includes a transfer belt or medium transporting path that runs through the transfer point; and a neutralizing cloth disposed on a side of the transfer belt or medium transporting path remote from the photoconductive drum, the neutralizing cloth being disposed between a preceding transfer section and a following transfer section.
The image-recording apparatus may further include an electrically conductive member attached to a surface that opposes the print medium.
The neutralizing cloth is at least 5 mm away from the transfer point.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
REFERENCES:
patent: 4984024 (1991-01-01), Ohkaji et al.
patent: 5189479 (1993-02-01), Matsuda et al.
patent: 5594538 (1997-01-01), Takekoshi et al.
patent: 06-019332 (1994-01-01), None
Chigira Nobutoshi
Nagaoka Kazuhiko
Shiraishi Toyokazu
Brase Sandra
Oki Data Corporation
Rabin & Berdo P.C.
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