Electrophotography – Image formation – Transfer
Reexamination Certificate
2000-09-21
2002-01-08
Grainger, Quana M. (Department: 2852)
Electrophotography
Image formation
Transfer
C399S302000, C399S308000
Reexamination Certificate
active
06337967
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-270895, filed Sep. 24, 1999, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
This invention relates to a color image forming apparatus for superposing monochrome images on each other to form a color image.
A color image forming apparatus using an electronic photography system is designed to execute color separation of an original document image into three primary colors, thereby forming four monochrome images (i.e. images of four colors in total) using toners of C (cyan), M (magenta) and Y (yellow), as complementary colors, and K (black) for emphasizing the black, superposing the monochrome color images and transferring them onto an output material (i.e. a sheet of paper). The process of superposing monochrome images can use a method for superposing toner images on an intermediate transfer member and then simultaneously transferring them onto a paper sheet, or a method for directly superposing toner images on a paper sheet.
Japanese Patent Application KOKAI Publication No. 7-281577, for example, discloses the use of such an intermediate transfer member. Specifically, it discloses an example where an intermediate transfer drum
2
is provided below a photosensitive belt
1
.
The method using an intermediate transfer member is employed in many color image forming apparatuses. However, the speed of forming a color image is ¼ the speed of forming a black-and-white image. Further, in color image forming apparatuses, the process of temporarily transferring a toner image onto an intermediate transfer member is included even when forming a black-and-white image. Accordingly, the black-and-white image forming speed (copy speed) of color image forming apparatuses is lower than that of black-and-white image forming apparatuses. The problem in copying speed is conspicuous, particularly in the case of the first copying period that is required for copying only one page.
BRIEF SUMMARY OF THE INVENTION
It is the object of the invention to provide a color image forming apparatus capable of forming a black-and-white image at high speed.
According to a first aspect of the invention, there is provided a color image forming apparatus comprising:
a charger unit for charging a photosensitive member;
an exposing unit for forming an electrostatic latent image on the charged photosensitive member;
a developing unit for visualizing the electrostatic latent image formed on the photosensitive member to form a toner image;
a first transfer unit for directly transferring the toner image on the photosensitive member onto an image receiving material;
a second transfer unit including an intermediate transfer member for transferring the toner image, formed on the photosensitive member, onto the intermediate transfer member, and for transferring the toner image, transferred to the intermediate transfer member, onto the image receiving material; and
a fixing unit for fixing the toner image on the image receiving material transferred to the image receiving material by the first and second transfer units and held thereon, thereby.
According to a second aspect of the invention, there is provided a color image forming method in a color image forming apparatus includes a charger unit for charging a photosensitive member; an exposing unit for an electrostatic latent image on the charged photosensitive member charged by the charger unit; a developing unit for visualizing the electrostatic latent image formed on the photosensitive member to formed toner image; an intermediate transfer member for holding the toner image formed on the photosensitive member; a first transfer unit for transferring the toner image on the photosensitive member; a second transfer unit for transferring the toner image on the intermediate transfer member; and a fixing unit for fixing the toner image on an image receiving material; comprising steps of:
forming a first image on the photosensitive member;
forming a second image on the photosensitive member;
directly transferring the first image on the image receiving material by using the first transfer unit;
transferring the second image on the intermediate transfer member; and
transferring the transferred second image on an image receiving material by using the second transfer unit.
According to a third aspect of the invention, there is provided a color image forming method in a color image forming apparatus includes a charger unit for charging a photosensitive member; an exposing unit for an electrostatic latent image on the charged photosensitive member charged by the charger unit; a developing unit for visualizing the electrostatic latent image formed on the photosensitive member to formed toner image; an intermediate transfer member for holding the toner image formed on the photosensitive member; a first transfer unit for transferring the toner image on the photosensitive member; a second transfer unit for transferring the toner image on the intermediate transfer member; a first image receiving material supply mechanism for supplying an image receiving material to the first transfer unit along first route; a second image receiving material supply mechanism for supplying an image receiving material to the second transfer unit along second route different from the first route; and a fixing unit for fixing the toner image on an image receiving material; comprising steps of:
forming a first image on the photosensitive member;
forming a second image on the photosensitive member;
directly transferring the first image on the image receiving material supplied from the first image receiving material supply mechanism by using the first transfer unit;
transferring the second image on the intermediate transfer member by the voltage between the photosensitive member and the intermediate transfer member; and
transferring the transferred second image on the image receiving material supplied from the second image receiving material supply mechanism by using the second transfer unit.
According to a fourth aspect of the invention, there is provided a color image forming method comprising steps of:
forming a first image on a photosensitive member;
forming a second image on the photosensitive member;
directly transferring the first image formed on the photosensitive member on to a first image receiving material;
transferring the second image formed on the photosensitive member on to an intermediate transfer member; and
transferring the second image transferred on the intermediate transfer member on to a second image receiving material.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.
REFERENCES:
patent: 5666599 (1997-09-01), Miyasaka et al.
patent: 5815775 (1998-09-01), Miyasaka et al.
patent: 6085051 (2000-07-01), Miyasaka et al.
patent: 62-220977 (1987-09-01), None
patent: 7-43975 (1995-02-01), None
patent: 7-160088 (1995-06-01), None
patent: 7-281577 (1995-10-01), None
Hiroki Masashi
Izumi Takao
Kasai Toshihiro
Foley & Lardner
Grainger Quana M.
Toshiba Tec Kabushiki Kaisha
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