Electrophotography – Image formation – Transfer
Reexamination Certificate
1999-12-17
2001-07-10
Braun, Fred L. (Department: 2852)
Electrophotography
Image formation
Transfer
C399S302000, C399S308000
Reexamination Certificate
active
06259880
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to printing machines, and more particularly this invention relates to a printing machines having heat transfer of an image support surface.
BACKGROUND TO THE INVENTION
Electrostatographic printers are known in which a single color toner image is electrostatically formed on photoreceptive image bearing member. The toner image is transferred to a receiving substrate, typically paper or other print receiving materials. The toner image is subsequently fused to the substrate.
In one arrangement of an electrostatographic printer, a plurality of dry toner imaging systems each having an image bearing member, are used to develop multiple color toner images. Each color toner image is electrostatically transferred from the image bearing members and onto an intermediate transfer member to form a multilayer composite toner image. The composite toner image is electrostatically transferred to a transfuse member and finally transferred and fused to the final substrate. Such systems that use electrostatic transfer to transfer the composite toner image from the intermediate transfer member to the transfuse member, can have transfer limitations. In operation, the transfuse member is cooled below the glass transition temperature of the toner prior to the transfer nip with the intermediate transfer member. Cooling of the transfuse member requires the transfuse member to be relatively thin. A thin transfuse member however has low conformance therefore providing reduced transfer efficiency in the transfuse nip. The reduced conformance also increases the potential for glossing of the toner image in the transfuse nip. In addition, a thin transfuse member can have a reduced operational life.
SUMMARY OF THE INVENTION
Briefly stated, a printing apparatus operated in accordance with the invention has a toner image bearing member and a transfuse member. The toner image from the toner image bearing member is transferred to the transfuse member. The transfer from the toner image bearing member to the transfuse member is rheologically assisted. The transfer can further be electrostatically assisted.
The transfuse member and toner image bearing member are maintained at a temperature differential whereby transfer of the toner image is rheologically enhanced. The toner image bearing member is maintained at a lower temperature relative to the transfuse member. The transfuse member is maintained in a preferred temperature region and the toner image bearing member is maintained at a preselected temperature differential from the temperature of the transfuse member.
A temperature gradient is developed across the thickness of the toner image at the transfer nip of the toner image bearing member and the transfuse member. The upper layer of the toner image in contact with the relatively hotter transfuse member is softened by the heat of the transfuse member and therefore increases contact and adhesion with the transfuse member. The lower layer of the toner image remains relatively rigid due to the contact with the relatively cooler toner image member. Therefore transfer of the toner image to the transfuse member is enhanced by the temperature differential between the toner image bearing member and the transfuse member. Additional electrostatic transfer assist can be provided if desired to further enhance transfer efficiency.
The rheological assisted transfer in accordance with the invention provides improved transfer efficiency of toner images between transfuse members and toner image bearing members. The use of rheological assisted transfer at the transfer nip of the toner image member and the transfuse member can also reduce the amount or need to preheat the substrate prior to the transfuse nip.
A preferred electrostatographic printing machine in accordance with the invention has multiple toner image producing stations, each forming a developed toner image of a component color. The developed toner images are electrostatically transferred at the first transfer nip to an intermediate transfer member to form a composite toner image thereon. The composite toner image is then transferred electrostatically and with rheological assist at the second transfer nip to a transfuse member. The transfuse member preferably has improved conformability and other properties for improved transfusion of the composite toner image to a substrate. The composite toner image and the substrate are brought together in the third transfer nip to generally simultaneously transfer the composite toner image and fuse the composite toner image to the substrate to form a final document.
REFERENCES:
patent: 6088565 (2000-07-01), Jia et al.
patent: 63-34572 (1988-02-01), None
Berkes John S.
Fletcher Gerald M.
Jia Nancy Y.
Braun Fred L.
Cunningham Reid K.
Xerox Corporation
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