Electrophotography – Image formation – Development
Reexamination Certificate
2000-06-16
2001-10-30
Lee, Susan S.Y. (Department: 2852)
Electrophotography
Image formation
Development
C399S133000
Reexamination Certificate
active
06311035
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to latent image development systems, and, more particularly, relates to an imaging system for contact electrostatic development of a latent image, wherein the latent image is developed on an imaging member, and wherein the developed image is transferred directly from the imaging member to a copy substrate in a single adhesive transfer step.
BACKGROUND OF THE INVENTION
A typical electrostatographic printing process includes a development step whereby developing material, including toner or marking particles, is physically transported into the vicinity of a latent image, with the toner or marking particles being caused to migrate via electrical attraction to the image areas of the latent image so as to selectively adhere in an imaged configuration. Transfer of the developed image to a copy substrate typically occurs either by an electrostatic transfer technique or an adhesive transfer technique.
Adhesive transfer of the developed image to a copy substrate is advantageous for a broad range of substrates; however, it requires an application of high pressure and high temperature at the interface of the developed image and the copy substrate. In conventional electrophotographic systems, adhesive transfer is typically implemented after the developed image is transferred to an intermediate transfer member. Direct transfer from the imaging member, upon which the developed image is first formed, is typically not considered because the imaging member lacks the requisite compliance and the appropriate surface characteristics for successful adhesive transfer of the developed image directly to a copy substrate.
An example of a conventional approach may be found in U.S. Pat. No. 5,436,706, issued to Landa, wherein there is disclosed an intermediate transfer member which is in operative engagement with a photoconductive surface of a drum bearing the developed image. The intermediate transfer member is said to be operative for receiving the toner image from a photoconductive surface and for transferring the toner image to a final substrate. A heater to heat the intermediate transfer member may also be provided. Transfer of the image to the intermediate transfer member is said to be aided by providing an electric field between the intermediate transfer member and the image areas of the photoconductive surface. The intermediate transfer member is said to include a conducting layer underlying an elastomeric layer.
However, it is desirable that the developed image be directly transferable from an imaging member to a wide range of substrates. Direct, singlestep image transfer, that is, the transfer of the developed image from the imaging member upon which the developed image was first formed, incurs less of the image quality loss that is associated with conventional development and transfer techniques, such as those that employ an intermediate transfer member, additional bias, or an electrostatically-enabled transfer step.
SUMMARY OF THE INVENTION
An imaging system may be constructed according to the present invention for effecting contact electrostatic printing of an image onto a copy substrate. The imaging system includes at least one contact electrostatic printing engine, having a latent image carrier member that includes a latent image bearing surface for receiving a latent image; an imaging member having a developed image bearing surface; and a toner cake layer delivery apparatus operative for delivery of a toner cake layer to at least one of the developed image bearing surface and the latent image bearing surface. Subsequent engagement of the developed image bearing surface and the latent image bearing surface causes development of the latent image, wherein the toner cake layer is separated, in correspondence with the image and non-image regions of the latent image, into a developed image borne on the developed image bearing surface. The remainder of the toner cake layer lies on the latent image bearing surface. Subsequent engagement of the developed image bearing surface with a copy substrate allows direct transfer therefrom of the developed image to the copy substrate, wherein transfer of the developed image is provided in a single image transfer step.
For example, the toner cake layer delivery apparatus may be operative for delivery of a toner cake layer to the developed image bearing surface and the development step may occur as the toner cake layer is brought into pressure contact with the latent image bearing surface of the latent image carrier member, such that a developed image is created on the developed image bearing surface of the imaging member by separation of the toner cake layer, wherein selective portions of the toner cake layer are retained on the developed image bearing surface in correspondence with the image, and wherein non-image regions transfer to the latent image carrier member.
Alternatively, the latent image carrier member may be uniformly coated with the toner cake layer and charged in an image-wise fashion to create a latent image, whereupon the latent image development step may be carried out as the developed image bearing surface is brought into contact with the latent image bearing surface. The developed image is created on the developed image bearing surface by separation of the toner cake layer, wherein selective portions of the toner cake layer are transferred to the developed image bearing surface in correspondence with the image, and non-image regions remain on the latent image carrier member.
In accordance with a principal aspect of the present invention, the imaging member preferably includes a developed image bearing surface constructed to exhibit at least one of the following surface characteristics: substantial conformability, low surface energy, and electrical conductivity.
“Substantial conformability”, in reference to a surface characteristic of the developed image bearing surface, describes a surface characteristic of the imaging member wherein a portion of the developed image bearing surface conforms to a portion of the surface of a copy substrate during engagement of the developed image bearing surface with a copy substrate. Such engagement is contemplated as being effected in a transfer nip, wherein a portion of the copy substrate is constrained under pressure between a corresponding portion of the developed image bearing surface and a corresponding, opposing portion of the surface of a pressure resisting member, such as a pressure roller, such that the portion of the developed image thus constrained is subjected to substantially complete contact with the copy substrate, that is, contact without substantial voids or interfacial gaps. Such engagement may be accompanied by an application of thermal or acoustic energy so as to assist in the adhesive transfer step.
As a result, there is substantially complete adhesive transfer of the developed image in a single adhesive transfer step, and is useful for transfer to a copy substrate having surface characteristic(s) that are less than satisfactory for developed image transfer, such as a surface that has surface irregularities, or is rough, textured, porous, etc.
“Direct” and “single”, in reference to the adhesive transfer step, describes a process for adhesive transfer of the developed image that obviates the use of an intermediate transfer member for transfer of the developed image from the imaging member to the copy substrate.
The developed image bearing surface is preferably constructed to effect a substantial area of rolling contact with the copy substrate at the interface of the developed image bearing surface and the copy substrate, thus eliminating problems of variable tolerance in the gap between the copy substrate and the developed image bearing surface. Such a developed image bearing surface offers improved contact with the surface irregularities typically found in a wide range of copy substrate materials.
Accordingly, in certain applications of the present invention, the thickness of the toner cake layer present on the developed image b
Liu Chu-heng
Proulx Rodney B.
Dudley Mark Z.
Lee Susan S.Y.
Xerox Corporation
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