Electrophotography – Image formation – Transfer
Reexamination Certificate
1999-08-04
2001-04-03
Lee, Susan S. Y. (Department: 2852)
Electrophotography
Image formation
Transfer
C399S127000
Reexamination Certificate
active
06212353
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to cleaning of image transfer surfaces, particularly the surfaces of image transfer members used in liquid toner imaging.
BACKGROUND OF THE INVENTION
The use of image transfer members in electrostatic imaging is well known. Typically, an intermediate transfer surface is used to transfer a toner image from an imaging surface to a final substrate. This transfer is typically aided by heat and pressure.
Various types of intermediate transfer members are known and are described, for example in U.S. Pat. Nos. 3,862,848, 4,684,238, 4,690,539 and 4,531,825, the disclosures of all of which are incorporated herein by reference.
Belt-type intermediate transfer members for use in electrophotography are known in the art and are described, inter alia, in U.S. Pat. Nos. 3,893,761, 4,684,238 and 4,690,539, the disclosures of all of which are incorporated herein by reference.
The use of intermediate transfer members and members including transfer blankets for offset ink printing is also well known. Such blankets have characteristics which are suitable for ink transfer but are generally not usable, per se, for liquid toner imaging.
Desirably, the transfer of the toner image from the intermediate transfer surface onto the final substrate is complete. However, it is appreciated that some residual toner may remain on the surface after each transfer. The residual toner typically comprises deformed toner particles, some of which may be at least partially fused to other particles, which may adhere to the transfer surface and may accumulate to substantial amounts after many imaging cycles. This accumulation of the residual toner particles results in non-homogeneous and/or unclean transfer of the toner images onto the final substrate.
Cleaning of intermediate transfer members is known in the art. To enable continuous cleaning while avoiding erasure of the image being transferred, the cleaning station in other prior art devices is located downstream of the site at which the image is transferred onto the final substrate, prior to the transfer of a subsequent image to the intermediate transfer member.
In other known systems, the intermediate transfer member is periodically cleaned by printing a series of toner patterns, hereinafter referred to as “non-images”, onto the final substrate. Printing of the non-images is based on applying a substantially continuous layer of fresh toner onto the intermediate transfer member and transferring the layer of liquid toner onto a final substrate, whereby the deformed residual toner particles adhere to the fresh toner and are thus removed from the intermediate transfer member. A substantially continuous or continuous layer of toner on the intermediate transfer member is typically obtained by developing a substantially continuous non-image on the imaging surface and transferring the developed non-image onto the intermediate transfer member.
To economize on the use of liquid toner, the substantially continuous non-image can be formed of a plurality of screen images each of which covers only a predetermined portion of the surface area of the intermediate transfer member. A sequence of such screen images, each preferably using a different color toner, provides complete coverage of the intermediate transfer member and collects substantially all the residual toner of all the color toners. It is appreciated that different color toners have different physical properties and, therefore, some color toners are more effective, e.g. more adhesive, than others in removing residual toner particles.
Cleaning of the intermediate transfer member by printing on the final substrate, as described above, generally requires at least eight imaging cycles for each cleaning session. The final substrate bearing the printed non-images which are formed during the cleaning session cannot be re-used and is, thus, discarded after the cleaning session, increasing maintenance costs. When the imaging system is designed for printing on a continuous final substrate as described, for example, in PCT publications WO 96/01442 and 96/31809, each cleaning session introduces a series of undesired non-images between consecutive images, interrupting the sequence of images formed on the final substrate.
SUMMARY OF THE INVENTION
It is an object of some aspects of the present invention to provide a method and apparatus for cleaning an image transfer surface in imaging apparatus, especially in imaging apparatus using electrostatically charged liquid toner.
According to one aspect of the present invention, a cleaning roller having a sticky surface is selectively brought to contact with the image transfer surface. A toner pattern, hereinafter also referred to as a toner non-image, is developed on an imaging surface of the imaging apparatus, and is transferred onto the image transfer surface. Residual toner on the image transfer surface, from previous imaging cycles, adheres to the fresh toner of the non-image. When the cleaning roller engages the image transfer surface, toner of the non-image is transferred onto the sticky surface of the cleaning roller. Preferably, in this aspect of the present invention, the cleaning roller selectively engages the image transfer surface only during predefined cleaning sessions. Therefore, the cleaning roller can be positioned anywhere along the image transfer surface, e.g. upstream of the location at which images are transferred onto a final substrate during normal printing. Furthermore, according to this aspect of the present invention, the image transfer surface does not engage the final substrate during the cleaning sessions.
According to another aspect of the present invention, a cleaning roller having a sticky surface continuously engages the image transfer surface, collecting residual toner particles therefrom. Periodically, a predefined toner non-image is formed on the surface of the intermediate transfer member and is not transferred onto the final substrate. The non-image, which includes fresh liquid toner, is collected by the cleaning roller and a layer of fresh toner is coated onto the surface of the roller. Thus, according to this aspect of the present invention, printing of non-images is utilized to renew the stickiness of the sticky surface. Since the cleaning roller continuously engages the image transfer surface, the cleaning roller is positioned downstream of the location at which images are transferred onto the final substrate.
Under some circumstances, it may be desirable to increase the stickiness of the toner on the roller by heating the roller or by plasticizing the toner on the roller by wetting it with carrier liquid or with a heavy mineral oil having a very low volatility, a high viscosity and a high flash point, such as Marcol 82. However, under normal circumstances, utilizing a heated intermediate transfer member which heats the roller by conduction, such additional measures are generally unnecessary and may even result in less optimal operation of the system.
It is appreciated that residual toner from incompletely transferred images which is transferred onto the cleaning roller accumulates gradually, over many cleaning sessions, into a thick layer of dried toner which enlarges the effective diameter of the cleaning roller. Therefore, in preferred embodiments of the present invention, the accumulated layer of toner is removed periodically from the cleaning roller.
In some preferred embodiments of the present invention, the non-images printed during the cleaning/surface renewal sessions include “sky shot” images, i.e. images which provide a substantially full coverage of the usable area of the intermediate transfer surface. In other preferred embodiments of the present invention, the non-images include predefined patterns which do not fully cover the usable area on the image transfer surface but which are sufficiently dense to interact substantially with all the residual toner particles. Additionally or alternatively, the non-images include a series of complementary patterns which aggregate to provide a su
Douvdevani Shmuel
Feygelman Alex
Yitzhaik Shlomo
Fenster & Company Patent Attorneys Ltd.
Indigo N.V.
Lee Susan S. Y.
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