Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – To produce color reproduction
Patent
1993-03-12
1995-01-10
Goodrow, John
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
To produce color reproduction
430126, 355326R, G03G 1501
Patent
active
053806115
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to image transfer techniques and apparatus for use in electrostatic imaging using an intermediate transfer member.
BACKGROUND OF THE INVENTION
The use of an intermediate transfer member in electrostatic imaging is well known in the art.
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.
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 use of intermediate transfer members is well known in the printing art. In offset printing an image formed of a viscous ink is transferred from a drum to a second drum prior to transfer to the final substrate.
Conventional color electrostatic printers print three or four, partly transparent, color, generally half-tone, separations in cyan, magenta, yellow and (optionally) black to form a single full color image. The color density of these single color prints must be carefully controlled to produce the correct color in the final image.
An observer viewing an image printed on paper actually sees a color which is the result of light incident on the image, which passes through the image, is reflected from the paper and passes through the image again before being seen by the viewer. The light which the observer sees is thus filtered twice by the image. If the same conditions are used for printing on transparencies the colors appear to be washed out, i.e., they have a lower saturation than the same print on paper. This reduced saturation is caused by the fact that for transparencies light passes through the printed image only once before being viewed.
SUMMARY OF THE INVENTION
The present invention seeks to provide apparatus and techniques for improved electrostatic printing of transparencies. In a preferred embodiment of the invention transparencies and prints on opaque substrates can be produced utilizing the same developer system operating at the same voltages and utilizing the same developer liquid.
There is thus provided apparatus for electrostatic printing of transparencies including:
an image bearing surface;
an intermediate transfer member operative for transfer of toner images from the image bearing surface to a transparency;
apparatus for causing each toner image to be developed on the image bearing surface and transferred to the intermediate transfer member a plurality of times, before the image is transferred to the transparency, thereby to enhance the color density of the transparency.
In a preferred embodiment of the invention the transparencies are polychromatic transparencies and each color separation is imaged and developed on the image bearing surface and transferred to the intermediate transfer member at least twice before the combined superimposed image for that color separation on the intermediate transfer member is transferred to the transparency.
In a preferred embodiment of the invention, the apparatus for causing is operative, when the image is to be transferred to an opaque substrate, for causing each toner image to be developed on the image bearing surface and transferred to the intermediate transfer member only once, before the image is transferred to the opaque surface thereby to result in a color density substantially the same as that for a transparency.
There is further provided a method for electrostatic printing of transparencies including the steps of:
providing an electrostatic image on an electrostatic image bearing surface;
developing the image on the electrostatic image bearing surface;
transferring the developed image to an intermediate transfer member;
carrying out the foregoing steps at least twice for each image; and
subsequently transferring the developed image built up on the intermediate transfer member to the transparency, thereby to enhance the color density of the transparency.
In a preferred embodiment of the invention the transparencies are polyc
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Goodrow John
Indigo N.V.
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