Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Patent
1989-06-10
1991-06-04
Goodrow, John
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
430 42, G03G 1309
Patent
active
050213130
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to electrophotography and in particular to a novel process of preparing, by an electrophotographic process, multicolor pre-press proofs from negative color separation films and preferrably is accomplished by making appropriate adaptations to a conventional proofer device formerly capable of producing proofs from only positive color separation films.
BACKGROUND ART
The purpose of pre-press proofs, as is well known in the art, is to assess color balance and strength which can be expected from the final press run and accordingly to correct the separation transparencies before the printing plates are made therefrom. In many instances it is also required to produce so-called customer proofs for approval of subject, composition and general appearance of the print prior to press run. Thus it is essential that the pre-press proof should have the same appearance as the press print, that is to say in addition to matching the colors of the press print, the pre-press proof should be on the same paper as the press print.
On the basis of the pre-press proofs, the color separation transparencies are accepted or corrected if necessary and then used for the preparation of printing plates. There are so-called positive working and negative working printing plates, as is well known in the art. A positive working printing plate is exposed to a positive transparency or film positive wherein the information to be printed corresponds directly to opaque areas, whereas the non-printing background areas correspond to transparent areas contained on such film positive. By exposing such positive working plate to light through a film positive, the exposed areas contained thereon are rendered removable by chemical treatment and the underlying usually grained aluminum plate surface then forms the water receptive nonprinting or non-image areas, whereas the unexposed areas contained thereon form the ink receptive printing or image areas during the subsequent lithographic or offset printing.
A negative working printing plate is exposed to light through a film negative wherein the information to be printed corresponds to transparent areas, whereas the non-printing background areas correspond to opaque areas contained on such film negative. In this case the exposed areas become photo-hardened and form the ink receptive printing areas whereas the unexposed areas are removed by chemical treatment and the underlying water receptive usually grained aluminium plate surface forms the non-printing or non-image areas during subsequent lithographic or offset printing.
It is known to produce by electrophotographic processes lithographic and gravure pre-press proofs containing in general four colors, such as yellow, magenta, cyan and black. Such pre-press proofing processes are disclosed for instance in U.S. Pat. Nos. 3,337,340, 3,419,411 and 3,862,848.
It is customary to produce such electrophotographic pre-press proofs by charging a photoconductive recording member followed by exposure through a separation film positive corresponding to one color, followed by toning of the exposed photoconductor with a liquid toner of the appropriate color, followed by in-register transfer of the color toned image deposit to a receiving member surface, such as paper, usually of the same grade as the printing stock. These process steps are then repeated with separation film positives of the other three or more colors and appropriate color toners to produce a multi-color pre-press proof of print as required.
It should be noted that prior art electrophotographic pre-press proofing processes are so-called direct reproduction processes, that is to say the color separation transparencies employed include film positives wherein the image areas to be reproduced correspond directly to the opaque image areas on such film positives. Consequently in such prior art electrophotographic pre-press proofing processes the latent image formed on the photoconductor upon exposure to such positive separation films is developed by attracting thereto
REFERENCES:
patent: 4350749 (1982-09-01), Ohnuma et al.
patent: 4608327 (1986-08-01), Oka
patent: 4647182 (1987-03-01), Pierce
Cass Myron C.
Goodrow John
Stork Colorproofing B.V.
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