Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making printing plates
Patent
1997-09-18
2000-07-11
Codd, Bernard
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making printing plates
430156, 430166, 430328, 430329, 430394, 101465, 101467, G03F 722
Patent
active
060870737
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the production of so-called water-less lithographic plates.
Lithographic plates may be divided into two classes. Those which require dampening water which is fed to the non-image areas of the plate, forms a water film and acts as an ink-repellant layer; this is the so-called fount solution and those which require no fount solution are called driographs or water-less lithographic plates. Most lithographic plates at present in use are of the first type and require a fount-solution during printing. However, lithographic plates of this type suffer from a number of disadvantages. Some of these are: difficult and requires great experience. If the correct ink-water balance is not achieved scumming is occasioned when the printed ink image extends into the non-image areas ruining the printed image. particularly difficult and can not be stabilised until a large number of sheets have been printed, thus incurring waste, ink on to the plate which causes problems in colour reproduction and in dot reproduction, increasing its size and complexity. selection. Further plate cleaners contain significant levels of solvent which is not desirable.
However, with water-less plates in which the ink-releasing layer is, for example, a cured silicone layer there is no scumming and clearer images can be produced. Very often water-less plates comprise a base material, for example aluminium plate, on which a photosensitive layer is coated, on this photosensitive layer there is coated a silicone layer. After imagewise exposure and development in which selected areas of the photosensitive composition are altered, the overlying silicone layer is removed and the plate is inked up. The ink adheres only to those areas of the plate not covered by the silicone remaining after development. Thus the plate can be printed without the need to use a fount solution.
However, in practice it has proved difficult to get the silicone layer composition to adhere to the photosensitive layer. In spite of the idea of water-less plates having been described in patent specifications for at least fifteen years very little has been done to commercialise the idea and water-less plates which have been and are being sold are more expensive than the conventional plates which require a fount solution.
It is the object of the present invention to provide a novel method of preparing a water-less lithographic plate.
Therefore, according to the present invention there is provided a method of preparing a water-less lithographic plate by coating a positive working photosensitive composition onto an oleophilic base, imagewise exposing the plate and developing it to remove the areas of the photosensitive composition which have been light exposed, coating overall the surface of the plate with a layer of a composition which is ink releasing, or when cured becomes ink releasing, then either as a separate step or as a combined step, curing the ink releasing composition or drying the ink releasing composition and light exposing overall the plate, then redeveloping the plate to remove the photosensitive composition remaining after the first development and the ink releasing composition which overlaid it.
In order to minimise the possibility of the ink releasing substance remaining on the positive working composition after the redevelopment step an additional step between first developing step and coating overall the plate with the ink-releasing substance may be employed, which comprises treating the plate with an oleophilic coating composition which adheres to the remaining positive working composition but which does not adhere to the exposed base to form a thin optically light transparent coating on the remaining positive working composition. The ink-releasing substance does not adhere to this thin coating.
Suitable oleophilic substances to use are esters based on coconut fatty acid. Such substances are wiped on the plate after the first developing step to provide a very thin layer.
In one method of the present invention the ink-releasing composition is c
REFERENCES:
patent: 3910187 (1975-10-01), Cords
patent: 4564584 (1986-01-01), Fredericks et al.
patent: 4853313 (1989-08-01), Mori et al.
patent: 5635328 (1997-06-01), Higashino et al.
IBM Technical Disclosure Bulletin, vol. 19, No. 10, Mar. 1977, New York, U.S., p. 4014.
Bennett Peter Andrew Reath
Smith Carole-Anne
Codd Bernard
Kodak Polychrome Graphics L.L.C.
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