Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making printing plates
Patent
1997-05-05
1999-11-02
Nuzzolillo, Maria
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making printing plates
430309, 101451, 101452, 101465, 101466, G03F 700
Patent
active
059767642
DESCRIPTION:
BRIEF SUMMARY
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 fountain solution and those which require no fountain solution. These are called driographs or water-less lithographic plates. Most lithographic plates at present in use are of the first type and require a fountain-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. and 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 a cured silicone layer there is no scumming and clearer images can be produced. Very often water-less plates comprise a base material, often aluminium plate, on which a photosensitive layer is coated, on this photosensitive layer 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.
In some more recent patents relating to water-less lithographic plates a photosensitive layer is coated on to the base and an ink-releasing layer is coated on the photo-sensitive layer, for example U.S. Pat. No. 5,252,431. However, such an arrangement also suffers from photosensitive material/ink-releasing layer adhesion problems. Also the developer has to penetrate the irk-releasing layer in order to reveal the final printing image thus requiring the use of solvents.
However, in practice it has proved difficult to get the photosensitive composition to adhere to the silicone 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 the water-less plates which have been and are being sold are more expensive than conventional plates which require a fount solution.
In U.S. Pat. No. 3,910,187 there is described a method of preparing a water-less lithographic plate which comprises acting on an exposed but undeveloped negative working plate with a solvent developer which comprises a fluorine containing compound. In the areas which have been photohardened by exposure no development takes place but in the unexposed areas of the photosensitive composition the unexposed photosensitive composition is removed and the fluoro containing compound is deposited in its place. It is stated in U.S. Pat. No. 3,910,187 that a water-less plate is thus produced. However as a solvent developer is used which is stated in U.S. Pat. No. 3,910,187 to be a vaporisable solvent a health hazard is produced. Moreover some fluorine containing compound is likely t be deposited on the image areas of the plate during such solvent development. This will lead to poor image differentiation as the printing ink will be repulsed and developer will need to be regularly replenished.
It is the object of the present invention to provide a water-less lithographic plate in which a photosensitive layer is not coated on to a silicone layer and which does use a solvent-based developing solution.
According to the present invention there is provided a method of preparing water-less lithographic plate which comprises imagewise exposing a lithographic plate coated with a photosensitive compo
REFERENCES:
patent: 3907562 (1975-09-01), Crystal
patent: 3910187 (1975-10-01), Cords
patent: 4508814 (1985-04-01), Sakurai et al.
Bennett Peter Andrew Reath
Smith Carole-Anne
Kodak Polychrome Graphics LLC
Nuzzolillo Maria
Weiner Laura
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