Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making printing plates
Patent
1998-02-11
2000-10-10
Baxter, Janet
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making printing plates
G03F 7004
Patent
active
061300268
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to the production of so-called water-less lithographic plates.
BACKGROUND OF THE INVENTION
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 color reproduction and in dot reproduction, increasing its size and complexity. These dampening solutions contain volatile organic compounds. 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 aluminum 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. In practice it is difficult and costly to formulate and manufacture the silicone layer composition with sufficient adhesion to the photosensitive composition in these multilayer assemblies. Thus the only commercially available water-less lithographic plates are expensive and of complex design.
There exists in patent literature water-less lithographic plate designs which do not exhibit these disadvantages. These inventions disclose photosensitive water-less lithographic plate precursors comprising a support with an oleophilic surface and a single layer, photosensitive, ink-releasing composition such that imagewise exposure causes changes in developer solubility of the composition where development produces an ink accepting image pattern on the uncovered support surface and an ink-releasing non-image area corresponding to unremoved composition.
U.S. Pat. No. 3,953,212 discloses a plate comprising a support and a coating layer of a mixture of a photosensitive material and a silicone rubber. The photosensitive materials utilised in the invention are typical of standard pre-sensitised wet, lithographic printing plates. These include photosolubilising napthoquinonediazide systems and photoinsolubilising systems including diazo compounds and photopolymer systems such as poly vinyl cinnamates and copolymers of acrylates and methacrylates.
SUMMARY OF THE INVENTION
U.S. Pat. No. 4,724,195, U.S. Pat. No. 5,006,443 and U.S. Pat. No. 5,104,961 disclose a single layer waterless plate precursor which comprises a mixture of radiation sensitive material and a class of fluorinated polymers. These fluorinated polymers represent novel release materials over U.S. Pat. No. 3,953,212. A wide range of composition types which are sensitive to UV or Visible light are disclosed as useful in the invention.
EP 0,410,760 discloses single layer photosensitive compositions comprising polysiloxanes and conventional o-quinonediazides. The invention does not relate directly to the production of waterless lithographic plates though certain of the polysiloxane polymers claimed will pr
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Bennett Peter Andrew Reath
Smith Carole-Anne
Baxter Janet
Gilmore Barbara
Kodak Polychrome Graphics LLC
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