Method to remove unwanted, unexposed, positive-working, IR radiation sensitive layer
A method for eliminating unwanted ink-receptive sections in positive working printing plates resulting from shading of the surface layer during exposure by the clamps holding the plate on the exposure apparatus following development of an imagewise exposed precursor. Accordingly the areas that are shaded are identified prior to development and the surface layer is scored in those areas to a depth and density sufficient to result in the scored layer being removed during development but not deep enough to damage the underlying hydrophilic layer.
1. A method for eliminating at least one unwanted ink-receptive section in a printing plate following development of an imagewise exposed positive-working printing plate precursor, wherein said positive-working printing plate precursor comprises a developer resistant surface layer that remains effective in resisting development in areas of the positive-working printing plate precursor that are undesirably not exposed during exposure of the positive-working printing plate precursor, the method comprising:
(a) identifying at least one of said undesirably unexposed areas of said positive-working printing plate precursor; and
(b) prior to developing said positive-working printing plate precursor to form said printing plate, scoring said developer resistant layer in said at least one identified undesirably unexposed area to a depth and density sufficient to render said developer resistant layer ineffective to resist development of said at least one identified undesirably unexposed area.
2. The method according to claim 1 wherein said steps of identifying and scoring said at least one undesirably unexposed area of said imagewise exposed positive-working printing plate precursor occur prior to its imagewise exposure.
3. The method according to claim 1 wherein said developer resistant surface layer is thermally sensitive.
4. The method according to claim 1 wherein said step of identifying said undesirably unexposed areas comprises identifying a location on said positive-working printing plate precursor corresponding to a location where a clamp of a preselected exposure device contacts said positive-working printing plate precursor when said positive-working printing plate precursor is mounted on said exposure device.
5. The method according to claim 4 wherein said scoring of said positive-working printing plate precursor surface is controlled by a computer.
6. The method according to claim 5 wherein said computer includes a data base and said data base includes data identifying a plurality of locations where clamps of a plurality preselected exposure devices contact said positive-working printing plate precursor when said positive-working printing plate precursor is mounted on a selected one of said plurality of exposure devices.
7. A positive-working printing plate precursor comprising a surface layer that is developer resistant prior to exposure to imaging radiation wherein said surface layer is scored in selected areas of said positive-working printing plate precursor to a depth and density sufficient to render said surface layer ineffective to resist development.
8. A positive working printing plate precursor comprising a developer resistant surface layer that is rendered soluble in a developer following exposure to radiation wherein said surface layer has been scored in predetermined surface areas to a depth and density sufficient to render said surface layer ineffective in resisting development when immersed in said developer in said predetermined surface areas corresponding to areas on said positive-working printing plate precursor surface that remain unexposed to radiation due to undesirable shading of said areas during exposure to said radiation.
9. The positive-working printing plate precursor according to claim 8 wherein said predetermined surface areas are areas shaded during exposure by elements of an exposure device holding said positive-working printing plate precursor thereon.