| 摘要 |
PROBLEM TO BE SOLVED: To provide a positive original plate for a planographic printing plate for direct plate making adaptable to an IR laser recording system, excellent in development latitude in image formation and suppressing defects due to a flaw in an image area and to provide a plate making method for a planographic printing plate. SOLUTION: The original plate has an underlayer containing a water-insoluble and alkali-soluble resin and an upper heat sensitive layer containing a water- insoluble and alkali-soluble resin and an IR absorbing dye and having solubility in an alkaline aqueous solution increased by heating in order on a hydrophilic support, both the underlayer and upper heat sensitive layer separately contain different IR absorbing dyes and the original plate is imagewise exposed and then developed with an alkali developing solution. |
