| 摘要 |
PROBLEM TO BE SOLVED: To obtain a production method of an offset printing plate which gives copies having excellent reproducibility of gradation of an original image. SOLUTION: In this method, an original is first screened by frequency modulation screening method to obtain data. An image forming element is exposed to light for an image according to the screened data. This image forming element has an image accepting layer containing physical developing nuclei and a photosensitive layer containing one or more kinds of silver halide emulsions and having water permeability with the image accepting layer formed in this order on a hydrophilic surface of a base body. Then the image forming element is treated with an alkali soln. in the presence of a developing agent and a solvent for silver halide to remove the layer on the image accepting layer and to expose a silver image formed in the image accepting layer. Thereby, the alkali soln. does not substantially contain thio sulfate ion or bromide ion and contains 1-10ml aminoalcohol per 1l of the alkali soln. By this method, a planographic printing plate is produced from an original having a continuous gradation. |
