PRODUCTION OF WATERLESS PLANOGRAPHIC PRINTING PLATE

摘要

PURPOSE:To permit utilization of a waterless planographic printing plate for negative working as the printing plate for positive working as well by using a light source which has no transparent plate for shielding UV rays on the plate surface and projecting active rays contg. UV rays of a specific wavelength to the printing plate. CONSTITUTION:A planographic printing master disk is subjected to image exposing by using the light source having no transparent plate for shielding UV rays and projecting the active rays contg. the UV rays of <=350nm wavelength through, for example, a positive film which is brought into tight contact by a vacuum with the plate to said plate in the case of using the waterless planographic printing plate as the printing plate for positive working. The silicone rubber layer in the part subjected to the photoirradiation by this image exposing treatment remains at the time of development and the silicone rubber layer in the nonirradiated part exfoliates and dislodges. The easy use of the printing master plate for negative working as the printing plate for positive working is thereby enabled.