| 摘要 |
PURPOSE:To desensitize the non-image region of a planographic printing plate and, at the same time, to prevent the generation of printing omission even when the image region of said printing plate is preserved for a long period of time, by treating the surface of the planographic printing plate with the protective agent for the planographic printing plate containing a water-soluble resin having a film forming property and a specific nonionic surfactant. CONSTITUTION:A water-soluble resin having a film forming property such as gum arabic or a cellulose derivative and a nonionic surfactant represented by formula [wherein n is an integer of 1 or more, m is 0 or an integer of 1 or more and at least two of A+F are a hydrogen atom and at least two of A-F are COOR (wherein R is an alkyl group)] are contained in a plate surface protective agent and the protective agent having this constitution is provided. A PS plate is imagewise exposed and subsequently developed to form a planographic printing plate. This planographic printing plate is washed with water and, after the water on the surface of the plate is squeezed, a proper amount of the plate surface protective agent is poured on the surface of the plate and rubbed by sponge so as to be applied to the entire surface of the plate. By this method, the non-image region on the surface of the plate is protected and the planographic printing plate can be preserved. Further, the hydrophilicity of the non-image part and the oleophilicity of an image part can be held and the ink depositing property of a highlight spot in the low exposure of a negative plate is improved and the generation of inferior printed paper can be reduced. |
