BLOCK COPY SHEET FOR LITHOGRAPHIC PRINTING PLATE

摘要

PROBLEM TO BE SOLVED: To prevent the deviation of position without applying the adverse effect on the surface side of a lithographic printing plate and use the lithographic printing plate with a substrate formed of a material other than a metal applicable to the multi-color printing or the printing of a number of papers by setting the number of projections of height in the specified range at the ratio in the specified range in the formation of recesses and projections of a block copy sheet for recessing the back of the lithographic printing plate. SOLUTION: A block copy sheet 31 for adjusting the printing pressure is interposed between the back of a lithographic printing plate and the outer peripheral face of a plate cylinder. Recesses and projections 32 of the required shape are formed on the surface of a substrate 31a of the block copy sheet 31. The ratio R of the number of projections in the range of 7-50μm height to the total number of projections constituting the recesses and projections 32 is set as 20-80%. The sufficient position deviation control effect can be provided without applying the adverse effect on the surface side of the lithographic printing plate by the arrangement. The recesses and projections 32 are formed by a method of fixing fine particles 34 such as glass particles harder than the substrate of the lithographic printing plate on the surface of the substrate 31a or the like.