| 摘要 |
PROBLEM TO BE SOLVED: To improve the power of desensitizing a non-image area, the part of a flaw in particular, by using a malic acid salt. SOLUTION: As to a malic acid salt, an alkali metal salt, e.g. a sodium salt, a potassium salt, a lithium salt and an ammonium salt, can be cited. One or two kinds or more of these salts can be used jointly. The potassium salt is preferable. The concentration of the malic acid salt in a plate surface protecting agent is suitably 4.0-25wt.%. More preferably, it is 5.0-15wt.%. When it is less than 4.0wt.%, the power of preventing a flaw on a non-image area lessens. When it exceeds 25wt.%, the forming performance of ink on an image deteriorates. A main solvent in regard to the plate surface protecting agent is water. The plate surface protecting agent can be prepared by adding an acid salt of a malic acid, e.g. an acid sodium salt of the malic acid and an acid potassium salt of the malic acid, as the malic acid salt to the water. |
