TOPCOATING MATERIAL FOR IMPARTING SCRATCH RESISTANCE, GALLING RESISTANCE, AND SNOW-SLIPPING PROPERTIES TO METAL SHEET, SURFACE TREATMENT METHOD FOR METAL SHEET, AND COATED METAL SHEET EXCELLENT IN SCRATCH RESISTANCE, GALLING RESISTANCE, AND SNOW-SLIPPING PROPERTIES

摘要

PROBLEM TO BE SOLVED: To provide a topcoating material which forms a coating film improved in scratch resistance, galling resistance, and snow-slipping properties by compounding a vinylidene fluoride resin as the matrix resin with a ceramic-base inorganic aggregate, polyacrylonitrile beads, and a fluororesin powder. SOLUTION: This topcoating material comprises 100 pts.wt. vinylidene fluoride resin, 1-40 pts.wt. ceramic-base inorganic aggregate having an average particle size (r1) of 0.6-40μm, 1-40 pts.wt. polyacrylonitrile beads having an average particle size (r2) of 0.6-40μm, and 0.1-20 pts.wt. fluororesin powder having an average particle size (r3) of 0.6-40μm. The topcoating material is applied to the surface of a metal sheet which has been subjected to cleaning by alkali degreasing, warm water washing, water washing, etc., and then to undercoating. The topcoating material is applied so that the resultant coating film after drying has a thickness (T1) satisfying the relations: 0.04<=r1/T1<1.0, 0.04<=r2/T1<=1.0, and 0.04<=r3/T1<=1.0. After applied, the topcoating material is baked by heating at a temperature high enough and for a time long enough for the matrix resin to form a film and then dried.