Surface treatment composition for coated steel sheet, surface treated plated steel sheet and method of production of same, and coated plated steel sheet and method of production of same

摘要

Provided is a water-based substrate treating composition for a coated metal plate, said composition forming a substrate treating layer for imparting superior eave corrosion resistance while guaranteeing sufficient processing adhesion without chromium. A substrate treating composition containing a particular organosilicon compound, a hexafluoro metal acid, a urethane resin having a particular cationic group, a vanadium compound, and an aqueous medium, wherein a substrate layer that imparts superior eave corrosion resistance while guaranteeing sufficient processing adhesion is obtained due to the cationic group and total amine number of the urethane resin having particular values.