PURPOSE: To provide a coating compsn. for chromate-treated galvanized steel sheet, consisting of an oil-free alkyd resin which contains tannic acid as an acid component, and an amino resin, and producing a coating film excellent in the secondary adhesiveness after boiling water and corrosion tests.
CONSTITUTION: The compsn. consists of (a) 50W95wt% alkyd resin contg. 1W 20% tannic acid as an acid component and having an acid value ≤50KOHmg/g and a hydroxyl value of 50W250KOHmg/g and (b) 50W5wt% amino resin. When the tannic acid content in (a) is less than 1%, the secondary adhesiveness improving effect is not significant and when it exceeds 20wt%, the resultant cured film becomes brittle and inferior in weathering resistance. When the amount of (b) is less than 5wt%, the film properties are degraded and when it exceeds 50wt%, the characteristics inherent to (a) are lost.
SASAKI HIROJI
HIGUCHI YOSHIHIRO
