Surface treatment liquid for galvanized steel sheet, method for producing galvanized steel sheet having surface treatment film, and galvanized steel sheet having surface treatment film

摘要

The present invention provides a surface treatment liquid for the purpose of producing a galvanized steel sheet having a surface treatment film, in which the surface treatment film does not contain a chromium compound and the galvanized steel sheet having a surface treatment film exhibits excellent thermal discoloration resistance, thermal crack resistance, planar part corrosion resistance, corrosion resistance following alkali degreasing, blackening resistance, stacked blackening resistance, water staining resistance, solvent resistance, sweat resistance, coating adhesion and storage stability. This surface treatment liquid for a galvanized steel sheet is characterized by: the addition of a glycidyl group-containing silane coupling agent (A), a tetraalkoxysilane (B), a zirconium carbonate compound (C), an anionic polyurethane resin (D) having a glass transition point (Tg) of 80-130ºC, a vanadium compound (E), a molybdenum oxide (F) and water; and by having a pH of 8.0-10.0, with the added quantities of components satisfying prescribed relationships.