AQUEOUS FLUID FOR SURFACE TREATMENT OF ZINC-PLATED STEEL SHEETS AND ZINC-PLATED STEEL SHEETS

摘要

An aqueous fluid for treatment of zinc-plated steel sheets which comprises (A) ammonium zirconium carbonate, (B) a vanadium (IV) compound, (C) an organophosphonic acid represented by the general formula (I) or an ammonium salt thereof, (D) an anionic water-dispersible acrylic resin having a glass transition temperature (Tg) of 0 to 60°C as obtained by converting the absolute temperature (K) calculated by the numerical formula (1) to Celsius temperature (°C), and water and which has a content of (D) of 1 to 60% by mass based on the whole solid matter, a content of (B) of 0.5 to 8% by mass in terms of V based on the whole solid matter, a V/(C) mass ratio of 0.05 to 1.0, a Zr/(V+(C)) of 0.1 to 6.0% by mass (as calculated by converting (A) to Zr), and a pH of 7 to 10; and zinc-plated steel sheets bearing films resulting from the fluid on the surface. The steel sheets of the invention are excellent in corrosion resistance, alkali resistance, appearance, condensed dew resistance, coatability and groundability. The fluid can be used in treatment equipment similar to that of temporary rust preventive chromate treatment in the manufacturing line for zinc-plated steel sheets.