SURFACE TREATMENT OF GALVANIZED STEEL PRODUCTS

摘要

PURPOSE:To impart excellent corrosion resistance, paint adhesiveness and fingerprint resistance by forming a chromate film contg. a mixture composed if both aq. and dry colloidal silicas on the surface of galvanized steel products. CONSTITUTION:The chromate film into which the mixture composed of the dry colloidal silica and the aq. colloidal silica having 40-1000mmu grain size is incorporated at the ratio to make 0.2-5 weight ratio of SiO2/CrO3 is formed on the galvanized surface. The above-mentioned silica mixture is preferably so formulated that the aq. colloidal silica occupies about >=20% and <100% of the total silica weight. The above-mentioned film is preferably so formed that Cr is deposited at about 20-150mg/m2. Furthermore, the above-mentioned film is preferably formed by using a chromate treating liquid in which Cr<3+> occupies about 20-60% of the total Cr content and/or a chromate treating liquid contg. a small ratio of phosphoric acid or fluosilicic acid.