ORGANIC THIN FILM COATING TYPE CHROMIUM-CONTAINING ZINC-BASED DOUBLE-LAYER TYPE RUSTPROOF STEEL PLATE EXCELLENT IN LONG-TIME ADHESIVE PROPERTY OF ORGANIC THIN FILM AND CATIONIC ELECTRODEPOSITION COATING PROPERTY AND PRODUCTION THEREOF

摘要

PURPOSE:To develop a double-layer type rustproof steel plate which is excellent in long-time adhesive property of an organic thin film and cationic electrodeposition coating property by forming a layer plated with zinc alloy contg. Cr and a chromate film having specified composition on the steel plate and performing treatment for imparting permeability of moisture to form the double-layer organic thin film. CONSTITUTION:Plating wherein Zn-Cr alloy or the same furthermore contg. organic substance such as a cationic polymer is formed on a steel plate at 1-100mum thickness by an electroplating method. A chromate film described hereunder is formed on this plated layer and dried. This chromate film contains hexavalent Cr by weight ratio at 0.03-60% for total amount of chromium and also contains water or alcohol capable of being vaporized at a time of baking in a double-layer organic thin film coating stage following this treatment stage at 0.1-40% for the organic coated film. Then a wet film equal to 0.3-3mum film thickness is formed of coating for the solvent type double-layer organic thin film. This wet film is baked by vaporizing the residual moisture and alcohol in the chromate film. The unfixed type dispersion characteristics are imparted by performing treatment for imparting permeability of moisture.