▎ 摘　　要

NOVELTY - A galvanized steel sheet is coated with an organic-inorganic composite coating film comprising aqueous cationic polyurethane composite resin, complex organic silane coupling agent, composite lubricating particles, graphene oxide aqueous solution, water-soluble fluorine-containing compound, water-soluble phosphorus-containing compound and water-soluble salt of rare-earth compound. The composite lubricating particles comprise polytetrafluoroethylene particles and surface-modified high-density polyethylene particles. USE - Galvanized steel sheet (claimed). ADVANTAGE - The galvanized steel sheet coated with organic-inorganic composite coating film has excellent abrasion resistance, corrosion resistance, solvent resistance and acid-base resistance. DETAILED DESCRIPTION - A galvanized steel sheet is coated with an organic-inorganic composite coating film comprising 30-50 pts. wt. aqueous cationic polyurethane composite resin, 25-45 pts. wt. complex organic silane coupling agent, 15-25 pts. wt. composite lubricating particles, 0.1-0.5 pt. wt. graphene oxide aqueous solution, 0.5-1.5 pt. wt. water-soluble fluorine-containing compound, 1-2 pts. wt. water-soluble phosphorus-containing compound and 0.1-1.5 pt. wt. water-soluble salt of rare-earth compound. The aqueous cationic polyurethane composite resin is formed by copolymerizing polytetrahydrofuran ether, polyacrylate and/or polyperfluoroalkyl acrylate, and polyurethane prepolymer, and has relative molecular weight of 80000-150000. The complex organic silane coupling agent comprises bis-organic silane coupling agent and mono-organic silane coupling agent in weight ratio of 0.3-2. The composite lubricating particles comprise polytetrafluoroethylene particles and surface-modified high-density polyethylene particles. The content of graphene oxide in graphene oxide aqueous solution is 1-5 %mass. INDEPENDENT CLAIMS are included for the following: (1) aqueous surface treatment agent; and (2) preparation of galvanized steel sheet.