Weldable automotive high corrosion resistance surface treated steel sheet and a manufacturing method thereof

PROBLEM TO BE SOLVED: To provide a surface-treated steel sheet capable of obtaining excellent corrosion resistance without containing chromium in a film. SOLUTION: A polyalkylene glycol-modified epoxy obtained by reacting (a) a polyalkylene glycol having a specific molecular weight, a bisphenol type epoxy resin, an active hydrogen-containing compound and a polyisocyanate compound on the surface of a zinc-based plated steel sheet or the like. Aqueous epoxy resin dispersion of resin obtained by reacting resin, epoxy group-containing resin and hydrazine derivative having active hydrogen, (b) silane coupling agent, (c) phosphoric acid and / or hexafluorometal A surface treatment film is formed with a surface treatment composition containing an acid, and a high molecular weight epoxy group-containing resin having a number average molecular weight of 6000 to 20000, a non-chromium antirust additive, and a solid lubricant having a molecular weight of 5000 or less. An upper film containing an agent and a conductive pigment was formed. [Selection figure] None