Highly corrosion-resistant surface-treated steel sheet and method for producing same

A surface-treated steel sheet with excellent corrosion resistance comprising:

• a zinc-based plated steel sheet or an aluminum-based plated steel sheet;
• a surface-treatment coating having coating thicknesses ranging from 0.01 to 1 μm, and being formed by applying and drying a surface treatment coating composition which contains ingredients (α) through (δ) described below on a surface of the plated steel sheet;
• and
• a top coating having coating thicknesses ranging from 0.3 to 2 μm, and being formed by applying and drying a coating composition for top coating, containing an (E) high molecular weight epoxy group-containing resin having number average molecular weights ranging from 6000 to 20000 on the surface-treatment coating:
• (α) a water-epoxy resin dispersion which is prepared by dispersing in water a (Z) modified epoxy resin obtained by a reaction of a (W) epoxy group-containing resin, an (X) primary amine compound and/or secondary amine compound, and an active hydrogen-containing compound in which a part or entire of the compound is structured by a (Y) hydrazine derivative having active hydrogen;
• (β) a water dispersed polyurethane resin at amounts of mass ratio of the resin solid matter in the water-epoxy resin dispersion to the resin solid matter in the water dispersed polyurethane resine, [water-epoxy resin dispersion]/[water dispersed polyurethane resine], ranging from 95/5 to 5/95;
• (γ) a silane coupling agent at amounts ranging from 1 to 300 parts by mass of solid matter therein to 100 parts by mass of the resin solid matter in the water-epoxy resin dispersion;
• and
• (δ) phosphoric acid and/or a hexafluorometal acid at amounts ranging from 0.1 to 80 parts by mass of solid matter therein to 100 parts by mass of the resin solid matter in the water-epoxy resin dispersion.

A method for manufacturing surface-treated steel sheet with excellent corrosion resistance comprising the steps of:

• applying a surface treatment coating composition which contains ingredients (a) through (c) described below onto a surface of a zinc-based plated steel sheet or an aluminum-based plated steel sheet, and then drying the applied surface treatment coating composition at ultimate sheet temperatures ranging from 30° C. to 150° C., thus forming a surface-treatment coating having coating thicknesses ranging from 0.01 to 1 μm;
• and
• forming a top coating having coating thicknesses ranging from 0.3 to 2 μm on the surface-treatment coating by applying a coating composition for top coating containing an (E) high molecular weight epoxy group-containing resin having number average molecular weights ranging from 6000 to 20000, and then by drying the applied coating composition for top coating at ultimate sheet temperatures ranging from 30° C. to 150° C.:
• (a) a water-epoxy resin dispersion which is prepared by dispersing in water a resin obtained by a reaction of:
• an (A) polyalkyleneglycol-modified epoxy resin derived from a reaction of polyalkyleneglycol having number average molecular weights ranging from 400 to 20000, a bisphenol type epoxy resin, an active hydrogen-containing compound, and a polyisocyanate compound;
• a (B) epoxy group-containing resin other than the (A) polyalkyleneglycol-modified epoxy resin;
• and an active hydrogen-containing compound in which a part or entire of the compound is structured by a (C) hydrazine derivative having active hydrogen;
• (b) a silane coupling agent at amounts ranging from 1 to 300 parts by mass of solid matter therein to 100 parts by mass of the resin solid matter in the water-epoxy resin dispersion;
• and
• (c) phosphoric acid and/or a hexafluorometal acid at amounts ranging from 0.1 to 80 parts by mass of solid matter thereof to 100 parts by mass of the resin solid matter in the water-epoxy resin dispersion.

A method for manufacturing surface-treated steel sheet with excellent corrosion resistance comprising the steps of:

• applying a surface treatment coating composition which contains ingredients (α) through (δ) described below onto a surface of a zinc-based plated steel sheet or an aluminum-based plated steel sheet, and then drying the applied surface treatment coating composition at ultimate sheet temperatures ranging from 30° C. to 150° C., thus forming a surface-treatment coating having coating thicknesses ranging from 0.01 to 1 μm;
• and
• forming a top coating having coating thicknesses ranging from 0.3 to 2 μm on the surface treatment coating by applying a coating composition for top coating containing an (E) high molecular weight epoxy group-containing resin having number average molecular weights ranging from 6000 to 20000, and then by drying the applied coating composition for top coating at ultimate sheet temperatures ranging from 30° C. to 150° C.:
• (α) a water-epoxy resin dispersion which is prepared by dispersing in water a (Z) modified epoxy resin obtained by a reaction of a (W) epoxy group-containing resin, an (X) primary amine compound and/or secondary amine compound, and an active hydrogen-containing compound in which a part or entire of the compound is structured by a (Y) hydrazine derivative having active hydrogen;
• (β) a water dispersed polyurethane resine at amounts of mass ratio of the resin solid matter in the water-epoxy resin dispersion to the resin solid matter in the water dispersed polyurethane resine, [water-epoxy resin dispersion]/[water dispersed polyurethane resine], ranging from 95/5 to 5/95;
• (γ) a silane coupling agent at amounts ranging from 1 to 300 parts by mass of solid matter therein to 100 parts by mass of the resin solid matter in the water-epoxy resin dispersion;
• and
• (δ) phosphoric acid and/or a hexafluorometal acid at amounts ranging from 0.1 to 80 parts by mass of solid matter therein to 100 parts by mass of the resin solid matter in the water-epoxy resin dispersion.