Surface treatment agent for zinc or zinc alloy coated steel sheet, zinc or zinc alloy coated steel sheet, and method of producing the steel sheet

摘要

The present invention provides a chromium-free surface treatment agent, comprising: a resin compound having a specific bisphenol skeleton; cationic urethane resin emulsion; silane coupling agent; an organic titanium chelate compound; a quadrivalent vanadyl compound; a molybdic acid compound; and water, wherein these components are blended at predetermined ratios such that pH value of the surface treatment agent is in the range of 4 to 5. The one-pack type chromium-free surface treatment agent of the present invention exhibits good stability during storage and is capable of forming on a metal material surface a coating film excellent in corrosion resistance at a bending-processed portion of a steel sheet, solvent resistance and paintability after alkali degreasing.

主权项

1. A surface treatment agent for a zinc or zinc alloy coated steel sheet, comprising:
(A) resin compound having a bisphenol skeleton represented by general formula (I) below; (B) cationic urethane resin emulsion having at least one type of cationic functional group selected from primary amine, secondary amine, tertiary amine or quaternary ammonium salt; (C) at least one type of silane coupling agent having at least one type of reactive functional group selected from active hydrogen-containing amino group, epoxy group, mercapto group armor methacryloxy group; (D) organic titanium chelate compound; (E) quadrivalent vanadyl compound; (F) molybdic acid compound; and (G) water,such that conditions (1) to (5) below are satisfied, pH of the surface treatment agent being in the range of 4 to 5,
wherein: (1) [(Bs)/{(As)+(Bs)+(Cs)}] as a mass ratio of solid content (Bs) of the cationic urethane resin emulsion (B) with respect to total solid content {(As)+(Bs)+(Cs)} of the resin compound (A), the cationic urethane resin emulsion (B) and the silane coupling agent (C) is in the range of 0.1 to 0.3; (2) [(Cs)/{(As)+(Bs)+(Cs)}] as a mass ratio of solid content (Cs) of the silane coupling agent (C) with respect to total solid content {(As)+(Bs)+(Cs)} of the resin compound (A), the cationic urethane resin emulsion (B) and the silane coupling agent (C) is in the range of 0.6 to 0.85; (3) {(Cs)/(DTi)} as a mass ratio of solid content (Cs) of the silane coupling agent (C) with respect to mass content (DTi) in terms of titanium of the organic titanium chelate compound (D) is in the range of 50 to 70; (4) {(EV)/(DTi)} as a mass ratio of mass content (EV) in terms of vanadium of the quadrivalent vanadyl compound (E) with respect to mass content (DTi) in terms of titanium of the organic titanium chelate compound (D) is in the range of 0.3 to 0.5; (5) [(FMo)/{(As)+(Bs)+(Cs)}] as a mass ratio of mass content (FMo) in terms of molybdenum of the molybdic acid compound (F) with respect to total solid content {(As)+(Bs)+(Cs)} of the resin compound (A), the cationic urethane resin emulsion (B) and the silane coupling agent (C) is in the range of 0.003 to 0.03;in formula (I), Y1 and Y2 bonded to benzene rings, respectively, are each independently hydrogen or group z represented by general formula (II) or (III) below, the average substitution number of the group z per benzene ring is in the range of 0.2 to 1.0, and n represents integer in the range of 2 to 50:in formula (II) and formula (III), R1, R2, R3, R4 and R5 each independently represent hydrogen atom, C1-10 alkyl group or C1-10 hydroxyalkyl group, and A− represents hydroxyl ion or acid ion.