Hot-dip galvanized steel sheet and method for producing the same

A method for producing a hot-dip galvanized steel sheet, the method comprising:

• applying a surface treatment agent with a pH of 4 to 5 to a hot-dip galvanized steel sheet having a Ra of 0.5 to 2.0 μm and a PPI of 150 or more;
• and
• drying the surface treatment agent at an ultimate sheet temperature of 50° C. to 180° C. to form a surface treatment coating film having a coating weight of 0.2 to 1.0 g/m2 on the surface of the steel sheet, the surface treatment agent containing:
• (A) a resin compound having a bisphenol skeleton represented by general formula (I) described below (hereinafter referred to as “resin compound (A)”);
• (B) a cationic urethane resin emulsion having at least one cationic functional group selected from primary to tertiary amino groups and quaternary ammonium bases (hereinafter referred to as “cationic urethane (B)”);
• (C) at least one silane coupling agent having at least one reactive functional group selected from an active hydrogen-containing amino group, an epoxy group, a mercapto group, and a methacryloxy group;
• (D) an organic titanium chelate compound;
• (E) a tetravalent vanadyl compound;
• and
• (F) water,
• wherein the solid content of the cationic urethane (B) is 0.10 to 0.30 in terms of ratio by mass [(b)/{(a)+(b)+(c)}] relative to the total solid content of the resin compound (A), the cationic urethane (B), and the silane coupling agent (C);
• the solid content of the silane coupling agent (C) is 0.60 to 0.85 in terms of ratio by mass [(c)/{(a)+(b)+(c)}] relative to the total solid content of the resin compound (A), the cationic urethane (B), and the silane coupling agent (C);
• the solid content of the silane coupling agent (C) is 50 to 70 in terms of ratio by mass [(c)/Ti] relative to the content of the organic titanium chelate compound (D) in terms of titanium;
• and
• the content of the tetravalent vanadyl compound (E) in terms of vanadium is 0.30 to 0.50 in terms of ratio by mass (V/Ti) relative to the content of the organic titanium chelate compound (D) in terms of titanium;
• Ra represents arithmetic mean roughness according to JIS B 0601-1994, and PPI represents the number of peaks per 25.4 mm (1 inch) according to SAEJ911 determined from a roughness curve according to JIS B 0601-1994;
• and
• in each of the equations, (a) represents the solid content of the resin compound (A);
• (b), the solid content of the cationic urethane (B);
• (c), the solid content of the silane coupling agent (c);
• Ti, the content of the organic titanium chelate compound (D) in terms of titanium;
• and V, the content of the tetravalent vanadyl compound (E) in terms of vanadium;
• wherein in the formula (I), Y1 and Y2 bonded to benzene rings are each independently a hydrogen atom or a Z group represented by general formula (II) or (III) below, the average number of Z groups substituted per benzene ring is 0.2 to 1.0, and n represents an integer of 2 to 50;
• wherein in the formulae (II) and (III), R1, R2, R3, R4, and R5 each independently represent a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, or a hydroxyalkyl group having 1 to 10 carbon atoms, and A− represents a hydroxide ion or an acid ion.