Method for preparing cationic electrodeposition coating composition

A method for preparing a cationic electrodeposition coating composition, wherein the method comprises the steps of:

• preparing a resin emulsion (i) by respectively dissolving an aminated resin (A) and a blocked isocyanate curing agent (B) in organic solvents to prepare respective solutions, mixing the respective solutions to achieve a mixed solution, and then neutralizing the mixed solution with a neutralizing acid to obtain the resin emulsion (i) comprising the aminated resin (A) and the blocked isocyanate agent (B),
• preparing a pigment dispersion paste comprising a bismuth mixture (C) obtained by mixing a bismuth compound (c1) and an organic acid (c2) in advance;
• a pigment dispersion resin (D);
• an amine-modified epoxy resin emulsion (ii) comprising an amine-modified epoxy resin (E);
• and a pigment (F), according to any one of the following methods of:
• mixing the bismuth mixture (C) and the pigment dispersion resin (D), then the obtained mixture being mixed with the amine-modified epoxy resin emulsion (ii), and next, the pigment (F) being mixed in the obtained mixture;
• mixing the bismuth mixture (C), the pigment dispersion resin (D) and the amine-modified epoxy resin emulsion (ii), and then the pigment (F) being mixed in the obtained mixture;
• or
• mixing the bismuth mixture (C) and the amine-modified epoxy resin emulsion (ii), and then, the obtained mixture, the pigment dispersion resin (D) and the pigment (F) being mixed, and
• mixing the resin emulsion (i) and the pigment dispersion paste to obtain the cationic electrodeposition coating composition, wherein
• the pigment dispersion resin (D) has a hydroxyl value of 20 to 120 mg KOH/g, and
• the amine-modified epoxy resin (E) has a primary amino group, a hydroxyl value of 150 to 650 mg KOH/g, and an amine value of 20 to 80 mg KOH/g.