Method for preparing cationic electrodeposition coating composition

A method for preparing a cationic electrodeposition coating composition, comprising the following steps:

• a step of preparing a resin emulsion (i) comprising an aminated resin (A) and a blocked isocyanate curing agent (B);
• a step of preparing a pigment dispersion paste (ii) comprising a bismuth-metal oxide mixture liquid (C) comprising a bismuth compound (c1), a metal oxide (c2), a monohydroxycarboxylic acid (c3) having 3 to 5 carbon atoms in total and a solvent;
• a pigment dispersion resin (D);
• a polyvalent acid (E);
• and a pigment (F);
• and
• a step of mixing the resin emulsion (i) and the pigment dispersion paste (ii) to prepare a cationic electrodeposition coating composition, wherein
• the pigment dispersion paste (ii) is prepared by the following steps:
• a bismuth-metal oxide mixture liquid (C) preparation step of mixing the bismuth compound (c1), the metal oxide (c2), the monohydroxycarboxylic acid (c3) having 3 to 5 carbon atoms in total and the solvent to prepare the bismuth-metal oxide mixture liquid (C);
• and
• a pigment dispersion paste (ii) preparation step of mixing the obtained bismuth-metal oxide mixture liquid (C) and the polyvalent acid (E), and then mixing the obtained mixture, the pigment dispersion resin (D) and the pigment (F) to prepare the pigment dispersion paste (ii);
• the metal oxide (c2) contains one or more metal elements selected from the group consisting of La, Nd, Y, Pr, Yb and Ce,
• the monohydroxycarboxylic acid (c3) having 3 to 5 carbon atoms in total has an asymmetric carbon atom, the monohydroxycarboxylic acid (c3) containing 80% or more of an L-form among its optical isomers, and
• in the bismuth-metal oxide mixture liquid (C) preparation step, the viscosity of the bismuth-metal oxide mixture liquid (C) is within a range of 2.5 mPa·s to 15 mPa·s.