Abstract: The present invention provides a cationic electrodeposition coating composition with a rust prevention property enhanced by improving the adhesion and the blocking property of a coating film obtained from a cationic electrodeposition coating composition as compared with conventional ones. The present invention provides a cationic electrodeposition coating composition including an aminated epoxy resin and a blocked polyisocyanate curing agent, wherein the aminated epoxy resin is an aminated epoxy resin obtained by reacting an amine compound with an epoxy resin, the aminated epoxy resin has a molecular weight distribution of 2.7 or less, and a rate of elongation of an electrodeposition coating film formed by applying the cationic electrodeposition coating composition to a steel sheet such that a cured film thickness is 20 ?m, followed by baking at 160° C. for 15 minutes, is 0.1 to 4.5%.

Abstract: An object of the present invention is to provide a preparation method for improving the edge part rust prevention property in the preparation of a cationic electrodeposition coating composition containing a bismuth compound as a curing catalyst. The present invention provides a method for preparing a cationic electrodeposition coating composition, including a step of preparing a resin emulsion (i) containing an aminated resin (A) and a blocked isocyanate curing agent (B), a step of preparing a pigment dispersion paste (ii) containing a bismuth-metal oxide mixture liquid (C) containing 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).