Patent ID: 8728626

Claim:
A method for forming a coating film comprising the steps of: forming a cured coating film (A1) of a cationic electrodeposition coating composition (A) on a metal object to be coated; forming a first colored coated film (B1) by coating a first colored aqueous coating composition (B) on the cured coating film (A1); forming a second colored coated film (C1) by coating a second colored aqueous coating composition (C) on the uncured first colored coated film (B1); forming a clear coated film (D1) by coating a clear coating composition (D) on the uncured second colored coated film (C1); and simultaneously curing the uncured first colored coated film (B1), the uncured second colored coated film (C1), and the uncured clear coated film (D1), wherein the cured coating film (A1) comprising the cationic electrodeposition coating composition (A) has: (i) a center line mean roughness (Ra) of not greater than 0.50 μm in a roughness curve at a cutoff value of 2.5 mm; (ii) a centre line average (Wca) of not greater than 0.50 μm in a filtered central line waviness curve at a high-band cutoff value of 0.8 mm and a low-band cutoff value of 8 mm; and (iii) a solvent swelling ratio of not greater than 30.0 mass % after being immersed in an organic solvent selected from the group consisting of n-butyl alcohol, dipropylene glycol monobutyl ether, 2-ethyl-1-hexanol, 3-methoxybutyl acetate and diethylene glycol monoethyl ether at 80° C. for 10 minutes, wherein the cationic electrodeposition coating composition (A) comprises an amino group-containing modified epoxy resin (a1) modified with a xylene formaldehyde resin that is obtained by reacting an epoxy resin (a11) having an epoxy equivalent of 180 to 2,500, a phenolic hydroxyl group-containing xylene formaldehyde resin (a12), and an amino group-containing compound (a13).