Method for forming coating film and coated article

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).