Patent ID: 8906465

Claim:
A method for forming a multilayer coating film on a coating object, which comprises successively carrying out the following steps (1-6): (1) a step of applying a water-based intermediate paint (X), which comprises a hydroxyl-containing acrylic resin and a hydroxyl-containing polyester resin as a base resin, and an amino resin and a blocked polyisocyanate compound as a crosslinking agent, to form an intermediate coating film, (2) a step of adjusting a solid content of the intermediate coating film which is formed in the step (1) to 70-100 mass %, (3) a step of forming a base coating film by applying onto the intermediate coating film as obtained in the step (2) a water-based base coating paint (Y), which comprises a hydroxyl-containing acrylic resin and a hydroxyl-containing polyester resin as a base resin, and an amino resin as a crosslinking agent, and which comprises 30-55 mass parts, per 100 mass parts of a solid resin content of the paint (Y), of an alcoholic solvent having a boiling point of 170-250° C., (4) a step of adjusting a solid content of the base coating film which is formed in the step (3) to 70-100 mass % and pre-heating the intermediate coating film and the base coating film at 30-100° C. for 30 seconds-15 minutes, (5) a step of forming a clear coating film by applying onto the base coating film as obtained in the step (4) a clear paint (Z) containing 40-60 mass parts a of carboxyl-containing compound and 60-40 mass parts of a polyepoxide, per 100 mass parts of a solid resin content of the paint (Z), and (6) a step of curing the intermediate coating film, base coating film and clear coating film, which are formed in the steps (1)-(5), simultaneously, by heating them at 100-120° C. for 3-10 minutes and thereafter further heating them at 130-160° C. for 10-30 minutes.