Abstract: A water-based intermediate coating composition which contains a water-dispersible polyurethane composition is used. Here, the water-dispersible polyurethane composition is obtained from: a polyisocyanate component containing diisocyanate as an essential component; a polyol component containing polycarbonatediol with an average molecular weight of 500 to 5,000 and carboxyl group-containing diol as essential components; an amine component containing a monoamine compound as an essential component; a carboxyl group-neutralizing component; and water. A three-layered coating film including the water-based intermediate coating, a water-based base coating and a clear coating is formed through a wet-on-wet process on a material onto which an electrodeposited coating film is formed. Thereafter, the three coating films are baked and cured at the same time, thereby forming a multilayer coating film.

Abstract: The present invention is to provide a method for forming a plural-layered coated film which is excellent in surface smoothness while phase mixing between an intermediate coating film and a base coating film is effectively prevented. The method comprises coating successively an aqueous intermediate coating paint, an aqueous base paint and a clear paint on an electrodeposition coated film in a wet-on-wet manner, and baking and curing them at the same time, wherein an intermediate coating film formed of the aqueous intermediate coating paint has a water absorption rate of coating film of 10% or less and a water dissolving rate of coating film of 5%, and the aqueous intermediate coating paint contains an acrylic resin emulsion, a urethane resin emulsion, and a curing agent.