Honda Motor Co., Ltd.
Method for forming multilayer coating film

Abstract:

Disclosed is a method for forming a multilayer coating film, including applying a first and second aqueous base coat, and a clear coat to an object, and thereafter simultaneously heating and curing the three-layer coating film. The first aqueous base coat includes a water-soluble or water-dispersible polyurethane resin having a glass transition temperature of -20.degree. C. or below and a weight average molecular weight of 30,000 to 500,000, and a crosslinkable resin having a weight average molecular weight of 600 or more. The first aqueous base coat-coated film has a breaking strength of 2050 N/cm2 or more and a loss tangent (tan .delta.) at -20.degree. C. of 0.075 or more. The migration amount of a melamine resin from the second aqueous base coat-coated film layer to the first aqueous base coat-coated film layer is within 3% by mass of a total resin solid content of the first aqueous base coat.