Abstract: A method for forming a multilayer coating film which includes forming an uncured coating film by applying a first aqueous base coating composition, forming an uncured coating film by applying a second aqueous base coating composition, forming an uncured coating film by applying a clear coating composition, and simultaneously heat curing the obtained coating films. The first aqueous base coating composition contains a carbodiimide compound, the clear coating composition contains a hydroxyl group-containing acrylic resin (A) having a hydroxyl value of 120 to 160 mgKOH/g and an acid value of 5 to 10 mgKOH/g, a polyisocyanate compound (B), and a polycarbonate diol compound (C). The component (A) has a hydroxyl group-containing alkyl moiety having 3 or less carbon atoms, and the ratio of the numbers of moles of the isocyanate functional groups of the component (B) and the hydroxyl group functional groups of the component (A) is 1.15 to 1.35.

Abstract: A method for forming a multilayer coating film which includes forming an uncured coating film by applying a first aqueous base coating composition, forming an uncured coating film by applying a second aqueous base coating composition, forming an uncured coating film by applying a clear coating composition, and simultaneously heat curing the obtained coating films. The first aqueous base coating composition contains a carbodiimide compound, the clear coating composition contains a hydroxyl group-containing acrylic resin (A) having a hydroxyl value of 120 to 160 mgKOH/g and an acid value of 5 to 10 mgKOH/g, a polyisocyanate compound (B), and a polycarbonate diol compound (C). The component (A) has a hydroxyl group-containing alkyl moiety having 3 or less carbon atoms, and the ratio of the numbers of moles of the isocyanate functional groups of the component (B) and the hydroxyl group functional groups of the component (A) is 1.15 to 1.35.

Abstract: A first clear coating composition comprising (a) an acryl resin having a hydroxyl value of 110 to 160 mgKOH/g and an acid value of 5 to 35 mgKOH/g, (b) an acryl resin having a hydroxyl value of 10 to 150 mgKOH/g and an epoxy equivalent of 230 to 800 g/eq, and (c) a curing agent of a melamine resin, which has a solubility parameter (SP value) within a range of from 9.5 to 11.0, and which comprises no less than 50% by weight of an imino group-containing melamine resin. The composition is effective in a three coating and two baking (3C2B) coating process which includes applying a base coating composition, applying a first clear coating composition thereon by a wet-on-wet procedure, curing the coatings, applying a second clear coating composition thereon, and then curing the coating.