Clear coating with composition of acrylic and polyester polycarboxylic acids, polyepoxide and crosslinked resin particles

A method for forming a coated film, which comprises:

• (1) applying a water-based or solvent-based coating composition on an undercoated or intercoated substrate to form a base coating;
• (2) applying a clear coating composition thereon to form a clear coating, without curing the base coating, wherein the clear coating composition comprises, as a binder component, a curable resin composition comprising:
• (a) 10 to 70% by weight of an acrylic polycarboxylic acid having 2 or more carboxyl groups per molecule on an average, an acid value of 5 to 300 mg KOH/g (solid) and a number-average molecular weight of 500 to 8000 obtained by copolymerizing an acid anhydride group-containing ethylenically unsaturated monomer with an ethylenically unsaturated monomer having no acid anhydride group and then reacting the resulting copolymer with a monoalcohol;
• (b) 5 to 70% by weight of a polyester polycarboxylic acid having an acid value of 50 to 350 mg KOH/g (solid), a number-average molecular weight of 400 to 3500 and a ratio of weight-average molecular weight to number-average molecular weight of 1.8 or less, which is obtained by reacting a polyester polyol having 3 or more hydroxyl groups with an acid anhydride group-containing compound;
• and
• (c) 10 to 80% by weight of a polyepoxide with both an epoxy group and a hydroxyl group, having an epoxy equivalent of 50 to 700 and a number-average molecular weight of 200 to 10000;
• provided that the amounts of the components (a) to (c) are based on the weight of the total solid contained in the curable resin composition;
• and
• further comprising (d) crosslinked resin particles prepared in the presence of an amphoteric ionic group-containing polyester resin;
• and
• (3) heating and curing both the base coating and clear coating.