Method for forming coating film

A method for forming a coating film which comprises the steps of coating a member with a coating material containing a pigment for a thermosetting base coat, overcoating the coated member with a coating material for a thermosetting clear coat in a wet-on-wet coating manner, and then thermosetting the uncured coating films simultaneously;

• a binder component in said coating material for said base coat comprising
• (1) 50 to 90% by weight of an acrylic copolymer (A) having a hydroxyl value of from 40 to 80 mg KOH/g and an acid value of from 0.5 to 30 mg KOH/g and a glass transition temperature of from -40.degree. to 20.degree. C. which is obtained by copolymerizing
• (a) 10 to 40% by weight of a hydroxyl group-containing (meth)acrylic ester,
• (b) 0.2 to 10% by weight of a carboxyl group-containing vinyl monomer,
• (c) 30 to 89.8% by weight of a (meth)acrylic ester represented by the general formula (I) ##STR5## (wherein R.sup.1 is a hydrogen atom or a methyl group, and n (d) 0 to 30% by weight of another copolymerizable vinyl monomer, and
• (2) 10 to 50% by weight of a curing agent;
• a binder component in the coating material for the clear coat comprising
• (3) an acrylic copolymer (B) having a hydroxyl value of from 50 to 180 mg KOH/g, an acid value of from 2 to 40 mg KOH/g and a glass transition temperature of from -40.degree. to 20.degree. C. which is obtained by copolymerizing
• (e) 5 to 60% by weight of a (meth)acrylic ester containing a fluoroalkyl group or a perfluoroalkyl group,
• (f) 10 to 60% by weight of at least one hydroxyl group-containing (meth)acrylic ester represented by the general formula (II) ##STR6## (wherein R.sup.2 is a hydrogen atom or a methyl group, R.sup.3 is an organic substituent represented by the formula (III), (IV), (V) or (VI) ##STR7## wherein each of R.sup.4 and R.sup.5 is a straight-chain or branched alkylene group having 1 to 8 carbon atoms, each of R.sup.6, R.sup.7, R.sup.8 and R.sup.9 is a hydrogen atom or a methyl group, l is an integer of from 2 to 5, j is an integer of from 2 to 10, k is an integer of from 1 to 7, and m is an integer of from 1 to 3),
• (g) 0.2 to 10% by weight of a vinyl monomer containing at least one of a carboxylic group, a sulfonic group and a phosphoric acid group,
• (h) 15 to 70% by weight of a (meth)acrylic ester represented by the general formula (VII) ##STR8## (wherein R.sup.10 is a hydrogen atom or a methyl group, R.sup.11 is a hydrocarbon substituent having 4 or more carbon atoms) and
• (i) 5 to 50% by weight of another copolymerizable vinyl monomer, and
• (4) a polyisocyanate compound (C);
• a ratio X/Y of an equivalent (X) of the OH group present in said acrylic copolymer (B) to an equivalent (Y) of the NCO group in said polyisocyanate compound (C) being in the range of from 1/0.5 to 1/1.5.