Coating film formation method

1. A method for forming a coating film comprising:

Step (1): forming an uncured coating film by applying to a substrate an aqueous coating composition that contains a copolymer of monomer components comprising one or more N-substituted (meth)acrylamide compounds, the copolymer being a graft copolymer comprising (A) a main chain having a lower critical solution temperature T 1 in water within the range of 30 to 95° C., and (B) at least one hydrophobic side chain;

Step (2): preheating the uncured coating film formed in Step (1) under heating conditions such that a preheating temperature T 2 falls within the range of 60 to 100° C., and the preheating temperature T 2 and the lower critical solution temperature T 1 have a relationship represented by the formula T 2 −T 1 =−30 to 30° C.; and

Step (3): curing the uncured coating film formed in Step (2) by heating.

2. The method for forming a coating film according to claim 1 , which further comprises Step (2′) between Step (2) and Step (3):

Step (2′): applying a clear coating composition to the uncured base coating film formed in Step (2) to form a clear coating film,

the uncured base coating film and uncured clear coating film respectively formed in Steps (2) and (2′) being simultaneously cured by heating in Step (3).

3. The method for forming a coating film according to claim 1 , wherein the graft copolymer is a copolymer obtained by radical copolymerization of an unsaturated monomer mixture containing said one or more N-substituted (meth)acrylamide compound and a hydrophobic macromonomer.

4. The method for forming a coating film according to claim 3 , wherein the content of the N-substituted (meth)acrylamide compound is 1 to 99 parts by mass and the content of the hydrophobic macromonomer is 1 to 30 parts by mass relative to 100 parts by mass of unsaturated monomer mixture.

5. An article comprising a coating film formed by the method for forming a coating film according to claim 1 .