Method for Forming Multilayer Coating Film

A method for forming a multilayer coating film, the method comprising:

• (1) applying a first water-based paint (P1) onto an object to be coated to form a first coating film having a cured film thickness (TP1) in a range from 5 to 20 μm;
• (2) applying a second water-based colored paint (P2) onto the first coating film formed in (1) to form a second colored coating film having a cured film thickness (TP2) in a range from 0.5 to 7 μm, the second water-based colored paint (P2) comprising a binder component (AP2) and an effect pigment (BP2) and having a paint solid content concentration (NVP2) in a range greater than or equal to 1 mass % and less than 20 mass %;
• (3) applying a clear coat paint (P3) onto the second colored coating film formed in (2) to form a clear coating film;
• and
• (4) heating a multilayer coating film including the first coating film formed in (1), the second colored coating film formed in (2), and the clear coating film formed in (3), and thereby simultaneously curing the multilayer coating film,
• the first water-based paint (P1) comprising
• a hydroxyl group-containing acrylic resin (A),
• a crosslinking agent (B), and
• acrylic-urethane composite particles (C) containing an acrylic resin component having an acid value less than or equal to 20 mg KOH/g.