Method for forming multilayer coating film

A method for forming a multilayer coating film, comprising in sequence:

• step (1):
• applying a solvent-based intermediate paint (V) to a substrate to form an uncured first intermediate coating film;
• step (2):
• heating the uncured first intermediate coating film to cure the coating film;
• step (3):
• applying a solvent-based intermediate paint (W) to the cured first intermediate coating film to form an uncured second intermediate coating film;
• step (4):
• heating the uncured second intermediate coating film to cure the coating film;
• step (5):
• applying an aqueous base paint (X) to the cured second intermediate coating film to form an uncured base coating film;
• step (6):
• applying an effect pigment dispersion (Y) to the uncured base coating film to form an uncured effect coating film;
• step (7):
• applying a clear paint (Z) to the uncured effect coating film to form an uncured clear coating film;
• and
• step (8):
• heating the uncured base coating film, the uncured effect coating film, and the uncured clear coating film to simultaneously cure the coating films,
• wherein
• the aqueous base paint (X) is applied using a rotary-atomization bell-shaped coater under coating conditions of a shaping air pressure of 0.15 to 0.25 MPa and a paint discharge amount of 100 to 300 cm3/min, the viscosity 60 seconds after the application of the aqueous base paint (X), measured at a temperature of 23° C. and a shear rate of 0.1 sec−1, is 90 to 160 mPa·s, the solids content 60 seconds after the application is 20 to 40 mass %, and the film thickness 60 seconds after the application is 17 to 35 μm,
• wherein
• the effect pigment dispersion (Y) contains a flake-aluminum pigment (A) with an average thickness of 1 nm or more and less than 70 nm, a flake-aluminum pigment (B) with an average thickness of 70 nm to 250 nm, a hydroxy-containing acrylic resin (C), a rheology control agent (D), a surface-adjusting agent (E), and water, the effect pigment dispersion (Y) having a solids content of 2 to 9 mass %, and
• wherein
• the effect coating film after curing has a film thickness of 0.5 to 2.0 μm.