Method for forming multilayer coating film

A method for forming a multilayer coating film comprising forming an uncured coating film of a primer paint composition (A) as defined below on a substrate, forming a top coating film of a top paint composition (B) as defined below on the uncured coating film, and simultaneously drying the films,

• wherein the uncured coating film of the primer paint composition (A) during application of the top paint composition (B) has a viscosity of 5 Pa·s to 1000 Pa·s, and
• a value ΔNV obtained by subtracting a value (NV1) of application mass solids content (%) of the primer paint composition (A) from a value (NV2) of mass solids content (%) of the uncured coating film of the primer paint composition (A) during application of the top paint composition (B) is 15 or more;
• Primer Paint Composition (A):
• A paint composition comprising an epoxy resin (a1) having a weight average molecular weight of 20000 or more, a rust preventive pigment (a2), a color pigment (a3), and an extender pigment (a4), the composition containing the rust preventive pigment (a2) in an amount of 1 to 70 parts by mass, the color pigment (a3) in an amount of 40 to 150 parts by mass, and the extender pigment (a4) in an amount of 40 to 150 parts by mass, per 100 parts by mass of the total solids content of the epoxy resin (a1);
• Top Paint Composition (B):
• A paint composition comprising an acrylic resin (b1), a polyisocyanate compound (b2), a silane coupling agent (b3), and barium sulfate (b4) having an average particle size of 0.01 to 5.0 μm, the composition containing the acrylic resin (b1) and the polyisocyanate compound (b2) in a proportion of 60 to 90 parts by mass to 10 to 40 parts by mass, and the barium sulfate (b4) in an amount of 1 to 50 parts by mass, per 100 parts by mass of the total solids content of the acrylic resin (b1) and the polyisocyanate compound (b2).