Method for forming multi-layer coating film

A method of forming a multi-layer coating film, the method comprising steps (1) to (6):

• (1) applying an electrodeposition paint onto a steel sheet, heating and curing an applied electrodeposition paint to form a cured electrodeposited coating film;
• (2) applying a first colored paint (P1) onto the cured electrodeposited coating film obtained in step (1) to form a first colored coating film;
• (3) applying a second water-based paint (P2) onto the first colored coating film obtained in step (2) to form a second coating film having a cured film thickness (TP2) in a range of from 5 to 20 μm;
• (4) applying a third water-based colored paint (P3) onto the second coating film obtained in step (3) to form a third colored coating film having a cured film thickness (TP3) in a range of from 0.5 to 7 μm, the third water-based colored paint (P3) comprising a binder component (AP3) and a bright pigment (BP3), and a paint solid content concentration (NVP3) being in a range of from 2 to 17 mass %;
• (5) applying a clear coat paint (P4) onto the third colored coating film obtained in step (4) to form a clear coating film;
• and
• (6) heating a multi-layer coating film comprising the first colored coating film, the second coating film, the third colored coating film, and the clear coating film formed in steps (2) to (5) to simultaneously curing the multi-layer coating film, wherein
• a viscosity (V2P2) of the second water-based paint (P2) one minute after application is in a range of from 3 to 500 Pa·sec when measured under conditions including a shear rate of 0.1 sec−1 and a temperature of 23° C., and a ratio (V2P2)/(V1P2) of the viscosity (V2P2) one minute after application to a viscosity (V1P2) of the second water-based paint (P2) measured under conditions including a shear rate of 0.1 sec−1 and a temperature of 23° C. is in a range of from 1.1/1 to 5/1.