Water-based coating composition

A water-based coating composition to be used as a water-based first colored coating material (X) in a method for forming a multilayer coating film in which the following steps (1) to (4) are carried out in order:

• step (1):
• a step of applying the water-based first colored coating material (X) onto an article to be coated to form a first colored coating film,
• step (2):
• a step of applying a water-based second colored coating material (Y) onto the first colored coating film formed in step (1), to form a second colored coating film,
• step (3):
• a step of applying a clear coating material (Z) onto the second colored coating film formed in step (2) to form a clear coating film, and
• step (4):
• a step of heat curing the first colored coating film, the second colored coating film and the clear coating film formed in steps (1) to (3) all at once,
• wherein the water-based coating composition to be used as a water-based first colored coating material (X) comprises:
• at least one type of resin selected from among acrylic resin (A) and polyester resin (B),
• a curing agent (C), and
• urethane resin particles (D) obtained from a constituent component including a polyisocyanate component (d1) comprising at least one type of diisocyanate (d1-1) selected from among xylylene diisocyanates and hydrogenated xylylene diisocyanates, and a polyol component (d2),
• wherein a content ratio of the diisocyanate (d1-1) in the polyisocyanate component (d1) of the urethane resin particles (D) is in a range of 20 to 100 mass %, based on a total solid content of the polyisocyanate component (d1),
• wherein the polyol component (d2) comprises a polyether polyol (d2-1) and a polycarbonate polyol (d2-2), and
• the content ratio of the polyether polyol (d2-1) and the polycarbonate polyol (d2-2) in the polyol component (d2) is 90/10 to 60/40, as the mass ratio of polyether polyol (d2-1)/polycarbonate polyol (d2-2).