Polyester resin composition, aqueous dispersion, coating composition, and coating film

A polyester resin composition comprising a polyester resin (A) and one or more kinds of catalysts (B), wherein the polyester resin composition satisfies the following requirements (i) to (iv),

• (i) the polyester resin (A) has an acid value of 100 eq/ton or more,
• (ii) in terms of solid content, a content of a curing agent is smaller than 1 part by mass with respect to 100 parts by mass of the polyester resin (A),
• (iii) a content of tetrahydrofuran-insoluble matter obtained by the following equation when the polyester resin composition has been heated at 240° C. for one hour is 10 mass % or more:
• Content of tetrahydrofuran-insoluble matter (mass %)=[{(Y)−mass of copper foil}/{(X)−mass of copper foil}]×100,
• wherein the polyester resin composition is applied onto a copper foil such that the thickness is 10 μm after being dried, heat is applied at 240° C. for one hour, and a sample having a longitudinal direction of 10 cm and a transverse direction of 2.5 cm is obtained, and a mass of the sample before immersion in tetrahydrofuran is defined as (X), and a mass of the sample which has been immersed in 60 ml of tetrahydrofuran at 25° C. for one hour, and thereafter dried at 100° C. for 10 minutes, is defined as (Y) after immersion in tetrahydrofuran, and
• (iv) a content of the one or more kinds of catalysts (B) is 0.01 to 0.5 parts by mass with respect to 100 parts by mass of the polyester resin (A).