Method for producing water-based polyester resin, and water-based polyester resin, and method for producing water-based coating composition, and water-based coating composition

A method for producing a water-based polyester resin using a recycled polyester, the method comprising:

• a first step including performing an ester formation reaction and a depolymerization reaction using the recycled polyester, a first polycarboxylic acid component including a divalent polycarboxylic acid residue other than a terephthalic acid residue, and a polyalcohol component;
• a second step including performing an ester formation reaction using a reaction product of the first step and a second polycarboxylic acid component including a trivalent or higher valent polycarboxylic acid residue;
• and
• a third step including performing a polycondensation reaction by reducing pressure,
• the first step including using the recycled polyester to such an amount that makes proportion of the terephthalic acid residue with respect to a total of the terephthalic acid residue included in the recycled polyester and the respective polycarboxylic acid residues included in the first and second polycarboxylic acid components equal to or greater than 20% by mass and equal to or less than 72% by mass, and
• the water-based polyester resin thus produced having an acid value equal to or greater than 30 mgKOH/g and equal to or less than 120 mgKOH/g.