Copolymer latex and method for producing the same

A method for producing a copolymer latex for a chipping-resistant coating, wherein the copolymer latex has a number average particle size of 180 nm to 400 nm, toluene-insoluble matter in a dry substance obtained by drying the copolymer latex is 95% by mass to 100% by mass;

• a ratio of a mass of a toluene wet product of the toluene-insoluble matter to a mass of the dry substance of the toluene-insoluble matter (degree of swelling in toluene) are 3.0 to 6.5;
• and the dry substance obtained by drying the copolymer latex has a glass transition starting temperature in a range of −70° C. to −20° C., and a glass transition ending temperature in a range of 10° C. to 100° C., the method comprising:
• emulsion polymerizing through at least not less than two steps, a monomer mixture containing:
• (a) 30% by mass to 70% by mass of a conjugated diene monomer, (b) 0.1% by mass to 15% by mass of an ethylene unsaturated carboxylic acid monomer, and (c) 15% by mass to 69.9% by mass of one or more other copolymerizable monomers (wherein (a)+(b)+(c)=100% by mass),
• wherein a total of an amount of a chain transfer agent to be used in all the polymerization steps is not less than 0.050 parts by mass and less than 0.400 parts by mass based on 100 parts by mass of the total monomer mixture, the method comprising:
• a first step of preparing 40% by mass to 75% by mass of the total monomer mixture, and polymerizing the monomer mixture until the polymerization conversion reaches 50% by mass to 95% by mass, and then, second and subsequent steps of continuously or intermittently adding the remaining monomer mixture equivalent to 25% by mass to 60% by mass of the total monomer mixture to perform emulsion polymerization.