COPOLYMER POLYESTER RESIN

Abstract

With respect to a copolymer polyester resin in which diethylene glycol and sodium sulfoisophthalate are copolymerized, the present invention solves the problem of dirtiness of a die and adhesion of foreign material to a product during continuous production of a products such as films, molded articles, and fibers, and the problem of coloring of the resin and a reduction in the molecular weight thereof at the time of recycling. Provided is a copolymer polyester resin comprising terephthalic acid as the main component of a dicarboxylic acid component, and ethylene glycol as the main component of a diol component, said copolymer polyester resin being characterized in that: in the entirety of a polyester resin component, when the total amount of the dicarboxylic acid component is represented as 100 mol%, the proportion of a terephthalic acid component with respect to the entirety of the dicarboxylic acid component is 70-99.95 mol%, the proportion of sodium sulfoisophthalate with respect to the entirety of the dicarboxylic acid component is 0.05-10 mol%, and when the total amount of the diol component is represented as 100 mol%, the proportion of diethylene glycol with respect to the entirety of a glycol component is 1-10 mol%; the content of a free cyclic monomer constituted by diethylene glycol, ethylene glycol, sodium sulfoisophthalate, and terephthalic acid is not more than 20 ppm; and the content of a free cyclic trimer constituted by ethylene glycol, sodium sulfoisophthalate, and terephthalic acid is not more than 200 ppm.

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