Polyester resin composition and a production method therefor

A method for preparing copolymerized polyester resin composition, comprising the steps of:

• carrying out an esterification reaction or a trans-esterification reaction of dicarboxylic acid components, and diol components comprising isosorbide at the increased pressure of 0 to 10.0 kg/cm2 and the temperature of 150 to 300° C. during an average retention time of 2 to 24 hours;
• obtaining a copolymerized polyester resin composition by carrying out a polycondensation reaction for a product of the esterification reaction or the trans-esterification reaction at the reduced pressure of 400 to 0.1 mmHg and at the temperature of 150 to 300° C. during an average retention time of 1 to 24 hours;
• and
• adding an antioxidant selected from a group consisting of a hindered phenolic antioxidant, a phosphitic antioxidant, a thioetheric antioxidant and mixtures thereof during the esterification reaction or polycondensation reaction, or mixing the antioxidant with the produced copolymerized polyester resin, for 95 to 99.99 weight % of the copolymerized polyester resin to be mixed with 0.01 to 5 weight % of the antioxidant.