| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for producing a copolyester with little birefringence, excellent in impact resistance, thermal resistance, transparency and color tone, and suitable for use as films. SOLUTION: In a method for producing a copolyester mainly consisting of terephthalic acid and a glycol component consisting of ethylene glycol and a glycol represented by the formula (wherein R<1> and R<2> are each an alkyl group having 2 to 10 carbon atoms, and R<3> , R<4> , R<5> , and R<6> are each an alkyl, an alkoxy or a phenyl group having 1 to 10 carbon atoms) at a molar ratio of 95/5-70/30, a polycondensation reaction is carried out by adding a phosphorus compound in an amount of 1×10<-4> -2×10<-3> mol per mole of an acid component in the copolyester prior to the initiation of polycondensation, carrying out an esterification or an ester interchange reaction, and then adding the glycol represented by the formula and an antimony compound.
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