| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for polymerizing more safely and inexpensively a copolyester having a degree of polymerization sufficiently usable for a bottle and a film, and having excellent heat resistance, excellent mechanical properties and high transparency, without operational problems in polymerization reaction. SOLUTION: The method for producing the copolyester is characterized in that when producing the copolyester comprising, as a repeating unit constructing a the copolyester, from 97 to 70 mol% of a ethylene terephthalate unit and from 3 to 30 mol% of an ethylene naphthalate unit using an oligomer of polyethylene terephthalate obtained by a direct esterification reaction using as materials terephalic acid and ethylene glycol, naphthalene dicarboxylic acid and a lower alkyl ester thereof are added to the oligomer of polyethylene terephthalate for ester exchange and then the resulting oligomer is subjected to polycondensation reaction. COPYRIGHT: (C)2003,JPO
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