| 摘要 |
PROBLEM TO BE SOLVED: To obtain a polyester having a quality comparable or superior to that of conventional polyester while shortening the polymerization time by supplying and passing a polyester in molten state through a vertical stirring thinfilm evaporator. SOLUTION: A polyester or its oligomer is supplied to and passed through a vertical stirring thin-film evaporator in molten state to increase the polymerization degree of the polyester. Preferably, the polyester or its oligomer has an intrinsic viscosity of 0.3-1.0 before passing through the evaporator, the intrinsic viscosity of the polyester after passing through the evaporator is higher than that of the polyester before passing by >=0.1, the reaction is carried out under a pressure lower than atmospheric pressure or in an inert gas flow and the polyester is a polymer selected from among polybutylene terephthalate, polycyclohexylene dimethylene terephthalate and polyethylene terephthalate.
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