| 摘要 |
PROBLEM TO BE SOLVED: To obtain a polyester film, which has high strength and favorable flatness and the heat stability and dimensional stability of which are improved, by a method wherein the longitudinal heat shrinkage factor and cystalline size of the polyester film at the specified temperature are respectively set to be specified value or less. SOLUTION: The longitudinal heat shrinkage factor of a polyester film at 80 deg.C is set to be 0.25% or less, preferably 0.23% or less. The crystalline size Xc of the polyester film is set to be 6nm or less, preferably 5.8nm or less. Dimethyl terephthalate and ethylene glycol are polymerized together by the conventional procedure by employing calcium acetate as ester interchange catalyst, antimony trioxide as polymerization catalyst and phosphoric acid as stabilizer. Thus, a polyester film is obtained, which is excellent in dimensional stability through having high strength, at the same time, the amount of unsymmetrical elongation of which is small and the flatness of which is kept favorably. |
