| 摘要 |
PROBLEM TO BE SOLVED: To enhance thermal dimensional stability without lowering the modulus of elasticity and productivity by biaxially stretching an unstretched film based on polyethylene terephthalate and specified in the relaxing time of carbonyl carbon in structural analysis by solid high resolving power NMR to heat-treat the stretched film. SOLUTION: A molten extruded film comprising polyester based on polyethylene terephthalate is cooled on the surface of a cooling metal roll by a static electricity applying casting method to obtain an unstretched film. The melt extrusion temp. at this time is pref. higher than the m.p. of polyester by 25-60 deg.C. Herein, by biaxially stretching the unstretched film characterized by that the relaxing time of carbonyl carbon in structural analysis by solid high resolving power NMR is 55 msec or less, further pref., 45 msec or less and amorphous and high in amorphous motility is biaxially stretched and heat-treated to obtain a film very small in heat shrinkage factor. |
