| 摘要 |
PROBLEM TO BE SOLVED: To improve uniformity of thickness and to make processability good by a method wherein a substantially unoriented polyester film consisting of liq. crystal polyester and non-liq. crystal polyester is set in such a way that temp. coefficient of drawing stress satisfies a specified condition and it is at least uniaxially drawn. SOLUTION: A substantially unoriented polyester film consisting of liq. crystal polyester and non-liq. crystal polyester is set in such a way that temp. coefficient K of drawing stress satisfies an equation -0.35<=K<=0.1 (MPa/ deg.C) and it is at least uniaxially drawn. In addition, it is pref. that drawing is performed at a temp. of the glass transition temp. of the non-liq. crystal polyester +30 deg.C-+60 deg.C. In addition, it is pref. that fluctuation of thickness of at least uniaxially stretched polyester film is at most 5% and when wave shape of the fluctuation of thickness is Fourier-analysed, the ratio of sum of spectrum strength in the wave numbers of 1.00(1/m)-2.00(1/m) to the sum of spectrum strength of the whole wave number region is at most 0.15. |
