| 摘要 |
<p>There is disclosed a process for stretching a film of a highly polymerized polyester at least 90 mol% of which recurring units consist of ethylene 2,6-naphthalate both in the longitudinal direction and in the transverse direction. The process is characterized in that (1) the film is first stretched in the longitudinal direction at a stretch ratio of 3.0 to 5.0 at a temperature higher than the second order transition temperature of the film and up to 170.degree.C., and (2) the film is then stretched in the transverse direction at a temperature of 40 to 100.degree.C. at a stretch ratio expressed by the equation (A) below 1 < x ? 0.022 Tt + 1.65 (A) wherein x is the transverse stretch ratio, and Tt is the transverse stretching temperature in .degree.C.</p> |
