Processes and apparatus for making transversely drawn films with substantially uniaxial character

摘要

The present invention relates to a method of processing a film, the method comprising conveying a film (40) within a stretcher (30') along a machine direction while holding opposing edge portions of the film, and stretching the film to a draw ratio in excess of four within the stretcher by moving the opposing edge portions along diverging, non-linear, coplanar paths (64) to form a stretched film, wherein, during the stretching of the film, the minimum value of the extent of uniaxial character, U, is at least 0.8 over a final portion of the stretching after achieving a TDDR of 2.5 and U is less than 1 at the end of the stretching, wherein U is defined as U = (1/MDDR - 1) / (TDDR 1/2 - 1) wherein MDDR is the machine direction draw ratio corresponding to a divergence angle of the diverging paths and TDDR is the transverse direction draw ratio as measured between the diverging paths.