Patent ID: 7229271

Claim:
A stretcher for substantially uniaxially orienting a film, the stretcher comprising: a plurality of gripping members to hold opposing edge portions of the film; paths along which the gripping members travel to stretch the film in a stretching region, wherein at least a portion of die paths in the stretching region define diverging, substantially parabolic courses disposed in-plane; and a drive mechanism to convey the film and gripping members along a machine direction; wherein the paths in the stretching region are configured such that the film is stretched with an extent of uniaxial character, U, being between zero and unity and with a minimum value of U of at least 0.70 over a final portion of the stretching after achieving a TDDR of 2.0, wherein U is defined as U =(1 /MDDR− 1)/( TDDR 1/2 −1) with MDDR defined as cosine of a positive included divergence angle θ between a direction of travel of a centerline of the film and an instantaneous tangent of one of the diverging paths and TDDR defined as a ratio of a half-distance between current opposing points on the diverging paths and a half-distance between an initial position of the opposing points on the diverging paths.