Patent ID: 7740470
Filing Date: 2010-06-22
Classification: B29C,B29K,B29L,G02B,Y10S

Abstract:
1. 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 the paths in the stretching region define diverging, curvilinear courses disposed in-plane; and a drive mechanism to convey the film and gripping members along a machine direction; wherein the paths are configured such that during the stretching an extent of uniaxial character, U, is between zero and unity and a minimum value of an extent of uniaxial character, U, is at least 0.70 over a final portion of the stretching after achieving a TDDR of 2.5, wherein U is defined as 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, wherein TDDR is greater than 4 at an end of the stretching region.