Apparatus for making transversely drawn films with substantially uniaxial character

A stretcher for substantially uniaxially orinting 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, substantially parabolic 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 0.75 over a final portion of the stretching after achieving a TDDR of 1.5, wherein U is defined as
• U=(1/MDDR−1)/(TDDR1/2 −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 pats 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.

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 the paths in the stretching region define diverging 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 during the stretching an extent of uniaxial character, U, is below unity over a final portion of the stretching after achieving a TDDR of 1.5 and a minimum value of U is at least 0.80 over a final portion of the stretching after achieving a TDDR of 2.5, wherein U is defined as
• U=(1/MDDR−1)/(TDDR1/2 −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.

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 the paths in the stretching region define diverging courses disposed in-plane;
• and
• a drive mechanism to convey die film and gripping members along a machine direction;
• wherein the paths in the stretching region are configured such that the film is stretched to a draw ratio in excess of four and during the stretching an extent of uniaxial character, U, is below unity over a final portion of the stretching and a minimum value of U is at least 0.8 over a final portion of the stretching after achieving a TDDR of 2.0, wherein U is defined as
• U=(1/MDDR−1)/(TDDR1/2 −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.