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

• US 7,740,470 B2
• Filed: 01/18/2007
• Issued: 06/22/2010
• Est. Priority Date: 05/31/2001
• Status: Expired due to Term

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Ruff, Andrew T., Jackson, Jeffery N., Wheatley, John A., Merrill, William Ward, Krueger, Dennis L.
• Primary Examiner(s): Gupta; Yogendra
• Assistant Examiner(s): Luk; Emmanuel S
• Application Number:
  US11/624,374
• Publication Number:
  US 20070134364A1
• Time in Patent Office: 1,251 Days
• Field of Search: 425/325, 425/363, 425/DIG.41, 264/235.6, 264/235.8, 264/901
• US Class Current: 425/325
• CPC Class Codes: B29C 2793/009 after shaping
• CPC Class Codes: B29C 55/08 transverse to the direction of feed
• CPC Class Codes: B29C 55/20 Edge clamps
• CPC Class Codes: B29C 69/001 a shaping technique combined with cutting, e.g. in parts or slices combined with rearranging and joining the cut parts for reinforced material B29C70/545; B29C49/4278, B29C51/268 take precedence
• CPC Class Codes: B29K 2067/003 PET, i.e. poylethylene terephthalate
• CPC Class Codes: B29K 2995/0051 mono-axially
• CPC Class Codes: B29L 2011/00 Optical elements, e.g. lenses, prisms
• CPC Class Codes: G02B 5/3033 in the form of a thin sheet or foil, e.g. Polaroid
• CPC Class Codes: Y10S 425/041 Reshape

Abstract

A stretcher for substantially uniaxially orienting a film includes 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, and a drive mechanism to convey the film and gripping members along a machine direction. At least a portion of the paths in the stretching region define diverging, curvilinear courses disposed in-plane. 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. U is defined as U=(1/MDDR−1)/(TDDR^1/2−1), wherein TDDR is greater than 4 at an end of the stretching region.

Claims

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

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, wherein TDDR is greater than 4 at an end of the stretching region.

2. The stretcher of claim 1, wherein the paths are adjustable.

3. The stretcher of claim 1, wherein the paths in the stretching region are mirror symmetric trajectories diverging away from a machine direction centerline.

4. The stretcher of claim 1, wherein the paths in the stretching region comprise rails formed from a series of straight segments.

5. The stretcher of claim 1, wherein the paths in the stretching region comprise curved rails.

6. The stretcher of claim 1, wherein the stretcher applies active cooling to the gripping members.

7. The stretcher of claim 1, wherein the gripping members comprise clips.

8. The stretcher of claim 7, wherein the paths along which the clips travel to stretch the film define diverging, substantially parabolic courses throughout the entire stretching region.