Claims
- 1. A method of processing a film, the method comprising:
conveying a film within a stretcher along a machine direction while holding opposing edge portions of the film; and stretching the film within the stretcher by moving the opposing edge portions along diverging, substantially parabolic paths to form a stretched film.
- 2. The method of claim 1, wherein stretching the film comprises stretching the film to a draw ratio in excess of four within the stretcher by moving the opposing edge portions along diverging, substantially parabolic paths to form a stretched film.
- 3. The method of claim 1, wherein stretching the film comprises stretching the film under non-constant strain within the stretcher by moving the opposing edge portions along diverging, substantially parabolic paths to form a stretched film.
- 4. The method of claim 1, wherein the film has an initial thickness and initial width when conveyed into the stretcher and the stretched film has a stretched thickness and a stretched width; and
wherein, after stretching the film to a ratio of stretched width/initial width defined as λ, a ratio of stretched thickness/initial thickness is approximately λ−1/2.
- 5. The method of claim 1, wherein the step of stretching the film comprises stretching the film within the stretcher by moving the opposing edge portions along diverging, substantially parabolic paths, wherein the paths are coplanar.
- 6. The method of claim 1, wherein the step of stretching the film comprises stretching the film within the stretcher by moving the opposing edge portions along diverging, substantially parabolic paths, wherein the paths are substantially symmetrical about a center axis of the film.
- 7. The method of claim 1, further comprising providing the film to the stretcher in a continuous manner from a roll of film.
- 8. The method of claim 1, further comprising extruding or coextruding the film in-line with the stretcher.
- 9. The method of claim 1, wherein the stretched film comprises at least one layer with indices of refraction in a length direction, corresponding to the machine direction, and a thickness direction that are substantially the same but substantially different from an index of refraction in a width direction.
- 10. The method of claim 1, further comprising releasing the edge portions of the film at an end of the substantially parabolic paths.
- 11. The method of claim 1, wherein the film comprises a multilayer film having a plurality of alternating layers of different polymeric composition.
- 12. The method of claim 1, wherein the minimum value of the extent of uniaxial character, U, is at least 0.7, wherein U is defined as
- 13. The method of claim 1, wherein the diverging, substantially parabolic paths have a functional form:
- 14. The method of claim 1, wherein at least a portion of the diverging, substantially parabolic paths have a functional form:
- 15. The method of claim 1, wherein the opposing edge portion of the film are substantially continuously supported.
- 16. A method of forming an optical film, the method comprising:
forming a multilayer film comprising alternating layers of different polymeric compositions; conveying the multilayer film into a stretcher along a machine direction while holding opposing edge portions of the multilayer film; and stretching the multilayer film within the stretcher by moving the opposing edge portions along diverging, substantially parabolic paths to form a multilayer optical film.
- 17. The method of claim 16, wherein the multilayer optical film is a substantially uniaxially-oriented multilayer optical film.
- 18. The method of claim 16, wherein the multilayer film has an initial thickness and initial width when conveyed into the stretcher and the multilayer optical film has a stretched thickness and a stretched width; and
wherein, after stretching the multilayer film to a ratio of stretched width/initial width defined as λ, a ratio of stretched thickness/initial thickness is approximately λ−1/2.
- 19. The method of claim 16, wherein the minimum value of the extent of uniaxial character, U, is at least 0.7, wherein U is defined as
- 20. The method of claim 16, wherein the diverging, substantially parabolic paths have a functional form:
- 21. The method of claim 16, wherein at least a portion of the diverging, substantially parabolic paths have a functional form:
- 22. A method of processing a film, the method comprising:
conveying a film within a stretcher 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 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)/(TDDR1/2−1) 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.
- 23. The method of claim 22, wherein the minimum value of the extent of uniaxial character is at least 0.85.
- 24. The method of claim 22, wherein the film comprises a multilayer film having a plurality of alternating layers of different polymeric composition.
- 25. The method of claim 22, wherein the step of stretching the film comprises stretching the film within the stretcher by moving the opposing edge portions along diverging non-linear paths, wherein the paths are in a plane of the film.
- 26. The method of claim 22, wherein the step of stretching the film comprises stretching the film within the stretcher by moving the opposing edge portions along diverging non-linear paths, wherein the paths are substantially symmetrical about a center axis of the film.
- 27. The method of claim 22, wherein the extent of uniaxial character, U, is at least 0.8 over a final portion of the stretching after achieving a TDDR of 2.0.
- 28. A method of processing a film, the method comprising:
conveying a film within a stretcher along a machine direction while holding opposing edge portions of the film; and stretching the film within the stretcher by moving the opposing edge portions along diverging non-linear paths to form a stretched film, wherein, during the stretching of the film, the speed of the film along the machine direction decreases by a factor of approximately λ1/2 where λ is the transverse direction draw ratio.
- 29. The method of claim 28, wherein the film comprises a multilayer film having a plurality of alternating layers of different polymeric composition.
- 30. The method of claim 28, wherein the step of stretching the film comprises stretching the film within the stretcher by moving the opposing edge portions along diverging non-linear paths, wherein the paths are in a plane of the film.
- 31. The method of claim 28, wherein the step of stretching the film comprises stretching the film within the stretcher by moving the opposing edge portions along diverging non-linear paths, wherein the paths are substantially symmetrical about a center axis of the film.
- 32. A roll of multilayer optical film, the roll comprising a substantially uniaxially-oriented multilayer optical film, wherein at least one layer of the multilayer optical film has indices of refraction in a length direction and a thickness direction that are substantially the same, but substantially different from an index of refraction in a width direction.
- 33. The roll of claim 32, wherein the multilayer optical film is a reflective polarizer.
- 34. A stretcher for processing a film, the stretcher comprising:
a plurality of clips to hold opposing edge portions of the film; paths along which the clips travel, wherein at least a portion of the paths define diverging, substantially parabolic courses; and a drive mechanism to convey the film and clips along a machine direction.
- 35. The stretcher of claim 34, wherein the paths are adjustable.
- 36. A stretcher for processing a film, the stretcher comprising:
means for receiving a film; means for grasping edge portions of the film; means for conveying the film in a machine direction; and means for moving the opposing edge portions along diverging, substantially parabolic paths to form a stretched film.
Parent Case Info
[0001] This application claims the benefit of U.S. Provisional Application Serial No. 60/294,940, which is incorporated herein by reference.
Provisional Applications (1)
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Number |
Date |
Country |
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60294940 |
May 2001 |
US |