Method of forming a multilayer film having a continuous and disperse phase

• US 6,031,665 A
• Filed: 08/24/1998
• Issued: 02/29/2000
• Est. Priority Date: 02/29/1996
• Status: Expired due to Term

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Majumdar, Biswaroop, Weber, Michael F., Ouderkirk, Andrew J., Nevitt, Timothy J., Stover, Carl A., Allen, Richard C., Carlson, Lockwood W., Kotz, Arthur L.
• Primary Examiner(s): Spyrou, Cassandra
• Assistant Examiner(s): Juba, Jr., John
• Application Number:
  US09/139,175
• Time in Patent Office: 554 Days
• Field of Search: 359/490, 359/491, 359/492, 359/494, 359/495, 359/500, 359/900
• US Class Current: 359/487.02
• CPC Class Codes: G02B 5/3008 comprising dielectric particles, e.g. birefringent crystals embedded in a matrix
• CPC Class Codes: G02B 5/305 including organic materials, e.g. polymeric layers
• CPC Class Codes: Y10S 359/90 Methods

Abstract

An optical film is provided which comprises a disperse phase of polymeric particles disposed within a continuous birefringent matrix. The film is oriented, typically by stretching, in one or more directions. The size and shape of the disperse phase particles, the volume fraction of the disperse phase, the film thickness, and the amount of orientation are chosen to attain a desired degree of diffuse reflection and total transmission of electromagnetic radiation of a desired wavelength in the resulting film.

Claims

1. A method for making a polarizer, comprising the steps of:

creating a blend of first and second diverse thermoplastic polymers, wherein said first thermoplastic polymer is present as a continuous phase and is capable of undergoing strain-induced birefringence, and wherein said second thermoplastic polymer is present as a disperse phase; and

orienting the blend in at least one direction such that the first thermoplastic polymer develops a birefringence of at least about 0.05;

wherein the blend is stretched in a first direction to a first stretch ratio k and is stretched in a second direction to a second stretch ratio m, and wherein k>

m.

2. The method of claim 1, wherein the blend is oriented such that it has a total diffuse reflectivity of at least 30% over essentially all wavelengths of visible light.

3. The method of claim 1, wherein m is at least about 2.

4. The method of claim 1, wherein m is at least about 4.

5. The method of claim 1, wherein m is at least about 6.

6. The method of claim 1, wherein the blend is extruded into a film before it is oriented, wherein the first direction is along a first in-plane axis, and wherein the second direction is along a second in-plane axis.

7. The method of claim 6, wherein the first and second in-plane axes are essentially orthogonal.

8. The method of claim 1, wherein the disperse phase is present in an amount of about 5% to about 50% by volume relative to the volume of the continuous phase.

9. A method for making a polarizer, comprising the steps of:

creating a blend comprising first and second diverse thermoplastic polymers, wherein the first thermoplastic polymer is present as a continuous phase and is capable of undergoing strain-induced birefringence, and wherein the second thermoplastic polymer is present in the blend as a disperse phase which is essentially randomly distributed throughout the continuous phase;

extruding the blend into a film; and

orienting the film in at least one direction such that the first thermoplastic polymer develops a birefringence of at least about 0.05;

wherein the film is oriented by stretching it in a first in-plane direction while leaving the film unconstrained in a second in-plane direction.

10. The method of claim 9, wherein the second in-plane direction is essentially orthogonal to the first in-plane direction.

11. The method of claim 9, wherein the blend is oriented such that it has a total diffuse reflectivity of at least 30% over essentially all wavelengths of visible light.

12. The method of claim 9, wherein the blend is stretched in the first in-plane direction to a stretch ratio of at least about 2.

13. The method of claim 9, wherein the blend is stretched in the first in-plane direction to a stretch ratio of at least about 4.

14. The method of claim 9, wherein the blend is stretched in the first in-plane direction to a stretch ratio of at least about 6.

15. The method of claim 9, wherein the second in-plane direction is orthogonal to the first in-plane direction.

16. The method of claim 9, wherein said disperse phase is present in an amount of about 5% to about 50% by volume relative to the volume of the continuous phase.

17. A method for making a polarizer, comprising the steps of:

creating a blend comprising first and second diverse thermoplastic polymers and a compatibilizer, wherein the first thermoplastic polymer is present as a continuous phase and is capable of undergoing strain-induced birefringence, and wherein the second thermoplastic polymer is present in the blend as a disperse phase which is essentially randomly distributed throughout the continuous phase;

extruding the blend into a film; and

stretching the film in at least one direction such that the first thermoplastic polymer develops a birefringence of at least about 0.05.

18. The method of claim 17, wherein the stretched film has a total diffuse reflectivity of at least 30% over essentially all wavelengths of visible light.

19. The method of claim 17, wherein the film is stretched to a stretch ratio of at least about 2.

20. The method of claim 17, wherein the film is stretched to a stretch ratio of at least about 4.

21. The method of claim 17, wherein the film is stretched to a stretch ratio of at least about 6.

22. The method of claim 17, wherein the film is stretched in a first direction to a stretch ratio k and is stretched in a second direction to a stretch ratio m, and wherein k>

m.

23. The method of claim 17, wherein the film is stretched in a first in-plane direction to a stretch ratio of at least 2, while leaving the film unconstrained in a second in-plane direction.

24. The method of claim 23, wherein the second in-plane direction is orthogonal to the first in-plane direction.

25. The method of claim 17, wherein said disperse phase is present in an amount of about 5% to about 50% by volume relative to the volume of the continuous phase.

26. A method for making a polarizer, comprising the steps of:

creating a blend comprising first, second, and third diverse polymers, wherein the first and second polymers are thermoplastic, wherein the first polymer is present in the blend as a continuous phase and is capable of undergoing strain-induced birefringence, and wherein the second and third polymers are present in the blend as disperse phases which are essentially randomly distributed throughout the continuous phase; and

stretching the blend in at least one direction such that the first thermoplastic polymer develops a birefringence of at least about 0.05.

27. The method of claim 26, wherein the blend is oriented such that it has a total diffuse reflectivity of at least 30% over essentially all wavelengths of visible light.

28. The method of claim 26, wherein the blend is stretched to a stretch ratio of at least about 2.

29. The method of claim 26, wherein the blend is stretched to a stretch ratio of at least about 4.

30. The method of claim 26, wherein the blend is stretched to a stretch ratio of at least about 6.

31. The method of claim 26, wherein the blend is stretched in a first direction to a stretch ratio k, wherein the blend is stretched in a second direction to a stretch ratio m, and wherein k>

m.

32. The method of claim 26, wherein the blend is extruded as a film prior to being stretched, and wherein the film is stretched in a first in-plane direction to a stretch ratio of at least 2 while leaving the film unconstrained in a second in-plane direction.

33. The method of claim 26, wherein said disperse phase is present in an amount of about 5% to about 50% by volume relative to the volume of the continuous phase.

34. The method of claim 26, wherein the second in-plane direction is orthogonal to the first in-plane direction.

35. A method for making a polarizer, comprising the steps of:

creating a blend comprising first and second diverse thermoplastic polymers, wherein the first thermoplastic polymer is present as a continuous phase and is capable of undergoing strain-induced birefringence, and wherein the second thermoplastic polymer is present in the blend as a disperse phase which is essentially randomly distributed throughout the continuous phase;

extruding the blend into a film; and

stretching the film asymmetrically and biaxially such that the first thermoplastic polymer develops a birefringence of at least about 0.05.

36. The method of claim 35, wherein the film is stretched such that it has a total diffuse reflectivity of at least 30% over essentially all wavelengths of visible light.

37. The method of claim 35, wherein the film is stretched to a stretch ratio of at least about 2.

38. The method of claim 35, wherein the film is stretched to a stretch ratio of at least about 4.

39. The method of claim 35, wherein the film is stretched to a stretch ratio of at least about 6.

40. The method of claim 35, wherein the film is stretched in a first direction to a stretch ratio k, wherein the film is stretched in a second direction to a stretch ratio m, and wherein k>

m.

41. The method of claim 40, wherein the second in-plane direction is orthogonal to the first in-plane direction.

42. A method for making a polarizer, comprising the steps of:

creating a blend comprising first and second diverse thermoplastic polymers, wherein the first thermoplastic polymer is present as a continuous phase and is capable of undergoing strain-induced birefringence, and wherein the second thermoplastic polymer is present in the blend as a disperse phase which is essentially randomly distributed throughout the continuous phase;

extruding the blend into a film; and

stretching the film in at least one direction such that the first thermoplastic polymer develops a birefringence of at least about 0.05;

wherein the blend is extruded as a first layer in a recurrent sequence of at least two layers.

43. The method of claim 42, wherein the film is stretched such that it has a total diffuse reflectivity of at least 30% over essentially all wavelengths of visible light.

44. The method of claim 42, wherein the film is stretched to a stretch ratio of at least about 2.

45. The method of claim 42, wherein the film is stretched to a stretch ratio of at least about 4.

46. The method of claim 42, wherein the film is stretched to a stretch ratio of at least about 6.

47. The method of claim 42, wherein the film is stretched in a first direction to a stretch ratio k, wherein the film is stretched in a second direction to a stretch ratio m, and wherein k>

m.

48. The method of claim 42, wherein the film is stretched in a first in-plane direction to a stretch ratio of at least 2 while leaving the film unconstrained in a second in-plane direction.

49. The method of claim 48, wherein the second in-plane direction is orthogonal to the first in-plane direction.