Diffusely reflecting polarizing element including a first birefringent phase and a second phase

• US 5,825,543 A
• Filed: 02/29/1996
• Issued: 10/20/1998
• Est. Priority Date: 02/29/1996
• Status: Expired due to Term

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: Minnesota Mining and Manufacturing Co (3M Company)
• Inventors: Weber, Michael F., Ouderkirk, Andrew J., Nevitt, Timothy J., Stover, Carl A., Allen, Richard C., Majumdar, Biswaroop, Carlson, Lockwood W., Kotz, Arthur L.
• Primary Examiner(s): Dzierzynski, Paul M.
• Assistant Examiner(s): Schuberg, Darren E.
• Application Number:
  US08/610,092
• Time in Patent Office: 964 Days
• Field of Search: 359/491, 359/492, 359/494, 359/495, 359/500, 252/585, 427/163.1
• 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: G02B 5/3083 Birefringent or phase retarding elements G02B5/3008, G02B5/3016 take precedence; systems for polarisation control G02B27/286; manufacturing phase modulating patterns by lithographic processes G03F7/001
• CPC Class Codes: G02F 1/133545 Dielectric stack polarisers

Abstract

An optical film with 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. An optical body, comprising:

a first phase having a birefringence of at least about 0.05; and

a second phase, disposed within said first phase, whose index of refraction differs from said first phase by greater than about 0.05 along a first axis and by less than about 0.05 along a second axis orthogonal to said first axis;

wherein the diffuse reflectivity of said first and second phases taken together along at least one axis for at least one polarization state of electromagnetic radiation is at least about 30%.

2. The optical body of claim 1, wherein said first phase has a birefringence of at least about 0 1.

3. The optical body of claim 1, wherein said first phase has a birefringence of at least about 0.15.

4. The optical body of claim 1, wherein said first phase has a birefringence of at least about 0.2.

5. The optical body of claim 1, wherein said second phase has a birefringence of less than about 0.02.

6. The optical body of claim 1, wherein said second phase has a birefringence of less than about 0.01.

7. The optical body of claim 1, wherein said second phase has an index of refraction which differs from said first phase by more than about 0.1 along said first axis.

8. The optical body of claim 1, wherein said second phase has an index of refraction which differs from said first phase by more than about 0.15 along said first axis.

9. The optical body of claim 1, wherein said second phase has an index of refraction which differs from said first phase by more than about 0.2 along said first axis.

10. The optical body of claim 1, wherein said second phase has an index of refraction which differs from said first phase by less than about 0.03 along said second axis.

11. The optical body of claim 1, wherein said second phase has an index of refraction which differs from said first phase by less than about 0.01 along said second axis.

12. The optical body of claim 1, wherein said first and second phases taken together have a diffuse reflectivity along said at least one axis of at least about 50% for both polarizations of electromagnetic radiation.

13. The optical body of claim 1, wherein said optical body has a total reflectivity of greater than about 50% for a first polarization state of electromagnetic radiation and a total transmission of greater than about 50% for a second polarization state of electromagnetic radiation orthogonal to said first polarization state.

14. The optical body of claim 13, wherein said optical body has a total reflectivity of greater than about 60% for said first polarization state of electromagnetic radiation.

15. The optical body of claim 13, wherein said optical body has a total reflectivity of greater than about 70% for said first polarization state of electromagnetic radiation.

16. The optical body of claim 13, wherein said optical body has a total transmission of greater than about 60% for said second polarization state of electromagnetic radiation.

17. The optical body of claim 13, wherein said optical body has a total transmission of greater than about 70% for said second polarization state of electromagnetic radiation.

18. The optical body of claim 1, wherein at least about 40% of light polarized orthogonal to a first polarization state of light is transmitted through said optical body with an angle of deflection of less than about 8°

.

19. The optical body of claim 1, wherein at least about 60% of light polarized orthogonal to a first polarization state of light is transmitted through said optical body with an angle of deflection of less than about 8°

.

20. The optical body of claim 1, wherein at least about 70% of light polarized orthogonal to a first polarization of light is transmitted through said optical body with an angle of deflection of less than about 8°

.

21. The optical body of claim 1, wherein said first phase comprises a thermoplastic resin.

22. The optical body of claim 21, wherein said thermoplastic resin is a syndiotactic vinyl aromatic polymer derived from a vinyl aromatic monomer.

23. The optical body of claim 21, wherein said thermoplastic resin comprises interpolymerized units of syndiotactic polystyrene.

24. The optical body of claim 21, wherein said thermoplastic resin comprises polyethylene naphthalate.

25. The optical body of claim 24, wherein said second phase comprises syndiotactic polystyrene.

26. The optical body of claim 21, wherein said second phase also comprises at least one thermoplastic polymer.

27. The optical body of claim 1, wherein said optical body is stretched to a stretch ratio of at least about 2.

28. The optical body of claim 1, wherein said optical body is stretched to a stretch ratio of at least about 4.

29. The optical body of claim 1, wherein said optical body is stretched to a stretch ratio of at least about 6.

30. The optical body of claim 1, wherein said first and second phases are immiscible.

31. The optical body of claim 1, wherein said second phase comprises a plurality of elongated masses whose major axes are substantially aligned along a common axis.

32. The optical body of claim 31, wherein said elongated masses have an aspect ratio of at least about 2.

33. The optical body of claim 31, wherein said elongated masses have an aspect ratio of at least about 5.

34. The optical body of claim 1, wherein said second phase comprises a plurality of rod-like structures.

35. The optical body of claim 1, wherein said optical body is oriented in at least two directions.

36. The optical body of claim 1, wherein said second phase is present in an amount of at least about 1% by volume relative to said first phase.

37. The optical body of claim 1, wherein said second phase is present in an amount of about 5% to about 50% by volume relative to said first phase.

38. The optical body of claim 1, wherein said second phase is present in an amount of about 15% to about 30% by volume relative to said first phase.

39. The optical body of claim 1, wherein said second phase is discontinuous along at least two of any three mutually perpendicular axes.

40. The optical body of claim 1, wherein said second phase is discontinuous along any three mutually perpendicular axes.

41. The optical body of claim 1, wherein the diffuse reflectivity of said first and second phases taken together along at least one axis for at least one polarization state of visible, ultraviolet, or infrared electromagnetic radiation is at least about 30%.

42. The optical body of claim 1, wherein the extinction ratio of said optical body is greater than about 3.

43. The optical body of claim 1, wherein the extinction ratio of said optical body is greater than about 5.

44. The optical body of claim 1, wherein the extinction ratio of said optical body is greater than about 10.

45. The optical body of claim 1, wherein the optical body is a film, and wherein the index difference between said first and second phases is less than about 0.05 along an axis perpendicular to the surface of said film.

46. The optical body of claim 45, wherein the diffusely reflected electromagnetic radiation is distributed anisotropically about the axis of specular reflection.

47. The optical body of claim 46, wherein said optical body is stretched in at least one direction, and wherein the diffusely reflected portion of said at least one polarization state of electromagnetic radiation is distributed primarily along or near the surface of a cone whose axis is centered on the stretch direction and whose surface contains the specularly reflected direction.

48. The optical body of claim 46, wherein said second phase comprises elongated inclusions whose axes of elongation are aligned in a common direction, wherein said optical body is stretched in at least one direction, and wherein the diffusely reflected portion of said at least one polarization state of electromagnetic radiation is distributed primarily along or near the surface- of a cone whose axis is centered on the axis of elongation direction and whose surface contains the specularly reflected direction.

49. The optical body of claim 45, wherein diffusely transmitted the electromagnetic radiation is distributed anisotropically about an axis of specular transmission.

50. The optical body of claim 1, wherein said optical body is stretched in at least one direction, wherein at least about 40% of light polarized orthogonal to a first polarization state of light is diffusely transmitted through said optical body, and wherein said diffusely transmitted rays are distributed primarily along or near the surface of a cone whose surface contains the spectrally transmitted direction and whose axis is centered on the stretch direction.

51. The optical body of claim 1, wherein said second phase comprises elongated inclusions whose axes of elongation are aligned in a common direction, wherein said optical body is stretched in at least one direction, and wherein the diffusely transmitted portion of said at least one polarization state of electromagnetic radiation is distributed primarily along or near the surface of a cone whose axis is centered on the axis of elongation direction and whose surface contains the diffusely transmitted direction.

52. The optical body of claim 1, wherein the optical body is a film, and wherein the index difference between said first and second phases is less than about 0.02 along an axis perpendicular to the surface of said film.

53. An optical body, comprising:

a first phase having a birefringence of at least about 0.05; and

a second phase, disposed within said first phase;

wherein the absolute value of the difference in index of refraction of said first and second phases is Δ

n₁, along a first axis and Δ

n₂ along a second axis orthogonal to said first axis, wherein the absolute value of the difference between Δ

n₁, and Δ

n₂ is at least about 0.05, and wherein the diffuse reflectivity of said first and second phases taken together along at least one axis for at least one polarization state of electromagnetic radiation is at least about 30%.

54. The optical body of claim 53, wherein wherein the absolute value of the difference between Δ

n₁ and Δ

n₂ is at least about 0.1.

55. The optical body of claim 53, wherein said first phase has a larger birefringence than said second phase.

56. The optical body of claim 55, wherein the birefringence of said first phase is at least 0.02 greater than the birefringence of said second phase.

57. The optical body of claim 55, wherein the birefringence of said first phase is at least 0.05 greater than the birefringence of said second phase.

58. An optical body, comprising:

a first phase having a birefringence of at least about 0.05; and

a second phase which is discontinuous along at least two of any three mutually orthogonal axes;

wherein the absolute value of the difference in index of refraction of said first and second phases is Δ

n₁, along a first axis and Δ

n₂ along a second axis orthogonal to said first axis, wherein the absolute value of the difference between Δ

n₁, and Δ

n₂ is at least about 0.05, and wherein the diffuse reflectivity of said first and second phases taken together along at least one axis for at least one polarization state of electromagnetic radiation is at least about 30%.