Jonza, James M.; Weber, Michael F.; Ouderkirk, Andrew J.; Stover, Carl A.;

Optical film

An optical film comprising a plurality of layers wherein the refractive index difference between the layers along at least one in-plane axis is greater than the refractive index difference between the layers along an out-of-plane axis. The film has an average reflectivity of at least 60% for a predetermined bandwidth of light incident at 60.degree. from normal to the plane of the film, said light being polarized in a plane defined by the at least one in-plane axis and the out-of-plane axis.

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We claim:

1. A film, comprising:

a plurality of layers;

wherein at least two of the plurality of layers exhibit a refractive index difference between the layers along at least one in-plane axis that is greater than a refractive index difference between the layers along an out-of-plane axis;

and further wherein the film has an average reflectivity of at least 60% for light within an intended bandwidth incident at 60.degree. from normal to the plane of the film said light being polarized in a plane defined by the at least one in-plane axis and the out-of-plane axis.

2. The film of claim 1 wherein the at least two layers are adjacent.

3. The film of claim 1 wherein at least one of the at least two layers is birefringent.

4. The film of claim 3 wherein a refractive index along the out-of-plane axis of the birefringent layer is closer numerically to a refractive index along the out-of-plane axis of the other layer than to a highest in-plane refractive index of the birefringent layer.

5. The film of claim 1 wherein the plurality of layers comprise layers of at least two different materials.

6. The film of claim 5 wherein the plurality of layers comprise alternating layers of at least two different materials.

7. The film of claim 1 wherein the plurality of layers includes layers of a first material and layers of a second material.

8. The film of claim 7 wherein the first and second materials are coextrudable.

9. The film of claim 1 wherein the out-of-plane axis is perpendicular to the at least one in-plane axis.

10. The film of claim 1 wherein the film is oriented along the at least one in-plane axis.

11. The film of claim 1 wherein the refractive index difference along the at least one in-plane axis is at least 0.05.

12. The film of claim 1 wherein the refractive index difference along the at least one in-plane axis is at least 0.2.

13. The film of claim 1 wherein the refractive index difference along the at least one in-plane axis is at least 0.25.

14. The film of claim 1 wherein the refractive index difference along the at least one in-plane axis is at least 0.4.

15. The film of claim 1 wherein the refractive index difference along the out-of-plane axis is less than 0.25.

16. The film of claim 1 wherein the refractive index difference along the out-of-plane axis is less than 0.11.

17. The film of claim 1 wherein the refractive index difference along the out-of-plane axis is less than 0.075.

18. The film of claim 1 wherein the refractive index difference along the out-of-plane axis is less than 0.05.

19. The film of claim 1 wherein the refractive index difference along the out-of-plane axis is less than 0.04.

20. The film of claim 1 wherein the refractive index difference along the out-of-plane axis is less than 0.02.

21. The film of claim 1 wherein the refractive index difference along the out-of-plane axis is less than 0.01.

22. The film of claim 1 wherein the refractive index difference along the out-of-plane axis is about 0.

23. The film of claim 1 wherein a ratio of the refractive index difference along the out-of-plane axis to the refractive index difference along the first in-plane axis is less than 0.5.

24. The film of claim 1 wherein a ratio of the refractive index difference along the out-of-plane axis to the refractive index difference along the first in-plane axis is less than 0.25.

25. The film of claim 1 wherein a ratio of the refractive index difference along the out-of-plane axis to the refractive index difference along the first in-plane axis is less than 0.1.

26. The film of claim 1 wherein a ratio of the refractive index difference along the out-of-plane axis to the refractive index difference along the first in-plane axis is less than 0.05.

27. The film of claim 1 wherein the film is a reflective polarizer.

28. The film of claim 1 wherein the film is an infrared reflective polarizer.

29. The film of claim 1 wherein the film is oriented along the at least one in-plane axis.

30. The film of claim 1 wherein at least two of the plurality of layers exhibit a refractive index difference between layers along a first in-plane axis that is greater than a refractive index difference between layers along a second in-plane axis.

31. The film of claim 30 wherein light of a first polarization orientation which is polarized in a plane defined by the first in-plane axis and the out-of-plane axis is reflected and wherein light of a second polarization orientation which is polarized in a plane defined by the second in-plane axis and the out-of-plane axis is transmitted.

32. The film of claim 31 wherein the light of the first and second polarization orientations is visible light.

33. The film of claim 31 wherein the light of the first and second polarization orientations is infrared light.

34. The film of claim 31 wherein the light of the first and second polarization orientations is red light.

35. The film of claim 31 wherein the light of the first and second polarization orientations is yellow light.

36. The film of claim 31 wherein the light of the first and second polarization orientations is blue light.

37. The film of claim 31 wherein the light of the first and second polarization orientations is green light.

38. The film of claim 31 wherein the light of the first and second polarization orientations is cyan light.

39. The film of claim 31 wherein the light of the first and second polarization orientations is magenta light.

40. The film of claim 31 wherein the light of the first and second polarization orientations has a bandwidth in the visible spectrum.

41. The film of claim 31 wherein the light of the first and second polarization orientations has a bandwidth of about 100 nm in the visible spectrum.

42. The film of claim 30 wherein the refractive index difference along the second in-plane axis is nonzero when the refractive index difference along the out-of-plane axis is nonzero.

43. The film of claim 42 wherein the refractive index difference along the second in-plane axis is of the same sign as the refractive index difference along the out-of-plane axis.

44. The film of claim 43 wherein the refractive index difference along the second in-plane axis and the refractive index difference along the out-of-plane axis are positive.

45. The film of claim 43 wherein the refractive index difference along the second in-plane axis and the refractive index difference along the out-of-plane axis are negative.

46. The film of claim 43 wherein the refractive index difference along the out-of-plane axis is greater than the refractive index difference along the second in-plane axis.

47. The film of claim 30 wherein the refractive index difference along the second in-plane axis is less than 0.05.

48. The film of claim 30 wherein the refractive index difference along the second in-plane axis is less than 0.02.

49. The film of claim 30 wherein the refractive index difference along the second in-plane axis is about 0.

50. The film of claim 30 wherein a ratio of the refractive index difference along the second in-plane axis to the refractive index difference along the first in-plane axis is less than 0.5.

51. The film of claim 30 wherein a ratio of the refractive index difference along the second in-plane axis to the refractive index difference along the first in-plane axis is less than 0.25.

52. The film of claim 30 wherein a ratio of the refractive index difference along the second in-plane axis to the refractive index difference along the first in-plane axis is less than 0.1.

53. The film of claim 30 wherein a ratio of the refractive index difference along the second in-plane axis to the refractive index difference along the first in-plane axis is less than 0.05.

54. The film of claim 30 wherein a ratio of the refractive index difference along the second in-plane axis to the refractive index difference along the first in-plane axis is about 0.

55. The film of claim 30 further having an average transmission of at least 80% for light incident normal to the film for light within an intended bandwidth having a first polarization orientation.

56. The film of claim 55 further having an average transmission of at least 85% for light incident normal to the film for light within an intended bandwidth having the first polarization orientation.

57. The film of claim 46 further having an average transmission of at least 60% for light incident 60.degree. from normal to the film for light within an intended bandwidth having the first polarization orientation.

58. The film of claim 57 further having an average transmission of at least 80% for light incident 60.degree. from normal to the film for light within an intended bandwidth having the first polarization orientation.

59. The film of claim 58 further having an average transmission of at least 90% for light incident 60.degree. from normal to the film for light within an intended bandwidth having a first polarization orientation.

60. The film of claim 59 further having an average transmission of at least 95% for light incident 60.degree. from normal to the film for light within an intended bandwidth having a first polarization orientation.

61. The film of claim 55 further having an average reflectance of at least 60% for light incident normal to the film for light within an intended bandwidth having a second polarization orientation.

62. The film of claim 61 further having an average reflectance of at least 80% for light incident normal to the film for light within an intended bandwidth having the second polarization orientation.

63. The film of claim 62 further having an average reflectance of at least 90% for light incident normal to the film for light within an intended bandwidth having the second polarization orientation.

64. The film of claim 63 further having an average reflectance of at least 95% for light incident normal to the film for light within an intended bandwidth having the second polarization orientation.

65. The film of claim 1 wherein the film is oriented in a tenter along the at least one in-plane axis.

66. The film of claim 1 wherein the film is length oriented along the at least one in-plane axis.

67. The film of claim 1 further comprising an anti-reflective coating.

68. The film of claim 1 wherein at least two layers exhibit a refractive index difference between layers along a first in-plane axis and a refractive index difference between layers along a second in-plane axis, and a refractive index difference between layers along the out-of-plane axis such that there is no Brewster angle along the first in-plane axis.

69. The film of claim 1 wherein the at least two layers are birefringent.

70. The film of claim 1 wherein one of the at least two layers is birefringent and the other of the at least two layers is isotropic.

71. The film of claim 1 wherein the plurality of layers comprise birefringent materials.

72. The film of claim 1 wherein the plurality of layers comprise alternating layers of at least two birefringent materials.

73. The film of claim 1 wherein the plurality of layers comprise alternating layers of a birefringent material and an isotropic material.

74. The film of claim 1 wherein the refractive index difference along the out-of-plane axis, the refractive index difference along the first in-plane axis and a refractive index difference along a second in-plane axis are such that film has a Brewster angle of at least 45 degrees for light polarized along the first in-plane axis for an incident medium of index 1.6.

75. The film of claim 1 wherein the film is a mirror.

76. The film of claim 75 wherein the film is oriented along a first in-plane axis and is oriented along a second in-plane axis.

77. The film of claim 75 wherein the film is an infrared mirror.

78. The film of claim 75 wherein the film is a hot mirror.

79. The film of claim 75 wherein the film is a cold mirror.

80. The film of claim 1 wherein light of a first polarization orientation which is polarized in a plane defined by the at least one in-plane axis and the out-of-plane axis is reflected and wherein light of a second polarization orientation which is polarized in a plane defined by a second in-plane axis and the out-of-plane axis is reflected.

81. The film of claim 80 wherein the light of the first and second polarization orientations is visible light.

82. The film of claim 80 wherein the light of the first and second polarization orientations is infrared light.

83. The film of claim 80 wherein the light of the first and second polarization orientations is red light.

84. The film of claim 80 wherein the light of the first and second polarization orientations is yellow light.

85. The film of claim 80 wherein the light of the first and second polarization orientations is blue light.

86. The film of claim 80 wherein the light of the first and second polarization orientations is green light.

87. The film of claim 80 wherein the light of the first and second polarization orientations has a bandwidth in the visible spectrum.

88. The film of claim 80 wherein the light of the first and second polarization orientations has a bandwidth of about 100 nm in the visible spectrum.

89. The film of claim 1 wherein at least two of the plurality of layers exhibit a refractive index difference between layers along a second in-plane axis that is greater than a refractive index difference between layers along the out-of-plane axis.

90. The film of claim 89 wherein the refractive index difference along the first in-plane axis and a refractive index difference along the second in-plane axis are of the opposite sign as the refractive index difference along the out-of-plane axis.

91. The film of claim 90 wherein the refractive index differences along the first and second in-plane axes are negative and the refractive index difference along the out-of-plane axis is positive.

92. The film of claim 90 wherein the refractive index differences along the first and second in-plane axes are positive and the refractive index difference the out-of-plane axis is negative.

93. The film of claim 90 wherein the refractive index difference along the first in-plane axis is of the same sign as the refractive index difference along the second in-plane axis.

94. The film of claim 89 further having an average reflectance of at least 80% for light incident normal to the film for light within an intended bandwidth having the first and second polarization orientation.

95. The film of claim 94 further having an average reflectance of at least 90% for light incident normal to the film for light within an intended bandwidth having the first and second polarization orientations.

96. The film of claim 95 further having an average reflectance of at least 80% for light incident at sixty degrees from normal to the film for light within an intended bandwidth having the first and second polarization orientations.

97. The film of claim 96 further having an average reflectance of at least 90% for light incident normal at sixty degrees from normal to the film for light within an intended bandwidth having the first and second polarization orientations.

98. The film of claim 97 further having an average reflectance of at least 95% for light incident at sixty degrees from normal to the film for light within an intended bandwidth having the first and second polarization orientations.

99. The film of claim 89 wherein the refractive index differences along the first and second in-plane axes are at least 0.05.

100. The film of claim 89 wherein the refractive index differences along the first and second in-plane axes are at least 0.2.

101. The film of claim 89 wherein the refractive index differences along the first and second in-plane axes are at least 0.25.

102. The film of claim 89 wherein the refractive index differences along the first and second in-plane axes are at least 0.4.

103. The film of claim 89 wherein the film has no Brewster angle for light polarized along the first and second in-plane axes for an incident medium of any index.

104. The film of claim 89 wherein the refractive index difference along the out-of-plane axis is such that the film has no Brewster angle for light polarized along the first and second in-plane axes for an incident medium of any index.

105. The film of claim 89 wherein the refractive index difference along the out-of-plane axis and the refractive index differences along the first and second in-plane axes are such that film has a Brewster angle of at least 45 degrees for light polarized along the first and second in-plane axes for an incident medium of index 1.6.

106. The film of claim 105 wherein the refractive index difference along the out-of-plane axis and the refractive index differences along the first and second in-plane axes are such that film has a Brewster angle of at least 60 degrees for light polarized along the first and second in-plane axes for an incident medium of index 1.6.

107. The film of claim 106 wherein the refractive index difference along the out-of-plane axis and the refractive index differences along the first and second in-plane axes are such that film has a Brewster angle of at least 70 degrees for light polarized along the first and second in-plane axes for an incident medium of index 1.6.

108. The film of claim 107 wherein the refractive index difference along the out-of-plane axis and the refractive index differences along the first and second in-plane axes are such that film has a Brewster angle of at least 80 degrees for light polarized along the first and second in-plane axes for an incident medium of index 1.6.

109. The film of claim 1 wherein the film has more than 2 layers.

110. The film of claim 1 wherein the film has at least 100 layers.

111. The film of claim 1 wherein the film has less than 2000 layers.

112. The film of claim 111 wherein the film has less than 1000 layers.

113. The film of claim 112 wherein the film has less than 500 layers.

114. The film of claim 1 wherein at least one of the plurality of layers is birefringent, and wherein a refractive index of the birefringent layer along the first in-plane axis is at least 0.05 greater than a refractive index of the birefringent layer along the out-of-plane axis.

115. The film of claim 1 wherein at least one of the plurality of layers is birefringent, and wherein a refractive index of the birefringent layer along a second in-plane axis is at least 0.05 greater than the refractive index of the birefringent layer along the out-of-plane axis.

116. The film of claim 1 wherein at least one of the plurality of layers is birefringent, and wherein a refractive index of the birefringent layer along the first in-plane axis is at least 0.05 greater than a refractive index of the birefringent layer along a second in-plane axis.

117. The film of claim 1 wherein the first in-plane axis and a second in-plane axis are perpendicular to each other.

118. The film of claim 117 wherein the out-of-plane axis is perpendicular to both the first and second in-plane axes.

119. The film of claim 1 wherein at least two of the plurality of layers exhibit a refractive index difference between layers along a first in-plane axis that is greater than a refractive index difference between layers along a second in-plane axis;

the film offer having a % RMS color of less than 10% at an angle of at least 45 degrees from an axis perpendicular to the film.

120. The reflective polarizer of claim 119 wherein the % RMS color is determined according to the equation ##EQU3## 121.

121. The film of claim 1 wherein at least two of the plurality of layers exhibit a refractive index difference between layers along a first in-plane axis that is greater than a refractive index difference between layers along a second in-plane axis; the film further having a % RMS color of less than 10% at an angle of at least 60 degrees from an axis perpendicular to the film.

122. The film of claim 1 wherein at least two of the plurality of layers exhibit a refractive index difference between layers along a first in-plane axis that is greater than a refractive index difference between layers along a second in-plane axis;

the film farther having a % RMS color of less than 8% at an angle of at least 45 degrees from an axis perpendicular to the film.

123. The film of claim 1 wherein at least two of the plurality of layers exhibit a refractive index difference between layers along a first in-plane axis that is greater than a refractive index difference between layers along a second in-plane axis;

the film further having a % RMS color of less than 8% at an angle of at least 60 degrees from an axis perpendicular to the film.

124. The film of claim 1 wherein at least two of the plurality of layers exhibit a refractive index difference between layers along a first in-plane axis that is greater than a refractive index difference between layers along a second in-plane axis;

the film further having a % RMS color of less than 3.5% at an angle of at least 45 degrees from an axis perpendicular to the film.

125. The film of claim 1 wherein at least two of the plurality of layers exhibit a refractive index difference between layers along a first in-plane axis that is greater than a refractive index difference between layers along a second in-plane axis;

the film further having a % RMS color of less than 3.5% at an angle of at least 60 degrees from an axis perpendicular to the film.

126. The film of claim 1 wherein at least two of the plurality of layers exhibit a refractive index difference between layers along a first in-plane axis that is greater than a refractive index difference between layers along a second in-plane axis;

the film further having a % RMS color of less than 2.1% at an angle of at least 45 degrees from an axis perpendicular to the film.

127. The film of claim 1 wherein at least two of the plurality of layers exhibit a refractive index difference between layers along a first in-plane axis that is greater than a refractive index difference between layers along a second in-plane axis;

the film further having a % RMS color of less than 2.1% at an angle of at least 60 degrees from an axis perpendicular to the film.