Optical film and polarizing film using the same, and method for improving view angle of the polarizing film

• US 6,912,029 B2
• Filed: 12/17/2001
• Issued: 06/28/2005
• Est. Priority Date: 12/18/2000
• Status: Expired due to Term

• Current Assignee: Nippon Kayaku Company Limited, Polatechno Co.,Ltd.
• Original Assignee: Nippon Kayaku Company Limited, Polatechno Co.,Ltd.
• Inventors: Tanaka, Kouichi
• Primary Examiner(s): Dudek, James A.
• Application Number:
  US10/433,394
• Publication Number:
  US 20040066482A1
• Time in Patent Office: 1,289 Days
• Field of Search: 349/118
• US Class Current: 349/118
• 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 1/133634 the refractive index Nz perpendicular to the element surface being different from in-plane refractive indices Nx and Ny, e.g. biaxial or with normal optical axis

Abstract

The invention provides an optical film prepared by laminating at least one of a first retardation film (2), having a mean in-plane refractive index of n_o and refractive index in the thickness direction of n_e wherein n_e−n_o>0, and at least one of a second retardation film (3) having an in-plane refractive index of n_x in the direction showing the maximum refractive index, refractive index of n_y in the direction perpendicular to the direction described just before, and refractive index in the thickness direction of n_z wherein n_x>n_y≧n_z. The light leakage occurred as the observation point is tilted from the front direction to a direction different from the direction of each absorption axis can be reduced when a plolarizing film is arranged so that the absorption axes will be perpendicular to each other.

Claims

1. An optical film prepared by laminating at least a first retardation film having a mean in-plane refractive index of n_o and a refractive index of n_e in the thickness direction, wherein n_e−

n_o>

0 and Δ

n_p·

d_p=10 to 100 nm when n_e−

n₀=Δ

np and thickness is dp, and at least an achromatic second retardation film having a maximum in-plane refractive index of n_x, a refractive index of n_y in the direction perpendicular to the direction described just before, and a refractive index of n_z in the thickness direction, wherein n_x>

n_y≧

n_z, and Δ

n·

d=120 to 150 nm when n_x−

n_y=Δ

n and thickness is d.

2. An optical film according to claim 1 prepared by laminating at least a third retardation film having a mean in-plane refractive index of n_o and a refractive index in the thickness direction, wherein n_e−

n_o<

0 and |Δ

n_n·

d_n|=10 to 100 nm when n_e−

n_o=Δ

n_n and thickness is d_n.

3. The optical film according to claim 2, wherein the absolute value of the difference between the sum of Δ

n_p·

d_p of the first retardation film and the sum of Δ

n_n·

d_n of the third retardation film is 5 to 80 nm.

4. The optical film prepared by laminating an optical film according to claim 1 and a polarizing element so that the n_x direction of the achromatic second retardation film of the optical film coincides with the direction of the absorption axis of the polarizing element.

5. A polarizing film prepared by laminating an optical film according to claim 2, and a polarizing element so that the n_x direction of the achromatic second retardation film of the optical film coincides with the direction of the absorption axis of the polarizing element.

6. A polarizing film prepared by laminating an optical film according to claim 3, and a polarizing element so that the n_x direction of the achromatic second retardation film of the optical film coincides with the direction of the absorption axis of the polarizing element.

7. A method for improving the view angle of a polarizing element, wherein the optical film according to claim 1 is sandwiched between two polarizing elements disposed so that their absorption axes are perpendicular to each other.

8. A method for improving the view angle of a polarizing element, wherein the optical film according to claim 2 is sandwiched between two polarizing elements disposed so that their absorption axes are perpendicular to each other.

9. A method for improving the view angle of a polarizing element, wherein the optical film according to claim 3 is sandwiched between two polarizing elements disposed so that their absorption axes are perpendicular to each other.

10. The method for improving the view angle of a polarizing element according to claim 7, wherein any one of said polarizing elements is the polarizing film according to claim 5.

11. The method for improving the view angle of a polarizing element according to claim 7, wherein any one of said polarizing elements is the polarizing film according to claim 5.

12. The method for improving the view angle of a polarizing element according to claim 7, wherein any one of said polarizing elements is the polarizing film according to claim 6.

13. The method for improving the view angle of a polarizing element according to claim 8, wherein any one of said polarizing elements is the polarizing film according to claim 4.

14. The method for improving the view angle of a polarizing element according to claim 8, wherein any one of said polarizing elements is the polarizing film according to claim 5.

15. The method for improving the view angle of a polarizing element according to claim 8, wherein any one of said polarizing elements is the polarizing film according to claim 6.

16. The method for improving the view angle of a polarizing element according to claim 9, wherein any one of said polarizing elements is the polarizing film according to claim 4.

17. The method for improving the view angle of a polarizing element according to claim 9, wherein any one of said polarizing elements is the polarizing film according to claim 5.

18. The method for improving the view angle of a polarizing element according to claim 9, wherein any one of said polarizing elements is the polarizing film according to claim 6.

19. A liquid crystal display device comprising the optical film or the polarizing film according to any one of claims 1, 2 or 3.

20. A liquid crystal display device comprising the optical film or the polarizing film according to claim 4.

21. A liquid crystal display device comprising the optical film or the polarizing film according to claim 5.

22. A liquid crystal display device comprising the optical film or the polarizing film according to claim 6.