Optical film having controlled scattering/transmitting characteristics
View Patent ↗An optical film composed by laminating a light scattering film 1 scattering and transmitting light and comprising at least two phases or more different in refractive index and a reflective polarizer 2 selectively P/S converting the light. It is preferred that at least one phase of the light scattering film larger in the refractive index has a columnar structure extending in the thickness direction of the film and the transmittance of the film in the normal direction is 4% or more. The optical film is excellent in visibility, is small in light loss in order to provide an excellently visible and bright image, and has an excellent light collecting property when used in a liquid crystal display device or the like.
1. An optical film, for use in a liquid crystal display which comprises a liquid crystal cell and a back light unit, comprising a layered product of,
(1) a reflective polarizer by which light is selectively P/S converted, which is disposed on the back light unit, and
(2) a light scattering film that scatters and transmits light and comprises at least two phases having different refractive indices from each other, which is disposed on the reflective polarizer,
wherein at least one of the phases which has the greater refractive index in the light scattering film has pillar structures extending in the thickness direction of the film, and further where the refractive index changes gradually at the interface of the greater refractive index phase and another phase, and furthermore the transmittance of the light scattering film in the normal direction of the film is not less than 4%, and wherein an absolute value of a light incident angle where the scattering film has a maximum scattering performance is larger than zero degrees, when zero degrees is a light incident angle that light enters the film in the normal direction of the film.
2. The optical film according to claim 1 , wherein axis lines of the pillar structures extending in the thickness direction of the light scattering film are in parallel with each other and the direction of the axis lines thereof are orientated in the normal direction to the film.
3. The optical film according to claim 2 , wherein difference in refractive indices between at least two phases having different indices of the light scattering film is in a range of 0.005 to 0.1.
4. The optical film according to claim 2 , wherein said light scattering film is made from a polymer material having a radiation sensitive property.
5. The optical film according to claim 2 , wherein said reflective polarizer is of a lamination type.
6. The optical film according to claim 2 , wherein said reflective polarizer is of a cholesteric liquid crystal type.
7. The optical film according to claim 1 , wherein axis lines of the pillar structures extending in the thickness direction of the light scattering film are in parallel with each other and the direction of the axis lines are inclined with respect to the normal direction to the film.
8. The optical film according to claim 7 , wherein difference in refractive indices between at least two phases having different refractive indices of the light scattering film is in a range of 0.005 to 0.1.
9. The optical film according to claim 7 , wherein said light scattering film is made from a polymer material having a radiation sensitive property.
10. The optical film according to claim 7 , wherein said reflective polarizer is of a lamination type.
11. The optical film according to claim 7 , wherein said reflective polarizer is of a cholesteric liquid crystal type.
12. The optical film according to claim 1 , wherein difference in refractive indices between at least two phases having different refractive indices of the light scattering film is in a range of 0.005 to 0.1.
13. The optical film according to claim 1 , wherein said light scattering film is made from a polymer material having a radiation sensitive property.
14. The optical film according to claim 1 , wherein said reflective polarizer is of a lamination type.
15. The optical film according to claim 1 , wherein said reflective polarizer is of a cholesteric liquid crystal type.
16. The optical film according to claim 1 , wherein the scattering performance of the scattering film is enhanced when the absolute value of the incident angle changes from zero degrees to the absolute value of the incident angle with a maximum scattering performance, and the scattering performance decreases after the absolute value of the incident angle with maximum scattering performance.
17. The optical film according to claim 1 , wherein the absolute value of the incident angle with a maximum scattering performance is around 20 degrees.