Optical compensation films based on stretched polymer films
The present invention provides uniaxially stretched polymer films that have a refractive index profile suitable for use as negative A-plates or biaxial birefringent plates in a liquid crystal display (LCD) device. These wave plates can be used to compensate for the phase retardations existing in various modes of LCDs including TN (twisted nematic), VA (vertically aligned), IPS (in-plane switching), and OCB (optically compensated bend), and therefore improving the viewing quality of the displays.
1. A uniaxially stretched polymer film having a refractive index profile of n x <n y ≦n z , which satisfies the relation of n y −n x >0.001, wherein n x is the in-plane refractive index parallel to the film stretching direction, n y is the in-plane refractive index perpendicular to n x , and n z is the thickness refractive index, where the stretched polymer film is prepared by stretching an unstretched polymer film made from a polymer capable of being solution cast into a positive C plate with a refractive index profile of n x =n y <n z and the relation of n z −(n x +n y )/2>0.002, wherein the unstretched polymer film is prepared by solution casting a polymer solution comprising a polymer having a moiety of
wherein R 1 , R 2 , and R 3 are each independently hydrogen atoms, alkyl groups, substituted alkyl groups, or halogens, wherein OASU is an optically anisotropic sub-unit that is a substituted aromatic group, a disk-like group, or a mesogen, and wherein OASU is attached to the polymer backbone through a single covalent bond.
2. The uniaxially stretched polymer film of claim 1 , having a refractive index profile of n x <n y =n z .
3. The uniaxially stretched polymer film of claim 2 , wherein the unstretched polymer film has a positive birefringence, which satisfies the relations of n z >n x =n y and n z −(n x +n y )/2>0.002.
4. The uniaxially stretched polymer film of claim 3 , wherein the unstretched polymer film has a positive birefringence n z −(n x +n y )/2 greater than 0.003.
5. The uniaxially stretched polymer film of claim 3 , wherein the unstretched polymer film has a positive birefringence n z −(n x +n y )/2 greater than 0.005.
6. The uniaxially stretched polymer film of claim 2 , which satisfies the relation of n y −n x >0.002.
7. The uniaxially stretched polymer film of claim 2 , which satisfies the relation of n y −n x >0.003.
8. The uniaxially stretched polymer film of claim 1 , wherein the stretched polymer film is a free standing film, and wherein said stretched polymer film has n y −n x in the range of ≧0.001 to 0.05.
9. The uniaxially stretched polymer film of claim 8 , wherein n y −n x is in the range of 0.002 to 0.05.
10. The uniaxially stretched polymer film of claim 9 , wherein n y −n x is in the range of 0.003 to 0.05.
11. The uniaxially stretched polymer film of claim 10 , wherein n y −n x is in the range of 0.004 to 0.05.
12. The uniaxially stretched polymer film of claim 1 , wherein said polymer film is a coating deposited on a substrate, and wherein said polymer film has a refractive index profile of n x <n y =n z , and n y −n x in the range of 0.003 to 0.1.
13. The uniaxially stretched polymer film of claim 12 , wherein n y −n x in the range of 0.005 to 0.1.
14. The uniaxially stretched polymer film of claim 13 , wherein n y −n x in the range of 0.01 to 0.1.
15. The uniaxially stretched polymer film of claim 14 , wherein n y −n x in the range of 0.02 to 0.1.
16. The uniaxially stretched polymer film of claim 1 , wherein the extension ratio of the stretched polymer film is from 2% to 200% and the stretched polymer film has n y −n x in the range of ≧0.001 to 0.1.
17. The uniaxially stretched polymer film of claim 16 , wherein the extension ratio of the stretched polymer film is from 2% to 200% and the stretched polymer film has n y −n x in the range of ≧0.001 to 0.05.
18. The uniaxially stretched polymer film of claim 16 , wherein the extension ratio of the stretched polymer film is from 2% to 100% and the stretched polymer film has n y −n x in the range of ≧0.001 to 0.1.
19. The uniaxially stretched polymer film of claim 18 , wherein the extension ratio of the stretched polymer film is from 2% to 100% and the stretched polymer film has n y −n x in the range of ≧0.001 to 0.05.
20. The uniaxially stretched polymer film of claim 1 , wherein the polymer is selected from the group consisting of poly(nitrostyrene), poly(bromostyrene), poly(iodostyrene), poly(4-methylstyrene-co-nitrostyene), poly(cyanostyrene), poly(vinylbiphenyl), poly(N-vinyl-4-tert-butylphthalimide), poly(2-vinylnaphthalene), poly[2,5-bis(p-alkoxyphenyl)styrene], and poly {2,5-bis[5-(4-alkoxyphenyl)-1,3,4-oxadiazole]styrene}.
21. The uniaxially stretched polymer film of claim 1 , wherein the polymer is poly(nitrostyrene) or poly(bromostyrene).
22. The uniaxially stretched polymer film of claim 1 , having a refractive index profile of n x <n y <n z , which satisfies the relations of n y −n x >0.002 and n z −(n x +n y )/2>0.002.
23. The uniaxially stretched polymer film of claim 22 , wherein the unstretched polymer film has a positive birefringence n z −(n x +n y )/2 greater than 0.003.
24. The uniaxially stretched polymer film of claim 23 , wherein the unstretched polymer film has a positive birefringence n z −(n x +n y )/2 greater than 0.004.
25. The uniaxially stretched polymer film of claim 22 , which satisfies the relations of n y −n x >0.003 and n z −(n x +n y )/2>0.002.
26. The uniaxially stretched polymer film of claim 25 , which satisfies the relations of n y −n x >0.004 and n z −(n x +n y )/2>0.002.
27. The uniaxially stretched polymer film of claim 22 , wherein the extension ratio of the stretched polymer film is from about 2% to about 200%, and the stretched polymer film has n y −n x from about 0.002 to about 0.1 and n z −(n x +n y )/2 from ≧0.002 to 0.05.
28. The uniaxially stretched polymer film of claim 27 , wherein the extension ratio of the stretched polymer film is from 2% to 200% and the stretched polymer film has n y −n x from 0.002 to 0.05 and n z −(n x +n y )/2 from ≧0.002 to 0.025.
29. The uniaxially stretched polymer film of claim 17 , wherein the extension ratio of the stretched polymer film is from 2% to 100% and the stretched polymer film has n y −n x from 0.002 to 0.1 and n z −(n x +n y )/2 from ≧0.002 to 0.05.
30. The uniaxially stretched polymer film of claim 29 , wherein the extension ratio of the stretched polymer film is from 2% to 100% and the stretched polymer film has n y −n x from 0.002 to 0.05 and n z −(n x +n y )/2 from ≧0.002 to 0.025.
31. The uniaxially stretched polymer film of claim 22 , wherein the polymer is poly(bromostyrene).
32. An LCD device comprising a retardation compensation film that is a uniaxially stretched polymer film of claim 1 .
33. The LCD device of claim 32 , wherein the device is an IPS-LCD.