Low birefringent light redirecting film

• US 20070014020A1
• Filed: 07/13/2005
• Published: 01/18/2007
• Est. Priority Date: 07/13/2005
• Status: Abandoned Application

• Current Assignee: Rohm and Haas Denmark Finance A/S
• Original Assignee: Eastman Kodak Company
• Inventors: Bourdelais, Robert, Neerbasch, Steven, Brickey, Cheryl
• Application Number:
  US11/180,942
• Publication Number:
  US 20070014020A1
• Time in Patent Office: Days
• US Class Current: 359/619
• CPC Class Codes: G02B 6/0053 Prismatic sheet or layer; Brightness enhancement element, sheet or layer
• CPC Class Codes: G02B 6/0065 Manufacturing aspects; Material aspects

Abstract

The invention relates to a polymeric optical film comprising a base provided with integral optical features on at least one side, wherein the features have two or more sides that form a ridge line, wherein the optical film has light leakage through crossed polarizers of less than 1.0%.

Claims

1. A polymeric optical film comprising a base provided with integral optical features on at least one side, wherein the features have two or more sides that form a ridge line, wherein the optical film has light leakage through crossed polarizers of less than 1.0%.

2. The polymeric optical film of claim 1 wherein said light leakage is between 0.05 and 0.5%.

3. The polymeric optical film of claim 1 wherein said light leakage is between 0.05 and 0.2%.

4. The polymeric film of claim 1 wherein said film comprises individual integral features.

5. The polymeric film of claim 1 wherein said film comprises integral features comprises elongated parallel ridges.

6. The polymeric film of claim 1 wherein said film comprises individual integral features wherein at least one side of said features is curved.

7. The polymeric film of claim 1 wherein the polymeric film has a birefringence of between 1.0×

10<sup>−

5</sup> to 5.0×

10<sup>−

3</sup>.

8. The polymeric film of claim 1 wherein said polymeric film comprises cellulose triacetate polymer.

9. The polymeric film of claim 1 wherein said polymeric film comprises cyclo-olefin.

10. The polymeric film of claim 1 wherein said integral features comprise curved wedge shaped features in the plane of the film, having a length in the range of 800 to 3000 micrometers.

11. The polymeric film of claim 1 wherein said integral features comprise curved wedge shaped features in the plane of the film, having a length in the range of 100 to 600 micrometers.

12. A liquid crystal display device comprising a polymeric optical film comprising a base provided with integral optical features on at least one side, wherein the features have two or more sides that form a ridge line, wherein the optical film has light leakage through crossed polarizers of less than 1.0%.

13. The liquid crystal display device of claim 12 wherein said polymeric optical film is located between a reflective polarizer and a first absorptive polarizer of said liquid crystal display device.

14. The liquid crystal display device of claim 12 wherein said polymeric optical film is located between a polarizing light guide plate and the first occurrence of an absorptive polarizer.

15. The liquid crystal display device of claim 12 wherein said integral features comprise curved wedge shaped features in the plane of the film, having a length in the range of 800 to 3000 micrometers.

16. The liquid crystal display device of claim 12 wherein said integral features comprise curved wedge shaped features in the plane of the film, having a length in the range of 100 to 600 micrometers.

17. The liquid crystal display device of claim 12 wherein said film comprises individual integral features.

18. The liquid crystal display device of claim 12 wherein said polymeric optical film is located between the first occurrence of an absorptive polarizer and the second occurrence of an absorptive polarizer.

19. The liquid crystal display device of claim 12 wherein the polymeric film has a birefringence of between 1.0×

10<sup>−

5</sup> to 5.0×

10<sup>−

3</sup>.

20. The liquid crystal display device of claim 12 wherein said polymeric film comprises cellulose triacetate polymer.

21. The liquid crystal display device of claim 12 further comprising a visible low birefringence light diffuser having a birefringence between 1.0×

10<sup>−

5</sup> to 5.0×

10<sup>−

3</sup>.

22. A process of forming a polymeric optical film comprising solvent casting a low birefringent polymer, partially evaporating the solvent to form a base, embossing the base to form integral features, wherein the features have two or more sides that form a ridge line, wherein the optical film a light leakage through crossed polarizers of less than 1%.

23. The process of claim 22 wherein the low birefringent polymer containing the remaining solvent from the casting surface is removed from the casting surface prior to embossing.

24. The process of claim 22 wherein said low birefringent polymer is solvent cast onto a carrier sheet comprising an oriented sheet of polymer with an average surface roughness between 0.02 and 0.25 micrometers.

25. The process of claim 24 wherein carrier sheet comprises a pattern on at least one side.

26. The process of claim 22 wherein said low birefringent light redirecting film has birefringence between 1.0×

10<sup>−

5</sup> to 5.0×

10<sup>−

3</sup>.

27. The process of claim 22 wherein said integral features comprises individual integral features wherein at least one side of said features is curved.

28. The process of claim 22 wherein said solvent cast low birefringent polymer has a solvent content between 15 and 40% by weight of low birefringent polymer at the time of embossing.

29. The process of claim 22 wherein said low birefringent polymer is amorphous.

30. The process of claim 22 wherein said low birefringent polymer comprises polycarbonate.

31. The process of claim 22 wherein said low birefringent polymer comprises cellulose triacetate.

32. A process of forming a polymeric optical film comprising simultaneously melt casting a polymer and at least one sacrificial surface polymer layer polymer against a roller containing concave features having two or more sides that form a crevice line, removing the composite polymer sheet from said roller to form a composite having integral features, wherein the features have two or more sides that form a ridge line, and stripping said at least one sacrificial layer, wherein the optical film a light leakage through crossed polarizers of less than 1%.

33. The process of claim 32 wherein said at least one sacrificial surface polymer layer comprises two sacrificial surface layers.

34. The process of claim 32 wherein said optical film has a birefringence of between 1.0×

10<sup>−

5</sup> to 5.0×

10<sup>−

3</sup>.

35. The process of claim 32 wherein said sacrificial polymer comprises polyolefin.