Cholesteric liquid crystal optical bodies and methods of manufacture

• US 20020113937A1
• Filed: 02/22/2001
• Published: 08/22/2002
• Est. Priority Date: 02/22/2001
• Status: Active Grant

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Munter, John David, Kammin, Marvin Ray, Ouderkirk, Andrew John
• Granted Patent: US 6,573,963 B2
• Time in Patent Office: Days
• US Class Current: 349/187
• CPC Class Codes: G02B 5/3016 involving passive liquid crystal elements optical properties of liquid crystals G02F1/0063; polarising elements associated with active liquid crystal devices G02F1/133528

Abstract

An optical body can be formed using cholesteric liquid crystal materials. At least two different coating compositions containing cholesteric liquid crystal material are coated on a substrate. At least a portion of each composition is allowed to interdiffuse to generate a change in pitch along a thickness dimension of the optical body. This optical body can be used, for example, as a reflective polarizer in an optical display.

Claims

1. A method of making an optical body, the method comprising steps of:

coating a first coating composition and a second coating composition onto a substrate, the first coating composition being disposed between the substrate and the second coating composition, the first and second coating compositions being different and each comprising at least one cholesteric liquid crystal material selected from cholesteric liquid crystal compounds and cholesteric liquid crystal monomers;

interdiffusing at least a portion of the second coating composition with the first coating composition; and

forming at least one cholesteric liquid crystal layer from the first and second coating compositions after interdiffusing at least a portion of the second liquid crystal composition on the substrate with the first liquid crystal composition on the substrate.

2. The method of claim 1, wherein the step of coating the first and second coating compositions comprises simultaneously coating the first and second coating compositions on the substrate.

3. The method of claim 2, wherein the step of simultaneously coating the first and second coating compositions comprises simultaneously coating the first and second coating compositions on the substrate using a technique selected from slide coating, curtain coating, extrusion bar coating, and combinations thereof.

4. The method of claim 1, wherein the step of forming at least one cholesteric liquid crystal layer comprises forming at least one cholesteric liquid crystal layer wherein a pitch of the cholesteric liquid crystal layer substantially continuously changes along at least a portion of a thickness dimension of the at least one cholesteric liquid crystal layer.

5. The method of claim 4, wherein the step of forming at least one cholesteric liquid crystal layer comprises forming at least one cholesteric liquid crystal layer wherein a pitch of the cholesteric liquid crystal layer monotonically changes along at least a portion of a thickness dimension of the at least one cholesteric liquid crystal layer.

6. The method of claim 4, wherein the step of forming at least one cholesteric liquid crystal layer comprises forming at least one cholesteric liquid crystal layer wherein a pitch of the cholesteric liquid crystal layer increases to a first pitch value and then decreases to a second pitch value along at least a portion of a thickness dimension of the at least one cholesteric liquid crystal layer.

7. The method of claim 4, wherein the step of forming at least one cholesteric liquid crystal layer comprises forming at least one cholesteric liquid crystal layer wherein a pitch of the cholesteric liquid crystal layer increases to a first pitch value, decreases to a second pitch value, and then increases to a third pitch value along at least a portion of a thickness dimension of the at least one cholesteric liquid crystal layer.

8. The method of claim 1, wherein the first coating composition further comprises a first solvent and the second coating composition further comprises a second solvent and wherein the step of forming at least one cholesteric liquid crystal layer comprises eliminating substantially all of the first and second solvents.

9. The method of claim 1, wherein the at least one cholesteric liquid crystal material of the first coating composition comprises first liquid crystal monomers and the at least one cholesteric liquid crystal material of the second coating composition comprises second liquid crystal monomers and wherein the step of forming at least one cholesteric liquid crystal layer comprises polymerizing the first liquid crystal monomers and the second liquid crystal monomers to form first liquid crystal compounds and second liquid crystal compounds.

10. The method of claim 9, further comprising polymerizing at least a portion of at least one of the first and second liquid crystal monomers prior to completing the step of mixing at least a portion of the first coating composition with the second coating composition.

11. The method of claim 9, wherein the step of mixing at least a portion of the second coating composition into the first coating composition occurs prior to polymerizing any portion of the first and second liquid crystal monomers.

12. The method of claim 9, wherein the step of polymerizing the first liquid crystal monomers and the second liquid crystal monomers comprises copolymerizing at least a portion of the second liquid crystal monomers with at least a portion of the first liquid crystal monomers.

13. The method of claim 1, wherein the first coating composition further comprises a first nematic liquid crystal material and the second coating composition further comprises a second nematic liquid crystal material.

14. The method of claim 13, wherein the first and second cholesteric liquid crystal materials are the same.

15. The method of claim 14, wherein the first and second nematic liquid crystal materials are the same and a ratio by weight of first cholesteric liquid crystal material to first nematic liquid crystal material in the first coating composition is different than a ratio by weight of second cholesteric liquid crystal material to second nematic liquid crystal material in the second coating composition.

16. The method of claim 1, further comprising

coating a third coating composition onto the second coating composition, the second and third coating compositions being different, the third coating composition comprising at least one cholesteric liquid crystal material selected from cholesteric liquid crystals and cholesteric liquid crystal monomers;

and

interdiffusing at least a portion of the third coating composition with the second coating composition.

18. The method of claim 17, wherein disposing a first coating composition comprises disposing the first coating composition on the substrate, the first coating composition comprising cholesteric liquid crystal monomers and nematic liquid crystal monomers.

19. The method of claim 18, wherein disposing a second coating composition comprises disposing the second coating composition on the substrate, the second coating composition comprising the cholesteric liquid crystal monomers and the nematic liquid crystal monomers in a different ratio by weight than the first coating composition.

20. The method of claim 18, wherein forming an optical body comprises polymerizing the cholesteric liquid crystal monomers and the nematic liquid crystal monomers.

21. The method of claim 17, wherein disposing a first coating composition and disposing a second coating composition comprises substantially simultaneously disposing the first and second coating compositions on the substrate.

22. The method of claim 21, wherein the step of simultaneously disposing the first and second coating compositions comprises substantially simultaneously disposing the first and second coating compositions on the substrate using a technique selected from the group consisting of slide coating, coating, curtain coating, extrusion bar coating, and combinations thereof.

23. The method of claim 17, further comprising

disposing, over the second coating composition, a third coating composition comprising a third solvent and a third cholesteric liquid crystal material selected from the group consisting of cholesteric liquid crystals and cholesteric liquid crystal monomers;

and

interdiffusing at least a portion of the third coating composition with at least a portion of the second coating composition before eliminating substantially all of the second solvent and before eliminating substantially all of the third solvent.

24. The method of claim 23, wherein eliminating substantially all of the first and second solvents comprises eliminating substantially all of the first, second, and third solvents to form an optical body comprising at least one cholesteric liquid crystal layer, including the first, second, and third coating compositions, with a pitch that substantially continuously changes along at least a portion of the thickness dimension of the layer.

26. The optical body of claim 25, wherein, along a thickness dimension of the layer, a pitch of the cholesteric liquid crystal layer begins at a first pitch at a first major surface of the cholesteric liquid crystal layer, increases to a second pitch, decreases to a third pitch, and increases to a fourth pitch.

27. The optical body of claim 25, wherein, along a thickness dimension of the layer, a pitch of the cholesteric liquid crystal layer begins at a first pitch at a first major surface of the cholesteric liquid crystal layer, increases to a second pitch, decreases to a third pitch, and increases to a fourth pitch at a second major surface of the cholesteric liquid crystal layer.

17. A method of making an optical body, the method comprising:

disposing a first coating composition on a substrate, the first coating composition comprising a first solvent and a first cholesteric liquid crystal material selected from cholesteric liquid crystals and cholesteric liquid crystal monomers;

disposing a second coating composition on the first coating composition, the second coating composition comprising a second solvent and a second cholesteric liquid crystal material selected from the group consisting of cholesteric liquid crystals and cholesteric liquid crystal monomers, wherein the first and second coating compositions are different;

interdiffusing at least a portion of the second coating composition with at least a portion of the first coating composition before eliminating substantially all of the first solvent and before eliminating substantially all of the second solvent;

eliminating substantially all of the first and second solvents; and

forming at least one cholesteric liquid crystal layer from the first and second coating compositions, the cholesteric liquid crystal layer having a pitch that substantially continuously changes over a range of values along at least a portion of a thickness dimension of the layer.

25. An optical body, comprising:

a cholesteric liquid crystal layer wherein, along a thickness dimension of the layer, a pitch of the cholesteric liquid crystal layer begins at a first pitch, increases to a second pitch, decreases to a third pitch, and increases to a fourth pitch.

28. An optical display, comprising:

a display medium; and

a reflective polarizer comprising a cholesteric liquid crystal layer wherein, along a thickness dimension of the layer, a pitch of the cholesteric liquid crystal layer begins at a first pitch, increases to a second pitch, decreases to a third pitch, and increases to a fourth pitch.

29. A method of making an optical display, comprising:

coating a first coating composition and a second coating composition onto a substrate, the first coating composition being disposed between the substrate and the second coating composition, the first and second coating compositions being different and each comprising at least one cholesteric liquid crystal material selected from cholesteric liquid crystal compounds and cholesteric liquid crystal monomers;

interdiffusing at least a portion of the second coating composition with the first coating composition;

forming at least one cholesteric liquid crystal layer from the first and second coating compositions only after interdiffusing at least a portion of the second liquid crystal composition on the substrate with the first liquid crystal composition on the substrate;

forming a reflective polarizer comprising the at least one cholesteric liquid crystal layer and the substrate; and

forming a liquid crystal display using the reflective polarizer and a display medium.