Optical bodies containing cholesteric liquid crystal material and methods of manufacture

• US 20020159019A1
• Filed: 02/22/2001
• Published: 10/31/2002
• 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: Ebihara, Ikuko, Radcliffe, Marc Dudley, Pokorny, Richard John, Watson, Philip Edwin, Bowley, Christopher Chadwick
• Granted Patent: US 6,917,399 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 includes a substrate and a cholesteric liquid crystal layer disposed on the substrate. The cholesteric liquid crystal layer has a non-uniform pitch along a thickness direction of the layer and comprises a crosslinked polymer material that substantially fixes the cholesteric liquid crystal layer. The crosslinking hinders diffusion of cholesteric liquid crystal material within the cholesteric liquid crystal layer. In other methods of making an optical body, a reservoir of chiral material is provided during the process over a first cholesteric liquid crystal layer to diffuse into the layer and provide a non-uniform pitch. Alternatively, two coating compositions can be disposed on a substrate where the material of the first coating composition is not substantially soluble in the second coating composition.

Claims

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

forming a first cholesteric liquid crystal polymer layer on a substrate using a first coating composition;

coating a second coating composition on the first cholesteric liquid crystal polymer layer, the second coating composition comprising at least one chiral monomer material selected from reactive chiral monomers;

diffusing a portion of the chiral monomer material into a portion of the first cholesteric liquid crystal polymer layer adjacent the second coating composition; and

curing the chiral monomer material to generate at least one cholesteric liquid crystal layer from the first cholesteric liquid crystal polymer layer and the second coating composition, the at least one cholesteric liquid crystal layer having a non-uniform pitch.

2. The method of claim 1, wherein forming a first cholesteric liquid crystal polymer layer comprises coating a first coating composition onto a substrate, the first coating composition comprising at least one cholesteric liquid crystal material selected from cholesteric liquid crystal compounds and cholesteric liquid crystal monomers;

and

polymerizing the first coating composition to form the first cholesteric liquid crystal polymer layer.

3. The method of claim 2, wherein polymerizing the first coating composition comprises polymerizing the first coating composition when exposed to air to establish a gradient of molecular weight throughout at least a portion of the first cholesteric liquid crystal polymer layer, wherein the molecular weight is higher proximal to the substrate.

4. The method of claim 3, wherein diffusing a portion of the chiral monomer material comprises diffusing a portion of the chiral monomer material into a portion of the first cholesteric liquid crystal polymer layer wherein the diffusing is limited by the gradient of molecular weight throughout the first cholesteric liquid crystal polymer layer.

5. The method of claim 1, wherein coating the second coating composition comprising coating the second coating composition on the first cholesteric liquid crystal polymer layer, wherein the second coating composition further comprises a solvent in which the first cholesteric liquid crystal polymer layer is substantially insoluble.

6. The method of claim 1, wherein forming the first cholesteric liquid crystal polymer layer comprises coating the substrate with a first coating composition, the first coating composition comprising a cholesteric liquid crystal polymer.

7. The method of claim 1, wherein curing the chiral monomer material comprises crosslinking the chiral monomer material.

8. The method of claim 7, wherein curing the chiral monomer material comprises crosslinking the chiral monomer material and the first cholesteric liquid crystal polymer layer.

9. The method of claim 8, wherein crosslinking the chiral monomer material and the first cholesteric liquid crystal polymer layer fixes the at least one cholesteric liquid crystal layer to substantially hinder further diffusion of any remaining chiral monomer material.

10. 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.

11. The method of claim 10, 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.

14. The method of claim 13, wherein the chiral compounds of the chiral material of the second coating composition are selected from cholesteric liquid crystal compounds, and cholesteric liquid crystal monomers.

15. The method of claim 13, wherein forming the first layer comprises coating the first coating composition onto the substrate, wherein the at least one cholesteric liquid crystal material of the first coating composition is substantially insoluble in the solvent of the second coating composition.

16. The method of claim 13, wherein forming the first layer comprises coating the first coating composition onto the substrate and curing the first coating composition to form a polymeric liquid crystal material, wherein the polymeric liquid crystal material is substantially insoluble in the solvent of the second coating composition.

17. The method of claim 13, wherein the second coating composition comprises a chiral liquid crystal monomer material and an achiral material, wherein diffusing the second coating composition into the first layer comprises diffusing the chiral liquid crystal monomer material of the second coating composition into the first layer.

18. The method of claim 17, wherein diffusing the chiral liquid crystal monomer comprises diffusing the chiral liquid crystal monomer material into the first layer occurs at a faster rate than diffusing the achiral material into the first layer.

19. The method of claim 13, wherein the second coating composition comprises a chiral monomer material and wherein diffusing the second coating composition into the first layer comprises diffusing the chiral monomer material of the second coating composition into the first layer.

20. The method of claim 19, wherein the second coating composition further comprises an achiral material and wherein the step of diffusing, diffusion of the chiral material into the first layer occurs at a faster rate than diffusion of the achiral material into the first layer.

21. The method of claim 13, wherein the first and second coating compositions each comprise a liquid crystal compound having a spacer, wherein the spacers of the first and second coating compositions differ to provide a different solubility to the respective liquid crystal compounds.

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

forming a first layer on a substrate using a first coating composition, the first coating composition comprising at least one cholesteric liquid crystal material selected from cholesteric liquid crystal compounds and cholesteric liquid crystal monomers;

coating a second coating composition on the first layer, the second coating composition comprising at least one chiral monomer material selected from reactive chiral monomers;

diffusing a portion of the chiral monomer material into a portion of the first layer adjacent the second coating composition; and

crosslinking the chiral monomer material with the first layer to generate and fix at least one cholesteric liquid crystal layer, the at least one cholesteric liquid crystal layer having a non-uniform pitch, the crosslinking substantially hindering further diffusion of any remaining chiral monomer material.

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

forming a first layer on a substrate using a first coating composition;

coating a second coating composition onto the first layer, the first and second coating compositions being different and each of the first and second coating compositions comprising at least one chiral material selected from chiral compounds, the second coating composition further comprising a solvent, wherein the first layer is substantially insoluble in the solvent of the second coating composition; and

diffusing at least a portion of the second coating composition into a portion of the first layer adjacent the second coating composition; and

forming at least one cholesteric liquid crystal layer from the first layer and second coating composition after diffusing the second coating composition into the first layer.

22. An optical body, comprising:

a substrate; and

a cholesteric liquid crystal layer disposed on the substrate, the cholesteric liquid crystal layer having a non-uniform pitch along a thickness direction of the cholesteric liquid crystal layer, the cholesteric liquid crystal layer comprising a crosslinked polymer material that substantially fixes the cholesteric liquid crystal layer to hinder diffusion of cholesteric liquid crystal material within the cholesteric liquid crystal layer.

23. The optical body of claim 22, wherein the pitch of at least a portion of the cholesteric liquid crystal layer changes monotonically along a thickness direction.

24. The optical body of claim 22, wherein at least a portion of the cholesteric liquid crystal layer adjacent the substrate has a uniform pitch.

25. The optical body of claim 22, wherein a portion of the cholesteric liquid crystal layer opposite the substrate has a pitch such that the portion reflects light having a wavelength outside of a range from 400 to 750 nm.

26. An optical display, comprising:

a display medium; and

a reflective polarizer comprising

a substrate; and

a cholesteric liquid crystal layer disposed on the substrate, the cholesteric liquid crystal layer having a non-uniform pitch along a thickness direction of the cholesteric liquid crystal layer, the cholesteric liquid crystal layer comprising a crosslinked polymer material that substantially fixes the cholesteric liquid crystal layer to hinder diffusion of cholesteric liquid crystal material within the cholesteric liquid crystal layer.