Diffusively reflective circular polarizer formed by thermo phase separation

• US 20050052595A1
• Filed: 09/08/2003
• Published: 03/10/2005
• Est. Priority Date: 09/08/2003
• Status: Active Grant

• Current Assignee: Yao-Dong Ma
• Original Assignee: Yao-Dong Ma
• Inventors: Ma, Yao-Dong
• Granted Patent: US 7,095,466 B2
• Time in Patent Office: Days
• US Class Current: 349/112
• 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

The present invention relates to a circular polarizer, more specifically, to a diffusively reflective circular polarizer (DRCP), which is characterized by broadband reflection and transmission over a hemispheric viewing angle. A thermo phase separation process of a cholesteric liquid crystal polymer system creates the DRCP film. As a multi-functional optical material, the DRCP film combines the merits of polarizer, reflector and diffuser to form an all-in-one component in the electro-optical industry. Moreover, since the novel film has a “silver white” appearance and super “hiding power”, it will initiate many other applications.

Claims

1. A diffusively reflective polarizer comprising:

a. a cholesteric film of at least two polymeric liquid crystals having a discrete microchip structure, and

b. at least one alignment layer attached to at least one surface of the film;

wherein a plurality of microchips having discrete reflection wavelengths are dispersed at least two dimensionally in the cholesteric film confined by the alignment layer as a result of a phase separation process of the polymeric liquid crystals;

whereby a silver white broadband reflection of circular polarization with an approximately hemispherical viewing angle is displayed on the polarizer.

2. The diffusively reflective polarizer as in claim 1 wherein the polymeric liquid crystals have different mesomorphic structure.

3. The diffusively reflective polarizer as in claim 1 wherein the polymeric liquid crystals have different physic-chemical miscibility.

4. The diffusively reflective polarizer as in claim 1 wherein the cholesteric film is a thermoplastic polymer.

5. The diffusively reflective polarizer as in claim 1 wherein the cholesteric film is a UV cureable thermo-set polymer.

6. The diffusively reflective polarizer as in claim 1 wherein the discrete microchip structure is a composite structure of polymeric liquid crystals with different proportion.

7. The diffusively reflective polarizer as in claim 1 wherein the discrete microchip structure has a diameter in the range of 5˜

30 micrometer.

8. The diffusively reflective polarizer as in claim 1 wherein the discrete microchip structure has at least two dimensional randomized distribution within the cholesteric film.

9. The diffusively reflective polarizer as in claim 1 wherein the discrete microchip structure has a symmetry helical axis which is normally distributed along the normal direction of the cholesteric film.

10. The diffusively reflective polarizer as in claim 1 wherein the phase separation is a thermo phase separation.

11. The diffusively reflective polarizer as in claim 1 wherein the broadband reflection of circular polarization covers substantially the visible bandwidth.

12. The diffusively reflective polarizer as in claim 1 wherein the broadband reflection of circular polarization covers at least a portion of the invisible bandwidth.

13. A method of fabricating a diffusively reflective polarizer comprising the step of:

a. forming a substantially homogenous mixture of the first polymeric liquid crystal and the second polymeric liquid crystal at a sufficiently high temperature,

b. applying the mixture onto at least one substrate with a predetermined surface condition to form a layer with a predetermined thickness while maintaining the mixture at mesomorphic phase,

c. forming a film with a specula narrow band Bragg reflection,

d. cooling the film to the room temperature at a predetermined speed,

e. maintaining a sufficiently low temperature for a controllable duration to let the first polymeric liquid crystal and the second polymeric liquid crystal partially separated into a plurality of discrete microchips.

wherein the microchips having a plurality of reflection wavelengths are dispersed at least two dimensionally in the cholesteric film as a result of the thermo phase separation of the polymeric liquid crystals;

whereby a broadband diffusively reflective polarizer is formed.

14. The method of fabricating a diffusively reflective polarizer as in claim 13 wherein the layer with predetermined thickness has the thickness in the range of 5˜

40 μ

m.

15. The method of fabricating a diffusively reflective polarizer as in claim 13 wherein the sufficiently low temperature is in the range of −

30˜

30°

C.

16. The method of fabricating a diffusively reflective polarizer as in claim 13 wherein the controllable duration is in the range of 1˜

24 hours.

17. The method of fabricating a diffusively reflective polarizer as in claim 13 wherein the homogenous mixture is also including a UV initiator.

18. The method of fabricating a diffusively reflective polarizer as in claim 13 further including a UV-beam exposure step to make the polarizer high-temperature stable.

19. A method of fabricating an inter-convertible polarizer comprising the step of:

a. forming a substantially homogenous mixture of the first polymeric liquid crystal and the second polymeric liquid crystal at a sufficiently high temperature,

b. applying the mixture onto at least one substrate with a predetermined surface condition to form a layer with a predetermined thickness while maintaining the mixture at mesomorphic phase,

c. forming a film with a specula narrow band Bragg reflection,

d. cooling the film to the room temperature at a predetermined speed,

e. maintaining a sufficiently low temperature for a controllable duration to let the first polymeric liquid crystal and the second polymeric liquid crystal partially separated into a plurality of discrete microchip structure, f heating the polarizer film in the predetermined area at a sufficiently high temperature to make the discrete microchip structure to the homogenous cholesteric structure,

g. repeating step d., and e., whereby the diffusively broadband polarizer and the specula narrow band polarizer is interchangeable to each other.

20. The method of fabricating an inter-convertible polarizer as in claim 19 wherein the conversion from narrow band polarizer to broadband polarizer is through the phase separation step.

21. The method of fabricating an inter-convertible polarizer as in claim 19 wherein the conversion from broadband polarizer to narrow band polarizer is through the phase unification step.

22. The method of fabricating an inter-convertible polarizer as in claim 19 wherein the step of heating the polarizer film in a predetermined area is a thermo-scan imaging process.