Diffusively reflective circular polarizer formed by thermo phase separation

• US 7,095,466 B2
• Filed: 09/08/2003
• Issued: 08/22/2006
• Est. Priority Date: 09/08/2003
• Status: Expired due to Fees

• Current Assignee: Yao-Dong Ma
• Original Assignee: Yao-Dong Ma
• Inventors: Ma, Yao-Dong
• Primary Examiner(s): TON, MINH TOAN T
• Application Number:
  US10/657,676
• Publication Number:
  US 20050052595A1
• Time in Patent Office: 1,079 Days
• Field of Search: 349/115, 349/112, 349/176, 349/187
• US Class Current: 349/115
• 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 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,

c. 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.

2. The method of fabricating a diffusively reflective polarizer as in claim 1 wherein the layer with predetermined thickness has the thickness in the range of 5˜

40 μ

m.

3. The method of fabricating a diffusively reflective polarizer as in claim 1 wherein the sufficiently low temperature is in the range of −

30˜

30°

C.

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

24 hours.

5. The method of fabricating a diffusively reflective polarizer as in claim 1 wherein the homogenous mixture is also including a UV initiator.

6. The method of fabricating a diffusively reflective polarizer as in claim 1 further including a UV-beam exposure step to make the polarizer high-temperature stable.

7. The method of fabricating a difusively reflective polarizer as in claim 1 wherein the first polymeric liquid crystal and the second polymeric liquid crystal have different mesomorphic structure.

8. The method of fabricating a difusively reflective polarizer as in claim 1 wherein the first polymeric liquid crystal and the second polymeric liquid crystal have diferent physic-chemical miscibility.

9. The method of fabricating a difusively reflective polarizer as in claim 1 wherein the cholesteric film is a thermoplastic polymer.

10. The method of fabricating a difusively reflective polarizer as in claim 1 wherein the cholesteric film is a UV cureable thermo-set polymer.

11. The method of fabricating a difusively reflective polarizer as in claim 1 wherein the discrete microchip is a composite structure of polymeric liquid crystals with different proportion.

12. The method of fabricating a difusively reflective polarizer as in claim 1 wherein the discrete microchip has a diameter in the range of 5˜

30 micrometer.

13. The method of fabricating a difusively reflective polarizer as in claim 1 wherein the discrete microchips have at least two dimensional randomized distributions within the cholesteric film.

14. The method of fabricating a diffusively reflective polarizer as in claim 1 wherein the phase separation is a thermo phase separation.

15. The method of fabricating a diffusively reflective polarizer as in claim 1 wherein the broadband difusively reflective polarizer reflects a circular polarization covering substantially the visible bandwidth.

16. The method of fabricating a difusively reflective polarizer as in claim 1 wherein the broadband diffusively reflective polarizer reflects a circular polarization covering at least a portion of the invisible bandwidth.

17. The method of fabricating a difusively reflective polarizer as in claim 1 wherein the narrow band Bragg reflection and the broadband diffusive reflection is inter-convertible.

18. The method of fabricating a difusively reflective polarizer as in claim 17 wherein the conversion from broadband to narrow band is through the phase unification process.