Methods for Fabricating Thermochromic Filters

• US 20100045924A1
• Filed: 08/20/2009
• Published: 02/25/2010
• Est. Priority Date: 08/20/2008
• Status: Active Grant

• Current Assignee: Ravenbrick, LLC
• Original Assignee: Ravenbrick, LLC
• Inventors: Powers, Richard M., McCarthy, Wil
• Granted Patent: US 8,665,414 B2
• Time in Patent Office: Days
• US Class Current: 349/190
• CPC Class Codes: C09K 2219/13 used in the technical field of thermotropic switches
• CPC Class Codes: F24S 10/00 Solar heat collectors using working fluids
• CPC Class Codes: F24S 50/80 for controlling collection or absorption of solar radiation
• CPC Class Codes: G02B 5/23 Photochromic filters
• CPC Class Codes: G02F 1/132 Thermal activation of liquid crystals exhibiting a thermo-optic effect
• CPC Class Codes: G02F 1/133305 Flexible substrates, e.g. plastics, organic film
• CPC Class Codes: G02F 1/1334 based on polymer dispersed liquid crystals, e.g. microencapsulated liquid crystals
• CPC Class Codes: G02F 1/1339 Gaskets; Spacers; Sealing of cells
• CPC Class Codes: Y02E 10/44 Heat exchange systems

Abstract

Thermochromic liquid crystal filters are fabricated by providing two polarizers oriented at offset polarity with respect to each other; providing alignment structures adjacent the inner surfaces of the polarizers; placing a plurality of spacers between the polarizers; and filling a space created by the spacers with a thermotropic liquid crystal that acts as a wave block in an isotropic state and acts as a depolarizer in a nematic state. Alternatively, the filters can be created by encapsulating a thermochromic liquid crystal with a polymer material to form a flexible film and orienting the thermochromic liquid crystal in the polymer material to create a structure that functions as a thermochromic optical filter. Such filters can control the flow of light and radiant heat through selective reflection, transmission, absorption, and/or re-emission. The filters have particular application in passive or active light-regulating and temperature-regulating films, materials, and devices, and particularly as construction materials.

Claims

1. A method for constructing a flexible thermochromic liquid crystal filter comprising

providing a first polarizer film and a second polarizer film each having inner surfaces facing the other;

orienting the second polarizer film to provide an offset polarity with respect to the first polarizer film;

providing a first alignment structure adjacent the inner surface of the first polarizer film and a second alignment structure adjacent the inner surface of the second polarizer film

placing a plurality of spacers between the first polarizer film and the second polarizer film; and

filling a space created by the spacers between the first polarizer film and the second polarizer film with a thermotropic liquid crystal that acts as a wave block in an isotropic state and acts as a depolarizer film in a nematic state.

2. The method of claim 1, further comprising adhering an ultraviolet blocking film to either the first polarizer film or the second polarizer film.

3. The method of claim 1, further comprising adhering a low-emissivity film to either the first polarizer film or the second polarizer film.

4. The method of claim 1 further comprising applying a layer of adhesive to an outer surface of either the first polarizer film or the second polarizer film to adhere the thermochromic liquid crystal filter to a structure.

5. The method of claim 1 further comprising adhering a fixed or removable protective material or coating to an outer surface of either the first polarizer film or the second polarizer film.

6. The method of claim 1 further comprising selecting a reflective polarizer material as the first polarizer film, the second polarizer film, or both.

7. The method of claim 1, wherein the operation of providing the first and second alignment structures further comprises rubbing or scratching the inner surfaces of the first polarizer film and the second polarizer film parallel to the polarization of the first polarizer film and the second polarizer film, respectively.

8. The method of claim 1, wherein the operation of providing the first and second alignment structures further comprises patterning a surface imprint upon the first polarizer film and the second polarizer film to create the first and second alignment structures.

9. The method of claim 1, wherein

the operation of providing the first polarizer film and the second polarizer film further comprises providing a wire grid polarizer fixed within a polymer film for one or both of the first polarizer film or the second polarizer film, wherein the wire grid polarizer forms a surface pattern in the polymer film;

and

the operation of providing the first and second alignment structures further is fulfilled by the surface pattern in the polymer film formed by the wire grid polarizer.

10. The method of claim 1, wherein the operation of providing the first and second alignment structures further comprises selecting the first polarizer film, the second polarizer film, or both in the form of a stretched polymer sheet, wherein the first and second alignment structures are formed by polymer alignment in the stretched polymer sheet.

11. The method of claim 1, wherein the placing operation further comprises mixing the spacers with the thermotropic liquid crystal before the filling operation.

12. The method of claim 1, wherein the thermochromic liquid crystal filter is fabricated to be a flexible material.

13. The method of claim 1 further comprising selecting a size of the spacers to control a thickness of the thermotropic liquid crystal to ensure function of the thermotropic liquid crystal as a wave block.

14. The method of claim 1, wherein the operation of placing a plurality of spacers further comprises selecting the first polarizer film, the second polarizer film, or both to have a plurality of raised structures formed on the inner surface that separate the first polarizer film from the second polarizer film.

15. The method of claim 1 further comprising forming interconnections between the inner surface of the first polarizer film and the inner surface of the second polarizer film.

16. The method of claim 15, wherein the operation of forming interconnections further comprises mixing an adhesive with the thermotropic liquid crystal that provides adherence between the spacers, the first polarizer film, and the second polarizer film.

17. The method of claim 15, wherein the operation of forming interconnections further comprises coating the spacers with an adhesive to adhere the spacers to the first polarizer film and the second polarizer film.

18. The method of claim 15, wherein the interconnections limit the thickness of the thermochromic liquid crystal filter.

19. The method of claim 15, wherein the interconnections seal the thermotropic liquid crystal into a plurality of regions.

20. The method of claim 15, wherein operation of forming the interconnections further comprises one or more of the following:

melting the spacers, the first polarizer film and the second polarizer film, or all to attach the spacers to first and second polarizer films;

chemically attaching the spacers to the inner surfaces of the first and second polarizer films;

mixing the thermochromic liquid crystals with a polymer stabilizer that attaches to the inner surfaces of the first and second polarizer films;

fixing portions of the inner surfaces of the first and second polarizer films together using one or more of pressure, heat, radiation, or light;

or

forming spherical structures between the first and second polarizer films and filling the spherical structures with the thermochromic liquid crystal.

21. The method of claim 1, wherein the filling operation is performed by one or more if the following processes:

vacuum loading, inkjet application, capillary action, “

slop and glop,”

pressure, or immersion.

22. The method of claim 1 further comprising sealing the portions of the inner surface of the first polarizer film to corresponding portions of the inner surface of the second polarizer film to create independent sections of the flexible thermochromic liquid crystal filter that can be cut apart, wherein the sealing operation is performed by one or more of the following processes:

pressure, heat, radiation, or light;

laser cutting;

water cutting,

adhering with adhesives, glues, or polymers;

sealing with a heat sealing knife;

sealing with an adhesive installing, sealing knife;

or

inserting gaskets to subdivide the filter into independent sections, wherein each section is enclosed by a individual gasket.

23. The method of claim 1, further comprising inserting a conductive layer having multiple connection points between the first polarizer film and the second polarizer film to provide an electrochromic override, wherein it is possible to both cut and seal the filter and still provide a conductive channel.

24. The method of claim 1 further comprising removing or relocating air bubbles in the thermotropic liquid crystal filters using one or more of the following processes:

chemical or physical absorption of the components of the air in layers or components of the filter;

directed pressure;

gravity;

capillary action;

or

vibration.

25. The method of claim 1 further comprising balancing wettability, surface tension, and capillary forces of the liquid crystal such that the liquid crystal functions as the spacers and further as a tensioner between the first polarizer film and the second polarizer film.

26. The method of claim 1 further comprising

receiving the first polarizing film from a first continuous web or first substantially continuous roll;

receiving the second polarizing film from a second continuous web or second substantially continuous roll; and

transferring the flexible thermochromic liquid crystal filter once completed to a roll.

27. The method of claim 1 further comprising

receiving the first polarizing film from a first continuous web or first substantially continuous roll;

receiving the second polarizing film from a second continuous web or second substantially continuous roll; and

cutting the flexible thermochromic liquid crystal filter once completed into sheets.

28. A method for constructing a thermochromic filter comprising

encapsulating a thermochromic liquid crystal with a polymer material to form a flexible film;

and

orienting the thermochromic liquid crystal in the polymer material to create a structure that functions as a thermochromic optical filter.

29. The method of claim 28, wherein the operation of encapsulating further comprises sandwiching the thermochromic liquid crystal between sheets of the polymer material.

30. The method of claim 28, wherein

the orienting operation further comprises applying an electric field to the thermochromic liquid crystal to match an optical index of the thermochromic liquid crystal to an optical index of the polymer material;

and

the encapsulating operation further comprises

mixing the thermochromic liquid crystal with the polymer material; and

photopolymerizing the polymer material to create encapsulated regions of liquid crystal within the polymer material.

31. The method of claim 28 further comprising doping the thermochromic liquid crystal with an additive that together form the thermochromic optical filter.

32. The method of claim 31, wherein the additive comprises dye molecules.

33. The method of claim 31 further comprising selecting the thermochromic liquid crystal, the additive, or both to be one or more of thermoreflective, thermodarkening, thermodiffusive, or thermofluorescent.

34. The method of claim 28 further comprising adhering a polarizer film to the flexible material to effect changes in transmission, reflection, and absorption of the filter.