Temperature responsive optical limiter, composition and device

Patent metadata

Field	Value
Publication number	US-10073285-B2
Application number	US-201715458055-A
Country	US
Kind code	B2
Filing date	Mar 14, 2017
Priority date	Mar 17, 2016
Publication date	Sep 11, 2018
Grant date	Sep 11, 2018

Abstract

The present invention relates to optical power-limiting devices, and more particularly, to an optical power-limiting passive (self-adaptive) device and to a method for limiting solar power transmission in devices such as windows, using scattering level changes in a novel thermotropic composition that contains salt nano or microparticles embedded in a solid transparent host layer, where temperature change induces change in the refraction index of the matrix as well as of the embedded particles, creating a scattering layer, substantially reflecting the incident light thus limiting the amount of light passing through the window, green house covers, car sun roofs, solar panel windows and protection layers on housing roofs and walls, as a function of ambient temperature.

First claim

The invention claimed is:

1. A thermotropic coating, limiting transmission of solar energy there-through, comprising:
salt nanoparticles or salt microparticles, embedded in a solid transparent host matrix;
said coating being reversible between: a translucent and non-transmittant state; and
a transparent and transmittant state; said state depending on the ambient temperature;
wherein said host and said salt particles are selected such that a change in ambient temperature induces a change in the refraction index of said matrix at a first rate, and induces a change in the refraction index of said embedded salt particles at a second rate different from the first rate, to produce scattering and reflection of solar light and thus limit transmission of light passing there through, as a function of the ambient temperature.

2. The thermotropic coating of claim 1 , wherein said coating is formulated such that at a pre-determined temperature the refractive indices of said host matrix layer and of said embedded salt particles are similar, yielding minimal light scattering and relatively high transmittance.

3. The thermotropic coating of claim 1 wherein said coating is formulated to be transparent at low ambient temperature, thus allowing light and heat to enter a window coated with said coating, for maximal savings of lighting and heating expenses.

4. The thermotropic coating of claim 1 wherein said coating is formulated to be translucent when the ambient temperature reaches a predefined high temperature, said coating back-scattering the majority of the solar heat and light impinging on it, for maximal savings of lighting and cooling expenses.

5. The thermotropic coating of claim 1 wherein said matrix is formed of an organic polymer having a refractive index which varies as a function of the temperature.

6. The thermotropic coating of claim 1 wherein said salt particles are made of an inorganic material, having a refractive index which varies at a slower rate as a function of the temperature, than the rate of variation of said refractive index of said matrix.

7. The thermotropic coating of claim 1 , wherein said coating is formulated to be transparent at a predefined temperature, by selecting two compatible polymeric matrices, wherein a first matrix has a refractive index higher than that of the salt particles, and a second matrix has a lower refractive index than that of the salt particles, and said two polymers are mixed at a predetermined ratio, to select the exact temperature at which said coating is transparent.

8. The thermotropic coating of claim 1 , wherein said coating is sandwiched or laminated between two transparent layers of glass, polymer or crystal panes.

9. The thermotropic coating of claim 1 wherein said coating is present as a laminating layer adhered or glued to transparent glass or polymer window-panes.

10. The thermotropic coating of claim 1 , wherein said coating is comprised of environmentally friendly materials.

11. The thermotropic coating of claim 1 where said host matrix is organic and selected from: a polymer film, a polymerizable composition, or a transparent adhesive.

12. The thermotropic coating of claim 1 where said host matrix is inorganic and selected from: mineral glass, sol-gel.

13. The thermotropic coating of claim 1 where said host matrix is an inorganic-organic composite.

14. The thermotropic coating of claim 1 where the host is selected from: a UV cured transparent adhesive; an epoxy based transparent adhesive; a silicone based transparent adhesive; a polymer host matrix selected from: Polyvinyl butyral (PVB), Cellulose acetate butyrate (CAB), and Cellulose acetate (CA); Acrylic polymers; and combinations thereof.

15. The thermotropic coating of claim 1 where said salt microparticles or nanoparticles are selected from: LiF, LiCl, LiBr, LiI, NaF, NaCl, NaBr, NaI, KF, KCl, KBr, KI, RbF, RbCl, RbBr, RbI, CsF, CsCl, CsBr, CsI, BaF 2 , CaF 2 , MgF 2 , ZnSe, ZnS; and mixtures and combinations thereof.

16. The thermotropic coating of claim 1 , further comprising a stabilizer selected from: a hindered amine light stabilizer (HALS), a UV absorber, a thermal stabilizer, a singlet oxygen quencher, an antioxidant, and any combination thereof.

17. The thermotropic coating of claim 1 wherein said salt particles are encapsulated to prevent degradation and enhance the dispersability of said particles.

18. The thermotropic coating of claim 1 further comprising light absorbing materials embedded in the host material to increase the modulation of light attenuation between said two states of said coating.

19. The thermotropic coating of claim 1 further comprising thermochromic nano-particles to increase the modulation of light attenuation between said two states of said coating.

20. The thermotropic coating of claim 19 , wherein said thermochromic nano-particles are formed of vanadium dioxide (VO 2 ).

21. The thermotropic coating of claim 1 wherein said coating is positioned between two polarizers oriented in the same linear polarization, to increase the modulation of light attenuation between said two states of said coating.

22. The thermotropic coating of claim 1 , wherein said host matrix is present in a layer of maximal thickness of 500 microns.

23. A laminate article comprising the thermotropic coating of claim 1 , wherein said coating is present as an internal layer located within an upper window layer and a lower window layer.

24. An optical power-limiting article comprising the coating of claim 1 , wherein said article is selected from: a window, a green house cover, a sun roof, a solar panel, and a protection-layer on a roof or walls.

25. The article of claim 24 , wherein power limiting is passive and self-adaptive.

Assignees

• Oron Moshe
• Nevo Doron
• Gross Noam
• Donval Ariela
• Elbit Systems Ltd

Inventors

• Oron Moshe
• Nevo Doron
• Gross Noam
• Donval Ariela

Classifications

• E06B2009/2417

  Light path control; means to control reflection · CPC title

• G02F1/0147 Primary

  based on thermo-optic effects (G02F1/132 takes precedence) · CPC title

• E06B9/24

  Screens or other constructions affording protection against light, especially against sunshine; Similar screens for privacy or appearance; {Slat blinds}(operating, guiding or securing devices or arrangements for roll-type closures E06B9/56; free-hanging flexible screens A47H23/00) · CPC title

• C03C17/32

  with synthetic or natural resins (C03C17/30 takes precedence) · CPC title

• C03C17/007 Primary

  containing a dispersed phase, e.g. particles, fibres or flakes, in a continuous phase · CPC title