Thermal control interface coatings and pigments

Abstract

The invention provides an optical structure with low chroma and brightness in the visible region and low emissivity in the infrared region. The optical structure includes an interference structure having an infrared reflective layer and an infrared absorbing thin film layer. These layers are in turn separated by a thin film spacer of a dielectric or semiconductor material. The reflectivity and transmission of the layers are selectively controlled through the thickness of the layers such that the visual reflectivity and color is independent of the infrared properties of the absorber and reflector layers.

1 - 73 . (canceled)  
   
   
       74 . An optical structure comprising: 
 a reflector;    a spacer layer with a spacer thickness disposed on the reflector; and    an absorber layer disposed on the spacer layer, the absorber layer having an absorber thickness providing a transmittance through the absorber layer between 5-85% wherein the reflector has a reflector thickness, the spacer thickness and the absorber thickness are selected to achieve an average first reflectivity of not more than 50% between 400-700 nanometers and an average second reflectivity of not less than 50% between 4-40 microns.    
   
   
       75 . The optical structure of  claim 74  wherein the spacer thickness is between 1 quarter-wave optical thickness at 200 nm and 2 quarter-wave optical thicknesses at 700 nm.  
   
   
       76 . The optical structure of  claim 74  wherein the spacer thickness is selected to achieve a reflectivity minimum of the optical interference structure between 200-1500 nm.  
   
   
       77 . The optical structure of  claim 74  wherein the spacer thickness is less than one quarter-wave optical thickness at 700 nm and is selected to achieve a reflectivity minimum of the optical structure between 200-700 nm.  
   
   
       78 . The optical structure of  claim 74  wherein the reflector comprises aluminum, the spacer layer comprises magnesium fluoride and the absorber layer comprises chromium having an internal transmittance of not more than 50%.  
   
   
       79 . The optical structure of  claim 74  wherein the spacer layer is made of a selectively absorbing spacer material being more absorptive in the visible range than in the infrared range.  
   
   
       80 . The optical structure of  claim 79  wherein the selectively absorbing spacer material is selected from the group consisting of iron oxide, tungsten oxide, copper oxide, and cobalt oxide.  
   
   
       81 . The optical structure of  claim 74  wherein the spacer layer comprises a spacer material selected from the group consisting of zinc sulfide, zinc oxide, zirconium oxide, titanium dioxide, diamond-like carbon, indium oxide, indium-tin-oxide, tantalum pentoxide), ceric oxide, yttrium oxide, europium oxide, iron oxide, ferric oxide, hafnium nitride, hafnium carbide, hafnium oxide, lanthanum oxide, magnesium oxide, neodymium oxide, praseodymium oxide, samarium oxide, antimony trioxide, silicon, silicon monoxide, germanium, selenium trioxide, tin oxide, tungsten trioxide, and combinations thereof.  
   
   
       82 . The optical structure of  claim 74  wherein the spacer layer comprises a spacer material selected from the group consisting of silicon dioxide; aluminum oxide; metal fluoride, including magnesium fluoride, aluminum fluoride, cerium fluoride, lanthanum fluoride, sodium aluminum fluorides including Na 3 AlF 6  and Na 5 Al 3 F 14 , neodymium fluoride, samarium fluoride, barium fluoride, calcium fluoride, and lithium fluoride; and organic monomers and polymers, including dienes, alkenes, acrylates including methacrylate, perfluoroalkenes, polytetrafluoroethylene, and fluorinated ethylene propylene (“FEP”).  
   
   
       83 . The optical structure of  claim 74  wherein the absorber thickness is selected to achieve a reflectivity minimum of less than 10% reflectivity of the optical interference structure between 200-1500 nm.  
   
   
       84 . The optical structure of  claim 74  wherein the absorber thickness is selected to achieve a reflectivity minimum of the optical interference structure between 200-1500 nm.  
   
   
       85 . The optical structure of  claim 74  disposed on a plurality of pigment flakes in a paint vehicle to provide a paint formulation.  
   
   
       86 . The optical structure of  claim 85  wherein the paint vehicle has a low infrared emittance.  
   
   
       87 . The optical structure of  claim 85  disposed on a surface to provide a solar absorber.  
   
   
       88 . The optical structure of  claim 85  disposed on a surface to provide infrared camouflage.  
   
   
       89 . The optical structure of  claim 74  disposed on a plurality of pigment flakes in an ink vehicle to provide an ink.  
   
   
       90 . The optical structure of  claim 74  disposed on a surface to provide an infrared image.  
   
   
       91 . The optical structure of  claim 90  wherein the infrared image is not discernible by an unaided human eye.  
   
   
       92 . The optical structure of  claim 90  wherein the infrared image is incorporated in a heat-sensitive foil pressed onto a surface.  
   
   
       93 . The optical structure of  claim 74  wherein the optical structure has indiscernible color shift when viewed by a human eye through a viewing arc of 0-90 degrees measured from a normal to a major surface of the optical structure with a fixed illumination source.  
   
   
       94 . The optical structure of  claim 74  disposed on a plurality of pigment flakes in a polymeric sheet.  
   
   
       95 . The optical structure of  claim 94  wherein the polymeric sheet comprises a material selected from the group consisting of aqueous polymer, polyvinyl alcohol, polyvinyl acetate polyvinylpyrrolidone, poly(ethoxyethylene), poly(methoxyethylene), poly(acrylic) acid, poly(acrylamide), poly(oxyethylene), poly(maleic anhydride), hydroxyethyl cellulose, cellulose acetate and poly(sacchrides) including gum arabic and pectin, poly(acetals) including polyvinylbutyral, poly(vinyl halides) including polyvinyl chloride and polyvinylene chloride, poly(dienes) including polybutadiene, poly(alkenes) including polyethylene, poly(acrylates) including polymethyl acrylate, poly(methacrylates) including poly methylmethacrylate, poly(carbonates) including poly(oxycarbonyl oxyhexamethylene, poly(esters) including polyethylene terephthalate, poly(urethanes), poly(siloxanes), poly(suphides), poly(sulphones), poly(vinylnitriles), poly(acrylonitriles), poly(styrene), poly(phenylenes) including poly(2,5 dihydroxy-1,4-phenyleneethylene), poly(amides), natural rubbers, formaldahyde resins, and combinations thereof.  
   
   
       96 . The optical structure of  claim 94  wherein the polymeric sheet is an extruded sheet.  
   
   
       97 . The optical structure of  claim 94  wherein the polymeric sheet is stretched.  
   
   
       98 . The optical structure of  claim 74  disposed on a plurality of pigment flakes and mixed with a powder coating vehicle to provide a powder coating formulation.  
   
   
       99 . The optical structure of  claim 98  wherein the powder coating vehicle is clear at visible wavelengths.  
   
   
       100 . The optical structure of  claim 74  disposed on a film.  
   
   
       101 . The optical structure of  claim 100  wherein the film includes an adhesive layer.  
   
   
       102 . The optical structure of  claim 74  disposed on a foil.  
   
   
       103 . The optical structure of  claim 102  wherein the foil comprises aluminum or stainless steel.  
   
   
       104 . The optical structure of  claim 74  wherein the absorber thickness is less than 3 times tabs min , the minimum visible reflectance absorber thickness providing a minimum reflectivity of the optical interference structure between 200-1500 nm.  
   
   
       105 . The optical structure of  claim 74  wherein the absorber layer comprises an absorber material selected from the group consisting of chromium, nickel, iron, titanium, aluminum, tungsten, molybdenum, niobium, metal alloys, including Ni—Cr—Fe alloy, metal dispersed in a dielectric matrix, iron oxide (Fe 2 O 3 ), silicon monoxide (SiO), chromium oxide (Cr 2 O 3 ), carbon, titanium nitride (TiN), and titanium sub-oxide (TiO x  where x is less than 2.0).  
   
   
       106 . The optical structure of  claim 74  wherein the reflector, spacer layer, and absorber layer are chosen so as to achieve a chroma of less than 20 for the optical interference structure.  
   
   
       107 . The optical structure of  claim 74  wherein the reflector layer comprises a reflector material selected from the group consisting of aluminum, silver, iron, tantalum, iridium, rhenium, copper, silver, gold, platinum, palladium, nickel, cobalt, niobium, chromium, tin, alloys, metal carbides, metal oxides, metal nitrides, metal sulfides.  
   
   
       108 . The optical structure of  claim 74  wherein the reflector layer comprises a reflector material selected from the group consisting of indium oxide, indium tin oxide (ITO), europium oxide (Eu 2 O 3 ), vanadium pentoxide (V 2 O 5 ), rhenium oxide (ReO 3 ), lanthanum boride (LaB 6 ).  
   
   
       109 . The optical structure of  claim 74  wherein the spacer layer has a spacer layer thickness of 1 quarter-wave optical thickness for wavelengths between 100-500 nm and further comprising 
 a second spacer layer disposed on the absorber layer, the second spacer layer having a second spacer layer thickness of 1 quarter-wave optical thickness for wavelengths between 100-500 nm; and    a second absorber layer having an internal transmittance between 5% and 85% disposed on the second spacer layer.    
   
   
       110 . The optical structure of  claim 74  wherein the spacer thickness is one quarter-wave optical thickness between 200-800 nm, the reflector comprises aluminum reflector and the absorber layer comprises 20 nm of chromium.  
   
   
       111 . The optical structure of  claim 74  wherein the optical structure is formed on a flake substrate.  
   
   
       112 . The optical structure of  claim 111  wherein at least one of the reflector, the spacer layer, and the absorber layer surrounds the flake substrate.  
   
   
       113 . The optical structure of  claim 74  wherein the optical structure has an optical structure thickness not greater than 250 nm and is formed on a stiff flake substrate.  
   
   
       114 . The optical structure of  claim 74  further comprising a stiffening layer.  
   
   
       115 . The optical structure of  claim 74  further comprising an overcoat layer having an overcoat layer thickness.  
   
   
       116 . The optical structure of  claim 115  wherein the overcoat layer thickness is at least eight times the spacer layer thickness.  
   
   
       117 . The optical structure of  claim 115  wherein the overcoat layer thickness is less than eight times the spacer layer thickness.  
   
   
       118 . The optical structure of  claim 74  having a chroma less than 5.  
   
   
       119 . The optical structure of  claim 74  having an average reflectance not greater than 20% between 400-700 nm.  
   
   
       120 . An optical structure comprising: 
 a reflector;    a spacer layer with a spacer thickness disposed on the reflector; and    an absorber layer disposed on the spacer layer, the absorber layer having an absorber thickness providing a transmittance through the absorber layer between 5-85%, the spacer thickness being selected so as to provide an average reflectance of the optical interference structure less than 50% reflectivity between 400-700 nm and a chroma of the optical interference structure less than 20.    
   
   
       121 . The optical structure of  claim 120  wherein the spacer thickness is between one quarter-wave optical thickness at 300 nm and two quarter-wave optical thicknesses at 550 nm.  
   
   
       122 . The optical structure of  claim 120  wherein the spacer thickness is between 2 quarter-wave optical thicknesses at a first wavelength of 280 nm and  2  quarter-wave optical thicknesses at a second wavelength of 450 nm.  
   
   
       123 . The optical structure of  claim 120  wherein the spacer thickness is between 2 quarter-wave optical thickness at a first wavelength of 450 nm and 2 quarter-wave optical thicknesses at a second wavelength of 550 nm.  
   
   
       124 . An optical interference structure comprising: 
 a reflector having a reflectivity of at least 50% over a wavelength range of 4-40 microns;    a spacer layer disposed on the reflector having a spacer layer thickness of between 1 quarter-wave optical thickness at a first wavelength of 200 nm and 2 quarter-wave optical thicknesses at a second wavelength of 500 nm, the spacer layer having a refractive index less than 2; and    an absorber layer with an absorber layer thickness selected to provide an average reflectance of the optical interference structure less than 20% between 400-700 nm.    
   
   
       125 . The optical interference structure of  claim 124  wherein the optical interference structure has a chroma less than 20.  
   
   
       126 . The optical interference structure of  claim 124  further comprising: 
 a second spacer layer with a second spacer thickness disposed on the absorber layer; and    a second absorber layer disposed on the second spacer layer.    
   
   
       127 . The optical interference structure of  claim 126  wherein the spacer layer thickness is less than one quarter-wave optical thickness at a wavelength of 700 nm and the second spacer layer thickness is less than one quarter-wave optical thickness at the wavelength of 700 nm.  
   
   
       128 . The optical interference structure of  claim 124  wherein the substrate is an aluminum flake comprising the aluminum reflector and the second aluminum reflector.  
   
   
       129 . The optical interference structure of  claim 124  wherein the substrate is a substantially rigid dielectric flake.  
   
   
       130 . The optical interference structure of  claim 129  wherein the substantially rigid dielectric flake comprises glass, mica, alumina, iron oxide, graphite, bismuth oxychloride, boron nitride, or polymer.  
   
   
       131 . An optical interference structure comprising: 
 an aluminum reflector;    a first dielectric layer disposed on the aluminum reflector, the first dielectric layer comprising MgF 2  having a first dielectric thickness of 55 nm;    a first absorber layer comprising 7 nm of chromium disposed on the first dielectric layer; a second dielectric layer disposed on the first absorber layer, the second dielectric layer comprising MgF 2  having a second dielectric thickness of 55 nm; and    a second absorber layer comprising 2.5 nm of chromium disposed on the second dielectric layer, the second absorber layer.    
   
   
       132 . The optical interference structure of  claim 131  wherein the aluminum reflector is an opaque reflector layer not less than 30 nm thick.  
   
   
       133 . The optical interference structure of  claim 131  further comprising: 
 a substrate having a first surface and a second surface, the aluminum reflector being disposed on the first surface of the substrate;    a second aluminum reflector disposed on the second surface of the substrate;    a third dielectric layer disposed on the second aluminum reflector, the third dielectric layer comprising MgF 2  having a third dielectric thickness of 55 nm;    a third absorber layer disposed on the third dielectric layer comprising 7 nm of chromium;    a fourth dielectric layer disposed on the third absorber layer, the fourth dielectric layer comprising MgF 2  having a fourth dielectric thickness of 55 nm; and    a fourth absorber layer disposed on the fourth dielectric layer, the second absorber layer comprising 2.5 nm of chromium.    
   
   
       134 . An optical interference structure comprising: 
 a substantially opaque aluminum reflector    a dielectric layer comprising ZnS being 1 quarter-wavelength optical thickness at a wavelength between 200-1400 nm; and    an absorber layer having an internal transmittance between 5-85%.    
   
   
       135 . An optical interference structure comprising: 
 an aluminum reflector    a dielectric layer comprising MgF 2  being 1 quarter-wavelength optical thickness at a wavelength of 500 nm; and    an absorber layer comprising 20 nm of chromium.    
   
   
       136 . The optical interference structure of  claim 135  having a chroma less than 5.