Electrothermal heater made from thermally conducting electrically insulating polymer material

Abstract

Thermally conductive films, composite materials including the films, and electrothermal heaters including the films, are disclosed. The films include a polymer and a sufficient concentration of hexagonal boron nitride to provide adequate heat transfer properties, and have high thermal conductivity, peel strength, and shear strength. The films can include thermoset polymers, thermoplastic polymers, or blends thereof, and can also include electrically conductive materials, reinforcing materials such as fiberglass, carbon fiber, metal mesh, and the like, and thermally conductive fillers, such as aluminum oxide, aluminum nitride, and the like. The films can be included in composite materials. The films can be used as part of a layered structure, and used in virtually any application, for example, various locations in aircraft, where heating is desirable, including nacelle skins, airplane wings, heated floor panels, and the like. The electrothermal heaters provide a more even heat, and a more rapid heat, than current resistive heaters formed from metal foils adhered to an adhesive film.

1 . A film formed from a blend of hexagonal boron nitride and a polymerizable monomer, wherein the hexagonal boron nitride is present in a concentration of from about 12 percent to about 40 percent weight, based on total weight of the film. 
     
     
         2 . The film of  claim 1 , wherein the hexagonal boron nitride is present in a concentration of from about 27 percent to about 33 percent weight, based on total weight of the film. 
     
     
         3 . The film of  claim 1 , wherein the monomer is a thermoset resin selected from the group consisting of epoxy based resin systems, matrices of bismaleimide (BMI), phenolic, polyester, PMR15 polyimide, acetylene terminated resins, acrylics; polyurethanes, and free-radically induced thermosetting resins. 
     
     
         4 . The film of  claim 1 , wherein the monomer is an epoxy resin. 
     
     
         5 . The film of  claim 4 , wherein the epoxy resin is selected from diglycidyl ethers of bisphenol A (2,2-bis(4-hydroxyphenyl)propane) or sym-tris(4-hydroxyphenyl)propane, tris(4-hydroxyphenyl)methane, bisphenol, F, tetrabromobisphenol A, their polyepoxide condensation products, cycloaliphatic epoxides, epoxy-modified novolacs (phenoli-formaldehyde resins) and the epoxides derived from the reaction of epichlorohydrin with analine, o-, m- or p-aminophenol, and methylene dianaline. 
     
     
         6 . The film of  claim 1 , further comprising an electrically conductive material. 
     
     
         7 . The film of  claim 6 , wherein the electrically conductive material is selected from the group consisting of metal powders, metal-coated microspheres, metal-coated carbon-nanotubes, carbon nanofibers, carbon nanotubes, graphite nanoplatelets, copper screen, and aluminum screen. 
     
     
         8 . The film of  claim 6 , wherein the electrically conductive material is present in a concentration of from about 10 percent to about 60 percent by weight of the hexagonal boron nitride. 
     
     
         9 . The film of  claim 6 , wherein the electrically conductive material does not provide electrical conductivity. 
     
     
         10 . The film of  claim 1 , wherein the polymerizable monomer forms a thermoplastic polymer. 
     
     
         11 . The film of  claim 10 , wherein the thermoplastic polymer is selected from polyetheretherketone (PEEK), polyetherketone (PEK), polyphenylene sulfide (PPS), polyethylene sulfide (PES), polyetherimide (PEI), polyvinylidene fluoride (PVDF), polysulfone (PS), polycarbonate (PC), polyphenylene ether/oxide, nylons, aromatic thermoplastic polyesters, aromatic polysulfones, thermoplastic polyimides, liquid crystal polymers, and thermoplastic elastomers. 
     
     
         12 . The film of  claim 10 , wherein the hexagonal boron nitride is present in concentrations of from about 5 percent to about 50 percent by weight of the thermoplastic polymer. 
     
     
         13 . A composite material comprising a film and a thermally insulating layer, wherein the film is formed from a blend of hexagonal boron nitride and a polymerizable monomer, and wherein the hexagonal boron nitride is present in a concentration of from about 12 percent to about 40 percent weight, based on total weight of the film. 
     
     
         14 . The composite material of  claim 13 , further comprising an electrically conductive layer between the thermally insulating layer and the film. 
     
     
         15 . The composite material of  claim 13 , further comprising an additional layer overlying the film, wherein the additional layer is capable of dissipating energy from a lightning strike. 
     
     
         16 . A method for forming an thermally conductive film, comprising the steps of
 blending hexagonal boron nitride and a polymerizable monomer wherein the hexagonal boron nitride is present in a concentration of between about 12 and about 40 percent weight;   forming a layer of the resulting blend; and   polymerizing the polymerizable monomer to form the thermally conductive film.   
     
     
         17 . A method for forming an thermally conductive film, comprising the steps of blending hexagonal boron nitride and a melted thennoplastic polymer wherein the hexagonal boron nitride is present in a concentration of from about 12 to about 40 percent weight, based on total weight of the film;
 forming a layer of the resulting blend; and   cooling the melted polymer to form the thermally conductive film.   
     
     
         18 . A method of electrothermally heating an airplane component, comprising the steps of
 providing a thermally conductive film to the airplane component, wherein the thermally conductive film comprises hexagonal boron nitride and a polymer;   attaching at least one conductor to the thermally conductive film, wherein the conductor is further attached to a converter; and   supplying electrical energy to the film via the converter and conductor so as to heat the airplane component.   
     
     
         19 . The method of claim 18 , wherein the thermally conductive film is rectangular in shape with a length substantially greater than the width for covering at least a portion of a leading edge of an airfoil. 
     
     
         20 . The method of  claim 18 , wherein the airplane component is selected from the group consisting of at least one nacelle, fuselage, wing and stabilizer.