Flame retardant broadband millimeter wave absorbers

Abstract

Flame retardant broadband millimeter wave absorbing materials are disclosed comprising a polymeric matrix, carbon-containing electromagnetic wave absorbing particles comprising carbon black dispersed in the polymeric matrix, and a flame retardant material.

Description

FLAME RETARDANT BROADBAND MILLIMETER WAVE ABSORBERSCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Patent ApplicationNo. 63 / 706,410 filed October 11, 2024, and also claims the benefit of U.S. Provisional Patent Application No. 63 / 822,332 filed June 12, 2025, both of which are incorporated herein by reference.FIELD

[0002] Flame retardant broadband millimeter wave absorbers are disclosed.BACKGROUND

[0003] Electromagnetic (EM) energy directed toward various types of surfaces may typically be reflected from such surfaces. The present disclosure is directed to broadband millimeter wave absorbing materials that are capable of attenuating energy across selected frequency bands to reduce EM wave reflections.SUMMARY

[0004] Disclosed herein is a flame retardant broadband millimeter wave absorbing material comprising a polymeric matrix, carbon-containing electromagnetic wave absorbing particles comprising carbon black dispersed in the polymeric matrix, and a flame retardant material.BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Figs. 1-3 schematically illustrate a flame retardant broadband millimeter wave absorbent sheet.

[0006] Fig. 4 is a graph of reflectivity vs. frequency illustrating insertion loss performance of a flame retardant broadband millimeter wave absorbent sheet at frequencies of from 75 to 110 GHz.

[0007] Figs. 5 and 6 schematically illustrate measurement geometries for testing broadband millimeter wave absorbent sheets, without a backing mirror (Fig. 5) and with a backing mirror (Fig. 6).

[0008] Figs. 7 and 8 are graphs showing Sn return loss data for broadband millimeter wave absorbent sheets within a frequency range of from 140 to 220 GHz, with a backing mirror (Fig. 7) and without a backing mirror (Fig. 8).DETAILED DESCRIPTION

[0009] Figs. 1-3 schematically illustrate a sheet 10 of material that may comprise the flame retardant broadband millimeter wave absorbing material. The sheet 10 includes a base layer 12 and a texture layer 14, which includes an array of raised pyramid shapes. As shown in Fig. 2, the absorbing material sheet 10 has an overall or total thickness Tt, the base layer 12 has a base thickness Tb, and the texture layer 14 has a textured surface thickness Ts. As further shown in Fig. 2, the raised pyramid shapes may have a pyramid angle A, which is between 50° and 55° in the figure, but may be adjusted to any desired angle. While the texture layer 14 shown in Figs. 1 and 2 comprises uniformly shaped, sized and spaced pyramids, any other suitable geometrical shapes, sizes and spacings may be used. In addition, at least one additional surface layer may be provided, for example, an upper surface layer that fills in some or all of the spaces between the raised pyramids or other geometrical shapes of the texture layer.

[0010] Broadband millimeter wave absorbing materials with flame retardant properties are provided that may be used to reduce EM wave reflections. The absorptive materials may be provided in various forms such as sheets having controlled surface profiles that help attenuate EM energy across selected frequencies. The materials include a polymeric matrix material having at least one carbon-based EM absorbing material comprising carbon black and at least one flame-retardant material dispersed therein.

[0011] As used herein, the term “broadband millimeter wave”, when referring to EM absorbing materials, means that a material attenuates or reduces reflections of EM energy within one or more selected frequency ranges of from 10 to 500, such as from 30 to 300, or from 75 to 110 GHz.

[0012] As used herein, the term “absorbing material” means that a material of given total thickness, such as 4 mm, attenuates EM energy within frequency ranges described above by at least 15 dB. For example, a flexible polymeric sheet of absorbing material having a total thickness of 4 mm may demonstrate at least -15 dB of attenuation across a frequency band of 75 GHz to 110+ GHz as measured by a Vector Network Analyzer equipped with standard horn antennas.

[0013] As used herein, the term “flame retardant” means that an EM absorbing material containing flame retardant particles or other forms of flame retardant materials passes the standard Underwriters Laboratories UL94 V0 test.

[0014] Carbon-based particles including carbon black powder may be dispersed into an elastomer such as silicone along with flame-retardant particles such as aluminum trihydratc. When the broadband millimeter wave absorbers are provided in the form of sheets, they may comprise a relatively thin flexible layer that may be applied on various types of flat and / or contoured surfaces to attenuate EM energy across a wide high frequency band. The sheets may be formed by processes such as compression molding to create the absorptive sheets. The mold geometry may be used to form a desired surface pattern such as a pyramidal array profile that attenuates EM energy in a broadband manner at the targeted frequencies.Polymeric Matrix

[0015] The matrix material of the broadband millimeter wave absorbing materials may comprise one or more polymers such as silicone, urethane, polycarbonate, polyamide, polyester, polyolefin, epoxy, neoprene, and the like. Suitable silicone materials may include vinyl-addition cure silicones and RTV (room temperature vulcanizing) silicones, e.g., CHT silicones, QSIL 216, and the like. Other suitable elastomeric polymers may comprise one or more of polybutylene terephthalate, polypropylene, thermoplastic vulcanizate, thermoplastic elastomer and / or a mixture including polyolefin, e.g., the elastomer may comprise polypropylene and santoprene thermoplastic vulcanizate. The elastomeric matrix material may have a selected level of cross-linking, such as a relatively low cross-linked material.

[0016] The matrix material may comprise polydimethylsiloxane, a block copolymer system, an elastomeric system (e.g., cured elastomers, thermoplastic elastomers (TPEs), Santoprene thermoplastic vulcanizate, etc.), a thermoplastic system ( e.g., liquid silicone, urethane, polycarbonate, polyamide, polyester, polyolefin, polybutylene terephthalate, thermoplastic vulcanizate, thermoplastic elastomer, a mixture including polyolefin, acrylonitrile buta-diene styrene (ABS), polypropylene (PP), polyethylene (PE), etc.), injection moldable and / or polymer resin.

[0017] Block copolymer may be used as the matrix material. For example, polystyrene- block-poly (ethylene oxide) (PS-b-PEO) may be used as the matrix material. Or, for example, polystyrene and poly(methyl methacrylate) (PS-PMMA) may be used as the matrix material. Other matrix materials may be used, such as poly styrene-poly ethylene block copolymer, another polystyrene-acrylate block copolymer, styrene-diene block copolymer (e.g., styrene-butadiene (SB) diblock copolymer, styrene-isoprene diblock copolymer, styrene -butadiene-styrene (SBS)triblock copolymer, styrene-isoprene-styrene (SIS) triblock copolymer, styrene-butadiene (SB) star block copolymer, etc.), hydrogenated styrcnc-dicnc block copolymer ( c.g., hydrogenated SBS styrene-( ethylene-butylene )-styrene, etc.), segmented block copolymer (e.g., segmented polyester-polyether, segmented polyamide-polyether, etc.), polyolefinic block copolymer, ethylene oxide / propylene oxide block copolymer, organosilicone copolymer system ( e.g., siloxane / polysulfone copolymer, siloxane / polyurethane, siloxane / polyurea copolymer, siloxane / polyamide copolymer, siloxane / polyimide copolymer, siloxane / polyamide / polyimide copolymer, siloxane / polyester copolymer, siloxane / polycarbonate copolymer, siloxane / polystyrene copolymer, siloxane / epoxide resin networks, etc.), hard block copolymer, other block copolymers, and / or combinations thereof.

[0018] Epoxy-containing compounds may be used as the matrix material. Suitable epoxy-containing compounds may include aromatic epoxies that can be used include poly epoxides, epoxy adducts, or combinations thereof. The aromatic epoxy may comprise a monoepoxide. In some cases, the epoxy-containing compound may comprise an aliphatic epoxy including polyglycidyl ethers of polyhydric alcohols, polyglycidyl esters of polycarboxylic acids, polyepoxides that are derived from the epoxidation of an olefinically unsaturated alicyclic compound, or polyepoxides containing oxyalkylene groups in the epoxy molecule. The epoxy- containing compound may also comprise an epoxy-containing acrylic, such as copolymers comprising glycidyl methacrylate. The aliphatic epoxy may comprise a monoepoxide. The epoxy-containing compound may comprise a combination of any of the aromatic epoxides described above and any of the aliphatic epoxides described above.

[0019] The polymeric matrix may comprise at least 50 weight percent of the absorbing material, for example, at least 70 weight percent, or at least 80 weight percent. The polymeric matrix may comprise up to 98 weight percent of the absorbing material, for example, up to 95 weight percent, or up to 92 weight percent. The polymeric matrix may range from 50 to 98 weight percent of the absorbing material, for example, from 70 to 95 weight percent, or from 80 to 92 weight percent.

[0020] The polymeric matrix material may have selected physical properties such as an elongation of at least 20 percent, or at least 50 percent, or at least 70 percent, or at least 90 percent; and a tensile strength of at least 200 psi, or at least 500 psi, or at least 700 psi.

[0021] The polymeric matrix material may have selected electrical properties such as a dielectric constant of from 1 to 4, or from 2 to 3, at 1000 Hz, and a volume resistivity of at least 1 x 1010ohm-cm, or at least 1 x 1012ohm-cm, or at least 1 x 1014ohm-cm, or at least 1 x 1015ohm-cm. The polymeric matrix material may be non-magnetic.Carbon-Based EM Absorbing Materials

[0022] The carbon-based EM absorbing material may comprise carbon black, such as thermal black, furnace black, and the like. The carbon black may have an average particle size of at least 1 nanometer, for example, at least 10 nanometers, or at least 20 nanometers. The carbon black may have an average particle size up to 200 nanometers, for example, up to 100 nanometers, or up to 50 nanometers. The average particle size of carbon black may range from 1 to 200 nanometers, for example, from 10 to 100 nanometers, or from 20 to 50 nanometers. The average particle size of the carbon black may be reported by the manufacturer, may be determined by standard B.E.T. surface area techniques, or may be measured by standard TEM imaging techniques in which a TEM image of the carbon black powder undergoes image analysis by standard image analysis software.

[0023] The carbon-based EM absorbing material may comprise at least 50 weight percent carbon black based on total weight percent of the flame retardant broadband millimeter wave absorbing material, such as at least 90 weight percent.

[0024] The carbon-based EM absorbing material may be present in amounts of at least 2 weight percent of the absorbing material, for example, at least 4 weight percent, or at least 6 weight percent. The carbon-based EM absorbing material may comprise up to 30 weight percent of the absorbing material, for example, up to 20 weight percent, or up to 15 weight percent. The carbon-based EM absorbing material may range from 2 to 30 weight percent based upon the total weight of the broadband millimeter wave absorbing material, for example, from 4 to 20 weight percent, or from 6 to 15 weight percent.Flame Retardant Materials

[0025] The compositions provided by the present disclosure may comprise a single type of flame retardant or a combination of flame retardants. As used herein, “flame retardant” refers to a material that slows down or stops the spread of fire or reduces its intensity. For example, flame retardants may be available as a powder that may be mixed with a composition.

[0026] As set forth in more detail below, a flame retardant can include metal hydroxides, minerals, organic compounds, organohalogcn compounds, organophosphorous compounds, or combinations thereof.

[0027] Suitable flame retardant materials may include metal hydroxides such as aluminum trihydrate, aluminum hydroxide, magnesium hydroxide, and the like. For example, the flame retardant material may comprise an aluminum trihydrate commercially available from Huber Advanced Materials under the designation Spacerite S3 or commercially available from Cimbar Performance Minerals under the designations Polyfill and PolyJet.

[0028] Suitable examples of minerals include huntite, hydromagnesite, various hydrates, red phosphorous, boron compounds such as borates, carbonates such as calcium carbonate and magnesium carbonate, and combinations thereof.

[0029] Suitable examples of organic compounds include carboxylic acid, dicarboxylic acid, melamine, and organonitrogen compounds.

[0030] Suitable examples of organohalogcn compounds include organochlorines such as chlorendic acid derivatives and chlorinated paraffins; organobromines such as decabromodiphenyl ether (decaBDE), decabromodiphenyl ethane (a replacement for decaBDE), polymeric brominated compounds such as brominated polystyrenes, brominated carbonate oligomers (BCOs), brominated epoxy oligomers (BEOs), tetrabromophthalic anyhydride, tetrabromobisphenol A (TBBPA) and hexabromocyclododecane (HBCD). Such halogenated flame retardants may be used in conjunction with a synergist to enhance their efficiency.

[0031] Suitable examples of organophosphorous compounds include triphenyl phosphate (TPP), resorcinol bis(diphenylphosphate) (RDP), bisphenol A diphenyl phosphate (BADP), and tricresyl phosphate (TCP); phosphonates such as dimethyl methylphosphonate (DMMP); and phosphinates such as aluminum diethyl phosphinate. In one important class of flame retardants, compounds contain both phosphorus and a halogen. Such compounds include tris(2,3- dibromopropyl) phosphate (brominated tris) and chlorinated organophosphates such as tris( 1 ,3- dichloro-2-propyl)phosphate (chlorinated tris or TDCPP) and tetrakis(2- chlorethyl)dichloroisopentyldiphosphate (V6).

[0032] Other suitable flame retardants include ammonium polyphosphate, barium sulfate, antimony trioxide, antimony pentaoxide, and sodium antimonate.

[0033] Suitable flame retardant materials may also include boron nitride (for example, commercially available as CarboTherm from Saint-Gobain, as CoolFlow and PolarThcrm from Momentive, and as hexagonal boron nitride powder available from Panadyne), silicon nitride, or aluminum nitride (for example, commercially available as aluminum nitride powder available from Micron Metals Inc., and as Toyalnite from Toyal), metal oxides such as aluminum oxide (for example, commercially available as Microgrit from Micro Abrasives, as Nabalox from Nabaltec, as Aeroxide from Evonik, and as Alodur from Imerys), magnesium oxide, beryllium oxide, silicon dioxide, titanium oxide, zinc oxide, nickel oxide, copper oxide, or tin oxide, arsenides such as boron arsenide, carbides such as silicon carbide, minerals such as agate and emery, ceramics such as ceramic microspheres (for example, commercially available from Zeeospheres Ceramics or 3M), silicon carbide, and diamond. These flame retardant particles may be used alone or in a combination of two or more.

[0034] The flame retardant particles may have particle sizes that may be defined by d50 values of at least 0.1 micron, for example, at least 0.2 micron, or at least 0.5 micron. The flame retardant particles may have d50 values up to 100 microns, for example, up to 50 microns, or up to 20 microns, or up to 10 microns, or up to 5 microns, or up to 2 microns. The d50 values of the flame retardant particles may range from 0.1 to 100 microns, or from 0.2 to 50 microns, or from 0.5 to 20 microns, or from 1 to 10 microns or from 0.1 to 10 microns, or from 0.2 to 5 microns, or from 0.5 to 2 microns.

[0035] As used herein the term “d50” means the point in the particle size distribution in which 50 percent or more of the total volume of material in the sample is contained. For example, a d50 of 5 microns means that 50 percent of the particles of the sample have a size of 5 microns or smaller as measured by methods known to those skilled in the art, such as laser diffraction or Low Angle Laser Light Scattering (LALLS).

[0036] The flame retardant particles may be present in amounts of at least 0.5 weight percent of the absorbing material, for example, at least 1 weight percent, or at least 2 weight percent. The flame retardant particles may be present in amounts up to 30 weight percent of the absorbing material, for example, up to 10 weight percent, or up to 5 weight percent. The flame retardant particles may range from 0.5 to 30 weight percent based upon the total weight of the broadband millimeter wave absorbing material, for example, from 1 to 10 weight percent, or from 2 to 5 weight percent.

[0037] When the flame retardant broadband millimeter wave absorbing material is provided in sheet form, it may have a thickness of at least 0.1 mm, for example, at least 1 mm, or at least 2 mm. The sheet may have a thickness up to 10 mm of the absorbing material, for example, up to 5 mm, or up to 4 mm. The sheet thickness may range from 0.1 to 10 mm, or from 1 to 5 mm, or from 2 to 4 mm. When such sheets include a surface profile comprising projections that extend above a base planar layer of the sheet, such projections may have heights measured perpendicular to the plane of the base layer of from 5 to 90 percent of the total thickness of the sheet, or from 20 to 80 percent, or from 40 to 60 percent.

[0038] The flame retardant broadband millimeter wave absorbing materials may be produced in sheet form by any suitable process such as molding, compression molding, injection molding, casting, machining, roller-forming, extruding, curtain coating, screen printing, spraying, additive manufacturing, and the like. Additive manufacturing may include three- dimensional (3D) printing, extrusion, jetting, binder jetting and ambient reactive extrusion. Additive manufacturing refers to a process of producing a part or member by constructing it in layers, such as one layer at a time. 3D printing refers to a computerized process by which materials are printed or deposited in successive layers to produce a 3D part or member, such as the flame retardant broadband millimeter wave absorber sheets. Any suitable mixing, delivery, and 3D printing equipment as known to those skilled in the art, may be used.

[0039] The carbon-containing electromagnetic wave absorbing particles and / or flame retardant particles may be dispersed uniformly throughout the thickness of the sheet, for example, uniformly dispersed throughout the thickness Tb of the base layer 12, throughout the thickness Tsof the texture layer 14, or throughout the total thickness Ttof the sheet 10. Alternatively, the carbon-containing electromagnetic wave absorbing particles and / or flame retardant particles may be dispersed non-uniformly throughout the thickness of the sheet, e.g., non-uniformly dispersed throughout the total thickness Tt, base thickness Tb and / or surface thickness Ts. Non-uniform particle dispersions may be graded or multi-layered to provide different particle loadings in the matrix material at different locations on or in the matrix, such as at different locations through the thickness of the sheet. For example, a multiple layer sheet may be formed with selected particle loadings in each layer by additive manufacturing or any other suitable fabrication process.

[0040] The sheet may comprise a thin flexible carbon-loaded silicone based broadband absorber material. The material is a dielectric absorber with no magnetic properties. The absorptive sheets may have automotive applications such as blind spot detection, lane departure and collision avoidance, automotive radar systems, and reflectivity reduction in high frequency applications. The material may be electrically conductive and waterproof. Typical properties include: Frequency range 35-100 GHz, Service Temperature °C (°F) -50 to 160 (-58 to 320), Fire Retardancy UL94V-0. The sheet size may be, for example, 12” x 12” (305 mm x 305 mm) or any other desired size. The sheets may also be supplied with pressure sensitive adhesive (PSA) as C-RAM MMA / PSA supplied by Cuming Microwave.

[0041] The broadband millimeter wave absorbing sheets may enable the use of high frequency radar sensing technologies. For example, the sheets may be beneficial to automotive designers attempting to reduce the EM reflections in tight spaces, e.g., bumper, to maximize the accuracy of sensing technologies while meeting UL-94 flame retardancy standards. Similar types of examples can be imagined for test and measurement environments as well as robotics, among potentially many others.Additive Manufacturing of Articles including the Broadband Millimeter Wave Absorbing Materials

[0042] As described previously, sheets of broadband millimeter wave absorbing materials may be produced by any suitable manufacturing process, such as additive manufacturing. Additionally, and / or alternatively, articles comprising the broadband millimeter wave absorbing materials, either with or without flame retardancy, may also be produced by additive manufacturing techniques.

[0043] For instance, additive manufacturing using coreactive compositions, also referred to as ambient reactive extrusion or ARE type three-dimensional printing, typically utilizes at least two components that react with each other (that is, are coreactive). A first coreactive component and at least one second coreactive component, when extruded in combination and / or succession, chemically react with one another to form a coreactive composition. The coreactive composition may thereafter cure under ambient conditions or, depending on the chemistry of the reaction, with the assistance of, for example, heat, actinic radiation, catalysts, addition of curing agents-post extrusion, etc. to form an article, or a portion of an article, comprising a thermosetting polymer (sometimes referred to as a thermoset), a thermoplastic polymer, orcombinations thereof. At least the first coreactive component and the second coreactive component arc chosen by one skilled in the art to result in the desired final product (e.g., thermoset, thermoplastic, etc.). For instance, the coreactive composition may be selected, as based upon the previously described polymeric matrix material(s), such as silicones and (poly)urethanes.

[0044] One advantage of additive manufacturing using coreactive compositions may be that the coreactive compositions can be additively manufactured at relatively low viscosity (“viscosity” may refer to a value determined at 25°C and ambient pressure and reflects a fluid’s resistance to flow when subjected to a shear stress and / or a shear strain). Therefore, relatively large amounts (e.g., high relative weight percents) of additives and / or fillers can be included with the coreactive components while maintaining a printable viscosity. Both the type and / or the amount of additives can be selected or “tuned” to result in desirable chemical and / or physical properties of the printed article. For instance, coreactive compositions can be tuned with the addition of additives and / or fillers for desired mechanical performance (e.g., strength, elasticity, rigidity, sag resistance, etc.), surface features (e.g., hardness, texturing, smoothness, etc.), chemical resistance (e.g., solvent resistance, etc.), thermal resistance (including fire retardancy, etc.) or conductivity, and / or electrical insulation or conductivity. Coreactive compositions can also be tuned with the addition of one or more catalytic / activator / accelerant additives in any of the coreactive components to result in desirable reaction kinetics, such as rate of reaction.

[0045] Three dimensional articles formed from coreactive compositions are additively manufactured by extruding the coreactive composition, which may be in an at least partially reacted state, through a print nozzle and onto a surface, such as a build platform. The coreactive composition may be in an at least partially reacted state at the time of extrusion and thereafter fully react and cure under ambient conditions, forming a layer of the coreactive composition. Successive layers of the same and / or different coreactive compositions can be deposited, forming additional layers of material. The combination of layers forms the article. The coreactive composition may at least partially react when the coreactive components come together, such as in a mixing volume, just prior to extrusion through the print nozzle. Alternatively, the two coreactive components could be premixed before extrusion and treated in a way to arrest the reaction between the coreactive components, such as by freezing the composition upon mixing.

[0046] Additionally, thermal energy of various forms (i.e., radiative, conductive, and / or convective thermal energy) can be supplied to the corcactivc components and / or the resulting coreactive composition prior to, during, or post extrusion. The addition of the thermal energy assists in the ambient curing process, where the thermal energy increases or otherwise modifies the reaction rate between the coreactive components, thereby lowering the gel time, tack free time, and curing time associated with the resulting coreactive composition, as compared with the same coreactive composition additively manufactured without thermal assistance. Since the coreactive composition sets / gels faster, the printed material provides structural support for the part more quickly, thereby enabling printing of complex geometries. Furthermore, thermally assisted ambient reactive extrusion additive manufacturing may allow for objects to be printed without the need for support materials, such as tubular objects. Moreover, thermally assisted ambient reactive extrusion additive manufacturing may result in parts printed with less stack height errors, as compared to non-thermally assisted printing.

[0047] Such an additive manufacturing device arrangement may include one or more thermal energy sources which supply various forms of thermal energy to the coreactive components / compo sition. Specific examples of thermal energy sources include: convective thermal energy sources including a heat ring positioned circumferentially about the outer periphery of the print nozzle, and including a plurality of air ports configured to expel heated air at the distal end of the print nozzle; conductive thermal energy sources, such as heating elements (e.g., heat tape) positioned on any combination of the feed lines supplying the coreactive components to the pumping arrangements, the pumping arrangements themselves, and / or any suitable portion of the mixing volume / print nozzle arrangement; and radiative thermal energy sources including infrared emitter(s) that emit a beam of infrared radiation at either the distal end of the print nozzle (e.g., via a focused / point IR emitter) and / or the surface where the coreactive composition is being printed, such as the print bed (e.g., via a broad IR emitter).

[0048] The broadband millimeter wave absorber material, either with or without flame retardancy, may be included as an additive / filler in either, or both of, the first coreactive component and / or the second coreactive component and additively manufactured into articles via any the described devices. Therefore, layers of coreactive composition(s) that include the flameretardant broadband millimeter wave absorber material may be deposited successively to form sheets, such as those described previously, and / or articles (e.g., parts, members, etc.) comprisingthe broadband millimeter wave absorber material. Because either, or both of, the first coreactive component and the second corcactivc component can include relatively high weight percents of the broadband millimeter wave absorber materials (e.g., an additive and / or filler), the resulting additively manufactured article may comprise an appreciable amount of the broadband millimeter wave absorber material, with or without flame retardancy, thus exhibiting the beneficial effects as described herein. For instance, Example 2, described below, illustrates the additive manufacturing of an article from the broadband millimeter wave absorber material based upon a silicone matrix / base composition, without flame retardancy. Example 3 illustrates the additive manufacturing of an article from the broadband millimeter wave absorber material based upon a silicone matrix / base composition, with flame retardancy.

[0049] In view of the foregoing description the present disclosure thus relates to the following Aspects 1 to 67 without being limited thereto.

[0050] Aspect 1. A flame retardant broadband millimeter wave absorbing material comprising a polymeric matrix, carbon-containing electromagnetic wave absorbing particles comprising carbon black dispersed in the polymeric matrix, and a flame retardant material.

[0051] Aspect 2. The flame retardant broadband millimeter wave absorbing material of aspect 1, wherein the flame retardant material comprises flame retardant particles dispersed in the polymeric matrix.

[0052] Aspect 3. The flame retardant broadband millimeter wave absorbing material of aspect 1 or 2, wherein the flame retardant particles comprise a metal hydroxide, a mineral, an organic compound, an organohalogen compound, an organophosphorus compound, or a combination thereof.

[0053] Aspect 4. The flame retardant broadband millimeter wave absorbing material of any of aspects 1 through 3, wherein the flame retardant particles comprise aluminum trihydrate.

[0054] Aspect 5. The flame retardant broadband millimeter wave absorbing material of any of aspects 1 through 4, comprising the flame retardant particles in an amount of at least 0.5 weight percent based on total weight of the broadband millimeter wave absorbing material, such as at least 1 weight percent.

[0055] Aspect 6. The flame retardant broadband millimeter wave absorbing material of any of aspects 1 through 5, comprising the flame retardant particles in an amount of at least 2 weight percent based on total weight of the broadband millimeter wave absorbing material.

[0056] Aspect 7. The flame retardant broadband millimeter wave absorbing material of any of aspects 1 through 6, comprising the flame retardant particles in an amount up to 30 weight percent based on total weight of the broadband millimeter wave absorbing material, such as up to 10 weight percent.

[0057] Aspect 8. The flame retardant broadband millimeter wave absorbing material of any of aspects 1 through 6, comprising the flame retardant particles in an amount up to 5 weight percent based on total weight of the broadband millimeter wave absorbing material.

[0058] Aspect 9. The flame retardant broadband millimeter wave absorbing material of any of aspects 1 through 5 and 7, comprising the flame retardant particles in an amount of 0.5 to 30 weight percent based on total weight of the broadband millimeter wave absorbing material, such as 1 to 10 weight percent.

[0059] Aspect 10. The flame retardant broadband millimeter wave absorbing material of any of aspects 1 through 9, comprising the flame retardant particles in an amount of 2 to 5 weight percent based on total weight of the broadband millimeter wave absorbing material.

[0060] Aspect 11. The flame retardant broadband millimeter wave absorbing material of any of aspects 1 through 10, wherein the flame retardant particles have a d50 particle size of at least 0.1 micron as measured by low angle laser light scattering, such as at least 0.2 micron.

[0061] Aspect 12. The flame retardant broadband millimeter wave absorbing material of any of aspects 1 through 11, wherein the flame retardant particles have a d50 particle size of at least 0.5 micron as measured by low angle laser light scattering.

[0062] Aspect 13. The flame retardant broadband millimeter wave absorbing material of any of aspects 1 through 12, wherein the flame retardant particles have a d50 particle size up to 100 microns as measured by low angle laser light scattering, such as up to 50 microns.

[0063] Aspect 14. The flame retardant broadband millimeter wave absorbing material of any of aspects 1 through 13, wherein the flame retardant particles have a d50 particle size up to 20 microns as measured by low angle laser light scattering, such as up to 10 microns.

[0064] Aspect 15. The flame retardant broadband millimeter wave absorbing material of any of aspects 1 through 14, wherein the flame retardant particles have a d50 particle size up to 5 microns as measured by low angle laser light scattering, such as up to 2 microns.

[0065] Aspect 16. The flame retardant broadband millimeter wave absorbing material of any of aspects 1 through 11 and 13, wherein the flame retardant particles have a d50 particle size of 0.1 to 100 microns as measured by low angle laser light scattering, such as 0.2 to 50 microns.

[0066] Aspect 17. The flame retardant broadband millimeter wave absorbing material of any of aspects 1 through 10, 12 to 14, and 16, wherein the flame retardant particles have a d50 particle size of 0.5 to 20 microns as measured by low angle laser light scattering, such as 1 to 10 microns.

[0067] Aspect 18. The flame retardant broadband millimeter wave absorbing material of any of aspects 1 through 11 and 13 to 17, wherein the flame retardant particles have a d50 particle size of 0.1 to 10 microns as measured by low angle laser light scattering, such as 0.2 to 5 microns.

[0068] Aspect 19. The flame retardant broadband millimeter wave absorbing material of any of aspects 1 through 18, wherein the flame retardant particles have a d50 particle size of 0.5 to 2 microns as measured by low angle laser light scattering.

[0069] Aspect 20. The flame retardant broadband millimeter wave absorbing material of any of aspects 1 through 19, comprising the carbon-containing electromagnetic wave absorbing particles in an amount of at least 2 weight percent based on total weight of the broadband millimeter wave absorbing material, such as at least 4 weight percent.

[0070] Aspect 21. The flame retardant broadband millimeter wave absorbing material of any of aspects 1 through 20, comprising the carbon-containing electromagnetic wave absorbing particles in an amount of at least 6 weight percent based on total weight of the broadband millimeter wave absorbing material.

[0071] Aspect 22. The flame retardant broadband millimeter wave absorbing material of any of aspects 1 through 21 , comprising the carbon-containing electromagnetic wave absorbing particles in an amount up to 30 weight percent based on total weight of the broadband millimeter wave absorbing material, such as up to 20 weight percent.

[0072] Aspect 23. The flame retardant broadband millimeter wave absorbing material of any of aspects 1 through 22, comprising the carbon-containing electromagnetic wave absorbing particles in an amount up to 15 weight percent based on total weight of the broadband millimeter wave absorbing material.

[0073] Aspect 24. The flame retardant broadband millimeter wave absorbing material of any of aspects 1 through 20 and 22, comprising the carbon-containing electromagnetic wave absorbing particles in an amount of 2 to 30 weight percent based on total weight of the broadband millimeter wave absorbing material, such as 4 to 20 weight percent.

[0074] Aspect 25. The flame retardant broadband millimeter wave absorbing material of any of aspects 1 through 24, wherein the carbon-containing electromagnetic wave absorbing particles are present in an amount of 6 to 15 weight percent based on total weight of the broadband millimeter wave absorbing material.

[0075] Aspect 26. The flame retardant broadband millimeter wave absorbing material of any of aspects 1 through 25, wherein the carbon-containing particles have an average particle size of at least 1 nanometer, such as at least 10 nanometer, wherein average particle size is measured by B.E.T. surface area techniques or TEM imaging techniques.

[0076] Aspect 27. The flame retardant broadband millimeter wave absorbing material of any of aspects 1 through 26, wherein the carbon-containing particles have an average particle size of at least 20 nanometers, wherein average particle size is measured by B.E.T. surface area techniques or TEM imaging techniques.

[0077] Aspect 28. The flame retardant broadband millimeter wave absorbing material of any of aspects 1 through 27, wherein the carbon-containing particles have an average particle size of up to 200 nanometers, such as up to 100 nanometers, wherein average particle size is measured by B.E.T. surface area techniques or TEM imaging techniques.

[0078] Aspect 29. The flame retardant broadband millimeter wave absorbing material of any of aspects 1 through 28, wherein the carbon-containing particles have an average particle size of up to 50 nanometers, wherein average particle size is measured by B.E.T. surface area techniques or TEM imaging techniques.

[0079] Aspect 30. The flame retardant broadband millimeter wave absorbing material of any of aspects 1 through 26 and 28, wherein the carbon-containing particles have an average particle size of 1 to 200 nanometers, such as 10 to 100 nanometers, wherein average particle size is measured by B.E.T. surface area techniques or TEM imaging techniques.

[0080] Aspect 31. The flame retardant broadband millimeter wave absorbing material of any of aspects 1 through 30, wherein the carbon-containing particles have an average particlesize of 20 to 50 nanometers, wherein average particle size is measured by B.E.T. surface area techniques or TEM imaging techniques.

[0081] Aspect 32. The flame retardant broadband millimeter wave absorbing material of any of aspects 1 through 31, wherein the carbon-containing particles comprise at least 50 weight percent carbon black based upon the total weight percent of the flame retardant broadband millimeter wave absorbing material, such as at least 90 weight percent.

[0082] Aspect 33. The flame retardant broadband millimeter wave absorbing material of any of aspects 1 through 32, wherein the polymeric matrix comprises an elastomer.

[0083] Aspect 34. The flame retardant broadband millimeter wave absorbing material of any of aspects 1 through 33, wherein the polymeric matrix comprises silicone, urethane, polycarbonate, polyamide, polyester, polyolefin, epoxy, neoprene or combinations thereof.

[0084] Aspect 35. The flame retardant broadband millimeter wave absorbing material of any of aspects 1 through 33, wherein the polymeric matrix comprises silicone.

[0085] Aspect 36. The flame retardant broadband millimeter wave absorbing material of any of aspects 1 through 35, comprising the polymeric matrix in an amount of at least 50 weight percent based on total weight of the broadband millimeter wave absorbing material, such as at least 70 weight percent.

[0086] Aspect 37. The flame retardant broadband millimeter wave absorbing material of any of aspects 1 through 36, comprising the polymeric matrix in an amount of at least 80 weight percent based on total weight of the broadband millimeter wave absorbing material.

[0087] Aspect 38. The flame retardant broadband millimeter wave absorbing material of any of aspects 1 through 37, comprising the polymeric matrix in an amount up to 98 weight percent based on total weight of the absorbing material, such as up to 95 weight percent.

[0088] Aspect 39. The flame retardant broadband millimeter wave absorbing material of any of aspects 1 through 38, comprising the polymeric matrix in an amount up to 92 weight percent based on total weight of the absorbing material.

[0089] Aspect 40. The flame retardant broadband millimeter wave absorbing material of any of aspects 1 through 36 and 38, comprising the polymeric matrix in an amount of 50 to 98 weight percent based on total weight of the absorbing material, such as 70 to 95 weight percent.

[0090] Aspect 41 . The flame retardant broadband millimeter wave absorbing material of any of aspects 1 through 40, comprising the polymeric matrix in an amount of 80 to 92 weight percent based on total weight of the absorbing material.

[0091] Aspect 42. The flame retardant broadband millimeter wave absorbing material of any of aspects 1 through 41, wherein the polymeric matrix comprises a material.

[0092] Aspect 43. The flame retardant broadband millimeter wave absorbing material aspect 42, wherein the material has an elongation of at least 20 percent, such as at least 50 percent.

[0093] Aspect 44. The flame retardant broadband millimeter wave absorbing material of aspect 42 or aspect 43, wherein the material has an elongation of at least 70 percent, such as at least 90 percent.

[0094] Aspect 45. The flame retardant broadband millimeter wave absorbing material of any of aspects 42 through 44, wherein the material has a tensile strength of at least 200 psi, such as at least 500 psi.

[0095] Aspect 46. The flame retardant broadband millimeter wave absorbing material of any of aspects 42 through 45, wherein the material has a tensile strength of at least 700 psi.

[0096] Aspect 47. The flame retardant broadband millimeter wave absorbing material of any of aspects 42 through 46, wherein the material has a dielectric constant of 1 to 4 at 1000 Hz, such as 2 to 3 at 1000 Hz.

[0097] Aspect 48. The flame retardant broadband millimeter wave absorbing material of any of aspects 42 through 47, wherein the material has a volume resistivity of at least 1 x 1010ohm-cm, such as at least 1 x 1012ohm-cm.

[0098] Aspect 49. The flame retardant broadband millimeter wave absorbing material of any of aspects 42 through 48, wherein the material has a volume resistivity of at least 1 x 1014ohm-cm, such as at least 1 x 1015ohm-cm.

[0099] Aspect 50. The flame retardant broadband millimeter wave absorbing material of any of aspects 42 through 49, wherein the material is non-magnetic material.

[0100] Aspect 51. The flame retardant broadband millimeter wave absorbing material of any of aspects 1 through 50, wherein the flame retardant broadband millimeter wave absorbing material is in the form of a sheet.

[0101] Aspect 52. The flame retardant broadband millimeter wave absorbing material of aspect 51, wherein the sheet has a thickness of at least 0.1 mm, such as at least 1 mm.

[0102] Aspect 53. The flame retardant broadband millimeter wave absorbing material of aspect 51 or aspect 52, wherein the sheet has a thickness of at least 2 mm.

[0103] Aspect 54. The flame retardant broadband millimeter wave absorbing material of any of aspects 51 through 53, wherein the sheet has a thickness of up to 10 mm, such as up to 5 mm.

[0104] Aspect 55. The flame retardant broadband millimeter wave absorbing material of any of aspects 51 through 54, wherein the sheet has a thickness of up to 4 mm.

[0105] Aspect 56. The flame retardant broadband millimeter wave absorbing material of any of aspects 51, 52 and 54, wherein the sheet has a thickness of 0.1 to 10 mm, such as 1 to 5 mm.

[0106] Aspect 57. The flame retardant broadband millimeter wave absorbing material of any of aspects 51 through 56, wherein the sheet has a thickness of 2 to 4 mm.

[0107] Aspect 58. The flame retardant broadband millimeter wave absorbing material of any of aspects 51 through 57, wherein the sheet has a surface profile comprising a projection.

[0108] Aspect 59. The flame retardant broadband millimeter wave absorbing material of aspect 58, wherein the projection has a height measured perpendicular to a plane of a base layer of 5 to 90 percent of a total thickness of the sheet, such as 20 to 80 percent.

[0109] Aspect 60. The flame retardant broadband millimeter wave absorbing material of aspect 58 or aspect 59, wherein the projection has a height measured perpendicular to a plane of a base layer of 40 to 60 percent of a total thickness of the sheet.

[0110] Aspect 61. The flame retardant broadband millimeter wave absorbing material of any of aspects 51 through 60, wherein the sheet has a thickness less than or equal to 4 mm and has a broadband millimeter wave attenuation of at least -15 dB in a frequency band of from 75 to 110 GHz measured by a Vector Network Analyzer equipped with standard horn antennas.

[0111] Aspect 62. The flame retardant broadband millimeter wave absorbing material of any of aspects 51 through 61, wherein the sheet comprises a pyramidal surface pattern.

[0112] Aspect 63. The flame retardant broadband millimeter wave absorbing material of any of aspects 51 through 62, wherein the sheet has a flame retardancy passing a UL94 V0 standard test.

[0113] Aspect 64. A molded sheet comprising the flame retardant broadband millimeter wave absorbing material of any of aspects 1 through 63.

[0114] Aspect 65. An additively manufactured article comprising the flame retardant broadband millimeter wave absorbing material of any of aspects 1 through 63.

[0115] Aspect 66. A use of the flame retardant broadband millimeter wave absorbing material of any of aspects 62 through 63 for forming the sheet having the pyramidal surface pattern.

[0116] Aspect 67. The use of aspect 66, for forming the sheet, wherein the sheet has a flame retardancy passing a UL94 VO standard test.

[0117] The following examples are for illustration purposes, which, however, are not to be considered as limiting.Example 1

[0118] A formulation including the ingredients and amounts listed in Table 1 was prepared as follows: Charge mixing tank with silicone resin part A and carbon black. The carbon black had the following characteristics: B.E.T. surface area of 223 m2 / g, Iodine number 253 mg / g (ASTM D1510), OAN equal to 192 cc / lOOg (ASTM D2414), 325 mesh residual of less than 10 ppm (ASTM D1514), and tint equal to 87% (ASTM D3265). Aluminum trihydrate flame retardant was added. The formulation was mixed until homogenously dispersed. The silicone curing agent pail B was added, and the formulation was mixed thoroughly. The formulation was cast into a mold to impart a pyramidal array that was coated with a standard release agent. The mold was compressed under at least 30 psi of force and cured for 48 hours at room temperature, or for 2 hours at 100°C. The cured composite was demolded.Table 1

[0119] The compression molded sheet with pyramidal features has a total thickness of 4 mm similar’ to that shown in Figs. 1-3.

[0120] Fig. 4 demonstrates broadband absorption of EM energy across a frequency range of 75-100+ GHz for the flexible polymeric sheet as measured by a Vector Network Analyzer equipped with standard horn antennas.

[0121] The flexible polymeric sheet met UL-94 V0 flammability capability.Comparative Example 1

[0122] Example 1 was repeated except no alumina trihydrate was added to the formulation. Unlike the formulation of Example 1, the flame retardant-free material did not pass the UL-94 V0 flammability test.Example 2

[0123] Measurements were performed on a broadband millimeter wave absorbing sheet similar to that of Example 1 having a thickness of 3.6 mm in a frequency range of from 140 GHz to 220 GHz at 100 MHz spacing using a focused lens system calibrated to a mirror reflection of unity with the beam focused on the sample-to-air interface. System beam spot size at the sample was approximately 1 cm x 1.5 cm. Time gating was used to isolate sample Sn response. Direct measurements of Sn were taken at normal incident (0 deg) and 45-degree incident angles (as measured from the sample normal) for both vertical (p-pol) and horizontal (s-pol) polarizations and for absorber samples with and with a backing mirror. Figs. 5 and 6 schematically illustrate the measurement geometries without a backing mirror (Fig. 5) and with a backing mirror (Fig. 6). Return loss data represented as the complex Sn values and Sn in dB vs frequency were evaluated. Return loss (RL) is given by the equation,Su(dB)= RL= 20*Log10(|Sn|)

[0124] This definition of return loss docs not add a negative sign in front of the logarithm, so RL will be equal to Sn in dB and thus a negative value for the absorbing material. Plots of the return loss in dB vs frequency are shown in Figs. 7 and 8. Fig. 7 corresponds to a test sample using a backing mirror as schematically shown in Fig. 6. Fig. 8 corresponds to a test sample using no backing mirror as schematically shown in Fig. 5.Example 3Additively Manufactured Silicone-based Formulation without Flame Retardancy

[0125] A 2k silicone elastomer formulation incorporating a rheology modifier is 3D printed at ambient conditions and with a broad / short focal length IR emitter set to 100°C. The Aand B components of the formulation are formulated using the compositions below. The A component of the formulation is made from the components in Table 2.

[0126] From Table 2, the silicone Part A resin and rheology modifier(s) are weighed in a Max 300 L Flacktek DAC cup and dispersed via standard Speedmixer procedure.Table 2A component

[0127] The B component of the silicone elastomer composition is made according to the formulation in Table 3.

[0128] From Table 3, the silicone Part B resin and the rheology modifier arc weighed in a Max 300L Flacktek DAC cup and dispersed via standard Speedmixer procedure.Table 3B component

[0129] The A and B components for the formulation are transferred from the DAC cup to a 32 oz. cartridge via Flacktek SpeedDisc for optimal 3D printing by reactive extrusion via progressive cavity extruders mounted to a 3-axis gantry Printer. The gantry also supports a thermal energy source directed towards the nozzle tip. The A and B components are printed at print parameters listed in Table 4.

[0130] The silicone elastomer formulation is printed in single layer stacks ranging from 1 layer to 10 layers at a consistent layer time at ambient conditions and at 100°C using a broad / short focal length IR emitter. The resolution and buildability of the material under IR radiation at 100°C is measured to be better than ambient conditions with the material specified in this example.Table 4Print parameters for silicone elastomer formulation at ambient conditions and 100°CExample 4Additively Manufactured Silicon-based Formulation with Flame Retardancy

[0131] A 2k flame retardant silicone elastomer formulation incorporating additives and rheology modifiers is 3D printed at ambient conditions and with a broad / short focal length IR emitter set to 100°C. The A and B components of the formulation are formulated using the compositions below. The A component of the formulation is made from the components in Table 5.

[0132] From Table 5, the silicone Part A resin, additive, and rheology modifier(s) are weighed in a Max 300 E Flacktek DAC cup and dispersed via standard Speedmixer procedure.Table 5A component

[0133] The B component of the silicone elastomer composition is made according to the formulation in Table 6.

[0134] From Table 6, the silicone Part B resin, additive, and the rheology modifier are weighed in a Max 300E Flacktek DAC cup and dispersed via standard Speedmixer procedure.Table 6B component

[0135] The A and B components for the formulation are transferred from the DAC cup to a 32 oz. cartridge via Flacktek SpeedDisc for optimal 3D printing by reactive extrusion via progressive cavity extruders mounted to a 3-axis gantry 3D printer. The gantry also supports a thermal energy source directed towards the nozzle tip. The A and B components are printed at print parameters listed in Table 7.

[0136] The flame-retardant silicone elastomer formulation is printed in single layer stacks ranging from 1 layer to 10 layers at a consistent layer time at ambient conditions and at 100°C using a broad / short focal length IR emitter. The resolution and buildability of the material under IR radiation at 100°C is measured to be better than ambient conditions with the material specified in this example.Table 7Printing parameters for flame retardant silicone elastomer.

[0137] For purposes of the detailed description, it is to be understood that the disclosure may assume various alternative variations, except where expressly specified to the contrary.

[0138] The numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard variation found in their respective testing measurements.

[0139] Also, any numerical range recited herein is intended to include all sub-ranges subsumed therein. For example, a range of “1 to 10” is intended to include all sub-rangesbetween (and including) the recited minimum value of 1 and the recited maximum value of 10, that is, having a minimum value equal to or greater than 1 and a maximum value of equal to or less than 10.

[0140] In addition, in this application, the use of “or” means “and / or” unless specifically stated otherwise, even though “and / or” may be explicitly used in certain instances.

[0141] As used herein, “including,” “containing” and like terms are understood in the context of this application to be synonymous with “comprising” and are therefore open-ended and do not exclude the presence of additional undescribed or unrecited elements, materials, ingredients or method steps. As used herein, “consisting of’ is understood in the context of this application to exclude the presence of any unspecified element, ingredient or method step. As used herein, “consisting essentially of’ is understood in the context of this application to include the specified elements, materials, or ingredients and those that do not materially affect basic and novel characteristics of what is being described.

[0142] As used herein, the terms “on,” “onto,” “applied on,” “applied onto,” “formed on,” “deposited on,” “deposited onto,” mean formed, overlaid, deposited, or provided on but not necessarily in contact with the surface. For example, a coating composition “deposited onto” a substrate does not preclude the presence of one or more other intervening coating layers of the same or different composition located between the coating composition and the substrate.

[0143] Whereas particular examples of this disclosure have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details of the present disclosure may be made without departing from what is defined in the appended claims.

Claims

CLAIMS:

1. A flame retardant broadband millimeter wave absorbing material comprising: a polymeric matrix; carbon-containing electromagnetic wave absorbing particles comprising carbon black dispersed in the polymeric matrix; and a flame retardant material.

2. The flame retardant broadband millimeter wave absorbing material of claim 1, wherein the flame retardant material comprises flame retardant particles dispersed in the polmeric matrix.

3. The flame retardant broadband millimeter wave absorbing material of claim 2, wherein the flame retardant particles comprise a metal hydroxide, a mineral, an organic compound, an organohalogen compound, an organophosphorus compound, or a combination thereof.

4. The flame retardant broadband millimeter wave absorbing material of claim 2, wherein the flame retardant particles comprise aluminum trihydrate.

5. The flame retardant broadband millimeter wave absorbing material of claim 2, wherein the polymeric matrix comprises 50 to 98 weight percent based upon the total weight percent of the flame retardant broadband millimeter wave absorbing material, the carbon- containing particles comprise 2 to 30 weight percent based upon the total weight percent of the flame retardant broadband millimeter wave absorbing material, and / or the flame retardant particles comprise 0.5 to 30 weight percent based upon the total weight percent of the flame retardant broadband millimeter wave absorbing material.

6. The flame retardant broadband millimeter wave absorbing material of claim 5, wherein the carbon-containing particles comprise 4 to 20 weight percent.

7. The flame retardant broadband millimeter wave absorbing material of claim 5, wherein the carbon-containing particles comprise 6 to 15 weight percent.

8. The flame retardant broadband millimeter wave absorbing material of claim 5, wherein the flame retardant particles comprise 1 to 10 weight percent.

9. The flame retardant broadband millimeter wave absorbing material of claim 5, wherein the flame retardant particles comprise 2 to 5 weight percent.

10. The flame retardant broadband millimeter wave absorbing material of any of claims 2-9, wherein the flame retardant particles have a d50 particle size of 0.1 to 100 microns.

11. The flame retardant broadband millimeter wave absorbing material of any of claims 2-10, wherein the carbon-containing particles have an average particle size of 10 to 100 nanometers.

12. The flame retardant broadband millimeter wave absorbing material of any of claims 2-11, wherein the carbon-containing particles comprise at least 50 weight percent carbon black.

13. The flame retardant broadband millimeter wave absorbing material of any of claims 2-11, wherein the carbon-containing particles comprise at least 90 weight percent carbon black.

14. The flame retardant broadband millimeter wave absorbing material of any of claims 1-13, wherein the polymeric matrix comprises an elastomer.

15. The flame retardant broadband millimeter wave absorbing material of any of claims 1-14, wherein the polymeric matrix comprises silicone, urethane, polycarbonate, polyamide, polyester, polyolefin, epoxy, neoprene or combinations thereof.

16. The flame retardant broadband millimeter wave absorbing material of any of claims 1-15, wherein the polymeric matrix comprises silicone.

17. The flame retardant broadband millimeter wave absorbing material of any of claims 1-16, wherein the material is in the form of a sheet having a thickness of 0.1 to 10 mm.

18. The flame retardant broadband millimeter wave absorbing material of claim 17, wherein the sheet has a thickness less than or equal to 4 mm and has a broadband millimeter wave attenuation of at least -15 dB in a frequency band of 75 to 110 GHz.

19. The flame retardant broadband millimeter wave absorbing material of any of claims 1-18, wherein the sheet comprises a pyramidal surface pattern.

20. The flame retardant broadband millimeter wave absorbing material of any of claims 1-19, wherein the sheet has a flame retardancy passing a UL94 VO standard test.

21. A molded sheet comprising the flame retardant broadband millimeter wave absorbing material of any one of claims 1 through 20.

22. An additively manufactured article comprising the flame retardant broadband millimeter wave absorbing material of any one of claims 1 through 20.

23. A use of the flame retardant broadband millimeter wave absorbing material of any of claims 1 through 20 for forming a sheet having a pyramidal surface pattern.

24. The use of any of claims 1 through 20 for forming a sheet having a flame retardancy passing a UL94 V0 standard test.

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