WO2025099515A1

WO2025099515A1 - Composites containing graphene coated hollow particles useful in high frequency applications

Info

Publication number: WO2025099515A1
Application number: PCT/IB2024/060091
Authority: WO
Inventors: Dipankar Ghosh; Md Abdulla Al MASUD
Original assignee: 3M Innovative Properties Co
Current assignee: 3M Innovative Properties Co
Priority date: 2023-11-09
Filing date: 2024-10-15
Publication date: 2025-05-15
Anticipated expiration: 2026-05-09

Abstract

A composite comprising a polymeric matrix and coated particles dispersed within the polymeric matrix. The coated particles comprise hollow particles made from electrically resistive material, and a coating comprising graphene flakes in direct contact with the outer surface of the hollow particles. The hollow particles are made by mechanically exfoliating layered graphene to create graphene flakes and coating the hollow particles with the graphene flakes. The composites may be used as electromagnetic interference (EMI) mitigation materials in high frequency applications.

Description

COMPOSITES CONTAINING GRAPHENE COATED HOLLOW PARTICLES USEFUL IN HIGH FREQUENCY APPLICATIONS

Background

[0001] Electromagnetic interference (“EMI”) is becoming increasingly problematic in many commercial microelectronics applications due to the growing need for more powerful and compact electronic devices. EMI is a disturbance caused by electromagnetic radiation that can disrupt or, in some instances, completely disable an electronic device. There are many sources of EMI. In some instances, sources of EMI exist outside an electronic device. In other instances, however, components within an electronic device can be a source of EMI that can affect other components within the electronic device and/or other nearby electronic devices. Although normal performance of an electronic device is usually restored upon elimination of the EMI source, the temporary failure of an electronic device by EMI may be critically important.

[0002] Reducing or eliminating undesirable EMI, in general, can be achieved by either reflection of the electromagnetic radiation, absorption of the electromagnetic radiation, or both. A common solution is to use a highly conductive metal sheet, known as an electromagnetic (EM) shield, to reflect undesirable electromagnetic radiation away from a device. However, the shield may not provide sufficient reflectance or, depending upon the application, the reflecting radiation may cause additional problems, such as interference with other nearby electronic devices. In such instances, absorption of electromagnetic radiation is the preferred mitigation method. Therefore, there is considerable interest in next generation EMI mitigation materials that shield electronic devices by absorption of electromagnetic radiation or absorption in combination with reflectance of electromagnetic radiation, especially for applications in the higher frequency ranges, such as 1-40 GigaHertz (GHz) for telecommunication applications and 70-110 GHz for automobile applications.

Summary

[0003] The present disclosure provides composites that may be used as EMI mitigation materials in high frequency applications. The composites can exhibit high absorption, low reflection and/or minimal transmission of high frequency electromagnetic radiation.

[0004] In one embodiment, the present disclosure provides a composite comprising a polymeric matrix and coated particles dispersed within the polymeric matrix. The coated particles comprise hollow particles made from electrically resistive material, each hollow particle having an outer surface, and a coating comprising graphene flakes in direct contact with the outer surface. In some embodiments, the coating does not comprise a binder. In some embodiments, the hollow particles are glass bubbles, nanotubes, or combinations thereof.

[0005] In another embodiment, the present disclosure provides an article comprising the composite. In some embodiments, the article is an electronic mobile device. [0006] In a further embodiment, the present disclosure provides a method of making the composite, the method comprising combining the coated particles with a curable polymeric matrix material, and curing the polymeric matrix material to form the composite.

[0007] In another embodiment, the present disclosure provides the coated particles.

[0008] In yet another embodiment, the present disclosure provides a method of making the coated particles, the method comprising combining the hollow particles with layered graphene, mechanically exfoliating the layered graphene to create graphene flakes, and coating the hollow particles with the graphene flakes.

[0009] As used herein:

[0010] The term “comprises” and variations thereof do not have a limiting meaning where these terms appear in the description and claims. Such terms will be understood to imply the inclusion of a stated step or element or group of steps or elements but not the exclusion of any other step or element or group of steps or elements. By “consisting of’ is meant including, and limited to, whatever follows the phrase “consisting of.” Thus, the phrase “consisting of’ indicates that the listed elements are required or mandatory, and that no other elements may be present. By “consisting essentially of’ is meant including any elements listed after the phrase, and limited to other elements that do not interfere with or contribute to the activity or action specified in the disclosure for the listed elements. Thus, the phrase “consisting essentially of’ indicates that the listed elements are required or mandatory, but that other elements are optional and may or may not be present depending upon whether or not they materially affect the activity or action of the listed elements.

[0011] The terms “a,” “an,” and “the” are used interchangeably with “at least one” to mean one or more of the components being described.

[0012] The term “and/or” means one or all of the listed elements or a combination of any two or more of the listed elements.

[0013] The term “some embodiments” means that a particular feature, configuration, composition, or characteristic described in connection with the embodiment is included in at least one embodiment of the disclosure. Thus, the appearances of such phrases in various places throughout this specification are not necessarily referring to the same embodiment of the disclosure. Furthermore, the particular features, configurations, compositions, or characteristics may be combined in any suitable manner in one or more embodiments.

[0014] The terms “preferred” and “preferably” refer to embodiments of the disclosure that may afford certain benefits, under certain circumstances; however, other embodiments may also be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful, and is not intended to exclude other embodiments from the scope of the disclosure.

[0015] All numbers are assumed to be modified by the term “about”. As used herein in connection with a measured quantity, the term “about” refers to that variation in the measured quantity as would be expected by the skilled artisan making the measurement and exercising a level of care commensurate with the objective of the measurement and the precision of the measuring equipment used.

[0016] The recitations of numerical ranges by endpoints include all numbers subsumed within that range as well as the endpoints (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc.). The phrase “up to” a number (e.g., up to 50) includes the number (e.g., 50).

[0017] The term “composite” means a material in which two or more materials coexist without chemical interaction, and one or more phases can be discrete or continuous.

[0018] The above summary of the present disclosure is not intended to describe each disclosed embodiment or every implementation of the present disclosure. The description that follows more particularly exemplifies illustrative embodiments.

Brief Description of Drawings

[0019] FIG. 1 is a plot of the EMI performance of the composite in Example 3 A; and

[0020] FIG. 2 is a plot of the EMI performance of the composite in Example 3B.

Detailed Description

[0021] The composites of the present disclosure generally comprise a polymeric matrix and coated particles dispersed within the polymeric matrix. The coated particles comprise hollow particles made from electrically resistive material and a coating comprising graphene flakes in direct contact with the outer surface of the hollow particles. The term “direct contact” as used herein, means that the coating is in physical contact with the surface of the hollow particles (i.e., no intermediate coating or layer). The composites can be used as EMI mitigation materials at high frequency ranges (e.g., 1-110 GHz) in a variety of applications. Each of the components is described in further detail below.

[0022] Coated Particles

[0023] The coated particles include hollow particles having a thin graphene coating in direct contact with the outer surface of the hollow particles. The hollow particles are typically made of an electrically resistive material. Electrically resistive, as used herein, means materials having an electrical resistivity of at least 10¹⁰ Q«m. In some embodiments, the electrical resistivity is IO¹⁰ to IO²² Q«m, or more particularly 10¹⁰ to IO¹⁸ Q«m. In some embodiments, the hollow particles have a void volume greater than 70%, 75%, 80%, 85% of 90%. Void volume can be determined, for example, from the true density of the hollow particles and the bulk density of the material making up the shell or casing of the hollow particles, i.e. void volume = (mass of sample of hollow particles / true density) - (mass of sample of hollow particles / bulk density). The “true density” of hollow particles is the quotient obtained by dividing the mass of a sample of hollow particles by the true volume of that mass of hollow glass microspheres as measured by a gas pycnometer. The “true volume” is the aggregate total volume of the hollow glass microspheres, not the bulk volume. In some embodiments, the hollow particles have a void volume of 70-95%, more particularly 80-95%. Exemplary hollow particles include glass bubbles, nanotubes, or combinations thereof.

[0024] Glass Bubbles [0025] In some embodiments, the hollow particles are glass bubbles. Glass bubbles, as the term is used herein, refer to hollow spheres made of glass, each having a substantially single-cell structure (i.e., each bubble is defined by only the outer wall with no additional exterior walls, partial spheres, concentric spheres, or the like present in each individual bubble). The hollow spheres have a rounded shape, e.g., an egg-shape, a pearl shape, a head shape, an ellipsoidal shape, a spheroidal shape, or a spherical shape. Preferably, the hollow spheres have a spherical shape. The glass bubbles may have an aspect ratio ranging from 1: 1 to 50: 1, 1: 1 to 40: 1, 1: 1 to 30: 1, 1: 1 to 20: 1, 1: 1 to 10: 1, or 1: 1 to 5: 1. In some embodiments, the aspect ratio is 1: 1.

[0026] The size of the glass bubbles are not particularly limiting and will depend upon the application for which they are intended. The term “size”, as used in this context, refers to the largest diameter of a glass bubble. In some embodiments, the glass bubbles can have a median size by volume in a range from 1 to 500 micrometers (pm), 1 to 100 micrometers, 5 to 100 micrometers, or from 10 to 60 micrometers (in some embodiments from 15 to 40 micrometers, 10 to 25 micrometers, 20 to 45 micrometers, 20 to 40 micrometers, 10 to 50 micrometers, or 10 to 30 micrometers). The median size is also called the d₅₀ size, where 50 percent by volume of the glass bubbles in the distribution are smaller than the indicated size, and 50 percent by volume of the glass bubbles in the distribution are greater than the indicated size.

[0027] Glass bubbles according to and/or useful for practicing the present disclosure can be made by techniques known in the art (see, e.g., U.S. Pat. No. 2,978,340 (Veatch et al.), U.S. Pat. No. 3,030,215 (Veatch et al.), U.S. Pat. No. 3,129,086 (Veatch et al.), U.S. Pat. No. 3,230,064 (Veatch et al.), U.S. Pat. No. 3,365,315 (Beck et al.), U.S. Pat. No. 4,391,646 (Howell), U.S. Pat. No. 4,767,726 (Marshall), and U.S. Pat. App. Pub. No. 2006/0122049 (Marshall et. al)). Techniques for preparing glass bubbles typically include heating milled frit, commonly referred to as "feed", which contains a blowing agent (e.g., sulfur or a compound of oxygen and sulfur). The resultant product (that is, "raw product") obtained from the heating step typically contains a mixture of glass bubbles, broken glass bubbles, and solid glass beads, the solid glass beads generally resulting from milled frit particles that failed to form glass bubbles. The milled frit typically has a range of particle sizes that influences the size distribution of the raw product. During heating, the larger particles tend to form glass bubbles that are more fragile than the mean, while the smaller particles tend to increase the density of the glass bubble distribution. When preparing glass bubbles by milling frit and heating the resulting particles, the amount of sulfur in the glass particles (i.e., feed) and the amount and length of heating to which the particles are exposed (e.g., the rate at which particles are fed through a flame) can typically be adjusted to vary the density of the glass bubbles. Uower amounts of sulfur in the feed and faster heating rates lead to higher density bubbles as described in U.S. Pat. Nos. 4,391,646 (Howell) and 4,767,726 (Marshall). Furthermore, milling the frit to smaller sizes can lead to smaller, higher density glass bubbles.

[0028] Although the frit and/or the feed may have any composition that is capable of forming a glass, in some embodiments the frit comprises from 50 to 90 wt.% SiCf. from 2 to 20 wt.% alkali metal oxides (for example, NazO or K2O), from 1 to 30 wt.% B2O3, from 0.005 to 0.5 wt.% sulfur (for example, as elemental sulfur, sulfate or sulfite), from 0 to 25 wt.% divalent metal oxides (for example, CaO, MgO, BaO, SrO, ZnO, or PbO), from 0 to 10 wt.% tetravalent metal oxides other than Si O2 (for example, TiCf. MnCh, or ZrCE), from 0 to 20 wt.% trivalent metal oxides (for example, AI2O3, FezCh, or SbzCh), from 0 to 10 wt.% oxides of pentavalent atoms (for example, P2O5 or V2O5), and from 0 to 5 wt.% fluorine (as fluoride) which may act as a fluxing agent to facilitate melting of the glass composition. Additional ingredients are useful in frit compositions and can be included in the frit, for example, to contribute particular properties or characteristics (for example, hardness or color) to the resultant glass bubbles. [0029] In some embodiments, the glass bubbles comprise a soda-lime borosilicate glass.

[0030] In some embodiments, the glass bubbles comprise 50 to 90 wt.% silica (SiCE), 2 to 20 wt.% alkali metal oxides (R2O), and 1 to 30 wt.% boron oxide (B2O3), based on the total weight of the glass bubbles. In the same, or different embodiments, the glass bubbles comprise no greater than 25 wt.% divalent metal oxide (RO), more particularly calcium oxide (CaO). In the same, or different embodiments, the glass bubbles further comprise no greater than 10 wt.% phosphorus oxide (P2O5). As used herein, “R” refers to a metal having the valence indicated, R2O an alkali metal oxide and RO being a divalent metal oxide, preferably an alkaline earth metal oxide.

[0031] Suitable glass bubbles may also be obtained commercially from, for example, 3M Company (Saint Paul, MN) under the designation 3M™ Glass Bubbles K, S, iM, XLD, Floated and HGS Series, including Glass Bubbles iM16K, Glass Bubbles S60, Glass Bubbles K42HS, and Glass Bubbles S32HS. In some embodiments, the glass bubbles are Glass Bubbles iM16K, Glass Bubbles S32HS, and combinations thereof. In some embodiments, the glass bubbles are iM16K.

[0032] The glass bubbles of the present disclosure typically have an average true density of at least

0.2 grams per cubic centimeter (g/cm^), 0.25 g/cm^, or 0.3 g/cmA In some embodiments, the glass bubbles have an average true density of up to 0.65 g/cn . 0.6 g/cirP. or 0.55 g/cn . For example, the average true density of the glass bubbles may be in a range from 0.2 g/cnP to 0.65 g/cm^, 0.25 g/cnP to 0.6 g/cm^, 0 3 g/crrU to 0.60 g/cm-3, or 0.3 g/cnP to 0.55 g/cmA The "average true density" or “real density” of the glass bubbles is the quotient obtained by dividing the mass of a sample of glass bubbles by the true volume of that mass of glass bubbles. The "true volume" is the aggregate total volume of the glass bubbles, not the bulk volume. The average true density can be measured using a pycnometer according to DIN EN ISO 1183-3. The pycnometer may be obtained, for example, under the trade designation "ACCUPYC II 1340 PYCNOMETER" from Micromeritics, Norcross, Georgia, or under the trade designations “PENTAPYCNOMETER” or “ULTRAPYCNOMETER 1000” from Formanex, Inc., San Diego, CA. Average true density can typically be measured with an accuracy of 0.001 g/cmA [0033] Nanotubes

[0034] In some embodiments, the hollow particles are nanotubes. Nanotubes are materials having a tube-like structure where the length of the tube-like structure is typically greater than the diameter. In some embodiments, the mean outer diameter of the nanotubes is 2 nanometers (nm) to 200 nm, more particularly 2 nm to 100 nm, or even more particularly 50 nm to 70 nm. The mean diameter can be determined by averaging the outer diameter of 20 nanotubes as measured by scanning electron microscopy (SEM). Required magnification of the SEM images depends on the size of the nanotubes. In some embodiments, the lengths of the nanotubes are 3 nanometers to 5 micrometers, more particularly 3 nanometers to 2 micrometers.

[0035] In some embodiments, the nanotubes have a mean aspect ratio ranging from 5: 1 to 50: 1, 5: 1 to 40: 1, 5: 1 to 30: 1, 5: 1 to 20: 1, or 10: 1 to 20: 1. The mean aspect ratio can be determined by averaging the aspect ratio of 20 nanotubes obtained using SEM. The aspect ratio of a single nanotube is determined by measuring the length (longest dimension) and the diameter of the nanotube and calculating the ratio of the length to the diameter.

[0036] Nanotubes include inorganic nanotubes (e.g., BN, M0S2, WS2 and SnS2), clay nanotubes (e.g., halloysite and imogolite), core shell nanotubes (e.g., Pbl2/WS2, BH3AVS2 and Sbfi/W^), and traditional ceramic nanotubes (e.g., TiCf. ZrCE and ZnO). In some embodiments, the nanotubes comprise halloysite, imogolite, or a combination thereof. In some embodiments, the nanotubes comprise halloysite.

[0037] Coating

[0038] The coating comprises graphene flakes in direct contact with the outer surfaces of the hollow particles. Flakes may be derived from layered graphene precursors that comprise individual layers held together by weak chemical forces (i.e., Van der Waals forces). In contrast, the carbon atoms within each layer are held together by stronger chemical forces (i.e., sp² hybridized covalent bonds) to form a two- dimensional honeycomb lattice. Mechanical exfoliation can be used to sheer off layers from the layered graphene precursors to form graphene flakes. These flakes are thinner than the layered graphene precursors from which they are derived and, due to their smaller size, exhibit unique physical and chemical properties that are distinct from the bulk layered graphene precursors. In some embodiments, the graphene flakes have no more than 100, 50, 25, 10, 9, 8, 7, 6, 5, 4, 3, 2 or 1 layers. In some embodiments, the graphene flakes have 1 to 100 layers, 1 to 50 layers, 1 to 25 layers, 1 to 10 layers, 1 to 5 layers, or even 1 layer.

[0039] The graphene flakes typically have a mean aspect ratio of at least 2: 1, 15: 1, 30: 1, or 50: 1. In some embodiments, the mean aspect ratio of the graphene flakes range from 2: 1 to 50: 1 or 2: 1 to 30: 1. The mean aspect ratio can be determined by averaging the aspect ratio of 20 flakes obtained using SEM. The aspect ratio of a single graphene flake is determined by measuring the length (longest dimension) and the thickness of the flake and calculating the ratio of the length to the thickness.

[0040] In some embodiments, the mean length of the graphene flakes is at least 10, 15, 20, 25, 30, 35, 40, 45, or 50 micrometers. In some embodiments, the mean length of the graphene flakes ranges from 10 to 50, from 10 to 40, from 10 to 30, or from 10 to 20 micrometers. The mean length can be determined by averaging the length of 20 flakes using SEM.

[0041] The graphene flakes are generally electrically conductive. Although electrical conductivity will depend, for example, upon flake size and coating thickness, in some embodiments, the graphene flakes have an electrical conductivity of 10⁷ to 10⁸ S/m in the planar direction. [0042] Additionally, the graphene flakes are typically thermally conductive, which can facilitate the dissipation of heat. In some embodiments, the thermal conductivity of the graphene plates is 3,000 to 3,300 W/m«K in the planar direction at room temperature.

[0043] The graphene flakes directly adhere to the surface of the hollow particles to form a two- dimensional coating. By “adhere to the surface” it is meant that the flakes are fixed on the surface of the individual hollow particles. When the coated particles, as disclosed herein, are compounded with a polymeric matrix material, the graphene flakes remain adhered to the surface of the hollow particles. [0044] The coating of the coated particles, as disclosed herein, typically does not comprise a binder. As used herein, “binder” means an organic or inorganic compound that has the function of adhering the flakes to one another and/or to the surface of the hollow particles, and that has been added to the hollow particles and the graphene flakes in the process for making the coated particles.

[0045] The graphene flakes of the coating may be placed in layers one upon another, or may be placed in an irregular manner on the surface of the hollow particles. Individual graphene flakes may be oriented parallel to the surface of the hollow particles, or may be oriented in any direction not parallel to the surface of the hollow particles. Individual graphene flakes may also be oriented perpendicularly to the surface of the hollow particles, i.e., in a radial manner. In some embodiments, most of the graphene flakes, i.e., more than 50% of the graphene flakes, are oriented parallel to the surface of the hollow particles.

[0046] The coating may be continuous or discontinuous on the outer surface of the hollow particles. In some embodiments, the coating covers at least 50, 60, 70, 80, 90 or 100% of the outer surface of the hollow particles. In some embodiments, the coating covers at least 90, 95 or 100% of the outer surface of the hollow particles. In preferred embodiments, the coating covers 100% of the outer surface of the hollow particles.

[0047] The thickness of the coatings may be up to 100 nm, 90 nm, 80 nm, 70 nm, 60 nm, 50 nm, 40 nm, 30 nm, 20 nm, or 10 nm. Thinner coats are preferable since they are more conductive and exhibit higher dielectric loss. Typically, the coating thickness is less than the smallest dimension of the hollow particles to which it is applied. In some embodiments, the thickness of the coating is no more than 10 nm, 9 nm, 8 nm, 7 nm, 6 nm, 5 nm, 4 nm, 3 nm, or 2 nm. In some embodiments, the thickness of the coating ranges from 1 nm to 10 nm, 2 nm to 5 nm, or 3 nm to 5 nm. The thickness of the coating on the coated particles may be measured by scanning electron microscopy (SEM). For example, in the case of coated glass bubbles, the thickness of the coating may be measured by crushing or fracturing of a plurality of coated glass bubbles by uniaxially pressing with a load of 10 kN and measurement of the thickness of the coating on the obtained fractured pieces of the coated glass bubbles by scanning electron microscopy (SEM). The coating thickness of coated nanotubes can be measured in a similar manner.

[0048] In some embodiments, the graphene flakes comprise no more than 20, 18, 16, 14 or 12 wt.% of the coated particles. In some embodiments, the flakes comprise 5 to 20 wt.% or 10 to 20 wt.% of the coated particles. [0049] The coated hollow particles of the present disclosure typically exhibit a dielectric permittivity (s’) and a dielectric loss (tan 5) greater than the uncoated hollow particles.

[0050] Method of Making

[0051] The coated particles of the present disclosure can be made by combining the hollow particles with a layered graphene precursor, mechanically exfoliating the layered graphene precursor to create flakes, and coating the hollow particles with the graphene flakes. The weight ratio of hollow particles to layered graphene precursor is at least 20: 1, 25: 1, 30: 1, 35: 1 or at least 40: 1. Typically, the weight ratio of hollow particles to layered graphene precursor is up to 50: 1, 45: 1, or 40: 1. In some embodiments, the weight ratio of hollow particles to layered graphene precursor ranges from 20: 1 to 50: 1, 20: 1 to 40: 1, or 20: 1 to 30: 1. If the amount of layered graphene precursor is too high, sufficient exfoliation of the layers may not occur.

[0052] Mechanical exfoliation separates the layers within the layered graphene precursor to create flakes. Exfoliation is typically carried out in a ball milling roller using relatively low mixing speeds and long mixing times. In some embodiments, the exfoliation is carried out at mixing speeds of at least 20, 25, 30, or 40 revolutions per minute (rpm). In the same or alternative embodiments, the exfoliation is carried out at mixing speeds up to 60, 55, 50, 45, or 40 rpm. In some embodiments, the exfoliation is carried out at mixing speeds ranging from 20 to 60, or 20 to 40 rpm. In some embodiments, the mixing time is at least 12, 18, or 24 hours. In the same or alternative embodiments, the mixing time is up to 60, 50, 40, or 30 hours. In some embodiments, the mixing time ranges from 12 to 60, from 12 to 50, from 12 to 40, from 12 to 30, or from 12 to 24 hours.

[0053] The graphene flakes obtained through exfoliation are simultaneously buff coated onto the outer surface of the hollow particles in the ball milling roller. Simultaneously, as used in this context, means that exfoliation and buff coating are occurring within the mixing time mentioned above. Buff coating refers to an operation in which a pressure is applied normal to a subject surface (e.g., the outer surface of the hollow particle) coupled with movement of flakes (e.g., rotational, lateral, combinations thereof) in a plane parallel to said surface.

[0054] The coating method can be carried out at room temperature (i.e., the method does not require heat treatment). This provides a low cost alternative to those coating processes using heat treatment and eliminates the need to soften the surface of the hollow particles.

[0055] In some embodiments, the coating method is substantially free of added liquids (e.g., solvents). The word “substantially” in this instance means that no liquids are added to the mixture of hollow particles and layered graphene precursor during the coating process.

[0056] Polymeric Matrix

[0057] Composites disclosed herein comprise a polymeric matrix and the coated particles dispersed therein. The polymer matrix may comprise a thermoplastic polymer, a thermoset polymer, an elastomeric polymer, or mixture thereof. Suitable polymers for the composite may be selected by those skilled in the art, depending at least partially on the desired application. [0058] In some embodiments, the polymeric matrix comprises a thermoplastic polymer. Exemplary thermoplastic polymers include polyolefins, fluorinated polyolefins, polyimide, polyamide-imide, polyether-imide, polyetherketone resins, polystyrenes, polystyrene copolymers, polyacrylates, polymethacrylates, polyesters, polyvinylchloride (PVC), liquid crystal polymers (LCP), polyphenylene sulfides (PPS), polysulfones, polyacetals, polycarbonates, polyphenylene oxides (PPO), polyphenyl ether (PPE), and blends thereof.

[0059] In some embodiments, the polymeric matrix comprises a thermoset polymer. Exemplary thermoset polymers include epoxies, polyesters, polyurethanes, polyureas, silicones, polysulfides, phenolics, vulcanized rubber, polyoxybenzylmethylenglycolanhydride, vinyl ester resin, and blends thereof.

[0060] In some embodiments, the polymer matrix comprises an elastomeric polymer. Exemplary useful elastomeric polymers include polybutadiene, polyisobutylene, ethylene-propylene copolymers, ethylene-propylene-diene terpolymers, sulfonated ethylene-propylene-diene terpolymers, polychloroprene, poly(2,3-dimethylbutadiene), poly(butadiene-co-pentadiene), chlorosulfonated polyethylenes, polysulfide elastomers, silicone elastomers, poly(butadiene-co-nitrile), hydrogenated nitrile-butadiene copolymers, acrylic elastomers, ethylene -acrylate copolymers, fluorinated elastomers, fluorochlorinated elastomers, fluorobrominated elastomers and combinations thereof. The elastomeric polymer may be a thermoplastic elastomer. Exemplary useful thermoplastic elastomeric polymer resins include block copolymers, made up of blocks of glassy or crystalline blocks of, for example, polystyrene, poly(vinyltoluene), poly(t-butylstyrene), and polyester, and elastomeric blocks of, for example, polybutadiene, polyisoprene, ethylene-propylene copolymers, ethylene-butylene copolymers, polyether ester, and combinations thereof. Some thermoplastic elastomers are commercially available, for example, poly(styrene-butadiene-styrene) block copolymers marketed by Shell Chemical Company, Houston, TX, under the trade designation “KRATON”.

[0061] In some embodiments, the polymeric matrix comprises silicone.

[0062] Other additives may be incorporated into the polymeric matrix according to the present disclosure depending on the application, e.g., preservatives, curatives, mixing agents, colorants, dispersants, floating or anti-setting agents, flow or processing agents, wetting agents, air separation promoters, functional nanoparticles, acid/base or water scavengers, or combinations thereof.

[0063] In some embodiments, the polymeric matrix comprises an impact modifier (e.g., an elastomeric resin or elastomeric filler). Exemplary impact modifiers include polybutadiene, butadiene copolymers, polybutene, ground rubber, block copolymers, ethylene terpolymers, core-shell particles, and functionalized elastomers available, for example, from Dow Chemical Company, Midland, MI, under the trade designation "AMPLIFY GR-216".

[0064] In some embodiments, the polymeric matrix comprises other density modifying additives like plastic bubbles (e.g., those available under the trade designation “EXPANCEL” from Akzo Nobel, Amsterdam, The Netherlands), blowing agents, or heavy fillers. In some embodiments, polymeric matrix may further comprise at least one of glass fiber, wollastonite, talc, calcium carbonate, titanium dioxide (including nano-titanium dioxide), carbon black, wood flour, other natural fillers and fibers (e.g., walnut shells, hemp, and com silks), silica (including nano-silica), and clay (including nano-clay).

[0065] Composite

[0066] The composite described herein can be made by combining the coated particles with a curable polymeric matrix material and curing the polymeric matrix material to form the composite. [0067] In some embodiments, the composite may comprise up to 60, 55, 50, 45, 40, 35, 30, 25, 20, 15 or 10 percent by volume (vol.%) of the coated particles, based on the total volume of the composite. In some embodiments, the composite material may comprise from 2 to 60, from 20 to 50, or from 30 to 50 vol.% of the coated particles, based on the total volume of the composite.

[0068] In some embodiments, the composite may comprise up to 50, 45, 40, 35, 30, 25, 20 wt.% of the coated particles, based on the total weight of the composite. In some embodiments, the composite material may comprise from 1 to 50, 1 to 40, 1 to 30, or 1 to 20 wt.% of the coated particles, based on the total weight of the composite.

[0069] When the coated particles are coated nanotubes, it is possible to reduce the loading level of the coated particles in the composite due to the higher aspect ratio of the hollow nanotubes. Without wishing to be bound by theory, it is believed that the nanotubes may align with and touch adjacent nanotubes during processing to form a network throughout the matrix that allows for lower loading levels. This reduced loading level can be advantageous as composites with higher loading levels can be more difficult to process, negatively impact the mechanical performance of the resultant composite, and/or increase cost of manufacture. Therefore, in some embodiments, it is preferable that the composite comprise coated nanotubes.

[0070] In some embodiments, the composite may comprise up to 20, 18, 16, 14, 12, 10, 8, 6, 4 or 2 vol.% of the coated nanotubes, based on the total volume of the composite. In some embodiments, the composite material may comprise from 1 to 20, 2 to 20, or 2 to 10 vol.% of the coated nanotubes, based on the total volume of the composite.

[0071] In some embodiments, the composite may comprise up to 20, 18, 16, 14, 12, 10, 8, 6, 4 or 2 wt.% of the coated nanotubes, based on the total weight of the composite. In some embodiments, the composite material may comprise from 1 to 20, 2 to 20, or 4 to 15 wt.% of the coated nanotubes, based on the total weight of the composite.

[0072] The composites disclosed herein may be used in a variety of applications to reduce or eliminate undesirable EMI over a broad range of frequencies. Typically the composites mitigate electromagnetic interference at frequencies from 1 GHz to 110 GHz. The composites can be used in telecommunication devices (e.g., cell phones, tablets, laptops, and computers), in the automobile industry (e.g., automotive radar control and automotive blind spot detection), and the medical industry (e.g., high frequency scanners and tomography systems for diagnostics). In embodiments where the composites are used in telecommunication devices, the composites may mitigate electromagnetic interference at frequencies from 1 GHz to 40 GHz, 5 GHz to 40 GHz, 10 GHz to 40 GHz, 15 GHz to 40 GHz, 20 GHz to 40 GHz, or 25 GHz to 40 GHz. In some embodiments, the composites mitigate electromagnetic interference at frequencies from 26 GHz to 40 GHz. In other embodiments where the composites are used in the automobile industry, the composites may mitigate electromagnetic interference at frequencies from 70 GHz to 110 GHz.

Examples

[0073] Objects and advantages of this invention are further illustrated by the following examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to unduly limit this invention. These examples are merely for illustrative purposes only and are not meant to be limiting on the scope of the appended claims.

Table 1. Materials Used in the Examples

[0074] Test Methods

[0075] Electromagnetic (EM) Characterization Test Method for Composites

[0076] Complex dielectric and magnetic properties were calculated from Scattering (S) parameters obtained using an Agilent E8363C Network Analyzer (Agilent Technologies, Santa Clara, CA) over the frequency range of 18 to 26.5 GHz (K Band) using rectangular waveguides made from composites exemplified herein. Composite samples (smooth and uniform) were cut to fit into the transmission lines and sized to have as small an airgap as possible inside the transmission line.

[0077] Electromagnetic (EM) Characterization Test Method for Coated Particle

[0078] Samples of coated particles were measured using a TEO 15 mode dielectric resonator at room temperature and 2.45 GHz, using a vector network analyzer (Agilent E8363C Network Analyzer).

[0079] EMI Performance Analysis Test Method

[0080] The radar absorption or reflection loss model is a well-known model that assumes electromagnetic waves are normally incident on a single layer composite absorber which is adhered to a well conducting metal plate (that prevents transmission). The EM wave absorbing performance can be evaluated in terms of the reflection loss (RL) in decibel (dB) units. In this model, lower reflection loss indicates higher electromagnetic absorption performance.

[0081] The EM wave absorption performances were investigated based on the following equations:

RL = 20 log

^S [ ^Zin 1 (b) L (Zjn+Zo ) J ' where Zo is the impedance of free space, t is the thickness of the absorber, and c is the speed of light. As indicated in Equation (a), the input impedance of an absorber depends on six parameters: the real and imaginary parts of complex permeability (p_r = p’- jp”) and complex permittivity (s_r = s'- js") values, the thickness of an absorber (t), and the working frequency (f). An industry standard composite thickness (t) of 1.0 mm was used since, in the case of many real-world high frequency EMI applications, space is a premium for current microelectronic devices. A description of the radar absorption or reflection loss model can be found in “Structural and high GHz frequency EMI (Electromagnetic Interference) properties of carbonyl iron and boron nitride hybrid composites”, Materials Research Express 6(10), 106305, 2019.

[0082] Example 1 : Coated Clay Nanotubes

[0083] Clay nanotubes and graphene platelets were mixed together in a Nalgene® plastic bottle using a ball milling roller at 30 revolutions per minute (rpm) according to the stoichiometric ratios and times set forth in Table 2.

Table 2. Stoichiometric Amounts of Starting Material and Ball Milling Roller Times

[0084] Example 2: Coated Glass Bubbles

[0085] Glass bubbles and graphene platelets were mixed together in a Nalgene® plastic bottle using a ball milling roller at 30 rpm according to the stoichiometric ratios and times set forth in Table 3.

Table 3. Stoichiometric Amounts of Starting Material and Ball Milling Roller Times

[0086] Example 3: Composites

[0087] Composites were made using the coated nanotubes and coated glass bubbles as described in Examples 1 and 2. The required amount of SYLGARD Silicone Part A was added to a plastic cup. The required amount of SYLGARD Silicone Part B was then added to the SYLGARD Silicone Part A in the plastic cup. The coated particles were then added to this mixture in the amounts set forth in Table 4. The plastic cup was covered with a cap configured to allow speed mixing under vacuum (100 millibar) for 2 minutes and 15 seconds. The mixture was then poured onto a stainless-steel plate. A second stainless steel plate was placed on top of the mixture. Teflon sheets were place between the mixture and each of the steel plates to make smooth surface composites. Spacers were used between the two plates to separate them to a desired thickness of 1.0 mm. The plates containing the mixture were hot pressed at a temperature of 118 °C under a pressure of 3 tons for 45-60 minutes. The plates were allowed to cool for 30-45 minutes before the cured composite sheet was removed. [0088] The dielectric and magnetic properties were obtained using the Electromagnetic (EM)

Characterization Test Method for Composites. Results are reported in Tables 5 and 6.

Table 4. Composite Components

Table 5. Dielectric and Magnetic Properties of Composite 3A with Coated Clay Nanotubes

Table 6. Dielectric and Magnetic Properties of Composite 3B with Coated Glass Bubbles

[0089] Example 4: EMI Performance of Composites [0090] The EMI performance of the composites in Example 3 were analyzed using the radar absorption or reflection loss model set forth in the EMI Performance Analysis Test Method. The EMI performance plot for composite 3A is provided in FIG. 1. The EMI performance plot for composite 3B is provided in FIG. 2. [0091] Example 5 : Dielectric Properties of Coated Glass Bubbles

[0092] The dielectric properties of coated glass bubbles were compared to uncoated glass bubbles using the Electromagnetic (EM) Characterization Test Method for Powders at a frequency of 2.54 GHz. Results are provided in Table 7.

Table 7. Dielectric Properties of Coated and Uncoated Glass Bubbles

[0093] Thus, the present disclosure provides, among other things, composites containing graphene coated hollow particles useful in high frequency EMI applications. Various features and advantages of the present disclosure are set forth in the following claims.

Claims

What is claimed is:

1. A composite comprising: a polymeric matrix; and coated particles dispersed within the polymeric matrix, the coated particles comprising: hollow particles made from electrically resistive material, each hollow particle having an outer surface; and a coating comprising graphene flakes in direct contact with the outer surface.

2. The composite of claim 1, wherein the coating covers at least 50% of the outer surface of the hollow particles.

3. The composite of claim 1 or claim 2, wherein the coated particles comprise 5 to 20 wt.% of graphene flakes.

4. The composite of claim 1 or claim 2, wherein the coating has a thickness of less than 5 nanometers.

5. The composite of any one of the preceding claims, where the coating does not comprise a binder.

6. The composite of any one of the preceding claims, wherein the composite comprises up to 50 wt.% of the coated particles, based on the total weight of the composite.

7. The composite of any one of the preceding claims, wherein the hollow particles are glass bubbles, nanotubes, or combinations thereof.

8. The composite of any one of the preceding claims, wherein the hollow particles are nanotubes.

9. The composite of any one of the preceding claims, wherein the coated particles are coated nanotubes, and the composite comprises no more than 20 wt.% of the coated nanotubes.

10. The composite of any one of claims 7-9 wherein the nanotubes comprise inorganic nanotubes, clay nanotubes, core shell nanotubes, ceramic nanotubes, or combinations thereof.

11. The composite of any one of claims 7-10, wherein the nanotubes comprise halloysite, imogolite, or a combination thereof.

12. The composite of any one of claims 7-11, wherein the nanotubes have an aspect ratio of 5: 1 to 50: 1.

13. The composite of any one of claims 1-7, wherein the hollow particles are glass bubbles.

14. The composite of claim 13, wherein the glass bubbles have a median size by volume ranging from 1 micrometer to 500 micrometers.

15. The composite of any one of the preceding claims, wherein the polymeric matrix comprises a thermoplastic polymer selected from the group consisting of polyolefins, fluorinated polyolefins, polyimide, polyamide-imide, polyether-imide, polyetherketone resins, polystyrenes, polystyrene copolymers, polyacrylates, polymethacrylates, polyesters, polyvinylchloride (PVC), liquid crystal polymers (LCP), polyphenylene sulfides (PPS), polysulfones, polyacetals, polycarbonates, polyphenylene oxides (PPO), polyphenyl ether (PPE), and blends thereof.

16. The composite of any one of claims 1-14, wherein the polymeric matrix comprises a thermoset polymer selected from the group consisting of epoxies, polyesters, polyurethanes, polyureas, silicones, polysulfides, phenolics, vulcanized rubber, polyoxybenzylmethylenglycolanhydride, vinyl ester resin, and blends thereof.

17. The composite of any one of the preceding claims, wherein the polymeric matrix further comprises preservatives, curatives, mixing agents, colorants, dispersants, floating or anti-setting agents, flow or processing agents, wetting agents, air separation promoters, functional nanoparticles, acid/base or water scavengers, or combinations thereof.

18. An article comprising the composite of any one of the preceding claims.

19. The article of claim 18, wherein the article is an electronic mobile device.

20. A method of making a composite, the method comprising: combining coated particles with a curable polymeric matrix material; and curing the curable polymeric matrix material to form the composite, wherein the coated particles comprise: hollow particles made from electrically resistive material, each hollow particle having an outer surface; and a coating comprising graphene flakes in direct contact with the outer surface.

21. Coated particles comprising: hollow particles made from an electrically resistive material, each hollow particle having an outer surface; and a coating comprising graphene flakes in direct contact with the outer surface.

22. A method of making the coated particles of claim 21 comprising: combining the hollow particles with layered graphene; mechanically exfoliating the layered graphene to create graphene flakes; and coating the hollow particles with the graphene flakes.