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US-12628321-B2 - Electromagnetic absorbing composites

US12628321B2US 12628321 B2US12628321 B2US 12628321B2US-12628321-B2

Abstract

A composite comprising a polymeric matrix and EM absorbers dispersed within the polymeric matrix. Each EM absorber comprises a ceramic particle having a surface, and a magnetic coating on at least a portion of the surface of the ceramic particle. The EM absorbers function as dielectric and magnetic absorbers in the 1-100 GHz frequency range. The composite can be used as an electromagnetic shielding article to mitigate electromagnetic interference in, for example, high speed, high frequency (HSHF) consumer electronics.

Inventors

  • Adam D. Miller
  • Dipankar Ghosh

Assignees

  • 3M INNOVATIVE PROPERTIES COMPANY

Dates

Publication Date
20260512
Application Date
20211216

Claims (18)

  1. 1 . A composite comprising: a polymeric matrix; and EM absorbers dispersed within the polymeric matrix, each EM absorber comprising a ceramic particle having a spherical surface and an average particle diameter ranging from 0.1 μm to 50 μm, and a magnetic coating on at least a portion of the spherical surface of the ceramic particle, wherein the ceramic particle comprises copper(II) oxide, a metal nitride, a metal carbide, a metal sulfide, a metal silicide, a metal boride, a multiferroic compound, or combinations thereof, and wherein the EM absorbers function as dielectric and magnetic absorbers in the 1-100 GHz frequency range.
  2. 2 . The composite of claim 1 , wherein the magnetic coating completely encapsulates the ceramic particle.
  3. 3 . The composite of claim 1 , wherein the magnetic coating comprises a ferromagnetic material or ferrimagnetic material.
  4. 4 . The composite of claim 1 , wherein the magnetic coating comprises a metal, a metal alloy, a ceramic ferrite, or a combination thereof.
  5. 5 . The composite of claim 1 , wherein the magnetic coating comprises iron metal.
  6. 6 . The composite of claim 1 , wherein the EM absorbers have an average particle size of 0.1 micrometers to 50 micrometers.
  7. 7 . The composite of claim 1 , wherein the EM absorbers make up 10 to 90 wt % of the composite.
  8. 8 . The composite of claim 1 , wherein the polymeric matrix comprises a silicone, a cyclic olefin copolymer (COC), a low-density polyethylene (LDPE), a high-density polyethylene (HDPE), a polystyrene (PS), a polypropylene (PP), a polyphenylene sulfide (PPS), a polyimide (PI), a syndiotactic polystyrene (SPS), a polytetrafluoroethylene (PTFE), a butyl rubber, an acrylonitrile butadiene styrene (ABS), a polycarbonate (PC), a polyurethane, or a combination thereof.
  9. 9 . The composite of claim 1 , wherein the polymeric matrix comprises a silicone.
  10. 10 . The composite of claim 1 , wherein one or more of the EM absorbers comprise a ceramic particle having at least two magnetic coatings thereon.
  11. 11 . The composite of claim 10 , wherein each of the at least two magnetic coatings thereon comprise a different magnetic material.
  12. 12 . The composite of claim 10 , wherein each of the at least two magnetic coatings thereon have different thicknesses.
  13. 13 . The composite of claim 1 , wherein the composite comprises two or more different types of EM absorbers, wherein the two or more different types of EM absorbers comprise different ceramic particles, different magnetic coatings, different ratio of components in the magnetic coatings to components in the ceramic particles, or a combination thereof.
  14. 14 . The composite of claim 1 , wherein the polymeric matrix comprises an epoxy-based polymer, the ceramic material is copper(II) oxide, and the magnetic coating is iron metal.
  15. 15 . The composite of claim 14 , wherein the mass ratio of copper(II) oxide to iron metal in the EM absorber ranges from 1:1 to 32:1.
  16. 16 . The composite of claim 1 , wherein the composite mitigates electromagnetic interference in the frequency range from 1 GHz to 100 GHz.
  17. 17 . An electromagnetic interference shielding article comprising the composite of claim 1 .
  18. 18 . A method of making the composite of claim 1 comprising: forming the EM absorbers by at least partially covering the spherical surfaces of each ceramic particle with the magnetic coating; and dispersing the EM absorbers in the polymeric matrix.

Description

CROSS REFERENCE TO RELATED APPLICATIONS This application is a national stage filing under 35 U.S.C. 371 of PCT/IB2021/061849, filed Dec. 16, 2021, which claims the benefit of U.S. Provisional Patent Application No. 63/199,448, filed Dec. 29, 2020, the disclosure of which is incorporated by reference in its/their entirety herein. FIELD OF INVENTION The present invention relates to electromagnetic absorbing composites that may be used to shield electronic devices or radiation sources, articles containing the composites, and methods of making the composites. BACKGROUND Electromagnetic interference (EMI) is a common issue encountered in electronic systems, such as electronic communications systems. Outside electromagnetic radiation is well known to induce undesirable currents in electronic components, thereby disrupting their normal operations. In order to protect against such effects, it is common to completely shield an electronic device or component via highly conductive enclosures, such as coatings, gaskets, adhesives sealants, wire sleeves, metal meshes or filters, and the like. These types of shields operate by reflecting the unwanted electromagnetic fields away from the sensitive component. Another form of protection is offered by electromagnetic absorbing materials. These are typically not highly conductive and operate by absorbing the unwanted electromagnetic energy and converting it to heat. Absorbers are widely used in radar and stealth applications. They are also commonly found inside of electronic devices where they are used to control electromagnetic emissions from the device. Electromagnetic absorbers can be classified as magnetic absorbers if they interact principally with the magnetic field component of an electromagnetic wave or as dielectric absorbers if they interact principally with the electric field component of the electromagnetic wave. Electromagnetic absorbers are especially beneficial in a high frequency regime, for example, in the 1-40 GHz or 1-100 GHz frequency range and harmonics associated with such base frequencies. There remains a need for flexible and versatile electromagnetic absorbing materials that can be used to mitigate electromagnetic interference. These materials should be lightweight, readily handled in industrial processes, and have loss characteristics that are appropriate to the frequency range of interest for a particular application. SUMMARY The present disclosure provides a composite comprising a polymeric matrix and electromagnetic (EM) absorbers dispersed therein. The EM absorbers comprise magnetically coated ceramic particles. The magnetic coating adds magnetic loss (i.e. increases the value of the imaginary part of the magnetic permeability) to a nonmagnetic ceramic particle. The magnetic coating increases the permeability of the EM absorber so that it more closely matches the permittivity of the ceramic particle, thus reducing the electromagnetic reflection and enhancing the electromagnetic absorption of the EM absorber and the resultant composite. Composites of the present disclosure are capable of mitigating electromagnetic interference in the 1-100 GHz frequency range, more particularly the 1-20 GHz frequency range. In one embodiment, the present disclosure provides a composite comprising a polymeric matrix, and EM absorbers dispersed within the polymeric matrix, each EM absorber comprising a ceramic particle having a surface, and a magnetic coating on at least a portion of the surface of the ceramic particle, wherein the EM absorbers function as dielectric and magnetic absorbers in the 1-100 GHz frequency range. In another embodiment, the present disclosure provides an electromagnetic interference shielding article comprising the composite. In a further embodiment, the present disclosure provides a method of making the composite. The following definitions shall be applied to the defined terms through the entire application, unless otherwise stated to the contrary. As used herein: 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 whethe