Composite electromagnetic shielding material and preparation method and application thereof

Abstract

The invention discloses a multi-layer composite electromagnetic shielding material and a preparation method and application thereof.The multi-layer composite electromagnetic shielding material is composed of a wire mesh, a liquid metal gallium coating and a polymer packaging layer, a metal wire mesh base body serves as a carrier, and a good conductive network structure and mechanical support can be provided; the mechanical stability of the whole material is ensured; the liquid metal gallium plating layer forms a continuous conductive layer on the surface of the metal wire mesh to enhance the electromagnetic wave reflection and absorption capability, and forms a dual conductive path with the metal wire mesh to improve the shielding efficiency; the polymer packaging layer endows the material with excellent flexibility and environmental resistance, and liquid metal leakage or oxidation is avoided. The metal wire mesh and the gallium plating layer form a stable conductive-reflection composite structure, and the polymer layer further ensures the overall flexibility and durability, so that the multilayer composite structure shows efficient and stable electromagnetic shielding performance in a wide frequency band range.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of electromagnetic shielding, and particularly relates to a composite electromagnetic shielding material and a preparation method and application thereof. BACKGROUND

[0002] With the rapid development of wireless communication and intelligent electronic devices, electromagnetic interference (EMI) problems are increasingly serious, affecting device performance and use stability. Traditional electromagnetic shielding materials mostly use metal foils, metal meshes or metal coatings, which have good shielding effects, but have many shortcomings in practical applications: (1) lack of flexibility: traditional metal materials are rigid and difficult to meet the needs of flexible electronic devices and complex curved structures, limiting their application in the field of flexible electronics; (2) easy oxidation and poor durability: metal coatings and films are easily oxidized in air, leading to a decrease in electrical conductivity and degradation of shielding performance, shortening the service life of the material; (3) limited structural stability: although liquid metals have high electrical conductivity and good flexibility, they are prone to leakage and interface instability, making it difficult to form a long-term reliable composite structure; (4) complex preparation process and high cost: the preparation process of some flexible shielding materials is complicated, making it difficult to achieve large-scale production, and the cost is high, which is not conducive to popularization and application. Therefore, how to maintain high-efficiency electromagnetic shielding performance while improving the flexibility, environmental stability and structural reliability of the material has become a key technical problem to be solved in the field of electromagnetic shielding materials. SUMMARY

[0003] In order to overcome the problems existing in the prior art, one of the purposes of the present application is to provide a composite electromagnetic shielding material. The second purpose of the present application is to provide a preparation method of the composite electromagnetic shielding material. The third purpose of the present application is to provide an application of the composite electromagnetic shielding material.

[0004] In order to achieve the above purposes, the technical solution adopted by the present application is: The first aspect of the present application provides a composite electromagnetic shielding material, which comprises: a wire mesh; the wire mesh is selected from a metal wire mesh, or a composite wire mesh composed of a metal and a reinforcing material; a liquid metal coating layer; the liquid metal coating layer is loaded on the surface of the wire mesh; the liquid metal in the liquid metal coating layer is selected from liquid gallium or liquid gallium-based alloy; a polymer encapsulation layer; the polymer encapsulation layer encapsulates the liquid metal coating layer and the wire mesh.

[0005] Preferably, the metal material in the metal wire mesh, or the composite wire mesh composed of a metal and a polymer, comprises at least one of copper, nickel, aluminum, chromium, gold and silver.

[0006] Preferably, the metal wire mesh is woven into a grid shape by a plurality of metal wires.

[0007] Preferably, the metal wire mesh is woven by a plurality of composite wires into a grid shape; the composite wires take a reinforcing material as an internal support layer, and are covered with a metal layer on the surface to form the composite wires.

[0008] More preferably, the mesh holes of the wire mesh are in a rectangular shape. The mesh holes can also be made into other shapes according to requirements, such as a circular shape, a diamond shape, a honeycomb shape, etc.

[0009] Preferably, the reinforcing material is a high polymer material or an inorganic carbon material.

[0010] More preferably, the high polymer material is selected from at least one of polyimide (PI), polyethylene terephthalate (PET), and polytetrafluoroethylene (PTFE).

[0011] More preferably, the inorganic carbon material is selected from at least one of carbon fiber, carbon nanotube, and graphene.

[0012] Preferably, the thickness of the wire mesh is 75-100 μm.

[0013] Preferably, the thickness of the liquid metal plating layer is 40-70 μm.

[0014] Preferably, the thickness of the polymer encapsulation layer is 175-300 μm.

[0015] In addition to selecting a single metal wire mesh, the wire mesh substrate of the present application can also select a composite wire mesh, the wire of which takes a high polymer material / inorganic carbon material as an internal support layer, and is covered with a copper layer on the surface to form a composite structure. This design, on the one hand, takes advantage of the flexibility and light weight characteristics of the high polymer material (such as polyimide, polyethylene terephthalate, polytetrafluoroethylene, or polyolefin elastomer, etc.) to ensure that the overall substrate has good bending performance and mechanical stability; on the other hand, a continuous conductive network is constructed by the outer copper covering layer to provide a bonding interface for the plating of the liquid metal gallium, thereby combining flexibility, electrical conductivity, and structural stability.

[0016] Preferably, the liquid gallium-based alloy is selected from at least one of gallium-indium alloy, gallium-indium-tin alloy, gallium-aluminum alloy, and gallium-tin alloy.

[0017] Preferably, the polymer material of the polymer encapsulation layer includes at least one of polyurea, polyurethane, silicone elastomer, polyimide, epoxy resin, fluorinated polymer, acrylic resin, and styrene block copolymer.

[0018] More preferably, the polymer material of the polymer encapsulation layer includes polyurea.

[0019] The polyurea is used as the encapsulation layer, the encapsulation layer has good interface wettability with the liquid metal layer, and can ensure the mechanical integrity and stable electrical performance of the composite material as a whole. The polyurethane is the main flexible matrix, which gives the encapsulation layer good flexibility, adhesion and film-forming property. The organic solvent is used to adjust the viscosity of the formula system, so as to ensure uniform coating during construction. The curing agent promotes the rapid curing of the polyurea through cross-linking reaction, and forms a dense protective film layer. The formula system not only ensures that the polyurea encapsulation layer has excellent mechanical properties and environmental adaptability, but also effectively prevents the leakage and oxidation of liquid metal gallium, thereby improving the electromagnetic shielding stability and service life of the composite material as a whole.

[0020] The second aspect of the present application provides a preparation method of the composite electromagnetic shielding material according to the first aspect, comprising the following steps: dipping the wire mesh in liquid metal, so that the wire mesh is loaded with a liquid metal plating layer on the surface; and then encapsulating the wire mesh loaded with the liquid metal plating layer with a polymer to obtain the composite electromagnetic shielding material.

[0021] Preferably, the method further comprises a pretreatment of the wire mesh, and the pretreatment comprises the following steps: dipping the wire mesh in a hydrofluoric acid buffer solution.

[0022] More preferably, the volume ratio of hydrofluoric acid in the hydrofluoric acid buffer solution is 5-10% (v / v).

[0023] More preferably, the hydrofluoric acid buffer solution further contains ammonia water.

[0024] Further preferably, the molar concentration of the ammonia water in the hydrofluoric acid buffer solution is 0.1-1 mol / L.

[0025] More preferably, the dipping time is 30-120 s.

[0026] Preferably, the method comprises the following steps: dipping the wire mesh in liquid metal at 50-70℃ for 10-30 min.

[0027] In the present application, the wire mesh is dipped in liquid metal at 50-70℃. After heating, the viscosity of the liquid gallium becomes smaller, so that the liquid gallium can stably adhere to the surface and pores of the copper mesh under the action of capillary force and cross-section reaction, and a continuous and uniform plating layer is formed, i.e. the "hanging pulp" effect is achieved.

[0028] Preferably, the encapsulation comprises the following steps: oppositely arranging two polymer-coated film bodies, and placing the wire mesh loaded with the liquid metal plating layer between the two film bodies, so that the polymer encapsulation layer coats the liquid metal plating layer and the wire mesh after mechanical pressing and static curing, and the composite electromagnetic shielding material is obtained.

[0029] More preferably, the film body is a polytetrafluoroethylene (PTFE) film.

[0030] More preferably, the standing curing is standing curing at room temperature for 24-48 h.

[0031] The third aspect of the present application provides the use of the composite electromagnetic shielding material of the first aspect in an electromagnetic shielding product or an electronic and electrical equipment.

[0032] The present application has the following advantages: The present application provides a multilayer composite electromagnetic shielding material, which is composed of a wire mesh, a liquid metal gallium coating layer and a polymer encapsulation layer. The metal wire mesh substrate serves as a carrier to provide a good conductive network structure and mechanical support, ensuring the mechanical stability of the overall material. The liquid metal gallium coating layer forms a continuous conductive layer on the surface of the metal wire mesh, enhancing the electromagnetic wave reflection and absorption capacity, and at the same time forming a double conductive path with the metal wire mesh to improve the shielding efficiency. The polymer encapsulation layer endows the material with excellent flexibility and environmental resistance, avoiding liquid metal leakage or oxidation, and maintaining the integrity of the composite structure under external bending and compression conditions. The interface interaction and physical coating between the layers achieve synergy: the metal wire mesh and the gallium coating layer form a stable conductive-reflection composite structure, and the polymer layer further ensures the overall flexibility and durability, so that the multilayer composite structure exhibits high and stable electromagnetic shielding performance in a wide frequency range. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 Material element analysis of the cross section of the copper mesh of Example 1.

[0034] Figure 2 SEM image of the cross section of the copper mesh / liquid metal gallium / polyurea multilayer composite electromagnetic shielding material of Example 1; Figure 3 Element analysis of the copper mesh / liquid metal gallium / polyurea multilayer composite electromagnetic shielding material of Example 1; Figure 4 Mechanical property test of the copper mesh / liquid metal gallium / polyurea multilayer composite electromagnetic shielding material; Figure 5 EMI test chart of the copper mesh / liquid metal gallium / polyurea multilayer composite electromagnetic shielding material; Figure 6 EMI test chart of the copper mesh / gallium-indium alloy / polyurea multilayer composite electromagnetic shielding material; Figure 7 The copper mesh / liquid metal gallium of Comparative Example 1 was placed in a freeze dryer at -20°C and the sample was taken out; Figure 8 Copper mesh / liquid metal gallium / silica gel composite material of Comparative Example 2. DETAILED DESCRIPTION

[0035] The content of the present application is further illustrated in detail through specific examples. The raw materials used in the following examples, unless otherwise specified, can be obtained from conventional commercial channels or prepared and isolated by simple synthesis; the processes used, unless otherwise specified, are conventional processes in the art.

[0036] Example 1 This example gives a kind of composite electromagnetic shielding material, specifically copper mesh / liquid metal gallium / polyurea multilayer composite electromagnetic shielding material, its preparation method and structure are as follows: 1. Preparation method 1) Copper mesh preparation and surface treatment The preparation of this copper mesh is designed and prepared by the applicant, and the detailed process can refer to the literature DOI: 10.1016 / j.aiepr.2025.07.001. The obtained copper mesh is cut into small pieces of 5 cm × 5 cm, immersed in BHF buffer for 60 seconds to enhance the surface wettability and plating adhesion; BHF buffer preparation: deionized water 64.3 mL, HF 8.7 mL, 1 mol / L ammonia water 27 mL.

[0037] 2) Preparation of liquid metal gallium coating The pretreated copper mesh is immersed in liquid gallium at 60°C constant temperature for about 15-20 minutes to uniformly cover the coating on both sides.

[0038] 3) Preparation of polyurea component and layer This polyurea system is designed and prepared by the applicant, and the detailed components can refer to the literature DOI: 10.1016 / j.aiepr.2025.07.001. Since the assembly process of the present application is not suitable for using the scraping method, the polyurea coating is preferably pre-coated on the surface of the PTFE film. The specific steps are as follows: first, lay a piece of polytetrafluoroethylene film coated with polyurea on a steel plate (polytetrafluoroethylene is only used as a carrier to facilitate the coating of polyurea and demolding), place the gallium-coated copper mesh on it, and then cover another piece of polyurea layer on the copper mesh with the inner side of the polytetrafluoroethylene film to form a three-layer composite laminate structure. Then cover a steel plate on top of the laminate structure and apply about 200 g of weight to maintain constant pressure, so that the polyurea coating and the gallium-coated copper mesh are fully attached. Place the assembly in a room temperature and ventilated condition and let it cool naturally for 24-48 hours. After the polyurea is cured into a film, remove the outer steel plate and tear off the PTFE film to obtain the prepared copper mesh / liquid gallium / polyurea multilayer composite electromagnetic shielding material.

[0039] 2. Material structure composition Copper mesh substrate: high-purity red copper mesh, 500 mesh, pore size 75 μm, thickness 75 μm, the inside of the mesh hole is covered with a copper layer, such asFigure 1 Cross-sectional material element analysis of copper mesh; Liquid metal gallium coating: the purity of liquid metal gallium is 99.99%, and the coating thickness is 50 μm, located on the front and back symmetric surfaces of the copper mesh; Polyurea coating: the thickness is about 175 μm, covering the copper mesh substrate and the liquid metal gallium coating.

[0040] Characterization of composite electromagnetic shielding material 1. Microstructure characterization The scanning electron microscope (SEM) combined with the energy dispersive spectrometer (EDS or WDS) is used for qualitative and quantitative analysis of elements in the micro area (usually nanometer to micrometer scale) of the sample, Figure 2 SEM image of the cross section of the copper mesh / liquid metal gallium / polyurea multilayer composite electromagnetic shielding material of Example 1; Figure 3 Elemental analysis of the copper mesh / liquid metal gallium / polyurea multilayer composite electromagnetic shielding material of Example 1; from the SEM results, the liquid metal gallium coating of the composite electromagnetic shielding material of Example 1 is uniform, and the polyurea encapsulation layer and the coating interface are well combined; 2. Mechanical property characterization The sample is cut into 1cm×8cm in length and width, and the thickness is the original preparation thickness of the sample 0.8mm; the uniaxial tensile testing machine is used to test the mechanical properties (Shenzhen Sansi universal tensile testing machine).

[0041] Figure 4 The mechanical property test of the copper mesh / liquid metal gallium / polyurea multilayer composite electromagnetic shielding material, from the figure, the composite electromagnetic shielding material has good flexibility, and still maintains integrity even under bending and compression conditions.

[0042] 3. Electromagnetic shielding performance characterization The waveguide method is used to test the electromagnetic shielding (instrument model: American Agilent E5071c), Figure 5 EMI test graph of copper mesh / liquid metal gallium / polyurea multilayer composite electromagnetic shielding material, wherein each curve is the total EMI shielding effect (SET), microwave reflection (SER) and microwave absorption (SEA) performance of the composite material, wherein the average EMI shielding efficiency (SE) is as high as 30dB, realizing high-efficiency electromagnetic shielding and wave absorption performance in a wide frequency band (2-18 GHz).

[0043] Example 2 This example gives a kind of composite electromagnetic shielding material, specifically copper mesh / liquid metal gallium-indium alloy / polyurea multilayer composite electromagnetic shielding material, its preparation method refers to Example 1, the difference is that in step 2), liquid metal gallium is replaced by gallium-indium alloy.

[0044] Figure 6The EMI test chart of the copper mesh / liquid metal gallium / polyurea multilayer composite electromagnetic shielding material is shown in FIG. 6. Although the interface of the composite material is stable and the plating layer does not leak, the overall electromagnetic shielding performance is slightly lower than that of Example 1. The reason may be that the high-purity gallium can form a continuous and dense plating layer on the surface of the copper mesh, ensuring the stability of the interface and excellent electrical conductivity, which is sufficient to meet the performance requirements of the electromagnetic shielding of the present application. If other elements are introduced to form an alloy, it may cause a decrease in wettability, uneven interface, or a decrease in environmental stability, thereby affecting the overall performance of the material. In addition, the use of pure gallium can simplify the process and improve the controllability and repeatability of the preparation process, so the present application preferably uses high-purity gallium as the liquid metal layer.

[0045] Comparative Example 1 The present comparative example gives a composite electromagnetic shielding material, specifically a copper mesh / liquid metal gallium multilayer composite electromagnetic shielding material, and the preparation method is as follows: 1) and 2) are the same as in Example 1; 3) The copper mesh plated with liquid metal gallium is placed between two PTFE films and clamped with two steel plates, and a constant pressure of about 200 g of weight is applied to the surface. After being placed in a freeze dryer at -20°C for a period of time, the sample is taken out.

[0046] Figure 7 The copper mesh / liquid metal gallium of Comparative Example 1 is placed in a freeze dryer at -20°C to take out the sample. Observation of the composite electromagnetic shielding material of Comparative Example 1 shows that the liquid metal gallium is unevenly distributed on the surface of the copper mesh, with local accumulation, absence or migration phenomena, and the overall surface morphology is irregular. This comparative example shows that when PTFE film and mechanical pressure are used without polyurea encapsulation, it is difficult to achieve uniform coverage and stable fixation of the liquid metal plating layer, and the process effect is not good.

[0047] Comparative Example 2 The present comparative example gives a composite electromagnetic shielding material, specifically a copper mesh / liquid metal gallium / silicone rubber multilayer composite electromagnetic shielding material, and the preparation method is as follows: 1) and 2) are the same as in Example 1; 3) Preparation of the silicone rubber layer A piece of polytetrafluoroethylene film coated with silicone rubber was first laid flat on a steel plate (polytetrafluoroethylene was only used as a carrier to facilitate the coating of polyurea and demolding), and the gallium-plated copper mesh was placed on it. Then another piece of silicone rubber layer was covered on the copper mesh with the inner side of the polytetrafluoroethylene film, forming a three-layer composite laminated structure. Subsequently, a steel plate was covered on the laminated structure, and a weight of about 500 g was applied to maintain constant pressure, so that the polyurea coating and the gallium-plated copper mesh were fully attached. The assembly was placed in a room temperature and ventilated condition for natural standing and cooling for 24-48 hours. After the polyurea was cured into a film, the outer steel plate was removed and the PTFE film was torn off, thereby obtaining the prepared copper mesh / liquid gallium / polyurea multilayer composite electromagnetic shielding material.

[0048] Figure 8 For the copper mesh / liquid metal gallium / silicone rubber composite material of Comparative Example 2, it was observed that the gallium layer of the composite electromagnetic shielding material of Comparative Example 2 showed obvious oxidation and peeling after being stored in air for a short time.

[0049] As can be seen from Comparative Example 1 and Comparative Example 2, the polyurea layer has good wettability with the liquid metal layer, which ensures the mechanical integrity and electrical performance stability of the composite material as a whole. The polyurethane is the main flexible matrix, which gives the encapsulation layer good flexibility, adhesion and film-forming property. The organic solvent is used to adjust the viscosity of the formulation system, ensuring uniform coating during construction. The curing agent promotes rapid curing of polyurea through crosslinking reaction, forming a dense protective film layer. This formulation system not only ensures that the polyurea encapsulation layer has excellent mechanical properties and environmental adaptability, but also effectively prevents the leakage and oxidation of liquid metal gallium, thereby improving the overall electromagnetic shielding stability and service life of the composite material. The results prove that the polyurea encapsulation layer plays an irreplaceable role in maintaining the stability of liquid gallium and the long-term performance of the material.

[0050] Comparative Example 3 This comparative example gives a composite electromagnetic shielding material, the difference between its preparation method and Example 1 is that the copper mesh is not pretreated by BHF buffer solution, but directly plated with liquid gallium, and then the composite material is prepared according to Example 1.

[0051] The composite electromagnetic shielding material of Comparative Example 3 was characterized in the same way as Example 1. Due to the poor wettability of the copper mesh surface, the liquid gallium was not uniformly distributed, resulting in many defects in the shielding layer, and the electromagnetic shielding efficiency and mechanical properties were lower than those of Example 1. The results show that the surface treatment process is crucial for achieving uniform plating of liquid gallium and performance improvement.

[0052] The above examples are the preferred embodiments of the present application, but the embodiments of the present application are not limited by the above examples, and any changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principles of the present application shall be equivalent replacement methods and shall be within the scope of protection of the present application.

Claims

1. A composite electromagnetic shielding material, characterized by, The composite electromagnetic shielding material comprises: a wire mesh; the wire mesh is selected from a metal wire mesh, or a composite wire mesh composed of a metal and a reinforcing material; a liquid metal coating; the liquid metal coating is loaded on the surface of the wire mesh; the liquid metal in the liquid metal coating is selected from liquid gallium or liquid gallium-based alloy; a polymer encapsulation layer; the polymer encapsulation layer encapsulates the liquid metal coating and the wire mesh.

2. The composite electromagnetic shielding material of claim 1, wherein, The metal material in the metal wire mesh, or the composite wire mesh composed of a metal and a polymer, comprises at least one of copper, nickel, aluminum, chromium, gold, and silver.

3. The composite electromagnetic shielding material of claim 1, wherein, The liquid gallium-based alloy is selected from at least one of gallium-indium alloy, gallium-indium-tin alloy, gallium-aluminum alloy, and gallium-tin alloy.

4. The composite electromagnetic shielding material of claim 1, wherein, The polymer material of the polymer encapsulation layer comprises at least one of polyurea, polyurethane, silicone elastomer, polyimide, epoxy resin, fluorinated polymer, acrylic resin, and styrene block copolymer.

5. The composite electromagnetic shielding material of claim 1, wherein, The thickness of the liquid metal coating is 40-70 μm; and / or, the thickness of the polymer encapsulation layer is 175-300 μm.

6. The method of producing a composite electromagnetic shielding material according to any one of claims 1 to 5, characterized by, The method comprises the following steps: immersing the wire mesh in liquid metal so that the surface of the wire mesh is loaded with a liquid metal coating; and then encapsulating the wire mesh loaded with the liquid metal coating with a polymer to obtain the composite electromagnetic shielding material.

7. The method of claim 6, wherein the composite electromagnetic shielding material is prepared by the steps of: The method further comprises a pretreatment of the wire mesh; the pretreatment comprises the following steps: immersing the wire mesh in a hydrofluoric acid buffer solution.

8. The method of claim 6, wherein the composite electromagnetic shielding material is prepared by the steps of: The method specifically comprises the following steps: immersing the wire mesh in liquid metal at 50-70 °C for 10-30 min.

9. The method of claim 6, wherein the composite electromagnetic shielding material is prepared by the steps of: The encapsulation specifically comprises the following steps: placing two polymer-coated film bodies opposite to each other, and placing the wire mesh loaded with the liquid metal coating in between; after mechanical pressing and static curing, the polymer encapsulation layer encapsulates the liquid metal coating and the wire mesh to obtain the composite electromagnetic shielding material.

10. Use of the composite electromagnetic shielding material according to any one of claims 1-5 in electromagnetic shielding products or electronic and electrical equipment.

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