Thermal expansion microspheres, preparation method thereof, and electromagnetic shielding-thermal management foam material

Abstract

The present invention belongs to electromagnetic shielding foam materials and relates to a kind of heat-expandable microspheres and its preparation method and electromagnetic shielding thermal management foam material. The heat-expandable microspheres are sequentially composed of a microsphere core, an intermediate layer and an outer layer from the inside to the outside. During preparation, component A and component B are first mixed and emulsified in a high-speed shear emulsifier to obtain a suspension emulsion. The suspension emulsion is then transferred to an autoclave. Under nitrogen protection, the pressure is maintained at 0.5-1.5 MPa and polymerization is carried out at 50-70°C for 15-20 hours. The temperature is then raised to 90-110°C for polymerization for 2-4 hours. After the reaction is completed, the reaction is cooled and the pressure is released. The product is filtered, washed and dried in sequence to obtain the heat-expandable microspheres. The electromagnetic shielding thermal management foam material is prepared by using the above-mentioned heat-expandable microspheres through a heat expansion foaming process. The heat-expandable microspheres of the present invention have high stability and unique in-situ interfacial chemical bonding ability after expansion. The preparation method is simple and has a wide range of applications.

Description

Technical Field

[0001] The invention belongs to the technical field of electromagnetic shielding foam materials and relates to a thermal expansion microsphere and a preparation method thereof and an electromagnetic shielding-thermal management foam material. Background Art

[0002] With the development of emerging technologies such as 5G communications, high-speed trains, and electric vehicles, electronic devices are rapidly evolving towards high frequency, high density, and high power. The resulting electromagnetic interference (EMI) problem is becoming increasingly serious, posing a threat to equipment stability and personnel health. Therefore, the development of composite functional materials with efficient electromagnetic shielding performance, excellent thermal management capabilities, and lightweight structures has become a key demand in the field of electronic packaging and protective materials. Electromagnetic shielding materials primarily rely on conductive materials to construct reflective or absorbing layers. To achieve lightweight and multifunctional integration, foam structures are widely used in the design of absorbing layer materials. Traditional foams are mostly prepared using physical foaming agents, resulting in random pore structures and poor interfacial properties.

[0003] In recent years, the use of thermally expandable microspheres as foaming units to construct layered foams has become a research hotspot. However, most microspheres are physically embedded, unable to form a stable interface with the matrix, and are difficult to adapt to highly crystalline resin materials. The application of thermally expandable microspheres in electromagnetic shielding foams can effectively form a high-porosity closed-cell structure, reducing the dielectric constant and enhancing the absorption path. Coordinating the microsphere structure with the matrix material, particularly by incorporating chemical bonding mechanisms, can significantly improve the material's structural stability, electromagnetic wave dissipation efficiency, and thermal insulation capabilities.

[0004] For example, patent CN202311211516.6 discloses a method for preparing thermally self-expanding epoxy foam with electromagnetic shielding properties. The method introduces thermally expandable microspheres and conductive fillers into epoxy resin, and achieves foam structure formation and shielding performance improvement through thermal curing. However, the microspheres used are a two-layer structure with a narrow foaming temperature window, which makes it difficult to match a variety of matrix systems. In addition, there is only physical filling between the microspheres and the matrix, and there is a lack of a chemical bonding interface. The interface stability is poor and the service life is limited.

[0005] Patent CN114634617A discloses a carbon nano-conductive foam material with thermal foaming ability and its preparation method. It uses thermally expandable microspheres to blend and foam with conductive materials such as carbon nanotubes and MXene to construct a conductive foam composite material. However, the conductive filler is prone to agglomeration during the high-temperature foaming process, resulting in unstable shielding performance. In addition, the microsphere foaming structure is uneven and the size distribution range is wide, resulting in unstable internal structure of the material and poor mechanical properties.

[0006] Patent CN107262014A discloses a high-performance electromagnetic shielding composite foam material and its preparation method. It uses physical foaming to form a PU foam matrix, and sprays a nano-silver conductive coating on its surface to construct an electromagnetic shielding layer. However, the spray coating has weak bonding strength with the foam interface and is easily detached during bending or impact, causing the shielding layer to break or reduce shielding effectiveness. At the same time, nano-silver is expensive and organic solvents are required in the process, posing environmental and safety risks.

[0007] Therefore, it is of great significance to study a thermally expandable microsphere and a preparation method thereof and an electromagnetic shielding-thermal management foam material to solve the problems existing in the prior art. Summary of the Invention

[0008] The purpose of the present invention is to solve the problems existing in the prior art and to provide a thermal expansion microsphere and a preparation method thereof and an electromagnetic shielding-thermal management foam material.

[0009] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0010] A heat-expandable microsphere, which comprises a microsphere core, a middle layer and an outer layer from the inside to the outside;

[0011] The core of the microspheres is a low-boiling-point hydrocarbon;

[0012] The middle layer is a copolymer composed of acrylonitrile (AN) segments, methyl methacrylate (MMA) segments, ethylene glycol dimethacrylate (EGDMA) segments, and polyethylene glycol diacrylate (PEGDA) segments. The acrylonitrile and methyl methacrylate segments form the main chain skeleton of the copolymer, while the ethylene glycol dimethacrylate and polyethylene glycol diacrylate segments serve as bridging units, connecting to the main chain skeleton. EGDMA acts as a short-chain rigid crosslinker, connecting to AN / MMA units on different main chains through its two double bonds, forming short-spacing crosslinks. PEGDA acts as a long-chain flexible crosslinker, and its polyethylene glycol segments introduce flexible spacers, forming long-range crosslinks when connected to the main chain.

[0013] The outer layer comprises a cross-linked tetravinylsilane network, dicumyl peroxide (DCP), and maleic anhydride-grafted polyolefin (PP-g-MAH). The cross-linked tetravinylsilane network is a dense three-dimensional network formed by tetravinylsilane (TVS) through Si-O-Si bridges. This cross-linked network improves the thermal stability, airtightness, and structural integrity of the microspheres. DCP and maleic anhydride-grafted polyolefin provide reinforcement in the outer layer through different mechanisms. DCP acts as a latent initiator during foam molding, initiating the cross-linking reaction. The maleic anhydride-grafted polyolefin, through the dipole-dipole interaction of the anhydride groups, forms a gradient polarity interface with the non-polar matrix resin PP or PE, reducing interfacial tension.

[0014] Low boiling point hydrocarbons have a boiling point of less than 100°C.

[0015] The microspheres of the present invention are designed into the above three-layer structure in order to achieve functional separation and synergy, meeting the requirements of the entire process from microsphere synthesis to final foaming application:

[0016] Inner layer (microsphere core): The power source for foaming. During the composite material's thermal molding process, the heated vaporization generates internal pressure, driving the microspheres to expand, thus forming a cellular structure within the matrix resin. The choice of material determines the foaming starting temperature and expansion capacity.

[0017] Intermediate layer: provides basic mechanical strength and thermal stability for the microsphere shell.

[0018] Outer layer: Provides high-temperature structural support and airtightness, ensuring the microspheres can effectively expand without rupture or leakage at temperatures between 160°C and 200°C. PP-g-MAH acts as an interfacial "anchor," improving the interfacial compatibility and bond strength between the microspheres and the matrix through gradient polarity orientation of its maleic anhydride groups and the matrix resin (e.g., polyethylene (PE) or polypropylene (PP). DCP, a latent initiator, is activated during the final hot press molding of the composite (180°C to 200°C), initiating chemical crosslinking / grafting between the microsphere shell and the matrix resin, further locking the pore structure and improving the overall mechanical properties and thermal stability of the composite.

[0019] The heat-expandable microspheres of the present invention can be foamed at 160-200°C and grafted and cross-linked with the substrate at 180-200°C to form a stable structure. This ensures that the foaming temperature, cross-linking reaction temperature, and resin molding temperature are matched to each other. Specifically:

[0020] The three-layer structure and temperature responsiveness and functional classification of each component during the foaming (160-200°C) stage:

[0021] Inner layer (microsphere core): When the temperature rises to 160~200℃, low-boiling-point hydrocarbons vaporize, generating huge internal vapor pressure.

[0022] The middle layer is composed of an AN / MMA copolymer that provides the main structure, EGDMA that provides cross-linking strength, and PEGDA that forms a low-cross-linking, flexible network that gives the shell a certain degree of flexibility. At 160-200°C, this layer softens, above its glass transition temperature (Tg), allowing the microspheres to expand under internal vapor pressure without rupturing the shell.

[0023] Outer layer: At high temperatures of 160~200℃, the high cross-linking density Si-O-Si network has high thermal stability and good air tightness, while also maintaining sufficient strength to effectively bind the internal vaporized foaming agent and prevent premature gas leakage.

[0024] Grafting and cross-linking with the substrate (180~200℃) stage:

[0025] DCP decomposition: DCP decomposes at 180-200°C to produce highly active free radicals, which trigger the double bonds in the microsphere shell to graft with the matrix chain segments to form an interpenetrating network.

[0026] PP-g-MAH Reaction: The anhydride groups in PP-g-MAH can form a gradient polarity interface with the matrix resin at this temperature, reducing interfacial tension. The reaction between PP-g-MAH and the matrix provides a dipole interaction pathway, enhancing the interfacial compatibility and bonding strength between the microspheres and the matrix.

[0027] Synergistic Effect: Foaming expansion and interfacial grafting / crosslinking occur almost simultaneously within the processing window of 180-200°C. Expansion forms a porous structure, while chemical bonding firmly anchors the expanded microspheres in the matrix, improving the structural stability and mechanical properties of the composite material and helping to maintain the integrity of the cellular structure, preventing gas leakage.

[0028] As the preferred technical solution:

[0029] In the aforementioned heat-expandable microspheres, the low-boiling-point hydrocarbons are a combination of isopentane and isooctane, with a mass ratio of 1 to 3:1. This combination of isopentane (boiling point 28°C) and isooctane (boiling point 99°C) prevents microsphere breakage caused by rapid vaporization of either hydrocarbon alone, resulting in a narrow expansion temperature range. It also matches the melting temperature window of the resin matrix (PE / PP) (160-200°C).

[0030] The heat-expandable microspheres as described above have a particle size of 25-30 μm before expansion and a particle size of 180-200 μm after expansion, and an effective foaming temperature range of 150-200°C.

[0031] The core advantage of this three-layer thermally expandable microsphere lies in its high stability after expansion and unique in-situ interfacial chemical bonding ability. Its TVS highly cross-linked dense shell formed by high temperature and the secondary cross-linking initiated by DCP give the microspheres excellent structural stability and gas leakage resistance after expansion at 160-200°C, which is superior to the possible collapse or rupture risks of traditional structures. Secondly, the PP-g-MAH and DCP integrated in the outer layer can be activated during the composite material processing at 180-200°C. Through anhydride reaction and free radical initiation, a gradient polarity interface and cross-linking are achieved between the microsphere shell and the matrix resin, forming a physically and chemically bonded interface. This design synchronizes foaming expansion with strong interface construction, significantly improving the structural integrity, compatibility, mechanical properties and durability of the final foam composite material.

[0032] The present invention also provides a method for preparing heat-expandable microspheres as described in any of the above items, comprising: first, mixing and emulsifying component A and component B in a high-speed shear emulsifier to obtain a suspension emulsion; then transferring the suspension emulsion to a high-pressure reactor; and polymerizing the mixture at 50-70° C. for 15-20 hours at a pressure of 0.5-1.5 MPa under nitrogen protection. The mixture is then heated to 90-110° C. for 2-4 hours. After the reaction is completed, the mixture is naturally cooled and the pressure is released. The product is filtered, washed, and dried in sequence to obtain heat-expandable microspheres.

[0033] Component A is prepared by mixing deionized water, sodium chloride, nano-silica, polyvinyl pyrrolidone, anhydrous ethanol and sodium nitrite and then ultrasonically treating the mixture;

[0034] Deionized water: dispersion medium, provides reaction site, and adjusts the polarity of the system;

[0035] Sodium chloride: ionic strength regulator, stabilizes emulsion droplets;

[0036] Nano-silica: emulsifier, adsorbed at the oil-water interface to enhance emulsion stability;

[0037] Polyvinylpyrrolidone (PVP): steric stabilizer to prevent droplet coalescence;

[0038] Anhydrous ethanol: cosolvent, adjusts interfacial tension and promotes monomer dispersion;

[0039] Sodium nitrite: pH buffer and polymerization inhibitor, inhibiting premature polymerization;

[0040] Component B is obtained by uniformly mixing low-boiling-point hydrocarbons, azobisisobutyronitrile, ethylene glycol dimethacrylate, acrylonitrile, methyl methacrylate, maleic anhydride grafted polyolefin, polyethylene glycol diacrylate, tetravinylsilane and dicumyl peroxide.

[0041] Low boiling point hydrocarbons: foaming agents, which vaporize when heated to provide expansion power;

[0042] Azobisisobutyronitrile (AIBN): low-temperature initiator, starts the inner layer polymerization;

[0043] Ethylene glycol dimethacrylate (EGDMA): cross-linking agent, participates in the cross-linking of the middle layer to enhance mechanical strength;

[0044] Acrylonitrile (AN): Main monomer, building the middle layer copolymer backbone;

[0045] Methyl methacrylate (MMA): Main monomer, building the middle layer copolymer backbone;

[0046] Maleic anhydride grafted polyolefin (PP-g-MAH): interfacial compatibilizer, the anhydride group forms a gradient polarity guide with the matrix resin;

[0047] Polyethylene glycol diacrylate (PEGDA): A low-temperature crosslinker (activated at 70-90°C), forming a low-crosslink interface between the inner and middle layers. Other low-temperature crosslinkers (such as butyl diacrylate) lack the hydrophilic-hydrophobic balance of the PEG chain, making it difficult to achieve efficient encapsulation of the foaming agent. The ether oxygen atoms of PEGDA can form hydrogen bonds, enhancing the toughness of the inner layer.

[0048] Tetravinylsilane (TVS): high-temperature crosslinking agent (≥100°C activation), building a dense and highly cross-linked outer layer;

[0049] Dicumyl peroxide (DCP): A high-temperature free radical source that decomposes at the composite material processing temperature to produce active free radicals, initiating interchain crosslinking between the microsphere shell and the matrix.

[0050] 1. Inner layer and middle layer;

[0051] Low-boiling-point hydrocarbon foaming agents do not participate in chemical reactions. In the emulsification stage, component A (aqueous phase system) and component B (oil phase system) form water-in-oil tiny droplets. The droplets contain the oil phase. During the stirring process, as the temperature rises, the reaction temperature reaches the decomposition temperature of the initiator (70°C) and the initiator decomposes to generate primary free radicals. As the molecular chain grows, the solubility of the generated polymer gradually decreases in the monomer droplets, and the polymer continuously precipitates from the monomer droplets to cause solution precipitation polymerization.

[0052] Monomer polymerization: AN (high polarity) and MMA (high rigidity) are copolymerized under the initiation of AIBN. The cyano group of AN strengthens intermolecular forces, while the methyl group of MMA provides steric hindrance, forming a transition layer that is both rigid and flexible. PEGDA, containing a diacrylate structure, preferentially undergoes free radical polymerization above 70°C under the initiation of AIBN. Its long-chain PEG structure imparts flexibility and a low crosslink density (large spacing between crosslinks), forming a stretchable elastic network.

[0053] EGDMA synergistic cross-linking: The dimethacrylate structure forms a medium cross-linking network during polymerization, improving thermal stability.

[0054] 2. Intermediate layer spherical shell structure:

[0055] The main chain is a copolymer of AN and MMA, and EGDMA dimethacrylate cross-links are interspersed between the main chains, and the inner layer has a low cross-linked PEGDA retention inner layer.

[0056] As the preferred technical solution:

[0057] The preparation method of heat-expandable microspheres as described above comprises the following amounts, by mass, of the substances in component A: 300 parts of deionized water, 50-70 parts of sodium chloride, 15-25 parts of nano-silicon dioxide, 2-5 parts of polyvinyl pyrrolidone, 1-2 parts of anhydrous ethanol, and 0.5-1 part of sodium nitrite.

[0058] The above-mentioned method for preparing heat-expandable microspheres comprises the following amounts, by mass, of the substances in component B: 25-40 parts of low-boiling-point hydrocarbons, 1-1.5 parts of azobisisobutyronitrile, 0.5-1 part of ethylene glycol dimethacrylate, 30-40 parts of acrylonitrile, 35-50 parts of methyl methacrylate, 8-12 parts of maleic anhydride-grafted polyolefin, 2-5 parts of polyethylene glycol diacrylate, 1-2 parts of tetravinylsilane, and 0.8-1 part of dicumyl peroxide.

[0059] In the above-mentioned method for preparing heat-expandable microspheres, the rotation speed of the high-speed shear emulsifier is 14,000 to 20,000 rpm, and the mixing and emulsification time is 5 to 20 minutes.

[0060] An electromagnetic shielding-thermal management foam material, prepared by a thermal expansion foaming process using the thermal expansion microspheres described in any one of the above items;

[0061] The electromagnetic shielding-thermal management foam material comprises an absorption layer, a reflection layer and a heat insulation layer from the outside to the inside;

[0062] The absorption layer is a closed-cell composite foam containing amorphous metal magnetic nanoparticles, conductive fillers and thermally expandable microspheres;

[0063] The reflective layer has a surface density of 200~320g / m 2 Plain woven carbon fiber fabric; Plain woven carbon fiber fabric has excellent anisotropic effect, and the weaving process controls the surface density to 200~320g / m 2 High porosity can be achieved, the lower the surface density, the greater the porosity;

[0064] The thermal insulation layer is a low-density closed-cell composite foam containing thermal expansion microspheres. The density of the low-density closed-cell composite foam is 100~400kg / m 3 .

[0065] The present invention uses plain woven carbon fiber fabric to act as a bridge between the absorption layer and the thermal insulation layer, further improving the electromagnetic shielding performance and thermal insulation performance, and ensuring that the overall material has excellent mechanical properties. Specifically:

[0066] Electromagnetic shielding performance: The outer absorption layer containing amorphous metal magnetic nanoparticles and conductive fillers efficiently dissipates high-frequency electromagnetic waves through magnetic loss and dielectric loss; the carbon fiber fabric in the middle layer forms a continuous conductive network, which reflects the remaining electromagnetic waves and generates eddy current loss, forming an "absorption-reflection-reabsorption" gradient impedance matching with the absorption layer. Absorption and reflection jointly promote the electromagnetic shielding performance of the composite material, and the shielding effectiveness is greatly improved compared with the single-layer structure.

[0067] Thermal Insulation: The inner layer of low-density closed-cell foam inhibits heat conduction by creating an internal gas barrier. The middle layer of plain-woven carbon fiber fabric has a high porosity, reducing the solid conduction path. Its anisotropic thermal conductivity effectively blocks the longitudinal transfer of heat, making it difficult for heat to diffuse through the thickness, further inhibiting heat conduction and achieving efficient thermal isolation. In other words, the inner layer of closed-cell foam primarily blocks heat conduction, while the middle layer of plain-woven carbon fiber fabric blocks the longitudinal transfer of heat. The combination of the two forms a multi-layered thermal barrier structure, significantly improving overall thermal insulation performance.

[0068] Mechanical Properties: The foam structure of the insulation and absorption layers has excellent impact resistance and cushioning properties, can absorb and disperse external forces, and protect the internal structure. The carbon fiber fabric has high strength and rigidity, can withstand large mechanical loads, and enhance the stability of the overall structure. When heated, the microsphere shells cross-link with the interchain of the matrix to form covalent bonds, which greatly improves the interface strength between the microspheres and the resin matrix. In summary, the closed-cell foam provides lightweight cushioning, and the carbon fiber fabric provides high-strength support. The combination of the two maintains lightweight while significantly improving the overall structural strength.

[0069] In the electromagnetic shielding-thermal management foam material as described above, the amorphous metal magnetic nanoparticles are iron silicon boron nanoparticles, and the conductive filler is carbon nanotubes; in the closed-cell composite foam containing the amorphous metal magnetic nanoparticles and the conductive filler, the content of the amorphous metal magnetic nanoparticles is 2-5wt%, and the content of the conductive filler is 1-3wt%.

[0070] In the electromagnetic shielding-thermal management foam material described above, the pore diameter of the closed-cell composite foam containing amorphous metal magnetic nanoparticles is 130-180 μm, and the pore diameter of the low-density closed-cell composite foam is 150-200 μm.

[0071] In the electromagnetic shielding-thermal management foam material as described above, the plain woven carbon fiber fabric is a plain woven nickel-plated or non-nickel-plated carbon fiber fabric.

[0072] In the electromagnetic shielding-thermal management foam material as described above, the thermal conductivity of the plain woven carbon fiber fabric in the thickness direction is 0.5-2.5 W / m·K.

[0073] An electromagnetic shielding-thermal management foam material as described in any one of the above items, wherein the absorption layer has a thickness of 1 to 5 mm, the reflection layer has a thickness of 0.2 to 0.4 mm, and the insulation layer has a thickness of 2 to 10 mm;

[0074] In the range of 8.2~12.4GHz, the electromagnetic shielding-thermal management foam material has a shielding effect of 60~110dB; the thermal conductivity of the electromagnetic shielding-thermal management foam material is 0.03~0.2W / m·K, and the compressive strength is 1~10MPa.

[0075] Beneficial effects:

[0076] (1) The heat-expandable microspheres of the present invention are three-layer heat-expandable microspheres, which have high stability and unique in-situ interfacial chemical bonding ability after expansion.

[0077] (2) The present invention provides a method for preparing thermally expandable microspheres, wherein the plain-woven carbon fiber fabric acts as a bridge between the absorption layer and the thermal insulation layer, thereby further improving the electromagnetic shielding performance and thermal insulation performance, and ensuring that the material as a whole has excellent mechanical properties; the preparation method is simple.

[0078] (3) The electromagnetic shielding-thermal management foam material of the present invention has excellent electromagnetic shielding and thermal insulation properties and has a wide range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0079] Figure 1 Schematic diagram of the structure of thermally expandable microspheres;

[0080] Figure 2 This is a scanning electron microscope image of the heat-expandable microspheres after expansion in Example 5;

[0081] Figure 3 This is a cross-sectional scanning electron microscope image of the heat-expandable microspheres of Example 3 before expansion;

[0082] Among them, 1-microsphere core, 2-middle layer, 3-outer layer. DETAILED DESCRIPTION

[0083] Below in conjunction with specific embodiment, further set forth the present invention.Should be understood that these embodiments are only used to illustrate the present invention and are not used in limiting the scope of the present invention.In addition, should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall equally within the scope limited by the appended claims of the application.

[0084] The test methods involved in the performance indicators in the embodiments and comparative examples of the present invention are as follows:

[0085] Cell diameter: The cell diameter was observed and measured using a scanning electron microscope (SEM).

[0086] Electromagnetic shielding performance: A vector network analyzer (Rohde & Schwarz (China) Technology Co., Ltd., model ZNB20) was used to test the electromagnetic shielding performance of the electromagnetic shielding-thermal management foam material in the WR90 band (8.2-12.4 GHz). The microwave S parameters (S11, S12, S21, and S22) of the foam composite material were obtained using the waveguide method, and the electromagnetic shielding effectiveness was calculated.

[0087] Thermal conductivity: A TA Fox200 thermal conductivity meter was used to measure the thermal conductivity of rectangular foam composite samples. The sample size was 100 mm (length × width × thickness) 100 mm (length × width × thickness) and the temperature difference between the upper and lower heating plates was 30°C.

[0088] Compressive Strength: The compressive strength test of expanded foam composite materials with electromagnetic shielding properties is carried out in accordance with GB / T 8813-2020.

[0089] Some of the substances of the present invention are as follows:

[0090] Nano-silicon dioxide, manufacturer: MCC New Materials, brand: ZY-8.

[0091] Polyvinylpyrrolidone, manufacturer: Merrill, brand: K23-27.

[0092] Maleic anhydride grafted polyolefin, manufacturer: ExxonMobil, brand: PE 1040.

[0093] Polyethylene glycol diacrylate, manufacturer: Merrill, brand: M87272.

[0094] Polyethylene resin, manufacturer: Zhejiang Ruitang Plastic Technology Co., Ltd., brand: HD253P.

[0095] Polypropylene resin, manufacturer: Yanshan Petrochemical Company, brand: B8101.

[0096] D50 particle size refers to the particle size value when the cumulative distribution percentage reaches 50%.

[0097] Example 1

[0098] A method for preparing heat-expandable microspheres, comprising the following steps:

[0099] (1) 300 parts of deionized water, 50 parts of sodium chloride, 15 parts of nano-silica, 2 parts of polyvinyl pyrrolidone, 1 part of anhydrous ethanol and 0.5 parts of sodium nitrite were mixed and ultrasonically treated for 10 minutes to obtain component A, and the pH value was adjusted to 3;

[0100] (2) 20 parts of isopentane, 10 parts of isooctane, 1 part of azobisisobutyronitrile, 0.5 parts of ethylene glycol dimethacrylate, 35 parts of acrylonitrile, 45 parts of methyl methacrylate, 10 parts of maleic anhydride grafted polyolefin, 3 parts of polyethylene glycol diacrylate, 2 parts of tetravinylsilane and 0.8 parts of dicumyl peroxide were mixed and stirred to obtain component B;

[0101] (3) First, component A and component B were mixed and emulsified in a high-speed shear emulsifier at a speed of 14,000 rpm for 15 minutes to obtain a suspension emulsion. The suspension emulsion was then transferred to a high-pressure reactor. Under nitrogen protection, the pressure was maintained at 1 MPa and polymerization was carried out at 70°C for 15 hours. The temperature was then raised to 100°C for polymerization for 2 hours. After the reaction was completed, the mixture was naturally cooled and the pressure was released. The product was filtered, washed and dried in sequence to obtain thermal expansion microspheres.

[0102] like Figure 1 As shown, the final heat-expandable microspheres are composed of a microsphere core 1, an intermediate layer 2, and an outer layer 3 from the inside out. The microsphere core is a mixture of isopentane and isooctane. The intermediate layer is a copolymer composed of acrylonitrile segments, methyl methacrylate segments, ethylene glycol dimethacrylate segments, and polyethylene glycol diacrylate segments. The acrylonitrile segments and methyl methacrylate segments constitute the main chain skeleton of the copolymer, and the ethylene glycol dimethacrylate segments and polyethylene glycol diacrylate segments serve as bridging units connected to the main chain skeleton. The outer layer comprises a cross-linked tetravinylsilane network, dicumyl peroxide, and maleic anhydride-grafted polyolefin. The cross-linked tetravinylsilane network is a dense three-dimensional network formed by tetravinylsilane through Si-O-Si bridges. The average particle size of the heat-expandable microspheres before expansion is 25 μm, and the average particle size after expansion is 200 μm. The effective foaming temperature range is 150-200°C.

[0103] Example 2

[0104] A method for preparing heat-expandable microspheres, comprising the following steps:

[0105] (1) 300 parts of deionized water, 60 parts of sodium chloride, 20 parts of nano-silica, 3 parts of polyvinyl pyrrolidone, 1 part of anhydrous ethanol and 0.5 parts of sodium nitrite were mixed and ultrasonically treated for 10 minutes to obtain component A, and the pH value was adjusted to 3;

[0106] (2) 20 parts of isopentane, 10 parts of isooctane, 1 part of azobisisobutyronitrile, 0.5 parts of ethylene glycol dimethacrylate, 30 parts of acrylonitrile, 35 parts of methyl methacrylate, 10 parts of maleic anhydride grafted polyolefin, 3 parts of polyethylene glycol diacrylate, 1 part of tetravinylsilane and 0.8 parts of dicumyl peroxide were mixed and stirred to obtain component B;

[0107] (3) First, component A and component B were mixed and emulsified in a high-speed shear emulsifier at a speed of 15,000 rpm for 18 minutes to obtain a suspension emulsion. The suspension emulsion was then transferred to a high-pressure reactor. Under nitrogen protection, the pressure was maintained at 0.5 MPa and polymerization was carried out at 65°C for 16 hours. The temperature was then raised to 105°C for polymerization for 2.5 hours. After the reaction was completed, the mixture was naturally cooled and the pressure was released. The product was filtered, washed and dried in sequence to obtain thermal expansion microspheres.

[0108] The final heat-expandable microspheres are composed of a microsphere core, an intermediate layer, and an outer layer from the inside out. The microsphere core is a mixture of isopentane and isooctane. The intermediate layer is a copolymer composed of acrylonitrile segments, methyl methacrylate segments, ethylene glycol dimethacrylate segments, and polyethylene glycol diacrylate segments. The acrylonitrile segments and methyl methacrylate segments constitute the main chain skeleton of the copolymer, and the ethylene glycol dimethacrylate segments and polyethylene glycol diacrylate segments serve as bridging units connected to the main chain skeleton. The outer layer includes a cross-linked tetravinylsilane network, dicumyl peroxide, and maleic anhydride-grafted polyolefin. The cross-linked tetravinylsilane network is a dense three-dimensional network formed by tetravinylsilane through Si-O-Si bridges. The average particle size of the heat-expandable microspheres before expansion is 25 μm, and the average particle size after expansion is 180 μm. The effective foaming temperature range is 160-190°C.

[0109] Example 3

[0110] A method for preparing heat-expandable microspheres, comprising the following steps:

[0111] (1) 300 parts of deionized water, 65 parts of sodium chloride, 20 parts of nano-silica, 3 parts of polyvinyl pyrrolidone, 1.5 parts of anhydrous ethanol and 0.5 parts of sodium nitrite were mixed and ultrasonically treated for 10 minutes to obtain component A, and the pH value was adjusted to 2.5;

[0112] (2) 15 parts of isopentane, 10 parts of isooctane, 1 part of azobisisobutyronitrile, 0.5 parts of ethylene glycol dimethacrylate, 30 parts of acrylonitrile, 35 parts of methyl methacrylate, 8 parts of maleic anhydride grafted polyolefin, 3 parts of polyethylene glycol diacrylate, 1.5 parts of tetravinylsilane and 0.8 parts of dicumyl peroxide were mixed and stirred to obtain component B;

[0113] (3) First, component A and component B were mixed and emulsified in a high-speed shear emulsifier at a speed of 16,000 rpm for 20 minutes to obtain a suspension emulsion. The suspension emulsion was then transferred to a high-pressure reactor. Under nitrogen protection, the pressure was maintained at 1 MPa and polymerization was carried out at 60°C for 18 hours. The temperature was then raised to 110°C for polymerization for 2 hours. After the reaction was completed, the mixture was naturally cooled and the pressure was released. The product was filtered, washed and dried in sequence to obtain thermal expansion microspheres.

[0114] The final heat-expandable microspheres are composed of a microsphere core, an intermediate layer and an outer layer from the inside to the outside. The microsphere core is a mixture of isopentane and isooctane. The intermediate layer is a copolymer composed of acrylonitrile segments, methyl methacrylate segments, ethylene glycol dimethacrylate segments and polyethylene glycol diacrylate segments. The acrylonitrile segments and methyl methacrylate segments constitute the main chain skeleton of the copolymer. The ethylene glycol dimethacrylate segments and polyethylene glycol diacrylate segments serve as bridging units and are connected to the main chain skeleton. The outer layer includes a cross-linked tetravinylsilane network, dicumyl peroxide and maleic anhydride grafted polyolefin, wherein the cross-linked tetravinylsilane network is a dense three-dimensional network formed by tetravinylsilane through Si-O-Si bridges. Figure 3 As shown in the figure, the average particle size of the heat-expandable microspheres before expansion is 25 μm, the average particle size after expansion is 180 μm, and the effective foaming temperature range is 170~200℃.

[0115] Example 4

[0116] A method for preparing heat-expandable microspheres, comprising the following steps:

[0117] (1) 300 parts of deionized water, 70 parts of sodium chloride, 25 parts of nano-silica, 5 parts of polyvinyl pyrrolidone, 1.5 parts of anhydrous ethanol and 1 part of sodium nitrite were mixed and ultrasonically treated for 10 minutes to obtain component A, and the pH value was adjusted to 3.5;

[0118] (2) 30 parts of isopentane, 10 parts of isooctane, 1.2 parts of azobisisobutyronitrile, 0.8 parts of ethylene glycol dimethacrylate, 40 parts of acrylonitrile, 40 parts of methyl methacrylate, 12 parts of maleic anhydride grafted polyolefin, 5 parts of polyethylene glycol diacrylate, 1.5 parts of tetravinylsilane and 0.8 parts of dicumyl peroxide were mixed and stirred to obtain component B;

[0119] (3) First, component A and component B were mixed and emulsified in a high-speed shear emulsifier at a speed of 18,000 rpm for 10 minutes to obtain a suspension emulsion. The suspension emulsion was then transferred to a high-pressure reactor. Under nitrogen protection, the pressure was maintained at 1.2 MPa and polymerization was carried out at 50°C for 20 hours. The temperature was then raised to 95°C for polymerization for 3 hours. After the reaction was completed, the mixture was naturally cooled and the pressure was released. The product was filtered, washed and dried in sequence to obtain thermal expansion microspheres.

[0120] The final heat-expandable microspheres are composed of a microsphere core, an intermediate layer, and an outer layer from the inside out. The microsphere core is a mixture of isopentane and isooctane. The intermediate layer is a copolymer composed of acrylonitrile segments, methyl methacrylate segments, ethylene glycol dimethacrylate segments, and polyethylene glycol diacrylate segments. The acrylonitrile segments and methyl methacrylate segments constitute the main chain skeleton of the copolymer, and the ethylene glycol dimethacrylate segments and polyethylene glycol diacrylate segments serve as bridging units connected to the main chain skeleton. The outer layer includes a cross-linked tetravinylsilane network, dicumyl peroxide, and maleic anhydride-grafted polyolefin. The cross-linked tetravinylsilane network is a dense three-dimensional network formed by tetravinylsilane through Si-O-Si bridges. The average particle size of the heat-expandable microspheres before expansion is 30 μm, and the average particle size after expansion is 190 μm. The effective foaming temperature range is 160-200°C.

[0121] Example 5

[0122] A method for preparing heat-expandable microspheres, comprising the following steps:

[0123] (1) 300 parts of deionized water, 65 parts of sodium chloride, 25 parts of nano-silica, 5 parts of polyvinyl pyrrolidone, 2 parts of anhydrous ethanol and 0.5 parts of sodium nitrite were mixed and ultrasonically treated for 10 minutes to obtain component A, and the pH value was adjusted to 3.5;

[0124] (2) 20 parts of isopentane, 20 parts of isooctane, 1.5 parts of azobisisobutyronitrile, 1 part of ethylene glycol dimethacrylate, 35 parts of acrylonitrile, 50 parts of methyl methacrylate, 12 parts of maleic anhydride grafted polyolefin, 2 parts of polyethylene glycol diacrylate, 1.5 parts of tetravinylsilane and 1 part of dicumyl peroxide were mixed and stirred to obtain component B;

[0125] (3) First, component A and component B were mixed and emulsified in a high-speed shear emulsifier at a speed of 20,000 rpm for 5 minutes to obtain a suspension emulsion. The suspension emulsion was then transferred to a high-pressure reactor. Under nitrogen protection, the pressure was maintained at 1.5 MPa and polymerization was carried out at 55°C for 19 hours. The temperature was then raised to 90°C for polymerization for 4 hours. After the reaction was completed, the mixture was naturally cooled and the pressure was released. The product was filtered, washed and dried in sequence to obtain thermal expansion microspheres.

[0126] The final heat-expandable microspheres are composed of a microsphere core, an intermediate layer and an outer layer from the inside to the outside; the microsphere core is a mixture of isopentane and isooctane; the intermediate layer is a copolymer composed of acrylonitrile segments, methyl methacrylate segments, ethylene glycol dimethacrylate segments and polyethylene glycol diacrylate segments, the acrylonitrile segments and methyl methacrylate segments constitute the main chain skeleton of the copolymer, and the ethylene glycol dimethacrylate segments and polyethylene glycol diacrylate segments serve as bridging units and are connected to the main chain skeleton; the outer layer includes a cross-linked tetravinylsilane network, dicumyl peroxide and maleic anhydride grafted polyolefin, wherein the cross-linked tetravinylsilane network is a dense three-dimensional network formed by tetravinylsilane through Si-O-Si bridging; the average particle size of the heat-expandable microspheres before expansion is 30 μm, and the average particle size after expansion is 180 μm (such as Figure 2 As shown in Figure 2), the effective foaming temperature range is 170~200℃.

[0127] Example 6

[0128] An electromagnetic shielding-thermal management foam material is prepared by using the heat-expandable microspheres of Example 1 through a heat-expandable foaming process. The specific preparation steps are as follows:

[0129] (1) Preparation of thermal insulation foam prepreg sheet;

[0130] The polyethylene resin and heat-expandable microspheres are mixed and hot-pressed at 140°C for 20 minutes to prepare a thermal insulation foam prepreg sheet.

[0131] The content of heat-expandable microspheres in the thermal insulation layer foam prepreg sheet is 10wt%;

[0132] (2) Preparation of reflective layer materials;

[0133] Surface density 200g / m 2 Plain woven carbon fiber fabric; the thermal conductivity of the plain woven carbon fiber fabric in the thickness direction is 0.5W / m·K;

[0134] (3) Preparation of the absorption layer foam prepreg sheet;

[0135] Heat-expandable microspheres, carbon nanotubes, and iron-silicon-boron nanoparticles with a D50 particle size of 30 μm were added to polyethylene resin, and then hot-pressed at 140°C for 20 minutes to prepare an absorbent layer foam prepreg sheet.

[0136] The content of heat-expandable microspheres in the absorbing layer foam prepreg sheet is 3wt%, the content of iron silicon boron nanoparticles is 5wt%, and the content of carbon nanotubes is 3%;

[0137] (4) The absorption layer foam prepreg sheet, the plain woven carbon fiber fabric and the insulation layer foam prepreg sheet are placed in a mold in sequence, heated at 180°C for expansion and foaming for 60 minutes to obtain an electromagnetic shielding-thermal management foam material.

[0138] The final electromagnetic shielding-thermal management foam material is composed of an absorption layer, a reflective layer, and a thermal insulation layer from the outside to the inside. The thickness of the thermal insulation layer is 2 mm, the thickness of the reflective layer is 0.2 mm, and the thickness of the absorption layer is 1 mm. The absorption layer and the thermal insulation layer are both closed-cell composite foams. The pore diameter of the closed-cell composite foam in the absorption layer is 130-150 μm. The density of the closed-cell composite foam in the thermal insulation layer is 150 kg / m 3 , the pore diameter is 150~180μm; in the range of 8.2~12.4GHz, the electromagnetic shielding-thermal management foam material has a shielding effect of 70dB; the thermal conductivity of the electromagnetic shielding-thermal management foam material is 0.2W / m·K, and the compressive strength is 3MPa.

[0139] Comparative Example 1

[0140] An electromagnetic shielding foam material is basically the same as Example 6, except that the reflective layer is omitted, that is, the absorption layer foam prepreg rubber sheet and the insulation layer foam prepreg rubber sheet are placed in a mold in sequence for thermal expansion and foaming to obtain the electromagnetic shielding foam material.

[0141] In the range of 8.2~12.4GHz, the electromagnetic shielding foam material has a shielding effect of 40dB.

[0142] Comparing Comparative Example 1 with Example 6, it can be found that the electromagnetic shielding effect of Comparative Example 1 is significantly reduced. This is because the shielding efficiency is heavily dependent on the loss capacity of the absorption layer. The structure without the reflective layer cannot form multiple internal reflection paths, the reflection loss mechanism fails, and the overall shielding efficiency is significantly reduced.

[0143] Comparative Example 2

[0144] An electromagnetic shielding foam material is basically the same as Example 6, except that aluminum foil of the same thickness is used instead of plain woven carbon fiber fabric.

[0145] In the range of 8.2~12.4GHz, the electromagnetic shielding foam material has a shielding effect of 50dB; the thermal conductivity of the electromagnetic shielding foam material is 0.25W / m·K.

[0146] By comparing Comparative Example 2 with Example 6, it can be found that the electromagnetic shielding effect of Comparative Example 2 is significantly reduced and the thermal insulation performance is decreased. This is because although the aluminum foil has high conductivity, it lacks structural adaptability and cannot work together with the foam layer to form an effective multi-layer shielding system. Some electromagnetic waves are reflected and interfered at the aluminum foil interface, resulting in incomplete reflection and the formation of leakage points, thereby reducing the overall shielding performance; in addition, aluminum foil is an isotropic material and its thermal conductivity is much higher than that of carbon fiber fabric, which makes the thermal insulation performance of the electromagnetic shielding foam material of Comparative Example 2 worse.

[0147] Example 7

[0148] An electromagnetic shielding-thermal management foam material is prepared by using a thermal expansion foaming process using the thermal expansion microspheres of Example 2. The specific preparation steps are as follows:

[0149] (1) Preparation of thermal insulation foam prepreg sheet;

[0150] The polyethylene resin and heat-expandable microspheres are mixed and hot-pressed at 140°C for 20 minutes to prepare a thermal insulation foam prepreg sheet.

[0151] The content of heat-expandable microspheres in the insulation layer foam prepreg sheet is 11wt%;

[0152] (2) Preparation of reflective layer materials;

[0153] Surface density 240g / m 2 Plain woven nickel-plated carbon fiber fabric; the thermal conductivity of the plain woven nickel-plated carbon fiber fabric in the thickness direction is 1.5W / m·K;

[0154] (3) Preparation of the absorption layer foam prepreg sheet;

[0155] Thermal expansion microspheres, iron silicon boron nanoparticles, and carbon nanotubes with a D50 particle size of 20 nm were added to polyethylene resin, and then hot-pressed at 140°C for 20 minutes to prepare an absorption layer foam prepreg sheet.

[0156] The content of the thermal expansion microspheres in the absorbing layer foam prepreg sheet is 2 wt%, the content of the iron silicon boron nanoparticles is 2 wt%, and the content of the carbon nanotubes is 1 wt%.

[0157] (4) The absorption layer foam prepreg sheet, the plain woven carbon fiber fabric and the insulation layer foam prepreg sheet are placed in a mold in sequence, heated at 180°C for expansion and foaming for 60 minutes to obtain an electromagnetic shielding-thermal management foam material.

[0158] The final electromagnetic shielding-thermal management foam material is composed of an absorption layer, a reflective layer, and a thermal insulation layer from the outside to the inside. The thickness of the thermal insulation layer is 5 mm, the thickness of the reflective layer is 0.2 mm, and the thickness of the absorption layer is 3 mm. Both the absorption layer and the thermal insulation layer are closed-cell composite foams. The pore diameter of the closed-cell composite foam in the absorption layer is 130-150 μm. The density of the closed-cell composite foam in the thermal insulation layer is 200 kg / m 3 , the pore diameter is 180~200μm; in the range of 8.2~12.4GHz, the electromagnetic shielding-thermal management foam material has a shielding effect of 60dB; the thermal conductivity of the electromagnetic shielding-thermal management foam material is 0.15W / m·K, and the compressive strength is 5MPa.

[0159] Example 8

[0160] An electromagnetic shielding-thermal management foam material is prepared by using a thermal expansion foaming process using the thermal expansion microspheres of Example 3. The specific preparation steps are as follows:

[0161] (1) Preparation of thermal insulation foam prepreg sheet;

[0162] The polyethylene resin and heat-expandable microspheres are mixed and hot-pressed at 140°C for 20 minutes to prepare a thermal insulation foam prepreg sheet.

[0163] The content of heat-expandable microspheres in the insulation layer foam prepreg sheet is 12 wt%;

[0164] (2) Preparation of reflective layer materials;

[0165] Surface density 260g / m 2 Plain woven carbon fiber fabric; the thermal conductivity of the plain woven carbon fiber fabric in the thickness direction is 1.6W / m·K;

[0166] (3) Preparation of the absorption layer foam prepreg sheet;

[0167] Heat-expandable microspheres, carbon nanotubes, and iron-silicon-boron nanoparticles with a D50 particle size of 30 μm were added to polypropylene resin, and then hot-pressed at 140°C for 20 minutes to prepare an absorbent layer foam prepreg sheet.

[0168] The content of heat-expandable microspheres in the absorbing layer foam prepreg sheet is 5wt%, the content of iron silicon boron nanoparticles is 2wt%, and the content of carbon nanotubes is 3%;

[0169] (4) The absorption layer foam prepreg sheet, the plain woven carbon fiber fabric and the insulation layer foam prepreg sheet are placed in a mold in sequence, heated at 180°C for expansion and foaming for 60 minutes to obtain an electromagnetic shielding-thermal management foam material.

[0170] The final electromagnetic shielding-thermal management foam material comprises an absorption layer, a reflective layer, and a thermal insulation layer from the outside to the inside. The thermal insulation layer is 5 mm thick, the reflective layer is 0.2 mm thick, and the absorption layer is 3 mm thick. Both the absorption layer and the thermal insulation layer are closed-cell composite foams. The pore diameter of the closed-cell composite foam in the absorption layer is 130-150 μm. The density of the closed-cell composite foam in the thermal insulation layer is 100 kg / m 3 , the pore diameter is 180~200μm; in the range of 8.2~12.4GHz, the electromagnetic shielding-thermal management foam material has a shielding effect of 90dB; the thermal conductivity of the electromagnetic shielding-thermal management foam material is 0.05W / m·K, and the compressive strength is 1MPa.

[0171] Example 9

[0172] An electromagnetic shielding-thermal management foam material is prepared by using the heat-expandable microspheres of Example 4 through a heat-expandable foaming process. The specific preparation steps are as follows:

[0173] (1) Preparation of thermal insulation foam prepreg sheet;

[0174] The polyethylene resin and heat-expandable microspheres are mixed and hot-pressed at 140°C for 20 minutes to prepare a thermal insulation foam prepreg sheet.

[0175] The content of heat-expandable microspheres in the insulation layer foam prepreg sheet is 13wt%;

[0176] (2) Preparation of reflective layer materials;

[0177] Surface density 280g / m 2 Plain woven nickel-plated carbon fiber fabric; the thermal conductivity of the plain woven nickel-plated carbon fiber fabric in the thickness direction is 2W / m·K;

[0178] (3) Preparation of the absorption layer foam prepreg sheet;

[0179] Thermal expansion microspheres, iron silicon boron nanoparticles, and carbon nanotubes with a D50 particle size of 20 nm were added to polyethylene resin, and then hot-pressed at 140°C for 20 minutes to prepare an absorption layer foam prepreg sheet.

[0180] The content of the thermal expansion microspheres in the absorbing layer foam prepreg sheet is 5wt%, the content of the iron silicon boron nanoparticles is 3wt%, and the content of the carbon nanotubes is 2wt%.

[0181] (4) The absorption layer foam prepreg sheet, the plain woven carbon fiber fabric and the insulation layer foam prepreg sheet are placed in a mold in sequence, heated at 180°C for expansion and foaming for 60 minutes to obtain an electromagnetic shielding-thermal management foam material.

[0182] The final electromagnetic shielding-thermal management foam material comprises an absorption layer, a reflective layer, and a thermal insulation layer from the outside to the inside. The thermal insulation layer is 8 mm thick, the reflective layer is 0.4 mm thick, and the absorption layer is 4 mm thick. Both the absorption layer and the thermal insulation layer are closed-cell composite foams. The pore diameter of the closed-cell composite foam in the absorption layer is 150-180 μm. The density of the closed-cell composite foam in the thermal insulation layer is 300 kg / m 3 , the pore diameter is 180~200μm; in the range of 8.2~12.4GHz, the electromagnetic shielding-thermal management foam material has a shielding effect of 100dB; the thermal conductivity of the electromagnetic shielding-thermal management foam material is 0.05W / m·K, and the compressive strength is 7MPa.

[0183] Example 10

[0184] An electromagnetic shielding-thermal management foam material is prepared by using the heat-expandable microspheres of Example 5 through a heat expansion foaming process. The specific preparation steps are as follows:

[0185] (1) Preparation of thermal insulation foam prepreg sheet;

[0186] The polyethylene resin and heat-expandable microspheres are mixed and hot-pressed at 140°C for 20 minutes to prepare a thermal insulation foam prepreg sheet.

[0187] The content of heat-expandable microspheres in the insulation layer foam prepreg sheet is 15wt%;

[0188] (2) Preparation of reflective layer materials;

[0189] Surface density 320g / m 2 Plain woven carbon fiber fabric; the thickness of the plain woven carbon fiber fabric is 0.4 mm; the thermal conductivity coefficient of the plain woven carbon fiber fabric in the thickness direction is 2.5 W / m·K;

[0190] (3) Preparation of the absorption layer foam prepreg sheet;

[0191] Heat-expandable microspheres, carbon nanotubes, and iron-silicon-boron nanoparticles with a D50 particle size of 30 μm were added to polypropylene resin, and then hot-pressed at 140°C for 20 minutes to prepare an absorbent layer foam prepreg sheet.

[0192] The content of heat-expandable microspheres in the absorbing layer foam prepreg sheet is 5wt%, the content of iron silicon boron nanoparticles is 3wt%, and the content of carbon nanotubes is 2%;

[0193] (4) The absorption layer foam prepreg sheet, the plain woven carbon fiber fabric and the insulation layer foam prepreg sheet are placed in a mold in sequence, heated at 180°C for expansion and foaming for 60 minutes to obtain an electromagnetic shielding-thermal management foam material.

[0194] The final electromagnetic shielding-thermal management foam material comprises an absorption layer, a reflective layer, and a thermal insulation layer from the outside to the inside. The thermal insulation layer is 10 mm thick, the reflective layer is 0.4 mm thick, and the absorption layer is 5 mm thick. Both the absorption layer and the thermal insulation layer are closed-cell composite foams. The pore diameter of the closed-cell composite foam in the absorption layer is 150-180 μm. The density of the closed-cell composite foam in the thermal insulation layer is 400 kg / m 3 , the pore diameter is 180~200μm; in the range of 8.2~12.4GHz, the electromagnetic shielding-thermal management foam material has a shielding effect of 110dB; the thermal conductivity of the electromagnetic shielding-thermal management foam material is 0.03W / m·K, and the compressive strength is 10MPa.

Claims

1. An electromagnetic shielding-thermal management foam material, characterized by: It is prepared by thermal expansion microspheres through thermal expansion foaming process; The thermal expansion microspheres are composed of microsphere core, middle layer and outer layer from inside to outside; The core of the microspheres is a low-boiling-point hydrocarbon; The middle layer is a copolymer composed of acrylonitrile segments, methyl methacrylate segments, ethylene glycol dimethacrylate segments and polyethylene glycol diacrylate segments, wherein the acrylonitrile segments and methyl methacrylate segments constitute the main chain skeleton of the copolymer, and the ethylene glycol dimethacrylate segments and polyethylene glycol diacrylate segments serve as bridging units and are connected to the main chain skeleton; The outer layer comprises a cross-linked tetravinylsilane network, dicumyl peroxide and maleic anhydride grafted polyolefin, wherein the cross-linked tetravinylsilane network is a dense three-dimensional network formed by tetravinylsilane through Si-O-Si bridges; Low-boiling-point hydrocarbons have a boiling point of less than 100°C; The electromagnetic shielding-thermal management foam material comprises an absorption layer, a reflection layer and a heat insulation layer from the outside to the inside; The absorption layer is a closed-cell composite foam containing amorphous metal magnetic nanoparticles, conductive fillers and thermally expandable microspheres; The reflective layer has a surface density of 200~320g / m 2 plain-woven carbon fiber fabric; The thermal insulation layer is a low-density closed-cell composite foam containing thermal expansion microspheres. The density of the low-density closed-cell composite foam is 100~400kg / m 3 The matrix in the absorption layer and the heat insulation layer is polypropylene resin or polyethylene resin; The thickness of the absorption layer is 1~5mm, the thickness of the reflection layer is 0.2~0.4mm, and the thickness of the heat insulation layer is 2~10mm; In the range of 8.2~12.4GHz, the electromagnetic shielding-thermal management foam material has a shielding effect of 60~110dB.

2. The electromagnetic shielding-thermal management foam material according to claim 1, characterized in that: The low boiling point hydrocarbons are a combination of isopentane and isooctane, and the mass ratio of isopentane to isooctane is 1 to 3:

1.

3. The electromagnetic shielding-thermal management foam material according to claim 1, characterized in that: The particle size of the heat-expandable microspheres before expansion is 25~30μm, and the particle size after expansion is 180~200μm. The effective foaming temperature range is 150~200℃.

4. The electromagnetic shielding-thermal management foam material according to any one of claims 1 to 3, characterized in that: The preparation method of heat-expandable microspheres comprises the following steps: first, mixing and emulsifying component A and component B in a high-speed shear emulsifier to obtain a suspension emulsion; then transferring the suspension emulsion into a high-pressure reactor; and polymerizing the mixture at 50-70° C. for 15-20 hours under nitrogen protection while maintaining a pressure of 0.5-1.5 MPa; then heating the mixture to 90-110° C. for 2-4 hours; cooling the mixture after the reaction is completed and releasing the pressure; and filtering, washing, and drying the product in sequence to obtain heat-expandable microspheres; Component A is prepared by mixing deionized water, sodium chloride, nano-silica, polyvinyl pyrrolidone, anhydrous ethanol and sodium nitrite and then ultrasonically treating the mixture; Component B is obtained by uniformly mixing low-boiling-point hydrocarbons, azobisisobutyronitrile, ethylene glycol dimethacrylate, acrylonitrile, methyl methacrylate, maleic anhydride grafted polyolefin, polyethylene glycol diacrylate, tetravinylsilane and dicumyl peroxide.

5. The electromagnetic shielding-thermal management foam material according to claim 4, characterized in that: Calculated by mass, the amount of each substance in component A is: 300 parts of deionized water, 50-70 parts of sodium chloride, 15-25 parts of nano-silicon dioxide, 2-5 parts of polyvinyl pyrrolidone, 1-2 parts of anhydrous ethanol, and 0.5-1 part of sodium nitrite.

6. The electromagnetic shielding-thermal management foam material according to claim 4, characterized in that: Calculated by mass, the amount of each substance in component B is: 25-40 parts of low-boiling point hydrocarbons, 1-1.5 parts of azobisisobutyronitrile, 0.5-1 parts of ethylene glycol dimethacrylate, 30-40 parts of acrylonitrile, 35-50 parts of methyl methacrylate, 8-12 parts of maleic anhydride grafted polyolefin, 2-5 parts of polyethylene glycol diacrylate, 1-2 parts of tetravinylsilane, and 0.8-1 parts of dicumyl peroxide.

7. The electromagnetic shielding-thermal management foam material according to claim 4, characterized in that: The speed of the high-speed shear emulsifier is 14,000 to 20,000 rpm, and the mixing and emulsification time is 5 to 20 minutes.

8. The electromagnetic shielding-thermal management foam material according to claim 1, characterized in that: The amorphous metal magnetic nanoparticles are iron silicon boron nanoparticles, and the conductive filler is carbon nanotubes. In the closed-cell composite foam containing the amorphous metal magnetic nanoparticles and the conductive filler, the content of the amorphous metal magnetic nanoparticles is 2-5wt%, and the content of the conductive filler is 1-3wt%.

9. The electromagnetic shielding-thermal management foam material according to claim 1, characterized in that: The cell diameter of the closed-cell composite foam containing amorphous metal magnetic nanoparticles and conductive fillers is 130-180 μm, and the cell diameter of the low-density closed-cell composite foam is 150-200 μm.

10. The electromagnetic shielding-thermal management foam material according to claim 1, characterized in that: Plain woven carbon fiber fabric is a plain woven carbon fiber fabric with or without nickel plating.

11. The electromagnetic shielding-thermal management foam material according to claim 10, characterized in that: The thermal conductivity of plain woven carbon fiber fabric in the thickness direction is 0.5~2.5W / m·K.

12. The electromagnetic shielding-thermal management foam material according to any one of claims 8 to 11, characterized in that: The thermal conductivity of the electromagnetic shielding-thermal management foam material is 0.03~0.2W / m·K, and the compressive strength is 1~10MPa.

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