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

Abstract

The invention belongs to an electromagnetic shielding foam material, and relates to a thermal expansion microsphere, a preparation method thereof and an electromagnetic shielding-thermal management foam material, and the thermal expansion microsphere sequentially comprises a microsphere core, a middle layer and an outer layer from inside to outside; the preparation method comprises the following steps: mixing and emulsifying the component A and the component B in a high-speed shearing emulsifying machine to obtain a suspended emulsion, transferring the suspended emulsion into a high-pressure reaction kettle, polymerizing for 15-20 hours at 50-70 DEG C under the condition of nitrogen protection, heating to 90-110 DEG C, polymerizing for 2-4 hours, cooling and decompressing after the reaction is completed, and sequentially performing suction filtration, washing and drying on the product to obtain the high-performance polyurethane elastomer. Thermal expansion microspheres are prepared; the electromagnetic shielding-thermal management foam material is prepared from the thermal expansion microspheres through a thermal expansion foaming process. After being expanded, the thermal expansion microspheres have high stability and unique in-situ interface chemical bonding capability; the preparation method is simple; the application range is wide.

Description

Technical Field

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

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

[0003] In recent years, introducing thermally expandable microspheres as foaming units to construct layered-structured foams has become a research hotspot. However, most microspheres are physically embedded and cannot form a stable interface with the matrix, making it difficult to adapt to highly crystalline resin materials. Applying thermally expandable microspheres to electromagnetic shielding foams can effectively form a high-porosity closed-cell structure, reduce the dielectric constant, and enhance the wave absorption path. If the microsphere structure and the matrix material are synergistically designed, especially by introducing a chemical bonding mechanism, the structural stability, electromagnetic wave dissipation efficiency, and thermal insulation ability of the material can be significantly improved.

[0004] For example, Patent CN202311211516.6 discloses a preparation method of a thermally self-expandable epoxy foam with electromagnetic shielding characteristics. By introducing thermally expandable microspheres and conductive fillers into epoxy resin, foam structure formation and shielding performance improvement are achieved through thermal curing. However, the microspheres used have a two-layer structure, a narrow foaming temperature window, making it difficult to match multiple matrix systems. Moreover, there is only physical filling between the microspheres and the matrix, lacking a chemical bonding interface, resulting in poor interfacial stability and limited service life.

[0005] Patent CN114634617A discloses a carbon nanotube conductive foam material with thermal foaming ability and a preparation method thereof. By blending and foaming thermally expandable microspheres with conductive materials such as carbon nanotubes and MXene, a conductive foam composite material is constructed. However, the conductive fillers are prone to agglomeration during the high-temperature foaming process, resulting in unstable shielding performance. In addition, the microsphere foaming structure is uneven, with a wide size distribution range, leading to unstable internal structure and poor mechanical properties of the material.

[0006] Patent CN107262014A discloses a high-performance electromagnetic shielding composite foam material and its preparation method, which 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 bonding force between the spray coating and the foam interface is weak, and it is easy to fall off during bending or impact, resulting in the fracture of the shielding layer or the decrease of the shielding effectiveness. At the same time, the cost of nano-silver is high, and organic solvents are required in the process, which poses environmental and safety risks.

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

[0008] The object of the present invention is to solve the problems existing in the prior art and provide a thermally expandable microsphere, its preparation method and an electromagnetic shielding-thermal management foam material.

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

[0010] A thermally expandable microsphere, which sequentially comprises a microsphere core, an intermediate layer and an outer layer from the inside to the outside;

[0011] The microsphere core is a low-boiling hydrocarbon;

[0012] The intermediate 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 segments and the methyl methacrylate segments constitute the main chain skeleton of the copolymer, and the ethylene glycol dimethacrylate segments and the polyethylene glycol diacrylate segments serve as bridging units and are connected to the main chain skeleton; among them, EGDMA is used as a short-chain rigid cross-linking agent, and through its two double bonds, it is respectively connected to the AN / MMA units on different main chains to form short-spacing cross-linking points; PEGDA is used as a long-chain flexible cross-linking agent, and its polyethylene glycol segment introduces a flexible spacer and forms long-range cross-linking when connecting to the main chain;

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

[0014] Low-boiling 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 to achieve the separation and coordination of functions, meeting the requirements of the whole process from microsphere synthesis to final foaming application:

[0016] Inner layer (microsphere core): The foaming power source. During the heating and forming process of the composite material, it gasifies when heated, generating internal pressure to drive the expansion of the microspheres, thereby forming a pore structure in the matrix resin. The selection of its material determines the starting temperature and expansion ability of foaming.

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

[0018] Outer layer: Provides high-temperature structural support and airtightness, ensuring that the microspheres can expand effectively without cracking or leaking air at 160 - 200 °C. PP-g-MAH serves as an interface "anchor point", and through its maleic anhydride groups, it guides the gradient polarity with the matrix resin (such as polyethylene PE, polypropylene PP, etc.), improving the interfacial compatibility and bonding strength between the microspheres and the matrix. DCP, as a latent initiator, is activated during the final hot pressing of the composite material (180 - 200 °C), initiating chemical cross-linking / grafting between the microsphere shell layer and the matrix resin, further locking the pore structure and improving the overall mechanical properties and thermal stability of the composite material.

[0019] The thermally expandable microspheres of the present invention can achieve foaming at 160 - 200 °C and graft cross-linking with the matrix at 180 - 200 °C, forming a stable structure. It ensures the mutual matching of the foaming temperature, cross-linking reaction temperature, and resin forming temperature. Specifically:

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

[0021] Inner layer (microsphere core): When the temperature rises to 160 - 200 °C, the low-boiling hydrocarbons gasify, generating a huge internal vapor pressure.

[0022] Intermediate layer: The main structure is provided by the AN / MMA copolymer, EGDMA provides a certain cross-linking strength, and the low-crosslinking flexible network formed by PEGDA endows the shell layer with a certain flexibility. At 160 - 200 °C, the material of this layer will soften, higher than its glass transition temperature Tg, allowing the microspheres to expand under the internal vapor pressure without the outer shell cracking.

[0023] Outer layer: At a high temperature of 160 - 200 °C, the high-crosslinking density Si-O-Si network has high thermal stability and good airtightness, and can also maintain sufficient strength to effectively confine the internal gasified blowing agent and prevent gas from leaking prematurely.

[0024] Grafting crosslinking with the matrix (180 - 200 °C) stage:

[0025] DCP decomposition: DCP decomposes at 180 - 200 °C to generate highly active free radicals. The highly active free radicals initiate the grafting of double bonds in the microsphere shell layer 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 polar interface with the matrix resin at this temperature, reducing the 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. The 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 cell structure and prevent gas leakage.

[0028] As a preferred technical solution:

[0029] A kind of thermally expandable microsphere as described above, the low-boiling hydrocarbons are a combination of isopentane and isooctane, and the mass ratio of isopentane to isooctane is 1 - 3:1. The combination of isopentane (boiling point 28 °C) and isooctane (boiling point 99 °C) avoids the rupture of microspheres caused by the rapid gasification of a single hydrocarbon and has a narrow expansion temperature range; at the same time, it matches the melting temperature window (160 - 200 °C) of the resin matrix (PE / PP).

[0030] A kind of thermally expandable microsphere as described above, the particle size of the thermally expandable microsphere before expansion is 25 - 30 μm, the particle size after expansion is 180 - 200 μm, and the effective foaming temperature range is 150 - 200 °C.

[0031] The core advantage of this three-layer structure thermally expandable microsphere lies in its high stability after expansion and unique in-situ interfacial chemical bonding ability. Its high-crosslinked dense shell of TVS formed at high temperature and the secondary crosslinking initiated by DCP endow the microsphere with excellent structural stability and gas leakage resistance after expansion at 160 - 200 °C, superior to the possible risk of collapse or rupture of the traditional structure. Secondly, the integrated PP-g-MAH and DCP on the outer layer can be activated during the processing of the composite material at 180 - 200 °C. Through anhydride reaction and free radical initiation, a gradient polar interface and crosslinking between the microsphere shell layer and the matrix resin are achieved, forming an interface with physical and chemical bonding. This design synchronizes foaming expansion and 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 the thermally expandable microspheres as described in any one of the above. First, component A and component B are mixed and emulsified by a high-speed shear emulsifier to obtain a suspension emulsion. Then, the suspension emulsion is transferred to a high-pressure reaction kettle, and under the condition of 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, and then the temperature is raised to 90 - 110 °C for polymerization for 2 - 4 hours. After the reaction is completed, it is naturally cooled and depressurized, and the product is successively subjected to suction filtration, washing and drying to obtain the thermally expandable microspheres;

[0033] Component A is obtained by ultrasonic treatment after mixing deionized water, sodium chloride, nano-silica, polyvinylpyrrolidone, absolute ethanol and sodium nitrite;

[0034] Deionized water: dispersion medium, providing a reaction site and adjusting the system polarity;

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

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

[0037] Polyvinylpyrrolidone (PVP): steric hindrance stabilizer, preventing droplet coalescence;

[0038] Absolute ethanol: co-solvent, adjusting the interfacial tension to promote monomer dispersion;

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

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

[0041] Low-boiling hydrocarbons: blowing agent, gasifying when heated to provide expansion power;

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

[0043] Ethylene glycol dimethacrylate (EGDMA): crosslinking agent, participating in the middle layer crosslinking to enhance the mechanical strength;

[0044] Acrylonitrile (AN): main monomer, constructing the middle layer copolymer skeleton;

[0045] Methyl methacrylate (MMA): main monomer, constructing the middle layer copolymer skeleton;

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

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

[0048] Tetravinylsilane (TVS): A high-temperature crosslinking agent (activated at ≥100 °C), constructing a dense and highly crosslinked outer layer;

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

[0050] 1. Inner layer and middle layer;

[0051] The low-boiling hydrocarbon blowing agent does not participate in chemical reactions. In the emulsification stage, component A (aqueous phase system) and component B (oil phase system) form oil-in-water micro-droplets. The inside of the droplets is the oil phase, and the monomer micro-droplets dissolved with the initiator and the blowing agent, during the stirring process, as the temperature rises and the reaction temperature reaches the decomposition temperature of the initiator (70 °C), the initiator decomposes to generate primary free radicals. As the molecular chain grows, the solubility of the generated polymer in the monomer droplets gradually decreases, and the polymer continuously precipitates from the monomer droplets to occur solution precipitation polymerization.

[0052] Monomer polymerization: AN (high polarity) and MMA (high rigidity) copolymerize under the initiation of AIBN. The cyano group of AN enhances the intermolecular force, and the methyl group of MMA provides steric hindrance, forming a transition layer with both rigidity and flexibility. PEGDA contains a double acrylate structure and preferentially undergoes free radical polymerization at 70 °C under the initiation of AIBN. Its long-chain PEG structure endows the molecular chain with flexibility and low crosslinking density (large crosslinking point spacing), forming a stretchable elastic network.

[0053] EGDMA co-crosslinking: The double methacrylate structure forms a medium crosslinking network during polymerization, enhancing the thermal stability.

[0054] 2. Middle layer spherical shell structure:

[0055] The main chain is a copolymer of AN and MMA, and at the same time, the EGDMA dimethacrylate crosslinking is interspersed between the main chains. The inner layer has a low-crosslinking PEGDA intercepting the inner layer.

[0056] As a preferred technical solution:

[0057] A preparation method of the above-mentioned thermal expansion microspheres, by mass parts, the dosage of each substance in component A is as follows: 300 parts of deionized water, 50 - 70 parts of sodium chloride, 15 - 25 parts of nano-silica, 2 - 5 parts of polyvinylpyrrolidone, 1 - 2 parts of absolute ethanol, and 0.5 - 1 part of sodium nitrite.

[0058] A preparation method of the above-mentioned thermal expansion microspheres, by mass parts, the dosage of each substance in component B is as follows: 25 - 40 parts of low-boiling 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] A preparation method of the above-mentioned thermal expansion microspheres, the rotational speed of the high-speed shear emulsifier is 14000 - 20000 r / min, and the mixing and emulsifying time is 5 - 20 min.

[0060] An electromagnetic shielding-thermal management foam material is prepared by a thermal expansion foaming process using the above-mentioned thermal expansion microspheres.

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

[0062] The absorption layer is a closed-cell composite foam containing amorphous metal magnetic nanoparticles, conductive fillers, and thermal expansion microspheres.

[0063] The reflection layer is a plain weave carbon fiber fabric with a surface density of 200 - 320 g / m 2 ; the plain weave carbon fiber fabric has excellent anisotropic effects, and at the same time, by controlling the surface density to 200 - 320 g / m during the weaving process 2 a high porosity can be achieved, and the smaller the surface density, the larger the porosity.

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

[0065] In the present invention, the plain weave carbon fiber fabric plays a bridging role between the absorption layer and the heat insulation layer, further improving the electromagnetic shielding performance and heat insulation performance, and can ensure 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, reflects the remaining electromagnetic waves, and generates eddy current loss, forming a "absorption-reflection-reabsorption" gradient impedance matching with the absorption layer. The combination of absorption and reflection promotes the electromagnetic shielding performance of the composite material, and the shielding effectiveness is greatly improved compared with the single-layer structure.

[0067] Thermal insulation performance: The inner low-density closed-cell foam inhibits heat conduction through the gas barrier inside the closed cells. The plain-weave carbon fiber fabric in the middle layer has a high porosity, reducing the solid conduction path. At the same time, its anisotropic thermal conductivity effectively blocks the longitudinal transfer of heat flow, making it difficult for heat to diffuse in the thickness direction, further inhibiting heat conduction and achieving efficient thermal insulation. That is, the inner closed-cell foam mainly blocks heat conduction, while the middle plain-weave carbon fiber fabric blocks the longitudinal transfer of heat flow. The combination of the two forms a multi-layer thermal barrier structure, significantly improving the overall thermal insulation performance.

[0068] Mechanical properties: The foam structures of the thermal insulation layer and the absorption layer have excellent impact resistance and buffering performance, which can absorb and disperse external forces to protect the internal structure. The carbon fiber fabric has high strength and rigidity, and can withstand large mechanical loads, enhancing the stability of the overall structure. The microsphere shell forms covalent bonds through heat-induced cross-linking between the chains with the matrix, greatly improving the interfacial strength between the microspheres and the resin matrix. In summary, the closed-cell foam provides lightweight buffering, and the carbon fiber fabric provides high-strength support. The combination of the two not only maintains lightweight but also significantly improves the overall structural strength.

[0069] An 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 amorphous metal magnetic nanoparticles and conductive fillers, the content of amorphous metal magnetic nanoparticles is 2-5 wt%, and the content of conductive filler is 1-3 wt%.

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

[0071] An electromagnetic shielding-thermal management foam material as described above, the plain-weave carbon fiber fabric is a plain-weave carbon fiber fabric with or without nickel plating.

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

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

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

[0075] Beneficial effects:

[0076] (1) A kind of thermally expandable microsphere of the present invention is a three-layer structure thermally expandable microsphere, which has high stability and unique in-situ interfacial chemical bonding ability after expansion.

[0077] (2) A preparation method of a kind of thermally expandable microsphere of the present invention, in which the plain woven carbon fiber fabric plays a bridging role between the absorption layer and the heat insulation layer, further improving the electromagnetic shielding performance and heat insulation performance, and can ensure that the overall material has excellent mechanical properties; the preparation method is simple.

[0078] (3) An electromagnetic shielding-thermal management foam material of the present invention has excellent electromagnetic shielding and heat insulation performance and a wide range of applications. Description of the drawings

[0079] Figure 1 It is a schematic structural diagram of a thermally expandable microsphere;

[0080] Figure 2 It is a scanning electron microscope image of the thermally expandable microsphere after expansion in Example 5;

[0081] Figure 3 It is a cross-sectional scanning electron microscope image of the thermally expandable microsphere before expansion in Example 3;

[0082] Among them, 1-microsphere core, 2-intermediate layer, 3-outer layer. Detailed implementation manners

[0083] The present invention will be further described below in conjunction with specific implementation manners. It should be understood that these examples are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it 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 also fall within the scope defined by the appended claims of this application.

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

[0085] Cell diameter: Use a scanning electron microscope (SEM) to observe and measure the cell diameter.

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

[0087] Thermal conductivity: The thermal conductivity of the rectangular sample of the foam composite material was measured using a TA Fox200 thermal conductivity meter. The sample had a length × width × thickness of 100 mm × 100 mm × 10 mm, and the temperature difference between the upper and lower heating plates was 30°C.

[0088] Compressive strength: The compressive strength test of the expanded foam composite material with electromagnetic shielding characteristics was carried out in accordance with the GB / T 8813-2020 standard.

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

[0090] Nanosilica, manufacturer: Zhongye New Materials, grade: ZY-8.

[0091] Polyvinylpyrrolidone, manufacturer: Merck, grade: K23-27.

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

[0093] Polyethylene glycol diacrylate, manufacturer: Merck, grade: M87272.

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

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

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

[0097] Example 1

[0098] A preparation method of thermally expandable microspheres is as follows:

[0099] (1) 300 parts of deionized water, 50 parts of sodium chloride, 15 parts of nanosilica, 2 parts of polyvinylpyrrolidone, 1 part of absolute ethanol, and 0.5 part 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) Mix 20 parts of isopentane, 10 parts of isooctane, 1 part of azobisisobutyronitrile, 0.5 part 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 part of diisopropylbenzene peroxide and stir evenly to obtain Component B;

[0101] (3) First, mix and emulsify Component A and Component B in a high-speed shear emulsifier at a rotation speed of 14,000 rpm for 15 minutes to obtain a suspension emulsion. Then transfer the suspension emulsion to a high-pressure reaction kettle. Under the condition of nitrogen protection, maintain the pressure at 1 MPa and polymerize at 70 °C for 15 hours. Then raise the temperature to 100 °C and polymerize for 2 hours. After the reaction is completed, cool naturally and release the pressure. Filter, wash and dry the product in sequence to obtain thermally expandable microspheres.

[0102] As Figure 1 shown, the finally prepared thermally expandable microspheres are successively composed of a microsphere core 1, an intermediate layer 2 and an outer layer 3 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 chain segments, methyl methacrylate chain segments, ethylene glycol dimethacrylate chain segments and polyethylene glycol diacrylate chain segments. The acrylonitrile chain segments and methyl methacrylate chain segments form the main chain skeleton of the copolymer, and the ethylene glycol dimethacrylate chain segments and polyethylene glycol diacrylate chain segments serve as bridging units and are connected to the main chain skeleton; the outer layer includes a crosslinked tetravinylsilane network, diisopropylbenzene peroxide and maleic anhydride grafted polyolefin, wherein the crosslinked tetravinylsilane network is a dense three-dimensional network formed by bridging tetravinylsilane through Si-O-Si; the average particle size of the thermally expandable microspheres before expansion is 25 μm, and the average particle size after expansion is 200 μm, and the effective foaming temperature range is 150-200 °C.

[0103] Example 2

[0104] A preparation method of thermally expandable microspheres, the specific steps are as follows:

[0105] (1) Mix 300 parts of deionized water, 60 parts of sodium chloride, 20 parts of nano-silica, 3 parts of polyvinylpyrrolidone, 1 part of absolute ethanol and 0.5 part of sodium nitrite, and perform ultrasonic treatment for 10 minutes to obtain Component A, and adjust the pH value to 3;

[0106] (2) Mix 20 parts of isopentane, 10 parts of isooctane, 1 part of azobisisobutyronitrile, 0.5 part 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 part of diisopropylbenzene peroxide and stir evenly to obtain Component B;

[0107] (3) First, the component A and component B are mixed and emulsified for 18 min by a high-speed shear emulsifier at a rotation speed of 15,000 r / min to obtain a suspension emulsion. Then, the suspension emulsion is transferred to a high-pressure reactor. Under the condition of nitrogen protection, the pressure is maintained at 0.5 MPa and polymerization is carried out at 65 °C for 16 h, and then the temperature is raised to 105 °C and polymerization is carried out for 2.5 h. After the reaction is completed, it is naturally cooled and depressurized, and the product is successively subjected to suction filtration, washing and drying to obtain thermally expandable microspheres.

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

[0109] Example 3

[0110] A preparation method of thermally expandable microspheres, the specific steps are as follows:

[0111] (1) 300 parts of deionized water, 65 parts of sodium chloride, 20 parts of nano-silica, 3 parts of polyvinylpyrrolidone, 1.5 parts of absolute ethanol and 0.5 part of sodium nitrite are mixed and ultrasonically treated for 10 min to obtain component A, and the pH value is adjusted to 2.5;

[0112] (2) 15 parts of isopentane, 10 parts of isooctane, 1 part of azobisisobutyronitrile, 0.5 part 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 part of diisopropylbenzene peroxide are mixed and stirred evenly to obtain component B;

[0113] (3) First, the component A and component B are mixed and emulsified for 20 min by a high-speed shear emulsifier at a rotation speed of 16,000 r / min to obtain a suspension emulsion. Then, the suspension emulsion is transferred to a high-pressure reactor. Under the condition of nitrogen protection, the pressure is maintained at 1 MPa and polymerization is carried out at 60 °C for 18 h, and then the temperature is raised to 110 °C and polymerization is carried out for 2 h. After the reaction is completed, it is naturally cooled and depressurized, and the product is successively subjected to suction filtration, washing and drying to obtain thermally expandable microspheres.

[0114] The finally obtained thermally expandable microspheres from the inside to the outside are successively a microsphere core, an intermediate layer, and an outer layer; 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 form 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 crosslinked tetravinylsilane network, dicumyl peroxide, and maleic anhydride-grafted polyolefin, where the crosslinked tetravinylsilane network is a dense three-dimensional network formed by the bridging of tetravinylsilane through Si-O-Si; as Figure 3 shown, the average particle size of the thermally 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 °C.

[0115] Example 4

[0116] A preparation method of thermally expandable microspheres, the specific steps are as follows:

[0117] (1) Mix 300 parts of deionized water, 70 parts of sodium chloride, 25 parts of nano-silica, 5 parts of polyvinylpyrrolidone, 1.5 parts of absolute ethanol, and 1 part of sodium nitrite, and then perform ultrasonic treatment for 10 minutes to obtain component A, and adjust the pH value to 3.5;

[0118] (2) Mix 30 parts of isopentane, 10 parts of isooctane, 1.2 parts of azobisisobutyronitrile, 0.8 part 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 part of dicumyl peroxide, and stir evenly to obtain component B;

[0119] (3) First, mix and emulsify component A and component B in a high-speed shear emulsifier at a rotation speed of 18,000 rpm for 10 minutes to obtain a suspension emulsion. Then transfer the suspension emulsion to a high-pressure reaction kettle. Under the condition of nitrogen protection, maintain the pressure at 1.2 MPa and polymerize at 50 °C for 20 hours, and then raise the temperature to 95 °C and polymerize for 3 hours. After the reaction is completed, cool naturally and relieve the pressure. The product is successively subjected to suction filtration, washing, and drying to obtain thermally expandable microspheres.

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

[0121] Example 5

[0122] A preparation method of thermally expandable microspheres, the specific steps are as follows:

[0123] (1) Mix 300 parts of deionized water, 65 parts of sodium chloride, 25 parts of nano-silica, 5 parts of polyvinylpyrrolidone, 2 parts of absolute ethanol, and 0.5 part of sodium nitrite, and then perform ultrasonic treatment for 10 minutes to obtain component A, and adjust the pH value to 3.5;

[0124] (2) Mix 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 and stir evenly to obtain component B;

[0125] (3) First, mix and emulsify component A and component B in a high-speed shear emulsifier at a rotation speed of 20,000 rpm for 5 minutes to obtain a suspension emulsion. Then transfer the suspension emulsion to a high-pressure reaction kettle. Under the condition of nitrogen protection, maintain the pressure at 1.5 MPa and polymerize at 55 °C for 19 hours, and then raise the temperature to 90 °C and polymerize for 4 hours. After the reaction is completed, naturally cool and relieve the pressure, and successively perform suction filtration, washing, and drying on the product to obtain thermally expandable microspheres.

[0126] The finally obtained thermally expandable microspheres consist 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 form 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 crosslinked tetravinylsilane network, dicumyl peroxide, and maleic anhydride grafted polyolefin, where the crosslinked tetravinylsilane network is a dense three-dimensional network formed by bridging tetravinylsilane through Si-O-Si; the average particle size of the thermally expandable microspheres before expansion is 30μm, and the average particle size after expansion is 180μm (as Figure 2 shown), and the effective foaming temperature range is 170~200℃.

[0127] Example 6

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

[0129] (1) Preparation of the heat insulation layer foam pre-impregnated film;

[0130] Mix polyethylene resin and thermally expandable microspheres, and hot press at 140℃ for 20 min to make the heat insulation layer foam pre-impregnated film;

[0131] Among them, the content of thermally expandable microspheres in the heat insulation layer foam pre-impregnated film is 10wt%;

[0132] (2) Preparation of the reflective layer material;

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

[0134] (3) Preparation of the absorption layer foam pre-impregnated film;

[0135] Add thermally expandable microspheres, carbon nanotubes, and iron-silicon-boron nanoparticles with a D50 particle size of 30μm to polyethylene resin respectively, and hot press at 140℃ for 20 min to make the absorption layer foam pre-impregnated film;

[0136] Among them, the content of thermally expandable microspheres in the absorption layer foam pre-impregnated film is 3wt%, the content of iron-silicon-boron nanoparticles is 5wt%, and the content of carbon nanotubes is 3%;

[0137] (4) Place the absorbent layer foam pre-impregnated film, plain woven carbon fiber fabric, and heat insulation layer foam pre-impregnated film into the mold in sequence, heat and expand for foaming at 180 °C for 60 min to obtain the electromagnetic shielding-thermal management foam material.

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

[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 absorbent layer foam pre-impregnated film and the heat insulation layer foam pre-impregnated film are placed into the mold in sequence for thermal expansion and foaming to obtain the electromagnetic shielding foam material.

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

[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 highly depends on the loss ability of the absorbent layer. Without the reflective layer, the structure cannot form multiple internal reflection paths, the reflection loss mechanism fails, and the overall shielding efficiency drops significantly.

[0143] Comparative Example 2

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

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

[0146] 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 heat insulation performance decreases. This is because although aluminum foil has high conductivity, due to its lack of structural adaptability, it cannot work synergistically with the foam layer to form an effective multi-layer shielding system. Part of the electromagnetic wave is reflected and interfered at the aluminum foil interface, resulting in incomplete reflection and forming leakage points, thus reducing the overall shielding performance. In addition, aluminum foil is an isotropic material with much higher thermal conductivity than carbon fiber fabric, making the heat insulation performance of the electromagnetic shielding foam material in Comparative Example 2 poor.

[0147] Example 7

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

[0149] (1) Preparation of the heat insulation layer foam pre-impregnated film;

[0150] Mix polyethylene resin and thermally expandable microspheres, and hot press at 140 °C for 20 min to make the heat insulation layer foam pre-impregnated film;

[0151] Among them, the content of thermally expandable microspheres in the heat insulation layer foam pre-impregnated film is 11 wt%;

[0152] (2) Preparation of the reflective layer material;

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

[0154] (3) Preparation of the absorption layer foam pre-impregnated film;

[0155] Add thermally expandable microspheres, iron-silicon-boron nanoparticles, and carbon nanotubes with a D50 particle size of 20 nm into polyethylene resin respectively, and hot press at 140 °C for 20 min to make the absorption layer foam pre-impregnated film;

[0156] Among them, the content of thermally expandable microspheres in the absorption layer foam pre-impregnated film is 2 wt%, the content of iron-silicon-boron nanoparticles is 2 wt%, and the content of carbon nanotubes is 1 wt%;

[0157] (4) Put the absorption layer foam pre-impregnated film, plain weave carbon fiber fabric, and heat insulation layer foam pre-impregnated film into the mold in sequence, and heat and expand and foam at 180 °C for 60 min to obtain the electromagnetic shielding-thermal management foam material.

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

[0159] Example 8

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

[0161] (1) Preparation of the heat insulation layer foam pre-impregnated film;

[0162] Mix polyethylene resin and thermally expandable microspheres, and hot press at 140 °C for 20 min to make the heat insulation layer foam pre-impregnated film;

[0163] Among them, the content of thermally expandable microspheres in the heat insulation layer foam pre-impregnated film is 12 wt%;

[0164] (2) Preparation of the reflection layer material;

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

[0166] (3) Preparation of the absorption layer foam pre-impregnated film;

[0167] Add thermally expandable microspheres, carbon nanotubes, and iron-silicon-boron nanoparticles with a D50 particle size of 30 μm into polypropylene resin respectively, and hot press at 140 °C for 20 min to make the absorption layer foam pre-impregnated film;

[0168] Among them, the content of thermally expandable microspheres in the absorption layer foam pre-impregnated film is 5 wt%, the content of iron-silicon-boron nanoparticles is 2 wt%, and the content of carbon nanotubes is 3%;

[0169] (4) Put the absorption layer foam pre-impregnated film, the plain weave carbon fiber fabric, and the heat insulation layer foam pre-impregnated film into the mold in sequence, and heat and expand and foam at 180 °C for 60 min to obtain the electromagnetic shielding-thermal management foam material.

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

[0171] Example 9

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

[0173] (1) Preparation of the heat insulation layer foam pre-impregnated film material;

[0174] Mix polyethylene resin and thermally expandable microspheres, and hot press at 140 °C for 20 min to make the heat insulation layer foam pre-impregnated film material;

[0175] Among them, the content of thermally expandable microspheres in the heat insulation layer foam pre-impregnated film material is 13 wt%;

[0176] (2) Preparation of the reflection layer material;

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

[0178] (3) Preparation of the absorption layer foam pre-impregnated film material;

[0179] Add thermally expandable microspheres, iron-silicon-boron nanoparticles, and carbon nanotubes with a D50 particle size of 20 nm to polyethylene resin respectively, and hot press at 140 °C for 20 min to make the absorption layer foam pre-impregnated film material;

[0180] Among them, the content of thermally expandable microspheres in the absorption layer foam pre-impregnated film material is 5 wt%, the content of iron-silicon-boron nanoparticles is 3 wt%, and the content of carbon nanotubes is 2 wt%;

[0181] (4) Put the absorption layer foam pre-impregnated film material, the plain weave carbon fiber fabric, and the heat insulation layer foam pre-impregnated film material into a mold in sequence, and heat and expand and foam at 180 °C for 60 min to obtain the electromagnetic shielding-thermal management foam material.

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

[0183] Example 10

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

[0185] (1) Preparation of the heat insulation layer foam pre-impregnated film material;

[0186] Mix the polyethylene resin and the thermally expandable microspheres, and hot press at 140 °C for 20 min to make the heat insulation layer foam pre-impregnated film material;

[0187] Among them, the content of the thermally expandable microspheres in the heat insulation layer foam pre-impregnated film material is 15 wt%;

[0188] (2) Preparation of the reflection layer material;

[0189] Plain weave carbon fiber fabric with a surface density of 320 g / m 2 , the thickness of the plain weave carbon fiber fabric is 0.4 mm; the thermal conductivity in the thickness direction of the plain weave carbon fiber fabric is 2.5 W / m·K;

[0190] (3) Preparation of the absorption layer foam pre-impregnated film material;

[0191] Add thermally expandable microspheres, carbon nanotubes, and iron-silicon-boron nanoparticles with a D50 particle size of 30 μm into the polypropylene resin respectively, and hot press at 140 °C for 20 min to make the absorption layer foam pre-impregnated film material;

[0192] Among them, the content of the thermally expandable microspheres in the absorption layer foam pre-impregnated film material is 5 wt%, the content of the iron-silicon-boron nanoparticles is 3 wt%, and the content of the carbon nanotubes is 2%;

[0193] (4) Put the absorption layer foam pre-impregnated film material, the plain weave carbon fiber fabric and the heat insulation layer foam pre-impregnated film material into the mold in sequence, and heat and expand and foam at 180 °C for 60 min to obtain the electromagnetic shielding-thermal management foam material.

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

Claims

1. A heat-expandable microsphere, characterized in that: From inside to outside, they are the microsphere core, middle layer and outer layer; The core of the microspheres is low-boiling-point hydrocarbons; 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 the 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 less than 100°C.

2. The heat-expandable microsphere 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 heat-expandable microsphere 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. A method for preparing heat-expandable microspheres according to any one of claims 1 to 3, characterized in that: First, component A and component B are mixed and emulsified in a high-speed shear emulsifier to obtain a suspension emulsion, and then the suspension emulsion is transferred to a high-pressure reactor, and 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, and then the temperature is 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, and the product is filtered, washed and dried in turn to obtain thermal expansion microspheres; Component A is obtained by mixing deionized water, sodium chloride, nano-silicon dioxide, polyvinyl pyrrolidone, anhydrous ethanol and sodium nitrite and then ultrasonically treating the mixture; Component B is obtained by mixing and stirring low boiling point hydrocarbons, azobisisobutyronitrile, ethylene glycol dimethacrylate, acrylonitrile, methyl methacrylate, maleic anhydride grafted polyolefin, polyethylene glycol diacrylate, tetravinylsilane and dicumyl peroxide.

5. The method for preparing heat-expandable microspheres according to claim 4, characterized in that: Calculated by weight, 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 method for preparing heat-expandable microspheres 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 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 diisopropylbenzene peroxide.

7. The method for preparing heat-expandable microspheres according to claim 4, characterized in that: The rotation speed of the high-speed shear emulsifier is 14000~20000 rpm, and the mixing and emulsification time is 5~20min.

8. An electromagnetic shielding-thermal management foam material, characterized in that: The heat-expandable microspheres are prepared by a heat-expandable foaming process according to any one of claims 1 to 3; 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 thermal expansion microspheres; The reflective layer has a surface density of 200~320g / m 2 of 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 .

9. The electromagnetic shielding-thermal management foam material according to claim 8, 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%.

10. The electromagnetic shielding-thermal management foam material according to claim 8, 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.

11. The electromagnetic shielding-thermal management foam material according to claim 8, characterized in that: Plain woven carbon fiber fabric is a plain woven nickel plated or non-nickel plated carbon fiber fabric.

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

13. The electromagnetic shielding-thermal management foam material according to any one of claims 8 to 12, characterized in that: 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; 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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