Thermoplastic elastomer-based foamed composite material having excellent electrically conductive and electromagnetic shielding properties and method for preparing the same

Abstract

The present application belongs to the technical field of thermoplastic elastomer-based electromagnetic shielding foamed material, and provides a thermoplastic elastomer-based foamed composite material with excellent electric conductivity and electromagnetic shielding performance and a preparation method thereof.The foamed composite material is prepared by extrusion foaming of the following components after sufficient mixing by an extruder: 100 parts by weight of thermoplastic elastomer resin, 0.8-8 parts by weight of electrically conductive functional filler, 0.1-10 parts by weight of coupling agent, 0.1-10 parts by weight of photosensitive initiator, 0.1-10 parts by weight of cell stabilizer and 0.2-8 parts by weight of composite foaming agent.The thermoplastic elastomer-based foamed composite material has excellent electric conductivity and electromagnetic shielding performance, and also has good mechanical properties, and the production process is highly continuous, stable, safe and environmentally friendly, and is suitable for industrialized scale production.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of thermoplastic elastomer-based electromagnetic shielding foamed materials, and relates to a thermoplastic elastomer-based foamed composite material with excellent electric conduction and electromagnetic shielding performance and a preparation method thereof. BACKGROUND

[0002] As a communication carrier, electromagnetic waves bring many conveniences to the development of electronic technology and industry, but also inevitably bring many safety hazards, such as affecting the normal work of various military or civilian electronic equipment, and more seriously, causing harm to people's health. Preparing electromagnetic shielding materials with excellent performance is the main way to effectively prevent electromagnetic wave radiation propagation and diffusion. At present, electromagnetic shielding materials mainly include metal materials, ferromagnetic materials and conductive polymer composites (CPC), etc. Among them, CPC is focused and widely applied in the preparation of electromagnetic shielding materials due to its light weight, good flexibility, good corrosion resistance, low processing cost and other advantages, and thermoplastic elastomer is a preferred base material for preparing CPC.

[0003] Thermoplastic elastomer (TPE)-based CPC foam material is a novel functional material prepared by foaming a thermoplastic elastomer (TPE) matrix with conductive fillers. Its low density and lightweight properties make it an effective way to reduce structural weight and energy consumption in fields such as aerospace and automotive manufacturing. It not only inherits the flexibility of TPE and can recover its original shape after significant deformation, making it suitable for a variety of soft and elastic components such as cushioning and seals in electronic devices, but also the added conductive fillers form a conductive network within the matrix that reflects, absorbs, and dissipates electromagnetic waves, effectively blocking their propagation and providing reliable electromagnetic shielding for electronic devices, preventing signal interference and information leakage. It has broad application prospects in fields such as 5G communications and consumer electronics. Due to the properties of TPE, it can be formed using a variety of processing methods, such as extrusion, injection, and blow molding, offering high processing efficiency and short cycle times, making it easy to implement on a large scale. By adjusting the formulation and process parameters, the expansion ratio, cell structure, and performance can be flexibly controlled to meet the needs of different application scenarios. However, during the foaming process, the escape of gas and the cooling shrinkage of the polymer melt can easily lead to shrinkage of the material, affecting the dimensional accuracy and appearance quality of the product. In particular, for large or complex-shaped products, the shrinkage problem is more prominent and needs to be controlled by appropriate measures, such as optimizing the formula, adjusting the foaming process parameters, etc. CN118725282A discloses a thermoplastic polyether ester elastomer with strong microwave absorption and electromagnetic shielding in a wide band and a preparation method thereof. The elastomer involves a combination of one-dimensional conductive material liquid metal, high dielectric constant MXenes and its derivatives, and rare earth magnetic materials and their oxides. Although the electromagnetic shielding effect can be enhanced, the cost is relatively high. A multi-layer spatial structure shielding layer is used to form multiple heterogeneous interfaces, so that the electromagnetic interference field forms eddy currents in the shielding body and generates reflections at the interface between the shielding body and the protected space, thereby greatly weakening the field strength of the interference field in the protected space and curbing the influence of high-frequency electromagnetic fields to achieve shielding. effect, but it adopts autoclave foaming, and the preparation process is relatively complicated, which is not suitable for industrial continuous production; CN115260735B discloses a wave-absorbing thermoplastic elastomer foam material and a preparation method thereof, which is made of thermoplastic resin, wave-absorbing powder, and additives. The wave-absorbing powder is used as a reinforcing phase and is added to the matrix under the action of a foaming additive, a pore regulator, and a plasticizer. After foaming and molding, the bending strength and compression strength of the foam are greatly improved, which is conducive to application in aviation, aerospace, trains, ships and other fields. However, the foaming additive used in the invention is mainly a chemical foaming agent, which is not conducive to cost reduction and environmental protection.

[0004] Current research on thermoplastic elastomer-based foamed composites reveals that their preparation methods primarily rely on chemical foaming or physical foaming (primarily physical intermittent foaming). Chemical foaming agents inevitably leave residues in the finished product during the foam preparation process, impacting product performance and safety. Intermittent foaming, on the other hand, is difficult to achieve continuous production, making it difficult to ensure consistent and stable product quality, impacting subsequent processing and use. This not only reduces production efficiency but also increases production costs, limiting its application in large-scale industrial production. While physical foaming agents are often supercritical carbon dioxide or nitrogen, while environmentally friendly, the resulting foams can easily shrink. Therefore, the choice of foaming agent in the preparation of polymer foam materials directly influences the final foam's pore structure, leading to performance differences.

[0005] Based on this, the present invention adopts a composite foaming agent to continuously extrusion foam to prepare a thermoplastic elastomer-based foamed composite material with good mechanical properties, excellent electromagnetic shielding properties and conductive properties, which is of great significance for meeting the demand for electromagnetic shielding materials in modern electronic equipment, aerospace and other fields. Summary of the Invention

[0006] One objective of the present invention is to provide a novel thermoplastic elastomer-based foamed composite material exhibiting good mechanical properties, excellent electromagnetic shielding performance, electrical conductivity, and safety. Specifically, the foamed material is prepared by melt blending and continuous extrusion using a thermoplastic elastomer resin, a conductive functional filler, a coupling agent, a photoinitiator, a cell stabilizer, and a foaming agent as primary raw materials. This foamed material can be used in electronic equipment, communications equipment, transportation, aerospace, and medical devices.

[0007] Another object of the present invention is to provide a method for preparing the thermoplastic elastomer-based foamed composite material, wherein the production process is highly continuous and stable, the production process is safe and has no environmental pollution, and is suitable for industrial-scale production.

[0008] To achieve the above-mentioned purpose, the present invention provides a foamed composite material, which is mainly a thermoplastic elastomer-based foamed composite material prepared by continuous extrusion foaming of a composite foaming agent. Specifically, the foamed composite material is prepared by extruding and foaming the following components after being fully mixed in an extruder:

[0009] 100 parts by weight of thermoplastic elastomer resin;

[0010] 0.8-8 parts by weight of conductive functional filler;

[0011] 0.1-10 parts by weight of coupling agent;

[0012] 0.1-10 parts by weight of photoinitiator;

[0013] Cell stabilizer 0.1-10 parts by weight;

[0014] Composite foaming agent 0.2-8 parts by weight;

[0015] In the thermoplastic elastomer-based foamed composite provided by the application, the thermoplastic elastomer resin is one or more of ethylene-vinyl acetate copolymer (EVA), polyolefin elastomer (POE), nylon elastomer (TPAE), polyurethane elastomer (TPU), thermoplastic vulcanized rubber (TPV), thermoplastic polyester elastomer (TPEE), and styrene block copolymer-based thermoplastic elastomer, the conductive functional filler is one or more of carbon nanotube (CNT), carbon black, graphene, and carbon fiber, or a mixture formed by further mixing one or more of nano-magnetic iron oxide, nano-silver particles, and copper powder, and preferably a plurality of conductive fillers are compounded.

[0016] According to a specific embodiment of the application, in the thermoplastic elastomer-based foamed composite provided by the application, the composite foaming agent preferably consists of 0-3 parts by weight of an air foaming agent, 0.2-2 parts by weight of a supercritical carbon dioxide foaming agent, and 0-3 parts by weight of a supercritical nitrogen foaming agent, and more preferably, the air foaming agent is not 0; the total amount of the composite foaming agent is controlled to be 0.2-8 parts by weight, and preferably 0.5-3 parts by weight. The application adopts a double-stage screw extruder, especially a double-screw extruder connected in series with a single-screw extruder, to continuously extrude and foam, the mixing extrusion equipment used has strong shearing action so that the material can be fully mixed and dispersed, the extrusion and foaming temperature is 80-120℃, the extrusion and foaming pressure is 5-20 MPa, and the extrusion and foaming time is 8-20 min, and the foaming temperature, pressure, and time are important factors affecting gas diffusion, and further affect the final cell morphology.

[0017] In the application, the parts by weight are based on 100 parts by weight of the total amount of the thermoplastic elastomer resin. Unless otherwise specified, the proportions and contents in the application are weight proportions and contents.

[0018] In the thermoplastic elastomer-based foamed composite provided by the application, the conductive functional filler needs to be pretreated and modified with a coupling agent before being put into the extruder, and the main role of these conductive functional fillers is to build a perfect conductive network in the matrix material, thereby improving the conductive performance and electromagnetic shielding performance, in addition, these conductive functional fillers can also play the role of heterogeneous nucleation to improve the cell density.

[0019] In the thermoplastic elastomer-based foamed composite material provided herein, the coupling agent may be one or more of KH550, KH560, KH570, KH171, A-172, and A-174. The coupling agent primarily functions by dry-blending with the conductive functional filler to improve its dispersibility and interfacial compatibility in the matrix.

[0020] In the thermoplastic elastomer-based foamed composite material provided by the present invention, the photosensitive initiator is mainly used for cross-linking and curing after extrusion foaming. By rapidly absorbing electron radiation energy and converting it into chemical energy, it produces active centers that initiate cross-linking reactions, such as free radicals or cations, thereby greatly accelerating the cross-linking and curing rate of the thermoplastic elastomer, shortening the curing time, and improving production efficiency.

[0021] In the thermoplastic elastomer-based foamed composite material provided herein, the cell stabilizer is primarily used to increase the strength of the cell walls, prevent cell wall rupture, and stabilize the cells. The cell stabilizer employed may be one or a mixture of glycerol fatty acid ester cell stabilizers, propylene glycol fatty acid ester cell stabilizers, and isooctyl alcohol fatty acid ester cell stabilizers. Preferred cell stabilizers are glycerol fatty acid ester cell stabilizers, such as glyceryl monostearate (GMS). The preferred amount of the cell stabilizer is 0.1 to 2 parts by weight.

[0022] The thermoplastic elastomer-based foamed composite material provided by the present invention is prepared by continuously extruding and foaming the above raw materials through a double-stage screw extruder.

[0023] In another aspect, the present invention provides a method for preparing the thermoplastic elastomer-based foamed composite material, the method comprising the following steps:

[0024] S1. vacuum drying the thermoplastic elastomer resin and the conductive functional filler;

[0025] S2. Stirring the conductive functional filler and the coupling agent in a high-speed stirrer for dry mixing to obtain a pretreated conductive functional filler;

[0026] S3, then uniformly mixing the thermoplastic elastomer resin, the pretreated conductive functional filler, the photoinitiator, and the cell stabilizer to obtain a mixed material;

[0027] S4, adding the above-mentioned mixed material into a twin-screw extruder, injecting the composite foaming agent into the extruder at the same time, and after sufficient mixing, extruding and foaming molding;

[0028] S5. Finally, the foamed sample is quickly subjected to electron radiation treatment to promote cross-linking and curing to obtain the foamed composite material.

[0029] In the process of preparing the foamed composite material of the present invention, the continuous extrusion foaming extruder used is a twin-stage screw extruder, which is a twin-screw extruder connected in series with a single-screw extruder or a single-screw extruder connected in series with a single-screw extruder, preferably a twin-screw extruder connected in series with a single-screw extruder. According to a preferred embodiment of the present invention, the processing temperature of the present invention is controlled to be 80-120°C, the extrusion foaming pressure is 5-20 MPa, and the extrusion foaming time is 8-20 minutes.

[0030] The die used in the extruder is an annular or sheet-shaped die that is electrically heated or oil-bathed for temperature control. Furthermore, a foaming stabilization device can be installed at the rear of the die to control melt uniformity. In the present invention, all raw materials are commercially available, and all mechanical equipment used is state-of-the-art. Steps not specifically described in the process described herein can be performed according to conventional procedures in the art.

[0031] The present invention mainly combines the components in a certain proportion to prepare a thermoplastic elastomer-based foamed composite material with excellent electrical conductivity and electromagnetic shielding properties, wherein the composite foaming agent used is a physical foaming agent, which has no effect on the performance and safety of the product. Utilizing the formula of the present invention, a thermoplastic elastomer-based foamed composite material with good mechanical properties, excellent electrical conductivity and electromagnetic shielding properties can be prepared, and the production process is highly continuous and stable, safe and has no environmental pollution, and is suitable for industrial-scale production. The thermoplastic elastomer-based foamed composite material product of the present invention has excellent comprehensive evaluation of foaming ratio, pore size distribution and mechanical properties, and the foaming ratio can be determined according to the application requirements of different fields, generally less than 10 times. The thermoplastic elastomer-based foamed composite material of the present invention can be used to process various types of sheets, plates, pipes and other products in order to be applied to aerospace, electronic equipment manufacturing, military and other fields.

[0032] In summary, the present invention provides a method for preparing a thermoplastic elastomer-based foamed composite material having good mechanical properties, excellent electrical conductivity and electromagnetic shielding properties. Compared with the prior art, the present invention has the following beneficial effects and advantages:

[0033] 1. The present invention uses the method to prepare a thermoplastic elastomer foam material with excellent electrical conductivity, electromagnetic shielding and other properties on the basis of adding less conductive functional filler. Specifically, it can achieve an electromagnetic shielding efficiency of ≥65dB with ≤10 parts of conductive functional filler, breaking through the limitation of the amount of conductive functional filler used in traditional CPC foam materials.

[0034] 2. Pre-treating the conductive filler with a coupling agent improves the uneven dispersion of the conductive filler in thermoplastic elastomer-based foam materials. The organic functional groups on the coupling agent can chemically react or physically adsorb with the surface of the conductive filler, forming a coating that reduces the filler's surface energy and makes it easier to disperse in the matrix. This improves filler utilization and the uniformity of the composite material's performance, thereby enhancing conductivity. For example, the vinyl group in the vinyl coupling agent molecule can copolymerize with the double bonds in the resin matrix, while the functional group at the other end can bind to the surface of the conductive filler, forming a chemically bonded bridge between the conductive filler and the matrix. This significantly enhances the interfacial bonding between the two, helps overcome stress concentration and interfacial debonding caused by poor interfacial compatibility between the filler and the matrix, and improves the mechanical properties of the composite material, such as flexural strength and impact strength.

[0035] 3. The physical foaming agent used has no effect on the product's performance and safety, and improves the shrinkage problem of thermoplastic elastomer-based foam materials. Supercritical carbon dioxide has a high solubility and diffusion rate in polymers, which can increase the number of cells and reduce cell size, thereby improving the cell density and uniformity of the foamed material, making the material more elastic and less dense. Supercritical nitrogen is chemically stable, non-toxic, safe to use, and has strong solubility and diffusion ability in polymers. It is easy to control, forming a more uniform cell structure and high cell density during foaming, giving the foamed material better mechanical properties and dimensional stability. Air, as a foaming agent, is low-cost and easily available, relatively simple to operate during the foaming process, and can play a role in resisting shrinkage of thermoplastic elastomer foam.

[0036] 4. The thermoplastic elastomer-based foamed composite material prepared by continuous extrusion foaming using a two-stage screw extruder is cross-linked and cured using electron radiation. The composite material has good mechanical properties, excellent electrical conductivity and electromagnetic shielding properties. The production process is highly continuous and stable, safe and environmentally pollution-free, suitable for industrial-scale production. The product also has excellent comprehensive evaluation of foaming ratio, pore size distribution, electromagnetic shielding properties and mechanical properties. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0038] All test instruments and reagents are commercially available and can be purchased through commercial channels.

[0039] The preparation process of the thermoplastic elastomer-based foamed composite materials of Comparative Examples 1-10 and Examples 11-12 is as follows:

[0040] S1. Drying the thermoplastic elastomer resin and the conductive functional filler in vacuum at 60° C. for 8 h;

[0041] S2. Dry-mixing the conductive functional filler and the coupling agent in a high-speed mixer, i.e., pre-treating the conductive functional filler;

[0042] S3, then uniformly mixing the thermoplastic elastomer resin, the pretreated conductive functional filler, the photoinitiator, and the cell stabilizer to obtain a mixed material;

[0043] S4. The mixed material is then added to a twin-screw extruder, and the composite foaming agent is simultaneously injected into the extruder (air, supercritical carbon dioxide, and supercritical nitrogen are pumped into the air inlet of the extruder at a rate of 0.6 kg / h by a gas pressure pump, and the gas mass is converted by volume). Supercritical carbon dioxide or supercritical nitrogen is injected in the compression section, and air is injected in the homogenization section. In a second-stage twin-screw tandem single-screw extruder, the extruder conditions are set as follows: extrusion temperature of 100° C., extrusion foaming pressure of 15 MPa, and extrusion foaming time of 10 min. After sufficient mixing, extrusion foaming molding is performed;

[0044] S5. Finally, the foamed sample is quickly subjected to electron radiation treatment, with an electron beam irradiation dose of 60 kGy and an irradiation time of 10 s at room temperature to promote cross-linking and curing to obtain the thermoplastic elastomer-based foamed composite material.

[0045] Effect test

[0046] The foam density was measured using a density balance to calculate the expansion ratio; the compression rebound rate of the foam was measured using a universal testing machine; and the electromagnetic shielding performance of the foam was measured using an electromagnetic shielding vector meter. Table 1 shows a comparison of the components and test results of the thermoplastic elastomer-based foam composite materials prepared in the comparative examples and examples.

[0047] Table 1 Components and test results of Comparative Examples 1-10 and Examples 11-12

[0048]

[0049] Note: The composite foaming agent in the table is a mixture of supercritical carbon dioxide and air at a weight ratio of 1:2, and the composite conductive functional filler is a mixture of CNTs and graphene at a weight ratio of 1:1.

[0050] Compatibility has a significant impact on the thermoplastic elastomer-based foaming. It can be found from Comparative Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 4 that, since POE and EVA both belong to polyolefin polymers, the molecular structure has certain similarity, so that POE can be better compatible with EVA matrix to form a relatively uniform blending system, which can effectively improve the foaming performance and compression resilience. In contrast, the molecular structure of TPAE and TPU is quite different from that of EVA, and the compatibility with EVA is relatively poor, which may cause phase separation in the blending system and affect the overall performance of the material.

[0051] The foaming agent component also has a significant impact on the performance of the material. It can be found from Comparative Example 2 and Comparative Example 5 that, single-component foaming agent (supercritical carbon dioxide) can obtain high expansion ratio but uneven cell, poor compression resilience, fast gas release, and easy to cause cell collapse; composite foaming agent (supercritical carbon dioxide + air) can obtain moderate expansion ratio, uniform and small cell, excellent resilience, and air delay diffusion, which makes the process more stable.

[0052] CNTs, as a conductive functional filler with excellent electrical conductivity and mechanical properties, has a significant impact on the performance of EVA thermoplastic elastomer-based foam material. The addition of appropriate amount of CNTs can act as a heterogeneous nucleation point, which helps to improve the foaming ratio and promote the formation of cell structure, making the cell structure more uniform; the high elastic modulus of CNTs can improve the resilience of the foam material, making it recover faster after compression, thereby improving the compression resilience; the interaction between CNTs and the polymer matrix can enhance the mechanical properties of the material. In addition, CNTs can reflect and absorb electromagnetic waves, thereby improving the electromagnetic shielding effectiveness of the foam material. It can be seen from Comparative Example 5, Comparative Example 6, and Comparative Example 7 that, the conductive filler modified by coupling agent can improve the performance more significantly.

[0053] It can be seen from Comparative Example 8 and Comparative Example 9 that, when CNTs are mixed with other conductive fillers, the electromagnetic shielding effect can be further enhanced, in which the one-dimensional nanostructure of CNTs and the two-dimensional sheet structure of graphene form a more perfect conductive network, improving the electrical conductivity and electromagnetic shielding effect of the material; in addition, according to Comparative Example 9 and Comparative Example 10, increasing the amount of conductive functional filler can also have a significant impact on improving the performance of thermoplastic elastomer-based foaming composite material.

[0054] The addition of a photoinitiator to electron radiation crosslinking significantly improves tensile strength, compression rebound, and cell uniformity, although it slightly reduces the expansion ratio. Furthermore, the addition of a cell stabilizer, GMS, further enhances cell stability. Comparing the comparative examples and examples in Table 1, Example 12 is the optimal formulation, offering the best overall performance. During the electron radiation treatment after extrusion foaming, the photoinitiator in this invention rapidly absorbs the electron radiation energy and converts it into chemical energy, generating active centers that initiate the crosslinking reaction, thereby significantly accelerating the crosslinking and curing rate of the thermoplastic elastomer. This rapid crosslinking and curing process stabilizes the material's cell structure, preventing cell collapse and excessive expansion, and ensuring the material's dimensional accuracy and appearance quality. The vinyl acetate (VA) units in the EVA molecular chain contain highly reactive tertiary hydrogen atoms with low atomic bond energies. Under the action of the photoinitiator and electron radiation, they readily dehydrogenate to form carbon-centered free radicals, significantly accelerating the crosslinking reaction. Furthermore, the polar groups in VA enhance the initiator's compatibility with the matrix and its energy absorption efficiency. In contrast, pure polyolefins (such as POE) contain only secondary and primary hydrogen atoms with higher bond energies, resulting in slower crosslinking kinetics. Furthermore, electron radiation treatment not only promotes bonding between the matrix and the conductive functional filler but also enhances the matrix's crosslink density, improving the material's mechanical properties and thermal stability, thereby providing a strong foundation for achieving excellent electrical conductivity and electromagnetic shielding performance.

[0055] In addition, it should be noted that in the method of the present invention, different photosensitive initiators are suitable for different thermoplastic elastomer matrices, specifically:

[0056] ① For EVA, acylphosphine oxides or benzophenone photoinitiators are usually selected. Benzophenones are excited after absorbing ultraviolet light, transitioning from the ground state to the excited state. The excited benzophenone molecules generate free radicals through energy transfer or electron-donating groups capturing hydrogen atoms. The free radicals trigger cross-linking reactions at the double bonds in the EVA molecular chain or the reactive sites in the vinyl acetate unit, forming a three-dimensional network structure between the EVA molecular chains, improving the material's cross-linking density and thermal stability.

[0057] ② For POE, acylphosphine oxide photoinitiators are generally used. When acylphosphine oxides are exposed to ultraviolet light, double bonds or specific groups within the molecule absorb light energy and become excited, undergoing homolytic cleavage or generating free radicals through other pathways. These free radicals can initiate crosslinking and curing of the double bonds within the POE molecular chain. The presence of a small number of double bonds in POE improves material performance after crosslinking.

[0058] ③ For nylon elastomer (TPAE), choose iodonium salt photoinitiator. TPAE contains amide groups with lone pairs of electrons, which are suitable for cationic initiation. Ionium salts generate super acid (H +), which initiates ring-opening polymerization of the amide group, protonates the generated HX, and triggers ring-opening crosslinking.

[0059] ④For polyurethane elastomer (TPU), aromatic diazonium salt photosensitive initiator is selected. TPU contains urethane groups. After photolysis of the aromatic diazonium salt, nitrogen is released and a carbocation is generated, which can initiate cationic polymerization of the polyester segment and further initiate crosslinking and curing.

[0060] ⑤For thermoplastic vulcanized rubber (TPV), nitrobenzoxadiazole photosensitive initiator is mostly used. The rubber phase in TPV contains allyl hydrogen with low bond energy. Under the action of ultraviolet light, the electron-withdrawing groups such as nitro in the molecular structure of nitrobenzoxadiazole are excited after absorbing light. The excited state initiator abstracts hydrogen from the allyl site to generate rubber macromolecular radicals and crosslink to form a crosslinked network.

[0061] ⑥For thermoplastic polyester elastomer (TPEE), benzophenone photosensitive initiator and amine co-initiator are selected because TPEE contains ester groups and ether bonds but no easily activated hydrogen. Diphenyl ketone (BP) needs to abstract α-hydrogen from the amine co-initiator in the excited state to generate amine alkyl radicals to initiate crosslinking. That is, amine alkyl radicals attack the ether bond or ester group of TPEE to initiate crosslinking reaction.

[0062] ⑦For styrene block copolymer thermoplastic elastomer, azo photosensitive initiator is more suitable. The styrene unit contains benzyl hydrogen which is easy to be abstracted by radicals. After photolysis of azo initiator (such as AIBN), cyanoisopropyl radicals are generated to abstract benzyl hydrogen to form a crosslinked network.

[0063] As can be seen from the above, through the selection and regulation of components and ratio, and the optimization of preparation process, multiple mechanisms are used to play a role together, including: ①filler dispersion and interface effect: coupling agent pretreatment forms an organic coating layer on the surface of the filler, reducing agglomeration; ②complex filler synergy: building a multi-dimensional conductive network; ③optimizing the conduction path of the cell structure: complex foaming agent forms uniform micropores; ④distribution of conductive fillers on the cell wall, increasing the electromagnetic wave reflection / absorption interface; ⑤radiation crosslinking stabilizes the cell structure: electron beam curing rapidly crosslinks the cell wall to prevent collapse and ensure the stability of the filler network; ultimately, the preparation of a foamed composite material with excellent comprehensive performance based on a small amount of conductive functional filler is achieved, especially with very excellent conductive performance and electromagnetic shielding performance.

[0064] The above description is only a preferred embodiment of the present application, and does not limit the present application in any form. Any modification, equivalent change and modification of the above embodiment based on the technical essence of the present application, without departing from the technical solution content of the present application, still belongs to the scope of the technical solution of the present application.

Claims

1. A thermoplastic elastomer-based foamed composite material with excellent electrical conductivity and electromagnetic shielding properties, characterized in that: The foamed composite material is prepared by continuously extruding and foaming the following components through an extruder, and then rapidly subjecting the foamed product to electron radiation treatment: 100 parts by weight of thermoplastic elastomer resin; 0.8-8 parts by weight of conductive functional filler; 0.1-10 parts by weight of coupling agent; 0.1-10 parts by weight of photoinitiator; 0.1-10 parts by weight of cell stabilizer; 0.2-8 parts by weight of composite foaming agent; The thermoplastic elastomer resin is ethylene-vinyl acetate copolymer and polyolefin elastomer, the conductive functional filler is a mixture of CNTs and graphene in a weight ratio of 1:1, and the composite foaming agent is a mixture of supercritical carbon dioxide and air in a weight ratio of 1:2; The conductive functional filler needs to be pre-treated before being put into the extruder. The pre-treatment is to use the coupling agent to dry-blend the conductive functional filler to improve the dispersibility and interfacial compatibility of the conductive functional filler in the matrix. The coupling agent is one or more of KH570, KH171, A-172, and A-174. The photoinitiator is one or more of benzophenones, acylphosphine oxides, aromatic diazonium salts, nitrobenzoxadiazoles, iodonium salts, and azo groups; The cell stabilizer is one or a mixture of glycerol fatty acid ester cell stabilizers, propylene glycol fatty acid ester cell stabilizers and isooctyl alcohol fatty acid ester cell stabilizers; The extruder is a twin-screw extruder, which is a twin-screw extruder connected in series with a single-screw extruder; The thermoplastic elastomer-based foamed composite material with excellent electrical conductivity and electromagnetic shielding properties is prepared by the following method: S1. vacuum drying the thermoplastic elastomer resin and the conductive functional filler; S2. Stirring the conductive functional filler and the coupling agent in a high-speed stirrer for dry mixing to obtain a pretreated conductive functional filler; S3, then uniformly mixing the thermoplastic elastomer resin, the pretreated conductive functional filler, the photoinitiator, and the cell stabilizer to obtain a mixed material; S4, adding the above-mentioned mixed material into a twin-screw extruder, injecting the composite foaming agent into the extruder at the same time, and after sufficient mixing, extruding and foaming molding; S5. Finally, the foamed sample is quickly subjected to electron radiation treatment to promote cross-linking and curing to obtain the foamed composite material.

2. The method for preparing the foamed composite material according to claim 1, wherein: The following steps are involved: S1. vacuum drying the thermoplastic elastomer resin and the conductive functional filler; S2. Stirring the conductive functional filler and the coupling agent in a high-speed stirrer for dry mixing to obtain a pretreated conductive functional filler; S3, then uniformly mixing the thermoplastic elastomer resin, the pretreated conductive functional filler, the photoinitiator, and the cell stabilizer to obtain a mixed material; S4, adding the above-mentioned mixed material into a twin-screw extruder, injecting the composite foaming agent into the extruder at the same time, and after sufficient mixing, extruding and foaming molding; S5. Finally, the foamed sample is quickly subjected to electron radiation treatment to promote cross-linking and curing to obtain the foamed composite material; In a first-stage extruder of a twin-stage screw extruder, all the mixed materials are melt-blended, and the processing temperature is controlled at 80-120° C.; after uniform mixing, the materials are conveyed to a second-stage extruder, and the extrusion foaming temperature is controlled at 80-120° C., the extrusion foaming pressure is 5-20 MPa, and the extrusion foaming time is 8-20 minutes, for continuous extrusion foaming; and the foamed product is rapidly subjected to electron radiation treatment, with an electron beam irradiation dose of 40-80 kGy and an irradiation time of 5-30 seconds at room temperature, to promote cross-linking and curing, thereby obtaining the thermoplastic elastomer-based foamed composite material.

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