Functional network structure design method and application of high-thermal-conductivity wave-absorbing composite material

Abstract

The invention discloses a functional network structure design method and application of a high-thermal-conductivity wave-absorbing composite material. The method comprises the following steps: S1, adding wave-absorbing functional particles into a polymer matrix by a melt blending or solution mixing method to obtain a wave-absorbing composite material; and crushing or crushing the wave-absorbing composite material to obtain the wave-absorbing functional particles. S2, mixing the wave-absorbing functional particles with the heat-conducting functional particles, so that the wave-absorbing functional particles are coated with the heat-conducting functional particles to form composite particles; and then loading the composite particles into a mold, pre-pressing to discharge gas among the particles, then carrying out hot pressing, and cooling to obtain the composite material with the three-dimensional communicated heat-conducting and wave-absorbing dual-function network structure. According to the invention, the heat-conducting functional particles are selectively distributed at a polymer particle micro-area interface through a hot-pressing process to construct an isolation structure, a continuous heat-conducting network is formed, and the composite material with excellent heat-conducting property and wave-absorbing property is obtained and can be used as an electronic chip packaging material and used in the field of electromagnetic compatibility.

Description

Technical Field

[0001] This invention relates to the field of thermally conductive and microwave absorbing materials, and in particular to a functional network structure design method and application of a high thermal conductivity and microwave absorbing composite material. Background Technology

[0002] With the advent of the 5G era, electromagnetic interference (EMI) has become an increasingly prominent issue in highly integrated electronic devices. Due to limited internal space and poor airflow, most of the energy absorbed by electromagnetic wave absorbing materials is converted into waste heat during absorption, which can easily accumulate and damage electronic components. Combining high-efficiency wave absorption performance with high thermal conductivity is crucial for accelerating waste heat dissipation and ensuring the stability of electronic devices. However, in thermally conductive and wave-absorbing polymer composites, there is a mutually restrictive relationship between thermal conductivity and wave absorption performance. Therefore, overcoming the structural design contradiction between thermal conductivity and wave absorption performance in composite materials has become an urgent problem to be solved.

[0003] Combining or blending thermally conductive and microwave-absorbing functional particles is currently the main method for composite materials to simultaneously achieve both thermal conductivity and microwave absorption properties. For example, patent CN202411600638.9 provides a method for preparing a Fe@Si3N4 core-shell structured thermally conductive and microwave-absorbing material, in which Si3N4 is uniformly coated on the surface of iron powder, and then applied to an organosilicon pad to improve the material's thermal conductivity and microwave absorption properties. However, since all functional particles are still confined to one phase, the problem of a contradiction between thermal conductivity and microwave absorption properties remains after the combination of thermally conductive and microwave-absorbing functional particles. A method of pre-constructing a three-dimensional thermally conductive network and then impregnating it with a resin matrix can efficiently construct a complete thermally conductive network. For example, patent CN202510915355.1 provides a method for preparing a three-dimensional interpenetrating network structure thermally conductive and microwave-absorbing composite material. This method involves impregnating carbon fibers in an ethanol dispersion containing titanate, graphene quantum dots, and polydopamine, followed by low-temperature in-situ polymerization, filtration, and drying to obtain surface-functionalized carbon fibers. The functionalized carbon fibers are then mixed with an MXene / BNNS dispersion and freeze-dried to obtain a three-dimensional honeycomb network skeleton of functionalized carbon fibers. This functionalized carbon fiber three-dimensional honeycomb network skeleton is then impregnated in a resin precursor solution containing functional fillers and flame retardants to fill the network gaps with resin, followed by heating and curing to obtain the composite material. While this method reconciles the contradictory relationship between thermal conductivity and microwave absorption, the process is cumbersome and difficult to scale up.

[0004] In summary, constructing a complete three-dimensional heat-conducting network while ensuring microwave absorption performance is an effective means to simultaneously improve both thermal conductivity and microwave absorption performance. However, existing design schemes still cannot resolve the mutual constraints between the structural design of thermal conductivity and microwave absorption functions, and therefore cannot achieve simultaneous improvement of these two functions. Summary of the Invention

[0005] To address the problem that existing technologies still cannot solve the mutual constraints between thermal conductivity and microwave absorption functional structure design, and cannot achieve simultaneous improvement of thermal conductivity and microwave absorption functions, this invention provides a functional network structure design method for high thermal conductivity microwave absorption composite materials.

[0006] The functional network structure design method for high thermal conductivity microwave absorbing composite materials provided by this invention comprises the following steps: S1. Microwave-absorbing functional particles are added to a polymer matrix by melt blending or solution mixing to obtain a microwave-absorbing composite material; the microwave-absorbing composite material is crushed or pulverized to obtain microwave-absorbing functional microparticles.

[0007] The solution mixing method is as follows: microwave absorbing functional particles are added to a polymer matrix solution and ultrasonically dispersed to obtain a mixed solution; the mixed solution is dried and then crushed to obtain microwave absorbing functional microparticles.

[0008] The polymer matrix is ​​a thermoplastic polymer or a thermosetting polymer, including but not limited to styrene-butadiene-styrene block copolymer (SBS) or polyimide (PI).

[0009] When the polymer matrix is ​​a styrene-butadiene-styrene block copolymer (SBS), the method for step S1 is as follows: SBS is dissolved in an organic solvent, and then microwave-absorbing functional particles are added and ultrasonically dispersed to obtain a mixture. The mixture is placed in a container and dried in a vacuum oven at 40-60℃ to obtain a flexible film. The film is then broken up to obtain microwave-absorbing functional microparticles.

[0010] When the polymer matrix is ​​polyimide (PI), the method for step S1 is as follows: Microwave-absorbing functional particles were added to the PI precursor solution (i.e., polyamic acid solution, PAA) and ultrasonically dispersed to obtain a mixture. The mixture was then poured into deionized water for flocculation. Subsequently, the filtered flocculent was vacuum dried, and the dried sample was mechanically pulverized to obtain microwave-absorbing functional microparticles.

[0011] The microwave absorbing particles are a mixture of carbon-based material particles and magnetic material particles, such as a mixture of carbonyl iron powder (CIP) and carbon fiber (CF), and the amount used is 15-20% of the polymer matrix mass.

[0012] S2. Coat the surface of the microwave-absorbing microparticles with thermally conductive microparticles, so that the thermally conductive microparticles encapsulate the microwave-absorbing microparticles to form composite particles; then load the composite particles into a mold, first pre-press to expel the gas between the particles, then heat to 160-350℃ for constant temperature hot pressing, and finally cool to obtain a thermally conductive and microwave-absorbing composite material with a three-dimensional interconnected thermally conductive and microwave-absorbing dual-function network structure.

[0013] The thermally conductive functional particles are one of boron nitride, aluminum oxide, and barium titanate, and their amount is 10-40% of the polymer matrix mass.

[0014] Preferably, in step S2, the microwave absorbing particles and the thermally conductive particles are mixed and then ball-milled. The mechanical force of the ball milling causes the thermally conductive particles to coat the surface of the microwave absorbing particles, forming composite particles.

[0015] Compared with the prior art, the advantages of the present invention are: (1) The design method of this invention utilizes the volume repulsion effect of the polymer matrix on the thermally conductive functional particles during the molding process, forcing the thermally conductive functional particles to selectively distribute at the polymer particle interface to form a unique isolation structure, thereby forming a three-dimensional interconnected thermally conductive and microwave-absorbing dual-functional network structure. This three-dimensional functional network structure can promote the effective stacking and overlapping of functional particles, significantly reduce the existence of isolated functional particles in the composite material system, effectively improve the utilization efficiency of functional particles, and fully exert their functional role at a low content.

[0016] (2) The method of constructing a three-dimensional network structure by coating thermoplastic polymer particles with thermally conductive functional particles is easy to scale up for production. Moreover, the functional particles can be easily connected to form a three-dimensional network structure. The thermally conductive functional network and the microwave absorbing functional particles in the composite material do not affect each other, which can effectively solve the structural design contradiction between microwave absorption and thermal conductivity. The prepared composite material can be used as an electronic chip packaging material and in the field of electromagnetic compatibility.

[0017] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0018] Figure 1 This is a microscopic image of the microwave-absorbing functional microparticles prepared in Example 1.

[0019] Figure 2 This is a schematic diagram of the functional network structure of the high thermal conductivity microwave absorbing composite material prepared in the example. Detailed Implementation

[0020] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0021] Example 1 A functional network structure design method for high thermal conductivity microwave absorbing composite materials: (1) Preparation of SBS-based microwave absorbing functional microparticles First, styrene-butadiene-styrene block copolymer (SBS) was added to dichloromethane and stirred at 80°C until completely dissolved. The amount of dichloromethane used is not critical, as long as it completely dissolves the SBS; in this example, 1g of SBS was added to 30ml of dichloromethane. Then, 17% (by mass of SBS) of microwave-absorbing functional particles (CF and CIP in a 10:7 mass ratio) were added to the solution. The mixture was ultrasonically dispersed using a sonic cell disruptor for 10 minutes, with both the ultrasonic on / off time and frequency set to 1.0 second. After ultrasonic treatment, the mixture was poured into a 10cm diameter polytetrafluoroethylene mold and placed in a vacuum oven at 40°C to evaporate and remove the solvent for 6 hours, forming a 0.5mm thick flexible film. The flexible film was then mechanically crushed in a crusher for 10 minutes at a speed of 2000 rpm to obtain microwave-absorbing functional microparticles. The microstructure of these microparticles is shown below. Figure 1 As shown.

[0022] (2) Construction of SBS-based three-dimensional thermally conductive and microwave-absorbing dual-functional network composite material: The microwave-absorbing functional microparticles obtained in step (1) are mixed evenly with boron nitride (BN) particles and then ball-milled at a speed of 400 r / min for 20 min to coat the surface of the microwave-absorbing functional microparticles with BN, forming composite particles with a particle size of about 200 mesh. The amount of BN used is 10% of the mass of SBS. Then, the microwave-absorbing functional particles coated with BN are placed in a mold and pre-pressed at a pressure of 1-5 MPa for 1-5 minutes. This pre-pressing process can be repeated multiple times (1-20 times) to remove air bubbles between the particles. Subsequently, the temperature is raised to 170℃ and the pressure is raised to 10 MPa. The temperature is maintained at 1℃ for 20 minutes for hot pressing treatment, with a dynamic cooling rate of 1℃ / min. The final product is as follows. Figure 2 The composite material shown has a three-dimensional thermally conductive and wave-absorbing dual-function network structure. The mold used is a 2mm thick concave-convex mold, which can be circular or square in shape.

[0023] Example 2 Based on Example 1, the amount of boron nitride was adjusted to 20% of the mass of SBS, while other parameters remained unchanged, resulting in a composite material with a three-dimensional thermally conductive and microwave-absorbing dual-functional network structure.

[0024] Example 3 Based on Example 1, the amount of boron nitride was adjusted to 30% of the mass of SBS, while other parameters remained unchanged, resulting in a composite material with a three-dimensional thermally conductive and microwave-absorbing dual-functional network structure.

[0025] Example 4 Based on Example 1, the amount of boron nitride was adjusted to 40% of the mass of SBS, while other parameters remained unchanged, resulting in a composite material with a three-dimensional thermally conductive and microwave-absorbing dual-functional network structure.

[0026] Comparative Example 1 A thermally conductive and microwave-absorbing composite material based on a uniformly dispersed SBS system is prepared by the following method: First, styrene-butadiene-styrene triblock copolymer (SBS) was selected as the matrix material. SBS particles were ball-milled with microwave-absorbing functional particles and thermally conductive functional particles (BN). After ball milling and blending, uniformly dispersed SBS-based microwave-absorbing composite particles were obtained. Next, these composite particles were loaded into a mold and pre-pressed and hot-pressed according to the same method as in Example 1 to obtain a uniformly dispersed SBS-based thermally conductive and microwave-absorbing composite material.

[0027] The microwave absorbing functional particles are a mixture of CF and CIP at a mass ratio of 10:7. The amount of microwave absorbing functional particles is 17% of the mass of SBS. The amount of BN is 10% of the mass of SBS.

[0028] Comparative Example 2 Following the same method as Comparative Example 1, the amount of BN was adjusted to 20% of the mass of SBS, while other parameters remained unchanged, to obtain a thermally conductive and microwave-absorbing composite material based on a uniformly dispersed SBS system.

[0029] Comparative Example 3 Following the same method as Comparative Example 1, the amount of BN was adjusted to 30% of the mass of SBS, while other parameters remained unchanged, to obtain a thermally conductive and microwave-absorbing composite material based on a uniformly dispersed SBS system.

[0030] Comparative Example 4 Following the same method as Comparative Example 1, the amount of BN was adjusted to 40% of the mass of SBS, while other parameters remained unchanged, to obtain a thermally conductive and microwave-absorbing composite material based on a uniformly dispersed SBS system.

[0031] The microwave absorption and thermal conductivity properties of the composite materials prepared in Examples 1-4 and Comparative Examples 1-4 were tested.

[0032] Wave absorption performance test: The return loss of the composite materials of Examples 1-4 and Comparative Examples 1-4 was tested by a vector network analyzer (VNA) (frequency range 2-18GHz), and the results are shown in Table 1.

[0033] Thermal conductivity testing: Following ISO 22007-4, the laser flash method was used for testing. The test material was prepared into a 12.7 mm diameter disc, with a surface planarized and coated with graphite to ensure uniform laser absorption and infrared emission. The test was conducted at a constant temperature of 25°C using a laser flash thermal conductivity meter. The thermal diffusivity was calculated by measuring the temperature rise curve on the back of the sample and using the Cowan model or the algorithm specified in ASTM E1461. Combined with the measured specific heat capacity and sample density, the thermal conductivity λ was calculated. The test results are shown in Table 1.

[0034] Table 1. Test results of microwave absorption and thermal conductivity of the composite materials prepared in Examples 1-4 and Comparative Examples 1-4.

[0035] As can be seen, in Examples 1-4, the thermal conductivity of the composite material increases with the increase of the content of thermally conductive functional particles, and the microwave absorption performance also increases accordingly. With the microwave absorption functional particle content remaining constant, the microwave absorption performance is significantly improved, overcoming the technical problem of the difficulty in simultaneously achieving both microwave absorption and thermal conductivity in composite materials. In Comparative Examples 1-4, the thermal conductivity of the composite material improves to some extent with the increase of the content of thermally conductive functional particles, but the improvement is lower than that in Examples 1-4; furthermore, the microwave absorption performance does not improve. This indicates that the thermally conductive and microwave-absorbing composite material obtained from the SBS-based uniformly dispersed system cannot simultaneously achieve both microwave absorption and thermal conductivity performance, while the design method of this invention can effectively solve the contradiction between microwave absorption and thermal conductivity performance.

[0036] Example 5 A functional network structure design method for high thermal conductivity microwave absorbing composite materials: (1) Add 17% (by mass of polyamic acid) of microwave-absorbing functional particles to a polyamic acid solution (PAA solution, polyamic acid concentration of 10wt%). The microwave-absorbing functional particles are a mixture of CF and CIP in a mass ratio of 10:7. Use an ultrasonic cell disruptor to ultrasonically disperse the particles for 10 minutes (ultrasonic on / off time and frequency are both set to 1.0s) to form a mixture. Then pour the mixture into a beaker containing deionized water for flocculation. After filtration, place the filtered flocculent in a vacuum oven and dry it at 80℃ for 12 hours. Place the dried sample in a grinder for mechanical grinding for 10 minutes (speed 2000 rpm) to obtain CF / CIP / PI functional particles, which are microwave-absorbing functional microparticles.

[0037] (2) The microwave-absorbing functional microparticles obtained in step (1) are mixed evenly with boron nitride (BN) particles and then ball-milled at a speed of 400 r / min for 20 min to coat the surface of the microwave-absorbing functional microparticles with BN, forming composite particles with a particle size of about 200 mesh. The amount of BN is 10% of the mass of polyamic acid, and CF / CIP / PI / BN particles are obtained. The CF / CIP / PI / BN particles are placed in a mold and pre-pressed in a press at a pressure of 20 MPa for 3 minutes, and then 10 exhaust cycles are performed. Then, a stepped heating thermal imidization process is performed for hot pressing. Specifically, under the pressure of 20 MPa, thermal imidization is performed according to a stepped heating program of 80℃, 150℃, 250℃, 280℃, and 320℃, where the heating and holding time of each stage is 1 h, and finally, a CF / CIP / PI / BN composite material with a three-dimensional thermally conductive and microwave-absorbing dual-functional network structure is obtained.

[0038] Example 6 Based on Example 5, the amount of boron nitride was adjusted to 20% of the mass of polyamic acid, while other parameters remained unchanged, resulting in a composite material with a three-dimensional thermally conductive and microwave-absorbing dual-functional network structure.

[0039] Example 7 Based on Example 5, the amount of boron nitride was adjusted to 30% of the mass of polyamic acid, while other parameters remained unchanged, resulting in a composite material with a three-dimensional thermally conductive and microwave-absorbing dual-functional network structure.

[0040] Example 8 Based on Example 5, the amount of boron nitride was adjusted to 40% of the mass of polyamic acid, while other parameters remained unchanged, resulting in a composite material with a three-dimensional thermally conductive and microwave-absorbing dual-functional network structure.

[0041] Comparative Example 5 A polyimide (PI)-based uniformly dispersed thermally conductive and microwave-absorbing composite material is prepared by the following method: Polyimide (PI) was selected as the matrix material. PI powder was ball-milled with microwave-absorbing functional particles and thermally conductive functional particles (BN). After ball milling and blending, uniformly dispersed PI-based microwave-absorbing composite particles were obtained. Next, these composite particles were loaded into a mold and subjected to pre-pressing and hot-pressing treatments using the same method as in Example 5 to obtain a uniformly dispersed PI-based thermally conductive and microwave-absorbing composite material. The types of microwave-absorbing and thermally conductive functional particles were the same as in Example 5, and the proportions of polyimide, microwave-absorbing functional particles, and thermally conductive functional particles were also the same as in Example 5.

[0042] Table 2 shows the test results of the microwave absorption and thermal conductivity of the composite materials prepared in Examples 5-8 and Comparative Example 5. The test methods are the same as above. The data in the table show that in Examples 5-8, the thermal conductivity of the composite material increases with the increase of the content of thermally conductive functional particles, and the microwave absorption performance also increases accordingly; while the microwave absorption performance is significantly improved when the content of microwave-absorbing functional particles remains unchanged. Although the thermal conductivity of Comparative Example 5 is greater than that of Example 5, its microwave absorption performance is poor, far lower than that of Example 5. The composite material of Example 5 can balance microwave absorption and thermal conductivity, significantly improving microwave absorption performance while ensuring that the thermal conductivity meets the application requirements. This further illustrates that the thermally conductive and microwave-absorbing composite material obtained from a uniformly dispersed polymer matrix system cannot simultaneously achieve both microwave absorption and thermal conductivity. This further proves that the method of the present invention can effectively solve the structural design contradiction between microwave absorption and thermal conductivity in microwave-absorbing and thermally conductive materials.

[0043] Table 2 shows the test results of the microwave absorption and thermal conductivity properties of the composite materials prepared in Examples 5-8 and Comparative Example 5.

[0044] In summary, the design method of this invention, based on achieving ideal microwave absorption performance with composite absorbing microparticles, utilizes a hot-pressing process to selectively distribute thermally conductive functional particles at the interface of polymer particle microregions, constructing an isolation structure and forming a continuous thermally conductive network. By controlling the hot-pressing process, the thermally conductive network structure of the composite material can be precisely constructed, resulting in excellent thermal conductivity and microwave absorption performance. Moreover, the preparation method of this invention can further reduce the overall functional particle content, improve the utilization rate of functional particles, and overcome the technical bottleneck restricting the simultaneous improvement of the performance of thermally conductive and microwave-absorbing materials, potentially leading to industrialization.

[0045] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for designing a functional network structure of a high thermal conductivity microwave absorbing composite material, characterized in that, It includes the following two steps: S1. Disperse microwave absorbing functional particles in a polymer matrix to form microwave absorbing functional microparticles; S2. Thermally conductive particles are used to coat microwave-absorbing microparticles to form composite particles; then the composite particles are loaded into a mold for hot pressing, and finally cooled to obtain a composite material with a three-dimensional interconnected thermally conductive and microwave-absorbing dual-function network structure.

2. The functional network structure design method for high thermal conductivity microwave absorbing composite materials as described in claim 1, characterized in that, The specific method for step S1 is as follows: Microwave-absorbing composite materials are obtained by adding microwave-absorbing functional particles to a polymer matrix through melt blending or solution mixing; the microwave-absorbing composite materials are then crushed or pulverized to obtain microwave-absorbing functional microparticles.

3. The functional network structure design method for high thermal conductivity microwave absorbing composite materials as described in claim 2, characterized in that, The polymer matrix is ​​a thermoplastic polymer or a thermosetting polymer.

4. The functional network structure design method for high thermal conductivity microwave absorbing composite materials as described in claim 1, characterized in that, In step S2, the thermally conductive particles and the microwave-absorbing particles are mixed so that the thermally conductive particles coat the microwave-absorbing particles to form composite particles.

5. The functional network structure design method for high thermal conductivity microwave absorbing composite materials as described in claim 1, characterized in that, In step S2, the composite particles are loaded into the mold, pre-pressed to expel the gas between the particles, and then hot-pressed.

6. The functional network structure design method for high thermal conductivity microwave absorbing composite materials as described in claim 1, characterized in that, The microwave absorbing particles are a mixture of carbon-based material particles and magnetic material particles, or a composite material thereof.

7. The functional network structure design method for high thermal conductivity microwave absorbing composite materials as described in claim 1, characterized in that, The thermally conductive particles are at least one of boron nitride, aluminum oxide, and barium titanate.

8. An application of a high thermal conductivity microwave absorbing composite material with a functional network structure, characterized in that, It is used as a material for electronic chip packaging and in the field of electromagnetic compatibility.

Images