A wave-absorbing and heat-conducting flexible electromagnetic functional composite material and its preparation method

Abstract

The present invention discloses a flexible electromagnetic functional composite material with wave absorption and heat conduction, and its preparation method, belonging to the field of composite materials. The invention combines dendritic silver-coated copper powder, boron nitride nanosheets, and carbonyl iron powder, and simultaneously introduces boron nitride fabric into the matrix material. Through a multi-dimensional, cross-scale, and multi-component system, a multifunctional network structure is systematically constructed to produce a silicone rubber-based electromagnetic functional composite material with high-frequency wave absorption, high thermal conductivity, and low density. This composite material exhibits high-frequency attenuation, high thermal conductivity, and low density, meeting the application requirements of high-performance antenna systems for wave absorption and heat conduction materials.

Description

Technical Field

[0001] The present invention belongs to the field of composite materials, and in particular relates to a wave-absorbing, heat-conducting, flexible electromagnetic functional composite material and a preparation method thereof. Background Art

[0002] High-performance antenna systems are developing towards high-power radiation, high-frequency transmission and reception, and strong stealth. This puts forward comprehensive performance requirements for the electromagnetic functional materials supporting the antenna system, including high-frequency loss of clutter, control of surface current radiation, high temperature resistance, high thermal conductivity, and lightweight. However, with the high degree of integration of the overall space, the requirements for the integration of multifunctional materials are also becoming increasingly higher. Therefore, the development of an electromagnetic functional material with high-frequency attenuation function, high thermal conductivity, high temperature resistance, and low density has become one of the important links in solving the high-performance development of antenna systems. The present invention develops a high-thermal conductivity, lightweight, flexible electromagnetic functional composite material based on the dual mechanisms of electrical conductivity loss and magnetic loss.

[0003] Currently, multifunctional flexible electromagnetic materials primarily combine thermal conductivity and absorption by adding various absorbers and traditional thermally conductive fillers to a rubber matrix. One approach is to increase the filler network density within the matrix to achieve continuous and complete thermal conductivity, thereby achieving efficient heat conduction. The other approach is to add absorbing fillers with different loss mechanisms to impart excellent electromagnetic wave absorption. However, these two approaches exhibit performance trade-offs, necessitating careful design and optimization of filler type, structure, distribution ratio, interface characteristics, and molding process within flexible material technology to achieve the technical goals of multifunctionality and high performance.

[0004] Dendritic silver-coated copper powder has high electrical conductivity, thermal conductivity and dimensional structural integrity, but its impedance matching is poor, making it difficult to achieve electromagnetic wave absorption under a wide frequency band; boron nitride, as an insulating thermal conductive material, not only has a high thermal conductivity, but also has excellent electrical insulation and a low dielectric constant, making it a good choice for adjusting the impedance matching characteristics of absorbing materials; carbonyl iron powder is one of the absorbers with better magnetic characteristics at present, which helps to adjust the absorption bandwidth and absorption intensity, but it has a high density and poor intrinsic thermal conductivity. Adding too much is not conducive to reducing the weight of the overall absorbing material, and it cannot significantly improve the thermal conductivity. Summary of the Invention

[0005] The purpose of the present invention is to compound and mix dendritic silver-coated copper powder, boron nitride nanosheets, and carbonyl iron powder, and at the same time introduce boron nitride fabric into the matrix material, so as to systematically construct a multifunctional network structure through multi-dimensional, cross-scale, and multi-component methods to prepare a silicone rubber-based electromagnetic functional composite material with high-frequency absorption, high thermal conductivity, and low density.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] A method for preparing a wave-absorbing, heat-conducting, flexible electromagnetic functional composite material, comprising the following steps:

[0008] (1) pre-mixing dendritic silver-coated copper powder, P-type carbonyl iron powder, Q-type carbonyl iron powder, and boron nitride nanosheets to obtain a thermally conductive and wave-absorbing composite powder;

[0009] (2) adding a coupling agent to the obtained thermal conductive and wave absorbing composite powder, mixing the mixture, and obtaining an activated thermal conductive and wave absorbing composite powder;

[0010] (3) adding the activated heat-conducting and wave-absorbing composite powder to methylphenyl silicone rubber for initial mixing to obtain a wave-absorbing and heat-conducting electromagnetic slurry;

[0011] (4) adding a certain amount of fumed silica and diisopropylbenzene ditert-butyl peroxide to the obtained wave-absorbing and heat-conducting electromagnetic slurry, performing secondary mixing, and obtaining a flexible electromagnetic slurry after mixing evenly;

[0012] (5) repeatedly thinning the obtained flexible electromagnetic slurry material and then pressing it into a thin sheet of rubber material;

[0013] (6) calendering the obtained flaky rubber material and the boron nitride fabric to pre-shape, and then stacking them into an unvulcanized prepreg;

[0014] (7) placing the obtained unvulcanized prepreg between two magnets and arranging them, then cutting them into strips and laying them flat, then flipping the strips 90° horizontally and laminating them side by side to obtain a layered unvulcanized strip;

[0015] (8) The obtained layered unvulcanized rubber material is subjected to hot pressing and vulcanization molding to obtain a wave-absorbing, heat-conducting, flexible, and electromagnetic functional composite material.

[0016] Furthermore, 127.5-178.5 parts of dendritic silver-coated copper powder, 12.75-25.5 parts of P-type flaky carbonyl iron powder, 12.75-51 parts of Q-type spherical carbonyl iron powder, 51-63.75 parts of boron nitride nanosheets, 1.275-5.1 parts of coupling agent, 40-45 parts of methylphenyl silicone rubber, 0.5-1.2 parts of fumed silica, and 0.4-0.45 parts of di-tert-butyl peroxide diisopropylbenzene are weighed in parts by mass.

[0017] Furthermore, in step (1), the length of the dendritic silver-coated copper powder filler is 11-18 μm, the D50 particle size of the P-type flaky carbonyl iron powder is 3.5-6.0 μm, the D50 particle size of the Q-type spherical carbonyl iron powder is 3-5 μm, and the D50 particle size of the boron nitride nanosheet is 0.05-0.2 μm.

[0018] Furthermore, the premixing condition in step (1) is mixing at a rotation speed of 12-25 rpm for 1-2 hours.

[0019] Furthermore, in step (2), the coupling agent is one of KH-550, KH-560, A-151, and GR-401.

[0020] Furthermore, in step (2), the mixing treatment is carried out at room temperature for 0.5-2 hours.

[0021] Furthermore, in step (3), the initial mixing is 30-40 min, and the specific mixing conditions are 10-12 rpm for 12-15 min in the first stage, 15-20 rpm for 10-15 min in the second stage, and 8-10 rpm for 8-10 min in the third stage.

[0022] Furthermore, in step (4), the secondary mixing is performed for 10-15 minutes, and the order of adding materials is as follows: adding fumed silica in the first stage and adding diisopropylbenzene ditert-butyl peroxide in the second stage. The specific mixing conditions are 20-25 rpm for 8-11 minutes in the first stage and 15-18 rpm for 2-4 minutes in the second stage.

[0023] Furthermore, in step (5), the thinning process is repeated 10-16 times, and the thinning process is divided into three sections: the first section is thinning 3-5 times with a roller distance of 1-1.2 mm, the second section is thinning 5-7 times with a roller distance of 0.6-0.8 mm, and the third section is thinning 2-4 times with a roller distance of 0.2-0.4 mm.

[0024] Furthermore, the thickness of the flaky rubber material in step (5) is 0.25-0.3 mm.

[0025] Furthermore, in step (6), the diameter of the boron nitride fabric monofilament is 3-10 μm and the thickness is 0.1 mm.

[0026] Furthermore, the calendering preforming condition in step (6) is to calender the composite at 5-8 rpm, and then stack to form 7 layers, and the thickness of the unvulcanized prepreg is 2-2.5 mm.

[0027] Furthermore, in step (7), two NdFeB magnets with a spacing of 8-15 cm are placed in the middle for magnetron treatment, the magnetic field strength is 1200-1850 Gs, and the magnetron treatment time is 4-6 hours; and then the rubber material is cut into 1-3 cm wide strips.

[0028] Furthermore, in step (8), the hot pressing vulcanization molding conditions are hot pressing at 145-170° C. and 10-15 MPa for 10-15 minutes, and post-treatment at 200° C. for 30 minutes.

[0029] A wave-absorbing, heat-conducting, flexible, electromagnetic functional composite material is prepared by the above-mentioned preparation method.

[0030] The present invention uses phenyl silicone rubber as a flexible matrix, dendritic silver-coated copper powder, carbonyl iron powder, and boron nitride nanofiller as multifunctional composite components, pre-mixes them through a V-type mixer, and uses a kneader to mix the composite powder with the silicone rubber matrix to prepare a high-viscosity flexible electromagnetic thermal conductive slurry; the boron nitride fabric and the electromagnetic thermal conductive slurry are rolled out into sheets and cut and arranged through a calendering and laminating method, and finally layered and heated and pressed in sequence under a flat vulcanizer to prepare a lightweight flexible electromagnetic functional material with the characteristics of high-frequency attenuation, high thermal conductivity, low density, etc., which can meet the application requirements of high-performance antenna systems for absorbing / thermal conductive materials.

[0031] The innovation of the present invention is as follows:

[0032] Innovation 1: The main absorber formulation utilizes four different functionally modified fillers: dendritic silver-coated copper powder, flake carbonyl iron powder, spherical carbonyl iron powder, and boron nitride nanosheets. By varying their content ratios, the flexible electromagnetic loss material's electromagnetic wave attenuation performance in the high-frequency range is tuned. Furthermore, a V-shaped powder premixing method effectively reduces agglomeration between the composite powders of varying morphologies. The dendritic silver-coated copper powder in this invention utilizes a branched, micron-sized morphology that facilitates the formation of thermal pathways, serving as a thermal backbone. Furthermore, at the appropriate addition level, it enriches the material's electromagnetic loss mechanism, facilitating high-performance electromagnetic absorption. The present invention balances the content of flake and spherical carbonyl iron powders to form an electromagnetically functional structure. This invention utilizes a thermally conductive backbone structure formed by the dendritic silver-coated copper, an electromagnetically functional structure formed by the carbonyl iron powder, and a functional interlayer structure formed by the boron nitride nanosheets and boron nitride fabric. Through the functional integration of these structures, the material achieves enhanced high-frequency electromagnetic attenuation, ultimately significantly improving both attenuation and thermal conductivity.

[0033] Innovation 2: The thermally conductive filler formula utilizes a combination of nanoscale ultra-thin boron nitride nanosheets and submicron silver-coated copper powder. This ensures that electromagnetic parameters remain stable (dielectric constant and permeability remain stable) while also allowing for overlap and isolation with the absorbing components to form a thermally conductive microstructure network.

[0034] Innovation point 3: In the construction of flexible electromagnetic material structure, boron nitride fiber fabric and flexible electromagnetic slurry are stacked on each other and arranged through thin channels and magnetic control, thus constructing a dual-functional structure of wave absorption / heat conduction network from the perspective of structure and preparation method.

[0035] The present invention has achieved the following beneficial effects:

[0036] (1) The present invention aims to achieve the electromagnetic attenuation, impedance matching, and thermal conductivity characteristics unique to different types of fillers. By adjusting the ratio between conductive silver-coated copper, sheet / spherical carbonyl iron powder, and boron nitride nanosheets, a multi-scale and multi-morphological functional filler system is formed, which can achieve the characteristics of strong attenuation and high thermal conductivity of flexible materials at high frequencies.

[0037] (2) The present invention addresses the problem of differences and randomness in the heat transfer performance of thermal conductive and absorbing materials in omnidirectional paths. Boron nitride fiber fabrics are added to the three-dimensional structure of the material, and the heat conductive path structure is further improved through mechanical orientation and magnetic control arrangement. The material also has the characteristics of stable dielectric properties, dual absorption loss mechanism, and low density, thereby achieving the characteristics of high thermal conductivity and strong attenuation of the material. DETAILED DESCRIPTION

[0038] The present invention is further described below with reference to specific examples. However, the scope of protection of the products and methods of making the products of the present invention is not limited to the examples. The silicone rubber used in the examples is methylphenyl silicone rubber, which has a complex dielectric constant of 2.8-0.01J and a complex magnetic permeability of 1.1-0.01J.

[0039] Example 1

[0040] 127.5 g of dendritic silver-coated copper powder, 25.5 g of P-type flaky carbonyl iron powder, 51 g of Q-type spherical carbonyl iron powder, and 63.75 g of boron nitride nanosheets were weighed and mixed at 12 rpm for 1 hour. Then, 5.1 g of coupling agent was added to the barrel and mixed at room temperature for 0.5 hour to obtain an activated wave-absorbing and thermally conductive composite powder.

[0041] Weigh 40g of methylphenyl silicone rubber and composite powder and knead and mix them at 10rpm for 12min in the first stage, 15rpm for 10min in the second stage and 8rpm for 8min in the third stage. Then add 0.5g of fumed silica and 0.40g of di-tert-butyl peroxide diisopropylbenzene, and knead and mix them at 20rpm for 8min in the first stage and 15rpm for 2min in the second stage. Further, pass the rubber material through the roller with a roller distance of 1.0mm for 3 times and a roller distance of 1.0mm for 2 times. The 0.6mm thin pass was performed 5 times, and the three-section roller spacing was 0.2mm thin pass was performed 2 times; the sheet slurry was then calendered and compounded with 0.1mm thick boron nitride fiber and stacked in 7 layers; the sheet was then placed between two 1200Gs magnetic field strength neodymium iron boron magnets with a spacing of 8cm and treated for 4 hours, and further cut into 1cm wide strips of rubber, and each strip of rubber was turned over and then bonded to each other; finally, hot pressed at 145℃ and 10MPa for 15min, and then high-temperature treated in a 200℃ oven for 30min.

[0042] Example 2

[0043] 178.5 g of dendritic silver-coated copper powder, 12.75 g of P-type flaky carbonyl iron powder, 12.75 g of Q-type spherical carbonyl iron powder, and 51 g of boron nitride nanosheets were weighed and mixed at 25 rpm for 2 h. 1.275 g of a coupling agent was then added to the barrel and mixed at room temperature for 2.0 h to obtain an activated wave-absorbing and thermally conductive composite powder.

[0044] Weigh 45g of methylphenyl silicone rubber and composite powder and knead and mix them at 12rpm for 15min in the first stage, 20rpm for 15min in the second stage and 10rpm for 10min in the third stage. Then add 1.2g of fumed silica and 0.45g of di-tert-butyl peroxide diisopropylbenzene, and knead and mix them at 25rpm for 11min in the first stage and 18rpm for 4min in the second stage. Further, pass the rubber material through 5 times on a roller with a distance of 1.2mm in the first stage and 100rpm on the second stage. The sheet was rolled 7 times with a distance of 0.8mm and 4 times with a distance of 0.4mm between three rollers. The sheet was then calendered and compounded with 0.1mm thick boron nitride fiber and stacked in 7 layers. The sheet was then placed between two 1850Gs NdFeB magnets with a distance of 15cm and treated for 6 hours. The sheet was then cut into 3cm wide strips of rubber, and each strip was turned over and bonded to each other. Finally, the sheet was hot pressed at 170℃ and 15MPa for 10min, and then high-temperature treated in a 200℃ oven for 30min.

[0045] Example 3

[0046] 142.5 g of dendritic silver-coated copper powder, 17.5 g of P-type flaky carbonyl iron powder, 42.5 g of Q-type spherical carbonyl iron powder, and 57.5 g of boron nitride nanosheets were weighed and mixed at 20 rpm for 1.0 h. Then, 3.9 g of a coupling agent was added to the barrel and mixed at room temperature for 1.0 h to obtain an activated wave-absorbing and thermally conductive composite powder.

[0047] Weigh 40g of methylphenyl silicone rubber and composite powder and knead and mix them at 11rpm for 13min, 18rpm for 12min and 9rpm for 9min in the first stage, then add 1.0g of fumed silica and 0.40g of di-tert-butyl peroxide diisopropylbenzene, and knead and mix them at 23rpm for 10min in the first stage and 16rpm for 3min in the second stage; further, pass the rubber material through 4 times on a roller with a distance of 1.1mm in the first stage and 1.1mm in the second stage. The 0.7mm thin pass was performed 6 times, and the three-section roller spacing was 0.3mm thin pass was performed 3 times; the sheet slurry was then calendered and compounded with 0.1mm thick boron nitride fiber and stacked in 7 layers; the sheet was then placed between two 1700Gs magnetic field strength neodymium iron boron magnets with a spacing of 12cm and treated for 5 hours, and further cut into 2cm wide strips of rubber, and each strip of rubber was turned over and then bonded to each other; finally, hot pressed at 155℃ and 12MPa for 12min, and then high-temperature treated in a 200℃ oven for 30min.

[0048] Comparative Example

[0049] 220g of Q-type carbonyl iron powder and 40g of methylphenyl silicone rubber were weighed and added to an internal mixer. The mixture was kneaded and stirred for 1 hour to form a gray electromagnetic slurry. 0.5g of fumed silica and 0.4g of di-tert-butyl peroxide diisopropylbenzene were then weighed and added to the electromagnetic slurry and stirred for 10 minutes to form an uncured flexible electromagnetic slurry. The slurry was repeatedly thinned 16 times on an open mill with a 0.4mm roll gap, and then the roll gap was adjusted to 2.0mm to form a sheet. The sheet was placed in a flat mold and hot-pressed at 145°C and 10MPa for 10 minutes. It was then oven-heated at 200°C for 30 minutes.

[0050] The test results of electromagnetic parameters, attenuation coefficient and thermal conductivity in Examples 1-3 and Comparative Examples are listed in Table 1

[0051] Table 1 Test results of electromagnetic properties, thermal conductivity and density of wave-absorbing and heat-conducting flexible electromagnetic functional composite materials

[0052]

[0053]

[0054] It can be seen from the data in Table 1 that by optimizing the ratio of various types of fillers and applying magnetic control arrangement measures, the material's high-frequency electromagnetic attenuation, thermal conductivity, and lightweight are improved.

[0055] Although the present invention has been disclosed as above by way of embodiments, they are not intended to limit the present invention. Any appropriate modification or equivalent substitution of the technical solution of the present invention by a person skilled in the art should be included in the protection scope of the present invention. The protection scope of the present invention shall be based on that defined in the claims.

Claims

1. A method for preparing a wave-absorbing, heat-conducting, flexible electromagnetic functional composite material, characterized in that the steps include: (1) Premixing dendritic silver-coated copper powder, P-type flaky carbonyl iron powder, Q-type spherical carbonyl iron powder, and boron nitride nanosheets to obtain a thermally conductive and microwave-absorbing composite powder; (2) adding a coupling agent to the obtained thermal conductive and wave absorbing composite powder, mixing the mixture, and obtaining an activated thermal conductive and wave absorbing composite powder; (3) adding the activated heat-conducting and wave-absorbing composite powder to methylphenyl silicone rubber for initial mixing to obtain a wave-absorbing and heat-conducting electromagnetic slurry; (4) adding a certain amount of fumed silica and diisopropylbenzene ditert-butyl peroxide to the obtained wave-absorbing and heat-conducting electromagnetic slurry, performing secondary mixing, and obtaining a flexible electromagnetic slurry after mixing evenly; (5) repeatedly thin-passing the obtained flexible electromagnetic slurry material, and then pressing it into a thin sheet-like rubber material; (6) calendering the obtained sheet-like rubber material and the boron nitride fabric to pre-shape, and then stacking them into an unvulcanized prepreg; (7) The obtained unvulcanized prepreg is placed between two magnets and arranged, and then cut into strips and laid flat, and then the strips are flipped 90° in the horizontal direction and laminated side by side to obtain a layered unvulcanized rubber material; (8) The obtained layered unvulcanized rubber material is subjected to hot pressing and vulcanization molding to obtain a wave-absorbing, heat-conducting, flexible, and electromagnetic functional composite material.

2. The preparation method according to claim 1, wherein Weigh, by mass, 127.5-178.5 parts of dendritic silver-coated copper powder, 12.75-25.5 parts of P-type flaky carbonyl iron powder, 12.75-51 parts of Q-type spherical carbonyl iron powder, 51-63.75 parts of boron nitride nanosheets, 1.275-5.1 parts of coupling agent, 40-45 parts of methylphenyl silicone rubber, 0.5-1.2 parts of fumed silica, and 0.4-0.45 parts of di-tert-butyl diisopropyl peroxide.

3. The preparation method according to claim 1, wherein In step (1), the length of the dendritic silver-coated copper powder filler is 11-18 μm, the D50 particle size of the P-type flake carbonyl iron powder is 3.5-6.0 μm, the D50 particle size of the Q-type spherical carbonyl iron powder is 3-5 μm, and the D50 particle size of the boron nitride nanosheet is 0.05-0.2 μm; the pre-mixing condition is mixing at a rotation speed of 12-25 rpm for 1-2 hours.

4. The preparation method according to claim 1, wherein In step (2), the coupling agent is one of KH-550, KH-560, A-151, and GR-401; the mixture is mixed at room temperature for 0.5-2 hours.

5. The preparation method according to claim 1, wherein In step (3), the initial mixing is 30-40 minutes, and the specific mixing conditions are 10-12 rpm for 12-15 minutes in the first stage, 15-20 rpm for 10-15 minutes in the second stage, and 8-10 rpm for 8-10 minutes in the third stage. In step (4), the secondary mixing is 10-15 minutes, and the order of adding materials is as follows: adding fumed silica in the first stage and adding diisopropylbenzene ditert-butyl peroxide in the second stage. The specific mixing conditions are 20-25 rpm for 8-11 minutes in the first stage and 15-18 rpm for 2-4 minutes in the second stage.

6. The preparation method according to claim 1, wherein In step (5), the thinning process is repeated 10-16 times. The thinning process is divided into three sections: the first section is thinning 3-5 times with a roller distance of 1-1.2 mm, the second section is thinning 5-7 times with a roller distance of 0.6-0.8 mm, and the third section is thinning 2-4 times with a roller distance of 0.2-0.4 mm.

7. The preparation method according to claim 1, wherein The calendering preforming condition in step (6) is to calender the composite at 5-8 rpm and then stack it to form a 7-layer thickness.

8. The preparation method according to claim 1, wherein In step (7), two NdFeB magnets with a spacing of 8-15 cm are placed in the middle for magnetron treatment, the magnetic field strength is 1200-1850 Gs, and the magnetron treatment time is 4-6 hours; and then the rubber material is cut into 1-3 cm wide strips.

9. The preparation method according to claim 1, wherein The hot pressing vulcanization molding conditions in step (8) are hot pressing at 145-170°C and 10-15 MPa for 10-15 minutes, and post-treatment at 200°C for 30 minutes.

10. A wave-absorbing, heat-conducting, flexible electromagnetic functional composite material, characterized in that: Prepared by the preparation method according to any one of claims 1 to 9.

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