High-frequency wave-absorbing material and preparation method thereof

Abstract

The invention relates to the technical field of wave-absorbing materials, and particularly discloses a high-frequency wave-absorbing material and a preparation method thereof. The invention discloses a high-frequency wave-absorbing material and a preparation method thereof. The high-frequency wave-absorbing material comprises the following raw materials in parts by mass: 20-35 parts of engineering plastic particles, 60-75 parts of wave-absorbing powder, 3-5 parts of a flame retardant and 5-8 parts of an auxiliary agent, wherein the wave-absorbing powder is formed by compounding a resistance type wave-absorbing agent, a dielectric type wave-absorbing agent and soft magnetic wave-absorbing powder; in addition, the preparation method disclosed by the invention has the advantage of expanding the wave-absorbing frequency band of the wave-absorbing material.

Description

Technical Field

[0001] The present application relates to the technical field of absorbing materials, and more specifically, to a high-frequency absorbing material and a preparation method thereof. Background Art

[0002] With the development of electronic devices, all kinds of precision electronic components cannot do without the existence of absorbing materials. Absorbing materials can absorb and attenuate electromagnetic waves to reduce electromagnetic interference and electromagnetic compatibility problems. They can effectively convert incident electromagnetic waves into heat energy, thereby reducing the reflection and scattering of electromagnetic waves, and protecting surrounding electronic equipment and electronic components from electromagnetic interference. In addition, absorbing materials can also improve the performance and reliability of electronic equipment and reduce signal distortion and noise interference.

[0003] However, in various precision electronic components, such as high-speed connectors, the frequency span of electromagnetic waves is relatively large when they are working. The existing absorbing materials are generally targeted at a smaller frequency span of electromagnetic waves, such as targeting low-frequency bands or high-frequency bands, and cannot take both into account. This makes it easy for electromagnetic interference to occur when such electronic components are working, resulting in signal distortion and reduced transmission efficiency. Summary of the invention

[0004] In order to expand the absorbing frequency band of the absorbing material, the present application provides a high-frequency absorbing material and a preparation method thereof.

[0005] In a first aspect, the present application provides a high-frequency absorbing material, which adopts the following technical solution: A high-frequency absorbing material comprises the following raw materials in parts by weight: 20-35 parts of engineering plastic particles, 60-75 parts of absorbing powder, 3-5 parts of flame retardant, and 5-8 parts of auxiliary agent. The absorbing powder is composited by a resistive absorbing agent, a dielectric absorbing agent, and a soft magnetic absorbing powder.

[0006] By adopting the above technical solution, the absorbing powder is mixed with the engineering plastic particles, and the engineering plastic particles can be made into an integrally molded plastic product by injection or the like. The plastic product contains the absorbing powder, so that the injection molded product has an absorbing function and can be used in various types of precision electronic components. At the same time, the absorbing powder is composited by a resistive absorbing agent, a dielectric absorbing agent and a soft magnetic absorbing powder. The soft magnetic absorbing powder targets a lower absorbing frequency band, while the resistive absorbing agent and the dielectric absorbing agent target a higher absorbing frequency band, so that the plastic product can absorb waves in both low-frequency bands and high-frequency bands at the same time, and is suitable for electronic devices with a large frequency band span during operation.

[0007] Preferably, the engineering plastic particles are selected from one of polyamide, polycarbonate, polyimide, polyphenylene sulfide, aromatic polyamide, polyphenylene ester and polyarylate.

[0008] By adopting the above technical solution, the selected engineering plastic particles have good mechanical properties, heat resistance and easy processing, and have good insulation properties, are suitable for use in electronic devices, and can serve as a good carrier of absorbing materials.

[0009] Preferably, in the absorbing powder, the mass ratio of the resistive absorbing agent, the dielectric absorbing agent and the soft magnetic absorbing powder is (1.2-1.6):(0.5-0.8):(0.8-1.1).

[0010] By adopting the above technical solution and controlling the mass ratio of the resistive absorber, the dielectric absorber and the soft magnetic absorbing powder, the synergistic effect among the three can be optimized, so that the absorbing powder has a better absorbing effect for both low-frequency bands and high-frequency bands.

[0011] Preferably, the resistive wave absorbing agent comprises 20-36% conductive carbon black, 21-28% graphite, 11-17% carbon nanotubes, 15-23% carbon fiber, and 5-14% silicon carbide powder; The dielectric absorber comprises barium titanate and silicon nitride, wherein the mass ratio of barium titanate is 40-55%; The soft magnetic wave-absorbing powder comprises 25-40% of sendust, 35-45% of iron-silicon-chromium and 20-35% of carbonyl iron.

[0012] By adopting the above technical scheme, the resistive absorber is composed of a composite of conductive carbon black, graphite, carbon nanotubes, carbon fiber and silicon carbide powder, the dielectric absorber is composed of a composite of barium titanate and silicon nitride, and the combination of multiple components can effectively improve the absorbing effect in the high-frequency band. The soft magnetic absorbing powder is composed of a composite of iron silicon aluminum, iron silicon chromium and carbonyl iron, and the combination of the three can effectively absorb waves in the low-frequency band.

[0013] Preferably, the silicon carbide powder is selected from modified bamboo-shaped silicon carbide whiskers.

[0014] By adopting the above technical scheme, the bamboo-shaped silicon carbide whiskers have a large number of criss-crossed and overlapping microstructures. During crystallization, a large number of stacking fault defects are formed, and the density of the stacking fault defects is relatively large. A small amount of small silicon carbide particles are attached to the surface of the whiskers, and the specific surface area is large, which provides a large number of active sites for the scattering of electromagnetic waves and enhances the wave absorption capacity of the silicon nitride powder.

[0015] Preferably, the preparation method of the modified bamboo-shaped silicon carbide whisker comprises the following steps: dissolving barium nitrate and ferric nitrate in water, adding citric acid and adding bamboo-shaped silicon carbide whiskers after fully dissolving, adjusting the solution to neutrality with ammonia water while stirring, heating in a water bath at 85-90°C for 4-5h, drying at 110-120°C for 4-4.5h, heating to 850°C at a rate of 55-60°C / h, keeping warm for 1h, and cooling naturally to obtain modified bamboo-shaped silicon carbide whiskers.

[0016] By adopting the above technical scheme, barium ferrite is prepared by the citric acid sol-gel method, so that a layer of barium ferrite film is attached to the surface of the bamboo-shaped silicon carbide whisker. The barium ferrite can absorb electromagnetic waves by magnetic loss. When the barium ferrite is attached to the surface of the bamboo-shaped silicon carbide whisker, the modified bamboo-shaped silicon carbide whisker has the performance of absorbing low-frequency electromagnetic waves, which broadens the wave absorption frequency band of the modified bamboo-shaped silicon carbide whisker, and at the same time enhances the electromagnetic loss, effectively improving the wave absorption performance of the modified bamboo-shaped silicon carbide whisker.

[0017] Preferably, the graphite is treated as follows: adding the graphite to a mixed solution of concentrated sulfuric acid and ammonium persulfate, standing for 24 hours, washing and drying, then adding it to a potassium permanganate solution, mixing evenly, performing a hydrothermal reaction at 150-155° C. for 1 hour, filtering, washing, and drying.

[0018] By adopting the above technical scheme, graphite is treated with a mixed solution to obtain expanded graphite, and the expanded graphite is treated in a potassium permanganate solution to obtain expanded graphite composited with manganese dioxide. The hydrothermal reaction changes the morphology of manganese dioxide on the surface of the expanded graphite, increases the transmission path of electromagnetic waves inside the material, and improves the material's ability to resist polarization loss of electromagnetic waves.

[0019] In a second aspect, the present application provides a method for preparing a high-frequency absorbing material, using the following technical solution: A method for preparing a high-frequency absorbing material comprises the following steps: Mixing: After the resistive absorber and dielectric absorber are compounded by mechanical alloying, soft magnetic absorber powder, additives and flame retardant are added, and after ball milling and mixing evenly, engineering plastic particles are added and kneaded together; Granulation: Granulation temperature 160-330℃, rotation speed 15-45rpm, pelletizing speed 200-400rpm; Injection molding: The injection molding temperature is 180-350℃ and the pressure is 2-20Mpa to obtain the finished absorbing material.

[0020] By adopting the above technical solution, engineering plastic particles and absorbing powder are mixed and granulated together, and an integrally molded plastic product is obtained through injection molding. The plastic product has good absorbing effects for both low-frequency bands and high-frequency bands, and is suitable for electronic devices with a large frequency span when used.

[0021] In summary, this application has the following beneficial effects: 1. In the present application, the absorbing powder is mixed with the engineering plastic particles, and the engineering plastic particles can be made into an integrally molded plastic product by injection or the like. The plastic product contains the absorbing powder, so that the injection molded product has the function of absorbing waves and can be used in various precision electronic components. At the same time, the absorbing powder is compounded by a resistive absorbing agent, a dielectric absorbing agent and a soft magnetic absorbing powder. The soft magnetic absorbing powder has a smaller absorbing frequency band, while the resistive absorbing agent and the dielectric absorbing agent have a larger absorbing frequency band, so that the plastic product can absorb waves in both low-frequency bands and high-frequency bands at the same time, and is suitable for electronic devices with a larger frequency band span during operation; 2. In the present application, by controlling the mass ratio of the resistive absorber, the dielectric absorber and the soft magnetic absorber powder, the synergistic effect between the three can be optimized, so that the absorbing powder has a relatively good absorbing effect for both the low-frequency band and the high-frequency band; 3. In the present application, the resistive absorber is composed of conductive carbon black, graphite, carbon nanotubes, carbon fiber and silicon carbide powder, and the dielectric absorber is composed of barium titanate and silicon nitride. The multiple components cooperate with each other, which can effectively improve the absorbing effect for the high-frequency band. The soft magnetic absorbing powder is composed of iron silicon aluminum, iron silicon chromium and carbonyl iron. The three cooperate with each other to effectively absorb the low-frequency band. DETAILED DESCRIPTION

[0022] The present application is further described in detail below with reference to the embodiments.

[0023] Preparation Examples 1-4 of Modified Bamboo-Shaped Silicon Carbide Whiskers Preparation Example 1 The preparation method of bamboo-shaped silicon carbide whiskers comprises the following steps: mixing metal silicon powder and silicon dioxide, placing the mixture at the bottom of a crucible, placing a graphite paper with uniform small holes, placing bamboo charcoal powder on the graphite paper, wherein the mass ratio of metal silicon powder, silicon dioxide and bamboo charcoal powder is 1:1:3, sintering at 1400°C to obtain silicon carbide whiskers, decarbonizing the silicon carbide whiskers at 700°C, and desiliconizing them with hydrogen fluoride at room temperature to obtain pure silicon carbide whiskers.

[0024] The preparation method of modified bamboo-shaped silicon carbide whiskers comprises the following steps: dissolving barium nitrate and ferric nitrate in water at a molar ratio of 1:11, adding citric acid and fully dissolving the solution, wherein the molar ratio of citric acid to barium nitrate is 24:1, complexing ferric nitrate and barium nitrate with citric acid to obtain barium ferrite, adding bamboo-shaped silicon carbide whiskers, wherein the mass ratio of bamboo-shaped silicon carbide whiskers to barium ferrite is 1:1, adjusting the solution to be neutral with 28wt% ammonia water while stirring, heating the solution in a water bath at 85°C for 5h, drying the solution at 110°C for 4.5h, heating the solution to 850°C at a speed of 55°C / h, keeping the temperature for 1h, and cooling the solution naturally to obtain modified bamboo-shaped silicon carbide whiskers.

[0025] Preparation Example 2 The preparation method of bamboo-shaped silicon carbide whiskers comprises the following steps: mixing metal silicon powder and silicon dioxide, placing the mixture at the bottom of a crucible, placing a graphite paper with uniform small holes, placing bamboo charcoal powder on the graphite paper, wherein the mass ratio of metal silicon powder, silicon dioxide and bamboo charcoal powder is 1.1:1.2:2.9, sintering at 1400°C to obtain silicon carbide whiskers, decarbonizing the silicon carbide whiskers at 750°C, and desiliconizing them with hydrogen fluoride at room temperature to obtain pure silicon carbide whiskers.

[0026] The preparation method of modified bamboo-shaped silicon carbide whiskers comprises the following steps: dissolving barium nitrate and ferric nitrate in water at a molar ratio of 1:11, adding citric acid and fully dissolving the solution, wherein the molar ratio of citric acid to barium nitrate is 23.5:1, complexing ferric nitrate and barium nitrate with citric acid to obtain barium ferrite, adding bamboo-shaped silicon carbide whiskers, wherein the mass ratio of bamboo-shaped silicon carbide whiskers to barium ferrite is 1.1:1.2, adjusting the solution to be neutral with 30wt% ammonia water while stirring, heating the solution in a water bath at 90°C for 4h, drying the solution at 120°C for 4h, heating the solution to 850°C at a speed of 0°C / h, keeping the temperature for 1h, and cooling the solution naturally to obtain the modified bamboo-shaped silicon carbide whiskers.

[0027] Preparation Example 3 The difference between Preparation Example 3 and Preparation Example 1 is that the mass ratio of bamboo-shaped silicon carbide whiskers to barium ferrite is 1:0.5.

[0028] Preparation Example 4 The difference between Preparation Example 4 and Preparation Example 1 is that the mass ratio of bamboo-shaped silicon carbide whiskers to barium ferrite is 1:2. Example

[0029] Unless otherwise specified in this application, the conductive carbon black is XE2B produced by Orion, graphite is purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., carbon nanotubes are XFM13 produced by Jiangsu Xianfeng Nanomaterial Technology Co., Ltd., carbon fiber is purchased from Jiangxi Shuobang New Material Technology Co., Ltd., silicon carbide powder is XT-SIC-01 produced by Wuhu Jikang New Material Technology Co., Ltd., barium titanate is purchased from Shanghai Dianyang Industrial Co., Ltd., silicon nitride is purchased from Shanghai Xiangtian Nanomaterial Co., Ltd., iron silicon aluminum is purchased from Sichuan Xinjinchun Metal Materials Co., Ltd., iron silicon chromium is purchased from Sichuan Green Forest Technology Co., Ltd., and carbonyl iron is purchased from Xinxiang Sanyi Metal Materials Co., Ltd.

[0030] Example 1 A high-frequency absorbing material comprises the following raw materials in parts by mass: 20 kg of engineering plastic particles, 60 kg of absorbing powder, 3 kg of flame retardant, and 5 kg of auxiliary agent. The engineering plastic particles are polyamide purchased from Dongguan Wenteng Plastic Raw Material Co., Ltd., and the model is DuPont 101L of the United States. The flame retardant is Doher6333M produced by Dongguan Doher New Material Technology Co., Ltd., and the auxiliary agent is BYK-Max CT 4275 produced by BYK Chemical. The absorbing powder is composited by a resistive absorbing agent, a dielectric absorbing agent, and a soft magnetic absorbing powder in a mass ratio of 1.2:0.5:0.8, wherein the resistive absorbing agent comprises 30% of conductive carbon black, 25% of graphite, 12% of carbon nanotubes, 20% of carbon fiber, and 13% of silicon carbide powder. The dielectric absorbing agent comprises barium titanate and silicon nitride, wherein the mass ratio of barium titanate is 40%; and the soft magnetic absorbing powder comprises 30% of sendustine, 40% of iron silicon chromium, and 30% of carbonyl iron.

[0031] The method for preparing the high-frequency absorbing material comprises the following steps: Mixing: After the resistive absorber and the dielectric absorber are compounded by mechanical alloying, the soft magnetic absorber powder, the additive and the flame retardant are added, and after the mixture is evenly mixed by ball milling, the engineering plastic particles are added and kneaded together at 280°C for 10 minutes; Granulation: Granulation temperature 260℃, rotation speed 25rpm, pelletizing speed 280rpm; Injection molding: The injection molding temperature is 250°C and the pressure is 12Mpa to obtain the finished absorbing material.

[0032] Example 2 A high-frequency wave-absorbing material comprises the following raw materials in parts by weight: 35 kg of engineering plastic particles, 75 kg of wave-absorbing powder, 5 kg of flame retardant, and 8 kg of auxiliary agent. The engineering plastic particles are polyphenylene sulfide purchased from Dongguan Xinxin New Materials Co., Ltd., model A305M45 of Toray Japan. The flame retardant is MCA nitrogen flame retardant produced by Yueyang Petrochemical, and the auxiliary agent is 30610101 zinc stearate produced by Shanghai Better Chemical Co., Ltd.; The absorbing powder is composited by a resistive absorber, a dielectric absorber and a soft magnetic absorbing powder in a mass ratio of 1.6:0.8:1.1, wherein the resistive absorber includes 25% conductive carbon black, 28% graphite, 16% carbon nanotubes, 23% carbon fiber and 8% silicon carbide powder; the dielectric absorber includes barium titanate and silicon nitride, wherein the mass ratio of barium titanate is 55%; the soft magnetic absorbing powder includes 25% iron silicon aluminum, 40% iron silicon chromium and 35% carbonyl iron.

[0033] The method for preparing the high-frequency absorbing material comprises the following steps: Mixing: After the resistive absorber and the dielectric absorber are compounded by mechanical alloying, the soft magnetic absorber powder, the additive and the flame retardant are added, and after the mixture is evenly mixed by ball milling, the engineering plastic particles are added and kneaded together at 220°C for 10 minutes; Granulation: Granulation temperature 290℃, rotation speed 30rpm, pelletizing speed 300rpm; Injection molding: The injection molding temperature is 300°C and the pressure is 15Mpa to obtain the finished absorbing material.

[0034] Example 3 The difference between Example 3 and Example 1 is that in Example 3, the absorbing powder is composited by a resistive absorbing agent, a dielectric absorbing agent, and a soft magnetic absorbing powder in a mass ratio of 1.2:1.5:0.5.

[0035] Example 4 The difference between Example 4 and Example 1 is that in Example 4, the absorbing powder is composited by a resistive absorbing agent, a dielectric absorbing agent, and a soft magnetic absorbing powder in a mass ratio of 0.7:1.2:1.5.

[0036] Example 5 The difference between Example 5 and Example 1 is that in Example 5, the resistive absorber includes 30% conductive carbon black, 15% graphite, 28% carbon nanotubes, 10% carbon fiber, and 17% silicon carbide powder.

[0037] Example 6 The difference between Example 6 and Example 1 is that in Example 6, the resistive absorber includes 40% conductive carbon black, 15% graphite, 14% carbon nanotubes, 11% carbon fiber, and 20% silicon carbide powder.

[0038] Example 7 The difference between Example 7 and Example 1 is that in Example 7, the dielectric absorber includes barium titanate and silicon nitride, wherein the mass ratio of barium titanate is 30%.

[0039] Example 8 The difference between Example 8 and Example 1 is that in Example 8, the dielectric absorber includes barium titanate and silicon nitride, wherein the mass ratio of barium titanate is 60%.

[0040] Example 9 The difference between Example 9 and Example 1 is that in Example 9, the soft magnetic wave-absorbing powder includes 20% of sendustine, 50% of iron silicon chromium, and 30% of carbonyl iron.

[0041] Example 10 The difference between Example 10 and Example 1 is that in Example 10, the soft magnetic wave-absorbing powder includes 50% of sendustine, 25% of iron silicon chromium, and 25% of carbonyl iron.

[0042] Embodiment 11 The difference between Example 11 and Example 1 is that in Example 11, the silicon carbide powder is the modified bamboo-shaped silicon carbide whisker obtained in Preparation Example 1.

[0043] Example 12 The difference between Example 12 and Example 1 is that in Example 12, the silicon carbide powder is the modified bamboo-shaped silicon carbide whiskers prepared in Preparation Example 2.

[0044] Example 13 The difference between Example 13 and Example 1 is that in Example 13, the silicon carbide powder is the modified bamboo-shaped silicon carbide whiskers prepared in Preparation Example 3.

[0045] Embodiment 14 The difference between Example 14 and Example 1 is that in Example 14, the silicon carbide powder is the modified bamboo-shaped silicon carbide whiskers prepared in Preparation Example 4.

[0046] Embodiment 15 The difference between Example 15 and Example 1 is that in Example 15, the graphite is treated as follows: the graphite is added to a mixed solution of concentrated sulfuric acid and ammonium persulfate, the mass ratio of graphite, ammonium persulfate and concentrated sulfuric acid is 1:5:3, after standing for 24 hours, washed and dried, and then added to 70mL0.45g / L potassium permanganate solution, the mass ratio of expanded graphite to potassium permanganate is 6.4:1, mixed evenly, hydrothermally reacted at 150°C for 1 hour, filtered, washed and dried.

[0047] Example 16 The difference between Example 16 and Example 1 is that in Example 16, the graphite is treated as follows: the graphite is added to a mixed solution of concentrated sulfuric acid and ammonium persulfate, the mass ratio of graphite, ammonium persulfate and concentrated sulfuric acid is 1:5:3, after standing for 24 hours, washed and dried, and then added to 75mL0.48g / L potassium permanganate solution, the mass ratio of expanded graphite to potassium permanganate is 6:1, mixed evenly, and hydrothermally reacted at 155°C for 1 hour, filtered, washed, and dried.

[0048] Embodiment 17 The difference between Example 17 and Example 15 is that the mass ratio of expanded graphite to potassium permanganate is 4:1.

[0049] Embodiment 18 The difference between Example 18 and Example 15 is that the mass ratio of expanded graphite to potassium permanganate is 8:1.

[0050] Comparative Example Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that in Comparative Example 1, an equal amount of resistive absorbing agent is used to replace the absorbing powder.

[0051] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that in Comparative Example 2, an equal amount of dielectric absorbent is used to replace the absorbing powder.

[0052] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that in Comparative Example 3, an equal amount of soft magnetic absorbing powder is used to replace the absorbing powder.

[0053] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that in Comparative Example 4, the following raw materials are included in parts by mass: 40 kg of engineering plastic particles, 40 kg of absorbing powder, 3 kg of flame retardant, and 5 kg of auxiliary agent. The selection of engineering plastic particles, absorbing powder, flame retardant and auxiliary agent is the same as that in Example 1.

[0054] Comparative Example 5 The difference between Comparative Example 5 and Example 1 is that in Comparative Example 5, the following raw materials are included in parts by mass: 30 kg of engineering plastic particles, 90 kg of absorbing powder, 5 kg of flame retardant, and 8 kg of auxiliary agent. The selection of engineering plastic particles, absorbing powder, flame retardant and auxiliary agent is the same as that in Example 1.

[0055] Performance testing According to the raw materials and preparation methods of Examples 1-18 and Comparative Examples 1-5, absorbing materials were prepared. The thickness of the absorbing materials was 2 mm. The reflection loss in the frequency range of 1-100 GHz was tested using a vector network analyzer. The frequency bands with reflection loss <-10 dB and the reflection loss of each absorbing material at 25 GHz and 77 GHz were recorded. The results are recorded in Table 1.

[0056] Table 1 Absorption performance of absorbing materials According to Table 1, Examples 1-2 and Comparative Examples 1-5, it can be seen that the absorbing material prepared in Examples 1-2 has a wider absorbing frequency band, and the reflection loss of electromagnetic waves is smaller in the two frequency bands of 25 GHz and 77 GHz, indicating that the absorbing material prepared in Examples 1-2 has better absorbing performance. In Examples 1-2, absorbing powder is added to the engineering plastic particles, so that the injection molded absorbing material has good absorbing performance. The absorbing powder is composited by a resistive absorbing agent, a dielectric absorbing agent and a soft magnetic absorbing powder. The type absorber absorbs electromagnetic waves by interacting with the electric field, while the dielectric absorber absorbs electromagnetic waves by dielectric polarization relaxation loss. The combination of the two can make the absorbing material have good absorbing performance for electromagnetic waves in the high-frequency band. The soft magnetic absorbing powder can convert electromagnetic waves into other forms such as heat energy to absorb electromagnetic waves. The absorbing material formed by the combination of the three can have good absorbing performance for both low-frequency bands and high-frequency bands, thereby broadening the absorbing frequency band of the absorbing material and making the absorbing material have excellent absorbing performance in high-frequency bands and low-frequency bands.

[0057] Compared with Example 1-2, Comparative Example 1-3 uses equal amounts of resistive absorber, dielectric absorber and soft magnetic absorbing powder to replace the absorbing powder, indicating that the effects of the resistive absorber, dielectric absorber and soft magnetic absorbing powder used alone are reduced compared with the absorbing powder formed by compounding the three in a specific mass ratio. The resistive absorber, dielectric absorber and soft magnetic absorbing powder target different electromagnetic wave frequency bands and absorb electromagnetic waves in different ways. Their combined use has a synergistic effect and can take into account both low-frequency and high-frequency bands. When used alone, the absorbing material has a worse absorbing effect on the high-frequency band or a worse absorbing effect on the low-frequency band, and the absorbing frequency band of the absorbing material becomes narrower. At the same time, when used alone, the absorbing performance is reduced, thereby increasing the reflection loss of each frequency band.

[0058] Compared with Examples 1-2, Comparative Examples 4-5 changed the addition amounts of engineering plastic particles and absorbing powder in the raw materials, indicating that the addition amounts of engineering plastic particles and absorbing powder have an impact on the absorbing performance of the finished absorbing material. When the addition amount of absorbing powder is reduced, the content of absorbing powder in the finished absorbing material is reduced, thereby reducing the absorption performance of the absorbing material for electromagnetic waves. When the addition amount of absorbing powder is increased, the content of absorbing powder in the finished absorbing material is increased, which easily causes the absorbing powder to agglomerate and entangle, resulting in uneven distribution, thereby affecting the absorbing performance of the absorbing material.

[0059] Compared with Example 1, the absorbing frequency band of the absorbing material prepared in Example 3-4 is narrowed, and the reflection loss of electromagnetic waves increases in the two frequency bands of 25 GHz and 77 GHz. Example 3-4 changes the mass ratio of the resistive absorber, the dielectric absorber, and the soft magnetic absorbing powder in the absorbing powder, indicating that the resistive absorber, the dielectric absorber, and the soft magnetic absorbing powder have a synergistic effect, and the composite absorbing powder has good absorbing effects on both high-frequency and low-frequency bands, and has a better absorption effect on electromagnetic waves. When the mass ratio between the three is changed, the synergistic effect is weakened, the absorbing frequency band is narrowed, the reflection loss increases, and the absorbing performance is reduced.

[0060] Compared with Example 1, the absorbing frequency band of the absorbing material prepared in Example 5-10 is narrowed, and the reflection loss of electromagnetic waves increases at the two frequency bands of 25 GHz and 77 GHz. Example 5-6 changes the mass ratio of each component in the resistive absorbing agent, Example 7-8 changes the mass ratio of each component in the dielectric absorbing agent, and Example 9-10 changes the mass ratio of each component in the soft magnetic absorbing powder, indicating that the resistive absorbing agent is composed of conductive carbon black, graphite, carbon nanotubes, carbon fibers and silicon carbide powder, and there is a synergistic effect between the components. , which can effectively improve the absorbing performance of the resistive absorber in the high-frequency band. The dielectric absorber is composed of barium titanate and silicon nitride in a certain mass ratio, which can effectively improve the absorbing effect of the dielectric absorber in the high-frequency band. The soft magnetic absorbing powder is composed of iron silicon aluminum, iron silicon chromium and carbonyl iron. There is a good synergistic effect between the three, which improves the absorbing performance of the absorbing material in the low-frequency band. The composition of the resistive absorber, the dielectric absorber and the soft magnetic absorbing powder changes, which reduces the synergistic effect between the components and reduces the absorbing performance of the absorbing material.

[0061] Compared with Example 1, the absorbing materials prepared in Examples 11-12 have smaller reflection losses of electromagnetic waves at both 25 GHz and 77 GHz frequency bands. In Examples 11-12, modified bamboo-shaped silicon carbide whiskers are used instead of commercially available silicon carbide powder. The bamboo-shaped silicon carbide whiskers have a large number of criss-crossed and overlapping microstructures. A large number of stacking fault defects provide a large specific surface area, provide a large number of active sites for the scattering of electromagnetic waves, and enhance the absorbing ability of silicon nitride powder. The bamboo-shaped silicon carbide whiskers are modified, and a layer of barium ferrite film is attached to the surface. The barium ferrite can absorb electromagnetic waves by magnetic loss. The prepared modified bamboo-shaped silicon carbide whiskers also have good absorption capacity for low-frequency electromagnetic waves, thereby enhancing the absorbing ability of the absorbing powder.

[0062] Compared with Example 11, the absorbing materials prepared in Examples 13-14 have increased reflection loss of electromagnetic waves in the two frequency bands of 25 GHz and 77 GHz. During the preparation of the modified bamboo-shaped silicon carbide whiskers used in Examples 13-14, the mass ratio of the bamboo-shaped silicon carbide whiskers to the barium ferrite was changed. The mass ratio of the bamboo-shaped silicon carbide whiskers to the barium ferrite directly affects the thickness and morphology of the barium ferrite film on the surface of the bamboo-shaped silicon carbide whiskers. When the mass ratio is too high or too low, the morphology of the barium ferrite film is poor, the magnetic loss effect on electromagnetic waves is reduced, and the performance of the absorbing material is reduced.

[0063] Compared with Example 1, the absorbing materials prepared in Examples 15-16 have smaller reflection losses of electromagnetic waves at both 25 GHz and 77 GHz frequency bands. The graphite used in Examples 15-16 has been modified. After expansion and compounding with manganese dioxide, the graphite can adjust impedance matching, increase the transmission path of electromagnetic waves inside the material, and improve the material's ability to resist polarization loss of electromagnetic waves, thereby improving the absorbing ability of the absorbing powder.

[0064] Compared with Example 15, the absorbing materials prepared in Examples 17-18 have increased reflection losses of electromagnetic waves at the two frequency bands of 25 GHz and 77 GHz. When preparing the graphite used in Examples 17-18, the mass ratio of expanded graphite to potassium permanganate was changed. The mass ratio of expanded graphite to potassium permanganate affected the distribution of manganese dioxide on the surface of expanded graphite. A too high mass ratio reduced the content of manganese dioxide and weakened the reinforcing effect of manganese dioxide on graphite. A too low mass ratio resulted in uneven distribution of manganese dioxide on the surface of expanded graphite, thereby affecting the absorbing ability of the treated graphite.

[0065] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A high-frequency absorbing material, characterized in that: The invention comprises the following raw materials in parts by weight: 20-35 parts of engineering plastic particles, 60-75 parts of absorbing powder, 3-5 parts of flame retardant and 5-8 parts of auxiliary agent. The absorbing powder is compounded by resistive absorbing agent, dielectric absorbing agent and soft magnetic absorbing powder.

2. The high-frequency absorbing material according to claim 1, characterized in that: The engineering plastic particles are selected from one of polyamide, polycarbonate, polyimide, polyphenylene sulfide, aromatic polyamide, polyphenyl ester and polyarylate.

3. The high-frequency absorbing material according to claim 1, characterized in that: In the absorbing powder, the mass ratio of the resistive absorbing agent, the dielectric absorbing agent and the soft magnetic absorbing powder is (1.2-1.6):(0.5-0.8):(0.8-1.1).

4. The high-frequency absorbing material according to claim 3, characterized in that: The resistive wave absorbing agent comprises 20-36% conductive carbon black, 21-28% graphite, 11-17% carbon nanotubes, 15-23% carbon fiber, and 5-14% silicon carbide powder; The dielectric absorber comprises barium titanate and silicon nitride, wherein the mass ratio of barium titanate is 40-55%; The soft magnetic wave-absorbing powder comprises 25-40% of sendustine, 35-45% of iron silicon chromium and 20-35% of carbonyl iron.

5. The high-frequency absorbing material according to claim 4, characterized in that: The silicon carbide powder is selected from modified bamboo-shaped silicon carbide whiskers.

6. The high-frequency absorbing material according to claim 5, characterized in that: The preparation method of the modified bamboo-shaped silicon carbide whisker comprises the following steps: dissolving barium nitrate and ferric nitrate in water, adding citric acid and fully dissolving the solution, then adding the bamboo-shaped silicon carbide whisker, adjusting the solution to be neutral with ammonia water while stirring, heating the solution in a water bath at 85-90°C for 4-5h, drying the solution at 110-120°C for 4-4.5h, heating the solution to 850°C at a speed of 55-60°C / h, keeping the temperature for 1h, and cooling the solution naturally to obtain the modified bamboo-shaped silicon carbide whisker.

7. The high-frequency absorbing material according to claim 4, characterized in that: The graphite is treated as follows: adding the graphite to a mixed solution of concentrated sulfuric acid and ammonium persulfate, standing for 24 hours, washing and drying, then adding it to a potassium permanganate solution, mixing evenly, performing a hydrothermal reaction at 150-155° C. for 1 hour, filtering, washing, and drying.

8. A method for preparing a high-frequency absorbing material according to any one of claims 1 to 7, characterized in that: The following steps are involved: Mixing: After the resistive absorber and dielectric absorber are compounded by mechanical alloying, soft magnetic absorber powder, additives and flame retardant are added, and after ball milling and mixing evenly, engineering plastic particles are added and kneaded together; Granulation: Granulation temperature 160-330℃, rotation speed 15-45rpm, pelletizing speed 200-400rpm; Injection molding: The injection molding temperature is 180-350℃ and the pressure is 2-20Mpa to obtain the finished absorbing material.

Images