Magnetic wave-absorbing composite material, preparation method and application thereof

Abstract

The application relates to a magnetic wave-absorbing composite material and a preparation method and application thereof, and relates to the technical field of electromagnetic wave-absorbing materials.The composite material comprises a magnetic mixed-weaving fiber web tire preform and a resin matrix filled in the gap of the magnetic mixed-weaving fiber web tire preform; the magnetic mixed-weaving fiber web tire preform comprises a magnetic mixed-weaving fiber web tire single piece composed of magnetic wave-absorbing fibers and wave-transparent fibers.The magnetic component is introduced into the organic fibers in advance and is carbonized at high temperature, so that the magnetic wave-absorbing fibers and the wave-transparent fibers are uniformly mixed and woven, and the problems of poor wave-absorbing effect and narrow frequency band caused by uneven dispersion of wave-absorbing agents in traditional wave-absorbing materials are solved.The material has excellent wave-absorbing performance and mechanical strength.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electromagnetic wave absorbing materials, in particular to a magnetic wave-absorbing composite material and a preparation method and application thereof. BACKGROUND

[0002] With the development of electronic information technology, the rapid increase of electromagnetic radiation brings greater challenges. Therefore, the development of efficient electromagnetic wave absorbing materials has become the key to solving the above problems. Wave-absorbing materials can effectively absorb electromagnetic waves and convert them into heat or other forms of energy, which is of great significance for reducing electromagnetic interference and meeting the needs of civil electromagnetic protection.

[0003] Wave-absorbing materials are mainly divided into two categories: coating type and structural type. Coating type wave-absorbing materials are usually composed of conductive or magnetic particles dispersed in a polymer matrix and coated on the surface of the target. They have the advantages of simple preparation and flexible application, but have the problems of large mass, easy peeling, narrow absorption frequency band, etc. In contrast, structural type wave-absorbing materials combine wave-absorbing function with structural bearing, such as wave-absorbing honeycomb, sandwich structure and wave-absorbing foam, etc. They have good mechanical properties, thermal stability and designability, and can realize the integration of structure and function, which has become an important direction of wave-absorbing material development.

[0004] The existing technology for preparing fiber-reinforced resin-based structural wave-absorbing composite materials usually uses carbon materials as wave-absorbing agents, which have a single loss mechanism for electromagnetic waves and are prone to cause impedance mismatch. Meanwhile, the common preparation methods include mixing wave-absorbing particles into the resin matrix or loading wave-absorbing particles onto the surface of the fibers. However, these methods have the problem of uneven dispersion or loading of wave-absorbing particles, resulting in poor wave-absorbing effect. In addition, these methods have low production efficiency and poor repeatability, which brings difficulties to practical application. SUMMARY

[0005] In view of the above analysis, the present application aims to provide a magnetic wave-absorbing composite material and a preparation method and application thereof, which can solve one of the following technical problems: (1) coating type wave-absorbing materials are prone to peeling and falling off, and have a narrow effective absorption frequency band, which affects the overall wave-absorbing performance; (2) the existing preparation methods of wave-absorbing materials are complex, and have a single loss mechanism, resulting in poor reflection loss effect and a narrow wave-absorbing frequency band.

[0006] The magnetic wave-absorbing composite material of the present application does not need to add additional wave-absorbing agents, and can significantly improve the wave-absorbing performance while ensuring a certain mechanical strength by adjusting the components of the wave-absorbing composite, i.e., it can widen the effective absorption bandwidth under the condition of low reflection loss.

[0007] The first aspect of the present application provides a magnetic wave-absorbing composite material, which comprises a magnetic mixed fiber web tire preform and a resin matrix filled in the gap of the magnetic mixed fiber web tire preform.

[0008] The magnetic mixed fiber web tire preform comprises a magnetic mixed fiber web tire single piece composed of the magnetic wave-absorbing fiber and the wave-transparent fiber.

[0009] Further, in the mixed fiber web tire preform, the number of the magnetic mixed fiber web tire single pieces is greater than or equal to 5.

[0010] Further, in the mixed fiber web tire preform, the mass percentage of the magnetic wave-absorbing fiber is 10-50%.

[0011] Further, the magnetic wave-absorbing fiber is obtained by carbonizing the magnetic organic fiber.

[0012] Further, the magnetic organic fiber is obtained by modifying the organic fiber with a magnetic component.

[0013] Further, the magnetic component comprises at least one of iron, cobalt, nickel, and oxides of the above-mentioned metals.

[0014] Further, in the composite material, the content of the magnetic mixed fiber web tire preform is 30-50wt%, and the content of the resin matrix is 50-70wt%.

[0015] Further, the resin matrix is selected from at least one of phenolic resin, silicone resin and epoxy resin.

[0016] Further, the density of the magnetic mixed fiber web tire preform is 0.16-0.4g / cm 3 , and the thickness is 2-20mm.

[0017] The second aspect of the application provides a preparation method of the magnetic wave-absorbing composite material, comprising the following steps:

[0018] S1, after the surface of the organic fiber is pretreated, a magnetic component is introduced to obtain a magnetic organic fiber;

[0019] S2, the magnetic organic fiber is carbonized at high temperature in the presence of a protective gas to obtain a magnetic wave-absorbing fiber;

[0020] S3, the magnetic wave-absorbing fiber and the wave-transparent fiber are uniformly mixed to obtain a magnetic mixed fiber web tire single piece, and then a magnetic mixed fiber web tire preform is prepared by a needle punching process;

[0021] S4, the magnetic mixed fiber web tire preform is placed in a mold, a resin matrix is vacuum impregnated, and then cured to form a magnetic wave-absorbing composite material;

[0022] The conditions of the high-temperature carbonization include: the carbonization temperature is 600-900℃, the heating rate is 1-8℃ / min, and the holding time is 1-4h.

[0023] Further, in step S1, the surface pretreatment comprises: soaking the organic fiber with an organic solvent, cleaning, and then activating with an acid solution or an alkali solution.

[0024] Further, the concentration of the acid solution is 0.1-1 mol / L in terms of hydrogen ions.

[0025] Alternatively, the concentration of the alkali solution is 0.1-1 mol / L in terms of hydroxyl ions.

[0026] Further, in step S1, the step of introducing the magnetic component comprises: under stirring, soaking the organic fiber after surface pretreatment in a solution containing the magnetic component at 25-60℃ for 12-24h.

[0027] Further, the concentration of the magnetic component solution is 0.3-1.5 mol / L.

[0028] Further, the magnetic component is selected from at least one of iron salt, cobalt salt and nickel salt.

[0029] Further, in step S3, the vacuum degree during vacuum impregnation is -0.05 to -0.15 MPa.

[0030] Further, the solidification forming conditions comprise: a solidification temperature of 80-100℃ and a solidification time of 8-12h.

[0031] The third aspect of the present application provides a use of the wave-absorbing composite material of the first aspect in electromagnetic protection.

[0032] Compared with the prior art, the present application can achieve at least one of the following beneficial effects:

[0033] 1. The magnetic wave-absorbing composite material of the present application does not need to add wave-absorbing agents during the forming process, nor does it need to add auxiliary processes. It only relies on the co-solidification of the mixed fiber web tire preform and the resin matrix to form once, without the need to increase new production processes, with high production efficiency. The prepared composite material has excellent wave-absorbing performance and excellent mechanical strength, has certain load-bearing capacity, and meets the load-bearing-wave-absorbing integrated design requirements.

[0034] 2、The application can produce a large number of heterogeneous interfaces by uniformly dispersing the magnetic wave-absorbing fibers in the wave-transparent fibers, and the magnetic wave-absorbing fibers are connected with each other to form a three-dimensional conductive network, and synergize with the magnetic components, the magnetic wave-absorbing fibers bear the function of electromagnetic loss, the wave-transparent fibers maintain the dielectric window and transfer the load, the mixed weaving of the two avoids the reflection surge caused by local aggregation of the conductive / magnetic phase in three-dimensional space, enhances the interface polarization loss through electromagnetic loss and dielectric loss, enhances the electric conduction loss, further improves the wave-absorbing effect, and avoids the performance drop caused by narrow frequency band of a single loss mechanism.

[0035] 3、The wave-absorbing composite material prepared by the application has strong designability and simple process, and different wave-absorbing effects of the composite material can be prepared by changing the carbonization temperature of the organic fiber, the proportion of the magnetic wave-absorbing fiber and the wave-transparent fiber, the content of the magnetic component, the density and thickness of the mixed fiber web tire preform, so as to meet the application requirements of different scenes.

[0036] The above technical solutions can be combined with each other in the application to realize more preferred combination solutions. Other features and advantages of the application will be described in the subsequent specification, and some advantages will become apparent from the specification, or will be understood by implementing the application. The purpose and other advantages of the application can be realized and obtained from the contents specifically pointed out in the specification and the drawings. BRIEF DESCRIPTION OF DRAWINGS

[0037] The accompanying drawings are included to provide a further understanding of the application and are incorporated herein and constitute a part of the application. The drawings illustrate embodiments of the application and, together with the description, serve to explain the principles of the application. In the drawings:

[0038] Figure 1 A schematic diagram of the microstructure of the magnetic wave-absorbing composite material prepared in Example 1 of the application;

[0039] Figure 2a The reflection loss curve of the magnetic wave-absorbing composite material prepared in Example 1 under different matching thicknesses;

[0040] Figure 2b The reflection loss curve of the magnetic wave-absorbing composite material prepared in Example 2 under different matching thicknesses;

[0041] Figure 2c The reflection loss curve of the magnetic wave-absorbing composite material prepared in Example 3 under different matching thicknesses;

[0042] Figure 2d The reflection loss curve of the magnetic wave-absorbing composite material prepared in Example 4 under different matching thicknesses. DETAILED DESCRIPTION

[0043] Preferred embodiments of the present application are described in detail below with reference to the attached drawings, wherein:

[0044] The present application provides a magnetic wave-absorbing composite material, which comprises a magnetic mixed-weaving fiber web tire preform and a resin matrix filled in the gap of the magnetic mixed-weaving fiber web tire preform.

[0045] The magnetic mixed-weaving fiber web tire preform comprises a magnetic mixed-weaving fiber web tire monolithic piece composed of magnetic wave-absorbing fibers and wave-transparent fibers.

[0046] Compared with the prior art, the magnetic wave-absorbing composite material of the present application does not need to add wave-absorbing agents in the forming process, nor does it need to add auxiliary processes. It only relies on the co-curing of the mixed-weaving fiber web tire preform and the resin matrix to form once, without the need to increase new production processes, and has high production efficiency. The prepared composite material has excellent wave-absorbing performance and excellent mechanical strength, has certain load-carrying capacity, and meets the design requirements of load-absorption integration.

[0047] It should be noted that the magnetic mixed-weaving fiber web tire preform has a three-dimensional net-like structure, and the magnetic mixed-weaving fiber web tire monolithic piece is composed of magnetic wave-absorbing fibers and wave-transparent fibers by interweaving, winding or other methods.

[0048] In the present application, the magnetic wave-absorbing fibers are uniformly dispersed in the wave-transparent fibers to generate a large number of heterogeneous interfaces. At the same time, the magnetic wave-absorbing fibers are connected to each other to form a three-dimensional conductive network, and synergistically work with the magnetic component. That is, the magnetic wave-absorbing fibers bear the function of electromagnetic loss, the wave-transparent fibers maintain the dielectric window and transfer the load, and the mixed weaving of the two makes the electrically conductive / magnetically conductive phase avoid the reflection surge caused by local aggregation in three-dimensional space, enhances the interface polarization loss through electromagnetic loss and dielectric loss, enhances the electric conduction loss, further improves the wave-absorbing effect, and avoids the performance drop caused by the narrow frequency band of a single loss mechanism.

[0049] In the present application, considering the penetration of electromagnetic waves and the synergistic improvement of the wave-absorbing effect with the magnetic wave-absorbing fibers, the wave-transparent fibers are selected from at least one of glass fibers, quartz fibers, aramid fibers and high-silica fibers.

[0050] According to some embodiments of the present application, the number of magnetic mixed-weaving fiber web tire monolithic pieces in the mixed-weaving fiber web tire preform is greater than or equal to 5.

[0051] In the present application, the inventor found that the number of the magnetic mixed fiber web tire monolithic piece is greater than or equal to 5, which can ensure the thickness of the magnetic mixed fiber web tire preform, and further make the absorbed electromagnetic wave fully dissipate in the material, thereby improving the wave absorption effect of the composite material, for example, 5 pieces, 6 pieces, 7 pieces, 8 pieces, 10 pieces, 12 pieces, 14 pieces, 15 pieces, and preferably 6-10 pieces.

[0052] According to some embodiments of the present application, the mass percentage of the magnetic wave-absorbing fiber in the mixed fiber web tire preform is 10-50%.

[0053] In the present application, the inventor found that when the mass percentage of the magnetic wave-absorbing fiber is less than 10%, the magnetic loss capacity of the composite material is weak, and the overall wave absorption performance is poor. If the percentage is too high (>50%), the overall electrical conductivity or dielectric constant of the composite material is too high, the electromagnetic wave is reflected on the surface of the material in large quantities and cannot enter the interior (impedance mismatch), which also reduces the wave absorption effect.

[0054] For example, the mass percentage of the magnetic wave-absorbing fiber is 10%, 15%, 20%, 25%, 30%, 32%, 38%, 40%, 45%, 46%, 50%, and a range formed by any two of the above values. Considering the loss capacity and impedance matching balance of the composite material, the mass percentage of the magnetic wave-absorbing fiber in the mixed fiber web tire preform is preferably 20-35%.

[0055] According to some embodiments of the present application, the magnetic wave-absorbing fiber is obtained by carbonizing a magnetic organic fiber.

[0056] In the present application, the inventor found that after high-temperature carbonization of the organic fiber, non-carbon elements can be removed to construct a carbon skeleton. The carbon atoms are rearranged into continuous conjugated sp2 graphite microzones to form delocalized pi bonds, and the electrons can move freely in the entire network to form a conductive channel, realizing the conversion of electromagnetic energy into heat energy, and balancing the mechanical bearing and absorption bandwidth.

[0057] According to some embodiments of the present application, the magnetic organic fiber is obtained by modifying an organic fiber with a magnetic component.

[0058] In the present application, modifying the organic fiber with the magnetic component can make the organic fiber efficiently dissipate electromagnetic energy through hysteresis loss, natural resonance, eddy current loss, and other mechanisms, further improving the wave absorption effect.

[0059] In the present application, specifically, in order to provide an electromagnetic loss basis for the magnetic wave-absorbing composite material, the organic fiber is selected from at least one of phenolic fiber, polyimide fiber, biomass fiber, and viscose fiber.

[0060] According to some embodiments of the present application, the magnetic component comprises at least one of iron, cobalt, nickel, and oxides of the above-mentioned metals.

[0061] According to some embodiments of the present application, in the composite material, the content of the magnetic mixed fiber web tire preform is 30-50wt%, such as 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, and the content of the resin matrix is 50-70wt%, such as 50wt%, 55wt%, 65wt%, 65wt%, 70wt%.

[0062] In the present application, the content of the magnetic mixed fiber web tire preform meets the above range, which can ensure that the composite material has sufficient magnetic wave-absorbing fibers to ensure performance, and has sufficient resin to fully infiltrate the fibers and fill the pores, forming a dense and strong whole to ensure mechanical properties. Too little resin will lead to incomplete infiltration and defects such as pores, and the mechanical properties will decrease; too much resin will reduce the wave-absorbing efficiency.

[0063] According to some embodiments of the present application, the resin matrix is selected from at least one of phenolic resin, silicone resin, and epoxy resin. In the present application, the resin matrix is exemplarily a nanoporous silicone resin, and the average pore size of the resin matrix is 20-70nm.

[0064] According to some embodiments of the present application, the density of the magnetic mixed fiber web tire preform is 0.16-0.4g / cm 3 , such as 0.16g / cm 3 , 0.18g / cm 3 , 0.2g / cm 3 , 0.25g / cm 3 , 0.3g / cm 3 , 0.35g / cm 3 , 0.4g / cm 3 , and the thickness is 2-20mm, such as 2mm, 3mm, 5mm, 10mm, 12mm, 15mm, 16mm, 20mm.

[0065] In the present application, when the density of the mixed fiber web tire preform meets the above range, it can provide a certain storage space for the resin matrix, and also can accommodate and disperse the magnetic wave-absorbing fibers, form a large number of interfaces, induce multiple reflections and scattering, greatly extend the propagation path of electromagnetic waves in the material, increase the probability of being lost by the magnetic wave-absorbing fibers, and thus significantly improve the wave-absorbing efficiency.

[0066] The second aspect of the present application provides a preparation method of a magnetic wave-absorbing composite material, comprising the following steps:

[0067] S1, introducing a magnetic component to the organic fiber after surface pretreatment to obtain a magnetic organic fiber;

[0068] S2, carbonizing the magnetic organic fiber at high temperature in the presence of a protective gas to obtain a magnetic wave-absorbing fiber;

[0069] S3, uniformly mixing the magnetic wave-absorbing fiber with a wave-transparent fiber to prepare a magnetic mixed fiber web tire single piece, and then preparing a magnetic mixed fiber web tire preform through a needle punching process;

[0070] S4, placing the magnetic mixed fiber web tire preform in a mold, vacuum impregnating a resin matrix, and then curing to obtain a magnetic wave-absorbing composite material;

[0071] The high-temperature carbonization conditions include: a carbonization temperature of 600-900℃, a heating rate of 1-8℃ / min, and a holding time of 1-4h.

[0072] It should be noted that the inventors have found through a large number of experiments that the carbonization temperature has a great influence on the wave-absorbing effect of the final magnetic wave-absorbing composite material. A suitable carbonization temperature can make the obtained carbon fiber have a suitable electrical conductivity to fully utilize its dielectric loss effect, and at the same time, the electromagnetic loss provided by the magnetic component can be used together to consume electromagnetic waves. If the carbonization temperature is less than 600℃, there will be more non-carbon elements remaining and the ordered degree of the carbon skeleton is low, resulting in a low electrical conductivity, which is not conducive to the consumption of electromagnetic waves, thereby affecting the wave-absorbing effect. If the carbonization temperature is greater than 900℃, the graphitization trend will be increased, the electrical conductivity will be too high, and the electromagnetic waves will be totally reflected, which will also reduce the wave-absorbing effect. Illustratively, the carbonization temperature is 600℃, 650℃, 700℃, 800℃, 850℃, 900℃, or a range formed by any two of the above values, and is preferably 600-750℃.

[0073] Further specifically, the heating rate meets the above range, which helps the organic fiber to stably decompose small molecule gases and avoid fiber morphology damage (such as bubbling and fusion) caused by violent reaction, so as to maintain the morphological integrity of the fiber and obtain a magnetic wave-absorbing fiber with good structure. At the same time, the holding time meets the above range, which can further ensure sufficient and uniform carbonization.

[0074] According to some embodiments of the present application, in step S1, the surface pretreatment includes: soaking the organic fiber with an organic solvent, washing, and then activating with an acid solution or an alkali solution.

[0075] It should be noted that the surface of the organic fiber is pre-treated as above, so that the oil stains and impurities such as oligomers on the surface of the organic fiber are removed, so that the subsequent adsorption of the magnetic component is facilitated, and the acid solution or the alkali solution can further enhance the activity of the functional groups (such as carboxyl, hydroxyl, amino, etc.) in the organic fiber, promote the adsorption and coordination of the magnetic component, so that the wave absorption effect of the composite material is significantly improved through electromagnetic loss and dielectric loss under the premise of ensuring the mechanical properties of the composite material.

[0076] It can be understood that the soaking refers to standing in an organic solvent at 20-40℃ for 1-2h, and the cleaning can be ultrasonic cleaning for 30-60min.

[0077] It can be understood that the organic solvent includes at least one of ethanol, isopropanol and acetone.

[0078] According to some embodiments of the present application, the concentration of the acid solution is 0.1-1mol / L in terms of hydrogen ions; or the concentration of the alkali solution is 0.1-1mol / L in terms of hydroxyl ions.

[0079] In the present application, it should be noted that the acid solution or the alkali solution meeting the above concentration can not only enhance the activity of the functional groups (such as carboxyl, hydroxyl, amino, etc.) in the organic fiber, promote the adsorption and coordination of the magnetic component, but also increase the roughness of the surface of the organic fiber, greatly improve the adhesion and loading capacity of the subsequent magnetic component on the fiber surface, prevent shedding, and ensure the stability of the wave absorption effect.

[0080] It can be understood that the conditions for activating the organic fiber by the acid solution or the alkali solution include standing in the acid solution or the alkali solution for 10-30min, and then washing the activated organic fiber to neutral with deionized water.

[0081] According to some embodiments of the present application, in step S1, the step of introducing the magnetic component includes immersing the surface pre-treated organic fiber into an alcohol solution containing the magnetic component under stirring at 25-60℃ for 12-24h.

[0082] In the present application, low temperature (25-60℃) and long time immersion avoid the formation of a dense hydroxide film on the surface due to too fast hydrolysis, ensure the diffusion of the magnetic component into the fiber, make the magnetic component be fully and uniformly loaded on the organic fiber, and avoid shedding.

[0083] It can be understood that the alcohol solution can be an ethanol solution, a methanol solution or a propylene glycol solution.

[0084] According to some embodiments of the present application, the concentration of the magnetic component solution is specifically 0.3-1.5 mol / L, for example, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.5 mol / L.

[0085] It should be noted that the magnetic component can be a metal salt. When the concentration of the magnetic component solution is less than 0.3 mol / L, the adsorption sites of the organic fiber cannot be fully occupied, the number of magnetic particles formed subsequently is extremely small, the magnetism is weak, and the wave absorption effect is affected. Meanwhile, the "diffusion ability" of the low-concentration metal ions is weak, and it is difficult to uniformly penetrate into the internal pores of the organic fiber, resulting in uneven distribution. When the concentration of the metal salt solution is greater than 1.5 mol / L, after the adsorption sites of the organic fiber are saturated, the excess metal ions will directly precipitate / aggregate in the fiber surface or fiber gap, and the magnetic particles obtained after reduction have poor dispersibility and are prone to agglomeration. Meanwhile, the high-concentration metal salt solution can reduce the pH value of the solution and corrode the molecular chain of the organic fiber, resulting in a decrease in the mechanical strength of the organic fiber, and even the problems of fiber embrittlement and easy breakage.

[0086] According to some embodiments of the present application, the magnetic component is selected from at least one of iron salt, cobalt salt and nickel salt.

[0087] It can be understood that the iron salt can be at least one of FeCl3, Fe(NO3)3 and Fe(SO4)3, the cobalt salt can be at least one of CoCl2, Co(NO3)2 and CoSO4, and the nickel salt can be at least one of NiCl2, Ni(NO3)2 and NiSO4.

[0088] It can be understood that the above-mentioned magnetic component exists in the form of oxide after subsequent high-temperature carbonization. It should be noted that the organic fiber can play a reduction role after high-temperature carbonization, and therefore the above-mentioned magnetic component can also exist in the form of an element.

[0089] It should be noted that the concentration of the magnetic component in the solution containing the magnetic component is 0.1-0.8 mol / L.

[0090] It can be understood that in step S2, the protective gas can be nitrogen or inert gas.

[0091] It can be understood that in step S3, the preparation method of the magnetic mixed fiber web tire monolithic piece is prepared in a conventional manner in the art. For example, the magnetic wave-absorbing fiber and the wave-transparent fiber are dispersed by opening and carding, and are randomly and uniformly deposited on the web curtain by using mechanical webbing technology to form a fluffy two-dimensional web-shaped structure of the magnetic mixed fiber web tire monolithic piece.

[0092] Need to explain, in the needle punching process, the needle density is 20-30 needles / cm 2 .

[0093] Specifically, considering the subsequent processability and structural uniformity of the magnetic mixed fiber web tire preform, the diameter of the magnetic wave-absorbing fiber is 6-15 μm, and the length is 8-55 mm, the diameter of the wave-transparent fiber is 10-20 μm, and the length is 15-80 mm.

[0094] According to some embodiments of the present application, in step S4, the vacuum degree during vacuum impregnation is-0.05 to-0.15 MPa;

[0095] And / or, the curing forming conditions include: the curing temperature is 80-100℃, and the curing time is 8-12h.

[0096] In the present application, the web tire single piece is vertically reinforced by the above method and needle punching process, and the mechanical action of the needle makes the upper and lower fibers interlock and entangle, forming a solid three-dimensional network structure tightly connected in X, Y and Z directions. The resin matrix fills and wraps the network structure, which not only provides mechanical support for the composite material, but also presets the electromagnetic function, and the two together constitute a functional composite material that is strong, light and can effectively absorb electromagnetic waves.

[0097] Need to explain, the diameter and length of the wave-transparent fiber meet the above range, which ensures that the fiber has good processability and structural uniformity of the final preform, thereby ensuring the wave-absorbing effect of the wave-absorbing composite material. If the diameter is less than 8 μm, the fiber strength may be insufficient and prone to breakage in the needle punching process; if the diameter is greater than 20 μm, it is difficult to form a uniform and delicate network structure, which reduces the mechanical properties. Illustratively, the diameter of the wave-transparent fiber is 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 15 μm, 16 μm, 18 μm, 20 μm and a range composed of any two of the above values.

[0098] Similarly, the length of the wave-transparent fiber is less than 10 mm, which will cause the subsequent needle punching process to be unable to effectively entangle each other, so as to form a stable three-dimensional network skeleton structure, and the mechanical properties and wave-absorbing effect are reduced, and if the length is greater than 80 mm, the fiber will not be uniformly dispersed during mixing and laying, and will easily form a ball, affecting the smooth progress of the subsequent process.

[0099] The third aspect of the present application provides a wave-absorbing composite material of the first aspect or a preparation method of the second aspect in electromagnetic protection.

[0100] Specifically, the minimum reflection loss of the composite material reaches -56.2 dB, and the effective absorption bandwidth exceeds 10 GHz, which means that the composite material can absorb most of the incident electromagnetic wave energy and continuously effectively in a very wide frequency range. At the same time, the material has good mechanical properties, with tensile and bending stress better than 14 MPa, meeting the needs of structural bearing.

[0101] In order to more clearly describe the present application, the following examples and comparative examples are further illustrated.

[0102] In the following examples and comparative examples, the complex permittivity and complex permeability of the wave-absorbing composite material in the range of 2-18 GHz were tested by free space method according to GB / T42741-2023. According to the transmission line theory, the reflection loss of the wave-absorbing composite material under different thicknesses was calculated by using formula (1) and formula (2).

[0103] Formula (1)

[0104] In the formula, Z0 is the free space impedance, which is 377 ohms, Z in is the input impedance.

[0105] Formula (2)

[0106] In the formula, is the complex permittivity, is the complex permeability, j represents the imaginary part, d is the sample thickness, and c is the speed of light.

[0107] The tensile strength of the wave-absorbing composite material was tested according to GB / T1447-2005.

[0108] The bending performance of the wave-absorbing composite material was tested according to GB / T1449-2005.

[0109] Both tensile and bending tests: the loading speed of each experiment was 2 mm / min, and 5 samples were tested in parallel for each group and the average value was taken.

[0110] Example 1

[0111] S1: The polyimide fibers were soaked in acetone at 30°C for 1 h, then ultrasonically cleaned for 30 min, and then immersed in a 0.5 mol / L NaOH solution after vacuum drying at 100°C, 60°C water bath and stirring for 2 h, then repeatedly washed with deionized water until neutral, and vacuum dried at 60°C for 12 h to obtain the surface pretreated organic fibers. The surface pretreated organic fibers were placed in a 1 mol / L Ni(NO3)2 ethanol solution, ultrasonically treated at room temperature for 2 h, and then vacuum dried at 60°C for 12 h to obtain magnetic organic fibers;

[0112] S2, the magnetic organic fiber is placed in a carbonization furnace, and is heated from room temperature to 600 DEG C at a rate of 2 DEG C / min under a nitrogen atmosphere, and is naturally cooled to room temperature after being kept at 600 DEG C for 2 h, to obtain a magnetic wave-absorbing fiber;

[0113] S3, the magnetic wave-absorbing fiber is mixed with quartz fiber at a mass ratio of 1:3, and is dispersed by opening and carding, and is randomly and uniformly deposited on a net curtain by using a mechanical webbing technology, to form a fluffy two-dimensional net structure of a magnetic mixed fiber webbing single piece, which is cut into 6 pieces each having a size of 330 mm*330 mm*2 mm, and a magnetic mixed fiber webbing preform having a density of 0.2 g / cm 3 is obtained by a needle punching process;

[0114] S4, the magnetic mixed fiber webbing preform is laid in a mold, and is injected with silicone resin under a vacuum degree of -0.1 MPa, and then the mold after injection is placed in an oven at 120 DEG C for curing and forming for 24 h, and is dried at 100 DEG C for 24 h, to obtain a magnetic wave-absorbing composite material having a thickness of 2 mm.

[0115] In the mixed fiber webbing preform, the number of the magnetic mixed fiber webbing single pieces is 6, and the mass percentage of the magnetic wave-absorbing fiber is 25%, and in the composite material, the content of the magnetic mixed fiber webbing preform is 45 wt%.

[0116] It is tested that the tensile stress of the magnetic wave-absorbing composite material is 15.3 MPa, and the bending stress is 14.6 MPa, and the calculation results according to the formula (1) and the formula (2) are as shown in Figure 2a , and the minimum reflection loss is -27.4 dB when the material thickness is 3.45 mm, and the effective absorption bandwidth is 7.6 GHz.

[0117] Example 2

[0118] According to the method of Example 1, except that in step S2, the magnetic organic fiber is placed in a carbonization furnace, and is heated from room temperature to 700 DEG C at a rate of 2 DEG C / min under a nitrogen atmosphere, and is naturally cooled to room temperature after being kept at 700 DEG C for 2 h.

[0119] In the mixed fiber webbing preform, the number of the magnetic mixed fiber webbing single pieces is 6, and the mass percentage of the magnetic wave-absorbing fiber is 25%, and in the composite material, the content of the magnetic mixed fiber webbing preform is 45 wt%.

[0120] It is tested that the tensile stress of the magnetic wave-absorbing composite material is 16.5 MPa, and the bending stress is 14.2 MPa, and the calculation results according to the formula (1) and the formula (2) are as shown in Figure 2bAs shown, the minimum reflection loss is -43.3 dB when the material thickness is 6.07 mm, and the effective absorption bandwidth is 3.2 GHz.

[0121] Example 3

[0122] S1: The phenolic fibers were soaked in ethanol at 30℃ for 1h, then ultrasonic cleaning for 30min, vacuum drying at 100℃, then immersed in 1mol / L HCl solution, 50℃ water bath and stirring for 2h, then repeatedly washed with deionized water until neutral, vacuum drying at 60℃ for 12h, to obtain the surface pretreated organic fibers, and the surface pretreated organic fibers were placed in 1mol / L mixed aqueous solution , ultrasonic at room temperature for 2h, then vacuum drying at 60℃ for 12h, to obtain magnetic organic fibers;

[0123] S2, the magnetic organic fibers were placed in a carbonization furnace, under nitrogen atmosphere, the temperature was raised from room temperature to 700℃ at a rate of 2℃ / min, and kept for 2h, and then naturally cooled to room temperature, to obtain magnetic wave-absorbing fibers;

[0124] S3, the magnetic wave-absorbing fibers were mixed with quartz fibers according to a mass ratio of 1:4 to prepare a magnetic mixed fiber web tire single piece, which was cut into 6 pieces with a size of 330mm×330mm×2mm, and a magnetic mixed fiber web tire preform with a density of 0.2g / cm 3 was obtained by needling process;

[0125] S4, the magnetic mixed fiber web tire preform was laid in a mold, and silicone resin was poured into the mold under a vacuum degree of -0.1MPa, then the poured mold was placed in an oven at 120℃ for curing and forming for 24h, and then dried at 100℃ for 24h, to obtain a magnetic wave-absorbing composite material with a thickness of 2mm.

[0126] In the mixed fiber web tire preform, the number of magnetic mixed fiber web tire single pieces is 6, and the mass percentage of magnetic wave-absorbing fibers is 20%, and in the composite material, the content of the magnetic mixed fiber web tire preform is 45wt%.

[0127] Test results show that the tensile stress of the magnetic wave-absorbing composite material is 16.1MPa, and the bending stress is 17.3MPa, and the calculation results according to formula (1) and formula (2) are as Figure 2c As shown, the minimum reflection loss is -43.3 dB when the material thickness is 6.07 mm, and the effective absorption bandwidth is 3.2 GHz.

[0128] Example 4

[0129] The method of example 3 is followed, except that the magnetic wave-absorbing fiber and quartz fiber are mixed in a mass ratio of 3:7.

[0130] In the mixed fiber web tire preform, the number of magnetic mixed fiber web tire single pieces is 6, the mass percentage of magnetic wave-absorbing fiber is 30%, and in the composite material, the content of the magnetic mixed fiber web tire preform is 45wt%.

[0131] The tensile stress of the wave-absorbing composite material is 19.3MPa, and the bending stress is 17.2MPa, and the calculation results according to formula (1) and formula (2) are as shown in the table. Figure 2d As shown in the table, when the material thickness is 7.64mm, the minimum reflection loss is-53dB, and the effective absorption bandwidth is 10.6GHz.

[0132] Example 5

[0133] The method of example 3 is followed, except that the magnetic wave-absorbing fiber and quartz fiber are mixed in a mass ratio of 1:1.

[0134] In the mixed fiber web tire preform, the number of magnetic mixed fiber web tire single pieces is 6, the mass percentage of magnetic wave-absorbing fiber is 50%, and in the composite material, the content of the magnetic mixed fiber web tire preform is 45wt%.

[0135] The tensile stress of the wave-absorbing composite material is 9.8MPa, and the bending stress is 10.3MPa, and the calculation results according to formula (1) and formula (2) are as shown in the table.

[0136] Example 6

[0137] The method of example 3 is followed, except that in step S3, the magnetic wave-absorbing fiber and quartz fiber are mixed in a mass ratio of 3:2.

[0138] In the mixed fiber web tire preform, the number of magnetic mixed fiber web tire single pieces is 6, the mass percentage of magnetic wave-absorbing fiber is 60%, and in the composite material, the content of the magnetic mixed fiber web tire preform is 45wt%.

[0139] The tensile stress of the wave-absorbing composite material is 7.43MPa, and the bending stress is 6.9MPa, and the calculation results according to formula (1) and formula (2) are as shown in the table.

[0140] Example 7

[0141] The method of example 3 is followed, except that in step S1, the organic fiber after surface pretreatment is placed in 0.1mol / L in solution.

[0142] The number of magnetic mixed fiber web tire monopieces in the mixed fiber web tire preform is 6, the mass percentage of the magnetic wave-absorbing fiber is 25%, and the content of the magnetic mixed fiber web tire preform in the composite material is 45wt%.

[0143] The tensile stress of the wave-absorbing composite material is 14.3MPa, the bending stress is 13.7MPa, the minimum reflection loss is-40.9dB when the material thickness is 11.2mm, and the effective absorption bandwidth is 8.7GHz according to formula (1) and formula (2).

[0144] Example 8

[0145] According to the method of Example 3, except that in step S3, the number of magnetic mixed fiber web tire monopieces is 12, so that the density of the magnetic mixed fiber preform is 0.4g / cm 3 .

[0146] The number of magnetic mixed fiber web tire monopieces in the mixed fiber web tire preform is 12, the mass percentage of the magnetic wave-absorbing fiber is 25%, and the content of the magnetic mixed fiber web tire preform in the composite material is 45wt%.

[0147] The tensile stress of the wave-absorbing composite material is 20.4MPa, the bending stress is 25.8MPa, the minimum reflection loss is-11.6dB when the material thickness is 8.4mm, and the effective absorption bandwidth is 0.8GHz according to formula (1) and formula (2).

[0148] Example 9

[0149] According to the method of Example 3, except that in step S1, the concentration of the HCL solution is 1.2mol / L.

[0150] The number of magnetic mixed fiber web tire monopieces in the mixed fiber web tire preform is 6, the mass percentage of the magnetic wave-absorbing fiber is 25%, and the content of the magnetic mixed fiber web tire preform in the composite material is 45wt%.

[0151] The tensile stress of the wave-absorbing composite material is 6.3MPa, the bending stress is 5.9MPa, the minimum reflection loss is-30.5dB when the material thickness is 11.2mm, and the effective absorption bandwidth is 7.3GHz according to formula (1) and formula (2).

[0152] Example 10

[0153] S1: The polyimide fibers were soaked in acetone at 30℃ for 1h, then ultrasonic cleaning for 30min, vacuum drying at 100℃, then immersed in 0.5mol / L NaOH solution, 60℃ water bath and stirring for 2h, then washed with deionized water repeatedly to neutral, vacuum drying at 60℃ for 12h, to obtain the surface pretreated organic fibers;

[0154] S2, the organic fibers were placed in a carbonization furnace, under nitrogen atmosphere, from room temperature to 600℃ at a rate of 2℃ / min, and kept for 2h, and then naturally cooled to room temperature, to obtain the wave-absorbing carbon fibers;

[0155] S3, the wave-absorbing carbon fibers were mixed with quartz fibers according to a mass ratio of 1:3 to prepare a mixed fiber web tire single piece, a magnetic modified wave-absorbing slurry was prepared according to the method of Example 1 in patent CN120659305A, and was uniformly dispersed into the mixed fiber web tire single piece to obtain a magnetic mixed fiber web tire single piece. It was cut into 6 pieces of magnetic mixed fiber web tire single pieces with a size of 330mm×330mm×2mm, and a magnetic mixed fiber web tire preform with a density of 0.24g / cm 3 was obtained by needling process;

[0156] S4, the magnetic mixed fiber web tire preform was laid in a mold, and silicone resin was poured into the mold under a vacuum degree of-0.1MPa, then the poured mold was placed in an oven at 120℃ for curing and forming for 24h, and then dried at 100℃ for 24h to obtain a magnetic wave-absorbing composite material with a thickness of 2mm.

[0157] In the mixed fiber web tire preform, the number of magnetic mixed fiber web tire single pieces was 6, and the mass percentage of magnetic wave-absorbing fibers was 20%, and in the composite material, the content of the magnetic mixed fiber web tire preform was 45wt%.

[0158] Test results showed that the tensile stress of the magnetic wave-absorbing composite material was 15.3MPa, and the bending stress was 14.6MPa, and according to formula (1) and formula (2), the minimum reflection loss was-21.4dB and the effective absorption bandwidth was 6.3GHz when the thickness of the material was 3.45mm.

[0159] Comparative Example 1

[0160] According to the method of Example 3, except that the phenolic fibers were placed in a carbonization furnace under a nitrogen atmosphere, and the temperature was raised from room temperature to 200℃ at a rate of 5℃ / min, kept for 30min, and then raised to 500℃ at a rate of 3℃ / min, kept for 2.5h, and then naturally cooled to room temperature to obtain the magnetic wave-absorbing fibers.

[0161] The tensile stress of the magnetic wave-absorbing composite material is 13.2 MPa, and the bending stress is 14.7 MPa. According to formula (1) and formula (2), the minimum reflection loss is-9.7 dB when the thickness of the material is 18 mm.

[0162] Comparative Example 2

[0163] According to the method of Example 1, except that in step S1, the phenolic fibers are soaked in ethanol at 30℃ for 1h, then ultrasonic cleaning for 30min, then washed with deionized water, vacuum drying at 60℃ for 12h, to obtain the surface pretreated organic fibers, the surface pretreated organic fibers are placed in 1mol / L aqueous solution of FeCl3 , ultrasonic at room temperature for 2h, then vacuum drying at 60℃ for 12h, to obtain magnetic organic fibers.

[0164] The tensile stress of the magnetic wave-absorbing composite material is 14.3 MPa, and the bending stress is 14.6 MPa. According to formula (1) and formula (2), the minimum reflection loss is-21.4 dB when the thickness of the material is 7.58 mm, and the effective absorption bandwidth is 3.2 GHz.

[0165] Comparative Example 3

[0166] S1: The polyimide fibers are soaked in acetone at 30℃ for 1h, then ultrasonic cleaning for 30min, vacuum drying at 100℃, then immersed in 0.5mol / L NaOH solution, 60℃ water bath and stirring for 2h, then repeatedly washed with deionized water until neutral, vacuum drying at 60℃ for 12h, to obtain the surface pretreated organic fibers, the surface pretreated organic fibers are placed in 1mol / L aqueous solution of FeCl3

[0167] S3, the magnetic organic fibers and quartz fibers are mixed according to a mass ratio of 1:3 to prepare a mixed fiber, and a magnetic mixed fiber preform with a density of 0.2g / cm 3 is obtained by needling process;

[0168] S4, the magnetic mixed fiber preform is laid in a mold, and silicone resin is poured under a vacuum degree of-0.1MPa, then the poured mold is placed in an oven at 120℃ for curing and molding for 24h, and then dried at 100℃ for 24h, to obtain a magnetic composite material with a thickness of 2mm.

[0169] The tensile stress of the magnetic composite material is 8.5 MPa, and the bending stress is 7.3 MPa, but it does not have wave-absorbing performance.

[0170] Comparative Example 4

[0171] S1, multi-walled carbon nanotubes (MWCNTs) were placed in a concentrated mixture of 3:1 at 70°C for 4 hours of ultrasonic treatment, after cooling, filtration and washing, and vacuum drying at 80°C for 12 hours, 2g of dried MWCNTs were pre-mixed with 93g of high-density polyethylene (HDPE) particles and 5g of carbonyl iron powder in a high-speed mixer for 7 minutes. Then, a double-screw extruder was used to melt blend and pelletize at 180°C and 100 rpm to obtain a composite master batch;

[0172] S2, the composite master batch was added to the melt spinning machine barrel, and the temperature of each zone was set to 185°C, 190°C, and 195°C (spinneret), and the speed was set to 100 m / min to obtain the as-spun fiber. The as-spun fiber was passed through a hot-drawing roller with a temperature of 110°C for two-stage hot-drawing, and the total draw ratio was controlled at 10 times to obtain the magnetic wave-absorbing fiber.

[0173] S3, the magnetic wave-absorbing fiber (length 20mm, diameter 15μm) was mixed with quartz fiber (length 30mm, diameter 15μm) according to a mass ratio of 2:8 to prepare a mixed fiber web tire, and then a needle-punched process was used to obtain a mixed fiber web tire preform with a density of 0.2g / cm 3 , and then silicone resin was injected to obtain the wave-absorbing composite material.

[0174] Through testing, the tensile stress of the wave-absorbing composite material was 8.7MPa, the bending stress was 7.9MPa, and according to formula (1) and formula (2), the minimum reflection loss was -37.8dB and the effective absorption bandwidth was 4.3GHz when the thickness of the material was 10.8mm.

[0175] From the above examples and comparative examples, it can be seen that the magnetic mixed fiber reinforced resin-based wave-absorbing composite material prepared by the present application has excellent electromagnetic wave absorption performance. The thickness of the composite material is 5-11mm, the minimum reflection loss is ≤-25dB, and the effective absorption bandwidth is ≥6GHz. At the same time, the composite material has excellent mechanical properties, the maximum tensile stress is ≥14MPa, and the maximum bending stress is ≥14MPa.

[0176] From Figure 1 it can be seen that the magnetic wave-absorbing fiber and the quartz fiber in the composite material are uniformly dispersed, and there is no obvious agglomeration or aggregation phenomenon. Further, the feasibility of preparing the composite material is confirmed.

[0177] Figures 2a-2d The reflection loss curves of the wave-absorbing composite materials prepared in Examples 1-4 under different matching thicknesses. From the figure, the minimum reflection loss and effective absorption bandwidth of the composite material under different thicknesses, and their change trend can be more intuitively seen. ​

[0178] In order to further illustrate the superiority of the method of the present application, the magnetic wave-absorbing composite materials prepared in Example 3 and Example 10 were characterized by a thermal oxygen aging experiment for long-term performance: according to GB / T7141-2021, the sample was placed in a 200℃ oven, compressed air (50mL / min) was introduced, and was placed for 200h, then the reflection loss of the sample in the range of 2-18GHz was tested by the bow method according to GJB2038A-2011, the reflection loss after aging was obtained, and the wave-absorbing performance retention rate was calculated using the formula, wherein the wave-absorbing performance retention rate = (reflection loss after aging / reflection loss before aging) x 100%.

[0179] It was tested that the wave-absorbing performance retention rate of the magnetic wave-absorbing composite material prepared in Example 3 after the thermal oxygen aging experiment was 81%, and the wave-absorbing performance retention rate of the magnetic wave-absorbing composite material prepared in Example 10 after the thermal oxygen aging experiment was 57%. It can be seen that introducing the magnetic component into the composite material in situ can make the composite material have longer wave-absorbing performance.

[0180] The above is only a preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. A magnetic microwave absorbing composite material, characterized in that, The composite material includes a magnetic hybrid fiber mesh preform and a resin matrix filling the gaps in the magnetic hybrid fiber mesh preform; The magnetic hybrid fiber mesh preform includes: a single piece of magnetic hybrid fiber mesh made of magnetic absorbing fibers and wave-transmitting fibers; the magnetic absorbing fibers are prepared by the following method: immersing organic fibers in a solution containing magnetic components, stirring to load the magnetic components onto the fiber surface to obtain magnetic organic fibers, and then carbonizing the magnetic organic fibers at high temperature to obtain magnetic absorbing fibers. The conditions for high-temperature carbonization include: carbonization temperature of 600-900℃, heating rate of 1-8℃ / min, and holding time of 1-4h. In the composite material, the content of the magnetic hybrid fiber mesh preform is 30-50 wt%, the content of the resin matrix is ​​50-70 wt%, and the density of the magnetic hybrid fiber mesh preform is 0.16-0.4 g / cm³. 3 The thickness is 2-20mm.

2. The magnetic wave-absorbing composite material according to claim 1, characterized in that, In the magnetic hybrid fiber mesh preform, the number of individual magnetic hybrid fiber mesh pieces is ≥5; And / or, in the hybrid fiber mesh preform, the mass percentage of the magnetic wave-absorbing fiber is 10-50%.

3. The magnetic wave-absorbing composite material according to claim 1, characterized in that, The magnetic absorbing fiber is made by carbonizing magnetic organic fiber; And / or, the magnetic organic fiber is obtained by modifying organic fibers with magnetic components; And / or, the magnetic component includes iron, cobalt, nickel, and at least one of the corresponding oxides of the aforementioned metals.

4. The magnetic wave-absorbing composite material according to claim 1, characterized in that, The resin matrix is ​​selected from at least one of phenolic resin, silicone resin and epoxy resin.

5. A method for preparing the magnetic microwave absorbing composite material according to any one of claims 1-4, characterized in that, Includes the following steps: S1. After pretreating the surface of organic fibers, magnetic components are introduced to obtain magnetic organic fibers; S2. In the presence of a protective gas, the magnetic organic fiber is carbonized at high temperature to obtain magnetic absorbing fiber. S3. Mix the magnetic absorbing fiber and the wave-transmitting fiber evenly to obtain a single piece of magnetic hybrid fiber mesh, and then prepare a magnetic hybrid fiber mesh preform by needle punching process. S4. Place the magnetic hybrid fiber mesh preform in a mold, vacuum impregnate it with a resin matrix, and then cure it to obtain a magnetic wave-absorbing composite material. The conditions for high-temperature carbonization include: carbonization temperature of 600-900℃, heating rate of 1-8℃ / min, and holding time of 1-4h.

6. The preparation method according to claim 5, characterized in that, In step S1, the surface pretreatment includes: soaking and cleaning the organic fibers with an organic solvent, and then activating them with an acid solution or an alkaline solution; And / or, the concentration of the acid solution, calculated as hydrogen ions, is 0.1-1 mol / L; Alternatively, the concentration of the alkaline solution, calculated as hydroxide ions, is 0.1-1 mol / L.

7. The preparation method according to claim 6, characterized in that, In step S1, the step of introducing magnetic components includes: immersing the surface-pretreated organic fibers in a solution containing magnetic components for 12-24 hours at 25-60°C under stirring conditions. And / or, the concentration of the magnetic component solution is 0.3-1.5 mol / L.

8. The preparation method according to claim 5, characterized in that, The magnetic component is selected from at least one of iron salts, cobalt salts, and nickel salts.

9. The preparation method according to claim 7 or 8, characterized in that, In step S3, the vacuum degree during vacuum impregnation is -0.05 to -0.15 MPa; And / or, the curing conditions include: a curing temperature of 80-100℃ and a curing time of 8-12h.

10. The application of the microwave absorbing composite material according to any one of claims 1-4 in electromagnetic protection.

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