Wave-absorbing film and preparation method therefor

Abstract

A wave-absorbing film and a preparation method therefor. The wave-absorbing film comprises a base material and a wave-absorbing layer provided on the base material. The wave-absorbing layer comprises a base and wave-absorbing units, the plurality of wave-absorbing units being arranged inside the base in a dot array; and the wave-absorbing layer is made of a soft magnetic composite material and a polymer elastomer, the mass fraction ratio of the soft magnetic composite material in the wave-absorbing layer ranging from 10% to 80%. According to the present wave-absorbing film and the preparation method therefor, the wave-absorbing layer comprises the plurality of wave-absorbing units arranged inside in the base in a dot array. The regular arrangement structural design can effectively improve the degree of matching between the impedance of the wave-absorbing film and the impedance of free space, and increase the effective absorption bandwidth. The soft magnetic alloy composite material uses a two-dimensional flaky multilayer structure, and comprises, from inside to outside, a soft magnetic alloy, an Al2O3 layer and an amorphous carbon layer. Compared with a material using only the soft magnetic alloy, the soft magnetic alloy composite material using the multilayer structure has the excellent characteristics of various functional materials.

Description

A microwave-absorbing film and a preparation method thereof Technical Field

[0001] The present invention belongs to the technical field of wave-absorbing materials, and in particular relates to a wave-absorbing film and a preparation method thereof. Background Art

[0002] Electromagnetic interference (EMI) and radiation protection are often achieved through electromagnetic shielding and absorbing materials. Compared to electromagnetic shielding, absorbing materials are the most effective method for eliminating electromagnetic pollution. Absorbing materials absorb most electromagnetic waves that strike their surfaces, dissipating them as heat or other forms of energy. They are widely used in advanced technologies such as aviation, medical radiation safety, microwave processing, and autonomous vehicles.

[0003] The absorbing performance of electromagnetic absorbing materials depends on their impedance matching and attenuation characteristics. Good impedance matching and strong attenuation characteristics result in less electromagnetic wave reflection, greater dissipation of electromagnetic waves incident on the absorbing material, and excellent absorbing performance. Absorbing materials typically include resistive materials (such as SiC and graphite), dielectric materials (such as BaTiO3 and BiFeO3), and magnetic dielectric materials (such as ferrite and FeSiAl). Compared to other electromagnetic absorbing materials, soft magnetic materials offer advantages such as high magnetic permeability and magnetic loss, excellent impedance matching, and strong absorbing performance. They are the most practical absorbing materials and are widely used in the communications field. Therefore, there is great potential in developing high-performance soft magnetic materials for use in absorbing materials.

[0004] Furthermore, existing absorbing materials are mostly composed of a single-layer absorbing sheet, formed by combining the absorbing material with a substrate to achieve a specific thickness and achieve electromagnetic wave absorption performance within a specific frequency band. With the diversification of absorbing scenarios, there is great potential for developing a multi-layer absorbing material with broadband absorbing performance.

[0005] Therefore, the object of the present invention is to provide an absorbing film and a preparation method thereof to solve the above technical problems.

[0006] Summary of the Invention

[0007] Purpose of the invention: In order to overcome the above shortcomings, the purpose of the present invention is to provide an absorbing film and a preparation method thereof, which has a reasonable structural design and a simple preparation method. The absorbing layer adopts a plurality of absorbing units arranged in a lattice inside the substrate. Through the regularly arranged structural design, the matching degree between the impedance of the absorbing film and the impedance of free space can be effectively improved, and the effective absorption bandwidth can be increased. The soft magnetic alloy composite material adopts a two-dimensional sheet-like multilayer structure, which includes a soft magnetic alloy, an Al2O3 layer, and an amorphous carbon layer from the inside to the outside. Compared with a single type of soft magnetic alloy, its multilayer structure has the excellent characteristics of being able to take into account multiple functional materials and has broad application prospects.

[0008] The purpose of the present invention is achieved through the following technical solutions:

[0009] A wave-absorbing film, comprising a substrate and a wave-absorbing layer disposed on the substrate; wherein the wave-absorbing layer comprises a matrix and wave-absorbing units, and a plurality of the wave-absorbing units are disposed within the matrix in a lattice arrangement; the wave-absorbing layer is made of a soft magnetic composite material and a polymer elastomer, and the mass fraction of the soft magnetic composite material in the wave-absorbing layer ranges from 10 to 80%.

[0010] The absorbing film of the present invention has a reasonable structural design. The absorbing layer adopts a plurality of absorbing units arranged in a lattice inside the substrate. The regularly arranged structural design can effectively improve the matching degree between the impedance of the absorbing film and the impedance of free space, thereby increasing the effective absorption bandwidth.

[0011] Among them, the soft magnetic composite material has high saturation magnetic induction intensity and low coercive force, which can effectively isolate electromagnetic interference and magnetic field interference. The polymer elastomer plays the role of filler and binder in the absorbing layer, which can make the soft magnetic composite material evenly distributed in the absorbing layer and improve the absorbing effect. The close combination of the soft magnetic composite material and the polymer elastomer can enhance the mechanical strength and stability of the absorbing layer.

[0012] Furthermore, in the above-mentioned absorbing film, the soft magnetic composite material is a powder, the thickness of the powder is 0.5-1.5 μm, and the particle size D50 of the powder is in the range of 30-100 μm.

[0013] Furthermore, in the above-mentioned absorbing film, the soft magnetic composite material is a two-dimensional sheet-like multilayer structure, including a soft magnetic alloy, an Al2O3 layer, and an amorphous carbon layer from the inside to the outside.

[0014] Soft magnetic alloys have the advantages of low magnetocrystalline anisotropy constant and high magnetic permeability, but also have the disadvantages of excessively high dielectric constant and poor impedance matching. Therefore, in order to obtain more excellent microwave absorption performance, the present invention optimizes the soft magnetic alloy. The soft magnetic alloy composite material adopts a two-dimensional sheet-like multilayer structure, which includes a soft magnetic alloy, an Al2O3 layer, and an amorphous carbon layer from the inside to the outside. Its multilayer structure has the excellent characteristics of being able to take into account multiple functional materials compared to a single type of soft magnetic alloy, and plays a role in regulating dielectric constant, magnetic permeability, and enriching interface structure to achieve impedance matching and enhanced loss. By providing an Al2O3 layer between the soft magnetic alloy and the amorphous carbon layer, the formation of carbon nanomaterials on the surface of the soft magnetic alloy composite material is avoided and multiple scattering and reflection mechanisms can be introduced to improve its microwave absorption performance. At the same time, this multilayer structure can also play a barrier protection role and can also play an effect of enhancing corrosion resistance.

[0015] Furthermore, in the above-mentioned absorbing film, the soft magnetic alloy is selected from at least one of Sendust soft magnetic alloy, Iron-Silicon soft magnetic alloy, Iron-Nickel soft magnetic alloy, Iron-Nickel-Molybdenum soft magnetic alloy, Iron-Aluminum soft magnetic alloy, Sendust aluminum-nickel soft magnetic alloy, Iron-Chromium soft magnetic alloy, and Iron-Cobalt soft magnetic alloy.

[0016] Preferably, the soft magnetic alloy is an iron-silicon-aluminum soft magnetic alloy, also known as Sendust alloy, the main components of which are Fe9.6-Si5.4-Al.

[0017] Furthermore, in the above-mentioned absorbing film, the substrate is at least one of PET film, PI film, PP film, PEI film, polyetheretherketone, phenolic resin, PE film, PC film, PS film and PVC film, and the thickness of the substrate is 10-300 μm; the thickness of the absorbing layer is 0.1-2 mm.

[0018] Furthermore, in the above-mentioned absorbing film, the polymer elastomer is at least one of polyurethane, acrylic acid, silicone, and epoxy resin.

[0019] The present invention also relates to a method for preparing the absorbing film, comprising the following steps:

[0020] S1: uniformly mixing the soft magnetic composite material and the polymer elastomer to obtain a mixture 1;

[0021] S2: adding the mixture 1 into a blender, and then adding a solvent, with the mass ratio of the mixture 1 to the solvent being 1-5:1-5, and stirring until they are uniformly mixed to prepare a mixture 2;

[0022] S3: The mixture is coated on a substrate and evenly distributed on the substrate using a scraper, and then placed on an acrylic plate for 1-10 minutes. The acrylic plate is provided with a plurality of permanent magnetic cylinders with a dot matrix distribution and N poles facing upwards. After heating and curing, an absorbing film is obtained.

[0023] By setting up a lattice distribution of several permanent magnetic cylinders with N poles pointing upward on the acrylic plate, the soft magnetic composite material has a high magnetic induction intensity. Under the action of the magnetic field of the permanent magnetic cylinders, it will move towards the approaching direction, thereby gathering to form several absorbing units based on the lattice arrangement of the permanent magnetic cylinders. Moreover, based on the magnetic direction of the permanent magnetic cylinders with N poles pointing upward, the soft magnetic composite materials of the several absorbing units are not disturbed by adjacent magnets and can obtain a stable shape.

[0024] Furthermore, in the method for preparing the above-mentioned absorbing film, the absorbing powder is a soft magnetic composite material, and its preparation comprises the following steps:

[0025] S1: ammonium formate solution, soft magnetic alloy powder, and aluminum sulfate are mixed and ultrasonically dispersed for 10-30 minutes to obtain a mixed solution, the mixed solution is heated in a water bath to 75-85°C, stirred and reacted for 1-2 hours, washed with ethanol multiple times and subjected to magnetic separation, and then dried in an oven at 40-50°C for 1-3 days, and then annealed at 350-450°C for 2 hours to obtain a soft magnetic alloy powder coated with an Al2O3 layer;

[0026] S2: Spread the soft magnetic alloy powder coated with the Al2O3 layer on a quartz boat, and then place it in a CVD rotary tube furnace. Under a protective atmosphere of argon with a gas flow rate of 50-100mL / min, heat it to 400℃ at a rate of 3-6℃ / min, and then introduce acetylene gas at a flow rate of 20-30mL / min to react for 0.5-1h. After the reaction is completed, turn off the acetylene and start to slowly cool it to 25℃. Take it out to obtain a soft magnetic composite material.

[0027] First, an Al2O3 layer is coated on the surface of the soft magnetic alloy powder through the sol-gel method, and then an amorphous carbon layer is introduced on the surface of the soft magnetic alloy through the CCDV method. The high-resistance amorphous carbon layer can reduce the dielectric constant of the magnetic metal, achieve good impedance matching between the absorption material and the free space, and enhance the microwave absorption performance.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] (1) The absorbing film disclosed in the present invention has a reasonable structural design. The absorbing layer adopts a plurality of absorbing units arranged in a lattice inside the substrate. The regularly arranged structural design can effectively improve the matching degree between the impedance of the absorbing film and the impedance of free space, thereby increasing the effective absorption bandwidth. The absorbing layer is made of a soft magnetic composite material and a polymer elastomer. The soft magnetic composite material has a high saturation magnetic induction intensity and a low coercive force, and can effectively isolate electromagnetic interference and magnetic field interference. The close combination of the soft magnetic composite material and the polymer elastomer can enhance the mechanical strength and stability of the absorbing layer.

[0030] (2) The absorbing film disclosed in the present invention and the soft magnetic alloy composite material adopt a two-dimensional sheet-like multilayer structure, which includes a soft magnetic alloy, an Al2O3 layer, and an amorphous carbon layer from the inside to the outside. Compared with a single type of soft magnetic alloy, the multilayer structure has the excellent characteristics of being able to take into account multiple functional materials, and plays a role in regulating the dielectric constant, magnetic permeability and enriching the interface structure to achieve the effect of impedance matching and enhanced loss; by arranging an Al2O3 layer between the soft magnetic alloy and the amorphous carbon layer, it can avoid the formation of carbon nanomaterials on the surface of the soft magnetic alloy composite material and introduce multiple scattering and reflection mechanisms to improve its microwave absorption performance. At the same time, this multilayer structure can also play a barrier protection role and enhance the corrosion resistance.

[0031] (3) The preparation method of the absorbing film disclosed in the present invention has reasonable preparation steps, simple and controllable preparation steps and high flexibility. By setting a lattice distribution on the acrylic plate and a plurality of permanent magnetic cylinders with N poles facing upward, a plurality of absorbing units based on the lattice arrangement of the permanent magnetic cylinders are formed. Moreover, based on the magnetic direction of the permanent magnetic cylinders with N poles facing upward, the soft magnetic composite materials of the plurality of absorbing units can obtain a stable shape along the lattice without being interfered with by adjacent magnets. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] FIG1 is a schematic cross-sectional view of the absorbing film of the present invention;

[0033] In the figure: substrate 1, absorbing layer 2, base 21, absorbing unit 22. DETAILED DESCRIPTION

[0034] The following will combine Comparative Example 1, Example 1, Comparative Example 2, and Example 2 with specific experimental data and Figure 1 to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0035] The raw materials used in Comparative Example 1, Example 1, Comparative Example 2, and Example 2 are all commercially available industrial raw materials.

[0036] Comparative Example 1 and Example 1 provide a wave absorbing material.

[0037] Comparative Example 1

[0038] Comparative Example 1 is Sendai alloy, the main components of which are Fe9.6-Si5.4-Al.

[0039] Example 1

[0040] Example 1 is a soft magnetic composite material, and its preparation method is as follows: 12.612g of ammonium formate powder is added to every 1L of deionized water solution, and after dispersion, formic acid solution is added to adjust the pH to 4.4 to prepare an ammonium formate solution; the ammonium formate solution, soft magnetic alloy powder, and aluminum sulfate are mixed in a mass ratio of 506:6:3, ultrasonically dispersed for 15 minutes to obtain a mixed solution, the mixed solution is heated to 75°C in a water bath, stirred and reacted for 1.5 hours, washed with ethanol multiple times and magnetically separated, and then dried in an oven at 45°C for 2 days, and then Annealing at 380°C for 2h to obtain a soft magnetic alloy powder coated with an Al2O3 layer; the soft magnetic alloy powder coated with the Al2O3 layer was spread flat on a quartz boat, and then placed in a CVD rotary tube furnace. Under a protective atmosphere of argon with a gas flow rate of 50-100mL / min, the temperature was raised to 400°C at a rate of 5°C / min, and acetylene gas was introduced at a flow rate of 25mL / min to react for 1h to generate an amorphous carbon layer. After the reaction was completed, the acetylene was turned off and the temperature was slowly lowered to 25°C. The powder was taken out to obtain the soft magnetic composite material of Example 1.

[0041] Wave absorption performance test: The electromagnetic parameters of the Sendaisite alloy of comparative example 1 and the soft magnetic composite material of embodiment 1 were tested. The testing instrument was a vector analyzer, and the test frequency band was 0.5-18 GHz.

[0042] During the test, the Sendai alloy of comparative example 1 and the soft magnetic composite material of embodiment 1 were made into coaxial rings for testing, that is, paraffin and the Sendai alloy of comparative example 1 and the soft magnetic composite material of embodiment 1 were fully and evenly mixed in a mass ratio of 1:1 to form a coaxial ring with a thickness of about 2.5 mm, an inner diameter of about 3.0 mm, and an outer diameter of about 7.0 mm.

[0043] Absorption performance test results show that, generally speaking, a material is considered to have an effective absorption band when RL < -10 dB. Within the frequency range of 0.5-18.0 GHz, the RL value of the Sendaisite alloy in Comparative Example 1 is less than -10 dB in less than 0.2 GHz of the bandwidth, indicating that the Sendaisite alloy in Comparative Example 1 has significant limitations in practical applications. In contrast, the soft magnetic composite material in Example 1 achieves an RLmin of -23.9 dB at 6.8 GHz, with an effective absorption bandwidth of 3.4 GHz.

[0044] The above-mentioned absorption performance test results show that the two-dimensional lamellar multilayer structure of the soft magnetic composite material synthesized by first coating Al2O3 by the sol-gel method and then coating the amorphous carbon layer by CCDV has significantly improved the minimum microwave loss RLmin and effective bandwidth compared to the Sendai alloy of the comparison example 1 with a two-dimensional lamellar single layer structure, thereby greatly enhancing the absorption performance of the absorbing powder.

[0045] Comparative Example 2 and Example 2 provide a wave-absorbing film and a preparation method thereof.

[0046] Comparative Example 2

[0047] As shown in FIG1 , the absorbing film of Comparative Example 2 includes a substrate 1 and an absorbing layer 2 disposed on the substrate 1. The absorbing layer 2 is made of the Sendai alloy and polyurethane of Comparative Example 1, and the preparation method thereof is as follows:

[0048] S1: uniformly mixing Sendai alloy and polyurethane to obtain a mixture 1, wherein the mass ratio of Sendai alloy powder to polyurethane is 70:30;

[0049] S2: adding the mixture 1 into a blender, and then adding methyl isopropyl ketone (MIP) solvent, wherein the mass ratio of the MIP solvent to the mixture 1 is 1:1, and stirring to uniformly mix the mixture to prepare a mixture 2;

[0050] S3: The mixture 2 is coated on a PET film (substrate 1), evenly distributed on the surface of the PET film with a scraper, and then placed on an acrylic plate for 6 minutes. The acrylic plate is provided with a plurality of permanent magnetic cylinders (height 2 mm, diameter 2 mm, column spacing 6 mm) with a dot matrix distribution and N poles facing upward, and the residual magnetization intensity of the permanent magnetic cylinders is 1 T. After heating and curing, an absorbing layer 2 is formed to obtain the absorbing film of Comparative Example 2, wherein the thickness of the PET film is 100 μm and the thickness of the absorbing layer 2 is 1 mm.

[0051] The absorbing film of comparative example 2 was cut into a size of 300×300 mm, and then subjected to a wave absorbing performance test. The testing instrument was a vector analyzer, and the test frequency band was 1-40 GHz.

[0052] The test results of the wave absorption performance are: at 18GHz, RLmin is -20.1dB, and the effective wave absorption bandwidth can reach 7.9GHz.

[0053] Example 2

[0054] As shown in FIG1 , the absorbing film of Example 2 includes a substrate 1 and an absorbing layer 2 disposed on the substrate 1. The absorbing layer 2 is made of the soft magnetic composite material and polyurethane of Example 1. The preparation method thereof is as follows:

[0055] S1: uniformly mixing the soft magnetic composite material and polyurethane to obtain a mixture 1, wherein the mass ratio of the soft magnetic composite material to the polyurethane is 70:30;

[0056] S2: adding the mixture 1 into a blender, and then adding methyl isopropyl ketone (MIP) solvent in a mass ratio of methyl isopropyl ketone to the mixture of 1:1, and stirring to uniformly mix the mixture to prepare a mixture 2;

[0057] S3: The mixture 2 is coated on a PET film (substrate 1), evenly distributed on the surface of the PET film with a scraper, and then placed on an acrylic plate for 6 minutes. The acrylic plate is provided with a plurality of permanent magnetic cylinders (with a height of 2 mm, a diameter of 2 mm, and a column spacing of 6 mm) with a dot array distribution and N poles facing upward, and the residual magnetization intensity of the permanent magnetic cylinders is 1 T. After heating and curing, an absorbing layer 2 is formed to obtain the absorbing film of Example 2, wherein the thickness of the PET film is 100 μm and the thickness of the absorbing layer 2 is 1 mm.

[0058] After the absorbing film of Example 2 was cut into a size of 300×300 mm, a wave absorbing performance test was performed using a vector analyzer with a test frequency range of 1-40 GHz.

[0059] The test results of the wave absorption performance are: at 23GHz, RLmin is -32.3dB, and the effective wave absorption bandwidth can reach 15.1GHz.

[0060] The present invention has many specific application paths, and the above is only a preferred embodiment of the present invention. It should be noted that the above embodiments are only used to illustrate the present invention and are not intended to limit the scope of protection of the present invention. For those skilled in the art, several improvements can be made without departing from the principles of the present invention, and these improvements should also be considered as the scope of protection of the present invention.

Claims

1. A microwave absorbing film, characterized in that: The wave absorbing film comprises a substrate (1) and a wave absorbing layer (2) arranged on the substrate (1); wherein the wave absorbing layer (2) comprises a substrate (21) and wave absorbing units (22), and a plurality of the wave absorbing units (22) are arranged inside the substrate (21) in a lattice arrangement; the wave absorbing layer (2) is made of a soft magnetic composite material and a polymer elastomer, and the mass fraction of the soft magnetic composite material in the wave absorbing layer (2) is in the range of 10-80%.

2. The absorbing film according to claim 1, characterized in that: The soft magnetic composite material is a powder, the thickness of the powder is 0.5-1.5 μm, and the particle size D50 of the powder is in the range of 30-100 μm.

3. The absorbing film according to claim 2, characterized in that: The soft magnetic composite material is a two-dimensional sheet-like multilayer structure, which comprises a soft magnetic alloy, an Al2O3 layer, and an amorphous carbon layer from the inside to the outside.

4. The absorbing film according to claim 3, characterized in that: The soft magnetic alloy is selected from at least one of iron-silicon-aluminum soft magnetic alloy, iron-silicon soft magnetic alloy, iron-nickel soft magnetic alloy, iron-nickel-molybdenum soft magnetic alloy, iron-aluminum soft magnetic alloy, iron-silicon-aluminum-nickel soft magnetic alloy, iron-chromium soft magnetic alloy and iron-cobalt soft magnetic alloy.

5. The absorbing film according to claim 1, characterized in that: The substrate (1) is at least one of PET film, PI film, PP film, PEI film, polyetheretherketone, phenolic resin, PE film, PC film, PS film and PVC film; the thickness of the substrate (1) is 10-300 μm, and the thickness of the absorbing layer (2) is 0.1-2 mm.

6. The absorbing film according to claim 1, characterized in that: The polymer elastomer is at least one of polyurethane, acrylic acid, silicone and epoxy resin.

7. The method for preparing the microwave absorbing film according to any one of claims 1 to 6, characterized in that: The steps include: S1: uniformly mixing the soft magnetic composite material and the polymer elastomer to obtain a mixture 1; S2: adding the mixture 1 into a blender, and then adding a solvent, wherein the mass ratio of the mixture 1 to the solvent is 1-5:1-5, and stirring until they are uniformly mixed to prepare a mixture 2; S3: The mixture is coated on the substrate (1), evenly distributed on the substrate (1) by a scraper, and then placed on an acrylic plate for 1-10 minutes. The acrylic plate is provided with a plurality of permanent magnetic cylinders with a dot matrix distribution and N poles facing upwards. After heating and curing, an absorbing film is obtained.

8. The method for preparing the microwave absorbing film according to claim 7, characterized in that: The wave-absorbing powder is a soft magnetic composite material, and its preparation comprises the following steps: S1: Mix ammonium formate solution, soft magnetic alloy powder and aluminum sulfate, and ultrasonically disperse for 10-30 minutes to obtain a mixed solution, heat the mixed solution to 75-85°C in a water bath, keep it warm and stir it for 1-2 hours, wash it with ethanol several times and perform magnetic separation, dry it in an oven at 40-50°C for 1-3 days, and then anneal it at 350-450°C for 2 hours to obtain a soft magnetic alloy powder coated with an Al2O3 layer; S2: Spread the soft magnetic alloy powder coated with Al2O3 layer on a quartz boat, and then place it in a CVD rotary tube furnace. Under a protective atmosphere of argon with a gas flow rate of 50-100 mL / min, the temperature was raised to 400°C at a rate of 3-6°C / min, and acetylene gas was introduced at a flow rate of 20-30 mL / min to react for 0.5-1 h. After the reaction was completed, the acetylene was turned off and the temperature was slowly lowered to 25°C, and the mixture was taken out to obtain a soft magnetic composite material.

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