A low-frequency band high-permeability absorbing thin film material and its preparation method

Abstract

This invention belongs to the field of microwave absorbing composite materials technology, specifically relating to a high-permeability microwave absorbing thin film material in the low-frequency band and its preparation method. The microwave absorbing thin film material provided by this invention comprises the following raw materials in parts by weight: 25-60 parts of conjugated structure modified polyimide, 25-40 parts of magnetic absorber, 5-15 parts of carbon hollow fiber, and 0-10 parts of functional additives. The microwave absorbing thin film material provided by this invention exhibits good microwave absorption performance and mechanical properties in the low-frequency band, and shows promising application prospects.

Description

Technical Field

[0001] This invention belongs to the field of microwave absorbing materials technology, specifically relating to a low-frequency band high-permeability microwave absorbing thin film material and its preparation method. Background Technology

[0002] With the rapid development of electronic information technology, the problems caused by low-frequency electromagnetic interference are becoming increasingly prominent, making the demand for low-frequency absorbing materials more and more urgent. High-permeability absorbing materials can effectively absorb low-frequency electromagnetic waves and have important application value in fields such as electromagnetic shielding of electronic equipment and communication systems.

[0003] However, existing low-frequency absorbing materials are limited and suffer from poor overall performance, including insufficient magnetic permeability, limited absorption capacity, and poor mechanical properties, making it difficult to meet practical application requirements. Therefore, developing a microwave absorbing thin film material with high magnetic permeability and excellent overall performance in the low-frequency band is of great significance. Summary of the Invention

[0004] This invention provides a low-frequency band high-permeability absorbing thin film material and its preparation method. By optimizing the composition and structure of the absorbing thin film material, the invention solves the problems of poor absorption performance and mechanical properties of existing absorbing thin film materials in the low-frequency band, and achieves high permeability and excellent absorption performance in the low-frequency band, while also possessing good mechanical properties and stability.

[0005] In a first aspect, a low-frequency band high-permeability absorbing thin film material is provided, comprising the following raw materials in parts by weight: 25-60 parts of conjugated structure modified polyimide, 25-40 parts of magnetic absorber, 5-15 parts of carbon hollow fiber, and 0-10 parts of functional additives.

[0006] Furthermore, the conjugated structure modified polyimide is obtained by reacting raw materials including diaminophenyl ether monomer, dianhydride monomer, and substances containing conjugated structures.

[0007] Furthermore, the preparation method of the conjugated structure modified polyimide is as follows:

[0008] The dianhydride monomer, diaminophenyl ether monomer, and the substance containing the conjugated structure are dissolved in an organic solvent to prepare a mixed solution; under nitrogen protection, a prepolymerization reaction is carried out at 0-5℃ for 1-2 hours; then the temperature is raised to 100-150℃ and the reaction is continued for 3-5 hours, and then dried to obtain the conjugated structure modified polyimide.

[0009] Furthermore, the magnetic absorber is a conjugated structure modified polyimide-coated magnetic nanosheet intercalated modified graphene composite particle.

[0010] The magnetic absorbent is obtained by reacting diaminophenyl ether monomer, dianhydride monomer, and substances containing conjugated structures on the surface of magnetic nanosheet intercalated modified graphene composite particles.

[0011] Furthermore, the preparation method of the magnetic absorbent is as follows:

[0012] A mixed solution was prepared by dissolving dianhydride monomer, diaminophenyl ether monomer, and a substance containing a conjugated structure in an organic solvent. Magnetic nanosheet intercalated modified graphene composite particles were added to the mixed solution and prepolymerized at 0-5℃ for 1-2 hours under nitrogen protection. The temperature was then raised to 100-150℃ and the reaction continued for 3-5 hours. After solid-liquid separation and drying, a magnetic absorbent was obtained.

[0013] The mass ratio of the magnetic nanosheet intercalated modified graphene composite particles to the mixed solution is 1:10-1:20; in the mixed solution, the total mass percentage of the dianhydride monomer, diaminophenyl ether monomer, and substances containing conjugated structures is 10-20%.

[0014] Furthermore, it must meet at least one of the following characteristics:

[0015] (1) When the diaminophenyl ether monomer, dianhydride monomer, and substance containing a conjugated structure react, the mass ratio of the diaminophenyl ether monomer, dianhydride monomer, and substance containing a conjugated structure is 1:1:0.1-0.3;

[0016] (2) The substance containing the conjugated structure contains two amino groups. Further, the substance containing the conjugated structure is anthracene or naphthalene containing two amino groups.

[0017] Furthermore, it must meet at least one of the following characteristics:

[0018] (1) The substance containing a conjugated structure includes at least one of 2,6-diaminoanthracene, (E)-2-(3-(6-(dimethylamino)naphth-2-yl)allyl)malonitrile, 1,2-diamino-naphthalene-5-sulfonamide hydrochloride, 2,3-diaminonaphthalene, 1,8-diaminonaphthalene, and 1,5-diaminonaphthalene;

[0019] (2) The dianhydride monomer includes at least one of pyromellitic dianhydride, biphenyl dianhydride, and ether anhydride;

[0020] (3) The diaminophenyl ether monomer includes at least one of 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, and 2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl ether.

[0021] Furthermore, the preparation method of the magnetic nanosheet intercalated modified graphene composite particles is as follows:

[0022] S1. Add the magnetic nanosheets to an organic solvent or aqueous solution containing a dispersant, and sonicate them to disperse them fully, forming a uniform magnetic nanosheet suspension.

[0023] S2. Add graphene to another part of the solution containing dispersant and sonicate to obtain a graphene suspension.

[0024] S3. Under stirring conditions, the magnetic nanosheet suspension is slowly added dropwise to the graphene suspension. After the addition is complete, stirring is continued for a period of time. Then, the pH of the solution is adjusted to 4.5-7 to facilitate self-assembly.

[0025] S4. Separate the composite particles from the solution, wash them multiple times, and then dry them to obtain magnetic nanosheet intercalated modified graphene composite particles.

[0026] Furthermore, the preparation method of the magnetic nanosheet intercalated modified graphene composite particles meets at least one of the following characteristics:

[0027] (1) The magnetic nanosheets in the magnetic nanosheet suspension account for 15-40 wt% of the mass, and the graphene in the graphene suspension accounts for 10-30 wt% of the mass.

[0028] (2) The mass ratio of graphene in the graphene suspension to the mass ratio of magnetic nanosheets in the magnetic nanosheet suspension is 3-5:1;

[0029] (3) The magnetic nanosheets include at least one of two-dimensional sheet FeCoZr, two-dimensional sheet FeNi, two-dimensional sheet FeNiMo, two-dimensional sheet FeSi, and two-dimensional sheet FeSiCr soft magnetic metal powder;

[0030] (4) The particle size D50 of the magnetic nanosheets is less than 70 μm.

[0031] Furthermore, the functional additives include, but are not limited to, at least one of dispersants and leveling agents; the dispersants include, but are not limited to, at least one of PVP, oleic acid, stearic acid, and lauric acid; the leveling agents include, but are not limited to, at least one of polydimethylsiloxane (silicone oil) and acrylate leveling agents.

[0032] Furthermore, the method for preparing the carbon hollow fiber is as follows:

[0033] Step 1: Dissolve polyacrylonitrile in an organic solvent, add ferrite and antioxidant, mix well to obtain the shell spinning solution stock solution;

[0034] Step 2: Dissolve polyvinylpyrrolidone in an organic solvent, add an antioxidant and mix well to obtain the core spinning solution stock solution;

[0035] Step 3: Perform coaxial electrospinning on the outer shell spinning solution and the inner core spinning solution to obtain a carbon fiber precursor. Then, soak the carbon fiber precursor in water to obtain a carbon hollow fiber precursor.

[0036] Step 4: The carbon hollow fiber precursor is subjected to drying, pre-oxidation, high-temperature carbonization, acid leaching and roughening, and mechanical cutting in sequence to obtain the carbon hollow fiber.

[0037] Furthermore, the ferrite is manganese-zinc ferrite (MnZn), which has high permeability. This allows it to provide higher impedance in low-frequency applications, which is beneficial for the efficient conversion of electromagnetic energy.

[0038] Secondly, a method for preparing a low-frequency band high-permeability absorbing thin film material is provided, comprising the following steps:

[0039] Step 1: Mix the conjugated structure modified polyimide, magnetic absorber, carbon hollow fiber and functional additives, add organic solvent, and stir at room temperature for 2-4 hours to form a uniform slurry;

[0040] Step 2: Apply the obtained slurry to the substrate, dry it, and then calender and cool it to obtain a low-frequency band high magnetic permeability absorbing film.

[0041] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0042] 1. Through the synergistic effect of conjugated structure modified polyimide and magnetic absorber, the thin film material can achieve efficient electromagnetic wave absorption in the low frequency band by reducing the dielectric loss brought by the conjugated structure and the magnetic loss of the magnetic absorber, thus effectively improving the wave absorption capability.

[0043] 2. While possessing excellent microwave absorption performance, the conjugated structure modified polyimide endows the material with good mechanical properties, ensuring that the film has certain strength and flexibility; the addition of functional additives can further improve the processing performance of the material, expanding the application scenarios and service life of the material.

[0044] 3. The addition of carbon hollow fibers further optimizes the impedance matching of the material, reduces electromagnetic wave reflection, enhances the overall wave absorption performance, and meets the application requirements such as low-frequency electromagnetic shielding. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0046] This invention provides a high-permeability absorbing thin film material for the low-frequency band. By optimizing the composition and structure of the absorbing thin film material, it solves the problems of poor absorption performance and mechanical properties of existing absorbing thin film materials in the low-frequency band, and achieves high permeability and excellent absorption performance in the low-frequency band, while also possessing good mechanical properties and stability.

[0047] The low-frequency band high magnetic permeability absorbing thin film material provided by the present invention comprises the following raw materials in parts by weight: 25-60 parts of conjugated structure modified polyimide, 25-40 parts of magnetic absorber, 5-15 parts of carbon hollow fiber, and 0-10 parts of functional additives.

[0048] In some embodiments, the conjugated structure modified polyimide is obtained by reacting raw materials including diaminophenyl ether monomer, dianhydride monomer, and a substance containing a conjugated structure. More specifically, by mass ratio, the ratio of diaminophenyl ether monomer: dianhydride monomer: substance containing a conjugated structure is 1:1:0.1-0.3, for example, 1:1:0.1, 1:1:0.2, or 1:1:0.3.

[0049] Preferably, the magnetic absorbent is a conjugated structure modified polyimide-coated magnetic nanosheet intercalated modified graphene composite particle, which is obtained by reacting diaminophenyl ether monomer, dianhydride monomer, and a substance containing a conjugated structure on the surface of the magnetic nanosheet intercalated modified graphene composite particle. An exemplary mass ratio of diaminophenyl ether monomer, dianhydride monomer, and substance containing a conjugated structure is 1:1:0.1-0.3, for example, 1:1:0.1, 1:1:0.2, or 1:1:0.3; 4.

[0050] In some embodiments, the substance containing the conjugated structure contains two amino groups; through the amino groups, the substance containing the conjugated structure can react with the dianhydride monomer to participate in the polyimide formation reaction, thereby introducing the conjugated structure into the polyimide chain segment.

[0051] An exemplary substance containing a conjugated structure is anthracene or naphthalene containing two amino groups. The anthracene or naphthalene conjugated structure has a large π-bond conjugated system, which can change the dielectric constant of the material, enhance the polarization ability of the polyimide matrix, and give the material better absorption performance in the low-frequency band.

[0052] Exemplary anthracene or naphthalene compounds containing two amino groups include, but are not limited to, at least one of 2,6-diaminoanthracene, (E)-2-(3-(6-(dimethylamino)naphth-2-yl)allyl)malonitrile, 1,2-diamino-naphthalene-5-sulfonamide hydrochloride, 2,3-diaminonaphthalene, 1,8-diaminonaphthalene, and 1,5-diaminonaphthalene.

[0053] Exemplary dianhydride monomers include, but are not limited to, at least one of pyromellitic dianhydride (PMDA), biphenyl dianhydride (BPDA), and ether anhydride (ODPA); other dianhydride monomers may also be selected according to actual needs.

[0054] Exemplary diaminophenyl ether monomers include, but are not limited to, 4,4'-diaminodiphenyl ether (ODA), 3,4'-diaminodiphenyl ether (3,4'-ODA), or 2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl ether (TFMB), and combinations thereof. The presence of ether bonds in the diaminophenyl ether monomer molecule increases the flexibility of the polyimide molecular chain, which is beneficial for improving the film-forming properties and flexibility of the film, reducing the likelihood of cracking or embrittlement. The benzene ring structure in the diaminophenyl ether monomer exhibits high thermal stability, increasing the heat distortion temperature of the polyimide. The structural characteristics of the diaminophenyl ether monomer result in a lower dielectric constant for the polyimide. In the low-frequency band, the lower dielectric constant facilitates combination with magnetic absorbers to further optimize the electromagnetic matching characteristics of the material, reduce electromagnetic wave reflection on the material surface, and improve the absorption efficiency of electromagnetic waves, thereby enhancing the absorption performance of the absorbing material in the low-frequency band.

[0055] On the other hand, the present invention provides a method for preparing a high-permeability absorbing thin film material in the low-frequency band, comprising the following steps:

[0056] Step 1: Mix the conjugated structure modified polyimide, magnetic absorber, carbon hollow fiber and functional additives, add organic solvent, and stir at room temperature for 2-4 hours to form a uniform slurry;

[0057] Step 2: Apply the obtained slurry to the substrate, dry it, and then calender and cool it to obtain a low-frequency band high magnetic permeability absorbing thin film material.

[0058] In some embodiments, the functional additives include, but are not limited to, at least one of dispersants and leveling agents; the dispersants include, but are not limited to, at least one of PVP, oleic acid, stearic acid, and lauric acid; the leveling agents include, but are not limited to, at least one of polydimethylsiloxane (silicone oil) and acrylate leveling agents.

[0059] In some embodiments, the method for preparing the conjugated structure modified polyimide is as follows:

[0060] The dianhydride monomer, diaminophenyl ether monomer, and the substance containing the conjugated structure are dissolved in an organic solvent to prepare a mixed solution; under nitrogen protection, a prepolymerization reaction is carried out at 0-5℃ for 1-2 hours; then the temperature is raised to 100-150℃ and the reaction is continued for 3-5 hours, and then dried to obtain the conjugated structure modified polyimide.

[0061] Preferably, the magnetic absorber conjugated structure modified polyimide-coated magnetic nanosheet intercalated graphene composite particles are prepared by the following method:

[0062] A mixed solution was prepared by dissolving dianhydride monomers, diaminophenyl ether monomers, and substances containing conjugated structures in an organic solvent. Magnetic nanosheet-intercalated graphene composite particles were added to the mixed solution, and a prepolymerization reaction was carried out at 0-5℃ for 1-2 hours under nitrogen protection. The temperature was then raised to 100-150℃, and the reaction continued for 3-5 hours. Solid-liquid separation and drying were then performed to obtain conjugated structure-modified polyimide-coated magnetic nanosheet-intercalated graphene composite particles. A unique composite structure was constructed by using magnetic nanosheet-intercalated graphene composite particles and coating their surface with conjugated structure-modified polyimide. This structural design not only fully utilizes the high specific surface area and excellent electrical properties of graphene and the magnetic properties of magnetic nanosheets, but also leverages the film-forming properties of polyimide and the special properties of the conjugated structure to further optimize and improve the material's microwave absorption performance, mechanical properties, and stability.

[0063] In some embodiments, the mass ratio of the magnetic nanosheet-intercalated graphene composite particles to the mixed solution is 1:10 to 1:20, for example, 1:10, 1:12, 1:14, 1:16, or 1:20. In an exemplary mixed solution, the total mass percentage of the dianhydride monomer, the diaminophenyl ether monomer, and the substance containing the conjugated structure is 10-20%, for example, 10%, 12%, 15%, 18%, or 20%.

[0064] In some embodiments, the method for preparing the magnetic nanosheet intercalated modified graphene composite particles is as follows:

[0065] S1. Add the magnetic nanosheets to an organic solvent or aqueous solution containing a dispersant, and sonicate them to disperse them fully, forming a uniform magnetic nanosheet suspension.

[0066] S2. Add graphene to another part of the solution containing dispersant and sonicate to obtain a graphene suspension.

[0067] S3. Under stirring conditions, the magnetic nanosheet suspension is slowly added dropwise to the graphene suspension. After the addition is complete, stirring is continued for a period of time. Then, the self-assembly can be carried out by adjusting the pH value of the solution to 4.5-7.

[0068] S4. Separate the composite particles from the solution, wash them multiple times with deionized water or organic solvent, and finally dry them at low temperature to obtain magnetic nanosheet intercalated modified graphene composite particles.

[0069] In some embodiments, the dispersant includes, but is not limited to, one of polyvinylpyrrolidone (PVP) and sodium dodecylbenzenesulfonate (SDBS).

[0070] Exemplary magnetic nanosheets include at least one of two-dimensional sheet-like FeCoZr, two-dimensional sheet-like FeNi, two-dimensional sheet-like FeNiMo, two-dimensional sheet-like FeSiAl, and two-dimensional sheet-like FeSiCr soft magnetic metal powders.

[0071] In some implementations, the magnetic nanosheets have a particle size D50 < 70 μm.

[0072] In some embodiments, the magnetic nanosheets in the magnetic nanosheet suspension have a mass percentage of 15-40 wt%, for example, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, or 40 wt%; the graphene in the graphene suspension has a mass percentage of 10-30 wt%, for example, 10 wt%, 12 wt%, 14 wt%, 16 wt%, 20 wt%, 25 wt%, or 30 wt%; the mass ratio of graphene to magnetic nanosheets in the graphene suspension is 3-5:1, for example, 3:1, 3.5:1, 4:1, 4.5:1, or 5:1. The mass ratio of magnetic nanosheets to graphene affects the intercalation self-assembly effect of the magnetic nanosheets. Excessive addition of magnetic nanosheets can lead to agglomeration and poor intercalation self-assembly. In some embodiments, the method for preparing the carbon hollow fiber includes:

[0073] Step 1: Dissolve polyacrylonitrile in an organic solvent, add ferrite and antioxidant, and mix thoroughly to obtain the shell spinning solution stock solution; the shell spinning solution stock solution contains: polyacrylonitrile at a proportion of 8-20 wt%, for example 8 wt%, 12 wt%, 14 wt%, 16 wt%, 18 wt%, 20 wt%; ferrite at a proportion of 10-15 wt%, for example 10 wt%, 12 wt%, 15 wt%; and antioxidant (titanium oxide) at a proportion of 1-3 wt%, for example 1 wt%, 2 wt%, 3 wt%.

[0074] Step 2: Dissolve polyvinylpyrrolidone in an organic solvent, add an antioxidant, and mix thoroughly to obtain the core spinning solution stock solution; in the core spinning solution: the proportion of polyvinylpyrrolidone is 6-12wt%, for example, 6wt%, 8wt%, 10wt%, 12wt%; the proportion of antioxidant is 1-3wt%, for example, 1wt%, 2wt%, 3wt%.

[0075] Step 3: Perform coaxial electrospinning on the outer shell spinning solution and the inner core spinning solution to obtain a carbon fiber precursor. Then, soak the carbon fiber precursor in water to obtain a carbon hollow fiber precursor.

[0076] Step 4: The carbon hollow fiber precursor is dried, pre-oxidized, and carbonized at high temperature in sequence, and then roughened by acid immersion and mechanically cut or directly mechanically cut to obtain the carbon hollow fiber.

[0077] Preferably, the ferrite is manganese-zinc ferrite (MnZn), which has high permeability. This allows it to provide higher impedance in low-frequency applications, which is beneficial for the efficient conversion of electromagnetic energy. Exemplary manganese-zinc ferrites include, but are not limited to, TDG50 from Tiantong Holdings Co., Ltd., H5C2, H5C3, K5D, and H5E series from TDK; 12001H and 18000H materials from TOKIN; and T42 and T46 materials from Siemens.

[0078] The present invention will be further described below with specific embodiments.

[0079] The absorbent added in the following examples and comparative examples is carbon hollow fiber, wherein the preparation method of carbon hollow fiber®1 is as follows:

[0080] Step 1: Dissolve polyacrylonitrile in N,N-dimethylformamide, add manganese zinc ferrite and antioxidant titanium dioxide, and mix thoroughly to obtain the shell spinning solution stock solution; the proportion of polyacrylonitrile in the shell spinning solution stock solution is 15wt%, the proportion of ferrite is 15wt%, and the proportion of titanium dioxide is 2wt%.

[0081] Step 2: Dissolve polyvinylpyrrolidone in N,N-dimethylformamide, add titanium dioxide (an antioxidant), and mix thoroughly to obtain the core spinning solution stock solution; the proportion of polyvinylpyrrolidone in the core spinning solution is 12 wt%, and the proportion of titanium dioxide (an antioxidant) is 1 wt%.

[0082] Step 3: The outer shell spinning solution and the core spinning solution are coaxially electrospun at a flow rate ratio of 2:1 and a total supply rate of 8.0 mL / h to obtain a carbon fiber precursor. The carbon fiber precursor is then soaked in water at 50°C for 24 hours to obtain a hollow carbon fiber precursor. The loading voltage for the coaxial electrospinning is 18 kV, and the distance between the needle and the receiving cylinder is 16 cm.

[0083] Step 4: The carbon hollow fiber precursor is dried at 60°C for 12 hours, oxidized at 220°C for 3 hours, and heated to 800°C at a rate of 4°C / min and held for 2 hours under a nitrogen atmosphere to obtain the carbon hollow fiber to be treated. The carbon hollow fiber to be treated is then immersed in a hydrochloric acid solution at 40°C for 3 hours to roughen it, and then mechanically cut to obtain the carbon hollow fiber.

[0084] The preparation method of carbon hollow fiber®2 differs from that of carbon hollow fiber®1 in that the proportion of ferrite in the shell spinning solution is 0 wt%, that is, no ferrite is added to the shell spinning solution.

[0085] The preparation method of carbon hollow fiber®3 differs from that of carbon hollow fiber®1 in that the carbon hollow fiber to be treated is not subjected to acid immersion roughening, but is directly mechanically cut to obtain the carbon hollow fiber.

[0086] The addition and proportion of some raw materials in the above-mentioned carbon hollow fiber preparation process are shown in Table 1.

[0087] Table 1. Material composition for preparing carbon hollow fibers

[0088] carbon hollow fiber Manganese zinc ferrite Concentration of hydrochloric acid solution for acid leaching ®1 TianTong Holdings Co., Ltd. TDG50 10wt% ®2 - 10wt% ®3 TianTong Holdings Co., Ltd. TDG50 -

[0089] In addition, the examples and comparative examples involve graphene composite particles modified by magnetic nanosheet intercalation, and the preparation of such graphene composite particles is provided as follows:

[0090] S1. Two-dimensional sheet-like FeNi particles with a particle size D50 < 70 μm are added to an aqueous solution and ultrasonically dispersed to form a uniform magnetic nanosheet suspension; the mass percentage of the two-dimensional sheet-like FeNi in the magnetic nanosheet suspension is 20 wt%.

[0091] S2. Graphene is added to another portion of an aqueous solution containing SDS and subjected to ultrasonic treatment to obtain a graphene suspension; the mass percentage of graphene in the graphene suspension is 15 wt%.

[0092] S3. Under stirring conditions, the magnetic nanosheet suspension was slowly added dropwise to the graphene suspension at a mass ratio of graphene in the graphene suspension to two-dimensional sheet FeN in the magnetic nanosheet suspension of 4:1. After the addition was completed, stirring was continued for 5 hours. Then the pH of the solution was adjusted to 6 to carry out self-assembly.

[0093] S4. The obtained magnetic nanosheet intercalated graphene composite particles are separated from the solution, washed with deionized water, and finally dried at 40°C to obtain magnetic nanosheet intercalated graphene composite particles.

[0094] Furthermore, the preparation examples of conjugated structure modified polyimide-coated magnetic nanosheet intercalated modified graphene composite particles involved in the embodiments and comparative examples of the present invention are provided below:

[0095] A mixed solution was prepared by dissolving dianhydride monomer, diaminophenyl ether monomer, and a substance containing a conjugated structure in N,N-dimethylformamide. The total mass percentage of the dianhydride monomer, diaminophenyl ether monomer, and substance containing a conjugated structure in the mixed solution was 15%. Magnetic nanosheet intercalated graphene composite particles were added to the mixed solution and prepolymerized at 0°C for 2 hours under nitrogen protection. The temperature was then raised to 120°C and the reaction was continued for 5 hours. The resulting solid was then separated from the solid and dried at 60°C to obtain conjugated structure modified polyimide-coated magnetic nanosheet intercalated graphene composite particles.

[0096] The types and proportions of the substances added during the preparation of conjugated structure modified polyimide-coated magnetic nanosheet intercalated graphene composite particles are shown in Table 2.

[0097] Table 2. Ingredients for preparing the magnetic absorbent

[0098] Magnetic absorbent Types of dianhydride monomers Diaminophenyl ether monomers Types of substances containing conjugated structures The mass ratio of dianhydride monomer, diaminophenyl ether monomer, and substances containing conjugated structures The mass ratio of magnetic nanosheet intercalated modified graphene composite particles and mixed solution &1 PMDA 4,4'-Diaminodiphenyl ether 2,6-Diaminoanthracene 1:1:0.2 1:10 &2 BPDA 3,4'-Diaminodiphenyl ether (E)-2-(3-(6-(dimethylamino)naphth-2-yl)allyl)malonitrile 1:1:0.1 1:15 &3 BPDA 2,2'-Di(trifluoromethyl)-4,4'-diaminodiphenyl ether 2,3-Diaminonaphthalene 1:1:0.3 1:20 &4 PMDA 4,4'-Diaminodiphenyl ether 2,6-Diaminoanthracene 1:1:0.2 1:15

[0099] Furthermore, examples of the preparation of conjugated structure modified polyimides involved in the embodiments and comparative examples are provided below:

[0100] A dianhydride monomer, a diaminophenyl ether monomer (or a diamino ether monomer), and a substance containing a conjugated structure are dissolved in N,N-dimethylformamide to prepare a mixed solution. The total mass percentage of the dianhydride monomer, diaminophenyl ether monomer, and substance containing a conjugated structure in the mixed solution is 15%. Under nitrogen protection, a prepolymerization reaction is carried out at 5°C for 1 hour. Then, the temperature is raised to 120°C and the reaction is continued for 4 hours. The mixture is then dried at 60°C to obtain the conjugated structure modified polyimide.

[0101] The types and proportions of substances used to prepare conjugated structure modified polyimide are shown in Table 3.

[0102] Table 3. Types and proportions of substances used in the preparation of conjugated structure modified polyimide

[0103] Conjugated structure modified polyimide Types of dianhydride monomers Types of diaminophenyl ether monomers (or diamino monomers) Types of substances containing conjugated structures The mass ratio of dianhydride monomer, diaminophenyl ether monomer (or diamino ethylenediamine monomer), and substances containing conjugated structures #1 PMDA 4,4'-Diaminodiphenyl ether 2,6-Diaminoanthracene 1:1:0.2 #2 BPDA 3,4'-Diaminodiphenyl ether (E)-2-(3-(6-(dimethylamino)naphth-2-yl)allyl)malonitrile 1:1:0.1 #3 BPDA 2,2'-Di(trifluoromethyl)-4,4'-diaminodiphenyl ether 2,3-Diaminonaphthalene 1:1:0.3 #4 PMDA 4,4'-Diaminodiphenyl ether 2,6-Diaminoanthracene 1:1:0.2 #5 PMDA ethylenediamine 2,6-Diaminoanthracene 1:1:0.2 #6 PMDA ethylenediamine - 1：1.2

[0104] Preparation of high permeability absorbing thin film materials in the low-frequency band:

[0105] Step 1: Mix the conjugated structure modified polyimide, magnetic absorber, carbon hollow fiber and functional additives, add N,N-dimethylformamide (DMF), and stir at room temperature for 3 hours to form a uniform slurry with a solid content of 60%.

[0106] Step 2: Apply the obtained slurry to the substrate, dry it, and then calender and cool it to obtain a low-frequency band high magnetic permeability absorbing film with a thickness of 0.1 mm. The control parameters of the calendering process are: calendering roll temperature of 220℃ and cooling roll temperature of 60℃.

[0107] Table 4. Film Formulation of High Permeability Absorbing Thin Film Materials in Low-Frequency Bands for Examples and Comparative Examples

[0108]

[0109] The properties of the thin film materials prepared in the examples and comparative examples were tested, and the test results are shown in Table 5. Among them:

[0110] 1. The elongation at break of the thin film materials prepared in the examples and comparative examples was tested according to GB / T 1040.3-2006 standard;

[0111] 2. The microwave absorption properties of the thin film materials prepared in the examples and comparative examples were tested according to standard SJ-20512-1995;

[0112] 3. The heat distortion temperature of the thin film materials prepared in the examples and comparative examples was determined in accordance with GB / T 1634.2 standard.

[0113] Table 5. Wave absorption performance tests of thin film materials prepared in the examples and comparative examples.

[0114]

[0115] As can be seen from Table 5, the thin film material prepared in the embodiments of the present invention has high magnetic permeability and wave absorption performance in the low frequency band of 1GHz to 8GHz, and has high heat distortion temperature and high elongation at break, indicating that it has good stability and mechanical properties.

[0116] Furthermore, in Example 2, since no ferrite is added to the absorbing material, the magnetic permeability of the absorbing film material is reduced, which in turn affects its ability to absorb low-frequency electromagnetic waves, resulting in a decrease in absorbing performance.

[0117] In Example 3, the carbon hollow fiber is not subjected to acid immersion roughening treatment, and the surface of the material is relatively smooth. This reduces the number of times electromagnetic waves are scattered and reflected on the surface of the material, which is not conducive to electromagnetic waves entering the interior of the material, thus reducing the absorption performance. In addition, without acid immersion roughening treatment, the interfacial bonding between the components in the microwave absorbing film material is relatively poor, and delamination and peeling are prone to occur during use, affecting the stability of the material.

[0118] In Example 7, the polyimide with a conjugated structure was prepared using ethylenediamine instead of diaminophenyl ether. Due to the absence of ether groups and benzene rings, the thermal stability decreased, and the mechanical properties deteriorated due to the increased rigidity of the molecule. Furthermore, since the structure of diaminophenyl ether helps to improve the magnetic permeability of the material to a certain extent in conjunction with magnetic absorbers, the magnetic permeability and wave absorption performance of Example 7 decreased compared to Example 1.

[0119] In Comparative Example 1, no hollow carbon fiber was added. The hollow structure allows electromagnetic waves to undergo multiple reflections and scatterings within the material, prolonging the propagation path of electromagnetic waves and increasing the interaction time between electromagnetic waves and the material, thereby improving the absorption effect. In addition, hollow carbon fiber can interact with magnetic absorbers, affecting the distribution and orientation of magnetic particles, adjusting the permeability of the absorbing film material, and giving the absorbing film material more suitable magnetic properties and absorption performance in the low-frequency band. Carbon fiber itself has the characteristics of high strength and high modulus. Adding it to the polyimide matrix can enhance the mechanical strength and toughness of the absorbing film material, improving the mechanical properties of the absorbing film.

[0120] In Comparative Example 2, graphene was used instead of conjugated structure modified polyimide to coat magnetic nanosheets with intercalated graphene composite particles. Graphene has a high specific surface area, but it is prone to agglomeration in the matrix, making it difficult to achieve good uniform dispersion. Uneven dispersion will lead to non-uniformity of the performance of the microwave absorbing film material, affecting the consistency of the microwave absorption effect. As a result, the microwave absorbing film material prepared in Comparative Example 2 has relatively poor microwave absorption performance, mechanical properties and thermal stability.

[0121] In Comparative Example 3, polyimide was added to replace the conjugated structure modified polyimide. The conjugated structure in the conjugated structure modified polyimide can generate special electronic transitions and polarization phenomena in the low-frequency band, which helps to regulate the electromagnetic properties of the material. Although graphene has excellent electrical properties, it lacks the special effect brought by this conjugated structure and cannot achieve effective absorption and control of low-frequency electromagnetic waves. In addition, the conjugated system helps to enhance the polarization ability and electron cloud mobility of the material, so that it can interact with electromagnetic waves more effectively in the low-frequency band, generate greater dielectric loss, and improve the absorption performance. In Comparative Example 3, the matrix conjugated structure is reduced, and the absorption performance is relatively reduced.

Claims

1. A low-frequency band high-permeability absorbing thin film material, characterized in that, The raw materials include the following parts by weight: 25-60 parts of conjugated structure modified polyimide, 25-40 parts of magnetic absorber, 5-15 parts of carbon hollow fiber, and 0-10 parts of functional additives; The conjugated structure modified polyimide is obtained by reacting raw materials including diaminophenyl ether monomer, dianhydride monomer, and substances containing conjugated structures. The substance containing a conjugated structure includes at least one of 2,6-diaminoanthracene, (E)-2-(3-(6-(dimethylamino)naphth-2-yl)allyl)malonitrile, 1,2-diamino-naphthalene-5-sulfonamide hydrochloride, 2,3-diaminonaphthalene, 1,8-diaminonaphthalene, and 1,5-diaminonaphthalene. The magnetic absorber is a composite particle of conjugated polyimide-coated magnetic nanosheets intercalated with graphene.

2. The microwave absorbing thin film material according to claim 1, characterized in that, The preparation method of the conjugated structure modified polyimide is as follows: The dianhydride monomer, diaminophenyl ether monomer, and the substance containing the conjugated structure are dissolved in an organic solvent to prepare a mixed solution; under nitrogen protection, a prepolymerization reaction is carried out at 0-5℃ for 1-2 hours; then the temperature is raised to 100-150℃ and the reaction is continued for 3-5 hours, and then dried to obtain the conjugated structure modified polyimide.

3. The microwave absorbing thin film material according to claim 1, characterized in that, The magnetic absorbent is obtained by reacting diaminophenyl ether monomer, dianhydride monomer, and substances containing conjugated structures on the surface of magnetic nanosheet intercalated modified graphene composite particles.

4. The microwave absorbing thin film material according to claim 3, characterized in that, The magnetic absorbent is prepared by: A mixed solution was prepared by dissolving dianhydride monomer, diaminophenyl ether monomer, and a substance containing a conjugated structure in an organic solvent. Magnetic nanosheet intercalated modified graphene composite particles were added to the mixed solution and prepolymerized at 0-5℃ for 1-2 hours under nitrogen protection. The temperature was then raised to 100-150℃ and the reaction continued for 3-5 hours. After solid-liquid separation and drying, a magnetic absorbent was obtained. The mass ratio of the magnetic nanosheet intercalated modified graphene composite particles to the mixed solution is 1:10-1:20; in the mixed solution, the total mass percentage of the dianhydride monomer, diaminophenyl ether monomer, and substances containing conjugated structures is 10-20%.

5. The microwave absorbing thin film material according to any one of claims 1-4, characterized in that, It must meet at least one of the following characteristics: (1) When the diaminophenyl ether monomer, dianhydride monomer, and substance containing a conjugated structure react, the mass ratio of the diaminophenyl ether monomer, dianhydride monomer, and substance containing a conjugated structure is 1:1:0.1-0.3; (2) The substance containing the conjugated structure contains two amino groups.

6. The microwave absorbing thin film material according to claim 5, characterized in that, It must meet at least one of the following characteristics: (1) The dianhydride monomer includes at least one of pyromellitic dianhydride, biphenyl dianhydride, and ether anhydride; (2) The diaminophenyl ether monomer includes at least one of 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, and 2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl ether.

7. The microwave absorbing thin film material according to claim 4, characterized in that, The preparation method of the magnetic nanosheet intercalated modified graphene composite particles is as follows: S1. Add the magnetic nanosheets to an organic solvent or aqueous solution containing a dispersant, and sonicate them to disperse them fully, forming a uniform magnetic nanosheet suspension. S2. Add graphene to another part of the solution containing dispersant and sonicate to obtain a graphene suspension. S3. Under stirring conditions, the magnetic nanosheet suspension is slowly added dropwise to the graphene suspension. After the addition is complete, stirring is continued for a period of time. Then, the pH of the solution is adjusted to 4.5-7 to facilitate self-assembly. S4. Separate the composite particles from the solution, wash them multiple times, and then dry them to obtain magnetic nanosheet intercalated modified graphene composite particles.

8. The microwave absorbing thin film material according to claim 7, characterized in that, The preparation method of the magnetic nanosheet intercalated modified graphene composite particles meets at least one of the following characteristics: (1) The magnetic nanosheets in the magnetic nanosheet suspension account for 15-40 wt% of the mass, and the graphene in the graphene suspension accounts for 10-30 wt% of the mass. (2) The mass ratio of graphene in the graphene suspension to the mass ratio of magnetic nanosheets in the magnetic nanosheet suspension is 3-5:1; (3) The magnetic nanosheets include at least one of two-dimensional sheet FeCoZr, two-dimensional sheet FeNi, two-dimensional sheet FeNiMo, two-dimensional sheet FeSi, and two-dimensional sheet FeSiCr soft magnetic metal powder; (4) The particle size D50 of the magnetic nanosheets is less than 70 μm.

9. A method for preparing a low-frequency band high-permeability absorbing thin film material according to any one of claims 1-8, characterized in that, Includes the following steps: Step 1: Mix the conjugated structure modified polyimide, magnetic absorber, carbon hollow fiber and functional additives, add organic solvent, and stir at room temperature for 2-4 hours to form a uniform slurry; Step 2: Apply the obtained slurry to the substrate, dry it, and then calender and cool it to obtain a low-frequency band high magnetic permeability absorbing film.

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