Wave-absorbing foam prepreg, preparation and application thereof

Abstract

This invention discloses a microwave absorbing foam prepreg, comprising a pure resin film layer, a dual-foam structure microwave absorbing foam layer, and a microwave absorbing adhesive film layer; wherein, the dual-foam structure of the dual-foam structure microwave absorbing foam layer consists of resin foam and pure electromagnetic matrix foam; the microwave absorbing adhesive film is a resin film with added magnetic or dielectric microwave absorbing agents; the resin used in the resin film layer and the microwave absorbing adhesive film layer is the same. This invention also discloses its preparation and application. The microwave absorbing foam prepreg provided by this invention has good surface integrity, controllable film thickness, peelable and processable film, good resin processability, and strong electromagnetic wave absorption capacity, exhibiting excellent performance and microwave absorption properties. It can be applied in aerospace, communications, electronic equipment, security building materials, and shoe soles, among other fields.

Description

Technical Field

[0001] This invention relates to a microwave absorbing foam prepreg, its preparation, and its application. Background Technology

[0002] Microwave absorbing materials are special materials that can effectively absorb electromagnetic wave energy and have a wide range of applications. To improve the absorption efficiency, the most common method used in engineering applications is material composite, which combines materials with different absorption mechanisms and controls the composite ratio to achieve impedance matching and electromagnetic attenuation. Among them, microwave absorbing prepregs have advantages in engineering applications, including thickness advantage, microwave absorption performance advantage, shape designability, product type and performance advantage, etc., and have attracted widespread attention. However, there are still many bottlenecks in microwave absorbing prepregs that need to be overcome: (1) Large mass. After adding magnetic materials (generally with a large density), the mass is further increased, which is not conducive to its practical use, especially in the aerospace field, which requires a lighter density. (2) Narrow absorption bandwidth. Traditional prepregs often require complex multi-layer design and multiple experiments to broaden the absorption bandwidth. (3) The middle fabric layer is prone to debonding due to thermal stress or weak shear strength in actual applications.

[0003] Currently, there are various types of prepreg materials for foam sandwich layers. Foam sandwich layers can be divided into two main categories: resin-based foam and pure electromagnetic loss matrix foam. Resin-based foams can be further subdivided into: pure resin foam boards (CN 106147703A, CN106147702B, CN1929731A), which have low electromagnetic parameters, which are beneficial for impedance matching but not for electromagnetic attenuation; resin foam boards mixed with absorbents, or rigid microwave absorbing foams (CN 117246019A, CN 113942286A, CN 101700706A), which enhance electromagnetic attenuation, but the blending of absorbents and resins increases density to some extent, and the molding process needs to be modified accordingly based on the amount of absorbent filled; and complex structure foam layers, including hollow fabric cavities filled with microwave absorbing foam material (CN113524820B, microwave absorbing foam type not specified, CN 116512686A, resin microwave absorbing foam), which enhance the mechanical properties of the material, especially solving the debonding problem. The introduction of special hollow structure fabrics increases the complexity of fiber preparation and costs, and may also increase the material density.

[0004] Pure electromagnetic loss matrix foams include carbon-based foam (CN 118040340A), which is lightweight, porous, and has good electrical conductivity; and metal matrix foams, such as aluminum foam (CN 111805999B), which has low density and certain microwave absorption properties. However, pure electromagnetic loss matrix foams are less widely used and studied compared to resin-based foams, possibly due to their poor compatibility with resins. Summary of the Invention

[0005] This invention was made in order to simultaneously reduce material density and broaden the absorption bandwidth.

[0006] In this invention, resin foam and pure electromagnetic matrix foam (carbon-based foam or metal matrix foam) are combined to form a dual-foam structure, which effectively simplifies the process and improves the absorption performance of the material. A pure electromagnetic loss matrix foam is selected and embedded into the pure resin foam via vacuum impregnation. This is similar to a complex foam layer structure, but with significant improvements in both process and performance. Electromagnetic attenuation is mainly achieved by the pure electromagnetic loss matrix foam, eliminating the need to consider process changes caused by mixing electromagnetic absorption powder with the resin. The pure electromagnetic loss matrix foam has an interconnected pore structure, which further enhances its electromagnetic attenuation capability. The upper and lower encapsulating films are made of materials with a different electromagnetic loss mechanism from the foam, achieving co-loss of magneto-dielectric properties and optimizing wave absorption performance.

[0007] As one aspect of the present invention, a microwave absorbing foam prepreg is disclosed, comprising a pure resin film layer, a dual-foam structure microwave absorbing foam layer, and a microwave absorbing film layer arranged sequentially; wherein the dual-foam structure of the dual-foam structure microwave absorbing foam layer consists of resin foam and pure electromagnetic matrix foam; the microwave absorbing film layer comprises a resin mixed with a curing agent and a microwave absorbing agent, wherein the microwave absorbing agent is a magnetic microwave absorbing agent or a dielectric microwave absorbing agent; the resin in the resin film layer and the microwave absorbing film layer is the same.

[0008] In a specific embodiment, the resin is bisphenol A epoxy resin or liquefied bismaleimide resin.

[0009] In a specific embodiment, the magnetic absorbing agent is ferrite, carbonyl iron powder, or magnetic metal whiskers; the dielectric absorbing agent is silicon carbide fiber, graphite, carbon black, chopped carbon fiber, graphene, carbon nanotubes, or conductive polymer.

[0010] In a specific embodiment, the mass ratio of the magnetic absorbing agent in the microwave absorbing film to the resin mixed with the curing agent is 50-70:50-30, and the mass ratio of the dielectric absorbing agent to the resin mixed with the curing agent is 0.5-20:99.5-80.

[0011] In a specific embodiment, the thickness of both the pure resin film and the microwave absorbing film is 0.1mm-0.25mm.

[0012] In a specific embodiment, the pure resin film and the microwave absorbing film have the same thickness.

[0013] As another aspect of the present invention, a method for preparing the above-mentioned microwave absorbing foam prepreg is provided, the method comprising:

[0014] 1) Preparation of microwave absorbing film: Pure resin is coated with a curing agent to obtain a pure resin film; magnetic microwave absorbing agent or dielectric microwave absorbing agent is dispersed in resin mixed with curing agent and coated to obtain a microwave absorbing film.

[0015] 2) Preparation of dual-foam structure microwave absorbing foam: Pure electromagnetic matrix foam is laid on the surface of a mold and filled with pure resin foaming material. The foaming material is then composited with the pure electromagnetic loss matrix foam using a vacuum impregnation method. The composite foam material is placed in an oven for foaming to form a multi-layered hollow composite material. This produces a dielectric loss type or magnetic loss type dual-foam structure microwave absorbing foam.

[0016] 3) Preparation of microwave absorbing foam prepreg: Pure resin film, double foam structure microwave absorbing foam, and microwave absorbing film are laid out in sequence and formed by bag pressing, molding or autoclave method.

[0017] In a specific embodiment, in step 1), the magnetic absorbing agent is ferrite, carbonyl iron powder or magnetic metal whiskers, the dielectric absorbing agent is silicon carbide fiber, graphite, carbon black, short-cut carbon fiber, graphene, carbon nanotubes or conductive polymer, and the resin is bisphenol A epoxy resin or liquefied bismaleimide resin.

[0018] In a specific embodiment, in step 1), the thickness of both the pure resin film and the microwave absorbing film is 0.1mm-0.25mm, and the thicknesses of the pure resin film and the microwave absorbing film are the same.

[0019] In a specific embodiment, in step 1), the mass ratio of the magnetic absorbing agent to the resin mixed with the curing agent is 50-70:50-30, and the mass ratio of the dielectric absorbing agent to the resin mixed with the curing agent is 0.5-20:99.5-80.

[0020] In a specific embodiment, in step 2), the pure electromagnetic matrix foam is one of cobalt foam, nickel foam, graphite-based foam, cork-derived carbon-based foam, and polystyrene board-derived carbon-based foam, and the resin in the pure resin foaming material is bisphenol A epoxy resin or thermosetting 6216 phenolic resin.

[0021] As another aspect of the present invention, it relates to the application of the above-mentioned microwave absorbing foam prepreg in the fields of aerospace, communications, electronic equipment, building materials and shoe soles.

[0022] Compared with the prior art, the present invention has the following significant advantages:

[0023] This invention aims to reduce material density and broaden the absorption bandwidth by replacing the middle layer of conventional microwave-absorbing prepreg with foam. Different types of microwave-absorbing foam are used to meet different performance requirements. The microwave-absorbing foam of this invention effectively combines resin foam and pure electromagnetic matrix foam (carbon-based foam or metal matrix foam), utilizing the advantages of both. The prepreg film can also be selected according to performance requirements, incorporating magnetic absorbers, including magnetic alloy powders such as carbonyl iron, iron, cobalt, and nickel, ferrite powder, etc., or conductive absorbers, including carbon black, carbon fibers (continuous or chopped), etc.

[0024] Taking an epoxy resin absorbing film with a small amount of carbonyl iron embedded in a carbon-based foam as an example, the carbon-based foam has a three-dimensional interconnected conductive network that enhances conductivity loss. Combined with the magnetic loss of the magnetic resin film, the resulting continuous interface further introduces interfacial polarization. These multiple loss mechanisms work together to effectively enhance the material's attenuation capability for electromagnetic waves. Simultaneously, the numerous conductive foam pores introduce multiple reflections and scattering, further optimizing impedance matching. Therefore, excellent lightweight and broadband absorption performance is foreseeable. Furthermore, it requires no complex layer structure design and is simple to fabricate.

[0025] Due to its excellent performance and wave absorption properties, this material can be applied in aerospace, communications, electronic equipment, security building materials, and shoe soles (lightweight and high strength). Detailed Implementation

[0026] In the example:

[0027] The bisphenol A epoxy resin, model E51, was purchased from Guangzhou Dongjun Chemical Co., Ltd.

[0028] The liquid bismaleimide resin is N,N'-4,4'-diphenylmethane bismaleimide, purchased from Tiangong Sanhua Chemical Materials.

[0029] The thermosetting 6216 phenolic resin was purchased from Henan Borun New Materials.

[0030] The blowing agent used for the epoxy resin is azodicarbonamide, model AG-175, purchased from Foshan Jieheng New Materials Co., Ltd. The blowing agent used for the phenolic resin is analytical grade sodium bicarbonate, brand name Xilong Scientific.

[0031] The water-based resin adhesive is water-based epoxy resin F0704, purchased from Shenzhen Yoshida Chemical Co., Ltd.

[0032] The benzyl alcohol mentioned is analytical grade benzyl alcohol, branded by Xilong Scientific.

[0033] The polyetheramine is polyetheramine D230, which was purchased from Shandong Yousuo Chemical Technology Co., Ltd.

[0034] The carbon black was 5000 mesh and purchased from Huifeng Chemical.

[0035] The chopped carbon fiber is a thermoplastic 6mm chopped carbon fiber filament, purchased from Polycarbonate (Guangdong) Co., Ltd.

[0036] The graphite, with product number qd-056, was purchased from Lingshou County Qiangdong Mineral Products Processing Plant.

[0037] The carbonyl iron is designated as JC-Fe-1, and its specification is metallic carbonyl iron powder. The brand is Junchen Metal.

[0038] The iron oxide is of type 1 (Iron Black), 400 mesh, and brand name is Anhong.

[0039] The nickel powder is spherical, 500 mesh, and was purchased from Guangzhou Metal Metallurgy Co., Ltd.

[0040] The cobalt foam, with item number JY003, and the nickel foam, with item number JYS112, were both purchased from Kunshan Yizhongtian New Materials Co., Ltd.

[0041] The graphite polystyrene board and the thick polystyrene board, both grade B1, were purchased from Ningbo High-tech Zone Huadongxing Insulation Materials Co., Ltd.

[0042] The cork rolls were purchased from Pinghu Yijia Cork Manufacturing Co., Ltd.

[0043] The honeycomb core material was purchased from Zhongfangte Fiber Co., Ltd.

[0044] The bow-shaped test involves cutting the material to be tested into 300mm*300mm pieces, placing them on a metal plate, and during the wave absorption performance test, the transmitting antenna excites the wave-absorbing foam prepreg, and the reflected signal is picked up by the receiving antenna. By comparing the reflected signals with and without the wave-absorbing material, the reflectivity of the wave-absorbing material, i.e., the wave absorption performance, can be calculated.

[0045] Unless otherwise stated, parts referred to in this application are parts by mass, and proportions are mass ratios.

[0046] Example 1

[0047] 1) Preparation of microwave absorbing film:

[0048] Add 40 parts of 4,4'-diaminodiphenyl sulfone (curing agent) to 100 parts of bisphenol A epoxy resin to obtain a bisphenol A epoxy resin mixed with curing agent. Perform the coating operation:

[0049] Bisphenol A epoxy resin mixed with curing agent is added to the coating roller, which is then pressed tightly against the fixed wheel. The coating machine is started, and the resin is coated onto the continuous release paper to obtain a pure resin film. The film thickness is controlled to be 0.1 mm.

[0050] Carbon black is dispersed in the bisphenol A epoxy resin mixed with curing agent at a ratio of 0.5:99.5, and added to the coating roller. The roller is pressed tightly against the fixed wheel. The coating machine is started, and the resin is coated onto the continuous release paper to obtain a microwave absorbing film. The film thickness is controlled to be 0.1 mm.

[0051] 2) Preparation of dual-foam structure microwave absorbing foam:

[0052] 40 parts of 4,4'-diaminodiphenyl sulfone (curing agent) and 20 parts of azodicarbonamide (foaming agent) were added to 100 parts of bisphenol A epoxy resin to obtain bisphenol A epoxy resin with added curing agent and foaming agent.

[0053] Foamed cobalt (98% porosity, 2.3mm thickness, three-dimensional fully perforated mesh) was laid in a 320mm*320mm*40mm square mold, and the above-mentioned bisphenol A epoxy resin with added curing agent and foaming agent was filled into the barrel to obtain a mold containing foaming raw materials.

[0054] Place the mold containing the foaming raw material into a vacuum drying oven, maintain a vacuum of 0.6 MPa at room temperature, and leave it for 30 minutes. Introduce air into the vacuum drying oven to restore a non-vacuum state, then raise the temperature to 180℃ and maintain it for 2 hours. Partially embedded bisphenol A epoxy resin with added curing agent and foaming agent is embedded in the cobalt foam layer, forming a double-foam structure microwave-absorbing foam (2.3 mm). The yellow foam is epoxy resin foam, and the gray foam is cobalt foam. Remove the excess bisphenol A epoxy resin foam (pure yellow foam layer).

[0055] 3) Preparation of microwave absorbing foam prepreg:

[0056] The pure resin film prepared in step 1), the double-foam structure microwave absorbing foam prepared in step 2), and the microwave absorbing film prepared in step 1) are laid out in sequence to obtain uncured microwave absorbing foam prepreg. The prepreg is then prepared by bag pressing: the uncured microwave absorbing foam prepreg is placed in a flexible rubber bag and then placed in a vacuum drying oven. The vacuum degree is maintained at 0.6 MPa and the temperature is kept at 180°C for 2 hours to obtain cured microwave absorbing foam prepreg.

[0057] The aforementioned microwave absorbing foam prepreg, tested using the bow method, showed an effective absorption bandwidth close to 7 GHz (11.5 GHz - 18 GHz), indicating a wide absorption bandwidth. Furthermore, during the operation of the embodiments, there were no issues such as uncontrollable thickness of the pure resin film and the microwave absorbing film, incomplete peeling of the pure resin film and the microwave absorbing film, or incomplete mixing of the bisphenol A epoxy resin mixed with the curing agent with the carbon black (microwave absorbing agent). The resulting microwave absorbing foam prepreg had a smooth, intact surface without pores.

[0058] Example 2

[0059] 1) Preparation of microwave absorbing film:

[0060] Add 40 parts diallyl bisphenol A (curing agent) to 100 parts liquefied bismaleimide resin to obtain liquefied bismaleimide resin mixed with curing agent. Perform the coating operation:

[0061] The liquefied bismaleimide resin mixed with curing agent is added to the coating roller. The roller is pressed tightly against the fixed wheel. The coating machine is started, and the resin is coated onto the continuous release paper to obtain a pure resin film. The film thickness is controlled to be 0.2 mm.

[0062] Short carbon fibers are dispersed in the above-mentioned liquefied bismaleimide resin mixed with curing agent at a ratio of 15:85, and added to the coating roller. The coating roller is pressed tightly against the fixed wheel. The coating machine is started, and the resin is coated onto the continuous release paper to obtain a microwave absorbing film. The film thickness is controlled to be 0.2 mm.

[0063] 2) Preparation of dual-foam structure microwave absorbing foam:

[0064] Adding 20 parts of sodium bicarbonate (foaming agent) to 100 parts of thermosetting 6216 phenolic resin yields thermosetting 6216 phenolic resin with added foaming agent.

[0065] Nickel foam (98% porosity, 5mm thickness, three-dimensional fully perforated mesh) is laid in a 320mm*320mm*40mm square mold, and the above-mentioned thermosetting 6216 phenolic resin with added foaming agent is filled into the barrel to obtain a mold containing foaming raw materials.

[0066] Place the mold containing the foaming raw materials into a vacuum drying oven, maintain a vacuum of 0.6 MPa at room temperature, and leave it for 30 minutes. Introduce air into the vacuum drying oven to restore it to a non-vacuum state, then raise the temperature to 175℃ and maintain it for 2 hours. Partially embedded thermosetting 6216 phenolic resin with added foaming agent is embedded in the cobalt foam layer to form a double-foam structure microwave-absorbing foam (5mm). The yellow foam is thermosetting 6216 phenolic resin foam, and the gray foam is nickel foam. Remove the excess thermosetting 6216 phenolic resin foam (pure yellow foam layer).

[0067] 3) Preparation of microwave absorbing foam prepreg:

[0068] The pure resin film prepared in step 1), the double-foam structure microwave absorbing foam prepared in step 2), and the microwave absorbing film prepared in step 1) are laid out sequentially to obtain a layer of uncured prepreg. The two layers of uncured prepreg are stacked to obtain an uncured double-layer microwave absorbing foam prepreg. The prepreg is then molded using a compression molding method: the uncured double-layer microwave absorbing foam prepreg is placed in a hot press, a pressure of 0.05 MPa is applied, the temperature is raised to 180°C and held for 2 hours, then raised to 220°C and held for 10 hours to obtain a cured microwave absorbing foam prepreg.

[0069] The aforementioned microwave absorbing foam prepreg was tested using the bow method, and the resulting absorption bandwidth was 7 GHz (11 GHz - 18 GHz). Furthermore, during the operation of the embodiments, there were no issues such as uncontrollable thickness of the pure resin film and the microwave absorbing film, incomplete peeling of the pure resin film and the microwave absorbing film, or the inability to completely mix the liquefied bismaleimide resin mixed with the curing agent with the short-cut carbon fibers (wave absorbing agent). The resulting microwave absorbing foam prepreg had a smooth, intact surface without pores.

[0070] Example 3

[0071] 1) Preparation of microwave absorbing film:

[0072] Add 40 parts of 4,4'-diaminodiphenyl sulfone (curing agent) to 100 parts of bisphenol A epoxy resin to obtain a bisphenol A epoxy resin mixed with curing agent. Perform the coating operation:

[0073] Bisphenol A epoxy resin mixed with curing agent is added to the coating roller, which is then pressed tightly against the fixed wheel. The coating machine is started, and the resin is coated onto a continuous release paper to obtain a pure resin film. The film thickness is controlled to be 0.25 mm.

[0074] At a ratio of 20:80, graphite is dispersed in the bisphenol A epoxy resin mixed with curing agent and added to the coating roller. The roller is pressed tightly against the fixed wheel. The coating machine is started, and the resin is coated onto the continuous release paper to obtain a microwave absorbing film. The film thickness is controlled to be 0.25 mm.

[0075] 2) Preparation of dual-foam structure microwave absorbing foam:

[0076] 40 parts of 4,4'-diaminodiphenyl sulfone (curing agent) and 20 parts of azodicarbonamide (foaming agent) were added to 100 parts of bisphenol A epoxy resin to obtain bisphenol A epoxy resin with added curing agent and foaming agent.

[0077] Nickel foam (98% porosity, 10mm thickness, three-dimensional fully perforated mesh) is laid in a 320mm*320mm*40mm square mold, and the above-mentioned bisphenol A epoxy resin with added curing agent and foaming agent is filled into the barrel to obtain a mold containing foaming raw materials.

[0078] Place the mold containing the foaming raw materials into a vacuum drying oven, maintain a vacuum of 0.6 MPa at room temperature, and leave it for 30 minutes. Introduce air into the vacuum drying oven to restore it to a non-vacuum state, then raise the temperature to 180℃ and maintain it for 2 hours. Partially embedded in the cobalt foam layer with added curing agent and foaming agent, bisphenol A epoxy resin forms a double-foam structure microwave-absorbing foam (10 mm), where the yellow foam is bisphenol A epoxy resin foam and the gray foam is nickel foam. Remove the excess bisphenol A epoxy resin foam (pure yellow foam layer).

[0079] 3) Preparation of microwave absorbing foam prepreg:

[0080] The pure resin film prepared in step 1), the double-foam structure microwave absorbing foam prepared in step 2), and the microwave absorbing film prepared in step 1) are laid out sequentially to obtain an uncured microwave absorbing foam prepreg. The prepreg is then molded using an autoclave method: the uncured microwave absorbing foam prepreg is wrapped with two aluminum plates, placed in an autoclave, the temperature is raised to 180℃, and kept at that temperature for 2 hours while maintaining a vacuum of 0.6MPa to obtain a cured microwave absorbing foam prepreg.

[0081] The aforementioned microwave absorbing foam prepreg was tested using the bow method, and the resulting absorption bandwidth was 8 GHz (10 GHz - 18 GHz). Furthermore, during the operation of this embodiment, there were no issues such as uncontrollable thickness of the pure resin film and the microwave absorbing film, incomplete peeling of the pure resin film and the microwave absorbing film, or the inability to completely mix the bisphenol A epoxy resin mixed with the curing agent with the graphite (microwave absorbing agent). The resulting microwave absorbing foam prepreg had a smooth, intact surface without pores.

[0082] Example 4

[0083] 1) Preparation of microwave absorbing film:

[0084] Add 40 parts of 4,4'-diaminodiphenyl sulfone (curing agent) to 100 parts of bisphenol A epoxy resin to obtain a bisphenol A epoxy resin mixed with curing agent. Perform the coating operation:

[0085] Bisphenol A epoxy resin mixed with curing agent is added to the coating roller, which is then pressed tightly against the fixed wheel. The coating machine is started, and the resin is coated onto the continuous release paper to obtain a pure resin film. The film thickness is controlled to be 0.1 mm.

[0086] Carbonyl iron is dispersed in the above-mentioned bisphenol A epoxy resin mixed with curing agent at a ratio of 50:50, and added to the coating roller. The coating roller is pressed tightly against the fixed wheel. The coating machine is started, and the resin is coated onto the continuous release paper to obtain a microwave absorbing film. The film thickness is controlled to be 0.1 mm.

[0087] 2) Preparation of dual-foam structure microwave absorbing foam:

[0088] 40 parts of 4,4'-diaminodiphenyl sulfone (curing agent) and 20 parts of azodicarbonamide (foaming agent) were added to 100 parts of bisphenol A epoxy resin to obtain bisphenol A epoxy resin with added curing agent and foaming agent.

[0089] Graphite-based foam (obtained by holding a 20mm thick graphite polystyrene board at 500°C for 1 hour under a nitrogen atmosphere) is laid in a 320mm*320mm*40mm square mold, and the above-mentioned bisphenol A epoxy resin with added curing agent and foaming agent is filled into the barrel to obtain a mold containing foaming raw materials.

[0090] Place the mold containing the foaming raw material into a vacuum drying oven, maintain a vacuum of 0.6 MPa at room temperature, and leave it for 30 minutes. Introduce air into the vacuum drying oven to restore a non-vacuum state, then raise the temperature to 180℃ and maintain it for 2 hours. Partially embedded bisphenol A epoxy resin with added curing agent and foaming agent is embedded in the graphite-based foam layer, forming a double-foam structure microwave-absorbing foam (20 mm). The yellow foam is bisphenol A epoxy resin foam, and the gray foam is graphite-based foam. Remove the excess bisphenol A epoxy resin foam (pure yellow foam layer).

[0091] 3) Preparation of microwave absorbing foam prepreg:

[0092] The pure resin film prepared in step 1), the double-foam structure microwave absorbing foam prepared in step 2), and the microwave absorbing film prepared in step 1) are laid out in sequence to obtain uncured microwave absorbing foam prepreg. The prepreg is then prepared by bag pressing: the uncured microwave absorbing foam prepreg is placed in a flexible rubber bag and then placed in a vacuum drying oven. The vacuum degree is maintained at 0.6 MPa and the temperature is kept at 180°C for 2 hours to obtain cured microwave absorbing foam prepreg.

[0093] The above-mentioned microwave absorbing foam prepreg was tested using the bow method, and the resulting absorption bandwidth was 9 GHz (9 GHz - 18 GHz). Furthermore, during the operation of the embodiment, there were no issues such as uncontrollable thickness of the pure resin film and the microwave absorbing film, incomplete peeling of the pure resin film and the microwave absorbing film, or the inability to completely mix the bisphenol A epoxy resin mixed with the curing agent with the carbonyl iron (microwave absorbing agent). The resulting microwave absorbing foam prepreg had a smooth, intact surface without pores.

[0094] Example 5

[0095] 1) Preparation of microwave absorbing film:

[0096] Add 40 parts diallyl bisphenol A (curing agent) to 100 parts liquefied bismaleimide resin to obtain liquefied bismaleimide resin mixed with curing agent. Perform the coating operation:

[0097] The liquefied bismaleimide resin mixed with curing agent is added to the coating roller. The roller is pressed tightly against the fixed wheel. The coating machine is started, and the resin is coated onto the continuous release paper to obtain a pure resin film. The film thickness is controlled to be 0.2 mm.

[0098] At a ratio of 60:40, ferric oxide is dispersed in the above-mentioned liquefied bismaleimide resin mixed with curing agent, added to the coating roller, the roller is pressed tightly against the fixed wheel, the coating machine is started, and the resin is coated onto the continuous release paper to obtain a microwave absorbing film, the film thickness is controlled to be 0.2mm.

[0099] 2) Preparation of dual-foam structure microwave absorbing foam:

[0100] Adding 20 parts of sodium bicarbonate (foaming agent) to 100 parts of thermosetting 6216 phenolic resin yields thermosetting 6216 phenolic resin with added foaming agent.

[0101] Cork-derived carbon-based foam (obtained by holding 5mm thick cork roll at 500°C for 1 hour under nitrogen atmosphere) is laid in a 320mm*320mm*40mm square mold, and the above-mentioned thermosetting 6216 phenolic resin with added foaming agent is filled into the barrel to obtain a mold containing foaming raw materials.

[0102] Place the mold containing the foaming raw materials into a vacuum drying oven, maintain a vacuum of 0.6 MPa at room temperature, and leave for 30 minutes. Introduce air into the vacuum drying oven to restore a non-vacuum state, then raise the temperature to 175℃ and maintain this temperature for 2 hours. Partially embedding a portion of the thermosetting 6216 phenolic resin with added foaming agent into a cork-derived carbon-based foam layer forms a double-foam structure microwave-absorbing foam (5 mm). The yellow foam is thermosetting 6216 phenolic resin foam, and the gray foam is cork-derived carbon-based foam. Remove excess thermosetting 6216 phenolic resin foam (pure yellow foam layer).

[0103] 3) Preparation of microwave absorbing foam prepreg:

[0104] The pure resin film prepared in step 1), the double-foam structure microwave absorbing foam prepared in step 2), and the microwave absorbing film prepared in step 1) are laid out sequentially to obtain a layer of uncured prepreg. The two layers of uncured prepreg are stacked to obtain an uncured double-layer microwave absorbing foam prepreg. The prepreg is then molded using a compression molding method: the uncured double-layer microwave absorbing foam prepreg is placed in a hot press, a pressure of 0.05 MPa is applied, the temperature is raised to 180°C and held for 2 hours, then raised to 220°C and held for 10 hours to obtain a cured microwave absorbing foam prepreg.

[0105] The aforementioned microwave absorbing foam prepreg was tested using the bow method, and the resulting absorption bandwidth was 7 GHz (11 GHz - 18 GHz). Furthermore, during the operation of the embodiments, there were no issues such as uncontrollable thickness of the pure resin film and the microwave absorbing film, incomplete peeling of the pure resin film and the microwave absorbing film, or the inability to completely mix the liquefied bismaleimide resin mixed with the curing agent with iron oxide (the microwave absorbing agent). The resulting microwave absorbing foam prepreg had a smooth, intact surface without pores.

[0106] Example 6

[0107] 1) Preparation of microwave absorbing film:

[0108] Add 40 parts of 4,4'-diaminodiphenyl sulfone (curing agent) to 100 parts of bisphenol A epoxy resin to obtain a bisphenol A epoxy resin mixed with curing agent. Perform the coating operation:

[0109] Bisphenol A epoxy resin mixed with curing agent is added to the coating roller, which is then pressed tightly against the fixed wheel. The coating machine is started, and the resin is coated onto a continuous release paper to obtain a pure resin film. The film thickness is controlled to be 0.25 mm.

[0110] Nickel powder is dispersed in the bisphenol A epoxy resin mixed with curing agent at a ratio of 70:30, and added to the coating roller. The roller is pressed tightly against the fixed wheel. The coating machine is started, and the resin is coated onto the continuous release paper to obtain a microwave absorbing film. The film thickness is controlled to be 0.25 mm.

[0111] 2) Preparation of dual-foam structure microwave absorbing foam:

[0112] 40 parts of 4,4'-diaminodiphenyl sulfone (curing agent) and 20 parts of azodicarbonamide (foaming agent) were added to 100 parts of bisphenol A epoxy resin to obtain bisphenol A epoxy resin with added curing agent and foaming agent.

[0113] Polystyrene-derived carbon-based foam (obtained by holding a 30mm thick polystyrene board at 500°C for 1 hour under a nitrogen atmosphere) is laid in a 320mm*320mm*40mm square mold, and the above-mentioned bisphenol A epoxy resin with added curing agent and foaming agent is filled into the barrel to obtain a mold containing foaming raw materials.

[0114] Place the mold containing the foaming raw material into a vacuum drying oven, maintain a vacuum of 0.6 MPa at room temperature, and leave it for 30 minutes. Introduce air into the vacuum drying oven to restore it to a non-vacuum state, then raise the temperature to 180℃ and maintain it for 2 hours. Partially embedding a portion of the bisphenol A epoxy resin (with added curing agent and foaming agent) into a polystyrene-derived carbon-based foam layer forms a double-foam structure microwave-absorbing foam (30 mm). The yellow foam is bisphenol A epoxy resin foam, and the gray foam is polystyrene-derived carbon-based foam. Remove the excess bisphenol A epoxy resin foam (pure yellow foam layer).

[0115] 3) Preparation of microwave absorbing foam prepreg:

[0116] The pure resin film prepared in step 1), the double-foam structure microwave absorbing foam prepared in step 2), and the microwave absorbing film prepared in step 1) are laid in sequence to obtain an uncured microwave absorbing foam prepreg. The prepreg is then molded using a compression molding method: the uncured double-layer microwave absorbing foam prepreg is placed in a hot press, a pressure of 0.05 MPa is applied, the temperature is raised to 180°C and held for 2 hours, then raised to 220°C and held for 10 hours to obtain a cured microwave absorbing foam prepreg.

[0117] The aforementioned microwave absorbing foam prepreg was tested using the bow method, and the resulting absorption bandwidth was 10 GHz (8 GHz - 18 GHz). Furthermore, during the operation of this embodiment, there were no issues such as uncontrollable thickness of the pure resin film and the microwave absorbing film, incomplete peeling of the pure resin film and the microwave absorbing film, or the inability to completely mix the bisphenol A epoxy resin mixed with the curing agent with the nickel powder (microwave absorbing agent). The resulting microwave absorbing foam prepreg had a smooth, intact surface without pores.

[0118] Comparative Example 1

[0119] 1) Preparation of microwave absorbing film:

[0120] Add 40 parts of 4,4'-diaminodiphenyl sulfone (curing agent) to 100 parts of bisphenol A epoxy resin to obtain a bisphenol A epoxy resin mixed with curing agent. Perform the coating operation:

[0121] Bisphenol A epoxy resin mixed with curing agent is added to the coating roller, which is then pressed tightly against the fixed wheel. The coating machine is started, and the resin is coated onto a continuous release paper to obtain a pure resin film. The film thickness is controlled to be 0.2 mm.

[0122] Carbon black is dispersed in the bisphenol A epoxy resin mixed with curing agent at a ratio of 1:199, and added to the coating roller. The roller is pressed tightly against the fixed wheel. The coating machine is started, and the resin is coated onto the continuous release paper to obtain a microwave absorbing film. The film thickness is controlled to be 0.2 mm.

[0123] 2) Fabrication of absorbing honeycomb cells:

[0124] The honeycomb core material is made of Nomex material with a pore size of 2.6 mm and a height of 5 mm. 70 parts of carbonyl iron powder and 30 parts of deionized water are thoroughly mixed to obtain a carbonyl iron powder-deionized water mixture. Then, 100 parts of the carbonyl iron powder-deionized water mixture and 30 parts of water-based resin binder are poured into a mixer and mixed for 30 minutes. During the mixing process, 30 parts of benzyl alcohol are added in two batches to obtain an impregnation slurry. 160 parts of the impregnation slurry are ultrasonically treated for 30 minutes. During the ultrasonic mixing process, 30 parts of polyetheramine are added in three batches to obtain a viscous impregnation slurry. The viscous impregnation slurry is poured into an impregnation tank and allowed to stand for 30 minutes to obtain a viscous impregnation slurry after standing. The honeycomb core material is impregnated in the viscous impregnation slurry after standing. After impregnation, the honeycomb is placed in an oven at 80°C for 2 hours, and then placed on a wire rack at room temperature for 24 hours.

[0125] 3) Preparation of microwave absorbing honeycomb prepreg:

[0126] The pure resin film prepared in step 1), the microwave absorbing honeycomb prepared in step 2), and the microwave absorbing film prepared in step 1) are laid out sequentially to obtain an uncured microwave absorbing honeycomb prepreg. The prepreg is then prepared by bag pressing: the uncured microwave absorbing honeycomb prepreg is placed in a flexible rubber bag and then placed in a vacuum drying oven. The vacuum degree is maintained at 0.6 MPa and the temperature is kept at 180°C for 2 hours to obtain the cured microwave absorbing honeycomb prepreg.

[0127] Problem: The contact area between the pure resin film and the microwave absorbing film and the honeycomb is small, and the honeycomb pore size is large. During the curing process, some of the pure resin film and microwave absorbing film are unsupported, resulting in pores in the pure resin film and microwave absorbing film.

[0128] Comparative Example 2

[0129] 1) Preparation of microwave absorbing film:

[0130] Add 40 parts of 4,4'-diaminodiphenyl sulfone (curing agent) to 100 parts of bisphenol A epoxy resin to obtain a bisphenol A epoxy resin mixed with curing agent. Perform the coating operation:

[0131] Bisphenol A epoxy resin mixed with curing agent is added to the coating roller, which is then pressed tightly against the fixed wheel. The coating machine is started, and the resin is coated onto the continuous release paper to obtain a pure resin film. The film thickness is controlled to be 0.1 mm.

[0132] Carbonyl iron is dispersed in the above-mentioned bisphenol A epoxy resin mixed with curing agent at a ratio of 70:30, and added to the coating roller. The coating roller is pressed tightly against the fixed wheel. The coating machine is started, and the resin is coated onto the continuous release paper to obtain a microwave absorbing film. The film thickness is controlled to be 0.1 mm.

[0133] 2) Fabrication of absorbing honeycomb cells:

[0134] The honeycomb core material is made of Nomex material with a pore size of 2.6 mm and a height of 5 mm. One part carbon black and 199 parts deionized water are thoroughly mixed to obtain a carbon black-deionized water mixture. Then, 200 parts of the carbon black-deionized water mixture and 199 parts of water-based resin binder are poured into a mixer and mixed for 30 minutes. During the mixing process, 199 parts of benzyl alcohol are added in two batches to obtain an impregnation slurry. 598 parts of the impregnation slurry are ultrasonically treated for 30 minutes. During the ultrasonic mixing process, 199 parts of polyetheramine are added in three batches to obtain a viscous impregnation slurry. The viscous impregnation slurry is poured into an impregnation tank and allowed to stand for 30 minutes to obtain a viscous impregnation slurry after standing. The honeycomb core material is impregnated in the viscous impregnation slurry after standing. After impregnation, the honeycomb is placed in an oven at 80°C for 2 hours, and then placed on a wire rack at room temperature for 24 hours.

[0135] 3) Preparation of microwave absorbing honeycomb prepreg:

[0136] The pure resin film prepared in step 1), the microwave absorbing honeycomb prepared in step 2), and the microwave absorbing film prepared in step 1) are laid out sequentially to obtain an uncured microwave absorbing honeycomb prepreg. The prepreg is then prepared by bag pressing: the uncured microwave absorbing honeycomb prepreg is placed in a flexible rubber bag and then placed in a vacuum drying oven. The vacuum degree is maintained at 0.6 MPa and the temperature is kept at 180°C for 2 hours to obtain the cured microwave absorbing honeycomb prepreg.

[0137] Problem arises: Similarly, the contact area between the pure resin film and the microwave absorbing film and the honeycomb is small, and the honeycomb pore size is large. During the curing process, some of the pure resin film and microwave absorbing film are unsupported, resulting in pores in the pure resin film and microwave absorbing film.

[0138] Comparative Example 3

[0139] 1) Preparation of microwave absorbing film:

[0140] Add 40 parts of 4,4'-diaminodiphenyl sulfone (curing agent) to 100 parts of bisphenol A epoxy resin to obtain a bisphenol A epoxy resin mixed with curing agent. Perform the coating operation:

[0141] Bisphenol A epoxy resin mixed with curing agent is added to the coating roller, which is then pressed tightly against the fixed wheel. The coating machine is started, and the resin is coated onto a continuous release paper to obtain a pure resin film. The film thickness is controlled to be 0.3 mm.

[0142] Carbon black is dispersed in the bisphenol A epoxy resin mixed with curing agent at a ratio of 25:75, and added to the coating roller. The roller is pressed tightly against the fixed wheel. The coating machine is started, and the resin is coated onto the continuous release paper to obtain a microwave absorbing film. The film thickness is controlled to be 0.3 mm.

[0143] 2) Preparation of dual-foam structure microwave absorbing foam:

[0144] 40 parts of 4,4'-diaminodiphenyl sulfone (curing agent) and 20 parts of azodicarbonamide (foaming agent) were added to 100 parts of bisphenol A epoxy resin to obtain bisphenol A epoxy resin with added curing agent and foaming agent.

[0145] Foamed cobalt (98% porosity, 2mm thickness, three-dimensional fully perforated mesh) is laid in a 320mm*320mm*40mm square mold, and the above-mentioned bisphenol A epoxy resin with added curing agent and foaming agent is filled into the barrel to obtain a mold containing foaming raw materials.

[0146] Place the mold containing the foaming raw material into a vacuum drying oven, maintain a vacuum of 0.6 MPa at room temperature, and leave it for 30 minutes. Introduce air into the vacuum drying oven to restore a non-vacuum state, then raise the temperature to 180℃ and maintain it for 2 hours. Partially embedded bisphenol A epoxy resin with added curing agent and foaming agent is embedded in the cobalt foam layer to form a double-foam structure microwave-absorbing foam (2 mm). The yellow foam is epoxy resin foam, and the gray foam is cobalt foam. Remove the excess bisphenol A epoxy resin foam (pure yellow foam layer).

[0147] 3) Preparation of microwave absorbing foam prepreg:

[0148] The pure resin film prepared in step 1), the double-foam structure microwave absorbing foam prepared in step 2), and the microwave absorbing film prepared in step 1) are laid out in sequence to obtain uncured microwave absorbing foam prepreg. The prepreg is then prepared by bag pressing: the uncured microwave absorbing foam prepreg is placed in a flexible rubber bag and then placed in a vacuum drying oven. The vacuum degree is maintained at 0.6 MPa and the temperature is kept at 180°C for 2 hours to obtain cured microwave absorbing foam prepreg.

[0149] Problems encountered: The pure resin film and the microwave absorbing film were too thick, making the thickness difficult to control during the coating process. The high carbon black content resulted in two issues: firstly, increased resin viscosity, affecting the preparation process; and secondly, excessive conductivity, leading to impedance mismatch, with the absorption peak not exceeding -10dB (-8.5GHz) and an absorption bandwidth of 0. Furthermore, the resulting microwave absorbing foam prepreg had a smooth, intact surface without pores.

[0150] Comparative Example 4

[0151] 1) Preparation of microwave absorbing film:

[0152] Add 40 parts of 4,4'-diaminodiphenyl sulfone (curing agent) to 100 parts of bisphenol A epoxy resin to obtain a bisphenol A epoxy resin mixed with curing agent. Perform the coating operation:

[0153] Bisphenol A epoxy resin mixed with curing agent is added to the coating roller, which is then pressed tightly against the fixed wheel. The coating machine is started, and the resin is coated onto a continuous release paper to obtain a pure resin film. The film thickness is controlled to be 0.01 mm.

[0154] Carbon black is dispersed in the bisphenol A epoxy resin mixed with curing agent at a ratio of 1:999, and added to the coating roller. The roller is pressed tightly against the fixed wheel. The coating machine is started, and the resin is coated onto the continuous release paper to obtain a microwave absorbing film. The film thickness is controlled to be 0.01 mm.

[0155] 2) Preparation of dual-foam structure microwave absorbing foam:

[0156] 40 parts of 4,4'-diaminodiphenyl sulfone (curing agent) and 20 parts of azodicarbonamide (foaming agent) were added to 100 parts of bisphenol A epoxy resin to obtain bisphenol A epoxy resin with added curing agent and foaming agent.

[0157] Foamed cobalt (98% porosity, 1.5mm thickness, three-dimensional fully perforated mesh) was laid in a 320mm*320mm*40mm square mold, and the above-mentioned bisphenol A epoxy resin with added curing agent and foaming agent was filled into the barrel to obtain a mold containing foaming raw materials.

[0158] Place the mold containing the foaming raw material into a vacuum drying oven, maintain a vacuum of 0.6 MPa at room temperature, and leave it for 30 minutes. Introduce air into the vacuum drying oven to restore a non-vacuum state, then raise the temperature to 180℃ and maintain it for 2 hours. Partially embedded bisphenol A epoxy resin with added curing agent and foaming agent is embedded in the cobalt foam layer to form a double-foam structure microwave-absorbing foam (1.5 mm). The yellow foam is epoxy resin foam, and the gray foam is cobalt foam. Remove the excess bisphenol A epoxy resin foam (pure yellow foam layer).

[0159] 3) Preparation of microwave absorbing foam prepreg:

[0160] The pure resin film prepared in step 1), the double-foam structure microwave absorbing foam prepared in step 2), and the microwave absorbing film prepared in step 1) are laid out in sequence to obtain uncured microwave absorbing foam prepreg. The prepreg is then prepared by bag pressing: the uncured microwave absorbing foam prepreg is placed in a flexible rubber bag and then placed in a vacuum drying oven. The vacuum degree is maintained at 0.6 MPa and the temperature is kept at 180°C for 2 hours to obtain cured microwave absorbing foam prepreg.

[0161] Problems encountered: The thickness of both the pure resin film and the microwave-absorbing film was too thin, making them impossible to peel off from the release paper. Low-temperature treatment was required for partial lamination with the microwave-absorbing foam. Furthermore, the carbon black filler content was too low, and the microwave-absorbing foam thickness was too thin, resulting in insufficient material attenuation capacity; the absorption peak did not exceed -10dB (-7dB), and the absorption bandwidth was 0. Additionally, the obtained microwave-absorbing foam prepreg had a smooth, intact surface without pores.

[0162] Comparative Example 5

[0163] 1) Preparation of microwave absorbing film:

[0164] Add 40 parts of 4,4'-diaminodiphenyl sulfone (curing agent) to 100 parts of bisphenol A epoxy resin to obtain a bisphenol A epoxy resin mixed with curing agent. Perform the coating operation:

[0165] Bisphenol A epoxy resin mixed with curing agent is added to the coating roller, which is then pressed tightly against the fixed wheel. The coating machine is started, and the resin is coated onto the continuous release paper to obtain a pure resin film. The film thickness is controlled to be 0.1 mm.

[0166] Carbonyl iron is dispersed in the above-mentioned bisphenol A epoxy resin mixed with curing agent at a ratio of 40:60, and added to the coating roller. The coating roller is pressed tightly against the fixed wheel. The coating machine is started, and the resin is coated onto the continuous release paper to obtain a microwave absorbing film. The film thickness is controlled to be 0.1 mm.

[0167] 2) Preparation of dual-foam structure microwave absorbing foam:

[0168] 40 parts of 4,4'-diaminodiphenyl sulfone (curing agent) and 20 parts of azodicarbonamide (foaming agent) were added to 100 parts of bisphenol A epoxy resin to obtain bisphenol A epoxy resin with added curing agent and foaming agent.

[0169] Graphite-based foam (obtained by holding a 20mm thick graphite polystyrene board at 500°C for 1 hour under a nitrogen atmosphere) is laid in a 320mm*320mm*40mm square mold, and the above-mentioned bisphenol A epoxy resin with added curing agent and foaming agent is filled into the barrel to obtain a mold containing foaming raw materials.

[0170] Place the mold containing the foaming raw material into a vacuum drying oven, maintain a vacuum of 0.6 MPa at room temperature, and leave for 30 minutes. Introduce air into the vacuum drying oven to restore a non-vacuum state, then raise the temperature to 180℃ and maintain this temperature for 2 hours. Partially embedded in the graphite-based foam layer with added curing agent and foaming agent, bisphenol A epoxy resin forms a double-foam structure microwave-absorbing foam (20 mm), where the yellow foam is epoxy resin foam and the gray foam is graphite-based foam. Remove excess bisphenol A epoxy resin foam (pure yellow foam layer).

[0171] 3) Preparation of microwave absorbing foam prepreg:

[0172] The pure resin film prepared in step 1), the double-foam structure microwave absorbing foam prepared in step 2), and the microwave absorbing film prepared in step 1) are laid out in sequence to obtain uncured microwave absorbing foam prepreg. The prepreg is then prepared by bag pressing: the uncured microwave absorbing foam prepreg is placed in a flexible rubber bag and then placed in a vacuum drying oven. The vacuum degree is maintained at 0.6 MPa and the temperature is kept at 180°C for 2 hours to obtain cured microwave absorbing foam prepreg.

[0173] Problems arose: the carbonyl iron mass fraction was too low, resulting in insufficient material attenuation capacity; the absorption peak did not exceed -10dB (-7dB), and the absorption bandwidth was 0. Furthermore, during the comparative operation, issues arose such as uncontrollable thickness of the pure resin film and the microwave-absorbing film, incomplete peeling of the pure resin film and the microwave-absorbing film, and the inability to completely mix the bisphenol A epoxy resin mixed with the curing agent with the carbonyl iron (microwave-absorbing agent). The resulting microwave-absorbing foam prepreg had a smooth, intact surface without pores.

[0174] Comparative Example 6

[0175] 1) Preparation of microwave absorbing film:

[0176] Add 40 parts of 4,4'-diaminodiphenyl sulfone (curing agent) to 100 parts of bisphenol A epoxy resin to obtain a bisphenol A epoxy resin mixed with curing agent. Perform the coating operation:

[0177] Bisphenol A epoxy resin mixed with curing agent is added to the coating roller, which is then pressed tightly against the fixed wheel. The coating machine is started, and the resin is coated onto the continuous release paper to obtain a pure resin film. The film thickness is controlled to be 0.1 mm.

[0178] Carbonyl iron is dispersed in the above-mentioned bisphenol A epoxy resin mixed with curing agent at a ratio of 80:20, and added to the coating roller. The coating roller is pressed tightly against the fixed wheel. The coating machine is started, and the resin is coated onto the continuous release paper to obtain a microwave absorbing film. The film thickness is controlled to be 0.1 mm.

[0179] 2) Preparation of dual-foam structure microwave absorbing foam:

[0180] 40 parts of 4,4'-diaminodiphenyl sulfone (curing agent) and 20 parts of azodicarbonamide (foaming agent) were added to 100 parts of bisphenol A epoxy resin to obtain bisphenol A epoxy resin with added curing agent and foaming agent.

[0181] Graphite-based foam (obtained by holding a 35mm thick graphite polystyrene board at 500°C for 1 hour under a nitrogen atmosphere) is laid in a 320mm*320mm*40mm square mold, and the above-mentioned bisphenol A epoxy resin with added curing agent and foaming agent is filled into the barrel to obtain a mold containing foaming raw materials.

[0182] Place the mold containing the foaming raw material into a vacuum drying oven, maintain a vacuum of 0.6 MPa at room temperature, and leave for 30 minutes. Introduce air into the vacuum drying oven to restore a non-vacuum state, then raise the temperature to 180℃ and maintain this temperature for 2 hours. Partially embedded in the graphite-based foam layer with added curing agent and foaming agent, bisphenol A epoxy resin forms a dual-foam structure microwave-absorbing foam (35 mm), where the yellow foam is epoxy resin foam and the gray foam is graphite-based foam. Remove excess bisphenol A epoxy resin foam (pure yellow foam layer).

[0183] 3) Preparation of microwave absorbing foam prepreg:

[0184] The pure resin film prepared in step 1), the double-foam structure microwave absorbing foam prepared in step 2), and the microwave absorbing film prepared in step 1) are laid out in sequence to obtain uncured microwave absorbing foam prepreg. The prepreg is then prepared by bag pressing: the uncured microwave absorbing foam prepreg is placed in a flexible rubber bag and then placed in a vacuum drying oven. The vacuum degree is maintained at 0.6 MPa and the temperature is kept at 180°C for 2 hours to obtain cured microwave absorbing foam prepreg.

[0185] Problems encountered: The carbonyl iron mass fraction was too high, preventing complete mixing with the resin; the microwave absorbing foam content was too high, resulting in excessive dielectric loss and failure to achieve effective magnetic-dielectric co-loss; the absorption peak did not exceed -10dB (-8dB), and the absorption bandwidth was 0. Furthermore, during the comparative operation, issues such as uncontrollable thickness of the pure resin film and microwave absorbing film, and incomplete peeling of the pure resin film and microwave absorbing film did not occur; the obtained microwave absorbing foam prepreg had a smooth, intact, and non-porous surface.

[0186] The present invention evaluated the results from five different perspectives: film surface integrity, film thickness controllability, film peelability, resin processability, and electromagnetic wave absorption capability.

[0187] Based on the above embodiments and comparative examples, it is clear that the embodiments with six microwave absorbing foam prepregs and the comparative examples with four microwave absorbing foam prepregs, compared to the comparative example with two microwave absorbing honeycomb prepregs, have significant technical advantages in maintaining the integrity of the film surface and ensuring effective electromagnetic wave absorption. Therefore, the microwave absorbing foam prepreg of the present invention preferably uses a double-foam structure microwave absorbing foam. The microwave absorbing film is a resin film with added magnetic or dielectric microwave absorbing agents.

[0188] The magnetic absorbing agent is ferrite, carbonyl iron powder or magnetic metal whiskers, and the dielectric absorbing agent is silicon carbide fiber, graphite, carbon black, short carbon fiber, graphene, carbon nanotube or conductive polymer.

[0189] Examples 1-6 and Comparative Examples 5 and 6 are superior to Comparative Examples 3 and 4 in two aspects: controllable film thickness and peelable film processing. In summary, the thickness of the pure resin film and the microwave absorbing film is 0.1mm-0.25mm. Preferably, when the thickness of the pure resin film and the microwave absorbing film are the same, the thickness is controllable and the film can be peeled off. The preparation process is summarized as follows: During the coating operation, the film thickness is controlled to be 0.1mm-0.25mm.

[0190] Examples 1-6 are superior to Comparative Examples 3-6 in terms of resin processability and electromagnetic wave absorption capability. In summary, when the mass ratio of magnetic absorbing agent to resin mixed with curing agent in the microwave absorbing film is 50-70:50-30, or the mass ratio of dielectric absorbing agent to resin mixed with curing agent is 0.5-20:99.5-80, the resin has good processability and strong electromagnetic wave absorption capability.

[0191] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent substitutions, and improvements made by those skilled in the art to the above embodiments without departing from the scope of the technical solution of the present invention, based on the technical essence of the present invention, shall still fall within the protection scope of the technical solution of the present invention.

Claims

1. A wave-absorbing foam prepreg, characterized by, The pure resin adhesive film layer, the double-foam structure wave-absorbing foam layer and the wave-absorbing adhesive film layer are sequentially arranged; the double-foam structure wave-absorbing foam layer is composed of resin foam and pure electromagnetic matrix foam, and the pure electromagnetic matrix foam is one of foam cobalt, foam nickel, graphite-based foam, softwood-derived carbon-based foam and polystyrene board-derived carbon-based foam; the double-foam structure wave-absorbing foam is prepared by the following steps: laying the pure electromagnetic matrix foam on the surface of a mold, filling the pure resin foaming material, combining the foaming material and the pure electromagnetic loss matrix foam by vacuum impregnation, putting the combined foam material into an oven for foaming, and forming a multi-layered hollow composite material to prepare the double-foam structure wave-absorbing foam; The wave-absorbing adhesive film layer comprises resin mixed with a curing agent and a wave-absorbing agent, and the wave-absorbing agent is a magnetic wave-absorbing agent or a dielectric wave-absorbing agent; the resin in the resin adhesive film layer and the resin in the wave-absorbing adhesive film layer are the same; The mass ratio of the magnetic wave-absorbing agent to the resin mixed with the curing agent in the wave-absorbing adhesive film layer is 50-70:50-30, or the mass ratio of the dielectric wave-absorbing agent to the resin mixed with the curing agent is 0.5-20:99.5-80; The thickness of the pure resin adhesive film and the wave-absorbing adhesive film is 0.1 mm-0.25 mm.

2. The wave-absorbing foam prepreg according to claim 1, wherein The resin in the resin adhesive film layer and the resin in the wave-absorbing adhesive film layer is bisphenol A epoxy resin or liquefied bismaleimide resin.

3. The wave-absorbing foam prepreg of claim 1, wherein, The magnetic wave-absorbing agent is ferrite, carbonyl iron powder or magnetic metal whisker, and the dielectric wave-absorbing agent is silicon carbide fiber, graphite, carbon black, chopped carbon fiber, graphene, carbon nanotube or conductive high polymer.

4. The wave-absorbing foam prepreg of claim 1, wherein, The thickness of the pure resin adhesive film and the wave-absorbing adhesive film is the same.

5. A method of making the wave-absorbing foam prepreg as claimed in claim 1, characterized in that, The method comprises: 1) Preparation of wave-absorbing adhesive film: pure resin is mixed with a curing agent to obtain a pure resin adhesive film; a magnetic wave-absorbing agent or a dielectric wave-absorbing agent is dispersed in resin mixed with a curing agent to obtain a wave-absorbing adhesive film; 2) Preparation of double-foam structure wave-absorbing foam: pure electromagnetic matrix foam is laid on the surface of a mold, and pure resin foaming material is filled; the foaming material and the pure electromagnetic loss matrix foam are combined by vacuum impregnation; the combined foam material is put into an oven for foaming to form a multi-layered hollow composite material to prepare the double-foam structure wave-absorbing foams; The pure electromagnetic matrix foam is one of foam cobalt, foam nickel, graphite-based foam, soft wood-derived carbon-based foam and polystyrene board-derived carbon-based foam; 3) Preparation of wave-absorbing foam prepreg: pure resin adhesive film, double-foam structure wave-absorbing foam and wave-absorbing adhesive film are sequentially laid, and a bag pressing, mold pressing or autoclave method is used for molding.

6. The method of claim 5, wherein, In step 1), the magnetic wave-absorbing agent is ferrite, carbonyl iron powder or magnetic metal whiskers, the dielectric wave-absorbing agent is silicon carbide fiber, graphite, carbon black, short carbon fiber, graphene, carbon nanotube or conductive high polymer, and the resin is bisphenol A epoxy resin or liquefied bismaleimide resin.

7. The method of claim 5, wherein, In step 1), the thickness of the pure resin adhesive film and the wave-absorbing adhesive film is the same.

8. The method of claim 5, wherein, In step 2), the resin in the pure resin foaming material is bisphenol A epoxy resin or thermosetting 6216 phenolic resin.

9. Use of the wave-absorbing foam prepreg according to any one of claims 1-4 in the fields of aerospace, communication, electronic equipment, building materials.