A structural microwave absorbing composite material and its preparation method

Abstract

This invention discloses a structural microwave absorbing composite material and its preparation method. The structural microwave absorbing composite material is divided from top to bottom into: an upper skin, a microwave absorbing foam core layer, and a lower skin. The upper skin is a glass fiber cloth and / or quartz fiber cloth reinforced resin-based composite material, and the lower skin is a carbon fiber cloth reinforced resin-based composite material. The microwave absorbing foam core layer is divided from top to bottom into a single-layer flame-retardant PMI foam sheet and a single-layer or multi-layer flame-retardant microwave absorbing PMI foam sheet. The microwave absorbing foam core layer has drainage grooves and pores on both surfaces. The structural microwave absorbing composite material provided by this invention is divided from top to bottom into: a highly transparent upper skin, a microwave absorbing foam core layer, and a lower skin that reflects electromagnetic waves. Through the synergy of these three components, the structural microwave absorbing composite material provided by this invention has advantages such as lightweight, high strength, and good flame retardant properties, while also exhibiting good broadband microwave absorption performance in the 1–40 GHz range.

Description

Technical Field

[0001] This invention belongs to the field of functional materials technology and relates to a structural microwave absorbing composite material and its preparation method. Background Technology

[0002] To meet the urgent needs of some special fields, researchers have conducted extensive research and applications on coating-type and structural-type microwave absorbing materials. Under the current trend of lightweight materials, resin-based structural microwave absorbing materials have attracted much attention due to their dual advantages of load-bearing and microwave absorption.

[0003] Resin-based microwave absorbing composite materials with a sandwich-like structure include a highly transparent upper skin, a core layer composed of electromagnetic wave absorbing material, and a lower skin that reflects electromagnetic waves. To achieve better electromagnetic wave absorption, the design process requires allowing as much electromagnetic wave as possible to pass through the upper skin into the absorption layer, while the reflection layer needs to reflect as much electromagnetic wave as possible so that the absorption layer can perform secondary absorption. Honeycomb and foam are the main core layers of the resin-based microwave absorbing composite material. Traditional microwave absorbing honeycomb mainly uses an impregnation method, where the absorbent is fully deposited within the honeycomb wall to achieve the absorption effect. However, the microwave absorbing material prepared by this method has a significant directionality. To improve the directionality of the electromagnetic and mechanical properties of traditional microwave absorbing honeycomb, patent CN112126114A uses a method of filling the microwave absorbing honeycomb with rigid microwave absorbing foam. Patents CN108749229A and CN11216422A also use a method of filling ordinary honeycomb with microwave absorbing foam to prepare a sandwich-structured microwave absorbing composite material, but in this material, only the foam has the microwave absorption function, and the honeycomb only serves a load-bearing function. Compared with honeycomb-based microwave absorbing composites, structural foam has a larger contact area with the panel, is less prone to detachment, and can meet various molding processes. When made into composite panels, it also has better environmental resistance. In addition, the electromagnetic and mechanical properties of the prepared microwave absorbing foam are less different in all directions. Therefore, in recent years, structural microwave absorbing foam materials have become a hot topic in microwave absorbing materials research.

[0004] There are many types of foam used as core materials in composite materials, including PMI foam, PVC foam, PUR foam, PET foam, and PS foam. Among them, PMI foam, with its superior performance and ability to meet various composite material molding processes, has become a key focus of research in structural microwave absorbing foam materials. Patents CN109280306A and CN103923337A disclose a PMI composite foam microwave absorbing material and its preparation method. These foams are produced by foaming expandable polymethacrylimide resin particles. However, the foam produced by this method has high density, uneven foam structure, low strength, and significant performance differences at various locations. Patents CN115304879A, CN114806052A, and CN106939110A all employ a two-step method to prepare microwave absorbing PMI foam: first, a microwave absorbing PMI foam prepolymer is prepared, and then the microwave absorbing PMI foam is prepared through high-temperature foaming. This method can obtain microwave absorbing PMI foam with controllable density, uniform cell structure, and good performance. Patent CN115284700A discloses a lightweight, high-strength composite microwave-absorbing foam board and its preparation method. The microwave-absorbing foam board is composed of multiple layers of PMI foam boards of specific thicknesses bonded together with microwave-absorbing adhesive. The upper skin is made of a long-fiber resin-based reinforced composite material with good wave transmission, and the lower skin is made of a high-strength fiber-reinforced resin-based composite material. The reflective layer is made of aluminum foil, etc. Finally, each layer is pressed together with low-temperature cured low-viscosity epoxy adhesive to form a composite microwave-absorbing foam board. However, due to the disordered distribution of fibers, the microwave-absorbing foam produced by this method has obvious directionality. At the same time, the absorbent is mixed in the adhesive, which increases the viscosity of the adhesive. In order to ensure the bonding performance, the amount of adhesive used will be increased. Moreover, the separate design of the reflective layer and the lower skin further increases the weight of the board. In addition, the molding method of this composite material board makes it difficult to ensure that the microwave-absorbing foam is integrally molded with other components on larger components such as the surface of a shelter. Summary of the Invention

[0005] To address the shortcomings of existing structural microwave absorbing composite materials, the first objective of this invention is to provide a structural microwave absorbing composite material with low surface density, high panel bonding strength, good flame retardancy, excellent microwave absorption performance from 1 to 40 GHz, and reduced difference in electromagnetic wave absorption performance in the two incident angles of 0° and 30°.

[0006] The second objective of this invention is to provide a method for preparing structural microwave absorbing composite materials that is simple to mold, easy to operate, and suitable for producing large-size structures.

[0007] To achieve the above technical objectives, the following technical solution is adopted:

[0008] This invention discloses a structural microwave absorbing composite material, which is divided from top to bottom into: an upper skin, a microwave absorbing foam core layer, and a lower skin; the upper skin is a glass fiber cloth and / or quartz fiber cloth reinforced resin-based composite material, the lower skin is a carbon fiber cloth reinforced resin-based composite material, and the microwave absorbing foam core layer is divided from top to bottom into a single-layer flame-retardant PMI foam sheet and a single-layer or multi-layer flame-retardant microwave absorbing PMI foam sheet, wherein the microwave absorbing foam core layer has drainage grooves and holes on both surfaces.

[0009] The structural microwave absorbing composite material provided by this invention is divided into three parts from top to bottom: an upper skin with good wave transmission, a wave-absorbing foam core layer, and a lower skin that reflects electromagnetic waves. With the synergy of the three, the structural microwave absorbing composite material provided by this invention has advantages such as being lightweight, high-strength, and having good flame-retardant properties, while also having good broadband wave absorption performance in the range of 1 to 40 GHz.

[0010] In this invention, in order to better bond the absorbing foam core layers together, the invention provides flow channels and holes on both surfaces of the absorbing foam core layer, thereby enabling it to better bond with the upper and lower skins.

[0011] In a preferred embodiment, the flame-retardant PMI foam sheet has a thickness of 1-3 mm and a foam density of 100 kg / m³. 3 ~200kg / m 3 The foam pore size is 0.2mm~0.6mm.

[0012] The surface layer of the microwave-absorbing foam core in this invention is a flame-retardant PMI foam sheet. Flame-retardant PMI foam has a very low dielectric constant, providing excellent wave transmission while having minimal impact on the overall microwave absorption effect. The surface layer is composed of flame-retardant PMI foam with a pore size of 0.2mm to 0.6mm, offering superior panel adhesion. If the pore size is less than 0.2mm, panel peeling is weak; if the pore size is greater than 0.6mm, the adhesive holding capacity is too high, increasing the areal density.

[0013] The inventors discovered that using flame-retardant PMI foam sheets for the surface layer ensures a good bond with the panel and also allows for a good bond with the flame-retardant absorbing PMI foam sheets. However, if the absorbing foam core layer only uses flame-retardant PMI foam sheets, the overall absorbing performance will be reduced. Furthermore, if the absorbing foam core layer only uses flame-retardant absorbing PMI foam sheets, the panel will easily detach because the flame-retardant absorbing PMI foam contains particulate absorbers and has small pores.

[0014] In a preferred embodiment, the flame-retardant microwave absorbing PMI foam sheet has a multi-layer structure, wherein the number of layers is ≥2, and the thickness of any one layer of the flame-retardant microwave absorbing PMI foam sheet is 1~30mm.

[0015] In a preferred embodiment, the input impedance Z of the multi-layer flame-retardant absorbing PMI foam sheet is as follows: the Nth layer of flame-retardant PMI foam sheet and the (N+1)th layer of flame-retardant absorbing PMI foam sheet are... N The intrinsic impedance η of the N+1th layer of flame-retardant absorbing PMI foam sheet N+1 equal.

[0016] In this invention, the thickness of each layer of flame-retardant and microwave-absorbing PMI foam can be the same or different; the absorbent content of each piece of flame-retardant and microwave-absorbing PMI foam can be the same or different; the film resistance between layers can be the same or different, as long as the above design principles are met.

[0017] In a preferred embodiment, the preparation process of the flame-retardant microwave-absorbing PMI foam sheet is as follows: 50-100 parts by weight of methacrylic acid, 50-100 parts by weight of methacrylonitrile, 2-7 parts by weight of polymethyl methacrylate, 0.5-20 parts by weight of electromagnetic wave absorber, 10-30 parts by weight of flame retardant, 3-7 parts by weight of tert-butanol, 3-5 parts by weight of formamide, 5-12 parts by weight of isopropanol, 0.2-2 parts by weight of allyl methacrylate, 0.2-0.7 parts by weight of peroxide initiator, 0.1-0.3 parts by weight of zinc methacrylate, and 0.01 parts by weight of hydroquinone are mixed evenly, polymerized at a constant temperature of 30℃-40℃ for 200-230 hours to form a solid prepolymer, and then foamed at 140℃-210℃ for 5-8 hours to obtain flame-retardant microwave-absorbing PMI foam. The foam is then sliced ​​to obtain flame-retardant microwave-absorbing PMI foam sheets.

[0018] In actual operation, after obtaining a whole piece of flame-retardant microwave-absorbing PMI foam using the above method, it is cut into sheets using a common gantry saw to obtain flame-retardant microwave-absorbing PMI foam sheets.

[0019] In a further preferred embodiment, the flame retardant is an NP-based liquid flame retardant, preferably at least one of dimethyl methylphosphonate and diethyl methylphosphonate.

[0020] In a further preferred embodiment, the electromagnetic wave absorber is a mixed absorber composed of magnetic carbon fiber and Cu / Co / C composite absorber, wherein, by weight ratio, the ratio of magnetic carbon fiber to Cu / Co / C composite absorber in the electromagnetic wave absorber is 1:0.1~10.

[0021] In this invention, the Cu / Co / C composite absorbent is prepared by adsorption-calcination method.

[0022] More preferably, the Cu / Co / C composite absorbent is prepared by first mixing 50-70 parts of cobalt nitrate and 30-200 parts of ethanol to form a Co-containing absorbent. 2+Mixture I, then take 50-100 parts of A and 50-100 parts of Cu3(BTC)2 particles and mix them evenly to form Mixture II. Finally, take 50-200 parts of Mixture II and treat it at 600℃-800℃ for 1.5-3 hours. After cooling, the Cu / Co / C composite absorbent is obtained.

[0023] The inventors discovered that mixing magnetic carbon fibers with a ternary Cu / Co / C composite absorber to form a mixed absorber results in superior electromagnetic wave absorption.

[0024] The magnetic carbon fiber is a carbon fiber with a nickel-plated coating and has a length of 0.5~5mm.

[0025] In a preferred embodiment, the flame-retardant microwave-absorbing PMI foam sheet has a pore size ≤ 0.2 mm and a density of 30~150 kg / m³. 3 It has a compressive strength of 0.5~5MPa and self-extinguishes within 30s after being removed from the flame.

[0026] In a preferred embodiment, the width of the guide channel is 0.5~5mm, the depth is 0.5~5mm, and the spacing between the channels is 10~40mm. Guide channels and holes are formed on the upper surface of the microwave-absorbing foam core layer, i.e., the flame-retardant PMI foam sheet, to facilitate the fabrication of a sandwich-structured microwave-absorbing composite material using a vacuum infusion process.

[0027] In a preferred embodiment, the diameter of the hole is 1~4mm and the spacing between the holes is 10~40mm.

[0028] In a preferred embodiment, the glass fiber cloth or quartz fiber cloth in the upper skin is one or more layers.

[0029] In a preferred embodiment, the thickness of the upper skin is 0.1~0.2mm.

[0030] In a preferred embodiment, the carbon fiber cloth in the lower skin is one or more layers, and the resistivity of the carbon fiber cloth is 1.0 × 10⁻⁶. 2 S / m ~ 5.0 × 10 2 S / m.

[0031] In a preferred embodiment, the thickness of the lower skin carbon fiber cloth is 0.1~0.2mm.

[0032] This invention also provides a method for preparing a structural microwave absorbing composite material. First, a single-layer flame-retardant PMI foam and a single-layer or multi-layer flame-retardant microwave absorbing PMI foam sheet are bonded together with an adhesive film. Then, the PMI foam core material is obtained by hot pressing at a temperature of 60~100℃ and a pressure of 0.1~3MPa. Next, channeling grooves and holes are opened on both surfaces of the PMI foam core material. Finally, glass fiber cloth and / or quartz fiber cloth, the PMI foam core material, and carbon fiber cloth are sequentially layered and laid. Then, vacuum-assisted resin infusion molding is performed at a temperature of 60~100℃ and a pressure of 0.1~3MPa to obtain the structural microwave absorbing composite material.

[0033] In a preferred embodiment, the surface resistivity of the adhesive film is 20~600Ω / c and the film thickness is 0.1~1mm.

[0034] In a preferred embodiment, the resin used in the vacuum-assisted resin casting molding is epoxy resin with a viscosity of 200 mPa·s to 1000 mPa·s. The inventors have discovered that controlling the viscosity of the resin added during vacuum-assisted resin casting molding within the above-mentioned range yields the optimal vacuum casting effect.

[0035] In this invention, by opening and perforating the double surfaces of the microwave-absorbing PMI foam core material, the resin is embedded in the channels and holes during the vacuum-assisted resin injection molding process. Finally, it is combined with the glass fiber cloth and / or quartz fiber cloth reinforced resin matrix composite material or carbon fiber cloth reinforced resin matrix composite material obtained by vacuum-assisted resin injection molding to form a structural microwave-absorbing composite material.

[0036] The through holes and grooves on the microwave absorbing foam core layer are machined using CNC machine tools.

[0037] Beneficial effects

[0038] (1) The structural microwave absorbing composite material provided by the present invention has advantages such as low surface density, high panel bonding strength and good flame retardant performance, and at the same time has good broadband microwave absorption performance in 1~40GHz.

[0039] (2) The foam core material adopts microwave absorbing PMI foam and conductive adhesive film. The main components of the microwave absorbing PMI foam absorber are magnetized carbon fiber and Cu / Co / C high-efficiency powder absorber, which can further reduce the difference in electromagnetic wave absorption performance between the two directions of incident angle 0° and 30°.

[0040] (3) The structural wave-absorbing composite material molding method of the present invention is simple and easy to operate. It is suitable for producing large-size structural wave-absorbing composite materials. It is also suitable for placing the wave-absorbing foam core material on the surface of large components and molding it as an integral part with other components, thus avoiding the splicing of scattered components.

[0041] (4) The structural microwave absorbing composite material of the present invention can be flexibly designed and molded according to the changes in the external environment's requirements for the material's strength, weight, load-bearing capacity and microwave absorption performance.

[0042] (5) A multi-layered absorbing structure is made by using absorbing film and flame-retardant absorbing PMI foam. After design, the absorption effect of electromagnetic waves in broadband and low frequency is better.

[0043] (6) Flame-retardant PMI foam with a pore size of 0.2~0.6mm is used as the core foam surface and bonded to the glass fiber wave-transparent layer, which further ensures the peel strength of the composite material surface and avoids bulging and cracking of the composite material surface caused by the small pore size and low peel strength of the flame-retardant wave-absorbing PMI foam.

[0044] (7) The flame-retardant and microwave-absorbing PMI foam uses short-cut magnetized carbon fibers and three-dimensional Cu / Co / C absorbers, which improve the electromagnetic wave absorption performance while also reducing the directionality.

[0045] (8) The structural wave-absorbing composite material of the present invention has both load-bearing and wave-absorbing functions and can be widely used in fields such as stealth cabins. Attached Figure Description

[0046] Figure 1 Schematic diagram of structural microwave absorbing composite material.

[0047] Figure 2 The microwave absorbing PMI foam core material prepared in Example 1.

[0048] Figure 3 The microwave-absorbing PMI foam core material after surface grooving and perforation in Example 1.

[0049] Figure 4 The front side of the structural microwave absorbing composite material prepared in Example 1.

[0050] Figure 5 The side surface of the structural microwave absorbing composite material prepared in Example 1. Detailed Implementation

[0051] The present invention will be further described below with reference to specific embodiments, but it should be noted that the scope of the present invention is not limited to the following embodiments.

[0052] The preparation process of the Cu / Co / C composite absorbent in the following examples is as follows:

[0053] Preparation of Cu / Co / C composite absorbent: Mix 50 parts by weight of cobalt nitrate and 80 parts by weight of ethanol to prepare mixture I. Then, take 60 parts by weight of A and 90 parts by weight of Cu3(BTC)2 particles and mix them evenly. Treat at 700℃ for 2 hours and cool to obtain Cu / Co / C composite absorbent.

[0054] Example 1

[0055] Preparation of Flame-Retardant Microwave-Absorbing PMI Foam: The mixture consists of 50 parts by weight of methacrylic acid, 45 parts by weight of methacrylonitrile, 7 parts by weight of polymethyl methacrylate, 3 parts by weight of 3mm magnetic carbon fiber absorber, 6 parts by weight of Cu / Co / C composite absorber, 20 parts by weight of dimethyl phosphonate, 4 parts by weight of tert-butanol, 4 parts by weight of formamide, 10 parts by weight of isopropanol, 0.25 parts by weight of allyl methacrylate, 0.3 parts by weight of benzoyl peroxide, 0.12 parts by weight of zinc methacrylate, and 0.005 parts by weight of hydroquinone. After uniform mixing, the mixture is polymerized at 35℃ for 200 hours to form a solid prepolymer. This prepolymer is then foamed at 140℃, 170℃, and 200℃ for 7 hours each to obtain the flame-retardant microwave-absorbing PMI foam. The prepared flame-retardant microwave-absorbing PMI foam has a pore size ≤0.2mm and a density of 79kg / m³. 3 It has a compressive strength of 1.8 MPa and self-extinguishes within 23 seconds after being removed from the flame.

[0056] 1) A 2mm thick material with a density of 114kg / m³ 3 Flame-retardant PMI foam sheets are bonded to 1mm, 3mm, 5mm, and 8mm flame-retardant microwave-absorbing foams using an adhesive film, and then hot-pressed at 80℃ and 2MPa to create a microwave-absorbing PMI foam core material. Figure 1 As shown.

[0057] 2) Grooving and perforating the obtained microwave-absorbing PMI foam core material on the surface of the flame-retardant PMI foam.

[0058] 3) After laying one layer of quartz fiber cloth, microwave absorbing PMI foam core material and one layer of carbon fiber cloth in sequence, they are placed together on the mold and vacuum-assisted resin injection molding is carried out at a temperature of 80℃ and a pressure of 0.1MPa to obtain the structural microwave absorbing composite material; the resin used in the vacuum-assisted resin injection molding is epoxy resin with a viscosity of 200mPa.s.

[0059] The resulting board exhibits a peel strength ≥ 6 N / cm between the top skin and the absorbent foam core layer, a compressive strength ≥ 1.5 MPa, and a core material areal density ≤ 3.5 g / cm³. 2 The surface density of the structural microwave absorbing composite material is ≤6g / cm³. 2 Both the microwave-absorbing foam core material and the structural microwave-absorbing composite material are self-extinguishing within 30 seconds of being removed from the fire. Their microwave absorption performance is shown in Table 1.

[0060] Table 1

[0061]

[0062] Example 2

[0063] Preparation of Flame-Retardant Microwave-Absorbing PMI Foam①: 50 parts by weight of methacrylic acid, 45 parts by weight of methacrylonitrile, 5 parts by weight of polymethyl methacrylate, 3 parts by weight of 3mm magnetic carbon fiber absorber, 6 parts by weight of Cu / Co / C composite absorber, 20 parts by weight of dimethyl phosphonate, 4 parts by weight of tert-butanol, 4 parts by weight of formamide, 10 parts by weight of isopropanol, 0.25 parts by weight of allyl methacrylate, 0.3 parts by weight of benzoyl peroxide, 0.12 parts by weight of zinc methacrylate, and 0.005 parts by weight of hydroquinone were mixed evenly and polymerized at 35℃ for 200 hours to form a solid prepolymer. This prepolymer was then foamed at 140℃, 170℃, and 200℃ for 7 hours each to obtain flame-retardant microwave-absorbing PMI foam. The prepared flame-retardant microwave-absorbing PMI foam has a pore size ≤0.2mm and a density of 79kg / m³. 3 It has a compressive strength of 1.8 MPa and self-extinguishes after 23 seconds of flameout.

[0064] Preparation of Flame-Retardant Microwave-Absorbing PMI Foam ②: 50 parts by weight of methacrylic acid, 45 parts by weight of methacrylonitrile, 6 parts by weight of polymethyl methacrylate, 5 parts by weight of 3mm magnetic carbon fiber absorber, 9 parts by weight of Cu / Co / C composite absorber, 20 parts by weight of dimethyl phosphonate, 6 parts by weight of tert-butanol, 5 parts by weight of formamide, 8 parts by weight of isopropanol, 0.15 parts by weight of allyl methacrylate, 0.3 parts by weight of benzoyl peroxide, 0.12 parts by weight of zinc methacrylate, and 0.005 parts by weight of hydroquinone were mixed evenly and polymerized at 35℃ for 200 hours to form a solid prepolymer. This prepolymer was then foamed at 140℃, 170℃, and 200℃ for 7 hours each to obtain the flame-retardant microwave-absorbing PMI foam. The prepared flame-retardant microwave-absorbing PMI foam has a pore size ≤0.2mm and a density of 85kg / m³. 3 It has a compressive strength of 2.0 MPa and self-extinguishes within 20 seconds after being removed from the flame.

[0065] 2) A 1.5mm thick material with a density of 114kg / m³ 3 Flame-retardant PMI foam sheets, 4mm flame-retardant microwave-absorbing PMI foam①, and 10mm flame-retardant microwave-absorbing PMI foam② are bonded together with an adhesive film and then hot-pressed at a temperature of 80℃ and a pressure of 2MPa to form microwave-absorbing PMI foam core material.

[0066] 2) Grooving and perforating the obtained microwave-absorbing PMI foam core material on the surface of the flame-retardant PMI foam.

[0067] 3) After laying two layers of quartz fiber cloth, microwave absorbing PMI foam core material and two layers of carbon fiber cloth in sequence, they are placed together on the mold. The structure microwave absorbing composite material is obtained by vacuum-assisted resin injection molding at a temperature of 80℃ and a pressure of 0.1MPa. The resin used in the vacuum-assisted resin injection molding is epoxy resin with a viscosity of 200mPa.s.

[0068] The resulting board exhibits a peel strength between the top skin and the absorbent foam core layer ≥ 6 N / cm, a compressive strength ≥ 1.8 MPa, and a core material areal density ≤ 3.0 g / cm³. 2 The surface density of the structural microwave absorbing composite material is ≤5g / cm³. 2 Both the microwave-absorbing foam core material and the structural microwave-absorbing composite material are self-extinguishing within 30 seconds of being removed from the fire. Their microwave absorption performance is shown in Table 2.

[0069] Table 2

[0070]

[0071] Example 3

[0072] Preparation of Flame-Retardant Microwave-Absorbing PMI Foam①: 50 parts by weight of methacrylic acid, 45 parts by weight of methacrylonitrile, 5 parts by weight of polymethyl methacrylate, 3 parts by weight of 3mm magnetic carbon fiber absorber, 6 parts by weight of Cu / Co / C composite absorber, 20 parts by weight of dimethyl phosphonate, 4 parts by weight of tert-butanol, 4 parts by weight of formamide, 10 parts by weight of isopropanol, 0.25 parts by weight of allyl methacrylate, 0.3 parts by weight of benzoyl peroxide, 0.12 parts by weight of zinc methacrylate, and 0.005 parts by weight of hydroquinone were mixed evenly and polymerized at 35℃ for 200 hours to form a solid prepolymer. This prepolymer was then foamed at 140℃, 170℃, and 200℃ for 7 hours each to obtain flame-retardant microwave-absorbing PMI foam. The prepared flame-retardant microwave-absorbing PMI foam has a pore size ≤0.2mm and a density of 79kg / m³. 3 It has a compressive strength of 1.8 MPa and self-extinguishes after 23 seconds of flameout.

[0073] Preparation of Flame-Retardant Microwave-Absorbing PMI Foam ②: 50 parts by weight of methacrylic acid, 45 parts by weight of methacrylonitrile, 6 parts by weight of polymethyl methacrylate, 5 parts by weight of 3mm magnetic carbon fiber absorber, 9 parts by weight of Cu / Co / C composite absorber, 20 parts by weight of dimethyl phosphonate, 6 parts by weight of tert-butanol, 5 parts by weight of formamide, 8 parts by weight of isopropanol, 0.15 parts by weight of allyl methacrylate, 0.3 parts by weight of benzoyl peroxide, 0.12 parts by weight of zinc methacrylate, and 0.005 parts by weight of hydroquinone were mixed evenly and polymerized at 35℃ for 200 hours to form a solid prepolymer. This prepolymer was then foamed at 140℃, 170℃, and 200℃ for 7 hours each to obtain the flame-retardant microwave-absorbing PMI foam. The prepared flame-retardant microwave-absorbing PMI foam has a pore size ≤0.2mm and a density of 85kg / m³. 3 It has a compressive strength of 2.0 MPa and self-extinguishes within 20 seconds after being removed from the flame.

[0074] 3) A 1.5mm thick material with a density of 114kg / m³ 3Flame-retardant PMI foam sheets and 1mm, 3mm flame-retardant microwave-absorbing PMI foam①, 5mm, and 10mm flame-retardant microwave-absorbing PMI foam② are bonded together with an adhesive film and then hot-pressed at 80℃ and 2MPa to form microwave-absorbing PMI foam core material.

[0075] 2) Grooving and perforating the obtained microwave-absorbing PMI foam core material on the surface of the flame-retardant PMI foam.

[0076] 3) After laying one layer of quartz fiber cloth, microwave absorbing PMI foam core material and one layer of carbon fiber cloth in sequence, they are placed together on the mold and vacuum-assisted resin injection molding is carried out at a temperature of 80℃ and a pressure of 0.1MPa to obtain the structural microwave absorbing composite material; the resin used in the vacuum-assisted resin injection molding is epoxy resin with a viscosity of 200mPa.s.

[0077] The resulting structural microwave absorbing composite material exhibits a peel strength ≥6 N / cm between the skin and the microwave absorbing foam core, a compressive strength ≥1.8 MPa, and a core material areal density ≤3.3 g / cm³. 2 The surface density of the structural microwave absorbing composite material is ≤5.5g / cm³. 2 Both the microwave-absorbing foam core material and the structural microwave-absorbing composite material are self-extinguishing within 30 seconds of being removed from the fire. Their microwave absorption performance is shown in Table 3.

[0078] Table 3

[0079]

[0080] Comparative Example 1

[0081] Preparation of Flame-Retardant Microwave-Absorbing PMI Foam ③: 50 parts by weight of methacrylic acid, 45 parts by weight of methacrylonitrile, 7 parts by weight of polymethyl methacrylate, 5 parts by weight of 3mm magnetic carbon fiber absorber, 20 parts by weight of dimethyl phosphonate, 4 parts by weight of tert-butanol, 4 parts by weight of formamide, 10 parts by weight of isopropanol, 0.25 parts by weight of allyl methacrylate, 0.3 parts by weight of benzoyl peroxide, 0.12 parts by weight of zinc methacrylate, and 0.005 parts by weight of hydroquinone were mixed evenly and polymerized at 35℃ for 200 hours to form a solid prepolymer. This prepolymer was then foamed at 140℃, 170℃, and 200℃ for 7 hours each to obtain the flame-retardant microwave-absorbing PMI foam. The prepared flame-retardant microwave-absorbing PMI foam has a pore size ≤0.4mm and a density of 70kg / m³. 3 It has a compressive strength of 1.4 MPa and self-extinguishes within 15 seconds after being removed from the flame.

[0082] 4) A 2mm thick material with a density of 114kg / m³ 3 Flame-retardant PMI foam sheets with 1mm, 3mm, 5mm, and 8mm flame-retardant microwave absorption membranes

[0083] After being bonded with adhesive film, it is hot-pressed at 80℃ and 2MPa to form microwave-absorbing PMI foam core material, such as... Figure 1 As shown.

[0084] 2) Grooving and perforating the obtained microwave-absorbing PMI foam core material on the surface of the flame-retardant PMI foam.

[0085] 3) After laying out the quartz fiber cloth, microwave-absorbing PMI foam core material and carbon fiber cloth in sequence, place them together on the mold and vacuum-inject them at a temperature of 80℃ and a pressure of 0.1MPa to form a structural microwave-absorbing composite material.

[0086] The resulting board exhibits a peel strength ≥ 6 N / cm, a compressive strength ≥ 1.3 MPa, and a core material areal density ≤ 3.0 g / cm³. 2 The surface density of the component is ≤5.4g / cm³. 2 Both the microwave-absorbing foam core material and the structural microwave-absorbing composite material are self-extinguishing within 30 seconds of being removed from the fire. Their microwave absorption performance is shown in Table 4.

[0087] Table 4

[0088]

[0089] Comparative Example 2

[0090] Preparation of Flame-Retardant Microwave-Absorbing PMI Foam: The mixture consists of 50 parts by weight of methacrylic acid, 45 parts by weight of methacrylonitrile, 7 parts by weight of polymethyl methacrylate, 5 parts by weight of 3mm magnetic carbon fiber absorber, 10 parts by weight of Cu / Co / C composite absorber, 20 parts by weight of dimethyl phosphonate, 4 parts by weight of tert-butanol, 4 parts by weight of formamide, 10 parts by weight of isopropanol, 0.25 parts by weight of allyl methacrylate, 0.3 parts by weight of benzoyl peroxide, 0.12 parts by weight of zinc methacrylate, and 0.005 parts by weight of hydroquinone. After uniform mixing, the mixture is polymerized at 35℃ for 200 hours to form a solid prepolymer. This prepolymer is then foamed at 140℃, 170℃, and 200℃ for 7 hours each to obtain the flame-retardant microwave-absorbing PMI foam. The prepared flame-retardant microwave-absorbing PMI foam has a pore size ≤0.2mm and a density of 80kg / m³. 3 It has a compressive strength of 2.0 MPa and self-extinguishes within 10 seconds after being removed from the flame.

[0091] 5) Flame-retardant and microwave-absorbing PMI foam sheets of 1mm, 3mm, 5mm, and 8mm thickness are bonded together with an adhesive film and then hot-pressed at 80℃ and 2MPa to form microwave-absorbing PMI foam core material. Figure 1 As shown.

[0092] 2) Grooving and perforating the obtained microwave-absorbing PMI foam core material on the surface of the flame-retardant PMI foam.

[0093] 3) After laying out the quartz fiber cloth, microwave-absorbing PMI foam core material and carbon fiber cloth in sequence, place them together on the mold and vacuum-inject them at a temperature of 80℃ and a pressure of 0.1MPa to form a structural microwave-absorbing composite material.

[0094] The resulting board exhibits weak peel strength (≤3.7 N / cm) and is prone to blistering and delamination; compressive strength ≥1.5 MPa; and core material surface density ≤3.3 g / cm³. 2 The surface density of the component is ≤5.2g / cm³. 2 Both the microwave-absorbing foam core material and the structural microwave-absorbing composite material are self-extinguishing within 30 seconds of being removed from the fire.

Claims

1. A structural microwave absorbing composite material, characterized in that: The structural microwave absorbing composite material is divided into three parts from top to bottom: an upper skin, a microwave absorbing foam core layer, and a lower skin. The upper skin is a glass fiber cloth and / or quartz fiber cloth reinforced resin-based composite material, and the lower skin is a carbon fiber cloth reinforced resin-based composite material. The microwave absorbing foam core layer is divided into a single-layer flame-retardant PMI foam sheet and a flame-retardant microwave absorbing PMI foam sheet. The microwave absorbing foam core layer has drainage grooves and holes on both surfaces. The flame-retardant microwave absorbing PMI foam sheet has a multi-layer structure, with ≥2 layers, and the thickness of any one layer of the flame-retardant microwave absorbing PMI foam sheet is 1~30mm. The multi-layer flame-retardant absorbing PMI foam sheet has an input impedance Z between the Nth and N+1th flame-retardant absorbing PMI foam layers. N The intrinsic impedance η of the N+1th layer of flame-retardant absorbing PMI foam sheet N+1 equal; The preparation process of the flame-retardant microwave-absorbing PMI foam sheet is as follows: 50-100 parts by weight of methacrylic acid, 50-100 parts by weight of methacrylonitrile, 2-7 parts by weight of polymethyl methacrylate, 0.5-20 parts by weight of electromagnetic wave absorber, 10-30 parts by weight of flame retardant, 3-7 parts by weight of tert-butanol, 3-5 parts by weight of formamide, 5-12 parts by weight of isopropanol, 0.2-2 parts by weight of allyl methacrylate, 0.2-0.7 parts by weight of peroxide initiator, 0.1-0.3 parts by weight of zinc methacrylate, and 0.01 parts by weight of hydroquinone are mixed evenly and then polymerized at a constant temperature of 30℃-40℃ for 200-230 hours to form a solid prepolymer. Then, it is foamed at 140℃-210℃ for 5-8 hours to obtain flame-retardant microwave-absorbing PMI foam, and sliced ​​to obtain flame-retardant microwave-absorbing PMI foam sheets. The electromagnetic wave absorber is a mixed absorber composed of magnetic carbon fiber and Cu / Co / C composite absorber. In the electromagnetic wave absorber, the ratio of magnetic carbon fiber to Cu / Co / C composite absorber by weight is 1:0.1~10.

2. The structural microwave absorbing composite material according to claim 1, characterized in that: The flame-retardant PMI foam sheet has a thickness of 1-3 mm and a foam density of 100 kg / m³. 3 ~200kg / m 3 The foam pore size is 0.2mm~0.6mm.

3. The structural microwave absorbing composite material according to claim 1, characterized in that: The flame retardant is an NP-based liquid flame retardant.

4. The structural microwave absorbing composite material according to claim 1, characterized in that: The preparation method of the Cu / Co / C composite absorbent is as follows: First, 50-70 parts of cobalt nitrate and 30-200 parts of ethanol are mixed to prepare a Co-containing absorbent. 2+ Mixture I, then take 50-100 parts of A and 50-100 parts of Cu3(BTC)2 particles and mix them evenly to form Mixture II. Finally, take 50-200 parts of Mixture II and treat it at 600℃-800℃ for 1.5-3 hours. After cooling, the Cu / Co / C composite absorbent is obtained.

5. The structural microwave absorbing composite material according to claim 1, characterized in that: The magnetic carbon fiber is a carbon fiber with a nickel-plated coating and has a length of 0.5~5mm.

6. The structural microwave absorbing composite material according to claim 1, characterized in that: The flame-retardant microwave-absorbing PMI foam sheet has a pore size ≤0.2mm and a density of 30~150kg / m³. 3 It has a compressive strength of 0.5~5MPa and self-extinguishes within 30s after being removed from the flame.

7. The structural microwave absorbing composite material according to claim 1, characterized in that: The width of the guide channel is 0.5~5mm, the depth is 0.5~5mm, and the spacing between channels is 10~40mm; The diameter of the holes is 1~4mm, and the spacing between the holes is 10~40mm.

8. The structural microwave absorbing composite material according to claim 1, characterized in that: The glass fiber cloth or quartz fiber cloth in the upper skin is one or more layers; The carbon fiber cloth in the lower skin is one or more layers, and the resistivity of the carbon fiber cloth is 1.0 × 10⁻⁶. 2 S / m ~ 5.0 × 10 2 S / m.

9. A structural microwave absorbing composite material according to claim 1 or 8, characterized in that: The thickness of the upper skin is 0.1~0.2mm; The thickness of the lower skin is 0.1~0.2mm.

10. A method for preparing a structural microwave absorbing composite material according to any one of claims 1-9, characterized in that: First, a single-layer flame-retardant PMI foam and a single-layer or multi-layer flame-retardant microwave-absorbing PMI foam sheet are bonded together with an adhesive film. Then, the foam is hot-pressed at a temperature of 60~100℃ and a pressure of 0.1~3MPa to obtain a microwave-absorbing PMI foam core material. Next, channel grooves and holes are opened on both surfaces of the microwave-absorbing PMI foam core material. Finally, glass fiber cloth and / or quartz fiber cloth, microwave-absorbing PMI foam core material, and carbon fiber cloth are sequentially layered and laid. Then, vacuum-assisted resin injection molding is performed at a temperature of 60~100℃ and a pressure of 0.1~3MPa to obtain a structural microwave-absorbing composite material.

11. The method for preparing a structural microwave absorbing composite material according to claim 10, characterized in that: The surface resistivity of the adhesive film is 20~600Ω / c, and the film thickness is 0.1~1mm.

12. The method for preparing a structural microwave absorbing composite material according to claim 10, characterized in that: The resin used in the vacuum-assisted resin injection molding is epoxy resin with a viscosity of 200 mPa.s to 1000 mPa.s.

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