A lightweight, broadband wave-absorbing PMI foam core composite wave-absorbing structure

Abstract

The present invention discloses a lightweight, broadband wave-absorbing composite material wave-absorbing structure with a PMI foam core, relating to the technical field of wave-absorbing materials. The structure comprises a bottom fiber cloth, wherein a material AP is provided at the upper end of the bottom fiber cloth, a material BP is provided at the end of the material AP away from the bottom fiber cloth, a material CP is provided at the end of the material BP away from the material AP, and a surface fiber cloth is provided at the end of the material CP away from the material BP. In the present invention, foaming and fiber curing are completed in one step, which reduces one step compared to the conventional method of first making the wave-absorbing foam and then compounding the skin layer with the wave-absorbing foam. In addition, no obvious interface is formed between the wave-absorbing foam and the skin layer. In the present invention, the absorbent content increases from the upper surface to the lower surface, forming a gradient. This takes into account the impedance matching of the wave-absorbing structure, is beneficial to the entry and loss of electromagnetic waves, significantly improves the low-frequency absorption effect of electromagnetic waves, and increases the effective wave-absorbing bandwidth.

Description

Technical Field

[0001] The invention relates to the technical field of wave-absorbing materials, in particular to a light-weight, broadband wave-absorbing PMI foam sandwich composite material wave-absorbing structure. Background Art

[0002] Currently, radar stealth for weapons and equipment primarily relies on absorbing coatings and patches to reduce the target's RCS. However, these coatings' relatively high surface density increases the weight of the equipment, and their easy peeling and high maintenance costs limit their application in many situations. The rapid development of modern weaponry toward low energy consumption, high payload, stealth, and high mobility places higher demands on manufacturing materials. Sandwich composite materials with absorbing properties offer an effective solution to these challenges. By combining a wave-transparent material as the outer skin and an absorbing foam core, the composite material achieves an integrated absorption, load-bearing, and lightweight design.

[0003] Polymethacrylimide (PMI) foam is a rigid closed-cell foam material that is lightweight, high-strength, high-temperature resistant, easy to process, and easy to bond. As the core material for composite sandwich structures, it is widely used in the field of high-performance composite materials. Its research and application are relatively mature, but the development of PMI foam plastics with wave-absorbing functions is still in the exploratory stage. In addition, due to its inherent defects, foam materials cannot be used as load-bearing structural components alone and need to be compounded with fiber materials to meet load-bearing and weather-resistant requirements.

[0004] Chinese patent 2014101804170, entitled "Polymethacrylimide Composite Foam Absorbing Material," discloses a method for obtaining a PMI absorbing composite foam by foaming expandable PMI particles in a mold. This method provides a PMI foam absorbing material with good absorbing properties. However, the expandable PMI particles used in this method are obtained by mechanical crushing, and the particle size specifications after foaming vary greatly, resulting in unstable mechanical properties of the material. In addition, when the amount of absorbent added is small, a good absorption effect cannot be achieved. When a large amount of absorbent is added, the surface impedance matching is poor, and electromagnetic waves cannot effectively enter the material and are lost. At the same time, this method can only produce a single absorbing foam, which, in practical applications, needs to be compounded again with a wave-transmitting fiber skin to ensure the strength and weather resistance of the product.

[0005] In order to solve the above problems, an improved lightweight, broadband wave-absorbing PMI foam sandwich composite material wave-absorbing structure is designed. Summary of the Invention

[0006] The object of the present invention is to provide a lightweight, broadband wave-absorbing composite material wave-absorbing structure with a PMI foam core, so as to solve the problems raised in the above-mentioned background technology.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] A lightweight, broadband wave-absorbing PMI foam sandwich composite material wave-absorbing structure includes a bottom fiber cloth, a material AP is provided on the upper end of the bottom fiber cloth, a material BP is provided on the end of the material AP away from the bottom fiber cloth, a material CP is provided on the end of the material BP away from the material AP, and a surface fiber cloth is provided on the end of the material CP away from the material BP.

[0009] As a further solution of the present invention: the preparation of the material AP, the material BP and the material CP comprises the following steps:

[0010] Step 1: Preparation of expandable PMI particles

[0011] Mix 100 parts of methacrylonitrile, 90-140 parts of methacrylic acid, 5-10 parts of the third monomer, 3-6 parts of the stabilizer, 0.5-4 parts of the initiator, 5-15 parts of the foaming agent, 0.5-4 parts of the crosslinking agent, and 0.5-4 parts of the heat stabilizer in a uniform ratio;

[0012] The mixed solution is poured into a special mold by vacuuming. The mold cavity is composed of connected spheres with a diameter of 1-5 mm. The polymerization reaction is carried out in a water bath at 25-35°C. The polymerization in the mold can obtain spherical expandable PMI particles of the same size connected together.

[0013] The connected spherical expandable PMI resin plates are broken along the connection points to obtain expandable PMI particles of uniform size.

[0014] Step 2: Preparation of absorbing slurry

[0015] Absorbing slurry A: Add 100 parts of adhesive, 15-30 parts of absorbent, and 5-50 parts of solvent to a stirring tank and stir for 0.5 hours to evenly mix the materials. Then, add the materials to a grinding mortar and add an equal weight of zirconium beads (1-3 mm in size). Grind at 800 rpm for 2 hours to evenly disperse the absorbent in the adhesive. Filter out the zirconium beads from the ground material, add the material to a stirring tank, add 35 parts of curing agent, and stir for 0.5 hours to obtain the desired absorbing slurry.

[0016] Absorbing slurry B: Add 100 parts of adhesive, 10-15 parts of absorbent, and 5-30 parts of solvent to a stirring tank and stir for 0.5 hours to evenly mix the materials. Then, add the materials to a grinding mortar and add an equal weight of zirconium beads (1-3 mm in size). Grind at 600 rpm for 2 hours to evenly disperse the absorbent in the adhesive. Filter out the zirconium beads from the ground material, add the material to a stirring tank, add 35 parts of curing agent, and stir for 0.5 hours to obtain the desired absorbing slurry.

[0017] Absorbing slurry C: Add 100 parts of adhesive, 5-10 parts of absorbent, and 5-15 parts of solvent to a stirring tank and stir for 0.5 hours to evenly mix the materials. Then, add the materials to a grinding mortar and add an equal weight of zirconium beads (1-3 mm in size). Grind at 600 rpm for 2 hours to evenly disperse the absorbent in the adhesive. Filter out the zirconium beads from the ground material, add the material to a stirring tank, add 35 parts of curing agent, and stir for 0.5 hours to obtain the desired absorbing slurry.

[0018] The contents of absorbent in the three types of absorbing slurries, namely absorbing slurry A, absorbing slurry B and absorbing slurry C, decrease in sequence.

[0019] Step 3: Mix expandable PMI particles with the absorbing slurry for foaming

[0020] 100 parts of expandable PMI particles are uniformly mixed with 30-50 parts of absorbing slurry A to obtain material AP, ensuring that all expandable PMI particles are covered by absorbing slurry A; 100 parts of expandable PMI particles are uniformly mixed with 20-40 parts of absorbing slurry B to obtain material BP, ensuring that all expandable PMI particles are covered by absorbing slurry B; 100 parts of expandable PMI particles are uniformly mixed with 10-30 parts of absorbing slurry C to obtain material CP, ensuring that all expandable PMI particles are covered by absorbing slurry C;

[0021] Step 4: Apply a release agent to the foaming mold cavity, lay a bottom fiber cloth on the bottom of the cavity, lay material AP on the bottom fiber cloth and flatten it, lay material BP on material AP and flatten it, lay material CP on material BP and flatten it;

[0022] Mix 100 parts of epoxy resin and 35 parts of diethylenetriamine evenly, use the mixture to completely soak the surface fiber cloth, and then lay the surface fiber cloth flat on the upper surface of the foaming mold cavity so that it will not fall due to gravity;

[0023] After the mold is closed, the mold is sent to an oven at 180~235℃ for foaming for 5 hours. During this process, the expansion of the expandable PMI particles will press the fiber cloth tightly to the mold surface, making its shape match; after demolding, heat treatment for 3 hours is carried out to obtain the composite material absorbing structure described in this invention.

[0024] As a further embodiment of the present invention, the third monomer is one of acrylamide and methacrylamide, the stabilizer is one of triphenyl phosphite and diisooctylphenyl phosphite, and the initiator is one or more of dibenzoyl peroxide, dodecyl peroxide, dicarbonate peroxide, and azobisisobutyronitrile.

[0025] As a further solution of the present invention: the foaming agent is one or more of methylformamide, butanol, and isopropanol.

[0026] As a further solution of the present invention: the cross-linking agent is one or more of 2-methylallyl acrylate and allyl methacrylate.

[0027] As a further solution of the present invention: the thermal stabilizer is one of N-phenylmaleimide and 4,4'-methylenediphenylbismaleimide.

[0028] As a further solution of the present invention: the adhesive is one of epoxy resin and cyanate resin, the curing agent is one of ethylenediamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, and diethylaminopropylamine, and the solvent is acetone.

[0029] As a further solution of the present invention: the absorbent is one or more of superconducting carbon black, single-layer graphene, and multi-walled carbon nanotubes.

[0030] As a further solution of the present invention: the bottom fiber cloth is one of glass fiber cloth, quartz fiber cloth, aramid fiber cloth, and basalt fiber cloth. When it is necessary to add a reflective surface to the bottom surface of the absorbing structure in the application, carbon fiber cloth or other conductive metal film or conductive cloth is selected.

[0031] As a further solution of the present invention: the surface fiber cloth is one of glass fiber cloth, quartz fiber cloth, aramid fiber cloth and basalt fiber cloth.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] 1. The foaming and fiber curing of the present invention are completed in one step, which reduces one step compared to the conventional method of first making the absorbing foam and then compounding the skin layer with the absorbing foam. In addition, no obvious interface is formed between the absorbing foam and the skin layer, thereby improving the efficiency of electromagnetic waves entering the absorbing structure.

[0034] 2. The absorbent content of the present invention increases from the upper surface to the lower surface, forming a gradient. Taking into account the impedance matching of the absorbing structure, it is beneficial to the entry and loss of electromagnetic waves, significantly improves the low-frequency absorption effect of electromagnetic waves, and increases the effective absorbing bandwidth.

[0035] 3. The expandable PMI particles of the present invention are uniform in size, so that the particles after foaming are also relatively uniform, the particles are more tightly combined, the enrichment of the absorbing slurry between the particles is reduced, and the overall density of the foam is effectively reduced, thereby reducing the overall density of the absorbing structure and improving the mechanical properties of the absorbing structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a structural schematic diagram of the present invention.

[0037] Figure 2 This is a test curve of an embodiment of the present invention.

[0038] Among them: 1. Bottom fiber cloth; 2. Material AP; 3. Material BP; 4. Material CP; 5. Surface fiber cloth. DETAILED DESCRIPTION

[0039] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention. Example 1

[0040] See also Figure 1-Figure 2 In an embodiment of the present invention, a lightweight, broadband absorbing PMI foam sandwich composite material absorbing structure includes a bottom fiber cloth 1, a material AP2 is provided on the upper end of the bottom fiber cloth 1, a material BP3 is provided on the end of the material AP2 away from the bottom fiber cloth 1, a material CP4 is provided on the end of the material BP3 away from the material AP2, and a surface fiber cloth 5 is provided on the end of the material CP4 away from the material BP3.

[0041] The preparation of the material AP2, the material BP3 and the material CP4 comprises the following steps:

[0042] Step 1: Preparation of expandable PMI particles

[0043] Mix 100 parts of methacrylonitrile, 125 parts of methacrylic acid, 6.5 parts of methylpropionamide, 4.5 parts of triphenyl phosphite, 1.5 parts of azobisisobutyronitrile, 10 parts of foaming agent, 3.25 parts of propyl methacrylate, and 12.5 parts of N-phenylmaleimide according to the ratio; the ratio of methylformamide to isopropyl alcohol in the foaming agent is 3:1;

[0044] The mixed solution is poured into a special mold by vacuuming. The mold cavity is composed of connected spheres with the same diameter of 2.5mm. The polymerization reaction is carried out in a water bath at 29℃. The polymerization in the mold can obtain spherical expandable PMI particles of the same size connected together.

[0045] The connected spherical expandable PMI resin plates were broken along the connection to obtain spherical expandable PMI particles with a diameter of 2.5 mm.

[0046] Step 2: Preparation of absorbing slurry

[0047] Absorbing slurry A: Add 100 parts of epoxy resin, 40.5 parts of superconducting carbon black, and 20 parts of acetone to a stirring tank and stir for 0.5 hours to evenly mix the materials. Then, add the materials to a grinding mortar and add an equal weight of zirconium beads (1-3 mm in size). Grind at 800 rpm for 2 hours to evenly disperse the absorbent in the adhesive. Filter the zirconium beads from the ground material, add the material to a stirring tank, add 35 parts of diethylenetriamine, and stir for 0.5 hours to obtain the desired absorbing slurry.

[0048] Absorbing slurry B: Add 100 parts of epoxy resin, 27 parts of superconducting carbon black, and 10 parts of acetone to a stirring tank and stir for 0.5 hours to evenly mix the materials. Then, add the materials to a grinding mortar and add an equal weight of zirconium beads (1-3 mm in size). Grind at 600 rpm for 2 hours to evenly disperse the absorbent in the adhesive. Filter the zirconium beads from the ground material, add the material to a stirring tank, add 35 parts of diethylenetriamine, and stir for 0.5 hours to obtain the desired absorbing slurry.

[0049] Absorbing slurry C: Add 100 parts of epoxy resin, 13.5 parts of superconducting carbon black, and 5 parts of acetone to a stirring tank and stir for 0.5 hours to evenly mix the materials. Then, add the materials to a grinding mortar and add an equal weight of zirconium beads (1-3 mm in size). Grind at 600 rpm for 2 hours to evenly disperse the absorbent in the adhesive. Filter the zirconium beads from the ground material, add the material to a stirring tank, add 35 parts of diethylenetriamine, and stir for 0.5 hours to obtain the desired absorbing slurry.

[0050] The absorbent contents in the three types of absorbing slurries, namely absorbing slurry A, absorbing slurry B and absorbing slurry C, decrease in sequence.

[0051] Step 3: Mix expandable PMI particles with the absorbing slurry for foaming

[0052] 100 parts of expandable PMI particles are evenly mixed with 40 parts of absorbing slurry A to obtain material AP2, ensuring that all expandable PMI particles are wrapped by absorbing slurry A; 100 parts of expandable PMI particles are evenly mixed with 30 parts of absorbing slurry B to obtain material BP3, ensuring that all expandable PMI particles are wrapped by absorbing slurry B; 100 parts of expandable PMI particles are evenly mixed with 20 parts of absorbing slurry C to obtain material CP4, ensuring that all expandable PMI particles are wrapped by absorbing slurry C.

[0053] Step 4: Apply a release agent to the foaming mold cavity, lay a bottom fiber cloth 1 on the bottom surface of the mold cavity, lay material AP2 on the bottom fiber cloth 1 and flatten it, lay material BP3 on material AP2 and flatten it, and lay material CP4 on material BP3 and flatten it;

[0054] Mix 100 parts of epoxy resin and 35 parts of diethylenetriamine evenly, completely soak the surface fiber cloth 5 with the mixture, and then lay the surface fiber cloth 5 flat on the upper surface of the foaming mold cavity;

[0055] After closing the mold, the mold was placed in an oven at 215° C. for foaming for 5 hours, and then heat-treated for 3 hours after demoulding to obtain the sandwich composite material absorbing structure prepared in this embodiment.

[0056] The surface density of the absorbing plate prepared in this embodiment is 240-300 kg / m 2 , thickness 30mm, compression strength ≥6MPa. Example 2

[0057] See also Figure 1-Figure 2 In an embodiment of the present invention, a lightweight, broadband absorbing PMI foam sandwich composite material absorbing structure includes a bottom fiber cloth 1, a material AP2 is provided on the upper end of the bottom fiber cloth 1, a material BP3 is provided on the end of the material AP2 away from the bottom fiber cloth 1, a material CP4 is provided on the end of the material BP3 away from the material AP2, and a surface fiber cloth 5 is provided on the end of the material CP4 away from the material BP3.

[0058] The preparation of the material AP2, the material BP3 and the material CP4 comprises the following steps:

[0059] Step 1: Preparation of expandable PMI particles

[0060] Mix 100 parts of methacrylonitrile, 125 parts of methacrylic acid, 6.5 parts of methylpropionamide, 4.5 parts of triphenyl phosphite, 1.5 parts of azobisisobutyronitrile, 10 parts of foaming agent, 3.25 parts of propyl methacrylate, and 12.5 parts of N-phenylmaleimide according to the ratio; the ratio of methylformamide to isopropyl alcohol in the foaming agent is 3:1;

[0061] The mixed solution is poured into a special mold by vacuuming. The mold cavity is composed of connected spheres with the same diameter of 2.5mm. The polymerization reaction is carried out in a water bath at 29℃. The polymerization in the mold can obtain spherical expandable PMI particles of the same size connected together.

[0062] The connected spherical expandable PMI resin plates were broken along the connection to obtain spherical expandable PMI particles with a diameter of 2.5 mm.

[0063] Step 2: Preparation of absorbing slurry

[0064] Absorbing slurry A: Add 100 parts of cyanate resin, 40.5 parts of superconducting carbon black, and 20 parts of acetone to a stirring tank and stir for 0.5 h to evenly mix the materials; then add the materials to a grinding mortar, add an equal weight of zirconium beads with a size of 1-3 mm, and grind at a speed of 800 rpm for 2 h to evenly disperse the absorbent in the adhesive; then filter out the zirconium beads from the ground material, add the material to a stirring tank, add 35 parts of diethylenetriamine, and stir for 0.5 h to obtain the desired absorbing slurry.

[0065] Absorbing slurry B: Add 100 parts of cyanate resin, 27 parts of superconducting carbon black, and 10 parts of acetone to a stirring tank and stir for 0.5 h to evenly mix the materials; then add the materials to a grinding mortar, add an equal weight of zirconium beads with a size of 1-3 mm, and grind at a speed of 600 rpm for 2 h to evenly disperse the absorbent in the adhesive; then filter out the zirconium beads from the ground material, add the material to a stirring tank, add 35 parts of diethylenetriamine, and stir for 0.5 h to obtain the desired absorbing slurry.

[0066] Absorbing slurry C: Add 100 parts of cyanate resin, 13.5 parts of superconducting carbon black, and 5 parts of acetone to a stirring tank and stir for 0.5 h to evenly mix the materials; then add the materials to a grinding mortar, add an equal weight of zirconium beads with a size of 1-3 mm, and grind at a speed of 600 rpm for 2 h to evenly disperse the absorbent in the adhesive; then filter out the zirconium beads from the ground material, add the material to a stirring tank, add 35 parts of diethylenetriamine, and stir for 0.5 h to obtain the desired absorbing slurry.

[0067] Step 3: Mix expandable PMI particles with the absorbing slurry for foaming

[0068] 100 parts of expandable PMI particles are evenly mixed with 40 parts of absorbing slurry A to obtain material AP2, ensuring that all expandable PMI particles are wrapped by absorbing slurry A; 100 parts of expandable PMI particles are evenly mixed with 30 parts of absorbing slurry B to obtain material BP3, ensuring that all expandable PMI particles are wrapped by absorbing slurry B; 100 parts of expandable PMI particles are evenly mixed with 20 parts of absorbing slurry C to obtain material CP4, ensuring that all expandable PMI particles are wrapped by absorbing slurry C.

[0069] Step 4: Apply a release agent to the foaming mold cavity, lay a bottom fiber cloth 1 on the bottom surface of the mold cavity, lay material AP2 on the bottom fiber cloth 1 and flatten it, lay material BP3 on material AP2 and flatten it, and lay material CP4 on material BP3 and flatten it;

[0070] Mix 100 parts of epoxy resin and 35 parts of diethylenetriamine evenly, completely soak the surface fiber cloth 5 with the mixture, and then lay the surface fiber cloth 5 flat on the upper surface of the foaming mold cavity;

[0071] After closing the mold, the mold was placed in an oven at 215° C. for foaming for 5 hours, and then demoulded and heat treated for 3 hours to obtain the sandwich absorbing structure prepared in this embodiment.

[0072] The surface density of the absorbing plate prepared in this embodiment is 240-300 kg / m 2 , thickness 30mm, compression strength ≥5.2MPa. Example 3

[0073] See also Figure 1-Figure 2 In an embodiment of the present invention, a lightweight, broadband absorbing PMI foam sandwich composite material absorbing structure includes a bottom fiber cloth 1, a material AP2 is provided on the upper end of the bottom fiber cloth 1, a material BP3 is provided on the end of the material AP2 away from the bottom fiber cloth 1, a material CP4 is provided on the end of the material BP3 away from the material AP2, and a surface fiber cloth 5 is provided on the end of the material CP4 away from the material BP3.

[0074] The preparation of the material AP2, the material BP3 and the material CP4 comprises the following steps:

[0075] Step 1: Preparation of expandable PMI particles

[0076] Mix 100 parts of methacrylonitrile, 125 parts of methacrylic acid, 6.5 parts of methylpropionamide, 4.5 parts of triphenyl phosphite, 1.5 parts of azobisisobutyronitrile, 10 parts of foaming agent, 3.25 parts of propyl methacrylate, and 12.5 parts of N-phenylmaleimide according to the ratio; the ratio of methylformamide to isopropyl alcohol in the foaming agent is 3:1;

[0077] The mixed solution is poured into a special mold by vacuuming. The mold cavity is composed of connected spheres with the same diameter of 2.5mm. The polymerization reaction is carried out in a water bath at 29℃. The polymerization in the mold can obtain spherical expandable PMI particles of the same size connected together.

[0078] The connected spherical expandable PMI resin plates were broken along the connection to obtain spherical expandable PMI particles with a diameter of 2.5 mm.

[0079] Step 2: Preparation of absorbing slurry

[0080] Absorbing slurry A: Add 100 parts of cyanate resin, 40.5 parts of absorbent (graphene: multi-walled carbon nanotubes: carbon black = 1:2:1), and 20 parts of acetone to a stirring tank and stir for 0.5 h to evenly mix the materials. Then, add the materials to a grinding mortar and add an equal weight of zirconium beads (1-3 mm in size). Grind at 800 rpm for 2 h to evenly disperse the absorbent in the adhesive. Filter out the zirconium beads from the ground material, add the material to a stirring tank, add 35 parts of diethylenetriamine, and stir for 0.5 h to obtain the desired absorbing slurry.

[0081] Absorbing slurry B: Add 100 parts of cyanate resin, 40.5 parts of absorber (graphene: multi-walled carbon nanotubes: carbon black = 1:2:1), and 10 parts of acetone to a stirring tank and stir for 0.5 h to evenly mix the materials. Then add the materials to a grinding mortar and add an equal weight of zirconium beads with a size of 1-3 mm. Grind at 600 rpm for 2 h to evenly disperse the absorber in the adhesive. Filter out the zirconium beads from the ground material, add the material to a stirring tank, add 35 parts of diethylenetriamine, and stir for 0.5 h to obtain the desired absorbing slurry.

[0082] Absorbing slurry C: Add 100 parts of cyanate resin, 40.5 parts of absorbent (graphene: multi-walled carbon nanotubes: carbon black = 1:2:1), and 5 parts of acetone to a stirring tank and stir for 0.5 h to evenly mix the materials. Then add the materials to a grinding mortar and add an equal weight of zirconium beads with a size of 1-3 mm. Grind at 600 rpm for 2 h to evenly disperse the absorbent in the adhesive. Filter out the zirconium beads from the ground material, add the material to a stirring tank, add 35 parts of diethylenetriamine, and stir for 0.5 h to obtain the desired absorbing slurry.

[0083] Step 3: Mix expandable PMI particles with the absorbing slurry for foaming

[0084] 100 parts of expandable PMI particles are evenly mixed with 40 parts of absorbing slurry A to obtain material AP2, ensuring that all expandable PMI particles are wrapped by absorbing slurry A; 100 parts of expandable PMI particles are evenly mixed with 30 parts of absorbing slurry B to obtain material BP3, ensuring that all expandable PMI particles are wrapped by absorbing slurry B; 100 parts of expandable PMI particles are evenly mixed with 20 parts of absorbing slurry C to obtain material CP4, ensuring that all expandable PMI particles are wrapped by absorbing slurry C.

[0085] Step 4: Apply a release agent to the foaming mold cavity, lay a bottom fiber cloth 1 on the bottom surface of the mold cavity, lay material AP2 on the bottom fiber cloth 1 and flatten it, lay material BP3 on material AP2 and flatten it, and lay material CP4 on material BP3 and flatten it;

[0086] Mix 100 parts of epoxy resin and 35 parts of diethylenetriamine evenly, completely soak the surface fiber cloth 5 with the mixture, and then lay the surface fiber cloth 5 flat on the upper surface of the foaming mold cavity;

[0087] After closing the mold, the mold was placed in an oven at 215° C. for foaming for 5 hours, and then demoulded and heat treated for 3 hours to obtain the sandwich absorbing structure prepared in this embodiment.

[0088] The surface density of the absorbing plate prepared in this embodiment is 240-300 kg / m 2 , thickness 30mm, compression strength ≥5.2MPa.

[0089] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention.

Claims

1. A lightweight, broadband PMI foam core composite material absorbing structure, characterized in that: The invention comprises a bottom fiber cloth (1), wherein a material AP (2) is provided on the upper end of the bottom fiber cloth (1), a material BP (3) is provided on the end of the material AP (2) away from the bottom fiber cloth (1), a material CP (4) is provided on the end of the material BP (3) away from the material AP (2), and a surface fiber cloth (5) is provided on the end of the material CP (4) away from the material BP (3); The preparation of the material AP (2), the material BP (3) and the material CP (4) comprises the following steps: Step 1: Preparation of expandable PMI particles Mix 100 parts of methacrylonitrile, 90-140 parts of methacrylic acid, 5-10 parts of the third monomer, 3-6 parts of the stabilizer, 0.5-4 parts of the initiator, 5-15 parts of the foaming agent, 0.5-4 parts of the crosslinking agent, and 0.5-4 parts of the heat stabilizer in a uniform ratio; The mixed solution is poured into a special mold by vacuuming. The mold cavity is composed of connected spheres with a diameter of 1-5 mm. The polymerization reaction is carried out in a water bath at 25-35°C. The polymerization in the mold can obtain spherical expandable PMI particles of the same size connected together. Break the connected spherical expandable PMI resin plates along the joints to obtain expandable PMI particles of uniform size; Step 2: Preparation of absorbing slurry Absorbing slurry A: Add 100 parts of adhesive, 15-30 parts of absorbent, and 5-50 parts of solvent to a stirring tank and stir for 0.5 hours to evenly mix the materials. Then, add the materials to a grinding mortar and add an equal weight of zirconium beads (1-3 mm in size). Grind at 800 rpm for 2 hours to evenly disperse the absorbent in the adhesive. Filter out the zirconium beads from the ground material, add the material to a stirring tank, add 35 parts of curing agent, and stir for 0.5 hours to obtain the desired absorbing slurry. Absorbing slurry B: Add 100 parts of adhesive, 10-15 parts of absorbent, and 5-30 parts of solvent to a stirring tank and stir for 0.5 hours to evenly mix the materials. Then, add the materials to a grinding mortar and add an equal weight of zirconium beads (1-3 mm in size). Grind at 600 rpm for 2 hours to evenly disperse the absorbent in the adhesive. Filter out the zirconium beads from the ground material, add the material to a stirring tank, add 35 parts of curing agent, and stir for 0.5 hours to obtain the desired absorbing slurry. Absorbing slurry C: Add 100 parts of adhesive, 5-10 parts of absorbent, and 5-15 parts of solvent to a stirring tank and stir for 0.5 hours to evenly mix the materials. Then, add the materials to a grinding mortar and add an equal weight of zirconium beads (1-3 mm in size). Grind at 600 rpm for 2 hours to evenly disperse the absorbent in the adhesive. Filter out the zirconium beads from the ground material, add the material to a stirring tank, add 35 parts of curing agent, and stir for 0.5 hours to obtain the desired absorbing slurry. The content of absorbent in the three types of absorbing slurries, namely absorbing slurry A, absorbing slurry B and absorbing slurry C, decreases in sequence; Step 3: Mix expandable PMI particles with the absorbing slurry for foaming 100 parts of expandable PMI particles are uniformly mixed with 30-50 parts of absorbing slurry A to obtain material AP (2), ensuring that all expandable PMI particles are covered by absorbing slurry A; 100 parts of expandable PMI particles are uniformly mixed with 20-40 parts of absorbing slurry B to obtain material BP (3), ensuring that all expandable PMI particles are covered by absorbing slurry B; 100 parts of expandable PMI particles are uniformly mixed with 10-30 parts of absorbing slurry C to obtain material CP (4), ensuring that all expandable PMI particles are covered by absorbing slurry C; Step 4: Apply a release agent to the cavity of the foaming mold, lay a bottom fiber cloth (1) on the bottom surface of the cavity, lay the material AP (2) on the bottom fiber cloth (1) and flatten it, lay the material BP (3) on the material AP (2) and flatten it, and lay the material CP (4) on the material BP (3) and flatten it; 100 parts of epoxy resin and 35 parts of diethylenetriamine are mixed evenly, and the surface fiber cloth (5) is completely soaked with the mixture, and then the surface fiber cloth (5) is laid flat on the upper surface of the foaming mold cavity so that it will not fall due to gravity; After the mold is closed, the mold is sent to an oven at 180~235℃ for foaming for 5 hours. During this process, the expansion of the expandable PMI particles will press the fiber cloth tightly to the mold surface, making its shape match; after demolding and heat treatment for 3 hours, the composite material absorbing structure is obtained.

2. The lightweight, broadband wave-absorbing PMI foam core composite wave-absorbing structure according to claim 1, characterized in that: The third monomer is one of acrylamide and methacrylamide, the stabilizer is one of triphenyl phosphite and diisooctylphenyl phosphite, and the initiator is one or more of dibenzoyl peroxide, dodecyl peroxide, dicarbonate peroxide, and azobisisobutyronitrile.

3. The lightweight, broadband wave-absorbing PMI foam core composite wave-absorbing structure according to claim 1, characterized in that: The foaming agent is one or more of methylformamide, butanol and isopropanol.

4. The lightweight, broadband wave-absorbing PMI foam core composite wave-absorbing structure according to claim 1, characterized in that: The cross-linking agent is one or more of 2-methylallyl acrylate and allyl methacrylate.

5. The lightweight, broadband wave-absorbing PMI foam core composite wave-absorbing structure according to claim 1, characterized in that: The thermal stabilizer is one of N-phenylmaleimide and 4,4'-methylenediphenylbismaleimide.

6. The lightweight, broadband wave-absorbing PMI foam core composite wave-absorbing structure according to claim 1, characterized in that: The adhesive is one of epoxy resin and cyanate resin, the curing agent is one of ethylenediamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine and diethylaminopropylamine, and the solvent is acetone.

7. The lightweight, broadband wave-absorbing PMI foam core composite wave-absorbing structure according to claim 1, characterized in that: The absorbent is one or more of superconducting carbon black, single-layer graphene, and multi-walled carbon nanotubes.

8. The lightweight, broadband microwave-absorbing PMI foam core composite material microwave-absorbing structure according to claim 1, characterized in that: The bottom fiber cloth (1) is one of glass fiber cloth, quartz fiber cloth, aramid fiber cloth, and basalt fiber cloth. When a reflective surface needs to be added to the bottom surface of the absorbing structure, carbon fiber cloth is selected.

9. The lightweight, broadband microwave-absorbing composite material microwave-absorbing structure with a PMI foam core according to claim 1, characterized in that: The surface fiber cloth (5) is one of glass fiber cloth, quartz fiber cloth, aramid fiber cloth, and basalt fiber cloth.

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