A wave-absorbing foam / honeycomb core composite panel, a preparation method and application thereof

Abstract

The application discloses a wave-absorbing foam / honeycomb core composite board and a preparation method and application thereof. The composite board comprises a honeycomb core substrate layer, a wave-absorbing foam embedding layer and a wave-transparent foam filling layer which are sequentially stacked. The honeycomb core substrate layer is a honeycomb core with a plurality of hollow regions, and the surfaces of the honeycomb core are provided with a wave-absorbing coating. The wave-absorbing foam embedding layer comprises a plurality of filling parts and protruding parts. The filling parts are filled in the hollow regions of the honeycomb core substrate layer, and the protruding parts are protruded on the surfaces of the honeycomb core substrate layer and form a relief structure. The wave-absorbing foam embedding layer is made of a wave-absorbing material. The wave-transparent foam filling layer is filled in the protruding parts and forms a flat surface on the side away from the honeycomb core substrate layer. The application improves the low-frequency absorption performance without increasing the total thickness, retains the multiple wave-absorbing characteristics of the wave-absorbing foam embedding layer, and ensures the excellent performance of the planar board in bearing, cutting and splicing.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of composite wave-absorbing materials, and particularly relates to a wave-absorbing foam / honeycomb core composite panel and a preparation method and application thereof. BACKGROUND

[0002] Wave-absorbing materials refer to a class of functional materials that can absorb and attenuate incident electromagnetic waves and effectively convert electromagnetic energy into heat or other forms of energy, thereby reducing or eliminating the intensity of electromagnetic waves. The design of wave-absorbing materials is usually based on the transmission line theory of electromagnetic waves in a medium, while meeting two basic requirements: 1. Surface impedance matching: the incident electromagnetic wave should enter the material interior to the maximum extent without being reflected at the surface. This requires that the impedance of the material surface should be matched with the impedance of free space; 2. High-efficiency attenuation characteristics: the electromagnetic wave entering the material interior should be maximally absorbed and attenuated.

[0003] In recent years, the structural design of wave-absorbing materials has been highly valued, such as foam porous structure, honeycomb structure, sandwich structure, laminated structure and pyramid structure, etc. In particular, the foam porous structure material with impedance matching characteristics can effectively improve the matching of the material surface impedance with the impedance of free space, which is beneficial to the maximum entry of electromagnetic waves into the material interior and the loss attenuation. The honeycomb structure and the pyramid structure promote multiple reflection and refraction of electromagnetic waves in the material interior, increase the effective path of electromagnetic wave propagation, and thus enhance the loss effect of the material on electromagnetic waves. The wave-absorbing foam is usually prepared by foaming the mixture of A agent (mainly composed of expandable resin) and B agent (foaming agent and other additives) under specific temperature and pressure conditions. The absorber needs to be uniformly mixed with A agent or B agent before foaming, and the wave-absorbing foam with a surface having a relief structure can be prepared by mechanical processing or direct foaming molding. This structure helps to further improve the wave-absorbing performance. However, for the wave-absorbing foam, a low content of absorber will result in poor wave-absorbing performance; and increasing the content of absorber may cause the absorber to aggregate in the foam, forming defects, and thus reducing the mechanical properties and wave-absorbing performance. In order to achieve excellent low-frequency wave-absorbing performance, it is usually necessary to greatly increase the thickness of the wave-absorbing foam, which is contrary to the design intention of thin, light, wide and strong wave-absorbing materials. The existing three-dimensional wave-absorbing materials with relief structures mainly use prisms and pyramids as structural units. These materials have more protruding structures on the surface, which are easy to be damaged by external forces during transportation or actual use, and do not have good load-bearing capacity and are not convenient for cutting and splicing during installation.

[0004] In view of the above problems, it is necessary to provide a wave-absorbing panel with excellent wave-absorbing performance, moderate thickness and smooth surface. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application aims to provide a wave-absorbing foam / honeycomb core composite panel and a preparation method and application thereof.

[0006] The object of the present application is achieved by the following technical solutions:

[0007] A wave-absorbing foam / honeycomb core composite panel comprises a honeycomb core substrate layer, a wave-absorbing foam embedding layer and a wave-transparent foam filling layer which are sequentially stacked.

[0008] The honeycomb core substrate layer is a honeycomb core having a plurality of hollow regions, and each surface of the honeycomb core is provided with a wave-absorbing coating.

[0009] The wave-absorbing foam embedding layer comprises a plurality of filling portions and protruding portions, the filling portions are filled in the hollow regions of the honeycomb core substrate layer, and the protruding portions are protrudingly arranged on the surface of the honeycomb core substrate layer and form a relief structure; the wave-absorbing foam embedding layer is made of a wave-absorbing material.

[0010] The wave-transparent foam filling layer is filled in the protruding portions and forms a flat surface on the side away from the honeycomb core substrate layer.

[0011] Preferably, the thickness of the wave-absorbing foam / honeycomb core composite panel is 10-30 mm, and the thickness ratio of the honeycomb core substrate layer to the protruding portions is 1:1-4.

[0012] Preferably, the wave-absorbing foam embedding layer comprises a plurality of filling portions and protruding portions, the filling portions are filled in the hollow regions of the honeycomb core substrate layer, and the protruding portions are protrudingly arranged on the surface of the honeycomb core substrate layer and form an array structure composed of a plurality of pyramids or prisms, wherein the sizes of adjacent pyramids or prisms are the same or different.

[0013] Preferably, the plurality of pyramids are any one of a trihedral pyramid, a tetrahedral pyramid, a pentahedral pyramid and a hexahedral pyramid.

[0014] Preferably, the plurality of prisms are any one of a trihedral prism, a tetrahedral prism, a pentahedral prism and a hexahedral prism.

[0015] Preferably, the wave-absorbing foam / honeycomb core composite panel further comprises a first skin and a second skin, the first skin is adhered to the side of the honeycomb core substrate layer away from the wave-transparent foam filling layer, and the second skin is adhered to the side of the wave-transparent foam filling layer away from the honeycomb core substrate layer.

[0016] Preferably, the first skin and the second skin are glass fiber reinforced resin-based composite materials or quartz fiber reinforced resin-based composite materials, and the thicknesses of the first skin and the second skin are both 0.1-0.5 mm.

[0017] The preparation method of the wave-absorbing foam / honeycomb core composite panel comprises the following steps:

[0018] (1) spraying the wave-absorbing coating on the surface of the honeycomb core to obtain a honeycomb core base layer;

[0019] (2) placing the wave-absorbing foam premix on the honeycomb core base layer to foam, so that the wave-absorbing foam is embedded into the hollow area of the honeycomb core and forms a filling part, and at the same time, the protruding wave-absorbing foam material is trimmed and a protruding part with an array of undulating structures in the processing height direction is formed, to obtain a wave-absorbing foam embedded layer;

[0020] (3) filling the wave-transparent foam material into the undulating structures of the protruding part, after the foaming is completed, cutting off the excess foam on the surface and around to make the surface of the plate flat, to obtain a wave-transparent foam filling layer, thereby obtaining the wave-absorbing foam / honeycomb core composite plate.

[0021] Preferably, the wave-absorbing coating in step (1) uses any one of polymethacrylimide, polyurethane, polyethylene, polyvinyl chloride and polystyrene as a foaming system.

[0022] Preferably, the wave-absorbing foam premix in step (2) uses any one of polymethacrylimide, polyurethane, polyethylene, polyvinyl chloride and polystyrene as a foaming system.

[0023] Preferably, the wave-absorbing coating in step (1) and the wave-absorbing foam premix in step (2) both use at least one of carbon black, graphene, carbon nanotube, chopped carbon fiber and ferrite as an absorbent.

[0024] Preferably, the thickness of the wave-absorbing coating sprayed in step (1) is 0.01-1mm.

[0025] Preferably, in step (1), the material of the honeycomb core is aramid fiber, the thickness of the honeycomb core is 5mm, and the pore size is 2.75-4.5mm.

[0026] Preferably, in step (2), the wave-absorbing foam layer is processed into a form with undulating structures in the height direction by mechanical processing or mold-assisted processing.

[0027] Preferably, in step (3), the wave-transparent foam material uses any one of PMI (polymethacrylimide), polyurethane, polyethylene, polyvinyl chloride and PS (polystyrene) as a foaming system.

[0028] Preferably, step (3) further comprises setting a first skin and a second skin, the first skin is adhered to the side of the honeycomb core base layer away from the wave-transparent foam filling layer, and the second skin is adhered to the side of the wave-transparent foam filling layer away from the honeycomb core base layer.

[0029] The above wave-absorbing foam / honeycomb core composite plate is applied in the field of electromagnetic shielding and electromagnetic barrier devices.

[0030] Compared with the prior art, the beneficial effects of the present application include:

[0031] (1) By embedding the wave-absorbing foam into the wave-absorbing honeycomb core, the impedance matching is optimized, and the electromagnetic wave absorption performance of the wave-absorbing foam in the medium and low frequency range can be significantly improved. The design of the embedded composite honeycomb core improves the low-frequency absorption performance without increasing the total thickness.

[0032] (2) A normal-temperature foaming system without absorbent is used to freely foam in the undulating structure of the wave-absorbing foam embedded layer, filling the undulating structure into a flat plate structure. Since the filled foam does not contain absorbent and is freely foamed, its density is low and it belongs to a wave-transparent material, so it will not affect the multiple wave-absorbing mechanism of the wave-absorbing foam embedded layer. This method not only retains the multiple wave-absorbing characteristics of the wave-absorbing foam embedded layer, but also ensures good performance of the flat panel in terms of bearing, cutting and splicing. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 A cross-sectional structure diagram of the wave-absorbing foam / honeycomb core composite board prepared in Example 1 along the thickness direction;

[0034] Figure 2 Structure diagrams of ordered combination and disordered combination of different sizes of multi-prism platforms;

[0035] In the figure, 1-honeycomb core base layer, 11-honeycomb core, 12-wave-absorbing coating layer, 2-wave-absorbing foam embedded layer, 21-filling part, 22-protruding part, 3-wave-transparent foam filling layer, 4-first skin, 5-second skin. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solutions and advantages of the present application clearer and more apparent, the present application will be further described in detail below in combination with examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application.

[0037] Figure 1 A cross-sectional structure diagram of the wave-absorbing foam / honeycomb core composite board prepared in Example 1 along the thickness direction; from Figure 1We can see that each surface of the honeycomb core 11 is provided with a wave-absorbing coating 12, the wave-absorbing foam embedded layer 2 is divided into a filling part 21 and a protruding part 22, the filling part 21 is filled in the hollow area of the honeycomb core base layer 1, the protruding part is protrudingly arranged on the surface of the honeycomb core base layer 1 and forms a protruding structure of a regular quadrangular pyramid, the wave-transparent foam filling layer 3 is filled in the protruding part 22 and forms a flat surface on the side away from the honeycomb core base layer 1. Further, in order to better protect the overall structure of the material, a first skin and a second skin are further arranged, the first skin 4 is adhered to the surface of the honeycomb core base layer 1, and the second skin 5 is adhered to the surface of the wave-transparent foam filling layer 3.

[0038] Figure 2 Structure schematic diagram of ordered combination and disordered combination of different sizes of multi-pyramids. According to the present application, the protruding part of the wave-absorbing foam embedded layer can adopt ordered or disordered free combination of multi-pyramids.

[0039] Embodiment 1

[0040] A preparation method of a wave-absorbing foam / honeycomb core composite board, steps are as follows:

[0041] (1) A PMI foaming system is adopted, 600 parts of deionized water are added into a reaction kettle and 1 part of a polyvinyl alcohol dispersant is dissolved, then 60 parts of a methacrylic acid monomer and 40 parts of an acrylonitrile monomer are added, stirring is carried out at a speed of 100 r / min for 30 min to form a suspension, 5 parts of carbon black are added, the stirring speed is increased to 200 r / min, after stirring for 45 min, 0.7 parts of an azobisisobutyronitrile initiator and 6 parts of an azodicarbonamide foaming agent are added, and the temperature is controlled at 60-70°C, the stirring speed is maintained at 200 r / min for 4 h, and then a PMI prepolymer is obtained by suspension collection; 2.5 parts of an acrylamide crosslinking agent are added into the PMI prepolymer, the mixture is uniformly mixed by using a roller and the excess water is removed, and then a sheet-shaped prepolymer is prepared.

[0042] (2) First, 10 parts of phenolic resin are dissolved in 25 parts of anhydrous ethanol to prepare a glue solution, then 2 parts of carbon black are added into the glue solution and mechanically stirred at a speed of 200 r / min for 30 min, finally, a high-speed homogenizer is used to continue to disperse the mixture for 10 min, and a wave-absorbing coating is obtained. The wave-absorbing coating is applied to the surface of an aramid honeycomb core by using a dipping or spraying method, and a honeycomb core base layer with a wave-absorbing coating is obtained; wherein the thickness of the aramid honeycomb core is 5 mm, the pore size is 2.75 mm, and the thickness of the wave-absorbing coating is in the range of 0.3±0.1 mm.

[0043] (3) Place the honeycomb core substrate layer with the wave-absorbing coating on the bottom of a 330x330 mm rectangular hot-pressing mold, then place the flaky prepolymer into the mold, preheat at 80°C for 0.5 h, and foam in the mold at 150°C for 2 h on a flat-plate vulcanizing machine, so that the wave-absorbing foam is embedded in the hollow area of the honeycomb core and part of the wave-absorbing foam material protrudes from the surface, and the foaming process is carried out at a pressure of 0.5 MPa, and the density of the obtained wave-absorbing foam is 75 kg / m 3 After completion, trim the protruding wave-absorbing foam material, cut and trim the excess foam at the bottom of the honeycomb core, and perform a sheet cutting process on the wave-absorbing foam, and finally obtain a wave-absorbing foam layer with a total thickness of 25 mm.

[0044] (4) Process the wave-absorbing foam layer into a form with a relief structure in the height direction to obtain a wave-absorbing foam embedded layer, specifically: a plurality of solid right tetrapods with the same size are arranged, the upper base length of the right tetrapod is 15 mm, the lower base length is 20 mm, and the height is 20 mm.

[0045] (5) Use the 902 type hard polyurethane foaming agent generated by Beijing Haibaisi Technology Co., Ltd. to fill the relief structure of the wave-absorbing foam embedded layer with free foaming, and after the foaming is completed, the excess foam on the surface and around is cut off to make the surface of the plate flat, thereby obtaining the wave-absorbing foam / honeycomb core composite board.

[0046] The total thickness of the wave-absorbing foam / honeycomb core composite board prepared in Example 1 is 25 mm, of which the upper part of 20 mm is a region with a relief structure in the height direction, mainly used for air impedance matching and realizing multi-layer scattering of electromagnetic waves; the lower part of 5 mm is an absorbing layer, mainly used for absorbing and dissipating electromagnetic waves. The mass ratio of the honeycomb core substrate layer, the wave-absorbing foam filling part, the wave-absorbing foam relief structure, and the wave-absorbing foam filling layer is 120:37:80:30.

[0047] The pure wave-absorbing foam prepared by using the prepolymer described in step (1) of Example 1 is obtained by the following process: preheat at 80°C for 0.5 h, then foam in the mold at 0.5 MPa pressure using a flat-plate vulcanizing machine at 150°C for 2 h, and finally obtain a sample with the same size (300x300x25 mm) and thickness. In order to evaluate the wave-absorbing performance, the wave-absorbing foam / honeycomb core composite board prepared in Example 1 (size: 300x300x25 mm) and the pure wave-absorbing foam are tested, and the test results are shown in Table 1.

[0048] Table 1 Comparison of wave-absorbing performance

[0049]

[0050] From the data in Table 1, it can be seen that the wave-absorbing foam / honeycomb core composite board prepared in the application has significantly better wave-absorbing performance in each frequency band than the pure wave-absorbing foam, showing more excellent electromagnetic wave absorption effect. In addition, there is no obvious difference in compressive strength between the existing wave-absorbing foam and the wave-absorbing foam / honeycomb core composite board prepared in the application.

[0051] Example 2

[0052] The present embodiment provides a preparation method of a wave-absorbing foam / honeycomb core composite board, except that the thickness of the aramid honeycomb core in step (2) is 10 mm, the pore size is 4.5 mm; the thickness of the wave-absorbing coating is 0.6 mm±0.1 mm; the upper base length of the right quadrangular frustum in step (4) is 15 mm, the lower base length is 20 mm, the height is 15 mm, and the other conditions and steps are the same as in Example 1. The mass ratio of the honeycomb core base layer, the wave-absorbing foam filling part, the wave-absorbing foam undulating structure and the wave-transparent foam filling layer is 20:9:10:5.

[0053] A pure wave-absorbing foam prepared by using the prepolymer in step (1) of Example 1 is obtained by the following process: preheating at 80℃ for 0.5h, then foaming in a mold at 150℃ for 2h under a pressure of 0.5MPa, and finally obtaining a sample with the same size (300×300×25mm) and thickness. In order to evaluate the wave-absorbing performance, the wave-absorbing foam / honeycomb core composite board prepared in Example 2 (size: 300×300×25mm) and the pure wave-absorbing foam are tested, and the test results are shown in Table 2.

[0054] Table 2 Comparison of wave-absorbing performance

[0055]

[0056] From the data in Table 2, it can be seen that the wave-absorbing foam / honeycomb core composite board prepared in Example 2 has significantly better wave-absorbing performance in each frequency band than the pure wave-absorbing foam, showing more excellent electromagnetic wave absorption effect.

[0057] Example 3

[0058] The present embodiment provides a preparation method of a wave-absorbing foam / honeycomb core composite board, except that the foaming process in step (3) is carried out under a pressure of 0.7MPa, and the density of the obtained wave-absorbing foam is 105kg / m 3After completion, the protruding wave-absorbing foam material is trimmed, the excess foam at the bottom of the honeycomb core is cut and trimmed, and the wave-absorbing foam is sheeted, to finally obtain a wave-absorbing foam layer with a total thickness of 20 mm; the upper base of the regular quadrangular frustum in step (4) has a length of 15 mm, the lower base has a length of 20 mm, and the height is 15 mm, and the other conditions and steps are the same as in Example 1. The mass ratio of the honeycomb core base layer, the wave-absorbing foam filling part, the wave-absorbing foam undulating structure, and the wave-transparent foam filling layer is 240: 103: 210: 60.

[0059] The pure wave-absorbing foam prepared from the prepolymer described in step (1) of Example 1 is obtained by the following process: preheating at 80℃ for 0.5 h, then foaming in a mold at 150℃ for 2 h under a pressure of 0.5 MPa, to finally obtain a sample with the same size (300×300×20 mm) and thickness. In order to evaluate the wave-absorbing performance, the wave-absorbing foam / honeycomb core composite board prepared in Example 3 (size: 300×300×20 mm) and the pure wave-absorbing foam are tested, and the test results are shown in Table 3.

[0060] Table 3 Comparison of wave-absorbing performance

[0061]

[0062] As can be seen from the data in Table 3, the wave-absorbing foam / honeycomb core composite board prepared in Example 3 has significantly better wave-absorbing performance in each frequency band than the pure wave-absorbing foam, showing a more excellent electromagnetic wave absorption effect.

[0063] The specific embodiments of the application described above do not constitute a limitation on the scope of protection of the application. Any various other corresponding changes and modifications made in accordance with the technical concept of the application should be included in the scope of protection of the claims of the application.

Claims

1. A method for preparing a wave-absorbing foam / honeycomb core composite panel, characterized by, The method comprises the following steps: (1) spraying wave-absorbing paint on the surface of the honeycomb core to obtain a honeycomb core base layer; (2) placing wave-absorbing foam premix on the honeycomb core base layer to foam, embedding the wave-absorbing foam into the hollow area of the honeycomb core and forming a filling part, and simultaneously, trimming the protruding wave-absorbing foam material and forming a protruding part with an array of undulating structures in the processing height direction to obtain a wave-absorbing foam embedded layer; (3) filling wave-transparent foam material into the undulating structure of the protruding part, and after foaming, cutting off the excess foam on the surface and around to make the surface of the plate flat to obtain a wave-transparent foam filling layer, thereby obtaining the wave-absorbing foam / honeycomb core composite board; The wave-absorbing foam / honeycomb core composite board comprises a honeycomb core base layer, a wave-absorbing foam embedded layer and a wave-transparent foam filling layer which are sequentially stacked; The honeycomb core base layer is a honeycomb core with a plurality of through hollow areas, and each surface of the honeycomb core is provided with a wave-absorbing coating; The wave-absorbing foam embedded layer comprises a plurality of filling parts and protruding parts, the filling parts are filled in the hollow areas of the honeycomb core base layer, the protruding parts are protrudingly arranged on the surface of the honeycomb core base layer and form undulating structures, and the wave-absorbing foam embedded layer is made of wave-absorbing material; The wave-transparent foam filling layer is filled in the protruding parts and forms a flat surface away from the honeycomb core base layer.

2. The method of claim 1, wherein the method further comprises the steps of: In step (1), the wave-absorbing paint uses any one of polymethacrylimide, polyurethane, polyethylene, polyvinyl chloride and polystyrene as a foaming system; ​ In step (2), the wave-absorbing foam premix uses any one of polymethacrylimide, polyurethane, polyethylene, polyvinyl chloride and polystyrene as a foaming system; In step (1), the wave-absorbing paint and in step (2), the wave-absorbing foam premix both use at least one of carbon black, graphene, carbon nanotube, chopped carbon fiber and ferrite as an absorbent.

3. The method of claim 1, wherein the method further comprises the steps of: providing a plurality of honeycomb cores; and providing a plurality of wave-absorbing foams; and combining the plurality of honeycomb cores and the plurality of wave-absorbing foams to form the wave-absorbing foam / honeycomb core composite panel. In step (1), the thickness of the wave-absorbing paint is 0.01-1 mm; In step (1), the material of the honeycomb core is aramid fiber, the thickness of the honeycomb core is 4-10 mm, and the pore size is 2.75-4.5 mm; In step (2), the wave-absorbing foam layer is processed into an undulating structure in the height direction by mechanical processing or mold assistance.

4. The method for preparing the microwave absorbing foam / honeycomb core composite panel according to claim 1, characterized in that, In step (3), the wave-transparent foam material uses any one of polymethacrylimide, polyurethane, polyethylene, polyvinyl chloride and polystyrene as a foaming system; Step (3) further comprises setting a first skin and a second skin, the first skin is adhered to the side of the honeycomb core base layer away from the wave-transparent foam filling layer, and the second skin is adhered to the side of the wave-transparent foam filling layer away from the honeycomb core base layer to obtain the wave-absorbing foam / honeycomb core composite board.

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