Wave-absorbing foam / honeycomb core composite board as well as preparation method and application thereof

Abstract

The invention discloses a wave-absorbing foam / honeycomb core composite board as well as a preparation method and application thereof. Comprising 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 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 hollow area of the honeycomb core substrate layer is filled with the filling parts, and the protruding parts are arranged on the surface of the honeycomb core substrate layer in a protruding mode and form a fluctuating structure; the wave-absorbing foam embedded layer is made of a wave-absorbing material; the wave-transparent foam filling layer is filled in the protruding parts, and a flat surface is formed on the side, away from the honeycomb core substrate layer, of the wave-transparent foam filling layer. The low-frequency absorption performance is improved on the premise that the total thickness is not increased, the multiple wave-absorbing characteristics of the wave-absorbing foam embedded layer are reserved, and meanwhile the excellent performance of the plane plate in the aspects of bearing, cutting and splicing is ensured.

Description

Technical Field

[0001] The invention belongs to the field of composite wave-absorbing materials, and in particular relates to a wave-absorbing foam / honeycomb core composite board and a preparation method and application thereof. Background Art

[0002] 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 weakening or eliminating the intensity of electromagnetic waves. The design of absorbing materials is usually based on the transmission line theory of electromagnetic waves in the medium, and should meet two basic requirements: 1. Surface impedance matching: the incident electromagnetic wave should enter the material to the maximum extent without reflecting on the surface. This requires the impedance of the material surface to match the impedance of free space; 2. High-efficiency attenuation characteristics: the electromagnetic waves entering the material should be absorbed and attenuated to the maximum extent.

[0003] In recent years, the structural design of absorbing materials has received great attention, such as foam porous structure, honeycomb structure, sandwich structure, layer structure and pyramid structure. In particular, the foam porous structure material with impedance matching characteristics has been found to effectively improve the matching between the surface impedance of the material and the impedance of the free space, which is conducive to the maximum entry of electromagnetic waves into the material and attenuation. Honeycomb structure and pyramid structure promote multiple reflections and refractions of electromagnetic waves inside the material, increase the effective path of electromagnetic wave propagation, and thus enhance the material's loss effect on electromagnetic waves. Absorbing foam is usually prepared by mixing agent A (the main component is expandable resin) and agent B (foaming agent and other additives) and foaming under specific temperature and pressure conditions. The absorbent needs to be evenly mixed with agent A or agent B before foaming. By mechanical processing or direct foaming molding using a mold, an absorbing foam with an undulating structure on the surface can be prepared. This structure helps to further improve the absorbing performance. However, for absorbing foam, low absorbent content will lead to poor absorbing performance; while increasing the absorbent content may cause the absorbent to aggregate in the foam, forming defects, thereby reducing its mechanical properties and absorbing performance. In order to achieve excellent low-frequency absorbing performance, it is usually necessary to significantly increase the thickness of the absorbing foam, but this is contrary to the design intention of the absorbing material to be "thin, light, wide, and strong". Existing three-dimensional absorbing materials with undulating structures mainly use prisms and pyramids as structural units. These materials have many protruding structures on the surface and are easily damaged by external forces during transportation or actual use. They do not have good load-bearing capacity and are not easy to cut and splice during installation.

[0004] In view of the above problems, it is necessary to provide an absorbing plate material with excellent absorbing performance, moderate thickness and smooth surface. Summary of the invention

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

[0006] The purpose of the present invention is achieved through the following technical solutions: A wave-absorbing foam / honeycomb core composite panel, comprising a honeycomb core base layer, a wave-absorbing foam embedding layer and a wave-transmitting foam filling layer which are stacked in sequence; The honeycomb core base layer is a honeycomb core having a plurality of through hollow areas, and each surface of the honeycomb core is provided with a microwave absorbing coating; The absorbing foam embedding layer comprises a plurality of filling parts and protruding parts, wherein the filling parts are all filled in the hollow area of ​​the honeycomb core base layer, and the protruding parts are all protruding from the surface of the honeycomb core base layer to form an undulating structure; the absorbing foam embedding layer is made of absorbing material; The wave-transmitting foam filling layer is filled in the protruding portion and forms a flat surface on a side away from the honeycomb core base layer.

[0007] Preferably, the thickness of the wave-absorbing foam / honeycomb core composite board is 10-30 mm, and the thickness ratio of the honeycomb core base layer to the protruding portion is 1:1-4.

[0008] Preferably, the absorbing foam embedded layer includes a plurality of filling parts and raised parts, wherein the filling parts are all filled in the hollow area of ​​the honeycomb core base layer, and the raised parts are all protruding from the surface of the honeycomb core base layer to 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.

[0009] Preferably, the polygonal pyramid is any one of a triangular pyramid, a quadrangular pyramid, a pentagonal pyramid and a hexagonal pyramid.

[0010] Preferably, the multi-prism is any one of a triangular prism, a quadrangular prism, a pentagonal prism and a hexagonal prism.

[0011] Preferably, it also includes a first skin and a second skin, wherein the first skin is adhered to the side of the honeycomb core base layer away from the wave-transmitting foam filling layer; the second skin is adhered to the side of the wave-transmitting foam filling layer away from the honeycomb core base layer.

[0012] 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 their thicknesses are both 0.1 mm to 0.5 mm.

[0013] The method for preparing the above-mentioned wave-absorbing foam / honeycomb core composite board comprises the following steps: (1) Spraying the radar absorbing coating on the surface of the honeycomb core to obtain a honeycomb core base layer; (2) placing the absorbing foam premix on the honeycomb core base layer and foaming it so that it is embedded in the hollow area of ​​the honeycomb core and forms a filling part. At the same time, the protruding absorbing foam material is trimmed and a protrusion with an undulating structure array is formed in the processing height direction to obtain an absorbing foam embedding layer; (3) Filling the wave-transmitting foam material into the undulating structure of the raised portion, and after the foaming is completed, cutting off the excess foam on the surface and around to make the surface of the board smooth, thereby obtaining a wave-transmitting foam filling layer, thereby obtaining the wave-absorbing foam / honeycomb core composite board.

[0014] Preferably, the absorbing coating in step (1) uses any one of polymethacrylimide, polyurethane, polyethylene, polyvinyl chloride and polystyrene as the foaming system.

[0015] Preferably, the wave-absorbing foam premix in step (2) uses any one of polymethacrylimide, polyurethane, polyethylene, polyvinyl chloride and polystyrene as the foaming system.

[0016] Preferably, the absorbents used in the absorbing coating in step (1) and the absorbing foam premix in step (2) are at least one of carbon black, graphene, carbon nanotubes, chopped carbon fibers and ferrite.

[0017] Preferably, the thickness of the radar absorbing coating sprayed in step (1) is 0.01-1 mm.

[0018] Preferably, in step (1), the material of the honeycomb core is aramid, the thickness of the honeycomb core is 5 mm, and the pore size is 2.75-4.5 mm.

[0019] Preferably, in step (2), the absorbing foam layer is processed into a form having an undulating structure in the height direction by mechanical processing or mold-assisted methods.

[0020] Preferably, in step (3), the wave-transmitting foam material adopts any one of PMI (polymethacrylimide), polyurethane, polyethylene, polyvinyl chloride and PS (polystyrene) as the foaming system.

[0021] Preferably, step (3) further comprises providing a first skin and a second skin, wherein the first skin is adhered to a side of the honeycomb core base layer away from the wave-transmitting foam filling layer; and the second skin is adhered to a side of the wave-transmitting foam filling layer away from the honeycomb core base layer.

[0022] The above-mentioned absorbing foam / honeycomb core composite board is used in the preparation of electromagnetic shielding and electromagnetic blocking devices.

[0023] Compared with the prior art, the beneficial effects of the present invention include: (1) By embedding the absorbing foam into the absorbing honeycomb core to optimize impedance matching, the electromagnetic wave absorption performance of the absorbing foam in the medium and low frequency range can be significantly improved. This embedded composite honeycomb core design improves the low-frequency absorption performance without increasing the total thickness.

[0024] (2) A room temperature foaming system without an absorbent is used to perform free foaming in the undulating structure of the absorbing foam embedding layer, and the undulating structure is filled into a flat plate structure. Since the filled foam does not contain an absorbent and is free foaming, its density is low and it is a wave-transmitting material, so it will not affect the multiple wave-absorbing mechanism of the absorbing foam embedding layer. This method not only retains the multiple wave-absorbing characteristics of the absorbing foam embedding layer, but also ensures the good performance of the flat plate in terms of load-bearing, cutting and splicing. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic diagram of the cross-sectional structure of the wave-absorbing foam / honeycomb core composite panel prepared in Example 1 along the thickness direction; Figure 2 It is a schematic diagram of the structure of ordered and disordered combinations of multi-prisms of different sizes; In the figure, 1-honeycomb core base layer, 11-honeycomb core, 12-wave-absorbing coating layer, 2-wave-absorbing foam embedding layer, 21-filling part, 22-raised part, 3-wave-transmitting foam filling layer, 4-first skin, 5-second skin. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0027] Figure 1 Schematic diagram of the cross-sectional structure of the wave-absorbing foam / honeycomb core composite panel prepared in Example 1 along the thickness direction; Figure 1 We can see that each surface of the honeycomb core 11 is provided with an absorbing coating 12, and the absorbing foam embedded layer 2 is divided into a filling portion 21 and a protruding portion 22. The filling portion 21 is filled in the hollow area of ​​the honeycomb core base layer 1, and the protruding portion is protruding from the surface of the honeycomb core base layer 1, and forms a protruding structure of a regular quadrangular pyramid. The wave-transmitting foam filling layer 3 is filled in the protruding portion 22, and forms a flat surface on the side away from the honeycomb core base layer 1. Furthermore, in order to better protect the overall structure of the material, a first skin and a second skin are also provided, wherein 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-transmitting foam filling layer 3.

[0028] Figure 2The schematic diagram is a structural diagram of ordered and disordered combinations of polygonal pyramids of different sizes. According to the present invention, the protrusions of the absorbing foam embedding layer can be in the form of ordered or disordered free combinations of polygonal pyramids.

[0029] Example 1 A method for preparing a wave-absorbing foam / honeycomb core composite board, the steps are as follows: (1) Using the PMI foaming system, add 600 parts of deionized water and dissolve 1 part of polyvinyl alcohol dispersant in a reactor, then add 60 parts of methacrylic acid monomer and 40 parts of acrylonitrile monomer, stir at a rate of 100 r / min for 30 minutes to form a suspension, add 5 parts of carbon black, increase the stirring rate to 200 r / min, stir for 45 minutes, add 0.7 parts of azobisisobutyronitrile initiator and 6 parts of azodicarbonamide foaming agent, and control the temperature at 60-70°C, maintain the stirring rate of 200 r / min for 4 hours, and obtain the PMI prepolymer through suspension aggregation; add 2.5 parts of acrylamide crosslinking agent to the PMI prepolymer, mix and remove excess water by roller, and make a thin sheet of prepolymer.

[0030] (2) First, 10 parts of phenolic resin were dissolved in 25 parts of anhydrous ethanol to make a glue solution. Then, 2 parts of carbon black were added to the glue solution and mechanically stirred at a rate of 200 r / min for 30 minutes. Finally, a high-speed homogenizer was used to disperse the mixture for 10 minutes to obtain an absorbing coating. The absorbing coating was applied to the surface of the aramid honeycomb core by dipping or spraying to obtain a honeycomb core substrate with an absorbing coating. The thickness of the aramid honeycomb core was 5 mm and the pore size was 2.75 mm. The thickness of the absorbing coating ranged from 0.3±0.1 mm.

[0031] (3) A honeycomb core substrate layer with an absorbing coating was placed at the bottom of a 330×330 mm rectangular hot pressing mold, and then a thin sheet of prepolymer was placed in the mold. The mold was preheated at 80°C for 0.5 h, and foamed in the mold at 150°C on a flat vulcanizer for 2 h, so that the absorbing foam was embedded in the hollow area of ​​the honeycomb core and part of the absorbing foam material protruded from the surface. The foaming process was carried out under a pressure of 0.5 MPa, and the density of the obtained absorbing foam was 75 kg / m 3 After completion, the protruding absorbing foam material is trimmed, the excess foam at the bottom of the honeycomb core is cut and trimmed, and the absorbing foam is sliced ​​to finally obtain an absorbing foam layer with a total thickness of 25 mm.

[0032] (4) The absorbing foam layer is processed into a form with an undulating structure in the height direction to obtain an absorbing foam embedded layer. Specifically, a plurality of solid regular tetrahedral structures of the same size are arranged, wherein the upper base length of the regular tetrahedral structure is 15 mm, the lower base length is 20 mm, and the height is 20 mm.

[0033] (5) Using the 902 type rigid polyurethane foaming agent produced by Beijing Haibeisi Technology Co., Ltd., free foaming filling is performed in the undulating structure of the absorbing foam embedding layer. After the foaming is completed, the excess foam on the surface and around is cut off to make the surface of the board smooth, thereby obtaining the absorbing foam / honeycomb core composite board.

[0034] The total thickness of the absorbing foam / honeycomb core composite board prepared in Example 1 is 25 mm, wherein the upper 20 mm is a region with an undulating structure in the height direction, which is mainly used to match the air impedance and realize multi-layer scattering of electromagnetic waves; the lower 5 mm is an absorption layer, which is mainly used to absorb and dissipate electromagnetic waves. The mass ratio of the honeycomb core base layer, the absorbing foam filling part, the absorbing foam undulating structure and the transparent foam filling layer is 120:37:80:30.

[0035] The pure absorbing foam prepared by the prepolymer of step (1) of Example 1 was obtained by the following process: preheating at 80°C for 0.5h, and then foaming in the mold at 150°C for 2h under a pressure of 0.5MPa using a flat vulcanizer, and finally obtaining samples of the same size (300×300×25mm) and thickness. In order to evaluate the absorbing performance, the absorbing foam / honeycomb core composite board (size: 300×300×25mm) prepared in Example 1 and the pure absorbing foam were tested, and the test results are shown in Table 1.

[0036] Table 1 Comparison of wave absorption performance

[0037] It can be seen from the data in Table 1 that the absorbing foam / honeycomb core composite panel prepared by the present invention has significantly better absorbing performance in each frequency band than pure absorbing foam, showing a more excellent electromagnetic wave absorption effect. In addition, there is no obvious difference in compression strength between the existing absorbing foam and the absorbing foam / honeycomb core composite panel prepared by the present invention.

[0038] Example 2 This embodiment provides a method for preparing an absorbing foam / honeycomb core composite board, except that the thickness of the aramid honeycomb core in step (2) is 10 mm and the pore size is 4.5 mm; the thickness of the absorbing coating is 0.6 mm±0.1 mm; the upper base length of the regular tetrahedron in step (4) is 15 mm, the lower base length is 20 mm, and the height is 15 mm, and other conditions and steps are the same as those in Example 1. The mass ratio of the honeycomb core base layer, the absorbing foam filling part, the absorbing foam undulating structure, and the transparent foam filling layer is 20:9:10:5.

[0039] The pure absorbing foam prepared by the prepolymer of step (1) of Example 1 was obtained by the following process: preheating at 80°C for 0.5h, and then foaming in the mold at 150°C for 2h under a pressure of 0.5MPa using a flat vulcanizer, and finally obtaining samples of the same size (300×300×25mm) and thickness. In order to evaluate the absorbing performance, the absorbing foam / honeycomb core composite board (size: 300×300×25mm) prepared in Example 2 and the pure absorbing foam were tested, and the test results are shown in Table 2.

[0040] Table 2 Comparison of microwave absorption performance

[0041] It can be seen from the data in Table 2 that the absorbing foam / honeycomb core composite panel prepared in Example 2 has significantly better absorbing performance than pure absorbing foam in each frequency band, showing a more excellent electromagnetic wave absorption effect.

[0042] Example 3 This embodiment provides a method for preparing a microwave-absorbing foam / honeycomb core composite board, except that the foaming process in step (3) is carried out under a pressure of 0.7 MPa, and the density of the microwave-absorbing foam obtained is 105 kg / m 3 After completion, the protruding absorbing foam material is trimmed, the excess foam at the bottom of the honeycomb core is cut and trimmed, and the absorbing foam is sliced ​​to finally obtain an absorbing foam layer with a total thickness of 20 mm; the upper base length of the regular tetrahedron in step (4) is 15 mm, the lower base length is 20 mm, and the height is 15 mm. Other conditions and steps are the same as in Example 1. The mass ratio of the honeycomb core base layer, the absorbing foam filling part, the absorbing foam undulating structure and the transparent foam filling layer is 240:103:210:60.

[0043] The pure absorbing foam prepared by the prepolymer of step (1) of Example 1 was obtained by the following process: preheating at 80°C for 0.5h, and then foaming in the mold at 150°C for 2h under a pressure of 0.5MPa using a flat vulcanizer, and finally obtaining samples of the same size (300×300×20mm) and thickness. In order to evaluate the absorbing performance, the absorbing foam / honeycomb core composite board (size: 300×300×20mm) prepared in Example 3 and the pure absorbing foam were tested, and the test results are shown in Table 3.

[0044] Table 3 Comparison of microwave absorption performance

[0045] It can be seen from the data in Table 3 that the absorbing foam / honeycomb core composite panel prepared in Example 3 has significantly better absorbing performance than pure absorbing foam in each frequency band, showing a more excellent electromagnetic wave absorption effect.

[0046] The specific implementation of the present invention described above does not constitute a limitation on the protection scope of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A wave-absorbing foam / honeycomb core composite panel, characterized in that: It comprises a honeycomb core base layer, a wave-absorbing foam embedding layer and a wave-transmitting foam filling layer which are stacked in sequence; The honeycomb core base layer is a honeycomb core having a plurality of through hollow areas, and each surface of the honeycomb core is provided with a microwave absorbing coating; The absorbing foam embedded layer includes a plurality of filling parts and protruding parts, the filling parts are all filled in the hollow area of ​​the honeycomb core base layer, and the protruding parts are all protruding from the surface of the honeycomb core base layer to form an undulating structure; the absorbing foam embedded layer is made of absorbing material; The wave-transmitting foam filling layer is filled in the protruding portion and forms a flat surface on a side away from the honeycomb core base layer.

2. The wave-absorbing foam / honeycomb core composite panel according to claim 1, characterized in that: The thickness of the wave-absorbing foam / honeycomb core composite board is 10-30 mm, and the thickness ratio of the honeycomb core base layer to the protrusion is 1:1-4; The absorbing foam embedded layer includes a plurality of filling parts and protruding parts, wherein the filling parts are all filled in the hollow area of ​​the honeycomb core base layer, and the protruding parts are all protruding from the surface of the honeycomb core base layer to 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.

3. The wave-absorbing foam / honeycomb core composite panel according to claim 2, characterized in that: The polygonal pyramid is any one of a triangular pyramid, a quadrangular pyramid, a pentagonal pyramid and a hexagonal pyramid; The multi-sided pyramid is any one of a triangular pyramid, a quadrangular pyramid, a pentagonal pyramid and a hexagonal pyramid.

4. The wave-absorbing foam / honeycomb core composite panel according to claim 1, characterized in that: It also includes a first skin and a second skin, wherein the first skin is adhered to a side of the honeycomb core base layer away from the wave-transmitting foam filling layer; and the second skin is adhered to a side of the wave-transmitting foam filling layer away from the honeycomb core base layer.

5. The wave-absorbing foam / honeycomb core composite panel according to claim 4, characterized in that: The first skin and the second skin are glass fiber reinforced resin-based composite materials or quartz fiber reinforced resin-based composite materials, and their thicknesses are both 0.1 mm to 0.5 mm.

6. The method for preparing the microwave-absorbing foam / honeycomb core composite panel according to any one of claims 1 to 5, characterized in that: The steps include: (1) Spraying the radar absorbing coating on the surface of the honeycomb core to obtain a honeycomb core base layer; (2) placing the absorbing foam premix on the honeycomb core base layer and foaming it so that it is embedded in the hollow area of ​​the honeycomb core and forms a filling part. At the same time, the protruding absorbing foam material is trimmed and a protrusion with an undulating structure array is formed in the processing height direction to obtain an absorbing foam embedding layer; (3) Filling the wave-transmitting foam material into the undulating structure of the raised portion, and after the foaming is completed, cutting off the excess foam on the surface and around to make the surface of the board smooth, thereby obtaining a wave-transmitting foam filling layer, thereby obtaining the wave-absorbing foam / honeycomb core composite board.

7. The method for preparing the wave-absorbing foam / honeycomb core composite board according to claim 6, characterized in that: The absorbing coating in step (1) uses any one of polymethacrylimide, polyurethane, polyethylene, polyvinyl chloride and polystyrene as a foaming system; The wave-absorbing foam premix in step (2) uses any one of polymethacrylimide, polyurethane, polyethylene, polyvinyl chloride and polystyrene as the foaming system; The absorbents used in the absorbing coating in step (1) and the absorbing foam premix in step (2) are at least one of carbon black, graphene, carbon nanotubes, chopped carbon fibers and ferrite.

8. The method for preparing the wave-absorbing foam / honeycomb core composite board according to claim 6, characterized in that: The thickness of the absorbing coating sprayed in step (1) is 0.01-1 mm; The honeycomb core in step (1) is made of aramid, has a thickness of 4-10 mm, and a pore size of 2.75-4.5 mm; In step (2), the absorbing foam layer is processed into a form having an undulating structure in the height direction by mechanical processing or mold-assisted methods.

9. The method for preparing the wave-absorbing foam / honeycomb core composite board according to claim 6, characterized in that: The wave-transmitting foam material in step (3) uses any one of polymethacrylimide, polyurethane, polyethylene, polyvinyl chloride and polystyrene as a foaming system; Step (3) also includes providing a first skin and a second skin, wherein the first skin is adhered to a side of the honeycomb core base layer away from the wave-transmitting foam filling layer; and the second skin is adhered to a side of the wave-transmitting foam filling layer away from the honeycomb core base layer, to obtain the wave-absorbing foam / honeycomb core composite panel.

10. Use of the microwave-absorbing foam / honeycomb core composite board according to any one of claims 1 to 5 in the field of electromagnetic shielding and electromagnetic blocking devices.

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