A microsphere carrier-based broadband wave-absorbing honeycomb sandwich foam and a preparation method thereof

Abstract

The application belongs to the technical field of electromagnetic functional materials and composite material manufacturing, and discloses a wideband wave-absorbing honeycomb sandwich foam based on a microsphere carrier and a preparation method thereof. The wideband wave-absorbing honeycomb sandwich foam based on the microsphere carrier is composed of a composite core layer (composed of a honeycomb framework and a gradient wave-absorbing foam), a wave-transparent skin layer and an electromagnetic shielding skin layer. The gradient wave-absorbing foam is formed by in-situ foaming and fusion bonding of at least two layers of functionalized thermal expansion microspheres with different wave-absorbing properties inside the cells of the honeycomb framework. The preparation method comprises the following steps: first, obtaining the functionalized thermal expansion microspheres with different wave-absorbing properties by using a wave-absorbing particle and a thermal expansion microsphere dispersion liquid; then, mixing the functionalized thermal expansion microspheres with a base resin respectively, and then extruding and calendering to form a precursor adhesive film; finally, laying the precursor adhesive film according to the set order, and then limiting and molding and foaming to obtain the product. The application realizes zero sedimentation dispersion under high filling amount, full-band impedance matching, and ensures the integrity of the wave-absorbing network under foaming large deformation.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic functional materials and composite material manufacturing technology, and relates to a broadband absorbing honeycomb sandwich foam based on microsphere carrier and its preparation method. Background Technology

[0002] As radar detection spectrum continues to expand, comprehensive requirements for absorbing structures have been placed on "wide bandwidth, high strength, and lightweight". Honeycomb sandwich structures are widely used due to their excellent specific strength; however, traditional honeycomb absorbing materials face many technical bottlenecks:

[0003] Firstly, there is the challenge of filler settling and dispersion. To achieve strong low-frequency absorption, a high proportion of magnetic metal powder is usually added. However, in traditional foaming processes, since the density of metal powder is much greater than that of the resin matrix, the filler is prone to settling due to gravity during the resin melting and foaming process, resulting in a "lighter at the top and heavier at the bottom" foam, poor uniformity of wave absorption performance, and easy collapse of the foam cells.

[0004] Secondly, there is the bandwidth limitation of a single formulation. Due to the Snoek limit, it is difficult for a single-formulation absorbing material to simultaneously achieve both low-frequency magnetic loss and high-frequency dielectric loss. Although gradient absorption can be achieved through multilayer bonding, the adhesive between the layers introduces impedance abrupt changes, causing electromagnetic waves to reflect at the interface and reducing absorption efficiency.

[0005] Third, interfacial bonding fails. Traditional thermally expandable microspheres have smooth surfaces and weak bonding with inorganic fillers. During foaming, the microspheres expand 30 to 50 times in volume, resulting in a dramatic increase in surface area. Simple physical adsorption or rigid chemical bonding (such as silane coupling agents) fails, and the filler detaches from the microsphere surface, disrupting the continuity of the conductive / magnetic network.

[0006] To address these issues, researchers have explored various improvement methods. For instance, patent CN117343381B discloses a method for preparing thermally self-expanding epoxy foam with electromagnetic shielding properties. This method grafts thermally expandable microspheres onto the surface of conductive fillers, solving the problem of difficult dispersion of conductive fillers in the resin matrix. During foaming, the microspheres expand to form a uniform conductive network, improving electromagnetic shielding performance. However, this technology focuses on electromagnetic shielding, has a narrow frequency coverage, primarily targets low-frequency signals, and does not consider broadband absorption design.

[0007] For example, patent application CN117820802A discloses a melamine foam with broadband microwave absorption properties and the structural / microwave absorption integrated composite material prepared therefrom. This patent combines reduced graphene oxide (RGO) with melamine foam (MF) to prepare a broadband microwave absorption foam material, which is then filled into aramid honeycomb and applied in the aerospace field. The microwave absorption effect covers the 3~18GHz frequency band, but it does not involve microwave absorption designs for a wider frequency band.

[0008] For example, patent application CN116423936A discloses a structural microwave absorbing composite material and its preparation method. This patented structural microwave absorbing composite material consists of an upper skin, a microwave absorbing foam core layer, and a lower skin. The microwave absorbing foam core layer uses PMI foam, and the multi-layer structure enhances electromagnetic wave absorption performance. However, this solution has significantly insufficient absorption efficiency in the low-frequency band (1~4GHz), and the composite material has a long preparation time and low production efficiency.

[0009] In summary, the development of a broadband absorbing honeycomb sandwich foam based on microsphere carriers aims to achieve uniform and stable dispersion of functional fillers, effective matching of broadband impedance, and strong and reliable interfacial bonding, so that the broadband absorbing honeycomb sandwich foam based on microsphere carriers meets the comprehensive requirements of "broadband, high strength, and lightweight". Summary of the Invention

[0010] The purpose of this invention is to solve the problems existing in the prior art and to provide a broadband absorbing honeycomb sandwich foam based on microsphere carrier and its preparation method.

[0011] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0012] A broadband absorbing honeycomb sandwich foam based on microsphere carrier is a multi-layer composite structure formed by a one-time hot pressing molding process, consisting of a composite core layer and a wave-transparent skin layer and an electromagnetic shielding skin layer located on both sides thereon.

[0013] The composite core layer consists of a honeycomb skeleton and gradient absorbing foam filling the pores of the honeycomb skeleton;

[0014] The gradient absorbing foam is formed by in-situ foaming and melting bonding of at least two layers of functionalized thermally expandable microspheres with different absorbing properties inside the pores of a honeycomb skeleton.

[0015] Functionalized thermally expandable microspheres consist of thermally expandable microspheres and a layer of microwave-absorbing particles that are mechanically interlocked on their surface through a semi-embedded manner;

[0016] Inside the gradient absorbing foam, absorbing particles accumulate along the foam pore walls (i.e., the resin matrix network), forming a continuous three-dimensional isolation absorbing network distribution.

[0017] As a preferred technical solution:

[0018] The broadband absorbing honeycomb sandwich foam based on microsphere carriers, as described above, has a honeycomb skeleton made of aramid paper honeycomb.

[0019] As described above, a broadband microwave absorbing honeycomb sandwich foam based on a microsphere carrier has a core-shell structure for thermally expanding microspheres. The core is a low-boiling-point liquid alkane, and the outer shell is a thermoplastic polymer. At a certain temperature, the internal gas expands, causing the microspheres to increase in volume, and they maintain their expanded shape after cooling.

[0020] As described above, in a broadband absorbing honeycomb sandwich foam based on a microsphere carrier, the gradient absorbing foam has a volume filling rate of 90%~100% within the honeycomb skeleton pores, and the density of the gradient absorbing foam is 0.2~0.4 g / cm³. 3 .

[0021] As described above, a broadband absorbing honeycomb sandwich foam based on a microsphere carrier is divided into at least two absorbing functional layers along the thickness direction from the incident surface (transparent skin layer) to the back surface (electromagnetic shielding skin layer), and the center absorption frequency of each absorbing functional layer decreases sequentially from the incident surface to the back surface.

[0022] As described above, a broadband absorbing honeycomb sandwich foam based on a microsphere carrier is a gradient absorbing foam composed of a high-frequency absorption functional layer and a low-frequency absorption functional layer.

[0023] The high-frequency absorption functional layer is formed by foaming first-type functionalized thermally expanding microspheres loaded with high-frequency responsive absorbing particles. The high-frequency responsive absorbing particles are one or more of amorphous metal powder and nano-ferrite, mainly targeting the dielectric loss and eddy current loss in the Ku and K bands. The loading mass fraction of the high-frequency responsive absorbing particles in the first-type functionalized thermally expanding microspheres is 15~30%.

[0024] The low-frequency absorption functional layer is formed by foaming second-type functionalized thermal expansion microspheres loaded with low-frequency responsive absorbing particles. The low-frequency responsive absorbing particles are one or more of carbonyl iron powder and iron-silicon-aluminum alloy powder, which mainly target the S and C bands to reduce hysteresis loss. The mass fraction of the low-frequency responsive absorbing particles in the second-type functionalized thermal expansion microspheres is 20~50%.

[0025] The broadband absorbing honeycomb sandwich foam based on microsphere carriers described above has a wave-transparent skin layer made of quartz fiber prepreg and an electromagnetic shielding skin layer made of carbon fiber prepreg.

[0026] The thickness of the composite core layer is 3~8mm, the thickness of the wave-transparent skin layer is 0.5~1mm, and the thickness of the electromagnetic shielding skin layer is 0.5~1mm.

[0027] The broadband microwave absorbing honeycomb sandwich foam based on microsphere carriers described above has a density of 0.3~0.5 g / cm³. 3The effective absorption bandwidth of RL (reflection loss) ≤ -10dB is 30~38GHz (RL is the industry standard for measuring the microwave absorption performance of materials, RL≤-10dB represents the absorption of more than 90% of electromagnetic waves), and the effective absorption bandwidth fluctuation of RL≤-10dB between the same test points in multiple samples along the thickness direction does not exceed ±0.5GHz; the roller peel strength of the broadband microwave absorbing honeycomb sandwich foam based on microsphere carrier is 28~40 (N·mm / mm), and the peak impact load is 4871~5466N.

[0028] The present invention also provides a method for preparing a broadband absorbing honeycomb sandwich foam based on a microsphere carrier as described above, comprising the following steps:

[0029] (1) Add microwave absorbing particles to two or more groups of thermal expansion microsphere dispersions and shear them at a speed of not less than 3000 rpm. Then, add cold ethanol at a temperature of 0~5℃ within 30 seconds to dilute the dispersions. The amount of cold ethanol added is 3 times the volume of the thermal expansion microsphere dispersions. Then filter and dry to obtain functionalized thermal expansion microspheres with different microwave absorbing properties.

[0030] (2) The matrix resin is mixed with functionalized thermally expandable microspheres with different microwave absorption properties, and extruded and calendered to form multiple precursor films;

[0031] (3) A carbon fiber prepreg is laid at the bottom of the mold and a quartz fiber prepreg is laid at the top. Between the carbon fiber prepreg and the quartz fiber prepreg, multiple precursor films are laid alternately in order from bottom to top according to the increasing central absorption frequency of the response, with the honeycomb skeleton as the interval. After the laying is completed, the broadband absorbing honeycomb sandwich foam based on the microsphere carrier is obtained by limiting molding and foaming.

[0032] As a preferred technical solution:

[0033] The method for preparing broadband absorbing honeycomb sandwich foam based on microsphere carriers, as described above, uses polyamide 6 (PA6), polyethylene (PE), or epoxy resin as the matrix resin.

[0034] The method for preparing broadband absorbing honeycomb sandwich foam based on microsphere carriers as described above further includes a dielectric loss filler in the matrix resin, wherein the dielectric loss filler is one or more of carbon nanotubes, graphene, and carbon black.

[0035] Invention principle:

[0036] To address the shortcomings of existing honeycomb absorbing materials, such as insufficient absorption performance, poor uniformity, and easy filler detachment, this invention provides a broadband absorbing honeycomb sandwich foam based on a functionalized microsphere carrier. The core design principles of this invention are: First, carrier effect: Thermally expandable microspheres are used as "buoyancy carriers," and absorbing particles are fixed to the surface of the microspheres through a special anchoring technique. The spatial steric hindrance generated by the expansion of the microspheres physically locks the absorbing particles within the resin matrix, preventing gravitational settling and achieving zero-settling dispersion even with high filler content. Second, frequency gradient: Within the confined space of the honeycomb pores, the in-situ expansion of the solid adhesive film constructs an ordered gradient of "high-frequency absorption in the upper layer and low-frequency absorption in the lower layer," achieving impedance matching across the entire frequency band. Third, anti-detachment modification: To address the problem of filler detachment caused by microsphere expansion, a "semi-embedded" modification process is developed to ensure the integrity of the absorbing network under large foaming deformation.

[0037] Beneficial effects:

[0038] (1) The present invention fixes the microwave absorbing particles on the surface of the microspheres through a special anchoring technology. By utilizing the spatial steric hindrance generated by the expansion of the microspheres, the microwave absorbing particles are physically locked in the resin matrix, avoiding gravity settling and achieving zero settling dispersion under high filling volume.

[0039] (2) The present invention utilizes the in-situ expansion of solid film within the confined space of the honeycomb lattice to construct an ordered gradient of “high frequency absorption in the upper layer and low frequency absorption in the lower layer”, thereby achieving impedance matching across the entire frequency band.

[0040] (3) In view of the problem that microsphere expansion can easily cause filler to fall off, the present invention developed a “semi-embedded” modification process to ensure the integrity of the microwave absorption network under large deformation of foaming, avoid the problem of easy particle fall-off in traditional methods, and provide a more stable and durable microwave absorption effect.

[0041] (4) The present invention uses solid film layering + in-situ hot pressing, which avoids the problem of formula miscibility in liquid injection, and the lateral extrusion force generated by the expansion of microspheres realizes the physical anchoring of foam and honeycomb wall, and the flat pressure strength is significantly improved; in addition, the present invention is formed by thermal expansion foam in one piece, which is low cost and can achieve fast cycle and mass production. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of the cross-sectional structure of the broadband absorbing honeycomb sandwich foam based on microsphere carrier of the present invention;

[0043] Figure 2 This is a microstructure morphology diagram of the first type of functionalized thermally expandable microspheres prepared in Example 4 of the present invention;

[0044] Figure 3This is a microstructure image of the three-dimensional isolation network of broadband absorbing honeycomb sandwich foam based on microsphere carrier in Embodiment 3 of the present invention.

[0045] Figure 4 This is a graph showing the iron distribution of the broadband absorbing honeycomb sandwich foam based on microsphere carrier in Embodiment 3 of the present invention.

[0046] In the figure, 1-wave-transparent skin layer, 2-high frequency absorption functional layer, 3-low frequency absorption functional layer, 4-electromagnetic shielding skin layer. Detailed Implementation

[0047] The present invention will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0048] The manufacturers and brands mentioned in the following embodiments are merely examples. The core of this invention lies in the technical solution itself, and it is not intended to limit specific manufacturers or brands. Products from other manufacturers and brands that meet the technical requirements and performance indicators specified in this invention can also meet the application requirements of this invention and are all feasible choices.

[0049] The following are the manufacturers and brands of some of the substances used in each embodiment:

[0050] Thermally expandable microspheres: Manufacturer: AkzoNobel, brand name: Expancel 930 DU120; Manufacturer: Crestor Technology (Shanghai) Co., Ltd., brand name: DU608; Manufacturer: AkzoNobel, brand name: Expancel 930 DU120;

[0051] Carbonyl iron powder: Manufacturer: Shanghai Shenganda Metal Materials Co., Ltd., Grade: W-01;

[0052] Iron-silicon-aluminum alloy powder: Manufacturer is Qinghe County Huichu Welding Materials Co., Ltd., grade is HC;

[0053] Amorphous metal powder: Iron-based amorphous metal powder, manufactured by Yancheng Bimudi New Material Technology Co., Ltd., brand name: Nano Amorphous;

[0054] Nano ferrite: Manufacturer is Kunshan City Huaqiao Town Yuhua Magnetic Materials Trading Company, grade NC-10;

[0055] Polyamide 6 (PA6): Manufacturer: Yueyang Petrochemical Co., Ltd., Grade: PA6-YH800;

[0056] Polyethylene (PE): Manufacturer: Zhejiang Ruitang Plastics Technology Co., Ltd., Grade: HD253P;

[0057] Epoxy resin: The manufacturer is Baling Branch of China Petroleum & Chemical Corporation, and the grade is bisphenol A type epoxy resin E20;

[0058] Carbon nanotubes: Manufacturer: Shenzhen Suiheng Technology Co., Ltd., Grade: 99% CNTs;

[0059] Graphene: The manufacturer is Shenzhen Suiheng Technology Co., Ltd., and the grade is high-purity multilayer graphene;

[0060] Carbon black: Manufacturer is Cabot Corporation, USA, grade VXC-72;

[0061] Aramid paper honeycomb: Manufacturer is Shandong Fanglei Composite Materials Co., Ltd., grade is SD-NH-1.83-48;

[0062] Nickel-zinc ferrite: Manufacturer is Kunshan City Huaqiao Town Yuhua Magnetic Materials Store, brand name YH-N;

[0063] Quartz fiber prepreg: Manufacturer is Foshan Changyu New Material Technology Co., Ltd., grade is QW200;

[0064] Carbon fiber prepreg: Manufacturer is Baihe Aerospace Composite Materials Co., Ltd., grade BAC 448.

[0065] The test methods for the relevant performance indicators in the following embodiments and comparative examples are as follows:

[0066] Effective absorption bandwidth RL≤-10dB: The sample was tested using the bow-shaped method in GB / T 30142-2013 "Method for Measurement of Shielding Effectiveness of Electromagnetic Shielding Materials". The specific steps were as follows: the bow-shaped frame test system was used to place the sample in front of the metal backplate and measure the curve of its reflection loss (RL) as a function of frequency. The width of the continuous frequency range with RL≤-10dB was taken as the effective absorption bandwidth. The frequency range was 1~40GHz. The test instrument was a vector network analyzer (manufacturer: Rohde & Schwarz) with a standard gain horn antenna. The test environment was a microwave anechoic chamber.

[0067] Absorption bandwidth fluctuation of RL≤-10dB between the same test points in multiple samples along the thickness direction: Select 5 samples, and then use the above-mentioned test method for effective absorption bandwidth of RL≤-10dB to measure the same test point of the 5 samples. At the same time, the effective absorption bandwidth of RL≤-10dB of the 5 samples is statistically analyzed, and finally the fluctuation error range is calculated.

[0068] Roller peel strength: Referring to GB / T 1457-2005 "Test method for roller peel strength of sandwich structure", a sample with a width of 60 mm and a length of not less than 300 mm was peeled at a speed of 25 mm / min, and then the peel strength was calculated to characterize the reliability of the interface bonding between the skin and the core layer.

[0069] Peak impact load: The peak impact load of the specimen was tested in accordance with GB / T 1453-2005 "Test method for flat crush performance of sandwich structure or core". The peak load (unit: N) during the impact process was recorded as the peak impact load, which can be used to characterize the impact resistance of the material; the impact energy was set to 40J.

[0070] Example 1

[0071] A broadband microwave absorbing honeycomb sandwich foam based on microsphere carriers is a multi-layer composite structure formed by a one-time hot-pressing molding process, such as... Figure 1 As shown, it consists of a composite core layer and a wave-transparent skin layer 1 and an electromagnetic shielding skin layer 4 located on both sides of it.

[0072] The wave-transparent skin layer 1 is made of quartz fiber prepreg, and the electromagnetic shielding skin layer 4 is made of carbon fiber prepreg.

[0073] The composite core layer consists of a honeycomb skeleton and gradient absorbing foam filling the cells of the honeycomb skeleton; the honeycomb skeleton is aramid paper honeycomb.

[0074] The gradient absorbing foam is formed by in-situ foaming and melting bonding of two layers of functionalized thermally expandable microspheres with different absorbing properties inside the pores of a honeycomb skeleton; the functionalized thermally expandable microspheres consist of thermally expandable microspheres and a layer of absorbing particles that are mechanically interlocked on their surface through a semi-embedded manner.

[0075] The gradient absorbing foam is divided into a high-frequency absorption functional layer 2 and a low-frequency absorption functional layer 3 along the thickness direction from the incident surface to the back surface. The center absorption frequency of each absorption functional layer decreases sequentially from the incident surface to the back surface.

[0076] Inside the gradient absorbing foam, absorbing particles accumulate along the foam pore walls, forming a continuous three-dimensional isolated absorbing network.

[0077] The method for preparing the above-mentioned broadband absorbing honeycomb sandwich foam based on microsphere carriers comprises the following steps:

[0078] (1) Preparation of second-type functionalized thermally expandable microspheres;

[0079] Thermally expandable microspheres A (manufacturer: AkzoNobel, brand name: Expancel 930 DU120) were dispersed in a mixed solution of water and ethanol (volume ratio of water to ethanol: 9:1) and stirred at 40°C for 15 min. At this point, the thermoplastic shell on the surface of thermally expandable microspheres A was in a slightly swollen viscoelastic state. Then, carbonyl iron powder was added and dispersed at high speed of 3000 rpm for 10 min. Then, cold ethanol at 5°C was added within 30 seconds to dilute the microsphere shell, hardening the microsphere shell and "freezing" the carbonyl iron powder onto the surface of the microspheres. The microspheres were then filtered and dried to obtain the second type of functionalized thermally expandable microspheres. The mass ratio of thermally expandable microspheres A to the mixed solution of water and ethanol was 1:2, the amount of cold ethanol added was 3 times the volume of the thermally expandable microsphere dispersion, and the mass fraction of carbonyl iron powder in the second type of functionalized thermally expandable microspheres was 30%.

[0080] (2) Preparation of the first type of functionalized thermally expandable microspheres;

[0081] Thermally expandable microspheres B (manufacturer: AkzoNobel, brand name: Expancel 930 DU120) were dispersed in a mixed solution of water and ethanol (volume ratio of water to ethanol: 9:1) and stirred at 40°C for 15 min. Then, amorphous metal powder was added and dispersed by high-speed shearing at 4000 rpm for 15 min. Cold ethanol at 5°C was then added within 30 seconds to dilute the microspheres, hardening the microsphere shells and "freezing" the amorphous metal powder onto the microsphere surface. The microspheres were then filtered and dried to obtain the first type of functionalized thermally expandable microspheres. The mass ratio of thermally expandable microspheres B to the mixed solution of water and ethanol was 1:2, the amount of cold ethanol added was three times the volume of the thermally expandable microsphere dispersion, and the mass fraction of amorphous metal powder in the first type of functionalized thermally expandable microspheres was 15%.

[0082] (3) Preparation of precursor film;

[0083] (3.1) The matrix resin A (composed of polyethylene and carbon nanotubes in a mass ratio of 99:1) was mixed with second-type functionalized thermally expandable microspheres, and extruded and calendered to form a low-frequency precursor film with a thickness of 0.8 mm; wherein the content of the second-type functionalized thermally expandable microspheres was 15 wt%.

[0084] (3.2) The matrix resin B (composed of polyethylene and carbon nanotubes in a mass ratio of 98:2) is mixed with the first type of functionalized thermally expandable microspheres, and extruded and calendered to form a high-frequency precursor film with a thickness of 0.5 mm; wherein the content of the first type of functionalized thermally expandable microspheres is 15 wt%.

[0085] (4) In the mold, carbon fiber prepreg, low frequency precursor film, aramid paper honeycomb, high frequency precursor film and quartz fiber prepreg are laid from bottom to top. Then, the foam is limited and molded for 60 minutes at a temperature of 160℃ and a pressure of 2MPa to obtain broadband absorbing honeycomb sandwich foam based on microsphere carrier.

[0086] The final broadband absorbing honeycomb sandwich foam based on microsphere carrier has a composite core layer thickness of 5 mm, a wave-transparent skin layer thickness of 0.5 mm, and an electromagnetic shielding skin layer thickness of 0.5 mm.

[0087] The gradient absorbing foam has a volume filling rate of 90%~100% within the honeycomb skeleton cells (the size of the honeycomb skeleton cells is not exactly the same, so the actual measured volume filling rate varies in different cells; this range is between the minimum and maximum measured values ​​of the volume filling rate across all cells), and the density of the gradient absorbing foam is 0.2 g / cm³. 3 ;

[0088] The density of the broadband absorbing honeycomb sandwich foam based on microsphere carriers is 0.3 g / cm³. 3 The effective absorption bandwidth (RL≤-10dB) is 34GHz, and the effective absorption bandwidth fluctuation (RL≤-10dB) at the same test point in multiple samples along the thickness direction is ±0.3GHz. The roller peel strength is 32N·mm / mm, and the peak impact load is 5129N. The specific absorption performance is shown in the table below:

[0089] Reflection loss (RL) -14.3 dB -18.6 dB -22.4 dB -24.5 dB -26.8 dB -25.2 dB -24.7 dB 34 GHz

[0090] Example 2

[0091] A broadband absorbing honeycomb sandwich foam based on microsphere carrier is a multi-layer composite structure formed by a one-time hot pressing molding process, consisting of a composite core layer and a wave-transparent skin layer and an electromagnetic shielding skin layer located on both sides thereon.

[0092] The wave-transparent skin layer is made of quartz fiber prepreg, and the electromagnetic shielding skin layer is made of carbon fiber prepreg.

[0093] The composite core layer consists of a honeycomb skeleton and gradient absorbing foam filling the cells of the honeycomb skeleton; the honeycomb skeleton is aramid paper honeycomb.

[0094] The gradient absorbing foam is formed by in-situ foaming and melting bonding of two layers of functionalized thermally expandable microspheres with different absorbing properties inside the pores of a honeycomb skeleton; the functionalized thermally expandable microspheres consist of thermally expandable microspheres and a layer of absorbing particles that are mechanically interlocked on their surface through a semi-embedded manner.

[0095] The gradient absorbing foam is divided into a high-frequency absorption functional layer and a low-frequency absorption functional layer along the thickness direction from the incident surface to the back surface. The center absorption frequency of each absorption functional layer decreases sequentially from the incident surface to the back surface.

[0096] Inside the gradient absorbing foam, absorbing particles accumulate along the foam pore walls, forming a continuous three-dimensional isolated absorbing network.

[0097] The method for preparing the above-mentioned broadband absorbing honeycomb sandwich foam based on microsphere carriers comprises the following steps:

[0098] (1) Preparation of second-type functionalized thermally expandable microspheres;

[0099] Thermally expandable microspheres A (manufacturer: AkzoNobel, brand name: Expancel 930 DU120) were dispersed in a mixed solution of water and ethanol (volume ratio of water to ethanol: 9:1) and stirred at 42°C for 12 min. At this point, the thermoplastic shell on the surface of thermally expandable microspheres A was in a slightly swollen viscoelastic state. Then, iron-silicon-aluminum alloy powder was added and dispersed at high speed of 3500 rpm for 10 min. Then, cold ethanol at 3°C ​​was added within 30 seconds to dilute the microsphere shell, hardening the microsphere shell and "freezing" the iron-silicon-aluminum alloy powder on the surface of the microspheres. The microspheres were then filtered and dried to obtain the second type of functionalized thermally expandable microspheres. The mass ratio of thermally expandable microspheres A to the mixed solution of water and ethanol was 1:2, the amount of cold ethanol added was 3 times the volume of the thermally expandable microsphere dispersion, and the loading mass fraction of iron-silicon-aluminum alloy powder in the second type of functionalized thermally expandable microspheres was 20%.

[0100] (2) Preparation of the first type of functionalized thermally expandable microspheres;

[0101] Thermally expandable microspheres B (manufactured by AkzoNobel, brand name Expancel 930 DU120) were dispersed in a mixed solution of water and ethanol (volume ratio of water to ethanol 9:1) and stirred at 42°C for 12 min. Then, nano-ferrite was added and dispersed by high-speed shearing at 3500 rpm for 10 min. Next, cold ethanol at 3°C ​​was added within 30 seconds to dilute the microspheres, hardening the shells and "freezing" the nano-ferrite onto the surface. The microspheres were then filtered and dried to obtain the first type of functionalized thermally expandable microspheres (the microstructure of which is shown below). Figure 2 (As shown in the figure). Among them, the mass ratio of thermally expandable microspheres B to the mixed solution of water and ethanol is 1:2, the amount of cold ethanol added is 3 times the volume of the thermally expandable microsphere dispersion, and the loading mass fraction of nano-ferrite in the first type of functionalized thermally expandable microspheres is 15%.

[0102] (3) Preparation of precursor film;

[0103] (3.1) The matrix resin A (composed of epoxy resin and carbon nanotubes in a mass ratio of 99:1) is mixed with the second type of functionalized thermally expandable microspheres, and extruded and calendered to form a low-frequency precursor film with a thickness of 0.5 mm; wherein the content of the second type of functionalized thermally expandable microspheres is 10 wt%.

[0104] (3.2) The matrix resin B (composed of epoxy resin and carbon nanotubes in a mass ratio of 98:2) is mixed with the first type of functionalized thermally expandable microspheres, and extruded and calendered to form a high-frequency precursor film with a thickness of 0.5 mm; wherein the content of the first type of functionalized thermally expandable microspheres is 10 wt%.

[0105] (4) In the mold, carbon fiber prepreg, low frequency precursor film, aramid paper honeycomb, high frequency precursor film and quartz fiber prepreg are laid from bottom to top. Then, the foam is limited and molded for 60 minutes at a temperature of 140℃ and a pressure of 2MPa to obtain broadband absorbing honeycomb sandwich foam based on microsphere carrier.

[0106] The final broadband absorbing honeycomb sandwich foam based on microsphere carrier has a composite core layer thickness of 3 mm, a wave-transparent skin layer thickness of 0.8 mm, and an electromagnetic shielding skin layer thickness of 0.5 mm.

[0107] The gradient absorbing foam achieves a volume filling rate of 95%–100% within the honeycomb skeleton pores, and its density is 0.3 g / cm³. 3 ;

[0108] The density of the broadband absorbing honeycomb sandwich foam based on microsphere carriers is 0.3 g / cm³. 3 The effective absorption bandwidth (RL≤-10dB) is 31GHz, and the effective absorption bandwidth fluctuation (RL≤-10dB) at the same test point in multiple samples along the thickness direction is ±0.5GHz. The roller peel strength is 28N·mm / mm, and the peak impact load is 4871N. The specific absorption performance is shown in the table below:

[0109] Reflection loss (RL) -10.5 dB -12.8 dB -15.4 dB -17.3 dB -18.6 dB -19.2 dB -20.1 dB 31 GHz

[0110] Comparative Example 1

[0111] A broadband absorbing honeycomb sandwich foam based on microsphere carriers is basically the same as in Example 2, except that:

[0112] Gradient microwave absorbing foam is formed by in-situ foaming and melting bonding of two layers of functionalized thermally expandable microspheres with the same microwave absorbing properties inside the pores of a honeycomb skeleton.

[0113] The gradient absorbing foam is divided into a high-frequency absorption functional layer and a high-frequency absorption functional layer along the thickness direction from the incident surface to the back surface. The center absorption frequency of each absorption functional layer is equal from the incident surface to the back surface.

[0114] The method for preparing the broadband absorbing honeycomb sandwich foam based on microsphere carrier is basically the same as in Example 2, except that steps (1) and (3.1) are not performed. In step (4), the order of laying the mold from bottom to top is carbon fiber prepreg, high frequency precursor film, aramid paper honeycomb, high frequency precursor film, and quartz fiber prepreg.

[0115] The final broadband absorbing honeycomb sandwich foam based on microsphere carriers has a microwave absorbing foam density of 0.5 g / cm³. 3 ;

[0116] The density of the broadband absorbing honeycomb sandwich foam based on microsphere carriers is 0.7 g / cm³. 3 The effective absorption bandwidth (RL≤-10dB) is 16GHz, and the effective absorption bandwidth fluctuation (RL≤-10dB) at the same test point in multiple samples along the thickness direction is ±1.2GHz. The roller peel strength is 19N·mm / mm, and the peak impact load is 4200N. The specific absorption performance is shown in the table below:

[0117] Reflection loss (RL) -6.5 dB -8.2 dB -9.8 dB -11.5 dB -13.2 dB -12.4 dB -14.6 dB 16 GHz

[0118] Comparing Comparative Example 1 and Example 2, it can be seen that the effective absorption bandwidth of the broadband absorbing honeycomb sandwich foam based on microsphere carrier prepared in this comparative example is significantly narrowed, the bandwidth fluctuation is increased, the overall density is relatively high, and the interfacial bonding strength is reduced. This is because a low-frequency absorption functional layer is not set, so it is impossible to achieve broadband impedance matching and gradual absorption effect; at the same time, the two layers use the same high-frequency microspheres, which lacks a gradient structure, resulting in deterioration of broadband performance.

[0119] Example 3

[0120] A broadband absorbing honeycomb sandwich foam based on microsphere carrier is a multi-layer composite structure formed by a one-time hot pressing molding process, consisting of a composite core layer and a wave-transparent skin layer and an electromagnetic shielding skin layer located on both sides thereon.

[0121] The wave-transparent skin layer is made of quartz fiber prepreg, and the electromagnetic shielding skin layer is made of carbon fiber prepreg.

[0122] The composite core layer consists of a honeycomb skeleton and gradient absorbing foam filling the cells of the honeycomb skeleton; the honeycomb skeleton is aramid paper honeycomb.

[0123] The gradient absorbing foam is formed by in-situ foaming and melting bonding of two layers of functionalized thermally expandable microspheres with different absorbing properties inside the pores of a honeycomb skeleton; the functionalized thermally expandable microspheres consist of thermally expandable microspheres and a layer of absorbing particles that are mechanically interlocked on their surface through a semi-embedded manner.

[0124] The gradient absorbing foam is divided into a high-frequency absorption functional layer and a low-frequency absorption functional layer along the thickness direction from the incident surface to the back surface. The center absorption frequency of each absorption functional layer decreases sequentially from the incident surface to the back surface.

[0125] Inside the gradient absorbing foam, absorbing particles accumulate along the foam pore walls, forming a continuous three-dimensional isolated absorbing network.

[0126] The method for preparing the above-mentioned broadband absorbing honeycomb sandwich foam based on microsphere carriers comprises the following steps:

[0127] (1) Preparation of second-type functionalized thermally expandable microspheres;

[0128] Thermally expandable microspheres A (manufacturer: Crestor Technology (Shanghai) Co., Ltd., brand name: DU608) were dispersed in a mixed solution of water and ethanol (volume ratio of water to ethanol: 9:1) and stirred at 45°C for 12 min. At this time, the thermoplastic shell on the surface of thermally expandable microspheres A was in a slightly swollen viscoelastic state. Then, low-frequency responsive microwave absorbing particles (composed of carbonyl iron powder and iron-based amorphous powder in a mass ratio of 1:1) were added and dispersed at high speed at 3500 rpm for 10 min. Then, cold ethanol at 0°C was added within 30 seconds to dilute the microsphere shell, hardening the microsphere shell and "freezing" the low-frequency responsive microwave absorbing particles on the surface of the microspheres. The microspheres were then filtered and dried to obtain the second type of functionalized thermally expandable microspheres. The mass ratio of thermally expandable microspheres A to the mixed solution of water and ethanol was 1:2, the amount of cold ethanol added was 3 times the volume of the thermally expandable microsphere dispersion, and the loading mass fraction of low-frequency responsive microwave absorbing particles in the second type of functionalized thermally expandable microspheres was 35%.

[0129] (2) Preparation of the first type of functionalized thermally expandable microspheres;

[0130] Thermally expandable microspheres B (manufacturer: Crestor Technology (Shanghai) Co., Ltd., brand name: DU608) were dispersed in a mixed solution of water and ethanol (volume ratio of water to ethanol: 9:1) and stirred at 45°C for 12 min. Then, nano-ferrite was added and dispersed by high-speed shearing at 3500 rpm for 10 min. Then, cold ethanol at 0°C was added within 30 seconds to dilute the microspheres, hardening the shells and "freezing" the nano-ferrite onto the surface of the microspheres. The microspheres were then filtered and dried to obtain the first type of functionalized thermally expandable microspheres. The mass ratio of thermally expandable microspheres B to the mixed solution of water and ethanol was 1:2, the amount of cold ethanol added was 3 times the volume of the thermally expandable microsphere dispersion, and the mass fraction of nano-ferrite in the first type of functionalized thermally expandable microspheres was 20%.

[0131] (3) Preparation of precursor film;

[0132] (3.1) A matrix resin A (composed of polyamide 6 and dielectric loss filler (composed of graphene and carbon black in a mass ratio of 1:1)) was mixed with second-type functionalized thermal expansion microspheres and extruded and calendered to form a low-frequency precursor film with a thickness of 0.5 mm; wherein, the mass ratio of polyamide 6 to dielectric loss filler in matrix resin A is 98:2, and the content of second-type functionalized thermal expansion microspheres in the low-frequency precursor film is 20 wt%;

[0133] (3.2) The matrix resin B (composed of polyamide 6 and dielectric loss filler (composed of graphene and carbon black in a mass ratio of 1:1)) is mixed with the first type of functionalized thermal expansion microspheres, and extruded and calendered to form a high-frequency precursor film with a thickness of 0.5 mm; wherein, the mass ratio of polyamide 6 to dielectric loss filler in the matrix resin B is 96:4, and the content of the first type of functionalized thermal expansion microspheres in the high-frequency precursor film is 20 wt%;

[0134] (4) Carbon fiber prepreg, low-frequency precursor film, aramid paper honeycomb, high-frequency precursor film, and quartz fiber prepreg are sequentially laid in the mold from bottom to top. Then, the mold is limited and molded for 90 minutes at a temperature of 210℃ and a pressure of 2MPa to obtain a broadband microwave absorbing honeycomb sandwich foam based on a microsphere carrier. Its microstructure is as follows: Figure 3 As shown, its iron element distribution is as follows Figure 4 As shown, from Figure 3 , Figure 4 As can be seen, the absorbing particles are mainly enriched along the bubble wall, forming a continuous three-dimensional isolation network. The particles are tightly bonded to the matrix interface. The distribution of iron (marked in yellow) highly coincides with the position of the bubble wall, further confirming that the absorbing particles are selectively enriched along the bubble wall. This distribution feature is conducive to the formation of an efficient absorbing network.

[0135] The final broadband absorbing honeycomb sandwich foam based on microsphere carrier has a composite core layer thickness of 8 mm, a wave-transparent skin layer thickness of 0.5 mm, and an electromagnetic shielding skin layer thickness of 0.5 mm.

[0136] The gradient absorbing foam achieves a volume filling rate of 95%–100% within the honeycomb skeleton pores, and its density is 0.3 g / cm³. 3 ;

[0137] The density of the broadband absorbing honeycomb sandwich foam based on microsphere carriers is 0.5 g / cm³. 3 The effective absorption bandwidth (RL≤-10dB) is 38GHz, and the effective absorption bandwidth fluctuation (RL≤-10dB) at the same test point in multiple samples along the thickness direction is ±0.3GHz. The roller peel strength is 40N·mm / mm, and the peak impact load is 5364N. The specific absorption performance is shown in the table below:

[0138] Reflection loss (RL) -18.5 dB -22.4 dB -26.7 dB -28.3 dB -30.5 dB -29.1 dB -27.8 dB 38 GHz

[0139] Example 4

[0140] A broadband absorbing honeycomb sandwich foam based on microsphere carrier is a multi-layer composite structure formed by a one-time hot pressing molding process, consisting of a composite core layer and a wave-transparent skin layer and an electromagnetic shielding skin layer located on both sides thereon.

[0141] The wave-transparent skin layer is made of quartz fiber prepreg, and the electromagnetic shielding skin layer is made of carbon fiber prepreg.

[0142] The composite core layer consists of a honeycomb skeleton and gradient absorbing foam filling the cells of the honeycomb skeleton; the honeycomb skeleton is aramid paper honeycomb.

[0143] The gradient absorbing foam is formed by in-situ foaming and melting bonding of two layers of functionalized thermally expandable microspheres with different absorbing properties inside the pores of a honeycomb skeleton; the functionalized thermally expandable microspheres consist of thermally expandable microspheres and a layer of absorbing particles that are mechanically interlocked on their surface through a semi-embedded manner.

[0144] The gradient absorbing foam is divided into a high-frequency absorption functional layer and a low-frequency absorption functional layer along the thickness direction from the incident surface to the back surface. The center absorption frequency of each absorption functional layer decreases sequentially from the incident surface to the back surface.

[0145] Inside the gradient absorbing foam, absorbing particles accumulate along the foam pore walls, forming a continuous three-dimensional isolated absorbing network.

[0146] The method for preparing the above-mentioned broadband absorbing honeycomb sandwich foam based on microsphere carriers comprises the following steps:

[0147] (1) Preparation of second-type functionalized thermally expandable microspheres;

[0148] Thermally expandable microspheres A (manufacturer: AkzoNobel, brand name: Expancel 930 DU120) were dispersed in a mixed solution of water and ethanol (volume ratio of water to ethanol: 9:1) and stirred at 45°C for 15 min. At this point, the thermoplastic shell on the surface of thermally expandable microspheres A was in a slightly swollen viscoelastic state. Then, carbonyl iron powder was added and dispersed at high speed of 3000 rpm for 10 min. Then, cold ethanol at 0°C was added within 30 seconds to dilute the microspheres, hardening the shell and "freezing" the carbonyl iron powder onto the surface of the microspheres. The microspheres were then filtered and dried to obtain the second type of functionalized thermally expandable microspheres. The mass ratio of thermally expandable microspheres A to the mixed solution of water and ethanol was 1:2, the amount of cold ethanol added was 3 times the volume of the thermally expandable microsphere dispersion, and the mass fraction of carbonyl iron powder in the second type of functionalized thermally expandable microspheres was 50%.

[0149] (2) Preparation of the first type of functionalized thermally expandable microspheres;

[0150] Thermally expandable microspheres B (manufacturer AkzoNobel, brand name Expancel 930 DU120) were dispersed in a mixed solution of water and ethanol (volume ratio of water to ethanol 9:1) and stirred at 45°C for 15 min. Then, high-frequency responsive microwave absorbing particles (composed of amorphous metal powder and nano-ferrite in a mass ratio of 1:1) were added and dispersed at a high speed of 3000 rpm for 10 min. Then, cold ethanol at 0°C was added within 30 seconds to dilute the microspheres, hardening the shells and "freezing" the high-frequency responsive microwave absorbing particles onto the surface of the microspheres. The microspheres were then filtered and dried to obtain the first type of functionalized thermally expandable microspheres. The mass ratio of thermally expandable microspheres B to the mixed solution of water and ethanol was 1:2, the amount of cold ethanol added was 3 times the volume of the thermally expandable microsphere dispersion, and the mass fraction of high-frequency responsive microwave absorbing particles in the first type of functionalized thermally expandable microspheres was 30%.

[0151] (3) Preparation of precursor film;

[0152] (3.1) The matrix resin A (composed of polyethylene and graphene in a mass ratio of 97:3) was mixed with the second type of functionalized thermally expandable microspheres, and extruded and calendered to form a low-frequency precursor film with a thickness of 1 mm; wherein the content of the second type of functionalized thermally expandable microspheres was 20 wt%.

[0153] (3.2) The matrix resin B (composed of polyethylene and graphene in a mass ratio of 96:4) is mixed with the first type of functionalized thermally expandable microspheres, and extruded and calendered to form a high-frequency precursor film with a thickness of 0.5 mm; wherein the content of the first type of functionalized thermally expandable microspheres is 20 wt%.

[0154] (4) In the mold, carbon fiber prepreg, low frequency precursor film, aramid paper honeycomb, high frequency precursor film and quartz fiber prepreg are laid from bottom to top. Then, the foam is limited and molded for 60 minutes at a temperature of 150℃ and a pressure of 2MPa to obtain broadband absorbing honeycomb sandwich foam based on microsphere carrier.

[0155] The final broadband absorbing honeycomb sandwich foam based on microsphere carrier has a composite core layer thickness of 8 mm, a wave-transparent skin layer thickness of 1 mm, and an electromagnetic shielding skin layer thickness of 0.8 mm.

[0156] The gradient absorbing foam has a volume filling rate of 90%~95% within the honeycomb skeleton pores, and its density is 0.4 g / cm³. 3 ;

[0157] The density of the broadband absorbing honeycomb sandwich foam based on microsphere carriers is 0.5 g / cm³. 3 The effective absorption bandwidth (RL≤-10dB) is 32GHz, and the effective absorption bandwidth fluctuation (RL≤-10dB) at the same test point in multiple samples along the thickness direction is ±0.4GHz. The roller peel strength is 40N·mm / mm, and the peak impact load is 5466N. The specific absorption performance is shown in the table below:

[0158] Reflection loss (RL) -12.5 dB -16.8 dB -20.5 dB -22.1 dB -24.3 dB -23.5 dB -22.8 dB 32 GHz

[0159] Example 5

[0160] A broadband absorbing honeycomb sandwich foam based on microsphere carrier is a multi-layer composite structure formed by a one-time hot pressing molding process, consisting of a composite core layer and a wave-transparent skin layer and an electromagnetic shielding skin layer located on both sides thereon.

[0161] The wave-transparent skin layer is made of quartz fiber prepreg, and the electromagnetic shielding skin layer is made of carbon fiber prepreg.

[0162] The composite core layer consists of a honeycomb skeleton and gradient absorbing foam filling the cells of the honeycomb skeleton; the honeycomb skeleton is aramid paper honeycomb.

[0163] The gradient absorbing foam is formed by in-situ foaming and melting bonding of two layers of functionalized thermally expandable microspheres with different absorbing properties inside the pores of a honeycomb skeleton; the functionalized thermally expandable microspheres consist of thermally expandable microspheres and a layer of absorbing particles that are mechanically interlocked on their surface through a semi-embedded manner.

[0164] The gradient absorbing foam is divided into a high-frequency absorption functional layer and a low-frequency absorption functional layer along the thickness direction from the incident surface to the back surface. The center absorption frequency of each absorption functional layer decreases sequentially from the incident surface to the back surface.

[0165] Inside the gradient absorbing foam, absorbing particles accumulate along the foam pore walls, forming a continuous three-dimensional isolated absorbing network.

[0166] The method for preparing the above-mentioned broadband absorbing honeycomb sandwich foam based on microsphere carriers comprises the following steps:

[0167] (1) Preparation of second-type functionalized thermally expandable microspheres;

[0168] Thermally expandable microspheres A (manufacturer: Crestor Technology (Shanghai) Co., Ltd., brand name: DU608) were dispersed in a mixed solution of water and ethanol (volume ratio of water to ethanol: 9:1) and stirred at 50°C for 10 min. At this time, the thermoplastic shell on the surface of thermally expandable microspheres A was in a slightly swollen viscoelastic state. Then, carbonyl iron powder was added and dispersed at high speed of 3500 rpm for 10 min. Then, cold ethanol at 5°C was added within 30 seconds to dilute the microsphere shell, so that the microsphere shell hardened and the carbonyl iron powder was "frozen" on the surface of the microspheres. Then, the microspheres were filtered and dried to obtain the second type of functionalized thermally expandable microspheres. The mass ratio of thermally expandable microspheres A to the mixed solution of water and ethanol was 1:2, the amount of cold ethanol added was 3 times the volume of the thermally expandable microsphere dispersion, and the mass fraction of carbonyl iron powder in the second type of functionalized thermally expandable microspheres was 50%.

[0169] (2) Preparation of the first type of functionalized thermally expandable microspheres;

[0170] Thermally expandable microspheres B (manufacturer: Crestor Technology (Shanghai) Co., Ltd., brand name: DU608) were dispersed in a mixed solution of water and ethanol (volume ratio of water to ethanol: 9:1) and stirred at 50°C for 10 min. Then, amorphous metal powder was added and dispersed by high-speed shearing at 3500 rpm for 10 min. Then, cold ethanol at 5°C was added within 30 seconds to dilute the microspheres, hardening the shells and "freezing" the amorphous metal powder onto the surface of the microspheres. The microspheres were then filtered and dried to obtain the first type of functionalized thermally expandable microspheres. The mass ratio of thermally expandable microspheres B to the mixed solution of water and ethanol was 1:2, the amount of cold ethanol added was 3 times the volume of the thermally expandable microsphere dispersion, and the mass fraction of amorphous metal powder in the first type of functionalized thermally expandable microspheres was 30%.

[0171] (3) Preparation of precursor film;

[0172] (3.1) The matrix resin A (composed of epoxy resin and carbon black in a mass ratio of 98:2) is mixed with the second type of functionalized thermally expandable microspheres, and extruded and calendered to form a low-frequency precursor film with a thickness of 0.3 mm; wherein the content of the second type of functionalized thermally expandable microspheres is 15 wt%.

[0173] (3.2) The matrix resin B (composed of epoxy resin and graphene in a mass ratio of 98:2) is mixed with the first type of functionalized thermally expandable microspheres, and extruded and calendered to form a high-frequency precursor film with a thickness of 0.5 mm; wherein the content of the first type of functionalized thermally expandable microspheres is 15 wt%.

[0174] (4) In the mold, carbon fiber prepreg, low frequency precursor film, aramid paper honeycomb, high frequency precursor film and quartz fiber prepreg are laid from bottom to top. Then, the foam is limited and molded for 60 minutes at a temperature of 150℃ and a pressure of 2MPa to obtain broadband absorbing honeycomb sandwich foam based on microsphere carrier.

[0175] The final broadband absorbing honeycomb sandwich foam based on microsphere carrier has a composite core layer thickness of 5 mm, a wave-transparent skin layer thickness of 0.5 mm, and an electromagnetic shielding skin layer thickness of 0.5 mm.

[0176] The gradient absorbing foam achieves a volume filling rate of 95%–100% within the honeycomb skeleton pores, and its density is 0.3 g / cm³. 3 ;

[0177] The density of the broadband absorbing honeycomb sandwich foam based on microsphere carriers is 0.4 g / cm³. 3 The effective absorption bandwidth (RL≤-10dB) is 33GHz, and the effective absorption bandwidth fluctuation (RL≤-10dB) at the same test point in multiple samples along the thickness direction is ±0.3GHz. The roller peel strength is 35N·mm / mm, and the peak impact load is 5075.418N. The specific absorption performance is shown in the table below:

[0178] Reflection loss (RL) -13.8 dB -17.5 dB -21.6 dB -23.2 dB -25.4 dB -24.8 dB -23.9 dB 33 GHz

[0179] Example 6

[0180] A broadband microwave absorbing honeycomb sandwich foam based on microsphere carrier is basically the same as in Example 5, except that the gradient microwave absorbing foam is formed by in-situ foaming and melting bonding of three layers of functionalized thermally expanding microspheres with different microwave absorption properties inside the pores of the honeycomb skeleton.

[0181] The gradient absorbing foam is divided into a high-frequency absorption functional layer, a mid-frequency absorption functional layer and a low-frequency absorption functional layer along the thickness direction from the incident surface to the back surface; the mid-frequency absorption functional layer is formed by foaming third-type functionalized thermal expansion microspheres loaded with mid-frequency responsive absorbing particles.

[0182] The method for preparing the broadband absorbing honeycomb sandwich foam based on microsphere carriers described above is basically the same as in Example 5, except that after preparing the first type of functionalized thermally expandable microspheres, a third type of functionalized thermally expandable microspheres also needs to be prepared. The specific process is as follows: thermally expandable microspheres C (manufacturer: AkzoNobel, brand name: Expancel 930 DU120) are dispersed in a mixed solution of water and ethanol (volume ratio 9:1), stirred at 40°C for 12 min, then nickel-zinc ferrite is added and dispersed at high speed of 3500 rpm for 10 min, and then cold ethanol at 5°C (volume 3 times that of the dispersion) is added within 30 seconds, filtered and dried to obtain the third type of functionalized thermally expandable microspheres; wherein, the mass ratio of thermally expandable microspheres B to the mixed solution of water and ethanol is 1:2, the amount of cold ethanol added is 3 times the volume of the thermally expandable microsphere dispersion, and the loading mass fraction of nickel-zinc ferrite in the third type of functionalized thermally expandable microspheres is 20%;

[0183] Then, epoxy resin was mixed with type III functionalized thermally expandable microspheres, and extruded and calendered to form a mid-frequency precursor film with a thickness of 0.5 mm; wherein, the content of type III functionalized thermally expandable microspheres was 20 wt%.

[0184] Finally, the hot pressing process in the mold is as follows: carbon fiber prepreg, low-frequency precursor film, aramid paper honeycomb, medium-frequency precursor film, aramid paper honeycomb, high-frequency precursor film, and quartz fiber prepreg are laid in the mold from bottom to top. Then, the foam is limited and molded for 60 minutes at a temperature of 150℃ and a pressure of 2MPa to obtain broadband microwave absorbing honeycomb sandwich foam based on microsphere carrier.

[0185] The final broadband absorbing honeycomb sandwich foam based on microsphere carrier has a composite core layer thickness of 8 mm, a wave-transparent skin layer thickness of 0.5 mm, and an electromagnetic shielding skin layer thickness of 0.5 mm.

[0186] The gradient absorbing foam achieves a volume filling rate of 95%–100% within the honeycomb skeleton pores, and its density is 0.3 g / cm³. 3 ;

[0187] The density of the broadband absorbing honeycomb sandwich foam based on microsphere carriers is 0.4 g / cm³. 3 The effective absorption bandwidth (RL≤-10dB) is 36GHz, and the effective absorption bandwidth fluctuation (RL≤-10dB) at the same test point in multiple samples along the thickness direction is ±0.3GHz. The roller peel strength is 37N·mm / mm, and the peak impact load is 5300N. The specific absorption performance is shown in the table below:

[0188] Reflection loss (RL) -16.2 dB -20.5 dB -25.1 dB -27.6 dB -31.2 dB -28.4 dB -26.3 dB 36 GHz

[0189] Example 7

[0190] A broadband absorbing honeycomb sandwich foam based on microsphere carrier is basically the same as in Example 5, except that the center absorption frequency of each absorbing functional layer in the gradient absorbing foam increases sequentially from the incident wave surface to the back wave surface.

[0191] The method for preparing the broadband absorbing honeycomb sandwich foam based on microsphere carrier is basically the same as in Example 5, except that the order of laying the mold from bottom to top in step (4) is: carbon fiber prepreg, high frequency precursor film, aramid paper honeycomb, low frequency precursor film, and quartz fiber prepreg.

[0192] The final fabricated broadband absorbing honeycomb sandwich foam based on microsphere carriers exhibited an effective absorption bandwidth of 32 GHz with an RL ≤ -10 dB. Furthermore, the effective absorption bandwidth fluctuation along the thickness direction at the same test points in multiple samples was ±0.5 GHz with an RL ≤ -10 dB. The roller peel strength was 31 N·mm / mm, and the peak impact load was 5000 N. The specific absorption performance is shown in the table below.

[0193] Reflection loss (RL) -11.2 dB -13.4 dB -16.5 dB -18.2 dB -19.4 dB -20.6 dB -21.3 dB 32 GHz

[0194] As can be seen from the above embodiments, the present invention, by separately controlling the type of absorbing particles, the mass fraction of the load, the number and arrangement order of the gradient functional layers, and using functionalized thermal expansion microspheres semi-embedded loading and in-situ molding foaming process, produces broadband absorbing honeycomb sandwich foams with different structures. The resulting products have excellent absorption performance in the 1~40 GHz test frequency band, with an effective absorption bandwidth of 31~38 GHz and RL≤-10 dB. They also exhibit good consistency in the thickness direction and are lightweight, have high peel strength and impact resistance. This fully demonstrates that the technical solution of the present invention can achieve synergistic optimization of broadband high-efficiency absorption and structural load-bearing capacity.

Claims

1. A broadband absorbing honeycomb sandwich foam based on microsphere carriers, characterized in that: It is a multi-layer composite structure formed by a one-time hot pressing molding process, consisting of a composite core layer and a wave-transparent skin layer and an electromagnetic shielding skin layer located on both sides of it. The composite core layer consists of a honeycomb skeleton and gradient absorbing foam filling the pores of the honeycomb skeleton; The gradient absorbing foam is formed by in-situ foaming and melting bonding of at least two layers of functionalized thermally expandable microspheres with different absorbing properties inside the pores of a honeycomb skeleton. The gradient absorbing foam is divided into at least two absorbing functional layers along the thickness direction from the incident surface to the back surface, and the center absorption frequency of each absorbing functional layer decreases sequentially from the incident surface to the back surface. Functionalized thermally expandable microspheres consist of thermally expandable microspheres and a layer of microwave-absorbing particles that are mechanically interlocked on their surface through a semi-embedded manner; Thermally expanded microspheres were dispersed in a mixed solution of water and ethanol to obtain a thermally expanded microsphere dispersion, with a volume ratio of water to ethanol of 9:

1. Microwave-absorbing particles were added to the thermal expansion microsphere dispersion and sheared at a speed of not less than 3000 rpm. Then, cold ethanol at a temperature of 0~5℃ was added within 30 seconds to dilute the dispersion. After filtration and drying, functionalized thermal expansion microspheres were obtained. Inside the gradient absorbing foam, absorbing particles accumulate along the foam pore walls, forming a continuous three-dimensional isolated absorbing network.

2. The broadband absorbing honeycomb sandwich foam based on microsphere carrier according to claim 1, characterized in that, The honeycomb skeleton is made of aramid paper honeycomb.

3. The broadband absorbing honeycomb sandwich foam based on microsphere carrier according to claim 1, characterized in that, The thermally expandable microspheres have a core-shell structure, with a core of low-boiling-point liquid alkane and a shell of thermoplastic polymer.

4. A broadband absorbing honeycomb sandwich foam based on a microsphere carrier according to claim 1, characterized in that, The gradient absorbing foam has a volume filling rate of 90%~100% within the honeycomb skeleton pores, and its density is 0.2~0.4 g / cm³. 3 .

5. A broadband absorbing honeycomb sandwich foam based on a microsphere carrier according to claim 1, characterized in that, Gradient absorbing foam consists of a high-frequency absorption functional layer and a low-frequency absorption functional layer. The high-frequency absorption functional layer is formed by foaming first-type functionalized thermally expandable microspheres loaded with high-frequency responsive microwave absorbing particles. The high-frequency responsive microwave absorbing particles are one or more of amorphous metal powder and nano-ferrite. The mass fraction of the high-frequency responsive microwave absorbing particles in the first-type functionalized thermally expandable microspheres is 15~30%. The low-frequency absorption functional layer is formed by foaming second-type functionalized thermal expansion microspheres loaded with low-frequency responsive microwave absorbing particles. The low-frequency responsive microwave absorbing particles are one or more of carbonyl iron powder and iron-silicon-aluminum alloy powder. The mass fraction of the low-frequency responsive microwave absorbing particles in the second-type functionalized thermal expansion microspheres is 20~50%.

6. A broadband absorbing honeycomb sandwich foam based on a microsphere carrier according to claim 1, characterized in that, The wave-transparent skin layer is made of quartz fiber prepreg, and the electromagnetic shielding skin layer is made of carbon fiber prepreg. The thickness of the composite core layer is 3~8mm, the thickness of the wave-transparent skin layer is 0.5~1mm, and the thickness of the electromagnetic shielding skin layer is 0.5~1mm.

7. A method for preparing broadband absorbing honeycomb sandwich foam based on microsphere carriers as described in any one of claims 1 to 6, characterized in that... Includes the following steps: (1) Add microwave absorbing particles to two or more groups of thermal expansion microsphere dispersions and shear them at a speed of not less than 3000 rpm. Then, add cold ethanol at a temperature of 0~5℃ within 30 seconds to dilute the dispersions. The amount of cold ethanol added is 3 times the volume of the thermal expansion microsphere dispersions. Then filter and dry to obtain functionalized thermal expansion microspheres with different microwave absorbing properties. (2) The matrix resin is mixed with functionalized thermally expandable microspheres with different microwave absorption properties, and extruded and calendered to form multiple precursor films; (3) A carbon fiber prepreg is laid at the bottom of the mold and a quartz fiber prepreg is laid at the top. Between the carbon fiber prepreg and the quartz fiber prepreg, multiple precursor films are laid alternately in order from bottom to top according to the increasing central absorption frequency of the response, with the honeycomb skeleton as the interval. After the laying is completed, the broadband absorbing honeycomb sandwich foam based on the microsphere carrier is obtained by limiting molding and foaming.

8. The method for preparing a broadband absorbing honeycomb sandwich foam based on a microsphere carrier according to claim 7, characterized in that, The base resin is polyamide 6, polyethylene, or epoxy resin.

9. The method for preparing a broadband absorbing honeycomb sandwich foam based on a microsphere carrier according to claim 8, characterized in that, The matrix resin also contains dielectric loss fillers, which are one or more of carbon nanotubes, graphene, and carbon black.

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