A dual-mart foam wave-absorbing material plate and a preparation method thereof

Abstract

The present application relates to satellite stealth technology field, specifically a kind of double-male foam wave-absorbing material plate and preparation method thereof.The present application uses double-male imide resin and its curing agent, carbon fiber and foaming agent as raw material, prepares a variety of different broadband complex permittivity double-male foam wave-absorbing material finished sheet, the finished sheet is bonded according to the order of broadband complex permittivity from small to large to obtain three layers of matching combination double-male foam wave-absorbing material plate, then the slurry of carbon black powder is sprayed to the side surface of the double-male foam wave-absorbing material plate.The present application only uses carbon fiber as wave-absorbing agent, and prepares three layers of matching combination double-male foam wave-absorbing material plate with the advantages of broadband wave-absorbing, low density, high heat insulation performance;The dispersion problem of carbon fiber as wave-absorbing agent in all azimuth orientation is solved by using "spiral scraping" process;The blackening process of "atomization spraying" meets the requirement of low visible light reflectivity, so as to realize the multispectral stealth of satellite.

Description

Technical Field

[0001] This invention relates to the field of satellite stealth technology, specifically to a bismaleimide foam absorbing material plate and its preparation method. Background Technology

[0002] With the advancement of human science and technology, military competition among world powers has gradually expanded from land, sea, and air to the outer space domain. Space warfare will inevitably be a key focus of future military technology, and satellite stealth is one of the necessary means to conduct space warfare. Therefore, it is necessary to equip satellites with stealth materials to form a "stealth cloak." Based on the principle of satellite design around its payload, the stealth materials used in satellite shells must first meet the requirements of space environment adaptability and lightweight, broadband stealth, while also addressing the technical challenges of multi-angle, multi-polarization, and multi-spectral stealth.

[0003] The Institute of Metal Research, Chinese Academy of Sciences, has developed a microwave absorbing material, referred to as "bismaleimide foam absorbing material," prepared through a foaming process. This material uses bismaleimide resin as a matrix and incorporates varying amounts of short-cut carbon fibers, carbon nanotubes, graphene, carbonyl iron powder, and flake iron-silicon-aluminum powder as absorbing agents to modulate electromagnetic properties. This material exhibits excellent broadband absorption performance and has already been applied in the aerospace field. The matrix of bismaleimide foam absorbing material is a polyimide resin. Polyimide resins are suitable for high and low temperature variations and radiation damage in space, making them commonly used load-bearing materials in space environments. However, to address the challenge of low-frequency broadband absorption, the bismaleimide foam absorbing material used in aerospace incorporates a large amount of magnetic absorbing agents (such as carbonyl iron powder and flake iron-silicon-aluminum powder), resulting in higher density and poorer thermal insulation, making it unsuitable for satellite stealth applications. In addition to solving the problem of lightweight broadband stealth for satellites, it is also necessary to further optimize and improve the preparation process of bi-mammalian foam absorbing materials, which serve as the "stealth cloak" for satellites, to address the technical challenges of multi-angle, multi-polarization, and multi-spectral stealth for satellites, taking into account the special characteristics of satellite stealth.

[0004] During flight, satellites face illumination from ground-based and space-based microwave radars at various azimuth angles and polarizations. This ultimately manifests in the absorption capabilities of the microwave absorbing material, acting as the satellite's "stealth cloak," to absorb microwaves from different electric field directions. Bismaleimide foam microwave absorbing materials use chopped carbon fibers as the absorbing agent. Compared to powdered absorbing agents, a very small amount of chopped carbon fibers can achieve broadband and efficient microwave absorption, thus ensuring the lightweight and high thermal insulation performance of the bismaleimide foam. However, due to the high conductivity and orientation of chopped carbon fibers, the angular relationship between the orientation of the chopped carbon fibers and the electric field direction of the incident microwaves significantly affects the microwave absorption performance of the bismaleimide foam (see...). Figure 3This means that the absorption capacity of bismaleimide foam absorbing material varies when exposed to microwave radar illumination from different angles and with different polarizations. This is obviously not conducive to the overall multi-angle and multi-polarization stealth of satellites. Therefore, finding a way to solve the problem of omnidirectional angular orientation dispersion of short-cut carbon fiber absorbing agent in bismaleimide foam absorbing material is the key to enabling this absorbing material to be used in satellite stealth.

[0005] During flight, satellites face detection not only from microwave radar but also from optical and infrared radar. The radar-absorbing materials used as a satellite's "stealth cloak" need to possess multi-spectral stealth capabilities across microwaves, visible light, and infrared. Bismaleimide foam radar-absorbing materials possess high thermal insulation properties; when installed on the satellite's outer shell, they effectively suppress heat dissipation within the satellite, benefiting thermal control and thus meeting the satellite's infrared stealth performance requirements. The visible light background in space is dark, requiring materials with sufficiently "black" surfaces to achieve low visible light reflectivity and meet visible light stealth requirements. However, the resin matrix of bismaleimide foam radar-absorbing materials is not black, falling far short of these requirements.

[0006] In summary, there is an urgent need to develop a new type of satellite absorbing material that combines lightweight, broadband microwave absorption, multi-angle / multi-polarization compatibility, and visible-infrared multi-spectral stealth capabilities. Furthermore, by optimizing the orientation distribution and surface optical properties of the absorbing agent, we can overcome the comprehensive technical bottlenecks of existing bismaleimide foam absorbing materials in terms of density, thermal insulation, electromagnetic response anisotropy, and visible-light stealth performance. Summary of the Invention

[0007] To address the problems existing in the prior art, this invention provides a bismaleimide foam absorbing material panel and its preparation method. This invention prepares a three-layer matched combination bismaleimide foam absorbing material panel with different lengths and a small amount of carbon fiber as the absorbing agent, leveraging its unique advantages of broadband absorption, low density, and high thermal insulation performance, thus solving the problem of broadband stealth technology for lightweight satellites. Further improvements are made to the omnidirectional angular orientation dispersion of the carbon fiber absorbing agent in the matrix and the surface porous "blackening" technology, solving the problems of multi-angle, multi-polarization, and multi-spectral stealth technology for satellites, ultimately enabling the bismaleimide foam absorbing material panel to be applied in the field of satellite stealth.

[0008] The technical solution of this invention is:

[0009] A method for preparing a bismaleimide foam absorbing material board is characterized by: using bismaleimide resin and its curing agent, carbon fiber and foaming agent as raw materials to prepare a variety of bismaleimide foam absorbing material sheets with different broadband complex dielectric constants; bonding the three bismaleimide foam absorbing material sheets with broadband complex dielectric constants in ascending order to obtain a three-layer matched combination of bismaleimide foam absorbing material boards; and then spraying a slurry of carbon black powder onto one side surface of the bismaleimide foam absorbing material board to obtain a blackened bismaleimide foam absorbing material board.

[0010] The method includes the following steps:

[0011] (1) Mixing

[0012] The bismaleimide resin, curing agent DDM, carbon fiber, and foaming agent are mixed in the following weight percentages: 60~85wt% : 11.5~36.5wt% : 0.09~0.51wt% : 2.9-3.1wt%.

[0013] (2) Prepolymerization

[0014] Heat the above-mentioned mixed raw materials to 120-130℃ and keep warm for 10-20 minutes;

[0015] (3) Finalization

[0016] The prepolymerized fluid hot raw material is poured onto a polyimide plate. The carbon fiber orientation in the hot raw material is distributed in a spiral pattern by spiral coating. After spiral coating, the material is left to stand for 20-30 minutes. The material cools down, forms a thin sheet, and detaches from the polyimide plate, thus completing the shaping process.

[0017] (4) Foaming

[0018] The pre-shaped raw material sheet is laid flat in the mold, and the mold is placed in an oven preheated to 180-200℃. The temperature is raised to 240-280℃ and kept at that temperature for 40-60 minutes to complete the curing. After natural cooling, the material is demolded to obtain a 40-60mm thick bismaleimide foam microwave absorbing material block.

[0019] (5) Slicing

[0020] The hard skin on the surface of the bismaleimide foam absorbing material block was cut off, and the broadband complex permittivity of the bismaleimide foam absorbing material block after the hard skin was cut off was tested; the bismaleimide foam absorbing material block after the hard skin was cut off was cut into finished sheets with a thickness of 4-15mm.

[0021] (6) Combination

[0022] By using carbon fiber absorbing agents of different lengths as raw materials and repeating the above operations, a variety of finished bismaleimide foam absorbing materials with different broadband complex dielectric constants and different thicknesses were prepared.

[0023] Using GD414 silicone rubber suitable for the space environment, three kinds of bismaleimide foam absorbing material sheets with different broadband complex dielectric constants and different thicknesses are bonded together in order of increasing broadband complex dielectric constant. The temperature is raised to 80-100℃ and held for 20-30 minutes until fully cured to prepare a three-layer matched combination of bismaleimide foam absorbing material board, achieving broadband and efficient microwave absorption.

[0024] (7) Darkening

[0025] GD414 silicone rubber, carbon black powder, and solvent are mixed in a certain proportion to obtain a carbon black powder slurry. The carbon black powder slurry is atomized and sprayed onto one side of a three-layer matched combination of bismaleimide foam absorbing material board. The nozzle diameter of the spray gun is controlled at 2-3 mm, and the distance from the bismaleimide foam absorbing material board is 0.4 m-0.6 m. After drying, it is kept at 180-200℃ for 30-40 minutes until the black film is completely cured. The atomization spraying of carbon black powder slurry and curing is repeated 1-3 times to obtain a blackened bismaleimide foam absorbing material board.

[0026] Furthermore, the carbon fiber described in step (1) has a length of 2-6 mm and a diameter of 5-8 μm;

[0027] The foaming agent is one or more of azobisisobutyronitrile, diisopropyl azodicarbonate, and dinitrospentamethylenetetramine.

[0028] Furthermore, the heating method described in step (2) is oil bath heating, with stirring during heating.

[0029] Furthermore, the coating thickness described in step (3) is 1 to 3 mm.

[0030] Furthermore, the mold reserved space in step (4) is 10 times the volume of the raw material sheet; the heating time is 30-40 minutes.

[0031] Furthermore, the density of the bismaleimide foam absorber block after the hard outer layer is cut off in step (5) is 0.13–0.15 g / cm³. 3 The thermal conductivity is less than 0.06 W / m·K.

[0032] Furthermore, the real part of the dielectric constant of the three different broadband complex dielectric constants described in step (6) is 1 to 30 and the imaginary part is 0 to 15 in the frequency range of 0.75 to 18 GHz.

[0033] Further, in step (7), the weight percentage of GD414 silicone rubber, carbon black powder and solvent is 15~25wt% : 1~3wt% : 72~82wt%; the carbon black powder is required to have a particle size of 5~50nm and is an electrically insulating powder; the solvent is one or more of ethyl acetate, n-butane and tetrahydrofuran.

[0034] A bismaleimide foam microwave absorbing material board prepared according to the above preparation method.

[0035] The design concept of this invention is:

[0036] This invention addresses the specific requirements of lightweight, broadband, multi-angle, multi-polarization, and multi-spectral stealth for satellites. It optimizes and improves the fabrication process of bipolar foam absorbing materials already applied in the aerospace field, as detailed below:

[0037] To address the requirements for lightweight, broadband stealth satellites, a three-layer matched combination of bismaleimide foam absorbing material panels was prepared using carbon fibers of varying lengths and in small quantities as the absorbing agent. On one hand, carbon fibers are ultrafine, highly conductive materials; a small amount (0.1~0.5wt%) of fully dispersed carbon fibers can achieve high-loss absorption of electromagnetic waves. The addition of a small amount of carbon fibers will not adversely affect the unique advantages of the foam material's low density and high thermal insulation performance. On the other hand, bismaleimide foam absorbing materials with different lengths of carbon fibers exhibit different electromagnetic properties, which is beneficial for multi-layer matched combination design to achieve broadband absorption. Therefore, replacing the thermal insulation foam material of the satellite shell with a three-layer matched combination of low-density, high-thermal-insulation bismaleimide foam absorbing material panel can meet the requirements for lightweight, broadband stealth satellites.

[0038] To address the multi-angle, multi-polarization stealth requirements of satellites, a "spiral coating" process was employed to solve the problem of omnidirectional angular orientation dispersion of carbon fiber absorbing agents (see...). Figure 4 The orientation of carbon fibers greatly affects the microwave absorption performance of the material. The "spiral coating" process can make the dispersed carbon fibers form a spiral distribution. In this way, the bimaleimide foam microwave absorbing material has a consistent broadband and high-efficiency microwave absorption capability under microwave irradiation at different angles and polarizations, which can meet the requirements of satellite stealth at multiple angles and polarizations.

[0039] To address the multi-spectral stealth requirements of satellites, a "foaming spraying" blackening process is employed to achieve low visible light reflectivity on the surface of the bismaleimide foam absorbing material. A high-airflow spray gun propels the black slurry outwards, maintaining a sufficient distance between the nozzle and the surface of the bismaleimide foam absorbing material. This atomized state upon reaching the material surface is termed "foaming spraying." This process blackens the bismaleimide foam absorbing material while preserving its porous scattering characteristics, resulting in a sufficiently "black" surface that meets the optical stealth requirements for low visible light reflectivity. Furthermore, the high thermal insulation capability of the bismaleimide foam absorbing material's outer shell effectively suppresses heat dissipation within the satellite, fulfilling the satellite's infrared stealth requirements and ultimately satisfying microwave, optical, and infrared multi-spectral stealth requirements.

[0040] Advantages and beneficial effects of the present invention:

[0041] This invention optimizes and improves the preparation process of bismaleimide foam microwave absorbing material in three aspects: First, it uses only carbon fibers of different lengths and a small amount as the microwave absorbing agent to prepare a material with broadband microwave absorption and low density (0.13 g / cm³). 3 ~0.15g / cm 3 The system employs a three-layer matching combination of bismaleimide foam absorbing material panels with high thermal insulation (thermal conductivity <0.06w / m·K) to achieve lightweight broadband stealth by replacing the thermal insulation foam material on the satellite's outer shell. Secondly, the "spiral coating" process solves the problem of omnidirectional angular orientation dispersion of carbon fiber as a microwave absorbing agent, enabling the bismaleimide foam absorbing material panels to possess broadband and efficient microwave absorption capabilities under different angles and polarizations of microwave irradiation, thus achieving multi-angle and multi-polarization stealth for the satellite. Thirdly, leveraging the porous scattering characteristics of the bismaleimide foam absorbing material surface, a "foaming spraying" blackening process is used to meet the requirements for low visible light reflectivity, thereby achieving multi-spectral stealth for the satellite.

[0042] The foam absorbing material board prepared by this invention has the advantages of being lightweight and having high thermal insulation, and can be mass-produced into various shapes according to the shape design and assembly requirements of satellite stealth (see...). Figure 2 , Figure 6 and Figure 8 ). Attached Figure Description

[0043] Figure 1 The broadband electromagnetic parameters of bismaleimide foam absorbing materials prepared using carbon fiber absorbing agents of different lengths and contents are shown; among them, Figure 1 (a) is bismaleimide foam absorbing material A. Figure 1 (b) is bismaleimide foam absorbing material B. Figure 1 (c) is bismaleimide foam absorbing material C. Figure 1 (d) is bismaleimide foam absorbing material D. Figure 1 (e) is bismaleimide foam absorbing material E.

[0044] Figure 2 A partial view of the unblackened bismaleimide foam absorbing material plate prepared in Example 1.

[0045] Figure 3 This is a comparison chart showing the correlation between the orientation of short-cut carbon fiber microwave absorbers and the electromagnetic properties of bismaleimide foam microwave absorbers.

[0046] Figure 4 The diagram shows the effect of the spiral coating process on the orientation of carbon fiber microwave absorbing agent and on the electromagnetic properties of bismaleimide foam microwave absorbing material; among them... Figure 4 (a) is a schematic diagram of the spiral coating process. Figure 4 (b) is a schematic diagram of the distribution of carbon fiber microwave absorber after spiral coating. Figure 4 (c) Comparison of electromagnetic properties of bimafic foam absorbing material in the X and Y axes after spiral coating.

[0047] Figure 5 This is a schematic diagram of the blackening process of atomized spray coating on the surface of smothermal foam microwave absorbing material.

[0048] Figure 6 This is a picture of a blackened bismaleimide foam microwave absorbing material board after atomized spraying.

[0049] Figure 7 The visible light reflectance of the blackened bismaleimide foam absorbing material plate prepared in Example 1.

[0050] Figure 8 Photos of blackened bimethane foam absorbing material boards of various shapes for mass production.

[0051] Figure 9 The broadband absorption performance of the blackened bismaleimide foam absorbing material board prepared in Example 1.

[0052] Figure 10 The broadband absorption performance of the blackened bismaleimide foam absorbing material board prepared in Example 2.

[0053] Figure 11 The broadband absorption performance of the blackened bismaleimide foam absorbing material board prepared in Example 3.

[0054] Figure 12 The broadband absorption performance of the blackened bismaleimide foam absorbing material board prepared in Example 4.

[0055] Figure 13 The visible light reflectance of the blackened bismaleimide foam absorbing material plate prepared in Example 2.

[0056] Figure 14 The visible light reflectance of the blackened bismaleimide foam absorbing material plate prepared in Example 3 is shown.

[0057] Figure 15 The visible light reflectance of the blackened bismaleimide foam absorbing material plate prepared in Example 4 is shown.

[0058] Figure 16 The broadband absorption performance of the blackened bismaleimide foam absorbing material board prepared for Comparative Example 1.

[0059] Figure 17 The broadband absorption performance of the blackened bismaleimide foam absorbing material board prepared for Comparative Example 2. Detailed Implementation

[0060] The present invention will be further illustrated 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.

[0061] Preparation of Bismaleimide Foam Absorbing Material A: 800g of bismaleimide resin, 200g of curing agent DDM (4,4'-diaminodiphenylmethane), 1g of 2mm long carbon fibers (5-8μm in diameter) as the absorbing agent, and 30g of azobisisobutyronitrile as the foaming agent are mixed in a container and stirred continuously for 10 minutes until uniformly dispersed. The mixed raw materials are heated in an oil bath to 130℃ until they are in a fluid state. After holding at this temperature for 20 minutes, the mixture is poured onto a polyimide plate (at this state, the bismaleimide resin is moderately pre-crosslinked). The hot raw material is then spirally coated using a thin plate, controlling the thickness of the coated hot raw material to 2mm, so that the orientation of the carbon fiber absorbing agent in the raw material is also spirally distributed. Figure 4 As shown. This ensures omnidirectional angular dispersion. After the hot raw material is spirally coated, it is left to stand for 20 minutes to cool and form a thin sheet that detaches from the polyimide plate, completing the shaping process. The sheet is laid flat in a 450mm × 450mm square mold. The mold cover is tightened with a 50mm limit screw according to the total height of the mold cavity. The mold is then placed in an oven preheated to 180℃, heated to 260℃ for 30 minutes, and held at that temperature for 1 hour to cure. After natural cooling to room temperature, the mold is demolded, and the hard skin on the surface of the foamed block (the so-called "hard skin" refers to the dense resin layer formed when the resin is in contact with the inner wall of the mold during foaming) is cut off, resulting in a density of 0.13g / cm³. 3 A 45mm thick bismaleimide foam microwave absorbing material block A, with a thermal conductivity of less than 0.06 W / m·K, has the following broadband electromagnetic parameters (broadband complex permittivity) in the range of 0.75–18 GHz: [See attached table]. Figure 1 (a) Cut the smothermal foam absorbing material block A into finished sheets of two thicknesses: 4 mm and 10 mm.

[0062] Preparation of Bismaleimide Foam Absorbing Material B: 700g of bismaleimide resin, 300g of DDM, 3g of 3mm long carbon fiber microwave absorbing agent, and 30g of azobisisobutyronitrile (AIBN) foaming agent were mixed in a container and continuously stirred. The mixture was heated to 120℃ and kept at this temperature for 10 minutes. The mixture was then poured onto a polyimide plate. A thin sheet was used to spirally coat the hot material, controlling the thickness of the coated material to 2mm. After spiral coating, the material was left to cool for 20 minutes, forming a thin sheet that detached from the polyimide plate. The sheet was then laid flat in a 450mm × 450mm square mold. The mold cover was tightened with a 50mm limit screw. The mold was then placed in an oven preheated to 180℃. The temperature was increased to 240℃ for 30 minutes and held for 1 hour to cure. After cooling, the material was demolded, and the hardened outer layer on the surface of the foam block was removed, yielding a material with a density of 0.13g / cm³. 3 A 45mm thick bismaleimide foam microwave absorbing material block B with a thermal conductivity of less than 0.06 W / m·K has the following broadband electromagnetic parameters in the range of 0.75–18 GHz: Figure 1 (b) Cut the smothermal foam absorbing material block B into finished sheets of two thicknesses: 6mm and 13mm.

[0063] Preparation of Bismaleimide Foam Absorbing Material C Finished Sheet: 700g of bismaleimide resin, 300g of DDM, 2.5g of 4mm long carbon fiber absorber, and 30g of diisopropyl azodicarbonate foaming agent were mixed in a container and continuously stirred. The raw material was heated to 120℃ and kept at this temperature for 10 minutes. The mixture was then poured onto a polyimide plate. A thin plate was used to spirally coat the hot material, controlling the thickness of the coated material to 2mm. After spiral coating, the material was left to cool for 20 minutes, forming a thin sheet that detached from the polyimide plate. The sheet was laid flat in a 450mm×450mm square mold. The mold cover was tightened with a 50mm limit screw. The mold was then placed in a preheated oven at 180℃. The temperature was increased to 240℃ for 30 minutes and held for 50 minutes to cure. After cooling, the material was demolded, and the hardened outer layer on the surface of the foam block was removed, yielding a density of 0.14g / cm³. 3 A 45mm thick bismaleimide foam microwave absorbing material block C with a thermal conductivity of less than 0.06 W / m·K has the following broadband electromagnetic parameters in the range of 0.75–18 GHz: Figure 1 (c). Cut the smothermal foam absorbing material block C into finished sheets of two thicknesses: 6mm and 13mm.

[0064] Preparation of the D-sheet of bismaleimide foam microwave absorbing material: 600g of bismaleimide resin, 360g of DDM, 3.5g of 5mm long carbon fiber microwave absorbing agent, and 30g of diisopropyl azodicarbonate foaming agent were mixed in a container and continuously stirred. The raw material was heated to 120℃ and kept at this temperature for 15 minutes. The mixture was then poured onto a polyimide plate. A thin plate was used to spirally coat the hot material, controlling the thickness of the coated material to 2mm. After spiral coating, the material was left to cool for 20 minutes, forming a thin sheet that detached from the polyimide plate. The sheet was then laid flat in a 450mm×450mm square mold. The mold cover was tightened with a 50mm limit screw. The mold was then placed in an oven preheated to 180℃. The temperature was increased to 250℃ for 30 minutes and held for 40 minutes to cure. After cooling, the material was demolded, and the hardened outer layer on the surface of the foam block was removed, yielding a material with a density of 0.14g / cm³. 3 A 45mm thick bismaleimide foam microwave absorbing material block D with a thermal conductivity of less than 0.06 W / m·K has the following broadband electromagnetic parameters in the range of 0.75–18 GHz: Figure 1 (d). Cut the smothermal foam absorbing material block D into finished sheets of two thicknesses: 5mm and 8mm.

[0065] Preparation of the finished bismaleimide foam microwave absorbing material sheet E: 600g of bismaleimide resin, 360g of DDM, 5g of 6mm long carbon fiber microwave absorbing agent, and 30g of azobisisobutyronitrile foaming agent were mixed in a container and continuously stirred. The raw material temperature was heated to 130℃ and kept at this temperature for 20 minutes. The mixture was then poured onto a polyimide plate. A thin plate was used to spirally coat the hot material, controlling the thickness of the coated material to 3mm. After spiral coating, the material was left to cool for 20 minutes, forming a sheet that detached from the polyimide plate. The sheet was laid flat in a 450mm×450mm square mold. The mold cover was tightened with a 50mm limit screw. The mold was then placed in an oven preheated to 180℃. The temperature was increased to 260℃ for 30 minutes and held for 1 hour to cure. After cooling, the material was demolded, and the hardened outer layer on the surface of the foamed block was removed, yielding a density of 0.15g / cm³. 3 A 40mm thick bismaleimide foam microwave absorbing material block E with a thermal conductivity of less than 0.06 W / m·K has the following broadband electromagnetic parameters in the range of 0.75–18 GHz: Figure 1 (e). Cut the smothermal foam absorbing material block E into 10mm thick finished sheets.

[0066] Example 1

[0067] Using GD414 silicone rubber, 4mm thick bismaleimide foam absorbing material A, 6mm thick bismaleimide foam absorbing material B, and 5mm thick bismaleimide foam absorbing material D are bonded and compacted in a top-to-bottom order (pressure ≥1MPa). The mixture is then heated to 80℃ for 30 minutes and kept at that temperature for 20 minutes to cure, resulting in a 15mm thick bismaleimide foam absorbing material board with three matched layers (the thickness of the silicone rubber adhesive here is 5-10μm).

[0068] 100g of GD414 silicone rubber, 10g of insulating carbon black powder with a particle size range of 5-50nm, and 400g of n-hexane solvent were ball-milled (using zirconia balls, ball-to-powder ratio of 1:2, rotation speed of 150-200r / min, ball milling for 20-30min). After filtration, a black slurry was obtained. The black slurry was loaded into a spray gun, and the nozzle diameter was controlled at 2mm. The slurry was atomized and sprayed from a distance of 0.5m from one side of the surface of the bismuth foam microwave absorbing material board until the black slurry completely covered the front of the material board, forming a porous blackened surface (see the atomized spraying blackening process). Figure 5 (As shown), air dry for 1 hour, then heat to 180℃ in an oven for 30 minutes and hold for 30 minutes to cure the black film. Repeat the atomization spraying-curing process twice to obtain the blackened bismaleimide foam absorbing material board. The thickness of the cured black film is 2-5μm. Figure 6 As shown. The visible light reflectance of the blackened bismaleimide foam absorbing material plate in this embodiment is shown in the figure. Figure 7 The absorption performance in the 2–18 GHz wideband is shown below. Figure 9 (Visible light reflectance was measured using a UV-VIS-NIR spectrophotometer; broadband absorption performance was tested using the RCS method in an anechoic environment according to the national military standard GJB2038A-2011.) This bismaleimide foam absorbing material board possesses multi-spectral, high-efficiency stealth capabilities in the 2–18 GHz microwave broadband and visible light bands. Further work can be carried out on the shape processing and assembly hole forming of the stealth board to meet the requirements of satellite shape design and lightweighting.

[0069] Example 2

[0070] Using GD414 silicone rubber, 4mm thick bismaleimide foam absorbing material A, 6mm thick bismaleimide foam absorbing material C, and 8mm thick bismaleimide foam absorbing material D were bonded together in a top-to-bottom order. The mixture was then heated to 80℃ for 30 minutes and kept at that temperature for 30 minutes to cure, resulting in a 18mm thick bismaleimide foam absorbing material board with three matching layers.

[0071] 100g of GD414 silicone rubber, 10g of insulating carbon black powder with a particle size range of 5-50nm, and 400g of tetrahydrofuran solvent were ball-milled and mixed, then filtered to obtain a black slurry. The black slurry was loaded into a spray gun, and the nozzle diameter was controlled at 2mm. The slurry was atomized and sprayed from a distance of 0.5m from one side of the bismaleimide foam absorbing material board to form a porous blackened surface. After drying for 1 hour, the surface was heated to 180℃ in an oven for 30 minutes and held for 40 minutes to cure the black film. This atomization and curing process was repeated twice to obtain the blackened bismaleimide foam absorbing material board. The visible light reflectance of this bismaleimide foam absorbing material board is shown in the figure. Figure 13 The absorption performance in the 2–18 GHz wideband is shown below. Figure 10 This bismaleimide foam absorbing material plate possesses multi-spectral high-efficiency stealth capabilities in the 2-18 GHz microwave broadband and visible light bands. Further work can be carried out on the shape processing and assembly hole forming of the stealth plate to meet the requirements of satellite shape design and lightweighting.

[0072] Example 3

[0073] Using GD414 silicone rubber, 10mm thick bismaleimide foam absorbing material A, 13mm thick bismaleimide foam absorbing material C, and 10mm thick bismaleimide foam absorbing material E were bonded together in a top-to-bottom order. The mixture was then heated to 100℃ for 30 minutes and kept at that temperature for 30 minutes to cure, resulting in a 33mm thick bismaleimide foam absorbing material board with three matched layers.

[0074] 100g of GD414 silicone rubber, 10g of insulating carbon black powder with a particle size range of 5-50nm, and 400g of ethyl acetate solvent were ball-milled and mixed, then filtered to obtain a black slurry. The black slurry was loaded into a spray gun, with the nozzle diameter controlled at 3mm and the distance from one side surface of the bismaleimide foam absorbing material board at 0.6m. Two atomized spraying passes were performed to form a porous blackened surface. The mixture was then air-dried for 2 hours, followed by curing in an oven at 200℃ for 40 minutes after a 30-minute heating period. This process of atomization spraying and curing was repeated twice to obtain the blackened bismaleimide foam absorbing material board. The visible light reflectance of this bismaleimide foam absorbing material board is shown in the figure. Figure 14 The absorption performance in the 0.8–12 GHz wideband range is shown in [reference needed]. Figure 11 This bismaleimide foam absorbing material plate possesses multi-spectral high-efficiency stealth capabilities in the 0.8–12 GHz microwave broadband and visible light bands. Further work can be carried out on the shape processing and assembly hole forming of the stealth plate to meet the requirements of satellite shape design and lightweighting.

[0075] Example 4

[0076] Using GD414 silicone rubber, 4mm thick bismaleimide foam absorbing material A, 13mm thick bismaleimide foam absorbing material B, and 10mm thick bismaleimide foam absorbing material E are bonded together in a top-to-bottom order. The mixture is then heated to 100℃ for 30 minutes and kept at that temperature for 30 minutes to cure, resulting in a 27mm thick bismaleimide foam absorbing material board with three matching layers.

[0077] 100g of GD414 silicone rubber, 10g of insulating carbon black powder with a particle size range of 5-50nm, and 400g of ethyl acetate solvent were ball-milled and mixed, then filtered to obtain a black slurry. The black slurry was loaded into a spray gun, with the nozzle diameter controlled at 3mm and the distance from the bismaleimide foam absorbing material board at 0.6m. Two atomized spray coats were applied to form a porous blackened surface. The mixture was allowed to dry for 2 hours, then heated to 200℃ in an oven for 30 minutes and held for 40 minutes to cure the black film. This atomized spraying and curing process was repeated three times to obtain the blackened bismaleimide foam absorbing material board. The visible light reflectance of this bismaleimide foam absorbing material board is shown in the figure. Figure 15 The absorption performance in the 0.8–12 GHz wideband range is shown in [reference needed]. Figure 12 This bismaleimide foam absorbing material plate possesses multi-spectral high-efficiency stealth capabilities in the 0.8–12 GHz microwave broadband and visible light bands. Further work can be carried out on the shape processing and assembly hole forming of the stealth plate to meet the requirements of satellite shape design and lightweighting.

[0078] Comparative Example 1

[0079] Using GD414 silicone rubber, 10mm thick bismaleimide foam absorbing material A and 10mm thick bismaleimide foam absorbing material E are bonded together from top to bottom. The mixture is heated to 100℃ for 30 minutes and kept at that temperature for 20 minutes to cure, resulting in a 20mm thick bismaleimide foam absorbing material board with two matched layers.

[0080] The bismaleimide foam absorbing material board was not blackened; only its 2–18 GHz microwave broadband absorption performance was tested. Figure 16 Comparing Examples 1 and 2, it can be seen that although the total thickness of the bismaleimide foam absorbing material board is increased to 20mm, its broadband absorption performance is significantly inferior to that of the bismaleimide foam absorbing material board with a thickness of 15mm and 18mm, which is due to the fact that it is a two-layer matching combination. In other words, it is not conducive to lightweight broadband and efficient wave absorption.

[0081] Comparative Example 2

[0082] 700g of bismaleimide resin, 300g of curing agent DDM (4,4'-diaminodiphenylmethane), 35g of carbon nanotubes, 120g of sheet-like iron-silicon-aluminum (D50=70μm), and 30g of azobisisobutyronitrile foaming agent were mixed in a container and stirred continuously for 10 minutes until uniformly dispersed. The mixture was heated in an oil bath to 120℃ until it reached a fluid state. After holding at this temperature for 15 minutes (at which point the bismaleimide resin was moderately pre-crosslinked), the mixture was poured into a 450mm×450mm square mold. The mold cover was tightened with a 50mm limit screw to maintain the total height of the mold cavity. The mold was then placed in an oven preheated to 180℃ and heated to 240℃ for 30 minutes, then held at this temperature for 40 minutes to cure. After naturally cooling to room temperature, the mold was demolded, and the hardened outer layer on the surface of the foamed block was removed, yielding a density of 0.51g / cm³. 3 A 45mm thick bismaleimide foam absorbing material block I with a thermal conductivity of 0.43W / m·K was prepared and then cut into 10mm thick finished sheets.

[0083] 800g of bismaleimide resin, 200g of curing agent DDM (4,4'-diaminodiphenylmethane), 55g of carbon nanotubes, and sheet-like iron-silicon-aluminum (D... 50 Mix 360g of bismaleimide (70-80μm) and 30g of azobisisobutyronitrile (DIBON) foaming agent in a container and stir continuously for 15 minutes until evenly dispersed. Heat the mixture in an oil bath until the temperature reaches 130℃ and it is in a fluid state. After holding at this temperature for 20 minutes (at which point the bismaleimide resin is moderately pre-crosslinked), pour the mixture into a 450mm × 450mm square mold. Tighten the mold cover with the 50mm limit screws for the total height of the mold cavity. Then place the mold in an oven preheated to 180℃, heat to 260℃ for 30 minutes, and hold for 1 hour to cure. Allow it to cool naturally to room temperature, demold, and cut off the hardened skin on the surface of the foamed block to obtain a density of 1.89g / cm³. 3 A 42mm thick bismaleimide foam absorbing material block II with a thermal conductivity of 2.16W / m·K was prepared and then cut into 20mm thick finished sheets.

[0084] Using GD414 silicone rubber, 10mm thick bismaleimide foam absorbing material I and 20mm thick bismaleimide foam absorbing material II finished sheets are bonded together from top to bottom. The temperature is raised to 100℃ for 30 minutes and kept at that temperature for 30 minutes to cure, resulting in a 30mm thick bismaleimide foam absorbing material board with two matched layers.

[0085] The bismaleimide foam absorbing material board was not blackened; only its microwave broadband absorption performance from 0.8 to 12 GHz was tested. Figure 17Comparing Examples 3 and 4, it can be seen that the bismaleimide foam absorbing material board also has a wideband high-efficiency absorbing capability of 0.8-12GHz, and the "spiral coating" preparation process is reduced. However, the use of carbon nanotubes, especially sheet-like iron-silicon-aluminum magnetic absorbing agents, greatly increases the density and thermal conductivity of the material board. The bismaleimide foam absorbing material board cannot meet the requirements of lightweight, wideband, and high-efficiency absorbing capability to replace satellite heat shields.

[0086] The implementation results of Examples 1-4 demonstrate that, addressing the specific requirements of lightweight, broadband, multi-polarization, multi-angle, and multi-spectral stealth for satellites, this invention proposes a new optimized preparation method based on existing bismaleimide foam absorbing material manufacturing processes. This method utilizes only a small amount of carbon fiber of varying lengths as the absorbing agent to regulate broadband electromagnetic properties, combining foaming molding and multilayer impedance matching techniques to develop a highly heat-insulating, lightweight, broadband stealth bismaleimide foam absorbing material plate. A spiral coating process solves the multi-polarization and multi-angle stealth issues of the bismaleimide foam absorbing material plate; and an atomized spraying blackening process solves the optical stealth problem, thereby achieving multi-spectral stealth. Through these optimized preparation methods, a bismaleimide foam absorbing material plate suitable for satellite stealth applications has been developed.

Claims

1. A method for preparing a bismaleimide foam microwave absorbing material board, characterized in that: Using bismaleimide resin and its curing agent, carbon fiber and foaming agent as raw materials, a variety of bismaleimide foam absorbing material sheets with different broadband complex dielectric constants are prepared. The three bismaleimide foam absorbing material sheets with broadband complex dielectric constants are bonded together in order of increasing broadband complex dielectric constant to obtain a three-layer matched combination of bismaleimide foam absorbing material board. Then, a slurry of carbon black powder is sprayed onto one side surface of the bismaleimide foam absorbing material board to obtain a blackened bismaleimide foam absorbing material board. The method includes the following steps: (1) Mixing: The bismaleimide resin, curing agent DDM, carbon fiber, and foaming agent are mixed in the following weight percentages: 60~85wt% : 11.5~36.5wt% : 0.09~0.51wt% : 2.9-3.1wt%. (2) Prepolymerization: Heat the above-mentioned mixed raw materials to 120-130℃ and keep warm for 10-20 minutes; (3) Finalization: The prepolymerized fluid hot raw material is poured onto a polyimide plate. The carbon fiber orientation in the hot raw material is distributed in a spiral pattern by spiral coating. After spiral coating, the material is left to stand for 20-30 minutes. The material cools down, forms a thin sheet, and detaches from the polyimide plate, thus completing the shaping process. (4) Foaming: The pre-shaped raw material sheet is laid flat in the mold, and the mold is placed in an oven preheated to 180-200℃. The temperature is raised to 240-280℃ and kept at that temperature for 40-60 minutes to complete the curing. After natural cooling, the material is demolded to obtain a 40-60mm thick bismaleimide foam microwave absorbing material block. (5) Slicing: The hard skin on the surface of the bismaleimide foam absorbing material block was cut off, and the broadband complex permittivity of the bismaleimide foam absorbing material block after the hard skin was cut off was tested; the bismaleimide foam absorbing material block after the hard skin was cut off was cut into finished sheets with a thickness of 4-15mm. (6) Combination: By using carbon fibers of different lengths as raw materials and repeating the above operations, a variety of bismaleimide foam absorbing material sheets with different broadband complex dielectric constants and different thicknesses were prepared. Using GD414 silicone rubber suitable for the space environment, three kinds of bismaleimide foam absorbing material sheets with different broadband complex dielectric constants and different thicknesses are bonded together in order of increasing broadband complex dielectric constant. The temperature is raised to 80-100℃ and held for 20-30 minutes until fully cured to prepare a three-layer matched combination of bismaleimide foam absorbing material board, achieving broadband and efficient microwave absorption. (7) Darkening: GD414 silicone rubber, carbon black powder, and solvent are mixed in a weight percentage ratio of 15-25 wt% : 1-3 wt% : 72-82 wt% to obtain a carbon black powder slurry. The carbon black powder slurry is atomized and sprayed onto one side of a three-layer matched combination of bismaleimide foam absorbing material board. The nozzle diameter of the spray gun is controlled at 2-3 mm, and the distance from the bismaleimide foam absorbing material board is 0.4 m-0.6 m. After drying, it is kept at 180-200℃ for 30-40 minutes until the black film is completely cured. The atomized spraying of carbon black powder slurry and curing is repeated 1-3 times to obtain a blackened bismaleimide foam absorbing material board.

2. The method for preparing the bismaleimide foam absorbing material plate according to claim 1, characterized in that: The carbon fiber mentioned in step (1) has a length of 2-6 mm and a diameter of 5-8 μm; The foaming agent is one or more of azobisisobutyronitrile, diisopropyl azodicarbonate, and dinitrospentamethylenetetramine.

3. The method for preparing the bismaleimide foam absorbing material plate according to claim 1, characterized in that: The heating method described in step (2) is oil bath heating, with stirring during heating.

4. The method for preparing the bismaleimide foam absorbing material plate according to claim 1, characterized in that: The coating thickness described in step (3) is 1 to 3 mm.

5. The method for preparing the bismaleimide foam absorbing material plate according to claim 1, characterized in that: The reserved space of the mold in step (4) is 10 times the volume of the raw material sheet; the heating time is 30-40 minutes.

6. The method for preparing the bismaleimide foam absorbing material plate according to claim 1, characterized in that: The density of the bismaleimide foam absorber block after the hard outer layer is cut off in step (5) is 0.13–0.15 g / cm³. 3 The thermal conductivity is less than 0.06 W / m·K.

7. The method for preparing the bismaleimide foam absorbing material plate according to claim 1, characterized in that: The real part of the dielectric constant of the three different broadband complex dielectric constants mentioned in step (6) is 1 to 30 and the imaginary part is 0 to 15 in the frequency range of 0.75 to 18 GHz.

8. The method for preparing the bismaleimide foam absorbing material plate according to claim 1, characterized in that: The carbon black powder in step (7) has a particle size of 5-50 nm and is an electrically insulating powder; the solvent is one or more of ethyl acetate, n-butane and tetrahydrofuran.

9. A bismaleimide foam absorbing material board prepared by the preparation method of the bismaleimide foam absorbing material board according to any one of claims 1-8.

Images