Radar wave-absorbing coating for entrance and exit camouflage device

Abstract

The invention relates to the technical field of wave-absorbing coatings, and discloses a radar wave-absorbing coating for an entrance and exit camouflage device, the radar wave-absorbing coating comprises the following raw materials by mass: 100-120 parts of a waterborne polyurethane emulsion, 1-2 parts of graphene oxide, 0.5-1.5 parts of acetylene carbon black, 1.5-2 parts of a wave-absorbing filler, 0.5-1 part of a dispersant, 0.3-0.8 part of an antifoaming agent, and 0.2-0.5 part of an anti-settling agent. The radar wave-absorbing coating prepared by taking the waterborne polyurethane emulsion as a matrix and compounding the wave-absorbing filler, the acetylene carbon black, the graphene oxide, the defoaming agent and the wetting agent has better wave-absorbing performance and mechanical performance, and the wave-absorbing filler, the acetylene carbon black and the graphene oxide can construct a two-dimensional network structure to form multiple reflection and scattering paths, so that the propagation distance of electromagnetic waves is prolonged, and the service life of the radar wave-absorbing coating is prolonged. The energy dissipation efficiency is improved, and the wave-absorbing performance is improved.

Description

Technical Field

[0001] This invention relates to the field of radar-absorbing coating technology, and more specifically to a radar-absorbing coating for an entrance / exit camouflage device. Background Technology

[0002] Radar-absorbing coatings for entrance / exit camouflage devices are functional coatings used to reduce the likelihood of entrance / exit targets being detected by radar. They have the function of absorbing and scattering radar waves, thus weakening radar echoes and achieving camouflage purposes. The radar-absorbing materials in the coating can weaken or absorb the electromagnetic wave energy received on its surface, reducing electromagnetic interference. The radar-absorbing materials mainly include ferrites, carbon materials, and conductive polymers, and can be made into radar-absorbing coatings, radar-absorbing fabrics, radar-absorbing silicone, etc., which are widely used in radar absorption and military stealth technology, communication and electronic systems, etc. Radar absorbing coatings prepared by using waterborne polyurethane emulsion as the matrix and compounding acetylene black, graphene oxide, defoamer, and wetting agent have good absorption and mechanical properties, but the absorption performance of a single absorbing material for electromagnetic waves is limited. Summary of the Invention

[0003] Technical problems to be solved To address the shortcomings of existing technologies, this invention provides a radar-absorbing coating for entrance / exit camouflage devices, which solves the problem of limited electromagnetic wave absorption performance of single absorbing materials.

[0004] Technical solution To achieve the above objectives, the present invention provides the following technical solution: A radar-absorbing coating for an entrance / exit camouflage device comprises the following raw materials in parts by weight: 100-120 parts of waterborne polyurethane emulsion, 1-2 parts of graphene oxide, 0.5-1.5 parts of acetylene black, 1.5-2 parts of radar-absorbing filler, 0.5-1 part of dispersant, 0.3-0.8 parts of defoamer, and 0.2-0.5 parts of anti-settling agent; The microwave absorbing filler is obtained by synthesizing iron carbide composite nanoparticles on the surface of pretreated carbon fibers, and then reacting them with pyromellitic anhydride, 4,4'-diaminodiphenyl ether and triethylamine.

[0005] Furthermore, the microwave absorbing filler is specifically prepared by the following steps: A1. Add carbon fiber to nitric acid aqueous solution, stir and react, cool to room temperature, filter, wash and dry to obtain pretreated carbon fiber; A2. Add the pretreated carbon fiber to octanol and stir evenly. Add iron pentacarbonyl and stir evenly. Pour in oxygen and place in an ultrasonic water bath. React at 60-70℃ and 40-50kHz for 2-3 hours. Pour in oxygen and continue the reaction for 1-2 hours. Cool to room temperature, remove, wash and dry to obtain carbon fiber loaded with iron carbide composite nanoparticles. A3. Add pyromellitic anhydride and 4,4'-diaminodiphenyl ether to N,N-dimethylacetamide, stir evenly, purge with nitrogen, seal, place in an ice-water bath, and stir to form a viscous liquid. Place the viscous liquid in deionized water to form a precipitate. After the precipitate is dried, grind it into powder, add it to ethanol, stir evenly, add carbon fibers loaded with iron carbide composite nanoparticles and triethylamine, stir to react and form a gel. After freeze-drying the gel, obtain the microwave absorbing filler.

[0006] Furthermore, in the A1 reaction process described above, nitric acid is used to treat the carbon fiber, causing an oxidation reaction on the carbon fiber surface. This introduces a large number of carboxyl and hydroxyl functional groups onto the carbon fiber surface, resulting in pretreated carbon fiber, which enhances the interaction force between the carbon fiber and the iron carbide composite nanoparticles.

[0007] Furthermore, in the A2 reaction process described above, the pretreated carbon fibers and iron pentacarbonyl are mixed in octanol. The iron pentacarbonyl is treated with the aid of oxygen and then treated in an ultrasonic bath. When the ultrasound propagates in the octanol medium, it generates alternating high-pressure and low-pressure regions. In the low-pressure region, tiny bubbles that form rapidly in the octanol solvent collapse rapidly in the high-pressure region, generating strong local shock waves, microjets, and shear forces in the liquid. This causes the iron pentacarbonyl to decompose and decompose, releasing iron atoms, which then react with carbon or oxygen atoms on the surface of the pretreated carbon fibers. Iron carbide is generated on the surface of the carbon fibers as nucleation sites. Since the vapor pressure of iron pentacarbonyl is lower than that of the solvent octanol, the iron carbide continuously nucleates and crystallizes, forming iron carbide nanoparticles. Furthermore, the generated iron carbide nanoparticles continue to interact with oxygen, thereby forming a 6-10 nm thick ferrous oxide nanolayer on the iron carbide surface. This layer is coated on the iron carbide surface as an anti-corrosion layer. After the ferrous oxide is formed on the iron carbide surface, the hydroxyl functional groups on the surface can bind with the acid-treated carbon fibers through hydrogen bonds, allowing the iron carbide composite nanoparticles to be adsorbed on the carbon fiber surface, thus obtaining carbon fibers loaded with iron carbide composite nanoparticles.

[0008] Furthermore, in the A3 reaction process described above, in the organic solvent N,N-dimethylacetamide, the two anhydride groups in pyromellitic anhydride undergo a condensation reaction with the amino groups of 4,4'-diaminodiphenyl ether, and are linked together by amide bonds to form long-chain polyamic acid molecules, which serve as the aerogel framework. The carbon fibers loaded with iron carbide composite nanoparticles serve as the reinforcing phase and can be cross-linked with the carboxyl groups in the polyamic acid through chemical bonds to form a porous aerogel, which serves as a microwave absorbing filler.

[0009] Further, in step A1, the mass ratio of the carbon fiber to the nitric acid aqueous solution is (1-2):(70-80).

[0010] Further, in step A2, the mass ratio of the pretreated carbon fiber, octanol and pentacarbonyl iron is (1.5-2):(40-50):(2-3).

[0011] Further, in step A3, the mass ratio of pyromellitic anhydride, 4,4'-diaminodiphenyl ether, N,N-dimethylacetamide, ethanol, carbon fiber loaded with iron carbide composite nanoparticles, and triethylamine is (4.2-4.5):(4.5-4.8):(70-80):(90-110):(1-2):(1.1-1.3).

[0012] Furthermore, the defoamer is selected from any one of defoamer BYK-065, defoamer BYK-035, and defoamer BYK-071.

[0013] Furthermore, the anti-settling agent is a polyamide wax anti-settling agent.

[0014] Furthermore, the dispersant is selected from any one of BYK-163 dispersant, BYK-162 dispersant, and BYK0-180 dispersant.

[0015] Furthermore, the solid content of the aqueous polyurethane emulsion is 38-45%.

[0016] Furthermore, the graphene oxide sheet has a diameter of 2-3 μm.

[0017] Furthermore, the carbon content in the acetylene black is 99.6-99.7%.

[0018] Furthermore, a method for preparing a radar-absorbing coating for an entrance / exit camouflage device includes the following steps: Aqueous polyurethane emulsion, graphene oxide, acetylene black, microwave absorbing filler, and dispersant are mixed evenly, and then defoamer and anti-settling agent are added. The mixture is stirred at 50-60℃ and 600-800r / min for 40-60min to obtain radar absorbing coating.

[0019] Beneficial technical effects (1) In the technical solution of the present invention, carbon fiber is treated with nitric acid to introduce a large number of carboxyl and hydroxyl functional groups on the surface of carbon fiber, thereby increasing the force of carbon fiber on iron carbide composite nanoparticles and increasing the specific surface area of ​​carbon fiber, thereby increasing the area for receiving electromagnetic waves, improving the reflection efficiency of electromagnetic waves, providing electromagnetic loss medium, and completing the absorption of electromagnetic waves. In addition, carbon fiber has an excellent aspect ratio, which can absorb and weaken the energy generated by external forces and improve the mechanical properties of radar absorbing coating.

[0020] (2) In the technical solution of this invention, iron pentacarbonyl is treated with oxygen and then ultrasonically to form iron carbide nanoparticles. The generated iron carbide nanoparticles continue to interact with oxygen, thereby forming an iron oxide nanolayer on the surface of the iron carbide, thus forming iron carbide composite nanoparticles. On the one hand, the formed iron oxide nanolayer is coated on the surface of the iron carbide as an anti-corrosion layer to prevent the iron carbide as an iron-based absorbing material from being easily corroded, which would cause a decrease in its absorbing performance and improve its absorbing performance. Moreover, the formed iron oxide, as an electromagnetic loss type absorbing material, can absorb electromagnetic waves incident on the surface of the coating and convert them into heat energy, thereby achieving the absorption of electromagnetic waves. On the other hand, iron carbide can convert electromagnetic wave energy into heat energy for dissipation, and has good absorbing performance, which improves the absorbing performance of radar absorbing coatings. Furthermore, the formed iron carbide composite nanoparticles have a core-shell structure, which can serve as a buffer layer for absorbing coatings and improve the mechanical properties of absorbing coatings. During the formation of iron carbide composite nanoparticles, these nanoparticles can be deposited on the surface of carbon fibers. On one hand, the carbon fiber acts as a carrier, improving the dispersibility of the iron carbide composite nanoparticles and preventing them from agglomerating in the radar-absorbing coating, thus affecting its absorption performance. On the other hand, carbon fibers possess excellent electrical conductivity. The iron carbide composite nanoparticles coated with an electromagnetic loss medium can effectively absorb electromagnetic waves. Furthermore, electromagnetic waves passing through the iron carbide composite nanoparticles are reflected by the carbon fibers and re-enter the electromagnetic loss medium, further dissipating the electromagnetic waves and resulting in high absorption efficiency.

[0021] (3) In the technical solution of the present invention, pyromellitic anhydride and 4,4-diaminodiphenyl ether form a long chain of polyamic acid molecules as the aerogel skeleton, and carbon fibers loaded with iron carbide composite nanoparticles as the reinforcing phase to form a porous aerogel. This allows the carbon fibers loaded with iron carbide composite nanoparticles to form a cross-linked network structure inside the aerogel, which can effectively extend the propagation path of electromagnetic waves. Combined with the magnetic loss medium, it can realize the absorption and consumption of electromagnetic waves. Moreover, the cross-linked network structure inside the porous aerogel can also enhance the mechanical properties of the microwave absorbing coating.

[0022] (4) In the technical solution of the present invention, waterborne polyurethane emulsion is used as the matrix, and radar absorbing filler, acetylene black, graphene oxide, defoamer and wetting agent are compounded to prepare radar absorbing coating with good absorption performance and mechanical properties. The radar absorbing filler, acetylene black and graphene oxide construct a two-dimensional network structure to form multiple reflection and scattering paths, extend the electromagnetic wave propagation distance, improve energy dissipation efficiency and improve absorption performance. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] The raw materials used in the embodiments of this invention are shown below, and all reagents used are analytical grade.

[0025] The waterborne polyurethane emulsion has a solid content of 40%, is model number Guoshibang GG025, and originates from Jining Ribuluo Biotechnology Co., Ltd.

[0026] The defoamer is defoamer BYK-065, the antisettling agent is polyamide wax antisettling agent, and the dispersant is BYK-163 dispersant.

[0027] The graphene oxide sheet has a diameter of 2.5 μm.

[0028] The carbon content in acetylene black is 99.65%.

[0029] The carbon fiber diameter is 0.2 mm. m, length 10 m.

[0030] Example 1 A radar-absorbing coating for an entrance / exit camouflage device comprises the following raw materials in parts by weight: 100 parts of waterborne polyurethane emulsion, 1 part of graphene oxide, 0.5 parts of acetylene black, 1.5 parts of radar-absorbing filler, 0.5 parts of BYK-163 dispersant, 0.3 parts of defoamer BYK-065, and 0.2 parts of polyamide wax anti-settling agent; A method for preparing a radar-absorbing coating for an entrance / exit camouflage device includes the following steps: Waterborne polyurethane emulsion, graphene oxide, acetylene black, microwave absorbing filler, and BYK-163 dispersant are mixed evenly, and then defoamer BYK-065 and polyamide wax anti-settling agent are added. The mixture is stirred at 50℃ and 600r / min for 40min to obtain radar absorbing coating.

[0031] The microwave absorbing filler is prepared by the following steps: A1. Add carbon fiber to a 65% nitric acid aqueous solution, stir at 80°C for 30 min, cool to room temperature, filter, wash three times with deionized water, and dry in an oven at 80°C for 10 min to obtain pretreated carbon fiber; the mass ratio of carbon fiber to nitric acid aqueous solution is 1:70. A2. Add the pretreated carbon fiber to octanol and stir until homogeneous. Add iron pentacarbonyl and stir until homogeneous. Purge with oxygen and place in an ultrasonic water bath. React at 60℃ and 40kHz for 2 hours. Purge with oxygen and continue the reaction for 1 hour. Cool to room temperature, remove, wash three times with deionized water, and dry in a 70℃ oven for 10 minutes to obtain carbon fiber loaded with iron carbide composite nanoparticles. The mass ratio of pretreated carbon fiber, octanol and iron pentacarbonyl is 1.5:40:2. A3. Add pyromellitic anhydride and 4,4'-diaminodiphenyl ether to N,N-dimethylacetamide, stir evenly, purge with nitrogen, seal, and place in an ice-water bath at 0°C. Stir for 3 hours to form a viscous liquid. Place the viscous liquid in deionized water to form a precipitate. Dry the precipitate in a 70°C oven for 10 minutes, grind it into powder, and then add it to ethanol. Stir evenly, add carbon fibers loaded with iron carbide composite nanoparticles and triethylamine, and stir to react for 12 hours to form a gel. Freeze-dry the gel at -20°C for 24 hours to obtain the microwave absorbing filler. The mass ratio of pyromellitic anhydride, 4,4'-diaminodiphenyl ether, N,N-dimethylacetamide, ethanol, carbon fibers loaded with iron carbide composite nanoparticles, and triethylamine is 4.2:4.5:70:90:1:1.1.

[0032] Example 2 A radar-absorbing coating for an entrance / exit camouflage device comprises the following raw materials in parts by weight: 110 parts of waterborne polyurethane emulsion, 1.5 parts of graphene oxide, 1 part of acetylene black, 1.8 parts of radar-absorbing filler, 0.8 parts of BYK-163 dispersant, 0.6 parts of defoamer BYK-065, and 0.3 parts of polyamide wax anti-settling agent; A method for preparing a radar-absorbing coating for an entrance / exit camouflage device includes the following steps: Waterborne polyurethane emulsion, graphene oxide, acetylene black, microwave absorbing filler and BYK-163 dispersant are mixed evenly, and then defoamer BYK-065 and polyamide wax anti-settling agent are added. The mixture is stirred at 55℃ and 700r / min for 50min to obtain radar absorbing coating.

[0033] The microwave absorbing filler is prepared by the following steps: A1. Add carbon fiber to a 65% nitric acid aqueous solution, stir at 80°C for 30 min, cool to room temperature, filter, wash three times with deionized water, and dry in an oven at 80°C for 10 min to obtain pretreated carbon fiber; the mass ratio of carbon fiber to nitric acid aqueous solution is 1.5:75. A2. Add the pretreated carbon fibers to octanol and stir until homogeneous. Add iron pentacarbonyl and stir until homogeneous. Purge with oxygen and place in an ultrasonic water bath. React at 65℃ and 45kHz for 2.5h. Purge with oxygen and continue the reaction for 1.5h. Cool to room temperature, remove, wash three times with deionized water, and dry in a 70℃ oven for 10min to obtain carbon fibers loaded with iron carbide composite nanoparticles. The mass ratio of pretreated carbon fibers, octanol, and iron pentacarbonyl is 1.8:45:2.5. A3. Add pyromellitic anhydride and 4,4'-diaminodiphenyl ether to N,N-dimethylacetamide, stir evenly, purge with nitrogen, seal, and place in an ice-water bath at 0°C. Stir for 3 hours to form a viscous liquid. Place the viscous liquid in deionized water to form a precipitate. Dry the precipitate in a 70°C oven for 10 minutes, grind it into powder, and then add it to ethanol. Stir evenly, add carbon fibers loaded with iron carbide composite nanoparticles and triethylamine, and stir to react for 12 hours to form a gel. Freeze-dry the gel at -20°C for 24 hours to obtain the microwave absorbing filler. The mass ratio of pyromellitic anhydride, 4,4'-diaminodiphenyl ether, N,N-dimethylacetamide, ethanol, carbon fibers loaded with iron carbide composite nanoparticles, and triethylamine is 4.3:4.7:75:100:1.5:1.2.

[0034] Example 3 A radar-absorbing coating for an entrance / exit camouflage device comprises the following raw materials in parts by weight: 120 parts of waterborne polyurethane emulsion, 2 parts of graphene oxide, 1.5 parts of acetylene black, 2 parts of radar-absorbing filler, 1 part of BYK-163 dispersant, 0.8 parts of defoamer BYK-065, and 0.5 parts of polyamide wax anti-settling agent; A method for preparing a radar-absorbing coating for an entrance / exit camouflage device includes the following steps: Waterborne polyurethane emulsion, graphene oxide, acetylene black, microwave absorbing filler, and BYK-163 dispersant are mixed evenly, and then defoamer BYK-065 and polyamide wax anti-settling agent are added. The mixture is stirred at 60℃ and 800r / min for 60min to obtain radar absorbing coating.

[0035] The microwave absorbing filler is prepared by the following steps: A1. Add carbon fiber to a 65% nitric acid aqueous solution, stir at 80°C for 30 min, cool to room temperature, filter, wash three times with deionized water, and dry in an oven at 80°C for 10 min to obtain pretreated carbon fiber; the mass ratio of carbon fiber to nitric acid aqueous solution is 2:80. A2. Add the pretreated carbon fiber to octanol and stir until homogeneous. Add iron pentacarbonyl and stir until homogeneous. Purge with oxygen and place in an ultrasonic water bath. React at 70℃ and 50kHz for 3 hours. Purge with oxygen and continue the reaction for 2 hours. Cool to room temperature, remove, wash three times with deionized water, and dry in a 70℃ oven for 10 minutes to obtain carbon fiber loaded with iron carbide composite nanoparticles. The mass ratio of pretreated carbon fiber, octanol and iron pentacarbonyl is 2:50:3. A3. Add pyromellitic anhydride and 4,4'-diaminodiphenyl ether to N,N-dimethylacetamide, stir evenly, purge with nitrogen, seal, and place in an ice-water bath at 0°C. Stir for 3 hours to form a viscous liquid. Place the viscous liquid in deionized water to form a precipitate. Dry the precipitate in a 70°C oven for 10 minutes, grind it into powder, and then add it to ethanol. Stir evenly, add carbon fibers loaded with iron carbide composite nanoparticles and triethylamine, and stir to react for 12 hours to form a gel. Freeze-dry the gel at -20°C for 24 hours to obtain the microwave absorbing filler. The mass ratio of pyromellitic anhydride, 4,4'-diaminodiphenyl ether, N,N-dimethylacetamide, ethanol, carbon fibers loaded with iron carbide composite nanoparticles, and triethylamine is 4.5:4.8:80:110:2:1.3.

[0036] Comparative Example 1 The only difference between this comparative example and Example 3 is the preparation of the microwave absorbing filler, as detailed below: The microwave absorbing filler is prepared by the following steps: A1. Add carbon fiber to octanol and stir until homogeneous. Add iron pentacarbonyl and stir until homogeneous. Purge with oxygen and place in an ultrasonic water bath. React at 70℃ and 50kHz for 3 hours. Purge with oxygen and continue the reaction for 2 hours. Cool to room temperature, remove, wash three times with deionized water, and dry in a 70℃ oven for 10 minutes to obtain carbon fiber loaded with iron carbide composite nanoparticles. The mass ratio of carbon fiber, octanol and iron pentacarbonyl is 2:50:3. A2. Add pyromellitic anhydride and 4,4'-diaminodiphenyl ether to N,N-dimethylacetamide, stir evenly, purge with nitrogen, seal, and place in an ice-water bath at 0℃. Stir for 3 hours to form a viscous liquid. Place the viscous liquid in deionized water to form a precipitate. Dry the precipitate in an oven at 70℃ for 10 minutes, grind it into powder, and then add it to ethanol. Stir evenly, add carbon fibers loaded with iron carbide composite nanoparticles and triethylamine, and stir to react for 12 hours to form a gel. Freeze-dry the gel at -20℃ for 24 hours to obtain the microwave absorbing filler. The mass ratio of pyromellitic anhydride, 4,4'-diaminodiphenyl ether, N,N-dimethylacetamide, ethanol, carbon fibers loaded with iron carbide composite nanoparticles, and triethylamine is 4.5:4.8:80:110:2:1.3.

[0037] Comparative Example 2 The only difference between this comparative example and Example 3 is the preparation of the microwave absorbing filler, as detailed below: The microwave absorbing filler is prepared by the following steps: A1. Add carbon fiber to a 65% nitric acid aqueous solution, stir at 80°C for 30 min, cool to room temperature, filter, wash three times with deionized water, and dry in an oven at 80°C for 10 min to obtain pretreated carbon fiber; the mass ratio of carbon fiber to nitric acid aqueous solution is 2:80. A2. Add pyromellitic anhydride and 4,4'-diaminodiphenyl ether to N,N-dimethylacetamide, stir evenly, purge with nitrogen, seal, and place in an ice-water bath at 0℃. Stir for 3 hours to form a viscous liquid. Place the viscous liquid in deionized water to form a precipitate. Dry the precipitate in an oven at 70℃ for 10 minutes, grind it into powder, and then add it to ethanol. Stir evenly, add pretreated carbon fiber and triethylamine, and stir to react for 12 hours to form a gel. Freeze-dry the gel at -20℃ for 24 hours to obtain the microwave absorbing filler. The mass ratio of pyromellitic anhydride, 4,4'-diaminodiphenyl ether, N,N-dimethylacetamide, ethanol, pretreated carbon fiber, and triethylamine is 4.5:4.8:80:110:2:1.3.

[0038] Comparative Example 3 The only difference between this comparative example and Example 3 is the preparation of the microwave absorbing filler, as detailed below: The microwave absorbing filler is prepared by the following steps: A1. Add carbon fiber to a 65% nitric acid aqueous solution, stir at 80°C for 30 min, cool to room temperature, filter, wash three times with deionized water, and dry in an oven at 80°C for 10 min to obtain pretreated carbon fiber; the mass ratio of carbon fiber to nitric acid aqueous solution is 2:80. A2. Add the pretreated carbon fiber to octanol, stir evenly, add iron pentacarbonyl, stir evenly, introduce oxygen, place in an ultrasonic water bath, react at 70℃ and 50kHz for 3 hours, cool to room temperature, take out, wash 3 times with deionized water, and dry in an oven at 70℃ for 10 minutes to obtain carbon fiber loaded with iron carbide; the mass ratio of pretreated carbon fiber, octanol and iron pentacarbonyl is 2:50:3. A3. Add pyromellitic anhydride and 4,4'-diaminodiphenyl ether to N,N-dimethylacetamide, stir evenly, purge with nitrogen, seal, and place in an ice-water bath at 0°C. Stir for 3 hours to form a viscous liquid. Place the viscous liquid in deionized water to form a precipitate. Dry the precipitate in an oven at 70°C for 10 minutes, grind it into powder, and then add it to ethanol. Stir evenly, add carbon fibers loaded with iron carbide and triethylamine, and stir to react for 12 hours to form a gel. Freeze-dry the gel at -20°C for 24 hours to obtain the microwave absorbing filler. The mass ratio of pyromellitic anhydride, 4,4'-diaminodiphenyl ether, N,N-dimethylacetamide, ethanol, carbon fibers loaded with iron carbide, and triethylamine is 4.5:4.8:80:110:2:1.3.

[0039] Comparative Example 4 The only difference between this comparative example and Example 3 is the preparation of the microwave absorbing filler, as detailed below: The microwave absorbing filler is prepared by the following steps: A1. Add carbon fiber to a 65% nitric acid aqueous solution, stir at 80°C for 30 min, cool to room temperature, filter, wash three times with deionized water, and dry in an oven at 80°C for 10 min to obtain pretreated carbon fiber; the mass ratio of carbon fiber to nitric acid aqueous solution is 2:80. A2. Add the pretreated carbon fiber to octanol and stir until homogeneous. Add iron pentacarbonyl and stir until homogeneous. Purge with oxygen and place in an ultrasonic water bath. React at 70℃ and 50kHz for 3 hours. Purge with oxygen and continue the reaction for 2 hours. Cool to room temperature, remove, wash three times with deionized water, and dry in a 70℃ oven for 10 minutes to obtain carbon fiber loaded with iron carbide composite nanoparticles. The mass ratio of pretreated carbon fiber, octanol and iron pentacarbonyl is 2:50:3. A3. Add 4,4'-diaminodiphenyl ether to N,N-dimethylacetamide, stir evenly, purge with nitrogen, seal, place in an ice-water bath at 0℃, stir for 3 hours, place in deionized water to form a precipitate, dry the precipitate in a 70℃ oven for 10 minutes, grind into powder, add to ethanol, stir evenly, add carbon fiber loaded with iron carbide composite nanoparticles and triethylamine, stir to react for 12 hours, freeze dry at -20℃ for 24 hours to obtain microwave absorbing filler; the mass ratio of 4,4'-diaminodiphenyl ether, N,N-dimethylacetamide, ethanol, carbon fiber loaded with iron carbide composite nanoparticles and triethylamine is 9.3:80:110:2:1.3.

[0040] Comparative Example 5 The only difference between this comparative example and Example 3 is the preparation of the microwave absorbing filler, as detailed below: The microwave absorbing filler is prepared by the following steps: A1. Add carbon fiber to a 65% nitric acid aqueous solution, stir at 80°C for 30 min, cool to room temperature, filter, wash three times with deionized water, and dry in an oven at 80°C for 10 min to obtain pretreated carbon fiber; the mass ratio of carbon fiber to nitric acid aqueous solution is 2:80. A2. Add the pretreated carbon fiber to octanol and stir until homogeneous. Add iron pentacarbonyl and stir until homogeneous. Purge with oxygen and place in an ultrasonic water bath. React at 70℃ and 50kHz for 3 hours. Purge with oxygen and continue the reaction for 2 hours. Cool to room temperature, remove, wash three times with deionized water, and dry in a 70℃ oven for 10 minutes to obtain carbon fiber loaded with iron carbide composite nanoparticles. The mass ratio of pretreated carbon fiber, octanol and iron pentacarbonyl is 2:50:3. A3. Add pyromellitic anhydride to N,N-dimethylacetamide, stir evenly, purge with nitrogen, seal, place in an ice-water bath at 0℃, stir for 3 hours, place in deionized water to form a precipitate, dry the precipitate in a 70℃ oven for 10 minutes, grind into powder, add to ethanol, stir evenly, add carbon fiber loaded with iron carbide composite nanoparticles and triethylamine, stir to react for 12 hours, freeze dry at -20℃ for 24 hours to obtain microwave absorbing filler; the mass ratio of pyromellitic anhydride, N,N-dimethylacetamide, ethanol, carbon fiber loaded with iron carbide composite nanoparticles and triethylamine is 9.3:80:110:2:1.3.

[0041] The performance of the radar absorbing coatings prepared in Examples 1-3 and Comparative Examples 1-5 will now be tested. The specific test methods are as follows: The radar-absorbing coating prepared above was applied to the surface of tinplate and baked at 80°C for 6 hours to form a coating with a thickness of 2 mm and a surface density of 4 kg / m³. 2 Using a vector network analyzer, and in accordance with the GJB2038A-2011 standard "Test Method for Reflectivity of Radar Absorbing Materials", the bow-shaped method was used to test the reflection loss and absorption performance of the coating, with a test frequency range of 2-18 GHz.

[0042] Tensile properties were tested according to GB / T528-2009 standard.

[0043] The specific results of the stability test are shown in Table 1.

[0044] Table 1 Performance testing of radar absorbing coatings prepared in Examples 1-3 and Comparative Examples 1-5

[0045] As shown in Table 1, the radar absorbing coatings of all embodiments outperform the reference product, and the prepared radar absorbing coatings possess superior absorption and mechanical properties. This fully demonstrates the effectiveness of the radar absorbing coating provided by this invention.

[0046] Comparative Example 1 replaced the pretreated carbon fiber with a carbon fiber-based absorber added to the radar absorbing coating. The absorption performance and mechanical properties of the coating decreased, demonstrating that introducing a large number of carboxyl and hydroxyl functional groups on the carbon fiber surface enhances the interaction force between the carbon fiber and the iron carbide composite nanoparticles, increases the specific surface area of ​​the carbon fiber, thereby increasing the area for receiving electromagnetic waves, improving the reflection efficiency of electromagnetic waves, providing an electromagnetic loss medium, and completing the absorption of electromagnetic waves. In addition, carbon fiber has an excellent aspect ratio, which can absorb and reduce the energy generated by external forces, thus improving the mechanical properties of the radar absorbing coating.

[0047] Comparative Example 2 replaced the carbon fibers loaded with iron carbide composite nanoparticles with a microwave absorbing filler prepared from pretreated carbon fibers and added it to the radar absorbing coating. Its microwave absorption performance and mechanical properties decreased, proving that the formation of iron carbide composite nanoparticles on the carbon fiber surface, as an electromagnetic loss type microwave absorbing material, can absorb electromagnetic waves incident on the coating surface and convert them into heat energy, thus achieving the absorption of electromagnetic waves. Moreover, the iron carbide composite nanoparticles can convert electromagnetic wave energy into heat energy dissipation, exhibiting good microwave absorption performance and improving the microwave absorption performance of the radar absorbing coating. In addition, the formed iron carbide composite nanoparticles have a core-shell structure, which can serve as a buffer layer for the microwave absorbing coating, improving the mechanical properties of the microwave absorbing coating.

[0048] In Comparative Example 3, the microwave absorbing filler prepared in step A2 without the introduction of oxygen was added to the radar absorbing coating. Its microwave absorption performance and mechanical properties decreased, proving that iron pentacarbonyl, with the help of oxygen and then treated by ultrasonic bath, forms iron carbide nanoparticles. The generated iron carbide nanoparticles continue to interact with oxygen, thereby forming a ferrous oxide nanolayer on the surface of the iron carbide. This serves as an anti-corrosion layer to prevent the iron carbide, as an iron-based microwave absorbing material, from being easily corroded, which would cause a decrease in microwave absorption performance and improve the microwave absorption performance. Furthermore, the formed ferrous oxide, as an electromagnetic loss type microwave absorbing material, can absorb electromagnetic waves incident on the surface of the coating and convert them into heat energy, thus achieving the absorption of electromagnetic waves.

[0049] Comparative Example 4, in which pyromellitic anhydride was replaced by 4,4'-diaminodiphenyl ether by mass, and Comparative Example 5, in which 4,4'-diaminodiphenyl ether was replaced by pyromellitic anhydride by mass, were added to radar absorbing coatings. The absorption performance and mechanical properties of these coatings decreased, demonstrating that pyromellitic anhydride and 4,4'-diaminodiphenyl ether form long-chain polyamic acid molecules, which serve as the aerogel framework. The carbon fibers loaded with iron carbide composite nanoparticles act as the reinforcing phase, forming a porous aerogel. This allows the carbon fibers loaded with iron carbide composite nanoparticles to form a cross-linked network structure inside the aerogel, which can effectively extend the electromagnetic wave propagation path. Combined with the magnetic loss medium, this achieves the absorption and consumption of electromagnetic waves. Furthermore, the cross-linked network structure inside the porous aerogel also enhances the mechanical properties of the radar absorbing coating.

[0050] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0051] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

[0052] Those skilled in the art should understand that the above descriptions are merely several specific embodiments of the present invention, and not all embodiments.

Claims

1. A radar-absorbing coating for an entrance / exit camouflage device, characterized in that, The raw materials include the following parts by weight: 100-120 parts of waterborne polyurethane emulsion, 1-2 parts of graphene oxide, 0.5-1.5 parts of acetylene black, 1.5-2 parts of microwave absorbing filler, 0.5-1 part of dispersant, 0.3-0.8 parts of defoamer, and 0.2-0.5 parts of anti-settling agent; The microwave absorbing filler is obtained by synthesizing iron carbide composite nanoparticles on the surface of pretreated carbon fibers, and then reacting them with pyromellitic anhydride, 4,4'-diaminodiphenyl ether and triethylamine.

2. The radar-absorbing coating for an entrance / exit camouflage device according to claim 1, characterized in that, The microwave absorbing filler is specifically prepared by the following steps: A1. Add carbon fiber to nitric acid aqueous solution, stir and react, cool to room temperature, filter, wash and dry to obtain pretreated carbon fiber; A2. Add the pretreated carbon fiber to octanol and stir evenly. Add iron pentacarbonyl and stir evenly. Pour in oxygen and place in an ultrasonic water bath. React at 60-70℃ and 40-50kHz for 2-3 hours. Pour in oxygen and continue the reaction for 1-2 hours. Cool to room temperature, remove, wash and dry to obtain carbon fiber loaded with iron carbide composite nanoparticles. A3. Add pyromellitic anhydride and 4,4'-diaminodiphenyl ether to N,N-dimethylacetamide, stir evenly, purge with nitrogen, seal, place in an ice-water bath, and stir to form a viscous liquid. Place the viscous liquid in deionized water to form a precipitate. After the precipitate is dried, grind it into powder, add it to ethanol, stir evenly, add carbon fibers loaded with iron carbide composite nanoparticles and triethylamine, stir to react and form a gel. After freeze-drying the gel, obtain the microwave absorbing filler.

3. The radar-absorbing coating for an entrance / exit camouflage device according to claim 2, characterized in that, In step A1, the mass ratio of the carbon fiber to the nitric acid aqueous solution is (1-2):(70-80).

4. The radar-absorbing coating for an entrance / exit camouflage device according to claim 2, characterized in that, In step A2, the mass ratio of the pretreated carbon fiber, octanol and pentacarbonyl iron is (1.5-2):(40-50):(2-3).

5. The radar-absorbing coating for an entrance / exit camouflage device according to claim 2, characterized in that, In step A3, the mass ratio of pyromellitic anhydride, 4,4'-diaminodiphenyl ether, N,N-dimethylacetamide, ethanol, carbon fiber loaded with iron carbide composite nanoparticles, and triethylamine is (4.2-4.5):(4.5-4.8):(70-80):(90-110):(1-2):(1.1-1.3).

6. The radar-absorbing coating for an entrance / exit camouflage device according to claim 1, characterized in that, The defoamer is selected from any one of defoamer BYK-065, defoamer BYK-035, and defoamer BYK-071.

7. The radar-absorbing coating for an entrance / exit camouflage device according to claim 1, characterized in that, The anti-settling agent is a polyamide wax anti-settling agent.

8. The radar-absorbing coating for an entrance / exit camouflage device according to claim 1, characterized in that, The dispersant is selected from any one of BYK-163 dispersant, BYK-162 dispersant, and BYK0-180 dispersant.

9. The radar-absorbing coating for an entrance / exit camouflage device according to claim 1, characterized in that, The solid content of the waterborne polyurethane emulsion is 38-45%; The graphene oxide sheets have a diameter of 2-3 μm; The carbon content in the acetylene black is 99.6-99.7%.

10. The radar-absorbing coating for an entrance / exit camouflage device according to claim 1, characterized in that, The preparation method of the radar absorbing coating includes the following steps: Aqueous polyurethane emulsion, graphene oxide, acetylene black, microwave absorbing filler, and dispersant are mixed evenly, and then defoamer and anti-settling agent are added. The mixture is stirred at 50-60℃ and 600-800r / min for 40-60min to obtain radar absorbing coating.

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