A corrosion-resistant radar absorbing coating and a preparation method thereof

Abstract

The present invention provides a corrosion-resistant radar absorbing coating and its preparation method, belonging to the field of functional composite materials. The coating comprises a three-layer structure: a base layer, an intermediate layer, and a surface layer. The base layer is made of fluorinated polyurethane, modified FeSiCr, modified graphene microplatelets, zinc phosphate, and propylene glycol methyl ether acetate; the intermediate layer is made of fluorinated polyurethane, a mixture of modified FeSiCr and modified FeSiAl, hydroxyl-functionalized multi-walled carbon nanotubes, and propylene glycol methyl ether acetate; and the surface layer is made of UV-curable polyurethane, glass flakes, hydroxylated nano-boron nitride, a UV absorber, modified fumed silica, and propylene glycol methyl ether acetate. The present invention achieves broadband radar absorbing performance in the L / S / C bands through a gradient composite structure design. Furthermore, through component and structural optimization, the resulting coating exhibits excellent resistance to salt spray, UV radiation, and humidity and heat.

Description

Technical Field

[0001] The present invention relates to the technical field of functional composite materials, and in particular to a corrosion-resistant radar absorbing coating and a preparation method thereof. Background Art

[0002] Wind turbine equipment in marine environments (such as wind turbine towers, blades, and offshore platforms) reflects electromagnetic waves over a large area. Coating wind turbine towers and blades with absorbing materials can significantly reduce electromagnetic reflectivity in the L, S, and C bands. However, long-term exposure to extreme conditions such as high salt spray, high humidity, strong UV radiation, and heat and humidity cycles poses severe challenges to the material's corrosion resistance, weatherability, and functionality.

[0003] Currently, the application of traditional protective radar absorbing materials (RAM) in marine environments faces the following key issues: (1) Salt spray corrosion: Chloride ions in seawater penetrate the coating, accelerating the electrochemical corrosion of the metal substrate, causing blistering and peeling of the coating. (2) Ultraviolet aging: Long-term ultraviolet radiation causes degradation of the polymer matrix, manifesting as powdering, discoloration, and decreased mechanical properties of the coating.

[0004] At the same time, existing radar-absorbing coatings have narrow frequency coverage: single absorbers (such as FeSiAl) are only effective in specific frequency bands (such as the L / S band), making it difficult to cover the L / S / C broadband requirements (1-8 GHz). They also suffer from poor environmental adaptability: magnetic alloy powders (such as FeSiAl) are susceptible to oxidation, and carbon fibers are susceptible to galvanic corrosion in high-salt fog environments, leading to coating failure. Thick coatings and low efficiency: To achieve broadband absorption, traditional solutions require increased coating thickness (>4 mm) and rely on a thermal curing process (taking >4 hours), making them difficult to meet the rapid construction requirements of offshore applications.

[0005] Therefore, there is an urgent need for an absorbing coating that can achieve strong L / S / C broadband absorption and has strong salt spray resistance and corrosion resistance. Summary of the Invention

[0006] In light of this, the present invention aims to provide a corrosion-resistant radar absorbing coating and its preparation method. This coating utilizes FeSiCr / FeSiAl magnetic alloy powder as the core absorber, achieving broadband absorbing performance in the L / S / C bands through a gradient composite structure design. Furthermore, through optimized composition and structure, the resulting coating exhibits excellent resistance to salt spray, UV rays, and heat and humidity.

[0007] In order to achieve the above-mentioned objectives, the present invention provides the following technical solutions: One of the technical solutions of the present invention is a corrosion-resistant radar absorbing coating, which comprises a three-layer structure consisting of a base layer, an intermediate layer and a surface layer; the raw materials of the base layer are fluorinated polyurethane, modified FeSiCr, modified graphene microplatelets, zinc phosphate and propylene glycol methyl ether acetate; the raw materials of the intermediate layer are fluorinated polyurethane, a mixture of modified FeSiCr and modified FeSiAl, hydroxyl-functionalized multi-walled carbon nanotubes and propylene glycol methyl ether acetate; the raw materials of the surface layer are UV-cured polyurethane, glass flakes, hydroxylated nano-boron nitride, ultraviolet absorber, modified fumed silica and propylene glycol methyl ether acetate.

[0008] A second technical solution of the present invention is a method for preparing the above-mentioned corrosion-resistant radar absorbing coating, comprising the following steps:

[0009] The modified FeSiCr, modified graphene microsheets, zinc phosphate, propylene glycol methyl ether acetate and fluorinated polyurethane are uniformly mixed, applied to a substrate, and cured to obtain a bottom layer;

[0010] Mixing a mixture of modified FeSiCr and modified FeSiAl, hydroxyl-functionalized multi-walled carbon nanotubes, propylene glycol methyl ether acetate, and fluorinated polyurethane uniformly, coating the mixture on the surface of the bottom layer, and curing the mixture to obtain an intermediate layer;

[0011] Glass flakes, hydroxylated nano-boron nitride, ultraviolet absorber, modified fumed silica, propylene glycol methyl ether acetate and UV curing polyurethane are uniformly mixed, coated on the surface of the intermediate layer, and cured for 3 to obtain the radar absorbing coating.

[0012] The present invention discloses the following technical effects:

[0013] The present invention adopts a three-layer structure, with a gradient structure of a bottom layer (high FeSiCr content), an intermediate layer (FeSiCr / FeSiAl mixture), and a surface layer (protective / conductive layer). Through the synergistic effect of FeSiCr and FeSiAl, impedance gradient and L, S, and C wide-band absorption are achieved; at the same time, the surface layer not only plays an impedance transition role, but also enhances the weather resistance of the entire structure.

[0014] The alloy absorbent selected in the present invention has strong salt spray resistance and corrosion resistance. Fluorinated modified polyurethane (hydrolysis and salt spray resistance) is used, and nano-boron nitride (h-BN) is added to improve thermal conductivity. Glass flakes are introduced to extend the corrosion path, and ultraviolet absorbers are used to inhibit light aging, thereby comprehensively achieving enhanced weather resistance.

[0015] The bottom layer and the middle layer of the present invention adopt a spraying process, and the surface layer is UV-cured (completed within 60 seconds), which is suitable for on-site construction requirements at sea. DETAILED DESCRIPTION

[0016] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0017] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value within any stated value or stated range, and each smaller range between any other stated value or intermediate value within the stated range, is also encompassed within the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0018] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0019] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be exemplary only.

[0020] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0021] Unless otherwise specified, room temperature in the present invention refers to 25±5°C.

[0022] A first aspect of the present invention provides a corrosion-resistant radar absorbing coating, comprising a three-layer structure consisting of a base layer, an intermediate layer, and a surface layer; the base layer is made of fluorinated polyurethane, modified FeSiCr, modified graphene microplatelets, zinc phosphate, and propylene glycol methyl ether acetate; the intermediate layer is made of fluorinated polyurethane, a mixture of modified FeSiCr and modified FeSiAl, hydroxyl-functionalized multi-walled carbon nanotubes, and propylene glycol methyl ether acetate; and the surface layer is made of UV-cured polyurethane, glass flakes, hydroxylated nano-boron nitride, an ultraviolet absorber, modified fumed silica, and propylene glycol methyl ether acetate.

[0023] In a preferred embodiment of the present invention, the modified FeSiCr is FeSiCr modified by a silane coupling agent; the modified FeSiAl is FeSiAl modified by a silane coupling agent; the modified graphene microplatelets are graphene microplatelets modified by a silane coupling agent; the modified fumed silica is fumed silica that has been hydrophobically treated; and the silane coupling agent is silane coupling agent KH-550.

[0024] In the present invention, the preparation method of the modified FeSiCr is as follows: adding pretreated FeSiCr to a silane coupling agent (KH-550) aqueous solution for stirring reaction; the pretreatment is washing and drying; the concentration of the silane coupling agent aqueous solution is 1.0-2.0wt%; the mass volume ratio of the FeSiCr to the silane coupling agent aqueous solution is 1g:10mL; the stirring reaction temperature is 50°C, the time is 90min, and the rotation speed is 300rpm; after the stirring reaction is completed, the product is further washed and dried in sequence; the particle size of the FeSiCr is 2-5μm, and the morphology is irregular particles, which are spherical.

[0025] The preparation method of the modified FeSiAl comprises: adding pretreated FeSiAl to a silane coupling agent (KH-550) aqueous solution for stirring reaction; the pretreatment comprises washing and drying; the concentration of the silane coupling agent aqueous solution is 1.0-2.0 wt%; the mass volume ratio of the FeSiAl to the silane coupling agent aqueous solution is 1 g:10 mL; the stirring reaction is carried out at a temperature of 50° C., for 90 minutes, and at a rotation speed of 300 rpm; and after the stirring reaction is completed, the obtained product is sequentially washed and dried; the FeSiAl has a flake diameter of 1-3 μm and a flaky morphology.

[0026] The preparation method of the modified graphene microsheets comprises: adding graphene microsheets to a silane coupling agent (KH-550) aqueous solution and subjecting the mixture to a reflux reaction; the concentration of the silane coupling agent aqueous solution is 1.0-2.0wt%; the mass volume ratio of the graphene microsheets to the silane coupling agent aqueous solution is 1g:500mL; the reflux reaction is carried out at a temperature of 120°C, for a time of 4h, under an inert gas protective atmosphere; after the reflux reaction is completed, the steps of washing and drying the obtained product are further included; the thickness of the graphene microsheets is 2-5nm.

[0027] The modified fumed silica preparation method comprises: adding silica to a mixed solution of ethanol and water, performing ultrasonic treatment to obtain a mixture 1; adding a silane coupling agent (KH-550) to the mixture 1 for reaction 1, and then spray drying to obtain the modified fumed silica; the volume ratio of ethanol to water in the mixed solution of ethanol and water is 9:1; the silica accounts for 15-20 wt% of the mixed solution of ethanol and water; the ultrasonic treatment power is 500 W, and the time is 30 minutes; the silane coupling agent accounts for 10-25 wt% of the mass of the silica; the temperature of reaction 1 is 60° C., and the time is 3 hours; and the particle size of the modified fumed silica is 5-20 nm.

[0028] The preparation method of the hydroxyl-functionalized multi-walled carbon nanotubes is as follows: thinly spread multi-walled carbon nanotubes are treated with a 100W water vapor radio frequency discharge low-temperature plasma for 10-15 minutes to achieve hydroxyl functionalization; the particle size of the hydroxyl-functionalized multi-walled carbon nanotubes is 10-20nm and the length is 1-10μm.

[0029] The hydroxylated nano-boron nitride has a sheet diameter of 200 nm and a thickness of 5-20 nm.

[0030] In a preferred embodiment of the present invention, the bottom layer comprises, by mass percentage, 40% fluorinated polyurethane, 45% modified FeSiCr, 8% modified graphene microsheets, 3% zinc phosphate and the balance propylene glycol methyl ether acetate.

[0031] In a preferred embodiment of the present invention, in the mixture of modified FeSiCr and modified FeSiAl, the mass ratio of modified FeSiCr to modified FeSiAl is 3:(2-7).

[0032] Optionally, the mass ratio of the modified FeSiCr to the modified FeSiAl is 3:2, 3:3, 3:4, 3:5, 3:6, 3:7 or any value between the foregoing two ratios.

[0033] In a preferred embodiment of the present invention, the intermediate layer comprises, by mass percentage, 35% fluorinated polyurethane, 50% a mixture of modified FeSiCr and modified FeSiAl, 5% hydroxyl-functionalized multi-walled carbon nanotubes, and the balance propylene glycol methyl ether acetate.

[0034] In a preferred embodiment of the present invention, the surface layer comprises, by mass percentage, 45% UV-cured polyurethane, 25%-30% glass flakes, 15% hydroxylated nano-boron nitride, 5% ultraviolet absorber, 0.8% modified fumed silica and the balance propylene glycol methyl ether acetate.

[0035] In a preferred embodiment of the present invention, the thickness of the glass flakes is 1-3 μm; and the ultraviolet absorber is Tinuvin 1130.

[0036] In a preferred embodiment of the present invention, the thickness of the bottom layer is 1.8-2.0 mm, the thickness of the middle layer is 1.3-1.5 mm, and the thickness of the surface layer is 0.5 mm.

[0037] In a preferred embodiment of the present invention, the thickness of the bottom layer is 1.8 mm, the thickness of the middle layer is 1.5 mm, and the thickness of the surface layer is 0.5 mm.

[0038] In a preferred embodiment of the present invention, the thickness of the bottom layer is 1.9 mm, the thickness of the middle layer is 1.3 mm, and the thickness of the surface layer is 0.5 mm.

[0039] In a preferred embodiment of the present invention, the thickness of the bottom layer is 2.0 mm, the thickness of the middle layer is 1.5 mm, and the thickness of the surface layer is 0.5 mm.

[0040] A second aspect of the present invention provides a method for preparing the above-mentioned corrosion-resistant radar absorbing coating, comprising the following steps:

[0041] The modified FeSiCr, modified graphene microsheets, zinc phosphate, propylene glycol methyl ether acetate and fluorinated polyurethane are uniformly mixed, applied to a substrate, and cured to obtain a bottom layer;

[0042] Mixing a mixture of modified FeSiCr and modified FeSiAl, hydroxyl-functionalized multi-walled carbon nanotubes, propylene glycol methyl ether acetate, and fluorinated polyurethane uniformly, coating the mixture on the surface of the bottom layer, and curing the mixture to obtain an intermediate layer;

[0043] Glass flakes, hydroxylated nano-boron nitride, ultraviolet absorber, modified fumed silica, propylene glycol methyl ether acetate and UV curing polyurethane are uniformly mixed, coated on the surface of the intermediate layer, and cured for 3 to obtain the radar absorbing coating.

[0044] In a preferred embodiment of the present invention, the parameters of the curing 1 are set as follows: curing at 50-60°C for 10-15 minutes; the parameters of the curing 2 are set as follows: curing at room temperature for 25-30 minutes; and the parameters of the curing 3 are set as follows: UV curing with a wavelength of 365 nm and an intensity of 80 mW / cm² for 30-60 seconds.

[0045] The present invention does not impose any particular limitation on the method for uniform mixing, and conventional technical means known to those skilled in the art may be used, such as stirring and ultrasound.

[0046] The present invention does not impose any particular limitation on the coating method, and conventional techniques used by those skilled in the art may be used, such as high-pressure spraying and roller coating.

[0047] Unless otherwise specified, the technical solutions described in the present invention are all conventional solutions in the field, and the reagents or raw materials used, unless otherwise specified, are purchased from commercial channels or have been disclosed.

[0048] In an embodiment of the present invention, the preparation method of the modified FeSiCr is as follows: 10 g of FeSiCr powder that has been ultrasonically cleaned with anhydrous ethanol is dried and placed in 100 mL of a 2.0 wt% KH550 aqueous solution, stirred at 300 rpm for 90 minutes under a heat preservation condition of 50°C, then filtered and rinsed once with 5 mL of anhydrous ethanol / g of powder, centrifuged to remove the residual liquid, and then dried at 80°C for 1 hour.

[0049] The preparation method of modified FeSiAl is as follows: 10g of FeSiAl powder that has been ultrasonically cleaned with anhydrous ethanol is dried and placed in 100mL of a 2.0wt% KH550 aqueous solution. The mixture is stirred at 300 rpm for 90 minutes at 50°C. The mixture is then filtered and rinsed once with 5mL of anhydrous ethanol / g of powder. The residual liquid is removed by centrifugation and then dried at 80°C for 1 hour.

[0050] The preparation method of modified graphene microsheets is as follows: 1 g of graphene microsheets is added to 500 mL of a 1.5 wt% KH550 aqueous solution, refluxed under nitrogen protection at 120°C for 4 hours, then washed with ethanol three times for 15 minutes each time, and finally dried at 60°C for 10 hours.

[0051] The preparation method of hydroxyl functionalized multi-walled carbon nanotubes is as follows: thinly spread multi-walled carbon nanotubes are treated with a water vapor radio frequency discharge low-temperature plasma with a power of 100W for 15 minutes to achieve hydroxyl functionalization.

[0052] The preparation method of modified fumed silica is as follows: 20 wt% of silica is placed in an alcohol-water solvent with an ethanol:water ratio of 9:1 (volume ratio), ultrasonically treated at a power of 500 W for 30 minutes, and then KH550 (accounting for 25 wt% of silica) is added. The reaction is carried out at 60°C for 3 hours, and then spray-dried to obtain the modified fumed silica.

[0053] The preparation method of hydroxylated nano-boron nitride is as follows: the nano-boron nitride is ultrasonically cleaned in ethanol for 30 minutes, vacuum dried at 80°C for 12 hours, and then thinly spread and treated with a water vapor radio frequency discharge low-temperature plasma with a power of 100W for 30 minutes. After the plasma is turned off, Ar gas is continuously introduced for 5 minutes.

[0054] In the embodiments of the present invention, the microwave reflection loss test complies with GJB 2038-94, using a vector network analyzer and the bow method; the salt spray test complies with ASTM B117, and the 0.1 Hz low-frequency impedance of the coating is tested using an electrochemical workstation; the UV aging test complies with ISO 11507, and the experiment is carried out using a box-type UV aging test chamber combined with a colorimeter; the humidity and heat cycle test complies with GJB150.9A, and the test is carried out using a high and low temperature humidity and heat test chamber.

[0055] In order to better understand the present invention, the content of the present invention is further illustrated below in conjunction with the examples, but the content of the present invention is not limited to the following examples. Example 1

[0056] The coating of this embodiment adopts a gradient three-layer absorbing coating structure, with a bottom layer thickness of 1.8 mm, a middle layer thickness of 1.5 mm, a surface layer thickness of 0.5 mm, and a total thickness of 3.8 mm. The corresponding formula of each layer is shown in Table 1.

[0057] Table 1 Corresponding components of each layer

[0058] ,

[0059] The steps for preparing the coating are as follows:

[0060] Bottom layer spraying: After uniformly mixing modified FeSiCr, modified graphene microsheets, zinc phosphate, propylene glycol methyl ether acetate and fluorinated polyurethane, spray them onto the substrate under high pressure and cure at 60°C for 10 minutes;

[0061] Intermediate layer spraying: a mixture of modified FeSiCr and modified FeSiAl, hydroxyl-functionalized multi-walled carbon nanotubes, propylene glycol methyl ether acetate, and fluorinated polyurethane were uniformly mixed, sprayed onto the bottom layer surface, and then cured at room temperature for 30 minutes;

[0062] Surface UV curing: Mix hydroxylated nano-boron nitride, glass flakes, Tinuvin 1130, modified fumed silica, propylene glycol methyl ether acetate, and UV-curable polyurethane, then roll-coat the surface of the intermediate layer. Then, cure with UV light at a wavelength of 365 nm and an intensity of 80 mW / cm² for 40 seconds.

[0063] The total curing time of this embodiment is less than 2 hours, which is suitable for on-site operation.

[0064] The obtained coating was tested for microwave reflection loss, corrosion resistance, and weather resistance. The results are as follows:

[0065] 1) Reflection loss (Table 2):

[0066] Table 2

[0067]

[0068] L-band (1-2GHz): Return loss is less than or equal to -10dB and the effective bandwidth is greater than or equal to 300MHz; S-band (2-4GHz): Return loss is less than or equal to -10dB and the effective bandwidth is greater than or equal to 800MHz; C-band (4-8GHz): Return loss is less than or equal to -10dB and the effective bandwidth is greater than or equal to 2.2GHz.

[0069] 2) Corrosion resistance:

[0070] Salt spray test (2000 h, ASTM B117): no blistering, no peeling, adhesion loss <3%;

[0071] Electrochemical impedance spectroscopy (EIS, 0.1 Hz): |Z| > 5×10 8 Ω·cm².

[0072] 3) Weather resistance:

[0073] UV aging (2500 h, ISO 11507): color difference ΔE < 1.2, no surface chalking;

[0074] Humidity and heat cycling (70℃ / 95% RH, 30 days): No delamination, adhesion ≥7 MPa. Example 2

[0075] The only difference from Example 1 is that the thickness of the bottom layer is 1.9 mm, the thickness of the middle layer is 1.3 mm, the thickness of the surface layer is 0.5 mm, the total thickness is 3.7 mm, the mass ratio of modified FeSiCr to modified FeSiAl is 3:7, the curing time during the spraying of the middle layer is 35 min, and the other steps and parameters are the same as those in Example 1.

[0076] The total curing time of this embodiment is less than 2 hours, which is suitable for on-site operation.

[0077] The obtained coating was tested for microwave reflection loss, corrosion resistance, and weather resistance. The results are as follows:

[0078] 1) Absorption performance (Table 3):

[0079] Table 3

[0080]

[0081] L-band (1-2GHz): Return loss is less than or equal to -10dB and the effective bandwidth is greater than or equal to 380MHz. S-band (2-4GHz): Return loss is less than or equal to -10dB and the effective bandwidth is greater than or equal to 800MHz.

[0082] 2) Corrosion resistance:

[0083] Salt spray test (2000 h, ASTM B117): Adhesion loss <2%, no blistering on the surface.

[0084] Electrochemical impedance spectroscopy (0.1 Hz): |Z| = 6×10 8 Ω·cm².

[0085] 3) Weather resistance:

[0086] UV aging (2500 h): color difference ΔE = 1.0, no surface chalking.

[0087] Moisture-heat cycle (30 days): Adhesion ≥7.5 MPa.

[0088] From the above results, it can be seen that increasing the FeSiAl ratio enhances the low-frequency absorption (RL in the L-band increases to -28 dB), but the high-frequency performance (C-band) decreases. Example 3

[0089] The only difference from Example 1 is that the thickness of the bottom layer is 2.0 mm, the thickness of the middle layer is 1.5 mm, the thickness of the surface layer is 0.5 mm, the total thickness is 4.0 mm, the mass percentage of glass flakes is 30%, the curing time in the surface layer UV curing is 60 minutes, and the other steps and parameters are the same as in Example 1.

[0090] The total curing time of this embodiment is less than 2 hours, which is suitable for on-site operation.

[0091] The obtained coating was tested for microwave reflection loss, corrosion resistance, and weather resistance. The results are as follows:

[0092] 1) Absorption performance (Table 4):

[0093] Table 4

[0094]

[0095] L-band (1-2GHz): Return loss is less than or equal to -10dB and the effective bandwidth is greater than or equal to 290MHz; S-band (2-4GHz): Return loss is less than or equal to -10dB and the effective bandwidth is greater than or equal to 900MHz; C-band (4-8GHz): Return loss is less than or equal to -10dB and the effective bandwidth is greater than or equal to 2.2GHz.

[0096] 2) Corrosion resistance enhancement results:

[0097] Salt spray test (2500 h, ASTM B117): Adhesion loss <1%, no corrosion penetration.

[0098] 3) Weathering resistance enhancement results:

[0099] UV aging (3000 h): ΔE = 0.8, surface gloss retention > 90%.

[0100] It can be seen from the above results that by increasing the proportion of glass flakes, the corrosion resistance and UV protection are significantly improved, but the absorption performance is slightly reduced.

[0101] Comparative Example 1

[0102] The coating of this comparative example is a single-layer structure with a coating thickness of 4.0 mm. The corresponding coating formulation is shown in Table 5.

[0103] Table 5

[0104]

[0105] The steps for preparing the coating are as follows:

[0106] Mix polyurethane, modified FeSiCr, modified fumed silica, and propylene glycol methyl ether acetate, spray onto the substrate under high pressure, and cure at 80°C for 2 hours. The application period is long (>4 hours).

[0107] The obtained coating was tested for microwave reflection loss and corrosion resistance. The results are as follows:

[0108] 1) Absorption performance: L-band: -9 dB @1.2 GHz (failed); S-band: -12 dB @2.8 GHz; C-band: -13 dB @5.5 GHz.

[0109] 2) Salt spray test (500 h, ASTM B117): Surface powdering and adhesion decreased by 40%.

[0110] It can be seen from the above results that the low-frequency performance is poor and the salt spray resistance is also poor.

[0111] Comparative Example 2

[0112] The only difference from Example 1 is that the surface layer is omitted, and other steps and parameters are the same as those in Example 1.

[0113] The total curing time of this comparative example is about 1 hour.

[0114] The obtained coating was tested for microwave reflection loss, corrosion resistance, and weather resistance. The results are as follows:

[0115] 1) Absorption performance (Table 6):

[0116] Table 6

[0117]

[0118] L-band (1-2 GHz): Return loss ≤ -10 dB, effective bandwidth ≥ 280 MHz; S-band (2-4 GHz): Return loss ≤ -10 dB, effective bandwidth ≥ 750 MHz; C-band (4-8 GHz): RL ≤ -10 dB, bandwidth only extends to 5.0 GHz. Due to the lack of a surface conductive layer and impedance transition structure, high-frequency absorption capacity is significantly reduced, and C-band performance does not meet standards.

[0119] 2) Corrosion resistance:

[0120] Salt spray test (2000 h, ASTM B117): The surface was slightly blistering and the adhesion loss was 8% (compared to <3% in Example 1);

[0121] Electrochemical impedance spectroscopy (0.1 Hz): |Z|=1×10 8 Ω·cm² (Compared with Example 1>5×10 8 Ω·cm²).

[0122] Due to the lack of glass flakes and nano-boron nitride on the surface, the corrosion path is shortened and the protective performance is greatly reduced.

[0123] 3) Weather resistance:

[0124] UV aging (2500 h): color difference ΔE = 2.5, slight surface powdering (Comparative Example 1: ΔE < 1.2);

[0125] Humidity and heat cycle (30 days): Adhesion dropped to 5 MPa (compared to ≥7 MPa in Example 1).

[0126] Due to the lack of UV absorber (Tinuvin 1130) and dense surface layer, weather resistance is significantly deteriorated.

[0127] Comparative Example 3

[0128] The coating of this comparative example adopts a gradient three-layer absorbing coating structure, with a middle layer thickness of 1.8 mm, a bottom layer thickness of 1.5 mm, a surface layer thickness of 0.5 mm, and a total thickness of 3.8 mm. The corresponding formula of each layer is shown in Table 7 (the difference from Example 1 is that the bottom layer of Example 1 is set as the middle layer, and the middle layer of Example 1 is set as the bottom layer).

[0129] Table 7 Corresponding components of each layer

[0130] ,

[0131] The steps for preparing the coating are as follows:

[0132] Bottom layer spraying: Mix the mixture of modified FeSiCr and modified FeSiAl, hydroxyl-functionalized multi-walled carbon nanotubes, propylene glycol methyl ether acetate and fluorinated polyurethane evenly, spray it onto the substrate surface and cure it at room temperature for 30 minutes;

[0133] Intermediate layer spraying: After uniformly mixing modified FeSiCr, modified graphene microsheets, zinc phosphate, propylene glycol methyl ether acetate and fluorinated polyurethane, spray them onto the bottom layer under high pressure and cure at 60°C for 10 minutes;

[0134] Surface UV curing: Mix hydroxylated nano-boron nitride, glass flakes, Tinuvin 1130, modified fumed silica, propylene glycol methyl ether acetate, and UV-curable polyurethane, then roll-coat the surface of the intermediate layer. Then, cure with UV light at a wavelength of 365 nm and an intensity of 80 mW / cm² for 40 seconds.

[0135] The obtained coating was tested for microwave reflection loss and corrosion resistance. The results are as follows:

[0136] Absorption performance (Table 8):

[0137] Table 8

[0138]

[0139] 2) Corrosion resistance:

[0140] Salt spray test (2000 h, ASTM B117): no blistering, adhesion loss 5%.

[0141] Electrochemical impedance spectroscopy (0.1 Hz): |Z| = 3×10 8 Ω·cm².

[0142] Comparative Example 4

[0143] The only difference from Example 1 is that in the bottom layer, the modified FeSiCr and modified graphene microsheets are replaced with unmodified FeSiCr and graphene microsheets, and the other steps and parameters are the same as those in Example 1.

[0144] The properties of the absorbing material obtained in this comparative example are shown in Table 9:

[0145] Table 9

[0146]

[0147] Comparative Example 5

[0148] The only difference from Example 1 is that in the surface layer, the hydroxylated nano-boron nitride is replaced by non-hydroxylated nano-boron nitride. Other steps and parameters are the same as those in Example 1.

[0149] The properties of the absorbing material obtained in this comparative example are shown in Table 10:

[0150] Table 10

[0151]

[0152] Comparative Example 6

[0153] The only difference from Example 1 is that the proportion of modified graphene microplatelets in the base layer was adjusted from 8% to 12%, and the modified FeSiCr content was adjusted from 45% to 41%. The other steps and parameters were the same as in Example 1. Sagging occurred during high-pressure spraying of the base layer. After curing at 60°C, the surface roughness was Ra = 3.8 μm (Ra < 1.5 μm in Example 1). The properties of the resulting absorbing material are shown in Table 11:

[0154] Table 11

[0155]

[0156] Comparative Example 7

[0157] The only difference from Example 1 is that the proportion of glass flakes in the surface layer was adjusted from 25% to 35%, and the proportion of hydroxylated nano-boron nitride was adjusted from 15% to 5%. All other steps and parameters were the same as in Example 1. The UV curing of the surface layer required an extension of 70 seconds (40 seconds in Example 1), and some areas remained incompletely cured. The properties of the resulting absorbing material are shown in Table 12:

[0158] Table 12

[0159]

[0160] Comparative Example 8

[0161] The only difference from Example 1 is that the mass ratio of modified FeSiCr to modified FeSiAl in the intermediate layer is adjusted from 6:4 to 8:2. All other steps and parameters are the same as in Example 1. After spraying, the intermediate layer is cured at room temperature for 30 minutes, and the coating hardness reaches 2H (the coating hardness in Example 1 is 3H). The properties of the resulting absorbing material are shown in Table 13:

[0162] Table 13

[0163]

[0164] Comparative Example 9

[0165] The only difference from Example 1 is that the mass ratio of modified FeSiCr to modified FeSiAl in the intermediate layer was adjusted from 6:4 to 2:8. All other steps and parameters were the same as in Example 1. Poor leveling was observed after spraying the intermediate layer, and the toughness of the cured coating decreased, with the elongation at break decreasing from 25% in Example 1 to 15%. The properties of the resulting absorbing material are shown in Table 14 below:

[0166] Table 14

[0167]

[0168] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A corrosion-resistant radar absorbing coating, characterized in that: The coating consists of a three-layer structure consisting of a bottom layer, an intermediate layer and a surface layer; the raw materials of the bottom layer are fluorinated polyurethane, modified FeSiCr, modified graphene microsheets, zinc phosphate and propylene glycol methyl ether acetate; the raw materials of the intermediate layer are fluorinated polyurethane, a mixture of modified FeSiCr and modified FeSiAl, hydroxyl-functionalized multi-walled carbon nanotubes and propylene glycol methyl ether acetate; the raw materials of the surface layer are UV-cured polyurethane, glass flakes, hydroxylated nano-boron nitride, ultraviolet absorber, modified fumed silica and propylene glycol methyl ether acetate; The modified FeSiCr is FeSiCr modified by a silane coupling agent; the modified FeSiAl is FeSiAl modified by a silane coupling agent; The modified graphene microsheets are graphene microsheets modified with a silane coupling agent; The modified fumed silica is fumed silica that has been hydrophobically treated; the silane coupling agent is silane coupling agent KH-550; Calculated by mass percentage, the bottom layer includes 40% fluorinated polyurethane, 45% modified FeSiCr, 8% modified graphene microsheets, 3% zinc phosphate and the balance propylene glycol methyl ether acetate; In the mixture of modified FeSiCr and modified FeSiAl, the mass ratio of modified FeSiCr to modified FeSiAl is 3:(2-7); The intermediate layer comprises, by mass percentage, 35% fluorinated polyurethane, 50% a mixture of modified FeSiCr and modified FeSiAl, 5% hydroxyl-functionalized multi-walled carbon nanotubes, and the balance propylene glycol methyl ether acetate; Calculated by mass percentage, the surface layer includes 45% UV-cured polyurethane, 25%-30% glass flakes, 15% hydroxylated nano-boron nitride, 5% ultraviolet absorber, 0.8% modified fumed silica and the balance propylene glycol methyl ether acetate.

2. The corrosion-resistant radar absorbing coating according to claim 1, characterized in that: The thickness of the glass flakes is 1-3 μm; the ultraviolet absorber is Tinuvin 1130.

3. The corrosion-resistant radar absorbing coating according to claim 1, characterized in that: The thickness of the bottom layer is 1.8-2.0 mm, the thickness of the middle layer is 1.3-1.5 mm, and the thickness of the surface layer is 0.5 mm.

4. A method for preparing the corrosion-resistant radar absorbing coating according to any one of claims 1 to 3, characterized in that: The following steps are involved: The modified FeSiCr, modified graphene microsheets, zinc phosphate, propylene glycol methyl ether acetate and fluorinated polyurethane are uniformly mixed, applied to a substrate, and cured to obtain a bottom layer; Mixing a mixture of modified FeSiCr and modified FeSiAl, hydroxyl-functionalized multi-walled carbon nanotubes, propylene glycol methyl ether acetate, and fluorinated polyurethane uniformly, coating the mixture on the surface of the bottom layer, and curing the mixture to obtain an intermediate layer; Glass flakes, hydroxylated nano-boron nitride, ultraviolet absorber, modified fumed silica, propylene glycol methyl ether acetate and UV curing polyurethane are uniformly mixed, coated on the surface of the intermediate layer, and cured for 3 to obtain the radar absorbing coating.

Images