Multiband compatible stealth and camouflage integrated material and preparation method thereof

Abstract

The invention provides a multiband compatible stealth and camouflage integrated material and a preparation method thereof, and belongs to the technical field of functional stealth materials, and a composite coating comprises a primer layer, a conductive layer, a first electromagnetic coating layer, a second electromagnetic coating layer, a finish paint layer and a low infrared emissivity layer which are sequentially arranged on the surface of a base material. An electromagnetic coating with flaky magnetically soft alloy as a filler is adopted, gradient transition of electromagnetic parameters is formed in the thickness direction and magnetic loss and interface polarization loss are enhanced by regulating and controlling the morphology and the filling proportion of the magnetically soft alloy, broadband radar wave absorption from the X-Ka wave band is achieved under the limited thickness, and the broadband radar wave absorption rate is increased. Stable radar cross section reduction performance is maintained under the condition of a large incident angle; and the low infrared emissivity layer is used for reducing infrared radiation characteristics and realizing visible light camouflage, so that multiband compatible stealth is realized. Through collaborative design of a multi-layer structure and a multi-time thin coating film forming process, the coating has excellent interlayer binding force, mechanical property and environmental durability, and the total thickness is controlled within a small range.

Description

Technical Field

[0001] This invention relates to the field of functional materials technology, specifically to a multi-band wide-angle ultrathin stealth composite coating and its preparation method. Background Technology

[0002] Stealth technology is one of the key technologies for modern weaponry to enhance battlefield survivability in the face of reconnaissance, guidance, and fire control systems. With the continuous development of detection and countermeasures, battlefield detection methods include visible light imaging reconnaissance, infrared imaging and infrared search and track (IRST), and multi-mode, multi-band radar detection (such as air / ground surveillance radar, imaging radar, airborne or spaceborne side-looking synthetic aperture radar SAR, etc.). Under these conditions, if equipment only implements stealth in a single spectral band, it may still be exposed in other spectral bands, making it difficult to meet comprehensive stealth requirements.

[0003] In radar stealth, radar-absorbing coatings (RAMs) typically dissipate electromagnetic energy through mechanisms such as dielectric loss, magnetic loss, eddy current loss, and interface polarization, and achieve impedance matching through structural design to reduce reflection and weaken the radar cross section (RCS). With the expansion of radar frequencies and the increasing application of imaging radar, radar-absorbing coatings need to maintain effective absorption over a wider frequency band (e.g., X to Ka) and maintain stable performance under large incident angles to adapt to large-angle illumination scenarios such as side-looking SAR. Simultaneously, engineering applications require coatings to possess good adhesion, flexibility, impact resistance, and environmental adaptability to high and low temperatures, humidity, salt spray, and solar radiation, while also considering thickness, areal density, and ease of construction and maintenance. Infrared stealth typically reduces infrared radiation signature through low-emissivity materials; visible light camouflage mainly relies on color and pattern matching with the environment.

[0004] In existing technologies, to achieve multi-spectral compatible stealth, a multi-layer stacked composite coating structure is often used, which involves sequentially setting different functional layers such as a conductive loss layer / absorbing layer, an infrared modulation layer, and a camouflage surface layer on the surface of a substrate. For example, patent CN202510201697.7 discloses a type of radar-infrared multi-spectral compatible stealth composite material and its preparation method, which uses a multi-layer structure to achieve the superposition of different functional layers (but is not limited to this approach).

[0005] However, the above-mentioned scheme, which is mainly characterized by simple physical stacking, still has the following shortcomings in practical applications: (1) Poor matching of electromagnetic parameters and thermal properties of different functional layers can easily lead to impedance mismatch, making it difficult to achieve both wideband and ultrathin thickness within a limited thickness. (2) Absorption performance is easily significantly attenuated under large incident angle conditions, making it difficult to adapt to large-angle detection scenarios such as side-looking SAR. Furthermore, the interlayer interface bonding is insufficient, limiting environmental durability. (3) The multilayer stacking results in a large coating thickness and surface density, limiting its engineering application on shape and weight-sensitive platforms.

[0006] In summary, while multi-layer stacking is a straightforward path to achieving multi-spectral stealth, existing technologies generally suffer from poor performance synergy, insufficient environmental durability, and excessive thickness and weight. The root cause lies in the lack of cross-scale, integrated, and collaborative design encompassing electromagnetics, thermodynamics, materials mechanics, and manufacturing processes. Therefore, there is an urgent need to invent a novel multi-layer composite coating solution that can achieve highly efficient stealth capabilities across visible light, infrared, and broadband radar waves while remaining ultra-thin (e.g., <1.5mm), and possess excellent interlayer bonding, environmental durability, and broad substrate adaptability, thereby truly meeting the practical requirements of next-generation weaponry. Summary of the Invention

[0007] In view of the above problems, the present invention provides a multi-band compatible stealth and camouflage integrated material and its preparation method, so as to solve the following technical problems existing in the current multi-spectral stealth coatings: (1) The problem of simultaneously achieving broadband radar stealth and infrared and visible light camouflage under limited thickness conditions; (2) The absorption performance is sensitive to the incident angle, and the stealth performance is significantly reduced under large incident angle conditions; (3) Insufficient interlayer bonding strength of multilayer coatings leads to limited mechanical properties and environmental durability; (4) Engineering applicability issues caused by excessive coating thickness and areal density to meet multi-spectral performance requirements.

[0008] This invention provides a method for preparing a multi-band compatible stealth and camouflage integrated material, comprising: Step 1. Grind the iron-based soft magnetic alloy to obtain sheet-like soft magnetic alloy powder; Step 2. Add the solvent to the dispersion container, premix it with the surfactant and dispersant, then add the flake soft magnetic alloy powder for primary dispersion, then add the anti-settling agent for secondary dispersion, and finally add the two-component modified epoxy resin and mix it evenly. Vacuum degassing is performed to obtain the first electromagnetic coating and the second electromagnetic coating. Step 3 involves pretreating the composite substrate to be coated to obtain a pretreated substrate. Step 4. On the surface of the pretreated substrate, a primer layer, a conductive layer, a first electromagnetic coating, a second electromagnetic coating, a topcoat layer, and a low infrared emissivity layer are sprayed sequentially to obtain a coating system. Step 5. Curing the coating system to obtain an integrated material that is compatible with stealth and camouflage.

[0009] Optionally, the particle size of the sheet-like soft magnetic alloy powder is 5-50 μm, and the aspect ratio is 0.05-0.3.

[0010] Optionally, the ratio of the rotational speeds of the primary dispersion to the secondary dispersion is 5-15:4-10; The ratio of the time spent in the first dispersion to the time spent in the second dispersion is 2-12:1-6.

[0011] Optionally, the anti-settling agent is organic modified bentonite, silica, modified silicate thixotropic agent, organic wax anti-settling agent and / or polyamide wax anti-settling agent.

[0012] Optionally, the surfactant is a nonionic surfactant, a silicone-modified nonionic surfactant, and / or a weakly polar surfactant.

[0013] Optionally, in the first electromagnetic coating, the volume fraction ratio of the flake soft magnetic alloy powder, the two-component modified epoxy resin, the dispersant, the additives and the solvent is: 50-60:35-45:1-1.5:1.3-2:2. Optionally, in the second electromagnetic coating, the volume fraction ratio of the flake soft magnetic alloy powder, the two-component modified epoxy resin, the dispersant, the additives and the solvent is: 60-66:31-37:0.9-1:1.2-1.5:0.9-1.

[0014] Optionally, the aspect ratio of the first electromagnetic coating is 0.05-0.1; the aspect ratio of the second electromagnetic coating is 0.1-0.15. The thickness of the low infrared emissivity layer is 3-14 μm.

[0015] The second objective of this invention is to provide a multi-band compatible stealth and camouflage integrated material, which includes a primer layer, a conductive layer, a first electromagnetic coating layer, a second electromagnetic coating layer, a topcoat layer, and a low infrared emissivity layer. The total dry film thickness of the integrated material compatible with stealth and camouflage is <1.2 mm; The electromagnetic response of the integrated material, which is compatible with stealth and camouflage, is in the X-Ka band.

[0016] Compared with the prior art, the present invention has at least the following beneficial effects: (1) By using sheet-like soft magnetic alloy high solid filler and conductive layer-double absorbing layer in synergistic design, broadband radar stealth in the X to Ka bands is achieved under ultra-thin conditions, and stable RCS reduction performance is maintained in the range of large incident angles. (2) By combining a low infrared emissivity camouflage layer with a surface optical camouflage layer, multi-spectral compatible stealth with radar, infrared and visible light can be achieved; (3) By using multi-layer structure synergy and multiple thin coating processes, the total coating thickness is controlled within a small range while ensuring mechanical properties and environmental durability; (4) It is applicable to a variety of substrates such as metals, alloys and composite materials. The construction process is simple and it has good engineering application value. Attached Figure Description

[0017] The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of the invention.

[0018] Figure 1 This is a schematic diagram of an ultra-thin stealth composite coating product in an embodiment of the present invention; Figure 2 This is a schematic diagram of the multilayer coating structure in an embodiment of the present invention; Figure 3 This is a schematic diagram illustrating the formation of a sheet-like structure with obvious anisotropic characteristics in soft magnetic alloy powder in an embodiment of the present invention; Figure 4 (a)-(d) are schematic diagrams of the point-frequency RCS of the composite coating at 10 GHz, 15 GHz and 35 GHz in the embodiments of the present invention; Figure 5 (e)-(f) are schematic diagrams of the point-frequency RCS of the composite coating at 15 GHz (and 35 GHz) with HH polarization and VV polarization in the embodiments of the present invention. Detailed Implementation

[0019] To better understand the above-described objectives, features, and advantages of the present invention, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other. Furthermore, the present invention can be implemented in other ways different from those described herein; therefore, the scope of protection of the present invention is not limited to the specific embodiments disclosed below.

[0020] A specific embodiment of the present invention, such as Figure 1-5 A method for preparing a multi-band compatible stealth and camouflage integrated material is disclosed, including: Step 1. Grind the iron-based soft magnetic alloy to obtain sheet-like soft magnetic alloy powder; The iron-based soft magnetic alloy has a granular or blocky structure; The iron-based soft magnetic alloy is used as a high-solids-content microwave absorbing filler. Optionally, the particle size of the sheet-like soft magnetic alloy powder is 5-50 μm, and the aspect ratio is 0.05-0.3.

[0021] Optionally, the transverse dimension of the sheet-like soft magnetic alloy powder is 5–50 μm, and the longitudinal thickness is 0.25–5 μm.

[0022] Optionally, the grinding process can be a three-roll milling method or a ball milling method; Optionally, the grinding speed is 200-500 rpm, the ball-to-material ratio is 5:1-20:1, and the grinding time is 4-24 h.

[0023] This invention controls the grinding time, ball-to-material ratio, rotation speed, and parameters to form a lamellar structure with obvious anisotropic characteristics in the obtained soft magnetic alloy powder.

[0024] This invention, by processing iron-based soft magnetic alloys into sheets, facilitates the formation of a larger specific surface area and a more complex electromagnetic propagation path in subsequent coatings, thereby enhancing magnetic loss, eddy current loss, and interface polarization loss, enabling radar waves to achieve more efficient absorption under conditions of smaller thickness.

[0025] Step 2. Add the solvent to the dispersion container, premix it with the surfactant and dispersant, then add the flake soft magnetic alloy powder for primary dispersion, then add the anti-settling agent for secondary dispersion, and finally add the two-component modified epoxy resin and mix it evenly. Vacuum degassing is performed to obtain the first electromagnetic coating and the second electromagnetic coating. Optionally, the ratio of the rotational speeds of the primary dispersion to the secondary dispersion is 5-15:4-10; The ratio of the time spent in the first dispersion to the time spent in the second dispersion is 2-12:1-6; Optionally, the primary dispersion speed is 1000–3000 rpm and the primary dispersion time is 10–60 min; the secondary dispersion speed is 800–2000 rpm and the secondary dispersion time is 5–30 min.

[0026] Optionally, the dispersant is a polyester-type dispersant, a polyurethane-type dispersant, an acrylic polymeric dispersant, or a dispersant containing phosphate ester groups and / or phosphonic acid groups.

[0027] Optionally, the anti-settling agent is organic modified bentonite, silica, modified silicate thixotropic agent, organic wax anti-settling agent and / or polyamide wax anti-settling agent.

[0028] The surfactant is a nonionic surfactant, a silicone-modified nonionic surfactant, and / or a weakly polar surfactant.

[0029] This invention utilizes the synergistic effect of anti-settling agents and surfactants as additives to improve powder wetting and dispersion, and enhance anti-settling stability, thereby reducing local defects caused by agglomeration and sedimentation, which is conducive to the formation of a dense and continuous electromagnetic functional layer and improves film formation consistency.

[0030] This application utilizes dispersants and additives to perform surface modification treatment on sheet-like soft magnetic alloy powder, making it suitable for uniform dispersion in a high-solids-content resin system. By adjusting the ratio of dispersants and additives, modified sheet-like soft magnetic alloy powder is obtained.

[0031] Optionally, in the electromagnetic coating, the volume fraction of the flake soft magnetic alloy powder is 40.0–80.0 wt%, the volume fraction of the two-component modified epoxy resin is 20.0–50.0 wt%, the volume fraction of the dispersant is 0.5–2.0 wt%, the volume fraction of the anti-settling agent is 0.5–2.0 wt%, the volume fraction of the surfactant is 0.1–1.0 wt%, and the remainder is solvent.

[0032] Optionally, the solvent is an ester, alcohol, ketone, or aromatic hydrocarbon solvent, or a mixture thereof; Furthermore, the solvent is a mixture of propylene glycol methyl ether acetate and n-butanol.

[0033] The amount of solvent added is based on the viscosity required for spraying, preferably so that the viscosity of the coating is in the range of 100 to 2000 mPa·s at 25 ℃.

[0034] Optionally, the particle size of the first electromagnetic coating is 10-30 μm, wherein the volume fraction ratio of the flake soft magnetic alloy powder, the two-component modified epoxy resin, the dispersant, the additives and the solvent is: 50-60:35-45:1-1.5:1.3-2:2; Optionally, in the two-component modified epoxy resin, the mass ratio of the main agent to the curing agent is 100:(20-50); Furthermore, in the two-component modified epoxy resin, the mass ratio of the main agent to the curing agent is 100:(25-35).

[0035] For example, in the first electromagnetic coating, the mass of sheet-like soft magnetic alloy powder accounts for 55.0 wt% of the total, the mass of two-component modified epoxy resin is 40.0 wt%, the mass of dispersant is 1.5 wt%, the mass of anti-settling agent is 1.0 wt%, the mass of surfactant is 0.5 wt%, and the remainder is solvent.

[0036] Optionally, the particle size of the second electromagnetic coating is 20-50 μm, wherein the volume fraction ratio of the flake soft magnetic alloy powder, the two-component modified epoxy resin, the dispersant, the additives and the solvent is: 60-66:31-37:0.9-1:1.2-1.5:0.9-1; For example, the second electromagnetic coating powder contains 63.0 wt% flake-shaped soft magnetic alloy powder, 34.0 wt% two-component modified epoxy resin, 0.9 wt% dispersant, 0.9 wt% anti-settling agent, 0.4 wt% surfactant, and the remainder is solvent.

[0037] Optionally, the aspect ratio of the first electromagnetic coating is 0.05-0.1; and the aspect ratio of the second electromagnetic coating is 0.1-0.15.

[0038] It is understandable that the thickness-to-diameter ratio is the ratio of the longitudinal thickness to the transverse dimension of the electromagnetic coating.

[0039] Optionally, the first electromagnetic coating has a filling amount of 50%-60%; the second electromagnetic coating has a filling amount of 60%-70%.

[0040] This invention adjusts the particle size / gradation and thickness-to-diameter ratio of the sheet-like soft magnetic alloy powder, as well as the filling ratio of the powder in the resin matrix, so that the first electromagnetic coating and the second electromagnetic coating have differences and complementary relationships in terms of equivalent dielectric constant, equivalent permeability and loss characteristics.

[0041] By altering the particle size and aspect ratio of the sheet-like soft magnetic alloy, the resonant frequency of the alloy is adjusted. Furthermore, by optimizing the filling ratio and coating thickness, the coating formed by the two coatings exhibits strong absorption performance in different frequency bands. The superposition of the two electromagnetic coatings creates a gradient impedance change and a complementary and superimposed absorption band, thereby broadening the absorption band and reducing sensitivity to changes in the incident angle.

[0042] Step 3 involves pretreating the composite substrate to be coated to obtain a pretreated substrate. The composite substrate includes an alloy substrate and a carbon fiber composite material substrate; Optionally, the alloy substrate is an aluminum alloy, titanium alloy, magnesium alloy, steel alloy, and / or nickel alloy.

[0043] The carbon fiber composite material matrix is ​​a carbon fiber / epoxy resin composite material, a carbon fiber / aramid fiber composite material, or a carbon fiber / polyimide composite material.

[0044] Optionally, pretreatment may include degreasing and cleaning, sanding and roughening, dust removal and drying, surface activation and / or primer activation to improve the adhesion and interfacial bonding strength between the coating and the substrate. For metal or alloy substrates, pretreatment may also include sandblasting or conversion coating treatment; for carbon fiber composite substrates, pretreatment may also include surface decontamination and activation treatment to enhance wetting.

[0045] Step 4. On the surface of the pretreated substrate, a primer layer, a conductive layer, a first electromagnetic coating, a second electromagnetic coating, a topcoat layer, and a low infrared emissivity layer are sprayed sequentially to obtain a coating system. Optionally, in step 4, the following spraying operations are performed sequentially on the pretreated substrate surface: 4-1. Apply primer layer; 4-2. Spray a conductive layer over the primer layer; Optionally, the conductive layer is a conductive silver paint layer or a conductive coating containing highly conductive metal fillers; 4-3. Spray a first electromagnetic coating onto the conductive layer to form a first absorbing layer; 4-4. Spray a second electromagnetic coating with different filling ratios on top of the first absorbing layer to form a second absorbing layer; 4-5. Apply a topcoat layer over the second absorbing layer; 4-6. A low infrared emissivity layer is sprayed on the outermost layer to give the coating both infrared stealth and surface optical camouflage capabilities, resulting in a multi-band wide-angle ultra-thin stealth composite coating.

[0046] Optionally, the thickness of the low infrared emissivity layer is 3-14 μm; Optionally, the infrared emissivity of the 3-5 μm low infrared emissivity layer is 0.3-0.35, and the infrared emissivity of the 8-14 μm low infrared emissivity layer is 0.25-0.3.

[0047] Optionally, the electromagnetic response of the integrated material compatible with stealth and camouflage is in the X-Ka band, 8-40 GHz.

[0048] The electromagnetic response of the integrated material, which is compatible with stealth and camouflage, covers the X-band, Ku-band, and Ka-band, with an incident angle range of 0° to ±75°.

[0049] Optionally, the total dry film thickness of the integrated material compatible with stealth and camouflage is <1.2 mm.

[0050] For example, the total dry film thickness of an integrated material compatible with stealth and camouflage is 1.0-1.2 mm.

[0051] Optionally, the spraying method is air spraying and / or airless spraying; the nozzle diameter can be selected according to the viscosity of the coating and the atomization effect; the distance between the spray gun and the substrate surface is 15-30 cm; the spraying method is cross-flow or multi-directional flow.

[0052] Optionally, the spraying method is a multi-layer thin-coating method, which forms the target dry film thickness. A drying process is set between adjacent spraying passes. After all spraying is completed, the coating system is cured to form a stable bonding structure between the layers, resulting in a multi-band wide-angle ultra-thin stealth composite coating.

[0053] Step 5. Curing the coating system to obtain an integrated material that is compatible with stealth and camouflage.

[0054] The integrated material that is compatible with stealth and camouflage includes a primer layer, a conductive layer, a dual absorbing layer, a topcoat layer, and a low infrared emissivity layer.

[0055] The curing process employs a phased curing system, including a pre-curing stage and a post-curing stage.

[0056] Optionally, the pre-curing stage temperature is 60–90 °C and the pre-curing stage time is 1–3 h; The post-curing stage temperature can be 100–140 ℃ and the post-curing stage time can be 1–4 h; room temperature leveling can be performed before curing to improve surface leveling and interlayer bonding.

[0057] In the six-layer structure of this invention: the primer layer is used to construct a reliable bonding interface with the substrate and form a wetting transition and stress buffer between the substrate and the functional layer, thereby improving adhesion and reducing interface defects; the conductive layer and the dual absorbing layer work together to form a secondary attenuation mechanism of "transmission-absorption-reflection-reabsorption", thereby improving broadband absorption efficiency; the dual absorbing layer adopts gradient impedance, quarter-wavelength resonant design and complementary and superimposed absorption frequency bands, thereby improving absorption performance under wide incident angle conditions; the topcoat layer is used to effectively resist the erosion of environmental factors such as ultraviolet rays, rain, and salt spray, ensuring the long-term stability of the electromagnetic performance of the internal functional layer; the low infrared emissivity / camouflage layer is used to reduce infrared radiation characteristics and take into account visible light / near infrared camouflage, enabling the coating to achieve multi-spectral compatibility.

[0058] This invention employs a multi-layer thin-coating method, which helps reduce defects such as sagging, pinholes, solvent retention, and internal pores caused by single-layer thick coating, thereby improving film density and thickness uniformity. Simultaneously, it facilitates control of solvent evaporation and curing shrinkage, reducing residual stress concentration, thus improving interlayer bonding reliability and reducing the risk of cracking. Furthermore, it ensures consistent coverage of complex curved surfaces and edge areas, improving engineering applicability and construction repeatability. The curing method can be room temperature curing, heat curing, or staged curing; staged curing is preferred to balance interlayer bonding and film quality.

[0059] The integrated material of the present invention, which is compatible with stealth and camouflage, is a multi-band wide-angle ultra-thin stealth composite coating. It forms a multi-layer structure on the surface of the substrate, including a primer layer, a conductive layer, a first absorbing layer, a second absorbing layer, a topcoat layer, and a low infrared emissivity / camouflage layer, with a total thickness of less than 1.2 mm; in a specific embodiment, it is about 1.13 mm. Thus, while ensuring good mechanical properties and environmental adaptability, it achieves synergy of radar stealth, infrared stealth, and visible light camouflage performance.

[0060] Example 1 This embodiment provides a multi-band wide-angle ultrathin stealth composite coating suitable for alloy substrate surfaces and its preparation method. The alloy substrate can be selected from aluminum alloys, titanium alloys, magnesium alloys, steel alloys, or combinations thereof, preferably aluminum alloy or titanium alloy structural components commonly used in aerospace and weaponry equipment. Through the coordinated design of the substrate surface state, the underlying interface structure, and the parameters of the multi-layer coating, multi-spectral compatible stealth effects are achieved, including wide-band radar stealth, wide-angle RCS reduction, and infrared and visible light camouflage, while ensuring good adhesion and environmental resistance. The composite coating sequentially comprises a primer layer, a conductive layer, a first electromagnetic absorbing layer, a second electromagnetic absorbing layer, a topcoat layer, and a low infrared emissivity camouflage layer, forming a six-layer composite structure. Through the coordinated design of the material system and spraying process of each layer, the total dry film thickness of the resulting coating can be controlled within the range of less than 1.5 mm, preferably less than 1.2 mm; in this embodiment, the total dry film thickness of the six-layer composite structure is 1.13 mm.

[0061] 1. In this embodiment, the first absorbing layer and the second absorbing layer are formed using a first electromagnetic coating and a second electromagnetic coating with different filling ratios, respectively; The electromagnetic coating uses a two-component modified epoxy resin as the matrix, flake-shaped soft magnetic alloy powder as a high-solids filler, and is formulated with dispersants, anti-settling agents, surfactants, and solvents to obtain a sprayable system. Specifically, the flake-shaped soft magnetic alloy powder constitutes 40.0–80.0 wt% of the electromagnetic coating, preferably 50.0–70.0 wt%; the two-component modified epoxy resin constitutes 20.0–50.0 wt% of the electromagnetic coating, preferably 30.0–40.0 wt%; the dispersant constitutes 0.5–2.0 wt% of the electromagnetic coating, preferably 0.5–1.5 wt%; the anti-settling agent constitutes 0.5–2.0 wt% of the electromagnetic coating, preferably 0.5–1.5 wt%; the surfactant constitutes 0.1–1.0 wt% of the electromagnetic coating, preferably 0.2–0.5 wt%; the remainder is solvent. The amount of solvent added is based on the viscosity required for spraying, preferably so that the viscosity of the coating is in the range of 100 to 2000 mPa·s at 25 ℃.

[0062] The first electromagnetic coating comprises, by mass percentage: 55.0 wt% flake soft magnetic alloy powder, 40.0 wt% two-component modified epoxy resin, 1.5 wt% dispersant, 1.0 wt% anti-settling agent, 0.5 wt% surfactant, and the remainder being solvent; the second electromagnetic coating comprises, by mass percentage: 63.0 wt% flake soft magnetic alloy powder, 34.0 wt% two-component modified epoxy resin, 0.9 wt% dispersant, 0.9 wt% anti-settling agent, 0.4 wt% surfactant, and the remainder being solvent.

[0063] In the two-component modified epoxy resin, the mass ratio of the main agent to the curing agent can be 100:(20-50), preferably 100:(25-35); in this embodiment, it is preferably 100:30 to balance the construction period and the curing speed.

[0064] The main difference between the first and second electromagnetic coatings lies in the particle size and thickness of the flake-shaped soft magnetic alloy powder used. Specifically, the first electromagnetic coating uses smaller soft magnetic alloy powder (10-30 μm), while the second electromagnetic coating uses larger powder (20-50 μm). The advantage of this design is that the smaller particle size enhances the high-frequency absorption capability of the coating, while the larger particle size helps to improve the absorption efficiency in the low-frequency range and the structural stability of the coating.

[0065] In the two-component modified epoxy resin, the mass ratio of the main agent to the curing agent can be 100:(20-50), preferably 100:(25-35); in this embodiment, it is preferably 100:30 to balance the construction period and the curing speed.

[0066] 2. Preparation of sheet-like soft magnetic alloy powder The sheet-like soft magnetic alloy powder is prepared by a grinding process. The grinding parameters can be adjusted within the following ranges: grinding speed 200-500 rpm, ball-to-powder ratio 5:1-20:1, grinding time 4-24 h; during the grinding process, intermittent shutdown or external cooling can be used to control the temperature rise, and ball milling can be carried out under an inert atmosphere or in a closed environment to reduce the risk of powder oxidation.

[0067] In this embodiment, zirconia balls were used as the grinding medium, with a ball diameter combination of 5 mm and 10 mm, a mass ratio of 7:3, and a ball-to-material ratio of 10:1. Grinding was carried out at 380 rpm for 12 hours under argon protection or a sealed environment, with intermittent grinding (stopping for 10 minutes every 30 minutes) to reduce temperature rise. The resulting soft magnetic alloy powder exhibited a lamellar structure with a transverse dimension of approximately 5–50 μm and a longitudinal thickness of approximately 0.25–5 μm, thus forming an anisotropic morphology conducive to electromagnetic loss and multi-scale scattering.

[0068] 3. Preparation of electromagnetic coatings In preparing electromagnetic coatings, the solvent is first added to a dispersion container, followed by the addition of a surfactant and dispersant for premixing. Then, flake-shaped soft magnetic alloy powder is added and dispersed. After initial dispersion, an anti-settling agent is added to construct a thixotropic network and improve storage and application stability. Finally, a two-component modified epoxy resin and curing agent are added and mixed thoroughly. Vacuum degassing is performed if necessary to reduce coating defects. The high-speed dispersion speed can be 1000–3000 rpm, and the dispersion time can be 10–60 min. The secondary dispersion speed after adding the anti-settling agent can be 800–2000 rpm, and the time can be 5–30 min. The vacuum degassing pressure can be [not specified]. 0.05~ 0.095 MPa, degassing time can be 5 to 30 min.

[0069] In this embodiment, the solvent is first added to the dispersion container, followed by the addition of surfactant and dispersant, and stirred at 800 rpm for about 5 minutes. Then, the flake-shaped soft magnetic alloy powder is slowly added and dispersed at high speed at about 2000 rpm for about 25 minutes. Next, the anti-settling agent is added and dispersed at 1500 rpm for about 10 minutes. Then, the epoxy resin main agent is added and stirred evenly, followed by the addition of curing agent and stirring. Finally, the resulting coating system is subjected to vacuum degassing treatment at -0.08 MPa for about 10 minutes, thereby obtaining the first electromagnetic coating and the second electromagnetic coating.

[0070] 4. Substrate Pretreatment Before coating, the carbon fiber composite substrate is pretreated. Pretreatment may include degreasing, roughening, dust removal, and surface activation steps to improve coating adhesion and interface stability. As a non-limiting example, in this embodiment, isopropanol is used for degreasing and cleaning, the surface is uniformly sanded to a matte finish using #320 sandpaper, and dust is removed using a lint-free cloth and compressed air. If necessary, 30–120 s plasma treatment or application of a primer activator can be used to further improve adhesion.

[0071] 5. Spray coating of a six-layer composite structure A six-layer composite coating structure is sequentially formed on the pretreated substrate surface using a spraying method. The spraying method can be air spraying, airless spraying, or a combination thereof; the spray gun nozzle diameter can be selected according to the viscosity and atomization effect of the coating; the distance between the spray gun and the substrate surface can be adjusted within the range of 15–30 cm, preferably within the range of 18–22 cm; the spray gun path can be cross-path or multi-directional path; the number of passes can be adjusted equivalently according to the film thickness of a single pass; and the layers can be flash-dried at room temperature or at low temperature.

[0072] As a specific example without limitation, this embodiment adopts an air spraying method, wherein the nozzle diameter of the spray gun used for the primer layer, topcoat layer and low infrared emissivity camouflage layer is 1.8 mm, the nozzle diameter of the spray gun used for the first and second electromagnetic wave absorbing layers is 2.0 mm, the distance between the spray gun and the substrate surface is controlled at 18 to 22 cm, and a cross-passing spraying method is adopted during spraying. First, a primer layer is sprayed, formed by two coats, with a dry film thickness of approximately 40 μm. Each coat is allowed to flash-dry for approximately 10 minutes at room temperature. Next, a conductive layer, preferably a conductive silver paint layer, is sprayed over the primer layer, forming a dry film thickness of approximately 30 μm through two coats (the conductive layer can also be an equivalent conductive coating containing metallic conductive fillers). A first electromagnetic absorbing layer, using a first electromagnetic coating, is sprayed over the conductive layer, forming a dry film thickness of approximately 260 μm through four coats, with each coat allowed to flash-dry for approximately 15 minutes at room temperature between coats. Then, a second electromagnetic absorbing layer, using a second electromagnetic coating, is sprayed over five coats, forming a dry film thickness of approximately 320 μm (with flash-drying between coats as before). A topcoat layer is sprayed over the double absorbing layers, forming a dry film thickness of approximately 60 μm through two coats. Finally, a low-infrared emissivity camouflage layer is sprayed over the topcoat layer, forming a dry film thickness of approximately 420 μm through six coats. The thickness of each layer is approximately μm, and each layer is flash-dried at room temperature for approximately 15 minutes. The resulting six-layer composite coating has a total dry film thickness of approximately 1130 μm, or approximately 1.13 mm.

[0073] 6. Solidify the system After spraying, the coating system is cured. Overall curing can be performed in stages, with a pre-curing temperature of 60–90 °C for 1–3 h and a post-curing temperature of 100–140 °C for 1–4 h. Room temperature leveling can be performed before curing to improve surface leveling and interlayer bonding. As a non-limiting example, this embodiment uses room temperature leveling for 30 min, followed by pre-curing at 80 °C for 2 h, and then post-curing at 120 °C for 2 h, followed by oven cooling to room temperature.

[0074] 7. Testing Under laboratory conditions, radar scattering characteristics, visible / near-infrared camouflage, and infrared characteristics were tested on the sample samples. Radar stealth performance testing was conducted in an electromagnetic anechoic chamber using a vector network analyzer combined with a standard radar testing system. Based on the principle of reflection coefficient and radar cross section (RCS) measurement, the stealth effect was evaluated by comparing the changes in electromagnetic response of the substrate before and after coating under different frequency bands and incident angles. The test frequency bands covered the X-band, Ku-band, and Ka-band, with an incident angle range of 0° to ±75°, to assess the performance stability of the coating under wide-angle conditions, especially its adaptability to large-angle detection scenarios such as side-looking SAR. Figure 4As shown in Table 1, the results indicate that under the condition of a total dry film thickness of less than 1.2 mm, the coating exhibits significant electromagnetic wave absorption and scattering suppression effects in the X, Ku, and Ka bands, and maintains a stable RCS reduction effect when the incident angle increases to ±75°. The angle sensitivity is significantly reduced, and the RCS stealth performance improvement under large incident angle conditions can reach approximately 70%. In visible light and near-infrared camouflage performance tests, the coating demonstrates good camouflage effects through color, reflectance characteristics, and background matching analysis. In infrared performance tests, the outermost low-infrared emissivity camouflage layer effectively reduces infrared radiation characteristics, with an infrared emissivity of 0.3-0.35 in the 3-5 μm band and 0.25-0.3 in the 8-14 μm band, while also maintaining camouflage effects in both visible and near-infrared bands, further achieving multi-spectral compatible countermeasures based on electromagnetic stealth. Thickness and areal density tests show that the total dry film thickness of the coating is stably controlled below 1.2 mm, which helps meet the requirements of lightweight design. To evaluate the engineering applicability, mechanical properties, and environmental adaptability, the sample of the example was tested for appearance, areal density, thickness, adhesion, flexibility, impact resistance, operating temperature, temperature shock, solar radiation, corrosion resistance (salt spray), damp heat, and water resistance. The test results are summarized in Table 2.

[0075] Table 1. Summary of the mean RCS values ​​of the composite coating at 10 GHz, 15 GHz and 35 GHz for HH polarization and VV polarization at specific frequencies.

[0076]

[0077] Table 2 Summary of various test indicators for composite coatings

[0078] Example 2 This embodiment provides a multi-band wide-angle ultrathin stealth composite coating suitable for the surface of a carbon fiber composite substrate and its preparation method. The carbon fiber composite substrate has excellent lightweight and mechanical properties and is widely used in aerospace, military equipment and other fields. By ensuring the surface condition of the substrate, the interface structure of the bottom layer and the parameters of the multi-layer coating, this embodiment achieves multi-spectral compatible stealth effects such as wide-band radar stealth, wide-angle RCS reduction and infrared and visible light camouflage. The composite coating sequentially includes a primer layer, a conductive layer, a first electromagnetic absorbing layer, a second electromagnetic absorbing layer, a topcoat layer and a low infrared emissivity camouflage layer, forming a six-layer composite structure. Through the coordinated design of the material system of each layer and the spraying process, the total dry film thickness of the resulting coating can be controlled within the range of less than 1.5 mm, preferably less than 1.2 mm; in this embodiment, the total dry film thickness of the six-layer composite structure is approximately 1.13 mm.

[0079] 1. In this embodiment, the first electromagnetic absorbing layer and the second electromagnetic absorbing layer are formed using first electromagnetic coatings and second electromagnetic coatings with different filling ratios, respectively. The electromagnetic coating uses a two-component modified epoxy resin as the matrix, flake soft magnetic alloy powder as a high-solids filler, and is combined with dispersants, anti-settling agents, surfactants and solvents to obtain a sprayable system. The mass percentage of the flake-shaped soft magnetic alloy powder in the electromagnetic coating can be 40.0–80.0 wt%, preferably 50.0–70.0 wt%; the mass percentage of the two-component modified epoxy resin in the electromagnetic coating can be 20.0–50.0 wt%, preferably 30.0–40.0 wt%; the mass percentage of the dispersant in the electromagnetic coating can be 0.5–2.0 wt%, preferably 0.5–1.5 wt%; the mass percentage of the anti-settling agent in the electromagnetic coating can be 0.5–2.0 wt%, preferably 0.5–1.5 wt%; the mass percentage of the surfactant in the electromagnetic coating can be 0.1–1.0 wt%, preferably 0.2–0.5 wt%; the remainder is solvent. The amount of solvent added is based on the viscosity required for spraying, preferably ensuring that the viscosity of the coating is in the range of 100–2000 mPa·s at 25 °C.

[0080] The types and amounts of the dispersant, anti-settling agent, surfactant, and solvent can be selected and adjusted according to the range described in Example 1, and will not be repeated here.

[0081] 2. Preparation of sheet-like soft magnetic alloy powder The sheet-like soft magnetic alloy powder is prepared by a grinding process. The grinding parameters can be adjusted within the following range: rotation speed 200-500 rpm, ball-to-powder ratio 5:1-20:1, grinding time 4-24 h; during the grinding process, intermittent shutdown or external cooling can be used to control the temperature rise, and ball milling can be carried out under an inert atmosphere or in a closed environment to reduce the risk of powder oxidation.

[0082] In this embodiment, zirconia balls were used as the grinding medium, with a ball diameter combination of 5 mm and 10 mm, a mass ratio of 7:3, and a ball-to-material ratio of 10:1. Grinding was carried out at 380 rpm for 12 hours under argon protection or a sealed environment, with intermittent grinding (stopping for 10 minutes every 30 minutes) to reduce temperature rise. The soft magnetic alloy powder obtained after ball milling exhibited a lamellar structure with a transverse dimension of approximately 5–50 μm and a thickness of approximately 0.5–2 μm, thus forming an anisotropic morphology conducive to electromagnetic loss and multi-scale scattering.

[0083] 3. Preparation of electromagnetic coatings In preparing electromagnetic coatings, the solvent is first added to a dispersion container, followed by the addition of a surfactant and dispersant for premixing. Then, flake-shaped soft magnetic alloy powder is added and dispersed. After initial dispersion, an anti-settling agent is added to construct a thixotropic network and improve storage and application stability. Finally, a two-component modified epoxy resin and curing agent are added and mixed thoroughly. Vacuum degassing is performed if necessary to reduce coating defects. The high-speed dispersion rotation speed can be 1000–3000 rpm, and the dispersion time can be 10–60 min. The secondary dispersion speed after adding the anti-settling agent can be 800–2000 rpm, and the time can be 5–30 min. The vacuum degassing pressure can be… 0.05~ 0.095 MPa, degassing time can be 5 to 30 min.

[0084] As a specific example without limitation, in this embodiment, the solvent is first added to the dispersion container, followed by the addition of a surfactant and a dispersant, and stirred at 800 rpm for about 5 minutes. Then, the flake-shaped soft magnetic alloy powder is slowly added and dispersed at high speed at about 2000 rpm for about 25 minutes. Next, an anti-settling agent is added, and dispersion continues at 1500 rpm for about 10 minutes. Then, the epoxy resin base is added and stirred until homogeneous, followed by the addition of a curing agent and continued stirring. Finally, the resulting coating system is subjected to vacuum degassing treatment under the following conditions: At a pressure of 0.08 MPa and a degassing time of approximately 10 minutes, electromagnetic coating A and electromagnetic coating B were obtained, respectively.

[0085] 4. Substrate Pretreatment Before coating, the carbon fiber composite substrate is pretreated. Pretreatment may include degreasing, roughening by sanding, dust removal, and surface activation steps to improve coating adhesion and interface stability. As a specific example without limitation, this embodiment uses isopropanol for degreasing and cleaning, uses #320 sandpaper to uniformly sand the surface to a matte state, and removes dust with a lint-free cloth and compressed air; if necessary, plasma treatment (30-120 s) or application of a primer activator may be used to further improve adhesion performance.

[0086] 5. Spray coating of a six-layer composite structure A six-layer composite coating structure is sequentially formed on the pretreated substrate surface using a spraying method. The spraying method can be air spraying, airless spraying, or a combination thereof; the spray gun nozzle diameter can be selected according to the viscosity and atomization effect of the coating; the distance between the spray gun and the substrate surface can be adjusted within the range of 15–30 cm, preferably within the range of 18–22 cm; the spray gun path can be cross-path or multi-directional path; the number of passes can be adjusted equivalently according to the film thickness of a single pass; and the layers can be flash-dried at room temperature or at low temperature.

[0087] As a specific example without limitation, this embodiment adopts an air spraying method, wherein the nozzle diameter of the spray gun used for the primer layer, topcoat layer and low infrared emissivity camouflage layer is 1.8 mm, the nozzle diameter of the spray gun used for the first and second electromagnetic wave absorbing layers is 2.0 mm, the distance between the spray gun and the substrate surface is controlled at 18 to 22 cm, and a cross-passing spraying method is adopted during spraying. First, a primer layer is sprayed, formed by two coats, with a dry film thickness of approximately 40 μm. Each coat is allowed to flash dry for approximately 10 minutes at room temperature. Next, a conductive layer, preferably a conductive silver paint layer, is sprayed over the primer layer, forming a dry film thickness of approximately 30 μm through two coats. Then, a first electromagnetic absorbing layer, using electromagnetic paint A, is sprayed over the conductive layer, forming a dry film thickness of approximately 260 μm through four coats, with each coat allowed to flash dry for approximately 15 minutes at room temperature between coats. Following this, a second electromagnetic absorbing layer, using electromagnetic paint B, is sprayed over five coats, forming a dry film thickness of approximately 320 μm. A topcoat layer is sprayed over the dual absorbing layers, forming a dry film thickness of approximately 60 μm through two coats. Finally, a low-infrared emissivity camouflage layer is sprayed over the topcoat layer, forming a dry film thickness of approximately 420 μm through six coats, with each coat allowed to flash dry for approximately 15 minutes at room temperature between coats. The resulting six-layer composite coating has a total dry film thickness of approximately 1130 μm, or about 1.13 mm.

[0088] 6. Solidify the system After spraying, the coating system is cured. Overall curing can be performed in stages, with a pre-curing temperature of 60–90 °C for 1–3 h and a post-curing temperature of 100–140 °C for 1–4 h. Room temperature leveling can be performed before curing to improve surface leveling and interlayer bonding. As a non-limiting example, this embodiment uses room temperature leveling for 30 min, followed by pre-curing at 80 °C for 2 h, and then post-curing at 120 °C for 2 h, followed by oven cooling to room temperature.

[0089] 7. Testing Under laboratory conditions, radar scattering characteristics, visible / near-infrared camouflage, and infrared characteristics were tested on the sample. Radar stealth performance testing was conducted in an electromagnetic anechoic chamber using a vector network analyzer combined with a standard radar testing system. Based on the principle of reflection coefficient and radar cross section (RCS) measurement, the stealth effect was evaluated by comparing the changes in electromagnetic response of the substrate before and after coating under different frequency bands and incident angles. The test frequency bands covered the X-band, Ku-band, and Ka-band, with an incident angle range of 0° to ±75°, to assess the performance stability of the coating under wide-angle conditions, especially its adaptability to large-angle detection scenarios such as side-looking SAR. Test results show that, with a total dry film thickness of less than 1.2 mm, the coating exhibits significant electromagnetic wave absorption and scattering suppression effects in the X, Ku, and Ka bands, and maintains a stable RCS reduction effect when the incident angle increases to ±75°. The angle sensitivity is significantly reduced, and the RCS stealth performance improvement under large incident angle conditions can reach approximately 70%. In visible and near-infrared camouflage performance tests, the coating demonstrated excellent camouflage effects through analysis of color, reflectance characteristics, and background matching. In infrared performance tests, the outermost low-infrared emissivity camouflage layer effectively reduced infrared radiation characteristics, with an infrared emissivity of 0.3-0.35 in the 3-5 μm band and 0.25-0.3 in the 8-14 μm band, while maintaining camouflage effects in both visible and near-infrared bands, further achieving multi-spectral compatible countermeasures based on electromagnetic stealth. Thickness and areal density tests showed that the total dry film thickness of the coating was consistently controlled below 1.2 mm, helping to meet lightweight design requirements. To evaluate engineering applicability, mechanical properties, and environmental adaptability, the sample samples were tested for appearance, areal density, thickness, adhesion, flexibility, impact resistance, operating temperature, temperature shock, solar radiation, corrosion resistance (salt spray), damp heat resistance, and water resistance. The test results are summarized in Table 2.

[0090] Table 3

[0091] This invention achieves multi-spectral compatible stealth effects—broadband radar stealth, wide-angle stable absorption, and infrared and visible light camouflage—under finite thickness conditions through the systematic design of sheet-like soft magnetic alloy high-solid-weight fillers, a dual-absorbing layer structure with complementary electromagnetic parameters, and a multi-layer synergistic interface and spraying process. Compared to existing stealth coating solutions that mainly rely on simple physical stacking, this invention has significant improvements in spectral coverage, incident angle adaptability, interlayer interface stability, and engineering applicability, enabling ultra-thin and lightweight structural designs while balancing mechanical performance and environmental durability.

[0092] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a multi-band compatible stealth and camouflage integrated material, characterized in that, include: Step 1. Grind the iron-based soft magnetic alloy to obtain sheet-like soft magnetic alloy powder; Step 2. Add the solvent to the dispersion container, premix it with the surfactant and dispersant, then add the flake soft magnetic alloy powder for primary dispersion, then add the anti-settling agent for secondary dispersion, and finally add the two-component modified epoxy resin and mix it evenly. Vacuum degassing is performed to obtain the first electromagnetic coating and the second electromagnetic coating. Step 3 involves pretreating the composite substrate to be coated to obtain a pretreated substrate. Step 4. On the surface of the pretreated substrate, a primer layer, a conductive layer, a first electromagnetic coating, a second electromagnetic coating, a topcoat layer, and a low infrared emissivity layer are sprayed sequentially to obtain a coating system. Step 5. Curing the coating system to obtain an integrated material that is compatible with stealth and camouflage.

2. The method for preparing the multi-band compatible stealth and camouflage integrated material according to claim 1, characterized in that, The particle size of the sheet-like soft magnetic alloy powder is 5-50 μm; the aspect ratio is 0.05-0.

3.

3. The method for preparing the multi-band compatible stealth and camouflage integrated material according to claim 1, characterized in that, The ratio of the rotational speeds for primary dispersion to secondary dispersion is 5-15:4-10; The ratio of the time spent in the first dispersion to the time spent in the second dispersion is 2-12:1-6.

4. The method for preparing the multi-band compatible stealth and camouflage integrated material according to claim 1, characterized in that, The anti-settling agent is an organically modified bentonite, silica, a modified silicate thixotropic agent, an organic wax anti-settling agent, and / or a polyamide wax anti-settling agent.

5. The method for preparing the multi-band compatible stealth and camouflage integrated material according to claim 1, characterized in that, The surfactant is a nonionic surfactant, a silicone-modified nonionic surfactant, and / or a weakly polar surfactant.

6. The method for preparing the multi-band compatible stealth and camouflage integrated material according to claim 1, characterized in that, In the first electromagnetic coating, the volume fraction ratio of flake soft magnetic alloy powder, two-component modified epoxy resin, dispersant, additives and solvent is: 50-60:35-45:1-1.5:1.3-2:

2.

7. The method for preparing the multi-band compatible stealth and camouflage integrated material according to claim 1, characterized in that, In the second electromagnetic coating, the volume fraction ratio of sheet-like soft magnetic alloy powder, two-component modified epoxy resin, dispersant, additives and solvent is: 60-66:31-37:0.9-1:1.2-1.5:0.9-1.

8. The method for preparing the multi-band compatible stealth and camouflage integrated material according to claim 1, characterized in that, The thickness of the low infrared emissivity layer is 3-14 μm.

9. The method for preparing the multi-band compatible stealth and camouflage integrated material according to claim 1, characterized in that, The thickness-to-diameter ratio of the first electromagnetic coating is 0.05-0.1; the thickness-to-diameter ratio of the second electromagnetic coating is 0.1-0.

15.

10. The multi-band compatible stealth and camouflage integrated material prepared by the preparation method according to any one of claims 1-9, characterized in that, The integrated material that is compatible with stealth and camouflage includes a primer layer, a conductive layer, a first electromagnetic coating layer, a second electromagnetic coating layer, a topcoat layer, and a low infrared emissivity layer. The total dry film thickness of the integrated material compatible with stealth and camouflage is <1.2 mm; The electromagnetic response of the integrated material, which is compatible with stealth and camouflage, is in the X-Ka band.

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