Optical absorbent, thermal control black paint and aerospace thermal control coating preparation method

Abstract

The invention discloses a preparation method of an optical absorbent, thermal control black paint and a spaceflight thermal control coating, and relates to the technical field of new materials. The optical absorbent is prepared into a carbon nanotube coating structure with silicon dioxide as a core. And a core-shell composite structure with a stable interface coupling effect is constructed. According to the structure, an effective optical and thermal synergistic channel is formed at an interface between a polar group on the surface of silicon dioxide and a carbon nanotube defect site or an introduced functional group through an intermolecular acting force between the polar group and the carbon nanotube defect site. In the thermal control black paint, vinyl organic silicon resin with high phenyl content is selected, and the refractive index of the vinyl organic silicon resin is matched with that of a carbon nanotube shell layer, so that the light scattering loss of an interface between a binder and an absorbent can be remarkably reduced, and the efficient absorption of the coating on a solar spectrum is guaranteed; through the microstructure effect of the core-shell absorbent, the interface matching effect of the resin matrix and the network construction effect of the addition curing reaction, a mutually reinforced chemical and physical synergistic system is formed.

Description

Technical Field

[0001] This invention relates to the field of new materials technology, specifically to an optical absorber, its preparation method, and a method for preparing aerospace thermal control coatings. Background Technology

[0002] During their operation in orbit, spacecraft (such as satellites, space stations, and deep space probes) face harsh space thermal environments, including direct solar radiation, Earth's albedo, and their own thermal radiation into the cold deep space. To maintain the stable operation of internal instruments and equipment within a suitable temperature range, the design of the spacecraft's thermal control system is crucial. Among these, thermal control coatings, as a core means of passive thermal control, adjust the solar absorptivity (α) of their surface. S ) and hemispherical emissivity (ε H This achieves a balance between absorbed heat and radiant heat, thereby achieving the purpose of temperature control.

[0003] Aerospace thermal control black paint is a widely used type of thermal control coating. However, existing thermal control black paints, such as E51-M black paint using epoxy resin E51 as a binder, have α... S and ε H All are low (e.g., α) S The value is 0.93 ± 0.02, ε HThe photothermal performance parameter is 0.88±0.02, resulting in limited thermal control efficiency. This low photothermal performance parameter leads to limited thermal control efficiency of the coating. To achieve the same heat dissipation effect, it is often necessary to increase the coating area or coating thickness, which is not conducive to the development trend of lightweight and miniaturized spacecraft. In addition, traditional black paints often use carbon black as an optical absorber. It is easy to form a dense surface structure with abrupt refractive index changes in the binder matrix, resulting in high Fresnel reflection in the solar spectrum, thereby reducing the absorption performance of the coating. At the same time, the emission characteristics of carbon black as an absorber in the infrared band are limited. Its absorption and emission mechanism mainly depends on electrical conductivity loss. In the mid-to-far infrared band (2.5~25μm), which determines the hemispherical emissivity, its emission performance strongly depends on the lattice vibration inside the material. Due to the lack of strong polar molecular bonds and efficient phonon excitation modes, carbon black has a small absorption cross section in the infrared band, which cannot effectively excite and maintain broadband, high-intensity thermal radiation, thus limiting the thermal radiation heat dissipation capability of the coating in the space environment. Furthermore, the condensable volatile matter (CVCM) content of existing thermal control black paints often fails to meet the stringent requirements of high-performance spacecraft in the space environment. In the vacuum of space, small-molecule additives and unreacted components in the thermal control black paint easily volatilize and condense on the surfaces of critical components at lower temperatures, causing contamination, performance degradation, or even functional failure, thus failing to meet the demands of long-life, high-reliability space missions. This mismatch in broadband optical properties and poor compatibility with the space environment makes it difficult for traditional thermal control coatings to simultaneously achieve high solar absorptivity, high infrared hemispherical emissivity, and low CVCM, failing to meet the urgent needs of future high-performance spacecraft for lightweight, high-reliability, and efficient thermal control. Summary of the Invention

[0004] The present invention provides an optical absorber, a thermal control black paint and a method for preparing aerospace thermal control coating, the thermal control coating formed having the characteristics of high solar absorptivity, high hemispherical emissivity and resistance to ultraviolet radiation.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] The specific implementation process of preparing a thermally controlling black paint based on an optical absorber, and then preparing a thermally controlling coating for hot weather based on the thermally controlling black paint, is as follows:

[0007] Step S1: Weigh carbon nanotube powder, dispersant DA345 and ethanol solvent in a certain proportion, and place them in a container for preliminary stirring and mixing;

[0008] Step S2: Transfer the premixed liquid from step S1 to a sand mill, add grinding media, and then perform mechanical grinding and dispersion;

[0009] Step S3: After dispersion, the resulting slurry is passed through a filtration device to obtain a uniform and stable carbon nanotube ethanol dispersion.

[0010] Step S4: Mix inorganic silica powder with carbon nanotube dispersion prepared in step S3 in a certain proportion;

[0011] Step S5: The mixture in step S4 is subjected to high-speed shearing to ensure that the carbon nanotubes are fully coated on the surface of the silica particles.

[0012] Step S6: The mixture obtained in step S5 is subjected to solvent evaporation treatment to obtain composite powder;

[0013] Step S7: The composite powder obtained in step S6 is pulverized and sieved to obtain an optical absorber;

[0014] Step S8: Using high phenyl content silicone resin as a binder, add the carbon nanotube optical absorber with silica core obtained in step 7, and add dispersant, substrate wetting agent and propylene glycol methyl ether acetate as solvent. Mix and disperse using a high-speed mixer to obtain a uniform A component slurry.

[0015] Step S9: Using hydrogen-containing silicone oil as a crosslinking agent, denoted as component B, and platinum-containing compounds as a catalyst, denoted as component C, the mixture is mixed and dispersed by mechanical stirring to obtain the thermal control black paint spray liquid;

[0016] Step S10: Spray the coating diluent prepared in step S9 onto the surface of a metal substrate commonly used in the aerospace field, and perform heat curing to obtain an aerospace thermal control black coating.

[0017] In some specific implementations, in step S1, the carbon nanotube powder is a multi-walled carbon nanotube with a diameter ranging from 10 to 30 nm and a length ranging from 10 to 50 µm. The mass concentration of the carbon nanotube in the final dispersion ranges from 3% to 5%, and the amount of dispersant DA345 added is 20% to 50% of the mass of the carbon nanotube.

[0018] In some specific implementations, in step S2, the grinding medium is zirconia beads with a particle size range of 0.4-0.8 mm, the grinding mill speed is 1500-2500 rpm, the dispersion time is 2-5 hours, and the temperature is controlled at 20-40℃ using a circulating cooling water system during the dispersion process.

[0019] In some specific implementations, step S3 involves filtering with a 100-200 mesh sieve to ensure the purity of the carbon nanotube dispersion.

[0020] In some specific embodiments, the average particle size of the inorganic silica powder is 50-100 nm; the mixing mass ratio of the inorganic silica powder and the carbon nanotube dispersion is calculated on a dry basis, that is, the mass ratio of silica to carbon nanotubes is 5-20:1.

[0021] In some specific implementations, the high-speed shearing process described in step S5 must be carried out immediately after the carbon nanotube dispersion is mixed with silica, and the shearing speed is not less than 5000 rpm, and the processing time is not less than 60 minutes, so as to ensure that the carbon nanotubes are fully and uniformly coated on the silica surface to form a stable core-shell structure. If simple mechanical mixing or low-speed shearing is used, effective coating cannot be achieved, resulting in a significant decrease in optical performance.

[0022] In some specific implementations, in step S6, the temperature of the evaporation treatment is 60-80°C, and it is carried out under continuous stirring at a stirring rate of 200-500 rpm until the ethanol solvent is completely evaporated.

[0023] In some specific implementations, in step S8, the high-content phenyl silicone resin is 100 parts; the optical absorber is 10-30 parts; the dispersing agent is 0.5-2 parts, wherein the dispersing agent is BYK-163 or BYK-2155; and the solvent propylene glycol methyl ether acetate is appropriate, so that the solid content of the slurry is controlled at 25% to 40%.

[0024] In some specific implementations, in step S8, the molar ratio (Ph / Si) of phenyl to silicon atoms in the high-phenyl content organosilicon resin ranges from 0.3 to 0.6:1.

[0025] In some specific implementations, in step S9, the hydrogen-containing silicone oil is a terminal-group hydrogen-containing silicone oil or a side-chain hydrogen-containing silicone oil, with an active hydrogen content of 1.0% to 1.8%; the catalyst containing platinum compounds is a platinum-vinylsiloxane complex.

[0026] Furthermore, the metal substrates commonly used in the aerospace field in step S10 include aluminum alloys, titanium alloys, aluminum-based silicon carbide, and magnesium alloys. The nozzle diameter used is 1-3 mm, the air pressure is 1-3 atm, the spraying distance is 10-30 cm, and the number of sprays is 3-5. The thermosetting conditions are: maintaining a temperature of 60-80℃ for 2-6 hours, then raising the temperature to 80-120℃ and holding for 8-12 hours; the coating thickness is controlled at 60-100 μm.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] This invention achieves uniform coating of carbon nanotubes on the surface of a silica core using a high-speed shearing process, constructing a core-shell composite structure with stable interfacial coupling. This structure forms an effective optical and thermal synergistic channel at the interface between the polar groups on the silica surface and the defect sites or introduced functional groups of the carbon nanotubes through intermolecular forces. The strong phonon vibrations excited by the polar silicon-oxygen bonds in the silica core can be effectively transferred to the carbon nanotube shell through this coupling interface, and the energy is rapidly dissipated and converted by its highly conductive network. This achieves an effective combination of infrared radiation enhancement and photothermal absorption effects at the microstructure level, overcoming the spectral response limitations of single materials.

[0029] The high-phenyl-content vinyl silicone resin selected in this invention has a refractive index that matches the carbon nanotube shell, significantly reducing light scattering loss at the binder-absorbent interface and ensuring efficient absorption of the solar spectrum by the coating. Replacing it with other resins with significantly different refractive indices (such as fluorocarbon or epoxy resins) would lead to increased interfacial reflection and decreased solar absorption performance. Furthermore, the high-phenyl-content vinyl silicone resin selected in this invention, through the formation of π-π bonds and van der Waals interactions between its conjugated π electrons and sp²-hybridized carbon nanotubes, significantly improves the interfacial compatibility and bonding strength between the resin and the absorbent shell. Simultaneously, the steric hindrance effect and chemical stability of the phenyl group effectively enhance the rigidity and environmental resistance of the cured coating network. The vinyl functional groups at the resin terminals undergo efficient and complete hydrosilylation reactions with the hydroxyl bonds in the hydrogen-containing silicone oil under the action of a platinum catalyst. This reaction is a stepwise polymerization process with very few byproducts, enabling in-situ construction of dense three-dimensional network structures from linear or branched polymers. The core-shell absorber is anchored within it through chemical bonding and physical entanglement, inhibiting the aggregation and migration of nanomaterials under complex stress, thereby enabling the thermal control coating to achieve high adhesion and long-term optical stability.

[0030] In this invention, the microstructure effect of the core-shell absorber, the interfacial matching effect of the resin matrix, and the network building effect of the addition-curing reaction collectively form a mutually reinforcing chemical and physical synergistic system. The binary core-shell optical absorber provides a functional filler with optimized intrinsic optical properties; the interaction between the high-phenyl resin and the core-shell optical absorber at the interfacial scale optimizes stress transfer and light transmission; and the byproduct-free addition-curing fixes the optimized microstructure in a highly cross-linked rigid network, fundamentally eliminating the source of low molecular weight volatiles.

[0031] This invention solves the contradiction in traditional technologies of simultaneously achieving high solar absorptivity, high infrared emissivity, and low condensable volatiles by designing and chemically coupling a core-shell structured absorber with a specific organosilicon resin system. The thermal control coating prepared by this invention maintains high α-value. S With high εH At the same time, it also features low CVCM, good adhesion, and resistance to space environment. This coating can achieve efficient heat dissipation without increasing the coating area or thickness, which strongly supports the development trend of lightweight, miniaturized, and high power density of future spacecraft, and provides a coating solution that combines efficient thermal control performance with excellent adaptability to the space environment. Attached Figure Description

[0032] Figure 1 An optical photograph of the black thermal control coating sprayed on an aluminum alloy substrate in Embodiment 1 of the present invention;

[0033] Figure 2 The integrated sphere reflectance spectrum of the black thermal control coating in the visible-near infrared band of 400-2000 nm in Embodiment 1 of the present invention;

[0034] Figure 3 The infrared reflectance spectrum of the black thermal control coating in the far-infrared band of 2.5–20 μm in Embodiment 1 of the present invention is shown.

[0035] Figure 4 This is an optical photograph of the adhesion test of the black thermal control coating sprayed on an aluminum alloy substrate in Embodiment 1 of the present invention after the cross-cut adhesion test. Detailed Implementation

[0036] The following description is provided in the specific applications and requirements thereof, which will enable those skilled in the art to make and use this application. It will be apparent to those skilled in the art that various changes can be made to the disclosed embodiments, and the general principles defined herein can be applied to other embodiments and application scenarios without departing from the principles and scope of this application. Therefore, this application is not limited to the described embodiments, but should be given the broadest scope consistent with the claims.

[0037] It should be understood that the expression “one or more of…” individually includes each of the objects described after the expression, as well as various different combinations of two or more of the described objects, unless otherwise understood from the context and usage. The expression “and / or” combined with three or more described objects should be understood to have the same meaning, unless otherwise understood from the context.

[0038] The terms “including,” “having,” or “containing,” including the use of their grammatical synonyms, should generally be understood as open-ended and non-restrictive, for example, not excluding other unstated elements or steps, unless otherwise specifically stated or understood from the context.

[0039] It should be understood that the order of the steps or the order in which certain actions are performed is not important as long as the invention remains operational. Furthermore, two or more steps or actions can be performed simultaneously.

[0040] The use of any and all instances or exemplary language such as “e.g.” or “including” in this document is merely intended to better illustrate the invention and is not intended to limit the scope of the invention unless the claims are made. No language in this specification should be construed as indicating that any unclaimed element is essential to the practice of the invention.

[0041] This invention discloses an optical absorber, a thermal control black paint, and a method for preparing an aerospace thermal control coating. To test the performance indicators of the obtained thermal control coating, the coating formed on the aerospace metal substrate needs to undergo solar absorptivity test, infrared emissivity test, and coating adhesion test.

[0042] The required performance target range for the thermal control coating is as follows:

[0043] Solar absorptivity: 0.95±0.02; Infrared hemispherical reflectivity: 0.92±0.02; CVCM (%)≤0.01%; Cross-cut adhesion rating: 0.

[0044] 1. The experimental method for solar absorptivity testing is: "GJB 2502.2-2015 Test Methods for Thermal Control Coatings of Spacecraft Part 2: Solar Absorptivity Testing", with a test band of 400-2000nm.

[0045] 2. The infrared emissivity test method is: "GJB 2502.3-2015 Test Methods for Thermal Control Coatings of Spacecraft Part 3: Emissivity Test", with a test band of 2.5~20um.

[0046] 3. The CVCM test method is: QJ1558A-2012 "Test Method for Volatilization Properties of Materials under Vacuum Conditions".

[0047] 4. The test method for coating adhesion is GB / T 9286-2021 "Cross-cut test for paints and varnishes".

[0048] Example 1

[0049] Preparation of optical absorbers:

[0050] Weigh 20g of multi-walled carbon nanotubes (CNTs) with a diameter of 10-20 nm and a length of 10-30 μm, 6g of dispersant DA345 (accounting for 30% of the mass of CNTs), and 474g of ethanol solvent, and stir at 800 rpm for 30 min.

[0051] The premixed liquid was transferred to a sand mill, and 0.6 mm zirconia beads were added (the volume ratio of material to zirconia beads was 1:1.5). The mixture was then sand-milled at 2000 rpm for 3 hours, with the temperature controlled at 30±5℃.

[0052] After dispersion, the solution was filtered through a 150-mesh sieve to obtain a carbon nanotube ethanol dispersion with a solid content of 4%.

[0053] 200 g of fumed silica powder with an average particle size of 50 nm was weighed and mixed with the above-mentioned carbon nanotube dispersion (containing 20 g of CNTs) to achieve a SiO2 to CNT mass ratio of 10:1. The mixture was treated at 5000 rpm for 60 min using a high-speed shear emulsifier. Subsequently, the solvent was evaporated at 70 °C and 300 rpm with stirring to obtain a composite powder.

[0054] Finally, the powder was pulverized and passed through a 400-mesh sieve to obtain the final binary composite optical absorber with a particle size of less than 38 μm.

[0055] Preparation of thermal control coatings:

[0056] Group A formulation: Weigh 100g of high-phenyl-content silicone resin (phenyl Ph: silicon atom Si = 0.4:1), add 20g of the above-mentioned optical absorber, 1g of dispersant BYK-163, and sufficient propylene glycol methyl ether acetate solvent, and adjust the slurry solid content to 30%. Disperse at high speed at 2000 rpm for 2 hours.

[0057] Component B: Hydrogen-terminated silicone oil (active hydrogen content 1.5%).

[0058] Component C: Platinum-vinylsiloxane complex.

[0059] Mix components A, B, and C in a certain proportion and stir for 20 minutes.

[0060] Preparation of aerospace thermal control black coating:

[0061] Thermal control coating is sprayed onto an aluminum alloy substrate.

[0062] Spraying parameters: nozzle diameter 1.5mm, air pressure 2 atm, distance 20cm, 4 coats. Then cure at 70℃ for 4 hours, then heat to 100℃ and cure for 10 hours to obtain a coating with a thickness of approximately 80μm.

[0063] In this embodiment, the performance indicators of the black coating obtained after adjusting the proportions of components A, B, and C are shown in Table 1.

[0064] Table 1: Performance indicators of black coatings formed with components A, B, and C as variables.

[0065]

[0066] Figure 1 and Figure 4 Optical photographs of the black thermal control coating sprayed on an aluminum alloy substrate with component A being 100g, component B being 4g, and component C being 0.3g are shown, as well as optical photographs of the black thermal control coating after the adhesion test using the cross-cut adhesion method.

[0067] Figure 2 The integral sphere reflectance spectrum of the black thermal control coating in the visible-near infrared band of 400–2000 nm is shown when component A is 100 g, component B is 4 g, and component C is 0.3 g.

[0068] Figure 3 The infrared reflectance spectrum of the black thermal control coating in the 2.5–20 μm mid-far infrared band is shown when component A is 100 g, component B is 4 g, and component C is 0.3 g.

[0069] Example 2

[0070] Preparation of optical absorbers:

[0071] Weigh 20g of multi-walled carbon nanotubes (CNTs) with a diameter of 10-20 nm and a length of 10-30 μm, 6g of dispersant DA345 (accounting for 30% of the mass of CNTs), and 474g of ethanol solvent, and stir at 800 rpm for 30 min.

[0072] The premixed liquid was transferred to a sand mill, and 0.6 mm zirconia beads were added (the volume ratio of material to zirconia beads was 1:1.5). The mixture was then sand-milled at 2000 rpm for 3 hours, with the temperature controlled at 30±5℃.

[0073] After dispersion, the solution was filtered through a 150-mesh sieve to obtain a carbon nanotube ethanol dispersion with a solid content of 4%.

[0074] 200 g of fumed silica powder with an average particle size of 50 nm was weighed and mixed with the above-mentioned carbon nanotube dispersion (containing 20 g of CNTs) to achieve a SiO2 to CNT mass ratio of 10:1. The mixture was treated at 5000 rpm for 60 min using a high-speed shear emulsifier. Subsequently, the solvent was evaporated at 70 °C and 300 rpm with stirring to obtain a composite powder.

[0075] Finally, the powder was pulverized and passed through a 400-mesh sieve to obtain the final binary composite optical absorber with a particle size of less than 38 μm.

[0076] Preparation of thermal control coatings:

[0077] Group A formulation: Weigh 100g of binder, add 20g of the above-mentioned optical absorber, 1g of dispersant BYK-163, and sufficient propylene glycol methyl ether acetate solvent to adjust the slurry solids content to 30%. Disperse at high speed at 2000 rpm for 2 hours.

[0078] Component B: Hydrogen-containing silicone oil with end groups (1% active hydrogen content);

[0079] Component C: Platinum-vinylsiloxane complex.

[0080] Mix 100g of component A, 4g of component B, and 0.3g of component C, and stir for 20 minutes.

[0081] Preparation of aerospace thermal control black coating:

[0082] Thermal control coating is sprayed onto a magnesium alloy substrate.

[0083] Spraying parameters: nozzle diameter 1.5mm, air pressure 2 atm, distance 20cm, 4 coats. Then cure at 70℃ for 4 hours, then heat to 100℃ and cure for 10 hours to obtain a coating with a thickness of approximately 80μm.

[0084] Table 2: Performance indicators of black coatings formed with binder as a variable.

[0085]

[0086] By adjusting the molar ratio (Ph / Si) of phenyl to silicon atoms in the silicone resin, the optical, thermal, and mechanical properties of the adhesive can be synergistically optimized, thereby improving the overall performance of the thermal control coating. When the Ph / Si molar ratio is 0.3-0.6:1, the resin refractive index matches the surface of the core-shell structure absorber, reducing interfacial light scattering loss and enabling the coating to achieve a high solar absorptivity. Phenyl groups enhance the rigidity of the molecular chain, improve the thermal stability of the resin, and inhibit the generation of condensable volatiles. The π-π interaction between the benzene ring and carbon nanotubes improves interfacial bonding and enhances coating adhesion. When the Ph / Si ratio is below 0.3, the low refractive index leads to enhanced interfacial reflection and decreased absorption, while the resin's thermal stability is insufficient and the content of condensable volatiles is high. When the Ph / Si ratio is above 0.6, the resin becomes more brittle, optical scattering increases, and both adhesion and absorption performance decrease.

[0087] Example 3

[0088] Preparation of optical absorbers:

[0089] Weigh 20g of multi-walled carbon nanotubes (CNTs) with a diameter of 10-20 nm and a length of 10-30 μm, 6g of dispersant DA345 (accounting for 30% of the mass of CNTs), and 474g of ethanol solvent, and stir at 800 rpm for 30 min.

[0090] The premixed liquid was transferred to a sand mill, and 0.6 mm zirconia beads were added (the volume ratio of material to zirconia beads was 1:1.5). The mixture was then sand-milled at 2000 rpm for 3 hours, with the temperature controlled at 30±5℃.

[0091] After dispersion, the solution was filtered through a 150-mesh sieve to obtain a carbon nanotube ethanol dispersion with a solid content of 4%.

[0092] Weigh out fumed silica powder with an average particle size of 50 nm and mix it with the above carbon nanotube dispersion. Treat the mixture at 5000 rpm for 60 min using a high-speed shear emulsifier. Then evaporate the solvent at 70°C and 300 rpm with stirring to obtain a composite powder.

[0093] Finally, the powder was pulverized and passed through a 400-mesh sieve to obtain the final binary composite optical absorber with a particle size of less than 38 μm.

[0094] Preparation of thermal control coatings:

[0095] Group A preparation: Weigh 100g of high phenyl content silicone resin (Ph / Si=0.4:1), add 20g of the above-mentioned optical absorber, 1g of dispersant BYK-163, and sufficient propylene glycol methyl ether acetate solvent, and adjust the slurry solid content to 30%. Disperse at high speed at 2000 rpm for 2 hours.

[0096] Component B: Hydrogen-terminated silicone oil (active hydrogen content 1.8%).

[0097] Component C: Platinum-vinylsiloxane complex.

[0098] Mix 100g of component A, 4g of component B, and 0.3g of component C, and stir for 20 minutes.

[0099] Preparation of aerospace thermal control black coating:

[0100] Thermal control coating is sprayed onto an aluminum-based silicon carbide substrate.

[0101] Spraying parameters: nozzle diameter 1.5mm, air pressure 2 atm, distance 20cm, 4 coats. Then cure at 70℃ for 4 hours, then heat to 100℃ and cure for 10 hours to obtain a coating with a thickness of approximately 80μm.

[0102] In this embodiment, the performance indicators of the black coating obtained after adjusting the mass ratio of SiO2 to CNT in the optical absorber are shown in Table 3.

[0103] Table 3: Performance indicators of black coatings formed with SiO2 to CNT mass ratio as the variable.

[0104]

[0105] When the SiO2 to CNT mass ratio is less than 5:1, carbon nanotubes are relatively excessive, and some carbon nanotubes agglomerate. Agglomerated carbon nanotubes form light scattering centers in the coating, reducing solar absorptivity. Simultaneously, the excessively thick carbon nanotube shell hinders the transfer of infrared vibrational energy from the silica core to the shell, reducing infrared hemispherical emissivity. When the mass ratio is greater than 20:1, the carbon nanotube content is insufficient, resulting in incomplete coating and partial exposure of silica. Exposed silica has weak absorption capacity for sunlight, reducing solar absorptivity; simultaneously, the lack of interfacial coupling between silica and the carbon nanotube shell reduces infrared hemispherical emissivity. Therefore, the SiO2 to CNT mass ratio needs to be controlled within the range of 5:1 to 20:1 to obtain a uniform and continuous core-shell coating structure and a coating with satisfactory optical properties.

[0106] Example 4

[0107] Preparation of optical absorbers:

[0108] Weigh 20g of multi-walled carbon nanotubes (CNTs) with a diameter of 10-20 nm and a length of 10-30 μm, 6g of dispersant DA345 (accounting for 30% of the mass of CNTs), and 474g of ethanol solvent, and stir at 800 rpm for 30 min.

[0109] The premixed liquid was transferred to a sand mill, and 0.6 mm zirconia beads were added (the volume ratio of material to zirconia beads was 1:1.5). The mixture was sand milled and dispersed at 2000 rpm for 3 hours, with the temperature controlled at 30±5℃.

[0110] After dispersion, the solution was filtered through a 150-mesh sieve to obtain a carbon nanotube ethanol dispersion with a solid content of 4%.

[0111] 200 g of fumed silica powder with an average particle size of 50 nm was weighed and mixed with the above-mentioned carbon nanotube dispersion (containing 20 g of CNTs) to achieve a SiO2 to CNT mass ratio of 10:1. The mixture was treated at 5000 rpm for 60 min using a high-speed shear emulsifier. Subsequently, the solvent was evaporated at 70 °C and 300 rpm with stirring to obtain the composite powder.

[0112] Finally, the powder was pulverized and passed through a 400-mesh sieve to obtain the final binary composite optical absorber with a particle size of less than 38 μm.

[0113] Preparation of thermal control coatings:

[0114] Group A preparation: Weigh out high-phenyl-content silicone resin (phenyl Ph: silicon atom Si = 0.4:1), add optical absorber, dispersant BYK-163, and sufficient propylene glycol methyl ether acetate solvent, and adjust the slurry solid content to 30%. Disperse at high speed at 2000 rpm for 2 hours.

[0115] Component B: Hydrogen-terminated silicone oil (active hydrogen content 1.5%).

[0116] Component C: Platinum-vinylsiloxane complex.

[0117] Mix 100g of component A, 4g of component B, and 0.3g of component C, and stir for 20 minutes.

[0118] Preparation of aerospace thermal control black coating:

[0119] Thermal control coating is sprayed onto the aluminum alloy substrate.

[0120] Spraying parameters: nozzle diameter 1.5mm, air pressure 2 atm, distance 20cm, 4 coats. Then cure at 70℃ for 4 hours, then heat to 100℃ and cure for 10 hours to obtain a coating with a thickness of approximately 80μm.

[0121] In this embodiment, the performance indicators of the black coating obtained after adjusting the proportions of each component in component A are shown in Table 4.

[0122] Table 4: Performance indicators of the black coating formed by varying the proportions of each component in component A.

[0123]

[0124] When the amount of optical absorber added is too low, the absorber content in the coating is insufficient, and the incident light cannot be fully captured, resulting in a decrease in solar absorptivity. Simultaneously, the increased proportion of resin matrix in the coating leads to a lower intrinsic infrared emissivity, resulting in a decrease in the overall infrared emissivity of the coating. When the amount of optical absorber added is too high, the dispersion uniformity deteriorates, making agglomeration more likely. The optical absorber cannot be effectively and fully wetted by the resin, leading to increased internal defects in the coating, decreased cohesive strength, and weakened adhesion to the substrate. Therefore, the amount of optical absorber must be controlled within a reasonable range to balance optical performance and coating adhesion.

[0125] Example 5

[0126] Preparation of optical absorbers:

[0127] Weigh 20g of multi-walled carbon nanotubes (CNTs) with a diameter of 10-20 nm and a length of 10-30 μm, 6g of dispersant DA345 (accounting for 30% of the mass of CNTs), and 474g of ethanol solvent, and stir at 800 rpm for 30 min.

[0128] The premixed liquid was transferred to a sand mill, and 0.6 mm zirconia beads were added (the volume ratio of material to zirconia beads was 1:1.5). The mixture was then sand-milled at 2000 rpm for 3 hours, with the temperature controlled at 30±5℃.

[0129] After dispersion, the solution was filtered through a 150-mesh sieve to obtain a carbon nanotube ethanol dispersion with a solid content of 4%.

[0130] 200 g of fumed silica powder with an average particle size of 50 nm was weighed and mixed with the above-mentioned carbon nanotube dispersion (containing 20 g of CNTs) to achieve a SiO2 to CNT mass ratio of 10:1. The mixture was treated at 5000 rpm for 60 min using a high-speed shear emulsifier. Subsequently, the solvent was evaporated at 70 °C and 300 rpm with stirring to obtain a composite powder.

[0131] Finally, the powder was pulverized and passed through a 400-mesh sieve to obtain the final binary composite optical absorber with a particle size of less than 38 μm.

[0132] Preparation of thermal control coatings:

[0133] Group A preparation: Weigh 100g of high phenyl content silicone resin (phenyl Ph: silicon atom Si = 0.4:1), add 20g of the above-mentioned optical absorber, 1g of dispersant BYK-2155, and sufficient propylene glycol methyl ether acetate solvent, and adjust the slurry solid content to 30%. Disperse at high speed at 2000 rpm for 2 hours.

[0134] Component B: Hydrogen-containing silicone oil with side chains (active hydrogen content 1.2%).

[0135] Component C: Platinum-vinylsiloxane complex.

[0136] Mix 100g of component A, 4g of component B, and 0.3g of component C, and stir for 20 minutes.

[0137] Preparation of aerospace thermal control black coating:

[0138] Thermal control coating is sprayed onto a titanium alloy substrate.

[0139] Spraying parameters: nozzle diameter 1.5mm, air pressure 2 atm, distance 20cm, 4 coats. Then cure at 70℃ for 4 hours, then heat to 100℃ and cure for 10 hours to obtain a coating with a thickness of approximately 80μm.

[0140] Compared to Example 1, in this Example 1, component B uses a side-chain hydrogen-containing silicone oil, the dispersant used in the preparation of the thermal control coating is BYK-2155, and the coating substrate is a titanium alloy.

[0141] The performance indicators of the coating obtained in this embodiment are as follows:

[0142] Solar absorptivity: 0.95; Infrared hemispherical reflectivity: 0.93; CVCM (%): 0.008; Cross-cut adhesion rating: 0.

[0143] Comparative Example 1

[0144] Optical absorbent: Traditional carbon black is used as the absorbent without special treatment.

[0145] Preparation of thermal control coatings:

[0146] Component A: Weigh 100g of high-phenyl-content silicone resin (Ph / Si=0.4:1), add 20g of high-pigment carbon black, 1g of dispersant BYK-163, and sufficient propylene glycol methyl ether acetate solvent to adjust the slurry solids content to 30%. Disperse at 2000 rpm for 2 hours. Component B: Hydrogen-terminated silicone oil (active hydrogen content 1.5%). Component C: Platinum-vinylsiloxane complex.

[0147] The aerospace thermal control black coating is prepared by mixing 100g of component A, 4g of component B, and 0.3g of component C and stirring for 20 minutes.

[0148] Preparation of aerospace thermal control black coating:

[0149] Thermal control coating is sprayed onto an aluminum alloy substrate.

[0150] Spraying parameters: nozzle diameter 1.5mm, air pressure 2 atm, distance 20cm, 4 coats. Then cure at 70℃ for 4 hours, then heat to 100℃ and cure for 10 hours to obtain a coating with a thickness of approximately 80μm.

[0151] The performance indicators of the coating obtained in this embodiment are as follows:

[0152] Solar absorptivity: 0.92; Infrared hemispherical reflectivity: 0.87; CVCM (%): 0.009; Cross-cut adhesion rating: Grade 1.

[0153] In this embodiment, the optical absorber was replaced with traditional carbon black, but the solar absorptivity, infrared hemispherical reflectivity, CVCM, and cross-cut adhesion were all substandard.

[0154] Comparative Example 2

[0155] Preparation of optical absorbers:

[0156] Weigh 20g of multi-walled carbon nanotubes (CNTs) with a diameter of 10-20 nm and a length of 10-30 μm, 6g of dispersant DA345 (accounting for 30% of the mass of CNTs), and 474g of ethanol solvent, and stir at 800 rpm for 30 min.

[0157] The premixed liquid was transferred to a sand mill, and 0.6 mm zirconia beads were added (the volume ratio of material to zirconia beads was 1:1.5). The mixture was then sand-milled at 2000 rpm for 3 hours, with the temperature controlled at 30±5℃.

[0158] After dispersion, the solution was filtered through a 150-mesh sieve to obtain a carbon nanotube ethanol dispersion with a solid content of 4%.

[0159] 200 g of fumed silica powder with an average particle size of 50 nm was weighed and mixed with the above-mentioned carbon nanotube dispersion (containing 20 g of CNTs) to achieve a SiO2 to CNT mass ratio of 10:1. The mixture was treated at 5000 rpm for 60 min using a high-speed shear emulsifier. Subsequently, the solvent was evaporated at 70 °C and 300 rpm with stirring to obtain a composite powder.

[0160] Finally, the powder was pulverized and passed through a 400-mesh sieve to obtain the final binary composite optical absorber with a particle size of less than 38 μm.

[0161] Preparation of thermal control coatings:

[0162] Group A formulation: Weigh 100g of high-phenyl-content silicone resin (phenyl Ph: silicon atom Si = 0.4:1), add 20g of the above-mentioned optical absorber, 1g of dispersant BYK-163, and sufficient propylene glycol methyl ether acetate solvent, and adjust the slurry solid content to 30%. Disperse at high speed at 2000 rpm for 2 hours.

[0163] Component B: Methyltrimethoxysilane, added at 5% of the mass of Component A resin.

[0164] Component C: Dibutyltin dilaurate, added at 0.2% of the mass of component A resin.

[0165] Mix components A, B, and C in the specified ratio, stir for 20 minutes, and then use the mixture for the preparation of aerospace thermal control black coating.

[0166] Preparation of aerospace thermal control black coating:

[0167] Thermal control coating is sprayed onto an aluminum alloy substrate.

[0168] Spraying parameters: nozzle diameter 1.5mm, air pressure 2 atm, distance 20cm, spray 4 coats. The coating is then cured for 7 days at room temperature (25℃) with a relative humidity of 50%±5% to achieve full curing and a coating thickness of approximately 80μm.

[0169] The performance indicators of the coating obtained in this embodiment are as follows:

[0170] Solar absorptivity: 0.95; Infrared hemispherical reflectivity: 0.91; CVCM (%): 0.045; Cross-cut adhesion rating: Grade 1.

[0171] In this embodiment, instead of using hydrogen-containing silicone oil as a crosslinking agent and platinum catalyst in the addition-type curing system, methyltrimethoxysilane is used as the crosslinking agent in the condensation-type system.

[0172] Comparative Example 3

[0173] Preparation of optical absorbers:

[0174] Weigh 20g of multi-walled carbon nanotubes (CNTs) with a diameter of 10-20 nm and a length of 10-30 μm, 6g of dispersant DA345 (accounting for 30% of the mass of CNTs), and 474g of ethanol solvent, and stir at 800 rpm for 30 min.

[0175] The premixed liquid was transferred to a sand mill, and 0.6 mm zirconia beads were added (the volume ratio of material to zirconia beads was 1:1.5). The mixture was then sand-milled at 2000 rpm for 3 hours, with the temperature controlled at 30±5℃.

[0176] After dispersion, the solution was filtered through a 150-mesh sieve to obtain a carbon nanotube ethanol dispersion with a solid content of 4%.

[0177] 200 g of fumed silica powder with an average particle size of 50 nm was weighed and mixed with the above-mentioned carbon nanotube dispersion (containing 20 g of CNTs) to achieve a SiO2 to CNT mass ratio of 10:1. The mixture was treated with low-speed stirring at 1000 rpm for 60 min, followed by standing. After standing, the solvent was evaporated at 70 °C and stirring at 300 rpm to obtain the composite powder.

[0178] Finally, the powder was pulverized and passed through a 400-mesh sieve to obtain the final binary composite optical absorber with a particle size of less than 38 μm.

[0179] Preparation of thermal control coatings:

[0180] Group A formulation: Weigh 100g of high-phenyl-content silicone resin (phenyl Ph: silicon atom Si = 0.4:1), add 20g of the above-mentioned optical absorber, 1g of dispersant BYK-163, and sufficient propylene glycol methyl ether acetate solvent, and adjust the slurry solid content to 30%. Disperse at high speed at 2000 rpm for 2 hours.

[0181] Component B: Hydrogen-terminated silicone oil (active hydrogen content 1.5%).

[0182] Component C: Platinum-vinylsiloxane complex.

[0183] Mix 100g of component A, 4g of component B, and 0.3g of component C, and stir for 20 minutes.

[0184] Preparation of aerospace thermal control black coating:

[0185] Thermal control coating is sprayed onto the aluminum alloy substrate.

[0186] Spraying parameters: nozzle diameter 1.5mm, air pressure 2 atm, distance 20cm, 4 coats. Then cure at 70℃ for 4 hours, then heat to 100℃ and cure for 10 hours to obtain a coating with a thickness of approximately 80μm.

[0187] The performance indicators of the coating obtained in this embodiment are as follows:

[0188] Solar absorptivity: 0.92; Infrared hemispherical reflectivity: 0.88; CVCM (%): 0.012; Cross-cut adhesion rating: Grade 1.

[0189] In the preparation of the optical absorber, the carbon nanotube dispersion was mixed with silica and then stirred at a low speed without high-speed shearing. Low-speed shearing cannot provide sufficient energy to allow the carbon nanotubes to spread uniformly on the silica surface and form a stable coating, resulting in incomplete or uneven coating and a decrease in optical performance.

[0190] Comparative Example 4

[0191] Preparation of optical absorbers:

[0192] Weigh 20g of multi-walled carbon nanotubes (CNTs) with a diameter of 10-20 nm and a length of 10-30 μm, 6g of dispersant DA345 (accounting for 30% of the mass of CNTs), and 474g of ethanol solvent, and stir at 800 rpm for 30 min.

[0193] The premixed liquid was transferred to a sand mill, and 0.6 mm zirconia beads were added (the volume ratio of material to zirconia beads was 1:1.5). The mixture was sand milled and dispersed at 2000 rpm for 3 hours, with the temperature controlled at 30±5℃.

[0194] After dispersion, the solution was filtered through a 150-mesh sieve to obtain a carbon nanotube ethanol dispersion with a solid content of 4%.

[0195] 200 g of fumed silica powder with an average particle size of 50 nm was weighed and mixed with the above carbon nanotube dispersion (containing 20 g of CNTs) to achieve a SiO2 to CNT mass ratio of 10:1. The mixture was stirred at 500 rpm for 30 min. Subsequently, the solvent was evaporated at 70 °C and 300 rpm to obtain the composite powder.

[0196] Finally, the powder was pulverized and passed through a 400-mesh sieve to obtain the final optical absorber with a particle size of less than 38 μm.

[0197] Preparation of thermal control coatings:

[0198] Group A preparation: Weigh 100g of high phenyl content silicone resin (Ph / Si=0.4:1), add 20g of the above-mentioned optical absorber, 1g of dispersant BYK-163, and sufficient propylene glycol methyl ether acetate solvent, and adjust the slurry solid content to 30%. Disperse at high speed at 2000 rpm for 2 hours.

[0199] Component B: Hydrogen-terminated silicone oil (active hydrogen content 1.5%).

[0200] Component C: Platinum-vinylsiloxane complex.

[0201] Mix 100g of component A, 4g of component B, and 0.3g of component C, and stir for 20 minutes.

[0202] Preparation of aerospace thermal control black coating:

[0203] Thermal control coating is sprayed onto an aluminum alloy substrate.

[0204] Spraying parameters: nozzle diameter 1.5mm, air pressure 2 atm, distance 20cm, 4 coats. Then cure at 70℃ for 4 hours, then heat to 100℃ and cure for 10 hours to obtain a coating with a thickness of approximately 80μm.

[0205] The performance indicators of the coating obtained in this embodiment are as follows:

[0206] Solar absorptivity: 0.91; Infrared hemispherical reflectivity: 0.89; CVCM (%): 0.011; Cross-cut adhesion rating: Grade 1.

[0207] In this embodiment, a core-shell structured absorbent is not used; instead, carbon nanotubes and silica powder are physically mixed without any coating treatment.

[0208] Although the carbon nanotube dispersion was mixed with silica and stirred at low speed, the main difference was that no high-speed shear coating treatment was performed, and the solvent was directly evaporated after mixing. In effect, this was equivalent to physically mixing the carbon nanotubes and silica without forming a core-shell coating structure. The purpose was to verify the necessity of the core-shell structure: even using the same raw materials, without coating, effective interfacial coupling cannot be formed through physical mixing alone, resulting in a decrease in optical properties and adhesion.

[0209] The present invention can be well implemented according to the above embodiments. It is worth noting that, based on the above structural design, even if some non-substantial modifications or refinements are made to the present invention to solve the same technical problem, the essence of the technical solution adopted is still the same as that of the present invention, and therefore it should also be within the protection scope of the present invention.

Claims

1. An optical absorber, characterized in that, Its preparation method is as follows: The carbon nanotube powder, dispersant, and solvent are stirred, mixed, and then ground and dispersed. The slurry obtained after dispersion is filtered to obtain a uniform and stable dispersion. The dispersion was mixed with inorganic silica powder and then immediately subjected to high-speed shearing to coat the surface of the silica particles with carbon nanotubes, resulting in a mixture. The shearing speed was ≥5000 rpm and the processing time was ≥60 min. The composite absorbent is obtained by evaporating the solvent from the mixture. The mass ratio of inorganic silica powder to carbon nanotube powder is 5-20:

1.

2. The optical absorber according to claim 1, characterized in that, The particle size of the powder in the composite absorbent is less than 50µm.

3. The optical absorber according to claim 1, characterized in that, The carbon nanotube powder is a multi-walled carbon nanotube with a diameter ranging from 10 to 30 nm and a length ranging from 10 to 50 µm.

4. A heat-controlled black paint, characterized in that, It includes 1000 parts by weight of component A, 35-45 parts by weight of component B, and 2-4 parts by weight of component C; Component A comprises: the optical absorber, organosilicon resin, dispersant, and solvent as described in any one of claims 1-4; Component B includes: crosslinking agent; Component C includes: catalyst.

5. The thermally controlled black paint according to claim 4, characterized in that, The crosslinking agent is hydrogen-containing silicone oil.

6. An optical absorber according to claim 4, characterized in that, The catalyst is a platinum-containing catalyst.

7. An optical absorber according to claim 4, characterized in that, In the organosilicon resin, the molar ratio of phenyl to silicon atoms is 0.3-0.6:

1.

8. A method for preparing an aerospace thermal control coating, characterized in that, Thermal control black paint is sprayed onto an aerospace metal substrate and cured to form a thermal control coating.

9. The method for preparing an aerospace thermal control coating according to claim 8, characterized in that, The aerospace metal substrate is made of aluminum alloy, titanium alloy, aluminum-based silicon carbide, or magnesium alloy.

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