Highly thermally conductive radiant refrigeration coating and method of making same

Abstract

The application belongs to the technical field of coating preparation, and provides high-thermal-conductivity radiation refrigeration coating and a preparation method thereof; surface-modified hexagonal boron nitride is prepared through steps such as ball milling stripping, oxidation and hydroxylation, and is further subjected to surface organic modification to improve its dispersibility and interfacial bonding force; dendritic silicon carbide is prepared by using a molten salt method, and an aluminum oxide nanolayer is in-situ grown on the surface of the silicon carbide, and the silicon carbide is modified by silane and phosphoric acid in cooperation to enhance the interfacial compatibility and heat conduction capacity of the silicon carbide with a resin; through preparation of aluminum nitride in an ammonia atmosphere at high temperature and borax activation treatment, combined with hydrothermal method coating of calcium fluoride, a composite filler with high thermal conductivity and infrared emission performance is obtained; the above various functional fillers are combined with a resin matrix such as water-based fluorocarbon emulsion, acrylic emulsion and polyimide emulsion, and the prepared coating significantly improves the conduction efficiency of heat from the inside of equipment to the outside, and realizes high-efficiency passive radiation cooling.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of coating preparation, and relates to high-thermal-conductivity radiation refrigeration coating and a preparation method thereof. BACKGROUND

[0002] Traditional radiation refrigeration coating usually relies on the addition of low-thermal-conductivity fillers such as hollow glass microbeads in the design to improve the solar reflectivity and thermal insulation performance of the coating. Such materials can effectively reflect incident solar radiation and reduce the absorption of external heat, thereby achieving passive cooling to a certain extent. Hollow glass microbeads can form a large number of scattering interfaces in the coating due to their unique hollow structure and low density characteristics, thereby enhancing the multiple scattering effect of visible light and near-infrared light and further improving the solar reflectivity of the coating. In addition, the introduction of low-thermal-conductivity fillers can also reduce the overall thermal conductivity of the coating, slowing down the transfer of external heat to the substrate and helping to improve the thermal insulation effect.

[0003] However, the thermal conductivity of hollow glass microbeads is lower than that of metals or other high-thermal-conductivity inorganic materials. When such coating is applied to the surface of equipment with internal heat sources, such as 5G communication base station cabinets, LED lighting equipment, etc., the low-thermal-conductivity fillers will form a thermal resistance barrier inside the coating, hindering the transfer of heat generated inside the equipment to the outside. Due to the difficulty of heat to pass through the low-thermal-conductivity coating, the heat energy inside the equipment gradually accumulates, causing local temperature rise and affecting the normal operation and service life of the equipment. At the same time, the heat cannot be efficiently transferred to the surface of the coating, so it cannot be released to the external environment in a timely manner through radiation, and the radiation refrigeration function of the coating is thus severely limited. SUMMARY

[0004] In view of the deficiencies of the prior art, the purpose of the present application is to provide high-thermal-conductivity radiation refrigeration coating and a preparation method thereof. Hexagonal boron nitride is modified by hydroxylation and fluorination to endow it with excellent infrared emission and thermal conductivity performance. Secondly, SiC@delta-Al2O3 composite material with high thermal conductivity and surface functionalization is prepared by salt dissolution method and hydrothermal treatment. Thirdly, AlN@CaF2 composite material is prepared by pyrolysis and melting treatment of aluminum foil in ammonia atmosphere to improve its infrared emission ability in the atmospheric window band. Finally, the modified fillers and water-based matrix material are fully mixed, supplemented with functional additives, and subjected to three-roll grinding and defoaming treatment to prepare coating with high solar reflectivity, hemispherical emittance and thermal conductivity performance, thereby meeting the needs of actual production.

[0005] To achieve this purpose, the technical scheme adopted by the present application is as follows:

[0006] In a first aspect, the present application provides a preparation method of high-thermal-conductivity radiation refrigeration coating, which comprises:

[0007] S1, mixing cubic silicon carbide, potassium chloride and sodium chloride, and keeping warm to obtain silicon carbide dendrite, immersing the silicon carbide dendrite into aluminum isopropyl alcohol sol, airing the surface liquid, transferring to an autoclave to obtain SiC@δ-Al2O3, mixing ethanol and γ-aminopropyl triethoxysilane, adding phosphoric acid, SiC@δ-Al2O3 to react to obtain modified SiC@δ-Al2O3;

[0008] S2, mixing aluminum foil fragments and urea, and then placing them in a tube furnace in an ammonia atmosphere, keeping warm to obtain aluminum nitride, melting borax and then vibrating and immersing into the aluminum nitride to obtain activated aluminum nitride, and then adding the activated aluminum nitride into a mixed solution to hydrothermally react to obtain AlN@CaF2;

[0009] S3, mixing deionized water, leveling agent and dispersant, and then adding water-based fluorocarbon emulsion, acrylic emulsion and polyimide emulsion in sequence, mixing uniformly, and then adding titanium dioxide, modified boron nitride, SiC@δ-Al2O3, AlN@CaF2 and calcium carbonate in sequence, mixing uniformly, and then adding defoaming agent, rheological agent, HDI water dispersion and aluminum dihydrogen phosphate solution to obtain high-thermal-radiation refrigeration coating.

[0010] Specifically includes:

[0011] A1, mixing hexagonal boron nitride and isopropyl alcohol to obtain slurry, mixing the slurry, sodium bisulfite and hydrogen peroxide solution, stirring at a first temperature, and then filtering and washing to obtain pretreated boron nitride, dispersing the pretreated boron nitride in ethylene glycol, heating to a second temperature for reflux reaction, and then vacuum drying to obtain hydroxylated boron nitride, dispersing the hydroxylated boron nitride, (1H, 1H, 2H, 2H-heptadecafluorodecyl) phosphonic acid, dicyclohexyl carbodiimide and 4-dimethylamino pyridine in anhydrous tetrahydrofuran, heating to a third temperature for reflux reaction under nitrogen atmosphere, filtering and washing after the reaction, and then drying to obtain modified boron nitride;

[0012] S1, mixing cubic silicon carbide, potassium chloride and sodium chloride, and keeping warm to obtain silicon carbide dendrite, immersing the silicon carbide dendrite into aluminum isopropyl alcohol sol, airing the surface liquid, transferring to an autoclave to obtain SiC@δ-Al2O3, mixing ethanol and γ-aminopropyl triethoxysilane, adding phosphoric acid, SiC@δ-Al2O3 to react to obtain modified SiC@δ-Al2O3;

[0013] S2, the aluminum foil fragments are mixed with urea and placed in a tube furnace in an ammonia atmosphere, heated to a sixth temperature, and cooled to obtain aluminum nitride. Borax is melted and then added to the aluminum nitride and vibrated for impregnation. After pouring out the aluminum nitride, cooling and washing, activated aluminum nitride is obtained. The activated aluminum nitride is added to the mixed solution for hydrothermal reaction, and AlN@CaF2 is obtained after washing and drying.

[0014] S3, deionized water, leveling agent, and dispersant are mixed, and then water-based fluorocarbon emulsion, acrylic emulsion, and polyimide emulsion are added in sequence. After mixing evenly, titanium dioxide, modified boron nitride, SiC@δ-Al2O3, AlN@CaF2, and calcium carbonate are added in sequence. After mixing evenly, defoaming agent, rheological agent, HDI water dispersion, and aluminum dihydrogen phosphate solution are added. Three-roll grinding, defoaming, and filtering obtain high-thermal-radiation refrigeration coating.

[0015] Hexagonal boron nitride is first peeled off by ball milling into a larger sheet structure. Ball milling not only helps to disperse the sheet, but also exposes more edge and surface active sites to some extent. Subsequently, the oxidation treatment of sodium bisulfite and hydrogen peroxide further introduces polar functional groups such as hydroxyl groups on the surface of boron nitride sheets. The polar groups improve the interfacial affinity of boron nitride and the polar resin matrix, allowing boron nitride to disperse uniformly in the coating system and reduce agglomeration. During the ethylene glycol reflux treatment stage, the hydroxyl content on the surface of boron nitride is further increased, and the sheet surface is more activated, providing reaction sites for subsequent modification. Boron nitride and (1H, 1H, 2H, 2H-heptadecafluorodecyl) phosphonic acid undergo esterification under the catalysis of dicyclohexyl carbodiimide and 4-dimethylaminopyridine. The phosphonic acid group is connected to the surface of boron nitride through covalent bonds, further improving the dispersibility and stability of boron nitride in the resin, and enhancing the interfacial bonding strength between boron nitride and the resin matrix. Since boron nitride itself has excellent thermal conductivity, and after surface modification it is tightly bonded to the resin matrix, heat can be efficiently transferred from the resin to the boron nitride sheet and rapidly spread along the sheet direction, reducing the thermal conduction resistance in the coating interior. This allows heat from the internal heat source to be transferred more quickly to the coating surface, avoiding the accumulation of heat inside the object.

[0016] Cubic silicon carbide is mixed with potassium chloride and sodium chloride and treated at high temperature, the eutectic salt system formed by potassium chloride and sodium chloride at high temperature can reduce the sintering temperature of silicon carbide and promote the dendritic growth of silicon carbide particles. Silicon carbide forms a dendritic structure under the wrapping and wetting effect of the molten salt at high temperature. The silicon carbide dendrites are immersed in an isopropyl alcohol aluminum sol, and the isopropyl alcohol aluminum is partially hydrolyzed in a mixed solvent of ethanol and water to form a nano-sized aluminum oxide precursor. Immersing the silicon carbide dendrites in the sol and vacuumizing the exhaust helps the sol to fully penetrate and coat the surface of the silicon carbide, and then transferring the silicon carbide dendrites coated with aluminum oxide precursors to an autoclave to grow δ-Al2O3 on the surface of the silicon carbide dendrites in situ. The δ-Al2O3 has high thermal conductivity and good chemical stability. Ethanol is mixed with γ-aminopropyl triethoxysilane, and after adding phosphoric acid, the mixture is continuously stirred to form a composite solution containing silane and phosphoric acid groups. SiC@δ-Al2O3 is added to the solution and heated to reflux. The γ-aminopropyl triethoxysilane hydrolyzes in the presence of ethanol and water, and the generated silanol groups can undergo condensation reaction with the hydroxyl groups on the surface of δ-alumina to form a firm Si-O-Al covalent bond. At the same time, phosphoric acid molecules can also react with surface hydroxyl groups to further introduce phosphoric acid groups. Finally, an organic-inorganic composite interface layer containing silane and phosphoric acid groups is formed on the surface of the silicon carbide dendrites. The silicon carbide dendrites themselves have excellent thermal conductivity, and the dendritic structure can form a continuous heat conduction channel in the coating. The introduction of the δ-Al2O3 coating layer and the organic modification layer improves the interfacial bonding between the silicon carbide and the resin matrix, enabling heat to be efficiently transferred from the resin to the silicon carbide dendrites and rapidly spread along the dendritic direction, thereby improving the overall thermal conductivity of the coating.

[0017] The aluminum foil pieces are mixed with urea and placed in a tube furnace, heated to high temperature in an ammonia atmosphere, and kept at high temperature. During this process, urea decomposes under heating to produce ammonia and a small amount of reducing gas, providing sufficient nitrogen source and partial reducing atmosphere for the reaction system. At high temperature, aluminum reacts with ammonia, and the surface gradually converts to aluminum nitride. The prepared aluminum nitride is contacted with molten borax and vibrated for impregnation. The borax melts at high temperature, forming a glassy phase with good fluidity, which can coat the surface of the aluminum nitride particles. The activated aluminum nitride is added to a mixed solution containing calcium and fluoride salts, and a hydrothermal reaction is carried out. Under hydrothermal conditions, calcium ions and fluoride ions react on the surface of aluminum nitride to generate a layer of calcium fluoride coating in situ. Calcium fluoride has low infrared absorption and excellent chemical stability, and this coating can effectively protect the aluminum nitride main phase from hydrolysis or oxidation during subsequent coating preparation and service, while not significantly reducing its thermal conductivity and infrared emission performance. The flaky aluminum nitride itself has excellent thermal conductivity and can form efficient heat flow channels in the coating. Surface activation and calcium fluoride coating not only improve the interfacial bonding between aluminum nitride and the resin matrix, but also reduce the interfacial thermal resistance, allowing heat to be transferred smoothly from the resin to the aluminum nitride layers and efficiently spread along the layer direction.

[0018] As a preferred technical solution of the present application, in A1, the mass ratio of hexagonal boron nitride, isopropanol, sodium bisulfite, aqueous hydrogen peroxide solution and ethylene glycol is (200-215):(780-800):(10-12):(20-22):700, for example, it can be (200, 201.5, 203, 204.5, 206, 207.5, 209, 210.5, 212, 213.5 or 215):(780, 782, 784, 786, 788, 790, 792, 794, 796, 798 or 800):(10, 10.2, 10.4, 10.6, 10.8, 11, 11.2, 11.4, 11.6, 11.8 or 12):(20, 20.2, 20.4, 20.6, 20.8, 21, 21.2, 21.4, 21.6, 21.8 or 22):700, but not limited to the listed values. Other values not listed in this range are also applicable.

[0019] In some optional examples, the mass fraction of the aqueous hydrogen peroxide solution is 30wt.%.

[0020] In some optional examples, the first temperature is 70-75℃, for example, it can be 70℃, 70.5℃, 71℃, 71.5℃, 72℃, 72.5℃, 73℃, 73.5℃, 74℃, 74.5℃ or 75℃, but not limited to the listed values. Other values not listed in this range are also applicable.

[0021] In some optional examples, the first temperature stirring time is 90-100 min, for example, can be 90 min, 91 min, 92 min, 93 min, 94 min, 95 min, 96 min, 97 min, 98 min, 99 min or 100 min, but not only limited to the listed values, other values not listed in the range of values are also applicable.

[0022] In some optional examples, the second temperature is 170-175℃, for example, can be 170℃, 170.5℃, 171℃, 171.5℃, 172℃, 172.5℃, 173℃, 173.5℃, 174℃, 174.5℃ or 175℃, but not only limited to the listed values, other values not listed in the range of values are also applicable.

[0023] In some optional examples, the second temperature reflux reaction time is 2-2.5h, for example, can be 2h, 2.05h, 2.1h, 2.15h, 2.2h, 2.25h, 2.3h, 2.35h, 2.4h, 2.45h or 2.5h, but not only limited to the listed values, other values not listed in the range of values are also applicable.

[0024] In some optional examples, the mass ratio of the hydroxylated boron nitride, (1H, 1H, 2H, 2H-heptadecafluorodecyl) phosphonic acid, dicyclohexyl carbodiimide, 4-dimethyl amino pyridine and anhydrous tetrahydrofuran is 300:(30-35):(15-18):1:900, for example, can be 300:(30, 30.5, 31, 31.5, 32, 32.5, 33, 33.5, 34, 34.5 or 35):(15, 15.3, 15.6, 15.9, 16.2, 16.5, 16.8, 17.1, 17.4, 17.7 or 18):1:900, but not only limited to the listed values, other values not listed in the range of values are also applicable.

[0025] In some optional examples, the third temperature is 85-90℃, for example, can be 85℃, 85.5℃, 86℃, 86.5℃, 87℃, 87.5℃, 88℃, 88.5℃, 89℃, 89.5℃ or 90℃, but not only limited to the listed values, other values not listed in the range of values are also applicable.

[0026] In some optional examples, the third temperature reflux reaction time is 3-3.5h, for example, can be 3h, 3.05h, 3.1h, 3.15h, 3.2h, 3.25h, 3.3h, 3.35h, 3.4h, 3.45h or 3.5h, but not only limited to the listed values, other values not listed in the range of values are also applicable.

[0027] As a preferred technical solution of the present application, in S1, the mass ratio of cubic silicon carbide, potassium chloride and sodium chloride is (20-23):(30-35):(30-35), for example, it can be (20, 20.3, 20.6, 20.9, 21.2, 21.5, 21.8, 22.1, 22.4, 22.7 or 23):(30, 30.5, 31, 31.5, 32, 32.5, 33, 33.5, 34, 34.5 or 35):(30, 30.5, 31, 31.5, 32, 32.5, 33, 33.5, 34, 34.5 or 35), but not limited to the listed values, other values not listed in the range are also applicable.

[0028] In some optional examples, the fourth temperature is 900-920℃, for example, it can be 900℃, 902℃, 904℃, 906℃, 908℃, 910℃, 912℃, 914℃, 916℃, 918℃ or 920℃, but not limited to the listed values, other values not listed in the range are also applicable.

[0029] In some optional examples, the time for the fourth temperature holding is 1-1.5h, for example, it can be 1h, 1.05h, 1.1h, 1.15h, 1.2h, 1.25h, 1.3h, 1.35h, 1.4h, 1.45h or 1.5h, but not limited to the listed values, other values not listed in the range are also applicable.

[0030] In some optional examples, the concentration of the hydrochloric acid solution is 1M.

[0031] In some optional examples, the mass ratio of aluminum isopropyl alcohol, deionized water and ethanol is 51:9:790.

[0032] In some optional examples, the mass ratio of the silicon carbide dendrite and aluminum isopropyl alcohol sol is 26:85.

[0033] In some optional examples, the time for the silicon carbide dendrite to be immersed in the aluminum isopropyl alcohol sol is 30-40min, for example, it can be 30min, 31min, 32min, 33min, 34min, 35min, 36min, 37min, 38min, 39 or 40min, but not limited to the listed values, other values not listed in the range are also applicable.

[0034] In some optional examples, the fifth temperature is 250-260℃, for example, can be 250℃, 251℃, 252℃, 253℃, 254℃, 255℃, 256℃, 257℃, 258℃, 259℃ or 260℃, but not only limited to the listed values, other values not listed in the range of values are also applicable.

[0035] In some optional examples, the time of the fifth temperature reaction is 4-5h, for example, can be 4h, 4.1h, 4.2h, 4.3h, 4.4h, 4.5h, 4.6h, 4.7h, 4.8h, 4.9h or 5h, but not only limited to the listed values, other values not listed in the range of values are also applicable.

[0036] In some optional examples, the mass ratio of the ethanol, γ-aminopropyl triethoxysilane, phosphoric acid and SiC@δ-Al2O3 is 450:4:1.5:(280-300), for example, can be 450:4:1.5:(280, 282, 284, 286, 288, 290, 292, 294, 296, 298 or 300), but not only limited to the listed values, other values not listed in the range of values are also applicable.

[0037] In some optional examples, the mass fraction of the phosphoric acid is 85wt.%.

[0038] In some optional examples, the time of the first temperature reflux reaction is 3-3.5h, for example, can be 3h, 3.05h, 3.1h, 3.15h, 3.2h, 3.25h, 3.3h, 3.35h, 3.4h, 3.45h or 3.5h, but not only limited to the listed values, other values not listed in the range of values are also applicable.

[0039] As a preferred technical solution of the present application, in S2, the mass ratio of the aluminum foil fragments and urea is 15:(45-50), for example, can be 15:(45, 45.5, 46, 46.5, 47, 47.5, 48, 48.5, 49, 49.5 or 50), but not only limited to the listed values, other values not listed in the range of values are also applicable.

[0040] In some optional examples, the flow rate of the ammonia gas is 500mL / min.

[0041] In some optional examples, the sixth temperature is 900-920℃, for example, can be 900℃, 902℃, 904℃, 906℃, 908℃, 910℃, 912℃, 914℃, 916℃, 918℃ or 920℃, but not only limited to the listed values, other values not listed in the range are also applicable.

[0042] In some optional examples, the time for the sixth temperature holding is 2-2.5h, for example, can be 2h, 2.05h, 2.1h, 2.15h, 2.2h, 2.25h, 2.3h, 2.35h, 2.4h, 2.45h or 2.5h, but not only limited to the listed values, other values not listed in the range are also applicable.

[0043] In some optional examples, the time for the vibration immersion is 10-15min, for example, can be 10min, 10.5min, 11min, 11.5min, 12min, 12.5min, 13min, 13.5min, 14min, 14.5min or 15min, but not only limited to the listed values, other values not listed in the range are also applicable.

[0044] In some optional examples, the mixed solution is calcium nitrate solution and ammonium fluoride solution, the volume ratio is 1:1, the concentration of calcium nitrate solution is 2M, and the concentration of ammonium fluoride solution is 2M.

[0045] In some optional examples, the mass-volume ratio of the activated aluminum nitride and the mixed solution is 1g:3mL.

[0046] In some optional examples, the temperature of the hydrothermal reaction is 200-210℃, for example, can be 200℃, 201℃, 202℃, 203℃, 204℃, 205℃, 206℃, 207℃, 208℃, 209℃ or 210℃, but not only limited to the listed values, other values not listed in the range are also applicable.

[0047] In some optional examples, the time for the hydrothermal reaction is 4-4.5h, for example, can be 4h, 4.05h, 4.1h, 4.15h, 4.2h, 4.25h, 4.3h, 4.35h, 4.4h, 4.45h or 4.5h, but not only limited to the listed values, other values not listed in the range are also applicable.

[0048] As a preferred technical solution of the present application, in S3, the mass ratio of the deionized water, the leveling agent, the dispersant, the water-based fluorocarbon emulsion, the acrylic emulsion, the polyimide emulsion, the titanium dioxide, the modified boron nitride, the SiC@δ-Al2O3, the AlN@CaF2, the calcium carbonate, the defoaming agent, the rheological agent, the HDI water dispersion and the aluminum dihydrogen phosphate solution is 450:15:10:(1450-1500):(180-200):(880-900):500:(280-300):(280-300):(180-190):200:10:40:15:60, which may be, for example, 450:15:10:(1450, 1455, 1460, 1465, 1470, 1475, 1480, 1485, 1490, 1495 or 1500):(180, 182, 184, 186, 188, 190, 192, 194, 196, 198 or 200):(880, 882, 884, 886, 888, 890, 892, 894, 896, 898 or 900):500:(280, 282, 284, 286, 288, 290, 292, 294, 296, 298 or 300):(280, 282, 284, 286, 288, 290, 292, 294, 296, 298 or 300):(180, 181, 182, 183, 184, 185, 186, 187, 188, 189 or 190):200:10:40:15:60, but is not limited to the listed values, and other values not listed in the range are also applicable.

[0049] In some optional examples, the mass fraction of the aluminum dihydrogen phosphate solution is 50 wt.%.

[0050] In a second aspect, the present application provides a high-thermal-conductivity radiation refrigeration coating prepared by the preparation method of the first aspect.

[0051] Compared with the prior art, the present application has the following beneficial effects: (1) the present application introduces high-thermal-conductivity inorganic fillers such as surface-modified hexagonal boron nitride, dendritic silicon carbide and surface-activated aluminum nitride to build a continuous and efficient heat conduction network, significantly reduce the thermal resistance inside the coating, solve the problem of heat conduction obstruction caused by traditional low-thermal-conductivity fillers, and enable the heat generated by the internal heat source to be transferred to the surface of the coating more quickly; (2) the present application maintains the high reflectivity of sunlight and the high emissivity of mid-infrared while improving the thermal conductivity, and the synergistic effect of multiple functional fillers not only ensures the passive cooling effect of the coating but also makes it suitable for complex application scenarios with internal heat sources; (3) the present application grafts long-chain fluorine-containing organic matter onto the surface of hydroxylated boron nitride, so that the surface energy of the modified boron nitride filler is extremely low and exhibits hydrophobic characteristics, and the water-based fluorocarbon emulsion as one of the main film-forming substances also provides hydrophobic effect for the coating. DETAILED DESCRIPTION

[0052] The technical solutions of the present application will be described in detail below in combination with specific embodiments. The embodiments described herein are specific embodiments of the present application and are used to illustrate the concept of the present application; all the descriptions are explanatory and exemplary and should not be construed as limiting the embodiments of the present application and the protection scope of the present application. In addition to the embodiments described herein, those skilled in the art can also employ other technical solutions that are obvious based on the content disclosed in the claims and the description of the present application, which include technical solutions that make any obvious substitutions and modifications to the embodiments described herein.

[0053] The chemical reagents used in the embodiments and comparative examples of the present application are all commercially available and are not subjected to any further purification treatment.

[0054] Embodiment 1

[0055] The present embodiment provides a high-thermal-conductivity radiation refrigeration coating and a preparation method thereof, and the preparation method specifically comprises the following steps:

[0056] A1, 215 g of hexagonal boron nitride is mixed with 800 g of isopropyl alcohol to obtain a slurry, the slurry, 12 g of sodium bisulfite and 22 g of 30 wt.% hydrogen peroxide aqueous solution are mixed, and the temperature is raised to 75℃ for 100 min of stirring, then filtered and washed to obtain pretreated boron nitride, the pretreated boron nitride is dispersed in 700 g of ethylene glycol, the temperature is raised to 175℃ for 2.5 h of reflux reaction, and then vacuum dried to obtain hydroxylated boron nitride, 300 g of hydroxylated boron nitride, 35 g of (1H, 1H, 2H, 2H-heptadecafluorodecyl) phosphonic acid, 18 g of dicyclohexyl carbodiimide and 1 g of 4-dimethylaminopyridine are dispersed in 900 g of anhydrous tetrahydrofuran, the nitrogen atmosphere is raised to 90℃ for 3.5 h of reflux reaction, and then filtered, washed and dried after the reaction to obtain modified boron nitride;

[0057] S1, 22 g cubic silicon carbide, 34 g potassium chloride and 32 g sodium chloride were mixed, heated to 910 °C for 1.2 h, after cooling, the salt was dissolved in deionized water, filtered, soaked in 1M hydrochloric acid solution and washed and dried to obtain silicon carbide dendrites; 51 g aluminum isopropoxide, 9 g deionized water and 790 g ethanol were mixed to obtain an aluminum isopropoxide sol, 260 g silicon carbide dendrites were immersed in 850 g aluminum isopropoxide sol for 38 min and vacuumed to exhaust, the surface liquid was dried, transferred to an autoclave and added with aluminum isopropoxide sol, heated to 258 °C for 4.7 h to obtain SiC@δ-Al2O3; 450 g ethanol was mixed with 4 g γ-aminopropyl triethoxysilane and stirred, 1.5 g of 85 wt.% phosphoric acid was added and stirred, and then 295 g SiC@δ-Al2O3 was added, heated to 74 °C for reflux reaction for 3.4 h, filtered, washed and dried to obtain modified SiC@δ-Al2O3;

[0058] S2, 15 g aluminum foil fragments were mixed with 47 g urea and placed in a tube furnace, ammonia atmosphere, flow rate 500 mL / min, heated to 915 °C for 2.2 h, after cooling, washed and dried to obtain aluminum nitride, borax was melted and then added to the aluminum nitride and vibrated for 12 min, the aluminum nitride was poured out, cooled and washed to obtain activated aluminum nitride, which was then added to a mixed solution for hydrothermal reaction, the mixed solution was a 2M calcium nitrate solution and a 2M ammonium fluoride solution, the volume ratio was 1:1, the mass-volume ratio of activated aluminum nitride to the mixed solution was 1 g:3 mL, the hydrothermal reaction temperature was 205 °C, the reaction time was 4.2 h, and after washing and drying, AlN@CaF2 was obtained;

[0059] S3, 450 g deionized water, 15 g leveling agent and 10 g dispersant were mixed, then 1450 g water-based fluorocarbon emulsion, 180 g acrylic emulsion and 880 g polyimide emulsion were added in sequence, mixed uniformly, then 500 g titanium dioxide, 280 g modified boron nitride, 280 g SiC@δ-Al2O3, 180 g AlN@CaF2 and 200 g calcium carbonate were added in sequence, mixed uniformly, then 10 g defoaming agent, 40 g rheological agent, 15 g HDI water dispersion and 60 g, 50 wt.% aluminum dihydrogen phosphate solution were added, three-roll grinding, defoaming and filtering to obtain high-thermal-radiation refrigeration coating.

[0060] Example 2

[0061] The present embodiment provides a high-thermal-radiation refrigeration coating and a preparation method thereof, and the preparation method specifically comprises the following steps:

[0062] A1, 200 g of hexagonal boron nitride was mixed with 780 g of isopropyl alcohol and ball milled to obtain a slurry. The slurry, 10 g of sodium bisulfite and 20 g of 30 wt.% hydrogen peroxide aqueous solution were mixed, heated to 70 °C and stirred for 90 min. After filtration and washing, a pretreated boron nitride was obtained. The pretreated boron nitride was dispersed in 700 g of ethylene glycol, heated to 170 °C and refluxed for 2 h. After vacuum drying, a hydroxylated boron nitride was obtained. 300 g of the hydroxylated boron nitride, 30 g of (1H, 1H, 2H, 2H-heptadecafluorodecyl) phosphonic acid, 15 g of dicyclohexyl carbodiimide and 1 g of 4-dimethylaminopyridine were dispersed in 900 g of anhydrous tetrahydrofuran under a nitrogen atmosphere, heated to 85 °C and refluxed for 3 h. After the reaction was completed, the product was obtained by filtration, washing and drying;

[0063] S1, 23 g of cubic silicon carbide, 30 g of potassium chloride and 34 g of sodium chloride were mixed, heated to 900 °C and kept for 1.5 h. After cooling, the salt was dissolved in deionized water, filtered, soaked in 1M hydrochloric acid solution and washed and dried to obtain silicon carbide dendrites. 51 g of aluminum isopropoxide, 9 g of deionized water and 790 g of ethanol were mixed to obtain an aluminum isopropoxide sol. 260 g of silicon carbide dendrites were immersed in 850 g of aluminum isopropoxide sol for 30 min and vacuumed to exhaust air. After the surface liquid was dried, it was transferred to an autoclave and aluminum isopropoxide sol was added. After being heated to 250 °C for 4 h, SiC@δ-Al2O3 was obtained. 450 g of ethanol was mixed with 4 g of γ-aminopropyl triethoxysilane and stirred. 1.5 g of 85 wt.% phosphoric acid was added and stirred. Then 280 g of SiC@δ-Al2O3 was added. After being heated to 70 °C and refluxed for 3 h, the modified SiC@δ-Al2O3 was obtained by filtration, washing and drying;

[0064] S2, 15 g of aluminum foil fragments were mixed with 45 g of urea and placed in a tube furnace. Under an ammonia atmosphere, the flow rate was 500 mL / min, and the temperature was increased to 900 °C and kept for 2 h. After cooling, washing and drying, aluminum nitride was obtained. After borax was melted and immersed in aluminum nitride for 10 min, the aluminum nitride was cooled, washed and dried to obtain activated aluminum nitride. The activated aluminum nitride was added to a mixed solution for hydrothermal reaction. The mixed solution was a 2M calcium nitrate solution and a 2M ammonium fluoride solution with a volume ratio of 1:1. The mass-volume ratio of activated aluminum nitride to the mixed solution was 1 g:3 mL. The hydrothermal reaction temperature was 200 °C, and the reaction time was 4 h. After washing and drying, AlN@CaF2 was obtained.

[0065] S3, 450 g of deionized water, 15 g of leveling agent, 10 g of dispersing agent were mixed, and then 1500 g of water-based fluorocarbon emulsion, 200 g of acrylic emulsion and 900 g of polyimide emulsion were added in turn, and then 500 g of titanium dioxide, 300 g of modified boron nitride, 300 g of SiC@δ-Al2O3, 190 g of AlN@CaF2 and 200 g of calcium carbonate were added in turn, and then 10 g of defoaming agent, 40 g of rheological agent, 15 g of HDI water dispersion and 60 g of 50 wt.% aluminum dihydrogen phosphate solution were added, and then three-roll grinding, defoaming and filtering were carried out to obtain a high-thermal-conductivity radiation refrigeration coating.

[0066] Example 3

[0067] The present embodiment provides a high-thermal-conductivity radiation refrigeration coating and a preparation method thereof, and the preparation method specifically comprises the following steps:

[0068] A1, 213 g of hexagonal boron nitride was mixed with 795 g of isopropyl alcohol to obtain a slurry, and then the slurry, 11 g of sodium bisulfite and 21 g of 30 wt.% hydrogen peroxide aqueous solution were mixed, and then the temperature was increased to 73°C and stirred for 95 min, and then the pre-treatment boron nitride was obtained by filtration and washing, and then the pre-treatment boron nitride was dispersed in 700 g of ethylene glycol, and then the temperature was increased to 172°C and refluxed for 2.2 h, and then vacuum drying was carried out to obtain hydroxylated boron nitride, and then 300 g of hydroxylated boron nitride, 32 g of (1H, 1H, 2H, 2H-heptadecafluorodecyl) phosphonic acid, 16 g of dicyclohexyl carbodiimide and 1 g of 4-dimethylaminopyridine were dispersed in 900 g of anhydrous tetrahydrofuran, and then the temperature was increased to 88°C and refluxed for 3.2 h under nitrogen atmosphere, and then the reaction was completed, and then the modified boron nitride was obtained by filtration, washing and drying;

[0069] S1, 20 g of cubic silicon carbide, 35 g of potassium chloride and 30 g of sodium chloride were mixed, and then the temperature was increased to 920°C and kept for 1 h, and then the salt was dissolved in deionized water after cooling, and then the salt was filtered, soaked in 1M hydrochloric acid solution and washed and dried to obtain silicon carbide dendrites; 51 g of aluminum isopropyl alcohol, 9 g of deionized water and 790 g of ethanol were mixed to obtain an aluminum isopropyl alcohol sol, 260 g of silicon carbide dendrites were immersed in 850 g of aluminum isopropyl alcohol sol for 40 min and vacuum exhaust, the surface liquid was dried, and then the SiC@δ-Al2O3 was obtained by transferring to an autoclave and adding aluminum isopropyl alcohol sol, increasing the temperature to 260°C and reacting for 5 h; 450 g of ethanol was mixed with 4 g of γ-aminopropyl triethoxysilane and stirred, 1.5 g of 85 wt.% phosphoric acid was added and stirred, and then 300 g of SiC@δ-Al2O3 was added, and then the temperature was increased to 75°C and refluxed for 3.5 h to obtain modified SiC@δ-Al2O3;

[0070] S2, 15 g aluminum foil fragments were mixed with 50 g urea and placed in a tube furnace, ammonia atmosphere, flow rate 500 mL / min, heated to 920°C for 2.5 h, washed and dried after cooling to obtain aluminum nitride, borax was melted and then added to the aluminum nitride and vibrated for 15 min, the aluminum nitride was poured out and cooled and washed to obtain activated aluminum nitride, which was then added to a mixed solution of 2M calcium nitrate solution and 2M ammonium fluoride solution with a volume ratio of 1:1, and the mass-volume ratio of activated aluminum nitride to the mixed solution was 1 g:3 mL, the hydrothermal reaction temperature was 210°C, and the reaction time was 4.5 h, and AlN@CaF2 was obtained after washing and drying;

[0071] S3, 450 g of deionized water, 15 g of leveling agent, and 10 g of dispersant were mixed, and then 1470 g of water-based fluorocarbon emulsion, 190 g of acrylic emulsion, and 890 g of polyimide emulsion were added in turn, and then 500 g of titanium dioxide, 285 g of modified boron nitride, 285 g of SiC@δ-Al2O3, 185 g of AlN@CaF2, and 200 g of calcium carbonate were added, and then 10 g of defoaming agent, 40 g of rheological agent, 15 g of HDI water dispersion, and 60 g of 50 wt.% aluminum dihydrogen phosphate solution were added, and then three-roll grinding, defoaming, and filtration were performed to obtain a high-thermal-radiation refrigeration coating.

[0072] Example 4

[0073] The present embodiment provides a high-thermal-radiation refrigeration coating and a preparation method thereof, which specifically comprises the following steps:

[0074] A1, 208 g of hexagonal boron nitride was mixed with 790 g of isopropyl alcohol and ball milled to obtain a slurry, the slurry, 11.5 g of sodium bisulfite, and 21.5 g of 30 wt.% hydrogen peroxide aqueous solution were mixed, heated to 72°C and stirred for 97 min, and then filtered, washed and dried to obtain pretreated boron nitride, 300 g of the pretreated boron nitride, 33 g of (1H, 1H, 2H, 2H-heptadecafluorodecyl) phosphonic acid, 17 g of dicyclohexyl carbodiimide, and 1 g of 4-dimethylaminopyridine were dispersed in 900 g of anhydrous tetrahydrofuran under a nitrogen atmosphere, heated to 87°C and refluxed for 3.3 h, and then filtered, washed and dried after the reaction to obtain modified boron nitride;

[0075] S1, 21 g of cubic silicon carbide, 32 g of potassium chloride and 35 g of sodium chloride were mixed, heated to 915℃ for 1.4 h, and after cooling, the salt was dissolved in deionized water, filtered, soaked in 1M hydrochloric acid solution and washed and dried to obtain silicon carbide dendrites; 51 g of aluminum isopropoxide, 9 g of deionized water and 790 g of ethanol were mixed to obtain an aluminum isopropoxide sol, 260 g of silicon carbide dendrites were immersed in 850 g of aluminum isopropoxide sol for 35 min and vacuumed to exhaust, the surface liquid was dried, transferred to an autoclave and added with aluminum isopropoxide sol, heated to 255℃ for 4.3 h to obtain SiC@δ-Al2O3; 450 g of ethanol was mixed with 4 g of γ-aminopropyl triethoxysilane and stirred, 1.5 g of 85 wt.% phosphoric acid was added and stirred, and then 285 g of SiC@δ-Al2O3 was added, heated to 72℃ for reflux reaction for 3.2 h, filtered, washed and dried to obtain modified SiC@δ-Al2O3;

[0076] S2, 15 g of aluminum foil fragments were mixed with 48 g of urea and placed in a tube furnace, under an ammonia atmosphere, with a flow rate of 500 mL / min, heated to 910℃ for 2.3 h, and after cooling, washed and dried to obtain aluminum nitride, borax was melted and then added to the aluminum nitride and vibrated for 13 min, the aluminum nitride was poured out and cooled and washed to obtain activated aluminum nitride, which was then added to a mixed solution for hydrothermal reaction, the mixed solution was a 2M calcium nitrate solution and a 2M ammonium fluoride solution with a volume ratio of 1:1, and the mass-volume ratio of activated aluminum nitride to the mixed solution was 1 g:3 mL, the hydrothermal reaction temperature was 208℃, and the reaction time was 4.3 h, and after washing and drying, AlN@CaF2 was obtained;

[0077] S3, 450 g of deionized water, 15 g of leveling agent and 10 g of dispersant were mixed, and then 1480 g of water-based fluorocarbon emulsion, 195 g of acrylic emulsion and 895 g of polyimide emulsion were added in sequence, mixed uniformly, and then 500 g of titanium dioxide, 295 g of modified boron nitride, 295 g of SiC@δ-Al2O3, 188 g of AlN@CaF2 and 200 g of calcium carbonate were added in sequence, mixed uniformly, and then 10 g of defoaming agent, 40 g of rheological agent, 15 g of HDI water dispersion and 60 g of 50 wt.% aluminum dihydrogen phosphate solution were added, three-roll grinding, defoaming and filtering to obtain a high-thermal-radiation refrigeration coating.

[0078] Comparative Example 1

[0079] The present embodiment provides a high-thermal-radiation refrigeration coating and a preparation method thereof, which is different from Example 1 in that the mass of modified boron nitride in S3 is 0, and other process parameters and operating conditions are exactly the same as those of Example 1.

[0080] Comparative Example 2

[0081] The embodiment provides high-thermal-conductivity radiation refrigeration paint and a preparation method thereof, which are different from those of the embodiment 1 in that the mass of SiC@delta-Al2O3 in S3 is 0, and other process parameters and operation conditions are completely same as those of the embodiment 1.

[0082] Comparative example 3

[0083] The embodiment provides high-thermal-conductivity radiation refrigeration paint and a preparation method thereof, which are different from those of the embodiment 1 in that the mass of SiC@delta-Al2O3 in S3 is 0, and other process parameters and operation conditions are completely same as those of the embodiment 1.

[0084] The test method of solar reflectance and hemispherical emittance is GB / T25261-2018. The test method of atmospheric window (8-13 mu m) emittance is that a reflectometer such as SOC-100 Hemispherical Directional Reflectometer (SOC-100 hemispherical directional reflectometer) is used to test the infrared emittance of 8-13 mu m wavelength, that is, the atmospheric window emittance. The test method of thermal conductivity is ASTM-E1530-06. The test results are shown in Table 1.

[0085] Table 1 Test results of high-thermal-conductivity radiation refrigeration paint of the embodiment 1, the embodiment 4 and comparative examples 1-3

[0086]

[0087] It can be known from Table 1 that, compared with the embodiment 1, the solar reflectance, hemispherical emittance, atmospheric window (8-13 mu m) emittance and thermal conductivity of the comparative example 1 all decrease; the solar reflectance, hemispherical emittance, atmospheric window (8-13 mu m) emittance and thermal conductivity of the comparative example 2 all decrease; and the solar reflectance, hemispherical emittance, atmospheric window (8-13 mu m) emittance and thermal conductivity of the comparative example 3 all decrease. The hexagonal boron nitride sheet has excellent transverse thermal conductivity and high infrared emission capacity, and the sheet structure is easy to form a continuous heat flow channel in the plane of the coating, which helps the heat to quickly spread and uniformly distribute on the surface of the coating. The modified boron nitride is lacked in the comparative example 1, so the in-plane heat conduction capacity of the coating is weakened, and the radiation effect is weakened. The dendritic silicon carbide has excellent thermal conductivity, which promotes the internal heat to be transferred to the surface, and the delta-alumina coating layer not only improves the interface bonding with the resin, but also enhances the infrared emission capacity of the coating. The SiC@delta-Al2O3 is lacked in the comparative example 2, so the thermal conductivity decreases, and the radiation effect is weakened. The sheet structure of the aluminum nitride has high thermal conductivity and good infrared emission capacity, and the CaF2 coating layer improves the chemical stability and infrared window emittance of the material. The AlN@CaF2 is lacked in the comparative example 3, so the overall thermal conductivity is reduced, and the radiation capacity is weakened.

[0088] The above merely describes the specific embodiments of the present application, but the protection scope of the present application is not limited thereto, and it should be understood by those skilled in the art that any changes or replacements within the technical scope disclosed by the present application can be easily conceived by those skilled in the art, and all such changes and replacements fall within the protection scope and disclosure scope of the present application.

Claims

1. A method for preparing a high thermal conductivity radiation cooling coating, characterized in that, The preparation method includes: S1, cubic silicon carbide, potassium chloride and sodium chloride are mixed and kept at a constant temperature to obtain silicon carbide dendrites. The silicon carbide dendrites are immersed in aluminum isopropoxide sol, the surface liquid is dried off, and the mixture is transferred to a hydrothermal reactor to obtain SiC@δ-Al2O3. Ethanol and γ-aminopropyltriethoxysilane are mixed, and phosphoric acid and SiC@δ-Al2O3 are added to react and obtain modified SiC@δ-Al2O3. S2, aluminum foil fragments are mixed with urea and placed in a tube furnace under an ammonia atmosphere to obtain aluminum nitride. Borax is melted and added to the aluminum nitride and vibrated to impregnate it, thus obtaining activated aluminum nitride. The activated aluminum nitride is then added to the mixed solution for hydrothermal reaction to obtain AlN@CaF2. S3, after mixing deionized water, leveling agent, and dispersant, add waterborne fluorocarbon emulsion, acrylic emulsion, and polyimide emulsion in sequence, mix evenly, then add titanium dioxide, modified boron nitride, SiC@δ-Al2O3, AlN@CaF2, and calcium carbonate in sequence, mix evenly, then add defoamer, rheology modifier, HDI aqueous dispersion, and aluminum dihydrogen phosphate solution to obtain a high thermal conductivity radiation cooling coating; The method for preparing the modified boron nitride includes: ball milling hexagonal boron nitride with isopropanol to obtain a slurry; mixing the slurry with sodium bisulfite and an aqueous solution of hydrogen peroxide to obtain pretreated boron nitride; dispersing the pretreated boron nitride in ethylene glycol and reacting to obtain hydroxylated boron nitride; and dispersing the hydroxylated boron nitride, (1H,1H,2H,2H-heptadecyl)phosphonic acid, dicyclohexylcarbodiimide, and 4-dimethylaminopyridine in anhydrous tetrahydrofuran under a nitrogen atmosphere to obtain modified boron nitride. The mass ratio of cubic silicon carbide, potassium chloride and sodium chloride is (20-23):(30-35):(30-35); The mass ratio of the hexagonal boron nitride, isopropanol, sodium bisulfite, hydrogen peroxide aqueous solution, and ethylene glycol is (200-215):(780-800):(10-12):(20-22):700; The mass ratio of the hydroxylated boron nitride, (1H,1H,2H,2H-heptadecyl)phosphonic acid, dicyclohexylcarbodiimide, 4-dimethylaminopyridine to anhydrous tetrahydrofuran is 300:(30-35):(15-18):1:

900.

2. The method for preparing the high thermal conductivity radiation cooling coating according to claim 1, characterized in that, In S1: The mass ratio of ethanol, γ-aminopropyltriethoxysilane, phosphoric acid and SiC@δ-Al2O3 is 450:4:1.5:(280-300).

3. The method for preparing the high thermal conductivity radiation cooling coating according to claim 1, characterized in that, In S2: The mass ratio of the aluminum foil fragments to urea is 15:(45-50). The flow rate of the ammonia gas is 500 mL / min.

4. The method for preparing the high thermal conductivity radiation cooling coating according to claim 1, characterized in that, In S2: The mixed solution is a calcium nitrate solution and an ammonium fluoride solution in a volume ratio of 1:1, with the calcium nitrate solution having a concentration of 2M and the ammonium fluoride solution having a concentration of 2M. The mass-to-volume ratio of the activated aluminum nitride to the mixed solution is 1 g: 3 mL.

5. The method for preparing the high thermal conductivity radiation cooling coating according to claim 1, characterized in that, In S3: The mass ratio of the deionized water, leveling agent, dispersant, aqueous fluorocarbon emulsion, acrylic emulsion, polyimide emulsion, titanium dioxide, modified boron nitride, SiC@δ-Al2O3, AlN@CaF2, calcium carbonate, defoamer, rheology modifier, HDI aqueous dispersion, and aluminum dihydrogen phosphate solution is 450:15:10:(1450-1500):(180-200):(880-900):500:(280-300):(280-300):(180-190):200:10:40:15:

60.

6. A high thermal conductivity radiation cooling coating obtained by the preparation method according to any one of claims 1-5.

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