Self-cleaning daytime radiation cooling coating and preparation method thereof

Abstract

The application discloses a self-cleaning daytime radiation cooling coating and a preparation method thereof, and the preparation method comprises the following steps: (1) adding a modifier into a dispersion liquid of inorganic particles to modify the inorganic particles, and after separation, washing and drying, modified inorganic particles are obtained; (2) adding the modified inorganic particles into a dispersion liquid of organic polymers, and after uniform stirring, a coating is obtained; and (3) coating the coating on a surface of a substrate, and after standing and drying, the self-cleaning daytime radiation cooling coating is obtained. The preparation method is simple in operation and short in preparation period. On the basis of adding the modified inorganic particles, by adjusting the doping proportion of the modified inorganic particles and the thickness of the coating, the self-cleaning daytime radiation cooling coating has high reflectivity, good cooling and self-cleaning effects, and is easy to be industrially produced.

Description

Technical Field

[0001] This invention relates to the field of passive daytime radiation cooling technology, and more particularly to a self-cleaning daytime radiation cooling coating and its preparation method. Background Technology

[0002] During the hot summer months, the demand for cooling equipment increases, leading to higher energy consumption and a heavier environmental impact. Traditional cooling methods often produce large amounts of carbon dioxide and ozone, exacerbating the greenhouse effect.

[0003] Passive daytime radiative cooling (PDRC) is a novel method for energy conservation and reducing ambient temperature, characterized by zero energy consumption and no environmental pollution. PDRC materials strongly reflect sunlight in the ultraviolet-visible-near-infrared band (0.3–2.5 μm) while simultaneously transmitting infrared heat into space through an atmospheric transparency window (8–13 μm). Therefore, the materials must possess both high reflectivity and high emissivity.

[0004] Chinese patent document CN103740205A discloses a water-based white coating. The raw materials for preparing the coating include the following components in parts by weight: 30-50 parts water-based resin; 10-20 parts pigment; 30-51 parts solvent; 0.3-1.2 parts water-based wetting and dispersing agent; 0.05-0.2 parts water-based defoamer; 0.1-0.3 parts AMP-95; 0.1-1.0 parts water-based leveling agent; 0.3-1.5 parts water-based drier; 0.3-0.8 parts anti-yellowing agent; and 0.1-0.5 parts ultraviolet absorber. This coating has a good cooling effect when applied to outdoor substrates. However, during outdoor use, it is easily contaminated and damaged by rainwater, dust, etc., which weakens the cooling performance of the material in outdoor environments and makes it unsuitable for long-term use.

[0005] Chinese patent document CN205348892B discloses a radiation cooling coating and its preparation method, which includes a reflective upper layer composed of nanoparticles with a particle size range of 200-1000nm and a lower emitting layer composed of nanoparticles with a particle size range of 40-100nm. The coating is sprayed onto the surface of a substrate and is used in fields such as building energy conservation, heat dissipation of electronic equipment and food preservation. However, its preparation method is complex and time-consuming.

[0006] Therefore, due to the harsh outdoor conditions and the preparation process, there is an urgent need for a self-cleaning daytime radiation cooling coating with a simple preparation method and a short preparation cycle. Summary of the Invention

[0007] This invention provides a method for preparing a self-cleaning daytime radiation cooling coating. The preparation method is simple to operate, the raw materials are readily available, which meets outdoor needs, and the prepared self-cleaning daytime radiation cooling coating has good cooling and self-cleaning effects.

[0008] The technical solution of the present invention is as follows:

[0009] A method for preparing a self-cleaning daytime radiation cooling coating includes:

[0010] (1) Add a modifier to the dispersion of inorganic particles to modify the inorganic particles. After separation, washing and drying, the modified inorganic particles are obtained.

[0011] (2) Add the modified inorganic particles to the dispersion of the organic polymer and stir until uniform to obtain the coating.

[0012] (3) Apply the coating to the surface of the substrate, let it stand and dry to obtain a self-cleaning daytime radiation cooling coating.

[0013] This invention can prepare a coating using a scraping method. During the drying process, the modified inorganic particles deposit and stack to form a rough structure. At the same time, the addition of modified inorganic particles increases the low surface energy of the coating surface, which not only makes the coating more effective at backscattering sunlight and increasing its infrared emissivity, but also makes the radiative cooling effect more obvious. The low surface energy and rough structure can also have a hydrophobic effect. Moreover, the selected particles are inorganic particles, which are easy to disperse, stable, durable, and have better acid and alkali resistance.

[0014] The self-cleaning daytime radiation cooling coating prepared by this invention is not limited to any substrate. It can be applied to substrates made of materials such as glass, ceramics, wood, aluminum alloy, steel plate, stainless steel, copper, and iron. It can also be applied to fabrics or buildings as needed.

[0015] Preferably, the substrate is one or more of the following: glass plate, ceramic, wood, aluminum alloy substrate, steel plate substrate, stainless steel substrate, copper substrate, and iron substrate.

[0016] Preferably, the inorganic particles are one or more of silicon dioxide, barium sulfate, barium titanate, calcium carbonate, titanium dioxide, aluminum oxide, and aluminum oxide.

[0017] Preferably, the average particle size of the inorganic particles is 500–5000 nm.

[0018] Larger particles are more likely to scatter light, thus increasing the reflectivity of an object, while smaller particles scatter light forward more, reducing the reflectivity of the object. As the particle size of inorganic nanoparticles increases, the reflectivity of the prepared coating will increase accordingly.

[0019] More preferably, the average particle size of the inorganic particles is 500–2000 nm.

[0020] Inorganic particles in the 500–2000 nm range have superior reflectivity, achieving a high solar reflectivity of over 90%.

[0021] Preferably, the modifier is one or more of γ-methacryloxypropyltrimethoxysilane, vinyltriethoxysilane, vinyltrimethoxysilane, palmitic acid, stearic acid, and sodium dodecyl sulfonate.

[0022] The aforementioned modifiers can introduce other functional groups onto the surface of inorganic particles, altering the chemical properties of the inorganic particle surface and improving the hydrophobicity and dispersion stability of the inorganic particles.

[0023] Too much or too little modifier will result in poor final modified inorganic particles.

[0024] Preferably, the modifier accounts for 2-5% of the mass of the inorganic particles.

[0025] In coatings, as the mass fraction of modified inorganic particles increases, the reflectivity of the coating also increases, but the mechanical properties of the coating decrease accordingly.

[0026] Preferably, the modified inorganic particles in the self-cleaning daytime radiation cooling coating have a mass fraction of 80-90%.

[0027] Organic polymers play a role in crosslinking and improving the mechanical strength of coatings.

[0028] Preferably, the organic polymer is one or more selected from polyurethane, polyester, vinyl resin, polyether resin, and acrylate.

[0029] The vibrational peaks of the aforementioned organic polymers are concentrated in the infrared fingerprint region (1300–400 cm⁻¹). -1 (Corresponding to the atmospheric window band, it can provide a high mid-infrared emissivity, and at the same time play a role in high cross-linking of the coating, providing the coating with certain mechanical properties.)

[0030] Preferably, the organic polymer is at least one of an organosilicon-modified polyurethane polymer and a fluorinated acrylate copolymer.

[0031] More preferably, the organic polymer is a silicone-modified polyurethane polymer and a fluorinated acrylate copolymer.

[0032] A self-cleaning daytime radiative cooling coating was prepared by uniformly blending an organosilicon-modified polyurethane polymer (due to the tensile vibrations of Si-O-Si bonds in the mid-infrared band) with an organofluorine-modified acrylate copolymer (which also exhibits CF bonds in the mid-infrared band) and then mixing it with high-reflectivity inorganic particles in a solvent. The inorganic particles improve the overall reflectivity of the material, giving the coating high reflectivity spectral characteristics. Simultaneously, the large number of functional groups in the organic polymer-inorganic particle composite system contributes to the material's high emissivity in the mid-infrared band, while the organic polymer also imparts good mechanical and hydrophobic properties.

[0033] Preferably, the mass ratio of the silicone-modified polyurethane polymer to the fluorinated acrylate copolymer is 1:0.5–2. This technical solution yields a coating with superior reflectivity and hydrophobicity.

[0034] Preferably, the preparation method of the organosilicon modified polymer includes: adding isophorone diisocyanate, polycarbonate diol, and hydroxyl-terminated silicone oil to an organic solvent, then adding a catalyst, and stirring the mixture at 80-90°C for 1-5 hours under inert gas protection; then adding 1,4-butanediol for chain extension reaction for 1-2 hours; then adding ethylene glycol for post-chain extension; and finally obtaining the organosilicon modified polyurethane polymer after the isophorone diisocyanate has completely reacted.

[0035] Hydroxyl-terminated silicone oil accounts for 6-12% of the total monomer mass; the molar mass ratio of isocyanate groups in isophorone diisocyanate to that in polycarbonate diol, 1,4-butanediol, ethylene glycol, and hydroxyl groups in hydroxyl-terminated silicone oil is 1.5-2.

[0036] The R-value is the ratio of the molar mass of isocyanate groups in isophorone diisocyanate to the molar mass of hydroxyl groups in polycarbonate diol, 1,4-butanediol, ethylene glycol, and hydroxyl-terminated silicone oil. A higher R-value results in a harder coating with poorer mechanical properties; a lower R-value results in a softer coating with better mechanical properties. The R-value can be adjusted depending on the substrate being applied.

[0037] Preferably, the preparation method of the fluoropolymer includes: mixing tridecyl fluorooctyl acrylate, butyl acrylate, methyl methacrylate and an initiator evenly, adding an emulsifier and water to mix and homogenize, and then pulverizing under an ice-water bath to obtain an emulsion; stirring a portion of the emulsion in an inert atmosphere at 60-80°C, and when the emulsion emits blue light, adding the remaining emulsion dropwise, and keeping it warm for 2-5 hours after the addition is complete to obtain a fluorinated acrylate emulsion; and drying to obtain a fluorinated acrylate copolymer.

[0038] Tridecafluorooctyl acrylate accounts for 25-50% of the total monomer mass; the molar mass ratio of butyl acrylate to methyl methacrylate is 1:0.5-2.

[0039] Butyl acrylate is a soft monomer, while methyl methacrylate is a hard monomer. The ratio of butyl acrylate to methyl methacrylate monomers is the soft-hard monomer ratio. A higher soft-hard monomer ratio results in a softer coating with better mechanical properties. A lower soft-hard monomer ratio results in a harder coating with worse mechanical properties. The soft-hard monomer ratio can be adjusted according to the substrate being applied.

[0040] In step (2), the dispersion of the organic polymer is obtained by dispersing the organic polymer in an organic solvent; the organic solvent is one or more of tetrahydrofuran, acetone, propylene glycol methyl ether acetate, ethyl acetate, and dimethylformamide.

[0041] Furthermore, in the dispersion of the organic polymer, the mass ratio of the organic polymer to the organic solvent is 1:8 to 13.

[0042] The coating thickness has a certain influence on the average reflectivity of the coating in the visible light band.

[0043] Preferably, the thickness of the self-cleaning daytime radiation cooling coating is 100–500 μm.

[0044] This invention optimizes the fixed particle density per unit area by controlling the thickness of the self-cleaning daytime radiative cooling coating, enabling the coating to reflect visible and near-infrared light while further emitting heat through atmospheric windows via infrared radiation, thus achieving optimal radiative cooling effect. The reflectivity increases with increasing coating thickness; after reaching a certain thickness, the reflectivity reaches its maximum value and then decreases with further increases in thickness.

[0045] When the coating thickness is 147±5μm, the average reflectivity of the coating in the visible light band does not reach 90.0%. As the coating thickness increases, the reflectivity also increases. When the thickness is 191±5μm, the average reflectivity in the visible light band reaches its maximum value. As the coating thickness continues to increase to 199±5μm, the reflectivity does not increase significantly. After the coating thickness is 200μm, the reflectivity gradually decreases with the increase of coating thickness. This is because the characteristics of inorganic particles lead to a maximum reflectivity effect on sunlight.

[0046] More preferably, the thickness of the self-cleaning daytime radiation cooling coating is 150–200 μm.

[0047] The preparation method of this invention is simple to operate and has a short preparation cycle. By adding modified inorganic particles and adjusting the doping ratio of the modified inorganic particles and the thickness of the coating, it can achieve high reflectivity and good cooling and self-cleaning effects, making it easy to industrialize.

[0048] The present invention also provides a self-cleaning daytime radiation cooling coating prepared by the above preparation method.

[0049] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0050] (1) The manufacturing method of the present invention is simple, low in cost, and easy to industrialize.

[0051] (2) The self-cleaning daytime radiation cooling coating prepared by the present invention has good cooling effect, good self-cleaning effect, good mechanical properties, and stable coating.

[0052] (3) The self-cleaning daytime radiation cooling coating prepared by the present invention can be used in the field of outdoor metal substrates to solve problems such as high-temperature volatilization and coating pollution of chemical storage tanks. At the same time, the self-cleaning daytime radiation cooling coating prepared by the present invention can be used in the fields of glass plates, ceramics, wood and building cooling. Attached Figure Description

[0053] Figure 1 The image shows a surface SEM image of the self-cleaning daytime radiation cooling coating prepared in Example 4.

[0054] Figure 2 The outdoor cooling test results of the self-cleaning daytime radiation cooling coating prepared in Example 4 and the coating in Comparative Example 1 are shown in the figure.

[0055] Figure 3 The water contact angle is the self-cleaning daytime radiation cooling coating prepared in Example 4.

[0056] Figure 4 The images show the self-cleaning effect of the self-cleaning daytime radiation cooling coating prepared in Example 4 and the coating in Comparative Example 1; (a) is the coating of Example 4, and (b) is the coating of Comparative Example 1.

[0057] Figure 5 The spectral characteristics of the self-cleaning daytime radiation cooling coating prepared in Example 4 and the coating in Comparative Example 1 are shown in the figure. Detailed Implementation

[0058] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be noted that the embodiments described below are intended to facilitate the understanding of the present invention and do not limit it in any way.

[0059] The modified inorganic particles, polyurethane, and fluorinated acrylate copolymers in the following examples were prepared through the following steps:

[0060] (1) Purified barium sulfate particles (average particle size of about 1000 nm) were dispersed in water and stirred at 70 °C. In another beaker, palmitic acid aqueous solution was added to the barium sulfate dispersion, and the resulting mixture was stirred at 70 °C for 90 min. After filtration, centrifugation, washing, and drying for 24 h, modified barium sulfate particles were obtained. The modifier accounted for 2-5% of the mass of the inorganic particles.

[0061] (2) A certain proportion of isophorone diisocyanate (IPDI), polycarbonate diol (PCDL), hydroxyl-terminated silicone oil (PDMS-OH), acetone and catalyst dibutyltin dilaurate (DBTDL) were added to a three-necked flask. Nitrogen gas was passed through the condenser in an oil bath at 80-90°C. After stirring at 400 r / min for 2 h, 1,4-butanediol (BDO) was added for chain extension. After one hour, ethylene glycol (EG) was added for further chain extension. After the isocyanate reaction was complete, the organosilicon-modified polyurethane polymer was obtained.

[0062] Hydroxyl-terminated silicone oil accounts for 10% of the total monomer mass. Among the monomers, the ratio of the molar mass of isocyanate groups in isophorone diisocyanate to the molar mass of hydroxyl groups in polycarbonate diol, 1,4-butanediol, ethylene glycol, and hydroxyl-terminated silicone oil is the R value, which is 1.8.

[0063] (3) Tridecafluorooctyl acrylate (GO6C), butyl acrylate (BA), methyl methacrylate (MMA), and the initiator azobisisobutyronitrile (AIBN) were mixed evenly. The emulsifier nonylphenol ethoxysulfate (DNS-86) and water were mixed evenly. The mixture was then homogenized and subjected to cell disruption in an ice-water bath for 30 min. One-third of the emulsion was poured into a three-necked flask, condensed, and protected with nitrogen. The mixture was stirred at 70°C and 300 r / min. When the emulsion emitted a blue light, the remaining two-thirds were added dropwise. After the addition was complete, the mixture was kept at this temperature for 3 h to obtain a fluorinated acrylate emulsion. The emulsion was then dried in an oven to obtain a fluorinated acrylate copolymer.

[0064] Tridecafluorooctyl acrylate accounts for 50% of the total monomer mass. The molar ratio of butyl acrylate to methyl methacrylate is 1:1.

[0065] Example 1

[0066] A self-cleaning daytime radiation cooling coating is prepared by the following steps:

[0067] (1) Add 0.2g of fluorinated acrylate copolymer and 0.2g of silicone-modified polyurethane to 5.0g of propylene glycol methyl ether acetate and stir for 30min.

[0068] (2) After the organic polymer is evenly dispersed, add 3.6g of modified barium sulfate particles and continue stirring until the particles are evenly dispersed to obtain the coating.

[0069] (3) The coating prepared in step (2) is applied to the aluminum alloy substrate by scraping. After standing for 2 hours, it is dried in an oven. After drying, a self-cleaning daytime radiation cooling coating is obtained on the substrate.

[0070] The coating thickness is controlled within the range of 191±5μm.

[0071] Example 2

[0072] A self-cleaning daytime radiation cooling coating is prepared by the following steps:

[0073] (1) Add 0.4g of fluorinated acrylate copolymer and 0.4g of silicone-modified polyurethane to 10.0g of propylene glycol methyl ether acetate and stir for 30min.

[0074] (2) After the organic polymer is evenly dispersed, add 6.4g of modified barium sulfate particles and continue stirring until the particles are evenly dispersed to obtain the coating.

[0075] (3) The coating prepared in step (2) is applied to the aluminum alloy substrate by scraping. After standing for a period of time, it is dried in an oven. After drying, a self-cleaning daytime radiation cooling coating is obtained on the substrate.

[0076] The coating thickness is controlled within the range of 191±5μm.

[0077] Example 3

[0078] A self-cleaning daytime radiation cooling coating is prepared by the following steps:

[0079] (1) Add 0.6g of fluorinated acrylate copolymer and 0.6g of silicone-modified polyurethane to 15.0g of propylene glycol methyl ether acetate and stir for 30min.

[0080] (2) After the organic polymer is evenly dispersed, add 8.7g of modified barium sulfate particles and continue stirring until the particles are evenly dispersed to obtain the coating.

[0081] (3) The coating prepared in step (2) is applied to the aluminum alloy substrate by scraping. After standing for a period of time, it is dried in an oven. After drying, a self-cleaning daytime radiation cooling coating is obtained on the substrate.

[0082] The coating thickness is controlled within the range of 191±5μm.

[0083] Example 4

[0084] A self-cleaning daytime radiation cooling coating is prepared by the following steps:

[0085] (1) Add 0.8g of fluorinated acrylate copolymer and 0.8g of silicone-modified polyurethane to 20.0g of propylene glycol methyl ether acetate and stir for 30min.

[0086] (2) After the organic polymer is evenly dispersed, add 10g of modified barium sulfate particles and continue stirring until the particles are evenly dispersed to obtain the coating.

[0087] (3) The coating prepared in step (2) is applied to the aluminum alloy substrate by scraping. After standing for a period of time, it is dried in an oven. After drying, a self-cleaning daytime radiation cooling coating is obtained on the substrate.

[0088] The coating thickness is controlled within the range of 191±5μm.

[0089] Comparative Example 1

[0090] Commercial white paint was applied to an aluminum alloy substrate by scraping and dried in an oven to obtain the coating of Comparative Example 1.

[0091] The coating thickness is controlled within the range of 191±5μm.

[0092] Figure 1 The surface microstructure of the coating prepared in Example 4 is shown. The inorganic particles are tightly bound together by the cross-linking effect of the polymer, and the disordered accumulation of the particles gives the coating surface a certain rough structure. This, combined with the synergistic effect of the organofluorine / silicon segments, results in a low surface energy and a hydrophobic coating surface. The water contact angle of the coating surface prepared under the conditions of Example 4 is 151°. Figure 3 It achieves a superhydrophobic effect.

[0093] The coating thicknesses of Example 4 and Comparative Example 1 were controlled within the range of 191±5 μm, and their spectral characteristics were tested and compared. Figure 5 Compared to the commercial radiative cooling coating (Comparative Example 1), which has an average reflectance of 83.3% in the 0.3–2.5 μm solar spectrum and an average emissivity of 74.2% in the mid-infrared 8–13 μm band, the daytime radiative cooling coating prepared in Example 4 achieves an average reflectance of 91.8% in the visible light band. For the entire atmospheric window band, due to the vibration of the CF and Si-O-Si structures within the atmospheric window, the average emissivity in the mid-infrared of Example 4 reaches 92.5%, demonstrating spectral characteristics significantly superior to the commercial PDRC coating. Both coatings were placed outdoors for cooling tests. Compared to Example 4, the coating prepared in Comparative Example 1 showed a poorer radiative cooling effect. Figure 2 As shown, the temperature difference between the two is 4.6℃, therefore the coating prepared in Example 4 has better cooling performance.

[0094] The self-cleaning performance of the prepared daytime radiation cooling coating of Example 4 was compared with that of a commercially available daytime radiation cooling coating (Comparative Example 1). Figure 4 Aqueous dye solution was dropped onto the coating prepared in Example 4. Due to the coating's high contact angle and low roll-off angle, it was not easily contaminated or penetrated, and the droplets formed spherical shapes and slid directly down. Simultaneously, as the droplets slid down the coating, they carried away solid contaminants from the surface. In contrast, the surface of commercially available daytime radiation cooling coatings (Comparative Example 1) became contaminated after the dye solution adhered to it, affecting their spectral characteristics and leading to a decrease in cooling performance. Furthermore, their application to outdoor substrates required additional cleaning costs.

[0095] Example 5

[0096] A self-cleaning daytime radiation cooling coating is prepared by the following steps:

[0097] (1) Add 10.0g of fluorinated acrylate copolymer and 10.0g of silicone-modified polyurethane to 25.0g of propylene glycol methyl ether acetate and stir for 30min.

[0098] (2) After the organic polymer is evenly dispersed, add 11.5g of modified barium sulfate particles and continue stirring until the particles are evenly dispersed to obtain the coating.

[0099] (3) The coating prepared in step (2) is applied to the aluminum alloy substrate by scraping. After standing for a period of time, it is dried in an oven. After drying, a self-cleaning daytime radiation cooling coating is obtained on the substrate.

[0100] The coating thickness is controlled within the range of 191±5μm.

[0101] Example 6

[0102] A self-cleaning daytime radiation cooling coating is prepared by the following steps:

[0103] (1) Add 1.2g of fluorinated acrylate copolymer and 1.2g of organosilicon modified polyurethane to 30.0g of propylene glycol methyl ether acetate and stir for 30min.

[0104] (2) After the organic polymer is evenly dispersed, add 12.6g of modified barium sulfate particles and continue stirring until the particles are evenly dispersed to obtain the coating.

[0105] (3) The coating prepared in step (2) is applied to the aluminum alloy substrate by scraping. After standing for a period of time, it is dried in an oven. After drying, a self-cleaning daytime radiation cooling coating is obtained on the substrate.

[0106] The coating thickness is controlled within the range of 191±5μm.

[0107] Example 7

[0108] A self-cleaning daytime radiation cooling coating is prepared by the following steps:

[0109] (1) Add 1.4g of fluorinated acrylate copolymer and 1.4g of silicone-modified polyurethane to 35.0g of propylene glycol methyl ether acetate and stir for 30min.

[0110] (2) After the organic polymer is evenly dispersed, add 14.0g of modified barium sulfate particles and continue stirring until the particles are evenly dispersed to obtain the coating.

[0111] (3) The coating prepared in step (2) is applied to the aluminum alloy substrate by scraping. After standing for a period of time, it is dried in an oven. After drying, a self-cleaning daytime radiation cooling coating is obtained on the substrate.

[0112] The coating thickness is controlled within the range of 191±5μm.

[0113] Example 8

[0114] A self-cleaning daytime radiation cooling coating is prepared by the following steps:

[0115] (1) Add 1.6g of fluorinated acrylate copolymer and 1.6g of silicone-modified polyurethane to 40.0g of propylene glycol methyl ether acetate and stir for 30min.

[0116] (2) After the organic polymer is evenly dispersed, add 14.4g of modified barium sulfate particles and continue stirring until the particles are evenly dispersed to obtain the coating.

[0117] (3) The coating prepared in step (2) is applied to the aluminum alloy substrate by scraping. After standing for a period of time, it is dried in an oven. After drying, a self-cleaning daytime radiation cooling coating is obtained on the substrate.

[0118] The coating thickness is controlled within the range of 191±5μm.

[0119] Example 9

[0120] A self-cleaning daytime radiation cooling coating is prepared by the following steps:

[0121] (1) Add 1.8g of fluorinated acrylate copolymer and 1.8g of silicone-modified polyurethane to 45.0g of propylene glycol methyl ether acetate and stir for 30min.

[0122] (2) After the organic polymer is evenly dispersed, add 15.3g of modified barium sulfate particles and continue stirring until the particles are evenly dispersed to obtain the coating.

[0123] (3) The coating prepared in step (2) is applied to the aluminum alloy substrate by scraping. After standing for a period of time, it is dried in an oven. After drying, a self-cleaning daytime radiation cooling coating is obtained on the substrate.

[0124] The coating thickness is controlled within the range of 191±5μm.

[0125] Example 10

[0126] A self-cleaning daytime radiation cooling coating is prepared by the following steps:

[0127] (1) Add 2.0g of fluorinated acrylate copolymer and 2.0g of silicone-modified polyurethane to 50.0g of propylene glycol methyl ether acetate and stir for 30min.

[0128] (2) After the organic polymer is evenly dispersed, add 16.0g of modified barium sulfate particles and continue stirring until the particles are evenly dispersed to obtain the coating.

[0129] (3) The coating prepared in step (2) is applied to the aluminum alloy substrate by scraping. After standing for a period of time, it is dried in an oven. After drying, a self-cleaning daytime radiation cooling coating is obtained on the substrate.

[0130] The coating thickness was controlled within the range of 191±5μm. As the proportion of modified inorganic particles increased, the reflectivity of the coating also increased, and the cooling performance of the coating improved. However, the mechanical properties of the coating decreased accordingly. Considering the practicality of the coating, Example 4 was selected for testing and comparison.

[0131] The embodiments described above provide a detailed explanation of the technical solutions and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, additions, and equivalent substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a self-cleaning daytime radiation cooling coating, characterized in that, include: (1) Add a modifier to the dispersion of inorganic particles to modify the inorganic particles. After separation, washing and drying, modified inorganic particles are obtained. The inorganic particles are barium sulfate. The average particle size of the inorganic particles is 500~5000 nm. (2) Add the modified inorganic particles to the dispersion of the organic polymer and stir until uniform to obtain the coating. The organic polymers are silicone-modified polyurethane polymers and fluorinated acrylate copolymers. The preparation method of the silicone-modified polyurethane polymer includes: adding isophorone diisocyanate, polycarbonate diol, and hydroxyl-terminated silicone oil to an organic solvent, then adding a catalyst, and stirring and reacting at 80-90 °C for 1-5 h under inert gas protection; then adding 1,4-butanediol for chain extension reaction for 1-2 h; then adding ethylene glycol for post-chain extension; and obtaining the silicone-modified polyurethane polymer after the isophorone diisocyanate has completely reacted. The preparation method of the fluorinated acrylate copolymer includes: mixing tridecyl fluorooctyl acrylate, butyl acrylate, methyl methacrylate, and an initiator evenly, adding an emulsifier and water, mixing and homogenizing, and then pulverizing under an ice-water bath to obtain an emulsion; stirring and reacting a portion of the emulsion at 60-80 °C under an inert atmosphere; when the emulsion emits blue light, adding the remaining emulsion dropwise, and then maintaining the temperature for 2-5 hours. h, to obtain a fluorinated acrylate emulsion; after drying, to obtain a fluorinated acrylate copolymer; (3) Apply the coating to the surface of the substrate, let it stand and dry to obtain a self-cleaning daytime radiation cooling coating; the mass fraction of the modified inorganic particles in the self-cleaning daytime radiation cooling coating is 80~90%.

2. The method for preparing the self-cleaning daytime radiation cooling coating according to claim 1, characterized in that, The modifier is one or more of γ-methacryloxypropyltrimethoxysilane, vinyltriethoxysilane, vinyltrimethoxysilane, palmitic acid, stearic acid, and sodium dodecyl sulfonate.

3. The method for preparing the self-cleaning daytime radiation cooling coating according to claim 1, characterized in that, In step (2), the dispersion of the organic polymer is obtained by dispersing the organic polymer in an organic solvent; the organic solvent is one or more of tetrahydrofuran, acetone, propylene glycol methyl ether acetate, ethyl acetate, and dimethylformamide.

4. The method for preparing the self-cleaning daytime radiation cooling coating according to claim 3, characterized in that, In the dispersion of the organic polymer, the mass ratio of the organic polymer to the organic solvent is 1:8~13.

5. The method for preparing the self-cleaning daytime radiation cooling coating according to claim 1, characterized in that, The thickness of the self-cleaning daytime radiation cooling coating is 100~500 μm.

6. The method for preparing the self-cleaning daytime radiation cooling coating according to claim 5, characterized in that, The thickness of the self-cleaning daytime radiation cooling coating is 150~200 μm.

7. A self-cleaning daytime radiation cooling coating prepared by the preparation method according to any one of claims 1 to 6.

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