Preparation method of coating material with radiation refrigeration function

Abstract

The invention discloses a preparation method of a radiation refrigeration functional coating material, and belongs to the technical field of thermal management material preparation. The preparation method comprises the following steps: weighing the deionized water, the emulsion and the functional additive in parts by weight, stirring and dispersing to form a mixed solution; adding the multi-component rare earth oxide filler, titanium dioxide, hollow glass beads and silicon dioxide into the mixed solution in parts by weight, and stirring and dispersing to form a radiation refrigeration coating; a base material is coated with the radiation refrigeration coating, and the radiation refrigeration functional coating is obtained after curing. The thickness of the prepared radiation refrigeration coating ranges from 200 micrometers to 500 micrometers, the sunlight emissivity is larger than or equal to 0.95, the atmospheric window emissivity is larger than or equal to 0.95, and the radiation refrigeration coating is remarkable in heat insulation effect, simple in process, low in preparation cost, suitable for industrial production and wide in application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of thermal management material preparation, and in particular to a method for preparing a radiation refrigeration functional coating material. Background Art

[0002] Summer cooling in buildings consumes significant amounts of electricity and emits significant amounts of greenhouse gases. With the growing demand for building cooling and climate change, energy pressures are becoming even more severe. Radiative cooling coatings are green materials based on the principle of passive radiative cooling. By increasing solar reflectivity (>90% reflectivity at 0.3–2.5 μm) and mid-infrared emissivity (>90% emissivity in the 8–13 μm atmospheric window band), they achieve radiative cooling, enabling low-energy cooling.

[0003] Traditional radiative cooling coatings primarily consist of a polymer matrix (such as styrene-acrylic emulsion) and functional fillers (such as titanium dioxide). The core material is the functional filler (titanium dioxide, barium sulfate, and silicon dioxide) in the coating. To improve the cooling performance of radiative cooling coatings, it is necessary to balance broadband reflectivity with high emissivity. However, the functional fillers commonly used in radiative cooling coatings currently have spectral matching limitations. For example, titanium dioxide exhibits significant absorption in the ultraviolet (<400 nm) (absorption rate of approximately 20-30%), resulting in reduced reflectivity across the entire solar spectrum. Barium sulfate exhibits weak absorption in the 8–13 μm atmospheric window (emissivity of only approximately 70-80%), potentially interfering with thermal radiation efficiency. Furthermore, its reflectivity in the near-infrared (700–2500 nm) is lower than that of titanium dioxide, necessitating compounding with highly reflective materials. Silicon dioxide's emissivity drops sharply (<50%) in the >13 μm band, preventing it from effectively covering wider infrared wavelengths (such as 14–16 μm), limiting its full-band heat dissipation potential. In addition, silicon dioxide has a low refractive index in the visible light band (about 1.45), and its solar reflectivity is only about 80%, which cannot meet the demand.

[0004] On this basis, it is necessary to propose a radiative cooling coating material with high reflectivity and high emissivity and a preparation method thereof. Summary of the Invention

[0005] The main purpose of the present invention is to provide a method for preparing a radiative cooling functional coating material to solve the technical problems of low full solar spectrum reflectivity and mid-infrared emissivity, poor radiative cooling performance, and low radiative cooling efficiency of radiative cooling coatings in the prior art.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A method for preparing a radiation cooling functional coating material comprises the following steps:

[0008] (1) Weighing deionized water, emulsion, and functional additives by weight and stirring to disperse them to form a mixed solution;

[0009] (2) adding multi-component rare earth oxide filler, titanium dioxide, hollow glass microspheres, and silicon dioxide to a mixed solution according to weight, and stirring and dispersing the mixture to form a radiant cooling coating;

[0010] (3) The radiant cooling coating is applied on a substrate, and after curing, a radiant cooling functional coating is obtained.

[0011] Preferably, in step (1) and step (2), the deionized water is 30-40 parts, the emulsion is 50-60 parts, the functional additive is 8-15 parts, the multi-component rare earth oxide filler is 40-50 parts, the titanium dioxide is 20-30 parts, the hollow glass microspheres are 8-10 parts, and the silicon dioxide is 8-10 parts.

[0012] Preferably, the stirring rate of the stirring and dispersing in step (1) is 500 r / min, and the stirring time is 30-60 minutes; the stirring rate of the stirring and dispersing in step (2) is 1200 r / min, and the stirring time is 120-180 minutes.

[0013] Preferably, the emulsion in step (1) is one of pure acrylic emulsion, polyurethane emulsion, acrylic emulsion, styrene acrylic emulsion, and silicone acrylic emulsion.

[0014] Preferably, the functional additives in step (1) include the following raw materials in parts by weight: 1 to 3 parts of dispersant, 1 to 3 parts of leveling agent, 0.5 to 2 parts of defoaming agent, 1 to 3 parts of wetting agent, and 2 to 5 parts of film-forming aid.

[0015] Preferably, the dispersant is BYK333, the leveling agent is H421 organosilicon leveling agent, the defoaming agent is organosilicon defoaming agent, the wetting agent is PE-100 nonionic wetting agent, and the film-forming aid is water-based dodecyl alcohol ester film-forming aid.

[0016] Preferably, the preparation method of the multi-component rare earth oxide filler in step (2) is:

[0017] Lanthanum oxide, yttrium oxide, cerium oxide and europium oxide are mixed and ball-milled once to obtain ball-milled material;

[0018] The ball mill material is calcined at high temperature, and after cooling in the furnace, a secondary ball milling is performed to refine the material, thereby obtaining a multi-component rare earth oxide filler;

[0019] Wherein, the mass ratio of lanthanum oxide, yttrium oxide, cerium oxide and europium oxide is (0.8-1.2): (1.2-1.5): (0.8-1.2): (0.8-1.2);

[0020] The calcination temperature during the high-temperature calcination is 1000-1400°C, the heating rate is 5°C / min, and the calcination time is 10-12 hours;

[0021] The parameters of the primary and secondary ball milling are as follows: ball milling time ≥ 20 h, ball milling speed 400-600 r / min, ball-to-material mass ratio 8:2;

[0022] The particle size of the multi-component rare earth oxide filler is 50-1000 nm.

[0023] Preferably, in step (2), the particle sizes of titanium dioxide, hollow glass microspheres and silicon dioxide are all 50-1000 nm.

[0024] Preferably, the coating method in step (3) is one of spraying, brushing, and rolling; the coating thickness after coating is 200-500 μm; the curing temperature is 25-100° C., and the curing time is 10-30 hours.

[0025] Preferably, the solar reflectivity of the radiative cooling functional coating is ≥94%, and the atmospheric window emissivity is ≥94%.

[0026] The beneficial effects of the present invention are:

[0027] 1. The present invention utilizes multi-component rare earth oxide fillers to overcome the spectral matching limitations of traditional functional fillers, thereby improving the full solar spectrum reflectivity and mid-infrared emissivity. Due to the 4f electron transitions and rich energy level structures of rare earth elements (such as lanthanum, cerium, yttrium, and europium), they exhibit high reflectivity in the visible to near-infrared band (0.3–2.5 μm). By doping or compounding them into wide-bandgap semiconductors (such as CeO2 and Y2O3), they can effectively scatter sunlight and reduce photothermal conversion, thereby improving solar reflectivity. Furthermore, the lattice vibration modes (such as phonon resonances) of rare earth oxides are highly matched to the atmospheric transparency window in the mid-infrared band (8–13 μm, the atmospheric window). The infrared-active vibrations of their highly polar chemical bonds (such as YO and La-O) enhance photon emission efficiency, prompting the coating to dissipate heat into the cold universe in the form of electromagnetic waves through radiative heat dissipation. In addition, the ff transition of rare earth ions can further broaden the infrared emission band, and through nanostructure design (such as porous structure and photonic crystal arrangement), the photon scattering and thermal radiation performance can be synergistically optimized to achieve efficient passive radiative cooling.

[0028] 2. The radiative cooling coating prepared by the present invention has a thickness of 200-500 μm, and its solar emissivity and atmospheric window emissivity are both ≥0.95. Under direct sunlight, the surface temperature can be significantly lower than the ambient temperature, achieving a low-energy cooling effect and a significant thermal insulation effect.

[0029] 3. The preparation method of the present invention is simple, low-cost, suitable for industrial production, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a test diagram of the thermal insulation effect of the radiant cooling coating prepared in Example 1 of the present invention and Comparative Example 1;

[0031] Figure 2 This is a graph showing the effect of multi-component rare earth oxide fillers on the performance of radiant cooling functional coating materials in Examples 1-2 and Comparative Examples 2-3 of the present invention;

[0032] Figure 3 This is a comparison chart of the powder particle sizes of the multi-component rare earth oxides in Example 1, Comparative Example 4, and Comparative Example 5 of the present invention;

[0033] Figure 4 This is a diagram of coating thickness in Example 1 and Example 3 of the present invention. DETAILED DESCRIPTION

[0034] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0035] Example 1

[0036] 1.1 This embodiment discloses a method for preparing a rare earth radiation cooling coating, comprising the following steps:

[0037] (1) According to weight, 30 parts of deionized water, 50 parts of acrylic emulsion, 1 part of dispersant BYK333, 1 part of silicone leveling agent H421, 0.5 parts of silicone defoamer, 1 part of nonionic wetting agent PE-100, and 2 parts of water-based lauryl alcohol ester film-forming aid were weighed and stirred and dispersed at a speed of 500 r / min for 30 minutes to form a mixed solution.

[0038] (2) Preparation of multi-component rare earth oxides: 0.8 parts of lanthanum oxide, 1.2 parts of yttrium oxide, 0.8 parts of cerium oxide, and 0.8 parts of europium oxide were weighed and mixed evenly by ball milling (ball milling time 20 hours, ball milling speed of 500 r / min, ball-to-material mass ratio of 8:2), and calcined at high temperature (calcination temperature 1400°C, heating rate 5°C / min, calcination time 10 hours). After furnace cooling, ball milling was performed to obtain multi-component rare earth oxide filler. After ball milling, the particle size of the multi-component rare earth oxide was 50-1000 nm.

[0039] (3) 40 parts of multi-component rare earth oxide, 20 parts of titanium dioxide, 8 parts of hollow glass microspheres, and 8 parts of silicon dioxide were poured into the mixed solution, stirred and dispersed (stirring rate was 1200 r / min, stirring time was 180 minutes) to form a radiant cooling coating, and the oxide particle size was 50-1000 nm.

[0040] (4) The radiation cooling coating was sprayed onto an aluminum alloy substrate with a thickness of 1 mm using an air spray method. The coating thickness was 200 μm. After curing at 20° C. for 24 hours, the desired radiation cooling coating was obtained.

[0041] 1.2 Performance test:

[0042] (1) Solar reflectance: tested in accordance with the standard JG / T235-2014 "Architectural Reflective Thermal Insulation Coatings", with a wavelength range of 0.3 to 2.5 μm;

[0043] (2) Atmospheric window emissivity: tested in accordance with the standard T / ZZB 2304-2021 “Radiative Cooling Film”, with a wavelength range of 8 to 13 μm;

[0044] (3) Coating adhesion: Conduct a cross-cut test according to the standard GB / T 9286-2021 “Paints and varnishes”;

[0045] (4) Cooling effect: The test was conducted using a self-designed model house device. The device was made of an insulated styrene foam box with a 100*100mm test hole reserved on the top of the device. Ordinary white paint on the market and the radiant cooling paint prepared above were applied to a square aluminum plate with a size of 100*100*1mm to make a test plate. The test plate was placed in the reserved hole of the test device, and a 250W infrared lamp was used to simulate sunlight irradiation of the coating. The distance between the infrared lamp and the test plate was fixed during each test. A thermocouple was strictly attached to the center point below the test plate and placed in the device. The temperature was recorded after the temperature was balanced and stabilized (about 30 minutes).

[0046] Comparative Example 1

[0047] This comparative example serves as a blank control group, i.e., a 1 mm thick aluminum alloy substrate is not coated, to compare the thermal insulation performance of the radiant cooling coating.

[0048] Comparison of thermal performance of Example 1 and Comparative Example 1, as shown in Table 1 and Figure 1 The results show that compared with pure aluminum alloy (Comparative Example 1), the outer surface temperature of the coating (Example 1) was reduced by 42.4°C and the inner surface temperature was reduced by 38.3°C, with a significant temperature drop effect. The test effect diagram is shown in FIG. Figure 1 shown.

[0049] Table 1 Temperature drop performance of aluminum alloy substrate with and without coating

[0050]

[0051] Example 2

[0052] The difference between this embodiment and embodiment 1 is that the weight portion of the multi-component rare earth oxide in step (3) is 50 parts.

[0053] Comparative Example 2

[0054] The difference between this comparative example and Example 1 is that the weight portion of the multi-component rare earth oxide filler in step (3) is 35 parts.

[0055] Comparative Example 3

[0056] The difference between this comparative example and Example 1 is that the weight portion of the multi-component rare earth oxide filler in step (3) is 55 parts.

[0057] The effects of the multi-component rare earth oxide fillers in Example 1, Example 2, Comparative Example 2 and Comparative Example 3 on the performance of the radiant cooling functional coating material are shown in Tables 2 and Figure 2 The results show that when the weight fraction of the multi-component rare earth oxide filler is 40-50 parts by weight, the radiative cooling functional coating has a higher solar reflectivity (94.4-96.61%) and atmospheric window emissivity (94.88-95.25%), as well as a lower external surface temperature (67.6-71.2°C) and internal surface temperature (29.3-30.1°C). In summary, the optimal mass fraction of the multi-component rare earth oxide filler is 40-50 parts by weight.

[0058] Table 2 Effect of multi-component rare earth oxide fillers on the performance of radiative cooling functional coating materials

[0059]

[0060] Comparative Example 4

[0061] The difference between this comparative example and Example 1 is that the oxide particle sizes are both 10-30 μm.

[0062] Comparative Example 5

[0063] The difference between this comparative example and Example 1 is that the oxide particle size is 20-100 μm.

[0064] The roughness of the coating materials prepared in Example 1, Comparative Example 4, and Comparative Example 5 is compared. The effect of powder particle size on the performance of the radiative cooling functional coating material is shown in Table 3. The results show that when the oxide particle size is nanopowder, the solar reflectivity is improved and the internal and external surface temperatures are reduced. However, in order to obtain a fine and smooth coating surface, the powder particle size must be controlled to achieve a balance between high solar reflectivity and low internal and external surface temperatures; the powder particle size of the multi-component rare earth oxide filler in Example 1, Comparative Example 4, and Comparative Example 5 is as follows: Figure 3 shown.

[0065] Table 3 Effect of powder particle size on the performance of radiative cooling functional coating materials

[0066]

[0067] Example 3

[0068] The difference between this embodiment and embodiment 1 is that the coating thickness is 300 μm.

[0069] Example 4

[0070] The difference between this embodiment and embodiment 1 is that the coating thickness is 400 μm.

[0071] Example 5

[0072] The difference between this embodiment and embodiment 1 is that the coating thickness is 500 μm.

[0073] Comparative Example 6

[0074] This embodiment adopts the method of Example 1 to prepare the radiative cooling functional coating material, except that the coating thickness is 600 μm.

[0075] Comparative Example 7

[0076] The difference between this comparative example and Example 1 is that the coating thickness is 700 μm.

[0077] Comparative Example 8

[0078] The difference between this comparative example and Example 1 is that the coating thickness is 800 μm.

[0079] The effects of coating thickness on the performance of the radiant cooling functional coating material in Comparative Example 1, Examples 3-5, and Comparative Examples 6-8 are shown in Table 4; the coating thickness of Example 3 and Example 5 is shown in Table 4. Figure 4The results show that as the coating thickness increases, the solar reflectivity changes slightly, the atmospheric window emissivity gradually increases, and the internal and external surface temperatures change slightly. This is because the thinner the coating, the greater the transmittance. According to Kirchhoff's law, the coating's infrared transmittance T + infrared reflectivity R + infrared emissivity (absorption) rate E = 1. Therefore, as the coating transmittance increases, the emissivity decreases. However, when the coating thickness exceeds 500 μm, the emissivity changes little. This is because when the coating thickens to a certain extent, the transmittance changes little, and therefore the emissivity changes little.

[0080] Table 4 Effect of coating thickness on the performance of radiative cooling functional coating materials

[0081]

[0082]

[0083] Example 6

[0084] This embodiment discloses a method for preparing a rare earth radiation cooling coating, comprising the following steps:

[0085] (1) According to weight, 35 parts of deionized water, 55 parts of acrylic emulsion, 2 parts of dispersant BYK333, 2 parts of silicone leveling agent H421, 1 part of silicone defoamer, 2 parts of nonionic wetting agent PE-100, and 4 parts of water-based dodecyl alcohol ester film-forming aid were weighed and stirred and dispersed at a speed of 500 r / min for 45 minutes to form a mixed solution.

[0086] (2) Preparation of multi-component rare earth oxide filler: 1.0 part of lanthanum oxide, 1.3 parts of yttrium oxide, 1.0 part of cerium oxide, and 1.0 part of europium oxide were weighed and mixed evenly by ball milling (ball milling time 18 hours, ball milling speed 400r / min, ball-to-material mass ratio 8:2), and calcined at high temperature (calcination temperature 1000℃, heating rate 5℃ / min, calcination time 11 hours). After furnace cooling, ball milling was performed to obtain a multi-component rare earth oxide filler. After ball milling, the particle size of the multi-component rare earth oxide filler was 50-1000nm.

[0087] (3) 40 parts of multi-component rare earth oxide filler, 25 parts of titanium dioxide, 9 parts of hollow glass microspheres, and 9 parts of silicon dioxide were poured into the mixed solution, stirred and dispersed (stirring rate of 1200 r / min, stirring time of 150 minutes) to form a radiant cooling coating, and the oxide particle size was 50-1000 nm.

[0088] (4) The above-mentioned radiation cooling coating is brushed on an aluminum alloy substrate with a thickness of 1 mm. The coating thickness is 400 μm. After 10 hours at 50°C, the desired radiation cooling coating is obtained.

[0089] Example 7

[0090] This embodiment discloses a method for preparing a rare earth radiation cooling coating, comprising the following steps:

[0091] (1) According to weight, 40 parts of deionized water, 60 parts of acrylic emulsion, 3 parts of dispersant BYK333, 3 parts of silicone leveling agent H421, 2 parts of silicone defoamer, 3 parts of nonionic wetting agent PE-100, and 5 parts of water-based dodecyl alcohol ester film-forming aid were weighed and stirred and dispersed at a speed of 500 r / min for 60 minutes to form a mixed solution.

[0092] (2) Preparation of multi-component rare earth oxide filler: 1.2 parts of lanthanum oxide, 1.5 parts of yttrium oxide, 1.2 parts of cerium oxide, and 1.2 parts of europium oxide were weighed and mixed evenly by ball milling (ball milling time 20 hours, ball milling speed 600r / min, ball-to-material mass ratio 8:2), and calcined at high temperature (calcination temperature 1200℃, heating rate 5℃ / min, calcination time 12 hours). After furnace cooling, ball milling was performed to obtain a multi-component rare earth oxide filler. After ball milling, the particle size of the multi-component rare earth oxide filler was 50-1000nm.

[0093] (3) 40 parts of multi-component rare earth oxide filler, 30 parts of titanium dioxide, 10 parts of hollow glass microspheres, and 10 parts of silicon dioxide were poured into the mixed solution, stirred and dispersed (stirring rate was 1200 r / min, stirring time was 180 minutes) to form a radiant cooling coating, and the oxide particle size was 50-1000 nm.

[0094] (4) The radiation cooling coating is rolled onto an aluminum alloy substrate having a thickness of 1 mm by roller coating. The coating thickness is 500 μm. After 30 hours at 100°C, the desired radiation cooling coating is obtained.

[0095] The radiative cooling functional coatings prepared in Example 6 and Example 7 also effectively improved the full solar spectrum reflectivity and mid-infrared emissivity, thereby improving the radiative cooling performance of the coating and enhancing the radiative cooling efficiency.

[0096] In summary, the present invention utilizes multi-component rare earth oxide fillers to overcome the spectral matching limitations of traditional functional fillers, thereby improving full solar spectrum reflectivity and mid-infrared emissivity. Due to the 4f electron transitions and rich energy level structure of rare earth elements (such as lanthanum, cerium, yttrium, and europium), they exhibit high reflectivity in the visible to near-infrared range (0.3–2.5 μm). By doping or compounding them into wide-bandgap semiconductors (such as CeO2 and Y2O3), they effectively scatter sunlight and reduce photothermal conversion, thereby improving solar reflectivity. Furthermore, the lattice vibration modes (such as phonon resonances) of rare earth oxides are highly aligned with the atmospheric transparency window in the mid-infrared range (8–13 μm, the atmospheric window). The infrared-active vibrations of their highly polar chemical bonds (such as YO and La-O) enhance photon emission efficiency, enabling the coating to dissipate heat into the cold universe in the form of electromagnetic waves through radiative heat dissipation. In addition, the ff transition of rare earth ions can further broaden the infrared emission band, and through nanostructure design (such as porous structure and photonic crystal arrangement), the photon scattering and thermal radiation performance can be synergistically optimized to achieve efficient passive radiative cooling.

[0097] The above detailed description of the specific embodiments of the invention is intended to be illustrative only, and the present invention is not limited to the specific embodiments described above. For those skilled in the art, any equivalent modifications or substitutions to the invention are also within the scope of the present invention. Therefore, equivalent changes, modifications, and improvements made without departing from the spirit and scope of the present invention are also encompassed within the scope of the present invention.

Claims

1. A method for preparing a radiation cooling functional coating material, characterized in that: The steps include: (1) Weighing deionized water, emulsion, and functional additives by weight and stirring to disperse them to form a mixed solution; (2) adding multi-component rare earth oxide filler, titanium dioxide, hollow glass microspheres, and silicon dioxide to a mixed solution according to weight, and stirring and dispersing the mixture to form a radiant cooling coating; (3) The radiant cooling coating is applied on a substrate, and after curing, a radiant cooling functional coating is obtained.

2. The method for preparing the radiation cooling functional coating material according to claim 1, wherein: In step (1) and step (2), 30-40 parts of deionized water, 50-60 parts of emulsion, 8-15 parts of functional additives, 40-50 parts of multi-component rare earth oxide filler, 20-30 parts of titanium dioxide, 8-10 parts of hollow glass microspheres, and 8-10 parts of silicon dioxide are prepared.

3. The method for preparing the radiation cooling functional coating material according to claim 1, wherein: The stirring rate of the stirring and dispersing in step (1) is 500 r / min, and the stirring time is 30-60 minutes; the stirring rate of the stirring and dispersing in step (2) is 1200 r / min, and the stirring time is 120-180 minutes.

4. The method for preparing the radiation cooling functional coating material according to claim 1, wherein: The emulsion in step (1) is one of pure acrylic emulsion, polyurethane emulsion, acrylic emulsion, styrene acrylic emulsion, and silicone acrylic emulsion.

5. The method for preparing the radiation cooling functional coating material according to claim 1, wherein: The functional additives in step (1) include the following raw materials in parts by weight: 1 to 3 parts of a dispersant, 1 to 3 parts of a leveling agent, 0.5 to 2 parts of a defoaming agent, 1 to 3 parts of a wetting agent, and 2 to 5 parts of a film-forming aid.

6. The method for preparing the radiation cooling functional coating material according to claim 5, wherein: The dispersant is BYK333, the leveling agent is H421 organic silicon leveling agent, the defoaming agent is an organic silicon defoaming agent, the wetting agent is PE-100 nonionic wetting agent, and the film-forming aid is a water-based dodecyl alcohol ester film-forming aid.

7. The method for preparing the radiation cooling functional coating material according to claim 1, wherein: The preparation method of the multi-component rare earth oxide filler in step (2) is: Lanthanum oxide, yttrium oxide, cerium oxide and europium oxide are mixed and ball-milled once to obtain a ball-milled material; The ball mill material is calcined at high temperature, and after cooling in the furnace, a secondary ball milling is performed to refine the material, thereby obtaining a multi-component rare earth oxide filler; Wherein, the mass ratio of lanthanum oxide, yttrium oxide, cerium oxide and europium oxide is (0.8-1.2): (1.2-1.5): (0.8-1.2): (0.8-1.2); The calcination temperature during the high-temperature calcination is 1000-1400°C, the heating rate is 5°C / min, and the calcination time is 10-12 hours; The parameters of the primary and secondary ball milling are as follows: ball milling time ≥ 20 h, ball milling speed 400-600 r / min, ball-to-material mass ratio 8:2; The particle size of the multi-component rare earth oxide filler is 50-1000 nm.

8. The method for preparing the radiation cooling functional coating material according to claim 1, wherein: In step (2), the particle sizes of titanium dioxide, hollow glass microspheres and silicon dioxide are all 50-1000 nm.

9. The method for preparing the radiation cooling functional coating material according to claim 1, wherein: The coating method in step (3) is one of spraying, brushing and rolling; the coating thickness after coating is 200-500 μm; the curing temperature is 25-100° C. and the curing time is 10-30 hours.

10. The method for preparing the radiation cooling functional coating material according to claim 1, wherein: The solar reflectivity of the radiative cooling functional coating is ≥94%, and the atmospheric window emissivity is ≥94%.

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