Radiation refrigeration coating material and preparation method of radiation refrigeration double-layer coating

Abstract

The invention provides a radiation refrigeration coating material and a preparation method of a radiation refrigeration double-layer coating. The radiation refrigeration coating material is composed of a bottom layer material and an upper layer material. The bottom-layer material and the upper-layer material both comprise reflective filler, resin and other raw materials, and the two raw materials are subjected to high-speed mixing, twin-screw melt extrusion, fine grinding and screening, cooling and packaging respectively to obtain the bottom-layer powder coating and the upper-layer powder coating. When in use, the two coatings are sequentially sprayed on the surface of a grounding metal workpiece through an electrostatic spray gun, and then are heated and cured to form a radiation refrigeration double-layer coating; the radiation refrigeration double-layer coating has the reflectivity as high as 90.5% in the solar spectrum wave band of 0.3-2.5 m, and meanwhile has the emissivity as high as 96.5% in the atmosphere infrared window wave band of 8-13 m. An outdoor actual measurement result shows that the temperature of the inner surface of the power cabinet sprayed with the coating can be reduced by 21.3 DEG C at most compared with that of untreated equipment under the condition of strong solar irradiation of about 900 W / m, and efficient daytime radiation refrigeration can be achieved without energy consumption.

Description

Technical Field

[0001] This invention belongs to the technical field of powder coatings and radiation cooling materials, specifically relating to a radiation cooling coating material and a method for preparing a radiation cooling double-layer coating that can be scalably prepared based on electrostatic spraying. Background Technology

[0002] Global warming has led to frequent extreme heat events, posing a serious threat to the stable operation of outdoor power facilities. Radiative cooling technology, as a passive cooling method that requires no external energy input, has significant application potential. This technology achieves continuous cooling by efficiently reflecting sunlight (wavelength 0.3–2.5 μm) and primarily utilizing the "atmospheric window" (8–13 μm) to release heat into the low-temperature outer space in the form of infrared radiation. However, current research and applications of radiative cooling technology are mostly concentrated in the field of building energy conservation, aiming to reduce building energy consumption, while research on heat dissipation management for outdoor power equipment is relatively scarce. There are significant differences in their technical approaches: radiative cooling coatings commonly used in the building sector are mostly applied to cement-based surfaces and can achieve excellent cooling performance with the help of high volumetric filler concentrations, but this strategy is difficult to directly transfer to the power equipment scenario. This is because the adhesion between the metal casing and the coating is poor, and the coating needs to withstand various extreme climatic conditions during long-term outdoor exposure. In addition, existing brush-applied radiative cooling coatings usually rely on organic solvents to disperse fillers, which also poses environmental pollution risks. Therefore, developing a radiation-cooling coating material that has strong adhesion to metal substrates, is environmentally friendly, low-cost, and suitable for large-scale preparation is of great value for improving the thermal management capabilities of outdoor power facilities. Summary of the Invention

[0003] To address the problem that existing radiative cooling technology is difficult to directly apply to the metal casing surface of outdoor power facilities, this invention provides a radiative cooling coating material and a method for preparing a radiative cooling double-layer coating based on the radiative cooling coating material.

[0004] A radiation cooling coating material is composed of a base material and an upper material; the raw materials of the base material and the upper material respectively include 40-70% reflective filler, 25-60% resin, 0-20% curing agent, 0.5-1% brightening agent, 0-1% leveling agent, 0-1% degassing agent and 0.5-1% additives;

[0005] The resin is one of polyester resin, hydroxyl acrylic resin, polyvinylidene fluoride, polymethylpentene, and fluorinated ethylene propylene copolymer;

[0006] The curing agent is one of triglycidyl isocyanate, β-hydroxyalkylamide, and blocked isocyanate;

[0007] The brightening agent is one of polyacrylate, silicone acrylate, and perfluoroalkoxy resin;

[0008] The leveling agent is one of fatty acid organic polymers or polyethylene-vinyl acetate.

[0009] The degassing agent is benzoin;

[0010] The additive is one of polyethylene wax, silica powder, and fluorinated wax;

[0011] The reflective filler in the bottom layer material is nano-titanium dioxide powder;

[0012] The reflective filler in the upper layer material is at least one of nano-zirconia powder, boron nitride nanosheets, nano-alumina powder, and barium sulfate powder.

[0013] The raw materials for the base material are mixed at high speed, melt-extruded by twin screws, and pressed into brittle sheets by cooling rollers. The brittle sheets are then finely ground, sieved, cooled, and packaged to obtain the base powder coating.

[0014] The raw materials for the upper layer are mixed at high speed, melt-extruded by twin screws, and pressed into brittle sheets by cooling rollers. The brittle sheets are then finely ground, sieved, cooled, and packaged to obtain the upper layer powder coating.

[0015] In use, the base powder coating and the top powder coating are successively sprayed onto the surface of the grounded metal workpiece using an electrostatic spray gun, and then heated and cured to form a radiation-cooled double-layer coating. A schematic diagram is shown below. Figure 1 As shown in (a);

[0016] The average particle size D50 of the base powder coating is controlled between 20μm and 30μm, with the content of fine powder with a particle size less than 10μm not exceeding 10% and the content of coarse particles with a particle size greater than 50μm not exceeding 5%, to ensure good fluidity and powder application rate during electrostatic spraying. The base powder coating does not clump or stick under storage and transportation conditions from room temperature to 40℃. When measured on a hot plate at 180℃ to 330℃, its gelation time is 40s to 80s to adapt to the construction requirements of different curing conditions.

[0017] The average particle size D50 of the upper powder coating is controlled between 20μm and 30μm, the content of fine powder with a particle size less than 10μm is not higher than 10%, and the content of coarse particles with a particle size greater than 50μm is not higher than 5%, to ensure good fluidization and powder application rate during electrostatic spraying. The upper powder coating does not clump or stick under storage and transportation conditions from room temperature to 40℃. When measured on a hot plate at 180℃~330℃, its gelation time is 80s to 120s to adapt to the construction requirements of different curing conditions.

[0018] Further technical solutions for radiation-cooling coating materials are as follows:

[0019] The nano-titanium dioxide powder has a particle size of 150nm to 500nm; the nano-zirconium dioxide powder and nano-aluminum oxide powder both have a particle size of 200nm to 700nm; the boron nitride nanosheets have a sheet diameter of 1 to 3μm; and the barium sulfate powder has a particle size of 1 to 2μm.

[0020] The extrusion temperature of the twin-screw melt extrusion is 100–330°C.

[0021] Fine grinding is carried out in a high-speed pulverizer at a speed of 20,000–26,000 rpm, a feed rate of 20–50 kg / h, and a cold air temperature of ≤15℃; sieving is carried out in a fully enclosed vibrating screen or rotary screen at a screen mesh of 160–200 mesh, with continuous sieving and a sealed and moisture-proof material collection system.

[0022] The preparation steps for fabricating a radiation-cooling bilayer coating based on radiation-cooling coating materials are as follows:

[0023] (1) Pre-treat the surface of the metal workpiece by degreasing and rust removal to thoroughly remove oil and oxide scale from the surface of the metal workpiece, and thoroughly wash and dry it with water; and ground the clean metal workpiece.

[0024] (2) The bottom layer powder coating and the top layer powder coating are respectively delivered to different electrostatic spray guns by compressed air; the bottom layer powder coating is first sprayed onto the surface of the grounded metal workpiece through the spray gun, and then heated and shaped for the first time to obtain the bottom layer on the surface of the metal workpiece;

[0025] (3) The upper powder coating is sprayed onto the surface of the lower layer using a spray gun, and then heated and shaped a second time to obtain the upper layer on the surface of the lower layer. The lower and upper layers are cured to form a radiation-cooled double-layer coating. The thickness of the radiation-cooled double-layer coating is 150-300 micrometers, and its coating structure diagram is shown below. Figure 1 As shown in (b);

[0026] The weighted average reflectivity of the radiation-cooling double-layer coating is greater than 0.90 in the solar radiation band of 0.3–2.5 μm, and the average emissivity is greater than 0.96 in the atmospheric window band of 8–13 μm. According to GB / T 9286, the coating adhesion is tested and the cross-cut test result is ≤1. According to GB / T 1771, the coating's salt spray resistance is tested and the unidirectional corrosion spread width at the crisscross mark is ≤2.0 mm after 1000 h of neutral salt spray testing. According to GB / T 1865, the coating's resistance to artificial weathering is tested and after 500 h of exposure, the coating's discoloration level is ≤2, with no abnormal phenomena such as chalking, blistering, cracking, or peeling.

[0027] The further preparation technology for the radiation-cooled double-layer coating is as follows:

[0028] In steps (2) and (3), the electrostatic spraying process conditions are the same: the spraying voltage is 60-90 kV, the atomizing pressure is 0.2-0.8 atmospheres, the spray gun distance is 100-300 mm, and the spray gun moving speed is 0.1-0.5 m / s.

[0029] In step (2), the oven temperature for the first heating and shaping is 100-330℃, and the baking time is 1-3 minutes.

[0030] In step (2), the thickness of the bottom layer is 100 to 200 micrometers.

[0031] In step (3), the oven temperature for the second heating and shaping is 100-330℃, and the baking time is 10-15 minutes.

[0032] In step (3), the thickness of the upper layer is 50 to 100 micrometers.

[0033] The beneficial technical effects of this invention are reflected in the following aspects:

[0034] 1. This invention provides a design concept for a scalable double-layer radiation-cooling coating based on electrostatic spraying. The bottom layer mainly reflects solar radiation in the visible to near-infrared band, while the top layer reflects solar radiation in the ultraviolet band and provides high emissivity characteristics in the mid- and far-infrared bands. The two layers work together to achieve a weighted average reflectivity greater than 0.90 in the solar radiation band of 0.3–2.5 μm and an average emissivity greater than 0.96 in the atmospheric window band of 8–13 μm. Its innovative mechanism lies in the following: the lower titanium dioxide layer, with its extremely high refractive index, achieves efficient reflection of solar radiation in the visible to near-infrared bands, blocking heat input at the source; the upper zirconium oxide / alumina / boron nitride / barium sulfate layer performs a dual function. On the one hand, it utilizes its inherent high infrared emission characteristics to achieve an emissivity exceeding 0.96 in the 8–13 μm atmospheric window, radiating heat to outer space to the extreme; on the other hand, as a stable wide-bandgap material, it can strongly reflect ultraviolet rays and form a dense physical barrier, overcoming the defects of traditional titanium dioxide coatings that are prone to photoaging. The addition of barium sulfate can also significantly reduce the cost of the coating. This design of vertical decoupling of functions and integration of advantages allows the surface temperature of the metal shell coating to be 3–6°C lower than the ambient temperature in sunny and dry weather, with a net cooling power of 40–150 watts per square meter. When applied to the surface of power equipment, it can significantly reduce the internal surface temperature and enhance the operational stability in high-temperature outdoor environments. In addition, the radiation cooling coating material of this invention is easy to prepare in a large area and uniformly through electrostatic spraying, with stable and scalable cooling performance, perfectly adaptable to outdoor power equipment of different sizes.

[0035] 2. The preparation method of this invention is highly compatible with existing production lines. The preparation method of the radiation-cooled double-layer coating has the outstanding advantages of low cost, high efficiency, and ease of large-scale production. Moreover, it adopts electrostatic spraying as the core process, which has the characteristics of high material utilization and low pollution. It can achieve a clean and environmentally friendly preparation process, providing a solid technical foundation for the rapid implementation and promotion of new productive forces. Attached Figure Description

[0036] Figure 1 A schematic diagram of a double-layer radiation cooling coating;

[0037] Figure 2 This is a flowchart illustrating the preparation process of a double-layer radiation-cooled coating.

[0038] Figure 3 Images showing the microscopic characterization of powder coatings;

[0039] Figure 4 It is a large-area double-layer radiation cooling coating prepared on planar and curved surfaces based on electrostatic spraying process;

[0040] Figure 5 The solar band (0.3~2.5 micrometers) reflectance of Example 1 and Comparative Example 1;

[0041] Figure 6 Emissivity in the infrared band (2.5~25 micrometers) of Example 1;

[0042] Figure 7 These are schematic diagrams of Example 1, Comparative Example 2, and Comparative Example 3;

[0043] Figure 8 The diagrams and temperature curves for the cooling process throughout the day are for Example 1, Comparative Example 2, and Comparative Example 3. Detailed Implementation

[0044] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments.

[0045] Example 1

[0046] See Figure 2 The preparation steps of a radiation-cooling coating material are as follows:

[0047] (1) Take the raw materials of the bottom layer material: the reflective filler is selected as nano titanium dioxide powder with a particle size of 150-500nm.

[0048] Take 400g of nano titanium dioxide powder, 550g of polyester resin, 30g of triglycidyl isocyanate curing agent, 5g of polyacrylate, 5g of fatty acid organic polymer, 5g of benzoin, and 5g of polyethylene wax. (By weight percentage: 40% reflective filler, 55% resin, 3% curing agent, 0.5% brightening agent, 0.5% leveling agent, 0.5% degassing agent, and 0.5% additives).

[0049] (2) Take the raw materials of the upper layer: the reflective filler is selected from nano zirconium dioxide powder with a particle size of 200-700nm and barium sulfate particles with a particle size of 1-2μm.

[0050] Take 200g of nano-zirconia powder, 500g of barium sulfate powder, 260g of polyester resin, 25g of triglycidyl isocyanate curing agent, 5g of polyacrylate, 5g of fatty acid organic polymer, and 5g of polyethylene wax. (By weight percentage: 70% reflective filler, 26% resin, 2.5% curing agent, 0.5% brightening agent, 0.5% leveling agent, and 0.5% additives)

[0051] (3) The raw materials for the bottom layer and the top layer are respectively fed into a high-speed mixer for preliminary mixing. Then, the premixed materials are continuously and uniformly fed into a melt extruder. The temperature of the extruder's feeding section is 100℃, the temperature of the discharge section is 110℃, and the screw speed is 500r / min, so that the solid mixture melts into a viscous flow state. Under strong shear force, each component achieves full micro-dispersion and homogenization, so that the reflective filler is completely broken up and encapsulated in the resin. Two homogeneous melts are obtained respectively.

[0052] (4) The two uniform melts are immediately pressed into thin and continuous sheets by cooling rollers and then rapidly cooled by cooling steel belts to form two brittle sheets.

[0053] (5) The two types of brittle flakes are fed into a high-speed pulverizer for pulverization, and then classified by a vibrating screen. Finally, the bottom layer powder coating and the top layer powder coating with a particle size of 20-30 micrometers are collected separately, i.e., the bottom layer material and the top layer material. Figure 3 As shown, scanning electron microscopy revealed that the powder particles had a dense surface, and the functional fillers were uniformly dispersed in the resin matrix at submicron size. There were no obviously coarse (>90μm) or fine (<5μm) particles, which is beneficial to the uniformity of powder application during electrostatic spraying.

[0054] The average particle size D50 of the base layer powder coating prepared in Example 1 was controlled between 20 μm and 30 μm, with the content of fine powder with a particle size less than 10 μm not exceeding 10% and the content of coarse particles with a particle size greater than 50 μm not exceeding 5%, to ensure good fluidization and powder application rate during electrostatic spraying. The base layer powder coating did not clump or stick under storage and transportation conditions from room temperature to 40°C; its gelation time was measured to be 50 s on a hot plate at 180°C.

[0055] The average particle size D50 of the upper powder coating prepared in Example 1 was controlled between 20 μm and 30 μm, with the content of fine powder with a particle size less than 10 μm not exceeding 10% and the content of coarse particles with a particle size greater than 50 μm not exceeding 5%. The upper powder coating did not clump or stick under storage and transportation conditions from room temperature to 40°C; its gelation time was measured to be 90 s on a hot plate at 180°C.

[0056] Example 2

[0057] The method for preparing a radiation-cooling coating material in Example 2 differs from that in Example 1 only in that:

[0058] In step (2), the raw materials for the upper powder coating are boron nitride nanosheets with a diameter of 1-3 μm and barium sulfate powder with a particle size of 1-2 μm as reflective fillers.

[0059] Take 150g boron nitride nanosheets, 500g barium sulfate powder, 300g polyester resin, 30g triglycidyl isocyanate curing agent, 5g polyacrylate, 10g fatty acid organic polymer, and 5g polyethylene wax. (By weight percentage: 65% reflective filler, 30% resin, 3% curing agent, 0.5% brightening agent, 1% leveling agent, and 0.5% additives)

[0060] The average particle size D50 of the upper powder coating prepared in Example 2 is controlled between 20μm and 30μm, the content of fine powder with a particle size less than 10μm is not higher than 10%, and the content of coarse particles with a particle size greater than 50μm is not higher than 5%. The upper powder coating does not clump or stick under storage and transportation conditions from room temperature to 40℃. The gelation time is measured to be 110s on a hot plate at 180℃.

[0061] Example 3

[0062] The method for preparing a radiation-cooling coating material in Example 3 differs from that in Example 1 only in that:

[0063] In step (2), the raw materials for the upper powder coating are selected as nano-alumina powder with a particle size of 200-700 nm and barium sulfate powder with a particle size of 1 μm-2 μm as reflective fillers. Take 250 g of nano-alumina powder, 450 g of barium sulfate powder, 250 g of polyester resin, 25 g of β-hydroxyalkylamide, 10 g of polyacrylate, 10 g of fatty acid organic polymer, and 5 g of polyethylene wax. (Based on the following mass percentages: 70% reflective filler, 25% resin, 2.5% curing agent, 1% brightening agent, 1% leveling agent, and 0.5% additives)

[0064] The average particle size D50 of the upper powder coating prepared in Example 3 is controlled between 20μm and 30μm, the content of fine powder with a particle size less than 10μm is not higher than 10%, and the content of coarse particles with a particle size greater than 50μm is not higher than 5%. The upper powder coating does not clump or stick under storage and transportation conditions from room temperature to 40℃. The gelation time is measured to be 90s on a hot plate at 180℃.

[0065] Example 4

[0066] The method for preparing a radiation-cooling coating material in Example 4 differs from that in Example 1 only in that:

[0067] In step (1), the raw material for the bottom powder coating is nano titanium dioxide powder with a particle size of 150-500nm.

[0068] Take 400g of nano titanium dioxide powder, 400g of hydroxyl acrylic resin, 170g of blocked isocyanate, 5g of polyacrylate, 10g of fatty acid organic polymer, 5g of benzoin, and 10g of polyethylene wax. (By weight percentage: 40% reflective filler, 40% resin, 17% curing agent, 0.5% brightening agent, 1% leveling agent, 0.5% degassing agent, and 1% additives).

[0069] In step (2), the raw materials for the upper powder coating are selected as nano-zirconia powder with a particle size of 200-700nm and barium sulfate powder with a particle size of 1-2μm as reflective fillers.

[0070] Take 200g of nano-zirconia powder, 430g of barium sulfate powder, 250g of hydroxyl acrylic resin, 100g of triglycidyl isocyanate curing agent, 5g of polyacrylate, 10g of fatty acid organic polymer, and 5g of polyethylene wax. (By weight percentage: 63% reflective filler, 25% resin, 10% curing agent, 0.5% brightening agent, 1% leveling agent, and 0.5% additives)

[0071] The average particle size D50 of the base powder coating prepared in Example 4 is controlled between 20μm and 30μm, the content of fine powder with a particle size less than 10μm is not higher than 10%, and the content of coarse particles with a particle size greater than 50μm is not higher than 5%. The base powder coating does not clump or stick under storage and transportation conditions from room temperature to 40℃. The gelation time is measured to be 45s on a hot plate at 180℃.

[0072] The average particle size D50 of the upper powder coating prepared in Example 4 is controlled between 20 μm and 30 μm, the content of fine powder with a particle size less than 10 μm is not higher than 10%, and the content of coarse particles with a particle size greater than 50 μm is not higher than 5%. The upper powder coating does not clump or stick under storage and transportation conditions from room temperature to 40°C. The gelation time is measured to be 85 s on a hot plate at 180°C.

[0073] Example 5

[0074] The method for preparing a radiation-cooling coating material in Example 5 differs from that in Example 1 only in that:

[0075] In step (1), the raw material for the bottom powder coating is nano titanium dioxide powder with a particle size of 150~500nm.

[0076] Take 400g of nano titanium dioxide powder, 400g of hydroxyl acrylic resin, 170g of blocked isocyanate, 5g of polyacrylate, 10g of fatty acid organic polymer, 5g of benzoin, and 10g of polyethylene wax. (By weight percentage: 40% reflective filler, 40% resin, 17% curing agent, 0.5% brightening agent, 1% leveling agent, 0.5% degassing agent, and 1% additives).

[0077] In step (2), the raw materials for the upper powder coating are boron nitride nanosheets with a diameter of 1-3 μm and barium sulfate powder with a particle size of 1-2 μm as reflective fillers.

[0078] Take 150g boron nitride nanosheets, 480g barium sulfate powder, 250g hydroxyl acrylic resin, 100g triglycidyl isocyanate curing agent, 5g polyacrylate, 10g fatty acid organic polymer, and 5g polyethylene wax. (By weight percentage: 63% reflective filler, 25% resin, 10% curing agent, 0.5% brightening agent, 1% leveling agent, and 0.5% additives)

[0079] The average particle size D50 of the base powder coating prepared in Example 5 is controlled between 20μm and 30μm, the content of fine powder with a particle size less than 10μm is not higher than 10%, and the content of coarse particles with a particle size greater than 50μm is not higher than 5%. The base powder coating does not clump or stick under storage and transportation conditions from room temperature to 40℃. The gelation time is measured to be 45s on a hot plate at 180℃.

[0080] The average particle size D50 of the upper powder coating prepared in Example 5 is controlled between 20 μm and 30 μm, the content of fine powder with a particle size less than 10 μm is not higher than 10%, and the content of coarse particles with a particle size greater than 50 μm is not higher than 5%. The upper powder coating does not clump or stick under storage and transportation conditions from room temperature to 40°C. The gelation time is 100 s when measured on a hot plate at 180°C.

[0081] Example 6

[0082] The method for preparing a radiation-cooling coating material in Example 6 differs from that in Example 1 only in that:

[0083] In step (1), the raw material for the bottom powder coating is nano titanium dioxide powder with a particle size of 150-500nm.

[0084] Take 400g of nano titanium dioxide powder, 400g of hydroxyl acrylic resin, 170g of blocked isocyanate, 5g of polyacrylate, 10g of polyethylene-vinyl acetate, 5g of benzoin, and 10g of polyethylene wax. (By weight percentage: 40% reflective filler, 40% resin, 17% curing agent, 0.5% brightening agent, 1% leveling agent, 0.5% degassing agent, and 1% additives).

[0085] In step (2), the raw materials for the upper powder coating are selected as nano-alumina powder with a particle size of 200-700nm and barium sulfate particles with a particle size of 1-2μm as reflective fillers.

[0086] Take 250g of nano-alumina powder, 450g of barium sulfate powder, 200g of hydroxyl acrylic resin, 80g of triglycidyl isocyanate curing agent, 5g of polyacrylate, 10g of polyethylene-vinyl acetate, and 5g of polyethylene wax. (By weight percentage: 70% reflective filler, 20% resin, 8% curing agent, 0.5% brightening agent, 1% leveling agent, and 0.5% additives)

[0087] The average particle size D50 of the base powder coating prepared in Example 6 is controlled between 20μm and 30μm, the content of fine powder with a particle size less than 10μm is not higher than 10%, and the content of coarse particles with a particle size greater than 50μm is not higher than 5%. The base powder coating does not clump or stick under storage and transportation conditions from room temperature to 40℃. The gelation time is measured to be 45s on a hot plate at 180℃.

[0088] The average particle size D50 of the upper powder coating prepared in Example 6 is controlled between 20 μm and 30 μm, the content of fine powder with a particle size less than 10 μm is not higher than 10%, and the content of coarse particles with a particle size greater than 50 μm is not higher than 5%. The upper powder coating does not clump or stick under storage and transportation conditions from room temperature to 40°C. The gelation time is 90 s when measured on a hot plate at 180°C.

[0089] Example 7

[0090] The method for preparing a radiation-cooling coating material in Example 7 differs from that in Example 1 only in that:

[0091] In step (1), the raw material for the bottom powder coating is nano titanium dioxide powder with a particle size of 150-500nm.

[0092] Take 400g of nano titanium dioxide powder, 570g of polyvinylidene fluoride, 5g of silicone acrylate, 10g of fatty acid organic polymer, 5g of benzoin, and 10g of silica powder. (By weight percentage: 40% reflective filler, 57% resin, 0.5% brightening agent, 1% leveling agent, 0.5% degassing agent, and 1% additives).

[0093] In step (2), the raw materials for the upper powder coating are boron nitride nanosheets with a diameter of 1-3 μm and barium sulfate powder with a particle size of 1-2 μm as reflective fillers.

[0094] Take 150g boron nitride nanosheets, 480g barium sulfate powder, 350g polyvinylidene fluoride, 5g silicone-containing acrylate, 10g fatty acid organic polymer, and 5g silica powder. (By weight percentage: 63% reflective filler, 35% resin, 0.5% brightening agent, 1% leveling agent, and 0.5% additives)

[0095] In step (3), the temperature of the extruder feeding section is 200℃, the temperature of the discharge section is 210℃, and the screw speed is 350r / min.

[0096] The average particle size D50 of the base layer powder coating prepared in Example 7 is controlled between 20μm and 30μm, the content of fine powder with a particle size less than 10μm is not higher than 10%, and the content of coarse particles with a particle size greater than 50μm is not higher than 5%. The base layer powder coating does not clump or stick under storage and transportation conditions from room temperature to 40℃. The gelation time is measured to be 80s on a hot plate at 220℃.

[0097] The average particle size D50 of the upper powder coating prepared in Example 7 is controlled between 20 μm and 30 μm, the content of fine powder with a particle size less than 10 μm is not higher than 10%, and the content of coarse particles with a particle size greater than 50 μm is not higher than 5%. The upper powder coating does not clump or stick under storage and transportation conditions from room temperature to 40°C. The gelation time is measured to be 90 s on a hot plate at 220°C.

[0098] Example 8

[0099] The method for preparing a radiation-cooling coating material in Example 8 differs from that in Example 1 only in that:

[0100] In step (1), the raw material for the bottom powder coating is nano titanium dioxide powder with a particle size of 150-500nm.

[0101] Take 400g of nano titanium dioxide powder, 570g of polyvinylidene fluoride, 5g of silicone acrylate, 10g of fatty acid organic polymer, 5g of benzoin, and 10g of silica powder. (By weight percentage: 40% reflective filler, 57% resin, 0.5% brightening agent, 1% leveling agent, 0.5% degassing agent, and 1% additives).

[0102] In step (2), the raw materials for the upper powder coating are selected as nano-alumina powder with a particle size of 200-700nm and barium sulfate powder with a particle size of 1-2μm as reflective fillers.

[0103] Take 250g of nano-alumina powder, 430g of barium sulfate powder, 300g of polyvinylidene fluoride, 5g of silicone-containing acrylate, 10g of fatty acid organic polymer, and 5g of silica powder. (By weight percentage: 68% reflective filler, 30% resin, 0.5% brightening agent, 1% leveling agent, and 0.5% additives)

[0104] In step (3), the temperature of the extruder feeding section is 190℃, the temperature of the discharge section is 205℃, and the screw speed is 400r / min.

[0105] The average particle size D50 of the base layer powder coating prepared in Example 8 was controlled between 20 μm and 30 μm, the content of fine powder with a particle size less than 10 μm was not higher than 10%, and the content of coarse particles with a particle size greater than 50 μm was not higher than 5%. The base layer powder coating did not clump or stick under storage and transportation conditions from room temperature to 40°C; its gelation time was measured to be 80 s on a hot plate at 220°C.

[0106] The average particle size D50 of the upper powder coating prepared in Example 8 was controlled between 20 μm and 30 μm, the content of fine powder with a particle size less than 10 μm was not higher than 10%, and the content of coarse particles with a particle size greater than 50 μm was not higher than 5%. The upper powder coating did not clump or stick under storage and transportation conditions from room temperature to 40°C; its gelation time was measured to be 90 s on a hot plate at 220°C.

[0107] Example 9

[0108] The method for preparing a radiation-cooling coating material in Example 9 differs from that in Example 1 only in that:

[0109] In step (1), the raw material for the bottom powder coating is nano titanium dioxide powder with a particle size of 150-500nm.

[0110] Take 400g of nano titanium dioxide powder, 580g of polymethylpentene, 10g of perfluoroalkoxy resin, and 10g of fluorinated wax. (By weight percentage: 40% reflective filler, 58% resin, 1% brightening agent, and 1% additives).

[0111] In step (2), boron nitride nanosheets with a diameter of 1-3 μm and barium sulfate particles with a particle size of 1-2 μm are selected as reflective fillers for the upper powder coating raw materials.

[0112] Take 250g of boron nitride nanosheets, 430g of barium sulfate powder, 300g of polymethylpentene, 10g of perfluoroalkoxy resin, and 5g of fluorinated wax. (By weight percentage: 68% reflective filler, 30% resin, 1% brightening agent, and 1% additives)

[0113] In step (3), the temperature of the extruder feeding section is 240℃, the temperature of the discharge section is 260℃, and the screw speed is 400r / min.

[0114] The average particle size D50 of the base layer powder coating prepared in Example 9 was controlled between 20 μm and 30 μm, the content of fine powder with a particle size less than 10 μm was not higher than 10%, and the content of coarse particles with a particle size greater than 50 μm was not higher than 5%. The base layer powder coating did not clump or stick under storage and transportation conditions from room temperature to 40°C; its gelation time was measured to be 80 s on a hot plate at 270°C.

[0115] The average particle size D50 of the upper powder coating prepared in Example 9 was controlled between 20 μm and 30 μm, with the content of fine powder with a particle size less than 10 μm not exceeding 10% and the content of coarse particles with a particle size greater than 50 μm not exceeding 5%. The lower powder coating did not clump or stick under storage and transportation conditions from room temperature to 40°C; its gelation time was measured to be 90 s on a hot plate at 270°C.

[0116] Example 10

[0117] The method for preparing a radiation-cooling coating material in Example 10 differs from that in Example 1 only in that:

[0118] In step (1), the raw material for the bottom powder coating is titanium dioxide powder with a particle size of 150-500nm.

[0119] Take 400g of nano titanium dioxide powder, 580g of polymethylpentene, 10g of perfluoroalkoxy resin, and 10g of fluorinated wax. (By weight percentage: 40% reflective filler, 58% resin, 1% brightening agent, and 1% additives).

[0120] In step (2), the raw materials for the upper powder coating are selected as nano-alumina powder with a particle size of 200-700nm and barium sulfate powder with a particle size of 1-2μm as reflective fillers.

[0121] Take 250g of nano-alumina powder, 430g of barium sulfate powder, 300g of polymethylpentene, 10g of perfluoroalkoxy resin, and 10g of fluorinated wax. (By weight percentage: 30% resin, 68% reflective filler, 1% brightening agent, 1% additives)

[0122] In step (3), the temperature of the extruder feeding section is 240℃, the temperature of the discharge section is 260℃, and the screw speed is 400r / min.

[0123] The average particle size D50 of the base layer powder coating prepared in Example 10 is controlled between 20 μm and 30 μm, the content of fine powder with a particle size less than 10 μm is not higher than 10%, and the content of coarse particles with a particle size greater than 50 μm is not higher than 5%. The base layer powder coating does not clump or stick under storage and transportation conditions from room temperature to 40°C; its gelation time is measured to be 80 s on a hot plate at 270°C.

[0124] The average particle size D50 of the upper powder coating prepared in Example 10 was controlled between 20 μm and 30 μm, the content of fine powder with a particle size less than 10 μm was not higher than 10%, and the content of coarse particles with a particle size greater than 50 μm was not higher than 5%. The lower powder coating did not clump or stick under storage and transportation conditions from room temperature to 40°C; its gelation time was measured to be 90 s on a hot plate at 270°C.

[0125] Example 11

[0126] The method for preparing a radiation-cooling coating material in Example 11 differs from that in Example 1 only in that:

[0127] In step (1), the raw material for the bottom powder coating is nano titanium dioxide powder with a particle size of 150-500nm.

[0128] Take 400g of titanium dioxide powder, 580g of fluorinated ethylene propylene copolymer, 10g of perfluoroalkoxy resin and 10g of fluorinated wax. (By weight percentage: 40% reflective filler, 58% resin, 1% brightening agent, 1% additives).

[0129] In step (2), the raw materials for the upper powder coating are boron nitride nanosheets with a diameter of 1-3 μm and barium sulfate powder with a particle size of 1-2 μm as reflective fillers.

[0130] Take 250g of boron nitride nanosheets, 430g of barium sulfate powder, 300g of fluorinated ethylene propylene copolymer, 10g of perfluoroalkoxy resin, and 5g of fluorinated wax. (By weight percentage: 68% reflective filler, 30% resin, 1% brightening agent, 1% additives)

[0131] In step (3), the temperature of the extruder feeding section is 300℃, the temperature of the discharge section is 320℃, and the screw speed is 400r / min.

[0132] The average particle size D50 of the base layer powder coating prepared in Example 11 was controlled between 20 μm and 30 μm, the content of fine powder with a particle size less than 10 μm was not higher than 10%, and the content of coarse particles with a particle size greater than 50 μm was not higher than 5%. The base layer powder coating did not clump or stick under storage and transportation conditions from room temperature to 40°C; its gelation time was measured to be 80 s on a hot plate at 330°C.

[0133] The average particle size D50 of the upper powder coating prepared in Example 11 was controlled between 20 μm and 30 μm, the content of fine powder with a particle size less than 10 μm was not higher than 10%, and the content of coarse particles with a particle size greater than 50 μm was not higher than 5%. The upper powder coating did not clump or stick under storage and transportation conditions from room temperature to 40°C; its gelation time was measured to be 90 s on a hot plate at 330°C.

[0134] Example 12

[0135] The method for preparing a radiation-cooling coating material in Example 12 differs from that in Example 1 only in that:

[0136] In step (1), the raw material for the bottom powder coating is nano titanium dioxide powder with a particle size of 150-500nm.

[0137] Take 400g of titanium dioxide powder, 580g of fluorinated ethylene propylene copolymer, 10g of perfluoroalkoxy resin and 10g of fluorinated wax. (By weight percentage: 40% reflective filler, 58% resin, 1% brightening agent, 1% additives).

[0138] In step (2), the raw materials for the upper powder coating are selected as nano-alumina powder with a particle size of 200-700nm and barium sulfate powder with a particle size of 1-2μm as reflective fillers.

[0139] Take 250g of nano-alumina powder, 430g of barium sulfate powder, 300g of fluorinated ethylene propylene copolymer, 10g of perfluoroalkoxy resin, and 10g of fluorinated wax. (By weight percentage: 30% resin, 68% reflective filler, 1% brightening agent, 1% additives)

[0140] In step (3), the temperature of the extruder feeding section is 300℃, the temperature of the discharge section is 320℃, and the screw speed is 400r / min.

[0141] The average particle size D50 of the base layer powder coating prepared in Example 12 was controlled between 20 μm and 30 μm, the content of fine powder with a particle size less than 10 μm was not higher than 10%, and the content of coarse particles with a particle size greater than 50 μm was not higher than 5%. The base layer powder coating did not clump or stick under storage and transportation conditions from room temperature to 40°C; its gelation time was measured to be 80 s on a hot plate at 330°C.

[0142] The average particle size D50 of the upper powder coating prepared in Example 12 was controlled between 20 μm and 30 μm, with the content of fine powder with a particle size less than 10 μm not exceeding 10% and the content of coarse particles with a particle size greater than 50 μm not exceeding 5%. The upper powder coating did not clump or stick under storage and transportation conditions from room temperature to 40°C; its gelation time was measured to be 90 s on a hot plate at 330°C.

[0143] Example 13

[0144] The preparation steps for fabricating a radiation-cooling bilayer coating based on radiation-cooling coating materials are as follows:

[0145] (1) Before electrostatic spraying, the surface of the metal workpiece to be treated is pretreated; the oil and oxide scale on the surface of the metal workpiece are thoroughly removed by degreasing and rust removal.

[0146] (2) Suspend or place the grounded metal workpiece in the powder recovery device and send it to the front of the spray gun. Adjust the electrostatic voltage of the spray gun to 60 kV, adjust the atomizing pressure to 0.5 atmospheres, and the spray gun distance to 150 mm.

[0147] (3) The bottom powder coating prepared in Example 1 is preferentially adsorbed onto the grounded metal workpiece surface by a spray gun, and the spray gun moves at a speed of 0.1 meters per second.

[0148] (4) Perform the first heating and shaping. The oven temperature for the first heating and shaping is 180℃ and the baking time is 2 minutes.

[0149] (5) The upper powder coating prepared in Example 1 is then adsorbed onto the surface of the workpiece again through a spray gun, and then heated and shaped for the second time. The oven temperature for the second heating and shaping is 200°C and the baking time is 10 minutes to obtain a double-layer radiation cooling coating.

[0150] See Figure 4 The radiation-cooling double-layer coating prepared in Example 13 can be uniformly applied to complex or flat surfaces, wherein the thickness of the bottom layer coating is 150±20 micrometers and the thickness of the top layer coating is 75±20 micrometers.

[0151] Depend on Figure 5 It can be seen that by using a UV-Vis-NIR spectrophotometer to analyze the radiation-cooled bilayer coating prepared in Example 1, its spectral reflectance in the range of 0.3 to 2.5 micrometers can be obtained, and further weighted calculation shows that its reflectance is 90.5%.

[0152] Depend on Figure 6 It can be seen that the radiation-cooled bilayer coating prepared in Example 1 was analyzed using a Fourier transform infrared spectrometer with an integrating sphere, and its weighted average emissivity in the 8-13 micrometer band was found to be 96.0%.

[0153] The radiation-cooling double-layer coating prepared in Example 13 has an adhesion grade of 1, a unidirectional corrosion propagation width of 0.5 mm at the scribing point after 1000 h of neutral salt spray, a discoloration grade of 0 after 500 h of exposure in an artificial climate aging atmosphere, and no abnormal phenomena such as chalking, blistering, cracking, or peeling.

[0154] Example 14

[0155] The method for preparing the double-layer radiation-cooling coating in Example 14 differs from that in Example 13 only in that:

[0156] The underlying coating material used in step (3) is the product of Example 2.

[0157] The upper coating material used in step (5) is the product of Example 2.

[0158] The thickness of the bottom coating is 150±20 micrometers, and the thickness of the top coating is 75±20 micrometers.

[0159] The double-layer radiation-cooling coating prepared in Example 14 has a weighted average reflectivity of 90.3% in the 0.3–2.5 μm band and a weighted average emissivity of 96.4% in the 8–13 μm band. The adhesion is grade 1, and the unidirectional corrosion propagation width at the scribing point after 1000 h of neutral salt spray is 0.5 mm.

[0160] Example 15

[0161] The preparation method of the double-layer radiation-cooling coating in Example 15 differs from that in Example 13 only in that:

[0162] The underlying coating material used in step (3) is the product of Example 3.

[0163] The upper coating material used in step (5) is the product of Example 3.

[0164] The thickness of the bottom coating is 150±20 micrometers, and the thickness of the top coating is 75±20 micrometers.

[0165] The double-layer radiation-cooling coating prepared in Example 15 has a weighted average reflectivity of 90.1% in the 0.3–2.5 μm band, a weighted average emissivity of 96.5% in the 8–13 μm band, an adhesion grade of 1, and a unidirectional corrosion propagation width of 0.5 mm at the scribing point after 1000 h of neutral salt spray.

[0166] Example 16

[0167] The preparation method of the double-layer radiation cooling coating in Example 16 differs from that in Example 13 only in that:

[0168] The underlying coating material used in step (3) is the product of Example 4.

[0169] The upper coating material used in step (5) is the product of Example 4.

[0170] The thickness of the bottom coating is 150±20 micrometers, and the thickness of the top coating is 75±20 micrometers.

[0171] The double-layer radiation-cooling coating prepared in Example 16 has a weighted average reflectivity of 90.5% in the 0.3 to 2.5 micrometer band and a weighted average emissivity of 96.2% in the 8 to 13 micrometer band.

[0172] Example 17

[0173] The method for preparing the double-layer radiation-cooling coating in Example 17 differs from that in Example 13 only in that:

[0174] The underlying coating material used in step (3) is the product of Example 5.

[0175] The upper coating material used in step (5) is the product of Example 5.

[0176] The thickness of the bottom coating is 150±20 micrometers, and the thickness of the top coating is 75±20 micrometers.

[0177] The double-layer radiation-cooling coating prepared in Example 17 has a weighted average reflectivity of 90.3% in the 0.3–2.5 μm band and a weighted average emissivity of 96.0% in the 8–13 μm band.

[0178] Example 18

[0179] The preparation method of the double-layer radiation cooling coating in Example 18 differs from that in Example 13 only in that:

[0180] The underlying coating material used in step (3) is the product of Example 6.

[0181] The upper coating material used in step (5) is the product of Example 6.

[0182] The thickness of the bottom coating is 150±20 micrometers, and the thickness of the top coating is 75±20 micrometers.

[0183] The double-layer radiation-cooling coating prepared in Example 18 has a weighted average reflectivity of 90.0% in the 0.3–2.5 μm band and a weighted average emissivity of 96.5% in the 8–13 μm band.

[0184] Example 19

[0185] The method for preparing the double-layer radiation-cooling coating in Example 19 differs from that in Example 13 only in that:

[0186] The underlying coating material used in step (3) is the product of Example 7.

[0187] The oven temperature for heating and shaping in step (4) is 220℃.

[0188] The upper coating material used in step (5) is the product of Example 7, and the final oven temperature for heating and shaping is 240°C.

[0189] The thickness of the bottom coating is 150±20 micrometers, and the thickness of the top coating is 75±20 micrometers.

[0190] The double-layer radiation-cooling coating prepared in Example 19 has a weighted average reflectivity of 90.7% in the 0.3–2.5 μm band and a weighted average emissivity of 96.0% in the 8–13 μm band.

[0191] Example 20

[0192] The preparation method of the double-layer radiation cooling coating in Example 20 differs from that in Example 13 only in that:

[0193] The underlying coating material used in step (3) is the product of Example 8.

[0194] The oven temperature for heating and shaping in step (4) is 220℃.

[0195] The upper coating material used in step (5) is the product of Example 8, and the final oven temperature for heating and shaping is 240°C.

[0196] The thickness of the bottom coating is 150±20 micrometers, and the thickness of the top coating is 75±20 micrometers.

[0197] The double-layer radiation-cooling coating prepared in Example 20 has a weighted average reflectivity of 90.5% in the 0.3–2.5 μm band and a weighted average emissivity of 96.3% in the 8–13 μm band.

[0198] Example 21

[0199] The method for preparing the double-layer radiation-cooling coating in Example 21 differs from that in Example 13 only in that:

[0200] The underlying coating material used in step (3) is the product of Example 9.

[0201] The oven temperature for heating and shaping in step (4) is 270℃.

[0202] The upper coating material used in step (5) is the product of Example 9, and the final oven temperature for heating and shaping is 290°C.

[0203] The thickness of the bottom coating is 150±20 micrometers, and the thickness of the top coating is 75±20 micrometers.

[0204] The double-layer radiation-cooling coating prepared in Example 21 has a weighted average reflectivity of 91.0% in the 0.3–2.5 μm band and a weighted average emissivity of 96.0% in the 8–13 μm band.

[0205] Example 22

[0206] The preparation method of the double-layer radiation cooling coating in Example 22 differs from that in Example 13 only in that:

[0207] The underlying coating material used in step (3) is the product of Example 10.

[0208] The oven temperature for heating and shaping in step (4) is 270℃.

[0209] The upper coating material used in step (5) is the product of Example 10, and the final oven temperature for heating and shaping is 290°C.

[0210] The thickness of the bottom coating is 150±20 micrometers, and the thickness of the top coating is 75±20 micrometers.

[0211] The double-layer radiation-cooling coating prepared in Example 22 has a weighted average reflectivity of 90.7% in the 0.3–2.5 μm band and a weighted average emissivity of 96.2% in the 8–13 μm band.

[0212] Example 23

[0213] The preparation method of the double-layer radiation cooling coating in Example 23 differs from that in Example 13 only in that:

[0214] The underlying coating material used in step (3) is the product of Example 11.

[0215] The oven temperature for heating and shaping in step (4) is 330℃.

[0216] The upper coating material used in step (5) is the product of Example 11, and the final oven temperature for heating and shaping is 350°C.

[0217] The thickness of the bottom coating is 150±20 micrometers, and the thickness of the top coating is 75±20 micrometers.

[0218] The double-layer radiation-cooling coating prepared in Example 23 has a weighted average reflectivity of 90.6% in the 0.3–2.5 micrometer band and a weighted average emissivity of 96.3% in the 8–13 micrometer band.

[0219] Example 24

[0220] The preparation method of the double-layer radiation-cooling coating in Example 24 differs from that in Example 13 only in that:

[0221] The underlying coating material used in step (3) is the product of Example 12.

[0222] The oven temperature for heating and shaping in step (4) is 330℃.

[0223] The upper coating material used in step (5) is the product of Example 12, and the final oven temperature for heating and shaping is 350°C.

[0224] The thickness of the bottom coating is 150±20 micrometers, and the thickness of the top coating is 75±20 micrometers.

[0225] The double-layer radiation-cooling coating prepared in Example 24 has a weighted average reflectivity of 90.3% in the 0.3–2.5 micrometer band and a weighted average emissivity of 96.7% in the 8–13 micrometer band.

[0226] Comparative Example 1

[0227] A sample of commercial white powder coating, measuring 5 cm × 10 cm.

[0228] Comparative Example 2

[0229] A commercial white powder-coated electrical cabinet, measuring 25 cm × 15 cm × 30 cm.

[0230] Comparative Example 3

[0231] The electrical cabinet is made of stainless steel and measures 25 cm × 15 cm × 30 cm.

[0232] Example 1

[0233] The optical properties of the bilayer radiation-cooled coating obtained by the preparation method of Example 13 and the commercial white coating of Comparative Example 1 were characterized using a UV-Vis-NIR spectrometer. To demonstrate the superior performance of the present invention, the optical properties of the bilayer radiation-cooled coating prepared in Example 1 and the commercial white coating of Comparative Example 1 were tested. Characterization was performed in the solar band of 0.3–2.5 micrometers using a UV-Vis-NIR spectrometer equipped with an integrating sphere, and the reflectance in the atmospheric window band of 8–13 micrometers was measured using a Fourier transform infrared spectrometer equipped with an integrating sphere. The emissivity of the examples was obtained according to Kirchhoff's laws.

[0234] Test results show that the optical performance of the coating of this invention is significantly better than that of the comparative example. The weighted average solar reflectance of the double-layer radiation-cooling coating of Example 1 can reach 90.5%, especially maintaining extremely high reflectance in the visible light band; while the solar reflectance of the commercial coating of Comparative Example 1 is only 81.3%. Figure 5 As shown. Regarding the key thermal radiation performance, the coating of Example 1 achieved an average thermal emissivity of 96.5% in the atmospheric window band, exhibiting strong selective radiation characteristics, such as... Figure 6 As shown above, the data demonstrates that this invention, through its unique dual-layer synergistic design—the bottom coating primarily reflects solar radiation in the visible to infrared bands, while the top coating reflects solar radiation in the ultraviolet band and provides high emissivity characteristics in the infrared band—achieves a weighted average reflectivity greater than 0.90 in the 0.3-2.5μm solar radiation band and an average emissivity greater than 0.96 in the 8-13μm atmospheric window band. Its comprehensive optical performance far surpasses that of traditional commercial white coatings, providing a key guarantee for achieving efficient daytime passive radiative cooling.

[0235] Example 2

[0236] The power cabinet with the double-layer radiation cooling coating prepared in Example 1 above, along with Comparative Examples 2 and 3, was tested in an open area under clear weather conditions. The test methods are as follows:

[0237] Experiments were conducted on the surface of a metal power cabinet measuring 25 cm × 15 cm × 30 cm, as well as on Comparative Examples 2 and 3. (See attached text.) Figure 7 High-precision thermocouples are installed at the same location inside each power cabinet and connected to a data logger to continuously monitor and record internal temperature changes. Simultaneously, a total solar radiation meter is used to monitor ambient solar irradiance. Figure 8As shown, the double-layer radiation cooling coating of this invention exhibits excellent cooling performance: the average solar irradiance is approximately 900 W / m² during the period from 9:00 to 12:00. 2 In the case of Example 1, the highest temperature difference on the inner surface can reach 21.3°C compared to Comparative Example 3, and the highest temperature difference on the inner surface can reach 12.5°C compared to Example 2.

[0238] The results of Examples 1-2 above fully demonstrate that the double-layer radiative cooling coating provided by this invention can provide strong cooling protection for outdoor power equipment through an efficient daytime passive radiative cooling mechanism without consuming any energy, effectively improving the safety and lifespan of equipment operation, and has broad application prospects in the fields of building energy conservation and outdoor equipment thermal management.

[0239] Those skilled in the art will readily understand that the above embodiments 1 to 24 are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A radiation-cooling coating material, characterized in that: The radiation cooling coating material consists of a base material and an upper material; the raw materials of the base material and the upper material respectively include 40-70% reflective filler, 25-60% resin, 0-20% curing agent, 0.5-1% brightening agent, 0-1% leveling agent, 0-1% degassing agent and 0.5-1% additives; The resin is one of polyester resin, hydroxyl acrylic resin, polyvinylidene fluoride, polymethylpentene, and fluorinated ethylene propylene copolymer; The curing agent is one of triglycidyl isocyanate, β-hydroxyalkylamide, and blocked isocyanate; The brightening agent is one of polyacrylate, silicone acrylate, and perfluoroalkoxy resin; The leveling agent is one of fatty acid organic polymers or polyethylene-vinyl acetate. The degassing agent is benzoin; The additive is one of polyethylene wax, silica powder, and fluorinated wax; The reflective filler in the bottom layer material is nano-titanium dioxide powder; The reflective filler in the upper layer material is at least one of nano-zirconia powder, boron nitride nanosheets, nano-alumina powder, and barium sulfate powder. The raw materials for the base material are mixed at high speed, melt-extruded by twin screws, and pressed into brittle sheets by cooling rollers. The brittle sheets are then finely ground, sieved, cooled, and packaged to obtain the base powder coating. The raw materials for the upper layer are mixed at high speed, melt-extruded by twin screws, and pressed into brittle sheets by cooling rollers. The brittle sheets are then finely ground, sieved, cooled, and packaged to obtain the upper layer powder coating. In use, the bottom powder coating and the top powder coating are sprayed onto the surface of the grounded metal workpiece one after another through an electrostatic spray gun and then heated and cured to form a radiation cooling double coating. The average particle size D50 of the base powder coating is controlled between 20μm and 30μm, the content of fine powder with a particle size less than 10μm is not higher than 10%, and the content of coarse particles with a particle size greater than 50μm is not higher than 5%. The base powder does not clump or stick under storage and transportation conditions from room temperature to 40℃. When measured on a hot plate at 180℃ to 330℃, its gelation time is 40s to 80s. The average particle size D50 of the upper powder coating is controlled between 20μm and 30μm, the content of fine powder with a particle size less than 10μm is not higher than 8%, and the content of coarse particles with a particle size greater than 50μm is not higher than 5%. The upper powder does not clump or stick under storage and transportation conditions from room temperature to 40℃. When measured on a hot plate at 180℃ to 330℃, its gelation time is 80s to 100s.

2. The radiation-cooling double-layer coating material according to claim 1, characterized in that: The nano-titanium dioxide powder has a particle size of 150nm to 500nm; the nano-zirconium dioxide powder and nano-aluminum oxide powder both have a particle size of 200nm to 700nm; the boron nitride nanosheets have a sheet diameter of 1 to 3μm; and the barium sulfate powder has a particle size of 1 to 2μm.

3. The radiation-cooling double-layer coating material according to claim 1, characterized in that: The extrusion temperature of the twin-screw melt extrusion is 100–330°C.

4. The radiation-cooling double-layer coating material according to claim 1, characterized in that: The fine grinding and screening process conditions are as follows: fine grinding is carried out in a high-speed pulverizer at a rotation speed of 20,000 to 26,000 rpm, a feed rate of 20-50 kg / h, and a cold air temperature of ≤15℃; screening is carried out in a fully enclosed vibrating screen or rotary screen at a screen mesh of 160 to 200 mesh, continuous screening, and a sealed and moisture-proof material collection system.

5. A method for preparing a radiation-cooling double-layer coating using the radiation-cooling coating material of claim 1, characterized in that, The operation steps are as follows: (1) Pre-treat the surface of the metal workpiece by degreasing and rust removal to thoroughly remove oil and oxide scale from the surface of the metal workpiece, and thoroughly wash and dry it with water; and ground the clean metal workpiece. (2) The bottom layer powder coating and the top layer powder coating are respectively delivered to different electrostatic spray guns by compressed air; the bottom layer powder coating is first sprayed onto the surface of the grounded metal workpiece through the spray gun, and then heated and shaped for the first time to obtain the bottom layer on the surface of the metal workpiece; (3) The upper powder coating is sprayed onto the surface of the bottom layer through a spray gun and then heated and shaped a second time to obtain the upper layer on the surface of the bottom layer. The bottom layer and the upper layer are cured and shaped to obtain a radiation cooling double layer coating. The thickness of the radiation-cooled double-layer coating is 150–300 micrometers; The weighted average reflectivity of the radiation-cooling double-layer coating is greater than 0.90 in the solar radiation band of 0.3–2.5 μm, and the average emissivity is greater than 0.96 in the atmospheric window band of 8–13 μm. According to GB / T 9286, the coating adhesion is tested and the cross-cut test result is ≤1. According to GB / T 1771, the coating's salt spray resistance is tested and the unidirectional corrosion spread width at the crisscross mark is ≤2.0 mm after 1000 h of neutral salt spray testing. According to GB / T 1865, the coating's resistance to artificial weathering is tested and after 500 h of exposure, the coating's discoloration level is ≤2, with no abnormal phenomena such as chalking, blistering, cracking, or peeling.

6. The method for preparing the radiation-cooled double-layer coating according to claim 5, characterized in that: In steps (2) and (3), the electrostatic spraying process conditions are the same: the spraying voltage is 60-90 kV, the atomizing pressure is 0.2-0.8 atmospheres, the spray gun distance is 100-300 mm, and the spray gun moving speed is 0.1-0.5 m / s.

7. The method for preparing the radiation-cooled double-layer coating according to claim 5, characterized in that: In step (2), the oven temperature for the first heating and shaping is 100-350℃, and the baking time is 1-3 minutes.

8. The method for preparing the radiation-cooled double-layer coating according to claim 5, characterized in that: In step (2), the thickness of the bottom layer is 100 to 200 micrometers.

9. The method for preparing the radiation-cooled double-layer coating according to claim 5, characterized in that: In step (3), the oven temperature for the second heating and shaping is 100-350℃, and the baking time is 10-15 minutes.

10. The method for preparing the radiation-cooled double-layer coating according to claim 5, characterized in that: In step (3), the thickness of the upper layer is 50 to 100 micrometers.

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