High refractive index contrast radiative cooling paint

Abstract

This invention discloses a high-refractive-index contrast radiation-cooling coating, belonging to the technical field of radiation-cooling coatings. The raw materials of this invention's high-refractive-index contrast radiation-cooling coating include hollow microspheres, high-refractive-index pigments, film-forming substances, solvents, and additives. The coating process of this invention's radiation-cooling coating is a two-coat process. First, an inner coating is applied to the substrate surface using the radiation-cooling coating with rutile titanium dioxide as the high-refractive-index pigment. Then, an outer coating is applied to the surface of the inner coating using the radiation-cooling coating with zirconium dioxide and / or zirconium silicate as the high-refractive-index pigments. This invention introduces a closed, independent bubble structure into the coating using hollow microspheres, combined with a preferred high-refractive-index pigment, to increase the refractive index difference between adjacent components in the coating, significantly enhancing its solar reflectance, thereby achieving excellent radiation-cooling performance under strong sunlight.

Description

Technical Field

[0001] This invention relates to the field of radiation cooling coating technology, and in particular to a radiation cooling coating with high refractive index contrast. Background Technology

[0002] Radiation cooling technology refers to the process of releasing excess heat into outer space by allowing the spontaneous infrared thermal radiation from an object's surface to penetrate the Earth's atmosphere through the 8-13μm wavelength "atmospheric window." Due to its energy-saving and environmentally friendly characteristics, it has become a research hotspot in academia and industry in recent years.

[0003] High-performance radiative cooling depends on high solar reflectance and high long-wave infrared (LWIR) thermal emissivity. The film-forming material of coatings is generally a polymer resin, which naturally possesses high infrared emissivity in the LWIR thermal radiation band due to its intrinsic material properties. On the other hand, the irradiance of the Earth's surface AM 1.5 standard solar spectrum is approximately 1000 W / m². 2 The theoretical maximum radiative exitance of radiative cooling technology is approximately 150 W / m². 2 The two differ by nearly an order of magnitude, and under sunlight, the heat absorption of the coating by sunlight easily offsets the energy of outward heat radiation cooling. Therefore, the key to designing high-performance radiation-cooling coatings lies in maximizing the solar reflectance of the coating in the solar wavelength range (0.3-2.5μm). One publicly disclosed technical approach for radiation-cooling coatings is to increase the amount of pigments and fillers. Essentially, this is to make the pigment volume concentration (PVC) of the dry coating film exceed the critical pigment volume concentration (CPVC). This results in the film-forming material being insufficient to completely coat the pigment particles, forming pores in the coating. The difference in refractive index between the air (refractive index n≈1) and the polymeric film-forming material (n≈1.5) in these pores scatters sunlight, thus increasing the solar reflectance. However, this structure also leads to the following adverse effects: the open, interconnected pore network allows liquids and gases to transport within the resin base, weakening the toughness and adhesion of the coating film, making it more prone to peeling, cracking, or delamination, and deteriorating its mechanical properties; the pores in the coating film also allow external substances (such as moisture, rainwater, and chemicals) to more easily erode and penetrate, weakening the coating's protective performance, shortening its lifespan, and reducing its durability. Therefore, further improvements are still needed. Summary of the Invention

[0004] The purpose of this invention is to provide a radiation-cooling coating with high refractive index contrast to solve the above-mentioned problems in the prior art.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] One of the technical solutions of this invention: provides a radiation-cooling coating with high refractive index contrast, wherein the raw materials, by volume, include:

[0007] Hollow microspheres 5-30 parts, high refractive index pigment 2-15 parts, film-forming substance 40-60 parts, solvent 10-40 parts and additives 0.1-10 parts;

[0008] The high refractive index pigment has a refractive index ≥ 1.95;

[0009] The boundary particle size D90 of the hollow microspheres is ≤30μm;

[0010] Preferably, the median particle size of the high refractive index pigment is 0.2-1 μm; the particle size distribution dispersion of the high refractive index pigment is ≥1.0.

[0011] The formula for calculating the dispersion is:

[0012] Dispersion = (D90 - D10) / D50;

[0013] Wherein, D90 and D10 are the boundary particle sizes of the high refractive index pigment, and D50 is the median particle size of the high refractive index pigment.

[0014] Preferably, the hollow microspheres are one or more of polymer hollow microspheres, glass hollow microspheres, and ceramic hollow microspheres.

[0015] Preferably, the high refractive index pigment is one or more of rutile titanium dioxide, anatase titanium dioxide, zinc sulfide, antimony trioxide, tin dioxide, zirconium dioxide, and zirconium silicate.

[0016] Preferably, the film-forming substance is acrylic resin, silicone-modified acrylic resin, fluorocarbon resin, polyurethane resin, or epoxy resin; the additives include one or more of dispersants, wetting agents, defoamers, film-forming aids, curing accelerators, thickeners, leveling agents, bactericides, fungicides, pH adjusters, and antifreeze agents.

[0017] The second technical solution of the present invention provides a method for preparing the above-mentioned high refractive index contrast radiation-cooling coating, comprising the following steps:

[0018] The raw materials are mixed to obtain the radiation-cooling coating with high refractive index contrast.

[0019] The third technical solution of the present invention provides an application of the above-mentioned high refractive index contrast radiation-cooling coating in the preparation of radiation-cooling coating films.

[0020] The fourth technical solution of the present invention provides a method for preparing a radiation-cooling coating film, using the above-mentioned radiation-cooling coating film with high refractive index contrast as raw material;

[0021] The coating process of the radiation-cooling coating film is a two-coat process. First, the inner coating film is coated on the substrate surface using the radiation-cooling coating material with rutile titanium dioxide as a high-refractive-index pigment. Then, the outer coating film is coated on the surface of the inner coating film using the radiation-cooling coating material with zirconium dioxide and / or zirconium silicate as a high-refractive-index pigment.

[0022] Preferably, the pigment volume concentration (PVC) of the hollow microspheres and high refractive index pigment in the dry coating film formed by the radiation-cooled coating is ≤ critical pigment volume concentration (CPVC).

[0023] Preferably, the thickness of the radiation cooling coating is 300 μm, and the thickness ratio of the inner coating to the outer coating is 2:1.

[0024] Fifth technical solution of the present invention: to provide a radiation cooling coating film obtained according to the above preparation method.

[0025] The beneficial technical effects of the present invention are as follows:

[0026] This invention improves the refractive index difference between the hollow microspheres, white pigment, and film-forming material in the coating film, thereby optimizing the solar reflectance without sacrificing other coating properties and achieving excellent radiative cooling performance under strong sunlight.

[0027] The high refractive index contrast radiation cooling coating of the present invention can provide high scattering performance of sunlight in the ultraviolet, visible and near-infrared full bands. It can be applied to the roofs, exterior walls and outdoor facilities of various buildings to achieve the effect of effectively reducing solar heat absorption and passive cooling in outdoor environments. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 The diagram illustrates the coating structure of Example 1 and the principle of scattering sunlight at different wavelengths.

[0030] Figure 2 The results of the cement board temperature test are shown in Example 1 and the blank group. Detailed Implementation

[0031] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0032] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, are also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0033] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention.

[0034] The terms “comprising,” “including,” “having,” “containing,” etc., used in this invention are all open-ended terms, meaning that they include but are not limited to.

[0035] This invention discloses a radiation-cooling coating with high refractive index contrast. The raw materials of the coating include hollow microspheres, high refractive index pigments, film-forming substances, solvents, and additives.

[0036] In coating systems, achieving a high solar reflectance hinges on the ability of microparticles dispersed in the film-forming material to effectively scatter incident light within the wavelength range of sunlight. The greater the difference in refractive index between the microparticles and the surrounding film-forming material and other components, the stronger the scattering effect. The film-forming material in the coating of this invention can be selected from polymer resins such as acrylic resin (refractive index n≈1.49), silicone-modified acrylic resin (n≈1.45), fluorocarbon resin (n≈1.40), polyurethane resin (n≈1.52), and epoxy resin (n≈1.54).

[0037] Unlike existing methods that enhance refractive index difference by creating open, continuous pores (refractive index close to 1) between particles exceeding the CPVC (continuously pore-forming polyvinyl chloride) structure, this invention introduces a closed, independent bubble structure into the coating film using hollow microspheres to create a high refractive index contrast. Furthermore, unlike existing thermal insulation coatings that utilize the low thermal conductivity of hollow structures to reduce heat conduction, this invention relies on the high refractive index contrast of the sealed gas inside the hollow microspheres, the microsphere shell walls, and the surrounding medium to efficiently scatter the solar spectrum. The boundary particle size D90 of the hollow microspheres in this invention is ≤30μm. By reducing the particle size, the number of high refractive index contrast scattering units per unit volume of the coating film is increased, thereby optimizing the scattering of sunlight in the 0.3-2.5μm wavelength range. Simultaneously, the smaller size of the hollow microspheres results in greater compressive strength, ensuring they can withstand the requirements of coating preparation and application processes without breaking.

[0038] The hollow microspheres of this invention are preferably at least one of polymer hollow microspheres, glass hollow microspheres, and ceramic hollow microspheres. Regardless of whether the shell of the hollow microsphere is made of polymer, glass, or ceramic material, its refractive index is significantly greater than that of the internal enclosed space, which is close to 1, thus meeting the high refractive index contrast design requirement of this invention.

[0039] While using hollow microspheres to construct a low refractive index (n≈1) component, the radiation-cooling coating of this invention introduces high refractive index pigment particles (n≥1.95) into the coating to enhance the refractive index contrast. The total pigment volume concentration (PVC) of the hollow microspheres and high refractive index pigments in this invention is ≤ the critical pigment volume concentration (CPVC), which ensures the density and continuity of the coating without negatively impacting its performance.

[0040] The CPVC of a coating is mainly affected by factors such as the particle size and distribution of pigments and fillers, the dispersion process of pigments and fillers, and the particle size of latex in the film-forming material. The CPVC calculation formula of this invention is as follows:

[0041] CPVC=1 / (1+OA*ρ / 93.5)

[0042] Where OA is the oil absorption value of the pigment and filler, and ρ is the density of the pigment and filler.

[0043] Calculations show that, under the raw materials and preparation process specified in this invention, the CPVC value is within the range of 50-60%.

[0044] Preferably, the high refractive index pigment is one or more of rutile titanium dioxide, anatase titanium dioxide, zinc sulfide, antimony trioxide, tin dioxide, zirconium dioxide, and zirconium silicate. The rutile titanium dioxide selected in this invention has an extremely high refractive index (refractive index n = 2.73 for 560nm wavelength light), making it an ideal formulation component. However, a drawback of rutile titanium dioxide is its narrow band gap (E...).g Because of its inherent absorption in the ultraviolet and short-wave violet light bands of sunlight with wavelengths less than 408 nm (≈3.03 eV), it limits the total solar reflectance. Anatase titanium dioxide (n≈2.55, E...) g ≈3.20eV), zinc sulfide (n≈2.37, E g ≈3.54eV), antimony trioxide (n≈2.29, E g ≈3.60eV), tin dioxide (n≈2.0, E g (≈3.60eV), zirconium dioxide (n≈2.13, E) g (≈5.55eV), zirconium silicate (n≈1.95, E) g Although its refractive index is slightly lower than that of rutile titanium dioxide (n≈5.90eV), it has the advantage of a wider band gap. It absorbs little or no ultraviolet and violet light from sunlight, and its absorption rate is lower than that of rutile titanium dioxide. The combined advantages of its refractive index and band gap are the reasons why it is the preferred pigment in this invention. In contrast, other pigments (fillers) such as calcium carbonate (n≈1.49, E...)... g ≈7.21eV), barium sulfate (n≈1.64, E g (≈8.64eV), alumina (n≈1.7, E) g ≈7.72eV), zinc oxide (n≈2.02, E g (≈3.2eV) Due to insufficient refractive index and / or band gap, its scattering efficiency for sunlight is limited when used alone below CPVC, and it is not suitable for use in this invention.

[0045] Preferably, the median particle size of the high-refractive-index pigment is 0.2-1 μm. Preferably, the particle size distribution dispersion of the high-refractive-index pigment of the present invention is ≥1.0, i.e., a wide particle size distribution range. This can be achieved by using a single-size pigment with a wider boundary particle size range, or by mixing multiple pigments of different particle sizes. The aforementioned preferred particle size and wide particle size distribution range can generate strong Mie scattering in the 0.3-2.5 μm solar spectrum band, achieving efficient reflection of sunlight and avoiding heat absorption by the coating. Furthermore, increasing the particle size distribution range of the pigment also helps to improve the CPVC of the coating film, thereby helping to prevent the PVC of the formulation from exceeding the CPVC.

[0046] The formula for calculating the dispersion of the particle size distribution of the high refractive index pigment of the present invention is as follows:

[0047] Dispersion = (D90 - D10) / D50;

[0048] Wherein, D90 and D10 are the boundary particle sizes of the high refractive index pigment, and D50 is the median particle size of the high refractive index pigment.

[0049] To further improve the scattering of sunlight across the entire wavelength range while reducing costs, more preferably, the high refractive index contrast radiation-cooling coating of this invention employs a double-layer structure. The high refractive index pigment in the outer layer is zirconium dioxide and / or zirconium silicate, while the high refractive index pigment in the inner layer is rutile titanium dioxide. In application, the inner layer is first applied to the substrate surface, and after it dries, the outer layer is applied. This coating scheme utilizes the characteristic that shorter wavelengths of light penetrate shallower into the coating. By designing the outer layer as high refractive index wide-bandgap particles that completely do not absorb the ultraviolet band, combined with hollow microspheres that effectively scatter the ultraviolet and part of the visible and near-infrared bands of the solar spectrum, it is difficult for ultraviolet and short-wave violet light to penetrate the outer layer. The visible and near-infrared light reaching the inner layer is strongly scattered due to the high refractive index contrast between the ultra-high refractive index rutile titanium dioxide in the inner layer and the film-forming material and hollow microspheres (e.g., Figure 1 (As shown).

[0050] The film-forming substance in this invention can be a solvent-based film-forming substance or an aqueous film-forming substance. When a solvent-based substance is used, the solvent is a suitable organic solvent; when an aqueous substance is used, the solvent is water. Additives include one or more of the following: dispersants, wetting agents, defoamers, film-forming aids, curing accelerators, thickeners, leveling agents, bactericides, fungicides, pH adjusters, and antifreeze agents.

[0051] In the following embodiments and comparative examples of the present invention, the percentage content of each component in the coating formulation is a volume percentage.

[0052] All raw materials used in the following embodiments and comparative examples of the present invention are commercially available products.

[0053] Example 1

[0054] A method for preparing a radiation-cooling coating with high refractive index contrast:

[0055] Take 19.55% water, 0.5% sodium polyacrylate dispersant, 0.3% hydroxyethyl cellulose thickener, 0.3% polyether siloxane defoamer, 0.2% Kathon bactericide, 0.2% nonionic surfactant wetting agent, and 4% rutile titanium dioxide (D50 = 0.5 μm, particle size distribution dispersion = 0.7), and grind and disperse them in a high-speed disperser at a linear velocity of 18-25 m / s for 20 min; then... Paint preparation: Add 52% acrylic resin emulsion, 0.2% polyether siloxane defoamer, 0.7% alcohol ester dodecyl film-forming aid, 0.3% IPBC mildew inhibitor, 0.15% AMP-95 pH adjuster, 1.6% propylene glycol antifreeze, and 20% glass hollow microspheres (D90 = 20 μm) to the ground and dispersed pigment slurry. Stir at a linear speed of 2 m / s for 15 min to obtain the radiation cooling coating. The PVC content of this coating is 45.6%.

[0056] Example 2

[0057] A method for preparing a radiation-cooling coating with high refractive index contrast:

[0058] 11% FEVE fluorocarbon resin, 18% butyl acetate, 0.3% alkyl hydroxyl ammonium salt dispersant, 0.3% polyacrylate defoamer, and 4% zirconium silicate (D50 = 0.5 μm) were ground and dispersed using a high-speed disperser at a linear velocity of 18-25 m / s for 20 min. Then, 36.7% FEVE fluorocarbon resin, 9.1% butyl acetate, 0.2% polyacrylate defoamer, 0.2% acrylic leveling agent, 0.2% DBTDL curing accelerator, and 20% ceramic hollow microspheres (D90 = 24 μm) were added to the dispersed pigment slurry. The mixture was stirred at a linear velocity of 2 m / s for 15 min to obtain a radiation-cooling coating. The PVC content of this coating was 45.6%.

[0059] Example 3

[0060] A method for preparing a radiation-cooling coating with high refractive index contrast:

[0061] 19.55% water, 0.5% sodium polyacrylate dispersant, 0.3% hydroxyethyl cellulose thickener, 0.3% polyether siloxane defoamer, 0.2% Kathon bactericide, 0.2% nonionic surfactant wetting agent, and 4% zirconium dioxide (D50 = 0.53 μm) were mixed and dispersed using a high-speed disperser at a linear velocity of 18-25 m / s for 20 min. Then, 52% silicone-modified acrylic resin emulsion, 0.2% polyether siloxane defoamer, 0.7% alcohol ester dodecyl film-forming aid, 0.3% IPBC mildew inhibitor, 0.15% AMP-95 pH adjuster, 1.6% propylene glycol antifreeze, and 20% high-molecular hollow microspheres (D90 = 2 μm) were added to the dispersed pigment slurry and stirred at a linear velocity of 2 m / s for 15 min to obtain a radiation cooling coating. The PVC content of this coating is 45.6%.

[0062] Example 4

[0063] The only difference from Example 3 is that zirconium dioxide (D50 = 0.53 μm) was replaced with an equal volume of zirconium dioxide (D50 = 2 μm). The PVC of this coating is 45.6%.

[0064] Example 5

[0065] The only difference from Example 1 is that the 4% rutile titanium dioxide (D50 = 0.5 μm, particle size distribution dispersion = 0.7) in Example 1 is replaced with 2% rutile titanium dioxide (D50 = 0.5 μm) and 2% rutile titanium dioxide (D50 = 0.23 μm), resulting in a particle size distribution dispersion of 1.3. The PVC of this coating is 45.6%.

[0066] Comparative Example 1

[0067] The only difference from Example 1 is that the hollow glass microspheres (D90 = 20 μm) are replaced with hollow glass microspheres of the same volume (D90 = 65 μm). The PVC content of this coating is 45.6%.

[0068] Comparative Example 2

[0069] The only difference from Example 1 is that rutile titanium dioxide (D50 = 0.5 μm) is replaced with an equal volume of calcium carbonate (D50 = 0.5 μm). The PVC of this coating is 45.6%.

[0070] Comparative Example 3

[0071] A method for preparing a radiation-cooling coating:

[0072] 15.25% water, 2% sodium polyacrylate dispersant, 0.2% hydroxyethyl cellulose thickener, 0.3% polyether siloxane defoamer, 0.2% Kathon bactericide, 0.2% nonionic surfactant wetting agent, and 17% rutile titanium dioxide (D50 = 0.5 μm) were mixed and dispersed using a high-speed disperser at a linear velocity of 18-25 m / s for 20 min. Then, 42% acrylic resin emulsion, 0.2% polyether siloxane defoamer, 0.6% alcohol ester dodecyl film-forming aid, 0.3% IPBC mildew inhibitor, 0.15% AMP-95 pH adjuster, 1.6% propylene glycol antifreeze, and 20% glass hollow microspheres (D90 = 20 μm) were added to the dispersed pigment slurry and stirred at a linear velocity of 2 m / s for 15 min to obtain a radiation cooling coating. The PVC content of this coating is 61.6%.

[0073] Comparative Example 4

[0074] A method for preparing a radiation-cooling coating:

[0075] Take 17.05% water, 3% sodium polyacrylate dispersant, 0.3% hydroxyethyl cellulose thickener, 0.3% polyether siloxane defoamer, 0.2% Kathon bactericide, 0.2% nonionic surfactant wetting agent, and 24% alumina (D50 = 0.3 μm), and disperse them in a high-speed disperser at a linear velocity of 18-25 m / s for 20 min. Add 52% acrylic resin emulsion, 0.2% polyether siloxane defoamer, 0.7% alcohol ester dodecyl film-forming aid, 0.3% IPBC mildew inhibitor, 0.15% AMP-95 pH adjuster, and 1.6% propylene glycol antifreeze to the dispersed pigment slurry, and stir at a linear velocity of 2 m / s for 15 min to obtain a radiation cooling coating. The PVC content of this coating is 45.6%.

[0076] Comparative Example 5

[0077] The only difference from Comparative Example 4 is that aluminum oxide (D50 = 0.3 μm) was replaced with an equal volume of zinc oxide (D50 = 0.3 μm). The PVC of this coating is 45.6%.

[0078] Comparative Example 6

[0079] The only difference from Comparative Example 4 is that alumina (D50 = 0.3 μm) was replaced with an equal volume of zirconium dioxide (D50 = 0.53 μm). The PVC of this coating is 45.6%.

[0080] Comparative Example 7

[0081] The only difference from Comparative Example 4 is that the alumina (D50 = 0.3 μm) was replaced with 12% rutile titanium dioxide (D50 = 0.5 μm) and 12% rutile titanium dioxide (D50 = 0.23 μm). The PVC of this coating is 45.6%.

[0082] Effect verification

[0083] (1) To verify the technical effect of the present invention, the coatings prepared in each embodiment and comparative example of the present invention were applied to a standard cement board with dimensions of 15cm×7cm. The specific construction method was as follows: the construction process adopted two coats. The second coat was applied after the first coat was completely dry. The final coating thickness on the cement board was about 300μm (the thickness ratio of the first coating layer to the second coating layer was 2:1). Among them, the coating of Example 2 was first mixed with the isocyanate curing agent at a molar ratio of OH / NCO = 1 / 1.05 before construction.

[0084] Furthermore, by preparing the first coating with the coating of Example 5 and the second coating with the coating of Example 3, effect example 1 was obtained; by preparing the first coating with the coating of Comparative Example 5 and the second coating with the coating of Comparative Example 4, effect example 2 was obtained; by preparing the first coating with the coating of Comparative Example 7 and the second coating with the coating of Comparative Example 6, effect example 3 was obtained; and by simply replacing the zirconium dioxide (D50 = 0.53 μm) in the coating scheme of effect example 1 with an equal volume of aluminum oxide (D50 = 0.53 μm), effect example 4 was obtained.

[0085] The radiative cooling performance of the coated samples was compared with that of the uncoated standard cement board (blank group) under the same open-air sunlight conditions. The test results are shown in Table 1.

[0086] Table 1

[0087]

[0088] As shown in Table 1, the high refractive index contrast radiation-cooling coating provided by this invention exhibits excellent radiation-cooling performance and good durability. Examples 3, 5, and Effect Example 1 demonstrate that the double-layer structure design can further enhance the scattering of sunlight by the coating film and optimize its radiation-cooling performance. Comparing Comparative Examples 1 and 2 with Example 1, it can be seen that the boundary particle size D90 ≤ 30 μm of the hollow microspheres and the refractive index of the white pigment not less than 1.95 have a significant impact on the cooling performance of the coating. Comparative Example 3 has a higher PVC than CPVC, and although it also has outstanding radiation-cooling performance, it significantly sacrifices the mechanical properties and protective function of the coating. Although Effect Examples 2-4 also employ a double-layer structure design where the outer coating mainly scatters the ultraviolet band and the inner coating mainly scatters the visible and near-infrared portions, the insufficient refractive index of the pigment used (Effect Examples 2 and 4) or the absence of low-refractive-index hollow microsphere components (Effect Examples 2 and 3) results in insufficient refractive index difference between the dispersed and continuous phases of the coating system, leading to less than ideal cooling performance.

[0089] Figure 1 The diagram illustrates the coating structure of Example 1 and the principle of scattering sunlight at different wavelengths.

[0090] (2) Under the same open-air sunlight conditions, the cement slab temperature of Example 1 and the control group during August 23-August 31 was measured. The results are as follows: Figure 2 As shown.

[0091] Figure 2 The results of the cement board temperature test are shown in Example 1 and the blank group.

[0092] Figure 2 In the diagram, the coated cement board represents the temperature of the cement board in Example 1, while the uncoated cement board represents the temperature of the blank group.

[0093] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a radiation-cooled coating, characterized in that, It is prepared using radiation-cooling coatings with high refractive index contrast as raw materials; The coating process of the radiation cooling coating film is a two-coat process. First, the inner coating film is coated on the substrate surface using the radiation cooling coating material with rutile titanium dioxide as a high refractive index pigment. Then, the outer coating film is coated on the surface of the inner coating film using the radiation cooling coating material with zirconium dioxide and / or zirconium silicate as a high refractive index pigment. The thickness of the radiation cooling coating is 300 μm, and the thickness ratio of the inner coating to the outer coating is 2:

1. The raw materials of the high refractive index contrast radiation-cooling coating, by volume, include: Hollow microspheres 5-30 parts, high refractive index pigment 2-15 parts, film-forming substance 40-60 parts, solvent 10-40 parts and additives 0.1-10 parts; The high refractive index pigment has a refractive index ≥ 1.95; The boundary particle size D90 of the hollow microspheres is ≤30μm; The median particle size of the high refractive index pigment is 0.2-1 μm; the particle size distribution dispersion of the high refractive index pigment is ≥1.0; The formula for calculating the dispersion is: Dispersion = (D90 - D10) / D50; Wherein, D90 and D10 are the boundary particle sizes of the high refractive index pigment, and D50 is the median particle size of the high refractive index pigment. The preparation method of the high refractive index contrast radiation-cooling coating includes the following steps: The raw materials are mixed to obtain the radiation-cooling coating with high refractive index contrast; The hollow microspheres are one or more of polymer hollow microspheres, glass hollow microspheres, and ceramic hollow microspheres; The film-forming substance is acrylic resin, silicone-modified acrylic resin, fluorocarbon resin, polyurethane resin, or epoxy resin; the additives include one or more of the following: dispersant, wetting agent, defoamer, film-forming aid, curing accelerator, thickener, leveling agent, bactericide, mildew inhibitor, pH adjuster, and antifreeze.

2. A radiation-cooling coating obtained by the preparation method according to claim 1.

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