Radiation refrigeration coating with high refractive index contrast

Abstract

The invention discloses a radiation refrigeration coating with high refractive index contrast, and belongs to the technical field of radiation refrigeration coatings. The radiation refrigeration coating with high refractive index contrast comprises the following raw materials: hollow microspheres, a high refractive index pigment, a film-forming substance, a solvent and an auxiliary agent. The coating process of the radiation refrigeration coating film comprises two coating steps: firstly, coating an inner layer coating film on the surface of a base material by using the radiation refrigeration coating with rutile type titanium dioxide as a high-refractive-index pigment as a raw material; and coating the surface of the inner-layer coating film with an outer-layer coating film by using the radiation refrigeration coating with high-refractive-index pigment being zirconium dioxide and / or zirconium silicate as a raw material. According to the invention, a closed and independent bubble structure is introduced into the coating by adopting the hollow microspheres, and the preferable high-refractive-index pigment is matched, so that the refractive index difference value between adjacent components in a coating film is increased, and the sunlight reflectivity of the coating film is remarkably enhanced, thereby realizing excellent radiation refrigeration performance under strong sunlight irradiation.

Description

Technical Field

[0001] The invention relates to the technical field of radiation cooling coatings, in particular to a radiation cooling coating with high refractive index contrast. Background Art

[0002] Radiative cooling technology refers to the use of spontaneous infrared thermal radiation from the surface of an object to penetrate the 8-13μm band "atmospheric window" of the earth's atmosphere and discharge excess heat into outer space. 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 the coating is generally made of polymer resin, which has a high infrared emissivity in the LWIR band of thermal radiation due to its intrinsic characteristics. On the other hand, the irradiance of the AM 1.5 standard solar spectrum on the ground is about 1000W / m 2 , while the theoretical maximum radiation output of radiative cooling technology is about 150W / m 2 There is a gap of nearly one order of magnitude between the two. In a sunny environment, the heat absorption of sunlight by the coating can easily offset the energy of outward thermal radiation cooling. Therefore, the key to designing high-performance radiant cooling coatings is to maximize the solar reflectance of the coating in the sunlight band (0.3-2.5μm). One of the disclosed technical routes for radiant cooling coatings is to increase the amount of pigments and fillers, which is essentially to make the pigment volume concentration (PVC) of the dry coating exceed the critical pigment volume concentration (CPVC). This will cause the film-forming substance to be insufficient to completely cover the pigment particles and form pores in the coating, thereby utilizing the refractive index difference between the air in the pores (refractive index n≈1) and the polymer film-forming substance (n≈1.5) to scatter sunlight and increase the solar reflectance. However, this structure also leads to the following adverse effects: the open, interconnected pore network allows liquids and gases to be transmitted in the resin base, the toughness and adhesion of the coating are weakened, it is more likely to peel, crack or delaminate, and the mechanical properties are deteriorated; because the pores in the coating make it easier for foreign substances (such as moisture, rain, chemicals) to erode and penetrate, the protective performance of the coating is weakened, the life span is shortened, and the durability is reduced. Therefore, further improvement is still needed. Summary of the invention

[0004] The object of the present invention is to provide a radiant cooling coating with high refractive index contrast to solve the above-mentioned problems in the background technology.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] One of the technical solutions of the present invention is to provide a radiant cooling coating with a high refractive index contrast, wherein the raw materials, measured by volume, include:

[0007] 5-30 parts of hollow microspheres, 2-15 parts of high refractive index pigments, 40-60 parts of film-forming substances, 10-40 parts of solvents and 0.1-10 parts of additives;

[0008] The refractive index of the high refractive index pigment is ≥1.95;

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

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

[0011] The calculation formula of the discreteness is:

[0012] Discreteness = (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, mildewicides, pH adjusters and antifreeze agents.

[0017] The second technical solution of the present invention is to provide a method for preparing the above-mentioned radiation cooling coating with high refractive index contrast, 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 is to provide an application of the above-mentioned radiation cooling coating with high refractive index contrast in the preparation of radiation cooling coating film.

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

[0021] The coating process of the radiation cooling coating is a two-layer coating process, firstly, an inner layer coating is coated on the surface of the substrate using the radiation cooling coating whose high refractive index pigment is rutile titanium dioxide as a raw material, and then an outer layer coating is coated on the surface of the inner layer coating using the radiation cooling coating whose high refractive index pigment is zirconium dioxide and / or zirconium silicate as a raw material.

[0022] Preferably, the pigment volume concentration (PVC) of the hollow microspheres and the high refractive index pigment in the dry coating film formed by the radiation cooling coating is ≤ the 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] The fifth technical solution of the present invention: provides a radiation cooling coating obtained according to the above preparation method.

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

[0026] The present invention improves the refractive index difference between the hollow microspheres, white pigment and film-forming material components in the coating film, optimizes the solar reflectance without losing other properties of the coating, thereby achieving excellent radiation cooling performance under strong sunlight.

[0027] The high refractive index contrast radiation cooling coating of the present invention can provide high scattering performance of ultraviolet, visible and near-infrared full-band sunlight, and can be applied to roofs, exterior walls and outdoor facilities of various buildings to effectively reduce solar heat absorption and passively cool down in outdoor environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0029] Figure 1 This is a schematic diagram of the coating structure of Effect Example 1 and the scattering principle of different wavelengths of sunlight.

[0030] Figure 2 The temperature test results of cement board of effect example 1 and blank group are shown. DETAILED DESCRIPTION

[0031] Now, various exemplary embodiments of the present invention are described in detail, and this detailed description should not be considered as a limitation of the present invention, but should be understood as a more detailed description of certain aspects, characteristics and embodiments of the present invention. It should be understood that the terms described in the present invention are only for describing specific embodiments and are not used to limit the present invention.

[0032] In addition, for the numerical range in the present invention, it is understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value in any stated value or stated range, and each smaller range between any other stated value or intermediate value in the range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0033] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the invention pertains. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention.

[0034] The words “include,” “including,” “have,” “contain,” etc. used in the present invention are open-ended terms, meaning including but not limited to.

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

[0036] In a coating system, to achieve a high solar reflectance, the key is that the particles dispersed in the film-forming material can effectively scatter incident light within the wavelength range of sunlight. The greater the difference between the refractive index of the particles and the surrounding film-forming material and other components, the stronger the scattering effect. The film-forming material of the coating of the present 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] Different from the existing scheme of increasing the refractive index difference by forming open continuous pores (refractive index close to 1) between particles exceeding CPVC, the present invention introduces a closed, independent bubble structure in the coating film through hollow microspheres with a hollow structure to create a high refractive index contrast. In addition, unlike the principle of existing thermal insulation coatings that use the low thermal conductivity of the hollow structure to reduce heat conduction, the present invention relies on the high refractive index contrast of the sealed gas inside the hollow microspheres, the microsphere shell wall and the medium surrounding the microspheres to efficiently scatter the solar light spectrum. The boundary particle size D90 of the hollow microspheres of the present invention is ≤30μm, and the number of high refractive index contrast scattering units per unit volume of the coating film is increased by reducing the particle size, thereby optimizing the scattering of the 0.3-2.5μm sunlight band. At the same time, smaller-sized hollow microspheres have greater compressive strength, which can ensure that they can withstand the corresponding coating preparation and construction process requirements without breaking.

[0038] The hollow microspheres of the present invention are preferably at least one of polymer hollow microspheres, glass hollow microspheres, and ceramic hollow microspheres. Regardless of whether the shell wall of the hollow microspheres is a polymer, glass, or ceramic material, its refractive index is significantly greater than the refractive index of the internal enclosed space close to 1, and can meet the design requirements of the present invention for high refractive index contrast.

[0039] While hollow microspheres are used to construct low refractive index (n≈1) components, the radiative cooling coating of the present 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 of the present invention is ≤ the critical pigment volume concentration (CPVC), which can ensure the compactness and continuity of the coating and has no negative impact on the performance of the coating.

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

[0041] CPVC=1 / (1+OA*ρ / 93.5)

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

[0043] According to calculation, under the conditions of the raw materials and preparation process defined in the present invention, the CPVC values ​​are all 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 the present invention has a very high refractive index (refractive index n = 2.73 for 560nm wavelength light) and is an ideal formula component, but the disadvantage of rutile titanium dioxide is that the band gap is narrow (Eg ≈3.03eV), so there is inherent absorption of the ultraviolet and short-wave violet bands of sunlight with a wavelength less than 408nm, which will limit the total sunlight 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 ≈5.90eV) has a slightly lower refractive index than rutile titanium dioxide, but has the advantage of a wider band gap and does not absorb sunlight ultraviolet and violet light at all or has a lower absorption rate than rutile titanium dioxide. The combined advantages of refractive index and band gap are the reasons why it is the preferred pigment of the present 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), aluminum oxide (n≈1.7, E g ≈7.72eV), zinc oxide (n≈2.02, E g ≈3.2eV) has limited sunlight scattering efficiency when used alone below CPVC due to insufficient refractive index and / or band gap, and is therefore not suitable for use in the present invention.

[0045] Preferably, the median particle size of the high refractive index pigment is 0.2-1 μm. Preferably, the discreteness of the particle size distribution of the high refractive index pigment of the present invention is ≥1.0, that is, the particle size distribution range is wide, which can be achieved by using a single specification pigment with a wider boundary particle size range, or by mixing and using multiple pigments of different particle size specifications. The above-mentioned preferred particle size and wide particle size distribution range can form strong Mie scattering in the 0.3-2.5 μm solar spectrum band, achieve efficient reflection of sunlight, and avoid the coating absorbing light and heat to cause temperature rise. In addition, increasing the particle size distribution range of the pigment also helps to improve the CPVC of the coating, thereby helping to prevent the PVC of the formula from exceeding the CPVC.

[0046] The calculation formula of the discreteness of the particle size distribution of the high refractive index pigment of the present invention is:

[0047] Discreteness = (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] In order to further improve the scattering of the coating film to the full-band sunlight and reduce the cost at the same time, it is more preferred that the coating film of the radiation cooling coating with high refractive index contrast of the present invention adopts an inner and outer double-layer structure, the high refractive index pigment in the outer coating film is zirconium dioxide and / or zirconium silicate, and the high refractive index pigment in the inner coating film is rutile titanium dioxide. When in use, the inner coating film is first applied to the surface of the substrate, and then the outer coating film is applied to its surface after the inner coating film is dried. This coating scheme utilizes the characteristic that the shorter the wavelength of the light wave, the shallower the penetration depth of the coating. By designing the outer coating film to be high-refractive index wide-bandgap particles that do not absorb the ultraviolet band at all, and cooperating with hollow microspheres to effectively scatter the ultraviolet and part of the visible and near-infrared bands of the solar spectrum, it is difficult for the ultraviolet and short-wave purple bands to penetrate the outer coating film; this part of the visible and near-infrared light that reaches the inner coating film is strongly scattered (such as ultraviolet light) due to the high refractive index contrast between the ultra-high refractive index rutile titanium dioxide in the inner coating film and the film-forming material and the hollow microspheres. Figure 1 shown).

[0050] The film-forming material in the present invention can be a solvent-based film-forming material or an aqueous film-forming material. When a solvent-based material is used, the solvent is a corresponding suitable organic solvent; when an aqueous material is used, the solvent is water. The auxiliary agent includes one or more of a dispersant, a wetting agent, a defoaming agent, a film-forming auxiliary agent, a curing accelerator, a thickener, a leveling agent, a bactericide, a mildew-proof agent, a pH adjuster, an antifreeze agent, and the like.

[0051] The content percentages of the various components in the coating formulations in the following embodiments and comparative examples of the present invention are all volume percentages.

[0052] All raw materials used in the following examples 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] 19.55% of water, 0.5% of sodium polyacrylate dispersant, 0.3% of hydroxyethyl cellulose thickener, 0.3% of polyether siloxane defoamer, 0.2% of kason bactericide, 0.2% of nonionic surfactant wetting agent and 4% of rutile titanium dioxide (D50 = 0.5 μm, particle size distribution dispersion = 0.7) were taken and ground and dispersed at a linear speed of 18-25 m / s for 20 min using a high-speed disperser; then Paint mixing: add 52% acrylic resin emulsion, 0.2% polyether siloxane defoamer, 0.7% alcohol ester film-forming aid, 0.3% IPBC mildew inhibitor, 0.15% AMP-95 pH regulator, 1.6% propylene glycol antifreeze agent and 20% glass hollow microspheres (D90 = 20 μm) to the pigment slurry after grinding and dispersion, and stir at a linear speed of 2 m / s for 15 minutes to obtain a radiation cooling paint. The PVC of this paint 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% alkylhydroxyl ammonium salt dispersant, 0.3% polyacrylate defoamer and 4% zirconium silicate (D50 = 0.5 μm) were taken and ground and dispersed for 20 minutes at a linear speed of 18-25 m / s using a high-speed disperser; 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 ground and dispersed pigment slurry, and stirred at a linear speed of 2 m / s for 15 minutes to obtain a radiant cooling coating. The PVC of this coating is 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% polyacrylic acid sodium salt dispersant, 0.3% hydroxyethyl cellulose thickener, 0.3% polyether siloxane defoamer, 0.2% kason bactericide, 0.2% nonionic surfactant wetting agent and 4% zirconium dioxide (D50=0.53μm) are taken, and the mixture is ground and dispersed at a linear speed of 18-25m / s for 20min by a high-speed disperser; 52% organosilicon modified acrylic resin emulsion, 0.2% polyether siloxane defoamer, 0.7% alcohol ester twelve film-forming aid, 0.3% IPBC mildewproofing agent, 0.15% AMP-95 pH regulator, 1.6% propylene glycol antifreeze agent and 20% high molecular hollow microspheres (D90=2μm) are added to the ground and dispersed pigment slurry, and stirred at a linear speed of 2m / s for 15min to obtain a radiant cooling coating. The PVC of the coating is 45.6%.

[0062] Example 4

[0063] The only difference from Example 3 is that zirconium dioxide (D50=0.53 μm) is replaced by 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 by 2% rutile titanium dioxide (D50 = 0.5 μm) and 2% rutile titanium dioxide (D50 = 0.23 μm), and the particle size distribution dispersion after replacement = 1.3. The PVC of this coating is 45.6%.

[0066] Comparative Example 1

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

[0068] Comparative Example 2

[0069] The only difference from Example 1 is that the rutile titanium dioxide (D50=0.5 μm) is replaced by 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 radiant cooling coating:

[0072] 15.25% water, 2% polyacrylic acid sodium salt dispersant, 0.2% hydroxyethyl cellulose thickener, 0.3% polyether siloxane defoamer, 0.2% kason bactericide, 0.2% nonionic surfactant wetting agent and 17% rutile titanium dioxide (D50=0.5μm) are taken, and ground and dispersed for 20 minutes at a linear speed of 18-25m / s by a high-speed disperser; 42% acrylic resin emulsion, 0.2% polyether siloxane defoamer, 0.6% alcohol ester twelve film-forming aid, 0.3% IPBC mildewproofing agent, 0.15% AMP-95 pH regulator, 1.6% propylene glycol antifreeze agent and 20% glass hollow microspheres (D90=20μm) are added to the pigment slurry after grinding and dispersion, and stirred at a linear speed of 2m / s for 15 minutes to obtain a radiation cooling coating. The PVC of this coating is 61.6%.

[0073] Comparative Example 4

[0074] A method for preparing a radiant cooling coating:

[0075] 17.05% water, 3% polyacrylic acid sodium salt dispersant, 0.3% hydroxyethyl cellulose thickener, 0.3% polyether siloxane defoamer, 0.2% kason bactericide, 0.2% nonionic surfactant wetting agent and 24% aluminum oxide (D50=0.3μm) are taken, and grind and dispersed for 20 minutes at a linear speed of 18-25m / s using a high-speed disperser; 52% acrylic resin emulsion, 0.2% polyether siloxane defoamer, 0.7% alcohol ester twelve film-forming aid, 0.3% IPBC mildewproofing agent, 0.15% AMP-95 pH regulator, 1.6% propylene glycol antifreeze agent are added to the grinded and dispersed pigment slurry, and stirred at a linear speed of 2m / s for 15 minutes to obtain a radiation cooling coating. The PVC of this coating is 45.6%.

[0076] Comparative Example 5

[0077] The only difference from Comparative Example 4 is that the aluminum oxide (D50=0.3 μm) is replaced by 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 the aluminum oxide (D50=0.3 μm) is replaced by 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 aluminum oxide (D50=0.3 μm) is replaced by 12% of rutile titanium dioxide (D50=0.5 μm) and 12% of 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 the embodiments and comparative examples of the present invention were applied on a standard cement board with a size of 15 cm×7 cm. The specific construction method is as follows: the construction process adopts two coats of coating, and the second coat of coating is applied after the first coat is completely dry. The final coating film thickness on the cement board is about 300 μm (the thickness ratio of the first coat to the second coat is 2:1); wherein, the coating of Example 2 is first mixed evenly with the isocyanate curing agent according to the molar ratio of OH / NCO=1 / 1.05 before the coating is applied.

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

[0085] Under the same open-air sunlight conditions, the radiant cooling performance of the above-mentioned coating sample was compared with the standard cement board without coating (blank group) in a horizontal comparison test. The test results are shown in Table 1.

[0086] Table 1

[0087]

[0088] As can be seen from Table 1, the radiation cooling coating with high refractive index contrast provided by the present invention has excellent radiation cooling performance and good durability. Example 3, Example 5, and Effect Example 1 show that the double-layer structure design can further enhance the scattering of sunlight by the coating and optimize its radiation cooling performance. Comparing Comparative Example 1 and Comparative Example 2 with Example 1, it can be seen that the importance of the hollow microsphere boundary particle size D90≤30μm and the refractive index of the white pigment not less than 1.95 on the cooling performance of the coating. The PVC of Comparative Example 3 is higher than CPVC. Although it also has outstanding radiation cooling performance, it significantly sacrifices the mechanical properties and protective functions of the coating. Although Effect Examples 2-4 also adopt a double-layer structure design in which the outer coating mainly scatters the ultraviolet band and the inner coating mainly scatters the visible and near-infrared parts, the refractive index of the pigment used is not high enough (Effect Examples 2 and 4), or the hollow microsphere component with a low refractive index is not introduced (Effect Examples 2 and 3), resulting in the difference in the refractive index between the dispersed phase and the continuous phase of the coating system is not large enough, and the cooling performance is not ideal.

[0089] Figure 1 This is a schematic diagram of the coating structure of Effect Example 1 and the scattering principle of different wavelengths of sunlight.

[0090] (2) Under the same outdoor sunshine conditions, the cement board temperature of Example 1 and the blank group from August 23 to August 31 was statistically analyzed. The test results are as follows Figure 2 shown.

[0091] Figure 2 The temperature test results of cement board of effect example 1 and blank group are shown.

[0092] Figure 2 In the figure, the coated cement board temperature represents the effect example 1, and the uncoated cement board temperature represents the blank group.

[0093] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A radiative cooling coating with high refractive index contrast, characterized in that: The raw materials are calculated by volume and include: 5-30 parts of hollow microspheres, 2-15 parts of high refractive index pigments, 40-60 parts of film-forming substances, 10-40 parts of solvents and 0.1-10 parts of additives; The refractive index of the high refractive index pigment is ≥1.95; The boundary particle size D90 of the hollow microspheres is ≤30 μm.

2. The high refractive index contrast radiant cooling coating according to claim 1, characterized in that: The median particle size of the high refractive index pigment is 0.2-1 μm; the dispersion of the particle size distribution of the high refractive index pigment is ≥1.0; The calculation formula of the discreteness is: Discreteness = (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.

3. The high refractive index contrast radiant cooling coating according to claim 1, characterized in that: The hollow microspheres are one or more of polymer hollow microspheres, glass hollow microspheres and ceramic hollow microspheres.

4. The high refractive index contrast radiant cooling coating according to claim 1, characterized in that: 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.

5. The high refractive index contrast radiant cooling coating according to claim 1, characterized in that: The film-forming substance is acrylic resin, silicone-modified acrylic resin, fluorocarbon resin, polyurethane resin or epoxy resin; the auxiliary agent includes one or more of a dispersant, a wetting agent, a defoaming agent, a film-forming auxiliary agent, a curing accelerator, a thickener, a leveling agent, a bactericide, a mildewproof agent, a pH adjuster and an antifreeze agent.

6. A method for preparing the radiation cooling coating with high refractive index contrast according to any one of claims 1 to 5, characterized in that: The following steps are involved: The raw materials are mixed to obtain the radiation cooling coating with high refractive index contrast.

7. Use of the radiation cooling coating with high refractive index contrast according to any one of claims 1 to 5 in preparing a radiation cooling coating film.

8. A method for preparing a radiation cooling coating, characterized in that: The method is prepared by using the radiation cooling coating with high refractive index contrast as described in any one of claims 1 to 5 as a raw material; The coating process of the radiation cooling coating is a two-layer coating process, firstly, an inner layer coating is coated on the surface of the substrate using the radiation cooling coating whose high refractive index pigment is rutile titanium dioxide as a raw material, and then an outer layer coating is coated on the surface of the inner layer coating using the radiation cooling coating whose high refractive index pigment is zirconium dioxide and / or zirconium silicate as a raw material.

9. The preparation method according to claim 8, characterized in that: 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.

10. A radiation cooling coating film obtained according to the preparation method of claim 8 or 9.

Images