A room temperature cured inorganic based radiative cooling coating and methods of making and using the same

Abstract

The application discloses a room-temperature-cured inorganic-based radiation refrigeration coating and a preparation method and application thereof, relates to the technical fields of passive daytime radiation refrigeration materials, building energy-saving coatings and inorganic functional coatings, and discloses the room-temperature-cured inorganic-based radiation refrigeration coating. The inorganic-based radiation refrigeration coating enhances sunlight reflection through white inorganic light scattering particles, enhances infrared emission of an atmospheric window through a silicon dioxide network formed by nano-silica sol curing, and achieves good radiation refrigeration performance, wherein the solar reflectivity can reach 94.38%, and the infrared emissivity of the 8-13 mu m atmospheric window can reach 92.76%. The inorganic-based radiation refrigeration coating can achieve a 13.21 DEG C cooling effect in an outdoor test box and can achieve sub-environmental cooling of about 1.52 DEG C lower than the ambient temperature in a self-made building model. The inorganic-based radiation refrigeration coating has fire safety, stable adhesion and high surface hardness, and can maintain stable optical performance after cyclic abrasion, ultraviolet irradiation and outdoor placement.

Description

Technical Field

[0001] This invention relates to the fields of passive daytime radiation cooling materials, building energy-saving coatings, and inorganic functional coatings. In particular, it relates to a room-temperature curing inorganic-based radiation cooling coating, its preparation method, and its application. Background Technology

[0002] With rising global temperatures and an increasing number of extreme heat events, building cooling energy consumption continues to rise, making the development of low-energy, environmentally friendly building thermal management materials of great significance. Passive daytime radiation cooling is a thermal management technology that requires no external energy input. Its basic principle is to reflect solar radiation as much as possible within the 0.3-2.5 μm solar spectrum, reducing the absorption of solar energy by the material surface; simultaneously, it radiates heat into the external environment within an 8-13 μm atmospheric transparency window, thereby achieving surface cooling or reducing the thermal load of the building envelope. Therefore, high-performance passive daytime radiation cooling coatings not only need to have high solar reflectivity and high mid-infrared emissivity, but also need to meet practical application requirements such as room temperature application, long-term weather resistance, fire safety, mechanical stability, and environmental friendliness.

[0003] In recent years, researchers have developed various radiation cooling material systems, including inorganic / organic composite coatings, polymer-based coatings, porous polymer films, aerogels, fiber membranes, ceramic materials, and inorganic binder coatings. Among these, polymer-based coatings typically exhibit good film-forming properties and ease of application, enabling coatings to be formed on large-area substrate surfaces through spraying, scraping, or roller coating. However, polymer-based coatings are prone to aging, yellowing, chalking, or mechanical property degradation under long-term ultraviolet radiation, thermo-oxidative aging, and outdoor humid and hot environments, leading to decreased solar reflectivity and shortened coating service life. Furthermore, some polymer-based radiation cooling coatings rely on volatile organic solvents in their preparation, posing limitations in terms of environmental safety, construction safety, and large-area application; the organic components themselves may also present problems such as flammability and insufficient heat resistance, making it difficult to meet the safety requirements for long-term service on building exterior surfaces.

[0004] To improve the weather resistance and safety of radiation-cooled coatings, all-inorganic or inorganic-based radiation-cooled materials have attracted attention. Ceramic coatings and porous inorganic materials typically possess good heat resistance, fire resistance, and UV resistance; however, these materials often require high-temperature sintering, complex molding, or post-processing, making room-temperature in-situ application to existing building roofs, exterior walls, cement-based substrates, and ceramic-based substrates unsuitable. While some inorganic water-based adhesive systems can cure at lower temperatures, they also suffer from potential structural damage and decreased adhesion under long-term UV exposure and thermo-oxidative aging environments, affecting the long-term stability of the coating. Therefore, existing inorganic radiation-cooled systems still struggle to simultaneously achieve room-temperature application, high optical performance, structural integrity, fire resistance, and outdoor service stability.

[0005] Nano-silica sol is an aqueous inorganic colloid whose surface silanol groups can form a Si-O-Si inorganic network through dehydration condensation during drying, exhibiting potential applications such as environmental friendliness, non-flammability, and room temperature curing. However, when using nano-silica sol alone to prepare thicker coatings, shrinkage stress and capillary stress are easily generated during the drying and gelation process, leading to coating cracking, delamination, or insufficient integrity. Furthermore, pure silica sol coatings have limited solar light scattering capabilities, making it difficult to meet the high solar reflectivity requirements of daytime radiation cooling coatings on their own.

[0006] For inorganic-based radiation-cooling coatings, high solar reflectivity typically requires the introduction of white inorganic light-scattering particles with low solar absorption and strong scattering capabilities. However, if the content of inorganic light-scattering particles is too low, the coating will not adequately scatter sunlight multiple times; if the content is too high, it may weaken the bridging and fixing effect of the nano-silica sol on the particles, thus affecting the structural integrity, surface hardness, and adhesion stability of the coating. Therefore, how to rationally control the ratio between nano-silica sol and white inorganic light-scattering particles under room temperature curing conditions, so that the coating maintains high solar reflectivity and infrared emissivity through an 8–13 μm atmospheric window while also possessing good structural integrity, mechanical stability, and fire resistance, is a problem that needs to be solved in the practical application of inorganic-based radiation-cooling coatings.

[0007] Therefore, there is still a need to develop an inorganic-based radiation cooling coating system that is based on nano-silica sol and white inorganic light scattering particles, can be applied at room temperature, and takes into account high solar reflectivity, high infrared emissivity, structural integrity, fire resistance, mechanical stability, and applicability to building substrates. Summary of the Invention

[0008] To address the shortcomings of existing technologies, the present invention aims to provide a room-temperature curing inorganic-based radiation-cooling coating. This inorganic-based radiation-cooling coating uses a silica network formed by the curing of nano-silica sol as the inorganic binder phase and white inorganic light-scattering particles as the solar light scattering component. It can be prepared on the surface of building substrates at room temperature through spraying, scraping, brushing, or roller coating, exhibiting high solar reflectivity, high infrared emissivity, and good structural stability. Furthermore, the present invention can selectively incorporate layered silicate suspending agents, aqueous polycarboxylate dispersants, wetting agents, or organic resins to meet different practical application requirements, depending on the needs for construction stability, wettability and spreadability of the metal substrate, or anti-dusting properties.

[0009] Another objective of this invention is to provide a method for preparing an inorganic-based radiation-cooling coating that cures at room temperature.

[0010] Another object of the present invention is to provide an application of a room temperature curing inorganic-based radiation cooling coating in building envelope.

[0011] To achieve the above objectives, the present invention is accomplished through the following technical solutions.

[0012] An inorganic-based radiation-cooling coating that cures at room temperature is prepared from the following components in parts by weight: 5-40 parts of nano-silica sol; 40-90 parts of white inorganic light-scattering particles; 0-5 parts of layered silicate suspension; 0-5 parts of water-based polycarboxylate dispersant; 0-3 parts wetting agent; 0-5 parts of organic resin; 4-30 parts water; The white inorganic light-scattering particles are one or more of the following: white metal oxide particles, white silicate particles, and glassy inorganic particles.

[0013] In the above technical solution, the particle size of silica gel in nano silica sol is 5~30 nm and the solid content is 20~40 wt%.

[0014] In the above technical solution, the preferred particle size of the silica gel in the nano silica sol is 8~15 nm, and the solid content is 20-30 wt%.

[0015] In the above technical solution, the white metal oxide particles are one or more of aluminum oxide, zirconium oxide, yttrium oxide, magnesium oxide, titanium oxide, zinc oxide, and tin oxide; the white silicate particles include kaolin or zeolite; and the glassy inorganic particles include glass powder.

[0016] In the above technical solution, the glass powder can be obtained by cleaning, removing impurities, crushing, grinding and screening waste flat glass, architectural glass, container glass or other colorless old glass, and the whiteness of the glass powder is ≥95%.

[0017] In the above technical solution, the morphology of the white metal oxide particles is one or more of the following: spherical, near-spherical, irregular granular, flake-like, rod-like, porous, and hollow; preferably spherical, near-spherical, or irregular granular.

[0018] In the above technical solution, the median particle size of the white inorganic light scattering particles is 0.7~9 μm; preferably 0.7~5 μm.

[0019] In the above technical solution, the aqueous polycarboxylate dispersant includes ammonium polyacrylate; the layered silicate suspending agent includes lithium magnesium silicate; the wetting agent is one or more of the following: fluorinated non-silicone polymer wetting agent, polyether-modified siloxane wetting agent, acetylsadiol wetting agent, and phosphate ester wetting agent; the fluorinated non-silicone polymer wetting agent includes KYC-643.

[0020] In the above technical solution, the organic resin is one or more of acrylic resin, pure acrylic resin, and silicone acrylic resin.

[0021] In the above technical solution, the thickness of the inorganic-based radiation cooling coating is 300~450 μm.

[0022] In the above technical solution, the room temperature curing inorganic-based radiation cooling coating is preferably prepared from the following components in parts by weight: 10-30 parts of nano-silica sol; 40-70 parts of white inorganic light-scattering particles; 0-2 parts of layered silicate suspension; 0-2 parts of water-based polycarboxylate dispersant; 0-2 parts of wetting agent; 0-2 parts of organic resin; Water 4-20 parts.

[0023] A method for preparing an inorganic-based radiation-cooling coating includes the following steps: Step 1: Mix all components of the above inorganic-based radiation cooling coating evenly and mechanically stir for 1-2 hours to uniformly disperse the white inorganic light scattering particles and obtain an aqueous suspension. Step 2: Coat the obtained aqueous suspension onto one side of the substrate surface, and allow it to dry and cure naturally at room temperature to obtain an inorganic radiation cooling coating on one side of the substrate surface.

[0024] In step 1, when the inorganic-based radiation cooling coating includes layered silicate suspending agents in all its components, the layered silicate suspending agents are first stirred with deionized water for 4-6 hours, then allowed to stand for 10-12 hours, and then mechanically stirred with the remaining components for 1-2 hours.

[0025] In step 1, when all components of the inorganic-based radiation cooling coating include organic resin or wetting agent, the organic resin or wetting agent is added to the system after the remaining components have been mechanically stirred for 1-2 hours to ensure full and uniform dispersion.

[0026] In step 1, the mechanical stirring speed is 350~450 rpm.

[0027] In step 2, the coating includes spraying, scraping, brushing, or roller coating; In step 2, the substrate is a porous inorganic building material or a metal substrate.

[0028] In the above technical solution, the porous inorganic building substrate includes cement fiberboard, cement substrate, concrete, mortar layer, ceramic plate, calcium silicate board, stone, brick, tile or gypsum board.

[0029] In the above technical solution, the metal substrate includes aluminum plate, stainless steel plate, galvanized steel plate, color steel plate, copper plate, titanium plate or alloy plate.

[0030] Application of a room temperature curing inorganic-based radiation cooling coating in building envelope.

[0031] In the above technical solution, the substrate used for the building envelope is a porous inorganic building material or a metal substrate.

[0032] In the above technical solution, the porous inorganic building substrate includes cement fiberboard, cement substrate, concrete, mortar layer, ceramic plate, calcium silicate board, stone, brick, tile or gypsum board.

[0033] In the above technical solution, the metal substrate includes aluminum plate, stainless steel plate, galvanized steel plate, color steel plate, copper plate, titanium plate or alloy plate.

[0034] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The inorganic-based radiation cooling coating of the present invention enhances the reflection of sunlight through white inorganic light scattering particles and enhances the infrared emission of the atmospheric window through the silicon dioxide network formed by the curing of nano-silica sol, thereby achieving good radiation cooling performance. The solar reflectivity can reach 94.38% and the infrared emissivity of the 8-13 μm atmospheric window can reach 92.76%. It can achieve a cooling effect of 13.21 ℃ in the outdoor test chamber and a sub-environmental cooling effect of about 1.52 ℃ below the ambient temperature in the self-made building model.

[0035] (2) The inorganic-based radiation cooling coating of the present invention reduces the problem of easy cracking of thick coatings of silica sol by limiting the median particle size of white inorganic light scattering particles and working synergistically with the nano-silica sol structure. It also forms a Si-O-Si inorganic network, inorganic interface connection and solid bridging structure between particles, which improves the integrity, hardness and adhesion stability of the inorganic-based radiation cooling coating. The surface hardness can reach 6H and it maintains relatively stable optical performance after cyclic wear, ultraviolet irradiation and outdoor placement. It has the potential for building energy conservation and outdoor passive thermal management applications.

[0036] (3) The inorganic-based radiation cooling coating of the present invention is based on nano-silica sol and white inorganic light scattering particles. The basic system does not rely on organic resin as the main binder, has good fire resistance and safety, and is not prone to combustion, dripping or obvious structural collapse under high temperature flame. At the same time, it does not require the use of highly volatile organic solvents. It is a water-based system with low pollution and good construction safety.

[0037] (4) The preparation method of the present invention can be used to prepare an inorganic radiation cooling coating at room temperature by spraying, scraping, brushing or rolling, without high temperature sintering, and is suitable for in-situ construction on the surface of building substrates such as cement fiberboard, cement, concrete and ceramic board.

[0038] (5) The inorganic-based radiation-cooling coating of the present invention uses nano-silica sol and white inorganic light-scattering particles as basic components. It can be prepared and used immediately without adding layered silicate suspending agents, aqueous polycarboxylate dispersants, wetting agents, and organic resins, and can form an inorganic-based coating with radiation-cooling properties. In a further embodiment, by adding layered silicate suspending agents and / or aqueous polycarboxylate dispersants, the dispersion stability and storage stability of the aqueous suspension can be improved; by adding organic resins, the interparticle bonding stability can be enhanced, and the anti-dusting performance of the coating can be improved.

[0039] (6) The present invention broadens the practical application scenarios. In the embodiment containing a wetting agent and applied to a metal substrate, the wetting agent can improve the wetting and spreading properties of the aqueous suspension on the surface of the metal substrate, so that the inorganic-based radiation cooling coating can form a continuous coating film on the surface of metal substrates such as aluminum plate, stainless steel plate, galvanized steel plate, and color steel plate, and maintain a high solar reflectivity and infrared emissivity.

[0040] (7) In the embodiment of the present invention using glass powder as white inorganic light scattering particles, glass powder can replace high-purity white metal oxide particles as the solar light scattering component, which is beneficial to reducing the raw material cost of inorganic-based radiation cooling coating. The inorganic-based radiation cooling coating prepared using glass powder has a solar reflectance of 94.28% in the 0.3-2.5 μm range and an infrared emissivity of 95.37% in the 8-13 μm atmospheric window. Attached Figure Description

[0041] Figure 1 This is a flowchart illustrating the preparation process of the inorganic-based radiation-cooling coating prepared in Example 1 of the present invention. Figure 2 Macroscopic photograph of the inorganic-based radiation-cooling coating prepared in Example 1 of this invention under natural light; Figure 3 Scanning electron microscope images of the (a) surface and (b) cross section of the inorganic-based radiation-cooling coating prepared in Example 1 of the present invention; Figure 4 (a) is a schematic diagram of an outdoor test box. Figure 4 (b) shows the temperature change curves of the air inside the outdoor test chamber and the inorganic-based radiation cooling coating; Figure 5 The images show three sets of self-made building models. The left image shows a self-made building model of cement fiberboard loaded with the inorganic-based radiation cooling coating prepared in Example 1 of this invention; the middle image shows a self-made building model of cement fiberboard coated with a commercial white coating; and the right image shows a self-made building model of cement fiberboard. Figure 6 This is a scanning electron microscope image of the inorganic-based radiation-cooling coating prepared in Example 1 of the present invention after undergoing cyclic tribological wear. Figure 7 The inorganic-based radiation-cooling coating prepared in Example 1 of this invention has (a) solar reflectance curves and (b) infrared emissivity curves after undergoing cyclic friction and wear, ultraviolet aging, and outdoor placement treatment. Figure 8 Temperature change curves of the inorganic-based radiation cooling coating, commercial coating, cement fiberboard, and outdoor environment prepared in Example 1 of the present invention; Figure 9 The image shows the fire resistance test of the inorganic-based radiation cooling coating prepared in Example 1 of the present invention under a high-temperature flame of 1300 °C. Figure 10 Thermogravimetric analysis curves of the inorganic-based radiation cooling coating prepared in Example 1 of the present invention in the high temperature range of 0~1400 °C; Figure 11 The results of pencil hardness testing are shown for the inorganic-based radiation-cooling coating prepared in Example 1 of this invention. Figure 12 (a) Solar reflectance curve and (b) Infrared emissivity curve of the inorganic-based radiation-cooling coating prepared in Example 1 of the present invention after being treated at 1200 °C for 5 h; Figure 13 This is a test diagram of the adhesion stability of the inorganic-based radiation cooling coating prepared in Example 1 of the present invention under a 10 kg load; Figure 14 This is a schematic diagram of a building energy consumption simulation model; Figure 15 (a) shows the reflectance curve of the inorganic-based radiation-cooling coating prepared in Example 3 of the present invention in the solar spectral range of 0.3-2.5 μm. Figure 15 (b) is the emissivity curve of the inorganic-based radiation-cooling coating prepared in Example 3 of the present invention in the mid-infrared band; Figure 16 (a) is a macroscopic photograph of the inorganic-based radiation-cooling coating prepared in Example 4 of the present invention on a metal substrate. Figure 16(b) is a comparison curve of the solar reflectance of the inorganic-based radiation-cooling coatings prepared in Example 4 and Example 1 of the present invention; Figure 17 (a) shows the reflectance curve of the inorganic-based radiation-cooling coating prepared in Example 5 of the present invention in the solar spectral range of 0.3-2.5 μm. Figure 17 (b) is the emissivity curve of the inorganic-based radiation-cooling coating prepared in Example 5 of the present invention in the mid-infrared band.

[0042] Among them, 1: sample, 2: PE film, 3: aluminum film, 4: PS foam, 5: K-type thermocouple. Detailed Implementation

[0043] The following examples are intended to enable those skilled in the art to more fully understand the present invention, but do not limit the invention in any way.

[0044] Unless otherwise specified, the materials used in the embodiments of the present invention can be obtained commercially or prepared according to conventional methods known to those skilled in the art.

[0045] In the following examples, the alumina used is in the form of white microspheres with a purity of 99.9%; the particle size of the silica gel in the nano silica sol is 8~15 nm, and the solid content is about 30 wt%.

[0046] In the following embodiments, the cement fiberboard or aluminum plate must be cleaned of surface dust and loose particles before spraying, and if necessary, cleaned with deionized water and dried.

[0047] Example 1 An inorganic-based radiation-cooling coating that cures at room temperature is prepared from the following components in parts by weight: 20 parts of nano-silica sol; 60 parts of alumina; 5 parts deionized water.

[0048] The preparation method of the above-mentioned inorganic-based radiation cooling coating is as follows: Figure 1 As shown, it includes the following steps: Step 1: Place the above components in a container and mechanically stir at 400 rpm for 2 h to uniformly disperse the alumina and obtain an aqueous suspension, wherein the median particle size of the alumina is approximately 1 μm.

[0049] Step 2: The obtained aqueous suspension is sprayed onto one side of the cement fiberboard surface. After spraying, it is allowed to dry and cure naturally at room temperature. During the evaporation of water, the nano-silica sol undergoes dehydration and condensation to form a silica inorganic network. At the same time, interparticle bridging structures are formed between the alumina particles. Finally, an inorganic-based radiation cooling coating is obtained on one side of the cement fiberboard surface. Its macroscopic photograph is shown below. Figure 2 As shown.

[0050] Depend on Figure 2 It can be seen that the inorganic-based radiation cooling coating prepared in Example 1 is uniformly bright white under natural light because it uses white inorganic light scattering particles (alumina).

[0051] The surface and cross-sectional micromorphology of the inorganic-based radiation-cooling coating prepared in Example 1 were characterized using scanning electron microscopy (SEM), and the results are as follows: Figure 3 As shown. By Figure 3 The inorganic-based radiation-cooling coating has a thickness of approximately 400 μm. The coating is composed of densely packed alumina microspheres and a silica network formed by the gelation of nano-silica sol, with solid-state bridging structures between the particles. This solid-state bridging structure facilitates strong multiple scattering within the solar spectrum and exhibits good infrared emissivity within the 8-13 μm atmospheric window. The inorganic-based radiation-cooling coating prepared in Example 1 was tested and found to have a solar reflectance of 94.38% and an infrared emissivity of 92.76% within the 8-13 μm atmospheric window.

[0052] The inorganic-based radiation-cooling coating prepared in Example 1 was placed in an outdoor test chamber for outdoor radiation-cooling performance testing. The temperature of the air inside the outdoor test chamber and the inorganic-based radiation-cooling coating were monitored throughout the process. A schematic diagram of the outdoor test chamber is shown below. Figure 4 As shown in (a), the temperature change curve is as follows: Figure 4 As shown in (b). By Figure 4 It can be seen that the polyethylene film (PE film) in the outdoor test chamber insulates against heat convection, causing the internal air temperature to rise. The temperature on the back of the inorganic-based radiation cooling coating (substrate temperature) is lower than the internal air temperature of the test chamber, with an average temperature difference of 13.21 ℃. This result indicates that the inorganic-based radiation cooling coating can reflect solar radiation and dissipate heat through mid-infrared radiation, reducing the heat load transferred into the test chamber from the top, and exhibiting good passive daytime radiation cooling performance.

[0053] Building models were fabricated using cement fiberboard coated with the inorganic-based radiation cooling coating prepared in Example 1, cement fiberboard coated with a commercial white coating, and cement fiberboard, respectively. The internal temperature was monitored under sufficient sunlight (10-16 AM). The commercial white coating was obtained by rolling white paint purchased from Challenger New Materials (Guangdong) Co., Ltd. onto the surface of the cement fiberboard. Figure 5 As shown, the internal temperature of the building model can be detected to be approximately 1.52 °C lower than the ambient temperature, demonstrating a sub-environmental cooling effect.

[0054] Cyclic triboelectric wear test was conducted on the inorganic-based radiation cooling coating prepared in Example 1: The inorganic-based radiation cooling coating on one side of a cement fiberboard was brought into contact with 400-grit sandpaper, and a 200 g weight was loaded (the weight was pressed onto the sandpaper). The weight was pushed back and forth 10 cm in a single cycle, and the cycle was repeated 10 times. The surface morphology of the inorganic-based radiation cooling coating after wear is shown in the figure below. Figure 6 As shown, by Figure 6 It can be seen that after wear, the inorganic-based radiation-cooling coating surface did not show obvious exposure of the substrate, large-scale peeling, or continuous cracking, with a mass loss rate of 4.21%. Its solar reflectance curve in the 0.3-2.5 μm solar spectral range and its infrared emissivity curve in the mid-infrared band are shown below. Figure 7 As shown in the "Cyclic Friction and Wear Experiment", by Figure 7 It can be seen that the solar reflectivity and infrared emissivity remain relatively stable after the cyclic friction and wear test.

[0055] The inorganic-based radiation-cooling coating prepared in Example 1 was subjected to an ultraviolet aging experiment: the inorganic-based radiation-cooling coating was placed in an ultraviolet aging chamber, the peak value of the ultraviolet aging lamp was approximately 340 nm, and the irradiation time was 168 h. Its solar reflectance curve in the 0.3-2.5 μm solar spectrum range and its infrared emissivity curve in the mid-infrared band are shown below. Figure 7 As shown in the "UV aging test", by Figure 7 It can be seen that the solar reflectivity and infrared emissivity remain relatively stable after the ultraviolet aging experiment.

[0056] The inorganic-based radiation-cooling coating prepared in Example 1 was subjected to a two-week outdoor placement experiment under natural outdoor conditions. The solar reflectance curves in the 0.3-2.5 μm solar spectral range and the infrared emissivity curves in the mid-infrared band after the outdoor placement experiment are shown below. Figure 7 As shown in the "Outdoor Placement Experiment".

[0057] In summary, after undergoing cyclic friction and wear, ultraviolet aging, and outdoor placement treatment, the inorganic-based radiation cooling coating prepared in Example 1 still maintains high solar reflectivity and infrared emissivity, indicating that the inorganic-based radiation cooling coating has good stability and can be applied to building exterior surfaces. The formulation components of Example 1 need to be prepared and used immediately.

[0058] Furthermore, the inorganic-based radiation-cooling coating prepared in Example 1, the commercial white coating, and the uncoated cement fiberboard were placed under the same outdoor solar irradiation conditions for comparative testing, and the ambient temperature and the temperature of each sample were recorded simultaneously. The temperature change curves are shown below. Figure 8 As shown. By Figure 8It can be seen that, under the same outdoor solar irradiation conditions, the uncoated cement fiberboard had the highest temperature, the commercial white coating sample had a lower temperature than the uncoated cement fiberboard, and the inorganic-based radiation cooling coating prepared in Example 1 had a further reduced temperature, even falling below the ambient temperature during the test. These results indicate that, compared to the uncoated cement fiberboard and the commercial white coating, the inorganic-based radiation cooling coating of this invention has a better passive cooling effect.

[0059] like Figure 9 As shown, the inorganic-based radiation cooling coating prepared in Example 1 was exposed to a high-temperature flame at 1300 °C for fire resistance testing. The presence of ignition, dripping, or significant structural collapse was observed. Since the inorganic-based radiation cooling coating prepared in Example 1 is primarily composed of white inorganic light-scattering particles and a silica inorganic network, and does not use organic resin as the main film-forming material, it did not exhibit ignition, dripping, or significant structural damage under direct exposure to a high-temperature flame.

[0060] Thermogravimetric analysis (TGA) was performed on the inorganic-based radiation-cooling coating prepared in Example 1 to evaluate its mass loss in the high-temperature range of 0–1400 °C. The TGA curves are shown below. Figure 10 As shown, by Figure 10 It can be seen that the inorganic-based radiation cooling coating prepared in Example 1 has very little mass loss in the high-temperature range, showing good thermal stability.

[0061] The inorganic-based radiation-cooling coating prepared in Example 1 was subjected to a pencil hardness test, and the results are as follows: Figure 11 As shown, by Figure 11 It can be seen that the inorganic-based radiation cooling coating prepared in Example 1 can withstand 6H pencil scratches without significant damage, and its hardness is 6H.

[0062] The inorganic-based radiation-cooling coating prepared in Example 1 was subjected to high-temperature treatment at 1200 °C for 5 h. The solar reflectance and infrared emissivity of the treated inorganic-based radiation-cooling coating were then tested. The results are as follows: Figure 12 As shown. By Figure 12 It can be seen that the inorganic-based radiation cooling coating prepared in Example 1 can still maintain a high solar reflectance of 96.55% and an infrared emissivity of 92.9% under an atmospheric window of 8-13 μm after being treated at 1200 ℃ for 5 h, indicating that its optical performance has a certain degree of stability.

[0063] Referring to the preparation method of Example 1, after the obtained aqueous suspension is sprayed onto one side of a cement fiberboard, another cement fiberboard is placed against it and allowed to dry and cure naturally at room temperature, serving as a bonding carrier. Figure 13As shown, a water bottle with a total weight of 10 kg was suspended by a hoist and lifted vertically. Under a continuous load of 10 kg, the inorganic-based radiation cooling coating did not detach or crack from the cement fiberboard, demonstrating that the inorganic-based radiation cooling coating has excellent interfacial bonding strength.

[0064] Referring to the preparation method of Example 1, the cement fiberboard was replaced with cement board or ceramic board. The solar reflectance and infrared emissivity of the inorganic-based radiation-cooling coating prepared on different substrates in Example 1 were tested. The solar reflectance of the inorganic-based radiation-cooling coating prepared on the cement board was 94.41%, and the infrared emissivity was 92.52% in the 8-13 μm atmospheric window. The solar reflectance of the inorganic-based radiation-cooling coating prepared on the ceramic board was 94.53%, and the infrared emissivity was 92.37% in the 8-13 μm atmospheric window. This indicates that the inorganic-based radiation-cooling coating and preparation method are suitable for a variety of building exterior wall substrates and have good substrate adaptability and versatility.

[0065] A building energy consumption simulation model is built using EnergyPlus building energy consumption simulation software, such as... Figure 14 As shown, building energy consumption simulations were conducted across multiple climate zones in China. The results indicate that, under the climatic conditions of most Chinese cities, applying inorganic-based radiative cooling coatings to the surface of building envelopes can reduce building cooling loads and has certain energy-saving potential. Therefore, the inorganic-based radiative cooling coating of this invention can be used in passive cooling scenarios such as building roofs, exterior walls, cold storage shells, outdoor equipment shells, tank exteriors, and corrugated steel roofs.

[0066] Example 2 An inorganic-based radiation-cooling coating that cures at room temperature is prepared from the following components in parts by weight: 20 parts of nano-silica sol; 60 parts of alumina; 0.1 parts of lithium magnesium silicate; 0.1 parts of ammonium polyacrylate; 5 parts deionized water.

[0067] The preparation method of the inorganic-based radiation cooling coating in Example 2 is basically the same as that in Example 1, except that lithium magnesium silicate is first stirred with deionized water for 6 hours, then allowed to stand for 12 hours before being mechanically stirred with the remaining components.

[0068] The aqueous suspension obtained in step 1 of Example 2 can be stored for more than 2 weeks and exhibits stability. This is because ammonium polyacrylate, as an aqueous polycarboxylate dispersant, can be adsorbed onto the surface of white inorganic light-scattering particles, reducing particle agglomeration through electrostatic repulsion and steric hindrance; lithium magnesium silicate, as a layered silicate suspending agent, can form a thixotropic network in the aqueous system, improving particle suspension stability and inhibiting sedimentation and stratification.

[0069] The inorganic-based radiation-cooling coating prepared in Example 2 has a solar reflectance of 94.56% and an infrared emissivity of 92.68% in an 8-13 μm atmospheric window.

[0070] In summary, based on the needs of paint storage and spraying, a small amount of ammonium polyacrylate and lithium magnesium silicate can be added to prepare an aqueous suspension with excellent construction stability. At the same time, the system can maintain good solar reflectivity and infrared emissivity.

[0071] Example 3 An inorganic-based radiation-cooling coating that cures at room temperature is prepared from the following components in parts by weight: 20 parts of nano-silica sol; 60 parts glass powder; 15 parts deionized water.

[0072] The preparation method of the inorganic-based radiation-cooling coating in Example 3 is the same as that in Example 1. The median particle size of the glass powder (D...) 50 The thickness is 2.7 μm.

[0073] The reflectance curves of the inorganic-based radiation-cooling coating prepared in Example 3 and the emissivity curves in the mid-infrared band of the solar spectrum in the 0.3-2.5 μm range were tested. Figure 15 As shown, the inorganic-based radiation-cooling coating prepared in Example 3 has a solar reflectance of 94.28% and an infrared emissivity of 95.37% in an atmospheric window of 8-13 μm.

[0074] Example 3 demonstrates that the use of glass powder can significantly reduce raw material costs and achieve resource utilization of waste glass. The resulting inorganic-based radiation cooling coating can form a continuous white film and has excellent solar reflection and mid-infrared emission capabilities, making it suitable for cost-sensitive building roofs, exterior walls, cement-based materials, and outdoor facility surfaces.

[0075] Example 4 An inorganic-based radiation-cooling coating that cures at room temperature is prepared from the following components in parts by weight: 20 parts of nano-silica sol; 60 parts of alumina; 0.5 parts of fluorinated non-silicone polymer KYC-643; 5 parts deionized water.

[0076] The preparation method of the inorganic-based radiation cooling coating in Example 4 is basically the same as that in Example 1, except that the fluorinated non-silicone polymer wetting agent KYC-643 needs to be added to the system after the other components have been fully dispersed by mechanical stirring. The cement fiberboard is replaced with an aluminum plate, and an inorganic-based radiation cooling coating is obtained on one side of the aluminum plate. Figure 16 As shown in (a).

[0077] Depend on Figure 16 As shown in (a), after adding KYC-643, the aqueous suspension forms a continuous and uniform inorganic radiation-cooling coating on the metal substrate surface. For porous inorganic building substrates, whose surfaces have porous, rough, or uneven structures, the aqueous suspension can enter these porous or rough structures during the coating process and form mechanical interlocking or physical anchoring after curing at room temperature. However, for metal substrates, whose surfaces are smooth and lack such physical anchoring points, the cohesive force driven by surface tension during the spreading process of the aqueous suspension is greater than its adhesion to the substrate, which easily leads to pinholes and dewetting defects. Therefore, when using metal substrates, it is preferable to add a small amount of wetting agent to improve the wetting and spreading properties of the aqueous suspension on the metal surface and reduce problems such as pinholes, local dewetting, and coating discontinuity.

[0078] Following the preparation method of Example 1, an inorganic-based radiation-cooling coating was prepared by replacing the cement fiberboard with an aluminum plate. The solar reflectance curves of the inorganic-based radiation-cooling coating with and without a wetting agent were tested in the 0.3-2.5 μm solar spectral range. Figure 16 As shown in (b), the inorganic-based radiation-cooling coating prepared in Example 4 has a solar reflectance of 93.86% and an infrared emissivity of 95.59% in the 8-13 μm atmospheric window. After the addition of a wetting agent, the inorganic-based radiation-cooling coating can still maintain high solar reflectance and infrared emissivity while forming a continuous coating film on the surface of the metal substrate.

[0079] Example 5 An inorganic-based radiation-cooling coating that cures at room temperature is prepared from the following components in parts by weight: 20 parts of nano-silica sol; 60 parts of zirconium oxide; 10 parts deionized water.

[0080] The preparation method of the inorganic-based radiation-cooling coating in Example 5 is the same as that in Example 1. Specifically, the D of zirconium oxide... 50 It is 0.7 μm.

[0081] The reflectance curves of the inorganic-based radiation-cooling coating prepared in Example 5 and the emissivity curves in the mid-infrared band of the solar spectrum in the 0.3-2.5 μm range were tested. Figure 17 As shown, the inorganic-based radiation-cooling coating prepared in Example 5 has a solar reflectance of 95.45% and an infrared emissivity of 95.04% in an 8-13 μm atmospheric window.

[0082] Examples 6-8 An inorganic-based radiation-cooling coating that cures at room temperature is described. The preparation method of the inorganic-based radiation-cooling coating in Examples 6-8 is basically the same as that in Example 1, except that the water-based acrylic resin is added to the system only after the other components have been fully dispersed by mechanical stirring. The components used in Examples 6-8 and their mass fractions are shown in Table 1.

[0083] Table 1

[0084] The solar reflectance and infrared emissivity of the inorganic-based radiation-cooling coatings prepared in Examples 6-8 are shown in Table 2.

[0085] Table 2

[0086] Comparative Examples 6-8 were used to investigate the effect of organic resin content on solar reflectivity and infrared emissivity under the 8-13 μm atmospheric window. Compared with Example 6, when the amount of organic resin added was 5 parts, the solar reflectivity of the inorganic-based radiation cooling coating prepared in Example 8 showed a decreasing trend, while the infrared emissivity under the 8-13 μm atmospheric window changed little and remained above 90%.

[0087] The inorganic-based radiation cooling coatings prepared in Examples 6-8, due to the addition of water-based acrylic resin, form an auxiliary bonding phase in the particle contact area, which enhances the bonding between particles and further improves the anti-powdering performance.

[0088] The inorganic-based radiation cooling coatings prepared in Examples 6-8 were subjected to fire resistance tests. It was observed that Example 6 did not exhibit ignition, dripping, or significant structural damage under an 800°C flame, indicating that 1 part of water-based acrylic resin does not affect the fire resistance of the inorganic-based radiation cooling coating. The inorganic-based radiation cooling coatings prepared in Examples 7-8 showed localized blackening on their surface under an 800°C flame, but the overall structure remained intact, without large-area charring or peeling, demonstrating good high-temperature stability.

[0089] Examples 9-11 An inorganic-based radiation cooling coating that cures at room temperature. The components and preparation methods used in Examples 9-11 are the same as those in Example 1, except that the mass fractions of the components are different. The mass fractions of the components used in Examples 9-11 are shown in Table 3.

[0090] Table 3

[0091] The solar reflectance and infrared emissivity of the inorganic-based radiation-cooling coatings prepared in Examples 9-11 are shown in Table 4.

[0092] Table 4

[0093] Examples 1 and 9-11 were compared to investigate the effect of the content of white inorganic light-scattering particles on solar reflectivity and infrared emissivity within the 8-13 μm atmospheric window. With a nano-silica sol content of 20 parts, as the alumina content increased from 40 parts to 80 parts, the inorganic-based radiation-cooling coatings maintained high solar reflectivity and infrared emissivity within the 8-13 μm atmospheric window. In Example 11, with an alumina content of 80 parts, the solar reflectivity of the inorganic-based radiation-cooling coating further increased to 95.35%, indicating that increasing the content of white inorganic light-scattering particles is beneficial for enhancing the coating's light-scattering ability within the solar spectrum. Simultaneously, the surface hardness of the coating obtained in Example 11 still reached 3H, indicating that the inorganic-based radiation-cooling coating at this formulation still possesses a certain degree of mechanical stability.

[0094] Examples 12-13 and Comparative Examples 1-3 An inorganic-based radiation cooling coating that cures at room temperature. The components, mass fractions of the components and preparation methods used in Examples 12-13 and Comparative Examples 1-3 are the same as those in Example 1. The difference is the median particle size of the alumina used. The median particle size of the alumina used in Examples 12-13 and Comparative Examples 1-3 is shown in Table 5.

[0095] Table 5

[0096] The solar reflectance and infrared emissivity of the inorganic-based radiation-cooling coatings prepared in Examples 12-13 and Comparative Examples 1-3 are shown in Table 6.

[0097] Table 6

[0098] Comparative Examples 1, 12-13, and 1-3 were used to investigate the effects of white inorganic light-scattering particles with different median particle sizes on solar reflectivity and infrared emissivity under an 8-13 μm atmospheric window. As the median particle size of the white inorganic light-scattering particles decreased, the solar reflectivity and infrared emissivity of the inorganic-based radiation-cooling coating under an 8-13 μm atmospheric window gradually increased. However, a smaller median particle size is not necessarily better. Comparative Examples 1-3 demonstrate that the median particle size of the white inorganic light-scattering particles should be selected within an appropriate range in order to prepare an inorganic-based radiation-cooling coating with excellent performance.

[0099] The layered silicate suspending agent, aqueous polycarboxylate dispersant, wetting agent, and organic resin of this invention are not essential components for achieving the formation and radiation cooling performance of the inorganic-based radiation cooling coating. The inorganic-based radiation cooling coating of this invention is suitable for immediate use without the addition of the above components. Specifically, the addition of the layered silicate suspending agent and the aqueous polycarboxylate dispersant improves the storage stability of the aqueous suspension, facilitating practical storage; the addition of the wetting agent improves dispersion stability, enhances the spreadability and film continuity of the aqueous suspension, and is suitable for metal substrates; the addition of the organic resin improves the interparticle bonding stability.

[0100] The solar reflectivity and infrared emissivity of this invention are based on the weighted average solar spectral reflectivity in the literature (Lin K, Chen S, Zeng Y, et al. Hierarchically structured passive radiative cooling ceramic with high solar reflectivity[J]. Science, 2023, 382(6671): 691-697). R Formula and mid-infrared emissivity ( MIR ) Formula calculation.

[0101] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the implementation. The scope of protection of the present invention should be determined by the scope defined in the claims. Other variations or modifications can be made based on the above description. Obvious variations or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. A room-temperature curing inorganic-based radiation-cooling coating, characterized in that, It is prepared from the following components in parts by weight: 5-40 parts of nano-silica sol; 40-90 parts of white inorganic light-scattering particles; 0-5 parts of layered silicate suspension; 0-5 parts of water-based polycarboxylate dispersant; 0-3 parts wetting agent; 0-5 parts of organic resin; 4-30 parts water; The white inorganic light-scattering particles are one or more of the following: white metal oxide particles, white silicate particles, and glassy inorganic particles.

2. The inorganic-based radiation cooling coating according to claim 1, characterized in that, The silica particles in the nano-silica sol have a particle size of 5–30 nm and a solid content of 20–40 wt%. The median particle size of the white inorganic light-scattering particles is 0.7~9 μm.

3. The inorganic-based radiation cooling coating according to claim 1, characterized in that, The thickness of the inorganic-based radiation cooling coating is 300~450 μm.

4. The inorganic-based radiation cooling coating according to claim 1, characterized in that, The white metal oxide particles are one or more of aluminum oxide, zirconium oxide, yttrium oxide, magnesium oxide, titanium oxide, zinc oxide, and tin oxide; the white silicate particles include kaolin or zeolite; and the glassy inorganic particles include glass powder.

5. The inorganic-based radiation cooling coating according to claim 1, characterized in that, The white metal oxide particles have one or more of the following morphologies: spherical, near-spherical, irregular granular, flake-like, rod-like, porous, and hollow.

6. The inorganic-based radiation cooling coating according to claim 1, characterized in that, The aqueous polycarboxylate dispersant includes ammonium polyacrylate; The layered silicate suspending agent includes lithium magnesium silicate; The wetting agent is one or more of the following: fluorinated non-silicone polymer wetting agent, polyether modified siloxane wetting agent, acetylenic diol wetting agent, and phosphate ester salt wetting agent; The organic resin is one or more of acrylic resin, pure acrylic resin, and silicone acrylic resin.

7. A method for preparing an inorganic-based radiation-cooling coating as described in any one of claims 1 to 6, characterized in that, Includes the following steps: Step 1: Mix all components of the inorganic-based radiation cooling coating as described in any one of claims 1 to 6 evenly and mechanically stir for 1 to 2 hours to obtain an aqueous suspension; Step 2: Coat the obtained aqueous suspension onto one side of the substrate surface, and allow it to dry and cure naturally at room temperature to obtain an inorganic radiation cooling coating on one side of the substrate surface.

8. Application of a room temperature curing inorganic-based radiation cooling coating in building envelope.

9. The application according to claim 8, characterized in that, The substrate used for the building envelope is a porous inorganic building material or a metal substrate.

10. The application according to claim 9, characterized in that, The porous inorganic building substrate includes cement fiberboard, cement substrate, concrete, mortar layer, ceramic board, calcium silicate board, stone, brick, tile or gypsum board; the metal substrate includes aluminum plate, stainless steel plate, galvanized steel plate, color steel plate, copper plate, titanium plate or alloy plate.

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