Interlayer spectral synergistic radiative cooling coating system and preparation method and application thereof

Abstract

This application provides an interlayer spectral synergistic radiation-cooling coating system, its preparation method, and its application, belonging to the field of functional coating materials. The coating system, from the inside out, is sequentially disposed on the surface of a substrate and includes: a primer layer, a primary reflective functional layer, and a spectral synergistic enhancement layer. The primary reflective functional layer contains a first functional filler selected from one or more of rutile titanium dioxide and barium sulfate. The average reflectivity R1 of the primary reflective functional layer in the 400–2500 nm wavelength band is ≥0.95. The spectral synergistic enhancement layer contains a second functional filler with a core-shell structure, its core being rutile titanium dioxide and its outer shell being alumina or barium sulfate. The average reflectivity R2 of this coating system in the 300–400 nm wavelength band is ≥0.80, and the overall solar reflectance (TSR) is ≥0.96. This application utilizes the interlayer spectral synergistic enhancement effect to achieve a significant improvement in reflectivity across the entire wavelength band.

Description

Technical Field

[0001] This invention relates to the field of functional coating materials technology, specifically to a radiation-cooling coating system with interlayer spectral synergy, its preparation method, and its application. Background Technology

[0002] Passive radiative cooling technology achieves energy-free cooling by radiating heat from an object's surface into the cold outer space via the mid-infrared band (especially through the atmospheric transparency window of 8-13 μm). The key to achieving efficient radiative cooling lies in the coating possessing two core optical properties: extremely high reflectivity (R) in the solar spectrum (approximately 300-2500 nm) to minimize temperature rise caused by solar irradiation; and extremely high emissivity (ε) in the atmospheric window band to maximize radiative heat dissipation.

[0003] Currently, high-performance radiative cooling coatings generally aim to achieve extremely high reflectivity across the entire solar spectrum. To achieve this goal, existing technologies typically employ a design scheme that adds a high proportion of reflective and heat-insulating fillers, such as titanium dioxide, to a single-layer topcoat. However, this design has the following inherent drawbacks: Insufficient ultraviolet reflectivity: Due to its intrinsic bandgap absorption, TiO2 exhibits a sharp decrease in reflectivity in the 300-400 nm ultraviolet band, creating a shortcoming in ultraviolet reflection. Simply increasing the amount of TiO2 cannot compensate for this deficiency. The optical performance of the single-layer structure is nearing its limit: High-whiteness, high-scattering fillers such as zirconium oxide and Al2O3, introduced to compensate for the ultraviolet shortcoming, offer limited improvement in reflectivity in the 700-2500 nm near-infrared band, failing to address the fundamental issues in the ultraviolet band. This single-layer, all-functional design requires optimization across all bands when combining the same filler, resulting in its optical performance approaching its theoretical limit, making further breakthroughs difficult.

[0004] In view of this, it is necessary to design a radiation-cooling coating system with interlayer spectral synergy, as well as its preparation method and application, to solve the above problems. Summary of the Invention

[0005] In view of the technical problems existing in the background art, this application provides a radiation-cooling coating system with interlayer spectral synergy, its preparation method and application, aiming to solve the technical problems of low ultraviolet reflectivity, mutual restriction of optical properties of different bands in a single coating, and difficulty in synergistic enhancement in the existing radiation-cooling coating system.

[0006] In a first aspect, this application provides a radiation cooling coating system with interlayer spectral synergy, which is disposed sequentially on the surface of a substrate from the inside to the outside, including: a primer layer, a main reflection functional layer and a spectral synergy enhancement layer; The primary reflective functional layer includes a first functional filler, which is selected from one or more of rutile titanium dioxide and barium sulfate. The average reflectivity R1 of the primary reflective functional layer in the 400~2500nm band is ≥0.95. The spectral synergistic enhancement layer includes a second functional filler with a core-shell structure, wherein the core of the second functional filler is rutile titanium dioxide and the shell is alumina or barium sulfate; The radiation-cooling coating system has an average reflectance R2 ≥ 0.80 in the 300~400nm wavelength band, and the overall solar reflectance TSR of the radiation-cooling coating system is ≥ 0.96.

[0007] As a further improvement of this application, the dry film thickness of the main reflection functional layer is 80~150μm, and the dry film thickness of the spectral synergistic enhancement layer is 40~80μm.

[0008] As a further improvement of this application, the core particle size of the second functional filler is 200~250nm, and the shell thickness is 30~300nm.

[0009] As a further improvement of this application, the radiation-cooled coating system has an average emissivity ε ≥ 0.94 in the 8~13μm atmospheric window.

[0010] Secondly, this application provides a method for preparing a radiation-cooling coating system with interlayer spectral synergy as described in the first aspect, comprising the following steps: Apply a primer layer to the substrate surface; Prepare a primary reflective functional layer coating and apply the primary reflective functional layer to the surface of the primer layer; A spectral synergistic enhancement layer coating is prepared and a spectral synergistic enhancement layer is disposed on the surface of the main reflective functional layer.

[0011] As a further improvement of this application, the main reflective functional layer coating comprises, by weight, 30-40 parts of acrylic emulsion, 30-40 parts of first functional filler, 0.5-3 parts of first additive, and 20-30 parts of water.

[0012] As a further improvement of this application, the spectral synergistic enhancement layer coating comprises, by weight, 15-35 parts of acrylic emulsion, 40-60 parts of second functional filler, 0.5-3 parts of second auxiliary agent, and 15-20 parts of water.

[0013] As a further improvement of this application, the preparation method of the second functional filler is as follows: using rutile titanium dioxide particles as the core, aluminum oxide or barium sulfate is coated on the surface of the rutile titanium dioxide particles by sol-gel method.

[0014] As a further improvement of this application, the first additive and the second additive are each independently selected from one or more of the following: dispersant, wetting agent, defoamer, film-forming aid, thickener, leveling agent, pH adjuster, mildew inhibitor, and antifreeze.

[0015] Thirdly, this application provides an application of the interlayer spectral synergistic radiation cooling coating system described in the first aspect in building roofs, outdoor equipment, or spacecraft ground equipment.

[0016] The beneficial effects of this application are as follows: This application provides an interlayer spectrally synergistic radiation-cooling coating system, its preparation method, and its application. The coating system is sequentially disposed on the surface of a substrate from the inside out, comprising: a primer layer, a primary reflective functional layer, and a spectrally synergistic enhancement layer. The primary reflective functional layer includes a first functional filler selected from one or more of rutile titanium dioxide and barium sulfate. The average reflectance R1 of the primary reflective functional layer in the 400–2500 nm wavelength band is ≥0.95. The spectrally synergistic enhancement layer includes a second functional filler with a core-shell structure. The core of the second functional filler is rutile titanium dioxide, and the outer shell is alumina or barium sulfate. The average reflectance R2 of the radiation-cooling coating system in the 300–400 nm wavelength band is ≥0.80, and the overall solar reflectance (TSR) of the radiation-cooling coating system is ≥0.96. This application utilizes an interlayer synergistic system comprising a high-reflectivity primary reflective layer and a spectrally synergistic enhancement layer with a core-shell structured filler to increase the average reflectivity of the coating in the ultraviolet band (300-400nm) to over 0.80. This overcomes the ultraviolet reflectance limitations of traditional titanium dioxide fillers, while simultaneously achieving a breakthrough overall solar reflectance (TSR) of over 0.96 and an atmospheric window emissivity of no less than 0.95. This achieves full-band synergistic enhancement of reflectance in the ultraviolet and visible-near-infrared bands, breaking through the performance limits of traditional single-layer structures and providing an ultra-efficient, low-cost, and process-compatible solution for radiative cooling technology. This coating system can be used for ultra-efficient passive radiative cooling on surfaces requiring extreme heat dissipation efficiency, such as outdoor communication base stations, data center roofs, and spacecraft ground equipment.

[0017] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0019] Figure 1 This is a schematic diagram of the structure of the radiation-cooling coating system with interlayer spectral synergy provided in the embodiments of this application; Explanation of reference numerals in the attached drawings: 1. Substrate; 2. Primer layer; 3. Main reflective functional layer; 31. First functional filler; 4. Spectral synergistic enhancement layer; 41. Second functional filler. Detailed Implementation

[0020] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0022] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0023] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0024] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0025] In existing technologies, high-performance radiation cooling coatings generally employ a design that adds a high proportion of reflective and heat-insulating functional fillers such as titanium dioxide to a single coating. However, due to the intrinsic band gap absorption of TiO2, its reflectivity in the 300-400nm ultraviolet band drops sharply, forming an ultraviolet bottleneck. Simply increasing the amount of TiO2 cannot compensate for this defect. On the other hand, the high-whiteness, high-scattering fillers introduced to compensate for this bottleneck can only improve the reflectivity in the near-infrared band and cannot solve the ultraviolet defect. This results in the optical performance of different bands within a single coating being mutually constrained and difficult to enhance synergistically. Its optical performance has approached the theoretical limit and cannot achieve a step-by-step improvement.

[0026] To address the technical challenges of low ultraviolet reflectivity and near-limit optical performance of single-layer structures in existing radiation-cooling coatings, which hinders the improvement of overall solar reflectance, this application provides a radiation-cooling coating system with interlayer spectral synergy, its preparation method, and its application. By setting a main reflective functional layer and a spectral synergy enhancement layer containing a core-shell structure filler, the spectral synergy enhancement effect between the two layers is utilized to achieve a step-wise improvement in full-band reflectance performance.

[0027] Firstly, embodiments of this application provide a radiation-cooling coating system with interlayer spectral synergy, such as... Figure 1 As shown, the following layers are sequentially disposed on the surface of the substrate 1 from the inside out: primer layer 2, main reflection functional layer 3, and spectral synergistic enhancement layer 4; The main reflective functional layer 3 includes a first functional filler 31, which is selected from one or more of rutile titanium dioxide and barium sulfate. The average reflectivity R1 of the main reflective functional layer 3 in the 400~2500nm band is ≥0.95. The spectral synergistic enhancement layer 4 includes a second functional filler 41 with a core-shell structure. The core of the second functional filler 41 is rutile titanium dioxide, and the shell is alumina or barium sulfate. The radiation-cooling coating system has an average reflectance R2 ≥ 0.80 in the 300~400nm wavelength band, and the overall solar reflectance TSR of the radiation-cooling coating system is ≥ 0.96.

[0028] In the technical solution of this application embodiment, the main reflective functional layer 3 provides basic high reflectivity in the 400~2500nm band, while the core-shell structure filler in the spectral synergistic enhancement layer 4 utilizes the refractive index difference between the core and the shell and the multiple interface backscattering effect to generate strong reflection in the ultraviolet band to compensate for the ultraviolet shortcomings of traditional TiO2. On the other hand, it forms superimposed scattering with the main reflective layer in the visible-near infrared band, so that the reflectivity of the whole band is enhanced twice, thereby synergistically realizing the high reflectivity of the coating system in the ultraviolet band and the improvement of the overall solar reflectance.

[0029] Furthermore, in some embodiments, the dry film thickness of the main reflection functional layer 3 is 80~150μm, and the dry film thickness of the spectral synergistic enhancement layer 4 is 40~80μm.

[0030] In the technical solution of this application embodiment, the dry film thickness of the main reflective functional layer 3 helps to provide sufficient optical paths for the first functional filler 31 such as rutile titanium dioxide inside, thereby forming a stable and extremely high basic reflection in the 400~2500nm band; the thickness of the spectral synergistic enhancement layer 4 is controlled within an appropriate range, which helps to accommodate the core-shell structure filler and utilize its multiple interface scattering effect to efficiently enhance ultraviolet and visible-near infrared reflection, while avoiding excessive absorption or scattering weakening of the lower layer reflected light by an excessively thick coating, ensuring that the upper enhancement layer and the lower main reflective layer form a gain superposition rather than a shielding loss, thereby synergistically achieving an overall leap in reflectivity across the entire band.

[0031] Furthermore, in some embodiments, the core particle size of the second functional filler 41 is 200~250nm, and the outer shell thickness is 30~300nm.

[0032] In the technical solution of this application embodiment, a rutile TiO2 core with a suitable particle size is selected to give it strong scattering capability in the 400~2500 nm wavelength band. Simultaneously, the shell thickness is controlled, and by utilizing the refractive index difference between the core and shell and the multiple interface backscattering effect, reflection is significantly enhanced in the 300~400 nm ultraviolet band. At the same time, superimposed scattering is formed in the visible-near infrared band, synergistically improving the overall reflectivity with the main reflective functional layer 3. This core-shell structure avoids the decrease in scattering efficiency due to an excessively thick shell or the inability to form an effective interface due to an excessively thin shell, thus achieving balanced and efficient optical gain in the ultraviolet and visible-near infrared bands.

[0033] Furthermore, in some embodiments, the radiation-cooled coating system has an average emissivity ε ≥ 0.94 in an atmospheric window of 8–13 μm.

[0034] In the technical solution of this application embodiment, the inorganic fillers in the main reflection functional layer 3 and the spectral synergistic enhancement layer 4 also possess a certain mid-infrared emission capability. These fillers have abundant lattice vibration absorption bands in the mid-infrared region, which can effectively emit heat from the object surface in the form of thermal radiation. At the same time, the film-forming materials such as acrylic emulsion used in the coating system have weak absorption peaks in the atmospheric window band, which will not significantly hinder the radiative heat dissipation of the fillers. Through the synergy of the two-layer structure, the coating maintains an ultra-high solar reflectance while possessing excellent atmospheric window emission capability, thereby efficiently radiating heat to the cold outer space and achieving passive radiative cooling.

[0035] Secondly, embodiments of this application provide a method for preparing a radiation-cooling coating system with interlayer spectral synergy, comprising the following steps: A primer layer 2 is applied to the surface of substrate 1; Prepare the main reflective functional layer coating, and set the main reflective functional layer 3 on the surface of the primer layer 2; A spectral synergistic enhancement layer coating is prepared, and a spectral synergistic enhancement layer 4 is set on the surface of the main reflection functional layer 3.

[0036] The process involves applying a primer layer 2 to the surface of substrate 1 to provide adhesion, sealing, and alkali resistance, thereby strengthening the substrate and providing a stable base for the upper coating. Then, a primary reflective functional layer coating is prepared and applied to the surface of primer layer 2 to form primary reflective functional layer 3, laying the foundation for high reflectivity across the entire wavelength range. Finally, a spectral synergistic enhancement layer coating is applied to the surface of the primary reflective layer to further enhance reflectivity in the ultraviolet (300-400 nm) and visible-near-infrared bands. A sequential coating process, allowing each layer to dry completely before applying the next, ensures that each functional layer forms an independent film with clear interfaces, avoiding interlayer miscibility that could lead to optical degradation. Ultimately, this results in an overall solar reflectance (TSR) ≥ 0.96 and an ultraviolet reflectance (R²) ≥ 0.80 for the coating system. This method is fully compatible with existing conventional coating processes such as roller coating, spraying, or brushing, and has good industrial applicability.

[0037] Furthermore, in some embodiments, the main reflective functional layer coating comprises, by weight, 30-40 parts of acrylic emulsion, 30-40 parts of first functional filler, 0.5-3 parts of first additive, and 20-30 parts of water.

[0038] In the technical solution of this application embodiment, acrylic emulsion is used as the film-forming substance to provide the cohesiveness of the coating and the adhesion to the primer layer 2; the first functional filler 31 acts as a key scatterer, utilizing its high refractive index to generate strong reflection in the 400~2500nm wavelength band, ensuring that the main reflective layer achieves a basic high reflectivity of R1≥0.95; the first additive is used to improve the dispersion, wetting, defoaming, and application performance of the filler; water is used as a solvent to adjust the viscosity of the coating to adapt to processes such as spraying and roller coating. This formulation, through the scientific ratio of high filler content and appropriate amount of emulsion, maximizes the optical reflection efficiency in the solar spectrum band while ensuring the mechanical integrity of the coating, laying a solid foundation for the secondary gain of the upper spectral synergistic enhancement layer 4.

[0039] Furthermore, in some embodiments, the spectral synergistic enhancement layer coating comprises, by weight, 15-35 parts of acrylic emulsion, 40-60 parts of a second functional filler, 0.5-3 parts of a second auxiliary agent, and 15-20 parts of water.

[0040] In the technical solution of this application embodiment, acrylic emulsion is used as the film-forming substance to provide the coating with the necessary mechanical properties and interlayer adhesion, while avoiding the negative impact of excessive organic resin on infrared emissivity. The second functional filler 41, as the core functional component, utilizes the multiple interface backscattering effect between its high-refractive-index core and low-refractive-index shell to generate strong reflection in the ultraviolet band (300~400 nm) to compensate for the ultraviolet shortcomings of traditional fillers. At the same time, it forms superimposed scattering with the lower main reflective functional layer 3 in the visible-near-infrared band (400~2500 nm), achieving secondary enhancement of reflectivity across the entire band. The second additive is used to improve the dispersion stability of the filler, the leveling properties of the coating, and the defoaming and other process performance. Water is used as a diluent to adjust the application viscosity. This formulation, through the scientific ratio of high content of core-shell filler and appropriate amount of emulsion, maximizes the spectral synergistic enhancement function while ensuring the integrity of the coating film, resulting in a final coating system with an average reflectivity ≥0.80 in the ultraviolet band and an overall solar reflectance ≥0.96.

[0041] Furthermore, in some embodiments, the second functional filler 41 is prepared by: using rutile titanium dioxide particles as the core, coating the surface of the rutile titanium dioxide particles with alumina or barium sulfate by a sol-gel method.

[0042] In the technical solution of this application embodiment, the sol-gel method can achieve precise control of the shell thickness and morphology, ensuring that the shell is intact, dense, and firmly bonded to the core. This core-shell structure utilizes the refractive index difference between the core and shell to form multiple optical interfaces, thereby generating strong backscattering in the ultraviolet band and simultaneously forming superimposed scattering with the lower primary reflective layer in the visible-near-infrared band, achieving synergistic enhancement of reflection across the entire wavelength range. This method offers process controllability and good repeatability, and the resulting core-shell filler can be directly used in the formulation of spectrally synergistic enhancement layer coatings.

[0043] Furthermore, in some embodiments, the first and second additives are each independently selected from one or more of the following: dispersants, wetting agents, defoamers, film-forming aids, thickeners, leveling agents, pH adjusters, fungicides, and antifreeze agents.

[0044] In the technical solution of this application embodiment, the reasonable compounding of the above-mentioned additives ensures that the coating of the main reflection functional layer and the spectral synergistic enhancement layer possesses excellent processability, workability, and storage stability, thereby guaranteeing the full utilization of the optical performance and long-term durability of the coating system. It should be noted that the above-mentioned additives are all commercially available industrial-grade products commonly used in the art, and those skilled in the art can make conventional selections according to specific construction requirements and coating systems.

[0045] Thirdly, embodiments of this application provide an application of a radiation-cooling coating system with interlayer spectral synergy in building roofs, outdoor equipment, or spacecraft ground equipment.

[0046] In the technical solution of this application embodiment, the coating system achieves ultra-high optical performance with a solar reflectance ≥0.96 and an atmospheric window emissivity ≥0.94 through the synergistic effect of the main reflective functional layer 3 and the spectral synergistic enhancement layer 4. This allows it to reflect most of the solar heat back under intense solar irradiation, while simultaneously efficiently radiating the heat from the substrate to the cold outer space through the atmospheric window in the form of infrared radiation, thus achieving zero-energy passive radiative cooling. When applied to building roofs, it can significantly reduce indoor temperatures and decrease air conditioning energy consumption; when applied to outdoor equipment (such as communication base stations, containers, and outdoor equipment shells), it can prevent overheating and extend the service life; when applied to spacecraft ground equipment, it can simulate the space heat dissipation environment, ensuring the thermal control stability of the equipment. This coating system is compatible with existing coating processes and has advantages such as convenient construction, controllable cost, and excellent durability, providing an efficient, energy-saving, and environmentally friendly cooling solution for high-temperature sensitive scenarios.

[0047] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0048] Example 1 This embodiment provides a radiation cooling coating system with interlayer spectral synergy, which is sequentially disposed on the surface of substrate 1 from the inside to the outside, including: primer layer 2, main reflection functional layer 3 and spectral synergy enhancement layer 4; The specific preparation method includes the following steps: S1. Mix 20 parts water, 0.5 parts dispersant, 0.3 parts defoamer, 0.2 parts wetting agent, 1 part film-forming aid, 0.3 parts thickener, 15 parts rutile titanium dioxide (chlorination process), 10 parts kaolin, 15 parts 800-mesh heavy calcium carbonate, and 35 parts acrylic emulsion (solid content 40-50%) until homogeneous. Apply the mixture to a clean substrate 1 (aluminum plate) surface by spraying. The dry film thickness is 80μm. S2. Mix 20 parts water, 0.5 parts dispersant, 0.3 parts defoamer, 0.2 parts wetting agent, 1.2 parts film-forming aid, 0.3 parts thickener, 40 parts rutile titanium dioxide (chlorination process), and 35 parts acrylic emulsion (solid content 40-50%) evenly to prepare the main reflective functional layer coating. Spray the main reflective functional layer 3 onto the surface of the primer layer 2, with a dry film thickness of 90μm. S3. Using commercially available rutile TiO2 (particle size 220 nm) as the core, a BaSO4 coating layer with a shell thickness of 250 nm was prepared by the sol-gel method. The specific steps are as follows: TiO2@BaSO4 core-shell filler was prepared by sol-gel method: Rutile TiO2 particles were dispersed in ethanol aqueous solution, pH was adjusted to 9-10, BaCl2 solution and Na2SO4 solution were added dropwise, the reaction temperature was controlled at 50℃, the reaction was stirred for 2 hours, and the core-shell structured filler was obtained after centrifugation, washing and drying. Mix 20 parts water, 0.5 parts dispersant, 0.3 parts defoamer, 0.2 parts wetting agent, 0.6 parts film-forming aid, 0.2 parts thickener, 45 parts TiO2@BaSO4 core-shell filler, and 15 parts acrylic emulsion (solid content 40-50%) evenly to prepare a spectral synergistic enhancement layer coating. Spray the spectral synergistic enhancement layer 4 onto the surface of the main reflective functional layer 3, with a dry film thickness of 60μm.

[0049] Optical performance tests were performed on the complete coating system described above: Solar reflectance (TSR): The reflectance of the 300-2500nm spectrum was measured using an ultraviolet-visible-near-infrared spectrophotometer, and the calculated TSR = 0.972; Average reflectance in the ultraviolet band: The average reflectance was calculated in the 300-400nm band, R² = 0.901; Atmospheric window emissivity: The average emissivity in the 8-13 μm band was measured using a Fourier transform infrared spectrometer (FTIR), ε=0.951.

[0050] Example 2 This embodiment provides a radiation-cooling coating system with interlayer spectral synergy. The only difference from Embodiment 1 is that the shell of the second functional filler 41 is aluminum oxide. Other experimental parameters and conditions are basically the same as those in Embodiment 1, and will not be repeated here.

[0051] Example 3 This embodiment provides a radiation-cooling coating system with interlayer spectral synergy. Compared with Embodiment 1, the only difference is that the dry film thickness of the main reflection functional layer 3 is 80 μm and the dry film thickness of the spectral synergy enhancement layer 4 is 40 μm. Other experimental parameters and conditions are basically the same as those in Embodiment 1, and will not be repeated here.

[0052] Example 4 This embodiment provides a radiation-cooling coating system with interlayer spectral synergy. Compared with Embodiment 1, the only difference is that the dry film thickness of the main reflection functional layer 3 is 150 μm and the dry film thickness of the spectral synergy enhancement layer 4 is 80 μm. Other experimental parameters and conditions are basically the same as those in Embodiment 1, and will not be repeated here.

[0053] Example 5 This embodiment provides a radiation-cooling coating system with interlayer spectral synergy. Compared with Embodiment 1, the only difference is that the thickness of the BaSO4 shell is 30 nm. Other experimental parameters and conditions are basically the same as those in Embodiment 1, and will not be repeated here.

[0054] Example 6 This embodiment provides a radiation-cooling coating system with interlayer spectral synergy. Compared with Embodiment 1, the only difference is that the thickness of the BaSO4 shell is 300 nm. Other experimental parameters and conditions are basically the same as those in Embodiment 1, and will not be repeated here.

[0055] Comparative Example 1 Comparative Example 1 provides a radiation-cooling coating system with interlayer spectral synergy, which is a traditional single-layer (primer plus topcoat) full-band high-reflectivity coating. The specific preparation method includes the following steps: S1. Mix 20 parts water, 0.5 parts dispersant, 0.3 parts defoamer, 0.2 parts wetting agent, 1 part film-forming aid, 0.3 parts thickener, 15 parts rutile titanium dioxide (chlorination process), 10 parts kaolin, 15 parts 800-mesh heavy calcium carbonate, and 35 parts acrylic emulsion (solid content 40-50%) until homogeneous. Apply the mixture to a clean substrate (aluminum plate) using a spraying method. The dry film thickness is 80μm. S2. Mix 15 parts water, 0.5 parts dispersant, 0.3 parts defoamer, 0.2 parts wetting agent, 1 part film-forming aid, 0.3 parts thickener, 60 parts nano alumina (particle size 200nm), and 20 parts acrylic emulsion (solid content 40-50%) evenly to prepare the topcoat layer. Spray the topcoat layer onto the surface of the primer layer, and the dry film thickness is 100μm.

[0056] Comparative Example 2 Comparative Example 2 provides a radiation-cooling coating system with interlayer spectral synergy. Compared with Example 1, the only difference is that the main reflection functional layer 3 is not provided, and the dry film thickness of the spectral synergy enhancement layer 4 is 150 μm. Other experimental parameters and conditions are basically the same as those in Example 1, and will not be repeated here.

[0057] Comparative Example 3 Comparative Example 3 provides a radiation-cooling coating system with interlayer spectral synergy. Compared with Example 1, the only difference is that the spectral synergy enhancement layer 4 is not provided, and the dry film thickness of the main reflection functional layer 3 is 150 μm. Other experimental parameters and conditions are basically the same as those in Example 1, and will not be repeated here.

[0058] Comparative Example 4 Comparative Example 4 provides a radiation-cooling coating system with interlayer spectral synergy. The only difference from Example 1 is that the thickness of the BaSO4 shell is 350 nm. Other experimental parameters and conditions are basically the same as those in Example 1, and will not be repeated here.

[0059] Comparative Example 5 Comparative Example 5 provides a radiation-cooling coating system with interlayer spectral synergy. The only difference from Example 1 is that the thickness of the BaSO4 shell is 15 nm. Other experimental parameters and conditions are basically the same as those in Example 1, and will not be repeated here.

[0060] Comparative Example 6 Comparative Example 6 provides a radiation-cooling coating system with interlayer spectral synergy. The only difference from Example 1 is that the shell of the second functional filler 41 is silicon dioxide. Other experimental parameters and conditions are basically the same as those in Example 1, and will not be repeated here.

[0061] Table 1. Test results of the examples and comparative examples. Note: Reflectivity and emissivity were tested according to the test methods in GB / T25261-2018; Cooling effect test conditions: at noon in summer (solar irradiance 1000 W / m²). 2 Under ambient temperature of 35±2℃ and no wind, the coating was applied to the light-receiving surface of the aluminum plate, and the temperature difference between the surface of the coating and the surface of the uncoated aluminum plate was measured. The adhesion was tested according to the cross-cut test of GB / T 9286-2021. The artificial weathering resistance was tested according to GB / T 1865-2009, and the time when the coating did not chalk or crack was recorded.

[0062] As shown in Table 1, the interlayer spectral synergistic radiation cooling coating systems prepared in Examples 1-6 of this application are significantly superior to the comparative examples in terms of optical performance, cooling effect, and durability. Comparative Example 1 uses a traditional single-layer high-reflectivity coating with an R2 of only 0.807, while Comparative Example 3, without a spectral synergistic enhancement layer, has an R2 of only 0.101. This indicates that relying solely on a single-layer structure or increasing the amount of filler in the bottom layer cannot effectively compensate for the ultraviolet reflection shortcomings caused by the intrinsic bandgap absorption of TiO2. In contrast, the core-shell structure enhancement layer of this application significantly improves the ultraviolet reflection capability through the refractive index difference between the core and the shell and the multiple interface backscattering effects. Although Comparative Example 2 uses a core-shell structure filler alone but does not have a main reflection functional layer 3, its TSR is only 0.900, further demonstrating that only the interlayer synergistic architecture of the spectral synergistic enhancement layer 4 and the main reflection functional layer 3 can achieve a leapfrog breakthrough in full-band reflection performance. The cooling effect test results show that the cooling range of Examples 1-6 is 10.0℃~14.1℃, which is much better than that of Comparative Examples 1-3 (5.2℃~7.5℃), verifying the key role of the spectral synergistic enhancement layer in improving the actual radiative cooling performance.

[0063] Comparative data from Examples 1, 5, 6, and Comparative Examples 4-5 show that when the BaSO4 shell thickness is 30-300 nm, the average reflectance R2 of the coating in the 300-400 nm wavelength band can reach above 0.8, TSR ≥ 0.96, and the cooling effect ≥ 10.0 °C. When the shell thickness of Comparative Example 4 is further increased to 350 nm, although the optical performance is still acceptable, the excessively thick shell leads to increased surface roughness of the filler, increased brittleness of the coating layer, and a significant reduction in adhesion and durability. When the shell thickness of Comparative Example 5 is only 15 nm, due to the thin shell, an effective core-shell optical interface cannot be formed, R2 drops to 0.1, TSR drops to 0.93, and the cooling effect is only 6.6 °C. Comparative Example 6 uses SiO2 as the shell, and its performance is lower than that of Example 1 using a BaSO4 shell, confirming that BaSO4 is superior to SiO2 in terms of refractive index matching and ultraviolet scattering efficiency.

[0064] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A radiation-cooling coating system with interlayer spectral synergy, wherein the coating is sequentially disposed on the surface of a substrate from the inside out, characterized in that, include: Primer layer, main reflection functional layer and spectral synergistic enhancement layer; The primary reflective functional layer includes a first functional filler, which is selected from one or more of rutile titanium dioxide and barium sulfate. The average reflectivity R1 of the primary reflective functional layer in the 400~2500nm band is ≥0.

95. The spectral synergistic enhancement layer includes a second functional filler with a core-shell structure, wherein the core of the second functional filler is rutile titanium dioxide and the shell is alumina or barium sulfate; The radiation-cooling coating system has an average reflectance R2 ≥ 0.80 in the 300~400nm wavelength band, and the overall solar reflectance TSR of the radiation-cooling coating system is ≥ 0.

96.

2. The interlayer spectral synergistic radiation-cooling coating system according to claim 1, characterized in that, The dry film thickness of the main reflective functional layer is 80~150μm, and the dry film thickness of the spectral synergistic enhancement layer is 40~80μm.

3. The interlayer spectral synergistic radiation-cooling coating system according to claim 1, characterized in that, The core particle size of the second functional filler is 200~250nm, and the outer shell thickness is 30~300nm.

4. The interlayer spectral synergistic radiation-cooling coating system according to claim 1, characterized in that, The radiation-cooled coating system has an average emissivity ε≥0.94 in the 8~13μm atmospheric window.

5. A method for preparing a radiation-cooling coating system with interlayer spectral synergy as described in any one of claims 1-4, characterized in that, Includes the following steps: Apply a primer layer to the substrate surface; Prepare a primary reflective functional layer coating and apply the primary reflective functional layer to the surface of the primer layer; A spectral synergistic enhancement layer coating is prepared and a spectral synergistic enhancement layer is disposed on the surface of the main reflective functional layer.

6. The method for preparing the interlayer spectral synergistic radiation-cooling coating system according to claim 5, characterized in that, The main reflective functional layer coating comprises, by weight, 30-40 parts of acrylic emulsion, 30-40 parts of first functional filler, 0.5-3 parts of first additive, and 20-30 parts of water.

7. The method for preparing the interlayer spectral synergistic radiation-cooling coating system according to claim 6, characterized in that, The spectral synergistic enhancement layer coating comprises, by weight, 15-35 parts of acrylic emulsion, 40-60 parts of secondary functional filler, 0.5-3 parts of secondary additive, and 15-20 parts of water.

8. The method for preparing the interlayer spectral synergistic radiation-cooling coating system according to claim 7, characterized in that, The preparation method of the second functional filler is as follows: using rutile titanium dioxide particles as the core, aluminum oxide or barium sulfate is coated on the surface of the rutile titanium dioxide particles by sol-gel method.

9. The method for preparing the interlayer spectral synergistic radiation-cooling coating system according to claim 8, characterized in that, The first and second additives are each independently selected from one or more of the following: dispersants, wetting agents, defoamers, film-forming aids, thickeners, leveling agents, pH adjusters, fungicides, and antifreeze agents.

10. The application of the interlayer spectral synergistic radiation cooling coating system according to any one of claims 1-4 in building roofs, outdoor equipment or spacecraft ground equipment.

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