Preparation method of colored passive radiation cooling coating

Abstract

The invention discloses a preparation method of a colored passive radiation cooling coating, the colored passive radiation cooling coating is composed of a thermal radiation base layer and a colloid photonic crystal reflecting layer, monodisperse colloid particles are assembled on the surface of the thermal radiation base layer by means of spray coating, roll coating, brush coating or blade coating, and the colored passive radiation cooling coating is prepared. The preparation method is simple and easy to implement, high in compatibility and capable of achieving large-area construction. The prepared passive radiation cooling coating has high sunlight reflectivity and infrared thermal emissivity, shows excellent passive radiation cooling performance, and can greatly save refrigeration energy consumption. Meanwhile, the coating is stable and adjustable in appearance color, green and environment-friendly, can meet the color requirements of decoration, appreciation and the like, and has high commercial popularization value.

Description

Technical Field

[0001] The invention relates to a method for preparing a colored passive radiation cooling coating, and in particular to a method for preparing a passive radiation cooling coating capable of producing bright and stable structural colors. Background Art

[0002] The many negative effects caused by climate warming have become a major challenge facing mankind. In order to ensure the normal operation of human production and life, the global demand for refrigeration is growing rapidly. The commonly used cooling systems based on air compression require a lot of electricity and coolants. According to statistics, these cooling systems consume 15% of the world's electricity and emit 10% of the world's greenhouse gases, posing the threat of greenhouse effect and urban heat island effect. The development of passive radiation cooling materials makes it possible to achieve effective and environmentally friendly cooling. Passive radiation cooling coatings achieve efficient cooling based on the material's high reflectivity of incident sunlight (0.3-2.5 microns) and high thermal emission capabilities within the atmospheric window (8-13 microns).

[0003] In order to meet the requirements of high reflection of solar radiation, passive radiation cooling coatings are usually processed into white and metallic colors. These monotonous colors are difficult to meet the decorative and ornamental requirements of the application occasions, and even cause light pollution problems. In order to achieve colored passive radiation cooling coatings, the most commonly used solution is to introduce chemical coloring dyes into the cooling coating. For example, the article Science 2018, 362, 315-319 discloses a poly (vinylidene fluoride-hexafluoropropylene) (P (VDF-HFE)) passive daytime radiation cooling coating with a hierarchical porous structure. This work adds chemical coloring dyes during the coating construction process to achieve the design of a colored passive radiation cooling coating. However, the use of chemical dyes exacerbates the absorption of sunlight by the cooling coating, thereby weakening the cooling effect of the material. In addition, the problems of photooxidation and photobleaching of chemical dyes also need to be solved. The article Adv.Optical Mater.2018, 6, 1800707 discloses a colored passive radiation cooling coating based on a thin film optical resonator. The construction of this coating relies on the layer-by-layer deposition of precious metal-insulating materials, which often requires multiple steps to complete, has many restrictions, is time-consuming and labor-intensive, and the construction cost of the coating is high, which limits its further industrial development. The article Langmuir 2020, 36, 6589-6596 discloses a colloidal photonic crystal composed of tightly and orderly arranged monodispersed colloidal particles of uniform size. Through the effective regulation of the construction unit size, it can selectively reflect solar radiation while producing bright and stable structural colors. Coupled with its own low thermal conductivity, it shows great potential in the development of colored passive cooling materials. However, the colloidal photonic crystal material only achieves selective visible light reflection with a narrow band gap, the reflectivity of solar radiation is insufficient, the thermal emission performance is not prominent enough, and the passive radiation cooling effect is not good. Therefore, it is very urgent and of great significance to effectively make up for the defects of light reflectivity and thermal emission of colloidal photonic crystal materials and obtain a colored passive radiation cooling coating with stable and adjustable color and good cooling effect. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing a colored passive radiation cooling coating, wherein the passive radiation cooling coating prepared by the method has a bright and adjustable, stable green structural color and excellent cooling performance, and can be extended to daytime cooling of various substrate materials. The preparation method is simple and easy to operate, has strong compatibility, and is suitable for large-area construction, and is an effective strategy for developing passive radiation cooling coatings.

[0005] The present invention is mainly realized by the following technical scheme: a method for preparing a colored passive radiation cooling coating, and the specific steps are as follows:

[0006] a. Prepare a thermal radiation base precursor: measure and mix the components of polymer gel prepolymer, inorganic microspheres and curing agent, wherein the weight parts of each component are: 46-61 parts of polymer gel prepolymer, 30-47 parts of inorganic microspheres, and 6-14 parts of curing agent; wherein the polymer gel prepolymer is one of polydimethylsiloxane prepolymer, polyurethane prepolymer or epoxy resin prepolymer;

[0007] b. Coat the prepared thermal radiation base precursor on the substrate and allow it to stand for pre-curing. The thickness of the thermal radiation base is controlled at 0.3-0.7 mm;

[0008] c. Preparation of monodisperse colloidal particle dispersion: measure each component and stir and mix, the monodisperse colloidal particle dispersion is a mixture of water, monodisperse colloidal particles and aqueous polyurethane emulsion, wherein the mass ratio of water, monodisperse colloidal particles and aqueous polyurethane emulsion is 1:(0.40-0.60):(0.03-0.06);

[0009] d. The prepared monodisperse colloidal particle dispersion is coated on the surface of the pre-cured thermal radiation base layer, and further allowed to stand and cure. The monodisperse colloidal particles evaporate and self-assemble on the surface of the thermal radiation base layer to form a colloidal photonic crystal reflective layer with a stable structural color, thereby obtaining a colored passive radiation cooling coating, wherein the thickness of the colloidal photonic crystal reflective layer is controlled to be 0.18-0.30 mm.

[0010] Preferably, the inorganic microspheres described in step a are one or more of SiO2, SiC, Al2O3 or TiO2 inorganic microspheres; these inorganic microspheres have strong thermal emissivity in the atmospheric window band and can achieve effective thermal radiation; the particle size of the inorganic microspheres is 3-8 μm; the micrometer-scale inorganic microspheres can achieve effective reflection of near-infrared sunlight by relying on the Mie scattering of their own structure;

[0011] Preferably, the curing agent described in step a is a corresponding curing agent of the polymer gel prepolymer, wherein the curing agent of the polydimethylsiloxane prepolymer is diphenylbutyl carbamate; the curing agent of the polyurethane prepolymer is one of diisocyanate carbamate or diisocyanate urea; the curing agent of the epoxy resin prepolymer is one of ethylenediamine, hexamethylenediamine, diethylenetriamine or triethylenetetramine. The polymer gel prepolymer can be cross-linked and cured under the action of the corresponding curing agent.

[0012] Preferably, the stirring and mixing speed in step a is 200-400 rpm, and the stirring and mixing time is 40-90 min.

[0013] Preferably, the coating method in step b is one of rolling, brushing or scraping.

[0014] Preferably, the substrate in step b is one of a plastic board, a cement board, an iron sheet or a glass sheet; the pre-curing time is 0.2-2 hours, and the curing temperature is 25-50°C.

[0015] Preferably, the monodisperse colloidal particle dispersion described in step c has high monodispersity, and the particle aggregation index (PDI value) is 0.02-0.05; the monodisperse colloidal particles are one of carboxylated polymethyl methacrylate monodisperse colloidal particles, amino polymethyl methacrylate monodisperse colloidal particles, hydroxylated polymethyl methacrylate monodisperse colloidal particles, carboxylated polystyrene monodisperse colloidal particles, amino polystyrene monodisperse colloidal particles, hydroxylated polystyrene monodisperse colloidal particles or silica monodisperse colloidal particles, and the particle size of the monodisperse colloidal particles is 180-320nm; based on the Bragg diffraction law, by regulating the particle size of the monodisperse colloidal particles, the construction of a colloidal photonic crystal reflective layer with structural color covering the entire visible spectrum can be achieved;

[0016] Preferably, the solid content of the aqueous polyurethane emulsion in step c is 10-20%; the long-chain hydroxyl groups of the flexible polyurethane can establish hydrogen bonding interactions with the monodisperse colloidal particles, thereby enhancing the mechanical stability of the colloidal photonic crystal reflective layer;

[0017] The stirring and mixing speed in step c is 100-300 rpm, and the stirring and mixing time is 20-40 min.

[0018] Preferably, the coating method in step d is one of spraying, rolling, brushing or scraping.

[0019] Preferably, the curing time in step d is 4-8 hours and the curing temperature is 25-50°C.

[0020] The colored passive radiation cooling coating prepared by the present invention has stable and adjustable structural color, excellent passive radiation cooling performance, solar reflectivity of 0.87-0.93, infrared thermal emissivity of 0.91-0.97, and 600-1200W / m 2 Under simulated solar radiation, a temperature drop of 5-22°C below the substrate surface can be achieved.

[0021] Beneficial effects:

[0022] 1. The colored passive radiation cooling coating prepared by the present invention has a bright, stable and color-adjustable structural color. The color generated by the structure avoids the problems of photooxidation and photobleaching, and also avoids the environmental pollution caused by chemical coloring;

[0023] 2. The colored passive radiation cooling coating prepared by the present invention has high solar reflectivity and infrared thermal emittance, exhibits excellent passive radiation cooling performance, and can greatly save refrigeration energy consumption;

[0024] 3. The present invention provides a method for preparing a colored passive radiation cooling coating. The entire preparation process is simple to operate and has a wide range of applications. It can be applied to daytime cooling of a variety of substrate materials and is an effective method for constructing a large-area colored passive radiation cooling coating. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic diagram of the structure of a colored passive radiation cooling coating;

[0026] Figure 2 The optical image and normalized reflection spectrum of the colored passive radiation cooling coating prepared in Example 1;

[0027] Figure 3 The solar band reflectivity and infrared emissivity spectra of the colored passive radiation cooling coating prepared in Example 1;

[0028] Figure 4 The optical image and normalized reflection spectrum of the colored passive radiation cooling coating prepared in Example 2;

[0029] Figure 5 The optical image and normalized reflection spectrum of the colored passive radiation cooling coating prepared in Example 3;

[0030] Figure 6 The optical image and normalized reflection spectrum of the colored passive radiation cooling coating prepared in Example 4;

[0031] Figure 7 The temperature tracking curves of the prepared colored passive radiation cooling coating and the corresponding blank substrate in the passive radiation cooling test, wherein (a) is Example 1, (b) is Example 2, (c) is Example 3, and (d) is Example 4. DETAILED DESCRIPTION

[0032] The present invention is described below by means of specific embodiments, but the present invention is not limited to the following embodiments, which are only intended to provide a better understanding of the present invention rather than to limit the scope of protection of the present invention.

[0033] Example 1

[0034] Weigh 42g of polydimethylsiloxane prepolymer, 36g of SiO2 inorganic microspheres with a particle size of 5 microns and 12g of diphenylcarbamate in a 200mL beaker, stir and mix at a speed of 200rpm for 90min to prepare a thermal radiation base precursor; apply the prepared thermal radiation base precursor on the purchased cement board by scraping, and the thickness of the thermal radiation base is controlled to be 0.3mm; transfer the cement board coated with the thermal radiation base precursor into an oven at 25°C and pre-cure for 2 hours; weigh 4.4g of carboxylated polymethyl methacrylate monodisperse colloidal particles with a particle size of 180nm, 0.3g of aqueous polyurethane (quality 10g of monodisperse colloidal particle dispersion was prepared by mixing 10g of colloid (with a molar fraction of 10wt.%) and 10g of water in a 25mL beaker, stirring and mixing at a speed of 300rpm for 20min. The prepared monodisperse colloidal particle dispersion had a PDI value of 0.02. The prepared monodisperse colloidal particle dispersion was sprayed on the surface of the pre-cured thermal radiation base layer. The monodisperse colloidal particles volatilized and self-assembled on the surface of the thermal radiation base layer to form a colloidal photonic crystal reflective layer with stable structural color. The thickness of the colloidal photonic crystal reflective layer was controlled at 0.2mm. The coating was then transferred to a 25°C oven for curing for 8h to obtain a colored passive radiation cooling coating. The schematic diagram of its structure is shown in Figure (1). As shown in Figure (2), the coating exhibits a bright blue structural color with a reflection peak wavelength at 430nm. The obtained colored passive radiation cooling coating was tested for solar band reflectivity and atmospheric window thermal emissivity. As shown in Figure (3), the solar reflectivity of the coating was 0.87 and the infrared thermal emissivity was 0.91. At 1000W / m 2 Under simulated solar radiation, the coating was subjected to a passive radiation cooling test. The real-time temperature curve of the test is shown in Figure (7a). It can be seen from the figure that the colored passive radiation cooling coating can achieve a temperature drop of 22°C on the surface of the cement board.

[0035] Example 2

[0036] Weigh 12g of polydimethylsiloxane prepolymer, 10g of SiO2 inorganic microspheres with a particle size of 5 microns, 2g of SiC inorganic microspheres with a particle size of 8 microns and 2g of diphenylbutyl carbamate in a 50mL beaker, stir and mix at a speed of 360rpm for 50min to prepare a thermal radiation base precursor; apply the prepared thermal radiation base precursor on the purchased iron sheet by brushing, and the thickness of the thermal radiation base is controlled to be 0.35mm; transfer the iron sheet coated with the thermal radiation base precursor into an oven at 30℃ and pre-cure for 1.6 hours; weigh 5g of amino-modified polystyrene monodisperse colloidal particles with a particle size of 230nm, 0.5g of waterborne polyurethane (mass fraction of 15wt.%) and 10g of water were placed in a 25mL beaker and stirred at 250rpm for 30min to prepare a monodisperse colloidal particle dispersion. The PDI value of the prepared monodisperse colloidal particle dispersion was 0.027. The prepared monodisperse colloidal particle dispersion was brushed on the surface of the pre-cured thermal radiation base. The monodisperse colloidal particles volatilized and self-assembled on the surface of the thermal radiation base to form a colloidal photonic crystal reflective layer with stable structural color. The thickness of the colloidal photonic crystal reflective layer was controlled at 0.18mm. The coating was then transferred to a 30°C oven for curing for 6h to form a colored passive radiation cooling coating. As shown in Figure (4), the coating exhibited a bright green structural color with a reflection peak wavelength at 487nm. The obtained colored passive radiation cooling coating was tested for solar band reflectivity and atmospheric window thermal emissivity. The coating had a solar reflectivity of 0.91 and an infrared thermal emissivity of 0.95. At 1200W / m 2 Under simulated solar radiation, the coating was subjected to a passive radiation cooling test. The real-time temperature curve of the test is shown in Figure (7b). It can be seen from the figure that the colored passive radiation cooling coating can achieve a temperature drop of 14°C on the surface of the iron sheet.

[0037] Example 3

[0038] Weigh 20g of polyurethane prepolymer, 10g of TiO2 inorganic microspheres with a particle size of 7 microns and 3g of diisocyanate urethane in a 50mL beaker, stir and mix at a speed of 300rpm for 70min to prepare a thermal radiation base precursor; apply the prepared thermal radiation base precursor on the purchased glass sheet by roller coating, and the thickness of the thermal radiation base is controlled to be 0.47mm; transfer the glass sheet coated with the thermal radiation base precursor into an oven at 40℃ and pre-cure for 0.8h; weigh 6g of silica monodisperse colloidal particles with a particle size of 270nm, 0.5g of waterborne polyurethane (quality 10g of water (with a molar fraction of 20wt.%) and 10g of water were added to a 25mL beaker, and stirred at a speed of 180rpm for 40min to prepare a monodisperse colloidal particle dispersion. The PDI value of the prepared monodisperse colloidal particle dispersion was 0.034; the prepared monodisperse colloidal particle dispersion was roll-coated on the surface of the pre-cured thermal radiation base layer, and the monodisperse colloidal particles volatilized and self-assembled on the surface of the thermal radiation base layer to form a colloidal photonic crystal reflective layer with stable structural color. The thickness of the colloidal photonic crystal reflective layer was controlled at 0.26mm, and then transferred to a 40°C oven for curing for 4h to obtain a colored passive radiation cooling coating. As shown in Figure (5), the coating exhibits a bright orange structural color with a reflection peak wavelength at 580nm. The obtained colored passive radiation cooling coating was tested for solar band reflectivity and atmospheric window thermal emissivity. The coating had a solar reflectivity of 0.90 and an infrared thermal emissivity of 0.92. At 800W / m 2 Under simulated solar radiation, the coating was subjected to a passive radiation cooling test. The real-time temperature curve of the test is shown in Figure (7c). It can be seen from the figure that the colored passive radiation cooling coating can achieve a temperature drop of 9°C on the surface of the glass sheet.

[0039] Example 4

[0040] Weigh 35g of epoxy resin prepolymer, 20g of SiO2 inorganic microspheres with a particle size of 3 microns, 5g of Al2O3 inorganic microspheres with a particle size of 4 microns and 4g of triethylenetetramine in a 100mL beaker, stir and mix at a speed of 400rpm for 40min to prepare a thermal radiation base precursor; apply the prepared thermal radiation base precursor on the purchased plastic plate by scraping, and the thickness of the thermal radiation base is controlled to be 0.7mm; transfer the plastic plate coated with the thermal radiation base precursor into an oven at 50℃ and pre-cure for 0.2h; weigh 5.4g of carboxylated polystyrene monodisperse colloidal particles with a particle size of 320nm, 0 .6g of waterborne polyurethane (mass fraction of 10wt.%) and 10g of water were placed in a 25mL beaker and stirred at 100rpm for 40min to prepare a monodisperse colloidal particle dispersion. The PDI value of the prepared monodisperse colloidal particle dispersion was 0.050. The prepared monodisperse colloidal particle dispersion was scraped onto the surface of the pre-cured thermal radiation base layer. The monodisperse colloidal particles volatilized and self-assembled on the surface of the thermal radiation base layer to form a colloidal photonic crystal reflective layer with stable structural color. The thickness of the colloidal photonic crystal reflective layer was controlled at 0.30mm. The coating was then transferred to a 50℃ oven for curing for 4h to form a colored passive radiation cooling coating. As shown in Figure (6), the coating exhibited a bright red structural color with a reflection peak wavelength at 620nm. The obtained colored passive radiation cooling coating was tested for solar band reflectivity and atmospheric window thermal emissivity. The solar reflectivity of the coating was 0.93 and the infrared thermal emissivity was 0.97. At 600W / m 2 Under simulated solar radiation, the coating was subjected to a passive radiation cooling test. The real-time temperature curve of the test is shown in Figure (7d). It can be seen from the figure that the colored passive radiation cooling coating can achieve a temperature drop of 5°C on the surface of the plastic plate.

Claims

1. A method for preparing a colored passive radiation cooling coating, the specific steps of which are as follows: a. Prepare a thermal radiation base precursor: measure and mix the components of polymer gel prepolymer, inorganic microspheres and curing agent, wherein the weight parts of each component are: 46-61 parts of polymer gel prepolymer, 30-47 parts of inorganic microspheres, and 6-14 parts of curing agent; wherein the polymer gel prepolymer is one of polydimethylsiloxane prepolymer, polyurethane prepolymer or epoxy resin prepolymer; b. Coat the prepared thermal radiation base precursor on the substrate and allow it to stand for pre-curing. The thickness of the thermal radiation base is controlled at 0.3-0.7 mm; c. Preparation of monodisperse colloidal particle dispersion: measure each component and stir and mix, the monodisperse colloidal particle dispersion is a mixture of water, monodisperse colloidal particles and aqueous polyurethane emulsion, wherein the mass ratio of water, monodisperse colloidal particles and aqueous polyurethane emulsion is 1:(0.40-0.60):(0.03-0.06); d. The prepared monodisperse colloidal particle dispersion is coated on the surface of the pre-cured thermal radiation base layer, and further allowed to stand and cure. The monodisperse colloidal particles evaporate and self-assemble on the surface of the thermal radiation base layer to form a colloidal photonic crystal reflective layer with a stable structural color, thereby obtaining a colored passive radiation cooling coating, wherein the thickness of the colloidal photonic crystal reflective layer is controlled to be 0.18-0.30 mm.

2. The preparation method according to claim 1, characterized in that The inorganic microspheres described in step a are one or more of SiO2, SiC, Al2O3 or TiO2 inorganic microspheres; the particle size of the inorganic microspheres is 3-8 μm.

3. The preparation method according to claim 1, characterized in that The curing agent described in step a is the corresponding curing agent of the polymer gel prepolymer, wherein the curing agent of the polydimethylsiloxane prepolymer is diphenylbutyl carbamate; the curing agent of the polyurethane prepolymer is one of diisocyanate carbamate or diisocyanate urea; the curing agent of the epoxy resin prepolymer is one of ethylenediamine, hexamethylenediamine, diethylenetriamine or triethylenetetramine.

4. The preparation method according to claim 1, characterized in that The stirring and mixing in step a has a rotation speed of 200-400 rpm and a stirring and mixing time of 40-90 min.

5. The preparation method according to claim 1, characterized in that The coating method described in step b is one of rolling, brushing or scraping.

6. The preparation method according to claim 1, characterized in that The substrate described in step b is one of a plastic board, a cement board, an iron sheet or a glass sheet; the pre-curing time is 0.2-2 hours, and the curing temperature is 25-50°C.

7. The preparation method according to claim 1, characterized in that The PDI value of the monodisperse colloidal particle dispersion described in step c is 0.02-0.05; the monodisperse colloidal particles are one of carboxylated polymethyl methacrylate monodisperse colloidal particles, amino polymethyl methacrylate monodisperse colloidal particles, hydroxylated polymethyl methacrylate monodisperse colloidal particles, carboxylated polystyrene monodisperse colloidal particles, amino polystyrene monodisperse colloidal particles, hydroxylated polystyrene monodisperse colloidal particles or silica monodisperse colloidal particles, and the particle size of the monodisperse colloidal particles is 180-320nm.

8. The preparation method according to claim 1, characterized in that The mass solid content of the aqueous polyurethane emulsion described in step c is 10-20%; the stirring and mixing speed described in step c is 100-300rpm, and the stirring and mixing time is 20-40min.

9. The preparation method according to claim 1, characterized in that The coating method described in step d is one of spraying, rolling, brushing or scraping.

10. The preparation method according to claim 1, characterized in that The curing time in step d is 4-8 hours, and the curing temperature is 25-50°C.

Images