Preparation method of ultra-thin radiation refrigeration coating with enhanced heat dissipation

Abstract

The present application belongs to the field of functional coating and film technology, and proposes a preparation method of an ultra-thin radiation cooling coating with enhanced heat dissipation. The coating comprises 10 wt%-40 wt% zinc oxide, 10 wt%-40 wt% hollow glass microbeads and 20 wt%-80 wt% resin. By reasonably designing the coating structure, fully utilizing the high refractive index of zinc oxide and the multi-stage cavity structure of hollow glass microbeads, and combining the ideal inherent characteristics of the polymer itself, the ultra-thin cooling coating exhibits an ultra-high average solar reflectance of 0.92 and a long-wave infrared emissivity of 0.93 in the state of 100 mu m ultra-thin, while having a high thermal conductivity, thus simultaneously exhibiting excellent sub-environment and higher-than-environment temperature cooling performance. In addition, the coating has excellent optical performance, hiding power, weather resistance, universality and other advantages, and is a heat dissipation and cooling coating with practical application value.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of functional coating and film technology, and particularly relates to a super-thin radiation refrigeration coating with enhanced heat dissipation and a preparation method thereof. BACKGROUND

[0002] Daytime passive radiative cooling technology is a completely environmentally friendly refrigeration technology without any energy consumption, which realizes temperature reduction by reflecting sunlight and emitting its own heat, and is expected to reduce the pressure of traditional air conditioning refrigeration system. The various advanced passive radiative cooling materials reported at present exhibit excellent cooling performance, but these thin films / coatings all need to reach a sufficient thickness (300-800 pm) to meet the requirements of high reflectivity and emissivity, and obviously the excessively large thickness greatly limits the application range of passive radiative cooling materials.

[0003] For refrigeration in the self-heating scenario, the radiative cooling coating is required to have a high thermal conductivity so as to conduct the self-heat, and therefore, it is a great challenge to develop a super-thin high-thermal-conductivity radiative cooling material at present. SUMMARY

[0004] The present application aims to provide a super-thin radiation refrigeration coating with enhanced heat dissipation and a preparation method thereof.

[0005] The super-thin radiation refrigeration coating with enhanced heat dissipation provided by the present application has a raw material composition of zinc oxide, hollow glass microbeads and resin,

[0006] The zinc oxide is 10wt%-40wt%, the hollow glass microbeads are 10wt%-40wt%, and the rest is resin, and the total weight satisfies 100%.

[0007] In the present application, the diameter of the zinc oxide is 100-500 nm, the diameter of the hollow glass microbeads is 1-30 pm, and the hollow glass microbeads are mainly alkali lime borosilicate glass.

[0008] In the present application, the resin is solvent-based resin and water-soluble resin.

[0009] In the present application, the resin is any two of polydimethylsiloxane, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polymethyl methacrylate, water-based polyurethane, polyacrylate, epoxy resin or silicone resin.

[0010] The method for preparing the coating of the super-thin radiation refrigeration coating with enhanced heat dissipation provided by the present application has the following specific steps: (1) uniformly mixing the nano-zinc oxide and the hollow glass microbeads with the resin respectively to form a nano-zinc oxide-resin dispersion liquid and a hollow glass microbead-resin dispersion liquid;

[0011] (2), the nanometer zinc oxide-resin dispersion liquid is coated on the substrate first, and then the hollow glass microsphere-resin dispersion liquid is coated on the nanometer zinc oxide coating after drying, so as to form a double-layer coating, and if the coating is peeled off from the surface of the substrate, a corresponding film can be obtained;

[0012] The thickness of the obtained coating is 100 mu m, the average solar reflectivity is greater than or equal to 0.90, the long-wave infrared emissivity is greater than or equal to 0.90, and the thermal conductivity is greater than or equal to 1.5 W M m -1 K -1 At noon, the temperature of the silica gel heating plate is 2-9 DEG C lower than the ambient temperature. Compared with the traditional coating, the coating can reduce the temperature of the silica gel heating plate by 15-20 DEG C.

[0013] In the present application, the mixing method in step (1) is any one of magnetic stirring, mechanical stirring or ultrasonic; the film forming method in step (2) is any one of drop coating, spraying or spin coating; in step (2), the material of the substrate is any one of glass, wood, metal or plastic.

[0014] In the above preparation method, attention should be paid to avoiding damage to the first coating during the second coating, for example, the solvent-based resin can be selected for the first coating, and the water-soluble resin is used for the second coating, so that a clear double-layer structure can be formed. In addition, the viscosity, dispersibility and other properties of the resin should also be considered to ensure that the fillers can be uniformly dispersed therein, so that a uniform and smooth coating can be obtained.

[0015] The present application has the following beneficial effects:

[0016] According to the preparation method of the ultra-thin radiation cooling coating provided by the application, nano zinc oxide and hollow glass microspheres are uniformly mixed with resin respectively to form nano zinc oxide-resin dispersion liquid and hollow glass microsphere-resin dispersion liquid, the nano zinc oxide-resin dispersion liquid is coated on a substrate first, and then the hollow glass microsphere-resin dispersion liquid is coated on the nano zinc oxide coating after drying, so as to form a double-layer coating. The nano zinc oxide shows strong scattering to visible light, which is the result of the synergistic effect of size distribution and high refractive index (2.0); the hollow glass microspheres have a standard spherical structure and a symmetrical hollow structure, and the size distribution is very wide, which can effectively scatter ultraviolet and near-infrared light. In addition, the extinction coefficient of the polymer in the solar wave band can be ignored, so it is almost not heated by the sun, and there are multiple extinction peaks in the long-wave infrared region, which can effectively radiate heat to the ultra-cold outer space through the first atmospheric transparent window. Therefore, by combining the advantages of different scatterers and selecting a reasonable polymer, the prepared coating shows an ultra-high average solar reflectivity of 0.92 and a long-wave infrared emissivity of 0.93 at a thickness of 100 μm. The coating shows good cooling effect, and its own temperature is 2-9℃ lower than the ambient temperature at noon. In the presence of metal oxides and the ultra-thin characteristics, the coating has high thermal conductivity and shows excellent cooling capacity above the ambient temperature. Compared with the traditional coating, the coating can reduce the silicone heating plate by 15-20℃.

[0017] The application adopts a simple blending technology and a layered film forming method, combines the cheap and environmentally friendly nano zinc oxide and hollow glass microspheres to form a coating dispersion system through a unique structural design, and the coating has good coating performance on substrates such as glass, wood, metal and plastic. The prepared ultra-thin cooling coating has obvious advantages in whiteness, integrity and uniformity. Overall, the preparation process of the ultra-thin cooling coating is simple, convenient for large-scale preparation, and is expected to contribute to the protection of the earth's ecology. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 Fig. 1 is a scanning electron microscope photo of the cross section of the ultra-thin cooling film, hollow glass microspheres and nano zinc oxide in Example 1 of the application; wherein a is the cross section of the ultra-thin cooling film, b is the hollow glass microspheres, and c is the nano zinc oxide;

[0019] Figure 2 Fig. 2 is a macro photo of the ultra-thin cooling coating in Example 1 of the application;

[0020] Figure 3 Fig. 3 is the solar reflectance spectrum and long-wave infrared emission spectrum of the ultra-thin cooling coating in Example 1 of the application; wherein a is the solar reflectance spectrum, and b is the long-wave infrared emission spectrum;

[0021] Figure 4 Thermal conductivity of the ultra-thin refrigeration coating in Example 1 of the present application at different temperatures;

[0022] Figure 5 Ambient temperature tracking curve of the ultra-thin refrigeration coating in Example 1 of the present application;

[0023] Figure 6 Temperature tracking curve of the silica gel heating plate covered with the ultra-thin refrigeration coating and the traditional coating in Example 1 of the present application in indoor and outdoor environments; wherein: a is the temperature change curve of the silica gel heating plate covered with the ultra-thin refrigeration coating and the traditional coating under the condition of no direct sunlight, and b is the temperature change curve of the silica gel heating plate covered with the ultra-thin refrigeration coating and the traditional coating under the condition of direct sunlight. DETAILED DESCRIPTION

[0024] In order to make the technical means, creative features, purposes and effects achieved by the present application easy to understand, the following will specifically describe a kind of ultra-thin radiation refrigeration coating for enhancing heat dissipation, a kind of coating and a preparation method thereof according to the embodiments and the drawings.

[0025] The methods in the embodiments of the present application are all conventional methods unless otherwise specified, and the raw materials in the embodiments of the present application can be obtained from public commercial channels unless otherwise specified.

[0026] Example 1:

[0027] First, 0.25 g of polyvinylidene fluoride-hexafluoropropylene copolymer (P(VdF-HFP)) was dissolved in 8 g of N,N-dimethylformamide to form a uniform transparent solution, then 1 g of nano-zinc oxide was added to the solution and magnetically stirred at room temperature for 2 h. The obtained 1.75 mL of zinc oxide dispersion solution was drop-coated on glass (5 cm*5 cm), and then dried at 60°C. In addition, a suitable coating method and base layer can also be selected according to the actual situation. Secondly, 0.3 g of hollow glass microspheres and 0.25 g of waterborne polyurethane (WPU) were uniformly dispersed in 2 g of deionized water, and magnetically stirred at room temperature for 2 h. 0.45 mL of hollow glass microsphere dispersion solution was drop-coated on the P(VdF-HFP)-nano-zinc oxide coating. Finally, the obtained ultra-thin coating was dried at 60°C for 1 hour.

[0028] A heat reduction test device was built using heat-insulating polystyrene foam, and the surface was covered with high-reflective aluminum foil to reflect sunlight. The sample film for heat reduction test was 5 cm*5 cm in size, and was placed in a 5 cm deep groove in the center of the incubator. A temperature probe was closely attached to the back of the sample to monitor the temperature change of the film, and another probe was placed in the same heat-insulating box to monitor the change of the ambient temperature, and one point was recorded every 30 s.

[0029] Figure 1 a is a scanning electron microscope photo of the cross section of the ultra-thin refrigeration film in Example 1 of the present application, b and c are scanning electron microscope photos of hollow glass microspheres and nano-zinc oxide, respectively.

[0030] As shown in Figure 1 , a clear double-layer structure can be observed, in which the top layer is composed of polymer and hollow glass microspheres, and the lower layer is composed of polymer and nano-zinc oxide, and the thickness is only 100 μm. The hollow glass microspheres have a standard spherical structure and a symmetrical hollow structure, and the size is mainly distributed between 6-15 μm; the nano-zinc oxide presents a cubic structure, and the size is mainly distributed between 200-650 nm.

[0031] Figure 2 is a macroscopic photo of large-scale preparation of the ultra-thin refrigeration coating in Example 1 of the present application, which presents a super-white appearance, and has good hiding power, flowability, film-forming property, universality, etc.

[0032] Figure 3 a describes the reflectance spectrum of the ultra-thin refrigeration coating in the solar wave band (0.3-2.5 μm), and the average solar reflectance is as high as ~0.92, Figure 3 b describes the infrared emissivity spectrum of the ultra-thin refrigeration coating in 3-15 μm, and the long-wave infrared (8-13 μm) emissivity can reach ~0.93. Due to the high reflectivity and high emissivity, the coating hardly absorbs the heat of the sunlight, and at the same time, it can emit its own heat through the atmospheric transparent window to the cold outer space, which meets the basic optical requirements of passive radiation cooling during the day.

[0033] Figure 4 is the overall thermal conductivity of the ultra-thin refrigeration coating at different temperatures, and the coating shows a stable high thermal conductivity of ~1.72 W m -1 K -1 at different temperatures (20-70℃), which indicates that the coating can conduct the heat below to the outside, and is suitable for cooling the scene higher than the ambient temperature.

[0034] Figure 5 is the temperature tracking curve of the ultra-thin refrigeration coating and the environment in Example 1, and the coating is averagely 8.1℃ lower than the ambient temperature during 11:00-14:00, which indicates that the coating has obvious cooling effect for the scene lower than the ambient temperature.

[0035] Figure 6 The temperature tracking curves of the silica gel heating plate coated with the ultra-thin refrigeration coating and the traditional coating are compared, and the silica gel heating plate coated with the ultra-thin refrigeration coating is 7.6℃ lower than that coated with the traditional coating under no solar irradiance, and the maximum solar irradiance is 960 W m -2The ultra-thin cooling coating reduced the temperature of the silicone heating plate by 18.1°C compared to the traditional coating, indicating that the coating also has a significant cooling effect in scenarios with temperatures higher than the ambient temperature, greatly expanding the application range of the coating.

[0036] Example 2:

[0037] The experimental setup and operation were the same as in Example 1. First, 0.25g of polydimethylsiloxane (PDMS) was dissolved in 5g of toluene to form a uniform and transparent solution. Then, 1g of nano-zinc oxide was added to the solution, and the mixture was magnetically stirred for 2 hours at room temperature. The resulting zinc oxide dispersion was sprayed onto glass / metal / wood (5cm*5cm) and then dried at 60°C. Next, 0.3g of hollow glass microspheres and 0.25g of waterborne polyurethane (WPU) were uniformly dispersed in 2g of deionized water, and the mixture was magnetically stirred for 2 hours at room temperature. The hollow glass microsphere dispersion was then sprayed onto the PDMS-nano-zinc oxide coating. Finally, the resulting ultrathin coating was dried at 60°C for 1 hour. The methods for testing sample temperature and ambient temperature were the same as in Example 1.

[0038] Example 3:

[0039] The experimental setup and operation were the same as in Example 1. First, 0.25g of polymethyl methacrylate (PMMA) and 1g of nano-zinc oxide were dissolved in 8g of acetone and magnetically stirred at 45°C for 2 hours to form a nano-zinc oxide dispersion. The obtained zinc oxide dispersion was spin-coated onto glass / metal / wood (5cm*5cm) and then dried at room temperature. Next, 0.3g of hollow glass microspheres and 0.25g of waterborne polyurethane (WPU) were uniformly dispersed in 2g of deionized water and magnetically stirred at room temperature for 2 hours. The hollow glass microsphere dispersion was spin-coated onto a PDMS-nano-zinc oxide coating. Finally, the resulting ultrathin coating was dried at 60°C for 1 hour. The methods for testing sample temperature and ambient temperature were the same as in Example 1.

[0040] The function and effect of this embodiment:

[0041] According to embodiments of the present invention, an ultrathin radiative cooling coating for enhanced heat dissipation and a double-layer coating are provided. The nano-zinc oxide exhibits strong scattering of visible light, a result of the synergistic effect of its size distribution and high refractive index (2.0). The hollow glass microspheres possess a standard spherical structure and a symmetrical hollow structure, with a very wide size distribution, effectively scattering ultraviolet and near-infrared light. Furthermore, since the polymer's extinction coefficient is negligible in the solar wavelength range, it is hardly heated by the sun, while exhibiting multiple extinction peaks in the long-wave infrared region, effectively radiating heat to the ultracool outer space through the first atmospheric transparency window. Therefore, by combining the advantages of different scatterers and selecting a suitable polymer, the prepared coating, at a thickness of 100 μm, exhibits an ultra-high average solar reflectance of 0.92 and a long-wave infrared emissivity of 0.93. This coating demonstrates excellent cooling effects, with its temperature at noon being 2°C to 9°C lower than the ambient temperature. In the presence of metal oxides and its ultra-thin properties, this coating exhibits high thermal conductivity and demonstrates excellent cooling capacity above ambient temperature. Compared to traditional coatings, this coating can lower the temperature of a silicone heating plate by 15°C to 20°C. This invention employs a simple blending technique and a layered film-forming method. Through a unique structural design, it combines inexpensive and environmentally friendly nano-zinc oxide and hollow glass microspheres to form a coating dispersion system. This coating exhibits good coating performance on substrates such as glass, wood, metal, and plastic. The resulting ultra-thin cooling coating shows significant advantages in whiteness, integrity, and uniformity. Overall, the preparation process of this ultra-thin cooling coating is simple and convenient for large-scale production, and it is expected to contribute to the protection of the Earth's ecology.

[0042] The above embodiments are preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention.

Claims

1. A method for preparing an ultrathin radiation-cooling coating to enhance heat dissipation, characterized in that... The ultrathin radiative cooling coating is composed of zinc oxide, hollow glass microspheres, and resin. Zinc oxide is 10 wt% - 40 wt%; Hollow glass microspheres: 10 wt% - 40 wt%; The remainder is resin, and its total weight is 100%. The specific steps are as follows: (1) Nano zinc oxide and hollow glass microspheres are mixed with resin to form nano zinc oxide-resin dispersion and hollow glass microsphere-resin dispersion, respectively. (2) First, the nano zinc oxide-resin dispersion is coated on the substrate. After drying, the hollow glass microspheres-resin dispersion is coated on the nano zinc oxide coating to form a double coating. If the coating is peeled off from the substrate surface, the corresponding film can be obtained. The resulting coating has a thickness of 100 μm, an average solar reflectance ≥0.90, a long-wave infrared emissivity ≥0.90, and a thermal conductivity ≥1.5 W / m². -1 K -1 At noon, its own temperature is 2℃ to 9℃ lower than the ambient temperature.

2. The method for preparing an ultrathin radiative cooling coating to enhance heat dissipation according to claim 1, characterized in that: The zinc oxide has a diameter of 100-500 nm, and the hollow glass microspheres have a diameter of 1-30 μm, with the main component being soda lime borosilicate glass.

3. The method for preparing an ultrathin radiative cooling coating to enhance heat dissipation according to claim 1, characterized in that: The resin is a solvent-based resin or a water-soluble resin.

4. The method for preparing an ultrathin radiative cooling coating to enhance heat dissipation according to claim 3, characterized in that: The resin is any two of the following: polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polymethyl methacrylate, waterborne polyurethane, polyacrylate, epoxy resin, or silicone resin.

5. The method for preparing an ultrathin radiative cooling coating to enhance heat dissipation according to claim 1, characterized in that... The mixing method in step (1) is any one of magnetic stirring, mechanical stirring or ultrasonication; the film forming method in step (2) is any one of drop coating, spray coating or spin coating; in step (2), the substrate material is any one of glass, wood, metal or plastic.

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