Radiative cooling element and method of making the same

Abstract

Disclosed are a radiative cooling element and a method of manufacturing the same. The radiative cooling element according to an embodiment of the present application includes a reflection layer that reflects sunlight having a wavelength in the ultraviolet, visible, and near-infrared regions, and a radiative cooling layer that is formed on the reflection layer to absorb sunlight having a wavelength in the mid-infrared region and radiate the same as heat. The radiative cooling layer can include a first radiative layer including a concave-convex pattern, and a second radiative layer formed on the first radiative layer and having a different refractive index from the first radiative layer.

Description

[0001] Related divisional application

[0002] This application is a divisional application of Chinese invention patent application (application number: 202080003155.4, application date: October 14, 2020, invention title: radiative cooling element and method of manufacturing thereof). Technical Field

[0003] This invention relates to a radiative cooling element and its manufacturing method. Background Technology

[0004] Generally speaking, cooling requires energy. Common cooling devices such as refrigerators and air conditioners use energy to compress the refrigerant and then absorb the heat generated when the refrigerant expands during compression to achieve cooling. In contrast, radiant cooling is a technology that can perform cooling without consuming energy.

[0005] In order to achieve radiative cooling, the absorption, reflection, and radiation of light in each wavelength band must be carefully controlled.

[0006] In most cases, the heat source is incoming sunlight, and the heat of sunlight is distributed in the UV-visible-near-infrared band. By reflecting light in this band, heat can be prevented from flowing in through sunlight.

[0007] If a material has a reflectivity of 100% in the UV-visible-near-infrared band, it means that it can reflect 100% of the incoming sunlight without any absorption.

[0008] For example, in bright sunlight, the interior temperature of a black car, which absorbs light easily, tends to rise. In contrast, the interior temperature of a white car, which does not absorb light and reflects it more readily, rises relatively slowly.

[0009] If the surface of a car reflects all light in the UV-visible-near-infrared bands, it can prevent heat energy from solar energy from flowing in.

[0010] All objects radiate heat to the outside in the form of light, and the wavelength of the emitted light depends on the surface temperature of the object.

[0011] The reason the sun radiates light in the UV-visible-near-infrared band to the outside is that the sun's surface temperature is 6000℃.

[0012] Objects with a surface temperature of tens of degrees Celsius emit mid-infrared light (wavelength from a few to tens of micrometers) to the outside.

[0013] If the surface of an object is coated with a material that suppresses or re-reflects mid-infrared radiation, heat loss due to mid-infrared radiation is reduced, thus providing a heat-insulating effect.

[0014] The Earth's atmosphere contains water vapor and carbon dioxide, which absorb some of the mid-infrared wavelengths emitted by the Earth, thus suppressing radiation.

[0015] However, the mid-infrared radiation in the 8 to 13 micrometer band, commonly known as the sky window, is not absorbed by the Earth's atmosphere, hence the name sky window. Furthermore, infrared radiation in this band is not absorbed by the atmosphere but is emitted into outer space.

[0016] If the wavelength band reflects all incoming sunlight (radiated from the sun) as UV-visible-near-infrared rays and can effectively radiate mid-infrared rays in the 8-13μm region of the sky window to the outside, then the material can be cooled without consuming energy by maximizing the release of heat while preventing heat inflow.

[0017] The reflective material used for sunlight is metal, which is transparent to sunlight and is a material that can radiate long-wavelength infrared rays very well. Therefore, the exterior of almost all radiative cooling components has the same color as the metal mirror.

[0018] The color of these metallic mirrors and similar materials could be a drawback in the application of radiation cooling materials.

[0019] Radiative cooling elements can reduce the energy burden required for cooling by being used in automobiles, buildings, and containers. Since colors are limited to those of metallic mirrors, there is an urgent need for a radiative cooling element that can achieve the same cooling performance but with different colors. Summary of the Invention

[0020] Technical issues

[0021] The purpose of embodiments of the present invention is to provide a radiative cooling element and a method for manufacturing the same, wherein the surface area of ​​the radiative cooling layer is increased by including a raised or recessed pattern, thereby increasing the mid-infrared emissivity and thus significantly improving the cooling efficiency of the radiative cooling element.

[0022] The purpose of embodiments of the present invention is to provide a radiative cooling element and a method for manufacturing the same, wherein the element and the method thereof can increase the mid-infrared emissivity by forming a radiative cooling layer from oxides, nitrides or polymers capable of radiating mid-infrared rays, thereby improving the cooling efficiency of the radiative cooling element.

[0023] The purpose of embodiments of the present invention is to provide a radiation cooling element and a method for manufacturing the same, wherein the element and the method thereof can increase mid-infrared emissivity and improve the cooling efficiency of the radiation cooling element by forming a radiation cooling layer composed of fine particles, polymers or mixtures thereof made of oxides or nitrides.

[0024] The purpose of embodiments of the present invention is to provide a radiative cooling element and a method thereof, which maximizes the reflectivity of visible light by forming a radiative cooling layer made of a material having a high refractive index and a low refractive index for visible light, thereby improving the cooling efficiency of the radiative cooling element.

[0025] The purpose of embodiments of the present invention is to provide a radiation cooling element that can reflect and scatter visible light onto a white radiation cooling layer, and the radiation cooling element may be white by also containing fine particles including metal oxides or polymers.

[0026] The purpose of embodiments of the present invention is to provide a white radiative cooling element that reflects all incoming sunlight to improve cooling performance.

[0027] The purpose of embodiments of the present invention is to provide a white radiative cooling element that, because it contains a white radiative cooling layer comprising a polymer matrix and fine polymer particles, is easy to mass-produce, has low manufacturing costs, and can adjust various physical properties.

[0028] The purpose of embodiments of the present invention is to provide a white radiative cooling element that improves visible light reflectivity by including a reflectance enhancement layer beneath the white radiative cooling layer, thereby enhancing cooling performance.

[0029] The purpose of embodiments of the present invention is to provide a white radiation cooling element that, through a white radiation cooling layer containing fluorescent particles, can not only display white, but also various colors.

[0030] Technical solution

[0031] According to an embodiment of the present invention, a radiative cooling element is characterized in that it comprises: a reflective layer that reflects sunlight having wavelengths in the ultraviolet, visible, and near-infrared regions; and a radiative cooling layer formed on the reflective layer that absorbs sunlight having wavelengths in the mid-infrared region and radiates it as heat, wherein the radiative cooling layer may comprise: a first radiative layer comprising a raised or recessed pattern; and a second radiative layer formed on the first radiative layer and having a refractive index different from that of the first radiative layer.

[0032] According to an embodiment of the present invention, the first radiation layer and the second radiation layer of the radiation cooling layer can be repeatedly formed.

[0033] According to an embodiment of the present invention, the reflective layer of the radiative cooling element may include at least one of silver (Ag), aluminum (Al), and platinum (Pt). According to an embodiment of the present invention, the first radiative layer and the second radiative layer may include at least one of fine particles composed of oxides or nitrides and a polymeric material.

[0034] According to an embodiment of the present invention, the diameter of the fine particles in the radiative cooling element can be from 10 nm to 20 μm.

[0035] According to embodiments of the present invention, the fine particles in the radiative cooling element may include at least one of silicon dioxide (SiO2), zirconium oxide (ZrO2), aluminum oxide (Al2O3), titanium dioxide (TiO2), and silicon nitride (Si3N4).

[0036] According to embodiments of the present invention, the polymer material in the radiative cooling element may be PDMS (polydimethylsiloxane) or DPHA (dipentaerythritol penta / hexa acrylate).

[0037] According to an embodiment of the present invention, the thickness of the first radiating layer and the second radiating layer can be from 10 nm to 2,000 nm, respectively.

[0038] According to an embodiment of the present invention, the radiative cooling element may include: a mid-infrared absorption layer formed on a reflective layer, which absorbs sunlight with wavelengths in the mid-infrared region and radiates it as heat; and coatings, wherein a first coating and a second coating are formed on the mid-infrared absorption layer and have different refractive indices for sunlight with wavelengths in the visible light region, wherein the first coating may have a larger refractive index than the second coating for sunlight with wavelengths in the visible light region.

[0039] According to an embodiment of the present invention, the coating of the radiative cooling element can reflect sunlight with wavelengths in the visible light region.

[0040] According to an embodiment of the present invention, the coating can be repeatedly formed into the first coating and the second coating.

[0041] According to an embodiment of the present invention, the refractive index difference between the first coating and the second coating can be 0.7 to 2.

[0042] According to an embodiment of the present invention, the first coating may include at least one of ZnS, Si and Ge, and the second coating may include CaF2.

[0043] The method for manufacturing a radiative cooling element according to the present invention is characterized by comprising: a step of forming a reflective layer on a substrate capable of reflecting sunlight with wavelengths having ultraviolet, visible, and near-infrared regions; and a step of forming a radiative cooling layer on the reflective layer capable of absorbing sunlight with wavelengths having mid-infrared regions and radiating it as heat, wherein the step of forming the radiative cooling layer may include: a step of forming a first radiative layer including a raised or recessed pattern on the reflective layer; and a step of forming a second radiative layer on the first radiative layer having a refractive index different from that of the first radiative layer.

[0044] According to the method for manufacturing a radiative cooling element of the present invention, the first radiative layer and the second radiative layer of the radiative cooling layer can be repeatedly formed on the reflective layer.

[0045] According to the method for manufacturing a radiative cooling element of the present invention, after the first radiative layer is coated on the reflective layer with at least one of fine particles made of oxides or nitrides and a polymer, it can be patterned by a die.

[0046] According to the method for manufacturing a radiative cooling element of the present invention, the second radiative layer can be formed by spin-coating at least one of fine particles made of oxides or nitrides and a polymeric substance onto a substrate.

[0047] According to the method for manufacturing a radiative cooling element of the present invention, the spin coating can be performed for 30 to 40 seconds.

[0048] According to an embodiment of the present invention, a method for manufacturing a radiative cooling element includes the step of forming the radiative cooling layer, comprising: forming a mid-infrared absorbing layer on the reflective layer that absorbs sunlight with wavelengths in the mid-infrared region and radiates it as heat; and forming a coating on the mid-infrared absorbing layer that has different refractive indices for sunlight with wavelengths in the visible light region, wherein the coating forming step is a process of forming a first coating and a second coating with different refractive indices for sunlight with wavelengths in the visible light region on the mid-infrared absorbing layer, and the first coating may have a larger refractive index for sunlight with wavelengths in the visible light region than the second coating.

[0049] According to the method for manufacturing a radiative cooling element according to an embodiment of the present invention, the coating can be repeatedly formed into the first coating and the second coating.

[0050] A white radiative cooling element according to an embodiment of the present invention is characterized in that it comprises: a substrate; and a white radiative cooling layer formed on the substrate, wherein metal oxide particles containing sunlight of wavelengths having a visible light region and fluorescent particles that radiate fluorescence are mixed within a polymer matrix that absorbs sunlight of wavelengths having a mid-infrared region and then radiates it as heat, wherein the white radiative cooling layer absorbs sunlight of wavelengths having a mid-infrared region and radiates it as heat, while simultaneously reflecting and scattering sunlight of wavelengths having a visible light region.

[0051] According to an embodiment of the present invention, the white radiative cooling element appears white by reflecting and scattering sunlight with wavelengths in the visible light region through fine particles of the metal oxide contained in the white radiative cooling layer.

[0052] According to an embodiment of the present invention, a white radiative cooling element comprising a polymer matrix and fine particles of the polymer having different refractive indices, and the white radiative cooling layer is white by the reflection and scattering of sunlight with wavelengths in the visible light region by the fine particles of the polymer contained in the white radiative cooling layer.

[0053] According to embodiments of the present invention, the white radiative cooling element may include at least one of PDMS (polydimethylsiloxane), PMMA (polymethyl methacrylate), DPHA (dipentaerythritolpenta / hexa acrylate), PVDF (polyvinylidene fluoride), and PUA (polyurethane acrylate).

[0054] According to an embodiment of the present invention, the white radiative cooling element may be at least one of titanium dioxide (TiO2), zirconium oxide (ZrO2), aluminum oxide (Al2O3), and zinc oxide (ZnO).

[0055] According to an embodiment of the present invention, the white radiative cooling element may be at least one of PVDF (polyvinylidene fluoride) and PUA (polyurethane acrylate).

[0056] According to an embodiment of the present invention, the white radiative cooling element may further include a reflection enhancement layer, which further reflects sunlight with wavelengths in the visible light region below the white radiative cooling layer.

[0057] According to an embodiment of the present invention, the white radiative cooling element may further include at least one of silver (Ag), aluminum (Al) and platinum (Pt) in its reflection enhancement layer.

[0058] According to an embodiment of the present invention, the white radiation cooling element, wherein the reflection enhancement layer and the white radiation cooling layer can be repeatedly formed.

[0059] A white radiative cooling element according to an embodiment of the present invention is characterized in that it comprises: a substrate; and a white radiative cooling layer formed on the substrate, wherein metal oxide particles containing sunlight with wavelengths having a visible light region and fluorescent particles that radiate fluorescence are mixed in a polymer matrix that absorbs sunlight with wavelengths having a mid-infrared region and then radiates it as heat, wherein the white radiative cooling layer absorbs sunlight with wavelengths having a mid-infrared region and radiates it as heat, while simultaneously reflecting and scattering sunlight with wavelengths having a visible light region.

[0060] Invention Effects

[0061] According to an embodiment of the present invention, the surface area of ​​the radiative cooling layer is increased due to the inclusion of a raised or recessed pattern, thereby increasing the mid-infrared emissivity and thus significantly improving the cooling efficiency of the radiative cooling element.

[0062] According to embodiments of the present invention, the mid-infrared emissivity is increased by forming a radiative cooling layer with oxides, nitrides, or polymers capable of radiating mid-infrared rays, and the cooling efficiency of the radiative cooling element can be improved.

[0063] According to embodiments of the present invention, the mid-infrared emissivity is increased and the cooling efficiency of the radiative cooling element is improved by forming a radiative cooling layer composed of fine particles, polymers, or mixtures thereof made of oxides or nitrides.

[0064] According to embodiments of the present invention, the reflectivity of visible light is maximized by forming a radiation cooling layer made of a material having a high refractive index and a low refractive index for visible light, thereby improving the cooling efficiency of the radiation cooling element.

[0065] According to embodiments of the present invention, visible light can be reflected and scattered onto a white radiative cooling layer, and the radiative cooling element is white by also containing fine particles including metal oxides or polymers.

[0066] According to an embodiment of the invention, all incoming sunlight is reflected to improve cooling performance.

[0067] According to embodiments of the present invention, because the white radiation cooling layer comprising a polymer matrix and fine polymer particles is easy to mass-produce and has low manufacturing cost, various physical properties can also be adjusted.

[0068] According to an embodiment of the present invention, the reflectivity of visible light is improved by including a reflectance enhancement layer below the white radiation cooling layer, thereby improving the cooling performance.

[0069] According to embodiments of the present invention, a white radiation cooling layer containing fluorescent particles can not only display white, but also various colors. Attached Figure Description

[0070] Figure 1a and Figure 1b This is a cross-sectional view showing the specific state of the radiative cooling element according to an embodiment of the present invention.

[0071] Figure 2a and Figure 2b This is a cross-sectional view showing the specific state of a radiative cooling element according to another embodiment of the present invention.

[0072] Figure 3 This is a flowchart illustrating a method for manufacturing a radiative cooling element according to an embodiment of the present invention.

[0073] Figure 4 This is a flowchart illustrating a method for manufacturing a radiative cooling element according to another embodiment of the present invention.

[0074] Figure 5 This is a graph showing the absorption rate depending on whether the first and second radiative layers are repeatedly laminated, according to embodiments and comparative examples of the present invention.

[0075] Figure 6 This is a graph showing the absorptivity and emissivity of the radiative cooling element according to the second embodiment of the present invention.

[0076] Figure 7 This is a graph showing the temperature of the radiative cooling element during each time period of daytime in Embodiment 2 of the present invention, based on the amount of sunlight.

[0077] Figure 8 It is a graph showing the absorptivity and emissivity of the radiative cooling element according to Embodiment 3-1 of the present invention.

[0078] Figure 9 This is a graph showing the external temperature of the radiative cooling element of Embodiment 3-1 and Comparative Example 2 of the present invention during each time period of the day, based on the amount of sunlight.

[0079] Figure 10 This is a graph showing the temperature of the radiative cooling element during each time period at night for Embodiments 3-1, 3-2, and Comparative Example 2 of the present invention.

[0080] Figure 11 This is a graph showing the absorbance of the radiative cooling elements of Embodiments 4-1, 4-2 and Comparative Example 3 of the present invention.

[0081] Figure 12 It is a graph showing the temperature of the radiative cooling element and the external temperature during each daytime period according to Embodiments 4-1 and 4-2 of the present invention.

[0082] Figure 13 This is a graph showing the temperature of the radiative cooling element and the external temperature during each nighttime period according to Embodiments 4-1 and 4-2 of the present invention.

[0083] Figures 14a to 14c It is a SEM (scanning electron spectroscopy) image showing a cross-section of the radiative cooling element according to Embodiment 5 of the present invention.

[0084] Figure 15 This is a graph showing the absorption rate of the radiative cooling element according to the DPHA content of Embodiment 5 of the present invention.

[0085] Figure 16 This is a graph showing the temperature of the radiative cooling element during various observation periods based on the amount of sunlight, according to Embodiment 5 of the present invention.

[0086] Figure 17 This is a graph showing the absorption rate of the radiative cooling element according to the fine particle content of the embodiment 6-1 according to the present invention.

[0087] Figure 18 This is a graph showing the absorption rate of the radiative cooling element according to the fine particle diameter of the embodiment 6-2 according to the present invention.

[0088] Figure 19 It is a graph showing the solar radiation according to the temperature based on the fine particle content of the radiative cooling element according to Embodiment 5 of the present invention.

[0089] Figure 20 This is a graph showing the absorption rate depending on the presence or absence of the embossed pattern according to Embodiment 7 and Comparative Example 4 of the present invention.

[0090] Figure 21 This is a graph showing the mid-infrared emissivity of the radiative cooling elements of Embodiment 8, Comparative Example 5-1, and Comparative Example 5-2 of the present invention.

[0091] Figures 22a to 22cThis is a graph showing the temperature and temperature change over time of the radiative cooling elements of Embodiment 8, Comparative Example 5-1 and Comparative Example 5-2 of the present invention.

[0092] Figures 23a to 23c This is a cross-sectional view showing the specific state of the white radiative cooling element according to an embodiment of the present invention.

[0093] Figure 24a and Figure 24b This is a graph showing the absorption rate of a white radiative cooling element according to the fine particle content, based on an embodiment of the present invention.

[0094] Figure 25 It is a graph showing the temperature change over time of a white radiative cooling element comprising fine particles according to an embodiment of the present invention.

[0095] Figure 26a It is an image showing the current state of the existing radiative cooling elements. Figure 26b This is an image showing the state of a white radiative cooling element according to an embodiment of the present invention.

[0096] Figure 27 This is a graph showing the absorption rate of the white radiation cooling element, which varies according to the type of polymer, included in the white radiation cooling element according to an embodiment of the present invention.

[0097] Figure 28 It is a graph showing the temperature change over time of a white radiative cooling element comprising fine particles of polymer material according to an embodiment of the present invention. Detailed Implementation

[0098] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings and the descriptions therein. The present invention is not limited to or restricted by these embodiments.

[0099] The terminology used in this specification is for illustrative purposes and is not intended to limit the invention. In this specification, the singular form includes the plural form unless otherwise explicitly stated. The use of "comprises" and / or "comprising" in this specification does not exclude the presence or addition of one or more other elements or steps to the mentioned components or steps.

[0100] Any style or design described in this document, such as “example,” “side,” “exemplary,” etc., should not be construed as being better or more advantageous than other styles or designs.

[0101] Furthermore, the term "or" indicates "inclusive or" rather than "exclusive or". That is, unless otherwise stated or explicitly known from the context, the expression "x using a or b" indicates any of the natural inclusive permutations.

[0102] Furthermore, the singular expressions (“a” or “an”) used in this specification and claims should generally be interpreted as “more than one” unless otherwise stated or clearly known from the context.

[0103] The terms used in the following description are general and common in the relevant art, but other terms may be used due to technological developments and / or changes, conventions, preferences of those skilled in the art, etc. Therefore, the terms used in the following description should not be construed as limiting the technical intent, but should be understood as exemplary terms used to describe embodiments.

[0104] Furthermore, in certain cases, there are terms that the applicant may choose arbitrarily; in the description section for such cases, their meanings will be described in detail. Therefore, the terms used in the following description should be understood based on their meanings and the content of the entire specification, not just their names.

[0105] Unless otherwise defined, all terms used in this specification (including technical and scientific terms) are to be understood in a manner that would be commonly understood by one of ordinary skill in the art to which this invention pertains. Furthermore, unless explicitly defined, terms as defined in common dictionaries are not to be interpreted ideally or excessively.

[0106] On the other hand, in the description of this invention, detailed descriptions of known functions or configurations will be omitted if it is determined that such detailed descriptions would unnecessarily obscure the spirit of the invention. Furthermore, the terminology used in this specification is for the proper expression of embodiments of the invention and may vary according to the intent of the user or operator or the conventions of the art to which this invention pertains. Therefore, these terms should be defined based on the entirety of this specification.

[0107] According to an embodiment of the present invention, the radiative cooling element absorbs mid-infrared rays and radiates them as heat, and is formed on the surface of the target object, such that the temperature of the target object located below the radiative cooling element according to the embodiment of the present invention is lower than the external temperature.

[0108] For example, the radiative cooling element according to an embodiment of the present invention is formed on the surface of a car, which can make the temperature of the vehicle frame lower than the external temperature or the temperature inside the car lower than the external temperature.

[0109] At this point, the target object is an object installed in the radiative cooling element. The target object can be a building such as a car, apartment, shopping mall or office building, or it can be a heat exchange tube installed in an air / water cooling cooler.

[0110] The example is not limited to any object that can be equipped with a radiative cooling element according to an embodiment of the present invention.

[0111] At this time, the external temperature refers to the ambient temperature, and may be the temperature outside the radiative cooling element according to an embodiment of the present invention.

[0112] Figure 1a and Figure 1b This is a cross-sectional view showing the specific state of the radiative cooling element according to an embodiment of the present invention.

[0113] First, refer to Figure 1a According to an embodiment of the present invention, a radiation cooling element 100 includes: a reflective layer 120 that reflects sunlight with wavelengths in the visible and near-infrared regions onto a substrate 110; and a radiation cooling layer 130 formed on the reflective layer 120 that absorbs sunlight with wavelengths in the mid-infrared region and radiates it as heat. The radiation cooling layer may include: a first radiation layer including a raised pattern; and a second radiation layer formed on the first radiation layer and having a refractive index different from that of the first radiation layer.

[0114] Typically, because the surface temperature of the sun reaches about 6,000°C, sunlight has wavelengths in various regions, including ultraviolet, visible, and near-infrared.

[0115] The reflective layer 120 reflects ultraviolet, visible, and near-infrared light from sunlight, so that the temperature of the radiative cooling element 100 according to the embodiment of the present invention will not rise due to sunlight.

[0116] That is, the reflective layer 120 reflects sunlight to minimize the amount of sunlight absorbed by the radiative cooling element 100 according to the embodiment of the present invention, and to maximize the reflection of sunlight.

[0117] Preferably, the reflective layer 120 can be made of a material that can reflect sunlight very well, especially having a reflectivity of more than 90% for light in the visible light region.

[0118] For example, the reflective layer 120 may be made of at least one of metallic materials such as silver (Ag), aluminum (Al) and platinum (Pt), but is not limited to said materials.

[0119] According to an embodiment, the reflective layer 120 can be formed from a commercially available solar reflective film such as 3M sunglasses film.

[0120] According to an embodiment, the reflective layer 120 may be formed of a multilayer thin film made of polymeric or inorganic materials.

[0121] The multilayer film can be a shape in which materials with different refractive indices are repeatedly laminated.

[0122] According to an embodiment, the substrate 110 may be formed of any one of a flexible polymer film, glass, quartz, silicon wafer, and metal, and is not limited to said materials.

[0123] For example, the substrate 110 may be made of any of the following substances: polyester resin such as polyethylene naphthalate (PEN), acetate resin, polyethersulfone resin, polycarbonate resin, polyamide resin, polyimide resin, polyolefin resin, (meth)acrylic resin, polyvinyl chloride resin, polyvinylidene chloride resin, polystyrene resin, polyvinyl alcohol resin, polyacrylate resin, polyphenylene sulfide resin, and polyphenylene sulfide-based resin.

[0124] The radiative cooling layer 130 absorbs mid-infrared radiation and radiates it as heat by being formed on the reflective layer 120, thereby reducing the temperature of the target object on which the radiative cooling element 100 according to an embodiment of the present invention is disposed.

[0125] Typically, objects on Earth emit mid-infrared radiation in the 8μm to 13μm band due to surface temperatures reaching tens of degrees Celsius.

[0126] This mid-infrared radiation can reduce the temperature of an object. According to an embodiment of the present invention, the radiation cooling element 100 may include a radiation cooling layer 130, which is made of a material that can effectively radiate mid-infrared radiation in the known atmospheric window transmittance or sky window band of 8 μm to 13 μm, so that the temperature of the target object can be kept lower than the external temperature.

[0127] The radiation cooling layer 130 according to an embodiment of the present invention is made of a material capable of effectively radiating mid-infrared rays and may have a single-layer shape.

[0128] According to an embodiment, the radiation cooling layer 130 is formed by laminating two thin films made of different materials capable of effectively radiating mid-infrared rays, and the radiation cooling layer 130 may include a first radiation layer 131 and a second radiation layer 132.

[0129] Specifically, according to the embodiments, the first radiating layer 131 may be formed as a thin film on the reflective layer 120, and may be formed to include a raised or recessed pattern on the reflective layer 120.

[0130] Since the first radiating layer 131 includes a raised and recessed pattern, the surface area of ​​the first radiating layer 131 can be increased, thereby improving the mid-infrared emissivity.

[0131] The raised or recessed pattern can be a plurality of cylindrical, prism, and line-shaped raised or recessed patterns, and the shape is not limited to the shape described herein.

[0132] The second radiative layer 132 can be formed as a thin film on the first radiative layer 131.

[0133] According to an embodiment, the second radiating layer 132 may be formed in the form of a thin film on the first radiating layer 131, which includes a raised or recessed pattern.

[0134] The second radiative layer 132, designed for sunlight with wavelengths in the mid-infrared region, can be formed of a material with a different refractive index than the first radiative layer 131.

[0135] That is, the materials constituting the first radiation layer 131 and the second radiation layer 132 have different refractive indices, and therefore have high infrared emissivity due to the phonon-polariton resonance effect.

[0136] According to an embodiment, the difference in refractive index between the first radiating layer 131 and the second radiating layer 132 relative to sunlight with wavelengths in the mid-infrared region can be 0.7 to 2.

[0137] The first radiating layer 131 and the second radiating layer 132 according to embodiments of the present invention may include at least one of oxides, nitrides or polymers.

[0138] The first radiative layer 131 and the second radiative layer 132 may include at least one of different types of oxides, nitrides or polymers.

[0139] The oxide may include, but is not limited to, silicon dioxide (SiO2), zirconium oxide (ZrO2), aluminum oxide (Al2O3) and titanium dioxide (TiO2).

[0140] The nitride may be silicon nitride (Si3N4), but is not limited to this material.

[0141] According to the embodiments, the polymer can be an acrylic polymer such as PDMS (polydimethylsiloxane) or DPHA (dipentaerythritol penta / hexa acrylate), but is not limited to the materials described above.

[0142] The acrylic polymer exhibits CO stretching vibration, resulting in high emissivity in the mid-infrared region.

[0143] In particular, the DPHA exhibits high emissivity in the mid-infrared region due to C-0 stretching vibration and C=C= bending vibration.

[0144] For example, the first radiative layer 131 can be formed by depositing silicon dioxide as an oxide, and the second radiative layer 132 can be formed by depositing aluminum oxide, but is not limited to the examples described.

[0145] Additionally, the first radiating layer 131 may have a layer shape formed by spin-coating PDMS, and the second radiating layer 132 may have a layer shape formed by depositing silicon nitride, but is not limited to the examples described.

[0146] The first radiating layer 131 and the second radiating layer 132 according to embodiments of the present invention may include at least one of fine particles and polymeric materials.

[0147] According to an embodiment, the first radiation layer 131 or the second radiation layer 132 may be formed from a mixture of fine particles and polymeric substances.

[0148] As the content of fine particles in the mixture increases, the emissivity of mid-infrared radiation increases.

[0149] The fine particles can be mixed with the polymer in an amount of 1% to 20% by weight based on the total weight of the mixture.

[0150] The mixture was prepared by mixing 30% by weight of zinc oxide (ZnO) particles with a diameter of 20 nm as fine particles, based on the total weight of PDMS as a polymer.

[0151] The mixture was prepared by mixing 30% by weight of zinc oxide (ZnO) particles with a diameter of 20 nm as fine particles with the total weight of PDMS based on polymer.

[0152] When the content of the fine particles exceeds 20% by weight, the mid-infrared emissivity no longer increases.

[0153] The fine particles may be made of oxides or nitrides, and may include at least one of, for example, silicon dioxide (SiO2), zirconium oxide (ZrO2), aluminum oxide (Al2O3), titanium dioxide (TiO2), and silicon nitride (Si3N4).

[0154] According to embodiments of the present invention, the smaller the size of the fine particles included in the radiation cooling layer 130 of the radiation cooling element 100, the higher the emissivity for mid-infrared radiation it can have.

[0155] According to an embodiment, the fine particles may have a diameter of 10 nm to 20 μm.

[0156] Preferably, fine particles with a nanometer unit size have a higher mid-infrared emissivity compared to fine particles with a micrometer unit size.

[0157] As an example, the first radiative layer 131 may be made of a mixture of fine particles and polymers, while the second radiative layer 132 may be made of polymers alone.

[0158] For example, the first radiating layer 131 may be made of alumina as fine particles and PDMS as a polymer, and the second radiating layer 132 may be made of silicon nitride (Si-3N4) as a polymer, and is not limited to the examples described.

[0159] In another example, the first radiative layer 131 and the second radiative layer 132 are made of a mixture of the fine particles and the polymeric material, but the types of fine particles and polymeric materials forming the first radiative layer 131 and the second radiative layer 132 can be different from each other.

[0160] For example, the first radiating layer 131 may be made of a mixture of silica as fine particles and PDMS as a polymer, and the second radiating layer 132 may be made of alumina as fine particles and DPHA as a polymer, and is not limited to the examples described.

[0161] The thicknesses of the first radiation layer 131 and the second radiation layer 132 may be the same or different from each other.

[0162] According to an embodiment, the first radiating layer 131 and the second radiating layer 132 can be formed with a thickness of 10 nm to 2,000 nm, respectively.

[0163] At this time, when the first radiating layer 131 includes a raised pattern, the height from the surface of the reflective layer 120 to the top of the raised portion of the raised pattern can be set by the thickness of the first radiating layer 131.

[0164] According to one embodiment, the radiative cooling layer 130 may include a first radiative layer 131, a second radiative layer 132, and a third radiative layer (not shown).

[0165] According to one embodiment, the first radiating layer 131, the second radiating layer 132, and the third radiating layer can radiate mid-infrared rays and can be made of materials having different refractive indices.

[0166] Reference Figure 1b , refer to Figure 1b According to an embodiment of the present invention, the radiation cooling element 100 may include a radiation cooling layer 130, which repeatedly forms a first radiation layer 131 and a second radiation layer 132.

[0167] For example, the radiative cooling layer 130 is repeatedly laminated onto the reflective layer 120 in the order of first radiative layer 131-second radiative layer 132-first radiative layer 131-second radiative layer 132.

[0168] According to an embodiment, although not shown, the radiative cooling layer 130 may be repeatedly laminated onto the reflective layer 120 in the order of first radiative layer 131-second radiative layer 132-first radiative layer 131-second radiative layer 132-first radiative layer 131-second radiative layer 132-first radiative layer 131-second radiative layer 132-...

[0169] For example, the radiative cooling layer 130 can be a shape in which a single layer is repeatedly laminated onto the reflective layer 120 in the order of aluminum oxide-silicon nitride-silicon dioxide.

[0170] As another example, the radiation cooling layer 130 can have a shape in which PDMS-silicon nitride-silicon dioxide are laminated in a single layer repeatedly.

[0171] because Figure 1a The first radiation layer 131 and the second radiation layer 132 have already been described in detail, so repeated descriptions will be omitted.

[0172] The radiative cooling element 100 according to an embodiment of the present invention includes: a reflective layer 120 that reflects sunlight in the ultraviolet, visible and near-infrared bands; and a radiative cooling layer 130 made of a material that radiates mid-infrared rays, thereby performing excellent cooling of a target object without consuming energy through effective mid-infrared radiation.

[0173] The structure and characteristics of a radiative cooling element according to another embodiment of the present invention will be described below.

[0174] Figure 2a and Figure 2b This is a cross-sectional view showing the specific state of a radiative cooling element according to another embodiment of the present invention.

[0175] First, refer to Figure 2a In another embodiment of the radiative cooling element 200 according to the present invention, the radiative cooling layer 230 may include: a mid-infrared absorbing layer 231 formed on the reflective layer 220 and absorbing sunlight with wavelengths having a mid-infrared region and radiating it as heat; and a coating formed on the mid-infrared absorbing layer 231 to reflect sunlight in the visible light region.

[0176] A mid-infrared absorbing layer 231 is formed on the reflective layer 220 and absorbs mid-infrared rays and radiates them as heat, thereby reducing the temperature of the radiative cooling element 200 according to another embodiment of the present invention.

[0177] The mid-infrared absorbing layer 231 is made of a material that can effectively radiate mid-infrared rays and can have a single-layer shape.

[0178] The material forming the mid-infrared absorption layer 231 has high emissivity to mid-infrared radiation, while being transparent to sunlight with wavelengths in the ultraviolet, visible, and near-infrared regions.

[0179] According to an embodiment, the mid-infrared absorbing layer 231 may be made of a polymer material.

[0180] For example, the polymer can be PDMS (polydimethylsiloxane) or DPHA (dipentaerythritol penta / hexa acrylate).

[0181] According to an embodiment, the mid-infrared absorbing layer 231 may be formed from at least one of oxides, nitrides and polymers.

[0182] The oxide may include, but is not limited to, silicon dioxide (SiO2), zirconium oxide (ZrO2), aluminum oxide (Al2O3) and titanium dioxide (TiO2).

[0183] The nitride may be silicon nitride (Si3N), but is not limited to this material.

[0184] According to the embodiments, the polymer may be PDMS (polydimethylsiloxane) or DPHA (dipentaerythritol penta / hexa acrylate).

[0185] For example, the mid-infrared absorbing layer 231 may have a layered structure formed by depositing silicon dioxide as an oxide, and is not limited to the example described.

[0186] As an example, the mid-infrared absorbing layer 231 may have a layered structure formed by spin-coating PDMS as a polymeric material, and is not limited to the example described.

[0187] According to an embodiment, the mid-infrared absorbing layer 231 may be formed from a mixture of fine particles and polymeric substances.

[0188] The fine particles may be made of oxides or nitrides, and may include at least one of, for example, silicon dioxide (SiO2), zirconium oxide (ZrO2), aluminum oxide (Al2O3), titanium dioxide (TiO2), and silicon nitride (Si3N4).

[0189] According to embodiments of the present invention, the radiative cooling element 200 can have a higher emissivity to mid-infrared radiation as the size of the fine particles included in the radiative cooling layer 230 decreases.

[0190] According to an embodiment, the fine particles may have a diameter of 10 nm to 20 μm.

[0191] For example, the mid-infrared absorbing layer 231 can be formed from PDMS or DPHA, and can be a single layer formed by spin coating a mixture thereof.

[0192] In addition, the mid-infrared absorption layer 231 can be a monolayer formed by spin-coating a mixture of silica as fine particles and PDMS as a polymer.

[0193] The coating reflects light in the visible light region and can be layered from a material with a high refractive index for the visible light region in order to effectively reflect light in the visible light region.

[0194] At this point, high refractive index can refer to a refractive index of 1.5 or higher for light in the visible region.

[0195] Accordingly, the coating can be a layer made of a material having a refractive index of 1.5 or higher for light in the visible light region.

[0196] Specifically, the coating may be a layer made of a material having a refractive index of 1.6 to 6 for light in the visible light region.

[0197] The coating can be made of defect-free single-crystal ceramic materials, and can also be made of materials that are transparent to visible and mid-infrared light.

[0198] For example, the coating can be made of at least one of yttrium oxide (Y2O3), alon and spinel structures of Mg, Si, Ge, ZnS, ZnSe, NaCl, CaF2, KBr, PE and PS, and is not limited to said materials.

[0199] Preferably, the coating may be made of a material having a high refractive index for light in the visible light region, and is made of at least one of ZnS, Si and Ge.

[0200] According to an embodiment of the invention, the coating is made of a material with a refractive index greater than that of the mid-infrared absorption layer 231, and effectively reflects light in the visible light region. Thus, according to another embodiment of the invention, the radiative cooling element 200 can improve cooling efficiency by reducing the heat absorption rate.

[0201] According to an embodiment, the coating may have a multilayer structure made of materials with different refractive indices for light in the visible light region.

[0202] Specifically, the coating is formed on the mid-infrared absorbing layer 231 and may include a first coating 232 and a second coating 233 that have different refractive indices for light in the visible light region.

[0203] The first coating 232 is formed on the mid-infrared absorption layer 231 and may be a layer made of a material whose refractive index in the visible light region is greater than that of the second coating 233.

[0204] The second coating 233 is formed on the first coating 232 and may be a layer made of a material whose refractive index to light in the visible light region is less than that of the first coating 232.

[0205] Specifically, the refractive index difference between the first coating 232 and the second coating 233 can be 0.7 to 2.

[0206] According to an embodiment, in another embodiment of the present invention, a second coating 233 of the radiative cooling element 200 is formed on a mid-infrared absorption layer 231, and a first coating 232 is formed on the second coating 233.

[0207] According to an embodiment, the first coating 232 may have a layered structure including at least one of ZnS, Si, Ge and ZrO2, wherein ZnS, Si, Ge and ZrO2 are materials whose refractive index in the visible light region is greater than that of the second coating 233, but are not limited to the above materials.

[0208] According to an embodiment, the second coating 233 may have a layered structure including at least one of CaF2 and SiO2, wherein CaF2 and SiO2 are materials that have a lower refractive index for light in the visible light region than the first coating 232, but are not limited to said materials.

[0209] The first coating 232 and the second coating 233 included in the coating can have different refractive indices for light in the visible light region, and therefore can have high reflectivity for visible light.

[0210] The first coating 232 and the second coating 233, being composed of materials with high or low refractive indices for visible light, can maximize the reflection of visible light and minimize the light reaching the visible light region of the reflective layer 220. Accordingly, the cooling efficiency of the radiative cooling element 200 according to another embodiment of the present invention can be improved.

[0211] Reference Figure 2b According to another embodiment of the present invention, the radiative cooling element may include a coating that repeatedly forms a first coating and a second coating.

[0212] Specifically, the coating can be formed by sequentially laminating a first coating - a second coating - a first coating - a second coating - a first coating - a second coating - ... onto a mid-infrared absorbing layer.

[0213] According to an embodiment, the first and second coatings of repeated lamination can be formed from different materials.

[0214] Because in Figure 2a The first and second coatings have already been described in detail, so repeated descriptions will be omitted.

[0215] Since the coating comprises a first coating and a second coating that are repeatedly formed, the reflection of visible light can be maximized by using a first coating and a second coating that have a high or low refractive index for light in the visible light region. Accordingly, the cooling efficiency of a radiative cooling element according to another embodiment of the present invention can be improved.

[0216] The radiative cooling element according to embodiments of the present invention can reflect more than 95% of sunlight and emit more than 90% of mid-infrared rays, thereby cooling the target object without consuming energy.

[0217] Hereinafter, a method for manufacturing a radiative cooling element according to an embodiment of the present invention will be described.

[0218] Since the manufacturing method of the radiative cooling element according to the embodiments of the present invention includes all the constituent elements of the radiative cooling element described above, the repeated description of the radiative cooling element will be omitted in the following description.

[0219] Figure 3 This is a flowchart illustrating a method for manufacturing a radiative cooling element according to an embodiment of the present invention.

[0220] Reference Figure 3According to the method for manufacturing a radiative cooling element of the present invention, the method includes: a step of forming a reflective layer on a substrate capable of reflecting sunlight with wavelengths having ultraviolet, visible and near-infrared regions (S110); and a step of forming a radiative cooling layer on the reflective layer capable of absorbing sunlight with wavelengths having mid-infrared regions and radiating it as heat (S120).

[0221] The substrate can be made of any of the following materials: flexible polymer film, glass, quartz, silicon wafer, and metal, but is not limited to these materials.

[0222] In step S110, a reflective layer can be formed by depositing metallic materials such as silver (Ag), aluminum (Al) and platinum (Pt) on the substrate.

[0223] Because in Figure 1a The substrate has already been described in detail in the description, so repeated descriptions will be omitted.

[0224] In step S110, a reflective layer can be formed by depositing metallic materials such as silver (Ag), aluminum (Al) and platinum (Pt) on the substrate.

[0225] The reflective layer deposition method, under reduced pressure, normal pressure, or pressurized conditions, includes sputtering, atomic layer deposition (ALD), chemical vapor deposition (CVD), thermal evaporation, co-evaporation, plasma-enhanced chemical vapor deposition (PECVD), electron beam evaporation, radio frequency sputtering, magnetron sputtering, vacuum deposition, or chemical vapor deposition, and is not limited to the aforementioned deposition methods.

[0226] In step S120, a radiation cooling layer can be formed by coating the reflective layer with a material that radiates mid-infrared rays.

[0227] According to one embodiment, step S120 may use different materials that radiate mid-infrared radiation to form a multi-layered radiation cooling layer comprising a first radiation layer and a second radiation layer on the reflective layer.

[0228] That is, in step S120, a layered first radiation layer and a second radiation layer can be formed on the reflective layer by using at least one of oxides, nitrides or polymers.

[0229] When the first and second radiative layers comprise oxides or nitrides, a deposition method can be used to form the first or second radiative layer.

[0230] For example, the first radiative layer can be formed in a layered manner by depositing silicon dioxide as an oxide, and the second radiative layer can be formed by depositing aluminum oxide.

[0231] The deposition method, under reduced pressure, normal pressure, or pressurized conditions, includes sputtering, atomic layer deposition (ALD), chemical vapor deposition (CVD), thermal evaporation, co-evaporation, plasma-enhanced chemical vapor deposition (PECVD), electron beam evaporation, radio frequency sputtering, magnetron sputtering, vacuum deposition, or chemical vapor deposition, and is not limited to the aforementioned deposition method.

[0232] When the first and second radiation layers contain polymeric substances, they can be formed by coating.

[0233] For example, the first radiative layer can be formed by spin-coating PDMS, and the second radiative layer can be formed by depositing silicon nitride as a nitride.

[0234] The coating method can be any one of spin coating, spray coating, ultra-spray coating, electrospinning, slot die coating, gravure coating, bar coating, roll coating, dip coating, shear coating, screen printing, inkjet printing, or nozzle printing, but is not limited to this method.

[0235] According to one embodiment, the first radiation layer and the second radiation layer may include at least one of fine particles and polymeric materials.

[0236] For example, the first radiative layer may be made of a mixture of fine particles and polymers, while the second radiative layer may be made of polymers alone.

[0237] When the first and second radiation layers comprise a mixture of the fine particles and the polymer, a coating method can be used to form the first and second radiation layers.

[0238] The coating method can be any one of spin coating, spray coating, ultra-spray coating, electrospinning, slot die coating, gravure coating, bar coating, roll coating, dip coating, shear coating, screen printing, inkjet printing, or nozzle printing, but is not limited to this method.

[0239] According to an embodiment, the first radiating layer may include a raised or recessed pattern to have a large area, thereby improving mid-infrared emissivity.

[0240] Specifically, step S120 may include: forming a first radiation layer including a concave-convex pattern on the reflective layer (S121); and forming a second radiation layer having a refractive index different from that of the first radiation layer on the first radiation layer (S122).

[0241] In step S121, a first radiating layer comprising an embossed pattern can be formed on the reflective layer by using at least one of oxides, nitrides, or polymers and fine particles made from any of them.

[0242] In step S121, a first radiating layer including the concave and convex patterns can be formed on the reflective layer using a mold having a pattern corresponding to the concave and convex patterns and by an optical lithography process or a non-optical lithography process.

[0243] The optical-based lithography process can be any of photolithography, laser interference lithography, and electron beam lithography, and is not limited to the aforementioned processes.

[0244] The non-optical lithography process can be any of nanoimprint lithography, nanotransfer printing, and roll imprint lithography, but is not limited to these processes.

[0245] According to an embodiment, in step S121, after coating with at least one of fine particles and polymeric substances consisting of oxides, nitrides, or any of them, the coating can be cut off from top to bottom to form a raised or recessed pattern.

[0246] The raised or recessed pattern can be multiple cylinders, prisms, and lines, and the shape is not limited to these.

[0247] In step S122, a second radiation layer may be formed on the first radiation layer having a concave-convex pattern using a material having a different refractive index than the first radiation layer.

[0248] Specifically, in step S122, a second radiation layer can be formed by spin-coating a material having a refractive index different from that of the first radiation layer onto the first radiation layer.

[0249] In step S122, the thickness of the second radiation layer can be adjusted according to the spin coating time.

[0250] According to an embodiment, the spin coating can be performed for 30 to 40 seconds.

[0251] At this point, even if spin coating is performed for 40 seconds or longer, the thickness of the second radiation layer will no longer increase.

[0252] According to an embodiment, the method for manufacturing a radiation cooling element according to an embodiment of the present invention can repeatedly perform steps S121 and S122 to form a radiation cooling layer formed by repeating the first radiation layer and the second radiation layer.

[0253] Specifically, a first radiation layer, which is layered or has a raised or recessed pattern, is formed on the reflective layer, and after a second radiation layer is formed on the first radiation layer, the second radiation layer can be repeatedly formed after the first radiation layer is formed in a layered manner on the second radiation layer or has a raised or recessed pattern.

[0254] The method for manufacturing a radiative cooling element according to an embodiment of the present invention can produce a radiative cooling element with a simple structure and a small number of layers through a simple process.

[0255] The radiation cooling element manufactured by the method of manufacturing a radiation cooling element according to an embodiment of the present invention increases the surface area by including a concave-convex pattern in the radiation cooling layer, thereby improving the cooling efficiency and thus improving the mid-infrared radiation efficiency.

[0256] In the following, a method for manufacturing a radiative cooling element according to another embodiment of the present invention will be described.

[0257] A method for manufacturing a radiative cooling element according to another embodiment of the present invention includes the following: Figure 2a and Figure 2b The components of the radiative cooling element described herein will be omitted, and therefore repeated descriptions will be omitted.

[0258] Figure 4 This is a flowchart illustrating a method for manufacturing a radiative cooling element according to another embodiment of the present invention.

[0259] refer to Figure 4 The method for manufacturing a radiative cooling element according to an embodiment of the present invention includes: a step (S210) of forming a reflective layer on a substrate capable of reflecting sunlight with wavelengths having ultraviolet, visible, and near-infrared regions; a step (S220) of forming a mid-infrared absorbing layer on the reflective layer capable of absorbing sunlight with wavelengths having mid-infrared regions and radiating it as heat; and a step (S230) of forming a coating on the mid-infrared absorbing layer that reflects sunlight with wavelengths having visible light regions.

[0260] Since step S210 includes and Figure 3 The same constituent elements as step S110 described herein will be omitted from the repeated description.

[0261] In steps S220 and S230, a radiation cooling layer comprising a mid-infrared absorption layer and a coating is formed by forming a coating on the layered infrared absorption layer.

[0262] First, in step S220, a mid-infrared absorbing layer can be formed by using a material capable of emitting mid-infrared rays on the reflective layer.

[0263] The mid-infrared absorption layer may have a monolayer shape including at least one of oxides, nitrides, or polymers.

[0264] When the mid-infrared absorbing layer comprises oxides or nitrides, the mid-infrared absorbing layer can be formed using a vapor deposition method.

[0265] The deposition method, under reduced pressure, normal pressure, or pressurized conditions, includes sputtering, atomic layer deposition (ALD), chemical vapor deposition (CVD), thermal evaporation, co-evaporation, plasma-enhanced chemical vapor deposition (PECVD), electron beam evaporation, radio frequency sputtering, magnetron sputtering, vacuum deposition, or chemical vapor deposition, and is not limited to the aforementioned deposition method.

[0266] When the mid-infrared absorption layer comprises a polymer material, it can be formed by coating.

[0267] The coating method can be any one of the following: spin coating, spray coating, ultra-spray coating, electrospinning, slot die coating, gravure coating, bar coating, roll coating, dip coating, shear coating, screen printing, inkjet printing, or nozzle printing, but is not limited to the coating method described above.

[0268] In step S230, in order to reflect light from the visible light region while effectively reflecting light from the visible light region, a layered coating made of a material with a high refractive index for light from the visible light region can be formed.

[0269] Specifically, in step S230, a coating can be formed by depositing or coating a material with a high refractive index for light in the visible light region onto the mid-infrared absorption layer, so as to effectively reflect light in the visible light region onto the infrared absorption layer.

[0270] The deposition method, under reduced pressure, normal pressure, or pressurized conditions, includes sputtering, atomic layer deposition (ALD), chemical vapor deposition (CVD), thermal evaporation, co-evaporation, plasma-enhanced chemical vapor deposition (PECVD), electron beam evaporation, radio frequency sputtering, magnetron sputtering, vacuum deposition, or chemical vapor deposition, and is not limited to the aforementioned deposition method.

[0271] The coating methods include, but are not limited to, spin coating, spray coating, ultra-spray coating, electrospinning, slot die coating, gravure coating, bar coating, roll coating, dip coating, shear coating, screen printing, inkjet printing, or nozzle printing.

[0272] According to an embodiment, the coating may have a multilayer shape made of materials having different refractive indices for light in the visible light region.

[0273] Specifically, in step S230, a first coating and a second coating with different refractive indices for visible light can be formed on the mid-infrared absorption layer.

[0274] Specifically, the first coating is formed on the mid-infrared absorbing layer, and a material with a greater refractive index than the second coating can be coated to form light in the visible light region.

[0275] The second coating is formed on the first coating and can be formed by coating a substance with a smaller refractive index than the first coating for light in the visible light region.

[0276] The first and second coatings can be formed using a deposition process or a coating process.

[0277] Since examples of the deposition methods and coating techniques have already been described above, repeated descriptions will be omitted.

[0278] According to an embodiment, a method for manufacturing a radiative cooling element according to another embodiment of the present invention can repeatedly form the first coating and the second coating.

[0279] According to another embodiment of the present invention, a method for manufacturing a radiative cooling element can easily produce a radiative cooling element with excellent cooling efficiency through a simple process.

[0280] The radiative cooling element manufactured by the method of manufacturing a radiative cooling element according to another embodiment of the present invention can have a simpler structure with fewer layers than existing radiative cooling elements, and can have excellent cooling efficiency due to its high infrared emissivity.

[0281] According to this embodiment, two radiative cooling elements based on the present invention are manufactured, and the characteristics and effects of the radiative cooling elements of the present invention are demonstrated through characteristic evaluation.

[0282] Examples and Comparative Examples

[0283] [Example 1-1]

[0284] A reflective layer made of silver (Ag) is formed on a glass substrate using an electron beam evaporator.

[0285] After spin-coating silica onto the reflective layer, a first radiating layer with a raised or recessed pattern is formed using a nanoimprinting process.

[0286] The radiation cooling element is then manufactured by spin-coating aluminum oxide onto the first radiation layer to form a layered second radiation layer.

[0287] [Examples 1-2]

[0288] After spin-coating silicon dioxide onto the second radiating layer, a first radiating layer with an embossed pattern is formed using a nanoimprinting process. Then, except that aluminum oxide is spin-coated onto the first radiating layer to form a layered second radiating layer again, the radiative cooling element is manufactured in the same manner as described in [Example 1-1].

[0289] [Example 2]

[0290] A reflective layer made of silver (Ag) is formed on a glass substrate using an electron beam evaporator.

[0291] Alumina is deposited on the reflective layer to form a first radiative layer, silicon nitride (Si3N4) is deposited on the first radiative layer to form a second radiative layer, and then silicon dioxide is deposited on the second radiative layer to form a third radiative layer, thereby manufacturing a radiative cooling element.

[0292] [Example 3-1]

[0293] A reflective layer made of silver (Ag) is formed on a glass substrate using an electron beam evaporator.

[0294] PDMS is spin-coated onto a reflective layer to form a first radiating layer, silicon dioxide is deposited onto the first radiating layer to form a second radiating layer, and silicon nitride is deposited onto the second radiating layer to form a third radiating layer, thereby forming a radiative cooling element.

[0295] [Example 3-2]

[0296] A reflective layer made of silver (Ag) is formed on a glass substrate using an electron beam evaporator.

[0297] After spin-coating PDMS onto the reflective layer to form the first radiative layer, silicon dioxide is deposited on the first radiative layer to form the second radiative layer, thereby manufacturing a radiative cooling element.

[0298] [Example 4]

[0299] A reflective layer made of silver (Ag) is formed on a glass substrate using an electron beam evaporator.

[0300] The mixture was prepared by adding 10% by weight of fine silica particles with a diameter of 10 μm to PDMS.

[0301] Radiation cooling elements are manufactured by spin-coating the mixture onto a reflective layer to form a single-layer radiation cooling layer.

[0302] [Example 4-1]

[0303] A reflective layer made of silver (Ag) is formed on a glass substrate using an electron beam evaporator.

[0304] Radiation-cooled elements are manufactured by spin-coating PDMS onto a reflective layer to form a single-layer radiation-cooling layer.

[0305] [Example 5]

[0306] Each reflective layer made of silver (Ag) was formed on three glass substrates using an electron beam evaporator.

[0307] Three radiative cooling elements were fabricated by spin-coating three solutions containing 60 wt%, 80 wt%, and 90 wt% DPHA, respectively, onto three reflective layers to form a single-layer radiative cooling layer.

[0308] [Example 6-1]

[0309] Each reflective layer made of silver (Ag) was formed on three glass substrates using an electron beam evaporator.

[0310] Three mixtures were prepared by adding 1.9 wt%, 3.8 wt%, and 7.7 wt% of fine alumina particles with a diameter of 20 nm to DPHA, respectively.

[0311] Three radiative cooling elements are manufactured by spin-coating each of the three mixtures onto three reflective layers to form a single layer of radiative cooling.

[0312] [Example 6-2]

[0313] Each reflective layer made of silver (Ag) was formed on three glass substrates using an electron beam evaporator.

[0314] Three mixtures were prepared by adding alumina fine powder with diameters of 20 nm, 1 μm, and 3 μm to DPHA, respectively.

[0315] Three radiative cooling elements are manufactured by spin-coating each of the three mixtures onto three reflective layers to form a single layer of radiative cooling.

[0316] [Example 7]

[0317] A 100nm reflective layer made of silver (Ag) was formed on a glass substrate using an electron beam evaporator.

[0318] A second radiative layer of 130 nm is formed by spin-coating fine silica particles onto the reflective layer.

[0319] After fine particles made of zirconium oxide are coated onto the second radiative layer, a first radiative layer with an embossed pattern is formed thereon by a nanoimprinting process.

[0320] At this point, the width of the embossed pattern in the first radiation layer is 24 μm and the height is 10.2 μm.

[0321] [Example 8]

[0322] Each reflective layer made of silver (Ag) is formed on a silicon substrate using an electron beam evaporator.

[0323] A radiation cooling element is manufactured by depositing ZrO2 on a reflective layer to form a first coating, and then depositing SiO2 on the first coating to form a second coating.

[0324] [Example 1-1]

[0325] A reflective layer made of silver (Ag) is formed on a glass substrate using an electron beam evaporator.

[0326] Silicon dioxide (SiO2) is deposited on the reflective layer to form a layered first radiative layer, and then aluminum oxide (Al2O3) is deposited on the first radiative layer to form a layered second radiative layer, thereby manufacturing a radiative cooling element.

[0327] [Examples 1-2]

[0328] The radiative cooling element is manufactured in the same manner as in [Comparative Example 1-1], except that silicon dioxide is deposited on the second radiative layer to form a layered first radiative layer, and aluminum oxide is deposited to further form a layered second radiative layer.

[0329] [Comparative Example 2]

[0330] Cooling elements are manufactured by forming a reflective layer made of silver (Ag) on ​​a glass substrate using an electron beam evaporator.

[0331] [Example 3]

[0332] Glass substrate.

[0333] [Example 4]

[0334] The radiative cooling element was manufactured in the same manner as in Example 7, except that zirconium oxide was coated onto the second radiative layer with a thickness of 7.33 μm to form the first radiative layer.

[0335] [Example 5-1]

[0336] Cooling elements are manufactured by forming a reflective layer made of silver (Ag) on ​​a silicon substrate using an electron beam evaporator.

[0337] [Example 5-2]

[0338] silicon substrate

[0339] Evaluation characteristics

[0340] 1. The emissivity of the radiation cooling element depends on whether there is a raised or recessed pattern.

[0341] Figure 5 This is a graph showing the absorption rate depending on whether the first and second radiative layers are repeatedly laminated, according to embodiments and comparative examples of the present invention.

[0342] Reference Figure 5 For areas outside the central red line ( Figure 5 The absorption rate of light at the wavelength of the yellow region in Example 1-1 (1 pair of Al2O3 / PSS layers) is higher than that of Comparative Example 1-1 (1 pair of Al2O3 / SiO2 layers).

[0343] Therefore, it can be confirmed that the embodiment 1-1 with the raised pattern emits more mid-infrared rays than the comparative example 1-1 without the raised pattern.

[0344] In addition, it can be confirmed that the absorption rate of the embodiments 1-2 (periodic Al2O3 / PSS layer) in the mid-infrared region is higher than that of the comparative embodiments 1-2 (periodic Al2O3 / SiO2 layer).

[0345] Therefore, it can be confirmed that the embodiments 1-2 with the raised pattern emit more mid-infrared rays than the comparative examples 1-2 without the raised pattern.

[0346] In summary, the radiative cooling element according to embodiments of the present invention can improve mid-infrared emissivity by including embossed patterns.

[0347] 2. Evaluate the cooling efficiency of radiative cooling elements based on material type.

[0348] After comparing the cooling efficiency of the radiation cooling element in Example 2 with the cooling efficiency obtained through simulation, the following results were obtained.

[0349] Figure 6 This is a graph showing the absorptivity and emissivity of the radiative cooling element according to the second embodiment of the present invention.

[0350] at this time, Figure 6 The yellow area represents the incoming sunlight.

[0351] Reference Figure 6 Simulation results show that the temperature change is -8.18℃ and the cooling efficiency is 81.8W / m2.

[0352] At this point, the temperature change refers to the temperature change after cooling from the initial temperature of the radiative cooling element. A temperature change of -8.18℃ means that the temperature of the radiative cooling element is 8.18℃ lower than the initial temperature.

[0353] In addition, it can be confirmed that the average solar absorptivity and the mid-infrared region ( Figure 6 The blue area showed no significant difference in emissivity between the simulation and the second embodiment.

[0354] That is, it can be confirmed that the second embodiment was manufactured in good agreement with the simulation results.

[0355] Figure 7 It is a graph showing the temperature of the radiative cooling element during each time period of daytime according to Embodiment 2 of the present invention.

[0356] Reference Figure 7 For Example 2, the temperature of the radiative cooling element was measured over a three-day period from midnight on May 9, 2019 to midnight on May 11, 2019.

[0357] As a result, in the second embodiment, although the temperature rises or falls depending on the intensity of sunlight, it can be confirmed that the maximum temperature change is -8°C during the day and -2°C at night.

[0358] Figure 8 It is a graph showing the absorptivity and emissivity of the radiative cooling element according to Embodiment 3-1 of the present invention.

[0359] refer to Figure 8 As a simulation result, the predicted radiative cooling element of Example 3-1 has a temperature change of -9.132℃ and a cooling efficiency of 80.44W / m².

[0360] The actual absorptivity measurements from Example 3-1 confirm that the region exhibits the lowest emissivity and the highest reflectivity in the solar energy region, and also in the mid-infrared region (…). Figure 8 The blue area in the image has the highest emissivity.

[0361] Figure 9 This is a graph showing the external temperature of the radiative cooling element of Embodiment 3-1 and Comparative Example 2 of the present invention at each time period during the day, based on the amount of sunlight.

[0362] Reference Figure 9 By observing the temperatures of Example 3-1 and Comparative Example 2 during the daytime (10:00 AM to 4:00 PM) on April 13, 2019, it can be confirmed that the temperature change of Comparative Example 2 compared to the ambient temperature (Ambient T) was -3°C, and the temperature change of Example 3-1 was 3°C and -5.95°C.

[0363] At this time, due to heat loss through the air, the outside temperature (Outside T) is lower than the temperature of Example 3-1 and Comparative Example 2.

[0364] Therefore, the radiative cooling element of the present invention can have excellent cooling efficiency through a radiative cooling layer made of a material capable of emitting mid-infrared rays.

[0365] Figure 10 This is a graph showing the temperature of the radiative cooling element during each time period at night for Embodiments 3-1, 3-2, and Comparative Example 2 of the present invention.

[0366] Reference Figure 10 Based on the results of observing the temperatures of Examples 3-1, 3-2, and Comparative Example 2 on the night of April 13, 2019 (10 pm to 4 am), it can be confirmed that the temperature change of Comparative Example 2 compared with the ambient temperature (Ambient T) was -0.5℃, and the temperature change of Examples 3-1 and 3-2 was -2.5℃.

[0367] Figure 11 These are graphs showing the absorbance of the radiative cooling elements of Embodiments 4-1, 4-2 and Comparative Example 3 of the present invention.

[0368] refer to Figure 11 It can be confirmed that, compared with Comparative Example 3, Examples 4-1 and 4-2 exhibit higher emissivity in the mid-infrared region.

[0369] In particular, Embodiment 4-1 absorbs almost no light in the visible light region and exhibits high absorption in the long wavelength region.

[0370] Therefore, the temperature change in Example 4-1 is -9.5℃, and the cooling efficiency is 99.16W / m².

[0371] Figure 12 It is a graph showing the temperature of the radiative cooling element and the external temperature during each daytime period according to Embodiments 4-1 and 4-2 of the present invention.

[0372] refer to Figure 12 The results of temperature measurements of Examples 4-1 and 4-2 taken over a continuous 5-hour period from 10:39 AM to 3:39 PM on April 25, 2019, confirm that the temperature is lower than that of the ambient temperature.

[0373] In particular, it can be confirmed that the maximum temperature change in Example 4-1 is -8°C.

[0374] Figure 13 This is a graph showing the temperature of the radiative cooling element and the external temperature at each time period during the night according to Embodiments 4-1 and 4-2 of the present invention.

[0375] Reference Figure 13 Based on the temperature measurements taken during a five-hour period from 10:49 PM to 3:49 AM on April 25, 2019, for Examples 4-1 and 4-2, it can be confirmed that the temperature of the radiative cooling element is lower than that of the ambient temperature.

[0376] In particular, it can be confirmed that the temperature change in Example 4-1 is at most -3°C.

[0377] Therefore, the radiative cooling element of the present invention, by comprising a radiative cooling layer formed of fine particles or polymer materials capable of emitting mid-infrared rays, can have excellent cooling efficiency even during the day and night.

[0378] In particular, it can be confirmed that the temperature change in Example 4-1 is at most -3°C.

[0379] Therefore, the radiative cooling element of the present invention has excellent cooling efficiency both day and night by including a radiative cooling layer formed of fine particles or polymers capable of emitting mid-infrared rays.

[0380] Figures 14a to 14c It is a SEM (scanning electron spectroscopy) image showing a cross-section of the radiative cooling element according to Embodiment 5 of the present invention.

[0381] Reference Figures 14a to 14c It can be confirmed that when the DPHA content in the radiative cooling layer of Example 5 is 60% by weight, 80% by weight, and 90% by weight, the thickness of the radiative cooling layer is 10.5 μm, 16.5 μm, and 25.7 μm, respectively, and the thickness of the radiative cooling layer increases with the increase of DPHA content.

[0382] This is because the higher the DPHA content spin-coated on the reflective layer, the higher the viscosity, and even under the same spin-coating conditions, the thickness of the radiation cooling layer will increase.

[0383] Figure 15 This is a graph showing the absorption rate of the radiative cooling element according to the DPHA content of Embodiment 5 of the present invention.

[0384] refer to Figure 15 It can be confirmed that as the DPHA content in the radiation cooling layer of Example 5 increases, it exhibits high emissivity for wavelengths in the 10μm to 12μm region.

[0385] Therefore, the higher the DPHA content in the radiative cooling layer, the higher the mid-infrared emissivity in the mid-infrared region, which can improve the cooling efficiency of the radiative cooling element.

[0386] Figure 16 This is a graph showing the temperature of the radiative cooling element during various observation periods based on the amount of sunlight, according to Embodiment 5 of the present invention.

[0387] refer to Figure 16 The results of temperature measurements taken over three days from April 28, 2019 to April 30, 2019 in Example 5 confirm that the higher the DPHA content in Example 5, the higher the mid-infrared emissivity and temperature field, and thus the greater the variation.

[0388] In particular, it can be confirmed that in Example 5, when the DPHA content is 90% by weight, the temperature change is -10.1°C.

[0389] Therefore, the radiation cooling element of the present invention comprises a radiation cooling layer made of a polymer material that has a resonance effect due to molecular chemical bonding, and thus has excellent radiation cooling efficiency due to its high mid-infrared emissivity.

[0390] Figure 17 This is a graph showing the absorption rate of the radiative cooling element according to the fine particle content of the embodiment 6-1 according to the present invention.

[0391] refer to Figure 17 It can be confirmed that as the content of alumina fine particles in Example 6-1 increases, the emissivity in the mid-infrared region increases.

[0392] Figure 18 This is a graph showing the absorption rate of the radiative cooling element according to the fine particle diameter of the embodiment 6-2 according to the present invention.

[0393] refer to Figure 18 It can be confirmed that as the diameter of the alumina fine particles in Example 6-2 increases, the emissivity in the mid-infrared region decreases.

[0394] Therefore, it can be confirmed that the radiative cooling element according to the embodiment of the present invention preferably contains a high content of nano-sized fine particles in order to have excellent cooling efficiency.

[0395] Figure 19 It is a graph showing the solar radiation according to the temperature based on the fine particle content of the radiative cooling element according to Embodiment 5 of the present invention.

[0396] Reference Figure 9 By measuring the temperature of Example 6-1 from May 28, 2019 to May 30, 2019, it can be confirmed that as the content of fine alumina particles increases, the mid-infrared emissivity increases, thereby improving the cooling efficiency.

[0397] In particular, when the content of fine alumina particles is 7.7% by weight, it can be confirmed that the temperature change in Example 6-1 is at most -11.9°C.

[0398] Therefore, the radiative cooling element according to an embodiment of the present invention comprises fine particles capable of radiating mid-infrared rays, and thus exhibits excellent radiative cooling efficiency as the emissivity of mid-infrared rays increases.

[0399] 3. Absorption rate depends on the presence or absence of embossed patterns.

[0400] Figure 20 This is a graph showing the absorption rate depending on the presence or absence of the embossed pattern according to Embodiment 7 and Comparative Example 4 of the present invention.

[0401] In this case, the first radiating layer of both Example 7 and Comparative Example 4 is made of oxide semiconductor of the same volume.

[0402] Reference Figure 20 It can be confirmed that the absorption rate of Example 7 (Patterm) in the red region, which is the mid-infrared region, is generally higher than that of Comparative Example 4 (Thin film).

[0403] That is, since the first radiating layer of the seventh embodiment includes a concave-convex pattern, it can be confirmed that the absorption of mid-infrared rays is increased by the resonance of electric field and magnetic field at a specific wavelength.

[0404] Accordingly, when the radiative cooling element according to the embodiment of the present invention forms a concave-convex pattern at the micrometer scale, the mid-infrared absorption rate can be selectively increased in the mid-infrared region, thereby exhibiting excellent radiation of mid-infrared rays and thus achieving a superior cooling effect.

[0405] 4. Evaluate the efficiency of radiative cooling elements based on the presence or absence of coatings with different refractive indices.

[0406] Figure 21 This is a graph showing the mid-infrared emissivity of the radiative cooling elements of Embodiment 8, Comparative Example 5-1, and Comparative Example 5-2 of the present invention.

[0407] refer to Figure 21 Compared with Comparative Example 5-1 (Ag / Si) and Comparative Example 5-2 (Si), it can be confirmed that Example 8 (RC (Radiative cooling) / Ag / Si) has increased emissivity in the 8 to 13 μm band of the infrared region.

[0408] Figures 22a to 22c This is a graph showing the temperature and temperature change over time of the radiative cooling elements of Embodiment 8, Comparative Example 5-1 and Comparative Example 5-2 of the present invention.

[0409] Figure 22a The results are from observing the temperature and temperature change of the radiative cooling elements of Example 8, Comparative Example 5-1, and Comparative Example 5-2 over one day. Figure 22b The results were obtained by observing the temperature and temperature change of the radiative cooling elements in Example 8, Comparative Example 5-1, and Comparative Example 5-2 during the daytime (10:00 to 18:00).

[0410] Figure 22c The results are from nighttime (22:00 to 06:00) observations of the temperature and temperature change of the heat dissipation cooling elements of Example 8, Comparative Example 5-1 and Comparative Example 5-2.

[0411] First, refer to Figure 22a It can be confirmed that the temperature of Example 8 (RC / Ag / Si) is lower than that of Comparative Example 5-1 (Ag / Si) and Comparative Example 5-2 (Si), and since the temperature is lower than the ambient temperature, it can be confirmed that it has excellent cooling efficiency.

[0412] Reference Figure 22b and Figure 22c Example 8 (RC / Ag / Si) was compared with Comparative Example 5-1 (Ag / Si) and Comparative Example 5-2 (Si), and it was confirmed that the temperature was very low both during the day and at night.

[0413] In particular, the temperature change (RC / Ag / Si) of Example 8 is higher than that of Comparative Example 5-1 (Ag / Si) and Comparative Example 5-2 (Si), thus confirming that it has excellent cooling efficiency.

[0414] Therefore, it can be confirmed that the radiative cooling element according to another embodiment of the present invention includes a coating comprising materials having different refractive indices, thereby having an excellent cooling effect.

[0415] According to an embodiment of the present invention, the white radiative cooling element absorbs mid-infrared rays and radiates them as heat, while reflecting or scattering visible light, and is formed on the surface of the target object, such that the temperature of the target object located below the white radiative cooling element according to an embodiment of the present invention is lower than the external temperature.

[0416] For example, according to an embodiment of the present invention, a white radiative cooling element is disposed on the surface of a car to radiate mid-infrared rays and reflect or scatter visible light, thereby reducing the temperature of the white radiative cooling element and the temperature of the vehicle frame, making it lower than the external temperature, or making the interior temperature of the vehicle lower than the outdoor temperature.

[0417] At this time, the target object can be a target equipped with a white radiative cooling element, such as a car, apartment, shopping mall, or office building, and if it is an object that can be equipped with a white radiative cooling element according to an embodiment of the present invention, it is not limited to the embodiment described.

[0418] At this time, the external temperature refers to the ambient temperature, and may be the temperature outside the white radiative cooling element according to an embodiment of the present invention.

[0419] The white radiative cooling element according to an embodiment of the present invention comprises fine particles or polymeric materials having different refractive indices, thereby appearing white by reflecting and scattering sunlight with wavelengths in the visible light region.

[0420] In the following description, the configuration of a white radiative cooling element according to an embodiment of the present invention will be described with reference to the accompanying drawings.

[0421] Figures 23a to 23c This is a cross-sectional view showing the specific state of the white radiative cooling element according to an embodiment of the present invention.

[0422] First, refer to Figure 23a According to a first embodiment of the present invention, a white radiation cooling element includes: a substrate 110; and a white radiation cooling layer 120 formed on the substrate 110, wherein metal oxide particles containing sunlight with wavelengths having a visible light region and fluorescent particles that radiate fluorescence are mixed in a polymer matrix that absorbs sunlight with wavelengths having a mid-infrared region and radiates it as heat.

[0423] The substrate 110 can be formed from any of the following materials: polymer film, glass, quartz, silicon wafer and metal, and is not limited to these materials.

[0424] For example, the substrate 110 may be a polymer film made of any of the following: polyester resin such as polyethylene naphthalate (PEN), acetate-based resin, polyethersulfone resin, polycarbonate resin, polyamide resin, polyimide resin, polyolefin resin, (meth)acrylic resin, polyvinyl chloride resin, polyvinylidene chloride resin, polystyrene resin, polyvinyl alcohol resin, polyacrylate resin, polyphenylene sulfide resin, and polyphenylene sulfide-based resin, but is not limited to the materials mentioned above.

[0425] A white radiative cooling layer 120 is formed on a substrate 110 to absorb mid-infrared or long-wavelength infrared light, and fine particles 122 containing reflected and scattered visible light are mixed in a polymer matrix 121 that radiates heat. The temperature of the target object can be lower than the external temperature by means of the white radiative cooling element 100 according to the first embodiment of the present invention.

[0426] Typically, because the surface temperature of objects on Earth reaches tens of degrees Celsius, they emit mid-infrared radiation with wavelengths ranging from 8μm to 13μm.

[0427] This mid-infrared radiation can reduce the temperature of the object, and the white radiation cooling layer 120 comprises a polymer matrix made of a material that can well radiate mid-infrared radiation in the known atmospheric window transmittance or skywindow band of 8 μm to 13 μm, so that as the temperature of the white radiation cooling element 100 according to the first embodiment of the present invention decreases, the temperature of the target object can be maintained below the external temperature.

[0428] The polymer matrix 121 can absorb sunlight with wavelengths in the mid-infrared region and radiate it as heat.

[0429] According to an embodiment, the polymer matrix 121 may include an acrylic polymer.

[0430] The acrylic polymer exhibits high emissivity in the mid-infrared region due to its CO stretching vibration.

[0431] For example, the polymer matrix 121 may include at least one of PDMS (polydimethylsiloxane), PMMA (polymethylmethacrylate) and DPHA (dipentaerythritol penta / hexa acrylate), but is not limited to the materials mentioned above.

[0432] In particular, the DPHA has high emissivity in the mid-infrared region due to C-O stretching vibration and C=C= bending vibration.

[0433] According to the embodiments, the polymer matrix 121 may be made of PVDF (polyvinylidene fluoride) or PUA (polyurethane acrylate).

[0434] The white radiation cooling layer 120 may have a morphology in which fine particles 122, including metal oxides or polymers, are mixed in a polymer matrix 121.

[0435] The fine particles 122 containing the metal oxide can reflect and scatter sunlight with wavelengths in the visible light region, and the white radiative cooling element 100 according to the first embodiment of the present invention can appear white due to the reflection and scattering of visible light through the fine particles 122.

[0436] Specifically, the white radiative cooling element 100 according to the first embodiment of the present invention reflects visible light in all directions by comprising fine particles 122 of metal oxides that do not absorb visible light, so that it does not have a mirror appearance like existing radiative cooling elements and can be white.

[0437] Furthermore, in the white radiative cooling element 100 according to the first embodiment of the present invention, when the fine particles 122 include a polymer material, the polymer matrix 121 and the fine particles 122 including the polymer material can have different refractive indices, and the scattering or reflection of visible light can be enhanced by the different refractive indices.

[0438] According to an embodiment, the polymer matrix 121 and the fine particles 122 can be made of a material with a refractive index of 1.4 to 1.7, and the scattering or reflection of visible light can be further enhanced as the difference in refractive index increases.

[0439] According to an embodiment, the polymer may be at least one of PVDF (polyvinylidene fluoride) and PUA (polyurethane acrylate).

[0440] For example, the white radiation cooling layer 120 may have a shape in which fine particles 122 including PUA (refractive index of about 1.55) are mixed in a polymer matrix 121 (refractive index of about 1.426) made of PVDF.

[0441] As another example, the white radiation cooling layer 120 may have a shape in which fine particles 122 including PVDF are mixed in a polymer matrix 121 made of PUA.

[0442] If the polymer matrix 121 and the fine particles 122 containing the polymer have different refractive indices, then when visible light enters the interface between the fine particles 122 and the polymer matrix 121, the visible light can be scattered and reflected, thus achieving excellent cooling performance without consuming energy.

[0443] According to one embodiment, fine particles 122 may be mixed into the polymer matrix 121 in an amount of 1% to 50% by weight based on the total weight of the polymer matrix 121.

[0444] According to embodiments, the metal oxide may be at least one selected from titanium dioxide (TiO2), zirconium oxide (ZrO2), aluminum oxide (Al2O3), zinc oxide (ZnO), silicon oxide (SiO2), and silicon nitride (Si3N4), but is not limited to the materials described above.

[0445] The smaller the diameter of the fine particles 122, the higher their reflectivity and scattering rate for visible light.

[0446] According to an embodiment, the diameter of the fine particles 122 can be from 10 nm to 20 μm.

[0447] When the diameter of the fine particles 122 is as small as nanometers, all sunlight can be reflected or scattered.

[0448] When the diameter of fine particles 122 is greater than 3 μm, the absorption in the long wavelength region increases, thereby improving heat radiation.

[0449] Preferably, fine particles 122 with a nanometer unit size have a higher visible light reflectivity (or scattering rate) than fine particles 122 with a micrometer unit size.

[0450] The white radiative cooling element 100 according to the first embodiment of the present invention can have excellent cooling performance through the white radiative cooling layer 120, which includes fine particles 122 on a polymer matrix 121 that reflects and scatters visible light and radiates mid-infrared or long-wavelength infrared light well.

[0451] Furthermore, the white radiative cooling element 100 according to the first embodiment of the present invention is white by means of fine particles 122 that reflect and scatter visible light, thereby improving its aesthetics.

[0452] Reference Figure 23b The white radiative cooling element 200 according to the second embodiment of the present invention further includes a reflection enhancement layer 230, which further reflects sunlight having wavelengths in the visible light region below the white radiative cooling layer 220.

[0453] Accordingly, the white radiation cooling element 200 according to the second embodiment of the present invention includes: a substrate 210; a reflection enhancement layer 230; and a white radiation cooling layer 220, which includes fine particles 222 mixed in a polymer matrix 221.

[0454] Since the white radiative cooling element 200 according to the second embodiment of the present invention includes the constituent elements of the white radiative cooling element 200 according to the first embodiment, repeated descriptions will be omitted.

[0455] The reflective enhancement layer 230 further reflects light in the ultraviolet, visible, and near-infrared regions of sunlight, thereby preventing the temperature of the white radiative cooling element 200 according to the second embodiment of the present invention from rising due to sunlight.

[0456] Preferably, the reflection enhancement layer 230 can be made of a material that can reflect sunlight well, especially the material should have a reflectivity of more than 90% for light in the visible light region.

[0457] The reflection enhancement layer 230 may be a layer in which a metal material is deposited on the substrate 210.

[0458] According to an embodiment, the reflection enhancement layer 230 is formed on the substrate 210 by depositing a metallic material using one of the following methods: sputtering, atomic layer deposition (ALD), chemical vapor deposition (CVD), thermal evaporation, co-evaporation, plasma-enhanced chemical vapor deposition (PECVD), electron beam evaporation, radio frequency sputtering, magnetron sputtering, vacuum deposition, or chemical vapor deposition.

[0459] According to an embodiment, the reflection enhancement layer 230 may be made of at least one of metallic materials such as silver (Ag), aluminum (Al) and platinum (Pt), but is not limited to said materials.

[0460] According to an embodiment, the reflective layer 120 can be formed from a commercially available solar reflective film such as 3M sunglasses film.

[0461] According to an embodiment, the white radiative cooling element 200 of the second embodiment of the present invention can be repeatedly formed with a reflection enhancement layer 230 and a white radiative cooling layer 220.

[0462] Specifically, the white radiation cooling element 200 according to the second embodiment of the present invention can be formed by laminating it onto the substrate 210 in the order of reflection enhancement layer 230-white radiation cooling layer 220-reflection enhancement layer 230-white radiation cooling layer 220-...

[0463] Reference Figure 23c In the white radiation cooling element 300 according to the third embodiment of the present invention, fluorescent particles 323 that emit radiation fluorescence can be further mixed in the white radiation cooling layer 320.

[0464] Accordingly, the white radiation cooling element according to the third embodiment of the present invention includes: a substrate 310; and a white radiation cooling layer formed on the substrate 310, wherein metal oxide particles containing sunlight with wavelengths having visible light regions and fluorescent particles 323 emitting fluorescence are mixed in a polymer matrix 321 that absorbs sunlight with wavelengths having mid-infrared regions and radiates it as heat.

[0465] Since the white radiative cooling element 300 according to the third embodiment of the present invention may include all the constituent elements of the white radiative cooling element 300 according to the first and second embodiments, repeated descriptions will be omitted.

[0466] The fluorescent particles 323 included in the white radiation cooling layer 320 emit visible light by absorbing sunlight, and according to embodiments, can emit visible light of at least one color.

[0467] Accordingly, by mixing colors using fluorescent particles 323 having at least one color, the white radiative cooling element 300 according to the third embodiment of the present invention can not only present white, but also present various colors.

[0468] According to an embodiment, the fluorescent particles 323 may be made of manganese (Mn) that emits red fluorescence and antimony (Sb) that emits blue fluorescence.

[0469] According to an embodiment, the fluorescent particles 323 may be formed of ruthenium aluminum garnet (LuAG) or yttrium aluminum garnet (YAG), nitrides, sulfides, silicates or mixtures thereof.

[0470] According to an embodiment, the white radiative cooling element 300 of the third embodiment of the present invention may include fine particles 322 and a color developer 323 within a polymer matrix 321.

[0471] The color developer 323 can be a commonly known metamaterial or dye, but is not limited to the materials mentioned above.

[0472] Accordingly, the white radiative cooling element 300 according to the third embodiment of the present invention also includes fluorescent particles 323, so that the color is different from that of the mirror and can present a variety of colors, thereby improving the aesthetics.

[0473] Hereinafter, the white radiative cooling element according to the present invention is manufactured according to an embodiment, and the characteristics and effects of the white radiative cooling element are demonstrated by evaluating the characteristics of the white radiative cooling element of the embodiment.

[0474] [Example 1-1]

[0475] The mixture was prepared by mixing zinc oxide (ZnO) particles with a diameter of 20 nm as fine particles, based on 30% by weight of the total weight of PDMS as a polymer.

[0476] Subsequently, an electron beam evaporator was used to form a reflection enhancement layer made of silver (Ag) on ​​the glass substrate.

[0477] The mixture is then spin-coated onto the reflectivity enhancement layer to create a white radiative cooling element.

[0478] [Examples 1-2]

[0479] The white radiative cooling element was manufactured in the same manner as in [Example 1-1], except that the zinc oxide particles were mixed in at 50% by weight.

[0480] [Example 2-1]

[0481] The mixture was prepared by mixing alumina (Al2O3) particles with a diameter of 20 nm as fine particles, based on 1.9% by weight of the total weight of DPHA as a polymer.

[0482] Subsequently, an electron beam evaporator was used to form a reflection enhancement layer made of silver (Ag) on ​​the glass substrate.

[0483] The mixture is then spin-coated onto the reflectivity enhancement layer to create a white radiative cooling element.

[0484] [Example 2-2]

[0485] The white radiative cooling element was manufactured in the same manner as in [Example 1-1], except that the mixture was made by mixing alumina particles in an amount of 3.8% by weight based on the total weight of DPHA.

[0486] [Examples 2-3]

[0487] The white radiative cooling element was manufactured in the same manner as in [Example 1-1], except that the mixture was made by mixing alumina particles in an amount of 7.7% by weight based on the total weight of DPHA.

[0488] [Comparative Example 1]

[0489] After forming a reflective layer made of silver (Ag) on ​​a glass substrate using an electron beam evaporator, DPHA is spin-coated onto the reflective layer to manufacture a radiative cooling element.

[0490] [Example 3]

[0491] The mixture was prepared by mixing 33% by weight of PVDF particles with a diameter of 20 nm as fine particles, based on the total weight of the polymer PUA.

[0492] White radiative cooling elements are manufactured by spin-coating the mixture onto a glass substrate.

[0493] [Comparative Example 2-1]

[0494] Radiation cooling elements are manufactured by spin-coating PUA onto a glass substrate.

[0495] [Comparative Example 2-2]

[0496] silver substrate

[0497] Feature evaluation

[0498] 1. White radiative cooling element containing fine metal oxide particles

[0499] Figure 24a and Figure 24b This is a graph showing the absorption rate of a white radiative cooling element according to the fine particle content, based on an embodiment of the present invention.

[0500] Reference Figure 24a and Figure 24b It can be confirmed that both Example 1-1 and Example 1-2 have high reflectivity for visible light.

[0501] Furthermore, by measuring the reflectance of Examples 1-1 and 1-2, it can be confirmed that the reflectance of Example 1-2, which has a higher zinc oxide particle content, is higher than that of Example 1-1.

[0502] That is, it can be confirmed that the higher the content of fine particles in the white radiation cooling element according to the embodiments of the present invention, the lower the transmittance of visible light, that is, the higher the reflectance of visible light.

[0503] Figure 25 This is a graph showing the temperature change over time of a white radiative cooling element comprising fine particles according to an embodiment of the present invention.

[0504] refer to Figure 25 It can be confirmed that, under clear weather conditions on May 28, 2019, the temperature of Example 2-3 was -11.9℃, Example 2-2 was -11.3℃, Example 2-1 was -9.2℃, and Comparative Example 1 was -8.8℃.

[0505] In addition, it can be confirmed that under clear weather conditions on May 29, 2019, the temperature of Example 2-3 was -11.6℃, Example 2-2 was -11.3℃, Example 2-1 was -9.21℃, and Comparative Example 1 was -8.7℃.

[0506] In addition, it can be confirmed that on a cloudy day on May 29, 2019, the temperature was -7.2°C for Example 2-3, -6.6°C for Example 2-2, -5.9°C for Example 2-1, and -5.4°C for Comparative Example 1.

[0507] That is, it can be confirmed that there is a large temperature change in the order of Examples 2-3, Examples 2-2, Examples 2-1 and Comparative Example 1, and the mid-infrared emissivity and visible light reflectivity / scattering rate increase with the increase of fine particle content, thereby improving the cooling efficiency of the white radiation cooling element.

[0508] Figure 26aIt is an image showing the current state of the existing radiative cooling elements. Figure 26b This is an image showing the state of a white radiative cooling element according to an embodiment of the present invention.

[0509] First, refer to Figure 26a It can be confirmed that existing radiation cooling elements that form a polymer layer on the reflective layer have the same color as a metallic mirror.

[0510] However, reference Figure 26b It can be confirmed that the white radiative cooling element of the third embodiment is white.

[0511] Therefore, it can be confirmed that the white radiative cooling element of Embodiment 2 appears white by reflecting and scattering visible light through PUA particles.

[0512] Figure 27 This is a graph showing the absorption rate of the white radiation cooling element, which varies according to the type of polymer included in the white radiation cooling layer according to an embodiment of the present invention.

[0513] refer to Figure 27 It can be confirmed that Example 3 (PUA+PVDF) has high reflectivity for visible light and high emissivity in the mid-infrared region.

[0514] Furthermore, by observing the solar light absorptivity in the visible, near-infrared, and mid-infrared regions of Example 3 (PUA PVDF) and Comparative Example 2-1 (PUA), it can be confirmed that the cooling power efficiency is 35.42 W / m2 at an ambient temperature of 40°C.

[0515] In the yellow region, which represents the visible light region, the absorption rate of Example 3 is lower than that of Comparative Example 2-1, thus confirming that the visible light reflectance of Example 3 is higher than that of Comparative Example 2-1.

[0516] Furthermore, the emissivity of Example 3 and Comparative Example 2-1 in the blue areas of the near-infrared and mid-infrared regions is substantially similar, thus the mid-infrared emissivity is not affected even if PUA particles are included.

[0517] Furthermore, according to embodiments of the present invention, the white radiative cooling element comprising fine polymer particles has the highest emissivity in the mid-infrared region, and even increasing the content of fine particles has almost no impact on the emissivity.

[0518] Figure 28 This is a graph showing the temperature change over time of a white radiative cooling element comprising fine polymer particles according to an embodiment of the present invention.

[0519] at this time, Figure 28 The ambient temperature shown is the temperature inside the chamber where the radiative cooling elements of Example 3 and Comparative Example 2-2 are installed, and is used to compare the cooling degree of Example 3 and Comparative Example 2-2.

[0520] In addition, the external temperature is the temperature outside the chamber, which is determined by convection measurement and is lower than the ambient temperature.

[0521] Reference Figure 28 The results of comparing the temperature of Example 3 (PUA+PVDF) with the ambient temperature (Ambient T) confirm that Example 3 was on average about 5.7°C cooler than the ambient temperature.

[0522] Furthermore, comparing the temperatures of Example 3 and Comparative Example 2-2, it can be confirmed that Example 3 is on average about 1.6°C cooler than Comparative Example 2-2.

[0523] It can be confirmed that, according to the embodiments of the present invention, the polymer matrix that emits mid-infrared rays also includes fine particles that reflect and scatter visible light, thereby having higher cooling performance than existing radiation cooling elements.

[0524] As described above, although the invention has been described with reference to defined embodiments and accompanying drawings, the invention is not limited to the above embodiments, and various modifications and variations can be made by those skilled in the art based on these descriptions. Therefore, the scope of the invention should not be limited to the described embodiments, but should be defined by the equivalent scope of the claims described below.

Claims

1. A radiative cooling element, characterized in that, include: A reflective layer that reflects sunlight with wavelengths in the ultraviolet, visible, and near-infrared regions; and a radiative cooling layer formed on the reflective layer that absorbs sunlight with wavelengths in the mid-infrared region and radiates it as heat, wherein the radiative cooling layer comprises: A mid-infrared absorbing layer, formed on the reflective layer, absorbs sunlight with wavelengths in the mid-infrared region and radiates it as heat; and A coating is formed on the mid-infrared absorbing layer. The coating comprises: A first radiating layer, comprising an embossed pattern; and A second radiating layer is formed on the first radiating layer and has a different refractive index than the first radiating layer. The coating described above reflects sunlight with wavelengths in the visible light region. The first radiating layer and the second radiating layer have different refractive indices for sunlight of the wavelengths in the visible light region, wherein the refractive index of the first radiating layer for sunlight of the wavelengths in the visible light region is greater than the refractive index of the second radiating layer for sunlight of the wavelengths in the visible light region. The first radiating layer and the second radiating layer are repeatedly formed, and the refractive index difference between the first radiating layer and the second radiating layer is 0.7 to 2.

2. The radiative cooling element according to claim 1, characterized in that, The reflective layer includes at least one of silver, aluminum, and platinum.

3. The radiative cooling element according to claim 1, characterized in that, The first radiating layer and the second radiating layer comprise at least one of fine particles composed of oxides or nitrides and a polymeric material. The fine particles have a diameter of 10 nm to 20 μm and include at least one of silicon dioxide, zirconium oxide, aluminum oxide, titanium dioxide, and silicon nitride. The polymeric material is PDMS or DPHA.

4. The radiative cooling element according to claim 1, characterized in that, The thicknesses of the first radiating layer and the second radiating layer are 10 nm to 2000 nm, respectively.

5. The radiative cooling element according to claim 1, characterized in that, The first radiating layer comprises at least one of ZnS, Si, and Ge, and the second radiating layer comprises CaF2.

6. A method of manufacturing a radiative cooling element, characterized by, include: The step of forming a reflective layer on a substrate that can reflect sunlight with wavelengths in the ultraviolet, visible and near-infrared regions; as well as In the step of forming a radiative cooling layer on the reflective layer, the radiative cooling layer is capable of absorbing sunlight with wavelengths in the mid-infrared region and radiating it as heat. The steps for forming the radiation cooling layer include: The steps of forming a mid-infrared absorbing layer on the reflective layer for absorbing sunlight with wavelengths in the mid-infrared region and radiating it as heat; and The step of forming a coating on the mid-infrared absorption layer. The coating formation step includes: The step of forming a first radiating layer including a concave-convex pattern on the mid-infrared absorbing layer; and The step of forming a second radiation layer with a refractive index different from that of the first radiation layer on the first radiation layer. The coating described above reflects sunlight with wavelengths in the visible light region. Wherein, the refractive index of the first radiating layer for sunlight of the wavelengths in the visible light region is greater than the refractive index of the second radiating layer for sunlight of the wavelengths in the visible light region. The first radiating layer and the second radiating layer are repeatedly formed, and the refractive index difference between the first radiating layer and the second radiating layer is 0.7 to 2.

7. The method for manufacturing a radiative cooling element according to claim 6, characterized in that, The first radiating layer is formed into a raised pattern by molding after coating the mid-infrared absorbing layer with at least one of fine particles made of oxides or nitrides and a polymer.

8. The method for manufacturing a radiative cooling element according to claim 6, characterized in that, The second radiation layer is formed by spin-coating at least one of fine particles made of oxides or nitrides and polymeric substances over a period of 30 to 40 seconds on the first radiation layer.

Images