Radiative cooling material and method of making the same

Abstract

The application discloses a radiation refrigeration material and a preparation method thereof. The radiation refrigeration material comprises a top layer and a bottom layer. The top layer is an ultraviolet light reflecting layer, and the ultraviolet light reflecting layer is a polymer multilayer film which is regularly alternately compounded by polymethyl methacrylate and polycarbonate. The bottom layer is a polymer resin layer doped with refractive particles. The application also provides a preparation method of the radiation refrigeration material. The radiation refrigeration material can strongly reflect ultraviolet light, and the ultraviolet light aging resistance is greatly improved. The radiation refrigeration material overcomes the refrigeration power loss problem caused by the absorption of ultraviolet light by a traditional ultraviolet light absorber, and has the advantages of strong ultraviolet light aging resistance and excellent radiation refrigeration performance.

Description

Technical Field

[0001] This invention belongs to the field of radiation cooling materials technology, specifically relating to a radiation cooling material with strong ultraviolet reflection and its preparation method. Background Technology

[0002] Building cooling energy consumption is rising steadily in summer. Statistics show that building cooling energy consumption accounts for 15% of global energy consumption, and this proportion is continuously increasing. Traditional air conditioning methods consume large amounts of energy while increasing carbon dioxide emissions, which will further exacerbate the greenhouse effect. To address the problem of cooling energy consumption, improving existing cooling technologies or seeking new temperature control methods are effective approaches. Among these, daytime radiative cooling relies on infrared radiation through atmospheric windows (8-13 μm) to directly exchange heat with outer space, reducing the surface temperature of objects with zero energy consumption. Various radiative cooling materials can be prepared to achieve daytime radiative cooling. Current daytime radiative cooling materials can be broadly classified into photonic crystals, polymers, and metamaterials. Among these, polymers, due to their low preparation cost and ease of processing, are the most promising type of radiative cooling materials for industrial production.

[0003] However, polymer materials often lack stability in complex outdoor environments. This is mainly because strong ultraviolet (UV) radiation in sunlight causes photoaging within the polymer material, which severely damages its structure, significantly shortens its lifespan, and rapidly deteriorates its radiative cooling performance. Currently, there are two main solutions to this problem: one is to use UV absorbers, such as titanium dioxide, to absorb some of the UV radiation from sunlight, effectively slowing down UV-induced aging and greatly improving the polymer's resistance to UV aging; however, the absorbed UV energy is converted into heat, weakening the cooling capacity of the radiative cooling material. The other solution is to use UV-stabilized plastics, primarily fluoroplastics such as polytetrafluoroethylene (PTFE). These polymers have high CF bond energies, thus generally exhibiting good resistance to UV aging. However, these plastics are expensive, and the production process uses fluorine-containing raw materials, which can easily cause environmental pollution. Summary of the Invention

[0004] In view of this, the primary objective of the present invention is to provide a radiation cooling material that can effectively reflect ultraviolet rays, significantly improve its resistance to ultraviolet aging, and at the same time have excellent radiation cooling performance.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] The first aspect of the present invention provides a radiation cooling material comprising a top layer and a bottom layer, wherein:

[0007] The top layer is an ultraviolet reflective layer, which is a polymer multilayer film composed of polymethyl methacrylate and polycarbonate in a regular alternating composite.

[0008] The bottom layer is a polymer resin layer doped with refractive particles.

[0009] In a further embodiment, the refracting particles are titanium dioxide, barium strontium titanate, or zirconium dioxide.

[0010] In a further embodiment, the refracting particles are titanium dioxide.

[0011] In a further embodiment, the titanium dioxide has a particle size of 200nm-400nm.

[0012] In a further embodiment, the polymer resin is epoxy resin, polyurethane, polyoxymethylene, or polyethersulfone.

[0013] In a further embodiment, the polymer resin is an epoxy resin.

[0014] In a further embodiment, the polymer resin layer is also doped with silicon dioxide.

[0015] In a further embodiment, the particle size of the silica is 6μm-8μm.

[0016] In a further embodiment, the thickness of the ultraviolet reflective layer is 16 μm.

[0017] In a further embodiment, the thickness of the polymer resin layer is 1mm-3mm.

[0018] The present invention further provides a method for preparing the radiation cooling material as described above, comprising the following steps:

[0019] Forms an ultraviolet reflective layer;

[0020] The refractory particles and polymer resin pre-cured material are mixed evenly to form a mixture;

[0021] The mixture is evenly applied to the ultraviolet reflective layer, dried and cured to obtain a radiation cooling material.

[0022] In a further embodiment, the ultraviolet reflective layer is prepared by a micro-nano layering co-extrusion process of polymethyl methacrylate and polycarbonate.

[0023] In a further embodiment, the micro / nano laminated co-extrusion process includes the following steps:

[0024] The melts of polymethyl methacrylate and polycarbonate are stacked to form two polymer melts;

[0025] The two polymer melts are multiplied to obtain a multilayer polymer melt.

[0026] The polymer multilayer melt is extruded, cooled, and stretched to form a polymer multilayer film.

[0027] In a further embodiment, the multiplication is achieved through a multiplication system containing a multiplier;

[0028] In a further embodiment, the multiplier includes at least one of an equal-division multiplier and an unequal-division multiplier.

[0029] In a further embodiment, the multiplier type includes at least one of a 1-to-2 splitter and a 1-to-4 splitter.

[0030] In a further embodiment, the multiplier includes two equally divided "one-to-four" multipliers, one equally divided "one-to-two" multiplier, and two unequally divided "one-to-two" multipliers; or, it includes three equally divided "one-to-four" multipliers and one unequally divided "one-to-two" multiplier.

[0031] The beneficial effects of this invention:

[0032] The radiative cooling material of this invention has a top layer consisting of a polymer multilayer film composed of alternating layers of polymethyl methacrylate and polycarbonate to achieve high ultraviolet reflection; while the bottom layer is a polymer resin layer doped with refractive particles to achieve efficient solar radiation scattering and infrared emission through the "atmospheric window". This radiative cooling material improves its overall resistance to ultraviolet aging through the synergistic effect of the above composite structure and overcomes the cooling power loss problem caused by ultraviolet absorption in traditional ultraviolet absorbers, exhibiting advantages such as strong resistance to ultraviolet aging and excellent radiative cooling performance.

[0033] The preparation process of the radiation cooling material in this invention is simple and low-cost, and it can be mass-produced, making it possible for the industrial-scale mass production of radiation cooling materials resistant to ultraviolet aging. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the structure of the radiative cooling material in a preferred embodiment of the present invention.

[0035] Figure 2 for Figure 1 A schematic diagram of the radiation cooling principle of a medium-radiation cooling material.

[0036] Figure 3 This is a flowchart illustrating the preparation process of the radiation cooling material in a preferred embodiment of the present invention.

[0037] Figure 4 The solar spectral reflectance diagram is shown for the radiative cooling material prepared in Example 1.

[0038] Figure 5The image shows the infrared emissivity of the radiation cooling material prepared in Example 1.

[0039] Figure 6 This is a diagram showing the actual cooling effect obtained in Example 1. Detailed Implementation

[0040] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0041] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0042] The first aspect of this invention provides a radiation-cooling material comprising a top layer and a bottom layer. The top layer is an ultraviolet-reflective layer, which serves to achieve high ultraviolet reflection. The bottom layer is a polymer resin layer doped with refractive particles, which serves to achieve efficient solar radiation scattering and infrared emission through an "atmospheric window."

[0043] The ultraviolet reflective layer in this invention is a polymer multilayer film, which is composed of polymethyl methacrylate (PMMA) and polycarbonate (PC) in a regular alternating composite. Based on the principle of optical interference, the regular alternating composite of PMMA and PC can give the ultraviolet reflective layer extremely high ultraviolet reflective ability, avoid ultraviolet damage to the underlying polymer resin, and greatly improve the outdoor service life of the underlying polymer resin.

[0044] In this article, the underlying polymer resin refers to a polymer with radiative cooling properties, especially a polymer that is prone to aging. These polymers possess excellent radiative cooling properties and exhibit multiple absorption peaks in the 8-13 μm "atmospheric window" band. However, during outdoor use, they are susceptible to aging problems such as yellowing due to ultraviolet radiation. Specific examples include epoxy resin, polyurethane, polyoxymethylene, or polyethersulfone, but are not limited to these. In some specific embodiments of this invention, epoxy resin is preferably used as the underlying polymer resin.

[0045] The refractive particles described herein refer to nanoparticles with a high refractive index (refractive index greater than 2), including inorganic oxides or salts, such as titanium dioxide, barium strontium titanate, or zirconium dioxide, but not limited to these. In some specific embodiments of the present invention, titanium dioxide (with a refractive index as high as approximately 2.6) is preferably used as the nano-refractive particles. It is understood that the particle size of the refractive particles can be selected and adjusted according to the properties of the final material. Specifically, refractive particles of different sizes have different light reflection intensities. To design the reflection peak to be within the required wavelength range, in some specific embodiments of the present invention, the particle size of titanium dioxide is preferably 200 nm-400 nm.

[0046] This invention incorporates refractive particles into the polymer resin layer, thereby endowing the composite material with excellent solar radiation shielding capabilities through the high refractive index of these particles. Furthermore, the bottom polymer resin exhibits multiple absorption peaks in the 8-13 μm "atmospheric window" band. According to Kirchhoff's law, an object in thermal equilibrium has an absorptivity equal to its emissivity; multiple absorption peaks indicate high infrared emissivity. This allows the polymer resin and the refractive particles to work synergistically to ensure excellent infrared emission performance. However, these polymer resins typically yellow under ultraviolet radiation during outdoor use. This invention addresses this by adding an ultraviolet-reflective layer to the top layer, significantly preventing UV damage to the bottom polymer resin and extending its outdoor lifespan.

[0047] In a further embodiment, the number of layers and the thickness of the ultraviolet reflective layer described in this paper are designed according to the principle of optical interference to achieve high reflection of ultraviolet rays. In a specific embodiment of the present invention, its thickness is 16 μm.

[0048] The bottom polymer resin layer, serving as the substrate, emits infrared radiation into outer space in the infrared transparent band. Its thickness should not be too thin (less than 1 mm), as this would result in insufficient mechanical strength, difficult processing, and weak radiation capability. Conversely, its thickness should not be too thick, as this would increase costs. Therefore, considering all factors, the preferred thickness of the bottom polymer resin layer is 1 mm to 3 mm, with 2 mm being the most desirable.

[0049] Furthermore, as a preferred embodiment, silica is also doped into the underlying polymer resin. Since silica nanoparticles contain Si-O bonds, doping with silica can enhance the infrared emissivity of the material in the "atmospheric window," thereby enhancing the emission capability through resonance. It is understood that the particle size of the silica can be selected or adjusted as needed; preferably, in this paper, the particle size of the silica is 6μm-8μm.

[0050] The second aspect of this invention provides a method for preparing a radiation-cooling material as described in the first aspect of this invention, the main steps of which are as follows:

[0051] S1, Forming an ultraviolet reflective layer

[0052] The ultraviolet reflective layer in this paper is prepared by a micro-nano layered co-extrusion process of polymethyl methacrylate and polycarbonate. Specifically, firstly, a melt of polymethyl methacrylate and polycarbonate is formed; then, the melts of polymethyl methacrylate and polycarbonate are stacked to form two polymer melts; subsequently, the layered polymer melts are multiplied to obtain a multilayer polymer melt; finally, the multilayer polymer melt is extruded, cooled and stretched to form a multilayer polymer film.

[0053] There are no particular limitations on the formation of the melt of polymethyl methacrylate and polycarbonate. In some specific embodiments of the present invention, the melt can be formed by mixing, melting and extruding polymethyl methacrylate and polycarbonate using a corresponding extruder, by means well known in the art.

[0054] The multiplication described herein refers to multiplication achieved through a multiplication system containing multipliers. Generally, a multiplication system can contain multiple multipliers of the same or different types, connected in series. The specific number and type of multipliers are designed according to needs. The multipliers include equally divided multipliers and unequally divided multipliers, and the types include 1-to-2 and 1-to-4 multipliers. In some specific embodiments of the present invention, the multipliers include two equally divided "1-to-4" multipliers, one equally divided "1-to-2" multiplier, and two unequally divided "1-to-2" multipliers (separation ratios of 1:0.96 and 1.04:1, respectively); or, three equally divided "1-to-4" multipliers and one unequally divided "1-to-2" multiplier (separation ratio of 1.04:1); or, three equally divided "1-to-4" multipliers and one unequally divided "1-to-2" multiplier (separation ratio of 0.96:1).

[0055] It is understood that the reflection band range of the ultraviolet reflective layer can be adjusted by changing the thickness of the ultraviolet reflective layer and the type of multiplier (including type, separation, etc.) to meet the practical application requirements of radiation cooling materials. In some specific embodiments of the present invention, the reflection band range of the ultraviolet reflective layer is 340-400nm, which covers the main wavelengths of ultraviolet radiation in solar radiation.

[0056] S2. Prepare a polymer resin layer to obtain a radiation cooling material.

[0057] The preparation of the polymer resin layer in this paper can be carried out using methods well known to those skilled in the art. In some specific embodiments of the present invention, a mold method is employed. Specifically, refractive particles and silica (if present) are added to the pre-cured base polymer resin, and the mixture is stirred thoroughly until homogeneous. The mixture is then placed in a vacuum chamber for defoaming, and the solution is poured into a mold to evenly cover the ultraviolet reflective layer prepared in step S1. Finally, the mold is transferred to a vacuum drying oven for drying and curing, thus obtaining the base polymer resin layer and simultaneously acquiring a radiation cooling material. It should be noted that the specific curing method is selected according to the type of polymer resin. For example, the curing of epoxy resin requires a corresponding curing agent, which is then added to the mixture. Other types of resins are similar and will not be elaborated upon here.

[0058] The content of refractive particles and silica (if present) in the underlying polymer resin layer can be designed according to performance requirements. The content of refractive particles should not be too high, as this will cause optical congestion and reduce reflectivity; if the content is too low, the concentration will be insufficient, and the reflectivity will not meet requirements. Conversely, if the silica content is too low, the reinforcing effect will be insignificant; if it is too high, it will easily lead to a decrease in the mechanical properties of the underlying polymer resin. Therefore, in some specific embodiments of the present invention, the volume fraction of titanium dioxide in the mixture is 2.5% to 15%, specifically 2.5%, 5%, 10%, or 15%; and the volume fraction of silica is 1% to 5%, specifically 1%, 2%, 3%, 4%, or 5%.

[0059] Furthermore, as is well known to those skilled in the art, while traditional photonic crystals can effectively reflect ultraviolet light, their fabrication primarily relies on magnetron sputtering or vacuum deposition methods, the high cost of which limits their application in the field of radiation cooling materials. This invention, however, employs a method combining a polymer multilayer reflective film and a polymer resin. The polymer multilayer reflective film can be mass-produced through a stacking and multiplication process, with a cost only about one-thousandth that of traditional photonic crystal materials, demonstrating a significant cost advantage.

[0060] The present invention will be described below through specific embodiments. It should be noted that the specific embodiments below are for illustrative purposes only and do not limit the scope of the present invention in any way. In addition, unless otherwise specified, methods that do not specifically describe conditions or steps are conventional methods, and the reagents and materials used can be obtained commercially.

[0061] Example 1

[0062] The structure of the radiative cooling material provided in this embodiment is as follows: Figure 1As shown, the radiation cooling material consists of two parts: a top layer is an ultraviolet reflective layer composed of polymer multilayer films, used to achieve high ultraviolet reflection; and a bottom layer is an epoxy resin layer doped with titanium dioxide and silicon dioxide, used to achieve efficient solar radiation scattering and infrared emission through the "atmospheric window".

[0063] The radiation cooling principle of this radiation cooling material is as follows: Figure 2 As shown, when solar radiation reaches the material surface, the top ultraviolet reflective layer reflects the ultraviolet rays from the solar radiation. This ultraviolet reflective layer is highly transparent to other wavelengths of solar radiation, and the transmitted solar radiation is highly scattered by the bottom epoxy resin layer. Therefore, the material exhibits extremely high reflectivity in the solar radiation band. Regarding infrared reflectivity, both epoxy resin and silicon dioxide have absorption peaks within the 8-13 μm atmospheric window. According to Kirchhoff's law, when an object is in thermal equilibrium, its absorptivity equals its emissivity. Therefore, this material has excellent infrared emission performance. Furthermore, since ultraviolet rays are primarily reflected by the top ultraviolet reflective layer, damage to the bottom epoxy resin layer from ultraviolet rays is prevented, improving the outdoor lifespan of the epoxy resin layer. Simultaneously, it avoids the problem of reduced cooling performance caused by titanium dioxide absorbing ultraviolet energy.

[0064] This embodiment also provides Figure 1 The preparation method of the radiation cooling material shown can be found in the detailed preparation process. Figure 3 The specific steps are as follows:

[0065] S1. Preparation of the ultraviolet reflective layer: PC and PMMA are selected as raw materials, with PC having a refractive index of 1.58 and PMMA having a refractive index of 1.48. In this embodiment, the total number of film layers is designed to be 256, and the film structure is designed as Air|(HL)^ 32 0.96(HL)^ 32 1.04(HL)^ 32 (HL)^ 32|Air, the reflective bandwidth of the film layer is 340-400nm, covering the main ultraviolet bands in solar radiation. In this embodiment, the total thickness of the ultraviolet reflective layer is designed to be 16μm. The preparation method is a polymer micro-nano layering multiplication process, using two equally divided quadruple multipliers, one equally divided bispinator, and two unequally divided bispinators. The specific preparation steps are as follows: all raw materials are first dried in a vacuum drying oven at 90℃ for 9h, and then added to an extruder. The melting temperature is selected as 270℃. The polymer melt is pre-formed into a two-layer structure. One equally divided quadruple multiplier can multiply the two melt layers into eight layers. Two equally divided quadruple multipliers can multiply the initial two melt layers into 32 layers, and then multiply them into 64 layers through the equally divided bispinator. Finally, it is multiplied by the first unequally divided bispinator. The multiplier (with a separation ratio of 1:0.96) multiplies 64 layers into 128 layers, but the total thickness ratio of the upper and lower 64 layers is 1:0.96. Similarly, after passing through a second unequally divided "one-to-two" multiplier (with a separation ratio of 1.04:1), the 128 layers are multiplied into 256 layers, but the total thickness ratio of the upper and lower 128 layers is 1.04:1. After multiplication, the fluid is extruded and shaped by the extrusion die, and then cooled and stretched into a film. The film thickness can be controlled by the extrusion screw speed.

[0066] S2. Preparation of Radiative Cooling Material: In this embodiment, transparent epoxy resin of type 204 (purchased from Shenzhen Juhengchuang Electronic Materials) is used. This type of epoxy resin consists of epoxy resin pre-cured material and curing agent. 10% by volume of titanium dioxide and 5% by volume of silica nanoparticles are added to the epoxy resin pre-cured material. The titanium dioxide has a particle size of 400 nm and the silica has a particle size of 8 μm. The mixture is stirred thoroughly, and then the curing agent is added. The mass ratio of pre-cured material to curing agent is 3:1. After adding the curing agent, the mixture is stirred thoroughly until it is uniform. Then, it is placed in a vacuum chamber to defoam. The mixture is then poured into a silicone mold and smoothly covered with the ultraviolet multilayer reflective film from step S1. Finally, it is transferred to a vacuum drying oven for drying and curing to form an epoxy resin layer with a thickness of 2 mm, thus obtaining the radiative cooling material.

[0067] Performance testing

[0068] Those skilled in the art know that excellent radiative cooling materials must possess extremely high solar radiation reflectivity and a high "atmospheric window" emissivity. The present invention conducted relevant performance tests on the radiative cooling material prepared in Example 1, and the results are as follows:

[0069] 1. Solar radiation reflectivity

[0070] The reflectivity of the radiative cooling material in Example 1 within the range of 0.3-2.5 μm was tested as follows: Figure 4As shown, due to the use of a double-layer structure, the radiative cooling material has a high reflectivity to solar radiation. In particular, the average reflectivity of the material is 95% in the 0.3-1.5μm range where solar radiation energy is concentrated, and the average reflectivity of the material is 93% (>90%) in the entire solar radiation band of 0.3-2.5μm. This indicates that the radiative cooling material has extremely high solar radiation reflection capability.

[0071] 2. Infrared emissivity

[0072] The infrared emission pattern of the radiation cooling material in Example 1 is shown below. Figure 5 As shown, by Figure 5 It can be seen that the average emissivity of this radiative cooling material in the 8-13 μm band is 93.2%, indicating that the radiative cooling material has good atmospheric window emissivity.

[0073] 3. Ultraviolet reflectance

[0074] Figure 4 The results of the ultraviolet reflectance test of the radiation cooling material in Example 1 are also shown. The epoxy resin underlayer refers to the material that is not covered with an ultraviolet reflective layer but is doped with titanium dioxide particles, and the transparent epoxy resin refers to the material that is not covered with an ultraviolet reflective film and is not doped with titanium dioxide.

[0075] Depend on Figure 4 It can be seen that in the ultraviolet band of 300-400nm, the radiation cooling material prepared in Example 1 has an ultraviolet reflectivity of over 90%, which ensures that the radiation cooling material has excellent resistance to ultraviolet aging. Furthermore, since epoxy resin itself has good mechanical properties, the radiation cooling material has good environmental stability in harsh outdoor environments.

[0076] 4. The radiative cooling material was directly subjected to outdoor field testing on March 11, 2024, when the weather was clear and the maximum solar irradiance exceeded 800 W / m². 2 During the test, no shielding measures, including sunshade and convection shielding, were used, and its cooling performance was as follows: Figure 6 As shown, the results indicate that under direct sunlight during the day, the sample temperature remains consistently lower than the ambient temperature, with a maximum temperature difference of approximately 6°C and an average temperature difference of approximately 2.5°C. This demonstrates the enormous cooling potential and practical applicability of this radiative cooling material.

[0077] Example 2

[0078] This embodiment provides another method for preparing the radiation cooling material of the present invention, the specific steps of which are as follows:

[0079] S1. Preparation of the ultraviolet reflective layer: PC and PMMA are selected as raw materials, with PC having a refractive index of 1.58 and PMMA having a refractive index of 1.48. In this embodiment, the total number of film layers is designed to be 256, and the film structure is designed as Air|(HL)^ 64 1.04(HL)^ 64 |Air, the reflectance bandwidth of the film layer is 350-390nm. In this embodiment, the total thickness of the ultraviolet reflective layer is designed to be 16μm. The preparation method is a polymer micro-nano layer multiplication process, and three equally divided quadruple multipliers and one divisor with a separation ratio of "1.04:1" are selected. The specific preparation steps are as follows: All raw materials are first dried in a vacuum drying oven at 90°C for 9 hours, and then added to an extruder. The melting temperature is selected as 270°C. The polymer melt is pre-formed into a two-layer structure. One equally divided "one-to-four" multiplier can multiply the two-layer melt into eight layers. Three identical "one-to-four" multipliers form a 128-layer structure. Then, it passes through an unequally divided "one-to-two" multiplier (with a separation ratio of 1.04:1), and the 128 layers are multiplied into 256 layers. The total thickness ratio of the upper and lower 128 layers is 1.04:1. After multiplication, the fluid is extruded and formed by the extrusion die, and then cooled and stretched into a film. The film thickness can be controlled by the extrusion screw speed.

[0080] S2. Preparation of Radiation Cooling Material: In this embodiment, transparent epoxy resin of type 204 (purchased from Shenzhen Juhengchuang Electronic Materials) is used. This type of epoxy resin consists of epoxy resin pre-cured material and curing agent. 10% by volume of titanium dioxide particles with a particle size of 400nm are added to the epoxy resin pre-cured material. After thorough stirring, the curing agent is added. The mass ratio of pre-cured material to curing agent is 3:1. After adding the curing agent, the mixture is stirred thoroughly until homogeneous. Then, it is placed in a vacuum chamber to defoam. The mixture is then poured into a silicone mold and smoothly covered with the ultraviolet multilayer reflective film from step one. Finally, it is transferred to a vacuum drying oven for drying and curing to form an epoxy resin bottom layer with a thickness of 2mm, thus obtaining the radiation cooling material.

[0081] Example 3

[0082] This embodiment provides a method for preparing this radiation cooling material, the specific steps of which are as follows:

[0083] S1. Preparation of the ultraviolet reflective layer: PC and PMMA are selected as raw materials, with PC having a refractive index of 1.58 and PMMA having a refractive index of 1.48. In this embodiment, the total number of film layers is designed to be 256, and the film structure is designed as Air|(HL)^ 64 0.96(HL)^ 64|Air, the reflectance bandwidth of the film layer is 340-380nm. In this embodiment, the total thickness of the ultraviolet reflective layer is designed to be 16μm. The preparation method is a polymer micro-nano layer multiplication process, and three equally divided quadruple multipliers and one divisor with a separation ratio of "0.96:1" are selected. The specific preparation steps are as follows: All raw materials are first dried in a vacuum drying oven at 90°C for 9 hours, and then added to an extruder. The melting temperature is selected as 270°C. The polymer melt is pre-formed into a two-layer structure. One equally divided "one-to-four" multiplier can multiply the two-layer melt into eight layers. Three identical "one-to-four" multipliers form a 128-layer structure. Then, it passes through an unequally divided "one-to-two" multiplier (with a separation ratio of 0.96:1), and the 128 layers are multiplied into 256 layers. The total thickness ratio of the upper and lower 128 layers is 0.96:1. After multiplication, the fluid is extruded and shaped by the extrusion die, and then cooled and stretched into a film. The film thickness can be controlled by the extrusion screw speed.

[0084] S2. Preparation of Radiation Cooling Material: In this embodiment, transparent epoxy resin of type 204 (purchased from Shenzhen Juhengchuang Electronic Materials) is used. This type of epoxy resin consists of epoxy resin pre-cured material and curing agent. 10% by volume of titanium dioxide particles with a particle size of 400nm are added to the epoxy resin pre-cured material. After thorough stirring, the curing agent is added. The mass ratio of pre-cured material to curing agent is 3:1. After adding the curing agent, the mixture is stirred thoroughly until homogeneous. Then, it is placed in a vacuum chamber to defoam. The mixture is then poured into a silicone mold and smoothly covered with the ultraviolet multilayer reflective film from step one. Finally, it is transferred to a vacuum drying oven for drying and curing to form an epoxy resin bottom layer with a thickness of 2mm, thus obtaining the radiation cooling material.

[0085] It should be noted that, based on the basic concept of this invention, changing some features and parameters in the technical solution can also achieve the purpose of this invention:

[0086] Specifically, the refracting particles could be barium strontium titanate or zirconium dioxide.

[0087] Regarding the doping amount of the refracting particles, when the refracting particles are titanium dioxide, it can specifically be 2.5%, 5%, or 15%.

[0088] The specific doping amount of silicon dioxide can be 1%, 2%, or 4%.

[0089] The underlying polymer resin can be polyurethane, polyoxymethylene, or polyethersulfone.

[0090] The thickness of the underlying polymer resin can be either 1 mm or 3 mm.

[0091] Those skilled in the art can make appropriate selections of the above features and parameters according to actual needs, and all of them can achieve the purpose of this invention.

[0092] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0093] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A radiation cooling material, characterized in that, Including the top layer and the bottom layer, where: The top layer is an ultraviolet reflective layer based on the principle of optical interference. The ultraviolet reflective layer is a polymer multilayer film composed of polymethyl methacrylate and polycarbonate in a regular alternating composite. The top layer is configured to have high reflectivity for ultraviolet light in the 300-400nm band and high transparency for visible light, near-infrared light, and infrared radiation in the 8-13μm atmospheric window band. The bottom layer is a polymer resin layer doped with refractive particles. The bottom layer is configured to have high scattering and reflection capability in the solar radiation band and high infrared emissivity in the 8-13μm atmospheric window band. The total thickness of the ultraviolet reflective layer is 16 μm, the total number of film layers is designed to be 256, and the film layer structure is designed as Air|(HL)^ 32 0.96(HL)^ 32 1.04(HL)^ 32 (HL)^ 32 |Air, or Air|(HL)^ 64 1.04(HL)^ 64 |Air, or Air|(HL)^ 64 0.96(HL)^ 64 |Any structure in Air.

2. The radiative cooling material as described in claim 1, characterized in that, The refracting particles are titanium dioxide, barium strontium titanate, or zirconium dioxide.

3. The radiative cooling material as described in claim 2, characterized in that, The refracting particles are titanium dioxide.

4. The radiative cooling material as described in claim 3, characterized in that, The titanium dioxide has a particle size of 200nm-400nm.

5. The radiative cooling material as described in claim 1, characterized in that, The polymer resin is epoxy resin, polyurethane, polyoxymethylene, or polyethersulfone.

6. The radiative cooling material as described in claim 5, characterized in that, The polymer resin is epoxy resin.

7. The radiative cooling material as described in claim 1, characterized in that, The polymer resin layer is also doped with silicon dioxide.

8. The radiative cooling material as described in claim 7, characterized in that, The silica has a particle size of 6μm-8μm.

9. The radiative cooling material as described in claim 1, characterized in that, The thickness of the polymer resin layer is 1mm-3mm.

10. A method for preparing a radiation-cooling material as described in any one of claims 1-9, characterized in that, Includes the following steps: Forms an ultraviolet reflective layer; The refractory particles and polymer resin pre-cured material are mixed evenly to form a mixture; The mixture is evenly applied to the ultraviolet reflective layer, dried and cured to obtain a radiation cooling material.

11. The preparation method according to claim 10, characterized in that, The ultraviolet reflective layer is prepared by a micro-nano layering co-extrusion process of polymethyl methacrylate and polycarbonate.

12. The preparation method according to claim 11, characterized in that, The micro / nano laminated co-extrusion process includes the following steps: The melts of polymethyl methacrylate and polycarbonate are stacked to form a double-layer polymer melt; The bilayer polymer melt is multiplied to obtain a multilayer polymer melt; The polymer multilayer melt is extruded, cooled, and stretched to form a polymer multilayer film.

13. The preparation method according to claim 12, characterized in that, The multiplication is achieved through a multiplication system containing a multiplier; The multiplier includes equal-division multipliers and unequal-division multipliers.

14. The preparation method according to claim 13, characterized in that, The multiplier includes two equally divided "one-to-four" multipliers, one equally divided "one-to-two" multiplier, and two unequally divided "one-to-two" multipliers; or, it includes three equally divided "one-to-four" multipliers and one unequally divided "one-to-two" multiplier.

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