Radiative cooling flexible film and preparation method and application thereof

Abstract

The application discloses a radiation refrigeration flexible film, which comprises at least one radiation layer and at least one heat resistance layer, wherein the outermost layer on at least one side is the radiation layer, the material of the radiation layer has an absorption rate of more than 80% in the middle infrared wave band, and the material of the heat resistance layer comprises an organic base material and inorganic nanoparticles doped in the organic base material, wherein the inorganic nanoparticles have an absorption rate of more than 80% in the near infrared wave band. The application further discloses a preparation method of the radiation refrigeration flexible film and application thereof. The radiation refrigeration flexible film has a high visible light transmittance, can passively radiate heat while blocking the near infrared sunlight from heating the internal space, and has a simple film preparation method, low material price, large-scale preparation and wide application prospect in the fields of buildings and vehicle windows.

Description

Technical Field

[0001] This invention belongs to the field of radiation cooling materials technology, specifically relating to a radiation cooling flexible thin film, its preparation method, and its application. Background Technology

[0002] In recent years, with the continuous intensification of the global greenhouse effect, the development of green and clean materials has become a hot research topic. Traditional cooling methods (such as fans and air conditioners) not only consume a large amount of electricity during use, but also produce a lot of greenhouse gases, further exacerbating the greenhouse effect. Therefore, finding environmentally friendly and clean cooling methods is an urgent problem to be solved.

[0003] Radiative cooling is a zero-energy, zero-emission cooling method. According to Kirchhoff's third law, absorption equals radiation. Objects on Earth radiate their heat into the 3K universe through "atmospheric windows" using electromagnetic waves in the mid-infrared band (8–13 μm), thus achieving cooling. In applications such as automobiles and construction, there is not only a need for cooling but also a high requirement for the visible light (450–780 nm) transparency of windows. Therefore, while blocking near-infrared (780–2100 nm) solar radiation from heating the interior space, it is necessary to ensure visible light transmittance. Combining solar wavelength light modulation with passive radiation technology, without any energy input or emission, can maximize the cooling performance of thin films, showing broad application prospects in automotive, construction, and other fields.

[0004] Patent document CN115838490A discloses a flexible radiation-cooling film with self-cleaning function and its preparation method. The preparation method includes: selecting and cleaning a substrate material; preparing a uniform mixed solution of polydimethylsiloxane and alumina particles; drop-coating the uniform mixed solution onto the substrate surface; and peeling off the film after curing to obtain a flexible radiation-cooling film. The materials used in this method are all readily available industrial raw materials, resulting in low cost and simple preparation, enabling large-scale production. However, the low transmittance of the film prepared by this method in the visible light band limits its application in scenarios such as vehicle windows and building windows.

[0005] Patent document CN115572939A discloses a transparent radiation-cooling thin film based on a biomimetic silver ant hair micro-nano structure, its preparation method, and its application. This invention provides a transparent radiation-cooling thin film based on a biomimetic silver ant hair micro-nano structure, comprising a biomimetic silver ant hair micro-nano structure layer and a multilayer dielectric film layer arranged from top to bottom. The biomimetic silver ant hair micro-nano structure layer is made of PET material, and its surface is arrayed with conical micro-nano structures, with microsphere wrinkled structures arrayed on the surface of each conical micro-nano structure. This invention achieves the functions of selectively transmitting visible light, blocking near-infrared light, and exchanging heat with space, making it applicable to facilities with high requirements for light transmission and appearance, such as various large commercial buildings, solar cells, and car windows. However, due to the high requirements for the fabrication process of the micro-nano structures involved, large-scale production is difficult.

[0006] Patent document CN113698645A discloses a method for preparing a PMMA-based mixed porous radiation cooling film. The main preparation method involves mixing solid PMMA with the solvent tetrahydrofuran and the non-solvent deionized water, magnetically stirring to disperse the mixture evenly, obtaining a transparent solution. An acrylic sheet is then cleaned with laundry detergent, sonicated in clean water, cleaned with anhydrous ethanol, cleaned again with deionized water, and dried. Using a BEVS1806B / 150 adjustable scraper, the transparent solution is dripped onto the cleaned acrylic surface, and then the adjustable scraper is used to uniformly scrape the sample surface to form a smooth coating. After being left at room temperature for half an hour, the tetrahydrofuran and moisture are evaporated to remove them. Due to the low cost of the materials and the simple preparation method, this film has broad application prospects in outdoor high-voltage electrical equipment, building exterior walls and roofs, outdoor products, and agricultural greenhouses. However, under prolonged exposure to ultraviolet radiation from sunlight, the aging of organic matter can reduce its cooling performance.

[0007] Although existing technologies have yielded considerable research on radiation-cooled thin films, they still suffer from problems such as low transmittance, easy aging, and complex preparation methods. Therefore, providing a radiation-cooled flexible thin film with a simple preparation process and high transmittance in the visible light band is of great significance for applications such as automobiles and buildings that require both lighting and cooling. Summary of the Invention

[0008] In view of the shortcomings of the prior art, the present invention provides a radiation-cooling flexible film, which includes a radiation layer and a heat-insulating layer. It can passively radiate heat while blocking near-infrared sunlight from heating the internal space, and the film has a high visible light transmittance.

[0009] A radiation-cooled flexible thin film includes at least one radiation layer and at least one heat-resistant layer, wherein the outermost layer on at least one side is the radiation layer, the radiation layer material is an organic material with an absorption rate greater than 80% in the mid-infrared band, and the heat-resistant layer material includes an organic substrate material and inorganic nanoparticles dispersed in the organic substrate material, wherein the inorganic nanoparticles have an absorption rate greater than 80% in the near-infrared band.

[0010] The radiative cooling flexible thin film of this invention combines the optical properties of different organic and inorganic materials across various wavelength ranges. While blocking near-infrared sunlight from heating the internal space, it can passively radiate heat. The heat-blocking layer of the structure exhibits high absorption in the near-infrared band, preventing near-infrared light from entering the internal space for heating. By adjusting the size and mixing ratio of the inorganic nanoparticles, the film can achieve high visible light transmittance. Furthermore, the number and order of the radiative and heat-insulating layers can be adjusted according to the actual materials, making it promising for applications in automobiles, buildings, and other locations requiring both lighting and cooling.

[0011] Preferably, the thickness of the radiating layer is 5–500 μm. More preferably, the thickness of the radiating layer is 50–500 μm. More preferably, the thickness of the radiating layer is 200 μm, which ensures the film's radiative capacity while accelerating the transfer of heat from the internal space to the radiating layer.

[0012] Preferably, the thickness of the heat-insulating layer is 5–500 μm. More preferably, the thickness of the heat-insulating layer is 50–500 μm.

[0013] Preferably, the overall thickness of the radiation-cooled flexible film is 10–1000 μm.

[0014] Preferably, the organic material with an absorption rate greater than 80% in the mid-infrared band is at least one of polymethyl methacrylate (PMMA), polyvinylidene fluoride (PVDF), or polydimethylsiloxane (PDMS).

[0015] Preferably, the organic substrate material is at least one of polymethyl methacrylate (PMMA) or polydimethylsiloxane (PDMS).

[0016] Preferably, the inorganic nanoparticle material has a visible light transmittance >25%.

[0017] More preferably, the inorganic nanoparticle material has a transmittance of <20% in the ultraviolet band.

[0018] More preferably, the inorganic nanoparticle material of the heat-insulating layer is cesium tungsten bronze (CWO) nanoparticles. CWO nanoparticles have high absorption rates in both the ultraviolet and near-infrared bands, and their particle size can be adjusted through processes such as beading, making it easy to control their transmittance in the visible light band. The cesium tungsten bronze (CWO) nanoparticles are uniformly dispersed in the organic substrate material, and their absorption rates in the ultraviolet and near-infrared bands change with the doping concentration. The higher the doping concentration, the higher the absorption rate of the CWO nanoparticles, and the stronger the heat-insulating effect; furthermore, the stronger the light intensity, the more obvious the effect of the CWO nanoparticles in preventing near-infrared light from entering the internal space for heating, and the more significant the cooling effect.

[0019] Preferably, the inorganic nanoparticle material has a size of 1–600 nm. More preferably, the nanoparticle size is 30 nm, at which the radiation-cooled flexible film has high visible light transmittance.

[0020] Preferably, the mass of the inorganic nanoparticle material is 3% to 30% of the mass of the heat-resistant layer material. More preferably, the mass of the inorganic nanoparticle material is 3% to 20% of the mass of the heat-resistant layer material. More preferably, the mass of the inorganic nanoparticle material is 6% of the mass of the heat-resistant layer material. This doping concentration ensures that the film has high transparency while also having good near-infrared light absorption capability.

[0021] Preferably, the outermost layer of the radiation-cooled flexible film includes a scratch-resistant and abrasion-resistant layer and / or an anti-aging layer.

[0022] The present invention also provides a method for preparing the above-mentioned radiation-cooled flexible thin film. The preparation method is simple, mature and low in cost, and is suitable for large-scale industrial production.

[0023] A method for preparing the above-mentioned radiation-cooled flexible thin film includes the following steps:

[0024] (1) Inorganic nanoparticle dispersant is prepared by encapsulating inorganic nanoparticles with solvents that have thermal volatilization and isolation coating functions. The organic substrate material and the inorganic nanoparticle dispersant are mechanically mixed and then extruded and calendered to prepare a heat-insulating film.

[0025] (2) Prepare a radiation layer film by extruding and calendering organic materials with an absorption rate greater than 80% in the mid-infrared band;

[0026] (3) Prepare a flexible radiation-cooling film by combining a radiation layer film and a heat-insulating layer film, and ensure that the outermost layer on at least one side is a radiation layer film.

[0027] Preferably, the solvent with thermal evaporation and isolation coating functions includes white oil, waxy solvents, or MMA-type solvents.

[0028] The organic substrate material and organic material used in this invention for preparing the heat-resistant layer film and radiation layer film are flexible. Furthermore, the mixing of the organic substrate material with inorganic nanoparticles does not affect the flexibility of the heat-resistant layer film, thus making the prepared radiation-cooling film flexible. Compared to rigid films that can only be adhered to smooth substrates, the flexible radiation-cooling film of this invention has lower requirements for substrate surface flatness and can be used on some irregularly shaped substrates.

[0029] Preferably, the mechanical mixing is performed using an ultrasonic method or a magnetic field method.

[0030] Preferably, a functional coating of a hardening layer and / or an anti-aging layer is applied to the outer surface of the radiation-cooling flexible film.

[0031] This invention also provides the application of the aforementioned radiation-cooling flexible film in the preparation of energy-saving building materials, heat dissipation and cooling equipment, and outdoor products.

[0032] The present invention also provides a radiation cooling product, comprising a substrate and the above-mentioned radiation cooling flexible film, wherein the radiation cooling flexible film is disposed on the substrate, and the outermost layer of the radiation cooling flexible film away from the substrate is a radiation layer, and the substrate is a metal substrate, a plastic substrate, a building material substrate or a glass substrate.

[0033] The flexible radiative cooling film of the present invention can be directly attached to the surface of a window. The window conducts the temperature of the interior space to the radiative layer. According to Planck's blackbody radiation law, the wavelength corresponding to the peak energy density of blackbody radiation heat near 300K is in the range of 8 to 13μm. According to the third law of thermodynamics, the radiation capacity of an object is the same as its absorption capacity. The radiative layer can radiate heat to outer space at 3K through the atmospheric transmission window (8 to 13μm) to achieve cooling.

[0034] Compared with the prior art, the present invention has at least the following beneficial effects:

[0035] (1) This invention uses organic materials with low material cost to prepare a flexible radiative cooling film that combines transmittance and cooling performance. By combining the optical properties of the material in the near-infrared and mid-infrared bands, it blocks sunlight from heating the internal space while improving heat dissipation capacity, thereby improving the cooling performance of the film. By adjusting the size and concentration of doped particles to control the performance of the film, the complexity of the preparation process is effectively reduced by using a simple film structure and uniform doping technology.

[0036] (2) The radiation-cooling flexible film of the present invention has high absorption rates in the near-infrared, ultraviolet and mid-infrared bands, effectively improving its cooling performance, even under average solar light intensity of 800 W / m². 2Under irradiation, the maximum temperature drop can reach 7.5°C, with an average temperature drop of 4.5°C. Because it blocks the near-infrared rays of sunlight from heating the internal space, the cooling transparent film of this invention has a more significant cooling effect under high light intensity.

[0037] (3) This invention successfully applies near-infrared and mid-infrared high-absorbing materials to radiation-cooling films, achieving the preparation of low-cost cooling transparent films. The radiation-cooling flexible film of this invention exhibits excellent cooling effects under both high and low light intensities due to its high near-infrared and mid-infrared absorption rates, showing promising application prospects in large-area windows such as building windows and car windows. Attached Figure Description

[0038] Figure 1 This is a schematic diagram and working principle diagram of the radiation-cooled flexible thin film in the embodiment, wherein... Figure 1 (a) is a schematic diagram of the thin film structure; Figure 1 (b) is a schematic diagram of the working principle of the thin film.

[0039] Figure 2 The diagram shows the optical properties of the radiation-cooled flexible thin film in the embodiment. Figure 2 (a) shows the visible and near-infrared spectra of the thin film and the AM1.5G standard solar spectrum; Figure 2 (b) shows the mid-infrared absorption spectrum and atmospheric transmission spectrum of the thin film.

[0040] Figure 3 This is a schematic diagram of the experimental testing device.

[0041] Figure 4 The relevant data graphs for the experimental tests are shown below. Figure 4 (a) is based on Figure 3 The temperature measured by the device Figure 4 (b) represents the intensity of sunlight in the experimental environment. Figure 4 (c) represents the calculated temperature difference within the cavity with and without the thin film. Detailed Implementation

[0042] Exemplary embodiments of the present invention will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present invention are shown in the drawings, it should be understood that the present invention may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0043] The structure of the radiation-cooling flexible thin film in this embodiment is as follows: Figure 1As shown, the film consists of a double-layer structure: an organic radiative layer made of PMMA and a substrate + nanoparticle heat-resistant layer made of CWO-doped PMMA. The PMMA radiative layer has a thickness of 200 μm, and the heat-resistant layer doped with inorganic particles has a thickness of 100 μm. The average size of the CWO nanoparticles is 30 nm, and the mass of the inorganic nanoparticle material is 15% of the mass of the heat-resistant layer material.

[0044] By combining the optical properties of CWO and PMMA and utilizing a simple multilayer thin film structure, selective optical properties of a radiation-cooling thin film are achieved. It allows visible light to pass through while blocking ultraviolet and near-infrared light, and radiates mid-infrared light to achieve heat exchange with space. Under outdoor sunlight, it can simultaneously achieve the effects of light transmission and cooling.

[0045] like Figure 2 As shown, the optical properties of the thin film in the wavelength range of 300–2100 nm and 4–20 μm were measured using a Cary 5000 ultraviolet-visible-near-infrared spectrophotometer and a Fourier transform infrared spectrometer (FTIR). In the visible light range, the average transmittance of the thin film was 43.2%, while the transmittance in the ultraviolet and near-infrared bands was less than 12% and 17%, respectively, indicating that it can effectively block ultraviolet and near-infrared light. The average absorption rate in the atmospheric transparent window (8–13 μm) was 93%, which can effectively radiate heat into space.

[0046] Figure 3 This is a schematic diagram of the outdoor experimental testing device for the cooling film. As shown, the main body of the experimental temperature measuring chamber uses 270mm*500mm*270mm thick polystyrene foam. A 200mm*430mm*40mm groove is centrally located at the top. An 80mm*80mm*80mm cavity is set in the middle of the foam, and a graphite plate is placed inside the cavity to simulate the absorption of internal objects. The exterior of the foam box is covered with 500μm thick aluminum foil to reduce heat conduction from the surrounding environment. The top of the foam box is covered with a 100μm thick polyethylene film to reduce heat convection with the environment. The surface of the cavity is covered with a glass plate and a glass plate covered with the film. Four-channel K-type thermocouples (TA612C) are placed inside to record real-time temperature changes, recording temperature changes in the environment and inside the two cavities.

[0047] On October 3, 2023, in a residential building in Jinhua City, Zhejiang Province, China, Figure 3 The temperature test chamber shown was placed on an open rooftop for testing. The test lasted from 10:00 AM to 3:00 PM, a total of five hours. Figure 4 (a) is the measured internal temperature of the cavity covered with the corresponding sample. Figure 4 (b) represents the light intensity of the experimental test environment. Figure 4 (c) The calculated temperature difference, at an average strength of 800 W / m2 Under sunlight, the film can achieve a maximum temperature drop of 7.5℃ and an average temperature drop of 4.5℃.

[0048] The above are merely embodiments of this application and are not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

Claims

1. A radiation-cooled flexible thin film, characterized in that, It includes at least one radiating layer and at least one heat-resistant layer, wherein the outermost layer on at least one side is the radiating layer. The radiating layer material is an organic material with an absorption rate greater than 80% in the mid-infrared band. The heat-resistant layer material includes an organic substrate material and inorganic nanoparticles dispersed in the organic substrate material. The inorganic nanoparticles have an absorption rate greater than 80% in the near-infrared band. The inorganic nanoparticle material has a visible light transmittance >25% and an ultraviolet light transmittance <20%. The inorganic nanoparticle material of the heat-resistant layer is cesium tungsten bronze nanoparticles.

2. The radiation-cooled flexible thin film according to claim 1, characterized in that, The thickness of the radiation layer is 5~500µm, and the thickness of the heat-insulating layer film is 5~500µm.

3. The radiation-cooled flexible thin film according to claim 1, characterized in that, The organic substrate material is at least one of polymethyl methacrylate or polydimethylsiloxane.

4. The radiation-cooled flexible thin film according to claim 1, characterized in that, The inorganic nanoparticle material has a size of 1~600nm.

5. The radiation-cooled flexible thin film according to claim 4, characterized in that, The mass of the inorganic nanoparticle material is 3% to 30% of the mass of the heat-insulating layer material.

6. The method for preparing a radiation-cooled flexible thin film according to any one of claims 1-5, characterized in that, Includes the following steps: (1) Inorganic nanoparticle dispersant is prepared by encapsulating inorganic nanoparticles with solvents that have thermal volatilization and isolation coating functions. The organic substrate material and the inorganic nanoparticle dispersant are mechanically mixed and then extruded and calendered to prepare a heat-insulating film. (2) Prepare a radiation layer film by extruding and calendering organic materials with an absorption rate greater than 80% in the mid-infrared band; (3) Prepare a flexible radiation cooling film by combining a radiation layer film and a heat-insulating layer film, and ensure that the outermost layer on at least one side is a radiation layer film.

7. The application of the radiation-cooling flexible film according to any one of claims 1-5 in the preparation of energy-saving building materials, heat dissipation and cooling equipment and outdoor products.

8. A radiation cooling product, characterized in that, The invention includes a substrate and a radiation-cooling flexible film as described in any one of claims 1-5, wherein the radiation-cooling flexible film is disposed on the substrate, and the outermost layer of the radiation-cooling flexible film away from the substrate is a radiation layer, and the substrate is a metal substrate, a plastic substrate, a building material substrate, or a glass substrate.

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