A method, apparatus and thin film for preparing a radiation-cooled film

Abstract

This invention belongs to the field of radiation cooling technology, and discloses a method, apparatus, and thin film for preparing a radiation cooling film. The preparation method includes: S1, forming an imprinting roller by setting a raised structure on the surface of a roller, and performing a heat imprinting treatment on a film substrate through the imprinting roller to form the corresponding raised structure on the surface of the film substrate; S2, filling the spaces between the raised structures on the surface of the film substrate with nanoparticles; S3, setting a protective film on the surface of the raised structures to form a radiation cooling film. This invention proposes a complete method for preparing a radiation cooling film based on a roller manufacturing process. Its production method is simple and low-cost, enabling efficient and large-scale production, thus improving the feasibility of promoting radiation cooling technology and showing broad application prospects in fields such as construction, automobiles, and agriculture.

Description

Technical Field

[0001] This invention belongs to the field of radiation cooling technology, and more specifically, relates to a method, apparatus and thin film for preparing radiation cooling films. Background Technology

[0002] Energy consumption for cooling is increasing daily, especially in densely populated and built-up urban centers, where the heat island effect will further amplify energy consumption and emissions. Therefore, developing a green and environmentally friendly cooling method is an urgent problem to be solved.

[0003] In recent years, an increasing number of researchers have turned their attention to radiative cooling technology, which boasts zero energy consumption and zero emissions, making it an ideal cooling technology. Its main principle consists of two parts: First, the atmosphere has excellent transmission properties for electromagnetic waves with wavelengths of 8-13 μm. If an object has high emissivity in this band (according to Kirchhoff's law, emissivity equals absorptivity at the same temperature under thermal equilibrium conditions), the object can emit its own heat into outer space in the form of radiation. The cosmic background radiation temperature is only 3K, making it a vast and ideal radiative cooling source. Second, the sun is the primary source of radiative heat on the Earth's surface, with its total radiative heat flux within its coverage band (0.3-2.5 μm) reaching up to nearly 1 kW / m². 2 If an object has high reflectivity in this wavelength band, it can reduce the absorption of solar radiation. When an object meets both of these conditions, it can emit more radiative heat flux than it absorbs, thus achieving a passive radiative cooling effect around the clock.

[0004] Radiation-cooled thin films prepared using this technology can be widely applied in agriculture, construction, automobiles, photovoltaics, and many other fields, saving significant amounts of cooling energy. However, most current research remains at the small-scale experimental stage. The preparation process of radiation-cooled thin films typically involves complex and costly processes such as magnetron sputtering and vacuum deposition, hindering large-scale deployment. Therefore, it is necessary to develop a large-scale, low-cost preparation technology to improve the feasibility of widespread application of radiation-cooling technology. Summary of the Invention

[0005] In view of the above-mentioned defects or improvement needs of the prior art, the present invention provides a method, apparatus and thin film for preparing radiation-cooled films, which solves the problem that the existing radiation-cooled film preparation process usually has complex and costly processes such as magnetron sputtering and vacuum deposition, which are difficult to promote on a large scale.

[0006] To achieve the above objectives, according to a first aspect of the present invention, a method for preparing a radiation-cooled thin film is provided, comprising:

[0007] S1, a raised structure is provided on the surface of the roller to form an printing roller, and the film substrate is subjected to thermal printing treatment by the printing roller to form the corresponding raised structure on the surface of the film substrate.

[0008] S2, nanoparticles are filled between the protrusions on the surface of the thin film substrate;

[0009] S3, a protective film is provided on the surface of the protruding structure to form a radiation cooling film.

[0010] According to the radiation-cooling thin film preparation method provided by the present invention, step S1 further includes, before performing heat printing treatment on the thin film substrate by the printing roller:

[0011] The thin film substrate is preheated, wherein the preheating temperature is within the range of 0-5°C below the viscous flow temperature of the thin film substrate.

[0012] According to the radiation-cooling thin film preparation method provided by the present invention, the heat-pressing treatment of the thin film substrate by the printing roller in step S1 specifically includes:

[0013] The hot printing temperature of the printing roller on the film substrate is controlled so that the hot printing temperature is higher than the viscous flow temperature of the film substrate;

[0014] Furthermore, the hot printing temperature is adjusted according to the rolling speed of the film substrate, and the hot printing temperature increases as the rolling speed of the film substrate increases.

[0015] According to the radiation-cooling thin film preparation method provided by the present invention, the hot-printing temperature T in S1 is... r Specifically, control and adjustment should be performed according to the following formula:

[0016] T f +5V≤T r ≤T f +20V;

[0017] Among them, T f V is the viscous flow temperature of the thin film substrate; V is the rolling speed of the thin film substrate.

[0018] According to the method for preparing a radiation-cooled thin film provided by the present invention, S2 specifically includes:

[0019] S21, the nanoparticles are sprayed onto the side of the thin film substrate with the protruding structure using an electrostatic spray gun, and the nanoparticles are electrostatically adsorbed onto the thin film substrate.

[0020] S22, the thin film substrate after the nanoparticles are sprayed by extrusion through a roller;

[0021] S23, excess nanoparticles are scraped off the surface of the raised structure by a grounded scraper for recycling, thus completing the filling of nanoparticles.

[0022] The method for preparing a radiation-cooled thin film according to the present invention further includes:

[0023] S4, the transmittance of the radiation cooling film in the near-infrared band is detected. If the transmittance is less than a preset value, the radiation cooling film is determined to be a qualified product.

[0024] Near-infrared light specifically refers to light with wavelengths in the range of 2.5-20μm.

[0025] According to a second aspect of the present invention, a radiation-cooled thin film preparation apparatus is provided, comprising: a first unwinding roller wound with a thin film substrate, an imprinting roller assembly, a spraying device, a second unwinding roller wound with a protective film, a hot-pressing roller assembly, and a take-up roller; the imprinting roller assembly includes a support roller and an imprinting roller with a raised structure on its surface, wherein the thin film substrate is unwound from the first unwinding roller and conveyed between the support roller and the imprinting roller for hot-pressing treatment, thereby forming the corresponding raised structure on the surface of the thin film substrate through the hot-pressing treatment;

[0026] The spraying device is located after the printing roller assembly and is used to spray nanoparticles onto the side surface of the film substrate with the raised structure. The second unwinding roller and the hot pressing roller assembly are located after the spraying device. The second unwinding roller is used to release the protective film and transport it to the side surface of the film substrate with the raised structure. The hot pressing roller assembly is used to perform hot pressing treatment on the protective film and the film substrate after the protective film is laid to form a radiation-cooling film. The winding roller is used to wind up and store the radiation-cooling film.

[0027] The radiation-cooled thin film preparation apparatus provided by the present invention further includes an extrusion roller assembly and a doctor blade assembly disposed between the spraying device and the second unwinding roller; the extrusion roller assembly is used to extrude the thin film substrate after the nanoparticles are sprayed by the roller; the doctor blade assembly includes a doctor blade and a recycling container; the doctor blade is used to scrape off excess nanoparticles from the surface of the raised structure and recycle them into the recycling container.

[0028] The spraying device includes an electrostatic spray gun, and the scraper is connected to a grounding wire.

[0029] According to a third aspect of the present invention, a radiation-cooling thin film is provided, which is prepared by any of the radiation-cooling thin film preparation methods described above, comprising: a thin film substrate, nanoparticles and a protective film, wherein one side surface of the thin film substrate is provided with a raised structure, the nanoparticles fill the gaps between the raised structures, and the protective film is disposed on the side of the raised structures opposite to the thin film substrate.

[0030] According to the radiation-cooling thin film provided by the present invention, the protrusion structure includes an array of rectangular or circular protrusions. The side length of the rectangular protrusion is 2-20 μm, the distance between the centroids of two adjacent rectangular protrusions is 1.5-5 times the side length, and the height of the rectangular protrusion is 0.2-1 times the side length. The radius of the circular protrusion is 1-10 μm, the distance between the centers of two adjacent circular protrusions is 2.5-6 times the radius, and the height of the circular protrusion is 0.4-2 times the radius.

[0031] In summary, compared with the prior art, the present invention provides a method, apparatus, and thin film for preparing radiation-cooled films:

[0032] 1. After constructing a uniformly arranged protrusion structure on the thin film substrate and fully filling it with nanoparticles, the impedance difference between the organic polymer and the nanoparticles will enhance the electromagnetic wave oscillation at the interface, especially the electromagnetic waves in the mid-infrared band, thereby increasing the absorption rate in this band. According to Kirchhoff's thermal radiation law, this effect can also further enhance the emission performance of the thin film substrate in the "atmospheric window" band.

[0033] 2. The nanoparticles filling the protruding structure have a band gap that is higher than or slightly lower than the maximum photon energy of solar radiation (300nm ultraviolet photon energy is 4.13eV). Photons cannot excite electrons to undergo energy level transitions, so they can hardly be absorbed by the nanoparticles. This greatly reduces the absorption of solar radiation energy, thereby further improving the radiation cooling performance.

[0034] 3. A complete method for preparing radiation-cooled thin films based on roll manufacturing process is proposed, which does not require metal or metal oxide coatings and does not involve complex processes such as magnetron sputtering or vacuum deposition. Its production method is simple and low-cost, and can be carried out in a high-efficiency and large-scale manner, which improves the feasibility of radiation-cooling technology and has broad application prospects in the fields of construction, automobiles, and agriculture. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the radiation-cooled thin film preparation apparatus provided by the present invention;

[0036] Figure 2This is a cross-sectional schematic diagram of the radiation-cooling thin film provided by the present invention;

[0037] Figure 3 This is a schematic diagram of the protrusion structure provided by the present invention;

[0038] In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0039] 1. First unwinding roll; 2. Preheating roll assembly; 3. Printing roll assembly; 4. Cooling and demolding roll; 5. First cooling roll assembly; 6. Spraying device; 7. Extrusion roll assembly; 8. Scraper; 9. Recycling container; 10. Second unwinding roll; 11. Hot pressing roll assembly; 12. Second cooling roll assembly; 13. Light transmittance monitoring device; 14. Rewinding roll; 101. Film substrate; 102. Nanoparticles; 103. Protective film; 111. Circular boss; 112. Rectangular boss. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0041] Please see Figure 1 and Figure 2 This invention provides a method for preparing a radiation-cooled thin film, the method comprising:

[0042] S1, a raised structure is provided on the surface of the roller to form an printing roller, and the film substrate 101 is subjected to heat printing treatment by the printing roller to form the corresponding raised structure on the surface of the film substrate 101.

[0043] S2, nanoparticles 102 are filled between the protrusions on the surface of the thin film substrate 101;

[0044] S3, a protective film 103 is provided on the surface of the protruding structure to form a radiation cooling film.

[0045] In this embodiment, the surface of the printing roller can be processed using precision machining, chemical etching, photolithography, and other techniques to create the desired raised structure. Then, the printing roller is used to thermally print the surface of the thin film substrate 101, thus obtaining a raised structure of the corresponding size on the surface of the thin film substrate 101. This process for preparing the raised structure on the thin film substrate 101 is simple and easy to manufacture. Furthermore, nanoparticles 102 can be directly filled into the gaps of the raised structure, and then a protective film 103 can be encapsulated on the surface of the raised structure to form a radiation-cooling thin film. Both the direct filling of nanoparticles 102 and the encapsulation of the protective film 103 are simple to operate, do not involve complex or costly processes, and are easy to manufacture.

[0046] The radiation cooling film preparation method provided by the present invention uses a film substrate 101. Because the film substrate 101 contains a large number of chemical bonds with characteristic wavelengths in the "atmospheric window" band, such as CC and CO bonds, the polymer film substrate 101 itself has a high emissivity in the "atmospheric window" band of 8-13μm, and can provide certain radiation cooling performance.

[0047] After constructing a uniformly arranged protrusion structure on the thin film substrate 101 and fully filling the nanoparticles 102, the impedance difference between the organic polymer and the nanoparticles 102 will enhance the electromagnetic wave oscillation at the interface, especially the electromagnetic waves in the mid-infrared band, thereby increasing the absorption rate in this band. According to Kirchhoff's thermal radiation law, this effect can also further enhance the emission performance of the thin film substrate 101 in the "atmospheric window" band.

[0048] The nanoparticles 102 filling the protruding structure have a band gap that is higher than or slightly lower than the maximum photon energy of solar radiation (300nm ultraviolet photon energy is 4.13eV). Since photons cannot excite electrons to undergo energy level transitions, they can hardly be absorbed by the nanoparticles 102, thus greatly reducing the absorption of solar radiation energy and further improving the radiation cooling performance.

[0049] This invention proposes a complete method for preparing radiation-cooled thin films based on roll manufacturing technology. It does not require metal or metal oxide coatings and does not involve complex processes such as magnetron sputtering or vacuum deposition. The production method is simple and low-cost, and can be carried out in a high-efficiency and large-scale manner, which improves the feasibility of radiation-cooling technology and has broad application prospects in fields such as construction, automobiles, and agriculture.

[0050] Furthermore, S1 further includes the following step before performing heat printing on the film substrate 101 via the printing roller:

[0051] The thin film substrate 101 is preheated, wherein the preheating temperature is within the range of 0-5°C below the viscous flow temperature of the thin film substrate 101.

[0052] Further, the hot printing process of the film substrate 101 by the printing roller in S1 specifically includes:

[0053] The hot printing temperature of the printing roller on the film substrate 101 is controlled so that the hot printing temperature is higher than the viscous flow temperature of the film substrate 101;

[0054] Furthermore, the hot printing temperature is adjusted according to the rolling speed of the thin film substrate 101, and the hot printing temperature increases as the rolling speed of the thin film substrate 101 increases.

[0055] Furthermore, the hot stamping temperature T in S1 is... r Specifically, control and adjustment should be performed according to the following formula:

[0056] T f +5V≤T r ≤T f +20V;

[0057] Among them, T f V is the viscous flow temperature of the thin film substrate 101; V is the rolling speed of the thin film substrate 101.

[0058] Specifically, preheating is required before the hot stamping process using preheating rollers. The polymer material is in its glassy state at temperature T. g When it is in the glassy state, its molecular chains cannot move, resulting in hard and brittle properties; when it is in the glassy state at temperature T... g To the viscous flow temperature T f When the temperature is between these two states, the molecular chains transform into a highly elastic state where the molecular chains can move locally and undergo elastic deformation under external force; however, its temperature is higher than the viscous flow temperature T. f Subsequently, the molecular chains can move significantly, and the material transforms into a viscous fluid, capable of irreversible deformation, a state known as the viscous flow state. At room temperature, the selected thin film substrate 101 is in the glassy state at temperature T. g To the viscous flow temperature T f Between these states, it is in a highly elastic state. This is to ensure that the temperature can be raised to the viscous flow temperature T in time during subsequent hot stamping. f To ensure successful plasticity, first preheat it to the viscous flow temperature T. f Below 0-5℃.

[0059] The preheated film substrate 101 is shaped by an impression roller with raised structures. The temperature of the impression roller must be adjusted according to the material of the film substrate 101 and the production line speed to ensure that the microstructure protrusions can locally heat the surface in contact with the film substrate 101 during impression, converting it into a viscous flow state, thus ensuring successful shaping and preventing springback. Considering that the faster the production line operates, the shorter the contact time between the film substrate 101 and the impression roller, and the larger the heating temperature difference to reach the required temperature, but excessively high temperatures will completely melt the film substrate 101, the viscous flow temperature T of the material is adjusted accordingly. f (unit: °C), and the temperature T of the printing roller. r (Unit: °C), given the following empirical formula for a temperature range:

[0060] T f +5V≤T r ≤T f +20V;

[0061] The specific processing procedure can be reasonably adjusted in terms of temperature and speed according to the actual situation to achieve a balance between processing efficiency and processing reliability. Among them, the roller pressing speed of the film substrate 101 is set to 0-2m / min; that is, the film substrate 101 is released from the self-unwinding roller at a speed of 0-2m / min.

[0062] Furthermore, S2 specifically includes:

[0063] S21, the nanoparticles 102 are sprayed onto the side of the thin film substrate 101 with the protruding structure using an electrostatic spray gun, and the nanoparticles 102 are electrostatically adsorbed onto the thin film substrate 101.

[0064] S22, the thin film substrate 101 after the nanoparticles 102 are sprayed by the extrusion of the roller;

[0065] S23, the excess nanoparticles 102 are scraped off from the surface of the raised structure by the grounded scraper 8 for recycling, thus completing the filling of the nanoparticles 102.

[0066] Furthermore, S3 specifically includes:

[0067] A protective film 103 is laid on the surface of the raised structure and then fused and fixed to the raised structure by hot pressing. The protective film 103 mainly forms a protective layer on the surface of the raised structure, preventing damage to the raised structure and shedding of nanopowder, and enhancing the overall mechanical properties and durability of the film.

[0068] Furthermore, the method for preparing radiation-cooled thin films also includes:

[0069] S4, the transmittance of the radiation cooling film in the near-infrared band is detected. If the transmittance is less than a preset value, the radiation cooling film is determined to be a qualified product.

[0070] Near-infrared light specifically refers to light with wavelengths in the range of 2.5-20μm.

[0071] Further, the nanoparticles 102 are at least one of the first type of particles, or a combination of at least one of the first type of particles and at least one of the second type of particles, wherein the first type of particles includes barium sulfate, titanium dioxide, zirconium oxide, zinc oxide, and calcium carbonate, and the second type of particles includes silicon dioxide and indium tin oxide; and when the nanoparticles 102 are a combination of at least one of the first type of particles and at least one of the second type of particles, the volume ratio of the first type of particles to the second type of particles is between 1:1 and 1:10; the particle size of the nanoparticles 102 is in the range of 20-500 nm.

[0072] The nanoparticles 102 can be selected from at least one of barium sulfate, titanium dioxide, zirconium oxide, zinc oxide, and calcium carbonate, or a combination of at least one of silicon dioxide, indium tin oxide, and at least one of the above, with a volume ratio between 1:1 and 1:10. All nanoparticles 102 have a particle size in the range of 20-500 nm. The selected types and proportions of nanoparticles 102 filling the protruding structure have band gaps higher than or slightly lower than the maximum photon energy of solar radiation (300 nm ultraviolet photon energy is 4.13 eV). Photons cannot excite electrons to undergo energy level transitions, so they are almost not absorbed by the nanoparticles, thus greatly reducing the absorption of solar radiation energy.

[0073] The particle size of the nanoparticles 102 selected to fill the protruding structure is close to the wavelength of solar radiation. Due to the Mie scattering effect, the particles can reflect or refract most of the solar radiation, further reducing the absorption of solar radiation energy and improving the cooling performance.

[0074] Furthermore, the film substrate 101 is made of PE (polyethylene), PET (polyethylene terephthalate), TPU (thermoplastic polyurethane elastomer), or PS (polystyrene), and its thickness is in the range of 20-200 micrometers.

[0075] The protective film 103 is made of polyethylene, polyethylene terephthalate, thermoplastic polyurethane elastomer, or polystyrene, with a thickness in the range of 20-200 micrometers. The material of the protective film 103 can be the same as that of the film substrate 101, or any of the above-mentioned film materials can be selected.

[0076] In another embodiment, the present invention also provides an apparatus for preparing a radiation-cooled thin film, as described above. Figure 1 The preparation apparatus includes: a first unwinding roller 1 wound with a thin film substrate 101, an imprinting roller assembly 3, a spraying device 6, a second unwinding roller 10 wound with a protective film 103, a hot pressing roller assembly 11, and a take-up roller 14; the imprinting roller assembly 3 includes a support roller and an imprinting roller with a raised structure on its surface. The thin film substrate 101 is unwound from the first unwinding roller 1 and conveyed between the support roller and the imprinting roller for hot pressing treatment, thereby forming the corresponding raised structure on the surface of the thin film substrate 101 through the hot pressing treatment;

[0077] The spraying device 6 is located after the printing roller assembly 3 and is used to spray nanoparticles 102 onto the side surface of the film substrate 101 where the protrusion structure is provided. The second unwinding roller 10 and the hot pressing roller assembly 11 are located after the spraying device 6. The second unwinding roller 10 is used to release the protective film 103 and transport it to the side surface of the film substrate 101 where the protrusion structure is provided. The hot pressing roller assembly 11 is used to perform hot pressing treatment on the protective film 103 and the film substrate 101 after the protective film 103 is laid to form a radiation cooling film. The take-up roller 14 is used to take up and store the radiation cooling film.

[0078] Furthermore, the preparation apparatus also includes an extrusion roller assembly 7 and a scraper assembly disposed between the spraying device 6 and the second unwinding roller 10; the extrusion roller assembly 7 is used to extrude the film substrate 101 after the nanoparticles 102 are sprayed by the roller; the scraper assembly includes a scraper 8 and a recycling container 9; the scraper 8 is used to scrape off excess nanoparticles 102 from the surface of the raised structure and recycle them into the recycling container 9.

[0079] The spraying device 6 includes an electrostatic spray gun, and the scraper 8 is connected to a grounding wire.

[0080] Furthermore, the preparation apparatus also includes a transmittance monitoring device 13 disposed between the hot press roller assembly 11 and the take-up roller 14. The transmittance monitoring device 13 includes a light emitting component and a light receiving component. The light emitting component is used to emit near-infrared light with a wavelength in the range of 2.5-20μm.

[0081] Furthermore, the preparation apparatus also includes a preheating roller assembly 2, a cooling and demolding roller 4, a first cooling roller assembly 5, and a second cooling roller assembly 12. The preheating roller assembly 2 is disposed between the first unwinding roller 1 and the printing roller assembly 3 for preheating the film substrate 101. The cooling and demolding roller 4 is in contact with the printing roller. After the film substrate 101 is heat-pressed between the support roller and the printing roller, it is output between the printing roller and the cooling and demolding roller 4 for cooling and demolding. The first cooling roller assembly 5 is disposed between the cooling and demolding roller 4 and the spraying device 6 for cooling and reducing the temperature of the film substrate 101 with raised structures. The second cooling roller assembly 12 is disposed between the hot pressing roller assembly 11 and the take-up roller 14 for cooling and reducing the temperature of the radiation-cooled film after the hot pressing protective film 103.

[0082] Furthermore, the radiation-cooled thin film preparation apparatus corresponds to the aforementioned radiation-cooled thin film preparation method, and the apparatus is used to implement the aforementioned radiation-cooled thin film preparation method. The specific operation flow of the radiation-cooled thin film preparation apparatus is as follows:

[0083] The first unwinding roller 1 releases the film substrate 101 and conveys it to the preheating roller assembly 2 for preheating treatment, and then conveys it to the printing roller assembly 3 for hot printing and shaping treatment, forming a raised structure on the surface of the film substrate 101.

[0084] After being shaped, the film is first pre-cooled and demolded, and then cooled by the first cooling roller assembly 5 until the film material is completely restored to room temperature.

[0085] An electrostatic spray gun is arranged 5-10 cm above the thin film substrate 101. The nanoparticles 102 with radiation cooling function are fully atomized and evenly sprayed onto the surface of the microstructure through the electrostatic spray gun. At the same time, the high voltage electrode at the nozzle of the electrostatic spray gun makes the particles charge so that they can be better adsorbed onto the surface of the thin film substrate 101.

[0086] The nanoparticles 102 are then fully filled into the raised structure by the extrusion of the rollers in the extrusion roller assembly 7. Excess powder is then removed and its charge is released using a grounded scraper 8. The removed excess powder is then recycled. The scraper 8 can be a metal scraper connected to a conductive wire, which is grounded.

[0087] The protective film 103 is then placed over the film substrate 101, and the two are hot-pressed together by the hot press roller assembly 11, and then cooled and shaped.

[0088] After the above preparation is completed, the transmittance of the film in the infrared band will be measured by a spectral transmittance monitoring device to verify whether the optical performance of the product is qualified. Generally, if the transmittance of the film in the near-infrared band (2.5-20μm) is less than 10%, the batch of products is considered to be able to effectively block infrared thermal radiation and have radiation cooling performance, and is considered a qualified product.

[0089] Finally, the composite film product that has passed the test is wound onto the take-up roller 14 to obtain the final product.

[0090] In another embodiment, the present invention also provides a radiation-cooling thin film, which is prepared by any of the radiation-cooling thin film preparation methods described above, with reference to... Figure 3 The radiation cooling film includes: a thin film substrate 101, nanoparticles 102 and a protective film 103. One side surface of the thin film substrate 101 is provided with a raised structure. The nanoparticles 102 fill the gaps between the raised structures. The protective film 103 is provided on the side of the raised structures away from the thin film substrate 101.

[0091] The protruding structure is an integral structure with the thin film substrate 101.

[0092] Further, refer to Figure 3 The protruding structure includes an array of rectangular protrusions 112 or circular protrusions 111. The side length of the rectangular protrusions 112 is 2-20 μm, the distance d2 between the centroids of two adjacent rectangular protrusions 112 is 1.5-5 times the side length, and the height of the rectangular protrusions 112 is 0.2-1 times the side length. The radius of the circular protrusions 111 is 1-10 μm, the distance d1 between the centers of two adjacent circular protrusions 111 is 2.5-6 times the radius, and the height of the circular protrusions 111 is 0.4-2 times the radius.

[0093] The present invention constructs a uniformly arranged protrusion structure on a thin film substrate 101. Within a given range of size and arrangement, the protrusion structure forms a microstructure. After fully filling the surface of the microstructure with nanoparticles 102, the impedance difference between the organic polymer and the nanoparticles 102 will enhance the electromagnetic wave oscillation at the interface, especially the electromagnetic waves in the mid-infrared band, thereby increasing the absorption rate in this band. According to Kirchhoff's thermal radiation law, this effect can also further enhance the emission performance of the thin film in the "atmospheric window" band.

[0094] To address the problems of complex manufacturing processes, high costs, and inconvenience for large-scale production of radiation-cooled thin films, this invention proposes a roll-to-roll thin film manufacturing process. In this process, the thin film substrate 101 is preheated and then surface-shaped using an imprinting roller with microstructured protrusions of a specific size, resulting in a thin film substrate 101 with a uniformly distributed microporous structure (i.e., a protruding structure) on one side. High solar radiation reflectivity nanoparticle powder is sprayed onto the microstructured side of the film and mechanically rolled to fully fill the micropores. After removing excess powder, a protective film 103 is applied on top, and finally, the layers are hot-pressed together to form a radiation-cooled thin film product with a three-layer composite microstructure. The roll-to-roll thin film manufacturing process provided by this invention is described below with reference to specific embodiments:

[0095] Example 1

[0096] like Figure 1 As shown, a roll-to-roll process for preparing radiation-cooled thin films mainly includes the following steps:

[0097] Unwinding: The PE film substrate 101 with a width of 1m and a thickness of 20μm is taken off from the first unwinding roller 1 at a uniform speed of 1m / min and transported to the next process by the rotation of the winding roller.

[0098] Preheating: Viscous flow temperature T of PE film f The temperature is 110℃, and it is preheated by the preheating roller assembly 2 to raise its temperature to the range of 105℃-110℃.

[0099] Hot roll forming microstructure: The PE film is printed by a microstructure surface printing roller at a temperature of 120℃-130℃, forming a uniformly distributed microporous structure on the surface. The structure consists of circular protrusions 111 with a radius of 2μm, a depth of 2μm, and a spacing of 5μm.

[0100] Cooling: The PE film first passes through the cooling demolding roller 4 at a temperature of 10℃-15℃ to complete the initial cooling, shaping and demolding. Then it passes through the first cooling roller assembly 5 to cool to room temperature or below to ensure that it fully recovers its high elasticity state.

[0101] Sprayed particles: Barium sulfate powder with an average particle size of 400 nm and silica powder with an average particle size of 300 nm (volume ratio 5:1) are uniformly mixed and loaded into an electrostatic spray gun. The electrostatic spray gun atomizes and sprays out the mixed powder in the filling chamber using high-pressure gas. The high-voltage electrode at the nozzle of the spray gun charges the sprayed powder, causing it to cover the side of the film with microstructures and adhere to the surface.

[0102] Mechanical rolling: The film passes through the mechanical extrusion roller assembly 7, which fully fills the micropores with powder from the surface.

[0103] Cleaning excess powder: The scraper 8 is grounded, and the excess powder on the film surface is removed and discharged by the scraper 8. The excess powder is recycled through the recycling container 9.

[0104] Covering with protective film 103: A PE protective film 103 with a width of 1m and a thickness of 20μm is taken off from the second unwinding roller 10 at a speed of 1m / min and covered on the side of the PE film filled with powder microstructure. The two are then heated and softened by the hot press roller assembly 11 at a temperature of 120℃-130℃ and pressed together.

[0105] Cooling: The composite film is cooled and shaped by the second cooling roller assembly 12 at a temperature of 10℃-15℃.

[0106] Testing: The prepared film is passed through the transmittance monitoring device 13. If the transmittance of the product in the near-infrared band (2.5-20μm) is less than 10%, the batch of products is considered to be able to effectively block infrared thermal radiation and have radiation cooling performance, and is a qualified product.

[0107] Winding: The prepared composite radiation cooling film is collected onto the winding roller 14.

[0108] The radiation-cooling thin film prepared in this embodiment has an average emissivity of 92% in the 8-13 μm atmospheric window band and a transmittance of 72% in the visible light band. Under clear, cloudless weather conditions, it can achieve a maximum emissivity of 79 W / m. 2 Radiative cooling power.

[0109] Example 2

[0110] like Figure 1 As shown, a roll-to-roll process for preparing radiation-cooled thin films mainly includes the following steps:

[0111] Unwinding: The TPU film substrate 101 with a width of 1m and a thickness of 50μm is taken off from the first unwinding roller 1 at a speed of 0.5m / min and transported to the next process by the rotation of the winding roller.

[0112] Preheating: TPU film viscous flow temperature T f The temperature is 170℃. It is preheated by the heating and preheating roller assembly 2 to raise its temperature to the range of 165℃-170℃.

[0113] Hot roll forming of microstructure: The TPU film is printed on the surface of the microstructure by a microstructure surface printing roller at a temperature of 173℃-175℃, forming a uniformly distributed microporous structure on the surface. The structure consists of square micropores with a side length of 5μm, a depth of 3μm, and a spacing of 10μm.

[0114] Cooling: The TPU film first passes through the cooling demolding roller 4 at a temperature of 10℃-15℃ to complete the initial cooling, shaping and demolding. Then it passes through the first cooling roller assembly 5 to cool to room temperature or below to ensure that it fully recovers its high elasticity state.

[0115] Spraying Particles: Titanium dioxide rutile powder with an average particle size of 60 nm and silicon dioxide powder with an average particle size of 300 nm (volume ratio 4:1) are uniformly mixed and loaded into an electrostatic spray gun. The electrostatic spray gun atomizes and sprays out the mixed powder in the filling chamber using high-pressure gas. The high-voltage electrode at the nozzle of the spray gun charges the sprayed powder, causing it to cover the side of the film with microstructures and adhere to the surface.

[0116] Mechanical rolling: The film passes through the mechanical extrusion roller assembly 7, which fully fills the micropores with powder from the surface.

[0117] Cleaning excess powder: The scraper 8 is grounded, and the excess powder on the film surface is removed and discharged by the scraper 8. The excess powder is recycled through the recycling container 9.

[0118] Covering with protective film 103: A TPU protective film 103 with a width of 1m and a thickness of 50μm is taken off from the second unwinding roller 10 at a speed of 0.5m / min and covered on the side of the TPU film filled with powder microstructure. The two are then heated and softened by a hot press roller assembly 11 at a temperature of 173℃-175℃ and pressed together.

[0119] Cooling: The composite film is cooled and shaped by the second cooling roller assembly 12 at a temperature of 10℃-15℃.

[0120] Testing: The prepared film is passed through the transmittance monitoring device 13. If the transmittance of the product in the near-infrared band (2.5-20μm) is less than 10%, the batch of products is considered to be able to effectively block infrared thermal radiation and have radiation cooling performance, and is a qualified product.

[0121] Winding: The prepared composite radiation cooling film is collected onto the winding roller 14.

[0122] The radiation-cooling thin film prepared in this embodiment exhibits an average emissivity of 91% in the 8-13 μm atmospheric window band and a transmittance of 75% in the visible light band, achieving a maximum of 58 W / m under clear, cloudless weather conditions. 2 Radiative cooling power.

[0123] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a radiation-cooled thin film, characterized in that, include: S1, a raised structure is provided on the surface of the roller to form an printing roller, and the film substrate is subjected to thermal printing treatment by the printing roller to form the corresponding raised structure on the surface of the film substrate. S2, nanoparticles are filled between the protrusions on the surface of the thin film substrate; the particle size of the nanoparticles is in the range of 20-500 nm. S3, A protective film is provided on the surface of the protruding structure to form a radiation cooling film; S1 heat printing temperature Specifically, control and adjustment should be performed according to the following formula: ； in, The viscous flow temperature of the thin film substrate, in °C; The rolling speed of the film substrate is set to 0-2 m / min; the hot stamping temperature is... The temperature of the printing roller, in °C; S2 specifically includes: S21, the nanoparticles are sprayed onto the side of the thin film substrate with the protruding structure using an electrostatic spray gun, and the nanoparticles are electrostatically adsorbed onto the thin film substrate. S22, the thin film substrate after the nanoparticles are sprayed by extrusion through a roller; S23, excess nanoparticles are scraped off the surface of the raised structure by a grounded scraper for recycling, thus completing the filling of nanoparticles.

2. The method for preparing a radiation-cooled thin film as described in claim 1, characterized in that, S1 further includes, before the film substrate is heat-pressed by the printing roller: The thin film substrate is preheated, wherein the preheating temperature is within the range of 0-5°C below the viscous flow temperature of the thin film substrate.

3. The method for preparing a radiation-cooled thin film as described in claim 1, characterized in that, S1 specifically includes the following steps for performing hot printing treatment on the film substrate using the printing roller: The hot printing temperature of the printing roller on the film substrate is controlled so that the hot printing temperature is higher than the viscous flow temperature of the film substrate; Furthermore, the hot printing temperature is adjusted according to the rolling speed of the film substrate, and the hot printing temperature increases as the rolling speed of the film substrate increases.

4. The method for preparing a radiation-cooled thin film as described in claim 1, characterized in that, Also includes: S4, the transmittance of the radiation cooling film in the near-infrared band is detected. If the transmittance is less than a preset value, the radiation cooling film is determined to be a qualified product. Near-infrared light specifically refers to light with wavelengths in the range of 2.5-20μm.

5. An apparatus for preparing a radiation-cooled thin film, characterized in that, The apparatus for implementing the radiation-cooling thin film preparation method according to any one of claims 1-4 includes: a first unwinding roller wound with a thin film substrate, an imprinting roller assembly, a spraying device, a second unwinding roller wound with a protective film, a hot-pressing roller assembly, and a take-up roller; the imprinting roller assembly includes a support roller and an imprinting roller with a raised structure on its surface, the thin film substrate is unwound from the first unwinding roller and conveyed between the support roller and the imprinting roller for hot-pressing treatment, and the corresponding raised structure is formed on the surface of the thin film substrate through the hot-pressing treatment. The spraying device is located after the printing roller assembly and is used to spray nanoparticles onto the side surface of the film substrate with the raised structure. The second unwinding roller and the hot pressing roller assembly are located after the spraying device. The second unwinding roller is used to release the protective film and transport it to the side surface of the film substrate with the raised structure. The hot pressing roller assembly is used to perform hot pressing treatment on the protective film and the film substrate after the protective film is laid to form a radiation-cooling film. The winding roller is used to wind up and store the radiation-cooling film.

6. The radiation-cooled thin film preparation apparatus as described in claim 5, characterized in that, It also includes a squeeze roller assembly and a scraper assembly disposed between the spraying device and the second unwinding roller; the squeeze roller assembly is used to squeeze the film substrate after the nanoparticles are sprayed by the roll roller, and the scraper assembly includes a scraper and a recycling container, the scraper being used to scrape off excess nanoparticles from the surface of the raised structure and recycle them into the recycling container; The spraying device includes an electrostatic spray gun, and the scraper is connected to a grounding wire.

7. A radiation-cooling thin film, characterized in that, The method for preparing a radiation-cooled thin film according to any one of claims 1-4 includes: a thin film substrate, nanoparticles, and a protective film. One side surface of the thin film substrate is provided with a raised structure, the nanoparticles fill the gaps between the raised structures, and the protective film is provided on the side of the raised structures opposite to the thin film substrate.

8. The radiation-cooling thin film as described in claim 7, characterized in that, The protruding structure includes an array of rectangular or circular protrusions. The rectangular protrusions have a side length of 2-20 μm, the distance between the centroids of two adjacent rectangular protrusions is 1.5-5 times the side length, and the height of the rectangular protrusions is 0.2-1 times the side length. The circular protrusions have a radius of 1-10 μm, the distance between the centers of two adjacent circular protrusions is 2.5-6 times the radius, and the height of the circular protrusions is 0.4-2 times the radius.

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