High-transmittance radiative cooling protective film and its use

Abstract

The present invention relates to a high-transmittance radiative cooling protective film. The film includes a spectral control layer, which comprises alternating layers of low-refractive-index and high-refractive-index materials, with six or more layers of high-refractive-index material and five or more layers of low-refractive-index material. The film achieves spectral control through the structural design of a multilayer film, ensuring high visible light transmittance while effectively blocking the incidence of other energies in the solar spectrum, and achieving maximum radiative cooling effect by releasing heat in the form of electromagnetic waves through the thermal infrared spectrum to the natural cooling source in space.

Description

Technical Field

[0001] The present invention relates to a protective film, and particularly to a high transmittance radiative cooling protective film and its use.

Background Art

[0002] With the increase in the world population and the continuous development of society, the problem of climate warming has become increasingly serious, and as a result, the demand for cooling energy consumption is also increasing. Conventional active cooling means rely on a compression cooling system, consume a large amount of electric power, and generate a large amount of carbon dioxide. On the other hand, refrigerants such as Freon used in the compression cooling system can destroy the ozone layer and cause serious environmental problems. Radiative cooling is a passive cooling method that is significantly different from conventional cooling means and releases heat to the cold universe by thermal radiation. The Earth's atmosphere has different electromagnetic wave transmittances depending on the wavelength, and the transmittance for electromagnetic waves in the 8-13 μm band is very high, which is known as the "atmospheric window". Therefore, an excellent radiative cooling surface strongly reflects sunlight (0.3-2.5 μm) while having the highest possible emissivity in the 8-13 μm band, thereby achieving natural cooling without consuming energy. As described above, radiative cooling technology can save energy while reducing problems such as the greenhouse effect and environmental pollution caused by conventional cooling.

[0003] With the development of nanophotonics and advanced manufacturing technologies, photonic crystals and metamaterials have been first used in radiative cooling materials. Nanophotonic crystals refer to nanophotonic materials with various layer structures and metasurface structures formed by processing some semiconductor materials through coating processes such as magnetron sputtering or electron beam evaporation, or micro-nano processing processes, thereby achieving selective high radiation in a specific mid-infrared band.

[0004] While the radiation spectra of conventional materials are typically very broad, the use of photonic materials allows for the design of heat sources with controllable, narrow-band radiation spectra, which are particularly necessary for radiative cooling. In the literature (Nature, 2014, 515(7528):540-544), a radiative cooler was fabricated by assembling a planar, layered one-dimensional photonic crystal. This cooler is designed with a photonic crystal consisting of seven alternating layers of SiO2 and HfO2 on a silver (Ag) mirror. Here, the SiO2 layer exhibits extremely high emissivity in the 8-13 μm mid-infrared band due to phonon polaritons. The spectral emissivity in the mid-infrared band is further adjusted by superimposing the SiO2 and HfO2 layers. Furthermore, the Ag mirror can improve the reflectivity of the composite film layer to the ultraviolet portion of sunlight. Due to the multilayer film structure design, the radiative cooler reflects approximately 97% of solar radiation, exhibiting strong radiation within an atmospheric window, reaching 900 W·m². -2 Under solar radiation, it has a cooling effect of 5°C lower than the ambient temperature and 40.1 W·m -2 This enables the realization of cooling power.

[0005] However, currently, radiative cooling materials are mainly used in outdoor buildings such as walls and roofs, and are rarely used in display devices. This is because display devices have higher spectral requirements for radiative cooling materials. [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] The object of the present invention is to provide a radiative cooling film suitable for display devices. Based on this object, a high-transmittance radiative cooling protective film is provided. This protective film has selectively high radiation in the mid-infrared band, thereby achieving low-energy-consuming passive cooling, while also having extremely high transmittance in the visible light band. [Means for solving the problem]

[0007] The technical solution to be adopted is as follows: A high-transmittance radiative cooling protective film comprising a spectral control layer, the spectral control layer comprising alternating layers of high-refractive-index material and low-refractive-index material, the high-refractive-index material comprising 6 or more layers and the low-refractive-index material comprising 5 or fewer layers, wherein when light passes through the spectral control layer, visible light has a transmittance of 90% or more, near-infrared light has a reflectance of 80% or more, thereby effectively blocking near-infrared light and mid-infrared light has an emissivity of 95% or more.

[0008] In one preferred configuration, the low refractive index material of each layer is either identical or different, and is one or more materials selected from SiO2, SiO, Al2O3, AlF3, and MgF2.

[0009] In one preferred configuration, the high refractive index material of each layer is either identical or different, and is one or more materials selected from TiO2, Ti3O5, Ti2O3, ZrO2, CeO2, and HfO2.

[0010] In one preferred embodiment, the spectral control layer is composed of a non-metallic layer material.

[0011] In one preferred embodiment, both the low refractive index material and the high refractive index material are formed by electron beam deposition coating, and the coating process is The coating speed is 0.1 to 1.0 nm / s. The particle size of the material used for coating should be between 1 and 20 mm. The film deposition temperature is 80-200°C. The vacuum level during the coating process is 1 × 10⁻⁶ -2 ~1 × 10 -4 To be maintained, and An ion source is used to assist in the coating process, and the ion source energy parameters satisfy one or more combinations of the following: voltage 150-220V and current 3-6A.

[0012] In one preferred configuration, the materials of the top and bottom layers of the spectral control layer are all high refractive index materials.

[0013] In one preferred embodiment, the spectral control layer comprises TiO2, SiO, TiO2, SiO2, TiO2, SiO, TiO2, SiO, TiO2, SiO, TiO2, SiO, TiO2, TiO2, arranged sequentially from the bottom layer to the top layer, and when light rays are incident from the outside, they first reach the top layer, then pass through each intermediate layer, and finally reach the bottom layer.

[0014] In one preferred embodiment, the organic packaging layer further comprises a hydrophobic layer.

[0015] In one preferred embodiment, the control layer is provided as a series of material layers, TiO2 material layer with a thickness of 10-20 nm, A layer of SiO material with a thickness of 20-50 nm. A TiO2 material layer with a thickness of 100-150 nm. A SiO material layer with a thickness of 150-200 nm. TiO2 material layer with a thickness of 80-110 nm, A SiO material layer with a thickness of 150-200 nm. TiO2 material layer with a thickness of 90-130 nm, A SiO material layer with a thickness of 150-200 nm. TiO2 material layer with a thickness of 90-130 nm, A layer of SiO material with a thickness of 20-50 nm, and It contains a TiO2 material layer with a thickness of 10-20 nm.

[0016] In another aspect, the present invention provides for the use of a highly transmissive radiative cooling protective film, which, as a screen film, is adhered onto the screen of an electronic product, particularly a mobile phone, to effect radiative cooling under outdoor conditions and prevent the temperature of the mobile phone from becoming too high. As shown in Figure 1, the radiative cooling film includes a package layer, a base film, a radiative cooling layer, and an AB adhesive layer provided sequentially. The base film is a reinforced glass film for mobile phones and may also be a commercially available reinforced glass film for mobile phones. The radiative cooling layer is deposited on the reinforced glass film for mobile phones, and the AB adhesive layer is used to adhere the radiative cooling protective film onto the screen.

Advantages of the Invention

[0017] The advantageous effects of the present invention include the following. Through the structural design of the multilayer film, the protection film achieves spectral control, effectively blocks the incidence of other energies in the solar band while ensuring a high visible light transmittance, and releases heat in the form of electromagnetic waves through the thermal infrared band to the natural cold source of the universe, thereby achieving the maximum radiative cooling effect. Specifically, the radiative cooling protective film achieves a visible light transmittance of 90% or more, a near-infrared blocking rate of 80% or more, and a mid-infrared emissivity of 95% or more, and finally realizes a temperature reduction effect of 5 to 10 °C.

[0018] Through the structural design of the multilayer film with alternating high refractive index layers and low refractive index layers, by utilizing the optical interference effect and stacking different materials, the transmittance of a specific band is increased and the reflectivity of a specific band is increased, thereby achieving spectral control in a specific band.

[0019] The protection film can be pasted onto the surface of almost any material to achieve a temperature reduction effect. Specific practical scenarios include not only outdoor buildings such as glass, walls, and roofs, but also display devices such as electronic devices. It is an effective tool for energy conservation and emission reduction. Additionally, by further adding an organic package layer, excellent anti-aging properties can be imparted to the product, and it can have excellent hydrophobicity, antifouling properties, and abrasion resistance during use.

Brief Description of the Drawings

[0020] [Figure 1] It is a structural schematic diagram of a high transmittance radiative cooling protection film in the present invention. [Figure 2] It is a structural diagram of a spectral control layer in the present invention. [Figure 3] It is a test of the transmittance of glass before and after coating in the visible light and near-infrared bands. [Figure 4] It is the emissivity of glass before and after coating in the mid-infrared band. [Figure 5] It is a test of the temperature reduction performance of glass before and after coating. [Figure 6] It is the contact angle between glass with an organic package layer and water. [Figure 7] It is the contact angle between glass without an organic package layer and water.

Embodiments for Carrying Out the Invention

[0021] Hereinafter, the present invention will be described in more detail with reference to specific embodiments, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments.

[0022] The high-transmittance radiative cooling protective film of the present invention comprises a base film and a spectral control layer, the spectral control layer being deposited on the base film, and the spectral control layer comprising alternating layers of high-refractive-index material and low-refractive-index material, wherein the high-refractive-index material comprises 6 or more layers and the low-refractive-index material comprises 5 or more layers. By alternating the arrangement of two materials with different refractive indices, the refraction angle of light rays within the film is adjusted, and the transmission paths of light of different bands within the film are adjusted, thereby achieving control of spectral performance. When light rays pass through the film layers, visible light has a transmittance of 90% or more, near-infrared light has a blockage rate of 80% or more, and mid-infrared light has an emissivity of 95% or more. The organic package layer is formed by electron beam deposition using a fluorine-containing organic material, the thickness of the package layer is preferably in the range of 5 to 40 nm, the evaporation resistance current is preferably in the range of 30 to 200 mA, and the coating speed is 0.3 to 1.0 nm / s.

[0023] In this invention, both the low-refractive-index and high-refractive-index materials are ceramic materials and do not contain metal layers, thus simplifying the design of the film system. By controlling the thickness of each layer of the ceramic material and the coating process, the reflectance, transmittance, and emissivity can be controlled. Here, the refractive index difference between the low-refractive-index and high-refractive-index materials is 0.5 to 0.9.

[0024] Each low refractive index material in the spectral control layer may be identical or different, and may be a single material or multiple materials. Each low refractive index material may be partially identical or entirely identical, and may be one or more materials selected from SiO2, SiO, Al2O3, AlF3, and MgF2. Each high refractive index material may be identical or different, may be partially identical or entirely identical, and may be one or more materials selected from TiO2, Ti3O5, Ti2O3, ZrO2, CeO2, and HfO2. To simplify the process, it is preferable that each low refractive index material and each high refractive index material are identical.

[0025] The base film in this invention may be a tempered glass film for mobile phones, and the radiative cooling protective film further comprises an organic packaging layer and an AB adhesive layer, the organic packaging layer and the spectral control layer are deposited or sputtered on both sides of the base film, preferably by electron beam deposition coating. The film layer formed by this coating process has a dense structure and high stability, the particle size of the material during the coating process can be 1 to 20 mm, the film formation temperature range is 80 to 200°C, and the vacuum degree is 1 × 10⁻⁶ -4 ~1 × 10 -1 The coating speed is maintained at Pa, and is selected according to the thickness of the film layer. When the film layer thickness is less than 50 nm, the coating speed is preferably 0.1 to 0.5 nm / s, and when the film layer thickness is 50 nm or more, the coating speed is preferably 0.6 to 1.0 nm / s. This configuration facilitates control of the precision of the film layer while also being beneficial for the stability of film formation.

[0026] To ensure tight bonding between the multilayer film structures, an ion source is used to assist in the coating process of each material, with the energy parameters of the ion source being a voltage of 150-220V and a current of 3-6A.

[0027] In the present invention, the protective film is preferably made up of TiO2, SiO, TiO2, SiO, TiO2, SiO, TiO2, SiO, TiO2, SiO, TiO2, and TiO2 in order from the glass substrate outward, with the thickness of each film layer being as follows. The TiO2 material layer has a thickness of 10-20 nm. The SiO material layer has a thickness of 20-50 nm. The TiO2 material layer has a thickness of 100-150 nm. The SiO material layer has a thickness of 150-200 nm. The TiO2 material layer has a thickness of 80-110 nm. The SiO material layer has a thickness of 150-200 nm. The TiO2 material layer has a thickness of 90-130 nm. The SiO material layer has a thickness of 150-200 nm. The TiO2 material layer has a thickness of 90-130 nm. The SiO material layer has a thickness of 20-50 nm. The TiO2 material layer has a thickness of 10-20 nm.

[0028] The present invention will be described in more detail below based on specific embodiments.

[0029] Example 1 The radiative cooling protective film comprises an organic package layer 1, a base film 2, a spectral control layer 3, and an AB adhesive layer 4. The organic package layer 1 is a fluorine-containing organic material layer, and the base film is a mobile phone film, which may be a commercially available tempered glass film for mobile phones or a soft film for mobile phones with high light transmission properties. In this embodiment, the spectral control layer 3 is formed by coating a tempered glass film for mobile phones as a base, and the AB adhesive layer 4 is used to bond the radiative cooling protective film to the mobile phone. The spectral control layer 3 has an 11-layer structure, of which high refractive index materials and low refractive index materials are alternately laminated, with 6 layers of high refractive index material and 5 layers of low refractive index material. Each low refractive index material uses SiO2 (n=1.46@550nm, i.e., the refractive index of light at a wavelength of 550nm is 1.46), and the high refractive index material uses TiO2 (n=2.35@500nm). Each film layer is manufactured by coating by electron beam deposition, and an ion source is also used to assist in the coating. The coating temperature for electron beam deposition was 120°C, and the vacuum level was 1*10⁻¹⁰. -3 The particle size of the low refractive index material is set to 1-3 mm, and the particle size of the high refractive index material is set to 3-5 mm. The energy of the SiO ion source for coating assistance is 150 V, 3 A, the energy of the TiO2 ion source for coating assistance is 200 V, 6 A, and the vapor resistance current of the fluorine-containing organic material is 100 mA.

[0030] The configuration of each film layer is shown in Figures 1 and 2, and the spectral control layer 3 includes TiO2 layer 21, SiO layer 22, TiO2 layer 23, SiO layer 24, TiO2 layer 25, SiO layer 26, TiO2 layer 27, SiO layer 28, TiO2 layer 29, SiO layer 210, and TiO2 layer 211.

[0031] The film layer material, thickness, and coating speed are shown in Table 1.

[0032] [Table 1]

[0033] The hydrophobicity of one side of the organic packaging layer of the obtained radiative cooling protective film was tested using a Theta contact angle tester (LSA100, LAUDA Scientific). The test results are shown in Figure 6. The average static contact angle after coating exceeded 140°.

[0034] Example 2 The main difference from Example 1 is that, as shown in Table 2, the material of the spectral control layer is different, and the thickness of each film layer and the coating speed are also different.

[0035] [Table 2]

[0036] Example 3 The difference from Example 1 is that the number of film layers is different, and the material, thickness, and coating speed of each film layer are specifically shown in Table 3.

[0037] [Table 3]

[0038] Example 4 Compared to Example 1, the only difference is that the particle size of the materials is different; the particle size of the low refractive index material is selected to be 5-8 mm, and the particle size of the high refractive index material is selected to be 8-10 mm.

[0039] Comparative Example 1 The base film of Example 1 is a tempered glass film for mobile phones that does not have a spectral control layer deposited on it.

[0040] The properties of the radiative cooling protective film of Example 1 and the tempered glass film for mobile phones of Comparative Example 1 were tested.

[0041] The reflectance in the sunlight band of the tempered glass film for mobile phones of Comparative Example 1 and the radiative cooling protective film of Example 1 was compared. The instrument used was a UV-Vis-NIR spectrophotometer (uv3600, Shimadzu Corporation) equipped with an integrating sphere model (ISR-3100). The measurement band range was 0.3 to 2.5 μm. The results are shown in Figure 3. The radiative cooling protective film of Example 1 was able to further improve the transmittance in the visible light band from 0.90 to 0.94. The radiative cooling protective film of the present invention achieved the effect of improving the transmittance of tempered glass films for mobile phones, and the reflectance in the near-infrared band was significantly improved, rising from less than 0.1 for conventional tempered glass films for mobile phones to 0.8 or higher, thus preventing the temperature rise of mobile phones due to high temperatures from the outside.

[0042] For the emissivity in the mid-infrared band of the tempered glass film for mobile phones in Comparative Example 1 and the radiative cooling protective film of Example 1, the equipment used was a Fourier transform infrared (FT-IR) spectrometer (Nicolet IS50, ThermoFisher), a gold-plated integrating sphere (IntergatIR MIR, Pike), and a cadmium mercury telluride detector. As shown in Figure 4, it was found that the radiative cooling protective film can significantly improve the emissivity in the mid-infrared and far-infrared bands, especially in the atmospheric window (8-13 μm), from less than 0.7 of the original glass to 0.95 or higher. This indicates that the radiative cooling protective film of the present invention can effectively and efficiently dissipate heat generated from the mobile phone to the outside, thereby preventing the mobile phone from overheating.

[0043] A temperature comparison test was conducted between the tempered glass film for mobile phones of Comparative Example 1 and the radiative cooling protective film of Example 1. Thermometers were placed in the radiative cooling protective film, the tempered glass film for mobile phones (attached to a commercially available mobile phone, with the screen turned on and continuously operated), and the air. Temperature changes under these three conditions were recorded simultaneously. Lower temperatures indicate better cooling performance. The equipment used was a K-type Omega thermocouple. As shown in Figure 5, under outdoor conditions with an ambient temperature of approximately 30°C, the radiative cooling protective film was able to lower the operating temperature of the mobile phone by 5-10°C, demonstrating a significant radiative cooling effect.

[0044] Comparative Example 2 Compared to Example 1, the only difference is the absence of the fluorine-containing organic layer 1. The hydrophobicity of the radiative cooling protective film was tested using a theta contact angle tester (LSA100, LAUDA Scientific). The test results are shown in Figure 7. The contact angle of the coated glass was only 23.7°. This indicates that the fluorine-containing organic layer significantly improves the hydrophobicity of the entire film system, thereby ensuring antifouling and abrasion resistance during use.

[0045] Comparative Example 3 Compared to Example 1, the only difference is the particle size of the materials. The particle size of both the low refractive index material and the high refractive index material is 0.5 to 1 mm.

[0046] The performance of the radiative cooling protective films in Examples 1, 2, 4, and 5, and Comparative Examples 1 and 2, was tested, and the results are shown in Table 4.

[0047] [Table 4]

[0048] The above embodiments are merely for illustrative purposes and not limiting purposes, and the invention has been described in detail with reference to preferred embodiments. Those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the invention without departing from the spirit and scope of the technical solutions of the invention.

Claims

1. A high-transmittance radiative cooling protective film, A high-transmittance radiative cooling protective film comprising a spectral control layer, wherein the spectral control layer comprises alternating layers of low-refractive-index material and high-refractive-index material, with six or more layers of high-refractive-index material and five or more layers of low-refractive-index material.

2. The high-transmittance radiative cooling protective film according to claim 1, characterized in that when light rays pass through the spectral control layer, visible light has a transmittance of 90% or more, near-infrared light has a blocking rate of 80% or more, and mid-infrared light has an emissivity of 95% or more.

3. The high refractive index materials of each layer are the same or different, and are one or more materials selected from TiO ２ , Ti ３ O ５ , Ti ２ O ３ , ZrO ２ , CeO ２ , HfO ２ . The low refractive index materials of each layer are the same or different, and are one or more materials selected from SiO ２ , SiO, Al ２ O ３ , AlF ３ , MgF ２ . The high transmittance radiation cooling protection film according to claim 1, characterized in that it is such.

4. The high transmittance radiative cooling protective film according to claim 1, characterized in that the spectral control layer is composed of a non-metallic layer material.

5. The low refractive index material and the high refractive index material are both formed by electron beam deposition coating, and the coating process is as follows: The coating speed is 0.1 to 1.0 nm / s. The particle size of the material used for coating should be between 1 and 20 mm. The film deposition temperature is 80 to 200°C. The vacuum level during the coating process is 1 x 10⁻⁶ －２ ~1 x 10 －４ To be maintained, and The high-transmittance radiative cooling protective film according to claim 1, characterized in that an ion source is used to assist in coating, and the ion source energy parameters satisfy one or more combinations of a voltage of 150 to 220 V and a current of 3 to 6 A.

6. The high transmittance radiative cooling protective film according to claim 1, characterized in that the materials of the uppermost and lowermost layers of the spectral control layer are all high refractive index materials.

7. The spectral control layer is provided sequentially from the bottom layer to the top layer, and contains TiO ２ SiO, TiO ２ SiO, TiO ２ SiO, TiO ２ SiO, TiO ２ SiO, TiO ２ The high-transmittance radiative cooling protective film according to claim 1, characterized in that, when light rays are incident from the outside, they first reach the uppermost layer, then pass through each intermediate layer, and finally reach the bottom layer.

8. The high transmittance radiative cooling protective film according to claim 1, further comprising an organic packaging layer, a base film, and an adhesive layer, wherein the organic packaging layer is a hydrophobic layer, the base film is a tempered glass film, the organic packaging layer and the radiative cooling layer are provided on both sides of the base film, and the adhesive layer is used to bond the radiative cooling protective film onto an electronic screen.

9. The control layer is provided as a series of material layers, TiO2 with a thickness of 10-20 nm ２ material layer, SiO material layer with a thickness of 20-50 nm, TiO2 with a thickness of 100-150 nm ２ material layer, A SiO material layer with a thickness of 150-200 nm, TiO2 with a thickness of 80-110 nm ２ material layer, A SiO material layer with a thickness of 150-200 nm, TiO2 with a thickness of 90-130 nm ２ material layer, A SiO material layer with a thickness of 150-200 nm, TiO2 with a thickness of 90-130 nm ２ material layer, A SiO material layer with a thickness of 20 to 50 nm, and TiO2 with a thickness of 10-20 nm ２ The high-transmittance radiative cooling protective film according to claim 1, characterized by including a material layer.

10. Use of the high-transmittance radiative cooling protective film described in claim 1 as a screen film for electronic equipment.

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