High-transmittance radiation refrigeration film and preparation method thereof

Abstract

The invention discloses a preparation method of a high-transmittance radiation refrigeration film, which comprises the following steps: mixing a transparent resin matrix with a diluted monomer solution, adding an ultraviolet light absorber, a surface additive and a photoinitiator, and carrying out ultrasonic dispersion to obtain a coating liquid; the surface of a transparent polymer base material is coated with the coating liquid, and the coating liquid is irradiated and cured by 365nm ultraviolet light to form the radiation refrigeration film. The visible light transmittance of the obtained film is larger than or equal to 92%, the ultraviolet rejection rate is larger than or equal to 99%, the infrared emissivity in the atmosphere window wave band is larger than or equal to 0.90, and cooling can be effectively achieved through radiation heat dissipation. The surface of the film is hydrophobic, the water contact angle is larger than 90 degrees, and the film has potential self-cleaning maintaining capacity. The method is simple in process, can be quickly cured at room temperature, is suitable for large-area continuous production, and has the advantages of low cost and high industrialization potential.

Description

Technical Field

[0001] This invention relates to the technical field of thin film material preparation, and in particular to a high-transmittance radiation-cooling thin film and its preparation method. Background Technology

[0002] Existing radiative cooling materials typically rely on extremely high solar reflectivity to achieve efficient daytime cooling. However, this high reflectivity inevitably leads to opacity, which fundamentally contradicts the light transmittance requirements of applications such as architectural glass and automotive sunroofs. Recent developments of transmissive radiative cooling films have attempted to address this issue, but they often suffer from challenges such as the difficulty in balancing light transmittance and cooling performance, complex fabrication processes, and high production costs.

[0003] For example, utility model patent application number 202322825631.4 discloses a transmissive radiation-cooling thin film, comprising a multilayer structure of a self-cleaning layer, a base film, a metal layer, a cooling layer, and an adhesive layer, with a transmittance >30% and haze <2%. Although this scheme achieves a certain level of light transmittance, the visible light transmittance is still relatively low, and the multilayer structure increases the manufacturing difficulty. Another Chinese invention patent application number 202510042753.7 discloses a high-transmittance radiation-cooling coating and its preparation method, employing a three-dimensional ordered porous structure, which can achieve high light transmittance, but its preparation relies on a template method, resulting in poor mass production. Therefore, there is an urgent need to develop a high-transmittance radiation-cooling thin film that combines high visible light transmittance, high atmospheric window infrared emissivity, simple manufacturing process, and suitability for large-scale production. Summary of the Invention

[0004] This application provides a high-transmittance radiation-cooling film and its preparation method, aiming to solve the problems of existing radiation-cooling materials, such as difficulty in balancing light transmittance and cooling performance, complex preparation processes, and high costs. By employing ultraviolet curing technology, a functional coating is constructed using a specific ratio of transparent resin matrix, diluent monomers, ultraviolet absorbers, surface additives, and photoinitiators. This achieves high atmospheric window infrared emissivity while maintaining high visible light transmittance, and also possesses excellent ultraviolet blocking and surface self-cleaning properties. This process can cure rapidly at room temperature, is suitable for large-area continuous production, and has significant potential for industrial application.

[0005] This application provides a method for preparing a high-transmittance radiation-cooling thin film, comprising the following steps:

[0006] Step 1: Mix 40–60% transparent resin matrix and 20–40% diluted monomer solution evenly by mass fraction, then add 1–3% UV absorber, 1–3% surface additives and 3–5% photoinitiator in sequence, and then disperse by ultrasonication to prepare a uniformly dispersed coating solution.

[0007] Step 2: Apply the coating liquid from Step 1 to the surface of the transparent polymer substrate to form a wet film;

[0008] Step 3: The wet film from Step 2 is cured by irradiating it with ultraviolet light at a wavelength of 365nm to obtain the high-transmittance radiation cooling film.

[0009] Preferably, the transparent resin matrix is ​​one or more selected from bifunctional aliphatic polyurethane acrylate and cyclophenol A epoxy acrylate.

[0010] Preferably, the diluted monomer solution is selected from one or more of isobornyl acrylate and methyl methacrylate.

[0011] Preferably, the ultraviolet absorber is one or more selected from UV1130, UV571, and Tinuvin 477.

[0012] Preferably, the surface additive is one or more selected from BYK-310, BYK-333, and BYK-3456.

[0013] Preferably, the photoinitiator is one or more selected from 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, 2-hydroxy-2-methylphenylacetone, and 1-hydroxycyclohexylphenyl ketone.

[0014] Preferably, the diluted monomer solution is a mixture of isoborneol acrylate and methyl methacrylate in a mass ratio of 9:1.

[0015] Preferably, the photoinitiator is a mixture of 2-hydroxy-2-methylphenylacetone and 1-hydroxycyclohexylphenyl ketone in a mass ratio of 8:1.

[0016] Preferably, the ultraviolet absorber is Tinuvin 477.

[0017] The present invention also provides the high-transmittance radiation cooling film prepared by any of the above preparation methods.

[0018] One technical solution provided in this application embodiment has at least the following technical effects:

[0019] (1) The radiation cooling film prepared by the present invention has excellent comprehensive optical performance, with visible light transmittance ≥92% and ultraviolet blocking rate ≥99%, and good optical clarity. In particular, in the atmospheric transparent window band of 8–13 μm, its infrared emissivity ≥0.90 can effectively dissipate heat to the low-temperature outer space in the form of radiation, thereby significantly enhancing its passive radiation cooling effect.

[0020] (2) The thin film prepared by the present invention exhibits hydrophobic properties, with a water contact angle >90°, and can achieve a self-cleaning function. In outdoor applications, it can keep the surface clean with the help of rainwater or simple rinsing, thereby maintaining high light transmittance and stable cooling effect for a long time, and significantly reducing maintenance costs.

[0021] (3) This invention uses ultraviolet light curing technology, and the entire preparation process can be completed quickly at room temperature. The curing time is only a few seconds to tens of seconds, and the coating is dense and uniform with strong adhesion to the transparent PET substrate. This process can efficiently and stably realize the large-area and continuous preparation of wide films with low production cost and high industrialization potential. Attached Figure Description

[0022] Figure 1 The diagram shows the water contact angles of pure PET film and the radiation-cooling film prepared in Example 3. Detailed Implementation

[0023] This application provides a high-transmittance radiation cooling film and its preparation method. It mainly forms a functional coating on the surface of a transparent polymer substrate through an ultraviolet curing process. While maintaining high visible light transmittance, it achieves high atmospheric window infrared emissivity and has excellent ultraviolet blocking and surface self-cleaning properties.

[0024] The technical solution in this application is to solve the above problems, and the overall approach is as follows:

[0025] A high-transmittance crosslinked network is constructed using a transparent resin matrix and specific diluted monomers. Ultraviolet shielding is achieved by adding an ultraviolet absorber, and surface additives optimize the coating's smoothness and adhesion. Simultaneously, by controlling the component ratios and curing process, the coating acquires high infrared emissivity in the atmospheric window band, thus achieving radiative heat dissipation without affecting visible light transmittance. The following examples will demonstrate the influence of different components and ratios on the optical properties and cooling effect of the thin film, verifying the feasibility and superiority of this invention.

[0026] To better understand the above technical solution, the following will provide a detailed explanation of the above technical solution using specific implementation methods.

[0027] Example 1

[0028] (1) After mixing 5.00g of polyurethane acrylate (PUA) and 2.00g of isobornyl acrylate (IBOA) evenly, 0.05g of ultraviolet absorber UV571, 0.10g of surface additive BYK-333 and 0.36g of 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (TPO) were added in sequence. After ultrasonic dispersion treatment, a uniformly dispersed coating liquid was obtained.

[0029] (2) The coating liquid in step (1) is uniformly coated onto the surface of the transparent PET substrate with a wet film thickness of 50 μm using a coating machine to form a wet film;

[0030] (3) The wet film was irradiated with ultraviolet light with a wavelength of 365nm and a power of 400W and cured for 10s to obtain a high-transmittance radiation cooling film.

[0031] The optical performance data of the high-transmittance radiation-cooling thin film prepared in this embodiment are shown in Table 1.

[0032] The thin film prepared in this embodiment has excellent optical performance data, with a visible light transmittance of up to 92.6% and an ultraviolet blocking rate of 99.9%, successfully achieving a highly efficient synergy between high light transmittance and near-complete ultraviolet shielding.

[0033] It is worth noting that the thin film can achieve an infrared emissivity of up to 0.90 in the 8–13 μm atmospheric window band, indicating that the material system can improve the infrared emission characteristics of the thin film surface, and then transfer its own heat outward in the form of radiation through thermal radiation, thereby realizing the function of radiative cooling.

[0034] Example 2

[0035] The only difference between Example 2 and Example 1 is that, except that 2.00g of isobornyl acrylate (IBOA) is replaced with 2.00g of methyl methacrylate (MMA), the other raw material types, amounts, preparation processes and conditions are the same as in Example 1, and a high-transmittance radiation cooling film is finally obtained.

[0036] The relevant optical performance data of the high-transmittance radiation-cooling thin film prepared in this embodiment are shown in Table 1.

[0037] The thin film prepared in this second embodiment has excellent optical performance data. While maintaining a visible light transmittance of 92.2% and an ultraviolet light blocking rate of 99.9%, the thin film also achieves a solar infrared blocking rate of 8.3% and a high infrared emissivity of 0.90.

[0038] This indicates that the thin film prepared in Example 2 can not only effectively regulate the solar energy spectrum, but also improve the cooling effect of the thin film through the synergistic mechanism of "blocking part of the incident heat" and "enhancing radiative heat dissipation".

[0039] Example 3

[0040] The only difference between Example 3 and Example 1 is that, except that 2.00g of isoborneol acrylate is adjusted to 1.80g of isoborneol acrylate and 0.20g of methyl methacrylate, the types and amounts of other raw materials, preparation processes and conditions are the same as in Example 1, and a high-transmittance radiation cooling film is finally obtained.

[0041] The relevant optical performance data of the high-transmittance radiation-cooling film prepared in this embodiment 3 are shown in Table 1.

[0042] Based on the optical performance data of the high-transmittance radiation cooling film prepared in Example 3, while maintaining a high visible light transmittance of 92.3% and an extremely high ultraviolet blocking rate of 99.5%, the film's solar infrared blocking rate of 9.9% and infrared emissivity of 0.92 are both improved compared to Example 2.

[0043] This indicates that the introduction of IBOA and the adjustment of monomer ratio further optimized the film's ability to manage near-infrared heat and its radiative heat dissipation efficiency in the mid-infrared band, thus synergistically enhancing the overall cooling effect.

[0044] Please refer to Figure 1 , Figure 1 The diagram shows the water contact angles of pure PET film and the radiation-cooling film prepared in Example 3.

[0045] The water contact angle of the film prepared in Example 3 is 97.98°, which is significantly improved compared to the 95.11° contact angle of the pure PET substrate. This data confirms the effective control of the substrate surface properties by the coating, indicating that the functionalized film, while maintaining high light transmittance and heat insulation performance, possesses superior surface moisture resistance and potential self-cleaning ability, providing favorable conditions for its long-term stable application in complex environments such as outdoors.

[0046] Example 4

[0047] The only difference between Example 4 and Example 3 is that, except that 0.36g of 2,4,6-trimethylbenzoyl-diphenylphosphine oxide is replaced with 0.32g of 2-hydroxy-2-methylphenylacetone (HMPP) and 0.04g of 1-hydroxycyclohexylphenyl ketone (IGM), the other raw material types, amounts, preparation processes and conditions are the same as in Example 3, and a high-transmittance radiation cooling film is finally obtained.

[0048] The relevant optical performance data of the high-transmittance radiation-cooling thin film prepared in this embodiment four are shown in Table 1.

[0049] In this fourth embodiment, by adjusting the photoinitiator to a compound system of HMPP and IGM, the solar infrared blocking rate is increased to 12.4% and the infrared emissivity is increased to 0.924 while maintaining a visible light transmittance of 92.2% and an ultraviolet blocking rate of 99.3%.

[0050] This indicates that the optimized initiation system further improved the distribution of functional components and synergistically enhanced the thermal barrier and radiative heat dissipation capabilities of the thin film.

[0051] The radiation cooling coating prepared in Example 4 is continuously and densely distributed on the PET substrate with a smooth surface, and no obvious particle aggregation was observed at different magnifications.

[0052] Example 5

[0053] The only difference between Example 5 and Example 4 is that, except for changing 0.05g UV571 to 0.05g Tinuvin477, the other raw material types, amounts, preparation processes and conditions are the same as in Example 4, and a high-transmittance radiation cooling film is finally obtained.

[0054] The relevant optical performance data of the high-transmittance radiation-cooling thin film prepared in this embodiment are shown in Table 1.

[0055] In this fifth embodiment, after replacing the ultraviolet absorber with Tinuvin 477, the film maintained excellent levels of visible light transmittance (92.4%) and ultraviolet blocking rate (99.9%), while achieving the highest values ​​in the series for solar infrared blocking rate (16.8%) and infrared emissivity (0.92).

[0056] This confirms that the UV absorber can better synergize with the entire system, significantly enhancing the film's comprehensive management of solar thermal radiation and passive heat dissipation efficiency without compromising basic optical properties, making it one of the optimal embodiments of this system.

[0057] The radiation cooling coating prepared in Example 5 is continuously and densely distributed on the PET substrate with a smooth surface, and no obvious particle aggregation was observed at different magnifications.

[0058] Table 1

[0059] Example Visible light transmittance UV blocking rate Infrared blocking rate Infrared emissivity Example 1 92.6% 99.9% 0.0% 0.900 Example 2 92.2% 99.9% 8.3% 0.907 Example 3 92.3% 99.5% 9.9% 0.922 Example 4 92.2% 99.3% 12.4% 0.924 Example 5 92.4% 99.9% 16.8% 0.927

[0060] The relevant data from Examples 1 to 5 in Table 1 also show that, in order to synergistically enhance the cooling effect, the thin film prepared in the embodiments of this application can selectively block thermal radiation in the near-infrared part (about 780-2500 nm) of the solar spectrum (i.e., solar infrared blocking) through component design, while maintaining high visible light transmittance, so as to reduce heat input.

[0061] It should be noted that the above embodiments are only for more specific demonstration of the technical solution and effects of the present invention, and are not intended to limit the present invention. Those skilled in the art can choose equivalent substitutions or combinations of other ultraviolet absorbers, surface additives, and other materials described in the claims and specification according to actual needs, and all can achieve the objectives of the present invention.

[0062] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for preparing a high-transmittance radiation-cooling thin film, characterized in that, Includes the following steps: Step 1: Mix 40–60% transparent resin matrix and 20–40% diluted monomer solution evenly by mass fraction, then add 1–3% UV absorber, 1–3% surface additives and 3–5% photoinitiator in sequence, and then disperse by ultrasonication to prepare a uniformly dispersed coating solution. Step 2: Apply the coating liquid from Step 1 to the surface of the transparent polymer substrate to form a wet film; Step 3: The wet film from Step 2 is cured by irradiating it with ultraviolet light at a wavelength of 365nm to obtain the high-transmittance radiation cooling film.

2. The preparation method according to claim 1, characterized in that, The transparent resin matrix is ​​selected from one or more of bifunctional aliphatic polyurethane acrylate and cyclophenol A epoxy acrylate.

3. The preparation method according to claim 1, characterized in that, The diluted monomer solution is selected from one or more of isobornyl acrylate and methyl methacrylate.

4. The preparation method according to claim 1, characterized in that, The ultraviolet absorber is selected from one or more of UV1130, UV571, and Tinuvin 477.

5. The preparation method according to claim 1, characterized in that, The surface additive is one or more selected from BYK-310, BYK-333, and BYK-3456.

6. The preparation method according to claim 1, characterized in that, The photoinitiator is one or more selected from 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, 2-hydroxy-2-methylphenylacetone, and 1-hydroxycyclohexylphenyl ketone.

7. The preparation method according to claim 3, characterized in that, The diluted monomer solution is a mixture of isobornyl acrylate and methyl methacrylate in a mass ratio of 9:

1.

8. The preparation method according to claim 7, characterized in that, The photoinitiator is a mixture of 2-hydroxy-2-methylphenylacetone and 1-hydroxycyclohexylphenyl ketone in a mass ratio of 8:

1.

9. The preparation method according to claim 8, characterized in that, The ultraviolet absorber is Tinuvin 477.

10. The high-transmittance radiation-cooling thin film prepared by the preparation method according to any one of claims 1 to 9.

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