High-reflectivity high-thermal-conductivity self-cooling coating material, and preparation method and application thereof

Abstract

The present application relates to the technical field of functional coating materials, and particularly relates to a high-reflectivity high-thermal-conductivity self-cooling coating material and a preparation method and application thereof.The high-reflectivity high-thermal-conductivity self-cooling coating material comprises a composite structure formed by a modified hexagonal boron nitride, nano-silver powder and a silicone rubber matrix through a hot-pressing process.In the coating, the hexagonal boron nitride is arranged in parallel under hot pressing, and the nano-silver powder is distributed between the boron nitride layers to form a "BN-Ag-BN" thermal conduction path, thereby solving the trade-off effect between thermal conduction and optical performance in the hexagonal boron nitride coating, and simultaneously achieving high solar reflectivity, high atmospheric window emissivity, high thermal conductivity and self-cooling functions.By introducing the nano-silver powder and the hot-pressing process, the present application realizes the synergistic improvement of the optical performance and the thermal conduction performance of the coating, and is particularly suitable for energy storage electric cabinets, transformers and other power equipment with strong self-heating requirements.

Description

Technical Field

[0001] This invention relates to the field of functional coating materials technology, specifically to a high-reflectivity, high-thermal-conductivity self-cooling coating material, its preparation method, and its application. Background Technology

[0002] With the continuous increase in power density of power electronic equipment, especially the widespread application of self-heating devices such as energy storage cabinets and transformers, heat dissipation has become a key factor restricting their performance and lifespan. Traditional heat dissipation methods, such as air cooling and liquid cooling, often suffer from high energy consumption and complex structures. Radiation cooling coating, as a passive heat dissipation technology, dissipates heat into outer space in the form of infrared radiation through high emissivity in the atmospheric window (8~13 μm) band, while reducing solar heat absorption through high reflectivity in the solar spectrum region (0.3~2.5 μm), thereby achieving zero-energy cooling.

[0003] Hexagonal boron nitride (h-BN) is considered an ideal filler for radiation-cooling coatings due to its high band gap, high reflectivity in the solar spectrum, and high emissivity in the atmospheric window. Furthermore, hexagonal boron nitride possesses a unique lamellar structure and extremely high in-plane thermal conductivity (300~600 W / m·K), making it a promising candidate for applications in power equipment where both heat dissipation and cooling are required.

[0004] However, the sheet-like structure of hexagonal boron nitride also presents a typical technical challenge: a trade-off exists between thermal conductivity and optical performance. When the hexagonal boron nitride sheets are arranged in parallel within the coating, high solar reflectivity can be achieved, but its out-of-plane thermal conductivity is extremely poor. When the hexagonal boron nitride sheets are arranged perpendicularly, although the out-of-plane thermal conductivity is excellent, the optical performance (reflectivity and emissivity) decreases significantly. This contradiction limits its application in high-self-heating electrical equipment.

[0005] Therefore, developing a self-cooling coating that can overcome the above trade-offs and achieve high reflectivity, high thermal conductivity, and high emissivity is of great practical significance and application value. Summary of the Invention

[0006] Purpose of the invention: The technical problem to be solved by the present invention is to address the technical difficulty in achieving both high solar reflectivity and high thermal conductivity of hexagonal boron nitride coatings in the prior art. The invention provides a high reflectivity, high thermal conductivity, and self-cooling coating material, its preparation method, and its application. The present invention achieves the following synergistic innovations by introducing nano silver powder (Ag) and combining it with a segmented hot-pressing curing process: (1) During the hot-pressing process, vertical pressure is applied to force the sheet-like BN to undergo forced orientation in the silicone oil matrix, and its sheet plane is basically parallel to the coating surface, thereby maximizing the solar reflectivity of the coating; (2) The uniformly dispersed nano silver powder acts as a "thermal bridge" and forms close contact with the edges or surfaces of adjacent BN sheets during the hot-pressing process, constructing a three-dimensional thermal conduction path of BN-Ag-BN across the BN sheet interface, which significantly improves the thermal conductivity of the coating in the vertical direction (thickness direction); (3) The silicone oil matrix itself has excellent chemical inertness and hydrophobicity, giving the coating long-term anti-corrosion performance.

[0007] To address the aforementioned technical problems, this invention discloses a high-reflectivity, high-thermal-conductivity, self-cooling coating material, its preparation method, and its application. The specific technical solution is as follows: In a first aspect, the present invention provides a method for preparing a high-reflectivity, high-thermal-conductivity, self-cooling coating material, comprising the following steps: (1) A first slurry is obtained by mixing modified hexagonal boron nitride (BN), vinyl silicone oil and nano silver powder; (2) The hydrogen-containing silicone oil (curing agent) and the first slurry are mixed to obtain the second slurry. After vacuum degassing, the slurry is cured by segmented hot pressing to obtain the high reflectivity, high thermal conductivity and self-cooling coating material.

[0008] The vinyl silicone oil and hydrogen-containing silicone oil curing agent are organosilicon matrices; the modified hexagonal BN and nano silver powder are functional fillers, which are dispersed within the organosilicon matrix.

[0009] In step (1), the modified hexagonal BN is a hexagonal BN modified with a silane coupling agent, and its particle size is 1~10 µm; the silane coupling agent includes dodecyltriethoxysilane, whose long alkyl chain can effectively improve the compatibility between BN and silicone oil matrix and reduce interfacial thermal resistance.

[0010] In step (1), the average size of the nano-silver powder is 0.1~0.12 µm and the particle size distribution is 80~300 nm.

[0011] In step (1), taking the mass of the prepared high-reflectivity, high-thermal-conductivity, self-cooling coating material as 100%, the modified hexagonal BN accounts for 30%~40% of the mass, and the nano-silver powder accounts for 5%~10% of the mass. The mass ratio of the modified hexagonal BN to the nano-silver powder is 3~8:1. Too low an Ag content cannot form an effective thermally conductive network, while too high an Ag powder content will reduce reflectivity and increase cost due to the absorption of sunlight by the metal itself. In the preparation method described in this invention, the mass loss during the preparation process is negligible.

[0012] In some embodiments of the present invention, in step (1), the mixing is carried out by high-speed shear dispersion, wherein the rotation speed of the high-speed shear machine is 2500~6000 r / min and the stirring time is 20~80 min. In some embodiments of the present invention, in step (1), the mixing is carried out by first dispersing vinyl silicone oil and nano silver powder at 2500 r / min for 20 min using a high-speed shear machine to obtain a silver powder pre-dispersion liquid, and then adding modified hexagonal boron nitride and dispersing at 5000 r / min for 60 min to obtain a first slurry.

[0013] In step (2), the molar ratio of Si-H groups in the hydrogen-containing silicone oil to vinyl groups in the vinyl silicone oil in step (1) is 1.5 to 1.8:1. In some embodiments of the present invention, the molar ratio of Si-H groups in the hydrogen-containing silicone oil in step (2) to vinyl groups in the vinyl silicone oil in step (1) is 1.7:1.

[0014] In step (2), the segmented hot pressing includes the following three stages: First stage: Temperature 60~150 ℃, pressure 1~2 MPa, time 5~30 min; Second stage: temperature 60~150 ℃, pressure 8~10 MPa, time 10~30 min; Third stage: room temperature, pressure 10 MPa, time 10 min.

[0015] In some embodiments of the present invention, step (2) of the segmented hot pressing includes the following three stages: First stage: temperature 60 ℃, pressure 1 MPa, time 20~30 min; then gradually increase the temperature to 150 ℃; Second stage: Temperature 150 ℃, pressure 10 MPa, time 30 min; Third stage: room temperature, pressure 10 MPa, time 10 min.

[0016] In step (2), a 200-500 μm hot pressing mold is used for segmented hot pressing. In some embodiments of the present invention, a 200 μm hot pressing mold is used for segmented hot pressing.

[0017] In some embodiments of the present invention, in step (2), the mixing is performed by using a mechanical stirrer to stir evenly, and the rotation speed of the mechanical stirrer is 300~1000 r / min. Preferably, it is 400 r / min.

[0018] In a second aspect, the present invention provides a high-reflectivity, high-thermal-conductivity, self-cooling coating material prepared by the preparation method described in the first aspect. The coating has a thickness of 200 μm or 500 μm; the coating has a reflectivity ≥90% in the solar spectral region (0.3–2.5 μm) and an emissivity ≥90% in the atmospheric window (8–13 μm); the coating prepared using a hot-pressing process has a thermal conductivity ≥2.0 W / (m·K).

[0019] Thirdly, the present invention provides the application of the high-reflectivity, high-thermal-conductivity self-cooling coating material described in the second aspect in the thermal management of electronic devices, building energy-saving cooling, or radiative cooling of outdoor equipment. The high-reflectivity, high-thermal-conductivity self-cooling coating material is adhered to or coated on the surface of a target substrate in the form of a thin film. The target substrate is an object that needs to dissipate heat or requires passive cooling, including but not limited to electronic devices, buildings, or outdoor equipment.

[0020] Beneficial effects: The present invention has the following advantages over the prior art: (1) By introducing nano silver powder as a thermal bridge and combining it with hot-pressing directional alignment technology, this invention can significantly improve the vertical thermal conductivity of the coating (≥2 W / m·K) while maintaining the parallel alignment of BN sheets (high solar reflectivity), thus solving the fundamental contradiction that traditional BN coatings have high reflectivity but poor thermal conductivity and good thermal conductivity but low reflectivity. (2) The coating prepared by the present invention can synergistically enhance self-cooling and heat dissipation. On the one hand, the coating achieves passive radiation cooling through high solar reflectivity (≥90%) and infrared emissivity (≥90% at 8~13μm), and on the other hand, it rapidly dissipates heat from the inside of the equipment through high thermal conductivity. The combination of the two achieves a comprehensive cooling effect that is superior to that of a single-function coating. (3) By optimizing the segmented hot pressing process, this invention ensures the density of the coating material and the uniformity of the internal structure, effectively eliminates internal bubbles and defects, and obtains a dense thin film material with good mechanical properties. (4) The coating prepared by the present invention has excellent anti-corrosion properties, can effectively protect the underlying metal substrate, and extend the service life of the equipment. It is especially suitable for outdoor power equipment such as energy storage cabinets and transformers. Attached Figure Description

[0021] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, and the advantages of the present invention in the above and / or other aspects will become clearer.

[0022] Figure 1 This is a schematic diagram illustrating the design concept of the present invention.

[0023] Figure 2 The images are SEM images of hexagonal boron nitride raw materials; where the scale bar of (a) is 5 μm and the scale bar of (b) is 2 μm.

[0024] Figure 3 The images are SEM images of the nano silver powder raw material; where the scale bar of (a) is 10 μm and the scale bar of (b) is 1 μm.

[0025] Figure 4 SEM image of the cross-section of a coating prepared by hot pressing with 30% BN and 5% silver powder.

[0026] Figure 5 The solar reflectance spectra of Example 1 (with added silver powder) and Comparative Example 1 (without added silver powder) are shown.

[0027] Figure 6 The solar reflectance spectra of Example 1 (using hot pressing) and Comparative Example 2 (not using hot pressing) are shown.

[0028] Figure 7 The solar reflectance spectra of Example 1 (thickness 200 μm) and Comparative Example 3 (thickness 500 μm) are shown.

[0029] Figure 8 The images are long-wave mid-infrared spectra of Examples 1-3. Detailed Implementation

[0030] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0031] The substances used in the embodiments of this invention include: dodecyltriethoxysilane, hexagonal boron nitride (flake-like), nano-spherical silver powder (average size 0.1~0.12 µm, particle size distribution 80~300 nm), and vinyl silicone oil, specifically vinyl-terminated silicone oil (25℃, 190-230 mm). 2 / s) and curing agent containing hydrogen-containing silicone oil (25℃, 55-65 mm) 2 All (s) are commercially available. The vinyl silicone oil used in this invention has a vinyl content of 0.68 wt%, and the hydrogen content (Si-H group content) of the hydrogen-containing silicone oil used is 1.23 wt% (i.e., the sum of the mass of hydrogen elements in all Si-H groups in every 100 g of hydrogen-containing silicone oil is 1.23 g). The amount of vinyl in the vinyl silicone oil is n. Vi The amount of Si-H in hydrogen-containing silicone oil n Si-H Calculate according to the following formulas: n Vi = n Si-H = ; Where m1 is the mass (g) of vinyl silicone oil and m2 is the mass (g) of hydrogen-containing silicone oil.

[0032] Example 1 This embodiment is used to prepare a boron nitride-based high-reflectivity, high-thermal-conductivity, anti-corrosion, and self-cooling coating with a BN mass fraction of 30% and an Ag mass fraction of 5%. The design concept is as follows: Figure 1 As shown, the specific preparation method is as follows: (1) Preparation of modified hexagonal boron nitride (BN): Dissolve 3 g of dodecyltriethoxysilane in 100 g of anhydrous ethanol, and add it dropwise to 100 g of hexagonal BN powder (e.g., ...) using a dropper. Figure 2 As shown, the modified hexagonal boron nitride was obtained by stirring at 300 r / min for 30 min at room temperature in a particle size of 1~10 µm and then drying in an oven at 100℃ for 12 h. (2) Based on the total mass of 100 g of coating, weigh 62.81 g of vinyl silicone oil, and first add 5 g of nano silver powder (its SEM image is shown in Figure 1). Figure 3 As shown), the silver powder pre-dispersion liquid was obtained by dispersing at 2500 r / min for 20 min using a high-speed shear machine; then 30 g of the modified hexagonal boron nitride prepared in step (1) was added to the pre-dispersion liquid, and the mixture was further dispersed at 5000 r / min for 60 min to obtain a uniform coating slurry. (3) Add 2.19 g of hydrogen-containing silicone oil curing agent (the molar ratio of Si-H groups in hydrogen-containing silicone oil to vinyl groups in vinyl silicone oil is 1.7:1) to the coating slurry obtained in step (2), and stir evenly using a mechanical stirrer at 400 r / min; (4) Place the coating obtained in step (3) in a vacuum drying oven for degassing treatment for 15 min, then take an appropriate amount of coating and use a 200 μm hot press mold to transfer it to a flat vulcanizing machine for segmented hot pressing and curing (the mass loss during the preparation process can be ignored). The specific parameters are: First stage: Temperature 60 ℃, pressure 1-2 MPa (1 MPa in this embodiment), time 20 min, then gradually increase the temperature to 150 ℃; Second stage: temperature 150 ℃, pressure 8-10 MPa (specifically 10 MPa in this embodiment), time 30 min; Third stage: At room temperature, pressure 10 MPa, time 10 min.

[0033] After demolding, a boron nitride-based high-reflectivity, high-thermal-conductivity, corrosion-resistant, and self-cooling coating is obtained, such as... Figure 4 As shown.

[0034] This invention also optimized the ratio of vinyl silicone oil and hydrogen-containing silicone oil. In order to prepare silicone rubber with a better degree of crosslinking, the influence of the content of crosslinking agent hydrogen-containing silicone oil on the curing degree of silicone rubber was investigated. Vinyl silicone oil and hydrogen-containing silicone oil were cured at 80°C for 30 min to prepare silicone rubber with different molar ratios of hydrogen-containing silicone oil Si-H group value (i.e. hydrogen value) to vinyl group value of vinyl silicone oil. The molar ratio of different hydrogen values ​​to vinyl values ​​was controlled at 1.2~3:1, and the hardness was tested. The results are shown in Table 1.

[0035] Table 1. Effect of different hydrogen and vinyl values ​​molar ratios on the hardness of cured silicone rubber.

[0036] Table 1 shows that a hydrogen to vinyl number molar ratio of 1.7 achieves a hardness of 50 HA, falling within the optimal window of 1.5–1.8. This ratio ensures a moderate excess of hydrogen-containing silicone oil to prevent incomplete curing while also preventing excessive crosslinking density that could lead to material brittleness. It represents the best balance between hardness, mechanical properties, and process stability. Therefore, a hydrogen to vinyl number molar ratio of 1.7:1 is preferred. Subsequent experiments were conducted using this ratio.

[0037] Example 2 This embodiment is used to prepare a boron nitride-based high-reflectivity, high-thermal-conductivity, corrosion-resistant, and self-cooling coating with a BN mass fraction of 40% and an Ag mass fraction of 5%. The specific preparation method is as follows: (1) The preparation method of modified hexagonal boron nitride is the same as in Example 1; (2) Based on the total mass of 100 g of coating, weigh 53.15 g of vinyl silicone oil, add 5 g of nano silver powder, and disperse it for 20 min at 2500 r / min using a high-speed shear machine to obtain silver powder pre-dispersion liquid; then add 40 g of modified hexagonal boron nitride obtained in step (1) to the pre-dispersion liquid, and continue to disperse it for 60 min at 6000 r / min to obtain uniform coating slurry; (3) Add 1.85 g of hydrogen-containing silicone oil curing agent (the molar ratio of hydrogen content of hydrogen-containing silicone oil to vinyl content of vinyl silicone oil is 1.7:1) to the coating slurry obtained in step (2), and stir evenly at 400 r / min using a mechanical stirrer. (4) Place the coating obtained in step (3) in a vacuum drying oven for degassing treatment for 15 min, then take an appropriate amount of coating and use a 200 μm hot press mold to transfer it to a flat vulcanizing machine for segmented hot pressing and curing. The specific parameters for segmented hot pressing are the same as in Example 1. After demolding, a boron nitride-based high reflectivity, high thermal conductivity, anti-corrosion, and self-cooling coating is obtained.

[0038] Example 3 This embodiment is used to prepare a boron nitride-based high-reflectivity, high-thermal-conductivity, corrosion-resistant, and self-cooling coating with a BN mass fraction of 30% and an Ag mass fraction of 10%. The specific preparation method is as follows: (1) The preparation method of modified hexagonal BN is the same as in Example 1; (2) Based on the total mass of 100 g of coating, weigh 57.98 g of vinyl silicone oil, add 10 g of nano silver powder, and disperse it for 20 min at 2500 r / min using a high-speed shear machine to obtain silver powder pre-dispersion liquid; then add 30 g of modified hexagonal boron nitride obtained in step (1) to the pre-dispersion liquid, and continue to disperse it for 60 min at 5000 r / min to obtain uniform coating slurry; (3) Add 2.02 g of hydrogen-containing silicone oil curing agent (the molar ratio of hydrogen content of hydrogen-containing silicone oil to vinyl content of vinyl silicone oil is 1.7:1) to the coating slurry obtained in step (2), and stir evenly at 400 r / min using a mechanical stirrer. (4) Place the coating obtained in step (3) in a vacuum drying oven for degassing treatment for 15 min, then take an appropriate amount of coating and use a 200 μm hot press mold to transfer it to a flat vulcanizing machine for segmented hot pressing and curing. The specific parameters are: First stage: Temperature 60℃, pressure 1-2 MPa (1 MPa in this embodiment), time 30 min, then gradually increase the temperature to 150℃; Second stage: Temperature 150℃, pressure 8-10 MPa (specifically 8 MPa in this embodiment), time 30 min; Third stage: At room temperature, pressure 10 MPa, time 10 min.

[0039] After demolding, a boron nitride-based high-reflectivity, high-thermal-conductivity, corrosion-resistant, and self-cooling coating is obtained.

[0040] Comparative Example 1 This comparative example was used to prepare a boron nitride-based coating with a BN mass fraction of 30% and without nano-silver powder. The specific preparation method is as follows: (1) The preparation method of modified hexagonal BN is the same as in Example 1; (2) Based on the total mass of 100 g of coating, weigh 67.65 g of vinyl silicone oil, add 30 g of the modified hexagonal BN obtained in step (1), and disperse at 5000 r / min for 60 min to obtain a uniform coating slurry. (3) Add 2.35 g of hydrogen-containing silicone oil curing agent to the coating slurry obtained in step (2) and stir evenly using a mechanical stirrer at a speed of 400 r / min; (4) Place the coating obtained in step (3) in a vacuum drying oven for degassing treatment for 15 min, then take an appropriate amount of coating and use a 200 μm hot press mold to transfer it to a flat vulcanizing machine for segmented hot pressing and curing. The specific parameters are: First stage: Temperature 60℃, pressure 1-2 MPa (2 MPa in this embodiment), time 5 min, then gradually increase the temperature to 85℃; Second stage: Temperature 85℃, pressure 8-10 MPa (specifically 10 MPa in this embodiment), time 15 min; Third stage: At room temperature, pressure 10 MPa, time 10 min.

[0041] After demolding, a boron nitride-based coating material is obtained.

[0042] This invention also optimized the segmented hot pressing process using the experimental method of the comparative example. The preparation method was the same as that of the comparative example, except that the initial experiment used a single temperature of 85℃, a constant pressure of 10MPa, and a holding pressure of 15 min in the curing and molding stage of step (4). The results showed that there were many voids on the surface of the coating. It was analyzed that although vacuum degassing was performed before hot pressing, there were still tiny air bubbles inside the coating. Applying high pressure at once would cause the air bubbles in the coating to not be discharged in time. At the same time, the BN flakes were rapidly oriented under high pressure but lacked sufficient flow time to form a uniform orientation structure. Therefore, the idea of ​​segmented hot pressing was proposed: first, a lower pressure was used to preliminarily shape the slurry and discharge the air bubbles, then the pressure was increased to promote the full orientation of the BN flakes, and finally, the pressure was maintained and cooled at room temperature to eliminate internal stress.

[0043] Subsequently, the parameters of the segmented hot pressing process were systematically optimized. In the initial experimental optimization of the segmented hot pressing process, the first stage involved directly heating to 85 ℃ and applying a pressure of 2 MPa for 5 min; the second stage involved a temperature of 85 ℃ and a pressure of 10 MPa for 15 min; and the third stage involved a temperature of room temperature and a pressure of 10 MPa for 10 min. The results showed that tiny bubbles appeared on the coating surface, and the uniformity of the coating near the edges was slightly worse. Analysis suggests that a one-time heating to 85 ℃ causes residual air or trace amounts of moisture in the slurry to expand rapidly, failing to completely expel them, thus forming microscopic defects. Therefore, the first stage was divided into two sub-stages: first, at 60 ℃ and 2 MPa for 5 min, then gradually increasing the temperature to 85 ℃, with the latter two stages remaining unchanged (i.e., the segmented hot pressing process described in this comparative example). The consideration for using 60 ℃ as the intermediate temperature is as follows: on the one hand, the viscosity of the silicone oil system at 60 ℃ is moderate, ensuring sufficient flow of the slurry under pressure to expel bubbles, while preventing the slurry from overflowing the mold due to excessively low viscosity. Experimental results show that the coating formed by using a strategy of pre-pressing at 60 ℃ for 5 min and then gradually increasing the temperature to 85 ℃, while keeping the latter two stages unchanged, is uniform and dense.

[0044] However, when nano-silver powder was introduced into the formulation (as in Example 1), the coating was found not to be fully cured when the same hot-pressing process was used. Adding nano-silver powder increased the curing time of the coating. Subsequently, by adjusting the temperature, time, and pressure of the first and second stages, the specific hot-pressing curing parameters described in Examples 1-3 were finally obtained.

[0045] Comparative Example 2 This comparative example was used to prepare a boron nitride-based coating with a BN mass fraction of 30% and an Ag mass fraction of 5% (naturally cured without hot pressing). The specific preparation method is as follows: (1) The preparation method of modified hexagonal BN is the same as in Example 1; (2) Based on the total mass of 100 g of coating, weigh 62.81 g of vinyl silicone oil, add 5 g of nano silver powder, and disperse it for 20 min at 2500 r / min using a high-speed shear machine to obtain silver powder pre-dispersion liquid; then add 30 g of modified hexagonal boron nitride obtained in step (1) to the pre-dispersion liquid, and continue to disperse it for 60 min at 5000 r / min to obtain uniform coating slurry; (3) Add 2.19 g of hydrogen-containing silicone oil curing agent to the coating slurry obtained in step (2) and stir evenly using a mechanical stirrer at a speed of 400 r / min; (4) Place the coating obtained in step (3) in a vacuum drying oven for degassing treatment for 15 min, then pour it directly into a mold (mold thickness 200 μm), place it in a 150 ℃ oven for curing for 2 h, without hot pressing treatment, to obtain boron nitride-based coating material.

[0046] Comparative Example 3 This comparative example was used to prepare a boron nitride-based high-reflectivity, high-thermal-conductivity, corrosion-resistant, and self-cooling coating with a thickness of 500 micrometers, containing 30% BN and 5% Ag. The specific preparation method is as follows: (1) The preparation method of modified hexagonal BN is the same as in Example 1; (2) Based on the total mass of 100 g of coating, weigh 62.81 g of vinyl silicone oil, add 5 g of nano silver powder, and disperse it for 20 min at 2500 r / min using a high-speed shear machine to obtain silver powder pre-dispersion liquid; then add 30 g of modified hexagonal boron nitride obtained in step (1) to the pre-dispersion liquid, and continue to disperse it for 60 min at 5000 r / min to obtain uniform coating slurry; (3) Add 2.19 g of hydrogen-containing silicone oil curing agent to the coating slurry obtained in step (2) and stir evenly using a mechanical stirrer at a speed of 400 r / min; (4) Place the coating obtained in step (3) in a vacuum drying oven for degassing treatment for 15 min, then take an appropriate amount of coating and use a 500-micron hot press mold to transfer it to a flat vulcanizing machine for segmented hot pressing and curing to obtain a boron nitride-based coating material. The specific parameters for segmented hot pressing are the same as in Example 1.

[0047] The optical performance of Examples 1-3 and Comparative Examples 1-3 was tested using an ultraviolet-visible spectrophotometer (equipped with an integrating sphere attachment) to measure the reflectance of the coatings prepared in each example and comparative example in the solar spectral region (0.3-2.5 μm).

[0048] Table 2. Solar reflectance of coatings in comparative examples and embodiments

[0049] Table 2 shows that, firstly, the addition of nano-silver powder can improve the solar reflectivity of the coating. Comparing Comparative Example 1 (reflectivity 86.16%) without silver powder with Examples 1-3 with silver powder, it can be seen that the reflectivities of Examples 1-3 reach 90.46%, 91.50%, and 92.33%, respectively, all higher than the system without nano-silver powder. Figure 5The solar reflectance spectra of Example 1 and Comparative Example 1, as shown, reveal that Example 1 with added silver powder exhibits a higher solar reflectance of 90.46%, compared to coatings with the same thickness of 200 micrometers. This improvement is primarily attributed to two factors: firstly, the nano-silver powder itself possesses extremely high reflectivity in the solar spectrum, especially after the hot-pressing process, where the silver powder forms a tight composite structure with the parallel hexagonal boron nitride (BN) sheets, further enhancing light scattering and reflection efficiency; secondly, the uniform dispersion of the silver powder fills the microscopic gaps between the BN sheets, reducing light transmission loss and thus improving the overall reflectance.

[0050] Secondly, the fabrication process is equally crucial to optical performance. Figure 6 The solar reflectance spectra of Example 1 and Comparative Example 2, and the calculated solar reflectance (Table 2), show that although their formulations contain silver nanoparticles, their reflectance is 87.85% due to the lack of hot-pressing treatment, which is lower than that of the hot-pressed sample with the same formulation. This indicates that the hot-pressing process can maximize the parallel orientation of BN sheets.

[0051] Furthermore, coating thickness also affects reflectivity. Figure 7 The solar reflectance spectra of Example 1 and Comparative Example 3, as shown, reveal that under the same formulation conditions, the solar reflectance of the coating decreases with increasing film thickness. This is mainly attributed to the decreased uniformity of filler orientation and increased light scattering paths within a thicker coating. A thinner coating facilitates the formation of a more uniform parallel orientation of the hexagonal boron nitride sheets during hot pressing, thereby constructing a more efficient light-reflecting structure.

[0052] The present invention then used a Fourier transform infrared spectrometer (equipped with an integrating sphere accessory) to test the long-wave infrared spectra of each coating in Examples 1-3, such as... Figure 8 As shown in Table 3, the infrared emissivity of the coating in the range of 8–13 micrometers was calculated.

[0053] Table 3 Infrared emissivity of the coatings in the example at 8–13 μm

[0054] The data in Tables 2 and 3 show that the coating of the example has good optical properties, with a solar reflectance (≥90%) and infrared emissivity (≥90% at 8~13μm).

[0055] Next, the thermal conductivity of Examples 1-3 and Comparative Examples 1-3 was tested using a thermal constant analyzer (Hot Disk method). The results are shown in Table 4.

[0056] Table 4 Thermal conductivity of coatings in comparative examples and embodiments

[0057] As shown in Table 4, firstly, the synergistic effect of nano-silver powder and hexagonal boron nitride significantly improves the thermal conductivity of the coating. Comparing Comparative Example 1 (thermal conductivity only 0.88 W / (m·K)) without silver powder with Examples 1-3 containing silver powder, it can be seen that silver powder acts as a highly efficient thermal bridge, greatly improving the thermal conductivity of the substrate. Simultaneously, with the increase of hexagonal boron nitride content, the thermal conductivity of the coating shows an upward trend, with Example 3 exhibiting the highest thermal conductivity at 2.54 W / (m·K). This confirms that the BN sheets form a more continuous and efficient thermally conductive network under hot pressing.

[0058] Secondly, the coating thickness has a significant impact on thermal conductivity. Comparing Example 1 (200 μm, 2.21 W / (m·K)) and Comparative Example 3 (500 μm, 1.76 W / (m·K)) with the same formulation, it can be seen that the thinner coating actually has a higher thermal conductivity. This is mainly because the thicker coating has poorer uniformity of filler orientation and is more prone to defects during drying, leading to impeded heat transfer; while the thinner coating makes it easier to achieve one-dimensional oriented alignment of fillers during hot pressing, thereby reducing thermal resistance.

[0059] Finally, the hot-pressing process is key to realizing the material's potential. Comparative Example 2, which was not hot-pressed, had a thermal conductivity of only 1.56 W / (m·K), far lower than that of Example 1 (2.21 W / (m·K)) after hot pressing. This indicates that only by inducing the orderly alignment of hexagonal boron nitride sheets along the heat flow direction through hot pressing can the phonon scattering barrier be broken, thus constructing a continuous internal heat conduction pathway.

[0060] The mechanical properties of Examples 1-3 and pure silicone rubber (prepared when the hydrogen value / vinyl value shown in Table 1 was 1.7) were also tested in this invention, with a sample thickness of 200 μm for all samples. The test results are shown in Table 5: Table 5. Results of Hardness and Tensile Strength Tests

[0061] This invention provides a high-reflectivity, high-thermal-conductivity self-cooling coating material, its preparation method, and its application. Many methods and approaches exist for implementing this technical solution; the above description is merely a preferred embodiment of the invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications should also be considered within the scope of protection of this invention. All components not explicitly stated in this embodiment can be implemented using existing technologies.

Claims

1. A method for preparing a high-reflective high-thermal-conductive self-cooling coating material, characterized in that, Includes the following steps: (1) A first slurry is obtained by mixing modified hexagonal boron nitride, vinyl silicone oil and nano silver powder; (2) The hydrogen-containing silicone oil and the first slurry are mixed to obtain the second slurry. After vacuum degassing, the slurry is cured by segmented hot pressing to obtain the high-reflectivity, high-thermal-conductivity, self-cooling coating material.

2. The production method according to claim 1, characterized by, In step (1), the modified hexagonal boron nitride is hexagonal boron nitride modified with a silane coupling agent, and its particle size is 1~10 µm; The silane coupling agent mentioned includes dodecyltriethoxysilane.

3. The production method according to claim 1, characterized by, In step (1), the average size of the nano silver powder is 0.1~0.12 µm and the particle size distribution is 80~300 nm.

4. The method of claim 1, wherein, Based on the mass of the prepared high-reflectivity, high-thermal-conductivity, self-cooling coating material as 100%, the mass percentage of the modified hexagonal boron nitride in step (1) is 30%~40%, and the mass percentage of the nano silver powder is 5%~10%.

5. The preparation method according to claim 1, characterized in that, The molar ratio of Si-H groups in the hydrogen-containing silicone oil described in step (2) to vinyl groups in the vinyl silicone oil described in step (1) is 1.5~1.8:

1.

6. The method of claim 1, wherein, In step (2), the segmented hot pressing includes the following three stages: First stage: Temperature 60~150 ℃, pressure 1~2 MPa, time 5~30 min; Second stage: Temperature 60~150 ℃, pressure 8~10 MPa, time 10~30 min; Third stage: room temperature, pressure 10 MPa, time 10 min.

7. The preparation method according to claim 1, characterized in that, In step (2), a 200~500 μm hot pressing mold is used for segmented hot pressing.

8. The high-reflectivity, high-thermal-conductivity, self-cooling coating material prepared by the preparation method according to any one of claims 1 to 7.

9. The application of the high-reflectivity, high-thermal-conductivity self-cooling coating material as described in claim 8 in the thermal management of electronic devices, building energy-saving cooling, or radiative cooling of outdoor equipment.

10. Use according to claim 9, characterized in that, The high-reflectivity, high-thermal-conductivity, self-cooling coating material is applied to the surface of the target substrate in the form of a thin film.

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