A composite coating with long-lasting anti-fog effect, preparation method thereof and application thereof

Abstract

The present invention provides a composite coating with long-lasting anti-fog effect, and its preparation method and application. The composite coating includes a photothermal layer with photothermal conversion performance and a hygroscopic layer with hygroscopic function, which are arranged in sequence; the photothermal layer includes cesium tungsten bronze nanoparticles. The composite coating effectively combines active and passive anti-fog modes. The hygroscopic layer on the outside can absorb condensed fog droplets, which plays an initial anti-fog effect. At the same time, the photothermal layer on the inside quickly converts the incident solar energy into thermal energy, causing the condensed fog droplets to evaporate, and finally achieves a long-lasting anti-fog effect. In addition, the composite coating has a high light transmittance in the visible light region, which can reach up to 75% or more. It also has good mechanical properties and photothermal cycle stability. Therefore, it has broad application prospects in scenes such as car windshields, aircraft windows, goggles, and building glass.

Description

Technical Field

[0001] The present invention belongs to the field of coating materials, and specifically comprises a composite coating with long-lasting anti-fog properties, a preparation method thereof, and an application thereof. Background Art

[0002] Fog can cause image distortion, seriously affecting the normal use of transparent equipment, and even pose a potential risk to our health and safety. Therefore, it is critical to develop effective anti-fog technology. Current anti-fog technologies are divided into active and passive categories based on whether external energy input is required. Passive anti-fog is based on surface wettability to construct super-hydrophobic, super-hydrophilic or hygroscopic surfaces. Although it consumes zero energy, the super-hydrophobic surface is only effective for large water droplets in the micron range, and the structural design is complex. Super-hydrophilic surfaces are easily contaminated by the outside world and have a short shelf life. Hygroscopic coatings rely on hydrogen bonding interactions between or within polymer molecules rich in polar groups to achieve an anti-fog effect, but due to their limited water absorption capacity, if the inhaled fog droplets cannot evaporate in time, it will not only affect the anti-fog performance of the coating, but may also form frost and ice in low temperature environments, and will not be long-lasting and durable.

[0003] Active anti-fog is based on the principles of thermodynamics, using external input energy to heat the surface, which can fundamentally solve the fogging problem. However, this method requires additional equipment and consumes energy such as electricity, which is contrary to the requirements of energy conservation and environmental protection. Recently, a very promising new strategy is to use photothermal materials to convert solar energy into thermal energy, which is expected to be applied in the field of anti-fog coatings. However, most photothermal materials show full-spectrum absorption of sunlight, which is inconsistent with the high transparency required for anti-fog. In addition, since it takes a certain amount of time for the photothermal surface to heat up under light, it cannot resist the condensation of fog in time at the beginning of light exposure. It can be seen that both active and passive anti-fog technologies have certain defects. Therefore, it is urgent to develop a new long-term anti-fog technology. Summary of the Invention

[0004] To address the aforementioned issues with the prior art, the first objective of the present invention is to provide a composite coating with long-lasting anti-fog properties. This composite coating combines high transparency with excellent photothermal performance, achieving long-lasting anti-fog properties driven by sunlight. This addresses the short anti-fog performance of single hygroscopic coatings and the delayed anti-fog performance of single photothermal coatings.

[0005] The second object of the present invention is to provide a method for preparing the composite coating as described above.

[0006] The third object of the present invention is to provide an application of the composite coating as described above in the anti-fog field.

[0007] To achieve the above first object, the technical solution adopted by the present invention includes:

[0008] The present invention discloses a composite coating with long-lasting anti-fog effect, wherein the composite coating comprises a photothermal layer with photothermal conversion performance and a moisture absorbing layer with moisture absorbing function, which are sequentially arranged;

[0009] The photothermal layer includes cesium tungsten bronze nanoparticles.

[0010] The composite coating provided by the present invention is used to solve the problem of short anti-fog effectiveness of a single hygroscopic coating and the problem of delayed anti-fog effect of a single photothermal coating. It effectively combines active and passive anti-fog modes. Once fogging begins, the hygroscopic layer located on the outside can be used to absorb condensed fog droplets, achieving an initial anti-fog effect in the absence of sunlight or when just exposed to sunlight. Thereafter, as the cesium tungsten bronze nanoparticles continuously and rapidly convert the incident solar energy into thermal energy, the condensed fog droplets evaporate, achieving a long-term anti-fog effect driven by sunlight. Therefore, the composite coating provided by the present invention has broad application prospects in scenarios such as automobile windshields, aircraft windows, goggles, and building glass.

[0011] In the technical solution of the present invention, screening suitable photothermal materials is particularly critical. We should not only pay attention to the photothermal conversion efficiency of the photothermal material, which is the key to directly affecting the evaporation rate of droplets, but also pay attention to the absorption spectrum of the photothermal material. If the absorption spectrum is not suitable (for example, full spectrum absorption), the transmittance of the composite coating cannot be effectively guaranteed, and it will be difficult to meet the application requirements. Finally, through a large number of experimental screenings, it was determined that the photothermal material that is compatible with the material used in the hygroscopic layer of the present invention is cesium tungsten bronze nanoparticles. This compatibility means that the heat energy converted by the photothermal material is sufficient to gradually establish a dynamic balance between the condensation and evaporation of the droplets, so that fog will not be generated during the entire process, and at the same time, the composite coating can maintain a high transmittance.

[0012] Furthermore, the cesium tungsten bronze nanoparticles are hexagonal and have a size of 10-100 nm.

[0013] Furthermore, the thickness of the photothermal layer in the composite coating is 200-600 nm, and the thickness of the hygroscopic layer is 20-150 μm;

[0014] The composite coating has an average light transmittance of ≥60% in the range of 400-720nm, and a maximum light transmittance of 75% or more;

[0015] The water contact angle of the composite coating decreases from 50-70° to 20-40° within 800 seconds.

[0016] To achieve the above second purpose, the technical solutions adopted by the present invention include:

[0017] The present invention discloses a method for preparing the composite coating as described above, comprising the following steps:

[0018] 1) Preparation of photothermal layer slurry:

[0019] Cesium tungsten bronze nanoparticles are added to a solvent under stirring, and a nanopowder dispersion is obtained by ultrasonic dispersion;

[0020] A film-forming agent is obtained by mixing a water-based coating emulsion with deionized water;

[0021] Mixing the film-forming agent with the nanopowder dispersion to obtain a photothermal layer slurry;

[0022] 2) Preparation of moisture absorbing layer slurry:

[0023] The first component and the second component are mixed evenly, stirred, ultrasonically or allowed to stand for degassing to obtain a moisture absorbing layer slurry;

[0024] Wherein, the first component is selected from an aqueous solution of a polymer containing a hydroxyl group in the main chain or a side chain or an aqueous solution of a polymer containing an amino group in the main chain or a side chain;

[0025] The second component is selected from an inorganic metal ion compound solution or an aqueous solution of a polymer containing carboxyl groups in the main chain or side chain;

[0026] 3) Preparation of photothermal layer:

[0027] Coating the photothermal layer slurry obtained in step 1) on a clean substrate and drying to obtain a photothermal layer;

[0028] 4) Preparation of composite coating:

[0029] The moisture absorption layer slurry obtained in step 2) is coated again on the photothermal layer obtained in step 3) and dried to obtain the product.

[0030] Furthermore, in step 1), the cesium tungsten bronze nanoparticles in the nanopowder dispersion account for 15-25wt%; illustratively, the cesium tungsten bronze nanoparticles in the nanopowder dispersion may account for 15wt%, 16wt%, 17wt%, 18wt%, 19wt%, 20wt%, 21wt%, 22wt%, 23wt%, 24wt%, 25wt%, and so on;

[0031] The cesium tungsten bronze nanoparticles in the photothermal layer slurry account for 5-20wt%; illustratively, the cesium tungsten bronze nanoparticles in the photothermal layer slurry may account for 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, 19wt%, 20wt% and the like.

[0032] Furthermore, in step 1), the water-based coating emulsion includes but is not limited to one of a water-based acrylic emulsion, a silicone acrylic emulsion and a styrene acrylic emulsion.

[0033] Furthermore, in the film-forming agent, the mass ratio of the aqueous coating emulsion to deionized water is 1:0-5; illustratively, the film-forming agent may not contain deionized water. When deionized water is contained, the mass ratio of the aqueous coating emulsion to deionized water may be 1:1, 1:2, 1:3, 1:4, 1:5, and the like.

[0034] Furthermore, the polymer contained in the first component includes, but is not limited to, one or more of polyvinyl alcohol, polyethylene glycol, block copolymers of polyethylene glycol, polyvinylamine, and polyacrylamine;

[0035] Inorganic metal ion compounds include, but are not limited to, compounds such as copper chloride, zinc chloride, and ferric chloride that can form coordination bonds with lone pairs of electrons on hydroxyl oxygen;

[0036] The polymer contained in the second component includes, but is not limited to, one or more of polyacrylic acid, polymethacrylic acid, polybutenoic acid, and polyvalenoic acid.

[0037] Further, when the hygroscopic layer slurry is composed of a polymer in the first component and an inorganic metal ion compound solution, the molar ratio of the polymer contained in the first component to the inorganic metal ion compound is 10-50:1; illustratively, the molar ratio of the polymer contained in the first component to the inorganic metal ion compound can be 10:1, 20:1, 30:1, 40:1, 50:1, and the like.

[0038] Further, when the hygroscopic layer slurry is composed of a polymer in a first component and a polymer in a second component, the molar ratio of the polymer contained in the first component to the polymer contained in the second component is 1-50:1; illustratively, the molar ratio of the polymer contained in the first component to the polymer contained in the second component can be 1:1, 5:1, 10:1, 15:1, 20:1, 25:1, 30:1, 35:1, 40:1, 45:1, 50:1 and the like.

[0039] Furthermore, the substrate is selected from acrylic glass, automobile glass, window glass or equipment glass. When cleaning the substrate, the following steps can be used:

[0040] The substrate was ultrasonically cleaned with acetone, anhydrous ethanol, and deionized water for 5-20 min, respectively, and then cleaned with oxygen plasma after drying;

[0041] The oxygen plasma cleaning time is 5-10 minutes, the voltage is 600-800V, and the oxygen flow rate is 800-1000mL / min.

[0042] Furthermore, the coating methods used in step 3) and step 4) are conventional coating methods used in the art, including but not limited to spin coating, spray coating, pulling, scraping, roller coating or manual application.

[0043] Furthermore, in step 3), the drying temperature of the photothermal layer is 20-40° C., and the drying time is 10-30 min.

[0044] Furthermore, in step 4), the drying temperature of the hygroscopic layer is 40-80° C., and the drying time is 2-8 hours.

[0045] Furthermore, the cesium tungsten bronze nanoparticles are prepared by a classic solvothermal method, the steps of which are as follows:

[0046] dissolving a tungsten-containing compound in anhydrous ethanol, and then adding a cesium-containing compound to obtain a mixed solution;

[0047] Acetic acid was added dropwise into the mixed solution, and cesium tungsten bronze nanoparticles were prepared by a solvothermal method.

[0048] Of course, those skilled in the art can also use other preparation methods to prepare cesium tungsten bronze nanoparticles, such as hydrothermal method, chemical vapor deposition method, solid phase method, etc., all of which can achieve similar anti-fog effects. Therefore, the specific preparation method of cesium tungsten bronze nanoparticles is not limited.

[0049] Furthermore, the tungsten-containing compound includes but is not limited to one or more of tungsten chloride, sodium tungstate and tungstic acid; the cesium-containing compound includes but is not limited to one or more of cesium hydroxide monohydrate, cesium carbonate and cesium sulfate.

[0050] Furthermore, the concentration of the tungsten-containing compound in the mixed solution is 0.7-1 wt %. For example, the concentration of the tungsten-containing compound in the mixed solution may be 0.7 wt %, 0.8 wt %, 0.9 wt %, 1 wt %, and the like.

[0051] Furthermore, the concentration of the cesium-containing compound in the mixed solution is 0.1-0.3 wt %; illustratively, the concentration of the cesium-containing compound in the mixed solution can be 0.1 wt %, 0.2 wt %, 0.3 wt %, and the like.

[0052] Furthermore, the volume ratio of the anhydrous ethanol to the acetic acid is 8:1.5-3; illustratively, the volume ratio of the anhydrous ethanol to the acetic acid can be 8:1.5, 8:2, 8:2.5, 8:3, and the like.

[0053] Furthermore, the reaction temperature in the solvent thermal method is 200-240° C., and the reaction time is 18-24 hours.

[0054] To achieve the third objective, the present invention employs the following technical solutions:

[0055] The present invention discloses a film-coated glass, which is obtained by coating the composite coating as described above on a glass substrate.

[0056] Furthermore, the glass substrate includes but is not limited to acrylic glass, automobile glass, window glass or equipment glass.

[0057] Beneficial effects of the present invention:

[0058] The present invention provides a composite coating with long-lasting anti-fog properties, as well as its preparation method and application. This composite coating effectively combines active and passive anti-fog modes. The outer adsorption layer absorbs condensed fog droplets, achieving initial anti-fog effects. Simultaneously, the inner photothermal layer rapidly converts incident solar energy into thermal energy, gradually evaporating condensed fog droplets and ultimately achieving a long-lasting anti-fog effect. The composite coating specifically includes the following advantages:

[0059] 1. The composite coating has good visible light transmittance. The average transmittance in the wavelength range of 400-720nm is ≥60%, and the highest transmittance is over 75%.

[0060] 2. The composite coating has good light-to-heat conversion performance, and the surface temperature can reach above 57°C in 600 seconds under the intensity of one sun.

[0061] 3. The composite coating has good anti-frost performance and will not frost after being placed in a -20℃ refrigerator for 24 hours.

[0062] 4. The composite coating can maintain a clear view for at least 6 hours when placed 5 cm above 65°C hot water under sunlight simulated by a xenon lamp.

[0063] 5. The composite coating has good mechanical properties. The surface of the composite coating was rubbed repeatedly 5000 times with a fiber cloth at a pressure of 55 kPa, and the transmittance of the composite coating did not change significantly.

[0064] 6. The composite coating has good light-heat cycle stability. The composite coating was subjected to 50 heating and cooling cycles. All temperature curves in these 50 heating and cooling cycles were similar and no significant changes occurred. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0066] Figure 1 The powder XRD spectrum and transmission electron microscope image of the cesium tungsten bronze nanoparticles prepared in Example 1 are shown; wherein, Figure 1 a is the powder XRD spectrum, and b is the transmission electron microscopy image.

[0067] Figure 2 The scanning electron microscope image and AFM image of the surface and cross section of the photothermal layer prepared in Example 2 are shown; wherein, Figure 2 a is a scanning electron microscope image, and b is an AFM image.

[0068] Figure 3 The scanning electron microscope image and AFM image of the surface of the composite coating prepared in Example 3 are shown; wherein, Figure 3 a is a scanning electron microscope image, and b is an AFM image.

[0069] Figure 4 The light transmittance curve of the composite coating prepared in Example 3 is shown.

[0070] Figure 5 The change of the water contact angle of the composite coating prepared in Example 3 over time is shown.

[0071] Figure 6 The temperature change curve of the composite coating prepared in Example 3 under a xenon lamp and the anti-fog test photos of the coatings of Comparative Example 4 and Example 3 are shown; wherein, Figure 6 In the figure a is a temperature change curve, and in the figure b is a photo showing a comparative anti-fog test of the hygroscopic layer of comparative example 4 and the composite coating of example 3.

[0072] Figure 7 The anti-fog test photos of the coating prepared in Comparative Example 5 and the anti-frost test photos of the coating prepared in Example 3 and Comparative Example 5 are shown, wherein: Figure 7 Part a is a photo of the anti-fog test of the coating prepared in Comparative Example 5 at different times, and part b is a photo of the anti-frost test of the blank glass substrate, the coating prepared in Comparative Example 5, and the composite coating prepared in Example 3.

[0073] Figure 8 The transmittance spectrum of the composite coating prepared in Example 3 before and after the wear resistance test and the temperature change curve during 50 heating and cooling cycles are shown; wherein, Figure 8 In the figure a is the transmittance spectrum, and in the figure b is the temperature change curve during 50 heating and cooling cycles.

[0074] Figure 9 The following is a photograph showing the outdoor anti-fog test of the composite coating prepared in Example 3. DETAILED DESCRIPTION

[0075] To more clearly illustrate the present invention, the present invention is further described below in conjunction with preferred embodiments and accompanying drawings. It should be understood that the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0076] In addition, unless otherwise specified, the raw materials used in the present invention can be obtained commercially, and any range recorded in the present invention includes the end value and any numerical value between the end values ​​and any sub-range formed by the end value or any numerical value between the end values.

[0077] Example 1 Preparation of Photothermal Nanomaterial Powder and Photothermal Layer Slurry

[0078] 0.6 g of tungsten chloride was dissolved in 80 ml of anhydrous ethanol and stirred at room temperature for 15 min. 0.13 g of cesium hydroxide monohydrate was then added and stirred at room temperature for 10 min to obtain a mixed solution. 20 ml of acetic acid was added dropwise to the mixed solution and stirred for 15 min. The solution was then transferred to a polytetrafluoroethylene-lined reactor and subjected to a solvothermal reaction at 220°C for 20 h. After the reaction, the solid sample was centrifuged and washed at least three times with anhydrous ethanol and deionized water, dried in a vacuum oven at 60°C overnight, and ground to obtain cesium tungsten bronze nanoparticle powder.

[0079] Under vigorous stirring, 12 parts by mass of nanoparticle powder were added to 60 parts by mass of deionized water, and ultrasonically dispersed for 10 minutes to obtain a uniform nanopowder dispersion; 8 parts by mass of aqueous acrylic emulsion was mixed with 10 parts by mass of deionized water to obtain a film-forming agent, which was then mixed with 50 parts by mass of the above-mentioned nanopowder dispersion and stirred, and ultrasonically dispersed for 15 minutes to obtain a photothermal layer slurry with a cesium tungsten bronze nanoparticle content of 12wt%.

[0080] The X-ray diffraction peaks of the cesium tungsten bronze nanoparticle powder obtained by the solvothermal method correspond to the diffraction peaks of the standard hexagonal cesium tungsten bronze (such as Figure 1 As shown in a), it is a rod-like structure with a diameter of about 10 nm and a length of 40-60 nm (as shown in Figure 1 (as shown in b).

[0081] Example 2 Preparation of photothermal layer

[0082] The photothermal layer slurry obtained in Example 1 was applied on a cleaned glass substrate by spin coating and dried at room temperature for 10 minutes to obtain a photothermal layer with near-infrared shielding performance.

[0083] The obtained photothermal layer was subjected to scanning electron microscopy to observe its surface morphology and cross-section. The detailed test results are as follows: Figure 2 As shown in Figure a, the thickness of the photothermal layer is about 400 nm. Due to the presence of nanoparticles, its surface is very rough. The surface roughness of the photothermal layer is further characterized by AFM, as shown in Figure 4. Figure 2 As shown in b, the root mean square roughness of the photothermal layer surface is 22.3 nm.

[0084] Example 3 Preparation of photothermal / hygroscopic composite coating

[0085] (1) Preparation of moisture absorbing layer slurry:

[0086] 8 parts by mass of PVA were dissolved in 92 parts by mass of deionized water and stirred in an 85°C water bath for 1 hour to obtain an 8 wt% PVA aqueous solution; 2.05 parts by mass of zinc chloride were dissolved in 30 parts by mass of 3M dilute hydrochloric acid and stirred uniformly to obtain a zinc chloride solution; 2.4 parts by mass of the zinc chloride solution was dropwise added to 20 parts by mass of the 8 wt% PVA aqueous solution and stirred at room temperature until thoroughly mixed to obtain a moisture absorbing layer slurry;

[0087] (2) The hygroscopic layer slurry prepared in step (1) is coated on the photothermal layer obtained in Example 2 by a doctor blade method, and is placed in a 60°C oven and dried for 4 hours to obtain a photothermal / hygroscopic composite coating; wherein the thickness of the hygroscopic layer is controlled to 20 μm by the program setting of the coating machine.

[0088] The obtained photothermal / hygroscopic composite coating was subjected to scanning electron microscopy to observe its surface morphology. The detailed test results are as follows: Figure 3 As shown in Figure a, the surface of the composite coating after coating the hygroscopic layer is very smooth; the surface roughness of the photothermal / hygroscopic composite coating is further characterized by AFM, as shown in Figure 5. Figure 3 As shown in b, the root mean square roughness of the surface of the photothermal / hygroscopic composite coating is 0.44 nm.

[0089] The light transmittance of the photothermal / hygroscopic composite coating was tested by Figure 4 It can be seen that the maximum transmittance of the photothermal / hygroscopic composite coating in the light wavelength range of 400-720nm is 80.92%, the average transmittance is 76.38%, and the transmittance in the near-infrared region is as low as 20.60%.

[0090] The water contact angle of the photothermal / hygroscopic composite coating was tested by dropping a 5 μl water droplet on the composite coating surface and taking pictures of the water contact angle at intervals. For the objectivity of the data, three different points were taken for each sample. Figure 5 As shown in the figure, the water contact angle of the photothermal / hygroscopic composite coating gradually decreases with time, decreasing from 67.13° to 31.33° within 800 seconds, while the water contact angle of the control blank glass remains basically unchanged, indicating that the surface of the composite coating has good hygroscopicity.

[0091] The surface temperature of the photothermal / hygroscopic composite coating and the control blank glass was measured under the irradiation of one sun. Figure 6 As shown in (a), the photothermal / hygroscopic composite coating has good photothermal conversion performance, and the surface temperature can reach at least 64°C within 600s.

[0092] The anti-fog test of the photothermal / hygroscopic composite coating was conducted. The photothermal / hygroscopic composite coating was exposed to sunlight simulated by a xenon lamp with a light intensity of 1000W m -2 The coated side was placed 5 cm above 65°C hot water. Figure 6 As shown in b, the photothermal / hygroscopic composite coating has a long-lasting anti-fog function and maintains a clear field of view at the 6th hour of the test; the glass sheet coated with the photothermal / hygroscopic composite coating is placed in a refrigerator at -20°C for 24 hours for anti-frost test. Figure 7 As shown in b, the surface of the photothermal / hygroscopic composite coating remains transparent and has anti-frost function.

[0093] The wear resistance of the photothermal / hygroscopic composite coating was tested. The photothermal / hygroscopic composite coating was rubbed repeatedly 5000 times with a fiber cloth at a pressure of 55 kPa, and the changes in the light transmittance of the coating before and after friction were compared. Figure 8 As shown in middle a, after friction, the maximum transmittance of the photothermal / hygroscopic composite coating in the range of 400-720 nm is 80.85%, and the average transmittance is 76.15%, which is almost unchanged compared with before friction.

[0094] In order to evaluate the effects of repeated and long-term illumination on the photothermal conversion performance of the photothermal / hygroscopic composite coating, the sample was repeatedly heated and cooled for 50 cycles under one sun intensity. Figure 8 As shown in middle b, all the cycle curves of the photothermal / hygroscopic composite coating during repeated heating (xenon lamp on) and cooling (xenon lamp off) are similar, with no significant changes, showing good photothermal stability.

[0095] The feasibility of the anti-fog performance of the photothermal / hygroscopic composite coating was tested. A glass sheet coated with the composite coating was placed 5 cm above 65°C hot water in the sun. The anti-fog test results are as follows: Figure 9 The photothermal / hygroscopic composite coating maintained a clear view throughout the experiment, but the control sample coated with only the hygroscopic layer was severely fogged.

[0096] Example 4 Preparation of Photothermal / Hygroscopic Composite Coating

[0097] (1) Preparation of photothermal layer slurry:

[0098] 0.6 g of tungsten chloride was dissolved in 80 ml of anhydrous ethanol and stirred at room temperature for 15 min. 0.13 g of cesium hydroxide monohydrate was then added and stirred at room temperature for 10 min to obtain a mixed solution. 20 ml of acetic acid was added dropwise to the mixed solution and stirred for 15 min. The solution was then transferred to a polytetrafluoroethylene-lined reactor and subjected to a solvothermal reaction at 220°C for 20 h. After the reaction, the solid sample was centrifuged and washed at least three times with anhydrous ethanol and deionized water, dried in a vacuum oven at 60°C overnight, and ground to obtain cesium tungsten bronze nanoparticle powder.

[0099] Under vigorous stirring, 12 parts by mass of nanoparticle powder were added to 60 parts by mass of deionized water, and ultrasonically dispersed for 15 minutes to obtain a uniform nanopowder dispersion; 8 parts by mass of aqueous acrylic emulsion was mixed with 18 parts by mass of deionized water to obtain a film-forming agent, which was then mixed and stirred with 24 parts by mass of the above nanopowder dispersion, and ultrasonically dispersed for 15 minutes to obtain a photothermal layer slurry with a cesium tungsten bronze nanoparticle content of 8wt%.

[0100] (2) Preparation of moisture absorbing layer slurry:

[0101] 8 parts by mass of PVA were weighed and dissolved in 92 parts by mass of deionized water, and stirred in a water bath at 85°C for 1 hour to obtain an 8 wt% PVA aqueous solution; 2.05 parts by mass of zinc chloride were dissolved in 30 parts by mass of 3M dilute hydrochloric acid to obtain a zinc chloride solution, which was stirred evenly and then 2.4 parts by mass of the zinc chloride solution was added dropwise to 20 parts by mass of the 8 wt% PVA aqueous solution. The mixture was stirred at room temperature until fully mixed to obtain a hygroscopic layer slurry.

[0102] (3) The photothermal layer slurry obtained in step (1) is applied to a clean glass substrate by spin coating, and dried at room temperature for 10 minutes to obtain a photothermal layer with near-infrared shielding performance.

[0103] The hygroscopic layer slurry prepared in step (2) is coated on the photothermal layer obtained in step (3) by a doctor blade method, and is placed in a 60° C. oven to dry for 4 hours to obtain a photothermal / hygroscopic composite coating.

[0104] The light transmittance, light-to-heat conversion performance, and anti-fog performance of the photothermal / hygroscopic composite coating obtained in Example 4 were measured, and the results are shown in Table 1.

[0105] Example 5 Preparation of Photothermal / Hygroscopic Composite Coating

[0106] (1) Preparation of photothermal layer slurry:

[0107] 0.6 g of tungsten chloride was dissolved in 80 ml of anhydrous ethanol and stirred at room temperature for 15 min. 0.13 g of cesium hydroxide monohydrate was then added and stirred at room temperature for 10 min to obtain a mixed solution. 20 ml of acetic acid was added dropwise to the mixed solution and stirred for 15 min. The solution was then transferred to a polytetrafluoroethylene-lined reactor and subjected to a solvothermal reaction at 220°C for 20 h. After the reaction, the solid sample was centrifuged and washed at least three times with anhydrous ethanol and deionized water, dried in a vacuum oven at 60°C overnight, and ground to obtain cesium tungsten bronze nanoparticle powder.

[0108] Under vigorous stirring, 12 parts by mass of nanoparticle powder was added to 60 parts by mass of deionized water, and ultrasonic dispersion was performed for 15 minutes to obtain a uniform nanopowder dispersion; 5 parts by mass of aqueous acrylic emulsion was taken, mixed and stirred with 50 parts of the above nanopowder dispersion, and ultrasonic dispersion was performed for 15 minutes to obtain a photothermal layer slurry with a cesium tungsten bronze nanoparticle content of 15wt%.

[0109] (2) Preparation of moisture absorbing layer slurry:

[0110] 8 parts by mass of PVA were weighed and dissolved in 92 parts by mass of deionized water, and stirred in a water bath at 85°C for 1 hour to obtain an 8 wt% PVA aqueous solution; 2.05 parts by mass of zinc chloride were dissolved in 30 parts by mass of 3M dilute hydrochloric acid to obtain a zinc chloride solution, which was stirred evenly and then 2.4 parts by mass of the zinc chloride solution was added dropwise to 20 parts by mass of the 8 wt% PVA aqueous solution. The mixture was stirred at room temperature until fully mixed to obtain a hygroscopic layer slurry.

[0111] (3) The photothermal layer slurry obtained in step (1) is applied to a clean glass substrate by spin coating, and dried at room temperature for 10 minutes to obtain a photothermal layer with near-infrared shielding performance.

[0112] The hygroscopic layer slurry prepared in step (2) is coated on the photothermal layer obtained in step (3) by a doctor blade method, and is placed in a 60° C. oven to dry for 4 hours to obtain a photothermal / hygroscopic composite coating.

[0113] The light transmittance, light-to-heat conversion performance, and anti-fog performance of the photothermal / hygroscopic composite coating obtained in Example 5 were measured. The results are shown in Table 1.

[0114] Example 6 Preparation of Photothermal / Hygroscopic Composite Coating

[0115] The preparation method is basically the same as that of Example 3, except that the zinc chloride solution in step (1) is replaced by a copper chloride solution of the same concentration.

[0116] The light transmittance, light-to-heat conversion performance, and anti-fog performance of the photothermal / hygroscopic composite coating obtained in Example 6 were measured. The results are shown in Table 1.

[0117] Example 7 Preparation of Photothermal / Hygroscopic Composite Coating

[0118] The preparation method is basically the same as that of Example 3, except that the zinc chloride solution in step (1) is replaced with a polyacrylic acid aqueous solution. The specific implementation method is:

[0119] (1) Preparation of photothermal nanomaterial powder and photothermal layer slurry:

[0120] 0.6 g of tungsten chloride was dissolved in 80 ml of anhydrous ethanol and stirred at room temperature for 15 min. 0.13 g of cesium hydroxide monohydrate was then added and stirred at room temperature for 10 min to obtain a mixed solution. 20 ml of acetic acid was added dropwise to the mixed solution and stirred for 15 min. The solution was then transferred to a polytetrafluoroethylene-lined reactor and subjected to a solvothermal reaction at 220°C for 20 h. After the reaction, the solid sample was centrifuged and washed at least three times with anhydrous ethanol and deionized water, dried in a vacuum oven at 60°C overnight, and ground to obtain cesium tungsten bronze nanoparticle powder.

[0121] Under vigorous stirring, 12 parts by mass of nanoparticle powder were added to 60 parts by mass of deionized water, and ultrasonically dispersed for 10 minutes to obtain a uniform nanopowder dispersion; 8 parts by mass of aqueous acrylic emulsion was mixed with 10 parts by mass of deionized water to obtain a film-forming agent, which was then mixed with 50 parts by mass of the above-mentioned nanopowder dispersion and stirred, and ultrasonically dispersed for 15 minutes to obtain a photothermal layer slurry with a cesium tungsten bronze nanoparticle content of 12wt%.

[0122] (2) Preparation of moisture absorbing layer slurry:

[0123] 8 parts of PVA were weighed and dissolved in 92 parts of deionized water, and stirred in an 85°C water bath for 1 hour to obtain an 8wt% PVA aqueous solution; 53wt% polyacrylic acid aqueous solution was prepared, 5ml of which was added dropwise to 45ml of the 8wt% PVA aqueous solution, and stirred at room temperature until fully mixed; the pH of the resulting mixture was adjusted to 4 with hydrochloric acid, and the mixture was stirred and degassed by ultrasonication or standing to obtain a hygroscopic layer slurry.

[0124] (3) The photothermal layer slurry obtained in step (1) is applied to a clean glass substrate by spin coating, and dried at room temperature for 10 minutes to obtain a photothermal layer with near-infrared shielding performance.

[0125] The hygroscopic layer slurry prepared in step (2) is coated on the photothermal layer obtained in step (3) by a doctor blade method, and is placed in a 60° C. oven and dried for 6 hours to obtain a photothermal / hygroscopic composite coating.

[0126] The light transmittance, light-to-heat conversion performance, and anti-fog performance of the photothermal / hygroscopic composite coating obtained in Example 7 were measured. The results are shown in Table 1.

[0127] Example 8 Preparation of Photothermal / Hygroscopic Composite Coating

[0128] The preparation method is basically the same as that of Example 7, except that the polyacrylic acid aqueous solution in step (2) is replaced by a polymethacrylic acid aqueous solution of the same concentration.

[0129] The light transmittance, light-to-heat conversion performance, and anti-fog performance of the photothermal / hygroscopic composite coating obtained in Example 8 were measured. The results are shown in Table 1.

[0130] Example 9 Preparation of Photothermal / Hygroscopic Composite Coating

[0131] The preparation method is basically the same as that of Example 7, except that the PVA aqueous solution in step (2) is replaced by a polyethylene glycol aqueous solution of the same concentration.

[0132] The light transmittance, light-to-heat conversion performance, and anti-fog performance of the photothermal / hygroscopic composite coating obtained in Example 9 were measured. The results are shown in Table 1.

[0133] Example 10 Preparation of photothermal / hygroscopic composite coating

[0134] The preparation method is basically the same as that of Example 9, except that the polyethylene glycol aqueous solution in step (2) is replaced by a polyvinylamine aqueous solution.

[0135] The light transmittance, light-to-heat conversion performance, and anti-fog performance of the photothermal / hygroscopic composite coating obtained in Example 10 were measured, and the results are shown in Table 1.

[0136] Comparative Example 1

[0137] The difference between Comparative Example 1 and Example 3 is that the preparation and mixing steps of the film-forming agent are missing in Comparative Example 1. The specific implementation method is:

[0138] (1) Preparation of photothermal layer slurry:

[0139] 0.6 g of tungsten chloride was dissolved in 80 ml of anhydrous ethanol and stirred at room temperature for 15 min. 0.13 g of cesium hydroxide monohydrate was then added and stirred at room temperature for 10 min to obtain a mixed solution. 20 ml of acetic acid was added dropwise to the mixed solution and stirred for 15 min. The solution was then transferred to a polytetrafluoroethylene-lined reactor and subjected to a solvothermal reaction at 220°C for 20 h. After the reaction, the solid sample was centrifuged and washed at least three times with anhydrous ethanol and deionized water, dried in a vacuum oven at 60°C overnight, and ground to obtain cesium tungsten bronze nanoparticle powder.

[0140] Under vigorous stirring, 12 parts by mass of nanoparticle powder was added to 60 parts by mass of deionized water, and ultrasonically dispersed for 10 minutes to obtain a uniform nanopowder dispersion; 18 parts by mass of deionized water was taken, mixed with 50 parts by mass of the above nanopowder dispersion, and ultrasonically dispersed for 15 minutes to obtain a photothermal layer slurry.

[0141] (2) Preparation of moisture absorbing layer slurry:

[0142] 8 parts by mass of PVA were weighed and dissolved in 92 parts by mass of deionized water, and stirred in an 85°C water bath for 1 hour to obtain an 8wt% PVA aqueous solution; 2.05 parts by mass of zinc chloride were dissolved in 30 parts by mass of 3M dilute hydrochloric acid to obtain a zinc chloride solution, and 2.4 parts by mass of the zinc chloride solution were added dropwise to 20 parts by mass of the 8wt% PVA aqueous solution. After stirring at room temperature until fully mixed, a moisture absorbing layer slurry was obtained.

[0143] (3) The nanopowder dispersion obtained in step (1) is coated on a clean glass substrate by spin coating, and dried at room temperature for 10 minutes to obtain a photothermal layer.

[0144] The hygroscopic layer slurry prepared in step (2) is coated on the photothermal layer obtained in step (3) by a doctor blade method, and is placed in a 60° C. oven to dry for 4 hours to obtain a photothermal / hygroscopic composite coating.

[0145] The light transmittance, photothermal conversion performance, and anti-fog performance of the photothermal / hygroscopic composite coating obtained in Comparative Example 1 were measured, and the results are shown in Table 1. Because no film-forming agent was added, the nanopowder dispersion had low viscosity and poor film-forming properties on the substrate. The resulting coating had low absorption in the near-infrared region, poor photothermal conversion performance, and ineffective long-term anti-fog performance.

[0146] Comparative Example 2

[0147] The difference between Comparative Example 2 and Example 3 is that in Comparative Example 2, the content of cesium tungsten bronze nanoparticles in the photothermal layer slurry is increased to 30 wt %. The specific implementation method is as follows:

[0148] (1) Preparation of photothermal layer slurry:

[0149] 0.6 g of tungsten chloride was dissolved in 80 ml of anhydrous ethanol and stirred at room temperature for 15 min. 0.13 g of cesium hydroxide monohydrate was then added and stirred at room temperature for 10 min to obtain a mixed solution. 20 ml of acetic acid was added dropwise to the mixed solution and stirred for 15 min. The solution was then transferred to a polytetrafluoroethylene-lined reactor and subjected to a solvothermal reaction at 220°C for 20 h. After the reaction, the solid sample was centrifuged and washed at least three times with anhydrous ethanol and deionized water, dried in a vacuum oven at 60°C overnight, and ground to obtain cesium tungsten bronze nanoparticle powder.

[0150] Under vigorous stirring, 5 parts by mass of nanoparticle powder were added to 5 parts by mass of deionized water, and ultrasonically dispersed for 10 minutes to obtain a uniform nanopowder dispersion; 26 parts by mass of aqueous acrylic emulsion were mixed with 54 parts by mass of deionized water to obtain a film-forming agent, which was then mixed with 120 parts by mass of the above-mentioned nanopowder dispersion and stirred, and ultrasonically dispersed for 15 minutes to obtain a photothermal layer slurry with a cesium tungsten bronze nanoparticle content of 30wt%.

[0151] (2) Preparation of hygroscopic layer slurry: 8 parts by mass of PVA were weighed and dissolved in 92 parts by mass of deionized water, and stirred in a water bath at 85°C for 1 hour to obtain an 8 wt% PVA aqueous solution; 2.05 parts by mass of zinc chloride were dissolved in 30 parts by mass of 3M dilute hydrochloric acid to obtain a zinc chloride solution, and after stirring evenly, 2.4 parts by mass of the zinc chloride solution was added dropwise to 20 parts by mass of the 8 wt% PVA aqueous solution, and stirred at room temperature until fully mixed to obtain a hygroscopic layer slurry.

[0152] (3) The nanopowder dispersion obtained in step (1) is coated on a clean glass substrate by spin coating, and dried at room temperature for 10 minutes to obtain a photothermal layer.

[0153] The hygroscopic layer slurry prepared in step (2) is coated on the photothermal layer obtained in step (3) by a doctor blade method, and is placed in a 60° C. oven to dry for 4 hours to obtain a photothermal / hygroscopic composite coating.

[0154] The photothermal / hygroscopic composite coating obtained in Comparative Example 2 has a high content of nanoparticles. Observation with the naked eye reveals that the coating has high haze and poor transparency, and therefore has no application value in anti-fogging on transparent substrates.

[0155] Comparative Example 3

[0156] The difference between Comparative Example 3 and Example 3 is that the preparation and addition steps of the zinc chloride solution are missing in the preparation process of the moisture absorption layer slurry in Comparative Example 3. The specific implementation method is:

[0157] (1) Preparation of photothermal layer slurry:

[0158] 0.6 g of tungsten chloride was dissolved in 80 ml of anhydrous ethanol and stirred at room temperature for 15 min. 0.13 g of cesium hydroxide monohydrate was then added and stirred at room temperature for 10 min to obtain a mixed solution. 20 ml of acetic acid was added dropwise to the mixed solution and stirred for 15 min. The solution was then transferred to a polytetrafluoroethylene-lined reactor and subjected to a solvothermal reaction at 220°C for 20 h. After the reaction, the solid sample was centrifuged and washed at least three times with anhydrous ethanol and deionized water, dried in a vacuum oven at 60°C overnight, and ground to obtain cesium tungsten bronze nanoparticle powder.

[0159] Under vigorous stirring, 12 parts by mass of nanoparticle powder were added to 60 parts by mass of deionized water, and ultrasonically dispersed for 10 minutes to obtain a uniform nanopowder dispersion; 8 parts by mass of aqueous acrylic emulsion was mixed with 10 parts by mass of deionized water to obtain a film-forming agent, which was then mixed with 50 parts by mass of the above-mentioned nanopowder dispersion and stirred, and ultrasonically dispersed for 15 minutes to obtain a photothermal layer slurry.

[0160] (2) Preparation of moisture absorbing layer slurry:

[0161] 8 parts by mass of PVA were weighed and dissolved in 92 parts by mass of deionized water, and stirred in a water bath at 85° C. for 1 hour to obtain an 8 wt % PVA aqueous solution; the 8 wt % PVA aqueous solution was directly used as the slurry for the moisture absorption layer.

[0162] (3) The photothermal layer slurry obtained in step (1) is applied to a clean glass substrate by spin coating, and dried at room temperature for 10 minutes to obtain a photothermal layer with near-infrared shielding performance.

[0163] The hygroscopic layer slurry prepared in step (2) is coated on the photothermal layer obtained in step (3) by a doctor blade method, and is placed in a 60° C. oven to dry for 4 hours to obtain a photothermal / hygroscopic composite coating.

[0164] Comparative Example 3 and Example 3 were immersed in deionized water at the same time. After 24 hours, the comparative example 3 was found to be severely wrinkled, while the appearance of Example 3 was not damaged at all, which proved that the zinc chloride added in Example 3 could enhance the adhesion and water resistance of the polymer.

[0165] Comparative Example 4

[0166] The difference between Comparative Example 4 and Example 3 is that the step of coating the photothermal layer is missing in Comparative Example 4. The specific implementation method is as follows:

[0167] (1) Preparation of moisture absorbing layer slurry:

[0168] 8 parts by mass of PVA were weighed and dissolved in 92 parts by mass of deionized water, and stirred in a water bath at 85°C for 1 hour to obtain an 8 wt% PVA aqueous solution; 2.05 parts by mass of zinc chloride were dissolved in 30 parts by mass of 3M dilute hydrochloric acid to obtain a zinc chloride solution, which was stirred evenly and then 2.4 parts by mass of the zinc chloride solution was added dropwise to 20 parts by mass of the 8 wt% PVA aqueous solution. The mixture was stirred at room temperature until fully mixed to obtain a hygroscopic layer slurry.

[0169] The hygroscopic layer slurry prepared in step (1) was coated on a cleaned glass substrate by a doctor blade method, and dried in an oven at 60° C. for 4 h to obtain a coating having only a hygroscopic layer.

[0170] After removing the first photothermal layer with photothermal conversion performance, the prepared hygroscopic layer does not have photothermal conversion performance, and the surface temperature does not increase significantly under the sunlight simulated by a xenon lamp; the anti-fog test of the hygroscopic layer coating obtained in Comparative Example 4 was carried out, and the test process was referred to Example 3. The results are as follows Figure 6 As shown in Figure b, in the initial stage of the anti-fog test, the hygroscopic layer has an anti-fog effect. However, as the test time increases, the hygroscopic layer gradually reaches its water absorption saturation limit, condensation droplets appear on the surface of the hygroscopic layer, and eventually aggregate into a water film, which cannot provide long-term anti-fog effect.

[0171] Comparative Example 5

[0172] The difference between Comparative Example 5 and Example 3 is that the step of coating the moisture absorbing layer is missing in Comparative Example 5. The specific implementation method is:

[0173] (1) Preparation of photothermal nanomaterial powder and photothermal layer slurry:

[0174] 0.6 g of tungsten chloride was dissolved in 80 ml of anhydrous ethanol and stirred at room temperature for 15 min. 0.13 g of cesium hydroxide monohydrate was then added and stirred at room temperature for 10 min to obtain a mixed solution. 20 ml of acetic acid was added dropwise to the mixed solution and stirred for 15 min. The solution was then transferred to a polytetrafluoroethylene-lined reactor and subjected to a solvothermal reaction at 220°C for 20 h. After the reaction, the solid sample was centrifuged and washed at least three times with anhydrous ethanol and deionized water, dried in a vacuum oven at 60°C overnight, and ground to obtain cesium tungsten bronze nanoparticle powder.

[0175] Under vigorous stirring, 12 parts by mass of nanoparticle powder were added to 60 parts by mass of deionized water, and ultrasonically dispersed for 10 minutes to obtain a uniform nanopowder dispersion; 8 parts by mass of aqueous acrylic emulsion was mixed with 10 parts by mass of deionized water to obtain a film-forming agent, which was then mixed with 50 parts by mass of the above-mentioned nanopowder dispersion and stirred, and ultrasonically dispersed for 15 minutes to obtain a photothermal layer slurry with a cesium tungsten bronze nanoparticle content of 12wt%.

[0176] (2) The photothermal layer slurry obtained in step (1) is applied to a clean glass substrate by spin coating, and dried at room temperature for 10 minutes to obtain a photothermal layer with near-infrared shielding performance.

[0177] After removing the second hygroscopic layer, the prepared photothermal layer still has photothermal conversion performance. The change in surface temperature under sunlight simulated by a xenon lamp is basically consistent with that of the photothermal / hygroscopic composite coating obtained in Example 3. The photothermal layer obtained in Comparative Example 5 was subjected to an anti-fog test. The test process was similar to that of Example 3. The results are shown in FIG. Figure 7As shown in a. In the initial stage of the anti-fog test, the photothermal layer was not anti-fog, but because the surface temperature of the photothermal layer rose rapidly under simulated sunlight, the condensed droplets evaporated completely within 5 minutes and no more fogging occurred. The photothermal layer obtained in Comparative Example 5 was placed in a refrigerator at -20°C for 24 hours for anti-frost test. Figure 7 As shown in b, the photothermal layer does not have anti-frost properties.

[0178] Table 1 Performance comparison data of the coatings obtained in Examples 3-10 and Comparative Examples 1, 4-5

[0179]

[0180] Note: Long-term anti-fog means that the sample coated with the coating is placed 5 cm above 65℃ hot water under one sunlight intensity and there is no fogging on the surface for at least 6 hours.

[0181] It can be seen from Table 1 that the composite coatings prepared in Examples 3-10 all have long-lasting anti-fog properties driven by sunlight, among which Example 3 has the best spectral selectivity, with an average transmittance of 76.38% in the visible light region and an average transmittance as low as 20.60% in the near-infrared region. After irradiation with one sunlight intensity for 600 seconds, the surface temperature is higher than 64°C, showing long-lasting anti-fog properties driven by sunlight.

[0182] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the scope of protection of the present invention.

Claims

1. A composite coating with long-lasting anti-fog properties, characterized in that: The composite coating comprises a photothermal layer with photothermal conversion performance and a moisture absorbing layer with moisture absorbing function, which are arranged in sequence; The photothermal layer includes cesium tungsten bronze nanoparticles; The preparation of the composite coating comprises the following steps: 1) Preparation of photothermal layer slurry: Cesium tungsten bronze nanoparticles are added to a solvent and dispersed by ultrasonication to obtain a nanopowder dispersion. A film-forming agent is obtained by mixing a water-based coating emulsion with deionized water; Mixing the film-forming agent with the nanopowder dispersion to obtain a photothermal layer slurry; 2) Preparation of moisture absorbing layer slurry: The first component and the second component are mixed evenly, stirred, ultrasonically or allowed to stand for degassing to obtain a moisture absorbing layer slurry; Wherein, the first component is selected from an aqueous solution of a polymer containing a hydroxyl group in the main chain or a side chain or an aqueous solution of a polymer containing an amino group in the main chain or a side chain; The second component is selected from an inorganic metal ion compound solution or an aqueous solution of a polymer containing carboxyl groups in the main chain or side chain; 3) Preparation of photothermal layer: Coating the photothermal layer slurry obtained in step 1) on a clean substrate and drying it to obtain a photothermal layer; 4) Preparation of composite coating: The hygroscopic layer slurry obtained in step 2) is again coated on the photothermal layer obtained in step 3), and dried to obtain a composite coating; In step 1), the cesium tungsten bronze nanoparticles account for 15-25wt% of the nanopowder dispersion; the cesium tungsten bronze nanoparticles account for 5-20wt% of the photothermal layer slurry; The polymer contained in the first component is selected from one or more of polyvinyl alcohol, polyethylene glycol, block copolymers of polyethylene glycol, polyvinylamine and polyacrylamine; The inorganic metal ion compound is selected from one or more of copper chloride, zinc chloride and ferric chloride; The polymer contained in the second component is selected from one or more of polyacrylic acid and polymethacrylic acid.

2. The composite coating according to claim 1, characterized in that The cesium tungsten bronze nanoparticles are hexagonal crystals with a size of 10-100 nm.

3. The composite coating according to claim 1, characterized in that The thickness of the photothermal layer in the composite coating is 200-600 nm, and the thickness of the hygroscopic layer is 20-150 μm; The average light transmittance of the composite coating in the range of 400-720nm is ≥60%; The water contact angle of the composite coating decreases from 50-70° to 20-40° within 800 seconds.

4. The method for preparing a composite coating according to any one of claims 1 to 3, wherein: The steps include: 1) Preparation of photothermal layer slurry: Cesium tungsten bronze nanoparticles are added to a solvent and dispersed by ultrasonication to obtain a nanopowder dispersion. A film-forming agent is obtained by mixing a water-based coating emulsion with deionized water; Mixing the film-forming agent with the nanopowder dispersion to obtain a photothermal layer slurry; 2) Preparation of moisture absorbing layer slurry: The first component and the second component are mixed evenly, stirred, ultrasonically or allowed to stand for degassing to obtain a moisture absorbing layer slurry; Wherein, the first component is selected from an aqueous solution of a polymer containing a hydroxyl group in the main chain or a side chain or an aqueous solution of a polymer containing an amino group in the main chain or a side chain; The second component is selected from an inorganic metal ion compound solution or an aqueous solution of a polymer containing carboxyl groups in the main chain or side chain; 3) Preparation of photothermal layer: Coating the photothermal layer slurry obtained in step 1) on a clean substrate and drying it to obtain a photothermal layer; 4) Preparation of composite coating: The hygroscopic layer slurry obtained in step 2) is again coated on the photothermal layer obtained in step 3), and dried to obtain a composite coating; In step 1), the cesium tungsten bronze nanoparticles account for 15-25wt% of the nanopowder dispersion; the cesium tungsten bronze nanoparticles account for 5-20wt% of the photothermal layer slurry; The polymer contained in the first component is selected from one or more of polyvinyl alcohol, polyethylene glycol, block copolymers of polyethylene glycol, polyvinylamine and polyacrylamine; The inorganic metal ion compound is selected from one or more of copper chloride, zinc chloride and ferric chloride; The polymer contained in the second component is selected from one or more of polyacrylic acid and polymethacrylic acid.

5. The preparation method according to claim 4, characterized in that In step 1), the water-based coating emulsion is selected from water-based acrylic emulsion.

6. The preparation method according to claim 4, characterized in that In the film-forming agent, the mass ratio of the aqueous coating emulsion to deionized water is 1:0-5.

7. The preparation method according to claim 4, characterized in that In the moisture absorption layer slurry, the molar ratio of the polymer to the inorganic metal ion compound in the first component is 10-50:

1.

8. The preparation method according to claim 4, characterized in that In the moisture absorption layer slurry, the molar ratio of the polymer contained in the first component to the polymer contained in the second component is 1-50:

1.

9. The preparation method according to claim 4, characterized in that The cesium tungsten bronze nanoparticles are prepared according to the following steps: dissolving a tungsten-containing compound in anhydrous ethanol, and then adding a cesium-containing compound to obtain a mixed solution; Acetic acid was added dropwise into the mixed solution, and cesium tungsten bronze nanoparticles were prepared by a solvothermal method.

10. The preparation method according to claim 4, characterized in that The substrate is selected from glass.

11. A film-coated glass, characterized in that: The composite coating according to any one of claims 1 to 3 is coated on a glass substrate.

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