ZnS-coated AZO composite filler, preparation method thereof and full-wave-band water-based reflective coating

Abstract

The invention relates to a ZnS-coated AZO composite filler and a preparation method thereof and a full-wave-band water-based reflective paint.The preparation method of the filler comprises the steps that ZnS powder subjected to surface activation through a silane coupling agent is dispersed in deionized water, ZnS dispersion liquid is obtained, and the ZnS dispersion liquid is heated to the first temperature; the preparation method comprises the following steps: dissolving zinc salt and aluminum salt in an alcohol-water mixed solvent to form a precursor solution; dropwise adding the precursor solution and an alkaline precipitant into the ZnS dispersion liquid under continuous stirring, and enabling the whole reaction system to react under the conditions that the temperature is kept unchanged and the pH value is kept in a weakly alkaline range by controlling the dropwise adding speed and the amount of the precipitant in the dropwise adding process; and after the reaction is finished, aging and filtering the obtained slurry, washing the precipitate, drying and calcining to form the composite filler. Limitation of traditional filler is broken through in optical performance, efficient full-wave-band reflection is achieved, and durability of the coating is improved in material chemical essence.

Description

Technical Field

[0001] This invention relates to the field of reflective coating technology, and in particular to a ZnS@AZO composite filler, its preparation method, and a full-band waterborne reflective coating. Background Technology

[0002] With the continuous growth of global energy consumption and the increasing sophistication of building energy efficiency standards, the development of efficient building envelope insulation technologies is of great significance. Solar radiation is the main source of external heat load on buildings, with its energy primarily distributed in the visible light (VIS, 400-780 nm, accounting for approximately 43% of total energy) and near-infrared light (NIR, 780-2500 nm, accounting for approximately 52% of total energy) bands. Reflective thermal insulation coatings, applied to the exterior surface of buildings, directly reflect the light energy from solar radiation back into the atmosphere, thereby reducing heat gain in the building envelope and indoor air conditioning energy consumption at the source. This is an economical and effective proactive energy-saving technology.

[0003] The solar reflectivity of coatings hinges on the optical properties of their functional fillers. Currently, technological development in this field primarily revolves around two types of material systems, both of which suffer from significant performance bottlenecks or application limitations: One approach is the reflective system based on high-refractive-index white pigments (represented by rutile titanium dioxide). These materials, with their extremely high refractive index (rutile TiO2 has a refractive index of approximately 2.7), exhibit excellent reflectivity in the visible light band through Mie scattering (reflectivity typically >80%), providing both superior hiding power and whiteness, thus becoming the benchmark filler for high-performance reflective coatings. However, this system suffers from two inherent drawbacks: First, the refractive index of TiO2 decreases significantly in the near-infrared band, resulting in severely insufficient scattering ability for near-infrared light, which accounts for more than half of solar energy, making it difficult to break through the 90% bottleneck in total solar reflectance (TSR). More seriously, titanium dioxide (especially its anatase phase) exhibits strong photocatalytic activity (i.e., "photocatalytic degradation effect") under ultraviolet light excitation, irreversibly catalyzing the degradation of the organic resin matrix in the coating, leading to aging phenomena such as chalking, discoloration, and loss of gloss, severely impairing the long-term durability of the coating.

[0004] Second, there are near-infrared reflective systems based on doped oxide semiconductors (represented by aluminum-doped zinc oxide (AZO)). To compensate for the shortcomings of TiO2 in the near-infrared band, researchers have developed doped semiconductor materials such as AZO. These materials achieve strong reflection in specific near-infrared bands (typically 1000-2000 nm) by introducing localized surface plasmon resonance effects generated by free carriers. However, these materials themselves have relatively low refractive indices (ZnO is approximately 2.0), exhibiting transparency or weak scattering of visible light, and cannot provide effective shielding on their own. Therefore, in practical applications, they must be physically compounded with white pigments such as TiO2. This simple mechanical mixing method raises new problems: (a) Poor interfacial compatibility: Particles with different polarities, densities and surface properties are difficult to disperse stably and uniformly in the resin system, and are prone to phase separation or sedimentation, resulting in uneven optical properties of the coating. (b) Excessive filler volume fraction: In order to meet the requirements of both covering and heat insulation at the same time, the total filler addition is forced to increase, which often impairs the film-forming properties, flexibility and adhesion of the coating. (c) Failure to eliminate photocatalytic risk: TiO2 components still exist in the system, and the risk of long-term damage to the resin matrix by its photocatalytic degradation remains.

[0005] In summary, existing reflective heat insulation coating technologies face common problems such as "performance shortcomings" (single materials cannot simultaneously achieve efficient visible light scattering and efficient near-infrared reflection), "durability risks" (high-performance scattering materials are often accompanied by photocatalytic side effects), and "defects in composite processes" (physical mixing leads to poor interfaces and low stability).

[0006] Therefore, there is an urgent need in this field for an innovative filler design that can synergistically manage full-spectrum sunlight at the microstructure level and fundamentally improve the overall performance and service life of the coating. Summary of the Invention

[0007] To address the aforementioned issues, this paper presents a ZnS@AZO composite filler, its preparation method, and a full-band waterborne reflective coating, aiming to effectively solve the functional limitations of single fillers in existing technologies.

[0008] The specific technical solution is as follows: The first aspect of this invention is to provide a method for preparing ZnS@AZO composite filler, comprising: ZnS powder, after surface activation with silane coupling agent, is dispersed in deionized water to obtain ZnS dispersion, and the ZnS dispersion is heated to a first temperature. Zinc and aluminum salts are dissolved in an alcohol-water mixed solvent to form a precursor solution; The precursor solution and alkaline precipitant were added dropwise to the ZnS dispersion under continuous stirring. During the addition process, the addition rate and the amount of precipitant were controlled to ensure that the entire reaction system was kept at a constant temperature and the pH value was kept within a weakly alkaline range. After the reaction is complete, the resulting slurry is aged, filtered, and the precipitate is washed clean, dried, and calcined to form ZnS@AZO composite filler.

[0009] Furthermore, the ZnS powder surface activation method is as follows: micron-sized ZnS powder is dispersed to form a suspension, a silane coupling agent is added to the suspension, the reaction is carried out, and the powder is separated and washed after the reaction is completed.

[0010] Furthermore, the first temperature is 50-80℃.

[0011] Furthermore, the Al / Zn molar ratio in the zinc salt and aluminum salt is (1-5):100; the mass ratio of aluminum in ZnS powder to that in zinc salt is 1:(0.5-0.8).

[0012] Furthermore, the calcination method is as follows: under an inert atmosphere, the temperature is increased to 400-600℃ at a rate of 5-10℃ / min, and calcined for 1-3 hours.

[0013] A second aspect of the present invention is to provide a ZnS@AZO composite filler prepared according to the above method.

[0014] A third aspect of the present invention is to provide a full-band waterborne reflective coating based on ZnS@AZO composite filler, comprising, by weight percentage: 20-40% silicone-acrylic emulsion, 15-35% ZnS@AZO composite filler, 14.6-20.1% additives, and the balance being water, wherein the ZnS@AZO composite filler is provided by claim 6.

[0015] Furthermore, the silicone-acrylic emulsion is a single-component silicone-acrylic emulsion with a solid content ≥45%.

[0016] Furthermore, by weight, the additives include 1-2% pigment, 1-5% thickening thixotropic agent, 1-5% dispersant, 1-5% film-forming aid, 0.1-1% anti-flash rust inhibitor, 1-5% defoamer, 1-5% wetting and leveling agent, and 0.1-1% pH adjuster.

[0017] Furthermore, the pigment is rutile titanium dioxide; the thickening thixotropic agent is fumed silica with a particle size of 200-300 nm; the dispersing and anti-settling agent is a siloxane; the film-forming aid is a dodecyl alcohol ester; the flash rust inhibitor is an organozinc chelate solution; the defoamer is an aqueous organosilicon; the wetting and leveling agent is a dimethylsiloxane; and the pH adjuster is an aminomethylbenzene alcohol.

[0018] The beneficial effects of the above scheme are: This invention creatively integrates a high-refractive-index ZnS core (responsible for visible light scattering) and a plasma-enhanced AZO shell (responsible for near-infrared reflection) into a single particle, producing a synergistic effect of "1+1>2". Testing showed that the coating (approximately 150 μm thick) prepared using the filler from this invention consistently achieved a solar reflectance (TSR, 280-2500 nm) of 88%-92% across the entire solar spectrum. This indicates that the invention effectively fills the "shortcoming" in near-infrared reflection through structural design, achieving more comprehensive blocking of solar radiation. In actual heat insulation tests (irradiation for 1 hour at 500 W / m² irradiance), the temperature at the center of the back of the test panel coated with the coating from this invention only increased by 7.1-8.5℃ compared to the ambient temperature, while the temperature rise of the control samples was generally 10-15℃.

[0019] This invention selects ZnS, a chemically stable material completely devoid of photocatalytic activity, as the core scatterer, thus eliminating the risk of resin degradation due to the catalytic effect of the filler itself from the material's origin. This is fundamentally different from the prior art methods that rely on TiO2 (even after coating treatment, the risk of photocatalytic degradation in the core may still exist for a long time). Ultraviolet accelerated aging (QUV-A) tests conducted according to GB / T 1865 standard show that after 1000 hours of aging, the gloss retention rate of the coating of this invention remains above 84%, with no chalking or cracking.

[0020] This invention utilizes a chemically bonded encapsulation structure to enable the composite filler to exhibit excellent dispersion stability and interfacial compatibility in coating systems. Since the core and shell are integrated, sedimentation and stratification issues caused by density and polarity differences during physical mixing are completely avoided. Storage stability tests (50℃, 30 days) show a viscosity change rate ≤10% with no hard sedimentation. Furthermore, this integrated structure allows the filler to achieve higher reflectivity at the same addition amount, which helps reduce VOCs and improve the density, flexibility, and adhesion of the coating film.

[0021] The preparation method of this invention (in-situ co-precipitation-calcination method) uses readily available raw materials and operates under mild reaction conditions (atmospheric pressure, medium temperature). The shell thickness and doping concentration can be precisely controlled by adjusting parameters such as the precursor ratio, pH value, and calcination temperature, thereby optimizing the LSPR response band and intensity of the filler. The process exhibits good repeatability and is suitable for large-scale production. Furthermore, the final water-based coating formulation does not contain toxic heavy metals and has low VOC content, meeting environmental protection requirements.

[0022] In summary, this invention not only breaks through the limitations of traditional fillers in terms of optical performance, achieving efficient full-band reflection, but also improves the durability of the coating from the perspective of material chemistry. Furthermore, through innovative structural design, it improves the processing and application performance of the coating, making it an advanced energy-saving coating solution that combines high performance, high durability, and high environmental adaptability. Attached Figure Description

[0023] Figure 1 These are TEM images of uncoated ZnS (a) and ZnS@AZO composite fillers (b, c) provided in this invention. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0026] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but this is not intended to limit the scope of the invention.

[0027] Example 1 This embodiment provides a ZnS@AZO composite filler, the preparation of which includes: 10.0 g of spherical zinc sulfide (ZnS) powder with an average particle size D50 of 1.5 μm was taken and added to 200 mL of anhydrous ethanol. The ZnS powder was then ultrasonically dispersed in an ultrasonic cell disruptor to form a uniform suspension. The suspension was transferred to a 250 mL three-necked flask, a reflux condenser was installed, and 2.0 mL of KH-550 (γ-aminopropyltriethoxysilane) was slowly added dropwise under magnetic stirring. The system was then heated to 70 °C and stirred at this temperature for 4 hours. After the reaction was completed, the mixture was centrifuged, and the obtained solid was washed three times with anhydrous ethanol to remove the physically adsorbed coupling agent. The surface-activated ZnS solid was redispersed in 200 mL of deionized water. The resulting ZnS aqueous dispersion was placed in a 500 mL three-necked flask and placed in a 65 °C constant temperature water bath with moderate mechanical stirring for later use. Zinc salt and aluminum salt (ZnS powder and aluminum in zinc salt in a mass ratio of 1:0.6) were dissolved together in 150 mL of ethanol-water mixed solvent with a volume ratio of 1:1, with an Al / Zn molar ratio of 2.5%, and stirred to form a completely clear and transparent precursor solution.

[0028] Two precision constant flow pumps were used to extract the precursor solution and a 0.5 mol / L ammonia solution, respectively. The dropping rate of the two pumps was controlled to allow the precursor solution and ammonia solution to be added slowly and concurrently to the vigorously stirred ZnS dispersion. The pH value of the entire reaction system was kept stable at 8.0 ± 0.2 by real-time monitoring and adjustment of the ammonia dropping rate. After the addition was complete, the mixture was kept at 65°C and stirred at the same speed for 2 hours for further aging. Heating was then stopped, and the reaction mixture was allowed to cool naturally to room temperature and allowed to stand for 12 hours. This process allowed the AZO (aluminum-doped zinc oxide) precursor to fully hydrolyze, condense, and deposit in an orderly manner on the ZnS core surface. The aged slurry was filtered using a Buchner funnel, and the resulting filter cake was washed with deionized water until the conductivity of the filtrate was below 50 μS / cm. It was then washed twice with anhydrous ethanol to replace the water. The washed wet filter cake was dried to obtain a light gray precursor powder. Finally, the dried powder was placed in an alumina crucible and placed in a tubular atmosphere furnace. High-purity nitrogen (flow rate 200 sccm) was first introduced for 30 minutes to purge the air. Then, under nitrogen protection, the furnace was heated to 550°C at a heating rate of 5°C / min and calcined at this temperature for 2 hours to obtain a ZnS@AZO composite filler with a spherical zinc sulfide core and an aluminum-doped zinc oxide shell.

[0029] Figure 1 These are TEM images of uncoated ZnS (a) and ZnS@AZO composite fillers (b, c) provided in this invention. Figure (a) shows the morphology of the uncoated micron-sized ZnS particles; Figures (b) and (c) show the morphology of the ZnS@AZO composite filler at different magnifications. It can be clearly observed that the AZO shell is uniformly and continuously coated on the surface of the ZnS core, forming a distinct core-shell structure.

[0030] Example 2 This embodiment provides a ZnS@AZO composite filler, the preparation of which includes: The surface-activated ZnS solid (activation method is described in Example 1) was redispersed in 200 mL of deionized water. The resulting ZnS aqueous dispersion was placed in a 500 mL three-necked flask and placed in a constant temperature water bath at 50°C with moderate mechanical stirring for later use. Zinc salt and aluminum salt (ZnS powder and aluminum in zinc salt in a mass ratio of 1:0.8) were dissolved together in 150 mL of ethanol-water mixed solvent with a volume ratio of 1:1, with an Al / Zn molar ratio of 5.0%, and stirred to form a completely clear and transparent precursor solution.

[0031] Two precision constant flow pumps were used to extract the precursor solution and a 0.5 mol / L ammonia solution, respectively. The dropping rate of the two pumps was controlled to allow the precursor solution and ammonia solution to be added slowly and concurrently to the vigorously stirred ZnS dispersion. The pH value of the entire reaction system was kept stable at 8.5 ± 0.2 by real-time monitoring and adjustment of the ammonia dropping rate. After the addition is complete, continue to heat and mature at 50℃ and the same stirring speed for 1 hour. Then stop heating and allow the reaction mixture to cool naturally to room temperature and stand for 12 hours. Then filter the aged slurry using a Buchner funnel. Wash the filter cake with deionized water and anhydrous ethanol in sequence to replace the water. Dry it. Finally, place the dried powder in an alumina crucible and put it into a tube furnace. First, purge the air with high-purity nitrogen. Then, under nitrogen protection, heat it to 600℃ at a heating rate of 8℃ / min and calcine it at this temperature for 1 hour to obtain a ZnS@AZO composite filler.

[0032] Example 3 This embodiment provides a ZnS@AZO composite filler, the preparation of which includes: The surface-activated ZnS solid (activation method is described in Example 1) was redispersed in 200 mL of deionized water. The resulting ZnS aqueous dispersion was placed in a 500 mL three-necked flask and placed in a constant temperature water bath at 80°C with moderate mechanical stirring for later use. Zinc salt and aluminum salt (ZnS powder and aluminum in zinc salt in a mass ratio of 1:0.5) were dissolved together in 150 mL of ethanol-water mixed solvent with a volume ratio of 1:1, with an Al / Zn molar ratio of 1.0%, and stirred to form a completely clear and transparent precursor solution.

[0033] Two precision constant flow pumps were used to extract the precursor solution and a 0.5 mol / L ammonia solution, respectively. The dropping rate of the two pumps was controlled to allow the precursor solution and ammonia solution to be added slowly and concurrently to the vigorously stirred ZnS dispersion. The pH value of the entire reaction system was kept stable at 9.0 ± 0.2 by real-time monitoring and adjustment of the ammonia dropping rate. After the addition is complete, continue to maintain the temperature at 80℃ and the same stirring speed for 4 hours. Then, stop heating and allow the reaction mixture to cool naturally to room temperature and stand for 12 hours. Then, filter the aged slurry using a Buchner funnel. Wash the filter cake with deionized water and anhydrous ethanol in sequence to replace the water. Dry it. Finally, place the dried powder in an alumina crucible and put it into a tube furnace. First, purge the air with high-purity nitrogen. Then, under nitrogen protection, heat it to 400℃ at a heating rate of 10℃ / min and calcine it at this temperature for 3 hours to obtain a ZnS@AZO composite filler.

[0034] In this invention, the ZnS@AZO composite filler obtained in Examples 1-3 above is added to a high-speed disperser along with the formulated amounts of silicone-acrylic emulsion, additives, and deionized water. The mixture is physically stirred until all components are evenly dispersed, forming a stable slurry, thus obtaining an antimony-doped titanium dioxide near-infrared water-based reflective heat insulation material (corresponding to Examples 4-6, which use the filler from Examples 1-3 respectively). Specific formulations are as follows:

[0035] The specific test results for the reflective heat insulation data of the above-mentioned coating are as follows:

[0036] The test items above correspond to the following test standards / methods: ASTM E903, film thickness 150 micrometers; ASTM E903, film thickness 150 micrometers; 500W / m 2 Back temperature measurement under halogen lamp irradiation; GB / T 1865; Sedimentation degree and viscosity change; GB / T 16777.

[0037] Note: Comparative Example 2 showed slight microcracks in the later stage of aging due to preferential resin degradation at the interface of physically mixed fillers.

[0038] Comparative Example 1: An equal amount of rutile TiO2 (D50=0.3 μm) was used to replace the ZnS@AZO filler in Example 4, and the rest of the formulation and process were exactly the same.

[0039] Comparative Example 2: An equal amount of physically mixed filler (21 parts of ZnS from the same batch as in Example 1 + 7 parts of commercial AZO powder (Al doping content 3.%)) was used to replace the ZnS@AZO filler in Example 4, with the rest remaining the same.

[0040] The above description is merely a preferred embodiment of the present invention and does not limit the implementation and protection scope of the present invention. Those skilled in the art should realize that any equivalent substitutions and obvious changes made based on the description and illustrations of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing ZnS@AZO composite filler, characterized in that, include: ZnS powder, after surface activation with silane coupling agent, is dispersed in deionized water to obtain ZnS dispersion, and the ZnS dispersion is heated to a first temperature. Zinc and aluminum salts are dissolved in an alcohol-water mixed solvent to form a precursor solution; The precursor solution and alkaline precipitant were added dropwise to the ZnS dispersion under continuous stirring. During the addition process, the addition rate and the amount of precipitant were controlled to ensure that the entire reaction system was kept at a constant temperature and the pH value was kept within a weakly alkaline range. After the reaction is complete, the resulting slurry is aged, filtered, and the precipitate is washed clean, dried, and calcined to form ZnS@AZO composite filler.

2. The preparation method according to claim 1, characterized in that, The surface activation method for ZnS powder is as follows: micron-sized ZnS powder is dispersed to form a suspension, a silane coupling agent is added to the suspension, the reaction is carried out, and the powder is separated and washed after the reaction is completed.

3. The preparation method according to claim 1, characterized in that, The first temperature is 50-80℃.

4. The preparation method according to claim 1, characterized in that, The Al / Zn molar ratio in zinc salts and aluminum salts is (1-5):100; the mass ratio of aluminum in ZnS powder to that in zinc salts is 1:(0.5-0.8).

5. The preparation method according to claim 1, characterized in that, The calcination method is as follows: calcination is carried out in an inert atmosphere at 400-600℃ for 1-3 hours.

6. A ZnS@AZO composite packing, characterized in that, Prepared by the preparation method according to any one of claims 1-5.

7. A full-band water-based reflective coating, characterized in that, The product comprises, by weight percentage: 20-40% silicone-acrylic emulsion, 15-35% ZnS@AZO composite filler, 14.6-20.1% additives, and the balance being water, wherein the ZnS@AZO composite filler is provided by claim 6.

8. The temperature-adaptive coating according to claim 7, characterized in that, The silicone-acrylic emulsion is a single-component silicone-acrylic emulsion with a solid content ≥45%.

9. The temperature-adaptive coating according to claim 7, characterized in that, The additives, by weight ratio, include 1-2% pigment, 1-5% thickening thixotropic agent, 1-5% dispersant, 1-5% film-forming aid, 0.1-1% anti-flash rust inhibitor, 1-5% defoamer, 1-5% wetting and leveling agent, and 0.1-1% pH adjuster.

10. The temperature-adaptive coating according to claim 7, characterized in that, The pigment is rutile titanium dioxide; the thickening thixotropic agent is fumed silica with a particle size of 200-300 nm; the dispersing and anti-settling agent is siloxane; the film-forming aid is dodecyl alcohol ester; the flash rust inhibitor is an organozinc chelate solution; the defoamer is an aqueous organosilicon; the wetting and leveling agent is dimethylsiloxane; and the pH adjuster is aminomethylbenzene alcohol.

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