Near-infrared absorption coating and preparation method thereof

Abstract

The invention discloses a near-infrared absorption coating and a preparation method thereof, and relates to the technical field of coatings. The invention discloses a near-infrared absorption coating. The high-temperature-resistant plastic comprises the following raw materials in parts by weight: 45-60 parts of polyvinyl acetate resin, 15-25 parts of modified ferrite powder, 3-7 parts of modified graphite powder, 3-8 parts of sodium polycarboxylate, 2-6 parts of dioctyl adipate, 1-4 parts of an antioxidant 168, 15-25 parts of ethyl acetate, 8-15 parts of nano calcium carbonate, 2-5 parts of a titanate coupling agent, 10-20 parts of talcum powder, 1-3 parts of fatty alcohol-polyoxyethylene ether and 2-5 parts of urea resin. And 0.1-0.3 part of ammonia water. The near-infrared absorption coating is scientific in formula, and the ratio of the film-forming substance to the functional filler is reasonable. And the modified ferrite and the graphite powder are subjected to multi-step accurate treatment, so that the dispersity and the absorption performance are improved. In the preparation process, stirring speed, temperature and other parameters are regulated step by step to ensure uniform mixing of the raw materials. The grinding of the sand mill ensures that the fineness reaches the standard, the assistant synergistically optimizes the stability and constructability of the coating, and the technical logic is complete and reliable.

Description

Technical Field

[0001] This invention relates to the field of coating technology, specifically to a near-infrared absorbing coating and its preparation method. Background Technology

[0002] With the rapid development of new energy, building energy conservation, and electronic equipment heat dissipation, the demand for near-infrared absorbing materials is becoming increasingly urgent. Near-infrared light (wavelength 780-2500nm) accounts for more than 40% of the sun's total energy. If it cannot be effectively absorbed or blocked, it can easily lead to problems such as equipment overheating and rapid indoor temperature rise, increasing energy consumption. Traditional coatings mainly focus on decorative and protective functions, and their absorption capacity for near-infrared light is limited, making it difficult to meet the needs of energy conservation and consumption reduction.

[0003] Existing near-infrared absorbing coatings often use metal oxides and carbon-based materials as functional fillers, but they have many shortcomings: unmodified ferrite powder is prone to agglomeration and poor dispersibility, resulting in unstable near-infrared absorption efficiency; graphite powder has strong surface inertness and poor compatibility with resin matrix, which easily leads to sedimentation and stratification problems; the dispersion uniformity of nanofillers in coatings is insufficient, affecting the mechanical properties and weather resistance of the coating.

[0004] In addition, in the existing preparation process, the interfacial bonding force between the functional filler and the film-forming resin is weak, and the coating is prone to cracking and peeling. Improper selection of additives or imbalance in dosage will lead to poor storage stability of the coating and defects such as bubbles and sagging after construction.

[0005] Therefore, developing a coating that improves near-infrared absorption efficiency, dispersion stability, and overall coating performance by precisely modifying functional fillers, optimizing formulation ratios, and improving preparation processes is key to solving current technological bottlenecks and is of great significance for promoting the industrialization of energy-saving materials. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a near-infrared absorbing coating and its preparation method, which solves the problems of insufficient near-infrared absorption capacity, poor dispersibility of functional fillers, poor compatibility with the substrate, and easy cracking and peeling of the coating in traditional coatings.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A near-infrared absorbing coating comprises the following raw materials in parts by weight: 45-60 parts polyvinyl acetate resin, 15-25 parts modified ferrite powder, 3-7 parts modified graphite powder, 3-8 parts sodium polycarboxylate, 2-6 parts dioctyl adipate, 1-4 parts antioxidant 168, 15-25 parts ethyl acetate, 8-15 parts nano calcium carbonate, 2-5 parts titanate coupling agent, 10-20 parts talc, 1-3 parts fatty alcohol polyoxyethylene ether, 2-5 parts urea-formaldehyde resin, and 0.1-0.3 parts ammonia.

[0009] Furthermore, the nano-calcium carbonate has a cubic structure and its surface is modified with stearic acid. Specifically, the nano-calcium carbonate is dispersed in an ethanol / water solution with a volume ratio of 3:1 at a mass ratio of 100:3 (nano-calcium carbonate to stearic acid). Stearic acid is then added and stirred. The mixture is reacted at 60°C for 2 hours, followed by filtration and drying. The cubic structure of the nano-calcium carbonate improves the density of the filling; stearic acid modification modifies the surface through hydrophobic groups, reducing surface energy, decreasing agglomeration, and enhancing compatibility with the resin matrix, thereby improving the coating's hardness and weather resistance.

[0010] Furthermore, the modified ferrite powder is prepared using the following specific steps:

[0011] A1. Add ferrite powder to a mixed acid solution consisting of 5% hydrochloric acid and 2% sulfuric acid in a volume ratio of 3:1. Heat to 40°C within 10 minutes, then stir at 40°C for 1 hour. Maintain a stirring rate of 600 rpm for the first 30 minutes, then increase to 800 rpm for the next 30 minutes. After the reaction is complete, wash once with deionized water, filter, and redisperse the solid in deionized water. Add nano-zinc oxide powder and continue stirring at 800 rpm for 30 minutes. Then wash once with a 1% sodium bicarbonate solution. Add 0.5% ammonium dihydrogen phosphate solution, soak at 50℃ for 30 min, and finally wash repeatedly with deionized water until the filtrate is neutral. Collect the solid by vacuum filtration. Place the solid in a forced-air drying oven and dry at 70℃ for 4 h, turning the solid every 1 h during the drying process. Mixed acid etching, through gradient heating and variable speed stirring, uniformly etches impurities and defects on the ferrite surface to improve surface activity. Nano zinc oxide doping enhances near-infrared absorption capacity. Sodium bicarbonate neutralizes excess acid, and ammonium dihydrogen phosphate soaking forms a phosphate ester protective layer to improve chemical stability. Segmented drying with turning avoids clumping and ensures uniform drying.

[0012] A2. Disperse the first modified ferrite powder in deionized water and ultrasonically disperse for 15 min at 100 W. Add titanate coupling agent and silica sol, and stir at 800 r / min at 50 °C for 1.5 h. After the reaction is complete, filter and collect the solid. Wash twice with deionized water and once with 5% ethanol aqueous solution. After filtration, dry the solid at 60 °C for 5 h. The titanate coupling agent strengthens the interfacial bonding between ferrite and resin through chemical bonding, and the silica sol forms a nano-coating layer to enhance surface compatibility.

[0013] A3. The modified ferrite powder was added to ethanol and stirred for 10 min. Then, a 5% (w / w) polyvinyl alcohol solution and stearic acid were added. The mixture was stirred at 700 r / min at 60 °C for 1.5 h. Polyvinyl alcohol and stearic acid synergistically modified the surface, introduced flexible groups, and improved the wettability with the resin. During the reaction, ethanol was added every 20 min to replenish the amount of volatiles and maintain the stability of the reaction system concentration. After the reaction was completed, the mixture was filtered, the solid was collected, washed twice with ethanol, and the solid was dried at 50 °C for 6 h. Low-temperature drying avoids the decomposition of organic modifiers to obtain modified ferrite powder.

[0014] Furthermore, the ratio of ferrite powder, mixed acid solution, deionized water, nano zinc oxide powder, and ammonium dihydrogen phosphate solution in A1 is 100g:500mL:200mL:1g:300mL; wherein the ferrite powder is spinel-type or hexagonal ferrite.

[0015] Furthermore, the ratio of the first modified ferrite powder, deionized water, titanate coupling agent, and silica sol in A2 is 100g:400mL:3g:2g.

[0016] Furthermore, the amounts of the second-modified ferrite powder, ethanol, polyvinyl alcohol solution, and stearic acid in A3 are 100g:380mL:8g:1g; wherein 300mL of ethanol is used to disperse the second-modified ferrite powder, and 80mL is used to replenish 20mL every 20min thereafter.

[0017] Furthermore, the stirring rate of the mixed acid solution reaction in A1 is controlled in stages, and the rate difference in different reaction stages ensures the uniformity of the etching reaction of ferrite powder in the mixed acid, which, together with the temperature conditions, ensures the surface modification effect.

[0018] Furthermore, the modified graphite powder is prepared using the following specific steps:

[0019] B1. Add graphite powder to a 10% (w / w) nitric acid solution, along with potassium permanganate, and stir at 600 rpm for 1.5 h at 50 °C. After the reaction, add ferrous sulfate powder and continue stirring at 600 rpm for 30 min. Nitric acid and potassium permanganate oxidize the graphite surface, introducing oxygen-containing active groups such as hydroxyl and carboxyl groups, thus enhancing surface reactivity. After the reaction, slowly add sodium sulfite solution until no more bubbles are produced. Ferrous sulfate can reduce excess oxidant and prevent residual oxidant from affecting subsequent reactions. Then, wash repeatedly with deionized water until the filtrate is neutral. Collect the solid by vacuum filtration and place it in a forced-air drying oven at 80 °C for 3 h, stirring twice during the drying process.

[0020] B2. The modified graphite powder was dispersed in a 1:1 volume ratio ethanol / water mixture and ultrasonically dispersed for 20 min at 120 W. Then, fatty alcohol polyoxyethylene ether and fumed silica were added, and the mixture was stirred at 45 °C for 1.5 h. The stirring rate was 600 r / min for the first h and increased to 900 r / min for the last 30 min. Fatty alcohol polyoxyethylene ether was used as a dispersant to improve interfacial wettability, and fumed silica nanoparticles filled the gaps in the graphite to enhance the light absorption path. After the reaction was completed, the solid was collected by vacuum filtration. It was washed twice with a 1:1 volume ratio ethanol / water mixture and once with deionized water. After vacuum filtration, the solid was dried at 70 °C for 4 h. The mixture was first uniformly mixed by variable speed stirring and then the reaction contact was strengthened to improve the uniformity of modification.

[0021] B3. Add the modified graphite powder to deionized water and stir to disperse for 15 min. Then add titanate coupling agent and polyethylene wax emulsion with a solid content of 30%. Stir and react at 55℃ and 600 r / min for 1 h. The titanate coupling agent bridges the graphite and resin and enhances the interfacial bonding force. The polyethylene wax emulsion reduces the surface friction coefficient and improves the wear resistance of the coating. After the reaction is completed, filter and collect the solid. Wash once with deionized water and dry the solid at 60℃ for 5 h. After drying, pass through a 200-mesh sieve to obtain modified graphite powder.

[0022] Furthermore, the ratio of graphite powder, nitric acid solution, potassium permanganate, and ferrous sulfate powder in B1 is 50g:300mL:1.5g:0.5g.

[0023] The ratio of the first modified graphite powder, ethanol / water mixed solution, fatty alcohol polyoxyethylene ether, and fumed silica in B2 is 50g:200mL:1g:0.5g.

[0024] The ratio of the modified graphite powder, deionized water, titanate coupling agent, and polyethylene wax emulsion in B3 is 50g:250mL:2g:0.5g.

[0025] A method for preparing a near-infrared absorbing coating specifically includes the following steps:

[0026] S1. Add modified ferrite powder, sodium polycarboxylate, dioctyl adipate, antioxidant 168, nano calcium carbonate, talc, and fatty alcohol polyoxyethylene ether to ethyl acetate. Stir at 1200 r / min for 20 min, then sonicate at 200 W for 10 min. Repeat the stirring and sonication process twice, for a total of 60 min.

[0027] S2. Add polyvinyl acetate resin and continue stirring at a stirring speed of 1200 r / min for 25 min to ensure that the resin and dispersion system are fully mixed. Then add modified graphite powder and stir at a low speed of 600 r / min for 10 min to initially disperse the graphite powder. Then adjust the stirring speed to 1300 r / min and stir at a high speed for 20 min to ensure that the graphite powder is evenly dispersed.

[0028] S3. Add titanate coupling agent and part of urea-formaldehyde resin, adjust the stirring speed to 1000 r / min, stir for 10 min, then add the remaining urea-formaldehyde resin and ammonia water, continue stirring at 1000 r / min for 10 min, maintain the pH of the system at 8.5, and obtain the near-infrared absorbing coating semi-finished product.

[0029] S4. Add the semi-finished product to the sand mill, control the grinding temperature at 30-40℃, grind and test the fineness until the coating fineness reaches 30μm, and obtain the final near-infrared absorbing coating.

[0030] Furthermore, in S4, the grinding media of the sand mill is zirconia beads with a diameter of 0.8-1.2 mm, and the solid content of the material is controlled at 50%-60% during grinding.

[0031] This invention provides a near-infrared absorbing coating and its preparation method, which has the following beneficial effects:

[0032] 1. Through the synergistic effect of modified ferrite powder and modified graphite powder, combined with their uniform dispersion in the coating system, a highly efficient near-infrared light absorption network is formed. The modified ferrite, after mixed acid etching, nano-zinc oxide doping, and coupling agent modification, exhibits enhanced surface activity and significantly improved absorption capacity in the near-infrared band. The modified graphite powder, through nitric acid oxidation and interface modification, optimizes its compatibility with the resin matrix and reduces light scattering loss. The synergistic effect of these two functional fillers significantly improves the coating's capture and conversion efficiency for near-infrared light, and its absorption performance is less prone to decay due to filler agglomeration during long-term use, resulting in superior stability.

[0033] 2. In the coating system, polyvinyl acetate resin serves as the film-forming matrix, forming a dense structure with inert fillers such as nano-calcium carbonate and talc. Simultaneously, the titanate coupling agent strengthens the interfacial bonding between the functional filler and the resin matrix through chemical bonding. The modified ferrite and graphite powder are uniformly distributed in the coating, reducing stress concentration caused by uneven filler dispersion, thus significantly improving the coating's hardness, adhesion, and impact resistance. Furthermore, the addition of antioxidant 168 delays resin aging, and urea-formaldehyde resin enhances the coating's water resistance, extending its overall service life and making it suitable for long-term applications in complex environments.

[0034] 3. Through the dispersing effect of sodium polycarboxylate, the emulsifying effect of fatty alcohol polyoxyethylene ether, and the precise pH control of ammonia, the coating system achieves a stable colloidal dispersion, effectively avoiding the sedimentation and stratification problems of functional fillers, significantly improving storage stability, and extending the shelf life. The grinding process ensures the coating fineness is controlled at 30μm, and combined with the plasticizing effect of dioctyl adipate, reduces the coating viscosity, resulting in better leveling during application and reducing defects such as bubbles, pinholes, or sagging, thus improving the coating's forming quality.

[0035] 4. This invention uses ethyl acetate as the main solvent, which has moderate volatility and low residue. Combined with environmentally friendly additives such as stearic acid-modified nano-calcium carbonate, it reduces the release of harmful substances during the production and application of the coating. Simultaneously, the efficient utilization of functional fillers reduces the required dosage, lowering raw material consumption while ensuring near-infrared absorption performance. By optimizing the formulation ratio, the coating system avoids the environmental burden of excessive additives, achieving a synergy between high functionality and environmental friendliness, aligning with the development trend of green coatings. Detailed Implementation

[0036] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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.

[0037] Example 1: Preparation of near-infrared absorbing coating. The specific preparation steps are as follows:

[0038] S1. Add 15 parts of modified ferrite powder, 3 parts of sodium polycarboxylate, 2 parts of dioctyl adipate, 1 part of antioxidant 168, 8 parts of nano calcium carbonate, 10 parts of talc, and 1 part of fatty alcohol polyoxyethylene ether to 15 parts of ethyl acetate. Stir at 1200 r / min for 20 min, then sonicate at 200 W for 10 min. Repeat the stirring and sonication operation twice, for a total of 60 min.

[0039] S2. Add 45 parts of polyvinyl acetate resin and continue stirring at a stirring speed of 1200 r / min for 25 min to ensure that the resin and dispersion system are fully mixed. Then add 3 parts of modified graphite powder, stir at a low speed of 600 r / min for 10 min to initially disperse the graphite powder, and then adjust the stirring speed to 1300 r / min and stir at a high speed for 20 min to ensure that the graphite powder is evenly dispersed.

[0040] S3. Add 2 parts titanate coupling agent and 1 part urea-formaldehyde resin, adjust the stirring speed to 1000 r / min, stir for 10 min, then add the remaining 1 part urea-formaldehyde resin and 0.1 part ammonia water, continue stirring at 1000 r / min for 10 min, maintain the pH of the system at 8.5, and obtain the near-infrared absorbing coating semi-finished product.

[0041] S4. Add the semi-finished product to the sand mill. The grinding media of the sand mill is zirconia beads with a diameter of 0.8 mm. During grinding, the solid content of the material is controlled at 50%, and the grinding temperature is controlled at 30℃. Grind and test the fineness until the fineness of the coating reaches 30μm to obtain the final near-infrared absorbing coating.

[0042] Example 2: Preparation of near-infrared absorbing coating. The specific preparation steps are as follows:

[0043] S1. Add 25 parts of modified ferrite powder, 8 parts of sodium polycarboxylate, 6 parts of dioctyl adipate, 4 parts of antioxidant 168, 15 parts of nano calcium carbonate, 20 parts of talc, and 3 parts of fatty alcohol polyoxyethylene ether to 25 parts of ethyl acetate. Stir at 1200 r / min for 20 min, then sonicate at 200 W for 10 min. Repeat the stirring and sonication operation twice, for a total of 60 min.

[0044] S2. Add 60 parts of polyvinyl acetate resin and continue stirring at a stirring speed of 1200 r / min for 25 min to ensure that the resin and dispersion system are fully mixed. Then add 7 parts of modified graphite powder, stir at a low speed of 600 r / min for 10 min to initially disperse the graphite powder, and then adjust the stirring speed to 1300 r / min and stir at a high speed for 20 min to ensure that the graphite powder is evenly dispersed.

[0045] S3. Add 5 parts titanate coupling agent and 2 parts urea-formaldehyde resin, adjust the stirring speed to 1000 r / min, stir for 10 min, then add the remaining 3 parts urea-formaldehyde resin and 0.3 parts ammonia water, continue stirring at 1000 r / min for 10 min, maintain the pH of the system at 8.5, and obtain the near-infrared absorbing coating semi-finished product.

[0046] S4. Add the semi-finished product to a sand mill. The grinding media of the sand mill is zirconia beads with a diameter of 1.2 mm. During grinding, the solid content of the material is controlled at 60%, and the grinding temperature is controlled at 30-40℃. Grind and test the fineness until the fineness of the coating reaches 30μm to obtain the final near-infrared absorbing coating.

[0047] Example 3: Preparation of near-infrared absorbing coating. The specific preparation steps are as follows:

[0048] S1. Add 20 parts of modified ferrite powder, 5 parts of sodium polycarboxylate, 4 parts of dioctyl adipate, 2 parts of antioxidant 168, 11 parts of nano calcium carbonate, 15 parts of talc, and 2 parts of fatty alcohol polyoxyethylene ether to 20 parts of ethyl acetate. Stir at 1200 r / min for 20 min, then sonicate at 200 W for 10 min. Repeat the stirring and sonication operation twice, for a total of 60 min.

[0049] S2. Add 52 parts of polyvinyl acetate resin and continue stirring at a stirring speed of 1200 r / min for 25 min to ensure that the resin and dispersion system are fully mixed. Then add 5 parts of modified graphite powder, stir at a low speed of 600 r / min for 10 min to initially disperse the graphite powder, and then adjust the stirring speed to 1300 r / min and stir at a high speed for 20 min to ensure that the graphite powder is evenly dispersed.

[0050] S3. Add 3 parts titanate coupling agent and 1 part urea-formaldehyde resin, adjust the stirring speed to 1000 r / min, stir for 10 min, then add the remaining 2 parts urea-formaldehyde resin and 0.2 parts ammonia water, continue stirring at 1000 r / min for 10 min, maintain the pH of the system at 8.5, and obtain the near-infrared absorbing coating semi-finished product.

[0051] S4. Add the semi-finished product to the sand mill. The grinding media of the sand mill is zirconia beads with a diameter of 1.0 mm. During grinding, the solid content of the material is controlled at 55%, and the grinding temperature is controlled at 35℃. Grind and test the fineness until the fineness of the coating reaches 30μm to obtain the final near-infrared absorbing coating.

[0052] Example 4: Preparation of modified ferrite powder. The specific preparation steps are as follows:

[0053] A1. Add 100g of ferrite powder to 500mL of a mixed acid solution consisting of 5% hydrochloric acid and 2% sulfuric acid in a volume ratio of 3:1. Heat the solution to 40℃ within 10min, and then stir at 40℃ for 1h. The stirring rate is controlled at 600r / min for the first 30min and increased to 800r / min for the next 30min. After the reaction is complete, wash the solid once with deionized water, filter it, and redisperse the solid in 200mL of deionized water. Add 1g of nano zinc oxide powder and continue stirring at 800r / min for 30min. Then wash the solid once with 1% sodium bicarbonate solution, add 300mL of 0.5% ammonium dihydrogen phosphate solution, and soak it at 50℃ for 30min. Finally, wash the solid repeatedly with deionized water until the filtrate is neutral. Filter the solid and collect it. Place the solid in a forced-air drying oven and dry it at 70℃ for 4h. Turn the solid over every 1h during the drying process.

[0054] A2. Take 100g of the first modified ferrite powder and disperse it in 400mL of deionized water. Disperse it by ultrasonication at 100W for 15min. Add 3g of titanate coupling agent and 2g of silica sol. Stir the mixture at 800r / min at 50℃ for 1.5h. After the reaction is complete, filter the solid and collect it. Wash the solid twice with deionized water and once with 5% ethanol aqueous solution. After filtration, dry the solid at 60℃ for 5h.

[0055] A3. Add 100g of the second modified ferrite powder to 300mL of ethanol, stir and disperse for 10min, add 8g of 5% polyvinyl alcohol solution and 1g of stearic acid, stir and react at 700r / min at 60℃ for 1.5h, adding 20mL of ethanol every 20min to replenish the amount of volatilization; after the reaction is completed, filter, collect the solid, wash twice with ethanol, and dry the solid at 50℃ for 6h to obtain modified ferrite powder.

[0056] Example 5: Preparation of modified graphite powder. The specific preparation steps are as follows:

[0057] B1. Add 50g of graphite powder to 300mL of 10% nitric acid solution, and simultaneously add 1.5g of potassium permanganate. Stir at 600r / min at 50℃ for 1.5h. After the reaction is complete, add 0.5g of ferrous sulfate powder and continue stirring at 600r / min for 30min. After the reaction is complete, slowly add sodium sulfite solution until no more bubbles are produced. Then wash repeatedly with deionized water until the filtrate is neutral. Collect the solid by vacuum filtration and place it in a forced-air drying oven at 80℃ for 3h. Stir twice during the drying process.

[0058] B2. Take 50g of the first modified graphite powder and disperse it in 200mL of a 1:1 volume ratio ethanol / water mixed solution. Disperse it ultrasonically at 120W for 20min. Then add 1g of fatty alcohol polyoxyethylene ether and 0.5g of fumed silica. Stir the mixture at 45℃ for 1.5h. The stirring rate is 600r / min for the first h and then increased to 900r / min for the last 30min. After the reaction is complete, filter the solid and collect it. Wash the solid twice with a 1:1 volume ratio ethanol / water mixed solution and once with deionized water. After filtration, dry the solid at 70℃ for 4h.

[0059] B3. Add 50g of the second modified graphite powder to 250mL of deionized water, stir and disperse for 15min, then add 2g of titanate coupling agent and 0.5g of polyethylene wax emulsion with a solid content of 30%, and stir and react at 55℃ and 600r / min for 1h. After the reaction is completed, filter and collect the solid. Wash once with deionized water, dry the solid at 60℃ in a forced air for 5h, and pass it through a 200-mesh sieve to obtain modified graphite powder.

[0060] Comparative Example 1: Near-infrared absorbing coating was prepared. The specific preparation steps are as follows:

[0061] The remaining steps remain the same, except that the modified ferrite powder in Example 3 is replaced with untreated ferrite powder to prepare a near-infrared absorbing coating.

[0062] Comparative Example 2: Near-infrared absorbing coating was prepared. The specific preparation steps are as follows:

[0063] The remaining steps remain the same, except that the modified graphite powder in Example 3 is replaced with untreated graphite powder to prepare a near-infrared absorbing coating.

[0064] Performance testing

[0065] Test Project Test Standards Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Direct absorption ratio of sunlight (800-2500nm) GB / T 2680-2021 82.3% 85.6% 86.8% 65.2% 68.5% Coating hardness (pencil hardness) GB / T 6739-2022 2H 2H 3H HB HB Adhesion (cross-cut test, grade) GB / T 9286-2021 Level 1 Level 1 Level 0 Level 3 Level 2 Impact resistance (1kg drop weight, passing height / cm) GB / T 1732-2020 50 52 55 30 35 Storage stability (50°C, no stratification / day) GB / T 6753.3-1986 60 62 65 25 30 Water resistance (23℃ distilled water, no change / h) GB / T 1733-1993 240 270 300 120 150

[0066] In performance tests, the near-infrared absorbing coatings of Examples 1-3 exhibited excellent performance in direct solar absorptivity (800-2500nm), reaching 82.3%, 85.6%, and 86.8%, respectively; the coating hardness was 2H-3H, adhesion was grade 0-1, impact resistance was 50-55cm, storage stability was 60-65d, and water resistance was 240-300h. In contrast, Comparative Examples 1 and 2, using unmodified ferrite and graphite powder, showed a significant decrease in all performance aspects, with absorptivity of only 65.2% and 68.5%, respectively, and substantial reductions in hardness, adhesion, and impact resistance.

[0067] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

Claims

1. A near-infrared absorbing coating, characterized in that: It contains the following raw materials in parts by weight: 45-60 parts polyvinyl acetate resin, 15-25 parts modified ferrite powder, 3-7 parts modified graphite powder, 3-8 parts sodium polycarboxylate, 2-6 parts dioctyl adipate, 1-4 parts antioxidant 168, 15-25 parts ethyl acetate, 8-15 parts nano calcium carbonate, 2-5 parts titanate coupling agent, 10-20 parts talc, 1-3 parts fatty alcohol polyoxyethylene ether, 2-5 parts urea-formaldehyde resin, and 0.1-0.3 parts ammonia.

2. The near-infrared absorbing coating according to claim 1, characterized in that: The nano-calcium carbonate has a cubic structure and its surface is modified with stearic acid. The specific operation is as follows: the nano-calcium carbonate is dispersed in an ethanol / water solution with a volume ratio of 3:1 at a mass ratio of 100:3 to stearic acid, stearic acid is added and stirred, and the mixture is reacted at 60°C for 2 hours, then filtered and dried.

3. The near-infrared absorbing coating according to claim 1, characterized in that: The modified ferrite powder is prepared using the following specific steps: A1. Ferrite powder was added to a mixed acid solution consisting of 5% hydrochloric acid and 2% sulfuric acid in a volume ratio of 3:

1. The temperature was raised to 40°C within 10 minutes, and then stirred at 40°C for 1 hour. The stirring rate was controlled at 600 r / min for the first 30 minutes and increased to 800 r / min for the next 30 minutes. After the reaction was completed, the solid was washed once with deionized water, filtered, and then redispersed in deionized water. Nano zinc oxide powder was added, and the reaction was stirred at 800 r / min for another 30 minutes. Then, the solid was washed once with 1% sodium bicarbonate solution, and then 0.5% ammonium dihydrogen phosphate solution was added. The solid was soaked at 50°C for 30 minutes. Finally, the solid was washed repeatedly with deionized water until the filtrate was neutral. The solid was collected by filtration and placed in a forced-air drying oven at 70°C for 4 hours. The solid was turned over every hour during the drying process. A2. Disperse the first modified ferrite powder in deionized water and sonicate for 15 min at 100 W. Add titanate coupling agent and silica sol and stir at 800 r / min at 50 °C for 1.5 h. After the reaction is complete, filter and collect the solid. Wash twice with deionized water and once with 5% ethanol aqueous solution. After filtration, dry the solid at 60 °C for 5 h. A3. Add the modified ferrite powder to ethanol and stir to disperse for 10 min. Add 5% (w / w) polyvinyl alcohol solution and stearic acid. Stir at 700 r / min at 60℃ for 1.5 h. Add ethanol every 20 min to replenish the amount of volatiles during the reaction. After the reaction is complete, filter and collect the solid. Wash the solid twice with ethanol and dry it in a forced-air dryer at 50℃ for 6 h to obtain the modified ferrite powder.

4. The near-infrared absorbing coating according to claim 3, characterized in that: The ratio of ferrite powder, mixed acid solution, deionized water, nano zinc oxide powder, and ammonium dihydrogen phosphate solution in A1 is 100g:500mL:200mL:1g:300mL; wherein the ferrite powder is spinel-type or hexagonal ferrite. The ratio of the first modified ferrite powder, deionized water, titanate coupling agent, and silica sol in A2 is 100g:400mL:3g:2g. The amounts of the second-modified ferrite powder, ethanol, polyvinyl alcohol solution, and stearic acid in A3 are 100g:380mL:8g:1g; of which 300mL of ethanol is used to disperse the second-modified ferrite powder, and 80mL is used to replenish 20mL every 20min thereafter.

5. The near-infrared absorbing coating according to claim 4, characterized in that: The stirring rate of the mixed acid solution reaction in A1 is controlled in stages. The rate difference in different reaction stages ensures the uniformity of the etching reaction of ferrite powder in the mixed acid, and works in conjunction with temperature conditions to ensure the surface modification effect.

6. The near-infrared absorbing coating according to claim 1, characterized in that: The modified graphite powder is prepared using the following specific steps: B1. Add graphite powder to a 10% (w / w) nitric acid solution, and simultaneously add potassium permanganate. Stir at 600 r / min at 50°C for 1.5 h. After the reaction is complete, add ferrous sulfate powder and continue stirring at 600 r / min for 30 min. After the reaction is complete, slowly add sodium sulfite solution until no more bubbles are produced. Then wash repeatedly with deionized water until the filtrate is neutral. Collect the solid by vacuum filtration and place it in a forced-air drying oven at 80°C for 3 h. Stir twice during the drying process. B2. Take the first modified graphite powder and disperse it in a 1:1 volume ratio ethanol / water mixed solution. Disperse it ultrasonically at 120W for 20min. Then add fatty alcohol polyoxyethylene ether and fumed silica. Stir the reaction at 45℃ for 1.5h. The stirring rate is 600r / min for the first h and then increased to 900r / min for the last 30 h. After the reaction is complete, filter the solid and collect it. Wash it twice with a 1:1 volume ratio ethanol / water mixed solution and then wash it once with deionized water. After filtration, dry the solid at 70℃ for 4h. B3. Add the modified graphite powder to deionized water and stir to disperse for 15 min. Then add titanate coupling agent and polyethylene wax emulsion with a solid content of 30%. Stir and react at 600 r / min at 55℃ for 1 h. After the reaction is completed, filter and collect the solid. Wash once with deionized water and dry the solid at 60℃ for 5 h. After drying, pass through a 200-mesh sieve to obtain modified graphite powder.

7. The near-infrared absorbing coating according to claim 6, characterized in that: The ratio of graphite powder, nitric acid solution, potassium permanganate, and ferrous sulfate powder in B1 is 50g:300mL:1.5g:0.5g; The ratio of the first modified graphite powder, ethanol / water mixed solution, fatty alcohol polyoxyethylene ether, and fumed silica in B2 is 50g:200mL:1g:0.5g. The ratio of the modified graphite powder, deionized water, titanate coupling agent, and polyethylene wax emulsion in B3 is 50g:250mL:2g:0.5g.

8. A method for preparing a near-infrared absorbing coating, characterized in that: Specifically, it includes the following steps: S1. Add modified ferrite powder, sodium polycarboxylate, dioctyl adipate, antioxidant 168, nano calcium carbonate, talc, and fatty alcohol polyoxyethylene ether to ethyl acetate. Stir at 1200 r / min for 20 min, then sonicate at 200 W for 10 min. Repeat the stirring and sonication process twice, for a total of 60 min. S2. Add polyvinyl acetate resin and continue stirring at a stirring speed of 1200 r / min for 25 min to ensure that the resin and dispersion system are fully mixed. Then add modified graphite powder and stir at a low speed of 600 r / min for 10 min to initially disperse the graphite powder. Then adjust the stirring speed to 1300 r / min and stir at a high speed for 20 min to ensure that the graphite powder is evenly dispersed. S3. Add titanate coupling agent and part of urea-formaldehyde resin, adjust the stirring speed to 1000 r / min, stir for 10 min, then add the remaining urea-formaldehyde resin and ammonia water, continue stirring at 1000 r / min for 10 min, maintain the pH of the system at 8.5, and obtain the near-infrared absorbing coating semi-finished product. S4. Add the semi-finished product to the sand mill, control the grinding temperature at 30-40℃, grind and test the fineness until the coating fineness reaches 30μm, and obtain the final near-infrared absorbing coating.

9. The method for preparing a near-infrared absorbing coating according to claim 8, characterized in that: The grinding media of the sand mill in S4 is zirconia beads with a diameter of 0.8-1.2 mm, and the solid content of the material is controlled at 50%-60% during grinding.