Building exterior wall coating and preparation method thereof

Abstract

The present application relates to a kind of building outer wall paint and its preparation method, belong to building paint technical field.The paint is composed of composite inorganic-organic hybrid film-forming binder, nano composite flame-retardant filler, biological base thickening agent, light response type hydrophobic auxiliary agent, low-foaming wetting dispersant and deionized water.Composite binder is formed by interpenetrating network structure by compounding sodium silicate and phosphate modified polyacrylate emulsion, with inorganic phase hardness and organic phase flexibility;Nanometer flame-retardant filler uses Mg-Al layered double hydroxide and cerium dioxide core-shell structure, and realizes multistage flame-retardant by loading zinc borate.Preparation method includes ultrasonic assisted emulsion polymerization, electrostatic self-assembly filler composite and gradient curing process, and adopts layered spraying in construction, combined with ultraviolet activation technology.The present application has excellent flame retardancy, super-hydrophobic self-cleaning and long-acting weather resistance.

Description

Technical Field

[0001] This invention relates to the field of architectural coatings technology, specifically to an exterior wall coating and its preparation method. Background Technology

[0002] Exterior wall coatings, as a crucial component of building protection systems, directly impact the durability, safety, and aesthetics of buildings. Traditional exterior wall coatings primarily consist of organic resins or inorganic silicate materials as film-forming bases, supplemented with pigments, fillers, and functional additives. Based on functional requirements, commercially available products are mainly categorized into decorative, waterproof, heat-insulating, and flame-retardant types. With rising building safety standards and increasingly stringent environmental regulations, modern exterior wall coatings must possess high flame retardancy, weather resistance, self-cleaning capabilities, and environmental friendliness, placing higher demands on material formulation design and manufacturing processes. However, existing technologies still face the following bottlenecks that urgently need to be addressed:

[0003] Traditional inorganic coatings, while possessing high hardness and weather resistance, are brittle, have poor adhesion, and are prone to cracking due to substrate deformation. Organic coatings, on the other hand, exhibit excellent flexibility but suffer from poor high-temperature resistance, insufficient flame retardancy, and are susceptible to yellowing and aging upon prolonged exposure to ultraviolet light. A single-base system cannot achieve a synergistic optimization of hardness and flexibility, failing to meet the long-term protection requirements under complex climatic conditions. Existing flame-retardant coatings often employ a single flame retardant, resulting in issues such as high addition amounts and uneven dispersion. Coating thickeners generally rely on synthetic polymers, leading to poor biodegradability and high VOC emissions. While natural polymers are environmentally friendly, their poor shear stability makes them prone to water separation and sedimentation during storage, failing to meet the rheological performance requirements of high-solids coatings. Traditional superhydrophobic coatings often use fluorinated resins or silicone materials, which, while exhibiting high static contact angles, lack dynamic self-cleaning capabilities. Contaminants easily adhere to the coating surface, and long-term ultraviolet radiation causes degradation of fluorinated segments, significantly reducing hydrophobic properties. Furthermore, existing hydrophobic additives and flame-retardant fillers have poor compatibility, easily causing microstructural defects in the coating. The dispersion stability of nanofillers in high-solids coatings is poor, and traditional mechanical stirring easily introduces air bubbles, leading to defects such as pinholes and orange peel in the coating film. In addition, single spraying processes are difficult to achieve a gradient distribution of functional components, and inorganic-organic phase separation is common during curing, affecting the coating's density and interfacial bonding strength.

[0004] The aforementioned issues limit the application of exterior wall coatings in high-rise buildings, extreme climate zones, and scenarios with stringent fire safety requirements. Therefore, developing an exterior wall coating that combines high flame retardancy, long-lasting weather resistance, intelligent self-cleaning, and environmental friendliness is of particular importance. Summary of the Invention

[0005] To address the problems existing in the background art, the present invention provides an exterior wall coating for buildings, which is made from the following raw materials in parts by weight:

[0006] Composite inorganic-organic hybrid film-forming base material: 50 parts, which is composed of potassium sodium silicate solution and modified polyacrylate emulsion with 3% by mass of phosphate functional monomer at a mass ratio of 1:1.2;

[0007] Nanocomposite flame retardant filler: 28 parts, including Mg-Al layered dihydroxy composite metal oxide LDH and nano-cerium oxide in a mass ratio of 3:1. The complex, wherein the LDH loading is 5% zinc borate;

[0008] Bio-based thickener: 2 parts, a mixture of hydroxypropyl guar gum and sodium alginate in a mass ratio of 2:1;

[0009] Photoresponsive hydrophobic additive: 0.8 parts, which is titanium dioxide nanoparticles modified with fluorinated siloxane;

[0010] Low-foaming wetting and dispersing agent: 0.7 parts, which is polyether-modified polysiloxane;

[0011] Deionized water: Balance.

[0012] Furthermore, the chemical formula of the Mg-Al layered dihydroxy complex metal oxide is as follows: The preparation process is as follows:

[0013] First, and Prepare a mixed salt solution at a 3:1 molar ratio, and under pH 9.5, 60-70℃, and nitrogen protection, react with... The precipitant co-precipitation reaction was carried out for 2 hours, and the precursor was obtained by centrifugation and washing. Subsequently, it was hydrothermally treated at 120-140℃ for 12 hours, followed by spray drying to obtain a highly crystalline intermediate; finally, it was dispersed in... In solution, ion exchange was performed at 50°C for 24 hours, so that... Completely replace interlayer The target product was obtained after washing and drying. .

[0014] Furthermore, the preparation method of the bio-based thickener is as follows: using natural guar gum as raw material, it is reacted with propylene oxide at a molar ratio of 1:1.2 under alkaline conditions at 60℃ for 4 hours to introduce hydroxyl groups through a hydroxypropyl substitution reaction. After precipitation with ethanol and drying, hydroxypropyl guar gum is obtained. Using brown algae as raw material, it is decalcified with dilute hydrochloric acid, extracted with sodium carbonate, filtered, and precipitated with ethanol to obtain high-purity sodium alginate. Hydroxypropyl guar gum and sodium alginate are dissolved in deionized water at a mass ratio of 2:1 and stirred at 50℃ for 1 hour to form a hydrogen bond-ionic bond synergistic network, finally obtaining the bio-based thickener.

[0015] Furthermore, the preparation method of the photoresponsive hydrophobic additive is as follows: Tetrabutyl titanate is mixed with anhydrous ethanol, dilute nitric acid is added dropwise for hydrolysis, and the mixture is aged at 60°C for 12 hours. Centrifugation yields particles with a diameter of 20-50 nm. ;Will Dispersed in isopropanol, perfluorooctyltriethoxysilane was added, and the mixture was refluxed at 80°C for 6 hours, resulting in the hydrolysis and condensation of the siloxane. Surface grafting with fluorine-containing segments; enhanced photoresponse properties: UV irradiation treatment for 2 hours, final product specific surface area ≥150. .

[0016] Furthermore, the preparation method of the low-foaming wetting and dispersing agent is as follows:

[0017] Using octamethylcyclotetrasiloxane D4 as monomer and hexamethyldisiloxane as end-capping agent, ring-opening polymerization was carried out at 90℃ for 6 h under 1% (w / w) sulfuric acid catalysis to obtain polydimethylsiloxane PDMS with a viscosity of 500-800 mPa·s. PDMS and allyl polyoxyethylene ether were reacted with a platinum catalyst at a molar ratio of 1:1.2 via hydrosilylation at 110℃ for 5 h to introduce polyether segments and form a polyether-siloxane block structure. Through the steric hindrance effect of the polyether segments, the dynamic surface tension was reduced to ≤30 mN / m, and the final product had a foaming height of <10 mm.

[0018] This invention provides a method for preparing building exterior wall coatings, comprising the following steps:

[0019] S1. Potassium sodium silicate solution and modified polyacrylate emulsion are premixed at 50°C and 300 rpm for 1 hour to form a composite base material;

[0020] S2. Combining LDH with nano Dispersed in deionized water for 30 min under ultrasonic assistance, zinc borate was added and the temperature was raised to 80℃ for 2 h. After drying and grinding, nano-composite flame retardant filler was obtained.

[0021] S3. Mix the composite base material obtained in S1, the filler obtained in S2, and the bio-based thickener, photoresponsive hydrophobic additive, and low-foaming wetting and dispersing agent, and disperse them in a disperser at 1200 rpm for 40 min.

[0022] S4. Adjust the pH to 9.0, filter and package.

[0023] Furthermore, the detailed steps of S1 are as follows:

[0024] S11. Mix butyl methacrylate and ethylene glycol phosphate methacrylate in a mass ratio of 9:1 with deionized water, add 0.1% ammonium persulfate as an initiator, and react at 75-80℃ for 4 hours under nitrogen protection to obtain a phosphate-functionalized polyacrylate emulsion.

[0025] S12. The initiator was added dropwise in three batches during the reaction, with an interval of 1 hour between each batch, and the reaction was assisted by ultrasound at a frequency of 40 kHz throughout the process.

[0026] S13. Preheat the potassium sodium silicate solution to 45°C, slowly add the modified emulsion obtained in S11, control the mass ratio of the two to be 1:1, and adjust the pH to 8.8-9.0 with ammonia.

[0027] S14. Under stirring at 500 rpm, add 0.5% (w / w) of silane coupling agent KH-570 dropwise to the mixture at a dropping rate of 2 mL / min. After the addition is complete, raise the temperature to 60℃ and continue the reaction for 2 hours to form an inorganic phase. Interpenetrating structure of network and organic phase polyacrylate chains.

[0028] Furthermore, the specific steps of S2 are as follows:

[0029] S21. Nanoparticles The mixture was mixed with a 5% citric acid solution at a mass ratio of 1:10, treated at 60℃ and ultrasonic power of 200W for 30 min, and centrifuged to obtain citric acid-modified material with a negatively charged surface. ;

[0030] S22. Modification of Mg-Al layered dihydroxy composite metal oxide LDH with the product obtained in S21 Add the LDH to deionized water at a mass ratio of 3:1, disperse for 30 minutes under ultrasonic assistance at a frequency of 40 kHz, and control the pH of the system to 9.0, so that the positive charge of the LDH layer is neutralized by the surrounding environment. Negative charges self-assemble through electrostatic adsorption, forming LDH as the core. A complex of shells;

[0031] S23. Add zinc borate to the resulting mixture. Its mass is LDH- 5% of the total mass of the composite was heated to 80℃ and reacted for 2 hours, allowing zinc borate to form between the LDH layers and... The surface is bonded through hydroxyl condensation reaction to form a stable supported structure;

[0032] S24. Spray dry the reaction solution to obtain the particle size. The primary particles were then ball-milled for 2 hours under an inert atmosphere to obtain a specific surface area of ​​180-200. Nanocomposite flame-retardant fillers.

[0033] This invention provides a method for applying building exterior wall coatings, comprising the following steps:

[0034] Q1. Substrate pretreatment: Use high-pressure water jet with a pressure ≥20MPa to remove floating dust and loose layer from the substrate surface, then spray with silane coupling agent KH-570 solution with pH=9.0, and let stand for 30 minutes to form a chemical anchoring layer.

[0035] Q2. Layered spraying and photoactivation: Dilute the paint to a viscosity of 30-35s, and apply the first coat using an airless sprayer at a speed of 0.5m / s, achieving a wet film thickness of 80-100 mm. Immediately after spraying, irradiate with a 365nm wavelength UV lamp with an irradiance of 1.0W / cm² for 5 minutes to activate the superhydrophobic properties of the photoresponsive hydrophobic additive; after the base coat is surface dry, spray the second coat of undiluted paint, with a wet film thickness of 120mm. The spraying direction is perpendicular to the base layer at 90°. After spraying, let it stand for 10 minutes, and then irradiate it with ultraviolet light for another 10 minutes.

[0036] Q3. Gradient curing; Stage 1: Curing in a 40-50℃ drying oven for 24 hours, humidity ≤40%, to promote LDH- Interlayer hydroxyl condensation of flame-retardant fillers; Stage 2: Curing for 7 days at 15-35℃ and 50-80% humidity, with daily spraying of deionized water to promote the bonding between the potassium sodium silicate base and the filler. The carbonization reaction forms a dense... network;

[0037] Q4. Post-treatment: After curing, spray the surface with a fluorinated siloxane curing agent to form a self-healing hydrophobic film.

[0038] LDH (Mg-Al layered dihydroxy complex metal oxide);

[0039] Chemical formula: It is a layered structure formed by magnesium and aluminum hydroxide plates bridged by common edge hydroxyl groups. The interlayer adsorption can exchange anions and water molecules, and has functions such as flame retardancy and adsorption.

[0040] Nano-cerium dioxide;

[0041] Cerium oxide nanoparticles possess UV shielding and catalytic properties. After modification with citric acid, their surface carries a negative charge, enhancing their flame retardant and photocatalytic activity.

[0042] Zinc borate;

[0043] Chemical formula: A flame retardant that decomposes upon heating, absorbs heat, and releases flame-retardant gas, and is loaded between LDH layers.

[0044] KH-570 (silane coupling agent);

[0045] Chemical name: γ-methacryloyloxypropyltrimethoxysilane; used for interfacial bonding of inorganic-organic phases to enhance material compatibility.

[0046] Perfluorooctyltriethoxysilane;

[0047] Chemical formula: Fluorosilane compounds, used for modification Nanoparticles impart superhydrophobicity and photoresponsive properties.

[0048] D4 (octamethylcyclotetrasiloxane);

[0049] Chemical formula: Monomers of polydimethylsiloxane are used to prepare low-foaming wetting and dispersing agents.

[0050] Electrostatic self-assembly;

[0051] Core-shell structures spontaneously form through electrostatic attraction between particles with opposite charges.

[0052] Interpenetrating network structure;

[0053] The inorganic silicon-oxygen network and the organic polyacrylate chain interpenetrate with each other, improving the mechanical strength and weather resistance of the coating.

[0054] Photoresponsive hydrophobicity;

[0055] Fluorosiloxane modified Under ultraviolet light, the surface chemical structure changes, forming a superhydrophobic state.

[0056] Dynamic surface tension;

[0057] Wetting and dispersing agents reduce the surface tension of coatings, reduce foaming, and improve the dispersibility of fillers.

[0058] Specific surface area;

[0059] High specific surface area enhances the interfacial interaction between filler and matrix, improving flame retardancy and catalytic efficiency.

[0060] Particle size ;

[0061] Nanocomposite flame retardant filler This indicates that 50% of the particles have a particle size smaller than this value, which affects the leveling and film-forming properties of the coating.

[0062] PDMS (polydimethylsiloxane);

[0063] structure: The base polymer of the low-foaming wetting and dispersing agent is modified with polyether to reduce surface tension.

[0064] APS (ammonium persulfate);

[0065] Chemical formula: Free radical initiators are used in the polymerization of polyacrylate emulsions.

[0066] OI (Oxygen Index);

[0067] The minimum oxygen concentration required for a material to sustain combustion in an oxygen-nitrogen mixture, such as OI ≥ 30%, is classified as A2 flame retardant.

[0068] Contact angle;

[0069] Characterizes surface hydrophobicity; the larger the angle, the stronger the hydrophobicity.

[0070] Smoke density (SDR);

[0071] Definition: The concentration of smoke produced when a material burns; the lower the value, the less harmful the smoke.

[0072] Peak heat release rate;

[0073] unit: The maximum amount of heat released per unit area when a material burns; the lower the value, the better the flame retardancy.

[0074] The beneficial effects achieved by this invention are as follows:

[0075] I. This invention constructs an interpenetrating structure of inorganic silicon-oxygen network and organic polymer chains by compounding potassium sodium silicate solution with phosphate-functionalized polyacrylate emulsion. The inorganic phase imparts high hardness and weather resistance to the coating, while the organic phase provides flexibility and adhesion. The synergistic effect of the two overcomes the performance limitations of traditional single-base materials. This hybrid design significantly improves the mechanical strength and environmental adaptability of the coating, while enhancing its bonding ability with the substrate, solving the problems of easy cracking and poor water resistance of traditional coatings.

[0076] II. This invention employs a core-shell structure of layered dihydroxyl composite metal oxide (LDH) and nano-cerium oxide (cerium dioxide), loaded with zinc borate flame retardant. The layered barrier effect of LDH complements the UV shielding properties of cerium dioxide, while the thermal decomposition endothermic effect of zinc borate further enhances the flame retardant layers. This multi-level structure not only achieves highly efficient flame retardancy but also delays material aging through photocatalysis and free radical capture mechanisms, significantly improving the fire safety and long-term durability of the coating.

[0077] Third, this invention, through the compounding of hydroxypropyl guar gum and sodium alginate, utilizes the synergistic formation of a three-dimensional network structure through hydrogen and ionic bonds, pioneering a new application model for natural polymer materials in coating thickening. This system possesses both excellent rheological control capabilities and environmentally friendly properties, ensuring the storage stability of coatings while avoiding the ecological burden of traditional synthetic thickeners, embodying an innovative concept of sustainable resource utilization.

[0078] IV. This invention achieves a smart combination of hydrophobicity and photocatalytic activity through fluorinated siloxane-modified titanium dioxide nanoparticles. Ultraviolet irradiation triggers surface chemical reconstruction, forming a dynamic superhydrophobic interface that endows the coating with self-cleaning and anti-fouling capabilities. Simultaneously, the photocatalytic properties decompose pollutants, overcoming the limitations of traditional hydrophobic materials with their single function and providing an innovative solution for long-term cleanliness of building coatings.

[0079] V. This invention designs a polyether-siloxane block dispersant, which achieves efficient dispersion of fillers and suppression of bubbles through steric hindrance effect and dynamic surface tension regulation. It overcomes the industry problem of easy foaming and uneven dispersion in high-solids coatings, ensuring film uniformity and surface smoothness, while simplifying the construction process and significantly improving coating efficiency and quality stability.

[0080] VI. This invention employs a multi-level composite and interfacial synergistic method in its preparation. A silane coupling agent bridges the inorganic silicon-oxygen network with the organic polymer chain, achieving chemical bonding and interpenetrating structure between the inorganic and organic phases. Electrostatic self-assembly technology is used to construct an LDH-cerium dioxide core-shell filler, which, combined with in-situ loaded zinc borate, forms a multi-level flame-retardant system. Simultaneously, the rheological properties of the system are regulated through the hydrogen-ionic bond synergistic network of a bio-based thickener. This method overcomes the limitations of simple mixing of traditional coating components, significantly enhancing material compatibility, filler dispersion uniformity, and system stability. It endows the coating with excellent mechanical properties and flame-retardant efficiency while reducing production energy consumption and process complexity.

[0081] VII. Regarding the construction method, this invention is based on a dynamic functional activation and gradient structure control scheme. Through layered spraying combined with in-situ UV-triggered hydrophobic interface reconstruction, the superhydrophobic properties of the coating are activated on demand. Cross-spraying and staged curing strategies promote the carbonization of the inorganic network and the orderly arrangement of the flexible chains of the organic phase, forming a dense, gradient composite structure. This method effectively solves the problems of single function and weak interfacial bonding in traditional coatings, significantly improving the coating's environmental adaptability, self-cleaning ability, and long-term durability, while reducing construction energy consumption and maintenance costs, meeting the high-performance building protection needs under complex climatic conditions. Attached Figure Description

[0082] Figure 1 This is a flowchart of the method for preparing building exterior wall coatings according to the present invention. Detailed Implementation

[0083] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. In addition, the forms of the various structures described in the following embodiments are merely illustrative. The present invention is not limited to the structures described in the following embodiments. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0084] The building exterior wall coating of the present invention is composed of the following core components;

[0085] A composite inorganic-organic hybrid film-forming matrix; composed of potassium sodium silicate solution and phosphate-functionalized polyacrylate emulsion at a mass ratio of 1:1.2. Potassium sodium silicate provides inorganic silicon oxides. The network framework enhances weather resistance and hardness; the phosphate-modified polyacrylate emulsion bonds with the inorganic phase through phosphate groups to form an organic-inorganic interpenetrating network, which improves adhesion and flexibility.

[0086] Nanocomposite flame retardant filler; nano-cerium oxide modified with Mg-Al layered dihydroxyoxide LDH and citric acid. It is composed of a 3:1 composite. The LDH interlayer is loaded with 5% zinc borate, which decomposes upon heating, absorbing heat and releasing flame-retardant gases. By reducing free radical generation through ultraviolet shielding, and in conjunction with the "lamellar barrier effect" of LDH, flame propagation is blocked. Both components form a core-shell structure through electrostatic self-assembly, achieving a specific surface area of ​​180-200 nm. This enhances the dispersibility and flame retardant efficiency of the filler.

[0087] Auxiliary functional components; the bio-based thickener hydroxypropyl guar gum / sodium alginate is formulated to stabilize the system through a hydrogen-ionic bond network;

[0088] Photoresponsive hydrophobic additives modified with fluorosiloxane Under ultraviolet light irradiation, a superhydrophobic surface is formed with a contact angle >150°;

[0089] Low-foaming wetting and dispersing agent polyether modified polysiloxane reduces dynamic surface tension to below 30 mN / m, reducing foaming and improving filler dispersibility.

[0090] The preparation method of the composite matrix is ​​as follows: preheat the potassium sodium silicate solution to 45°C, slowly add it to the phosphate ester modified polyacrylate emulsion, add silane coupling agent KH-570 dropwise, react at 60°C for 2 hours to form an interpenetrating structure of inorganic silicon oxygen network and organic chain.

[0091] The preparation method of flame-retardant filler is as follows: Mg-AlLDH is synthesized by co-precipitation, followed by hydrothermal crystallization and ion exchange, and then modified with citric acid. Sonicational self-assembly at pH 9.0 forms an LDH-based core. A composite material with a shell was then loaded with zinc borate and subjected to a spray-drying-ball milling process to obtain high specific surface area nanofillers 5-8. Particle size.

[0092] nanometer Modification; hydrolysis of tetrabutyl titanate to generate nanoparticles Then, it was refluxed with perfluorooctyltriethoxysilane at 80°C for 6 hours, and the superhydrophobic properties were activated by grafting fluorine-containing segments through siloxane condensation and ultraviolet irradiation for 2 hours.

[0093] Bio-based thickener: Guar gum modified with hydroxypropylation is mixed with sodium alginate at a ratio of 2:1 and stirred at 50°C to form a synergistic thickening network.

[0094] Low-foaming dispersant; polydimethylsiloxane (PDMS) and allyl polyoxyethylene ether are introduced into the polyether chain via hydrosilylation to form a block structure to reduce foaming.

[0095] Coating mixing and application method: Mix the composite base material, nano filler, thickener, hydrophobic additive and dispersant, disperse at 1200 rpm for 40 minutes, adjust the pH to 9.0 and then filter.

[0096] The application process employs layered spraying; immediately after the first wet film is applied, the hydrophobicity is activated with 365nm ultraviolet light, followed by a second cross-coating and secondary curing. Finally, a dense structure is formed through gradient curing at 40-50℃ followed by drying and then carbonization at room temperature. The network surface is coated with a fluorinated siloxane protective agent to achieve a self-healing hydrophobic film.

[0097] An exterior wall coating of the present invention is preferably made from the following raw materials in parts by weight:

[0098] Composite inorganic-organic hybrid film-forming base material: 50 parts, which is composed of potassium sodium silicate solution and modified polyacrylate emulsion with 3% by mass fraction of phosphate ester functional monomer at a mass ratio of 1:1.2;

[0099] Nanocomposite flame retardant filler: 28 parts, including Mg-Al layered dihydroxy composite metal oxide LDH and nano-cerium oxide in a mass ratio of 3:1. The complex, wherein the LDH loading is 5% zinc borate;

[0100] Bio-based thickener: 2 parts, a mixture of hydroxypropyl guar gum and sodium alginate in a mass ratio of 2:1;

[0101] Photoresponsive hydrophobic additive: 0.8 parts, which is titanium dioxide nanoparticles modified with fluorinated siloxane;

[0102] Low-foaming wetting and dispersing agent: 0.7 parts, which is polyether-modified polysiloxane;

[0103] Deionized water: Balance.

[0104] Preparation of Mg-Al layered dihydroxy complex metal oxide; the chemical formula of the Mg-Al layered dihydroxy complex metal oxide is as follows: The preparation process is as follows:

[0105] Will and Prepare a mixed salt solution at a 3:1 molar ratio, and under pH 9.5, 60-70℃, and nitrogen protection, react with... The precipitant co-precipitation reaction was carried out for 2 hours, and the precursor was obtained by centrifugation and washing. ;

[0106] Subsequently, the intermediate was hydrothermally treated at 120-140℃ for 12 hours and then spray-dried to obtain a highly crystalline intermediate.

[0107] Finally, disperse it. In solution, ion exchange was performed at 50°C for 24 hours, so that... Completely replace interlayer The target product was obtained after washing and drying. .

[0108] Surface modification and composite of nano-cerium oxide; the nano-cerium oxide After surface modification with citric acid, it forms a core-shell structure with LDH through electrostatic self-assembly, in which... Uniformly coated on the LDH surface, with a specific surface area of ​​180-200. The main LDH tiered panel is composed of and brucite formed by bridging of shared edge hydroxyl groups Layered structure, Partially In isomorphous substitution, the layers are positively charged; the interlayers adsorb exchangeable anions and water molecules through electrostatic interactions, forming an interlayer structure with an interlayer spacing of 0.77 nm.

[0109] Preparation of bio-based thickener: Natural guar gum was reacted with propylene oxide at a molar ratio of 1:1.2 at 60℃ for 4 hours under alkaline conditions to introduce hydroxyl groups through a hydroxypropyl substitution reaction. After precipitation with ethanol and drying, hydroxypropyl guar gum was obtained. High-purity sodium alginate was obtained by decalcification with dilute hydrochloric acid, alkaline extraction with sodium carbonate, filtration, and ethanol precipitation. Hydroxypropyl guar gum and sodium alginate were dissolved in deionized water at a mass ratio of 2:1 and stirred at 50℃ for 1 hour to form a hydrogen-ionic bond synergistic network, finally obtaining the bio-based thickener.

[0110] Preparation of photoresponsive hydrophobic additives: Tetrabutyl titanate was mixed with anhydrous ethanol, hydrolyzed by dropwise addition of dilute nitric acid, aged at 60℃ for 12 h, and centrifuged to obtain particles with a diameter of 20-50 nm. ;Will Dispersed in isopropanol, perfluorooctyltriethoxysilane was added, and the mixture was refluxed at 80°C for 6 hours, resulting in the hydrolysis and condensation of the siloxane. Surface grafting with fluorine-containing segments; enhanced photoresponse properties: UV irradiation treatment for 2 hours, final product specific surface area ≥150. .

[0111] Preparation of low-foaming wetting and dispersing agent: Using octamethylcyclotetrasiloxane D4 as monomer and hexamethyldisiloxane as end-capping agent, ring-opening polymerization was carried out at 90℃ for 6h under 1% mass fraction sulfuric acid catalysis to obtain polydimethylsiloxane PDMS with a viscosity of 500-800 mPa·s; PDMS and allyl polyoxyethylene ether were reacted with a platinum catalyst at 1:1.2 molar ratio via hydrosilylation reaction at 110℃ for 5h to introduce polyether segments and form a polyether-siloxane block structure; through the steric hindrance effect of polyether segments, the dynamic surface tension was reduced to ≤30mN / m, and the foaming height of the final product was <10mm.

[0112] Preparation methods of building exterior wall coatings; preparation of composite base materials S1; synthesis of phosphate ester functionalized polyacrylate emulsions:

[0113] Monomers: Butyl methacrylate (BA) + ethylene glycol phosphate methacrylate (PEG-PMA);

[0114] Initiator: Ammonium persulfate (APS);

[0115] Reaction formula: ;

[0116] Phosphate groups provide bonding sites with the inorganic phase.

[0117] Sodium potassium silicate Reaction with silane coupling agent KH-570:

[0118] Reaction formula: ;

[0119] It forms an interpenetrating network with the polyacrylate chains, enhancing mechanical strength.

[0120] Preparation of nanocomposite flame-retardant fillers S2; Preparation of Mg-AlLDH precursor:

[0121] Coprecipitation reaction ;

[0122] Ion exchange It then forms a stable layered structure.

[0123] Surface modification and lamination:

[0124] Citric acid and Surface hydroxyl groups coordinate with negative charges:

[0125]

[0126] LDH positive charge and Core-shell structures are formed through electrostatic self-assembly.

[0127] Hydroxyl condensation reaction:

[0128]

[0129] Synthesis of bio-based thickeners; Ring-opening reaction of guar gum with propylene oxide:

[0130]

[0131] The introduction of hydroxypropyl groups improves water solubility and thickening efficiency.

[0132] Sodium alginate extraction:

[0133] Brown algae acid Decalcification, alkali Sodium alginate was extracted and precipitated. .

[0134] Preparation of photoresponsive hydrophobic additives; tetrabutyl titanate hydrolysis:

[0135]

[0136] Hydrolysis and condensation of perfluorooctyltriethoxysilane (PFOTES):

[0137]

[0138] Synthesis of low-foaming wetting and dispersing agents; D4 polymerization of octamethylcyclotetrasiloxane:

[0139]

[0140] Hydrosilylation reaction of PDMS with allyl polyoxyethylene ether:

[0141]

[0142] Inorganic The network barrier prevents moisture penetration and enhances weather resistance. Phosphate ester groups strengthen interfacial bonding and improve adhesion. LDH and zinc borate undergo endothermic decomposition to release... and This forms a glassy barrier layer. Fluorosilicone segments reduce surface energy, imparting superhydrophobicity. Photocatalytic decomposition of pollutants enhances self-cleaning performance. The hydrogen-bonded network of the bio-thickener inhibits filler sedimentation and stabilizes the system.

[0143] Example 1: The exterior wall coating in this example uses the following components:

[0144] Table 1. Components of the building exterior wall coating used in Example 1

[0145] Ingredient name weight Specific parameters and composition Composite inorganic-organic hybrid film-forming matrix 50 A mixture of potassium sodium silicate solution and 3% phosphate-modified polyacrylate emulsion was prepared at a mass ratio of 1:1.2, comprising 22.7 parts potassium sodium silicate solution and 27.3 parts modified emulsion. Nanocomposite flame retardant filler 28 21 parts of Mg-AlLDH and 7 parts of citric acid-modified nano-cerium dioxide were compounded in a 3:1 ratio, with 1.05 parts of LDH loaded with 5% zinc borate. Bio-based thickeners 2 Hydroxypropyl guar gum 1.33 parts and sodium alginate 0.67 parts were compounded in a 2:1 ratio. Photoresponsive hydrophobic additives 0.8 Fluorosiloxane-modified titanium dioxide nanoparticles have a particle size of 35 nm and a specific surface area of ​​160 m² / g. Low-foaming wetting and dispersing agents 0.7 The polyether-modified polysiloxane has a viscosity of 650 mPa·s and a foaming height of 8 mm. Deionized water margin pH=9.0, replenish to 100%

[0146] The preparation process is as follows:

[0147] Nine kg of butyl methacrylate and one kg of ethylene glycol methacrylate were reacted at 80°C under nitrogen protection for 4 hours. 10 g of ammonium persulfate initiator was added in three portions, with ultrasound at 40 kHz throughout the reaction, to prepare a phosphate-modified polyacrylate emulsion. Subsequently, 22.7 kg of potassium sodium silicate solution, preheated to 45°C, was mixed with 27.3 kg of the modified emulsion at a mass ratio of 1:1.2. The pH was adjusted to 9.0, and 1.25 kg of silane coupling agent KH-570 was added dropwise. The mixture was reacted at 60°C for 2 hours to form an inorganic-organic interpenetrating network. Seven kg of nano-cerium dioxide and 70 kg of 5% citric acid solution were ultrasonically treated at 60°C and 200 W for 30 minutes. After centrifugation, the mixture was combined with 21 kg of Mg-AlLDH (pH=9.0) and ultrasonically self-assembled at 40 kHz to form a core-shell structure. Add 1.05 kg of zinc borate (5% of the total mass), react at 80°C for 2 hours, and spray dry to obtain particles with D50=6 μm. After ball milling, the specific surface area reaches 190 m² / g.

[0148] 50 kg of composite base material, 28 kg of nano filler, 2 kg of bio-thickener, 1.33 kg of hydroxypropyl guar gum, 0.67 kg of sodium alginate, 0.8 kg of fluorosilicone modified titanium dioxide with a particle size of 35 nm, and 0.7 kg of polyether modified polysiloxane dispersant were mixed and dispersed at 1200 rpm for 40 minutes. The pH was adjusted to 9.0, and 0.3 kg of ammonia water was added. After filtering through a 200-mesh sieve, the final coating viscosity was stable at 32 s. No sedimentation was observed during long-term storage, and the viscosity change was only 2%.

[0149] Comparative Example 1: In this comparative example, a commercially available brand of silicone-acrylic emulsion exterior wall paint was used. The main components of the paint are pure acrylic emulsion, titanium dioxide, heavy calcium carbonate, and APEO wetting agent.

[0150] Experimental methods:

[0151] Water resistance test: Prepare 150mm×70mm cement mortar test panels, coat them with a coating, and dry them for 7 days. Immerse the test panels in deionized water at 23±2℃ for 168 hours, remove them, wipe them dry, and observe whether the coating blisters or peels off. According to the standard rating: Level 0 no change to Level 5 severe damage.

[0152] Adhesion test: Use a cross-cutting tool to draw 100 1mm × 1mm squares on the coating surface, with the scratch depth reaching the substrate. Apply transparent tape to the marked areas and quickly peel it off. Calculate the peeling rate, which is the percentage of the total area where the peeling occurred. Rating standard: Grade 0: 0% peeling to Grade 5: >65% peeling.

[0153] Flame retardancy oxygen index test: Prepare a 100mm×10mm×3mm sample, place it in an oxygen indexer, adjust the oxygen / nitrogen ratio, and determine the minimum oxygen concentration (OI) required for the material to burn continuously for 30 seconds or a length of 50mm. Classification: A2 grade OI ≥ 30%, B1 grade 24% ≤ OI < 30%.

[0154] In the ultraviolet aging test, a UVA-340 lamp was used to simulate sunlight ultraviolet radiation, with an irradiance of 0.76 W / m², a blackboard temperature of 63±3℃, and a relative humidity of 50±5%. After 2000 hours, the color difference of the coating was measured using a colorimeter. ΔE ≤ 1 indicated no change, while ΔE ≥ 3 indicated significant color change.

[0155] Self-cleaning test: Simulated contaminants, consisting of a 1:1 mixture of graphite powder and vegetable oil, were uniformly sprayed onto the coating surface and allowed to stand for 24 hours. The surface was then rinsed with 0.2 MPa water for 30 seconds, and the contaminant removal rate was calculated as (clean area / contaminated area × 100%).

[0156] Storage stability test: The coating was sealed in a 500mL container and left to stand at room temperature (23±2℃) for 6 months. Observe whether it separates into layers or clumps, and use a rotational viscometer to measure the percentage difference between the initial viscosity and the final viscosity.

[0157] Contact angle testing method: The static contact angle is determined using the seat drop method with a contact angle measuring instrument. The sample is flatly coated on a glass substrate, the test drop volume is 2μL, and the average value of three measurements is taken.

[0158] Self-cleaning efficiency test method: Graphite powder and soybean oil were mixed at a ratio of 1:1 to prepare a simulated contaminant. The contaminant was evenly coated with a spray gun at a coating amount of 2.0±0.2g / m². After curing at room temperature for 24h, the area was rinsed for 30s using a spray device with a water pressure of 0.2MPa, a nozzle diameter of 1mm, and a vertical distance of 30cm. The percentage of the cleaned area was then analyzed.

[0159] Table 2 Experimental data and results of Example 1 and Comparative Example 1

[0160]

[0161] As shown in Table 2, the composite base material, sodium potassium silicate + phosphate ester modified emulsion, forms an interpenetrating network structure, with the inorganic phase filling the pores of the organic phase and preventing water penetration. In Comparative Example 1, the pure organic emulsion has poor water resistance due to its numerous hydrophilic groups; in Example 1, the inorganic-organic hybrid structure significantly reduces water absorption.

[0162] In the LDH-cerium dioxide composite filler, the decomposition of zinc borate between LDH layers is endothermic, and the ultraviolet shielding effect of cerium dioxide reduces the generation of free radicals. Example 1 showed an OI value of 38%, far exceeding the comparative example's 124%, and an ultraviolet aging ΔE of only 1.2 compared to the comparative example's 13.8.

[0163] Photoresponsive hydrophobic additive fluorosilicone-modified titanium dioxide exhibits superhydrophilic-superhydrophobic switching properties under ultraviolet excitation, making contaminants easily washed away by rainwater. Example 1 shows a contact angle of 152° and a self-cleaning efficiency of 95%; Comparative Example 1, without hydrophobic additive, has an efficiency of only 40%.

[0164] The bio-based thickeners guar gum and sodium alginate stabilize filler dispersion and inhibit sedimentation through hydrogen bonding and electrostatic interactions. In Example 1, the viscosity change was only 2%, while in Comparative Example 1, the traditional thickener HEC easily separated into layers after 3 months of storage.

[0165] The coating of this invention is significantly superior to commercially available products in terms of water resistance, flame retardancy, self-cleaning properties, and storage stability, verifying the synergistic effect of composite base material, nanofiller, and bio-thickener.

[0166] Example 2: Based on the formulation of Example 1, the composite base material is potassium sodium silicate solution to modified polyacrylate emulsion in a mass ratio of 1:1.2. The construction process is as follows:

[0167] Substrate Pretreatment: Remove surface dust from cement-based surfaces using a 20MPa high-pressure water jet. Spray with a pH 9.0 silane coupling agent KH-570 solution and allow to stand for 30 minutes to form a chemical anchoring layer. Layered Spraying and Photoactivation: Dilute the coating to a 32s Forte 4 cup viscosity. Apply the first coat with a wet film thickness of 90μm, immediately followed by irradiation with a 365nm UV lamp at 1.0W / cm² for 5 minutes. The second coat has a wet film thickness of 120μm, applied cross-sprayed at a 90° angle, allowed to stand for 10 minutes, and then irradiated again with UV light for 10 minutes. Gradient Curing: The first stage involves curing in a 45℃ oven for 24 hours at ≤40% humidity. The second stage involves curing at 25℃ and 60% humidity for 7 days, with daily spraying with deionized water. Post-treatment: Spray with a fluorinated siloxane curing agent to form a self-healing hydrophobic film.

[0168] Comparative Example 2: Only 50 parts of potassium sodium silicate solution were used. The preparation method was the same as in Example 1, but no polyacrylate emulsion was added, and the UV activation step was omitted during the construction process.

[0169] Comparative Example 3: Only 50 parts of phosphate-modified polyacrylate emulsion were used, without the addition of potassium sodium silicate solution, and the construction and curing conditions were the same as in Example 2.

[0170] Experimental methods and test indicators:

[0171] Impact resistance: Drop a 1kg hammer from a height of 50cm onto the coating surface and observe for cracking. Rating standard: Level 0: No cracks to Level 4: Severe cracking.

[0172] Pencil hardness: The coating hardness is determined by scratching the coating surface at a 45° angle with a Mitsubishi pencil with a hardness range of 6B-9H. The highest hardness level that does not produce a scratch is the coating hardness.

[0173] Table 3 Experimental data and results of Example 2 and Comparative Examples 2 and 3

[0174] index Example 2 Comparative Example 2 Comparative Example 3 Water resistance and foaming rate after 168 hours 0% 100%, severe bubbling 40%, localized blistering Adhesion detachment rate 0%, Level 1 18%, Level 3 8%, Level 2 Pencil hardness 4H 2H 3H Impact resistance 50cm No cracks Crack level 4 Minor crack, grade 2

[0175] Example 2, through the Si-O-Si network of the inorganic-organic hybrid base material sodium potassium silicate and the flexible chain interpenetration of polyacrylate, combined with a layered UV curing process, significantly improved water resistance, eliminating blistering and achieving 0% adhesion loss. Simultaneously, its hardness (4H) and impact resistance were superior to single-component systems. Comparative Example 2, due to the high brittleness of the pure inorganic phase, resulted in poor adhesion loss (18%) and impact cracking. Comparative Example 3, due to insufficient water resistance of the organic phase, experienced blistering of 40%. This demonstrates that the composite base material and the gradient application process work synergistically, resulting in overall performance superior to traditional single-component coatings.

[0176] Example 3: Based on the formulation and preparation process of Example 1, the nanofiller is an LDH-cerium dioxide composite with a mass ratio of 3:1, loaded with 5% zinc borate. Preparation step S2: LDH and citric acid-modified cerium dioxide are ultrasonically self-assembled, then loaded with zinc borate, spray-dried, and ball-milled to a specific surface area of ​​190 m² / g. The construction method is the same as in Example 2.

[0177] Comparative Example 4: Only LDH28 parts were used, without the addition of cerium dioxide and zinc borate.

[0178] Comparative Example 5: Only 28 parts of cerium dioxide were used, without zinc borate loading.

[0179] Experimental methods and test indicators:

[0180] Smoke density SDR: The maximum smoke density value SDR was determined by burning the sample under a radiant heat flux of 50 kW / m² using a smoke density meter.

[0181] Peak heat release rate: The peak heat release rate per unit area (kW / m²) was recorded using a cone calorimeter at a radiant power of 50 kW / m².

[0182] Smoke density SDR test method: Use a smoke density meter, sample size 75×75×3mm, radiant heat flux 50kW / m², and record the maximum smoke density within 600s.

[0183] Peak heat release rate test method: The sample size is 100×100×3mm, placed horizontally under the radiation cone, the radiation power is 50kW / m², and the peak heat release rate per unit area is recorded within 180s.

[0184] Table 4. Experimental data and results of Example 3 and Comparative Examples 4 and 5

[0185] index Example 3 Comparative Example 4 Comparative Example 5 Oxygen Index (OI) 38% A2 grade 28% B1 grade 22% B1 grade Smoke density SDR 45 78 92 UV aging △E2000h 1.2 3.5 4.8 Peak heat release rate 85kW / m² 145kW / m² 180kW / m²

[0186] In Example 3, the LDH-cerium dioxide core-shell structure with cerium dioxide-coated LDH, through a triple mechanism of "layer barrier + UV shielding + zinc borate endothermic effect," improved the OI value to A2 level by 38%, reduced smoke density by 58% (SDR=45), and exhibited a UV aging color difference ΔE of only 1.2. Comparative Example 4, lacking the UV shielding effect of cerium dioxide, had an ΔE of 3.5, and Comparative Example 5, lacking the LDH barrier effect, had a peak heat release of 180 kW / m², resulting in significantly reduced flame retardant and anti-aging properties. The multi-level structural design of the nanocomposite filler significantly improved the flame retardancy and durability of the coating.

[0187] Example 4: Based on the formulation and preparation method of Example 1, 0.8 parts of fluorosilicone modified titanium dioxide were added, and perfluorooctyltriethoxysilane was grafted onto tetrabutyl titanate after hydrolysis. The mixture was then irradiated with ultraviolet light for 2 hours. The construction method was the same as in Example 2.

[0188] Comparative Example 6: Titanium dioxide without fluorine-silicon modification, other components are the same as in Example 1.

[0189] Experimental methods and test indicators:

[0190] Contact angle testing method: The static contact angle is determined using the seat drop method with a contact angle measuring instrument. The sample is flatly coated on a glass substrate, the test drop volume is 2μL, and the average value of three measurements is taken.

[0191] Experimental method for surface energy: The contact angles of water (a polar liquid) and diiodomethane (a nonpolar liquid) were measured using a contact angle meter, and the surface energy (mN / m) was calculated using the Owens-Wendt formula.

[0192] Photocatalytic degradation rate test method: Prepare a 10 mg / L methylene blue solution, immerse a 50 × 50 mm sample in the solution, and irradiate it vertically with a 365 nm ultraviolet light source with an intensity of 1.0 mW / cm² for 4 h. Measure the change in absorbance at 664 nm using a UV-Vis spectrophotometer.

[0193] Supplement to the surface energy calculation method: The Owens-Wendt two-liquid method was adopted. The contact angles of deionized water (polar liquid) and diiodomethane (nonpolar liquid) were measured using a contact angle meter. The dispersed and polar components of the surface energy were calculated, and the sum of them was the total surface energy.

[0194] Table 5. Experimental data and results of Example 4 and Comparative Example 6

[0195] index Example 4 Comparative Example 6 Contact angle 152° 85° Self-cleaning efficiency 95% 40% Photocatalytic degradation rate 4h 88% 5% Surface energy 12mN / m 45mN / m

[0196] In Example 4, the fluorosilicone-modified titanium dioxide, after UV activation, forms a superhydrophobic surface with a contact angle of 152° and a surface energy as low as 12 mN / m. Pollutants are easily washed away by rainwater, resulting in a self-cleaning efficiency of 95%, and a photocatalytic degradation rate of 88%. In contrast, Comparative Example 6, with its hydrophilic surface and 85° contact angle, easily adsorbs pollutants, resulting in a self-cleaning efficiency of only 40%. The photoresponsive hydrophobic additive significantly improves the self-cleaning and stain resistance of the coating through the synergistic effect of "low surface energy + photocatalysis."

[0197] Example 5: Based on the formulation and preparation method of Example 1, the thickener is a 2:1 mixture of hydroxypropyl guar gum and sodium alginate. The hydroxypropyl guar gum undergoes a propylene oxide substitution reaction at 60°C, and the sodium alginate is dissolved in water using the alginic acid extraction method, then stirred at 50°C for 1 hour. The application method is the same as in Example 2.

[0198] Comparative Example 7: Only 2 parts of hydroxypropyl guar gum were used.

[0199] Comparative Example 8: Only 2 parts of sodium alginate were used.

[0200] Experimental methods and test indicators:

[0201] Zeta potential test method: Using a Malvern Zetasizer Nano ZS90 instrument, take a paint suspension diluted to 0.1% by mass, measure it three times at 25°C and take the average value.

[0202] Quantification method of settlement phenomenon: The coating is put into a 250mL stoppered graduated cylinder, and the settlement layer height ratio is recorded after standing at room temperature for 6 months.

[0203] Where H0 is the initial height and Ht is the height of the supernatant after settling.

[0204] Table 6. Experimental data and results of Example 5 and Comparative Examples 7 and 8

[0205] index Example 5 Comparative Example 7 Comparative Example 8 Initial viscosity (mPa·s) 3200 2800 2500 6-month viscosity change rate +2% +15% +12% Zeta potential mV -45 -20 -35 Settlement phenomenon none 5% of the clear liquid in the stratified layer flocculation and agglomeration

[0206] In Example 5, the hydrogen bonding of hydroxypropyl guar gum combined with the electrostatic repulsion of sodium alginate anions formed a three-dimensional network with a zeta potential of -45 mV. After 6 months of storage, the viscosity changed by only 2%, with no sedimentation. Comparative Example 7, due to its single hydrogen bond network and a zeta potential of -20 mV, experienced stratification; Comparative Example 8, due to insufficient electrostatic repulsion and a zeta potential of -35 mV, exhibited flocculation. The synergistic effect of the bio-based thickener significantly improved the storage stability of the coating, meeting the requirements for green and environmentally friendly practices.

[0207] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A building exterior wall coating, characterized in that, It is made from the following raw materials in parts by weight: Composite inorganic-organic hybrid film-forming base material: 50 parts, which is composed of potassium sodium silicate solution and modified polyacrylate emulsion with 3% by mass of phosphate functional monomer at a mass ratio of 1:1.2; Nanocomposite flame retardant filler: 28 parts, including a composite of Mg-Al layered dihydroxy composite metal oxide LDH and nano-cerium dioxide in a mass ratio of 3:1; Bio-based thickener: 2 parts, a mixture of hydroxypropyl guar gum and sodium alginate in a mass ratio of 2:1; Photoresponsive hydrophobic additive: 0.8 parts, which is titanium dioxide nanoparticles modified with fluorinated siloxane; Low-foaming wetting and dispersing agent: 0.7 parts, which is polyether-modified polysiloxane; Deionized water: Balance; The chemical formula of the Mg-Al layered dihydroxy complex metal oxide is: Its preparation process is as follows: First, and Prepare a mixed salt solution at a 3:1 molar ratio, and under pH 9.5, 60-70℃, and nitrogen protection, react with... The co-precipitation reaction with the precipitant lasted for 2 hours, followed by centrifugation and washing to obtain the precursor. Subsequently, it was hydrothermally treated at 120-140℃ for 12 hours, followed by spray drying to obtain a highly crystalline intermediate; finally, it was dispersed in... In solution, ion exchange was performed at 50°C for 24 hours, so that... Completely replace interlayer The target product was obtained after washing and drying. ; The preparation method of the bio-based thickener is as follows: using natural guar gum as raw material, it is reacted with propylene oxide at a molar ratio of 1:1.2 under alkaline conditions at 60℃ for 4 hours to introduce hydroxyl groups through a hydroxypropyl substitution reaction. After precipitation with ethanol and drying, hydroxypropyl guar gum is obtained. Using brown algae as raw material, it is decalcified with dilute hydrochloric acid, extracted with sodium carbonate, filtered, and precipitated with ethanol to obtain high-purity sodium alginate. Hydroxypropyl guar gum and sodium alginate are dissolved in deionized water at a mass ratio of 2:1 and stirred at 50℃ for 1 hour to form a hydrogen bond-ionic bond synergistic network, finally obtaining the bio-based thickener. The preparation method of the photoresponsive hydrophobic additive is as follows: Tetrabutyl titanate is mixed with anhydrous ethanol, dilute nitric acid is added dropwise for hydrolysis, and the mixture is aged at 60℃ for 12 hours. After centrifugation, particles with a diameter of 20-50 nm are obtained. ;Will Dispersed in isopropanol, perfluorooctyltriethoxysilane was added, and the mixture was refluxed at 80°C for 6 hours, resulting in the hydrolysis and condensation of the siloxane. Surface grafting with fluorine-containing segments; enhanced photoresponse properties: UV irradiation treatment for 2 hours, final product specific surface area ≥150. ; The preparation method of low-foaming wetting and dispersing agent is as follows: Using octamethylcyclotetrasiloxane D4 as monomer and hexamethyldisiloxane as end-capping agent, ring-opening polymerization was carried out at 90℃ for 6 h under 1% (w / w) sulfuric acid catalysis to obtain polydimethylsiloxane PDMS with a viscosity of 500-800 mPa·s. PDMS and allyl polyoxyethylene ether were reacted with a platinum catalyst at a molar ratio of 1:1.2 via hydrosilylation at 110℃ for 5 h to introduce polyether segments and form a polyether-siloxane block structure. Through the steric hindrance effect of the polyether segments, the dynamic surface tension was reduced to ≤30 mN / m, and the final product had a foaming height of <10 mm.

2. The method for preparing building exterior wall coating as described in claim 1, characterized in that, Includes the following steps: S1. Potassium sodium silicate solution and modified polyacrylate emulsion are premixed at 50°C and 300 rpm for 1 hour to form a composite base material; S2. Combining LDH with nano Dispersed in deionized water for 30 min under ultrasonic assistance, zinc borate was added and the temperature was raised to 80℃ for 2 h. After drying and grinding, nano-composite flame retardant filler was obtained. S3. Mix the composite base material obtained in S1, the filler obtained in S2, and the bio-based thickener, photoresponsive hydrophobic additive, and low-foaming wetting and dispersing agent, and disperse them in a disperser at 1200 rpm for 40 min. S4. Adjust the pH to 9.0, filter and package.

3. The preparation method according to claim 2, characterized in that, The detailed steps for S1 are as follows: S11. Mix butyl methacrylate and ethylene glycol phosphate methacrylate in a mass ratio of 9:1 with deionized water, add 0.1% ammonium persulfate as an initiator, and react at 75-80℃ for 4 hours under nitrogen protection to obtain a phosphate-functionalized polyacrylate emulsion. S12. The initiator was added dropwise in three batches during the reaction, with an interval of 1 hour between each batch, and the reaction was assisted by ultrasound at a frequency of 40 kHz throughout the process. S13. Preheat the potassium sodium silicate solution to 45°C, slowly add the modified emulsion obtained in S11, control the mass ratio of the two to be 1:1, and adjust the pH to 8.8-9.0 with ammonia. S14. Under stirring at 500 rpm, add 0.5% (w / w) of silane coupling agent KH-570 dropwise to the mixture at a dropping rate of 2 mL / min. After the addition is complete, raise the temperature to 60℃ and continue the reaction for 2 hours to form an inorganic phase. Interpenetrating structure of network and organic phase polyacrylate chains.

4. The preparation method according to claim 3, characterized in that, The specific steps of S2 are as follows: S21. Nanoparticles The mixture was mixed with a 5% citric acid solution at a mass ratio of 1:10, treated at 60℃ and ultrasonic power of 200W for 30 min, and centrifuged to obtain citric acid-modified material with a negatively charged surface. ; S22. Modification of Mg-Al layered dihydroxy composite metal oxide LDH with the product obtained in S21 Add the LDH to deionized water at a mass ratio of 3:1, disperse for 30 minutes under ultrasonic assistance at a frequency of 40 kHz, and control the pH of the system to 9.0, so that the positive charge of the LDH layer is neutralized by the surrounding environment. Negative charges self-assemble through electrostatic adsorption, forming LDH as the core. A complex of shells; S23. Add zinc borate to the resulting mixture. Its mass is LDH- 5% of the total mass of the composite was heated to 80℃ and reacted for 2 hours, allowing zinc borate to form between the LDH layers and... The surface is bonded through hydroxyl condensation reaction to form a stable supported structure; S24. Spray dry the reaction solution to obtain the particle size. The primary particles were then ball-milled for 2 hours under an inert atmosphere to obtain a specific surface area of ​​180-200. Nanocomposite flame-retardant fillers.

5. The construction method of the building exterior wall coating as described in claim 2, characterized in that, The steps include the following: Q1. Substrate pretreatment: Use high-pressure water jet with pressure ≥20MPa to remove floating dust and loose layer from the substrate surface, then spray with silane coupling agent KH-570 solution with pH=9.0, and let stand for 30min to form chemical anchoring layer. Q2. Layered spraying and photoactivation: Dilute the paint to a viscosity of 30-35s, and apply the first coat using an airless sprayer at a speed of 0.5m / s, achieving a wet film thickness of 80-100 mm. Immediately after spraying, irradiate with a 365nm wavelength UV lamp with an irradiance of 1.0W / cm² for 5 minutes to activate the superhydrophobic properties of the photoresponsive hydrophobic additive; after the base coat is surface dry, spray the second coat of undiluted paint, with a wet film thickness of 120mm. The spraying direction is perpendicular to the base layer at 90°. After spraying, let it stand for 10 minutes, and then irradiate it with ultraviolet light for another 10 minutes. Q3. Gradient curing; Stage 1: Curing in a 40-50℃ drying oven for 24 hours, humidity ≤40%, to promote LDH- Interlayer hydroxyl condensation of flame-retardant fillers; Stage 2: Curing for 7 days at 15-35℃ and 50-80% humidity, with daily spraying of deionized water to promote the bonding between the potassium sodium silicate base and the filler. The carbonization reaction forms a dense... network; Q4. Post-treatment: After curing, spray the surface with a fluorinated siloxane curing agent to form a self-healing hydrophobic film.

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