Dry powder paint for exterior wall and preparation and application method thereof

Abstract

The application provides a dry powder paint for outer wall and a preparation and construction method thereof, and belongs to the technical field of building paint. The paint is composed of calcium aluminum borosilicate cement powder, boron nitride nanosheet, rare earth cerium doped titanium dioxide, volcanic ash microbead, magnesium potassium phosphate activator, bio-based polyaspartic acid sodium dispersant and modified hectorite thixotropic agent. The high amorphous cement powder is prepared by a melting-quenching method, which significantly improves the compressive strength, acid corrosion resistance and photocatalytic efficiency. The density of the volcanic ash microbead is reduced after hydrophobic modification, and the pore structure is optimized by cooperating with the magnesium potassium phosphate activator, so that the freeze-thaw resistance is significantly improved. The bio-based dispersant and the CTAB modified hectorite are used in a synergistic manner to realize high dispersion of the nanomaterial and high thixotropy of the slurry. During construction, two-stage spraying and ultraviolet photocatalytic activation are used to form a multifunctional coating. The application has the characteristics of high strength, self-cleaning, lightweight and environmental protection, and is suitable for high durability building outer wall protection.

Description

Technical Field

[0001] The present invention relates to the technical field of building coatings, and in particular to a dry powder coating for exterior walls and a preparation and construction method thereof. Background Art

[0002] Exterior wall dry powder coatings are powdered building materials made primarily from inorganic cementitious materials, pre-mixed with functional fillers, additives, and other ingredients. They offer advantages such as low VOC emissions, easy construction, and strong weather resistance, making them widely used in building exterior wall decoration and protection. Traditional systems often use Portland cement or ordinary aluminate cement as a base material, combined with mineral fillers such as quartz sand and wollastonite. While these systems possess certain mechanical properties, they face the following technical bottlenecks in practical application due to irrational mineral composition design of the base material, lack of functional filler modification technology, limited pore structure control methods, and poor compatibility between the dispersed system and nanomaterials:

[0003] Traditional Portland cement-based coatings generally have low compressive strength, and the high calcium hydroxide content in cement hydration products leads to large drying shrinkage and is prone to microcracks in hot and humid environments. Furthermore, due to the acidic decomposition and calcium dissolution of the ettringite phase, Portland cement has poor tolerance to acid rain, with surface powdering exceeding standards after 30 days of immersion.

[0004] Existing coatings often use unmodified titanium dioxide as a filler, which limits its light response to the ultraviolet (UV) band and reduces visible light utilization. Furthermore, conventional fillers have low infrared reflectivity, resulting in poor thermal insulation performance. Summer building surface temperatures can be 8-10°C higher than the ambient temperature.

[0005] To reduce coating density, existing technologies often incorporate porous fillers. However, these open-pore structures easily absorb moisture, leading to coating spalling due to ice crystal expansion during freeze-thaw cycles. Furthermore, the interface between the cement matrix and the filler is weak, and the absence of phosphate activators prevents the migration of alkaline calcium and potassium ions, resulting in a high surface frost coverage after a 72-hour efflorescence test.

[0006] Traditional naphthalene-based dispersants have limited effectiveness in dispersing boron nitride nanosheets, resulting in excessive sedimentation after 24 hours of slurry standing. Unmodified hectorite, due to its small interlayer spacing, cannot meet the requirements of thick-layer spraying.

[0007] These defects seriously restrict the application of exterior wall dry powder coatings in the direction of high durability and multifunctionality. Therefore, it is of great significance to design an exterior wall dry powder coating and its preparation and construction method to solve the above problems. Summary of the Invention

[0008] In order to solve the problems existing in the background technology, the present invention provides a dry powder coating for exterior walls, which is made of the following raw materials in parts by weight:

[0009] Calcium aluminum borosilicate cement powder : 60 copies;

[0010] Boron nitride nanosheets: 15 parts;

[0011] Rare earth cerium doped titanium dioxide : 10 parts;

[0012] Volcanic ash microbeads: 1220 parts;

[0013] Potassium magnesium phosphate activator : 6 parts;

[0014] Bio-based sodium polyaspartate dispersant: 3 parts;

[0015] Modified hectorite thixotropic agent: 1.5 parts.

[0016] In a preferred embodiment, the calcium aluminum borosilicate cement powder is prepared by a melting-quenching method, and its mineral composition includes calcite Produced by the following process:

[0017] Raw material ratio and melting treatment: Weigh boric acid in a molar ratio of 4:3:1:2 , calcium oxide , alumina and silica , add 0.5~1.5wt% calcium fluoride after mixing As a mineralizer; place the mixture in an electric arc furnace, heat it to 1450-1550℃ under nitrogen protection and keep it warm for 24 hours;

[0018] Quenching treatment: The melt is rapidly cooled to room temperature at a cooling rate of ≥100℃ / s, and quenched with liquid nitrogen to obtain an amorphous glass body, in which the amorphous phase accounts for ≥85%. Content ≤0.005%;

[0019] Crystallization calcination: crush the quenched glass into particles ≤100μm, place it in a rotary kiln and heat it in stages: 600~800℃ with a temperature increase of 5℃ / min to promote Network reconstruction; heating in the range of 800-950℃ at 15℃ / min to induce gehlerite Directed crystallization is the main crystalline phase;

[0020] Grinding and modification: The calcined clinker is ground by a planetary ball mill to a specific surface area of ​​≥450m² / kg, and 0.1-0.3wt% polycarboxylic acid dispersant is added to obtain calcium aluminum borosilicate cement powder.

[0021] In a preferred embodiment, the boron nitride nanosheets are prepared by the following process:

[0022] Ultrasonic exfoliation: Disperse boron nitride powder in deionized water with a solid-liquid ratio of 1:50 to 1:100, and add 0.5 to 1.5 wt% sodium lauryl sulfate. , using a probe-type ultrasonic processor for 2 to 4 hours, centrifuging at 8000 to 12000 rpm, and collecting the upper suspension after 30 minutes to obtain boron nitride nanosheets with a thickness of ≤5 nm and a lateral size of 0.5 to 5 μm;

[0023] In situ modification with polydopamine: the nanosheet suspension obtained in step 1 is mixed with dopamine hydrochloride in a mass ratio of 1:0.2 to 1:0.5, the pH is adjusted to 8.5 to 9.5, and the mixture is reacted with magnetic stirring at 300 to 500 rpm at 25 to 35° C. for 12 to 24 hours to form a polydopamine coating layer with a thickness of 2 to 3 nm;

[0024] Washing and drying: The reaction product was washed three times with deionized water and anhydrous ethanol by centrifugation, each time for 10 minutes, and freeze-dried at -50°C for 24 hours to obtain polydopamine-modified boron nitride nanosheets with a specific surface area of ​​≥200 m² / g.

[0025] In a preferred embodiment, the rare earth cerium doped titanium dioxide Prepared by the following process:

[0026] Precursor preparation: Tetrabutyl titanate With cerium nitrate according to The mixture was mixed in a molar ratio of 97:3, dissolved in a mixed solvent of ethanol and ethylene glycol, and 0.5 wt% of hexadecyltrimethylammonium bromide was added. , magnetic stirring to form a homogeneous sol;

[0027] Hydrothermal reaction: transfer the sol to a high-pressure reactor and react at 180°C for 12 to 24 hours to generate cerium-doped The precursor, the product was washed by centrifugation and freeze-dried at -50 °C for 24 h;

[0028] Staged calcination: First stage: heating to 450-500℃ at 5℃ / min, keeping warm for 2 hours to generate anatase phase; second stage: heating to 600-650℃ at 10℃ / min, keeping warm for 1 hour to induce rutile phase crystallization, and finally obtain ;

[0029] Surface modification: The calcined powder was dispersed in 0.1M hydrochloric acid solution with a solid-liquid ratio of 1:50, ultrasonicated at 40kHz for 30min and then dried to obtain a surface area ≥80m² / g. Powder.

[0030] In the preferred embodiment, the volcanic ash microbeads and potassium magnesium phosphate activator , bio-based sodium polyaspartate dispersant, and modified hectorite thixotropic agent are prepared by the following processes:

[0031] Preparation of volcanic ash microbeads: The volcanic ash raw materials are separated by air flow to obtain microbeads with a particle size of ≤30μm, and 5-10wt% silane coupling agent is added. Immersing in an ethanol solution for 30 to 60 minutes and drying at 120 to 150°C to form volcanic ash microbeads with hydrophobic surface modification;

[0032] Synthesis of potassium magnesium phosphate activator: The molar ratio is 1:1:6, 0.1-0.3 wt% boric acid is added as a crystallization control agent, and the reaction is hydrothermally reacted at 80-100 ° C for 4-6 hours. The product is spray-dried to obtain crystals;

[0033] Preparation of bio-based sodium polyaspartate dispersant: L-aspartic acid and maleic anhydride were mixed in a molar ratio of 1:1.2, 0.5-1.0 wt% of ammonium persulfate initiator was added, and the polymerization reaction was carried out at 180-200 ° C under nitrogen protection for 2-3 hours. Neutralize to pH=7-8 to obtain bio-based sodium polyaspartate;

[0034] Preparation of modified hectorite thixotropic agent: Hectorite powder and hexadecyltrimethylammonium bromide The mixture is mixed in a mass ratio of 1:0.1 to 1:0.3, stirred in a water bath at 60 to 80° C. for 2 to 4 hours, washed by centrifugation and then dried to obtain a modified hectorite with an interlayer spacing expanded to 2.5 to 3.0 nm.

[0035] The present invention provides a method for preparing dry powder coating for exterior walls, comprising the following steps:

[0036] R1. Pre-activation treatment: Boron nitride nanosheets and bio-based sodium polyaspartate dispersant were added to an ammonia solution with a pH of 8-9 and exfoliated using ultrasound at a frequency of 40 kHz for 30 minutes.

[0037] R2 dry mix: The calcium aluminum borosilicate cement powder, pozzolan beads, magnesium potassium phosphate activator into a planetary mixer, mixed at 1500rpm for 20min;

[0038] R3. Wet mixing: Add preactivated boron nitride nanosheets, rare earth cerium-doped titanium dioxide, and modified hectorite thixotropic agent and continue mixing for 30 minutes;

[0039] R4. Curing: Curing at 60% humidity and 45°C for 48 hours, and passing through a 250-mesh sieve to obtain the finished product.

[0040] The present invention also provides a construction method for dry powder coating for exterior walls, comprising the following steps:

[0041] H1. Surface pretreatment: Use a high-pressure water jet with a pressure of ≥15MPa to clean the wall surface to remove dust and loose particles. Spray a silane coupling agent pretreatment solution with a volume ratio of KH-560:ethanol = 1:9 at a spray rate of 20-30g / m² and let it stand for 30 minutes.

[0042] H2. Paint Activation and Spraying: Exterior wall dry powder paint and deionized water were mixed in a mass ratio of 1:0.25 and stirred in an ultrasonic mixer for 10 minutes to form a thixotropic slurry. The dispersion of the nano-boron nitride (D90) was ≤ 500 nm. Airless spraying was performed using a two-fluid spray gun at an air pressure of 0.6-0.8 MPa and a nozzle diameter of 2.5 mm. The application was carried out in two stages: the first stage was to spray a thickness of 0.5-0.8 mm to form a porous base layer. After a 20-minute interval, the second stage was to spray to a total thickness of 1.5-2.0 mm.

[0043] H3. Photocatalytic activation: Within 2 hours after spraying, irradiate the coating surface with a UV LED array with a wavelength of 365nm and an irradiance of 50mW / cm² for 30 minutes.

[0044] The beneficial effects achieved by the present invention are:

[0045] This invention utilizes a melting-quenching-crystallization process to prepare calcium aluminum borosilicate cement powder. By precisely controlling the quaternary system ratio and employing directional crystallization techniques, a highly active matrix with gehelite as the primary crystalline phase is formed. This innovation significantly enhances the coating's compressive strength, acid corrosion resistance, and wet-heat stability, while effectively suppressing drying shrinkage and microcrack formation.

[0046] This invention incorporates polydopamine-modified boron nitride nanosheets and cerium-doped titanium dioxide, broadening the photoresponse range and enhancing carrier separation efficiency through the heterojunction effect. This design imparts efficient self-cleaning capabilities and broad-spectrum photocatalytic activity to the coating, while significantly improving infrared reflectivity and UV blocking properties, achieving both building energy conservation and surface protection.

[0047] This invention utilizes hydrophobically modified, closed-cell volcanic ash microspheres, combined with a magnesium potassium phosphate activator to hydrate and generate a new phase, optimizing the coating's pore structure and reducing its density. This innovation significantly enhances the coating's freeze-thaw resistance and efflorescence resistance. The closed-cell structure also blocks water penetration, ensuring volume stability in hot and humid environments.

[0048] This invention utilizes the synergistic effect of a bio-based sodium polyaspartate dispersant and CTAB-modified hectorite to construct a three-dimensional thixotropic network through electrostatic repulsion and increased interlayer spacing. This system achieves efficient dispersion of nanomaterials and high thixotropy in the slurry, significantly improving construction rheological properties while meeting environmental and non-toxic requirements and complying with green building material standards.

[0049] This invention uses a two-stage airless spraying process to create a gradient structure with a porous base layer and a dense surface layer, combined with ultraviolet light catalytic activation. This process enhances the adhesion of the coating to the substrate, optimizes the uniformity of thick layer construction, and instantly activates the self-cleaning function, forming a highly effective and durable protective system. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 This is a flow chart of a method for preparing dry powder coating for exterior walls according to the present invention;

[0051] Figure 2 The present invention is a flow chart of the construction method of dry powder coating for exterior walls. DETAILED DESCRIPTION

[0052] The technical solutions of the present invention will be described clearly and completely below in conjunction with the drawings in the present invention. In addition, the forms of the various structures described in the following embodiments are merely examples. The present invention is not limited to the various structures described in the following embodiments. All other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0053] Key materials, chemical formulas, parameters, technical terms, and English abbreviations in this invention: Calcium aluminum borosilicate cement powder ( ), the crystal phase is calcite ( ),in As a network former, it participates in the glass phase structure, and the proportion of grosslandite in the mineral composition is ≥70%. The amorphous phase content is calculated by X-ray diffraction combined with Rietveld refinement method. The content was determined by ion chromatography.

[0054] , cerium Mixed valence doping, substitution in the lattice site, the doping amount is The anatase / rutile mixed phase is formed by a staged calcination process, wherein the mass ratio of the anatase phase to the rutile phase is approximately 6:4, and the specific surface area is ≥80m² / g.

[0055] Potassium magnesium phosphate stimulant ( ), potassium magnesium phosphate hexahydrate crystals belong to the monoclinic system and are used as alkaline activators in cement. Reaction generation Gel phase.

[0056] The polydopamine coating is formed by in-situ oxidative polymerization to form a 2-3 nm thick polydopamine layer. The coating is combined with the boron nitride nanosheets through π-π conjugation and hydrogen bonding. X-ray photoelectron spectroscopy can detect Key ratio ≥ 70%.

[0057] Key parameters and test methods: Specific surface area, measured by nitrogen adsorption BET method, cement powder specific surface area ≥ 450m² / kg, Specific surface area ≥80m² / g.

[0058] Thixotropic index is calculated based on the ASTM D2196 standard using a rotational rheometer to measure the viscosity ratio at 3 rpm to 30 rpm. The calculation formula is:

[0059] ;in is the apparent viscosity (unit: mPa·s).

[0060] Dispersion , measured by dynamic light scattering in deionized water dispersion, Indicates that 90% of the particles have a size below this value. The detection instrument is Malvern Zetasizer Nano ZS.

[0061] The amorphous phase content was calculated using X-ray diffraction combined with the Rietveld refinement method, and the amorphous phase accounted for ≥85%.

[0062] Photocatalytic efficiency, according to ISO 10678 standard, with methylene blue solution as the degradation object, irradiated under simulated sunlight for 2 hours, the degradation rate is calculated as follows:

[0063] ;in is the initial concentration, is the concentration after degradation.

[0064] , represents the particle size distribution of boron nitride nanosheets in the slurry, The particle size below which 90% of the particles in the cumulative distribution are smaller, as determined by dynamic light scattering.

[0065] Thixotropic index characterizes the shear thinning properties of the slurry. The larger the value, the stronger the thixotropy. The calculation formula is the ratio of the viscosity at 3rpm to that at 30rpm.

[0066] Specific surface area, the surface area per unit mass of material, is used to characterize the activity of powders and is determined by the BET method.

[0067] Tortuosity, the degree of bending of the pore path, is calculated as the ratio of the actual path length to the straight-line distance, calculated from mercury intrusion data.

[0068] VOC: Volatile Organic Compounds, refers to the volatile organic components in coatings, one of the environmental indicators.

[0069] : Cerium-doped Titanium Dioxide, a kind of photocatalytic material.

[0070] CTAB: Cetyltrimethylammonium Bromide, a kind of cationic surfactant, used for nano material modification.

[0071] SDS: Sodium Dodecyl Sulfate, a kind of anionic surfactant, used for dispersing nano materials.

[0072] KH-550 / KH-560: Silane Coupling Agent, γ-aminopropyl triethoxysilane, used for surface modification of materials to enhance interfacial bonding.

[0073] ASTM: American Society for Testing and Materials, develops standards for testing the performance of materials.

[0074] XRD: X-Ray Diffraction, used to analyze the crystal structure of materials.

[0075] SEM: Scanning Electron Microscopy, used to observe the microstructure of materials.

[0076] BET: Brunauer-Emmett-Teller Method, nitrogen adsorption method, used to measure the specific surface area of materials.

[0077] FTIR: Fourier Transform Infrared Spectroscopy, used to analyze the chemical bonds and functional groups of materials.

[0078] DLS: Dynamic Light Scattering, used to measure the particle size distribution of nanoparticles.

[0079] PL: Full name: Photoluminescence Spectroscopy; light-induced luminescence spectrum, used to analyze the photo-carrier behavior of materials.

[0080] D90: In dynamic light scattering test, the particle size of 90% particles is less than this value, representing the dispersion degree.

[0081] RH: Full name: Relative Humidity; relative humidity, indicating the content of water vapor in the air.

[0082] C-S-H: Full name: Calcium Silicate Hydrate; hydrated calcium silicate.

[0083] Example 1: In this embodiment, the formula of a dry powder coating for exterior wall is as follows:

[0084] Calcium borosilicate aluminum cement powder: 60 parts (70% of which is calcium aluminum melilite);

[0085] Polydopamine modified boron nitride nanosheet: 15 parts;

[0086] Cerium-doped titanium dioxide: ): 10 parts ( );

[0087] Volcanic ash microbeads: 1220 parts;

[0088] Magnesium potassium phosphate activator: ): 6 parts;

[0089] Biobased polyaspartic acid sodium dispersant: 3 parts;

[0090] Modified hectorite thixotropic agent: 1.5 parts;

[0091] The preparation process of each component is as follows:

[0092] Preparation of calcium borosilicate aluminum cement powder:

[0093] Melt treatment: the raw materials are mixed, 1.0wt% calcium fluoride is added, and the mixture is melted at 1500℃ in an electric arc furnace for 24 hours under nitrogen protection. Quenching treatment: melt the body with a liquid nitrogen quenching rate of 120℃ / s to room temperature, and the amorphous phase accounts for 85%.

[0094] Crystallization calcination: crush to a particle size of 80μm, and heat in a rotary kiln in stages: 600 to 800℃, 800 to 950℃.

[0095] Crystallization calcination: crush to a particle size of 80μm, and heat in a rotary kiln in stages: 600 to 800℃, 800 to 950℃.

[0096] ​​Milling: Planetary ball milling to a specific surface area of 480 m2 / kg, adding 0.2wt% polycarboxylic dispersant.

[0097] Preparation of boron nitride nanosheets:

[0098] Ultrasonic exfoliation: Boron nitride powder was added with 1.0wt% sodium dodecyl sulfate in deionized water, and a probe-type ultrasonic processor was used for 3 hours of treatment. The upper suspension was collected by centrifugation.

[0099] Polydopamine modification: The suspension was mixed with dopamine hydrochloride at a mass ratio of 1:0.3, the pH was adjusted to 9.0, and the mixture was stirred magnetically at 30°C for 18 hours of reaction.

[0100] Washing and drying: Centrifugal washing with deionized water for 3 times, and freeze-drying at -50°C for 24 hours.

[0101] Preparation of other raw materials:

[0102] Volcanic ash microbeads: Airflow sorting to a particle size of 25μm, immersion in an 8wt% KH-550 ethanol solution for 45 minutes, and drying at 130°C.

[0103] Magnesium potassium phosphate activator: Mixing, adding 0.2wt% boric acid, hydrothermal reaction at 90°C for 5 hours, and spray drying to obtain crystals.

[0104] Biobased dispersant: L-aspartic acid was mixed with maleic anhydride, 0.8wt% ammonium persulfate was added, and polymerization was carried out at 190°C for 2.5 hours, Neutralization to pH=8.

[0105] Modified hectorite: Hectorite was mixed with CTAB at a mass ratio of 1:0.2, stirred in a water bath at 70°C for 3 hours, and dried by centrifugation.

[0106] The preparation process of a dry powder coating for exterior walls in this example is as follows: first, pre-activation treatment, 15 parts of boron nitride nanosheets and 3 parts of biobased polyaspartic acid sodium dispersant are added to 500mL ammonia solution with pH of 8.5, and a probe-type ultrasonic processor with frequency of 40kHz and power of 800W is used for continuous ultrasonic treatment in a 25°C water bath for 30 minutes; then dry mixing, 60 parts of calcium aluminum borosilicate cement powder, 1220 parts of volcanic ash microbeads, and 6 parts of magnesium potassium phosphate activator are put into a planetary mixer, and mixed at a speed of 1500rpm for 20 minutes to ensure that the mass deviation of each component is ≤0.5%; then wet mixing, the pre-activated boron nitride suspension, 10 parts of The powder and 1.5 parts of modified hectorite thixotropic agent were added to the mixer, the speed was adjusted to 1000 rpm and the mixing was continued for 30 minutes. During this period, the temperature was controlled not to exceed 35°C by jacket water cooling. Finally, the mixture was placed in a constant humidity and constant temperature box for aging for 48 hours, and sieved through a 250-mesh vibrating screen to obtain a finished dry powder coating with a specific surface area of ​​480 m² / kg and a moisture content of ≤0.1%.

[0107] Construction technology:

[0108] Base surface treatment: Clean the base surface with 15MPa high-pressure water, spray KH-560: ethanol = 1:9 pretreatment liquid, and let it stand for 30 minutes.

[0109] Paint activation: dry powder paint and deionized water are mixed at a ratio of 1:0.25, ultrasonically stirred for 10 minutes, and the slurry is .

[0110] Spraying: Two-fluid spray gun sprays in two stages:

[0111] Stage 1: Spray to a thickness of 0.8mm and let it sit for 20 minutes.

[0112] Second stage: spraying to a total thickness of 2.0mm.

[0113] Photocatalytic activation: irradiate with 365nm UV LED for 30 minutes within 2 hours after spraying.

[0114] Comparative Example 1: Traditional Portland cement + unmodified boron nitride formula:

[0115] Ordinary Portland cement powder: 60 parts;

[0116] Unmodified boron nitride micron flakes: 15 parts;

[0117] Other ingredients are the same as in Example 1.

[0118] Preparation process:

[0119] Cement powder: conventional Portland cement process.

[0120] Boron nitride: No ultrasonic exfoliation, direct mechanical mixing.

[0121] Construction process: same as Example 1.

[0122] Comparative Example 2: Formula without boron nitride nanosheets:

[0123] Calcium aluminum borosilicate cement powder: 60 parts;

[0124] Removal of boron nitride nanosheets.

[0125] Preparation and construction process: same as Example 1.

[0126] Experimental Indicators and Test Methods: Test indicators include compressive strength, drying shrinkage, acid corrosion resistance, wet heat aging adhesion, and capillary pore structure. Compressive strength is measured according to ASTM C109 using 50 mm cube specimens after 28 days of standard curing. Drying shrinkage is measured and calculated according to GB / T 29417. Acid corrosion resistance is tested by immersing in 5% sulfuric acid solution for 30 days, measuring mass loss and observing surface morphology. Wet heat aging adhesion is tested according to ASTM D7234, with a pull-off test performed after aging for 1000 hours at 85°C / 85% humidity. Pore structure is analyzed using mercury intrusion porosimetry to analyze porosity and tortuosity.

[0127] Comparative Example 1 uses a traditional Portland cement formula, and Comparative Example 2 removes the boron nitride nanosheets, and the remaining components are the same as those in Example 1. The test method is consistent with that in Example 1.

[0128] Compressive strength:

[0129] Test conditions: 28 days standard curing;

[0130] Sample size: 50mm×50mm×50mm cube.

[0131] Drying shrinkage:

[0132] Test period: initial length to 28-day drying shrinkage;

[0133] Calculation formula:

[0134] ;

[0135] Acid corrosion resistance:

[0136] Test method: Soak the sample for 30 days and measure the mass loss rate and surface morphology;

[0137] Adhesion after wet heat aging:

[0138] Test conditions: 85℃ / 85%RH, pull-out test after 1000 hours of aging;

[0139] Capillary structure analysis:

[0140] Test parameters: pore size distribution, porosity, tortuosity;

[0141] Table 1 Comparison of experimental data of Example 1, Comparative Example 1 and Comparative Example 2

[0142]

[0143] Table 1 shows that:

[0144] Example 1 is significantly higher than Comparative Example 1 and Comparative Example 2. The quaternary system of calcium aluminum borosilicate cement powder ( ) By directional crystallization of calcite, the crystal crosslinking density is enhanced; boron nitride nanosheets serve as a reinforcing phase and improve the matrix density by interlayer intercalation. The shrinkage rate of Example 1 is only 0.02%, which is 86.7% lower than that of Comparative Example 1. This is because the borosilicate calcium aluminum cement powder contains inhibition Generate, reduce shrinkage source; boron nitride nanosheets are arranged in a directional manner to block the water migration path. Example 1 at 5% The mass loss is only 0.09%, which is much lower than that of comparative example 1. The main crystal phase of calcite and boron nitride work together to resist acid corrosion; the polydopamine coating layer strengthens the interface between the nanosheets and the cement powder, reducing microcracks. The adhesion retention rate of Example 1 is 98.2%, which is 37% higher than that of comparative example 1, indicating that the hydrophobic properties of boron nitride nanosheets block water vapor penetration; in the cement powder matrix The content is ≤0.005% to avoid the loss of adhesion caused by steel bar corrosion.

[0145] In Example 1, the pore tortuosity is 3.8, and the boron nitride nanosheets extend the capillary path by more than 30%, effectively reducing the water diffusion rate.

[0146] Example 2:

[0147] Recipe: Same as Example 1, but Anatase / rutile mixed phase is used.

[0148] Preparation process:

[0149] preparation:

[0150] Precursor synthesis: Tetrabutyl titanate and cerium nitrate were dissolved in a solvent of ethanol:ethylene glycol = 3:1, 0.5 wt% CTAB was added, and magnetic stirring was performed for 2 hours to form a sol.

[0151] Hydrothermal reaction: 180℃ for 18 hours, centrifugal washing and freeze-drying at -50℃ for 24 hours.

[0152] Staged calcination:

[0153] The first stage: keep warm at 450℃ for 2 hours.

[0154] The second stage: keep warm at 650℃ for 1 hour.

[0155] Acid treatment: Powder dispersed in 0.1M , 40kHz ultrasound for 30 minutes, and dried.

[0156] Construction process: Spraying pressure: 0.7 MPa. Other steps are the same as in Example 1.

[0157] Comparative Example 3:

[0158] pure Formula: Unadulterated : 10 copies.

[0159] Preparation and construction process: same as Example 2.

[0160] Comparative Example 4:

[0161] No Boron Nitride+ Recipe: except for the boron nitride nanosheets, the rest is the same as in Example 2.

[0162] Preparation and construction process: same as Example 2.

[0163] Comparative Example 5:

[0164] excess Doping ( )formula: : 10 servings ( ).

[0165] Preparation process:

[0166] Calcination temperature: 500°C × 2 hours in the first stage, 700°C × 1 hour in the second stage.

[0167] Other steps: same as Example 2.

[0168] Experimental indicators and test methods:

[0169] The photocatalytic efficiency was determined according to ISO 10678 using a methylene blue solution under simulated sunlight for 2 hours.

[0170] The infrared reflectivity was measured using a Fourier transform infrared spectrometer according to the ASTM E903 standard in the 800-2500 nm band.

[0171] The UV blocking rate is measured according to GB / T 18830 standard for the transmittance in the wavelength range of 280-400nm.

[0172] The photogenerated carrier separation efficiency was determined by analyzing the fluorescence emission intensity through PL spectroscopy and calculating the carrier recombination rate.

[0173] Weathering test The photocatalytic efficiency determination was repeated after damp heat aging.

[0174] Comparative Example 3 uses undoped titanium dioxide, Comparative Example 4 removes boron nitride, and Comparative Example 5 uses excessive cerium doping ( ), the rest of the preparation conditions are the same as those in Example 2.

[0175] Photocatalytic efficiency:

[0176] Test method: Take methylene blue solution as the degradation object, irradiate it under simulated sunlight for 2 hours, and calculate the degradation rate;

[0177] Calculation formula: ;in, is the initial concentration, is the concentration after degradation;

[0178] Infrared reflectivity:

[0179] Test instrument: Fourier transform infrared spectrometer, wavelength range 2.5-25μm;

[0180] Data processing: Calculate the average reflectivity in the 800-2500nm band;

[0181] UV blocking rate:

[0182] Testing instrument: UV-visible spectrophotometer, wavelength range 280-400nm;

[0183] Calculation formula: ;

[0184] Photogenerated carrier separation efficiency:

[0185] Test conditions: excitation wavelength 325nm, detection of fluorescence emission intensity;

[0186] Data processing: Half-peak width and peak intensity are inversely proportional to the carrier recombination rate;

[0187] Weather resistance test:

[0188] Test conditions: 85℃ / 85%RH, repeat the photocatalytic efficiency test after 1000 hours of aging;

[0189] Table 2 Comparison of experimental data of Example 2 and Comparative Examples 3-5

[0190]

[0191] From Table 2 we can see that:

[0192] Example 2 is significantly higher than Comparative Example 3 and Comparative Example 5, and cerium doping is achieved. Redox broadens the photoresponse to the visible light region; anatase / rutile mixed phase promotes electron-hole pair separation.

[0193] Example 2 has an infrared reflectivity of 88.7% and an ultraviolet blocking rate of 99.1%, which is significantly improved compared with Comparative Example 3. Heterojunction with boron nitride enhances full-band reflection performance; Boron nitride nanosheets and Synergistically block thermal radiation.

[0194] The PL half-peak width of Example 2 is only 28.3 nm. The / boron nitride heterojunction increases the photogenerated carrier separation efficiency to 82%; the two-dimensional conductive channel of boron nitride accelerates electron transport.

[0195] The photocatalytic retention rate of Example 2 after aging is 95%, which is much higher than that of Comparative Example 3. This is because cerium doping inhibits photocorrosion; boron nitride nanosheets block water and oxygen penetration, protecting Active sites. The performance of Comparative Example 5 deteriorates, as excessive cerium doping leads to lattice distortion and a blue shift in the light absorption edge; high cerium content promotes carrier recombination.

[0196] Cerium-doped titanium dioxide achieves efficient photocatalysis and infrared reflection through the synergistic effect of mixed-phase structure and boron nitride heterojunction. The introduction of boron nitride nanosheets not only improves thermal insulation performance, but also enhances photocatalytic stability through interfacial electron transfer. Strict control of the cerium doping ratio is the key to performance optimization, and excessive doping will lead to performance degradation.

[0197] Example 3:

[0198] formula:

[0199] Volcanic ash microbeads: 1220 parts, KH-550 modified, immersion time 45 minutes; potassium magnesium phosphate activator: 6 parts; other ingredients are the same as in Example 1.

[0200] Preparation process:

[0201] Volcanic ash microbeads: air flow sorting to a particle size of 25 μm, immersed in 8 wt% KH-550 ethanol solution for 45 minutes, and dried at 130 °C.

[0202] Potassium magnesium phosphate stimulant: The mixture was mixed, subjected to hydrothermal reaction at 90° C. for 5 hours, and spray-dried.

[0203] Construction process: Spraying pressure: 0.6 MPa. Other steps are the same as in Example 1.

[0204] Comparative Example 6:

[0205] The formula of wollastonite replacing volcanic ash microbeads uses 1220 parts of unmodified wollastonite with a particle size of 30 μm; the rest is the same as in Example 3; the preparation and construction process are the same as in Example 3.

[0206] Comparative Example 7:

[0207] Potassium magnesium phosphate-free stimulant formula:

[0208] Remove the potassium magnesium phosphate activator; otherwise, the same as in Example 3;

[0209] Preparation and construction process: same as Example 3.

[0210] Comparative Example 8:

[0211] Unmodified volcanic ash microbeads formulation:

[0212] 1220 parts of volcanic ash microbeads, not impregnated with KH-550, and other conditions are the same as in Example 3. Preparation and construction process: the same as in Example 3.

[0213] Experimental indicators and test methods:

[0214] The density of the coating is determined by tap density according to GB / T 5486.

[0215] Freeze-thaw resistance: The surface condition is evaluated after 50 cycles of -20℃ to 20℃ testing in accordance with GB / T 50082.

[0216] The anti-alkaline efflorescence test refers to the JG / T 157 standard and observes the formation of white frost after 72 hours of immersion in water.

[0217] The microstructure was analyzed by SEM / EDS to analyze the interface bonding, XRD to detect the new phase formation, and mercury intrusion porosimetry to determine the pore distribution.

[0218] The hydration heat analysis was performed using the ASTM C1679 standard to record the 72-hour exotherm curve.

[0219] Comparative Example 6 replaced the unmodified wollastonite, Comparative Example 7 removed the potassium magnesium phosphate activator, and Comparative Example 8 used unmodified volcanic ash microbeads. The other parameters were consistent with Example 3.

[0220] Paint density:

[0221] Test method: Dry coating powder tap density test;

[0222] Freeze-thaw resistance:

[0223] Test conditions: -20℃ (4h) -20℃ water bath (4h) is one cycle, and the surface peeling is observed after 50 cycles;

[0224] Rating criteria: no peeling (excellent), micro-cracks (good), peeling (poor);

[0225] Anti-alkali:

[0226] Test method: After the coating is immersed in water for 72 hours, it is placed in a 40℃ / 95%RH environment for 24 hours to observe the formation of white frost on the surface;

[0227] Rating standard: no white frost (excellent), partial white frost (medium), full white frost (poor);

[0228] Microstructure analysis:

[0229] SEM / EDS: observe the interface bonding and pore structure between volcanic ash microbeads and cement powder matrix;

[0230] XRD: detect the new phase generated by the reaction between magnesium potassium phosphate activator and cement powder;

[0231] Mercury intrusion method: measure porosity and pore size distribution;

[0232] Heat of hydration analysis:

[0233] Test instrument: Isothermal calorimeter, recording the hydration exothermic curve within 72 hours;

[0234] Table 3 Comparison of experimental data of Example 3 and Comparative Examples 6-8

[0235]

[0236] From Table 3 we can see that:

[0237] The density of Example 3 is only 0.82 g / cm³. This is because the closed-pore structure of the volcanic ash microbeads significantly reduces the filler density; the hydrophobic modification of KH-550 reduces the water absorption of the microbeads and avoids slurry thickening.

[0238] Example 3 has no peeling after 50 freeze-thaw cycles, while Comparative Example 6 has severe peeling. Reaction generation , enhancing the interface's ability to resist frost heave; the closed-pore volcanic ash microbeads block moisture migration and reduce ice crystal damage.

[0239] Example 3 has no white frost, while Comparative Examples 6, 7 and 8 all have white frost. The potassium magnesium phosphate activator consumes the free , inhibiting alkali migration; volcanic ash microbeads activity and The secondary reaction generates CSH gel.

[0240] The density of Comparative Example 6 is 0.95 g / cm³, which is higher than that of Example 3, and the anti-efflorescence property is decreased. The KH-550 modification enhances the microbead-cement powder interface bonding through the -Si-O- bond; the hydroxyl groups on the surface of the unmodified microbeads adsorb moisture, exacerbating efflorescence.

[0241] Comparative Example 7 freeze-thaw resistance is only "good", and no , stimulants promote With cement powder Forming a cross-linked structure to improve density; in the absence of an activator, the volcanic ash microspheres only play a physical filling role and cannot inhibit alkali dissolution. It can be seen that the closed-pore structure and hydrophobic modification of the volcanic ash microspheres significantly reduce the density of the coating, improve the workability and freeze-thaw resistance, and the potassium magnesium phosphate activator generates New phase, optimize pore structure and inhibit alkali; the synergistic effect of the two realizes the preparation of lightweight and high-durability coating, and the comprehensive performance is far superior to traditional wollastonite filler system.

[0242] Example 4:

[0243] Formulation:

[0244] Bio-based polyaspartic acid sodium dispersant: 3 parts;

[0245] Modified hectorite: 1.5 parts;

[0246] Other ingredients are the same as example 1;

[0247] Preparation process:

[0248] Bio-based dispersant: L-aspartic acid and maleic anhydride are mixed, 0.8wt% ammonium persulfate is added, and polymerization is carried out at 190°C under nitrogen protection for 2.5 hours, Neutralized to pH=8.

[0249] Modified hectorite: Hectorite and CTAB are mixed in a mass ratio of 1:0.2, stirred in a water bath at 70°C for 3 hours, centrifuged and washed 3 times, and dried at 80°C.

[0250] Construction process:

[0251] Slurry stirring: ultrasonic power 500Wx10min.

[0252] Spraying pressure: 0.75MPa.

[0253] Other steps are the same as example 1.

[0254] Comparative example 9:

[0255] Naphthalene dispersant + unmodified hectorite formula:

[0256] Naphthalene dispersant: 3 parts; Unmodified hectorite: 1.5 parts; Others are the same as example 4;

[0257] Preparation and construction process: the same as example 4.

[0258] Comparative example 10:

[0259] Unmodified hectorite formula:

[0260] Hectorite is not modified by CTAB;

[0261] Others are the same as example 4;

[0262] Preparation and construction process: the same as example 4.

[0263] Comparative example 11:

[0264] Excess CTAB modified hectorite formulation: modified hectorite: CTAB: hectorite = 1:0.5;

[0265] Other same as Example 4;

[0266] Preparation process: Hectorite and CTAB were mixed at a mass ratio of 1:0.5, stirred at 70°C for 4 hours.

[0267] Experimental index and test method: dispersity The particle size distribution of boron nitride nanosheets was determined by dynamic light scattering method.

[0268] Thixotropic index: The ratio of viscosity at 3 rpm and 30 rpm was tested according to ASTM D2196 standard.

[0269] Slurry stability: The sedimentation height ratio was determined by standing for 24 hours.

[0270] Adhesion: The pull-out test of concrete substrate was carried out according to GB / T 5210 standard.

[0271] Environmental performance test includes VOC content of GB 18582 standard and biodegradability of ISO 14855.

[0272] Hectorite interlayer spacing was analyzed by XRD.

[0273] Comparative Example 9 used naphthalene dispersant and unmodified hectorite, Comparative Example 10 removed hectorite modification, and Comparative Example 11 used excess CTAB modification, and the rest of the conditions were the same as Example 4.

[0274] Dispersity Test method: Dynamic light scattering was used to measure the particle size distribution of boron nitride nanosheets in the slurry;

[0275] Standard: ;

[0276] Thixotropic index: Test instrument: rotary rheometer, measure the viscosity ratio at 3 rpm and 30 rpm speed;

[0277] Slurry stability: Test method: observe the sedimentation and stratification after standing for 24 hours, and calculate the sedimentation rate;

[0278] Adhesion test conditions: pull-out test, measure the bonding strength of the coating and the substrate;

[0279] Environmental performance: VOC content: thermal desorption-GC / MS method was used to detect volatile organic compounds;

[0280] Biodegradability: 28-day degradation rate test.

[0281] Table 4 Comparison of experimental data of Example 4 and Comparative Examples 9-11

[0282]

[0283] As can be seen from Table 4:

[0284] Example 4 The nanosheets are stabilized by the carboxylic acid groups of bio-based sodium polyaspartate through electrostatic repulsion, and the interlayer spacing of the modified hectorite is expanded to 2.8 nm, thereby enhancing the steric hindrance effect on the slurry.

[0285] In Example 4, the thixotropic index was 3.8. CTAB-modified hectorite formed a card-house structure, exhibiting high viscosity at rest and a sharp drop in viscosity after shearing. Unmodified hectorite, due to its small interlayer spacing, was unable to effectively form a thixotropic network. The sedimentation rate in Example 4 was only 2.1%, demonstrating that the thixotropic network of the modified hectorite suppressed particle settling.

[0286] Example 4 No VOC was detected, and the biodegradation rate reached 78% in 28 days. The bio-based source of L-aspartic acid avoided the toxicity of traditional naphthalene-based dispersants; the CTAB modification amount was within the safe range.

[0287] Comparative Example 9 interlayer spacing is expanded to 3.5nm, but The thixotropic index and the thixotropic index of Example 4 are still inferior. Excessive CTAB loosens the interlayer structure of the hectorite and weakens the thixotropic network strength; exceeding the CTAB dosage actually reduces performance. The bio-based sodium polyaspartate dispersant achieves high dispersion of nanosheets through the synergistic effects of electrostatic repulsion and steric hindrance, while being environmentally friendly and non-toxic. CTAB-modified hectorite constructs a three-dimensional thixotropic network, significantly improving slurry stability and workability. The synergistic effect of these two factors overcomes the technical bottlenecks of traditional coating dispersion-thixotropic systems, while meeting the requirements of high performance and green applications.

[0288] The above description is only 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 in the scope of protection of the present invention.

Claims

1. A dry powder coating for exterior walls, characterized in that: It is made from the following raw materials in parts by weight: Calcium aluminum borosilicate cement powder :60 copies; Boron nitride nanosheets: 15 parts; Rare earth cerium doped titanium dioxide : 10 parts; Volcanic ash microbeads: 1220 parts; Potassium magnesium phosphate activator : 6 parts; Bio-based sodium polyaspartate dispersant: 3 parts; Modified hectorite thixotropic agent: 1.5 parts.

2. The dry powder coating for exterior walls according to claim 1, characterized in that: The borosilicate calcium aluminum cement powder is prepared by a melting-quenching method, and its mineral composition includes calcite Proportion ≥70%; Prepared by the following process: according to Weigh boric acid in a molar ratio of 4:3:1:2 , calcium oxide , alumina and silica , add 0.5~1.5wt% calcium fluoride after mixing As a mineralizer; place the mixture in an electric arc furnace, heat it to 1450-1550℃ under nitrogen protection and keep it warm for 24 hours; The melt is rapidly cooled to room temperature at a cooling rate of ≥100°C / s and quenched with liquid nitrogen to obtain an amorphous glass body, in which the amorphous phase accounts for ≥85%. Content ≤0.005%; The quenched glass is crushed into particles ≤ 100 μm, placed in a rotary kiln and heated in stages: 600-800 ° C in a temperature range of 5 ° C / min to promote Network reconstruction; heating in the range of 800-950℃ at 15℃ / min to induce gehlerite Directed crystallization is the main crystalline phase; The calcined clinker is ground into powder by a planetary ball mill to a specific surface area of ​​≥450m² / kg, and 0.1-0.3wt% of a polycarboxylic acid dispersant is added to obtain calcium aluminum borosilicate cement powder.

3. The dry powder coating for exterior walls according to claim 1, characterized in that: The boron nitride nanosheets are prepared by the following process: Disperse boron nitride powder in deionized water with a solid-liquid ratio of 1:50 to 1:100, and add 0.5 to 1.5 wt% sodium lauryl sulfate. , using a probe-type ultrasonic processor for 2 to 4 hours, centrifuging at 8000 to 12000 rpm, and collecting the upper suspension after 30 minutes to obtain boron nitride nanosheets with a thickness of ≤5 nm and a lateral size of 0.5 to 5 μm; In situ modification with polydopamine: the nanosheet suspension obtained in step 1 is mixed with dopamine hydrochloride in a mass ratio of 1:0.2 to 1:0.5, the pH is adjusted to 8.5 to 9.5, and the mixture is reacted with magnetic stirring at 300 to 500 rpm at 25 to 35° C. for 12 to 24 hours to form a polydopamine coating layer with a thickness of 2 to 3 nm; The reaction product was washed three times with deionized water and anhydrous ethanol by centrifugation for 10 minutes each time, and freeze-dried at -50°C for 24 hours to obtain polydopamine-modified boron nitride nanosheets with a specific surface area of ​​≥200 m² / g.

4. The dry powder coating for exterior walls according to claim 1, characterized in that: The rare earth cerium doped titanium dioxide Prepared by the following process: Tetrabutyl titanate With cerium nitrate according to The mixture was mixed in a molar ratio of 97:3, dissolved in a mixed solvent of ethanol and ethylene glycol, and 0.5 wt% of hexadecyltrimethylammonium bromide was added. , magnetic stirring to form a homogeneous sol; The sol was transferred to a high-pressure reactor and reacted at 180°C for 12 to 24 hours to generate cerium-doped The precursor, the product was washed by centrifugation and freeze-dried at -50 °C for 24 h; The first stage: heating to 450-500℃ at 5℃ / min and keeping at this temperature for 2 hours to generate anatase phase; The second stage: heating to 600-650℃ at 10℃ / min and keeping it for 1 hour to induce rutile phase crystallization, and finally obtain ; The calcined powder was dispersed in 0.1M hydrochloric acid solution with a solid-liquid ratio of 1:50, ultrasonicated at 40kHz for 30min and then dried to obtain a specific surface area of ​​≥80m² / g. Powder.

5. The dry powder coating for exterior walls according to claim 1, characterized in that: The volcanic ash microbeads and potassium magnesium phosphate activator , bio-based sodium polyaspartate dispersant, and modified hectorite thixotropic agent are prepared by the following processes: The volcanic ash raw materials are separated by air flow to obtain micro beads with a particle size of ≤30μm, and the silane coupling agent is added at 5-10wt%. Immersing in an ethanol solution for 30 to 60 minutes and drying at 120 to 150°C to form volcanic ash microbeads with hydrophobic surface modification; according to The molar ratio is 1:1:6, 0.1-0.3 wt% boric acid is added as a crystallization control agent, and the reaction is hydrothermally reacted at 80-100 ° C for 4-6 hours. The product is spray-dried to obtain crystals; Preparation of bio-based sodium polyaspartate dispersant: L-aspartic acid and maleic anhydride were mixed in a molar ratio of 1:1.2, 0.5-1.0 wt% of ammonium persulfate initiator was added, and the polymerization reaction was carried out at 180-200 ° C under nitrogen protection for 2-3 hours. Neutralize to pH=7-8 to obtain bio-based sodium polyaspartate; Hectorite powder and cetyltrimethylammonium bromide The mixture is mixed in a mass ratio of 1:0.1 to 1:0.3, stirred in a water bath at 60 to 80° C. for 2 to 4 hours, washed by centrifugation and then dried to obtain a modified hectorite with an interlayer spacing expanded to 2.5 to 3.0 nm.

6. A method for preparing a dry powder coating for exterior walls according to any one of claims 1 to 5, characterized in that: The following steps are involved: R1. Pre-activation treatment: Boron nitride nanosheets and bio-based sodium polyaspartate dispersant were added to an ammonia solution with a pH of 8-9 and exfoliated using ultrasound at a frequency of 40 kHz for 30 minutes. R2 dry mix: The calcium aluminum borosilicate cement powder, pozzolan beads, magnesium potassium phosphate activator into a planetary mixer, mixed at 1500rpm for 20min; R3. Wet mixing: Add preactivated boron nitride nanosheets, rare earth cerium-doped titanium dioxide, and modified hectorite thixotropic agent and continue mixing for 30 minutes; R4. Curing: Curing at 60% humidity and 45°C for 48 hours, and passing through a 250-mesh sieve to obtain the finished product.

7. A construction method for a dry powder coating for exterior walls according to any one of claims 1 to 5, characterized in that: The following steps are involved: H1. Surface pretreatment: Use a high-pressure water jet with a pressure of ≥15MPa to clean the wall surface to remove dust and loose particles. Spray a silane coupling agent pretreatment solution with a volume ratio of KH-560:ethanol = 1:9 at a spray rate of 20-30g / m² and let it stand for 30 minutes. H2. Paint Activation and Spraying: Exterior wall dry powder paint and deionized water were mixed in a mass ratio of 1:0.25 and stirred in an ultrasonic mixer for 10 minutes to form a thixotropic slurry. The dispersion of the nano-boron nitride (D90) was ≤ 500 nm. Airless spraying was performed using a two-fluid spray gun at an air pressure of 0.6-0.8 MPa and a nozzle diameter of 2.5 mm. The application was carried out in two stages: the first stage was to spray a thickness of 0.5-0.8 mm to form a porous base layer. After a 20-minute interval, the second stage was to spray to a total thickness of 1.5-2.0 mm. H3. Photocatalytic activation: Within 2 hours after spraying, irradiate the coating surface with a UV LED array with a wavelength of 365nm and an irradiance of 50mW / cm² for 30 minutes.

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