Waterproof composite coating and preparation method thereof

Abstract

The application discloses a kind of waterproof composite coating and preparation method thereof, belong to coating technical field.The method includes: preparation aqueous polyurethane dispersion, aqueous bisphenol A type epoxy resin and fluorine-containing acrylic emulsion of aqueous resin premix fluid;With nano silicon dioxide, nano titanium dioxide, nano zinc oxide as matrix, after hydrolysis and polycondensation of gamma-aminopropyl triethoxysilane and perfluorooctyl triethoxysilane, fluorinated modified nano inorganic composite sol is prepared by polydopamine coating;With multi-walled carbon nanotube and graphene oxide as matrix, carbon-based nano composite dispersion liquid is prepared by in-situ coating of polydopamine;Cellulose nanocrystals are modified by polyethylene glycol to prepare bio-based nanodispersion;The above three kinds of nanodispersion are added to resin premix fluid, defoaming agent, leveling agent and epoxy curing agent are stirred uniformly.The application is suitable for long-term protection of various substrates by the synergy of fluorinated polydopamine-mediated multi-level micro-nano structure and low surface energy resin.

Description

Technical Field

[0001] This invention belongs to the field of coating technology, specifically, it relates to a waterproof composite coating and its preparation method. Background Technology

[0002] With the rapid development of modern industry, construction, transportation, marine engineering, and aerospace, the demand for waterproof, antifouling, anticorrosive, anti-icing, and self-cleaning properties of material surfaces is becoming increasingly urgent. Especially in humid, rainy, salt spray, or heavily polluted environments, traditional material surfaces are prone to water accumulation, icing, dirt adhesion, or corrosion, leading to performance degradation, shortened service life, and even safety hazards. For example, on building exteriors, bridges, ships, oil pipelines, power transmission lines, and the surfaces of automobiles and aircraft, moisture penetration and accumulation not only accelerate material aging but also induce mold, rust, and icing, causing significant economic losses and maintenance costs. Therefore, the development of efficient and durable waterproof coatings has become a research hotspot in the field of material protection.

[0003] Traditional waterproof coatings mainly include asphalt-based waterproof coatings, polyurethane waterproof coatings, acrylic waterproof coatings, and cement-based waterproof coatings. These coatings played an important role in early waterproof applications. Asphalt-based waterproof coatings are inexpensive and have reliable waterproof performance, but they have problems such as poor weather resistance, easy aging and cracking, and the generation of harmful gases during construction. Polyurethane waterproof coatings have good flexibility and dense film formation, but the curing process is sensitive to humidity, prone to bubbling, and some products contain free isocyanates, which are harmful to human health and the environment. Acrylic waterproof coatings form a film quickly and have rich colors, but their water resistance and alkali resistance are insufficient, and they are prone to powdering and peeling after long-term immersion. Cement-based waterproof coatings have good compatibility with concrete substrates, but they have poor flexibility, are prone to cracking, and their waterproof effect depends on the thickness of the application. The common defects of these traditional waterproof coatings are: their waterproof mechanism mainly relies on the density of the coating to block water penetration, and once the coating develops micro-cracks or ages, the waterproof performance drops significantly; in addition, they generally lack self-cleaning function, and dust and oil stains easily accumulate on the surface, further weakening the protective effect; their environmental performance is also poor, with many products containing volatile organic compounds (VOCs), which does not meet the current development requirements of green building materials.

[0004] In recent years, inspired by the "lotus leaf effect" in nature, research on superhydrophobic surfaces has made groundbreaking progress. The surface of a lotus leaf possesses a micron-nano composite rough structure and a low surface energy waxy layer. Water droplets on its surface form spheres and easily roll off, carrying away dirt and achieving self-cleaning. Scientists have developed artificial superhydrophobic coatings by constructing similar micro-nano composite rough structures and combining them with low surface energy materials. These coatings typically have a water contact angle greater than 150° and a roll-off angle less than 10°. They not only possess excellent waterproof performance but also combine self-cleaning, anti-fouling, anti-icing, and drag-reducing functions, showing broad application prospects in building exteriors, solar panels, textiles, and metal corrosion protection.

[0005] The existing methods for preparing superhydrophobic coatings mainly include the following categories: (1) Template method: using natural or artificial templates (such as lotus leaves and rose petals) to replicate micro-nano structures, and then combining them with low surface energy modification. This method can accurately replicate the morphology of biological surfaces, but the template preparation is complex, costly, and difficult to apply on a large scale. (2) Etching method: constructing rough structures on the surface of the substrate through chemical etching (such as acid and alkali corrosion) or physical etching (such as plasma and laser), and then performing fluorination treatment. This method is suitable for hard substrates such as metals and glass, but the etching process is prone to damaging the substrate and generating waste liquid, and the rough structure has low mechanical strength and poor wear resistance. (3) Sol-gel method: using tetraethyl orthosilicate as a precursor, hydrolysis and condensation are used to form nano-silica sol, which is then modified with fluorosilanes or long-chain alkylsilanes and coated into a film. This method is simple and transparent, but the gel network is fragile, and the micro-nano structure of the coating is easily destroyed after friction or scratching, resulting in rapid loss of superhydrophobicity; in addition, the commonly used alcohol solvent system has a high VOC content, which does not meet environmental protection requirements. (4) Nanoparticle deposition method: Directly spray or dip-coat fluorinated modified nanoparticles (such as fluorinated SiO2, TiO2) to construct a rough surface. This method is simple to operate, but the bonding force between the nanoparticles and the substrate or resin matrix is ​​weak and easy to fall off; the coating has poor durability, and the contact angle usually drops below 150° after several hundred friction cycles. (5) Polymer composite method: Fluorinated polymers (such as PTFE, fluorinated acrylates) are composited with nanofillers to form an interpenetrating network. This method can improve flexibility, but the amount of fluoride used is large and the cost is high, and the environmental durability of fluorine is increasingly concerned.

[0006] Although the above methods can achieve excellent superhydrophobic properties under laboratory conditions, several bottlenecks remain in practical engineering applications: First, poor mechanical durability is the most prominent problem with superhydrophobic coatings. The realization of superhydrophobicity highly depends on the surface micro / nano rough structure; once subjected to mechanical wear, scratching, or abrasive impact, this structure is easily damaged, leading to increased surface energy and decreased contact angle. Existing literature reports that many superhydrophobic coatings lose their superhydrophobicity after only 100-300 cycles of sandpaper abrasion under a 500g load, failing to meet the requirements for long-term outdoor use. Second, insufficient adhesion and interfacial compatibility. The lack of effective chemical bonding between nanoparticles and organic resin matrices or inorganic substrates (such as concrete and metals) makes the coating prone to blistering and peeling under thermal expansion and contraction, humid heat cycling, or salt spray environments. Especially with porous substrates such as concrete, existing coatings have poor permeability, making it difficult to form a strong anchor. Third, chemical corrosion resistance and weather resistance need improvement. Superhydrophobic coatings are susceptible to degradation of low-energy substances or collapse of rough structures under long-term exposure to acids, alkalis, salt spray, or ultraviolet radiation, leading to protective failure. For example, in marine environments, chloride ion penetration accelerates the corrosion of metal substrates. Fourth, environmental and construction issues are prominent. Many superhydrophobic coatings rely on organic solvents (such as ethanol and acetone) or fluorinated compounds, resulting in high VOC emissions and a significant risk of bioaccumulation; some preparation processes involve strong acid and alkali etching, generating hazardous waste. Meanwhile, the development of water-based superhydrophobic coatings is difficult, and existing water-based systems often struggle to form stable micro / nano structures due to high surface tension, leading to unstable superhydrophobic properties. Fifth, multifunctionality is insufficient. Most existing superhydrophobic coatings only possess waterproof and self-cleaning functions, failing to simultaneously achieve additional properties such as conductivity, antistatic properties, photothermal de-icing, antibacterial properties, or high transparency, thus failing to meet the "one coating, multiple uses" requirements under complex working conditions. Sixth, cost and large-scale production barriers exist. High-end fluorosilanes, nanomaterials, and complex processes result in expensive products, hindering widespread adoption in fields such as construction and infrastructure.

[0007] In recent years, researchers have attempted to improve these shortcomings by introducing functional nanofillers. For example, adding carbon nanotubes and graphene can enhance mechanical strength and conductivity; introducing titanium dioxide can achieve photocatalytic self-cleaning; and using cellulose nanocrystals can enhance biocompatibility and flexibility. However, these attempts still have limitations: carbon-based materials have poor dispersibility and are prone to aggregation, leading to uneven coatings; photocatalytic nanoparticles can easily trigger resin degradation; and bio-based materials are highly hydrophilic, requiring complex modifications to achieve compatibility with low surface energy systems. In addition, polydopamine, as a biomimetic material mimicking mussel adhesion proteins, has been used to improve interfacial adhesion, but existing technologies are mostly limited to single matrix modification, failing to achieve synergistic optimization of multiple components including inorganic, organic, carbon-based, and bio-based materials.

[0008] Some existing patented technologies also reflect the above problems. For example, some patents disclose superhydrophobic coatings composed of fluorinated nano-silica and acrylic resin, but the wear resistance is only a few hundred cycles and the adhesion is grade 1 to 2; other patents use polydopamine to coat nanoparticles to improve adhesion, but do not introduce fluorinated low surface energy components, and the contact angle is difficult to reach more than 160°; other patents attempt waterborne polyurethane-based superhydrophobic systems, but due to the lack of multi-level rough structure and functional fillers, the salt spray resistance time is less than 1000h and there are no obvious multifunctional characteristics.

[0009] In summary, while existing waterproof and superhydrophobic coating technologies have made some progress, they still cannot simultaneously meet the comprehensive requirements of high durability, strong adhesion, multifunctionality, environmentally friendly water-based properties, and low-cost scalability. Especially in harsh environments (such as offshore platforms, northern icy regions, and highly polluted urban buildings), there is an urgent need for a new type of waterproof composite coating that can achieve a balance between superhydrophobicity and multiple functions such as mechanical strength, corrosion resistance, self-cleaning, and photothermal properties through the rational design of micro / nano structures, interface modification, and component synergy, while simultaneously reducing environmental impact through a water-based system. This not only has significant theoretical implications but also has substantial practical value for promoting green building materials, extending the lifespan of infrastructure, and reducing maintenance costs.

[0010] Therefore, developing a nano-superhydrophobic composite coating with simple preparation process, environmentally friendly raw materials, excellent performance and multiple functions has become an urgent technical problem to be solved in this field. Summary of the Invention

[0011] To address the prominent shortcomings of existing superhydrophobic coatings, such as poor mechanical durability, insufficient interfacial adhesion, poor chemical corrosion resistance and weather resistance, poor environmental performance, complex construction, limited multifunctionality, and high cost, this invention provides a waterproof composite coating and its preparation method. This coating uses a water-based resin as a matrix and employs a multi-component synergistic construction of a multi-level micro-nano rough structure through polydopamine-mediated fluorinated modified nano-inorganic particles, polydopamine-coated carbon-based nanomaterials, and modified bio-based nanocrystals. This structure forms an interpenetrating network with a low surface energy fluorinated acrylic resin, achieving an organic unity of superhydrophobicity, high mechanical strength, strong adhesion, corrosion resistance, and photothermal conversion capabilities. Furthermore, the all-water-based system results in low VOC emissions, simple construction, and suitability for long-term protection of various substrates such as concrete, metal, and wood.

[0012] The present invention adopts the following technical solution: a method for preparing a waterproof composite coating, comprising the following steps by weight: (1) preparing an aqueous resin premix: adding 15-35 parts of aqueous polyurethane dispersion (solid content 45-65wt%, average particle size 50-300nm), 10-30 parts of aqueous bisphenol A epoxy resin (epoxy equivalent 500-1000g / eq, solid content 50-70wt%), and 5-20 parts of fluorinated acrylic emulsion to deionized water, and stirring at high speed to form a uniform premix, with the solid content controlled at 35-55wt%; (2) preparing a polydopamine-modified nano-inorganic composite sol: taking 3-12 parts of nano silica (average particle size 20-80nm, CAS No.: 7631-86-9), 1-6 parts of nano-titanium dioxide (average particle size 10-40nm, anatase type, CAS No.: 13463-67-7), 0.5-4 parts of nano-zinc oxide (average particle size 20-100nm, CAS No.: 1314-13-2), add to a mixed solvent of 10-30 parts anhydrous ethanol and 10-25 parts deionized water, first add 0.5-4 parts of γ-aminopropyltriethoxysilane (CAS No.: 919-30-2) and 0.5-4 parts of 1H,1H,2H,2H-perfluorooctyltriethoxysilane (CAS No.: 51851-37-7), and hydrolyze and condense at pH 3-5 and 25-45℃ for 1-3 hours. Then add 0.2-2 parts of dopamine hydrochloride (CAS No.: 51-61-6) and 0.1-1 parts of tris(hydroxymethyl)aminomethane (CAS No.: 77-86-1), adjust the pH to 8.0-9.0, and continue the reaction at 20-40℃ for 2-6 hours to form a polydopamine-coated and fluorinated nano-inorganic composite sol with a total solid content of 8-30wt%; (3) Prepare polydopamine-coated carbon-based nanocomposite dispersion: take 0.2-3 parts of multi-walled carbon nanotubes (outer diameter 10-50nm, length 5-20μm, CAS No.: 308068-56-6), 0.2-3 parts of graphene oxide (sheet diameter 1-10μm, oxygen content 30-50wt%), and add 10-3 In 0 parts of deionized water and 0.5-3 parts of sodium dodecyl sulfate (CAS No.: 151-21-3), ultrasonically disperse for 0.5-2h, then add 0.1-1 parts of dopamine hydrochloride (CAS No.: 51-61-6), adjust the pH to 8.0-9.0, and react at 30-50℃ for 3-8h to form a polydopamine-coated carbon-based nanocomposite dispersion in situ; (4) Prepare modified bio-based nanodispersion: Take 0.2-3 parts of cellulose nanocrystals (length 200-500nm, diameter 10-30nm, CAS No.: 9004-34-6, surface sulfate ester content 0.1-0.4mmol / g), add to 10-25 parts of deionized water, and add 0.1~1 part of polyethylene glycol (molecular weight 4000~8000, CAS No.: 25322-68-3), adjust pH to 6~8, high shear dispersion for 1~3h to obtain bio-based nano-dispersion; (5) Composite ingredients: add the polydopamine modified nano-inorganic composite sol of step (2), the carbon-based nano-composite dispersion of step (3) and the bio-based nano-dispersion of step (4) to the aqueous resin premix of step (1) at a total nano solid mass of 8~30wt% of the final coating solid mass. Meanwhile, 0.5-3 parts of polyether-modified silicone defoamer, 0.5-3 parts of polyether siloxane copolymer leveling agent, and 1-6 parts of water-based modified fatty amine epoxy curing agent (amine hydrogen equivalent 250-450 g / eq) are added. The mixture is mechanically stirred at 15-30℃ for 1-3 hours, and the D90 particle size of the system is controlled to be less than 3 μm. (6) Filtration and curing: The coating obtained in step (5) is filtered through an 80-150 mesh filter and placed at 20-35℃ for 24-72 hours to cure, thereby obtaining a waterproof composite coating.

[0013] Preferably, the aqueous polyurethane dispersion in step (1) is prepared by a prepolymer method: polytetrahydrofuran ether diol (molecular weight 1000, hydroxyl value 110 mg KOH / g) is vacuum dehydrated at 80°C for 1.5 h, cooled to 65°C, and isophorone diisocyanate is added to make the R value (-NCO / -OH) 1.8. 0.02 wt% dibutyltin dilaurate is added, and the mixture is stirred at 85°C for 3 h. After cooling to 70°C, dihydroxyl group is added. Methylbutyric acid (5wt% of the total mass of the preceding raw materials) was subjected to chain extension reaction at 80℃ for 2h, cooled to 35℃, and neutralized with triethylamine (molar ratio of 1.0:1 to dimethylolbutyric acid) for 30min. Then, deionized water at 50℃ was added under stirring at 1000r / min for emulsification, with the solid content controlled at 60wt%. After standing for 24h, an aqueous polyurethane dispersion with pH 7.5~8.5 and an average particle size of 80~200nm was obtained; Step (1) The preparation method of the fluorinated acrylic emulsion is as follows: it is prepared by emulsion polymerization of hexafluorobutyl methacrylate (CAS No.: 36405-47-7), butyl acrylate (CAS No.: 141-32-2) and acrylic acid (CAS No.: 79-10-7), wherein the mass ratio of the three monomers is: 20 parts of hexafluorobutyl methacrylate, 60 parts of butyl acrylate and 10 parts of acrylic acid. During preparation, sodium dodecylbenzenesulfonate with a total monomer mass of 4wt% is added to deionized water to prepare a pre-emulsion. One-third of the mass of the pre-emulsion is prepolymerized with 0.2wt% persulfate initiator at 75℃ for 1h. The remaining pre-emulsion is added dropwise at 80℃ for 3h. The temperature is kept at 85℃ for 3h. After cooling, the pH is adjusted to 8.5 and the solid content is controlled at 50wt% to obtain a stable fluorinated acrylic emulsion. The parameters of high-speed stirring in step (1) are as follows: speed 1500r / min, stirring time 40min.

[0014] Preferably, in step (2), the mass ratio of nano-silica, nano-titanium dioxide and nano-zinc oxide is (2~6):(1~3):(0.5~2), the mass ratio of γ-aminopropyltriethoxysilane to 1H,1H,2H,2H-perfluorooctyltriethoxysilane is (1~3):(1), the amount of dopamine hydrochloride added is such that the mass of the polydopamine coating layer accounts for 5~25wt% of the total mass of the inorganic nanoparticles, the hydrolysis and polycondensation stirring speed is 400~1000r / min, and the water:alcohol volume fraction ratio is (1~2):1, forming a fluorinated polydopamine modified composite particle with a dual-size hierarchical rough structure and enhanced interfacial adhesion.

[0015] Preferably, in step (3), the mass ratio of multi-walled carbon nanotubes to graphene oxide is (1~4):1, the total carbon-based nanomaterials account for 0.5~8wt% of the solid mass of the coating, the mass of the polydopamine coating layer accounts for 15~50wt% of the total mass of the carbon-based nanomaterials, and 0.2~1 part of ascorbic acid (CAS No.: 50-81-7) is added before the reaction to assist in the partial reduction of graphene oxide, improve dispersion stability, conductive pathways and photothermal conversion efficiency, and form a through network to enhance mechanical strength and multifunctionality.

[0016] Preferably, in step (4), the absolute value of the zeta potential of the cellulose nanocrystals is 35~60mV, the solid content of the dispersion liquid is 2~8wt%, the amount of polyethylene glycol added is 10~40wt% of the mass of the cellulose nanocrystals, and the high shear speed is 8000~15000r / min, so as to provide three-dimensional skeleton support and inhibit agglomeration, and improve the transparency and flexibility of the coating.

[0017] Preferably, in step (5), the mass ratio (dry basis) of polydopamine modified nano-inorganic composite sol to carbon-based nano-composite dispersion is (3~12):1, and the mass ratio of inorganic:carbon-based:bio-based in the total nano-solids is (5~15):(1~5):1. Before adding the curing agent, the system temperature is lowered to 10~20℃, and after stirring for 30~120min, low-speed stirring is continued to avoid bubbles, ensuring that the curing agent is uniformly dispersed and controlling the NH to epoxy equivalent ratio to be 0.9~1.1.

[0018] Preferably, the coating is applied to the surface of concrete, metal or wood substrates, the substrate pretreatment roughness is Ra1~8μm, and the moisture content is less than 6wt%; the coating viscosity is adjusted to 800~4000mPa·s, the single-coat wet film thickness of spraying or roller coating is 80~250μm, the interval between multiple coatings is 10~40min, the surface drying time is 20~60min at 15~35℃, the full curing time is 48~96h, and the final dry film thickness is 50~200μm.

[0019] Preferably, the composite nanomaterials obtained in steps (2) and (3) are treated with ultrasonic power of 300~1000W for 20~60min before being added to the aqueous resin premix, which promotes the entanglement of polydopamine-mediated nanoparticles with carbon-based materials, forming a multi-level micro-nano composite framework, and improving the mechanical durability and multifunctional synergy of the coating.

[0020] A waterproof composite coating, wherein the waterproof composite coating is obtained by the preparation method described above.

[0021] Compared with existing technologies, this invention has the following significant advantages and innovations: (1) Revolutionary improvement in superhydrophobic durability: This invention innovatively uses γ-aminopropyltriethoxysilane and 1H,1H,2H,2H-perfluorooctyltriethoxysilane bissilane for synergistic hydrolysis and condensation, and constructs a fluorinated dual-size hierarchical micro-nano rough structure under in-situ polydopamine coating, which is deeply synergistic with the low surface energy interpenetrating network resin matrix formed by fluorinated acrylic emulsion. The water contact angle is stable at 154°~160° or higher, and the roll-off angle is less than 7°. Even after 1250~1420 sandpaper abrasion cycles under a 500g load (data from Examples 1~12) or 1500~1680h salt spray test, it still maintains superhydrophobic performance. Compared with the existing superhydrophobic coatings, which usually fail after 100 to 500 wear cycles when the contact angle drops below 140°, the durability of the present invention is improved by 3 to 10 times, and the bottleneck of easy mechanical friction damage of traditional superhydrophobic surfaces is completely solved. (2) Comprehensive enhancement of interface adhesion and mechanical strength: The polydopamine mussel-like adhesion mechanism plays a core "molecular bridge" role in the present invention. Its rich catechol, amino and indole groups form multiple hydrogen bonds, coordination bonds and potential Michael addition / Schiff base covalent bonds with the surface of inorganic nanoparticles, carbon-based materials π-π stacking, cellulose nanocrystal hydroxyl groups and waterborne resins (polyurethane / epoxy), realizing strong anchoring between heterogeneous components. The coating adhesion reaches grade 0 (GB / T 9286-1998), and the pencil hardness is ≥4H (Examples 1, 3, and 5 reach 4H~5H). Simultaneously, the interconnected conductive network constructed from multi-walled carbon nanotubes / graphene oxide synergistically provides excellent flexibility and impact resistance, avoiding blistering, peeling, and brittleness defects caused by weak bonding between nanofillers and resin in existing technologies. Comparative Example 3 (lacking polydopamine) showed adhesion reduced to grade 2 and abrasion resistance of only 350 cycles, fully verifying the criticality of this innovation. (3) High integration and synergy of multifunctionality: This invention is the first to precisely composite three nanosystems—polydopamine-modified inorganic nanomaterials (SiO2 / TiO2 / ZnO), polydopamine-coated carbon-based nanomaterials (CNTs / GO), and polyethylene glycol-modified bio-based nanomaterials (CNC)—in an aqueous resin. Optional combined ultrasonic treatment promotes the formation of a multi-level entangled network, achieving deep functional synergy: the carbon-based material imparts conductivity (antistatic properties) and photothermal conversion capabilities (rapid ice melting and de-icing) to the coating; anatase nano-TiO2 provides photocatalytic self-cleaning and antibacterial properties; ZnO enhances UV shielding; and cellulose nanocrystals improve the coating's transparency, flexibility, and biocompatibility. Compared to existing technologies that mostly offer only single waterproof and self-cleaning functions, this invention achieves "one coating, multiple uses," suitable for complex scenarios such as marine corrosion protection, northern anti-icing and de-icing, antibacterial and antifouling in highly polluted environments, and drag reduction for solar panels. Its functional diversity is significantly superior.(4) Excellent environmental protection and construction friendliness: The entire process uses a water-based dispersion and a mixed solvent of deionized water / a small amount of ethanol, with near-zero VOC emissions, complying with strict environmental regulations; it avoids the hazardous waste generated by organic solvent systems (such as large amounts of alcohol solvents in sol-gel methods) or strong acid and alkali etching commonly found in existing technologies. The coating viscosity can be easily adjusted to 800~4000 mPa·s, spraying / roller coating is simple, single-coat wet film is 80~250μm, multiple coats have short intervals (10~40min), surface drying is fast (20~60min), and full curing is 48~96h. It is suitable for large-area projects on various substrates such as concrete (roughness Ra1~8μm), metal, and wood. The construction efficiency and compatibility are far superior to existing solvent-based or etching-type superhydrophobic coatings. (5) Controllable cost and great potential for large-scale production: The raw materials used are industrial-grade nanoparticles (SiO2, TiO2, ZnO, CNTs), renewable bio-based cellulose nanocrystals, and low-volume fluorosilane / fluorinated acrylic emulsions (fluorine monomers account for only 10~30wt%), avoiding the large dependence of existing technologies on expensive long-chain perfluorinated compounds (such as heptadecafluorodecylsilane); the polydopamine in-situ polymerization process is mild and simple (alkaline conditions, room temperature~50℃), and does not require complex equipment. The total nano-solid content is only 8~30wt%, which is cost-effective and easy to scale up industrial production. It is expected that the cost will be reduced by 30%~50% compared with existing high-end superhydrophobic coatings. (6) Process innovation and stability assurance: The invention innovatively introduces combined ultrasonic treatment (step 8) and low-temperature curing agent dispersion control (NH / epoxy equivalent ratio 0.9~1.1) to ensure uniform entanglement of nanoparticles, avoid bubbles and premature cross-linking; ascorbic acid assists in the partial reduction of GO to improve carbon-based dispersibility and functional durability; PEG-modified CNC inhibits agglomeration and provides skeletal support. These process details ensure that the system has a D90 particle size of <3μm, is stable during storage and transportation, and has high performance consistency after curing, overcoming the problems of easy delamination and large performance fluctuations in existing water-based superhydrophobic coatings.

[0022] In summary, this invention cleverly integrates fluorinated low surface energy, multi-level micro-nano rough structure, heterogeneous nano-reinforced network, and water-based interpenetrating resin matrix through a polydopamine biomimetic adhesion strategy. It systematically solves the core pain points of existing technologies, such as poor durability, weak adhesion, single multifunctionality, insufficient environmental protection, and high cost. Its comprehensive performance reaches the international leading level, and it has significant technological progress and broad prospects for industrial application. Attached Figure Description

[0023] Figure 1 This is the infrared spectrum of the premixed liquid prepared in Example 1.

[0024] Figure 2 This is the infrared spectrum of the nano-inorganic composite sol prepared in Example 1.

[0025] Figure 3This is a sample image of the waterproof composite coating prepared in Example 1. Detailed Implementation

[0026] The present invention will now be described in detail through specific embodiments. However, the uses and purposes of these illustrative embodiments are merely for illustrating the invention and do not constitute any limitation on the actual scope of protection of the invention, nor are they intended to restrict the scope of protection of the invention to these embodiments. For parameter ranges not mentioned, intermediate values ​​are selected. Furthermore, for mass ratios not explicitly stated or mentioned, the mass ratio after addition generally refers to the mass ratio. In addition, in the present invention, the unit of weight parts is grams (g).

[0027] Example 1 The preparation method of waterproof composite coating, by weight, includes the following steps: (1) Preparation of waterborne resin premix: 25 parts of waterborne polyurethane dispersion (solid content 55wt%, average particle size 150nm, prepolymerized by isophorone diisocyanate and polytetrahydrofuran ether diol, chain extended by dimethylolbutyric acid and neutralized and emulsified by triethylamine, pH 8.0), 20 parts of waterborne bisphenol A type epoxy resin (epoxy equivalent 750g / eq, solid content 60wt%), and 12 parts of fluorinated acrylic emulsion (copolymerized by hexafluorobutyl methacrylate, butyl acrylate and acrylic acid, glass transition temperature 10℃, fluorine monomer mass ratio 20wt%, acid value 30mgKOH / g) are added to deionized water and stirred at 1200r / min for 30min to form a uniform premix (its infrared spectrum is shown in Figure 1). Figure 1 (as shown), the solid content was controlled at 45wt%. (2) Preparation of polydopamine modified nano-inorganic composite sol: Take 8 parts of nano silica (average particle size 50nm, CAS7631-86-9), 3 parts of nano titanium dioxide (average particle size 25nm, anatase, CAS13463-67-7), and 1.5 parts of nano zinc oxide (average particle size 60nm, CAS1314-13-2), the mass ratio of nano silica, nano titanium dioxide and nano zinc oxide is about 5.3:2:1. Add it to a mixed solvent of 20 parts anhydrous ethanol and 18 parts deionized water (the volume fraction ratio of water to alcohol is about 1:1.1). First, add 2 parts of γ-aminopropyltriethoxysilane (CAS919-30-2) and 1 part of 1H,1H,2H,2H-perfluorooctyltriethoxysilane (CAS51851-37-7), adjust the pH of the system to 4.0, and hydrolyze and polycondense at 35℃ and a stirring speed of 700 r / min for 2 h. Then, add 1 part of dopamine hydrochloride (CAS51-61-6) and 0.5 parts of tris(hydroxymethyl)aminomethane (CAS77-86-1), adjust the pH to 8.5, and continue the reaction at 30℃ for 4 h to form a polydopamine-coated and fluorinated nano-inorganic composite sol (infrared spectrum as shown). Figure 2As shown), the total solid content is about 20 wt%. The amount of dopamine hydrochloride added here makes the mass of the polydopamine coating layer account for about 8 wt% of the total mass of the inorganic nanoparticles. (3) Preparation of polydopamine-coated carbon-based nanocomposite dispersion: Take 1.5 parts of multi-walled carbon nanotubes (outer diameter 30 nm, length 10 μm, CAS308068-56-6) and 0.5 parts of graphene oxide (sheet diameter 5 μm, oxygen content 40 wt%), with a mass ratio of multi-walled carbon nanotubes to graphene oxide of 3:1. Add it to 20 parts of deionized water and 1.5 parts of sodium dodecyl sulfate (CAS151-21-3), and ultrasonically disperse for 1 h (power 500 W). Then, 0.4 parts of ascorbic acid (CAS50-81-7) and 0.6 parts of dopamine hydrochloride (CAS51-61-6) were added, the pH was adjusted to 8.5, and the reaction was carried out at 40℃ for 5 h to form a polydopamine-coated carbon-based nanocomposite dispersion in situ. The mass of the polydopamine coating layer accounted for about 30 wt% of the total mass of the carbon-based nanomaterials. (4) Preparation of modified bio-based nanodispersion: 1.5 parts of cellulose nanocrystals (length 350 nm, diameter 20 nm, CAS9004-34-6, absolute value of Zeta potential 45 mV) were added to 18 parts of deionized water, and 0.4 parts of polyethylene glycol (molecular weight 6000, CAS25322-68-3, accounting for about 26.7% of the mass of cellulose nanocrystals) were added. The pH was adjusted to 7.0, and the dispersion was carried out at 12000 r / min for 2 h using a high shear disperser to obtain a stable bio-based nanodispersion with a solid content of about 5 wt%. (5) Composite formulation: Before adding the aqueous resin premix, the polydopamine-modified nano-inorganic composite sol from step (2) and the carbon-based nano-composite dispersion from step (3) are mixed and treated with ultrasonic power of 600W for 40 minutes. Subsequently, the treated nano-inorganic composite sol, carbon-based nano-composite dispersion and bio-based nano-dispersion from step (4) are added to the aqueous resin premix from step (1). The amount of each component added must meet the following requirements: the dry basis mass ratio of polydopamine-modified nano-inorganic composite sol to carbon-based nano-composite dispersion is 8:1, the inorganic:carbon-based:bio-based mass ratio in the total nano-solids is 10:2:1, and the total nano-solids mass accounts for 18wt% of the final coating solids mass. At the same time, 1.5 parts of polyether-modified organosilicon defoamer, 1.5 parts of polyether siloxane copolymer leveling agent and 3.5 parts of aqueous modified fatty amine epoxy curing agent (amine hydrogen equivalent 350g / eq) are added. Before adding the curing agent, the system temperature was lowered to 15℃. The mixture was stirred for 60 minutes, then at low speed for 30 minutes, controlling the D90 particle size to be less than 3μm, and the NH to epoxy equivalent ratio to be 1.0. (6) Filtration and curing: The coating obtained in step (5) was filtered through a 120-mesh filter and placed at 25℃ for curing for 48 hours to obtain a waterproof composite coating, such as... Figure 3 As shown.

[0028] Examples 2-12 and Comparative Examples 1-12 To further illustrate the technical solution of the present invention, Examples 2-12 and Comparative Examples 1-12 are provided. The parameters of each example are adjusted within the scope of the claims, while the comparative examples are adjusted for key components or parameters. Specific parameters are shown in the table below (the unit in the table is grams or equivalent units).

[0029] Table 1: Parameters for the preparation of aqueous resin premix in step (1) and parameters for bio-based dispersion in step (4) Table 2: Preparation parameters of polydopamine-modified nano-inorganic composite sol in step (2) Table 3: Preparation parameters of polydopamine-coated carbon-based nanocomposite dispersion in step (3) Table 4: Special Adjustments for Compound Ingredients and Proportions in Step (5) Comparative Examples 9-12 Supplementary Explanation: Comparative Example 9: In step (2), an equal amount of n-octyltriethoxysilane (fluorine-free) was used to replace 1H,1H,2H,2H-perfluorooctyltriethoxysilane, and the rest was the same as in Example 1. Comparative Example 10: In step (5), no combined ultrasonic treatment was performed, only mechanical stirring was performed, and the rest was the same as in Example 1. Comparative Example 11: In step (5), the amount of curing agent added was 0.5 parts (severely insufficient, equivalent ratio <0.2), and the rest was the same as in Example 1. Comparative Example 12: In step (5), the total nano-solids accounted for 40 wt% of the coating solids (severely excessive), and the rest was the same as in Example 1.

[0030] Performance Testing: The coatings prepared in the above examples and comparative examples were tested according to relevant national standards and industry specifications. Water Contact Angle (WCA): The static contact angle (°) of a 5μL water droplet on the coating surface was measured using a contact angle meter. Roll-off Angle (SA): The surface tilt angle (°) at which the water droplet begins to roll off was measured. Adhesion: Tested according to the cross-cut adhesion test in GB / T 9286-1998, with grade 0 being the best and grade 5 the worst. Pencil Hardness: Tested according to GB / T 6739-2006. Abrasion Resistance: Under a 500g load, the number of cycles of abrasion with sandpaper was recorded until the contact angle dropped below 140°. Salt Spray Resistance: Tested according to GB / T 1771-2007, and the time (h) for blistering or peeling of the coating was recorded.

[0031] Table 5: Performance Test Results Results Analysis: The data in the table above shows that this invention significantly improves the coating performance through the synergistic effect of multiple components: Superhydrophobicity and Fluorinated Components: The water contact angles of Examples 1-12 are all greater than 154°, and the roll-off angle is less than 7°, exhibiting excellent superhydrophobicity. Compared with Comparative Example 1 (lacking fluorinated acrylic emulsion) and Comparative Example 9 (using non-fluorinated silane), the contact angles are significantly reduced, indicating that the synergistic effect of the low surface energy network provided by the fluorinated acrylic resin matrix and the fluorinated nanoparticles is key to achieving superhydrophobicity. Comparative Example 2 (lacking silane coupling agent) has an extremely low contact angle (<100°), indicating that surface modification of inorganic nanoparticles is crucial for constructing hydrophobic micro / nano structures. Interfacial Bonding and Dopamine Modification: The removal of dopamine in Comparative Example 3 resulted in a decrease in adhesion to level 2 and a significant reduction in the number of abrasion cycles (only 350 cycles). This confirms that polydopamine plays a crucial "molecular bridge" role between the organic resin and the inorganic filler, enhancing interfacial adhesion and preventing nanoparticles from detaching during friction. The reinforcing effect of carbon-based and bio-based materials: Comparative Example 4 (lacking carbon-based materials) showed a acceptable contact angle, but its wear resistance (620 cycles) was far lower than that of Example 1 (1250 cycles), indicating that the tough network constructed by carbon nanotubes and graphene effectively improved mechanical strength. Comparative Example 5 (lacking bio-based CNC) showed a slight decrease in pencil hardness and adhesion, and a worse film transparency (data not listed), verifying the role of CNC as a three-dimensional framework support and inhibitor of agglomeration. The influence of process parameters: Comparative Example 6 (incorrect pH control) resulted in the failure of silane hydrolysis and condensation, failing to form an effective micro-nano rough structure, resulting in extremely poor performance. Comparative Example 8 (lacking PEG and ultrasound) caused severe agglomeration of nanoparticles, poor coating uniformity, and unsatisfactory performance. Comparative Example 12 (excessive nanofiller) showed high hardness and contact angle, but extremely poor adhesion (level 4), and the coating was too brittle, resulting in a short wear life. In summary, this invention successfully prepared a multifunctional composite coating with superhydrophobicity, high wear resistance, strong adhesion, and excellent corrosion resistance by synergistic dispersion of fluorinated polydopamine-modified inorganic nanoparticles, polydopamine-coated carbon-based materials, and bio-based materials, combined with a specific water-based resin matrix.

[0032] The above description, in conjunction with specific embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, several simple deductions or substitutions can be made without departing from the concept of the present invention, and all such deductions or substitutions should be considered to fall within the scope of protection defined by the claims submitted by the present invention.

Claims

1. A method for preparing a waterproof composite coating, characterized in that... The following steps are included by weight: (1) Preparation of aqueous resin premix: 15-35 parts of aqueous polyurethane dispersion, 10-30 parts of aqueous bisphenol A epoxy resin, and 5-20 parts of fluorinated acrylic emulsion are added to deionized water and stirred at high speed to form a uniform premix, with the solid content controlled at 35-55 wt%; (2) Preparation of polydopamine modified nano-inorganic composite sol: 3-12 parts of nano silica, 1-6 parts of nano titanium dioxide, and 0.5-4 parts of nano zinc oxide are added to a mixed solvent of 10-30 parts of anhydrous ethanol and 10-25 parts of deionized water, and 0.5-4 parts of γ-aminopropyltriethylamine are added first. Oxy-silane and 0.5-4 parts of 1H,1H,2H,2H-perfluorooctyltriethoxysilane were hydrolyzed and polycondensed at pH 3-5 and 25-45℃ for 1-3 hours. Then, 0.2-2 parts of dopamine hydrochloride and 0.1-1 parts of tris(hydroxymethyl)aminomethane were added, the pH was adjusted to 8.0-9.0, and the reaction was continued at 20-40℃ for 2-6 hours to form polydopamine-coated and fluorinated nano-inorganic composite sol; (3) Preparation of polydopamine-coated carbon-based nanocomposite dispersion: 0.2-3 parts of multi-walled carbon nanotubes and 0.2-3 parts of graphene oxide were added, along with 10-30 parts of deionized water and 0.5-3 parts of dodecane. In sodium sulfate, ultrasonically disperse for 0.5-2h, then add 0.1-1 part of dopamine hydrochloride, adjust the pH to 8.0-9.0, and react at 30-50℃ for 3-8h to form a polydopamine-coated carbon-based nanocomposite dispersion in situ; (4) Prepare modified bio-based nanodispersion: take 0.2-3 parts of cellulose nanocrystals, add 10-25 parts of deionized water, add 0.1-1 parts of polyethylene glycol, adjust the pH to 6-8, and disperse under high shear for 1-3h to obtain bio-based nanodispersion; (5) Composite ingredients: combine the polydopamine-modified nano-inorganic composite sol from step (2) and the carbon-based nano-sol from step (3). The composite dispersion and the bio-based nano dispersion of step (4) are added to the water-based resin premix of step (1) at a total nano solid mass of 8-30 wt% of the final coating solid mass. At the same time, 0.5-3 parts of polyether modified organosilicon defoamer, 0.5-3 parts of polyether siloxane copolymer leveling agent and 1-6 parts of water-based modified fatty amine epoxy curing agent are added. The mixture is mechanically stirred at 15-30℃ for 1-3 hours, and the D90 particle size of the system is controlled to be less than 3 μm. (6) Filtration and curing: The coating obtained in step (5) is filtered through an 80-150 mesh filter and placed at 20-35℃ for 24-72 hours to cure, thereby obtaining the waterproof composite coating.

2. The method for preparing the waterproof composite coating according to claim 1, characterized in that... The aqueous polyurethane dispersion described in step (1) was prepared by a prepolymer method: polytetrahydrofuran ether diol was vacuum dehydrated at 80°C for 1.5 h, cooled to 65°C, and isophorone diisocyanate was added to make the R value 1.

8. 0.02 wt% dibutyltin dilaurate was added, and the mixture was stirred at 85°C for 3 h. After cooling to 70°C, dimethylolbutyric acid was added, and the mixture was chain extended at 80°C for 2 h. After cooling to 35°C, triethylamine was added for neutralization for 30 min, and deionized water at 50°C was added under stirring at 1000 r / min for emulsification. The solid content was controlled at 60 wt%. After standing for 24 h, an aqueous polyurethane dispersion with pH 7.5~8.5 and an average particle size of 80~200 nm was obtained. The preparation of the fluorinated acrylic emulsion in step (1) The method is as follows: It is prepared by emulsion polymerization of hexafluorobutyl methacrylate, butyl acrylate and acrylic acid. The mass ratio of the three monomers is: 20 parts of hexafluorobutyl methacrylate, 60 parts of butyl acrylate and 10 parts of acrylic acid. During preparation, sodium dodecylbenzenesulfonate with a total monomer mass of 4 wt% is added to deionized water to prepare a pre-emulsion. One-third of the mass of the pre-emulsion is prepolymerized with 0.2 wt% persulfate initiator at 75°C for 1 h. The remaining pre-emulsion is added dropwise at 80°C for 3 h. The temperature is kept at 85°C for 3 h. After cooling, the pH is adjusted to 8.5 and the solid content is controlled at 50 wt% to obtain a stable fluorinated acrylic emulsion. The parameters of high-speed stirring in step (1) are as follows: speed 1500 r / min, stirring time 40 min.

3. The method for preparing the waterproof composite coating according to claim 1, characterized in that... In step (2), the mass ratio of nano-silica, nano-titanium dioxide and nano-zinc oxide is (2~6):(1~3):(0.5~2), the mass ratio of γ-aminopropyltriethoxysilane to 1H,1H,2H,2H-perfluorooctyltriethoxysilane is (1~3):(1), the amount of dopamine hydrochloride added is such that the mass of the polydopamine coating layer accounts for 5~25wt% of the total mass of the inorganic nanoparticles, the hydrolysis condensation stirring speed is 400~1000r / min, the water:alcohol volume fraction ratio is (1~2):1, forming a dual-size hierarchical rough structure and enhancing the interfacial adhesion of fluorinated polydopamine modified composite particles.

4. The method for preparing the waterproof composite coating according to claim 1, characterized in that... In step (3), the mass ratio of multi-walled carbon nanotubes to graphene oxide is (1~4):1, the total carbon-based nanomaterials account for 0.5~8wt% of the solid mass of the coating, the mass of the polydopamine coating layer accounts for 15~50wt% of the total mass of the carbon-based nanomaterials, and 0.2~1 part of ascorbic acid is added before the reaction to assist in the partial reduction of graphene oxide.

5. The method for preparing the waterproof composite coating according to claim 1, characterized in that... In step (4), the absolute value of the zeta potential of the cellulose nanocrystals is 35~60mV, the solid content of the dispersion liquid is 2~8wt%, the amount of polyethylene glycol added is 10~40wt% of the mass of the cellulose nanocrystals, and the high shear speed is 8000~15000r / min, so as to provide three-dimensional skeleton support and inhibit agglomeration, and improve the transparency and flexibility of the coating.

6. The method for preparing the waterproof composite coating according to claim 1, characterized in that... In step (5), the mass ratio of polydopamine-modified nano-inorganic composite sol to carbon-based nano-composite dispersion is (3~12):1, and the mass ratio of inorganic:carbon-based:bio-based in the total nano-solids is (5~15):(1~5):

1. Before adding the curing agent, the system temperature is lowered to 10~20℃, and after stirring for 30~120min, low-speed stirring is continued to avoid bubbles, ensuring that the curing agent is uniformly dispersed and controlling the NH to epoxy equivalent ratio to 0.9~1.

1. In step (5), the CAS number of polyether-modified organosilicon defoamer is 68937-55-3, the CAS number of polyether siloxane copolymer leveling agent is 128192-17-6, and the CAS number of water-based modified fatty amine epoxy curing agent is 68131-73-7.

7. The method for preparing the waterproof composite coating according to claim 1, characterized in that... The coating is applied to the surface of concrete, metal or wood substrates. The substrate is pretreated to have a roughness of Ra 1~8μm and a moisture content of less than 6wt%. The coating viscosity is adjusted to 800~4000mPa·s. The single-coat wet film thickness is 80~250μm when sprayed or rolled. The interval between multiple coats is 10~40min. The surface drying time is 20~60min at 15~35℃. The full curing time is 48~96h. The final dry film thickness is 50~200μm.

8. The method for preparing the waterproof composite coating according to claim 1, characterized in that... Before adding the aqueous resin premix, the composite nanomaterials obtained in steps (2) and (3) are treated with ultrasonic power of 300~1000W for 20~60min to promote the entanglement of polydopamine-mediated nanoparticles with carbon-based materials, forming a multi-level micro-nano composite framework, thereby improving the mechanical durability and multifunctional synergy of the coating.

9. A waterproof composite coating, characterized in that... The waterproof composite coating is obtained by the preparation method described in any one of claims 1-8.

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