High-stability coating and preparation method thereof

Abstract

The application belongs to the technical field of water-based functional coating and specifically relates to a high-stability coating and a preparation method thereof. The coating comprises the following components in parts by weight: a water-based polyurethane dispersion liquid 120-150 parts, boron nitride nanosheets 6-10 parts, amino-modified carbon nanotubes 3-7 parts, carboxylated nanocellulose fibers 1-3 parts, an additive 1-6 parts, and deionized water 50-100 parts. The application successfully constructs a three-dimensional synergistic network with physical barrier, chemical bonding and rheological stability by compounding a certain proportion of boron nitride nanosheets, amino-modified carbon nanotubes and carboxylated nanocellulose fibers in the water-based polyurethane. The coating has excellent comprehensive performance in terms of adhesion, salt mist corrosion resistance and the like, is high in stability, simple in preparation process, friendly to the environment, and has a wide application prospect in the field of coating corrosion prevention.

Description

Technical Field

[0001] This invention belongs to the field of water-based functional coatings technology. Specifically, it relates to a highly stable coating and its preparation method, which can be widely used for surface protection and decorative coating of various substrates such as metals. Background Technology

[0002] With increasing global awareness of environmental protection, the coatings industry is undergoing a profound transformation from solvent-based to water-based coatings. Water-based polyurethane coatings, with their environmental advantages such as low VOC emissions, non-toxicity, odorlessness, and non-flammability, as well as excellent film-forming properties, high elasticity, and good wear resistance, have been widely used in wood coating, leather finishing, plastic decoration, and textile finishing.

[0003] However, when waterborne polyurethane coatings are applied to the more demanding field of corrosion protection for metal substrates, their inherent performance shortcomings become apparent, severely restricting their adoption in high-end equipment manufacturing industries such as automobile manufacturing, marine engineering, oil pipelines, and power facilities. Specifically, waterborne polyurethane coatings face three main technical bottlenecks in metal corrosion protection applications: (a) Insufficient adhesion and weak interfacial bonding Metal substrates typically have a trace amount of oxide layer or hydroxyl groups on their surface, exhibiting strong polarity. While waterborne polyurethane molecules contain urethane groups, their overall polarity is still less than that of metal oxides. More importantly, during film formation, as water evaporates, the hydrophilic groups on the molecular chains of waterborne polyurethane tend to gravitate towards the interior of the coating, reducing the number of active sites for forming effective hydrogen bonds or chemical bonds with the metal surface. This weak interfacial bonding makes the coating highly susceptible to peeling off from the substrate surface when subjected to external impacts or alternating hot and cold temperatures, thus compromising the first line of defense.

[0004] (ii) The permeability of corrosive media and short salt spray resistance life. Compared to solvent-based polyurethane, waterborne polyurethane has poorer barrier properties. In salt spray environments, chloride ions can easily penetrate the coating and reach the metal interface, inducing pitting and under-film corrosion, leading to blistering and peeling of the coating. Traditional physical blending modifications, such as directly adding micron-sized fillers, often fail to effectively block the penetration path due to poor compatibility between the filler and the matrix, and instead create new defects at the interface.

[0005] (III) The contradiction between the dispersion and storage stability of nanofillers To address these issues, researchers have attempted to introduce inorganic nanoparticles such as carbon nanotubes, graphene, and nano-silica into waterborne polyurethane systems, hoping to leverage the labyrinth effect of nanomaterials to extend the diffusion path of corrosive media or utilize their mechanical properties to enhance coating cohesion. However, the enormous specific surface energy and strong aggregation tendency of nanoparticles make it difficult to achieve monodispersity in aqueous media. To achieve stable dispersion, large amounts of surfactants or dispersants are often added, which inevitably introduces new hydrophilic species, thus degrading the water resistance of the coating. Even more problematic is that these highly reactive nanoparticles are prone to sedimentation or aggregation during storage, leading to coating failure and severely impacting the commercial value of the product.

[0006] In summary, there is an urgent need to develop a highly stable waterborne polyurethane coating solution that can simultaneously achieve strong interfacial adhesion and long-lasting salt spray resistance. Summary of the Invention

[0007] This invention aims to overcome the shortcomings of the prior art and provide a highly stable coating and its preparation method. By constructing a three-dimensional functional network, this invention simultaneously addresses the comprehensive technical challenges of poor adhesion and insufficient salt spray resistance of waterborne polyurethane coatings in the protection of metal and other substrates through physical barrier, chemical bonding, and interface regulation.

[0008] To achieve the above-mentioned objectives, the present invention provides the following technical solution: A highly stable coating comprises the following components in parts by weight: 120-150 parts of waterborne polyurethane dispersion, 6-10 parts of boron nitride nanosheets, 3-7 parts of amino-modified carbon nanotubes, 1-3 parts of carboxylated nanocellulose fibers, 1-6 parts of additives, and 50-100 parts of deionized water.

[0009] The key to achieving excellent adhesion and salt spray resistance in this invention lies in the construction of a multi-level, multi-scale synergistic reinforcement network in the waterborne polyurethane system, consisting of two-dimensional sheet materials (boron nitride nanosheets), one-dimensional tubular materials (amino-modified carbon nanotubes), and naturally derived biomass nanofibers (carboxylated cellulose nanofibers).

[0010] First, boron nitride nanosheets (BNNS) possess an atomically flat two-dimensional sheet structure and an extremely high aspect ratio, with lateral dimensions typically ranging from 1 to 10 µm. Their atomically flat surfaces can form strong van der Waals forces and π-π interactions with the polyurethane matrix, effectively improving interfacial stress transfer and preventing interfacial debonding. After being uniformly dispersed in an aqueous polyurethane matrix, the BNNS sheets are stacked layer by layer or arranged in parallel orientation within the coating film, forming a physical barrier. When water molecules and chloride ions attempt to penetrate from the coating surface to the substrate, they must bypass these insoluble nanosheets, forcing their diffusion path from a straight line to a curve, significantly increasing the penetration time. In particular, the addition of BNNS also improves the thermal conductivity of the coating, facilitating heat diffusion and allowing it to function as a thermally conductive coating to prevent heat accumulation. However, simple two-dimensional sheets are prone to stacking within the matrix, forming penetrating microcracks. To address this, the present invention introduces one-dimensional amino-modified carbon nanotubes (A-CNTs). These rigid tubular structures, interspersed between BNNS sheets, act as spacers, effectively preventing the tight stacking and aggregation of BNNS. Simultaneously, the A-CNTs themselves also function as nanoscale fibers, further filling the gaps between the sheets, making the barrier network denser and more complete. Carboxylated cellulose nanofibers (C-CNF) act as flexible connectors, firmly linking the BNNS sheets and A-CNTs together, preventing filler migration and re-aggregation due to capillary forces during film drying, ensuring a uniform distribution of the barrier network throughout the entire coating thickness direction. Furthermore, the addition of boron nitride nanosheets, amino-modified carbon nanotubes, and carboxylated cellulose nanofibers provides a micro / nano-rough surface structure, which improves the hydrophobic properties of the coating, thereby further enhancing its corrosion resistance.

[0011] In one embodiment, the aqueous polyurethane dispersion has a solid content of 50-70%, and the high solid content helps to reduce drying shrinkage stress and improve coating performance.

[0012] In one embodiment, the amino-modified carbon nanotubes are carbon nanotubes modified with an aminosilane coupling agent. As a common carbon material, carbon nanotubes typically have an average length of 1-50 µm and a diameter of 10-100 nm. After modification with the aminosilane coupling agent, the carbon nanotubes have active amino groups grafted onto their surface. These amino groups can form covalent or hydrogen bonds with residual isocyanate and carboxyl groups on the waterborne polyurethane molecular chain, thereby fixing A-CNTs in the three-dimensional polyurethane network through covalent bonds, achieving chemical fusion of the filler and matrix at the molecular level. As a strongly polar group, amino groups can also form hydrogen or coordinate bonds with hydroxyl groups on the metal surface, establishing a continuous chemical bond chain between the filler, resin, and metal substrate. Simultaneously, hydrogen or chemical bonds can form between the amino groups on the A-CNTs surface and the carboxyl groups on the C-CNF surface, promoting uniform dispersion and synergistic arrangement of both during coating preparation and film formation.

[0013] In one embodiment, the aminosilane coupling agent is one or more of γ-aminopropyltrimethoxysilane, γ-aminopropyltriisopropoxysilane, and γ-aminopropyltriethoxysilane.

[0014] In one embodiment, the amino-modified carbon nanotube modification process is as follows: first, the carbon nanotubes are activated with an oxidizing acid; then, the activated carbon nanotubes and an aminosilane coupling agent are dispersed in a solvent, and the amino-modified carbon nanotubes are obtained after the reaction. Acid activation treatment can introduce active sites such as hydroxyl and carboxyl groups onto the surface of the carbon nanotubes, providing a chemical basis for subsequent grafting of silane coupling agents.

[0015] In one embodiment, the oxidizing acid can be a mixed acid solution of concentrated sulfuric acid and concentrated nitric acid. Specifically, a mixed acid solution of 98% concentrated sulfuric acid and 68% concentrated nitric acid can be used. This mixed acid system possesses both strong oxidizing and nitrifying properties, enabling efficient opening of carbon nanotube ports and sidewall defects, introducing abundant oxygen-containing functional groups.

[0016] Specifically, the amino-modified carbon nanotube modification process is as follows: carbon nanotubes are dispersed in a mixed solution of concentrated sulfuric acid and concentrated nitric acid with a volume ratio of 3:1, reacted at 70-90℃ for 5-6 hours, centrifuged, washed, and dried to obtain activated carbon nanotubes, and then the activated carbon nanotubes are dispersed in an ethanol solution, γ-aminopropyltriethoxysilane is added (the mass ratio of γ-aminopropyltriethoxysilane to activated carbon nanotubes is (0.5-1):1), reacted at 60-80℃ for 2-4 hours, filtered, washed, and dried to obtain amino-modified carbon nanotubes.

[0017] In one embodiment, the carboxylated cellulose nanofibers contain 1-3 mmol / g of carboxyl groups. Carboxylated cellulose nanofibers are nanoscale biomass materials extracted from natural plant fibers. Their surface contains a large number of carboxyl groups (-COOH), which can react with hydroxyl and amino groups on aqueous polyurethane molecular chains or carbon nanotubes during film formation or form hydrogen bonds, creating chemical crosslinking points and significantly increasing the crosslinking density and cohesive strength of the coating. Carboxyl groups can also undergo strong coordination complexation reactions with metal ions or oxides on metal surfaces, forming a stable chemisorption layer. The strength of this chemisorption is much higher than that of physical adsorption, giving the coating extremely strong adhesion. In particular, C-CNF, due to its flexible long-chain fiber morphology, can intertwine and entangle rigid BNNS sheets and A-CNTs, making it a key component in constructing a three-dimensional physical network throughout the entire coating system.

[0018] In one embodiment, a high-stability coating comprises the following components in parts by weight: 120-150 parts of aqueous polyurethane dispersion, 6-10 parts of boron nitride nanosheets, 4-6 parts of amino-modified carbon nanotubes, 1-3 parts of carboxylated cellulose nanofibers, 2-5 parts of additives, and 60-90 parts of deionized water. Adjusting the amount of each component in the coating can improve the coating performance. It is worth noting that, as a hydrophilic component, the amount of carboxylated cellulose nanofibers should not be excessive. Excessive hydrophilic cellulose fibers will form a continuous hydrophilic phase, leading to a sharp increase in the water absorption rate of the coating film. Simultaneously, excessive carboxyl groups will cause over-crosslinking, resulting in gelation of the system and a decrease in salt spray resistance. At the same time, an appropriate amount of NNS can balance reinforcement and dispersion effects. If the amount is excessive, it cannot be effectively wetted and dispersed in the matrix, instead acting as a stress concentration point to induce microcracks or causing severe agglomeration, thus destroying the continuity and density of the coating film. Specifically, in one embodiment, 7-9 parts of boron nitride nanosheets and 3-6 parts of amino-modified carbon nanotubes are included. An appropriate amount of carbon nanotubes can both promote the dispersion of boron nitride nanosheets and carboxylated cellulose nanofibers, and avoid excessive use from affecting the formation of a dense coating structure.

[0019] When BNNS (two-dimensional sheets), A-CNTs (one-dimensional tubes), and C-CNF (flexible nanofibers) are dispersed in water, these nanoparticles of different dimensions and flexibility spontaneously assemble into a network structure through electrostatic repulsion and steric hindrance. Due to its flexible long-chain structure, C-CNF can interweave the rigid BNNS sheets and A-CNTs, constructing a sparse but fully distributed elastic network. This not only imparts storage stability to the coating but also, through the self-stabilizing mechanism achieved by the three-dimensional nanonetwork, effectively avoids the hydrophilic side effects caused by the traditional addition of large amounts of thickeners.

[0020] In one embodiment, the additive is one or more of the following: anti-settling agent, defoamer, dispersant, leveling agent, and light stabilizer.

[0021] In one embodiment, the anti-settling agent is one or more of BYK420, BYK425, and BYK430.

[0022] In one embodiment, the defoamer is one or more of the following: silicone defoamer, mineral oil defoamer, and polyether defoamer.

[0023] In one embodiment, the dispersant is one or more of sodium polyacrylate, ammonium polyacrylate, polyphosphate, and polyether-modified polycarboxylate.

[0024] On the other hand, the present invention also provides a method for preparing a highly stable coating, comprising the following steps: (1) Mix and disperse boron nitride nanosheets, amino-modified carbon nanotubes, carboxylated nanocellulose fibers, and deionized water evenly; (2) Add water-based polyurethane dispersion and additives, and stir to disperse, and a high-stability coating is obtained.

[0025] Beneficial effects: (1) This invention successfully constructs a three-dimensional synergistic network that combines physical barrier, chemical bonding, and rheological stability by compounding a certain proportion of boron nitride nanosheets (BNNS), amino-modified carbon nanotubes (A-CNTs), and carboxylated cellulose nanofibers into waterborne polyurethane. This coating exhibits excellent comprehensive performance in terms of metal adhesion, salt spray corrosion resistance, and storage stability. It has high stability, a simple preparation process, and is environmentally friendly, showing broad application prospects in the field of metal corrosion protection.

[0026] (2) Boron nitride nanosheets (BNNS) have an atomically flat two-dimensional sheet structure and an extremely high aspect ratio. Their atomically flat surface can form strong van der Waals forces and π-π interactions with the polyurethane matrix, which effectively improves the interfacial stress transfer and prevents interfacial debonding. One-dimensional amino-modified carbon nanotubes (A-CNTs) and carboxylated cellulose nanofibers (C-CNF) effectively prevent the tight stacking and agglomeration of BNNS; at the same time, A-CNTs further fill the gaps between the sheets, making the barrier network more compact and perfect, and improving the adhesion and corrosion resistance of the coating. Attached Figure Description

[0027] Figure 1 Scanning electron microscope image of the high-stability coating prepared in Example 9.

[0028] Figure 2 Scanning electron microscope image of the high-stability coating prepared for Comparative Example 1.

[0029] Figure 3 Scanning electron microscope image of the high-stability coating prepared for Comparative Example 2. Detailed Implementation

[0030] The following embodiments are provided to better understand the present invention and do not constitute a limitation on the content and scope of protection of the present invention. The present invention is not limited to the described preferred embodiments. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0031] The preparation methods of amino-modified carbon nanotubes and high-stability coatings in the following examples and comparative examples are the same.

[0032] The specific preparation process of amino-modified carbon nanotubes is as follows: carbon nanotubes are dispersed in a mixed solution of concentrated sulfuric acid and concentrated nitric acid with a volume ratio of 3:1, reacted at 80°C for 5.5 h, centrifuged, washed, and dried to obtain activated carbon nanotubes, and then the activated carbon nanotubes are dispersed in an ethanol solution, γ-aminopropyltriethoxysilane (the mass ratio of γ-aminopropyltriethoxysilane to activated carbon nanotubes is 0.8:1) is added, reacted at 70°C for 3 h, filtered, washed, and dried to obtain amino-modified carbon nanotubes.

[0033] The preparation method of high-stability coatings is as follows: (1) Mix and disperse boron nitride nanosheets, amino-modified carbon nanotubes, carboxylated nanocellulose fibers, and deionized water evenly; (2) Add water-based polyurethane dispersion and additives (anti-settling agent, defoamer, dispersant), and stir to disperse to obtain a high-stability coating.

[0034] Performance testing: Under the same conditions, the adhesion (refer to GB / T 5210-2006) and salt spray resistance (refer to GB / T 1771-2007) of the high-stability coatings prepared in the following examples and comparative examples were tested.

[0035] Example 1

[0036] A highly stable coating comprises the following components in parts by weight: The composition consists of 120 parts waterborne polyurethane dispersion (60% solids content), 6 parts boron nitride nanosheets, 3 parts amino-modified carbon nanotubes, 1 part carboxylated nanocellulose fibers (carboxyl content 2 mmol / g), 2 parts anti-settling agent BYK420, 0.5 parts defoamer polydimethylsiloxane, 1 part dispersant sodium polyacrylate, and 85 parts deionized water. Testing showed that the coating had an adhesion of 4.5 MPa and a salt spray resistance of 850 h.

[0037] Example 2

[0038] A highly stable coating comprises the following components in parts by weight: The composition consists of 150 parts waterborne polyurethane dispersion (60% solids content), 9.5 parts boron nitride nanosheets, 6 parts amino-modified carbon nanotubes, 3 parts carboxylated cellulose nanofibers (carboxyl content 2 mmol / g), 0.5 parts anti-settling agent BYK425, 2 parts defoamer polydimethylsiloxane, 0.5 parts dispersant sodium polyacrylate, and 100 parts deionized water. The coating exhibits an adhesion of 4.9 MPa and a salt spray resistance of 970 h.

[0039] Example 3

[0040] A highly stable coating comprises the following components in parts by weight: The composition consists of 135 parts waterborne polyurethane dispersion (60% solids content), 10 parts boron nitride nanosheets, 5 parts amino-modified carbon nanotubes, 2 parts carboxylated cellulose nanofibers (carboxyl content 2 mmol / g), 2 parts anti-settling agent BYK425, 1 part defoamer polydimethylsiloxane, 1.5 parts dispersant sodium polyacrylate, and 90 parts deionized water. The coating exhibits an adhesion of 4.3 MPa and a salt spray resistance of 940 h.

[0041] Example 4

[0042] A highly stable coating comprises the following components in parts by weight: The composition of the coating consists of 125 parts of waterborne polyurethane dispersion (60% solids content), 9 parts of boron nitride nanosheets, 3.5 parts of amino-modified carbon nanotubes, 1.2 parts of carboxylated cellulose nanofibers (carboxyl content 2 mmol / g), 1.5 parts of anti-settling agent BYK420, 1.5 parts of defoamer polydimethylsiloxane, 1.2 parts of dispersant sodium polyacrylate, and 80 parts of deionized water. The coating exhibits an adhesion of 4.6 MPa and a salt spray resistance of 840 h.

[0043] Example 5

[0044] A highly stable coating comprises the following components in parts by weight: The composition includes 135 parts of waterborne polyurethane dispersion (60% solids content), 8 parts of boron nitride nanosheets, 5 parts of amino-modified carbon nanotubes, 2 parts of carboxylated nanocellulose fibers (carboxyl content 2 mmol / g), 2 parts of anti-settling agent BYK425, 1 part of defoamer polydimethylsiloxane, 1.5 parts of dispersant sodium polyacrylate, and 90 parts of deionized water. The coating's adhesion was tested to be 5.1 MPa, and its salt spray resistance was 950 h.

[0045] Example 6

[0046] A highly stable coating comprises the following components in parts by weight: The composition of the coating consists of 130 parts of waterborne polyurethane dispersion (60% solids content), 7 parts of boron nitride nanosheets, 4 parts of amino-modified carbon nanotubes, 1.6 parts of carboxylated nanocellulose fibers (carboxyl content 2 mmol / g), 0.8 parts of anti-settling agent BYK420, 1.8 parts of defoamer polydimethylsiloxane, 0.8 parts of dispersant sodium polyacrylate, and 95 parts of deionized water. The coating exhibits an adhesion of 5.0 MPa and a salt spray resistance of 910 h.

[0047] Example 7

[0048] A highly stable coating comprises the following components in parts by weight: The composition of the coating consists of 140 parts of waterborne polyurethane dispersion (60% solids content), 8.5 parts of boron nitride nanosheets, 5.5 parts of amino-modified carbon nanotubes, 2.5 parts of carboxylated cellulose nanofibers (carboxyl content 2 mmol / g), 1.2 parts of anti-settling agent BYK425, 1.2 parts of defoamer polydimethylsiloxane, 1.7 parts of dispersant sodium polyacrylate, and 90 parts of deionized water. The coating exhibits an adhesion of 4.7 MPa and a salt spray resistance of 860 h.

[0049] Example 8

[0050] A highly stable coating comprises the following components in parts by weight: The composition of the coating consists of 145 parts of waterborne polyurethane dispersion (60% solids content), 7.5 parts of boron nitride nanosheets, 4.5 parts of amino-modified carbon nanotubes, 1.5 parts of carboxylated nanocellulose fibers (carboxyl content 2 mmol / g), 1.8 parts of anti-settling agent BYK420, 0.8 parts of defoamer polydimethylsiloxane, 1.8 parts of dispersant sodium polyacrylate, and 85 parts of deionized water. The coating exhibits an adhesion of 5.3 MPa and a salt spray resistance of 880 h.

[0051] Example 9

[0052] A highly stable coating comprises the following components in parts by weight: The composition includes 135 parts of waterborne polyurethane dispersion (60% solids content), 8 parts of boron nitride nanosheets, 7 parts of amino-modified carbon nanotubes, 2 parts of carboxylated nanocellulose fibers (carboxyl content 2 mmol / g), 2 parts of anti-settling agent BYK425, 1 part of defoamer polydimethylsiloxane, 1.5 parts of dispersant sodium polyacrylate, and 90 parts of deionized water. The coating's adhesion was tested to be 4.7 MPa, and its salt spray resistance was 920 h.

[0053] Comparative Example 1 A highly stable coating comprises the following components in parts by weight: The composition of the coating consists of 135 parts of waterborne polyurethane dispersion (60% solids content), 9.1 parts of boron nitride nanosheets, 7.9 parts of amino-modified carbon nanotubes, 0 parts of carboxylated nanocellulose fibers (carboxyl content 2 mmol / g), 2 parts of anti-settling agent BYK425, 1 part of defoamer polydimethylsiloxane, 1.5 parts of dispersant sodium polyacrylate, and 90 parts of deionized water. The coating's adhesion was tested to be 3.4 MPa, and its salt spray resistance was 690 h.

[0054] Comparative Example 2 A highly stable coating comprises the following components in parts by weight: The composition of the coating consists of 135 parts of waterborne polyurethane dispersion (60% solids content), 13.6 parts of boron nitride nanosheets, 0 parts of amino-modified carbon nanotubes, 3.4 parts of carboxylated nanocellulose fibers (carboxyl content 2 mmol / g), 2 parts of anti-settling agent BYK425, 1 part of defoamer polydimethylsiloxane, 1.5 parts of dispersant sodium polyacrylate, and 90 parts of deionized water. The coating's adhesion was tested to be 3.6 MPa, and its salt spray resistance was 720 h.

[0055] Comparative Example 3 A highly stable coating comprises the following components in parts by weight: The composition of the coating consists of 135 parts of waterborne polyurethane dispersion (60% solids content), 0 parts of boron nitride nanosheets, 13.2 parts of amino-modified carbon nanotubes, 3.8 parts of carboxylated nanocellulose fibers (carboxyl content 2 mmol / g), 2 parts of anti-settling agent BYK425, 1 part of defoamer polydimethylsiloxane, 1.5 parts of dispersant sodium polyacrylate, and 90 parts of deionized water. The coating's adhesion was tested to be 4.5 MPa, and its salt spray resistance was 660 h.

[0056] Comparative Example 4 A highly stable coating comprises the following components in parts by weight: The composition includes 135 parts of waterborne polyurethane dispersion (60% solids content), 8 parts of boron nitride nanosheets, 7 parts of amino-modified carbon nanotubes, 5 parts of carboxylated nanocellulose fibers (carboxyl content 2 mmol / g), 2 parts of anti-settling agent BYK425, 1 part of defoamer polydimethylsiloxane, 1.5 parts of dispersant sodium polyacrylate, and 90 parts of deionized water. The coating's adhesion was tested to be 4.3 MPa, and its salt spray resistance was 770 h.

[0057] Figure 1 This is a scanning electron microscope (SEM) image of the coating formed by the high-stability coating prepared in Example 9. Figure 2 , Figure 3 The images show scanning electron microscope (SEM) images of the coatings formed by the highly stable coatings prepared in Comparative Examples 1 and 2, respectively. Figure 1 As can be seen, the coating prepared by this invention forms a coating without obvious agglomerates, exhibiting a uniform, smooth, and crack-free morphology. The overall structure is dense, without obvious penetrating pores, which is beneficial for improving the coating's adhesion and corrosion resistance. Furthermore, the coating's... Figure 2 and Figure 3 It can be seen that the coatings formed exhibit a loose, independent aggregate state, unable to form an interwoven network, and show varying degrees of filler agglomeration. The coating structure is loose, with micron-level cracks and pores, allowing corrosive media to easily penetrate.

[0058] Combined with specific embodiments and comparative experimental data, it can be seen that the atomically flat surface of boron nitride nanosheets can form strong van der Waals forces and π-π interactions with the polyurethane matrix, effectively improving interfacial stress transmission and preventing interfacial debonding. After being uniformly dispersed in the waterborne polyurethane matrix, the BNNS sheets are stacked or arranged in parallel orientation within the coating film, forming a physical barrier wall. Amino-modified carbon nanotubes are interspersed between the BNNS sheets, acting as spacers and effectively preventing the tight stacking and aggregation of BNNS; at the same time, A-CNTs themselves also act as nanoscale fibers, further filling the gaps between the sheets, making the barrier network more compact and complete. C-CNFs act as flexible connectors, firmly linking the BNNS sheets and A-CNTs together, preventing filler migration and re-agglomeration caused by capillary forces during film drying, and ensuring the uniform distribution of the barrier network throughout the entire coating thickness direction.

[0059] Compared to Example 9, Comparative Examples 1-3 lacked carboxylated cellulose nanofibers, amino-modified carbon nanotubes, and boron nitride nanosheets, respectively, resulting in varying degrees of performance degradation. Specifically, Comparative Example 1, lacking carboxylated cellulose nanofibers, exhibited significantly reduced adhesion and corrosion resistance. This is because the surface of carboxylated cellulose nanofibers contains a large number of carboxyl groups, which can react with hydroxyl and amino groups on the waterborne polyurethane molecular chains during film formation or form hydrogen bonds, creating chemical crosslinking points and significantly increasing the crosslinking density and cohesive strength of the coating. Moreover, C-CNF, due to its flexible long-chain fiber morphology, can intertwine and entangle rigid BNNS sheets and A-CNTs, making it a key component in constructing a three-dimensional physical network throughout the entire coating system. The lack of carboxylated cellulose nanofibers in Comparative Example 1 prevented the formation of a dense structure, leading to decreased coating stability. The lack of amino-modified carbon nanotubes in Comparative Example 2 also resulted in decreased adhesion and corrosion resistance. This is because after carbon nanotubes are modified with aminosilane coupling agents, the amino groups on their surface can form covalent or hydrogen bonds with the residual isocyanate and carboxyl groups on the molecular chains of waterborne polyurethane. This fixes A-CNTs within the three-dimensional polyurethane network through covalent bonds, achieving chemical fusion between the filler and the matrix at the molecular level. Simultaneously, hydrogen or chemical bonds can form between the amino groups on the A-CNTs surface and the carboxyl groups on the C-CNF surface, promoting uniform dispersion and synergistic arrangement during coating preparation and film formation. When amino-modified carbon nanotubes are lacking, the cross-linking effect between fillers decreases, leading to a decline in coating performance. Comparative Example 3, lacking boron nitride nanosheets, showed little change in adhesion, but its barrier properties decreased, and its salt spray resistance significantly declined. Comparative Example 4 shows that the amount of carboxylated nanocellulose fibers used as a modifying agent should not be excessive. When the amount of C-CNF is moderate, it is uniformly dispersed and encapsulated by polyurethane, with the carboxyl groups primarily participating in interfacial chemical bonding. However, when there is an excess, the excess cellulose fibers cannot be completely wetted and coated by the polyurethane matrix. The hydrophilicity of the cellulose molecular chains themselves will form continuous hydrophilic microdomains or water molecule channels inside the coating. In salt spray or humid environments, water molecules and ions preferentially penetrate rapidly along these hydrophilic cellulose fiber networks, causing coating blistering, a sharp decrease in wet adhesion, and disruption of the coating continuity, resulting in a significant reduction in barrier performance.

[0060] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A highly stable coating, characterized in that, It contains the following components in parts by weight: 120-150 parts of waterborne polyurethane dispersion, 6-10 parts of boron nitride nanosheets, 3-7 parts of amino-modified carbon nanotubes, 1-3 parts of carboxylated nanocellulose fibers, 1-6 parts of additives, and 50-100 parts of deionized water.

2. The high-stability coating as described in claim 1, characterized in that, The waterborne polyurethane dispersion has a solid content of 50-70%.

3. The high-stability coating as described in claim 1, characterized in that, The amino-modified carbon nanotubes are carbon nanotubes modified with an aminosilane coupling agent.

4. The high-stability coating as described in claim 3, characterized in that, The aminosilane coupling agent is one or more of γ-aminopropyltrimethoxysilane, γ-aminopropyltriisopropoxysilane, and γ-aminopropyltriethoxysilane.

5. The high-stability coating as described in claim 3, characterized in that, The modification process of amino-modified carbon nanotubes is as follows: first, carbon nanotubes are activated with an oxidizing acid, and then the activated carbon nanotubes and aminosilane coupling agent are dispersed in a solvent. After the reaction, amino-modified carbon nanotubes are obtained.

6. The high-stability coating as described in claim 1, characterized in that, The additive is one or more of the following: anti-settling agent, defoamer, dispersant, leveling agent, and light stabilizer.

7. The high-stability coating as described in claim 6, characterized in that, The anti-settling agent is one or more of BYK420, BYK425, and BYK430.

8. The high-stability coating as described in claim 6, characterized in that, The defoamer is one or more of the following: silicone defoamer, mineral oil defoamer, and polyether defoamer.

9. A high-stability coating as described in claim 6, characterized in that, The dispersant is one or more of sodium polyacrylate, ammonium polyacrylate, polyphosphate, and polyether-modified polycarboxylate.

10. The method for preparing a high-stability coating as described in claim 1, characterized in that, Includes the following steps: (1) Mix and disperse boron nitride nanosheets, amino-modified carbon nanotubes, carboxylated nanocellulose fibers, and deionized water evenly; (2) Add water-based polyurethane dispersion and additives, and stir to disperse, and a high-stability coating is obtained.

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