A modified high-strength one-component polyurea coating and its preparation method

Abstract

The invention belongs to the technical field of coating preparation and provides a modified high-strength one-component polyurea coating and a preparation method thereof. First, PDA@electrospun carbon nanofibers are prepared by reacting a Tris-HCl buffer solution under alkaline conditions, and the functional properties and interfacial bonding strength of the fibers are enhanced by surface dopamine coating. Secondly, a metal coordination microgel is prepared by an emulsion polymerization method, and a high-strength, corrosion-resistant functional microgel structure is constructed through the synergistic effect of acrylamide monomer, metal salt and benzotriazole. Then, a matrix resin is prepared by reacting isocyanate with an amino-terminated polyether under a nitrogen atmosphere, and its storage stability and curing behavior are regulated by combining a latent amine and a composite blocking agent. Finally, the PDA@nanofibers, the metal coordination microgel and an auxiliary agent are uniformly dispersed in the matrix resin to prepare a modified high-strength one-component polyurea coating suitable for application in complex environments.

Description

Technical Field

[0001] The invention belongs to the technical field of coating preparation and relates to a modified high-strength single-component polyurea coating and a preparation method thereof. Background Art

[0002] Polyurea coatings, as high-performance protective coating systems, have attracted widespread attention for their rapid curing, high mechanical strength, and excellent corrosion and weather resistance. Their unique chemical reaction system enables them to demonstrate exceptional performance in waterproofing, industrial protection, transportation infrastructure, and other fields. Traditional polyurea coatings primarily rely on two-component systems, which rapidly react with isocyanates and amines to form a strong crosslinked network. Despite their excellent performance, these two-component systems face numerous technical challenges in practical application, including complex construction, poor environmental adaptability, and inconvenient storage and transportation. First, these two-component systems require precise proportioning and thorough mixing of the isocyanate and amine components during application, which typically requires specialized high-pressure spray equipment and rigorous application procedures. Second, these systems are highly sensitive to ambient temperature and humidity, significantly affecting curing speed and coating quality in high humidity or low temperatures. Furthermore, two-component systems present chemical stability issues during storage. The isocyanate component is prone to hydrolysis or self-polymerization, while the amine component can delaminate or aggregate, leading to performance degradation. This makes long-term storage and transportation of the material difficult.

[0003] To overcome the above-mentioned shortcomings of two-component systems, one-component polyurea coatings have gradually become a research hotspot. By integrating isocyanate and latent curing agent into the same system, one-component polyurea avoids the reliance of two-component systems on precise proportioning and mixing, thereby significantly simplifying the construction process and improving construction convenience. The development of one-component polyurea coatings is also accompanied by the continuous advancement of functional design. In recent years, the performance of one-component polyurea coatings has been further improved by the introduction of nanomaterials, inorganic fillers or functional additives. In addition, one-component polyurea coatings can also be multifunctionalized through molecular design to meet the special needs of different scenarios. However, due to the limitations of one-component polyurea in crosslinking density and network structure design, the mechanical properties of its coating are usually lower than those of the two-component system, resulting in incomplete coating formation or unstable performance, which further limits its practical application under complex environmental conditions. Therefore, it is necessary to prepare a modified high-strength one-component polyurea coating to meet the needs of actual production. Summary of the Invention

[0004] In response to the shortcomings of the existing technology, the present invention aims to provide a modified, high-strength, one-component polyurea coating and its preparation method. First, PDA@electrospun carbon nanofibers are prepared using a Tris-HCl buffer solution under suitable conditions to functionalize their surfaces and enhance interfacial bonding properties. Second, metal coordination microgels are prepared using emulsion polymerization. The mechanical properties and corrosion resistance of the coating are improved by introducing a metal salt solution and coordination structure. Finally, a storage-stable, one-component polyurea matrix resin is prepared using HDI trimer and isophorone diisocyanate as the main raw materials, combined with a composite blocking agent and a latent amine component. Finally, the functionalized PDA@ nanofibers, metal coordination microgels, and additives are uniformly dispersed in the matrix resin to produce a modified, high-strength, one-component polyurea coating that meets the needs of actual production.

[0005] To achieve this object, the present invention adopts the following technical solutions:

[0006] In a first aspect, the present invention provides a method for preparing a modified high-strength one-component polyurea coating, the preparation method comprising:

[0007] S1, preparing a Tris-HCl buffer solution and adjusting the pH to 8.5, dispersing dopamine hydrochloride in the Tris-HCl buffer solution, then dispersing the ball-milled electrospun carbon nanofibers in an SDBS solution, sonicating, filtering, and adding the solution to the Tris-HCl buffer solution, adjusting the temperature to a first temperature, then adding ferric chloride and stirring the reaction, washing, filtering, and vacuum drying to obtain PDA@ nanofibers;

[0008] S2, uniformly mixing cyclohexane and an emulsifier to obtain an oil phase, dispersing acrylamide, acrylic acid, and N,N'-methylenebisacrylamide in deionized water, adjusting the pH to 7, and adding ammonium persulfate to obtain an aqueous phase, adding the aqueous phase to the oil phase, adjusting the temperature to a second temperature, stirring and reacting, filtering the product, washing, and drying to obtain a pre-product, immersing the pre-product in a metal salt solution, adding benzotriazole and cyclic carbonate, and freeze-drying to obtain a metal coordination microgel;

[0009] S3, in a nitrogen atmosphere, HDI trimer and isophorone diisocyanate are mixed, the temperature is adjusted to the second temperature, and amino-terminated polyether is added for reaction. After the reaction is completed, the temperature is adjusted to 40°C, a composite blocking agent is added and stirred, and then a latent amine component is added and stirred to obtain a base resin;

[0010] S4, heating the base resin to 40° C., adding propylene glycol monomethyl ether acetate, PDA@ nanofiber, metal coordination microgel, leveling agent, defoaming agent and anti-settling agent, and mixing evenly to obtain a modified high-strength one-component polyurea coating.

[0011] Tris-HCl is a commonly used buffer solution system. In the present invention, by adjusting the pH of the Tris-HCl solution to 8.5, a suitable alkaline environment is provided for the oxidative self-polymerization of dopamine. Under alkaline conditions, the hydroxide ion concentration in the solution increases, effectively promoting the oxidation reaction of dopamine. The dopamine molecule itself contains a catechol group and a secondary amine group. The catechol group is easily oxidized to an o-quinone structure under alkaline conditions. This oxidation process is the key starting point for the oxidative self-polymerization of dopamine to form polydopamine. Dopamine hydrochloride is a water-soluble compound that dissociates into dopamine cations and chloride ions upon dissolution in water. Under alkaline conditions, the amino group in the dopamine cation becomes less protonated, gradually deprotonating to form a neutral dopamine molecule. The dopamine molecule is then oxidized in the solution, and its catechol group is converted to dopaquinone in the presence of oxygen. This reaction is driven by dissolved oxygen, with the oxygen in the solution acting as an oxidant and directly participating in the reaction, oxidizing dopamine to dopaquinone. Dopaquinone is a highly active compound with an o-quinone structure that can rapidly undergo intramolecular or intermolecular chemical reactions. After its formation, dopaquinone can be rapidly converted into more complex products through a series of intramolecular or intermolecular reactions due to its active chemical properties. Specifically, dopaquinone can achieve self-polymerization through the following two main reaction pathways: (1) The quinone group in dopaquinone can react with its own amino group to form an indole-type structure through an intramolecular Schiff base reaction. The reaction mechanism includes electrophilic addition of the quinone group and an intramolecular ring closure reaction. This cyclization reaction is the key step in the dopamine polymerization reaction and generates a highly stable conjugated molecular structure; (2) Dopaquinone reacts with the amino or hydroxyl groups of other molecules through addition to further form a complex covalent cross-linked network. The addition reaction enables dopamine molecules to be connected to each other through intermolecular bonding, gradually forming a three-dimensional cross-linked polymer network. As the reaction proceeds, polydopamine is gradually generated, forming a continuous coating through covalent and non-covalent bonding. This complex polymerization process gives polydopamine a highly stable chemical structure. Its surface is also rich in functional groups such as catechol, quinone, and amine, providing excellent chemical activity and reactivity for subsequent applications. Carbon nanofibers are widely used in functional materials due to their unique mechanical strength and high specific surface area. However, the surface chemical inertness and easy agglomeration of carbon nanofibers limit their dispersibility and interfacial bonding properties in composite materials. Therefore, in this experiment, ball milling and surfactant modification were used to improve the dispersibility and surface activity of carbon nanofibers. SDBS is an anionic surfactant whose dispersing effect comes from the dual functions of sulfonate groups and long-chain hydrocarbon groups. The sulfonate groups prevent carbon nanofiber agglomeration through electrostatic repulsion, while the long-chain hydrocarbon groups enhance the dispersibility of the fibers in non-polar or weakly polar environments through hydrophobic interaction.

[0012] After the dispersed carbon nanofibers are added to a Tris-HCl buffer, the oxidative autopolymerization reaction of dopamine continues, while polydopamine gradually deposits on the carbon nanofiber surface. The aromatic rings in the dopamine molecules can non-covalently adsorb to the aromatic graphitic carbon structure of the carbon nanofibers through π-π interactions. This stacking effect provides the initial binding force for the uniform deposition of polydopamine on the carbon nanofiber surface. The dopaquinone structures generated during the polydopamine polymerization process can covalently bond with hydroxyl or carboxyl functional groups that may exist on the carbon nanofiber surface. This chemical bonding enhances the interfacial strength between the polydopamine coating and the carbon nanofibers. As the polydopamine polymerization reaction proceeds, more polydopamine molecules adhere to the carbon nanofiber surface through π-π stacking and covalent bonding, ultimately forming a uniform and dense polydopamine coating. This coating not only provides a rich surface functional group but also improves the interfacial chemical properties of the carbon nanofibers. To further enhance the functionality of PDA@carbon nanofibers, ferric chloride is added for modification. Dopamine hydrochloride dissociates into a cationic form and chloride ions in water. Under alkaline conditions, dopamine is oxidized to dopaquinone. However, the introduction of ferric ions increases the rate of the oxidation reaction, primarily due to the strong oxidizing ability of ferric ions and their redox cycling properties in solution. As a strong oxidant, ferric ions can directly oxidize dopamine molecules, converting their catechol groups into dopaquinone. During this process, the ferric ions accept electrons and are reduced to ferrous ions, simultaneously generating highly chemically active dopaquinone molecules. Dopaquinone is a key intermediate in the oxidative self-polymerization of dopamine. It has strong electrophilicity and can react with other molecules through intramolecular or intermolecular addition reactions to form the primary polymer segments of polydopamine (PDA). The presence of ferric ions increases the oxidation rate of dopamine, thereby accelerating the formation of PDA. Furthermore, ferric ions act as catalysts in the reaction system. The ferrous ions generated during the reaction can be oxidized to ferric ions by dissolved oxygen, thus achieving a redox cycle. This cycle ensures a continuous supply of ferric ions, allowing them to repeatedly participate in the oxidation reaction of dopamine, not only improving the reaction efficiency but also reducing its dependence on dissolved oxygen concentration. Especially in an environment with low dissolved oxygen, the presence of ferric ions significantly enhances the oxidative polymerization ability of dopamine, ultimately improving the thickness and quality of the PDA coating.

[0013] In addition to its oxidative catalytic effect, ferric ions further influence the structure and properties of PDA coatings by reacting with catechol groups or quinone structures in PDA molecules. Catechol groups can form stable metal-ligand complexes with ferric ions, and this coordination effect optimizes the properties of PDA coatings on multiple levels. First, the coordination reaction enhances the chemical stability of the PDA coating, making it less soluble or difficult to dissolve in aqueous solutions. Second, the introduction of ferric ions can induce further cross-linking reactions between PDA molecules, increasing the thickness and uniformity of the coating. Furthermore, the formation of metal-ligand complexes enhances the electrochemical activity of the PDA coating, providing further possibilities for material functionalization. Fe(III) ions not only promote the oxidation of dopamine but also have a significant impact on the subsequent reaction processes of dopaquinone. In the oxidative polymerization of dopamine, dopaquinone typically forms polymer segments through intramolecular Schiff base reactions or intermolecular addition reactions. Fe(III) ions can reduce the activation energy of these reactions, thereby accelerating the reaction rate. In particular, during the intramolecular cyclization of dopaquinone, the presence of trivalent iron ions stabilizes the reaction intermediates and promotes the formation of indole-type structures. This complex conjugated structure is an important source of the chemical stability and mechanical properties of the PDA coating. In the present invention, the oxidative self-polymerization of dopamine and the surface binding of carbon nanofibers occur simultaneously. Ball milling and dispersion treatment with SDBS (sodium dodecylbenzenesulfonate) significantly increase the specific surface area of ​​the carbon nanofibers and enhance their dispersibility in aqueous solution. SDBS prevents the agglomeration of carbon nanofibers through the electrostatic repulsion of its sulfonate groups, while its long-chain hydrocarbon structure provides a hydrophobic effect, further improving the dispersion stability of the fibers. When the dispersed carbon nanofibers are added to Tris-HCl buffer, PDA gradually deposits on the surface of the carbon nanofibers through oxidative self-polymerization in an alkaline environment. Dopamine molecules undergo non-covalent adsorption with the aromatic graphite structure on the surface of the carbon nanofibers through π-π stacking, while the quinone structure generated during the PDA polymerization undergoes covalent bonding with hydroxyl or carboxyl functional groups that may exist on the surface of the carbon nanofibers. This interfacial chemical reaction ensures the uniformity and firmness of the PDA coating. The introduction of trivalent iron ions further improved the thickness and uniformity of the PDA coating. Its oxidative catalytic properties accelerated the formation of PDA molecules, allowing more PDA molecules to be deposited on the surface of carbon nanofibers in a short period of time. In addition, the trivalent iron ions, through coordination with PDA molecules, increased the degree of cross-linking of the coating, forming a denser coating structure. The uniformity of the coordination reaction also effectively avoided local polymerization or agglomeration, thereby ensuring the uniformity of the coating. In summary, trivalent iron ions play multiple roles in the oxidative polymerization of dopamine and the formation of PDA coatings. They not only directly participate in the oxidation reaction of dopamine, increasing the reaction rate, but also achieve catalyst regeneration through redox cycles, allowing the reaction to continue.At the same time, trivalent iron ions enhance the stability and functionality of the coating through coordination with PDA, and improve the mechanical strength and chemical properties of the coating.

[0014] Cyclohexane is a commonly used nonpolar solvent. Its excellent chemical stability and low polarity make it an ideal oil-phase material in emulsion systems. In this invention, cyclohexane serves as the continuous phase of the oil phase, providing a nonpolar reaction environment for emulsion formation and paving the way for the stable existence of aqueous phase droplets. To achieve uniform dispersion of the aqueous phase within the oil phase, an emulsifier is introduced into the system. By reducing the oil-water interfacial tension, the aqueous phase can be stably suspended in the oil phase as droplets, thus forming an oil-in-water emulsion system. The emulsifier molecules have an amphiphilic structure: their hydrophilic heads bind to aqueous phase molecules, while their hydrophobic tails embed within the oil phase, forming a stable monolayer at the oil-water interface. This intermolecular interaction significantly reduces the surface energy of the oil-water interface, resulting in a more uniform dispersion of aqueous phase droplets within the oil phase and inhibiting droplet coalescence and sedimentation. The core components of the aqueous phase are acrylamide, acrylic acid, and N,N'-methylenebisacrylamide, which serve as monomers and crosslinkers, respectively, and together construct the three-dimensional network structure of the hydrogel. Acrylamide, a hydrophilic monomer, contains both a double bond and an amide group in its molecular structure. The double bond is the active site for free radical polymerization, participating in chain propagation reactions to form the polymer backbone. The polarity and hydrogen bonding of the amide group impart excellent hydrophilicity and mechanical flexibility to the hydrogel, allowing it to maintain structural stability even in a swollen state. Acrylic acid, a monomer containing a carboxyl group, exhibits functionality primarily in two ways: first, its double bond participates in free radical polymerization, forming the polymer backbone with acrylamide; second, the carboxyl group provides additional chemical functionality, including electronegativity and chemical activity to the hydrogel. In particular, the carboxyl group can coordinate with metal ions in subsequent steps, imparting metal coordination properties to the hydrogel, further expanding its functional applications. N,N'-methylenebisacrylamide is a commonly used crosslinker. Its molecule contains two double bonds, which can crosslink with acrylamide and acrylic acid chains during free radical polymerization to form a three-dimensional network structure.

[0015] To ensure a smooth polymerization reaction, the monomers and crosslinker are dispersed in deionized water, and the pH of the solution is adjusted to neutral. This ensures uniform dispersion and dissociates the carboxyl groups of acrylic acid, generating carboxyl groups. The presence of carboxyl groups provides active sites for the subsequent metal coordination reaction. Ammonium persulfate is used as an initiator in the polymerization reaction. Ammonium persulfate is a thermally decomposable free radical initiator that decomposes upon heating to generate free radicals. The generated free radicals have high oxidizing properties and can attack the double bonds in the acrylamide and acrylic acid molecules, forming reactive monomer radicals. These reactive radicals undergo chain propagation reactions with other monomer molecules, gradually forming linear polymer chains. Simultaneously, the double bonds of the crosslinker N,N'-methylenebisacrylamide also participate in the reaction, bonding with multiple polymer chains to form crosslinks, ultimately forming a hydrogel with a three-dimensional network structure. The role of the emulsifier is particularly important in this process, as its stable interface ensures the isolation of the aqueous phase droplets, confining the polymerization reaction to their interior. After the polymerization reaction is complete, the resulting hydrogel microspheres are the pre-product. These pre-products are further processed to improve their functionality. Specifically, the hydrogel microspheres are immersed in a metal salt solution and undergo coordination reactions with metal ions. In this process, the carboxyl groups in acrylic acid or their dissociated carboxyl groups are the main coordination groups. Carboxyl groups have strong electron-donating capabilities and can form stable coordination bonds with metal ions, thereby introducing metal ions into the hydrogel. The introduction of metal ions may also trigger cross-linking between some carboxyl groups, thereby further enhancing the mechanical strength of the hydrogel and making it exhibit higher structural stability under external forces.

[0016] To further functionalize the metal coordination microgel, the present invention introduces benzotriazole and cyclic carbonate. Benzotriazole is an excellent corrosion inhibitor, containing nitrogen atoms and aromatic rings in its structure. These properties enable it to coordinate with metal ions, forming an additional metal-ligand network. The introduction of benzotriazole into the microgel significantly enhances the microgel's corrosion resistance through its binding to metal ions, while also improving its chemical stability, enabling it to maintain functional and structural integrity in harsh environments. The cyclic carbonate, through its cyclic structure, undergoes a ring-opening reaction with hydroxyl or amine groups in the hydrogel, further crosslinking the hydrogel network. This chemical crosslinking enhances the microgel's thermal stability and mechanical strength, ensuring its application in high-temperature or complex environments. After this functionalization treatment, the resulting metal coordination microgel is a multifunctional material with excellent mechanical strength, electrochemical activity, corrosion resistance, and chemical stability. The porous structure of this material is retained during the freeze-drying process, and its internally crosslinked three-dimensional network enables uniform dispersion in subsequent composite materials, offering potential for enhancing the performance of functional coatings. In the subsequent preparation of polyurea coatings, metal coordination microgels will serve as key reinforcing components, not only providing mechanical reinforcement effects, but also giving the coating system higher corrosion resistance and chemical stability.

[0017] The formation of the polyurea matrix centers on the addition reaction between isocyanates and amino-terminated polyethers. This reaction forms the basic backbone of polyurea coatings and imparts their excellent mechanical properties and chemical stability. Isocyanates are highly reactive compounds. The isocyanate groups in their molecules act as electrophilic centers, allowing for rapid nucleophilic addition reactions with the amine groups in amino-terminated polyethers to form urea bonds. HDI trimer is an aliphatic isocyanate, composed of multiple HDI units linked together in a trimer-like structure. This highly cross-linked structure imparts exceptional hardness, abrasion resistance, and weatherability to polyurea coatings. Isophorone diisocyanate is an alicyclic isocyanate, whose cyclic groups possess high chemical stability, imparting excellent flexibility and impact resistance to the coating. The alicyclic structure of isophorone diisocyanate effectively mitigates localized stress concentrations in the material under external forces, thereby improving the coating's ductility and low-temperature performance. Furthermore, its excellent chemical stability makes it resistant to corrosion and degradation in complex environments. HDI trimer provides highly crosslinked hard segments, while isophorone diisocyanate introduces flexible segments into the polyurea matrix. The hard segments form a densely crosslinked network through strong intermolecular interactions, providing excellent mechanical strength, wear resistance, and chemical resistance. The soft segments, through their dispersed flexible segments, impart excellent flexibility, elasticity, and low-temperature impact toughness to the material. Amino-terminated polyethers are the primary component of the soft segments in the polyurea matrix. Their molecular structure contains amine groups as reactive sites. These long polymer chains not only provide the structural foundation for the flexible segments but also significantly improve the low-temperature performance and impact resistance of the polyurea coating. The long-chain structure of amino-terminated polyethers, with their high molecular weight and excellent molecular mobility, enables the formation of flexible regions within the polyurea, thereby enhancing the material's ductility and crack resistance. During the reaction, the amine groups in the amino-terminated polyethers react rapidly with the isocyanate to form urea bonds, which are then linked into the polymer chain.

[0018] After the main reaction is complete, the system temperature is lowered to 40°C, and a composite sealant is added. The sealant is introduced to adjust the coating's latency and workability, addressing storage stability issues that may arise from the high reactivity of isocyanates. Unreacted isocyanates readily react with moisture in the environment to form amines and carbon dioxide, causing system instability and even premature curing. The composite sealant reacts with residual isocyanate to form a temporary, blocked state, preventing side reactions with moisture or other impurities. This blocked state is very stable at room temperature, but at elevated temperatures or under specific triggering conditions (such as moisture or a catalyst), it can release active isocyanates, restoring reactivity. Through this mechanism, the sealant significantly reduces the coating's reactivity, extending its shelf life and pot life, and avoiding waste or performance loss caused by premature curing. After the composite sealant is added, a latent amine component is added. Latent amines are a class of amine compounds that have low room-temperature activity but can be rapidly activated under specific conditions. This type of compound barely reacts with isocyanates during the coating's storage phase. However, during the coating's application and curing phase, when triggered by elevated temperatures or moisture, the latent amines rapidly react with isocyanates, further crosslinking the polyurea matrix. The introduction of latent amine components not only extends the coating's shelf life but also prevents premature curing during application, thereby improving its operability and applicability. The resulting matrix resin is a high-performance prepolymer system with excellent mechanical properties, chemical stability, and storage suitability. This matrix resin not only provides the polyurea coating with a balanced balance of hardness, flexibility, and impact resistance, but also ensures long-term storage and application.

[0019] The introduction of the reinforcing component, PDA@nanofibers, improves the coating's performance in many aspects. Carbon nanofibers, with their extremely high tensile strength and modulus, significantly enhance the coating's mechanical properties, including tensile strength, impact resistance, and wear resistance. The PDA molecules, through their rich functional groups, chemically react with isocyanate or amine groups in the matrix resin, forming a strong interfacial bond, further enhancing the coating's overall mechanical properties. Furthermore, the phenolic hydroxyl groups in the PDA molecules coordinate with the metal surface, forming a dense protective film when the coating is applied to the metal substrate, thereby preventing oxygen and moisture penetration and reducing the likelihood of metal corrosion. The metal ions in the microgel further enhance the crosslinking density of the polyurea coating by coordinating with amine or urea groups in the matrix resin. This chemical crosslinking not only improves the coating's mechanical strength but also enhances its chemical stability. The metal ions in the microgel form a dense protective layer on the coating surface, preventing the penetration of external moisture and oxygen.

[0020] As a preferred technical solution of the present invention, in S1, the volume mass ratio of the Tris-HCl buffer solution to dopamine hydrochloride is 150 mL:1 g.

[0021] In some optional embodiments, the mass volume ratio of the ball-milled electrospun carbon nanofibers to the SDBS solution is 1 g:40 mL.

[0022] In some optional embodiments, the mass fraction of the SDBS solution is 1 wt.%.

[0023] In some optional embodiments, the ultrasonic time is 30-40 min, for example, it can be 30 min, 31 min, 32 min, 33 min, 34 min, 35 min, 36 min, 37 min, 38 min, 39 min or 40 min, but is not limited to the listed times, and other unlisted times within the time range are also applicable.

[0024] In some optional embodiments, the mass ratio of the dopamine hydrochloride to the ball-milled electrospun carbon nanofibers is 2:5.

[0025] In some optional embodiments, the first temperature is 30-40°C, for example, it can be 30°C, 31°C, 32°C, 33°C, 34°C, 35°C, 36°C, 37°C, 38°C, 39°C or 40°C, but is not limited to the listed temperatures, and other unlisted temperatures within this temperature range are also applicable.

[0026] In some optional embodiments, the stirring reaction time is 15-20h, for example, it can be 15h, 15.5h, 16h, 16.5h, 17h, 17.5h, 18h, 18.5h, 19h, 19.5h or 20h, but is not limited to the listed times, and other unlisted times within the time range are also applicable.

[0027] In some optional embodiments, the mass ratio of ferric chloride to dopamine hydrochloride is 3:2.

[0028] As a preferred technical solution of the present invention, in S2, the volume mass ratio of cyclohexane to emulsifier is 100mL:1g.

[0029] In some optional embodiments, the emulsifier is Span 80.

[0030] In some optional embodiments, the mass ratio of acrylamide, acrylic acid, N,N'-methylenebisacrylamide and ammonium persulfate is 25:15:1:0.5.

[0031] In some optional embodiments, the mass volume ratio of acrylamide to deionized water is 1 g:6 mL.

[0032] In some optional embodiments, the volume ratio of the oil phase to the water phase is 20:3.

[0033] In some optional embodiments, the second temperature is 60-70°C, for example, it can be 60°C, 61°C, 62°C, 63°C, 64°C, 65°C, 66°C, 67°C, 68°C, 69°C or 70°C, but is not limited to the listed temperatures, and other unlisted temperatures within this temperature range are also applicable.

[0034] In some optional embodiments, the second temperature stirring reaction time is 3-4h, for example, it can be 3.0h, 3.1h, 3.2h, 3.3h, 3.4h, 3.5h, 3.6h, 3.7h, 3.8h, 3.9h or 4.0h, but is not limited to the listed times, and other times not listed within the time range are also applicable.

[0035] In some optional embodiments, the mass volume ratio of the pre-product to the metal salt solution is 4g:15mL.

[0036] In some optional embodiments, the mass fraction of the metal salt solution is 9 wt.%.

[0037] In some optional embodiments, the mass ratio of the pre-product, benzotriazole and cyclic carbonate is 8:1:2.

[0038] As a preferred technical solution of the present invention, in S3, the mass ratio of the HDI trimer, isophorone diisocyanate, amino-terminated polyether, composite blocking agent and latent amine component is 12:5:20:4:4.

[0039] In some optional embodiments, the HDI trimer is hexamethylene diisocyanate trimer.

[0040] In some optional embodiments, the amino-terminated polyether is LHD-1200.

[0041] In some optional embodiments, the reaction time of adding the amino-terminated polyether is 1-2h, for example, it can be 1.0h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, 1.6h, 1.7h, 1.8h, 1.9h or 2.0h, but is not limited to the listed times, and other times not listed within the time range are also applicable.

[0042] In some optional embodiments, the composite blocking agent is 2-imidazolidinone.

[0043] In some optional embodiments, the latent amine component is a ketimine curing agent.

[0044] As a preferred technical solution of the present invention, in S4, the mass ratio of the base resin, propylene glycol monomethyl ether acetate, PDA@ nanofiber, metal coordination microgel, leveling agent, defoaming agent and anti-settling agent is 450:150:10:15:2:1:3.

[0045] In some optional embodiments, the leveling agent is polyether-modified polysiloxane.

[0046] In some optional embodiments, the defoaming agent is polydimethylsiloxane.

[0047] In some optional embodiments, the anti-settling agent is one or more of kaolin, bentonite, and talc.

[0048] In a second aspect, the present invention provides a modified high-strength one-component polyurea coating prepared by the preparation method described in the first aspect.

[0049] Compared with the prior art, the present invention has the following advantages: (1) electrospun carbon nanofibers are used as reinforcing materials, and the functionalization treatment of polydopamine gives the nanofibers rich surface functional groups, which can react chemically with the isocyanate in the matrix resin to form a strong interface bond. In addition, the surface coating of polydopamine can also improve the dispersibility of the carbon nanofibers and prevent them from agglomerating in the coating system; (2) the prepared metal coordination microgel realizes a three-dimensional cross-linked network through the emulsion polymerization process, and introduces the metal ions through the coordination effect between the carboxyl group of acrylic acid and the metal ions. The metal coordination network is formed. The coordination of metal ions can enhance the cross-linking density of the coating and improve the tensile strength of the coating. The porous structure of the microgel provides more interface bonding points for the coating, which helps to enhance the overall uniformity of the material. (3) By combining HDI trimer and isophorone diisocyanate, a hard segment-soft segment structure is constructed. The HDI trimer provides the hardness and wear resistance of the coating through its regular trimer structure and high cross-linking density. The alicyclic structure of isophorone diisocyanate improves the impact resistance and flexibility of the coating by introducing flexible chain segments. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 This is a SEM image of the metal coordination microgel provided in Example 1 of the present invention;

[0051] Figure 2 This is a TEM image of the metal coordination microgel provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0052] The technical solutions of the present invention are described in detail below in conjunction with specific embodiments and their accompanying drawings. The embodiments described herein are specific embodiments of the present invention and are used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary and should not be understood as limiting the embodiments of the present invention and the scope of protection of the present invention. In addition to the embodiments described herein, those skilled in the art can also adopt other obvious technical solutions based on the contents disclosed in the claims of this application and its specification, including technical solutions that adopt any obvious replacements and modifications to the embodiments described herein.

[0053] The chemical reagents used in the examples and comparative examples of the present invention are all commercially available products and have not been subjected to any further purification treatment.

[0054] Example 1

[0055] This embodiment provides a modified high-strength one-component polyurea coating, the preparation method of which specifically includes the following steps:

[0056] S1, prepare Tris-HCl buffer solution and adjust the pH to 8.5, disperse 2 g of dopamine hydrochloride in 300 mL of Tris-HCl buffer solution, then disperse 5 g of ball-milled electrospun carbon nanofibers in 200 mL of 1 wt.% SDBS solution, sonicate for 33 min, filter, and add to Tris-HCl buffer solution. Adjust the temperature to 38°C, add 3 g of ferric chloride, and stir for 15.2 h. Wash, filter, and vacuum dry to obtain PDA@ nanofibers.

[0057] S2, 200 mL of cyclohexane and 2 g of Span 80 were uniformly mixed to obtain an oil phase, 25 g of acrylamide, 15 g of acrylic acid, and 1 g of N,N'-methylenebisacrylamide were dispersed in 150 mL of deionized water, the pH was adjusted to 7, and 0.5 g of ammonium persulfate was added to obtain an aqueous phase, 30 mL of the aqueous phase was added to 200 mL of the oil phase, the temperature was adjusted to 66° C., and the reaction was stirred for 3.2 h. The product was filtered, washed, and dried to obtain a pre-product, 8 g of the pre-product was immersed in 30 mL of a 9 wt.% zinc nitrate solution, 1 g of benzotriazole and 2 g of a cyclic carbonate were added, and the product was freeze-dried to obtain a metal coordination microgel;

[0058] S3, under nitrogen atmosphere, 120 g of hexamethylene diisocyanate trimer and 50 g of isophorone diisocyanate were mixed, the temperature was adjusted to 66°C, 200 g of LHD-1200 was added, and the mixture was reacted for 1.3 h. After the reaction, the temperature was adjusted to 40°C, 40 g of 2-imidazolidone was added, and the mixture was stirred. Then, 40 g of the latent amine component was added and stirred to obtain a base resin;

[0059] S4, heating 450g of the base resin to 40°C, adding 150g of propylene glycol monomethyl ether acetate, 10g of PDA@ nanofiber, 15g of metal coordination microgel, 2g of polyether-modified polysiloxane, 1g of polydimethylsiloxane and 3g of kaolin, and mixing them evenly to obtain a modified high-strength one-component polyurea coating.

[0060] Figure 1 This is the SEM image of the metal coordination microgel prepared in this example; Figure 2 This is the TEM image of the metal coordination microgel prepared in this example. The internal structure of the gel shows obvious porous characteristics.

[0061] Example 2

[0062] This embodiment provides a modified high-strength one-component polyurea coating, the preparation method of which specifically includes the following steps:

[0063] S1, prepare Tris-HCl buffer solution and adjust the pH to 8.5, disperse 2 g of dopamine hydrochloride in 300 mL of Tris-HCl buffer solution, then disperse 5 g of ball-milled electrospun carbon nanofibers in 200 mL of 1 wt.% SDBS solution, sonicate for 39 min, filter, and add to Tris-HCl buffer solution. Adjust the temperature to 30°C, add 3 g of ferric chloride, and stir for 17.6 h. Wash, filter, and vacuum dry to obtain PDA@ nanofibers.

[0064] S2, 200 mL of cyclohexane and 2 g of Span 80 were uniformly mixed to obtain an oil phase, 25 g of acrylamide, 15 g of acrylic acid, and 1 g of N,N'-methylenebisacrylamide were dispersed in 150 mL of deionized water, the pH was adjusted to 7, and 0.5 g of ammonium persulfate was added to obtain an aqueous phase, 30 mL of the aqueous phase was added to 200 mL of the oil phase, the temperature was adjusted to 69° C., and the reaction was stirred for 3.8 hours. The product was filtered, washed, and dried to obtain a pre-product, 8 g of the pre-product was immersed in 30 mL of a 9 wt.% zinc nitrate solution, 1 g of benzotriazole and 2 g of a cyclic carbonate were added, and the product was freeze-dried to obtain a metal coordination microgel;

[0065] S3, under nitrogen atmosphere, 120 g of hexamethylene diisocyanate trimer and 50 g of isophorone diisocyanate were mixed, the temperature was adjusted to 69°C, 200 g of LHD-1200 was added, and the mixture was reacted for 1.5 h. After the reaction, the temperature was adjusted to 40°C, 40 g of 2-imidazolidone was added, and the mixture was stirred. Then, 40 g of the latent amine component was added and stirred to obtain a base resin;

[0066] S4, heating 450g of the base resin to 40°C, adding 150g of propylene glycol monomethyl ether acetate, 10g of PDA@ nanofiber, 15g of metal coordination microgel, 2g of polyether-modified polysiloxane, 1g of polydimethylsiloxane and 3g of bentonite, and mixing them evenly to obtain a modified high-strength one-component polyurea coating.

[0067] Example 3

[0068] This embodiment provides a modified high-strength one-component polyurea coating, the preparation method of which specifically includes the following steps:

[0069] S1, prepare Tris-HCl buffer solution and adjust the pH to 8.5, disperse 2 g of dopamine hydrochloride in 300 mL of Tris-HCl buffer solution, then disperse 5 g of ball-milled electrospun carbon nanofibers in 200 mL of 1 wt.% SDBS solution, sonicate for 31 min, filter, and add to Tris-HCl buffer solution. Adjust the temperature to 34°C, add 3 g of ferric chloride, and stir for 19.4 h. Wash, filter, and vacuum dry to obtain PDA@ nanofibers.

[0070] S2, 200 mL of cyclohexane and 2 g of Span 80 were uniformly mixed to obtain an oil phase, 25 g of acrylamide, 15 g of acrylic acid, and 1 g of N,N'-methylenebisacrylamide were dispersed in 150 mL of deionized water, the pH was adjusted to 7, and 0.5 g of ammonium persulfate was added to obtain an aqueous phase, 30 mL of the aqueous phase was added to 200 mL of the oil phase, the temperature was adjusted to 61° C., and the reaction was stirred for 3.4 hours. The product was filtered, washed, and dried to obtain a pre-product, 8 g of the pre-product was immersed in 30 mL of a 9 wt.% zinc nitrate solution, 1 g of benzotriazole and 2 g of a cyclic carbonate were added, and the product was freeze-dried to obtain a metal coordination microgel;

[0071] S3, under nitrogen atmosphere, 120 g of hexamethylene diisocyanate trimer and 50 g of isophorone diisocyanate were mixed, the temperature was adjusted to 61°C, 200 g of LHD-1200 was added, and the reaction was carried out for 1.9 h. After the reaction was completed, the temperature was adjusted to 40°C, 40 g of 2-imidazolidone was added, and stirred, and then 40 g of the latent amine component was added and stirred to obtain a base resin;

[0072] S4, heating 450g of the base resin to 40°C, adding 150g of propylene glycol monomethyl ether acetate, 10g of PDA@ nanofiber, 15g of metal coordination microgel, 2g of polyether-modified polysiloxane, 1g of polydimethylsiloxane and 3g of talc, and mixing them evenly to obtain a modified high-strength one-component polyurea coating.

[0073] Example 4

[0074] This embodiment provides a modified high-strength one-component polyurea coating, the preparation method of which specifically includes the following steps:

[0075] S1, prepare Tris-HCl buffer solution and adjust the pH to 8.5, disperse 2 g of dopamine hydrochloride in 300 mL of Tris-HCl buffer solution, then disperse 5 g of ball-milled electrospun carbon nanofibers in 200 mL of 1 wt.% SDBS solution, sonicate for 37 min, filter, and add to Tris-HCl buffer solution. Adjust the temperature to 36°C, add 3 g of ferric chloride, and stir for 16.3 h. Wash, filter, and vacuum dry to obtain PDA@ nanofibers.

[0076] S2, 200 mL of cyclohexane and 2 g of Span 80 were uniformly mixed to obtain an oil phase, 25 g of acrylamide, 15 g of acrylic acid, and 1 g of N,N'-methylenebisacrylamide were dispersed in 150 mL of deionized water, the pH was adjusted to 7, and 0.5 g of ammonium persulfate was added to obtain an aqueous phase, 30 mL of the aqueous phase was added to 200 mL of the oil phase, the temperature was adjusted to 63°C, and the reaction was stirred for 3.6 hours. The product was filtered, washed, and dried to obtain a pre-product, 8 g of the pre-product was immersed in 30 mL of a 9 wt.% zinc nitrate solution, 1 g of benzotriazole and 2 g of a cyclic carbonate were added, and the product was freeze-dried to obtain a metal coordination microgel;

[0077] S3, under nitrogen atmosphere, 120 g of hexamethylene diisocyanate trimer and 50 g of isophorone diisocyanate were mixed, the temperature was adjusted to 63°C, 200 g of LHD-1200 was added, and the mixture was reacted for 1.7 h. After the reaction, the temperature was adjusted to 40°C, 40 g of 2-imidazolidone was added, and the mixture was stirred. Then, 40 g of the latent amine component was added and stirred to obtain a base resin;

[0078] S4, heating 450g of the base resin to 40°C, adding 150g of propylene glycol monomethyl ether acetate, 10g of PDA@ nanofiber, 15g of metal coordination microgel, 2g of polyether-modified polysiloxane, 1g of polydimethylsiloxane and 3g of kaolin, and mixing them evenly to obtain a modified high-strength one-component polyurea coating.

[0079] Comparative Example 1

[0080] This comparative example provides a modified high-strength one-component polyurea coating, which differs from Example 1 in that the mass of the hexamethylene diisocyanate trimer in S3 is 220 g, which is 100 g more than that in Example 1, and the other process parameters and operating conditions are exactly the same as those in Example 1.

[0081] Comparative Example 2

[0082] This comparative example provides a modified high-strength one-component polyurea coating, which differs from Example 1 in that the mass of the hexamethylene diisocyanate trimer in S3 is 20 g, which is 100 g less than that in Example 1, and the other process parameters and operating conditions are exactly the same as those in Example 1.

[0083] Comparative Example 3

[0084] This comparative example provides a modified high-strength one-component polyurea coating, which differs from Example 1 in that the mass of the PDA@ nanofibers in S4 is 20 g, which is 10 g more than that in Example 1, and the other process parameters and operating conditions are exactly the same as those in Example 1.

[0085] Comparative Example 4

[0086] This comparative example provides a modified high-strength one-component polyurea coating, which differs from Example 1 in that the mass of the PDA@ nanofiber in S4 is 1 g, which is 10 g less than that in Example 1, and the other process parameters and operating conditions are exactly the same as those in Example 1.

[0087] Adhesion testing was conducted according to GB / T 9286-2021; tensile strength testing was conducted according to GB / T 528-2009; hardness testing was conducted according to GB / T 6739-2022; and impact resistance testing was conducted according to GB / T 1732-2020. The test results are shown in Table 1.

[0088] Table 1 Test results of a modified high-strength one-component polyurea coating of Examples 1-4 and Comparative Examples 1-4

[0089] Adhesion Tensile strength (MPa) hardness Impact resistance (cm) Example 1 Level 0 18.6 3H 65 Example 2 Level 0 19.5 3H 70 Example 3 Level 0 18.2 3H 70 Example 4 Level 0 19.1 3H 65 Comparative Example 1 Level 1 15.9 H 75 Comparative Example 2 Level 2 21.5 4H 40 Comparative Example 3 Level 2 12.1 F 45 Comparative Example 4 Level 2 16.2 2H 50

[0090] As can be seen from the data in Table 1, compared with Example 1, the adhesion, tensile strength and hardness of Comparative Example 1 decreased, while the impact resistance increased; the tensile strength and hardness of Comparative Example 2 increased, while the adhesion and impact resistance decreased. This is because the trifunctional structure of the HDI trimer enables it to form a highly cross-linked network structure during the reaction. In Comparative Example 1, the HDI trimer is insufficient, reducing the hard segment ratio, thereby reducing the overall mechanical properties of the coating. The lower hard segment ratio and cross-linking density increase the flexibility of the coating, enabling it to absorb more impact energy and improve impact resistance. In Comparative Example 2, the HDI trimer is excessive, and the high cross-linking density causes the coating to become brittle and lack flexibility, making it more prone to cracking or peeling when the interface is subjected to mechanical stress. The high cross-linking density and increased hard segment ratio make the coating exhibit a higher surface hardness. Excessive hard segments make the coating brittle and difficult to absorb and disperse energy under impact loads, causing the coating to crack more easily.

[0091] Compared with Example 1, the adhesion, tensile strength, hardness and impact resistance of Comparative Example 3 are reduced; the adhesion, tensile strength, hardness and impact resistance of Comparative Example 4 are reduced. This is because there are too few PDA@ nanofibers in Comparative Example 3, the number of phenolic hydroxyl groups and amine groups of PDA is reduced, the interface bonding points between the matrix resin and the substrate are reduced, and the paint film lacks sufficient high-strength reinforcing components, and the mechanical properties of the coating are reduced. In Comparative Example 4, when the PDA@ nanofiber content is too much, the nanofibers are difficult to disperse evenly and are prone to agglomeration. The agglomeration phenomenon leads to uneven interface bonding, weakened interfacial interaction between the nanofibers and the matrix resin, weak bonding points are formed in some areas, adhesion is reduced, and brittle points are formed in the agglomerated areas. The coating is more likely to crack or break under impact loads.

[0092] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a modified high-strength one-component polyurea coating, characterized in that: The preparation method comprises: S1, preparing a Tris-HCl buffer solution and adjusting the pH to 8.5, dispersing dopamine hydrochloride in the Tris-HCl buffer solution, then dispersing the ball-milled electrospun carbon nanofibers in an SDBS solution, filtering and adding the solution to the Tris-HCl buffer solution, and adding ferric chloride to react to obtain PDA@ nanofibers; S2, mixing cyclohexane with an emulsifier to obtain an oil phase, dispersing acrylamide, acrylic acid, and N,N'-methylenebisacrylamide in deionized water, adjusting the pH to 7, and adding ammonium persulfate to obtain an aqueous phase, adding the aqueous phase to the oil phase to react to obtain a pre-product, immersing the pre-product in a metal salt solution, and adding benzotriazole and cyclic carbonate to obtain a metal coordination microgel; S3, mixing HDI trimer and isophorone diisocyanate, adding amino-terminated polyether to react, adjusting the temperature to 40°C, adding a composite blocking agent and a latent amine component to obtain a base resin; S4, heating the base resin to 40° C., adding propylene glycol monomethyl ether acetate, PDA@ nanofibers, metal coordination microgel, leveling agent, defoaming agent and anti-settling agent to obtain a modified high-strength one-component polyurea coating; The mass ratio of the dopamine hydrochloride to the ball-milled electrospun carbon nanofibers is 2:5; The mass ratio of the ferric chloride to dopamine hydrochloride is 3:2; The mass ratio of acrylamide, acrylic acid, N,N'-methylenebisacrylamide and ammonium persulfate is 25:15:1:0.5; The volume ratio of the oil phase to the water phase is 20:3; The mass volume ratio of the pre-product to the metal salt solution is 4g:15mL; The mass ratio of the pre-product, benzotriazole and cyclic carbonate is 8:1:2; The mass ratio of the HDI trimer, isophorone diisocyanate, amino-terminated polyether, composite blocking agent and latent amine component is 12:5:20:4:4; The mass ratio of the base resin, propylene glycol monomethyl ether acetate, PDA@ nanofiber, metal coordination microgel, leveling agent, defoaming agent and anti-settling agent is 450:150:10:15:2:1:3; The composite sealing agent is 2-imidazolidinone.

2. The method for preparing a modified high-strength one-component polyurea coating according to claim 1, characterized in that: In S4, The leveling agent is polyether modified polysiloxane; The defoaming agent is polydimethylsiloxane; The anti-settling agent is one or more of kaolin, bentonite and talc.

3. A modified high-strength one-component polyurea coating obtained according to the preparation method according to any one of claims 1-2.

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