Modified high-strength single-component polyurea coating and preparation method thereof

Abstract

The invention belongs to the technical field of coating preparation, and provides a modified high-strength single-component polyurea coating and a preparation method thereof. Firstly, a Tris-HCl buffer solution is utilized to react under the alkaline condition to prepare PDA electrospinning carbon nanofibers, and the functional characteristics and interface bonding force of the fibers are enhanced through surface dopamine coating; secondly, preparing metal coordination microgel by adopting an emulsion polymerization method, and constructing a high-strength and corrosion-resistant functional microgel structure through the synergistic effect of an acrylamide monomer, metal salt and benzotriazole; then, in a nitrogen atmosphere, preparing matrix resin through reaction of isocyanate and amine-terminated polyether, and regulating and controlling the storage stability and curing behavior of the matrix resin by combining latent amine and a composite sealing agent; and finally, uniformly dispersing the PDA nanometer fiber, the metal coordination microgel and an auxiliary agent in matrix resin to prepare the modified high-strength single-component polyurea coating which is suitable for application in a complex environment.

Description

Technical Field

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

[0002] As a high-performance protective coating system, polyurea coatings have received extensive attention due to their rapid curing, high mechanical strength, excellent corrosion resistance and weather resistance. Their unique chemical reaction system enables them to exhibit excellent performance in waterproofing projects, industrial protection, transportation infrastructure and other fields. Traditional polyurea coatings mainly rely on a two-component system, that is, a high-strength cross-linked network is formed through the rapid reaction of isocyanate and amine compounds. Although this two-component system has excellent performance, it faces many technical problems in practical applications, such as complex construction, poor environmental adaptability, and inconvenient storage and transportation. First of all, the two-component system requires precise proportioning and thorough mixing of the isocyanate and amine components during construction, which usually requires special high-pressure spraying equipment and strict construction processes. Secondly, this system is highly sensitive to environmental temperature and humidity, and the curing speed and coating quality are easily significantly affected under high humidity or low temperature conditions. In addition, there are chemical stability problems in the storage process of the two-component system. The isocyanate component is prone to hydrolysis or self-polymerization, while the amine component may cause performance degradation due to stratification or aggregation, making the long-term storage and transportation of materials difficult.

[0003] To overcome the above defects of the two-component system, one-component polyurea coatings have gradually become a research hotspot. One-component polyurea integrates isocyanate and latent curing agents in the same system, avoiding the dependence on precise proportioning and mixing of the two-component system, thus significantly simplifying the construction process and improving the 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 introducing nanomaterials, inorganic fillers or functional additives. In addition, one-component polyurea coatings can also be functionalized through molecular design to meet special requirements in different scenarios. However, due to the limitations in the crosslinking density and network structure design of one-component polyurea, the mechanical properties of its coatings are usually lower than those of the two-component system, resulting in incomplete coating formation or unstable performance, which further restricts 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] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a modified high-strength one-component polyurea coating and its preparation method. First, PDA@electrospun carbon nanofibers are prepared through a Tris-HCl buffer solution under suitable conditions to functionalize their surfaces and enhance the interfacial bonding performance. Secondly, metal coordination microgels are prepared by emulsion polymerization, and the mechanical properties and corrosion resistance of the coating are improved by introducing metal salt solutions and coordination structures. Then, using HDI trimer and isophorone diisocyanate as the main raw materials, combined with a composite blocking agent and a latent amine component, a storage-stable one-component polyurea matrix resin is prepared. Finally, the functionalized PDA@nanofibers, metal coordination microgels and additives are uniformly dispersed in the matrix resin to obtain a modified high-strength one-component polyurea coating, thus meeting the needs of actual production.

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

[0006] In the first aspect, the present invention provides a preparation method of a modified high-strength one-component polyurea coating, and the preparation method includes:

[0007] S1, Prepare a Tris-HCl buffer solution and adjust the pH to 8.5. Disperse dopamine hydrochloride in the Tris-HCl buffer solution, then disperse the ball-milled and pulverized electrospun carbon nanofibers in the SDBS solution, filter after ultrasonic treatment and add them to the Tris-HCl buffer solution. Adjust the temperature to the first temperature, then add ferric chloride and stir for reaction. Wash, filter and vacuum dry to obtain PDA@nanofibers;

[0008] S2, Mix cyclohexane and an emulsifier evenly to obtain an oil phase. Disperse acrylamide, acrylic acid and N,N'-methylenebisacrylamide in deionized water, adjust the pH to 7 and add ammonium persulfate to obtain an aqueous phase. Add the aqueous phase to the oil phase, adjust the temperature to the second temperature and stir for reaction. Filter the product, wash and dry to obtain a pre-product. Immerse the pre-product in a metal salt solution and add benzotriazole and cyclic carbonate, and freeze-dry to obtain metal coordination microgels;

[0009] S3, In a nitrogen atmosphere, mix HDI trimer and isophorone diisocyanate, adjust the temperature to the second temperature and add a terminal amino polyether for reaction. After the reaction, adjust the temperature to 40°C, add a composite blocking agent and stir, then add a latent amine component and stir to obtain a matrix resin;

[0010] S4, Heat the matrix resin to 40°C, then add propylene glycol monomethyl ether acetate, PDA@nanofibers, metal coordination microgels, a leveling agent, an antifoaming agent and an anti-settling agent, and mix evenly to obtain a modified high-strength one-component polyurea coating.

[0011] Tris-HCl is a commonly used buffer solution system. In this 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 concentration of hydroxide ions in the solution increases, which can effectively promote the oxidation reaction of dopamine. The dopamine molecule itself has a catechol group and a secondary amine group in its structure. Among them, the catechol group is easily oxidized to the o-quinone structure under alkaline conditions, and 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, which dissociates into dopamine cations and chloride ions after dissolving in water. Under alkaline conditions, the degree of protonation of the amino group of dopamine cations decreases, and it gradually deprotonates to form neutral dopamine molecules. Subsequently, the dopamine molecules are oxidized in the solution, and their catechol groups are converted into dopaquinone in the presence of oxygen. This reaction is driven by dissolved oxygen, and the oxygen in the solution participates directly in the reaction as an oxidant, oxidizing dopamine to dopaquinone. Dopaquinone is a compound with relatively high activity and has an o-quinone structure, which can quickly undergo intra- or intermolecular chemical reactions. After the formation of dopaquinone, due to its active chemical properties, it quickly transforms into more complex products through a series of intra- or intermolecular reactions. Specifically, dopaquinone can achieve self-polymerization through the following two main reaction pathways: (1) The quinone group in dopaquinone can undergo an intramolecular Schiff base reaction with its own amino group to form an indole-type structure. The reaction mechanism includes the electrophilic addition of the quinone group and the intramolecular cyclization reaction. This cyclization reaction is a key step in the dopamine polymerization reaction, generating 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-linking network. The addition reaction enables dopamine molecules to be connected to each other through intermolecular bonding, gradually forming a three-dimensional cross-linked polymerization network. As the reaction progresses, polydopamine is gradually generated and forms a continuous coating through a combination of covalent and non-covalent bonds. This complex polymerization process endows polydopamine with a highly stable chemical structure, and at the same time, the surface is rich in functional functional groups such as catechol, quinone, and amino groups, providing excellent chemical activity and reactivity for subsequent applications. Carbon nanofibers have a wide range of applications in functional materials due to their unique mechanical strength and high specific surface area. However, the surface chemical inertness and easy agglomeration characteristics of carbon nanofibers limit their dispersibility and interfacial bonding properties in composite materials. Therefore, in the experiment, ball milling and surfactant modification are used to improve the dispersibility and surface activity of carbon nanofibers. SDBS is an anionic surfactant, and its dispersing effect comes from the dual functions of the sulfonate group and the long-chain hydrocarbon group. The sulfonate group prevents the agglomeration of carbon nanofibers through electrostatic repulsion, and the long-chain hydrocarbon group enhances the dispersibility of the fibers in non-polar or weakly polar environments through hydrophobic interaction.

[0012] After the dispersed carbon nanofibers are added to the Tris-HCl buffer solution, the oxidative self-polymerization reaction of dopamine continues, and polydopamine gradually deposits on the surface of the carbon nanofibers. The aromatic ring in the dopamine molecule can undergo non-covalent adsorption with the aromatic graphite carbon structure of the carbon nanofibers through π-π interactions. This stacking effect provides an initial binding force for the uniform deposition of polydopamine on the surface of the carbon nanofibers; during the polymerization process of polydopamine, the generated dopaquinone structure can form covalent bonds with the hydroxyl or carboxyl functional groups that may exist on the surface of the carbon nanofibers. This chemical bonding enhances the interfacial strength between the polydopamine coating and the carbon nanofibers. As the polydopamine polymerization reaction proceeds, more polydopamine molecules attach to the surface of the carbon nanofibers through π-π stacking and covalent bonding methods, ultimately forming a uniform and dense polydopamine coating. This coating not only provides abundant surface functional functional groups 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 in this invention. Dopamine hydrochloride dissociates into cationic form and chloride ions in water and is oxidized to dopaquinone under alkaline conditions. However, after the introduction of ferric ions, the rate of the oxidation reaction increases, which is mainly attributed to the strong oxidation ability of ferric ions and their redox cycling characteristics in the solution. As a strong oxidant, ferric ions can directly oxidize dopamine molecules and convert their catechol groups into dopaquinone. During this process, ferric ions accept electrons and are reduced to ferrous ions, while generating highly chemically active dopaquinone molecules. Dopaquinone is a key intermediate in the oxidative self-polymerization reaction of dopamine and has strong electrophilicity. It can react with other molecules through intra- or intermolecular addition reactions to generate the primary polymerization segments of polydopamine (PDA). The participation of ferric ions increases the oxidation rate of dopamine, thus accelerating the formation process of PDA. At the same time, ferric ions exhibit the characteristics of a catalyst in the reaction system. The generated ferrous ions in the reaction can be oxidized to ferric ions by dissolved oxygen, thus realizing the redox cycle. This cycle ensures the continuous supply of ferric ions, enabling them to repeatedly participate in the oxidation reaction of dopamine, not only improving the reaction efficiency but also reducing the dependence on the 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 increasing the thickness and quality of the PDA coating.

[0013] In addition to its oxidation catalytic effect, ferric ions also further affect the structure and properties of the PDA coating through coordination reactions 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 characteristics of the PDA coating at multiple levels. First, the coordination reaction enhances the chemical stability of the PDA coating, making it more difficult to dissolve or peel off 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. In addition, the formation of metal-ligand complexes also enhances the electrochemical activity of the PDA coating, providing more possibilities for material functionalization. Ferric ions not only promote the oxidation of dopamine but also have an important impact on the subsequent reaction process of dopaquinone. In the oxidative polymerization of dopamine, dopaquinone usually forms polymer segments through intramolecular Schiff base reactions or intermolecular addition reactions. Ferric ions can lower the activation energy of these reactions, thus accelerating the reaction rate. Especially in the intramolecular cyclization process of dopaquinone, the presence of ferric ions stabilizes the reaction intermediate 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 is carried out simultaneously with the surface binding of carbon nanofibers. Ball milling and dispersion treatment with SDBS (sodium dodecylbenzenesulfonate) significantly increase the specific surface area of carbon nanofibers and enhance their dispersibility in aqueous solutions. SDBS prevents the aggregation of carbon nanofibers through the electrostatic repulsion of its sulfonate groups, and at the same time its long-chain hydrocarbon structure provides a hydrophobic effect, further enhancing the dispersion stability of the fibers. When the dispersed carbon nanofibers are added to Tris-HCl buffer solution, PDA is gradually deposited on the surface of 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 carbon nanofibers through π-π stacking, and the quinone structures generated during the PDA polymerization process form covalent bonds with the hydroxyl or carboxyl functional groups that may exist on the surface of carbon nanofibers. This interfacial chemical effect ensures the uniformity and firmness of the PDA coating. The introduction of ferric ions further increases the thickness and uniformity of the PDA coating. Its oxidation catalytic characteristics accelerate the generation of PDA molecules, enabling more PDA molecules to be deposited on the surface of carbon nanofibers in a short time. In addition, through the coordination with PDA molecules, ferric ions increase the degree of cross-linking of the coating, forming a denser coating structure. The uniformity of the coordination reaction effectively avoids local polymerization or aggregation phenomena, thus ensuring the uniformity of the coating. In summary, ferric ions play multiple roles in the oxidative polymerization of dopamine and the formation of the PDA coating. It not only directly participates in the oxidation reaction of dopamine, increasing the reaction rate, but also realizes the regeneration of the catalyst through redox cycling, enabling the reaction to continue.Meanwhile, ferric ions enhance the stability and functionality of the coating through coordination with PDA, improving the mechanical strength and chemical properties of the coating.

[0014] Cyclohexane is a commonly used non-polar solvent. Its good chemical stability and low polarity make it an ideal oil-phase material in the emulsion system. In this invention, cyclohexane serves as the continuous phase of the oil phase, providing a non-polar reaction environment for the formation of the emulsion and laying the foundation for the stable existence of water-phase droplets. To achieve the uniform dispersion of the water phase in the oil phase, an emulsifier is introduced into the system. The emulsifier reduces the oil-water interfacial tension, enabling the water phase to stably suspend in the oil phase in the form of droplets, thus forming an oil-in-water emulsion system. The emulsifier molecule has an amphiphilic structure. Its hydrophilic head can bind to water-phase molecules, while its hydrophobic tail embeds into the interior of 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, making the dispersion of water-phase droplets in the oil phase more uniform and suppressing the coalescence and sedimentation of droplets. The core components of the water phase are acrylamide, acrylic acid, and N,N'-methylenebisacrylamide, which serve as monomers and crosslinking agents respectively to jointly construct the three-dimensional network structure of the hydrogel. Acrylamide, as a hydrophilic monomer, contains a double bond and an amide group in its molecular structure. The double bond is the active site for free radical polymerization and can participate in the chain growth reaction to form the polymer backbone; while the polarity and hydrogen bonding of the amide group endow the hydrogel with excellent hydrophilicity and mechanical flexibility, enabling its structure to remain stable in the swollen state. Acrylic acid is a monomer containing a carboxyl group, and its functionality is mainly reflected in two aspects: on the one hand, its double bond participates in free radical polymerization and forms the polymerization backbone together with acrylamide; on the other hand, the carboxyl group provides additional chemical functionality, including endowing the hydrogel with electronegativity and chemical activity. In particular, the carboxyl group can undergo a coordination reaction with metal ions in subsequent steps, endowing the hydrogel with metal coordination characteristics and further expanding its functional applications. N,N'-methylenebisacrylamide is a commonly used crosslinking agent. Its molecule contains two double bonds and can crosslink with the molecular chains of acrylamide and acrylic acid during the free radical polymerization process to form a three-dimensional network structure.

[0015] To ensure the smooth progress of the polymerization reaction, the monomer and the cross-linking agent are dispersed in deionized water, and at the same time, the pH of the solution is adjusted to neutral. This operation can ensure the uniform dispersion of the system and, at the same time, dissociate the carboxyl group of acrylic acid to generate carboxylate. The presence of carboxylate provides active sites for subsequent metal coordination reactions. In the polymerization reaction, ammonium persulfate is used as an initiator. Ammonium persulfate is a thermal decomposition type free radical initiator that decomposes to generate free radicals under heating conditions. The generated free radicals have high oxidizing properties and can attack the double bonds in acrylamide and acrylic acid molecules to form active monomer free radicals. These active free radicals undergo chain growth reactions with other monomer molecules to gradually form linear polymer chains. At the same time, the double bonds of the cross-linking agent N,N'-methylenebisacrylamide also participate in the reaction and combine with multiple polymer chains to form cross-linking points, ultimately generating a hydrogel with a three-dimensional network structure. The role of the emulsifier is particularly important in this process. Its stable interfacial action ensures the independence of the aqueous phase microdroplets, confining the polymerization reaction within the interior of the aqueous phase microdroplets. After the polymerization reaction is completed, the obtained hydrogel microspheres are the pre-products. These pre-products are further processed to improve their functionality. Specifically, the hydrogel microspheres are immersed in a metal salt solution to undergo a coordination reaction with metal ions. In this process, the carboxyl group in acrylic acid or its dissociated carboxylate is the main coordination group. The carboxylate has a strong electron donating ability and can form stable coordination bonds with metal ions, thereby introducing metal ions into the interior of the hydrogel. The introduction of metal ions may also trigger cross-linking between some carboxyl groups, further enhancing the mechanical strength of the hydrogel and enabling it to exhibit higher structural stability under external forces.

[0016] To further functionalize the metal coordination microgels, benzotriazole and cyclic carbonate are introduced in the present invention. Benzotriazole is an excellent corrosion inhibitor. Its structure contains nitrogen atoms and aromatic rings, and these characteristics enable it to undergo coordination reactions with metal ions to form additional metal-ligand networks. After introducing benzotriazole into the microgels, its binding with metal ions significantly enhances the corrosion resistance of the microgels, while improving the chemical stability, enabling them to maintain the integrity of their functions and structures in harsh environments. The cyclic carbonate undergoes ring-opening reactions with the hydroxyl or amine groups in the hydrogel through its cyclic structure, further crosslinking the hydrogel network. This chemical crosslinking improves the thermal stability and mechanical strength of the microgels, providing a guarantee for their applications in high-temperature or complex environments. After the above functionalization treatment, the finally obtained metal coordination microgels are a kind of multifunctional material, and its characteristics include 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 it to be uniformly dispersed in the subsequent composite material system, thus providing the possibility for improving the performance of functional coatings. In the subsequent preparation of polyurea coatings, the metal coordination microgels will serve as key reinforcing components, not only providing mechanical reinforcement effects, but also endowing the coating system with higher corrosion resistance and chemical stability.

[0017] The formation of the polyurea matrix is centered around the addition reaction between isocyanates and amino-terminated polyethers. This reaction constructs the basic framework of the polyurea coating and endows it with excellent mechanical properties and chemical stability. Isocyanates are highly reactive compounds, and the isocyanate groups in their molecules, as electrophilic centers, can rapidly undergo nucleophilic addition reactions with the amino groups in amino-terminated polyethers to form urea bonds. HDI trimer is an aliphatic isocyanate, and its molecular structure consists of multiple HDI units connected in a trimer form, with a regular spatial configuration and a relatively high crosslinking density. This highly crosslinked structure endows the polyurea coating with extremely high hardness, wear resistance, and weather resistance. Isophorone diisocyanate is an alicyclic isocyanate, and the cyclic groups in its molecular structure have high chemical stability, while also endowing the coating with good flexibility and impact resistance. The alicyclic structure of isophorone diisocyanate can effectively relieve local stress concentration in the material under external forces, thereby improving the ductility and low-temperature performance of the coating. In addition, the excellent chemical stability of isophorone diisocyanate enables it to resist corrosion and degradation in complex environments. HDI trimer provides high-crosslinking hard segments, while isophorone diisocyanate introduces flexible chain segments into the polyurea matrix. The hard segments form a high-density crosslinked network through strong intermolecular interactions, providing excellent mechanical strength, wear resistance, and chemical corrosion resistance; while the soft segments endow the material with good flexibility, elasticity, and impact toughness at low temperatures through their dispersed flexible chain segment regions. Amino-terminated polyethers are the main components forming the soft segments of the polyurea matrix, and their molecular structures contain amino groups as reactive sites. Such polymer chains not only provide a structural basis for the flexible chain segments but also significantly improve the low-temperature performance and impact resistance of the polyurea coating. The long-chain structure of amino-terminated polyethers has a high molecular weight and good molecular mobility, and can form flexible regions in the polyurea, thereby improving the ductility and crack resistance of the material. During the reaction process, the amino groups in amino-terminated polyethers rapidly react with isocyanates to form urea bonds and connect into high-molecular chains.

[0018] After the main reaction is completed, the temperature of the system is lowered to 40 °C, and a composite blocking agent is added. The introduction of the blocking agent is to adjust the latency and construction performance of the coating, and to solve the storage stability problem that may be caused by the high reactivity of isocyanates. Isocyanates are extremely prone to react with moisture in the environment in the unreacted state, generating amines and carbon dioxide, resulting in system instability or even premature curing. The composite blocking agent forms a temporary blocked state by reacting with residual isocyanates, preventing side reactions of isocyanates with moisture or other impurities. This blocked state is very stable at room temperature, but at high temperatures or under specific triggering conditions (such as the action of moisture or catalysts), it can release active isocyanates again, thus restoring its reactivity. Through this mechanism, the blocking agent significantly reduces the activity of the coating, extends its storage time and construction applicable period, and avoids waste or performance loss caused by premature curing. After adding the composite blocking agent, a latent amine component is further added. Latent amines are a class of amine compounds with low room temperature activity but can be rapidly activated under specific conditions. These compounds hardly react with isocyanates during the storage stage of the coating, but during the construction and curing stages of the coating, when the temperature rises or is triggered by moisture, the latent amines can rapidly react with isocyanates to further crosslink the polyurea matrix. The introduction of the latent amine component not only extends the storage period of the coating, but also avoids premature curing of the coating during construction, thus improving the operability and applicability of the coating. The prepared matrix resin is a high-performance prepolymer system, which has excellent mechanical properties, chemical stability and storage applicability. This matrix resin not only provides a balance of hardness, flexibility and impact resistance for the polyurea coating, but also provides guarantee for the long-term storage and construction of the coating.

[0019] The introduction of the reinforcing component of PDA@ nanofibers improves the coating performance in many aspects. Carbon nanofibers have extremely high tensile strength and modulus, and their introduction can significantly improve the mechanical properties of the coating, including tensile strength, impact resistance and wear resistance; PDA molecules undergo chemical reactions with isocyanates or amino groups in the matrix resin through their rich functional groups to form strong interfacial bonding, further improving the overall mechanical properties of the coating; at the same time, the phenolic hydroxyl groups in PDA molecules can coordinate with the metal surface to form a dense protective film when the coating is applied to metal substrates, thus preventing the penetration of oxygen and moisture and reducing the possibility of metal corrosion. Metal ions in the microgel further enhance the crosslinking density of the polyurea coating through coordination reactions with amino or ureido groups in the matrix resin. This chemical crosslinking not only improves the mechanical strength of the coating, but also enhances the chemical stability of the coating; metal ions in the microgel can form a dense protective layer on the coating surface to prevent 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 alternative embodiments, the mass-volume ratio of the ball-milled electrospun carbon nanofibers to the SDBS solution is 1 g:40 mL.

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

[0023] In some alternative 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 this time range are equally applicable.

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

[0025] In some alternative 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 equally applicable.

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

[0027] In some alternative 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 the emulsifier is 100 mL:1 g.

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

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

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

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

[0033] In some alternative 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 equally applicable.

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

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

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

[0037] In some alternative embodiments, the mass ratio of the pre-product, benzotriazole to 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 to latent amine component is 12:5:20:4:4.

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

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

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

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

[0043] In some alternative 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 matrix resin, propylene glycol monomethyl ether acetate, PDA@nanofibers, metal coordination microgel, leveling agent, defoaming agent and anti-settling agent is 450:150:10:15:2:1:3.

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

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

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

[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 beneficial effects of the present invention are as follows: (1) Using electrospun carbon nanofibers as reinforcing materials, through the functionalization treatment of polydopamine, the nanofibers are endowed with rich surface functional groups, which can chemically react with the isocyanate in the matrix resin to form a strong interfacial bond. In addition, the surface coating of polydopamine can also improve the dispersibility of carbon nanofibers and prevent their agglomeration in the coating system; (2) The prepared metal coordination microgel realizes a three-dimensional cross-linked network through an emulsion polymerization process, and introduces a metal coordination network through the coordination of the carboxyl group of acrylic acid with metal ions. 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 interfacial bonding points for the coating, which helps to enhance the overall uniformity of the material; (3) By using a combination of 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 SEM image of the metal coordination microgel provided in Example 1 of the present invention;

[0051] Figure 2 TEM image of the metal coordination microgel provided in Example 1 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0052] The technical solution of the present invention will be described in detail below in conjunction with specific embodiments and their accompanying drawings. The embodiments described herein are specific specific embodiments of the present invention and are used to illustrate the concept of the present invention; these descriptions are all explanatory and exemplary and should not be construed as limiting the embodiments of the present invention and the protection scope of the present invention. Except for the embodiments described herein, those skilled in the art can also adopt other obvious technical solutions based on the content disclosed in the claims and the specification of the present application. These technical solutions include technical solutions that make any obvious substitutions and modifications to the embodiments described herein.

[0053] The chemical reagents used in the embodiments and comparative examples of the present invention are all commercially available products and have not been further purified.

[0054] Example 1

[0055] This example provides a modified high-strength one-component polyurea coating, and its preparation method specifically includes the following steps:

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

[0057] S2, Mix 200 mL of cyclohexane with 2 g of Span 80 to obtain an oil phase. Disperse 25 g of acrylamide, 15 g of acrylic acid, and 1 g of N,N'-methylenebisacrylamide in 150 mL of deionized water, adjust the pH to 7, and add 0.5 g of ammonium persulfate to obtain an aqueous phase. Add 30 mL of the aqueous phase to 200 mL of the oil phase, adjust the temperature to 66°C, and stir for reaction for 3.2 h. Filter the product, wash and dry to obtain a pre-product. Immerse 8 g of the pre-product in 30 mL of a 9 wt.% zinc nitrate solution, add 1 g of benzotriazole and 2 g of cyclic carbonate, and freeze-dry to obtain a metal coordination microgel;

[0058] S3, Under a nitrogen atmosphere, mix 120 g of hexamethylene diisocyanate trimer with 50 g of isophorone diisocyanate, adjust the temperature to 66°C, add 200 g of LHD-1200 and react for 1.3 h. After the reaction, adjust the temperature to 40°C, add 40 g of 2-imidazolidinone and stir, then add 40 g of a latent amine component and stir to obtain a matrix resin;

[0059] S4. Heat 450 g of the matrix resin to 40 °C, then add 150 g of propylene glycol monomethyl ether acetate, 10 g of PDA@ nanofibers, 15 g of metal coordination microgel, 2 g of polyether-modified polysiloxane, 1 g of polydimethylsiloxane, and 3 g of kaolin. After mixing evenly, a modified high-strength one-component polyurea coating is obtained.

[0060] Figure 1 SEM image of the metal coordination microgel prepared in this example; Figure 2 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 example provides a modified high-strength one-component polyurea coating, and its preparation method specifically includes the following steps:

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

[0064] S2. Mix 200 mL of cyclohexane and 2 g of Span 80 evenly to obtain the oil phase. Disperse 25 g of acrylamide, 15 g of acrylic acid, and 1 g of N,N'-methylenebisacrylamide in 150 mL of deionized water, adjust the pH to 7, and add 0.5 g of ammonium persulfate to obtain the water phase. Add 30 mL of the water phase to 200 mL of the oil phase, adjust the temperature to 69 °C, and stir for 3.8 h. Filter the product, wash, and dry to obtain the pre-product. Immerse 8 g of the pre-product in 30 mL of a 9 wt.% zinc nitrate solution, add 1 g of benzotriazole and 2 g of cyclic carbonate, and freeze-dry to obtain the metal coordination microgel;

[0065] S3. Under a nitrogen atmosphere, mix 120 g of hexamethylene diisocyanate trimer and 50 g of isophorone diisocyanate, adjust the temperature to 69 °C, add 200 g of LHD-1200 and react for 1.5 h. After the reaction, adjust the temperature to 40 °C, add 40 g of 2-imidazolidinone and stir, then add 40 g of the latent amine component and stir to obtain the matrix resin;

[0066] S4. Heat 450 g of the matrix resin to 40 °C, then add 150 g of propylene glycol monomethyl ether acetate, 10 g of PDA@nanofibers, 15 g of metal coordination microgels, 2 g of polyether-modified polysiloxane, 1 g of polydimethylsiloxane and 3 g of bentonite. After mixing evenly, a modified high-strength one-component polyurea coating is obtained.

[0067] Example 3

[0068] This example provides a modified high-strength one-component polyurea coating, and its preparation method specifically includes the following steps:

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

[0070] S2. Mix 200 mL of cyclohexane and 2 g of Span 80 evenly to obtain an oil phase. Disperse 25 g of acrylamide, 15 g of acrylic acid and 1 g of N,N'-methylenebisacrylamide in 150 mL of deionized water, adjust the pH to 7, and add 0.5 g of ammonium persulfate to obtain an aqueous phase. Add 30 mL of the aqueous phase to 200 mL of the oil phase, adjust the temperature to 61 °C and stir for 3.4 h. Filter the product, wash and dry to obtain a pre-product. Immerse 8 g of the pre-product in 30 mL of 9 wt.% zinc nitrate solution and add 1 g of benzotriazole and 2 g of cyclic carbonate, and freeze-dry to obtain metal coordination microgels.

[0071] S3. Under a nitrogen atmosphere, mix 120 g of hexamethylene diisocyanate trimer and 50 g of isophorone diisocyanate, adjust the temperature to 61 °C, add 200 g of LHD-1200 and react for 1.9 h. After the reaction, adjust the temperature to 40 °C, add 40 g of 2-imidazolidinone and stir, then add 40 g of the latent amine component and stir to obtain the matrix resin.

[0072] S4. Heat 450 g of the matrix resin to 40 °C, then add 150 g of propylene glycol monomethyl ether acetate, 10 g of PDA@nanofibers, 15 g of metal coordination microgels, 2 g of polyether-modified polysiloxane, 1 g of polydimethylsiloxane and 3 g of talc powder. After mixing evenly, a modified high-strength one-component polyurea coating is obtained.

[0073] Example 4

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

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

[0076] S2, Mix 200 mL of cyclohexane and 2 g of Span 80 evenly to obtain an oil phase. Disperse 25 g of acrylamide, 15 g of acrylic acid, and 1 g of N,N'-methylenebisacrylamide in 150 mL of deionized water, adjust the pH to 7, and add 0.5 g of ammonium persulfate to obtain an aqueous phase. Add 30 mL of the aqueous phase to 200 mL of the oil phase, adjust the temperature to 63°C, and stir for 3.6 h. Filter the product, wash, and dry to obtain a pre-product. Immerse 8 g of the pre-product in 30 mL of a 9 wt.% zinc nitrate solution, add 1 g of benzotriazole and 2 g of cyclic carbonate, and freeze-dry to obtain a metal coordination microgel;

[0077] S3, Under a nitrogen atmosphere, mix 120 g of hexamethylene diisocyanate trimer and 50 g of isophorone diisocyanate, adjust the temperature to 63°C, add 200 g of LHD-1200 and react for 1.7 h. After the reaction, adjust the temperature to 40°C, add 40 g of 2-imidazolidinone and stir, then add 40 g of a latent amine component and stir to obtain a matrix resin;

[0078] S4, Heat 450 g of the matrix resin to 40°C, then add 150 g of propylene glycol monomethyl ether acetate, 10 g of PDA@nanofibers, 15 g of the metal coordination microgel, 2 g of polyether-modified polysiloxane, 1 g of polydimethylsiloxane, and 3 g of kaolin, and mix 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 is different from Example 1 in that the mass of hexamethylene diisocyanate trimer in S3 is 220 g, an increase of 100 g compared to Example 1, and 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 is different from Example 1 in that the mass of hexamethylene diisocyanate trimer in S3 is 20 g, which is 100 g less than that in Example 1, and 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 is different from Example 1 in that the mass of PDA@ nanofibers in S4 is 20 g, which is 10 g more than that in Example 1, and 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 is different from Example 1 in that the mass of PDA@ nanofibers in S4 is 1 g, which is 10 g less than that in Example 1, and other process parameters and operating conditions are exactly the same as those in Example 1.

[0087] The adhesion test standard is GB / T 9286-2021; the tensile strength test standard is GB / T 528-2009; the hardness test standard is GB / T 6739-2022; the impact resistance test standard is 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 for Examples 1-4 and Comparative Examples 1-4

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

[0090] It can be seen from the data in Table 1 that compared with Example 1, the adhesion, tensile strength and hardness of Comparative Example 1 decrease, and the impact resistance increases; the tensile strength and hardness of Comparative Example 2 increase, while the adhesion and impact resistance decrease. This is because the trifunctional group structure of HDI trimer enables it to form a highly cross-linked network structure during the reaction. In Comparative Example 1, the amount of HDI trimer is insufficient, reducing the hard segment ratio, thus decreasing the overall mechanical properties of the coating film. The lower hard segment ratio and cross-linking density increase the flexibility of the coating film, enabling it to absorb more impact energy and resulting in an increase in impact resistance. In Comparative Example 2, the amount of HDI trimer is excessive, and the high cross-linking density makes the coating film brittle and lack flexibility, making it more prone to cracking or peeling when subjected to mechanical stress at the interface. The increase in the high cross-linking density and the ratio of hard segments makes the coating film exhibit a higher surface hardness. The excessive hard segments make the coating film brittle and difficult to absorb and disperse energy under impact loads, resulting in the coating film being more likely to crack.

[0091] Compared with Example 1, the adhesion, tensile strength, hardness, and impact resistance of Comparative Example 3 decreased; the adhesion, tensile strength, hardness, and impact resistance of Comparative Example 4 decreased. This is because in Comparative Example 3, there was too little PDA@nanofiber, the number of phenolic hydroxyl groups and amino groups of PDA decreased, the number of interfacial bonding points between the matrix resin and the substrate decreased, and there was a lack of sufficient high-strength reinforcing components in the paint film, resulting in a decline in the mechanical properties of the coating film. In Comparative Example 4, when the content of PDA@nanofiber was too high, the nanofibers were difficult to disperse evenly and easily agglomerated. The agglomeration phenomenon led to uneven interfacial bonding, weakened the interfacial interaction between the nanofibers and the matrix resin, formed weak bonding points in some areas, resulting in a decrease in adhesion, and formed brittle points in the agglomerated areas, making the coating film more prone to cracks or breakage under impact loads.

[0092] The above are only specific embodiments 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, prepare a Tris-HCl buffer solution and adjust the pH to 8.5, disperse dopamine hydrochloride in the Tris-HCl buffer solution, disperse the electrospun carbon nanofibers after ball milling in a SDBS solution, filter and add the solution to the Tris-HCl buffer solution, add ferric chloride, and react to obtain PDA@ nanofibers; S2, 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, reacting 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 with isophorone diisocyanate, adding amino-terminated polyether for reaction, adjusting the temperature to 40°C, adding a composite sealing agent and a latent amine component, and obtaining a base resin; 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 to obtain a modified high-strength one-component polyurea coating.

2. The method for preparing a modified high-strength one-component polyurea coating according to claim 1, characterized in that: In S1, The mass ratio of the dopamine hydrochloride to the electrospun carbon nanofibers after ball milling is 2:

5.

3. The method for preparing a modified high-strength one-component polyurea coating according to claim 1, characterized in that: In S1, The mass ratio of the ferric chloride to dopamine hydrochloride is 3:

2.

4. The method for preparing a modified high-strength one-component polyurea coating according to claim 1, characterized in that: In S2, 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.

5. The method for preparing a modified high-strength one-component polyurea coating according to claim 1, characterized in that: In S2, The mass volume ratio of the pre-product to the metal salt solution is 4 g:15 mL; The mass ratio of the pre-product, benzotriazole and cyclic carbonate is 8:1:

2.

6. The method for preparing a modified high-strength one-component polyurea coating according to claim 1, characterized in that: 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.

7. The method for preparing a modified high-strength one-component polyurea coating according to claim 1, characterized in that: In S3, The HDI trimer is hexamethylene diisocyanate trimer.

8. The method for preparing a modified high-strength one-component polyurea coating according to claim 1, characterized in that: 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.

9. 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.

10. A modified high-strength one-component polyurea coating obtained according to the preparation method according to any one of claims 1 to 9.

Images