High-adhesion low-solvent coating and preparation method thereof

Abstract

The invention provides a high-adhesion low-solvent coating and a preparation method thereof, and belongs to the field of coatings. The performance of the water-based paint is synergistically improved through various modification strategies; a phosphate group of the phosphorylated water-based polyurethane dispersion and a base material form a coordinate bond, so that the adhesive force is enhanced; thiol groups react with unsaturated groups to construct a stable cross-linked network. Oxidized and aminated graphene quantum dots improve the dispersity and form hydrogen bonds and crosslinking points, so that the mechanical property is improved; the quaternized cellulose nanocrystals improve the compatibility, and double bonds participate in a cross-linked network to enhance the structural stability; polydopamine modified by sulfydryl and boric acid groups strengthens the network strength and flexibility and improves the interface bonding force. The mechanisms provide a solid foundation for developing high-adhesion, low-solvent and high-performance coatings.

Description

Technical Field

[0001] The invention belongs to the technical field of coatings and relates to a high-adhesion low-solvent coating and a preparation method thereof. Background Art

[0002] As an important functional material, coatings are used in construction, automobiles, electronics, home appliances, aerospace and other industrial fields. Coatings not only protect substrates from environmental factors (such as moisture, corrosion, ultraviolet rays, chemicals, etc.), but also improve product appearance and increase surface decorative effects, thereby significantly improving the overall value and service life of the product. In industrial production, the widespread use of coatings can also reduce equipment wear and improve energy efficiency, so they occupy an indispensable position in modern manufacturing.

[0003] Solvent-based coatings are widely used due to their superior adhesion, durability and adaptability. Solvent-based coatings use organic solvents as dispersion media to evenly mix film-forming substances, pigments, fillers and additives to form a stable coating system. This type of coating is easy to level during the coating process, dries quickly, and can form high-quality coatings on the surfaces of various substrates with excellent weather resistance and decorative properties. Therefore, solvent-based coatings have been widely used in the fields of building exterior walls, automobile surfaces, and home appliance coatings. However, the outstanding performance of solvent-based coatings is also accompanied by significant shortcomings.

[0004] First, solvent-based coatings require a large amount of organic solvents during production and use. The volatilization of these solvents will release a large amount of volatile organic compounds (VOCs), causing serious pollution to the environment. VOCs are the main factor causing photochemical smog, ozone generation and air quality degradation, posing a threat to both the ecosystem and human health. Secondly, solvent-based coatings can pose a potential hazard to the health of construction workers during construction. Long-term exposure to high concentrations of solvent vapor may cause respiratory, nervous and other health problems. In addition, organic solvents are flammable and explosive, and their safety hazards in storage, transportation and use cannot be ignored, which also significantly increases the operating costs and risk management difficulties of the coatings industry. Summary of the invention

[0005] In view of the above problems, the object of the present invention is to provide a high-adhesion low-solvent coating and a preparation method thereof. In the present invention, the phosphate groups introduced by phosphorylation in the aqueous polyurethane dispersion form stable coordination bonds with the surface of the metal substrate, which significantly enhances the interfacial bonding force; the introduction of thiol groups further enhances the stability and durability of the cross-linked network through the Michael addition reaction with the unsaturated groups. The graphene quantum dots are oxidized and amino-treated, which not only improves their dispersibility in the aqueous system, but also forms a hydrogen bond network and chemical cross-linking points through the amino groups, greatly improving the mechanical properties and adhesion of the coating. Cellulose nanocrystals are modified by quaternization to improve their compatibility with the coating system, and the double bonds introduced can serve as reactive sites and participate in the construction of the cross-linked network, thereby improving the structural stability and mechanical properties of the coating. Polydopamine is double-modified by thiol and boric acid groups, and its thiol participates in chemical cross-linking to enhance the network strength, while the boric acid groups give the coating better flexibility and self-healing ability through dynamic cross-linking characteristics, while further enhancing the bonding force of the substrate interface.

[0006] To achieve this object, the present invention adopts the following technical solutions: In a first aspect, the present invention provides a method for preparing a high-adhesion low-solvent coating, the method for preparing the high-adhesion low-solvent coating comprising: S1: mixing an aqueous polyurethane dispersion with phosphoric acid to obtain a reaction solution A, mechanically stirring at a constant temperature, adjusting the pH with aqueous ammonia after the reaction, and dialyzing to obtain a phosphorylated aqueous polyurethane dispersion; mixing the phosphorylated aqueous polyurethane dispersion with 2-mercaptoethanol and triethylamine to obtain a reaction solution B, stirring the reaction, and dialyzing to obtain a modified aqueous polyurethane dispersion; S2: mixing graphene quantum dots with hydrogen peroxide solution to obtain reaction solution C, stirring at constant temperature, centrifuging, washing, and drying to obtain graphene oxide quantum dots; dispersing graphene oxide quantum dots in water, adding 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide to obtain reaction solution D, stirring at room temperature, adding ethylenediamine and continuing to stir the reaction, dialyzing, and freeze-drying to obtain amino graphene oxide quantum dots; S3: preparing a cellulose nanocrystal dispersion, adding 3-chloro-2-hydroxypropyltrimethylammonium chloride, stirring, and then dropping a sodium hydroxide solution to obtain a reaction solution E, and after the reaction, dialyzing and freeze-drying to obtain quaternized cellulose nanocrystals; dispersing the quaternized cellulose nanocrystals in anhydrous ethanol to obtain a quaternized cellulose nanocrystal dispersion, adding glycidyl methacrylate and tetrabutylammonium bromide to obtain a reaction solution F, reacting at a constant temperature, precipitating, centrifuging, washing, and vacuum drying to obtain modified cellulose nanocrystals; S4: Disperse polydopamine in phosphate buffer, add 2-mercaptoethylamine hydrochloride, stir at room temperature, dialyze to obtain thiolated polydopamine; disperse thiolated polydopamine in water, add 4-carboxyphenylboronic acid, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide, stir at room temperature for reaction, dialyze, and freeze-dry to obtain double-modified polydopamine; S5: Using the modified waterborne polyurethane dispersion as a matrix, adding amino-modified graphene oxide quantum dots, modified cellulose nanocrystals, double-modified polydopamine and deionized water in sequence, stirring, ultrasonically dispersing and vacuum degassing to obtain the high-adhesion low-solvent coating.

[0007] As a preferred technical solution of the present invention, in step S1, the amount of phosphoric acid added is 10-15% of the mass of the aqueous polyurethane dispersion, for example, 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14% or 15%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0008] In some optional embodiments, the constant temperature stirring temperature of the reaction liquid A is 50-60°C, for example, it can be 50°C, 51°C, 52°C, 53°C, 54°C, 55°C, 56°C, 57°C, 58°C, 59°C or 60°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0009] In some optional embodiments, the constant temperature stirring time of the reaction liquid A is 3-4h, for example, it can be 3h, 3.1h, 3.2h, 3.3h, 3.4h, 3.5h, 3.6h, 3.7h, 3.8h, 3.9h or 4h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0010] In some optional embodiments, the mass fraction of the ammonia water is 20-25wt.%, for example, it can be 20wt.%, 20.5wt.%, 21wt.%, 21.5wt.%, 22wt.%, 22.5wt.%, 23wt.%, 23.5wt.%, 24wt.% or 25wt.%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0011] In some optional embodiments, the pH is adjusted to 7-8 with aqueous ammonia, for example, 7, 7.1, 7.2, 7.3, 7.4, 7.5, 7.6, 7.7, 7.8, or 8, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0012] In some optional embodiments, the feeding amount of the 2-mercaptoethanol is 8-12% of the mass of the phosphorylated aqueous polyurethane dispersion, for example, it can be 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5% or 12%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0013] In some optional embodiments, the amount of triethylamine fed is 4-8% of the mass of 2-mercaptoethanol, for example, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5% or 8%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0014] In some optional embodiments, the stirring reaction temperature of the reaction liquid B is 40-50°C, for example, it can be 40°C, 41°C, 42°C, 43°C, 44°C, 45°C, 46°C, 47°C, 48°C, 49°C or 50°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0015] In some optional embodiments, the stirring reaction time of the reaction liquid B is 2-3h, for example, it can be 2h, 2.1h, 2.2h, 2.3h, 2.4h, 2.5h, 2.6h, 2.7h, 2.8h, 2.9h or 3h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0016] As a preferred technical solution of the present invention, in step S2, the concentration of the hydrogen peroxide solution is 10-15%, for example, it can be 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14% or 15%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0017] In some optional embodiments, the mass fraction of the graphene quantum dots in the hydrogen peroxide solution is 5-10wt.%, for example, it can be 5wt.%, 5.5wt.%, 6wt.%, 6.5wt.%, 7wt.%, 7.5wt.%, 8wt.%, 8.5wt.%, 9wt.% or 10wt.%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0018] In some optional embodiments, the constant temperature stirring temperature of the reaction liquid C 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 values, and other unlisted values ​​within the numerical range are also applicable.

[0019] In some optional embodiments, the constant temperature stirring time of the reaction liquid C is 2-3h, for example, it can be 2h, 2.1h, 2.2h, 2.3h, 2.4h, 2.5h, 2.6h, 2.7h, 2.8h, 2.9h or 3h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0020] In some optional embodiments, the mass fraction of the graphene oxide quantum dots dispersed in water is 2-5wt.%, for example, it can be 2.0wt.%, 2.3wt.%, 2.6wt.%, 2.9wt.%, 3.2wt.%, 3.5wt.%, 3.8wt.%, 4.1wt.%, 4.4wt.%, 4.7wt.% or 5.0wt.%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0021] In some optional embodiments, the feeding amount of the 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride is 50-60% of the mass of the graphene oxide quantum dots, for example, it can be 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59% or 60%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0022] In some optional embodiments, the mass ratio of N-hydroxysuccinimide to 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride is 1:1-2, for example, it can be 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9 or 1:2, but it is not limited to the listed ratios, and other ratios not listed within the ratio range are also applicable.

[0023] In some optional embodiments, the reaction solution D is stirred at room temperature for 30-40 min, for example, 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 values, and other unlisted values ​​within the numerical range are also applicable.

[0024] In some optional embodiments, the mass ratio of ethylenediamine to graphene oxide quantum dots is 5-10:1, for example, it can be 5:1, 5.5:1, 6:1, 6.5:1, 7:1, 7.5:1, 8:1, 8.5:1, 9:1, 9.5:1 or 10:1, but is not limited to the listed ratios, and other unlisted ratios within the ratio range are also applicable.

[0025] In some optional embodiments, the time for continuing to stir the reaction after adding ethylenediamine is 10-12 hours, for example, it can be 10 hours, 10.2 hours, 10.4 hours, 10.6 hours, 10.8 hours, 11 hours, 11.2 hours, 11.4 hours, 11.6 hours, 11.8 hours or 12 hours, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0026] As a preferred technical solution of the present invention, in step S3, the mass fraction of the cellulose nanocrystal dispersion is 10-20wt.%, for example, it can be 10wt.%, 11wt.%, 12wt.%, 13wt.%, 14wt.%, 15wt.%, 16wt.%, 17wt.%, 18wt.%, 19wt.% or 20wt.%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0027] In some optional embodiments, the mass ratio of 3-chloro-2-hydroxypropyltrimethylammonium chloride to cellulose nanocrystals is 1:1-2, for example, it can be 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9 or 1:2, but is not limited to the listed ratios, and other ratios not listed within the ratio range are also applicable.

[0028] In some optional embodiments, the mass fraction of the sodium hydroxide solution is 20-30wt.%, for example, it can be 20wt.%, 21wt.%, 22wt.%, 23wt.%, 24wt.%, 25wt.%, 26wt.%, 27wt.%, 28wt.%, 29wt.% or 30wt.%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0029] In some optional embodiments, the volume mass ratio of sodium hydroxide to cellulose nanocrystals is 2-3:1, for example, it can be 2:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, 2.5:1, 2.6:1, 2.7:1, 2.8:1, 2.9:1 or 3:1, but is not limited to the listed ratios, and other unlisted ratios within the ratio range are also applicable.

[0030] In some optional embodiments, the reaction temperature of the reaction liquid E is 60-65°C, for example, it can be 60°C, 60.5°C, 61°C, 61.5°C, 62°C, 62.5°C, 63°C, 63.5°C, 64°C, 64.5°C or 65°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0031] In some optional embodiments, the reaction time of the reaction liquid E is 4-5h, for example, it can be 4h, 4.1h, 4.2h, 4.3h, 4.4h, 4.5h, 4.6h, 4.7h, 4.8h, 4.9h or 5h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0032] In some optional embodiments, the mass fraction of the quaternized cellulose nanocrystal dispersion is 10-20wt.%, for example, it can be 10wt.%, 11wt.%, 12wt.%, 13wt.%, 14wt.%, 15wt.%, 16wt.%, 17wt.%, 18wt.%, 19wt.% or 20wt.%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0033] In some optional embodiments, the mass ratio of the glycidyl methacrylate to the quaternized cellulose nanocrystals is 3-4:10, for example, 3:10, 3.1:10, 3.2:10, 3.3:10, 3.4:10, 3.5:10, 3.6:10, 3.7:10, 3.8:10, 3.9:10 or 4:10, but is not limited to the listed ratios, and other ratios not listed within the ratio range are also applicable.

[0034] In some optional embodiments, the mass ratio of tetrabutylammonium bromide to quaternized cellulose nanocrystals is 1-2:10, for example, 1:10, 1.1:10, 1.2:10, 1.3:10, 1.4:10, 1.5:10, 1.6:10, 1.7:10, 1.8:10, 1.9:10 or 2:10, but is not limited to the listed ratios, and other ratios not listed within the ratio range are also applicable.

[0035] In some optional embodiments, the temperature of the constant temperature reaction of the reaction liquid F is 40-50°C, for example, it can be 40°C, 41°C, 42°C, 43°C, 44°C, 45°C, 46°C, 47°C, 48°C, 49°C or 50°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0036] In some optional embodiments, the isothermal reaction time of the reaction liquid F is 5-6h, for example, it can be 5h, 5.1h, 5.2h, 5.3h, 5.4h, 5.5h, 5.6h, 5.7h, 5.8h, 5.9h or 6h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0037] As a preferred technical solution of the present invention, in step S4, the pH of the phosphate buffer is 8-9, for example, it can be 8.0, 8.1, 8.2, 8.3, 8.4, 8.5, 8.6, 8.7, 8.8, 8.9 or 9.0, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0038] In some optional embodiments, the mass fraction of polydopamine in phosphate buffer is 2-3wt.%, for example, it can be 2.0wt.%, 2.1wt.%, 2.2wt.%, 2.3wt.%, 2.4wt.%, 2.5wt.%, 2.6wt.%, 2.7wt.%, 2.8wt.%, 2.9wt.% or 3.0wt.%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0039] In some optional embodiments, the mass ratio of 2-mercaptoethylamine hydrochloride to polydopamine is 3-4:10, for example, it can be 3:10, 3.1:10, 3.2:10, 3.3:10, 3.4:10, 3.5:10, 3.6:10, 3.7:10, 3.8:10, 3.9:10 or 4:10, but is not limited to the listed ratios, and other ratios not listed within the ratio range are also applicable.

[0040] In some optional embodiments, the mass fraction of the thiolated polydopamine in water is 2-3wt.%, for example, it can be 2.0wt.%, 2.1wt.%, 2.2wt.%, 2.3wt.%, 2.4wt.%, 2.5wt.%, 2.6wt.%, 2.7wt.%, 2.8wt.%, 2.9wt.% or 3.0wt.%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0041] In some optional embodiments, the feeding amount of the 4-carboxyphenylboronic acid is 40-50% of the mass of the thiolated polydopamine, for example, it can be 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49% or 50%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0042] In some optional embodiments, the mass ratio of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride to 4-carboxyphenylboric acid is 1-1.5:1, for example, it can be 1:1, 1.05:1, 1.1:1, 1.15:1, 1.2:1, 1.25:1, 1.3:1, 1.35:1, 1.4:1, 1.45:1 or 1.5:1, but is not limited to the listed ratios, and other ratios not listed within the ratio range are also applicable.

[0043] In some optional embodiments, the mass ratio of N-hydroxysuccinimide to 4-carboxyphenylboric acid is 0.5-0.6:1, for example, it can be 0.5:1, 0.51:1, 0.52:1, 0.53:1, 0.54:1, 0.55:1, 0.56:1, 0.57:1, 0.58:1, 0.59:1 or 0.6:1, but is not limited to the listed ratios, and other unlisted ratios within the ratio range are also applicable.

[0044] In a second aspect, the present invention provides a high-adhesion low-solvent coating, wherein the mass ratio of the components of the high-adhesion low-solvent coating is: modified aqueous polyurethane dispersion: amino-containing graphene oxide quantum dots: modified cellulose nanocrystals: double-modified polydopamine: deionized water is (75-85): (0.5-1): (1-5): (0.5-2): (7-23).

[0045] In the present invention, waterborne polyurethane dispersion is selected as the matrix material. Waterborne polyurethane dispersion is an emulsion polyurethane, and its molecular structure is usually composed of a flexible segment and a rigid segment. The flexible segment has a long molecular chain and a relatively soft structure, which gives the coating good flexibility and ductility, thereby improving the impact resistance and adaptability of the coating. The rigid segment has a rigid molecular structure and high mechanical strength, so that the coating exhibits excellent scratch resistance and chemical corrosion resistance.

[0046] In addition, the molecules of waterborne polyurethane dispersions contain a large number of polar groups, such as hydroxyl and amino groups. These polar groups can be closely combined with the surface of the substrate through hydrogen bonds or physical adsorption, thereby significantly enhancing the adhesion of the coating and preventing the coating from falling off or cracking during long-term use. At the same time, compared with traditional solvent-based polyurethanes, waterborne polyurethanes have obvious environmental advantages. Their low volatile organic compound content meets the development requirements of modern green and environmentally friendly coatings, and they are non-toxic and low in odor, making them suitable for fields with high requirements for environmental performance.

[0047] In order to further improve the performance of waterborne polyurethane coating, phosphoric acid is used to modify the polyurethane dispersion in the present invention. Phosphoric acid is a compound with high electronegativity and chemical activity. The phosphorus atom in its molecule has an empty orbital and can be combined with the hydroxyl or amino group on the molecular chain of the polyurethane dispersion through hydrogen bonding or electrostatic action. During the modification process, part of the phosphoric acid may also form a stable phosphate ester structure with the polyurethane through a chemical reaction, which further enhances the binding force between the phosphoric acid and the polyurethane molecular chain.

[0048] The introduction of phosphoric acid groups adds highly polar functional groups to the polyurethane dispersion molecules. This polar group has strong hydrophilicity and chemical reactivity, and can form coordination bonds or hydrogen bonds with the silanol groups on the surface of metal oxides or glass substrates. Through these effects, the modified polyurethane dispersion significantly improves the adhesion performance of the coating, especially on high-hardness substrates such as glass and metal. At the same time, the presence of phosphoric acid groups improves the hydrophilicity of the waterborne polyurethane dispersion, making it more evenly dispersed in the waterborne system. This uniform dispersion not only reduces surface defects in the coating film-forming process, but also improves the overall appearance and performance of the coating, making it more practical.

[0049] In order to further enhance the performance of the aqueous polyurethane dispersion, the present invention also uses 2-mercaptoethanol to modify it. 2-mercaptoethanol is a sulfur-containing compound, and the thiol group in its molecule has high nucleophilicity and can form a metal-sulfur bond with the metal atoms on the surface of the metal substrate through coordination. This metal-sulfur bond significantly improves the adhesion of the coating to the metal substrate in practical applications, making the coating more firm and durable during use.

[0050] In addition, the thiol groups can generate disulfide bonds through intermolecular interactions in an oxidative environment, thereby further enhancing the crosslinking density inside the coating. The formation of this internal crosslinking structure not only improves the mechanical properties of the coating, such as tensile strength and elastic modulus, but also makes it exhibit higher impact resistance and wear resistance during use. At the same time, the introduction of thiol groups also effectively enhances the chemical corrosion resistance of the coating. For example, in a harsh chemical environment, the modified coating can resist the erosion of acids, alkalis and organic solvents, thereby extending the service life of the coating.

[0051] Graphene quantum dots are introduced as nano cross-linking points in the present invention. Graphene quantum dots show excellent performance potential due to their unique two-dimensional structure, large specific surface area and edge defect area. Their ultra-high conductivity, thermal stability and mechanical properties make them have broad application prospects in the fields of multifunctional composite materials, electronic devices, coatings, etc. However, unmodified graphene quantum dots have a limited number of polar functional groups and show high chemical inertness due to their surface mainly composed of carbon-carbon bonds. This characteristic leads to poor dispersibility in aqueous systems and easy agglomeration, which further reduces the uniformity of the material and limits its direct application in the field of coatings.

[0052] In order to overcome the above problems and give full play to the potential of graphene quantum dots, it is necessary to perform surface chemical modification on them. First, they are converted into graphene oxide quantum dots by oxidation treatment. In this process, hydrogen peroxide is selected as an oxidant to selectively oxidize graphene quantum dots under suitable temperature and reaction time conditions. The oxidation reaction is mainly concentrated in the edge defect area and carbon-carbon double bond site of graphene quantum dots. By introducing polar functional groups such as hydroxyl and carboxyl, its hydrophilicity and surface reactivity are significantly improved. These polar functional groups give graphene oxide quantum dots excellent dispersibility in the aqueous phase and effectively avoid agglomeration. In addition, these functionalized functional groups provide reaction sites for subsequent chemical modification, and at the same time enable graphene oxide quantum dots to combine with hydroxyl, amino and other groups in polar matrix materials (such as polyurethane dispersions) through hydrogen bonds or electrostatic interactions, thereby significantly improving the uniformity and compatibility of the coating system.

[0053] On the basis of oxidation treatment, in order to further improve the performance of graphene quantum dots, they are subjected to amino modification. Specifically, 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide are used to activate the carboxyl groups on the surface of graphene oxide quantum dots to generate acyl active intermediates. Subsequently, amidation reaction occurs with ethylenediamine under neutral or weakly acidic conditions to successfully introduce free amino groups. Amide modification has multiple advantages: the introduced free amino groups can form stable covalent bonds with active groups such as carbonyl groups in polyurethane dispersions through chemical cross-linking reactions, thereby further enhancing the strength of the internal network structure of the coating and improving the mechanical properties; the amino groups can form stable bonds with the thiol or boric acid groups in polydopamine through hydrogen bonds or covalent bonds, for example, the thiol oxidation cross-linking of amino groups with thiol groups can generate disulfide bonds, significantly enhancing the adhesion of the coating while improving impact resistance and durability; the graphene quantum dots after amino modification provide additional chemical stability and environmental adaptability, which can effectively improve the chemical corrosion resistance of the coating in complex or harsh environments.

[0054] The present invention introduces cellulose nanocrystals. Cellulose nanocrystals are highly crystalline nano-scale materials extracted from plant fibers, with a rod-like structure with a diameter ranging from a few nanometers to tens of nanometers and a length of up to hundreds of nanometers. This material has attracted much attention due to its natural origin, biocompatibility, high strength and high modulus, especially in the field of green materials and nano-reinforced composite materials, and has broad application prospects.

[0055] However, the surface of unmodified cellulose nanocrystals is rich in polar hydroxyl groups, which gives them good dispersibility in aqueous systems. However, in non-polar or weakly polar organic systems, they have poor compatibility and are prone to agglomeration, which significantly limits their wide application in composite materials, coatings and other fields.

[0056] In order to overcome the dispersibility and compatibility problems of cellulose nanocrystals, the present invention first adopts 3-chloro-2-hydroxypropyltrimethylammonium chloride to quaternize and modify cellulose nanocrystals. By reacting in an alkaline environment, the hydroxyl groups on the cellulose surface are deprotonated under the action of sodium hydroxide to form a highly active nucleophilic reagent, thereby reacting with 3-chloro-2-hydroxypropyltrimethylammonium chloride to introduce quaternary ammonium salt groups on the cellulose surface. This modification process significantly improves the hydrophilicity of cellulose nanocrystals, greatly improves its dispersion stability in aqueous systems, and overcomes agglomeration at the same time. In addition, the positive charge introduced by the quaternary ammonium salt group enhances the electrostatic interaction between the coating and the substrate surface, significantly improving the adhesion performance of the coating. This modification also gives the material a certain antibacterial ability, enhances the environmental stability of the coating, and enables it to show excellent performance in a demanding environment.

[0057] In further modification, the present invention uses glycidyl methacrylate to modify cellulose nanocrystals, and generates ester bonds containing double bonds on the cellulose surface by means of a ring-opening reaction between the hydroxyl groups on the cellulose surface and the epoxy groups of glycidyl methacrylate. By introducing double bonds, cellulose nanocrystals have the ability to participate in free radical polymerization or cross-linking reactions, enabling them to be more efficiently integrated into the chemical cross-linking network of the coating matrix. The presence of double bonds significantly improves the mechanical strength of the coating film, while giving it higher wear resistance and durability, so that the cellulose nanocrystal-modified coating exhibits superior use effects in multifunctional, high-performance coating systems.

[0058] The present invention introduces polydopamine as a system crosslinking agent. Polydopamine is a biomimetic polymer with abundant chemical reaction sites. The molecular structure of polydopamine is rich in catechol groups and amine groups, which enable it to strongly adhere to the surfaces of various materials, such as metals, glass and polymer materials, and exhibit excellent interfacial adhesion. In addition, the multifunctional modification potential of polydopamine makes it an ideal modified substrate that can meet a variety of application requirements. However, unmodified polydopamine also exposes some shortcomings during use, such as low tolerance in complex environments, limited chemical reactivity, and lack of directional design for specific functions. These problems significantly limit its practical application range.

[0059] In order to overcome the above problems, the present invention uses 2-mercaptoethylamine hydrochloride to chemically modify polydopamine, aiming to simultaneously introduce active thiol groups and more amino groups to enhance its chemical reactivity and surface functionality. Specifically, the thiol groups in 2-mercaptoethylamine hydrochloride react with the quinone groups in the polydopamine molecule through a thiol-quinone addition reaction to generate modified polydopamine containing thiol groups. The core advantage of this modification strategy is that the thiol groups can form stable metal-sulfur bonds with the surface of the metal substrate, thereby significantly improving the adhesion and durability of the coating on the metal surface. In addition, the amino groups in 2-mercaptoethylamine hydrochloride can further undergo amino addition reactions with the quinone groups in the polydopamine molecules, thereby introducing more amino groups on the surface of polydopamine. These newly introduced amino groups provide abundant chemical active sites for subsequent cross-linking reactions, so that the modified polydopamine can form a stronger chemical network structure with other carboxyl or epoxy-containing components (such as graphene oxide quantum dots), thereby greatly enhancing the mechanical properties and stability of the coating.

[0060] In order to further enrich the functional properties of polydopamine, the present invention performs secondary modification on it by 4-carboxyphenylboronic acid, and introduces boronic acid groups to enhance the compactness and adhesion of the coating. In this process, 4-carboxyphenylboronic acid undergoes amidation reaction with the amino group in the polydopamine molecule through its carboxyl group to generate modified polydopamine containing boronic acid groups. The introduction of boronic acid groups gives the material a unique reversible boron ester bond characteristic, enabling it to combine with the hydroxyl or carboxyl group in the coating matrix to form a dynamic chemical cross-linking network. In addition, the boronic acid group can form a stable chemical bond with the metal oxide surface, thereby further strengthening the adhesion ability of the coating on the metal substrate. This dual modification strategy has comprehensively improved the performance of polydopamine and can better meet the application requirements of high-performance coatings.

[0061] This system uses water as the main medium and a small amount of low-toxic, easily removable solvents to complete the necessary functional modifications, minimizing the use of organic solvents that are potentially harmful to the environment and human body. In the post-processing process, the solvent residue is further reduced through effective separation and drying processes, so that the final coating not only maintains excellent adhesion and other functionalities, but also meets the environmental protection requirements of "low solvent" and even low VOC.

[0062] There is also a synergistic enhancement effect in the present invention: in terms of adhesion: the phosphoric acid group in the modified waterborne polyurethane dispersion can form a stable coordination bond with the surface of the metal substrate through chemical action. This coordination bond not only provides excellent chemical adhesion, but also maintains a high bonding strength under a variety of environmental conditions, thereby significantly enhancing the adhesion effect between the coating and the substrate. At the same time, the catechol group of polydopamine plays a key role in the system, which further improves the adhesion performance of the coating through hydrogen bonding and chelation. This multi-point bonding mechanism ensures a firm bond between the coating and the substrate, and maintains excellent adhesion even in high humidity, high salt or other harsh environments.

[0063] In addition, the boric acid groups introduced into the double-modified polydopamine provide dynamic reversible binding properties. This reversible binding mechanism enables the coating to adapt to the slight deformation or stress concentration that may occur on the surface of the substrate in a dynamic environment, thereby showing higher stability and durability in terms of adhesion performance. At the same time, the amino groups in the amino-modified graphene oxide quantum dots further enhance the binding force of the coating by forming a hydrogen bond network. The hydrogen bond network not only strengthens the interaction between the molecules within the coating, but also optimizes the overall bonding effect between the coating and the substrate.

[0064] The synergistic effect of these different mechanisms significantly improves the adhesion of the coating, achieving a multi-level enhancement effect from chemical adhesion to physical enhancement. This synergistic enhancement is particularly prominent in highly dynamic and complex environments.

[0065] In the design of the cross-linked network, the present invention constructs a stable and functional cross-linked structure through multiple reaction mechanisms. First, the thiol groups in the modified waterborne polyurethane dispersion can undergo Michael addition reaction with unsaturated groups to form stable chemical cross-linking points. Such cross-linking points not only give the coating higher mechanical strength, but also improve its heat resistance and aging resistance to a certain extent.

[0066] The thiol groups in the double-modified polydopamine can also participate in the construction of the cross-linked network, and cooperate with other components to form a complex cross-linked structure. More importantly, its boric acid group can dynamically cross-link with the hydroxyl groups on the surface of cellulose nanocrystals. This dynamic cross-linking point gives the coating good flexibility and self-healing properties, allowing it to quickly recover and maintain high mechanical properties under the action of external forces.

[0067] The role of graphene oxide quantum dots in the cross-linked network is that the rich functional groups on its surface can serve as nano-scale cross-linking points, which not only improves the density of the cross-linked network, but also effectively improves the overall mechanical properties and toughness of the coating. Through its excellent nano-enhancement effect, graphene oxide quantum dots significantly optimize the stress transfer ability of the coating, making the coating show a more uniform stress distribution under external loads.

[0068] The combined effect of multiple cross-linking mechanisms not only builds a highly stable chemical cross-linking network, but also achieves comprehensive optimization of the mechanical properties, durability and functional characteristics of the coating through dynamic cross-linking points and nano-enhancement. This composite cross-linking structure ensures the reliable performance of the coating in a variety of complex usage scenarios.

[0069] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention uses a combined modification of phosphoric acid and 2-mercaptoethanol to maintain the original environmental protection characteristics of the waterborne polyurethane dispersion. The synergistic effect of the phosphoric acid group and the thiol group significantly improves the hydrophilicity and adhesion of the coating.

[0070] (2) By oxidizing and amino-modifying graphene quantum dots, the dispersibility, activity and compatibility of graphene quantum dots are significantly improved, which is beneficial to their application in coatings.

[0071] (3) The two-step modification significantly improved the dispersibility, compatibility and functionality of cellulose nanocrystals. Quaternary ammonium modification improved the application performance of the material in aqueous systems, and the introduction of double bonds enabled cellulose nanocrystals to participate in free radical polymerization, thereby improving the overall performance of the composite material.

[0072] (4) The multi-level functionalization of polydopamine using 2-mercaptoethylamine hydrochloride and 4-carboxyphenylboronic acid not only significantly enhanced its chemical reactivity and environmental tolerance, but also benefited the adhesion, mechanical properties and structural stability of the coating.

[0073] (5) The present invention provides excellent adhesion properties for the coating by complementing chemical bonding and physical reinforcement mechanisms; through the combined action of multiple chemical reactions and nano-enhancement effects, a cross-linked structure with high strength, high flexibility and high stability is constructed, thereby improving the overall performance of the coating. BRIEF DESCRIPTION OF THE DRAWINGS

[0074] Figure 1 This is a flow chart of the preparation method of the high-adhesion low-solvent coating provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0075] The technical solution of the present invention is described in detail below in conjunction with specific embodiments and their accompanying drawings. The embodiments recorded herein are specific embodiments of the present invention, which are used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary and should not be construed as limitations on the embodiments of the present invention and the scope of protection of the present invention. In addition to the embodiments recorded 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 recorded herein.

[0076] The chemical reagents used in the examples and comparative examples of the present invention are all commercially available products without further purification or treatment.

[0077] Example 1

[0078] like Figure 1 As shown, this embodiment provides a high-adhesion low-solvent coating and a preparation method thereof, and the preparation method specifically comprises the following steps: S1: Mixing an aqueous polyurethane dispersion with phosphoric acid to obtain a reaction solution A, wherein the amount of phosphoric acid added is 12% of the mass of the aqueous polyurethane dispersion, mechanically stirring at a constant temperature of 58°C for 3 hours, adjusting the pH to 7.8 with 23% ammonia water after the reaction, and dialyzing to obtain a phosphorylated aqueous polyurethane dispersion; mixing the phosphorylated aqueous polyurethane dispersion with 2-mercaptoethanol and triethylamine to obtain a reaction solution B, wherein the amount of 2-mercaptoethanol added is 10% of the mass of the phosphorylated aqueous polyurethane dispersion, and the amount of triethylamine added is 4% of the mass of the 2-mercaptoethanol, stirring and reacting at 44°C for 2.6 hours, and dialyzing to obtain a modified aqueous polyurethane dispersion; S2: Mixing graphene quantum dots with a hydrogen peroxide solution having a concentration of 12% to obtain a reaction solution C, wherein the mass fraction of graphene quantum dots in the hydrogen peroxide solution is 8wt.%, stirring at a constant temperature of 66°C for 3h, centrifuging, washing, and drying to obtain graphene oxide quantum dots; dispersing graphene oxide quantum dots in water at a mass fraction of 3wt.%, adding 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride in an amount of 50% of the mass of graphene oxide quantum dots and N-hydroxysuccinimide in a mass ratio of 1:1 to 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride to obtain a reaction solution D, stirring at room temperature for 35min, adding ethylenediamine in a mass ratio of 5:1 to graphene oxide quantum dots, and continuing to stir for 10h, dialyzing, and freeze-drying to obtain amino graphene oxide quantum dots; S3: Prepare a 14wt.% cellulose nanocrystal dispersion, add 3-chloro-2-hydroxypropyltrimethylammonium chloride in a mass ratio of 1:1 to the cellulose nanocrystals, stir and dropwise add a 27wt.% sodium hydroxide solution to obtain a reaction solution E, wherein the volume mass ratio of sodium hydroxide to cellulose nanocrystals is 2.3:1, react at 62°C for 4.6h, dialyze and freeze-dry to obtain quaternized cellulose nanocrystals; disperse the quaternized cellulose nanocrystals in anhydrous ethanol to obtain a 18wt.% quaternized cellulose nanocrystal dispersion, add glycidyl methacrylate in a mass ratio of 3.4:10 to the quaternized cellulose nanocrystals and tetrabutylammonium bromide in a mass ratio of 1.8:10 to the quaternized cellulose nanocrystals to obtain a reaction solution F, react at a constant temperature of 40°C for 6h, precipitate, centrifuge, wash and vacuum dry to obtain modified cellulose nanocrystals; S4: Disperse polydopamine at a mass fraction of 2.3wt.% in a phosphate buffer solution with a pH of 8.7, add 2-mercaptoethylamine hydrochloride at a mass ratio of 3.4:10 to polydopamine, stir at room temperature, dialyze to obtain thiolated polydopamine; disperse thiolated polydopamine at a mass fraction of 2.6wt.% in water, add 4-carboxyphenylboric acid in an amount of 45% of the mass of thiolated polydopamine, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride at a mass ratio of 1:1 to 4-carboxyphenylboric acid, and N-hydroxysuccinimide at a mass ratio of 0.5:1 to 4-carboxyphenylboric acid, stir at room temperature for reaction, dialyze, and freeze-dry to obtain double-modified polydopamine; S5: Using 75 g of modified aqueous polyurethane dispersion as a matrix, 0.5 g of amino-modified graphene oxide quantum dots, 5 g of modified cellulose nanocrystals, 1 g of double-modified polydopamine and 18.5 g of deionized water were added in sequence, and the mixture was stirred, ultrasonically dispersed and vacuum degassed to obtain the high-adhesion low-solvent coating.

[0079] Example 2

[0080] This embodiment provides a high-adhesion low-solvent coating and a preparation method thereof, wherein the preparation method specifically comprises the following steps: S1: Mixing an aqueous polyurethane dispersion with phosphoric acid to obtain a reaction solution A, wherein the amount of phosphoric acid added is 15% of the mass of the aqueous polyurethane dispersion, mechanically stirring at a constant temperature of 55°C for 3.5 hours, adjusting the pH to 8 with 20% ammonia water after the reaction, and dialyzing to obtain a phosphorylated aqueous polyurethane dispersion; mixing the phosphorylated aqueous polyurethane dispersion with 2-mercaptoethanol and triethylamine to obtain a reaction solution B, wherein the amount of 2-mercaptoethanol added is 12% of the mass of the phosphorylated aqueous polyurethane dispersion, and the amount of triethylamine added is 5% of the mass of the 2-mercaptoethanol, stirring the reaction at 40°C for 3 hours, and dialyzing to obtain a modified aqueous polyurethane dispersion; S2: Mixing graphene quantum dots with a 10% hydrogen peroxide solution to obtain a reaction solution C, wherein the mass fraction of graphene quantum dots in the hydrogen peroxide solution is 10wt.%, stirring at a constant temperature of 60°C for 2.3h, centrifuging, washing, and drying to obtain graphene oxide quantum dots; dispersing graphene oxide quantum dots in water at a mass fraction of 4wt.%, adding 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride in an amount of 55% of the mass of graphene oxide quantum dots and N-hydroxysuccinimide in a mass ratio of 1:1.5 to 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride to obtain a reaction solution D, stirring at room temperature for 37min, adding ethylenediamine in a mass ratio of 10:1 to graphene oxide quantum dots and continuing to stir for 11h, dialyzing, and freeze-drying to obtain amino graphene oxide quantum dots; S3: Prepare a 10wt.% cellulose nanocrystal dispersion, add 3-chloro-2-hydroxypropyltrimethylammonium chloride in a mass ratio of 1:2 to the cellulose nanocrystal, stir and dropwise add a 30wt.% sodium hydroxide solution to obtain a reaction solution E, wherein the volume mass ratio of sodium hydroxide to cellulose nanocrystals is 2:1, react at 65°C for 5h, dialyze and freeze-dry to obtain quaternized cellulose nanocrystals; disperse the quaternized cellulose nanocrystals in anhydrous ethanol to obtain a 20wt.% quaternized cellulose nanocrystal dispersion, add glycidyl methacrylate in a mass ratio of 3:10 to the quaternized cellulose nanocrystals and tetrabutylammonium bromide in a mass ratio of 1.6:10 to the quaternized cellulose nanocrystals to obtain a reaction solution F, react at a constant temperature of 45°C for 5.6h, precipitate, centrifuge, wash and vacuum dry to obtain modified cellulose nanocrystals; S4: Disperse polydopamine at a mass fraction of 3 wt.% in a phosphate buffer having a pH of 9, add 2-mercaptoethylamine hydrochloride at a mass ratio of 4:10 to polydopamine, stir at room temperature, dialyze to obtain thiolated polydopamine; disperse thiolated polydopamine at a mass fraction of 3 wt.% in water, add 4-carboxyphenylboric acid in an amount of 50% of the mass of thiolated polydopamine, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride at a mass ratio of 1.2:1 to 4-carboxyphenylboric acid, and N-hydroxysuccinimide at a mass ratio of 0.56:1 to 4-carboxyphenylboric acid, stir at room temperature for reaction, dialyze, and freeze-dry to obtain double-modified polydopamine; S5: Using 80 g of modified aqueous polyurethane dispersion as a matrix, 0.8 g of amino-modified graphene oxide quantum dots, 2 g of modified cellulose nanocrystals, 2 g of double-modified polydopamine and 15.2 g of deionized water were added in sequence, and after stirring and ultrasonic dispersion, vacuum degassing was performed to obtain the high-adhesion low-solvent coating.

[0081] Example 3

[0082] This embodiment provides a high-adhesion low-solvent coating and a preparation method thereof, wherein the preparation method specifically comprises the following steps: S1: Mixing an aqueous polyurethane dispersion with phosphoric acid to obtain a reaction solution A, wherein the amount of phosphoric acid added is 10% of the mass of the aqueous polyurethane dispersion, mechanically stirring at a constant temperature of 50°C for 3.7 hours, adjusting the pH to 7 with 25% ammonia water after the reaction, and dialyzing to obtain a phosphorylated aqueous polyurethane dispersion; mixing the phosphorylated aqueous polyurethane dispersion with 2-mercaptoethanol and triethylamine to obtain a reaction solution B, wherein the amount of 2-mercaptoethanol added is 8% of the mass of the phosphorylated aqueous polyurethane dispersion, and the amount of triethylamine added is 7% of the mass of the 2-mercaptoethanol, stirring the reaction at 50°C for 2.5 hours, and dialyzing to obtain a modified aqueous polyurethane dispersion; S2: Mixing graphene quantum dots with a hydrogen peroxide solution having a concentration of 14% to obtain a reaction solution C, wherein the mass fraction of graphene quantum dots in the hydrogen peroxide solution is 5wt.%, stirring at a constant temperature of 70°C for 2.8h, centrifuging, washing, and drying to obtain graphene oxide quantum dots; dispersing graphene oxide quantum dots in water at a mass fraction of 5wt.%, adding 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride in an amount of 58% of the mass of graphene oxide quantum dots and N-hydroxysuccinimide in a mass ratio of 1:1.7 to 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride to obtain a reaction solution D, stirring at room temperature for 40min, adding ethylenediamine in a mass ratio of 8:1 to graphene oxide quantum dots, and continuing to stir for 12h, dialyzing, and freeze-drying to obtain amino graphene oxide quantum dots; S3: Prepare a cellulose nanocrystal dispersion with a mass fraction of 20wt.%, add 3-chloro-2-hydroxypropyltrimethylammonium chloride in a mass ratio of 1:1.5 to the cellulose nanocrystals, stir and dropwise add a sodium hydroxide solution with a mass fraction of 20wt.% to obtain a reaction solution E, wherein the volume mass ratio of sodium hydroxide to cellulose nanocrystals is 3:1, react at 63°C for 4.8h, dialyze and freeze-dry to obtain quaternized cellulose nanocrystals; disperse the quaternized cellulose nanocrystals in anhydrous ethanol to obtain a quaternized cellulose nanocrystal dispersion with a mass fraction of 15wt.%, add glycidyl methacrylate in a mass ratio of 3.8:10 to the quaternized cellulose nanocrystals and tetrabutylammonium bromide in a mass ratio of 1:10 to the quaternized cellulose nanocrystals to obtain a reaction solution F, react at a constant temperature of 48°C for 5.8h, precipitate, centrifuge, wash and vacuum dry to obtain modified cellulose nanocrystals; S4: Disperse polydopamine at a mass fraction of 2 wt.% in a phosphate buffer having a pH of 8, add 2-mercaptoethylamine hydrochloride at a mass ratio of 3.7:10 to polydopamine, stir at room temperature, dialyze to obtain thiolated polydopamine; disperse thiolated polydopamine at a mass fraction of 2 wt.% in water, add 4-carboxyphenylboric acid in an amount of 47% of the mass of thiolated polydopamine, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride at a mass ratio of 1.4:1 to 4-carboxyphenylboric acid, and N-hydroxysuccinimide at a mass ratio of 0.57:1 to 4-carboxyphenylboric acid, stir at room temperature for reaction, dialyze, and freeze-dry to obtain double-modified polydopamine; S5: Using 82 g of modified aqueous polyurethane dispersion as a matrix, 0.7 g of amino-modified graphene oxide quantum dots, 4 g of modified cellulose nanocrystals, 0.5 g of double-modified polydopamine and 12.8 g of deionized water were added in sequence, and the mixture was stirred, ultrasonically dispersed and vacuum degassed to obtain the high-adhesion low-solvent coating.

[0083] Example 4

[0084] This embodiment provides a high-adhesion low-solvent coating and a preparation method thereof, wherein the preparation method specifically comprises the following steps: S1: Mixing an aqueous polyurethane dispersion with phosphoric acid to obtain a reaction solution A, wherein the amount of phosphoric acid added is 14% of the mass of the aqueous polyurethane dispersion, mechanically stirring at a constant temperature of 60°C for 4 hours, adjusting the pH to 7.5 with 22% ammonia water after the reaction, and dialyzing to obtain a phosphorylated aqueous polyurethane dispersion; mixing the phosphorylated aqueous polyurethane dispersion with 2-mercaptoethanol and triethylamine to obtain a reaction solution B, wherein the amount of 2-mercaptoethanol added is 11% of the mass of the phosphorylated aqueous polyurethane dispersion, and the amount of triethylamine added is 8% of the mass of 2-mercaptoethanol, stirring and reacting at 47°C for 2 hours, and dialyzing to obtain a modified aqueous polyurethane dispersion; S2: Mixing graphene quantum dots with a 15% hydrogen peroxide solution to obtain a reaction solution C, wherein the mass fraction of graphene quantum dots in the hydrogen peroxide solution is 7wt.%, stirring at a constant temperature of 68°C for 2h, centrifuging, washing, and drying to obtain graphene oxide quantum dots; dispersing graphene oxide quantum dots in water at a mass fraction of 2wt.%, adding 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride in an amount of 60% of the mass of graphene oxide quantum dots and N-hydroxysuccinimide in a mass ratio of 1:2 to 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride to obtain a reaction solution D, stirring at room temperature for 30min, adding ethylenediamine in a mass ratio of 7:1 to graphene oxide quantum dots, and continuing to stir for 11.4h, dialyzing, and freeze-drying to obtain amino graphene oxide quantum dots; S3: Prepare a cellulose nanocrystal dispersion with a mass fraction of 18wt.%, add 3-chloro-2-hydroxypropyltrimethylammonium chloride in a mass ratio of 1:1.8 to the cellulose nanocrystals, stir and dropwise add a sodium hydroxide solution with a mass fraction of 25wt.% to obtain a reaction solution E, wherein the volume mass ratio of sodium hydroxide to cellulose nanocrystals is 2.7:1, react at 60°C for 4h, dialyze and freeze-dry to obtain quaternized cellulose nanocrystals; disperse the quaternized cellulose nanocrystals in anhydrous ethanol to obtain a quaternized cellulose nanocrystal dispersion with a mass fraction of 10wt.%, add glycidyl methacrylate in a mass ratio of 4:10 to the quaternized cellulose nanocrystals and tetrabutylammonium bromide in a mass ratio of 2:10 to the quaternized cellulose nanocrystals to obtain a reaction solution F, react at a constant temperature of 50°C for 5h, precipitate, centrifuge, wash and vacuum dry to obtain modified cellulose nanocrystals; S4: Disperse polydopamine at a mass fraction of 2.7wt.% in a phosphate buffer having a pH of 8.4, add 2-mercaptoethylamine hydrochloride at a mass ratio of 3:10 to polydopamine, stir at room temperature, dialyze to obtain thiolated polydopamine; disperse thiolated polydopamine at a mass fraction of 2.8wt.% in water, add 4-carboxyphenylboric acid in an amount of 40% of the mass of thiolated polydopamine, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride at a mass ratio of 1.5:1 to 4-carboxyphenylboric acid, and N-hydroxysuccinimide at a mass ratio of 0.6:1 to 4-carboxyphenylboric acid, stir at room temperature for reaction, dialyze, and freeze-dry to obtain double-modified polydopamine; S5: Using 85 g of modified aqueous polyurethane dispersion as a matrix, 1 g of amino-modified graphene oxide quantum dots, 1 g of modified cellulose nanocrystals, 1.5 g of double-modified polydopamine and 11.5 g of deionized water were added in sequence, and after stirring and ultrasonic dispersion, vacuum degassing was performed to obtain the high-adhesion low-solvent coating.

[0085] Comparative Example 1 This comparative example provides a high-adhesion low-solvent coating and a preparation method thereof, which is different from Example 1 in that, in step S1, the amount of phosphoric acid added is 20% of the mass of the aqueous polyurethane dispersion, and the other operating steps and process parameters are exactly the same as those in Example 1.

[0086] Comparative Example 2 This comparative example provides a high-adhesion low-solvent coating and a preparation method thereof. The difference from Example 1 is that in step S1, the amount of phosphoric acid added is 5% of the mass of the aqueous polyurethane dispersion, and the other operating steps and process parameters are exactly the same as those in Example 1.

[0087] Comparative Example 3 This comparative example provides a high-adhesion low-solvent coating and a preparation method thereof, which is different from Example 1 in that, in step S3, the mass ratio of glycidyl methacrylate to quaternized cellulose nanocrystals is 7:10, and the other operating steps and process parameters are exactly the same as those in Example 1.

[0088] Comparative Example 4 This comparative example provides a high-adhesion low-solvent coating and a preparation method thereof, which is different from Example 1 in that, in step S3, the mass ratio of glycidyl methacrylate to quaternized cellulose nanocrystals is 1:10, and the other operating steps and process parameters are exactly the same as those in Example 1.

[0089] The performance test of the high adhesion low solvent coatings of the above Examples 1-4 and Comparative Examples 1-4 was carried out, and the specific process is as follows: Test the adhesion of samples according to GB / T 9286-2021; Test the hardness of the sample according to GB / T 6739-2022; Test the water resistance of samples according to GB / T 1733-1993; The test results are shown in Table 1.

[0090] Table 1: Performance test results of high adhesion low solvent coatings of Examples 1-4 and Comparative Examples 1-4

[0091] From the test results of Example 1 and Comparative Examples 1 and 2, it can be seen that in the process of modifying the waterborne polyurethane dispersion, when the amount of phosphoric acid added is too much, the interaction between the phosphoric acid groups or the interaction with the solvent may lead to enhanced attraction between the particles, thereby reducing the stability of the dispersion, inducing agglomeration and sedimentation, and reducing the adhesion, water resistance and hardness of the coating. In addition, the competition between the excessive phosphoric acid groups and the hydrogen bonds of the hard segments may weaken the microphase separation and reduce the water resistance of the coating; when the amount of phosphoric acid added is too little, the number of introduced phosphoric acid groups is insufficient, resulting in insufficient modification of the waterborne polyurethane dispersion, resulting in limited effect of improving the adhesion of the coating and insufficient bonding with the substrate.

[0092] From the test results of Example 1 and Comparative Examples 3 and 4, it can be seen that when modifying cellulose nanocrystals, introducing too much glycidyl methacrylate will lead to too many epoxy groups being introduced, and the epoxy groups on the surface of the cellulose nanocrystals are excessive, which will reduce the hydrophilicity after reacting with the hydroxyl group, and at the same time induce self-crosslinking, resulting in a decrease in the dispersibility of the cellulose nanocrystals. This decrease in dispersibility and increase in crosslinking density will make the coating too hard but not flexible enough, and it will easily crack under external force or environmental stress. On the contrary, when the amount of glycidyl methacrylate introduced is insufficient, the number of epoxy groups on the surface of the cellulose nanocrystals is reduced, the lack of active groups leads to insufficient chemical crosslinking points, and the interfacial bonding force is weakened, which is ultimately manifested as a decrease in the water resistance and adhesion of the coating.

[0093] The above description is only a specific implementation mode 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 are within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a high-adhesion low-solvent coating, characterized in that: The preparation method comprises: S1: mixing an aqueous polyurethane dispersion with phosphoric acid to obtain a reaction solution A, mechanically stirring at a constant temperature, adjusting the pH with aqueous ammonia after the reaction, and dialyzing to obtain a phosphorylated aqueous polyurethane dispersion; mixing the phosphorylated aqueous polyurethane dispersion with 2-mercaptoethanol and triethylamine to obtain a reaction solution B, stirring the reaction, and dialyzing to obtain a modified aqueous polyurethane dispersion; S2: mixing graphene quantum dots with hydrogen peroxide solution to obtain reaction solution C, stirring at constant temperature, centrifuging, washing, and drying to obtain graphene oxide quantum dots; dispersing graphene oxide quantum dots in water, adding 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide to obtain reaction solution D, stirring at room temperature, adding ethylenediamine and continuing to stir the reaction, dialyzing, and freeze-drying to obtain amino graphene oxide quantum dots; S3: preparing a cellulose nanocrystal dispersion, adding 3-chloro-2-hydroxypropyltrimethylammonium chloride, stirring, and then dropping a sodium hydroxide solution to obtain a reaction solution E, and after the reaction, dialyzing and freeze-drying to obtain quaternized cellulose nanocrystals; dispersing the quaternized cellulose nanocrystals in anhydrous ethanol to obtain a quaternized cellulose nanocrystal dispersion, adding glycidyl methacrylate and tetrabutylammonium bromide to obtain a reaction solution F, reacting at a constant temperature, precipitating, centrifuging, washing, and vacuum drying to obtain modified cellulose nanocrystals; S4: Disperse polydopamine in phosphate buffer, add 2-mercaptoethylamine hydrochloride, stir at room temperature, dialyze to obtain thiolated polydopamine; disperse thiolated polydopamine in water, add 4-carboxyphenylboronic acid, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide, stir at room temperature for reaction, dialyze, and freeze-dry to obtain double-modified polydopamine; S5: Using the modified waterborne polyurethane dispersion as a matrix, adding amino-modified graphene oxide quantum dots, modified cellulose nanocrystals, double-modified polydopamine and deionized water in sequence, stirring, ultrasonically dispersing and vacuum degassing to obtain the high-adhesion low-solvent coating.

2. The method for preparing a high-adhesion low-solvent coating according to claim 1, characterized in that: In S1: the amount of phosphoric acid added is 10-15% of the mass of the aqueous polyurethane dispersion.

3. The method for preparing a high-adhesion low-solvent coating according to claim 1, characterized in that: In S1: The amount of 2-mercaptoethanol added is 8-12% of the mass of the phosphorylated aqueous polyurethane dispersion; The feeding amount of the triethylamine accounts for 4-8% of the mass of 2-mercaptoethanol.

4. The method for preparing a high-adhesion low-solvent coating according to claim 1, characterized in that: In S2: the mass fraction of the graphene quantum dots in the hydrogen peroxide solution is 5-10 wt.%.

5. The method for preparing a high-adhesion low-solvent coating according to claim 1, characterized in that: In S2: The amount of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride is 50-60% of the mass of graphene oxide quantum dots; The mass ratio of N-hydroxysuccinimide to 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride is 1:1-2; The mass ratio of the ethylenediamine to the graphene oxide quantum dots is 5-10:

1.

6. The method for preparing a high-adhesion low-solvent coating according to claim 1, characterized in that: In S3: The mass ratio of the 3-chloro-2-hydroxypropyltrimethylammonium chloride to the cellulose nanocrystals is 1:1-2; The volume mass ratio of the sodium hydroxide to the cellulose nanocrystals is 2-3:

1.

7. The method for preparing a high-adhesion low-solvent coating according to claim 1, characterized in that: In S3: The mass ratio of glycidyl methacrylate to quaternized cellulose nanocrystals is 3-4:10; The mass ratio of the tetrabutylammonium bromide to the quaternized cellulose nanocrystals is 1-2:

10.

8. The method for preparing a high-adhesion low-solvent coating according to claim 1, characterized in that: In S4: The mass fraction of the polydopamine in the phosphate buffer is 2-3wt.%; The mass ratio of the 2-mercaptoethylamine hydrochloride to polydopamine is 3-4:

10.

9. The method for preparing a high-adhesion low-solvent coating according to claim 1, characterized in that: In S4: The feeding amount of the 4-carboxyphenylboronic acid is 40-50% of the mass of the thiolated polydopamine; The mass ratio of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride to 4-carboxyphenylboronic acid is 1-1.5:1; The mass ratio of the N-hydroxysuccinimide to 4-carboxyphenylboronic acid is 0.5-0.6:

1.

10. A high-adhesion, low-solvent coating prepared by the preparation method according to any one of claims 1 to 9, characterized in that: The mass ratio of the components of the high-adhesion low-solvent coating is: modified waterborne polyurethane dispersion: amino-modified graphene oxide quantum dots: modified cellulose nanocrystals: double-modified polydopamine: deionized water is (75-85): (0.5-1): (1-5): (0.5-2): (7-23).

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