A high-adhesion low-solvent coating and its preparation method

Abstract

The present invention provides a high-adhesion low-solvent coating and a preparation method thereof, belonging to the field of coatings. The present invention synergistically improves the performance of waterborne coatings through a variety of modification strategies: the phosphate groups of the phosphorylated waterborne polyurethane dispersion form coordination bonds with the substrate to enhance adhesion; the thiol groups react with unsaturated groups to construct a stable crosslinked network. Oxidation and amination of graphene quantum dots improve dispersibility and form hydrogen bonds and crosslinking points to enhance mechanical properties; quaternized cellulose nanocrystals improve compatibility, and double bonds participate in the crosslinked network to enhance structural stability; mercapto- and borate-group modified polydopamine strengthens the network strength and flexibility and improves the interfacial binding force. These mechanisms provide a solid foundation for the development of high-adhesion, low-solvent high-performance coatings.

Description

Technical Field

[0001] The present 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 applied in various fields such as construction, automotive, electronics, household appliances, aerospace, and other industrial fields. Coatings can not only protect the substrate from environmental factors (such as moisture, corrosion, ultraviolet rays, chemicals, etc.), but also improve the appearance of products and enhance the surface decoration effect, thereby significantly increasing the overall value and service life of products. In industrial production, the extensive use of coatings can also reduce equipment wear and improve energy efficiency, so it occupies an indispensable position in modern manufacturing.

[0003] Solvent-based coatings are widely used due to their excellent adhesion, durability, and adaptability. Solvent-based coatings use organic solvents as the dispersion medium to uniformly 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, has a fast drying speed, can form high-quality coating films on the surfaces of various substrates, and has excellent weather resistance and decorative properties. Therefore, solvent-based coatings are widely used in fields such as exterior building walls, automotive surfaces, and household appliance painting. However, the outstanding performance of solvent-based coatings is also accompanied by significant deficiencies.

[0004] Firstly, a large amount of organic solvents are required in the production and use of solvent-based coatings, and the volatilization of these solvents will release a large amount of volatile organic compounds (VOCs), causing serious environmental pollution. VOCs are the main factors leading to photochemical smog, ozone formation, and air quality degradation, posing threats to both the ecological system and human health. Secondly, solvent-based coatings can pose potential hazards to the health of construction workers during the construction process. Long-term exposure to high-concentration solvent vapors may cause respiratory, nervous system, 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 coating industry. Summary of the Invention

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

[0006] To achieve this purpose, the present invention adopts the following technical solutions:

[0007] In the first aspect, the present invention provides a preparation method of a high-adhesion low-solvent coating, and the preparation method of the high-adhesion low-solvent coating includes:

[0008] S1: Mix the aqueous polyurethane dispersion with phosphoric acid to obtain reaction solution A, mechanically stir at a constant temperature, adjust the pH with ammonia water after the reaction ends, and obtain phosphorylated aqueous polyurethane dispersion after dialysis; mix the phosphorylated aqueous polyurethane dispersion with 2-mercaptoethanol and triethylamine to obtain reaction solution B, stir and react, and obtain modified aqueous polyurethane dispersion after dialysis;

[0009] S2: Mix graphene quantum dots with hydrogen peroxide solution to obtain reaction solution C, centrifuge, wash and dry after stirring at a constant temperature to obtain oxidized graphene quantum dots; disperse the oxidized graphene quantum dots in water, add 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide to obtain reaction solution D, stir at room temperature, add ethylenediamine and continue to stir and react, and obtain amino-functionalized oxidized graphene quantum dots after dialysis and freeze-drying;

[0010] S3: Prepare a cellulose nanocrystal dispersion, add 3-chloro-2-hydroxypropyltrimethylammonium chloride, stir and then dropwise add sodium hydroxide solution to obtain reaction solution E, dialyze and freeze-dry after the reaction to obtain quaternized cellulose nanocrystals; disperse the quaternized cellulose nanocrystals in absolute ethanol to obtain a quaternized cellulose nanocrystal dispersion, add glycidyl methacrylate and tetrabutylammonium bromide to obtain reaction solution F, precipitate after reacting at a constant temperature, centrifuge, wash and vacuum-dry to obtain modified cellulose nanocrystals;

[0011] S4: Disperse polydopamine in phosphate buffer solution, add 2-mercaptoethylamine hydrochloride, stir at room temperature and dialyze to obtain thiolated polydopamine; disperse the thiolated polydopamine in water, add 4-carboxyphenylboronic acid, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide, stir and react at room temperature, dialyze and freeze-dry to obtain doubly modified polydopamine;

[0012] S5: Using the modified aqueous polyurethane dispersion as the matrix, sequentially add amino-functionalized graphene oxide quantum dots, modified cellulose nanocrystals, doubly modified polydopamine and deionized water, stir, ultrasonically disperse and then degas under vacuum to obtain the high-adhesion low-solvent coating.

[0013] As a preferred technical solution of the present invention, in step S1, the feeding amount of the phosphoric acid accounts for 10-15% of the mass of the aqueous polyurethane dispersion, 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 this numerical range are equally applicable.

[0014] In some alternative embodiments, the temperature of the constant-temperature stirring of the reaction solution 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 this numerical range are equally applicable.

[0015] In some alternative embodiments, the time of the constant-temperature stirring of the reaction solution A is 3-4 h, for example, it can be 3 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 h, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0016] In some alternative embodiments, the mass fraction of the ammonia water is 20-25 wt.%, for example, it can be 20 wt.%, 20.5 wt.%, 21 wt.%, 21.5 wt.%, 22 wt.%, 22.5 wt.%, 23 wt.%, 23.5 wt.%, 24 wt.% or 25 wt.%, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0017] In some alternative embodiments, the pH is adjusted to 7-8 with ammonia water, for example, it can be 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 this numerical range are equally applicable.

[0018] In some alternative embodiments, the feeding amount of 2-mercaptoethanol accounts for 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. Other unlisted values within this numerical range are equally applicable.

[0019] In some alternative embodiments, the feeding amount of triethylamine accounts for 4-8% of the mass of 2-mercaptoethanol. For example, it can be 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5% or 8%, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0020] In some alternative embodiments, the temperature for the stirring reaction of reaction solution 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. Other unlisted values within this numerical range are equally applicable.

[0021] In some alternative embodiments, the time for the stirring reaction of reaction solution B is 2-3 h. For example, it can be 2 h, 2.1 h, 2.2 h, 2.3 h, 2.4 h, 2.5 h, 2.6 h, 2.7 h, 2.8 h, 2.9 h or 3 h, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0022] 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. Other unlisted values within this numerical range are equally applicable.

[0023] In some alternative embodiments, the mass fraction of the graphene quantum dots in the hydrogen peroxide solution is 5-10 wt.%. For example, it can be 5 wt.%, 5.5 wt.%, 6 wt.%, 6.5 wt.%, 7 wt.%, 7.5 wt.%, 8 wt.%, 8.5 wt.%, 9 wt.% or 10 wt.%, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0024] In some alternative embodiments, the temperature for the constant-temperature stirring of the reaction solution 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. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0025] In some alternative embodiments, the time for the constant-temperature stirring of the reaction solution C is 2 - 3 h. For example, it can be 2 h, 2.1 h, 2.2 h, 2.3 h, 2.4 h, 2.5 h, 2.6 h, 2.7 h, 2.8 h, 2.9 h or 3 h. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0026] In some alternative embodiments, the mass fraction of the graphene oxide quantum dots dispersed in water is 2 - 5 wt.%. For example, it can be 2.0 wt.%, 2.3 wt.%, 2.6 wt.%, 2.9 wt.%, 3.2 wt.%, 3.5 wt.%, 3.8 wt.%, 4.1 wt.%, 4.4 wt.%, 4.7 wt.% or 5.0 wt.%. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0027] In some alternative embodiments, the feeding amount of 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%. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0028] In some alternative 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. However, it is not limited to the listed ratios, and other unlisted ratios within this ratio range are equally applicable.

[0029] In some alternative embodiments, the time for the room-temperature stirring of the reaction solution D 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. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0030] In some alternative 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. However, it is not limited to the listed ratios, and other unlisted ratios within this ratio range are equally applicable.

[0031] In some alternative embodiments, the time for continuous stirring reaction after adding ethylenediamine is 10-12 h. For example, it can be 10 h, 10.2 h, 10.4 h, 10.6 h, 10.8 h, 11 h, 11.2 h, 11.4 h, 11.6 h, 11.8 h or 12 h. However, it is not limited to the listed values, and other unlisted values within this value range are equally applicable.

[0032] As a preferred technical solution of the present invention, in step S3, the mass fraction of the cellulose nanocrystal dispersion is 10-20 wt.%. For example, it can be 10 wt.%, 11 wt.%, 12 wt.%, 13 wt.%, 14 wt.%, 15 wt.%, 16 wt.%, 17 wt.%, 18 wt.%, 19 wt.% or 20 wt.%. However, it is not limited to the listed values, and other unlisted values within this value range are equally applicable.

[0033] In some alternative 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. However, it is not limited to the listed ratios, and other unlisted ratios within this ratio range are equally applicable.

[0034] In some alternative embodiments, the mass fraction of the sodium hydroxide solution is 20-30 wt.%. For example, it can be 20 wt.%, 21 wt.%, 22 wt.%, 23 wt.%, 24 wt.%, 25 wt.%, 26 wt.%, 27 wt.%, 28 wt.%, 29 wt.% or 30 wt.%. However, it is not limited to the listed values, and other unlisted values within this value range are equally applicable.

[0035] In some alternative 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. However, it is not limited to the listed ratios, and other unlisted ratios within this ratio range are equally applicable.

[0036] In some alternative embodiments, the reaction temperature of the reaction solution 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. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0037] In some alternative embodiments, the reaction time of the reaction solution E is 4 - 5 h. For example, it can be 4 h, 4.1 h, 4.2 h, 4.3 h, 4.4 h, 4.5 h, 4.6 h, 4.7 h, 4.8 h, 4.9 h, or 5 h. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0038] In some alternative embodiments, the mass fraction of the quaternized cellulose nanocrystals dispersion is 10 - 20 wt.%. For example, it can be 10 wt.%, 11 wt.%, 12 wt.%, 13 wt.%, 14 wt.%, 15 wt.%, 16 wt.%, 17 wt.%, 18 wt.%, 19 wt.%, or 20 wt.%. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0039] In some alternative embodiments, the mass ratio of glycidyl methacrylate to quaternized cellulose nanocrystals 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. However, it is not limited to the listed ratios, and other unlisted ratios within this ratio range are equally applicable.

[0040] In some alternative embodiments, the mass ratio of tetrabutylammonium bromide to quaternized cellulose nanocrystals is 1 - 2:10. For example, it can be 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. However, it is not limited to the listed ratios, and other unlisted ratios within this ratio range are equally applicable.

[0041] In some alternative embodiments, the temperature of the constant-temperature reaction of the reaction solution 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. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0042] In some alternative embodiments, the reaction solution F is subjected to a constant-temperature reaction for 5 - 6 h. For example, it can be 5 h, 5.1 h, 5.2 h, 5.3 h, 5.4 h, 5.5 h, 5.6 h, 5.7 h, 5.8 h, 5.9 h, or 6 h. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0043] 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. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0044] In some alternative embodiments, the mass fraction of polydopamine in the phosphate buffer is 2 - 3 wt.%. For example, it can be 2.0 wt.%, 2.1 wt.%, 2.2 wt.%, 2.3 wt.%, 2.4 wt.%, 2.5 wt.%, 2.6 wt.%, 2.7 wt.%, 2.8 wt.%, 2.9 wt.%, or 3.0 wt.%. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0045] In some alternative 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. However, it is not limited to the listed ratios, and other unlisted ratios within this ratio range are equally applicable.

[0046] In some alternative embodiments, the mass fraction of thiolated polydopamine in water is 2 - 3 wt.%. For example, it can be 2.0 wt.%, 2.1 wt.%, 2.2 wt.%, 2.3 wt.%, 2.4 wt.%, 2.5 wt.%, 2.6 wt.%, 2.7 wt.%, 2.8 wt.%, 2.9 wt.%, or 3.0 wt.%. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0047] In some alternative embodiments, the feeding amount of 4-carboxyphenylboronic acid is 40 - 50% of the mass of thiolated polydopamine. For example, it can be 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, or 50%. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0048] In some alternative embodiments, the mass ratio of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride to 4-carboxyphenylboronic 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. However, it is not limited to the listed ratios, and other unlisted ratios within this range are equally applicable.

[0049] In some alternative embodiments, the mass ratio of N-hydroxysuccinimide to 4-carboxyphenylboronic 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. However, it is not limited to the listed ratios, and other unlisted ratios within this range are equally applicable.

[0050] In a second aspect, the present invention provides a high-adhesion low-solvent coating. The mass ratio of each component of the high-adhesion low-solvent coating is: modified aqueous polyurethane dispersion: amino-functionalized graphene oxide quantum dots: modified cellulose nanocrystals: double-modified polydopamine: deionized water = (75-85):(0.5-1):(1-5):(0.5-2):(7-23).

[0051] In the present invention, aqueous polyurethane dispersion is selected as the matrix material. Aqueous polyurethane dispersion is an emulsion-type polyurethane, and its molecular structure is usually composed of a flexible segment and a rigid segment. The molecular chain of the flexible segment is relatively long and the structure is relatively soft, which endows the coating with good flexibility and ductility, thereby improving the impact resistance and adaptability of the coating. The molecular structure of the rigid segment is rigid and has high mechanical strength, making the coating exhibit excellent scratch resistance and chemical corrosion resistance.

[0052] In addition, the molecules of aqueous polyurethane dispersion contain a large number of polar groups, such as hydroxyl groups, amino groups, etc. These polar groups can be tightly combined with the surface of the substrate through hydrogen bonding or physical adsorption, thereby significantly enhancing the adhesion of the coating and avoiding the phenomenon of coating peeling or cracking during long-term use. At the same time, compared with traditional solvent-based polyurethanes, aqueous polyurethanes have obvious environmental protection advantages. Their low volatile organic compound content meets the development requirements of modern green environmental protection coatings, and they are non-toxic and have a low odor, making them suitable for fields with high requirements for environmental protection performance.

[0053] In order to further improve the performance of waterborne polyurethane coatings, 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 empty orbitals and can bind to the hydroxyl or amino groups on the molecular chain of the polyurethane dispersion through hydrogen bonds or electrostatic interactions. During the modification process, part of the phosphoric acid may also form a stable phosphate ester structure with the polyurethane through chemical reactions, which further enhances the binding force between the phosphoric acid and the polyurethane molecular chain.

[0054] The introduction of phosphate groups adds highly polar functional groups to the polyurethane dispersion molecules. Such polar groups have 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 the adhesion effect on high-hardness substrates such as glass and metal is more excellent. At the same time, the presence of phosphate groups improves the hydrophilicity of the waterborne polyurethane dispersion, making it more uniformly dispersed in the aqueous system. This dispersion uniformity not only reduces the surface defects during the film-forming process of the coating but also improves the overall appearance and performance of the coating, making it more practical.

[0055] To further enhance the performance of the waterborne polyurethane dispersion, 2-mercaptoethanol is also used to modify it in the present invention. 2-Mercaptoethanol is a sulfur-containing compound. The thiol group in its molecule has high nucleophilicity and can form metal-sulfur bonds with metal atoms on the surface of metal substrates 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.

[0056] 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 crosslinked structure not only improves the mechanical properties of the coating, such as tensile strength and elastic modulus, but also makes it show higher impact resistance and wear resistance during use. At the same time, the introduction of thiol groups 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, bases, and organic solvents, thereby extending the service life of the coating.

[0057] In the present invention, graphene quantum dots are introduced as nano-crosslinking points. Due to their unique two-dimensional structure, large specific surface area, and edge defect regions, graphene quantum dots exhibit excellent performance potential. Their ultra-high electrical 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 mainly have carbon-carbon bonds on the surface, with a limited number of polar functional groups, showing high chemical inertness. This characteristic leads to poor dispersibility in aqueous systems and easy agglomeration, further reducing the uniformity of the material and restricting its direct application in the coating field.

[0058] To overcome the above problems and fully exploit the potential of graphene quantum dots, surface chemical modification treatment is required. First, it is transformed into oxidized graphene quantum dots through oxidation treatment. In this process, hydrogen peroxide is selected as the oxidant, and graphene quantum dots are selectively oxidized under appropriate temperature and reaction time conditions. The oxidation reaction mainly focuses on the edge defect regions and carbon-carbon double bond sites of graphene quantum dots. By introducing polar functional groups such as hydroxyl and carboxyl groups, its hydrophilicity and surface reactivity are significantly improved. These polar functional groups endow oxidized graphene quantum dots with excellent dispersibility in the aqueous phase, effectively avoiding the agglomeration phenomenon. In addition, these functionalized functional groups provide reaction sites for subsequent chemical modification, and at the same time enable oxidized graphene quantum dots to combine with groups such as hydroxyl and amino 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.

[0059] On the basis of the oxidation treatment, to further enhance the performance of graphene quantum dots, amination modification treatment is carried out. Specifically, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide are used to activate the carboxyl groups on the surface of oxidized graphene quantum dots to generate acyl active intermediates. Subsequently, amidation reaction occurs with ethylenediamine under neutral or weakly acidic conditions, successfully introducing free amino groups. The amination modification has multiple advantages: the introduced free amino groups can form stable covalent bonds with active groups such as carbonyl groups in the polyurethane dispersion through chemical crosslinking reactions, thereby further enhancing the strength of the internal network structure of the coating and improving the mechanical properties; the amino group can form stable bonds with the thiol or borate group in polydopamine through hydrogen bonds or covalent bonds. For example, the thiol oxidation crosslinking of the amino group and the thiol group can generate disulfide bonds, significantly enhancing the adhesion of the coating and at the same time improving the impact resistance and durability; the aminated graphene quantum dots provide additional chemical stability and environmental adaptability, and can effectively improve the chemical corrosion resistance of the coating in complex or harsh environments.

[0060] The present invention introduces cellulose nanocrystals. Cellulose nanocrystals are highly crystalline nanoscale materials extracted from plant fibers, with a rod-like structure having a diameter between a few nanometers and dozens of nanometers and a length that can reach hundreds of nanometers. This material has attracted much attention due to its natural source, biocompatibility, high strength, and high modulus, especially having broad application prospects in the fields of green materials and nano-reinforced composite materials.

[0061] However, the surface of unmodified cellulose nanocrystals is rich in polar hydroxyl groups, which, although endowing it with good dispersibility in aqueous systems, is prone to agglomeration in non-polar or weakly polar organic systems due to poor compatibility, significantly limiting its wide application in fields such as composite materials and coatings.

[0062] To overcome the dispersion and compatibility problems of cellulose nanocrystals, the present invention first quaternizes cellulose nanocrystals with 3-chloro-2-hydroxypropyl trimethyl ammonium chloride. By carrying out the reaction in an alkaline environment, the hydroxyl groups on the cellulose surface are deprotonated under the action of sodium hydroxide to form highly reactive nucleophiles, which then undergo a nucleophilic substitution reaction with 3-chloro-2-hydroxypropyl trimethyl ammonium chloride to introduce quaternary ammonium salt groups on the cellulose surface. This modification process significantly improves the hydrophilicity of cellulose nanocrystals, greatly enhancing their dispersion stability in aqueous systems and overcoming the agglomeration phenomenon. In addition, the positive charges introduced by the quaternary ammonium salt groups enhance the electrostatic interaction between the coating and the substrate surface, significantly improving the adhesion performance of the coating film. This modification also endows the material with certain antibacterial ability, enhancing the environmental stability of the coating film, enabling it to exhibit excellent performance in environments with higher requirements.

[0063] In further modification, the present invention modifies cellulose nanocrystals with glycidyl methacrylate. By means of the ring-opening reaction between the hydroxyl groups on the cellulose surface and the epoxy groups of glycidyl methacrylate, ester bonds containing double bonds are formed on the cellulose surface. 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 incorporated into the chemical cross-linking network of the coating matrix. The presence of double bonds significantly improves the mechanical strength of the coating film and endows it with higher wear resistance and durability, making the coatings modified with cellulose nanocrystals show excellent use effects in multifunctional and high-performance coating systems.

[0064] 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 amino groups, which enable it to strongly adhere to the surfaces of various materials, such as metal, glass, and polymer material surfaces, demonstrating excellent interfacial adhesion ability. In addition, the multifunctional modification potential of polydopamine makes it an ideal modified substrate, capable of meeting various application requirements. However, unmodified polydopamine also exposes some deficiencies during use, such as low tolerance in complex environments, limited chemical reaction activity, and lack of targeted design for specific functions. These problems significantly limit its practical application scope.

[0065] To overcome the above problems, the present invention chemically modifies polydopamine with 2-mercaptoethylamine hydrochloride, aiming to introduce active thiol groups and more amino groups simultaneously to enhance its chemical reaction activity and surface functionality. Specifically, the thiol group in 2-mercaptoethylamine hydrochloride reacts with the quinone group in the polydopamine molecule through a thiol-quinone addition reaction to generate thiol-containing modified polydopamine. The core advantage of this modification strategy is that the thiol group 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 group in 2-mercaptoethylamine hydrochloride can further react with the quinone group in the polydopamine molecule through an amino addition reaction, thereby introducing more amino groups on the surface of polydopamine. These newly introduced amino groups provide abundant chemical active sites for subsequent crosslinking reactions, enabling the modified polydopamine to form a stronger chemical network structure with other components containing carboxyl or epoxy groups (such as graphene oxide quantum dots), thus greatly enhancing the mechanical properties and stability of the coating.

[0066] To further enrich the functional characteristics of polydopamine, the present invention conducts a secondary modification on it with 4-carboxyphenylboronic acid to introduce boronic acid groups to enhance the denseness and adhesion of the coating. During this process, 4-carboxyphenylboronic acid undergoes an amidation reaction with the amino group in the polydopamine molecule through its carboxyl group to generate boronic acid group-containing modified polydopamine. The introduction of boronic acid groups endows the material with unique reversible borate ester bond characteristics, enabling it to combine with hydroxyl or carboxyl groups in the coating matrix to form a dynamic chemical crosslinking 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 comprehensively improves the performance of polydopamine and can better meet the application requirements of high-performance coatings.

[0067] This system uses water as the main medium and is combined with a small amount of solvents with low toxicity and easy removal to complete the necessary functional modification, minimizing the usage of organic solvents that are potentially harmful to the environment and the human body. During the post-treatment process, the solvent residues are further reduced through effective separation and drying processes, enabling the final coating to not only maintain excellent adhesion and other functionalities but also meet the environmental protection requirements of "low solvent" and even low VOC.

[0068] There is also a synergistic enhancement effect in the present invention: In terms of adhesion: The phosphate groups in the modified aqueous polyurethane dispersion can form stable coordination bonds with the surface of the metal substrate through chemical interactions. This coordination binding not only provides excellent chemical adhesion but also maintains a high binding strength under various environmental conditions, thus significantly enhancing the adhesion effect between the coating and the substrate. At the same time, the catechol groups of polydopamine play a key role in the system, further enhancing the adhesion performance of the coating through hydrogen bonding and chelation. This multi-point binding mechanism ensures the firm binding between the coating and the substrate, and excellent adhesion can be maintained even in high-humidity, high-salt, or other harsh environments.

[0069] In addition, the introduced borate groups in the double-modified polydopamine provide dynamic reversible binding characteristics. This reversible binding mechanism enables the coating to adapt to the possible minor deformations or stress concentrations on the substrate surface in a dynamic environment, thus showing higher stability and durability in terms of adhesion performance. Meanwhile, the amino groups in the amino-functionalized 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 intermolecular interactions within the coating but also optimizes the overall binding effect between the coating and the substrate.

[0070] 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 strengthening. Especially in high-dynamic and complex environments, this synergistic enhancement is particularly prominent.

[0071] In the design of the crosslinking network, the present invention constructs a stable and functionalized crosslinking structure through various reaction mechanisms. First, the thiol groups in the modified aqueous polyurethane dispersion can undergo Michael addition reactions with unsaturated groups to form stable chemical crosslinking points. These crosslinking points not only endow the coating with higher mechanical strength but also improve its heat resistance and aging resistance to a certain extent.

[0072] The thiol groups in the double-modified polydopamine can also participate in the construction of the crosslinking network and form a complex crosslinking structure in cooperation with other components. More importantly, its borate groups can undergo dynamic crosslinking with the hydroxyl groups on the surface of cellulose nanocrystals. These dynamic crosslinking points endow the coating with good flexibility and self-healing properties, enabling it to quickly recover and maintain high mechanical properties under external forces.

[0073] The role of graphene oxide quantum dots in the crosslinked network is that the abundant functional groups on their surface can serve as nanoscale crosslinking points, not only improving the density of the crosslinked network, but also effectively enhancing the overall mechanical properties and toughness of the coating. Through its excellent nano-reinforcement effect, graphene oxide quantum dots significantly optimize the stress transfer ability of the coating, making the coating exhibit a more uniform stress distribution under external loads.

[0074] The combined action of multiple crosslinking mechanisms not only constructs a highly stable chemical crosslinked network, but also comprehensively optimizes the coating in terms of mechanical properties, durability, and functional characteristics through dynamic crosslinking points and nano-reinforcement. This composite crosslinked structure ensures the reliable performance of the coating in various complex usage scenarios.

[0075] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0076] (1) Through the combined modification of phosphoric acid and 2-mercaptoethanol, on the basis of maintaining the original environmental protection characteristics of the aqueous polyurethane dispersion, the synergistic effect of the phosphate group and the thiol group significantly improves the hydrophilicity and adhesion of the coating.

[0077] (2) By oxidizing and aminating graphene oxide quantum dots, the dispersibility, activity, and compatibility of graphene oxide quantum dots are significantly improved, which is beneficial to their application in coatings.

[0078] (3) The two-step modification significantly improves the dispersibility, compatibility, and functionality of cellulose nanocrystals. Quaternization modification improves the application performance of the material in aqueous systems, and the introduction of double bonds enables cellulose nanocrystals to participate in free radical polymerization, thus improving the overall performance of the composite material.

[0079] (4) By using 2-mercaptoethylamine hydrochloride and 4-carboxyphenylboric acid to perform multi-level functionalization modification on polydopamine, not only significantly enhances its chemical reactivity and environmental tolerance, but also is beneficial to the adhesion, mechanical properties, and structural stability of the coating.

[0080] (5) By complementing chemical bonding and physical enhancement mechanisms, the present invention provides excellent adhesion performance for the coating; through the combined action of various chemical reactions and nano-reinforcement effects, a crosslinked structure with high strength, high flexibility, and high stability is constructed, improving the comprehensive performance of the coating. BRIEF DESCRIPTION OF THE DRAWINGS

[0081] Figure 1 It is a flow chart of the preparation method of the high-adhesion and low-solvent coating provided in Example 1 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0082] 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.

[0083] 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 or treated.

[0084] Example 1

[0085] As Figure 1 shown, this example provides a high-adhesion low-solvent coating and a preparation method thereof. The preparation method specifically includes the following steps:

[0086] S1: Mix an aqueous polyurethane dispersion with phosphoric acid to obtain reaction solution A, where the feeding amount of phosphoric acid accounts for 12% of the mass of the aqueous polyurethane dispersion. Mechanically stir at a constant temperature of 58 °C for 3 h. After the reaction, adjust the pH to 7.8 with 23% ammonia water, and obtain a phosphorylated aqueous polyurethane dispersion after dialysis; Mix the phosphorylated aqueous polyurethane dispersion with 2-mercaptoethanol and triethylamine to obtain reaction solution B, where the feeding amount of 2-mercaptoethanol accounts for 10% of the mass of the phosphorylated aqueous polyurethane dispersion, and the feeding amount of triethylamine accounts for 4% of the mass of 2-mercaptoethanol. Stir and react at 44 °C for 2.6 h, and obtain a modified aqueous polyurethane dispersion after dialysis;

[0087] S2: Mix graphene quantum dots with a 12% hydrogen peroxide solution to obtain reaction solution C, where the mass fraction of graphene quantum dots in the hydrogen peroxide solution is 8 wt.%. After stirring at a constant temperature of 66 °C for 3 h, centrifuge, wash, and dry to obtain oxidized graphene quantum dots; Disperse the oxidized graphene quantum dots in water at a mass fraction of 3 wt.%, add 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride with a feeding amount of 50% of the mass of the oxidized graphene quantum dots and N-hydroxysuccinimide with a mass ratio of 1:1 to 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride to obtain reaction solution D. After stirring at room temperature for 35 min, add ethylenediamine with a mass ratio of 5:1 to the oxidized graphene quantum dots and continue to stir and react for 10 h. After dialysis, freeze-dry to obtain amino-functionalized oxidized graphene quantum dots;

[0088] S3: Prepare a cellulose nanocrystal dispersion with a mass fraction of 14 wt.%, add 3-chloro-2-hydroxypropyltrimethylammonium chloride with a mass ratio of 1:1 to the cellulose nanocrystals, stir and then dropwise add a sodium hydroxide solution with a mass fraction of 27 wt.% to obtain reaction solution E, where the volume-mass ratio of sodium hydroxide to cellulose nanocrystals is 2.3:1. React at 62 °C for 4.6 h, then dialyze and freeze-dry to obtain quaternized cellulose nanocrystals; Disperse the quaternized cellulose nanocrystals in absolute ethanol to obtain a quaternized cellulose nanocrystal dispersion with a mass fraction of 18 wt.%, add glycidyl methacrylate with a mass ratio of 3.4:10 to the quaternized cellulose nanocrystals and tetrabutylammonium bromide with a mass ratio of 1.8:10 to the quaternized cellulose nanocrystals to obtain reaction solution F. React at a constant temperature of 40 °C for 6 h, then precipitate, centrifuge, wash, and vacuum dry to obtain modified cellulose nanocrystals;

[0089] S4: Disperse polydopamine in a phosphate buffer solution with a pH of 8.7 at a mass fraction of 2.3 wt.%, add 2-mercaptoethylamine hydrochloride with a mass ratio of 3.4:10 to the polydopamine, stir at room temperature and then dialyze to obtain thiolated polydopamine; Disperse the thiolated polydopamine in water at a mass fraction of 2.6 wt.%, add 4-carboxyphenylboronic acid with a feed amount of 45% of the mass of the thiolated polydopamine, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride with a mass ratio of 1:1 to the 4-carboxyphenylboronic acid, and N-hydroxysuccinimide with a mass ratio of 0.5:1 to the 4-carboxyphenylboronic acid. Stir and react at room temperature, dialyze, and freeze-dry to obtain double-modified polydopamine;

[0090] S5: Using 75 g of modified aqueous polyurethane dispersion as the matrix, sequentially add 0.5 g of amino-functionalized graphene oxide quantum dots, 5 g of modified cellulose nanocrystals, 1 g of double-modified polydopamine, and 18.5 g of deionized water. Stir, ultrasonically disperse, and then vacuum degas to obtain the high-adhesion low-solvent coating.

[0091] Example 2

[0092] This example provides a high-adhesion low-solvent coating and its preparation method. The preparation method specifically includes the following steps:

[0093] S1: Mix the aqueous polyurethane dispersion with phosphoric acid to obtain reaction solution A, where the feeding amount of phosphoric acid accounts for 15% of the mass of the aqueous polyurethane dispersion. Mechanically stir at a constant temperature of 55 °C for 3.5 h. After the reaction, adjust the pH to 8 with 20% ammonia water by mass, and obtain the phosphorylated aqueous polyurethane dispersion after dialysis; Mix the phosphorylated aqueous polyurethane dispersion with 2-mercaptoethanol and triethylamine to obtain reaction solution B, where the feeding amount of 2-mercaptoethanol accounts for 12% of the mass of the phosphorylated aqueous polyurethane dispersion, and the feeding amount of triethylamine accounts for 5% of the mass of 2-mercaptoethanol. Stir and react at 40 °C for 3 h, and obtain the modified aqueous polyurethane dispersion after dialysis;

[0094] S2: Mix graphene quantum dots with a 10% hydrogen peroxide solution to obtain reaction solution C, where the mass fraction of graphene quantum dots in the hydrogen peroxide solution is 10 wt.%. Stir at a constant temperature of 60 °C for 2.3 h, then centrifuge, wash, and dry to obtain oxidized graphene quantum dots; Disperse the oxidized graphene quantum dots in water at a mass fraction of 4 wt.%, add 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride with a feeding amount of 55% of the mass of the oxidized graphene quantum dots and N-hydroxysuccinimide with a mass ratio of 1:1.5 to 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride to obtain reaction solution D. Stir at room temperature for 37 min, then add ethylenediamine with a mass ratio of 10:1 to the oxidized graphene quantum dots and continue to stir and react for 11 h. After dialysis, freeze-dry to obtain amino-functionalized oxidized graphene quantum dots;

[0095] S3: Prepare a cellulose nanocrystal dispersion with a mass fraction of 10 wt.%, add 3-chloro-2-hydroxypropyltrimethylammonium chloride with a mass ratio of 1:2 to the cellulose nanocrystals, stir, and then dropwise add a 30 wt.% sodium hydroxide solution to obtain reaction solution E, where the volume-mass ratio of sodium hydroxide to cellulose nanocrystals is 2:1. React at 65 °C for 5 h, then dialyze and freeze-dry to obtain quaternized cellulose nanocrystals; Disperse the quaternized cellulose nanocrystals in absolute ethanol to obtain a quaternized cellulose nanocrystal dispersion with a mass fraction of 20 wt.%, add glycidyl methacrylate with a mass ratio of 3:10 to the quaternized cellulose nanocrystals and tetrabutylammonium bromide with a mass ratio of 1.6:10 to the quaternized cellulose nanocrystals to obtain reaction solution F. React at a constant temperature of 45 °C for 5.6 h, then precipitate, centrifuge, wash, and vacuum-dry to obtain modified cellulose nanocrystals;

[0096] S4: Disperse polydopamine at a mass fraction of 3 wt.% in a phosphate buffer solution with a pH of 9, add 2-mercaptoethylamine hydrochloride with a mass ratio to polydopamine of 4:10, stir at room temperature and then dialyze to obtain thiolated polydopamine; Disperse the thiolated polydopamine at a mass fraction of 3 wt.% in water, add 4-carboxyphenylboronic acid with a dosage of 50% of the mass of the thiolated polydopamine, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride with a mass ratio to 4-carboxyphenylboronic acid of 1.2:1, and N-hydroxysuccinimide with a mass ratio to 4-carboxyphenylboronic acid of 0.56:1, stir and react at room temperature, dialyze, and freeze-dry to obtain doubly modified polydopamine;

[0097] S5: Using 80 g of modified aqueous polyurethane dispersion as the matrix, sequentially add 0.8 g of amino-functionalized graphene quantum dots, 2 g of modified cellulose nanocrystals, 2 g of doubly modified polydopamine, and 15.2 g of deionized water, stir, ultrasonically disperse, and then degas under vacuum to obtain the high-adhesion low-solvent coating.

[0098] Example 3

[0099] This example provides a high-adhesion low-solvent coating and its preparation method. The preparation method specifically includes the following steps:

[0100] S1: Mix the aqueous polyurethane dispersion with phosphoric acid to obtain reaction solution A, where the dosage of phosphoric acid accounts for 10% of the mass of the aqueous polyurethane dispersion, mechanically stir at a constant temperature of 50 °C for 3.7 h, after the reaction, adjust the pH to 7 with 25% ammonia water, and dialyze to obtain phosphorylated aqueous polyurethane dispersion; Mix the phosphorylated aqueous polyurethane dispersion with 2-mercaptoethanol and triethylamine to obtain reaction solution B, where the dosage of 2-mercaptoethanol accounts for 8% of the mass of the phosphorylated aqueous polyurethane dispersion and the dosage of triethylamine accounts for 7% of the mass of 2-mercaptoethanol, stir and react at 50 °C for 2.5 h, and dialyze to obtain modified aqueous polyurethane dispersion;

[0101] S2: Mix graphene quantum dots with a 14% hydrogen peroxide solution to obtain reaction solution C, where the mass fraction of graphene quantum dots in the hydrogen peroxide solution is 5 wt.%, stir at a constant temperature of 70 °C for 2.8 h, then centrifuge, wash, and dry to obtain graphene oxide quantum dots; Disperse the graphene oxide quantum dots at a mass fraction of 5 wt.% in water, add 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride with a dosage of 58% of the mass of the graphene oxide quantum dots and N-hydroxysuccinimide with a mass ratio to 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride of 1:1.7 to obtain reaction solution D, stir at room temperature for 40 min, then add ethylenediamine with a mass ratio to the graphene oxide quantum dots of 8:1 and continue to stir and react for 12 h, dialyze, and freeze-dry to obtain amino-functionalized graphene quantum dots;

[0102] S3: Prepare a cellulose nanocrystal dispersion with a mass fraction of 20 wt.%, add 3-chloro-2-hydroxypropyltrimethylammonium chloride with a mass ratio of 1:1.5 to the cellulose nanocrystals, stir and then dropwise add a sodium hydroxide solution with a mass fraction of 20 wt.% to obtain reaction solution E, where the volume-mass ratio of sodium hydroxide to cellulose nanocrystals is 3:1. React at 63 °C for 4.8 h, then dialyze and freeze-dry to obtain quaternized cellulose nanocrystals; Disperse the quaternized cellulose nanocrystals in absolute ethanol to obtain a quaternized cellulose nanocrystal dispersion with a mass fraction of 15 wt.%, add glycidyl methacrylate with a mass ratio of 3.8:10 to the quaternized cellulose nanocrystals and tetrabutylammonium bromide with a mass ratio of 1:10 to the quaternized cellulose nanocrystals to obtain reaction solution F. React at a constant temperature of 48 °C for 5.8 h, then precipitate, centrifuge, wash, and vacuum-dry to obtain modified cellulose nanocrystals;

[0103] S4: Disperse polydopamine at a mass fraction of 2 wt.% in a phosphate buffer solution with a pH of 8, add 2-mercaptoethylamine hydrochloride with a mass ratio of 3.7:10 to the polydopamine, stir at room temperature and then dialyze to obtain thiolated polydopamine; Disperse the thiolated polydopamine at a mass fraction of 2 wt.% in water, add 4-carboxyphenylboronic acid with a feed amount of 47% of the mass of the thiolated polydopamine, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride with a mass ratio of 1.4:1 to the 4-carboxyphenylboronic acid, and N-hydroxysuccinimide with a mass ratio of 0.57:1 to the 4-carboxyphenylboronic acid. Stir and react at room temperature, dialyze, and freeze-dry to obtain double-modified polydopamine;

[0104] S5: Using 82 g of modified aqueous polyurethane dispersion as the matrix, sequentially add 0.7 g of amino-functionalized graphene oxide quantum dots, 4 g of modified cellulose nanocrystals, 0.5 g of double-modified polydopamine, and 12.8 g of deionized water. Stir, ultrasonically disperse, and then vacuum degas to obtain the high-adhesion low-solvent coating.

[0105] Example 4

[0106] This example provides a high-adhesion low-solvent coating and its preparation method. The preparation method specifically includes the following steps:

[0107] S1: Mix the aqueous polyurethane dispersion with phosphoric acid to obtain reaction solution A, where the feeding amount of phosphoric acid accounts for 14% of the mass of the aqueous polyurethane dispersion. Mechanically stir for 4 h at a constant temperature of 60 °C. After the reaction, adjust the pH to 7.5 with 22% ammonia water by mass, and obtain the phosphorylated aqueous polyurethane dispersion after dialysis. Mix the phosphorylated aqueous polyurethane dispersion with 2-mercaptoethanol and triethylamine to obtain reaction solution B, where the feeding amount of 2-mercaptoethanol accounts for 11% of the mass of the phosphorylated aqueous polyurethane dispersion, and the feeding amount of triethylamine accounts for 8% of the mass of 2-mercaptoethanol. Stir and react at 47 °C for 2 h, and obtain the modified aqueous polyurethane dispersion after dialysis.

[0108] S2: Mix graphene quantum dots with a 15% hydrogen peroxide solution to obtain reaction solution C, where the mass fraction of graphene quantum dots in the hydrogen peroxide solution is 7 wt.%. After stirring at a constant temperature of 68 °C for 2 h, centrifuge, wash, and dry to obtain oxidized graphene quantum dots. Disperse the oxidized graphene quantum dots in water at a mass fraction of 2 wt.%, add 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride with a feeding amount of 60% of the mass of the oxidized graphene quantum dots and N-hydroxysuccinimide with a mass ratio of 1:2 to 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride to obtain reaction solution D. After stirring at room temperature for 30 min, add ethylenediamine with a mass ratio of 7:1 to the oxidized graphene quantum dots and continue to stir and react for 11.4 h. After dialysis, freeze-dry to obtain amino-functionalized oxidized graphene quantum dots.

[0109] S3: Prepare a cellulose nanocrystal dispersion with a mass fraction of 18 wt.%, add 3-chloro-2-hydroxypropyltrimethylammonium chloride with a mass ratio of 1:1.8 to the cellulose nanocrystals, stir, and then dropwise add a 25 wt.% sodium hydroxide solution to obtain reaction solution E, where the volume-mass ratio of sodium hydroxide to cellulose nanocrystals is 2.7:1. React at 60 °C for 4 h, then dialyze and freeze-dry to obtain quaternized cellulose nanocrystals. Disperse the quaternized cellulose nanocrystals in absolute ethanol to obtain a 10 wt.% quaternized cellulose nanocrystal dispersion, add glycidyl methacrylate with a mass ratio of 4:10 to the quaternized cellulose nanocrystals and tetrabutylammonium bromide with a mass ratio of 2:10 to the quaternized cellulose nanocrystals to obtain reaction solution F. React at a constant temperature of 50 °C for 5 h, then precipitate, centrifuge, wash, and vacuum-dry to obtain modified cellulose nanocrystals.

[0110] S4: Disperse polydopamine at a mass fraction of 2.7 wt.% in a phosphate buffer solution with a pH of 8.4, add 2-mercaptoethylamine hydrochloride with a mass ratio of 3:10 to polydopamine, stir at room temperature and dialyze to obtain thiolated polydopamine; Disperse the thiolated polydopamine at a mass fraction of 2.8 wt.% in water, add 4-carboxyphenylboronic acid with a feeding amount of 40% of the mass of the thiolated polydopamine, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride with a mass ratio of 1.5:1 to 4-carboxyphenylboronic acid, and N-hydroxysuccinimide with a mass ratio of 0.6:1 to 4-carboxyphenylboronic acid, stir and react at room temperature, dialyze, and freeze-dry to obtain doubly modified polydopamine;

[0111] S5: Using 85 g of modified aqueous polyurethane dispersion as the matrix, sequentially add 1 g of amino-functionalized graphene oxide quantum dots, 1 g of modified cellulose nanocrystals, 1.5 g of doubly modified polydopamine, and 11.5 g of deionized water, stir, ultrasonically disperse, and then degas under vacuum to obtain the high-adhesion low-solvent coating.

[0112] Comparative Example 1

[0113] This comparative example provides a high-adhesion low-solvent coating and its preparation method. The difference from Example 1 is that in step S1, the feeding amount of phosphoric acid accounts for 20% of the mass of the aqueous polyurethane dispersion, and the other operation steps and process parameters are exactly the same as those in Example 1.

[0114] Comparative Example 2

[0115] This comparative example provides a high-adhesion low-solvent coating and its preparation method. The difference from Example 1 is that in step S1, the feeding amount of phosphoric acid accounts for 5% of the mass of the aqueous polyurethane dispersion, and the other operation steps and process parameters are exactly the same as those in Example 1.

[0116] Comparative Example 3

[0117] This comparative example provides a high-adhesion low-solvent coating and its preparation method. The difference from Example 1 is that in step S3, the mass ratio of glycidyl methacrylate to quaternized cellulose nanocrystals is 7:10, and the other operation steps and process parameters are exactly the same as those in Example 1.

[0118] Comparative Example 4

[0119] This comparative example provides a high-adhesion low-solvent coating and its preparation method. The difference from Example 1 is that in step S3, the mass ratio of glycidyl methacrylate to quaternized cellulose nanocrystals is 1:10, and the other operation steps and process parameters are exactly the same as those in Example 1.

[0120] The performance of the high-adhesion low-solvent coatings in the above Examples 1-4 and Comparative Examples 1-4 was tested, and the specific process is as follows:

[0121] The adhesion of the test samples was tested according to GB / T 9286-2021;

[0122] The hardness of the test samples was tested according to GB / T 6739-2022;

[0123] The water resistance of the test samples was tested according to GB / T 1733-1993;

[0124] The test results are shown in Table 1.

[0125] Table 1: Performance test results of the high-adhesion low-solvent coatings in Examples 1-4 and Comparative Examples 1-4

[0126]

[0127] From the test results of Example 1 and Comparative Examples 1 and 2, it can be seen that during the modification of the aqueous polyurethane dispersion, when the feeding amount of phosphoric acid is too much, the interaction between phosphoric acid groups or the interaction with the solvent may lead to enhanced attraction between particles, thereby reducing the stability of the dispersion, causing agglomeration and sedimentation, and the adhesion, water resistance and hardness of the coating decrease. In addition, the competition of excessive phosphoric acid groups with hard segment hydrogen bonds may weaken the microphase separation and reduce the water resistance of the coating; when the feeding amount of phosphoric acid is too little, the number of introduced phosphoric acid groups is insufficient, resulting in insufficient modification of the aqueous polyurethane dispersion, limited improvement in the adhesion of the coating, and insufficient binding force with the substrate.

[0128] From the test results of Example 1 and Comparative Examples 3 and 4, it can be seen that introducing too much glycidyl methacrylate during the modification of cellulose nanocrystals will result in too many introduced epoxy groups, excessive epoxy groups on the surface of cellulose nanocrystals, reduced hydrophilicity after reaction with hydroxyl groups, and at the same time triggering self-crosslinking, resulting in a decrease in the dispersibility of cellulose nanocrystals. This reduction in dispersibility and the increase in crosslinking density will make the hardness of the coating too high but the flexibility insufficient, and it is easy to crack under the action of 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 cellulose nanocrystals decreases, the lack of active groups leads to insufficient chemical crosslinking points, and the interfacial binding force weakens, ultimately resulting in a decrease in the water resistance and adhesion of the coating.

[0129] The above are only the 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 the disclosure scope of the present invention.

Claims

1. A preparation method of a high-adhesion and low-solvent coating, characterized in that The preparation method includes: S1: Mix an aqueous polyurethane dispersion with phosphoric acid to obtain reaction solution A. The feeding amount of phosphoric acid accounts for 10-15% of the mass of the aqueous polyurethane dispersion. Mechanically stir at a constant temperature. After the reaction, adjust the pH with ammonia water, and obtain a phosphorylated aqueous polyurethane dispersion after dialysis; Mix the phosphorylated aqueous polyurethane dispersion with 2-mercaptoethanol and triethylamine to obtain reaction solution B. Stir and react, and obtain a modified aqueous polyurethane dispersion after dialysis; S2: Mix graphene quantum dots with a hydrogen peroxide solution to obtain reaction solution C. After stirring at a constant temperature, centrifuge, wash, and dry to obtain oxidized graphene quantum dots; Disperse the oxidized graphene quantum dots in water, add 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide to obtain reaction solution D. Stir at room temperature, then add ethylenediamine and continue to stir and react. After dialysis, freeze-dry to obtain amino-functionalized oxidized graphene quantum dots; S3: Prepare a cellulose nanocrystal dispersion, add 3-chloro-2-hydroxypropyltrimethylammonium chloride, stir, and then dropwise add a sodium hydroxide solution to obtain reaction solution E. After the reaction, dialyze and freeze-dry to obtain quaternized cellulose nanocrystals; Disperse the quaternized cellulose nanocrystals in anhydrous ethanol to obtain a quaternized cellulose nanocrystal dispersion, add glycidyl methacrylate and tetrabutylammonium bromide to obtain reaction solution F. The mass ratio of glycidyl methacrylate to quaternized cellulose nanocrystals is 3-4:

10. After reacting at a constant temperature, precipitate, centrifuge, wash, and vacuum-dry to obtain modified cellulose nanocrystals; S4: Disperse polydopamine in a phosphate buffer solution, add 2-mercaptoethylamine hydrochloride, stir at room temperature and dialyze to obtain mercapto-functionalized polydopamine; Disperse the mercapto-functionalized polydopamine in water, add 4-carboxyphenylboronic acid, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide, stir and react at room temperature, dialyze, and freeze-dry to obtain doubly modified polydopamine; S5: Using the modified aqueous polyurethane dispersion as the matrix, sequentially add amino-functionalized oxidized graphene quantum dots, modified cellulose nanocrystals, doubly modified polydopamine and deionized water, stir, ultrasonically disperse, and then vacuum degas to obtain the high-adhesion low-solvent coating.

2. The preparation method of a high-adhesion and low-solvent coating according to claim 1, characterized in that, In S1: The feeding amount of the 2-mercaptoethanol accounts for 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 the 2-mercaptoethanol.

3. The preparation method of a high-adhesion and 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.%.

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

1.

5. The preparation method of a high-adhesion and 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.

6. The preparation method of a high-adhesion and low-solvent coating according to claim 1, characterized in that, In S3: The mass ratio of the tetrabutylammonium bromide to the quaternized cellulose nanocrystals is 1-2:

10.

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

10.

8. The preparation method of a high-adhesion and 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 mercapto-functionalized polydopamine; The mass ratio of the 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride to the 4-carboxyphenylboronic acid is 1-1.5:1; The mass ratio of the N-hydroxysuccinimide to the 4-carboxyphenylboronic acid is 0.5-0.6:

1.

9. A high-adhesion low-solvent coating prepared by the preparation method according to any one of claims 1-8, characterized in that, The mass ratio of each component of the high-adhesion low-solvent coating is as follows: modified aqueous polyurethane dispersion: amino-functionalized 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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