A waterborne acrylic polyurethane paint and a preparation method thereof

Abstract

The application discloses a kind of water-based acrylic polyurethane paint and preparation method thereof, belong to water-based paint preparation technical field, the water-based acrylic polyurethane paint includes A component and B component, the A component includes modified hydroxyl acrylic resin aqueous dispersion, auxiliary agent and deionized water, the B component includes aliphatic isocyanate and solvent B.The methyl methacrylate monomer of the application is functionally modified, and the histidinol containing imidazole group and hydroxymethyl is connected into the methyl methacrylate structure containing carbon-carbon double bond through amide bond, to form new functional monomer;The monomer is copolymerized into the main chain of acrylic resin by double bond, so that the modified resin side chain has imidazole group, hydroxymethyl group.Relying on weak base catalysis and metal coordination effect of imidazole group, the adhesion and crosslinking density of paint film can be improved, and it is suitable for the protection and decoration of various metal, non-metal substrate.

Description

Technical Field

[0001] This invention relates to the field of water-based paint preparation technology, specifically to a water-based acrylic polyurethane paint and its preparation method. Background Technology

[0002] Solvent-based coatings, due to their high emissions of volatile organic compounds (VOCs) and significant pollution, are facing increasingly limited application scenarios. Waterborne coatings, with their advantages of being environmentally friendly, low in toxicity, safe to apply, and convenient to store and transport, have become the core development direction in the field of industrial protective and decorative coatings. Waterborne polyurethane coatings, using water as the dispersion medium, are non-toxic, odorless, environmentally friendly, and safe, and are gradually replacing traditional solvent-based coatings. Among them, waterborne two-component polyurethane coatings consist of a hydroxyl-containing waterborne polyol component and an isocyanate-containing curing agent component. During application, the two components are mixed, and a coating film with high cross-linking density is formed through the cross-linking reaction of hydroxyl groups and isocyanates. Its performance is comparable to that of solvent-based polyurethane coatings, and it has been widely used in automotive, wood, plastic, and metal protection fields.

[0003] Chinese Patent CN113308180B discloses a two-component waterborne hydroxyl acrylic polyurethane topcoat emulsion and its preparation method. The emulsion comprises 1-2% emulsifier, 45-50% water, 7-12% hydroxy acrylate monomer, 10-20% styrene, 20-28% acrylate monomer, 0.3-1.5% vinylsiloxane, 0.1-1% chain transfer agent, and 0.1-1% initiator. It is prepared by seed emulsion and semi-continuous dropwise addition polymerization. The product can improve the gloss of waterborne topcoat emulsion and reduce production costs. Chinese patent CN118725714B discloses a water-based two-component polyurethane clear varnish and its preparation process, comprising component A and component B. Component A includes the following raw materials by weight: 85-110 parts of water-based polyurethane dispersion, 40-45 parts of modified acrylic dispersion, 10-25 parts of modified silica, 30-40 parts of modified titanium dioxide, 4-6 parts of dispersant, 0.5-2 parts of defoamer, 0.5-2 parts of leveling agent, and 10-20 parts of water. Component B is a polyisocyanate curing agent. In this scheme, the modified acrylic dispersion gives the coating film excellent physical properties such as hardness and gloss, the modified silica can improve the hardness and wear resistance of the coating film, and the modified titanium dioxide improves the thermal stability and flame retardant properties of the material. However, none of the above schemes mention the design of functional monomers, nor do they involve the design of achieving adhesion to metal substrates by introducing specific functional groups. Summary of the Invention

[0004] The purpose of this invention is to provide a waterborne acrylic polyurethane paint and its preparation method. A modified functional monomer is prepared by introducing histidine containing hydroxymethyl and imidazole groups into the structure of methacrylic acid containing polymerizable carbon-carbon double bonds via amide bonds. This monomer is then polymerized with methyl methacrylate, butyl acrylate, and methacrylic acid under the action of an initiator to form a modified hydroxy acrylic resin. The side chain groups of this resin include ester groups, hydroxymethyl groups, imidazole groups, and carboxyl groups. Specifically, the hydroxymethyl group can undergo a crosslinking reaction with the aliphatic isocyanate in component B to form a polyurethane crosslinking network; the imidazole group can form coordination bonds with the metal substrate, effectively improving the adhesion of the paint film to the substrate; and the carboxyl group can maintain the stable dispersibility of the modified hydroxy acrylic resin in the aqueous phase, ensuring the stability of the paint during storage and application.

[0005] To achieve the above objectives, in a first aspect, the present invention provides a waterborne acrylic polyurethane paint, wherein the waterborne acrylic polyurethane paint comprises component A and component B; the mass ratio of component A to component B is 100:(18~25).

[0006] Furthermore, component A comprises a modified hydroxyl acrylic resin aqueous dispersion, an additive, and deionized water, wherein the hydroxyl value of the modified hydroxyl acrylic resin aqueous dispersion is 25~40 mgKOH / g.

[0007] Furthermore, the modified hydroxyl acrylic resin aqueous dispersion is obtained by double bond polymerization of modified functional monomers, methyl methacrylate, butyl acrylate and methacrylic acid under the action of an initiator, followed by neutralization, phase inversion and self-emulsification.

[0008] Furthermore, the modified functional monomer contains carbon-carbon double bonds, imidazole groups, and hydroxymethyl groups.

[0009] Furthermore, component B is a water-dispersible hexamethylene diisocyanate polyisocyanate; the NCO content of the water-dispersible hexamethylene diisocyanate polyisocyanate is 19 wt.%~22 wt.%.

[0010] Furthermore, the molar ratio of isocyanate groups (NCO) in component B to hydroxyl groups (OH) in component A is 1.2 to 1.5.

[0011] Further, in component A, the mass ratio of the modified hydroxyl acrylic resin aqueous dispersion, the additives, and deionized water is (70~80):(3~7):(13~27); the additives include nonionic dispersants, nonionic defoamers, nonionic leveling agents, film-forming aids, and pH adjusters; the mass ratio of the nonionic dispersants, nonionic defoamers, nonionic leveling agents, film-forming aids, and pH adjusters is (4~10):(1~3):4:(20~50):(1~3); the solid content of the modified hydroxyl acrylic resin aqueous dispersion is 38%~42%.

[0012] A second aspect of this invention provides a method for preparing a waterborne acrylic polyurethane paint, comprising the following steps: S1. Mix the additive with deionized water, filter, and obtain the additive pre-prepared solution; S2. Add the pre-mixed additive solution to the modified hydroxyl acrylic resin aqueous dispersion, stir, filter, and obtain component A; S3. Before use, stir components A and B in the dark and let stand to obtain water-based acrylic polyurethane paint.

[0013] Furthermore, in step S1, the mixing speed is 200~400 rpm, the mixing time is 8~12 min, and the sieve mesh size for filtration is 150~200 mesh.

[0014] Furthermore, in step S2, the stirring speed is 800~1200 rpm, the stirring time is 15~30 min, and the sieve mesh size for filtration is 150~200 mesh.

[0015] Furthermore, in step S3, the stirring speed in the dark is 200~400 rpm, the stirring time in the dark is 5~10 min, and the settling time is 10~20 min.

[0016] Thirdly, the present invention provides a process for preparing a modified hydroxyl acrylic resin aqueous dispersion, comprising the following steps: A1. Methacrylic acid and a polymerization inhibitor are dispersed in anhydrous N,N-dimethylformamide (DMF), N-hydroxysuccinimide (NHS) is added, the mixture is stirred, and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC·HCl) is added in an ice bath. The mixture is reacted in an ice bath to obtain an activated methacrylic acid solution. A2. Histidine is dispersed in anhydrous DMF to obtain a histidine solution; A3. Histidine solution was added dropwise to methacrylic acid activation solution, reacted in an ice bath, the reaction was quenched, and purified to obtain the modified functional monomer. A4. Under nitrogen protection, the modified functional monomer, methyl methacrylate, butyl acrylate, methacrylic acid and initiator are dissolved in anhydrous propylene glycol methyl ether acetate to carry out the polymerization reaction. The mixture is then cooled and distilled under reduced pressure to obtain a modified hydroxyl acrylic resin solution. A5. Adjust the pH of the modified hydroxyl acrylic resin solution to 7.1~7.5 with triethylamine, stir, add deionized water dropwise to homogenize, mix, filter, and obtain the modified hydroxyl acrylic resin aqueous dispersion.

[0017] Further, in A1, the mass-to-volume ratio of methacrylic acid, polymerization inhibitor, NHS, EDC·HCl, and anhydrous DMF is (0.8~0.9) g : (0.0004~0.00045) g : 1.4 g : 2.1 g : 30 mL; the polymerization inhibitor is either hydroquinone monomethyl ether or phenothiazine; the stirring speed is 100~200 rpm, and the stirring time is 10~20 min; the ice bath reaction speed is 200~300 rpm, and the ice bath reaction time is 30~60 min.

[0018] Furthermore, in A2, the mass-to-volume ratio of histidine to anhydrous DMF is 1 g: (20~30) mL.

[0019] Histidine contains a hydroxymethyl group, an imidazole ring, and an amino group. Under the influence of EDC (electrodeionization), the amino group reacts with the carboxyl group in methacrylic acid to form an amide bond, which then connects the hydroxymethyl group and the imidazole ring to the methacrylic acid structure. The nitrogen atom in the imidazole group contains a lone pair of electrons, which can form coordinate bonds with empty orbitals on the metal surface, enhancing the interfacial adhesion between the paint film and the substrate and improving the coating's adhesion performance. Simultaneously, the crosslinking reaction of the hydroxymethyl group with the aliphatic isocyanate forms a polyurethane network, giving the paint film a moderate crosslinking density, balancing the coating's hardness and flexibility.

[0020] Further, in A3, the dropping rate of the histidine solution is 0.3~0.5 mL / min; the volume ratio of the histidine solution to the methacrylic acid activating solution is (20~30):30; the rotation speed of the ice bath reaction is 200~300 rpm, and the ice bath reaction time is 2~3 h.

[0021] Further, in A3, the quenching reaction process is as follows: after the ice bath reaction is completed, a 10% acetic acid aqueous solution is added dropwise to the reaction solution to adjust the pH of the system to 5.5~6.0, and the mixture is stirred at 100 rpm for 5 min to obtain reaction solution 1.

[0022] Further, in A3, the purification process is as follows: Add an equal volume of ethyl acetate to reaction solution 1, stir evenly, allow to stand and separate into layers, collect the organic phase, add an equal volume of acetic acid to the aqueous phase to inhibit extraction twice, combine the organic phases, wash the organic phases sequentially with deionized water and saturated brine, add anhydrous sodium sulfate to dry, and filter; remove the solvent from the filtrate by vacuum distillation.

[0023] Further, in A4, the mass-to-volume ratio of the modified functional monomer, methyl methacrylate, butyl acrylate, methacrylic acid, initiator, and anhydrous propylene glycol methyl ether acetate is (15~30) g : (35~50) g ​​: (25~35) g : 3 g : (0.8~1.5) g : (100~150) mL; the initiator is either azobisisobutyronitrile or benzoyl peroxide; the polymerization method is semi-continuous solution polymerization, the polymerization temperature is 80~90℃, the polymerization speed is 200~300 rpm, and the total polymerization time is 4~6 h; the final cooling temperature is 60~65℃; the vacuum degree of the vacuum distillation is -0.085~-0.098 MPa, the vacuum distillation temperature is 65~70℃, and the vacuum distillation is carried out until the solid content of the system is 75~80%.

[0024] Further, in A4, the specific operation of the semi-continuous solution polymerization method is as follows: First, add 1 / 3 mass of monomer, 1 / 4 mass of initiator, and 1 / 2 volume of anhydrous propylene glycol methyl ether acetate. After heating to 80~90℃, stir at 200~300 rpm for 15 min. Then, maintain stirring and add 2 / 3 mass of monomer and 1 / 2 mass of initiator dropwise over 3 h. Finally, add 1 / 2 volume of anhydrous propylene glycol methyl ether acetate and 1 / 4 mass of initiator. Stir at 200~300 rpm until the total polymerization time is 4~6 h. The monomer includes modified functional monomers, methyl methacrylate, butyl acrylate, and methacrylic acid.

[0025] Further, in A5, the stirring speed is 200-300 rpm, and the stirring time is 8-15 min; the homogenization speed is 800-1200 rpm; the rate of adding deionized water is 5-10 mL / min; the mixing speed is 1500-2000 rpm, and the mixing time is 20-30 min; the sieve mesh size for filtration is 150-200 mesh.

[0026] The modified hydroxyl acrylic resin side chain contains carboxyl groups provided by methacrylic acid resin, which are converted into carboxylates under the action of triethylamine, thus maintaining the water dispersibility of the system.

[0027] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: This invention provides a waterborne acrylic polyurethane paint and its preparation method. This waterborne paint can be sprayed onto the surfaces of metal objects such as steel and iron, exhibiting excellent adhesion. This invention introduces histidine containing imidazole and hydroxymethyl groups into the structure of methacrylic acid via amide bonds, preparing a modified functional monomer containing imidazole and hydroxymethyl groups. This monomer is then copolymerized with methyl methacrylate, butyl acrylate, and methacrylic acid, allowing the imidazole and hydroxymethyl groups to be distributed as side groups on the acrylic resin backbone. The hydroxymethyl group can react with NCO in component B to form a polyurethane crosslinking network, providing crosslinking density to the paint film; the imidazole group can form coordination with the metal substrate, helping to enhance the adhesion of the paint film. Furthermore, the reversible reaction characteristics of the imidazole group with isocyanate help to regulate the pot life and curing rate of the system. Compared with physically adding imidazole catalysts or post-grafting modification, this copolymerization method allows the functional groups to be bound to the polymer chain, avoiding the migration and precipitation of small molecule additives during film formation. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of a process for preparing an aqueous dispersion of modified hydroxyl acrylic resin. Detailed Implementation

[0029] The technical solution of the present invention will be described in detail below through specific embodiments. It should be understood that the embodiments of the present invention and the specific features in the embodiments are detailed descriptions of the technical solution of the present invention, rather than limitations on the technical solution of the present invention. In the absence of conflict, the embodiments of the present invention and the technical features in the embodiments can be combined with each other.

[0030] The term "and / or" simply describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. Additionally, the character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0031] The chemical reagents used in the embodiments and comparative examples of this invention are all commercially available products and have not undergone further purification or processing.

[0032] Example 1 like Figure 1 As shown, the preparation process of a modified hydroxyl acrylic resin aqueous dispersion includes the following steps: A1. Methacrylic acid and hydroquinone monomethyl ether were dispersed in anhydrous DMF, NHS was added, and the mixture was stirred at 150 rpm for 15 min. Then, EDC·HCl was added in an ice bath, and the mixture was reacted at 250 rpm in an ice bath for 45 min to obtain an activated methacrylic acid solution. The mass-to-volume ratio of methacrylic acid, hydroquinone monomethyl ether, NHS, EDC·HCl and anhydrous DMF was 0.86 g : 0.00043 g : 1.4 g : 2.1 g : 30 mL. A2. Disperse histidine in anhydrous DMF at a mass-to-volume ratio of 1g:25mL to obtain a histidine solution. A3. Histidine solution was added dropwise to methacrylic acid activation solution at a rate of 0.4 mL / min, with a volume ratio of histidine solution to methacrylic acid activation solution of 25:30. The reaction was carried out under ice bath conditions with a stirring speed of 250 rpm for 2.5 h. After the reaction was completed, 10% acetic acid aqueous solution was added dropwise to the reaction solution to adjust the pH of the system to 5.7. The mixture was stirred at 100 rpm for 5 min to obtain reaction solution 1. An equal volume of ethyl acetate was added to reaction solution 1, and the mixture was stirred evenly and allowed to stand for separation. The organic phase was collected, and an equal volume of ethyl acetate was added to the aqueous phase for extraction twice. The organic phases were combined and washed successively with deionized water and saturated brine. The organic phase was dried with anhydrous sodium sulfate and filtered. The filtrate was subjected to vacuum distillation to remove the solvent, yielding the modified functional monomer. A4. Under nitrogen protection, first add 1 / 3 of the total monomer mass; 1 / 4 of the total azobisisobutyronitrile mass; and 1 / 2 of the total volume of anhydrous propylene glycol methyl ether acetate. Heat to 85°C and stir at 250 rpm for 15 minutes. Then, maintain stirring and add dropwise 1 / 2 of the total azobisisobutyronitrile mass and 2 / 3 of the total monomer mass over 3 hours. Finally, add 1 / 2 of the total volume of anhydrous propylene glycol methyl ether acetate and 1 / 4 of the total azobisisobutyronitrile mass, stirring at 250 rpm. The total reaction time to polymerization was 5 hours. After polymerization, the temperature was lowered to 62°C, followed by vacuum distillation at a vacuum level of -0.09 MPa and a temperature of 67°C until the solid content reached 77%, yielding a modified hydroxyl acrylic resin solution. The monomers included modified functional monomers, methyl methacrylate, butyl acrylate, and methacrylic acid. The mass-to-volume ratio of the modified functional monomers, methyl methacrylate, butyl acrylate, methacrylic acid, azobisisobutyronitrile, and anhydrous propylene glycol methyl ether acetate was 21 g: 42 g: 30 g: 3 g: 1.2 g: 120 mL. A5. Adjust the pH of the modified hydroxy acrylic resin solution to 7.3 with triethylamine, stir at 250 rpm for 12 min, homogenize at 1000 rpm, and simultaneously add deionized water dropwise at a rate of 7 mL / min until the solid content is 40%; mix at 1800 rpm for 25 min, and after mixing, filter through an 180-mesh sieve to obtain the modified hydroxy acrylic resin aqueous dispersion.

[0033] Example 2 like Figure 1 As shown, the preparation process of a modified hydroxyl acrylic resin aqueous dispersion includes the following steps: A1. Methacrylic acid and phenothiazine were dispersed in anhydrous DMF, NHS was added, and the mixture was stirred at 200 rpm for 10 min. Then, EDC·HCl was added in an ice bath and reacted at 300 rpm in an ice bath for 30 min to obtain an activated methacrylic acid solution. The mass-to-volume ratio of methacrylic acid, phenothiazine, NHS, EDC·HCl and anhydrous DMF was 0.8 g: 0.0004 g: 1.4 g: 2.1 g: 30 mL. A2. Disperse histidine in anhydrous DMF at a mass-to-volume ratio of 1g:30mL to obtain a histidine solution. A3. Histidine solution was added dropwise to methacrylic acid activation solution at a rate of 0.5 mL / min, with a volume ratio of 30:30 between the histidine solution and the methacrylic acid activation solution. The reaction was carried out at 300 rpm under ice bath conditions for 2 h. After the reaction was completed, 10% acetic acid aqueous solution was added dropwise to the reaction solution to adjust the pH of the system to 5.5. The mixture was stirred at 100 rpm for 5 min to obtain reaction solution 1. An equal volume of ethyl acetate was added to reaction solution 1, and the mixture was stirred until homogeneous. The mixture was allowed to stand and separate into layers. The organic phase was collected, and an equal volume of ethyl acetate was added to the aqueous phase for extraction twice. The organic phases were combined and washed successively with deionized water and saturated brine. The mixture was dried with anhydrous sodium sulfate and filtered. The filtrate was subjected to vacuum distillation to remove the solvent, yielding the modified functional monomer. A4. Under nitrogen protection, first add 1 / 3 of the total mass of monomer, 1 / 4 of the total mass of benzoyl peroxide, and 1 / 2 of the total volume of anhydrous propylene glycol methyl ether acetate. After heating to 80°C, stir at 200 rpm for 15 min. Then, maintain stirring and add 1 / 2 of the total mass of benzoyl peroxide and 2 / 3 of the total mass of monomer dropwise over 3 h. Finally, add 1 / 2 of the total volume of anhydrous propylene glycol methyl ether acetate and 1 / 4 of the total mass of benzoyl peroxide. Stir at 200 rpm until the total polymerization time is 6 h. After polymerization, the temperature was lowered to 60°C, followed by vacuum distillation at a vacuum level of -0.098 MPa and a temperature of 65°C until the solid content reached 75%, yielding a modified hydroxyl acrylic resin solution. The monomers included modified functional monomers, methyl methacrylate, butyl acrylate, and methacrylic acid. The mass-to-volume ratio of the modified functional monomers, methyl methacrylate, butyl acrylate, methacrylic acid, benzoyl peroxide, and anhydrous propylene glycol methyl ether acetate was 15 g: 35 g: 25 g: 3 g: 0.8 g: 100 mL. A5. Adjust the pH of the modified hydroxyl acrylic resin solution to 7.5 with triethylamine, stir at 300 rpm for 8 min, homogenize at 1200 rpm, and simultaneously add deionized water dropwise at a rate of 5 mL / min until the solid content is 38%; mix at 2000 rpm for 20 min, and after mixing, filter through a 200-mesh sieve to obtain the modified hydroxyl acrylic resin aqueous dispersion.

[0034] Example 3 like Figure 1 As shown, the preparation process of a modified hydroxyl acrylic resin aqueous dispersion includes the following steps: A1. Methacrylic acid and phenothiazine were dispersed in anhydrous DMF, NHS was added, and the mixture was stirred at 100 rpm for 20 min. Then, EDC·HCl was added in an ice bath and reacted at 200 rpm in an ice bath for 60 min to obtain an activated methacrylic acid solution. The mass-to-volume ratio of methacrylic acid, phenothiazine, NHS, EDC·HCl and anhydrous DMF was 0.9 g : 0.00045 g : 1.4 g : 2.1 g : 30 mL. A2. Disperse histidine in anhydrous DMF at a mass-to-volume ratio of 1g:20mL to obtain a histidine solution. A3. Histidine solution was added dropwise to methacrylic acid activation solution at a rate of 0.3 mL / min, with a volume ratio of histidine solution to methacrylic acid activation solution of 20:30. The reaction was carried out at 200 rpm under ice bath conditions for 3 h. After the reaction was completed, 10% acetic acid aqueous solution was added dropwise to the reaction solution to adjust the pH of the system to 6.0. The mixture was stirred at 100 rpm for 5 min to obtain reaction solution 1. An equal volume of ethyl acetate was added to reaction solution 1, and the mixture was stirred evenly and allowed to stand for separation. The organic phase was collected, and an equal volume of ethyl acetate was added to the aqueous phase for extraction twice. The organic phases were combined and washed successively with deionized water and saturated brine. The organic phase was dried with anhydrous sodium sulfate and filtered. The filtrate was subjected to vacuum distillation to remove the solvent, yielding the modified functional monomer. A4. Under nitrogen protection, first add 1 / 3 of the total mass of monomer, 1 / 4 of the total mass of benzoyl peroxide, and 1 / 2 of the total volume of anhydrous propylene glycol methyl ether acetate. After heating to 90°C, stir at 300 rpm for 15 min. Then, maintain stirring and add 1 / 2 of the total mass of benzoyl peroxide and 2 / 3 of the total mass of monomer dropwise over 3 h. Finally, add 1 / 2 of the total volume of anhydrous propylene glycol methyl ether acetate and 1 / 4 of the total mass of benzoyl peroxide. Stir at 300 rpm until the total polymerization time is 4 h. After polymerization, the temperature was lowered to 65°C, followed by vacuum distillation at a vacuum level of -0.085 MPa and a temperature of 70°C until the solid content reached 80%, yielding a modified hydroxyl acrylic resin solution. The monomers included modified functional monomers, methyl methacrylate, butyl acrylate, and methacrylic acid. The mass-to-volume ratio of the modified functional monomers, methyl methacrylate, butyl acrylate, methacrylic acid, benzoyl peroxide, and anhydrous propylene glycol methyl ether acetate was 30 g: 50 g: 35 g: 3 g: 1.5 g: 150 mL. A5. Adjust the pH of the modified hydroxyl acrylic resin solution to 7.1 with triethylamine, stir at 200 rpm for 15 min, homogenize at 800 rpm, and simultaneously add deionized water dropwise at a rate of 10 mL / min until the solid content is 42%; mix at 1500 rpm for 30 min, and after mixing, filter through a 150-mesh sieve to obtain the modified hydroxyl acrylic resin aqueous dispersion.

[0035] Example 4 A water-based acrylic polyurethane paint, the preparation method of which includes: S1. Add the additives to deionized water. The additives are a mixture of nonionic dispersant, nonionic defoamer, nonionic leveling agent, film-forming aid, and pH adjuster in a mass ratio of 7:2:4:35:2. Mix at 300 rpm for 10 minutes, then filter through a 180-mesh sieve to obtain the additive pre-prepared solution. The mass ratio of additives to deionized water is 5:20. S2. Add the pre-prepared additive solution to the modified hydroxyl acrylic resin aqueous dispersion prepared in Example 1. The mass ratio of the modified hydroxyl acrylic resin aqueous dispersion to the pre-prepared additive solution is 75:25. The hydroxyl value of the modified hydroxyl acrylic resin aqueous dispersion is 33 mg KOH / g. Stir at 1000 rpm for 22 min, and then filter through a 180-mesh sieve to obtain component A. S3. Before use, stir component A and component B with an NCO content of 20 wt.% at 300 rpm in the dark for 7 min, and let stand for 15 min to degas, to obtain water-based acrylic polyurethane paint. The molar ratio of NCO in component B to OH in component A is 1.3.

[0036] Example 5 A water-based acrylic polyurethane paint, the preparation method of which includes: S1. Add the additives to deionized water. The additives are a mixture of nonionic dispersant, nonionic defoamer, nonionic leveling agent, film-forming aid, and pH adjuster in a mass ratio of 10:3:4:50:3. Mix at 400 rpm for 8 minutes, then filter through a 200-mesh sieve to obtain the additive pre-prepared solution. The mass ratio of additives to deionized water is 7:13. S2. Add the pre-prepared additive solution to the modified hydroxyl acrylic resin aqueous dispersion prepared in Example 2. The mass ratio of the modified hydroxyl acrylic resin aqueous dispersion to the pre-prepared additive solution is 80:20. The hydroxyl value of the modified hydroxyl acrylic resin aqueous dispersion is 25 mg KOH / g. Stir at 800 rpm for 30 min, and then filter through a 200-mesh sieve to obtain component A. S3. Before use, stir component A and component B with an NCO content of 19 wt.% at 400 rpm in the dark for 5 min, and let stand for 10 min to degas, to obtain water-based acrylic polyurethane paint. The molar ratio of NCO in component B to OH in component A is 1.5.

[0037] Example 6 A water-based acrylic polyurethane paint, the preparation method of which includes: S1. Add the additives to deionized water. The additives are a mixture of nonionic dispersant, nonionic defoamer, nonionic leveling agent, film-forming aid, and pH adjuster in a mass ratio of 4:1:4:20:1. Mix at 200 rpm for 12 minutes, then filter through a 150-mesh sieve to obtain the additive pre-prepared solution. The mass ratio of additives to deionized water is 3:27. S2. Add the pre-prepared additive solution to the modified hydroxyl acrylic resin aqueous dispersion prepared in Example 3. The mass ratio of the modified hydroxyl acrylic resin aqueous dispersion to the pre-prepared additive solution is 70:30. The hydroxyl value of the modified hydroxyl acrylic resin aqueous dispersion is 40 mg KOH / g. Stir at 1200 rpm for 15 min, and then filter through a 150-mesh sieve to obtain component A. S3. Before use, stir component A and component B with an NCO content of 22 wt.% at 200 rpm in the dark for 10 min, and let stand for 20 min to remove bubbles to obtain water-based acrylic polyurethane paint. The molar ratio of NCO in component B to OH in component A is 1.2.

[0038] Comparative Example 1 A waterborne acrylic polyurethane paint differs from Example 4 in that the modified hydroxyl acrylic resin prepared in Example 1 is not used. Instead, a hydroxyl acrylic resin is used, which is formed by polymerizing N-(hydroxymethyl)acrylamide, methyl methacrylate, butyl acrylate and methacrylic acid in the same mass ratio under the action of an initiator. Other operating steps and process parameters are exactly the same as in Example 4.

[0039] Comparative Example 2 A waterborne acrylic polyurethane paint differs from Example 4 in that the modified hydroxyl acrylic resin prepared in Example 1 is not used; instead, the hydroxyl acrylic resin prepared in Comparative Example 1 is used, and 2-thiol-benzoimidazole is added to component A. Other operating steps and process parameters are exactly the same as in Example 4.

[0040] Performance testing: Paint film adhesion test: In accordance with GB / T9286-2021, the waterborne acrylic polyurethane paint prepared in Examples 4 to 6 and Comparative Example 1 was sprayed onto a hard metal substrate. The paint film thickness was 50±5μm. After the paint film was completely dry, a cross-cut test was performed. The test results are shown in Table 1.

[0041] Film separation adhesion test: Waterborne acrylic polyurethane paints prepared in Examples 4-6 and Comparative Examples 1-2 were sprayed onto a hard metal substrate. The film thickness was 50±5μm. After the film was completely dry, the test column was vertically bonded to the coating surface of the sample to be tested with adhesive. After the adhesive was completely cured, a tensile testing machine was used to apply a tensile force perpendicular to the coating surface at an acceleration of 5mm / min. The force that the coating was pulled apart was taken as the pull-off adhesion of the coating, and the force that the film was pulled apart was taken as the film separation adhesion. The test results are shown in Table 1.

[0042] Table 1 Performance test results of the waterborne acrylic polyurethane coatings prepared in Examples 4-6 and Comparative Examples 1-2

[0043] As shown in Table 1, the waterborne acrylic polyurethane paints prepared in Examples 4-6 and Comparative Examples 1-2 all exhibited good adhesion properties. However, the separation adhesion of the paint film in Comparative Example 1 was significantly lower than that in Examples 4-6. This may be because the adhesion of the waterborne acrylic polyurethane paint prepared in Comparative Example 1 relies entirely on the cross-linking network formed by NCO and OH groups, thus exhibiting good adhesion. However, the lack of imidazole group coordination results in insufficient anti-separation performance between the paint film and the metal substrate, leading to lower separation adhesion. Comparative Example 2 added 2-thiol-benzoimidazole containing imidazole groups to Comparative Example 1, slightly improving the separation adhesion, but it was still lower than that in Examples 4-6. This may be because the 2-thiol-benzoimidazole was added only through physical mixing, and the imidazole groups were not chemically bonded to the resin backbone, preventing them from integrating into the polyurethane cross-linking network. Although chemical bonding with the metal substrate was achieved, the polyurethane cross-linking network could not be further fixed, and only a small amount could be fixed through molecular chain entanglement.

[0044] The embodiments of the present invention have been described above. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. A water-based acrylic polyurethane paint, characterized in that, The product comprises component A and component B. Component A includes a modified hydroxyl acrylic resin aqueous dispersion, additives, and deionized water. The hydroxyl value of the modified hydroxyl acrylic resin aqueous dispersion is 25-40 mg KOH / g. The modified hydroxyl acrylic resin aqueous dispersion is obtained by double bond polymerization of modified functional monomers, methyl methacrylate, butyl acrylate, and methacrylic acid under the action of an initiator, followed by neutralization, phase inversion, and self-emulsification. The modified functional monomers contain carbon-carbon double bonds, imidazole groups, and hydroxymethyl groups. Component B is a water-dispersible hexamethylene diisocyanate polyisocyanate. The NCO content of the water-dispersible hexamethylene diisocyanate polyisocyanate is 19 wt.% to 22 wt.%.

2. The waterborne acrylic polyurethane paint according to claim 1, characterized in that, The molar ratio of NCO in component B to OH in component A is 1.2~1.

5.

3. The waterborne acrylic polyurethane paint according to claim 1, characterized in that, In component A, the mass ratio of the modified hydroxyl acrylic resin aqueous dispersion, the additives, and deionized water is (70~80):(3~7):(13~27); the additives include nonionic dispersants, nonionic defoamers, nonionic leveling agents, film-forming aids, and pH adjusters; the mass ratio of the nonionic dispersants, nonionic defoamers, nonionic leveling agents, film-forming aids, and pH adjusters is (4~10):(1~3):4:(20~50):(1~3); the solid content of the modified hydroxyl acrylic resin aqueous dispersion is 38%~42%.

4. A method for preparing a waterborne acrylic polyurethane paint according to any one of claims 1-3, characterized in that, Includes the following steps: S1. Mix the additive with deionized water, filter, and obtain the additive pre-prepared solution; S2. Add the pre-mixed additive solution to the modified hydroxyl acrylic resin aqueous dispersion, stir, filter, and obtain component A; S3. Before use, stir components A and B in the dark and let stand to obtain water-based acrylic polyurethane paint.

5. The method for preparing a waterborne acrylic polyurethane paint according to claim 4, characterized in that, In step S1, the mixing speed is 200-400 rpm, and the mixing time is 8-12 min; the sieve mesh size for filtration is 150-200 mesh. In step S2, the stirring speed is 800~1200 rpm, and the stirring time is 15~30 min; the sieve mesh size for filtration is 150~200 mesh. In step S3, the stirring speed in the dark is 200~400 rpm, the stirring time in the dark is 5~10 min, and the settling time is 10~20 min.

6. The method for preparing a waterborne acrylic polyurethane paint according to claim 4, characterized in that, In step S1, the preparation process of the modified hydroxyl acrylic resin aqueous dispersion includes the following steps: A1. Disperse methacrylic acid and polymerization inhibitor in anhydrous DMF, add NHS, stir, add EDC·HCl in an ice bath, and react in an ice bath to obtain methacrylic acid activated solution; A2. Histidine is dispersed in anhydrous DMF to obtain a histidine solution; A3. Histidine solution was added dropwise to methacrylic acid activation solution, reacted in an ice bath, the reaction was quenched, and purified to obtain the modified functional monomer. A4. Under nitrogen protection, the modified functional monomer, methyl methacrylate, butyl acrylate, methacrylic acid and initiator are dissolved in anhydrous propylene glycol methyl ether acetate to carry out the polymerization reaction. The mixture is then cooled and distilled under reduced pressure to obtain a modified hydroxyl acrylic resin solution. A5. Adjust the pH of the modified hydroxyl acrylic resin solution with triethylamine, stir, add deionized water dropwise to homogenize, mix, filter, and obtain an aqueous dispersion of modified hydroxyl acrylic resin.

7. The method for preparing a waterborne acrylic polyurethane paint according to claim 6, characterized in that, In A1, the mass-to-volume ratio of methacrylic acid, polymerization inhibitor, NHS, EDC·HCl, and anhydrous DMF is (0.8~0.9) g : (0.0004~0.00045) g : 1.4 g : 2.1 g : 30 mL; the polymerization inhibitor is either hydroquinone monomethyl ether or phenothiazine; the stirring speed is 100~200 rpm, and the stirring time is 10~20 min; the ice bath reaction speed is 200~300 rpm, and the ice bath reaction time is 30~60 min. In A2, the mass-to-volume ratio of histidine to anhydrous DMF is 1 g: (20~30) mL.

8. The method for preparing a waterborne acrylic polyurethane paint according to claim 6, characterized in that, In A3, the dropping rate of the histidine solution is 0.3~0.5 mL / min; the volume ratio of the histidine solution to the methacrylic acid activating solution is (20~30):30; the rotation speed of the ice bath reaction is 200~300 rpm, and the ice bath reaction time is 2~3 h.

9. The method for preparing a waterborne acrylic polyurethane paint according to claim 6, characterized in that, In A4, the mass-to-volume ratio of the modified functional monomer, methyl methacrylate, butyl acrylate, methacrylic acid, initiator, and anhydrous propylene glycol methyl ether acetate is (15~30) g : (35~50) g ​​: (25~35) g : 3 g : (0.8~1.5) g : (100~150) mL; the initiator is either azobisisobutyronitrile or benzoyl peroxide; the polymerization method is semi-continuous solution polymerization, the polymerization temperature is 80~90℃, the polymerization speed is 200~300 rpm, and the total polymerization time is 4~6 h; the final cooling temperature is 60~65℃; the vacuum degree of the vacuum distillation is -0.085~-0.098 MPa, the vacuum distillation temperature is 65~70℃, and the vacuum distillation is carried out until the solid content of the system is 75~80%.

10. The method for preparing a waterborne acrylic polyurethane paint according to claim 6, characterized in that, In A5, the stirring speed is 200-300 rpm, and the stirring time is 8-15 min; the homogenization speed is 800-1200 rpm; the rate of adding deionized water is 5-10 mL / min; the mixing speed is 1500-2000 rpm, and the mixing time is 20-30 min; the filtration sieve mesh size is 150-200 mesh.

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