A safe and environmentally friendly water-based coating for toys and its preparation method

Abstract

This invention relates to a safe and environmentally friendly water-based coating for toys and its preparation method, belonging to the field of coating technology. The coating components include a bio-based waterborne polyurethane-acrylic interpenetrating network polymer, a dynamic covalent self-healing resin, functional fillers, and antibacterial agents. The bio-based waterborne polyurethane-acrylic interpenetrating network polymer is prepared by reacting castor oil-modified polyol, lysine diisocyanate, ethylhexyl palmitate, and dimethylolpropionic acid to obtain a prepolymer, which is then reacted with butyl acrylate, methyl methacrylate, and hydroxyethyl methacrylate. The dynamic covalent self-healing resin is prepared by reacting 3,3'-thiodipropionic acid, glycidyl methacrylate, and isobutyl palmitate to obtain a product, which is then reacted with methyl methacrylate and ethylene glycol dimethacrylate to obtain an oligomer, and finally reacted with a waterborne acrylic resin. The combined use of these components exhibits excellent adhesion, crack resistance, water resistance, abrasion resistance, and self-healing ability, and is safe and environmentally friendly.

Description

Technical Field

[0001] This invention belongs to the field of coating technology, specifically relating to a safe and environmentally friendly water-based coating for toys and its preparation method. Background Technology

[0002] In the children's products sector, toys, as important companions in children's growth, have always been a focus of attention regarding safety and environmental friendliness. With socio-economic development and rising living standards, parents have increasingly higher demands for toy quality, not only focusing on fun and educational value but also prioritizing safety. As the part of a toy that comes into direct contact with children, the performance of the toy's surface coating directly impacts children's health. Traditional solvent-based coatings, containing large amounts of volatile organic compounds (VOCs), heavy metals, and other harmful substances, are gradually failing to meet market demands. Against this backdrop, safe and environmentally friendly water-based coatings have emerged and become a research hotspot and development direction in the toy coating field.

[0003] Traditional solvent-based coatings once dominated toy manufacturing. These coatings use organic solvents such as benzene, toluene, and xylene as dispersion media. During the coating process, large amounts of these organic solvents evaporate into the air, causing severe air pollution and harming the health of workers. Furthermore, organic solvents are flammable and explosive, posing significant safety hazards. More importantly, traditional solvent-based coatings often contain heavy metals such as lead, cadmium, and mercury, as well as harmful substances like formaldehyde. Children may ingest these harmful substances by biting or sucking on the toy surface, and long-term accumulation can cause irreversible damage to their nervous and immune systems.

[0004] Water-based coatings use water as the primary solvent or dispersion medium, offering significant advantages such as environmental friendliness, safety, and low toxicity. Compared to traditional solvent-based coatings, water-based coatings produce virtually no VOC emissions during production and use, effectively reducing atmospheric pollution and aligning with green development principles. Furthermore, water-based coatings contain no organic solvents, eliminating flammable and explosive hazards and reducing risks during production and storage. In terms of safety, water-based coatings utilize non-toxic and harmless film-forming substances, pigments, and additives, avoiding the introduction of harmful substances such as heavy metals. This ensures the safety of toys in contact with children from the source, providing strong protection for children's healthy growth.

[0005] Despite the numerous advantages of water-based coatings, they still face some technical challenges in practical applications. For example, the water resistance and abrasion resistance of water-based coatings are still somewhat inferior to those of solvent-based coatings, requiring further improvement through formulation optimization and process refinement. Summary of the Invention

[0006] To meet the usage requirements of toys and ensure human health while improving the performance of water-based coatings, this invention provides a safe and environmentally friendly water-based coating for toys and its preparation method. A special method is used to prepare a bio-based water-based polyurethane-acrylic interpenetrating network polymer and a dynamically covalently bonded self-healing resin. Using water as a solvent, VOC emissions are effectively reduced. When used in combination with functional fillers, antibacterial agents, and other components in a certain proportion, it exhibits excellent adhesion, crack resistance, water resistance, and abrasion resistance, as well as superior self-healing capabilities. The specific technical solution is as follows:

[0007] A safe and environmentally friendly water-based coating for toys, comprising the following raw materials in parts by weight: 40-45 parts of bio-based waterborne polyurethane-acrylic interpenetrating network polymer, 8-10 parts of dynamic covalent self-healing resin, 20-25 parts of functional filler, 6-8 parts of antibacterial agent, 0.5-1 part of thickener, 1-2 parts of dispersant, 0.2-0.5 parts of leveling agent, 8-12 parts of pigment, 0.5-1 part of defoamer, with the balance being deionized water, and a solid content of 45%-55%.

[0008] The bio-based waterborne polyurethane-acrylic acid interpenetrating network polymer is a product obtained by reacting castor oil modified polyol, lysine diisocyanate, ethylhexyl palmitate and dimethylolpropionic acid to obtain a bio-based waterborne polyurethane prepolymer, and then reacting it with butyl acrylate, methyl methacrylate and hydroxyethyl methacrylate.

[0009] The dynamic covalent self-healing resin is prepared by reacting 3,3'-thiodipropionic acid, glycidyl methacrylate, and isobutyl palmitate to obtain product A, which is then reacted with methyl methacrylate and ethylene glycol dimethacrylate to obtain an oligomer, and finally reacted with an aqueous acrylic resin to obtain the product.

[0010] The antibacterial agent is a catechin β-cyclodextrin inclusion complex.

[0011] The preparation method of the bio-based waterborne polyurethane-acrylic interpenetrating network polymer in the above coating includes:

[0012] S1: By mass, add 100-120 parts of castor oil-modified polyol to 80-100 parts of acetone and stir until homogeneous. Then, add 35-40 parts of lysine diisocyanate, 10-15 parts of ethylhexyl palmitate, and 0.1-0.2 parts of dibutyltin dilaurate in sequence. Reflux at 80-85°C for 3-4 hours. Add 8-10 parts of dimethylolpropionic acid and reflux at 50-60°C for 1-1.5 hours. Add triethylamine at 1-1.1 times the mass of dimethylolpropionic acid for neutralization and stir until homogeneous to obtain a prepolymer solution.

[0013] S2: Under stirring, add the prepolymer solution to 2.5 to 3.5 times the mass of the prepolymer solution in deionized water, stir to emulsify, remove acetone and part of the deionized water by vacuum distillation, and achieve a solid content of 45 wt% to 50 wt% to obtain a bio-based waterborne polyurethane prepolymer.

[0014] S3: Add 100-120 parts of bio-based waterborne polyurethane prepolymer to 50-80 parts of deionized water and stir until homogeneous. Then add 30-35 parts of butyl acrylate, 20-25 parts of methyl methacrylate, and 5-8 parts of hydroxyethyl methacrylate in sequence and stir until homogeneous. Add 10-12 parts of ammonium persulfate aqueous solution with a concentration of 4wt%-6wt% and reflux at 75℃-80℃ for 3-4 hours to obtain a bio-based waterborne polyurethane-acrylic acid interpenetrating network polymer.

[0015] In the preparation method of the above-mentioned bio-based waterborne polyurethane-acrylic acid interpenetrating network polymer, in S1, the stirring is carried out at 200 r / min to 300 r / min for 15 min to 20 min, and the stirring speed of the reflux reaction is carried out at 250 rpm to 300 rpm.

[0016] In the preparation method of the above-mentioned bio-based waterborne polyurethane-acrylic interpenetrating network polymer, in step S2, the stirring speed is 1000 r / min to 1200 r / min, and the stirring emulsification time is 30 min to 40 min.

[0017] In the preparation method of the above-mentioned bio-based waterborne polyurethane-acrylic acid interpenetrating network polymer, in step S3, the stirring is carried out at 200 r / min to 300 r / min for 15 min to 20 min, and the reflux reaction speed is 250 r / min to 300 rpm.

[0018] The preparation method of the dynamic covalent self-healing resin in the above-mentioned coating includes:

[0019] N1: By mass, under nitrogen protection, 20-25 parts of 3,3'-thiodipropionic acid, 40-45 parts of glycidyl methacrylate, 10-12 parts of isobutyl palmitate, 50-60 parts of ethyl acetate, and 2-3 parts of triethylamine were refluxed at 80-85°C for 3-4 hours, cooled to room temperature, and the filtrate was collected to obtain product A. Under nitrogen protection, all of product A, 30-35 parts of methyl methacrylate, 5-8 parts of ethylene glycol dimethacrylate, 0.8-1.2 parts of azobisisobutyronitrile, and 60-80 parts of ethyl acetate were refluxed at 75-80°C for 6-8 hours, cooled to room temperature, and product B was obtained. Product B was poured into cold methanol to precipitate, and the solid was collected by filtration. The solid was washed with methanol and dried under vacuum to obtain the oligomer.

[0020] N2: By mass, add 100-120 parts of waterborne acrylic resin to 15-25 parts of deionized water, stir until homogeneous, add 13-17 parts of oligomer, stir until homogeneous, add 8-10 parts of potassium persulfate aqueous solution with a concentration of 4wt%-6wt%, and reflux at 80℃-85℃ for 3-4 hours to obtain dynamic covalent bond self-healing resin.

[0021] In the above-mentioned method for preparing the dynamic covalent self-healing resin, in N1, the stirring speed of the reflux reaction is 250 rpm to 300 rpm, the sieve mesh size for filtration is 100 mesh to 200 mesh, the temperature of the cold methanol is 2℃ to 6℃, the amount of cold methanol is 10 to 12 times the volume of product B, the sieve mesh size for filtration to collect the solid is 200 mesh to 325 mesh, the number of methanol washings is 3 to 5 times, and the vacuum drying is performed at 35℃ to 40℃ for 24 to 30 hours.

[0022] In the above-mentioned method for preparing dynamic covalent self-healing resin, in N2, the stirring is carried out at 200 r / min to 300 r / min for 15 min to 20 min; the stirring speed of the reflux reaction is 250 rpm to 300 rpm.

[0023] The preparation method of the catechin β-cyclodextrin inclusion complex in the above coating includes: preparing a 15 g / L to 18 g / L β-cyclodextrin aqueous mixture; preparing a 4.5 g / L to 5.0 g / L catechin ethanol solution; adding the catechin ethanol solution dropwise to the β-cyclodextrin aqueous mixture at a volume ratio of β-cyclodextrin aqueous mixture: catechin ethanol solution = (4 to 5): (1 to 1.2) under stirring, stirring the mixture at 30°C to 40°C for 2 to 4 hours to allow it to react, allowing it to stand at 4°C to 6°C to precipitate the inclusion complex, centrifuging at 4000 rpm to 6000 rpm for 10 to 15 minutes, collecting the precipitate, drying it under vacuum at 40°C to 50°C to constant weight, and then breaking it up to obtain the catechin β-cyclodextrin inclusion complex.

[0024] In the above coating, the mass ratio of the functional filler components is: calcium carbonate: talc: kaolin: titanium dioxide = (30-35): (20-25): (8-12): (5-10); the functional filler passes through a 325-460 mesh sieve.

[0025] In the above coatings, the thickener is hydroxyethyl cellulose or xanthan gum.

[0026] In the above coating, the dispersant is lecithin.

[0027] In the above coatings, the leveling agent is an acrylic leveling agent.

[0028] In the above-mentioned coatings, the pigments are natural plant pigments.

[0029] In the above-mentioned coatings, the defoamer is a polyether defoamer.

[0030] The preparation method of the above-mentioned safe and environmentally friendly water-based coating for toys includes the following steps:

[0031] According to the mass fraction, add the bio-based waterborne polyurethane-acrylic interpenetrating network polymer to the reactor and stir at a low speed of 200 rpm to 250 rpm. Then, add the dynamic covalent self-healing resin, functional filler, antibacterial agent, and pigment in sequence, and continue stirring for 30 min to 40 min to obtain mixture A. Add the dispersant, leveling agent, and thickener to 8 parts to 10 parts of deionized water and mix evenly to obtain mixture B. Add mixture B and defoamer to mixture A and stir at 800 rpm to 1200 rpm for 30 min to 40 min. Adjust the solid content of the coating to 45 wt% to 55 wt% with deionized water and filter through a 150-200 mesh sieve to obtain the coating.

[0032] This invention provides a safe and environmentally friendly water-based coating for toys and its preparation method, with the following beneficial effects:

[0033] I. The preparation method and parameter design can achieve complete reaction and improve the reasonable regulation of polymerization, with good structural uniformity. The solvent evaporates more completely during the preparation process, with less monomer residue and reduced VOC emissions.

[0034] II. Bio-based waterborne polyurethane-acrylic interpenetrating polymer networks contain a large number of active groups such as hydroxyl and carboxyl groups. During the coating film formation process, these active groups can chemically react with oxides or other polar groups on the surface of the substrate material to form covalent bonds; simultaneously, through intermolecular van der Waals forces and hydrogen bonds, they exhibit strong physical adsorption with the substrate. Furthermore, with the appropriate ratio and increased amount of functional fillers, they can fill the voids in the resin network, enhancing the density and cohesion of the coating film, resulting in a stronger bond between the coating film and the substrate.

[0035] III. The dynamic covalent bonds within the self-healing resin (including disulfide bonds and dynamic chemical bonds related to transesterification reactions) possess unique reversible properties. During temperature changes or bending, when the coating is subjected to stress, these dynamic covalent bonds can break and recombine, alleviating stress concentration through the movement and rearrangement of molecular chains. Simultaneously, the bio-based waterborne polyurethane-acrylic interpenetrating network polymer enhances the coating's flexibility, allowing it to maintain structural integrity even under greater deformation. After drying, the resulting coating is more dense, with significantly reduced porosity, effectively blocking water molecule penetration channels. The synergistic effect of the bio-based waterborne polyurethane-acrylic interpenetrating network polymer and the dynamic covalent bond self-healing resin constructs a stable three-dimensional network structure, enhancing the coating's resistance to water erosion. The catechin β-cyclodextrin inclusion complex is uniformly dispersed in the system, not only exerting antibacterial effects but also stabilizing the coating structure through interactions with resin molecules, reducing the destructive effects of water molecules on the coating.

[0036] IV. Optimized formulation of bio-based waterborne polyurethane-acrylic interpenetrating network polymer and functional fillers significantly alters the microstructure of the coating film. The functional fillers, uniformly dispersed within the resin matrix, act as a reinforcing skeleton, improving the surface hardness and abrasion resistance of the coating. The continuous phase formed by the bio-based waterborne polyurethane-acrylic interpenetrating network polymer exhibits excellent toughness and cohesive strength, effectively dispersing stress and reducing coating wear under abrasive friction.

[0037] V. Optimized preparation and rational formulation of the dynamic covalent bond self-healing resin significantly increased the number of dynamic covalent bonds in the coating film. When scratches occur on the coating surface, under the influence of ambient temperature and molecular thermal motion, the dynamic covalent bonds can break and recombine, promoting the diffusion and migration of molecular chains towards the scratched area. Through the mutual entanglement and cross-linking of molecular chains, the scratch gaps are gradually filled, achieving the self-healing function. Simultaneously, the bio-based waterborne polyurethane-acrylic interpenetrating polymer network provides a favorable matrix environment, which is conducive to the function of the dynamic covalent bond self-healing resin.

[0038] V. In the bio-based waterborne polyurethane-acrylic interpenetrating polymer network reaction system, an appropriate amount of ethylhexyl palmitate can participate in promoting monomer reactions, improving the stability and homogeneity of the reaction system, obtaining suitable molecular weights, enhancing subsequent crosslinking, reducing monomer residues, and thus effectively reducing VOC volatilization. If the amount added is too small, the improvement effect is insufficient, the internal plasticizing effect of the molecular chain is weak, and the flexibility and impact resistance of the coating film cannot be effectively improved. If the amount added is excessive, ethylhexyl palmitate will reduce the crosslinking density of the polymer, resulting in a decrease in the mechanical properties of the coating film and a deterioration in water resistance.

[0039] VI. In the synthesis of dynamic covalent self-healing resins, an appropriate amount of isobutyl palmitate promotes monomer reactions, and isobutyl palmitate has a significant impact on the flexibility and flowability of molecular chains. If the amount added is too small, the improvement effect is not obvious, the mobility of molecular chains is limited, affecting the exchange and recombination of dynamic covalent bonds, resulting in unsatisfactory self-healing performance and crack resistance. If too much is added, it interferes with the exchange of thioester bonds, resulting in the loss of dynamic response capability and a decrease in the hardness and wear resistance of the coating film. Detailed Implementation

[0040] The present invention will be further described below with reference to specific implementation examples, but the present invention is not limited to these embodiments.

[0041] Example 1

[0042] A safe and environmentally friendly water-based coating for toys comprises the following raw materials in parts by weight: 40 parts of bio-based waterborne polyurethane-acrylic interpenetrating network polymer, 8 parts of dynamic covalent self-healing resin, 20 parts of functional filler, 6 parts of antibacterial agent, 0.5 parts of thickener, 1 part of dispersant, 0.2 parts of leveling agent, 8 parts of pigment, 0.5 parts of defoamer, with the balance being deionized water, and a solid content of 45%. The functional filler has a composition ratio of calcium carbonate: talc: kaolin: titanium dioxide = 30:20:8:5; the functional filler passes through a 325-mesh sieve. The antibacterial agent is catechin β-cyclodextrin inclusion complex. The thickener is hydroxyethyl cellulose. The dispersant is lecithin. The leveling agent is an acrylate leveling agent. The pigment is a natural plant pigment. The defoamer is a polyether defoamer.

[0043] The preparation method of the bio-based waterborne polyurethane-acrylic acid interpenetrating network polymer includes:

[0044] S1: By mass, add 100 parts of castor oil-modified polyol to 80 parts of acetone, stir at 200 r / min for 15 min, then add 35 parts of lysine diisocyanate, 10 parts of ethylhexyl palmitate and 0.1 parts of dibutyltin dilaurate in sequence, reflux at 80℃ and 250 rpm for 3 h, add 8 parts of dimethylolpropionic acid, reflux at 50℃ for 1 h, add triethylamine with a mass equal to that of dimethylolpropionic acid for neutralization, stir at 200 r / min for 15 min to obtain the prepolymer solution;

[0045] S2: Under stirring at 1000 r / min, the prepolymer solution is added to 2.5 times the mass of deionized water, stirred and emulsified at 1000 r / min for 30 min, and acetone and part of the deionized water are removed by vacuum distillation to achieve a solid content of 45 wt%, thus obtaining a bio-based waterborne polyurethane prepolymer.

[0046] S3: Add 100 parts of bio-based waterborne polyurethane prepolymer to 50 parts of deionized water, stir at 200 r / min for 15 min, then add 30 parts of butyl acrylate, 20 parts of methyl methacrylate, and 5 parts of hydroxyethyl methacrylate in sequence, stir at 200 r / min for 15 min, then add 10 parts of 4 wt% ammonium persulfate aqueous solution dropwise, and reflux at 75℃ and 250 rpm for 3 h to obtain a bio-based waterborne polyurethane-acrylic acid interpenetrating network polymer.

[0047] The preparation methods of dynamic covalent self-healing resin include:

[0048] N1: By mass, under nitrogen protection, 20 parts of 3,3'-thiodipropionic acid, 40 parts of glycidyl methacrylate, 10 parts of isobutyl palmitate, 50 parts of ethyl acetate, and 2 parts of triethylamine were refluxed at 80°C and 250 rpm for 3 hours. After cooling to room temperature, the mixture was filtered through a 100-mesh sieve to obtain product A. Under nitrogen protection, all of product A, 30 parts of methyl methacrylate, 5 parts of ethylene glycol dimethacrylate, 0.8 parts of azobisisobutyronitrile, and 60 parts of ethyl acetate were refluxed at 75°C and 250 rpm for 6 hours. After cooling to room temperature, product B was obtained. Product B was poured into 10 times its volume of methanol at 2°C to precipitate the product. The solid was collected by filtration through a 200-mesh sieve. The product was washed three times with methanol and dried under vacuum at 35°C for 24 hours to obtain the oligomer.

[0049] N2: By mass, 100 parts of waterborne acrylic resin were added to 15 parts of deionized water and stirred at 200 r / min for 18 min. Then, 13 parts of oligomer were added and stirred at 200 r / min for 18 min. Finally, 8 parts of 4 wt% potassium persulfate aqueous solution were added dropwise. The mixture was refluxed at 80℃ and 250 rpm for 3 h to obtain a dynamic covalent bond self-healing resin.

[0050] The preparation method of catechin β-cyclodextrin inclusion complex includes: preparing a 15 g / L β-cyclodextrin aqueous solution; preparing a 4.5 g / L catechin ethanol solution; adding the catechin ethanol solution dropwise to the β-cyclodextrin aqueous solution at a volume ratio of 4:1 under stirring, stirring the mixture at 30°C for 2 h, allowing it to stand at 4°C to precipitate the inclusion complex, centrifuging at 4000 rpm for 10 min, collecting the precipitate, drying it under vacuum at 40°C to constant weight, and then breaking it up to obtain the catechin β-cyclodextrin inclusion complex.

[0051] The preparation method of the above-mentioned safe and environmentally friendly water-based coating for toys includes the following steps:

[0052] According to the mass fraction, the bio-based waterborne polyurethane-acrylic interpenetrating network polymer was added to the reactor and stirred at a low speed of 200 rpm. The dynamic covalent self-healing resin, functional filler, antibacterial agent, and pigment were added in sequence, and stirring was continued for 30 min to obtain mixture A. The dispersant, leveling agent, and thickener were added to 8 parts of deionized water and mixed evenly to obtain mixture B. Mixture B and defoamer were added to mixture A and stirred at 800 rpm for 30 min. The solid content of the coating was adjusted to 45 wt% with deionized water and filtered through a 150-mesh sieve to obtain the coating.

[0053] Example 2

[0054] A safe and environmentally friendly water-based coating for toys comprises the following raw materials in parts by weight: 43 parts of bio-based waterborne polyurethane-acrylic interpenetrating network polymer, 9 parts of dynamic covalent self-healing resin, 22 parts of functional filler, 7 parts of antibacterial agent, 0.7 parts of thickener, 1.5 parts of dispersant, 0.35 parts of leveling agent, 10 parts of pigment, 0.7 parts of defoamer, with the balance being deionized water, and a solid content of 50%. The functional filler has a composition ratio of calcium carbonate: talc: kaolin: titanium dioxide = 32:23:10:8; the functional filler passes through a 400-mesh sieve. The antibacterial agent is catechin β-cyclodextrin inclusion complex. The thickener is hydroxyethyl cellulose. The dispersant is lecithin. The leveling agent is an acrylate leveling agent. The pigment is a natural plant pigment. The defoamer is a polyether defoamer.

[0055] The preparation method of the bio-based waterborne polyurethane-acrylic acid interpenetrating network polymer includes:

[0056] S1: By mass, 110 parts of castor oil modified polyol were added to 90 parts of acetone and stirred at 250 r / min for 18 min. Then, 38 parts of lysine diisocyanate, 13 parts of ethylhexyl palmitate and 0.15 parts of dibutyltin dilaurate were added sequentially and refluxed at 82℃ and 280 rpm for 3.5 h. Then, 9 parts of dimethylolpropionic acid were added and refluxed at 55℃ for 1 h. Finally, triethylamine with a mass equal to that of dimethylolpropionic acid was added for neutralization and stirred at 250 r / min for 18 min to obtain the prepolymer solution.

[0057] S2: Under stirring at 1100 r / min, the prepolymer solution is added to deionized water with a mass of 3 times that of the prepolymer solution, and the mixture is stirred and emulsified at 1100 r / min for 35 min. The acetone and some deionized water are removed by vacuum distillation to achieve a solid content of 48 wt%, thus obtaining a bio-based waterborne polyurethane prepolymer.

[0058] S3: 110 parts of bio-based waterborne polyurethane prepolymer were added to 65 parts of deionized water and stirred at 250 r / min for 20 min. Then, 32 parts of butyl acrylate, 23 parts of methyl methacrylate, and 6.5 parts of hydroxyethyl methacrylate were added sequentially and stirred at 250 r / min for 20 min. Then, 11 parts of 5 wt% ammonium persulfate aqueous solution were added dropwise and refluxed at 78℃ and 280 rpm for 3.5 h to obtain a bio-based waterborne polyurethane-acrylic acid interpenetrating network polymer.

[0059] The preparation methods of dynamic covalent self-healing resin include:

[0060] N1: By mass, under nitrogen protection, 22 parts of 3,3'-thiodipropionic acid, 43 parts of glycidyl methacrylate, 11 parts of isobutyl palmitate, 55 parts of ethyl acetate, and 2.5 parts of triethylamine were refluxed at 82°C and 280 rpm for 3.5 h. After cooling to room temperature, the mixture was filtered through a 150-mesh sieve to obtain product A. Under nitrogen protection, all of product A, 32 parts of methyl methacrylate, 7 parts of ethylene glycol dimethacrylate, 1 part of azobisisobutyronitrile, and 70 parts of ethyl acetate were refluxed at 78°C and 280 rpm for 7 h. After cooling to room temperature, product B was obtained. Product B was poured into 11 times its volume of methanol at 4°C to precipitate the product. The solid was collected by filtration through a 250-mesh sieve. The product was washed four times with methanol and dried under vacuum at 38°C for 26 h to obtain the oligomer.

[0061] N2: By mass, 110 parts of waterborne acrylic resin were added to 20 parts of deionized water and stirred at 250 r / min for 15 min. Then, 15 parts of oligomer were added and stirred at 250 r / min for 15 min. Finally, 9 parts of 5 wt% potassium persulfate aqueous solution were added dropwise. The mixture was refluxed at 82℃ and 280 rpm for 3.5 h to obtain a dynamic covalent bond self-healing resin.

[0062] The preparation method of catechin β-cyclodextrin inclusion complex includes: preparing a 16 g / L β-cyclodextrin aqueous solution; preparing a 4.8 g / L catechin ethanol solution; adding the catechin ethanol solution dropwise to the β-cyclodextrin aqueous solution at a volume ratio of 4.5:1.1 under stirring, stirring the mixture at 35°C for 3 h, allowing it to stand at 5°C to precipitate the inclusion complex, centrifuging at 5000 rpm for 12 min, collecting the precipitate, drying it under vacuum at 45°C to constant weight, and then breaking it up to obtain the catechin β-cyclodextrin inclusion complex.

[0063] The preparation method of the above-mentioned safe and environmentally friendly water-based coating for toys includes the following steps:

[0064] According to the mass fraction, the bio-based waterborne polyurethane-acrylic interpenetrating network polymer was added to the reactor and stirred at a low speed of 220 rpm. The dynamic covalent self-healing resin, functional filler, antibacterial agent, and pigment were added in sequence, and stirring was continued for 35 min to obtain mixture A. The dispersant, leveling agent, and thickener were added to 9 parts of deionized water and mixed evenly to obtain mixture B. Mixture B and defoamer were added to mixture A and stirred at 1000 rpm for 35 min. The solid content of the coating was adjusted to 50 wt% with deionized water and filtered through a 150-mesh sieve to obtain the coating.

[0065] Example 3

[0066] A safe and environmentally friendly water-based coating for toys comprises the following raw materials in parts by weight: 45 parts of bio-based waterborne polyurethane-acrylic interpenetrating network polymer, 10 parts of dynamic covalent self-healing resin, 25 parts of functional filler, 8 parts of antibacterial agent, 1 part of thickener, 2 parts of dispersant, 0.5 parts of leveling agent, 12 parts of pigment, 1 part of defoamer, with the balance being deionized water, and a solid content of 55%. The functional filler has a composition ratio of calcium carbonate: talc: kaolin: titanium dioxide = 35:25:12:10; the functional filler passes through a 460-mesh sieve. The antibacterial agent is catechin β-cyclodextrin inclusion complex. The thickener is xanthan gum. The dispersant is lecithin. The leveling agent is an acrylic leveling agent. The pigment is a natural plant pigment. The defoamer is a polyether defoamer.

[0067] The preparation method of the bio-based waterborne polyurethane-acrylic acid interpenetrating network polymer includes:

[0068] S1: By mass, 120 parts of castor oil modified polyol were added to 100 parts of acetone and stirred at 300 r / min for 20 min. Then, 40 parts of lysine diisocyanate, 15 parts of ethylhexyl palmitate and 0.2 parts of dibutyltin dilaurate were added sequentially and refluxed at 85℃ and 300 rpm for 4 h. Then, 10 parts of dimethylolpropionic acid were added and refluxed at 60℃ for 1.5 h. Finally, triethylamine with a mass of 1.1 times that of dimethylolpropionic acid was added for neutralization and stirred at 300 r / min for 20 min to obtain a prepolymer solution.

[0069] S2: Under stirring at 1200 r / min, the prepolymer solution is added to 3.5 times the mass of deionized water, stirred and emulsified at 1200 r / min for 40 min, and acetone and part of the deionized water are removed by vacuum distillation to achieve a solid content of 50 wt% to obtain a bio-based waterborne polyurethane prepolymer.

[0070] S3: Add 120 parts of bio-based waterborne polyurethane prepolymer to 80 parts of deionized water and stir at 300 r / min for 18 min. Then add 35 parts of butyl acrylate, 25 parts of methyl methacrylate, and 8 parts of hydroxyethyl methacrylate in sequence and stir at 300 r / min for 18 min. Add 12 parts of 6 wt% ammonium persulfate aqueous solution dropwise and reflux at 80℃ and 300 rpm for 4 h to obtain a bio-based waterborne polyurethane-acrylic acid interpenetrating network polymer.

[0071] The preparation methods of dynamic covalent self-healing resin include:

[0072] N1: By mass, under nitrogen protection, 25 parts of 3,3'-thiodipropionic acid, 45 parts of glycidyl methacrylate, 12 parts of isobutyl palmitate, 60 parts of ethyl acetate, and 3 parts of triethylamine were refluxed at 85°C and 300 rpm for 4 hours. After cooling to room temperature, the mixture was filtered through a 200-mesh sieve to obtain product A. Under nitrogen protection, all of product A, 35 parts of methyl methacrylate, 8 parts of ethylene glycol dimethacrylate, 1.2 parts of azobisisobutyronitrile, and 80 parts of ethyl acetate were refluxed at 80°C and 300 rpm for 8 hours. After cooling to room temperature, product B was obtained. Product B was poured into 12 times its volume of methanol at 6°C to precipitate the product. The solid was collected by filtration through a 325-mesh sieve. The product was washed 5 times with methanol and dried under vacuum at 40°C for 30 hours to obtain the oligomer.

[0073] N2: By mass, 120 parts of waterborne acrylic resin were added to 25 parts of deionized water and stirred at 300 r / min for 20 min. Then, 17 parts of oligomer were added and stirred at 300 r / min for 20 min. Finally, 10 parts of 6 wt% potassium persulfate aqueous solution were added dropwise. The mixture was refluxed at 85℃ and 300 rpm for 4 h to obtain a dynamic covalent bond self-healing resin.

[0074] The preparation method of catechin β-cyclodextrin inclusion complex includes: preparing an 18 g / L β-cyclodextrin aqueous solution; preparing a 5.0 g / L catechin ethanol solution; adding the catechin ethanol solution dropwise to the β-cyclodextrin aqueous solution at a volume ratio of 5:1.2 under stirring, stirring the mixture at 40°C for 4 h, allowing it to stand at 6°C to precipitate the inclusion complex, centrifuging at 6000 rpm for 15 min, collecting the precipitate, drying it under vacuum at 50°C to constant weight, and then breaking it up to obtain the catechin β-cyclodextrin inclusion complex.

[0075] The preparation method of the above-mentioned safe and environmentally friendly water-based coating for toys includes the following steps:

[0076] According to the mass fraction, the bio-based waterborne polyurethane-acrylic interpenetrating network polymer was added to the reactor and stirred at a low speed of 250 rpm. The dynamic covalent self-healing resin, functional filler, antibacterial agent, and pigment were added in sequence, and stirring was continued for 40 min to obtain mixture A. The dispersant, leveling agent, and thickener were added to 10 parts of deionized water and mixed evenly to obtain mixture B. Mixture B and defoamer were added to mixture A and stirred at 1200 rpm for 40 min. The solid content of the coating was adjusted to 55 wt% with deionized water and filtered through a 200-mesh sieve to obtain the coating.

[0077] The raw materials used in the above embodiments are as follows: Calcium carbonate is from Shijiazhuang Jingsen Mineral Products Co., Ltd., light calcium carbonate. Talc powder is from Lingshou County Qiangdong Mineral Products Processing Plant, high-whiteness talc powder. Kaolin is from Shijiazhuang Qiantong Mineral Products Co., Ltd., calcined kaolin. Titanium dioxide is from Xinhao Energy Saving Technology (Tianjin) Co., Ltd., rutile titanium dioxide. Catechins are from Xi'an Ruiying Biotechnology Co., Ltd., 98% purity. β-Cyclodextrin is from Henan Anrui Biotechnology Co., Ltd. Hydroxyethyl cellulose is from Zouping Anlan Chemical Co., Ltd. Xanthan gum is from Zhengzhou Xinke Chemical Products Co., Ltd. Lecithin is from Anhui Weimao Biotechnology Co., Ltd., soybean lecithin. Acrylic ester leveling agent is BYK-381 (Germany). Natural plant pigment is madder pigment. Polyether defoamer is from Guangdong Nanhui New Materials Co., Ltd., model Cl-318. Castor oil modified polyol is Polycin D290. Lysine diisocyanate is from Wuhan Huaxiang Kejie Biotechnology Co., Ltd., L-lysine diisocyanate. Ethylhexyl palmitate is sourced from Shanghai Xiangu Chemical Co., Ltd. Dibutyltin dilaurate is sourced from Shanghai Gaoming Chemical Co., Ltd., tin-dibutyltin dilaurate. Dimethylolpropionic acid is sourced from Guangzhou Tengli Chemical Co., Ltd., 2,2-dimethylolpropionic acid. Triethylamine is sourced from Shandong Chongcheng Energy Technology Co., Ltd. Butyl acrylate is sourced from Jinan Yuansite New Material Technology Co., Ltd. Methyl methacrylate is sourced from Shandong Xinheng Chemical Co., Ltd. Hydroxyethyl methacrylate is sourced from Shanghai Yuanye Biotechnology Co., Ltd. Ammonium persulfate is sourced from Changzhou Jiaye Chemical Co., Ltd. 3,3'-Thiodipropionic acid is sourced from Wuhan Xinxin Jiali Biotechnology Co., Ltd. Glycidyl methacrylate is sourced from Shanghai Yuanye Biotechnology Co., Ltd. Isobutyl palmitate is sourced from Hubei Rishengchang New Material Technology Co., Ltd. Ethyl acetate is sourced from Jinan Bada Chemical Co., Ltd. Ethyl glycol dimethacrylate is sourced from Hubei Zhenbo Chemical Co., Ltd. Azobisisobutyronitrile is sourced from Shandong Yukang Chemical Co., Ltd. Waterborne acrylic resin is sourced from Dongguan Taikang Polymer Technology Co., Ltd., waterborne acrylic resin emulsion with a solid content of 36±2%. Potassium persulfate was sourced from Hubei Xinrunde Chemical Co., Ltd.

[0078] Comparative Example 1

[0079] The bio-based waterborne polyurethane-acrylic interpenetrating network polymer was replaced with a waterborne acrylic resin; other parameters and methods were the same as in Example 1.

[0080] Comparative Example 2

[0081] In method S1 for preparing bio-based waterborne polyurethane-acrylic interpenetrating network polymer, ethylhexyl palmitate is not added; other parameters and methods are the same as in Example 1.

[0082] Comparative Example 3

[0083] In method S1 for preparing bio-based waterborne polyurethane-acrylic interpenetrating network polymer, 3 parts of ethylhexyl palmitate are added (too little); other parameters and methods are the same as in Example 1.

[0084] Comparative Example 4

[0085] In method S1 for preparing bio-based waterborne polyurethane-acrylic acid interpenetrating network polymer, 25 parts of ethylhexyl palmitate are added (too much); other parameters and methods are the same as in Example 1.

[0086] Comparative Example 5

[0087] In the preparation method S1 of the bio-based waterborne polyurethane-acrylic acid interpenetrating network polymer, 2 parts of dimethylolpropionic acid are added (too little); other parameters and methods are the same as in Example 1.

[0088] Comparative Example 6

[0089] In method S1 for preparing bio-based waterborne polyurethane-acrylic acid interpenetrating network polymer, 20 parts of dimethylolpropionic acid are added (too much); other parameters and methods are the same as in Example 1.

[0090] Comparative Example 7

[0091] In method S3 for preparing bio-based waterborne polyurethane-acrylic interpenetrating network polymer, 50 parts of bio-based waterborne polyurethane prepolymer are added (too little); other parameters and methods are the same as in Example 1.

[0092] Comparative Example 8

[0093] In method S3 for preparing bio-based waterborne polyurethane-acrylic interpenetrating network polymer, 200 parts of bio-based waterborne polyurethane prepolymer are added (too much); other parameters and methods are the same as in Example 1.

[0094] Comparative Example 9

[0095] The dynamic covalent self-healing resin was replaced with a water-based acrylic resin; other parameters and methods were the same as in Example 1.

[0096] Comparative Example 10

[0097] Add 30 parts of dynamic covalent self-healing resin (too much); other parameters and methods are the same as in Example 1.

[0098] Comparative Example 11

[0099] In method N1 for preparing dynamic covalent self-healing resin, isobutyl palmitate is not added; other parameters and methods are the same as in Example 1.

[0100] Comparative Example 12

[0101] In method N1 for preparing dynamic covalent self-healing resin, 3 parts of isobutyl palmitate were added (too little); other parameters and methods were the same as in Example 1.

[0102] Comparative Example 13

[0103] In method N1 for preparing dynamic covalent self-healing resin, 20 parts of isobutyl palmitate were added (too much); other parameters and methods were the same as in Example 1.

[0104] Comparative Example 14

[0105] In method N2 for preparing dynamic covalent self-healing resin, 3 parts of oligomer are added (too little); other parameters and methods are the same as in Example 1.

[0106] Comparative Example 15

[0107] In method N2 for preparing dynamic covalent self-healing resin, 30 parts of oligomer are added (too much); other parameters and methods are the same as in Example 1.

[0108] Comparative Example 16

[0109] The catechin β-cyclodextrin inclusion complex was replaced with catechin; other parameters and methods were the same as in Example 1.

[0110] (a) VOC emission testing:

[0111] A 150mm × 75mm × 0.8mm glass plate was sprayed with a coating to form a wet film with a thickness of 100±5μm. The plate was then dried in an environment at 25℃ and 50% relative humidity for 7 days to ensure complete curing. The dried sample was placed in a 100L environmental testing chamber, with the chamber temperature controlled at 25℃ and relative humidity at 50%. After equilibration for 1 hour, gas samples were collected using gas chromatography-mass spectrometry (GC-MS). GC conditions: DB-5MS capillary column (30m × 0.25mm × 0.25μm), injection port temperature 250℃, initial column oven temperature 40℃, held for 2 min, then increased to 250℃ at 5℃ / min, held for 5 min; Mass spectrometry conditions: electron impact source (EI), electron energy 70eV, ion source temperature 230℃, scan range 35-350m / z. VOC emissions were determined (unit: mg / m³). 3 ).

[0112] (II) Adhesion Testing:

[0113] According to GB / T 9286 "Cross-cut test for paint and varnish films". The coating was applied to ABS plastic sheet (dry film thickness 80±2μm) and dried for 7 days at 25℃ and 50% relative humidity. The cross-cut test (1mm spacing, 6×6 squares) was used to evaluate the peeling grade; standard rating: Grade 0 indicates completely smooth cut edges with no peeling; Grade 1 indicates a small amount of thin flakes peeling off at the cut intersections, with the affected area not exceeding 5%; and so on, with Grade 5 indicating a peeling area greater than 65%.

[0114] (III) Crack resistance test:

[0115] The coating was applied to a flexible polyvinyl chloride (PVC) substrate (dry film thickness 80±2μm) and dried for 7 days at 25℃ and 50% relative humidity. A bending test was conducted on a 3mm diameter shaft to observe the maximum crack length (in mm).

[0116] (iv) Water resistance test:

[0117] The coating was applied to an aluminum plate, with the wet film thickness controlled at 120±5μm, and dried for 7 days at 25℃ and 50% relative humidity. The dried sample was then completely immersed in deionized water at 25℃, with the water level 20mm above the sample. After 240 hours of immersion, the sample was removed, and the degree of blistering, peeling, discoloration, or loss of gloss on the coating surface was observed. The severity levels were: Level 0: No blistering, peeling, discoloration, or loss of gloss on the coating surface; the coating remained completely intact. Level 1: Slight discoloration or loss of gloss on the coating surface; no blistering or peeling. Level 2: A small number of fine bubbles (diameter ≤0.5mm, area ≤5%) on the coating surface; no peeling; noticeable discoloration or loss of gloss. Level 3: Numerous bubbles (diameter ≤1mm, area ≤15%) on the coating surface; localized slight peeling (area ≤10%); severe discoloration or loss of gloss. Level 4: The coating surface has a large number of bubbles (diameter > 1 mm, area > 15%), with obvious peeling (area > 10%), seriously affecting the integrity of the coating. Level 5: The coating has failed (bubbling and peeling area > 50%, substrate exposed), and has lost its protective performance.

[0118] (v) Abrasion resistance test:

[0119] According to GB / T 1768 "Determination of Abrasion Resistance of Paints and Varnishes". The coating was applied to an aluminum plate (dry film thickness 80±2μm) and cured at room temperature for 7 days. The mass loss (unit: mg) was recorded using a Taber abrasion tester (CS-10 grinding wheel, 500g load, 1000 rpm).

[0120] (vi) Self-healing performance test:

[0121] The coating was applied to an ABS board (dry film thickness 80 μm) and dried for 7 days at 25°C and 50% relative humidity. A blade was used to make a vertical cut into the scratch: depth 50 μm, width 30 μm, length 10 mm; then the board was heated in a 60°C oven for 30 min, and the average width of the repaired scratch (in μm) was measured under a microscope.

[0122] Table 1 Performance Test Results

[0123]

[0124] The results above show that the coatings of Examples 1 to 3 exhibit superior performance, complete reaction, reasonable improvement and adjustment of polymerization, good structural uniformity, more complete solvent evaporation during preparation, lower monomer residue, and reduced VOC emissions. The bio-based waterborne polyurethane-acrylic interpenetrating polymer network contains a large number of active groups such as hydroxyl and carboxyl groups. During the coating film formation process, these active groups can chemically react with oxides or other polar groups on the substrate surface to form covalent bonds; simultaneously, through intermolecular van der Waals forces and hydrogen bonds, they generate strong physical adsorption with the substrate. Furthermore, with the reasonable ratio and increased amount of functional fillers, they can fill the voids in the resin network, enhancing the density and cohesion of the coating film, making the bond between the coating film and the substrate stronger. The dynamic covalent bonds (including disulfide bonds and dynamic chemical bonds related to transesterification reactions) within the self-healing resin possess unique reversible characteristics. During temperature changes or bending, when the coating is subjected to stress, the dynamic covalent bonds can break and recombine, alleviating stress concentration through the movement and rearrangement of molecular chains. Simultaneously, the bio-based waterborne polyurethane-acrylic interpenetrating network polymer enhances the coating's flexibility, allowing it to maintain structural integrity even under greater deformation. After drying, the resulting coating is denser with significantly reduced porosity, effectively blocking water molecule penetration channels. The synergistic effect of the bio-based waterborne polyurethane-acrylic interpenetrating network polymer and the dynamic covalent bond self-healing resin constructs a stable three-dimensional network structure, enhancing the coating's resistance to water erosion. Catechin β-cyclodextrin inclusion complexes are uniformly dispersed in the system, not only exerting antibacterial effects but also stabilizing the coating structure through interactions with resin molecules, reducing the destructive effects of water molecules. The optimized ratio of the bio-based waterborne polyurethane-acrylic interpenetrating network polymer and functional fillers significantly alters the coating's microstructure. The functional fillers, uniformly dispersed in the resin matrix, act as a reinforcing skeleton, improving the coating's surface hardness and wear resistance. The continuous phase formed by the bio-based waterborne polyurethane-acrylic interpenetrating network polymer exhibits excellent toughness and cohesive strength, effectively dispersing stress and reducing coating wear under abrasive friction. The increased content of the dynamically covalently self-healing resin significantly increases the number of dynamic covalent bonds in the coating. When scratches occur on the coating surface, under the influence of ambient temperature and molecular thermal motion, these dynamic covalent bonds break and recombine, promoting the diffusion and migration of molecular chains towards the scratched area. Through the entanglement and cross-linking of molecular chains, the scratch gaps are gradually filled, achieving self-healing functionality. Simultaneously, the bio-based waterborne polyurethane-acrylic interpenetrating network polymer provides a favorable matrix environment, which is conducive to the effective functioning of the dynamically covalently self-healing resin.

[0125] Comparative Example 1: When ordinary acrylic resin was used as a substitute, no interpenetrating network was formed. The acrylic resin itself had low monomer conversion rate and contained volatile monomers, leading to increased VOC emissions. Replacing the bio-based waterborne polyurethane-acrylic interpenetrating network polymer with ordinary waterborne acrylic resin resulted in the coating system losing the unique advantages of bio-based materials. Ordinary waterborne acrylic resin has a relatively simple molecular chain structure and lacks active groups capable of forming strong chemical bonds with the substrate, leading to decreased adhesion. Its low crosslinking density and weak intermolecular forces result in poor performance in terms of abrasion resistance, crack resistance, and water resistance. Acrylic resin has high rigidity but insufficient flexibility, making it prone to cracking.

[0126] Comparative Examples 2 to 4: Ethylhexyl palmitate promotes monomer reactions; its absence or inadequacy leads to increased unreacted monomer residue and elevated VOC volatilization. Excess ethylhexyl palmitate migrates to the surface, causing some esters to volatilize and increasing VOC volatilization. In the synthesis of bio-based waterborne polyurethane-acrylic interpenetrating polymer networks, ethylhexyl palmitate plays a crucial role in plasticizing, improving compatibility, and enhancing polymerizability. In Comparative Example 2, without added ethylhexyl palmitate, the interaction forces between polymer molecular chains are too strong, restricting the movement of molecular chain segments, resulting in poor coating flexibility and reduced abrasion resistance due to the lack of flexible buffering in the molecular chains. In Comparative Example 3, the addition amount is too small, resulting in insufficient improvement; the internal plasticizing effect of the molecular chains is weak, and the flexibility and impact resistance of the coating are not effectively improved. In Comparative Example 4, the addition of excessive ethylhexyl palmitate reduces the crosslinking density of the polymer, causing a decrease in the mechanical properties of the coating; water resistance deteriorates, and coating swelling occurs.

[0127] Comparative Examples 5 and 6: Insufficient dimethylolpropionic acid (DMPA) led to incomplete neutralization, resulting in the volatilization of residual triethylamine; excessive DMPA introduced excess carboxylic acid groups, requiring more triethylamine for neutralization, and causing the volatilization of residual amines. DMPA is an important raw material for introducing hydrophilic groups and plays a role in regulating water dispersibility and crosslinking structure in polymer synthesis. In Comparative Example 5, insufficient addition resulted in insufficient hydrophilic groups on the polymer molecular chains, preventing the formation of a stable emulsion system during water dispersion. This led to numerous defects in the coating film, affecting its density and mechanical properties, and reducing adhesion and water resistance. In Comparative Example 6, excessive addition caused over-branching of the polymer molecular chains, increasing the degree of entanglement between chains, hindering the uniformity of the crosslinking reaction, and resulting in an uneven crosslinking network structure. This reduced the flexibility and crack resistance of the coating film and also affected the adhesion between the coating and the substrate, leading to decreased adhesion.

[0128] Comparative Examples 7 to 8: The reduced amount of bio-based polyurethane prepolymer resulted in an incomplete interpenetrating network structure and increased unreacted monomer residues. Simultaneously, insufficient prepolymer affected emulsification, leading to increased solvent residues such as acetone. Excessive prepolymer hindered the reaction of acrylic monomers, resulting in more residual monomers. In Comparative Example 7, the amount of bio-based waterborne polyurethane prepolymer added was too small, resulting in insufficient effective components participating in the subsequent acrylate copolymerization reaction and an inability to form a complete interpenetrating network structure. This led to a decrease in the mechanical properties and stability of the coating film. In abrasion resistance tests, due to the lack of sufficient polymer support, the coating film was more easily damaged by abrasives, increasing mass loss. In Comparative Example 8, excessive addition significantly increased the viscosity of the system. During the reaction, uneven mixing of materials hindered the reaction from proceeding fully, resulting in an uneven distribution of polymer molecular weight. The coating film's performance became unstable, phase separation led to structural inhomogeneity, stress concentration, and varying degrees of decline in all performance indicators.

[0129] Comparative Example 9: When the dynamic covalent resin was replaced by ordinary acrylic resin, the dynamic stability of the thioester bonds was lost, and the residue of unreacted glycidyl methacrylate monomers from the resin synthesis increased; the monomers remaining in the acrylic resin itself volatilized. After replacing the dynamic covalent self-healing resin with ordinary waterborne acrylic resin, the coating almost lost its self-healing ability. The coating film formed by ordinary waterborne acrylic resin has a static cross-linked structure. When scratches occur on the coating surface, the molecular chains cannot move and recombine autonomously to repair the damage. At the same time, the mechanical properties and environmental resistance of this resin are relatively weak. In abrasion resistance, crack resistance, and water resistance tests, it performed worse than the coating containing the dynamic covalent self-healing resin.

[0130] In Comparative Example 10, the excessive amount of dynamic covalent self-healing resin resulted in excessive cross-linking of the coating film, causing it to become hard. The excessive dynamic bonds inhibited the continuity of the acrylic resin, limiting the repair efficiency. The self-healing performance was not as good as in Example 1, and the crack resistance was poor. The excessively high degree of cross-linking also affected the adhesion between the coating film and the substrate, resulting in a decrease in adhesion. In the abrasion resistance test, due to the increased brittleness of the coating film, it was more prone to cracking and peeling, leading to an increase in quality loss.

[0131] Comparative Examples 11 to 13: Isobutyl palmitate promotes monomer reaction; its absence or inadequacy leads to an increase in unreacted monomer residue, decreased chain segment flexibility during dynamic bond resin synthesis, reduced plasticity resulting in poor emulsion stability, and increased ethyl acetate solvent residue. Excessive isobutyl palmitate migrates to the surface, causing some esters to volatilize and increasing VOC emissions. In the synthesis of dynamic covalent bond self-healing resins, isobutyl palmitate has a significant impact on the flexibility and flowability of molecular chains. In Comparative Example 11, without the addition of isobutyl palmitate, the synthesized oligomer molecular chains are relatively rigid, making it difficult to form a uniform network structure during subsequent copolymerization with waterborne acrylic resin, resulting in decreased mechanical properties and self-healing properties of the coating. In Comparative Example 12, the addition amount was too small, resulting in insignificant improvement; the limited mobility of molecular chains affected the exchange and recombination of dynamic covalent bonds, leading to unsatisfactory self-healing properties and crack resistance. Excessive addition in Comparative Example 13 interfered with the exchange of thioester bonds, resulting in loss of dynamic response capability, decreased hardness and abrasion resistance of the coating film, and increased mass loss in abrasion resistance tests.

[0132] Comparative Examples 14 and 15: Insufficient oligomer addition resulted in an incomplete dynamic bond network, inadequate cross-linking, and residual monomer volatilization. Simultaneously, insufficient oligomer led to uneven filler dispersion and increased volatiles. Excessive oligomer resulted in an overly dense dynamic bond network, with some thioester bonds remaining unreacted. Furthermore, excessive oligomer hindered the emulsification process, leading to uneven dispersion, uneven cross-linking, and increased volatiles. In Comparative Example 14, insufficient oligomer addition resulted in an insufficient number of dynamic covalent bonds provided during copolymerization with waterborne acrylic resin, failing to effectively achieve self-healing. Additionally, the low oligomer content limited its improvement on the mechanical properties of the coating, affecting abrasion resistance and crack resistance. In Comparative Example 15, excessive addition resulted in an excessively high cross-linking density in the coating, reducing the flexibility of the molecular chains and causing the coating to become brittle and prone to cracking during crack resistance testing. Adhesion also decreased due to poor compatibility between the coating and the substrate.

[0133] Comparative Example 16: Replacing catechin β-cyclodextrin inclusion complex with catechin reduced the stability of catechin in the coating system. Catechins are prone to oxidation or aggregation during water dispersion. The free state of catechin can react adversely with resin molecules, destroying the cross-linking structure of the resin and leading to a decrease in the water resistance and self-healing properties of the coating film.

Claims

1. A safe and environmentally friendly water-based coating for toys, characterized in that, The coating comprises the following raw materials in parts by weight: 40-45 parts of bio-based waterborne polyurethane-acrylic interpenetrating network polymer, 8-10 parts of dynamic covalent self-healing resin, 20-25 parts of functional filler, 6-8 parts of antibacterial agent, 0.5-1 part of thickener, 1-2 parts of dispersant, 0.2-0.5 parts of leveling agent, 8-12 parts of pigment, 0.5-1 part of defoamer, with the balance being deionized water, and a solid content of 45%-55%. The antibacterial agent is a catechin β-cyclodextrin inclusion complex; The preparation method of the bio-based waterborne polyurethane-acrylic acid interpenetrating network polymer includes: S1: By mass, add 100-120 parts of castor oil-modified polyol to 80-100 parts of acetone and stir until homogeneous. Then, add 35-40 parts of lysine diisocyanate, 10-15 parts of ethylhexyl palmitate, and 0.1-0.2 parts of dibutyltin dilaurate in sequence. Reflux at 80-85°C for 3-4 hours. Add 8-10 parts of dimethylolpropionic acid and reflux at 50-60°C for 1-1.5 hours. Add triethylamine at 1-1.1 times the mass of dimethylolpropionic acid for neutralization and stir until homogeneous to obtain a prepolymer solution. S2: Under stirring, add the prepolymer solution to 2.5 to 3.5 times the mass of the prepolymer solution in deionized water, stir to emulsify, remove acetone and part of the deionized water by vacuum distillation, and achieve a solid content of 45 wt% to 50 wt% to obtain a bio-based waterborne polyurethane prepolymer. S3: Add 100-120 parts of bio-based waterborne polyurethane prepolymer to 50-80 parts of deionized water and stir until homogeneous. Then add 30-35 parts of butyl acrylate, 20-25 parts of methyl methacrylate, and 5-8 parts of hydroxyethyl methacrylate in sequence and stir until homogeneous. Add 10-12 parts of ammonium persulfate aqueous solution with a concentration of 4wt%-6wt% and reflux at 75℃-80℃ for 3-4 hours to obtain a bio-based waterborne polyurethane-acrylic acid interpenetrating network polymer. The preparation method of the dynamic covalent self-healing resin includes: N1: By mass, under nitrogen protection, 20-25 parts of 3,3'-thiodipropionic acid, 40-45 parts of glycidyl methacrylate, 10-12 parts of isobutyl palmitate, 50-60 parts of ethyl acetate, and 2-3 parts of triethylamine were refluxed at 80-85°C for 3-4 hours, cooled to room temperature, and the filtrate was collected to obtain product A. Under nitrogen protection, all of product A, 30-35 parts of methyl methacrylate, 5-8 parts of ethylene glycol dimethacrylate, 0.8-1.2 parts of azobisisobutyronitrile, and 60-80 parts of ethyl acetate were refluxed at 75-80°C for 6-8 hours, cooled to room temperature, and product B was obtained. Product B was poured into cold methanol to precipitate, and the solid was collected by filtration. The solid was washed with methanol and dried under vacuum to obtain the oligomer. N2: By mass, add 100-120 parts of waterborne acrylic resin to 15-25 parts of deionized water, stir until homogeneous, add 13-17 parts of oligomer, stir until homogeneous, add 8-10 parts of potassium persulfate aqueous solution with a concentration of 4wt%-6wt%, and reflux at 80℃-85℃ for 3-4 hours to obtain dynamic covalent bond self-healing resin.

2. The safe and environmentally friendly water-based coating for toys according to claim 1, characterized in that, In S1, the stirring is performed at 200 r / min to 300 r / min for 15 min to 20 min, and the stirring speed for the reflux reaction is 250 rpm to 300 rpm. In S2, the stirring speed is 1000 r / min to 1200 r / min, and the stirring emulsification time is 30 min to 40 min. In S3, the stirring is performed at 200 r / min to 300 r / min for 15 min to 20 min, and the stirring speed for the reflux reaction is 250 rpm to 300 rpm.

3. The safe and environmentally friendly water-based coating for toys according to claim 1, characterized in that, In N1, the stirring speed of the reflux reaction is 250 rpm to 300 rpm, the sieve mesh size for filtration is 100 mesh to 200 mesh, the temperature of the cold methanol is 2℃ to 6℃, the amount of cold methanol is 10 to 12 times the volume of product B, the sieve mesh size for filtration to collect the solid is 200 mesh to 325 mesh, the number of methanol washings is 3 to 5 times, and the vacuum drying is performed at 35℃ to 40℃ for 24 to 30 hours.

4. The safe and environmentally friendly water-based coating for toys according to claim 1, characterized in that, In N2, the stirring is carried out at 200 r / min to 300 r / min for 15 min to 20 min; the stirring speed for the reflux reaction is 250 rpm to 300 rpm.

5. The safe and environmentally friendly water-based coating for toys according to claim 1, characterized in that, The preparation method of the catechin β-cyclodextrin inclusion complex includes: preparing a 15 g / L to 18 g / L β-cyclodextrin aqueous solution; preparing a 4.5 g / L to 5.0 g / L catechin ethanol solution; adding the catechin ethanol solution dropwise to the β-cyclodextrin aqueous solution under stirring, stirring at 30℃ to 40℃ for 2 h to 4 h for inclusion reaction, allowing it to stand at 4℃ to 6℃ to precipitate the inclusion complex, centrifuging at 4000 rpm to 6000 rpm for 10 min to 15 min, collecting the precipitate, drying it under vacuum at 40℃ to 50℃ to constant weight, and breaking it up to obtain the catechin β-cyclodextrin inclusion complex.

6. The safe and environmentally friendly water-based coating for toys according to claim 1, characterized in that, The component mass ratio of the functional filler is: calcium carbonate: talc: kaolin: titanium dioxide = (30-35): (20-25): (8-12): (5-10); the functional filler passes through a 325-460 mesh sieve.

7. The safe and environmentally friendly water-based coating for toys according to claim 1, characterized in that, The thickener is hydroxyethyl cellulose or xanthan gum; the dispersant is lecithin; the leveling agent is acrylate leveling agent; the pigment is a natural plant pigment; and the defoamer is a polyether defoamer.

8. The method for preparing a safe and environmentally friendly water-based coating for toys according to claim 1, characterized in that, Includes the following steps: According to the mass fraction, add the bio-based waterborne polyurethane-acrylic interpenetrating network polymer to the reactor and stir at a low speed of 200 rpm to 250 rpm. Then, add the dynamic covalent self-healing resin, functional filler, antibacterial agent, and pigment in sequence, and continue stirring for 30 min to 40 min to obtain mixture A. Add the dispersant, leveling agent, and thickener to 8 parts to 10 parts of deionized water and mix evenly to obtain mixture B. Add mixture B and defoamer to mixture A and stir at 800 rpm to 1200 rpm for 30 min to 40 min. Adjust the solid content of the coating to 45 wt% to 55 wt% with deionized water and filter through a 150-200 mesh sieve to obtain the coating.

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