Non-toxic environment-friendly water-based protective coating and preparation method thereof

Abstract

The invention relates to a non-toxic environment-friendly water-based protective paint and a preparation method thereof, and belongs to the technical field of paints.The paint is prepared from siloxane-bio-based polyester composite emulsion, a cyclodextrin-sodium phytate-ketimine composite cross-linking agent, composite nanometer reinforcing slurry, talcum powder, hydrophilic vapor-phase silicon dioxide, sodium glycinate and deionized water. The siloxane-bio-based polyester composite emulsion is prepared from D4, tetramethylammonium hydroxide, AGE, a trimethylolpropane triglycidyl ether mixed solution, bio-based polyester polyol, an emulsifier and isodecanol polyoxyethylene ether. The cyclodextrin-sodium phytate-ketimine composite cross-linking agent is prepared from beta-cyclodextrin, epoxy chloropropane, sodium phytate, ketimine and the like. The composite nano reinforced slurry is prepared by modifying and dispersing magnesium lithium silicate and nano silicon dioxide through NDZ-201 titanate, KH550, sodium glycolate, sodium polyacrylate and the like. The coating is non-toxic and low in emission, and the adhesive force and the medium infiltration resistance are improved.

Description

Technical Field

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

[0002] With increasingly stringent environmental regulations and the popularization of green manufacturing concepts, traditional solvent-based coatings, due to their high emissions of volatile organic compounds, strong irritation, and flammability and explosiveness, are gradually being replaced by environmentally friendly coatings. Water-based protective coatings, using water as the main dispersion medium, contain little or no organic solvents. They possess advantages such as low toxicity, odorless, pollution-free, safe application, and convenient storage and transportation, and have been widely used in metal corrosion protection, building decoration, rail transportation, shipbuilding, and machinery equipment, becoming the mainstream development direction of modern protective coating systems.

[0003] Currently, waterborne protective coatings primarily use waterborne acrylic, waterborne epoxy, waterborne polyurethane, waterborne alkyd, and their modified copolymer systems as core base materials. Films are formed through emulsification polymerization, physical dispersion, and cross-linking curing, providing basic anti-corrosion, anti-rust, decorative, and protective functions under normal conditions. Compared to traditional solvent-based products, waterborne coatings offer significant upgrades in environmental performance, meeting the requirements of most indoor and conventional outdoor applications. However, due to the inherent characteristics of waterborne systems, existing waterborne protective coatings still have significant shortcomings in overall performance, failing to fully meet the stringent requirements of high-end equipment, heavily corrosive environments, and long-term service.

[0004] The most prominent problem with water-based protective coatings currently lies in their insufficient protective stability. Slow water evaporation rates lead to poor early water resistance, causing whitening, stickiness, and blistering upon contact with water, severely impacting construction efficiency and film quality. Simultaneously, the weak wetting ability of water-based resins at the substrate interface and insufficient chemical bonding result in low coating adhesion, making them prone to peeling, flaking, and cracking under thermal cycling, mechanical vibration, and salt spray corrosion, significantly shortening their protective lifespan. Regarding corrosion resistance and media resistance, water-based coatings often retain micropores after curing, forming channels for water vapor, chloride ions, and acid / alkali media penetration, making it difficult to achieve a dense barrier. Long-term service can lead to substrate corrosion and coating blistering and peeling.

[0005] In summary, existing water-based protective coatings struggle to achieve a balanced approach in terms of environmental friendliness, adhesion, and corrosion resistance, failing to meet the dual demands of high-end applications for non-toxicity, high protection, and long-term stability. Therefore, there is a need to develop novel water-based protective coatings that, while ensuring non-toxicity and environmental friendliness, also improve performance indicators. Summary of the Invention

[0006] To address the challenge of simultaneously achieving environmental safety and superior protective performance in existing water-based protective coatings, this invention provides a non-toxic, environmentally friendly water-based protective coating and its preparation method. Through resin structure optimization, additive-free film-forming technology, interface enhancement modification, and a non-toxic crosslinking system design, the coating achieves low emissions and improves density, adhesion, and resistance to media penetration, truly unifying environmental friendliness and protective performance to meet the high-end green protection needs of multiple fields. The specific technical solution is as follows:

[0007] A non-toxic and environmentally friendly water-based protective coating comprises the following raw materials in parts by weight: 60-65 parts of siloxane-bio-based polyester composite emulsion, 4-6 parts of cyclodextrin-sodium phytate-ketimine composite crosslinking agent, 7-11 parts of composite nano-reinforcing paste, 4-7 parts of talc, 0.9-1.3 parts of hydrophilic fumed silica, 0.2-0.4 parts of sodium glycine, and 18-24 parts of deionized water; The siloxane-bio-based polyester composite emulsion is prepared by adding tetramethylammonium hydroxide to D4 and refluxing at 90-95°C; adding a mixture of AGE and trimethylolpropane triglycidyl ether dropwise at 65-70°C, maintaining the temperature at 65-70°C, and reacting at 80-85°C; adding bio-based polyester polyol and reacting at 85-90°C; adding emulsifier and isomeric decayl alcohol polyoxyethylene ether at 40-45°C for shearing; and adding deionized water dropwise to obtain a product with a solid content of 40-45 wt%. The bio-based polyester polyol is prepared by adding PDO, SA, and MA at 155-165°C, adding tetrabutyl titanate and reacting at 195-205°C; and adding hydroquinone and phenothiazine at 145-155°C with stirring. The cyclodextrin-sodium phytate-ketoimine composite crosslinking agent is prepared by dissolving β-cyclodextrin in deionized water, activating it by adjusting the pH to 11-12 at 40-45℃, adding epichlorohydrin dropwise and reacting at 55-60℃; adding 20-22wt% sodium phytate aqueous solution at 45-50℃, maintaining pH > 9, and reacting at 65-70℃; adding ketoimine at 50-55℃ and stirring; neutralizing with sodium glycinate to pH 7-8 at 35-40℃, and filtering to obtain the final product. The composite nano-reinforced paste is prepared by first adding lithium magnesium silicate and nano silica to a mixer; then diluting NDZ-201 titanate with anhydrous ethanol and spraying it into the mixer in a mist and stirring; then pre-hydrolyzing KH550 with an ethanol aqueous solution and spraying it into the mixer in a mist and stirring; finally adding a mixture of sodium glycolate, sodium polyacrylate and deionized water, ball milling, aging, and filtration.

[0008] Furthermore, the siloxane-bio-based polyester composite emulsion comprises D4, tetramethylammonium hydroxide, AGE, trimethylolpropane triglycidyl ether, bio-based polyester polyol, emulsifier, isomeric decayl alcohol polyoxyethylene ether, and deionized water in a mass ratio of (25-30):(0.12-0.18):(10-14):(4-5):(6-9):(1.5-2.0):(0.2-0.4):(40-45), with D4 added at 80-85°C. After ammonium chloride is added, the mixture is refluxed at 90–95 °C for 3–4 h; a mixture of AGE and trimethylolpropane triglycidyl ether is added dropwise at 65–70 °C, and the mixture is kept at 65–70 °C for 1.5–2 h, and then reacted at 80–85 °C for 1–1.5 h; bio-based polyester polyol is added, and the mixture is reacted at 85–90 °C for 2.5–3 h; an emulsifier and isomeric decayl alcohol polyoxyethylene ether are added at 40–45 °C, the mixture is sheared at 800–1000 rpm, and deionized water is added dropwise to obtain a product with a solid content of 40–45 wt%. The bio-based polyester polyol is prepared by mixing PDO, SA, MA, tetrabutyl titanate, hydroquinone, and phenothiazine in a mass ratio of (145-155):(115-120):(95-100):(0.4-0.6):(0.2-0.4):(0.05-0.1). PDO, SA, and MA are heated at 155-165℃ for 1-1.5 hours, and tetrabutyl titanate is added and reacted at 195-205℃ for 4-6 hours. Hydroquinone and phenothiazine are added at 145-155℃ and stirred to obtain the final product.

[0009] Furthermore, the preparation method of the siloxane-bio-based polyester composite emulsion includes the following steps: N1: By weight, 145-155 parts of PDO, 115-120 parts of SA, and 95-100 parts of MA are kept at 155-165℃ for 1-1.5 hours, 0.4-0.6 parts of tetrabutyl titanate are added, and the mixture is reacted at 195-205℃ for 4-6 hours until the acid value is <10mg KOH / g; 0.2-0.4 parts of hydroquinone and 0.05-0.1 parts of phenothiazine are added at 145-155℃, and the mixture is stirred to obtain a bio-based polyester polyol; N2: By weight, 25-30 parts of D4 are stirred at 80-85℃, 0.12-0.18 parts of tetramethylammonium hydroxide are added, and the mixture is refluxed at 90-95℃ for 3-4 hours to obtain hydroxyl-terminated polysiloxane; a mixture of 10-14 parts of AGE and 4-5 parts of trimethylolpropane triglycidyl ether is added dropwise at 65-70℃, and the mixture is kept at 65-70℃ for 1.5-2 hours, and reacted at 80-85℃ for 1-1.5 hours; 6-9 parts of bio-based polyester polyol are added, and the mixture is reacted at 85-90℃ for 2.5-3 hours; 1.5-2.0 parts of emulsifier and 0.2-0.4 parts of isomeric decaol polyoxyethylene ether are added at 40-45℃, sheared at 800-1000 rpm, 40-45 parts of deionized water are added dropwise, the temperature is lowered to 25-30℃, the solid content is adjusted to 40-45 wt%, and the mixture is filtered to obtain a siloxane-bio-based polyester composite emulsion.

[0010] Furthermore, the cyclodextrin-sodium phytate-ketoimine composite crosslinking agent is prepared by mixing β-cyclodextrin, epichlorohydrin, 20-22 wt% sodium phytate aqueous solution, and ketoimine in a mass ratio of (12-15):(3-3.5):(8-10):(2.5-3.5). β-cyclodextrin is dissolved in deionized water and activated at pH 11-12 at 40-45℃. Epichlorohydrin is added dropwise and the reaction is carried out at 55-60℃ for 4.5-5 hours. At 45-50℃, 20-22 wt% sodium phytate aqueous solution is added, and the reaction is carried out at 65-70℃ while maintaining pH > 9 for 3.5-4 hours. Ketoimine is added at 50-55℃ and stirred for 1-1.5 hours. The mixture is then neutralized to pH 7-8 with sodium glycinate at 35-40℃ and filtered to obtain the final product.

[0011] Further, the preparation method of the cyclodextrin-sodium phytate-ketoimine composite crosslinking agent includes the following steps: 12-15 parts by weight of β-cyclodextrin are added to 90-100 parts of deionized water, stirred and dissolved at 60-70°C, cooled to 40-45°C, and the pH is adjusted to 11-12 for activation. 3-3.5 parts of epichlorohydrin are added dropwise, and the reaction is carried out at 55-60°C for 4.5-5 hours to obtain an epoxy-modified β-cyclodextrin solution. The temperature is then lowered to 45-50°C, and 8-10 parts of 20-22 wt% sodium phytate aqueous solution are added. The pH is maintained >9, and the reaction is carried out at 65-70°C for 3.5-4 hours. The temperature is then lowered to 50-55°C, and 2.5-3.5 parts of ketoimine are added and stirred for 1-1.5 hours. The temperature is then lowered to 35-40°C, neutralized to pH 7-8 with sodium glycinate, and filtered to obtain the cyclodextrin-sodium phytate-ketoimine composite crosslinking agent.

[0012] Furthermore, the preparation method of the ketimine includes: reacting 80-90 parts by weight of IPDA, 95-105 parts by weight of MIBK and 5-10 parts by weight of toluene under reflux at 105-115°C for 5.5-6.5 h, followed by vacuum distillation to obtain a ketimine with a solid content >98wt%.

[0013] Furthermore, the composite nano-reinforced slurry is prepared by mixing lithium magnesium silicate, nano silica, NDZ-201 titanate, KH550, sodium glycolate, sodium polyacrylate, and deionized water in a mass ratio of (25-35):(4-6):(2-3):(1.0-1.5):(1.2-1.8):(0.3-0.6):(65-70). First, lithium magnesium silicate and nano silica are added to a mixer. NDZ-201 titanate is diluted with anhydrous ethanol and then sprayed into the mixer in a mist and stirred. Next, KH550 is pre-hydrolyzed with an ethanol-water solution and then sprayed into the mixer in a mist and stirred. Finally, a mixture of sodium glycolate, sodium polyacrylate, and deionized water is added, ball-milled for 3-3.5 hours, stirred and matured at 25-35°C for 5.5-6.5 hours, and then filtered to obtain the final product.

[0014] Furthermore, the preparation method of the composite nano-reinforced slurry includes the following steps: 25-35 parts by weight of lithium magnesium silicate and 4-6 parts by weight of nano-silica are added to a mixer; 2-3 parts by weight of NDZ-201 titanate are diluted with anhydrous ethanol and then sprayed into the mixer in a mist and stirred; 1.0-1.5 parts by weight of KH550 are pre-hydrolyzed with an ethanol aqueous solution and then sprayed into the mixer in a mist and stirred; a mixture of 1.2-1.8 parts by weight of sodium glycolate, 0.3-0.6 parts by weight of sodium polyacrylate and 65-70 parts by weight of deionized water is added, and the mixture is ball-milled for 3-3.5 hours to obtain a slurry with a particle size D90 < 500 nm; the slurry is stirred and matured at 25-35°C for 5.5-6.5 hours; and then filtered to obtain the composite nano-reinforced slurry.

[0015] The preparation method of the above-mentioned non-toxic and environmentally friendly water-based protective coating includes the following steps: According to the coating formulation, sodium glycinate was added to deionized water and stirred; hydrophilic fumed silica was added and stirred; talc powder and composite nano-reinforcing paste were added and stirred; siloxane-bio-based polyester composite emulsion was added and stirred; cyclodextrin-sodium phytate-ketimine composite crosslinking agent was added and stirred; vacuum degassing and filtration were performed to obtain the coating.

[0016] In the above-mentioned preparation method of the coating, according to the coating formula, sodium glycinate is added to deionized water and stirred at 200-300 rpm for 3-5 min; hydrophilic fumed silica is added and stirred at 400-600 rpm for 8-12 min; talc powder and composite nano-reinforcing slurry are added and stirred at 600-800 rpm for 15-20 min; siloxane-bio-based polyester composite emulsion is added and stirred at 600-800 rpm for 15-20 min; cyclodextrin-sodium phytate-ketimine composite crosslinking agent is added and stirred at 600-800 rpm for 10-15 min; vacuum degassing is performed at -0.07 MPa to -0.09 MPa for 5-10 min, and the mixture is filtered through a 100-150 mesh filter to obtain the coating.

[0017] The present invention provides a non-toxic and environmentally friendly water-based protective coating and its preparation method, which have the following beneficial effects: I. This non-toxic and environmentally friendly water-based protective coating achieves a synergistic balance between non-toxicity, environmental friendliness, and long-lasting high protective performance, fundamentally solving the industry pain point of traditional water-based protective coatings that struggle to balance environmental friendliness and protective properties. Through the integrated design of resin structure optimization, additive-free film-forming technology, interface enhancement modification, and a non-toxic crosslinking system, it achieves extremely low VOC emissions while significantly improving coating density, interfacial adhesion, and resistance to media penetration. The coating forms a microstructure with high crosslinking density, high compactness, strong interfacial bonding, and efficient shielding, maintaining long-lasting and stable protective performance even under harsh conditions such as thermal cycling, salt spray corrosion, and acid and alkali media, while also possessing good mechanical properties, making it suitable for high-end green protection needs in multiple fields.

[0018] II. In the preparation of siloxane-bio-based polyester composite emulsion, precise control of the mass ratio of D4, AGE, and trimethylolpropane triglycidyl ether, as well as the reaction temperature and time at each stage, results in denser molecular packing and a significant reduction in coating porosity. The siloxane Si-O-Si backbone endows the coating with hydrophobic, high and low temperature resistance, and media resistance properties, while the bio-based polyester polyol enhances the affinity between the resin and the metal substrate. The two are grafted together through covalent bonds to avoid phase separation, achieving a coating that is both rigid and flexible. The compound emulsifier of alkyl glycoside and isomeric decayl alcohol polyoxyethylene ether, as well as the control of parameters such as shearing and water addition, ensure stable dispersion of the emulsion, resulting in a defect-free film formation channel. At the same time, it is low in toxicity and free of APEO, reducing VOC emissions.

[0019] III. In the preparation of the cyclodextrin-sodium phytate-ketimine composite crosslinking agent, the activation pH of β-cyclodextrin, the reaction temperature of epichlorohydrin, and the addition ratio of sodium phytate are controlled to enable the epoxy-activated cyclodextrin to form multi-point bonds with sodium phytate and ketimine. Ketoimine, as a latent curing agent, combined with room temperature reaction parameters, achieves slow and uniform crosslinking at room temperature, reducing the internal stress of the coating and VOC emissions. Sodium phytate forms a chelated conversion film with the metal substrate, and the cavity structure of cyclodextrin enables the anchoring and controlled release of sodium phytate, ultimately constructing a non-toxic interpenetrating crosslinking network, which significantly improves the crosslinking density and interfacial adhesion of the coating.

[0020] IV. In the preparation of composite nano-reinforced paste, precise control of the ratio of lithium magnesium silicate to nano silica, as well as the dilution, hydrolysis, and spraying parameters of NDZ-201 and KH550 dual coupling agents, achieves efficient organic modification of inorganic nanoparticles and constructs a three-phase covalent bond between resin, filler, and substrate. Control of ball milling time and curing temperature ensures uniform dispersion in the system, filling the micropores inside the coating and improving density. The dispersion and stabilization system of sodium glycolate and sodium polyacrylate prevents nanoparticle aggregation, eliminates internal defects in the coating, and further enhances the shielding and barrier effect.

[0021] 5. The epoxy and hydroxyl groups of the siloxane-bio-based polyester composite emulsion covalently bond with the amino and epoxy groups of the cyclodextrin-sodium phytate-ketimine crosslinking agent, further increasing the crosslinking density, making the interpenetrating crosslinking network more complete, and significantly enhancing the coating cohesion.

[0022] VI. After being modified by a dual coupling agent, the inorganic nanoparticles of the composite nano-reinforced paste form covalent bonds with the emulsion resin. Talc and hydrophilic fumed silica serve as auxiliary fillers, forming macroscopic and microscopic multi-level filling with the nano-paste, further reducing the porosity of the coating, strengthening the labyrinth effect, and improving the shielding and barrier capabilities. VII. Sodium phytate in the crosslinking agent forms a chelated conversion film with the metal substrate, the bio-based polyester in the emulsion enhances the affinity with the substrate, and the nano-particles are covalently bonded to the substrate. The three work together to construct a strong interfacial bonding system, which solves the problems of low adhesion and easy peeling of traditional water-based coatings.

[0023] 8. Sodium glycinate serves as a neutralizing agent in the preparation of crosslinking agents and also plays a role in dispersing and pH adjustment in coating mixing. Hydrophilic fumed silica enhances the thixotropy and film density of the coating. All additives work in combination with the main agent, with no superfluous components, while ensuring that the system is non-toxic and low in VOCs.

[0024] Overall, the synergistic effect of the various components in the formula can achieve good film-forming effect without the need for additional additives such as leveling agents, defoamers, and anti-settling agents. This enables the coating to simultaneously possess four core characteristics: high crosslinking density, high density, strong interfacial bonding, and efficient shielding and barrier. Ultimately, it achieves the dual performance requirements of being non-toxic and environmentally friendly while providing long-lasting and high protection. Detailed Implementation

[0025] Some embodiments are given below, but the present invention is not limited to these embodiments.

[0026] Glossary: ​​PDO is 1,3-propanediol; SA is succinic acid; MA is maleic anhydride; D4 is octamethylcyclotetrasiloxane; AGE is allyl glycidyl ether; IPDA is isophorone diamine; MIBK is methyl isobutyl ketone; KH550 is γ-aminopropyltriethoxysilane.

[0027] Example 1 A non-toxic and environmentally friendly water-based protective coating, comprising the following raw materials in parts by weight: 62 parts of siloxane-bio-based polyester composite emulsion, 5 parts of cyclodextrin-sodium phytate-ketimine composite crosslinking agent, 9 parts of composite nano-reinforcing paste, 5.5 parts of talc, 1.1 parts of hydrophilic fumed silica, 0.3 parts of sodium glycine, and 20 parts of deionized water.

[0028] The preparation method of the siloxane-bio-based polyester composite emulsion includes the following steps: N1: Under nitrogen protection, 150 parts PDO, 118 parts SA, and 97 parts MA were mixed by mass, heated to 155-165℃, and kept at this temperature for 1 hour until the materials were melted and mixed evenly. 0.5 parts tetrabutyl titanate were added, and the temperature was increased to 195-205℃ at a rate of 6℃ / h. The mixture was stirred at 250 rpm for 5 hours until the acid value was <10 mg KOH / g, during which water was continuously separated by a water separator. The temperature was then lowered to 145-155℃, and 0.3 parts hydroquinone and 0.08 parts phenothiazine were added. The mixture was stirred at 250 rpm for 30 minutes to obtain bio-based polyester polyol. Under nitrogen protection, 28 parts by weight of D4 were stirred at 250 rpm for 15 min at 80–85 °C. 0.15 parts of tetramethylammonium hydroxide were added, and the mixture was heated to 90–95 °C and refluxed at 250 rpm for 3.5 h to obtain hydroxyl-terminated polysiloxane. The mixture was then cooled to 65–70 °C, and a mixture of 12 parts of AGE and 4.5 parts of trimethylolpropane triglycidyl ether was added dropwise at a rate of 1.2 mL / min. After the addition was complete, the mixture was maintained at 65–70 °C at 250 rpm. Stir for 1.5 h, heat to 80-85℃ and stir at 250 rpm for 1 h; add 7.5 parts of bio-based polyester polyol and stir at 85-90℃ and 250 rpm for 3 h; cool to 40-45℃, add 1.8 parts of emulsifier and 0.3 parts of isomeric decaol polyoxyethylene ether, shear at 900 rpm for 25 min; add 42 parts of deionized water dropwise, cool to 28℃, adjust the solid content to 43 wt% with deionized water, filter through 200 mesh to obtain siloxane-bio-based polyester composite emulsion.

[0029] The preparation method of the cyclodextrin-sodium phytate-ketoimine composite crosslinking agent includes the following steps: M1: By mass, 85 parts IPDA, 100 parts MIBK, and 8 parts toluene were mixed and refluxed at 105–115°C and 250 rpm for 6 hours, with continuous water separation using a water separator; MIBK and toluene were recovered by vacuum distillation at 80–90°C to obtain ketimine with a solid content of 98.9 wt%. M2: By mass, 14 parts of β-cyclodextrin were added to 95 parts of deionized water, heated to 60-70℃ and stirred until completely dissolved, cooled to 42℃, and the pH was adjusted to 11.5 with sodium hydroxide. The mixture was activated for 35 min. 3.2 parts of epichlorohydrin were added dropwise, and the mixture was stirred at 250 rpm for 4.5 h at 55-60℃ to obtain an epoxy-modified β-cyclodextrin solution. The mixture was cooled to 48℃, and 9 parts of 21 wt% sodium phytate aqueous solution were added. The pH of the reaction system was kept >9 (if the pH decreased, it was adjusted with sodium hydroxide). The mixture was stirred at 250 rpm for 3.5 h at 65-70℃. The mixture was cooled to 50-55℃, and 3 parts of ketoimine were added. The mixture was stirred at 250 rpm for 1 h. The mixture was cooled to 38℃ and neutralized to pH 7.5 with sodium glycinate. The insoluble matter was removed by filtration through a 200 mesh to obtain the cyclodextrin-sodium phytate-ketoimine composite crosslinking agent.

[0030] The preparation method of the composite nano-reinforced slurry includes the following steps: 30 parts by mass of lithium magnesium silicate and 5 parts by mass of nano-silica are dried at 110–120℃ for 2 hours, cooled to room temperature, and then added to a mixer; 2.5 parts by mass of NDZ-201 titanate are diluted with 2.8 times the mass of anhydrous ethanol and sprayed into the mixer in a mist, stirred at 400 rpm for 12 minutes; 1.2 parts by mass of KH550 are pre-hydrolyzed with 4 times the mass of 88 vol% ethanol aqueous solution for 35 minutes, sprayed into the mixer in a mist, stirred at 400 rpm for 18 minutes, transferred to a ball mill (zirconium bead particle size range 0.5–1.0 mm), and a mixture of 1.5 parts by mass of sodium glycolate, 0.5 parts by mass of sodium polyacrylate, and 68 parts by mass of deionized water is added, ball-milled for 3 hours to obtain a slurry with a particle size D90 of 463 nm, stirred and matured at 250 rpm at 25–35℃ for 6 hours; filtered through a 200-mesh screen to obtain the composite nano-reinforced slurry.

[0031] The preparation method of the above-mentioned non-toxic and environmentally friendly water-based protective coating includes the following steps: According to the coating formulation, sodium glycinate was added to deionized water and stirred at 250 rpm for 4 min; hydrophilic fumed silica was added and stirred at 500 rpm for 10 min; talc powder and composite nano-reinforcing slurry were added and stirred at 700 rpm for 18 min; siloxane-bio-based polyester composite emulsion was added and stirred at 700 rpm for 18 min; cyclodextrin-sodium phytate-ketimine composite crosslinking agent was added and stirred at 700 rpm for 12 min; vacuum degassing at -0.08 MPa was performed for 8 min; and the mixture was filtered through a 100-mesh sieve to obtain the coating.

[0032] Example 2 A non-toxic and environmentally friendly water-based protective coating, comprising the following raw materials in parts by weight: 60 parts of siloxane-bio-based polyester composite emulsion, 4 parts of cyclodextrin-sodium phytate-ketimine composite crosslinking agent, 7 parts of composite nano-reinforcing paste, 4 parts of talc, 0.9 parts of hydrophilic fumed silica, 0.2 parts of sodium glycine, and 18 parts of deionized water.

[0033] The preparation method of the siloxane-bio-based polyester composite emulsion includes the following steps: N1: Under nitrogen protection, 145 parts PDO, 115 parts SA, and 95 parts MA were mixed by mass, heated to 155-165℃, and kept at this temperature for 1 hour until the materials were melted and mixed evenly. 0.4 parts tetrabutyl titanate were added, and the temperature was increased to 195-205℃ at a rate of 5℃ / h. The mixture was stirred at 200 rpm for 4 hours until the acid value was <10 mg KOH / g, during which water was continuously separated by a water separator. The temperature was then lowered to 145-155℃, and 0.2 parts hydroquinone and 0.05 parts phenothiazine were added. The mixture was stirred at 200 rpm for 25 minutes to obtain bio-based polyester polyol. Under nitrogen protection, 25 parts by weight of D4 were stirred at 200 rpm for 10 min at 80–85 °C. 0.12 parts of tetramethylammonium hydroxide were added, and the mixture was heated to 90–95 °C and refluxed at 200 rpm for 3 h to obtain hydroxyl-terminated polysiloxane. The mixture was then cooled to 65–70 °C, and a mixture of 10 parts of AGE and 4 parts of trimethylolpropane triglycidyl ether was added dropwise at a rate of 1.0 mL / min. After the addition was complete, the mixture was kept at 65–70 °C and stirred at 200 rpm. After 1.5 hours, the temperature was raised to 80-85℃ and stirred at 200 rpm for 1 hour. 6 parts of bio-based polyester polyol were added, and the mixture was stirred at 200 rpm for 2.5 hours at 85-90℃. The temperature was lowered to 40-45℃, and 1.5 parts of emulsifier and 0.2 parts of isomeric decaol polyoxyethylene ether were added. The mixture was sheared at 800 rpm for 20 minutes. 40 parts of deionized water were added dropwise, and the temperature was lowered to 25℃. The solid content was adjusted to 40 wt% with deionized water, and the mixture was filtered through a 200-mesh filter to obtain a siloxane-bio-based polyester composite emulsion.

[0034] The preparation method of the cyclodextrin-sodium phytate-ketoimine composite crosslinking agent includes the following steps: M1: By mass, 80 parts IPDA, 95 parts MIBK, and 5 parts toluene were mixed and refluxed at 200 rpm for 5.5 h at 105–115 °C, with continuous water separation using a water separator; MIBK and toluene were recovered by vacuum distillation at 80–90 °C to obtain ketimine with a solid content of 99.1 wt%. M2: By mass, 12 parts of β-cyclodextrin were added to 90 parts of deionized water, heated to 60-70℃ and stirred until completely dissolved, then cooled to 40℃, and the pH was adjusted to 11 with sodium hydroxide. The mixture was activated for 30 min. 3 parts of epichlorohydrin were added dropwise, and the mixture was stirred at 200 rpm for 4.5 h at 55-60℃ to obtain an epoxy-modified β-cyclodextrin solution. The mixture was cooled to 45℃, and 8 parts of 20 wt% sodium phytate aqueous solution were added. The pH of the reaction system was kept >9 (if the pH decreased, it was adjusted with sodium hydroxide). The mixture was stirred at 200 rpm for 3.5 h at 65-70℃. The mixture was cooled to 50-55℃, and 2.5 parts of ketoimine were added. The mixture was stirred at 200 rpm for 1 h. The mixture was cooled to 35℃ and neutralized to pH 7 with sodium glycinate. The insoluble matter was removed by filtration through a 200-mesh filter to obtain the cyclodextrin-sodium phytate-ketoimine composite crosslinking agent.

[0035] The preparation method of the composite nano-reinforced slurry includes the following steps: 25 parts by mass of lithium magnesium silicate and 4 parts by mass of nano-silica are dried at 110–120℃ for 2 hours, cooled to room temperature, and then added to a mixer; 2 parts by mass of NDZ-201 titanate are diluted with 2.5 times the mass of anhydrous ethanol and sprayed into the mixer in a mist, stirred at 300 rpm for 10 minutes; 1.0 part by mass of KH550 is pre-hydrolyzed with 3 times the mass of 85 vol% ethanol aqueous solution for 30 minutes, sprayed into the mixer in a mist, stirred at 300 rpm for 15 minutes, transferred to a ball mill (zirconium bead particle size range 0.5–1.0 mm), and a mixture of 1.2 parts by mass of sodium glycolate, 0.3 parts by mass of sodium polyacrylate, and 65 parts by mass of deionized water is added, ball-milled for 3 hours to obtain a slurry with a particle size D90 of 485 nm, and matured at 25–35℃ and 200 rpm for 5.5 hours; filtered through a 200-mesh screen to obtain the composite nano-reinforced slurry.

[0036] The preparation method of the above-mentioned non-toxic and environmentally friendly water-based protective coating includes the following steps: According to the coating formulation, sodium glycinate was added to deionized water and stirred at 200 rpm for 5 min; hydrophilic fumed silica was added and stirred at 400 rpm for 12 min; talc powder and composite nano-reinforcing slurry were added and stirred at 600 rpm for 20 min; siloxane-bio-based polyester composite emulsion was added and stirred at 600 rpm for 20 min; cyclodextrin-sodium phytate-ketimine composite crosslinking agent was added and stirred at 600 rpm for 15 min; vacuum degassing at -0.07 MPa was performed for 10 min; and the mixture was filtered through a 100-mesh sieve to obtain the coating.

[0037] Example 3 A non-toxic and environmentally friendly water-based protective coating, the coating comprising the following raw materials in parts by weight: 65 parts of siloxane-bio-based polyester composite emulsion, 6 parts of cyclodextrin-sodium phytate-ketimine composite crosslinking agent, 11 parts of composite nano-reinforcing paste, 7 parts of talc, 1.3 parts of hydrophilic fumed silica, 0.4 parts of sodium glycine, and 24 parts of deionized water.

[0038] The preparation method of the siloxane-bio-based polyester composite emulsion includes the following steps: N1: Under nitrogen protection, 155 parts PDO, 120 parts SA, and 100 parts MA were mixed by mass, heated to 155-165℃, and kept at this temperature for 1.5 hours until the materials were melted and mixed evenly. 0.6 parts tetrabutyl titanate were added, and the temperature was increased to 195-205℃ at a rate of 8℃ / h. The mixture was stirred at 300 rpm for 6 hours until the acid value was <10 mg KOH / g, during which water was continuously separated by a water separator. The temperature was then lowered to 145-155℃, and 0.4 parts hydroquinone and 0.1 parts phenothiazine were added. The mixture was stirred at 300 rpm for 35 minutes to obtain bio-based polyester polyol. Under nitrogen protection, 30 parts by weight of D4 were stirred at 300 rpm for 20 min at 80–85 °C. 0.18 parts of tetramethylammonium hydroxide were added, and the mixture was heated to 90–95 °C and refluxed at 300 rpm for 4 h to obtain hydroxyl-terminated polysiloxane. The mixture was then cooled to 65–70 °C, and a mixture of 14 parts of AGE and 5 parts of trimethylolpropane triglycidyl ether was added dropwise at a rate of 1.5 mL / min. After the addition was complete, the mixture was kept at 65–70 °C and stirred at 300 rpm. After 2 hours, the temperature was raised to 80-85℃ and stirred at 300 rpm for 1.5 hours. Then, 9 parts of bio-based polyester polyol were added and stirred at 85-90℃ for 3 hours. The temperature was lowered to 40-45℃, and 2.0 parts of emulsifier and 0.4 parts of isomeric decayl alcohol polyoxyethylene ether were added. The mixture was sheared at 1000 rpm for 30 minutes. 45 parts of deionized water were added dropwise, and the temperature was lowered to 30℃. The solid content was adjusted to 45 wt% with deionized water and filtered through a 250-mesh filter to obtain a siloxane-bio-based polyester composite emulsion.

[0039] The preparation method of the cyclodextrin-sodium phytate-ketoimine composite crosslinking agent includes the following steps: M1: By mass, 90 parts IPDA, 105 parts MIBK, and 10 parts toluene were mixed and refluxed at 300 rpm for 6.5 h at a temperature range of 105–115 °C, with continuous water separation using a water separator; MIBK and toluene were recovered by vacuum distillation at a temperature range of 80–90 °C to obtain ketimine with a solid content of 98.5 wt%. M2: By mass, 15 parts of β-cyclodextrin were added to 100 parts of deionized water, heated to 60-70℃ and stirred until completely dissolved, then cooled to 45℃, and the pH was adjusted to 12 with sodium hydroxide. Activation was carried out for 40 min. 3.5 parts of epichlorohydrin were added dropwise, and the reaction was carried out at 55-60℃ and stirred at 300 rpm for 5 h to obtain an epoxy-modified β-cyclodextrin solution. The temperature was lowered to 50℃, and 10 parts of 22wt% sodium phytate aqueous solution were added. The pH of the reaction system was kept >9 (if the pH decreased, it was adjusted with sodium hydroxide), and the reaction was carried out at 65-70℃ and stirred at 300 rpm for 4 h. The temperature was lowered to 50-55℃, and 3.5 parts of ketimine were added. The mixture was stirred at 300 rpm for 1.5 h. The temperature was lowered to 40℃, and the pH was neutralized to 8 with sodium glycinate. Insoluble matter was removed by 250 mesh filtration to obtain the cyclodextrin-sodium phytate-ketimine composite crosslinking agent.

[0040] The preparation method of the composite nano-reinforced slurry includes the following steps: 35 parts by mass of lithium magnesium silicate and 6 parts by mass of nano-silica are dried at 110–120℃ for 2.5 h, cooled to room temperature, and then added to a mixer; 3 parts by mass of NDZ-201 titanate are diluted with 3 times the mass of anhydrous ethanol and sprayed into the mixer in a mist, stirred at 500 rpm for 15 min; 1.5 parts by mass of KH550 are pre-hydrolyzed with 5 times the mass of 90 vol% ethanol aqueous solution for 40 min, sprayed into the mixer in a mist, stirred at 500 rpm for 20 min, transferred to a ball mill (zirconium bead particle size range 0.5–1.0 mm), and a mixture of 1.8 parts by mass of sodium glycolate, 0.6 parts by mass of sodium polyacrylate, and 70 parts by mass of deionized water is added, ball-milled for 3.5 h to obtain a slurry with a particle size D90 of 450 nm, and matured at 25–35℃ and 300 rpm for 6.5 h; filtered through a 250 mesh to obtain the composite nano-reinforced slurry.

[0041] The preparation method of the above-mentioned non-toxic and environmentally friendly water-based protective coating includes the following steps: According to the coating formulation, sodium glycinate was added to deionized water and stirred at 300 rpm for 3 min; hydrophilic fumed silica was added and stirred at 600 rpm for 8 min; talc powder and composite nano-reinforcing slurry were added and stirred at 800 rpm for 15 min; siloxane-bio-based polyester composite emulsion was added and stirred at 800 rpm for 15 min; cyclodextrin-sodium phytate-ketimine composite crosslinking agent was added and stirred at 800 rpm for 10 min; vacuum degassing was performed at -0.09 MPa for 5 min; and the mixture was filtered through a 150-mesh sieve to obtain the coating.

[0042] In the above embodiments, the "mass fractions" recorded in steps N1, N2 and M1, M2 are all equivalent to mass ratios, and are only the basis for material proportioning when each step is executed independently, and are only applicable to the material addition and reaction process within the corresponding step.

[0043] The raw materials used in the above embodiments are as follows: Talc powder is from Wuhan Kanos Technology Co., Ltd., 1250 mesh. Lithium magnesium silicate is from Wuhan Jiyesheng Chemical Co., Ltd., pulverized to the nanoscale. Hydrophilic fumed silica is from Hubei Huifu Nanomaterials Co., Ltd., with a specific surface area of ​​380±30m². 2 / g, 45μm sieve residue ≤250mg / kg. Nano-silica is sourced from Hangzhou Jiupeng New Materials Co., Ltd., with a median particle size of 30±5nm and a specific surface area of ​​150-300m². 2 / g, purity 99.5%. Tetrabutyl titanate is from Wuhan Jiyesheng Chemical Co., Ltd., used as a condensation catalyst. NDZ-201 titanate is from Hubei Rishengchang New Material Technology Co., Ltd., used as a coupling agent. D4 is octamethylcyclotetrasiloxane, from Shanghai Jiachen Chemical Co., Ltd., purity 99%. Bio-based polyester polyol is from Asahikawa Chemical (Suzhou) Co., Ltd., model XCP-B2000-JS, hydroxyl value 53-59mg KOH / g. Alkyl glycoside emulsifier is used, from Yangzhou Chenhua New Material Co., Ltd., APG CH-1214. Isomeric decayl alcohol polyoxyethylene ether is from Shandong Yonglida New Material Technology Co., Ltd., E-1006. β-Cyclodextrin is hydroxypropyl-β-cyclodextrin, from Chongqing Ruiya Biotechnology Co., Ltd. Sodium polyacrylate is from Hubei Zhonglong Kangsheng Fine Chemical Co., Ltd. Sodium glycinate is anhydrous sodium glycinate. Sodium phytate is sodium phytate dodecahydrate. Sodium glycolate is anhydrous sodium glycolate. The purity of all other substances is greater than 98%. The sources of the raw materials mentioned above are merely illustrative examples and are not intended to limit the scope of this invention.

[0044] Comparative Example 1 The difference from Example 1 is that the cyclodextrin-sodium phytate-ketoimine composite crosslinking agent is changed to 1 part.

[0045] Comparative Example 2 The difference from Example 1 is that the composite nano-reinforced paste is changed to 3 parts.

[0046] Comparative Example 3 The difference from Example 1 is that in the preparation of the siloxane-bio-based polyester composite emulsion, allyl glycidyl ether is not added to N2.

[0047] Comparative Example 4 The difference from Example 1 is that in the preparation of the siloxane-bio-based polyester composite emulsion, trimethylolpropane triglycidyl ether is not added to N2.

[0048] Comparative Example 5 The difference from Example 1 is that no emulsifier and isomeric deca-ol polyoxyethylene ether are added to N2 in the preparation of the siloxane-bio-based polyester composite emulsion.

[0049] Comparative Example 6 The difference from Example 1 is that epichlorohydrin is not added in the preparation of the cyclodextrin-sodium phytate-ketoimine composite crosslinking agent.

[0050] Comparative Example 7 The difference from Example 1 is that KH550, sodium glycolate, and sodium polyacrylate are not added in the preparation of the composite nano-reinforced paste.

[0051] Comparative Example 8 The difference from Example 1 is that NDZ-201 titanate and KH550 are not added in the preparation of the composite nano-reinforced paste.

[0052] I. VOC content detection: Sample specifications: Take 2.0g of the mixed coating, without dilution, and conduct three parallel tests.

[0053] Detection parameters: Refer to standard GB / T 23986 "Determination of Volatile Organic Compounds (VOCs) in Paints and Varnishes by Gas Chromatography". Gas chromatography was used. After accurate weighing, the sample was injected into the headspace. The column temperature was increased from 60℃ to 220℃. An FID detector was used. Retention time was used for qualitative analysis, and peak area was used for quantitative analysis. The total amount of volatiles was calculated, and the result was taken as the arithmetic mean.

[0054] II. Adhesion Test (Cross-Cut Test): Sample specifications: Q235 cold-rolled steel sheet, dry film thickness 30±2μm, cured at room temperature for 7 days at 23±2℃ and 50±5% relative humidity, 3 samples were tested in parallel.

[0055] Test parameters: Refer to standard GB / T 9286 "Cross-cut test for paints and varnishes", use a cross-cut tester, cut at 1mm intervals, cut the coating perpendicularly to the substrate at a uniform speed, and cut horizontally and vertically to form a grid; clean up debris with a soft brush, apply special tape, press firmly to remove air bubbles, and quickly tear at a 60° angle. Observe the grid detachment under sufficient light and rate it.

[0056] Grading Standards: Level 0: The coating is completely intact within the grid area, with no peeling at grid intersections and edges. Even under 10x magnification, there are no signs of coating separation from the substrate, indicating tight adhesion and no risk of peeling or detachment. Level 1: A very small amount of coating peels off at grid intersections, with a peeling area ≤5%. There are no continuous peeling bands along the lines, and the adhesion is good, meeting the needs of most protection scenarios. Level 2: The peeling area is 5%-15%, mainly concentrated at grid intersections or lines. The adhesion is average, suitable for light protection scenarios without severe external impact. Level 3: The peeling area is 15%-35%. The coating on some grid units is completely peeled off, exposing the substrate. The adhesion is insufficient, and peeling is easy. It can only be used for temporary protection. Level 4 and above: The peeling area is ≥35%. Most of the coating is peeled off and cannot effectively adhere to the substrate, losing its protective function and failing to meet the technical requirements of this invention.

[0057] III. Pencil Hardness Testing: Sample specifications: tinplate, dry film thickness 30±2μm, cured at room temperature for 7 days at 23±2℃ and 50±5% relative humidity, with 3 parallel tests.

[0058] Test parameters: Refer to standard GB / T 6739 "Determination of paint film hardness by pencil method for paints and varnishes", select 6B to 6H drawing pencils, load 750g, the pencil is at a 45° angle with the coating, and draw at a uniform speed for at least 6.5mm. The highest pencil hardness that does not puncture the coating is taken as the test result.

[0059] IV. Flexibility Testing (Shaft Bar Method): Sample specifications: tinplate, dry film thickness 30±2μm, cured at room temperature for 7 days at 23±2℃ and 50±5% relative humidity, 3 samples were tested in parallel.

[0060] Test parameters: Refer to standard GB / T 1731 "Test method for flexibility of paint film and putty film", bend the test plate 180° along the shaft and record the minimum shaft diameter without cracks.

[0061] V. Neutral Salt Spray Test (NSS): Sample specifications: Q235 cold-rolled steel sheet, total dry film thickness 60±3μm, cured at room temperature for 7 days at 23±2℃ and 50±5% relative humidity; the coating was sealed with molten paraffin around the edges and back, leaving only the front test surface. The coating was vertically scratched through the surface of the test plate to the substrate, and 3 samples were tested in parallel.

[0062] Test parameters: Referencing standard GB / T 10125 "Artificial Atmosphere Corrosion Test - Salt Spray Test", salt spray chamber temperature 35±2℃, sodium chloride solution concentration 50g / L, pH 7.0, continuous spraying, and settling rate 2.0mL / (80cm). 2 •h), test cycle 1000h. Measure the corrosion spread on one side of the scribing line.

[0063] VI. Acid and alkali resistance testing: Sample specifications: Q235 cold-rolled steel sheet, total dry film thickness 60±3μm, cured at room temperature for 7 days at 23±2℃ and 50±5% relative humidity, 3 samples were tested in parallel.

[0064] Test parameters: Refer to standard GB 9274 "Determination of resistance to liquid media for paints and varnishes", immerse at 23±2℃, with 2 / 3 of the test panel immersed in the medium; immerse in 5wt% H2SO4 acidic solution for 168h, immerse in 5wt% NaOH alkaline solution for 48h; after immersion, rinse with deionized water and dry, let stand for 2h to observe the coating condition and rate.

[0065] Grading Standards: Grade 0: No changes in coating, no blistering, no discoloration, no peeling, no corrosion; extremely strong acid and alkali resistance; suitable for scenarios with acidic or alkaline media. Grade 1: Slight discoloration of coating, no blistering, no peeling, no corrosion; good acid and alkali resistance; can withstand mild acid and alkali contact. Grade 2: Slight blistering or significant discoloration of coating, no peeling, no significant corrosion; moderate acid and alkali resistance; suitable for scenarios without direct acid or alkali contact. Grade 3: Significant blistering and discoloration of coating; slight corrosion; no large-area peeling; only suitable for environments without acid or alkali. Grade 4 and above: Severe blistering, peeling, and corrosion of coating; loss of protective ability; unsuitable for scenarios where contact with acid or alkali is possible.

[0066] VII. Thermal Cycling Test: Sample specifications: Q235 cold-rolled steel sheet, dry film thickness 30±2μm, cured at room temperature for 7 days at 23±2℃ and 50±5% relative humidity, 3 samples were tested in parallel.

[0067] Test parameters: 1 cycle: 80℃ high temperature for 2 hours, -40℃ low temperature for 2 hours, for a total of 25 cycles. After the cycle, the coating condition is observed and rated after restoring to room temperature for 2 hours.

[0068] 8. Early water resistance testing: Sample specifications: tinplate, dry film thickness 30±2μm, cured at room temperature for 24h at 23±2℃ and 50±5% relative humidity (early stage), 3 samples were tested in parallel.

[0069] Test parameters: Refer to standard GB / T 1733 "Test method for water resistance of paint film" (Method A), soak in deionized water at 23±2℃ for 24h, take it out, wipe it dry and let it stand for 1h for observation, and then rate it.

[0070] The grading standards for thermal cycling tests and early water resistance tests are as follows: Grade 0: The coating shows no change, no cracks, no peeling, no blistering, and no whitening. It has extremely strong resistance to environmental changes and water resistance, and is suitable for environments with large temperature differences and high humidity. Grade 1: The coating has no cracks, no peeling, and no blistering, with only slight whitening. It has good resistance to environmental changes and water resistance, and is suitable for normal environments. Grade 2: The coating has slight blistering or slight cracking, with no peeling. It has moderate resistance to environmental changes and water resistance, and can be used in dry environments with small temperature differences. Grade 3: The coating has obvious blistering and cracking, with no large-area peeling. It has insufficient resistance to environmental changes and water resistance, and can only be used in dry and stable environments. Grade 4 and above: The coating has severe blistering, cracking, and peeling. It cannot withstand environmental changes or water erosion and does not meet the protection requirements.

[0071] Table 1 Average test results Table 1 (continued) Average test results Note: " / " indicates not detected. The data range of parallel samples is statistically significant.

[0072] In Examples 1 to 3, the synergistic effect of the three major systems—siloxane-bio-based polyester composite emulsion, cyclodextrin-sodium phytate-ketimine composite crosslinking agent, and composite nano-reinforcing paste—constructed a high-protection, environmentally friendly coating from four aspects: molecular structure, film-forming process, interfacial bonding, and coating structure. The topological structure allows for dense molecular packing and low porosity; the Si-O-Si backbone of the siloxane imparts hydrophobicity and resistance to high and low temperatures; the bio-based polyester enhances affinity with the substrate; and the covalent grafting of the three components prevents phase separation, achieving a balance between rigidity and flexibility. The ketimine acts as a latent curing agent, enabling slow and uniform crosslinking at room temperature, reducing internal stress and VOCs; the epoxy-activated cyclodextrin bonds with sodium phytate and resin at multiple points, while sodium phytate forms a chelate conversion film with the metal substrate, constructing a non-toxic interpenetrating crosslinking network and improving crosslinking density and interfacial adhesion. NDZ-201 and KH550 dual coupling agents achieve the organic modification of inorganic nanoparticles, constructing a three-phase covalent bond between resin, filler, and substrate. Lithium magnesium silicate and nano-silica form a sheet-like, fan-shaped effect, filling micropores and improving density. Dispersing stabilizers ensure uniform dispersion of nanoparticles and avoid defect formation. Alkyl glycosides and isomeric decayl alcohol polyoxyethylene ethers, combined with emulsifiers, achieve stable dispersion of the emulsion, eliminating defect channels during film formation, ensuring coating continuity, and are low in toxicity and APEO-free, reducing VOC emissions. The three systems synergistically form a coating structure with high crosslinking density, high density, strong interfacial bonding, and efficient shielding, ultimately achieving the dual performance requirements of non-toxicity, environmental friendliness, and long-term protection.

[0073] In Comparative Example 1, insufficient dosage of the cyclodextrin-sodium phytate-ketoimine composite crosslinking agent directly led to a significant decrease in the crosslinking density of the coating, an incomplete crosslinking network, and insufficient bonding of resin molecular chains. This resulted in a loose coating structure with increased internal micropores and wider media penetration channels after film formation. Simultaneously, insufficient sodium phytate content resulted in a weak chelate conversion film formed with the metal substrate, reducing interfacial adhesion and consequently causing a simultaneous decline in adhesion, corrosion resistance, and media resistance.

[0074] In Comparative Example 2, the reduction in the amount of composite nano-reinforced paste resulted in the coating losing sufficient inorganic nanofilling and interfacial reinforcement effects. The labyrinth effect of lithium magnesium silicate and nano-silica was significantly weakened, failing to effectively fill the micropores inside the coating, leading to a significant decrease in density. The synergistic effect between the inorganic and organic phases weakened, the bonding force between the resin and the substrate, and within the resin itself decreased, allowing for rapid penetration of corrosive media such as water vapor and chloride ions, resulting in a decline in corrosion barrier properties and mechanical properties.

[0075] In Comparative Example 3, no AGE (Advanced Glycol Age) was added during the preparation of the siloxane-bio-based polyester composite emulsion. AGE is a core monomer for structural construction, providing covalent grafting sites for siloxane and polyester, and introducing side-chain epoxy groups and branching nodes. Its absence resulted in ineffective structural construction, with the resin molecular chains being predominantly linear, exhibiting loose molecular packing and increased porosity. The compatibility between siloxane and polyester decreased significantly, leading to poor coating uniformity. Simultaneously, the number of crosslinking sites was greatly reduced, resulting in lower crosslinking density and consequently decreased coating water resistance, corrosion resistance, and adhesion.

[0076] In Comparative Example 4, the preparation of the siloxane-bio-based polyester composite emulsion did not include trimethylolpropane triglycidyl ether (TMT). TMT is a multifunctional epoxy crosslinking center and a branching auxiliary component in the structure. Its absence only led to a slight decrease in the degree of resin branching and the density of crosslinking points; the integrity of the crosslinking network was not completely destroyed, and only local defects existed. The coating cohesion and density were slightly lower than those of the examples, but the grafting reaction between siloxane and polyester could still be achieved through AGE, so the performance degradation was small. Only the salt spray resistance, acid and alkali resistance, and early water resistance were slightly reduced; the adhesion, hardness, and flexibility were slightly reduced, but were at the same level as those of the examples.

[0077] In Comparative Example 5, no emulsifier or isomeric decayl alcohol polyoxyethylene ether was added during the preparation of the siloxane-bio-based polyester composite emulsion. The emulsifier and isomeric decayl alcohol polyoxyethylene ether are crucial for the stable dispersion of the emulsion. Their absence prevents the hydrophobic modified resin from forming stable micelles in the aqueous phase. The latex particles are large, unevenly distributed, and prone to agglomeration and demulsification. The resulting coating surface is rough, with pinholes and microcracks. The continuous resin phase is discontinuous, forming interconnected pores that allow corrosive media to penetrate unimpeded. Simultaneously, the interfacial compatibility is extremely poor, resulting in weak adhesion between the coating and the substrate, leading to a comprehensive and significant deterioration of all properties.

[0078] In Comparative Example 6, epichlorohydrin was not added to the preparation of the cyclodextrin-sodium phytate-ketoimine composite crosslinking agent. Epichlorohydrin is the activating core of β-cyclodextrin; its absence prevents cyclodextrin from introducing reactive epoxy groups, allowing it to exist only in the system as a physical blend. It cannot form covalent bonds with sodium phytate, ketoimine, or resin, and only exhibits weak hydrogen bonding. This results in decreased crosslinking density, cohesive strength, and stability. Simultaneously, cyclodextrin cannot anchor and control the release of sodium phytate through epoxy groups, leading to decreased coating resistance to media, salt spray, and thermal cycling. Adhesion, hardness, and flexibility remain relatively unchanged, slightly inferior to the examples, but still within the same range.

[0079] In Comparative Example 7, KH550, sodium glycolate, and sodium polyacrylate were not added during the preparation of the composite nano-reinforced slurry. KH550 is a silane coupling agent, while sodium glycolate and sodium polyacrylate are dispersants and stabilizers. The absence of these three components resulted in the inorganic nanoparticles lacking both effective surface organic modification and a stable dispersion system. The nanoparticles agglomerated and failed to form a good, dense nanoscale filling, instead becoming defect centers and stress initiation points within the coating. The absence of KH550 led to the lack of covalent bonds at the inorganic-organic interface, resulting in extremely weak interfacial adhesion and easy debonding and porosity in the coating. The lack of dispersants resulted in poor slurry stability, uneven coating structure, high internal stress, decreased flexibility, impact resistance, and adhesion, and the failure of the barrier effect also led to deterioration in corrosion resistance and media resistance.

[0080] In Comparative Example 8, the composite nano-reinforced paste was prepared without the addition of NDZ-201 titanate and KH550 dual coupling agent. The dual coupling agent is crucial for achieving interfacial bridging between inorganic nanoparticles and organic resins. Its absence resulted in complete lack of interfacial modification between the inorganic powder and the organic system, leading to extremely poor wettability, compatibility, and bonding strength. This caused severe agglomeration of nanoparticles, resulting in numerous macroscopic and microscopic defects and pore channels within the coating. The filler was merely a simple physical filler, completely losing its nano-reinforcement and interfacial strengthening effects. Consequently, the coating's cohesion, hardness, adhesion, impact resistance, and flexibility all deteriorated. Water vapor and corrosive media rapidly penetrated the coating, significantly reducing its anti-corrosion barrier performance.

Claims

1. A non-toxic, environmentally friendly water-based protective coating, characterized in that, The coating comprises the following raw materials in parts by weight: 60-65 parts of siloxane-bio-based polyester composite emulsion, 4-6 parts of cyclodextrin-sodium phytate-ketimine composite crosslinking agent, 7-11 parts of composite nano-reinforcing paste, 4-7 parts of talc, 0.9-1.3 parts of hydrophilic fumed silica, 0.2-0.4 parts of sodium glycinate, and 18-24 parts of deionized water; The siloxane-bio-based polyester composite emulsion is prepared by adding tetramethylammonium hydroxide to D4 and refluxing at 90-95°C; adding a mixture of AGE and trimethylolpropane triglycidyl ether dropwise at 65-70°C, maintaining the temperature at 65-70°C, and reacting at 80-85°C; adding bio-based polyester polyol and reacting at 85-90°C; adding emulsifier and isomeric decayl alcohol polyoxyethylene ether at 40-45°C for shearing; and adding deionized water dropwise to obtain a product with a solid content of 40-45 wt%. The bio-based polyester polyol is prepared by adding PDO, SA, and MA at 155-165°C, adding tetrabutyl titanate and reacting at 195-205°C; and adding hydroquinone and phenothiazine at 145-155°C with stirring. The cyclodextrin-sodium phytate-ketoimine composite crosslinking agent is prepared by dissolving β-cyclodextrin in deionized water, activating it by adjusting the pH to 11-12 at 40-45℃, adding epichlorohydrin dropwise and reacting at 55-60℃; adding 20-22wt% sodium phytate aqueous solution at 45-50℃, maintaining pH > 9, and reacting at 65-70℃; adding ketoimine at 50-55℃ and stirring; neutralizing with sodium glycinate to pH 7-8 at 35-40℃, and filtering to obtain the final product. The composite nano-reinforced paste is prepared by first adding lithium magnesium silicate and nano silica to a mixer; then diluting NDZ-201 titanate with anhydrous ethanol and spraying it into the mixer in a mist and stirring; then pre-hydrolyzing KH550 with an ethanol aqueous solution and spraying it into the mixer in a mist and stirring; finally adding a mixture of sodium glycolate, sodium polyacrylate and deionized water, ball milling, aging, and filtration.

2. The non-toxic and environmentally friendly water-based protective coating according to claim 1, characterized in that, The siloxane-bio-based polyester composite emulsion comprises D4, tetramethylammonium hydroxide, AGE, trimethylolpropane triglycidyl ether, bio-based polyester polyol, emulsifier, isomeric decaol polyoxyethylene ether, and deionized water in a mass ratio of (25-30):(0.12-0.18):(10-14):(4-5):(6-9):(1.5-2.0):(0.2-0.4):(40-45). Tetramethylammonium hydroxide is added to D4 at 80-85°C. The mixture was then refluxed at 90–95 °C for 3–4 h; a mixture of AGE and trimethylolpropane triglycidyl ether was added dropwise at 65–70 °C, and the mixture was kept at 65–70 °C for 1.5–2 h, and then reacted at 80–85 °C for 1–1.5 h; a bio-based polyester polyol was added, and the mixture was reacted at 85–90 °C for 2.5–3 h; an emulsifier and isomeric decayl alcohol polyoxyethylene ether were added at 40–45 °C, the mixture was sheared at 800–1000 rpm, and deionized water was added dropwise to obtain a product with a solid content of 40–45 wt%. The bio-based polyester polyol is prepared by mixing PDO, SA, MA, tetrabutyl titanate, hydroquinone, and phenothiazine in a mass ratio of (145-155):(115-120):(95-100):(0.4-0.6):(0.2-0.4):(0.05-0.1). PDO, SA, and MA are heated at 155-165℃ for 1-1.5 hours, and tetrabutyl titanate is added and reacted at 195-205℃ for 4-6 hours. Hydroquinone and phenothiazine are added at 145-155℃ and stirred to obtain the final product.

3. The non-toxic and environmentally friendly water-based protective coating according to claim 2, characterized in that, The preparation method of the siloxane-bio-based polyester composite emulsion includes the following steps: N1: By weight, 145-155 parts of PDO, 115-120 parts of SA, and 95-100 parts of MA are kept at 155-165℃ for 1-1.5h, 0.4-0.6 parts of tetrabutyl titanate are added, and the mixture is reacted at 195-205℃ for 4-6h; 0.2-0.4 parts of hydroquinone and 0.05-0.1 parts of phenothiazine are added at 145-155℃, and the mixture is stirred to obtain a bio-based polyester polyol; N2: By weight, 25-30 parts of D4 are stirred at 80-85℃, 0.12-0.18 parts of tetramethylammonium hydroxide are added, and the mixture is refluxed at 90-95℃ for 3-4 hours to obtain hydroxyl-terminated polysiloxane; a mixture of 10-14 parts of AGE and 4-5 parts of trimethylolpropane triglycidyl ether is added dropwise at 65-70℃, and the mixture is kept at 65-70℃ for 1.5-2 hours, and reacted at 80-85℃ for 1-1.5 hours; 6-9 parts of bio-based polyester polyol are added, and the mixture is reacted at 85-90℃ for 2.5-3 hours; 1.5-2.0 parts of emulsifier and 0.2-0.4 parts of isomeric decaol polyoxyethylene ether are added at 40-45℃, sheared at 800-1000 rpm, 40-45 parts of deionized water are added dropwise, the temperature is lowered to 25-30℃, the solid content is adjusted to 40-45 wt%, and the mixture is filtered to obtain a siloxane-bio-based polyester composite emulsion.

4. The non-toxic and environmentally friendly water-based protective coating according to claim 1, characterized in that, The cyclodextrin-sodium phytate-ketoimine composite crosslinking agent is composed of β-cyclodextrin, epichlorohydrin, 20-22 wt% sodium phytate aqueous solution, and ketoimine in a mass ratio of (12-15):(3-3.5):(8-10):(2.5-3.5). β-cyclodextrin is dissolved in deionized water and activated at pH 11-12 at 40-45℃. Epichlorohydrin is added dropwise and the reaction is carried out at 55-60℃ for 4.5-5 hours. At 45-50℃, 20-22 wt% sodium phytate aqueous solution is added, and the reaction is carried out at 65-70℃ while maintaining pH > 9 for 3.5-4 hours. Ketoimine is added at 50-55℃ and stirred for 1-1.5 hours. The mixture is then neutralized to pH 7-8 with sodium glycinate at 35-40℃ and filtered to obtain the final product.

5. The non-toxic and environmentally friendly water-based protective coating according to claim 4, characterized in that, The preparation method of the cyclodextrin-sodium phytate-ketoimine composite crosslinking agent includes the following steps: 12-15 parts by weight of β-cyclodextrin are added to 90-100 parts of deionized water, stirred and dissolved at 60-70℃, cooled to 40-45℃, and the pH is adjusted to 11-12 for activation. 3-3.5 parts of epichlorohydrin are added dropwise, and the reaction is carried out at 55-60℃ for 4.5-5 hours to obtain an epoxy-modified β-cyclodextrin solution. The temperature is then lowered to 45-50℃, and 8-10 parts of 20-22wt% sodium phytate aqueous solution are added. The pH is maintained >9, and the reaction is carried out at 65-70℃ for 3.5-4 hours. The temperature is then lowered to 50-55℃, and 2.5-3.5 parts of ketoimine are added and stirred for 1-1.5 hours. The temperature is then lowered to 35-40℃, neutralized to pH 7-8 with sodium glycinate, and filtered to obtain the cyclodextrin-sodium phytate-ketoimine composite crosslinking agent.

6. The non-toxic and environmentally friendly water-based protective coating according to claim 4, characterized in that, The method for preparing the ketimine includes: reacting 80-90 parts by weight of IPDA, 95-105 parts by weight of MIBK and 5-10 parts by weight of toluene under reflux at 105-115°C for 5.5-6.5 h, followed by vacuum distillation to obtain a ketimine with a solid content >98wt%.

7. The non-toxic and environmentally friendly water-based protective coating according to claim 1, characterized in that, The composite nano-reinforced slurry is prepared by mixing lithium magnesium silicate, nano silica, NDZ-201 titanate, KH550, sodium glycolate, sodium polyacrylate, and deionized water in a mass ratio of (25-35):(4-6):(2-3):(1.0-1.5):(1.2-1.8):(0.3-0.6):(65-70). First, lithium magnesium silicate and nano silica are added to a mixer. NDZ-201 titanate is diluted with anhydrous ethanol and then sprayed into the mixer in a mist and stirred. Next, KH550 is pre-hydrolyzed with an ethanol-water solution and then sprayed into the mixer in a mist and stirred. Finally, a mixture of sodium glycolate, sodium polyacrylate, and deionized water is added, ball-milled for 3-3.5 hours, stirred and matured at 25-35°C for 5.5-6.5 hours, and then filtered to obtain the final product.

8. The non-toxic and environmentally friendly water-based protective coating according to claim 7, characterized in that, The preparation method of the composite nano-reinforced slurry includes the following steps: 25-35 parts by weight of lithium magnesium silicate and 4-6 parts by weight of nano-silica are added to a mixer; 2-3 parts by weight of NDZ-201 titanate are diluted with anhydrous ethanol and then sprayed into the mixer in a mist and stirred; 1.0-1.5 parts by weight of KH550 are pre-hydrolyzed with an ethanol aqueous solution and then sprayed into the mixer in a mist and stirred; a mixture of 1.2-1.8 parts by weight of sodium glycolate, 0.3-0.6 parts by weight of sodium polyacrylate and 65-70 parts by weight of deionized water is added, and the mixture is ball-milled for 3-3.5 hours to obtain a slurry with a particle size D90 < 500 nm; the slurry is stirred and matured at 25-35°C for 5.5-6.5 hours; and then filtered to obtain the composite nano-reinforced slurry.

9. The method for preparing a non-toxic and environmentally friendly water-based protective coating according to claim 1, characterized in that, Includes the following steps: According to the coating formulation, sodium glycinate was added to deionized water and stirred; hydrophilic fumed silica was added and stirred; talc powder and composite nano-reinforcing paste were added and stirred; siloxane-bio-based polyester composite emulsion was added and stirred; cyclodextrin-sodium phytate-ketimine composite crosslinking agent was added and stirred; vacuum degassing and filtration were performed to obtain the coating.

10. The method for preparing a non-toxic and environmentally friendly water-based protective coating according to claim 9, characterized in that, According to the coating formulation, sodium glycinate is added to deionized water and stirred at 200-300 rpm for 3-5 minutes; hydrophilic fumed silica is added and stirred at 400-600 rpm for 8-12 minutes; talc powder and composite nano-reinforcing paste are added and stirred at 600-800 rpm for 15-20 minutes; siloxane-bio-based polyester composite emulsion is added and stirred at 600-800 rpm for 15-20 minutes; cyclodextrin-sodium phytate-ketimine composite crosslinking agent is added and stirred at 600-800 rpm for 10-15 minutes; vacuum degassing is performed at -0.07 MPa to -0.09 MPa for 5-10 minutes, and the mixture is filtered through a 100-150 mesh filter to obtain the coating.

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