Environment-friendly alkyd resin coating and preparation method thereof

Abstract

The invention discloses an environment-friendly alkyd resin coating and a preparation method of the environment-friendly alkyd resin coating, and the preparation method comprises the following steps: carrying out vacuum dehydration on soybean oleic acid; raising the temperature to 230-240 DEG C in a stepped manner with pentaerythritol, nano-zinc oxide dispersed slurry, sebacic acid, limonene with the rest 70% of the total amount of limonene, an antioxidant, hydrogenated castor oil and isophthalic acid premixed liquid, and reacting to prepare bio-based alkyd resin; the preparation method comprises the following steps: respectively adding bio-based alkyd resin, epoxy resin and glycidyl methacrylate premixed liquid into a reaction kettle, and reacting at 110-120 DEG C to obtain an alkyd resin prepolymer; the preparation method comprises the following steps: respectively adding N-methyl pyrrolidone, polysulfonamide, an alkyd resin prepolymer and maleic anhydride castor oil, carrying out multi-stage high-speed shearing to obtain a modified prepolymer, adding a diluent, a curing agent, an antifoaming agent, a leveling agent and an anti-settling agent, and carrying out a reaction at 50-55 DEG C to obtain the environment-friendly alkyd resin coating. Therefore, the obtained alkyd resin coating is green, environment-friendly, excellent in performance and high in adhesiveness.

Description

Technical Field

[0001] The present invention relates to the technical field of alkyd resin coatings, in particular to an environmentally friendly alkyd resin coating and a preparation method thereof. Background Art

[0002] Coatings primarily provide protection and decoration for various materials and are essential for people's production and daily lives. By evenly applying and firmly adhering to surfaces, coatings protect, decorate, mark, and perform other special functions. These coatings primarily include alkyd resin coatings, epoxy resin coatings, polyurethane coatings, acrylic coatings, and fluorocarbon coatings. Alkyd resins, as a paint raw material, are readily available and offer a wide variety of paint products. They are the most important raw material in paint production, and the paint films they form offer excellent overall performance. Therefore, they are the most widely used resin raw material in synthetic coatings, occupying a key position in the coatings industry.

[0003] Alkyd resin paint is a key coating type based on alkyd resin as its primary film-forming substance. Its core component, alkyd resin, is a polyester resin synthesized through the esterification and polycondensation of polyols, polyacids, and fatty acids (or oils). While alkyd resin paint boasts weather resistance, strong adhesion, and excellent brushability, making it easy to apply, it also produces high VOC (volatile organic compound) emissions, exhibits slow drying, low hardness, poor alkali resistance, and poor outdoor weatherability, making it unable to meet increasingly demanding application requirements.

[0004] At present, alkyd resins are mainly modified by chemical methods to improve the comprehensive properties of alkyd resin coatings, mainly including acrylic resin modified alkyd resin coatings, silicone modified alkyd resin coatings, styrene modified alkyd resin coatings and nanomaterial modified alkyd resin coatings. Although great improvements have been made in the drying properties, hardness, water resistance, electrical insulation, high temperature resistance, moisture resistance, atmospheric corrosion resistance, aging resistance and wear resistance of the paint film, the problem of large VOC emissions is still the biggest limitation of solvent-based alkyd resins. Therefore, developing an environmentally friendly alkyd resin coating that can minimize its VOC emissions while optimizing the various properties of alkyd resin coatings is an important issue that technicians in this field urgently need to solve. Summary of the Invention

[0005] In light of this, the present invention provides an environmentally friendly alkyd resin coating and a preparation method thereof. The environmentally friendly alkyd resin coating is prepared using bio-based raw materials, nanocatalysts, and green solvents, resulting in low VOC emissions and environmental friendliness. Furthermore, the coating utilizes epoxy resin modification to form an alkyd resin prepolymer. Maleic anhydride-grafted castor oil effectively bridges the polysulfoneamide and alkyd resin prepolymers. Combining the advantageous properties of epoxy resin, polysulfoneamide, and alkyd resin, the coating effectively enhances its chemical stability, flexibility, and weatherability. The coating exhibits strong adhesion, high hardness, and easy drying to form a film.

[0006] In order to achieve the above object, the present invention provides a method for preparing an environmentally friendly alkyd resin coating, comprising the following steps: S1, after vacuum dehydration, soybean oleic acid is reacted with pentaerythritol, nano zinc oxide dispersion, sebacic acid, the remaining 70% of the total amount of limonene, antioxidant, hydrogenated castor oil and isophthalic acid premix by stepwise heating to 230-240°C to prepare a bio-based alkyd resin; S2, adding the premixed solution of bio-based alkyd resin, epoxy resin and glycidyl methacrylate into a reactor respectively, and reacting at 110-120° C. to obtain an alkyd resin prepolymer; S3. Add N-methylpyrrolidone, polysulfoneamide, alkyd resin prepolymer and maleic anhydride castor oil respectively, and obtain a modified prepolymer through multi-stage high-speed shearing. Add diluent, curing agent, defoaming agent, leveling agent and anti-settling agent, and react at 50-55°C to obtain an environmentally friendly alkyd resin coating.

[0007] In some embodiments of the present invention, in step S1, the biobased content of the soybean oleic acid is ≥95%, and the acid value is 190-200 mgKOH / g; the biobased content of the pentaerythritol is 100%, and the particle size is ≤50 μm; the nano-zinc oxide dispersion slurry is a pre-dispersed slurry formed by ball-milling nano-zinc oxide and 20% soybean oleic acid at 2000-3000 rpm for 20-30 minutes; the biobased content of the sebacic acid is 100%; the biobased content of the isophthalic acid is ≥95%; the isophthalic acid premix is a solution formed by mixing isophthalic acid with 30% limonene preheated to 90° C.; the biobased content of the limonene is ≥95%; and the antioxidant is 2,6-di-tert-butyl-4-methylphenol.

[0008] In some embodiments of the present invention, in step S1, the mass ratio of the soybean oleic acid to the pentaerythritol is 3-5:1-3, the amount of the nano-zinc oxide dispersion is 0.05-0.08% of the mass of the bio-based alkyd resin, the mass ratio of the sebacic acid and the isophthalic acid premix is 1-3:2-5, the total amount of the limonene is 5-8% of the mass of the bio-based alkyd resin, the amount of the antioxidant is 0.03-0.05% of the mass of the bio-based alkyd resin, and the amount of the hydrogenated castor oil is 0.01-0.03% of the mass of the bio-based alkyd resin.

[0009] In some embodiments of the present invention, step S1 includes: S1.1. Dehydrate soybean oleic acid at 100-120°C and -0.095 MPa vacuum for 1-1.5 h. Add it, along with pentaerythritol and nano-zinc oxide dispersion, to a reactor under nitrogen protection. Raise the temperature to 220-240°C at a rate of 5°C / min and react for 1-2 h. S1.2. Cool the mixture to 170-180°C, first add sebacic acid, the remaining 70% of the total amount of limonene, an antioxidant, and hydrogenated castor oil, stir at 200-300 rpm for 10-15 min, then slowly add the isophthalic acid premix dropwise, heat the mixture to 190-200°C at a rate of 2°C / min, react for 45-60 min, then heat the mixture to 210-220°C, react for 60-80 min, and finally heat the mixture to 230-240°C, react for 60-90 min to obtain a bio-based alkyd resin.

[0010] In some embodiments of the present invention, in step S2, the epoxy resin is epoxy resin E-51, the catalyst is dibutyltin dilaurate, the polymerization inhibitor is hydroquinone, the mass ratio of the bio-based alkyd resin to the epoxy resin is 4-10:1-3, the amount of glycidyl methacrylate is 12-15% of the mass of the alkyd resin prepolymer, and the mass ratio of the catalyst to the polymerization inhibitor is 2-5:1-3.

[0011] In some embodiments of the present invention, step S2 includes: S2.1. Dehydrate the bio-based alkyd resin under vacuum at 100-120°C and -0.095 MPa for 30-40 minutes. Then, add it to the reactor and heat it to 110-120°C. Under nitrogen protection, slowly add epoxy resin preheated to 60°C and stir at 400-600 rpm for 20-25 minutes. S2.2. Slowly dropwise add the premix of glycidyl methacrylate, catalyst, and polymerization inhibitor, and continue the reaction at a stirring speed of 300-400 rpm for 50-70 minutes to obtain an alkyd resin prepolymer.

[0012] In some embodiments of the present invention, in step S3, the purity of the N-methylpyrrolidone is ≥99.9%, the moisture content is ≤50ppm, the diluent is epoxy limonene butyl ether, the bio-based content is ≥90%, the curing agent is cardanolamine T-31, the defoamer is defoamer BYK-066N, the leveling agent is leveling agent BYK-358, the anti-settling agent is hydrogenated castor oil wax, and the amount of the N-methylpyrrolidone is 75% to 80% of the mass of the modified prepolymer. 5%, the mass ratio of the polysulfoneamide and the maleic anhydride grafted castor oil is 8-10:1-3, the amount of the diluent is 15-20% of the mass of the alkyd resin coating, the amount of the curing agent is 8-10% of the mass of the alkyd resin coating, the amount of the defoamer is 0.3-0.5% of the mass of the alkyd resin coating, the amount of the leveling agent is 0.5-0.8% of the mass of the alkyd resin coating, and the amount of the anti-settling agent is 2-5% of the mass of the alkyd resin coating.

[0013] In some embodiments of the present invention, step S3 includes: S3.1. Place N-methylpyrrolidone in a reactor and heat to 70-80°C. Under nitrogen, add polysulfoneamide that has been vacuum-dehydrated at 70-80°C and -0.095 MPa for 3-4 hours in batches. Stir at 200-300 rpm for 2-3 hours. Add alkyd resin prepolymer preheated to 110-120°C. Premix at 800-1000 rpm for 10-15 minutes. Then, high-speed shear reaction is carried out at 110-120°C and -0.05 MPa at 5000-6000 rpm for 15-18 minutes. S3.2. Atomize maleic anhydride-grafted castor oil preheated to 50-60°C and perform a stepwise shear reaction at 120-125°C, -0.08 MPa, and 3500-4000 rpm for 8-10 minutes. Then, perform a high-speed shear reaction at 110-120°C, -0.09 MPa, and 2000-2500 rpm for 3-5 minutes to obtain a modified prepolymer. S3.3. Preheat the modified prepolymer in a water bath at 50-60°C for 25-30 min, add the diluent dropwise at a rate of 5 mL / min, stir at 50-55°C at 300-500 rpm for 8-10 min, add curing agent, defoaming agent, leveling agent and anti-settling agent respectively, and stir at 50-55°C at a speed of 600-1200 rpm for 12-18 min. After vacuum degassing at -0.08 MPa and 50-55°C for 10-15 min, place in a constant temperature box at 40°C and let it stand for 30 min to obtain an environmentally friendly alkyd resin coating.

[0014] The present invention provides an environmentally friendly alkyd resin coating, which is prepared by the above-mentioned preparation method of the environmentally friendly alkyd resin coating, and comprises soybean oleic acid, pentaerythritol, nano zinc oxide, sebacic acid, limonene, an antioxidant, hydrogenated castor oil, isophthalic acid, epoxy resin, glycidyl methacrylate, a catalyst, a polymerization inhibitor, N-methylpyrrolidone, polysulfoneamide, maleic anhydride grafted castor oil, a diluent, a curing agent, a defoaming agent, a leveling agent and an anti-settling agent; wherein, The soybean oleic acid is used to provide a long-chain fatty acid structure to enhance the flexibility and bio-based content of the alkyd resin coating; The pentaerythritol is used to construct multifunctional cross-linking nodes to increase the branching degree and hardness of the alkyd resin; The nano zinc oxide is used to replace the traditional lead / tin catalyst to catalyze the esterification reaction and at the same time impart ultraviolet shielding function to the alkyd resin coating; The sebacic acid is used to introduce a long-chain dibasic acid structure to improve the low-temperature toughness of the alkyd resin; The limonene is used to replace traditional petroleum-based solvents and serves as a green solvent to disperse nanoparticles and reduce the viscosity of the alkyd resin reaction system; The isophthalic acid is used to provide a rigid aromatic ring structure to improve the heat resistance of the alkyd resin coating; The epoxy resin is used to modify the alkyd resin, construct a covalent cross-linked main chain, and enhance the chemical stability of the alkyd resin coating; The glycidyl methacrylate is used to introduce carbon-carbon double bonds to achieve the ultraviolet light-assisted curing function of the alkyd resin coating; The polysulfoneamide is used to provide a strong polar bond and a rigid skeleton of the sulfone group, thereby enhancing the dielectric strength of the alkyd resin coating and imparting high insulation, heat resistance and high-frequency stability to the alkyd resin coating; The maleic anhydride grafted castor oil is used to bridge the polysulfoneamide and the alkyd resin prepolymer to form chemical bonds, physical bonds and entangled structures, thereby improving the interface compatibility of the alkyd resin coating.

[0015] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention uses bio-based alkyd resin, epoxy resin, polysulfoneamide and maleic anhydride grafted castor oil to prepare an environmentally friendly alkyd resin coating, avoiding petroleum-based sources, having low VOC emissions, reducing environmental impact, and being relatively green and environmentally friendly. At the same time, the epoxy groups of the epoxy resin and the carboxyl groups of the alkyd resin undergo a ring-opening reaction to form ester bonds and hydroxyl groups. The epoxy groups cross-link to form a rigid network, which interpenetrates with the flexible chains of the alkyd resin to form an interpenetrating network. The dense structure of the epoxy cured product and the aromatic ring structure of the epoxy resin are introduced, significantly enhancing the mechanical strength, chemical resistance and thermal stability of the alkyd resin coating. The amide bonds of the polysulfoneamide react with the anhydride of the maleic anhydride-grafted castor oil to form amide-ester bonds, creating a rigid-flexible interfacial structure. Furthermore, the proximity of the maleic anhydride-grafted castor oil and alkyd resin prepolymer chains allows the castor oil segments to intercalate into the prepolymer interstices through diffusion and van der Waals forces. The castor oil hydroxyl groups form hydrogen bonds with the ester groups of the prepolymer, forming a stable entangled network. The introduction of the flexible, long chains of the maleic anhydride-grafted castor oil effectively enhances the prepolymer's flexibility and impact resistance. Through the bridging effect of the maleic anhydride-grafted castor oil, the sulfone groups of the polysulfoneamide react with the hydroxyl groups of the alkyd resin prepolymer to form hydrogen bonds. Polysulfoneamide fibrils interpenetrate the epoxy-alkyd network, forming a topological interpenetrating structure. Furthermore, the introduction of sulfone groups and aromatic rings enhances the prepolymer's electrical insulation, rigidity, high-temperature stability, and chemical resistance, imparting excellent mechanical properties and chemical stability.

[0016] (2) The present invention uses bio-based soybean oleic acid, pentaerythritol, sebacic acid and isophthalic acid to prepare bio-based alkyd resin. The carboxyl group of soybean oleic acid reacts with the hydroxyl group of pentaerythritol to form a pre-ester. The reaction rate is controlled by step-by-step heating. Sebacic acid reacts with the pre-ester to form a linear segment. The flexible segment of sebacic acid is introduced. Isophthalic acid is then condensed with the remaining hydroxyl group to form a cross-linked network, providing a rigid aromatic ring structure. The prepared bio-based alkyd resin has good flexibility, strong heat resistance and high hardness. In addition, the reactants, catalysts and solvents are environmentally friendly, avoiding petroleum-based sources and toxic heavy metal catalysts, reducing the VOC emissions of the system, and being relatively green and environmentally friendly. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0018] The present invention provides a method for preparing an environmentally friendly alkyd resin coating, comprising the following steps: S1, soybean oleic acid after vacuum dehydration, and pentaerythritol, nano zinc oxide dispersion, sebacic acid, the remaining 70% of the total amount of limonene, antioxidant, hydrogenated castor oil and isophthalic acid premix were reacted by step-wise heating to 230-240 °C to prepare bio-based alkyd resin.

[0019] In step S1, the biobased content of soybean oleic acid is ≥95%, the acid value is 190-200 mgKOH / g, the biobased content of pentaerythritol is 100%, the particle size is ≤50 μm, the nano zinc oxide dispersion slurry is a pre-dispersed slurry formed by ball milling nano zinc oxide and 20% soybean oleic acid at 2000-3000 rpm for 20-30 minutes, the biobased content of sebacic acid is 100%, the biobased content of isophthalic acid is ≥95%, the isophthalic acid premix is a solution formed by mixing isophthalic acid with 30% limonene preheated to 90° C., the biobased content of limonene is ≥95%, and the antioxidant is 2,6-di-tert-butyl-4-methylphenol.

[0020] In step S1, the mass ratio of soybean oleic acid and pentaerythritol is 3-5:1-3, the amount of nano zinc oxide dispersion is 0.05-0.08% of the mass of the bio-based alkyd resin, the mass ratio of sebacic acid and isophthalic acid premix is 1-3:2-5, the total amount of limonene is 5-8% of the mass of the bio-based alkyd resin, the amount of antioxidant is 0.03-0.05% of the mass of the bio-based alkyd resin, and the amount of hydrogenated castor oil is 0.01-0.03% of the mass of the bio-based alkyd resin.

[0021] Step S1 includes: S1.1. Dehydrate soybean oleic acid at 100-120°C and -0.095 MPa vacuum for 1-1.5 h. Add it into the reactor simultaneously with pentaerythritol and nano zinc oxide dispersion under nitrogen protection. Raise the temperature to 220-240°C at a rate of 5°C / min and react for 1-2 h.

[0022] Vacuum dehydration of soybean oleic acid effectively removes moisture from the raw material and prevents esterification side reactions. The dehydration temperature is controlled at 100-120°C, above the boiling point of water but below the oxidation temperature of oleic acid, ensuring that water evaporation does not destroy the fatty acid structure. The vacuum degree is -0.095MPa, which effectively lowers the boiling point of water, accelerates the escape of water molecules, and avoids double bond isomerization caused by high temperature. Dehydration at this temperature and vacuum degree for 1-1.5 hours can effectively control the moisture content and ensure the complete removal of free water and trace bound water. The introduction of nitrogen protection can effectively prevent the high-temperature oxidation of unsaturated fatty acids. Controlling the heating rate at 5°C / min can balance the reaction rate and side reaction control, preventing the risk of gelation. Controlling the reaction temperature at 220-240°C can meet the esterification activation energy requirements, while being lower than the decomposition temperature of pentaerythritol and the deactivation temperature of the zinc catalyst, avoiding the deactivation of the catalyst affecting the reaction. Reacting at this reaction temperature and heating rate for 1-2 hours can significantly reduce the acid value of the system, increase the conversion rate of the alkyd resin, and lay the foundation for the subsequent modification reaction.

[0023] S1.2. Cool the mixture to 170-180°C, first add sebacic acid, the remaining 70% of the total amount of limonene, an antioxidant, and hydrogenated castor oil, stir at 200-300 rpm for 10-15 min, then slowly add the isophthalic acid premix dropwise, heat the mixture to 190-200°C at a rate of 2°C / min, react for 45-60 min, then heat the mixture to 210-220°C, react for 60-80 min, and finally heat the mixture to 230-240°C, react for 60-90 min to obtain a bio-based alkyd resin.

[0024] The addition temperature is controlled at 170-180°C, which is below the decarboxylation temperature of sebacic acid to prevent the decarboxylation side reaction, yet above its melting point to ensure fluidity. At this temperature, stirring at 200-300 rpm for 10-15 minutes ensures complete melt dispersion of the solid sebacic acid and maintains system homogeneity. The addition of antioxidants and hydrogenated castor oil effectively blocks free radical chain reactions and inhibits the organic reactions of limonene. A controlled heating rate of 2°C / min balances reaction rate and side reaction control.

[0025] The esterification temperature program can effectively avoid limonene cracking. The first stage reaction temperature is controlled at 190-200℃, which can reach the melting point of sebacic acid, ensure complete melting of sebacic acid, and avoid local concentration gradients. The reaction is carried out at this temperature for 45-60 minutes, which can ensure the full esterification of the flexible chain of sebacic acid while avoiding the risk of gelation. The second stage reaction temperature is controlled at 210-220℃, which can effectively balance reaction efficiency and raw material loss and inhibit the side reaction of hydroxyl dehydration to ether bond. The reaction is carried out at this temperature for 60-80 minutes, which can promote the full esterification of the rigid chain of isophthalic acid and ensure high heat resistance and impact resistance of the coating. The third stage reaction temperature is controlled at 230-240℃, which can fully expand the free volume fraction of the resin, fully entangle the long-chain fatty acids with the aromatic ring segments, and avoid the side reaction of sebacic acid decarboxylation. The reaction is carried out at this temperature for 60-90 minutes, which can achieve a high molecular weight and a rigid-flexible structure of the bio-based alkyd resin, providing the coating with excellent mechanical strength and heat resistance while avoiding the formation of gel.

[0026] S2. Add the premixed solution of bio-based alkyd resin, epoxy resin and glycidyl methacrylate into a reactor respectively, and react at 110-120° C. to obtain an alkyd resin prepolymer.

[0027] Step S2 includes: S2.1. Dehydrate the bio-based alkyd resin under vacuum at 100-120°C and -0.095 MPa for 30-40 min, then add it to the reactor and heat it to 110-120°C. Under nitrogen protection, slowly add epoxy resin preheated to 60°C and stir at 400-600 rpm for 20-25 min.

[0028] The bio-based alkyd resin is vacuum-dehydrated to control the moisture content of the raw materials and ensure the efficiency of the epoxy-carboxyl primary reaction. The dehydration temperature is controlled between 100 and 120°C, above the boiling point of water but below the softening point of the alkyd resin to prevent resin coking. The vacuum level is -0.095 MPa, which effectively lowers the boiling point of water and efficiently removes hydrogen-bonded water. Reaction at this dehydration temperature and vacuum level for 30 to 40 minutes significantly reduces the water content of the bio-based alkyd resin, meeting the requirements of the epoxy ring-opening reaction. Preheating the epoxy resin to 60°C effectively reduces its viscosity and ensures its uniform dispersion, achieving micron-level dispersion. The reaction temperature is controlled between 110 and 120°C, above the glass transition temperature of the alkyd resin to promote molecular chain motion, but below the epoxy autopolymerization temperature, effectively balancing reaction rate and side reaction suppression. Introducing nitrogen protection can effectively prevent the oxidation of unsaturated fatty acids, and controlling the stirring speed at 400-600 rpm can effectively avoid laminar flow leading to uneven dispersion of the system. Reacting at this reaction temperature and stirring speed for 20-25 minutes can make the reaction system reach macroscopic homogeneity.

[0029] Epoxy resins are thermosetting polymers containing two or more epoxy groups in their molecules. They are typically formed by the polycondensation of epichlorohydrin and bisphenol A and exhibit high reactivity, strong adhesion, chemical stability, and excellent mechanical properties. As a modifier, the epoxy groups of the epoxy resin and the carboxyl groups of the alkyd resin undergo a ring-opening reaction to form ester bonds and hydroxyl groups. The epoxy groups cross-link to form a rigid network that interpenetrates with the flexible chains of the alkyd resin, forming an interpenetrating network and enhancing the mechanical strength of the alkyd resin coating. The dense structure of the epoxy cured product shields the penetration of corrosive media, improving the chemical resistance of the alkyd resin coating. At the same time, the aromatic ring structure of the epoxy resin and the ester bonds synergistically resist thermal motion of the chain segments, effectively optimizing the thermal stability of the alkyd resin coating.

[0030] S2.2. Slowly dropwise add the premix of glycidyl methacrylate, catalyst, and polymerization inhibitor, and continue the reaction at 110-120° C. with a stirring speed of 300-400 rpm for 50-70 min to obtain an alkyd resin prepolymer.

[0031] The reaction temperature is controlled at 110-120°C, which is higher than the glass transition temperature of the alkyd resin to ensure the mobility of the molecular chain, but lower than the autopolymerization temperature of glycidyl methacrylate to avoid premature polymerization of double bonds. The stirring speed is controlled at 300-400 rpm to uniformly disperse the glycidyl methacrylate premix in the resin. The reaction is carried out for 50-70 minutes at this reaction temperature and stirring speed to ensure the conversion rate of the epoxy group and prevent excessive loss of double bonds due to side reactions, which may affect the reaction results.

[0032] In step S2, the epoxy resin is epoxy resin E-51, the catalyst is dibutyltin dilaurate, the inhibitor is hydroquinone, the mass ratio of bio-based alkyd resin to epoxy resin is 4-10:1-3, the amount of glycidyl methacrylate is 12-15% of the mass of the alkyd resin prepolymer, and the mass ratio of the catalyst to the inhibitor is 2-5:1-3.

[0033] S3. Add N-methylpyrrolidone, polysulfoneamide, alkyd resin prepolymer and maleic anhydride castor oil respectively, and obtain a modified prepolymer through multi-stage high-speed shearing. Add diluent, curing agent, defoaming agent, leveling agent and anti-settling agent, and react at 50-55°C to obtain an environmentally friendly alkyd resin coating.

[0034] In step S3, the purity of N-methylpyrrolidone is ≥99.9%, the moisture content is ≤50ppm, the diluent is epoxy limonene butyl ether, the bio-based content is ≥90%, the curing agent is cardanolamine T-31, the defoamer is defoamer BYK-066N, the leveling agent is leveling agent BYK-358, the anti-settling agent is hydrogenated castor oil wax, the amount of N-methylpyrrolidone is 75-85% of the mass of the modified prepolymer, the mass ratio of polysulfoneamide and maleic anhydride grafted castor oil is 8-10:1-3, the amount of diluent is 15-20% of the mass of the alkyd resin coating, the amount of curing agent is 8-10% of the mass of the alkyd resin coating, the amount of defoamer is 0.3-0.5% of the mass of the alkyd resin coating, the amount of leveling agent is 0.5-0.8% of the mass of the alkyd resin coating, and the amount of anti-settling agent is 2-5% of the mass of the alkyd resin coating.

[0035] Step S3 includes: S3.1. Place N-methylpyrrolidone in a reactor and heat it to 70-80°C. Under the protection of nitrogen, add polysulfoneamide that has been vacuum dehydrated at 70-80°C and -0.095 MPa for 3-4 hours in batches. Stir at 200-300 rpm for 2-3 hours. Add alkyd resin prepolymer preheated to 110-120°C, premix at 800-1000 rpm for 10-15 minutes, and then carry out high-speed shear reaction at 110-120°C and -0.05 MPa at 5000-6000 rpm for 15-18 minutes.

[0036] Controlling the dissolution temperature between 70 and 80°C, the optimal dissolution window for N-methylpyrrolidone, effectively promotes the dissolution of polysulfoneamide. Vacuum dehydration of polysulfoneamide controls the system's moisture content and effectively prevents its hydrolysis. The dehydration temperature is controlled at 70 to 80°C, above half the glass transition temperature (Tg) of polysulfoneamide, promoting the diffusion of water molecules but below its decomposition temperature. A vacuum of -0.095 MPa significantly lowers the boiling point of water and, combined with thermal motion, completely removes bound water. Vacuum dehydration at this temperature and vacuum for 3 to 4 hours significantly reduces the water content of polysulfoneamide. Controlling the stirring speed between 200 and 300 rpm creates a laminar flow state, preventing high-speed shear-induced depolymerization of polysulfoneamide.

[0037] Preheating the alkyd resin prepolymer to 110-120°C, which is both below the epoxy ring-opening temperature and above its softening point, effectively reduces the prepolymer's viscosity and facilitates its dispersion. Controlling the stirring speed to 800-1000 rpm creates turbulence, enabling the fibrillation of the polysulfoneamide. Premixing at this stirring speed for 10-15 minutes evenly disperses the polysulfoneamide fibrils and improves the solution's transmittance. Controlling the reaction temperature to 110-120°C maintains system fluidity, below the polysulfoneamide's glass transition temperature to prevent embrittlement. A vacuum of -0.05 MPa removes low-boiling substances while avoiding excessive decompression that could vaporize N-methylpyrrolidone. Controlling the stirring speed at 5000~6000rpm can significantly increase the shear rate, which can nano-size the polysulfoneamide fibrils and break up the polysulfoneamide aggregates. At this stirring speed, high-speed shearing for 15~18 minutes can form a continuous network of polysulfoneamide fibrils and achieve polysulfoneamide fibril breakage, laying the foundation for nano-enhancement of maleic anhydride castor oil grafting.

[0038] Polysulfoneamide is a high-performance engineering plastic containing sulfone groups and amide bonds in its backbone. It exhibits excellent high-temperature resistance, mechanical strength, chemical stability, and electrical insulation. The regularity and compactness of its molecular chains contribute to its high crystallinity, further enhancing its strength and hardness. Polysulfoneamide is also recyclable, contributing to reduced environmental pollution. The amide bonds of polysulfoneamide react with the anhydride of maleic anhydride-grafted castor oil to form amide-ester bonds, which lowers interfacial energy and creates a rigid-flexible interface structure. The sulfone groups of polysulfoneamide react with the hydroxyl groups of the alkyd resin prepolymer to form hydrogen bonds, allowing polysulfoneamide fibrils to interpenetrate the epoxy-alkyd network, forming a topological interpenetrating structure. Furthermore, the introduction of sulfone groups and aromatic rings in the prepolymer's structure binds free electrons through its highly polar bonds, inhibiting conductive pathways and enhancing the prepolymer's electrical insulation. The sulfone groups and aromatic rings of polysulfoneamide enhance the prepolymer's rigidity, inhibiting high-temperature relaxation of the resin segments, and improving its high-temperature stability. Furthermore, the prepolymer imparts excellent mechanical properties and outstanding chemical resistance.

[0039] S3.2. Atomize and add maleic anhydride grafted castor oil preheated to 50-60°C, adopt a step-by-step shearing method, and carry out high-speed shear reaction at 120-125°C, -0.08 MPa, 3500-4000 rpm for 8-10 minutes, and then carry out high-speed shear reaction at 110-120°C, -0.09 MPa, 2000-2500 rpm for 3-5 minutes to obtain a modified prepolymer.

[0040] The addition of maleic anhydride castor oil by atomization ensures instantaneous dispersion and avoids gelation caused by excessive local concentration. The maleic anhydride grafted castor oil is preheated to 50-60°C, which is lower than the double bond activation temperature of the maleic anhydride grafted castor oil, to avoid prepolymerization. A step-by-step shearing method is used, with the initial shear temperature controlled at 120-125°C to reach the anhydride ring-opening activation energy and promote interfacial amidation. The vacuum degree is -0.08MPa, which can remove the byproduct water and push the reaction equilibrium to the right. The shear speed is controlled at 3500-4000rpm, with a shear rate γ≈5×10³s⁻¹, so that the maleic anhydride grafted castor oil droplets are dispersed to 1-2μm. The reaction is carried out for 8-10 minutes at this temperature, vacuum degree, and shear speed, significantly improving the anhydride conversion rate. Avoid excessive loss of double bonds, then lower the temperature and control the shear temperature at 110~120℃, which is lower than the dangerous temperature of double bonds of maleic anhydride grafted castor oil, and can effectively protect unsaturated bonds. The vacuum degree is -0.09MPa, which can completely remove free acid and residual solvent. The shear speed is controlled at 2000~2500rpm, presenting a laminar flow state to avoid bubble entanglement. React at this temperature, vacuum degree and shear speed for 3~5min, effectively improving the volatile matter removal rate and eliminating local concentration gradients.

[0041] Maleic anhydride grafted castor oil is a modified bio-based material produced through the esterification reaction of castor oil with maleic anhydride. Derived from renewable castor oil, it has a 100% biobased content, contributing to reduced environmental pollution. The maleic anhydride grafted castor oil is close to the chain segments of the alkyd resin prepolymer. The castor oil segments diffuse into the alkyd resin prepolymer and, through van der Waals forces, insert into the interstices of the prepolymer chains. Simultaneously, the hydroxyl groups of the castor oil form hydrogen bonds with the ester groups of the prepolymer, forming a stable entanglement network. The long, flexible chains of the maleic anhydride grafted castor oil absorb impact energy, inhibit crack propagation, and enhance the flexibility and impact resistance of the alkyd resin prepolymer.

[0042] S3.3. Preheat the modified prepolymer in a water bath at 50-60°C for 25-30 min, add the diluent dropwise at a rate of 5 mL / min, stir at 50-55°C at 300-500 rpm for 8-10 min, add curing agent, defoaming agent, leveling agent and anti-settling agent respectively, and stir at 50-55°C at a speed of 600-1200 rpm for 12-18 min. After vacuum degassing at -0.08 MPa and 50-55°C for 10-15 min, place in a constant temperature box at 40°C and let it stand for 30 min to obtain an environmentally friendly alkyd resin coating.

[0043] The preheating temperature is controlled at 50-60°C, which is higher than the glass transition temperature of the prepolymer, to facilitate diluent penetration. Preheating at this temperature for 25-30 minutes can ensure uniform core temperature and avoid uneven dilution caused by local high viscosity. The dripping rate is controlled at 5mL / min to match the prepolymer absorption rate to avoid phase separation caused by local excessive concentration. The stirring speed is controlled at 300-500rpm to form laminar flow, reduce shear rate, and achieve gentle mixing. The stirring temperature is 50-55°C, which can effectively control the diluent volatility while maintaining the system viscosity. Stirring at this stirring speed and temperature for 8-10 minutes can fully participate in the reaction of the diluent, reduce the system viscosity, and improve its workability. After adding curing agent, defoamer, and other additives, maintain a stirring speed of 600-1200 rpm to transition the system from transitional flow to turbulent flow, increasing mixing rate and effectively spreading the defoamer. Maintaining the stirring temperature at 50-55°C prevents premature reaction of the amine curing agent. Stirring at this speed and temperature for 12-18 minutes effectively balances the molecular orientation time of the leveling agent and the formation of the thixotropic network of the anti-settling agent. Maintaining the degassing vacuum at -0.08 MPa effectively increases the bubble expansion rate and facilitates rapid bubble removal. Maintaining the degassing temperature at 50-55°C effectively maintains the system viscosity. Degassing at this vacuum and temperature for 10-15 minutes effectively removes bubbles and reduces the system's bubble density. Maintaining the curing temperature at 40°C—above the coating's glass transition temperature but below the reaction temperature—allows the leveling agent to achieve molecular orientation. Allowing the coating to stand at this temperature for 30 minutes effectively relaxes internal stress and prevents cratering.

[0044] The present invention provides an environmentally friendly alkyd resin coating, which is prepared by the above-mentioned preparation method of the environmentally friendly alkyd resin coating, and comprises soybean oleic acid, pentaerythritol, nano zinc oxide, sebacic acid, limonene, an antioxidant, hydrogenated castor oil, isophthalic acid, epoxy resin, glycidyl methacrylate, a catalyst, a polymerization inhibitor, N-methylpyrrolidone, polysulfoneamide, maleic anhydride grafted castor oil, a diluent, a curing agent, a defoaming agent, a leveling agent and an anti-settling agent; wherein, Soybean oleic acid is used to provide long-chain fatty acid structure, enhancing the flexibility and biobased content of alkyd resin coatings; Pentaerythritol is used to construct multifunctional cross-linking nodes and improve the branching degree and hardness of alkyd resin; Nano zinc oxide is used to replace traditional lead / tin catalysts to catalyze esterification reactions and also impart UV shielding properties to alkyd resin coatings; Sebacic acid is used to introduce long-chain dibasic acid structure to improve the low-temperature toughness of alkyd resin; Limonene is used to replace traditional petroleum-based solvents as a green solvent to disperse nanoparticles and reduce the viscosity of alkyd resin reaction systems; Isophthalic acid is used to provide a rigid aromatic ring structure and improve the heat resistance of alkyd resin coatings; Epoxy resin is used to modify alkyd resin, build a covalent cross-linked backbone, and enhance the chemical stability of alkyd resin coatings; Glycidyl methacrylate is used to introduce carbon-carbon double bonds to achieve UV-assisted curing of alkyd resin coatings; Polysulfoneamide is used to provide strong polar bonds and rigid skeletons of sulfone groups, enhance the dielectric strength of alkyd resin coatings, and give alkyd resin coatings high insulation, heat resistance and high-frequency stability; Maleic anhydride grafted castor oil is used to bridge polysulfoneamide and alkyd resin prepolymer to form chemical bonds, physical bonds and entanglement structures, thereby improving the interfacial compatibility of alkyd resin coatings.

[0045] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing an environmentally friendly alkyd resin coating, characterized in that the steps include: S1, after vacuum dehydration, soybean oleic acid is reacted with pentaerythritol, nano zinc oxide dispersion, sebacic acid, the remaining 70% of the total amount of limonene, antioxidant, hydrogenated castor oil and isophthalic acid premix by stepwise heating to 230-240°C to prepare a bio-based alkyd resin; S2, adding the premixed solution of bio-based alkyd resin, epoxy resin and glycidyl methacrylate into a reactor respectively, and reacting at 110-120° C. to obtain an alkyd resin prepolymer; S3. Add N-methylpyrrolidone, polysulfoneamide, alkyd resin prepolymer and maleic anhydride castor oil respectively, and obtain a modified prepolymer through multi-stage high-speed shearing. Add diluent, curing agent, defoaming agent, leveling agent and anti-settling agent, and react at 50-55°C to obtain an environmentally friendly alkyd resin coating.

2. The method for preparing an environmentally friendly alkyd resin coating according to claim 1, wherein: In step S1, the biobased content of the soybean oleic acid is ≥95%, and the acid value is 190-200 mgKOH / g; the biobased content of the pentaerythritol is 100%, and the particle size is ≤50 μm; the nano zinc oxide dispersion slurry is a pre-dispersed slurry formed by ball milling nano zinc oxide and 20% soybean oleic acid at 2000-3000 rpm for 20-30 minutes; the biobased content of the sebacic acid is 100%; the biobased content of the isophthalic acid is ≥95%; the isophthalic acid premix is a solution formed by mixing isophthalic acid with 30% limonene preheated to 90° C.; the biobased content of the limonene is ≥95%; and the antioxidant is 2,6-di-tert-butyl-4-methylphenol.

3. The method for preparing an environmentally friendly alkyd resin coating according to claim 1, wherein: In step S1, the mass ratio of the soybean oleic acid to the pentaerythritol is 3-5:1-3; the amount of the nano-zinc oxide dispersion is 0.05-0.08% of the mass of the bio-based alkyd resin; the mass ratio of the sebacic acid to the isophthalic acid premix is 1-3:2-5; the total amount of the limonene is 5-8% of the mass of the bio-based alkyd resin; the amount of the antioxidant is 0.03-0.05% of the mass of the bio-based alkyd resin; and the amount of the hydrogenated castor oil is 0.01-0.03% of the mass of the bio-based alkyd resin.

4. The method for preparing an environmentally friendly alkyd resin coating according to claim 1, wherein: Step S1 includes: S1.

1. Dehydrate soybean oleic acid at 100-120°C and -0.095 MPa vacuum for 1-1.5 h. Add it, along with pentaerythritol and nano-zinc oxide dispersion, to a reactor under nitrogen protection. Raise the temperature to 220-240°C at a rate of 5°C / min and react for 1-2 h. S1.

2. Cool the mixture to 170-180°C, first add sebacic acid, the remaining 70% of the total amount of limonene, an antioxidant, and hydrogenated castor oil, stir at 200-300 rpm for 10-15 min, then slowly add the isophthalic acid premix dropwise, heat the mixture to 190-200°C at a rate of 2°C / min, react for 45-60 min, then heat the mixture to 210-220°C, react for 60-80 min, and finally heat the mixture to 230-240°C, react for 60-90 min to obtain a bio-based alkyd resin.

5. The method for preparing an environmentally friendly alkyd resin coating according to claim 1, wherein: Step S2 includes: S2.

1. Dehydrate the bio-based alkyd resin under vacuum at 100-120°C and -0.095 MPa for 30-40 minutes. Then, add it to the reactor and heat it to 110-120°C. Under nitrogen protection, slowly add epoxy resin preheated to 60°C and stir at 400-600 rpm for 20-25 minutes. S2.

2. Slowly dropwise add the premix of glycidyl methacrylate, catalyst, and polymerization inhibitor, and continue the reaction at a stirring speed of 300-400 rpm for 50-70 minutes to obtain an alkyd resin prepolymer.

6. The method for preparing an environmentally friendly alkyd resin coating according to claim 5, characterized in that: In step S2, the epoxy resin is epoxy resin E-51; the catalyst is dibutyltin dilaurate; the polymerization inhibitor is hydroquinone; the mass ratio of the bio-based alkyd resin to the epoxy resin is 4-10:1-3; the amount of glycidyl methacrylate is 12-15% of the mass of the alkyd resin prepolymer; and the mass ratio of the catalyst to the polymerization inhibitor is 2-5:1-3.

7. The method for preparing an environmentally friendly alkyd resin coating according to claim 1, characterized in that: In step S3, the purity of the N-methylpyrrolidone is ≥99.9%, and the moisture content is ≤50ppm; the diluent is epoxy limonene butyl ether, and the bio-based content is ≥90%; the curing agent is cardanolamine T-31; the defoamer is defoamer BYK-066N; the leveling agent is leveling agent BYK-358; the anti-settling agent is hydrogenated castor oil wax; the amount of the N-methylpyrrolidone is 75-85% of the mass of the modified prepolymer; the polymer is The mass ratio of sulfoneamide to the maleic anhydride grafted castor oil is 8-10:1-3; the amount of the diluent is 15-20% of the mass of the alkyd resin coating; the amount of the curing agent is 8-10% of the mass of the alkyd resin coating; the amount of the defoamer is 0.3-0.5% of the mass of the alkyd resin coating; the amount of the leveling agent is 0.5-0.8% of the mass of the alkyd resin coating; and the amount of the anti-settling agent is 2-5% of the mass of the alkyd resin coating.

8. The method for preparing an environmentally friendly alkyd resin coating according to claim 1, characterized in that: Step S3 includes: S3.

1. Place N-methylpyrrolidone in a reactor and heat to 70-80°C. Under nitrogen, add polysulfoneamide that has been vacuum-dehydrated at 70-80°C and -0.095 MPa for 3-4 hours in batches. Stir at 200-300 rpm for 2-3 hours. Add alkyd resin prepolymer preheated to 110-120°C. Premix at 800-1000 rpm for 10-15 minutes. Then, high-speed shear reaction is carried out at 110-120°C and -0.05 MPa at 5000-6000 rpm for 15-18 minutes. S3.

2. Atomize maleic anhydride-grafted castor oil preheated to 50-60°C and perform a stepwise shear reaction at 120-125°C, -0.08 MPa, and 3500-4000 rpm for 8-10 minutes. Then, perform a high-speed shear reaction at 110-120°C, -0.09 MPa, and 2000-2500 rpm for 3-5 minutes to obtain a modified prepolymer. S3.

3. Preheat the modified prepolymer in a water bath at 50-60°C for 25-30 min, add the diluent dropwise at a rate of 5 mL / min, stir at 50-55°C at 300-500 rpm for 8-10 min, add curing agent, defoaming agent, leveling agent and anti-settling agent respectively, and stir at 50-55°C at a speed of 600-1200 rpm for 12-18 min. After vacuum degassing at -0.08 MPa and 50-55°C for 10-15 min, place in a constant temperature box at 40°C and let it stand for 30 min to obtain an environmentally friendly alkyd resin coating.

9. An environmentally friendly alkyd resin coating, characterized in that: The environmentally friendly alkyd resin coating is prepared by the preparation method of any one of claims 1 to 8, comprising soybean oleic acid, pentaerythritol, nano zinc oxide, sebacic acid, limonene, antioxidant, hydrogenated castor oil, isophthalic acid, epoxy resin, glycidyl methacrylate, catalyst, polymerization inhibitor, N-methylpyrrolidone, polysulfoneamide, maleic anhydride grafted castor oil, diluent, curing agent, defoamer, leveling agent and anti-settling agent; wherein, The soybean oleic acid is used to provide a long-chain fatty acid structure to enhance the flexibility and bio-based content of the alkyd resin coating; The pentaerythritol is used to construct multifunctional cross-linking nodes to increase the branching degree and hardness of the alkyd resin; The nano zinc oxide is used to replace the traditional lead / tin catalyst to catalyze the esterification reaction and at the same time impart ultraviolet shielding function to the alkyd resin coating; The sebacic acid is used to introduce a long-chain dibasic acid structure to improve the low-temperature toughness of the alkyd resin; The limonene is used to replace traditional petroleum-based solvents and serves as a green solvent to disperse nanoparticles and reduce the viscosity of the alkyd resin reaction system; The isophthalic acid is used to provide a rigid aromatic ring structure to improve the heat resistance of the alkyd resin coating; The epoxy resin is used to modify the alkyd resin, construct a covalent cross-linked main chain, and enhance the chemical stability of the alkyd resin coating; The glycidyl methacrylate is used to introduce carbon-carbon double bonds to achieve the ultraviolet light-assisted curing function of the alkyd resin coating; The polysulfoneamide is used to provide a strong polar bond and a rigid skeleton of the sulfone group, thereby enhancing the dielectric strength of the alkyd resin coating and imparting high insulation, heat resistance and high-frequency stability to the alkyd resin coating; The maleic anhydride grafted castor oil is used to bridge the polysulfoneamide and the alkyd resin prepolymer to form chemical bonds, physical bonds and entangled structures, thereby improving the interface compatibility of the alkyd resin coating.