Preparation method of environment-friendly rust inhibitor with rust based on gallic acid-tung oil ester

Abstract

The invention relates to an environment-friendly rust inhibitor based on gallic acid-tung oil ester and a preparation method of the environment-friendly rust inhibitor. The environment-friendly rust inhibitor comprises the following components in percentage by weight: 98-98.5% of gallic acid-oligomerization tung oil acid amino diester emulsion and 1.5-2% of a drier. According to the environment-friendly antirust agent with rust, tung oil serves as a raw material, gallic acid-oligomerization tung oil acid diester is obtained through the saponification-esterification-amidation-oligomerization-esterification technology, and the prepared antirust agent with rust has the advantages of being good in environmental protection property (containing no heavy metal or strong acid), free of corrosion, low in VOC emission, high in weather resistance and wide in applicability.

Description

Technical Field

[0001] This invention relates to a method for preparing a rust remover, specifically a method for preparing an environmentally friendly rust inhibitor based on gallic acid-tung oil ester. Background Technology

[0002] Rust inhibitors are chemical treatment agents specifically designed for rusted metal surfaces. They work by reacting acidic components with the rust to form a stable passivation layer, or by using resin to encapsulate the rust layer, thus preventing further corrosion. Their core components include rust conversion agents, film-forming resins, and corrosion inhibitors. Suitable for lightly to moderately rusted steel, cast iron, and other metals, they are widely used in industrial equipment, automotive repair, shipbuilding, and home DIY projects. Before application, the surface must be cleaned. After drying, a protective coating can be applied directly or layered. Products are available in conversion, stabilizing, and penetrating types, offering advantages such as time-saving, labor-saving, and wide applicability. However, their effectiveness is limited for severe rust, requiring attention to environmental conditions and safety precautions.

[0003] Currently, similar products on the market mainly fall into three technical categories: First, traditional phosphoric acid-tannic acid system coatings, which have defects such as low conversion rate (≤80%), poor salt spray resistance (≤300h), and high VOC content (>120g / L); second, composite water-based rust-inducing coatings, which have good adhesion but lack chemical rust conversion function and contain heavy metals; and third, new chelated coatings, which have problems such as high cost and poor film-forming properties.

[0004] Compared to traditional rust inhibitors (such as chromates and phosphates), gallic acid-based rust inhibitors offer significant environmental advantages (degradable and low-toxicity), highly efficient corrosion inhibition (multi-active-site film formation and broad-spectrum rust prevention), and multifunctionality (antioxidant and antibacterial properties), making them suitable for applications with high safety requirements, such as food and medical fields. However, their cost is relatively high, and their long-term stability requires further verification.

[0005] CN111393956B discloses a water-based two-component conversion-type rust-resistant anti-corrosion coating, which uses a compound of phosphoric acid and gallic acid modified by polyol monoether esterification as a rust-converting agent and a modified acrylic emulsion as a film-forming medium. Existing gallic acid-based rust inhibitors typically require the addition of resins (styrene-acrylic emulsion, water-soluble epoxy resin, water-soluble acrylic resin, etc.) as film-forming media, which is highly environmentally harmful. Summary of the Invention

[0006] The first technical problem to be solved by the present invention is to provide an environmentally friendly rust inhibitor based on gallic acid-tung oil ester.

[0007] The second technical problem to be solved by the present invention is to provide a method for preparing the environmentally friendly rust inhibitor based on gallic acid-tung oil ester.

[0008] The technical solution adopted by the present invention to solve its first technical problem is an environmentally friendly rust inhibitor based on gallic acid-tung oil ester, comprising the following components: gallic acid-oligomeric tung oil ester emulsion 93-98.5wt%, nonionic surfactant 0-5wt%, and drying agent 1.5-2wt%.

[0009] Furthermore, the preparation method of the gallic acid-oligomeric tung oil amine diester emulsion includes the following steps: Step 1: Methyl tung oil acid and diethanolamine are subjected to amidation reaction to obtain tung oil acid amine diol, heated to 140-150℃ and kept at the temperature for 4-6 hours, and then cooled to obtain oligomeric tung oil acid amine diol; Step 2: Using gallic acid and oligotung oil acid amine diol as raw materials, p-toluenesulfonic acid is used as a catalyst to carry out an esterification reaction in a solvent to introduce ortho-phenolic hydroxyl groups. After the reaction is completed, the mixture is washed with saturated sodium bicarbonate solution until the pH is neutral. The organic phase is dried, filtered, and the solvent is removed by rotary evaporation to obtain gallic acid-oligotung oil acid amine diol. The solvent is toluene or xylene; The molar ratio of gallic acid to oligomeric tung oil acid diol is 1-1.5:1. Step 3: Emulsify gallic acid-oligomeric tung oil amine diester to obtain gallic acid-oligomeric tung oil amine diester emulsion.

[0010] Furthermore, the preparation method of the methyl tung oil ester includes the following steps: (1) Dissolve 0.08-0.12 mol tung oil and 0.3-0.4 mol potassium hydroxide in a container containing methanol aqueous solution, heat to 60-80℃, reflux for 1-1.5h, adjust the pH value to 3.0-3.5 with concentrated sulfuric acid, continue stirring for 1-1.5h, cool to room temperature and let stand to separate the layers; take the upper organic phase and wash it once with 10wt% NaCl solution and twice with water, then remove the water with anhydrous CaCl2 to obtain tung oil acid; (2) Add 8-12 g of tung oil acid and 40-60 ml of methanol to a three-necked flask, and add concentrated sulfuric acid for catalysis. After reflux for 4-6 hours, add saturated sodium bicarbonate solution or triethanolamine solution to adjust the pH to neutral. After separation, take the upper layer and wash it with water 2-3 times. Then separate the layers again and take the upper layer. Remove excess water by rotary evaporation to obtain methyl tung oil acid.

[0011] The emulsification process can be either ultrasonic emulsification or high-speed shearing.

[0012] Preferably, the emulsifier used in the emulsification treatment is a mixture of Tween-80 and Span-80 in a mass ratio of 9:1.

[0013] The ultrasonic emulsification specifically involves mixing gallic acid-oligomeric tung oil amine diester (15%), emulsifier (5%), cosolvent (8%), and deionized water (72%) and then performing ultrasonic emulsification.

[0014] The high-speed shearing process specifically involves: mixing 15% gallic acid-oligomeric tung oil amine diester, 5% emulsifier, and 8% cosolvent, heating to 65-70°C, and stirring until completely clear and homogeneous; heating 72% deionized water to the same temperature as the oil phase; adding the oil phase dropwise to the aqueous phase under high-speed shearing; observing the system thicken from dilute to thick, and then suddenly thinning and brightening upon reaching the phase inversion point, forming a bluish emulsion; continuing shearing for 5-10 minutes after phase inversion, and then slowly cooling to room temperature under stirring to obtain the gallic acid-oligomeric tung oil amine diester emulsion.

[0015] Preferably, the co-solvent is isopropanol.

[0016] Preferably, the drying agent is a manganese-based drying agent, a cerium-based drying agent, or a cobalt-zirconium composite drying agent.

[0017] Preferably, the emulsification process is a phase inversion emulsification method.

[0018] Preferably, in step 3, diethanolamine is heated to 70-80℃, potassium hydroxide is added and stirred until completely dissolved, then methyl tung oil acid (methyl tung oil acid: diethanolamine: KOH = 100:61:8) is added, and the mixture is vacuumed to 0.08-0.1 MPa and reacted for 4-6 hours. After cooling to 45-50℃, ethyl acetate is added for extraction to obtain the crude product. The crude product is then washed 3-4 times with saturated brine, and water is removed using anhydrous magnesium sulfate. Finally, ethyl acetate is removed using a rotary evaporator to obtain tung oil acid diol.

[0019] Preferably, in step 2, the esterification reaction conditions are: oil bath at 110-120°C, reflux for 4-6 hours.

[0020] The technical solution adopted by this invention to solve its second technical problem is a method for preparing an environmentally friendly rust inhibitor based on gallic acid-tung oil ester, comprising the following steps: Step S1: Dissolve 0.1 mol tung oil and 0.35 mol potassium hydroxide in a three-necked flask containing 140 mL methanol and 70 mL water. Heat to 70 °C, reflux for 1-1.5 h, adjust the pH to 3.0-3.5 with 98% H2SO4 solution, continue stirring for 1-1.5 h, cool to room temperature, and allow to separate into layers. Take the upper organic phase, wash once with 80 mL 10% NaCl solution and twice with 80 mL deionized water, then remove water with anhydrous CaCl2 to obtain tung oil acid. Step S2: Add 10g of tung oil acid and 50ml of methanol to a three-necked flask, and add 1ml of concentrated sulfuric acid for catalysis. After reflux for 4-6 hours, add saturated sodium bicarbonate solution to adjust the pH to neutral. After separation, take the upper layer and wash it with water 2-3 times. Then separate the layers again and take the upper layer. Remove excess water by rotary evaporation to obtain methyl tung oil acid. Step S3: Methyl tung oil ester and diethanolamine undergo an amidation reaction to obtain tung oil amine diol, which is heated to 140-150℃ and kept at that temperature for 4-6 hours. After cooling, oligomeric tung oil amine diol is obtained. The reaction equation is as follows:

[0021] Step S4: Using gallic acid and oligotung oil acid amine diol as raw materials, p-toluenesulfonic acid is used as a catalyst to carry out an esterification reaction in toluene solvent, and an ortho-phenolic hydroxyl group is introduced. After the reaction is completed, the mixture is washed with saturated sodium bicarbonate solution until the pH is neutral, the organic phase is dried, filtered, and the solvent is removed by rotary evaporation to obtain gallic acid-oligotung oil acid amine diol. The molar ratio of gallic acid to oligomeric tung oil acid diol is 1-1.5:1. Step S5: Emulsify gallic acid-oligomeric tung oil amine diester, add nonionic surfactant and drying agent to obtain an environmentally friendly rust inhibitor based on gallic acid-tung oil ester.

[0022] In this invention, oligomeric tung oil acid amine diol with excellent film-forming properties is prepared through an amidation reaction of methyl tung oil acid with diethanolamine and a subsequent oligomerization process at 150°C for 4-6 hours. Secondly, an ortho-phenolic hydroxyl group is introduced by the esterification reaction of gallic acid with the oligomer, endowing the coating with chemical rust conversion function (XPS detection chelation rate ≥95%). In terms of process, ultrasonic-assisted emulsification (300W, 20min) is used to achieve an emulsion particle size ≤200nm, and a manganese / cobalt-zirconium composite drying agent is used to achieve rapid curing with surface drying ≤30min and actual drying ≤8h. This coating exhibits a triple synergistic protection mechanism of rust transformation, passivation, and shielding: gallic acid esters chemically transform the rust layer (cross-cut adhesion grade 1), tung oil derivatives form a dense hydrophobic film, and oligomeric structures enhance permeability, ultimately achieving a salt spray resistance of over 600 hours (ASTM B117) and a VOC content of <50g / L. Compared with traditional alkyd coatings (salt spray resistance ≤200 hours, VOC >350g / L), it has significant environmental advantages and performance improvements.

[0023] In this invention, gallic acid-tung oil ester possesses excellent antioxidant, antibacterial, UV-resistant, and film-forming properties, while also exhibiting good biocompatibility and biodegradability. The phenolic hydroxyl groups in its molecular structure endow it with strong free radical scavenging ability, while the long-chain fatty acid ester provides hydrophobicity and flexibility.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) Performance advantages Strong adhesion: The flexible long chain of oligomeric tung oil acid amine diol is balanced with the rigid benzene ring structure, which improves the coating's penetration and adhesion to rust and substrate. Excellent weather resistance: The unsaturated bonds of tung oil undergo oxidative cross-linking to form a dense film, and gallic acid provides antioxidant protection, delaying coating aging; Easy to apply: The water-based system can be directly applied to rusted surfaces, simplifying the pretreatment process; (2) Environmental protection and economy: The raw materials are renewable, the wastewater in the process is easy to treat, and the cost is lower than that of synthetic resin coatings; the amount of drying agent used is small, which further reduces costs; (3) Process controllability: Key parameters are clear, repeatability is good, and it is suitable for industrial scale-up. Attached Figure Description

[0025] Figure 1 The images show the XPS spectra of the rust inhibitor prepared in Example 2 before and after treatment. Detailed Implementation

[0026] Numerous specific details are set forth in the following description to provide a full understanding of the invention. However, the invention can be practiced in many other ways different from those described herein, and similar modifications can be made by those skilled in the art without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0028] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0029] It should be noted that the reagents and other materials used in the embodiments of this invention are all commercially available products.

[0030] Example 1

[0031] In this embodiment, the mass ratio of gallic acid-tung oil ester emulsion to manganese-based drying agent in the environmentally friendly rust inhibitor is 98:2.

[0032] This embodiment describes a method for preparing an environmentally friendly rust inhibitor based on gallic acid-tung oil ester, which includes the following steps: Step S1: Dissolve 0.1 mol tung oil and 0.35 mol potassium hydroxide in a mixed solution consisting of 140 mL methanol and 70 mL water, reflux at 75 °C for 1.2 h, then adjust the pH to 3.2 with 98% concentrated sulfuric acid, continue stirring for the same time, cool, and allow to stand for separation; take the upper organic phase and wash it once with 80 mL 10% sodium chloride solution and twice with 80 mL deionized water, then dehydrate it with anhydrous calcium chloride to obtain tung oil acid; Step S2: Add 10g of the above tung oil acid, 50mL of methanol and 1mL of concentrated sulfuric acid as catalyst to a three-necked flask. After reflux for 4 hours, add saturated sodium bicarbonate solution to adjust the pH to neutral. Take the upper liquid after separation, wash it twice with water, and then separate it again. Remove the residual water by rotary evaporation to obtain methyl tung oil acid. Step S3: Methyl tung oil acid and diethanolamine are reacted at 0.08 MPa and 145 °C for 5 h to obtain oligomeric tung oil acid amine diol; Step S4: Using p-toluenesulfonic acid as a catalyst (5% p-toluenesulfonic acid), gallic acid and oligomeric tung oil acid amine diol are esterified in toluene solvent at a molar ratio of 1:1.2:1 to introduce ortho-phenolic hydroxyl groups; after the reaction, the mixture is washed with saturated sodium bicarbonate solution until neutral, the organic phase is dried and filtered, and the solvent is removed by rotary evaporation to obtain the final product gallic acid-oligomeric tung oil acid amine diol. Step S5: Sonic emulsify the following mixture (300W, 20min): 15wt% gallic acid-oligomeric tung oil amine diester, 5wt% compound emulsifier (Tween-80:Span-80 = 9:1), 8wt% isopropanol (co-solvent), and 72wt% deionized water. After emulsification, gallic acid-oligomeric tung oil amine diester emulsion is obtained. Add manganese-based drier at a mass ratio of 98:2 (emulsion / drier) to obtain an environmentally friendly rust inhibitor.

[0033] Example 2

[0034] In this embodiment, the mass ratio of gallic acid-oligomeric tung oil ester emulsion to cobalt-zirconium composite drying agent in the environmentally friendly rust inhibitor is 98.5:1.5.

[0035] This embodiment describes a method for preparing an environmentally friendly rust inhibitor based on gallic acid-tung oil ester, which includes the following steps: Step S1: Dissolve 0.1 mol tung oil and 0.35 mol potassium hydroxide in a mixed solution consisting of 140 mL methanol and 70 mL water, reflux at 70 °C for 1.5 h, then adjust the pH to 3.0 with 98% concentrated sulfuric acid, continue stirring for the same time, cool, and allow to stand for separation; take the upper organic phase and wash it once with 80 mL 10% sodium chloride solution and twice with 80 mL deionized water, then dehydrate it with anhydrous calcium chloride to obtain tung oil acid; Step S2: Add 10g of the above tung oil acid, 50mL of methanol and 1mL of concentrated sulfuric acid as catalyst to a three-necked flask. After reflux for 4 hours, add saturated sodium bicarbonate solution to adjust the pH to neutral. Take the upper liquid layer, wash it with water 3 times, and then separate the layers again. Remove the residual water by rotary evaporation to obtain methyl tung oil acid. Step S3: Methyl tung oil acid and diethanolamine are reacted at 0.06 MPa and 140 °C for 4 h to obtain oligomeric tung oil acid amine diol; Step S4: Using p-toluenesulfonic acid as a catalyst (5 wt% p-toluenesulfonic acid), gallic acid and oligomeric tung oil acid amine diol are esterified in toluene solvent at a molar ratio of 1:1 to introduce ortho-phenolic hydroxyl groups; after the reaction, the mixture is washed with saturated sodium bicarbonate solution until neutral, the organic phase is dried and filtered, and the solvent is removed by rotary evaporation to obtain the final product gallic acid-oligomeric tung oil acid amine diol. Step S5: Mix 15% gallic acid-oligomeric tung oil amine diester, 5% of the compound emulsifier—a mixture of Tween-80: Span-80 = 9:1, and 8% of the cosolvent—isopropanol. Heat to 65°C and stir until completely clear and homogeneous. Heat 72% deionized water to the same temperature as the oil phase, 65°C. Under high-speed shearing, slowly and dropwise add the oil phase to the aqueous phase. At this point, the system will be observed to thicken from dilute, and after dropping to the phase inversion point, it will suddenly become thinner and brighter, forming a bluish emulsion. After phase inversion, continue shearing for 5 minutes, and then slowly cool to room temperature under stirring to obtain gallic acid-oligomeric tung oil amine diester emulsion. Add cobalt-zirconium composite drier to the emulsion according to the (emulsion / drier) mass ratio of 98.5:1.5 to obtain the rust inhibitor.

[0036] Example 3

[0037] In this embodiment, the mass ratio of gallic acid-tung oil ester-based environmentally friendly rust inhibitor to nonionic surfactant (Tween-80) and manganese-based drier is 94:5:1.

[0038] This embodiment describes a method for preparing an environmentally friendly rust inhibitor based on gallic acid-tung oil ester, which includes the following steps: Step S1: Dissolve 0.1 mol tung oil and 0.35 mol potassium hydroxide in a mixed solution consisting of 140 mL methanol and 70 mL water, reflux at 80 °C for 1 h, then adjust the pH to 3.5 with 98% concentrated sulfuric acid, continue stirring for the same time, cool, and allow to stand for separation; take the upper organic phase and wash it once with 80 mL 10% sodium chloride solution and twice with 80 mL deionized water, then dehydrate it with anhydrous calcium chloride to obtain tung oil acid; Step S2: Add 10g of the above tung oil acid, 50mL of methanol and 1mL of concentrated sulfuric acid as catalyst to a three-necked flask. After reflux for 6 hours, add saturated sodium bicarbonate solution to adjust the pH to neutral. Take the upper liquid after separation, wash it twice with water, and then separate it again. Remove the residual water by rotary evaporation to obtain methyl tung oil acid. Step S3: Methyl tung oil acid and diethanolamine are reacted at 0.1 MPa and 140 °C for 4 h to obtain oligomeric tung oil acid amine diol; Step S4: Using p-toluenesulfonic acid as a catalyst (5 wt% p-toluenesulfonic acid), gallic acid and oligomeric tung oil amine diol are esterified in toluene solvent at a molar ratio of 1:1.5:1 to introduce ortho-phenolic hydroxyl groups. After the reaction, the mixture is washed with saturated sodium bicarbonate solution until neutral, the organic phase is dried and filtered, and the solvent is removed by rotary evaporation to obtain the final product, gallic acid-oligomeric tung oil amine diol. Step S5: Gallic acid oligomeric tung oil amine diester is ultrasonically emulsified (power 300W, 20min) to obtain gallic acid oligomeric tung oil amine diester emulsion. Nonionic surfactant (Tween-80) and manganese-based drier are added according to the mass ratio of (emulsion / nonionic surfactant / drier) 94:5:1 to obtain rust inhibitor.

[0039] Comparative Example 1 The difference between this comparative example and Example 2 is that methyl tung oil ester does not undergo oligomerization at 150°C after reacting with diethanolamine. Other parameters and steps are the same as in Example 2.

[0040] Comparative Example 2 The difference between this comparative example and Example 2 is that gallic acid is replaced with common benzoic acid. Other parameters and steps are the same as in Example 2.

[0041] Comparative Example 3 The difference between this comparative example and Example 2 is that the gallic acid oligomeric tung oil amine diester was not emulsified and was directly dissolved in xylene, with 5% lead-chromium drying agent added. Other parameters and steps are the same as in Example 2.

[0042] Performance checks and results analysis The rust-coated coatings prepared in Examples 1-3 and Comparative Examples 1-3 were tested for adhesion, salt spray resistance, drying time, rust conversion effect, water resistance, emulsion stability, and coating flexibility according to the contents of Table 1. The test methods are shown in Table 1, and the test results are shown in Table 2.

[0043] Table 1 Test Methods

[0044] Table 2 Test Results

[0045] Gallic acid oligomeric tung oil amine diester and cobalt-zirconium composite drier exhibit a significant synergistic effect in this system. For example... Figure 1 As shown, XPS test data indicate that gallic acid oligomeric tung oil amine diester reacts with rust (Fe) through its ortho-phenolic hydroxyl group. 3+ The cobalt-zirconium composite chelate forms a stable iron gallate complex, achieving excellent chemical conversion of the rust layer (conversion rate ≥75% in Examples 1-3, with Example 2 reaching 85%). Simultaneously, its long-chain hydrophobic structure effectively improves coating adhesion (cross-cut test reaches grade 0-1). In contrast, Comparative Example 2, due to the substitution of gallic acid with benzoic acid, completely loses its chelating ability (conversion rate 0), resulting in adhesion dropping to grade 3 and salt spray resistance of only 200 hours. The cobalt-zirconium composite drier significantly accelerates coating curing through a synergistic catalytic mechanism, shortening the actual drying time to 7-9 hours (7 hours in Example 2), while the unoptimized Comparative Example 1 extends it to 10 hours.

[0046] Compared with traditional solvent-based systems, this water-based formulation exhibits comprehensive advantages: Although Comparative Example 3 has good initial adhesion (Grade 1) and a short drying time (6h), it lacks an effective rust conversion mechanism, and its salt spray resistance (400h) is significantly lower than that of this system (≥550h), and it contains harmful heavy metal components; while this solution, through bio-based molecular design, achieves excellent salt spray resistance (up to 600h), good water resistance (no bubbling after 240h immersion) and ideal flexibility (no cracking after 3mm shaft bending) while maintaining low VOC (<50g / L), perfectly meeting the current dual requirements of green environmental protection and long-term protection in the field of heavy-duty corrosion protection.

[0047] This synergistic effect is mainly reflected in three aspects: First, the chelation conversion of gallic esters complements the shielding protection of the long-chain tung oil acid; second, the optimized ratio of the drier ensures the kinetic balance between the conversion reaction and film-forming curing; finally, the water-based emulsification process achieves environmental friendliness while maintaining performance, providing a new solution for the development of rust protection technology. The above embodiments only illustrate several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that for those skilled in the art, several modifications and improvements can be made without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the claims.

Claims

1. An environmentally friendly rust inhibitor based on gallic acid-tung oil ester, characterized in that, It includes the following components: gallic acid-oligomeric tung oil amine diester emulsion 93-98.5wt%, nonionic surfactant 0-5wt%, and drying agent 1.5-2wt%.

2. The environmentally friendly rust inhibitor according to claim 1, characterized in that, The preparation method of the gallic acid-oligomeric tung oil amine diester emulsion includes the following steps: Step 1: Methyl tung oil acid and diethanolamine are subjected to amidation reaction to obtain tung oil acid amine diol, heated to 140-150℃ and kept at the temperature for 4-6 hours, and then cooled to obtain oligomeric tung oil acid amine diol; Step 2: Using gallic acid and oligotung oil acid amine diol as raw materials, p-toluenesulfonic acid is used as a catalyst to carry out an esterification reaction in a solvent to introduce ortho-phenolic hydroxyl groups. After the reaction is completed, the mixture is washed with saturated sodium bicarbonate solution until the pH is neutral. The organic phase is dried, filtered, and the solvent is removed by rotary evaporation to obtain gallic acid-oligotung oil acid amine diol. The solvent is toluene or xylene; The molar ratio of gallic acid to oligomeric tung oil acid diol is 1-1.5:

1. Step 3: Emulsify gallic acid-oligomeric tung oil amine diester to obtain gallic acid-oligomeric tung oil amine diester emulsion.

3. The environmentally friendly rust inhibitor according to claim 2, characterized in that, The preparation method of the methyl tung oil acid includes the following steps: (1) Dissolve 0.08-0.12 mol tung oil and 0.3-0.4 mol potassium hydroxide in a container containing methanol aqueous solution, heat to 60-80℃, reflux for 1-1.5h, adjust the pH value to 3.0-3.5 with concentrated sulfuric acid, continue stirring for 1-1.5h, cool to room temperature and let stand to separate the layers; take the upper organic phase and wash it once with 10wt% NaCl solution and twice with water, then remove the water with anhydrous CaCl2 to obtain tung oil acid; (2) Add 8-12 g of tung oil acid and 40-60 ml of methanol to a three-necked flask, and add concentrated sulfuric acid for catalysis. After reflux for 4-6 hours, add saturated sodium bicarbonate solution or triethanolamine solution to adjust the pH to neutral. After separation, take the upper layer and wash it with water 2-3 times. Then separate the layers again and take the upper layer. Remove excess water by rotary evaporation to obtain methyl tung oil acid.

4. The environmentally friendly rust inhibitor according to any one of claims 1-3, characterized in that, The drying agent is a manganese-based drying agent, a cerium-based drying agent, or a cobalt-zirconium composite drying agent.

5. The environmentally friendly rust inhibitor according to claim 2, characterized in that, In step 3, the emulsification process is ultrasonic emulsification or high-speed shearing.

6. The environmentally friendly rust inhibitor according to claim 5, characterized in that, The ultrasonic emulsification is specifically performed by mixing gallic acid-oligomeric tung oil amine diester 15%, emulsifier 5%, cosolvent 8%, and deionized water 72% in a ultrasonic emulsification ratio. The high-speed shearing process specifically involves: mixing 15% gallic acid-oligomeric tung oil amine diester, 5% emulsifier, and 8% cosolvent, heating to 65-70°C, and stirring until completely clear and homogeneous; heating 72% deionized water to the same temperature as the oil phase; adding the oil phase dropwise to the aqueous phase under high-speed shearing; observing the system thicken from dilute to thick, and then suddenly thinning and brightening upon reaching the phase inversion point, forming a bluish emulsion; continuing shearing for 5-10 minutes after phase inversion, and then slowly cooling to room temperature under stirring to obtain the gallic acid-oligomeric tung oil amine diester emulsion.

7. The environmentally friendly rust inhibitor according to claim 6, characterized in that, The cosolvent is isopropanol; the emulsifier is a mixture of Tween-80 and Span-80 in a mass ratio of 9:

1.

8. The environmentally friendly rust inhibitor according to claim 2, characterized in that, In step 1, the specific process of the amidation reaction is as follows: Diethanolamine is heated to 70-80℃, KOH is added and stirred until completely dissolved, then methyl tung oil is added and the reaction is carried out under vacuum to 0.08-0.1 MPa for 4-6 hours. After cooling to about 45-50℃, ethyl acetate is added for extraction to obtain the crude product. The crude product is then washed 3-4 times with saturated brine, and water is removed with anhydrous magnesium sulfate. Finally, ethyl acetate is removed by rotary evaporation to obtain tung oil amino diol, wherein methyl tung oil contains 59%-61%, diethanolamine 35%-36%, and KOH 3%-6%.

9. The environmentally friendly rust inhibitor according to claim 2, characterized in that, In step 2, the esterification reaction conditions are: oil bath at 110-120℃, reflux for 4-6 hours.

10. A method for preparing an environmentally friendly rust inhibitor based on gallic acid-tung oil ester as described in claim 1, characterized in that, Includes the following steps: Step S1: Dissolve 0.08-0.12 mol tung oil and 0.3-0.4 mol potassium hydroxide in a methanol-water solution, heat to 60-80℃, reflux for 1-1.5 h, adjust the pH to 3.0-3.5 with concentrated sulfuric acid, continue stirring for 1-1.5 h, cool to room temperature and allow to stand for separation; take the upper organic phase, wash once with 10wt% NaCl solution and twice with water, then remove water with anhydrous CaCl2 to obtain tung oil acid; Step S2: Add 8-12 g of tung oil acid and 40-60 ml of methanol to a three-necked flask, and add concentrated sulfuric acid for catalysis. After reflux for 4-6 hours, add saturated sodium bicarbonate solution or triethanolamine solution to adjust the pH to neutral. After separation, take the upper layer and wash it with water 2-3 times. Then separate the layers again and take the upper layer. Remove excess water by rotary evaporation to obtain methyl tung oil acid. Step S3: Methyl tung oil ester and diethanolamine undergo an amidation reaction to obtain tung oil amine diol, which is heated to 140-150℃ and kept at that temperature for 4-6 hours. After cooling, oligomeric tung oil amine diol is obtained. Step S4: Using gallic acid and oligotung oil acid amine diol as raw materials, p-toluenesulfonic acid is used as a catalyst to carry out an esterification reaction in toluene solvent, and an ortho-phenolic hydroxyl group is introduced. After the reaction is completed, the mixture is washed with saturated sodium bicarbonate solution until the pH is neutral, the organic phase is dried, filtered, and the solvent is removed by rotary evaporation to obtain gallic acid-oligotung oil acid amine diol. The molar ratio of gallic acid to oligomeric tung oil acid diol is 1:1-1.5:

1. Step S5: Emulsify gallic acid-oligomeric tung oil amine diester, add nonionic surfactant and drying agent to obtain an environmentally friendly rust inhibitor based on gallic acid-tung oil ester.

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