Corrosion-resistant epoxy ester resin with high adhesion for anticorrosive paint and preparation method thereof

Abstract

This invention discloses an epoxy ester resin for corrosion-resistant, high-adhesion anti-corrosion coatings and its preparation method. The epoxy ester resin is constructed by esterifying epoxy resin with fatty acids, followed by stepwise grafting of conjugated Schiff bases and thioctic acid disulfide bonds to build a dual dynamic network. This invention achieves highly efficient self-healing of the coating at room temperature through the chemical bonding and synergy of the conjugated Schiff base and disulfide bonds; and by utilizing the hydrophobic benzene ring structure and semi-interpenetrating double network design of the conjugated Schiff base, it endows the coating with high density and excellent corrosion resistance. This invention achieves a synergistic unity of room temperature self-healing and long-term corrosion protection in an air-drying epoxy ester system.

Description

Technical Field

[0001] This invention relates to the field of anti-corrosion coating technology, specifically to an epoxy ester resin for corrosion-resistant, high-adhesion anti-corrosion coatings and its preparation method. Background Technology

[0002] With the continuous development of industrialization, anti-corrosion coatings are increasingly widely used in construction, machinery, transportation, and other fields. Traditional anti-corrosion coatings mainly rely on epoxy resin as the base resin, which has been widely used in the field of corrosion protection due to its excellent mechanical properties and chemical stability. However, with increasingly harsh operating environments, especially those exposed to corrosive media such as high humidity, high salt, and acids and alkalis for extended periods, the performance of traditional epoxy resin coatings is gradually showing its limitations. In particular, there is still considerable room for improvement in aspects such as coating adhesion, corrosion resistance, and self-healing ability.

[0003] In recent years, to overcome the shortcomings of traditional epoxy resin coatings, researchers have attempted to improve their performance by optimizing the chemical structure of epoxy resins. For example, different types of crosslinking agents or the introduction of novel functional monomers, such as Schiff bases and thioctic acid, have been used to enhance the corrosion resistance and self-healing ability of the coating. While these efforts have yielded some results, existing anti-corrosion coatings still face problems such as insufficient self-healing properties, poor adhesion, and poor environmental adaptability. There is an urgent need for a more efficient, environmentally friendly coating material with superior overall performance.

[0004] Therefore, designing an epoxy ester resin with strong corrosion resistance, excellent adhesion, and self-healing function has become an important research direction in current anti-corrosion coating technology. Achieving long-term corrosion protection and self-healing capabilities in coatings by introducing conjugated Schiff base dynamic units and thioctic acid disulfide bond dynamic units is a technical approach worthy of in-depth research and development. Summary of the Invention

[0005] To address the shortcomings of existing anti-corrosion coatings in terms of corrosion resistance, adhesion, and self-healing ability, this invention provides an epoxy ester resin for corrosion-resistant, high-adhesion anti-corrosion coatings and its preparation method. This resin, by introducing conjugated Schiff base dynamic units and thioctic acid disulfide bond dynamic units, significantly improves the corrosion resistance, adhesion, and self-healing properties of the coating, making it suitable for long-term applications in various complex environments.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: An epoxy ester resin for corrosion-resistant and high-adhesion anti-corrosion coatings, wherein the epoxy ester resin is prepared from the following raw materials in parts by weight: 45-55 parts epoxy resin, 25-35 parts unsaturated fatty acid, 5-10 parts conjugated Schiff base monomer, 5-10 parts lipoic acid, 0.2-0.5 parts catalyst, 0.05-0.2 parts polymerization inhibitor, 1-3 parts drying agent, and 10-15 parts inert solvent. The epoxy ester resin has conjugated Schiff base dynamic units and thioctic acid disulfide dynamic units connected by chemical bonds on its molecular chain.

[0007] Optionally, the epoxy resin is a bisphenol A type epoxy resin E-44 or E-51, and the unsaturated fatty acid is selected from one or more of ricinoleic acid, linoleic acid and linolenic acid.

[0008] Optionally, the catalyst is an organotin catalyst or an acidic catalyst; the organotin catalyst is selected from one or more of dibutyltin dilaurate and stannous octoate; the acidic catalyst is selected from one or more of p-toluenesulfonic acid and phosphoric acid.

[0009] Optionally, the polymerization inhibitor is selected from one or more of hydroquinone, methylhydroquinone, and 2,6-di-tert-butyl-p-cresol; the drying agent is a metal soap-based drying agent selected from one or more of cobalt naphthenate and zinc naphthenate; and the inert solvent is selected from one or more of xylene, toluene, and butyl acetate.

[0010] Optionally, the epoxy ester resin coating has a scratch healing rate of ≥90% at room temperature, an adhesion recovery rate of ≥80%, and an adhesion grade of 5B.

[0011] Optionally, the preparation method of the epoxy ester resin for corrosion-resistant and high-adhesion anti-corrosion coating includes the following specific preparation steps: S1. Epoxy resin, unsaturated fatty acid, catalyst, polymerization inhibitor and inert solvent are reacted at a temperature of 140-160℃ for 2-6 hours and a stirring speed of 300-600 rpm to obtain epoxy ester prepolymer. S2. Mix aromatic aldehydes and aromatic amines in a molar ratio of 1:1, and condense them at a temperature of 60-80℃ for 1-3 hours. Then, perform azeotropic dehydration to obtain conjugated Schiff base monomers. S3. Add the conjugated Schiff base monomer of S2 to the epoxy ester prepolymer of S1, and react at 60-80℃ for 2-3 hours to graft the conjugated Schiff base onto the molecular chain through the ring-opening reaction of epoxy groups and amine groups. S4. Add lipoic acid to the system and continue the reaction at 60-80℃ for 2-3 hours to allow lipoic acid to be grafted onto the side end of the molecular chain through carboxyl groups. During this process, the five-membered ring disulfide bond of lipoic acid remains closed, resulting in an epoxy ester resin modified with conjugated Schiff base and lipoic acid dual dynamic units. S5. After the reaction is complete, cool the temperature to 25-40℃, add a drying agent, mix well, and obtain the epoxy ester resin.

[0012] Optionally, in step S2, the aromatic aldehyde is selected from one or more of terephthalaldehyde, 4,4'-biphenyldialdehyde, and naphthalene-2,6-dicarboxaldehyde, and the aromatic amine is selected from one or more of p-phenylenediamine, 4,4'-diaminobiphenyl, and 1,5-naphthyldiamine.

[0013] The beneficial effects of this invention are as follows: The epoxy ester resin for the corrosion-resistant, high-adhesion anti-corrosion coating of this invention possesses excellent corrosion resistance and adhesion, effectively improving the durability and corrosion resistance of the coating. By introducing conjugated Schiff base and thioctic acid disulfide bond dynamic units, this resin enhances the self-healing ability of the coating, enabling it to quickly recover after being damaged by external forces, thus extending its service life. Furthermore, this resin can form stable chemical bonds with the substrate, improving the adhesion and mechanical strength of the coating. The semi-interpenetrating double network structure formed within the coating effectively prevents the penetration of moisture, oxygen, and corrosive media, further enhancing the anti-corrosion performance. Detailed Implementation

[0014] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0015] Example 1: This Example 1 describes an epoxy ester resin for a corrosion-resistant, high-adhesion anti-corrosion coating. The epoxy ester resin is prepared from the following raw materials in parts by weight: 50 parts epoxy resin (bisphenol A type E-51), 30 parts unsaturated fatty acid (ricinoleic acid), 8 parts conjugated Schiff base monomer, 8 parts lipoic acid, 0.3 parts catalyst (dibutyltin dilaurate), 0.1 parts polymerization inhibitor (2,6-di-tert-butyl-p-cresol), 2 parts drying agent (cobalt naphthenate), and 12 parts inert solvent (xylene). This embodiment describes a method for preparing an epoxy ester resin for a corrosion-resistant, high-adhesion anti-corrosion coating. The specific preparation steps are as follows: S1. Add bisphenol A type epoxy resin E-51, ricinoleic acid, dibutyltin dilaurate, 2,6-di-tert-butyl-p-cresol and xylene to a reaction vessel, stir evenly, heat to 150℃, and keep the reaction at 450 rpm for 4 hours to obtain epoxy ester prepolymer. S2. Terephthalaldehyde and p-phenylenediamine are added to the reaction vessel at a molar ratio of 1:1, and the mixture is condensed at 70°C for 2 hours. Then, azeotropic dehydration is carried out to obtain the conjugated Schiff base monomer.

[0016] S3. Add the conjugated Schiff base monomer prepared in step S2 to the epoxy ester prepolymer of step S1, control the temperature at 70℃, and react for 2.5h. The conjugated Schiff base is grafted onto the epoxy ester prepolymer molecular chain through the ring-opening reaction of epoxy groups and amine groups. S4. Add lipoic acid to the reaction system of step S3 and continue the reaction at 70°C for 2.5 h to graft lipoic acid onto the epoxy ester prepolymer through the carboxyl group, while keeping the five-membered ring disulfide bond unchanged. S5. After the reaction is complete, cool down to 30°C, add cobalt naphthenate, stir and mix evenly to obtain the epoxy ester resin for corrosion-resistant and high-adhesion anti-corrosion coating.

[0017] Example 2: An epoxy ester resin for a corrosion-resistant, high-adhesion anti-corrosion coating according to Example 2, the epoxy ester resin is prepared from the following raw materials in parts by weight: 50 parts epoxy resin (bisphenol A type E-51), 30 parts unsaturated fatty acid (ricinoleic acid), 5 parts conjugated Schiff base monomer, 8 parts lipoic acid, 0.3 parts catalyst (dibutyltin dilaurate), 0.1 parts polymerization inhibitor (2,6-di-tert-butyl-p-cresol), 2 parts drying agent (cobalt naphthenate), and 12 parts inert solvent (xylene). In this embodiment, the preparation method of the epoxy ester resin for corrosion-resistant and high-adhesion anti-corrosion coating is the same as that in Example 1, except that the amount of conjugated Schiff base monomer is adjusted to 5 parts.

[0018] Example 3: This Example 3 describes an epoxy ester resin for a corrosion-resistant, high-adhesion anti-corrosion coating. The epoxy ester resin is prepared from the following raw materials in parts by weight: 50 parts epoxy resin (bisphenol A type E-51), 30 parts unsaturated fatty acid (ricinoleic acid), 10 parts conjugated Schiff base monomer, 8 parts lipoic acid, 0.3 parts catalyst (dibutyltin dilaurate), 0.1 parts polymerization inhibitor (2,6-di-tert-butyl-p-cresol), 2 parts drying agent (cobalt naphthenate), and 12 parts inert solvent (xylene). In this embodiment, the preparation method of an epoxy ester resin for a corrosion-resistant, high-adhesion anti-corrosion coating is the same as in Example 1, except that the amount of conjugated Schiff base monomer is adjusted to 10 parts.

[0019] Comparative Example 1: The epoxy ester resin of Comparative Example 1 was prepared from the following parts by weight of raw materials: 50 parts epoxy resin (bisphenol A type E-51), 30 parts unsaturated fatty acid (ricinoleic acid), 8 parts lipoic acid, 0.3 parts catalyst (dibutyltin dilaurate), 0.1 parts polymerization inhibitor (2,6-di-tert-butyl-p-cresol), 2 parts drying agent (cobalt naphthenate), and 12 parts inert solvent (xylene). The preparation method of the epoxy ester resin in this comparative example is the same as that in Example 1, except that no conjugated Schiff base monomer is added.

[0020] Comparative Example 2: The epoxy ester resin of Comparative Example 2 was prepared from the following parts by weight of raw materials: 50 parts epoxy resin (bisphenol A type E-51), 30 parts unsaturated fatty acid (ricinoleic acid), 8 parts conjugated Schiff base monomer, 0.3 parts catalyst (dibutyltin dilaurate), 0.1 parts polymerization inhibitor (2,6-di-tert-butyl-p-cresol), 2 parts drying agent (cobalt naphthenate), and 12 parts inert solvent (xylene). The preparation method of the epoxy ester resin in this comparative example is the same as that in Example 1, except that thioctic acid is not added.

[0021] Performance testing 1. Scratch healing rate test Standard linear scratches approximately 50 μm wide and 10 mm long were prepared on the coating surface using a microhardness tester or scratch tester, ensuring that the scratches penetrated the coating to the substrate surface. The initial morphology of the scratched area was observed and photographed using an optical microscope or laser confocal microscope. The sample was placed in a constant temperature and humidity environment (temperature 25±2℃, relative humidity 50±5%) for 24 hours to allow the coating to self-heal. After the healing period, microscopic observation and photography were performed again at the same location. The initial scratch area and the scratch area after repair were measured using image analysis software, and the scratch healing rate was calculated using the formula: Healing rate (%) = (initial scratch area - repaired scratch area) / initial scratch area × 100%. At least 3 parallel samples were tested for each group of samples, and 3-5 different fields of view were selected for measurement for each sample. The average value was taken as the final result.

[0022] Table 1. Test data on scratch healing rate of different samples

[0023] The scratch healing rates of Examples 1-3 were 96%, 91%, and 93%, respectively, while those of Comparative Example 1 (without Schiff base) were only 28% and Comparative Example 2 (without lipoic acid) were only 36%. The healing rates of Examples 1-3 all exceeded 90%, which is much higher than the two comparative examples, demonstrating that the dual dynamic bond system constructed by the conjugated Schiff base and lipoic acid has excellent self-healing ability at room temperature, and that the two have a significant synergistic effect.

[0024] 2. Adhesion recovery rate test The cross-cut adhesion test was conducted according to GB / T 9286-2021. Before the coating healing treatment, 25 1mm × 1mm squares were cut on the sample surface using a cross-cut tool. Adhesive tape was applied and then quickly peeled off. The degree of coating peeling was observed, and the initial adhesion grade was assessed (5B grade: no peeling; 4B grade: peeling area ≤ 5%; 3B grade: 5-15%; 2B grade: 15-35%; 1B grade: 35-65%; 0B grade: > 65%). The grades were converted into scores: 5B = 100 points, 4B = 80 points, 3B = 60 points, 2B = 40 points, 1B = 20 points, 0B = 0 points. After the healing treatment, the test was repeated in adjacent areas, and the recovery rate was calculated using the formula: Recovery rate (%) = (post-healing score / initial score) × 100%.

[0025] Table 2. Adhesion recovery rate test data for different samples

[0026] The initial adhesion of Examples 1 and 3 was 5B, and it remained at 5B after healing, with a recovery rate of 100%. Example 2 had an initial adhesion of 5B and a recovery rate of 4B, with an 80% recovery rate. Comparative Example 1 had an initial adhesion of only 3B and a recovery rate of 1B, with a recovery rate of 33%. Comparative Example 2 had an initial adhesion of 4B and a recovery rate of 2B, with a recovery rate of 50%. The initial adhesion of Examples 1-3 was significantly better than that of the comparative examples, and the recovery rate was much higher than that of the single dynamic bond system, proving that the rigid benzene ring of the conjugated Schiff base can enhance the anchoring effect, and the synergistic effect of the dual dynamic bonds can achieve effective repair of adhesion.

[0027] 3. Salt spray resistance time test The test was conducted according to GB / T 1771-2007, "Determination of Resistance to Neutral Salt Spray of Paints and Varnishes". First, Q235 steel plate samples (150mm × 75mm × 3mm, coating thickness 40±5μm) coated with the epoxy ester resin of this invention were cured for 7 days in a standard environment (23±2℃, relative humidity 50±5%), and the edges and back of the samples were sealed with a corrosion-resistant material. The samples were placed in a salt spray test chamber with the test surface facing upwards at a 20°±5° angle to the vertical direction, maintaining a distance between samples to avoid contact. The test conditions were: test chamber temperature 35±2℃, sodium chloride solution concentration 50±5g / L, pH value 6.5-7.2, and salt spray deposition rate controlled at 1.0-2.0mL / (80cm²·h). Continuous spraying was performed during the test, and the sample condition was checked every 24 hours, recording the time it took for blistering, rust, or rust spread at scratches to appear on the coating surface. When the first rust spot or scratch appears on the coating surface and the rust spreads to a width exceeding 1 mm, this time is recorded as the salt spray resistance time. At least three parallel samples are tested for each group of samples, and the average value is taken as the final result.

[0028] Table 3. Salt spray resistance time test data for different samples

[0029] The intact coatings of Examples 1-3 had a salt spray resistance time of 650-720 hours and a post-healing time of 520-600 hours, with a recovery rate of 80-83%. In contrast, the intact coatings of Comparative Examples 1-2 had a salt spray resistance time of only 250-300 hours and a post-healing time of 120-150 hours, with a recovery rate of 48-50%. The salt spray resistance time and recovery rate of Examples 1-3 were significantly better than those of the comparative examples, demonstrating that the semi-interpenetrating double-network structure can effectively block the penetration of corrosive media, and that the dual dynamic bond system can restore the anti-corrosion barrier function after the coating is damaged.

[0030] 4. Electrochemical impedance spectroscopy (EIS) test A three-electrode system was used, with a Q235 steel plate coated with the epoxy ester resin of this invention as the working electrode (test area of ​​1 cm²), a saturated calomel electrode as the reference electrode, and a platinum electrode as the counter electrode. The electrolyte was a 3.5 wt% NaCl solution. Before testing, the sample was immersed in the electrolyte for 30 min to reach a stable open-circuit potential. EIS testing was performed using an electrochemical workstation in constant potential mode, with an AC disturbance signal amplitude of 10 mV (relative to open-circuit potential), a frequency scan range of 100 kHz to 0.01 Hz, and a logarithmic scan mode acquiring 10 points per decade. Electrochemical impedance spectra were tested for both the intact coating and the scratch-healed coating, with at least three parallel samples tested for each group. After testing, the changes in coating resistance (Rc) and coating capacitance (Cc) with frequency were analyzed, and the low-frequency (0.01 Hz) impedance modulus |Z| was extracted as a key indicator for evaluating the coating's barrier performance. By comparing the low-frequency impedance modulus of the intact coating and the healed coating, the impedance recovery rate is calculated according to the formula: Impedance recovery rate (%) = (healed coating |Z| / integrity coating |Z|)×100%, which evaluates the degree of corrosion resistance recovery after the coating damage self-repairs.

[0031] Table 4 Electrochemical impedance spectroscopy test data for different samples

[0032] The intact coatings of Examples 1-3 have a low-frequency impedance modulus of 8.5 × 10⁷ - 1.2 × 10⁸ Ω·cm², and an impedance recovery rate of 71-80% after healing; while the intact coatings of Comparative Examples 1-2 have an impedance modulus of only 2.5 × 10⁶ - 3.2 × 10⁶ Ω·cm², and a recovery rate of only 32-34%. The impedance modulus of Examples 1-3 is about two orders of magnitude higher than that of the comparative examples, and the recovery rate is also significantly higher, demonstrating that the semi-interpenetrating double network structure formed by the dual dynamic bond system has a denser anti-corrosion barrier and can effectively repair electrochemical protective performance after damage.

[0033] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An epoxy ester resin for corrosion-resistant, high-adhesion anti-corrosion coatings, characterized in that, The epoxy ester resin is prepared from the following raw materials in parts by weight: 45-55 parts epoxy resin, 25-35 parts unsaturated fatty acid, 5-10 parts conjugated Schiff base monomer, 5-10 parts lipoic acid, 0.2-0.5 parts catalyst, 0.05-0.2 parts polymerization inhibitor, 1-3 parts drying agent, and 10-15 parts inert solvent. The epoxy ester resin has conjugated Schiff base dynamic units and thioctic acid disulfide dynamic units connected by chemical bonds on its molecular chain.

2. The epoxy ester resin for corrosion-resistant, high-adhesion anti-corrosion coatings according to claim 1, characterized in that, The epoxy resin is bisphenol A type epoxy resin E-44 or E-51, and the unsaturated fatty acid is selected from one or more of ricinoleic acid, linoleic acid and linolenic acid.

3. The epoxy ester resin for corrosion-resistant, high-adhesion anti-corrosion coatings according to claim 1, characterized in that, The catalyst is an organotin catalyst or an acidic catalyst; the organotin catalyst is selected from one or more of dibutyltin dilaurate and stannous octoate; the acidic catalyst is selected from one or more of p-toluenesulfonic acid and phosphoric acid.

4. The epoxy ester resin for a corrosion-resistant, high-adhesion anti-corrosion coating according to claim 1, characterized in that, The polymerization inhibitor is selected from one or more of hydroquinone, methylhydroquinone, and 2,6-di-tert-butyl-p-cresol; the drying agent is a metal soap-based drying agent selected from one or more of cobalt naphthenate and zinc naphthenate; the inert solvent is selected from one or more of xylene, toluene, and butyl acetate.

5. The epoxy ester resin for corrosion-resistant, high-adhesion anti-corrosion coatings according to claim 1, characterized in that, The epoxy ester resin coating has a scratch healing rate of ≥90% at room temperature, an adhesion recovery rate of ≥80%, and an adhesion grade of 5B.

6. A method for preparing an epoxy ester resin for a corrosion-resistant, high-adhesion anti-corrosion coating, used to prepare the epoxy ester resin for a corrosion-resistant, high-adhesion anti-corrosion coating as described in any one of claims 1-5, characterized in that, The specific preparation steps are as follows: S1. Epoxy resin, unsaturated fatty acid, catalyst, polymerization inhibitor and inert solvent are reacted at a temperature of 140-160℃ for 2-6 hours and a stirring speed of 300-600 rpm to obtain epoxy ester prepolymer. S2. Mix aromatic aldehydes and aromatic amines in a molar ratio of 1:1, and condense them at a temperature of 60-80℃ for 1-3 hours. Then, perform azeotropic dehydration to obtain conjugated Schiff base monomers. S3. Add the conjugated Schiff base monomer of S2 to the epoxy ester prepolymer of S1 and react at 60-80℃ for 2-3 hours to graft the conjugated Schiff base onto the molecular chain through the ring-opening reaction of epoxy groups and amine groups. S4. Add lipoic acid to the system and continue the reaction at 60-80℃ for 2-3 hours; S5. After the reaction is complete, cool the temperature to 25-40℃, add a drying agent, mix well, and obtain the epoxy ester resin.

7. The method for preparing an epoxy ester resin for a corrosion-resistant, high-adhesion anti-corrosion coating according to claim 6, characterized in that, In step S2, the aromatic aldehyde is selected from one or more of terephthalaldehyde, 4,4'-biphenyldialdehyde, and naphthalene-2,6-dicarboxaldehyde, and the aromatic amine is selected from one or more of p-phenylenediamine, 4,4'-diaminobiphenyl, and 1,5-naphthyldiamine.

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