Preparation method of anti-ultraviolet long corrosion-resistant composite epoxy coating

Abstract

The application belongs to the technical field of corrosion and protective coating, and particularly relates to a preparation method of an ultraviolet-resistant long-corrosion-resistant composite epoxy coating. The application prepares a two-dimensional sheet composite material modified by an ultraviolet-resistant aging agent loaded in a metal organic framework through a two-dimensional sheet, a metal salt, an organic ligand and the ultraviolet-resistant aging agent. The ultraviolet-resistant aging agent is loaded in the metal organic framework to avoid direct contact with the epoxy resin, and the structure integrity of the ultraviolet-resistant aging agent is ensured. Then, the composite material is added into the epoxy resin as a filler to improve the compatibility of the two-dimensional sheet and the epoxy resin, improve the dispersibility of the composite material, enhance the physical barrier performance of the coating, reduce internal defects of the coating, improve the compactness of the coating, prolong the time for corrosion medium to reach the metal surface, and finally make the modified epoxy coating exhibit excellent ultraviolet-resistant aging performance and long-term corrosion resistance, which has important application prospects in the field of corrosion and protection of marine equipment.

Description

Technical Field

[0001] This invention belongs to the field of corrosion and protective coating technology, specifically relating to a method for preparing an anti-ultraviolet long-term corrosion resistant composite epoxy coating. Background Technology

[0002] The development and utilization of various marine resources are the cornerstone of the rapid development of the national marine economy. The long-term and stable service of marine engineering equipment and vessels is crucial for the development of marine resources. Taking the South China Sea environment as an example, marine engineering equipment operates under harsh conditions of high salinity, high humidity, high temperature, and strong ultraviolet radiation. Corrosion and its coupled damage are among the main factors causing reduced lifespan and safety accidents. Practice has proven that organic coatings are one of the most important technologies for protecting marine engineering equipment and extending its service life. Waterborne epoxy coatings, in particular, are environmentally friendly and possess excellent corrosion resistance, making them widely used in the protection of marine engineering equipment. However, during curing and service, the coating can develop pores and cracks. Simultaneously, under strong sunlight, ultraviolet radiation can damage the internal structure of the coating through photo-oxidation, significantly accelerating coating aging. In this situation, the penetration of corrosive media accelerates the deterioration of metal properties, thereby shortening the service life of the equipment. Therefore, how to reduce internal defects in the coating while improving its resistance to ultraviolet aging, and thus extending the service life of marine engineering equipment, is a pressing scientific and technological problem that technicians in the field of corrosion and protection need to solve.

[0003] To address the insufficient UV aging resistance of epoxy coatings, current solutions typically involve directly adding UV aging inhibitors to the coating resin. However, not all UV aging inhibitors exhibit good compatibility with epoxy resins. Therefore, directly adding UV aging inhibitors may disrupt the internal structural integrity of the coating, leading to a decrease in its overall protective performance. Two-dimensional sheets are widely used to reduce internal defects in coatings and block the penetration of corrosive media. However, most two-dimensional sheets are inorganic and incompatible with organic resins, resulting in weak filler / resin interfaces and failing to improve the coating's UV aging resistance. Therefore, simultaneously improving the compatibility between fillers and resins, as well as the coating's UV aging resistance, could potentially significantly extend the coating's service life. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, this invention provides a method for preparing a UV-resistant and corrosion-resistant composite epoxy coating. The epoxy coating prepared by this method can greatly improve the compatibility between filler and resin, reduce internal defects in the coating, and enhance the coating's UV aging resistance and long-term corrosion resistance. It has important application prospects in the field of corrosion and protection of marine engineering equipment.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The first aspect of this invention provides a method for preparing a UV-resistant and corrosion-resistant composite epoxy coating, the method comprising the following steps: S1. Preparation of two-dimensional sheet composite materials modified with metal-organic framework-supported UV aging inhibitors: S11. Disperse the two-dimensional sheet in water, then add metal salt and organic ligand, stir to form a yellow turbid liquid, then separate and collect the yellow solid, and after washing and drying, obtain a yellow powdery metal-organic framework modified two-dimensional sheet nanomaterial. S12. The two-dimensional sheet nanomaterial of S11 is dispersed in a solvent, and an anti-UV aging agent is added. After vacuum loading, the pale yellow solid is separated and collected. After washing and drying, a pale yellow powdery metal-organic framework loaded with an anti-UV aging agent modified two-dimensional sheet composite material is obtained. S2. Modified epoxy resin for composite materials: Mix epoxy resin emulsion, the two-dimensional sheet composite material prepared in step S1 and diluent, then add curing agent and continue mixing to obtain modified epoxy resin. S3. Coating: The modified epoxy resin obtained in step S2 is coated on the surface of the metal substrate. After drying and curing, an anti-UV and corrosion-resistant composite epoxy coating (i.e., a two-dimensional sheet composite material modified epoxy coating modified with a metal-organic framework loaded with an anti-UV aging agent) is obtained on the surface of the metal substrate.

[0006] Metal-organic frameworks (MOFs) are crystalline materials with porous topologies formed by the chemical coordination of metal ions and organic ligands under certain conditions. This invention prepares a two-dimensional sheet composite material modified with an anti-UV aging agent and loaded with a MOF using two-dimensional sheets, metal salts, organic ligands, and an anti-UV aging agent. The two-dimensional sheets are industrially produced and of reliable quality. The organic ligands offer the advantage of versatility; by changing the type and amount of organic ligands, the size, number, and pore size of the MOF can be controlled. For example, organic ligands containing benzene rings have high steric hindrance, resulting in larger MOFs with higher porosity, which can increase the loading of the anti-UV aging agent. Adding these ligands as fillers to epoxy resin improves the compatibility between the two-dimensional sheets and the epoxy resin, enhances the physical barrier properties of the coating, reduces internal defects in the coating, and improves its anti-UV aging performance. Meanwhile, since the organic ligands of the metal-organic framework in the composite material contain imidazole rings and carboxyl / amino groups, the compatibility between the composite material and epoxy resin is increased, the dispersibility of the composite material is improved, the pores in the coating curing process are filled, the density and crosslinking density of the coating are improved, the time for corrosive media to reach the metal surface is extended, and the long-term corrosion resistance of the coating is ultimately increased.

[0007] Preferably, the two-dimensional sheet in S11 includes at least one of graphene, graphene oxide, reduced graphene oxide, hexagonal boron nitride, black phosphorus sheet, and transition metal sulfides.

[0008] Preferably, the metal salt in S11 is at least one of cerium nitrate, cerium chloride, cerium sulfate, cerium ammonium nitrate, or cerium acetate.

[0009] Preferably, the organic ligand in S11 is at least one of butynedioic acid, imidazole, 2-methylimidazolium, benzimidazole, 2-aminobenzimidazole, terephthalic acid, and 2-aminoterephthalic acid.

[0010] Preferably, the UV aging agent in S12 is at least one of benzotriazole, phenyl salicylate, 2,2,6,6-tetramethylpiperidine, and 3-[3-(2-H-benzotriazole-2-yl)-4-hydroxy-5-tert-butylphenyl]-propionic acid-polyethylene glycol 300 ester (UV-1130).

[0011] Preferably, the mass ratio of the two-dimensional sheet, metal salt and organic ligand in S1 is 0.1-0.5: 1-3: 0.5-2, and the mass ratio of the metal-organic framework modified two-dimensional sheet nanomaterial to the anti-UV aging agent is 0.1: 0.1-1.

[0012] By adjusting the mass ratio of the two-dimensional sheet and the metal salt to the organic ligand, the coverage of the metal-organic framework (MOF) on the two-dimensional sheet can be controlled, as can the size and number of the MOF, thereby improving the dispersibility of the composite material in epoxy resin. Simultaneously, by changing the amount of UV aging inhibitor added, the loading of the UV aging inhibitor in the composite material can be increased, thus enhancing the UV aging resistance of the coating. At the aforementioned mass ratio, full coverage of the two-dimensional sheet surface by the MOF can be achieved, ensuring that the size of the MOF is between 100 and 2000 nm, and the loading of the UV aging inhibitor reaches 10–30 wt.%.

[0013] Preferably, the vacuum loading time in S12 is 10 to 24 hours.

[0014] Preferably, the mass ratio of the epoxy emulsion, the two-dimensional sheet composite material, and the diluent in S2 is 12: 0.12-2.4: 2-12.

[0015] Preferably, the thickness of the UV-resistant and corrosion-resistant composite epoxy coating obtained by S3 on the metal substrate surface is 30–200 μm.

[0016] Preferably, the diluent in S2 is a mixture of anhydrous ethanol and deionized water, and the mass ratio of ethanol to deionized water is 1:5.

[0017] The introduction of diluents can improve the dispersibility of fillers in resin and reduce the viscosity of coatings, making coating application and leveling easier.

[0018] Preferably, the curing agent described in S2 is diethylenetriamine or triethylenetetramine, etc.

[0019] According to the experience values ​​provided by the coating supplier, the amount of hardener should be 50% of the epoxy emulsion. However, in actual construction, the coating will be diluted appropriately, and to ensure complete curing of the epoxy resin, the amount of hardener will be 10-20 wt.% in excess. The hardener used in this invention can cure at room temperature, thus increasing the workability of the coating.

[0020] Preferably, the metal substrate described in S3 is one of carbon steel, aluminum alloy, titanium alloy, magnesium alloy, and copper alloy.

[0021] Preferably, the drying and curing temperature in S3 is 25℃~60℃, and the curing time is 24h~72h.

[0022] The second aspect of the present invention provides an anti-ultraviolet long-term corrosion resistant composite epoxy coating prepared by the preparation method described in the first aspect.

[0023] Compared with the prior art, the beneficial effects of the present invention are: While two-dimensional sheets can enhance the physical barrier properties of coatings through their large specific surface area, impermeability, and "maze effect," their poor interfacial compatibility with resins can easily lead to coating failure. Adding only UV aging inhibitors may result in incompatibility with the resin or even direct reaction, thus reducing the overall performance of the coating or failing to achieve the desired UV resistance. Therefore, this invention develops a two-dimensional sheet composite material using a metal-organic framework (MOF) to modify the two-dimensional sheet material, thereby improving the compatibility between the sheet and epoxy resin and filling internal defects in the coating. Simultaneously, the UV aging inhibitor is loaded within the MOF, preventing direct contact with the epoxy resin and ensuring the structural integrity of the inhibitor. This ultimately allows the modified epoxy coating to exhibit excellent UV aging resistance and long-term corrosion resistance. Furthermore, this invention can control the number and size of the MOF on the two-dimensional sheet surface by adjusting the ratio of the two-dimensional sheet material, metal salt, and organic ligands, and can regulate the coverage of the MOF on the two-dimensional sheet surface within a certain range, thereby improving the physical barrier properties of the coating. Furthermore, the loading of UV aging inhibitors in composite materials can be increased by adjusting the porosity of the metal-organic framework and the amount of UV aging inhibitor added, thereby further improving the UV aging resistance of the coating while ensuring physical barrier properties. Detailed Implementation

[0024] The specific embodiments of the present invention will be further described below. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0025] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods, and the experimental materials used in the following embodiments are all available through conventional commercial channels.

[0026] Example 1 (1) Preparation of cerium-based metal-organic framework-supported UV-1130 modified graphene oxide composite material (GO-HHU-T): 0.25 g of graphene oxide was ultrasonically dispersed in 30 mL of deionized water, and then 1.5 g of cerium ammonium nitrate and 1.25 g of butynediic acid were added. The mixture was stirred at room temperature for 14 h on a magnetic stirrer to obtain a yellow turbid liquid. The liquid was then centrifuged and washed four times alternately with anhydrous ethanol and deionized water to obtain a yellow solid. Finally, the solid was dried in a vacuum drying oven at 60 °C for 17 h to obtain a yellow powder GO-HHU.

[0027] 0.1g of the above GO-HHU powder was ultrasonically dispersed in 20mL of anhydrous ethanol, and then 0.5g of UV-1130 anti-ultraviolet aging agent was added. The mixture was placed in a drying oven under vacuum for 17h (temperature 25℃, vacuum degree -0.1MPa), then centrifuged, and washed 4 times with anhydrous ethanol to obtain a light yellow solid. Finally, it was placed in a vacuum drying oven and dried at 60℃ for 24h to obtain a light yellow powder GO-HHU-T. (2) Preparation of composite material modified epoxy resin: An epoxy emulsion with a mass ratio of 12:0.2:2, GO-HHU-T, and a diluent were mixed, wherein the diluent was anhydrous ethanol and deionized water with a mass ratio of 1:5. After magnetic stirring for 20 minutes, 65 wt.% of the curing agent diethylenetriamine was added and stirred for 20 minutes. After mixing, the composite modified epoxy resin was obtained.

[0028] (3) Coating the film layer: The composite modified epoxy resin obtained in step (2) was coated on the surface of a carbon steel substrate that had been treated (polished from 220 mesh to 1000 mesh, then ultrasonically cleaned with anhydrous ethanol to remove oil and impurities from the surface, and finally dried with a cold air blower). After drying and curing at 25°C, a GO-HHU-T composite modified epoxy coating was obtained on the carbon steel surface. The dry film thickness of the composite coating was 50±5μm.

[0029] Comparative Example 1 In this embodiment, an epoxy emulsion and a diluent were directly mixed at a mass ratio of 12:2, wherein the diluent was anhydrous ethanol and deionized water at a mass ratio of 1:5. After magnetic stirring for 20 minutes, 65 wt.% of the curing agent diethylenetriamine was added, and the mixture was stirred for another 20 minutes to obtain an epoxy resin coating. This epoxy resin was then coated onto the surface of a pre-treated carbon steel substrate. After drying and curing, an epoxy coating was obtained on the carbon steel surface, with a dry film thickness of 50 ± 5 μm.

[0030] Electrochemical impedance spectroscopy experiments of the coatings after UV aging in Example 1 and Comparative Example 1: The coatings prepared in Example 1 and Comparative Example 1 were subjected to continuous accelerated aging with a UVB lamp (313 nm, 60 W) for 168 h according to ISO 16474–2021 standard. Subsequently, the UV-aged coatings of Example 1 and Comparative Example 1 were placed in a 3.5 wt.% sodium chloride solution for electrochemical testing. After 100 days of electrochemical testing, the low-frequency impedance modulus of Example 1 remained consistently at 10. 9 ~10 11 Ω·cm 2 Meanwhile, the low-frequency impedance modulus of Comparative Example 1 remained consistently at 10. 5 ~10 8 Ω·cm 2 This indicates that the corrosion resistance of the epoxy coating modified by GO-HHU-T composite material is improved by three orders of magnitude compared with that of the pure epoxy coating, demonstrating that the epoxy coating modified by GO-HHU-T composite material has good UV aging resistance and long-term corrosion resistance.

[0031] Example 2 (1) Preparation of cerium-based metal-organic framework-supported benzotriazole-modified hexagonal boron nitride composite material (hBN-CeMOF-BTA): 0.3 g of hexagonal boron nitride was ultrasonically dispersed in 30 mL of deionized water, and then 2 g of cerium ammonium nitrate and 1.5 g of terephthalic acid were added. The mixture was stirred at room temperature for 24 h on a magnetic stirrer to obtain a gray turbid liquid. The liquid was then centrifuged and washed four times alternately with anhydrous ethanol and deionized water to obtain a gray solid. Finally, the solid was placed in a vacuum drying oven and dried at 50 °C for 12 h to obtain a gray powder hBN-CeMOF.

[0032] 0.1g of the above-mentioned hBN-CeMOF powder was ultrasonically dispersed in 20mL of anhydrous ethanol, and then 0.6g of anti-UV aging agent BTA was added. The mixture was placed in a drying oven under vacuum for 15h, then centrifuged, and washed 4 times with anhydrous ethanol to obtain a light gray solid. Finally, it was placed in a vacuum drying oven and dried at 50℃ for 12h to obtain a light gray powder hBN-CeMOF-BTA. (2) Preparation of composite material modified epoxy resin: An epoxy emulsion with a mass ratio of 12:0.15:2.5, hBN-CeMOF-BTA, and a diluent (anhydrous ethanol and deionized water in a mass ratio of 1:5) were mixed. After magnetic stirring for 20 minutes, 55 wt.% of the curing agent triethylenetetramine was added and stirred for another 20 minutes. After mixing thoroughly, the composite modified epoxy resin was obtained.

[0033] (3) Coating the film layer: The composite modified epoxy resin obtained in step (2) was coated on the surface of the treated copper alloy substrate. After drying and curing, the hBN-CeMOF-BTA composite modified epoxy coating was obtained on the surface of the copper alloy. The dry film thickness of the composite coating was 80±10μm.

[0034] Electrochemical impedance spectroscopy experiments were conducted on the coating after UV aging according to the method in Example 1. In this example, the low-frequency impedance value of the hBN-CeMOF-BTA composite modified epoxy coating was maintained at 10. 9 ~10 11 Ω·cm 2 It exhibits stable and long-lasting corrosion resistance.

[0035] Example 3 (1) Preparation of cerium-ammonia-based metal-organic framework-supported phenyl salicylate-modified black phosphorus composite material (BP-NH2CeMOF-PS): 0.15 g of black phosphorus was ultrasonically dispersed in 30 mL of deionized water, and then 2.5 g of cerium ammonium nitrate and 1 g of aminoterephthalic acid were added. The mixture was stirred at room temperature for 20 h on a magnetic stirrer to obtain a gray turbid liquid. The liquid was then centrifuged and washed four times alternately with anhydrous ethanol and deionized water to obtain a gray solid. Finally, the solid was placed in a vacuum drying oven and dried at 70 °C for 10 h to obtain gray powder BP-NH2CeMOF.

[0036] 0.1g of the above-mentioned BP-NH2CeMOF powder was ultrasonically dispersed in 20mL of anhydrous ethanol, and then 0.4g of anti-UV aging agent PS was added. The mixture was placed in a drying oven under vacuum for 20h, then centrifuged, and washed 4 times with anhydrous ethanol to obtain a light gray solid. Finally, it was placed in a vacuum drying oven and dried at 40℃ for 24h to obtain a light gray powder BP-NH2CeMOF-PS. (2) Preparation of composite material modified epoxy resin: An epoxy emulsion with a mass ratio of 12:1.2:3, BP-NH2CeMOF-PS, and a diluent were mixed, wherein the diluent was anhydrous ethanol and deionized water with a mass ratio of 1:5. After magnetic stirring for 20 minutes, 60 wt.% of the curing agent diethylenetriamine was added to the emulsion and stirred for 20 minutes. After mixing, the composite modified epoxy resin was obtained.

[0037] (3) Coating the film layer: The composite modified epoxy resin obtained in step (2) is coated on the surface of the treated aluminum alloy substrate. After drying and curing, a BP-NH2CeMOF-PS composite modified epoxy coating is obtained on the aluminum alloy surface. The dry film thickness of the composite coating is 100±10μm.

[0038] Electrochemical impedance spectroscopy experiments were conducted on the coating after UV aging according to the method in Example 1. In this example, the low-frequency impedance value of the BP-NH2CeMOF-PS composite modified epoxy coating was maintained at 10. 9 ~10 11 Ω·cm 2 It exhibits excellent long-term corrosion resistance.

[0039] Example 4 (1) Preparation of cerium-based metal-organic framework-supported 2,2,6,6-tetramethylpiperidine-modified transition metal sulfide composite material (MoS2-CeMOF-TP): 0.5 g of transition metal sulfide (MoS2) was ultrasonically dispersed in 30 mL of deionized water, and then 3 g of cerium nitrate and 0.8 g of aminoterephthalic acid were added. The mixture was stirred at room temperature for 20 h on a magnetic stirrer to obtain a gray turbid liquid. The liquid was then centrifuged and washed four times alternately with anhydrous ethanol and deionized water to obtain a gray solid. Finally, the solid was placed in a vacuum drying oven and dried at 70 °C for 10 h to obtain gray powdered MoS2-CeMOF.

[0040] 0.1g of the above MoS2-CeMOF powder was ultrasonically dispersed in 20mL of anhydrous ethanol, and then 0.4g of anti-UV aging agent TP was added. The mixture was placed in a drying oven under vacuum for 20h, then centrifuged, and washed 4 times with anhydrous ethanol to obtain a light gray solid. Finally, it was placed in a vacuum drying oven and dried at 40℃ for 24h to obtain a light gray powder MoS2-CeMOF-TP. (2) Preparation of composite material modified epoxy resin: An epoxy emulsion, MoS2-CeMOF-TP, and a diluent with a mass ratio of 12:1.2:4 were mixed, wherein the diluent was anhydrous ethanol and deionized water with a mass ratio of 1:5. After magnetic stirring for 20 minutes, 60 wt.% of the curing agent diethylenetriamine was added to the emulsion and stirred for 20 minutes. After mixing, the composite modified epoxy resin was obtained.

[0041] (3) Coating the film layer: The composite modified epoxy resin obtained in step (2) is coated on the surface of the treated magnesium alloy substrate. After drying and curing, a MoS2-CeMOF-TP composite modified epoxy coating is obtained on the surface of the magnesium alloy. The dry film thickness of the composite coating is 100±10μm.

[0042] Electrochemical impedance spectroscopy experiments were conducted on the coating after UV aging according to the method in Example 1. In this example, the low-frequency impedance value of the MoS2-CeMOF-TP composite modified epoxy coating was maintained at 10. 9 ~10 11 Ω·cm 2 It exhibits excellent long-term corrosion resistance.

[0043] The embodiments of the present invention have been described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A method for preparing a UV-resistant and corrosion-resistant composite epoxy coating, characterized in that, Includes the following steps: S1. Preparation of two-dimensional sheet composite materials modified with metal-organic framework-supported UV aging inhibitors: S11. Disperse the two-dimensional sheet in water, then add a metal salt and an organic ligand, stir to form a yellow turbid liquid, separate and collect the yellow solid, and obtain a yellow powdery metal-organic framework modified two-dimensional sheet nanomaterial after washing and drying; the two-dimensional sheet includes at least one of graphene, graphene oxide, reduced graphene oxide, hexagonal boron nitride, black phosphorus sheets, and transition metal sulfides; the metal salt is at least one of cerium nitrate, cerium chloride, cerium sulfate, cerium ammonium nitrate, or cerium acetate; the organic ligand is at least one of butynedioic acid, terephthalic acid, and 2-aminoterephthalic acid; the mass ratio of the two-dimensional sheet, metal salt, and organic ligand is 0.1-0.5: 1-3: 0.5-2; S12. The two-dimensional sheet nanomaterials of S11 are dispersed in a solvent, and an anti-UV aging agent is added. After vacuum loading, the pale yellow solid is separated and collected. After washing and drying, a pale yellow powdery metal-organic framework-loaded anti-UV aging agent-modified two-dimensional sheet composite material is obtained. The anti-UV aging agent is at least one of benzotriazole, phenyl salicylate, 2,2,6,6-tetramethylpiperidine, and 3-[3-(2-H-benzotriazole-2-yl)-4-hydroxy-5-tert-butylphenyl]-propionic acid-polyethylene glycol 300 ester. The mass ratio of the metal-organic framework-modified two-dimensional sheet nanomaterials to the anti-UV aging agent is 0.1:0.1~1. S2. Modified epoxy resin for composite materials: Mix epoxy resin emulsion, the two-dimensional sheet composite material prepared in step S1 and diluent, then add curing agent and continue mixing to obtain modified epoxy resin. S3. Coating: The modified epoxy resin obtained in step S2 is coated on the surface of the metal substrate. After drying and curing, an anti-UV and corrosion-resistant composite epoxy coating is obtained on the surface of the metal substrate.

2. The method for preparing an anti-UV corrosion resistant composite epoxy coating according to claim 1, characterized in that, The vacuum loading time described in S12 is 10 to 24 hours.

3. The method for preparing an anti-UV corrosion resistant composite epoxy coating according to claim 1, characterized in that, The mass ratio of the epoxy resin emulsion, the two-dimensional sheet composite material, and the diluent in S2 is 12: 0.12~2.4: 2~12.

4. The method for preparing an anti-UV corrosion resistant composite epoxy coating according to claim 1, characterized in that, The thickness of the UV-resistant and corrosion-resistant composite epoxy coating obtained by S3 on the metal substrate surface is 30-200 μm.

5. An anti-ultraviolet corrosion resistant composite epoxy coating prepared by the preparation method according to any one of claims 1-4.