Waterborne epoxy coating as well as preparation method and application thereof

Abstract

The invention discloses a waterborne epoxy coating as well as a preparation method and application thereof, and belongs to the technical field of waterborne coating processing, and the waterborne epoxy coating specifically comprises the following components in parts by weight: 50 parts of waterborne cardanol modified epoxy resin, 14 parts of a waterborne amine curing agent, 6 parts of Fe2O3 / SiO2 composite pigment, 10 parts of deionized water and 0.9 part of an additive. The improved composite pigment is matched with the curing agent and the additive to prepare the waterborne epoxy coating, so that the VOC content is reduced, and the corrosion resistance and the mechanical property are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of waterborne coating processing, and in particular to a waterborne epoxy coating and a preparation method and application thereof. Background Art

[0002] An all-aluminum can is mainly composed of two parts: the can body (a barrel body integrated with the bottom surface, and its side can be printed), and the can lid (a lid with an easy-open system connected to the barrel body, and the surface is painted). 5182 aluminum alloy has high strength, good corrosion resistance and excellent formability, and is widely used in the can lid part of the can. The current production process of 5182 alloy coated can lid material is: smelting → refining → casting → sawing and milling → heating → hot rolling (rough rolling, finishing rolling) → cold rolling (middle trimming) → stretching, bending and straightening → coating and lamination. The production process is complex, the construction period is long, the technical requirements are high, and the index control is difficult.

[0003] As for the anti-corrosion coatings for the inner and outer walls of can lids, most of them use solvent-based epoxy resin coatings. This type of coating uses organic solvents. With the continuous improvement of environmental protection regulations and increasingly stringent atmospheric emissions, solvent-based epoxy resin coatings volatilize organic substances during the production and coating process, causing environmental pollution and posing occupational health hazards to operators. Most companies no longer purchase can lids using solvent-based epoxy resin coatings. In order to comply with the new development concept and environmental protection requirements, the original production process and material application are subverted. The raw materials of can lids use more environmentally friendly water-based epoxy coatings to meet customer needs.

[0004] In the existing technology, water-based epoxy coatings still have problems such as salt spray resistance and low adhesion. Most of them are composed of epoxy resin, amine curing agent, pigment filler, additives, co-solvent, water, etc. After curing, water-based epoxy resin may have residual micropores or incomplete cross-linked structures. Water molecules penetrate through capillary action. In a high humidity environment, water evaporates slowly, resulting in incomplete reaction between epoxy groups and amine curing agents, forming a loose network. Some water-based epoxy resins introduce hydrophilic groups to improve wettability, but instead reduce water resistance. Unmodified epoxy resin mainly relies on van der Waals force to combine with the substrate and lacks chemical bonding. Resins with high surface tension have difficulty penetrating the micropores of the substrate, resulting in insufficient mechanical anchoring. If the substrate has oil stains, rust or a loose layer, the adhesion will drop sharply. Summary of the Invention

[0005] The purpose of the present invention is to provide a water-based epoxy coating and its preparation method and application, so as to solve the technical problem in the prior art that the salt spray resistance and adhesion of the water-based epoxy coating applied on the 5182 aluminum alloy can lid material need to be further improved.

[0006] The object of the present invention can be achieved by the following technical solution: a water-based epoxy coating, comprising, by weight, 50 parts of a water-based cardanol-modified epoxy resin, 14 parts of a water-based amine curing agent, 6 parts of a Fe2O3 / SiO2 composite pigment, 10 parts of deionized water, and 0.9 parts of an additive; The preparation method of the water-based cardanol-modified epoxy resin is as follows: epoxy resin, cardanol, and propylene glycol methyl ether are added to a three-necked flask protected by nitrogen and stirred, the reaction temperature is increased to 60-80°C, a catalyst is added, the temperature is increased to 110-120°C, and the reaction is carried out for 2-3 hours. After the reaction is completed, the temperature is reduced to 60-80°C to obtain the cardanol-modified epoxy resin; maleic anhydride is added to the cardanol-modified epoxy resin, the reaction is carried out for 1 hour, the temperature is reduced to 4-50°C, a neutralizer is added to adjust the pH to 7-8, deionized water is added, high-speed shear emulsification is performed for 10-20 minutes, and post-treatment is performed to obtain the water-based cardanol-modified epoxy resin.

[0007] The synthesis mechanism of waterborne cardanol modified epoxy resin is: Under the conditions of a catalyst, the phenolic hydroxyl group of cardanol attacks the β-carbon of the epoxy group with the nucleophilic oxygen atom, causing a ring-opening reaction to form an ether bond connection; the secondary hydroxyl group on the epoxy resin modified by cardanol is esterified with the anhydride group of maleic anhydride.

[0008] Furthermore, the additives are composed of a dispersant, a defoamer, and an anti-settling agent in a dosage ratio of 1g:0.3g:0.5g, wherein the dispersant is polyacrylate, the defoamer is polyether-modified silicone, and the anti-settling agent is wax emulsion; and the water-based amine curing agent is diethylenetriamine.

[0009] Furthermore, the amount ratio of the epoxy resin, propylene glycol methyl ether, cardanol, and catalyst is 10g:5~7mL:2~4g:1g, the epoxy resin is bisphenol A epoxy resin E-51, and the catalyst is triphenylphosphine; the amount ratio of the cardanol-modified epoxy resin, maleic anhydride, neutralizer, and deionized water is 50g:5g:1g:60mL, wherein the neutralizer is 2-amino-2-methyl-1-propanol, and the post-treatment step is: after the reaction is completed, the solvent is evaporated under reduced pressure to obtain a water-based cardanol-modified epoxy resin.

[0010] Furthermore, the preparation method of the Fe2O3 / SiO2 composite pigment is as follows: add iron salt, sodium silicate and water into a three-necked flask and stir, increase the temperature to 60-80°C, add a precipitant, and perform post-processing to obtain the Fe2O3 / SiO2 composite pigment.

[0011] The reaction mechanism of Fe2O3 / SiO2 composite pigment is: Fe 3+ With SiO3 2−Hydrolysis generates Fe(OH)3 and Si(OH)4 respectively, and forms a Fe(OH)3·Si(OH)4 composite precursor under pH 9~11, which forms Fe-O-Si bonds through dehydration condensation, and finally converts into α-Fe2O3 / SiO2 during the calcination process to obtain Fe2O3 / SiO2 composite pigment.

[0012] Furthermore, the usage ratio of the iron salt, sodium silicate, water and precipitant is 5.4g:2.1g:50-100mL:1.4-1.8g; the iron salt is FeCl3·6H2O, and the precipitant is sodium hydroxide; the post-processing step is: after precipitation is completed, filtering and washing the precipitate with deionized water multiple times, transferring the precipitate to a drying oven and drying it to constant weight, and then transferring the dried precipitate to a muffle furnace and calcining it for 2-4 hours to obtain a Fe2O3 / SiO2 composite pigment.

[0013] Furthermore, the calcination temperature is 500-700° C., the heating rate is 2-5° C. / min, and the calcination atmosphere is air.

[0014] The present invention also provides a method for preparing a water-based epoxy coating, comprising: adding deionized water to a reaction kettle, stirring at a low speed, raising the temperature to 30-40°C, sequentially adding a water-based cardanol-modified epoxy resin and additives, and stirring evenly to obtain a water-based epoxy emulsion; adding a Fe2O3 / SiO2 composite pigment to the water-based epoxy emulsion, dispersing at a high speed for 15-20 minutes, adding a water-based amine curing agent to the system, and stirring for 10 minutes to obtain a water-based epoxy coating.

[0015] The present invention also proposes an application of a water-based epoxy coating, wherein the water-based epoxy coating prepared by the above-mentioned preparation method of a water-based epoxy coating is applied to the surface coating of cans.

[0016] The present invention has the following beneficial effects: 1. This invention improves epoxy coatings. Compared with traditional solvent-based epoxy coatings, water-based cardanol-modified epoxy coatings achieve a double breakthrough in environmental protection and performance. The long-chain alkyl group of cardanol forms a dense hydrophobic layer on the coating surface, providing hydrophobicity and flexibility, reducing water, Cl - 、SO4 2- The corrosive medium penetrates, and its phenolic hydroxyl group participates in the ring-opening reaction of the epoxy group, enhancing the adsorption of the phenolic hydroxyl group of the interfacial cross-linked cardanol on the metal surface to form Fe-O-CNSL bonds, inhibiting the anode Fe→Fe 2+ The long-chain alkyl group of cardanol weakens the rigidity of the epoxy resin and improves the impact resistance of the coating. The aromatic ring of cardanol and the epoxy resin synergistically absorb ultraviolet rays, thereby improving weather resistance.

[0017] 2. The present invention also achieves a breakthrough in performance by using Fe2O3 / SiO2 composite pigment to achieve a synergistic effect between structure and function. Silicon dioxide fills the gaps between red iron oxide particles to form a dense structure, reducing the penetration of corrosive media such as chloride ions and sulfate ions, thereby improving the corrosion resistance of the material. The inert surface of silicon dioxide SiO2 reduces the oxidation rate of Fe2O3 in a humid environment, preventing Fe 3+ Reduction to Fe 2+ The resulting pigment failure, the composite structure is stable in the pH range of 4 to 9, and is suitable for acid rain or marine environments; the co-precipitation method allows Fe2O3 and SiO2 to be evenly coated, avoiding the problem of easy agglomeration of single Fe2O3. The complementary surface charges reduce electrostatic adsorption between pigments, improving the storage stability of the material, and the elastic modulus of red iron oxide combined with the toughness of silicon dioxide enhances the impact resistance of the coating. The photocatalytic activity of Fe2O3 combined with the hydrophobicity of SiO2 accelerates the degradation of pollutants and prevents biofilm attachment; the high thermal stability of SiO2 protects Fe2O3 from phase change in high temperature environments.

[0018] 3. The present invention also uses water as a solvent, and the water-based system can be cured at 5-35°C without the need for high-temperature baking, saving energy and adapting to outdoor low-temperature environments; the water-based epoxy emulsion has strong permeability, higher adhesion to the substrate, forms a dense coating, and has a salt spray resistance time better than solvent-based coatings; it greatly reduces the VOC content, does not volatilize irritating solvents, reduces air quality pollution in the construction area and surrounding areas, avoids ozone layer depletion, and improves construction environmental safety; the water-based coating is non-flammable, and there is no risk of fire or explosion during storage and construction. The ester bond cross-linking of the epoxy matrix and cardanol maintains hardness, avoiding the cold brittleness problem of pure water-based epoxy. DETAILED DESCRIPTION

[0019] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0020] In this application, the epoxy resin is selected from Shandong Jinhong New Material Technology Co., Ltd., CAS No. 1675-54-3, selected from Shandong Jinhong New Material Technology Co., Ltd., with a viscosity of 11000-18000 and an epoxy equivalent (g / mol) of 183-200.

[0021] Example 1 This embodiment provides a method for preparing a water-based epoxy coating, comprising the following steps: S1. Preparation of waterborne cardanol-modified epoxy resin Weigh: 100 g of epoxy resin, 20 g of cardanol, and 50 mL of propylene glycol methyl ether, add them into a three-necked flask protected by nitrogen and stir, raise the reaction temperature to 60°C, add 10 g of triphenylphosphine, raise the temperature to 110°C, react for 2 hours, and after the reaction is completed, cool to 60°C to obtain cardanol-modified epoxy resin.

[0022] S2. Preparation of water-based cardanol-modified epoxy resin Weigh: add 10 g of maleic anhydride to 100 g of cardanol-modified epoxy resin, react for 1 hour, cool to 40 ° C, add 2 g of 2-amino-2-methyl-1-propanol to adjust the pH to 7, add 120 mL of deionized water, and emulsify at high speed for 10 minutes. After the reaction is completed, evaporate the solvent under reduced pressure to obtain a water-based cardanol-modified epoxy resin.

[0023] S3. Preparation of Fe2O3 / SiO2 composite pigment Add 54 g of FeCl3·6H2O, 21 g of sodium silicate and 75 mL of water into a three-necked flask and stir. The temperature is raised to 60°C, and 14 g of sodium hydroxide is added. After precipitation is completed, filter and wash the precipitate with deionized water several times. The washed precipitate is transferred to an 80°C drying oven and dried to constant weight. The dried precipitate is then transferred to a muffle furnace and calcined for 3 hours. After natural cooling, the Fe2O3 / SiO2 composite pigment is obtained.

[0024] S4. Preparation of waterborne epoxy coating Weigh by weight: 10 parts of deionized water are added to the reactor, stirred at low speed, the temperature is raised to 30°C, 50 parts of water-based cardanol-modified epoxy resin and 0.9 parts of additives are added in sequence and stirred evenly, 6 parts of Fe2O3 / SiO2 composite pigment are added, the stirring speed is set to 3000r / min, and high-speed dispersion is carried out for 15 minutes. 14 parts of water-based amine curing agent are added to the system and stirred for 10 minutes to obtain a water-based epoxy coating.

[0025] Example 2 This embodiment provides a method for preparing a water-based epoxy coating, comprising the following steps: S1. Preparation of water-based cardanol-modified epoxy resin Weigh: 100 g of epoxy resin, 20 g of cardanol, and 5 mL of propylene glycol methyl ether were added to a three-necked flask protected by nitrogen and stirred. The reaction temperature was raised to 70°C, 10 g of triphenylphosphine was added, and the temperature was raised to 115°C. The reaction was allowed to react for 2 hours. After the reaction was completed, the temperature was lowered to 60°C to obtain a cardanol-modified epoxy resin. S2. Preparation of water-based cardanol-modified epoxy resin Weigh: add 10 g of maleic anhydride to 100 g of cardanol-modified epoxy resin, react for 1 hour, cool to 40 ° C, add 2 g of 2-amino-2-methyl-1-propanol to adjust the pH to 7.5, add 120 mL of deionized water, and emulsify at high speed for 10 minutes. After the reaction is completed, evaporate the solvent under reduced pressure to obtain a water-based cardanol-modified epoxy resin.

[0026] S3. Preparation of Fe2O3 / SiO2 composite pigment Add 54 g of FeCl3·6H2O, 21 g of sodium silicate and 75 mL of water into a three-necked flask and stir. The temperature is raised to 80°C, and 14 g of sodium hydroxide is added. After precipitation is completed, filter and wash the precipitate with deionized water several times. The washed precipitate is transferred to a 70°C drying oven and dried to constant weight. The dried precipitate is then transferred to a muffle furnace and calcined for 3.5 hours. After natural cooling, the Fe2O3 / SiO2 composite pigment is obtained.

[0027] S4. Preparation of waterborne epoxy coating Weigh by weight: 10 parts of deionized water are added to the reactor, stirred at low speed, the temperature is raised to 35°C, 50 parts of water-based cardanol-modified epoxy resin and 0.9 parts of additives are added in sequence and stirred evenly, 6 parts of Fe2O3 / SiO2 composite pigment are added, the stirring speed is set to 3000r / min, and high-speed dispersion is carried out for 17 minutes, 14 parts of water-based amine curing agent are added to the system, and stirred for 10 minutes to obtain a water-based epoxy coating.

[0028] Example 3 This embodiment provides a method for preparing a water-based epoxy coating, comprising the following steps: S1. Preparation of water-based cardanol-modified epoxy resin Weigh: 100 g of epoxy resin, 20 g of cardanol, and 5 mL of propylene glycol methyl ether were added to a three-necked flask protected by nitrogen and stirred. The reaction temperature was raised to 80°C. 10 g of triphenylphosphine was added and the temperature was raised to 120°C. The reaction was allowed to react for 2 hours. After the reaction was completed, the temperature was lowered to 60°C to obtain a cardanol-modified epoxy resin. S2. Preparation of water-based cardanol-modified epoxy resin Weigh: add 10 g of maleic anhydride to 100 g of cardanol-modified epoxy resin, react for 1 hour, cool to 40 ° C, add 2 g of 2-amino-2-methyl-1-propanol to adjust the pH to 7, add 120 mL of deionized water, and emulsify at high speed for 10 minutes. After the reaction is completed, evaporate the solvent under reduced pressure to obtain a water-based cardanol-modified epoxy resin.

[0029] S3. Preparation of Fe2O3 / SiO2 composite pigment Add 54 g of FeCl3·6H2O, 21 g of sodium silicate and 75 mL of water into a three-necked flask and stir. The temperature is raised to 60°C, and 14 g of sodium hydroxide is added. After precipitation is completed, filter and wash the precipitate with deionized water several times. The washed precipitate is transferred to an 80°C drying oven and dried to constant weight. The dried precipitate is then transferred to a muffle furnace and calcined for 3 hours. After natural cooling, the Fe2O3 / SiO2 composite pigment is obtained.

[0030] S4. Preparation of waterborne epoxy coating Weigh by weight: 10 parts of deionized water are added to the reactor, stirred at low speed, the temperature is raised to 30°C, 50 parts of water-based cardanol-modified epoxy resin and 0.9 parts of additives are added in sequence and stirred evenly, 6 parts of Fe2O3 / SiO2 composite pigment are added, the stirring speed is set to 3000r / min, and high-speed dispersion is carried out for 15 minutes. 14 parts of water-based amine curing agent are added to the system and stirred for 10 minutes to obtain a water-based epoxy coating.

[0031] Comparative Example 1 The difference between this comparative example and Example 3 is that the epoxy resin is not modified in step S1.

[0032] Comparative Example 2 The difference between this comparative example and Example 3 is that in step S2, maleic anhydride is not added.

[0033] Comparative Example 3 The difference between this comparative example and Example 3 is that in step S3, the Fe2O3 / SiO2 composite pigment replaces the nano-SiO2 filler.

[0034] Performance testing: The hardness of the waterborne epoxy coatings prepared in Examples 1 to 3 and Comparative Examples 1 to 3 was measured with reference to the standard GB / T 6739-2022 “Paints and varnishes – Determination of film hardness by pencil method”; The organic compound (VOC) emissions of the waterborne epoxy coatings prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were measured with reference to the standard GB / T 37884-2019 “Determination of Volatile Organic Compound (VOC) Emission in Coatings”; The salt spray resistance of the waterborne epoxy coatings prepared in Examples 1 to 3 and Comparative Examples 1 to 3 was determined with reference to the standard HG / T 4759-2014 “Waterborne Epoxy Anticorrosive Coatings”; The adhesion of the waterborne epoxy coatings prepared in Examples 1 to 3 and Comparative Examples 1 to 3 was measured with reference to the standard GB / T 9286-1998 "Cross-cut test for paint and varnish films". The impact resistance of the waterborne epoxy coatings prepared in Examples 1 to 3 and Comparative Examples 1 to 3 was determined in accordance with the standard GB / T 1732-2020 "Determination of impact resistance of paint films". The specific test results are shown in Table 1 below: Table 1-Performance test data of the sample Data Analysis: A comparative analysis of the data in Table 1 above shows that the salt spray resistance of the waterborne epoxy coating prepared by the present invention achieves the paint film without blistering, peeling, rusting, or cracking, the pencil hardness reaches 4H, the impact resistance reaches 55J, the VOC content is less than 50g / L, and the adhesion test is all level 0. This shows that the present invention prepares a waterborne epoxy coating by modifying the epoxy resin, improving the composite pigment, and then cooperating with the curing agent and additives, which not only reduces the VOC content but also improves the corrosion resistance and mechanical properties.

[0035] Compared with the examples, the salt spray resistance time of comparative example 1 is significantly prolonged, indicating that the long-chain alkyl of cardanol forms a dense hydrophobic layer on the coating surface, which provides hydrophobicity and flexibility, reduces the penetration of corrosive media, and its phenolic hydroxyl group participates in the ring-opening reaction of the epoxy group, enhances the interfacial cross-linking, and the phenolic hydroxyl group of cardanol is adsorbed on the metal surface to form Fe-O-CNSL bonds, which inhibits the anode Fe→Fe 2+ Dissolved, improving its corrosion resistance; Compared with the embodiment, the mechanical properties of the material in Comparative Example 2 are significantly improved, indicating that after the anhydride group of maleic anhydride reacts with the epoxy group, a dense cross-linked network is formed, which reduces the penetration of the corrosive medium, and the long-chain alkyl group of cardanol provides physical anchoring, thereby improving the adhesion of the coating.

[0036] Compared with the embodiment, the mechanical properties and salt spray resistance of the material in Comparative Example 3 are improved the most, indicating that the Fe2O3 / SiO2 composite pigment achieves a breakthrough in performance through the synergy of structure and function, and silicon dioxide fills the gaps between red iron oxide particles to form a dense structure, thereby improving the corrosion resistance of the material; and the elastic modulus of red iron oxide is combined with the toughness of silicon dioxide to enhance the impact resistance of the coating; the photocatalytic activity of Fe2O3 is combined with the hydrophobicity of SiO2 to accelerate the degradation of pollutants and prevent biofilm adhesion; the high thermal stability of SiO2 protects Fe2O3 from phase change in high temperature environment.

[0037] The above contents are merely examples and explanations of the structure of the present invention. Those skilled in the art may make various modifications or additions to the described specific embodiments or replace them in a similar manner. As long as they do not deviate from the structure of the invention or exceed the scope defined by the claims, they shall fall within the scope of protection of the present invention.

[0038] Throughout this specification, references to terms such as "one embodiment," "example," or "specific example" indicate that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0039] The preferred embodiments of the present invention disclosed above are intended only to help illustrate the present invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the present invention to specific embodiments. Obviously, many modifications and variations are possible based on the contents of this specification. These embodiments are selected and described in detail in this specification to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to better understand and utilize the present invention. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A waterborne epoxy coating, characterized in that: The waterborne epoxy coating comprises, by weight, 50 parts of waterborne cardanol-modified epoxy resin, 14 parts of waterborne amine curing agent, 6 parts of Fe2O3 / SiO2 composite pigment, 10 parts of deionized water and 0.9 parts of additives; The preparation method of the water-based cardanol-modified epoxy resin comprises the following steps: adding epoxy resin, cardanol, and propylene glycol methyl ether into a three-necked flask protected by nitrogen, stirring, raising the reaction temperature to 60-80° C., adding a catalyst, raising the temperature to 110-120° C., reacting for 2-3 hours, and after the reaction is completed, cooling the temperature to 60-80° C. to obtain the cardanol-modified epoxy resin; Maleic anhydride was added to the cardanol-modified epoxy resin, reacted for 1 hour, cooled to 40-50°C, a neutralizer was added to adjust the pH to 7-8, deionized water was added, high-speed shear emulsification was performed for 10-20 minutes, and post-treatment was performed to obtain a water-based cardanol-modified epoxy resin.

2. A waterborne epoxy coating according to claim 1, characterized in that: The additives are composed of a dispersant, a defoamer, and an anti-settling agent in a weight ratio of 1:0.3:0.5, wherein the dispersant is polyacrylate, the defoamer is polyether-modified silicone, and the anti-settling agent is wax emulsion; and the water-based amine curing agent is diethylenetriamine.

3. A waterborne epoxy coating according to claim 1, characterized in that: The usage ratio of the epoxy resin, propylene glycol methyl ether, cardanol, and catalyst is 10g:5-7mL:2-4g:1g, the epoxy resin is bisphenol A epoxy resin E-51, and the catalyst is triphenylphosphine; the usage ratio of the cardanol-modified epoxy resin, maleic anhydride, neutralizer, and deionized water is 50g:5g:1g:60mL, and the neutralizer is 2-amino-2-methyl-1-propanol. The post-treatment step is: after the reaction is completed, distilling off the solvent under reduced pressure to obtain a water-based cardanol-modified epoxy resin.

4. A waterborne epoxy coating according to claim 1, characterized in that: The preparation method of the Fe2O3 / SiO2 composite pigment comprises the following steps: adding iron salt, sodium silicate and water into a three-necked flask and stirring, raising the temperature to 60-80°C, adding a precipitant, and performing post-processing to obtain the Fe2O3 / SiO2 composite pigment.

5. A waterborne epoxy coating according to claim 4, characterized in that: The dosage ratio of the iron salt, sodium silicate, water and precipitant is 5.4g:2.1g:50-100mL:1.4-1.8g; the iron salt is FeCl3·6H2O, and the precipitant is sodium hydroxide; the post-treatment step comprises: after precipitation is completed, filtering, washing the precipitate with deionized water multiple times, transferring the precipitate to an 80°C drying oven and drying it to a constant weight, and then transferring the dried precipitate to a muffle furnace and calcining it for 2-4 hours to obtain a Fe2O3 / SiO2 composite pigment.

6. A waterborne epoxy coating according to claim 5, characterized in that: The calcination temperature is 500-700°C, the heating rate is 2-5°C / min, and the calcination atmosphere is air.

7. A method for preparing a waterborne epoxy coating according to any one of claims 1 to 6, characterized in that: Add deionized water to the reactor and stir at low speed. Raise the temperature to 30-40°C. Add water-based cardanol-modified epoxy resin and additives in sequence and stir evenly. Add Fe2O3 / SiO2 composite pigment and disperse at high speed for 15-20 minutes. Add water-based amine curing agent to the system and stir for 10 minutes to obtain a water-based epoxy coating.

8. An application of a waterborne epoxy coating, characterized in that: The water-based epoxy coating prepared by the method for preparing a water-based epoxy coating as claimed in claim 7 is applied to the surface coating of cans.

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