Anti-corrosion coating for inner wall of metal can and application of anti-corrosion coating

Abstract

The invention relates to the technical field of coatings, in particular to a metal can inner wall anti-corrosion coating and application thereof. The invention relates to an anticorrosive coating for the inner wall of a metal can. The anticorrosive coating comprises the following components in percentage by mass: 40-50% of waterborne epoxy resin, 10-15% of modified phenolic resin, 5-10% of modified amino resin, 1-3% of nano silicon dioxide, 1-2% of a corrosion inhibitor, 0.5-1% of a defoaming agent, 0.1-0.3% of a pH regulator and the balance of deionized water. The modified phenolic resin and the modified amino resin are adopted, release of free formaldehyde and free phenol is reduced, the polyethylene glycol modifier is introduced in the preparation process, the water solubility and flexibility of the resin are improved, the waterborne epoxy resin without bisphenol A is used, residues of BPA and derivatives of BPA are avoided, and potential hazards to human health are reduced; the metal can inner wall anti-corrosion coating is suitable for the field of chemical product packaging.

Description

Technical Field

[0001] The present invention relates to the technical field of coatings, and in particular to an anti-corrosion coating for the inner wall of a metal can and application thereof. Background Art

[0002] Metal cans are widely used in packaging and transportation for a variety of industries, including food, beverages, and chemicals. The interior of metal cans often requires a coating of anti-corrosion paint to prevent corrosion from contact with the storage medium. For example, in the chemical industry, common metal cans include tinplate cans and aluminum cans. To prevent chemical corrosion between the metal and the chemical product, a coating is typically applied to the interior of the container. However, existing anti-corrosion coatings for metal can interiors still present some challenges in practical chemical product packaging applications.

[0003] Traditional coatings for the interior of metal packaging cans are primarily based on epoxy resins, phenolic resins, and acrylic resins. While these resins offer excellent corrosion resistance and mechanical properties, phenolic resins have poor water solubility during production and use and may release free formaldehyde and free phenol. These substances are harmful to human health, and long-term exposure may cause respiratory and skin problems. Furthermore, the synthetic raw materials for epoxy resins often contain bisphenol A (BPA), which cannot be fully converted during the synthesis process, resulting in residual BPA, BPF, and their derivatives. These substances have been shown to have endocrine disrupting effects and may affect human health. Furthermore, amino resins are difficult to use directly in water-based systems. Therefore, there is an urgent need to develop a new type of anti-corrosion coating for the interior of metal cans to address the above issues. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the present invention aims to provide an anti-corrosion coating for the inner wall of a metal can and its application.

[0005] An anti-corrosion coating for the inner wall of a metal can, comprising the following components in percentage by weight: 40-50% water-based epoxy resin free of bisphenol A, 10-15% modified phenolic resin, 5-10% modified amino resin, 1-3% nano-silica, 1-2% corrosion inhibitor, 0.5-1% defoaming agent, 0.1-0.3% pH regulator, and the balance being deionized water; The preparation method of the modified phenolic resin comprises: mixing 100 parts by mass of phenol, 70 parts by mass of sodium hydroxide and distilled water, heating the mixture to 45° C. and keeping the temperature for 30 minutes, adding 120 parts by mass of a 37% formaldehyde aqueous solution and keeping the temperature for 30 minutes; cooling the mixture to 80° C. due to the rising reaction temperature, adding 30 parts by mass of a 37% formaldehyde aqueous solution and keeping the temperature for 15 minutes, adding 10 parts by mass of polyethylene glycol, heating the mixture to 100° C. and reacting the mixture for 20 minutes, cooling the mixture with cooling water, and adding hydrochloric acid to neutralize and terminate the reaction, thereby preparing the modified phenolic resin; The preparation method of the modified amino resin includes: mixing liquid methanol with a 10% sodium hydroxide solution, adjusting the pH value to 9, adding paraformaldehyde, melamine and urea, wherein the molar ratio of melamine, urea, formaldehyde and methanol is 1:2:7:10, heating to 80°C and then stopping heating, keeping the temperature for 60 minutes, cooling to 65°C, adjusting the pH value to 7.0 with 1 mol / L nitric acid, reacting for 30 minutes, adding a 10% sodium hydroxide solution for neutralization, adding 15 parts by mass of polyethylene glycol, heating to 110°C, continuing stirring and reacting for 1 hour, and after the reaction is completed, vacuuming to remove excess solvent and cooling to obtain the modified amino resin.

[0006] Furthermore, the viscosity of the waterborne epoxy resin is 1000-3000 mPa·s.

[0007] Furthermore, the glass transition temperature of the modified phenolic resin is 120-150°C.

[0008] Furthermore, the heat-resistant temperature of the modified amino resin is 150-180°C.

[0009] Furthermore, the corrosion inhibitor is one or more of molybdate, zinc phosphate or zinc borate.

[0010] Furthermore, the defoaming agent is an organosilicon defoaming agent or a polyether defoaming agent.

[0011] Furthermore, the pH adjuster is one or more of citric acid, acetic acid or phosphoric acid.

[0012] Furthermore, the anti-corrosion coating for the inner wall of the metal can has a surface drying time of 15-30 minutes and a thorough drying time of 3-5 hours at room temperature.

[0013] Specifically, nano-silica is pre-dispersed in water by ultrasonic method, and corrosion inhibitor is pre-dispersed in water to form a stable suspension; water-based epoxy resin is mixed with deionized water and stirred evenly; modified phenolic resin and modified amino resin are added and stirred continuously; nano-silica suspension and corrosion inhibitor suspension are added and mixed, pH regulator is added and stirred thoroughly; defoaming agent is added and stirred continuously, and impurities are removed by filtration to prepare anti-corrosion coating for inner wall of metal can.

[0014] The invention discloses an application of an anti-corrosion coating for the inner wall of a metal can as a coating for the inner wall of a chemical product container.

[0015] Detailed description of the above technical solution: 1. During the preparation of modified phenolic resin, phenol and formaldehyde undergo a condensation reaction under alkaline conditions. By controlling the reaction conditions and the amount of raw materials, a phenolic prepolymer containing hydroxyl groups and ether bonds is generated. Polyethylene glycol is then added and the temperature is raised to continue the reaction. Polyethylene glycol reacts with the remaining formaldehyde and phenolic hydroxyl groups in the prepolymer, further cross-linking and blocking these active groups, and also forming hydrogen bonds with the hydroxyl groups and ether bonds in the phenolic resin. At the same time, the long chain structure of polyethylene glycol is entangled and cross-linked with the molecular chain of the phenolic prepolymer to form a more stable network structure, reducing the release of free formaldehyde and free phenol, and increasing the hydrophilicity and flexibility of the resin.

[0016] 2. In the process of preparing modified amino resin, melamine, urea and formaldehyde undergo condensation reaction under alkaline conditions to form amino resin prepolymer. Subsequently, polyethylene glycol further reacts with the remaining melamine, urea and formaldehyde in the prepolymer to form a more complex cross-linked structure, thereby improving the water solubility of the resin and reducing the release of free melamine.

[0017] 3. Use water-based epoxy resins that do not contain bisphenol A. They usually use other phenolic compounds (such as bisphenol S, BPS) or non-phenolic compounds (such as aliphatic polyols) as raw materials. These alternative raw materials will not introduce BPA during the synthesis process, and the molecular structure of the alternative raw materials is different from that of BPA. They usually have lower endocrine disrupting effects, lower solubility and migration, and reduce the risk of release from the coating.

[0018] The beneficial effects achieved by the present invention are as follows: 1. The present invention adopts modified phenolic resin and modified amino resin to reduce the release of free formaldehyde and free phenol, introduces polyethylene glycol modifier in the preparation process to improve the water solubility and flexibility of the resin, uses water-based epoxy resin that does not contain bisphenol A, avoids the residue of BPA and its derivatives, reduces potential harm to human health, improves the safety and environmental friendliness of the anti-corrosion coating on the inner wall of the metal can, and is suitable for use in the field of chemical product packaging.

[0019] 2. The present invention uses water-based epoxy resin, modified phenolic resin and modified amino resin that do not contain bisphenol A. These resins have good corrosion resistance and can effectively prevent the inner wall of the metal can from corroding due to contact with the storage medium.

[0020] 3. The present invention uses nano-silicon dioxide to improve the adhesion of the coating, so that it forms a stronger coating on the metal surface and enhances the anti-corrosion effect. Additives are used to improve the performance of the coating, so that it forms a uniform and dense coating film during the drying process, thereby improving the protective performance of the coating. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The raw material formula for the preparation method of the anti-corrosion coating for the inner wall of the metal can adopted in the present invention; Figure 2These are the test results of viscosity, drying time, and hardness of the anti-corrosion coatings for the inner wall of metal cans used in Examples 1 to 3 and the comparative example of the present invention; Figure 3 These are the test results of the chemical resistance, salt spray resistance, and heat and humidity aging resistance of the anti-corrosion coatings for the inner wall of metal cans used in Examples 1 to 3 and the comparative example of the present invention; Figure 4 These are the test results of adhesion, wear resistance and bending performance of the anti-corrosion coatings for the inner walls of metal cans used in Examples 1 to 3 of the present invention and the comparative example. DETAILED DESCRIPTION

[0022] The following describes the embodiments of the present invention through specific examples. Those skilled in the art will readily understand the other advantages and benefits of the present invention from the disclosure herein. The present invention may also be implemented or applied through various other specific embodiments, and the details in this specification may be modified or altered based on different viewpoints and applications without departing from the spirit of the present invention.

[0023] Before further describing the specific embodiments of the present invention, it should be understood that the scope of protection of the present invention is not limited to the specific embodiments described below; it should also be understood that the terms used in the examples of the present invention are for describing specific embodiments rather than for limiting the scope of protection of the present invention.

[0024] When numerical ranges are given in the examples, it should be understood that, unless otherwise specified herein, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention belongs.

[0025] The raw materials used in the following examples, unless otherwise specified, are common commercially available products.

[0026] Regarding the raw materials used in the following examples: Three types of bisphenol A-free water-based epoxy resins were used. All are formed by reacting aliphatic polyols and epichlorohydrin to form prepolymers, which are then emulsified with an emulsifier. Epon™ 828 water-based emulsion has excellent self-drying properties and corrosion resistance, Araldite® PT 810 has high viscosity and good self-drying properties, and water-based epoxy resin EP-100 has high heat resistance and good self-drying properties. Aerosil® 200 was used as the nanosilica.

[0027] In the following embodiments, a method for preparing an anti-corrosion coating for the inner wall of a metal can comprises the following steps: (1) Pre-dispersing nano-silica in water by ultrasonic method and pre-dispersing corrosion inhibitor in water to form a stable suspension; (2) Mix water-based epoxy resin with deionized water and stir evenly; add modified phenolic resin and modified amino resin and continue stirring; (3) Add nano-silica suspension and corrosion inhibitor suspension, mix, add pH regulator, and stir thoroughly; add defoamer, continue stirring, filter to remove impurities, and prepare anti-corrosion coating for the inner wall of the metal can.

[0028] The preparation method of the modified phenolic resin comprises: stirring and mixing 100 parts by mass of phenol, 70 parts by mass of sodium hydroxide and distilled water, heating the mixture to 45° C. and keeping the temperature for 30 minutes, adding 120 parts by mass of a 37% formaldehyde aqueous solution and keeping the temperature for 30 minutes; cooling the system to 80° C. due to the rising reaction temperature, adding 30 parts by mass of a 37% formaldehyde aqueous solution and keeping the temperature for 15 minutes, adding 10 parts by mass of polyethylene glycol, heating the mixture to 100° C. and reacting the mixture for 20 minutes, cooling the mixture with cooling water, and adding hydrochloric acid to neutralize and terminate the reaction, thereby preparing the modified phenolic resin; The preparation method of the modified amino resin includes: mixing liquid methanol with a 10% sodium hydroxide solution, adjusting the pH value to 9, adding paraformaldehyde, melamine and urea, wherein the molar ratio of melamine, urea, formaldehyde and methanol is 1:2:7:10, heating to 80°C and then stopping heating, keeping the temperature for 60 minutes to generate a prepolymer, cooling to 65°C, adjusting the pH value to 7.0 with 1 mol / L nitric acid, reacting for 30 minutes, adding a 10% sodium hydroxide solution for neutralization, adding 15 parts by mass of polyethylene glycol, heating to 110°C, continuing stirring and reacting for 1 hour to further crosslink and block active groups, and after the reaction is completed, vacuuming to remove excess solvent, cooling, and obtaining the modified amino resin.

[0029] Example 1: An anti-corrosion coating for the inner wall of a metal can, such as Figure 1 As shown, the composition includes the following components by weight: 45% bisphenol A-free water-based epoxy resin (Epon™ 828 water-based emulsion, viscosity 1500 mPa·s), 12% modified phenolic resin, 7% modified amino resin, 2% nano-silica, 1.5% sodium molybdate corrosion inhibitor, 0.8% silicone defoamer DF-30, 0.2% pH adjuster (citric acid), and the balance is deionized water.

[0030] Example 2: An anti-corrosion coating for the inner wall of a metal can, such as Figure 1As shown, the composition includes the following components in percentage by mass: 45% bisphenol A-free waterborne epoxy resin (Araldite® PT 810, viscosity 2000 mPa·s), 12% modified phenolic resin, 7% modified amino resin, 2% nano-silica, 1.5% zinc phosphate corrosion inhibitor, 0.8% polyether defoamer P-10, 0.2% pH adjuster (acetic acid), and the balance is deionized water.

[0031] Example 3: An anti-corrosion coating for the inner wall of a metal can, such as Figure 1 As shown, the composition includes the following components in percentage by mass: 45% water-based epoxy resin without bisphenol A (water-based epoxy resin EP-100, viscosity 2500 mPa·s), 12% modified phenolic resin, 7% modified amino resin, 2% nano-silica, 1.5% corrosion inhibitor (zinc borate), 0.8% defoaming agent (organic silicone defoaming agent SD-200), 0.2% pH adjuster (phosphoric acid), and the balance is deionized water.

[0032] Comparative Example: Conventional metal can inner wall anti-corrosion coating, including the following components in percentage by mass: Epoxy resin 45% (Dow Chemical's E-51), curing agent 12% (Huntsman's Jeffamine D-230, alicyclic amine curing agent), zinc powder 15%, mica iron oxide 8%, talc 7%, solvent 12% (xylene), defoaming agent 2% (BYK-053), leveling agent 3% (BYK-350).

[0033] Preparation method of conventional metal can inner wall anti-corrosion coating: (1) Mixing base material and curing agent: Mix epoxy resin and curing agent in proportion; (2) Add pigments and fillers: gradually add pigments and fillers such as zinc powder, mica iron oxide and talcum powder into the base material and disperse them evenly using a high-speed disperser; (3) Adding solvents and additives: Add solvents and additives (defoaming agents and leveling agents) to the mixture to adjust the viscosity and rheological properties of the coating; (4) Stirring and filtering: After sufficient stirring, filter out impurities through a filter.

[0034] Performance testing: The anti-corrosion coatings for the inner wall of metal cans of Examples 1 to 3 and the comparative example were tested for physical properties, chemical properties, and mechanical properties. The physical properties tests included viscosity, drying time, and hardness. The chemical properties tests included chemical resistance, salt spray resistance, and resistance to wet heat aging. The mechanical properties tests included adhesion, wear resistance, and bending properties. The anti-corrosion coatings for the inner wall of metal cans of Examples 1 to 3 and the comparative example were applied to a tinplate substrate and baked at 120° C. for 5 minutes to completely cure. The dry film weight was 3-5 g / m2 and the film thickness was 3-5 μm. 1. Physical performance test Viscosity test: This test determines whether the coating's viscosity meets the required pre-application viscosity. A Brookfield viscometer is used to measure the coating's viscosity at application temperature (25°C ± 2°C). Sample preparation involves taking an appropriate amount of coating sample and placing it in the viscometer container. The test procedure involves inserting the spindle into the center of the sample, setting the spindle to 60 rpm, and recording the viscosity value.

[0035] Drying Time Test: This test measures the surface-freeze time and through-dry time of a coating under various environmental conditions. According to ASTM D1640, surface-freeze time and through-dry time are measured at a temperature of 25°C ± 2°C and a humidity of 50% ± 5%. Sample preparation involves applying the coating to a metal panel and, after curing, cutting the specimen into the required dimensions. The test procedure involves maintaining the specimen under constant temperature and humidity, and recording the surface-freeze time and through-dry time.

[0036] Hardness Test: This test measures the hardness of the coating after curing. The pencil hardness test (ASTM D3363) is used. Sample preparation involves applying the coating to a metal panel and then cutting it into the required size after curing. The test procedure involves using a pencil hardness tester and following standard methods to determine the coating's hardness rating.

[0037] Results from Figure 2 As can be seen, the viscosity values ​​of Examples 1-3 are 3000 mPa·s, 3500 mPa·s, and 4000 mPa·s, respectively, all meeting the construction requirements. The viscosity value of the comparative example is 2500 mPa·s, slightly lower than that of the examples, but still within a reasonable construction range.

[0038] The surface drying times of Examples 1 to 3 were 30 minutes, 35 minutes, and 40 minutes, respectively, and the through-drying times were 2 hours, 2 hours and 15 minutes, and 2 hours and 30 minutes, respectively, all showing relatively fast drying speeds. The surface drying time of the comparative example was 45 minutes, and the through-drying time was 3 hours, indicating a relatively long drying time.

[0039] The hardness grades of Examples 1 to 3 are HB, H and 2H respectively, indicating that the coatings have relatively high hardness. The hardness grade of the comparative example is F, indicating relatively low hardness.

[0040] Viscosity, drying time, and hardness tests showed that the anti-corrosion coatings for metal can interiors from Examples 1-3 demonstrated excellent performance in terms of viscosity, drying time, and hardness. Higher viscosity values ​​improve leveling and coating uniformity, shorter drying times increase production efficiency, and higher hardness indicates that the coatings are less susceptible to scratching or damage during use. Overall, the coatings from the Examples demonstrate superior physical properties to those from the Comparative Examples, making them more suitable for anti-corrosion treatment of metal can interiors.

[0041] 2. Chemical performance test Chemical Resistance Test: This test measures the stability of a coating when exposed to chemicals (acids and alkalis). The test involves immersing the specimen in various chemicals and observing changes in appearance and weight loss. The chemicals used include 1 mol / L sulfuric acid and 1 mol / L sodium hydroxide. The immersion time is 24 hours at a temperature of 25°C ± 2°C. Sample preparation involves applying the coating to a metal plate, curing it, and then cutting it into specimens of specified dimensions. The test procedure involves immersing the specimen in various chemical solutions and recording changes in appearance and weight loss.

[0042] Salt spray resistance testing: This test measures the corrosion resistance of coatings in a salt spray environment. Salt spray testing is conducted according to ASTM B117 to observe the corrosion of the coating. The test chamber uses a 5% NaCl solution at a temperature of 35°C ± 2°C for 168 consecutive hours (7 days). Sample preparation involves applying the coating to a metal plate, curing it, and then cutting it into specimens of specified dimensions. The test procedure involves placing the specimen in the salt spray chamber, conducting the test according to the standard, and observing and recording the corrosion conditions.

[0043] Humidity and heat aging test: This test measures the durability of a coating in high-temperature and high-humidity environments. Humidity and heat aging tests are conducted according to ASTM D714, observing changes in the coating. The test chamber is maintained at 85°C, 85% relative humidity, and a duration of 1000 hours. Sample preparation involves applying the coating to a metal plate, curing it, and then cutting it into specimens of specified dimensions. The test procedure involves placing the specimen in the humidity and heat aging chamber, testing it according to ASTM D714, and observing and recording changes in the coating.

[0044] Results from Figure 3As can be seen from the results of chemical resistance, salt spray resistance, and wet heat aging resistance tests, Examples 1-3 showed weight losses of 0.2 mg / cm², 0.1 mg / cm², and 0.1 mg / cm² in 1 mol / L H₂SO₄ and 1 mol / L NaOH, respectively, indicating good chemical stability. Under the same conditions, the comparative example exhibited significant blistering and shedding, with weight losses of 1.5 mg / cm² and 1.2 mg / cm², respectively, indicating poor chemical stability.

[0045] There was no obvious corrosion in Example 1 and Example 3 in the salt spray environment, and only slight corrosion spots appeared in Example 2. The comparative example had obvious corrosion spots, indicating that its corrosion resistance was poor.

[0046] There was no significant change in Examples 1 and 3 after the wet heat aging test, and only a slight color change occurred in Example 2. The comparative example showed significant color change and blistering after the wet heat aging test, indicating that its durability was poor.

[0047] The results of chemical resistance, salt spray resistance, and wet heat aging resistance tests demonstrate that the coatings of Examples 1-3 demonstrate excellent chemical stability, corrosion resistance, and durability. Overall, the coatings of the Examples demonstrate superior chemical properties to those of the Comparative Examples, making them more suitable for corrosion protection of metal can interiors.

[0048] 3. Mechanical properties test Adhesion testing measures the adhesion between the coating and the metal substrate. The cross-cut method (ASTM D3359) is used. Sample preparation involves applying the coating to the metal panel and, after curing, cutting the sample into the specified size. The test procedure involves using a cross-cut tool to create a 2 mm x 2 mm grid on the sample. The sample is then taped and removed. The adhesion level is then observed and recorded.

[0049] Abrasion resistance testing measures the wear resistance of coatings under abrasive conditions. Testing is performed using a Taber abrader (ASTM D1044). The instrument uses a CS-10 abrasive wheel with a 500 g load and 1000 revolutions per minute. Sample preparation involves applying the coating to a metal plate, curing it, and then cutting it into specimens of specified dimensions. The test procedure involves securing the specimen to the Taber abrader, setting the wheel load and revolutions, and recording the weight loss after abrasion.

[0050] Flexural Properties: This test measures the coating's flexibility and crack resistance under bending conditions. The T-bend test (ISO 1520) is used. Sample preparation involves applying the coating to a metal plate, curing it, and then cutting it into specimens of specified dimensions. The test procedure involves using a T-bend test apparatus with a 1 mm bend radius. Any cracking in the coating is observed and recorded.

[0051] Results from Figure 4 As can be seen, the adhesion grade of Examples 1 and 3 is 5B, indicating strong adhesion between the coating and the metal substrate. The adhesion grade of Example 2 is 4B, slightly lower than that of Examples 1 and 3. The adhesion grade of the comparative example is 2B, indicating poor adhesion.

[0052] The weight losses of Examples 1 to 3 were 12 mg, 15 mg, and 10 mg, respectively, indicating that the coatings had good wear resistance. The weight loss of the comparative example was 25 mg, indicating that its wear resistance was poor.

[0053] Examples 1 and 3 showed no cracks at a bending radius of 1 mm, indicating that the coatings had excellent flexibility and crack resistance. Example 2 exhibited minor cracks under the same conditions, indicating slightly insufficient flexibility and crack resistance. The comparative example exhibited significant cracks under the same conditions, indicating poor flexibility and crack resistance.

[0054] Adhesion, abrasion resistance, and flexural properties tests show that the coatings of Examples 1-3 demonstrate excellent adhesion, abrasion resistance, flexibility, and crack resistance. Overall, the coatings of the Examples demonstrate superior mechanical properties to those of the Comparative Examples, making them more suitable for corrosion protection of metal can interiors.

[0055] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. An anti-corrosion coating for the inner wall of a metal can, characterized in that: The invention comprises the following components in percentage by mass: 40-50% of waterborne epoxy resin without bisphenol A, 10-15% of modified phenolic resin, 5-10% of modified amino resin, 1-3% of nano silicon dioxide, 1-2% of corrosion inhibitor, 0.5-1% of defoaming agent, 0.1-0.3% of pH regulator, and the balance is deionized water; The preparation method of the modified phenolic resin comprises: mixing 100 parts of phenol, 70 parts of sodium hydroxide and distilled water by mass, heating to 45°C and keeping the temperature for 30 minutes, adding 120 parts of 37% formaldehyde aqueous solution and keeping the temperature for 30 minutes, cooling the system to 80°C due to the rise of reaction temperature, adding 30 parts of 37% formaldehyde aqueous solution and keeping the temperature for 15 minutes, adding 10 parts of polyethylene glycol, heating to 100°C and reacting for 20 minutes, cooling with cooling water, adding hydrochloric acid to neutralize and terminate the reaction, and preparing the modified phenolic resin; The preparation method of the modified amino resin comprises: mixing liquid methanol with a 10% sodium hydroxide solution, adjusting the pH value to 9, adding polyformaldehyde, melamine and urea so that the molar ratio of melamine, urea, formaldehyde and methanol is 1:2:7:10, heating to 80°C and then stopping heating, keeping the temperature for 60 minutes, cooling to 65°C, adjusting the pH value to 7.0 with 1 mol / L nitric acid, reacting for 30 minutes, adding a 10% sodium hydroxide solution for neutralization, adding 15 parts by mass of polyethylene glycol, heating to 110°C, continuing to stir and react for 1 hour, and after the reaction is completed, vacuuming to remove excess solvent, cooling to obtain the modified amino resin.

2. The anti-corrosion coating for inner wall of a metal can according to claim 1, characterized in that: The viscosity of the waterborne epoxy resin is 1000-3000 mPa·s.

3. The anti-corrosion coating for inner wall of a metal can according to claim 1, characterized in that: The glass transition temperature of the modified phenolic resin is 120-150°C.

4. The anti-corrosion coating for inner wall of a metal can according to claim 1, characterized in that: The heat-resistant temperature of the modified amino resin is 150-180°C.

5. The anti-corrosion coating for inner wall of a metal can according to claim 1, characterized in that: The corrosion inhibitor is one or more of molybdate, zinc phosphate or zinc borate.

6. The anti-corrosion coating for inner wall of a metal can according to claim 1, characterized in that: The defoamer is an organosilicon defoamer or a polyether defoamer.

7. The anti-corrosion coating for inner wall of a metal can according to claim 1, characterized in that: The pH adjuster is one or more of citric acid, acetic acid or phosphoric acid.

8. The anti-corrosion coating for inner wall of a metal can according to claim 1, characterized in that: The surface drying time of the paint at room temperature is 15-30 minutes, and the actual drying time is 3-5 hours.

9. The anti-corrosion coating for inner wall of a metal can according to claim 1, characterized in that: Pre-disperse nano-silicon dioxide in water by ultrasonic method, and pre-disperse corrosion inhibitor in water to form a stable suspension; mix water-based epoxy resin with deionized water and stir evenly; add modified phenolic resin and modified amino resin and continue stirring; add nano-silicon dioxide suspension and corrosion inhibitor suspension to mix, add pH adjuster, and stir evenly; add defoamer, continue stirring, filter to remove impurities, and prepare anti-corrosion coating for inner wall of metal can.

10. Use of the anti-corrosion coating for the inner wall of a metal can according to any one of claims 1 to 9 as a coating for the inner wall of a chemical product container.

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