Composition of metal packaging coating for food and preparation method thereof, and metal packaging can

Abstract

This invention provides a composition for a metal packaging coating for food, a method for preparing the same, and a metal packaging can. The composition of this invention, based on 100 parts by weight of epoxy acrylate resin, comprises: 10-25 parts by weight of dimethylethanolamine, 0.5-3 parts by weight of wax paste, 5-10 parts by weight of crosslinking agent, 0.1-1.1 parts by weight of defoamer, and 200-350 parts by weight of deionized water. The composition of this invention requires a small amount of coating material, is easy to use, has a high bubble retention capacity, and is both environmentally friendly and food-safe.

Description

Technical Field

[0001] The invention belongs to the field of polymer technology, and in particular relates to a composition of a metal packaging coating for food and a preparation method thereof, and a metal packaging can. Background Art

[0002] The main function of traditional metal packaging is to isolate the contents from the external environment. On the one hand, it is convenient for logistics and transportation, and on the other hand, it slows down the speed of spoilage of the contents by isolating oxygen and microorganisms. For the contents, metal packaging is just a good sealed container. However, with the growing demand of consumers for fresh experiences, the call for functional innovation in traditional packaging is also growing. Especially in terms of beverages containing gas, these gases are indispensable elements for providing consumers with a good tasting experience and intuitive consumption experience. Under the current domestic technical conditions, after the gas-containing beverage is fully left to stand, the gas contained in it cannot migrate out of the liquid autonomously when the package is opened, forming visible foam. The abundant and dense foam has a good promoting effect on stimulating consumers' desire to drink and improving the consumer experience. Therefore, how to make the bubbles in the metal packaging overflow quickly has become one of the key factors to improve consumers' taste.

[0003] Among the methods for increasing the gas overflow rate, one method is to change the coating components of the metal packaging. Commonly used food contact metal packaging coatings on the market mainly include epoxy phenolic coatings, epoxy amino coatings, epoxy acrylic coatings, polyvinyl chloride organosol coatings, etc. Among them, epoxy acrylic coatings are a type of coating used for corrosion protection of the inner wall of two-piece cans. It is a water-based coating made by treating epoxy resin with modifiers such as acrylic acid and styrene. It combines the advantages of epoxy resin and acrylic resin. The coating film not only has good metal adhesion and corrosion resistance, but also has good water resistance and light and heat resistance.

[0004] Patent (JP20078493A) discloses a can for foaming beverages. The inner surface of the can for beverages is provided with an organic resin covering layer, in which a predetermined amount of organic resin covering material of large-diameter particles with a particle size of 0.3~7 μm occupies more than 20% and less than 60% of the inner area of ​​the can, and a predetermined amount of organic resin covering material of small-diameter particles with a particle size of 0.03~0.2 μm occupies the remaining part of the inner area of ​​the can; and the organic resin covering layer is formed with concave parts generated by the detachment of at least a part of the large-diameter particles or convex parts generated by the residue thereof, and concave parts generated by the detachment of small-diameter particles. The organic resin covering layer is formed by at least one of epoxy acrylic acid, epoxy phenolic or vinyl chloride-based organic materials, and at least one of polyethylene-based or polyester-based resins with a melting point higher than that of the corresponding particles. According to the above-disclosed technology, in order to meet the basic functional requirements of forming a complete and effective resin layer in the can, it is necessary to greatly increase the amount of coating used in the can, which not only leads to a significant increase in economic costs, but also increases the difficulty of construction, and may require equipment modification or the use of special equipment.

[0005] Therefore, it is hoped to provide an epoxy acrylic resin emulsion, the composition of the metal packaging coating for food prepared therefrom can not only maintain the original corrosion resistance, but also accelerate the overflow speed of bubbles in the metal packaging, and is simple to prepare and requires a small coating amount. Summary of the invention

[0006] The present invention aims to solve at least one of the above-mentioned technical problems existing in the prior art. To this end, the present invention provides a composition of a metal packaging coating for food, which is simple to prepare, easy to use, has a small coating amount, a fast bubble overflow speed, and is environmentally friendly and food safe.

[0007] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0008] In a first aspect, the present invention provides a composition for a metal packaging coating for food, wherein the composition, based on 100 parts by weight of epoxy acrylic resin, further comprises: 10-25 parts by weight of dimethylethanolamine, 0.5-3 parts by weight of wax slurry, 5-10 parts by weight of a cross-linking agent, 0.1-1.1 parts by weight, preferably 0.5-1.1 parts by weight, of a defoaming agent, and 200-350 parts by weight of deionized water.

[0009] In a preferred embodiment, the epoxy acrylic resin is obtained by chain extension and grafting of epoxy resin, bisphenol A, dimethylimidazole, ethylene glycol butyl ether, methacrylic acid, acrylic acid, ethyl acrylate, styrene, benzoyl peroxide, and n-butanol.

[0010] In a preferred embodiment, the weight ratio of the epoxy resin, bisphenol A, dimethylimidazole, ethylene glycol butyl ether, methacrylic acid, acrylic acid, ethyl acrylate, styrene, benzoyl peroxide, and n-butanol is 100:30-80:0.1-0.5:50-80:10-15:1-5:1-5:5-15:1-5:15-25.

[0011] In a preferred embodiment, the wax slurry is selected from at least one of montan wax, polypropylene wax, polytetrafluoroethylene wax, carnauba wax and paraffin wax.

[0012] In a preferred embodiment, the cross-linking agent is selected from at least one of polyester resin, polyurethane resin, melamine formaldehyde resin, isocyanate resin and phenolic resin.

[0013] In a preferred embodiment, the defoaming agent is selected from at least one of BYK-060, BYK-061, BYK-066N and BYK-088.

[0014] In a preferred embodiment, the composition is in the form of an emulsion, wherein the solid content of the emulsion is 22-26 wt % and the viscosity is 18-22 seconds.

[0015] In a preferred embodiment, the epoxy equivalent of the epoxy acrylic resin is 5000-6000 g / mol.

[0016] A second aspect of the present invention provides a metal packaging can for food, comprising a metal body and a coating formed on the inner wall of the metal body, wherein the coating is formed from the above composition.

[0017] In another aspect, the present invention provides a method for preparing a composition for a metal packaging coating for food, comprising the following steps:

[0018] Epoxy acrylic resin is obtained by chain extension and grafting of epoxy resin, bisphenol A, dimethyl imidazole, ethylene glycol butyl ether, methacrylic acid, acrylic acid, ethyl acrylate, styrene, benzoyl peroxide and n-butanol with a catalyst and an initiator;

[0019] The composition is prepared by mixing 100 parts by weight of the epoxy acrylic resin, 10-25 parts by weight of dimethylethanolamine, 0.5-3 parts by weight of wax slurry, 5-10 parts by weight of a crosslinking agent, 0.1-1.1 parts by weight of a defoaming agent, and 200-350 parts by weight of deionized water.

[0020] In a preferred embodiment, the epoxy acrylic resin is prepared by the following process:

[0021] (1) adding solvent ethylene glycol butyl ether, bisphenol A, and dimethylimidazole to an epoxy resin, heating to 175-185° C. and keeping the temperature for 2-3 hours until the epoxy equivalent of the epoxy resin reaches 5000-6000 g / mol, thereby obtaining a chain-extended epoxy resin;

[0022] (2) mixing n-butanol, acrylic acid, ethyl acrylate, methacrylic acid, styrene, and benzoyl peroxide to prepare a mixed solution of acrylic acid-based substances; and

[0023] (3) Cooling the chain-extended epoxy resin to 120-130° C., slowly adding the mixed solution of acrylic acid-based substances in step (2) at a rate of 1-2 kg / min, and keeping the temperature for 1-3 hours to obtain epoxy acrylic resin.

[0024] In a preferred embodiment, the composition is prepared as follows:

[0025] The epoxy acrylic resin is pumped into a stirring kettle, dimethylethanolamine and deionized water are added, and stirred for 2-4 hours to obtain a mixed emulsion, and the solid content of the emulsion is adjusted to 30-35wt%; and

[0026] Water is added to the obtained mixed emulsion, and a cross-linking agent, wax slurry, and defoaming agent are added to obtain a composition in the form of an emulsion, wherein the solid content of the emulsion is 22-26 wt %, and the viscosity is 18-22 seconds.

[0027] Compared with the prior art, the beneficial effects of the present invention include:

[0028] (1) The present invention provides a composition having a new formula, which has excellent corrosion resistance and food safety and is particularly suitable for forming a coating for metal packaging for food.

[0029] (2) The present invention uses bisphenol A and acrylic acid to extend the chain and graft the base epoxy resin to obtain epoxy acrylic resin. The resin has both flexibility and hardness, excellent adhesion and stability, and a molecular weight much higher than that of ordinary internal spray coating, thereby significantly improving the protection of packaging cans. Packaging cans, such as beer cans, have better protection against the destructive effects of the coating due to transportation damage and the rise of the bottom of the can under high-temperature storage conditions.

[0030] (3) The emulsion composition of the present invention is acid-resistant and corrosion-resistant, meets the performance requirements of metal can interior coatings, and does not contain melamine that is harmful to the human body and the environment, and is green and environmentally friendly. At the same time, compared with the metal can interior spray coating currently commonly used in China, it can make the canned liquid, such as beer, produce rich beer foam after opening the can under low temperature conditions, thereby improving the visual and taste effects of beer drinking. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Schematic diagram of a coating surface 10000X inside a can according to an exemplary embodiment of the present invention.

[0032] Figure 2 Schematic diagram of a coating surface 500X inside a can according to an exemplary embodiment of the present invention. DETAILED DESCRIPTION

[0033] In order to make the technical scheme of the present invention more clearly understood by those skilled in the art, the following embodiments are listed for illustration. It should be pointed out that the following embodiments do not limit the protection scope of the present invention.

[0034] It should be noted that the term "mixed solution of acrylic substances" refers to a mixture of solutions of multiple different substances containing acrylic monomers. Example

[0035] Example 1

[0036] A composition of a metal packaging coating for food, comprising epoxy acrylic resin, dimethylethanolamine, wax slurry, a cross-linking agent, a defoaming agent and deionized water, wherein based on 100 parts by weight of epoxy acrylic resin, the composition comprises 17.4 parts by weight of dimethylethanolamine, 1.3 parts by weight of wax slurry, 8.7 parts by weight of cross-linking agent, 0.78 parts by weight of defoaming agent and 270 parts by weight of deionized water.

[0037] The epoxy acrylic resin is obtained by chain extension and grafting of epoxy resin, bisphenol A, dimethylimidazole, ethylene glycol butyl ether, methacrylic acid, acrylic acid, ethyl acrylate, styrene, benzoyl peroxide and n-butanol in a mass ratio of 100:61:0.18:76:14:4:5:9:3:17 through a catalyst initiator.

[0038] The catalyst initiator of the present invention is not particularly limited, and those commonly used in the art can be used, including but not limited to dimethylimidazole.

[0039] Wherein, the cross-linking agent is phenolic resin; the wax slurry is carnauba wax; and the defoaming agent is BYK-088.

[0040] The composition of the metal packaging coating for food is prepared according to the following process:

[0041] (1) adding epoxy resin, ethylene glycol butyl ether, bisphenol A, and dimethylimidazole into a reaction kettle, heating to 175° C. and keeping the temperature for 2 hours until the epoxy equivalent of the epoxy resin reaches 5500 g / mol, thereby obtaining a chain-extended epoxy resin;

[0042] (2) mixing n-butanol, acrylic acid, ethyl acrylate, methacrylic acid, styrene, and benzoyl peroxide to prepare a mixed solution of acrylic acid-based substances; and

[0043] (3) cooling the chain-extended epoxy resin to 125° C., slowly adding the mixed solution of acrylic acid-based substances in step (2) at a dropping rate of 1 kg / min, and keeping the temperature for 1 hour to obtain epoxy acrylic resin;

[0044] (4) The epoxy acrylic resin was pumped into a stirred tank, dimethylethanolamine and deionized water were added, and stirred for 2 hours to obtain a mixed emulsion, and the solid content of the emulsion was adjusted to 30%;

[0045] (5) Add water to the mixed emulsion in step (4), and add phenolic resin, carnauba wax slurry, and BYK-088 to obtain a composition in the form of an emulsion, wherein the solid content of the emulsion is 22% and the viscosity is 18 seconds (25°C, Ford No. 4 cup). The viscosity of the emulsion of the present invention is measured by a method comprising the following steps: the emulsion is allowed to stand at 25°C to stabilize it, and a finger is placed under the hole of the Ford No. 4 cup to prevent the emulsion from flowing out. The emulsion is carefully poured from the top of the Ford cup until a small amount overflows, the finger is removed to allow the emulsion to flow out and a stopwatch is started, and the timing is stopped when the emulsion no longer flows out.

[0046] The solid content of the emulsion of the present invention is determined by a method comprising the following steps: 1 g of the emulsion is weighed with a 1 / 10,000 balance to 4 decimal places, the weight is recorded, the 1 g of the emulsion is placed in an oven and baked at 200° C. for 5 minutes, the emulsion is taken out and cooled, and the value obtained by subtracting the two weights is divided by the weight of the emulsion, and the obtained percentage value is the solid content of the emulsion.

[0047] The epoxy equivalent of the epoxy resin of the present invention is determined by a method comprising the following steps: a certain amount of epoxy resin is weighed (at least to three decimal places) and placed in a sample conical flask; 25 ml of butanone is added to the sample conical flask, and the same amount of butanone is also added to a control blank flask; the resin is dissolved on a magnetic stirrer (slightly heated), and 50 ml of a cyclohexanone-glacial acetic acid mixed solvent is added to the conical flask and the blank flask; 2.0±0.1 g of CTBA is added to the conical flask and the blank flask, respectively, and then 4 drops of crystal violet indicator are added to each, and titrated with a 0.1M perchloric acid glacial acetic acid solution, and the color changes from blue to blue-green to emerald green, which is the titration end point. The calculation formula of the epoxy equivalent is as follows:

[0048] EEW 1000 M / (AB) N

[0049] Wherein, EEW is the epoxy equivalent weight of the epoxy resin to be tested, A is the milliliters of perchloric acid solution consumed by the sample, B is the milliliters of perchloric acid solution consumed by the blank sample, N is the equivalent concentration of the perchloric acid solution, and M is the weight of the epoxy resin.

[0050] Example 2

[0051] The composition was prepared using substantially the same preparation method as in Example 1, except that the content of the defoaming agent was changed to 0.1 parts by weight.

[0052] Example 3

[0053] The composition was prepared by using substantially the same preparation method as in Example 1, except that the content of the defoaming agent was changed to 1.1 parts by weight.

[0054] Example 4

[0055] The composition was prepared by using a preparation method substantially the same as that in Example 1, except that the mass ratio of epoxy resin to bisphenol A was changed to 100:57, and the chain-extended epoxy resin was prepared by the following specific process:

[0056] Add epoxy resin, ethylene glycol butyl ether, bisphenol A and dimethylimidazole into the reaction kettle, heat to 180°C, and keep warm for 2.5 hours until the epoxy equivalent reaches 4000 g / mol to obtain a chain-extended epoxy resin.

[0057] Comparative Example 1

[0058] A composition of a metal packaging coating for food, comprising epoxy acrylic resin, dimethylethanolamine, wax slurry, a crosslinking agent and deionized water, wherein based on 100 parts by weight of epoxy acrylic resin, the composition comprises 14 parts by weight of dimethylethanolamine, 1 part by weight of wax slurry, 15 parts by weight of the crosslinking agent and 325 parts by weight of deionized water.

[0059] The epoxy acrylic resin is obtained by chain extension and grafting of epoxy resin, bisphenol A, dimethylimidazole, ethylene glycol butyl ether, methacrylic acid, acrylic acid, ethyl acrylate, styrene, benzoyl peroxide and n-butanol in a mass ratio of 100:57:0.2:91:11:4:13:5:4:27 through a catalyst initiator.

[0060] Wherein, the cross-linking agent is phenolic resin; and the wax slurry is carnauba wax.

[0061] The composition of the metal packaging coating for food is prepared according to the following process:

[0062] (1) adding epoxy resin, ethylene glycol butyl ether, bisphenol A, and dimethylimidazole into a reaction kettle, heating to 175° C. and keeping the temperature for 2 hours until the epoxy equivalent of the epoxy resin reaches 4000 g / mol, thereby obtaining a chain-extended epoxy resin;

[0063] (2) mixing n-butanol, acrylic acid, ethyl acrylate, methacrylic acid, styrene, and benzoyl peroxide to prepare a mixed solution of acrylic acid-based substances; and

[0064] (3) cooling the chain-extended epoxy resin to 125° C., slowly adding the mixed solution of acrylic acid-based substances in step (2) at a dropping rate of 1 kg / min, and keeping the temperature for 1 hour to obtain epoxy acrylic resin;

[0065] (4) The epoxy acrylic resin was pumped into a stirred tank, dimethylethanolamine and deionized water were added, and stirred for 2 hours to obtain a mixed emulsion, and the solid content of the emulsion was adjusted to 30wt%;

[0066] (5) Adding water, phenolic resin and carnauba wax slurry to the mixed emulsion in step (4) to obtain an emulsion composition, wherein the emulsion has a solid content of 18% and a viscosity of 18 seconds (25° C., Ford No. 4 cup).

[0067] Comparative Example 2

[0068] The composition was prepared using substantially the same preparation method as in Example 1, except that the content of the defoaming agent was increased to 1.2 parts by weight.

[0069] Coating performance test

[0070] The coating was prepared by a coating spraying process. The emulsions of Examples 1-4 and Comparative Examples 1-2 were sprayed onto the inner wall of the metal can to form a coating. Three metal cans were obtained by spraying each of the Examples and Comparative Examples. The initial baking temperature was 95°C.

[0071] The performance test method is as follows:

[0072] (1) Measurement of surface state: Scanning electron microscopy (ZEISS GeminiSEM 300, Germany) was used to obtain images of the coating surface inside the can. The pit structure density was further calculated from the images.

[0073] (2) Determination of gas escape amount: Pour 330 mL of beer into a metal can at 8-12 °C and seal it. Weigh the mass, let it stand for 3 minutes, and weigh it again after opening the can. The difference between the two masses is the gas escape amount.

[0074] (3) Determination of gas overflow time: Pour 330 ml of beer into the prepared metal can at 8-12°C and seal it. Then refrigerate the metal can and let it stand for 24 hours. Then open the can to observe the gas overflow and record the gas overflow time (gas overflows in the form of foam).

[0075] (4) Determination of conductivity: Add electrolyte [1% (m / v) sodium chloride solution] into the metal can, with the liquid level 3mm from the can mouth, and use an internal coating integrity tester with a minimum reading value of no more than 0.1mA to test the internal coating of the can, and read the current value at the 4th second. (Note: The national standard requires that the current value for each beer can be ≤75 and the average value be ≤35; the current value for each beverage can be ≤25 and the average value be ≤5, in mA).

[0076] Table 1 Pit structure density

[0077]

[0078] Combined with Table 1 and Appendix Figure 1-2 As shown, compared with Comparative Example 1, Examples 1-4 and Comparative Example 2 have obvious pit-like structures. The main reason for the pit-like structure is the use of defoamers in the composition. This is because the defoamer has poor compatibility with the composition system in the form of an emulsion, and dense pits and fine wrinkles can be formed on the surface of the emulsion during the curing process of the emulsion; in addition, the dense pits and fine wrinkles on the surface of the emulsion are related to the epoxy equivalent of the epoxy acrylic resin. When the epoxy equivalent is high, the epoxy resin has fewer side chains, so the grafted acrylic acid content is low, which leads to poor water compatibility of the epoxy acrylic resin, so that the surface of the coating is not smooth enough during curing, which promotes the formation of pits and wrinkles on the surface of the final coating. The dense pits and wrinkles on the surface of the coating can make the gas in the beer unevenly distributed in the can, so that when the can lid is opened, the pressure in the can changes instantly, and the gas can be concentrated and released quickly, resulting in a large amount of foam overflow.

[0079] On the other hand, compared with Example 1, Example 4 has a smaller epoxy equivalent formed in the epoxy resin chain extension reaction, and correspondingly has a smaller viscosity, so the number of pits per 1 mm² is less than that of Example 1. In addition, the difference between Example 1 and Examples 2-3 lies in the different defoamer content. It can be seen that the higher the defoamer content, the greater the number of pits per 1 mm².

[0080] Table 2 Gas Escape

[0081]

[0082] As shown in Table 2, the gas escape amount of Examples 1-4 is significantly greater than that of Comparative Example 1. In combination with Table 1, it can be seen that Examples 1-4 have a special pit-shaped structure, which can make the gas in the tank unevenly distributed. As the gas pressure in the tank changes when the tank is opened, the gas can be quickly released, which is specifically manifested in the gas escape amount. Compared with the smooth surface of Comparative Example 1, Examples 1-4 with pit structures can release a large number of bubbles. In addition, the gas escape amount of Example 4 is less than that of Example 1. This is because the pit structure should meet certain density requirements to achieve the effect of large-scale escape of gas when the tank is opened, and the number of pits in Example 4 is less than that in Example 1, so the gas escape amount is also less than that in Example 1. At the same time, it can be seen from Examples 1-3 that with the increase of the defoamer content, the gas escape amount shows an upward trend. Since the defoamer can form dense pits and fine wrinkles on the coating surface, when its content increases, the area and number of pit wrinkles formed also increase accordingly. The number of pits will affect the distribution of gas in the tank, so the increase of defoamer will increase the gas escape amount.

[0083] Table 3 Gas overflow time

[0084]

[0085] As shown in Table 3, there is no bubble overflow time in Comparative Example 1. Since Comparative Example 1 uses a common coating composition, the coating does not have a special pit-shaped structure, so there will be no gas overflow when opening the can, and there will be no gas overflow time. Compared with Example 4, the gas overflow time of Example 1 is shorter, and the reason is that the epoxy equivalent of Example 1 is larger, the pore size and number of pits are more than Example 4, and the effect of rapid gas overflow can be achieved. In addition, in Examples 1-3, as the defoamer content increases, the increase in pits and wrinkles also makes the gas overflow time of the can body faster, which is consistent with the conclusion of Table 2.

[0086] Table 4 Conductivity values ​​(mA)

[0087]

[0088] As shown in Table 4, the conductivity value of Comparative Example 2 is much greater than that of other examples. This is because the defoamer content of Comparative Example 2 is 1.2 parts by weight, which is greater than that of other embodiments and Comparative Example 1. Although the defoamer can increase the appearance of more pit-like structures on the coating surface, thereby showing a fast gas overflow rate, it also brings about an increase in the conductivity inside the can. The high conductivity problem may cause the coating to react with the acid-base components of the liquid in the can, resulting in a decrease in the chemical stability of the liquid, and it cannot play a role in protecting food safety. Therefore, the defoamer content should not be too high.

[0089] The present invention prepares a composition suitable for food packaging coating by mixing a defoamer with an epoxy acrylic resin. The use of the defoamer can cause a pit-like structure to appear on the surface of the coating formed by the composition, and the pits and wrinkles on the surface will make the gas distribution uneven, so that the gas is concentrated and quickly released when the can is opened; further, acrylic acid is grafted onto the epoxy resin by a chain extension grafting method to obtain an epoxy acrylic resin with a high epoxy equivalent, which also increases the pit degree on the coating surface. The packaging can with a coating formed by using the composition of the present invention forms dense foam visible to the naked eye when the package is opened, which brings visual stimulation to the user and increases the taste. At the same time, the coating composition maintains the original impact resistance and anti-corrosion functions, and has environmental friendliness and food safety.

[0090] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions of the technical solution of the present invention by ordinary technicians in this field do not deviate from the essence and scope of the technical solution of the present invention.

Claims

1. A composition for a metal packaging coating for food, wherein the composition comprises, based on 100 parts by weight of epoxy acrylic resin, 10-25 parts by weight of dimethylethanolamine, 0.5-3 parts by weight of wax slurry, 5-10 parts by weight of a crosslinking agent, 0.1-1.1 parts by weight of a defoaming agent, and 200-350 parts by weight of deionized water; the defoaming agent is selected from at least one of BYK-060, BYK-061, BYK-066N, and BYK-088; The epoxy acrylic resin is obtained by chain extension and grafting of epoxy resin, bisphenol A, dimethylimidazole, ethylene glycol butyl ether, methacrylic acid, acrylic acid, ethyl acrylate, styrene, benzoyl peroxide and n-butanol with a catalyst, and the epoxy equivalent is 5000-6000 g / mol; the weight ratio of the epoxy resin, bisphenol A, dimethylimidazole, ethylene glycol butyl ether, methacrylic acid, acrylic acid, ethyl acrylate, styrene, benzoyl peroxide and n-butanol is 100:30-80:0.1-0.5:50-80:10-15:1-5:1-5:5-15:1-5:15-25.

2. The composition of the metal packaging coating for food according to claim 1, characterized in that: The wax slurry is selected from at least one of montan wax, polypropylene wax, polytetrafluoroethylene wax, carnauba wax and paraffin wax.

3. The composition of the metal packaging coating for food according to claim 1, characterized in that: The cross-linking agent is selected from at least one of polyester resin, polyurethane resin, melamine formaldehyde resin, isocyanate resin and phenolic resin.

4. The composition of the metal packaging coating for food according to any one of claims 1 to 3, characterized in that: The composition is in the form of an emulsion, wherein the solid content of the emulsion is 22-26 wt % and the viscosity is 18-22 seconds.

5. A metal packaging can for food, comprising a metal body and a coating formed on the inner wall of the metal body, wherein the coating is formed from the composition according to any one of claims 1 to 4.

6. A method for preparing the composition of the metal packaging coating for food according to claim 1, comprising the following steps: The composition is prepared by mixing 100 parts by weight of the epoxy acrylic resin, 10-25 parts by weight of dimethylethanolamine, 0.5-3 parts by weight of wax slurry, 5-10 parts by weight of a crosslinking agent, 0.1-1.1 parts by weight of a defoaming agent, and 200-350 parts by weight of deionized water.

7. The preparation method according to claim 6, characterized in that: The epoxy acrylic resin is prepared by the following process: (1) adding solvent ethylene glycol butyl ether, bisphenol A, and dimethylimidazole to the epoxy resin, heating to 175-185° C. and keeping the temperature for 2-3 hours to obtain a chain-extended epoxy resin; (2) mixing n-butanol, acrylic acid, ethyl acrylate, methacrylic acid, styrene, and benzoyl peroxide to prepare a mixed solution of acrylic acid-based substances; and (3) Cooling the chain-extended epoxy resin to 120-130° C., slowly adding the mixed solution of acrylic acid-based substances in step (2) at a rate of 1-2 kg / min, and keeping the temperature for 1-3 hours to obtain epoxy acrylic resin.

8. The preparation method according to claim 6, characterized in that: The composition is prepared by: Pumping the epoxy acrylic resin into a stirring kettle, adding dimethylethanolamine and deionized water, stirring for 2-4 hours to obtain a mixed emulsion, and adjusting the solid content of the emulsion to 30-35wt%; and Water is added to the obtained mixed emulsion, and a cross-linking agent, wax slurry, and defoaming agent are added to obtain a composition in the form of an emulsion.

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