Coating composition for metal packages for food, preparation method therefor, and metal packaging can

Abstract

Provided in the present invention are a coating composition for metal packages for food, a preparation method therefor and a metal packaging can. Using 100 parts by weight of epoxy acrylate resin as reference, the composition of the present invention comprises: 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 defoamer and 200-350 parts by weight of deionized water. The composition of the present invention enables a small coating amount, convenient use and high bubble storage capacity, and has environmental friendliness and food safety.

Description

Compositions and preparation methods of metal packaging coatings for food, and metal packaging cans Technical Field

[0001] This invention belongs to the field of polymer technology, specifically relating to compositions of coatings for metal packaging for food and their preparation methods, as well as metal packaging cans. Background Technology

[0002] The primary function of traditional metal packaging is to isolate the contents from the external environment, facilitating logistics and slowing spoilage by isolating oxygen and microorganisms. For the contents, metal packaging is simply a good sealed container. However, with consumers' growing demand for fresh experiences, the call for functional innovation in traditional packaging is growing louder. This is especially true for carbonated beverages, where the gases are indispensable for providing consumers with a pleasant taste and a direct sensory experience. Under current domestic technology, after sufficient settling, the gases in carbonated beverages cannot spontaneously migrate out of the liquid upon opening the packaging to form visible foam. Abundant and dense foam effectively stimulates consumers' desire to drink and enhances the consumption experience. Therefore, enabling the bubbles inside the metal packaging to quickly escape has become a key factor in improving the consumer's taste.

[0003] One method to increase the gas overflow rate is to modify the coating composition of the metal packaging. Commonly used food contact metal packaging coatings include epoxy phenolic coatings, epoxy amino coatings, epoxy acrylic coatings, and polyvinyl chloride organic sol coatings. Among these, epoxy acrylic coatings are used for corrosion protection of the inner walls of two-piece cans. They are water-based coatings made from epoxy resin modified with acrylic and styrene modifiers, combining the advantages of both epoxy and acrylic resins. The coating film not only has good metal adhesion and corrosion resistance but also excellent water resistance and light and heat resistance.

[0004] Patent (JP20078493A) discloses a foaming beverage can. The inner surface of this beverage can is provided with an organic resin coating layer. In this coating layer, a predetermined amount of large-diameter particles (0.3-7 μm) constitute 20% to 60% of the inner area of ​​the can, while a predetermined amount of small-diameter particles (0.03-0.2 μm) constitute the remaining inner area. The organic resin coating layer has recesses caused by the detachment of at least some of the large-diameter particles, protrusions caused by their residue, and recesses caused by the detachment of small-diameter particles. The organic resin coating layer is formed from at least one of epoxy acrylic, epoxy phenolic, or vinyl chloride organic materials, and at least one of polyethylene or polyester resins with a melting point higher than that of the corresponding particles. According to the disclosed technology, to meet the basic functional requirement of forming a complete and effective resin layer inside the can, the amount of coating used inside the can needs to be significantly increased. This not only leads to a significant increase in economic costs but also increases the difficulty of construction, potentially requiring equipment modification or the use of special equipment.

[0005] Therefore, it is desirable to provide an epoxy acrylic resin emulsion, from which a composition for coating food metal packaging is prepared, which not only maintains the original corrosion resistance properties, but also accelerates the overflow rate of air bubbles inside the metal packaging, and is simple to prepare and requires a small amount of coating. Summary of the Invention

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

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0008] In a first aspect, the present invention provides a composition for a metal packaging coating for food, wherein, based on 100 parts by weight of epoxy acrylate resin, the composition further 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, preferably 0.5-1.1 parts by weight, and 200-350 parts by weight of deionized water.

[0009] In a preferred embodiment, the epoxy acrylate 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.

[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 paste is selected from at least one of montan wax, polypropylene wax, polytetrafluoroethylene wax, carnauba wax, and paraffin wax.

[0012] In a preferred embodiment, the crosslinking 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 defoamer 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 emulsion has a solid content of 22-26 wt% and a viscosity of 18-22 seconds.

[0015] In a preferred embodiment, the epoxy equivalent in the epoxy acrylate 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-described composition.

[0017] On the other hand, the present invention provides a method for preparing a composition of a metal packaging coating for food, comprising the following steps:

[0018] Epoxy acrylate 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 through a catalyst initiator.

[0019] The composition is prepared by mixing 100 parts by weight of the epoxy acrylate resin with 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.

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

[0021] (1) Add solvents ethylene glycol butyl ether, bisphenol A and dimethyl imidazole to epoxy resin, heat to 175-185℃ and keep warm for 2-3 hours until the epoxy equivalent of epoxy resin reaches 5000-6000 g / mol, to obtain chain-extended epoxy resin.

[0022] (2) A mixed solution of acrylic acid substances is prepared by mixing n-butanol, acrylic acid, ethyl acrylate, methacrylic acid, styrene, and benzoyl peroxide; and

[0023] (3) Cool the extended epoxy resin to 120-130℃, slowly add the mixed solution of acrylic substances in step (2) at a rate of 1-2 kg / min, keep warm for 1-3 hours, and obtain epoxy acrylic resin.

[0024] In a preferred embodiment, the composition is carried out in the following manner:

[0025] The epoxy acrylate resin was pumped into a stirred tank, dimethylethanolamine and deionized water were added, and the mixture was stirred for 2-4 hours to obtain a mixed emulsion. The solid content of the emulsion was adjusted to 30-35 wt%.

[0026] Water is added to the obtained mixed emulsion, and a crosslinking agent, a wax paste, and a defoamer 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 with a novel formulation, which has excellent corrosion resistance and food safety, and is particularly suitable for forming coatings for metal packaging for food.

[0029] (2) The present invention uses bisphenol A and acrylic acid to extend and graft the basic 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 spraying, thus significantly improving the protection of packaging cans. Packaging cans, such as beer cans, have better protection against damage to the coating due to transportation damage and the rise of the can bottom under high temperature storage conditions.

[0030] (3) The emulsion composition of the present invention is acid and corrosion resistant, meets the performance requirements of coatings for the inside of metal cans, and is free of melamine, which is harmful to human health and the environment, making it green and environmentally friendly. At the same time, compared with the metal can spraying commonly used in China, it can produce rich beer foam after opening the can under static low temperature conditions, such as beer, improving the visual and taste effects of drinking beer. Attached Figure Description

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

[0032] Figure 2 is a schematic diagram of the 500X surface of the coating inside the can according to an exemplary embodiment of the present invention. Detailed Implementation

[0033] To enable those skilled in the art to more clearly understand the technical solutions described in this invention, the following embodiments are provided for illustration. It should be noted that the following embodiments do not constitute a limitation on the scope of protection claimed by this invention.

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

[0035] Example

[0036] Example 1

[0037] A composition for a metal packaging coating for food uses comprises epoxy acrylate resin, dimethyl ethanolamine, wax paste, crosslinking agent, defoamer, and deionized water. Based on 100 parts by weight of epoxy acrylate resin, the composition comprises 17.4 parts by weight of dimethyl ethanolamine, 1.3 parts by weight of wax paste, 8.7 parts by weight of crosslinking agent, 0.78 parts by weight of defoamer, and 270 parts by weight of deionized water.

[0038] The epoxy acrylate 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 in a mass ratio of 100:61:0.18:76:14:4:5:9:3:17 with a catalyst initiator.

[0039] The catalyst initiator of this invention is not particularly limited, and those catalysts commonly used in the art can be used, including but not limited to dimethylimidazole.

[0040] The crosslinking agent is phenolic resin; the wax paste is carnauba wax; and the defoamer is BYK-088.

[0041] The composition of the metal packaging coating for food is prepared according to the following process:

[0042] (1) Add epoxy resin, ethylene glycol butyl ether, bisphenol A and dimethyl imidazole to the reaction vessel, heat to 175°C and keep warm for 2 hours until the epoxy equivalent of the epoxy resin reaches 5500 g / mol, and obtain the chain-extended epoxy resin.

[0043] (2) A mixed solution of acrylic acid substances is prepared by mixing n-butanol, acrylic acid, ethyl acrylate, methacrylic acid, styrene, and benzoyl peroxide; and

[0044] (3) Cool the chain-extended epoxy resin to 125°C, slowly add the mixed solution of acrylic substances in step (2) at a rate of 1 kg / min, keep warm for 1 hour, and obtain epoxy acrylic resin.

[0045] (4) Pump the epoxy acrylate resin into the mixing tank, add dimethyl ethanolamine and deionized water, stir for 2 hours to obtain a mixed emulsion, and adjust the solid content of the emulsion to 30%.

[0046] (5) Add water to the mixed emulsion in step (4), and add phenolic resin, carnauba wax paste, and BYK-088 to obtain a composition in emulsion form, 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 determined by a method comprising the following steps: allowing the emulsion to stand at 25°C to stabilize it, placing a finger under the hole of the Ford No. 4 cup to prevent the emulsion from flowing out. Carefully pouring the emulsion from the top of the Ford cup until a small amount overflows, removing the finger to allow the emulsion to flow out and starting a stopwatch, stopping the timer when the emulsion stops flowing out.

[0047] The solid content of the emulsion of the present invention is determined by a method comprising the following steps: 1g of emulsion is weighed using a balance of 0.01g, accurate to 4 decimal places, and the weight is recorded. This 1g of emulsion is placed in an oven and baked at 200°C for 5 minutes. After being removed and cooled, it is weighed again. The difference between the two weights is divided by the weight of the emulsion, and the percentage obtained is the solid content of the emulsion.

[0048] The epoxy equivalent of the epoxy resin of the present invention is determined by the following steps: a certain amount of epoxy resin is weighed (accurate to at least three decimal places) and placed in a sample conical flask; 25 ml of butanone is added to the sample conical flask, and the same volume of butanone is added to the control blank flask; the resin is dissolved on a magnetic stirrer (with slight heating), 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 each of the conical flask and the blank flask, and then 4 drops of crystal violet indicator are added to each. Titration is performed with a 0.1 M perchloric acid-glacial acetic acid solution, and the titration endpoint is reached when the color changes from blue through blue-green to emerald green. The epoxy equivalent is calculated using the following formula: EEW = 1000 * M / (AB) * N

[0049] Wherein, EEW is the epoxy equivalent of the epoxy resin to be tested, A is the number of milliliters of perchloric acid solution consumed by the sample, B is the number of 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 essentially the same preparation method as in Example 1, except that the content of the defoamer was changed to 0.1 parts by weight.

[0052] Example 3

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

[0054] Example 4

[0055] The composition was prepared using essentially the same preparation method as 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 obtained using the following specific process:

[0056] Epoxy resin, ethylene glycol butyl ether, bisphenol A, and dimethylimidazole were added to a reaction vessel, heated to 180°C, and kept at that temperature for 2.5 hours until the epoxy equivalent reached 4000 g / mol, thus obtaining the chain-extended epoxy resin.

[0057] Comparative Example 1

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

[0059] The epoxy acrylate 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 in a mass ratio of 100:57:0.2:91:11:4:13:5:4:27 with a catalyst initiator.

[0060] The crosslinking agent is phenolic resin; the wax paste is carnauba wax.

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

[0062] (1) Add epoxy resin, ethylene glycol butyl ether, bisphenol A and dimethyl imidazole to the reaction vessel, heat to 175°C and keep warm for 2 hours until the epoxy equivalent of the epoxy resin reaches 4000 g / mol, and obtain the chain-extended epoxy resin.

[0063] (2) A mixed solution of acrylic acid substances is prepared by mixing n-butanol, acrylic acid, ethyl acrylate, methacrylic acid, styrene, and benzoyl peroxide; and

[0064] (3) Cool the chain-extended epoxy resin to 125°C, slowly add the mixed solution of acrylic substances in step (2) at a rate of 1 kg / min, keep warm for 1 hour, and obtain epoxy acrylic resin.

[0065] (4) Pump the epoxy acrylate resin into the mixing tank, add dimethyl ethanolamine and deionized water, stir for 2 hours to obtain a mixed emulsion, and adjust the solid content of the emulsion to 30 wt%.

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

[0067] Comparative Example 2

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

[0069] Coating performance test

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

[0071] The performance testing method is as follows:

[0072] (1) Measurement of surface condition: Images of the coating surface inside the tank were obtained using a scanning electron microscope (ZEISS GeminiSEM 300, Germany). The pit structure density was further calculated from the images.

[0073] (2) Determination of gas escape: 330 mL of beer is poured steadily into a metal can at 8-12℃ and sealed. The mass is weighed, and after standing for 3 minutes, the mass is weighed again after opening the can. The difference between the two mass values ​​is the gas escape.

[0074] (3) Determination of gas overflow time: 330ml of beer was poured steadily into a prepared metal can at 8-12℃ and sealed. The metal can was then refrigerated and left to stand for 24 hours. After that, the can was opened to observe the gas overflow phenomenon and the gas overflow time was recorded (the gas was manifested in the form of foam overflow).

[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 opening. Use an inner coating integrity tester with a minimum reading of no more than 0.1mA to test the inner coating of the can and read the current value at the 4th second. (Note: The national standard requires that beer cans be ≤75mm individually and ≤35mm on average; and beverage cans be ≤25mm individually and ≤5mm on average, in mA).

[0076] Table 1. Density of pit structure

[0077] As shown in Table 1 and Figures 1-2, compared to Comparative Example 1, Examples 1-4 and Comparative Example 2 exhibit a distinct pitted structure. The pitted structure is primarily due to the use of defoamers in the composition. This is because defoamers have poor compatibility with the emulsion-based composition system, leading to the formation of dense pits and fine wrinkles on the emulsion surface during curing. Furthermore, the dense pits and fine wrinkles on the emulsion surface are related to the epoxy equivalent of the epoxy acrylate resin. A higher epoxy equivalent results in fewer branches in the epoxy resin, leading to less grafted acrylic acid content and thus poorer water compatibility. This results in an uneven coating surface during curing, promoting the formation of pits and wrinkles on the final coating surface. These dense pits and wrinkles on the coating surface cause uneven gas distribution in the can, resulting in a sudden pressure change when the can is opened, causing the gas to concentrate and release rapidly, producing a large amount of foam.

[0078] On the other hand, compared with Example 1, Example 4 produces a smaller epoxy equivalent in the epoxy resin chain extension reaction, resulting in a correspondingly lower viscosity. Therefore, each 1mm... 2 The number of pits in Example 1 is less than that in Example 2-3. Furthermore, the difference between Example 1 and Examples 2-3 lies in the content of the defoamer; it can be seen that the higher the defoamer content, the more pits are present per 1mm. 2 The number of pits will also increase accordingly.

[0079] Table 2 Gas Escape

[0080] As shown in Table 2, the gas escape amount of Examples 1-4 is significantly greater than that of Comparative Example 1. Referring to Table 1, Examples 1-4 have a special pitted structure that allows for uneven gas distribution within the can. The change in gas pressure upon opening the can enables rapid gas release, specifically in terms of gas escape amount. Compared to the smooth surface of Comparative Example 1, Examples 1-4 with the pitted structure release a large number of bubbles. Furthermore, the gas escape amount of Example 4 is less than that of Example 1. This is because the pitted structure must meet certain density requirements to achieve the effect of a large amount of gas escaping upon opening the can, and the number of pits in Example 4 is less than that in Example 1, thus resulting in less gas escape. Simultaneously, it can be seen from Examples 1-3 that the gas escape amount increases with the increase of defoamer content. Since defoamer can form dense pits and fine wrinkles on the coating surface, as its content increases, the area and number of pits and wrinkles also increase. The number of pits affects the gas distribution within the can; therefore, increasing the amount of defoamer increases the gas escape amount.

[0081] Table 3 Gas Escape Time

[0082] As shown in Table 3, Comparative Example 1 had no bubble overflow time. Since Comparative Example 1 used a common coating composition, the coating did not have a special pitted structure, therefore no gas overflow occurred upon opening the can, and thus no gas overflow time was observed. Compared to Example 4, Example 1 had a shorter gas overflow time. This is because Example 1 had a higher epoxy equivalent, and the pore size and number of pits were greater than in Example 4, enabling rapid gas overflow. Furthermore, in Examples 1-3, the increase in defoamer content led to an increase in pits and wrinkles, which also accelerated the gas overflow time of the can, consistent with the conclusions in Table 2.

[0083] Table 4 Conductivity values ​​(mA)

[0084] As shown in Table 4, the conductivity value of Comparative Example 2 is much higher than that of the other examples. This is because the defoamer content of Comparative Example 2 is 1.2 parts by weight, which is higher than that of the other examples and Comparative Example 1. Although the defoamer can increase the number of pitted structures on the coating surface, thus resulting in a faster gas overflow rate, it also increases the conductivity inside the can. High conductivity can cause the coating to react with the acidic or alkaline components of the liquid inside the can, leading to a decrease in the chemical stability of the liquid and failing to protect food safety. Therefore, the defoamer content should not be too high.

[0085] This invention provides a composition suitable for food packaging coatings by mixing a defoamer with epoxy acrylic resin. The use of the defoamer creates a pitted structure on the surface of the coating formed by this composition. These pits and wrinkles result in uneven gas distribution, leading to concentrated and rapid gas release upon opening the can. Furthermore, grafting acrylic acid onto epoxy resin using a grafting method to obtain a high epoxy equivalent epoxy acrylic resin further increases the pitting degree of the coating surface. Packaging cans with a coating formed using the composition of this invention create a dense, visible foam upon opening, providing visual stimulation and enhancing the taste for the user. Simultaneously, the coating composition retains its original impact resistance and corrosion protection properties, exhibiting both environmental friendliness and food safety.

[0086] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, and is not intended to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention do not depart from the essence and scope of the technical solution of the present invention.

Claims

1. A composition for a coating of metal packaging for food, wherein, based on 100 parts by weight of epoxy acrylate resin, the composition 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.

2. The composition of the metal packaging coating for food according to claim 1, characterized in that, The epoxy acrylate resin is obtained by chain extension and grafting of epoxy resin, bisphenol A, dimethylimidazolium, ethylene glycol butyl ether, methacrylic acid, acrylic acid, ethyl acrylate, styrene, benzoyl peroxide, and n-butanol with a catalyst.

3. The composition of the metal packaging coating for food according to claim 2, characterized in that, 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.

4. The composition of a metal packaging coating for food according to any one of claims 1-3, characterized in that, The wax paste is selected from at least one of montan wax, polypropylene wax, polytetrafluoroethylene wax, carnauba wax, and paraffin wax.

5. The composition of a metal packaging coating for food according to any one of claims 1-3, characterized in that, The crosslinking agent is selected from at least one of polyester resin, polyurethane resin, melamine-formaldehyde resin, isocyanate resin and phenolic resin.

6. The composition of a metal packaging coating for food according to any one of claims 1-3, characterized in that, The defoamer is selected from at least one of BYK-060, BYK-061, BYK-066N, and BYK-088.

7. The composition of a metal packaging coating for food according to any one of claims 1-3, 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; and / or the epoxy equivalent in the epoxy acrylate resin is 5000-6000 g / mol.

8. 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 by the composition of any one of claims 1-7.

9. A method for preparing a composition for a metal packaging coating for food, comprising the following steps: Epoxy acrylate 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 through a catalyst initiator. The composition is prepared by mixing 100 parts by weight of the epoxy acrylate resin with 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.

10. The preparation method according to claim 9, characterized in that, The epoxy acrylate resin is prepared by the following process: (1) Add solvents ethylene glycol butyl ether, bisphenol A and dimethyl imidazole to epoxy resin, heat to 175-185℃ and keep warm for 2-3 hours until the epoxy equivalent of epoxy resin reaches 5000-6000 g / mol, to obtain chain-extended epoxy resin. (2) Mix n-butanol, acrylic acid, ethyl acrylate, methacrylic acid, styrene, and benzoyl peroxide to prepare a mixed solution of acrylic substances; as well as (3) Cool the extended epoxy resin to 120-130℃, slowly add the mixed solution of acrylic substances in step (2) at a rate of 1-2 kg / min, keep warm for 1-3 hours, and obtain epoxy acrylic resin.

11. The preparation method according to claim 9, characterized in that, The composition is prepared in the following manner: The epoxy acrylate resin was pumped into a stirred tank, dimethylethanolamine and deionized water were added, and the mixture was stirred for 2-4 hours to obtain a mixed emulsion. The solid content of the emulsion was adjusted to 30-35 wt%. Water is added to the obtained mixed emulsion, and a crosslinking agent, a wax paste, and a defoamer 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.

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