A coating composition for two-piece cans and its preparation method and application

Abstract

The present invention discloses a coating composition for two-piece cans, its preparation method, and application, relating to the technical field of food packaging coatings. The present invention utilizes acrylic acid to esterify epoxy resin to obtain an epoxy ester containing polymerizable double bonds. The polymerizable double bonds in the epoxy ester are further copolymerized with the hard and tough monomer isobornyl acrylate, the functional monomer phosphate-containing acrylate, and epoxy-containing glycidyl methacrylate to improve the toughness, adhesion, and stability of the epoxy resin. Furthermore, by introducing epoxy groups, the loss of epoxy groups during the esterification modification process to prepare the epoxy ester is compensated, thereby improving curing efficiency. This results in an acrylic-modified epoxy resin with both flexibility and hardness, and excellent adhesion and stability. This reduces component migration and overflow, and the resulting coating composition is acid-resistant, sulfur-resistant, and high-temperature steam-resistant, meeting the performance requirements of metal can interior coatings. Furthermore, the coating composition is free of melamine, which is harmful to humans and the environment, and does not require the use of organic solvents, making it environmentally friendly.

Description

Technical Field

[0001] The present invention belongs to the technical field of food packaging coatings, and in particular relates to a coating composition for two-piece cans, a preparation method thereof, and an application thereof. Background Art

[0002] Aluminum two-piece cans with easy-open ends are currently widely used in my country for beer and beverages. The quality of the internal coating directly affects the safety of the filled product, a significant concern for customers and consumers. All metal cans require internal coating to isolate the metal from the filled product, preventing direct contact between the metal and the contents, thus preventing corrosion of the can and aluminum ion precipitation.

[0003] Commonly used coatings for food contact metal packaging on the market include epoxy phenolic coatings, epoxy amino coatings, water-based modified epoxy resin coatings, food can interior release coatings, and polyvinyl chloride organosol coatings. Epoxy phenolic and epoxy amino coatings are currently the primary internal coating materials for the bodies and bottoms of three-piece cans. The former is made from a specific ratio of epoxy and phenolic resins, while the latter is made from epoxy and amino resins. These coatings offer comprehensive performance, particularly in adhesion, flexibility, acid and sulfur resistance, and corrosion resistance. Currently, the internal coatings for three-piece cans are all solvent-based.

[0004] Water-based modified epoxy resin coating is 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 both 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.

[0005] Patent (CN104371492A) discloses a solvent-based coating for the inner wall of cans and its preparation method, relating to the technical field of can coatings. The coating comprises a primer and a topcoat. The primer is composed of 60% 6009 epoxy resin solution, 10% phenolic resin, 10% adhesion promoter, and 20% special diluent, while the topcoat is composed of 65% 6009 epoxy resin solution, 10% phenolic resin, 5% adhesion promoter, and 20% special diluent. The primer and topcoat are formulated separately. The primer has strong adhesion to tinplate, and the coating film has good flexibility and impact resistance. It can reduce the transmittance of food corrosion, thereby improving the barrier ability of the coating film and meeting food hygiene standards. However, this technical solution uses two separate primers, the primer and topcoat, which are formulated separately, resulting in a complex process. In addition, the solvent system is not environmentally friendly.

[0006] Patent (CN103013303A) discloses a coating for the interior of metal beverage and food cans, its preparation method, and its application. The coating is composed of the following components, by mass percentage: 35-70% saturated polyester, 1-15% amino resin, 3-20% phenolic resin, and 1.8-2.5% additives. The coating contains no toxic monomers, and the resulting coating is resistant to high-temperature sterilization and acid boiling, exhibiting excellent flexibility. It can be used as a coating for the interior of pull-off lids, two-piece deep-drawn food cans, and three-piece beverage cans. It can replace the double-coating process of epoxy primer and organosol topcoat in sheet coating. However, this technical solution uses a solvent-based coating, which is not environmentally friendly.

[0007] Patent CN115710449A provides an amino resin-free water-based interior spray coating and its preparation method, relating to the field of coating technology. The coating comprises components: a modified epoxy resin, a modified phenolic resin, an amine, an additive, a lubricant, and water, mixed in specific proportions and synergistically prepared by modifying the epoxy resin and phenolic resin. The resulting coating is corrosion-resistant, acid- and alkali-resistant, saltwater-resistant, high-temperature-resistant, and abrasion-resistant. Furthermore, since it does not use amino resin, it addresses the safety issue of melamine accumulation caused by amino resins in coatings. The coating can be widely used in the preparation of interior coatings for beverage cans, meat cans, and tableware. However, the above technical solution uses relatively complex ingredients.

[0008] Patent (CN102146248A) discloses a water-based coating for the inner wall of cans that is acid-resistant and heat-resistant. The coating comprises the following raw materials by weight: 15-30 parts of a water-based acrylic monomer graft-modified epoxy phosphate resin, 1-3 parts of a water-based amino resin, 0.2-0.8 parts of an acid catalyst, 0.1-0.5 parts of a wetting agent, 0.1-0.3 parts of a defoaming agent, and 2-5 parts of a cosolvent. The prepared coating has good acid and heat-resistant properties and is harmless to the environment and the human body, making it environmentally friendly. However, this technical solution can only achieve technical effects equivalent to those of existing products.

[0009] As can be seen, existing coating compositions for metal can interior coatings suffer from environmental concerns, complex processes, complex ingredients, and subpar performance. Based on these issues, the present invention proposes a coating composition for two-piece cans. This coating composition utilizes a water-based modified epoxy resin modified with various functional acrylic acid / acrylate monomers to achieve both hardness and flexibility. After neutralization, this resin is combined with a water-based curing agent and additives. The resulting coating composition is resistant to acid, sulfur, and high-temperature steam, meeting the performance requirements for metal can interior coatings. It also contains no melamine, which is harmful to humans and the environment, and eliminates the need for organic solvents, making it environmentally friendly. Summary of the Invention

[0010] The present invention addresses the problems existing in the prior art and provides a coating composition for two-piece cans, a preparation method thereof, and an application thereof. Epoxy resin is esterified and modified with acrylic acid to obtain epoxy ester containing polymerizable double bonds. The polymerizable double bonds in the epoxy ester are further copolymerized with hard and tough monomer isobornyl acrylate, functional monomer phosphate-containing acrylate, and epoxy-containing glycidyl methacrylate to improve the toughness, adhesion, and stability of the epoxy resin. Epoxy groups are introduced to compensate for the loss of epoxy groups in the esterification modification process for preparing the epoxy ester, thereby improving the curing efficiency. Thus, an acrylic modified epoxy resin having both flexibility and hardness and excellent adhesion and stability is prepared, and component migration and overflow are reduced. The prepared coating composition is resistant to acid, sulfur, and high-temperature steam, meeting the performance requirements of metal can interior coatings, and does not contain melamine harmful to humans and the environment, does not require the use of organic solvents, and is environmentally friendly.

[0011] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0012] In a first aspect, the present invention provides a coating composition for a two-piece can, comprising component A and component B, wherein component B is a water-based curing agent, and the mass ratio of component A to component B is 10:(2-4); and component A comprises, in parts by weight:

[0013] 30-65 parts of water-based modified epoxy resin emulsion, 0.1-1 part of additive and 5-25 parts of water.

[0014] In a preferred embodiment, the water-based modified epoxy resin emulsion is obtained by copolymerizing epoxy resin, acrylic acid, isobornyl acrylate, phosphate-containing acrylate, and glycidyl methacrylate with a free radical initiator, followed by neutralization and dispersion.

[0015] In a preferred embodiment, the mass ratio of the epoxy resin, acrylic acid, isobornyl acrylate, phosphate-containing acrylate, and glycidyl methacrylate is 10:1-2:1-2:1-2:1.5-3.

[0016] In a preferred embodiment, the preparation process of the water-based modified epoxy resin emulsion is as follows:

[0017] 3) adding epoxy resin, acrylic acid, polymerization inhibitor and catalyst into a reaction kettle, heating the reaction to obtain epoxy ester;

[0018] 4) adding a solvent to the epoxy ester obtained in step 1), and adding a mixed solution of isobornyl acrylate, phosphate-containing acrylate, glycidyl methacrylate, and a free radical initiator; after heat preservation and reaction, removing the solvent, cooling, adding a neutralizer, and after the temperature stabilizes, adding water to disperse to obtain a water-based modified epoxy resin emulsion.

[0019] More preferably, in step 1), the temperature reaction conditions are: reaction at 100-120° C. for 1-4 hours; the catalyst is triphenylphosphine, and the amount used is 1-4% of the mass of the epoxy resin; the polymerization inhibitor is selected from at least one of 2,6-di-tert-butyl-p-cresol, p-hydroxyanisole, hydroquinone, and 2,4-dimethyl-6-tert-butylphenol, and the amount used is 0.5-3% of the acrylic acid.

[0020] More preferably, in step 2), the insulation reaction conditions are: insulation reaction at 110-140°C for 2-5h, and the cooling condition is cooling to 50-70°C; the solid content of the water-based modified epoxy resin emulsion is 30-55%; the neutralizer is selected from at least one of N,N-dimethylethanolamine and / or AMP-95, and the molar ratio of the neutralizer to acrylic acid is (0.8-1.1):1; the solvent is selected from at least one of an alcohol organic solvent, an ether organic solvent, an ester organic solvent and a benzene organic solvent, and the amount of the solvent is 1.5-4 times the mass of the epoxy resin.

[0021] The invention adopts acrylic acid to esterify epoxy resin to obtain epoxy ester containing polymerizable double bonds, and further utilizes the polymerizable double bonds in the epoxy ester to copolymerize with isobornyl acrylate, acrylate containing phosphate ester and glycidyl methacrylate containing epoxy group. On the one hand, isobornyl acrylate contains a bridge ring, which is hard and tough, can give the coating appropriate hardness and improve toughness modification, and has good adhesion to various metal substrates, good tolerance to solvents and acids and alkalis, and good thermal stability, which can improve the toughness, adhesion and thermal stability of epoxy resins; on the other hand, phosphate-containing acrylates are usually used as adhesion promoters, and have a certain chain length, have good adhesion to various metal substrates, can improve flexibility, water resistance, acid and alkali resistance and corrosion resistance, and compared with silane modifiers, have better compatibility with epoxy resins, better modification effect, and can better improve flexibility compared with phosphate-esterified epoxy resins; thirdly, epoxy-containing glycidyl methacrylate can introduce epoxy groups to make up for the loss of epoxy groups in the esterification modification process to prepare epoxy esters, promote curing efficiency and the physical properties of the coating, and reduce component migration and overflow. Therefore, through the above modification, a water-based modified epoxy resin with both hardness and flexibility, excellent adhesion and stability can be prepared. No additional adhesion promoter is needed to prepare an acid-resistant, sulfur-resistant, and high-temperature steam-resistant coating composition, which meets the performance requirements of the coating inside the metal can, and does not leak harmful components such as melamine that are harmful to the human body and the environment. There is no need to use organic solvents, and it is green and environmentally friendly.

[0022] In a preferred embodiment, the phosphate-containing acrylate is selected from 2-hydroxyethyl methacrylate phosphate and / or alkyl acrylate phosphate.

[0023] In a preferred embodiment, the free radical initiator is selected from at least one of benzoyl peroxide, tert-butyl benzoyl peroxide, and methyl ethyl ketone peroxide, and is used in an amount of 1-4% of the total amount of acrylic acid, isobornyl acrylate, phosphate-containing acrylate, and glycidyl methacrylate.

[0024] In a preferred embodiment, the epoxy resin is selected from at least one of bisphenol A epoxy resin, bisphenol F epoxy resin, aliphatic epoxy resin, and alicyclic epoxy resin; and the water-based curing agent is selected from at least one of polyamide, modified polyamide, aliphatic amine, modified alicyclic amine, aromatic amine, and modified aliphatic amine.

[0025] In a second aspect, the present invention provides a method for preparing the coating composition for two-piece cans, comprising the following steps:

[0026] (1) Preparation of Component A: Weigh the water-based modified epoxy resin emulsion, the additive, and water according to the ratio, and mix them evenly to obtain Component A;

[0027] (2) Preparation of Component B: Weigh the water-based curing agent according to the ratio to obtain Component B;

[0028] (3) When in use, component A and component B are mixed evenly in proportion to obtain the coating composition for two-piece cans.

[0029] In a third aspect, the present invention provides use of the coating composition for two-piece cans in two-piece can packaging coatings.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1. The present invention uses acrylic acid to esterify epoxy resin to obtain epoxy ester containing polymerizable double bonds, and further utilizes the polymerizable double bonds in the epoxy ester to copolymerize with the hard and tough monomer isobornyl acrylate, the functional monomer phosphate-containing acrylate and epoxy-containing glycidyl methacrylate to improve the toughness, adhesion and stability of the epoxy resin. By introducing epoxy groups, the loss of epoxy groups in the process of esterification modification to prepare epoxy ester is compensated, the curing efficiency is improved, and an acrylic modified epoxy resin with both flexibility and hardness, and excellent adhesion and stability is prepared, and the migration and overflow of components are reduced. The prepared coating composition is acid-resistant, sulfur-resistant, and high-temperature steam-resistant, meeting the performance requirements of metal can interior coatings, and does not contain melamine that is harmful to humans and the environment, does not require the use of organic solvents, and is green and environmentally friendly.

[0032] 2. The coating composition for two-piece cans of the present invention has excellent wear resistance, as well as water resistance, salt resistance, acid resistance and sulfur resistance. The migration degree of bisphenol A epoxy derivatives is very small, which is much lower than the relevant limit requirements of the European Union. It can meet the use requirements of the inner wall coating of two-piece cans and can also be used as packaging coatings for other metal cans such as three-piece cans. DETAILED DESCRIPTION

[0033] It is worth noting that the raw materials used in the present invention are all common commercially available products, and their sources are not specifically limited.

[0034] Epoxy resin: GELR127, Hongchang Electronic Materials Co., Ltd.

[0035] Phosphate-containing acrylates: EM39, purchased from Changxing Chemical Materials (Zhuhai) Co., Ltd.; KM2140, purchased from Hangzhou Furuide Technology Co., Ltd.

[0036] Defoamer: BYK-024;

[0037] Dispersant: BYK-190;

[0038] Catalyst: triphenylphosphine, commercially available;

[0039] Free radical initiator: benzoyl peroxide, commercially available;

[0040] Inhibitor: 2,6-di-tert-butyl-p-cresol, commercially available;

[0041] Solvent: ethyl acetate, commercially available;

[0042] Neutralizer: N,N-dimethylethanolamine, AMP-95, commercially available;

[0043] Water-based curing agents: AB-HGF (aromatic amine epoxy curing agent) and AB-HGH-200 (modified alicyclic amine epoxy curing agent), purchased from Zhejiang Anbang New Materials Development Co., Ltd.

[0044] Other raw materials are commonly available on the market.

[0045] Example 1

[0046] A coating composition for a two-piece can, comprising a component A and a component B in a mass ratio of 10:3, wherein the component B is a water-based curing agent (AB-HGF), and the component A is composed, by weight, of 50 parts of a water-based modified epoxy resin emulsion, 0.1 parts of a defoaming agent, 0.5 parts of a dispersant, and 20 parts of water.

[0047] The water-based modified epoxy resin is prepared by copolymerizing epoxy resin, acrylic acid, isobornyl acrylate, phosphate-containing acrylate (EM39), and glycidyl methacrylate in a mass ratio of 10:2:2:2:3 with a free radical initiator, neutralizing, and dispersing. The preparation process is as follows:

[0048] 1) Add epoxy resin, acrylic acid, polymerization inhibitor, and catalyst to a reaction kettle, heat until the material becomes transparent, start stirring, and react at 110° C. for 3 hours until the acid value is ≤5 mg KOH / mg to obtain epoxy ester; wherein the amount of catalyst is 3% by weight of the epoxy resin, and the amount of polymerization inhibitor is 1% by weight of the acrylic acid;

[0049] 2) adding a solvent twice as much as the epoxy resin by weight to the epoxy ester obtained in step 1), and adding dropwise a mixed solution of isobornyl acrylate, phosphate-containing acrylate, glycidyl methacrylate, and a free radical initiator while stirring for 30 minutes. After the mixture is kept warm at 110° C. for 4 hours, the solvent is removed by distillation under reduced pressure, the temperature is lowered to 60° C., and a neutralizer (N,N-dimethylethanolamine, with a molar ratio of neutralizer to acrylic acid of 1:1) is added dropwise while stirring. After the temperature stabilizes, distilled water twice as much as the epoxy resin by weight is added and dispersed at high speed to obtain a water-based modified epoxy resin emulsion (solid content of approximately 49%).

[0050] Example 2

[0051] A coating composition for two-piece cans, comprising component A and component B in a mass ratio of 10:2, wherein the component B is a water-based curing agent (AB-HGH-200), and the component A is composed, by weight, of 30 parts of a water-based modified epoxy resin emulsion, 0.05 parts of a defoaming agent, 0.05 parts of a dispersant, and 5 parts of water.

[0052] The water-based modified epoxy resin emulsion is prepared by copolymerization, neutralization, and dispersion of epoxy resin, acrylic acid, isobornyl acrylate, phosphate-containing acrylate (KM2140), and glycidyl methacrylate in a mass ratio of 10:1:1.5:1.5:2.5 with a free radical initiator. The preparation process is as follows:

[0053] 1) Add epoxy resin, acrylic acid, polymerization inhibitor, and catalyst to a reaction kettle, heat until the material becomes transparent, start stirring, and react at 120° C. for 2.5 hours until the acid value is ≤5 mg KOH / mg to obtain epoxy ester; wherein the amount of catalyst is 4% by weight of the epoxy resin, and the amount of polymerization inhibitor is 3% by weight of the acrylic acid;

[0054] 2) raising the temperature to 140° C., adding a solvent in an amount 3 times the mass of the epoxy resin to the epoxy ester obtained in step 1), and adding dropwise a mixed solution of isobornyl acrylate, phosphate-containing acrylate, glycidyl methacrylate, and a free radical initiator while stirring for 30 minutes. After keeping the temperature at 140° C. for 3 hours, the solvent was removed by distillation under reduced pressure, and the temperature was lowered to 70° C., and a neutralizer (AMP-95, the molar ratio of the neutralizer to acrylic acid is 1.1:1) was added dropwise while stirring. After the temperature stabilized, distilled water in an amount 3 times the mass of the epoxy resin was added and dispersed at high speed to obtain a water-based modified epoxy resin emulsion (solid content of approximately 35%).

[0055] Example 3

[0056] A coating composition for a two-piece can, comprising a component A and a component B in a mass ratio of 10:4, wherein the component B is a water-based curing agent (AB-HGH-200), and the component A is composed, by weight, of 65 parts of a water-based modified epoxy resin emulsion, 0.2 parts of a defoaming agent, 0.8 parts of a dispersant, and 25 parts of water.

[0057] The water-based modified epoxy resin emulsion is prepared by copolymerization, neutralization, and dispersion of epoxy resin, acrylic acid, isobornyl acrylate, phosphate-containing acrylate (EM39), and glycidyl methacrylate in a mass ratio of 10:1:1:1:1.5 with a free radical initiator. The preparation process is as follows:

[0058] 1) Add epoxy resin, acrylic acid, polymerization inhibitor, and catalyst to a reaction kettle, heat until the material becomes transparent, start stirring, and react at 105° C. for 4 hours until the acid value is ≤5 mg KOH / mg to obtain epoxy ester; wherein the amount of catalyst is 2% by weight of the epoxy resin, and the amount of polymerization inhibitor is 0.5% by weight of the acrylic acid;

[0059] 2) raising the temperature to 130° C., adding a solvent in an amount 1.5 times the mass of the epoxy resin to the epoxy ester obtained in step 1), and adding dropwise a mixed solution of isobornyl acrylate, phosphate-containing acrylate, glycidyl methacrylate, and a free radical initiator while stirring for 30 minutes. After keeping the temperature at 130° C. for 3 hours, the solvent was removed by distillation under reduced pressure, and the temperature was lowered to 50° C., and a neutralizer (AMP-95, the molar ratio of the neutralizer to acrylic acid is 0.8:1) was added dropwise while stirring. After the temperature stabilized, distilled water in an amount 1 times the mass of the epoxy resin was added, and the mixture was dispersed at high speed to obtain a water-based modified epoxy resin emulsion (solid content of approximately 59%).

[0060] Comparative Example 1

[0061] Except that glycidyl methacrylate is not added, the rest is the same as Example 1.

[0062] Comparative Example 2

[0063] Except that an equal amount of KH570 was used instead of EM39, the rest was the same as in Example 1.

[0064] Comparative Example 3

[0065] Except that an equal amount of methyl methacrylate was used instead of isobornyl acrylate, the rest was the same as in Example 1.

[0066] Comparative Example 4

[0067] Except for using an equal amount of styrene instead of isobornyl acrylate, the rest is the same as Example 1.

[0068] Comparative Example 5

[0069] Except for the different process of preparing the waterborne modified epoxy resin emulsion (i.e., the waterborne modified epoxy resin emulsion is prepared by free radical polymerization grafting method), the rest is the same as Example 1. The specific process is as follows:

[0070] Add epoxy resin and solvent twice the mass of epoxy resin into a reaction kettle, heat to 110°C, and add dropwise a mixed solution of acrylic acid, isobornyl acrylate, phosphate-containing acrylate, glycidyl methacrylate and free radical initiator while stirring. The mixture is added dropwise for 30 minutes. After the mixture is kept warm at 110°C for 4 hours, the solvent is removed by distillation under reduced pressure, the temperature is lowered to 60°C, and a neutralizer (the molar ratio of neutralizer to acrylic acid is 1:1) is added dropwise while stirring. After the temperature stabilizes, distilled water twice the mass of epoxy resin is added and dispersed at high speed to obtain a water-based modified epoxy resin emulsion (solid content of approximately 49%).

[0071] Test example coating performance test

[0072] The coating was prepared by conventional coating spraying process. Component A and component B of the coating compositions of Examples 1-3 and Comparative Examples 1-5 were mixed in proportion and sprayed evenly onto the aluminum plate. The target dry film weight was 12 g / m 2 , bake in an oven at 200℃ for 10 minutes until it is completely cured.

[0073] 1. The performance test method is as follows:

[0074] 1) Coefficient of friction (COF) test: The prepared coating was tested using an American ALTEK9505A3 instrument with a weight of 2 kg and a speed of 508 mm / min.

[0075] 2) MEK resistance test: Wrap a 1kg iron hammer with cotton cloth, dip it in liquid MEK solvent, and rub the surface of the tested coating with a back-and-forth motion. One back-and-forth motion is counted as one stroke. The number of rubs is recorded as the MEK value.

[0076] 3) The coated aluminum samples were subjected to the following treatments: boiling in water at 121°C for 60 minutes (water resistance), boiling in 30g / L NaCl at 121°C for 60 minutes (salt resistance), boiling in a 2% by mass citric acid solution at 121°C for 30 minutes (acid resistance), and boiling in 0.5g / L sodium sulfide at 121°C for 60 minutes (sulfur resistance). Samples that showed no blistering, whitening, water spots, discoloration, or shifting during cooking were deemed qualified; otherwise, they were deemed unqualified. Adhesion before and after cooking was also verified using a 100-grid test, with 0 being the best and 5 being the worst. The adhesion of the coated sample without these treatments was designated F0, and the adhesion after treatment was designated F1.

[0077] 4) Detection of Bisphenol A Epoxy Derivatives: Coating samples were extracted with acetonitrile at 100°C for 1 hour. The extract was then concentrated to dryness by rotary evaporation and dissolved in a mixture of V (acetonitrile):V (water) = 50:50 and fixed to volume. High performance liquid chromatography (HPLC) separation was performed using a Lichrospher C18 column with acetonitrile / water as the mobile phase for gradient elution (elution gradient see Table 1). Detection was performed with a fluorescence detector at an excitation wavelength of 230 nm and an emission wavelength of 301 nm. (For specific methods, see the journal article "High Performance Liquid Chromatographic Analysis of Bisphenol A and Bisphenol F Epoxy Derivative Residues in Food Can Coatings").

[0078] Table 1 Elution parameters

[0079]

[0080] 2. The effect data of Examples 1-3 and Comparative Examples 1-5 are shown in Table 2-3.

[0081] Table 2

[0082]

[0083] As can be seen from Table 2, the coating compositions of Examples 1-3 have excellent wear resistance, as well as water resistance, salt resistance, acid resistance, and sulfur resistance, and are significantly better than Comparative Examples 1-5. Comparison of Example 1 with Comparative Example 1 shows that the addition of glycidyl methacrylate can significantly improve the wear resistance and water resistance, salt resistance, acid resistance, and sulfur resistance of the coating. This is because glycidyl methacrylate can increase the epoxy group content of the waterborne epoxy resin, thereby improving its curing effect and overall performance. Comparison of Example 1 with Comparative Examples 2-4 shows that the use of EM39 can better improve the overall performance of the coating than KH570, and the use of isobornyl acrylate can better improve the overall performance of the coating than methyl methacrylate or styrene. This is because EM39 has better compatibility with epoxy resin than KH570, and isobornyl acrylate, due to its bridged ring, has better adhesion and toughness than methyl methacrylate or styrene, which is beneficial to improving the overall performance of the coating. By comparing Example 1 and Comparative Example 5, it can be seen that the preparation method of the water-based epoxy resin emulsion defined in the present invention can better improve the comprehensive performance of the coating than the modification method of direct free radical copolymerization. This is because the present invention introduces a double bond after esterification modification, which can be better copolymerized with other modified monomers, which is beneficial to improving the reaction degree of the modified monomer on the epoxy resin.

[0084] Table 3

[0085]

[0086] As shown in Table 3, although Examples 1-3 of the present invention use bisphenol A epoxy resin as the raw material, the content of bisphenol A epoxy derivatives is very low, significantly below the requirements of relevant EU regulations. This is because the present invention modifies the epoxy resin, increasing its molecular chain length and reducing the content of low-molecular-weight bisphenol A epoxy derivatives. Furthermore, by introducing glycidyl methacrylate to further improve the curing efficiency, the presence and migration of low-molecular-weight bisphenol A epoxy derivatives can be significantly reduced. Comparing Example 1 with Comparative Example 1, it can be seen that glycidyl methacrylate can improve the curing efficiency and reduce the migration of bisphenol A epoxy derivatives. Comparing Example 1 with Comparative Example 5, it can be seen that the preparation method of the water-based epoxy resin emulsion defined by the present invention can increase the degree of modification of the epoxy resin and reduce the presence and migration of bisphenol A epoxy derivatives.

[0087] 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 coating composition for a two-piece can, characterized in that: The invention comprises component A and component B, wherein component B is a water-based curing agent, and the mass ratio of component A to component B is 10:(2-4); the component A comprises, by weight, 30-65 parts of a water-based modified epoxy resin emulsion, 0.1-1 part of an auxiliary agent, and 5-25 parts of water; The water-based modified epoxy resin emulsion is obtained by copolymerizing epoxy resin, acrylic acid, isobornyl acrylate, acrylate containing phosphoric acid ester, and glycidyl methacrylate through a free radical initiator, neutralizing, and dispersing. The mass ratio of the epoxy resin, acrylic acid, isobornyl acrylate, acrylate containing phosphoric acid ester, and glycidyl methacrylate is 10:1-2:1-2:1-2:1.5-3. The preparation process of the water-based modified epoxy resin emulsion is as follows: 1) Add epoxy resin, acrylic acid, polymerization inhibitor and catalyst into the reactor and heat to react to obtain epoxy ester; 2) adding a solvent to the epoxy ester obtained in step 1), and adding a mixed solution of isobornyl acrylate, phosphate-containing acrylate, glycidyl methacrylate, and a free radical initiator, keeping the mixture warm for reaction, removing the solvent, cooling the mixture, adding a neutralizing agent, and after the temperature stabilizes, adding water to disperse the mixture to obtain a water-based modified epoxy resin emulsion; The phosphate-containing acrylate is selected from 2-hydroxyethyl methacrylate phosphate and / or alkyl acrylate phosphate; The water-based curing agent is selected from at least one of polyamide, modified polyamide, fatty amine, modified alicyclic amine, aromatic amine or modified fatty amine.

2. The coating composition according to claim 1, wherein In step 1), the temperature reaction conditions are: reaction at 100-120°C for 1-4 hours; the catalyst is triphenylphosphine, and the amount used is 1-4% of the mass of the epoxy resin; the polymerization inhibitor is selected from at least one of 2,6-di-tert-butyl-p-cresol, p-hydroxyanisole, hydroquinone, and 2,4-dimethyl-6-tert-butylphenol, and the amount used is 0.5-3% of the acrylic acid.

3. The coating composition according to claim 1, wherein In step 2), the heat preservation reaction conditions are: heat preservation reaction at 110-140°C for 2-5 hours, and the cooling condition is cooling to 50-70°C; the solid content of the water-based modified epoxy resin emulsion is 30-55%; the neutralizing agent is selected from at least one of N,N-dimethylethanolamine and / or AMP-95, and the molar ratio of the neutralizer to acrylic acid is (0.8-1.1):1; the solvent is selected from at least one of an alcohol organic solvent, an ether organic solvent, an ester organic solvent, and a benzene organic solvent, and the amount of the solvent is 1.5-4 times the mass of the epoxy resin.

4. The coating composition according to claim 1, wherein The free radical initiator is selected from at least one of benzoyl peroxide, tert-butyl benzoyl peroxide, and methyl ethyl ketone peroxide, and the amount used is 1-4% of the total amount of acrylic acid, isobornyl acrylate, phosphate-containing acrylate, and glycidyl methacrylate; the epoxy resin is selected from at least one of bisphenol A epoxy resin, bisphenol F epoxy resin, aliphatic epoxy resin, and alicyclic epoxy resin.

5. The coating composition according to claim 1, wherein The auxiliary agent is selected from at least one of a dispersant, a defoamer, a leveling agent, and a thickener.

6. The method for preparing a coating composition for a two-piece can according to any one of claims 1 to 5, wherein: The steps include: (1) Preparation of Component A: Weigh the water-based modified epoxy resin emulsion, the additive, and water according to the ratio, and mix them evenly to obtain Component A; (2) Preparation of Component B: Weigh the water-based curing agent according to the ratio to obtain Component B; (3) When in use, component A and component B are mixed evenly in proportion to obtain the coating composition for two-piece cans.

7. Use of the coating composition for two-piece cans according to any one of claims 1 to 5 in two-piece can packaging coatings.

Images