A bisphenol A-free interior water-based coating and its preparation method and application

Abstract

The present invention belongs to the field of coating technology, and provides a bisphenol A-free water-based interior coating, and its preparation method and application. The water-based coating for the interior of cans is prepared from the following raw materials: an acrylate monomer, an epoxy vinyl monomer, a functional monomer, an initiator, and an organic solvent; the weight ratio of the acrylate monomer, the epoxy vinyl monomer, and the functional monomer is 1:0.1-0.2:0.05-0.1. The water-based coating prepared by the present invention combines the characteristics of acrylic resin, such as stable chemical properties, strong adhesion, and aging resistance, with the characteristics of epoxy resin, such as convenient curing and excellent mechanical properties, and has excellent anti-corrosion performance and flexibility, and excellent comprehensive performance; the coating does not contain bisphenol A, has high safety, and meets the market requirements for food packaging coatings; at the same time, the preparation process is simple, the equipment requirements are not high, and it is suitable for industrial production.

Description

Technical Field

[0001] The invention belongs to the technical field of coatings and relates to a bisphenol A-free interior water-based coating and a preparation method and application thereof. Background Art

[0002] The inner coating of metal cans, especially food and health care product cans, is mainly made of epoxy resin and organosol resin. On the one hand, the inner coating protects the metal can from corrosion by the contents, and on the other hand, it can prevent heavy metals in the metal can from migrating into food and health care products, thereby increasing the shelf life.

[0003] Currently, the two most common materials are epoxy-phenolic resin and vinyl organosol resin. These resins offer advantages in flexibility, adhesion, and oxidation resistance, making them widely used in metal can interior coatings. Epoxy-phenolic resin is primarily synthesized by reacting bisphenol A (BPA) with bisphenol-A diglycidyl ether (BADGE). Vinyl organosol resin requires the addition of bisphenol-A diglycidyl ether (BADGE) and bisphenol-F diglycidyl ether (BFDGE) during the production process to remove the hydrochloric acid produced by the curing reaction and prevent the coating from degrading. Studies have shown that bisphenol A can mimic estrogen, causing premature puberty, decreased sperm count, and prostate enlargement in animals, even at very low doses. Other studies have linked bisphenol A to heart disease and type 2 diabetes, and elevated levels of bisphenol A in the body can pose risks to liver, immune, and thyroid function. Therefore, developing products that combine excellent functionality with a bisphenol A-free structure is becoming increasingly important.

[0004] Chinese invention patent CN110511640A discloses a bisphenol A-free can coating and its preparation method. The coating is mainly composed of an epoxy-modified polyester resin, a phenolic resin, a catalyst, and a solvent. Due to the presence of a large number of ester bonds in the main chain of the epoxy-modified polyester, it provides better metal adhesion and processability, but the paint film is brittle and has poor flexibility.

[0005] Chinese invention patent CN10695467A discloses a method for preparing a self-drying epoxy-based water-soluble acrylic resin. The method uses acrylic acid monomers, methacrylic acid, and epoxy vinyl monomers with different Tgs as raw materials. By rationally designing the glass transition temperature and improving the polymerization process, the resin molecules are arranged more uniformly, thereby improving drying properties and corrosion resistance. The water-based self-drying acrylic resin is chemically modified by copolymerizing epoxy vinyl monomers into the resin's polymer chain segments, enhancing the resin's wet adhesion to the substrate, allowing the resin to better wrap pigments and further improving the resin's corrosion resistance. The epoxy groups, resulting from the chemical modification, are in the mid-range of the molecular weight, resulting in lower reactivity of the epoxy groups, thereby improving the storage stability of the resin.

[0006] The cured coating of epoxy-based water-soluble acrylic resin has the characteristics of high adhesion and excellent stability, and the raw material source is wide, so it has potential application in interior coatings for food cans and other products. However, water-based epoxy resins and water-based acrylic resins often have poor compatibility, which reduces the gloss of the coating after cold mixing, and the improvement in anti-corrosion performance is not obvious. Further improvement is still needed to achieve an improvement in overall performance. Summary of the Invention

[0007] In response to the problems existing in the prior art, the present invention provides a bisphenol A-free water-based interior coating, a preparation method thereof, and an application thereof. The water-based coating obtained by grafting epoxy groups onto an acrylic resin overcomes the problem of poor compatibility between water-based epoxy resin and water-based acrylic resin. The epoxy-grafted acrylic resin is modified by acrylic acid to further improve its corrosion resistance and flexibility. The obtained water-based coating has excellent comprehensive performance, a simple preparation process, and is easy to industrialize. It does not contain bisphenol A and has high safety, thus meeting market requirements for food packaging coatings.

[0008] The technical solutions of the present invention are as follows:

[0009] Provided is a bisphenol A-free water-based coating for the interior of cans. The water-based coating for the interior of cans is prepared from the following raw materials: an acrylate monomer, an epoxyethylene monomer, a functional monomer, an initiator, and an organic solvent; the functional monomer consists of an acrylamide monomer and acrylic acid.

[0010] Furthermore, the weight ratio of the acrylic acid ester monomer, the epoxy vinyl monomer and the functional monomer is 1:0.1-0.2:0.05-0.1.

[0011] Furthermore, the weight ratio of acrylamide monomer to acrylic acid in the functional monomer is 1:0.5-2.

[0012] Furthermore, the acrylic acid ester monomer is selected from one or more of methyl acrylate, ethyl acrylate, methyl 2-methacrylate and ethyl 2-methacrylate.

[0013] Furthermore, the epoxy vinyl monomer is selected from one or more of epoxybutene, allyl glycidyl ether, glycidyl methacrylate, and 4-vinylbenzyl glycidyl ether.

[0014] Furthermore, the acrylamide monomer is selected from one or more of methacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, methyl-acyloxyethyltrimethylammonium chloride and N-substituted acrylamide.

[0015] Furthermore, the initiator is selected from dibenzoyl peroxide and / or azobisisobutyronitrile.

[0016] Furthermore, the organic solvent is a polyol selected from one or more of ethylene glycol, glycerol, dipropylene glycol, 1,4-butanediol and 1,6-hexanediol.

[0017] The present invention also provides a method for preparing any of the above-mentioned water-based coatings for the interior of cans, which specifically comprises the following steps:

[0018] (1) adding an acrylic acid ester monomer to an organic solvent and preheating the solvent;

[0019] (2) adding epoxy vinyl monomer and initiator, and reacting at the same temperature to obtain epoxy group grafted acrylic resin solution;

[0020] (3) Adding acrylic acid and acrylamide monomers to the epoxy group grafted acrylic resin solution, and continuing to heat the reaction to obtain the product.

[0021] Furthermore, in step (1), the preheating temperature is 80-120°C.

[0022] Furthermore, in step (2), the insulation reaction time is 1-2 hours.

[0023] Furthermore, in step (3), the heating temperature is 100-150° C., and the reaction time is 30-60 min.

[0024] Preferably, the heating temperature in step (3) is higher than the insulation reaction temperature in step (2).

[0025] The present invention also provides the use of any of the above-mentioned inner water-based coatings or the inner water-based coatings prepared by any of the above-mentioned preparation methods in the packaging of food, health products, medicines or cosmetics.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) The present invention overcomes the problem of poor compatibility between water-based epoxy resin and water-based acrylic resin by grafting epoxy groups onto acrylic resin to obtain a water-based coating. At the same time, it combines the characteristics of acrylic resin such as stable chemical properties, strong adhesion, and aging resistance with the characteristics of epoxy resin such as convenient curing and excellent mechanical properties, and has excellent comprehensive performance.

[0028] (2) The epoxy grafted acrylic resin was further modified by synergistically using acrylamide monomers and acrylic acid, which were functional monomers with amide bonds and carboxyl groups, and its corrosion resistance and flexibility were further improved.

[0029] (3) The water-based coating raw materials of the present invention are free of formaldehyde or free phenol migration, do not contain bisphenol A, are highly safe, and meet the market requirements for food packaging coatings; at the same time, the preparation process is simple, the equipment requirements are not high, and it is suitable for industrial production. DETAILED DESCRIPTION

[0030] The following non-limiting examples are provided to enable those skilled in the art to more fully understand the present invention, but are not intended to limit the present invention in any way. The following contents are merely illustrative of the scope of the present invention, and those skilled in the art may make various changes and modifications to the present invention based on the disclosed contents, which should also fall within the scope of the present invention.

[0031] Example 1

[0032] The invention discloses a bisphenol A-free water-based coating for the inner layer of an easy-pull can. The coating is prepared from raw materials of methyl acrylate (1 part by weight), epoxybutene (0.1 part by weight), and functional monomers of 2-acrylamido-2-methylpropanesulfonic acid (0.05 part by weight) and acrylic acid (0.05 part by weight).

[0033] The preparation method is as follows:

[0034] (1) Add methyl acrylate to 500 mL of ethylene glycol and preheat to 100°C for 10 minutes;

[0035] (2) adding epoxybutene and initiator (dibenzoyl peroxide and azobisisobutyronitrile, 0.01 parts by weight each), and heating at 100° C. for 2 h to obtain an epoxy group-grafted acrylic resin solution;

[0036] (3) Add acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid to the epoxy group grafted acrylic resin solution, continue heating to 120° C. and react for 40 minutes to obtain the product.

[0037] Example 2

[0038] The invention discloses a bisphenol A-free water-based coating for the inner coating of an easy-pull can, which is prepared from raw materials of ethyl acrylate (1 part by weight), glycidyl methacrylate (0.2 part by weight), and functional monomers of methacrylamide (0.025 part by weight) and acrylic acid (0.025 part by weight).

[0039] The preparation method is as follows:

[0040] (1) Ethyl acrylate was added to 500 mL of a mixed solvent of ethylene glycol and 1,4-butanediol (1:1 v / v), and the mixture was preheated to 80°C for 10 min.

[0041] (2) adding glycidyl methacrylate and an initiator (0.01 parts by weight each of dibenzoyl peroxide and azobisisobutyronitrile), and reacting at 80° C. for 2 h to obtain an epoxy group-grafted acrylic resin solution;

[0042] (3) Add acrylic acid and methacrylamide to the epoxy group grafted acrylic resin solution, continue heating to 120°C and react for 40 minutes to obtain the product.

[0043] Example 3

[0044] The invention discloses a bisphenol A-free water-based coating for the inner coating of an easy-pull can, which is prepared from raw materials of 2-methyl methacrylate (1 part by weight), allyl glycidyl ether (0.15 part by weight), and functional monomers of N-substituted acrylamide (0.06 part by weight) and acrylic acid (0.04 part by weight).

[0045] The preparation method is as follows:

[0046] (1) Add 2-methyl methacrylate to 500 mL of glycerol and preheat to 120°C for 10 min;

[0047] (2) adding allyl glycidyl ether and an initiator (0.02 parts by weight of dibenzoyl peroxide and 0.01 parts by weight of azobisisobutyronitrile), and reacting at 120° C. for 1 hour to obtain an epoxy group-grafted acrylic resin solution;

[0048] (3) Add acrylic acid and N-substituted acrylamide to the epoxy group grafted acrylic resin solution, continue heating to 150° C. and react for 30 minutes to obtain the product.

[0049] Example 4

[0050] The invention discloses a bisphenol A-free water-based coating for the interior of cans, which is prepared from raw materials of 2-methyl methacrylate (1 part by weight), 4-vinylbenzyl glycidyl ether (0.2 part by weight), and functional monomers of methyl-acyloxyethyl trimethylammonium chloride (0.04 part by weight) and acrylic acid (0.06 part by weight).

[0051] The preparation method is as follows:

[0052] (1) Methyl 2-methacrylate was added to 500 mL of a mixed solvent of ethylene glycol and 1,6-ethylene glycol (1:1 v / v), and the mixture was preheated to 100 °C for 10 min.

[0053] (2) adding 4-vinylbenzyl glycidyl ether and an initiator (0.01 parts by weight of dibenzoyl peroxide and 0.02 parts by weight of azobisisobutyronitrile), and reacting at 100° C. for 2 h to obtain an epoxy group-grafted acrylic resin solution;

[0054] (3) Add acrylic acid and methyl-acyloxyethyl trimethylammonium chloride to the epoxy group grafted acrylic resin solution, continue to heat to 100 ° C and react for 50 minutes to obtain.

[0055] Comparative Example 1

[0056] Compared with Example 1, the only difference is that the functional monomer is 0.1 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid.

[0057] Comparative Example 2

[0058] Compared with Example 1, the only difference is that the functional monomer is 0.1 parts by weight of acrylic acid.

[0059] Comparative Example 3

[0060] Compared with Example 1, the only difference is that the functional monomers are 0.08 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid and 0.02 parts by weight of acrylic acid.

[0061] Comparative Example 4

[0062] Compared with Example 1, the only difference is that the functional monomers are 0.02 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid and 0.08 parts by weight of acrylic acid.

[0063] Comparative Example 5

[0064] Compared with Example 1, the only difference is that the raw material epoxybutene is 0.05 parts by weight.

[0065] Comparative Example 6

[0066] Compared with Example 1, the only difference is that the raw material epoxybutene is 0.25 parts by weight.

[0067] Comparative Example 7

[0068] Compared with Example 1, the only difference is that the preparation method is different, as follows:

[0069] (1) Add methyl acrylate and epoxybutene to 500 mL of ethylene glycol and preheat to 100 °C for 10 min;

[0070] (2) Acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid and initiator (0.01 parts by weight of dibenzoyl peroxide and azobisisobutyronitrile) were added, and the mixture was heated at 100° C. for 2 hours to obtain the product.

[0071] Comparative Example 8

[0072] Compared with Example 1, the only difference is that the preparation method is different, as follows:

[0073] (1) Add methyl acrylate to 500 mL of ethylene glycol and preheat to 100°C for 10 minutes;

[0074] (2) adding epoxybutene and initiator (dibenzoyl peroxide and azobisisobutyronitrile, 0.01 parts by weight each), and heating at 100° C. for 2 h to obtain an epoxy group-grafted acrylic resin solution;

[0075] (3) Add acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid to the epoxy group grafted acrylic resin solution, continue heating to 100° C. and react for 40 minutes to obtain the product.

[0076] Performance Testing

[0077] (1) Coating preparation: An equal amount of the coating prepared in the comparative example of the above embodiment was applied to a tinplate substrate and baked at 180° C. for 5 min to completely cure. The dry film thickness was about 10 μm.

[0078] (2) The performance test methods are shown in Table 1:

[0079] Table 1

[0080]

[0081]

[0082] The results are shown in Tables 2-4.

[0083] Table 2 Film forming performance results

[0084] Surface drying time (min) Drying time (h) Surface condition Gloss (60°) Example 1 10 2 No bubbles or fish eyes 95 Example 2 12 2.5 No bubbles or fish eyes 92 Example 3 14 3 No bubbles or fish eyes 94 Example 4 10 2 No bubbles or fish eyes 90 Comparative Example 1 18 3 No bubbles or fish eyes 82 Comparative Example 2 19 3 No bubbles or fish eyes 85 Comparative Example 3 15 3.5 No bubbles or fish eyes 88 Comparative Example 4 16 3.5 No bubbles or fish eyes 89 Comparative Example 5 8 1.83 No bubbles or fish eyes 81 Comparative Example 6 15 3.25 No bubbles or fish eyes 90 Comparative Example 7 20 3.5 There are bubbles and fish eyes 80 Comparative Example 8 23 4 There are bubbles and fish eyes 82

[0085] It can be seen from the above table:

[0086] During the preparation of the water-based coating of the present invention, the functional monomers in the raw materials, especially the type of monomers, have a significant impact on the drying time and film glossiness. The use of acrylamide monomers and acrylic acid in synergy can shorten the drying time of the coating film and also improve the surface gloss. The ratio of the two types of functional monomers has a certain influence on the film-forming performance, but it is not significant.

[0087] In addition, the preparation process also has a great influence on the film-forming properties of the coating. For example, the coating obtained by one-time polymerization in Comparative Example 7 has poor film-forming properties and a prolonged drying time. An excessively long drying process can easily cause the coating to pick up dust and impurities during the drying process, affecting the appearance and performance, thereby causing bubbles and fisheyes to appear on the surface of the paint film, and a significant decrease in glossiness. At the same time, it was unexpectedly discovered that the amount of epoxy vinyl monomer used in Comparative Example 5 was too small, and the drying time was short, which could easily cause the paint film to be rough and affect leveling.

[0088] Table 3 Mechanical properties results

[0089] Adhesion (grade) Pencil hardness Impact resistance (Kg·cm) Flexibility (mm) Example 1 0 2H 58.4 1 Example 2 1 2H 54.2 1 Example 3 1 2H 56.9 1 Example 4 1 3H 53.5 1 Comparative Example 1 2 2H 51.3 3 Comparative Example 2 3 2H 53.4 2 Comparative Example 3 1 2H 52.6 2 Comparative Example 4 1 2H 51.9 3 Comparative Example 5 2 2H 49.2 2 Comparative Example 6 2 2H 50.0 2 Comparative Example 7 3 HB 46.3 3 Comparative Example 8 3 HB 44.8 3

[0090] It can be seen from the above table that: in the preparation process of the water-based coating of the present invention, the type and amount of functional monomers in the raw materials have little effect on the hardness and impact resistance of the coating after film formation, but the adhesion and flexibility are significantly reduced; the preparation process has a great influence on the hardness, impact resistance, adhesion and flexibility, which may be due to the poor uniformity of the coating in the solvent caused by the one-time polymerization and the lack of secondary temperature polymerization.

[0091] Table 4 Anticorrosion performance results

[0092]

[0093]

[0094] It can be seen from the above table that the water-based coating prepared by the present invention has acid and alkali resistance, salt water resistance and boiling resistance, and has high stability; and does not contain bisphenol A, and is suitable for various environmental conditions, such as food, health products, and special medicines or preparations.

[0095] In general, the present invention improves functional monomers, especially adopts the synergistic effect of acrylamide monomers and acrylic acid to modify the waterborne epoxy grafted acrylic resin, and optimizes the raw material dosage and preparation process. The obtained waterborne coating has good film-forming properties, excellent mechanical properties, better anti-corrosion properties, and excellent comprehensive performance.

[0096] 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 bisphenol A-free interior water-based coating, characterized in that: The interior water-based coating is prepared from the following raw materials: acrylate monomers, epoxy vinyl monomers, functional monomers, an initiator, and an organic solvent; the functional monomers are composed of acrylamide monomers and acrylic acid; the weight ratio of the acrylate monomers, epoxy vinyl monomers, and functional monomers is 1:0.1-0.2:0.05-0.13; the weight ratio of the acrylamide monomers to acrylic acid in the functional monomers is 1:0.5-2; The method for preparing the interior water-based coating comprises the following steps: (1) Adding acrylic acid ester monomers to an organic solvent for preheating; (2) adding epoxy vinyl monomer and initiator, and reacting at a temperature of 100°C to obtain epoxy group grafted acrylic resin solution; (3) Add acrylic acid and acrylamide monomers to the epoxy group grafted acrylic resin solution and continue to heat the reaction to obtain: In step (1), the preheating temperature is 80-120°C; in step (2), the insulation reaction time is 1-2 hours; in step (3), the heating temperature is 120-150°C, and the reaction time is 30-60 minutes.

2. The interior water-based paint according to claim 1, characterized in that: The acrylic acid ester monomer is selected from one or more of methyl acrylate, ethyl acrylate, methyl 2-methacrylate and ethyl 2-methacrylate.

3. The interior water-based paint according to claim 1, characterized in that: The epoxyethylene monomer is selected from one or more of epoxybutene, allyl glycidyl ether, glycidyl methacrylate, and 4-vinylbenzyl glycidyl ether.

4. The interior water-based paint according to claim 1, characterized in that: The acrylamide monomer is selected from one or more of methacrylamide, 2-acrylamido-2-methylpropanesulfonic acid and N-substituted acrylamide.

5. The interior water-based paint according to claim 1, characterized in that: The initiator is selected from dibenzoyl peroxide and / or azobisisobutyronitrile; the organic solvent is a polyol selected from one or more of ethylene glycol, glycerol, dipropylene glycol, 1,4-butanediol and 1,6-hexanediol.

6. A method for preparing an interior water-based coating according to any one of claims 1 to 5, characterized in that: The following steps are involved: (1) Adding acrylic acid ester monomers to an organic solvent for preheating; (2) adding epoxy vinyl monomer and initiator, and reacting at the same temperature to obtain epoxy group grafted acrylic resin solution; (3) Add acrylic acid and acrylamide monomers to the epoxy group grafted acrylic resin solution and continue to heat the reaction to obtain the product.

7. The preparation method according to claim 6, characterized in that In step (1), the preheating temperature is 80-120°C; in step (2), the insulation reaction time is 1-2 hours; in step (3), the heating temperature is 120-150°C, and the reaction time is 30-60 minutes.

8. Use of the interior water-based coating according to any one of claims 1 to 5 or the interior water-based coating prepared by the preparation method according to claim 6 or 7 in the packaging of food, health products, medicines or cosmetics.

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