A method for the preparation of ultraviolet light-cured coatings for the field of metal packaging

Abstract

The application discloses a preparation method of ultraviolet light curing paint for metal packaging field, and the ultraviolet light curing paint is composed of the following components in parts by weight: special modified acrylate 10-30 parts, polyurethane acrylate 20-50 parts, functional active monomer 10-40 parts, photoinitiator 2-5 parts, and surface additive 0.5-3 parts. The final ultraviolet light curing paint can realize thin coating, high gloss, high leveling and fullness, and has the excellent characteristics that the scratch resistance is more than 2000g when the thickness is less than 5um, and the coating of 3cm deep-drawing cans is not cracked, and the ultraviolet light curing paint is widely applicable to the fields of metal can packaging and the like with various deep-drawing and stretching requirements.

Description

Technical Field

[0001] This invention belongs to the field of ultraviolet curable coating preparation technology, and specifically relates to a method for preparing ultraviolet curable coatings for use in the field of metal packaging. Background Technology

[0002] Metal packaging is ubiquitous in our lives, widely used in food, pharmaceuticals, daily necessities, industrial products, and instruments. The coatings used in these metal packaging products are crucial, requiring not only excellent adhesion and surface finish but also stringent requirements for rust prevention, scratch resistance, wear resistance, and metal processing. This is especially true for food packaging, which uses the largest quantities of coatings; the final cured coating must meet food packaging standards. The amount of coating used in metal packaging is enormous, yet the market still largely uses traditional solvent-based coatings. These require large ovens with temperatures exceeding 150°C, requiring approximately 15 minutes for complete curing. The large amounts of VOCs emitted during this process negatively impact human health and the environment.

[0003] Therefore, developing new pollution-free and low-energy-consumption metal coatings is of great significance, and UV-curable coatings are a very important direction, as they have advantages such as being solvent-free and environmentally friendly, curing quickly, and having high production efficiency.

[0004] Chinese patent CN201710307621.8 discloses a method for preparing UV printing coating, the main components of which are a mixture of thermoplastic acrylate and epoxy acrylate. This method cannot meet the deep-drawing requirements of two-piece cans, and the energy required for coating curing is 400 mJ / cm². 2 The above also does not apply to food packaging. Although the cationic curing technology disclosed in Chinese patent CN202110498122.8 can meet the needs of food packaging, the market price of cationic raw materials is currently high, the selection is limited, the curing speed is slow, and they are brittle, which cannot meet the requirements of high-depth drawing. Summary of the Invention

[0005] To address the VOC emissions and high energy consumption issues of traditional solvent-based baking coatings, and to further improve the performance of UV-curable coatings in the application of tinplate and other metal can manufacturing, accelerating the replacement of traditional solvent-based coatings with heat-baking technology in the metal packaging field, this invention provides a method for preparing UV-curable coatings for metal packaging. This invention proposes the synthesis of modified acrylates and polyurethane acrylates, combined with active monomers, additives, photoinitiators, and other components, enabling applications in tinplate and other metal packaging, achieving new breakthroughs in curing performance, deep-drawing properties, scratch resistance, surface finish, and safety performance.

[0006] The technical solution adopted in this invention is:

[0007] A method for preparing a UV-curable coating for use in metal packaging, characterized in that the UV-curable coating is composed of the following components in parts by weight:

[0008] Special modified acrylate: 10-30 parts

[0009] Polyurethane acrylate: 20-50 parts

[0010] Functional active monomer: 10-40 parts

[0011] Photoinitiator: 2-5 parts

[0012] Surface additives: 0.5-3 parts;

[0013] The synthesis steps of the special modified acrylate are as follows: a mixture of 2-acrylic acid-2-hydroxy-3-phenoxypropyl ester, 4-hydroxybutyl acrylate and styrene is added dropwise under nitrogen protection at a temperature of 75-80℃ for 4-4.5 hours. Then, the temperature is controlled at 55-60℃, 2,6-di-tert-butyl-p-cresol is added, ethyl isocyanate acrylate is added dropwise, and the reaction is carried out for 4-4.5 hours. After washing with ethyl acetate and rotary evaporation, polyether-modified siloxane is added at 50-55℃ and reacted fully for 1-2 hours. Then, modified nano-SiO2 and polytetrafluoroethylene micro powder are added separately, and the reaction is carried out for 4-5 hours to obtain the final product.

[0014] Furthermore, the components of 2-hydroxy-3-phenoxypropyl acrylate, 4-hydroxybutyl acrylate, styrene, ethyl isocyanate acrylate, modified nano-SiO2, polytetrafluoroethylene micro powder, polyether-modified siloxane, azobisisobutyronitrile, and 2,6-di-tert-butyl-p-cresol, by mass parts, are as follows: 40-60 parts of 2-hydroxy-3-phenoxypropyl acrylate, 20-30 parts of 4-hydroxybutyl acrylate, 30-40 parts of styrene, 28-42 parts of ethyl isocyanate acrylate, 3-6 parts of modified nano-SiO2, 3-5 parts of polytetrafluoroethylene micro powder, 1-3 parts of polyether-modified siloxane, 0.5-1.5 parts of azobisisobutyronitrile, and 0.2-1.0 parts of 2,6-di-tert-butyl-p-cresol.

[0015] Furthermore, the polyurethane acrylate is composed of the following components in parts by weight:

[0016] Polyester polyol: 40-50 parts

[0017] 4,4′-Dicyclohexylmethane diisocyanate: 10-14 parts

[0018] N-(3-aminopropyl)acrylamide: 5-7 parts

[0019] 4-tert-butylcyclohexyl acrylate: 5-20 parts

[0020] Catalyst: 0.05-0.20 parts

[0021] Polymerization inhibitor: 0.1-0.5 parts;

[0022] 4-tert-butylcyclohexyl acrylate and a polymerization inhibitor were added to 4,4′-dicyclohexylmethane diisocyanate under nitrogen protection. The temperature was controlled at 35-40℃, and N-(3-aminopropyl)acrylamide was slowly added dropwise. The temperature was then raised to 60-65℃ and reacted for 3-3.5 hours. Polyester polyol was then added, and a catalyst was added. The reaction was carried out at 68-73℃ for 2 hours, and then the temperature was raised to 75-80℃ for 2 hours to obtain the polyurethane acrylate.

[0023] Further, the synthesis steps of the modified nano-SiO2 are as follows: nano-SiO2 is dispersed in γ-methacryloxypropyltrimethoxysilane in butyl acetate solvent, reacted at 78-82℃ for 3-3.5h, washed and rotary evaporated, and dried at 60-65℃ for 12h to obtain the modified nano-SiO2; wherein the modified nano-SiO2, γ-methacryloxypropyltrimethoxysilane and butyl acetate are 10-30 parts, 15-30 parts and 40-100 parts by mass, respectively.

[0024] Furthermore, the polyester polyol has a number average molecular weight of 2000 g / mol and is a copolymer containing a carbonate structure.

[0025] The polymerization inhibitor is p-hydroxyanisole;

[0026] The catalyst is one or more of dimethylaminoethyl ether, dibutyltin dilaurate, organotin, organobismuth, and pentamethyldiethylenetriamine.

[0027] Furthermore, the functional active monomer is one or more of ethoxytrimethylolpropane triacrylate, 3,3,5-trimethylcyclohexyl acrylate, cyclohexyl methacrylate, cyclotrimethylolpropane methyl acetal acrylate, 2-phenoxyethyl acrylate, 1,6-hexanediol diacrylate, and tricyclodecanediethanol diacrylate.

[0028] Furthermore, the photoinitiator is one or more of the following: polymer [2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]acetone, bimolecular 2-hydroxy-2-methylphenylacetone, bimolecular hydroxycyclohexylphenyl ketone, bimolecular methyl o-benzoylbenzoate, and polymeric methyl benzoylbenzoate.

[0029] Furthermore, the UV-curable coatings used in the metal packaging field, configured as required, have a viscosity range of 200-800 mPa·s / 25℃ and are suitable for thin-coat roller coating processes.

[0030] Furthermore, the polytetrafluoroethylene micro powder refers to micro powder with a particle size of less than 5 μm.

[0031] Compared with the prior art, the beneficial effects of the present invention are reflected in:

[0032] 1. This invention relates to UV-curable coatings for the metal packaging industry, suitable for thin-coat roller coating processes, and can achieve a curing energy of less than 300 mJ / cm² under coating conditions with a film thickness of less than 5 μm. 2 It can be cured instantly. Compared with existing light curing technology, its scratch resistance can reach 2000g. It can meet the requirement of 3cm deep drawing of two-piece cans without cracking of the coating. It has a good surface effect, low toxicity and low migration, and is suitable for a variety of metal packaging needs.

[0033] 2. The polyurethane acrylate of this invention is specially designed to have strong antioxidant and polymerization inhibition capabilities, fast thin-coat curing speed, and excellent toughness, making an important contribution to the high deep-drawing performance of UV-curable coatings.

[0034] 3. This invention is widely applicable to various fields such as metal can manufacturing and packaging that require deep drawing and stretching. Detailed Implementation

[0035] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the present invention.

[0036] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0037] The present invention will now be described in detail with reference to exemplary embodiments.

[0038] The formulations used in this invention are all commercially available conventional products, as long as they are qualified industrial products and not limited to those from manufacturers.

[0039] In this invention, the following terms have specific meanings:

[0040]

[0041]

[0042] Example 1: Preparation of Modified Nano-SiO2

[0043] Prepare the product according to the ingredients listed in the table below.

[0044]

[0045] First, add component number 3 to the flask, then add components 1 and 2 above, react at 80℃ for 3 hours, wash with ethyl acetate multiple times and rotary evaporate, and dry at 60℃ for 12 hours to obtain the desired products of 29.5g and 23g respectively.

[0046] Example 2: Preparation of Special Modified Acrylates

[0047] Synthesize resins according to the formulations in the table below.

[0048]

[0049] Components 1, 2, 3, and 10 were added to a flask. Under nitrogen protection, the reaction temperature was controlled at 75-80℃, and 9 components were added slowly dropwise for 4 hours. Then, the temperature was controlled at 55-60℃, and 8 components were added slowly dropwise for 4 hours. The isocyanate content was tested to be less than 0.1%. After washing with ethyl acetate and rotary evaporation, 7 components were added at 50℃ and reacted completely for 1 hour. Then, components 4, 5, and 6 were added respectively, and after reacting for 5 hours, the final products were 119g and 117g, respectively. 、 150g, 135g.

[0050] Example 3: Preparation of polyurethane acrylate

[0051] Synthesize resins according to the formulations in the table below.

[0052]

[0053] Add components 4 and 6 to a flask. Under nitrogen protection, add two components and control the temperature at 35-40℃. Slowly add one component dropwise, then raise the temperature to 60-65℃ and react for 3 hours. Next, add components 3 and 5 separately and react at 70℃ for 2 hours. Finally, raise the temperature to 75-80℃ and react for 2 hours to obtain 70g of product. 、 72.5g, with isocyanate content less than 0.1% as tested.

[0054] Example 4: Preparation of UV-curable coatings

[0055]

[0056]

[0057] Example 5: Test Methods and Results

[0058] Substrate: Tinplate coated with white phthalate;

[0059] Light source for curing: medium-pressure mercury lamp;

[0060] Curing energy: 300 mJ / cm 2 Formulas that do not cure well will be cured several more times so that their performance can be tested.

[0061] Application method: Roller coating, with a film thickness of 3-5µm;

[0062] Impact resistance: 1kg, 50cm;

[0063] Deep drawing: forming 3cm in diameter using a stamping press.

[0064]

[0065]

[0066] The data above shows that, compared with market samples, the self-synthesized special modified acrylate and polyurethane acrylate have outstanding performance, greatly improving scratch resistance, curing effect and deep drawing performance. Through formula adjustment, a low-energy, fast-curing UV-curing coating was successfully developed. It has low migration, meets food packaging standards, and is suitable for various metal packaging requirements.

[0067] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing a UV-curable coating for use in the field of metal packaging, characterized in that, The UV-curable coating is composed of the following components in parts by weight: Special modified acrylate: 10-30 parts Polyurethane acrylate: 20-50 parts Functional active monomer: 10-40 parts Photoinitiator: 2-5 parts Surface additives: 0.5-3 parts; The synthesis steps of the special modified acrylate are as follows: a mixture of 2-acrylate-2-hydroxy-3-phenoxypropyl ester, 4-hydroxybutyl acrylate and styrene is reacted under nitrogen protection at a temperature of 75-80℃, and azobisisobutyronitrile is slowly added dropwise for 4-4.5h. Then, the temperature is controlled at 55-60℃, 2,6-di-tert-butyl-p-cresol is added, and ethyl isocyanate is slowly added dropwise for 4-4.5h. After washing with ethyl acetate and rotary evaporation, polyether-modified siloxane is added at 45-55℃ and reacted fully for 1-2h. Then, modified nano-SiO2 and polytetrafluoroethylene micro powder are added separately, and the reaction is carried out for 4-5h to obtain the final product. The polyurethane acrylate is composed of the following components in parts by weight: Polyester polyol: 40-50 parts 4,4′-Dicyclohexylmethane diisocyanate: 10-14 parts N-(3-aminopropyl)acrylamide: 5-7 parts 4-tert-butylcyclohexyl acrylate: 5-20 parts Catalyst: 0.05-0.20 parts Polymerization inhibitor: 0.1-0.5 parts; The polyurethane acrylate: 4-tert-butylcyclohexyl acrylate and a polymerization inhibitor were added to 4,4′-dicyclohexylmethane diisocyanate under nitrogen protection. The temperature was controlled at 35-40℃, and N-(3-aminopropyl)acrylamide was slowly added dropwise. The temperature was then raised to 60-65℃ and reacted for 3-3.5 hours. Polyester polyol was then added, and a catalyst was added. The reaction was carried out at 68-73℃ for 2 hours, and then the temperature was raised to 75-80℃ for 2 hours to obtain the polyurethane acrylate. The synthesis steps of the modified nano-SiO2 are as follows: nano-SiO2 is dispersed in butyl acetate solvent of γ-methacryloxypropyltrimethoxysilane, reacted at 78-82℃ for 3-3.5h, washed and rotary evaporated, and dried at 60-65℃ for 12h to obtain the modified nano-SiO2; wherein the modified nano-SiO2, γ-methacryloxypropyltrimethoxysilane and butyl acetate are 10-30 parts, 15-30 parts and 40-100 parts by mass, respectively.

2. The method for preparing a UV-curable coating for use in the field of metal packaging as described in claim 1, characterized in that, The components of 2-hydroxy-3-phenoxypropyl acrylate, 4-hydroxybutyl acrylate, styrene, ethyl isocyanate acrylate, modified nano-SiO2, polytetrafluoroethylene micro powder, polyether-modified siloxane, azobisisobutyronitrile, and 2,6-di-tert-butyl-p-cresol, by mass parts, are as follows: 40-60 parts of 2-hydroxy-3-phenoxypropyl acrylate, 20-30 parts of 4-hydroxybutyl acrylate, 30-40 parts of styrene, 28-42 parts of ethyl isocyanate acrylate, 3-6 parts of modified nano-SiO2, 3-5 parts of polytetrafluoroethylene micro powder, 1-3 parts of polyether-modified siloxane, 0.5-1.5 parts of azobisisobutyronitrile, and 0.2-1.0 parts of 2,6-di-tert-butyl-p-cresol.

3. The method for preparing a UV-curable coating for use in the field of metal packaging as described in claim 1, characterized in that, The polyester polyol has a number average molecular weight of 2000 g / mol and is a copolymer containing a carbonate structure. The polymerization inhibitor is p-hydroxyanisole; The catalyst is one or more of dimethylaminoethyl ether, dibutyltin dilaurate, organotin, organobismuth, and pentamethyldiethylenetriamine.

4. The method for preparing a UV-curable coating for use in the field of metal packaging as described in claim 1, characterized in that, The functional active monomer is one or more of the following: ethoxytrimethylolpropane triacrylate, 3,3,5-trimethylcyclohexyl acrylate, cyclohexyl methacrylate, cyclotrimethylolpropane methyl acetal acrylate, 2-phenoxyethyl acrylate, 1,6-hexanediol diacrylate, and tricyclodecanediethanol diacrylate.

5. The method for preparing a UV-curable coating for use in the field of metal packaging as described in claim 1, characterized in that, The photoinitiator is one or more of the following: polymer [2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]acetone, bimolecular 2-hydroxy-2-methylphenylacetone, bimolecular hydroxycyclohexylphenyl ketone, bimolecular methyl o-benzoylbenzoate, and polymeric methyl benzoylbenzoate.

6. A method for preparing a UV-curable coating for use in the field of metal packaging as described in any one of claims 1 to 5, characterized in that, The UV-curable coatings used in the metal packaging field, when configured as required, have a viscosity range of 200-800 mpa.s / 25℃ and are suitable for thin-coat roller coating processes.

7. The method for preparing a UV-curable coating for use in the field of metal packaging as described in claim 1, characterized in that, The polytetrafluoroethylene micro powder mentioned refers to micro powder with a particle size of less than 5 μm.

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