Environmentally friendly water-based varnish for packaging printing and preparation method thereof

Abstract

The present invention relates to the field of printing and packaging technology, and more particularly to an environmentally friendly water-based varnish for packaging printing and a preparation method thereof. The environmentally friendly water-based varnish for packaging printing of the present invention comprises the following raw materials in parts by weight: 50-70 parts of a water-soluble acrylic resin, 30-40 parts of a styrene-acrylic emulsion with a low benzene content, 20-30 parts of a styrene-acrylic emulsion with a high benzene content, 7-10 parts of a graphene-polyethylene wax emulsion, 0.1-0.2 parts of a defoamer, 0.1-0.3 parts of a leveling agent, 0.2-0.4 parts of a dispersant, and 15-20 parts of deionized water. By adding quantum-grade graphene and two styrene-acrylic emulsions with different contents, the environmentally friendly water-based varnish for packaging printing of the present invention has excellent abrasion resistance and gloss after film formation.

Description

Technical Field

[0001] The present invention relates to the technical field of printing and packaging, and in particular to an environmentally friendly water-based varnish for packaging printing and a preparation method thereof. Background Art

[0002] The printing industry typically uses varnishes to improve the appearance of paper products and enhance their water and friction resistance. Currently, traditional solvent-based varnishes are being gradually replaced by environmentally friendly water-based varnishes and ultraviolet (UV)-curing varnishes. Water-based varnishes primarily consist of a base, additives, and solvent. The base is typically a water-based resin, whose properties directly impact the varnish's gloss, friction resistance, water resistance, drying speed, and other parameters. Additives, which improve the varnish's performance, primarily include defoamers, leveling agents, wax additives, and thickeners. The solvent is typically water. Water-based varnishes offer advantages such as high transparency, good abrasion resistance, rapid film formation, non-toxicity, odorlessness, low cost, and strong anti-curling properties. Furthermore, they comply with environmental requirements, making them a promising varnish variety.

[0003] The wear resistance of water-based varnishes is primarily provided by the wax emulsion. During film formation, the wax floats to the top layer of the coating, where it is encapsulated within the varnish resin and partially exposed. When external forces act on the surface of the coating, the slippage of the protective wax layer mitigates damage. However, friction can cause wax emulsion particles to fall off during use, ultimately reducing the wear resistance of the water-based varnish. However, adding too much wax emulsion can also reduce gloss. Because traditional water-based varnishes lack ideal wear resistance, while maintaining good wear resistance, they also suffer from poor gloss, typically ranging from 55-75, resulting in subpar performance in the final printed product.

[0004] Patent document CN202210550717.8 discloses an environmentally friendly water-based varnish composition that improves gloss and friction resistance by adding a high-density polyethylene wax emulsion to the water-based varnish formula. The high-density polyethylene wax emulsion comprises a high-density polyethylene wax emulsion A and a high-density polyethylene wax emulsion B in a weight ratio of 1:(0.3-0.5); the pH value of the high-density polyethylene wax emulsion A is 8.5, the D90 is 0.2-1.0μm, and the D50 is 0.3-0.6μm; the pH value of the high-density polyethylene wax emulsion B is 9, the D90 is 0.2-2.0μm, and the D50 is 0.5-1.0μm. However, the polyethylene wax emulsion used in this invention has a small particle size. Although the high density helps to improve the wear resistance of the varnish after film formation, the improvement capacity is limited. In addition, the high-density polyethylene wax emulsion B used in this invention contains particles with a particle size of more than 1μm, which will reduce the gloss of the varnish after film formation to a certain extent. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide an environmentally friendly water-based varnish for packaging printing and a preparation method thereof, so as to solve the problem of poor gloss and wear resistance of water-based varnish.

[0006] Based on the above purpose, the present invention provides an environmentally friendly water-based varnish for packaging printing, comprising the following raw materials in parts by weight: 50-70 parts of a water-soluble acrylic resin, 30-40 parts of a styrene-acrylic emulsion with a low benzene content, 20-30 parts of a styrene-acrylic emulsion with a high benzene content, 7-10 parts of a graphene-polyethylene wax emulsion, 0.1-0.2 parts of a defoaming agent, 0.1-0.3 parts of a leveling agent, 0.2-0.4 parts of a dispersant, and 15-20 parts of deionized water;

[0007] The preparation steps of the graphene-polyethylene wax emulsion are as follows:

[0008] S1: Add vinyltrimethoxysilane and ethanol to deionized water and disperse them evenly. Then add ammonia to adjust the pH to 9-11. Then add graphene quantum dots and react at 55-65°C for 2-6 hours. Then filter, wash and dry to obtain vinylized graphene quantum dots.

[0009] Preferably, the mass ratio of vinyltrimethoxysilane, ethanol, deionized water and graphene quantum dots in S1 is 0.5-1:10-20:20-40:5-15.

[0010] S2: Under a nitrogen atmosphere, polyethylene wax is added to n-butanol and heated until fully dissolved. Then, olefin-modified graphene quantum dots are added and stirred at 80-120°C for 10-20 minutes. Then, an initiator is added and the mixture is reacted at 150-160°C for 1-2 hours. The mixture is washed, filtered, and dried to obtain graphene-polyethylene wax.

[0011] Preferably, the mass ratio of polyethylene wax, olefinic graphene quantum dots, n-butanol and initiator in S2 is 20-40:1-5:2-6:0.2-0.4.

[0012] Preferably, the initiator is a mixture of dibenzoyl peroxide and di-tert-butyl peroxide in a mass ratio of 1:1.

[0013] S3: adding graphene-polyethylene wax to deionized water, heating until fully dissolved, then adding an emulsifier, emulsifying at 80-90°C for 40-60 minutes, adjusting the pH to 7-8, and obtaining a graphene-polyethylene wax emulsion with a particle size D50 of 0.5-0.8 μm;

[0014] Preferably, the mass ratio of graphene-polyethylene wax, emulsifier and deionized water in S3 is 20-25:1-2:28-34.

[0015] Preferably, the emulsifier is a mixture of Tween-60 and Span-80 in a mass ratio of 4-8:1-3.

[0016] The high-benzene content styrene acrylic emulsion is prepared from styrene monomer, butyl acrylate monomer and methacrylic acid monomer, wherein the weight percentage of styrene monomer accounts for 50%-60% of the total monomer amount, and the weight percentage of methacrylic acid monomer accounts for 2%-4% of the total monomer amount;

[0017] Preferably, the preparation steps of the styrene-acrylic emulsion with high benzene content are as follows:

[0018] S21: 0.6-1.2 parts of an emulsifier, 0.4-1.0 parts of sodium bicarbonate, and 45-70 parts of water are mixed and stirred to obtain a preformed liquid;

[0019] S22: mixing styrene monomer, butyl acrylate monomer, methacrylic acid monomer and chain transfer agent, and dispersing them uniformly to obtain a monomer mixture;

[0020] S23: Add 10%-25% of the monomer mixture to the preformed solution, heat to 70-85°C, then add 0.2-0.5 parts of the initiator and mix. When the mixture turns light blue, keep it warm for 20-40 minutes to obtain the seed emulsion;

[0021] S24: taking the remaining monomer mixture and adding it dropwise to the seed emulsion, reacting at 80-90° C. for 40-80 minutes, then adding ammonia water dropwise, and adjusting the pH to 6-8 to obtain a styrene-acrylic emulsion with a high benzene content.

[0022] Preferably, the weight percentage of the styrene monomer in the total monomer amount is 50%-60%, the weight percentage of the methacrylic acid monomer in the total monomer amount is 2%-4%, and the weight percentage of the chain transfer agent monomer in the total monomer amount is 0.1%-0.5%.

[0023] The low-benzene-content styrene-acrylic emulsion is prepared from styrene monomer, butyl acrylate monomer and methacrylic acid monomer, wherein the weight percentage of styrene monomer accounts for 20%-30% of the total monomer amount, and the weight percentage of methacrylic acid monomer accounts for 2%-4% of the total monomer amount;

[0024] Preferably, the preparation steps of the styrene-acrylic emulsion with low benzene content are as follows:

[0025] S31: 0.6-1.2 parts of an emulsifier, 0.4-1.0 parts of sodium bicarbonate, and 45-70 parts of water are mixed and stirred to obtain a preformed liquid;

[0026] S32: mixing styrene monomer, butyl acrylate monomer, methacrylic acid monomer and chain transfer agent, and dispersing them uniformly to obtain a monomer mixture;

[0027] S33: Add 10%-25% of the monomer mixture to the preformed solution, heat to 70-85°C, then add 0.2-0.5 parts of the initiator and mix. When the mixture turns light blue, keep it warm for 20-40 minutes to obtain the seed emulsion;

[0028] S34: taking the remaining monomer mixture and adding it dropwise to the seed emulsion, reacting at 80-90° C. for 40-80 minutes, then adding ammonia water dropwise, and adjusting the pH to 6-8 to obtain a styrene-acrylic emulsion with a low benzene content.

[0029] Preferably, the weight percentage of the styrene monomer in the total monomer amount is 20%-30%, the weight percentage of the methacrylic acid monomer in the total monomer amount is 2%-4%, and the weight percentage of the chain transfer agent monomer in the total monomer amount is 0.1%-0.5%.

[0030] Preferably, the chain transfer agent is dodecanethiol.

[0031] Preferably, the emulsifier is a compound of sodium lauryl sulfate and octylphenol polyoxyethylene ether.

[0032] Preferably, the initiator is one of ammonium persulfate and potassium persulfate.

[0033] Preferably, the defoaming agent is one of polydimethylsiloxane, dimethylsiloxane, and higher fatty acid amide.

[0034] Preferably, the leveling agent is one of polydimethylsiloxane, polymethylphenylsiloxane, polyether polyester modified organic siloxane, and alkylhydroxy modified organic siloxane.

[0035] Preferably, the dispersant is one of calcium stearate, magnesium stearate, zinc stearate and barium stearate.

[0036] Furthermore, the present invention also provides a method for preparing an environmentally friendly water-based varnish for packaging printing, comprising the following preparation steps:

[0037] (1) adding water-soluble acrylic resin to deionized water and mixing uniformly;

[0038] (2) adding a defoamer, a leveling agent and a dispersant to the mixture in step (1) and mixing them uniformly;

[0039] (3) adding a styrene-acrylic emulsion with a low benzene content, a styrene-acrylic emulsion with a high benzene content, and a graphene-polyethylene wax emulsion to the mixture in step (2), mixing the mixture evenly, and filtering the mixture to obtain an environmentally friendly water-based varnish for packaging printing.

[0040] Beneficial effects of the present invention:

[0041] (1) The environmentally friendly water-based varnish for packaging printing of the present invention adds quantum-level graphene to the raw materials. On the one hand, it is beneficial to improve the wear resistance of the environmentally friendly water-based varnish for packaging printing after film formation. On the other hand, due to its small particle size, it will not affect the glossiness after film formation.

[0042] (2) The environmentally friendly water-based varnish for packaging printing of the present invention is prepared by adding two styrene acrylic emulsions with different contents into the raw materials. The high and low content styrene acrylic emulsions are matched with each other, so that the environmentally friendly water-based varnish has better film-forming properties, which is beneficial to improving the glossiness after film formation.

[0043] (3) The environmentally friendly water-based varnish for packaging printing of the present invention has excellent wear resistance and glossiness after film formation, can withstand 900 frictions without fading, and the glossiness can reach 94, which can meet the performance requirements of daily packaging printing for water-based varnish. DETAILED DESCRIPTION

[0044] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to specific embodiments.

[0045] The sources or properties of the raw materials used in the examples and comparative examples of the present invention are as follows:

[0046] Polyethylene wax: purchased from Guangzhou Haocheng New Materials Co., Ltd., specifically high-density polyethylene wax.

[0047] Example 1: An environmentally friendly water-based varnish for packaging printing, the specific preparation steps are as follows:

[0048] (1) Add 0.5 g of vinyltrimethoxysilane and 10 g of ethanol to 20 g of deionized water, disperse them evenly, then add ammonia water to adjust the pH to 9, then add 5 g of graphene quantum dots, react at 55 ° C for 2 h, filter, wash, and dry to obtain vinylized graphene quantum dots;

[0049] (2) Under a nitrogen atmosphere, 20 g of polyethylene wax was added to 2 g of n-butanol and heated until fully dissolved. Then, 1 g of olefin-modified graphene quantum dots was added and stirred at 80°C for 10 min. Then, a mixture of 0.1 g of dibenzoyl peroxide and 0.1 g of di-tert-butyl peroxide was added and reacted at 150°C for 1 h. The mixture was washed, filtered, and dried to obtain graphene-polyethylene wax.

[0050] (3) 20 g of graphene-polyethylene wax was added to 28 g of deionized water, heated until fully dissolved, and then a mixture of 0.8 g of Tween-60 and 0.2 g of Span-80 was added. The mixture was emulsified at 80 ° C for 40 min and the pH was adjusted to 7 to obtain a graphene-polyethylene wax emulsion with a particle size D50 of 0.65 μm.

[0051] (4) 0.6 g of a mixture of sodium lauryl sulfate and octylphenol polyoxyethylene ether, 0.4 g of sodium bicarbonate, and 45 g of water were mixed and stirred to obtain a preformed liquid;

[0052] (5) 50 g of styrene monomer, 36 g of butyl acrylate monomer, 2 g of methacrylic acid monomer and 0.1 g of dodecanethiol were mixed and dispersed uniformly to obtain a monomer mixture;

[0053] (6) Add 10% of the monomer mixture to the preformed solution, heat to 70°C, and then add 0.2g of ammonium persulfate and mix. When the mixture turns light blue, keep it warm for 20 minutes to obtain the seed emulsion;

[0054] (7) The remaining monomer mixture was added dropwise to the seed emulsion, reacted at 80°C for 40 min, and then ammonia was added dropwise, and the pH was adjusted to 6 to obtain a styrene-acrylic emulsion with a high benzene content;

[0055] (8) 0.6 g of a mixture of sodium lauryl sulfate and octylphenol polyoxyethylene ether, 0.4 g of sodium bicarbonate, and 45 g of water were mixed and stirred to obtain a preformed liquid;

[0056] (9) 20 g of styrene monomer, 66 g of butyl acrylate monomer, 2 g of methacrylic acid monomer, and 0.1 g of dodecanethiol were mixed and dispersed uniformly to obtain a monomer mixture;

[0057] (10) 10% of the monomer mixture was added to the preformed solution, heated to 70°C, and 0.2 g of ammonium persulfate was added and mixed. When the mixture turned light blue, the mixture was kept warm for 20 minutes to obtain the seed emulsion.

[0058] (11) The remaining monomer mixture was added dropwise to the seed emulsion, reacted at 80°C for 40 min, and then ammonia was added dropwise, and the pH was adjusted to 6 to obtain a styrene-acrylic emulsion with a high benzene content;

[0059] (12) Add 50 g of water-soluble acrylic resin to 15 g of deionized water and mix well;

[0060] (13) Add 0.1 g of dimethylsiloxane, 0.1 g of polydimethylsiloxane, and 0.2 g of magnesium stearate to the mixture of step (12) and stir evenly;

[0061] (14) 30 g of styrene-acrylic emulsion with low benzene content, 20 g of styrene-acrylic emulsion with high benzene content and 7 g of graphene-polyethylene wax emulsion were added to the mixture in step (13) and mixed evenly, and filtered to obtain an environmentally friendly water-based varnish for packaging printing.

[0062] Example 2: An environmentally friendly water-based varnish for packaging printing, the specific preparation steps are as follows:

[0063] (1) Add 0.8 g of vinyltrimethoxysilane and 15 g of ethanol to 30 g of deionized water and disperse them evenly. Then add ammonia water to adjust the pH to 10, and then add 10 g of graphene quantum dots. React at 60 ° C for 4 h, filter, wash, and dry to obtain vinylized graphene quantum dots.

[0064] (2) Under a nitrogen atmosphere, 30 g of polyethylene wax was added to 4 g of n-butanol and heated until fully dissolved. Then, 3 g of olefin-modified graphene quantum dots were added and stirred at 100 ° C for 15 min. Then, a mixture of 0.15 g of dibenzoyl peroxide and 0.15 g of di-tert-butyl peroxide was added and reacted at 155 ° C for 1.5 h. The mixture was washed, filtered, and dried to obtain graphene-polyethylene wax;

[0065] (3) 23 g of graphene-polyethylene wax was added to 31 g of deionized water, heated until fully dissolved, and then a mixture of 1.2 g of Tween-60 and 0.3 g of Span-80 was added. The mixture was emulsified at 85° C. for 50 min and the pH was adjusted to 8 to obtain a graphene-polyethylene wax emulsion with a particle size D50 of 0.66 μm.

[0066] (4) 0.9 g of a mixture of sodium lauryl sulfate and octylphenol polyoxyethylene ether, 0.7 g of sodium bicarbonate, and 60 g of water were mixed and stirred to obtain a preformed liquid;

[0067] (5) 55 g of styrene monomer, 42 g of butyl acrylate monomer, 3 g of methacrylic acid monomer and 0.1-0.5 g of dodecanethiol were mixed and dispersed uniformly to obtain a monomer mixture;

[0068] (6) Add 18% of the monomer mixture to the preformed solution, heat to 80°C, and then add 0.4g of ammonium persulfate and mix. When the mixture turns light blue, keep it warm for 30 minutes to obtain the seed emulsion;

[0069] (7) The remaining monomer mixture was added dropwise to the seed emulsion, reacted at 85°C for 60 min, and then ammonia was added dropwise, and the pH was adjusted to 7 to obtain a styrene-acrylic emulsion with a high benzene content;

[0070] (8) 0.9 g of a mixture of sodium lauryl sulfate and octylphenol polyoxyethylene ether, 0.7 g of sodium bicarbonate, and 60 g of water were mixed and stirred to obtain a preformed liquid;

[0071] (9) 25 g of styrene monomer, 72 g of butyl acrylate monomer, 3 g of methacrylic acid monomer, and 0.3 g of dodecanethiol were mixed and dispersed uniformly to obtain a monomer mixture;

[0072] (10) 18% of the monomer mixture was added to the preformed solution, heated to 80°C, and then 0.3 g of ammonium persulfate was added and mixed. When the mixture turned light blue, the mixture was kept warm for 30 minutes to obtain the seed emulsion;

[0073] (11) The remaining monomer mixture was added dropwise to the seed emulsion, reacted at 85°C for 60 min, and then ammonia was added dropwise, and the pH was adjusted to 7 to obtain a styrene-acrylic emulsion with a high benzene content;

[0074] (12) Add 60 g of water-soluble acrylic resin to 18 g of deionized water and mix well;

[0075] (13) Add 0.15 g of dimethylsiloxane, 0.23 g of polydimethylsiloxane, and 0.3 g of magnesium stearate to the mixture of step (12) and stir evenly;

[0076] (14) 35 g of styrene-acrylic emulsion with low benzene content, 25 g of styrene-acrylic emulsion with high benzene content, and 8 g of graphene-polyethylene wax emulsion were added to the mixture in step (13) and mixed evenly, and filtered to obtain an environmentally friendly water-based varnish for packaging printing.

[0077] Example 3: An environmentally friendly water-based varnish for packaging printing, the specific preparation steps are as follows:

[0078] (1) 1 g of vinyltrimethoxysilane and 20 g of ethanol were added to 40 g of deionized water and dispersed uniformly. Ammonia was then added to adjust the pH to 11. 15 g of graphene quantum dots were then added and reacted at 65 ° C for 6 h. The mixture was filtered, washed, and dried to obtain vinyl-based graphene quantum dots.

[0079] (2) Under a nitrogen atmosphere, 40 g of polyethylene wax was added to 6 g of n-butanol and heated until fully dissolved. Then, 5 g of olefin-modified graphene quantum dots were added and stirred at 120 ° C for 20 min. Then, a mixture of 0.2 g of dibenzoyl peroxide and 0.2 g of di-tert-butyl peroxide was added and reacted at 160 ° C for 2 h. The mixture was washed, filtered, and dried to obtain graphene-polyethylene wax;

[0080] (3) 25 g of graphene-polyethylene wax was added to 34 g of deionized water, heated until fully dissolved, and then a mixture of 1.6 g of Tween-60 and 0.4 g of Span-80 was added. The mixture was emulsified at 90 ° C for 60 min and the pH was adjusted to 8 to obtain a graphene-polyethylene wax emulsion with a particle size D50 of 0.65 μm.

[0081] (4) 1.2 g of a mixture of sodium lauryl sulfate and octylphenol polyoxyethylene ether, 1.0 g of sodium bicarbonate, and 70 g of water were mixed and stirred to obtain a preformed liquid;

[0082] (5) 60 g of styrene monomer, 48 g of butyl acrylate monomer, 4 g of methacrylic acid monomer and 0.1-0.5 g of dodecanethiol were mixed and dispersed uniformly to obtain a monomer mixture;

[0083] (6) Add 25% of the monomer mixture to the preformed solution, heat to 85°C, and then add 0.5g of ammonium persulfate and mix. When the mixture turns light blue, keep it warm for 40 minutes to obtain the seed emulsion;

[0084] (7) The remaining monomer mixture was added dropwise to the seed emulsion, reacted at 90°C for 80 min, and then ammonia was added dropwise, and the pH was adjusted to 8 to obtain a styrene-acrylic emulsion with a high benzene content;

[0085] (8) 1.2 g of a mixture of sodium lauryl sulfate and octylphenol polyoxyethylene ether, 1.0 g of sodium bicarbonate, and 70 g of water were mixed and stirred to obtain a preformed solution;

[0086] (9) 30 g of styrene monomer, 78 g of butyl acrylate monomer, 4 g of methacrylic acid monomer, and 0.5 g of dodecanethiol were mixed and dispersed uniformly to obtain a monomer mixture;

[0087] (10) Add 25% of the monomer mixture to the preformed solution, heat to 85°C, and then add 0.5g of ammonium persulfate and mix. When the mixture turns light blue, keep it warm for 40 minutes to obtain the seed emulsion;

[0088] (11) The remaining monomer mixture was added dropwise to the seed emulsion, reacted at 90°C for 80 min, and then ammonia was added dropwise, and the pH was adjusted to 8 to obtain a styrene-acrylic emulsion with a high benzene content;

[0089] (12) Add 70 g of water-soluble acrylic resin to 20 g of deionized water and mix well;

[0090] (13) Add 0.2 g of dimethylsiloxane, 0.3 g of polydimethylsiloxane, and 0.4 g of magnesium stearate to the mixture of step (12) and stir evenly;

[0091] (14) 40 g of styrene-acrylic emulsion with low benzene content, 30 g of styrene-acrylic emulsion with high benzene content and 10 g of graphene-polyethylene wax emulsion were added to the mixture in step (13) and mixed evenly, and filtered to obtain an environmentally friendly water-based varnish for packaging printing.

[0092] Comparative Example 1: A water-based varnish, the specific preparation steps are as follows:

[0093] The difference from Example 2 is that the polyethylene wax emulsion is directly added to the raw materials, and the other steps remain unchanged.

[0094] Comparative Example 2: A water-based varnish, the specific preparation steps are as follows:

[0095] The difference from Example 2 is that only the styrene-acrylic emulsion with a high benzene content is added to the raw materials, and the styrene-acrylic emulsion with a low benzene content is not added, and the other steps remain unchanged.

[0096] Comparative Example 3: A water-based varnish, the specific preparation steps are as follows:

[0097] The difference from Example 2 is that only the styrene-acrylic emulsion with a low benzene content is added to the raw materials, and the styrene-acrylic emulsion with a high benzene content is not added, and the other steps remain unchanged.

[0098] Performance testing:

[0099] Glossiness: The samples prepared in the examples and comparative examples were tested according to the national standard GB / T 7706-2008 "Letterpress Decorative Printings". The test results are shown in Table 1.

[0100] Abrasion resistance: The samples prepared in the examples and comparative examples were tested in accordance with the national standard GB / T23999-2009. The samples were evenly applied to a glass plate. After film formation and curing at room temperature, sandpaper was used to rub the paper in the same direction with uniform force until the glass plate was exposed. The number of frictions until the glass plate was exposed was calculated.

[0101] Drying property: Use a scraper fineness meter to scrape the water-based varnish prepared in the examples and comparative examples onto the scraper fineness meter until the grooves on the scraper fineness meter are filled. Touch the 15 μm groove with your hand to determine whether the varnish is dry, and record the drying time of the environmentally friendly water-based varnish.

[0102] Hardness: Samples prepared in the Examples and Comparative Examples were tested according to the national standard GB / T 23999-2009 using a pencil hardness tester. A set of 9B-9H high-grade Chinese drawing pencils was selected. The coating sample to be tested was placed on a horizontal surface. The pencils were held at an angle of approximately 45° to the horizontal plane. The hardest pencil was then tested, followed by the hardest pencil, and finally the softest. The coating was gently scratched across the pencil, each stroke approximately 6.5 mm long. The test was terminated if the pencil failed to penetrate or rub off the coating. The test results are shown in Table 1.

[0103] Table 1 Performance test results

[0104] Glossiness Wear resistance (times) Drying time(s) hardness Example 1 91 930 65 3H Example 2 94 945 64 3H Example 3 93 938 65 3H Comparative Example 1 75 502 68 2H Comparative Example 2 77 1028 70 3H Comparative Example 3 83 759 69 2H

[0105] Data analysis: Examples 1-3 show that the environmentally friendly water-based varnish for packaging printing of the present invention has excellent wear resistance and glossiness. It will not fade until it has been rubbed 945 times, and the glossiness can reach 94. In addition, it dries quickly, and its hardness can reach the same level as the water-based varnish in the prior art. Applying it to the surface of the substrate can provide good protection and increase the aesthetics.

[0106] It can be seen from Example 2 and Comparative Examples 1-3 that by adding polyethylene wax modified with graphene quantum dots and two styrene acrylic emulsions with different contents to the raw materials, the obtained water-based varnish has the best effect. The main reasons are: on the one hand, the wear resistance of graphene itself and the addition of high-quantum-level graphene are not only conducive to improving the wear resistance of the environmentally friendly water-based varnish for packaging and printing after film formation, but also because of its small particle size, it will not affect its gloss. On the other hand, the high and low content styrene acrylic emulsions match each other so that the environmentally friendly water-based varnish has better film-forming properties, which is conducive to improving its gloss, which is not achievable with a single styrene acrylic emulsion; more importantly, the benzene on the surface of the styrene acrylic emulsion with a high benzene content is very likely to form π-π conjugation with the graphene on the surface of the graphene-polyethylene wax, which promotes the uniform distribution of the graphene-polyethylene wax on the surface, further improving the wear resistance and gloss.

[0107] Those skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of the present invention (including the claims) is limited to these examples. Within the scope of the present invention, the technical features in the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of the different aspects of the present invention as described above, which are not provided in detail for the sake of simplicity.

[0108] The present invention is intended to cover all such substitutions, modifications and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An environmentally friendly water-based varnish for packaging printing, characterized in that: The invention comprises the following raw materials in parts by weight: 50-70 parts of water-soluble acrylic resin, 30-40 parts of styrene-acrylic emulsion with low benzene content, 20-30 parts of styrene-acrylic emulsion with high benzene content, 7-10 parts of graphene-polyethylene wax emulsion, 0.1-0.2 parts of defoaming agent, 0.1-0.3 parts of leveling agent, 0.2-0.4 parts of dispersant and 15-20 parts of deionized water; The preparation steps of the graphene-polyethylene wax emulsion are as follows: S1: adding vinyltrimethoxysilane and ethanol to deionized water and dispersing them uniformly, then adding ammonia water to adjust the pH to 9-11, then adding graphene quantum dots, reacting at 55-65°C for 2-6 hours, filtering, washing, and drying to obtain vinylized graphene quantum dots; wherein the mass ratio of vinyltrimethoxysilane, ethanol, deionized water, and graphene quantum dots is 0.5-1:10-20:20-40:5-15; S2: Under a nitrogen atmosphere, polyethylene wax is added to n-butanol, heated until fully dissolved, and then olefin-modified graphene quantum dots are added, stirred at 80-120° C. for 10-20 minutes, and then an initiator is added. The mixture is reacted at 150-160° C. for 1-2 hours, washed, filtered, and dried to obtain graphene-polyethylene wax; wherein the mass ratio of polyethylene wax, olefin-modified graphene quantum dots, n-butanol, and initiator is 20-40:1-5:2-6:0.2-0.4; S3: adding graphene-polyethylene wax to deionized water, heating until fully dissolved, then adding an emulsifier, emulsifying at 80-90°C for 40-60 minutes, adjusting the pH to 7-8, and obtaining a graphene-polyethylene wax emulsion with a particle size D50 of 0.5-0.8 μm; The monomers for preparing the styrene-acrylic emulsion with high benzene content are styrene monomer, butyl acrylate monomer and methacrylic acid monomer, wherein the weight percentage of styrene monomer accounts for 50%-60% of the total monomer amount, and the weight percentage of methacrylic acid monomer accounts for 2%-4% of the total monomer amount; The monomers for preparing the styrene-acrylic emulsion with low benzene content are styrene monomer, butyl acrylate monomer and methacrylic acid monomer, wherein the weight percentage of styrene monomer accounts for 20%-30% of the total monomer amount, and the weight percentage of methacrylic acid monomer accounts for 2%-4% of the total monomer amount.

2. The environmentally friendly water-based varnish for packaging printing according to claim 1, characterized in that: The defoaming agent is one of polydimethylsiloxane and higher fatty acid amide.

3. The environmentally friendly water-based varnish for packaging printing according to claim 1, characterized in that: The leveling agent is one of polydimethylsiloxane, polymethylphenylsiloxane, polyether polyester modified organic siloxane and alkylhydroxy modified organic siloxane.

4. The environmentally friendly water-based varnish for packaging printing according to claim 1, characterized in that: The dispersant is one of calcium stearate, magnesium stearate, zinc stearate and barium stearate.

5. The environmentally friendly water-based varnish for packaging printing according to claim 1, characterized in that: The initiator is a mixture of dibenzoyl peroxide and di-tert-butyl peroxide in a mass ratio of 1:

1.

6. The environmentally friendly water-based varnish for packaging printing according to claim 1, characterized in that: The mass ratio of graphene-polyethylene wax, emulsifier and deionized water in S3 is 20-25:1-2:28-34.

7. The environmentally friendly water-based varnish for packaging printing according to claim 1, characterized in that: The emulsifier is a mixture of Tween-60 and Span-80 in a mass ratio of 4-8:1-3.

8. A method for preparing the environmentally friendly water-based varnish for packaging printing according to any one of claims 1 to 7, characterized in that: The method comprises the following preparation steps: (1) Add water-soluble acrylic resin to deionized water and mix well; (2) adding a defoamer, a leveling agent and a dispersant to the mixture of step (1) and mixing them uniformly; (3) Adding a styrene-acrylic emulsion with a low benzene content, a styrene-acrylic emulsion with a high benzene content, and a graphene-polyethylene wax emulsion to the mixture of step (2) and mixing them evenly, filtering, and obtaining an environmentally friendly water-based varnish for packaging printing.