UV varnish, its preparation, application methods, and packaging film

Abstract

This invention provides a UV varnish, its preparation, application method, and packaging film. By weight, the UV varnish comprises the following components: 20-40 parts of a first prepolymer, 10-20 parts of a second prepolymer, 40-60 parts of an active monomer, 1-5 parts of an initiator, and 0-8 parts of an adhesion promoter. The first prepolymer is selected from polyurethane acrylic prepolymers, and its functionality is 6-10. The second prepolymer is a modified epoxy acrylic prepolymer, and its functionality is not greater than 2. This invention uses prepolymers and active monomers with low viscosity and good wetting properties, thus eliminating the need for leveling, defoaming, or other fluorosilicone additives, simplifying the formulation, reducing costs, and maintaining a high surface tension of the coating. It contains no organic solvents and uses a low-odor initiator, resulting in minimal odor during application and in the finished product. After curing, the varnish has a high gloss and a tough, smooth surface, providing excellent protection for printed materials in the printing and packaging industry.

Description

Technical Field

[0001] This invention relates to the field of UV varnish technology, and in particular to a UV varnish, its preparation, application method and packaging film. Background Technology

[0002] UV varnish is a transparent coating, also known as UV clear coat. Its function is to be sprayed or rolled onto the substrate surface, then irradiated by a UV lamp, causing it to transform from a liquid to a solid state, thus achieving surface hardening. It provides scratch and abrasion resistance, and the surface appears glossy, aesthetically pleasing, and has a smooth texture. With the development of the printing and packaging industry, the coating field has undergone tremendous changes. UV coatings, in particular, offer advantages such as fast curing speed, energy saving, room temperature curing, superior performance, and environmental friendliness. They provide rapid varnishing, high gloss, and a strong, heat-resistant film after drying, with excellent refractive effects, giving the substrate a strong sense of its own character. They are widely used in chemical, machinery, electronics, light industry, and communications fields. Due to its environmental advantages, UV curing has received strong support from relevant environmental regulations and close attention from industry. While the market demand for UV radiation-cured materials is growing rapidly, UV radiation curing systems are being integrated with various industries to overcome certain shortcomings and meet practical production applications. In today's printing and packaging industry, the application of UV varnishes enables packaging to achieve several unique effects: high gloss, excellent ink protection, controllable smoothness and abrasion resistance, low or no odor, low or undetectable extractables, and protection of inks. However, most existing UV varnishes contain small amounts of solvents, which can easily lead to residual odors and fire hazards, requiring VOC exhaust treatment equipment and drying processes during use; alternatively, they may contain small amounts of silicone additives, resulting in lower surface tension after coating curing, which may not meet the requirements for recoating or hot stamping of packaging films.

[0003] Currently, CN201710211753.0, "All-solid UV-coated glossy anti-scratch coating for BOPP pre-coated film and its preparation method," describes the synthesis of an all-solid glossy UV-coated anti-scratch coating using nano-composite polyurethane acrylic oligomers and reactive diluents. However, its high viscosity makes it unsuitable for gravure coating, and the high cost of the nano-composite oligomers limits its application and promotion. CN201810256792.7, "A low-odor UV glossy varnish and its preparation method," provides a VOC-free, low-odor glossy varnish that improves the product's abrasion resistance and color. Its main purpose is to improve the product's odor. CN201910895695.7, "Yellowing-resistant glossy UV paint and its production process," provides a yellowing-resistant glossy UV paint containing organic solvents. CN201910627906.9, "A high-wear-resistant and high-toughness UV glossy coating and its application," provides a high-wear-resistant and tough UV glossy coating that requires the addition of organic solvents and infrared baking during application, primarily for the 3C manufacturing industry. CN201611153902.4 describes a recoatable glossy UV coating for 3C products, solving the problem of uneven appearance caused by sanding during recoating. This patent contains organic solvents and is not applicable to the printing and packaging industry. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a UV varnish, its preparation, application method and packaging film.

[0005] To achieve the above objectives, the present invention employs the following technical invention:

[0006] In a first aspect, the present invention provides a UV varnish, which, by weight, comprises the following components: 20-40 parts of a first prepolymer, 10-20 parts of a second prepolymer, 40-60 parts of an active monomer, 1-5 parts of an initiator, and 0-8 parts of an adhesion promoter; the functionality of the first prepolymer is 6-10; and the functionality of the second prepolymer is not greater than 2.

[0007] Further, the first prepolymer is selected from polyurethane acrylic prepolymer with a viscosity of less than 1500 cps; preferably, the modulus of the first prepolymer is not less than 800 MPa; preferably, the solid content of the first prepolymer is 100%.

[0008] Further, the second prepolymer is a modified epoxy acrylic acid prepolymer with a viscosity of less than 2000 cps; preferably, the modulus of the second prepolymer is not less than 50 MPa; preferably, the solid content of the second prepolymer is 100%.

[0009] Further, the active monomer is selected from difunctional active monomers and multifunctional active monomers, and the mass ratio of the difunctional active monomer to the multifunctional active monomer is (1-3):(2-4); preferably, the multifunctional active monomer is selected from trifunctional active monomers and tetrafunctional active monomers.

[0010] Furthermore, the surface tension of the active monomer is 38-42 dynes; the viscosity is 10-750 cps.

[0011] Furthermore, the active monomer is selected from two or more of the following: triethylene glycol diacrylate (TEGDA), polyethylene glycol diacrylate (PEGDA), ethoxylated (3)trimethylolpropane triacrylate (EO-TMPTA), pentaerythritol tetraacrylate (PETA), and dipentaerythritol pentaacrylate.

[0012] Furthermore, the adhesion promoter is selected from diisocyanate modified acrylic resin, and the adhesion promoter has an acrylic functionality of ≤3, an NCO functionality of ≤2, and an NCO content of 5-10%.

[0013] In a second aspect, the present invention provides a method for preparing the UV varnish described in the first aspect, the method comprising the following steps: mixing an initiator and an active monomer in a proportion, heating to 50-60°C, stirring at a speed of 200-500 r / min for 15-20 min until the initiator is completely dissolved, and then adding a first prepolymer, a second prepolymer, and an adhesion promoter in a proportion to a dispersion tank, and stirring at a speed of 100-300 r / min at room temperature for 10-15 min.

[0014] Thirdly, the present invention provides a method for using the UV varnish described in the first aspect, the method comprising: (S1) subjecting the surface of a thin film substrate to corona treatment; (S2) applying the UV varnish to the corona-treated surface of the thin film substrate; and (S3) curing the coating obtained in step (S2) using a UV curing system protected by an inert gas. Preferably, the coating method in step (S2) is selected from gravure coating, microgravure coating, and slot coating.

[0015] Fourthly, the present invention provides a packaging film comprising a film substrate and a coating disposed on the film substrate, the coating being formed by UV varnish coating and curing as described in the first aspect.

[0016] Furthermore, the coating has a thickness of 2-3.5 micrometers; a gloss of 85-105 GU; a surface tension of 36-40; and the film substrate is one of biaxially oriented polypropylene film (BOPP), polyethylene terephthalate film (PET), nylon film (NY), or polyvinyl chloride (PVC).

[0017] Compared with the prior art, the present invention has the following advantages when applied:

[0018] (1) The present invention uses prepolymers and active monomers with low viscosity and good wettability, so there is no need to add fluorosilicone additives such as leveling and defoaming agents, which simplifies the formulation, reduces costs, and can maintain a high surface tension of the coating.

[0019] (2) The varnish provided by the present invention does not contain organic solvents and uses a low-odor initiator, so the odor during the construction process and the finished product is very small;

[0020] (3) The curing speed of the varnish provided by the present invention is very fast, which can effectively improve production efficiency and significantly reduce product costs.

[0021] (4) The varnish provided by the present invention has a high gloss after curing and a tough and smooth surface. When applied in the printing and packaging field, it can effectively protect printed products.

[0022] (5) The viscosity of the varnish prepared by the present invention is less than 500 cps, and it can be directly used for gravure coating. For different substrates, the amount of adhesion promoter and the second prepolymer can be adjusted to ensure that the varnish has good adhesion. Detailed Implementation

[0023] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the embodiments.

[0024] To enable those skilled in the art to better understand the present invention, the technical inventions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention. In addition, when describing the embodiments of the present invention, the use of terms such as "preferred," "more preferably," and "more preferably" refers to embodiments of the present invention that can provide certain beneficial effects in certain circumstances. However, in the same or other circumstances, other embodiments may also be preferred. Furthermore, the description of one or more preferred embodiments does not imply that other embodiments are unavailable, nor is it intended to exclude other embodiments from the scope of the present invention.

[0025] Unless otherwise defined, the technical or scientific terms used in this disclosure shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0026] Currently, most existing UV varnishes contain small amounts of solvents, which can easily leave residual odors and pose fire hazards. Their use requires VOC exhaust gas treatment equipment and drying processes. Alternatively, they may contain small amounts of silicone-based additives, resulting in low surface tension after coating curing, which cannot meet the requirements for recoating or hot stamping of packaging films. To address this issue, this application provides a UV varnish, its preparation and application methods, and a packaging film thereof.

[0027] In a typical embodiment of this application, the present invention provides a UV varnish, which, by weight, comprises the following components: 20-40 parts of a first prepolymer, 10-20 parts of a second prepolymer, 40-60 parts of an active monomer, 1-5 parts of an initiator, and 0-8 parts of an adhesion promoter. The first prepolymer has a functionality of 6-10. High-functionality polyurethane acrylate prepolymers can increase the crosslinking density of the coating formed after the UV varnish has cured, thereby improving the overall wear resistance, high-temperature resistance, and weather resistance of the coating. Low-functionality polyurethane acrylate prepolymers have good adhesion, good flexibility, low shrinkage, and high curing rate. However, if the functionality of the first prepolymer is lower than 6, the curing crosslinking density of the varnish will be low, thus reducing wear resistance. If the functionality of the first prepolymer is higher than 10, the viscosity will be relatively high, resulting in higher prices and increased viscosity, making application difficult. Furthermore, higher functionality leads to greater shrinkage after curing, causing film curling and unevenness. The functionality of the second prepolymer is no greater than 2. If the functionality of the second prepolymer is greater than 2, the shrinkage rate of the resulting UV varnish film will be too large, causing the product to warp after film formation.

[0028] In one specific embodiment of this application, the first prepolymer is selected from polyurethane acrylic prepolymer, which has good flexibility and high adhesion to metals; the viscosity of the first prepolymer is less than 1500 cps; if the viscosity of the first prepolymer is higher than 1500 cps, the viscosity is too high, making it unsuitable for roller coating, increasing the difficulty of construction, and worsening the uniformity of the coating appearance. Preferably, the modulus of the first prepolymer is not less than 800 MPa; if the modulus of the first prepolymer is lower than 800 MPa, the low modulus will result in insufficient toughness and poor wear resistance after the varnish cures into a film. Preferably, the solid content of the first prepolymer is 100%; if it is not 100% solid content, an oven or other means are needed to remove the solvent, leading to increased energy consumption, and the use of solvents is not environmentally friendly.

[0029] In one specific embodiment of this application, the second prepolymer is a modified epoxy acrylate prepolymer, which has a high curing rate and good adhesion to the base film. The viscosity of the second prepolymer is less than 2000 cps; if the viscosity of the second prepolymer is greater than 2000 cps, the resulting UV varnish will have excessively high viscosity, increasing the difficulty of application and affecting the uniformity of appearance. Preferably, the modulus of the second prepolymer is not less than 50 MPa; if the modulus of the second prepolymer is less than 50 MPa, the resulting UV varnish will have a low modulus, resulting in poor abrasion resistance after film formation. Preferably, the solid content of the second prepolymer is 100%; if the solid content of the second prepolymer is not 100%, an oven or other means are needed to remove the solvent, leading to increased energy consumption, and the use of solvents is not environmentally friendly.

[0030] In one specific embodiment of this application, the active monomer is selected from difunctional and polyfunctional active monomers, and the ratio of the difunctional and polyfunctional active monomers is (1-3):(2-4); preferably, the polyfunctional active monomer is selected from trifunctional and tetrafunctional active monomers. Difunctional monomers can adjust the viscosity of the system, impart flexibility to the coating, ensure that the film does not crack after formation, and improve the adhesion of the coating to the film. The presence of trifunctional or tetrafunctional monomers in the system results in a faster curing reaction, and polyfunctional active monomers have high reactivity, increasing the degree of crosslinking in the system, increasing the hardness of the film after formation, and providing scratch and abrasion resistance. If the ratio of the difunctional and polyfunctional active monomers is less than 1:4, the polyfunctional monomers generally have a higher viscosity, affecting construction and appearance, and the shrinkage rate after film formation is higher, leading to warping. However, multifunctional monomers can increase the crosslinking density of varnish and improve abrasion resistance, so their content cannot be too low. If the ratio of difunctional active monomers to multifunctional active monomers is higher than 3:2, the viscosity of monofunctional monomers is lower, mainly to adjust the application viscosity, but their strength is insufficient. Too much of this will affect the abrasion resistance after film formation.

[0031] In one specific embodiment of this application, the surface tension of the active monomer is 38-42 dynes; the viscosity is 10-750 cps. If the surface tension of the active monomer is not within the above range, and the dyne value of the active monomer is too low, the dyne value after the varnish film is formed will be low, making it unsuitable for processes such as hot stamping and UV screen printing in the printing and packaging industry. Monomers with a dyne value higher than 42 are rare and have no market significance. If the viscosity of the active monomer is not within the above range, it may lead to a higher overall viscosity of the varnish, increasing the difficulty of application.

[0032] In one specific embodiment of this application, the active monomer is selected from two or more of the following: triethylene glycol diacrylate (TEGDA), polyethylene glycol diacrylate (PEGDA), ethoxylated (3)trimethylolpropane triacrylate (EO-TMPTA), pentaerythritol tetraacrylate (PETA), and dipentaerythritol pentaacrylate (DPHA).

[0033] In one specific embodiment of this application, the adhesion promoter is selected from diisocyanate-modified acrylic resin. The adhesion promoter has an acrylic functionality ≤3, an NCO functionality ≤2, and an NCO content of 5-10%. The isocyanate-modified acrylic resin contains double bonds in its structure. During UV curing, it reacts with the prepolymer and monomer to form a link point. Simultaneously, the NCO in its structure reacts with the hydroxyl groups generated after corona treatment of the substrate, forming another link point. This connects the UV coating and the substrate together. Therefore, it can participate in the UV curing reaction and react with the hydroxyl groups generated after corona treatment on the film surface, improving the adhesion of the coating. This dual-curing mechanism enhances the adhesion of the varnish to the coating, expanding the film's applicability to various plastic substrates such as BOPP, PET, NY, and PVC. For different substrates, the amount of adhesion promoter and the second prepolymer can be adjusted to ensure good adhesion of the varnish. For example, on PVC surfaces, an adhesion promoter may not be needed; however, on BOPP substrate surfaces, the amount of the second prepolymer and the adhesion promoter needs to be increased to ensure good adhesion. If the acrylic functionality of the adhesion promoter is greater than 3, the resulting UV varnish will have high viscosity and shrinkage, and there are not many commercially available acrylic products with a functionality greater than 3. If the NCO functionality is greater than 2, the resulting UV varnish will have a short activation period, affecting the application time. If the NCO content is less than 5%, the adhesion promoter will not function effectively, or a large amount will be required to achieve the desired effect, increasing costs. If the NCO content is greater than 10%, the resulting UV varnish will have a short activation period, affecting the application time.

[0034] In specific embodiments of this application, the initiator is selected from commercially available low-odor photoinitiators to reduce the residue of low-molecular-weight products after initiator decomposition. Examples include 2,4,6-trimethylbenzoyl diphenylphosphine oxide (TPO), 2,4-diethylthioxanthone (DETX), and 2-hydroxy-2-methyl-1-[4-(2-hydroxyethoxy)phenyl]-1-propanone (2959).

[0035] In a second aspect, the present invention provides a method for preparing the UV varnish described in the first aspect, the method comprising the following steps: mixing an initiator and an active monomer in proportion, heating to 50-60°C, stirring at high speed for 15-20 min until the initiator is completely dissolved, and then adding a first prepolymer, a second prepolymer and an adhesion promoter in proportion to a dispersion tank, and stirring at room temperature at high speed for 10-15 min.

[0036] Thirdly, the present invention provides a method for using the UV varnish described in the first aspect, the method comprising: (S1) subjecting the surface of a thin film substrate to corona treatment; (S2) applying the UV varnish to the corona-treated surface of the thin film substrate; and (S3) curing the coating obtained in step (S2) using a UV curing system protected by an inert gas. Preferably, the coating method in step (S2) is selected from gravure coating, microgravure coating, and slot coating.

[0037] Fourthly, the present invention provides a packaging film comprising a film substrate and a coating disposed on the film substrate, the coating being formed by UV varnish coating and curing as described in the first aspect.

[0038] In a specific embodiment of this application, the coating thickness is 2-3.5 micrometers; the gloss is 85-105 GU; the surface tension is 36-40; and the film substrate is one of biaxially oriented polypropylene film (BOPP), polyethylene terephthalate film (PET), nylon film (NY), or polyvinyl chloride (PVC). The gloss is significantly different from existing packaging materials, which would hinder market promotion; if the surface tension of the coating is not within the above range, the resulting packaging film cannot be used for processes such as hot stamping and UV screen printing in the packaging industry.

[0039] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0040] Example 1

[0041] This embodiment provides a wear-resistant UV varnish for glossy BOPP surfaces. By weight, its composition includes: 30 parts of a first prepolymer, which is KDNM7531; the first prepolymer has a functionality of 8; a viscosity of 1300 cps; a modulus of 960 MPa; and a solid content of 100%; 10 parts of a second prepolymer, which is KDNM7329; the second prepolymer has a functionality of 2; a viscosity of 1700 cps; a modulus of 78 MPa; and a solid content of 100%; and 50 parts of an active monomer, which is composed of polyethylene. The mixture is composed of PEGDA (poly(ethylene glycol diacrylate)) and PETA (pentaerythritol tetraacrylate) in a ratio of 3:2. The surface tension of the active monomer is 39 dynes, and the viscosity is 150-210 cps. Two parts of photoinitiator (specifically 2-hydroxy-2-methyl-1-[4-(2-hydroxyethoxy)phenyl]-1-propanone (2959; manufacturer: Aijianmeng)) and eight parts of adhesion promoter (specifically JT680; manufacturer: Guangzhou Jintu) are included. The adhesion promoter has an acrylic functionality of 3, an NCO functionality of 2, and an NCO content of 8%. After mixing the initiator and active monomer according to the ratio, the mixture is heated to 50-60℃ and stirred at 200 rpm for 20 min until the initiator is completely dissolved. Then, the first and second prepolymers and the adhesion promoter are added to the dispersion tank according to the ratio and stirred at 300 rpm at room temperature for 10 min. The varnish was applied to the corona-treated BOPP outer surface at a speed of 100 mpm using gravure coating. After curing with a UV lamp in a nitrogen atmosphere, the varnish was rolled up and samples were taken for performance testing.

[0042] Example 2

[0043] Example 2 differs from Example 1 in that the weight percentage of the first prepolymer is 20, and the weight percentage of the second prepolymer is 20. Everything else is the same as in Example 1.

[0044] Example 3

[0045] Example 3 differs from Example 1 in that the first prepolymer has a weight percentage of 30, the second prepolymer has a weight percentage of 20, and the active monomer has a weight percentage of 40. Everything else is the same as in Example 1.

[0046] Example 4

[0047] Example 4 differs from Example 1 in that the first prepolymer has a weight percentage of 20 parts, the second prepolymer has a weight percentage of 10 parts, and the active monomer has a weight percentage of 60 parts. Everything else is the same as in Example 1.

[0048] Example 5

[0049] Example 5 differs from Example 1 in that it contains 5 parts of initiator and 5 parts of adhesion promoter. Everything else is the same as in Example 1.

[0050] Example 6

[0051] Example 6 differs from Example 1 in that: the initiator is 5 parts, the active monomer is 55 parts, and the adhesion promoter is 0 parts; the coating substrate is corona-treated PET. Everything else is the same as in Example 1.

[0052] Example 7

[0053] Example 7 differs from Example 1 in that the first prepolymer is KDNM7837, the functionality of the first prepolymer is 6, and the viscosity is 800-900 cps. Everything else is the same as in Example 1.

[0054] Example 8

[0055] Example 8 differs from Example 1 in that the first prepolymer is KDNM7415, the functionality of the first prepolymer is 10, and the viscosity is 1600 cps. Everything else is the same as in Example 1.

[0056] Example 9

[0057] Example 9 differs from Example 1 in that the active monomer is a mixture of polyethylene glycol diacrylate (PEGDA) and pentaerythritol tetraacrylate (PETA) in a ratio of 1:4. Everything else is the same as in Example 1.

[0058] Example 10

[0059] Example 10 differs from Example 1 in that the active monomer is a mixture of polyethylene glycol diacrylate (PEGDA) and pentaerythritol tetraacrylate (PETA) in a ratio of 1:2. Everything else is the same as in Example 1.

[0060] Example 11

[0061] Example 11 differs from Example 1 in that the active monomer is a mixture of polyethylene glycol diacrylate (PEGDA) and pentaerythritol tetraacrylate (PETA) in a ratio of 2:3. Everything else is the same as in Example 1.

[0062] Example 12

[0063] Example 12 differs from Example 1 in that the active monomer is a mixture of polyethylene glycol diacrylate (PEGDA) and pentaerythritol tetraacrylate (PETA) in a 1:1 ratio. Everything else is the same as in Example 1.

[0064] Example 13

[0065] Example 13 differs from Example 1 in that the active monomer is a mixture of polyethylene glycol diacrylate (PEGDA) and ethoxylated (3)trimethylolpropane triacrylate (EO-TMPTA) in a ratio of 3:2. Everything else is the same as in Example 1.

[0066] Example 14

[0067] Example 14 differs from Example 1 in that the active monomer is a mixture of polyethylene glycol diacrylate (PEGDA) and dipentaerythritol pentaacrylate (DPHA) in a ratio of 3:2. Everything else is the same as in Example 1.

[0068] Example 15

[0069] Example 15 differs from Example 1 in that the adhesion promoter has an acrylic acid functionality of 3, an NCO functionality of 2, and an NCO content of 7.5%. Everything else is the same as in Example 1.

[0070] Comparative Example 1

[0071] The difference between Comparative Example 1 and Example 1 is that the first prepolymer has a weight fraction of 10, and the second prepolymer has a weight fraction of 30. Everything else is the same as in Example 1.

[0072] Comparative Example 2

[0073] The difference between Comparative Example 2 and Example 1 is that: 35 parts of the first prepolymer, 20 parts of the second prepolymer, and 35 parts of the active monomer. Everything else is the same as in Example 1.

[0074] Comparative Example 3

[0075] The difference between Comparative Example 3 and Example 1 is that the first prepolymer is KDNM7158 and the functionality of the first prepolymer is 4. Everything else is the same as in Example 1.

[0076] Comparative Example 4

[0077] The difference between Comparative Example 4 and Example 1 is that the first prepolymer is KDNM7619 and the functionality of the first prepolymer is 12. Everything else is the same as in Example 1.

[0078] Comparative Example 5

[0079] The difference between Comparative Example 5 and Example 1 is that the second prepolymer is a modified epoxy acrylic acid prepolymer, and the functionality of the second prepolymer is 3. Everything else is the same as in Example 1.

[0080] Comparative Example 6

[0081] The difference between Comparative Example 6 and Example 1 is that the viscosity of the first prepolymer is 2000 cps. Everything else is the same as in Example 1.

[0082] Comparative Example 7

[0083] The difference between Comparative Example 7 and Example 1 is that the viscosity of the second prepolymer is 2500 cps. Everything else is the same as in Example 1.

[0084] Comparative Example 8

[0085] The difference between Comparative Example 8 and Example 1 is that the active monomer is a mixture of polyethylene glycol diacrylate (PEGDA) and dipentaerythritol pentaacrylate (DPHA) in a ratio of 1:5. Everything else is the same as in Example 1.

[0086] Comparative Example 9

[0087] The difference between Comparative Example 9 and Example 1 is that the active monomer is a mixture of polyethylene glycol diacrylate (PEGDA) and dipentaerythritol pentaacrylate (DPHA) in a ratio of 4:1. Everything else is the same as in Example 1.

[0088] Performance testing

[0089] (1) Coating thickness: According to the method of GB / T 6672, first detect the thickness H1 of the substrate before coating, and then detect the thickness H2 of the film after coating. Coating thickness H = H2 - H1.

[0090] (2) Gloss: The gloss at a 60° angle was tested according to the standard method of GB 8807.

[0091] (3) Surface tension: Performed in accordance with GB / T 14216.

[0092] (4) Pencil hardness: in accordance with GB / T 6739.

[0093] (5) Abrasion resistance: Using the RT-01 abrasion tester, the coating was rubbed against the coating 200 times under a 4LB load, and the friction marks of the coating were observed under natural light.

[0094] The materials prepared in Examples 1-15 and Comparative Examples 1-9 were subjected to performance testing, and the results are shown in Table 1.

[0095] Table 1

[0096]

[0097]

[0098] The data in the table shows that, compared with Example 1, Comparative Examples 3, 4, and 5 exhibit the following characteristics: If the functionality of the first prepolymer is lower than 6, the curing crosslinking density of the varnish will be lower, resulting in reduced abrasion resistance and scratches. If the functionality of the first prepolymer is higher than 10, the viscosity will be relatively high, leading to higher prices and increased viscosity of the varnish, making application difficult. Furthermore, higher functionality results in greater shrinkage after curing, causing film curling, unevenness, and inconsistent appearance. If the viscosity of the active monomer is not within the range of 10-750 cps, the overall viscosity of the varnish may be higher, increasing the difficulty of application. If the ratio of difunctional active monomers to multifunctional active monomers is lower than 1:4, the multifunctional monomers generally have higher viscosity, affecting application and appearance, and resulting in higher shrinkage after film formation, leading to warping. However, multifunctional monomers can increase the crosslinking density of varnish and improve abrasion resistance, so their content cannot be too low. If the ratio of difunctional active monomers to multifunctional active monomers is higher than 3:2, the viscosity of monofunctional monomers is lower, mainly to adjust the application viscosity, but their strength is insufficient. Too much of this will affect the abrasion resistance after film formation.

[0099] The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A UV varnish, characterized in that, By weight, the UV varnish is composed of the following components: 20-40 parts of a first prepolymer, 10-20 parts of a second prepolymer, 40-60 parts of an active monomer, 1-5 parts of an initiator, and 0-8 parts of an adhesion promoter; the functionality of the first prepolymer is 6-10; and the functionality of the second prepolymer is not greater than 2. The active monomer is selected from difunctional active monomers and multifunctional active monomers, and the mass ratio of the difunctional active monomers to the multifunctional active monomers is (1-3):(2-4). The surface tension of the active monomer is 38-42 dynes; The first prepolymer is selected from polyurethane acrylic prepolymer with a viscosity of less than 1500 cps; The second prepolymer is a modified epoxy acrylic acid prepolymer with a viscosity of less than 2000 cps; The multifunctional active monomer of the active monomer is selected from trifunctional and / or tetrafunctional active monomers.

2. The UV varnish according to claim 1, characterized in that, The modulus of the first prepolymer is not less than 800 MPa.

3. The UV varnish according to claim 1, characterized in that, The solid content of the first prepolymer is 100%.

4. The UV varnish according to claim 1, characterized in that, The modulus of the second prepolymer is not less than 50 MPa.

5. The UV varnish according to claim 1, characterized in that, The solid content of the second prepolymer is 100%.

6. The UV varnish according to claim 1, characterized in that, The viscosity of the active monomer is 10-750 cps.

7. The UV varnish according to claim 1, characterized in that, The active monomer is selected from two or more of the following: triethylene glycol diacrylate (TEGDA), polyethylene glycol diacrylate (PEGDA), ethoxylated (3) trimethylolpropane triacrylate (EO-TMPTA), pentaerythritol tetraacrylate (PETA), and dipentaerythritol pentaacrylate (DPHA).

8. The UV varnish according to claim 1, characterized in that, The adhesion promoter is selected from diisocyanate modified acrylic resin, and the acrylic functionality of the adhesion promoter is ≤3, the NCO functionality is ≤2, and the NCO content is 5-10%.

9. A method for preparing a UV varnish according to any one of claims 1 to 8, characterized in that, The method includes the following steps: after mixing the initiator and active monomer in proportion, heating to 50-60℃, stirring at a speed of 200-500r / min for 15-20min until the initiator is completely dissolved, then adding the first prepolymer, the second prepolymer and the adhesion promoter to the dispersion tank in proportion, and stirring at room temperature at a speed of 100-300r / min for 10-15min.

10. A method for using the UV varnish according to any one of claims 1 to 8, characterized in that, The method of use includes: (S1) corona treatment of the surface of the film substrate; (S2) application of UV varnish to the corona-treated surface of the film substrate; and (S3) curing the coating obtained in step (S2) using a UV curing system protected by inert gas.

11. The method of using the UV varnish according to claim 10, characterized in that, The coating method in step (S2) is selected from gravure coating, microgravure coating, and slot coating.

12. A packaging film, comprising a film substrate and a coating disposed on the film substrate, characterized in that, The coating is formed by UV varnish application and curing according to any one of claims 1 to 8.

13. The packaging film according to claim 12, characterized in that, The coating has a thickness of 2-3.5 micrometers; a gloss of 85-105 GU; a surface tension of 36-40 dynes; and the film substrate is one of biaxially oriented polypropylene film (BOPP), polyethylene terephthalate film (PET), nylon film (NY), or polyvinyl chloride (PVC).

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