A UV-curable coating composition, its preparation method and application

Abstract

This invention discloses a UV-curable coating composition, its preparation method, and its application. The UV-curable coating composition includes a UV-curable primer and a UV-curable topcoat. The UV-curable primer is composed of polyurethane acrylate resin, a first acrylate monomer, a photoinitiator, an adhesion promoter, and a wetting and leveling agent in a specific ratio, and after curing, it forms a coating with strong adhesion on a nickel-plated substrate. Furthermore, by optimizing the formulation of the UV-curable topcoat, it promotes efficient bonding between the topcoat and primer when used in conjunction with the primer, imparting excellent insulation properties to the coating. The UV-curable coating composition provided by this invention can form a composite coating with strong adhesion, excellent insulation properties, and high stability on the surface of a nickel-plated substrate. Its adhesion performance is grade 1 or higher, and it passes voltage resistance and electrolyte resistance tests. Even after aging under double 85 conditions for 1000 hours, it still maintains excellent adhesion and insulation stability.

Description

Technical Field

[0001] This application relates to the field of coating technology, specifically to a UV-curable coating composition, its preparation method, and its application. Background Technology

[0002] In power and energy storage batteries, individual battery cells are typically arranged in a specific manner, and their casings are generally made of metal to ensure that the battery cells can withstand external impacts and dissipate heat quickly, but this also introduces safety hazards such as short circuits. Therefore, cell insulation materials have become a key barrier to ensure battery safety.

[0003] For a long time, polyethylene terephthalate (PET) blue film has been the mainstream insulation solution for battery cells. However, with the development of new energy vehicle technology, PET blue film can no longer meet the technical requirements: on the one hand, its pressure-sensitive adhesive has limited bonding performance and is prone to aging. When the battery pack is subjected to external impact, the blue film is easy to fall off from the cell casing, leading to insulation failure; on the other hand, facing the rise of high-voltage platform vehicles, the breakdown voltage of traditional PET blue film cannot meet the new requirement of 3000-4000V.

[0004] UV-curable coatings, due to their fast curing speed, lack of high-temperature treatment, and tight adhesion to the casing, have become an important alternative to blue film coatings. However, battery casings are mainly divided into two categories: square aluminum casings and cylindrical nickel-plated steel casings. Existing UV-curable insulating coatings are primarily designed for aluminum casing surfaces. For example, patent CN120173501A discloses a dielectric insulating protective coating with high surface energy and high adhesion, obtained by combining flexible modified polyurethane acrylate, flexible acrylate, high glass transition temperature rigid acrylate, high functionality acrylate crosslinking agent, high dilution high glass transition temperature methyl methacrylate, and numerous photoinitiators, additives, and pigments and fillers. This coating can be applied to aluminum casings of battery cells or other external metal packaging materials (aluminum metal) of battery pack components. However, cylindrical battery casings are usually nickel-plated steel casings. The surface plating is prone to microscopic contamination or oxidation after electroplating, and its chemical state is completely different from the aluminum oxide layer on the aluminum casing surface. This leads to poor adhesion of existing UV-curable insulating coatings on nickel-plated substrates.

[0005] Therefore, developing a UV-curable insulating coating with excellent adhesion to the nickel-plated casing of cylindrical batteries is of urgent practical significance for improving battery safety and production reliability. Summary of the Invention

[0006] The primary objective of this invention is to overcome the problem of poor adhesion of existing UV-curable insulating coatings on nickel-plated substrates, and to provide a UV-curable primer that can be cured on the surface of a nickel-plated substrate to form a coating with strong adhesion.

[0007] Another object of the present invention is to provide a method for preparing the above-mentioned UV-curable primer.

[0008] Another object of the present invention is to provide a UV-curable topcoat.

[0009] Another object of the present invention is to provide a method for preparing the above-mentioned UV-curable topcoat.

[0010] Another object of the present invention is to provide a UV-curable coating composition comprising the above-described UV-curable primer and the above-described UV-curable topcoat. This UV-curable coating composition can form a composite coating with strong adhesion, excellent insulation properties, and high stability on the surface of a nickel-plated substrate.

[0011] Another object of the present invention is to provide the application of the above-described UV-curable coating composition as a coating for nickel-plated substrates.

[0012] Another object of the present invention is to provide a nickel-plated product.

[0013] Another object of the present invention is to provide a method for preparing the above-mentioned nickel-plated articles.

[0014] Another object of the present invention is to provide a nickel-plated casing for a cylindrical battery.

[0015] To achieve the above objectives, the present invention adopts the following technical solution: A UV-curable primer comprising the following components by weight percentage: 30-40% polyurethane acrylate resin; First acrylate monomer 48~64%; Photoinitiator 3-8%; Adhesion promoter 2-5%; Wetting and leveling agent 0.1-1%; The first acrylate monomer comprises a hard acrylate monomer, a functional acrylate monomer, and a specialty acrylate monomer; the mass ratio of the hard acrylate monomer to the functional acrylate monomer to the specialty acrylate monomer is 17.5~25:7.5~20:15~30; the glass transition temperature of the hard acrylate monomer is above 25°C; the functional acrylate monomer is an acrylate monomer containing at least one polar group; the polar group is one or more of phenoxy, hydroxy, vinyl ether, oxygen-containing heterocyclic, or nitrogen-containing heterocyclic groups; the specialty acrylate monomer contains a cyclic acetal structure or contains C6~C6 groups. 12 cycloalkyl acrylate monomers.

[0016] In UV-curable primer formulations, acrylate hard monomers can increase the hardness of the coating, acrylate functional monomers improve the adhesion of the coating through polar groups, and acrylate specialty monomers contain cyclic acetal structures or C6~C6 groups. 12 Cycloalkyl acrylate monomers possess a bulky group structure, which increases steric hindrance and interchain spacing, thereby effectively improving the curing shrinkage rate of coatings. This invention significantly enhances the adhesion and shrinkage resistance of primers to nickel-plated substrates by compounding the above three types of monomers in a specific ratio and synergistically combining them with polyurethane acrylate resin and an adhesion promoter.

[0017] In this field, primers are typically applied to the substrate surface using processes such as spraying, brushing, or printing. The viscosity of the primer directly affects its application. Preferably, the UV-curable primer has a viscosity of 30-80 cps at 25°C; and / or a viscosity of 20-40 cps at 50°C.

[0018] More preferably, the UV-curable primer has a viscosity of 50-65 cps at 25°C; and / or a viscosity of 25-35 cps at 50°C.

[0019] In the UV-curable primer of the present invention, the polyurethane acrylate resin can be selected from common polyurethane acrylate resins in the art, and generally commercial products are acceptable, such as, but not limited to: one or more of the following: polyurethane 93745 from Haohui New Materials Co., Ltd., 92511 from Haohui New Materials Co., Ltd., QW2141 from Qingwu Co., Ltd., or 6101 from Changxing Materials Co., Ltd.

[0020] Preferably, the polyurethane acrylate resin is a difunctional polyurethane acrylate resin. In this invention, a difunctional polyurethane acrylate resin refers to a resin molecule containing two acrylate groups.

[0021] It should be noted that any acrylate hard monomer with a glass transition temperature above 25°C is suitable for this invention. Preferably, in the UV-curable primer, the acrylate hard monomer has a glass transition temperature above 50°C, and is, for example, one or more of the following: trifluoroethyl methacrylate, isobornyl acrylate, cyclotrimethylolpropane methyl acetal acrylate, norbornyl acrylate, methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, or cyclohexyl methacrylate.

[0022] More preferably, in the UV-curable primer, the acrylate hard monomer is one or more of trifluoroethyl methacrylate, isoborneol acrylate, cyclotrimethylolpropane methyl acetal acrylate, or norborneol acrylate.

[0023] In this invention, the glass transition temperature of the acrylate hard monomer can be obtained by DSC instrument testing.

[0024] Preferably, in the UV-curable primer, the acrylate functional monomer is one or more of the following: acrylate monomer containing phenoxy groups, acrylate monomer containing hydroxy groups, acrylate monomer containing vinyl ether groups, acrylate monomer containing oxygen-containing heterocyclic groups, or acrylate monomer containing nitrogen-containing oxygen-containing heterocyclic groups.

[0025] More preferably, in the UV-curable primer, the acrylate functional monomer is one or more of 2-phenoxyethyl acrylate, tetrahydrofurfuryl acrylate, glyceryl monomethacrylate, or ethyl 2-ethyleneoxyethoxyacrylate.

[0026] Preferably, in the UV-curable primer, the molecular weight of the acrylate functional monomer is 100~1000.

[0027] More preferably, in the UV-curable primer, the molecular weight of the acrylate functional monomer is 100-500.

[0028] Preferably, in the UV-curable primer, the acrylate specialty monomer is an acrylate monomer containing a cyclic acetal structure and containing C6~C6 bonds. 12 A mixture of cycloalkyl acrylate monomers.

[0029] In this invention, acrylate monomers containing a cyclic acetal structure commonly used in the art can be selected, such as one or more of the following: acetone glyceryl ester acrylate, dioxane acrylate, dioxolane acrylate, and orthocarbonate acrylate. In this invention, monomers containing C6~C6 can be selected. 12 The cycloalkyl acrylate monomer is, for example, one or more of 3,5,5-trimethylcyclohexyl acrylate, 4-tert-butylcyclohexyl acrylate or isobornyl acrylate.

[0030] Preferably, in the UV-curable primer, the acrylate specialty monomer is a mixture of acrylate monomers containing a cyclic acetal structure and acrylate monomers containing a cyclohexyl group.

[0031] More preferably, in the UV-curable primer, the acrylate specialty monomer is a mixture of acetone glyceryl acrylate and 3,5,5-trimethylcyclohexyl acrylate.

[0032] Preferably, the mass ratio of acetone glyceryl acrylate to 3,5,5-trimethylcyclohexyl acrylate is 1:0.2~1.

[0033] More preferably, the mass ratio of the acetone glyceryl acrylate to 3,5,5-trimethylcyclohexyl acrylate is 1:0.5~1.

[0034] In the UV-curable primer of the present invention, the photoinitiator can be one or more of the photoinitiators commonly used in the art, such as photoinitiator 1173, photoinitiator 184, photoinitiator YS160, photoinitiator TMO, photoinitiator TPO or photoinitiator TPO-L.

[0035] In UV-curable coatings, photoinitiators with different absorption wavelengths are often combined to increase the curing rate, thereby achieving a more uniform and thorough curing effect. Preferably, in the UV-curable primer, the photoinitiator is a mixture of photoinitiator TMO and photoinitiator YS160. Preferably, the mass ratio of photoinitiator TMO to photoinitiator YS160 is 1:0.2~0.4.

[0036] In the UV-curable primer of the present invention, the adhesion promoter can be selected from commonly used adhesion promoters in the art, such as, but not limited to, one or more of phosphate ester adhesion promoters, siloxane adhesion promoters, or acrylate adhesion promoters. Preferably, the adhesion promoter is a mixture of phosphate ester adhesion promoters and siloxane adhesion promoters. More preferably, the adhesion promoter is a mixture of monofunctional phosphate ester adhesion promoters and siloxane adhesion promoters.

[0037] In the UV-curable primer of this invention, the wetting and leveling agent can be a commonly used wetting and leveling agent in the art, generally a commercially available product, such as, but not limited to, HC5800 from Haohui New Materials and 2300 from Digo. Preferably, in the UV-curable primer, the wetting and leveling agent is HC5800 from Haohui New Materials.

[0038] The preparation method of the above-mentioned UV-curable primer is also within the scope of protection of this invention, including the following steps: stirring polyurethane acrylate resin, first acrylate monomer and adhesion promoter evenly, adding photoinitiator and wetting leveling agent, stirring evenly, and thus obtaining the UV-curable primer.

[0039] In the preparation of the primer, to prevent moisture from the air from entering the system and causing degradation of the primer's performance, preparation is usually carried out under an inert gas atmosphere. Preferably, the inert gas is nitrogen.

[0040] Preferably, the stirring temperature is 50~60℃.

[0041] After optimizing the adhesion between the primer and the substrate, applying an insulating topcoat to the primer surface enables the resulting coating to possess insulating properties. The topcoat can be a known topcoat with similar functions, or the following preferred option can be used.

[0042] The present invention also provides a preferred UV-curable topcoat, comprising the following components by weight percentage: Polyurethane resins containing carbon-carbon double bonds: 4-12%; Epoxy resins containing carboxyl groups: 3-7%; Bisphenol A epoxy resin 3~11%; Second acrylate monomer 60-75%; Photoinitiator 5-10%; Wetting and leveling agent 0.1~2%; Pigment 0.5-5%; The sum of the mass percentages of the polyurethane resin containing carbon-carbon double bonds, the epoxy resin containing carboxyl groups, and the bisphenol A epoxy resin is 18-30%; the second acrylate monomer includes monofunctional acrylate monomers and difunctional acrylate monomers; the mass ratio of the monofunctional acrylate monomer to the difunctional acrylate monomer is 50-60:5-15; the monofunctional acrylate monomer includes isobornyl acrylate and 3,5,5-trimethylcyclohexyl acrylate.

[0043] The UV-curable topcoat of this invention is prepared by compounding polyurethane resin, carboxyl-containing epoxy resin, and bisphenol A type epoxy resin in a specific ratio, and introducing monofunctional acrylate monomers as reactive diluents and difunctional acrylate monomers as crosslinking agents. This topcoat can cure rapidly to form a film, and the cured coating exhibits excellent weather resistance, flexibility, and insulation properties. Further research has found that when this UV-curable topcoat is used in conjunction with the aforementioned UV-curable primer, a synergistic effect is produced, promoting efficient bonding between the topcoat and primer, further improving coating performance, and endowing the coating with excellent insulation properties.

[0044] In this field, topcoat is typically applied to the substrate surface using processes such as spraying, brushing, or printing, while the viscosity of the primer directly affects its application. Preferably, the UV-curable topcoat has a viscosity of 30-80 cps at 25°C; and / or, a viscosity of 20-40 cps at 50°C.

[0045] More preferably, the UV-curable topcoat has a viscosity of 50-65 cps at 25°C; and / or a viscosity of 30-38 cps at 50°C.

[0046] It should be noted that the polyurethane resin containing carbon-carbon double bonds used in the UV-curable topcoat of this invention is not particularly limited in structure. Commonly used polyurethane resins containing carbon-carbon double bonds in the art can be selected, and commercially available products are generally sufficient. Examples include: CR93745 from Haohui New Materials, CR92511 from Haohui New Materials, or QW2141 from Qingwu Company, or one or more of these. Preferably, the polyurethane resin is 93991 from Haohui New Materials.

[0047] Preferably, in the UV-curable topcoat, the carboxyl-containing epoxy resin is one or more of L6135A, L6136, or L6132A from Lancoro Company.

[0048] In the UV-curable topcoat of this invention, the bisphenol A epoxy resin can be any commonly used bisphenol A epoxy resin in the art, generally a commercially available product, such as, but not limited to, one or more of Sartorma 153NS, Haohui 421S, or Changxing 621A-80. Preferably, the bisphenol A epoxy resin is Sartorma 153NS.

[0049] Preferably, in the UV-curable topcoat, the sum of the mass percentages of isoborneol acrylate and 3,5,5-trimethylethyl acrylate accounts for more than 50% of the monofunctional acrylate monomer.

[0050] Preferably, in the UV-curable topcoat, the monofunctional acrylate monomer further includes one or more of acetone glyceryl acrylate, 2-ethyleneoxyethoxyethyl acrylate, or 2-phenoxyethyl acrylate.

[0051] Preferably, in the UV-curable topcoat, the difunctional acrylate monomer is one or more of dipropylene glycol diacrylate, propoxylated neopentyl glycol diacrylate, tricyclodecanediethanol diacrylate, or neopentyl glycol diacrylate.

[0052] Preferably, in the UV-curable topcoat, the mass ratio of the monofunctional acrylate monomer to the difunctional acrylate monomer is 55:10.

[0053] Preferably, in the UV-curable topcoat, the second acrylate monomer further includes an acrylate monomer with a functionality of 3 or higher. Those skilled in the art know that acrylate monomers with a functionality of 3 or higher can significantly increase the crosslinking density of the coating, thereby enhancing the coating's hardness, abrasion resistance, and chemical resistance. However, when the crosslinking density is too high, it can lead to decreased coating flexibility, increased brittleness, and may cause problems such as excessive shrinkage stress and reduced adhesion. Preferably, the amount of the acrylate monomer with a functionality of 3 or higher added is less than 5% of the total mass of the UV-curable topcoat.

[0054] In the UV-curable topcoat of the present invention, the photoinitiator can be a commonly used photoinitiator in the art, and generally commercial products are acceptable, such as one or more of photoinitiator 1173, photoinitiator 184, photoinitiator YS160, photoinitiator TMO, photoinitiator TPO or photoinitiator TPO-L.

[0055] In UV-curable coatings, photoinitiators with different absorption wavelengths are often combined to increase the curing rate, thereby achieving a more uniform and thorough curing effect. Preferably, in the UV-curable topcoat, the photoinitiator is a mixture of photoinitiator TMO and photoinitiator YS160. Preferably, the mass ratio of photoinitiator TMO to photoinitiator YS160 is 1:0.2~0.4.

[0056] In the UV-curable topcoat of the present invention, the wetting and leveling agent can be a commonly used wetting and leveling agent in the art, generally a commercially available product, such as, but not limited to, HC5800 from Haohui New Materials and 2300 from Digo. Preferably, in the UV-curable topcoat, the wetting and leveling agent is HC5800 from Haohui New Materials.

[0057] In the UV-curable topcoat of the present invention, the pigment can be any pigment commonly used in the art, and no limitation is made herein.

[0058] The preparation method of the above-mentioned UV-curable topcoat is also within the scope of protection of this invention, including the following steps: stirring polyurethane resin containing carbon-carbon double bonds, epoxy resin containing carboxyl groups, bisphenol A epoxy resin and second acrylate monomer evenly, adding photoinitiator, wetting and leveling agent and pigment, stirring evenly to obtain the UV-curable topcoat.

[0059] In the preparation of the topcoat, to prevent moisture from the air from entering the system and causing deterioration of the topcoat's performance, preparation is usually carried out under an inert gas atmosphere. Preferably, the inert gas is nitrogen.

[0060] Preferably, the stirring temperature is 50~60℃.

[0061] The present invention also provides a UV-curable coating composition, comprising the above-described UV-curable primer and the above-described UV-curable topcoat.

[0062] The application of the above-mentioned UV-curable coating composition as a coating for nickel-plated substrates is also within the scope of protection of this invention.

[0063] The present invention provides a nickel-plated product, the nickel-plated product comprising a nickel-plated substrate and a coating formed by curing the above-mentioned UV-curable coating composition.

[0064] The preparation method of the above-mentioned nickel-plated product is also within the scope of protection of the present invention, which includes the following steps: first, the above-mentioned UV-curable primer is adhered to the surface of the nickel-plated substrate for pre-curing, and then the above-mentioned UV-curable topcoat is adhered to the primer on the surface of the nickel-plated substrate for curing, thereby obtaining the nickel-plated product.

[0065] Preferably, the adhesion process is one of spraying, brushing, or printing.

[0066] Preferably, the thickness of the UV-curable primer is 20~25μm.

[0067] Preferably, the pre-curing time is 1 to 3 seconds.

[0068] Preferably, the energy of the ultraviolet light used for pre-curing is 300~500 mJ / cm². 2 .

[0069] Preferably, the thickness of the UV-curable topcoat is 80~85μm.

[0070] Preferably, the curing time is 6-8 seconds.

[0071] Preferably, the energy of the ultraviolet light used for curing is 28000~30000 mJ / cm². 2 .

[0072] Compared with the prior art, the beneficial effects of the present invention include: This invention successfully prepared a UV-curable primer with excellent adhesion to nickel-plated substrates by introducing acrylate hard monomers, acrylate functional monomers, and acrylate specialty monomers in a specific ratio, synergistically combining polyurethane acrylate resin and adhesion promoters. Specifically, the acrylate hard monomers effectively improve the hardness of the coating, the acrylate functional monomers significantly enhance the adhesion of the coating through polar groups, and the acrylate specialty monomers effectively increase steric hindrance and molecular chain spacing through large-volume groups, thereby improving the curing shrinkage rate of the coating. This invention optimizes the formulation ratio of the UV-curable primer to achieve a balance between the coating's hardness, adhesion, and curing shrinkage rate, enabling it to cure on nickel-plated substrates and form a highly adhesive coating. Furthermore, this invention optimizes the formulation of the UV-curable topcoat, allowing it to produce a synergistic effect when used in combination with the UV-curable primer, promoting efficient bonding between the topcoat and primer, further improving coating performance and imparting excellent insulation properties to the coating. Therefore, the UV-curable coating composition provided by this invention can form a composite coating with strong adhesion, excellent insulation performance, and high stability on the surface of a nickel-plated substrate. Its adhesion performance is grade 1 or higher, and it passes voltage resistance and electrolyte resistance tests. Furthermore, after aging for 1000 hours under conditions of 85°C and 85% relative humidity, it still maintains excellent adhesion and insulation stability, solving the problem of poor performance of existing UV-curable insulating coatings on nickel-plated substrates. Detailed Implementation

[0073] The present invention will be further described below with reference to embodiments and comparative examples. These embodiments are merely typical descriptions of the present invention, but the present invention is not limited thereto. Unless otherwise specified, the test methods used in the following embodiments and comparative examples are conventional methods, and the raw materials and reagents used are commercially available from conventional commercial sources.

[0074] The raw materials used in each embodiment and comparative example are shown in Table 1: Table 1. Raw material information for each embodiment and comparative example.

[0075] Examples 1-16 Examples 1-16 provide different UV-curable coating compositions, and the specific formulations are shown in Table 2.

[0076] Table 2 Formulation table of UV-curable coating compositions in Examples 1-16

[0077] The specific formulations of primers 1-11 in Table 2 are shown in Table 3. Their preparation method includes the following steps: According to the formulation, the polyurethane acrylate resin, the first acrylate monomer, and the adhesion promoter are stirred evenly; a photoinitiator and a wetting and leveling agent are added; and the mixture is stirred evenly to obtain the primer.

[0078] Table 3 Formulation table for primers 1-11 (unit: g)

[0079] The specific formulations of topcoats 1 to 6 in Table 2 are shown in Table 4. The preparation method includes the following steps: According to the formulation, polyurethane resin containing carbon-carbon double bonds, epoxy resin containing carboxyl groups, bisphenol A epoxy resin, and a second acrylate monomer are stirred evenly; a photoinitiator, wetting and leveling agent, and pigment are added; and the mixture is stirred evenly to obtain the topcoat.

[0080] Table 4 Formulation table for topcoat 1-6 (unit: g)

[0081] Comparative Examples 1-6 Comparative Examples 1-6 provide different UV-curable coating compositions, and the specific formulations are shown in Table 5.

[0082] Table 5 Formulation of UV-curable coating compositions for Comparative Examples 1-6

[0083] The specific formulations of primers 12-17 in Table 5 are shown in Table 6. Their preparation methods are the same as those for primer 1.

[0084] Table 6 Formulation table for primers 12-17 (unit: g)

[0085] Performance testing (1) Viscosity test of primer and topcoat: The viscosity of the primer and topcoat prepared above was tested, and the results are shown in Table 7. The specific test method is as follows: the test was conducted according to GB / T 2794-2022, at 25℃ and 50℃ respectively.

[0086] Table 7 Viscosity test results for each primer and topcoat

[0087] (2) Adhesion performance test of primer The adhesion of the primer prepared above was tested, and the results are shown in Table 8. The specific test method is as follows: First, the primer was printed onto a nickel-plated steel plate, and then pre-cured and cured. The pre-curing conditions were an ultraviolet light energy of 400 mJ / cm². 2 The pre-curing time is 1 second; the curing conditions are an ultraviolet light energy of 28000 mJ / cm². 2 The pre-curing time is 6 seconds. Then, according to GB / T 9286-2021, the nickel-plated steel sheet is placed on a horizontal rigid plane and cut perpendicularly to the sample using a cross-cutting tool, ensuring all cuts penetrate to the substrate surface. Subsequently, the same number of cuts are made in the direction intersecting the original cut lines at 90° to form a grid. Finally, a soft brush is used to sweep several times, and transparent tape is applied above the grid, flattened, and then peeled off. The adhesion rating is determined by referring to the adhesion grading table.

[0088] Table 8 Adhesion test results of each primer

[0089] Among them, 0~1 indicates that its adhesion level is 0 < adhesion level ≤ 1, that is, the adhesion level reaches level 1, but does not reach level 0; 1~2 indicates that its adhesion level is 1 < adhesion level ≤ 2; 2~3 indicates that its adhesion level is 2 < adhesion level ≤ 3; 3~4 indicates that its adhesion level is 3 < adhesion level ≤ 4; 4~5 indicates that its adhesion level is 4 < adhesion level ≤ 5.

[0090] As shown in Table 8, primers 1-11 all exhibit excellent adhesion to nickel-plated substrates, with adhesion performance of grade 1 or higher. In contrast, primers 12-17 fail to achieve grade 1 adhesion. This indicates that the primer formulation provided by this invention can effectively improve the problem of insufficient adhesion of existing primers to nickel-plated substrates.

[0091] (3) Preparation of nickel-plated products Using nickel-plated steel sheet as the substrate, the UV-curable coating compositions obtained in the above embodiments and comparative examples are used to prepare nickel-plated products. The specific preparation method includes the following steps: first, the primer is printed onto the nickel-plated steel sheet and pre-cured; then, the topcoat is printed onto the nickel-plated steel sheet and cured to obtain the nickel-plated product.

[0092] The pre-curing condition is an ultraviolet light energy of 400 mJ / cm. 2 The pre-curing time is 1 second; the curing conditions are an ultraviolet light energy of 28000 mJ / cm². 2 The pre-curing time is 6 seconds.

[0093] (4) Performance testing of nickel-plated steel sheets The nickel-plated steel sheets prepared above were subjected to performance tests, and the test results are shown in Table 9. The specific test methods are as follows: 1. Adhesion test: The test was conducted according to GB / T 9286-2021. The nickel-plated steel sheet was placed on a horizontal, rigid plane, and a cross-cutting tool was used to cut perpendicularly to the sample, ensuring all cuts penetrated to the substrate surface. Subsequently, the same number of cuts were made in a direction intersecting the original cut lines at 90° angles, forming a grid. Then, a soft brush was used to sweep the surface several times, and transparent tape was applied over the grid, pressed flat, and then peeled off. The adhesion rating was determined by referring to the adhesion grading table.

[0094] 2. Withstand voltage test: The nickel-plated steel sheet is placed in an insulation withstand voltage tester and subjected to a 60-second withstand voltage test at 3000V. This test is repeated 25 times. If the leakage current in each test is ≤0.1mA, the test is considered passed.

[0095] 3. Electrolyte resistance test: After the electrolyte is dripped onto the surface of the nickel-plated steel sheet, it is placed in a vacuum drying oven at 85°C and baked for 2 hours. The test is considered passed when there are no bubbles or wrinkles on the surface of the nickel-plated steel sheet.

[0096] 4. Double 85 Test Nickel-plated steel sheets were stored at 85℃ / 85% relative humidity for 1000 hours, and their adhesion grade, voltage resistance, and shear strength were tested after aging. The shear strength test method is as follows: the structural adhesive is overlapped with the nickel-plated steel plate, and the test is performed in accordance with the method of GB / T7124.

[0097] Table 9 Test Results of Nickel-Plated Steel Sheets

[0098] Among them, 0~1 indicates that its adhesion level is 0 < adhesion level ≤ 1, that is, the adhesion level reaches level 1, but does not reach level 0; 1~2 indicates that its adhesion level is 1 < adhesion level ≤ 2; 2~3 indicates that its adhesion level is 2 < adhesion level ≤ 3; 3~4 indicates that its adhesion level is 3 < adhesion level ≤ 4; 4~5 indicates that its adhesion level is 4 < adhesion level ≤ 5.

[0099] As shown in Table 9, the UV curing composition provided by the present invention can form a composite coating with strong adhesion, excellent insulation performance and high stability on a nickel-plated substrate. Specifically, its adhesion performance is level 1 or above, and it can pass the voltage resistance and electrolyte resistance tests. After double 85 aging, it can still maintain excellent adhesion, voltage resistance and shear performance.

[0100] As can be seen from Comparative Examples 1 to 6, if the primer formulation is changed, it is difficult to balance the hardness, adhesion and curing shrinkage of the coating at the same time, so it is impossible to form a strong and dense cured coating on the nickel-plated substrate.

[0101] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A UV-curable primer, characterized in that, The UV-curable primer comprises the following components by weight percentage: 30-40% polyurethane acrylate resin; First acrylate monomer 48~64%; Photoinitiator 3-8%; Adhesion promoter 2-5%; Wetting and leveling agent 0.1-1%; The first acrylate monomer comprises a hard acrylate monomer, a functional acrylate monomer, and a specialty acrylate monomer; the mass ratio of the hard acrylate monomer to the functional acrylate monomer to the specialty acrylate monomer is 17.5~25:7.5~20:15~30; the glass transition temperature of the hard acrylate monomer is above 25°C; the functional acrylate monomer is an acrylate monomer containing at least one polar group; the polar group is one or more of phenoxy, hydroxy, vinyl ether, oxygen-containing heterocyclic, or nitrogen-containing heterocyclic groups; the specialty acrylate monomer contains a cyclic acetal structure or contains C6~C6 groups. 12 cycloalkyl acrylate monomers.

2. The UV-curable primer according to claim 1, characterized in that, The viscosity of the UV-curable primer at 25°C is 30~80 cps; And / or, the viscosity is 20-40 cps at 50°C.

3. The method for preparing the UV-curable primer according to any one of claims 1 to 2, characterized in that, The process includes the following steps: mixing polyurethane acrylate resin, first acrylate monomer and adhesion promoter evenly, adding photoinitiator and wetting leveling agent, and mixing evenly to obtain the UV-curable primer.

4. A UV-curable topcoat, characterized in that, The UV-curable topcoat comprises the following components by weight percentage: Polyurethane resins containing carbon-carbon double bonds: 4-12%; Epoxy resins containing carboxyl groups: 3-7%; Bisphenol A epoxy resin 3~11%; Second acrylate monomer 60-75%; Photoinitiator 5-10%; Wetting and leveling agent 0.1~2%; Pigment 0.5-5%; The sum of the mass percentages of the polyurethane resin containing carbon-carbon double bonds, the epoxy resin containing carboxyl groups, and the bisphenol A epoxy resin is 18-30%; the second acrylate monomer includes monofunctional acrylate monomers and difunctional acrylate monomers; the mass ratio of the monofunctional acrylate monomer to the difunctional acrylate monomer is 50-60:5-15; the monofunctional acrylate monomer includes isobornyl acrylate and 3,5,5-trimethylcyclohexyl acrylate.

5. The method for preparing the UV-curable topcoat according to claim 4, characterized in that, The process includes the following steps: mixing polyurethane resin containing carbon-carbon double bonds, epoxy resin containing carboxyl groups, bisphenol A epoxy resin and second acrylate monomer evenly, adding photoinitiator, wetting and leveling agent and pigment, and mixing evenly to obtain the UV-curable topcoat.

6. A UV-curable coating composition, characterized in that, The UV-curable coating composition includes the UV-curable primer according to any one of claims 1 to 2 and the UV-curable topcoat according to claim 4.

7. The use of the UV-curable coating composition of claim 6 as a coating for nickel-plated substrates.

8. A nickel-plated product, characterized in that, The nickel-plated product comprises a nickel-plated substrate and a coating formed by curing the UV-curable coating composition of claim 6.

9. The method for preparing the nickel-plated article according to claim 8, characterized in that, The process includes the following steps: first, the UV-curable primer described in any one of claims 1 to 2 is adhered to the surface of the nickel-plated substrate for pre-curing; then, the UV-curable topcoat described in claim 4 is adhered to the primer on the surface of the nickel-plated substrate for curing, thereby obtaining the nickel-plated product.

10. A nickel-plated casing for a cylindrical battery, characterized in that, The nickel-plated outer shell comprises a coating formed by curing the UV-curable coating composition of claim 6.

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