A uv light-cured coating composition, its preparation method and use on aluminum substrates

Abstract

The application discloses a UV light-cured coating composition, a preparation method thereof and application thereof on an aluminum base. The UV light-cured coating composition comprises a UV light-cured primer and a UV light-cured topcoat. The UV light-cured primer is composed of polyurethane acrylate resin, first acrylate monomer, photoinitiator, adhesion promoter and wetting and leveling agent in a specific ratio, and can be directly cured on the surface of an aluminum base without pre-treatment to form a coating layer with excellent adhesion. The formula of the UV light-cured topcoat is optimized, so that when the topcoat is used in combination with the primer, the combination of the topcoat and the primer is effectively promoted, and the coating layer has excellent insulation performance. The UV light-cured coating composition provided by the application can form a composite coating layer with strong adhesion, excellent insulation performance and high stability on the surface of the aluminum base without pre-treatment such as laser texturing or chemical passivation.

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 on an aluminum substrate. 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 meet the requirements of resisting external impacts and rapid heat dissipation. However, metal casings also introduce safety hazards such as short circuits. Therefore, cell insulation materials become a crucial 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 rapid development of new energy vehicle technology, PET blue film has gradually become unable to meet new 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 surface of 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 insulation requirements of 3000-4000V and above.

[0004] Against this backdrop, UV-curable coatings, due to their fast curing speed, lack of high-temperature treatment, and ability to adhere tightly to the casing, have become an important alternative to blue film coatings. For example, Chinese patent CN120173501A discloses a dielectric insulating protective coating with high surface energy and high adhesion, obtained from a combination of 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 / fillers. This coating can be applied to aluminum casings of battery cells or other external metal packaging materials (aluminum) of battery pack components. Another example is Chinese patent CN112893064A, which discloses a construction process for a UV-curable leakage resistance protection coating. This involves first spraying a primer onto a steel or aluminum substrate and pre-curing it, followed by spraying a topcoat for deep curing. This primer comprises the following components: epoxy acrylate, polyurethane acrylate, monofunctional acrylate, difunctional acrylate, polyfunctional acrylate, pigments and fillers, photoinitiator, silane coupling agent, and additives. It can be applied to aluminum or steel substrates to form a uniform coating with good adhesion.

[0005] However, existing UV-curable coatings generally require pretreatment of the aluminum substrate surface, such as laser texturing or chemical passivation, before adhering to the substrate surface to increase the surface roughness and thus enhance coating adhesion. However, laser texturing requires complex specialized equipment, is costly, and is not conducive to large-scale industrial production; while chemical passivation can easily lead to excessive corrosion of the aluminum substrate surface, affecting its mechanical properties, and at the same time, it generates a large amount of wastewater during the process, causing environmental problems.

[0006] Therefore, developing a UV-curable insulating coating suitable for aluminum casings of square batteries that can achieve excellent adhesion without pretreatment is of great practical significance for improving battery safety, simplifying production processes, and reducing overall costs. Summary of the Invention

[0007] The primary objective of this invention is to overcome the shortcomings and defects of existing UV-curable insulating coatings and to provide a UV-curable primer. This UV-curable primer can directly form a coating with excellent adhesion on the surface of an untreated aluminum substrate.

[0008] Another object of the present invention is to provide a method for preparing the above-mentioned UV-curable primer.

[0009] Another object of the present invention is to provide a UV-curable topcoat.

[0010] Another object of the present invention is to provide a method for preparing the above-mentioned UV-curable topcoat.

[0011] 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 an untreated aluminum substrate.

[0012] Another object of the present invention is to provide the application of the above-described UV-curable coating composition as a coating for aluminum substrates.

[0013] Another object of the present invention is to provide an aluminum article.

[0014] Another object of the present invention is to provide a method for preparing the above-mentioned aluminum articles.

[0015] Another object of the present invention is to provide a square aluminum battery casing.

[0016] To achieve the above objectives, the present invention adopts the following technical solution: A UV-curable primer comprising the following components by weight percentage: 20-30% polyurethane acrylate resin; First acrylate monomer 60-70%; Photoinitiator 5-10%; Adhesion promoter 0.5~2%; 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 15~25:20~30:15~30; 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.

[0017] 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 inter-chain spacing, thereby effectively improving the curing shrinkage rate of coatings. This invention, by compounding the above three types of monomers in a specific ratio and synergistically combining polyurethane acrylate resin and an adhesion promoter, significantly enhances the adhesion and shrinkage resistance of the primer to aluminum substrates, enabling the formation of a firmly adhered coating even when the aluminum substrate has not undergone pretreatment and its surface roughness has not been increased.

[0018] 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.

[0019] More preferably, the UV-curable primer has a viscosity of 40~60 cps at 25°C; and / or a viscosity of 20~35 cps at 50°C.

[0020] 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.

[0021] 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.

[0022] 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, tricyclodecane monomethanol acrylate, or cyclohexyl methacrylate.

[0023] More preferably, in the UV-curable primer, the acrylate hard monomer is one or more of trifluoroethyl methacrylate, isoborneol acrylate, cyclotrimethylolpropane methyl acetal acrylate, tricyclodecane monomethanol acrylate, or norborneol acrylate.

[0024] In this invention, the glass transition temperature of the acrylate hard monomer can be obtained by DSC instrument testing.

[0025] 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.

[0026] More preferably, in the UV-curable primer, the acrylate functional monomer is one or more of 2-phenoxyethyl acrylate, tetrahydrofurfuryl acrylate, glyceryl monomethacrylate, (2-ethyl-2-methyl-1,3-dioxopentyl-4-yl) acrylate or 2-ethyleneoxyethoxyethyl acrylate.

[0027] Preferably, in the UV-curable primer, the molecular weight of the acrylate functional monomer is 100~1000.

[0028] More preferably, in the UV-curable primer, the molecular weight of the acrylate functional monomer is 100-500.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] More preferably, in the UV-curable primer, the acrylate specialty monomer is a mixture of acetone glyceryl acrylate and 3,5,5-trimethylcyclohexyl acrylate.

[0033] Preferably, the mass ratio of acetone glyceryl acrylate to 3,5,5-trimethylcyclohexyl acrylate is 1:0.2~1.

[0034] More preferably, the mass ratio of the acetone glyceryl acrylate to 3,5,5-trimethylcyclohexyl acrylate is 1:0.5~1.

[0035] In the UV-curable primer of the present invention, the photoinitiator can be a commonly used photoinitiator in the art, generally a commercially available product, such as one or more of photoinitiator 1173, photoinitiator 184, photoinitiator YS160, photoinitiator TMO, photoinitiator TPO, or photoinitiator TPO-L. Preferably, the photoinitiator is photoinitiator TMO.

[0036] In the UV-curable primer of this 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 phosphate ester adhesion promoter. The phosphate ester adhesion promoter can be a commonly used phosphate ester adhesion promoter in the art, and generally commercially available products are sufficient, such as HC5110 from Haohui New Materials.

[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 account for 13-23%; Epoxy resin 1~7%; Second acrylate monomer 60-75%; Photoinitiator 5-10%; Wetting and leveling agent 0.1~2%; Pigment 3-8%; The epoxy resin is one or both of bisphenol A epoxy resin and phenolic epoxy resin. The second acrylate monomer includes a monofunctional acrylate monomer and a difunctional acrylate monomer; 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] This invention relates to a novel UV-curable topcoat, prepared by introducing monofunctional acrylate monomers as reactive diluents and difunctional acrylate monomers as crosslinking agents, based on polyurethane resins and epoxy resins containing carbon-carbon double bonds. This topcoat can cure rapidly to form a film, and the cured coating exhibits excellent weather resistance, flexibility, and insulation properties. Further research revealed that when this UV-curable topcoat is used in conjunction with the aforementioned UV-curable primer, a synergistic effect is achieved, promoting efficient bonding between the topcoat and primer, further enhancing coating performance, and imparting excellent insulation properties to the coating.

[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 40~60 cps at 25°C; and / or a viscosity of 24~35 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 the present 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, QW2141 from Qingwu Company, or one or more of QW2145 from Qingwu Company. Preferably, the polyurethane resin containing carbon-carbon double bonds is CR92511 from Haohui New Materials.

[0047] 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 one or more of Sartorma 153NS, Haohui 421S, or Changxing 621A-80. Preferably, the bisphenol A epoxy resin is Sartorma 153NS.

[0048] In the UV-curable topcoat of this invention, the phenolic epoxy resin can be a commonly used phenolic epoxy resin in the art, generally a commercially available product, such as one or more of Dongguan Huihe New Materials' 321S, 421, 429, or Changxing Chemical's 621-8. Preferably, the phenolic epoxy resin is Dongguan Huihe New Materials' 321S.

[0049] Preferably, the epoxy resin is a phenolic epoxy resin.

[0050] 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.

[0051] Preferably, in the UV-curable topcoat, the monofunctional acrylate monomer further includes one or more of acetone glyceryl acrylate, 2-vinyloxyethoxyethyl acrylate, 2-phenoxyethyl acrylate, methacrylate monoglyceride, or tricyclodecane monomethanol acrylate.

[0052] Preferably, in the UV-curable topcoat, the difunctional acrylate monomer is one or more of dipropylene glycol diacrylate, neopentyl glycol diacrylate, propoxylated neopentyl glycol diacrylate, or tricyclodecanediethanol diacrylate.

[0053] Preferably, in the UV-curable topcoat, the mass ratio of the monofunctional acrylate monomer to the difunctional acrylate monomer is 53~57:8~10.

[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 YS160, photoinitiator TMO, photoinitiator TP67 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 TP67 and photoinitiator YS160. Preferably, the mass ratio of photoinitiator TP67 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 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 aluminum substrates is also within the scope of protection of this invention.

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

[0064] Preferably, the roughness of the aluminum substrate is 2~8μm.

[0065] More preferably, the roughness of the aluminum substrate is 4~8μm.

[0066] In this invention, the maximum height R of the contour is used. Z To evaluate the roughness of the substrate, the maximum height R of the profile is... Z The determination can be carried out in accordance with GB / T 1031-2009.

[0067] The above-mentioned method for preparing aluminum products is also within the scope of protection of this invention, and includes the following steps: first, the above-mentioned UV-curable primer is adhered to the surface of the aluminum substrate for pre-curing, and then the above-mentioned UV-curable topcoat is adhered to the primer on the surface of the aluminum substrate for curing, thereby obtaining the aluminum product.

[0068] Preferably, the adhesion process is one of spraying, brushing, or printing.

[0069] More preferably, the adhesion process is printing.

[0070] Preferably, the thickness of the UV-curable primer is 20~25μm.

[0071] Preferably, the pre-curing time is 1~3 seconds.

[0072] Preferably, the energy of the ultraviolet light used for pre-curing is 300~500 mJ / cm². 2 .

[0073] Preferably, the thickness of the UV-curable topcoat is 80~85μm.

[0074] Preferably, the curing time is 6-8 seconds.

[0075] Preferably, the energy of the ultraviolet light used for curing is 28000~30000 mJ / cm. 2 .

[0076] Compared with the prior art, the beneficial effects of the present invention include: This invention successfully prepared a novel UV-curable primer by introducing acrylate hard monomers, acrylate functional monomers, and acrylate specialty monomers in a specific ratio, synergistically combining polyurethane acrylate resin and adhesion promoters. The acrylate hard monomers effectively improve the hardness of the coating, the acrylate functional monomers significantly enhance the adhesion of the coating through their polar groups, and the acrylate specialty monomers effectively increase steric hindrance and molecular chain spacing through their 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 form a coating with excellent adhesion directly on untreated aluminum substrates. 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 aluminum substrates without requiring pretreatment such as laser texturing or chemical passivation. 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. This overcomes the limitation of existing UV-curable insulating coatings requiring pretreatment on aluminum substrates, simplifies the coating application process, and improves production efficiency. Detailed Implementation

[0077] 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.

[0078] 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.

[0079] Examples 1-20 Examples 1-20 provide different UV-curable coating compositions, and the specific formulations are shown in Table 2.

[0080] Table 2. Details of UV-curable coating compositions for Examples 1-20

[0081] The specific formulations of primers 1-13 in Table 2 are shown in Table 3. Their preparation method includes the following steps: According to the formulation, polyurethane acrylate resin, first acrylate monomer, and adhesion promoter are stirred evenly; then, photoinitiator and wetting / leveling agent are added and stirred evenly to obtain the primer.

[0082] Table 3 Formulation table for primers 1-13 (unit: g)

[0083] The specific formulations of topcoats 1-8 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, and 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.

[0084] Table 4 Formulation table for topcoat 1-8 (unit: g)

[0085] Comparative Examples 1-10 Comparative Examples 1 to 10 provide different UV-curable coating compositions, and the specific formulations are shown in Table 5.

[0086] Table 5. List of UV-curable coating compositions for Comparative Examples 1-10

[0087] The specific formulations of primers 14-21 in Table 5 are shown in Table 6. Their preparation methods are the same as those for primer 1.

[0088] Table 6 Formulation table for primers 14-21 (unit: g)

[0089] Primer 22 The preparation method, based on Chinese patent CN112893064A, includes the following steps: Weigh out 15g of bifunctional fatty acid-modified bisphenol A epoxy acrylate and 10g of bifunctional poly(H) 12MDI isocyanate acrylate, 15g tetrahydrofuran acrylate, 10g N-hydroxyethyl acrylamide, 20g tricyclodecanediethanol dimethyl diacrylate, 15g tri(2-hydroxyethyl)isocyanurate triacrylate, 10g pigments and fillers, 3g 2-hydroxy-2-methyl-1-phenyl-1-propanone, 2g (2,4,6-trimethylbenzyl)diphenylphosphine oxide, 3g silane coupling agent KH-560, 0.8g dispersant, 0.3g defoamer, and 0.5g leveling agent are mixed thoroughly to obtain primer 22.

[0090] Primer 23 The preparation method, referring to Chinese patent CN120173501A, includes the following steps: S1. Weigh 45g of a combination of norborneol acrylate and isooctyl acrylate (mass ratio 4:1). Under conditions of no light radiation and below 30 degrees Celsius, add 3g of photoinitiator (2,2-dimethoxy-phenylacetophenone), 8g of adhesion promoter (glycidyl methacrylate), and a combination of wetting, dispersing, and defoaming agent (Digo 2300) (mass ratio 1:1). Stir under vacuum until there are no bubbles or powders present. Stop vacuuming and add 19.3g of a combination of high-viscosity silicone-modified polyurethane acrylate, polyester polyurethane acrylate, and polyether polyurethane acrylate prepolymers (the above three prepolymers are in a mass ratio of 1:3:1), and 6.4g of dipentaerythritol hexaacrylate. Stir and heat to 50 degrees Celsius until the mixture is evenly dispersed. S2. To prevent moisture from being present in the premixed material, a vacuum can be applied appropriately. Finally, at 50 degrees Celsius, add 17.5g of powder, including insulating powder, thermally conductive filler, and pigment (the insulating powder is mainly precipitated silica, the thermally conductive filler is mainly alumina treated with coupling agent, and the pigment can be phthalocyanine or ultramarine, with a mass ratio of 10:5:1), and 0.8g of deacidifying agent (zinc phosphate). After high-speed dispersion for a certain period of time until uniform, the primer 23 is obtained.

[0091] 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.

[0092] Table 7 Viscosity test results for each primer and topcoat

[0093] (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: S1. Substrate treatment: Three aluminum substrates were immersed in an acidic degreasing solution to remove surface oil and dirt. After cleaning, they underwent pretreatment, the specific pretreatment method of which is as follows: The first aluminum substrate is prepared without any pretreatment to obtain the raw aluminum substrate. The second aluminum substrate is chemically passivated to obtain a chemically passivated aluminum substrate. The third aluminum substrate was subjected to laser texturing treatment to obtain a laser-textured aluminum substrate.

[0094] The chemical passivation process involves immersion or spraying with a commercially available chromium-free passivation solution for 10 minutes.

[0095] Roughness tests were performed on the original aluminum substrate, the chemically passivated aluminum substrate, and the laser-textured aluminum substrate, and the results are shown in Table 8. The roughness test method is as follows:

[0096] S2. Curing: The primer was applied to the aluminum substrates after the three pretreatment methods using both printing and spraying methods, and then pre-cured and cured.

[0097] 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.

[0098] S3. Adhesion Test: The test was conducted according to GB / T 9286-2021. The aluminum 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 the direction intersecting the original cut lines at 90° to form a grid. Finally, a soft brush was used to sweep the surface several times, and transparent tape was applied over the grid, flattened, and then peeled off. The adhesion grade was determined by referring to the adhesion grading table, ranging from 0 (best) to 5 (worst). The test results are shown in Table 9.

[0099] Table 9 Adhesion grade test results for each primer

[0100] 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.

[0101] As shown in Table 9, primers 1-13 all exhibit excellent adhesion to the original aluminum substrate, with adhesion performance of grade 1 or higher. In contrast, primers 14-23 all fail to achieve grade 1 adhesion on the original aluminum substrate. This indicates that the primers prepared by this invention can effectively improve the defect of poor adhesion of existing primers to the original aluminum substrate.

[0102] Primer 22 and primer 23 require pretreatment of the aluminum substrate, such as chemical passivation or laser texturing, to improve the surface roughness of the substrate before they can be cured to form a coating.

[0103] Primers 14-21, however, cannot achieve an effective balance between coating hardness, adhesion, and curing shrinkage, resulting in poor adhesion on both raw aluminum substrates and aluminum substrates that have undergone chemical passivation or laser texturing.

[0104] (3) Preparation of aluminum products The UV-curable coating compositions obtained in the above embodiments and comparative examples are adhered to a raw aluminum substrate to prepare aluminum products. The specific preparation method includes the following steps: first, a primer is printed onto the raw aluminum substrate and pre-cured; then, a topcoat is printed onto the raw aluminum substrate and cured to obtain an aluminum metal plate.

[0105] 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.

[0106] (4) Performance testing of aluminum metal plates The aluminum metal plates prepared above were subjected to performance tests, and the test results are shown in Table 10. The specific test methods are as follows: 1. Adhesion test: The test was conducted according to GB / T 9286-2021. An aluminum 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. The same number of cuts were then made in a direction intersecting the original cut lines at 90° angles, forming a grid. Afterward, 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.

[0107] 2. Withstand voltage test: Place the aluminum plate in an insulation withstand voltage tester and perform a 60s withstand voltage test at 3000V. Repeat the test 25 times. If the leakage current is ≤0.1mA in each test, the test is considered passed.

[0108] 3. Electrolyte resistance test: After the electrolyte is dripped onto the surface of the aluminum plate, 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 aluminum plate.

[0109] 4. Double 85 Test An aluminum sheet was stored at 85℃ / 85% relative humidity for 1000 hours, and its 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 aluminum metal plate, and the test is performed in accordance with the method of GB / T7124.

[0110] Table 10 Test Results of Aluminum Metal Plates

[0111] 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.

[0112] As shown in Table 10, the UV curing composition provided by the present invention can form a composite coating with strong adhesion, excellent insulation performance and high stability on the original aluminum substrate. Its adhesion performance is grade 1 or above, and it can pass the voltage resistance and electrolyte resistance tests. After aging with double 85 for 1000 hours, its adhesion performance can still be maintained at grade 1 or above, its shear strength is above 10 MPa, and it has excellent voltage resistance performance.

[0113] As can be seen from Comparative Examples 1 to 8, if the primer formulation is changed, it is difficult to achieve an effective balance between coating hardness, adhesion performance and curing shrinkage, resulting in the inability to form a strong and dense cured coating on the original aluminum substrate.

[0114] As can be seen from Comparative Examples 9 and 10, the adhesion of existing primers to the original aluminum substrate is poor, making it difficult to meet application requirements. This invention optimizes the primer formulation, enabling the prepared primer to form a strong and dense cured coating on the original aluminum substrate, effectively overcoming the shortcomings of existing technologies that generally require pretreatment of the aluminum substrate.

[0115] 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: 20-30% polyurethane acrylate resin; First acrylate monomer 60-70%; Photoinitiator 5-10%; Adhesion promoter 0.5~2%; 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 15~25:20~30:15~30; 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 account for 13-23%; Epoxy resin 1~7%; Second acrylate monomer 60-75%; Photoinitiator 5-10%; Wetting and leveling agent 0.1~2%; Pigment 3-8%; The epoxy resin is one or both of bisphenol A epoxy resin and phenolic epoxy resin. The second acrylate monomer includes a monofunctional acrylate monomer and a difunctional acrylate monomer; 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 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 aluminum substrates.

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

9. The method for preparing the aluminum product 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 an aluminum substrate for pre-curing; finally, the UV-curable topcoat described in claim 4 is adhered to the primer on the surface of the aluminum substrate for curing, thereby obtaining the aluminum product.

10. A square aluminum battery casing, characterized in that, The aluminum casing comprises a coating formed by curing the UV-curable coating composition of claim 6.

Images