Epoxy structural adhesive for metal bonding of automobiles and preparation method thereof

Abstract

This application relates to the field of structural adhesives, and particularly to an epoxy structural adhesive for automotive metal bonding and its preparation method. The epoxy structural adhesive for automotive metal bonding, by weight, comprises the following raw materials: 30-50 parts epoxy matrix, 20-35 parts toughening agent, 3-6 parts curing agent, 2-5 parts accelerator, 1-2 parts silane coupling agent, 0.2-0.3 parts defoamer, 0.8-1.5 parts leveling agent, 0.2-0.3 parts thickener, 3-8 parts composite functional agent, and 10-25 parts solid filler. This application provides a one-component epoxy structural adhesive that can be stored stably at room temperature for a long period, can be rapidly cured in standard automotive drying processes, further reduces the internal performance contradictions existing in the prior art, and maintains excellent overall application performance.

Description

Technical Field

[0001] This application relates to the field of structural adhesives, and in particular to an epoxy structural adhesive for bonding automotive metals and its preparation method. Background Technology

[0002] In the automotive manufacturing industry, structural adhesives have become one of the key materials for achieving lightweighting and improving vehicle body rigidity and durability. Among them, epoxy resin adhesives are widely used in the structural bonding of metal car bodies due to their excellent adhesion, chemical stability, high temperature resistance, and high mechanical strength. While traditional two-component epoxy adhesives offer a wide range of adjustable properties, they require precise mixing and proportioning before use, which not only increases the complexity and time cost of the production process but also introduces the risk of performance fluctuations due to uneven mixing. Therefore, single-component epoxy structural adhesives suitable for automated production lines and ready for immediate use have become an urgent technological direction for the industry.

[0003] Currently, to achieve a balance between room temperature storage stability and rapid curing upon heating in single-component epoxy adhesives, the industry generally employs latent curing systems. Among these, systems using dicyandiamide as a curing agent in combination with various accelerators are the mainstream technical solution. These adhesives typically require storage and transportation at low temperatures to inhibit premature reactions, which undoubtedly increases energy consumption and costs in the supply chain and creates inconvenience for material management on the production floor.

[0004] Regarding curing performance, to meet the stringent mechanical and durability requirements of the automotive industry, especially the high strength, high peel strength, and impact resistance required for substrates such as galvanized steel sheets in some applications, effective toughening components must be incorporated into the adhesive formulation. However, many existing toughening methods often sacrifice the rigidity or heat resistance of the adhesive layer, making it difficult to achieve an ideal balance between toughness and strength during high-speed curing cycles. Furthermore, in pursuit of shorter curing times or lower curing temperatures, some technical solutions employ highly reactive accelerators, but this typically further compromises the adhesive's storage stability, leading to a shortened shelf life at room temperature and excessively rapid viscosity increases.

[0005] In summary, existing epoxy structural adhesive technologies for automotive metal bonding mainly suffer from a prominent contradiction between storage stability and curing activity; difficulty in simultaneously achieving high shear strength, high peel toughness, and excellent impact resistance under rapid curing conditions; and difficulty in achieving excellent aging resistance and corrosion resistance. Summary of the Invention

[0006] The purpose of this invention is to provide a single-component epoxy structural adhesive that can be stored stably at room temperature for a long time, can be rapidly cured in a standard automotive drying process, and further reduces the internal performance contradictions existing in the prior art, while maintaining excellent overall application performance.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] The first aspect of this application provides an epoxy structural adhesive for bonding automotive metals, comprising, by weight, the following raw materials: 30-50 parts epoxy matrix, 20-35 parts toughening agent, 3-6 parts curing agent, 2-5 parts accelerator, 1-2 parts silane coupling agent, 0.2-0.3 parts defoamer, 0.8-1.5 parts leveling agent, 0.2-0.3 parts thickener, 3-8 parts composite functional agent, and 10-25 parts solid filler.

[0009] In a preferred embodiment, the epoxy resin is a combination of bisphenol F epoxy resin and flexible epoxy resin.

[0010] In a preferred embodiment, the mass ratio of the bisphenol F epoxy resin to the flexible epoxy resin is (20~30):(10~20).

[0011] A more preferred embodiment is that the mass ratio of the bisphenol F epoxy resin to the flexible epoxy resin is (26~30):(17~20).

[0012] In a preferred embodiment, the epoxy equivalent of the bisphenol F epoxy resin is 150~200 g / eq.

[0013] In a more preferred embodiment, the epoxy equivalent of the bisphenol F epoxy resin is 160~180 g / eq.

[0014] In a preferred embodiment, the mass ratio of the epoxy resin, toughening agent, and composite functional agent is (3.5~5):(2.5~3.3):(0.4~0.7).

[0015] In a more preferred embodiment, the mass ratio of the epoxy resin, toughening agent, and composite functional agent is (4~5):(2.75~3.3):(0.5~0.6).

[0016] In a preferred embodiment, the flexible epoxy resin is flexible epoxy resin BH-026 and / or flexible epoxy resin DER-3913.

[0017] A more preferred embodiment is that the flexible epoxy resin is flexible epoxy resin BH-026, manufactured by Taizhou Hengchuang in China.

[0018] A more preferred embodiment is that the flexible epoxy resin is DER-3913, manufactured by Dow Chemical Company, USA.

[0019] A more preferred embodiment is that the flexible epoxy resin is a combination of flexible epoxy resin BH-026 and flexible epoxy resin DER-3913.

[0020] In a preferred embodiment, the mass ratio of the flexible epoxy resin BH-026 to the flexible epoxy resin DER-3913 is (1~1.5):1.

[0021] In a preferred embodiment, the toughening agent is a combination of a core-shell polymer toughening agent and a modified polyurethane toughening agent.

[0022] In a preferred embodiment, the mass ratio of the core-shell polymer toughening agent to the modified polyurethane toughening agent is (2~2.5):(0.8~1.2).

[0023] In a more preferred embodiment, the mass ratio of the core-shell polymer toughening agent to the modified polyurethane toughening agent is (2.2~2.3):(0.9~1).

[0024] In a preferred embodiment, the core-shell polymer toughening agent is MX-154, manufactured by Kanekachi, Japan.

[0025] In a preferred embodiment, the modified polyurethane toughening agent is QR-9466, manufactured by Adico Japan.

[0026] The epoxy resin and toughening agent composite system used in this application achieves a balance between strength and toughness, and endows the structural adhesive with excellent comprehensive performance, constructing a more stable three-dimensional cross-linked network. Bisphenol F epoxy resin, as a rigid skeleton, provides strong cohesive strength and heat resistance, while flexible epoxy resin, like molecular springs, is interwoven within, effectively absorbing and dispersing stress. Simultaneously, core-shell polymer particles act as energy dissipation centers, preventing crack propagation through plastic deformation, and modified polyurethane long chains further interweave and strengthen the network, significantly improving impact and peel resistance. This combined effect ensures that the adhesive layer can firmly bond to metals under severe temperature differences and mechanical vibrations without cracking due to brittleness, ultimately achieving a highly reliable long-lasting bond.

[0027] In a preferred embodiment, the curing agent is a dicyandiamide curing agent.

[0028] In a preferred embodiment, the dicyandiamide curing agent is ultrafine dicyandiamide.

[0029] In a preferred embodiment, the average D50 particle size of the ultrafine dicyandiamide is 3~8μm.

[0030] In a more preferred embodiment, the average D50 particle size of the ultrafine dicyandiamide is 3~4.5μm.

[0031] In a preferred embodiment, the accelerator is at least one selected from substituted urea accelerators, modified amine accelerators, and organic guanidine accelerators.

[0032] A more preferred embodiment is that the accelerator is a substituted urea accelerator or a modified amine accelerator.

[0033] A more preferred embodiment is that the accelerator is a substituted urea accelerator.

[0034] A more preferred embodiment is that the substituted urea accelerator is LS-U400 or LS-U700, manufactured by Dalian Liansheng in China.

[0035] In a preferred embodiment, the silane coupling agent is at least one of KH-550, KH-560, and KH-540.

[0036] In a more preferred embodiment, the silane coupling agent is KH-550 or KH-560.

[0037] In a more preferred embodiment, the silane coupling agent is KH-560.

[0038] In a preferred embodiment, the defoamer is any one of the organosilicon defoamers.

[0039] In a preferred embodiment, the leveling agent is any one of BYK-333, BYK-354, and BYK-358N.

[0040] In a preferred embodiment, the leveling agent is BYK-333.

[0041] In a preferred embodiment, the thickener is at least one selected from fumed silica, organobentonite, polyamide wax, hydrogenated castor oil, and cellulose.

[0042] In a more preferred embodiment, the thickener is fumed silica or organobentonite.

[0043] In a more preferred embodiment, the thickener is fumed silica.

[0044] In a preferred embodiment, the composite functional agent is a combination of cocoyl monoethanolamide, isopropyl tris(dioctyl pyrophosphate) titanate, and acetylacetone.

[0045] In a preferred embodiment, the mass ratio of the cocoyl monoethanolamide, isopropyl tris(dioctylpyrophosphate)titanate and acetylacetone is (2~4):(2~3):(1~2).

[0046] In a more preferred embodiment, the mass ratio of the cocoyl monoethanolamide, isopropyl tris(dioctyl pyrophosphate) titanate, and acetylacetone is (3~4):(2.5~3):(1.6~2).

[0047] The addition of composite functional agents effectively improves the interfacial properties and long-term durability of the structural adhesive. As a compatibility and wetting medium, it promotes the uniform dispersion of each component and its spreading and penetration onto the metal surface, enhances the bonding ability with the metal oxide layer, and forms a strong interface. This significantly enhances the adhesive substrate and its resistance to environmental corrosion. Furthermore, by subtly regulating the curing reaction process, it helps to form a denser network structure. Together, these factors enable the adhesive layer to maintain extremely high bonding strength and reliability for a long time under harsh environments such as humidity, heat, and salt spray.

[0048] In a preferred embodiment, the solid filler is at least one selected from silica powder, calcium carbonate, barium sulfate, and talc.

[0049] In a more preferred embodiment, the solid filler is silica powder or calcium carbonate.

[0050] In a more preferred embodiment, the solid filler is silica powder.

[0051] In a preferred embodiment, the average D50 particle size of the silicon micropowder is 0.5~2μm.

[0052] In a more preferred embodiment, the average D50 particle size of the silicon micropowder is 0.5~1μm.

[0053] The second aspect of this application provides a method for preparing the above-mentioned epoxy structural adhesive for automotive metal bonding, specifically including the following steps: S1: Adding epoxy matrix, toughening agent, solid filler, silane coupling agent, leveling agent, thickener, and composite functional agent to a planetary mixer, dispersing at 20-30 rpm revolution, 500-600 rpm rotation, and a vacuum of -0.095 MPa for 25-35 min, controlling the temperature at 50-60℃ during the process, to obtain a uniform matrix mixture; S2: After cooling to 35-40℃, adding the remaining raw materials, and dispersing at 15-20 rpm revolution, 60-80 rpm rotation, and a vacuum of -0.095 MPa for 15-20 min to ensure uniform dispersion of the curing system; S3: After discharge, transferring the material to a homogenizer for final homogenization treatment in a vacuum environment at <40℃ for 5-10 min, and discharging the final product.

[0054] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0055] 1. The epoxy structural adhesive provided in this application, while ensuring excellent construction performance, achieves long-term stable storage of a single-component adhesive at room temperature, greatly facilitating transportation and inventory management. It achieves 10-minute curing at 140~150℃ via electrophoresis, meeting the requirements of automotive metal structural adhesives while significantly shortening curing time and improving production efficiency. Furthermore, the resulting structural adhesive not only exhibits high shear strength and flexibility in bonding with metals, especially galvanized steel sheets for automobiles, but also allows for storage at room temperature for more than 6 months, improving the product's storage cycle and reducing energy consumption during storage.

[0056] 2. This application achieves a balance between strength and toughness, constructing a stable three-dimensional cross-linked network. Bisphenol F epoxy resin acts as a rigid skeleton, providing strength and heat resistance; flexible epoxy resin is interspersed within to absorb and disperse stress; core-shell polymer particles prevent crack propagation through plastic deformation; modified polyurethane long-chain interwoven reinforcement network enhances impact resistance. Under these combined effects, the adhesive layer is firmly bonded and does not crack under severe working conditions, achieving highly reliable and long-lasting adhesion.

[0057] 3. The composite functional agent of this application improves the interfacial performance and durability. It promotes the dispersion of components and the spreading and penetration of the metal surface, and enhances the connection with the metal oxide layer to form a strong interface to improve the resistance to environmental corrosion. At the same time, it regulates the curing reaction process, which helps to form a denser network structure, so that the adhesive layer can maintain extremely high bonding strength and reliability in harsh environments for a long time. Attached Figure Description

[0058] Figure 1 This is a photograph of the epoxy structural adhesive for bonding automotive metals prepared in Example 1 of this application. Detailed Implementation

[0059] The technical solutions in the embodiments of this application will be clearly and completely described below. 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 are within the scope of protection of this application.

[0060] In the following specific embodiments, unless otherwise specified, the sources / preparation methods of some raw materials are as follows:

[0061] Bisphenol F epoxy resin NPEF-170, 170g / eq, Nan Ya Plastics, China.

[0062] Flexible epoxy resin BH-026, Taizhou Hengchuang, China.

[0063] Flexible epoxy resin DER-3913, Dow Chemical Co., Ltd.

[0064] Core-shell polymer toughening agent MX-154, Kanekachi, Japan.

[0065] The modified polyurethane toughening agent is QR-9466, manufactured by Adico Japan.

[0066] Dicyandiamide curing agent LS-D8, D50 average particle size is 4μm, manufactured by Dalian Liansheng, China.

[0067] LS-U400, a urea accelerator, is manufactured by Dalian Liansheng in China.

[0068] LS-U700, a urea accelerator, is manufactured by Dalian Liansheng in China.

[0069] Fumed silica H18, Wacker Chemie, Germany.

[0070] Example 1

[0071] An epoxy structural adhesive for bonding automotive metals comprises, by weight, 47.5 parts epoxy matrix, 32 parts toughening agent, 5.2 parts curing agent, 4 parts accelerator, 1 part silane coupling agent, 0.2 parts defoamer, 0.9 parts leveling agent, 0.3 parts thickener, 5.8 parts composite functional agent, and 10 parts solid filler.

[0072] The epoxy resin is a combination of bisphenol F epoxy resin NPEF-170 and flexible epoxy resin DER-3913 in a mass ratio of 29.5:18.

[0073] The toughening agent is a combination of core-shell polymer toughening agent MX-154 and modified polyurethane toughening agent QR-9466, with a mass ratio of 2.2:1.

[0074] The curing agent is ultrafine dicyandiamide curing agent LS-D8, with an average particle size of 4μm (D50).

[0075] The accelerator is the substituted urea accelerator LS-U700.

[0076] The silane coupling agent is KH-560; the defoamer is BYK-066N; the leveling agent is BYK-333; the thickener is fumed silica H18; and the solid filler is silica powder with an average particle size of 1 μm at D50.

[0077] The composite functional agent is a combination of cocoyl monoethanolamide, isopropyl tris(dioctyl pyrophosphate) titanate and acetylacetone in a mass ratio of 3.5:2.5:1.8.

[0078] A method for preparing the above-mentioned epoxy structural adhesive for automotive metal bonding specifically includes the following steps: S1: Add epoxy matrix, toughening agent, solid filler, silane coupling agent, leveling agent, thickener, and composite functional agent to a planetary mixer, and disperse at 25 rpm revolution, 500 rpm rotation, and a vacuum of -0.095 MPa for 30 min, while controlling the temperature at 60℃, to obtain a uniform matrix mixture; S2: After cooling to 40℃, add the remaining raw materials, and disperse at 20 rpm revolution, 70 rpm rotation, and a vacuum of -0.095 MPa for 20 min to ensure uniform dispersion of the curing system; S3: After discharge, transfer the material to a homogenizer and perform final homogenization treatment in a vacuum environment at <40℃ for 10 min, and discharge the final product.

[0079] The actual product of the epoxy structural adhesive for automotive metal bonding prepared in this embodiment is shown below. Figure 1 As shown.

[0080] Example 2

[0081] An epoxy structural adhesive for bonding automotive metals comprises, by weight, 47.5 parts epoxy matrix, 32 parts toughening agent, 5.2 parts curing agent, 4 parts accelerator, 1 part silane coupling agent, 0.2 parts defoamer, 0.9 parts leveling agent, 0.3 parts thickener, 5.8 parts composite functional agent, and 10 parts solid filler.

[0082] The epoxy resin is a combination of bisphenol F epoxy resin NPEF-170 and flexible epoxy resin BH-026 in a mass ratio of 29.5:18.

[0083] The toughening agent is a combination of core-shell polymer toughening agent MX-154 and modified polyurethane toughening agent QR-9466, with a mass ratio of 2.2:1.

[0084] The curing agent is ultrafine dicyandiamide curing agent LS-D8, with an average particle size of 4μm (D50).

[0085] The accelerator is the substituted urea accelerator LS-U400.

[0086] The silane coupling agent is KH-560; the defoamer is BYK-066N; the leveling agent is BYK-333; the thickener is fumed silica H18; and the solid filler is silica powder with an average particle size of 1 μm at D50.

[0087] The composite functional agent is a combination of cocoyl monoethanolamide, isopropyl tris(dioctyl pyrophosphate) titanate and acetylacetone in a mass ratio of 3.5:2.5:1.8.

[0088] A method for preparing the above-mentioned epoxy structural adhesive for automotive metal bonding specifically includes the following steps: S1: Add epoxy matrix, toughening agent, solid filler, silane coupling agent, leveling agent, thickener, and composite functional agent to a planetary mixer, and disperse at 25 rpm revolution, 500 rpm rotation, and a vacuum of -0.095 MPa for 30 min, while controlling the temperature at 60℃, to obtain a uniform matrix mixture; S2: After cooling to 40℃, add the remaining raw materials, and disperse at 20 rpm revolution, 70 rpm rotation, and a vacuum of -0.095 MPa for 20 min to ensure uniform dispersion of the curing system; S3: After discharge, transfer the material to a homogenizer and perform final homogenization treatment in a vacuum environment at <40℃ for 10 min, and discharge the final product.

[0089] Example 3

[0090] An epoxy structural adhesive for bonding automotive metals comprises, by weight, the following raw materials: 40 parts epoxy matrix, 32 parts toughening agent, 4 parts curing agent, 3 parts accelerator, 1 part silane coupling agent, 0.2 parts defoamer, 0.9 parts leveling agent, 0.3 parts thickener, 5.8 parts composite functional agent, and 15 parts solid filler.

[0091] The epoxy resin is a combination of bisphenol F epoxy resin NPEF-170, flexible epoxy resin BH-026 and flexible epoxy resin DER-3913, with a mass ratio of 20:10:10.

[0092] The toughening agent is a combination of core-shell polymer toughening agent MX-154 and modified polyurethane toughening agent QR-9466, with a mass ratio of 2.2:1.

[0093] The curing agent is ultrafine dicyandiamide curing agent LS-D8, with an average particle size of 4μm (D50).

[0094] The accelerator is the substituted urea accelerator LS-U700.

[0095] The silane coupling agent is KH-560; the defoamer is BYK-066N; the leveling agent is BYK-333; the thickener is fumed silica H18; and the solid filler is silica powder with an average particle size of 1 μm at D50.

[0096] The composite functional agent is a combination of cocoyl monoethanolamide, isopropyl tris(dioctyl pyrophosphate) titanate and acetylacetone in a mass ratio of 3.5:2.5:1.8.

[0097] A method for preparing the above-mentioned epoxy structural adhesive for automotive metal bonding specifically includes the following steps: S1: Add epoxy matrix, toughening agent, solid filler, silane coupling agent, leveling agent, thickener, and composite functional agent to a planetary mixer, and disperse at 25 rpm revolution, 500 rpm rotation, and a vacuum of -0.095 MPa for 30 min, while controlling the temperature at 60℃, to obtain a uniform matrix mixture; S2: After cooling to 40℃, add the remaining raw materials, and disperse at 20 rpm revolution, 70 rpm rotation, and a vacuum of -0.095 MPa for 20 min to ensure uniform dispersion of the curing system; S3: After discharge, transfer the material to a homogenizer and perform final homogenization treatment in a vacuum environment at <40℃ for 10 min, and discharge the final product.

[0098] Comparative Example 1

[0099] An epoxy structural adhesive for bonding automotive metals comprises, by weight, the following raw materials: 50 parts epoxy matrix, 33 parts toughening agent, 5.2 parts curing agent, 4 parts accelerator, 1 part silane coupling agent, 0.2 parts defoamer, 0.9 parts leveling agent, 0.3 parts thickener, 2.3 parts composite functional agent, and 10 parts solid filler.

[0100] The remaining implementation methods are the same as in Example 1.

[0101] Comparative Example 2

[0102] An epoxy structural adhesive for bonding automotive metals comprises, by weight, the following raw materials: 55 parts epoxy matrix, 27.5 parts toughening agent, 5.2 parts curing agent, 4 parts accelerator, 1 part silane coupling agent, 0.2 parts defoamer, 0.9 parts leveling agent, 0.3 parts thickener, 5.8 parts composite functional agent, and 10 parts solid filler.

[0103] The toughening agent is a combination of a core-shell polymer toughening agent and a modified polyurethane toughening agent, with a mass ratio of 2.5:0.25.

[0104] The remaining implementation methods are the same as in Example 1.

[0105] Comparative Example 3

[0106] An epoxy structural adhesive for bonding automotive metals, comprising, by weight, 47.5 parts epoxy matrix, 32 parts toughening agent, 5.2 parts curing agent, 4 parts accelerator, 1 part silane coupling agent, 0.2 parts defoamer, 0.9 parts leveling agent, 0.3 parts thickener, 5.8 parts composite functional agent, and 10 parts solid filler.

[0107] The toughening agent is a combination of core-shell polymer toughening agent MX-154 and modified polyurethane toughening agent QR-9466, with a mass ratio of 3:0.2.

[0108] The remaining implementation methods are the same as in Example 1.

[0109] Comparative Example 4

[0110] An epoxy structural adhesive for bonding automotive metals, comprising, by weight, 47.5 parts epoxy matrix, 32 parts toughening agent, 5.2 parts curing agent, 4 parts accelerator, 1 part silane coupling agent, 0.2 parts defoamer, 0.9 parts leveling agent, 0.3 parts thickener, 5.8 parts composite functional agent, and 10 parts solid filler.

[0111] The toughening agent is a combination of core-shell polymer toughening agent MX-154 and modified polyurethane toughening agent QR-9466, with a mass ratio of 1.5:1.7.

[0112] The remaining implementation methods are the same as in Example 1.

[0113] Comparative Example 5

[0114] An epoxy structural adhesive for bonding automotive metals, comprising, by weight, 47.5 parts epoxy matrix, 32 parts toughening agent, 5.2 parts curing agent, 4 parts accelerator, 1 part silane coupling agent, 0.2 parts defoamer, 0.9 parts leveling agent, 0.3 parts thickener, 5.8 parts composite functional agent, and 10 parts solid filler.

[0115] The composite functional agent is a combination of cocoyl monoethanolamide, isopropyl tris(dioctyl pyrophosphate) titanate and acetylacetone in a mass ratio of 5:1:1.8.

[0116] The remaining implementation methods are the same as in Example 1.

[0117] Comparative Example 6

[0118] An epoxy structural adhesive for bonding automotive metals, comprising, by weight, 47.5 parts epoxy matrix, 32 parts toughening agent, 5.2 parts curing agent, 4 parts accelerator, 1 part silane coupling agent, 0.2 parts defoamer, 0.9 parts leveling agent, 0.3 parts thickener, 5.8 parts composite functional agent, and 10 parts solid filler.

[0119] The composite functional agent is a combination of cocoyl monoethanolamide, isopropyl tris(dioctyl pyrophosphate) titanate and acetylacetone in a mass ratio of 3.5:3.5:0.8.

[0120] The remaining implementation methods are the same as in Example 1.

[0121] Performance testing

[0122] The epoxy structural adhesives prepared in the examples and comparative examples were electrophoretically cured at 150°C for 10 minutes to obtain corresponding samples. The specific testing methods are as follows:

[0123] 1. Shear strength: The test method is in accordance with ISO 4587:2003. The substrate specimen size shall be 25 mm × 100 mm, and the bonding plane shall be 25 mm × 12.5 mm. Unless otherwise specified in this specification, the lap shear gap of metal bonding shall be 0.2 mm ± 0.05 mm, and the lap shear specimen shall be subjected to tensile testing at a rate of 10 mm / min.

[0124] In addition, high and low temperature aging tests were conducted on the same batch of substrate samples: the high temperature test was conducted after aging at 80°C for 14 days, and the test was conducted after at least 24 hours of recovery after aging; the high temperature test was conducted after aging at -40°C for 1 day, and the test was conducted after at least 24 hours of recovery after aging.

[0125] All test results are calculated as the arithmetic mean of 10 tests and are included in Table 1.

[0126] 2. T-Peel Strength: The test method refers to ASTM D1876:2023. The size of a single specimen should be 30mm × 200mm, the bonding plane should be 30mm × 100mm, the bonding gap should be 0.2mm ± 0.05mm, and the T-peel specimen should be subjected to tensile testing at a rate of 50 mm / min.

[0127] In addition, high and low temperature aging tests were performed on the above-mentioned batch of samples: the high temperature test was performed after aging at 80℃ for 14 days, and the test was carried out after at least 24 hours of recovery after aging; the high temperature test was performed after aging at -40℃ for 1 day, and the test was carried out after at least 24 hours of recovery after aging.

[0128] All test results are calculated as the arithmetic mean of 10 tests and are included in Table 1.

[0129] 3. Wedge impact: The test method refers to ISO 11343:2019. The test sample is a symmetrical wedge shape. The size of a single sample piece should be 20mm×90mm, and the bonding plane should be 20mm×30mm. The bonding gap of the test sample for metal samples should be 0.2mm±0.05mm, and for non-metal samples it should be 0.8mm±0.25mm. The wedge impact peel test sample should be tested at a rate of 3 m / s (aluminum substrate). The test results are the arithmetic mean of 10 tests and are recorded in Table 1.

[0130] 4. Corrosion test: (1) Neutral salt spray (NSS) exposure (GMW3286-2011), the T peel strength sample should be tested for strength retention rate after 480h of exposure to NSS. The test should be carried out after the environment has recovered for at least 24h. The test results are the arithmetic mean of 10 tests and are included in Table 1.

[0131] (2) Cyclic corrosion laboratory test (GMW14124-2012) 10 cycles. The T peel strength sample should be tested for strength retention rate after the cycle is completed. The test should be carried out at least 24 hours after the last cycle. The test should be carried out on the test sample that has been pretreated and coated with electrophoretic primer. The test results are the arithmetic mean of 10 tests and are included in Table 1.

[0132] (3) Water test (GMW14729-2020): The T-strip strength sample should be completely immersed in deionized water at 55℃ for 168h before the strength retention rate is tested. The test should be conducted after the sample has recovered to the ambient temperature, but not more than 60min after it has been taken out of the environment. The test results are the arithmetic mean of 10 tests and are included in Table 1.

[0133] Table 1 Performance Test Results 1

[0134]

[0135] The test results, as shown in Table 1, confirm that Examples 1-3, through the corresponding technical solutions defined in this application, with appropriate raw material selection and proportions, use flexible epoxy resin to absorb and disperse stress, core-shell polymer particles to prevent crack propagation through plastic deformation, and modified polyurethane long-chain interwoven reinforcement network to improve impact resistance. Under these combined effects, the adhesive layer is firmly bonded and does not crack under severe working conditions, achieving highly reliable and long-lasting adhesion. Furthermore, the composite functional agent improves the interface performance and durability, promotes component dispersion and spreading penetration to the metal surface, and enhances the connection with the metal oxide layer, forming a strong interface to improve environmental corrosion resistance. Therefore, in terms of comprehensive application performance, Examples 1-6 are significantly superior. In contrast, Comparative Example 6, because it uses a different technical solution than those defined in this application, shows a significant decrease in the technical effect of the corresponding raw materials in the structural adhesive system, which directly leads to a decrease in the overall performance of the final structural adhesive.

[0136] 6. Storage properties: Store the sample in an environment with room temperature of 23±2℃ and humidity of 50%±3% in the dark. Use a rheometer to test the viscosity at 2.5 counts. The viscosity before storage is V1, and the viscosity after 6 months of storage is V2. V2 / V1 should be less than 2. Take the average value of V2 / V1 from 10 sets of tests and record it in Table 2.

[0137] Table 2 Performance Test Results 2

[0138]

[0139] As can be seen from the results in Table 2, Examples 1-3 are not only significantly stronger than Comparative Examples 1-6 of this application in terms of overall application performance, but also have clear advantages in terms of product storage and performance stability. During long-term storage, the corresponding products of Examples 1-3 have better system stability, which greatly improves their actual application quality and performance.

[0140] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An epoxy structural adhesive for bonding automotive metal parts, characterized in that: By weight, the raw materials include: 30-50 parts epoxy resin, 20-35 parts toughening agent, 3-6 parts curing agent, 2-5 parts accelerator, 1-2 parts silane coupling agent, 0.2-0.3 parts defoamer, 0.8-1.5 parts leveling agent, 0.2-0.3 parts thickener, 3-8 parts composite functional agent, and 10-25 parts solid filler; The epoxy resin is a combination of bisphenol F epoxy resin and flexible epoxy resin, with a mass ratio of (20~30):(10~20). The flexible epoxy resin is flexible epoxy resin BH-026 and / or flexible epoxy resin DER-3913. The toughening agent is a combination of a core-shell polymer toughening agent and a modified polyurethane toughening agent, with a mass ratio of (2~2.5):(0.8~1.2). The curing agent is a dicyandiamide curing agent; The composite functional agent is a combination of cocoyl monoethanolamide, isopropyl tris(dioctylpyrophosphoryloxy)titanate and acetylacetone, with a mass ratio of (2~4):(2~3):(1~2). The core-shell polymer toughening agent is MX-154, manufactured by Kanekachi, Japan. The modified polyurethane toughening agent is QR-9466, manufactured by Adico Japan.

2. The epoxy structural adhesive for automotive metal bonding as described in claim 1, characterized in that: The epoxy equivalent of the bisphenol F epoxy resin is 150~200 g / eq.

3. The epoxy structural adhesive for automotive metal bonding according to claim 2, characterized in that: The mass ratio of the epoxy resin, toughening agent, and composite functional agent is (3.5~5):(2.5~3.3):(0.4~0.7).

4. The epoxy structural adhesive for automotive metal bonding as described in claim 3, characterized in that: The flexible epoxy resin is a combination of flexible epoxy resin BH-026 and flexible epoxy resin DER-3913, with a mass ratio of (1~1.5):

1.

5. The epoxy structural adhesive for automotive metal bonding according to claim 4, characterized in that: The dicyandiamide curing agent is ultrafine dicyandiamide; the average D50 particle size of the ultrafine dicyandiamide is 3~8μm.

6. The epoxy structural adhesive for automotive metal bonding as described in claim 5, characterized in that: The accelerator is at least one of substituted urea accelerators, modified amine accelerators, and organic guanidine accelerators.

7. The epoxy structural adhesive for automotive metal bonding as described in claim 6, characterized in that: The silane coupling agent is at least one of KH-550, KH-560 and KH-540.

8. The epoxy structural adhesive for automotive metal bonding as described in claim 7, characterized in that: The thickener is at least one of fumed silica, organobentonite, polyamide wax, hydrogenated castor oil, and cellulose.

9. The epoxy structural adhesive for automotive metal bonding as described in claim 8, characterized in that: The solid filler is at least one of silica fume, calcium carbonate, barium sulfate, and talc.

10. A method for preparing an epoxy structural adhesive for automotive metal bonding according to any one of claims 1 to 9, characterized in that: Specifically, the following steps are included: S1: Add the epoxy resin, toughening agent, solid filler, silane coupling agent, leveling agent, thickener, and composite functional agent to a planetary mixer and disperse for 25-35 minutes at a revolution speed of 20-30 rpm, a rotation speed of 500-600 rpm, and a vacuum degree of -0.095 MPa, while controlling the temperature at 50-60℃, to obtain a homogeneous matrix mixture; S2: After cooling to 35-40℃, add the remaining raw materials. After all the materials are added, disperse for 15-20 minutes at a revolution speed of 15-20 rpm, a rotation speed of 60-80 rpm, and a vacuum degree of -0.095 MPa to ensure uniform dispersion of the curing system; S3: After discharge, transfer the material to a homogenizer and perform final homogenization treatment in a vacuum environment at <40℃ for 5-10 minutes, and the product is then discharged.

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