A structural adhesive epoxy composition and its preparation method

Abstract

This application relates to the field of adhesives, and more specifically to a structural adhesive epoxy composition and its preparation method. The structural adhesive epoxy composition comprises, as a raw material, epoxy resin, toughening agent, reinforcing agent, filler, latent curing agent, latent accelerator, chemical foaming agent, and physical foaming agent. The epoxy composition obtained in this application, as a structural adhesive raw material, possesses ultra-high expansion rate, low-temperature rapid curing capability, and structural bonding performance, while simultaneously maintaining good mechanical properties. Its comprehensive application effect is excellent, thus meeting the complex requirements of existing technology application fields for structural adhesive raw materials.

Description

Technical Field

[0001] This application relates to the field of adhesives, and more specifically to a structural adhesive epoxy composition and its preparation method. Background Technology

[0002] In the automotive manufacturing industry, structural adhesives are increasingly widely used as key materials for improving body rigidity, enhancing crash safety, and improving noise, vibration, and harshness (NVH) performance. Among them, intumescent epoxy structural adhesives have attracted much attention due to their unique properties. These adhesives expand in volume when heated during the electrophoretic painting process, effectively filling gaps and cavities between sheet metal parts, achieving excellent sealing, sound insulation, and reinforcement of the overall body structure. Currently, the typical expansion rate of commonly used intumescent epoxy structural adhesives ranges from 30% to 100%, which can meet filling requirements under certain conditions. However, as the automotive industry continues to develop towards lightweighting and increasingly complex structural designs, more cavities with larger gaps and more irregular shapes are appearing in the body. These new structural characteristics place higher demands on the filling capacity of structural adhesives. The limited expansion rate of existing products often fails to fully fill these spaces, potentially leading to stress concentration at incomplete filling points, decreased sound insulation performance, and a series of other problems.

[0003] Furthermore, automotive OEMs are actively exploring the possibility of lowering the electrophoresis process temperature. This requires that the curing and foaming processes of expandable epoxy structural adhesives adapted to electrophoresis also be able to be effectively carried out at relatively lower temperatures. Therefore, there is a clear and urgent market demand for structural adhesive products that combine higher expansion rates and lower curing temperatures. However, achieving these performance improvements is not easy technically; simply increasing the expansion rate or lowering the reaction temperature by increasing the amount of traditional foaming agents or accelerators often severely damages the mechanical properties after curing, such as significantly reducing shear strength, T-peel strength, and adhesion performance under high and low temperature environments. It also causes problems such as poor adhesive storage stability, making it difficult to meet the stringent requirements of automotive structural components for safety, reliability, and product shelf life. For example, Chinese patent application CN107674384A, although its expansion rate meets the requirements, requires a curing temperature of 165℃ / 20min that is too high, and the highest T-peel strength against metal after curing is only 3.8 N / mm, requiring superior adhesion to meet the requirements of structural components for long-term fatigue strength and safety.

[0004] Therefore, how to maintain the excellent mechanical properties and sufficient storage stability inherent in epoxy resin systems while successfully achieving high expansion rate and low temperature curing has become a core technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] Therefore, solving the aforementioned technical problems has become an important issue that those skilled in the art must address. Through in-depth research in this technical field, the applicant has ultimately proposed a structural adhesive epoxy composition and its preparation method in this application. This application provides a one-component epoxy structural adhesive, specifically designed to solve the contradiction between high expansion rate and curing and bonding performance inherent in current intumescent epoxy structural adhesives. Ultimately, the epoxy composition obtained in this application, as a structural adhesive raw material, possesses ultra-high expansion rate, low-temperature rapid curing capability, and structural bonding performance, while simultaneously maintaining good mechanical properties. Its comprehensive application effect is excellent, thus meeting the complex requirements of existing technology application fields for structural adhesive raw materials.

[0006] A structural adhesive epoxy composition, by weight, comprises the following raw materials: 40-60 parts epoxy resin, 10-30 parts toughening agent, 10-20 parts reinforcing agent, 10-50 parts filler, 1-3 parts thixotropic agent, 0.5-1.5 parts coupling agent, 0.5-1 part stabilizer, 4-9 parts latent curing agent, 0.1-3 parts latent accelerator, 0.5-3 parts chemical foaming agent, and 0.5-3 parts physical foaming agent.

[0007] Preferably, the epoxy resin is a composition of bisphenol A type resin and bisphenol F type resin.

[0008] Preferably, the mass ratio of the bisphenol A type resin to the bisphenol F type resin is (0.4~0.6):(4.5~5).

[0009] Preferably, the mass ratio of the epoxy resin, toughening agent, and reinforcing agent is (4.5~6):(1~2.5):(1.2~2).

[0010] Preferably, the mass ratio of the epoxy resin, toughening agent, and reinforcing agent is (4.5~5.5):(1.2~2.2):(1.2~1.5).

[0011] Preferably, the toughening agent is at least one of epoxy-terminated liquid nitrile rubber, core-shell rubber particles, and polyurethane prepolymer.

[0012] Preferably, the toughening agent is epoxy-terminated liquid nitrile rubber or core-shell rubber particles.

[0013] Preferably, the toughening agent is core-shell rubber particles.

[0014] Preferably, the core-shell rubber particles are MX-154, sourced from Kanebuchi, Japan.

[0015] Preferably, the reinforcing agent is a combination of liquid-terminated carboxyl-terminated butadiene-acrylonitrile rubber and 4,4'-oxobis(benzenesulfonyl)hydrazine.

[0016] Preferably, the mass ratio of the liquid-terminated carboxyl-terminated acrylonitrile rubber to 4,4'-oxobis(benzenesulfonyl)hydrazine is (8~15):(1~2.5).

[0017] Preferably, the mass ratio of the liquid-terminated carboxyl-terminated acrylonitrile rubber to 4,4'-oxobis(benzenesulfonyl)hydrazine is (9~12):(1.5~2).

[0018] This application employs a reinforcing composition consisting of liquid-terminated carboxyl-terminated nitrile butadiene rubber and 4,4'-oxobis(benzenesulfonyl)hydrazine, which significantly improves the overall performance of the core epoxy system. The carboxyl functional groups it carries can chemically react with the epoxy groups, thereby forming microphase separation in situ within the rigid epoxy network. This creates efficient stress dispersion centers that absorb a large amount of energy, maintaining good mechanical properties. Furthermore, both components assist in forming a fine, closed-cell foam structure within the epoxy system. The excellent flexible network structure prevents the epoxy composition from coalescing or rupturing during expansion, thus achieving extremely high expansion rates while ensuring the integrity and stability of the cell structure. Ultimately, this results in a material that simultaneously possesses excellent comprehensive properties such as lightweight, high strength, and impact resistance.

[0019] Preferably, the filler is at least one selected from precipitated calcium carbonate, calcium oxide, silica powder, aluminum hydroxide, and hollow glass microspheres.

[0020] Preferably, the filler is a composition of precipitated calcium carbonate and calcium oxide.

[0021] Preferably, the mass ratio of the precipitated calcium carbonate to calcium oxide is (10~14):(1~3).

[0022] Preferably, the mass ratio of the precipitated calcium carbonate to calcium oxide is (11~13):(1.5~2.2).

[0023] Preferably, the thixotropic agent is at least one of fumed silica, hydrogenated castor oil, polyamide wax, and organobentonite.

[0024] Preferably, the thixotropic agent is fumed silica or hydrogenated castor oil.

[0025] Preferably, the thixotropic agent is hydrogenated castor oil.

[0026] Preferably, the coupling agent is at least one of silane coupling agents.

[0027] Preferably, the coupling agent is KH-550 or KH-560.

[0028] Preferably, the stabilizer is at least one of hindered phenols, phosphites, and phosphites.

[0029] Preferably, the stabilizer is a hindered phenol or a phosphite.

[0030] Preferably, the stabilizer is a phosphite.

[0031] Preferably, the latent curing agent is a combination of epoxy resin and dicyandiamide.

[0032] Preferably, the mass ratio of the epoxy resin to the dicyandiamide is (7~10):(6~8).

[0033] Preferably, the mass ratio of the epoxy resin to the dicyandiamide is (9~10):(6~6.5).

[0034] Preferably, the epoxy resin is QR-9466, sourced from ADEKA, Japan.

[0035] Preferably, the dicyandiamide is Amicure CG-1400F, from Evonik GmbH, Germany.

[0036] Preferably, the latency promoter is an organic urea.

[0037] Preferably, the organic urea Dyhard UR300 or Dyhard UR500 is from Evonik, Germany.

[0038] Preferably, the organic urea is Dyhard UR500.

[0039] Preferably, the chemical foaming agent is azodicarbonamide.

[0040] Preferably, the physical foaming agent is thermally expandable microspheres Expansion 909 DU 80, sourced from Norinon.

[0041] Preferably, the thermally expandable microspheres are encapsulated in a thermoplastic polymer shell.

[0042] Preferably, the average particle size of the thermally expanded microspheres is 18~24 μm.

[0043] Preferably, the mass ratio of the epoxy resin, chemical foaming agent, and physical foaming agent is (4.5~6):(0.15~0.3):(0.15~0.3).

[0044] Preferably, the mass ratio of the epoxy resin, chemical foaming agent, and physical foaming agent is (4.5~5.5):(0.16~0.2):(0.16~0.2).

[0045] This application achieves a balance between high expansion rate and excellent mechanical properties by controlling the combined use of chemical and physical foaming agents and optimizing the selection of toughening agents and fillers. Through precise matching of the types, particle sizes, and ratios of physical and chemical foaming agents, a significant synergistic foaming effect is generated within the epoxy resin curing temperature range. Specifically, the physical foaming agent initiates the process at lower temperatures, providing controllable initial expansion and forming a preliminary cell structure; subsequently, the chemical foaming agent decomposes at slightly higher temperatures, generating a large amount of gas, which then expands efficiently within the pre-formed microbubble structure. This step-by-step synergistic foaming process ultimately leads to the formation of a uniform, dense foam structure dominated by closed cells, thus successfully achieving an expansion rate of up to 150%. This effectively meets the filling requirements of complex cavities. Furthermore, the toughening agent used is a reactive toughening agent to improve toughness, impact resistance, and peel adhesion. This compounding strategy cleverly avoids the problem of large cells or structural damage caused by excessive use of a single foaming agent, thus ensuring that the achievement of a high expansion rate does not come at the expense of foam quality.

[0046] Furthermore, this invention specifically selects and optimizes the toughening system and filler combination. Given the challenge that high-ratio foaming inevitably weakens the matrix strength, this optimized system effectively compensates for the performance loss that may result from foaming. As a result, even after significant expansion of the colloid, the cured product retains sufficiently high shear strength, modulus, and excellent impact toughness. All key mechanical properties strictly meet the stringent safety and reliability requirements of automotive structural components, ultimately overcoming the technical bottleneck of the difficulty in simultaneously achieving high expansion rate and high performance. This allows the final product to achieve excellent filling and sealing effects while also possessing a robust ability to withstand structural stress.

[0047] A method for preparing a structural adhesive epoxy composition includes the following steps: S1: Epoxy resin, toughening agent, filler, thixotropic agent, coupling agent, and stabilizer are added to a planetary mixer and mixed evenly under vacuum conditions to obtain premix A; S2: Premix A is cooled to below 40°C, the remaining raw materials are added, and the mixture is mixed evenly under vacuum conditions of 40~60 rpm, 5~10°C, to avoid premature reaction and foaming agent failure; S3: The evenly mixed adhesive is degassed and discharged, and packaged in an airtight container to obtain the final product.

[0048] The beneficial effects of this application are:

[0049] 1. The epoxy composition prepared in this application, as a structural adhesive raw material, can have ultra-high expansion rate, low temperature rapid curing ability and structural bonding performance, while maintaining good mechanical properties. It has excellent comprehensive application effect, thereby meeting the complex requirements of existing technology application fields for structural adhesive raw materials.

[0050] 2. This application achieves a balance between high expansion rate and excellent mechanical properties by controlling the combined use of chemical and physical foaming agents, and by optimizing the selection of toughening agents and fillers. Through precise matching of the types, particle sizes, and ratios of physical and chemical foaming agents, a significant synergistic foaming effect is generated within the epoxy resin curing temperature range. Specifically, the physical foaming agent initiates the process at lower temperatures, providing controllable initial expansion and forming a preliminary cell structure; subsequently, the chemical foaming agent decomposes at slightly higher temperatures, generating a large amount of gas, which then expands efficiently within the pre-formed microbubble structure. This step-by-step synergistic foaming process ultimately leads to the formation of a uniform, dense, and predominantly closed-cell foam structure, thus successfully achieving an expansion rate of up to 150%, effectively meeting the filling requirements of complex cavities.

[0051] 3. This application specifically selects and optimizes the toughening system and filler combination. Given the challenge that high-ratio foaming inevitably weakens the matrix strength, this optimized system effectively compensates for the performance loss that may result from foaming. As a result, even after significant expansion of the colloid, the cured product still retains sufficiently high shear strength, modulus, and excellent impact toughness. All key mechanical properties strictly meet the stringent safety and reliability requirements of automotive structural components. Attached Figure Description

[0052] Figure 1 This is a photograph showing the effect of tearing the structural adhesive epoxy composition prepared in Example 1 of this application. Detailed Implementation

[0053] Example 1

[0054] A structural adhesive epoxy composition, by weight, comprises the following raw materials: 51.2 parts epoxy resin, 21.6 parts toughening agent, 13.5 parts reinforcing agent, 14.4 parts filler, 1.2 parts thixotropic agent, 0.6 parts coupling agent, 0.6 parts stabilizer, 5.8 parts latent curing agent, 1.2 parts latent accelerator, 1.9 parts chemical foaming agent, and 1.9 parts physical foaming agent.

[0055] The epoxy resin is a composition of bisphenol A type resin and bisphenol F type resin in a mass ratio of 0.49:4.63. The bisphenol A type resin RA-1340 is from Volker, Germany; the bisphenol F type resin NPEF-170 is from Nan Ya Plastics.

[0056] The toughening agent is core-shell rubber granules MX-154, sourced from Kanekachi, Japan.

[0057] The reinforcing agent is a combination of liquid-terminated carboxyl-terminated nitrile butadiene rubber and 4,4'-oxobis(benzenesulfonyl)hydrazine, with a mass ratio of 10:1.8. The liquid-terminated carboxyl-terminated nitrile butadiene rubber is of industrial grade and sourced from Hubei Langbowan.

[0058] The filler is a composition of precipitated calcium carbonate and calcium oxide, with a mass ratio of precipitated calcium carbonate to calcium oxide of 12.4:1.9.

[0059] The thixotropic agent is hydrogenated castor oil; the coupling agent is KH-560; and the stabilizer is phosphite antioxidant 168.

[0060] The latent curing agent is a combination of epoxy resin and dicyandiamide in a mass ratio of 9.3:6.2. The epoxy resin is QR-9466, sourced from ADEKA, Japan; the dicyandiamide is Amicure CG-1400F, sourced from Evonik, Germany.

[0061] The latency promoter is an organic urea, Dyhard UR500, from Evonik in Germany.

[0062] The chemical blowing agent is azodicarbonamide; the physical blowing agent is thermally expandable microspheres Expansion 909 DU 80, which are derived from Norinon. The thermally expandable microspheres are encapsulated in a thermoplastic polymer shell and have an average particle size of 20 μm.

[0063] A method for preparing a structural adhesive epoxy composition includes the following steps: S1: Epoxy resin, toughening agent, filler, thixotropic agent, coupling agent, and stabilizer are added to a planetary mixer and mixed evenly under vacuum conditions to obtain premix A; S2: Premix A is cooled to below 40°C, the remaining raw materials are added, and the mixture is mixed evenly under 50 rpm, 7.5°C, and vacuum conditions to avoid premature reaction and foaming agent failure; S3: The evenly mixed adhesive is degassed and discharged, and packaged in an airtight container to obtain the final product.

[0064] The tear-resistant effect of the structural adhesive epoxy composition prepared in this embodiment is as follows: Figure 1 As shown.

[0065] Example 2

[0066] This embodiment differs from Embodiment 1 only in the following aspects: A structural adhesive epoxy composition, by weight, comprises the following raw materials: 51.2 parts epoxy resin, 18.8 parts toughening agent, 12.2 parts reinforcing agent, 14.4 parts filler, 1.2 parts thixotropic agent, 0.6 parts coupling agent, 0.6 parts stabilizer, 5.8 parts latent curing agent, 1.2 parts latent accelerator, 1.9 parts chemical foaming agent, and 1.9 parts physical foaming agent.

[0067] The remaining implementation methods are the same.

[0068] Example 3

[0069] This embodiment differs from Embodiment 1 only in the following aspects: A structural adhesive epoxy composition, by weight, comprises the following raw materials: 51.2 parts epoxy resin, 21.6 parts toughening agent, 13.5 parts reinforcing agent, 14.4 parts filler, 1.2 parts thixotropic agent, 0.6 parts coupling agent, 0.6 parts stabilizer, 5.8 parts latent curing agent, 1.2 parts latent accelerator, 1.6 parts chemical foaming agent, and 2.2 parts physical foaming agent.

[0070] The remaining implementation methods are the same.

[0071] Example 4

[0072] The only difference between this embodiment and Example 1 is that the reinforcing agent is a combination of liquid terminal carboxyl acrylonitrile rubber and 4,4'-oxobisbenzenesulfonyl hydrazine in a mass ratio of 9.5:2.5.

[0073] The latent curing agent is a combination of epoxy resin and dicyandiamide in a mass ratio of 10:5.5.

[0074] The remaining implementation methods are the same.

[0075] Comparative Example 1

[0076] This comparative example differs from Example 1 only in the following aspects: a structural adhesive epoxy composition, by weight, comprises: 51.2 parts epoxy resin, 21.6 parts toughening agent, 4.5 parts reinforcing agent, 14.4 parts filler, 1.2 parts thixotropic agent, 0.6 parts coupling agent, 0.6 parts stabilizer, 5.8 parts latent curing agent, 1.2 parts latent accelerator, 1.9 parts chemical foaming agent, and 1.9 parts physical foaming agent.

[0077] The remaining implementation methods are the same.

[0078] Comparative Example 2

[0079] This comparative example differs from Example 1 only in the following aspects: a structural adhesive epoxy composition, by weight, comprising: 51.2 parts epoxy resin, 21.6 parts toughening agent, 13.5 parts reinforcing agent, 14.4 parts filler, 1.2 parts thixotropic agent, 0.6 parts coupling agent, 0.6 parts stabilizer, 5.8 parts latent curing agent, 1.2 parts latent accelerator, 2.8 parts chemical foaming agent, and 0.5 parts physical foaming agent.

[0080] The remaining implementation methods are the same.

[0081] Comparative Example 3

[0082] The only difference between this comparative example and Example 1 is that the reinforcing agent is a combination of liquid-terminated carboxyl-terminated butadiene-acrylonitrile rubber and 4,4'-oxobis(benzenesulfonyl)hydrazine in a mass ratio of 11.8:0.2.

[0083] The remaining implementation methods are the same.

[0084] Comparative Example 4

[0085] This comparative example differs from Example 1 only in the following way: the reinforcing agent is a combination of liquid terminal carboxyl acrylonitrile rubber and 4,4'-oxobisbenzenesulfonyl hydrazine in a mass ratio of 3:1.

[0086] The remaining implementation methods are the same.

[0087] Comparative Example 5

[0088] The only difference between this comparative example and Example 1 is that the latent curing agent is a combination of epoxy resin and dicyandiamide in a mass ratio of 10:3.

[0089] The remaining implementation methods are the same.

[0090] Comparative Example 6

[0091] The only difference between this comparative example and Example 1 is that the latent curing agent is a combination of epoxy resin and dicyandiamide in a mass ratio of 5:6.5.

[0092] The remaining implementation methods are the same.

[0093] Performance testing

[0094] The adhesives prepared in the examples and comparative examples were made into specimens and test pieces, cured at 140°C for 30 minutes, and then subjected to the following tests:

[0095] 1. Expansion rate determination: Measure the volume change of the colloid before and after curing, and calculate the expansion rate. Expansion rate (%) = [(V2-V1) / V1] ×100%, where V1 is the volume before curing and V2 is the volume after curing. The result is the average of 10 tests and recorded in Table 1.

[0096] 2. Tensile shear strength: The strength of the steel plate-to-steel plate bond was tested according to GB / T 7124 standard, and the average value of 10 tests was recorded in Table 1.

[0097] 3. Peel strength: According to GB / T 2791 standard, the strength of the steel plate-to-steel plate bond was tested, and the result was the average of 10 tests and recorded in Table 1.

[0098] 4. Storage stability: Place in a 40℃ oven and observe the time required for viscosity to double. The results are recorded in Table 1.

[0099] 5. Resistance to damp heat: The sample was placed in a constant temperature and humidity chamber at 85℃ and 85% relative humidity for 500 hours. Before and after damp heat aging, its shear strength was tested according to ISO 9142:2021. The shear strength retention rate after damp heat aging was obtained. The average value of 10 tests was recorded in Table 1.

[0100] Table 1 Performance Test Results

[0101]

[0102] Ultimately, Examples 1-3 achieved superior overall performance compared to Comparative Examples 1-6. This was mainly due to the specific technical solutions employed in Examples 1-3, which precisely controlled the combined use of chemical and physical foaming agents, and optimized the selection of toughening agents and fillers, achieving a balance between high expansion rate and excellent mechanical properties. Furthermore, the addition of reinforcing agents and the optimization of the toughening system and filler combination effectively compensated for potential performance losses due to foaming. In particular, even after significant expansion, the cured product still maintained sufficiently high shear strength, modulus, and excellent impact toughness. Comparative Examples 1-6, however, employed technical solutions different from those specified in this application, resulting in a significant decrease in the effectiveness of their respective raw materials in the system, ultimately leading to a significant deviation between the comparative example compositions and the examples.

Claims

1. A structural adhesive epoxy composition, characterized in that: By weight, the raw materials include: 40-60 parts epoxy resin, 10-30 parts toughening agent, 10-20 parts reinforcing agent, 10-50 parts filler, 1-3 parts thixotropic agent, 0.5-1.5 parts coupling agent, 0.5-1 part stabilizer, 4-9 parts latent curing agent, 0.1-3 parts latent accelerator, 0.5-3 parts chemical foaming agent, and 0.5-3 parts physical foaming agent; The epoxy resin is a combination of bisphenol A type resin and bisphenol F type resin; the reinforcing agent is a combination of liquid terminal carboxyl-terminated butadiene-acrylonitrile rubber and 4,4'-oxobisbenzenesulfonyl hydrazine, with a mass ratio of (8~15):(1~2.5). The latent curing agent is a composition of epoxy resin and dicyandiamide; the mass ratio of the epoxy resin and dicyandiamide composition is (7~10):(6~8). The epoxy resin, in which the mass ratio of chemical foaming agent to physical foaming agent is (4.5~5.5):(0.16~0.2):(0.16~0.2); The epoxy resin, toughening agent and reinforcing agent are in a mass ratio of (4.5~6):(1~2.5):(1.2~2). The chemical foaming agent is azodicarbonamide; the physical foaming agent is thermally expanding microspheres Expansion 909 DU80, Norinon; The latency promoter is an organic urea.

2. The structural adhesive epoxy composition according to claim 1, characterized in that: The epoxy resin is composed of bisphenol A type resin and bisphenol F type resin in a mass ratio of (0.4~0.6):(4.5~5).

3. The structural adhesive epoxy composition according to claim 2, characterized in that: The toughening agent is at least one of epoxy-terminated liquid nitrile rubber, core-shell rubber particles, and polyurethane prepolymer.

4. The structural adhesive epoxy composition according to claim 3, characterized in that: The filler is at least one of precipitated calcium carbonate, calcium oxide, silica powder, aluminum hydroxide, and hollow glass microspheres.

5. The structural adhesive epoxy composition according to claim 4, characterized in that: The thixotropic agent is at least one of fumed silica, hydrogenated castor oil, polyamide wax, and organobentonite.

6. A method for preparing a structural adhesive epoxy composition according to any one of claims 1 to 5, characterized in that: Specifically, the following steps are included: S1: Add epoxy resin, toughening agent, filler, thixotropic agent, coupling agent and stabilizer into a planetary mixer and mix evenly under vacuum to obtain premix A; S2: Cool premix A to below 40℃, add the remaining raw materials, and mix evenly under 40~60rpm, 5~10℃ and vacuum conditions to avoid premature reaction and foaming agent failure; S3: Degas the evenly mixed rubber compound and discharge it into an airtight container to obtain the final product.

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