Dual-curing solvent-free high-temperature-resistant epoxy resin structural adhesive as well as preparation method and application thereof

Abstract

The invention discloses a dual-curing solvent-free high-temperature-resistant epoxy resin structural adhesive as well as a preparation method and application thereof. The structural adhesive comprises the following components in percentage by weight: 1.5-5% of a latent curing agent, 2-5% of a high-heat-resistant curing agent, 1-5% of nano filler, 0.1-0.3% of a curing accelerator and the balance of epoxy resin. By accurately screening epoxy resin monomers, optimizing a dual curing agent system and introducing the high-temperature-resistant nanofiller, room-temperature stability, medium-temperature rapid curing and gelling and high-temperature complete curing are realized, and the final heat-resistant temperature is greater than or equal to 300 DEG C. Through the synergistic effect of the epoxy resin, the medium-temperature curing agent and the high-temperature curing agent, the crosslinking stability at different temperature stages is ensured. In addition, through introduction of the inorganic nano filler, the high-temperature mechanical property and the heat-resistant stability of the material are further improved. The preparation method does not need to use a solvent, and the prepared epoxy resin structural adhesive has excellent heat resistance and mechanical strength and is suitable for the fields of high-temperature structural adhesives, aerospace composite materials, high-temperature-resistant coatings and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of adhesives, and in particular relates to a dual-curing solvent-free, high-temperature resistant epoxy resin structural adhesive, a preparation method thereof, and applications thereof. Background Art

[0002] Epoxy resin structural adhesives are widely used in industrial equipment, aerospace, automotive and other fields under high-temperature environments, and have excellent bonding properties and mechanical strength. However, traditional epoxy resin structural adhesives usually have a high viscosity at room temperature, which makes it difficult to achieve uniform coating and operation during processing and application. In actual applications, this high viscosity not only affects the workability of the adhesive, but also limits its bonding stability during medium-temperature pre-curing and high-temperature full curing. Therefore, how to reduce the viscosity at room temperature and achieve good curing and stable bonding properties at different temperature stages has become an important issue in improving the performance of epoxy resin structural adhesives.

[0003] Furthermore, traditional epoxy structural adhesives have poor thermal stability, particularly in high-temperature environments, where their mechanical properties and bonding strength often degrade significantly. The root cause of this problem lies in the ineffective incorporation of inorganic nanofillers into many traditional epoxy adhesives to enhance their high-temperature resistance. While inorganic fillers such as nanoalumina and nanosilica can effectively improve the thermal stability and mechanical strength of epoxy resins, the dispersibility and interfacial bonding strength of these fillers remain challenges hindering their performance improvement.

[0004] Furthermore, the curing agent systems of traditional epoxy structural adhesives often fail to meet the requirements for complete curing under high-temperature conditions. Many existing curing agents cannot provide sufficient crosslink density at high temperatures, which affects the long-term stability and high-temperature performance of the adhesive. As a result, traditional epoxy structural adhesives typically require a long curing time, and the cured adhesive layer often fails to maintain high bond strength and heat stability.

[0005] To address these issues, the present invention optimizes the curing agent system and introduces suitable inorganic nanofillers to develop a dual-curing, solvent-free, high-temperature-resistant epoxy structural adhesive. This adhesive can be pre-cured at moderate temperatures and fully cured at high temperatures, ultimately providing excellent high-temperature resistance and mechanical strength. This innovative improvement not only overcomes the curing and heat resistance issues of traditional epoxy structural adhesives but also effectively enhances their stability and bonding performance in high-temperature environments. Summary of the Invention

[0006] To address the issues of insufficient curing and unstable performance of existing epoxy resin structural adhesives in high-temperature environments, the present invention aims to provide a dual-curing, solvent-free, high-temperature-resistant epoxy resin structural adhesive that is simple to operate and requires minimal equipment, as well as its preparation method and application. Through rational formulation design and optimized curing process, the present invention achieves a high-crosslink density epoxy resin structural adhesive with excellent high-temperature resistance and high mechanical strength, making it particularly suitable for aerospace composite materials, high-temperature structural adhesives, and high-temperature-resistant coatings.

[0007] The technical solution adopted in the present invention is as follows:

[0008] A dual-curing solvent-free, high-temperature resistant epoxy resin structural adhesive comprises the following components by weight: 1.5-5% latent curing agent, 2-5% high-heat resistant curing agent, 1-5% nano filler, 0.1-0.3% curing accelerator, and the balance epoxy resin.

[0009] Furthermore, the following components are included by weight: 2.5-3% latent curing agent, 3-4% high heat-resistant curing agent, 2-2.5% nano filler, 0.2-0.25% curing accelerator, and the balance is epoxy resin, wherein the curing accelerator is ethylene thiourea.

[0010] Furthermore, the epoxy resin is at least one of E20, E44, E51, and TDE-85, or is a silicone-modified epoxy resin.

[0011] Furthermore, the latent curing agent is one or more of the following: dicyandiamide, 2-phenylimidazole, 2-ethyl-4-methylimidazole, 2-methylimidazole, N-imidazole, and a latent acid anhydride curing agent, and the latent acid anhydride curing agent is at least one of hexahydrophthalic anhydride and methyltetrahydrophthalic anhydride.

[0012] Furthermore, the high heat-resistant curing agent is one or more of the following: benzoxazine, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone, benzophenonetetracarboxylic dianhydride, hexafluorodianhydride, benzoxazine-modified curing agent, and bismaleimide.

[0013] Furthermore, the nanofiller is one or more of the following: nano-alumina, nano-silicon dioxide, nano-zirconium oxide, multi-walled carbon nanotubes, and graphene.

[0014] Furthermore, the nanofiller is modified with a silane coupling agent to improve the dispersibility and interfacial bonding strength of the filler in the epoxy resin.

[0015] Furthermore, the modification step is: adding nanofillers to a mass concentration of 1-

[0016] In a 5% γ-glycidyloxypropyltrimethoxysilane ethanol solution, the mass ratio of nanofiller to γ-glycidyloxypropyltrimethoxysilane is 1:0.2-0.6, heated to 55-65°C and stirred for reaction for 1-4 hours, and ultrasonically dispersed for 10-60 minutes to reduce agglomeration, then centrifuged, washed with ethanol to remove unreacted silane and by-products, and dried, and the modification treatment is completed.

[0017] The dual-curing solvent-free, high-temperature resistant epoxy resin structural adhesive of the present invention has a heat resistance temperature of ≥300°C after final curing, exhibits excellent heat resistance stability and high mechanical strength, and is suitable for aerospace composite materials, high-temperature structural adhesives and high-temperature resistant coatings and other fields.

[0018] The application of the dual-curing solvent-free, high-temperature resistant epoxy resin structural adhesive in adhesive materials of the present invention comprises the following steps of curing process:

[0019] Step 1: Mixing and preparing: According to the formula, mix the epoxy resin, latent curing agent, high heat-resistant curing agent, nano filler and curing accelerator, and stir at 70-90°C for 1-3 hours to fully mix the curing agent and epoxy resin.

[0020] Step 2, Pre-curing: Apply the mixture to a film and then pre-curing it at a temperature between 100°C and 150°C for 1-3 hours. Pre-curing allows the system to form a preliminary cross-linking structure during the initial heating process, thereby enhancing the stability of the colloidal system and providing conditions for subsequent complete curing.

[0021] Step 3, High-Temperature Curing: Bond the adhesive film to the objects to be bonded, press firmly, and fully cure at a temperature between 190°C and 220°C for 1-3 hours. This step ensures the epoxy resin structural adhesive forms a high cross-link density structure and high heat stability, ultimately resulting in an epoxy resin structural adhesive with excellent high-temperature resistance and strong mechanical strength.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1) The present invention achieves room temperature stability, medium temperature rapid curing to form a gel, high temperature complete curing, and final heat resistance temperature ≥300°C by accurately screening epoxy resin monomers, optimizing the dual curing agent system, and introducing high temperature resistant nanofillers.

[0024] 2) The present invention ensures crosslinking stability at different temperature stages by utilizing the synergistic effects of epoxy resin, medium-temperature curing agent, and high-temperature curing agent. In addition, the introduction of inorganic nanofillers further enhances the material's high-temperature mechanical properties and heat-resistant stability. The preparation method of the present invention does not require the use of solvents, and the resulting epoxy resin structural adhesive has excellent heat resistance and mechanical strength, making it suitable for use in high-temperature structural adhesives, aerospace composite materials, and high-temperature resistant coatings. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is the infrared spectrum of the structural adhesive in Example 1 of the present invention. DETAILED DESCRIPTION

[0026] The present invention will be further described below with reference to specific embodiments, but the protection scope of the present invention is not limited thereto.

[0027] Example 1

[0028] (1) Preparation of prepolymer and curing film

[0029] In order to improve the interfacial compatibility, the nano-silica filler is first modified with a silane coupling agent. The modification process is as follows: the nano-silica filler is mixed with an ethanol solution of γ-glycidyloxypropyltrimethoxysilane with a mass concentration of 3%, and the mass ratio of the filler to γ-glycidyloxypropyltrimethoxysilane is 1:0.3. The mixture is heated to 60°C and stirred for 2 hours, and ultrasonically dispersed for 30 minutes to reduce agglomeration. The mixture is then centrifuged, washed with ethanol, and dried to obtain the modified nano-silica filler.

[0030] E44 epoxy resin (150 g) and TDE-85 epoxy resin (50 g) were mixed, and 6 g of dicyandiamide was added as a latent curing agent while stirring, along with 5 g of modified nano-silica filler to improve the system's heat resistance and mechanical properties. 8 g of benzoxazine was added as a high-heat-resistant curing agent, and 0.5 g of ethylene thiourea curing accelerator was added to promote the subsequent high-temperature curing reaction. The mixture was then stirred at 80°C for 2 hours to allow the curing agent and epoxy resin to fully mix and form a uniform prepolymer. Pre-curing was then carried out at 100°C for 2 hours to form a partially cross-linked structure in the system, thereby improving the stability and heat resistance of the final cure.

[0031] (2) Preparation of high temperature resistant epoxy structural adhesive by dual curing

[0032] The pre-cured adhesive film is cut into appropriate sizes, sandwiched between two substrates to be bonded (aluminum alloy plates), and hot-pressed under a certain pressure (0.2MPa). Subsequently, it is cured at 200°C for 2 hours to complete the cross-linking reaction of the epoxy resin system and further enhance the bonding strength. The final decomposition temperature (Td10) of the structural adhesive obtained exceeds 300°C, the tensile strength reaches 85MPa, the shear strength is 40MPa, and after baking at 250°C for 2 hours and cooling to room temperature, the re-tested strength data error is less than 5%, showing excellent heat resistance. DSC (differential scanning calorimetry) is used to test the thermal curing process, TGA (thermogravimetric analysis) is used to test its heat decomposition temperature, and a universal material testing machine is used to determine the mechanical properties. The average value of 5 measurement results is taken for all tests.

[0033] The infrared spectrum of the structural adhesive in Example 1 is as follows Figure 1 As shown, the figure shows the presence of key functional groups such as epoxy group, cyano group, benzene ring, and siloxy group.

[0034] Example 2

[0035] (1) Preparation of prepolymer and curing film

[0036] The nano-silica filler is first modified with a silane coupling agent, and the steps of the modification process are the same as those in Example 1.

[0037] 6 g of 2-phenylimidazole was added to 200 g of E44 epoxy resin under stirring as a latent curing agent, along with 5 g of modified nano-silica filler to improve the system's heat resistance and mechanical properties. 8 g of benzoxazine was also added as a high-heat-resistant curing agent, and 0.5 g of ethylenethiourea curing accelerator was added to promote the subsequent high-temperature curing reaction. The mixture was then stirred at 80°C for 2 hours to thoroughly mix the curing agent and epoxy resin and form a uniform prepolymer. Pre-curing was then carried out at 100°C for 2 hours to form a partially cross-linked structure, thereby improving the stability and heat resistance of the final cure.

[0038] (2) Preparation of high temperature resistant epoxy structural adhesive by dual curing

[0039] The pre-cured adhesive film is cut into appropriate sizes, sandwiched between two substrates to be bonded (such as carbon fiber composite materials or aluminum alloy plates), and hot-pressed under a certain pressure (0.2MPa). Subsequently, it is cured at 200°C for 2 hours to complete the cross-linking reaction of the epoxy resin system and further enhance the bonding strength. The final decomposition temperature (Td10) of the structural adhesive is over 300°C, the tensile strength reaches 76MPa, the shear strength is 36MPa, and after baking at 250°C for 2 hours and cooling to room temperature, the re-tested strength data error is less than 5%, showing excellent heat resistance. DSC (differential scanning calorimetry) is used to test the thermal curing process, TGA (thermogravimetric analysis) is used to test its heat decomposition temperature, and a universal material testing machine is used to determine the mechanical properties. The average value of 5 measurement results is taken for all tests.

[0040] Example 3

[0041] (1) Preparation of prepolymer and curing film

[0042] The nano-silica filler is first modified with a silane coupling agent, and the steps of the modification process are the same as those in Example 1.

[0043] E44 epoxy resin (150 g) and TDE-85 epoxy resin (50 g) were mixed in a ratio of 3:1. Six grams of 2-ethyl-4-methylimidazole were added as a latent curing agent under stirring, along with 5 grams of modified nano-silica filler to improve the heat resistance and mechanical properties of the system. Six grams of benzoxazine were added as a high-heat-resistant curing agent, and 0.5 grams of ethylene thiourea curing accelerator were added to promote the subsequent high-temperature curing reaction. Subsequently, the mixture was stirred at 80°C for 2 hours to fully mix the curing agent and epoxy resin and form a uniform prepolymer. Pre-curing was then carried out at 100°C for 2 hours to form a partially cross-linked structure in the system, thereby improving the stability and heat resistance of the final cure.

[0044] (2) Preparation of high temperature resistant epoxy structural adhesive by dual curing

[0045] The pre-cured adhesive film is cut into appropriate sizes, sandwiched between two substrates to be bonded (such as carbon fiber composite materials or aluminum alloy plates), and hot-pressed under a certain pressure (0.2MPa). Subsequently, it is cured at 200°C for 2 hours to complete the cross-linking reaction of the epoxy resin system and further enhance the bonding strength. The final decomposition temperature (Td10) of the structural adhesive is over 300°C, the tensile strength reaches 70MPa, the shear strength is 34MPa, and after baking at 250°C for 2 hours and cooling to room temperature, the re-tested strength data error is less than 5%, showing excellent heat resistance. DSC (differential scanning calorimetry) is used to test the thermal curing process, TGA (thermogravimetric analysis) is used to test its heat decomposition temperature, and a universal material testing machine is used to determine the mechanical properties. The average value of 5 measurement results is taken for all tests.

[0046] Example 4

[0047] (1) Preparation of prepolymer and curing film

[0048] The nano-silica filler is first modified with a silane coupling agent, and the steps of the modification process are the same as those in Example 1.

[0049] E20 epoxy resin (130 g) and TDE-85 epoxy resin (50 g) were mixed, and 6 g of dicyandiamide was added as a latent curing agent under stirring, and 5 g of modified nano-silica filler was added to improve the heat resistance and mechanical properties of the system. 8 g of hexafluorodianhydride was added as a high-heat-resistant curing agent, and 0.5 g of ethylenethiourea curing accelerator was added to promote the subsequent high-temperature curing reaction. Subsequently, stirring was carried out at 80°C for 2 hours to fully mix the curing agent and epoxy resin and form a uniform prepolymer. Pre-curing was then carried out at 100°C for 2 hours to form a partially cross-linked structure in the system to improve the stability and heat resistance of the final cure.

[0050] (2) Preparation of high temperature resistant epoxy structural adhesive by dual curing

[0051] The pre-cured adhesive film is cut into appropriate sizes, sandwiched between two substrates to be bonded (such as carbon fiber composite materials or aluminum alloy plates), and hot-pressed under a certain pressure (0.2MPa). Subsequently, it is cured at 200°C for 2 hours to complete the cross-linking reaction of the epoxy resin system and further enhance the bonding strength. The final decomposition temperature (Td10) of the structural adhesive is over 300°C, the tensile strength reaches 84MPa, the shear strength is 41MPa, and after baking at 250°C for 2 hours and cooling to room temperature, the re-tested strength data error is less than 5%, showing excellent heat resistance. DSC (differential scanning calorimetry) is used to test the thermal curing process, TGA (thermogravimetric analysis) is used to test its heat decomposition temperature, and a universal material testing machine is used to determine the mechanical properties. The average value of 5 measurement results is taken for all tests.

[0052] Example 5

[0053] (1) Preparation of prepolymer and curing film

[0054] The nano-silica filler is first modified with a silane coupling agent, and the steps of the modification process are the same as those in Example 1.

[0055] E51 epoxy resin (150 g) and TDE-85 epoxy resin (50 g) were mixed in a ratio of 3:1. 6 g of dicyandiamide was added as a latent curing agent under stirring, and 5 g of modified nano-silica filler was added to improve the heat resistance and mechanical properties of the system. 8.5 g of benzoxazine was added as a high-heat-resistant curing agent, and 0.5 g of ethylene thiourea curing accelerator was added to promote the subsequent high-temperature curing reaction. Subsequently, stirring was carried out at 80°C for 2 hours to fully mix the curing agent and epoxy resin and form a uniform prepolymer. Pre-curing was then carried out at 100°C for 2 hours to form a partially cross-linked structure in the system to improve the stability and heat resistance of the final cure.

[0056] (2) Preparation of high temperature resistant epoxy structural adhesive by dual curing

[0057] The pre-cured adhesive film is cut into appropriate sizes, sandwiched between two substrates to be bonded (such as carbon fiber composite materials or aluminum alloy plates), and hot-pressed under a certain pressure (0.2MPa). Subsequently, it is cured at 200°C for 2 hours to complete the cross-linking reaction of the epoxy resin system and further enhance the bonding strength. The final decomposition temperature (Td10) of the structural adhesive obtained exceeds 300°C, the tensile strength reaches 86MPa, the shear strength is 38MPa, and after baking at 250°C for 2 hours and cooling to room temperature, the re-tested strength data error is less than 5%, showing excellent heat resistance. DSC (differential scanning calorimetry) is used to test the thermal curing process, TGA (thermogravimetric analysis) is used to test its heat decomposition temperature, and a universal material testing machine is used to determine the mechanical properties. The average value of 5 measurement results is taken for all tests.

[0058] Example 6

[0059] (1) Preparation of prepolymer and curing film

[0060] The nano-silica filler is first modified with a silane coupling agent, and the steps of the modification process are the same as those in Example 1.

[0061] E44 epoxy resin (150 g) and TDE-85 epoxy resin (50 g) were mixed in a ratio of 3:1. 6 g of dicyandiamide was added as a latent curing agent under stirring, and 5 g of modified nano-silica filler was added to improve the heat resistance and mechanical properties of the system. 8 g of 4,4'-diaminodiphenyl ether was added as a high heat-resistant curing agent, and 0.5 g of ethylene thiourea curing accelerator was added to promote the subsequent high-temperature curing reaction. Subsequently, the mixture was stirred at 80°C for 2 hours to fully mix the curing agent and epoxy resin and form a uniform prepolymer. Pre-curing was then carried out at 100°C for 2 hours to form a partially cross-linked structure in the system to improve the stability and heat resistance of the final cure.

[0062] (2) Preparation of high temperature resistant epoxy structural adhesive by dual curing

[0063] The pre-cured adhesive film is cut into appropriate sizes, sandwiched between two substrates to be bonded (such as carbon fiber composite materials or aluminum alloy plates), and hot-pressed under a certain pressure (0.2MPa). Subsequently, it is cured at 200°C for 2 hours to complete the cross-linking reaction of the epoxy resin system and further enhance the bonding strength. The final decomposition temperature (Td10) of the structural adhesive is over 300°C, the tensile strength reaches 81MPa, the shear strength is 40MPa, and after baking at 250°C for 2 hours and cooling to room temperature, the re-tested strength data error is less than 5%, showing excellent heat resistance. DSC (differential scanning calorimetry) is used to test the thermal curing process, TGA (thermogravimetric analysis) is used to test its heat decomposition temperature, and a universal material testing machine is used to determine the mechanical properties. The average value of 5 measurement results is taken for all tests.

[0064] Example 7

[0065] (1) Preparation of prepolymer and curing film

[0066] The nano-zirconia filler is first modified with a silane coupling agent. The steps of the modification process are the same as those in Example 1, except that the nano-silica filler is replaced with a nano-zirconia filler of the same mass.

[0067] E44 epoxy resin (150 g) and TDE-85 epoxy resin (50 g) were mixed in a ratio of 3:1. Six grams of dicyandiamide were added as a latent curing agent while stirring, along with 5 grams of modified nano-zirconia filler to improve the heat resistance and mechanical properties of the system. Eight grams of bismaleimide were added as a high-heat-resistant curing agent, and 0.5 grams of ethylene thiourea curing accelerator were added to promote the subsequent high-temperature curing reaction. The mixture was then stirred at 80°C for 2 hours to allow the curing agent and epoxy resin to fully mix and form a uniform prepolymer. Pre-curing was then carried out at 100°C for 2 hours to form a partially cross-linked structure in the system, thereby improving the stability and heat resistance of the final cure.

[0068] (2) Preparation of high temperature resistant epoxy structural adhesive by dual curing

[0069] The pre-cured adhesive film is cut into appropriate sizes, sandwiched between two substrates to be bonded (such as carbon fiber composite materials or aluminum alloy plates), and hot-pressed under a certain pressure (0.2MPa). Subsequently, it is cured at 200°C for 2 hours to complete the cross-linking reaction of the epoxy resin system and further enhance the bonding strength. The final decomposition temperature (Td10) of the structural adhesive obtained exceeds 300°C, the tensile strength reaches 82MPa, the shear strength is 41MPa, and after baking at 250°C for 2 hours and cooling to room temperature, the re-tested strength data error is less than 5%, showing excellent heat resistance. DSC (differential scanning calorimetry) is used to test the thermal curing process, TGA (thermogravimetric analysis) is used to test its heat decomposition temperature, and a universal material testing machine is used to determine the mechanical properties. The average value of 5 measurement results is taken for all tests.

[0070] Examples 1-7 are cases with better effects. Due to different raw materials and proportions, the corresponding tape performance varies according to different application scenarios.

[0071] Comparative Example 1

[0072] (1) Preparation of prepolymer and curing film

[0073] The nano-silica filler is first modified with a silane coupling agent, and the steps of the modification process are the same as those in Example 1.

[0074] E44 epoxy resin (150 g) and TDE-85 epoxy resin (50 g) were mixed in a ratio of 3:1. 6 g of dicyandiamide was added as a latent curing agent under stirring, and 0.1 g of modified nano-silica filler was added to improve the heat resistance and mechanical properties of the system. 8 g of benzoxazine was added as a high-heat-resistant curing agent, and 0.5 g of ethylene thiourea curing accelerator was added to promote the subsequent high-temperature curing reaction. Subsequently, stirring was carried out at 80°C for 2 hours to fully mix the curing agent and epoxy resin and form a uniform prepolymer. Pre-curing was then carried out at 100°C for 2 hours to form a partially cross-linked structure in the system to improve the stability and heat resistance of the final cure.

[0075] (2) Preparation of high temperature resistant epoxy structural adhesive by dual curing

[0076] The pre-cured adhesive film is cut into appropriate sizes, sandwiched between two substrates to be bonded (such as carbon fiber composite materials or aluminum alloy plates), and hot-pressed under a certain pressure (0.2MPa). Subsequently, it is cured at 200°C for 2 hours to complete the cross-linking reaction of the epoxy resin system and further enhance the bonding strength. The final decomposition temperature (Td10) of the structural adhesive obtained exceeds 300°C, the tensile strength reaches 85MPa, the shear strength is 40MPa, and after baking at 250°C for 2 hours and cooling to room temperature, the re-tested strength data error is greater than 25%, and the heat resistance is general. DSC (differential scanning calorimetry) is used to test the thermal curing process, TGA (thermogravimetric analysis) is used to test its heat decomposition temperature, and a universal material testing machine is used to determine the mechanical properties. The average value of 5 measurement results is taken for all tests.

[0077] Comparative Example 2

[0078] (1) Preparation of prepolymer and curing film

[0079] The nano-silica filler is first modified with a silane coupling agent, and the steps of the modification process are the same as those in Example 1.

[0080] E51 epoxy resin (100 g) and TDE-85 epoxy resin (50 g) were mixed, and 6 g of dicyandiamide was added as a latent curing agent while stirring, along with 5 g of modified nano-silica filler to improve the system's heat resistance and mechanical properties. 8.5 g of benzoxazine was added as a high-heat-resistant curing agent, and 0.5 g of ethylene thiourea curing accelerator was added to promote the subsequent high-temperature curing reaction. Subsequently, the mixture was stirred at 80°C for 2 hours to fully mix the curing agent and epoxy resin and form a uniform prepolymer. Pre-curing was then carried out at 100°C for 2 hours to form a partially cross-linked structure in the system, thereby improving the stability and heat resistance of the final cure.

[0081] (2) Preparation of high temperature resistant epoxy structural adhesive by dual curing

[0082] The pre-cured adhesive film is cut into appropriate sizes, sandwiched between two substrates to be bonded (such as carbon fiber composite materials or aluminum alloy plates), and hot-pressed under a certain pressure (0.2MPa). Subsequently, it is cured at 200°C for 2 hours to complete the cross-linking reaction of the epoxy resin system and further enhance the bonding strength. The final decomposition temperature (Td10) of the structural adhesive obtained exceeds 300°C, the tensile strength reaches 86MPa, the shear strength is 38MPa, and after baking at 250°C for 2 hours and cooling to room temperature, the re-tested strength data error is greater than 25%, and the heat resistance is general. DSC (differential scanning calorimetry) is used to test the thermal curing process, TGA (thermogravimetric analysis) is used to test its heat decomposition temperature, and a universal material testing machine is used to determine the mechanical properties. The average value of 5 measurement results is taken for all tests.

[0083] Comparative Example 3

[0084] (1) Preparation of prepolymer and curing film

[0085] The nano-silica filler is first modified with a silane coupling agent, and the steps of the modification process are the same as those in Example 1.

[0086] E44 epoxy resin (150 g) and TDE-85 epoxy resin (50 g) were mixed in a ratio of 3:1. 6 g of dicyandiamide was added as a latent curing agent under stirring, and 5 g of modified nano-silica filler was added to improve the heat resistance and mechanical properties of the system. 8 g of 4,4'-diaminodiphenyl ether was added as a high heat-resistant curing agent, and 0.5 g of ethylene thiourea curing accelerator was added to promote the subsequent high-temperature curing reaction. Subsequently, the mixture was stirred at 80°C for 2 hours to fully mix the curing agent and epoxy resin and form a uniform prepolymer. Pre-curing was then carried out at 100°C for 2 hours to form a partially cross-linked structure in the system to improve the stability and heat resistance of the final cure.

[0087] (2) Preparation of high temperature resistant epoxy structural adhesive by dual curing

[0088] The pre-cured adhesive film is cut into appropriate sizes, sandwiched between two substrates to be bonded (such as carbon fiber composite materials or aluminum alloy plates), and hot-pressed under a certain pressure (0.2MPa). Subsequently, it is cured at 200°C for 10 minutes to complete the cross-linking reaction of the epoxy resin system and further enhance the bonding strength. The final decomposition temperature (Td10) of the structural adhesive obtained exceeds 300°C, the tensile strength reaches 81MPa, the shear strength is 40MPa, and after baking at 250°C for 2 hours and cooling to room temperature, the re-tested strength data error is greater than 25%, and the heat resistance is general. DSC (differential scanning calorimetry) is used to test the thermal curing process, TGA (thermogravimetric analysis) is used to test its heat decomposition temperature, and a universal material testing machine is used to determine the mechanical properties. The average value of 5 measurement results is taken for all tests.

[0089] Comparative Example 4

[0090] (1) Preparation of prepolymer and curing film formation

[0091] The nano-silica filler is first modified with a silane coupling agent, and the steps of the modification process are the same as those in Example 1.

[0092] E44 epoxy resin (150g) and TDE-85 epoxy resin (50g) were mixed, and 5g of modified nano-silica filler was added under stirring to improve the system's heat resistance and mechanical properties. 8g of benzoxazine was added as a high-heat-resistant curing agent, and 0.5g of ethylene thiourea curing accelerator was added to promote the subsequent high-temperature curing reaction. Subsequently, the mixture was stirred at 80°C for 2 hours to fully mix the curing agent and epoxy resin and form a uniform prepolymer. Pre-curing was then carried out at 100°C for 2 hours to form a partially cross-linked structure in the system, thereby improving the stability and heat resistance of the final cure.

[0093] (2) Preparation of high temperature resistant epoxy structural adhesive by dual curing

[0094] The pre-cured adhesive film is cut into appropriate sizes, sandwiched between two substrates to be bonded (aluminum alloy plates), and hot-pressed under a certain pressure (0.2MPa). Subsequently, it is cured at 200°C for 2 hours to complete the cross-linking reaction of the epoxy resin system and further enhance the bonding strength. The final structural adhesive has a decomposition temperature (Td10) of 170°C, a tensile strength of 15MPa, and a shear strength of 12MPa. After baking at 250°C for 2 hours and cooling to room temperature, the retested strength data has an error of more than 25%, and the heat resistance is average. DSC (differential scanning calorimetry) is used to test the thermal curing process, TGA (thermogravimetric analysis) is used to test its heat decomposition temperature, and a universal material testing machine is used to determine the mechanical properties. The average value of 5 measurement results is taken for all tests.

[0095] Comparative Example 5

[0096] (1) Preparation of prepolymer and curing film formation

[0097] The nano-silica filler is first modified with a silane coupling agent, and the steps of the modification process are the same as those in Example 1.

[0098] E44 epoxy resin (150 g) and TDE-85 epoxy resin (50 g) were mixed, and 6 g of dicyandiamide was added as a latent curing agent while stirring, along with 5 g of modified nano-silica filler to improve the system's heat resistance and mechanical properties. 0.5 g of ethylene thiourea curing accelerator was also added to promote the subsequent high-temperature curing reaction. The mixture was then stirred at 80°C for 2 hours to allow the curing agent and epoxy resin to fully mix and form a uniform prepolymer. Pre-curing was then carried out at 100°C for 2 hours to form a partially cross-linked structure, which improved the stability and heat resistance of the final cure.

[0099] (2) Preparation of high temperature resistant epoxy structural adhesive by dual curing

[0100] The pre-cured adhesive film was cut to the appropriate size and sandwiched between two substrates (aluminum alloy plates) to be bonded. Hot-press bonding was performed under a constant pressure (0.2 MPa). Subsequently, the adhesive was cured at 200°C for 2 hours to complete the cross-linking reaction of the epoxy resin system and further enhance the bond strength. The resulting structural adhesive was incompletely cured, with some residual adhesive remaining, making mechanical property testing impossible.

[0101] Comparative Example 6

[0102] (1) Preparation of prepolymer and curing film

[0103] E44 epoxy resin (150 g) and TDE-85 epoxy resin (50 g) were mixed, and 6 g of dicyandiamide was added as a latent curing agent while stirring, along with 5 g of nanosilica filler to improve the system's heat resistance and mechanical properties. 8 g of benzoxazine was also added as a high-heat-resistant curing agent, and 0.5 g of ethylenethiourea curing accelerator was added to promote the subsequent high-temperature curing reaction. The mixture was then stirred at 80°C for 2 hours to thoroughly mix the curing agent and epoxy resin and form a uniform prepolymer. The resulting prepolymer film was then pre-cured at 100°C for 2 hours to form a partially cross-linked structure, improving the stability and heat resistance of the final cure.

[0104] (2) Preparation of high temperature resistant epoxy structural adhesive by dual curing

[0105] The pre-cured adhesive film is cut into appropriate sizes, sandwiched between two substrates to be bonded (aluminum alloy plates), and hot-pressed under a certain pressure (0.2MPa). Subsequently, it is cured at 200°C for 2 hours to complete the cross-linking reaction of the epoxy resin system and further enhance the bonding strength. The final decomposition temperature (Td10) of the structural adhesive is over 300°C, the tensile strength reaches 35MPa, the shear strength is 23MPa, and after baking at 250°C for 2 hours and cooling to room temperature, the re-tested strength data error is less than 5%, showing excellent heat resistance. DSC (differential scanning calorimetry) is used to test the thermal curing process, TGA (thermogravimetric analysis) is used to test its heat decomposition temperature, and a universal material testing machine is used to determine the mechanical properties. The average value of 5 measurement results is taken for all tests.

[0106] Compared with Example 1, Comparative Example 1 significantly reduced the amount of nano-silica filler. As shown in Table 1, the decomposition temperature, tensile strength, and shear strength of Comparative Example 1 were significantly reduced, indicating that the addition of nano-fillers has a significant impact on high-temperature resistance, but has little effect on the glass transition temperature of the polymer itself. Compared with Example 5, Comparative Example 2 reduced the epoxy resin content in the prepolymer. The results showed that due to overcuring during the prepolymer film formation stage, the initial adhesion of the prepolymer film was significantly reduced, and the subsequent deep curing reaction was limited, resulting in a significant decrease in the high-temperature resistance of the final structural adhesive. This shows that the ratio of resin to curing agent is crucial to the performance of the structural adhesive. Compared with Example 6, Comparative Example 3 reduced the high-temperature curing time, resulting in insufficient curing of the system. As a result, the glass transition temperature and decomposition temperature of the resulting structural adhesive were significantly reduced. Due to insufficient curing, the mechanical properties were also significantly reduced. Therefore, sufficient reaction is also an important factor in ensuring the performance of structural adhesives. Compared with Example 1, Comparative Example 4 eliminated the latent curing agent. The results showed that the deep curing was incomplete and the decomposition temperature of the glue was low. Compared with Example 1, Comparative Example 5 eliminated the high heat-resistant curing agent. The results showed that the glue could not be cured, residual glue was left, and subsequent mechanical property tests could not be carried out. Compared with Example 1, Comparative Example 6 showed that if the nanofiller was not pre-modified with a silane coupling agent, the particle distribution was uneven, and the improvement in strength and heat resistance was very limited.

[0107] Table 1 Performance test results of foam tapes in different embodiments and comparative examples

[0108]

[0109] *The decomposition temperature is based on the 10% mass loss temperature (Td10). 6# represents ball No. 6 (GB / T2792-2008).

[0110] The above description is only part of the embodiments of the present invention and is not intended to limit the present invention. All equivalent changes and modifications made based on the content of the present invention are within the scope of protection of the present invention.

Claims

1. A dual-curing solvent-free, high-temperature resistant epoxy resin structural adhesive, characterized in that The composition includes the following components by weight: 1.5-5% latent curing agent, 2-5% high heat-resistant curing agent, 1-5% nano filler, 0.1-0.3% curing accelerator, and the balance is epoxy resin.

2. A dual-curing solvent-free, high-temperature resistant epoxy resin structural adhesive according to claim 1, characterized in that The invention comprises the following components by weight: 2.5-3% latent curing agent, 3-4% high heat-resistant curing agent, 2-2.5% nano filler, 0.2-0.25% curing accelerator, and the balance is epoxy resin, wherein the curing accelerator is ethylene thiourea; The epoxy resin is at least one of E20, E44, E51, and TDE-85, or is a silicone-modified epoxy resin.

3. A dual-curing solvent-free, high-temperature resistant epoxy resin structural adhesive according to claim 1, characterized in that The latent curing agent is one or more of the following: dicyandiamide, 2-phenylimidazole, 2-ethyl-4-methylimidazole, 2-methylimidazole, N-imidazole, and a latent acid anhydride curing agent. The latent acid anhydride curing agent is at least one of hexahydrophthalic anhydride and methyltetrahydrophthalic anhydride.

4. A dual-curing solvent-free, high-temperature resistant epoxy resin structural adhesive according to claim 1, characterized in that The high heat-resistant curing agent is one or more of the following: benzoxazine, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone, benzophenone tetracarboxylic dianhydride, hexafluorodianhydride, benzoxazine modified curing agent, and bismaleimide.

5. The dual-curing solvent-free, high-temperature resistant epoxy resin structural adhesive according to claim 1, characterized in that The nanofiller is one or more of the following: nano-alumina, nano-silicon dioxide, nano-zirconium oxide, multi-walled nano-carbon tubes, and graphene.

6. A dual-curing solvent-free, high-temperature resistant epoxy resin structural adhesive as claimed in claim 5, characterized in that The nano filler is modified with a silane coupling agent to improve the dispersibility and interface bonding strength of the filler in the epoxy resin.

7. A dual-curing solvent-free, high-temperature resistant epoxy resin structural adhesive as claimed in claim 6, characterized in that The modification treatment comprises the following steps: adding the nanofiller to an ethanol solution of γ-glycidyloxypropyltrimethoxysilane with a mass concentration of 1-5%, wherein the mass ratio of the nanofiller to the γ-glycidyloxypropyltrimethoxysilane is 1:0.2-0.6; heating the solution to 55-65° C. and stirring for reaction for 1-4 hours; and ultrasonically dispersing the solution for 10-60 minutes to reduce agglomeration; then centrifuging the solution, washing the solution with ethanol to remove unreacted silane and by-products, and drying the solution. The modification treatment is then completed.

8. The method for preparing a dual-curing solvent-free, high-temperature resistant epoxy resin structural adhesive according to claim 1, characterized in that According to the formula, epoxy resin, latent curing agent, high heat-resistant curing agent, nano filler and ethylene thiourea curing accelerator are mixed and uniformly stirred to prepare the structural adhesive.

9. Use of the dual-curing solvent-free, high-temperature resistant epoxy resin structural adhesive as claimed in claim 1 in bonding materials.

10. The use according to claim 9, characterized in that The following steps are involved: 1) Mixing: According to the formula, mix the epoxy resin, latent curing agent, high heat-resistant curing agent, nano filler, and curing accelerator. Stir at 70-90°C for 1-3 hours to fully mix the curing agent and epoxy resin. 2) Pre-curing: Apply the mixture to a film and pre-curing at a temperature range of 100°C - 150°C for 1-3 hours to form a preliminary cross-linking structure; 3) High temperature curing: Use the adhesive film to bond the two objects to be bonded, press them tightly, and fully cure them at a temperature range of 190℃ - 220℃. The curing time is 1-3 hours, so that the material forms a structural adhesive system with a high cross-linking density.

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