High-temperature and high-humidity resistant epoxy structural adhesive and preparation method thereof

Abstract

The application discloses a high-temperature and wet heat resistant epoxy structural adhesive and a preparation method thereof, and belongs to the technical field of high-performance composite materials. The application constructs a water blocking path of chemical hydrophobic interception and physical lamellar structure network barrier through the cooperation of fluorine-containing modified nano-silicon dioxide and organic intercalation modified nano-montmorillonite. The perfluoroalkyl chain grafted on the surface of the fluorine-containing modified nano-silicon dioxide can intercept water; the organic intercalation montmorillonite is exfoliated into nano-lamellar, forms a lamellar structure network in the epoxy structural adhesive matrix, forms a lamellar labyrinth effect, hinders water penetration, and can also adsorb hydrogen ions in a humid heat environment to inhibit the hydrolysis of the crosslinked network. Finally, the tensile shear strength retention rate of the epoxy structural adhesive is greater than or equal to 81.3% after 1000h, 85 DEG C and 85% RH humid heat aging. The application has strong raw material adaptability, high industrialization feasibility, and can be suitable for multiple scenes such as building curtain walls, automobile structures and electronic packaging.

Description

Technical Field

[0001] This invention relates to the field of high-performance composite materials technology, and in particular to a high-temperature and humid heat resistant epoxy structural adhesive and its preparation method. Background Technology

[0002] Epoxy structural adhesives, with their excellent bonding strength, mechanical stability, and process adaptability, have become core materials in many fields, including building curtain wall bonding, automotive body structure connection, electronic device component encapsulation, and marine engineering component fixing. Especially in scenarios requiring long-term resistance to vibration, temperature differences, and environmental corrosion, their service reliability directly affects the safety and service life of the overall component. However, epoxy structural adhesives contain hydrophilic groups such as hydroxyl groups in their molecular chains, and the interface between the adhesive layer and the adherend (such as metals or inorganic materials) easily forms micropores. Under high temperature and humidity conditions, water molecules can easily penetrate into the adhesive layer and interface through diffusion and capillary action, causing problems such as resin matrix swelling, interfacial chemical bond breakage, and filler agglomeration. Ultimately, this leads to a significant decrease in bonding strength, interfacial debonding, and even component failure. Therefore, improving resistance to damp heat has become a key technical challenge in the epoxy structural adhesive field.

[0003] To address these issues, the industry has explored various technologies: conventional solutions often involve adding traditional silane coupling agents (such as KH550 and KH560) to optimize interfacial bonding, or introducing common nanofillers such as calcium carbonate to improve density. However, the former can only improve interfacial adhesion in the short term and cannot prevent long-term water penetration. Common nanofillers are also prone to forming new penetration channels due to uneven dispersion, resulting in limited improvement in resistance to damp heat. Another technology improves toughness by modifying a single epoxy resin (such as introducing flexible segments), but this often comes at the cost of sacrificing resistance to damp heat, making it difficult to achieve a synergistic balance between strength, toughness, and resistance to damp heat.

[0004] In existing technologies, hydrophobic groups are also used to modify epoxy resins. For example, patent CN10487711B discloses a fluorinated modified epoxy resin, which achieves hydrophobic modification of epoxy resin through a fluorinated curing agent. Although this improves the resistance to chemical media to a certain extent, it relies solely on a single hydrophobic mechanism. Under long-term high-temperature and humid environments, it is still prone to interfacial debonding due to water molecule penetration. Furthermore, it uses a single epoxy resin system and does not take into account the toughness of the material, making it difficult to meet the dynamic stress requirements in scenarios such as automobiles and construction machinery.

[0005] Meanwhile, when modifying epoxy resins with hydrophobic groups, additional reactive functional groups (such as epoxy groups in fluorinated copolymers and amine groups in fluorinated curing agents) are usually introduced. These functional groups participate in the epoxy curing reaction, making the crosslinking network denser. The strong hydrophobicity of fluorinated groups also reduces the compatibility between epoxy monomers and curing agents. To avoid phase separation, existing technologies often increase the degree of curing reaction, which inevitably further increases the crosslinking density. The increase in crosslinking density reduces the toughness of the structural adhesive system, making the system more brittle. This, in turn, limits the product's applicability to various scenarios, making it difficult to meet the requirements of long-term humid heat stability and high bonding toughness for epoxy structural adhesives in fields such as construction, automotive, and electronics. Summary of the Invention

[0006] To address the aforementioned technical problems in the prior art, this invention aims to provide a high-temperature and humid heat resistant epoxy structural adhesive and its preparation method.

[0007] One objective of this invention is to provide a high-temperature and moisture-resistant epoxy structural adhesive, wherein the epoxy structural adhesive comprises the following raw materials in parts by weight:

[0008] The composition includes 25-35 parts of bisphenol A type epoxy resin, 15-20 parts of core-shell modified epoxy resin, 10-15 parts of polyurethane modified epoxy resin, 3-8 parts of fluorine-containing modified nano-silica, 5-10 parts of organic intercalated modified nano-montmorillonite, 8-12 parts of curing agent, 1-3 parts of curing accelerator, 1-3 parts of silane coupling agent, and 0.5-1 parts of antioxidant.

[0009] The fluorine-modified nano-silica is obtained by modifying nano-silica with perfluoroalkyltrialkoxysilane as a modifier, wherein the carbon chain length of the perfluoroalkyl group is 6-10, and the alkoxy group is methoxy or ethoxy.

[0010] The organic intercalation modified nano-montmorillonite is a long-chain alkyl quaternary ammonium salt or a long-chain alkylamine salt modified montmorillonite, wherein the carbon chain length of the alkyl group is 12~20.

[0011] Preferably, the modifier includes one or more of tridecylfluorooctyltriethoxysilane, perfluorodecyltriethoxysilane, perfluorooctyltrimethoxysilane, or perfluorohexyltriethoxysilane.

[0012] Preferably, the nano-silica includes fumed nano-silica with a particle size of 5-20 nm.

[0013] Preferably, the amount of the modifier is 10-15% of the mass of nano-silica.

[0014] The preparation method of the fluorine-modified nano-silica includes:

[0015] (1) Add the modifier to anhydrous ethanol to obtain a silane solution with a mass concentration of 10~15%, and continue stirring for 30~50 min to complete the hydrolysis;

[0016] (2) Add the dried nano-silica to a high-speed stirred reactor, heat it to 60~80℃, and stir and disperse it at 800~1000r / min for 25~35min; then slowly add the hydrolyzed silane solution, and after the addition is complete, keep the temperature at 60~80℃ and continue stirring for 2~3h.

[0017] (3) The fluorine-modified nano-silica is obtained by vacuum drying at 60~70℃ for 4~6h.

[0018] Preferably, the mass ratio of the organic intercalated modified nano-montmorillonite to the fluorine-modified nano-silica is 1.5~2.5:1, and the sum of their masses does not exceed 18 parts.

[0019] Preferably, the nano-silica includes Cabot TS-720.

[0020] Preferably, the organic intercalated modified nano-montmorillonite includes Zhejiang Fenghong NANOLC-NP301.

[0021] Preferably, the bisphenol A type epoxy resin includes E-44 and / or E-51.

[0022] Preferably, the core-shell modified epoxy resin includes MX153 and / or MX154 from Kaneka Chemicals, Japan.

[0023] Preferably, the polyurethane-modified epoxy resin includes complexed high-tech EPU301.

[0024] Preferably, the curing agent includes one or more of dicyandiamide, sebacate dihydrazide, or adipic acid dihydrazide.

[0025] Preferably, the curing accelerator is an organic urea accelerator.

[0026] Preferably, the silane coupling agent includes KH560 and / or KH580.

[0027] A second objective of this invention is to provide a method for preparing the epoxy structural adhesive as described above, the method comprising:

[0028] Bisphenol A type epoxy resin, core-shell modified epoxy resin, and polyurethane modified epoxy resin are put into a stirring device and stirred for 30 to 40 minutes at 80~90℃ and 800~1000r / min to obtain an epoxy matrix mixture.

[0029] The temperature was lowered to below 60℃, and fluorine-modified nano-silica, organic intercalated modified nano-montmorillonite, and silane coupling agent were added. The mixture was stirred at 800~1200r / min for 1~2h to obtain a filler-matrix mixture.

[0030] Lower the temperature to below 40℃, add curing agent, curing accelerator and antioxidant, stir at 300~500r / min for 20~30min, and vacuum degas for 10~15min to obtain the high temperature and humid heat resistant epoxy structural adhesive.

[0031] The beneficial effects of this invention include:

[0032] This invention utilizes the synergistic effect of fluorinated modified nano-silica and organically intercalated modified nano-montmorillonite to construct a moisture-blocking pathway that combines chemical hydrophobic interception with a physical layered network barrier. The perfluoroalkyl chains grafted onto the surface of the fluorinated modified nano-silica intercept moisture; the organically intercalated montmorillonite is exfoliated into nanosheets, forming a layered network within the epoxy structural adhesive matrix. This network creates a layered maze effect, hindering moisture penetration and adsorbing hydrogen ions in humid and hot environments, thus inhibiting the hydrolysis of the cross-linked network. Ultimately, the epoxy structural adhesive retains ≥81.3% of its tensile shear strength after 1000 hours of humid and hot aging at 85°C and 85% RH.

[0033] Meanwhile, this invention employs a ternary matrix system of bisphenol A type epoxy resin, core-shell modified epoxy resin, and polyurethane modified epoxy resin. The bisphenol A type epoxy resin provides a rigid skeleton to ensure load-bearing capacity, the core-shell modified epoxy resin can inhibit the propagation of microcracks through the rubber core, and the polyurethane modified epoxy resin optimizes the flexibility of the molecular chain. The three work together to provide an epoxy resin matrix compatible with the damp heat protection system, which is conducive to achieving the comprehensive requirements of strong load-bearing capacity, impact resistance, and environmental corrosion resistance.

[0034] Meanwhile, the raw materials of this invention are highly adaptable and have high industrial feasibility, making it applicable to various scenarios such as building curtain walls, automotive structures, and electronic packaging. Detailed Implementation

[0035] The following description includes certain specific details to provide a comprehensive understanding of the various disclosed embodiments. However, those skilled in the art will recognize that embodiments can be implemented without employing one or more of these specific details, but using other methods, components, materials, etc.

[0036] Unless otherwise required by the present invention, throughout the specification and the following claims, the words “comprising” and “including” shall be interpreted in an open-ended, inclusive sense, meaning “including but not limited to”.

[0037] Throughout this specification, the terms "an embodiment," "an embodiment," "a preferred embodiment," or "some embodiments" refer to including, in at least one embodiment, a specific reference element, structure, or feature associated with that embodiment. Therefore, the phrases "in an embodiment," "in a preferred embodiment," or "in some embodiments" appearing in different places throughout the specification do not necessarily all refer to the same embodiment. Furthermore, specific elements, structures, or features may be combined in one or more embodiments in any suitable manner.

[0038] According to a first aspect of the present invention, a high-temperature and humid heat resistant epoxy structural adhesive is provided, the epoxy structural adhesive comprising the following raw materials in parts by weight:

[0039] The composition includes 25-35 parts of bisphenol A type epoxy resin, 15-20 parts of core-shell modified epoxy resin, 10-15 parts of polyurethane modified epoxy resin, 3-8 parts of fluorine-containing modified nano-silica, 5-10 parts of organic intercalated modified nano-montmorillonite, 8-12 parts of curing agent, 1-3 parts of curing accelerator, 1-3 parts of silane coupling agent, and 0.5-1 parts of antioxidant.

[0040] The fluorine-modified nano-silica is obtained by modifying nano-silica with perfluoroalkyltrialkoxysilane as a modifier, wherein the carbon chain length of the perfluoroalkyl group is 6-10, and the alkoxy group is methoxy or ethoxy.

[0041] The organic intercalation modified nano-montmorillonite is a long-chain alkyl quaternary ammonium salt or a long-chain alkylamine salt modified montmorillonite, wherein the carbon chain length of the alkyl group is 12~20.

[0042] In this invention, bisphenol A type epoxy resin, core-shell modified epoxy resin and polyurethane modified epoxy resin constitute an epoxy matrix system.

[0043] Bisphenol A type epoxy resin forms the basic framework, ensuring the system's mechanical load-bearing capacity and chemical inertness in humid and hot environments. Its molecular chain contains numerous rigid benzene rings and flexible ether bonds, giving it high strength, high modulus, and good chemical stability. The benzene rings enhance the system's heat resistance, while the ether bonds provide a small amount of molecular chain flexibility, facilitating high bonding toughness. Furthermore, the raw materials are readily available and cost-effective. The epoxy value of bisphenol A type epoxy resin is 0.4~0.55 eq / 100g, matching the reactivity of the curing agent, enabling the formation of a dense three-dimensional cross-linked network that provides core bonding strength. If the amount of bisphenol A type epoxy resin exceeds 35 parts, the cross-linked network becomes too dense, making it difficult for the molecular chains to slip and deform, leading to weakened impact strength and increased susceptibility to stress concentration fracture in humid and hot environments. If the amount of bisphenol A type epoxy resin is less than 25 parts, the main matrix framework of the epoxy structural adhesive is weak, making it difficult to support the toughening effect of the core-shell and polyurethane-modified epoxy, resulting in decreased tensile strength and failure to meet the load-bearing requirements of the structural adhesive. The amount of the bisphenol A type epoxy resin used is, for example, 25 parts, 26 parts, 27 parts, 28 parts, 29 parts, 30 parts, 31 parts, 32 parts, 33 parts, 34 parts or 35 parts, and any point value between any two of the above.

[0044] Preferably, the bisphenol A type epoxy resin includes E-44 and / or E-51.

[0045] Core-shell modified epoxy resin refers to epoxy resin toughened using core-shell particles. These particles have a soft core primarily composed of polybutadiene rubber and a hard shell layer with good compatibility with epoxy resin. This allows for the inhibition of microcrack propagation without reducing heat resistance. The shell layer and the main matrix can form an integrated cross-linked network under the action of a curing agent, thus avoiding the defects of general toughening agents that result in toughening without heat resistance. If the amount of core-shell modified epoxy resin is less than 15 parts, the toughening effect is insufficient; if the amount exceeds 20 parts, it will dilute the rigid groups of the main matrix, leading to a decrease in cross-linking density and glass transition temperature, failing to meet the 85°C damp heat aging requirement. In this invention, the amount of core-shell modified epoxy resin is, for example, 15 parts, 15.5 parts, 16 parts, 16.5 parts, 17 parts, 17.5 parts, 18 parts, 18.5 parts, 19 parts, 19.5 parts, or 20 parts, and any value between these two.

[0046] Preferably, the core-shell modified epoxy resin includes MX153 and / or MX154 from Kaneka Chemicals, Japan.

[0047] Polyurethane-modified epoxy resin is used as an auxiliary toughening agent to optimize low-temperature toughness and impact resistance. It can synergize with core-shell epoxy to compensate for the insufficient toughness of core-shell modified epoxy in low-temperature environments. Simultaneously, the long chains of polyurethane improve the interfacial wettability between the adhesive layer and the adherend, enhancing bonding reliability. If the amount of polyurethane-modified epoxy resin is less than 10 parts, it is difficult to effectively optimize low-temperature performance; the impact strength of the adhesive layer decreases at -40°C, making it prone to brittleness at extreme temperatures. If the amount of polyurethane-modified epoxy resin is greater than 15 parts, it will reduce the overall heat resistance of the system. The amount of polyurethane-modified epoxy resin used, for example, is 10 parts, 10.5 parts, 11 parts, 11.5 parts, 12 parts, 12.5 parts, 13 parts, 13.5 parts, 14 parts, 14.5 parts, or 15 parts, and any value between these two extremes.

[0048] Preferably, the polyurethane-modified epoxy resin includes complexed high-tech EPU301.

[0049] In this invention, a curing agent and a curing accelerator constitute a curing control system. The curing agent is a latent curing agent, matching the activity of the epoxy groups in the three epoxy resins mentioned above, enabling them to crosslink synchronously without phase separation, and is also compatible with industrial production. In this invention, when the amount of the curing agent is less than 8 parts, the epoxy resin system is prone to insufficient curing; when the amount of the curing agent exceeds 12 parts, the crosslinking density becomes too high, making it difficult for the molecular chains to slide, and weakening the impact strength of the adhesive layer. The amount of the curing agent is, for example, 8 parts, 8.5 parts, 9 parts, 9.5 parts, 10 parts, 10.5 parts, 11 parts, 11.5 parts, or 12 parts, and any value between these two.

[0050] Preferably, the curing agent includes one or more of dicyandiamide, sebacic acid dihydrazide, or adipic acid dihydrazide, with dicyandiamide being the most preferred. The CN bond formed by the reaction of the amino and epoxy groups in dicyandiamide has a high bond energy, approximately 305 kJ / mol, and is not easily hydrolyzed under humid and hot conditions.

[0051] The curing accelerator includes urea-based accelerators and / or imidazole-based accelerators, which can specifically activate the dicyandiamide curing agent and have good compatibility with the system. Furthermore, the urea bonds formed after curing by urea-based accelerators have strong hydrolysis resistance, and the nitrogen atoms of imidazole-based accelerators can form coordination bonds with the epoxy network, further enhancing the stability of the cross-linked network and preventing network degradation under humid heat. When the amount of the curing accelerator is less than 1 part, it is difficult to effectively activate the curing agent, and the curing time is long, resulting in low production efficiency and incomplete cross-linking. When the amount of the curing accelerator exceeds 3 parts, the curing reaction rate is too fast, and the heat inside the adhesive layer cannot be dissipated in time. The resulting internal stress easily leads to cracking of the adhesive layer after curing or peeling from the interface with the adhered object; moreover, excessive accelerator is prone to migration and precipitation, reducing the adhesive layer's resistance to humid heat. The amount of the curing accelerator is, for example, 1 part, 1.2 parts, 1.4 parts, 1.6 parts, 1.8 parts, 2 parts, 2.2 parts, 2.4 parts, 2.6 parts, 2.8 parts, or 3 parts.

[0052] Preferably, the curing accelerator is an organic urea accelerator, preferably including Azken UR700 and / or Ajinomoto PN50.

[0053] Preferably, the mass ratio of the curing agent to the curing accelerator is 4~8:1, which is more conducive to synergistically improving the toughness of the adhesive layer with other components.

[0054] Fluorine-modified nano-silica and organically intercalated modified nano-montmorillonite constitute a moisture- and heat-resistant protective system.

[0055] In this invention, perfluoroalkyltrialkoxysilane is used as a modifier to chemically graft and modify nano-silica, grafting hydrophobic fluorine-containing groups onto the surface of the nano-silica particles to form an organic hydrophobic layer. The carbon chain length of the perfluoroalkyl group is 6-10, and the alkoxy group is methoxy or ethoxy. Perfluoroalkyl groups have extremely low surface free energy and very strong hydrophobicity. The perfluoroalkyltrialkoxysilane can form Si-O-Si covalent bonds with the hydroxyl groups on the surface of the nano-silica through hydrolysis and condensation, forming a strong graft. The fluorine-modified nano-silica is uniformly distributed and fills the epoxy structural adhesive matrix, serving as both a hydrophobic barrier and a physical filler.

[0056] Meanwhile, after the siloxane groups of the fluorosilane modifier hydrolyze, in addition to reacting with the hydroxyl groups on the SiO2 surface, they will further react with the hydroxyl groups and ether bonds in the epoxy matrix to form stable Si-OC chemical bonds. This can reduce the interfacial gaps between the filler and the epoxy matrix, while improving the bonding force between the filler and the matrix, preventing interfacial peeling under humid and hot conditions, and playing a role in interfacial strengthening.

[0057] When the amount of fluorinated modified nano-silica is less than 3 parts, it is insufficient to form a complete hydrophobic coating layer, and moisture is easily absorbed and adsorbed. When the amount is more than 8 parts, the nano-fluorinated silica particles are prone to agglomeration due to van der Waals forces. The pores inside the agglomerates become channels for moisture penetration, and also lead to a decrease in the toughness of the adhesive layer. The amount of fluorinated modified nano-silica is, for example, 3 parts, 4 parts, 5 parts, 6 parts, 7 parts, or 8 parts, as well as any value between two of the above.

[0058] In this invention, the organic intercalation modified nano-montmorillonite is a long-chain alkyl quaternary ammonium salt or a long-chain alkylamine salt modified montmorillonite, wherein the carbon chain length of the alkyl group is 12-20.

[0059] Organically intercalated modified nano-montmorillonite refers to montmorillonite modified using long-chain alkyl quaternary ammonium salts or long-chain alkylamine salts as intercalating agents. The intercalating agent inserts between the montmorillonite layers, increasing the interlayer spacing and changing the montmorillonite surface from hydrophilic to hydrophobic, while also ensuring good compatibility with the epoxy organic resin matrix. The intercalating agent can increase the interlayer spacing from 1-2 nm in natural montmorillonite to 3-5 nm, allowing for full penetration by the epoxy resin. It can even be exfoliated into nanoscale monolayers during curing, uniformly dispersed in the epoxy matrix, forming a randomized layered network. This layered network can construct numerous tiny barriers within the adhesive layer, preventing moisture penetration into the adhesive layer and thus reducing moisture penetration to the bonding interface.

[0060] Meanwhile, the montmorillonite sheets themselves are negatively charged and form stable ionic bonds with quaternary ammonium salts or amine salts. They can adsorb trace amounts of hydrogen ions generated in humid and hot environments, preventing hydrogen ions from catalyzing the hydrolysis and breakage of the epoxy crosslinking network, thus protecting the stability of the matrix structure.

[0061] Meanwhile, the layered network structure possesses extremely high specific surface area and strength, and after uniform dispersion, it forms a composite structure of rigid layers and flexible matrix with the epoxy matrix. Under stress, the montmorillonite layers can share the load, inhibit the plastic deformation of the resin matrix, and improve the tensile shear strength and modulus of the adhesive layer; the layered structure can hinder the propagation of microcracks inside the adhesive layer, reduce brittle fracture caused by resin swelling and molecular chain degradation under humid and hot conditions, and improve bonding toughness.

[0062] When the amount of the organically intercalated modified nano-montmorillonite is less than 5 parts, it is insufficient to form a dense labyrinth network; when the amount is more than 10 parts, it will lead to an increase in the rigidity of the adhesive layer, an increase in internal stress, and easy cracking after hygrothermal aging, which will instead provide a channel for water to permeate. The amount of the organically intercalated modified nano-montmorillonite is, for example, 5 parts, 5.5 parts, 6 parts, 6.5 parts, 7 parts, 7.5 parts, 8 parts, 8.5 parts, 9 parts, 9.5 parts, or 10 parts, as well as any value between two of the above.

[0063] In summary, the organically intercalated modified nano-montmorillonite and fluorine-modified nano-silica form a synergistic layer barrier and hydrophobic protection, while also working synergistically with core-shell modified epoxy and polyurethane modified epoxy to improve resistance to damp heat while maintaining bonding toughness.

[0064] In this invention, the silane coupling agent is used to enhance interfacial adhesion and prevent interfacial delamination under humid and hot conditions. The amount of the silane coupling agent used is, for example, 1 part, 1.2 parts, 1.4 parts, 1.6 parts, 1.8 parts, 2 parts, 2.2 parts, 2.4 parts, 2.6 parts, 2.8 parts, or 3 parts.

[0065] The silane coupling agent preferably includes KH560 and / or KH580.

[0066] The antioxidant is used to inhibit the aging of the epoxy resin system, and the amount of the antioxidant is, for example, 0.5 parts, 0.6 parts, 0.7 parts, 0.8 parts, 0.9 parts, or 1 part. The antioxidant preferably includes antioxidant 1010.

[0067] In a preferred embodiment of the present invention, the modifier includes one or more of tridecafluorooctyltriethoxysilane, perfluorodecyltriethoxysilane, perfluorooctyltrimethoxysilane, or perfluorohexyltriethoxysilane.

[0068] In this invention, the molecular structural formula of tridecafluorooctyltriethoxysilane is CF3(CF2)5CH2CH2Si(OC2H5)3, the molecular structural formula of perfluorodecyltriethoxysilane is CF3(CF2)7CH2CH2Si(OC2H5)3, the molecular structural formula of perfluorooctyltrimethoxysilane is CF3(CF2)5CH2CH2Si(OCH3)3, and the molecular structural formula of perfluorohexyltriethoxysilane is CF3(CF2)3CH2CH2Si(OC2H5)3.

[0069] In a preferred embodiment of the present invention, the nano-silica includes fumed nano-silica with a particle size of 5-20 nm.

[0070] In this invention, the fumed silica nanoparticles exhibit good particle size uniformity, good dispersibility, and high surface hydroxyl density, resulting in better compatibility with the modifier. If the particle size is <5nm, the primary aggregates are dense, which easily leads to the modified fluorosilanes only being grafted onto the surface of the aggregates; if the particle size is >20nm, the excessively large particle size results in poor filling of the micro-gaps in the epoxy structural adhesive, and the excessively large particle size easily leads to local aggregation when dispersed in the epoxy matrix. When synergistic with montmorillonite layers, this will disrupt the continuity of the layer network structure and reduce the physical barrier effect.

[0071] The nano-silica is preferably Cabot TS-720.

[0072] In a preferred embodiment of the present invention, the amount of the modifier is 10-15% of the mass of nano-silica.

[0073] In this invention, when the amount of modifier is less than 10%, the grafting density is too low, which can easily lead to discontinuity of the hydrophobic layer; when the amount of modifier exceeds 15%, it exceeds the carrying capacity of the hydroxyl groups on the surface of nano-silica. Modifiers that do not participate in grafting may self-polymerize, generating small particulate impurities. These small particulate impurities may agglomerate in the epoxy matrix, forming micropores that become channels for water permeation.

[0074] In a preferred embodiment of the present invention, the method for preparing the fluorine-modified nano-silica includes:

[0075] (1) Add the modifier to anhydrous ethanol to obtain a silane solution with a mass concentration of 10~15%, and continue stirring for 30~50 min to complete the hydrolysis;

[0076] (2) Add the dried nano-silica to a high-speed stirred reactor, heat it to 60~80℃, and stir and disperse it at 800~1000r / min for 25~35min; then slowly add the hydrolyzed silane solution, and after the addition is complete, keep the temperature at 60~80℃ and continue stirring for 2~3h.

[0077] (3) The fluorine-modified nano-silica is obtained by vacuum drying at 60~70℃ for 4~6h.

[0078] In this invention, the nano-silica is vacuum dried at 105°C for 2 hours to remove surface-adsorbed moisture.

[0079] In step (1), the alkoxy group in the modifier perfluoroalkyltrialkoxysilane undergoes hydrolysis to generate silanol and ethanol. When the alkoxy group in the modifier is methoxy, its hydrolytic activity is low. The hydrolysis reaction can be promoted by adding dilute acetic acid to adjust the pH of the solution to 4-5.

[0080] In step (2), the dried nano-silica is first dispersed by high-speed stirring at 800-1000 r / min at 60-80℃, which can break up the agglomerates and activate the hydroxyl groups on the surface of the nano-silica.

[0081] Heating to 60-80℃ makes the residual hydroxyl groups on the surface of nano-silica more active, which is more conducive to the subsequent condensation reaction with the silanol groups generated by the hydrolysis of fluorosilanes, resulting in a stronger graft. When the temperature exceeds 80℃, the excessively high temperature may cause the subsequently added modifier to self-polymerize prematurely.

[0082] When using a low stirring speed of less than 800 r / min, the shear force is insufficient, making it difficult to break up stubborn agglomerates and resulting in poor modification treatment. When the speed exceeds 1000 r / min, the excessive speed may cause the system to generate a large amount of heat and may also cause the system to splash, increasing the difficulty of process control.

[0083] In step (2), after the silane solution is added, the hydroxyl groups on the surface of the nano-silica undergo a dehydration condensation reaction with the silanol groups generated by the hydrolysis of the modifier, forming stable Si-O-Si chemical bonds, and grafting the long-chain fluorine-containing groups in the modifier onto the surface of the nano-silica. The grafted fluorine-containing groups are oriented on the surface of the nano-silica, forming a fluorine-containing hydrophobic layer.

[0084] After the reaction in step (2) is completed, the product is transferred to a vacuum drying oven and dried under vacuum at 60~70℃ and -0.08~-0.1MPa for 4~6h to remove ethanol, by-product alkyl alcohol and unreacted trace amounts of water, to obtain fluorinated modified nano silica with fluorinated hydrophobic groups grafted on the surface.

[0085] In a preferred embodiment of the present invention, the mass ratio of the organic intercalated modified nano-montmorillonite to the fluorine-modified nano-silica is 1.5~2.5:1, and the sum of their masses does not exceed 18 parts.

[0086] In this invention, the mass ratio of organic intercalated modified nano-montmorillonite and fluorine-modified nano-silica is 1.5~2.5:1, which allows for a precise match between the physical barrier properties of montmorillonite and the chemical hydrophobicity of fluorine-silica, avoiding either excessive or insufficient functionality of a single filler. The total mass of these fillers does not exceed 18 parts, which avoids excessive filler damaging the crosslinking network, toughness, and workability of the adhesive layer, ensuring that the protective effect does not conflict with other properties.

[0087] When the mass ratio is <1.5:1, the amount of organically intercalated modified montmorillonite is insufficient, resulting in a weak lamellar network structure effect. When the mass ratio is >2.5:1, the amount of fluorine-modified nano-silica is insufficient, the hydrophobic layer is not fully covered, and the amount of water entering the adhesive layer increases. At the same time, excessive montmorillonite leads to decreased dispersibility and toughness.

[0088] The preferred mass ratio of the organically intercalated modified nano-montmorillonite to the fluorine-modified nano-silica is 2:1.

[0089] According to a second aspect of the present invention, the present invention provides a method for preparing the epoxy structural adhesive as described above, the method comprising:

[0090] S1 is added to bisphenol A type epoxy resin, core-shell modified epoxy resin and polyurethane modified epoxy resin, and stirred at 80~90℃ and 800~1000r / min for 30~40min to obtain epoxy matrix mixture.

[0091] S2 lowers the temperature to below 60℃, adds fluorine-modified nano-silica, organic intercalated modified nano-montmorillonite and silane coupling agent, and stirs at 800~1200r / min for 1~2h to obtain filler-matrix mixture;

[0092] S3 lowers the temperature to below 40℃, adds curing agent, curing accelerator and antioxidant, stirs at 300~500r / min for 20~30min, and vacuum degasses for 10~15min to obtain the high temperature and humid heat resistant epoxy structural adhesive.

[0093] In this invention, step S1 first involves mixing the epoxy resin matrix. The bisphenol A type epoxy resin, core-shell modified epoxy resin, and polyurethane modified epoxy resin are in the optimal flow range at 80~90℃. The mixture is stirred thoroughly at 800~1000r / min to form a homogeneous matrix, which provides a good carrier for the subsequent dispersion of fillers and avoids local enrichment of fillers due to uneven matrix.

[0094] In step S2, the epoxy resin matrix and filler are mixed. Cooling to below 60°C prevents premature hydrolysis and failure of the silane coupling agent due to high temperatures, and also moderately increases the matrix viscosity, enhancing the shear force's effect on dispersing the nanofiller agglomerates, while preventing the thermal decomposition of the hydrophobic groups on the surface of the fluorinated modified nano-silica. High-speed stirring at 800~1200 r / min disperses the loose agglomerates of the fluorinated modified nano-silica and the lamellar stacks of montmorillonite, ensuring the filler is uniformly dispersed in the epoxy matrix.

[0095] In step S3, the curing agent, curing accelerator and antioxidant are added last, and the mixture is stirred at a low speed of 300~500 r / min. This can prevent the curing agent from agglomerating locally due to high-speed stirring, which could lead to uneven cross-linking reaction and increased stress in the adhesive layer. It can also prevent the destruction of the filler-matrix stable system formed in step S2.

[0096] The present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other.

[0097] In the following embodiments, unless otherwise specified, all raw material components are commercially available products.

[0098] Example 1

[0099] A high-temperature and humid heat resistant epoxy structural adhesive, with the following raw material composition by weight:

[0100] Bisphenol A type epoxy resin: E-44, 30 parts;

[0101] Core-shell modified epoxy resin: Kanekachi Chemical MX153, 18 parts;

[0102] Polyurethane modified epoxy resin: complexed high-tech EPU301, 12 parts;

[0103] Fluorine-modified nano-silica: 4 parts, wherein the modifier is tridecafluorooctyltriethoxysilane, the nano-silica uses Cabot TS-720, and the amount of tridecafluorooctyltriethoxysilane is 13% of the mass of the nano-silica;

[0104] Organic intercalation modified nano-montmorillonite: Zhejiang Fenghong NANOLC-NP301, 8 parts;

[0105] Curing agent: Dicyandiamide, 10 parts;

[0106] Curing accelerator: UR700, 1.5 parts;

[0107] Silane coupling agent: KH560, 2 parts;

[0108] Antioxidant: 1010, 0.8 parts.

[0109] Preparation method of fluorine-modified nano-silica:

[0110] (1) Raw material pretreatment: Nano silica was vacuum dried at 105℃ for 2h to remove surface adsorbed water and activate surface hydroxyl groups;

[0111] (2) Silane hydrolysis: Take tridecafluorooctyltriethoxysilane, add it to anhydrous ethanol to prepare a silane solution with a mass concentration of 12%, and stir at room temperature for 40 min to complete the hydrolysis;

[0112] (3) Grafting reaction: The dried nano-silica was added to a high-speed stirred reactor, heated to 70°C, and stirred at 800 r / min for 30 min to disperse the original aggregates and further activate the surface hydroxyl groups; then the hydrolyzed silane solution was slowly added dropwise at a rate of 5 mL / min. After the addition was completed, the reaction was stirred at 70°C for 2.5 h to allow the surface hydroxyl groups of nano-silica to fully condense with the silanol groups generated by the hydrolysis of silane.

[0113] (4) Post-processing: The reaction product was transferred to a vacuum drying oven and dried under vacuum at 65℃ and -0.09MPa for 5h to remove ethanol and unreacted trace amounts of water, and fluorine-modified nano silica was obtained.

[0114] Preparation process of epoxy structural adhesives:

[0115] S1: Add bisphenol A type epoxy resin, core-shell modified epoxy resin, and polyurethane modified epoxy resin into a stirred tank and stir at 85℃ and 900r / min for 35min to form a homogeneous epoxy matrix mixture.

[0116] S2: Cool to 55℃, add fluorine-modified nano-silica, organic intercalated modified nano-montmorillonite, and silane coupling agent, stir at 1000r / min for 1.5h to achieve uniform dispersion and interfacial bonding of the filler;

[0117] S3: Cool to 35℃, add curing agent, curing accelerator and antioxidant, stir at 400r / min for 25min, then degas under vacuum at -0.09MPa for 12min to obtain the high temperature and humid heat resistant epoxy structural adhesive.

[0118] Example 2

[0119] A high-temperature and humid heat resistant epoxy structural adhesive, with the following raw material composition by weight:

[0120] Bisphenol A type epoxy resin: E-44, 28 parts;

[0121] Core-shell modified epoxy resin: Kanekachi Chemical MX153, 20 parts;

[0122] Polyurethane modified epoxy resin: complexed high-tech EPU301, 15 parts;

[0123] Fluorine-modified nano-silica: 6.4 parts, wherein the modifier and nano-silica are the same as in Example 1;

[0124] Organic intercalation modified nano-montmorillonite: Zhejiang Fenghong NANOLC-NP301, 9.6 parts;

[0125] Curing agent: Dicyandiamide, 11 parts;

[0126] Curing accelerator: UR700, 2 parts;

[0127] Silane coupling agent: KH560, 1.5 parts;

[0128] Antioxidant: 1010, 0.7 parts.

[0129] The preparation method of fluorine-modified nano-silica is the same as that in Example 1.

[0130] The preparation process of the epoxy structural adhesive is the same as that in Example 1.

[0131] Example 3

[0132] A high-temperature and humid heat resistant epoxy structural adhesive, with the following raw material composition by weight:

[0133] Bisphenol A type epoxy resin: E-44, 32 parts;

[0134] Core-shell modified epoxy resin: Kanekachi Chemical MX153, 15 parts;

[0135] Polyurethane modified epoxy resin: complexed high-tech EPU301, 10 parts;

[0136] Fluorine-modified nano-silica: 4 parts, wherein the modifier and nano-silica are the same as in Example 1;

[0137] Organic intercalation modified nano-montmorillonite: Zhejiang Fenghong NANOLC-NP301, 10 parts;

[0138] Curing agent: Dicyandiamide, 9 parts;

[0139] Curing accelerator: UR700, 1.2 parts;

[0140] Silane coupling agent: KH580, 2.5 parts;

[0141] Antioxidant: 1010, 0.9 parts.

[0142] The preparation method of fluorine-modified nano-silica is the same as that in Example 1.

[0143] The preparation process of the epoxy structural adhesive is the same as that in Example 1.

[0144] Example 4

[0145] A high-temperature and humid heat resistant epoxy structural adhesive, with the following raw material composition by weight:

[0146] Bisphenol A type epoxy resin: E-44, 30 parts;

[0147] Core-shell modified epoxy resin: Kanekachi Chemical MX153, 18 parts;

[0148] Polyurethane modified epoxy resin: complexed high-tech EPU301, 12 parts;

[0149] Fluorine-modified nano-silica: 3 parts, wherein the modifier and nano-silica are the same as in Example 1;

[0150] Organic intercalation modified nano-montmorillonite: Zhejiang Fenghong NANOLC-NP301, 10 parts;

[0151] Curing agent: Dicyandiamide, 10 parts;

[0152] Curing accelerator: UR700, 1.5 parts;

[0153] Silane coupling agent: KH560, 2 parts;

[0154] Antioxidant: 1010, 0.8 parts.

[0155] The preparation method of fluorine-modified nano-silica is the same as that in Example 1.

[0156] The preparation process of the epoxy structural adhesive is the same as that in Example 1.

[0157] Example 5

[0158] A high-temperature and humid heat resistant epoxy structural adhesive, with the following raw material composition by weight:

[0159] Bisphenol A type epoxy resin: E-44, 30 parts;

[0160] Core-shell modified epoxy resin: Kanekachi Chemical MX153, 18 parts;

[0161] Polyurethane modified epoxy resin: complexed high-tech EPU301, 12 parts;

[0162] Fluorine-modified nano-silica: 4 parts, wherein the modifier is tridecafluorooctyltriethoxysilane, the nano-silica uses Cabot TS-720, and the amount of tridecafluorooctyltriethoxysilane is 10% of the mass of the nano-silica;

[0163] Organic intercalation modified nano-montmorillonite: Zhejiang Fenghong NANOLC-NP301, 8 parts;

[0164] Curing agent: Dicyandiamide, 10 parts;

[0165] Curing accelerator: UR700, 1.5 parts;

[0166] Silane coupling agent: KH560, 2 parts;

[0167] Antioxidant: 1010, 0.8 parts.

[0168] The preparation method of fluorine-modified nano-silica is the same as that in Example 1.

[0169] The preparation process of the epoxy structural adhesive is the same as that in Example 1.

[0170] Example 6

[0171] A high-temperature and humid heat resistant epoxy structural adhesive, with the following raw material composition by weight:

[0172] Bisphenol A type epoxy resin: E-44, 30 parts;

[0173] Core-shell modified epoxy resin: Kanekachi Chemical MX153, 18 parts;

[0174] Polyurethane modified epoxy resin: complexed high-tech EPU301, 12 parts;

[0175] Fluorine-modified nano-silica: 4 parts, wherein the modifier is tridecafluorooctyltriethoxysilane, the nano-silica uses Cabot TS-720, and the amount of tridecafluorooctyltriethoxysilane is 8% of the mass of the nano-silica;

[0176] Organic intercalation modified nano-montmorillonite: Zhejiang Fenghong NANOLC-NP301, 8 parts;

[0177] Curing agent: Dicyandiamide, 10 parts;

[0178] Curing accelerator: UR700, 1.5 parts;

[0179] Silane coupling agent: KH560, 2 parts;

[0180] Antioxidant: 1010, 0.8 parts.

[0181] The preparation method of fluorine-modified nano-silica is the same as that in Example 1.

[0182] The preparation process of the epoxy structural adhesive is the same as that in Example 1.

[0183] Comparative Example 1

[0184] Unmodified nano-silica Cabot TS-720 was used instead of fluorine-modified nano-silica, and everything else was the same as in Example 1.

[0185] The preparation process of the epoxy structural adhesive is the same as that in Example 1.

[0186] Comparative Example 2

[0187] Organically intercalated modified nano-montmorillonite was not used in the raw materials. 12 parts of fluorine-modified nano-silica were used. The rest was the same as in Example 1.

[0188] The preparation method of fluorine-modified nano-silica is the same as that in Example 1.

[0189] The preparation process of the epoxy structural adhesive is the same as that in Example 1.

[0190] Performance testing

[0191] 1. Shear strength

[0192] Test standard: Refer to GB / T 7124-2008 "Determination of tensile shear strength of adhesives (rigid material to rigid material)"

[0193] The sample was a steel plate, measuring 100mm × 25mm × 2mm, after grinding and rust removal. The bonding area was 25mm × 12.5mm × 0.2mm. It was cured at 170℃ for 20 minutes and then placed in a humid heat aging chamber at 85℃ and 85% RH for 1000 hours. Before and after aging, the shear strength at room temperature was tested using a universal testing machine at a tensile rate of 10mm / min, and the strength retention rate was calculated.

[0194] 2. Impact strength test

[0195] Test standard: Refer to GB / T 36877-2018 "Determination of Impact Peel Strength of Structural Adhesives - Wedge Method"

[0196] Wedge-shaped impact specimens were prepared with steel plates measuring 90mm × 20mm × 1.6mm and adhesive layer thickness of 0.2mm. The specimens were cured at 170℃ for 20min and the impact strength at room temperature was tested using a drop hammer impact tester. Five specimens were tested in each group, and the average value was taken.

[0197] 3. Tensile strength and elastic modulus test

[0198] Test standard: Refer to GB / T 2567-2021 "Test Methods for Properties of Resin Castings"

[0199] Prepare dumbbell-shaped specimens according to the requirements of the tensile test in the standard, cure at 170℃ for 20 min, and use a universal testing machine to stretch them at a rate of 2 mm / min. Record the tensile strength and elastic modulus. Test 5 specimens in each group and take the average value.

[0200] 4. Interface peel strength test

[0201] Test standard: Refer to GB / T 2791-1995 "Adhesives - T-Pipe Strength Test Method - Flexible Materials to Flexible Materials"

[0202] Prepare steel-to-steel bonding samples with an adhesive layer thickness of 0.2 mm, steel sheet dimensions of 200 mm × 25 mm × 0.8 mm, and bonding area of ​​150 mm × 25 mm. Cure at 170 °C for 20 min. Perform a 180° peel test using a universal testing machine at a rate of 100 mm / min and record the peel strength (N / mm).

[0203] The performance test results of Examples 1-6 and Comparative Examples 1-2 are shown in Table 1.

[0204] Table 1 Performance Test Results

[0205]

[0206] As shown in Table 1, the epoxy structural adhesives obtained in Examples 1-6 all exhibited a strength retention rate of ≥81.3% after aging for 1000 hours at 85℃ and 85% RH, significantly exceeding that of the comparative examples. This indicates that the epoxy structural adhesives described in this invention can effectively block moisture penetration. The room temperature shear strength of the examples is ≥30.6 MPa, and the tensile strength is ≥30.3 MPa, meeting the load-bearing requirements of the structural adhesives. The impact strength is stable at 54.3~60.2 N / mm, indicating a good toughening effect of the technical solution described in this invention. The peel strength of the examples is ≥10.5 N / mm, higher than that of the comparative examples (9.1~9.3 N / mm), indicating that the silane coupling agent and the protective system work synergistically to improve interfacial stability.

[0207] The applicant declares that the present invention is illustrated by the above embodiments, but the present invention is not limited to the above process steps, nor does it mean that the present invention must rely on the above process steps for implementation. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, additions of auxiliary components, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A high-temperature and humid heat resistant epoxy structural adhesive, characterized in that, The epoxy structural adhesive comprises the following raw materials in parts by weight: The composition includes 25-35 parts of bisphenol A type epoxy resin, 15-20 parts of core-shell modified epoxy resin, 10-15 parts of polyurethane modified epoxy resin, 3-8 parts of fluorine-containing modified nano-silica, 5-10 parts of organic intercalated modified nano-montmorillonite, 8-12 parts of curing agent, 1-3 parts of curing accelerator, 1-3 parts of silane coupling agent, and 0.5-1 parts of antioxidant. The fluorine-modified nano-silica is obtained by modifying nano-silica with perfluoroalkyltrialkoxysilane as a modifier, wherein the carbon chain length of the perfluoroalkyl group is 6-10, and the alkoxy group is methoxy or ethoxy. The organic intercalation modified nano-montmorillonite is a long-chain alkyl quaternary ammonium salt or a long-chain alkylamine salt modified montmorillonite, wherein the carbon chain length of the alkyl group is 12~20. The mass ratio of the organic intercalated modified nano-montmorillonite to the fluorine-modified nano-silica is 1.5~2.5:1, and the sum of their masses does not exceed 18 parts.

2. The epoxy structural adhesive as described in claim 1, characterized in that, The modifier includes one or more of tridecylfluorooctyltriethoxysilane, perfluorodecyltriethoxysilane, perfluorooctyltrimethoxysilane, or perfluorohexyltriethoxysilane.

3. The epoxy structural adhesive as described in claim 1, characterized in that, The nano-silica includes fumed nano-silica with a particle size of 5-20 nm.

4. The epoxy structural adhesive as described in claim 1, characterized in that, The amount of the modifier used is 10-15% of the mass of nano-silica.

5. The epoxy structural adhesive as described in claim 1, characterized in that, The preparation method of the fluorine-modified nano-silica includes: (1) Add the modifier to anhydrous ethanol to obtain a silane solution with a mass concentration of 10~15%, and continue stirring for 30~50 min to complete the hydrolysis; (2) Add the dried nano-silica to a high-speed stirred reactor, heat it to 60~80℃, and stir and disperse it at 800~1000r / min for 25~35min; then slowly add the hydrolyzed silane solution, and after the addition is complete, keep the temperature at 60~80℃ and continue stirring for 2~3h. (3) The fluorine-modified nano-silica is obtained by vacuum drying at 60~70℃ for 4~6h.

6. The epoxy structural adhesive as described in claim 1, characterized in that, The nano-silica includes Cabot TS-720; The organic intercalated modified nano-montmorillonite includes Zhejiang Fenghong NANOLC-NP301.

7. The epoxy structural adhesive as described in claim 1, characterized in that, The bisphenol A type epoxy resin includes E-44 and / or E-51; the core-shell modified epoxy resin includes MX153 and / or MX154 from Kaneka Chemicals, Japan; and the polyurethane modified epoxy resin includes EPU301 from Complex High-Tech.

8. The epoxy structural adhesive according to any one of claims 1 to 7, characterized in that, The curing agent includes one or more of dicyandiamide, sebacic dihydrazide or adipic dihydrazide; The curing accelerator is an organic urea accelerator; The silane coupling agent includes KH560 and / or KH580.

9. A method for preparing an epoxy structural adhesive as described in any one of claims 1 to 8, characterized in that, The preparation method includes: Bisphenol A type epoxy resin, core-shell modified epoxy resin, and polyurethane modified epoxy resin are put into a stirring device and stirred for 30 to 40 minutes at 80~90℃ and 800~1000r / min to obtain an epoxy matrix mixture. The temperature was lowered to below 60℃, and fluorine-modified nano-silica, organic intercalated modified nano-montmorillonite, and silane coupling agent were added. The mixture was stirred at 800~1200r / min for 1~2h to obtain a filler-matrix mixture. Lower the temperature to below 40℃, add curing agent, curing accelerator and antioxidant, stir at 300~500r / min for 20~30min, and vacuum degas for 10~15min to obtain the high temperature and humid heat resistant epoxy structural adhesive.

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