Structural adhesive and method for producing same

Abstract

This application discloses a structural adhesive and its preparation method, belonging to the field of battery technology. The structural adhesive includes phase change microcapsules and flame-retardant microcapsules. The phase change core material of the phase change microcapsules undergoes a solid-liquid phase change when the battery temperature reaches its phase change point, absorbing a large amount of heat and providing instantaneous "peak shaving and valley filling" capabilities that surpass traditional thermal conductive materials. This effectively copes with the battery's peak heat load and effectively reduces the temperature of local hot spots. When the temperature further increases, the flame-retardant microcapsules rupture, precisely and rapidly releasing a high concentration of flame-retardant core material, i.e., flame retardant, to the heat source point. This achieves on-demand release of the flame retardant, preventing premature failure of the flame retardant under normal operating conditions, thereby greatly improving flame-retardant efficiency and ultimately enhancing the safety of the entire vehicle.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a structural adhesive and its preparation method. Background Technology

[0002] In advanced battery packaging technologies such as CTP (Cell to Pack) and CTC (Cell to Chassis), structural adhesives are key materials that provide structural bonding, fixation, and thermal management between the cell and the casing, and between the cell and the cooling plate.

[0003] In related technologies, structural adhesives generally use polyurethane, epoxy resin, etc. as the matrix, and by adding functional fillers, the thermal conductivity is increased, while good flame retardancy is obtained.

[0004] However, the structural adhesives used in these technologies have a constant thermal conductivity. When the battery is under conditions such as fast charging or high-rate discharging, generating a large amount of instantaneous heat, they cannot dynamically enhance heat dissipation, easily causing heat accumulation and leading to thermal runaway. Furthermore, flame retardants may slowly decompose or migrate under the long-term operating environment of the battery. As a result, when they are needed to play a role in extreme situations such as thermal abuse, their flame retardant efficiency has been greatly reduced, ultimately causing the battery to catch fire or explode, seriously threatening the safety of the entire vehicle. Summary of the Invention

[0005] This application provides a structural adhesive and its preparation method, which can effectively reduce local hot spot temperature, improve flame retardant efficiency, and thus improve the safety of the entire vehicle. The technical solution is as follows: On the one hand, a structural adhesive is provided, the structural adhesive comprising component A and component B; Component A comprises the following components in parts by weight: The composition includes 60 to 100 parts by weight of polyurethane prepolymer, 30 to 60 parts by weight of thermally conductive filler, 10 to 20 parts by weight of phase change microcapsules and flame retardant microcapsules, and 0.3 to 0.8 parts by weight of additives. The mass ratio of the phase change microcapsules to the flame retardant microcapsules is 1:2 to 2:1. The phase change microcapsule comprises: a phase change core material and a phase change shell, wherein the phase change core material is selected from at least one of n-eicosane, n-docosahexanes, and n-tetracosane, and the phase change shell is urea-formaldehyde resin; The flame-retardant microcapsule comprises: a flame-retardant core material and a flame-retardant shell, wherein the flame-retardant core material is selected from ammonium polyphosphate and pentaerythritol, and the flame-retardant shell is an ethylene-vinyl acetate copolymer; Component B is a curing agent.

[0006] In one possible implementation, the phase change core material is 30 to 50 parts by weight. Optionally, the urea-formaldehyde resin is obtained by reacting urea with formaldehyde solution, wherein the urea is present in the form of 10 to 15 parts by weight, the formaldehyde solution has a concentration of 37%, and the formaldehyde solution is present in the form of 20 to 30 parts by weight. Optionally, the phase change microcapsules have an average particle size of 5 μm to 25 μm.

[0007] In another possible implementation, the flame-retardant core material is 20 to 40 parts by weight. Optionally, the flame-retardant shell is 20% to 40% of the flame-retardant core material by weight. Optionally, the mass ratio of the ammonium polyphosphate to the pentaerythritol is 2.5:1 to 3.5:1.

[0008] In another possible implementation, the polyurethane prepolymer is obtained by reacting a polyol with an isocyanate; The polyol is selected from castor oil-modified polyester polyol and phosphorus-containing flame-retardant polyether polyol, and the isocyanate is selected from diphenylmethane diisocyanate or its modified form. Optionally, the castor oil modified polyester polyol is 40 to 80 parts by weight, the phosphorus-containing flame-retardant polyether polyol is 20 to 40 parts by weight, and the isocyanate is 20 to 60 parts by weight. Optionally, the isocyanate content in the isocyanate is 28% to 32%; Optionally, the molar ratio of isocyanate groups to hydroxyl groups in the polyurethane prepolymer is 1.5 to 2.5.

[0009] In another possible implementation, the hydroxyl value of the castor oil-modified polyester polyol is 100 mg KOH / g to 300 mg KOH / g; The phosphorus-containing flame-retardant polyether polyol has a phosphorus content of 5% to 10% and a hydroxyl value of 50 mg KOH / g to 100 mg KOH / g.

[0010] In another possible implementation, the thermally conductive filler is selected from boron nitride nanosheets and spherical alumina; The mass ratio of the boron nitride nanosheets to the spherical alumina is 1:2 to 2:1; Optionally, the boron nitride nanosheets have a diameter of 1 μm to 5 μm and a thickness of 3 nm to 10 nm, and the spherical alumina particles have a diameter of 1 μm to 5 μm.

[0011] In another possible implementation, the thermally conductive filler, the phase change microcapsule, and the flame-retardant microcapsule are all surface-modified with a silane coupling agent. Optionally, component B is selected from at least one of diols, diamines, and triols; Optionally, the molar ratio of the active hydrogen functional group in component B to the isocyanate group in the polyurethane prepolymer is 0.8:1 to 1.1:1.

[0012] On the other hand, a method for preparing a structural adhesive is provided, wherein the structural adhesive is as described in any of the above claims, and the preparation method includes: Phase change microcapsules, flame retardant microcapsules, and polyurethane prepolymers were prepared separately. The thermally conductive filler, the phase change microcapsule, and the flame-retardant microcapsule are surface modified using a silane coupling agent. The polyurethane prepolymer, additives, surface-modified thermally conductive fillers, phase change microcapsules, and flame-retardant microcapsules are mixed uniformly under vacuum conditions to obtain component A. The structural adhesive is obtained by mixing component A and component B thoroughly and then curing them through a stepped curing process.

[0013] In one possible implementation, the process of preparing the phase change microcapsules includes: The phase change core material and the emulsifier are emulsified in water to form an emulsion; Urea and formaldehyde solution are added to the emulsion. After the urea and formaldehyde solution react, a urea-formaldehyde resin phase change shell is formed on the surface of the phase change core material. After post-processing, the phase change microcapsules are obtained.

[0014] In another possible implementation, the process of preparing the flame-retardant microcapsules includes: The ethylene-vinyl acetate copolymer, ammonium polyphosphate, pentaerythritol and solvent were mixed to obtain the oil phase; The dispersant is dissolved in water to obtain an aqueous phase; The oil phase is poured into the aqueous phase to form an oil-in-water emulsion; The solvent in the oil-in-water emulsion is evaporated, and the resulting product is post-processed to obtain the flame-retardant microcapsules.

[0015] This application provides a structural adhesive comprising phase change microcapsules and flame-retardant microcapsules. The phase change core material of the phase change microcapsules undergoes a solid-liquid phase change when the battery temperature reaches its phase change point, absorbing a large amount of heat and providing instantaneous "peak shaving and valley filling" capabilities that surpass traditional thermal conductive materials. This effectively addresses the battery's peak heat load and significantly reduces local hot spot temperatures. When the temperature rises further, the flame-retardant microcapsules rupture, precisely and rapidly releasing a high concentration of flame-retardant core material, i.e., flame retardant, to the heat source. This achieves on-demand release of the flame retardant, preventing premature failure under normal operating conditions and greatly improving flame-retardant efficiency, thereby enhancing the overall vehicle safety. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of a structural adhesive smart response mechanism provided in an embodiment of this application. Detailed Implementation

[0017] To make the technical solution and advantages of this application clearer, the embodiments of this application will be described in further detail below.

[0018] On the one hand, embodiments of this application provide a structural adhesive, which includes component A and component B; Component A comprises the following components in parts by weight: The composition includes 60 to 100 parts by weight of polyurethane prepolymer, 30 to 60 parts by weight of thermally conductive filler, 10 to 20 parts by weight of phase change microcapsules and flame retardant microcapsules, and 0.3 to 0.8 parts by weight of additives. The mass ratio of phase change microcapsules to flame retardant microcapsules is 1:2 to 2:1. Phase change microcapsules include: a phase change core material and a phase change shell, wherein the phase change core material is selected from at least one of n-eicosane, n-docosahexanes, and n-tetracosane, and the phase change shell is urea-formaldehyde resin; The flame-retardant microcapsule comprises a flame-retardant core material and a flame-retardant shell. The flame-retardant core material is selected from ammonium polyphosphate and pentaerythritol, and the flame-retardant shell is ethylene-vinyl acetate copolymer (EVA). Component B is the curing agent.

[0019] The vinyl acetate (VA) content in the ethylene-vinyl acetate copolymer is 28%.

[0020] This application provides a structural adhesive comprising phase change microcapsules and flame-retardant microcapsules. The phase change core material of the phase change microcapsules undergoes a solid-liquid phase change when the battery temperature reaches its phase change point, absorbing a large amount of heat and providing instantaneous "peak shaving and valley filling" capabilities that surpass traditional thermal conductive materials. This effectively addresses the battery's peak heat load and significantly reduces local hot spot temperatures. When the temperature rises further, the flame-retardant microcapsules rupture, precisely and rapidly releasing a high concentration of flame-retardant core material, i.e., flame retardant, to the heat source. This achieves on-demand release of the flame retardant, preventing premature failure under normal operating conditions and greatly improving flame-retardant efficiency, thereby enhancing the overall vehicle safety.

[0021] For example, the weight percentages of the polyurethane prepolymer can be 60 parts by weight, 65 parts by weight, 70 parts by weight, 75 parts by weight, 80 parts by weight, 85 parts by weight, 90 parts by weight, 95 parts by weight, 100 parts by weight, etc. The weight percentages of the thermally conductive filler can be 30 parts by weight, 35 parts by weight, 40 parts by weight, 45 parts by weight, 50 parts by weight, 55 parts by weight, 60 parts by weight, etc. The total weight percentages of the phase change microcapsules and flame-retardant microcapsules can be 10 parts by weight, 11 parts by weight, 12 parts by weight, 13 parts by weight, 14 parts by weight, 15 parts by weight, 16 parts by weight, 17 parts by weight, 18 parts by weight, 19 parts by weight, 20 parts by weight, etc. The weight percentages of the additives can be 0.3 parts by weight, 0.4 parts by weight, 0.5 parts by weight, 0.6 parts by weight, 0.7 parts by weight, 0.8 parts by weight, etc. The mass ratio of phase change microcapsules to flame retardant microcapsules can be 1:2, 1:1.9, 1:1.8, 1:1.7, 1:1.6, 1:1.5, 1:1.4, 1:1.3, 1:1.2, 1:1.1, 1:1, 1.1:1, 1.2:1, 1.5:1, 1.8:1, 2:1, etc.

[0022] It's important to note that, based on the mass ratio of phase change microcapsules to flame-retardant microcapsules, the mass of the phase change microcapsules can be greater than, less than, or equal to that of the flame-retardant microcapsules. When the mass of the phase change microcapsules is greater than that of the flame-retardant microcapsules, the phase change microcapsules can better absorb the latent heat of phase change and better suppress temperature peaks. When the mass of the flame-retardant microcapsules is greater than that of the phase change microcapsules, the flame-retardant efficiency can be improved. In practical applications, the masses of both can be adjusted according to actual needs to better achieve thermal-safety synergy.

[0023] In one possible implementation, the phase change core material is 30 to 50 parts by weight. Optionally, urea-formaldehyde resin is obtained by reacting urea with formaldehyde solution, wherein the weight of urea is 10 to 15 parts by weight, the concentration of formaldehyde solution is 37%, and the weight of formaldehyde solution is 20 to 30 parts by weight. Optionally, the phase change microcapsules have an average particle size of 5 μm to 25 μm.

[0024] For example, the weight percentages of the phase change core material can be 30 parts by weight, 32 parts by weight, 35 parts by weight, 38 parts by weight, 40 parts by weight, 42 parts by weight, 45 parts by weight, 48 parts by weight, 50 parts by weight, etc. The weight percentages of urea can be 10 parts by weight, 11 parts by weight, 12 parts by weight, 13 parts by weight, 14 parts by weight, 15 parts by weight, etc. The weight percentages of formaldehyde solution can be 20 parts by weight, 21 parts by weight, 22 parts by weight, 23 parts by weight, 24 parts by weight, 25 parts by weight, 26 parts by weight, 27 parts by weight, 28 parts by weight, 29 parts by weight, 30 parts by weight, etc. The average particle size of the phase change microcapsules can be 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 22 μm, 25 μm, etc.

[0025] In this embodiment, urea-formaldehyde resin, which forms a rigid network structure through the reaction of urea and formaldehyde, is used as the phase change shell of the phase change microcapsules. This method offers the advantages of a uniform and dense shell layer, effectively preventing leakage of the phase change core material. Furthermore, urea-formaldehyde resin possesses a certain heat resistance temperature. When the phase change core material undergoes a solid-liquid phase change (phase change temperature 40℃~50℃), the urea-formaldehyde resin remains intact. This means that the phase change of the core material occurs while the phase change shell remains intact, thus meeting the battery thermal management requirements. Additionally, the average particle size of the phase change microcapsules is controlled between 5μm and 25μm, ensuring uniform dispersion in the polyurethane prepolymer, good interfacial bonding, and rapid thermal response, thus meeting the requirements for power battery applications.

[0026] In one possible implementation, the flame-retardant core material is 20 to 40 parts by weight. Optionally, the flame-retardant shell may comprise 20% to 40% of the flame-retardant core material by weight. Optionally, the mass ratio of ammonium polyphosphate (APP) to pentaerythritol (PER) is 2.5:1 to 3.5:1.

[0027] Among them, the average particle size of ammonium polyphosphate is <10μm.

[0028] For example, the weight percentage of the flame-retardant core material can be 20 parts by weight, 22 parts by weight, 25 parts by weight, 28 parts by weight, 30 parts by weight, 32 parts by weight, 35 parts by weight, 38 parts by weight, 40 parts by weight, etc. The weight percentage of the flame-retardant shell can be 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40% of the flame-retardant core material, etc. The mass ratio of ammonium polyphosphate to pentaerythritol can be 2.5:1, 2.6:1, 2.7:1, 2.8:1, 2.9:1, 3:1, 3.1:1, 3.2:1, 3.3:1, 3.4:1, 3.5:1, etc.

[0029] In this embodiment, the flame-retardant core material is released when the flame-retardant microcapsules rupture. Ammonium polyphosphate decomposes at high temperature to generate polyphosphoric acid and ammonia, while pentaerythritol serves as a carbon source, providing a char skeleton. The two work synergistically to rapidly form a dense, expanded, and continuous expanded char layer, isolating oxygen and heat, resulting in high flame-retardant efficiency. Using the amount of flame-retardant core material within the aforementioned range ensures the release of a high concentration of effective flame-retardant components while avoiding brittleness and cracking of the colloid due to excessive use of the flame-retardant core material.

[0030] The amount of flame-retardant shell and flame-retardant core material used meets the above requirements, which can ensure that the flame-retardant shell uniformly and completely covers the flame-retardant core material, preventing the flame-retardant core material from migrating or decomposing prematurely, and can also ensure that the flame-retardant shell has a moderate thickness and is not easily broken.

[0031] When the mass ratio of ammonium polyphosphate to pentaerythritol is within the above range, the synergistic flame-retardant effect of the two can be optimized.

[0032] In one possible implementation, the polyurethane prepolymer is obtained by reacting a polyol with an isocyanate; The polyol is selected from castor oil-modified polyester polyol and phosphorus-containing flame-retardant polyether polyol, and the isocyanate is selected from diphenylmethane diisocyanate (MDI) or its modified form. Optionally, the castor oil-modified polyester polyol is in the amount of 40 to 80 parts by weight, the phosphorus-containing flame-retardant polyether polyol is in the amount of 20 to 40 parts by weight, and the isocyanate is in the amount of 20 to 60 parts by weight. Optionally, the isocyanate content in the isocyanate is 28% to 32%; Optionally, the molar ratio of isocyanate groups to hydroxyl groups in the polyurethane prepolymer is 1.5 to 2.5.

[0033] For example, the weight parts of castor oil-modified polyester polyol can be 40 parts by weight, 45 parts by weight, 50 parts by weight, 55 parts by weight, 60 parts by weight, 65 parts by weight, 70 parts by weight, 75 parts by weight, 80 parts by weight, etc. The weight parts of phosphorus-containing flame-retardant polyether polyol can be 20 parts by weight, 25 parts by weight, 30 parts by weight, 35 parts by weight, 40 parts by weight, etc. The weight parts of isocyanate can be 20 parts by weight, 25 parts by weight, 30 parts by weight, 35 parts by weight, 40 parts by weight, 45 parts by weight, 50 parts by weight, 55 parts by weight, 60 parts by weight, etc. The content of isocyanate groups in the isocyanate can be 28%, 29%, 30%, 31%, 32%, etc. The molar ratio of isocyanate groups to hydroxyl groups in the polyurethane prepolymer can be 1.5, 1.8, 2.0, 2.1, 2.2, 2.5, etc.

[0034] In this embodiment, the castor oil groups in the castor oil-modified polyester polyol provide excellent flexibility, while the polyester polyol provides high adhesive strength and high modulus, meeting the structural fixation requirements. The phosphorus-containing flame-retardant polyether polyol imparts intrinsic flame retardancy to the matrix at the molecular chain level. Combining these two components allows the polyurethane prepolymer to possess flexibility, adhesive strength, aging resistance, and intrinsic flame retardancy. Based on this, the polyol obtained by combining the castor oil-modified polyester polyol and the phosphorus-containing flame-retardant polyether polyol is reacted with isocyanate to form a prepolymer with active NCO end groups. This prepolymer can then rapidly react with component B to cure, forming a polyurethane elastomer with adjustable mechanical properties, high adhesive strength, and excellent flexibility.

[0035] By controlling the amount of polyol and isocyanate, sufficient hydroxyl sites and isocyanate groups can be provided to ensure sufficient curing and stable mechanical properties of the polyurethane prepolymer.

[0036] By controlling the content of isocyanate groups, a balance can be ensured in the prepolymer's reactivity, viscosity, and curing speed. This prevents insufficient curing due to excessively low NCO content, as well as excessively high content leading to brittleness and poor weather resistance.

[0037] By controlling the molar ratio of isocyanate groups to hydroxyl groups, the prepolymer can have suitable viscosity, good workability and sufficient reactivity. After curing, it forms a polyurethane matrix with a balance of strength and toughness, reliable adhesion and resistance to humid heat aging, which is suitable for the long-term reliable service requirements of power batteries.

[0038] In one possible implementation, the hydroxyl value of the castor oil-modified polyester polyol is 100 mg KOH / g to 300 mg KOH / g; The phosphorus content of phosphorus-containing flame-retardant polyether polyols is 5%~10%, and the hydroxyl value is 50mgKOH / g~100mgKOH / g.

[0039] For example, the hydroxyl value of castor oil-modified polyester polyols can be 100 mg KOH / g, 120 mg KOH / g, 150 mg KOH / g, 180 mg KOH / g, 200 mg KOH / g, 220 mg KOH / g, 250 mg KOH / g, 280 mg KOH / g, 300 mg KOH / g, etc. The phosphorus content of phosphorus-containing flame-retardant polyether polyols can be 5%, 6%, 7%, 8%, 9%, 10%, etc. The hydroxyl value of phosphorus-containing flame-retardant polyether polyols can be 50 mg KOH / g, 60 mg KOH / g, 70 mg KOH / g, 80 mg KOH / g, 90 mg KOH / g, 100 mg KOH / g, etc.

[0040] In the embodiments of this application, controlling the hydroxyl value of the castor oil-modified polyester polyol within the aforementioned range ensures moderate reactivity and reasonable crosslinking density, achieving a balance between strength and toughness. Controlling the phosphorus content and hydroxyl value of the phosphorus-containing flame-retardant polyether polyol within their respective ranges imparts efficient and durable halogen-free flame retardancy to the matrix without compromising mechanical properties, and fosters good compatibility with the castor oil-based polyol. Ultimately, this yields a strong, tough, flame-retardant, aging-resistant, and highly workable polyurethane prepolymer, meeting the long-term reliable service requirements of power batteries.

[0041] In one possible implementation, the thermally conductive filler is selected from boron nitride nanosheets and spherical alumina; The mass ratio of boron nitride nanosheets to spherical alumina is 1:2 to 2:1; Optionally, the boron nitride nanosheets have a diameter of 1μm to 5μm and a thickness of 3nm to 10nm, and the spherical alumina particles have a diameter of 1μm to 5μm.

[0042] For example, the mass ratio of boron nitride nanosheets to spherical alumina can be 1:2, 1:1.9, 1:1.8, 1:1.7, 1:1.6, 1:1.5, 1:1.4, 1:1.3, 1:1.2, 1:1.1, 1:1, 1.1:1, 1.2:1, 1.5:1, 1.8:1, 2:1, etc. The diameter of the boron nitride nanosheets can be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, etc. The thickness of the boron nitride nanosheets can be 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, etc. The particle size of the spherical alumina can be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, etc.

[0043] In the embodiments of this application, boron nitride nanosheets are in the form of sheets, and spherical alumina is in the form of spheres. The sheets and spheres complement each other to form a three-dimensional thermally conductive network, which greatly improves the overall thermal conductivity.

[0044] When the mass ratio of boron nitride nanosheets to spherical alumina is within the above range, an optimal balance can be achieved in terms of thermal conductivity, filling density, and system viscosity.

[0045] By controlling the diameter and thickness of boron nitride nanosheets and the particle size of spherical alumina within their respective ranges, the filler and microcapsule sizes can be matched, the dispersion can be uniform, and the interfacial thermal resistance can be low. At the same time, the mechanical properties of the colloidal material and the compatibility of the thin adhesive layer construction can be guaranteed, thus meeting the requirements of efficient thermal management of battery modules.

[0046] In one possible implementation, the thermally conductive filler, phase change microcapsules, and flame-retardant microcapsules are all surface-modified with a silane coupling agent. Optionally, component B is selected from at least one of diols, diamines, and triols; Optionally, the molar ratio of active hydrogen functional groups in component B to isocyanate groups in the polyurethane prepolymer is 0.8:1 to 1.1:1.

[0047] For example, the molar ratio of the active hydrogen functional group in component B to the isocyanate group in the polyurethane prepolymer can be 0.8:1, 0.85:1, 0.9:1, 0.95:1, 1:1, 1.05:1, 1.1:1, etc.

[0048] In this implementation, the amount of silane coupling agent used is 2% to 5% of the total amount of thermally conductive filler, phase change microcapsules, and flame retardant microcapsules.

[0049] For example, the amount of silane coupling agent can be 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, etc., of the total amount of thermally conductive filler, phase change microcapsule, and flame retardant microcapsule.

[0050] The type of silane coupling agent can be set and changed as needed, and there is no specific limitation. For example, the silane coupling agent can be selected from KH-550 and KH-560.

[0051] The diol may be selected from at least one of 1,4-butanediol, ethylene glycol, and diethylene glycol; the diamine may be selected from at least one of ethylenediamine, hexamethylenediamine, and isophoronediamine; and the triol may be selected from at least one of glycerol, trimethylolpropane, and triethanolamine.

[0052] In this implementation, the active hydrogen functional group in component B can be a hydroxyl group (-OH) in a diol or triol, or an amino group (-NH2) in a diamine, without specific limitations.

[0053] In this embodiment, surface modification of the thermally conductive filler, phase change microcapsules, and flame-retardant microcapsules using a silane coupling agent enhances their interfacial bonding with the polyurethane prepolymer. This not only reduces interfacial thermal resistance but, more importantly, prevents the microcapsules from becoming mechanical defect points. This allows the colloid to maintain high adhesive strength and high toughness while incorporating a large number of multifunctional fillers.

[0054] For component B, the diols, diamines, and triols all contain active hydrogen functional groups (-OH or -NH2), which can efficiently crosslink and cure with the NCO groups in component A, making the curing speed controllable and the reaction complete. Furthermore, the molar ratio of active hydrogen functional groups to isocyanate groups within the aforementioned range ensures sufficient active hydrogen in the system, allowing for complete NCO conversion and the formation of a continuous crosslinked network, thus preventing incomplete curing and insufficient strength of the colloid.

[0055] In one possible implementation, the additives include defoamers and leveling agents.

[0056] The total weight of the defoamer and leveling agent is 0.3 to 0.8 parts by weight. The amount of each can be set and changed according to actual needs, and no specific limit is set.

[0057] The type of defoamer can be set and changed as needed, and there is no specific limitation. For example, the defoamer can be selected from BYK-A530. The type of leveling agent can also be set and changed as needed, and there is no specific limitation. For example, the leveling agent can be selected from BYK-306.

[0058] On the other hand, embodiments of this application provide a method for preparing a structural adhesive, the method comprising: Step 1: Prepare phase change microcapsules, flame retardant microcapsules and polyurethane prepolymers respectively.

[0059] In the embodiments of this application, the preparation order of phase change microcapsules, flame-retardant microcapsules, and polyurethane prepolymer can be set and changed as needed, and no specific limitation is made thereto. For example, phase change microcapsules can be prepared first, followed by flame-retardant microcapsules, and then polyurethane prepolymer. Alternatively, flame-retardant microcapsules can be prepared first, followed by phase change microcapsules, and then polyurethane prepolymer. Or, polyurethane prepolymer can be prepared first, followed by phase change microcapsules, and then flame-retardant microcapsules.

[0060] The preparation process of phase change microcapsules is described below. This process can be achieved through the following steps (A-1) to (A-2): (A-1) The phase change core material and the emulsifier are emulsified in water to form an emulsion.

[0061] The phase change core material and emulsifier are added to a container containing deionized water and emulsified at high speed of 800 rpm to 1500 rpm for 20 min to 40 min in a water bath at 60℃ to 70℃ to form a stable emulsion.

[0062] The emulsifier is present in a weight ratio of 1% to 3% of the phase change core material. For example, the weight ratio of the emulsifier can be 1%, 1.5%, 2%, 2.5%, 3%, etc. of the phase change core material.

[0063] The type of emulsifier can be set and changed as needed, and there is no specific limitation on it. For example, the emulsifier can be styrene-maleic anhydride copolymer (SMA).

[0064] The weight percentage of deionized water can be 100 to 150 parts by weight. For example, the weight percentage of deionized water can be 100, 110, 120, 130, 140, 150 parts by weight, etc.

[0065] The water bath temperature can be 60℃, 62℃, 65℃, 68℃, 70℃, etc. The rotation speed can be 800rpm, 900rpm, 1000rpm, 1100rpm, 1200rpm, 1300rpm, 1400rpm, 1500rpm, etc. The emulsification time can be 20min, 25min, 30min, 35min, 40min, etc.

[0066] (A-2) Urea and formaldehyde solution are added to the emulsion. After the urea and formaldehyde solution react, a urea-formaldehyde resin phase change shell is formed on the surface of the phase change core material. After post-treatment, phase change microcapsules are obtained.

[0067] Step (A-2) can be achieved through the following steps (A-2-1) to (A-2-3), including: (A-2-1) Adjust the pH of the emulsion to meet the requirements, add urea, and then slowly add formaldehyde solution. React at 70℃~80℃ for 1h~2h to form urea-formaldehyde resin prepolymer.

[0068] The pH of the emulsion can be adjusted to 3.5-4.0 using triethanolamine, then urea can be added, followed by the slow addition of formaldehyde solution.

[0069] For example, the pH of the adjusted emulsion can be 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, etc. The reaction temperature can be 70℃, 72℃, 75℃, 78℃, 80℃, etc. The reaction time can be 1h, 1.2h, 1.5h, 1.8h, 2h, etc.

[0070] (A-2-2) Heat the reaction system to 80℃~85℃, adjust the pH of the system to 1.5~2.5, and continue the reaction for 2h~3h.

[0071] The pH of the system can be adjusted to 1.5-2.5 using a 10% ammonium chloride solution.

[0072] For example, the reaction system can be heated to 80℃, 81℃, 82℃, 83℃, 84℃, 85℃, etc. The pH of the system can be adjusted to 1.5, 1.8, 2, 2.2, 2.5, etc. The reaction time can be 2h, 2.2h, 25h, 2.8h, 3h, etc.

[0073] (A-2-3) After the reaction is completed, the mixture is cooled to room temperature, filtered, washed, dried and sieved to obtain phase change microcapsules.

[0074] After the reaction was completed, the mixture was naturally cooled to room temperature, filtered, washed three times each with deionized water and ethanol, dried in a vacuum drying oven at 50℃~60℃ for 12h~24h, and sieved (400 mesh~600 mesh) to obtain white powdery phase change microcapsules.

[0075] The phase change microcapsules were measured by a laser particle size analyzer, and their average particle size was between 5 μm and 25 μm.

[0076] For example, the temperature of the vacuum drying oven can be 50℃, 52℃, 55℃, 58℃, 60℃, etc. The drying time can be 12h, 15h, 18h, 20h, 22h, 24h, etc.

[0077] In this embodiment, phase change microcapsules are prepared by in-situ polymerization. When the battery temperature reaches its phase change temperature, the core material of the phase change microcapsule undergoes a solid-liquid phase change, absorbing a large amount of latent heat and effectively reducing the temperature of local hot spots. This can solve the problem that the thermal management method of structural adhesives in related technologies is passive and cannot intelligently respond to the instantaneous thermal shock of the battery.

[0078] The preparation process of flame-retardant microcapsules is described below. This process can be achieved through the following steps (B-1) to (B-4): (B-1) Ethylene-vinyl acetate copolymer, ammonium polyphosphate, pentaerythritol and solvent are mixed to obtain an oil phase.

[0079] In this step, the ethylene-vinyl acetate copolymer can be dissolved in a solvent and stirred until completely dissolved. Then, a mixture of ammonium polyphosphate and pentaerythritol can be added and stirred at a speed of 400 rpm to 600 rpm to disperse it evenly, thus obtaining the oil phase.

[0080] The solvent is an organic solvent, which can be dichloromethane or other solvents, without specific limitations.

[0081] The speed can be 400rpm, 420rpm, 450rpm, 480rpm, 500rpm, 520rpm, 550rpm, 580rpm, 600rpm, etc.

[0082] (B-2) Dissolve the dispersant in water to obtain an aqueous phase.

[0083] The dispersant is dissolved in deionized water to obtain an aqueous phase. The concentration of the dispersant is 0.5% to 1%, and the weight of the aqueous phase is 200 to 300 parts by weight.

[0084] For example, the weight parts of the aqueous phase can be 200 parts by weight, 220 parts by weight, 250 parts by weight, 280 parts by weight, 300 parts by weight, etc. The concentration of the dispersant can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, etc.

[0085] The dispersant can be polyvinyl alcohol (PVA) or other dispersants, without specific limitations.

[0086] (B-3) Pour the oil phase into the aqueous phase to form an oil-in-water emulsion.

[0087] Slowly pour the oil phase into the aqueous phase and emulsify at high speed (1000 rpm to 2000 rpm) for 30 to 60 minutes at 25°C to 35°C to form a stable oil-in-water emulsion.

[0088] For example, the emulsification temperature can be 25℃, 28℃, 30℃, 32℃, 35℃, etc. The rotation speed can be 1000rpm, 1100rpm, 1200rpm, 1300rpm, 1400rpm, 1500rpm, 1600rpm, 1700rpm, 1800rpm, 1900rpm, 2000rpm, etc. The emulsification time can be 30min, 35min, 40min, 45min, 50min, 55min, 60min, etc.

[0089] (B-4) Evaporate the solvent in the oil-in-water emulsion, and after post-processing, obtain flame-retardant microcapsules.

[0090] The oil-in-water emulsion was transferred to a reaction vessel and slowly evaporated for 4-6 hours at 40-50°C and 300-500 rpm to remove the solvent. The mixture was then filtered, washed three times with deionized water, and dried in a vacuum drying oven at 50-60°C for 10-14 hours to obtain white powdery flame-retardant microcapsules. DSC (Differential Scanning Calorimetry) testing showed that the shell rupture temperature was adjustable within the range of 100-130°C.

[0091] For example, the solvent evaporation temperature can be 40℃, 42℃, 45℃, 48℃, 50℃, etc. The rotation speed can be 300rpm, 320rpm, 350rpm, 380rpm, 400rpm, 420rpm, 450rpm, 480rpm, 500rpm, etc. The evaporation time can be 4h, 4.2h, 4.5h, 4.8h, 5h, 5.2h, 5.5h, 5.8h, 6h, etc. The drying temperature can be 50℃, 52℃, 55℃, 58℃, 60℃, etc. The drying time can be 10h, 10.5h, 11h, 11.5h, 12h, 12.5h, 13h, 13.5h, 14h, etc. The bursting temperature of the flame-retardant shell can be 100℃, 102℃, 105℃, 110℃, 115℃, 120℃, 125℃, 130℃, etc.

[0092] In this embodiment, flame-retardant microcapsules are prepared by solvent evaporation, which can achieve precise and active safety protection: the outer shell of the flame-retardant microcapsule ruptures when the heat abuse causes high temperature, and the high concentration of phosphorus-nitrogen intumescent flame retardant is accurately and quickly released to the heat source point, realizing the on-demand release of the flame retardant, which has higher fire extinguishing efficiency and avoids the premature failure of the flame retardant under normal working conditions. It can solve the problem of low utilization efficiency and easy premature consumption caused by the uniform dispersion of flame retardant in colloid in related technologies.

[0093] The preparation process of polyurethane prepolymer is described below. This process can be achieved through the following steps (C-1) to (C-2): (C-1) Dehydration treatment of polyols.

[0094] Add the polyol to the reaction vessel, start stirring, and gradually increase the speed to 150 rpm. Dehydrate for 2 to 4 hours at 110℃~120℃ and a vacuum of -0.095 MPa until the moisture content is below 0.05% when sampled.

[0095] For example, the dehydration temperature can be 110℃, 112℃, 115℃, 118℃, 120℃, etc. The dehydration time can be 2h, 2.5h, 3h, 3.5h, 4h, etc.

[0096] (C-2) Isocyanate is added to the dehydrated polyol. The NCO content is detected during the reaction. The reaction is stopped when the NCO content reaches the theoretical value. After cooling and filtration, polyurethane prepolymer is obtained.

[0097] The dehydrated polyol was cooled to 60℃~80℃, and isocyanate was slowly added under nitrogen protection, controlling the reaction temperature to not exceed 85℃. After the addition was complete, the reaction was continued at 70℃~90℃ for 2h~4h, with samples taken every 0.5h to determine the NCO content, until the theoretical value (10%~20%) was reached, at which point the reaction was stopped. The mixture was then cooled to 40℃~50℃, filtered, and discharged to obtain the polyurethane prepolymer.

[0098] For example, the dehydrated polyol can be cooled to 60℃, 65℃, 70℃, 75℃, 80℃, etc. After feeding, the reaction temperature can be 70℃, 75℃, 80℃, 85℃, 90℃, etc. The reaction time can be 2h, 2.5h, 3h, 3.5h, 4h, etc. The NCO content at the end of the reaction can be 10%, 12%, 15%, 18%, 20%, etc. The cooling temperature after the reaction ends can be 40℃, 42℃, 45℃, 48℃, 50℃, etc.

[0099] In the embodiments of this application, polyol and isocyanate are subjected to a stepwise prepolymerization reaction under nitrogen protection and precise temperature control, and the NCO content is monitored in real time to ensure the accuracy of the reaction endpoint. Finally, a polyurethane prepolymer with uniform structure, stable activity, no bubbles and no gel is prepared, which provides a stable and reliable matrix guarantee for the subsequent preparation of structural adhesives.

[0100] Step 2: Surface modification treatment of thermally conductive fillers, phase change microcapsules and flame-retardant microcapsules using silane coupling agents.

[0101] The silane coupling agent was diluted with an equal part by weight of ethanol to obtain a silane coupling agent solution. The thermally conductive filler, phase change microcapsules and flame retardant microcapsules were mixed evenly with the silane coupling agent solution in a high-speed mixer and treated in an oven at 70℃~90℃ for 1h~3h to obtain surface-modified thermally conductive filler, phase change microcapsules and flame retardant microcapsules.

[0102] For example, the temperature of the oven can be 70℃, 75℃, 80℃, 85℃, 90℃, etc. The processing time can be 1h, 1.2h, 1.5h, 1.8h, 2h, 2.2h, 2.5h, 2.8h, 3h, etc.

[0103] In the embodiments of this application, surface treatment of phase change microcapsules, flame retardant microcapsules and thermally conductive fillers with silane coupling agents can increase their interfacial bonding force with polyurethane prepolymers. This not only reduces interfacial thermal resistance, but more importantly, prevents microcapsules from becoming mechanical defect points. This allows the colloid to maintain high bonding strength and high toughness while introducing a large number of multifunctional fillers, which can solve the problem in related technologies where it is difficult to balance high filler content with the excellent mechanical properties (especially flexibility) of the colloid.

[0104] Step 3: Mix the polyurethane prepolymer, additives, surface-modified thermally conductive fillers, phase change microcapsules, and flame-retardant microcapsules uniformly under vacuum conditions to obtain component A.

[0105] The polyurethane prepolymer, additives, surface-modified thermally conductive fillers, phase change microcapsules, and flame-retardant microcapsules were added to a planetary mixer and stirred at 20 rpm to 60 rpm for 30 min to 60 min under a vacuum of -0.095 MPa until a uniform, bubble-free paste-like component A was obtained.

[0106] For example, the stirring speed can be 20 rpm, 30 rpm, 40 rpm, 50 rpm, 60 rpm, etc. The stirring time can be 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min, etc.

[0107] Step 4: Mix component A and component B thoroughly, and cure them using a stepped curing process to obtain the structural adhesive.

[0108] The A component and B component are mixed evenly using a two-component adhesive applicator. The adhesive is then applied between the substrates and cured using a stepped curing process to obtain the structural adhesive.

[0109] The stepped curing process refers to a combination of curing at room temperature and curing at high temperature. Specifically, it involves first curing at 20℃~30℃ for 24h~72h, and then curing at 60℃~100℃ for 1h~4h.

[0110] For example, the curing temperature at room temperature can be 20℃, 22℃, 25℃, 28℃, 30℃, etc. The curing time at room temperature can be 24h, 26h, 28h, 30h, 40h, 50h, 60h, 70h, 72h, etc. The curing temperature at high temperature can be 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃, 100℃, etc. The curing time at high temperature can be 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, etc.

[0111] See Figure 1 , Figure 1 This is a schematic diagram illustrating the intelligent response mechanism of structural adhesive provided in an embodiment of this application. From Figure 1 As can be seen, under normal operating conditions, the phase change core material in the phase change microcapsules is in a solid state, and the flame-retardant microcapsules are also in a stable state. When the temperature rises to around 50°C, the phase change core material absorbs heat and changes from a solid to a liquid state, thus achieving intelligent thermal management. When the temperature continues to rise to >115°C, the flame-retardant shell of the flame-retardant microcapsule ruptures, releasing the flame-retardant core material, thereby achieving precise and active safety protection.

[0112] The technical solution of this application will be described in detail below through specific embodiments.

[0113] In the following specific embodiments, unless otherwise specified, all operations shall be performed under normal conditions or conditions recommended by the manufacturer.

[0114] Example 1 Example 1 provides a structural adhesive comprising component A and component B; Component A comprises the following components in parts by weight: The composition includes 70 parts by weight of polyurethane prepolymer, 12 parts by weight of surface-modified boron nitride nanosheets, 18 parts by weight of surface-modified spherical alumina, 6 parts by weight of surface-modified phase change microcapsules, 6 parts by weight of surface-modified flame retardant microcapsules, and 0.5 parts by weight of defoamer and leveling agent.

[0115] The phase change microcapsule comprises a phase change core material and a phase change shell. The phase change core material is n-dodecane, which accounts for 40 parts by weight. The phase change shell is urea-formaldehyde resin, in which urea accounts for 12 parts by weight and 37% formaldehyde solution accounts for 25 parts by weight.

[0116] The flame-retardant microcapsule comprises a flame-retardant core material and a flame-retardant shell. The flame-retardant core material is selected from ammonium polyphosphate and pentaerythritol in a mass ratio of 3:1, and the flame-retardant core material accounts for 30 parts by weight. The flame-retardant shell is EVA, and the VA content of EVA is 28%. The flame-retardant shell accounts for 9 parts by weight.

[0117] The polyurethane prepolymer comprises: a polyol and an isocyanate. The polyol is selected from 50 parts by weight of castor oil-modified polyester polyol (hydroxyl value of 120 mg KOH / g) and 25 parts by weight of phosphorus-containing flame-retardant polyether polyol (hydroxyl value of 80 mg KOH / g, phosphorus content of 8%). The isocyanate is selected from 28 parts by weight of carbodiimide-modified MDI (NCO content of 30%).

[0118] Component B is 1,4-butanediol.

[0119] The preparation method of structural adhesive is as follows: Step 1: Preparation of phase change microcapsules Phase change microcapsules were prepared by in-situ polymerization. First, 40 parts by weight of n-dodecane (phase change point about 44℃), 0.8 parts by weight of styrene-maleic anhydride copolymer, and 120 parts by weight of deionized water were added to a three-necked flask and emulsified at high speed of 1200 rpm for 30 min in a water bath at 65℃ to form a stable emulsion.

[0120] Next, the pH of the emulsion was adjusted to 3.8 with triethanolamine, 12 parts by weight of urea were added, and 25 parts by weight of 37% formaldehyde solution were slowly added dropwise. The mixture was reacted at 75°C for 1.5 hours to form urea-formaldehyde resin prepolymer.

[0121] The temperature was then raised to 85℃, and the pH was adjusted to 2.0 with a 10% ammonium chloride solution. The reaction was continued for 2.5 hours for polycondensation and solidification. After the reaction was completed, the mixture was allowed to cool naturally to room temperature, filtered, washed three times each with deionized water and ethanol, and dried in a vacuum drying oven at 55℃ for 18 hours. The resulting powdered phase change microcapsules were then passed through a 500-mesh sieve. The average particle size of the obtained phase change microcapsules was determined to be 15 μm by a laser particle size analyzer.

[0122] Step 2: Preparation of flame-retardant microcapsules First, 9 parts by weight of EVA (VA content of 28%) were dissolved in 156 parts by weight of dichloromethane and stirred until completely dissolved. Then, 30 parts by weight of a mixture of ammonium polyphosphate and pentaerythritol (mass ratio of the two is 3:1) were added and stirred at 500 rpm to disperse evenly, forming an oil phase.

[0123] Next, 250 parts by weight of PVA (concentration 0.8%) aqueous solution were prepared to obtain the aqueous phase.

[0124] Then, the oil phase was slowly poured into the aqueous phase in a 30°C water bath, and emulsified at a high speed of 1500 rpm for 45 minutes to form a stable oil-in-water emulsion. This emulsion was transferred to a reaction vessel and slowly evaporated for 5 hours at 45°C and 400 rpm to remove dichloromethane. After filtration, the emulsion was washed three times with deionized water and then dried in a 50°C vacuum drying oven for 12 hours to obtain white powdery flame-retardant microcapsules. DSC testing showed that the shell rupture temperature of the obtained flame-retardant microcapsules was approximately 115°C.

[0125] Step 3: Preparation of polyurethane prepolymer 50 parts by weight of castor oil-modified polyester polyol (hydroxyl value 120 mg KOH / g) and 25 parts by weight of phosphorus-containing flame-retardant polyether polyol (hydroxyl value 80 mg KOH / g, phosphorus content 8%) were added to a reactor. The mixture was initially stirred at 50 rpm. After stirring, the stirring speed was gradually increased to 150 rpm over 10 minutes, while the temperature was raised to 115°C. A vacuum was applied to -0.098 MPa, and dehydration was carried out for 2.5 hours. After the moisture content met the standard, the temperature was lowered to 75°C. Under nitrogen protection, 28 parts by weight of carbodiimide-modified MDI (NCO content 30%) was slowly added, controlling the feeding rate to ensure the reaction temperature was ≤85°C. After the feeding was completed, the reaction continued at 80°C and 150 rpm for 3 hours. Samples were taken every 0.5 hours to measure the NCO content. The reaction was stopped when the content met the standard. The mixture was cooled to 45°C, filtered, and the polyurethane prepolymer was obtained.

[0126] Step 4: Surface Modification Treatment 12 parts by weight of boron nitride nanosheets, 18 parts by weight of spherical alumina, 6 parts by weight of phase change microcapsules, 6 parts by weight of flame retardant microcapsules, and 1.2 parts by weight of silane coupling agent KH-550 (pre-diluted with an equal part by weight of ethanol) were mixed evenly in a high-speed mixer and then treated in an oven at 80°C for 2 hours to complete the surface modification treatment.

[0127] Step 5: Preparation of Component A 70 parts by weight of polyurethane prepolymer, 0.5 parts by weight of defoamer and leveling agent, along with the surface-modified boron nitride nanosheets, spherical alumina, phase change microcapsules and flame retardant microcapsules, were added to a planetary mixer and stirred at 20 rpm for 40 min under a vacuum of -0.095 MPa until a homogeneous, bubble-free paste-like component A was obtained.

[0128] Step 6: Mixing and Curing Mix 70 parts by weight of component A and 5.8 parts by weight of 1,4-butanediol evenly using a two-component dispensing device, apply the mixture between the substrates, cure at 25°C for 24 hours, and then cure in an 80°C forced-air oven for 2 hours to obtain the structural adhesive.

[0129] Example 2 Example 2 provides a structural adhesive that differs from Example 1 in that the amount of microcapsules is adjusted. Specifically, the amount of phase change microcapsules is 8 parts by weight and the amount of flame retardant microcapsules is 4 parts by weight. The remaining steps and parameters are the same as in Example 1.

[0130] Example 3 Example 3 provides a structural adhesive that differs from Example 1 in that the proportion of thermally conductive filler is adjusted. Specifically, the amount of boron nitride nanosheets is 18 parts by weight and the amount of spherical alumina is 12 parts by weight. The remaining steps and parameters are the same as in Example 1.

[0131] Comparative Example 1 Comparative Example 1 provides a structural adhesive that differs from Example 1 in that the phase change microcapsules and flame retardant microcapsules are replaced with 12 parts by weight of ammonium polyphosphate, while the remaining steps and parameters are the same as in Example 1.

[0132] Comparative Example 2 Comparative Example 2 provides a structural adhesive that differs from Example 1 in that the amounts of thermally conductive filler, phase change microcapsules, and flame-retardant microcapsules remain the same, but it is not surface-modified with a silane coupling agent; instead, it is directly mixed with the polyurethane prepolymer. The remaining steps and parameters are the same as in Example 1.

[0133] This application conducts performance tests on the structural adhesives provided in Examples 1-3 and Comparative Examples 1-2, and the test results are shown in Table 1.

[0134]

[0135] Among them, thermal conductivity, tensile shear strength, elongation at break, flame retardancy rating, and thermal abuse pass rate are all tested in accordance with the corresponding standards, which will not be elaborated here.

[0136] The temperature peak suppression effect was evaluated using a custom heat source method, i.e., by simulating battery thermal shock testing. The blank control group was compared with Comparative Example 1. The detailed test method is as follows: Test setup: The test platform is a self-built thermal shock test platform, including a controllable constant temperature heat source (50W power), thermocouple temperature sensor (accuracy ±0.1℃), data acquisition system, and fixtures for fixing samples.

[0137] Sample preparation: Structural adhesive is applied between the substrates, with the adhesive layer thickness controlled at 0.5±0.1mm. After curing using a stepped curing process, test samples are formed.

[0138] Test Procedure: Place the sample on the test platform, ensuring the heat source is in close contact with the lower surface of the sample, while allowing the upper surface to dissipate heat naturally. Turn on the heat source and continuously record the temperature change at the center point of the upper surface of the sample for 300 seconds.

[0139] Data processing: Record the highest temperature Tmax during the test and compare it with the highest temperature T0 of the blank control group to calculate the peak temperature suppression value ΔT = T0 - Tmax. Five parallel samples were tested for each sample, and the average value was taken.

[0140] As shown in Table 1, the structural adhesives prepared in Examples 1-3 of this application all exhibit excellent comprehensive performance, verifying the success of the synergistic design of microcapsule design and filler surface modification. Specifically, the structural adhesive prepared in Example 2 achieved the best temperature peak suppression effect (ΔT=9.0℃) by increasing the proportion of phase change microcapsules. The structural adhesive prepared in Example 3 achieved the highest thermal conductivity (1.8 W / m·K) by increasing the proportion of boron nitride nanosheets in the thermally conductive filler.

[0141] In contrast, Comparative Example 1 directly added traditional flame retardants instead of adding them in the form of microcapsules, resulting in disadvantages in flame retardant efficiency and mechanical properties.

[0142] In Comparative Example 2, the lack of surface modification treatment on the thermally conductive filler, phase change microcapsules, and flame-retardant microcapsules resulted in their disadvantages in strength and toughness, highlighting the decisive role of surface modification treatment in maintaining the high strength and high toughness of the colloid.

[0143] In summary, the microcapsule-type structural adhesive provided in this application is a thermally conductive and flame-retardant structural adhesive for battery modules that can achieve intelligent thermal-safety collaborative management and has excellent mechanical properties and reliability. Through the collaborative design of intelligent microcapsule system and filler surface engineering, it significantly improves active thermal management capabilities and safety protection level while maintaining excellent basic thermal conductivity, and also has high strength and high toughness.

[0144] The above description is only for the purpose of enabling those skilled in the art to understand the technical solution of this application, and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A structural adhesive, characterized in that, The structural adhesive comprises component A and component B; Component A comprises the following components in parts by weight: The composition includes 60 to 100 parts by weight of polyurethane prepolymer, 30 to 60 parts by weight of thermally conductive filler, 10 to 20 parts by weight of phase change microcapsules and flame retardant microcapsules, and 0.3 to 0.8 parts by weight of additives. The mass ratio of the phase change microcapsules to the flame retardant microcapsules is 1:2 to 2:

1. The phase change microcapsule comprises: a phase change core material and a phase change shell, wherein the phase change core material is selected from at least one of n-eicosane, n-docosahexanes, and n-tetracosane, and the phase change shell is urea-formaldehyde resin; The flame-retardant microcapsule comprises: a flame-retardant core material and a flame-retardant shell, wherein the flame-retardant core material is selected from ammonium polyphosphate and pentaerythritol, and the flame-retardant shell is an ethylene-vinyl acetate copolymer; Component B is a curing agent.

2. The structural adhesive of claim 1, wherein The phase change core material is 30 to 50 parts by weight. Optionally, the urea-formaldehyde resin is obtained by reacting urea with formaldehyde solution, wherein the urea is present in the form of 10 to 15 parts by weight, the formaldehyde solution has a concentration of 37%, and the formaldehyde solution is present in the form of 20 to 30 parts by weight. Optionally, the phase change microcapsules have an average particle size of 5 μm to 25 μm.

3. The structural adhesive of claim 1, wherein The flame-retardant core material is 20 to 40 parts by weight. Optionally, the flame-retardant shell is 20% to 40% of the flame-retardant core material by weight. Optionally, the mass ratio of the ammonium polyphosphate to the pentaerythritol is 2.5:1 to 3.5:

1.

4. The structural adhesive according to claim 1, characterized in that, The polyurethane prepolymer is obtained by reacting polyols and isocyanates; The polyol is selected from castor oil-modified polyester polyol and phosphorus-containing flame-retardant polyether polyol, and the isocyanate is selected from diphenylmethane diisocyanate or its modified form. Optionally, the castor oil modified polyester polyol is 40 to 80 parts by weight, the phosphorus-containing flame-retardant polyether polyol is 20 to 40 parts by weight, and the isocyanate is 20 to 60 parts by weight. Optionally, the isocyanate content in the isocyanate is 28% to 32%; Optionally, the molar ratio of isocyanate groups to hydroxyl groups in the polyurethane prepolymer is 1.5 to 2.

5.

5. The structural adhesive according to claim 4, characterized in that, The hydroxyl value of the castor oil-modified polyester polyol is 100mgKOH / g~300mgKOH / g; The phosphorus-containing flame-retardant polyether polyol has a phosphorus content of 5% to 10% and a hydroxyl value of 50 mg KOH / g to 100 mg KOH / g.

6. The structural adhesive according to claim 1, characterized in that, The thermally conductive filler is selected from boron nitride nanosheets and spherical alumina; The mass ratio of the boron nitride nanosheets to the spherical alumina is 1:2 to 2:1; Optionally, the boron nitride nanosheets have a diameter of 1 μm to 5 μm and a thickness of 3 nm to 10 nm, and the spherical alumina particles have a diameter of 1 μm to 5 μm.

7. The structural adhesive according to claim 1, characterized in that, The thermally conductive filler, the phase change microcapsule, and the flame-retardant microcapsule are all surface-modified with a silane coupling agent. Optionally, component B is selected from at least one of diols, diamines, and triols; Optionally, the molar ratio of the active hydrogen functional group in component B to the isocyanate group in the polyurethane prepolymer is 0.8:1 to 1.1:

1.

8. A method for preparing a structural adhesive, characterized in that, The structural adhesive is as described in any one of claims 1 to 7, and the preparation method comprises: Phase change microcapsules, flame retardant microcapsules, and polyurethane prepolymers were prepared separately. The thermally conductive filler, the phase change microcapsule, and the flame-retardant microcapsule are surface modified using a silane coupling agent. The polyurethane prepolymer, additives, surface-modified thermally conductive fillers, phase change microcapsules, and flame-retardant microcapsules are mixed uniformly under vacuum conditions to obtain component A. The structural adhesive is obtained by mixing component A and component B thoroughly and then curing them through a stepped curing process.

9. The preparation method according to claim 8, characterized in that, The process of preparing the phase change microcapsules includes: The phase change core material and emulsifier are emulsified in water to form an emulsion; Urea and formaldehyde solution are added to the emulsion. After the urea and formaldehyde solution react, a urea-formaldehyde resin phase change shell is formed on the surface of the phase change core material. After post-processing, the phase change microcapsules are obtained.

10. The preparation method according to claim 8, characterized in that, The process of preparing the flame-retardant microcapsules includes: The ethylene-vinyl acetate copolymer, ammonium polyphosphate, pentaerythritol and solvent were mixed to obtain the oil phase; The dispersant is dissolved in water to obtain an aqueous phase; The oil phase is poured into the aqueous phase to form an oil-in-water emulsion; The solvent in the oil-in-water emulsion is evaporated, and the resulting product is post-processed to obtain the flame-retardant microcapsules.

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