Green high-thermal-stability bi-component polyurethane heat-conducting structural adhesive for power battery PACK and preparation method thereof

Abstract

The invention discloses a green high-thermal-stability bi-component polyurethane heat-conducting structural adhesive for a power battery PACK, and belongs to the field of polyurethane heat-conducting structural adhesives. The structural adhesive comprises a component A and a component B which are used according to the volume ratio of 1: 1, wherein the component A comprises polycarbonate polyol obtained through ring-opening copolymerization of carbon dioxide and epoxypropane, bio-based polyol, a chain extender and / or a cross-linking agent, a heat-conducting filler, a flame retardant, a coupling agent, an interface wetting agent, a thixotropic agent, a water removal agent and a catalyst; and the component B comprises an NCO-containing prepolymer prepared from polycarbonate polyol, a heat-conducting filler, a water removal agent and a catalyst. According to the invention, the proportion of a non-petroleum-based carbon source is increased while high thermal conductivity, high thermal stability and high-damp-heat reliable bonding are met; and by virtue of relatively high carbonic ester / ester group density in the adhesive layer, the adhesive layer has controllable peptizing capacity under alcohol / alcohol amine-base catalysis and / or enzyme catalysis conditions, so that disassembly and assembly recovery of the power battery PACK are facilitated.

Description

Technical Field

[0001] This invention relates to the field of polyurethane thermally conductive structural adhesive technology, specifically to a green, high thermal stability two-component polyurethane thermally conductive structural adhesive for power battery PACK and its preparation method. Background Technology

[0002] With the rapid growth of new energy vehicles in recent years, the cumulative installed capacity of power batteries has exceeded 500 GWh. The safety, durability, and life-cycle resource utilization efficiency of power battery systems are directly related to the development of the new energy vehicle industry. Developing key power battery materials that combine high safety, high heat resistance, long lifespan, and green and low-carbon characteristics can reduce the frequency of battery replacement and disposal, saving manufacturing capacity and energy consumption from the source, which is of great practical significance.

[0003] In the structure of power battery packs, thermally conductive structural adhesives are typically used for bonding and filling between cells and between cells and the casing / cooling system. They must possess a certain thermal conductivity to effectively dissipate and diffuse the heat generated by the cells during operation, reducing the risk of localized overheating. They must also fulfill multiple functions, including structural load-bearing, buffering and vibration reduction, flame retardancy and thermal insulation, and pressure and impact resistance. They are one of the key functional materials ensuring the safe and reliable operation of power batteries under complex conditions such as high temperature, high humidity, and long-term vibration. With the development of highly integrated pack technologies such as CTP (Cell To Pack) and CTB (Cell To Body), the operating temperature range of battery packs has been further widened, and the heat flux density has increased. This places more stringent requirements on the modulus retention and bond strength retention of thermally conductive structural adhesives under humid and hot aging conditions such as 50–100℃ or even higher temperatures and 85℃ / 85%RH.

[0004] Existing thermally conductive structural adhesives for power batteries include epoxy, silicone, and polyurethane systems. Epoxy adhesives, while having a high modulus, lack sufficient toughness, making them prone to brittle cracking under long-term vibration and impact conditions in large modules or packs. Silicone adhesives, although possessing good weather resistance and flexibility, have low bonding strength, making it difficult to meet the high-strength structural bonding requirements of power battery packs. Polyurethane thermally conductive structural adhesives, due to their flexible formulation design, high bonding strength, and adjustable modulus, have become the mainstream direction for power battery thermally conductive structural adhesives. However, to achieve the required elongation at break and buffering performance with high filler content, existing polyurethane thermally conductive structural adhesives generally lower the softening point by increasing the proportion of soft segments. This results in a significant decrease in elastic modulus and a marked reduction in bonding strength under long-term high temperature or high temperature and humidity environments. Furthermore, they are prone to interfacial cracking under thermal cycling conditions, making it difficult to simultaneously achieve low modulus and high toughness at room temperature, as well as heat resistance and resistance to humid heat aging.

[0005] To address the bonding and thermal conductivity issues of power batteries, several published patents have proposed different solutions. For example, Chinese patent CN111303820B provides a two-component polyurethane structural adhesive for power battery bonding. By introducing bio-based polyols and a flame-retardant system, it achieves high shear strength and good flame retardancy on substrates such as aluminum and PET. However, the resin system mainly focuses on room temperature bonding performance and has not yet systematically considered high-temperature modulus and reliability under thermal shock conditions. Chinese patent CN115491159A proposes a solution that introduces aromatic polyols and polyether-modified silanes into the system, embedding organosilicon segments into the polyurethane backbone to improve the thermally conductive structural adhesive's resistance to damp heat and surface hydrophobicity, mitigating performance degradation caused by moisture. However, this solution mainly focuses on damp-heat aging conditions such as 85℃ / 85%RH, and its description of modulus control over a wide temperature range and reliability under thermal cycling remains relatively limited. Chinese patent CN115612433A discloses a two-component polyurethane thermally conductive structural adhesive that combines high thermal conductivity, V-0 flame retardancy, and fatigue resistance through a composite polyether / polyester polyol and high filler formulation design. This adhesive can meet the service life requirements of power battery packs under certain operating conditions. However, under high thermal conductivity and high filler conditions, the elastic modulus of the system is still relatively high, and there is room for further improvement in dimensional stability and interfacial stress buffering capacity. In summary, existing technical solutions mostly focus on optimizing thermal conductivity, initial bond strength, or single operating conditions (such as damp heat aging or fatigue). Under the comprehensive requirements of "high thermal conductivity, high thermal stability, and resistance to damp heat aging" for power battery packs, it is still difficult to simultaneously maintain low modulus at room temperature, modulus and bond strength in high temperature and high humidity environments, and interfacial stability under thermal shock conditions while maintaining high filler content.

[0006] In summary, existing two-component polyurethane thermally conductive structural adhesives for power battery packs have at least the following problems: (1) Based on traditional polyether polyols or polyester polyols, the raw materials are highly dependent on petroleum-based carbon sources, and the utilization rate of carbon dioxide resources is low, which makes it difficult to meet the requirements of the new energy vehicle industry for green and low-carbon materials. (2) Under the actual service conditions of power batteries, such as high temperature of 60-100℃ and humid heat of 85℃ / 85%RH, the modulus and shear strength retention of the adhesive layer are insufficient, and the load-bearing capacity and bonding reliability under high temperature and high humidity are difficult to achieve.

[0007] (3) In order to obtain a certain thermal conductivity, the system often requires high filler and high viscosity, which can easily lead to construction difficulties, insufficient interface wetting, and sedimentation and stratification during long-term storage. (4) Traditional polyurethane thermal conductive structural adhesives are mostly inert polyether soft segments, and the density of degradable bonds in the adhesive layer is low. During the retirement stage of the power battery, it is difficult to achieve controllable debonding and separation from the structural components under mild conditions, which is not conducive to the disassembly and high-value recycling of the power battery PACK.

[0008] Therefore, how to develop a polyurethane thermally conductive structural adhesive that is green and low-carbon, has a high bio-based content, and can be reliably applied to power battery PACKs under high temperature, high humidity and complex working conditions for a long time remains a technical problem that needs to be solved in this field.

[0009] In view of this, the present invention is hereby proposed. Summary of the Invention

[0010] The purpose of this invention is to provide a green, high thermal stability two-component polyurethane thermally conductive structural adhesive for power battery packs and its preparation method. It can achieve green and low carbon emissions at the raw material end while ensuring thermal conductivity, as well as high bulk strength and bond strength retention rate. At the same time, it takes into account the construction rheological properties under high filler system and the decomposability of adhesive layer and component recycling during the power battery retirement stage, thereby solving the technical problems existing in the prior art.

[0011] The objective of this invention is achieved through the following technical solution: A green, high-thermal-stability two-component polyurethane thermally conductive structural adhesive for power battery packs includes: component A and component B, wherein component A and component B are mixed in a mass ratio of 1:1 to 3, and the NCO:OH equivalent ratio in the mixed system is 0.9:1 to 1.3:1; wherein, Component A comprises the following raw materials in parts by mass: 5 to 30 parts of polycarbonate polyol obtained by ring-opening copolymerization of carbon dioxide and propylene oxide, 20-60 parts of bio-based polyols, 1 to 10 parts of chain extender and / or crosslinking agent, 40-80 parts of thermally conductive filler, 0.1 to 10 parts of thixotropic agent, 0.1 to 5 parts of silane coupling agent, 0.1 to 5 parts of interfacial wetting agent, 0.1 to 5 parts of dehydrating agent, 0.01 to 3 parts of catalyst A; Component B comprises the following raw materials in parts by mass: 20 to 80 parts of an NCO-containing prepolymer made from a polycarbonate polyol, wherein the polycarbonate polyol is obtained by ring-opening copolymerization of carbon dioxide and propylene oxide. 60-80 parts of thermally conductive filler; 0.01 to 3 parts of catalyst B; 0.1 to 5 parts of dehydrating agent.

[0012] Preferably, in the above structural adhesive, the NCO-containing prepolymer in component B is prepared by polycarbonate polyol and high symmetry diisocyanate under conditions where the NCO / OH molar ratio is 1.5 to 3.0. The high symmetry diisocyanate is one or more of terephthalic diisocyanate, naphthalene diisocyanate, and dimethylbiphenyl diisocyanate, as well as modified or derivatives of any of the above diisocyanates obtained by chemical modification, prepolymerization, end-capping, or substitution.

[0013] Preferably, in the above structural adhesive, the polycarbonate polyol used in component A and the NCO-containing prepolymer in component B has a hydroxyl value of 40-80 mgKOH / g and a number-average molecular weight M. n The range is 1000 to 4000.

[0014] Preferably, in the above structural adhesive, the polycarbonate polyol in component A and the polycarbonate polyol used in the NCO-containing prepolymer in component B are both obtained by ring-opening copolymerization of carbon dioxide and epoxide in the presence of a catalyst, wherein the carbon dioxide content accounts for 20 to 40 wt% of the total mass of the polyol.

[0015] Preferably, in the above-mentioned structural adhesive, the epoxide is a cyclic ether compound capable of undergoing a ring-opening copolymerization reaction with carbon dioxide; preferably, an aliphatic epoxide and / or its substituted derivatives are used; the aliphatic epoxide includes, but is not limited to, at least one of ethylene oxide, propylene oxide, butane oxide and their substituted derivatives; The catalyst is a catalytic system capable of catalyzing the ring-opening copolymerization of carbon dioxide and epoxides. Preferably, it is one or more of a bimetallic cyanide catalyst, a metal complex catalyst, or an organic catalyst.

[0016] Preferably, in the above-mentioned structural adhesive, the epoxide is at least one of propylene oxide, ethylene oxide, a derivative of propylene oxide, and a derivative of ethylene oxide. The catalyst used is a bimetallic cyanide catalyst.

[0017] Preferably, in the above structural adhesive, the bio-based polyol in component A is a castor oil-modified polyol or a castor oil-modified polyol. The chain extender is one or more of ethylene glycol, 1,4-butanediol, and 2-methyl-1,3-propanediol; The crosslinking agent is one or more of aliphatic polyamines and alicyclic polyamines; The silane coupling agent is one or a combination of several of γ-glycidoxypropyltrimethoxysilane and aminopropyltriethoxysilane. The thixotropic agent is one or a combination of fumed silica, bentonite, and polyamide wax. The interface wetting agent is one or a combination of polyether modified silicone oil and fluorocarbon surfactant.

[0018] Preferably, in the above structural adhesive, the thermally conductive fillers in both component A and component B are one or more of aluminum hydroxide, aluminum oxide, calcium carbonate, boron nitride, and aluminum nitride. The dehydrating agents in both component A and component B are one or a combination of 3A molecular sieve powder, 4A molecular sieve powder, and organic dehydrating agents. Catalyst A in component A and catalyst B in component B are both combinations of organometallic catalysts and tertiary amine catalysts. The organometallic catalysts are bismuth-based, zinc-based, or tin-based catalysts; the tertiary amine catalysts are triethylenediamine, bis(dimethylaminoethyl) ether, and their derivatives.

[0019] A method for preparing a green, high thermal stability, two-component polyurethane thermally conductive structural adhesive for power battery PACK according to the present invention, comprising the following steps: (The method involves taking the raw materials of component A and component B according to the formulation of the two-component polyurethane thermally conductive structural adhesive of the present invention.) Preparation of Component A: The bio-based polyol and polycarbonate polyol in the raw materials of Component A are mixed and dehydrated, and coupling agent, interface wetting agent, thixotropic agent, chain extender and / or crosslinking agent, thermally conductive filler, dehydrating agent and catalyst A are added. Component A is obtained by high-speed dispersion and vacuum degassing. Preparation of component B: The NCO-containing prepolymer, thermally conductive filler, dehydrating agent and catalyst B in the raw materials of component B are mixed, dispersed and degassed under vacuum to obtain component B; The A component and B component prepared above are mixed and used at a mass ratio of 1:1 to 3.

[0020] Preferably, in the above method, the NCO-containing prepolymer used in component B is prepared in the following manner, wherein each raw material, by mass, comprises: Under inert gas protection, polycarbonate polyol is added to highly symmetric diisocyanate and reacted at 60–120 °C, with the NCO / OH molar ratio controlled at 1.5–3.0, to obtain an NCO-containing prepolymer.

[0021] Preferably, in the above method, the polycarbonate multi-component used in component A and the polycarbonate multi-component used in the NCO-containing prepolymer in component B are prepared in the following manner, wherein each raw material comprises, by weight, parts of: Initiator polyol and catalyst are added to a reaction vessel equipped with stirring, heating and pressurization functions. After degassing and dehydration under vacuum and nitrogen purging conditions, carbon dioxide is introduced and the temperature and pressure are increased. Epoxide monomer is added dropwise in the presence of carbon dioxide, and the molar ratio of carbon dioxide to epoxide is controlled. Ring-opening copolymerization reaction is carried out at 60-140℃ and 1-5MPa to obtain polycarbonate polyol with a carbon dioxide content of 20-40wt% of polyol mass and a hydroxyl value of 40-80mgKOH / g.

[0022] Preferably, in the above method, after the reaction is completed, the preparation of the polycarbonate multi-component further includes: removing unreacted monomers and low-boiling substances under reduced pressure of 50-100°C and 5-10 kPa, and removing mechanical impurities by filtration; In the steps of preparing component A and component B, the vacuum degassing pressure is -0.08 to -0.095 MPa, and the time is 20 to 60 min.

[0023] Compared with the prior art, the green, high thermal stability two-component polyurethane thermally conductive structural adhesive for power battery PACK and its preparation method provided by the present invention have the following advantages: (1) This invention uses polycarbonate polyol obtained by ring-opening copolymerization of carbon dioxide and propylene oxide and introduces bio-based polyol to replace traditional petroleum-based polyether and polyester polyol, so that the thermally conductive structural adhesive for power battery PACK has a higher proportion of non-petroleum-based carbon source, providing a new material solution and choice for the high-value utilization of carbon dioxide in the atmosphere and the greening of thermally conductive structural adhesive.

[0024] (2) Through the synergistic design of “CO2-derived polycarbonate soft segment + bio-based soft segment + high symmetry isocyanate hard segment + graded thermally conductive filler”, the present invention achieves a high thermal conductivity while enabling the cured adhesive layer to have a moderate modulus and good flexibility at room temperature, and maintains a high bulk strength and bond strength retention rate under harsh working conditions such as 60-100℃ and 85℃ / 85%RH, which significantly improves the high heat resistance and damp heat aging reliability of the thermally conductive structural adhesive for power battery PACK.

[0025] (3) By increasing the density of carbonate bonds and ester groups in the adhesive layer, the present invention enables selective degradation under alcohol / alkanolamine solvent-alkaline catalyst and / or enzyme catalysis conditions, which facilitates the debonding and separation of the adhesive layer from the structural components during the retirement stage of the power battery, and provides technical support for the dismantling, recycling and green full life cycle management of the power battery PACK.

[0026] (4) Introducing polycarbonate polyols and bio-based polyols obtained by CO2 ring-opening copolymerization to achieve green and low carbon at the raw material end; and through the synergistic design of high symmetry diisocyanate, graded thermally conductive filler and interface additives, the structural adhesive still has high bulk strength and bond strength retention rate under harsh working conditions such as 60-100℃ and 85℃ / 85%RH, while taking into account the construction rheological properties under high filler system and the decomposable adhesive layer and component recycling during the power battery retirement stage. Detailed Implementation

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the specific content of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments, which do not constitute a limitation of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0028] First, the following explanations are provided for the terms that may be used in this article: The term "and / or" means that either or both can be achieved simultaneously. For example, X and / or Y means that it includes both "X" or "Y" as well as the three cases of "X and Y".

[0029] The terms "comprising," "including," "containing," "having," or other similar semantic descriptions should be interpreted as non-exclusive inclusion. For example, including a technical feature element (such as raw material, component, ingredient, carrier, dosage form, material, size, part, component, mechanism, device, step, process, method, reaction conditions, processing conditions, parameter, algorithm, signal, data, product or article of manufacture, etc.) should be interpreted as including not only the expressly listed technical feature element, but also other technical feature elements that are not expressly listed and are well-known in the art.

[0030] The term "composed of" excludes any technical features not expressly listed. When used in a claim, it closes the claim to exclude all technical features other than those expressly listed, except for associated conventional impurities. If the term appears only in a clause of a claim, it limits the claim to the elements expressly listed in that clause; elements recited in other clauses are not excluded from the overall claim.

[0031] The term "parts by mass" indicates the mass ratio between multiple components. For example, if component X is described as x parts by mass and component Y as y parts by mass, then the mass ratio of component X to component Y is x:y. One part by mass can represent any mass; for example, one part by mass can be expressed as 1 kg or 3.1415926 kg, etc. The sum of the parts by mass of all components is not necessarily 100 parts; it can be greater than 100 parts, less than 100 parts, or equal to 100 parts. Unless otherwise stated, parts, proportions, and percentages mentioned herein are all measured by mass.

[0032] When concentration, temperature, pressure, size, or other parameters are expressed as numerical ranges, such ranges should be understood to specifically disclose all ranges formed by any pairing of upper limits, lower limits, or preferred values ​​within that range, regardless of whether the range is explicitly stated; for example, if the numerical range "2 to 8" is stated, then that range should be interpreted to include ranges such as "2 to 7", "2 to 6", "5 to 7", "3 to 4 and 6 to 7", "3 to 5 and 7", "2 and 5 to 7", etc. Unless otherwise stated, the numerical ranges described herein include both their endpoints and all integers and fractions within that range.

[0033] The solution provided by this invention will be described in detail below. Contents not described in detail in the embodiments of this invention are prior art known to those skilled in the art. Where specific conditions are not specified in the embodiments of this invention, they shall be performed according to conventional conditions in the art or conditions recommended by the manufacturer. Reagents or instruments used in the embodiments of this invention whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0034] This invention provides a green, high thermal stability, two-component polyurethane thermally conductive structural adhesive for power battery packs. The thermally conductive structural adhesive includes two separate components, A and B. After mixing and curing components A and B in a 1:1 volume ratio, a thermally conductive structural adhesive layer is formed, which is used for thermal bonding and filling between battery cells, between battery cells and the casing or cooling system in power battery packs.

[0035] Component A comprises the following raw materials by mass: 5 to 30 parts of polycarbonate polyol obtained by ring-opening copolymerization of carbon dioxide and propylene oxide, 20-60 parts of bio-based polyol components, 1 to 10 parts of chain extender and / or crosslinking agent, 40-80 parts of thermally conductive filler, 0.1 to 10 parts of thixotropic agent, 0.1 to 5 parts of coupling agent, 0.1 to 5 parts of interfacial wetting agent, 0.1 to 5 parts of dehydrating agent, 0.01 to 3 parts of catalyst A, Component B comprises the following raw materials by mass: 20-80 parts of an NCO-containing prepolymer made from a polycarbonate polyol, wherein the polycarbonate polyol is obtained by ring-opening copolymerization of carbon dioxide and propylene oxide. 60-80 parts of thermally conductive filler, 0.01 to 3 parts of catalyst B, 0.1 to 5 parts of dehydrating agent; The components A and B are mixed in a mass ratio of 1:1 to 3, and the NCO:OH equivalent ratio in the mixed system is 0.9:1 to 1.3:1, more preferably 1.00:1 to 1.15:1.

[0036] In some preferred embodiments, in the above-mentioned thermally conductive structural adhesive, based on 100 parts by mass of the total mass of polyol and isocyanate in component A and component B, the total amount of thermally conductive filler is preferably 80 to 250 parts by mass, so that the thermal conductivity of the cured adhesive layer at 25°C is preferably 0.7 to 2.0 W / (m·K), and the room temperature shear bond strength is preferably greater than 8 MPa.

[0037] In some preferred embodiments, the polyol component in the above-mentioned thermally conductive structural adhesive includes at least carbon dioxide ring-opening copolymer polycarbonate polyol (PCE), and may further include one or more bio-based polyols. The preparation method of the self-made environmentally friendly polycarbonate polyol includes: adding an initiator polyol and a composite catalyst to a reactor equipped with stirring, heating, and pressurization functions; removing dissolved air and moisture from the system under vacuum and inert gas conditions; introducing carbon dioxide and increasing the temperature and pressure; adding propylene oxide and / or ethylene oxide dropwise in the presence of carbon dioxide; and carrying out a ring-opening copolymerization reaction at 60–140°C and 1–5 MPa; controlling the molar ratio of carbon dioxide to epoxide and the reaction time; the resulting polycarbonate polyol having a carbon dioxide content of 20–40 wt% of the polyol mass, a hydroxyl value of 40–80 mg KOH / g, preferably 50–70 mg KOH / g, and a number-average molecular weight M. n The concentration is 1000–4000. After the reaction is complete, unreacted monomers and low-boiling substances are removed under reduced pressure, and mechanical impurities are removed by filtration to obtain the environmentally friendly polycarbonate polyol. Specific implementation steps of this preparation method can be found in Example 1 later in this specification.

[0038] Furthermore, in order to introduce specific functional groups and tunable structures into polycarbonate polyols, the CO2 ring-opening copolymerization of the present invention is not limited to using propylene oxide as the sole epoxy monomer; other epoxides and / or functionalized epoxy monomers may also be selected or used in combination. The epoxy monomers may be aliphatic or cyclic epoxides such as ethylene oxide, butane oxide, and cyclohexane oxide, or functionalized epoxy monomers such as glycidyl ethers, glycidyl esters, fluorinated epoxides, and silane epoxides with specific side groups.

[0039] By adjusting the molar fraction of functionalized epoxy monomers in the total epoxy monomers (e.g., 10–30%), structural units such as fluorine atoms, alkenyl groups, hydroxyl groups, ester groups, or silane groups can be introduced into the polycarbonate polyol backbone to further control the polarity, glass transition temperature, compatibility with bio-based polyols and fillers, and dielectric properties of the soft segment. This provides a more diverse range of formulation design options for polyurethane thermally conductive structural adhesives used in power battery packs.

[0040] In some preferred embodiments, the bio-based polyol in the above-mentioned thermally conductive structural adhesive is selected from polyols prepared from renewable biomass resources, including one or more of plant oil-based polyols, sugar alcohol polyols, and lignin-modified polyols. The plant oil-based polyol is preferably obtained by introducing hydroxyl groups into vegetable oils such as castor oil, rapeseed oil, soybean oil, palm oil, cottonseed oil, linseed oil, tung oil, and cashew nut shell oil, or their fatty acids, through transesterification, epoxidation-ring-opening addition, or hydroxymethylation. Castor oil and castor oil-modified polyols, and aromatic bio-based polyols prepared from cashew nut shell liquid are more preferred. The above-mentioned bio-based polyols typically have a functionality of 2-3 and a hydroxyl value of 40-200 mgKOH / g, preferably a functionality of about 2.7 and a hydroxyl value of about 160 mgKOH / g. By adjusting the aliphatic chain length, unsaturation, and aromatic ring content, a reasonable balance between soft segment flexibility and thermal stability can be achieved.

[0041] In this invention, the bio-based polyol is mainly used in the construction of the soft segment of component A, accounting for 20-80 wt% of the total mass of component A, preferably 30-50 wt%. Castor oil and its modified polyols provide longer, more flexible fatty chains and a moderately branched structure, which is beneficial for reducing the room-temperature modulus of the adhesive layer, increasing elongation at break, and improving impact resistance under high filler content, thus improving the shock resistance reliability of the power battery during vehicle operation. The aromatic bio-based polyol derived from cashew nut shell oil improves the heat distortion temperature and heat oxidation stability of the soft segment by introducing a benzene ring structure, which is beneficial for maintaining mechanical properties under high humidity and heat conditions. Meanwhile, the bio-based polyol is derived from renewable resources, which can significantly increase the bio-based content of the structural adhesive of this invention, reduce dependence on petroleum-based polyether / polyester polyols, and, together with polycarbonate polyols prepared from carbon dioxide, achieve a green and low-carbon design for the thermally conductive structural adhesive used in power battery PACKs.

[0042] In some preferred embodiments, in the above-mentioned thermally conductive structural adhesive, the NCO-containing prepolymer in component B is prepared by reacting the above-mentioned polycarbonate / bio-based polyol and diisocyanate at a controlled temperature. The diisocyanate can be one or more of aliphatic, alicyclic, or aromatic diisocyanates and their prepolymers or modifiers; alicyclic and / or modified aromatic diisocyanates with high molecular symmetry, such as pentamethylene diisocyanate (PDI), hexamethylene diisocyanate (HDI), hexamethylene diisocyanate trimer (HDI trimer), hydrogenated diphenylmethane diisocyanate (HMDI), and dicyclohexylmethane diisocyanate (H... 12 The first one or more of MDI, isophorone diisocyanate (IPDI), terephthalic diisocyanate (PPDI), naphthalene diisocyanate (NDI), dimethyl biphenyl diisocyanate (TODI), triphenylmethane triisocyanate (TTI), and 3,3′-dimethylbiphenyl-4,4′-diisocyanate (DMMDI), as well as modified or derivatives of any of the above diisocyanates obtained by chemical modification, prepolymerization, end-capping, or substitution.

[0043] Preferably, the high-symmetry diisocyanate is PPDI, which produces hard segments with high regularity and density, which is beneficial for the orderly arrangement and physical cross-linking of the hard segment phase. This improves the bulk modulus, shear strength, and dimensional stability of the cured adhesive layer under high temperature and high humidity conditions of 60–100°C, and slows down the penetration and diffusion of moisture in the adhesive layer, thereby improving the long-term reliability of the interfacial adhesion. Without departing from the concept of the present invention, the diisocyanate can also be partially or wholly made of conventional aromatic diisocyanates such as 4,4′-diphenylmethane diisocyanate (MDI) and toluene diisocyanate (TDI) to suit different cost and process requirements.

[0044] The NCO mass fraction in the NCO-containing prepolymer is 5-25 wt%, preferably 10-18 wt%; the PCE mass fraction in the prepolymer is 20-80 wt%, more preferably 50-70 wt%, to balance the viscosity, reactivity and hard segment structure regularity of the prepolymer.

[0045] In some preferred embodiments, the chain extender and / or crosslinking agent in the above-mentioned thermally conductive structural adhesive is a low-molecular-weight polyol and / or polyamine compound containing active hydrogen. The polyol can be a C2-C6 straight-chain or branched diol, such as ethylene glycol, 1,3-propanediol, 1,4-butanediol, dipropylene glycol, diethylene glycol, 2-methyl-1,3-propanediol, etc., or a polyol with three or more hydroxyl groups, such as trimethylolpropane, glycerol, pentaerythritol, dipentaerythritol, etc.; the crosslinking agent can be an aliphatic or alicyclic polyamine, such as ethylenediamine, 1,4-butanediamine, diethylenetriamine, etc. Preferably, the chain extender is mainly a diol, and the crosslinking agent is a small amount of polyol and polyamine as auxiliary agents. By adjusting the type and amount of the above-mentioned aliphatic chain extender and crosslinking agent, and controlling the NCO:OH / NH equivalent ratio, a balance can be achieved between room temperature flexibility and high temperature modulus maintenance.

[0046] Furthermore, to improve the heat resistance and dimensional stability of the cured adhesive layer under humid and hot conditions, the chain extender and / or crosslinking agent may also contain aromatic polyols and / or polyamines with benzene rings, such as ortho-, meta-, or para-phenylenediol, dimethyloldiphenylmethane, hydroxylated diphenylmethane polyols, and one or more of m-phenylenediamine, p-phenylenediamine, and 4,4′-diaminodiphenylmethane. A combination of "aliphatic linear diol + a small amount of aromatic chain extender / crosslinking agent" is preferred. This combination utilizes linear aliphatic segments to impart a lower room temperature modulus and good elongation at break to the system, while the benzene ring structure improves the thermal stability and glass transition temperature of the hard segments. This allows the cured adhesive layer to maintain high bulk modulus and shear strength even under high temperature and humid and hot conditions of 60–100°C, and mitigates the risk of stress cracking under thermal cycling conditions.

[0047] In some preferred embodiments, the thermally conductive filler in the above-mentioned thermally conductive structural adhesive is an electrically insulating inorganic thermally conductive filler, including one or more of aluminum hydroxide, alumina, calcium carbonate, silica powder, and / or boron nitride, more preferably a mixture of two or three of aluminum hydroxide, alumina, and calcium carbonate. The total amount of thermally conductive filler is preferably 40%–80% by weight of the cured structural adhesive, more preferably 70%–80%, to ensure that the thermal conductivity of the system is in the range of 0.7–2.0 W / (m·K). To balance high thermal conductivity, low viscosity, and good settling stability, a graded filling method of large-particle-size filler and small-particle-size filler is preferred: large-particle-size filler is used to construct the thermally conductive skeleton and reduce the specific surface area, while small-particle-size filler fills the gaps in the skeleton, improving density and the continuity of the thermal conduction path, thereby increasing the effective filler volume fraction and improving flowability without excessively increasing the system viscosity.

[0048] In some preferred embodiments, the organometallic catalyst in the above-mentioned thermally conductive structural adhesive is selected from one or a combination of organobismuth catalysts, organotin catalysts, organozinc catalysts, and organotitanium catalysts. More preferably, the organometallic catalyst is a bismuth-based or zinc-based environmentally friendly catalyst, such as bismuth neodecanoate, bismuth octanoate, zinc 2-ethylhexanoate, etc., to reduce the potential hazards of organotin to the environment and operators and to reduce the content of volatile organic compounds. More preferably, where the use of organotin is permitted, the organometallic catalyst may also be dibutyltin dilaurate, tin octanoate, or a combination thereof with a bismuth-based catalyst to obtain a higher curing rate.

[0049] In some preferred embodiments, the coupling agent in the above-mentioned thermally conductive structural adhesive is a silane coupling agent, including one or more silanes containing functional groups such as amino, epoxy, methacryloyloxy, or mercapto groups, such as γ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane. The coupling agent, on the one hand, undergoes a condensation reaction with the hydroxyl groups on the surface of the inorganic filler to form an interfacial layer; on the other hand, its organic functional groups can participate in or embed into the polyurethane network, improving the interfacial adhesion between the organic and inorganic phases, reducing interfacial defects and micropores, and thus improving the shear strength, peel strength, and long-term resistance to damp heat of the adhesive layer.

[0050] In some preferred embodiments, the interfacial wetting agent in the above-mentioned thermally conductive structural adhesive is used to improve the wetting, spreading, and dispersion rheological behavior of inorganic thermally conductive fillers in a polyol matrix, thereby adjusting the initial viscosity and shear thinning characteristics of the system. The interfacial wetting agent can be selected from polyether-modified silicone surfactants, polyester-type or polyether-type polymeric dispersants, wetting and leveling agents containing phosphate esters or sulfonates, fluorinated surfactants, and combinations thereof. By introducing an interfacial wetting agent into the polyol / filler system, the surface tension and filler surface energy of the system can be reduced, improving the wetting and spreading of the thermally conductive powder, weakening secondary aggregation between powders, thereby significantly reducing the initial viscosity and low shear viscosity of the system under high filling conditions, reducing shear sensitivity, and improving the flowability and leveling properties during the dispensing process.

[0051] In some preferred embodiments, the thixotropic agent in the above-mentioned thermally conductive structural adhesive is organobentonite or modified fumed silica. The thixotropic agent constructs a reversible three-dimensional network structure in the system, causing the viscosity of the adhesive to decrease under shear conditions, facilitating flow and spreading. During static or curing processes, the viscosity recovers, forming a certain yield value, which helps prevent the adhesive from sagging on vertical surfaces and inhibits the settling of high-density thermally conductive fillers, thus achieving a better balance between workability and storage stability.

[0052] In some preferred embodiments, the dehydrating agent in the above-mentioned thermally conductive structural adhesive can be molecular sieve powder, specific water-absorbing pigments and fillers, or chemical dehydrating agents. These agents reduce the moisture content of the system, decrease the side reactions between isocyanate and water that produce CO2 gas and urea bonds, thereby reducing defects such as bubbles and pinholes, and improving the electrical insulation and mechanical property consistency of the adhesive layer. Depending on the requirements, conventional additives such as flame retardants, defoamers, antioxidants, light stabilizers, and pigments can also be added to the system to meet comprehensive requirements for flame retardancy, safety, weather resistance, and appearance.

[0053] Considering the dismantling and recycling needs of PACKs after the retirement of power lithium batteries, this invention increases the ratio of polycarbonate polyols and bio-based polyols, resulting in a significantly higher density of carbonate bonds and ester groups in the cured adhesive layer compared to traditional polyurethane structural adhesives dominated by inert polyether soft segments. This is more conducive to controlled degradation under controlled conditions. During the retirement stage of the power battery, alcohol / alkanolamine solvents can be selected under medium-temperature conditions, along with alkaline catalysts and / or biocatalysts such as esterases and lipases, to preferentially break the carbonate bonds and some ester bonds in the adhesive layer. This significantly reduces the adhesive layer's bonding strength while the structural components of the PACK, such as cells, casings, and cooling plates, remain largely intact. This facilitates the separation and recycling of each component under relatively mild conditions, providing a feasible technical path for the post-service adhesive layer treatment and green closed-loop management of the power battery system.

[0054] The pot life of components A and B after mixing at 25°C is controlled at 20–60 min, and the preferred mixing viscosity is 10–80 Pa. The adhesive layer should have good flowability and filling properties, as well as sufficient thixotropy to prevent sagging and collapse, under conditions such as automatic dispensing and manual touch-up of power battery packs. The thermal conductivity of the cured adhesive layer is preferably 0.7–2.0 W / (m²). K), with a volume resistivity preferably greater than 1.0 × 10⁻⁶. 14 Ω cm, to balance thermal management efficiency and electrical insulation safety.

[0055] This invention provides a two-component polyurethane thermally conductive structural adhesive and its preparation method. After curing, the thermally conductive structural adhesive exhibits good thermal conductivity and structural adhesion properties, with a preferred thermal conductivity of 0.7–2.0 W / (m²). The adhesive maintains high mechanical property retention and interface reliability (preferably ≥80%) even after 2000 hours of humid heat aging at 85℃ / 85%RH and thermal shock conditions ranging from -40℃ to 100℃. The structural adhesive can be used for thermally conductive bonding and structural fixation between metal and composite material substrates, and is preferably used for thermally conductive bonding and structural fixation between cells and cooling plates, cells and casings, and / or modules in power battery PACKs.

[0056] The two-component polyurethane thermally conductive structural adhesive of this invention is used in power battery packs for thermally conductive bonding and structural fixation between battery cells and cooling plates, battery cells and casings, and / or modules, to achieve a thermal conductivity of 0.7–2.0 W / (m²). While improving thermal conductivity, it also improves the mechanical property retention rate and interface reliability of the bonding interface under 2000h of humid heat aging at 85℃ / 85%RH and thermal shock conditions of −40~100℃.

[0057] This invention also provides a method for preparing the above-mentioned green, high thermal stability, two-component polyurethane thermally conductive structural adhesive for power battery PACK, including but not limited to the following steps: (1) Preparation of polyol mixture: PCE and bio-based polyol are added to a reaction vessel or stirred vessel according to the ratio, stirred evenly, and then dehydrated under reduced pressure or inert gas protection to obtain polyol mixture; (2) Preparation of component A: Thermally conductive filler, coupling agent, interfacial wetting agent, thixotropic agent, dehydrating agent and catalyst are added sequentially to the polyol mixture. The mixture is fully dispersed by high-speed dispersion and other methods, and then degassed under reduced pressure to obtain a uniform and stable component A. (3) Preparation of prepolymer and component B: PCE and high symmetry diisocyanate were added to the reactor in a set ratio and reacted under inert gas protection and controlled temperature. The NCO content was monitored until the target value was reached to obtain NCO-containing prepolymer. Then, thermally conductive filler, dehydrating agent and catalyst were added, dispersed and degassed to obtain component B. (4) Mixing and curing application: When using, mix component A and component B evenly according to the predetermined mass / volume ratio. During the applicable period, apply the mixture to the cells in the power battery PACK, between the cells, between the cells and the shell or cooling system, by dispensing, scraping or potting. Curing is carried out at room temperature or medium temperature to form an integrated structural adhesive layer with thermal conductivity, load-bearing and bonding functions.

[0058] The two-component polyurethane thermally conductive structural adhesive of the present invention is suitable for module or PACK structures composed of power cells of different shapes such as square, cylindrical and pouch, and is especially suitable for bonding and filling between cells and between cells and shell / cooling plate in highly integrated battery packs such as CTP and CTB. It is used to realize multiple functions such as heat conduction, structural load-bearing, flame retardant heat insulation and buffering and vibration reduction, thereby improving the safety and reliability of power battery systems under complex working conditions such as high temperature, high humidity and high vibration.

[0059] The structural adhesive of this invention can cure at room temperature, and the resulting adhesive layer has a thermal conductivity of 0.7–2.0 W / (m²) at 25°C. The aluminum-adhesive-aluminum composite exhibits a room temperature shear strength ≥8 MPa. After 2000 hours of humid heat aging at 85℃ / 85%RH and 2000 cycles of thermal shock at −40~80℃, the shear strength and bulk tensile strength retention rates are significantly higher than the comparative example, with no obvious cracking or peeling at the interface. This invention, through the synergistic design of CO2-derived polycarbonate soft segments, bio-based soft segments, and highly symmetric isocyanate hard segments, achieves high thermal conductivity, high thermal stability, and reliable adhesion under humid heat while increasing the proportion of non-petroleum-based carbon sources. Furthermore, the high carbonate / ester group density in the adhesive layer enables controllable debinding under alcohol / amine-base catalysis and / or enzyme catalysis, which is beneficial for the disassembly and recycling of power battery packs.

[0060] To more clearly demonstrate the technical solution and its effects provided by the present invention, the following detailed description of the low-temperature fast-curing two-component polyurethane structural adhesive provided by the present invention is based on specific embodiments.

[0061] Example 1 This embodiment provides a green, high thermal stability, two-component polyurethane thermally conductive structural adhesive for power battery PACKs, and its preparation method is as follows: (1) Preparation of self-made environmentally friendly polycarbonate diol PCE-1: In a 5L stirred high-pressure reactor that has been dried, 5 parts by mass of glycerol were added as a chain transfer agent, along with 0.05 parts by mass of a bimetallic cyanide catalyst (DMC). After purging with nitrogen three times, a vacuum was created, followed by the introduction of CO2 to 1.0 MPa and the heating to 110°C. While maintaining a reactor temperature of 110–115°C and a reactor pressure of 2.5–3.5 MPa, 100 parts by mass of propylene oxide were continuously fed, with appropriate CO2 replenishment to maintain a relatively stable pressure. The reaction was carried out for 4–6 hours to achieve a propylene oxide conversion rate of over 95%.

[0062] After the reaction is complete, the feed is stopped, and the unreacted CO2 is slowly released by depressurization. The temperature is lowered to below 60°C, and unreacted propylene oxide is removed under reduced pressure at 5–10 kPa until the residual pressure and mass in the reactor are basically stable. The system is cooled to room temperature, and an appropriate amount of dilute acid is added to neutralize the catalyst. After stirring for 30 min, solid impurities are removed by filtration. The filtrate is then vacuum-devoured at 80°C and <1 kPa for 1–2 h to obtain a pale yellow, transparent, viscous liquid, which is the self-made environmentally friendly polycarbonate diol PCE-1.

[0063] Tests showed that PCE-1 had a hydroxyl value of 56 mg KOH / g and a number-average molecular weight M. n With a content of approximately 2000 g / mol, a carbonate unit mass fraction of approximately 30%, a residual propylene oxide monomer content of less than 100 ppm, and a low free VOC content, it is suitable for use as a polyurethane thermally conductive structural adhesive soft segment polyol for power battery PACKs.

[0064] It should be noted that the polycarbonate polyol preparation process of the present invention does not require the use of highly toxic raw materials such as phosgene. CO2 is directly introduced into the main chain carbonate structure as a carbon source. While achieving partial carbon fixation, it has higher atom economy and lower by-product emissions compared with the traditional polyester polyol synthesis route, which meets the requirements of green chemistry.

[0065] (2) Preparation of NCO-containing prepolymer of component B: Considering the poor compatibility and tendency for localized phase separation when the self-made environmentally friendly polycarbonate polyol PCE-1 is directly blended with castor oil-based bio-based polyols at room temperature, this embodiment primarily uses PCE-1 to prepare the NCO-containing prepolymer in component B. Specifically, PCE-1 and the bio-based polyol are used together as polyol components and reacted with isocyanate to obtain the NCO-containing prepolymer, thereby forming a block copolymer between PCE-1 and the bio-based polyol, thus improving the compatibility of PCE-1 and the bio-based polyol in the system.

[0066] (2-1) Preparation of prepolymer P-B1: In a dry, stirred reactor, parts by weight of PCE-168 were added, and the mixture was heated to 70°C under nitrogen protection and stirred until homogeneous. Then, 30 parts by weight of PPDI were slowly added, ensuring the system temperature did not exceed 90°C. The reaction was maintained at 80°C for 2 hours, and the reaction progress was monitored by NCO titration. The reaction was terminated when the NCO mass fraction reached approximately 13.0 wt% and the change within 1 hour did not exceed 0.2 wt%. The temperature was then lowered to approximately 60°C to obtain the NCO-containing prepolymer P-B1.

[0067] P-B1 is a transparent liquid at 60℃, with an NCO mass fraction of approximately 13.0 wt% at 25℃ and a cone-plate viscosity of 10 Pa. s, suitable for the subsequent preparation and viscosity control of component B.

[0068] (3) Preparation of component B: At 50–60°C, add P-B130 by weight to the dispersion vessel, and add the following sequentially under stirring: 50 parts by weight of aluminum hydroxide (D50≈10μm); 10 parts by weight of spherical alumina (D50≈3μm); 10 parts by weight of light calcium carbonate (D50≈2μm); Molecular sieve powder (3A) 1 part by weight; 0.2 parts by mass of bismuth-based catalyst and 0.05 parts by mass of tertiary amine catalyst.

[0069] First, premix the mixture at medium speed for about 15 minutes, then disperse it at medium to high speed for 30 to 45 minutes to fully wet and uniformly disperse the thermally conductive filler. Afterward, transfer the system to a vacuum degassing tank and degas it at 50°C and –0.085 MPa for about 40 minutes to obtain component B-1.

[0070] The viscosity of component B-1 at 25°C and 2 rpm is approximately 220–300 Pa·s.

[0071] (4) Preparation of component A Add the following raw materials to a dispersion vessel equipped with stirring and heating functions: 30 parts by weight of castor oil-modified polyol; PCE-15 parts by weight; 5 parts of chain extender 1,4-butanediol.

[0072] The mixture was stirred and mixed at approximately 60°C, and then dehydrated at -0.09 MPa for about 1 hour to control the moisture content of the mixed polyols to below 0.05 wt%. Considering the general compatibility between PCE-1 and castor oil, the amount of PCE-1 in component A of this embodiment is relatively low. The main component is the castor oil-modified polyol, which provides compliant segments to improve the flexibility and low-temperature performance of the cured adhesive, while avoiding macroscopic phase separation caused by incompatibility between polyols.

[0073] To the above polyol mixture, add the following in sequence: 1 part by weight of γ-glycidoxypropyltrimethoxysilane; 1 part by weight of polyether-modified silicone oil-based interfacial wetting agent; Molecular sieve powder (3A) 1 part by weight; After stirring at medium speed for about 20 minutes, add in batches at 55-65°C: 40 parts by weight of aluminum hydroxide (D50≈10μm); 10 parts by weight of spherical alumina (D50≈5μm); 10 parts by weight of light calcium carbonate (D50≈2μm).

[0074] During the feeding process, control the stirring speed and feeding rate to prevent local agglomeration and excessive temperature rise in the system. After the thermally conductive filler is added, add 2 parts by mass of modified fumed silica as a thixotropic agent and disperse it under medium-high speed dispersion conditions for about 40 minutes.

[0075] Finally, 0.1 parts by mass of bismuth catalyst and 0.03 parts by mass of tertiary amine catalyst were added at around 50℃. After stirring at low speed until homogeneous, the system was transferred to a vacuum degassing tank and degassed for about 40 minutes at 45-55℃ and -0.085--0.095 MPa to obtain component A-1.

[0076] Component A-1 has a viscosity of approximately 180–260 Pa·s at 25°C and 2 rpm, exhibiting significant thixotropy.

[0077] The A component-1 prepared above and the B component-1 prepared in Example 2 were measured at a volume ratio of 1:1 and placed in a planetary mixer. The mixture was stirred at 20–25°C for 3–4 minutes to ensure thorough and uniform mixing, resulting in a two-component polyurethane thermally conductive structural adhesive. This adhesive was applied to a power battery pack, and its performance corresponds to that of Example 1 in Table 1. The pot life of the mixed adhesive at 25°C is approximately 40 minutes, making it suitable for automated dispensing or potting processes on power battery pack production lines.

[0078] Comparative Example 1 Using a conventional aromatic MDI prepolymer system: To investigate the effect of isocyanate structure on the reliability of the adhesive's heat resistance and humid heat resistance, the same polyol system and ratio as in Example 1 were used, except that all PPDI used in the prepolymer preparation was replaced with MDI-100, while the types and amounts of other raw materials remained unchanged, to obtain NCO-containing prepolymer P-B2. Components B and A were then prepared according to the same method as in Example 1 to obtain the structural adhesive of Comparative Example 1, whose performance corresponds to Comparative Example 1 in Table 1.

[0079] Comparative Example 2 Partial alternative systems excluding PCE: To investigate the effect of polycarbonate polyol PCE-1 on the performance of the structural adhesive, the same formulation structure and preparation process as in Example 1 were used. Only the PCE-1 in components A and B were replaced with conventional polyether polyols with similar hydroxyl values. Castor oil-modified polyols, polyester polyols, and PPDI remained unchanged, and the other components and their amounts were kept as consistent as possible. The thermally conductive structural adhesive of Comparative Example 2 was obtained, and its performance corresponds to that of Comparative Example 2 in Table 1.

[0080] Comparative Example 3 PCE-free and using a conventional polyether polyol system: To further compare the differences between the system of this invention and the traditional polyether / MDI system, the same formulation structure and preparation process as in Example 1 were used, except that the polyol system was completely replaced with conventional polyether polyol (hydroxyl value of about 163 mg KOH / g), and PCE-1 and castor oil-based bio-based polyols were not used. At the same time, the diisocyanate in component B was replaced with MDI-100, while the other components and their amounts remained the same, and the thermally conductive structural adhesive of Comparative Example 3 was obtained, with properties corresponding to Comparative Example 3 in Table 1.

[0081] Performance comparison of thermally conductive structural adhesives used in power battery packs: To facilitate a direct understanding of the overall performance of the material system of the present invention by those skilled in the art, the main performance characteristics of Example 1 of the present invention and Comparative Example 1, which does not contain PCE and uses conventional polyether polyols, are listed in Table 1.

[0082] Unless otherwise stated, the performance tests of the products in this manual shall be conducted in accordance with the following methods: (1) Thermal conductivity: The test was conducted at 25°C using the transient planar heat source method (e.g., a Hot Disk thermal conductivity tester) according to ASTM D5470 standard. The specimen was a block specimen, 2–3 mm thick, cast and fully cured with the structural adhesive of this invention. The test results are the average of three parallel tests.

[0083] (2) Tensile shear strength: Aluminum-adhesive-aluminum lap joint specimens were prepared according to GB / T 7124, with an overlap area of ​​12.5 mm × 25 mm and an adhesive layer thickness of approximately 1.0 mm. After curing the specimens at 25°C and 50% relative humidity for 7 days, they were tested on a universal testing machine at a tensile speed of 5 mm / min. The average value of 5 specimens was taken as the shear bond strength.

[0084] (3) Tensile properties of the body: The tensile modulus and elongation at break of the specimen were tested in accordance with GB / T1040. The specimen was a Type II standard dumbbell-shaped specimen cast and cured with the structural adhesive of this invention. The tensile speed was 500 mm / min.

[0085] (4) Damp heat aging performance: The damp heat aging test was conducted in a constant temperature and humidity chamber at 85℃ / 85%RH. Aluminum-adhesive-aluminum lap joint samples cured for 7 days were placed under the above conditions for 2000 hours, then removed and left at room temperature for 24 hours before being tested for shear bond strength using the same method. The shear strength retention rate is the percentage of the shear strength after aging to the shear strength before aging.

[0086] (5) Thermal shock performance: The thermal shock test was cyclically conducted between -40°C and 80°C. The aluminum-adhesive-aluminum samples cured for 7 days were placed in the thermal shock chamber, with each temperature plateau held for 30 minutes and a temperature transition time not exceeding 5 minutes, for a total of 2000 cycles. After the test, the appearance of the samples was inspected, and the shear bond strength was tested according to the aforementioned method to calculate the shear strength retention rate.

[0087] To facilitate a direct understanding of the overall performance of the material system of the present invention by those skilled in the art, the main performance of Example 4 and Comparative Examples 1 to 3 using the technical solution of the present invention is listed in Table 1.

[0088] Table 1 compares the performance of the structural adhesive of the present invention and the comparative structural adhesive under normal temperature, humid heat aging and thermal shock conditions. .

[0089] As can be seen from Table 1 above, the performance comparison between the structural adhesive of the present invention and the structural adhesive of the comparative examples under normal temperature, humid heat aging and thermal shock conditions shows that, under the condition that the thermal conductivity and initial shear strength are basically similar, Example 1 of the present invention is significantly better than Comparative Examples 1 to 3 in terms of humid heat aging retention rate and thermal shock retention rate. This indicates that the introduction of CO2-derived polycarbonate polyol PCE-1 and castor oil bio-based polyol, combined with high symmetry isocyanate to construct soft and hard segment structures, has a significant effect on improving the high temperature and high temperature and high humidity reliability of polyurethane thermally conductive structural adhesive for power battery PACK.

[0090] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims. The information disclosed in the background section is intended only to enhance the understanding of the overall background technology of the present invention and should not be construed as an admission or implication in any way that such information constitutes prior art known to those skilled in the art.

Claims

1. A green, high thermal stability, two-component polyurethane thermally conductive structural adhesive for power battery packs, characterized in that, include: Component A and component B are mixed in a mass ratio of 1:1 to 3, and the NCO:OH equivalent ratio in the mixed system is 0.9:1 to 1.3:1; wherein, Component A comprises the following raw materials in parts by mass: 5 to 30 parts of polycarbonate polyol obtained by ring-opening copolymerization of carbon dioxide and propylene oxide 20-60 parts of bio-based polyols, 1 to 10 parts of chain extender and / or crosslinking agent, 40-80 parts of thermally conductive filler, 0.1 to 10 parts of thixotropic agent, 0.1 to 5 parts of silane coupling agent, 0.1 to 5 parts of interfacial wetting agent, 0.1 to 5 parts of dehydrating agent, Catalyst A: 0.01–3 parts; Component B comprises the following raw materials in parts by mass: 20 to 80 parts of an NCO-containing prepolymer made from a polycarbonate polyol, wherein the polycarbonate polyol is obtained by ring-opening copolymerization of carbon dioxide and propylene oxide. 60-80 parts of thermally conductive filler; 0.01 to 3 parts of catalyst B; 0.1 to 5 parts of dehydrating agent.

2. The green, high thermal stability, two-component polyurethane thermally conductive structural adhesive for power battery PACK according to claim 1, characterized in that, The NCO-containing prepolymer in component B is prepared by reacting polycarbonate polyol with a highly symmetric diisocyanate at an NCO / OH molar ratio of 1.5 to 3.

0. The highly symmetric diisocyanate includes at least one or more of terephthalic diisocyanate, naphthalene diisocyanate, and dimethylbiphenyl diisocyanate, as well as modified or derivative products of any of the above diisocyanates obtained by chemical modification, prepolymerization, end-capping, or substitution.

3. The green, high thermal stability, two-component polyurethane thermally conductive structural adhesive for power battery PACK according to claim 1 or 2, characterized in that, The polycarbonate polyol in component A and the polycarbonate polyol used in the NCO-containing prepolymer in component B have hydroxyl values ​​of 40–80 mg KOH / g and number-average molecular weights of M. n The range is 1000 to 4000.

4. The green, high thermal stability, two-component polyurethane thermally conductive structural adhesive for power battery PACK according to claim 1 or 2, characterized in that, The polycarbonate polyol in component A and the polycarbonate polyol used in the NCO-containing prepolymer in component B are both obtained by ring-opening copolymerization of carbon dioxide and epoxide in the presence of a catalyst, wherein the carbon dioxide content accounts for 20 to 40 wt% of the total mass of the polyol.

5. The green, high thermal stability, two-component polyurethane thermally conductive structural adhesive for power battery PACK according to claim 4, characterized in that, The epoxide is a cyclic ether compound capable of undergoing ring-opening copolymerization with carbon dioxide; The catalyst is a catalytic system capable of catalyzing the ring-opening copolymerization of carbon dioxide and epoxide.

6. The green, high thermal stability, two-component polyurethane thermally conductive structural adhesive for power battery PACK according to claim 5, characterized in that, The epoxide is an aliphatic epoxide and / or its substituted derivatives; The catalyst is one or more of a bimetallic cyanide catalyst, a metal complex catalyst, or an organic catalyst.

7. The green, high thermal stability, two-component polyurethane thermally conductive structural adhesive for power battery PACK according to claim 1 or 2, characterized in that, In component A, the bio-based polyol is castor oil-modified polyol or castor oil-modified polyol. The chain extender is one or more of ethylene glycol, 1,4-butanediol, and 2-methyl-1,3-propanediol; The crosslinking agent is one or more of aliphatic polyamines and alicyclic polyamines; The silane coupling agent is one or a combination of several of γ-glycidoxypropyltrimethoxysilane and aminopropyltriethoxysilane. The thixotropic agent is one or a combination of fumed silica, bentonite, and polyamide wax. The interface wetting agent is one or a combination of polyether modified silicone oil and fluorocarbon surfactant. The thermally conductive fillers in both component A and component B are one or more of aluminum hydroxide, aluminum oxide, calcium carbonate, boron nitride, and aluminum nitride. The dehydrating agents in both component A and component B are one or a combination of 3A molecular sieve powder, 4A molecular sieve powder, and organic dehydrating agents. Catalyst A in component A and catalyst B in component B are both combinations of organometallic catalysts and tertiary amine catalysts. The organometallic catalysts are bismuth-based, zinc-based, or tin-based catalysts; the tertiary amine catalysts are triethylenediamine, bis(dimethylaminoethyl) ether, and their derivatives.

8. A method for preparing a green, high thermal stability, two-component polyurethane thermally conductive structural adhesive for a power battery PACK according to any one of claims 1 to 7, characterized in that, The formulation of the two-component polyurethane thermally conductive structural adhesive according to any one of claims 1-7 comprises taking the raw materials of component A and component B, and including the following steps: Preparation of Component A: The bio-based polyol and polycarbonate polyol in the raw materials of Component A are mixed and dehydrated, and coupling agent, interface wetting agent, thixotropic agent, chain extender and / or crosslinking agent, thermally conductive filler, dehydrating agent and catalyst A are added. Component A is obtained by high-speed dispersion and vacuum degassing. Preparation of component B: The NCO-containing prepolymer, thermally conductive filler, dehydrating agent and catalyst B in the raw materials of component B are mixed, dispersed and degassed under vacuum to obtain component B; The A component and B component prepared above are mixed and used at a mass ratio of 1:1 to 3.

9. The preparation method of the green, high thermal stability, two-component polyurethane thermally conductive structural adhesive for power battery PACK according to claim 8, characterized in that, The NCO-containing prepolymer used in component B is prepared as follows, with each raw material comprising, by mass, parts: Under inert gas protection, polycarbonate polyol is added to highly symmetric diisocyanate and reacted at 60–120 °C, with the NCO / OH molar ratio controlled at 1.5–3.0, to obtain an NCO-containing prepolymer. In the preparation of the polycarbonate multi-component, after the reaction is completed, the process further includes: removing unreacted monomers and low-boiling substances under reduced pressure conditions of 50-100℃ and 5-10kPa, and removing mechanical impurities by filtration; In the steps of preparing component A and component B, the vacuum degassing pressure is -0.08 to -0.095 MPa, and the time is 20 to 60 min.

10. The preparation method of the green, high thermal stability, two-component polyurethane thermally conductive structural adhesive for power battery PACK according to claim 8 or 9, characterized in that, The polycarbonate multi-component used in component A and the polycarbonate multi-component used in the NCO-containing prepolymer in component B are prepared in the following manner, with each raw material comprising, by weight: Initiator polyol and catalyst are added to a reaction vessel equipped with stirring, heating and pressurization functions. After degassing and dehydration under vacuum and nitrogen purging conditions, carbon dioxide is introduced and the temperature and pressure are increased. Epoxide monomer is added dropwise in the presence of carbon dioxide, and the molar ratio of carbon dioxide to epoxide is controlled. Ring-opening copolymerization reaction is carried out at 60-140℃ and 1-5MPa to obtain polycarbonate polyol with a carbon dioxide content of 20-40wt% of polyol mass and a hydroxyl value of 40-80mgKOH / g.