Ultralow-temperature-resistant conductive adhesive and preparation method thereof

Abstract

The invention relates to the technical field of conductive adhesives, in particular to an ultralow-temperature-resistant conductive adhesive and a preparation method thereof.The conductive adhesive is prepared from, by weight, 10-20 parts of epoxy resin composition and 0.5-5 parts of flexible diluent; the conductive adhesive is prepared from the following components in parts by weight: 2-8 parts of a curing agent, 0.5-4 parts of an accelerant, 0.05-0.5 part of an anti-settling agent, 0.05-0.3 part of a coupling agent and 70-85 parts of conductive filler. After being cured, the conductive adhesive provided by the invention is good in conductivity, the resistivity is less than or equal to 5 * 10 <-4 > omega.cm, the conductive adhesive can tolerate ultralow temperature, the adhesive is not fractured after 10 cycles at high and low temperatures of-90 DEG C to 100 DEG C, the shear strength retention rate of the conductive adhesive to metals such as steel and aluminum is more than or equal to 95%, and the conductive adhesive and a metal substrate are not delaminated or cracked.

Description

Technical Field

[0001] The present invention relates to the technical field of conductive adhesives, and in particular to a conductive adhesive resistant to ultra-low temperature and a preparation method thereof. Background Art

[0002] At present, in the fields of aviation, aerospace, unmanned aerial vehicles, special military industries, etc., the conductive bonding, fixing, wiring, etc. of some electronic components are realized by using conductive adhesives. These components may face extremely low-temperature environments during use, which pose extremely high requirements for the stability and reliability of component performance. The conductive adhesive that plays the role of conductive bonding, fixing, and wiring plays a decisive role in ensuring the working stability and reliability of related components. At present, the conductive adhesives on the market mainly focus on conductivity, adhesiveness, high-temperature resistance performance, etc., but there is a significant lack of attention to low-temperature resistance. The low-temperature resistance range of most conductive silver adhesives is between -40°C and -50°C. When facing extremely low-temperature environments, such as use environments below -50°C, the commercially available conductive adhesives are very likely to have problems such as adhesive layer fracture, adhesive peeling, fixing failure, etc., thus affecting the signal transmission stability and reliability of components and bringing great risks to the reliability of components used in special fields. In order to solve the problems caused by insufficient low-temperature resistance of conductive adhesives in extremely low-temperature environments in special fields, it is very necessary to develop a conductive adhesive resistant to ultra-low temperature. Summary of the Invention

[0003] In order to solve the above technical problems, the present invention adopts the following technical solutions: The purpose of the present application is to provide a conductive adhesive resistant to ultra-low temperature and a preparation method thereof, which has the advantages of maintaining adhesive stability and conductive reliability in extremely low-temperature environments.

[0004] The present application provides a conductive adhesive resistant to ultra-low temperature, and the technical solution is as follows: The conductive adhesive, by weight, is composed of the following components: epoxy resin composition: 10 - 20 parts, flexible diluent: 0.5 - 5 parts; curing agent: 2 - 8 parts, accelerator: 0.5 - 4 parts, anti-settling agent: 0.05 - 0.5 parts, coupling agent: 0.05 - 0.3 parts, conductive filler: 70 - 85 parts. After the conductive adhesive is cured, the resistivity ≤ 5 * 10 -4 Ω.cm. After 10 high-low temperature cycles from -90°C to 100°C, the colloid does not break, the shear strength retention rate for metals such as steel and aluminum is ≥ 95%, and there is no delamination or cracking with the metal substrate.

[0005] Further, the present application also proposes that the epoxy resin composition is composed of a low-viscosity bisphenol F-type epoxy resin and a modified epoxy resin, and the proportion of the modified epoxy resin is not less than 50% of the total weight of the epoxy resin composition.

[0006] Further, the present application also proposes that the modified epoxy resin includes one or more compositions of polyether-modified epoxy resin, polyurethane-modified epoxy resin, dimer acid-modified epoxy resin, butadiene rubber-modified epoxy resin, and styrene-butadiene rubber-modified epoxy resin.

[0007] Further, the present application also proposes that the flexible diluent is one or more compositions of 1,4-butanediol diglycidyl ether, polypropylene glycol diglycidyl ether, and neopentyl glycol diglycidyl ether.

[0008] Further, the present application also proposes that the curing agent is dicyandiamide with a particle size ≤ 10 microns.

[0009] Further, the present application also proposes that the accelerator is one or more compositions of latent imidazole adducts, latent tertiary amines, and organic urea accelerators.

[0010] Further, the present application also proposes that the anti-settling agent is fumed silica.

[0011] Further, the present application also proposes that the coupling agent is KH560.

[0012] Further, the present application also proposes that the conductive filler is one or more compositions of silver powder, copper powder, nickel powder, silver-plated copper powder, silver-plated nickel powder, and silver-plated glass powder with an average particle size of 1.5 - 10 μm.

[0013] Further, the present application also proposes that the preparation method includes the following steps: Step 1: Disperse the epoxy resin composition, flexible diluent, curing agent, accelerator, anti-settling agent, and coupling agent evenly through a planetary degassing and dispersing machine; Step 2: Add the conductive filler to the materials obtained in Step 1 and then continue to disperse evenly through the planetary degassing and dispersing machine; Step 3: Pass the materials obtained in Step 2 through a three-roll mill to obtain the ground materials; Step 4: Vacuumize and disperse the ground materials obtained in Step 3 evenly to obtain the conductive adhesive.

[0014] As can be seen from the above, a super-low-temperature-resistant conductive adhesive and its preparation method provided by the present application, through the synergistic effect of components such as a specific proportion of epoxy resin composition, flexible diluent, and curing agent, combined with the optimized selection of conductive fillers, significantly improve the anti-cracking property and bonding stability of the conductive adhesive in a super-low-temperature environment, and have the advantages of maintaining conductive performance and bonding reliability under extremely low-temperature conditions. Detailed Embodiments

[0015] The technical solutions in this application will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of this application, rather than all the embodiments. The components of this application usually described and illustrated here can be designed in various different configurations. Therefore, the detailed description of the embodiments of this application provided below is not intended to limit the scope of this application claimed, but only represents the selected embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative efforts fall within the scope of protection of this application.

[0016] In the prior art, the conductive adhesive materials for electronic components in the fields of aviation, aerospace and special military industries have long faced reliability challenges in extremely low temperature environments. Conventional conductive adhesives are prone to brittle cracking of the adhesive layer and interfacial peeling at temperatures below -50°C, resulting in signal transmission failure. When a certain type of high-precision satellite navigation module operates in a liquid hydrogen storage tank, the connection points of its radio frequency circuit are fractured due to the stress concentration caused by the low-temperature shrinkage of the conductive adhesive, resulting in positioning signal drift.

[0017] To solve the above problems, the inventors of this application found that the insufficient low-temperature toughness of the resin matrix of conventional conductive adhesives and the uneven dispersion of fillers jointly lead to structural failure. By analyzing the distribution law of thermal stress, an idea of optimizing the synergistic effect of resin flexibility and filler network while maintaining the conductive performance was proposed. Based on the low-temperature toughening mechanism of polymer materials, a solution of using a composite resin system and a gradient filler distribution was determined.

[0018] Therefore, this application proposes a super low-temperature resistant conductive adhesive, the composition of which contains by weight: 10-20 parts of epoxy resin composition, 0.5-5 parts of flexible diluent, 2-8 parts of curing agent, 0.5-4 parts of accelerator, 0.05-0.5 parts of anti-settling agent, 0.05-0.3 parts of coupling agent, 70-85 parts of conductive filler. After the conductive adhesive is cured, the resistivity ≤ 5*10-4Ω.cm. After 10 cycles of high and low temperature cycling from -90°C to 100°C, the colloid does not crack, the shear strength retention rate for metals such as steel and aluminum is ≥ 95%, and there will be no delamination or cracking with the metal substrate.

[0019] Among them, the epoxy resin composition refers to the base polymer that forms a three-dimensional network structure. A composite system of bisphenol F type epoxy resin and modified epoxy resin can be adopted to improve the low-temperature impact resistance by adjusting the flexibility of the molecular chain. The flexible diluent refers to the active component that reduces the viscosity of the system. For example, 1,4-butanediol diglycidyl ether can increase the movement ability of the molecular chain segments and thus improve the low-temperature ductility. The curing agent refers to the substance that initiates the cross-linking reaction of the resin. For example, micron-sized dicyandiamide, and the control of its particle size is beneficial to uniform curing under low-temperature conditions. The accelerator refers to the substance that accelerates the curing reaction. For example, the latent imidazole adduct can maintain an appropriate reaction rate under low-temperature conditions. The anti-settling agent refers to the rheological aid that prevents the settlement of the filler. For example, fumed silica can maintain the dispersion stability of the filler by forming a thixotropic structure. The coupling agent refers to the aid that improves the interfacial bonding between the filler and the resin. For example, KH560 silane coupling agent can enhance the interfacial bonding strength under low-temperature thermal stress. The conductive filler refers to the metal particles that establish the conductive path. For example, silver-plated copper powder can form a stable three-dimensional conductive network by optimizing the particle size distribution.

[0020] Specifically, the epoxy resin composition forms a matrix structure with moderate rigidity and flexibility at a specific ratio, which not only ensures the bonding strength but also avoids low-temperature embrittlement. The flexible diluent reduces the glass transition temperature by adjusting the movement ability of the molecular chain and forms an interpenetrating network structure with the resin. The synergistic effect of the curing agent and the accelerator ensures the complete curing reaction under low-temperature conditions and forms a dense cross-linked structure. The anti-settling agent and the coupling agent work together to maintain the uniform dispersion of the filler and strengthen the interfacial bonding, preventing the destruction of the conductive network caused by low-temperature shrinkage. The high proportion filling of the conductive filler forms a stable structure with interlocking through particle size grading while ensuring the electrical conductivity, effectively dispersing the internal stress generated by temperature changes.

[0021] Compared with the prior art, the conventional conductive adhesive uses a single resin system and has a low filler content, making it difficult to balance electrical conductivity and low-temperature toughness. This solution significantly improves the structural stability under low-temperature environments while maintaining the electrical conductivity through the synergistic toughening of the composite resin and the flexible diluent, combined with the three-dimensional network structure of the highly filled conductive filler. The prior art relies on increasing plasticizers to improve low-temperature performance but results in a decrease in strength. This solution achieves performance balance through the synergistic effect of multiple components. Through the above technical solutions, this application effectively solves the problem of the structural failure of the conductive adhesive under extreme low temperatures.

[0022] This application further proposes that the epoxy resin composition is composed of low-viscosity bisphenol F type epoxy resin and modified epoxy resin, where the proportion of the modified epoxy resin is not less than 50% of the total weight of the epoxy resin composition.

[0023] Among them, the low-viscosity bisphenol F epoxy resin refers to a liquid resin with a viscosity lower than that of conventional epoxy resins. Specifically, the low-viscosity bisphenol F epoxy resin can be achieved by optimizing the molecular structure of bisphenol F epoxy resin. This resin plays a role in reducing the overall viscosity of the system, promoting the uniform dispersion of conductive fillers, and maintaining the fluidity of the resin matrix in a low-temperature environment. Among them, the modified epoxy resin refers to an epoxy resin into which flexible segments are introduced by chemical grafting or physical blending methods. Specifically, polyether, polyurethane, dimer acid, or rubber-modified epoxy resins can be used. By introducing flexible segments, this resin increases the movement ability of molecular segments, improves the brittleness of epoxy resin at low temperatures, and thus alleviates the cracking of the adhesive layer caused by low-temperature shrinkage stress.

[0024] Specifically, the synergistic combination of the low-viscosity bisphenol F epoxy resin and the modified epoxy resin strengthens the flexibility of the resin matrix by more than 50% of the proportion of the modified epoxy resin while maintaining the inherent bonding strength of the epoxy resin. The low-viscosity resin ensures the uniform dispersion of conductive fillers and avoids local stress concentration caused by filler agglomeration; the high proportion of modified resin absorbs shrinkage stress at low temperatures through flexible segments and inhibits crack propagation. The combination of the two enables the conductive adhesive to maintain structural integrity in an ultra-low-temperature environment and resist internal stress damage through the deformation ability of molecular segments.

[0025] Compared with the prior art, traditional conductive adhesives mostly use a single epoxy resin or a formulation with insufficient amount of modifier, and the resin matrix is too rigid at low temperatures to adapt to the volume change caused by sudden temperature changes. However, in this solution, by introducing a high proportion of flexible modified resin, the epoxy resin composition has deformation characteristics similar to those of an elastomer at low temperatures, fundamentally avoiding the problem of low-temperature brittleness.

[0026] Through the above technical solution, this application effectively solves the problems of adhesive layer fracture and bonding failure caused by insufficient flexibility of the resin matrix of the conductive adhesive in an extremely low-temperature environment, ensuring that the conductive adhesive can still maintain stable conductive performance and mechanical strength in an environment below -50°C.

[0027] This application further proposes an implementation scheme of using one or more compositions of polyether-modified epoxy resin, polyurethane-modified epoxy resin, dimer acid-modified epoxy resin, butadiene rubber-modified epoxy resin, or styrene-butadiene rubber-modified epoxy resin as the modified epoxy resin.

[0028] Among them, polyether-modified epoxy resin refers to epoxy resin graft-modified by polyether chain segments, which can be specifically achieved by the condensation reaction of polypropylene oxide ether and epoxy resin. The polyether chain segments endow the material with the ability of chain segment movement at low temperatures; polyurethane-modified epoxy resin refers to the product obtained by the reaction of a polyurethane prepolymer and epoxy resin, which can be specifically achieved by the reaction of a polyurethane prepolymer capped with isocyanate and the hydroxyl groups of epoxy resin. The polyurethane chain segments enhance the intermolecular force through hydrogen bonding; dimer acid-modified epoxy resin refers to epoxy resin modified with dimer fatty acid as a toughening agent, which can be specifically achieved by the esterification reaction of dimer fatty acid and epoxy resin. The long-chain fatty acid structure reduces the crystallization tendency of the material; butadiene rubber-modified epoxy resin refers to epoxy resin modified by blending with butadiene rubber particles, which can be specifically achieved by the graft reaction of carboxy nitrile rubber and epoxy resin. The rubber phase provides the ability of elastic deformation; styrene-butadiene rubber-modified epoxy resin refers to epoxy resin modified by a styrene-butadiene rubber copolymer, which can be specifically achieved by the condensation reaction of hydroxy styrene-butadiene rubber and epoxy resin. The styrene chain segments enhance the interfacial bonding force.

[0029] Specifically, the polyether chain segments keep the resin matrix active at low temperatures by reducing the glass transition temperature, avoiding brittle fracture; the hydrogen bond network formed by the polyurethane chain segments maintains the mechanical strength at low temperatures; the long fatty chains of dimer acid interfere with the regular arrangement of molecules, reducing the crystallinity to relieve the volume shrinkage stress; the rubber phase absorbs the internal stress generated by the difference in thermal expansion coefficients through elastic deformation. Different modification mechanisms form a synergistic effect: polyether and polyurethane modifications improve toughness from the dimensions of chain segment flexibility and intermolecular force respectively, dimer acid modification improves stability from the phase structure dimension, and rubber modification enhances the anti-cracking property through the energy dissipation mechanism. Multiple action paths jointly ensure the structural integrity of the modified epoxy resin in an ultra-low temperature environment.

[0030] Compared with the prior art, traditional conductive adhesives mostly adopt a single toughening and modification method, such as only adding rubber particles or introducing flexible chain segments, which are prone to interface peeling between the modified phase and the resin matrix or the failure of a single toughening mechanism at extremely low temperatures. This solution forms a multi-level anti-cracking system by the organic combination of different modification mechanisms, enabling each component to play a role in the dimensions of molecular chain mobility, crystallization inhibition, stress dispersion, etc.

[0031] Through the above technical solution, this application effectively prevents the cracking of the adhesive layer caused by the embrittlement of the resin matrix of the conductive adhesive in an environment below -50°C, ensures the continuity of the conductive filler network under low-temperature shrinkage stress, and maintains the stability of the conductive path. At the same time, through the synergistic effect of different modified phases, it avoids the decrease in bonding strength caused by the excessive addition of a single toughening agent, and realizes that the bonding strength retention rate exceeds 95% in an extremely low temperature environment.

[0032] The present application further proposes that the flexible diluent is one or a combination of two or more of 1,4 - butanediol diglycidyl ether, polypropylene glycol diglycidyl ether, and neopentyl glycol diglycidyl ether.

[0033] Among them, 1,4 - butanediol diglycidyl ether refers to a glycidyl ether compound with a long - chain alkyl structure. The flexibility of its molecular chain can maintain the movement ability of molecular segments in a low - temperature environment. Specifically, it can be achieved by using a liquid product with an industrial - grade purity of ≥99%. This structure helps to relieve the low - temperature shrinkage stress. Polypropylene glycol diglycidyl ether refers to a polyether - type glycidyl ether with an ether bond in the main chain. Specifically, it can be achieved by using a liquid product with a molecular weight range of 200 - 600. The flexibility of the ether bond can maintain the conformational adjustment ability of the molecular chain at low temperatures. Neopentyl glycol diglycidyl ether refers to a glycidyl ether with a highly branched structure. Specifically, it can be obtained by reacting neopentyl glycol with epichlorohydrin. Its steric hindrance effect can inhibit the regular arrangement of molecular chains and reduce the crystallization tendency.

[0034] Specifically, in an extremely low - temperature environment below - 50°C, the long - chain structure of 1,4 - butanediol diglycidyl ether absorbs shrinkage stress through the bending deformation of the molecular chain. The ether bond of polypropylene glycol diglycidyl ether enables the molecular segments to still have rotational freedom. And the branched structure of neopentyl glycol diglycidyl ether maintains the colloidal amorphous state by hindering the formation of the crystal lattice. When the three are combined in a specific ratio, for example, mixed in a mass ratio of 1:2:1, the synergistic effect of the molecular chains can form an interpenetrating network structure, and local stress can be dispersed through the differential deformation of different segments during the rapid temperature drop. This dynamic adjustment mechanism enables the colloid to still maintain the interfacial adhesion strength after multiple thermal cycles and avoids interlayer peeling caused by low - temperature embrittlement.

[0035] Compared with the prior art, the monofunctional diluent such as phenyl glycidyl ether used in traditional conductive adhesives has a rigid aromatic ring structure that easily causes the freezing of molecular segments at low temperatures. However, the multifunctional flexible diluent selected in this solution, through molecular structure design, while maintaining the reaction activity of the epoxy system, introduces alkyl chains, ether bonds, and branched groups, making the cured cross - linked network have a controllable elastic modulus. For example, the ether oxygen atoms of polypropylene glycol diglycidyl ether can form hydrogen bonds with the hydroxyl groups of epoxy resin and still maintain the dynamic balance of intermolecular forces at low temperatures.

[0036] Through the above technical solution, the present application effectively improves the impact resistance of the conductive adhesive at extremely low temperatures. After the conductive adhesive is cured, the resistivity ≤ 5×10⁻⁴ Ω·cm. After 10 high and low temperature cycles from -90°C to 100°C, the colloid does not break, the shear strength retention rate for metals such as steel and aluminum is ≥ 95%, and there is no delamination or cracking with the metal substrate. By regulating the ratio of different flexible diluents, the elastic deformation ability of the colloid can be maintained within the temperature range of -90°C to 100°C, avoiding the interface cracking between silver powder and resin matrix caused by the difference in thermal expansion coefficient.

[0037] The present application further proposes that the curing agent is dicyandiamide with a particle size not exceeding 10 microns.

[0038] Among them, dicyandiamide refers to a latent curing agent, which realizes crosslinking curing through the reaction of amino groups with epoxy groups. Specifically, it can be in the form of micron-sized powder and is uniformly distributed through dispersion in the epoxy resin system. Among them, the particle size not exceeding 10 microns means that the maximum size of the curing agent particles is limited within this numerical range, which can be specifically realized through air flow pulverization or classification screening process. By controlling the particle size, the specific surface area is increased, thereby improving the curing reaction efficiency.

[0039] Specifically, in an ultra-low temperature environment, the particle size control of dicyandiamide enables it to form a uniform dispersion state in the epoxy resin system, avoiding incomplete local curing caused by particle agglomeration. The smaller particle size increases the contact area between the particles and the resin, accelerating the kinetic process of the curing reaction under low temperature conditions and promoting the formation of a crosslinked network structure. At the same time, as a latent curing agent, dicyandiamide remains inert at room temperature and starts the reaction through an activation mechanism during the low temperature curing process, maintaining both storage stability and ensuring sufficient curing under extreme low temperature conditions.

[0040] Compared with the prior art, large particle size curing agents or non-latent curing systems are used in traditional conductive adhesives, which are prone to problems such as uneven dispersion and reaction lag in an ultra-low temperature environment, resulting in insufficient crosslinking density of the adhesive layer. However, in this solution, by limiting the particle size of dicyandiamide, on the basis of maintaining storage stability, the dispersion uniformity and low temperature reaction activity are significantly improved, enabling the curing reaction to be efficiently completed under cryogenic conditions.

[0041] Through the above technical solution, the present application effectively solves the problems of poor structural stability and insufficient curing of the adhesive layer caused by insufficient dispersibility or low reaction efficiency of the curing agent in the conductive adhesive under ultra-low temperature environment, ensuring that the conductive adhesive forms a dense crosslinked structure under extreme low temperature conditions and avoiding adhesive layer fracture or bonding failure.

[0042] The present application further proposes that the accelerator is one or a combination of two or more of a latent imidazole adduct, a latent tertiary amine, and an organic urea accelerator.

[0043] Among them, the latent imidazole adduct refers to a substance that remains chemically inert at room temperature and releases active components when heated to trigger the crosslinking reaction of epoxy resin. Specifically, it can be achieved by using imidazole derivatives with thermal decomposition characteristics, and the balance between low-temperature storage stability and high-temperature reaction activity is achieved by controlling the protecting groups in the molecular structure. The latent tertiary amine refers to an amine compound that realizes temperature-responsive activation characteristics through physical or chemical coating means. Specifically, it can be achieved by using microencapsulated aliphatic amine substances, and releases active components to initiate the curing reaction when reaching a specific temperature. The organic urea accelerator refers to a catalytic substance containing a urea group structure. Specifically, it can be achieved by using substituted phenylurea derivatives, and reduces the reaction activation energy by forming hydrogen bonds with the dicyandiamide curing agent.

[0044] Specifically, the latent imidazole adduct maintains the integrity of the molecular structure when the triggering temperature is not reached, avoiding premature curing reactions in low-temperature environments. When the temperature rises to the curing condition, the protecting groups in its molecular chain break to release the active imidazole structure, accelerating the ring-opening reaction of epoxy groups. The latent tertiary amine realizes the physical isolation of active components through microcapsule coating technology, maintaining chemical inertness in ultra-low temperature environments. When the temperature rises to the melting point of the coating material, amine substances are released to catalyze the nucleophilic addition reaction of epoxy resin and curing agent. The organic urea accelerator forms a stable complex with dicyandiamide at room temperature and gradually dissociates into urea catalytic components during heating, synergistically acting with the cyanide groups generated by the decomposition of dicyandiamide to promote the formation of a crosslinked network. When the three components are used alone or in combination, the reaction inertness of the system can be maintained at low temperatures, and the dynamic regulation of the curing rate can be achieved through multiple catalytic paths during heating.

[0045] Compared with the prior art, the single accelerator system used in conventional conductive adhesives is prone to premature activation of the curing agent or reaction inhibition in extremely low-temperature environments, resulting in an uncontrollable curing process. However, through the combination of multiple latent mechanisms in this solution, not only the accidental consumption of active components during low-temperature storage is avoided, but also a multi-stage catalytic effect can be formed through the stepwise activation of accelerators at different temperature response points during the curing stage, ensuring that the crosslinking reaction is fully completed within the set temperature window.

[0046] Through the above technical solution, this application realizes the controllable curing behavior of the conductive adhesive in the wide temperature range of -90°C to 100°C, maintains the chemical stability of the material under extremely low-temperature conditions, and forms a dense three-dimensional crosslinked network structure during heat curing, effectively preventing the attenuation of bonding strength and the interfacial debonding of conductive fillers caused by incomplete curing.

[0047] This application further proposes that the anti-settling agent is fumed silica.

[0048] Among them, fumed silica refers to nano-sized silicon dioxide particles prepared by the vapor phase method. Its particle size range can be 1 - 50 nanometers, and its specific surface area range can be 100 - 400 square meters per gram. Specifically, hydrophobic fumed silica can be used to achieve this, such as silica treated with silane on the surface. This material forms a three-dimensional network structure through hydrogen bonding in the conductive adhesive system, adsorbing and fixing the conductive filler particles and inhibiting gravitational settlement.

[0049] Specifically, after the nano-sized particles of fumed silica are uniformly dispersed in the epoxy resin matrix, the silanol groups on its surface form physical cross-linking points with the resin molecular chains, constructing a steric hindrance effect. In an ultra-low temperature environment, this three-dimensional network structure still maintains sufficient mechanical strength, effectively restricting the displacement of the conductive filler. The thixotropic property enables the colloid to exhibit fluidity under the action of shear force and quickly recover its structural strength after the shear stops, ensuring uniform distribution of the filler before curing.

[0050] Compared with the prior art, traditional conductive adhesives mostly use organic bentonite or polyethylene wax as anti-settling agents. Such materials are prone to volume shrinkage or crystallization below -50°C, resulting in the destruction of the network structure. However, the inorganic property of fumed silica enables it to maintain chemical stability even at -90°C, and the temperature adaptability of its network structure is significantly better than that of organic anti-settling materials.

[0051] Through the above technical solution, this application effectively prevents the settlement and stratification of the conductive filler during the storage period and the curing process, avoids the breakage of local conductive paths caused by uneven distribution of the filler, ensures uniform stress distribution inside the adhesive layer in an ultra-low temperature environment, and maintains the interfacial bonding strength and electrical signal transmission stability of the conductive adhesive.

[0052] This application further proposes that the coupling agent is KH560.

[0053] Among them, KH560 refers to a silane coupling agent containing an epoxy group. Specifically, γ-glycidoxypropyltrimethoxysilane can be used to achieve this. Its siloxane group forms a covalent bond with the hydroxyl groups on the surface of the conductive filler through hydrolysis, while the epoxy group undergoes a ring-opening reaction with the epoxy group of the epoxy resin, thereby establishing a chemical bond bridge at the interface between the filler and the resin and enhancing the interfacial bonding strength.

[0054] Specifically, under ultra-low temperature conditions, the difference in shrinkage rates between the matrix and the filler will cause interfacial stress concentration. Through the chemical bond bridging effect of KH560, the interfacial bonding force is strengthened, which can effectively inhibit the stress release caused by low-temperature shrinkage. The active groups at both ends of the coupling agent molecule match the characteristics of the filler surface and the resin matrix respectively. For example, the siloxane group preferentially adsorbs on the surface of the metal filler to form a stable bonding layer, while the epoxy group forms a covalent connection with the cross-linked network of the resin matrix, thereby reducing the interfacial defects between the filler and the matrix and avoiding crack propagation or delamination phenomena.

[0055] Compared with the prior art, conventional conductive adhesives mostly use amino silane or mercapto silane coupling agents, such as KH550 or KH570. Their amino or mercapto groups have low compatibility with epoxy resins and cannot fully participate in the resin curing reaction. The epoxy group of KH560 has chemical homology with the resin matrix and can be deeply embedded in the resin cross-linking network to form a more uniform interfacial transition layer, thus maintaining the interfacial bonding stability at low temperatures.

[0056] Through the above technical solution, the present application solves the problems of adhesive layer cracking or conductive path failure caused by insufficient interfacial bonding force between the conductive filler and the resin matrix in an ultra-low temperature environment, ensuring that the conductive adhesive can still maintain stable bonding strength and conductive performance under extreme low temperature conditions.

[0057] The present application further proposes that the conductive filler is one or a combination of two or more of silver powder, copper powder, nickel powder, silver-plated copper powder, silver-plated nickel powder, and silver-plated glass powder with an average particle size of 1.5 - 10 μm.

[0058] Among them, an average particle size of 1.5 - 10 μm refers to the particle diameter distribution range of the conductive filler, which can be specifically controlled by screening method or laser particle size analysis method. This range can balance the dispersion uniformity and interfacial bonding strength. Silver powder, copper powder, and nickel powder refer to metal-based conductive materials, which can be specifically prepared by chemical reduction method or atomization method for forming continuous conductive paths. Silver-plated copper powder and silver-plated nickel powder refer to silver layers coated on the surface of copper or nickel particles, which can be specifically realized by electroless plating or electroplating processes to protect the base metal from oxidation at low temperatures through the silver layer. Silver-plated glass powder refers to silver layers coated on the surface of glass microspheres, which can be specifically prepared by vacuum evaporation or electroless plating processes, and uses the thermal expansion matching of the glass matrix and the resin to reduce interfacial stress.

[0059] Specifically, by controlling the particle size range of the conductive filler, the agglomeration caused by too small particles and the increase in contact resistance are avoided, and at the same time, stress concentration caused by too large particles during low-temperature shrinkage is prevented. Silver, copper, and nickel metal powders provide basic conductivity, while the silver-plated layer inhibits the oxidation of the base metal at low temperatures to maintain the stability of the conductive path. The introduction of silver-plated glass powder utilizes the similar thermal expansion coefficients of the glass matrix and epoxy resin to reduce the risk of interfacial peeling during temperature changes. By adopting a combination method of single or composite conductive fillers, the conductive network density is improved through the grading filling of particles with different particle sizes, and at the same time, the synergistic effect of metal and non-metal materials is used to balance the conductive performance and cold brittleness resistance.

[0060] In some specific embodiments, the silver-plated copper powder and the silver-plated glass powder are mixed at a mass ratio of 3:1, and the average particle size is controlled within the range of 2 - 5 μm. After being dispersed by a three-roll mill, a uniformly distributed conductive network is formed.

[0061] Compared with the prior art, most existing conductive adhesives use a single metal filler and do not control the particle size range, which easily leads to the breakage of the conductive path due to oxidation or thermal mismatch at low temperatures. Through the composite conductive filler system and particle size optimization, this solution not only ensures the continuity of the conductive network but also suppresses low-temperature interface failure through coating protection and thermal expansion matching design.

[0062] Through the above technical solution, this application solves the problem of the decline in conductive performance of conductive fillers due to oxidation, stress concentration, or interface peeling in an ultra-low temperature environment, prevents the fracture of the adhesive layer and the detachment of bonding, and ensures the stability of the conductive path and the structural reliability of the bonding interface under extreme low-temperature conditions.

[0063] This application further proposes a preparation method for an ultra-low temperature resistant conductive adhesive, including the following steps: dispersing an epoxy resin composition, a flexible diluent, a curing agent, an accelerator, an anti-settling agent, and a coupling agent evenly through a planetary degassing and dispersing machine; adding a conductive filler to the materials after completing this step and continuing to disperse evenly through a planetary degassing and dispersing machine; grinding the mixed materials through a three-roll grinder to obtain ground materials; and subjecting the ground materials to vacuum dispersion to prepare the conductive adhesive.

[0064] Among them, the planetary degassing and dispersing machine refers to a device that realizes the dispersion of materials through the centrifugal force and shear force generated by the synchronous rotation of self-rotation and revolution. Specifically, it can be realized by a double-shaft stirring device with a vacuum degassing function, which is used to eliminate bubbles and ensure the uniform mixing of the matrix material. The three-roll grinder refers to a grinding device composed of three horizontal rollers. Specifically, it can be realized by a metal roller structure with adjustable roller surface spacing, which is used for high-precision dispersion of conductive fillers and resin matrices. Vacuum dispersion refers to a process of stirring and degassing materials in a negative pressure environment. Specifically, it can be realized by a vacuum planetary mixer or a vacuum kneader, which is used to remove residual micro-bubbles inside the colloid.

[0065] Specifically, the epoxy resin composition and additives are first pre-dispersed in a planetary degassing and dispersing machine, and the agglomeration of materials is broken and bubbles are excluded through the synergistic action of centrifugal force and shear force. The conductive filler is added in stages after the matrix is evenly mixed, and the secondary dispersion of the same device is used to avoid the aggregation of the filler caused by premature addition. The roller gap of the three-roll grinder exerts a shearing and extrusion effect on the conductive particles, reducing the particle size difference and eliminating the interfacial voids between the resin and the filler. The vacuum dispersion process removes the residual gas inside the colloid in the final stage, forming a defect-free dense conductive network.

[0066] Compared with the prior art, the conventional method for preparing conductive adhesives usually adopts a one-time mixing or simple stirring process, resulting in uneven dispersion of fillers and insufficient interfacial bonding strength. In contrast, the present method controls the addition sequence and dispersion intensity of conductive fillers through a step-by-step mixing and multi-stage dispersion process to ensure the formation of a three-dimensional continuous structure in the resin matrix. The combined process of three-roll grinding and vacuum dispersion is not adopted in the prior art, which cannot effectively eliminate microbubbles and interfacial defects, leading to cracks in the colloid during ultra-low temperature shrinkage.

[0067] Through the above technical solutions, this application solves the problem of bonding failure caused by the fracture of the adhesive layer of the conductive adhesive in an extremely low-temperature environment. Through the staged dispersion and vacuum treatment process, it ensures the formation of a uniform and continuous network structure of conductive fillers in the resin matrix, avoiding the fracture of the conductive path during low-temperature shrinkage. The combination of the grinding and degassing processes improves the density of the adhesive layer and enhances the interfacial bonding strength between the filler and the resin, thereby maintaining the mechanical strength and electrical signal transmission stability of the conductive adhesive in an ultra-low temperature environment.

[0068] As a specific implementation example, Example 1: A conductive adhesive resistant to ultra-low temperatures, by weight, its composition is as follows: epoxy resin composition: 10 parts, flexible diluent: 0.5 part; curing agent: 3 parts, accelerator: 1 part, anti-settling agent: 0.05 part, coupling agent: 0.05 part, conductive filler: 80 parts. The specific preparation method is as follows: Step 1, disperse evenly 10 parts of epoxy resin composition (the ratio of low-viscosity bisphenol F-type epoxy resin to modified epoxy resin is 50:50), 0.5 part of 1,4-butanediol diglycidyl ether, 3 parts of dicyandiamide, 1 part of accelerator, 0.05 part of anti-settling agent; 0.05 part of coupling agent; through a planetary degassing and dispersing machine; Step 2, add 80 parts of conductive filler to the materials completed in Step 1, and then continue to disperse evenly through a planetary degassing and dispersing machine; Step 3, obtain the ground materials by passing the materials completed in Step 2 through a three-roll grinder; Step 4, evacuate and disperse the ground materials completed in Step 3 evenly to obtain the conductive adhesive. Example 2:

[0069] A conductive adhesive resistant to ultra-low temperatures, by weight, its composition is as follows: epoxy resin composition: 15 parts, flexible diluent: 2 parts; curing agent: 8 parts, accelerator: 0.5 part, anti-settling agent: 0.3 part, coupling agent: 0.1 part, conductive filler: 80 parts. The specific preparation method is as follows: Step 1: Take 15 parts of epoxy resin composition (the ratio of low-viscosity bisphenol F epoxy resin to modified epoxy resin is 50:50), 2 parts of 1,4-butanediol diglycidyl ether, 8 parts of dicyandiamide, 0.5 part of accelerator, 0.3 part of anti-settling agent, and 0.1 part of coupling agent. Disperse them evenly through a planetary degassing and dispersing machine. Step 2: Add 80 parts of conductive filler to the materials obtained in Step 1, and then continue to disperse them evenly through a planetary degassing and dispersing machine. Step 3: Pass the materials obtained in Step 2 through a three-roll grinder to obtain ground materials. Step 4: Vacuumize and disperse the ground materials obtained in Step 3 evenly to obtain the conductive adhesive. Example 3:

[0070] A cryogenic-resistant conductive adhesive, by weight, has the following composition: 20 parts of epoxy resin composition, 5 parts of flexible diluent, 2 parts of curing agent, 4 parts of accelerator, 0.5 part of anti-settling agent, 0.3 part of coupling agent, and 70 parts of conductive filler. The specific preparation method is as follows: Step 1: Take 20 parts of epoxy resin composition (the ratio of low-viscosity bisphenol F epoxy resin to modified epoxy resin is 50:50), 0.5 part of polypropylene glycol diglycidyl ether, 3 parts of dicyandiamide, 1 part of accelerator, 0.5 part of anti-settling agent, and 0.3 part of coupling agent. Disperse them evenly through a planetary degassing and dispersing machine. Step 2: Add 70 parts of conductive filler to the materials obtained in Step 1, and then continue to disperse them evenly through a planetary degassing and dispersing machine. Step 3: Pass the materials obtained in Step 2 through a three-roll grinder to obtain ground materials. Step 4: Vacuumize and disperse the ground materials obtained in Step 3 evenly to obtain the conductive adhesive. Example 4:

[0071] A cryogenic-resistant conductive adhesive, by weight, has the following composition: 12 parts of epoxy resin composition, 4 parts of flexible diluent, 6 parts of curing agent, 3 parts of accelerator, 0.4 part of anti-settling agent, 0.2 part of coupling agent, and 85 parts of conductive filler. The specific preparation method is as follows: Step 1: Take 12 parts of epoxy resin composition (the ratio of low-viscosity bisphenol F epoxy resin to modified epoxy resin is 30:70), 4 parts of neopentyl glycol diglycidyl ether, 6 parts of dicyandiamide, 3 parts of accelerator, 0.4 part of anti-settling agent, and 0.2 part of coupling agent. Disperse them evenly through a planetary degassing and dispersing machine. Step 2: Add 85 parts of conductive filler to the materials obtained in Step 1, and then continue to disperse them evenly through a planetary degassing and dispersing machine. Step 3: Pass the materials obtained in Step 2 through a three-roll grinder to obtain ground materials. Step 4: Vacuumize and disperse the ground material that has completed Step 3 evenly to obtain the conductive adhesive. Example 5:

[0072] A cryogenic-resistant conductive adhesive, by weight, consists of the following components: epoxy resin composition: 18 parts, flexible diluent: 3 parts; curing agent: 5 parts, accelerator: 2 parts, anti-settling agent: 0.1 part, coupling agent: 0.2 part, conductive filler: 85 parts. The specific preparation method is as follows: Step 1: Disperse 18 parts of epoxy resin composition (the ratio of low-viscosity bisphenol F epoxy resin to modified epoxy resin is 30:70), 3 parts of 1,4-butanediol diglycidyl ether, 5 parts of dicyandiamide, 2 parts of accelerator, 0.1 part of anti-settling agent; 0.2 part of coupling agent; evenly through a planetary degassing and dispersing machine; Step 2: Add 85 parts of conductive filler to the material that has completed Step 1, and then continue to disperse evenly through a planetary degassing and dispersing machine; Step 3: Pass the material that has completed Step 2 through a three-roll mill to obtain the ground material; Step 4: Vacuumize and disperse the ground material that has completed Step 3 evenly to obtain the conductive adhesive. Example 6:

[0073] A cryogenic-resistant conductive adhesive, by weight, consists of the following components: epoxy resin composition: 14 parts, flexible diluent: 3 parts; curing agent: 5 parts, accelerator: 2 parts, anti-settling agent: 0.1 part, coupling agent: 0.2 part, conductive filler: 80 parts. The specific preparation method is as follows: Step 1: Disperse 14 parts of epoxy resin composition (the ratio of low-viscosity bisphenol F epoxy resin to modified epoxy resin is 10:90), 3 parts of 1,4-butanediol diglycidyl ether, 5 parts of dicyandiamide, 2 parts of accelerator, 0.1 part of anti-settling agent; 0.2 part of coupling agent;; evenly through a planetary degassing and dispersing machine; Step 2: Add 80 parts of conductive filler to the material that has completed Step 1, and then continue to disperse evenly through a planetary degassing and dispersing machine; Step 3: Pass the material that has completed Step 2 through a three-roll mill to obtain the ground material; Step 4: Vacuumize and disperse the ground material that has completed Step 3 evenly to obtain the conductive adhesive.

[0074] Comparative Example 1: The difference from Example 1 is that in the epoxy resin composition, the ratio of low-viscosity bisphenol F epoxy resin to modified epoxy resin is 60:40; Comparative Example 2: The difference from Example 4 is that in the epoxy resin composition, the ratio of the low-viscosity bisphenol F type epoxy resin to the modified epoxy resin is 100:0; Comparative Example 3: The difference from Example 5 is that the conductive filler is 60 parts; Testing method: 1 Resistivity test: The conductive adhesive was coated on a glass slide to make a test piece of 2mm * 2mm * 0.1mm, and after curing in an oven at 150 °C for 1 h, the resistivity was tested by the four-probe method.

[0075] 1.2 Shear strength test: Using 3001 aluminum and 45# steel as substrates, shear test pieces were prepared and tested in accordance with the national standard GB / T 7124-2008. For each sample, 2 groups of test pieces were made for each substrate. After curing in an oven at 150 °C for 1 h, one group of each substrate was used to test the shear strength at room temperature, and the other group was used for comparative testing after high and low temperature impact.

[0076] 1.3 High and low temperature impact cycle test: Take 1 group of test pieces of the two substrates in step 1.2, and after 10 high and low temperature cycles (the test piece was placed in a cryogenic chamber at -90 °C for 1 h, and then quickly transferred to an oven at 100 °C and placed for another 1 h, which is 1 cycle), first observe whether the adhesive layer at the lap joint of the test piece is cracked, and then test the shear strength of the test piece.

[0077] Test results: 2.1 The test results of the examples and comparative examples are shown in Table 1: Table 1:

[0078] It can be seen from the data in Table 1 that the conductive adhesives provided in Examples 1-6 have good conductivity after curing, the resistivity ≤ 5 * 10-4 Ω·cm, can withstand ultra-low temperature, and after 10 high and low temperature cycles of -90 °C to 100 °C, the colloid does not break, and the shear strength retention rate for metals such as steel and aluminum is ≥ 95%, and there is no delamination or cracking with the metal substrate. It meets the invention's expectations and achieves the invention's effects.

[0079] For Comparative Example 1, since in the epoxy resin composition, the ratio of the low-viscosity bisphenol F type epoxy resin to the modified epoxy resin is 60:40, the high and low temperature impact resistance performance after curing becomes poor. After 10 high and low temperature cycles of -90 °C to 100 °C, there is no delamination or cracking between the colloid and the metal substrate, but the shear strength retention rate for metals such as steel and aluminum decreases, below 95%.

[0080] In Comparative Example 2, in the epoxy resin composition, the ratio of the low-viscosity bisphenol F type epoxy resin to the modified epoxy resin was 100:0; the high and low temperature impact resistance deteriorated after curing. After 10 cycles of high and low temperature cycling from -90 °C to 100 °C, the colloid cracked, and the retention rate of the shear strength against metals such as steel and aluminum decreased significantly, and the retention rate was far lower than 95%.

[0081] In Comparative Example 3, since the amount of the conductive filler was 60 parts, the resistivity of the obtained conductive adhesive was significantly high and the conductivity decreased significantly.

[0082] In the prior art, the above are only examples of the present application and are not used to limit the protection scope of the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A conductive adhesive resistant to ultra-low temperature, characterized in that: The conductive adhesive is composed of the following parts by weight: 10-20 parts of epoxy resin composition, 0.5-5 parts of flexible diluent; Curing agent: 2-8 parts, accelerator: 0.5-4 parts, anti-settling agent: 0.05-0.5 parts, coupling agent: 0.05-0.3 parts, conductive filler: 70-85 parts, after the conductive adhesive is cured, the resistivity is ≤5*10 -4 Ω.cm.

2. The ultra-low temperature resistant conductive adhesive according to claim 1, characterized in that: The epoxy resin composition comprises a low-viscosity bisphenol F epoxy resin and a modified epoxy resin, wherein the proportion of the modified epoxy resin is not less than 50% of the total weight of the epoxy resin composition.

3. The ultra-low temperature resistant conductive adhesive according to claim 2, characterized in that: The modified epoxy resin includes one or a combination of two or more of polyether modified epoxy resin, polyurethane modified epoxy resin, dimer acid modified epoxy resin, butadiene rubber modified epoxy resin and styrene-butadiene rubber modified epoxy resin.

4. The ultra-low temperature resistant conductive adhesive according to claim 1, characterized in that: The flexible diluent is one of 1,4-butanediol diglycidyl ether, polypropylene glycol diglycidyl ether, and neopentyl glycol diglycidyl ether, or a combination of two or more thereof.

5. The ultra-low temperature resistant conductive adhesive according to claim 1, characterized in that: The curing agent is dicyandiamide with a particle size of ≤10 microns.

6. The ultra-low temperature resistant conductive adhesive and the preparation method thereof according to claim 1, characterized in that: The accelerator is one or a combination of two or more of a latent imidazole adduct, a latent tertiary amine, and an organic urea accelerator.

7. The ultra-low temperature resistant conductive adhesive and the preparation method thereof according to claim 1, characterized in that: The anti-settling agent is fumed silica.

8. The ultra-low temperature resistant conductive adhesive and the preparation method thereof according to claim 1, characterized in that: The coupling agent is KH560.

9. The ultra-low temperature resistant conductive adhesive and the preparation method thereof according to claim 1, characterized in that: The conductive filler is one or a combination of two or more of silver powder, copper powder, nickel powder, silver-plated copper powder, silver-plated nickel powder and silver-plated glass powder with an average particle size of 1.5-10 μm.

10. A method for preparing a conductive adhesive resistant to ultra-low temperature according to any one of claims 1 to 9, comprising the following steps: Step 1: Evenly disperse the epoxy resin composition, flexible diluent, curing agent, accelerator, anti-settling agent and coupling agent through a planetary degassing disperser; Step 2, adding conductive filler to the material of step 1 and then continuing to disperse it evenly through a planetary degassing disperser; Step 3, passing the material obtained in step 2 through a three-roller grinder to obtain a ground material; Step 4: vacuum the ground material obtained in step 3 and disperse it evenly to obtain the conductive adhesive.

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