Low-temperature impact resistant epoxy structural adhesive and preparation method thereof

Abstract

The application provides a low-temperature impact resistant epoxy structural adhesive and a preparation method thereof, and belongs to the technical field of high-performance composite materials. The rigid matrix skeleton is constructed by using bisphenol F type epoxy resin and first bisphenol A type epoxy resin, the nano dot-molecular chain-flexible unit triple toughening system is constructed by using core-shell modified epoxy resin, HMC-polyurethane modified epoxy resin and a toughening agent, the core-shell particles induce small silver cracks, the HMC-polyurethane modified epoxy resin flexible chain segment restrains the silver crack expansion, the toughening agent absorbs residual impact energy, and high-efficiency energy dissipation is realized. The components such as fillers, moisture absorbents, thixotropic agents and silane coupling agents are synergistically enhanced: the rigid support of bisphenol A and F type epoxy resins is ensured, the flexible unit is supplemented, the toughening synergy is strengthened, the thixotropic agent prevents the fillers from settling and sagging, the moisture absorbent improves the weather resistance, the silane coupling agent enhances the interface bonding, the construction feasibility and appearance requirements are considered, and the contradiction between low-temperature embrittlement and high-temperature strength loss of the epoxy structural adhesive can be solved.

Description

Technical Field

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

[0002] As the automotive industry rapidly evolves towards lightweight, high-strength, and high-safety standards, epoxy structural adhesives, due to their excellent bonding strength, heat resistance, chemical corrosion resistance, and good compatibility with metals and composite materials, have been widely applied in key scenarios such as vehicle body structure bonding, component fixing, and weld replacement. They have become one of the core materials for achieving weight reduction and efficiency improvement, enhancing structural integrity, and improving collision safety in automobiles. Especially in the field of new energy vehicles, scenarios such as battery pack fixing and lightweight vehicle body components (aluminum alloys, carbon fiber composites) connections place even more stringent demands on the comprehensive performance of epoxy structural adhesives.

[0003] However, existing epoxy structural adhesives inherently present a contradiction between high strength and high toughness, especially in low-temperature environments where this deficiency becomes more pronounced. When automobiles are used in cold regions, they face extreme low-temperature conditions ranging from -30℃ to -45℃. The molecular chain mobility of traditional epoxy structural adhesives decreases sharply, and their glass transition temperature is higher than the low-temperature operating temperature, leading to severe material embrittlement: their low-temperature impact strength is typically less than 20 N / mm, their tensile shear strength easily decreases with decreasing temperature, and their T-peel strength is generally below 8 N / mm. Under vibration, collision, or external impact during vehicle operation, cracks easily form at the bonding interface and propagate rapidly, even causing structural failure, seriously threatening driving safety.

[0004] To improve the toughness of epoxy structural adhesives, various technologies have been explored: physical blending toughening is achieved by directly incorporating flexible components, but it suffers from poor compatibility, easy phase separation, strength decline, and weak interfacial bonding, making it difficult to completely eliminate low-temperature embrittlement; core-shell modification toughening relies on the physical dispersion of core-shell particles, but the dispersion uniformity is difficult to control, resulting in limited toughening effects and failing to meet the impact requirements at extreme low temperatures of -45°C; while chemical modification of epoxy compounds introduces flexible segments, traditional segments easily lead to an imbalance between weather resistance, heat resistance, and low-temperature toughness, and the soft segments modified by ordinary polyurethane lack sufficient flexibility, still failing to break through the bottleneck of the "rigidity-toughness" balance. Furthermore, existing solutions either rely on special monomers, complex processes, and toxic solvents, making large-scale application difficult; or they are designed for niche extremely low-temperature scenarios, failing to consider the comprehensive requirements of the automotive industry for low-temperature impact, room-temperature strength, and processability, and thus cannot be directly adapted to automotive operating conditions.

[0005] Therefore, developing an epoxy structural adhesive that can maintain high impact toughness at extreme low temperatures of -45℃ while also possessing excellent tensile shear strength, peel strength, and industrial processability, to solve the industry pain points of low-temperature embrittlement and imbalance between strength and toughness in traditional epoxy structural adhesives, and to meet the stringent requirements of cold-region automobiles and new energy vehicles, has become an urgent technical problem to be solved in the field of automotive epoxy structural adhesives. Summary of the Invention

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

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

[0008] 10-15 parts of bisphenol F type epoxy resin, 10-20 parts of first bisphenol A type epoxy resin, 10-20 parts of core-shell modified epoxy resin, 15-25 parts of HMC-polyurethane modified epoxy resin, 10-15 parts of toughening agent, 10-30 parts of filler, 0.1-0.5 parts of curing accelerator, 1-5 parts of curing agent, 3-5 parts of desiccant, 0.01-0.05 parts of pigment, 2-5 parts of thixotropic agent, and 0.1-0.5 parts of silane coupling agent;

[0009] The HMC-polyurethane modified epoxy resin contains 0.15~0.20 eq / 100g of residual epoxy groups and 0.05~0.10 eq / 100g of unreacted -NCO groups.

[0010] Preferably, the mass ratio of the core-shell modified epoxy resin, HMC-polyurethane modified epoxy resin and toughening agent is 1:(1~1.5):(0.5~1).

[0011] Preferably, the HMC-polyurethane modified epoxy resin uses polyhexamethylene carbonate diol (PHMC), synthesized from 1,6-hexanediol and dimethyl carbonate via transesterification, as a flexible segment precursor.

[0012] Preferably, the PHMC has a number-average molecular weight of 1000~2000 g / mol and a hydroxyl value of 56~112 mg KOH / g.

[0013] Preferably, the preparation method of the HMC-polyurethane modified epoxy resin includes:

[0014] (1) Synthesis of PHMC

[0015] 1,6-Hexanediol and dimethyl carbonate were fed in a molar ratio of 1:1.05~1.2 and reacted under nitrogen protection, 120~140℃, and 0.1~0.3MPa for 4~8h to obtain polyhexamethylene carbonate diol (PHMC).

[0016] (2) Preparation of polyurethane prepolymer

[0017] The dehydrated PHMC and diisocyanate were fed into the mixture at a molar ratio of 1:1.2~1.5 and reacted under nitrogen protection at 80~90℃ for 2~3 hours to obtain a polyurethane prepolymer with -NCO terminal.

[0018] (3) Epoxy resin modification

[0019] The HMC-polyurethane modified epoxy resin is prepared by feeding polyurethane prepolymer and second bisphenol A type epoxy resin with an epoxy equivalent of 160~180g / eq at a mass ratio of 1:1.5~2.5, treating at 50~80℃ for 5h, and then degassing under vacuum.

[0020] Preferably, the core-shell modified epoxy resin refers to an epoxy resin modified with core-shell particles, wherein the core-shell particles are polybutadiene rubber as the core and methyl methacrylate as the shell, the particle size of the core-shell particles is 50~200nm, and the content of the core-shell particles in the core-shell modified epoxy resin is 10~20%.

[0021] Preferably, the toughening agent is a polyurethane toughening agent, and the polyurethane toughening agent simultaneously meets the following technical characteristics:

[0022] (1) Viscosity at 25℃ is 3000~12000 mPa·s;

[0023] (2) The number-average molecular weight (Mn) is 1500~3000 g / mol, and the molecular weight distribution width (PDI) is ≤1.8;

[0024] (3) The content of terminal -NCO groups is 0.5~1.5 eq / 100g, or the content of terminal -OH is 0.3~0.8 eq / 100g.

[0025] Preferably, the polyurethane toughening agent includes one or more of Covestro Desmocap 11A, Lanxess Trixene BI 7774, or complexed high-tech EPU-133L.

[0026] Preferably, the filler comprises heavy calcium carbonate and / or modified aluminum hydroxide.

[0027] Preferably, the curing accelerator includes an organic urea accelerator.

[0028] Preferably, the curing agent includes one or more of dicyandiamide, sebacate dihydrazide, or adipic acid dihydrazide.

[0029] Preferably, the desiccant comprises calcium oxide desiccant.

[0030] Preferably, the thixotropic agent comprises nano-calcium carbonate and / or fumed silica.

[0031] Preferably, the epoxy equivalent of the bisphenol F type epoxy resin is 150~170 g / eq.

[0032] Preferably, the epoxy equivalent of the first bisphenol A type epoxy resin is 160~180 g / eq.

[0033] Preferably, the silane coupling agent includes KH560 and / or KH580.

[0034] A second objective of this invention is to provide a method for preparing the low-temperature impact-resistant epoxy structural adhesive as described above, the method comprising:

[0035] S1 matrix premix: Under normal temperature and nitrogen protection conditions, add bisphenol F type epoxy resin and first bisphenol A type epoxy resin, and stir at a speed of 150~250 rpm for 10~20 min to obtain epoxy matrix mixture;

[0036] S2 toughening system fusion: First, add core-shell modified epoxy resin and HMC-polyurethane modified epoxy resin sequentially to the epoxy matrix mixture, and stir at room temperature for 15-25 minutes while maintaining a rotation speed of 150-250 rpm; then add toughening agent, heat to 30-40℃, adjust the rotation speed to 200-300 rpm, and stir for 20-30 minutes to obtain epoxy-toughening composite system;

[0037] S3 Functional Component Dispersion: First, add filler and thixotropic agent to the epoxy-toughening composite system, increase the rotation speed to 350~500 rpm, and stir at room temperature for 30~40 min; then add silane coupling agent, desiccant and pigment in sequence, and keep the rotation speed at 300~400 rpm for 15~20 min.

[0038] S4 Curing System Mixing: Cool the system from step S3 to 25~30℃, add curing agent and curing accelerator, and stir at 200~250rpm for 10~15min;

[0039] S5 Vacuum Degassing and Finished Product: Degassing is performed for 20-30 minutes under vacuum conditions of -0.09 to -0.1 MPa and temperature of 30-40℃, with low-speed stirring at 50-100 rpm to assist in degassing, thus obtaining the low-temperature impact resistant epoxy structural adhesive.

[0040] Preferably, the heating rate after adding the toughening agent is controlled at 1~2℃ / min, and the system temperature is controlled to not exceed 45℃ during the entire preparation process.

[0041] Preferably, during the vacuum degassing process, the viscosity of the system needs to be controlled at 8000~12000 mPa·s. If the viscosity exceeds the range, it can be adjusted by fine-tuning the temperature or rotation speed.

[0042] The beneficial effects of this invention include:

[0043] This invention uses bisphenol F type epoxy resin and first bisphenol A type epoxy resin to construct a rigid matrix framework, and core-shell modified epoxy resin, HMC-polyurethane modified epoxy resin and toughening agent to construct a triple toughening system of "nanodot-molecular chain-flexible unit". It achieves efficient energy dissipation through "core-shell particles initiating micro-silver crazes, flexible chain segments of HMC-polyurethane modified epoxy resin constraining the expansion of silver crazes, and toughening agent absorbing residual impact energy".

[0044] At the same time, it works synergistically with fillers, desiccant, thixotropic agents, silane coupling agents and other components: it ensures the rigid support of the first bisphenol A type epoxy resin and bisphenol F type epoxy resin, and supplements the flexible unit to strengthen and toughen the synergistic effect; it also prevents filler sedimentation and sagging through thixotropic agents, improves weather resistance through desiccant, and enhances interfacial adhesion through silane coupling agents, taking into account both construction feasibility and appearance requirements.

[0045] This invention can solve the contradiction of low-temperature embrittlement and high-temperature strength loss of traditional epoxy structural adhesives, making the adhesive layer have an impact strength of ≥55N / mm at -45℃ and a tensile shear strength of ≥32MPa at 25℃, which is suitable for the harsh usage scenarios of automobiles and new energy vehicles in cold regions, and the raw materials and processes are suitable for industrial production. Detailed Implementation

[0046] The following description includes certain specific details to provide a comprehensive understanding of the various disclosed embodiments. However, those skilled in the art will recognize that embodiments can be implemented without employing one or more of these specific details, but using other methods, components, materials, etc.

[0047] Unless otherwise required by the present invention, throughout the specification and the following claims, the words “comprising” and “including” shall be interpreted in an open-ended, inclusive sense, meaning “including but not limited to”.

[0048] Throughout this specification, the terms "an embodiment," "an embodiment," "a preferred embodiment," or "some embodiments" refer to including, in at least one embodiment, a specific reference element, structure, or feature associated with that embodiment. Therefore, the phrases "in an embodiment," "in a preferred embodiment," or "in some embodiments" appearing in different places throughout the specification do not necessarily all refer to the same embodiment. Furthermore, specific elements, structures, or features may be combined in one or more embodiments in any suitable manner.

[0049] According to a first aspect of the present invention, a low-temperature impact epoxy structural adhesive is provided, the epoxy structural adhesive comprising the following raw materials in parts by weight:

[0050] 10-15 parts of bisphenol F type epoxy resin, 10-20 parts of first bisphenol A type epoxy resin, 10-20 parts of core-shell modified epoxy resin, 15-25 parts of HMC-polyurethane modified epoxy resin, 10-15 parts of toughening agent, 10-30 parts of filler, 0.1-0.5 parts of curing accelerator, 1-5 parts of curing agent, 3-5 parts of desiccant, 0.01-0.05 parts of pigment, 2-5 parts of thixotropic agent, and 0.1-0.5 parts of silane coupling agent;

[0051] The HMC-polyurethane modified epoxy resin contains 0.15~0.20 eq / 100g of residual epoxy groups and 0.05~0.10 eq / 100g of unreacted -NCO groups.

[0052] In this invention, HMC-polyurethane modified epoxy resin refers to polyhexamethylene carbonate diol polyurethane modified epoxy resin. The residual epoxy groups are determined according to the hydrochloric acid-acetone method in GB / T 1677-2008, and the unreacted -NCO groups are determined according to the di-n-butylamine titration method in GB / T12009.4-2016.

[0053] The HMC-polyurethane modified epoxy resin is, for example, 15 parts, 16 parts, 17 parts, 18 parts, 19 parts, 20 parts, 21 parts, 22 parts, 23 parts, 24 parts, or 25 parts.

[0054] The HMC-polyurethane modified epoxy resin is a block polymer of rigid and flexible segments. The rigid segments are epoxy segments containing benzene rings and ether bonds, and the flexible segments are polyhexamethylene carbonate diol segments (-O-(CH2)6-O-CO-O- repeating units). The rigid and flexible segments are connected by urethane bonds (-O-CO-NH-), which can avoid phase separation of the rigid and flexible segments during physical blending and ensure efficient stress transfer.

[0055] PHMC flexible segments (Tg approximately -60℃) have long methylene chains with low internal rotational resistance. At low temperatures, they can dissipate energy through chain oscillation, thus improving the intrinsic toughness of the matrix. Epoxy rigid segments, on the other hand, retain the high strength and heat resistance (Tg ≥ 120℃) of the epoxy matrix, forming a continuous phase (epoxy rigid skeleton) - dispersed phase (polyurethane flexible island) island structure. The flexible islands absorb impact energy, while the rigid skeleton supports the structural strength, helping the material achieve the characteristics of being strong but not brittle.

[0056] Meanwhile, the HMC-polyurethane modified epoxy resin molecule retains two types of active functional groups (epoxy groups and -NCO groups), which participate in the subsequent curing process and promote the formation of a dense and tough cross-linked network. The residual epoxy groups can react with the hydroxyl groups of the curing agent, the first bisphenol A type epoxy resin, and the bisphenol F type epoxy resin, while the residual -NCO groups can react with the epoxy hydroxyl groups and the amino groups of the curing agent to form urethane bonds / urea bonds, ultimately forming a polyurethane-epoxy interpenetrating network. The network has high density, which can improve both tensile shear strength and fatigue resistance of the adhesive layer.

[0057] Meanwhile, the carbonate bonds of the PHMC flexible segments are far more resistant to hydrolysis and automotive oil stains (such as engine oil and brake fluid) than traditional polyether bonds and polyester bonds, which can protect the epoxy group from moisture and chemical media corrosion, making it suitable for complex outdoor working conditions of automobiles.

[0058] The core-shell modified epoxy resin is an epoxy resin modified with core-shell particles, which are uniformly dispersed in the epoxy matrix. The core of the core-shell particles can undergo elastic deformation. Under stress, the core-shell particles become stress concentration points, inducing a large number of micro-crazes. At the same time, shear bands are generated at the particle-matrix interface. The formation of crazes and the expansion of shear bands consume a large amount of energy, and the elasticity of the core can also prevent the crazes from further developing into macroscopic cracks.

[0059] The core-shell modified epoxy resin is, for example, 10 parts, 11 parts, 12 parts, 13 parts, 14 parts, 15 parts, 16 parts, 17 parts, 18 parts, 19 parts or 20 parts.

[0060] The toughening agent further provides flexible units that can absorb instantaneous impact energy at extreme low temperatures through interface slippage and violent segment swinging.

[0061] The toughening agent is, for example, 10 parts, 10.5 parts, 11 parts, 11.5 parts, 12 parts, 12.5 parts, 13 parts, 13.5 parts, 14 parts, 14.5 parts, or 15 parts.

[0062] The core-shell modified epoxy resin, HMC-polyurethane modified epoxy resin, and toughening agent can synergistically construct a triple toughening system of "nanodots-molecular chains-flexible units", which can simultaneously achieve a four-dimensional balance of toughness, strength, weather resistance and processability, thereby solving the industry pain points of low-temperature embrittlement and imbalance between strength and toughness in traditional epoxy structural adhesives.

[0063] First, core-shell modified epoxy resin, HMC-polyurethane modified epoxy resin, and toughening agent improve the low-temperature impact energy absorption efficiency through full-scale energy dissipation, thereby effectively improving the toughening effect.

[0064] The first stage of dissipation involves initiating microcracks, with core-shell particles acting as stress concentration points, triggering numerous tiny crazes and increasing the energy dissipation area. The second stage of dissipation involves preventing craze propagation; the molecular chains of HMC-polyurethane modified epoxy resin penetrate the matrix, and flexible segments can wrap around the craze tips, alleviating stress concentration. At the same time, the density of the interpenetrating network prevents further craze propagation. The third stage of dissipation involves participating in energy absorption; the flexible units of the toughening agent fill the space between the craze and the shear band, absorbing residual impact energy through interface slippage and chain segment oscillation. These three stages work together to form a closed-loop dissipation mechanism of craze initiation → craze prevention → residual energy absorption.

[0065] Secondly, core-shell modified epoxy resin, HMC-polyurethane modified epoxy resin, and toughening agent can construct a stable composite matrix through chemical bonding and physical interweaving.

[0066] On the one hand, when the toughening agent is a polyurethane toughening agent, the -NCO and -OH groups react directly with the residual groups of HMC-polyurethane modified epoxy resin (HMC-EP) and the shell hydroxyl groups of the core-shell modified epoxy resin to form chemical bonds. On the other hand, through the bridging effect of the continuous phase matrix of the first bisphenol A type epoxy resin and bisphenol F type epoxy resin, multiple cross-linking reactions occur with the epoxy groups and residual hydroxyl groups of the first bisphenol A type epoxy resin and bisphenol F type epoxy resin, forming a three-dimensional cross-linked network with the first bisphenol A type epoxy resin and bisphenol F type epoxy resin matrix as the core and the core-shell particles-HMC-EP-toughening agent interwoven. This helps to avoid the peeling of core-shell particles and the separation of the HMC-EP phase, ensuring long-term stability.

[0067] Secondly, using the first bisphenol A type epoxy resin and bisphenol F type epoxy resin as the continuous phase (marine phase), the flexible segments of HMC-EP aggregate to form a nano- to micron-scale dispersed phase (island phase), constituting an island structure; the nanoparticles of the core-shell modified epoxy resin are uniformly filled in the interface of the island structure and the voids of the marine phase, forming discrete reinforcing points; the flexible segments of the toughening agent are wrapped around the surface of the core-shell particles, the island phase segments of HMC-EP, and the rigid segments of the first bisphenol A type epoxy resin and bisphenol F type epoxy resin, forming a flexible network that runs through the entire continuous phase. Ultimately, a three-dimensional interwoven structure was constructed, consisting of continuous phases of first bisphenol A epoxy resin and bisphenol F epoxy resin as the framework, core-shell particles (dots) - HMC-EP island phase segments / rigid segments (chains) of first bisphenol A epoxy resin / bisphenol F epoxy resin - flexible segments (network) of toughening agent. This structure, through the synergy of rigid framework support, discrete reinforcement points, and flexible network energy dissipation, retains the high strength of the epoxy matrix while ensuring extreme low-temperature toughness through multiple flexible units. At the same time, the dense interwoven structure increases the crosslinking density, enhancing the heat resistance and fatigue resistance of the adhesive layer.

[0068] Third, the point-type toughening of core-shell modified epoxy resin, the chain-type toughening of HMC-EP, and the unit-type toughening of toughening agent work together to offset the strength loss that may be caused by the addition of toughening agent. At the same time, the hydrolysis resistance of HMC-EP carbonate bonds, the interfacial strengthening effect of toughening agent, and the physical barrier effect of core-shell particles can enhance weather resistance and adapt to the complex working conditions of automobiles.

[0069] Fourth, the viscosity ranges of the three components can complement each other, stabilizing the viscosity of the mixed system. This avoids both filler sedimentation caused by excessive thinness and uneven mixing caused by excessive thickness. At the same time, the polarity of HMC-EP and toughening agent, as well as the matching of core-shell modified epoxy resin with the first bisphenol A type epoxy resin and bisphenol F type epoxy resin, reduce the agglomeration tendency of each added component, which helps to simplify the process.

[0070] In this invention, the bisphenol F type epoxy resin is, for example, 10 parts, 10.5 parts, 11 parts, 11.5 parts, 12 parts, 12.5 parts, 13 parts, 13.5 parts, 14 parts, 14.5 parts or 15 parts, and its epoxy equivalent is 150~170 g / eq.

[0071] The first bisphenol A type epoxy resin is, for example, 10 parts, 11 parts, 12 parts, 13 parts, 14 parts, 15 parts, 16 parts, 17 parts, 18 parts, 19 parts or 20 parts, and its epoxy equivalent is 160~180g / eq.

[0072] The filler is, for example, 10 parts, 12 parts, 14 parts, 16 parts, 18 parts, 20 parts, 22 parts, 24 parts, 26 parts, 28 parts, or 30 parts. The curing accelerator is 0.1 parts, 0.2 parts, 0.3 parts, 0.4 parts, or 0.5 parts. The curing agent is, for example, 1 part, 2 parts, 3 parts, 4 parts, or 5 parts. The desiccant is, for example, 3 parts, 3.2 parts, 3.4 parts, 3.6 parts, 3.8 parts, 4 parts, 4.2 parts, 4.4 parts, 4.6 parts, 4.8 parts, or 5 parts. The pigment is, for example, 0.01 parts, 0.02 parts, 0.03 parts, 0.04 parts, or 0.05 parts. The thixotropic agent is, for example, 2 parts, 2.2 parts, 2.4 parts, 2.6 parts, 2.8 parts, 3 parts, 3.2 parts, 3.4 parts, 3.6 parts, 3.8 parts, 4 parts, 4.2 parts, 4.6 parts, 4.8 parts, or 5 parts.

[0073] In a preferred embodiment of the present invention, the mass ratio of the core-shell modified epoxy resin, the HMC-polyurethane modified epoxy resin and the toughening agent is 1:(1~1.5):(0.5~1).

[0074] In this invention, using 1 part of core-shell modified epoxy resin and controlling HMC-EP at 1-1.5 parts ensures that the flexible segments (island phase) of HMC-EP are uniformly dispersed in the continuous phase (sea phase) of the first bisphenol A type epoxy resin and bisphenol F type epoxy resin. This avoids the lack of flexible segments and weak low-temperature toughness caused by insufficient HMC-EP (<1 part), while also preventing the island phase from agglomerating and fusing due to excessive HMC-EP (>1.5 parts), which would damage the rigid skeleton of the continuous phase and cause a decline in tensile shear strength. Simultaneously, at this ratio, the residual epoxy and -NCO groups in HMC-EP can fully react with the first bisphenol A type epoxy resin and bisphenol F type epoxy resin, which helps ensure the compactness of the interpenetrating network.

[0075] The core function of toughening agent is to supplement the residual energy absorption under extreme low temperature. The range of 0.5 to 1 part is not only conducive to filling the energy gap after the core-shell modified epoxy induces crazes and HMC-EP prevents crazes, but also helps to avoid excessive aggregation of flexible segments due to excessive toughening agent, dilute the rigid skeleton of the first bisphenol A type epoxy resin and bisphenol F type epoxy resin, and at the same time help to control the viscosity of the system and adapt to construction.

[0076] The preferred mass ratio of the core-shell modified epoxy resin, HMC-polyurethane modified epoxy resin, and toughening agent is 1:1.3:0.8.

[0077] In a preferred embodiment of the present invention, the HMC-polyurethane modified epoxy resin uses polyhexamethylene carbonate diol (PHMC) as a flexible segment precursor.

[0078] Preferably, the PHMC has a number-average molecular weight of 1000~2000 g / mol and a hydroxyl value of 56~112 mg KOH / g.

[0079] In this invention, the number-average molecular weight of the PHMC was determined by gel permeation chromatography (GPC, GB / T 36214.4-2018). The molecular weight of the core soft segment PHMC was controlled between 1000 and 2000 g / mol, with a hydroxyl value of 56 to 112 mg KOH / g. When the molecular weight is too low (<1000 g / mol), the flexible segments are too short, resulting in insufficient chain segment mobility at low temperatures, which may lead to ineffective absorption of impact energy; when the molecular weight is too high (>2000 g / mol), the flexible segments are too long, which can easily lead to a loose cross-linking network, thereby reducing tensile shear strength. A molecular weight between 1000 and 2000 g / mol is beneficial for ensuring sufficient chain segment mobility at low temperatures while minimizing damage to the compactness of the epoxy cross-linking network.

[0080] In a preferred embodiment of the present invention, the preparation method of the HMC-polyurethane modified epoxy resin includes:

[0081] (1) Synthesis of PHMC

[0082] 1,6-Hexanediol and dimethyl carbonate were fed in a molar ratio of 1:1.05~1.2 and reacted under nitrogen protection, 120~140℃, and 0.1~0.3MPa for 4~8h to obtain polyhexamethylene carbonate diol (PHMC).

[0083] (2) Preparation of polyurethane prepolymer

[0084] The dehydrated PHMC and diisocyanate were fed into the mixture at a molar ratio of 1:1.2~1.5 and reacted under nitrogen protection at 80~90℃ for 2~3 hours to obtain a polyurethane prepolymer with -NCO terminal.

[0085] (3) Epoxy resin modification

[0086] The HMC-polyurethane modified epoxy resin is prepared by feeding polyurethane prepolymer and second bisphenol A type epoxy resin with an epoxy equivalent of 160~180g / eq at a mass ratio of 1:1.5~2.5, treating at 50~80℃ for 5h, and then degassing under vacuum.

[0087] In this invention, during the PHMC synthesis process, tetrabutyl titanate (TBT) and / or sodium methoxide are used as catalysts, preferably tetrabutyl titanate, and the amount of catalyst used is 0.1~0.3% of the total mass of the raw materials.

[0088] In the preparation process of the polyurethane prepolymer, dibutyltin dilaurate (DBTDL) is used as a catalyst, and the amount of catalyst used is 0.05~0.1% of the total mass of the raw materials.

[0089] The vacuum degassing conditions described in step (3) are: -0.09~-0.1MPa, 30~40min.

[0090] In this invention, the first bisphenol A type epoxy resin and the second bisphenol A type epoxy resin are preferably the same bisphenol A type epoxy resin, and more preferably E-51.

[0091] In a preferred embodiment of the present invention, the core-shell modified epoxy resin refers to an epoxy resin modified with core-shell particles, wherein the core-shell particles are polybutadiene rubber as the core and methyl methacrylate as the shell, the particle size of the core-shell particles is 50~200nm, and the content of the core-shell particles in the core-shell modified epoxy resin is 10~20%.

[0092] In this invention, the glass transition temperature (Tg) of the polybutadiene (PB) rubber core is approximately -90°C. Even in extreme environments of -45°C, the PB core segments maintain efficient mobility. Upon impact, they can absorb a large amount of impact energy through elastic deformation and segment oscillation. Simultaneously, they act as stress concentration points, inducing high-density microcrazing (rather than macroscopic cracks), laying the foundation for subsequent energy dissipation of HMC-EP and toughening agents. The low modulus of the PB core (≈0.1 MPa) also creates a hardness contrast with the high modulus of the epoxy matrix (≈3 GPa), generating shear bands under stress, further consuming impact energy and preventing brittle fracture of the adhesive layer.

[0093] For the methyl methacrylate (MMA) shell, the solubility parameters of MMA and epoxy resin are highly matched, which helps to ensure that the core-shell particles can be uniformly dispersed in the epoxy matrix. During the polymerization process, the MMA shell will have trace amounts of hydroxyl groups (-OH), which can form hydrogen bonds or chemical bonds with epoxy groups, anchoring the core-shell particles in the epoxy matrix. This prevents the particles from peeling off from the matrix during low-temperature impact, ensuring the long-term stability of the toughening effect, while also improving the fatigue resistance of the adhesive layer.

[0094] If the particle size is <50nm, the core-shell particles have an excessively large specific surface area and extremely high surface energy, making them prone to irreversible aggregation. This causes stress concentration points to become defect points, which in turn reduces the strength of the adhesive layer; at the same time, the production cost is high. If the particle size is >200nm, the core-shell particles will disrupt the integrity of the continuous phase in the epoxy matrix, which is equivalent to embedding large-sized flexible impurities in a rigid framework. This can easily lead to a significant decline in tensile shear strength; moreover, excessively large particles cannot fill the interfacial voids of the HMC-EP island structure, making it difficult to form a dense interwoven point-chain-network structure, thus weakening the toughening synergy.

[0095] If the content is <10%, the core-shell particles are too sparsely distributed in the matrix, making it difficult to form high-density silver crazing; at the same time, the particle spacing is too large, the shear band is difficult to penetrate, and the energy dissipation efficiency is low; if the content is >20%, it will cause three major problems: (1) diluting the epoxy rigid skeleton, which easily leads to a decline in tensile shear strength; (2) easily leading to a sudden increase in the viscosity of the system; (3) the core-shell particles are prone to agglomeration, which destroys the dispersion uniformity.

[0096] The core-shell modified epoxy resin of the present invention includes complexed high-tech EPX-152 and / or Fujian refined enthalpy material YT-3154A, preferably Fujian refined enthalpy material YT-3154A.

[0097] In a preferred embodiment of the present invention, the toughening agent is a polyurethane toughening agent, which simultaneously satisfies the following technical features:

[0098] (1) Viscosity at 25℃ is 3000~12000 mPa·s;

[0099] In this invention, if the viscosity is too low, the viscosity of the entire system will be too low, which will cause the filler to settle and separate, resulting in poor storage stability. If the viscosity is too high, it will be difficult to mix, and additional shear force will be required during mixing, which will not only increase the energy consumption of the equipment, but may also damage the core and shell particles. It will also make the total viscosity of the system too high, making vacuum degassing difficult, and the adhesive layer will easily have residual bubbles after curing.

[0100] (2) The number-average molecular weight (Mn) is 1500~3000 g / mol, and the molecular weight distribution width (PDI) is ≤1.8;

[0101] In this invention, a molecular weight of 1500~3000 g / mol is beneficial to ensure that the flexible chain segment is long enough, thereby effectively absorbing impact energy and improving the toughening effect; it can also avoid the decrease in compatibility caused by excessively long flexible chain segments.

[0102] A narrow molecular weight distribution indicates good uniformity in toughening agent molecular chain length and consistent reactivity of terminal functional groups (NCO / OH). If the PDI is greater than 1.8, the molecular weight distribution is wider. Shorter-chain molecules are more likely to react prematurely, leading to local cross-linking, while longer-chain molecules are difficult to disperse, resulting in aggregation. This can lead to large fluctuations in adhesive layer performance, making it difficult to meet the quality control requirements for mass production of automotive structural adhesives.

[0103] (3) The content of terminal -NCO groups is 0.5~1.5 eq / 100g, or the content of terminal -OH is 0.3~0.8 eq / 100g.

[0104] In this invention, if -NCO is less than 0.5 eq / 100g, there are insufficient bonding points and weak interfacial bonding; if it is more than 1.5 eq / 100g, there is too much residual -NCO, which is easy to react with moisture in the air to generate CO2 bubbles, resulting in an increase in the porosity of the adhesive layer.

[0105] If the -OH group is less than 0.3 eq / 100g, the reaction with the epoxy group will be insufficient, making it difficult for the toughening agent to anchor in the matrix; if it is greater than 0.8 eq / 100g, the epoxy group will be excessively consumed, reducing the crosslinking density and affecting the strength and heat resistance of the adhesive layer.

[0106] In a preferred embodiment of the present invention, the polyurethane toughening agent includes one or more of Covestro Desmocap 11A, Lanxess Trixene BI 7774, or complexed high-tech EPU-133L.

[0107] In a preferred embodiment of the present invention, the filler comprises heavy calcium carbonate and / or modified aluminum hydroxide.

[0108] The curing accelerator includes an organic urea accelerator, preferably complexed high-tech HUA5050 and / or PN50.

[0109] The curing agent includes one or more of dicyandiamide, sebacic acid dihydrazide or adipic acid dihydrazide, preferably dicyandiamide.

[0110] The desiccant includes calcium oxide desiccant, preferably Hangxin CaO and / or CGX-3.

[0111] The thixotropic agent comprises nano-calcium carbonate and / or fumed silica, preferably fumed silica, and more preferably has a specific surface area of ​​100 m². 2 / g of fumed silica.

[0112] The silane coupling agent includes KH560 and / or KH580.

[0113] The epoxy equivalent of the bisphenol F type epoxy resin is 150~170 g / eq.

[0114] The epoxy equivalent of the first bisphenol A type epoxy resin is 160~180 g / eq.

[0115] The pigments include carbon black.

[0116] According to a second aspect of the present invention, a method for preparing the low-temperature impact-resistant epoxy structural adhesive as described above is provided, the method comprising:

[0117] S1 matrix premix: Under normal temperature and nitrogen protection conditions, add bisphenol F type epoxy resin and first bisphenol A type epoxy resin, and stir at a speed of 150~250 rpm for 10~20 min to obtain epoxy matrix mixture;

[0118] S2 toughening system fusion: First, add core-shell modified epoxy resin and HMC-polyurethane modified epoxy resin sequentially to the epoxy matrix mixture, maintaining a speed of 150~250 rpm and stirring at room temperature for 15~25 min; then add toughening agent, heat to 30~40℃, adjust the speed to 200~300 rpm, and stir for 20~30 min to ensure that the toughening component is completely compatible with the epoxy matrix, thus obtaining the epoxy-toughening composite system;

[0119] S3 Functional Component Dispersion: First, add filler and thixotropic agent to the epoxy-toughening composite system, increase the rotation speed to 350~500 rpm, and stir at room temperature for 30~40 min; then add silane coupling agent, desiccant and pigment in sequence, and keep the rotation speed at 300~400 rpm for 15~20 min.

[0120] S4 Curing System Mixing: Cool the system from step S3 to 25~30℃, add curing agent and curing accelerator, and stir at 200~250rpm for 10~15min to ensure that the curing components are evenly dispersed and do not cause premature curing.

[0121] S5 Vacuum Degassing: Degas for 20-30 minutes under vacuum conditions of -0.09 to -0.1 MPa and temperature of 30-40℃, with low-speed stirring at 50-100 rpm to assist in degassing, to obtain the low-temperature impact resistant epoxy structural adhesive.

[0122] The material is then discharged at room temperature and sealed in packaging.

[0123] In this invention, bisphenol A type epoxy resin and bisphenol F type epoxy resin are added first to establish a low-viscosity dispersion medium, which is beneficial for the subsequent dispersion of core-shell modified epoxy and HMC-polyurethane modified epoxy, ensuring uniform interweaving of toughening components. Solid components (fillers, curing agents, etc.) are easily dispersed in the low-viscosity system, reducing the risk of agglomeration. The viscosity gradient is controllable (from low to medium to high), the process is stable, and it is suitable for industrial production.

[0124] In a preferred embodiment of the present invention, the heating rate after adding the toughening agent is controlled at 1~2℃ / min, and the system temperature is controlled to not exceed 45℃ during the entire preparation process, so as to avoid premature reaction of the residual -NCO groups in the HMC-polyurethane modified epoxy resin or agglomeration of core-shell particles due to high temperature.

[0125] Preferably, during the vacuum degassing process, the viscosity of the system needs to be controlled at 8000~12000 mPa·s. If the viscosity exceeds the range, it can be adjusted by fine-tuning the temperature or rotation speed.

[0126] Preferably, in step S3, the filler and thixotropic agent need to be dried at 105~110℃ for 2~3 hours and then cooled to room temperature before being added to ensure that the moisture content is ≤0.1% and to avoid introducing air bubbles.

[0127] Preferably, in step S4, the curing agent and curing accelerator are pre-mixed and then added in batches: the curing agent and curing accelerator are mixed evenly at a mass ratio of 2~10:1, and then added to the system in 2~3 batches with an interval of 5 minutes between each batch to ensure that the curing system is evenly dispersed.

[0128] The present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other.

[0129] In the following embodiments, unless otherwise specified, all raw material components are commercially available products.

[0130] Example 1

[0131] Raw material formula, by weight

[0132] Bisphenol F type epoxy resin: Dow DER 354, 12 parts;

[0133] First bisphenol A type epoxy resin: E-51, 15 parts;

[0134] Core-shell modified epoxy resin: Fujian Jinghan Materials YT-3154A, 15 parts;

[0135] Toughening agent: Complexed high-tech EPU-133L, 12 parts;

[0136] Curing agent: Dicyandiamide, 3 parts;

[0137] Curing accelerator: Complexed high-tech HUA5050, 0.3 parts;

[0138] Filler: Heavy calcium carbonate, 20 parts;

[0139] Desiccant: Calcium oxide, 4 parts;

[0140] Thixotropic agent: Fumed silica, 3 parts;

[0141] Silane coupling agent: KH560, 0.3 parts;

[0142] Pigment: Carbon black, 0.03 parts;

[0143] HMC-polyurethane modified epoxy resin: 20 parts.

[0144] The preparation method of HMC-polyurethane modified epoxy resin is as follows:

[0145] (1) Synthesis of PHMC

[0146] 1,6-hexanediol and dimethyl carbonate were fed in a molar ratio of 1:1.1, with tetrabutyl titanate added as a catalyst. The amount of tetrabutyl titanate added was 0.2% of the sum of the mass of 1,6-hexanediol and dimethyl carbonate. The reaction was carried out under nitrogen protection, at 130°C and 0.1~0.3 MPa for 6 h to obtain polyhexamethylene carbonate diol (PHMC).

[0147] The number-average molecular weight of the PHMC was determined to be 1500 g / mol and the hydroxyl value was 74.8 mg KOH / g by gel permeation chromatography (GPC, GB / T 36214.4-2018).

[0148] (2) Preparation of polyurethane prepolymer

[0149] Dehydrated PHMC and diisocyanate were fed in a molar ratio of 1:1.35, and dibutyltin dilaurate (DBTDL) was used as a catalyst. The amount of catalyst was 0.08% of the total mass of PHMC and diisocyanate. The reaction was carried out under nitrogen protection and at 85°C for 2.5 h to obtain a polyurethane prepolymer with -NCO at the end.

[0150] (3) Epoxy resin modification

[0151] The polyurethane prepolymer and a second bisphenol A type epoxy resin with an epoxy equivalent of 160~180 g / eq were fed at a mass ratio of 1:2. The second bisphenol A type epoxy resin used was E-51. The mixture was treated at 70℃ for 5 h, followed by vacuum degassing at -0.09~-0.1 MPa for 30~40 min to obtain the HMC-polyurethane modified epoxy resin. The residual epoxy groups were determined to be 0.18 eq / 100 g using the hydrochloric acid-acetone method (GB / T 1677-2008), and the unreacted -NCO groups were determined to be 0.07 eq / 100 g using the di-n-butylamine titration method (GB / T 12009.4-2016).

[0152] The preparation method of low-temperature impact-resistant epoxy structural adhesive is as follows:

[0153] S1 matrix premix: Under normal temperature and nitrogen protection conditions, add bisphenol F type epoxy resin and first bisphenol A type epoxy resin, and stir at 200 rpm for 15 min to obtain epoxy matrix mixture.

[0154] S2 toughening system fusion: First, core-shell modified epoxy resin and HMC-polyurethane modified epoxy resin are added sequentially to the epoxy matrix mixture. The mixture is stirred at room temperature for 20 minutes while maintaining a rotation speed of 200 rpm. Then, the toughening agent is added, and the temperature is increased to 35°C at a rate of 1.5°C / min. The rotation speed is adjusted to 250 rpm, and the mixture is stirred for 25 minutes. The system temperature is controlled to not exceed 45°C throughout the entire preparation process to ensure that the toughening component is completely compatible with the epoxy matrix, thus obtaining an epoxy-toughening composite system.

[0155] S3 functional component dispersion: First, add filler and thixotropic agent to the epoxy-toughening composite system (the filler and thixotropic agent are first dried at 105~110℃ for 2~3h), increase the speed to 430rpm, and stir at room temperature for 35min; then add silane coupling agent, desiccant and pigment in sequence, and keep the speed at 350rpm for 18min.

[0156] S4 Curing System Mixing: Cool the system from step S3 to 25~30℃, add curing agent and curing accelerator, and stir at 230 rpm for 13 minutes to ensure that the curing components are evenly dispersed and do not cause premature curing.

[0157] The curing agent and curing accelerator are added as follows: first, the curing agent and curing accelerator are mixed evenly at a mass ratio of 2~10:1, and then added to the system in 2~3 batches;

[0158] S5 Vacuum Degassing: Under vacuum of -0.09 to -0.1 MPa and temperature of 30 to 40°C, the viscosity of the system is controlled at 8000 to 12000 mPa·s, and degassing is performed for 25 minutes. During this period, low-speed stirring at 80 rpm is used to assist in degassing, thus obtaining the low-temperature impact resistant epoxy structural adhesive.

[0159] The material is then discharged at room temperature and sealed in packaging.

[0160] Example 2

[0161] The difference between the raw material formulation and Example 1 is that:

[0162] The core-shell modified epoxy resin is 10 parts, the HMC-polyurethane modified epoxy resin is 15 parts, and the toughening agent is 10 parts.

[0163] The rest is the same as in Example 1.

[0164] The preparation methods for HMC-polyurethane modified epoxy resin and low-temperature impact resistant epoxy structural adhesive are the same as in Example 1.

[0165] Example 3

[0166] The difference between the raw material formulation and Example 1 is that:

[0167] The core-shell modified epoxy resin is 20 parts, the HMC-polyurethane modified epoxy resin is 25 parts, and the toughening agent is 15 parts.

[0168] The rest is the same as in Example 1.

[0169] The preparation methods for HMC-polyurethane modified epoxy resin and low-temperature impact resistant epoxy structural adhesive are the same as in Example 1.

[0170] Example 4

[0171] The difference between the raw material formulation and Example 1 is that:

[0172] The HMC-polyurethane modified epoxy resin is 22 parts, and the toughening agent is 10 parts;

[0173] The rest is the same as in Example 1.

[0174] The preparation methods for HMC-polyurethane modified epoxy resin and low-temperature impact resistant epoxy structural adhesive are the same as in Example 1.

[0175] Example 5

[0176] The difference between the raw material formulation and Example 1 is that:

[0177] The HMC-polyurethane modified epoxy resin is 17 parts, the toughening agent is 15 parts, and the other components are the same as in Example 1.

[0178] The preparation methods for HMC-polyurethane modified epoxy resin and low-temperature impact resistant epoxy structural adhesive are the same as in Example 1.

[0179] Example 6

[0180] The difference between the raw material formulation and Example 1 is that:

[0181] The core-shell modified epoxy resin was 12 parts, the toughening agent was 15 parts, and the rest was the same as in Example 1.

[0182] The preparation methods for HMC-polyurethane modified epoxy resin and low-temperature impact resistant epoxy structural adhesive are the same as in Example 1.

[0183] Example 7

[0184] The difference between the raw material formulation and Example 1 is that:

[0185] The toughening agent used was Lanxess Trixene BI 7774, and the other conditions were the same as in Example 1.

[0186] The preparation methods for HMC-polyurethane modified epoxy resin and low-temperature impact resistant epoxy structural adhesive are the same as in Example 1.

[0187] Example 8

[0188] The difference between the raw material formulation and Example 1 is that:

[0189] The core-shell modified epoxy resin used was complexed high-tech EPX-152, and the toughening agent was 15 parts. Other aspects were the same as in Example 1.

[0190] The preparation methods for HMC-polyurethane modified epoxy resin and low-temperature impact resistant epoxy structural adhesive are the same as in Example 1.

[0191] Example 9

[0192] The raw material formula is the same as that in Example 1.

[0193] The preparation method of HMC-polyurethane modified epoxy resin differs from that in Example 1 in that:

[0194] In step (3), the mass ratio of polyurethane prepolymer to second bisphenol A type epoxy resin is 1:2.3, the reaction temperature is 60℃, and the reaction time is 5h.

[0195] The remaining steps are the same as in Example 1.

[0196] The residual epoxy groups were determined to be 0.16 eq / 100g according to the hydrochloric acid-acetone method in GB / T 1677-2008, and the unreacted -NCO groups were determined to be 0.07 eq / 100g according to the di-n-butylamine titration method in GB / T12009.4-2016.

[0197] The preparation method of the low-temperature impact resistant epoxy structural adhesive is the same as in Example 1.

[0198] Example 10

[0199] The raw material formula is the same as that in Example 1.

[0200] The preparation method of HMC-polyurethane modified epoxy resin differs from that in Example 1 in that:

[0201] In step (2), the molar ratio of PHMC to diisocyanate is 1:1.3;

[0202] In step (3), the mass ratio of the prepolymer to the second bisphenol A epoxy resin is 1:2.0, the reaction temperature is 75℃, and the reaction time is 5h.

[0203] The remaining steps are the same as in Example 1.

[0204] The residual epoxy groups were determined to be 0.18 eq / 100g according to the hydrochloric acid-acetone method in GB / T 1677-2008, and the unreacted -NCO groups were determined to be 0.06 eq / 100g according to the di-n-butylamine titration method in GB / T12009.4-2016.

[0205] The preparation method of the low-temperature impact resistant epoxy structural adhesive is the same as in Example 1.

[0206] Example 11

[0207] The raw material formula is the same as that in Example 1.

[0208] The preparation method of HMC-polyurethane modified epoxy resin differs from that in Example 1 in that:

[0209] In step (2), the molar ratio of PHMC to diisocyanate is 1:1.4;

[0210] In step (3), the mass ratio of the prepolymer to the second bisphenol A epoxy resin is 1:1.8, the reaction temperature is 80℃, and the reaction time is 5.0h.

[0211] The remaining steps are the same as in Example 1.

[0212] The residual epoxy groups were determined to be 0.19 eq / 100g according to the hydrochloric acid-acetone method in GB / T 1677-2008, and the unreacted -NCO groups were determined to be 0.09 eq / 100g according to the di-n-butylamine titration method in GB / T12009.4-2016.

[0213] The preparation method of the low-temperature impact resistant epoxy structural adhesive is the same as in Example 1.

[0214] Comparative Example 1

[0215] The difference between the raw material formulation and Example 1 is that:

[0216] HMC-modified polyurethane epoxy resin was not used; otherwise, it was the same as in Example 1.

[0217] The preparation method of the epoxy structural adhesive is the same as in Example 1.

[0218] Performance testing

[0219] (1) Impact strength at -45℃ (N / mm)

[0220] Testing standard: Based on ISO 11343

[0221] Sample preparation: The substrate is Q235 cold-rolled steel sheet. Prepare a test plate with a width of 20 mm and a thickness of 1.0 mm. Apply the sample to the test plate with a coating area of ​​30 mm × 20 mm. Use 0.2 mm diameter wire as a spacer to maintain a certain bonding thickness. Overlap and stack the samples. Scrape off the excess sample on both sides. Then clamp the sample from both sides with iron clamps. Then bake at 170℃ for 20 min to cure and leave at room temperature for 24 h.

[0222] Test: Place the sample in an impact tester, set the temperature to -45℃, keep it at that temperature for 4 hours, and test the impact strength.

[0223] (2) Tensile shear strength at 25℃ (MPa)

[0224] Testing standard: Based on GB / T 7124;

[0225] Sample preparation: The substrate is a Q235 cold-rolled steel sheet with dimensions of 100mm×25mm×1.6mm. It is wiped with anhydrous ethanol and dried. The adhesive layer thickness is controlled at 0.2mm, the bonding area is 25mm×12.5mm, and it is cured by baking at 170℃ for 20min and left at room temperature for 24h.

[0226] Test: The tensile shear strength of the cured sample was tested at a stretching speed of 50 mm / min.

[0227] (3) T-type peel strength (N / mm)

[0228] Testing standard: Based on GB / T 2791-1995;

[0229] Sample preparation: The substrate is Q235 cold-rolled steel sheet (thickness 0.8mm), with dimensions of 200mm×25mm, adhesive layer thickness of 0.2mm, coating area of ​​25mm×150mm, baked at 170℃ for 20min for curing, and left at room temperature for 24h;

[0230] Test: The cured sample was subjected to a peel test at a tensile speed of 50 mm / min.

[0231] (4) Rate of decrease in humidity and heat (%)

[0232] Testing standard: Based on GB / T 14074-2017;

[0233] Sample preparation: Same as (2) 25℃ tensile shear strength sample, and measure the initial tensile shear strength (τ0).

[0234] Humid heat aging treatment: The specimens were placed in a humid heat aging test chamber and placed under constant temperature and humidity conditions of (95±2)% relative humidity and (50℃±2)% for 480 hours.

[0235] After aging, the sample was left at room temperature for 24 hours, and then the tensile shear strength (τ1) after aging was measured using the same method. The rate of decrease in damp heat was: η = (τ1 / τ1) 0- τ1) / τ0×100%.

[0236] The test results of Examples 1-11 and Comparative Example 1 are shown in Table 1.

[0237] Table 1 Test results of Examples 1-11 and Comparative Example 1

[0238] .

[0239] As shown in Table 1, this invention uses bisphenol F type epoxy resin and first bisphenol A type epoxy resin to construct a rigid matrix framework, and core-shell modified epoxy resin, HMC-polyurethane modified epoxy resin, and toughening agent to construct a triple toughening system of "nanodots-molecular chains-flexible units". Efficient energy dissipation is achieved through "core-shell particles inducing micro-cracks, HMC-polyurethane modified epoxy resin flexible segments constraining the expansion of cracks, and toughening agent absorbing residual impact energy". This successfully solves the industry pain points of traditional epoxy structural adhesives, such as low-temperature embrittlement, high-temperature strength loss, and imbalance between strength and toughness.

[0240] At the same time, it works synergistically with fillers, desiccant, thixotropic agents, silane coupling agents and other components: it ensures the rigid support of the first bisphenol A type epoxy resin and bisphenol F type epoxy resin, and supplements the flexible unit to strengthen and toughen the synergistic effect; it also prevents filler sedimentation and sagging through thixotropic agents, improves weather resistance through desiccant, and enhances interfacial adhesion through silane coupling agents, taking into account both construction feasibility and appearance requirements.

[0241] All performance characteristics of Examples 1-11 meet the stringent requirements of cold-region automobiles and new energy vehicles: impact strength ≥55N / mm at extreme low temperature of -45℃, tensile shear strength ≥32MPa at room temperature, peel strength ≥11N / mm, and strength reduction rate after damp heat aging ≤7%.

[0242] The performance of Comparative Example 1 was significantly inferior to that of the Example, demonstrating that HMC-polyurethane modified epoxy resin is the core component for achieving a balance between strength and toughness and weather resistance stability.

[0243] The applicant declares that the present invention is illustrated by the above embodiments, but the present invention is not limited to the above process steps, nor does it mean that the present invention must rely on the above process steps for implementation. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, additions of auxiliary components, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A low-temperature impact-resistant epoxy structural adhesive, characterized in that, The epoxy structural adhesive comprises the following raw materials in parts by weight: 10-15 parts of bisphenol F type epoxy resin, 10-20 parts of first bisphenol A type epoxy resin, 10-20 parts of core-shell modified epoxy resin, 15-25 parts of HMC-polyurethane modified epoxy resin, 10-15 parts of toughening agent, 10-30 parts of filler, 0.1-0.5 parts of curing accelerator, 1-5 parts of curing agent, 3-5 parts of desiccant, 0.01-0.05 parts of pigment, 2-5 parts of thixotropic agent, and 0.1-0.5 parts of silane coupling agent; The residual epoxy groups in the HMC-polyurethane modified epoxy resin are 0.15~0.20 eq / 100g, and the unreacted -NCO groups are 0.05~0.10 eq / 100g; The HMC-polyurethane modified epoxy resin uses polyhexamethylene carbonate diol, synthesized from 1,6-hexanediol and dimethyl carbonate via transesterification, as a flexible segment precursor. The core-shell modified epoxy resin refers to an epoxy resin modified with core-shell particles, wherein the core-shell particles are polybutadiene rubber as the core and methyl methacrylate as the shell, the particle size of the core-shell particles is 50~200nm, and the content of the core-shell particles in the core-shell modified epoxy resin is 10~20%.

2. The low-temperature impact-resistant epoxy structural adhesive as described in claim 1, characterized in that, The mass ratio of the core-shell modified epoxy resin, HMC-polyurethane modified epoxy resin and toughening agent is 1:(1~1.5):(0.5~1).

3. The low-temperature impact-resistant epoxy structural adhesive as described in claim 1, characterized in that, The polyhexamethylene carbonate diol has a number-average molecular weight of 1000~2000 g / mol and a hydroxyl value of 56~112 mg KOH / g.

4. The low-temperature impact-resistant epoxy structural adhesive as described in claim 1, characterized in that, The preparation method of the HMC-polyurethane modified epoxy resin includes: (1) Synthesis of polyhexamethylene carbonate diol 1,6-hexanediol and dimethyl carbonate were fed in a molar ratio of 1:1.05~1.2 and reacted under nitrogen protection, 120~140℃, and 0.1~0.3MPa for 4~8h to obtain polyhexamethylene carbonate diol; (2) Preparation of polyurethane prepolymer Dehydrated polyhexamethylene carbonate diol and diisocyanate were fed in a molar ratio of 1:1.2~1.5 and reacted under nitrogen protection at 80~90℃ for 2~3 hours to obtain a polyurethane prepolymer with -NCO terminal. (3) Epoxy resin modification The HMC-polyurethane modified epoxy resin is prepared by feeding polyurethane prepolymer and second bisphenol A type epoxy resin with an epoxy equivalent of 160~180g / eq at a mass ratio of 1:1.5~2.5, treating at 50~80℃ for 5h, and then degassing under vacuum.

5. The low-temperature impact-resistant epoxy structural adhesive as described in claim 1, characterized in that, The toughening agent is a polyurethane toughening agent, and the polyurethane toughening agent simultaneously meets the following technical characteristics: (1) Viscosity at 25℃ is 3000~12000 mPa·s; (2) The number-average molecular weight is 1500~3000 g / mol, and the molecular weight distribution width is ≤1.8; (3) The content of terminal -NCO groups is 0.5~1.5 eq / 100g, or the content of terminal -OH is 0.3~0.8 eq / 100g.

6. The low-temperature impact-resistant epoxy structural adhesive as described in claim 5, characterized in that, The polyurethane toughening agent includes one or more of Covestro Desmocap 11A, Lanxess Trixene BI 7774, or complexed high-tech EPU-133L.

7. The low-temperature impact-resistant epoxy structural adhesive according to any one of claims 1-6, characterized in that, The filler includes heavy calcium carbonate and / or modified aluminum hydroxide; The curing accelerator includes an organic urea accelerator; The curing agent includes one or more of dicyandiamide, sebacic dihydrazide or adipic dihydrazide; The desiccant includes calcium oxide desiccant; The thixotropic agent includes nano-calcium carbonate and / or fumed silica; The epoxy equivalent of the bisphenol F type epoxy resin is 150~170 g / eq; The epoxy equivalent of the first bisphenol A type epoxy resin is 160~180 g / eq; The silane coupling agent includes KH560 and / or KH580.

8. The method for preparing the low-temperature impact-resistant epoxy structural adhesive according to any one of claims 1-7, characterized in that, The preparation method includes: S1 matrix premix: Under normal temperature and nitrogen protection conditions, add bisphenol F type epoxy resin and first bisphenol A type epoxy resin, and stir at a speed of 150~250 rpm for 10~20 min to obtain epoxy matrix mixture; S2 toughening system fusion: First, add core-shell modified epoxy resin and HMC-polyurethane modified epoxy resin sequentially to the epoxy matrix mixture, and stir at room temperature for 15-25 minutes while maintaining a rotation speed of 150-250 rpm; then add toughening agent, heat to 30-40℃, adjust the rotation speed to 200-300 rpm, and stir for 20-30 minutes to obtain epoxy-toughening composite system; S3 Functional Component Dispersion: First, add filler and thixotropic agent to the epoxy-toughening composite system, increase the rotation speed to 350~500 rpm, and stir at room temperature for 30~40 min; then add silane coupling agent, desiccant and pigment in sequence, and keep the rotation speed at 300~400 rpm for 15~20 min. S4 Curing System Mixing: Cool the system from step S3 to 25~30℃, add curing agent and curing accelerator, and stir at 200~250rpm for 10~15min; S5 Vacuum Degassing: Degas for 20-30 minutes under vacuum conditions of -0.09 to -0.1 MPa and temperature of 30-40℃, with low-speed stirring at 50-100 rpm to assist in degassing, to obtain the low-temperature impact resistant epoxy structural adhesive.

9. The preparation method according to claim 8, characterized in that: The heating rate after adding the toughening agent is controlled at 1~2℃ / min, and the system temperature is controlled to not exceed 45℃ throughout the entire preparation process; During vacuum degassing, the viscosity of the system needs to be controlled at 8000~12000 mPa·s. If the viscosity exceeds the range, it can be adjusted by fine-tuning the temperature or rotation speed.