Wide-temperature-range cured epoxy structural adhesive composition for automobile manufacturing and preparation method of wide-temperature-range cured epoxy structural adhesive composition

Abstract

The invention relates to the technical field of thermosetting adhesives, in particular to a wide-temperature-range cured epoxy structural adhesive composition for automobile manufacturing and a preparation method of the wide-temperature-range cured epoxy structural adhesive composition. The invention discloses a wide-temperature-range cured epoxy structural adhesive composition for automobile manufacturing. The composition comprises the following components in parts by mass: 30-50 parts of epoxy resin; 3-10 parts of a microcapsule coated hydrazide curing agent; 2 to 6 parts of dicyandiamide; 10 to 30 parts of a toughening agent; 0.1 to 5 parts of a reactive diluent; 0.5 to 8 parts of a thixotropic agent; 10 to 20 parts of filler; and 0.5-5 parts of a moisture absorption agent. The wide-temperature-range cured epoxy structural adhesive composition for automobile manufacturing has a wide curing temperature window, has good storage stability at room temperature, and has high strength, high toughness and excellent impact resistance; the technical problems that an existing epoxy structural adhesive is poor in adaptability in different temperature zones, a curing window of a curing system is narrow, low-temperature curing is insufficient and poor in performance, and the existing epoxy structural adhesive becomes brittle due to excessive high-temperature curing crosslinking are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of thermosetting adhesives, and in particular to a wide-temperature-range curing epoxy structural adhesive composition for automobile manufacturing and a preparation method thereof. Background Art

[0002] Epoxy structural adhesives, due to their excellent bond strength and heat resistance, are widely used in automotive manufacturing, electronic packaging, and building structural bonding. In the automotive industry, epoxy structural adhesives are commonly used in processes such as spot welding, reinforcement bonding, and body structure bonding. The curing process typically relies on heat energy provided by an electrophoresis baking line. Conventional epoxy structural adhesives achieve optimal performance only at relatively high temperatures (e.g., 160°C to 180°C). This can lead to incomplete curing and insufficient strength for some manufacturers with lower process temperatures or for structural components in certain insulated or shielded areas of the vehicle body. In particular, some manufacturers set the electrophoresis baking temperature at only 160°C. As a result, certain areas (such as door reinforcements, door rings, and rear floor structures) reach actual temperatures of only 130°C to 150°C due to thermal shielding or thermal inertia, failing to meet the full curing requirements of traditional structural adhesives.

[0003] Dicyandiamide is a commonly used latent curing agent with good thermosetting properties, but its activity is relatively low, with an initial reaction temperature typically at 180°C. Higher temperatures are required to activate the cure. Even though the addition of a curing accelerator can lower the initial reaction temperature, high-temperature performance is affected, and the shelf life is correspondingly shortened. While hydrazide curing agent systems have a low reaction initial temperature, they are highly hygroscopic. Upon absorbing moisture, they hydrolyze to form free amines, which catalyze the epoxy resin curing reaction. This accelerates the viscosity increase at room temperature, causing premature colloid failure and shortening the shelf life. Existing single curing systems for epoxy structural adhesives struggle to meet the special requirements of large temperature variations in different electrophoretic processes. Summary of the Invention

[0004] In response to the problems raised in the background technology, the purpose of the present invention is to propose a wide-temperature range curing epoxy structural adhesive composition for automobile manufacturing, which has a wide curing temperature window, good storage stability at room temperature, high strength, high toughness and excellent impact resistance. It solves the technical problems of existing epoxy structural adhesives such as poor adaptability in different temperature zones, narrow curing window of the curing system, insufficient low-temperature curing and poor performance, and brittleness due to excessive cross-linking during high-temperature curing.

[0005] Another object of the present invention is to propose a preparation method for the above-mentioned wide-temperature-range curing epoxy structural adhesive composition for automobile manufacturing, which combines an aqueous in-situ polymerization method with a melt coating method. The method is simple to operate, has low equipment requirements, mild reaction conditions, and controllable costs, and is suitable for industrial-scale production.

[0006] To achieve this object, the present invention adopts the following technical solutions: A wide temperature range curing epoxy structural adhesive composition for automobile manufacturing, comprising the following components in parts by weight: 30-50 parts of epoxy resin; 3-10 parts of microcapsule-encapsulated hydrazide curing agent; 2-6 parts of dicyandiamide; 10-30 parts of toughening agent; 0.1 to 5 parts of active diluent; 0.5-8 parts of thixotropic agent; 10-20 parts of filler; 0.5-5 parts of moisture absorbent; The microcapsule-encapsulated hydrazide curing agent comprises a core material and a shell material, wherein the core material is a hydrazide-zinc acetylacetonate complex, the raw materials of the hydrazide-zinc acetylacetonate complex include hydrazide and zinc acetylacetonate, and the shell material comprises an inner shell and an outer shell, wherein the inner shell is a urea-formaldehyde resin and the outer shell is polycaprolactone.

[0007] Further, in the raw materials of the hydrazide-zinc acetylacetonate complex, the mass ratio of hydrazide to zinc acetylacetonate is 1:(0.05-0.2), and the hydrazide is any one of glutaric dihydrazide, adipic dihydrazide and sebacic dihydrazide; The raw materials of the inner shell include urea and formaldehyde solution; The mass ratio of the core material, the inner shell and the outer shell is 1: (0.5-1): (0.2-0.5).

[0008] To further illustrate, the mass ratio of the urea to the formaldehyde solution is 1:(1.5-2).

[0009] To further illustrate, the molecular weight of the polycaprolactone is 20,000 to 100,000 g / mol.

[0010] To further illustrate, the thickness of the outer shell is 5-10 μm, and the thickness of the inner shell is 20-30 μm.

[0011] To further illustrate, the epoxy resin is one or a combination of bisphenol A epoxy resin and bisphenol F epoxy resin.

[0012] It is further explained that the toughening agent includes at least two of polyurethane, core-shell rubber particles and carboxyl-terminated liquid nitrile rubber.

[0013] To further illustrate, the reactive diluent includes one or more of versatile glycidyl carbonate, benzyl glycidyl ether and p-tert-butylphenyl glycidyl ether.

[0014] It is further explained that the thixotropic agent is any one of fumed silica and organic bentonite; The filler is any one of calcium carbonate, alumina and quartz powder; The moisture absorbent is calcium oxide.

[0015] A method for preparing a wide-temperature-range curing epoxy structural adhesive composition for automobile manufacturing, comprising the following steps: Step A: preparing a hydrazide-zinc acetylacetonate complex: dissolving hydrazide in N,N-dimethylformamide to obtain a hydrazide solution, then dropping a suspension of zinc acetylacetonate in anhydrous ethanol into the hydrazide solution, heating under reflux for reaction, and filtering and drying the precipitate to obtain a hydrazide-zinc acetylacetonate complex after completion of the reaction; Step B: Preparing microcapsules encapsulating a hydrazide curing agent: dissolving polyvinyl alcohol in deionized water, adding a hydrazide-zinc acetylacetonate complex, and dispersing the mixture to obtain a suspension emulsion; adding urea and formaldehyde solutions; adjusting the pH to 7.5-8.0 with sodium tripolyphosphate; and heating the mixture to obtain a urea-formaldehyde resin. The urea-formaldehyde resin is coated on the outer surface of the hydrazide-zinc acetylacetonate complex to form the inner shell; heating and melting polycaprolactone, adding polycaprolactone dropwise under stirring, coating the surface of the inner shell with the polycaprolactone to form the outer shell, and cooling, filtering and drying to obtain microcapsules encapsulating the hydrazide curing agent; Step C: preparing an epoxy structural adhesive composition: uniformly mixing epoxy resin, toughening agent, reactive diluent, thixotropic agent, filler and moisture absorbent, adding microcapsule-encapsulated hydrazide curing agent and dicyandiamide and mixing evenly to obtain a wide temperature range curing epoxy structural adhesive composition for automobile manufacturing.

[0016] Compared with the prior art, the embodiments of the present invention have the following beneficial effects: 1. The double latent curing system of hydrazide curing agent and dicyandiamide is encapsulated in microcapsules. The shell material of the microcapsule encapsulated hydrazide curing agent is a double-shell composite structure composed of an inner shell urea-formaldehyde resin and an outer shell polycaprolactone. The shell material is wrapped in a double-shell composite structure, and the core material uses hydrazide-acetylacetonate zinc complex as the active substance, polycaprolactone as a flexible chain segment, and urea-formaldehyde resin as a thermally stable barrier. The outer shell begins to soften at around 60℃~70℃, allowing the urea-formaldehyde resin in the inner shell to begin to rupture at 100℃~130℃, releasing The core material hydrazide-acetylacetonate zinc complex, that is, the release temperature of the core material is 100°C to 130°C. At a lower temperature of 130°C to 160°C, the hydrazide-acetylacetonate zinc complex encapsulated in the microcapsules plays a major role, and at a higher temperature of 160°C to 210°C, dicyandiamide plays a major role. Hydrazide-acetylacetonate zinc and dicyandiamide are curing agents with two different reaction temperatures, thereby achieving a wide curing temperature window, and complete curing can be achieved within a wide temperature range of 130°C to 210°C.

[0017] 2. When stored at room temperature, the inner and outer shells of the microcapsules encapsulating the hydrazide curing agent can encapsulate the hydrazide-zinc acetylacetonate complex. The hydrazide-zinc acetylacetonate complex is not simply physically mixed with the urea-formaldehyde resin and polycaprolactone, but rather encapsulated within a double-shell composite structure of urea-formaldehyde resin and polycaprolactone. The hydrophobic polycaprolactone coating in the outer layer of the microcapsules significantly reduces the contact probability between the hydrazide groups and the epoxy groups in the composition, enhancing the inertness of the system and preventing the hydrazide-zinc acetylacetonate complex from simply physically mixing with other raw materials, which could lead to slow reaction at room temperature and affect storage stability. The urea-formaldehyde resin in the inner shell provides a tightly sealed package. Under storage conditions of 40°C for 30 days, the viscosity increase rate of the mixed system is less than 30%, and the shear strength decrease rate is less than 5%, which is superior to uncoated or single-shell latent curing agents.

[0018] 3. By using microcapsules to encapsulate a dual-curing system of hydrazide curing agent and dicyandiamide, the dual-curing system has a synergistic effect: the urea bond (-NH-CO-NH-) of the microcapsulated hydrazide-zinc acetylacetonate complex and the triazine ring (-C3N3-) of dicyandiamide are entangled with each other through hydrogen bonds and π-π conjugation, forming an interpenetrating network (IPN), which significantly improves the high-temperature shear resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The present invention is a schematic diagram of the encapsulation structure of a hydrazide curing agent encapsulated in microcapsules of a wide-temperature-range curing epoxy structural adhesive composition for automobile manufacturing according to an embodiment of the present invention.

[0020] Figure 2 Schematic diagram of a heat flow curve of a wide temperature range curing epoxy structural adhesive composition for automobile manufacturing according to one embodiment of the present invention. DETAILED DESCRIPTION

[0021] A wide temperature range curing epoxy structural adhesive composition for automobile manufacturing, comprising the following components in parts by weight: 30-50 parts of epoxy resin; 3-10 parts of microcapsule-encapsulated hydrazide curing agent; 2-6 parts of dicyandiamide; 10-30 parts of toughening agent; 0.1 to 5 parts of active diluent; 0.5-8 parts of thixotropic agent; 10-20 parts of filler; 0.5-5 parts of moisture absorbent; like Figure 1 As shown, the microcapsule encapsulating the hydrazide curing agent includes a core material and a shell material, wherein the core material is a hydrazide-zinc acetylacetonate complex, the raw materials of the hydrazide-zinc acetylacetonate complex include hydrazide and zinc acetylacetonate, the shell material includes an inner shell and an outer shell, the inner shell is a urea-formaldehyde resin, and the outer shell is polycaprolactone. Figure 1 From inside to outside, there are core material, inner shell and outer shell.

[0022] The wide temperature range curing epoxy structural adhesive composition for automobile manufacturing of the present invention comprises a dual latent curing system of a microcapsule-encapsulated hydrazide curing agent and dicyandiamide. The shell material of the microcapsule-encapsulated hydrazide curing agent is a double-shell composite structure consisting of an inner shell urea-formaldehyde resin and an outer shell polycaprolactone. The shell material is wrapped with the double-shell composite structure, and the core material adopts a hydrazide-acetylacetonate zinc complex as an active substance, polycaprolactone as a flexible chain segment, and urea-formaldehyde resin as a thermally stable barrier. The outer shell begins to soften at about 60°C to 70°C, so that the urea-formaldehyde resin of the inner shell can be heated at 100°C to 130°C. It starts to break at 0℃ and releases the core material hydrazide-acetylacetonate zinc complex, that is, the release temperature of the core material is 100℃~130℃. At the lower temperature of 130℃~160℃, the hydrazide-acetylacetonate zinc complex encapsulated in the microcapsules plays a major role, and at the higher temperature of 160℃~210℃, dicyandiamide plays a major role. Hydrazide-acetylacetonate zinc and dicyandiamide are curing agents with two different reaction temperatures, respectively, thereby achieving a wide curing temperature window, and complete curing can be achieved within the wide temperature range of 130℃~210℃.

[0023] Furthermore, when stored at room temperature, the inner and outer shells of the microcapsules encapsulating the hydrazide curing agent can encapsulate the hydrazide-zinc acetylacetonate complex. The hydrazide-zinc acetylacetonate complex is not simply physically mixed with the urea-formaldehyde resin and polycaprolactone, but rather encapsulated within a double-shell composite structure of urea-formaldehyde resin and polycaprolactone. The hydrophobic polycaprolactone coating in the outer layer of the microcapsules significantly reduces the probability of contact between the hydrazide groups and the epoxy groups in the composition, enhancing the system's inertness and preventing the hydrazide-zinc acetylacetonate complex from simply physically mixing with other raw materials, which could lead to slow reactions at room temperature and compromise storage stability. The urea-formaldehyde resin in the inner shell provides a tightly sealed package. Under storage conditions of 40°C for 30 days, the viscosity increase rate of the mixed system is less than 30%, and the shear strength decrease rate is less than 5%, surpassing unencapsulated or single-shell latent curing agents.

[0024] Furthermore, a dual-curing system of microcapsules encapsulating hydrazide curing agent and dicyandiamide has a synergistic effect: the urea bond (-NH-CO-NH-) of the microcapsulated hydrazide-zinc acetylacetonate complex and the triazine ring (-C3N3-) of dicyandiamide are entangled through hydrogen bonds and π-π conjugation to form an interpenetrating network (IPN), significantly improving the high-temperature shear resistance. The reaction mechanism of the hydrazide-zinc acetylacetonate complex is as follows: Step 1: Nucleophilic attack; A-NH2 of hydrazide acetylacetonate zinc acac - The carbonyl group (C=O) initiates a nucleophilic attack to form an intermediate with a hydroxyl group: Zn(acac)2+H2NNH-R→Zn(acac)(-CH(OH)NHR-)+acac - ; Step 2: Dehydration to form bonds; The intermediate removes one molecule of H2O to produce a urea bond (-NH-CO-NH-), and simultaneously protonates to release acacH: Zn(acac)(-CH(OH)NHR-)→Zn(acac)(-CO-NH-R-)+H2O; Step 3: Generate coordination structure; Zinc ion (Zn 2+ , tetracoordinate) binds to the following groups: 1 unreacted acac- (bidentate coordination, providing 2 O); urea ligand (from hydrazide): carbonyl oxygen (O) and hydrazide nitrogen (N) with Zn 2+ Coordinate to form a five-membered chelate ring.

[0025] The wide-temperature-curing epoxy structural adhesive composition for automotive manufacturing utilizes a dual latent curing system consisting of a microcapsule-encapsulated hydrazide curing agent and dicyandiamide. Fully curing is achieved within a wide temperature range (baking window) of 130°C to 210°C. After thermal curing within this range, the composition exhibits mechanical properties such as shear strength ≥20 MPa, T-peel strength ≥8 N / mm, and impact peel strength ≥20 N / mm. This significantly improves the adaptability and bonding reliability of vehicle body structural parts in various temperature zones. Furthermore, the composition can be stably stored for at least six months below 25°C and exhibits good storage stability at room temperature. It possesses high strength, high toughness, and excellent impact resistance, making it widely applicable in the bonding of automotive body structural parts. This overcomes the technical issues of existing epoxy structural adhesives, such as poor adaptability across temperature zones, a narrow curing window, insufficient and poor performance from low-temperature curing, and brittleness from excessive crosslinking during high-temperature curing.

[0026] Further, in the raw materials of the hydrazide-zinc acetylacetonate complex, the mass ratio of hydrazide to zinc acetylacetonate is 1:(0.05-0.2), and the hydrazide is any one of glutaric dihydrazide, adipic dihydrazide and sebacic dihydrazide; The raw materials of the inner shell include urea and formaldehyde solution; The mass ratio of the core material, the inner shell and the outer shell is 1: (0.5-1): (0.2-0.5).

[0027] To further illustrate, the mass ratio of the urea to the formaldehyde solution is 1:(1.5-2).

[0028] Preferably, the molecular weight of the polycaprolactone is 20,000 to 100,000 g / mol.

[0029] The softening temperature of the outer shell can be controlled by the molecular weight of the polycaprolactone; the higher the molecular weight, the higher the softening temperature.

[0030] Preferably, the outer shell has a thickness of 5 to 10 μm, and the inner shell has a thickness of 20 to 30 μm.

[0031] The unsealing temperature can be controlled by the cross-linking degree of the urea-formaldehyde resin (the mass ratio of urea to formaldehyde solution is controlled at 1:1.5 to 1:2.0) and the thickness of the shell material (the outer shell is 5 to 10 μm, and the inner shell is 20 to 30 μm). The lower the cross-linking degree of the urea-formaldehyde resin, the thinner the shell thickness and the lower the unsealing temperature, thereby achieving precise control of the unsealing temperature of the microcapsule-encapsulated hydrazide curing agent.

[0032] Preferably, the epoxy resin is one or a combination of bisphenol A epoxy resin and bisphenol F epoxy resin.

[0033] It is further explained that the toughening agent includes at least two of polyurethane, core-shell rubber particles and carboxyl-terminated liquid nitrile rubber.

[0034] To further illustrate, the reactive diluent includes one or more of versatile glycidyl carbonate, benzyl glycidyl ether and p-tert-butylphenyl glycidyl ether.

[0035] It is further explained that the thixotropic agent is any one of fumed silica and organic bentonite; The filler is any one of calcium carbonate, alumina and quartz powder; The moisture absorbent is calcium oxide.

[0036] A method for preparing a wide-temperature-range curing epoxy structural adhesive composition for automobile manufacturing, comprising the following steps: Step A: preparing a hydrazide-zinc acetylacetonate complex: dissolving hydrazide in N,N-dimethylformamide to obtain a hydrazide solution, then dropping a suspension of zinc acetylacetonate in anhydrous ethanol into the hydrazide solution, heating under reflux for reaction, and filtering and drying the precipitate to obtain a hydrazide-zinc acetylacetonate complex after completion of the reaction; Step B: Preparing microcapsules encapsulating a hydrazide curing agent: dissolving polyvinyl alcohol in deionized water, adding a hydrazide-zinc acetylacetonate complex, and dispersing the mixture to obtain a suspension emulsion; adding urea and formaldehyde solutions; adjusting the pH to 7.5-8.0 with sodium tripolyphosphate; and heating the mixture to obtain a urea-formaldehyde resin. The urea-formaldehyde resin is coated on the outer surface of the hydrazide-zinc acetylacetonate complex to form the inner shell; heating and melting polycaprolactone, adding polycaprolactone dropwise under stirring, coating the surface of the inner shell with the polycaprolactone to form the outer shell, and cooling, filtering and drying to obtain microcapsules encapsulating the hydrazide curing agent; Step C: preparing an epoxy structural adhesive composition: uniformly mixing epoxy resin, toughening agent, reactive diluent, thixotropic agent, filler and moisture absorbent, adding microcapsule-encapsulated hydrazide curing agent and dicyandiamide and mixing evenly to obtain a wide temperature range curing epoxy structural adhesive composition for automobile manufacturing.

[0037] Preferably, in step A, the reaction is refluxed at 60° C. for 4 hours. During the reaction, the solution gradually changes from turbid to clear, and a white precipitate is finally generated. The precipitate is filtered and dried to obtain a hydrazide-acetylacetonate zinc complex.

[0038] Preferably, in step B, the pH is adjusted to 7.5-8.0 with sodium tripolyphosphate, and the mixture is heated and stirred at 60°C for 2 hours to obtain a urea-formaldehyde resin. In step B, polyvinyl alcohol (PVA) is added as an emulsifier to form a stable emulsion through emulsification and steric hindrance, thereby assisting the urea-formaldehyde resin in film formation and promoting the deposition of the urea-formaldehyde resin.

[0039] Preferably, in the step C, polycaprolactone is added dropwise under high-speed stirring at a speed of 800 rpm, so that the polycaprolactone is evenly wrapped on the surface of the inner shell to form the flexible outer shell.

[0040] The preparation method of the wide-temperature-range curing epoxy structural adhesive composition for automobile manufacturing adopts a combination of an aqueous in-situ polymerization method and a melt coating method, which is simple to operate, has low equipment requirements, mild reaction conditions, and controllable costs, and is suitable for industrial-scale production.

[0041] For ease of understanding of the present invention, the present invention will be described more fully below. The present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0042] If no specific techniques or conditions are specified in the examples, the experiments were carried out according to the techniques or conditions described in the literature in the field or according to the product instructions. All reagents or instruments used without specifying the manufacturer are commercially available conventional products.

[0043] The raw materials used in the following examples and comparative examples are as follows: Epoxy resin: Guodu Chemical YD-128, YD-134, YDF-170.

[0044] Toughening agent: polyurethane from Japan ADICO QR-9466; core-shell rubber particles from Japan Kaneka MX-154; Huntsman CTBN 1300×13 from the United States.

[0045] Polyvinyl alcohol: Japan Kuraray POVALTM22-88.

[0046] Polycaprolactone: Swedish Perstorp Capa 6400, Capa 6500, Capa 6800.

[0047] Example 1 A wide temperature range curing epoxy structural adhesive composition for automobile manufacturing is composed of the following raw material components: 40 parts of epoxy resin (using epoxy resin YD-128); 6 parts of microcapsule-encapsulated hydrazide curing agent; 4 parts of dicyandiamide; 28 parts of toughening agent (8 parts of polyurethane QR-9466 and 20 parts of core-shell rubber particles MX-154); 1 part of active diluent (using tert-butyl glycidyl carbonate); 5 parts of thixotropic agent (using fumed silica); 15 parts of filler (calcium carbonate); 1 part of moisture absorbent (calcium oxide); The core material (hydrazide-zinc acetylacetonate complex) of the microcapsule-encapsulated hydrazide curing agent is made of hydrazide (adipyl dihydrazide) and zinc acetylacetonate, with a mass ratio of hydrazide to zinc acetylacetonate of 1:0.1. The inner shell is urea-formaldehyde resin, with a mass ratio of polyvinyl alcohol, urea, and formaldehyde solution of 1:3:4.5 among the raw materials of the inner shell. The outer shell uses polycaprolactone with a molecular weight of 37,000 g / mol.

[0048] A wide temperature range curing epoxy structural adhesive composition for automobile manufacturing is prepared by the following steps: Step A: Preparation of hydrazide-zinc acetylacetonate complex: Preparation of hydrazide solution: Dissolve 10 g of hydrazide (using adipic dihydrazide) in 100 mL of N,N-dimethylformamide, add 0.5 mL of triethylamine as a catalyst, and stir until completely dissolved to obtain a hydrazide solution; Pretreatment of zinc acetylacetonate: add 1 g of zinc acetylacetonate to 50 mL of anhydrous ethanol and ultrasonically disperse for 15 minutes to form an anhydrous ethanol suspension of zinc acetylacetonate; Complexation reaction: Slowly drop a suspension of zinc acetylacetonate in anhydrous ethanol into the hydrazide solution while mechanically stirring (at 200 rpm). After the addition is complete, heat the mixture to 60°C and reflux for 4 hours. During the reaction, the solution gradually changes from turbid to clear, eventually forming a white precipitate. After the reaction is complete, cool the mixture to room temperature, collect the precipitate by filtration, and wash it three times with 10 mL of cold ethanol (-5°C). Dry the product in a vacuum drying oven at 50°C for 12 hours to obtain a hydrazide (adipic acid hydrazide)-zinc acetylacetonate complex. Step B: Preparation of microcapsules encapsulating hydrazide curing agent: In-situ coating of urea-formaldehyde inner shell: 80 g of deionized water and 1.0 g of polyvinyl alcohol were added to a three-necked flask, heated to 60° C. and stirred until the PVA was completely dissolved. 10 g of dried hydrazide-zinc acetylacetonate complex was slowly added, and ultrasonic dispersion was used for 10 minutes to form a stable suspension emulsion. 3 g of urea and 4.5 g of formaldehyde solution were added to the system, and stirring was continued. The pH was adjusted to 7.5-8.0 with sodium tripolyphosphate, and the temperature was raised to 60° C. and heated and kept for 2 hours to form urea-formaldehyde resin, thereby generating microcapsules with a primary urea-formaldehyde cross-linked shell layer. The urea-formaldehyde resin was coated on the outer surface of the hydrazide-zinc acetylacetonate complex to form the inner shell; Polycaprolactone shell coating: 2.5 g of polycaprolactone Capa 6400 (molecular weight 37,000 g / mol) was heated to approximately 75°C in a small beaker to completely melt the polycaprolactone. The reaction solution obtained by in-situ coating of the urea-formaldehyde inner shell was cooled to approximately 45°C. The molten polycaprolactone was slowly added dropwise under high-speed stirring (800 rpm) and stirred for 20 minutes to uniformly coat the surface of the inner shell with the polycaprolactone to form a flexible outer shell. The resulting system was allowed to cool to form microcapsules with a composite double-shell structure. The microcapsules were filtered, washed twice with deionized water, and dried under vacuum at low temperature for 12 hours to obtain microcapsules encapsulated with hydrazide curing agent (powder). The yield of the hydrazide-zinc acetylacetonate complex is about 80%, the yield of the inner shell urea-formaldehyde resin is about 70%, and the yield of the outer shell polycaprolactone is about 90%. The mass ratio of the core material, inner shell, and outer shell in the obtained microcapsules encapsulating the hydrazide curing agent is 1:0.66:0.28. The thickness of the inner shell is about 22 μm, and the thickness of the outer shell is about 7 μm. Step C: Preparation of epoxy structural adhesive composition: Main mixing stage: add the formulated amount of epoxy resin into the high-speed dispersing kettle, add the formulated amount of toughening agent and reactive diluent, heat to 60°C, stir slowly and evenly, add the formulated amount of thixotropic agent, filler and moisture absorbent in batches, increase the speed to 1500rpm, stir for 20 minutes to mix evenly; Add curing components: cool to below 40°C, add dicyandiamide, and slowly add microencapsulated hydrazide curing agent. Stir at a low speed of 300 rpm to prevent shear breakage. Stir for 10 minutes to mix evenly, ensuring uniform dispersion without breaking the shell. Vacuum degassing (-0.08 MPa) for 30 minutes to remove residual air. Place in an aluminum tube or aluminum foil composite bag and seal for storage (storage temperature ≤ 25°C, shelf life at least 6 months) to prepare a wide-temperature-range curing epoxy structural adhesive composition for automotive manufacturing.

[0049] Example 2 A wide temperature range curing epoxy structural adhesive composition for automobile manufacturing is composed of the following raw material components: 48 parts of epoxy resin (using epoxy resin YD-134); 7.5 parts of microencapsulated hydrazide curing agent; 5 parts of dicyandiamide; 15 parts of toughening agent (9 parts of polyurethane QR-9466 and 20 parts of carboxyl-terminated liquid nitrile rubber CTBN 1300×13); 0.5 parts of active diluent (benzyl glycidyl ether); 3 parts of thixotropic agent (organic bentonite); 18 parts of filler (aluminum oxide); 3 parts of moisture absorbent (calcium oxide); The preparation method of Example 2 is the same as that of Example 1, except that: the added hydrazide is glutaric hydrazide, the mass of the added zinc acetylacetonate is 0.5 g, that is, the mass ratio of hydrazide to zinc acetylacetonate is 1:0.05, the mass of the added polycaprolactone is 3 g, and the added polycaprolactone is Capa 6500 (molecular weight 50,000 g / mol), the yield of the hydrazide-zinc acetylacetonate complex is approximately 80%, the yield of the inner shell urea-formaldehyde resin is approximately 70%, and the yield of the outer shell polycaprolactone is approximately 90%. The mass ratio of the core material, inner shell, and outer shell of the obtained microcapsule-encapsulated hydrazide curing agent is 1:0.66:0.34, the thickness of the inner shell is approximately 22 μm, and the thickness of the outer shell is approximately 8 μm. A wide temperature range curing epoxy structural adhesive composition for automobile manufacturing is prepared.

[0050] Example 3 A wide temperature range curing epoxy structural adhesive composition for automobile manufacturing is composed of the following raw material components: 50 parts of epoxy resin (using epoxy resin YDF-170); 6 parts of microcapsule-encapsulated hydrazide curing agent; 3 parts of dicyandiamide; 22 parts of toughening agent (using 20 parts of core-shell rubber particles MX-154 and 2 parts of carboxyl-terminated liquid nitrile rubber CTBN 1300×13); 1 part of active diluent (p-tert-butylphenyl glycidyl ether); 2 parts of thixotropic agent (using fumed silica); 15 parts of filler (quartz powder); 1 part of moisture absorbent (calcium oxide); The preparation method of Example 3 is the same as that of Example 1, except that: the added hydrazide is sebacic acid hydrazide, the mass of the added zinc acetylacetonate is 0.5 g, that is, the mass ratio of hydrazide to zinc acetylacetonate is 1:0.05, the added urea is 3 g, the formaldehyde solution is 6 g, the mass of the added polycaprolactone is 2 g, and the added polycaprolactone is Capa 6800 (molecular weight 80,000 g / mol), the yield of the hydrazide-zinc acetylacetonate complex is approximately 80%, the yield of the inner shell urea-formaldehyde resin is approximately 70%, and the yield of the outer shell polycaprolactone is approximately 90%. The mass ratio of the core material, inner shell, and outer shell in the obtained microcapsule-encapsulated hydrazide curing agent is 1:0.79:0.23, the thickness of the inner shell is approximately 26 μm, and the thickness of the outer shell is approximately 7 μm. A wide temperature range curing epoxy structural adhesive composition for automobile manufacturing is prepared.

[0051] Example 4 A wide temperature range curing epoxy structural adhesive composition for automobile manufacturing is composed of the following raw material components: 35 parts of epoxy resin (using epoxy resin YD-128); 4 parts of microcapsule-encapsulated hydrazide curing agent; 3 parts of dicyandiamide; 29 parts of toughening agent (5 parts of polyurethane QR-9466 and 24 parts of core-shell rubber particles MX-154); 4 parts of active diluent (using tert-butyl glycidyl carbonate); 6 parts of thixotropic agent (using fumed silica); 15 parts of filler (calcium carbonate); 4 parts of moisture absorbent (calcium oxide); The preparation method of Example 4 is the same as that of Example 1, except that: the mass of zinc acetylacetonate added is 1.5 g, that is, the mass ratio of hydrazide to zinc acetylacetonate is 1:0.15, the mass of polycaprolactone added is 3 g, and the added polycaprolactone is Capa 6500 (molecular weight 50,000 g / mol), the yield of hydrazide-zinc acetylacetonate complex is about 80%, the yield of inner shell urea-formaldehyde resin is about 70%, and the yield of outer shell polycaprolactone is about 90%. The mass ratio of the core material, inner shell, and outer shell of the obtained microcapsule-encapsulated hydrazide curing agent is 1:0.66:0.34, the thickness of the inner shell is about 22 μm, and the thickness of the outer shell is about 8 μm. A wide temperature range curing epoxy structural adhesive composition for automobile manufacturing is prepared.

[0052] Example 5 The raw materials of a wide temperature range curing epoxy structural adhesive composition for automobile manufacturing are composed of the following components: 30 parts of epoxy resin (using epoxy resin YD-128); 3 parts of microcapsule-encapsulated hydrazide curing agent; 2 parts of dicyandiamide; 10 parts of toughening agent (using 3 parts of polyurethane QR-9466 and 7 parts of core-shell rubber particles MX-154); 0.1 part of active diluent (using tert-butyl glycidyl carbonate); 0.5 parts of thixotropic agent (using fumed silica); 10 parts of filler (calcium carbonate); 0.5 parts of moisture absorbent (calcium oxide); The preparation method and other raw materials of Example 5 are the same as those of Example 1, and a wide temperature range curing epoxy structural adhesive composition for automobile manufacturing is prepared.

[0053] Example 6 The raw materials of a wide temperature range curing epoxy structural adhesive composition for automobile manufacturing are composed of the following components: 50 parts of epoxy resin (using epoxy resin YD-128); 10 parts of microcapsule-encapsulated hydrazide curing agent; 6 parts of dicyandiamide; 30 parts of toughening agent (using 10 parts of polyurethane QR-9466 and 20 parts of core-shell rubber particles MX-154); 5 parts of active diluent (using tert-butyl glycidyl carbonate); 8 parts of thixotropic agent (using fumed silica); 20 parts of filler (calcium carbonate); 5 parts of moisture absorbent (calcium oxide); The preparation method and other raw materials of Example 6 are the same as those of Example 1, and a wide temperature range curing epoxy structural adhesive composition for automobile manufacturing is prepared.

[0054] Comparative Example 1 The raw materials of an epoxy structural adhesive composition are composed of the following components: 45 parts of epoxy resin (using epoxy resin YD-128); 6 parts of hydrazide (adipic dihydrazide)-zinc acetylacetonate complex (the hydrazide-zinc acetylacetonate complex prepared in Example 1); 4 parts of dicyandiamide; 23 parts of toughening agent (8 parts of polyurethane QR-9466 and 15 parts of core-shell rubber particles MX-154); 1 part of active diluent (using tert-butyl glycidyl carbonate); 5 parts of thixotropic agent (using fumed silica); 15 parts of filler (calcium carbonate); 1 part of moisture absorbent (calcium oxide); An epoxy structural adhesive composition is prepared by the following steps: Step A, main mixing stage: add the formulated amount of epoxy resin to a high-speed dispersing kettle; add a toughening agent and a reactive diluent, heat to 60°C, and slowly stir to mix; add a thixotropic agent, a filler, and a moisture absorbent in batches, increase the speed to 1500 rpm, and stir for 20 minutes to form a uniform mixing system.

[0055] Step B, Adding Curing Components: Cool the mixture to below 40°C, then sequentially add dicyandiamide and hydrazide (adipic dihydrazide)-zinc acetylacetonate complex with low-speed stirring (300 rpm). Stir for 10 minutes to ensure uniform dispersion. Vacuum degassing (-0.08 MPa) for 30 minutes was performed to remove any residual air, thereby producing an epoxy structural adhesive composition.

[0056] Step C, Packaging and Storage: Pack into aluminum tubes or aluminum foil composite bags and seal for storage (recommended storage temperature ≤ 25°C).

[0057] Comparative Example 2 The raw materials of an epoxy structural adhesive composition are composed of the following components: 45 parts of epoxy resin (using epoxy resin YD-128); 6 parts of adipic dihydrazide; 4 parts of dicyandiamide; 23 parts of toughening agent (8 parts of polyurethane QR-9466 and 15 parts of core-shell rubber particles MX-154); 1 part of active diluent (using tert-butyl glycidyl carbonate); 5 parts of thixotropic agent (using fumed silica); 15 parts of filler (calcium carbonate); 1 part of moisture absorbent (calcium oxide); The preparation method of Comparative Example 2 is the same as that of Comparative Example 1, and an epoxy structural adhesive composition is prepared.

[0058] Storage stability and mechanical property tests were performed on the epoxy structural adhesive compositions prepared in Examples 1 to 6 and Comparative Examples 1 and 2: 1. Storage stability: After 30 days of storage at 40°C, measure the initial viscosity and the viscosity after storage, and calculate the viscosity change rate. The viscosity is tested using a Brookfield viscometer with a 7# rotor, 0.6 rpm, and a test temperature of 23°C. The initial shear strength and the shear strength after storage are measured, and the shear strength decrease rate is calculated. Observe for any precipitation or gelation.

[0059] 2. Mechanical properties: Shear strength, T-peel strength and impact peel strength were tested after baking at three conditions: low temperature 130℃*20 minutes, medium temperature 170℃*20 minutes, and high temperature 210℃*40 minutes. The test was conducted after standing at room temperature for 24 hours after baking.

[0060] The test results are shown in Tables 1 and 2 below.

[0061] Table 1 Storage stability test results As shown in Table 1, the viscosity change rate of the compositions using microcapsules to encapsulate the hydrazide curing agent (Examples 1 to 6) is approximately 100% lower than that of the unencapsulated complex (Comparative Example 1) and over 300% lower than that of the free hydrazide curing agent (Comparative Example 2). This is because the free hydrazide curing agent in Comparative Example 2 physically contacts the epoxy resin, causing a trace amount of slow crosslinking during storage, resulting in a gradual thickening of the system. This crosslinking density not only weakens the uniformity of the colloid but also reduces shear strength, leading to difficulties in application and coating, and the risk of mechanical property failure. Although the hydrazide curing agent in Comparative Example 1 is coordinated and complexed with zinc acetylacetonate, the lone pair of electrons on the amino nitrogen of the hydrazide curing agent is "bound" by the zinc ion, significantly reducing the nucleophilicity of the amino group and preventing it from effectively attacking the epoxy ring of the epoxy group, thus somewhat inhibiting the crosslinking rate at room temperature, it still tends to crosslink slowly during storage, resulting in a shear strength drop nearly 100% higher than that of the examples. In the embodiment, the hydrazide curing agent is encapsulated in microcapsules, and the hydrazide-acetylacetonate zinc complex is encapsulated in microcapsules to form a dual latent mechanism of "coordination bond chemical inhibition + microcapsule physical isolation", which greatly improves the storage stability of the wide temperature range curing epoxy structural adhesive composition for automobile manufacturing.

[0062] Table 2 Mechanical properties test results As shown in Table 2, Example 1 differs from Comparative Example 1 in whether the hydrazide curing agent utilizes microencapsulation technology. The similar mechanical properties indicate that microencapsulation technology does not affect the reaction between the hydrazide curing agent and the epoxy resin, while significantly improving storage stability. Comparative Example 2, on the other hand, differs from Comparative Example 1 in that it does not utilize coordination complexation technology. This results in poor storage stability and very poor mechanical properties at low temperatures of 130°C. (Comparative Example 2 does not fully cure at 130°C, resulting in very low adhesive strength. Impact peel testing requires very high adhesive strength, and the adhesive breaks when the strength is insufficient. Consequently, the sensor's force reading is 0, and the impact peel strength under these curing conditions is 0.) This is because zinc acetylacetonate blocks the active sites of the curing agent through coordination chemistry at room temperature. At high temperatures, the coordination bonds break, releasing the zinc ions from the complex and immediately coordinating with epoxy groups, triggering a catalytic mechanism. This "intelligent switching" mechanism enables the single-component epoxy adhesive to achieve the dual advantages of long shelf life and rapid high-temperature curing. The polycaprolactone of the outer shell of the microcapsule encapsulating the hydrazide curing agent in the embodiment of the present invention begins to soften at around 60°C, and the urea-formaldehyde resin of the inner shell softens and breaks at 100°C~130°C, releasing the hydrazide-zinc acetylacetonate complex. After the zinc ions dissociate, they activate adipic dihydrazide to react rapidly with the epoxy groups (amine crosslinking), forming an initial crosslinking network, providing basic mechanical strength (shear strength ≥20 MPa, T-peel strength ≥8 N / mm, impact peel strength ≥20 N / mm). When the temperature rises to 180°C~210°C, dicyandiamide completely decomposes and reacts with the epoxy groups to form a melamine-epoxy crosslinking reaction, generating a rigid structure containing triazine rings, which compensates for the insufficient crosslinking of the hydrazide-zinc acetylacetonate complex at high temperatures. Figure 2 The figure shows a heat flow curve for a wide-temperature curing epoxy structural adhesive composition for automotive manufacturing. The test was performed using differential scanning calorimetry (DSC) with a dynamic temperature ramp from 100°C to 250°C at a rate of 10°C / min. The test materials were epoxy resin E51: microencapsulated adipic dihydrazide-zinc acetylacetonate complex (prepared in Example 1): dicyandiamide in a ratio of 100:8:8. By leveraging the temperature difference between the reaction rates of the two curing agents, the combination achieves a synergistic effect of "medium-temperature rapid curing combined with high-temperature deep crosslinking," extending the pot life of the epoxy resin system. This makes it particularly suitable for complex applications requiring varying curing temperatures between 130°C and 210°C.

[0063] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A wide temperature range curing epoxy structural adhesive composition for automobile manufacturing, characterized in that: The composition comprises the following components in parts by weight: 30-50 parts of epoxy resin; 3-10 parts of microcapsule-encapsulated hydrazide curing agent; 2-6 parts of dicyandiamide; 10-30 parts of toughening agent; 0.1 to 5 parts of active diluent; 0.5-8 parts of thixotropic agent; 10-20 parts of filler; 0.5-5 parts of moisture absorbent; The microcapsule-encapsulated hydrazide curing agent comprises a core material and a shell material, wherein the core material is a hydrazide-zinc acetylacetonate complex, the raw materials of the hydrazide-zinc acetylacetonate complex include hydrazide and zinc acetylacetonate, and the shell material comprises an inner shell and an outer shell, wherein the inner shell is a urea-formaldehyde resin and the outer shell is polycaprolactone.

2. The wide temperature range curing epoxy structural adhesive composition for automobile manufacturing according to claim 1, characterized in that: In the raw materials of the hydrazide-zinc acetylacetonate complex, the mass ratio of hydrazide to zinc acetylacetonate is 1:(0.05-0.2), and the hydrazide is any one of glutaric dihydrazide, adipic dihydrazide and sebacic dihydrazide; The raw materials of the inner shell include urea and formaldehyde solution; The mass ratio of the core material, the inner shell and the outer shell is 1: (0.5-1): (0.2-0.5).

3. The wide temperature range curing epoxy structural adhesive composition for automobile manufacturing according to claim 2, characterized in that: The mass ratio of the urea to the formaldehyde solution is 1:(1.5-2).

4. The wide temperature range curing epoxy structural adhesive composition for automobile manufacturing according to claim 1, characterized in that: The molecular weight of the polycaprolactone is 20,000 to 100,000 g / mol.

5. The wide temperature range curing epoxy structural adhesive composition for automobile manufacturing according to claim 1, characterized in that: The outer shell has a thickness of 5 to 10 μm, and the inner shell has a thickness of 20 to 30 μm.

6. The wide temperature range curing epoxy structural adhesive composition for automobile manufacturing according to claim 1, characterized in that: The epoxy resin is one or a combination of bisphenol A epoxy resin and bisphenol F epoxy resin.

7. The wide temperature range curing epoxy structural adhesive composition for automobile manufacturing according to claim 1, characterized in that: The toughening agent comprises at least two of polyurethane, core-shell rubber particles and carboxyl-terminated liquid nitrile rubber.

8. The wide temperature range curing epoxy structural adhesive composition for automobile manufacturing according to claim 1, characterized in that: The active diluent includes one or more of versatile glycidyl carbonate, benzyl glycidyl ether and p-tert-butylphenyl glycidyl ether.

9. The wide temperature range curing epoxy structural adhesive composition for automobile manufacturing according to claim 1, characterized in that: The thixotropic agent is any one of fumed silica and organic bentonite; The filler is any one of calcium carbonate, alumina and quartz powder; The moisture absorbent is calcium oxide.

10. A method for preparing a wide temperature range curing epoxy structural adhesive composition for automobile manufacturing, characterized in that: The method for preparing the wide temperature range curing epoxy structural adhesive composition for automobile manufacturing according to any one of claims 1 to 9 comprises the following steps: Step A: preparing a hydrazide-zinc acetylacetonate complex: dissolving hydrazide in N,N-dimethylformamide to obtain a hydrazide solution, then dropping a suspension of zinc acetylacetonate in anhydrous ethanol into the hydrazide solution, heating under reflux for reaction, and filtering and drying the precipitate to obtain a hydrazide-zinc acetylacetonate complex after completion of the reaction; Step B: Preparing microcapsules encapsulating a hydrazide curing agent: dissolving polyvinyl alcohol in deionized water, adding a hydrazide-zinc acetylacetonate complex, and dispersing the mixture to obtain a suspension emulsion; adding urea and formaldehyde solutions; adjusting the pH to 7.5-8.0 with sodium tripolyphosphate; and heating the mixture to obtain a urea-formaldehyde resin. The urea-formaldehyde resin is coated on the outer surface of the hydrazide-zinc acetylacetonate complex to form the inner shell; heating and melting polycaprolactone, adding polycaprolactone dropwise under stirring, coating the surface of the inner shell with the polycaprolactone to form the outer shell, and cooling, filtering and drying to obtain microcapsules encapsulating the hydrazide curing agent; Step C: preparing an epoxy structural adhesive composition: uniformly mixing epoxy resin, toughening agent, reactive diluent, thixotropic agent, filler and moisture absorbent, adding microcapsule-encapsulated hydrazide curing agent and dicyandiamide and mixing evenly to obtain a wide temperature range curing epoxy structural adhesive composition for automobile manufacturing.

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