Latent curing agent, one-component epoxy resin composition and method for producing the same

Abstract

The application provides a latent curing agent, a single-component epoxy resin composition and a preparation method thereof, and belongs to the technical field of thermosetting resin curing.The preparation method of the latent curing agent comprises the following steps: after a vinyl monomer containing a tertiary amine group, an acrylic ester monomer, an emulsifier, an initiator and water are mixed, emulsion polymerization reaction is carried out, a copolymer emulsion is obtained, then a demulsifier is added to demulsify the copolymer emulsion, and after demulsification, drying is carried out to obtain copolymer powder; the copolymer powder and an organic acid are subjected to acid blocking reaction, and after the reaction is completed, the latent curing agent is obtained.The stable reversible acid amine salt is formed by the reaction of the tertiary amine functionalized vinyl polymer and the organic acid, the tertiary amine catalyzed epoxy resin is inhibited, the storage period of the curing agent and the epoxy resin mixture at 40 DEG C is prolonged to more than 3 months, the acid amine salt is dissociated when heated, the tertiary amine is released to restore the catalytic activity, rapid curing is realized, and good latency and reactivity are combined.

Description

Technical Field

[0001] This invention relates to the field of thermosetting resin curing technology, and more particularly to a latent curing agent, a one-component epoxy resin composition, and a method for preparing the same. Background Technology

[0002] Epoxy resins, as a crucial class of thermosetting polymers, have been a cornerstone material in fields such as electronic packaging, high-performance coatings, structural adhesives, and advanced composite materials since the mid-20th century, thanks to their superior mechanical properties, excellent adhesion, outstanding heat resistance, and good dimensional stability. From the micro-packaging of smartphone chips to the giant composite materials of wind turbine blades, from the high-temperature coatings of automotive engines to the lightweight structural components of aerospace, epoxy resins are ubiquitous, contributing to the development of modern industry towards precision and high performance.

[0003] In recent years, with the explosive growth of cutting-edge industries such as 5G communication, artificial intelligence, new energy vehicles, and semiconductors, electronic devices are evolving towards miniaturization, integration, and high reliability, while industrial production is transforming towards high efficiency, automation, and green practices. Single-component epoxy resin systems are gradually becoming a core research hotspot and key industrial focus in the field of materials science both domestically and internationally. Compared to traditional two-component epoxy resins (which require on-site mixing of resin and curing agent, resulting in cumbersome operation, short pot life, and waste), single-component systems achieve a disruptive breakthrough by pre-integrating epoxy resin and curing agent into the same package, achieving "stable storage at room temperature and instantaneous activation and curing upon heating." This characteristic essentially relies on a key material—latent curing agents.

[0004] Latent curing agents are considered the "heart" of single-component epoxy resin systems. Their unique feature lies in their ability, through sophisticated molecular design or physical isolation mechanisms, to "coexist peacefully" with the epoxy resin at room temperature (without significant cross-linking reactions), ensuring a sufficiently long pot life (typically ≥3 months, and even ≥6 months in high-end electronic packaging). When external heat is applied (e.g., to 120~200℃), the curing agent quickly "awakens," releasing active groups that react efficiently with the epoxy groups, completing cross-linking and curing in a short time (curing time can be reduced to several minutes to tens of minutes). This "intelligent response" characteristic not only drastically simplifies the application process (eliminating the need for on-site mixing and reducing human error) but also significantly improves production efficiency (suitable for automated dispensing and continuous production), while reducing volatile organic compound (VOC) emissions, aligning with the trend of green manufacturing.

[0005] The development of latent curing agent technology for epoxy resins aims to resolve the core contradiction between storage stability and rapid low-temperature curing. Currently, commonly used latent curing agents mainly include imidazoles, dicyandiamides, and acid anhydrides. Imidazole curing agents (such as 2-ethyl-4-methylimidazolium) have low curing temperatures (120~150℃) and high reactivity, but poor storage stability. They readily react with epoxy resins at room temperature, and unmodified imidazole compounds typically have a shelf life of less than 3 days at room temperature. Chemical modification methods such as salt formation, microencapsulation, or coordination with transition metals are needed to extend the shelf life to 3-6 months. While dicyandiamide curing agents offer a good shelf life of over 6 months, their compatibility with epoxy resins is poor, and they are prone to phase separation and crystallization during storage, leading to uneven curing. Acid anhydride curing agents (such as phthalic anhydride and tetrahydrophthalic anhydride) produce curing products with good heat resistance, but poor latency, requiring low-temperature storage. Furthermore, they are prone to absorbing moisture in humid environments, prematurely initiating the curing reaction.

[0006] More concerning is that most epoxy resin latent curing agents widely used in industry currently suffer from common problems such as complex synthesis processes, high energy consumption during production, and highly toxic raw materials. For example, the synthesis of some imidazole latent curing agents requires the use of highly corrosive reagents, and the production of some acid anhydride curing agents generates large amounts of organic wastewater, posing a significant pollution risk to the environment and contradicting current green chemistry and sustainable development concepts.

[0007] In recent years, researchers have developed a variety of novel latent curing agents. Patent US20080249258A1 employs a "core-shell" structure strategy of physical coating and cross-linking to prepare a latent curing agent, a relatively mature process: imidazole-epoxy adduct particles are coated with an ethyl cellulose membrane and then cross-linked with polyisocyanate, giving the curing agent excellent solvent resistance and storage stability, allowing it to remain stable at room temperature for extended periods. It rapidly releases the active ingredient to initiate curing at 110-130°C, with an exothermic peak temperature as low as 126°C. However, its drawbacks include the multi-step reaction process, strict requirements on solvents (such as saturated hydrocarbons with specific aniline points) and process conditions (such as stirring speed and temperature control), and the potential risk of uneven coating or shell rupture leading to decreased latent properties.

[0008] In contrast, patent WO2018 / 181045A1 demonstrates innovation at the molecular design level: achieving "self-latent" properties through the direct synthesis of novel bisphenol-imidazolium derivatives. The core advantages of this method are its well-defined molecular structure and more direct synthetic route, avoiding complex microencapsulation processes and simplifying production steps from the outset. Furthermore, precise functional group modification allows for flexible control of reactivity and latency, such as achieving long-term stability below 80°C and rapid curing above 100°C.

[0009] To address the issue of excessively high reactivity in traditional imidazole curing agents, CN115160229A proposes a chemical modification strategy: utilizing the reaction of epoxy resin and epoxy reactive diluent with imidazole, a coating layer is formed through the ring-opening addition of the epoxy group to the pyridine nitrogen at the 1-position of the imidazole and the molecular chain extension, effectively extending the latency by preventing contact between the active group and the epoxy group. This modification method is applicable to various imidazoles and their derivatives, significantly improving the applicability and latency control precision of imidazole curing agents, especially suitable for the stringent requirements of high-end electronics applications for curing triggering conditions. However, the synthesis of such compounds with specific structures is difficult and costly, and their broad applicability (such as compatibility with different epoxy resins) and long-term reliability still require a more comprehensive evaluation.

[0010] However, the aforementioned prior art has the following technical problems: 1) Insufficient latency: Existing imidazole curing agents are prone to react with epoxy resin at room temperature and have a short shelf life; 2) Excessively high curing temperature: Dicyandiamide-based curing agents have curing temperatures as high as 160~180℃, resulting in high energy consumption; 3) Complex preparation process: Existing modified imidazole curing agents have complicated synthesis steps and require the use of highly corrosive reagents; 4) Poor environmental friendliness: The production process of some curing agents generates a large amount of organic wastewater, polluting the environment; 5) Poor storage stability: Anhydride curing agents are hygroscopic and the curing reaction will be triggered prematurely in a humid environment.

[0011] Therefore, it is of great significance to provide a latent curing agent with good latency, excellent storage stability, adjustable curing temperature, simple preparation process, and environmental friendliness. Summary of the Invention

[0012] To address the aforementioned technical problems, the present invention aims to provide a latent curing agent, a one-component epoxy resin composition, and a method for preparing the same.

[0013] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing a latent curing agent, comprising the following steps: 1) A vinyl monomer containing a tertiary amine group, an acrylate monomer, an emulsifier, an initiator and water are mixed and subjected to emulsion polymerization to obtain a copolymer emulsion. Then, a demulsifier is added to demulsify the copolymer emulsion. After demulsification, the copolymer powder is dried to obtain a copolymer powder. 2) The copolymer powder and organic acid are subjected to an acid-blocking reaction. After the reaction is completed, a latent curing agent is obtained.

[0014] Furthermore, the vinyl monomer containing a tertiary amine group includes one or more of N-(3-dimethylaminopropyl)acrylamide, N,N-dimethylaminoethyl methacrylate, and N,N-diethylaminoethyl acrylate. The acrylate monomers include one or more of methyl acrylate, ethyl acrylate, butyl acrylate, and methyl methacrylate; The organic acids include one or more of fatty acids, hydroxycarboxylic acids, and aromatic carboxylic acids.

[0015] Furthermore, the emulsifier includes anionic emulsifiers and / or nonionic emulsifiers, wherein the anionic emulsifier includes one or more of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate and sodium fatty alcohol polyoxyethylene ether sulfate, and the nonionic emulsifier includes one or more of OP-10, Tween 80 and Span 80. The initiator includes one or more of potassium persulfate, ammonium persulfate, and sodium persulfate; The demulsifier includes one or more of calcium chloride, sodium chloride, and magnesium sulfate.

[0016] Furthermore, the molar ratio of the vinyl monomer containing the tertiary amine group to the acrylate monomer is 1:0.5~3; The molar ratio of the copolymer powder to the organic acid is 0.8~1.2:1.

[0017] Furthermore, the amount of the emulsifier used is 1-5% of the total mass of the vinyl monomers containing tertiary amine groups and the acrylate monomers; The amount of the initiator used is 0.1-1% of the total mass of the vinyl monomers containing tertiary amine groups and the acrylate monomers; The amount of water used is 2 to 5 times the total mass of the vinyl monomers and acrylate monomers containing tertiary amine groups; The amount of the demulsifier solution used is 1 to 5% of the mass of the copolymer emulsion.

[0018] Furthermore, a molecular weight regulator is added to the emulsion polymerization reaction; The molecular weight regulator includes one or more of n-dodecyl mercaptan, tert-dodecyl mercaptan, and mercaptoethanol; The amount of the molecular weight regulator is 0.1-1% of the total mass of the vinyl monomers and acrylate monomers containing tertiary amine groups.

[0019] Furthermore, the emulsion polymerization reaction is carried out at a temperature of 60-80°C for 2-6 hours. The acid blocking reaction is carried out at a temperature of 60-80°C for 1-3 hours.

[0020] This invention provides a latent curing agent prepared by the aforementioned preparation method.

[0021] This invention provides a one-component epoxy resin composition comprising an epoxy resin and the aforementioned latent curing agent; The amount of the latent curing agent added is 5-20% of the epoxy resin mass; The epoxy resin includes one or more of bisphenol A type epoxy resin, bisphenol F type epoxy resin, and phenolic epoxy resin.

[0022] The present invention also provides a method for preparing a one-component epoxy resin composition, wherein a latent curing agent is mixed with epoxy resin to obtain a one-component epoxy resin composition.

[0023] The beneficial effects of this invention are: 1) This invention utilizes the acid-blocking reaction between tertiary amine functionalized vinyl polymers and organic acids to form a stable and reversible acid amine salt structure at room temperature. This structure can effectively inhibit the catalytic activity of tertiary amine groups on epoxy resins, extending the storage period of the curing agent and epoxy resin blend at 40°C to more than 3 months. When heated to 80~120°C, the dissociation equilibrium of the acid amine salt shifts towards the free tertiary amine, thereby restoring catalytic activity and achieving rapid curing. It combines excellent latency with good curing reactivity. 2) By selecting different types of organic acids (such as fatty acids, hydroxycarboxylic acids, and aromatic carboxylic acids) and adjusting the copolymer composition, the present invention can flexibly control the curing start temperature in the range of 80~120℃, so as to meet the differentiated requirements of curing temperature for various application scenarios such as adhesives, coatings, and electronic packaging. 3) The cured product of this invention possesses a high glass transition temperature (typically >100℃) and excellent mechanical properties. Latent control is achieved through a dual mechanism of polymer structure fixation and reversible acid-amine salt chemical passivation. Furthermore, the polymer network formed after curing not only originates from the epoxy resin itself but also incorporates flexible acrylate polymer chains. This effectively improves the brittleness of the cured product without significantly negatively impacting the adhesive strength and heat resistance of the epoxy resin, giving it better toughness and impact resistance. Its tensile shear strength is not less than 20 MPa, and its impact strength is greater than 15 kJ / m². 2 ; 4) This invention uses a water-based emulsion polymerization process with mild reaction conditions. It does not require the use of highly corrosive reagents or large amounts of organic solvents. The production process is environmentally friendly and in line with the concepts of green chemistry and sustainable development. In addition, the raw materials are widely available and the synthesis steps are simple, making it suitable for large-scale industrial production and providing significant economic benefits. 5) The curing agent obtained by this invention has a polymer structure, which has excellent compatibility with epoxy resin. There are no phase separation or crystal precipitation during storage, and the curing reaction is uniform, ensuring the performance stability of the final product. Detailed Implementation

[0024] This invention provides a method for preparing a latent curing agent, comprising the following steps: 1) A vinyl monomer containing a tertiary amine group, an acrylate monomer, an emulsifier, an initiator and water are mixed and subjected to emulsion polymerization to obtain a copolymer emulsion. Then, a demulsifier is added to demulsify the copolymer emulsion. After demulsification, the copolymer powder is dried to obtain a copolymer powder. 2) The copolymer powder and organic acid are subjected to an acid-blocking reaction. After the reaction is completed, a latent curing agent is obtained.

[0025] In this invention, the vinyl monomer containing a tertiary amine group includes one or more of N-(3-dimethylaminopropyl)acrylamide, N,N-dimethylaminoethyl methacrylate and N,N-diethylaminoethyl acrylate, preferably N-(3-dimethylaminopropyl)acrylamide and / or N,N-dimethylaminoethyl methacrylate, and more preferably N-(3-dimethylaminopropyl)acrylamide.

[0026] In this invention, the acrylate monomers include one or more of methyl acrylate, ethyl acrylate, butyl acrylate and methyl methacrylate, preferably one or more of methyl acrylate, butyl acrylate and methyl methacrylate, and more preferably butyl acrylate and / or methyl methacrylate.

[0027] In this invention, the organic acid includes one or more of fatty acids, hydroxycarboxylic acids and aromatic carboxylic acids, preferably fatty acids and / or hydroxycarboxylic acids.

[0028] In this invention, the emulsifier includes anionic emulsifiers and / or nonionic emulsifiers. The anionic emulsifier includes one or more of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, and sodium fatty alcohol polyoxyethylene ether sulfate, preferably sodium dodecyl sulfate and / or sodium dodecylbenzene sulfonate, and more preferably sodium dodecyl sulfate. The nonionic emulsifier includes one or more of OP-10, Tween 80, and Span 80, preferably OP-10 and / or Tween 80, and more preferably OP-10.

[0029] In this invention, the initiator includes one or more of potassium persulfate, ammonium persulfate and sodium persulfate, preferably potassium persulfate and / or ammonium persulfate, and more preferably potassium ammonium persulfate.

[0030] In this invention, the demulsifier includes one or more of calcium chloride, sodium chloride and magnesium sulfate, preferably calcium chloride and / or sodium chloride, and more preferably calcium chloride.

[0031] In this invention, the molar ratio of the vinyl monomer containing the tertiary amine group to the acrylate monomer is 1:0.5~3, preferably 1:0.8~2.5, and more preferably 1:1~2; The molar ratio of the copolymer powder to the organic acid is 0.8~1.2:1, preferably 0.9~1.1:1, and more preferably 1:1.

[0032] In this invention, the amount of emulsifier used is 1-5% of the total mass of vinyl monomers containing tertiary amine groups and acrylate monomers, preferably 1.5-4%, and more preferably 2-3%; The amount of the initiator is 0.1-1% of the total mass of the vinyl monomers containing tertiary amine groups and the acrylate monomers, preferably 0.2-0.8%, and more preferably 0.3-0.5%. The amount of water used is 2 to 5 times the total mass of the vinyl monomers and acrylate monomers containing tertiary amine groups, preferably 2.5 to 4.5 times, and more preferably 3 to 4 times; The amount of the demulsifier solution used is 1-5% of the mass of the copolymer emulsion, preferably 1.5-4%, and more preferably 2-3%.

[0033] In this invention, a molecular weight regulator is added to the emulsion polymerization reaction; The molecular weight regulator includes one or more of n-dodecyl mercaptan, tert-dodecyl mercaptan, and mercaptoethanol, preferably n-dodecyl mercaptan and / or tert-dodecyl mercaptan, and more preferably n-dodecyl mercaptan.

[0034] In this invention, the amount of the molecular weight regulator is 0.1-1% of the total mass of the vinyl monomers containing tertiary amine groups and the acrylate monomers, preferably 0.2-0.8%, and more preferably 0.3-0.5%.

[0035] In this invention, the temperature of the emulsion polymerization reaction is 60~80℃, preferably 65~75℃, and more preferably 70℃; the time of the emulsion polymerization reaction is 2~6h, preferably 2.5~5.5h, and more preferably 3~5h.

[0036] In this invention, the temperature of the acid blocking reaction is 60~80℃, preferably 62~78℃, and more preferably 65~75℃; the time of the acid blocking reaction is 1~3h, preferably 1.5~2.5h, and more preferably 2h.

[0037] In this invention, after the acid blocking reaction is completed, vacuum distillation is also included. The purpose of vacuum distillation is to remove water and unreacted organic acids.

[0038] This invention provides a latent curing agent prepared by the aforementioned preparation method.

[0039] This invention provides a one-component epoxy resin composition comprising an epoxy resin and a latent curing agent; The amount of the latent curing agent added is 5-20% of the epoxy resin mass, preferably 7-18%, and more preferably 10-15%. The epoxy resin includes one or more of bisphenol A type epoxy resin, bisphenol F type epoxy resin and phenolic epoxy resin, preferably bisphenol A type epoxy resin and / or bisphenol F type epoxy resin, and more preferably bisphenol A type epoxy resin.

[0040] The present invention also provides a method for preparing a one-component epoxy resin composition, wherein a latent curing agent is mixed with epoxy resin to obtain a one-component epoxy resin composition.

[0041] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0042] Example 1

[0043] 15.6 g of N-(3-dimethylaminopropyl)acrylamide (DMAPAA), 12.8 g of butyl acrylate, 0.85 g of sodium dodecyl sulfate (SDS), 0.14 g of n-dodecyl mercaptan and 80 g of water were mixed and the mixture was left to stand for 30 minutes to obtain a pre-emulsion. 20g of water and 0.14g of potassium persulfate (KPS) were mixed to obtain an initiator solution. The pre-emulsion and the initiator solution were then subjected to emulsion polymerization under nitrogen protection at a temperature of 70℃ for 4 hours. After the reaction, a copolymer emulsion was obtained. The copolymer emulsion was demulsified, filtered, and washed with water using 3.8g of 10% calcium chloride solution. Finally, it was vacuum dried at 60℃ for 24 hours to obtain a white copolymer powder. 10g of copolymer powder and 1.61g of formic acid were subjected to an acid-blocking reaction at 65℃. After the reaction was completed in 2 hours, vacuum distillation was performed to remove water and unreacted formic acid, yielding a pale yellow solid product. After vacuum drying and low-temperature pulverization, a latent curing agent was obtained.

[0044] Example 2

[0045] 15.6g of N-(3-dimethylaminopropyl)acrylamide (DMAPAA), 10g of methyl methacrylate, 0.76g of emulsifier OP-10, 0.12g of n-dodecyl mercaptan and 80g of water were mixed and the mixture was left to stand for 30 minutes to obtain a pre-emulsion. 20g of water and 0.12g of ammonium persulfate (APS) were mixed to obtain an initiator solution. The pre-emulsion and the initiator solution were then subjected to emulsion polymerization under nitrogen protection at a temperature of 70℃ for 4 hours. After the reaction, a copolymer emulsion was obtained. The copolymer emulsion was demulsified, filtered, and washed with water using 3.7g of 10% calcium chloride solution. Finally, it was vacuum dried at 60℃ for 24 hours to obtain a white copolymer powder. 10g of copolymer powder and 3.15g of lactic acid were subjected to an acid-blocking reaction at 65℃. After the reaction was completed in 2 hours, vacuum distillation was performed to remove water and unreacted formic acid, yielding a pale yellow solid product. After vacuum drying and low-temperature pulverization, a latent curing agent was obtained.

[0046] Example 3

[0047] 15.6g of N-(3-dimethylaminopropyl)acrylamide (DMAPAA), 8.6g of methyl acrylate, 10g of ethyl acrylate, 1g of sodium dodecylbenzenesulfonate (SDBS), 0.17g of n-dodecyl mercaptan and 80g of water were mixed and the mixture was left to stand for 30 minutes to obtain a pre-emulsion. 20g of water and 0.17g of potassium persulfate (KPS) were mixed to obtain an initiator solution. The pre-emulsion and the initiator solution were then subjected to emulsion polymerization under nitrogen protection at a temperature of 70℃ for 4 hours. After the reaction, a copolymer emulsion was obtained. The copolymer emulsion was demulsified, filtered, and washed with water using 4g of 10% calcium chloride solution. Finally, it was vacuum dried at 60℃ for 24 hours to obtain a white copolymer powder. 10g of copolymer powder and 2.1g of acetic acid were subjected to an acid-blocking reaction at 65°C. After the reaction was completed in 2 hours, vacuum distillation was performed to remove water and unreacted formic acid, yielding a pale yellow solid product. After vacuum drying and low-temperature pulverization, a latent curing agent was obtained.

[0048] Comparative Example 1

[0049] Comparative Example 1 used an imidazole curing agent, 2-ethyl-4-methylimidazolium (2E4MI).

[0050] Comparative Example 2

[0051] Comparative Example 2 used dicyandiamide as a curing agent and Ajinomoto PN-23 from Japan as an accelerator.

[0052] Comparative Example 3

[0053] Compared with Example 1, the difference is that no organic acid was added to Comparative Example 3 for acid blocking reaction.

[0054] The curing agents and E51 epoxy resins of Examples 1-3, Comparative Examples 1 and 3 were mixed at a mass ratio of 15:100. Comparative Example 2 was mixed at a mass ratio of epoxy resin:curing agent:accelerator of 100:8:5. After stirring evenly, a single-component epoxy resin composition was obtained.

[0055] The curing characteristics of the one-component epoxy resin composition were tested using differential scanning calorimetry (DSC) at a heating rate of 10 °C / min. The test results are shown in Table 1.

[0056] Table 1 Latency Test Results

[0057] According to GB / T1 2007.7-1989, the single-component epoxy resin composition was stored in an oven at 40°C, and the gel time (120°C) was measured periodically. The test results are shown in Table 2.

[0058] Table 2 Storage stability test results

[0059] Note: "-" indicates that the system has gelled within the corresponding storage time and the gel time cannot be determined.

[0060] The single-component epoxy resin composition was cured at 120°C for 30 minutes to obtain a cured epoxy resin product. The properties of the cured epoxy resin product were tested according to GB / T1040.2-2006, and the test results are shown in Table 3.

[0061] Table 3 Performance test results of epoxy resin cured products

[0062] As shown in Tables 1-3, compared with the prior art, Examples 1-3 of the present invention show significant improvements in latency, curing activity and comprehensive mechanical properties.

[0063] Regarding latency, the curing initiation temperatures of Examples 1-3 were 85-92℃, significantly higher than those of Comparative Example 1 (70℃) with imidazole curing agents and Comparative Example 3 (80℃) without acid blocking. This indicates that blocking the tertiary amine groups with organic acids can effectively reduce their catalytic activity at low temperatures, thereby significantly delaying the premature reaction of the epoxy resin. Meanwhile, the gel time of the example systems remained relatively stable after 3 months of storage at 40℃, while Comparative Example 1 showed a significant reaction in a short period, and the gel time of Comparative Example 3 decreased rapidly. This suggests that unblocked or simply modified systems in the prior art cannot simultaneously achieve storage stability. Comparative Example 3, without acid blocking, showed a significantly shortened gel time during storage, indicating premature reaction, further demonstrating the crucial role of acid blocking in achieving latency control.

[0064] Regarding curing activity, the peak curing temperature of the embodiments of the present invention is 110~118℃, which is significantly lower than that of the dicyandiamide system comparative example 2 (140℃). This indicates that the present invention maintains good latency while avoiding the defect in the prior art that "high latency is necessarily accompanied by high curing temperature", and achieves synergistic optimization of latency and low-temperature curing performance.

[0065] Regarding the properties of the cured product, the glass transition temperature of the embodiments of the present invention is 118~120℃, the tensile shear strength is 24.8~25.5MPa, and the impact strength is 15.2~15.8kJ / m². While ensuring high heat resistance, it still possesses excellent mechanical properties and toughness. In contrast, although imidazole systems have lower curing temperatures, they have poor storage stability, while dicyandiamide systems, although having higher strength, have higher curing temperatures and limited process windows.

[0066] Therefore, by constructing a reversible acid amine salt structure, this invention effectively overcomes the problems of insufficient latency, high curing temperature, and difficulty in balancing performance in the prior art, achieving a good comprehensive balance between storage stability, curing activity, and mechanical properties, and has made significant technological progress.

[0067] As can be seen from the above embodiments, the present invention provides a latent curing agent, a one-component epoxy resin composition, and a method for preparing the same. The method for preparing the latent curing agent includes the following steps: mixing a vinyl monomer containing a tertiary amine group, an acrylate monomer, an emulsifier, an initiator, and water, and then performing an emulsion polymerization reaction to obtain a copolymer emulsion; subsequently adding a demulsifier to demulsify the copolymer emulsion; drying after demulsification to obtain a copolymer powder; and then performing an acid-blocking reaction between the copolymer powder and an organic acid. After the reaction is complete, the latent curing agent is obtained. The present invention utilizes the reaction of a tertiary amine-functionalized vinyl polymer with an organic acid to form a stable, reversible acid amine salt, inhibiting the tertiary amine catalysis of the epoxy resin, thus extending the storage period of the curing agent and epoxy resin mixture at 40°C to more than 3 months. Upon heating, the acid amine salt dissociates, releasing the tertiary amine and restoring catalytic activity, achieving rapid curing and exhibiting both good latency and reactivity.

[0068] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a latent curing agent, characterized in that, Includes the following steps: 1) A vinyl monomer containing a tertiary amine group, an acrylate monomer, an emulsifier, an initiator and water are mixed and subjected to emulsion polymerization to obtain a copolymer emulsion. Then, a demulsifier is added to demulsify the copolymer emulsion. After demulsification, the copolymer powder is dried to obtain a copolymer powder. 2) The copolymer powder and organic acid are subjected to an acid-blocking reaction. After the reaction is completed, a latent curing agent is obtained.

2. The method for preparing the latent curing agent according to claim 1, characterized in that, The vinyl monomers containing tertiary amine groups include one or more of N-(3-dimethylaminopropyl)acrylamide, N,N-dimethylaminoethyl methacrylate, and N,N-diethylaminoethyl acrylate. The acrylate monomers include one or more of methyl acrylate, ethyl acrylate, butyl acrylate, and methyl methacrylate; The organic acids include one or more of fatty acids, hydroxycarboxylic acids, and aromatic carboxylic acids.

3. The method for preparing the latent curing agent according to claim 1 or 2, characterized in that, The emulsifier includes anionic emulsifiers and / or nonionic emulsifiers. The anionic emulsifier includes one or more of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, and sodium fatty alcohol polyoxyethylene ether sulfate. The nonionic emulsifier includes one or more of OP-10, Tween 80, and Span 80. The initiator includes one or more of potassium persulfate, ammonium persulfate, and sodium persulfate; The demulsifier includes one or more of calcium chloride, sodium chloride, and magnesium sulfate.

4. The method for preparing the latent curing agent according to claim 3, characterized in that, The molar ratio of the vinyl monomer containing the tertiary amine group to the acrylate monomer is 1:0.5~3; The molar ratio of the copolymer powder to the organic acid is 0.8~1.2:

1.

5. The method for preparing the latent curing agent according to claim 4, characterized in that, The amount of the emulsifier used is 1-5% of the total mass of the vinyl monomers containing tertiary amine groups and the acrylate monomers; The amount of the initiator used is 0.1-1% of the total mass of the vinyl monomers containing tertiary amine groups and the acrylate monomers; The amount of water used is 2 to 5 times the total mass of the vinyl monomers and acrylate monomers containing tertiary amine groups; The amount of the demulsifier solution used is 1 to 5% of the mass of the copolymer emulsion.

6. The method for preparing the latent curing agent according to claim 4 or 5, characterized in that, A molecular weight regulator is added to the emulsion polymerization reaction; The molecular weight regulator includes one or more of n-dodecyl mercaptan, tert-dodecyl mercaptan, and mercaptoethanol; The amount of the molecular weight regulator is 0.1-1% of the total mass of the vinyl monomers and acrylate monomers containing tertiary amine groups.

7. The method for preparing the latent curing agent according to claim 6, characterized in that, The emulsion polymerization reaction is carried out at a temperature of 60-80°C for 2-6 hours. The acid blocking reaction is carried out at a temperature of 60-80°C for 1-3 hours.

8. A latent curing agent prepared by the preparation method according to any one of claims 1 to 7.

9. A one-component epoxy resin composition, characterized in that, Includes epoxy resin and the latent curing agent as described in claim 8; The amount of the latent curing agent added is 5-20% of the epoxy resin mass; The epoxy resin includes one or more of bisphenol A type epoxy resin, bisphenol F type epoxy resin, and phenolic epoxy resin.

10. A method for preparing the single-component epoxy resin composition according to claim 9, characterized in that, A one-component epoxy resin composition is obtained by mixing a latent curing agent with epoxy resin.

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