Epoxy resin latent curing accelerator and method for preparing the same

Abstract

This invention discloses a latent curing accelerator for epoxy resin and its preparation method. The latent curing accelerator has a structure as shown in formula (I). This latent curing accelerator remains chemically inert at room temperature, extending the shelf life of the epoxy resin and preventing viscosity increase or premature curing during storage. When the temperature is raised to a set level, the latent curing accelerator is activated, rapidly promoting the curing reaction of the epoxy resin. The curing speed and temperature can be adjusted by changing the amount of catalyst.

Description

Technical Field

[0001] This invention relates to the field of epoxy materials, and more particularly to epoxy resin latent curing accelerators and their preparation methods. Background Technology

[0002] Epoxy resins are among the most widely used thermosetting polymers, accounting for approximately 70% of the global thermosetting resin market. They are widely used in aerospace, electronics, automotive manufacturing, construction, composite materials, and coatings. This is due to their excellent mechanical properties, chemical stability, electrical insulation, and highly cross-linked structure. However, most epoxy resin formulations currently require individual storage of each component before use and must be prepared fresh for immediate application, which brings many inconveniences to industrial production. In large-scale industrial production, this requirement not only increases operational complexity and reduces production efficiency but also increases the risk of material waste.

[0003] To simplify production processes and reduce operational steps, achieving single-component storage and use of epoxy resins has become an important goal in the industry. Single-component formulations allow epoxy resins to be stored stably at room temperature for extended periods and cured by heating when needed. However, existing single-component formulations typically rely on latent curing agents, resulting in poor storage stability, a tendency for viscosity to rise, and premature curing of the resin. Furthermore, these formulations usually require high curing temperatures (typically around 150°C), which is detrimental to rapid production, increases process complexity and cost, and significantly raises energy consumption.

[0004] To address this issue, the introduction of latent catalysts provides an effective solution for achieving single-component epoxy resins. Latent catalysts remain inert at room temperature or lower temperatures, preventing premature curing of the epoxy resin and thus enabling long-term storage. Upon activation by heating, the catalyst is rapidly released, promoting rapid curing of the epoxy resin. This not only meets the storage requirements of epoxy resins but also ensures the mechanical properties and chemical stability of the cured material.

[0005] Therefore, developing a latent curing accelerator that can provide long-term storage stability for epoxy resin systems before activation and effectively promote rapid curing after activation has become the key to solving existing technical problems. Summary of the Invention

[0006] This invention aims to at least partially solve one of the technical problems in related technologies. The invention discloses a latent curing catalyst for epoxy resins, designed to improve the storage stability of epoxy resins and lower their curing temperature. This latent curing accelerator remains chemically inert at room temperature, extending the shelf life of epoxy resins and preventing viscosity increases or premature curing during storage. When the temperature is raised to a set level, the latent curing accelerator is activated, rapidly promoting the curing reaction of the epoxy resin. The curing speed and temperature can be adjusted by changing the catalyst dosage. This invention simplifies the production process, reduces energy consumption, and is particularly suitable for industrial applications requiring efficient production and storage. This latent curing accelerator is applicable to various epoxy systems, including epoxy-acid systems, epoxy-thiol systems, and epoxy-anhydride systems. Furthermore, the latent curing accelerator is also applicable to other alkali-catalyzed curing systems, including polyurethane, acrylate-thiol systems, cyanate ester resins, and polycarbonate.

[0007] In one aspect of the invention, a latent curing accelerator is provided. According to an embodiment of the invention, the latent curing accelerator has a structure as shown in formula (I):

[0008]

[0009] This latent curing accelerator remains chemically inert at room temperature, extending the shelf life of epoxy resins and preventing viscosity increases or premature curing during storage. When the set temperature is reached, the latent curing accelerator is activated, rapidly accelerating the curing reaction of the epoxy resin. The curing speed and temperature can be adjusted by changing the catalyst dosage. This latent curing accelerator is suitable for various epoxy systems, including epoxy-acid systems, epoxy-mercapto systems, and epoxy-anhydride systems. Furthermore, it is also suitable for other alkali-catalyzed curing systems, including polyurethane, acrylate-mercapto systems, cyanate ester resins, and polycarbonate.

[0010] In another aspect, the present invention also provides a method for preparing a latent curing accelerator. According to an embodiment of the present invention, the method includes:

[0011] Cyanoacetic acid was reacted with 1,5,7-triazabicyclo[4.4.0]decene-5-ene to obtain a latent curing accelerator having a structure as shown in formula (I).

[0012]

[0013] According to embodiments of the present invention, the method may further include at least one of the following additional technical features:

[0014] According to an embodiment of the present invention, the molar ratio of the cyanoacetic acid to the 1,5,7-triazabicyclo[4.4.0]decene-5-ene is (1-1.2):1.

[0015] According to an embodiment of the present invention, the cyanoacetic acid is pre-dissolved in methanol.

[0016] According to an embodiment of the present invention, the ratio of cyanoacetic acid to methanol is 0.893 g: 30 mL.

[0017] According to an embodiment of the present invention, the 1,5,7-triazabicyclo[4.4.0]decene-5-ene is pre-dissolved in 10% methanol.

[0018] According to an embodiment of the present invention, the ratio of the amount of 1,5,7-triazabicyclo[4.4.0]decene-5-ene to the amount of methanol is 1.392 g: 90 mL.

[0019] According to an embodiment of the present invention, the reaction time is 24 hours.

[0020] According to an embodiment of the present invention, the reaction temperature is room temperature.

[0021] In another aspect, the present invention also provides a method for preparing epoxy cured products. According to an embodiment of the present invention, the method includes:

[0022] Bisphenol A diglycidyl ether, an anhydride curing agent, and the previously mentioned latent curing accelerator or the latent curing accelerator prepared according to the previously mentioned method are mixed and cured to obtain an epoxy cured product.

[0023] According to embodiments of the present invention, the method may further include at least one of the following additional technical features:

[0024] According to an embodiment of the present invention, the molar ratio of bisphenol A diglycidyl ether to the anhydride curing agent is 0.5:(1-0.5), for example, 0.5:1 or 1:1.

[0025] According to an embodiment of the present invention, the latent curing accelerator is (0.25-1)% of the total mass of the bisphenol A diglycidyl ether and the anhydride curing agent, for example, 0.25%, 0.5%, 0.75% or 1%.

[0026] According to an embodiment of the present invention, the anhydride curing agent is methyltetrahydrophthalic anhydride.

[0027] According to an embodiment of the present invention, the mixing process is carried out at room temperature.

[0028] According to an embodiment of the present invention, the mixing process is carried out by stirring uniformly in a vortex.

[0029] According to an embodiment of the present invention, the curing process is carried out in a vacuum drying oven.

[0030] According to an embodiment of the present invention, the curing process is carried out in a polytetrafluoroethylene mold.

[0031] According to an embodiment of the present invention, the curing process is carried out at 80°C for 4 hours, then at 120°C for 4 hours, and finally at 150°C for 4 hours. Attached Figure Description

[0032] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0033] Figure 1 Synthetic route of latent curing accelerator LA-TBD;

[0034] Figure 2 The proton NMR spectrum of the latent curing accelerator LA-TBD;

[0035] Figure 3 Viscosity changes of formulations containing latent curing accelerator LA-TBD and curing accelerator BDMA at different room temperature storage times. Detailed Implementation

[0036] The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the invention, and should not be construed as limiting the invention.

[0037] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0038] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0039] Example 1: Preparation of latent curing accelerator LA-TBD

[0040] Synthetic routes such as Figure 1 As shown.

[0041] Cyanoacetic acid (10.5 mmol, 0.893 g) was dissolved in 30 mL of methanol to obtain a cyanoacetic acid solution. Then, 1,5,7-triazabicyclo[4.4.0]decen-5-ene (TBD, 10.0 mmol, 1.392 g) was dissolved in 90 mL of 10% methanol to obtain a TBD solution. Subsequently, the TBD solution was added dropwise to the cyanoacetic acid solution under vigorous stirring. After stirring at room temperature for 24 hours, methanol was removed using a rotary evaporator, and a white powder was observed to precipitate. The resulting powder was dispersed in diethyl ether to remove unreacted cyanoacetic acid, filtered to obtain a solid, and this process was repeated three times. Vacuum drying yielded the latent curing accelerator LA-TBD.

[0042] Depend on Figure 2 As shown 1 The H-NMR spectrum shows that the target latent curing accelerator LA-TBD was obtained in this embodiment.

[0043] Example 2: Rheological testing of catalyst latency

[0044] Epoxy Preparation: Bisphenol A diglycidyl ether (epoxy equivalent: 182-192 g / equivalent, epoxy group equivalent: 0.0535, 10.00 g), methyltetrahydrophthalic anhydride (anhydride curing agent, anhydride group equivalent: 0.0535, 8.89 g), latent curing accelerator LA-TBD (0.0472 g, determined based on 0.25% of the total mass of epoxy and anhydride) or commercial curing accelerator N,N-dimethylbenzylamine (BDMA, 0.0472 g, determined based on 0.25% of the total mass of epoxy and anhydride) were mixed and stirred uniformly in a vortex at room temperature. The mixture was poured into a polytetrafluoroethylene mold (4 cm × 4 cm × 0.5 cm) and cured in a vacuum drying oven using the following curing process: 80℃ for 4 h + 120℃ for 4 h + 150℃ for 4 h. The cured sample was removed from the mold to obtain the cured epoxy.

[0045] Rheological testing: The viscosity of the two glass-like polymer formulations in Example 2 was analyzed using a rheometer (after being placed at room temperature for different number of days, with a shear rate of 1 s⁻¹). The results are as follows: Figure 3 As shown, for the commercial curing accelerator BDMA system, the viscosity increased rapidly with the number of days, indicating that partial polymerization of epoxy and anhydride occurred, leading to the increase in system viscosity. This suggests that the BDMA catalyst lacks latency. In contrast, the viscosity of the latent curing accelerator LA-TBD system remained consistently low, indicating that the catalyst remained inert at room temperature for extended periods, effectively preventing the curing reaction. This demonstrates that LD-TBD possesses good latency, providing the possibility for one-pot storage of epoxy resin.

[0046] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0047] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. The application of a latent curing accelerator in promoting the curing reaction of epoxy resin, wherein the latent curing accelerator has a structure as shown in formula (I): Formula (I); The curing reaction is carried out under the action of an acid anhydride curing agent.

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