Latent amine curing agent as well as preparation method and application thereof

Abstract

The invention provides a latent amine curing agent as well as a preparation method and application thereof. The curing agent is a mixture containing a compound with a structure I and a compound with a structure II, the structure of the compound with the structure I is shown in the specification, and the structure of the compound with the structure II is shown in the specification. The preparation method comprises the following steps: S1, carrying out primary amine substitution reaction on diamine and Boc anhydride (di-tert-butyl dicarbonate) to generate a secondary amine compound intermediate; and S2, carrying out secondary amine reactive hydrogen substitution reaction on the secondary amine compound intermediate and anhydride containing a fluoroacetic acid structure to obtain a mixture containing a structure I compound and a structure II compound. The latent amine curing agent not only has an excellent storage period and can be stably stored for more than three months after being matched with epoxy resin at room temperature, but also endows a cured product with excellent toughness and solvent resistance due to introduction of a carbamate structure, and has a good application value in the fields of epoxy SMC (Sheet Molding Compound), prepreg and the like.

Description

Technical Field

[0001] This invention relates to the field of curing agents, and more particularly to a latent amine curing agent, its preparation method, and its application. Background Technology

[0002] Epoxy resin is a typical representative of important thermosetting polymers. Due to its excellent mechanical properties, bonding properties, dimensional stability, and chemical resistance, it is widely used in composite materials, adhesives, coatings, and other fields. Uncured epoxy resin is a single-chain thermoplastic material; only after reacting with a curing agent to form a three-dimensional cross-linked network structure can it exhibit its excellent thermosetting properties. For epoxy resin materials, the curing agent has a significant impact on its physical and processing properties. Epoxy curing agents can be divided into two types according to their curing process and characteristics: overt and latent. Overt curing agents react directly with epoxy resin after mixing, while latent curing agents do not immediately cure after mixing and have a storage period. Curing only occurs when external conditions are changed, such as light or heat. Compared to overt curing agents, latent curing agents can be pre-mixed with epoxy resin, eliminating the need for separate transportation and on-site weighing, which has significant commercial value, including shortened working time and stable performance.

[0003] In the field of composite materials, latent curing agents are widely used, such as dicyandiamide and imidazole. Among them, dicyandiamide is favored by downstream industries due to its low price and suitable shelf life. However, dicyandiamide itself has a curing temperature of 160℃-180℃, which is high and the curing rate is slow, so it needs to be used in conjunction with curing accelerators. Furthermore, dicyandiamide itself is incompatible with epoxy resin, and the cured products are prone to defects such as white spots and pinholes, resulting in a low yield of products.

[0004] Against this backdrop, the development of a latent curing agent with a storage period of more than three months, high curing efficiency, and excellent cured product performance has broad application prospects. Summary of the Invention

[0005] One of the objectives of this invention is to provide a latent amine curing agent. This latent amine curing agent not only has an excellent shelf life, but can also be stably stored for more than three months at room temperature when combined with epoxy resin. Furthermore, the introduction of the urethane structure endows the cured product with excellent toughness and solvent resistance. This latent amine curing agent has great application value in the fields of epoxy SMC and prepreg.

[0006] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0007] A latent amine curing agent, wherein the curing agent is a mixture containing a compound of structure I and a compound of structure II:

[0008] The structure of compound I is as follows:

[0009]

[0010] In the formula, R1 is selected from C1-C 10 Alkylene, C3-C 16 Cycloalkylene, C3-C 16 One of the ether groups, preferably C3-C 12 Cycloalkylene or C3-C 12 The ether group, more preferably one of the following groups:

[0011]

[0012] R2 has one or two of the following structures:

[0013] Preferred

[0014] The structure of structure II is as follows:

[0015]

[0016] In the formula, R3 is selected from One of them, preferred

[0017] Another object of the present invention is to provide a method for preparing a latent amine curing agent.

[0018] A method for preparing a latent amine curing agent, wherein the curing agent is the latent amine curing agent according to claim 1, and the preparation method comprises the following steps:

[0019] S1: A diamine undergoes a primary amine substitution reaction with Boc anhydride (di-tert-butyl dicarbonate) to generate a secondary amine intermediate.

[0020] S2: The secondary amine intermediate undergoes a substitution reaction with an acid anhydride containing a fluoroacetic acid structure to obtain a mixture containing compounds of structure I and structure II.

[0021] In one embodiment of the present invention, the structure of the diamine in S1 is as follows:

[0022] H2N——R1——NH2,

[0023] In the formula, R1 is selected from C1-C 10 Alkylene, C3-C 16Cycloalkylene, C3-C 16 One of the ether groups, preferably C3-C 12 Cycloalkylene or C3-C 12 The ether group, more preferably one of the following groups:

[0024]

[0025] In one embodiment of the present invention, the molar amount of Boc anhydride in S1 is 0.5 to 1.5 times the molar amount of the diamine, preferably 1.0 to 1.2 times.

[0026] In one embodiment of the present invention, the reaction in S1 is carried out under catalytic conditions. Preferably, the catalyst is an inorganic or organic alkaline catalyst, more preferably one or more of sodium hydroxide, sodium bicarbonate, and ethylenediamine, and most preferably sodium hydroxide. Preferably, the amount of catalyst used is 0.001 to 0.01 of the mass of the diamine, more preferably 0.0025 to 0.0075.

[0027] In one embodiment of the present invention, the reaction temperature in S1 is 20-100°C, preferably 40-50°C, and the reaction time is 1-8 hours, preferably 4-6 hours.

[0028] For example, when the diamine in S1 is selected from WANAMINE 2110, the relevant reaction process is as follows:

[0029]

[0030] In one embodiment of the present invention, the anhydride containing the fluoroacetic acid structure in S2 is an acetic anhydride with an F number of 1-5, preferably one or more of trifluoroacetic anhydride, difluoroacetic anhydride, and fluoroacetic anhydride, more preferably trifluoroacetic anhydride; preferably, the molar amount of the anhydride containing the fluoroacetic acid structure is 1.5 to 3.0 times the molar amount of the secondary amine compound intermediate, more preferably 2.0 to 2.5 times.

[0031] In one embodiment of the present invention, the reaction in S2 is carried out under catalytic conditions, preferably the catalyst is a nitrogen-containing heterocyclic organic basic catalyst, more preferably one or more of 4-dimethylaminopyridine, 4-pyrrolidinylpyridine, and 1-(pyridin-2-yl)piperidin-4-amine, most preferably 4-dimethylaminopyridine; preferably, the amount of the catalyst is 0.001 to 0.01 of the mass of the secondary amine compound intermediate, preferably 0.0025 to 0.0075.

[0032] In one embodiment of the present invention, the reaction temperature in S2 is 25-95°C, preferably 45-55°C, and the reaction time is 1-12 hours, preferably 4-8 hours.

[0033] For example, taking trifluoroacetic anhydride in S2, the reaction process is as follows:

[0034]

[0035] Based on the above preparation method, a latent amine curing agent was successfully prepared by protecting the amine groups. During the reaction, a segment carrying a urethane structure was introduced. This segment exists in the product after crosslinking with epoxy resin, which not only significantly improves the toughness of the cured product but also imparts excellent solvent resistance.

[0036] Another object of the present invention is to provide a use for a latent amine curing agent.

[0037] Use of a latent amine curing agent, wherein the curing agent is the curing agent described above, or a curing agent prepared by the above preparation method, and the curing agent is used in the fields of epoxy SMC and prepregs. For example, when used in epoxy SMC, the epoxy resin mixture is a mixture of liquid epoxy resin, solid epoxy resin, and other raw material additives.

[0038] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0039] (1) The latent amine curing agent was prepared by a stepwise substitution reaction of acid anhydrides under the action of a catalyst, through the protection of the amine groups. All the amine groups were protonated, so the latent amine curing agent has an excellent shelf life. It can be stably stored for more than three months at room temperature when combined with epoxy resin. Under high temperature (>100℃) conditions, the protecting groups on the amine groups are deprotected under the catalysis of fluorinated acetic acid, releasing the original activity of the amine groups.

[0040] (2) During the process of amine protection, the structure of urethane is introduced, which gives the cured product excellent toughness and solvent resistance, which can meet the requirements of this latent curing agent in composite materials, adhesives and other applications with higher requirements for impact strength, elongation at break and chemical resistance. Attached Figure Description

[0041] Figure 1 The infrared spectral characterization results are for the secondary amine intermediate prepared in Example 1.

[0042] Figure 2 The infrared spectral characterization results are for the latent amine curing agent prepared in Example 1. Detailed Implementation

[0043] The present invention will be further described in detail below with reference to specific embodiments and appendices, but the implementation methods and applicable substrates of the present invention are not limited thereto.

[0044] The latent amine curing agent prepared in the embodiments of the present invention was qualitatively characterized by infrared spectroscopy.

[0045] The raw materials and their sources are shown in Table 1:

[0046] Table 1 Raw Materials and Sources

[0047] Chemical name factory <![CDATA[WANAMINE 2110 (subcycloalkyl structure corresponding to R1)]]> Wanhua Chemical Group Co., Ltd. <![CDATA[WANAMINE IPDA (subcycloalkyl structure corresponding to R1)]]> Wanhua Chemical Group Co., Ltd. <![CDATA[WANAMINE 8100 (corresponding to the ether group and alkylene structure of R1)]]> Wanhua Chemical Group Co., Ltd. NPEL-128 Nan Ya Electronic Materials Co., Ltd. NPES-901 Nan Ya Electronic Materials Co., Ltd. Micronized dicyandiamide 100s Evonik Specialty Chemicals (Shanghai) Co., Ltd. Organic urea U500 Evonik Specialty Chemicals (Shanghai) Co., Ltd. BYK-A530 BYK Additives (Shanghai) Co., Ltd. BYK-W9010 BYK Additives (Shanghai) Co., Ltd. BYK-P9912 BYK Additives (Shanghai) Co., Ltd. methanol Shanghai Aladdin Biochemical Technology Co., Ltd. Dioxane Shanghai Aladdin Biochemical Technology Co., Ltd. DMF Maclean Chemical Reagents Co., Ltd. Sodium hydroxide Maclean Chemical Reagents Co., Ltd. Sodium bicarbonate Maclean Chemical Reagents Co., Ltd. ethylenediamine Shanghai Aladdin Biochemical Technology Co., Ltd. Trifluoroacetic anhydride Shanghai Aladdin Biochemical Technology Co., Ltd. difluoroacetic anhydride Shanghai Aladdin Biochemical Technology Co., Ltd. fluoroacetic anhydride Shanghai Aladdin Biochemical Technology Co., Ltd. 4-Dimethylaminopyridine Maclean Chemical Reagents Co., Ltd. 4-Pyrrolidinylpyridine Maclean Chemical Reagents Co., Ltd. 1-(pyridin-2-yl)piperidin-4-amine Maclean Chemical Reagents Co., Ltd.

[0048] The infrared testing instrument was a Thermo Fisher Nicolet iS5, and the characterization was performed using the reflection mode.

[0049] The mechanical properties of the epoxy SMC resin paste mixture were determined according to GB / T2567-2008. The resin tensile and flexural test specimens were prepared by vacuum degassing and casting. The curing conditions were 150℃×5min to obtain the epoxy resin cured casting.

[0050] Mechanical property testing of cured epoxy SMC sheet molding compound: The cured compound was rapidly cured in a mold with dimensions of 500mm*500mm*4mm at a curing temperature of 150*5min. The resulting cured compound sheet was cut into tensile, bending, and impact test strips according to GB / T15568-2008 standard and tested at a tensile speed of 50mm / min.

[0051] Glass transition temperature test of epoxy SMC sheet molding compound: The epoxy SMC resin paste was rapidly cured in a high-temperature gelation apparatus at a curing condition of 150°C for 5 minutes. The glass transition temperature of the resulting cured sheet was tested according to GB / T 19466.2-2004 standard.

[0052] Solvent resistance tests on cured epoxy SMC were conducted in accordance with GB / T1732-1993 standard.

[0053] The specific preparation process of the secondary amine intermediate and latent amine curing agent involved in this scheme is as follows.

[0054] Example 1

[0055] (1) Substitution of primary diamines with Boc anhydrides to generate secondary amine intermediates:

[0056] The reaction was carried out in a 1L three-necked flask. First, 200ml of methanol solution containing 0.5g sodium hydroxide was added. Nitrogen gas was then bubbled into the flask for 6 minutes to displace the air. Next, 210g of WANAMINE 2110 was added, and the stirrer was kept at 200 rpm. The temperature of the flask was maintained at 25°C using a water bath. Then, 218g of di-tert-butyl dicarbonate was weighed and added to a constant-pressure dropping funnel, and slowly added dropwise to the flask over 20 minutes. After the addition was complete, the system temperature was raised to 20°C, and the reaction was continued for 1 hour. After the reaction was complete, vacuum distillation was performed at 35°C and 150 mmHg to separate the excess methanol solvent, yielding the secondary amine intermediate A1, whose infrared spectrum is attached. Figure 1 As shown, at 3120cm -1 and 3350cm -1 The peak is attributed to the asymmetric stretching vibration of the NH bond in secondary amines.

[0057] (2) Preparation of latent amine curing agents by secondary amine substitution reaction:

[0058] First, 200g of methanol was added as a solvent to a three-necked flask after nitrogen purging, and the stirring speed was controlled at 200 rpm. Then, 41g of secondary amine intermediate A1 and 0.1g of 4-dimethylaminopyridine were added, and the reaction temperature was controlled at 25℃. 31.5g of trifluoroacetic anhydride was weighed and slowly added dropwise to the three-necked flask, and the reaction was continued for 1 hour. After the reaction was completed, the solvent was separated by thin-film evaporation at 45℃ to obtain latent amine curing agent B1, the infrared spectrum of which is attached. Figure 2 As shown, at 660cm -1 and 790cm -1 The peak is attributed to the stretching vibration of the CF bond in secondary amines.

[0059] Example 2

[0060] (1) Substitution of primary diamines with Boc anhydrides to generate secondary amine intermediates:

[0061] The reaction was carried out in a 1L three-necked flask. First, 200ml of a dioxane solution containing 0.85g sodium bicarbonate was added. Nitrogen gas was then introduced into the flask for 6 minutes to displace the air. Next, 170g of WANAMINE IPDA was added, and the stirrer was kept at 200 rpm. The temperature of the flask was maintained at 25°C using a water bath. Then, 262g of di-tert-butyl dicarbonate was weighed and added to a constant-pressure dropping funnel, and slowly added dropwise to the flask over 20 minutes. After the addition was complete, the system temperature was raised to 40°C, and the reaction was continued for 4 hours. After the reaction was complete, vacuum distillation was performed at 45°C and 150 mmHg to separate the excess dioxane solvent, yielding the secondary amine intermediate A2.

[0062] (2) Preparation of latent amine curing agents by secondary amine substitution reaction:

[0063] First, 200g of dioxane was added to a three-necked flask after nitrogen purging, and the stirring speed was controlled at 200r / min. Then, 37g of the secondary amine intermediate A2 obtained in Example 2 and 0.18g of 4-pyrrolidinylpyridine were added, and the reaction temperature was controlled at 45℃. 38g of difluoroacetic anhydride was weighed and slowly added dropwise to the three-necked flask, and the reaction was continued for 4h. After the reaction was completed, the solvent was separated by thin-film evaporation at 45℃ to obtain the latent amine curing agent B2.

[0064] Example 3

[0065] (1) Substitution of primary diamines with Boc anhydrides to generate secondary amine intermediates:

[0066] The reaction was carried out in a 1L three-necked flask. First, 200ml of DMF solution containing 1.7g of ethylenediamine was added. Nitrogen gas was then introduced into the flask for 6 minutes to displace the air. Next, 230g of WANAMINE 8100 was added, and the stirrer was kept at 200 rpm. The temperature of the flask was maintained at 25°C using a water bath. Then, 305g of di-tert-butyl dicarbonate was weighed and added to a constant-pressure dropping funnel, and slowly added dropwise to the flask over 20 minutes. After the addition was complete, the system temperature was raised to 50°C, and the reaction was continued for 6 hours. After the reaction was complete, vacuum distillation was performed at 55°C and 150 mmHg to separate the excess DMF solvent, yielding the secondary amine intermediate A3.

[0067] (2) Preparation of latent amine curing agents by secondary amine substitution reaction:

[0068] First, 200g of DMF was added as a solvent to a three-necked flask after nitrogen purging, and the stirring speed was controlled at 200r / min. Then, 43g of the secondary amine intermediate A3 obtained in Example 3 and 0.32g of 1-(pyridin-2-yl)piperidin-4-amine were added, and the reaction temperature was controlled at 55℃. 33g of fluoroacetic anhydride was weighed and slowly added dropwise to the three-necked flask, and the reaction was continued for 8h. After the reaction was completed, the solvent was separated by thin-film evaporation at 45℃ to obtain the latent amine curing agent B3.

[0069] Example 4

[0070] (1) Substitution of primary diamines with Boc anhydrides to generate secondary amine intermediates:

[0071] The reaction was carried out in a 1L three-necked flask. First, 200ml of methanol solution containing 0.5g sodium hydroxide was added. Nitrogen gas was then introduced into the flask for 6 minutes to displace the air. Next, 210g of WANAMINE 2110 was added, and the stirrer was kept at 200 rpm. The temperature of the flask was maintained at 25°C using a water bath. Then, 327g of di-tert-butyl dicarbonate was weighed and added to a constant-pressure dropping funnel, and slowly added dropwise to the flask over 20 minutes. After the addition was complete, the system temperature was raised to 100°C, and the reaction was continued for 8 hours. After the reaction was complete, vacuum distillation was performed at 55°C and 150 mmHg to separate the excess methanol solvent, yielding the secondary amine intermediate A4.

[0072] (2) Preparation of latent amine curing agents by secondary amine substitution reaction:

[0073] First, 200g of methanol was added to a three-necked flask after nitrogen purging, and the stirring speed was controlled at 200r / min. Then, 41g of the secondary amine intermediate A4 obtained in Example 4 and 0.2g of 4-dimethylaminopyridine were added, and the reaction temperature was controlled at 95℃. 63.6g of trifluoroacetic anhydride was weighed and slowly added dropwise to the three-necked flask, and the reaction was continued for 12h. After the reaction was completed, the solvent was separated by thin-film evaporation at 45℃ to obtain the latent amine curing agent B4.

[0074] Comparative Example 1

[0075] 8g of micronized dicyandiamide 100s and 2g of organic urea U500 were physically mixed evenly to obtain the control sample Dicy.

[0076] Example: Preparation of SMC sheet molding compound

[0077] 70g NPEL-128, 30g NPES-901, 6g BYK-P9912, 0.75g BYK-A530, and 0.75g BYK-W9010 were added to a reactor and stirred until the resin was melted and mixed evenly. Then, 100g aluminum hydroxide was added to the reactor and stirred at high speed until the mixture was homogeneous. Then, the latent amine curing agent synthesized in the preparation example was added in equimolar amounts (the number of moles of epoxy groups in the epoxy resin = the number of moles of hydrogen on the amine groups (primary and secondary amines) in the curing agent). The mixture was stirred and mixed evenly in the reactor and then degassed under vacuum to obtain SMC resin paste. The obtained epoxy SMC resin paste was impregnated with 25mm disordered chopped glass fibers, rolled by an SMC sheet press, and then cured in a 35℃ oven for 20 hours to obtain epoxy sheet molding compound PB.

[0078] Preparation of comparative SMC sheet molding compound

[0079] 70g NPEL-128, 30g NPES-901, 6g BYK-P9912, 0.75g BYK-A530, and 0.75g BYK-W9010 were added to a reactor and stirred until the resin was melted and mixed evenly. Then, 100g aluminum hydroxide was added to the reactor and stirred at high speed until evenly mixed. The comparative Dicy was then added to the reactor and stirred until evenly mixed. After vacuum degassing, SMC resin paste was obtained. The obtained epoxy SMC resin paste was impregnated with 25mm disordered chopped glass fibers, rolled by an SMC sheet press, and then cured in a 35℃ oven for 20 hours to obtain epoxy sheet molding compound P-Dicy.

[0080] Using the above-described method for preparing epoxy SMC sheet molding compounds, latent amine curing agents B1 to B4 from Preparation Examples 1 to 4 were used to prepare epoxy sheet molding compounds P-B1 to P-B4 according to the steps described above.

[0081] The epoxy SMC resin paste and epoxy sheet molding compound obtained in the examples and comparative examples were cured and tested respectively.

[0082] The test results are listed in Tables 2 and 3 below.

[0083] Table 2 Comparison of basic parameters and cured properties of epoxy SMC resin paste

[0084]

[0085]

[0086] Table 3 Comparison of Mechanical Properties of Epoxy SMC Sheet Molding Compounds

[0087] P-B1 P-B2 P-B3 P-B4 P-Dicy Tensile strength / MPa 262.3 255.8 255.9 261.2 223.54 Tensile modulus / GPa 13.4 12.2 16.2 15.8 10.1 Bending strength / MPa 350.4 344.6 348.3 349.2 310.2 Elongation at break % 4.2 4.3 3.9 4.3 2.3

[0088] As can be seen from the table above, this latent amine curing agent has significant advantages over the dicyandiamide system. Its reaction rate after 30 days of storage at room temperature is significantly lower than that of the dicyandiamide system, indicating that this latent curing agent has excellent storage stability at room temperature. This is due to the fact that after the diamine undergoes a stepwise substitution reaction with an anhydride, the amine groups are protected. Under high-temperature conditions, the original activity of the amine groups is released under the catalysis of fluorinated acetic acid, achieving the curing purpose. Furthermore, during the stepwise substitution reaction with the anhydride, a large number of urethane segments are introduced. These segments exist in the product after crosslinking with epoxy resin, which not only significantly improves the elasticity and elongation at break of the cured product but also imparts excellent solvent resistance.

[0089] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and additions without departing from the method of the present invention, and these improvements and additions should also be considered within the scope of protection of the present invention.

Claims

1. A latent amine curing agent characterized in that, The curing agent is a mixture containing a compound of structure I and a compound of structure II: The structure of the compound of structure I is: wherein R1is selected from one of the group consisting of C1-C 10 alkylene, C3-C 16 cycloalkylene, C3-C 16 ether, preferably C3-C 12 cycloalkylene or C3-C 12 ether, more preferably one of the following groups: The structure of R2 is one or both of the following structures: preferably The structure of the compound of structure II is: wherein R3is selected from one of R1and R2, preferably 2. A process for the preparation of the latent amine curing agent of claim 1, characterized in that, The preparation method comprises the following steps: S1: substitution reaction of primary amine of diamine with Boc anhydride (di-tert-butyl dicarbonate) to generate a secondary amine compound intermediate; S2: substitution reaction of active hydrogen of secondary amine of the secondary amine compound intermediate with anhydride containing a fluorine-containing acetic acid structure to obtain a mixture containing a compound of structure I and a compound of structure II.

3. The preparation method according to claim 2, characterized in that, The structure of the diamine in S1 is: H2N-R1-NH2, wherein R1is selected from one of the group consisting of C1-C 10 alkylene, C3-C 16 cycloalkylene, C3-C 16 ether, preferably C3-C 12 cycloalkylene or C3-C 12 ether, more preferably one of the following groups:

4. The production method according to claim 2 or 3, characterized by, The molar amount of the Boc anhydride in S1 is 0.5-1.5 times, preferably 1.0-1.2 times, of the molar amount of the diamine; And / or, the reaction in S1 is carried out under the condition of a catalyst, preferably the catalyst is an inorganic or organic alkaline catalyst, more preferably one or more of sodium hydroxide, sodium bicarbonate, ethylenediamine, most preferably sodium hydroxide; Preferably, the amount of the catalyst is 0.001-0.01, preferably 0.0025-0.0075, of the mass of the diamine; And / or, the temperature of the reaction in S1 is 20-100℃, preferably 40-50℃, and the reaction time is 1-8h, preferably 4-6h.

5. The production method according to claim 2 or 3, characterized by, The anhydride containing a fluorine-containing acetic acid structure in S2 is an anhydride of acetic acid with an F number of 1-5, preferably one or more of trifluoroacetic anhydride, difluoroacetic anhydride, fluoroacetic anhydride, more preferably trifluoroacetic anhydride; Preferably, the molar amount of the anhydride containing a fluorine-containing acetic acid structure is 1.5-3.0 times, preferably 2.0-2.5 times, of the molar amount of the secondary amine compound intermediate; And / or, the reaction in S2 is carried out under the condition of a catalyst, preferably the catalyst is an organic alkaline catalyst containing a nitrogen heterocycle, more preferably one or more of 4-dimethylaminopyridine, 4-pyrrolidinylpyridine, 1-(pyridin-2-yl)piperidin-4-amine, most preferably 4-dimethylaminopyridine; Preferably, the amount of the catalyst is 0.001-0.01, preferably 0.0025-0.0075, of the mass of the secondary amine compound intermediate; And / or, the temperature of the reaction in S2 is 25-95℃, preferably 45-55℃, and the reaction time is 1-12h, preferably 4-8h.

6. Use of a latent amine curing agent, the curing agent being the curing agent of claim 1 or being prepared by the preparation method of any one of claims 2-5, for the field of epoxy SMC, prepreg.

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