Latent aliphatic cyclic amide curing agent, method for preparing the same, and use thereof

Abstract

The application discloses a latent aliphatic amide curing agent, a preparation method thereof and application thereof. The latent aliphatic amide curing agent is obtained through an amidation reaction of an aliphatic amine compound and a formyl carboxylic acid compound. The secondary amine group in the latent curing agent obtained by the application does not react with an epoxy resin at a low temperature due to the influence of steric hindrance, and has latency. The latent modified aliphatic amine curing agent prepared by the application is a flowable liquid at normal temperature, and can be used in combination with a traditional solid powder type latent curing agent, thereby improving the poor miscibility of the solid powder type latent curing agent with the epoxy resin.

Description

Technical Field

[0001] This invention relates to the field of curing agents, and in particular to a latent cycloaliphatic amide curing agent, its preparation method, and its application. Background Technology

[0002] Epoxy resin is a high-performance thermosetting polymer synthetic material that, upon reaction with a curing agent, forms a complex cross-linked network structure, making it widely used in coatings, adhesives, and composite materials. Epoxy curing agents are divided into overt and covert curing agents. Overt curing agents must be packaged separately from epoxy resin; the two components are mixed in a specific ratio during application, and their pot life is relatively short, typically ranging from a few minutes to a few hours. Covert curing agents mainly consist of dicyandiamide, organic acid hydrazides, and modified imidazole compounds. When mixed with epoxy resin to form a single-component system, the covert curing agent has a longer shelf life at room temperature, exceeding one month. The single-component system formulated by mixing covert curing agents with epoxy resin offers advantages such as simple production processes and prevention of environmental pollution, making it particularly suitable for modern large-scale industrial production processes, such as in the field of fiber-reinforced composite materials.

[0003] Dicyandiamide is a commonly used latent epoxy resin curing agent with a shelf life of up to 6 months at room temperature. However, dicyandiamide is a latent curing agent in powder form at room temperature with a high melting point (above 180°C), making it difficult to mix uniformly with epoxy resin in actual production. This can lead to incomplete or over-curing, as well as low heat distortion temperature of the finished product, thus affecting its practical application.

[0004] Alicyclic amines are room-temperature curing agents with a rigid alicyclic structure in their molecular structure. Epoxy cured products have high heat distortion temperatures, reaching up to 150℃, and exhibit good heat resistance. However, due to their high reactivity, they cannot be used directly as latent curing agents.

[0005] Patent CN116751533A discloses a method for preparing a non-post-curing epoxy tape. It utilizes a combination of alicyclic amines and dicyandiamide, dissolving the dicyandiamide and alicyclic amines before adding them to the epoxy system. This method eliminates overflow and bubble formation at 220°C, improving the material's heat resistance. However, the rapid reaction between the alicyclic amines and epoxy resin in this system results in a short working time of only 6 hours at room temperature, significantly shortening the shelf life.

[0006] Patent CN105646843A proposes a method for latent modification of alicyclic amines, specifically by modifying them with aromatic isocyanates. This effectively blocks the activity of the alicyclic amines, resulting in a long pot life with epoxy resins. Simultaneously, the newly generated organic urea groups can enhance the bonding strength of the cured product, making it applicable to adhesives, coatings, and composite materials. However, the modified latent alicyclic amine is a solid powder, and uneven dispersion in the matrix resin is still difficult to avoid, leading to performance defects in the finished product.

[0007] To better achieve uniform dispersion of latent curing agents in resins and effectively solve the problems of incomplete or over-curing of products, it is necessary to develop a latent curing agent with a long storage period at room temperature to meet the increasingly urgent application needs. Summary of the Invention

[0008] To address the aforementioned problems, this invention provides a latent alicyclic amide curing agent and its preparation method. The alicyclic amine compound and a carboxylic acid compound are amidated to block the active hydrogen groups on the highly reactive primary amine. The active hydrogen groups on the secondary amine are influenced by sterically hindered groups such as benzene rings, alicyclic rings, and furan rings, effectively inhibiting the reactivity of the active hydrogen groups on the secondary amine and resulting in a longer pot life at room temperature. This latent modified alicyclic amine curing agent is a viscous liquid at room temperature and contains strongly polar formyl and amide groups. It exhibits good compatibility with traditional solid powder curing agents after melt blending, avoiding the complex and time-consuming dispersion process required for powder curing agents. This effectively solves the problems of uneven mixing, incomplete curing, or over-curing of solid powder latent curing agents in resins. Furthermore, the presence of the alicyclic structure can improve the heat resistance and mechanical strength of the cured product.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] This invention provides a latent alicyclic amide curing agent having the following structure:

[0011]

[0012] Wherein, R1 is selected from

[0013] R2 is selected from

[0014] This invention also provides a method for preparing a latent alicyclic amide curing agent, comprising mixing an alicyclic amine curing agent with a formylcarboxylic acid compound and reacting the mixture to obtain the latent alicyclic amide curing agent. The reaction temperature between the alicyclic amine curing agent and the formylcarboxylic acid compound is 120–180°C, preferably 140–160°C; the reaction time is 2–10 hours, preferably 5–8 hours.

[0015] The alicyclic amine is selected from one or more of 4,4'-diaminodicyclohexylmethane, isophorone diamine, 1,3-cyclohexanedimethylamine, 1-methyl-2,4-cyclohexanediamine, and 1,2-cyclohexanediamine, preferably 1,2-cyclohexanediamine;

[0016] The formyl carboxylic acid compound is selected from one or more of 3'-formyl(1,1'-biphenyl)-3-carboxylic acid, 2-formylpyridine-4-carboxylic acid, 3-benzoylthiophene-2-carboxylic acid, 2-formylfuran-3-carboxylic acid, 3-benzoyl-2-pyridine carboxylic acid, 1-benzoylpiperidine-4-carboxylic acid, 4-formyl-3-methylisoxazole-5-carboxylic acid, 1-aldehydepiperidine-4-carboxylic acid, and 1-(2-methyl-benzoyl)-piperidine-4-carboxylic acid.

[0017] The ratio of the molar amount of the primary amine in the alicyclic amine compound to the molar amount of the carboxylic acid group in the formyl carboxylic acid compound is n. 伯胺 :n COOH =1:(0.8-1.0), preferably 1:(0.85-0.95).

[0018] A latent cycloaliphatic amide curing agent composition comprises the aforementioned latent cycloaliphatic amide curing agent and a solid powder latent curing agent. Preferably, the solid powder latent curing agent is selected from one or more of dicyandiamide latent curing agents, hydrazides, and imidazole compounds.

[0019] A method for preparing the latent cycloaliphatic amide curing agent mixture involves melting a solid powder latent curing agent, adding a latent cycloaliphatic amide curing agent, mixing evenly, and obtaining the latent cycloaliphatic amide curing agent mixture.

[0020] The mass ratio of the latent cycloaliphatic amide curing agent to the solid powder latent curing agent is 1:(0.1-0.7), preferably 1:(0.3-0.6).

[0021] The present invention also provides the use of the latent cycloaliphatic amide curing agent described herein for use in coatings, impregnating materials, and potting compounds, preferably impregnating materials.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] (1) The latent cycloaliphatic amide curing agent obtained by the present invention is a viscous liquid at room temperature and can be mixed with epoxy resin at the molecular level;

[0024] (2) The molecular structure contains a large number of strong polar groups. When mixed with solid powder latent curing agents such as dicyandiamide, it is easy to form a large number of hydrogen bond structures, which has good compatibility and solves the problem of uneven mixing, incomplete curing or over-curing of traditional solid powder latent curing agents and epoxy resin.

[0025] (3) By amidation modification, the active hydrogen groups on the primary amine with high activity are blocked, while the active hydrogen on the secondary amine is affected by the large steric hindrance group, which effectively inhibits its reactivity and has a long service life at room temperature.

[0026] (4) The cycloaliphatic amide curing agent contains cycloaliphatic rings, benzene rings and other structures, and the resulting products have good heat resistance and mechanical strength;

[0027] (5) The latent cycloaliphatic amide curing agent of the present invention has a simple synthesis process and is highly practical. Attached Figure Description

[0028] Figure 1 The product described in Example 1 1 H NMP spectra were obtained using a Bruker AVANCE NEO 600M spectrometer with a 5mm BBO probe, CDCl3 as the solvent, and 25°C as the test temperature. Detailed Implementation

[0029] The following embodiments further illustrate the technical solutions provided by the present invention, but the present invention is not limited to the listed embodiments, and also includes any other known modifications within the scope of the present invention.

[0030] Table 1 Raw Materials and Sources

[0031] Chemical name factory purity 3'-Formyl(1,1'-biphenyl)-3-carboxylic acid Shanghai Aladdin Biochemical Technology Co., Ltd. 96％ 1-Aldehydepiperidine-4-carboxylic acid THIAI (Shanghai) Chemical Industry Development Co., Ltd. 95％ 1-Benzoylpiperidine-4-carboxylic acid Shanghai Titan Technology Co., Ltd. 98％ 2-Formylpyridine-4-carboxylic acid Shanghai Titan Technology Co., Ltd. 98％ 2-Formylfuran-3-carboxylic acid Shanghai Titan Technology Co., Ltd. 98％ 1,2-Cyclohexanediamine Zhengzhou Aikem Chemical Co., Ltd. 99％ 1,3-Cyclohexanedimethylamine Mitsubishi Chemical Company, Japan 99％ 4,4'-Diaminodicyclohexylmethane Wanhua Chemical Group Co., Ltd. 99％ Isoflurane diamine Wanhua Chemical Group Co., Ltd. 99％ Dicyandiamide Shanghai Aladdin Biochemical Technology Co., Ltd. 99％ Adipic acid dihydrazide Shanghai McLean Biochemical Technology Co., Ltd. 99％ QXE301 Wuhan Kemike Biomedical Technology Co., Ltd. 99％

[0032] Table 2 Test methods for main performance indicators

[0033]

[0034]

[0035] Example 1

[0036] Preparation of latent modified alicyclic amine curing agents:

[0037] 114 g of 1,2-cyclohexanediamine and 410 g of 3'-formyl(1,1'-biphenyl)-3-carboxylic acid were added to a reactor. The temperature was raised to 120 °C, and the mixture was stirred and reacted for 1 h. The temperature was then increased stepwise to 180 °C, and the reaction was carried out for 8 h to obtain a crude product. After vacuum dehydration at 100 °C for 2 h, the final latent alicyclic curing agent was obtained, with the structure shown below.

[0038]

[0039] Example 2

[0040] Preparation of latent modified alicyclic amine curing agents:

[0041] 142 g of 1,3-cyclohexanedimethylamine and 280 g of 1-aldehydepiperidine-4-carboxylic acid were added to a reactor. The temperature was raised to 120 °C, and the mixture was stirred and reacted for 1 h. The temperature was then gradually increased to 180 °C, and the reaction was continued for 8 h to obtain a crude product. After vacuum dehydration at 100 °C for 2 h, the final latent cycloaliphatic amide curing agent was obtained, with the structure shown below.

[0042]

[0043] Preparation of latent alicyclic amide curing agent mixture:

[0044] Weigh 50g of adipic acid dihydrazide and 100g of the latent cycloaliphatic amide curing agent prepared in this example and add them to a three-necked flask. Install a stirrer and a condenser, place the three-necked flask in a heating mantle and heat it to 160°C. After the dicyandiamide is completely dissolved, continue stirring for 1 hour. After returning to room temperature, discharge the material to obtain a viscous transparent liquid, which is the latent cycloaliphatic amide curing agent combination.

[0045] Example 3

[0046] Preparation of latent modified alicyclic amine curing agents:

[0047] 210g of 4,4'-diaminodicyclohexylmethane and 410g of 1-benzoylpiperidine-4-carboxylic acid were added to a reactor. The temperature was raised to 120℃, and the mixture was stirred and reacted for 1 hour. The temperature was then increased to 180℃ in stages, and the crude product was obtained after 8 hours of reaction. After vacuum dehydration at 100℃ for 2 hours, the final latent cycloaliphatic amide curing agent was obtained, with the structure shown below.

[0048]

[0049] Preparation of latent alicyclic amide curing agent mixture:

[0050] Weigh 50g of dicyandiamide and 100g of the latent cycloaliphatic amide curing agent prepared in this example and add them to a three-necked flask. Install a stirrer and a condenser, place the three-necked flask in a heating mantle and heat it to 150°C. After the two curing agents are completely dissolved, continue stirring for 1 hour. After returning to room temperature, discharge the material to obtain a viscous transparent liquid, which is the latent cycloaliphatic amide curing agent combination material.

[0051] Example 4

[0052] Preparation of latent modified alicyclic amine curing agents:

[0053] 170g of isophorone diamine and 310g of 2-formylpyridine-4-carboxylic acid were added to a reactor, the temperature was raised to 120℃, and the mixture was stirred and reacted for 1 hour. The temperature was then increased to 160℃ in stages, and the reaction was carried out for 7 hours to obtain a crude product. After vacuum dehydration at 100℃ for 2 hours, the final latent cycloaliphatic amide curing agent was obtained, with the structure shown below.

[0054]

[0055] Preparation of latent alicyclic amide curing agent mixture:

[0056] Weigh 30g of QXE301 and 100g of the latent cycloaliphatic amide curing agent prepared in this embodiment and add them to a three-necked flask. Install a stirrer and a condenser, place the three-necked flask in a heating mantle and heat it to 150°C. After the two curing agents are completely dissolved, continue stirring for 1 hour. After returning to room temperature, discharge the material to obtain a viscous transparent liquid, which is the latent cycloaliphatic amide curing agent combination material.

[0057] Example 5

[0058] Preparation of latent modified alicyclic amine curing agents:

[0059] 210g of 4,4'-diaminodicyclohexylmethane and 410g of 2-formylfuran-3-carboxylic acid were added to a reactor. The temperature was raised to 120℃, and the mixture was stirred and reacted for 1 hour. The temperature was then increased stepwise to 180℃, and the reaction was continued for 8 hours to obtain a crude product. After vacuum dehydration at 100℃ for 2 hours, the final latent cycloaliphatic amide curing agent was obtained, with the structure shown below.

[0060]

[0061] Preparation of latent alicyclic amide curing agent mixture:

[0062] Weigh 70g of dicyandiamide and 100g of the latent cycloaliphatic amide curing agent prepared in this example into a three-necked flask, install a stirrer and a condenser, place the three-necked flask in a heating mantle and heat to 150°C. After the adipic acid dihydrazide is completely dissolved, continue stirring for 1 hour, and then discharge the material after restoring to room temperature. Finally, a viscous transparent liquid is obtained, which is the latent cycloaliphatic amide curing agent combination material.

[0063] Comparative Example 1

[0064] Adipic acid dihydrazide, available on the market, was directly selected as the latent curing agent for Comparative Example 1.

[0065] Comparative Example 2

[0066] Weigh 50g of dicyandiamide and 70g of 4,4'-diaminodicyclohexylmethane into a three-necked flask. Install a stirrer and condenser, and place the flask in a heating mantle. Heat until the adipic acid dihydrazide is completely dissolved. Then add 300g of N,N-dimethylformamide and continue stirring for 30 minutes. After stirring until homogeneous, allow to return to room temperature and discharge to obtain the latent curing agent mixture of Comparative Example 2. Performance testing of the latent curing agent.

[0067] The latent epoxide amide curing agents prepared in Examples 1-5 were mixed with liquid epoxy resin E51 (EEW190) in equimolar amounts and curing experiments were conducted (molar amount of epoxy groups in epoxy resin = molar amount of active hydrogen on amino groups in curing agent). The performance test results of the epoxy curing agents are shown in Table 3.

[0068] Table 3. Heat resistance and mechanical strength data of cured products obtained from alicyclic amide latent curing agents.

[0069]

[0070] The latent epoxide amide curing agents prepared in Examples 1-5 and the curing agents obtained in Comparative Examples 1 and 2 were mixed with liquid epoxy resin E51 (EEW190) in equimolar amounts and a curing experiment was conducted (molar amount of epoxy groups in epoxy resin = molar amount of active hydrogen on amino groups in curing agent). The performance test results of the epoxy curing agents are shown in Table 4.

[0071] Table 4. Heat resistance and mechanical strength data of the cured products of the alicyclic amide latent curing agent combination and the comparative examples.

[0072]

[0073]

[0074] As can be seen from Table 3, referring to Example 1 and Comparative Example 1, the difference between the two is that Example 1 is the modified alicyclic amide latent curing agent prepared according to the present invention, while Comparative Example 1 is the commercially available latent curing agent adipate dihydrazide. According to the results in Table 3, adipate dihydrazide is a solid at room temperature and needs to be melted at a higher temperature before reacting with epoxy resin, resulting in a longer pot life. However, Example 1 is a viscous liquid with better compatibility with epoxy resin. Under high temperature, the secondary amine group will react with the epoxy resin, still maintaining a longer pot life. In addition, the alicyclic amide curing agent contains a large number of benzene rings and alicyclic structures, giving the epoxy cured material superior mechanical strength and heat resistance.

[0075] As can be seen from Table 4, referring to Example 2 and Comparative Example 1, the difference between the two is that Example 2 is a combination of alicyclic amide curing agent and adipic acid dihydrazide curing agent, while Comparative Example 1 is a commercially available latent curing agent, adipic acid dihydrazide. According to the data in Table 3, adipic acid dihydrazide is solid at room temperature and needs to be melted at a higher temperature before reacting with epoxy resin, resulting in a longer pot life. However, Example 2, being a molten combination of alicyclic amide curing agent and adipic acid dihydrazide, remains a viscous liquid at room temperature, exhibiting good compatibility with epoxy resin and effectively avoiding problems such as uneven mixing of solid powder and resin, incomplete curing, or over-curing. Under high temperature conditions, it has a longer pot life compared to alicyclic amide. Furthermore, the introduction of the alicyclic amide curing agent introduces a large number of alicyclic structures into the structure, resulting in superior mechanical strength and heat resistance compared to traditional solid powder latent curing agents.

[0076] As can be seen from Table 4, referring to Example 3 and Comparative Example 2, the difference between the two is that Example 3 is a melt combination of alicyclic amide curing agent and dicyandiamide powder, while Comparative Example 2 is a combination of alicyclic amine and dicyandiamide. According to the data in Table 3, the introduction of the alicyclic structure endows the combination with excellent mechanical strength and heat resistance; however, the alicyclic amine in Comparative Example 2 has high reactivity with epoxy resin, with only a 10-minute working period at 150°C, resulting in a short pot life. The modified alicyclic amide curing agent significantly increases the working period from 10 minutes to 40 minutes, giving the combination formulation a longer working life. In Tables 3 and 4, referring to the comparison of the curing agent and combination in Example 1, the difference is that Table 3 shows the modified alicyclic amide latent curing agent prepared according to this invention, while Table 4 shows the combination of the modified alicyclic amide latent curing agent and solid powder latent curing agents such as dicyandiamide. According to the comparison results in Tables 3 and 4, the modified cycloaliphatic amide latent curing agent contains a large number of strongly polar groups in its molecular structure. When mixed with dicyandiamide solid powder latent curing agent, the presence of hydrogen bonds improves the compatibility of the two, and a liquid latent curing agent mixture can be obtained. This solves the problem of uneven mixing between traditional solid powder latent curing agents and epoxy resins, and shows good compatibility with epoxy resins. After adding the conventional latent curing agent dicyandiamide, the viscosity of the mixture increases, the latency is extended, and its pot life is further improved, but the brittleness increases and the mechanical strength decreases slightly.

[0077] Unless otherwise specified, the terms used in this invention have the meanings commonly understood by those skilled in the art.

[0078] The embodiments described in this invention are for illustrative purposes only and are not intended to limit the scope of protection of this invention. Those skilled in the art can make various other substitutions, changes and improvements within the scope of this invention. Therefore, this invention is not limited to the above embodiments, but is only defined by the claims.

Claims

1. A method for preparing a latent alicyclic amide curing agent, characterized in that, A latent alicyclic amine curing agent is obtained by reacting a mixture of alicyclic amine curing agents and formyl carboxylic acid compounds. The alicyclic amine is selected from 1,2-cyclohexanediamine, 4,4'-diaminodicyclohexylmethane, isophoronediamine, and 1,3-cyclohexanedimethylamine; The formyl carboxylic acid compounds are selected from one or more of 3'-formyl(1,1'-biphenyl)-3-carboxylic acid, 2-formylpyridine-4-carboxylic acid, 2-formylfuran-3-carboxylic acid, 1-benzoylpiperidine-4-carboxylic acid, and 1-aldehydepiperidine-4-carboxylic acid; The latent cycloaliphatic amide curing agent is , , , or .

2. The preparation method according to claim 1, characterized in that, The reaction temperature between the alicyclic amine curing agent and the formyl carboxylic acid compound is 120~180℃.

3. The preparation method according to claim 2, characterized in that, The reaction temperature between the alicyclic amine curing agent and the formyl carboxylic acid compound is 140~160℃.

4. The preparation method according to claim 1, characterized in that, The reaction time between the alicyclic amine curing agent and the formyl carboxylic acid compound is 2 to 10 hours.

5. The preparation method according to claim 4, characterized in that, The reaction time between the alicyclic amine curing agent and the formyl carboxylic acid compound is 5-8 hours.

6. The preparation method according to claim 1, characterized in that, The ratio of the molar amount of the primary amine in the alicyclic amine compound to the molar amount of the carboxylic acid group in the formyl carboxylic acid compound is n. 伯胺 :n COOH =1:(0.8-1.0).

7. The preparation method according to claim 6, characterized in that, The ratio of the molar amount of the primary amine in the alicyclic amine compound to the molar amount of the carboxylic acid group in the formyl carboxylic acid compound is n. 伯胺 :n COOH =1:(0.85-0.95).

8. The application of the cycloaliphatic amide curing agent prepared by the preparation method according to any one of claims 1-7, which can be used directly as a curing agent or in combination with other curing agents, is used in the fields of coatings, impregnating materials, and potting compounds.

9. The application according to claim 8, which is used for impregnation materials.

10. A latent alicyclic amide curing agent composition, characterized in that, The invention comprises alicyclic amide curing agents and solid powder latent curing agents prepared by the preparation method according to any one of claims 1-7.

11. The latent cycloaliphatic amide curing agent composition according to claim 10, wherein the solid powder latent curing agent is selected from one or more of dicyandiamide, hydrazide, and imidazole compound latent curing agents.

12. The latent cycloaliphatic amide curing agent composition according to claim 10, wherein the mass ratio of the latent cycloaliphatic amide curing agent to the solid powder latent curing agent is 1:(0.1-0.7).

13. The latent cycloaliphatic amide curing agent composition according to claim 12, wherein the mass ratio of the latent cycloaliphatic amide curing agent to the solid powder latent curing agent is 1:(0.3-0.6).

14. The method for preparing the latent cycloaliphatic amide curing agent mixture according to claim 10, wherein a solid powder latent curing agent is melted, and then a latent cycloaliphatic amide curing agent is added and mixed evenly to obtain the latent cycloaliphatic amide curing agent mixture.

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