Latent alicyclic amide curing agent as well as preparation method and application thereof

Abstract

The invention discloses a latent alicyclic amide curing agent as well as a preparation method and application thereof. The latent alicyclic amide curing agent is obtained by carrying out amidation reaction on an alicyclic amine compound and a formyl carboxylic acid compound. The secondary amine group in the latent curing agent does not react with the epoxy resin at medium and low temperatures due to the influence of steric hindrance, and has latency. The latent modified alicyclic amine curing agent prepared by the invention is a flowable liquid at normal temperature, and can be mixed with a traditional solid powder type latent curing agent for use, so that the problem that the solid powder type latent curing agent is poor in miscibility with epoxy resin is solved.

Description

Technical Field

[0001] The invention relates to the field of curing agents, in particular to a latent alicyclic amide curing agent, a preparation method thereof and application thereof. Background Art

[0002] Epoxy resin is a thermosetting polymer synthetic material with excellent performance. After reacting with a curing agent, it can form a complex cross-linked network structure and is widely used in coatings, adhesives, composite materials and other fields. Epoxy curing agents are divided into explicit curing agents and latent curing agents. The explicit curing agent must be packaged separately from the epoxy resin. During construction, the two components are mixed in a certain proportion and have a short application period, generally a few minutes to a few hours; the latent curing agent is mainly dicyandiamide, organic acid hydrazide, modified imidazole compounds, etc. After the latent curing agent is mixed with the epoxy resin into a single component, it has a long storage period at room temperature, which can reach more than 1 month. The latent curing agent is mixed with the epoxy resin to form a single-component system, which has the advantages of simple production and operation process and prevention of environmental pollution. It is especially suitable for modern large-scale industrial production processes, such as the field of fiber-reinforced composite materials.

[0003] Dicyandiamide is a commonly used latent epoxy resin curing agent with a storage period 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). It is difficult to mix it evenly with epoxy resin in actual production, which can easily lead to incomplete curing or over-curing, and low thermal deformation temperature of the product, which affects its practical application.

[0004] Alicyclic amine is a room temperature curing agent with a rigid alicyclic structure in its molecular structure. The epoxy cured product has a high heat deformation temperature of up to 150°C and good heat resistance. However, it is highly active and cannot be used directly as a latent curing agent.

[0005] Patent CN116751533A discloses a method for preparing a non-post-curing epoxy tape. Alicyclic amine and dicyandiamide are used together. Dicyandiamide and alicyclic amine are dissolved in advance and then added to the epoxy system. There is no overflow of glue bubbles at a high temperature of 220°C, which improves the heat resistance of the material. However, the reaction speed of alicyclic amine and epoxy resin in this system is fast, and the operating period is only 6 hours at room temperature, and the storage period is greatly shortened.

[0006] Patent CN105646843A proposes to modify alicyclic amines latently, modify alicyclic amines with aromatic isocyanates, effectively block the activity of alicyclic amines, and prolong the application period with epoxy resins. At the same time, the newly generated organic urea groups can enhance the bonding strength of the cured product, and can be used in adhesives, coatings and composite materials. However, the modified latent alicyclic amine is a solid powder, and it is still difficult to avoid the problem of uneven dispersion in the matrix resin, resulting in performance defects in the product.

[0007] In order to better achieve uniform dispersion of latent curing agents in the resin and effectively solve the problem of incomplete curing 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] In order to solve the above problems, the present invention provides a latent alicyclic amide curing agent and a preparation method thereof. The alicyclic amine compound and the carboxylic acid compound are modified by amidation to seal the active hydrogen group on the primary amine with higher activity, while the active hydrogen on the secondary amine is affected by large steric hindered groups such as benzene ring, alicyclic ring, furan ring, etc., which effectively inhibits the reaction activity of the active hydrogen on the secondary amine, so that it has a longer applicable period at room temperature; the latent modified alicyclic amine curing agent is a viscous liquid at room temperature, and contains a strong polar group formyl group and an amide group in the structure. It has good compatibility with the traditional solid powder type curing agent after melt blending, avoiding the complex and time-consuming process required for the dispersion of the powder type curing agent, and effectively solving the problem of uneven mixing, incomplete curing or over-curing of the solid powder type latent curing agent in the resin; in addition, the presence of the alicyclic structure can improve the heat resistance and mechanical strength of the cured product.

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

[0010] The present 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] The present invention also provides a method for preparing a latent alicyclic amide curing agent, wherein the alicyclic amine curing agent and the formyl carboxylic acid compound are mixed and reacted to obtain the latent alicyclic amide curing agent. The reaction temperature of the alicyclic amine curing agent and the formyl carboxylic acid compound is 120 to 180° C., preferably 140 to 160° C.; the reaction time of the alicyclic amine curing agent and the formyl carboxylic acid compound is 2 to 10 hours, preferably 5 to 8 hours;

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

[0016] Among them, 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-pyridinecarboxylic acid, 1-benzoylpiperidine-4-carboxylic acid, 4-formyl-3-methylisoxazole-5-carboxylic acid, 1-formylpiperidine-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 alicyclic amide curing agent combination material comprises the above-mentioned latent alicyclic amide curing agent and a solid powder type latent curing agent. Preferably, the solid powder type latent curing agent is selected from one or more of dicyandiamide latent curing agents, hydrazides, and imidazole compounds.

[0019] A preparation method of the latent alicyclic amide curing agent combination material comprises the steps of melting a solid powder type latent curing agent, adding the latent alicyclic amide curing agent, and mixing the mixture evenly to obtain the latent alicyclic amide curing agent combination material.

[0020] Wherein, the mass ratio of the latent alicyclic amide curing agent to the solid powder type 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 alicyclic amide curing agent of the present invention, which is used for coatings, impregnation materials, and potting materials, preferably impregnation materials.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) The latent alicyclic 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 type latent curing agents such as dicyandiamide, it is easy to form a large number of hydrogen bond structures and has good compatibility, which solves the problem of uneven mixing of traditional solid powder type latent curing agents and epoxy resins, incomplete curing or over-curing;

[0025] (3) Through amidation modification, the active hydrogen groups on the more active primary amines are blocked, while the active hydrogen on the secondary amines is affected by the large steric hindrance groups, which effectively inhibits their reactivity and has a longer working life at room temperature;

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

[0027] (5) The latent alicyclic amide curing agent of the present invention has a simple synthesis process and strong practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 For the product described in Example 1 1 H NMP spectrum, the test instrument is Bruker AVANCE NEO 600M spectrometer, the test uses 5mmBBO probe, the test solvent is CDCl3, and the test temperature is 25℃. DETAILED DESCRIPTION

[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 changes 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-Aldehyde piperidine-4-carboxylic acid TCI (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 ACM Chemical Co., Ltd. 99％ 1,3-Cyclohexanedimethylamine Mitsubishi Chemical Corporation 99％ 4,4'-Diaminodicyclohexylmethane Wanhua Chemical Group Co., Ltd. 99％ Isophorone diamine Wanhua Chemical Group Co., Ltd. 99％ Dicyandiamide Shanghai Aladdin Biochemical Technology Co., Ltd. 99％ Adipic acid dihydrazide Shanghai MacLean Biochemical Technology Co., Ltd. 99％ QXE301 Wuhan Comic Biopharmaceutical Technology Co., Ltd. 99％

[0032] Table 2 Test methods for main performance and indicators

[0033]

[0034]

[0035] Example 1

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

[0037] 114 g of 1,2-cyclohexanediamine and 410 g of 3'-formyl(1,1'-biphenyl)-3-carboxylic acid were added to the reaction kettle, the temperature was raised to 120°C, the mixture was stirred and reacted for 1 hour, the temperature was increased stepwise to 180°C, and the crude product was obtained after the reaction for 8 hours. After vacuum dehydration at 100°C for 2 hours, the final latent alicyclic curing agent was obtained, the structure of which is shown below.

[0038]

[0039] Example 2

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

[0041] 142g of 1,3-cyclohexanedimethylamine and 280g of 1-formylpiperidine-4-carboxylic acid were added to the reaction kettle, the temperature was raised to 120°C, the mixture was stirred and reacted for 1h, the temperature was increased stepwise to 180°C, the reaction was performed for 8h to obtain a crude product, and the final latent alicyclic amide curing agent was obtained after vacuum dehydration at 100°C for 2h. The structure is shown below.

[0042]

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

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

[0045] Example 3

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

[0047] 210 g of 4,4'-diaminodicyclohexylmethane and 410 g of 1-benzoylpiperidine-4-carboxylic acid were added to the reaction kettle, the temperature was raised to 120°C, mixed and stirred for reaction for 1 hour, the temperature was increased stepwise to 180°C, and the crude product was obtained after reaction for 8 hours. After vacuum dehydration at 100°C for 2 hours, the final latent alicyclic amide curing agent was obtained, the structure of which is shown below.

[0048]

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

[0050] Weigh 50 g of dicyandiamide and 100 g of the latent alicyclic amide curing agent prepared in this example and add them into a three-necked flask. Install a stirrer and a condenser. Place the three-necked flask in a heating jacket and heat it at 150° C. After the two curing agents are completely dissolved, continue stirring for 1 hour, and then discharge the material after returning to room temperature to finally obtain a viscous transparent liquid, i.e., a latent alicyclic amide curing agent combination material.

[0051] Example 4

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

[0053] 170 g of isophorone diamine and 310 g of 2-formylpyridine-4-carboxylic acid were added to the reaction kettle, the temperature was raised to 120° C., the mixture was stirred and reacted for 1 hour, the temperature was increased stepwise to 160° C., and the crude product was obtained after reacting for 7 hours. After vacuum dehydration at 100° C. for 2 hours, the final latent alicyclic amide curing agent was obtained, and the structure is shown below.

[0054]

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

[0056] Weigh 30g QXE301 and 100g of the latent alicyclic 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 at 150°C. After the two curing agents are completely dissolved, continue stirring for 1h, and then discharge the material after returning to room temperature to finally obtain a viscous transparent liquid, i.e., a latent alicyclic amide curing agent combination material.

[0057] Example 5

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

[0059] 210 g of 4,4'-diaminodicyclohexylmethane and 410 g of 2-formylfuran-3-carboxylic acid were added to the reaction kettle, the temperature was raised to 120°C, mixed and stirred for reaction for 1 hour, the temperature was increased stepwise to 180°C, and the crude product was obtained after reaction for 8 hours. After vacuum dehydration at 100°C for 2 hours, the final latent alicyclic amide curing agent was obtained, and the structure is shown below.

[0060]

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

[0062] Weigh 70 g of dicyandiamide and 100 g of the latent alicyclic 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 it at 150° C. After adipic acid dihydrazide is completely dissolved, continue stirring for 1 h, and then discharge the material after returning to room temperature to finally obtain a viscous transparent liquid, i.e., a latent alicyclic 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 in 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 a condenser, place the three-necked flask in a heating jacket and heat it. After adipic acid dihydrazide is completely dissolved, add 300g of N,N-dimethylformamide, continue stirring for 30 minutes, stir evenly, and discharge the material after returning to room temperature to obtain the comparative example 2 latent curing agent combination material. Latent curing agent performance test

[0067] The latent ester cyclic amide curing agent prepared in the above Examples 1 to 5 was mixed with the liquid epoxy resin E51 (EEW190) in equimolar amounts, and a curing experiment was carried out (the molar amount of epoxy groups in the epoxy resin = the molar amount of active hydrogen on the amino group in the curing agent). The performance test results of the obtained epoxy curing agent are shown in Table 3.

[0068] Table 3 Heat resistance and mechanical strength data of cured products obtained by alicyclic amide latent curing agent

[0069]

[0070] The combination materials of the latent ester cyclic amide curing agent prepared in the above Examples 1 to 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 carried out (the molar amount of epoxy groups in the epoxy resin = the molar amount of active hydrogen on the amino group in the curing agent). The performance test results of the obtained epoxy curing agent 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 of the embodiment and the comparative example

[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 a modified alicyclic amide latent curing agent prepared by the present invention, and Comparative Example 1 is a latent curing agent adipic acid dihydrazide sold outside. According to the results of Table 3, adipic acid dihydrazide is a solid at room temperature and needs to be melted at a higher temperature before reacting with the epoxy resin, and its applicable period is longer, but Example 1 is a viscous liquid with good compatibility with the epoxy resin. Under high temperature, the secondary amine group will react with the epoxy resin and still have a long applicable period; in addition, the alicyclic amide curing agent structure contains a large number of benzene rings and alicyclic structures, which give the epoxy cured material better mechanical strength and heat resistance.

[0075] As can be seen from Table 4, with reference to Example 2 and Comparative Example 1, the difference between the two is that Example 2 is a curing agent combination of alicyclic amide curing agent and adipic acid dihydrazide, and Comparative Example 1 is a latent curing agent adipic acid dihydrazide sold outside. According to the data in Table 3, adipic acid dihydrazide is solid at room temperature, and needs to react with epoxy resin after melting at a higher temperature, and its application period is longer, but Example 2 is a molten combination of alicyclic amide curing agent and adipic acid dihydrazide, which is still a viscous liquid at room temperature, and is compatible with epoxy resin, and can effectively avoid the problem of uneven mixing of solid powder and resin, incomplete curing or excessive curing; under high temperature, the comparison of alicyclic amide has a longer application period; in addition, the introduction of alicyclic amide curing agent, the introduction of a large number of alicyclic structures in the structure, and the comparison of traditional solid powder type latent curing agent, Example 2 has more excellent mechanical strength and heat resistance.

[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 molten combination of alicyclic amide curing agent and dicyandiamide powder, and Comparative Example 2 is a combination of alicyclic amine and dicyandiamide. According to the data in Table 3, the introduction of the alicyclic structure gives the two combinations excellent mechanical strength and heat resistance; while the reaction activity of alicyclic amine and epoxy resin in Comparative Example 2 is relatively high, and the operation period is only 10 minutes at a temperature of 150°C, and the applicable period is relatively short. The modified alicyclic amide curing agent greatly increases the operation period, extending from 10 minutes to 40 minutes, so that the combination formula has a longer operating applicable period. In Tables 3 and 4, referring to the comparison of the curing agent and the combination in Example 1, the difference between the two is that Table 3 is a modified alicyclic amide latent curing agent prepared by the present invention, and Table 4 is a combination of a modified alicyclic amide latent curing agent and a solid powder type latent curing agent such as dicyandiamide. According to the comparison results in Tables 3 and 4, the modified alicyclic amide latent curing agent contains a large number of strong polar groups in its molecular structure. When mixed with the dicyandiamide solid powder type latent curing agent, the presence of the hydrogen bond structure improves the compatibility of the two, and finally a liquid latent curing agent combination can be obtained, which solves the problem of uneven mixing of traditional solid powder type latent curing agent and epoxy resin, and has good compatibility with epoxy resin; after adding the conventional latent curing agent dicyandiamide, the viscosity of the combination increases, the latency is extended, and its application period is further improved, but the brittleness increases and the mechanical strength decreases slightly.

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

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

Claims

1. A latent alicyclic amide curing agent, characterized in that, It has the following structure: Wherein R1 is selected from R2 is selected from 2. A method for preparing a latent alicyclic amide curing agent, characterized in that: The alicyclic amine curing agent and the formyl carboxylic acid compound are mixed and reacted to obtain a latent alicyclic amide curing agent.

3. The preparation method according to claim 2, characterized in that: The reaction temperature of the alicyclic amine curing agent and the formyl carboxylic acid compound is 120 to 180° C., preferably 140 to 160° C.; Preferably, the reaction time of the alicyclic amine curing agent and the formyl carboxylic acid compound is 2 to 10 hours, preferably 5 to 8 hours.

4. The preparation method according to claim 2, characterized in that: The alicyclic amine is selected from one or more of 4,4'-diaminodicyclohexylmethane, isophoronediamine, 1,3-cyclohexanedimethylamine, 1-methyl-2,4-cyclohexanediamine, and 1,2-cyclohexanediamine, preferably 1,2-cyclohexanediamine; Preferably, the formylcarboxylic 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-pyridinecarboxylic acid, 1-benzoylpiperidine-4-carboxylic acid, 4-formyl-3-methylisoxazole-5-carboxylic acid, 1-formylpiperidine-4-carboxylic acid, and 1-(2-methyl-benzoyl)-piperidine-4-carboxylic acid.

5. The preparation method according to claim 2, 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), preferably 1:(0.85-0.95).

6. Use of the latent alicyclic amide curing agent according to claim 1 or the alicyclic amide curing agent prepared by the preparation method according to any one of claims 2 to 5, which can be used directly as a curing agent or used in combination with other curing agents.

7. The use according to claim 6, which is used in the fields of coatings, impregnation materials, and potting materials, preferably in impregnation materials.

8. A latent alicyclic amide curing agent composition, characterized in that: Comprising the latent alicyclic amide curing agent according to claim 1 or the alicyclic amide curing agent prepared by the preparation method according to any one of claims 2 to 5 and a solid powder type latent curing agent, preferably, the solid powder type latent curing agent is selected from one or more of dicyandiamide latent curing agents, hydrazides, and imidazole compounds; Preferably, the mass ratio of the latent alicyclic amide curing agent to the solid powder type latent curing agent is 1:(0.1-0.7), preferably 1:(0.3-0.6).

9. The method for preparing the latent alicyclic amide curing agent combination according to claim 8, comprising melting the solid powder type latent curing agent, adding the latent alicyclic amide curing agent, and mixing them uniformly to obtain the latent alicyclic amide curing agent combination.

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