Imidazole epoxy resin curing agent as well as preparation method and application thereof

Abstract

The invention relates to the technical field of organic synthesis, in particular to an imidazole epoxy resin curing agent as well as a preparation method and application thereof. The imidazole epoxy resin curing agent is prepared from the following components in parts by weight: 82 to 144 parts of alkyl imidazole, 108 to 198 parts of quinone compound and 229 to 342 parts of solvent. A phenolic compound is connected to an imidazole ring, that is, alkyl imidazole and a quinone compound are subjected to a Michael addition reaction, and alkyl imidazole connected with the phenolic compound is generated. The phenolic hydroxyl group-containing alkyl imidazole curing agent fundamentally solves the problem of separation of an imidazole curing agent and a phenolic polymerization inhibitor.

Description

Technical Field

[0001] The present invention relates to the technical field of organic synthesis, and particularly to an imidazole-based epoxy resin curing agent, a preparation method thereof, and an application thereof. Background Art

[0002] Imidazole compounds belong to heat-curing epoxy resin curing agents, and the cured products have excellent heat resistance and insulation properties, and are widely used in the fields of electronics, electrical appliances, and composite materials. Its disadvantage is that the pot life after mixing with epoxy resin is relatively short, generally not exceeding eight hours at room temperature, which greatly limits the use of imidazole curing agents. CN114230767A uses a microcapsule method to encapsulate the imidazole curing agent and then disperse it into the epoxy resin for heat curing. However, it can only be used in a pure epoxy resin system and cannot be used in a system containing a diluent (or solvent) because the diluent or solvent will dissolve the wall of the microcapsule and release the imidazole curing agent, still resulting in a pot life problem.

[0003] JP58-13623 uses the addition of alkyl imidazole and epoxy resin, and the product is pulverized and then dispersed into the epoxy resin to extend the pot life of the alkyl imidazole curing agent. The principle is that the alkyl imidazole-epoxy resin adduct is insoluble in the epoxy resin, thereby extending the pot life. However, such imidazole-based adduct curing agents still cannot be used in the presence of a diluent or solvent because once the adduct dissolves and the imidazole ring is exposed, it can react with the epoxy resin, thus losing its latency and being equivalent to the pot life of conventional alkyl imidazoles.

[0004] Phenolic hydroxyl groups have the function of extending the pot life of imidazole curing agents. The principle is that phenolic hydroxyl groups can absorb the imidazole negative ion bond and interrupt the chain reaction, prompting the epoxy resin to terminate the curing reaction, thereby extending the pot life. JP52-3828 prepares a curing agent with a longer pot life by directly adding phenolic compounds to the alkyl imidazole-epoxy resin adduct. Such curing agents can dissolve in a formulation system containing a diluent or solvent, and the imidazole curing agent and the phenolic compound are in a separated state. The imidazole curing agent can directly cure the epoxy resin, while the phenolic compound loses its polymerization inhibition function. This method still cannot solve the disadvantage of short pot life in the presence of a diluent or solvent. Summary of the Invention

[0005] In order to solve the above problems, the present invention provides an imidazole-based epoxy resin curing agent, a preparation method thereof, and an application thereof. The present invention attaches a phenolic compound to the imidazole ring, that is, alkyl imidazole and quinone compounds are subjected to a Michael addition reaction to generate alkyl imidazole connected with phenolic compounds. This type of alkyl imidazole curing agent containing phenolic hydroxyl groups fundamentally solves the separation problem between imidazole curing agents and phenolic polymerization inhibitors.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] The present invention provides an imidazole-based epoxy resin curing agent, which is prepared from the following components in parts by weight:

[0008] 82-144 parts of alkyl imidazole, 108-198 parts of quinone compound, and 229-342 parts of solvent.

[0009] Preferably, it is prepared from the following components in parts by weight:

[0010] 110 parts of alkyl imidazole, 119-175 parts of quinone compound, and 235-357 parts of solvent.

[0011] Preferably, the alkyl imidazole includes 2-methylimidazole and / or 2-ethyl-4-methylimidazole.

[0012] Preferably, the quinone compound includes one or more of p-benzoquinone, o-benzoquinone, 1,4-naphthoquinone, and 1,2-naphthoquinone.

[0013] Preferably, the solvent includes one or more of tetrahydrofuran, dioxane, N,N-dimethylformamide, N,N-dimethylacetamide, and hexamethylphosphoric triamide.

[0014] The present invention also provides a preparation method of the imidazole-based epoxy resin curing agent described in the above technical solution, including the following steps: under nitrogen protection, mix the alkyl imidazole, quinone compound, and solvent, carry out an addition reaction at 80-120 °C for 5-8 h, and remove the solvent to obtain the imidazole-based epoxy resin curing agent.

[0015] The present invention also provides the application of the imidazole-based epoxy resin curing agent described in the above technical solution in curing epoxy resin.

[0016] Preferably, the application includes the following steps: mix the imidazole-based epoxy resin curing agent with a good solvent and epoxy resin and then carry out curing.

[0017] Preferably, the mass ratio of the imidazole-based epoxy resin curing agent to the good solvent and epoxy resin is 8.8-14.6:50:100.

[0018] Preferably, the good solvent includes N,N-dimethylformamide;

[0019] The conditions for curing include: temperature is 100 °C, and time is 2 h.

[0020] Beneficial effects:

[0021] In the present invention, an alkylimidazole and a quinone compound are subjected to a Michael addition reaction in a solvent environment to generate a phenolic hydroxyl group-containing imidazole compound curing agent. After this type of curing agent is mixed with an epoxy resin, the tertiary nitrogen atom on the imidazole ring attacks the epoxy group to form an oxygen anion, while the phenolic hydroxyl group prevents the chain reaction of the oxygen anion, thereby delaying the etherification cross-linking reaction of the epoxy resin. Ultimately, at the macroscopic level, it is manifested as an extended pot life at room temperature. When curing by heating, the kinetic energy of the oxygen anion becomes larger and can complete the etherification reaction, so it can be cured normally. The present invention utilizes the polymerization inhibition function of the phenolic hydroxyl group to prepare a phenolic imidazole-based curing agent with a long pot life at room temperature. Detailed implementation mode

[0022] The present invention provides an imidazole-based epoxy resin curing agent, which is prepared from the following components in parts by weight: 82-144 parts of alkylimidazole, 108-198 parts of quinone compound, and 229-342 parts of solvent. In the present invention, the imidazole-based epoxy resin curing agent is preferably prepared from the following components in parts by weight: 110 parts of alkylimidazole, 119-175 parts of quinone compound, and 235-357 parts of solvent. In the present invention, the alkylimidazole preferably includes 2-methylimidazole and / or 2-ethyl-4-methylimidazole. In the present invention, the quinone compound preferably includes one or more of p-benzoquinone, o-benzoquinone, 1,4-naphthoquinone, and 1,2-naphthoquinone. In the present invention, the solvent preferably includes one or more of tetrahydrofuran, dioxane, N,N-dimethylformamide, N,N-dimethylacetamide, and hexamethylphosphoric triamide. The present invention has no special limitation on the sources of the above reagents, and conventional commercially available products can be used.

[0023] The present invention also provides a preparation method of the imidazole-based epoxy resin curing agent described in the above technical solution, which includes the following steps: under nitrogen protection, mix the alkylimidazole, quinone compound, and solvent, and carry out an addition reaction at 80-120 °C for 5-8 h, and remove the solvent to obtain the imidazole-based epoxy resin curing agent.

[0024] The present invention also provides the application of the imidazole-based epoxy resin curing agent described in the above technical solution in curing epoxy resin. In the present invention, the application preferably includes the following steps: mix the imidazole-based epoxy resin curing agent with a good solvent and an epoxy resin and then carry out curing. In the present invention, the mass ratio of the imidazole-based epoxy resin curing agent to the good solvent and the epoxy resin is preferably 8.8-14.6:50:100. In the present invention, the good solvent preferably includes N,N-dimethylformamide. In the present invention, the curing conditions preferably include: temperature is 100 °C, and time is 2 h.

[0025] In order to further illustrate the present invention, the present invention will be described in detail below in conjunction with examples, but they cannot be understood as limiting the protection scope of the present invention.

[0026] Example 1

[0027] Under nitrogen protection, 82 g of 2-methylimidazole and 108 g of p-benzoquinone were dissolved in 190 g of tetrahydrofuran, and the mixture was heated under reflux for 8 hours. The tetrahydrofuran solvent was distilled off under reduced pressure to obtain 190 g of a brown solid (imidazole-based epoxy resin curing agent).

[0028] Example 2

[0029] Under nitrogen protection, 110 g of 2-ethyl-4-methylimidazole and 119 g of p-benzoquinone were dissolved in 229 g of dioxane, and the reaction was carried out at 100 °C for 5 hours. The dioxane solvent was distilled off under reduced pressure. The residue was extracted with 200 g of xylene to remove the unreacted substances. Then the residue was heated to dryness to obtain 206 g of a brown solid (imidazole-based epoxy resin curing agent).

[0030] Example 3

[0031] Under nitrogen protection, 110 g of 2-ethyl-4-methylimidazole and 125 g of o-benzoquinone were dissolved in 235 g of N,N-dimethylformamide, and the mixture was heated to 80 °C and reacted for 8 hours. The N,N-dimethylformamide solvent was distilled off under vacuum. The residue was extracted with 200 g of xylene to remove the unreacted substances. The residue was dried by evaporation to obtain 182 g of a light brown solid (imidazole-based epoxy resin curing agent).

[0032] Example 4

[0033] Under nitrogen protection, 82 g of 2-methylimidazole and 175 g of 1,4-naphthoquinone were dissolved in 257 g of N,N-dimethylformamide, and the reaction was carried out at 100 °C for 8 hours. The N,N-dimethylformamide solvent was distilled off under reduced pressure. The residue was extracted with 200 g of xylene to remove the unreacted substances. The residue was dried by evaporation to obtain 186 g of a dark brown solid (imidazole-based epoxy resin curing agent).

[0034] Example 5

[0035] Under nitrogen protection, 144 g of 2-phenylimidazole and 198 g of 1,2-naphthoquinone were dissolved in 342 g of N,N-dimethylacetamide, and the reaction was carried out at 120 °C for 8 hours. The N,N-dimethylacetamide solvent was distilled off under reduced pressure. The unreacted substances were extracted with 300 g of xylene, and the residue was dried by evaporation to obtain 233 g of a light brown solid (imidazole-based epoxy resin curing agent).

[0036] Example 6

[0037] Under nitrogen protection, 144 g of 2-phenylimidazole and 125 g of o-benzoquinone were dissolved in 235 g of hexamethylphosphoramide and reacted at 120 °C for 8 hours. The hexamethylphosphoramide solvent was distilled off under reduced pressure. The unreacted substances were extracted with 200 g of xylene, and the residue was evaporated to dryness to obtain 212 g of a light brown solid (imidazole-based epoxy resin curing agent).

[0038] Example 7

[0039] The products of Examples 1 to 6 were dissolved in N,N-dimethylformamide (DMF), and this solution was used to prepare a glue with epoxy resin. The dosage was converted to the corresponding 5% alkylimidazole. Among them, 128 was a bisphenol A liquid epoxy resin with an EEW of 190. The formula was as follows:

[0040] A. The mass ratio of 128 / Example 1 / DMF = 100 / 11.6 / 50;

[0041] B. The mass ratio of 128 / Example 2 / DMF = 100 / 9.9 / 50;

[0042] C. The mass ratio of 128 / Example 3 / DMF = 100 / 9.9 / 50;

[0043] D. The mass ratio of 128 / Example 4 / DMF = 100 / 14.6 / 50;

[0044] E. The mass ratio of 128 / Example 5 / DMF = 100 / 10.5 / 50;

[0045] F. The mass ratio of 128 / Example 6 / DMF = 100 / 8.8 / 50.

[0046] The curing method was: after mixing epoxy resin, imidazole-based epoxy resin curing agent and N,N-dimethylformamide, curing was carried out at 100 °C for 2 h.

[0047] The evaluation criteria were: curing was based on the needle not being able to penetrate, and the needle was a blunt needle on the market; the storage period was based on the viscosity doubling.

[0048] The results of the examples are shown in Table 1.

[0049] Table 1 Curing Results

[0050] Number A B C D E F Storage period at 25°C / day 24 35 30 23 18 16 Curing at 100°C for 2 hours Curing Curing Curing Curing Curing Curing

[0051] Comparative Example 1

[0052] The formula was as follows, the following were mass ratios:

[0053] G. 128 / 2-methylimidazole / DMF = 100 / 5 / 50;

[0054] H. 128 / 2 - ethyl - 4 - methylimidazole / DMF = 100 / 5 / 50;

[0055] I. 128 / 2 - phenylimidazole / DMF = 100 / 5 / 50.

[0056] 128 is a bisphenol A liquid epoxy resin with an EEW of 190, and the curing method and evaluation criteria are the same as those in Example 7.

[0057] The results of the comparative examples are shown in Table 2.

[0058] Curing results

[0059] Number G H I Storage period at 25°C / day <1 <1 <1 Curing at 100°C for 2 hours Curing Curing Curing

[0060] Although the above embodiments have described the present invention in detail, they are only some embodiments of the present invention, not all embodiments. People can also obtain other embodiments based on these embodiments without creative efforts, and these embodiments all fall within the protection scope of the present invention.

Claims

1. An imidazole-based epoxy resin curing agent, characterized in that, Prepared from the following components in parts by weight: 82 - 144 parts of alkyl imidazole, 108 - 198 parts of quinone compound, and 229 - 342 parts of solvent.

2. The imidazole-based epoxy resin curing agent according to claim 1, characterized in that, Prepared from the following components in parts by weight: 110 parts of alkyl imidazole, 119 - 175 parts of quinone compound, and 235 - 357 parts of solvent.

3. The imidazole-based epoxy resin curing agent according to claim 1 or 2, characterized in that, The alkyl imidazole includes 2 - methylimidazole and / or 2 - ethyl - 4 - methylimidazole.

4. The imidazole-based epoxy resin curing agent according to claim 1 or 2, characterized in that, The quinone compound includes one or more of p - benzoquinone, o - benzoquinone, 1,4 - naphthoquinone, and 1,2 - naphthoquinone.

5. The imidazole-based epoxy resin curing agent according to claim 1 or 2, characterized in that, The solvent includes one or more of tetrahydrofuran, dioxane, N,N - dimethylformamide, N,N - dimethylacetamide, and hexamethylphosphoric triamide.

6. A preparation method of the imidazole-based epoxy resin curing agent according to any one of claims 1 to 5, characterized in that, Including the following steps: Under nitrogen protection, mix the alkyl imidazole, quinone compound, and solvent, carry out an addition reaction at 80 - 120 °C for 5 - 8 h, remove the solvent, and obtain an imidazole - type epoxy resin curing agent.

7. Use of the imidazole - type epoxy resin curing agent according to any one of claims 1 - 5 in curing epoxy resin.

8. The application according to claim 7, wherein The use includes the following steps: Mix the imidazole - type epoxy resin curing agent with a good solvent and epoxy resin and then carry out curing.

9. The application according to claim 8, characterized in that The mass ratio of the imidazole - type epoxy resin curing agent to the good solvent and epoxy resin is 8.8 - 14.6:50:

100.

10. The application according to claim 8, wherein The good solvent includes N,N - dimethylformamide; The conditions for curing include: temperature is 100 °C and time is 2 h.