阅读说明：本技术 一种复合改性2-甲基咪唑固化剂及其制备方法 (Composite modified 2-methylimidazole curing agent and preparation method thereof ) 是由 杨建国 金众 徐琰 徐胜 金玲 高宏 于 2021-01-11 设计创作，主要内容包括：本发明公开了一种复合改性2-甲基咪唑固化剂及其制备方法,属于精细化工领域。该复合改性固化剂的制备过程为：先以2-甲基咪唑、有机碳酸酯反应制备中间产物,再将中间产物与金属盐反应得到常温下呈粘稠液态的复合改性2-甲基咪唑固化剂。所述的有机碳酸酯为碳酸乙烯酯、碳酸丙烯酯中的一种或者两者的混合物。所述的金属盐为乙酸锌、醋酸铜、葡萄糖酸锌、七水硫酸锌中的一种或者多种组成的混合物。本发明复合改性固化剂具有易与环氧树脂混合、常温条件下反应活性较低、潜伏性能优良、固化强度高等优点。此外,本发明利用有机碳酸酯对2-甲基咪唑进行改性,属于二氧化碳资源化利用技术的延伸。(The invention discloses a compound modified 2-methylimidazole curing agent and a preparation method thereof, belonging to the field of fine chemical engineering. The preparation process of the composite modified curing agent comprises the following steps: firstly, 2-methylimidazole reacts with organic carbonate to prepare an intermediate product, and then the intermediate product reacts with metal salt to obtain the composite modified 2-methylimidazole curing agent which is viscous and liquid at normal temperature. The organic carbonate is one of ethylene carbonate and propylene carbonate or a mixture of the ethylene carbonate and the propylene carbonate. The metal salt is a mixture consisting of one or more of zinc acetate, copper acetate, zinc gluconate and zinc sulfate heptahydrate. The composite modified curing agent has the advantages of easy mixing with epoxy resin, lower reaction activity under normal temperature, excellent latent property, high curing strength and the like. In addition, the invention utilizes organic carbonate to modify 2-methylimidazole, and belongs to the extension of carbon dioxide resource utilization technology.)

1. The composite modified 2-methylimidazole curing agent is characterized in that the curing agent is prepared from the following components in percentage by weight:

0.5-2 parts of 2-methylimidazole

1-5 parts of organic carbonate

0.1-0.5 part of metal salt.

2. The compound modified 2-methylimidazole curing agent as claimed in claim 1, wherein the organic carbonate is one of ethylene carbonate and propylene carbonate or a mixture of the two.

3. The compound modified 2-methylimidazole curing agent as claimed in claim 2, wherein the organic carbonate is propylene carbonate.

4. The compound modified 2-methylimidazole curing agent as claimed in claim 1, wherein the metal salt is a mixture of one or more of zinc acetate, copper acetate, zinc gluconate and zinc sulfate heptahydrate.

5. The compound-modified 2-methylimidazole curing agent as claimed in claim 4 wherein the metal salt is zinc gluconate.

6. The preparation method of the composite modified 2-methylimidazole curing agent as claimed in claim 1, characterized by comprising the steps of:

(1) adding 2-methylimidazole and organic carbonate into a three-neck flask provided with a reflux condensing device, reacting for 2-6 hours at 105-150 ℃, and cooling to room temperature to obtain an intermediate product;

(2) uniformly mixing the intermediate product prepared in the step (1) with metal salt, reacting at 100-140 ℃ for 0.5-5 hours, and cooling to room temperature to obtain a viscous liquid product, namely a target product: composite modified 2-methylimidazole curing agent.

7. The use method of the compound modified 2-methylimidazole curing agent as claimed in claim 1, wherein the use amount of the compound modified 2-methylimidazole curing agent is 2.5-40% of the mass of the pure liquid E-44 type epoxy resin; the curing process condition is to keep the temperature at 135-185 ℃ for 0.2-3.5 hours.

Technical Field

The invention belongs to the field of fine chemical engineering, and particularly relates to a composite modified 2-methylimidazole curing agent as well as a preparation method and a use method thereof.

Background

Imidazole compounds contain secondary amine groups and tertiary amine groups in the molecular structure, and can initiate epoxy groups to carry out anionic polymerization, so that the imidazole compounds are often used as catalytic polymerization type curing agents of epoxy resins. The imidazole curing agent has the following advantages: the toxicity and the volatility of the imidazole curing agent at normal temperature are lower than those of common aliphatic amine and aromatic amine curing agents, and the imidazole curing agent is hardly decomposed below 250 ℃; when the imidazole compound initiates epoxy group polymerization, chain transfer is not easy to occur at high temperature, and the cured product has higher heat resistance and mechanical strength.

Except for individual high-price varieties such as 2-ethyl-4-methylimidazole and 1-benzyl-2-methylimidazole, most of imidazole compounds such as 2-methylimidazole and the like are solid powder at normal temperature, are not easy to mix with epoxy resin uniformly, and are inconvenient to operate. Therefore, the imidazole compound is modified to be converted into a liquid state at normal temperature to improve the compatibility with the epoxy resin, and the imidazole compound is beneficial to improving the curing performance and expanding the application range of the imidazole compound in the field of epoxy resin curing agents.

The imidazole curing agent has another problem in the actual use process: the imidazole curing agent has high reaction activity and can quickly initiate the curing of the epoxy resin; when mixed with epoxy resin, the viscosity of the system rises rapidly at normal temperature, so that the imidazole compound cannot be directly used as a latent epoxy curing agent. In order to improve the latency, the most common method is to react imidazole compounds with metal salts such as copper, cobalt, nickel, zinc, etc. to form metal salt complexes which are stable at normal temperature, and the metal salt complexes will be dissociated into imidazole and metal salts when heated, thereby rapidly initiating the curing of the epoxy resin. In addition, the complex can be used as an accelerator for dicyandiamide to promote improvement in curability.

Chemical world (Zhao Ru thrifty, Liu Guo, Lin, A group of novel one-component epoxy resin curing systems [ J ]]The chemical world, 1989(07):323-325) reported a latent curing agent of zinc salicylate-2-methylimidazole complex (C)₂₂H₂₂N₄O₆Zn, the relative molecular mass is 503), the single-component epoxy adhesive prepared by the curing agent has long storage life and can be rapidly cured at 120-210 ℃. However, the zinc salicylate-2-methylimidazole complex has a high melting pointThe temperature reaches 177.6-178 ℃, and the epoxy resin is solid at normal temperature and is not easy to mix uniformly; and the preparation process of the zinc salicylate-2-methylimidazole complex is complicated. These problems limit the application of such curing agents.

Disclosure of Invention

Aiming at the defects of the prior art, the invention adopts organic carbonate and metal salt to carry out compound modification on 2-methylimidazole so as to prepare the compound modified 2-methylimidazole curing agent. The first purpose of the invention is to provide a compound modified 2-methylimidazole curing agent which is easy to mix with epoxy resin, has long room temperature gel time and excellent curing performance and a preparation method thereof; the second purpose of the invention is to provide a using process of the composite modified curing agent.

In order to realize the purpose, the invention adopts the following technical scheme:

the composite modified 2-methylimidazole curing agent has the following mass ratio of each component in the synthetic formula:

0.5-2 parts of 2-methylimidazole

1-5 parts of organic carbonate

0.1-0.5 part of metal salt.

The organic carbonate is one or a mixture of ethylene carbonate and propylene carbonate, and the propylene carbonate is preferred. The metal salt is a mixture consisting of one or more of zinc acetate, copper acetate, zinc gluconate and zinc sulfate heptahydrate, and preferably zinc gluconate.

The preparation method of the composite modified 2-methylimidazole curing agent provided by the invention is realized by the following two steps of reactions: (1) adding 2-methylimidazole and organic carbonate into a three-neck flask provided with a reflux condensing device, reacting for 2-6 hours at 105-150 ℃, and cooling to room temperature to obtain an intermediate product; (2) and (2) uniformly mixing the intermediate product prepared in the step (1) with metal salt, reacting for 0.5-5 hours at 100-140 ℃, and cooling to room temperature to obtain a viscous liquid product, namely the target product, namely the composite modified 2-methylimidazole curing agent. It should be noted that the reaction of the organic carbonate with 2-methylimidazole releases carbon dioxide, so that it is necessary to ensure that the exhaust passage of the reaction system is open in step (1) and step (2). The intermediate product prepared in the step (1) and the composite modified curing agent prepared in the step (2) may have a barrel expansion phenomenon in the storage process, because a carbon dioxide byproduct generated in the reaction process is partially dissolved in the corresponding product and can be released in the storage process; in addition, excessive or incompletely reacted organic carbonate in the intermediate product or the composite modified curing agent can slowly react to release carbon dioxide in the process of storage at normal temperature. In order to avoid the phenomenon of barrel expansion, the container for storing the intermediate product and the composite modified 2-methylimidazole curing agent must be periodically uncovered and deflated.

The organic carbonate in the composite modified 2-methylimidazole curing agent synthesis formula provided by the invention belongs to a strong polar molecule. The intermediate product is prepared by reacting organic carbonate with 2-methylimidazole, so that solid 2-methylimidazole is converted into liquid, the intermediate product has stronger polarity, and good miscibility of the metal salt and the liquid intermediate product is ensured. The nitrogen atom on the imidazole ring of the intermediate product and the metal ion in the metal salt form a coordination bond for complexing, so that the alkalinity and the nucleophilic ability of the nitrogen atom are reduced, and the reaction capability of catalyzing the polymerization of the epoxy resin by the imidazole ring under the normal temperature condition is weakened. Therefore, the sizing material prepared from the modified curing agent and the epoxy resin has longer gel time at room temperature. The composite modified 2-methylimidazole curing agent provided by the invention is liquid at normal temperature, has excellent compatibility with epoxy resin, is easy to be uniformly mixed with the epoxy resin, and is beneficial to uniform and full curing of the epoxy resin, so that the curing performance is improved. When heated, the coordination bond between the nitrogen atom and the metal ion in the composite modified curing agent is broken, and the alkalinity and the nucleophilic ability of the nitrogen atom are recovered, so that the epoxy resin is initiated to carry out a curing reaction.

The invention provides a composite modified 2-methylimidazole curing agent, which has the following use process: (1) the amount of the compound modified 2-methylimidazole curing agent is 2.5-40% of the mass of the pure liquid E-44 type epoxy resin; (2) the curing process condition is to keep the temperature at 135-185 ℃ for 0.2-3.5 hours.

Compared with the prior art, the invention has the following technical effects:

(1) according to the invention, 2-methylimidazole is modified to be changed from a solid state to a liquid state, so that the problems that solid 2-methylimidazole is difficult to be uniformly mixed with epoxy resin and the curing strength is influenced are solved.

(2) The compound modified 2-methylimidazole curing agent provided by the invention has low reaction activity at normal temperature and excellent latent performance, the gel time of a sizing material prepared from the modified curing agent and epoxy resin at room temperature can be more than 4400 hours, and the gel time of an adhesive prepared from unmodified 2-methylimidazole and epoxy resin at room temperature is only 6 hours.

(3) The disclosed metal salt modified 2-methylimidazole latent curing agent is mostly solid at normal temperature, while the metal salt compound modified 2-methylimidazole latent curing agent prepared according to the technical scheme of the invention is viscous liquid at normal temperature, is easy to mix with epoxy resin and has latency, which is the most outstanding advantage of the invention.

(4) By adopting a proper synthesis formula and synthesis conditions, dosage and curing conditions of the modified curing agent, the technical scheme provided by the invention can greatly improve the curing strength of the epoxy adhesive. Compared with the adhesive prepared by unmodified 2-methylimidazole, the adhesive prepared by the composite modified curing agent has the tensile shear strength increased by over 100 percent.

(5) The invention utilizes organic carbonate to modify 2-methylimidazole, and the raw material of the organic carbonate belongs to a chemical fixed product of carbon dioxide, so the technical scheme of the invention belongs to the extension of a carbon dioxide resource utilization technology.

Detailed Description

The present invention will be further described with reference to the following examples, but the present invention is not limited to the following examples.

I. Preparation of composite modified 2-methylimidazole curing agent

The composite modified 2-methylimidazole curing agent of examples 1 to 10 was prepared according to the synthesis formula shown in table 1 and the process conditions shown in table 2. The synthesis process of the corresponding compound modified 2-methylimidazole curing agent is illustrated by example 3: (1) adding 1 part of 2-methylimidazole and 2 parts of propylene carbonate into a three-neck flask with a reflux condensing device, stirring and refluxing for 4 hours at 135 ℃, and cooling to room temperature to obtain a viscous liquid intermediate product; (2) and (3) uniformly mixing the intermediate product obtained in the first step with 0.4 part of zinc gluconate, reacting at 120 ℃ for 1 hour, and cooling to room temperature to obtain a viscous liquid composite modified 2-methylimidazole curing agent, namely the target product.

TABLE 1 Synthesis formulation of composite modified 2-methylimidazole curative

TABLE 2 Synthesis Process conditions for composite modified 2-methylimidazole curing agent

II. Preparation of composite modified 2-methylimidazole curing agent and comparative epoxy adhesive

The epoxy adhesive is prepared from the compound modified 2-methylimidazole curing agent prepared in the following steps of table 1 and table 2, examples 1-10, E44 epoxy resin and propylene glycol ethyl ether, wherein the propylene glycol ethyl ether plays a role of an inert diluent. The adhesive formulations corresponding to the examples are shown in table 3, and the preparation process is described by taking example 3 as an example: 100 parts by weight of E44 epoxy resin, 19.6 parts by weight of the compound modified 2-methylimidazole curing agent prepared in example 3 (the preparation formula and the process are shown in the table 1 and 2 and the example 3), and 10 parts by weight of propylene glycol ethyl ether are weighed and fully and uniformly stirred to obtain the epoxy adhesive in example 3.

In order to compare the performance change conditions before and after 2-methylimidazole modification, 100 parts by weight of E44 epoxy resin, 4.4 parts by weight of 2-methylimidazole and 10 parts by weight of propylene glycol ethyl ether are weighed according to the formula of a comparison sample in Table 3, and the epoxy adhesive is obtained after fully stirring and uniformly mixing.

TABLE 3 composite modified 2-methylimidazole curative and comparative adhesive formulations (examples 1-10)

III, performance test of composite modified 2-methylimidazole curing agent and comparative epoxy adhesive

(1) Room temperature gel time test: about 10g of the epoxy adhesive which is just prepared according to the formula of each example and the reference sample in the table 3 is respectively filled into a transparent plastic bottle to be sealed and placed at room temperature, timing observation is started, and the time for the adhesive to lose fluidity is defined as the gel time at room temperature, so that the reaction activity of the curing agent and the working life of the adhesive are measured. The longer the room temperature gel time is, the lower the reaction activity of the curing agent is, and the longer the pot life of the corresponding epoxy adhesive is.

In table 4, the 2 nd column indicates the room temperature gel time of the comparative adhesive prepared from the composite modified 2-methylimidazole curing agent and unmodified 2-methylimidazole in examples 1 to 10, and it can be seen that the room temperature gel time of the adhesive prepared from the composite modified curing agent is tens of times to hundreds of times that of the unmodified 2-methylimidazole, and the longest gel time can reach 4400 hours.

(2) Testing the tensile shear strength of the compound modified 2-methylimidazole curing agent and the comparative adhesive: 2 stainless steel test pieces of 120mm in length by 30mm in length by 3mm in length by width by thickness were bonded in parallel by lapping along the longitudinal direction by using the adhesives of the examples and comparative examples in Table 3, respectively, and the length of the bonding surface was 10 mm. Placing the bonding test piece into an oven in a contact pressure mode, and respectively curing according to the curing process shown in the table 4; after the state adjustment was performed by leaving the bonded sample at room temperature for 24 hours, the state-adjusted bonded sample was subjected to a tensile shear strength test using a universal material testing machine, and the results are shown in the rightmost column of Table 4. As long as the formula and the process are proper, the tensile shear strength of the adhesive prepared by the composite modified curing agent can be increased by more than 100 percent compared with the tensile shear strength of the adhesive prepared by the unmodified 2-methylimidazole curing agent.

TABLE 4 Performance test results of composite modified 2-methylimidazole curing agent and comparative epoxy adhesive