Imidazole microcapsules, and methods of making and using the same

Abstract

The present application belongs to the technical field of imidazole curing agent, and particularly relates to an imidazole microcapsule, a preparation method and application thereof.The imidazole microcapsule has a core-shell structure; the core material of the core-shell structure comprises an imidazole compound; the shell layer of the core-shell structure comprises a polyurea-polyurethane composite; in the polyurea-polyurethane composite, polyurea segments and polyurethane segments are covalently crosslinked to form a composite hybrid network structure.The polyurea-polyurethane composite formed by covalent crosslinking of the polyurethane segments and the polyurea segments in the shell layer of the imidazole microcapsule coats the imidazole compound in the polyurea-polyurethane composite system, and has both sealing property and functionality, so that the imidazole microcapsule has the characteristics of high coating amount, fast curing speed and good storage stability.

Description

Technical Field

[0001] This invention belongs to the technical field of imidazole curing agents, and specifically relates to an imidazole microcapsule, its preparation method, and its application. Background Technology

[0002] Epoxy resin, a common thermosetting resin, possesses excellent mechanical properties, electrical insulation, and corrosion resistance, and has been widely used in electronics, aerospace, transportation, and building materials. However, epoxy resin needs to react with a curing agent to form a cross-linked structure to realize its properties; therefore, the type and performance of the curing agent directly determine the performance and application of epoxy resin products.

[0003] Imidazole compounds, due to the presence of an imidazole ring in their molecules, possess excellent catalytic activity and thermal stability, and are widely recognized as a promising latent curing agent for epoxy resin curing. Compared to traditional amine curing agents (such as ethylenediamine, which is volatile and highly toxic) and acid anhydride curing agents (such as phthalic anhydride, which requires high curing temperatures and long curing times), imidazole compounds offer advantages such as lower dosage, higher curing efficiency, and superior mechanical properties and resistance to humid heat of the cured products. They have become core curing agents in fields such as electronic packaging, high-end coatings, and composite materials.

[0004] Currently, imidazole compounds still face many challenges in their application as epoxy resin curing agents. Some imidazole compounds (such as 2-methylimidazole) are prone to absorbing moisture and clumping at room temperature, affecting their dispersibility in epoxy resins and consequently the performance of the cured product. Furthermore, the high volatility of some liquid imidazole compounds (such as 1-ethyl-2-methylimidazole) can lead to the loss of active ingredients during processing, reducing curing efficiency. More importantly, most imidazole compounds, when mixed with epoxy resins, lack sufficient storage stability, retaining curing activity at room temperature and easily curing prematurely, ultimately losing their flowability and processability. Therefore, there is an urgent need to develop an efficient and comprehensive technology to overcome the inherent shortcomings of imidazoles and further promote the application of imidazole curing agents.

[0005] In recent years, microencapsulation technology has been used to encapsulate imidazole, which not only limits the moisture absorption and volatilization of imidazole through the protection of the shell material, but also improves its storage stability. Furthermore, the release of imidazole can be controlled according to the characteristics of different wall materials. One study prepared 2-phenylimidazole microcapsules with polycaprolactone as the shell using a solvent evaporation method; however, the linear polymer nature of the shell severely affected its storage stability in epoxy resin. Another study disclosed a method for preparing imidazole microcapsules based on thiol-isocyanate click reaction and oil-in-oil interfacial polymerization, which significantly improved the imidazole encapsulation amount and microcapsule preparation efficiency, but did not address changes in storage stability. A study disclosed a microcapsule composition containing imidazole compounds, exhibiting excellent low-temperature curing properties and high storage stability; however, this process is only suitable for encapsulating specific solid imidazoles and requires adjusting the melting point of imidazole using low-molecular-weight amine compounds, resulting in a complex and time-consuming process. One study disclosed a latent curing agent for epoxy resins, formed by an amine-containing free radical polymer and imidazole compounds. However, this method also faces challenges such as complex synthesis processes and limited selection of imidazole compounds. Furthermore, researchers prepared microcapsules encapsulating 1-benzyl-2-methylimidazolium based on thiol-ene click chemistry. While this achieved encapsulation of liquid imidazole, the encapsulation amount was only 28%, resulting in a longer curing time (100℃-1h).

[0006] Therefore, it is of great significance to provide an imidazole curing agent with fast curing efficiency, good storage stability and high coating amount. Summary of the Invention

[0007] The present invention aims to solve one or more technical problems existing in the prior art, and at least provide a beneficial solution. Specifically, the present invention provides an imidazole microcapsule with fast curing efficiency, good storage stability, and high coating capacity.

[0008] The inventive concept of this invention is as follows: The imidazole microcapsules of this invention have a core-shell structure; the core material of the core-shell structure includes imidazole compounds; the shell layer of the core-shell structure includes a polyurea-polyurethane composite; in the polyurea-polyurethane composite, polyurea segments and polyurethane segments are covalently cross-linked to form a composite hybrid network structure.

[0009] The polyurea-polyurethane composite of this invention is a covalently cross-linked product of polyurea segments and polyurethane segments. The polyurethane segments and polyurea segments form a "rigid-flexible" polyurea-polyurethane composite through covalent cross-linking. The rigid segments of polyurea and the flexible segments of polyurethane are firmly connected by chemical bonds. By utilizing the difference in rigidity / flexibility of the segments, a hybrid network at the molecular level is constructed. This network encapsulates imidazole compounds in the polyurethane-polyurea composite system, achieving a balance between "high encapsulation, fast curing, and long storage".

[0010] Therefore, a first aspect of the present invention provides an imidazole microcapsule.

[0011] Specifically, the imidazole microcapsules have a core-shell structure; The core material of the core-shell structure includes imidazole compounds; The shell of the core-shell structure includes a polyurea-polyurethane composite; in the polyurea-polyurethane composite, polyurea segments and polyurethane segments are covalently cross-linked to form a composite hybrid network structure.

[0012] Preferably, the imidazole compound includes at least one of 1-methylimidazole, 1-ethylimidazole, 2-ethyl-4-methylimidazole, 1-cyanoethyl-2-methylimidazole, and 1-cyanoethyl-2-ethyl-4-methylimidazole.

[0013] Preferably, the core material content accounts for 60-80% of the total mass of the imidazole microcapsules; for example, 60%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 80%, etc.

[0014] A second aspect of the present invention provides a method for preparing the imidazole microcapsules described in the first aspect of the present invention.

[0015] Specifically, the preparation method of the imidazole microcapsules includes the following steps: (1) A continuous phase is obtained by mixing alkane nonpolar solvents and surfactants; a dispersed phase is obtained by mixing imidazole compounds, alcohol monomers and amine monomers. (2) The dispersed phase is added to the continuous phase for emulsification to form an emulsion; (3) The isocyanate solution and the emulsion are mixed and reacted to obtain the product.

[0016] Specifically, this invention prepares imidazole microcapsules through interfacial polymerization and utilizes the synergistic construction of alcohol / amine dual monomers to encapsulate imidazole in a polyurethane-polyurea composite system, achieving a balance between sealing and functionality, and realizing the three aspects of "high encapsulation amount, fast curing, and long storage". Moreover, the process is simple, requires low equipment, and has a low threshold for industrialization.

[0017] Preferably, in step (1), the alkane nonpolar solvent includes at least one of liquid paraffin and a mixed alkane containing liquid paraffin.

[0018] Preferably, the mixed alkane containing liquid paraffin further includes at least one of n-hexane, n-heptane, n-octane, and dodecane.

[0019] Preferably, the liquid paraffin accounts for 20-90% of the mass of the mixed alkane containing liquid paraffin; more preferably, the liquid paraffin accounts for 20-50% of the mass of the mixed alkane containing liquid paraffin, such as 20%, 30%, 40%, 50%, etc.

[0020] Specifically, the solvent system of this invention adopts an innovative design of "liquid paraffin + alkane nonpolar solvent". It is not a simple mixture of solvents. This design is based on the viscosity characteristics of different types of imidazole compounds and is specifically adapted to effectively control the viscosity and interfacial tension of the system, achieve stable emulsification, and thus ensure that the polymerization reaction proceeds smoothly, ultimately obtaining microcapsules with uniform structure and stable performance.

[0021] Preferably, in step (1), the mass ratio of the alkane nonpolar solvent to the surfactant is 100:(1-10); more preferably, in step (1), the mass ratio of the alkane nonpolar solvent to the surfactant is 100:(1-5); for example, 100:1, 100:2, 100:3, 100:4, 100:5, etc.

[0022] Preferably, in step (1), the surfactant includes at least one of stearate, fatty acid ester, polysiloxane, and polyoxyethylene ether.

[0023] Preferably, in step (1), the alcohol monomer includes at least one of ethylene glycol, hexanediol, 1,4-butanediol, polyethylene glycol, glycerol, and pentaerythritol.

[0024] Preferably, in step (1), the amine monomer includes at least one of diamines and polyamines.

[0025] Preferably, the polyamine includes at least one of diethylenetriamine, triethylenetetramine, tetraethylenepentamine, 1,3,5-phenyltriamine, and polyethyleneimine.

[0026] Preferably, in step (1), the mass ratio of the imidazole compound to the total mass of the alcohol monomer and the amine monomer is (40-400):100; more preferably, in step (1), the mass ratio of the imidazole compound to the total mass of the alcohol monomer and the amine monomer is (100-200):100.

[0027] Preferably, in step (1), the mixing is carried out at room temperature.

[0028] Preferably, in step (2), the mass ratio of the continuous phase to the dispersed phase is 100:(5-50); more preferably, in step (2), the mass ratio of the continuous phase to the dispersed phase is 100:(10-20); for example, 100:10, 100:11, 100:12, 100:13, 100:14, 100:15, 100:16, 100:17, 100:18, 100:19, 100:20, etc.

[0029] Preferably, in step (2), the rotation speed of the emulsification is ≥400 rpm.

[0030] Preferably, in step (2), the emulsification time is ≥5 min.

[0031] Preferably, step (3) involves adding the isocyanate solution to the emulsion, mixing, reacting, and obtaining the product.

[0032] Preferably, in step (3), the isocyanate in the isocyanate solution includes at least one of isophorone diisocyanate, hexamethylene diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, and toluene diisocyanate.

[0033] Preferably, in step (3), the solvent in the isocyanate solution includes a nonpolar alkane solvent.

[0034] Specifically, the types of alkane-based nonpolar solvents that can be selected in the isocyanate solution are the same as those used in the preparation of the continuous phase.

[0035] Preferably, in step (3), the mass ratio of the solvent to the isocyanate in the isocyanate solution is 100:(1-100); for example, 100:1, 100:10, 100:20, 100:30, 100:40, 100:50, 100:60, 100:70, 100:80, 100:90, 100:100, etc.

[0036] Preferably, in step (3), the reaction includes a first-stage reaction and a second-stage reaction; the temperature of the first-stage reaction is 10-30℃ and the time of the first-stage reaction is 0.5-8h; the temperature of the second-stage reaction is 30-50℃ and the time of the second-stage reaction is 0.5-4h.

[0037] Specifically, during the preparation process, when isocyanate reacts with the polyamine / polyol mixture, isocyanate preferentially reacts with the polyamine at a much faster rate than the polyol, forming polyurea. This is also the reason for the lower reaction temperature in the first stage. Subsequently, the polyol reacts with the isocyanate to form polyurethane, which forms a "rigid-flexible" composite cross-linked structure with the polyurea segments. This structure ultimately determines the performance of the system, rather than being a simple direct combination.

[0038] Preferably, the mass ratio of isocyanate, alcohol monomer, and amine monomer in the isocyanate solution is 100:(10-100):(10-100).

[0039] Preferably, the total mass of the alcohol monomer and the amine monomer does not exceed the total mass of the isocyanate monomer in the isocyanate solution.

[0040] A third aspect of the present invention provides an epoxy resin curing agent.

[0041] Specifically, the epoxy resin curing agent includes the imidazole microcapsules described in the first aspect of this invention.

[0042] Compared with the prior art, the beneficial effects of the technical solution provided by the present invention are as follows: (1) The shell of the imidazole microcapsule of the present invention includes a polyurea-polyurethane composite structure formed by covalent cross-linking of polyurethane segments and polyurea segments. It encapsulates imidazole compounds in the polyurea-polyurethane composite system, taking into account both sealing and functionality. This makes the imidazole microcapsule have the characteristics of high encapsulation amount, fast curing speed and good storage stability. At the same time, the cured film has good hardness.

[0043] (2) This invention prepares imidazole microcapsules by interfacial polymerization and utilizes the synergistic construction of alcohol / amine dual monomers to encapsulate imidazole in a polyurea-polyurethane composite system, achieving a balance of "high encapsulation, fast curing, and long storage". At the same time, the preparation process is simple, the equipment requirements are low, and the industrialization threshold is low.

[0044] (3) The solvent system of this invention adopts the creative design of liquid paraffin + alkane non-polar solvent. It is not a simple mixing of solvents, but a targeted adaptation based on the viscosity characteristics of different types of imidazoles to achieve a stable emulsification effect, thereby achieving high coating amount, fast curing and long storage. Attached Figure Description

[0045] Figure 1 This is an optical microscope image of the imidazole microcapsules of Example 1 of the present invention; Figure 2 This is an optical microscope image of the imidazole microcapsules of Comparative Example 1 of the present invention. Figure 3This is an optical microscope image of the imidazole microcapsules of Comparative Example 2 of the present invention; Figure 4 This is an optical microscope image of the comparative example 3 imidazole microcapsules of the present invention; Figure 5 Thermogravimetric curve of imidazole microcapsules in Example 1 of this invention; Figure 6 This is a particle size distribution diagram of the imidazole microcapsules in Example 1 of the present invention. Detailed Implementation

[0046] To enable those skilled in the art to more clearly understand the technical solutions described in this invention, the following embodiments are provided for illustration. It should be noted that the following embodiments do not constitute a limitation on the scope of protection claimed by this invention.

[0047] Unless otherwise specified, the raw materials, reagents or devices used in the following examples are available from conventional commercial sources or can be obtained by existing known methods.

[0048] Example 1 This embodiment provides a method for preparing imidazole microcapsules, the specific steps of which are as follows: Two parts of polyoxyethylene (30) dihydroxystearate, two parts of lauryl polydimethylsiloxane, 50 parts of liquid paraffin (Maclean, reagent grade) and 50 parts of dodecane were mixed evenly to form a continuous phase; 10 parts of 1-cyanoethyl-2-ethyl-4-methylimidazolium, 1 part of polyethyleneimine and 4 parts of 1,4-butanediol were mixed evenly to form a dispersed phase. Dissolve 15 parts of hexamethylene diisocyanate in 15 parts of liquid paraffin and place in a sample vial for later use. Add the prepared dispersed phase to the continuous phase and stir at 1000 rpm for 30 min to obtain a homogeneous emulsion. Reduce the stirring speed and slowly add the hexamethylene diisocyanate solution dropwise to the emulsion at a rate of 1.0 mL / min. React at 25 °C for 3 h. Then further heat to 40 °C and react for 1 h to obtain microcapsules. Wash, filter and dry the obtained microcapsules to obtain dried imidazole microcapsules coated with 1-cyanoethyl-2-ethyl-4-methylimidazolium.

[0049] Example 2 This embodiment provides a method for preparing imidazole microcapsules, the specific steps of which are as follows: 4 parts sorbitan trioleate, 2 parts nonylphenol polyoxyethylene ether, 150 parts liquid paraffin (Maclean, reagent grade) and 100 parts n-heptane were mixed evenly to prepare a continuous phase; 40 parts 2-ethyl-4-methylimidazole, 4 parts diethylenetriamine and 30 parts hexanediol were mixed evenly to prepare a dispersed phase. 30 parts of dicyclohexylmethane-4,4'-diisocyanate and 30 parts of hexamethylene diisocyanate were dissolved in 80 parts of liquid paraffin and placed in a sample vial for later use. The prepared dispersed phase was added to the continuous phase and stirred at 600 rpm for 20 min to obtain a homogeneous emulsion. The stirring speed was reduced, and the dicyclohexylmethane-4,4'-diisocyanate and hexamethylene diisocyanate solution was slowly added dropwise to the emulsion at a rate of 5.0 mL / min. The reaction was first carried out at 20 °C for 5 h, and then further heated to 30 °C for 2 h to obtain microcapsules. The obtained microcapsules were washed, filtered, and dried to obtain dried imidazole microcapsules coated with 2-ethyl-4-methylimidazolium.

[0050] Example 3 This embodiment provides a method for preparing imidazole microcapsules, the specific steps of which are as follows: 3 parts fatty alcohol polyoxyethylene ether, 40 parts n-hexane, 40 parts n-octane and 20 parts liquid paraffin were mixed evenly to form a continuous phase; 20 parts 1-methylimidazole, 2 parts tetraethylenepentamine, 1 part diethylenetriamine, 10 parts ethylene glycol and 5 parts pentaerythritol were mixed evenly to form a dispersed phase. 15 parts of isophorone diisocyanate and 5 parts of toluene diisocyanate were dissolved in 50 parts of liquid paraffin (Maclean, reagent grade) and placed in a sample vial for later use. The prepared dispersed phase was added to the continuous phase and stirred at 800 rpm for 40 min to obtain a homogeneous emulsion. The stirring speed was reduced, and the isophorone diisocyanate and toluene diisocyanate solutions were slowly added dropwise to the emulsion at a rate of 3.0 mL / min. The reaction was first carried out at 20 °C for 2 h. Then, the temperature was further increased to 50 °C and the reaction was carried out for 1 h to obtain microcapsules. The obtained microcapsules were washed, filtered, and dried to obtain dried imidazole microcapsules coated with 1-methylimidazole.

[0051] Comparative Example 1 Comparative Example 1, which does not use amine monomers, was prepared using the following method for its imidazole microcapsules: Two parts of polyoxyethylene (30) dihydroxystearate, two parts of lauryl polydimethylsiloxane, 50 parts of liquid paraffin (Maclean, reagent grade) and 50 parts of dodecane were mixed evenly to form a continuous phase; 10 parts of 1-cyanoethyl-2-ethyl-4-methylimidazolium and 4 parts of 1,4-butanediol were mixed evenly to form a dispersed phase. Dissolve 15 parts of hexamethylene diisocyanate in 15 parts of liquid paraffin and place in a sample vial for later use. Add the prepared dispersed phase to the continuous phase and stir at 1000 rpm for 30 min to obtain a homogeneous emulsion. Reduce the stirring speed and slowly add the hexamethylene diisocyanate solution dropwise to the emulsion at a rate of 1.0 mL / min. React at 25 °C for 3 h. Then further heat to 40 °C and react for 1 h to obtain microcapsules. Wash, filter and dry the obtained microcapsules to obtain dried imidazole microcapsules coated with 1-cyanoethyl-2-ethyl-4-methylimidazolium.

[0052] Comparative Example 2 Comparative Example 2 did not use liquid paraffin, but only dodecane as a solvent. Its imidazole microcapsules were prepared as follows: 2 parts of polyoxyethylene (30) dihydroxystearate, 2 parts of lauryl polydimethylsiloxane and 100 parts of dodecane were mixed evenly to form a continuous phase; 10 parts of 1-cyanoethyl-2-ethyl-4-methylimidazol, 1 part of polyethyleneimine and 4 parts of 1,4-butanediol were mixed evenly to form a dispersed phase. Dissolve 15 parts of hexamethylene diisocyanate in 15 parts of liquid paraffin and place in a sample vial for later use. Add the prepared dispersed phase to the continuous phase and stir at 1000 rpm for 30 min to obtain a homogeneous emulsion. Reduce the stirring speed and slowly add the hexamethylene diisocyanate solution dropwise to the emulsion at a rate of 1.0 mL / min. React at 25 °C for 3 h. Then further heat to 40 °C and react for 1 h to obtain microcapsules. Wash, filter and dry the obtained microcapsules to obtain dried imidazole microcapsules coated with 1-cyanoethyl-2-ethyl-4-methylimidazolium.

[0053] Comparative Example 3 Comparative Example 3 did not use dodecane, but only liquid paraffin as a solvent. Its imidazole microcapsules were prepared as follows: Two parts of polyoxyethylene (30) dihydroxystearate, two parts of lauryl polydimethylsiloxane, and 100 parts of liquid paraffin were mixed evenly to form a continuous phase; ten parts of 1-cyanoethyl-2-ethyl-4-methylimidazolium, one part of polyethyleneimine, and four parts of 1,4-butanediol were mixed evenly to form a dispersed phase. Dissolve 15 parts of hexamethylene diisocyanate in 15 parts of liquid paraffin and place in a sample vial for later use. Add the prepared dispersed phase to the continuous phase and stir at 1000 rpm for 30 min to obtain a homogeneous emulsion. Reduce the stirring speed and slowly add the hexamethylene diisocyanate solution dropwise to the emulsion at a rate of 1.0 mL / min. React at 25 °C for 3 h. Then further heat to 40 °C and react for 1 h to obtain microcapsules. Wash, filter and dry the obtained microcapsules to obtain dried imidazole microcapsules coated with 1-cyanoethyl-2-ethyl-4-methylimidazolium.

[0054] Performance testing 1. Morphological observation The imidazole microcapsule samples (approximately 0.1 g) from Examples 1, 1, 2, and 3 were dissolved in 10 mL of liquid paraffin. The morphology of the imidazole microcapsules was observed using an optical microscope, and the results are as follows: Figure 1 , 2 As shown in Figures 3 and 4.

[0055] Depend on Figure 1 As can be seen, the imidazole microcapsules in Example 1 exhibit a typical spherical / quasi-spherical structure. The microcapsules are relatively uniformly dispersed and do not show obvious agglomeration. Most of the microcapsules have a particle size of 10-100 μm.

[0056] Depend on Figure 2 It can be seen that the comparative example 1 imidazole microcapsules showed obvious aggregation and agglomeration, which will lead to poor product uniformity and short storage stability.

[0057] Depend on Figure 3 It can be seen that the imidazole microcapsules in Comparative Example 2 have irregular morphology and poor forming effect, making it difficult to collect dry powder with good flowability, which greatly affects the yield.

[0058] Depend on Figure 4 It can be seen that the comparative 3 imidazole microcapsules are difficult to disperse in a timely and effective manner, and are prone to phenomena such as particle adhesion, agglomeration, and even wall material damage.

[0059] 2. Thermal weight loss rate test Using a thermogravimetric analyzer, the imidazole microcapsule sample (approximately 10 mg) from Example 1 was sealed in an alumina crucible at a nitrogen temperature of 25-800°C, and the thermogravimetric rate was tested at a heating rate of 10°C / min. The thermogravimetric curve of the imidazole microcapsule from Example 1 is shown below. Figure 5 As shown.

[0060] The rapid weight loss segment of the thermogravimetric curve represents the temperature at which the core material decomposes. Figure 5 It can be deduced that the core material content is approximately 70%-80%.

[0061] 3. Average particle size test Take approximately 0.5 g of the imidazole microcapsule sample from Example 1 and dissolve it in 20 mL of water. Measure the average particle size of the imidazole microcapsules using a laser particle size analyzer. The particle size distribution is shown in the figure below. Figure 6 As shown.

[0062] Depend on Figure 6 It can be seen that the particle size distribution of the imidazole microcapsules in Example 1 is mostly in the range of 10-100 μm, which is basically consistent with the optical microscope images.

[0063] 4. Storage stability test In this invention, the viscosity change of imidazole microcapsules in epoxy resin N128 (Nanya, NPE-128) is used to evaluate storage stability. A longer storage time indicates higher storage stability of imidazole microcapsules. In the industry, a viscosity change of no more than 200% is generally considered the standard. When the viscosity change does not exceed 200%, it is considered that storage can continue.

[0064] 2g of imidazole microcapsule samples from Examples 1-3 and Comparative Examples 1-3 were uniformly dispersed in epoxy resin N128 (Nanya, NPE-128) (8g), sealed in glass sample bottles, and subjected to storage stability tests at a given temperature. The test results are shown in Table 1.

[0065] Table 1: Storage stability test results of imidazole microcapsules in Examples 1-3 and Comparative Examples 1-3

[0066] Comparative Example 2: The imidazole microcapsules had irregular morphology and poor forming effect, making it difficult to collect dry powder with good flowability and conduct storage stability tests. Therefore, “ / ” in Table 1 indicates that the test could not be performed.

[0067] As can be seen from Table 1, the imidazole microcapsules of the present invention have good storage stability, and their storage stability at -5℃, 25℃ and 40℃ is significantly better than that of comparative examples 1-3.

[0068] 5. Curing performance test In this invention, the curing speed is evaluated by the curing time required when imidazole microcapsules are applied to epoxy resin N128 (Nanya, NPE-128). A shorter curing time indicates a faster curing speed of the imidazole microcapsules.

[0069] Take 2g of imidazole microcapsule samples from Examples 1-3 and Comparative Examples 1-3 respectively, and disperse them evenly in epoxy resin N128 (Nanya, NPE-128) (8g). Use a film scraper to scrape films of different thicknesses, and conduct curing performance tests at a given temperature. The test results are shown in Table 2.

[0070] Table 2: Curing performance test results of imidazole microcapsules in Examples 1-3 and Comparative Examples 1-3

[0071] As can be seen from Table 2, the imidazole microcapsules of the present invention have a good curing speed.

[0072] Although Comparative Examples 1 and 3 had short curing times, their poor storage stability made them unsuitable for practical use and storage. The short curing time may be due to the varying degrees of agglomeration of the imidazole microcapsules in Comparative Examples 1 and 3. This agglomeration caused the microcapsules to easily compress against each other, leading to cracking and premature release of imidazole compounds from the core material, which then react with the epoxy resin. Simultaneously, agglomeration caused adhesion between the microcapsules, resulting in numerous defects in the outer shell, allowing resin to easily penetrate and contact the internal core material, thus causing premature curing. The imidazole microcapsules in Comparative Example 2 had irregular morphology and poor molding effect, making it difficult to collect free-flowing dry powder, thus preventing curing performance testing. The " / " in Table 2 indicates that testing was not possible.

[0073] 6. Hardness test The hardness of the films cured with imidazole microcapsules and epoxy resin N128 (Nanya, NPE-128) in Examples 1-3 and Comparative Examples 1-3 was tested using a Shore D hardness tester. The test results are shown in Table 3.

[0074] Table 3: Hardness test results of the films after curing imidazole microcapsules and epoxy resin N128 in Examples 1-3 and Comparative Example 1

[0075] In Table 3, " / " indicates that Comparative Example 2 could not be tested.

[0076] As can be seen from Table 3, the film formed by curing the imidazole microcapsules of the present invention with epoxy resin N128 (Nanya, NPE-128) has high hardness.

[0077] Comparative Example 1: No amine monomers were added during the preparation of the imidazole microcapsules. This resulted in the absence of polyurea segments in the shell structure of the microcapsules, preventing covalent cross-linking with polyurethane segments and consequently reducing the hardness of the microcapsules. Comparative Example 2: Only dodecane was used as a solvent in the preparation of the imidazole microcapsules. The system viscosity was too low, making it difficult to maintain the stability of the reaction system. This led to irregular morphology, poor molding effect, difficulty in collecting free-flowing dry powder, and inability to conduct hardness tests. Comparative Example 3: Only liquid paraffin was used as a solvent in the preparation of the imidazole microcapsules. This easily resulted in a high system viscosity, reduced dispersion rate, and difficulty in timely and effective dispersion of the microcapsules, affecting the structural integrity of the microcapsules and consequently reducing their hardness.

[0078] In summary, the polyurea-polyurethane composite formed by covalent cross-linking of polyurethane segments and polyurea segments in the shell of the imidazole microcapsules of the present invention encapsulates imidazole compounds in the polyurea-polyurethane composite system, taking into account both sealing and functionality, so that the imidazole microcapsules have the characteristics of high encapsulation amount, fast curing speed and good storage stability.

[0079] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. An imidazole microcapsule characterized in that, The imidazole microcapsules have a core-shell structure; The core material of the core-shell structure includes imidazole compounds; The shell layer of the core-shell structure comprises a polyurea-polyurethane composite; In the polyurea-polyurethane composite, polyurea segments and polyurethane segments are covalently cross-linked to form a composite hybrid network structure.

2. The imidazole microcapsule according to claim 1, characterized in that, The imidazole compound includes at least one of 1-methylimidazole, 1-ethylimidazole, 2-ethyl-4-methylimidazole, 1-cyanoethyl-2-methylimidazole, and 1-cyanoethyl-2-ethyl-4-methylimidazole; and / or, the core material accounts for 60-80% of the total mass of the imidazole microcapsules.

3. Process for the preparation of imidazole microcapsules according to any one of claims 1-2, characterized in that, The preparation method includes the following steps: (1) A continuous phase is obtained by mixing alkane nonpolar solvents and surfactants; a dispersed phase is obtained by mixing imidazole compounds, alcohol monomers and amine monomers. (2) The dispersed phase is added to the continuous phase for emulsification to form an emulsion; (3) The isocyanate solution and the emulsion are mixed and reacted to obtain the product.

4. The production method according to claim 3, characterized by, In step (1), the alkane nonpolar solvent includes at least one of liquid paraffin and a mixture of alkanes containing liquid paraffin; And / or, the mass ratio of the alkane nonpolar solvent to the surfactant is 100:(1-10).

5. The preparation method according to claim 4, characterized in that, In step (1), the mixed alkane containing liquid paraffin also includes at least one of n-hexane, n-heptane, n-octane, and dodecane; And / or, in the mixed alkane containing liquid paraffin, the mass percentage of liquid paraffin is 20-90%; And / or, the alcohol monomers include at least one of ethylene glycol, hexanediol, 1,4-butanediol, polyethylene glycol, glycerol, and pentaerythritol; And / or, the amine monomers include at least one of diamines and polyamines; And / or, the mass ratio of the imidazole compound to the total mass of the alcohol monomer and amine monomer is (40-400):

100.

6. The preparation method according to claim 3, characterized in that, In step (2), the mass ratio of the continuous phase to the dispersed phase is 100:(5-50). And / or, the emulsification rotation speed is ≥400 rpm; And / or, the emulsification time is ≥5 min.

7. The preparation method according to claim 3, characterized in that, In step (3), the isocyanate in the isocyanate solution includes at least one of isophorone diisocyanate, hexamethylene diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, and toluene diisocyanate. And / or, the solvent in the isocyanate solution includes nonpolar alkane solvents; And / or, in the isocyanate solution, the mass ratio of the solvent to the isocyanate is 100:(1-100).

8. The preparation method according to claim 3, characterized in that, In step (3), the reaction includes a first stage reaction and a second stage reaction; the temperature of the first stage reaction is 10-30℃ and the time of the first stage reaction is 0.5-8h; the temperature of the second stage reaction is 30-50℃ and the time of the second stage reaction is 0.5-4h.

9. The preparation method according to claim 3, characterized in that, The mass ratio of isocyanate, alcohol monomer, and amine monomer in the isocyanate solution is 100:(10-100):(10-100). And / or, the mass of the alcohol monomer and amine monomer does not exceed the mass of the isocyanate monomer in the isocyanate solution.

10. An epoxy resin curing agent, characterized in that, Includes the imidazole microcapsules according to any one of claims 1-2.

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