A microencapsulated epoxy resin latent curing agent, its preparation method and application

Abstract

A microcapsule epoxy resin latent curing agent, its preparation method, and its application belong to the technical field of epoxy resin curing agents. The specific solution is as follows: A microcapsule epoxy resin latent curing agent includes a microcapsule shell and a microcapsule core. The microcapsule shell material is a thermoplastic resin containing imidazole groups, and the microcapsule core material is an imidazole compound. Due to the presence of imidazole groups in the shell material, the shell material can play a curing role and release heat after melting, thereby accelerating the release and curing of the core material, reducing the amount of curing agent added and accelerating the curing speed. Furthermore, after curing, the thermoplastic resin of the shell and the epoxy resin form a semi-interpenetrating network structure, improving the mechanical properties of the cured product. Compared with traditional microcapsule curing agents where the shell material does not participate in the curing reaction, this method has the advantages of low curing agent dosage, fast curing speed, and high mechanical properties of the cured product.

Description

Technical Field

[0001] This invention belongs to the technical field of epoxy resin curing agents, and relates to a latent epoxy resin curing agent, its preparation method and application, specifically a microcapsule latent epoxy resin curing agent, its preparation method and application. Background Technology

[0002] Epoxy resins are an important class of thermosetting resins, including one-component and two-component epoxy resins. Two-component epoxy resins contain the epoxy resin and curing agent in separate containers and require mixing in a specific ratio before use. One-component epoxy resins are mixtures of epoxy resin, curing agent, solvent, and other components. They can be stored at room temperature and spontaneously cure under suitable temperature and humidity conditions, forming a network structure. Compared to two-component resins, one-component epoxy resins are more convenient and easier to use, avoiding the problems associated with mixing two-component components, and are beneficial for environmental protection and energy efficiency. One-component epoxy resins are suitable for electronic packaging materials, anti-corrosion coatings, and other fields. Latent curing agents are required in one-component epoxy resins. These agents are a key component, significantly impacting storage, curing processes, and performance, and have received widespread attention.

[0003] Latent curing agents are mainly classified into dicyandiamide-based curing agents, modified imidazole-based curing agents, and microencapsulated curing agents. Currently, microencapsulated curing agents have become the most popular type due to their longer latency. Microencapsulation technology uses polymers to encapsulate the curing agent, isolating it from the epoxy resin. When the polymer shell material of the microcapsule ruptures at a certain temperature, releasing the curing agent, the epoxy resin undergoes a curing reaction. This ensures the curing of the epoxy resin system while also providing a long latency. However, because the shell material of microencapsulated curing agents is usually a chemically inert polymer, it leads to problems such as higher curing agent dosage, slower curing speed, and weaker mechanical properties of the cured product.

[0004] The rapid development of industries such as electronic packaging has placed increasingly higher demands on single-component epoxy resins. Developing novel microcapsule curing agents to solve existing problems such as curing agent dosage, curing speed, and mechanical properties of cured products is of great significance. Summary of the Invention

[0005] In order to solve the technical problems in the prior art, such as the large amount of microcapsule curing agent required, slow curing speed, and weak mechanical properties of the cured product, the present invention provides a microcapsule epoxy resin latent curing agent and a preparation method thereof. This curing agent is prepared by the solvent evaporation method, using a thermoplastic resin containing an imidazole group as the microcapsule shell material and an imidazole compound as the microcapsule core material. Due to the presence of the imidazole group in the shell material, the shell material can play a curing role and release heat after melting, thereby accelerating the release and curing of the core material, reducing the amount of curing agent added and accelerating the curing speed. And after curing, the shell thermoplastic resin and the epoxy resin form a semi-interpenetrating network structure, improving the mechanical properties of the cured product. Compared with the traditional microcapsule curing agent shell material that does not participate in the curing reaction, it has the advantages of small amount of curing agent added, fast curing speed, and high mechanical properties of the cured product.

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

[0007] A microcapsule epoxy resin latent curing agent, comprising a microcapsule shell and a microcapsule core, wherein the microcapsule shell material is a thermoplastic resin containing an imidazole group, and the microcapsule core material is an imidazole compound.

[0008] Further, the chemical structural formula of the thermoplastic resin containing an imidazole group is as follows:

[0009]

[0010] Where R1 is any one of methyl, ethyl, propyl, and butyl, and R2 is any one of methyl, ethyl, propyl, and butyl; 0.2 < x < 0.4, 0.25 < y < 0.45, 0.3 < z < 0.5, and x + y + z = 1. Preferably, when R1 is butyl and R2 is methyl, the thermoplastic resin containing an imidazole group is called poly(butyl acrylate-methyl methacrylate-vinyl imidazole) random copolymer; when R1 is ethyl and R2 is ethyl, the thermoplastic resin containing an imidazole group is called poly(ethyl acrylate-ethyl methacrylate-vinyl imidazole) random copolymer.

[0011] Further, the imidazole compound includes any one or a combination of more than one of 1-benzyl-2-methylimidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-undecylimidazole, 2-phenylimidazole, and 2-phenyl-4-methylimidazole. Preferably, 1-benzyl-2-methylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, or 2-phenyl-4-methylimidazole.

[0012] A preparation method of the microcapsule epoxy resin latent curing agent described above is the solvent evaporation method, which specifically includes the following steps:

[0013] Step 1: Dissolve the thermoplastic resin containing imidazole groups and imidazole compounds in an organic solvent to obtain the oil phase; dissolve the emulsifier in water to obtain the aqueous phase.

[0014] Step 2: Disperse the oil phase into the aqueous phase to obtain an oil-in-water emulsion;

[0015] Step 3: Evaporate the organic solvent in the oil-in-water emulsion to obtain a suspension;

[0016] Step 4: Filter the suspension. After filtration, wash and freeze-dry the precipitate to obtain the microcapsule epoxy resin latent curing agent.

[0017] Furthermore, in step one, the mass ratio of the imidazole-containing thermoplastic resin, imidazole compound, organic solvent, emulsifier, and water is 1:(0.5-2):(10-30):(0.2-2):(50-120).

[0018] Furthermore, in step one, the organic solvent includes any one or more combinations of dichloromethane, chloroform, and ethyl acetate, preferably dichloromethane or ethyl acetate.

[0019] Furthermore, in step one, the emulsifier includes any one or more combinations of decaalkyltrimethylammonium chloride, dodecyltrimethylammonium chloride, sodium dodecyl sulfate, sodium dodecyl sulfonate, polyvinyl alcohol 1788, Tween 80, and Tween 60, preferably dodecyltrimethylammonium chloride, polyvinyl alcohol 1788, Tween 80, or Tween 60.

[0020] Furthermore, in step two, the oil phase is added to the aqueous phase and mechanically stirred and dispersed at 20°C and a rotation speed of 5000–10000 r / min for 30–60 min to obtain an oil-in-water emulsion.

[0021] Furthermore, in step three, the conditions for the evaporation of the organic solvent are: dispersion at 40–50°C under open conditions with mechanical stirring at a speed of 700–1000 r / min for 4–8 h.

[0022] The prepared microcapsule epoxy resin latent curing agent is macroscopically a pale yellow solid powder with a particle size range of 1–25 μm.

[0023] An application of the aforementioned microencapsulated epoxy resin latent curing agent involves mixing epoxy resin and the microencapsulated epoxy resin latent curing agent at a mass ratio of 100:8 to 14 at room temperature, stirring until homogeneous, and then curing at 90 to 130°C for 15 to 60 minutes.

[0024] Compared with the prior art, the beneficial effects of the present invention are:

[0025] (1) This invention prepares a microcapsule latent curing agent using a thermoplastic resin containing imidazole groups as the shell material and an imidazole compound as the core material via solvent evaporation. Since both the shell material and the core material play a curing role in the epoxy resin curing process, the amount of curing agent added is significantly reduced compared to traditional microcapsule latent curing agents.

[0026] (2) In the microcapsule latent curing agent of the present invention, the shell material plays a curing role after melting and releases heat, thereby accelerating the release and curing of the core material and speeding up the curing speed of the microcapsule latent curing agent.

[0027] (3) In the microcapsule latent curing agent of the present invention, after the curing reaction, the shell thermoplastic resin and epoxy resin form a semi-interpenetrating network structure, thereby improving the mechanical properties of the microcapsule latent curing agent and epoxy resin system.

[0028] (4) The preparation method of the microcapsule latent curing agent provided by the present invention is simple, easy to control, and the product has stable performance. Attached Figure Description

[0029] Figure 1 These are optical microscope images of the microcapsule latent curing agents prepared in Examples 1-4;

[0030] Figure 2 The non-isothermal DSC curves of the microcapsule latent curing agent and epoxy resin system prepared in Examples 1-4 are shown, with a heating rate of 10℃ / min.

[0031] Figure 3 These are the isothermal DSC curves of the microcapsule latent curing agent and epoxy resin system prepared in Example 2 at five temperatures; Detailed Implementation

[0032] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are only some embodiments of the invention, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0033] Example 1

[0034] The preparation steps of a microcapsule latent curing agent are as follows: 2.5g of poly(butyl acrylate-methyl methacrylate-vinyl imidazole) random copolymer and 2.5g of 1-benzyl-2-methylimidazolium are dissolved in 25g of dichloromethane to obtain an oil phase. 0.7g of Tween 80 is dissolved in 125g of water to obtain an aqueous phase. The obtained oil phase is added to the aqueous phase and dispersed at 20℃ with mechanical stirring at 5000r / min for 30min to obtain an oil-in-water emulsion. The oil-in-water emulsion is then heated to 40℃ and dispersed under open conditions with mechanical stirring at 800r / min for 4h to obtain a suspension. The suspension is filtered, and the precipitate after filtration is washed and freeze-dried to obtain the microcapsule epoxy resin latent curing agent.

[0035] A method for applying the microcapsule latent curing agent: E51 epoxy resin and the obtained microcapsule latent curing agent are stirred and mixed at a mass ratio of 100:14. After stirring evenly, the mixture is placed in a 90℃ constant temperature oven and cured for 60 minutes.

[0036] Example 2

[0037] The preparation steps of a microcapsule latent curing agent are as follows: 1.5g of poly(ethyl acrylate-ethyl methacrylate-vinyl imidazole) random copolymer and 3g of 2-phenylimidazolium are dissolved in 10g of dichloromethane and 10g of ethyl acetate to obtain an oil phase. 0.75g of Tween 60 is dissolved in 100g of water to obtain an aqueous phase. The obtained oil phase is added to the aqueous phase and dispersed at 20℃ with mechanical stirring at 7000r / min for 45min to obtain an oil-in-water emulsion. The oil-in-water emulsion is then heated to 45℃ and dispersed under open conditions with mechanical stirring at 900r / min for 6h to obtain a suspension. The suspension is filtered, and the precipitate after filtration is washed and freeze-dried to obtain the microcapsule epoxy resin latent curing agent.

[0038] A method for applying the microcapsule latent curing agent: E51 epoxy resin and the obtained microcapsule latent curing agent are stirred and mixed at a mass ratio of 100:12. After stirring evenly, the mixture is placed in a constant temperature oven at 100℃ and cured for 40 minutes.

[0039] Example 3

[0040] The preparation steps of a microcapsule latent curing agent are as follows: 1.0 g of poly(butyl acrylate-methyl methacrylate-vinyl imidazole) random copolymer and 1.5 g of 2-phenyl-4-methylimidazolium are dissolved in 15 g of dichloromethane to obtain an oil phase. 2.0 g of polyvinyl alcohol 1788 is dissolved in 100 g of water to obtain an aqueous phase. The obtained oil phase is added to the aqueous phase and dispersed at 20°C with mechanical stirring at 8000 r / min for 30 min to obtain an oil-in-water emulsion. The oil-in-water emulsion is then heated to 40°C and dispersed under open conditions with mechanical stirring at 700 r / min for 4 h to obtain a suspension. The suspension is filtered, and the precipitate after filtration is washed and freeze-dried to obtain the microcapsule epoxy resin latent curing agent.

[0041] A method for applying the microcapsule latent curing agent: E51 epoxy resin and the obtained microcapsule latent curing agent are stirred and mixed at a mass ratio of 100:10. After stirring evenly, the mixture is placed in a constant temperature oven at 110℃ and cured for 30 minutes.

[0042] Example 4

[0043] The preparation steps of a microcapsule latent curing agent are as follows: 0.5 g of poly(ethyl acrylate-ethyl methacrylate-vinyl imidazole) random copolymer and 0.25 g of 2-ethyl-4-methylimidazolium are dissolved in 15 g of ethyl acetate to obtain an oil phase. 0.6 g of dodecyltrimethylammonium chloride is dissolved in 60 g of water to obtain an aqueous phase. The obtained oil phase is added to the aqueous phase and dispersed at 20 °C with mechanical stirring at 4000 r / min for 30 min to obtain an oil-in-water emulsion. The oil-in-water emulsion is then heated to 50 °C and dispersed under open conditions with mechanical stirring at 600 r / min for 5 h to obtain a suspension. The suspension is filtered, and the precipitate after filtration is washed and freeze-dried to obtain the microcapsule epoxy resin latent curing agent.

[0044] A method for applying the microcapsule latent curing agent: E51 epoxy resin and the obtained microcapsule latent curing agent are stirred and mixed at a mass ratio of 100:8. After stirring evenly, the mixture is placed in a constant temperature oven at 130℃ and cured for 20 minutes.

[0045] Figure 1 These are optical microscope images of the microcapsule latent curing agents prepared in Examples 1-4, demonstrating that the microcapsules prepared by this invention are uniform in size, with a particle size range of 1-10 μm.

[0046] Figure 2 The figures are non-isothermal DSC curves of the microcapsule latent curing agent and epoxy resin system prepared in Examples 1-4, with a heating rate of 10℃ / min, demonstrating that the microcapsule latent curing agent prepared in this invention also has good curing activity at low addition levels.

[0047] Figure 3 These are the isothermal DSC curves of the microcapsule latent curing agent and epoxy resin system prepared in Example 2 at five temperatures. Figure 3 It can be seen that in Example 2, the curing reaction was completed in 15 minutes at 130°C; in 20 minutes at 120°C; in 30 minutes at 110°C; in 40 minutes at 100°C; and in 55 minutes at 90°C, demonstrating that the microcapsule latent curing agent of the present invention has the ability to rapidly cure epoxy resin at a certain temperature.

[0048] Table 1. Test results of latent properties, adhesive properties, and mechanical properties of the curing agent and epoxy resin in each embodiment.

[0049]

[0050] As can be seen from the above results, the microcapsule epoxy resin latent curing agent of the present invention has the ability to rapidly cure epoxy resin with a small amount of additive, and has a long latency period. At the same time, it has good adhesion strength and tensile strength with the cured epoxy resin.

[0051] It can be seen that the microcapsule latent epoxy resin curing agent prepared by this invention has the ability to rapidly cure epoxy resin even with a small addition amount because both the shell material and the core material of the microcapsule play a role in curing the epoxy resin during the curing process. Furthermore, after the curing reaction, the shell material, being a thermoplastic resin, forms a semi-interpenetrating network structure with the epoxy resin, thereby improving the mechanical and adhesive properties of the microcapsule latent curing agent and the epoxy resin system. Therefore, the microcapsule latent epoxy resin curing agent provided by this invention has excellent application value and development prospects.

[0052] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A microencapsulated epoxy resin latent curing agent, characterized in that: The device includes a microcapsule shell and a microcapsule core. The microcapsule shell is made of a thermoplastic resin containing imidazole groups, and the microcapsule core is made of an imidazole compound. The chemical structural formula of the thermoplastic resin containing imidazole groups is as follows: Where R1 is any one of methyl, ethyl, propyl, and butyl, and R2 is any one of methyl, ethyl, propyl, and butyl; 0.2 <x<0.4,0.25<y<0.45,0.3<z<0.5,x+y+z=1。 2. The microencapsulated epoxy resin latent curing agent according to claim 1, characterized in that: The imidazole compounds include any one or more combinations of 1-benzyl-2-methylimidazolium, 2-methylimidazolium, 2-ethyl-4-methylimidazolium, 2-undecylimidazolium, 2-phenylimidazolium, and 2-phenyl-4-methylimidazolium.

3. A method for preparing a microencapsulated epoxy resin latent curing agent according to any one of claims 1-2, characterized in that, Includes the following steps: Step 1: Dissolve the thermoplastic resin containing imidazole groups and imidazole compounds in an organic solvent to obtain the oil phase; dissolve the emulsifier in water to obtain the aqueous phase. Step 2: Disperse the oil phase into the aqueous phase to obtain an oil-in-water emulsion; Step 3: Evaporate the organic solvent in the oil-in-water emulsion to obtain a suspension; Step 4: Filter the suspension. After filtration, wash and freeze-dry the precipitate to obtain the microcapsule epoxy resin latent curing agent.

4. The preparation method according to claim 3, characterized in that: In step one, the mass ratio of the imidazole-containing thermoplastic resin, imidazole compound, organic solvent, emulsifier, and water is 1:(0.5~2):(10~30):(0.2~2):(50~120).

5. The preparation method according to claim 3, characterized in that: In step one, the organic solvent includes any one or more combinations of dichloromethane, chloroform, and ethyl acetate.

6. The preparation method according to claim 3, characterized in that: In step one, the emulsifier includes any one or a combination of decaalkyltrimethylammonium chloride, dodecyltrimethylammonium chloride, sodium dodecyl sulfate, sodium dodecyl sulfonate, polyvinyl alcohol 1788, Tween 80, and Tween 60.

7. The preparation method according to claim 3, characterized in that: In step two, the oil phase is added to the aqueous phase and mechanically stirred and dispersed at 20°C and a speed of 5000~10000 r / min for 30~60 min to obtain an oil-in-water emulsion.

8. The preparation method according to claim 3, characterized in that: In step three, the conditions for the evaporation of organic solvents are: dispersion at 40~50℃ and open conditions with mechanical stirring at a speed of 700~1000 r / min for 4~8 hours.

9. The application of the microencapsulated epoxy resin latent curing agent according to any one of claims 1-2, characterized in that: At room temperature, epoxy resin and the microcapsule epoxy resin latent curing agent are mixed and stirred evenly at a mass ratio of 100:8~14, and cured at 90~130℃ for 15min~60min.

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