Epoxy resin curing agent as well as preparation method and application thereof

Abstract

The invention relates to an epoxy resin curing agent as well as a preparation method and application thereof. The epoxy resin curing agent disclosed by the invention is prepared by taking amino trimethylene phosphonic acid and an imidazole compound as raw materials; the preparation method comprises the following steps: mixing the amino trimethylene phosphonic acid, the imidazole compound and the solvent, and reacting for 4-6 hours under the condition of stirring at 55-65 DEG C; and then, removing the solvent, washing and drying to obtain the phosphorus-containing imidazole flame-retardant latent curing agent. According to the epoxy resin curing agent disclosed by the invention, an imidazole group with high reaction activity and a phosphonate group with an efficient flame-retardant effect are constructed in a molecule, a novel bifunctional imidazole curing agent is successfully developed, and a single-component system formed by the curing agent and epoxy resin shows excellent room-temperature storage stability; meanwhile, the modified imidazole curing agent is endowed with good latent curing activity and flame retardant property to epoxy resin through a phosphorus-based flame retardant mechanism; the technical requirements of industrial application on the latent curing agent are met.

Description

Technical Field

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

[0002] As a high-performance thermosetting polymer material, epoxy resin has been widely used in key fields such as protective coatings, structural adhesives, composite laminates, and microelectronic packaging due to its excellent mechanical properties, outstanding interfacial adhesion characteristics, remarkable chemical corrosion resistance, excellent dielectric properties, and good dimensional stability.

[0003] However, the inherent flammability defect of this material significantly restricts its application expansion in scenarios with strict fire safety requirements such as aerospace and rail transit. There is an urgent need to endow it with flame retardant properties through molecular structure design or composite modification technology to meet higher safety standards.

[0004] It is worth noting that in recent years, the latent curing technology of epoxy resin systems has become a research hotspot in the field of polymer materials. Compared with traditional two-component curing systems, the one-component epoxy resin system based on the latent curing mechanism exhibits significant technical advantages: through the stable blending of pre-dispersed latent curing agents and epoxy matrices, it not only simplifies the process, but also effectively reduces the emission of volatile organic compounds, and improves the performance consistency of products due to the elimination of uneven component mixing, which has important engineering value for realizing green manufacturing and industrial continuous production.

[0005] Among many curing agent systems, imidazole compounds have attracted much attention due to their unique anionic catalytic polymerization mechanism. They can enable epoxy resins to achieve rapid curing under mild conditions, and the resulting cross-linked network structure exhibits excellent solvent resistance, mechanical strength retention rate, and electrical insulation properties, showing great application potential in the field of electronic packaging materials.

[0006] However, conventional imidazole derivatives generally have the problem of excessive room temperature reaction activity, which directly leads to pre-curing phenomena during the storage of one-component systems, manifested as a sharp increase in system viscosity or even gelation. Therefore, in the research, it is necessary to regulate the thermal response characteristics of imidazole compounds through molecular structure modification to solve the latency problem of imidazole-based curing agents. Summary of the Invention

[0007] To solve the above technical problems, the present invention provides an epoxy resin curing agent, a preparation method thereof, and an application thereof, which have the characteristics of good flame retardant effect, excellent latency, and high curing activity for epoxy resins.

[0008] The technical solution adopted by the present invention to solve its technical problems is: an epoxy resin curing agent, whose molecular structural formula is as follows:

[0009]

[0010] Among them, R1 is selected from one of hydrogen, methyl, ethyl, phenyl or undecyl, and R2 is selected from one of hydrogen, methyl or phenyl.

[0011] Furthermore, the epoxy resin curing agent is prepared from aminotrimethylphosphonic acid and an imidazole compound; wherein, the molar ratio of aminotrimethylphosphonic acid to the imidazole compound is 1:(6 - 6.2); the molecular structural formula of the imidazole compound is as follows:

[0012]

[0013] Among them, R1 is selected from one of hydrogen, methyl, ethyl, phenyl or undecyl, and R2 is selected from one of hydrogen, methyl or phenyl.

[0014] Furthermore, the imidazole compound is selected from one of imidazole, 2 - methylimidazole, 2 - ethylimidazole, 2 - phenylimidazole, 4 - phenylimidazole, 2 - undecylimidazole or 2 - ethyl - 4 - methylimidazole.

[0015] A preparation method of an epoxy resin curing agent, the synthesis route diagram is as follows:

[0016]

[0017] And it is specifically prepared according to the following steps:

[0018] S1. Mix aminotrimethylphosphonic acid, the imidazole compound and a solvent, and react at 55 - 65 °C under stirring for 4 - 6 h;

[0019] S2. Remove the solvent from the reaction product obtained in step S1, and after washing and drying, obtain a phosphorus - containing imidazole - based flame - retardant latent curing agent.

[0020] Furthermore, the solvent includes but is not limited to deionized water, ethanol, chlorobenzene, xylene, dimethyl sulfoxide, N,N - dimethylformamide or N,N - dimethylacetamide.

[0021] Furthermore, step S1 is: Mix aminotrimethylphosphonic acid, the imidazole compound and a solvent, and react at 60 °C under stirring for 5 h.

[0022] Furthermore, in step S2, the way to remove the solvent is rotary evaporation.

[0023] Furthermore, in step S2, the washing method is: Wash three times with water and ethanol respectively.

[0024] Further, in step S2, the drying method is: vacuum drying at 90°C for 24 h.

[0025] Application of an epoxy resin curing agent as a phosphorus-containing imidazole-based flame-retardant latent curing agent in an intrinsically flame-retardant one-component epoxy resin system.

[0026] Advantages of the present invention: For an epoxy resin curing agent, its preparation method and application thereof according to the present invention, the epoxy resin curing agent constructs an imidazole group with high reactivity and a phosphonate group with an efficient flame-retardant effect in one molecule, and successfully develops a new type of bifunctional imidazole-based curing agent. The one-component system composed of this curing agent and epoxy resin not only exhibits excellent room-temperature storage stability, but also endows the modified imidazole-based curing agent with good latent curing activity and flame-retardant performance for epoxy resin through a phosphorus-based flame-retardant mechanism; it meets the technical requirements of industrial applications for latent curing agents; the preparation method is simple, the yield is high, the raw materials are widely available, and it is suitable for industrial production; the synergistic optimization of the intrinsic flame retardancy of epoxy resin and process applicability is realized. Specific embodiments

[0027] To deepen the understanding of the present invention, the following will further describe the present invention in detail with reference to embodiments. These embodiments are only used to explain the present invention and do not limit the protection scope of the present invention.

[0028] Example 1

[0029] This embodiment provides an epoxy resin curing agent, and its molecular structural formula is as follows:

[0030] It is prepared from amino trimethylene phosphonic acid and imidazole as raw materials.

[0031] This embodiment also provides a preparation method of the above epoxy resin curing agent: sequentially add 20 g of amino trimethylene phosphonic acid, 28 g of imidazole and 100 mL of deionized water into a three-necked flask; then heat the mixture to 60°C and continuously stir for 5 h; after the reaction is completed, remove ethanol by rotary evaporation; wash the obtained product three times with deionized water and ethanol respectively, and then vacuum dry at 90°C for 24 h to obtain a phosphorus-containing imidazole-based flame-retardant latent curing agent.

[0032] Example 2

[0033] This embodiment provides an epoxy resin curing agent, and its molecular structural formula is as follows:

[0034] It is prepared from amino trimethylene phosphonic acid and 2-methylimidazole as raw materials.

[0035] This embodiment also provides a preparation method of the above epoxy resin curing agent: 20 g of aminotrimethylenephosphonic acid, 34 g of 2-methylimidazole and 100 mL of deionized water are sequentially added into a three-necked flask; then the mixture is heated to 60 °C and continuously stirred for 5 h; after the reaction is completed, ethanol is removed by rotary evaporation. The obtained product is washed three times with water and ethanol respectively, and then vacuum dried at 90 °C for 24 h to obtain a phosphorus-containing imidazole-based flame-retardant latent curing agent.

[0036] Example 3

[0037] This embodiment provides an epoxy resin curing agent, and its molecular structural formula is as follows:

[0038] It is prepared from aminotrimethylenephosphonic acid and 2-phenylimidazole as raw materials.

[0039] This embodiment also provides a preparation method of the above epoxy resin curing agent: 20 g of aminotrimethylenephosphonic acid, 59 g of 2-phenylimidazole and 100 mL of ethanol are sequentially added into a three-necked flask; then the mixture is heated to 60 °C and continuously stirred for 5 h; after the reaction is completed, ethanol is removed by rotary evaporation; the obtained product is washed three times with water and ethanol respectively, and then vacuum dried at 90 °C for 24 h to obtain a phosphorus-containing imidazole-based flame-retardant latent curing agent.

[0040] Example 4

[0041] This embodiment provides an epoxy resin curing agent, and its molecular structural formula is as follows:

[0042] It is prepared from aminotrimethylenephosphonic acid and 4-phenylimidazole as raw materials.

[0043] This embodiment also provides a preparation method of the above epoxy resin curing agent: 20 g of aminotrimethylenephosphonic acid, 59 g of 4-phenylimidazole and 100 mL of ethanol are sequentially added into a three-necked flask; then the mixture is heated to 60 °C and continuously stirred for 5 h; after the reaction is completed, ethanol is removed by rotary evaporation. The obtained product is washed three times with water and ethanol respectively, and then vacuum dried at 90 °C for 24 h to obtain a phosphorus-containing imidazole-based flame-retardant latent curing agent.

[0044] Example 5

[0045] This embodiment provides an epoxy resin curing agent, and its molecular structural formula is as follows:

[0046] It is prepared from aminotrimethylenephosphonic acid and 2-undecylimidazole as raw materials.

[0047] This embodiment also provides a preparation method of the above epoxy resin curing agent: 20 g of aminotrimethylphosphonic acid, 91 g of 2-undecylimidazole and 100 mL of ethanol are successively added into a three-necked flask; then the mixture is heated to 60 °C and continuously stirred for 5 h; after the reaction is completed, ethanol is removed by rotary evaporation; the obtained product is washed three times with water and ethanol respectively, and then vacuum dried at 90 °C for 24 h to obtain a phosphorus-containing imidazole-based flame-retardant latent curing agent.

[0048] Example 6

[0049] This embodiment provides an epoxy resin curing agent, and its molecular structural formula is as follows:

[0050] It is prepared from aminotrimethylphosphonic acid and 2-ethyl-4-methylimidazole as raw materials.

[0051] This embodiment also provides a preparation method of the above epoxy resin curing agent: 20 g of aminotrimethylphosphonic acid, 45 g of 2-ethyl-4-methylimidazole and 100 mL of ethanol are successively added into a three-necked flask; then the mixture is heated to 60 °C and continuously stirred for 5 h; after the reaction is completed, ethanol is removed by rotary evaporation; the obtained product is washed three times with water and ethanol respectively, and then vacuum dried at 90 °C for 24 h to obtain a phosphorus-containing imidazole-based flame-retardant latent curing agent.

[0052] Comparative Example

[0053] The unmodified imidazole-based curing agent is selected from imidazole, 2-methylimidazole, 2-ethylimidazole, 2-phenylimidazole, 4-phenylimidazole, 2-undecylimidazole or 2-ethyl-4-methylimidazole.

[0054] The phosphorus-containing imidazole-based latent curing agents prepared in Examples 1 to 6 were respectively mixed with bisphenol A epoxy resin (E-51 epoxy resin, trade name CYD-128, Yueyang Baling Huaxing Petrochemical Co., Ltd.) at a mass ratio of 25:100; various imidazole-based curing agents in the comparative examples were respectively mixed with bisphenol A epoxy resin (E-51 epoxy resin, trade name CYD-128, Yueyang Baling Huaxing Petrochemical Co., Ltd.) at a mass ratio of 5:100; a variable-temperature curing test was carried out using a differential scanning calorimeter, and the heating rate was 10 °C / min; the storage period of the samples was determined with reference to GB / T7123.2-2002. The prepared epoxy resin curing system was placed in a constant-temperature control box, and the temperature was maintained at 25 °C to determine the maximum storage time during which the curing system could still maintain its operating performance; the differential scanning calorimetry analysis results and the resin system storage period test results are shown in Table 1; the limiting oxygen index (LOI) of the epoxy resin cured product was determined with reference to the ASTM D2863 standard, and the vertical burning test was carried out with reference to the UL-94 test standard, and the results are shown in Table 2.

[0055] Table 1 Curing performance parameters of imidazole-based curing agents for epoxy resin

[0056]

[0057] Table 2 Flame retardant performance parameters of epoxy resin cured products

[0058] Curing Agent LOI (%) UL94 Flame Retardant Rating Comparative Example ≤22.0 No Rating Example 1 30.2 V-0 Example 2 27.6 V-1 Example 3 28.7 V-0 Example 4 27.9 V-1 Example 5 26.8 V-1 Example 6 31.7 V-0

[0059] As can be seen from Table 1, the storage periods of the single-component systems composed of various imidazole-based curing agents in the comparative examples and epoxy resin are all less than 1 day; while the storage periods of the single-component systems composed of the modified curing agents in Examples 1 to 6 of the present invention and epoxy resin are all more than 15 days, and the storage period is greatly extended. As can be seen from Table 2, the cured products obtained by curing epoxy resin with various imidazole-based curing agents in the comparative examples are flammable materials with poor flame retardant performance, while the cured products obtained by curing epoxy resin with the modified curing agents in Examples 1 to 6 of the present invention have excellent flame retardant performance.

[0060] The present invention uses aminotrimethylphosphonic acid and imidazole-based compounds as raw materials, and through the directional acid-base neutralization reaction between the 3-position nitrogen atom in the imidazole-based compound and the phosphate group in aminotrimethylphosphonic acid, the intermolecular self-assembly of the imidazole group and the phosphate group is realized, and at the same time, the modified imidazole-based curing agent is given good latent curing activity and flame retardant performance for epoxy resin.

[0061] In the present invention, an imidazole group with high reactivity and a phosphonate group with high flame retardancy effect are constructed in one molecule, and a novel bifunctional imidazole curing agent is successfully developed. The single-component system composed of this curing agent and epoxy resin not only exhibits excellent room-temperature storage stability, but also significantly improves the flame retardancy of the cured product through the phosphorus-based flame retardancy mechanism, realizing the synergistic optimization of the intrinsic flame retardancy of epoxy resin and process applicability.

[0062] In the present invention, through the electron-withdrawing effect and steric hindrance effect of the phosphonate group, the nucleophilic activity of the nitrogen atom at the 3-position of the imidazole ring is significantly reduced, thereby effectively regulating the curing reaction kinetics and endowing it with excellent latent characteristics at room temperature, meeting the technical requirements of industrial applications for latent curing agents.

[0063] The above embodiments should not limit the present invention in any way, and all technical solutions obtained by means of equivalent substitution or equivalent transformation fall within the protection scope of the present invention.

Claims

1. An epoxy resin curing agent, characterized in that: The molecular structure of the curing agent is as follows: Wherein, R1 is selected from one of hydrogen, methyl, ethyl, phenyl or undecyl, and R2 is selected from one of hydrogen, methyl or phenyl.

2. An epoxy resin curing agent according to claim 1, characterized in that: The epoxy resin curing agent is prepared using aminotrimethylenephosphonic acid and imidazole compounds as raw materials; wherein the molar ratio of aminotrimethylenephosphonic acid to imidazole compounds is 1:(6-6.2); the molecular structure of the imidazole compounds is as follows: Wherein, R1 is selected from one of hydrogen, methyl, ethyl, phenyl or undecyl, and R2 is selected from one of hydrogen, methyl or phenyl.

3. An epoxy resin curing agent according to claim 2, characterized in that: The imidazole compound is selected from one of imidazole, 2-methylimidazole, 2-ethylimidazole, 2-phenylimidazole, 4-phenylimidazole, 2-undecylimidazole or 2-ethyl-4-methylimidazole.

4. A method for preparing the epoxy resin curing agent according to any one of claims 1 to 3, characterized in that: The synthetic route is as follows: And specifically prepare according to the following steps: S1. Mix aminotrimethylenephosphonic acid, imidazole compound and solvent, and react for 4-6 hours at 55-65° C. with stirring; S2. Remove the solvent from the reaction product obtained in step S1, wash and dry it to obtain a phosphorus-containing imidazole flame retardant latent curing agent.

5. The method for preparing the epoxy resin curing agent according to claim 4, characterized in that: The solvent includes, but is not limited to, deionized water, ethanol, chlorobenzene, xylene, dimethyl sulfoxide, N,N-dimethylformamide or N,N-dimethylacetamide.

6. The method for preparing the epoxy resin curing agent according to claim 4, characterized in that: Step S1 is: aminotrimethylenephosphonic acid, an imidazole compound and a solvent are mixed, and reacted at 60° C. with stirring for 5 hours.

7. The method for preparing the epoxy resin curing agent according to claim 4, characterized in that: In step S2, the solvent is removed by rotary evaporation.

8. The method for preparing the epoxy resin curing agent according to claim 4, characterized in that: In step S2, the washing method is: washing with water and ethanol three times respectively.

9. The method for preparing the epoxy resin curing agent according to claim 4, characterized in that: In step S2, the drying method is: vacuum drying at 90° C. for 24 hours.

10. Use of the epoxy resin curing agent according to any one of claims 1 to 3, characterized in that: Application as phosphorus-containing imidazole flame retardant latent curing agent in intrinsically flame retardant one-component epoxy resin system.

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