Liquid modified dicyandiamide curing agent, preparation method and application
By grafting and compounding dicyandiamide, a liquid-modified dicyandiamide curing agent was prepared, which solved the problems of harsh curing conditions and poor compatibility of dicyandiamide in epoxy resin, achieved the effect of low-temperature curing and long-term storage, and improved the performance of epoxy slurry cured products.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-02-11
- Publication Date
- 2026-04-03
AI Technical Summary
Dicyandiamide curing agents have problems such as harsh curing conditions, uneven curing, and poor compatibility in epoxy resins, which affect their application value. Furthermore, the introduction of curing accelerators can lead to a decrease in storage stability.
A liquid-modified dicyandiamide curing agent was prepared by grafting dicyandiamide with aminophenyl ether monomer and then combining it with n-butyl glycidyl ether. This improved the reactivity and compatibility, reduced the curing temperature, and maintained a longer shelf life.
The prepared liquid-modified dicyandiamide curing agent reduced the curing temperature while maintaining a shelf life of more than 3 months and significantly improved the mechanical properties of the cured epoxy slurry.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of epoxy resin curing agent research and development technology, specifically to liquid modified dicyandiamide curing agent, its preparation method, and its application. Background Technology
[0002] Dicyandiamide (DICY) has excellent room temperature latency as a curing agent for epoxy resins. It can maintain the pot life of a single-component epoxy system for more than 6 months at room temperature. Its cured products exhibit excellent chemical stability, mechanical properties and electrical insulation properties, and are widely used in single-component epoxy adhesives, composite prepregs, electronic packaging materials, powder coatings and PCB materials.
[0003] However, the cyano (-CN) and imine (-C=NH) groups in the dicyandiamide molecule are highly polar and electron-withdrawing, which reduces the electron cloud density of the amino group and inhibits its activity in the curing reaction. Furthermore, dicyandiamide has significant structural differences and poor compatibility with epoxy resins, easily leading to macroscopic phase separation in epoxy systems. Therefore, dicyandiamide curing systems suffer from harsh curing conditions (170-180℃ / 20-60min) and uneven curing, severely limiting their application value.
[0004] Existing technologies show that introducing curing accelerators (urea derivatives, organic guanidine derivatives, imidazole derivatives, etc.) can effectively reduce the curing temperature of dicyandiamide, but this is usually accompanied by a significant decrease in the storage stability of the system.
[0005] Therefore, developing a modified dicyandiamide curing agent that can both lower the curing temperature and maintain a longer storage period is of great significance for expanding its industrial application value. Summary of the Invention
[0006] This invention first utilizes a self-developed aminophenyl ether monomer to graft and modify dicyandiamide via a nucleophilic addition reaction of an amino-cyano group. Then, it prepares a liquid-modified dicyandiamide curing agent by compounding n-butyl glycidyl ether through an amino-epoxy ring-opening reaction. This curing agent is suitable for single-component bisphenol A type epoxy resin systems. The epoxy slurry prepared in this way significantly reduces the curing temperature while maintaining a shelf life of more than 3 months, and its cured product exhibits excellent mechanical properties.
[0007] A liquid modified dicyandiamide curing agent, wherein the curing agent is prepared by compounding modified dicyandiamide with n-butyl glycidyl ether via an amino-epoxy ring-opening reaction; The modified dicyandiamide is modified dicyandiamide I or a mixture of modified dicyandiamide I and modified dicyandiamide II; Preferably, the molar ratio of modified dicyandiamide and n-butyl glycidyl ether in the curing agent is 1:(2.0-2.1).
[0008] Preferably, the molar ratio of modified dicyandiamide I to modified dicyandiamide II in the modified dicyandiamide is 1:(0-0.6).
[0009] A method for preparing a liquid modified dicyandiamide curing agent specifically involves: dispersing modified dicyandiamide and n-butyl glycidyl ether in anhydrous N,N-dimethylformamide solvent, heating to 85-95℃ and stirring to react, removing the solvent by rotary evaporation under reduced pressure, and obtaining a uniform, transparent, viscous liquid modified dicyandiamide curing agent.
[0010] Preferably, the modified dicyandiamide I is prepared by: Using 1 molar equivalent of bisphenol A and 2.01-2.05 molar equivalents of 4-nitrophenylethyl bromide as raw materials, a nucleophilic substitution reaction was carried out between the phenolic hydroxyl functional group of bisphenol A and the bromine functional group of 4-nitrophenylethyl bromide through a basic catalyst to obtain a dinitrophenyl ether monomer. Using tin dichloride as a reducing agent, the nitro functional group of the dinitrophenyl ether monomer was reduced by concentrated hydrochloric acid to obtain the diaminophenyl ether monomer; Using 1 molar equivalent of diaminophenyl ether monomer and 2.01-2.05 molar equivalents of dicyandiamide as raw materials, modified dicyandiamide I was obtained by nucleophilic addition reaction of the amino functional group of diaminophenyl ether monomer with the cyano functional group of dicyandiamide catalyzed by concentrated hydrochloric acid.
[0011] Preferably, the modified dicyandiamide II is prepared by: Using 1 molar equivalent of phloroglucinol and 3.01-3.05 molar equivalents of 4-nitrophenylethyl bromide as raw materials, a nucleophilic substitution reaction was carried out between the phenolic hydroxyl functional group of phloroglucinol and the bromine functional group of 4-nitrophenylethyl bromide through a basic catalyst to obtain trinitrophenyl ether monomers. Using tin dichloride as a reducing agent, the nitro functional group of the trinitrophenyl ether monomer was reduced by concentrated hydrochloric acid to obtain the triaminophenyl ether monomer; Using 1 molar equivalent of triaminophenyl ether monomer and 3.01-3.05 molar equivalents of dicyandiamide as raw materials, modified dicyandiamide II was obtained by nucleophilic addition reaction of the amino functional group of triaminophenyl ether monomer with the cyano functional group of dicyandiamide catalyzed by concentrated hydrochloric acid.
[0012] Preferably, the alkaline catalyst is one of sodium carbonate, sodium hydroxide, potassium carbonate, and potassium hydroxide.
[0013] Application of a liquid-modified dicyandiamide curing agent in bisphenol A type epoxy resin curing systems.
[0014] Preferably, the application method is as follows: 15-25 parts by weight of liquid modified dicyandiamide curing agent and 90-120 parts by weight of bisphenol A type epoxy resin are mixed evenly at 25-40°C to obtain epoxy slurry.
[0015] Beneficial effects: This invention uses bisphenol A or pyrogallol as raw materials, first reacts with 4-nitrophenylethyl bromide through a nucleophilic substitution reaction to introduce a nitro group, and then uses tin dichloride to convert the nitro group into an amino group to obtain a diaminophenyl ether monomer or a triaminophenyl ether monomer. Dicyandiamide was grafted onto diaminophenyl ether monomers or triaminophenyl ether monomers via a nucleophilic addition reaction of amino-cyano groups. This process improved the reactivity of dicyandiamide by disrupting its original regular structure and strong crystallinity, and enhanced its compatibility by introducing phenyl ether segments similar to bisphenol A type epoxy resins. Modified dicyandiamide was compounded with n-butyl glycidyl ether via an amino-epoxy ring-opening reaction. By introducing long chains to adjust the viscosity and improve flexibility, a liquid modified dicyandiamide curing agent was prepared. Epoxy slurry was prepared by using liquid-modified dicyandiamide curing agent as the crosslinking and curing component of bisphenol A type epoxy resin. The performance test results show that the liquid-modified dicyandiamide curing agent developed in this invention not only achieved the beneficial technical effect of significantly improving the curing performance of epoxy slurry, but also maintained a storage and applicability period of more than 3 months, and the epoxy cured product exhibited excellent mechanical properties. Detailed Implementation Example 1:
[0016] Preparation of liquid modified dicyandiamide curing agent I: Using 1 molar equivalent of modified dicyandiamide I and 2.04 molar equivalent of n-butyl glycidyl ether as raw materials, liquid modified dicyandiamide curing agent I is obtained by ring-opening reaction between the amino functional group of modified dicyandiamide I and the epoxy functional group of n-butyl glycidyl ether. The specific experimental steps for preparing liquid modified dicyandiamide curing agent I are as follows: 6.3g of modified dicyandiamide I, 2.7g of n-butyl glycidyl ether (CAS No. 2426-08-6) and 80mL of anhydrous N,N-dimethylformamide are added to a three-necked flask, stirred at room temperature until completely dissolved, heated to 90℃ and stirred for 4h, cooled to room temperature, and rotary evaporated under reduced pressure at 20mbr and 50℃ until no solvent is evaporated, to obtain a uniform and transparent viscous liquid modified dicyandiamide curing agent I; The chemical structural formula of modified dicyandiamide I is as follows: ; The preparation method of modified dicyandiamide I is as follows: Using 1 molar equivalent of bisphenol A and 2.02 molar equivalents of 4-nitrophenylethyl bromide as raw materials, a nucleophilic substitution reaction was carried out between the phenolic hydroxyl functional group of bisphenol A and the bromine functional group of 4-nitrophenylethyl bromide via a basic catalyst to obtain a dinitrophenyl ether monomer with the following chemical structural formula: ; The alkaline catalyst can be selected from sodium carbonate, sodium hydroxide, potassium carbonate, and potassium hydroxide. In this embodiment, potassium carbonate is selected. Using tin dichloride as a reducing agent, the nitro functional group of the dinitrophenyl ether monomer is reduced by concentrated hydrochloric acid to obtain the diaminophenyl ether monomer, whose chemical structural formula is as follows: ; Using 1 molar equivalent of diaminophenyl ether monomer and 2.03 molar equivalent of dicyandiamide as raw materials, a nucleophilic addition reaction was carried out between the amino functional group of the diaminophenyl ether monomer and the cyano functional group of the dicyandiamide via concentrated hydrochloric acid catalysis to obtain modified dicyandiamide I. The preparation steps of modified dicyandiamide I are as follows: 2.3 g of bisphenol A (CAS No. 80-05-7), 2.0 g of potassium carbonate and 100 mL of N,N-dimethylformamide were added to a three-necked flask and stirred at room temperature for 30 min to dissolve. Then, 40 mL of N,N-dimethylformamide solution containing 4.7 g of 4-nitrophenylethyl bromide (CAS No. 5339-26-4) was added to the three-necked flask. The mixture was heated to 80 °C and stirred for 6 h. After cooling to room temperature, the solvent was removed by rotary evaporation under reduced pressure. The mixture was washed three times with deionized water and dried under vacuum at 60 °C for 12 h to obtain the dinitrophenyl ether monomer. 5.0 g of dinitrophenyl ether monomer, 18 g of tin dichloride, 20 mL of concentrated hydrochloric acid and 200 mL of anhydrous ethanol were added to a three-necked flask and stirred at room temperature for 30 min. The mixture was then heated to 70 °C and stirred for 6 h. After cooling to room temperature, the mixture was poured into deionized water and the pH was adjusted to 10 using 20 wt% sodium hydroxide aqueous solution. The mixture was filtered, the filtrate was collected, extracted with dichloromethane, dried with anhydrous sodium sulfate, filtered, and the solvent was removed by rotary evaporation under reduced pressure. The mixture was then dried under vacuum at 60 °C for 12 h to obtain diaminophenyl ether monomer. Under nitrogen protection, 2.3 g of diaminophenyl ether monomer, 0.9 g of dicyandiamide and 30 mL of N,N-dimethylformamide were added to a three-necked flask and stirred at room temperature for 30 min. Then, 2 mL of concentrated hydrochloric acid was added dropwise to the three-necked flask, the temperature was raised to 80 °C and stirred for 10 h, the mixture was cooled to room temperature, filtered, washed three times with deionized water, and dried under vacuum at 60 °C for 12 h to obtain modified dicyandiamide I. The 1H NMR spectrum of modified dicyandiamide I is characterized as follows: 1H NMR (DMSO-d6, 400MHz) δ: 1.61 (s, 6H), 2.94-2.96 (t, 4H), 4.20-4.23 (t, 4H), 4.89 (s, 2H), 6.63 (s, 4H), 6.87-6.91(m, 6H), 7.09-7.16(m, 10H), 7.31(s, 2H), 7.49-7.50(d, 4H). Example 2:
[0017] Preparation of liquid modified dicyandiamide curing agent II: Using 0.7 mol equivalent of modified dicyandiamide I (self-made in Example 1), 0.3 mol equivalent of modified dicyandiamide II and 2.04 mol equivalent of n-butyl glycidyl ether as raw materials, liquid modified dicyandiamide curing agent II was obtained by ring-opening reaction between the amino functional groups of modified dicyandiamide I and modified dicyandiamide II and the epoxy functional groups of n-butyl glycidyl ether. The specific experimental steps for preparing liquid modified dicyandiamide curing agent II are as follows: 4.4g of modified dicyandiamide I, 2.2g of modified dicyandiamide II, 2.7g of n-butyl glycidyl ether and 100mL of anhydrous N,N-dimethylformamide are added to a three-necked flask, stirred at room temperature until completely dissolved, heated to 90℃ and stirred for 5h, cooled to room temperature, and rotary evaporated under reduced pressure at 20mbr and 50℃ until no solvent evaporates, to obtain a uniform and transparent viscous liquid modified dicyandiamide curing agent II; The chemical structural formula of modified dicyandiamide II is as follows: ; The preparation method of modified dicyandiamide II is as follows: Using 1 molar equivalent of resorcinol and 3.02 molar equivalents of 4-nitrophenylethyl bromide as raw materials, a nucleophilic substitution reaction was carried out between the phenolic hydroxyl functional group of resorcinol and the bromine functional group of 4-nitrophenylethyl bromide via a basic catalyst to obtain a trinitrophenyl ether monomer with the following chemical structural formula: ; The alkaline catalyst can be selected from sodium carbonate, sodium hydroxide, potassium carbonate, and potassium hydroxide. In this embodiment, potassium carbonate is selected. Using tin dichloride as a reducing agent, the nitro functional group of the trinitrophenyl ether monomer is reduced by concentrated hydrochloric acid to obtain the triaminophenyl ether monomer, whose chemical structural formula is as follows: ; Using 1 molar equivalent of triaminophenyl ether monomer and 3.03 molar equivalent of dicyandiamide as raw materials, a nucleophilic addition reaction was carried out between the amino functional group of the triaminophenyl ether monomer and the cyano functional group of the dicyandiamide catalyzed by concentrated hydrochloric acid to obtain modified dicyandiamide II. The preparation steps of modified dicyandiamide II are as follows: 1.3 g of phloroglucinol (CAS No. 108-73-6), 2.5 g of potassium carbonate and 100 mL of N,N-dimethylformamide were added to a three-necked flask and stirred at room temperature for 30 min to dissolve. Then, 60 mL of N,N-dimethylformamide solution containing 7.1 g of 4-nitrophenylethyl bromide was added to the three-necked flask, the temperature was raised to 80 °C and stirred for 8 h, the temperature was cooled to room temperature, the solvent was removed by rotary evaporation under reduced pressure, the mixture was washed three times with deionized water, and dried under vacuum at 60 °C for 12 h to obtain the trinitrophenyl ether monomer. 5.0 g of trinitrophenyl ether monomer, 25 g of tin dichloride, 20 mL of concentrated hydrochloric acid and 200 mL of anhydrous ethanol were added to a three-necked flask and stirred at room temperature for 30 min. The mixture was then heated to 70 °C and stirred for 8 h. After cooling to room temperature, the mixture was poured into deionized water and the pH was adjusted to 10 using 20 wt% sodium hydroxide aqueous solution. The mixture was filtered, and the filtrate was collected. The filtrate was extracted with dichloromethane, dried over anhydrous sodium sulfate, filtered, and the solvent was removed by rotary evaporation under reduced pressure. The mixture was then dried under vacuum at 60 °C for 12 h to obtain the triaminophenyl ether monomer. Under nitrogen protection, 2.4 g of triaminophenyl ether monomer, 1.3 g of dicyandiamide and 40 mL of N,N-dimethylformamide were added to a three-necked flask and stirred at room temperature for 30 min. Then, 5 mL of concentrated hydrochloric acid was added dropwise to the three-necked flask, the temperature was raised to 80 °C and stirred for 10 h, the mixture was cooled to room temperature, filtered, washed three times with deionized water, and dried under vacuum at 60 °C for 12 h to obtain modified dicyandiamide II. The 1H NMR characterization of modified dicyandiamide II is as follows: 1 H NMR (DMSO-d6, 400MHz) δ: 2.96-2.98(t, 6H), 4.23-4.25(t, 6H), 4.93(s, 3H), 6.21(s, 3H), 6.65(s, 6H) , 6.84(s, 3H), 7.09-7.10(d, 6H), 7.26(s, 3H), 7.31(s, 3H), 7.45-7.47(d, 6H). Example 3:
[0018] The application method of liquid modified dicyandiamide curing agent is as follows: 20 parts by weight of liquid modified dicyandiamide curing agent and 100 parts by weight of bisphenol A type epoxy resin (model E51) are added to a planetary mixer and stirred at a speed of 1500 r / min for 10 min. During the mixing process, the jacket cooling water is turned on to ensure that the material temperature does not exceed 40℃. Then, the vacuum is drawn to -0.1MPa, and the vacuum is maintained and defoamed at a speed of 100 r / min for 20 min to obtain epoxy slurry. Specifically, when liquid modified dicyandiamide curing agent I and liquid modified dicyandiamide curing agent II are used respectively, epoxy slurry I and epoxy slurry II are prepared sequentially. Comparative Example 1:
[0019] Epoxy slurry a is prepared, and its only difference from epoxy slurry I is that dicyandiamide is used instead of liquid modified dicyandiamide curing agent I. Comparative Example 2:
[0020] Epoxy slurry b is prepared, and its only difference from epoxy slurry I is that dicyandiamide is used to replace liquid modified dicyandiamide curing agent I, and 0.5 parts by weight of curing accelerator (2-ethyl-4-methylimidazole) is added. Performance testing:
[0021] I. Room Temperature Storage Stability Test: The viscosity of the epoxy slurry was determined using a single-cylinder rotary viscometer according to GB / T 2794-2022 standard. Its room temperature storage stability was characterized by the rate of viscosity change after 30, 60, and 90 days of storage at room temperature. The calculation method for the viscosity change rate is as follows: Viscosity change rate (%) = (Viscosity value after n days at room temperature - Initial viscosity value) / Initial viscosity value × 100%; II. Curing performance test: The gel time of epoxy grout was determined according to GB / T 12007.7-1989 standard, and its curing performance was characterized by the gel time at 120℃, 140℃ and 170℃. III. Mechanical property test: The epoxy slurry was poured into a polytetrafluoroethylene mold coated with a release agent, cured at 140℃ for 20 minutes and then demolded. The curing effect was judged by pressing with a finger to see if a fingerprint could be left. The tensile strength and impact toughness of the cured epoxy slurry (Type II specimen) were determined according to GB / T 2567-2021 standard. The results of the above performance experiments are shown in Table 1-3.
[0022] Table 1. Results of room temperature storage stability test of epoxy grout
[0023] Note: Industry standards require that the viscosity increase of single-component epoxy grout during its shelf life should not exceed 30%. Table 2. Test results of curing performance of epoxy grout
[0024] Table 3 Performance test results of epoxy grout cured products
[0025] A comprehensive analysis of the above experimental results leads to the following conclusions: Conclusion 1: The epoxy slurry prepared by the self-developed liquid modified dicyandiamide curing agent of this invention not only significantly improves the curing conditions (reduces the curing temperature) but also retains a long shelf life (>90 days). Conclusion 2: The epoxy slurry cured product prepared by the self-developed liquid modified dicyandiamide curing agent of this invention has achieved a significant improvement in mechanical properties compared with the conventional curing system composed of dicyandiamide and curing accelerator.
Claims
1. A liquid-modified dicyandiamide curing agent, characterized in that, The curing agent is prepared by compounding modified dicyandiamide with n-butyl glycidyl ether via an amino-epoxy ring-opening reaction; The modified dicyandiamide is modified dicyandiamide I or a mixture of modified dicyandiamide I and modified dicyandiamide II; The chemical structural formula of the modified dicyandiamide I is: ； The chemical structural formula of the modified dicyandiamide II is: 。 2. The liquid-modified dicyandiamide curing agent according to claim 1, characterized in that, The molar ratio of modified dicyandiamide and n-butyl glycidyl ether in the curing agent is 1:(2.0-2.1).
3. The liquid-modified dicyandiamide curing agent according to claim 1, characterized in that, The molar ratio of modified dicyandiamide I to modified dicyandiamide II in the modified dicyandiamide is 1:(0-0.6).
4. A method for preparing a liquid-modified dicyandiamide curing agent according to any one of claims 1-3, characterized in that, The specific preparation method of the curing agent is as follows: modified dicyandiamide and n-butyl glycidyl ether are dispersed in anhydrous N,N-dimethylformamide solvent, heated to 85-95℃ and stirred to react, and the solvent is removed by rotary evaporation under reduced pressure to obtain a uniform and transparent viscous liquid modified dicyandiamide curing agent.
5. The method for preparing a liquid-modified dicyandiamide curing agent according to claim 4, characterized in that, The preparation method of the modified dicyandiamide I is as follows: Using 1 molar equivalent of bisphenol A and 2.01-2.05 molar equivalents of 4-nitrophenylethyl bromide as raw materials, a nucleophilic substitution reaction was carried out between the phenolic hydroxyl functional group of bisphenol A and the bromine functional group of 4-nitrophenylethyl bromide through a basic catalyst to obtain a dinitrophenyl ether monomer. Using tin dichloride as a reducing agent, the nitro functional group of the dinitrophenyl ether monomer was reduced by concentrated hydrochloric acid to obtain the diaminophenyl ether monomer; Using 1 molar equivalent of diaminophenyl ether monomer and 2.01-2.05 molar equivalents of dicyandiamide as raw materials, modified dicyandiamide I was obtained by nucleophilic addition reaction of the amino functional group of diaminophenyl ether monomer with the cyano functional group of dicyandiamide catalyzed by concentrated hydrochloric acid.
6. The method for preparing a liquid-modified dicyandiamide curing agent according to claim 4, characterized in that, The preparation method of the modified dicyandiamide II is as follows: Using 1 molar equivalent of phloroglucinol and 3.01-3.05 molar equivalents of 4-nitrophenylethyl bromide as raw materials, a nucleophilic substitution reaction was carried out between the phenolic hydroxyl functional group of phloroglucinol and the bromine functional group of 4-nitrophenylethyl bromide through a basic catalyst to obtain trinitrophenyl ether monomers. Using tin dichloride as a reducing agent, the nitro functional group of the trinitrophenyl ether monomer was reduced by concentrated hydrochloric acid to obtain the triaminophenyl ether monomer; Using 1 molar equivalent of triaminophenyl ether monomer and 3.01-3.05 molar equivalents of dicyandiamide as raw materials, modified dicyandiamide II was obtained by nucleophilic addition reaction of the amino functional group of triaminophenyl ether monomer with the cyano functional group of dicyandiamide catalyzed by concentrated hydrochloric acid.
7. A method for preparing a liquid-modified dicyandiamide curing agent according to claim 5 or 6, characterized in that, The alkaline catalyst is one of sodium carbonate, sodium hydroxide, potassium carbonate, and potassium hydroxide.
8. The application of a liquid-modified dicyandiamide curing agent according to any one of claims 1-3, characterized in that, The application of the curing agent in the bisphenol A type epoxy resin curing system.
9. The application of the liquid-modified dicyandiamide curing agent according to claim 8, characterized in that, The application method is as follows: 15-25 parts by weight of liquid modified dicyandiamide curing agent and 90-120 parts by weight of bisphenol A type epoxy resin are mixed evenly at 25-40℃ to obtain epoxy slurry.