A novel low-temperature curing epoxy curing agent and a preparation method thereof

Abstract

The application discloses a novel low-temperature curing epoxy curing agent and a preparation method thereof, and belongs to the technical field of epoxy curing agents. The novel low-temperature curing epoxy curing agent is made of eugenol, cysteine and formaldehyde. The application selects raw materials through a large number of experiments, adopts new raw materials, i.e. eugenol and cysteine. The eugenol molecule contains a phenolic hydroxyl group, an allyl group and a methoxyl group; the cysteine molecule contains an amino group, a carboxyl group and a sulfydryl group (-SH). These groups increase the reactivity of the curing agent, and especially the sulfydryl group can greatly improve the curing speed of the curing agent in a low-temperature environment. The phenolic aldehyde amine curing agent synthesized by using eugenol and cysteine has a faster low-temperature curing speed than a general cardanol phenolic aldehyde amine curing agent, and also has a good heat deformation resistance, and thus a good technical effect is achieved.

Description

Technical Field

[0001] This invention relates to an epoxy curing agent, specifically a novel low-temperature curing epoxy curing agent and its preparation method, belonging to the field of polymer materials technology. Background Technology

[0002] In epoxy resin applications, curing agents are a crucial component. Currently, modified amine curing agents are commonly used in the market, mainly including polyamides and phenolic amines. Polyamide curing agents can cure epoxy resins into films at room temperature, but their low-temperature curing performance is poor; they cannot be properly applied below 15℃, and the drying time is long. Phenolic amine curing agents, compared to polyamide curing agents, can cure epoxy resins at lower temperatures and have a faster curing speed. The development and application of bio-based raw materials is a current global research hotspot. Eugenol, as a green, environmentally friendly, and abundant renewable raw material, can be used to replace or partially replace phenol in the production of phenolic amine epoxy curing agents, which will also be a research direction for epoxy curing agents.

[0003] Thiols have been used as a commercial epoxy curing agent for over 40 years. One of the most important characteristics of thiols is their rapid curing at room temperature, typically within 5 minutes. Another characteristic is low-temperature curing; when used with DMP as an accelerator, they can rapidly cure epoxy resins at -20°C. Their main limitations are their unpleasant odor, tendency to form a skin, and low heat distortion temperature.

[0004] Therefore, based on existing technologies, this invention, through extensive experimental screening, synthesizes a novel low-temperature curing epoxy curing agent using new raw materials—eugenol and cysteine. Due to the presence of a thiol group (-SH) in its molecular structure, eugenol-phenolic amine exhibits significantly improved low-temperature curing performance compared to conventional phenolic amine curing agents; furthermore, due to the presence of a benzene ring in its molecular structure, it has a higher heat distortion temperature and a reduced odor compared to thiol curing agents. This overcomes the shortcomings of existing technologies. Summary of the Invention

[0005] Purpose of the Invention: The purpose of this invention is to address the shortcomings of existing technologies. Through extensive experimental screening of raw materials, a new raw material—eugenol and cysteine—was synthesized into eugenol phenolic amine, which exhibits higher reactivity at low temperatures, significantly improving the curing speed. It can also rapidly cure into a film at low temperatures (-15℃ to 0℃). Moreover, compared to thiol curing agents, the introduction of a benzene ring into its molecule results in a substantial increase in heat distortion temperature, achieving excellent technical effects.

[0006] Technical solution: To achieve the above objectives, the technical solution adopted by this invention is as follows:

[0007] A low-temperature curing epoxy curing agent, made from eugenol, cysteine, and formaldehyde. Its structure is shown below:

[0008]

[0009] This invention provides a method for preparing a low-temperature curing epoxy curing agent, which includes the following steps:

[0010] (1) Add deionized water and cysteine ​​to the reaction flask in sequence, heat and stir, and control the temperature at 50±5℃ to dissolve cysteine ​​in water.

[0011] (2) Add eugenol and stir to disperse it evenly. Then add formaldehyde solution dropwise, controlling the dropping rate so that the temperature does not exceed 80℃.

[0012] (3) After the formaldehyde is added, maintain the temperature between 80±5℃ and the reaction time is 2-3 hours. After the reaction is completed, remove the water in the system by vacuuming to obtain the low-temperature curing epoxy curing agent.

[0013] As a preferred embodiment, in step (2), the formaldehyde is a 37% formaldehyde solution or solid paraformaldehyde.

[0014] As a preferred embodiment, in the above-described method for preparing a low-temperature curing epoxy curing agent, the molar ratio of eugenol, cysteine, and formaldehyde is 1:1 to 3:1 to 3.

[0015] As a particularly preferred embodiment, in the above-described method for preparing a low-temperature curing epoxy curing agent, the molar ratio of eugenol, cysteine, and formaldehyde is 1:2:2.

[0016] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0017] This invention obtained the optimal raw material ratio through extensive experimental screening. Eugenol, formaldehyde, and cysteine ​​were used to synthesize eugenol phenol-aldehyde-amine curing agent via Mannich condensation reaction. By introducing thiol groups (-SH) into the eugenol phenol-aldehyde-amine molecule, its reactivity was improved, which greatly accelerated the curing speed of epoxy resin at low temperature. Moreover, the heat distortion temperature was greatly improved compared with thiol curing agent, achieving very good technical results. Attached Figure Description

[0018] Figure 1 This is the synthetic reaction formula of the present invention. Detailed Implementation

[0019] Example 1

[0020] 1. A novel low-temperature curing epoxy curing agent, comprising the following raw materials: 164g eugenol, 121g cysteine, 81g 37% formaldehyde solution, and 400g deionized water.

[0021] 2. The method for preparing the curing agent includes the following steps:

[0022] (1) Add cysteine ​​and deionized water to the reaction flask in sequence, turn on heating and stirring, and raise the temperature to 50°C to dissolve all the cysteine.

[0023] (2) Add eugenol and stir well. Then add 37% formaldehyde solution dropwise. Control the dropping speed and complete the addition within half an hour, keeping the temperature below 80℃.

[0024] (3) After the formaldehyde is added, maintain the temperature at 80±5℃ and keep the reaction at this temperature for 2 hours.

[0025] (4) After the reaction is complete, the water in the system is removed by vacuuming, and after cooling, it is weighed to obtain 298g of the new low-temperature curing epoxy curing agent.

[0026] Example 2

[0027] 1. A novel low-temperature curing epoxy curing agent, comprising the following raw materials: 164g eugenol, 800g deionized water, 242g cysteine, and 162g 37% formaldehyde solution.

[0028] 2. The preparation method of the curing agent includes the following steps:

[0029] (1) Add cysteine ​​and deionized water to the reaction flask in sequence, turn on heating and stirring, and raise the temperature to 50°C to dissolve all the cysteine.

[0030] (2) Add eugenol and stir well. Then add 37% formaldehyde solution dropwise. Control the dropping rate and complete the addition within one hour, keeping the temperature below 80℃.

[0031] (3) After the formaldehyde is added, maintain the temperature at 80±5℃ and keep the reaction at this temperature for 3 hours.

[0032] (4) After the reaction is complete, the water in the system is removed by vacuuming, and after cooling, it is weighed to obtain 435g of the new low-temperature curing epoxy curing agent.

[0033] Example 3

[0034] 1. A novel low-temperature curing epoxy curing agent, comprising the following raw materials: 164g eugenol, 400g deionized water, 121g cysteine, and 30g paraformaldehyde.

[0035] 2. The preparation method of the curing agent includes the following steps:

[0036] (1) Add cysteine ​​and deionized water to the reaction flask in sequence, turn on heating and stirring, and raise the temperature to 50°C to dissolve all the cysteine.

[0037] (2) Add eugenol and stir well. Then add paraformaldehyde granules in batches, keeping the temperature below 80°C.

[0038] (3) After the formaldehyde is added, maintain the temperature at 80±5℃ and keep it warm for 3 hours.

[0039] (4) After the reaction is complete, the water in the system is removed by vacuuming, and after cooling, it is weighed to obtain 297g of the new low-temperature curing epoxy curing agent.

[0040] Comparative Example 1

[0041] 1. Cysteine ​​was replaced with conventional polyethylenepolyamine—diethylenetriamine—to synthesize a conventional eugenol phenol-amine curing agent for comparison of the product's low-temperature curing performance. The raw materials included: 164g eugenol, 103g diethylenetriamine, and 81g 37% formaldehyde solution.

[0042] 2. A method for preparing an epoxy curing agent, comprising the following steps:

[0043] (1) Add eugenol and diethylenetriamine to the reaction flask in sequence, and turn on heating and stirring.

[0044] (2) When the temperature reaches 50℃, start adding 37% formaldehyde solution dropwise. Control the dropping rate and complete the addition within half an hour, so that the temperature does not exceed 80℃.

[0045] (3) After the formaldehyde is added, maintain the temperature at 80±5℃ and keep the reaction at this temperature for 3 hours.

[0046] (4) After the reaction was completed, the water in the system was removed by vacuuming, and after cooling, it was weighed to obtain 280g of eugenol phenol amine.

[0047] Comparative Example 2

[0048] 1. Eugenol was replaced with phenol to synthesize a phenolic amine curing agent, which was used to compare the low-temperature curing performance of the product. Its raw materials included: 94g phenol, 121g cysteine, and 81g 37% formaldehyde solution.

[0049] 2. Its preparation method includes the following steps:

[0050] (1) Add cysteine ​​and deionized water to the reaction flask in sequence, turn on heating and stirring, and raise the temperature to 50°C to dissolve all the cysteine.

[0051] (2) Add phenol and stir well. Then add 37% formaldehyde solution dropwise over half an hour, keeping the temperature below 80°C.

[0052] (3) After the formaldehyde is added, maintain the temperature at 80±5℃ and keep the reaction at this temperature for 3 hours.

[0053] (4) After the reaction is complete, the water in the system is removed by vacuuming, and after cooling, it is weighed to obtain 227g of phenolic amine curing agent.

[0054] Comparative Example 3

[0055] 1. By replacing eugenol with cashew phenol and cysteine ​​with diethylenetriamine, a cashew phenol-aldehyde-amine curing agent was synthesized to compare the low-temperature curing performance of the product. Its raw materials include: 304g cashew phenol, 103g diethylenetriamine, and 81g 37% formaldehyde solution.

[0056] 2. Its preparation method includes the following steps:

[0057] (1) Add cashew phenol and diethylenetriamine to the reaction flask in sequence, and turn on heating and stirring.

[0058] (2) When the temperature reaches 50℃, start adding 37% formaldehyde solution dropwise. Control the dropping rate and complete the addition within half an hour, so that the temperature does not exceed 80℃.

[0059] (3) After the formaldehyde is added, maintain the temperature at 80±5℃ and keep the reaction at this temperature for 3 hours.

[0060] (4) After the reaction was completed, the water in the system was removed by vacuuming, and after cooling, it was weighed to obtain 420g of cashew phenol aldehyde amine.

[0061] Example 4: Surface Drying Temperature Test

[0062] Epoxy resin (Jiangsu Sanmu Chemical Co., Ltd.'s 828) was mixed with various epoxy curing agents prepared above and purchased polythiol curing agent (Toray QE-340M), and a curing accelerator (DMP-30) was added appropriately. The epoxy resin, curing agent, and curing accelerator were mixed in a mass ratio of 10:8:1 and uniformly coated onto a tinplate to form a film with a thickness of 40 μm. The surface drying time at different temperatures was recorded, and the results are shown in Table 1 below.

[0063] Table 1

[0064] Curing agent / temperature 0℃ -5℃ -10℃ -15℃ -20℃ Comparative Example 1 65min 125min Undried Undried Undried Comparative Example 2 33min 42min 68min 152min Undried Comparative Example 3 45min 113min 189min Undried Undried Example 1 24min 33min 55min 88min Undried Example 2 22min 28min 48min 74min Undried Example 3 23min 33min 55min 86min Undried QE-340M 16min 18min 23min 31min 45min .

[0065] Example 5: Heat distortion temperature test

[0066] Epoxy resin (Jiangsu Sanmu Chemical Co., Ltd.'s 828) was mixed with various epoxy curing agents prepared above and purchased polythiol curing agent (Toray QE-340M), and a curing accelerator (DMP-30) was added appropriately. The epoxy resin, curing agent, and curing accelerator were mixed in a mass ratio of 10:8:1. The mixture was poured into a mold, and after complete curing, a rectangular sample with a length of 120 mm, a width of 10 mm, and a height of 12 mm was formed. Its heat distortion temperature was tested according to the ISO 75 national standard, and the results are shown in Table 2 below.

[0067] Table 2

[0068]

[0069] The above experimental results show that the low-temperature curing agent of the present invention, compared with conventional phenolic amine curing agents and cashew phenolic amine curing agents, has a faster curing speed at the same low temperature and can cure epoxy resin at a lower temperature. Although its low-temperature curing speed is still relatively slower than that of polythiol curing agents, its heat distortion temperature is greatly improved, its application range is wider, and it has achieved very good technical results. Through comparison, Example 2 of the present invention has better overall performance in terms of low-temperature curing and heat distortion temperature resistance.

[0070] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A low temperature curing epoxy curing agent, characterized by, The curing agent has a structure as shown below: 。 2. The preparation method of the low-temperature curing epoxy curing agent according to claim 1, characterized in that, It comprises the following steps: (1) Deionized water and cysteine are sequentially added into a reaction bottle, heated and stirred, and the temperature is controlled at 50±5℃, so that the cysteine is dissolved in the water; (2) Eugenol is added and stirred to disperse uniformly, and then formaldehyde solution is added dropwise, and the dropping speed is controlled so that the temperature is not higher than 80℃; (3) After the formaldehyde is added dropwise, the temperature is maintained at 80±5℃, the reaction time is 2-3 hours, after the reaction is completed, the water in the system is removed by vacuum, and a novel low-temperature curing epoxy curing agent is obtained.

3. The production method according to claim 2, characterized by, The formaldehyde is a 37% formaldehyde solution or a solid paraformaldehyde.

4. The preparation method according to claim 2, characterized in that, The molar ratio of the eugenol, cysteine and formaldehyde is 1:1-3:1-3.

5. The preparation method according to claim 2, characterized in that, The molar ratio of the eugenol, cysteine and formaldehyde is 1:2:

2.

6. Application of the epoxy curing agent of claim 1 in curing epoxy resin.

Images