Novel low-temperature curing epoxy curing agent and preparation method thereof

Abstract

The invention 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 formaldehyde adsorbent is prepared from eugenol, cysteine and formaldehyde. Raw materials are screened through a large number of experiments, new raw materials-eugenol and cysteine are adopted, and eugenol molecules contain a phenolic hydroxyl group, an allyl group and a methoxyl group; a cysteine molecule contains an amino group, a carboxyl group and a sulfydryl group (-SH). The groups increase the reaction activity of the curing agent, especially sulfydryl, so that the curing speed of the curing agent in a low-temperature environment can be greatly increased. Compared with a common cardanol phenolic aldehyde amine curing agent, the phenolic aldehyde amine curing agent synthesized from eugenol and cysteine has the advantages that the low-temperature curing speed is higher, the good heat deformation resistance is achieved, and the good technical effect is achieved.

Description

Technical Field

[0001] The invention relates to an epoxy curing agent, in particular to a novel low-temperature curing epoxy curing agent and a preparation method thereof, and belongs to the technical field of polymer materials. Background Art

[0002] In the application of epoxy resin, curing agent is an important component. At present, the commonly used modified amine curing agents on the market are mainly polyamide and phenalkamine products. Among them, polyamide curing agents can be cured with epoxy resin to form a film at room temperature, but their low-temperature curing performance is poor. When the temperature is lower than 15°C, they cannot be constructed normally, and the drying time is long; compared with polyamide curing agents, phenalkamine curing agents can cure epoxy resin at a lower temperature and the curing speed is fast. The development and application of bio-based raw materials is currently a hot research direction in the world. Eugenol, as a green, environmentally friendly, resource-rich renewable raw material, is used to replace or partially replace phenol. It is used in the production of phenalkamine epoxy curing agents, which will also be a research direction for epoxy curing agents.

[0003] Mercaptan has been used as a commercial epoxy curing agent for more than 40 years. One of the main features of mercaptan is that it can achieve rapid curing at room temperature, generally in about 5 minutes. Another feature is low temperature curing. With DMP as an accelerator, it can quickly cure epoxy resin at -20°C. Its main limitations are that it has a bad odor, is prone to skinning, and has a low heat deformation temperature.

[0004] Therefore, based on the prior art, the present invention uses a new raw material, eugenol and cysteine, through a large number of experimental screenings, to synthesize a new low-temperature curing epoxy curing agent. Due to the presence of thiol (-SH) in its molecular structure, the low-temperature curing performance of eugenol phenol amine is significantly improved compared with the general phenol amine curing agent; and due to the presence of benzene ring in its molecular structure, compared with the thiol curing agent, its heat deformation temperature is high and the odor is also reduced. The shortcomings of the prior art are overcome. Summary of the invention

[0005] Purpose of the invention: The purpose of the present invention is to address the deficiencies of the prior art, screen the raw materials through a large number of experiments, and use new raw materials - eugenol and cysteine ​​to synthesize eugenol phenol amine, which has higher reactivity at low temperatures, greatly improves the curing speed, and can also quickly cure into a film at low temperatures (-15°C to 0°C). Moreover, compared with the mercaptan curing agent, the introduction of benzene rings in its molecules has greatly improved the heat deformation temperature, achieving very good technical effects.

[0006] Technical solution, in order to achieve the above purpose, the technical solution adopted by the present invention is:

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

[0008]

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

[0010] (1) Deionized water and cysteine ​​are added to a reaction bottle in sequence, heated and stirred, and the temperature is controlled at 50±5°C to dissolve cysteine ​​in water;

[0011] (2) Add eugenol and stir to make it evenly dispersed. Then add formaldehyde solution dropwise, controlling the dropping speed so that the temperature does not exceed 80°C.

[0012] (3) After the formaldehyde is added, the temperature is maintained at 80±5°C and the reaction time is 2-3 hours. After the reaction is completed, the water in the system is removed by vacuum to obtain a 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-mentioned method for preparing a low-temperature curing epoxy curing agent, the molar ratio of eugenol, cysteine ​​and formaldehyde is 1:1-3:1-3.

[0015] As a particularly preferred embodiment, in the above-mentioned 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] The invention obtains the best raw material ratio composition through a large number of experimental screenings, uses raw materials eugenol, formaldehyde and cysteine ​​to synthesize the eugenol phenalkamine curing agent through a Mannich condensation reaction, introduces a thiol (-SH) group into the eugenol phenalkamine molecule to improve its reaction activity, greatly accelerates the speed of curing epoxy resin at low temperature, and the heat deformation temperature is greatly improved compared with the mercaptan curing agent, thereby achieving very good technical effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is the synthetic reaction formula of the present invention. DETAILED DESCRIPTION

[0019] Example 1

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

[0021] 2. A method for preparing a curing agent, comprising the following steps:

[0022] (1) Cysteine ​​and deionized water were added to a reaction flask in sequence, and the temperature was raised to 50°C with stirring to dissolve all the cysteine.

[0023] (2) Add eugenol and stir evenly. Then add 37% formaldehyde solution dropwise. Control the dripping speed and finish dripping within half an hour. Keep the temperature below 80°C.

[0024] (3) After the addition of formaldehyde is complete, the temperature is maintained at 80±5°C and the reaction is carried out for 2 hours.

[0025] (4) After the reaction is completed, the water in the system is removed by vacuum, and the system is cooled and weighed to obtain 298 g of a 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: 164 g of eugenol, 800 g of deionized water, 242 g of cysteine, and 162 g of 37% formaldehyde solution.

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

[0029] (1) Cysteine ​​and deionized water were added to a reaction flask in sequence, and the temperature was raised to 50°C with stirring to dissolve all the cysteine.

[0030] (2) Add eugenol and stir evenly. Then add 37% formaldehyde solution dropwise. Control the dripping speed and complete the dripping within one hour. Keep the temperature below 80°C.

[0031] (3) After the addition of formaldehyde is complete, the temperature is maintained at 80±5°C and the reaction is carried out for 3 hours.

[0032] (4) After the reaction is completed, the water in the system is removed by vacuum, and the system is cooled and weighed to obtain 435 g of a 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: 164 g of eugenol, 400 g of deionized water, 121 g of cysteine, and 30 g of paraformaldehyde.

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

[0036] (1) Cysteine ​​and deionized water were added to a reaction flask in sequence, and the temperature was raised to 50°C with stirring to dissolve all the cysteine.

[0037] (2) Add eugenol and stir evenly. Then add paraformaldehyde particles in batches so that the temperature does not exceed 80°C.

[0038] (3) After the formaldehyde is added, the temperature is maintained at 80±5°C and the reaction is kept warm for 3 hours.

[0039] (4) After the reaction is completed, the water in the system is removed by vacuum, and the system is cooled and weighed to obtain 297 g of a novel low-temperature curing epoxy curing agent.

[0040] Comparative Example 1

[0041] 1. Replace cysteine ​​with conventional polyethylene polyamine-diethylenetriamine to synthesize conventional eugenol phenalkamine curing agent for comparison of the low temperature curing performance of the product. The raw materials include: 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 in a reaction flask in sequence, and start heating and stirring.

[0044] (2) When the temperature reaches 50°C, start dripping 37% formaldehyde solution. Control the dripping speed and complete the dripping within half an hour so that the temperature does not exceed 80°C.

[0045] (3) After the addition of formaldehyde is complete, the temperature is maintained at 80±5°C and the reaction is carried out for 3 hours.

[0046] (4) After the reaction is completed, the water in the system is removed by vacuum, and the system is cooled and weighed to obtain 280 g of eugenol phenalkamine.

[0047] Comparative Example 2

[0048] 1. Replace eugenol with phenol to synthesize phenalkamine curing agent to compare the low-temperature curing performance of the product. The raw materials include: 94g phenol, 121g cysteine, and 81g 37% formaldehyde solution.

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

[0050] (1) Cysteine ​​and deionized water were added to a reaction flask in sequence, and the temperature was raised to 50°C with stirring to dissolve all the cysteine.

[0051] (2) Add phenol and stir evenly. Then add 37% formaldehyde solution dropwise within half an hour and keep the temperature below 80°C.

[0052] (3) After the addition of formaldehyde is complete, the temperature is maintained at 80±5°C and the reaction is carried out for 3 hours.

[0053] (4) After the reaction was completed, the water in the system was removed by vacuum, and the system was cooled and weighed to obtain 227 g of phenalkamine curing agent.

[0054] Comparative Example 3

[0055] 1. Replace eugenol with cardanol and cysteine ​​with diethylenetriamine to synthesize cardanol phenol amine curing agent for comparing the low temperature curing performance of the product. The raw materials include: 304g cardanol, 103g diethylenetriamine, and 81g 37% formaldehyde solution.

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

[0057] (1) Add cardanol and diethylenetriamine in a reaction bottle in sequence, and start heating and stirring.

[0058] (2) When the temperature reaches 50°C, start dripping 37% formaldehyde solution. Control the dripping speed and complete the dripping within half an hour so that the temperature does not exceed 80°C.

[0059] (3) After the addition of formaldehyde is complete, the temperature is maintained at 80±5°C and the reaction is carried out for 3 hours.

[0060] (4) After the reaction is completed, the water in the system is removed by vacuum, and the system is cooled and weighed to obtain 420 g of cardanol phenolaldehyde amine.

[0061] Example 4 Surface Dry Temperature Test

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

[0063] Table 1

[0064] Curing agent / temperature 0℃ -5℃ -10℃ -15℃ -20℃ Comparative Example 1 65min 125min Not dry yet Not dry yet Not dry yet Comparative Example 2 33min 42min 68min 152min Not dry yet Comparative Example 3 45min 113min 189min Not dry yet Not dry yet Example 1 24min 33min 55min 88min Not dry yet Example 2 22min 28min 48min 74min Not dry yet Example 3 23min 33min 55min 86min Not dry yet QE-340M 16min 18min 23min 31min 45min .

[0065] Example 5 Heat Deformation Temperature Test

[0066] Epoxy resin (828 produced by Jiangsu Sanmu Chemical Co., Ltd.) was mixed with various epoxy curing agents prepared above and purchased polythiol curing agent (Toray QE-340M), and curing accelerator (DMP-30) was added appropriately. Epoxy resin, curing agent, and curing accelerator were mixed in a mass ratio of 10:8:1. They were poured into the mold and made into rectangular strips with a length of 120 mm, a width of 10 mm, and a height of 12 mm after being completely cured. The heat deformation temperature was tested according to the ISO75 national standard, and the results are shown in Table 2 below.

[0067] Table 2

[0068]

[0069] Shown by the above experimental result, low temperature curing agent of the present invention is faster than conventional phenol amine curing agent and cardanol phenol amine curing agent in the same low temperature, and can cure epoxy resin at a lower temperature. Although, compared to polythiol curing agent, its low temperature curing speed is still relatively slow, but its heat distortion temperature is greatly improved compared to polythiol curing agent, has a wider range of application, and has achieved excellent technical effect. Through comparison, embodiment 2 of the present invention has better comprehensive performance in low temperature curing and heat distortion temperature.

[0070] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A novel low temperature curing epoxy curing agent, characterized in that: The curing agent has the structure shown below:

2. The method for preparing the novel low temperature curing epoxy curing agent according to claim 1, characterized in that: The following steps are involved: (1) Deionized water and cysteine ​​are added to a reaction bottle in sequence, heated and stirred, and the temperature is controlled at 50±5°C to dissolve cysteine ​​in water; (2) adding eugenol, stirring to make it evenly dispersed, and then adding formaldehyde solution dropwise, controlling the dropping speed so that the temperature does not exceed 80° C.; (3) After the formaldehyde is added, the temperature is maintained at 80±5° C. and the reaction time is 2-3 hours. After the reaction is completed, the water in the system is removed by vacuum to obtain a novel low-temperature curing epoxy curing agent.

3. The preparation method according to claim 2, characterized in that: The formaldehyde is 37% formaldehyde solution or solid paraformaldehyde.

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

2.

6. Use of the epoxy curing agent according to claim 1 in curing epoxy resin.

7. A novel low temperature curing epoxy curing agent, characterized in that: It includes the following raw materials: Eugenol 164g, deionized water 800g, cysteine ​​242g, 37% formaldehyde solution 162g.

8. The method for preparing the novel low temperature curing epoxy curing agent according to claim 7, characterized in that: The following steps are involved: (1) Add cysteine ​​and deionized water to a reaction bottle in sequence, turn on heating and stirring, and raise the temperature to 50° C. to dissolve all the cysteine; (2) Add eugenol and stir evenly. Then add 37% formaldehyde solution dropwise, controlling the dropping speed so that the temperature does not exceed 80°C; (3) After the addition of formaldehyde is complete, the temperature is maintained at 80±5°C and the reaction is carried out for 3 hours. (4) After the reaction is completed, the water in the system is removed by vacuuming and the system is cooled to obtain a novel low-temperature curing epoxy curing agent.

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