A preparation method of an epoxy curing agent

Abstract

The present invention provides a preparation method of an epoxy curing agent. By selecting a flexible imidazole curing agent, carrying out flame retardant modification on it, and adding an active diluent to interact with it, an epoxy curing agent with rapid curing, excellent flame retardant performance, good water resistance and impact resistance is obtained.

Description

Technical Field

[0001] The present invention belongs to the technical field of curing agents, and particularly relates to a preparation method of an epoxy-based curing agent. Background Art

[0002] Epoxy resin is an oligomer. It is necessary to add a curing agent to it. After a cured product with a three-dimensional networked three-dimensional structure is formed, it will exhibit good mechanical strength and bonding ability. Therefore, the selection of the curing agent is one of the key factors determining the performance of epoxy resin. Imidazole-based curing agents such as imidazole, 2-phenylimidazole, and 2-methylimidazole are common medium and low-temperature curing agents for epoxy resins with high activity. They are used in small amounts and can cure epoxy resins in a short time at medium and low temperatures, and the cured products have good mechanical properties and resistance to heat and humidity. However, the pot life of the imidazole / epoxy single-component system is only a few days. Therefore, it is necessary to chemically modify it to reduce the reaction activity to improve the room-temperature storage period.

[0003] The commonly used imidazole-based latent curing agents have a single variety, a short pot life, and most imidazole-based curing agents are solids, with poor compatibility with epoxy resins. The goal of the present invention is to select a high-purity medium and normal-temperature latent curing agent with good compatibility with epoxy resins and a long pot life at room temperature.

[0004] The hydroxyl groups and ether bonds possessed by epoxy resin endow epoxy coatings with good adhesion, excellent chemical resistance, high bonding strength, etc. However, the disadvantages of slow curing speed and high viscosity of epoxy resin at room temperature limit the application of epoxy resin. The flammable characteristics of ordinary epoxy resin restrict its use in fields with fire prevention requirements. Therefore, improving the flame retardant performance of the epoxy resin system helps to expand the application range of epoxy resin.

[0005] At present, most of the flame retardants used for epoxy resins are additive flame retardants and do not have the inherent flame retardant characteristics; traditional flame retardant curing agents are mostly addition polymerization type curing agents. Compared with ionic catalytic polymerization type curing agents, their curing speed is slow and the curing efficiency is low. As for the modification research of imidazole-based curing agents, it mainly focuses on improving their latency and does not involve flame retardant modification, and the functions of the curing agents are single. In response to this, the present invention proposes a new method for preparing a high-performance epoxy resin system by combining the inherent flame retardant technology of epoxy resin and improving the curing to a certain extent.

[0006] Reactive diluents can not only replace and reduce the viscosity of liquid coating systems, but also have functional groups that can participate in cross-linking reactions. Therefore, they can participate in the epoxy curing process. Of course, different diluents not only affect the curing rate of resin curing, increase the cross-linking density of the resin system, but also control the properties of the resin after curing. Of course, for linear polymers, generally reducing the molecular weight is used to achieve the purpose of low viscosity, but it will also lead to a decrease in the curing speed and the properties of the resin after curing. Therefore, selecting a reactive diluent compatible with the imidazole epoxy curing system is the research focus of the present invention. Summary of the Invention

[0007] The present invention discloses a preparation method of an epoxy curing agent to solve any of the above and potential problems in the prior art. To solve the above technical problems, the preparation method of the present invention is as follows:

[0008] Resin mixing and casting: Mix epoxy resin AFG90 and epoxy reactive diluent at a mass ratio of 10:1 - 3, mechanically stir at a stirring speed of 500 - 800 r / min at 35°C for 30 min, add 10 - 15% of imidazole curing agent to the epoxy resin, and stir at 50°C for 20 min to obtain;

[0009] Among them, the imidazole curing agent is 1-trityl-1H-imidazole-4-carboxylic acid ethyl ester.

[0010] Among them, the reactive diluent is 4-vinylbenzyl glycidyl ether.

[0011] Among them, the imidazole curing agent also includes a flame retardant modification process: Dissolve 8 - 10 parts of flame retardant modifier, 5 - 8 parts of preheated imidazole curing agent and 4 - 6 parts of triethanolamine in 60 - 80 parts of dichloromethane, and dropwise add 2 - 4 parts of carbon tetrachloride into the bottle. After the dropping is completed in 2 h, continue to react at room temperature for 12 h to obtain the flame retardant modified curing agent.

[0012] The preheating treatment of the curing agent includes: heating the oil bath to 60°C, stirring at a stirring speed of 200 r / min for 30 min, and setting aside.

[0013] Among them, the flame retardant modifier is diethyl o-phenylenediaminomethylphosphonate.

[0014] The advantages and beneficial effects of the present invention are:

[0015] 1. The present invention provides a preparation method of an epoxy curing agent. By selecting a flexible imidazole curing agent, performing flame retardant modification on it, and interacting with a reactive diluent, an epoxy curing agent with fast curing, excellent flame retardant performance, good water resistance and impact resistance is obtained.

[0016] 2. The present invention selects ethyl 1-trityl-1H-imidazole-4-carboxylate as the curing agent, and pre-heats it to reduce the viscosity. Compared with the conventional imidazole-based curing agents that need to be modified, this curing agent does not need to be modified. Ethyl 1-trityl-1H-imidazole-4-carboxylate not only has the characteristics of imidazole-based curing agents, but also has more stable flexible chain segments, has good compatibility with epoxy resins, can toughen to a certain extent, increase the tensile strength, and improve the tensile strength of the system, and enhance the impact resistance; moreover, the carboxylic acid group of ethyl 1-trityl-1H-imidazole-4-carboxylate can undergo an amidation reaction with the amine group in the epoxy resin to adjust the rate and temperature range of the curing reaction, so as to better meet the curing requirements under different application environments.

[0017] 3. Moreover, the ester structure introduced into the structure of ethyl 1-trityl-1H-imidazole-4-carboxylate reduces the water absorption rate of the cured product participating in the curing, thereby further improving the water resistance of the epoxy resin-based material, and prolonging the service life of the material.

[0018] 4. 4-Vinylbenzyl glycidyl ether itself is an active diluent with good compatibility with resins, which is a simple linear epoxy resin. The ether bond in 4-vinylbenzyl glycidyl ether is grafted onto the imidazole-based curing agent molecule. 4-Vinylbenzyl glycidyl ether itself is a flexible chain segment. Grafting it onto the imidazole curing agent can destroy its original structure, increase its compatibility with epoxy resins, consume the active hydrogen of the imidazole curing agent, and increase the steric hindrance of the tertiary amine nitrogen atom in the imidazole ring, effectively improving the latency of the imidazole-based curing agent.

[0019] 5. By grafting the ether bond in 4-vinylbenzyl glycidyl ether onto the imidazole-based curing agent molecule, the structure of the curing agent can be effectively changed, and the compatibility with epoxy resins can be increased. This grafting reaction not only consumes the active hydrogen of the curing agent, but also increases the steric hindrance of the tertiary amine nitrogen atom in the imidazole ring, thereby improving the latency of the curing agent, that is, delaying the activation rate of the curing agent, which helps to control the curing process, improve the use efficiency of the curing agent and the performance of the epoxy resin system.

[0020] 6. Diethyl (phthaloyliminomethyl) phosphate belongs to phosphate flame retardants. Its molecular structure contains a P-C structure. Such flame retardants have good stability, water resistance, chemical corrosion resistance and other characteristics. The phosphorus-containing group in diethyl (phthaloyliminomethyl) phosphate has an electron-withdrawing effect and a steric hindrance effect, which inhibits the reactivity of the nitrogen atom at the 3-position on the imidazole ring in ethyl 1-trityl-1H-imidazole-4-carboxylate, avoiding the violent heat release during the mixing process of the curing agent and epoxy resin, and effectively preventing the shrinkage and fracture of the cured product caused by the violent reaction heat release. The phosphorus-containing group in diethyl (phthaloyliminomethyl) phosphate decomposes into phosphorus-containing derivatives after heating, promoting the carbonization of the resin matrix to form a dense, stable and continuous carbon layer, playing a covering effect, thereby enhancing the flame retardant performance; and the phosphorus-containing group and imidazole group in diethyl (phthaloyliminomethyl) phosphate act together to exert the covering effect, free radical quenching effect and non-combustible gas dilution effect, preventing the further combustion of the polymer matrix and achieving the characteristic of intrinsic flame retardancy, significantly improving the flame retardant performance of the epoxy resin system.

[0021] 7. In addition to increasing the flame retardant performance of the matrix, due to the strong epoxy-opening activity of the imidazole curing agent, it can initiate the polymerization of the epoxy system at room temperature, greatly limiting its application. Therefore, by carrying out a nucleophilic substitution reaction between diethyl (phthaloyliminomethyl) phosphate and it, the heat resistance and chemical resistance of the curing agent and the system can be improved, making it have better stability and performance under complex environmental conditions. And diethyl (phthaloyliminomethyl) phosphate has more active sites. During the mixing process with ethyl 1-trityl-1H-imidazole-4-carboxylate, the modified curing agent has good water dispersibility. When used in combination with waterborne epoxy resin, it can have multiple reaction types. Therefore, the formed curing agent has better adhesion, high gloss, hot water resistance and hardness than ordinary curing agents.

[0022] 8. Because after the nucleophilic substitution reaction between diethyl (phthaloyliminomethyl) phosphate and the imidazole curing agent, the activity of the curing agent may change, resulting in a change in the curing rate. And this process will lead to an increase in the brittleness of the epoxy group, thereby reducing the impact strength and fracture toughness of the system. In addition to the benefits of conventional active diluents, by grafting the ether bond in 4-vinylbenzyl glycidyl ether onto the imidazole curing agent molecule, the structure of the curing agent can be changed. 4-vinylbenzyl glycidyl ether has a higher molecular weight and a hyperbranched structure compared to conventional glycidyl esters, and can more effectively increase its compatibility with epoxy resin, reducing the competitive reaction between the curing agent and epoxy groups, thereby stabilizing the curing rate and curing process. 4-vinylbenzyl glycidyl ether, as a flexible chain segment, can form a soft elastic phase after curing, increasing the toughness of the epoxy resin system, inhibiting the increase in brittleness, and improving the impact strength and fracture toughness of the product. Detailed implementation mode

[0023] The present invention will be further described in detail below in conjunction with embodiments.

[0024] Example 1

[0025] Modified flame retardant curing agent: 9 parts of diethyl phthalimidomethylphosphonate, 6 parts heated to 60 °C, 1-trityl-1H-imidazole-4-carboxylic acid ethyl ester stirred for 30 min at a stirring speed of 200 r / min, and 5 parts of triethanolamine were dissolved in 70 parts of dichloromethane, and 3 parts of carbon tetrachloride were added dropwise into the bottle. After the addition was completed in 2 h, the reaction was continued at room temperature for 12 h to obtain the flame retardant modified curing agent.

[0026] Resin mixing and casting: Epoxy resin AFG90 and 4-vinylbenzyl glycidyl ether were mechanically stirred at a mass ratio of 10:2 and a stirring speed of 500 - 800 r / min at 35 °C for 30 min. 12% of the modified flame retardant curing agent was added to the epoxy resin and stirred at 50 °C for 20 min to obtain the product.

[0027] Example 2

[0028] Modified flame retardant curing agent: 8 - 10 parts of diethyl phthalimidomethylphosphonate, 5 - 8 parts heated to 60 °C, 1-trityl-1H-imidazole-4-carboxylic acid ethyl ester stirred for 30 min at a stirring speed of 200 r / min, and 4 - 6 parts of triethanolamine were dissolved in 60 - 80 parts of dichloromethane, and 2 - 4 parts of carbon tetrachloride were added dropwise into the bottle. After the addition was completed in 2 h, the reaction was continued at room temperature for 12 h to obtain the flame retardant modified curing agent.

[0029] Resin mixing and casting: Epoxy resin AFG90 and 4-vinylbenzyl glycidyl ether were mechanically stirred at a mass ratio of 10:1 - 3 and a stirring speed of 500 - 800 r / min at 35 °C for 30 min. 10 - 15% of the modified flame retardant curing agent was added to the epoxy resin and stirred at 50 °C for 20 min to obtain the product.

[0030] Example 3

[0031] Modified flame retardant curing agent: 8 - 10 parts of diethyl phthalimidomethylphosphonate, 5 - 8 parts heated to 60 °C, 1-trityl-1H-imidazole-4-carboxylic acid ethyl ester stirred for 30 min at a stirring speed of 200 r / min, and 4 - 6 parts of triethanolamine were dissolved in 60 - 80 parts of dichloromethane, and 2 - 4 parts of carbon tetrachloride were added dropwise into the bottle. After the addition was completed in 2 h, the reaction was continued at room temperature for 12 h to obtain the flame retardant modified curing agent.

[0032] Resin mixing and casting: Epoxy resin AFG90 and 4-vinylbenzyl glycidyl ether are mixed at a mass ratio of 10:1 - 3, mechanically stirred at 35°C with a stirring speed of 500 - 800 r / min for 30 min. Then, 10 - 15% of the modified flame retardant curing agent is added to the epoxy resin, and stirred at 50°C for 20 min to obtain the product.

[0033] Comparative Example 1

[0034] The difference between this comparative example and Example 1 is that ethyl 1-trityl-1H-imidazole-4-carboxylate in this comparative example is 2-phenylimidazole, and the rest is the same as in Example 1.

[0035] Comparative Example 2

[0036] The difference between this comparative example and Example 1 lies in the different addition amount of ethyl 1-trityl-1H-imidazole-4-carboxylate in this comparative example. The specific process of the modified flame retardant curing agent is as follows: 9 parts of diethyl (phthalimidomethyl)phosphonate, 12 parts of ethyl 1-trityl-1H-imidazole-4-carboxylate heated to 60°C and stirred at a stirring speed of 200 r / min for 30 min, and 5 parts of triethanolamine are dissolved in 70 parts of dichloromethane. Then, 3 parts of carbon tetrachloride are added dropwise into the bottle. After 2 h of dropping, the reaction continues at room temperature for 12 h to obtain the flame retardant modified curing agent; the rest is the same as in Example 1.

[0037] Comparative Example 3

[0038] The difference between this comparative example and Example 1 lies in the different addition amount of ethyl 1-trityl-1H-imidazole-4-carboxylate in this comparative example. The specific process of the modified flame retardant curing agent is as follows: 9 parts of diethyl (phthalimidomethyl)phosphonate, 3 parts of ethyl 1-trityl-1H-imidazole-4-carboxylate heated to 60°C and stirred at a stirring speed of 200 r / min for 30 min, and 5 parts of triethanolamine are dissolved in 70 parts of dichloromethane. Then, 3 parts of carbon tetrachloride are added dropwise into the bottle. After 2 h of dropping, the reaction continues at room temperature for 12 h to obtain the flame retardant modified curing agent; the rest is the same as in Example 1.

[0039] Comparative Example 4

[0040] The difference between this comparative example and Example 1 is that diethyl (phthalimidomethyl)phosphonate in this comparative example is triphenyl phosphate, and the rest is the same as in Example 1.

[0041] Comparative Example 5

[0042] The difference between this comparative example and Example 1 lies in the different addition amounts of diethyl phthalimidomethylphosphonate. Modified flame-retardant curing agent: Dissolve 15 parts of diethyl phthalimidomethylphosphonate, 6 parts of ethyl 1-trityl-1H-imidazole-4-carboxylate heated to 60°C and stirred at a stirring speed of 200 r / min for 30 min, and 5 parts of triethanolamine in 70 parts of dichloromethane. Then, add 3 parts of carbon tetrachloride dropwise into the bottle. After the dropping is completed in 2 h, continue the reaction at room temperature for 12 h to obtain the flame-retardant modified curing agent; the rest is the same as in Example 1.

[0043] Comparative Example 6

[0044] The difference between this comparative example and Example 1 lies in the different addition amounts of diethyl phthalimidomethylphosphonate. Modified flame-retardant curing agent: Dissolve 5 parts of diethyl phthalimidomethylphosphonate, 6 parts of ethyl 1-trityl-1H-imidazole-4-carboxylate heated to 60°C and stirred at a stirring speed of 200 r / min for 30 min, and 5 parts of triethanolamine in 70 parts of dichloromethane. Then, add 3 parts of carbon tetrachloride dropwise into the bottle. After the dropping is completed in 2 h, continue the reaction at room temperature for 12 h to obtain the flame-retardant modified curing agent; the rest is the same as in Example 1.

[0045] Comparative Example 7

[0046] The difference between this comparative example and Example 1 is that 4-vinylbenzyl glycidyl ether in this comparative example is n-butyl glycidyl ether, and the rest is the same as in Example 1.

[0047] Comparative Example 8

[0048] The difference between this comparative example and Example 1 lies in the different addition amounts of 4-vinylbenzyl glycidyl ether. The specific resin mixing and casting is as follows: Mix epoxy resin AFG90 and 4-vinylbenzyl glycidyl ether according to a mass ratio of 10:6, and mechanically stir at a stirring speed of 500 - 800 r / min at 35°C for 30 min. Then, add 12% of the modified flame-retardant curing agent to the epoxy resin and stir at 50°C for 20 min to obtain it; the rest is the same as in Example 1.

[0049] Comparative Example 9

[0050] The difference between this comparative example and Example 1 lies in the different addition amounts of 4-vinylbenzyl glycidyl ether. The specific resin mixing and casting is as follows: Mix epoxy resin AFG90 and 4-vinylbenzyl glycidyl ether according to a mass ratio of 10:0.5, and mechanically stir at a stirring speed of 500 - 800 r / min at 35°C for 30 min. Then, add 12% of the modified flame-retardant curing agent to the epoxy resin and stir at 50°C for 20 min to obtain it; the rest is the same as in Example 1.

[0051] Test 1: Performance Test

[0052] The degassed epoxy resin curing agents prepared in Examples 1-3 and Comparative Examples 1-9 were sprayed on the surface of a steel plate and dried at 70 °C for 45 minutes, and then cured at room temperature for 7 days before testing the film properties (the film thickness was 55-60 µm).

[0053] Test methods and standards: Hardness test standard GB / T 6739-2006; Adhesion test standard GB / T 9286—1998; GB / T 1731-2020; Salt spray resistance, GB / T 1771-2007; Impact strength test standard GB / T 1732—1993; Tensile strength standard GB / T 1040.2-2006; The test results are shown in Table 1.

[0054] The test results of Examples 1-3 and Comparative Examples 1-9 are shown in Table 1 below:

[0055] Table 1 Performance test results

[0056] Curing agent Hardness Adhesion (grade) Salt spray resistance (h) <![CDATA[Impact strength (kJ / m 2 )]]> Tensile strength (MPa) Example 1 8H Grade 3 1200h 36.7 238 Example 2 7H Grade 3 1100h 35.6 219 Example 3 7H Grade 3 1100h 35.4 227 Comparative example 1 2H Grade 0 600h 18.9 133 Comparative example 2 6H Grade 2 900h 29.8 211 Comparative example 3 4H Grade 1 700h 23.5 159 Comparative example 4 1H Grade 0 500h 19.4 148 Comparative example 5 5H Grade 1 1000h 28.6 192 Comparative example 6 4H Grade 0 800h 26.2 174 Comparative example 7 1H Grade 0 600h 18.7 150 Comparative example 8 5H Grade 2 900h 31.5 187 Comparative example 9 3H Grade 1 600h 25.3 172

Claims

1. A method for preparing an epoxy curing agent, characterized in that: The production process specifically comprises the following steps: Resin mixing and pouring: Mix epoxy resin AFG90 and epoxy reactive diluent in a mass ratio of 10:1-3, stir mechanically at 35°C at a stirring speed of 500-800r / min for 30 minutes, add 10-15% imidazole curing agent to the epoxy resin, stir at 50°C for 20 minutes, and obtain; The imidazole curing agent includes a flame retardant modification process: 8-10 parts of the flame retardant modifier, 5-8 parts of preheated 1-trityl-1H-imidazole-4-carboxylic acid ethyl ester and 4-6 parts of triethanolamine are dissolved in 60-80 parts of dichloromethane, and 2-4 parts of carbon tetrachloride are added dropwise into the bottle. After the addition is completed for 2 hours, the reaction is continued at room temperature for 12 hours to obtain a flame retardant modified curing agent; Wherein, the active diluent is 4-vinylbenzyl glycidyl ether; Wherein, the flame retardant modifier is diethyl phthalimide methyl phosphate.

2. The method for preparing an epoxy curing agent according to claim 1, characterized in that: The preheating treatment of the curing agent includes: heating the oil bath to 60° C., stirring at a stirring speed of 200 r / min for 30 minutes, and setting aside.