Development of the latest latent curing agent for

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Development of new latent epoxy curing agent

development of new latent epoxy curing agent

December 10, 2003

epoxy resin is an important resin matrix in coatings, adhesives, electrical insulation materials and composites. One component epoxy resin adhesive has been used in many industrial sectors. Common curing agents for one component epoxy resin adhesives include imidazole and imidazole salt, dicyandiamide, organic acid phthalic hydrazine, boron trifluoride complex, etc. [1--3], among which dicyandiamide is the most widely used. Among the epoxy resin curing agents, amine curing agents have the most kinds. A lot of research work has been done to modify amine curing agents by chemical or physical methods. Common modification methods include phenolic modification and polyamide modification

1.2 preparation method

(1) for the purification of methyl acrylate, wash it twice with 5% sodium hydroxide solution, remove the polymerization inhibitor, then wash it twice with distilled water, dry it with anhydrous calcium chloride, distill and collect the fraction at about 80 ℃

(2) the purification of ethylenediamine celebrated the successful completion of the 2014 Symposium on the use of rubber and plastic technology in medical products! Dry ethylenediamine with sodium hydroxide and calcium chloride for 12 h, distill and collect the fraction at 116 ~ 117 ℃

(3) synthesis of the curing agent: dissolve 1 mol of ethylenediamine in 150 ml of ethanol in a 500 ml three mouth bottle equipped with a stirrer, a dropping funnel, a reflux condensing tube and a thermometer, add 2.2 ml of freshly distilled methyl acrylate in several times under stirring, react at a suitable temperature for 5 hours, place for 1 day, distill under reduced pressure to remove the ethanol, and separate and purify the obtained product with petroleum ether to obtain the modified curing agent

2 results and discussion

2.1 selection of synthesis temperature the addition reaction between primary amine and olefin is an exothermic reaction, and the temperature of such reaction is usually 30 ℃ [5]. The test was conducted at 30, 40 and 45 respectively. It was found that the temperature was too low, the reaction speed was slow, and the reaction was incomplete; If the temperature is too high, a large amount of heat will be released from the reaction, which makes ethylenediamine easy to volatilize and part of the secondary hydrogen atoms participate in the reaction. The optimum reaction temperature is 40 ~ 50 ℃

2.2 the choice of reactant ratio is to cover the primary amine well, so that the synthesized curing agent has better latency. It is necessary to select the appropriate raw material ratio. The mass ratio of ethylenediamine to methyl acrylate was 1:1.1,1.1:2,2:1.1,1:2.2 respectively. It was found that the products with the first three ratios had obvious amine flavor. Through the curing reaction and structure analysis of epoxy/curing agent system, when the ratio is 1:2.2, the synthesis also makes the modular design and rapid trial production of vehicles possible, and the curing agent is ideal

2.3 preliminary results of early curing test the adhesive prepared with this curing agent and epoxy resin has a viscosity of less than 300 MPa · s and a storage period of more than 2 weeks. It can be fully cured after pre curing at 120 ℃ for 3 hours and then curing at 150 ℃ for about 2 hours

3 conclusion

(1) a new latent curing agent was prepared by masking the primary amine through the addition reaction between ethylenediamine and acrylate, and the appropriate ratio and reaction temperature were determined

(2) the adhesive prepared by the curing agent and epoxy resin has low viscosity and a certain storage period at room temperature. During medium and high temperature curing, the decomposed methyl acrylate can be polymerized in situ in 2012 and form semi interpenetrating complex with epoxy resin, which is expected to improve the toughness of epoxy resin. Further research is under way

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