As the requirements for environmental protection become more stringent, waterborne epoxy systems that do not contain volatile organic solvents (VOC) or low volatile organic solvents and do not contain harmful air pollutants (NHAP) have become the focus of current research. Among the epoxy resin curing agents, there are many types of amine curing agents, large dosage, and wide use, but the general amine curing agents evaporate quickly at room temperature, have high toxicity, fast curing speed, strict ratio requirements, and even absorb Carbon dioxide reduces the curing effect. The waterborne epoxy curing agent is obtained by modifying the traditional amine curing agent. It overcomes the shortcomings of the unmodified amine curing agent, does not affect the physical and chemical properties of the coating film, and uses water as a solvent, VOC The content meets environmental protection requirements. The research progress of waterborne epoxy resin curing agent is introduced below.
Ⅰtype waterborne epoxy curing agent
Type I water-based epoxy curing agent has made great progress since its development. The type I water-based epoxy curing agent that was successfully developed early was Casmide 360 of Thomas Swan Company and its modified product Casmide 362. It is mainly a modified fatty amine water-soluble curing agent that has undergone partial salt formation, such as Becker et al.  uses a low molecular weight epoxy resin to react with a polyethylene polyamine to form an amine-terminated epoxy-amine adduct, and then reuse It is blocked with a single epoxy compound, and part of the secondary amine is neutralized with acetic acid to adjust the HLB value of the curing agent and reduce the reactivity of the curing agent, extending the pot life. Low-molecular-weight liquid epoxy resin (E-51) is reacted with polyethylene glycol to form terminal epoxy compounds, and then with triethylenetetramine to form terminal amine epoxy-amine adducts, and then single epoxy The compound is capped and then neutralized with acetic acid to form a salt to prepare a type I waterborne epoxy curing agent. With the introduction of long-chain polyethylene glycol, the crosslink density is reduced and the flexibility of the coating film is improved. Because such curing agents need to rely on salt formation to reduce reaction activity and increase water solubility and stability, but excess acetic acid has a certain corrosive effect on steel, so it is not suitable for steel components.
Using epoxy resin to react with excess m-xylylenediamine to generate epoxy amine-end adducts, and then reacting with carboxyl-terminated polyether alcohol to generate amide-amines, and then end-capping to obtain Type I waterborne epoxy curing agent.
Epoxy resin curing agent
Type II waterborne epoxy curing agent
Type II waterborne epoxy curing agent refers to a type of curing agent that directly cures solid epoxy dispersions (epoxy equivalent of 500-650). Since the epoxy resin in the type II waterborne epoxy resin system has been formulated into an emulsion in advance, no waterborne epoxy curing agent is needed to emulsify the epoxy resin, so it only needs to have the function of a crosslinking agent. Due to the relatively high molecular weight of the epoxy resin used in Type II epoxy coatings and the high glass transition temperature (Tg), the low film formation temperature (MFT) of the coating film is high (it may exceed room temperature). Therefore, it is necessary to add 5% to 7% coalescing solvent to reduce Tg and MFT. The use of coalescing solvents means that it is impossible to make zero VOC coatings.
The currently used type II water-based epoxy curing agent is mainly an epoxy-amine curing agent prepared by reacting a fatty amine embedded with a hydrophilic polyoxyethylene segment and an epoxy resin, or using an embedded hydrophilic polymer A polyamide curing agent produced by the reaction of a fatty amine in an oxyethylene segment and a dimer acid. It utilizes the hydrophilicity of the polyoxyethylene segment, so that the curing agent can be stably dispersed in water, and the use of epoxy resin as a chain extender can improve the compatibility of the curing agent and epoxy resin.
Using the reaction of polyoxyethylene diglycidyl ether and bisphenol A epoxy resin to obtain epoxy resin self-dispersion, and then reacting with polyoxypropylene diamine and isophorone diamine to generate epoxy-amine curing agent. Using bisphenol A epoxy resin, polyoxyethylene diglycidyl ether and bisphenol A to obtain epoxy resin dispersion, and then reacted with polyethylene polyamine to produce terminal amine epoxy-amine adduct, and then blocked Type II waterborne epoxy curing agent is obtained.
Epoxy resin curing agent
For waterborne epoxy curing agent and waterborne epoxy resin technology, improving the compatibility of epoxy resin and curing agent, developing waterborne epoxy resin and its curing agent to replace epoxy resin containing organic volatile solvent greatly reduces the environmental impact Pollution, prolonging the application period, and achieving high performance have become research priorities in this field. Domestic researchers have developed waterborne epoxy resin curing agents with excellent performance. At present, biological resources and other clean resources that are not harmful to the environment are rarely used. my country’s abundant biological resources should be developed and researched and applied to the development and preparation of more efficient water-based epoxy curing agents as soon as possible. The future development direction is how to further reduce production costs, simplify process conditions, shorten curing time, improve mechanical properties, and expand application fields. With the continuous improvement of technology and the continuous innovation of processes, I believe that in the near future, more environmentally friendly and efficient waterborne epoxy curing agents will appear