6. Latent type
Latent curing agent refers to relatively long-term stability at room temperature after mixing with epoxy resin (epoxy resin generally requires more than 3 months to have greater practical value, and the most ideal requires more than half a year or more than 1 year ), and only needs to be exposed to heat, light, moisture and other conditions to start the curing reaction. This type of curing agent is basically a physical and chemical method to block the curing agent activity. Therefore, in some books, these varieties are also classified as latent curing agents, which can actually be called functional latent curing agents. Because the latent curing agent can be mixed with epoxy resin to make a one-liquid complex, simplifying the application procedures of epoxy resin. Its applications range from single-pack adhesives to coatings, dipping varnishes, potting compounds, powder coatings, and more. Latent curing agents have attracted increasing attention abroad, and can be said to be a key subject for research and development. New varieties of curing agents and new technologies have emerged endlessly and actively.
7. Amine curing agent
The curing effect of the primary and secondary amines on the epoxy resin is that the active hydrogen on the nitrogen atom opens the epoxy group, so that it is crosslinked and cured. Aliphatic polyamines such as ethylenediamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, diethylaminopropylamine, etc. have greater activity and can cross-link and cure epoxy resins at room temperature. While aromatic polyamines have low activity, such as m-phenylenediamine, which can only be fully cured at 150℃.
8. Anhydrides curing agent
Dibasic acids and their anhydrides such as maleic anhydride and phthalic anhydride can cure epoxy resins, but they must be baked at higher temperatures to cure completely. The acid anhydride first reacts with the hydroxyl group in the epoxy resin to form a monoester, and the carboxyl group in the monoester undergoes addition esterification with an epoxy group to form a diester.
9. Synthetic resin curing agent
The low molecular weight polyamide resin is a kind of amber-colored viscous resin formed by the reaction of linoleic acid dimer or tungoleic acid dimer with aliphatic polyamines such as ethylenediamine and diethylenetriamine.
10. Latent curing agent
This curing agent is stable under normal conditions, but when it is heated to a certain temperature, it shows its activity to cure the epoxy resin. Such as dicyandiamide, mixed with epoxy resin, is stable at room temperature. If the temperature is 145-165℃, the epoxy resin can be cured within 30 minutes. Boron trinitride ethylamine complex is also stable at room temperature, but can cure epoxy resins above 100℃.