Common types of epoxy resin curing agent and its curing mechanism
This article briefly summarizes the common types of epoxy resin curing agent and its curing mechanism.
1, alkaline class curing agent WTF. including aliphatic diamine and polyamine, aromatic polyamine, other nitrogenous compounds and modified aliphatic amine. The curing effect of primary and secondary amines on epoxy resin is to open the epoxy group by the active hydrogen on the nitrogen atom, and make it cross-linked curing. Aliphatic polyamines such as ethylenediamine, hexanediamine, diethylenetriamine, triethylenetetetramine, diethylaminopropylamine, etc. are more active and can make the epoxy resin cross-linked and cured at room temperature; while aromatic polyamines are less active, such as m-phenylenediamine, which can be cured at 150℃.
2、Acidic type curing agent. Including organic acids, acid anhydride, and boron trifluoride and its complexes. Dibasic acid and its anhydride such as maleic anhydride, phthalic anhydride can cure epoxy resin, but must be baked at a higher temperature to cure completely. The anhydride firstly reacts with the hydroxyl group in the epoxy resin to generate monoester, and the carboxyl group in the monoester and the epoxy group undergoes addition and esterification to make double ester.
3、Additive molding curing agent. This type of curing agent and epoxy addition reaction constitutes a part of the curing product chain segment, and through the gradual polymerization reaction so that the linear molecules cross-linked into the body structure molecules, this type of curing agent is also known as melon type curing agent.
4、Catalytic curing agent. This type of curing agent only on the epoxy resin initiation, open the epoxy group, the catalytic epoxy resin itself polymerization into a network structure, the generation of ether bonds as the main structure of the homopolymer.
5, apparent in the type of curing agent for the general use of curing agent, can be divided into addition polymerization and catalytic type. Addition polymerization type that opens the ring of epoxy group for addition polymerization reaction, the curing agent itself to participate in the three-dimensional network structure. This type of curing agent, such as adding too little, the curing product connected to the epoxy group at the end of the reaction. Therefore, for this type of curing agent, there is a suitable amount; and catalytic curing agent is a cationic way, or anionic way to make epoxy group ring addition polymerization, curing agent does not participate in the mesh structure, so there is no equivalent reaction of the appropriate amount. However, increasing the dosage will make the curing speed faster. In the apparent type curing agent, dicyandiamide, adipic acid dihydrazide such varieties, at room temperature is not dissolved in the epoxy resin, and at high temperatures after dissolution began to cure reaction, and therefore also presents a latent state, so it can be called a functional latent curing agent.
6, latent curing agent refers to the epoxy resin mixed with the relatively long-term stability at room temperature conditions. Generally require more than 3 months to have greater practical value, the ideal requires half a year or more than 1 year. And only need to be exposed to heat, light, moisture and other conditions, it begins to cure reaction. This type of curing agent is basically a physical and chemical method to close the curing agent activity, these varieties are called latent curing agent, in fact, can be called functional latent curing agent. Such as dicyandiamide and epoxy resin mixed together, at room temperature is stable. If at 145-165 ℃, the epoxy resin can be cured in 30 minutes; boron triazide ethylamine complex is also stable at room temperature, above 100 ℃ when the epoxy resin can be cured.
Latent curing agent can be mixed with epoxy resin to make a liquid type compound, simplify the application of epoxy resin products, its application range from a single package adhesive to coatings, impregnating paint, potting compounds, powder coatings and other aspects of development.