Epoxy Resin Hardener Classification
The curing agent of epoxy resin has the chemical reaction with epoxy resin to form a reticulated stereopolymer, which envelops the composite material in the reticulate. A solid additive makes linear resins tough, including many types. Epoxy floor is mostly used for underground garage floor, which is cheap and practical.
Alkaline curing agent WTF: including aliphatic diamines and polyamines, aromatic polyamines, other nitrogen-containing compounds and modified aliphatic amines.
Acidic curing agents include organic acids, anhydrides, boron trifluoride and their complexes.
Addition molding type:
Additive type curing agent: This kind of curing agent reacts with epoxy group to form part of the chain of curing product, and crosslinks linear molecules into structural molecules through step-by-step polymerization. This kind of curing agent is also called melon curing agent.
Catalytic curing agent: This kind of curing agent only has the reaction with the epoxy resin. After opening the epoxy group, it catalyzes the epoxy resin itself to polymerize into a network structure, forming a homopolymer with ether bond as the main structure.
The apparent curing agent is a common curing agent, which can be divided into additive polymerization type and catalytic type. The so-called additive polymerization is additive polymerization by opening the ring of the epoxy ring, and the curing agent itself participates in the three-dimensional network structure. For this kind of curing, if the amount of curing agent is too small, the curing product will connect to the epoxy group of the final reaction. Therefore, there is a suitable dosage for this kind of curing agent. Catalytic curing agent is existing as the cationic or anionic state to make epoxy ring-opening addition polymerization. Ultimately, curing agent does not participate in the network structure, so there is no suitable amount of equivalent reaction; however, increasing the amount of curing agent will accelerate the curing rate. Among the apparent curing agents, dicyandiamide and dihydrazide adipate are insoluble in epoxy resin at room temperature and begin to cure after dissolving at high temperature, thus showing a latent state. Therefore, it can be called functional latent curing agent.
Latent curing agent refers to the curing agent that has relatively long-term stability of epoxy resin at room temperature after mixing with epoxy resin (epoxy resin generally requires more than three months to have greater practical value, and the ideal one requires more than six months or one year). It only needs to be exposed to heat, light, humidity and other conditions to start curing reaction. This kind of curing agent basically uses physical and chemical methods to seal the activity of curing agent. Therefore, in some books, these varieties are also classified as latent curing agents, which can actually be called functional latent curing agents. Because latent curing agent can be mixed with epoxy resin to form a liquid-type complex, which simplifies the process of epoxy resin application. Its application range is from single packaging adhesive to coating, impregnating paint, filling material, powder coating and so on. Latent curing agents have attracted more and more attention in foreign countries, which can be said to be a key subject of research and development. Various new curing agents and new technologies emerge endlessly , which are very active.
Amine curing agent:
The curing effect of primary amine and secondary amine on epoxy resin is that active hydrogen on nitrogen atom opens epoxy group, making it cross-linked and cured. Aliphatic polyamines such as ethylenediamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine and diethylaminopropylamine have higher activity, which can cross-link epoxy resin at room temperature, while aromatic polyamines have lower activity, such as m-phenylenediamine, which can only be cured completely at 150 ℃.
Anhydride curing agent:
Dibasic acids and their anhydrides, such as maleic anhydride and phthalic anhydride, can cure epoxy resin, but they must be baked at a higher temperature to complete curing. Anhydride first reacts with hydroxyl groups in epoxy resin to form monoesters. Carboxyl groups in monoesters are added to epoxy groups to form diesters.
Synthetic resin curing agent
Low molecular weight polyamide resin is a kind of amber viscous resin produced by the reaction of linoleic acid dimer or tung oleic acid dimer with aliphatic polyamines such as ethylenediamine and diethylenetriamine.
Latent curing agent:
This kind of curing agent is stable under general conditions, but when heated to a certain temperature, it shows its activity and cures epoxy resin. For example, dicyandiamide, mixed with epoxy resin, is stable at room temperature. The epoxy resin can be cured in 30 minutes at 145 - 165 C. Boron trinitride ethylamine complex is also stable at room temperature, and can cure epoxy resin at 100 C or above.
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