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Epoxy resin hardener reacts with epoxy resin to form a network solid polymer. The composite is wrapped in the network, which can transform the linear resin into a tough bulk solid.

1. TYPES OF CURING AGENTS BASIC
Basic curing agent WTF: including aliphatic diamines and polyamines, aromatic polyamines, other nitrogen compounds and modified fatty amines.

Acidic type

Acid curing agents: organic acids, anhydrides, boron trifluoride and their complexes.

Addition molding

Addition of curing agent: the curing agent reacts with epoxy group to form a part of the curing product chain segment, and the linear molecule is crosslinked with the structure molecule of the cost body through gradual polymerization. This curing agent is also called melon curing agent.

Catalytic type

Catalytic curing agent: this curing agent only causes epoxy resin. After opening the epoxy group, the epoxy resin itself polymerizes into a network structure to form a homopolymer with ether bond as the main structure.

Manifest type

Apparent curing agent is a common curing agent, which can be further divided into addition polymerization type and catalytic type. The addition polymerization type is a ring that opens epoxy group for addition polymerization. The curing agent itself participates in the three-dimensional network structure. If too little is added, the curing agent will adhere to the final reactive epoxy group. Therefore, for this curing agent, there is an appropriate amount. The catalytic curing agent circularly adds and polymerizes epoxy groups in the form of cation or anion. Finally, the curing agent does not participate in the network structure, so there is no appropriate equivalent reaction amount. However, the dose is increased. Speed up curing. In the obvious curing agent, dicyandiamide and adipic acid diacylhydrazide are insoluble in epoxy resin at room temperature, and begin to cure after dissolving at high temperature, so they show latent state. Therefore, it can be called a functional latent curing agent.

Latent type

Latent curing agent refers to the relatively long-term stability at room temperature after mixing with epoxy resin (epoxy resin usually takes more than 3 months, which has great practical value. It is preferred to take half a year or more) , just expose to heat, light, moisture and other environment, and the curing reaction begins. This curing agent can prevent the activity of curing agent in physical and chemical aspects. Therefore, in some books, these varieties are also classified as latent curing agents. It can be called a functional latent curing agent. Because latent curing agent can be mixed with epoxy resin to make liquid composite, the matching procedure of epoxy resin application is simplified. Its application range is from single package adhesive to coating, impregnation varnish, potting material, powder coating, etc. More and more attention has been paid to the development of potential curing agents abroad. It can be said that it is a key topic of research and development. A variety of new curing agents and new technologies are emerging. Relevant R & D activities are very active.

Amine curing agent

The curing action of primary amine and secondary amine on the epoxy resin is to open the epoxy group through the active hydrogen on the nitrogen atom to crosslink and cure. Aliphatic polyamines, such as ethylenediamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine and diethylaminopropylamine, have high activity and can crosslink and solidify epoxy resin at room temperature. The reaction at low temperature, such as m-phenylenediamine, can be cured at 150 ℃

2. FORMULATION OF EPOXY RESIN HARDENER
Anhydrides curing agent

Binary acids and their anhydrides, such as maleic anhydride and phthalic anhydride, can cure epoxy resins. However, it must be baked at a higher temperature to fully cure. Anhydrides react with hydroxyl groups in epoxy resin to form monoesters, and the carboxyl groups in the monoesters are esterified by the epoxy group to form diesters.

Synthetic resin curing agent

Low molecular weight polyamide resin is an amber viscous resin formed by the reaction of linoleic acid dimer or tung oil dimer with aliphatic polyamines such as ethylenediamine or diethylenetriamine. The structure of the resin prepared from dimeric linoleic acid and ethylenediamine is as follows:

Latent curing agent

The curing agent is stable under ordinary conditions, but when heated to a certain temperature, its activity shows that the epoxy resin can be cured. If dicyandiamide is mixed with epoxy resin, it is stable at room temperature. If the temperature is 145-165 ℃, the epoxy resin can be cured within 30 minutes. Boron trichloride ethylamine complex is stable at room temperature. Cure the epoxy at a temperature higher than 100 ℃.

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