Classification of curing agents for epoxy resins
1.Epoxy resin is an amorphous viscous liquid that is plastic when heated and has no obvious melting point. It becomes soft when heated and gradually melts, but becomes sticky and insoluble in water.After the curing agent was added into gradually solidified form of chemicals with various properties, therefore, must add hardener, the formula of resin, and under certain conditions for curing reaction, generate the product of the three-dimensional network structure, will appear a variety of excellent performance, an epoxy material has actually use value.Common amine curing agent in engineering: ethylenediamine, ethylene polyamine, polyethylene polyamine, etc.
2. Curing agent is an indispensable additive, which is needed for adhesives, coatings and castables, otherwise epoxy resin cannot be cured.Name of packing function asbestos fiber, glass fiber increase toughness, impact resistance quartz powder, porcelain powder, iron powder, cement, emery improve hardness alumina, porcelain powder increase adhesion,Increase the mechanical strength of asbestos powder, silica gel powder, high temperature and increase the heat resistant asbestos cement powder, quartz powder, stone powder, reducing shrinkage aluminum powder, copper powder, iron powder and other metal powder Increase the thermal conductivity and electrical conductivity of graphite powder, talcum powder, quartz powder Improve abrasion performance and lubrication performance of silicon carbide and other abrasive Improve the antiwear properties of mica powder, porcelain powder, quartz powder increase the insulation performance of various pigments, graphite has the color epoxy resin curing agent is defined and the reaction of epoxy resin, a stereoscopic network polymers, the composite aggregate envelope in the mesh.An additive used to make linear resins tough and solid.
3. Classification of curing agent for epoxy resin
(1) basic and acidic curing agents: basic curing agents include aliphatic diamines and polyamines, aromatic polyamines, other nitrogenous compounds and modified aliphatic amines.Acidic hardeners include organic acids, anhydrides, and boron trifluoride and their complexes.
(2) addition molding and catalytic curing agents: the addition of molding curing agents and other curing agents to the epoxy group forms part of the chain segment of the curing products, and crosslinks the linear molecules to form structural molecules through gradual polymerization. Such curing agents are also called melon curing agents.This kind of curing agent can only initiate the action on the epoxy resin. After the epoxy group is opened, it can catalyze the epoxy resin itself to polymerize into the network structure and generate the homopolymer with ether bond as the main structure.
(3) apparent hardener and latent hardener.
Apparent curing agent is a common curing agent which can be divided into addition polymerization type and catalytic type.The so-called addition polymerization is to open the epoxy ring for addition polymerization reaction, the curing agent itself to participate in the three-dimensional network structure.If too little is added, the curing product is linked to the final reactive epoxy group.Therefore, there is an appropriate dosage for this type of curing agent.However, the catalytic curing agent can make the epoxy group open ring addition polymerization in the way of cation or anion. In the end, the curing agent does not participate in the network structure, so there is no appropriate amount of equivalent reaction.However, increasing the dosage will speed up the curing process.
A latent curing agent is one that, when mixed with an epoxy resin, is relatively stable at room temperature for a long period of time (generally, an epoxy resin needs more than 3 months to be of great practical value; ideally, it needs more than 6 months or 1 year), but only needs to be exposed to heat, light, moisture and other conditions to initiate the curing reaction.These hardeners essentially block hardener activity by physical and chemical means.In the apparent curing agent, the varieties of dicyandiamide and dihydrazide adipate are insoluble in epoxy resin at room temperature, but begin to cure after dissolution at high temperature, and thus present a latent state.So, also divide these breed in some books for latent hardener, can call function actually latent hardener.Because the latent curing agent can be mixed with epoxy resin to make a liquid compound, the application of epoxy resin can be simplified. Its application range has developed from single-package adhesive to coating, impregnating paint, filling and sealing material, powder coating and other aspects.Latent curing agent has been paid more and more attention in foreign countries. It can be said that it is a key subject of research and development.
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