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What is the classification of epoxy resin?

Feb 16, 2019


Epoxy resins can be roughly divided into five categories:

A
Bisphenol A type epoxy resin (also known as bisphenol A diglycidyl ether - DGEBA)
It is currently the largest amount of epoxy resin (type), the structure shown in Figure-1, accounting for more than 85% of the total output.


B
Bisphenol F type epoxy resin (DGEBF)
It is obtained by reacting bisphenol F with epichlorohydrin. DGEBA resin often crystallizes in winter and becomes an operational failure, but the use of DGEBF resin does not cause such trouble.

The curing activity of DGEBF resin is almost comparable to that of DGEBA. The performance of the cured product is slightly lower than the heat distortion temperature (HDT), and the other properties are slightly higher than that of DGEBA resin. Due to such excellent performance of DGEBF resins, there is a tendency for such resin compounds to rapidly increase in civil engineering and construction under natural conditions.


C
Bisphenol S type epoxy resin
Bisphenol S epoxy resin (DGEBS) is prepared by reacting bisphenol S with ECH. Its chemical structure is also very similar to that of DGEBA resin, and its viscosity is slightly higher than that of DGEBA resin of the same molecular weight. Its biggest feature is higher heat distortion temperature and better heat resistance than DGEBA resin cured products.


D
Hydrogenated bisphenol A epoxy resin
The hydrogenated bisphenol A type epoxy resin is obtained by reacting hexahydrobisphenol A obtained by hydrogenation of bisphenol A with ECH. It is characterized by a very low viscosity of the resin, comparable to DGEBF, but with a long gel time, it takes more than twice the gel time of the DGEBA resin to gel. The most important feature of hydrogenated bisphenol A type epoxy resin cured products is good weather resistance.


E
Linear novolac epoxy resin
The linear polyfunctional phenolic epoxy resin having practical value mainly includes phenol novolac epoxy resin (EPN) and o-cresol novolac epoxy resin (ECN).
EPN epoxy resin is blended with bisphenol A epoxy resin alone, and can be used as a printed circuit board that requires heat resistance and as an adhesive for electrical insulating materials, adhesives, and corrosion-resistant coatings.

The ECN resin has a higher softening point than the EPN resin, and the cured product has superior performance. Utilizing this property, ECN resin is used as an encapsulation material for integrated circuits and various electronic circuits and electronic components to protect them from the external environment. Such use is extremely demanding.
Further, there are polyfunctional glycidyl ether resins, polyfunctional glycidylamine resins, and halogenated epoxy resins having special properties.

Regarding halogenated epoxy resins, brominated epoxy resins and fluorinated epoxy resins are of practical value. Brominated epoxy resins have improved heat distortion temperature and are flame retardant; fluorinated epoxy resins have very low refractive index and surface tension. Brominated resin DGEBA resin has tetrabromobisphenol A (TBBA) as raw material, high brominated epoxy resin (HBR) with bromine content of 48 & 50%, and bromine content of 20% by copolymerization of TBBA and BA. -25% low brominated epoxy resin (LBR). HBR is directly used for printed wiring boards or reactive flame retardants for molding epoxy resins; LBR is mainly used for FR-4 type printed wiring boards.

If it is based on the number of epoxy groups, the epoxy resin can be classified into a bifunctional epoxy resin and a polyfunctional epoxy resin. For reactive resins, the amount of functional groups is very important.

According to the state of the resin at room temperature, it can also be classified into a liquid epoxy resin and a solid epoxy resin. This is important in actual use. Liquid resins can be used as castables, solventless adhesives and coatings. Solid resin can be used in powder coatings and solid molding materials.

According to the difference in molecular weight, it can be divided into high, medium and low molecular weight epoxy resins. Generally, an epoxy resin having a number average molecular weight of less than 400 is called a low molecular weight product, and its main component is diglycidyl ether; the number average molecular weight is 1400. As a basis for distinguishing medium and high molecular weight epoxy resins.


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