Epoxy Systems

Out of a total of over 500 million pounds of epoxy resin produced in the United States, more than half is used in the manufacture of composites, potting, casting molding and adhesives. The majority of epoxy resins produced are based on the condensation products of Bisphenol A (BPA) and epichlorohydrin. In general, these are low molecular weight resins. The demand for the higher molecular weight resins is limited because of the cost and high viscosity requiring special processing equipment. Low molecular weight Bisphenol F (BPF) epoxy resins are now in greater demand due to their excellent chemical resistance and low viscosities. Both BPA and BPF epoxies are used in the electrical and electronic industries because of their excellent electrical, mechanical and chemical resistance properties.

The hydroxyl and terminal epoxide groups in these resins provide good reactivity, wetting properties and compatibility. The epoxide group is capable of reacting with Amine, methylol, carboxylic acid, anhydride groups. These, in general, are addition reactions and lead to low shrinkage during polymerization.

The following table shows the comparison between one part, thermally cured and the two-part room temperature cure epoxy systems:

Properties	One Part	Two Part
Pot Life	Long	Short
Cure Time	Long	Short
Cure Temperature	Elevated	Ambient
Exotherm	Low	High
Chemical Resistance	Excellent	Fair/Good
Electrical Properties	Very Good	Good
Resist. To Thermal Shock	Good	Fair
Heat Deflection Temp	High	Low
Shrinkage	Very Low	Low
Reactive Groups on Crosslinker	Carboxyl	Amine
Curing Agent	DICY Tertiary amines	Aliphatic/Aromatic Amines Polyamides
Electrical/Electronic Applications	Impregnating Dip/Bake, VPI	Potting Encapsulation

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