Details
Material hierarchy: Polymer - Thermoset
These resins offer excellent electrical properties and dimensional stability, coupled with high strength and low moisture absorption.
The most important of the epoxy resins are based on bisphenol A and epichlorhydrin; they can be produced in either liquid or solid form. Epoxy novolacs are made by reacting a phenol formaldehyde with epichlorhydrin; the resulting resins have high heat resistance and low levels of ionic impurities. All epoxies have to be reacted with a hardening agent (e.g., an aliphatic amine or a polyamide) to crosslink into thermoset structures.
Epoxies are used by the plastics industry in several ways. One is in combination with glass fibers (i.e., impregnating fiber with epoxy resin) to produce high-strength composites that provide heightened strength, electrical and chemical properties, and heat resistance. Typical uses for epoxy-glass RP are in aircraft components, filament-wound rocket motor casings for missiles, pipes, tanks, pressure vessels, and tooling jigs and fixtures.
Epoxies also are used in the encapsulation or casting of various electrical and electronic components and in the coating of various metal substrates. Epoxy coatings are used on pipe, containers, appliances, and marine parts. Charged epoxy powders are electrostatically deposited on car bodies and other auto parts for corrosion protection.
Another major application area for epoxies is adhesives. The two-art systems cure with minimal shrinkage and without emitting volatiles. Formulations can be created to cure at different rates at room or elevated temperatures. The auto industry has started to use epoxy adhesives in place of welding and for assembling plastic body parts.
Epoxies can futher be transfer- or injection-molded. Transfer presses, for example, are being used today to encapsulate electronic components in epoxy or to mold epoxy electrical insulators. Injection molding presses also are available for liquid epoxy molding.
Epoxy molding compounds are available in a wide range of mineral-filled and glass-, carbon-, and aramid-fiber-reinforced versions. The low-glass-content (up to about 12-50%) or mineral-reinforced compounds are primarily used for electrical applications and can be molded at relatively low pressures and short cycles. The high-glass-content compounds (over 60%) offer extremely high mechanical strengths, but are more difficult to process. Carbon fiber-epoxy composites are used to produce strong, lightweight parts for military and aircraft uses.