Epoxy Resins

Uses

Cured epoxy resins have an outstanding resistance to heat and chemicals and find wide use in reinforced plastics, coatings, adhesives, casting, “potting,” and encapsulation. The typical resin is prepared by condensation of epichlorohydrin with a diphenol in the presence of a curing agent. Epoxy resins are cured by cross-linking agents known as “hardeners,” such as the polyamines (e.g., diethylenetriamine, triethylenetetramine, and piperazine) or the acid anhydrides and polybasic acids (e.g., phthalic anhydride and adipic acid). Catalysts perform a similar curing action but they do not themselves act as cross-linking agents. Common catalysts include various polyamides, monoethylamine, and tertiary amines, such as triethylamine and benzyl dimethylamine. Diluents (e.g., phenyl, allyl, and butyl glycidyl ether; styrene oxide; styrene; and other epoxides) may be used to reduce the viscosity of uncured resin systems.

Definition

epoxy resins: Synthetic resins producedby copolymerizing epoxidecompounds with phenols. They contain-O- linkages and epoxide groupsand are usually viscous liquids. Theycan be hardened by addition ofagents, such as polyamines, thatform cross-linkages. Alternatively,catalysts may be used to induce furtherpolymerization of the resin.Epoxy resins are used in electricalequipment and in the chemical industry(because of resistance tochemical attack). They are also usedas adhesives.

Industrial uses

Epoxy (Ep) resins comprise an extremely broadand diverse family of materials. They are usedin the form of protective coatings, adhesives,reinforced plastics, molding compounds, castingand potting compounds, and foams.Epoxies, perhaps best known as adhesives,are premium thermosetting plastics, and aregenerally employed in high-performance useswhere their high cost is justified. They areavailable in a wide variety of forms, both liquidand solid, and are cured into the finished plasticby a catalyst or with hardeners containingactive H2. Depending on the type, they arecured at either room temperature or at elevatedtemperatures.Liquid epoxies are used for casting, for pottingor encapsulation, and for laminating. Theyare used unfilled or with any of a number ofdifferent mineral or metallic powers. Moldingcompounds are available as liquids, and also aspowders with various types of fillers and reinforcements.
The epoxy resins have very high adhesion to metals and nonmetals, and high resistance to common solvents, oils, and chemicals.
An unlimited variety of epoxy resins is possible by varying the basic reactions with different chemicals or different catalysts, or both, by combination with other resins, or by cross-linking with organic acids, amines, and other agents. To reduce cost when used as laminating adhesives, they may be blended with furfural resins, giving adhesives of high strength and high chemical resistance. Blends with polyamides have high dielectric strength, mold well, and are used for encapsulating electrical components. By using a polyamide curing agent, an epoxy can be made water emulsifiable for use in waterbased paints.The epoxies have excellent electrical, thermal, and chemical resistance.

Synthesis

Epoxy resins, when mixed with a hardening agent, cross link on gentle heating; in this way, very strong and even vacuum-tight joints between the following materials are obtained: metal, glass, porcelain, thermosetting (not thermoplastic) synthetics, vulcanized rubber. Epoxy cements can be cooled to very low temperatures without cracking and have very low vapor pressures (10^-6 to10^-7 mm. at room temperature.