epoxy adhesive[ə′päk·sē ad′hē·siv]
any of a number of synthetic adhesives based on epoxy resins.
Epoxy adhesives contain curing agents (diamines, polyamines, dicyandiamide, phthalic anhydride, or maleic anhydride), fillers (aluminum oxide, silicon dioxide, carbon black, glass fiber, carbon fiber, or metal powders, such as nickel powder), plasticizers (certain polymers, such as rubbers, or esters of phthalic or phosphoric acid), modifiers (phenol-formaldehyde resins), and solvents (alcohols, xylene, or acetone); however, highly-reactive diluents, such as liquid Thiokol products, that react with epoxy resins during curing are often used instead of the solvent. Certain epoxy adhesives contain only an epoxy resin and a curing agent.
Epoxy adhesives may take the form of liquids, pastes, or solids (powders, sticks, or films). Liquid and paste expoxy adhesives with amine hardeners may be kept at room temperature for one to six hours; the components of such adhesives are usually mixed just before use. Epoxy adhesives with acid anhydride curing agents may be stored from five days to several months. The properties of solid epoxy adhesives are retained for one to three years.
Before the application of epoxy adhesives, surfaces are treated mechanically, ultrasonically, or by etching. Liquid and paste epoxy adhesives are applied with a brush or spatula or by spraying. Powders are applied by dusting, and sticks, by rubbing on heated surfaces. Epoxy adhesive films are applied between the parts to be joined. The curing temperature ranges from room temperature for cold-set epoxy adhesives to 140°–300°C for heatset adhesives. The pressure that must be applied may reach 0.5 meganewtons per square meter (MN/m2) and may have to be maintained from several hours to several days. The uniform breaking strength of the joints may be as high as 45 MN/m2. These joints are resistant to heat, air, oil, gasoline, dilute acids, and dilute bases, and they have good electrical insulation properties.
Epoxy adhesives are used in virtually all industries. For example, they are used in machine building for the manufacture of industrial equipment, in construction for the connection of reinforced concrete structures of bridges, in shipbuilding for the assembly of fiberglass boats, and in radio engineering and electronics for assembling parts.