Of equal significance are recent improvements in thermal stability for one- and two-component structural adhesives. Advanced epoxy adhesive systems now perform satisfactorily at temperatures of 500 °F and higher. Key to this development is the production of new heat-resistant epoxy resins based on novel chemical structures. These advanced resins can be cured over a wide temperature range with specially designed curing agents that yield impressive bond strengths.
Two-component epoxies are usually cured at ambient or moderately elevated temperatures in the 75 to 200 °F range and tend to achieve somewhat lower strengths and more limited service temperature capabilities compared to onecomponent formulas. Single-component paste and film epoxy adhesives are often used in the aerospace and transportation industries because they offer the highest shear strengths, service temperature capabilities, and ease of processing. These epoxies require elevated temperature cures, frequently in the 250 to 400 °F range.
Beyond punishing temperatures, epoxies are also finding use in highly corrosive environments, such as those in the chemical processing industries. Specialized two-component liquid and paste adhesives now feature superior resistance to strong mineral acids, bases, and organic solvents after only ambient temperature cures.
Today’s advanced epoxy resins often function as thermal and electrical insulators as well. In certain electronics applications, it is now required that adhesives conduct electricity, heat, or both. Electrically and thermally conductive adhesives have been developed in response to this demand. Electrically conductive epoxies contain metallic fillers — such as silver, copper, and nickel — in finely divided powder form. For less stringent requirements, graphite fillers are acceptable. Thermal conductivity is achieved using either specialized metals or inorganic fillers, including alumina. Both one- and two-component conductive adhesive systems are available with either ambient or elevated temperature cures. Advanced adhesive systems are also being utilized in NASA-compliant low-outgassing and fiber-optic applications.
This work was done by Master Bond. For more information, visit http://info.hotims.com/40433-122.