Epoxy adhesives are generally more resistant to a wide variety of liquid environments than other structural adhesives. However, they are generally considered to be very rigid systems, and as such they do not have exceptionally good impact or peel resistance unless modified with tougheners.
Many one component epoxies contain rubber toughening agents such as carboxylic acid terminated butadiene nitrile rubber (CTBN) or amine terminated butadiene nitrile rubber (ATBN). These elastomers are pre-reacted at the 5-15% level with the epoxy resin at high temperature. During the final cure, the rubber must precipitate out of solution into discrete particles within the epoxy resin matrix.
RESULTING PROPERTIES
The above table presents typical two component epoxy adhesive formulations using ATBN toughening agents. This adhesive formulation can cure at either room temperature or elevated temperatures. Tensile shear strength and temperature resistance of these adhesives are relatively high. Peel strength is also high and does not decrease rapidly with lower temperatures. The durability of ATBN modified epoxies is satisfactory as measured by most long term moisture tests.
