UV Activated, Thermally Cured Film Adhesive for On-Aircraft Bonded Repairs

A need currently exists for a structural adhesive which is long term storable, low temperature curable, vacuum processable, and good for 180 degrees F service. This new film adhesive is needed for on-aircraft repair of the Air Force's aircraft fleet. State-of-the-art 180 degreeF service adhesives for repair bonding of aluminum alloy surfaces are typically one-part nitrile epoxy cured with dicyanodiamide and aromatic amines. However, none of the currently available catalysts allows long term storage at room temperature or elevated storage temperatures of 90 degrees F or 120 degrees F, and also allows curing at 180 degrees F using vacuum in less than 4 hours. Active research has been conducted in this area, and quasimechanical means for segregating the epoxy from the curing agent curative by such techniques as microenscapsulation or zeolite molecular sieves have been proposed. However, these quasimechanical methods do not prevent premature gelling due to the closeness of the required long term storage temperatures of 90 degrees or 120 degrees to the allowable processing temperature of 180 degrees F. Triton proposes to use photoactivable but thermally curable compositions. Recent developments in radiation chemistry have led to photochemically latent catalysts which required UV for activation and heat for subsequent curing. Such compositions have been demonstrated on steel substrates. In this proposal, aluminum substrates and further optimization shall be done.