UV activiated adhesive for aluminum bonded repairs

A need currently exists for a structural adhesive which is long term storable, low curable, processable, and is good for 82°C service. Photochemically latent cationic photoinitiators were explored as catalysts. Epoxy formulations using Irgacure 261 from Ciba which is a ferrocenium salt showed good shelf lives at 49°C and 32°C up to 150 days. On UV activation, a Lewis acid was produced and this had good latency at room temperature which allowed laying up of aluminum substrates for bonding. At a curing temperature of 93°C for three hours, the UV activated samples containing 1.1 weight percent of Irgacure 261 showed complete cure as evidenced by differential scanning calorimetry. Single lap shear strengths of about 24 MPa were achieved using properly prepared aluminum substrates.