One-component toughened epoxy adhesives with improved adhesion to oily surfaces and high wash-off resistance

A method for adhering a first oily substrate to a second substrate, comprising

• 1) forming a layer of a one-component epoxy adhesive comprising in admixture:
• A) at least 25 weight percent, based on the weight of the adhesive, of one or more non-rubber-modified epoxy resins;
• B) 5 to 45 weight percent, based on the weight of the composition, of a reactive elastomeric toughener having capped isocyanate groups, which reactive elastomeric toughener includes a chain-extended and then isocyanate-capped mixture of i) a 1000 to 10,000 number average molecular weight isocyanate-terminated polyether and ii) a 1000 to 10,000 number average molecular weight isocyanate-terminated diene polymer;
• C) one or more latent epoxy curing agents in an amount sufficient to cure the adhesive;
• and
• D) 0.1 to 5 weight percent, based on the weight of the adhesive, of at least one urea compound having one or more urea groups and a molecular weight per urea group of up to 250, the adhesive being devoid of an aminophenol curing accelerator, at a bondline between the first oily substrate and the second substrate to form an assembly that includes the first and second substrates each in contact with the adhesive composition at the bondline;
• then
• 2) degreasing the assembly to remove oil from the first oily substrate;
• and then
• 3) heating the degreased assembly to an elevated temperature to cure the adhesive.