Structural adhesive and bonding application thereof

A two-part system for forming a structural adhesive comprising a resinous part (A) and a separate catalyst part (B),

• the resinous part (A) comprising:
• at least two different multifunctional epoxy resins with different epoxy functionality selected from di-functional, tri-functional, and tetra-functional epoxy resins;
• smaller core-shell rubber particles having particle sizes less than 100 nm and larger core-shell rubber particles having particle sizes greater than 100 nm, the weight ratio of smaller core-shell rubber particles to larger core-shell rubber particles being in the range of 3:1 to 5:1;
• at least one of (i) an elastomeric polymer with a functional group capable of reacting with the multifunctional epoxy resins and (ii) a polyethersulfone polymer having an average molecular weight in the range of 8,000-14,000;
• and
• inorganic filler particles in an effective amount to control rheology of the resinous part;
• the catalyst part (B) comprising:
• at least one amine curing agent selected from the group consisting of:
• dicyclohexylamine, amine-terminated piperazine, polyethylene polyamine, and combinations thereof;
• and
• inorganic filler particles present in an effective amount to control rheology of the catalyst part;
• wherein the weight ratio of part (A) to part (B) is within the range of 3:2 to 10:2;
• and
• wherein, when part (A) and part (B) are mixed and then cured in a temperature range of 65-93° C. (150-200° F.), the resulting structural adhesive has a glass transition temperature (Tg) of greater than 95° C. (203° F.), a lap shear strength of 33-37 MPa at 20° C.-25° C., 24-27 MPa at 82° C., and 15-18 MPa at 121° C. according to ASTM D3165, and a peel strength of 250-350 Nm/m at 20° C.-25° C. according to ASTM D3167.