Low-temperature curable, high glass transition temperature adhesive compositions for bonding magnets in electric and hybrid electric vehicle motors and associated methods for using the same

A one-component epoxy adhesive composition for bonding magnets to motor rotors, comprising:

• (a) 25-60 weight percent of a first epoxy resin comprising a diglycidyl ether of bisphenol F (DGEBF) having an epoxy equivalent weight of 160-180 g/eq, serving as a primary network former;
• (b) 5-20 weight percent of a second epoxy resin comprising a diglycidyl ether of bisphenol A (DGEBA) having an epoxy equivalent weight of 184-190 g/eq, providing metal adhesion properties;
• (c) 10-25 weight percent of a third epoxy resin selected from the group consisting of:
• trifunctional epoxy resins, dicyclopentadiene (DCPD) epoxy resins, and/or naphthalene-type multifunctional epoxy resins, providing enhanced thermal resistance;
• (d) 5-10 weight percent of an epoxy resin/ABS rubber blend and 5-10 weight percent of a bisphenol-capped polyurethane toughener, together providing impact resistance;
• (e) 5-15 weight percent of aluminum trihydrate as a thermal conductive filler;
• (f) 2-15 weight percent of a cycloaliphatic epoxy diluent for viscosity control;
• (g) a latent hardener system, comprising:
• (1) 2-10 weight percent dicyandiamide, (2) 0.5-5.0 weight percent imidazole catalyst, and 0.5-2.0 weight percent substituted urea accelerator;
• (h) 0.1-5.0 weight percent epoxy-functional silane adhesion promoter;
• (i) 0.1-5.0 weight percent phosphoric acid ester wetting agent;
• and
• (j) 0.1-2.0 weight percent fumed silica rheology modifier;
• and wherein the composition is curable at temperatures between 100° C. and 200° C. and achieves a glass transition temperature of at least 120° C. when cured.