Heat-resistant structural epoxy resins
View Patent ↗Epoxy adhesive compositions containing a rubber-modified epoxy resin contain a bisphenol. The bisphenol can be pre-reacted with the rubber-modified epoxy resin to advance the resin. The adhesives are resistant to thermal degradation as can occur in so-called “overbake” conditions, in which the adhesive is heated to high temperatures for prolonged periods of time. In addition, expanded microballoons are included in epoxy structural adhesives to promote a desired fracture mode.
1. A one-component structural adhesive, comprising:
A) from 5 to 30 weight percent of one or more rubber-modified epoxy resins, in which at least a portion of the rubber has a glass transition temperature of −40° C. or lower; and
B) from 5 to 25 parts by weight, per 100 parts by weight of the rubber component of the rubber-modified epoxy resin(s), of one or more bisphenol compounds,
wherein component B) is pre-reacted with all or a portion of component A) to form an advanced rubber-modified epoxy resin, the structural adhesive further comprising:
C) at least 8 weight percent of a reactive toughener; and
D) one or more epoxy curing agents;
wherein the structural adhesive further comprises particles of a core-shell rubber, the total rubber content is from 6 to 20 weight percent of the structural adhesive and the structural adhesive is curable at a temperature of 80° C. or higher.
2. A method comprising applying the structural adhesive of claim 1 between the surfaces of two metals, and curing the structural adhesive to form an adhesive bond between the two metals.