Structural epoxy resins containing core-shell rubbers
View Patent ↗Core-shell rubbers are incorporated into epoxy adhesives. The adhesives are structural type adhesives that contain an epoxy resin and a toughener, and may contain a liquid rubber in addition to the core-shell rubber. The adhesives have good modulus and tensile strength, which are obtained without loss of elongation and adhesive properties.
1. A method comprising applying a structural adhesive to the surfaces of two metals, and curing the structural adhesive at a temperature of from 140 to 200° C. to form an adhesive bond between the two metals wherein the structural adhesive comprises:
A) at least 10 weight percent up to about 20 weight percent, based on the weight of the adhesive, of one or more liquid rubber-modified epoxy resins, wherein the liquid rubber is a carboxyl-terminated butadiene/acrylonitrile copolymer and the epoxy resin is a glycidyl ether of a bisphenol;
B) from 3 to 8 weight percent, based on the weight of the adhesive, of at least one core-shell rubber in the form of particles having at least one rubbery core portion and at least one shell portion that has a T g of at least 50° C., the rubbery core constituting from 50 to 95% of the weight of the core-shell rubber particles;
C) from 12 to 30 weight percent, based on the weight of the adhesive, of a reactive toughener which is an isocyanate-terminated prepolymer formed from a polyether polyol and an aliphatic polyisocyanate in which the terminal isocyanate groups are blocked with a phenol, aminophenol, polyphenol or an allyl phenol;
D) at least one non-rubber-modified epoxy resin which is a diglycidyl ether of bisphenol A, bisphenol F, bisphenol K or tetramethylbiphenol; and
E) a guanidine curing agent,
wherein the structural adhesive has a total rubber content of from 8 to 15% by weight.
2. The method of claim 1 wherein at least one of the metals is a hot dip zinc coated steel.
3. The method of claim 2 wherein at least one of the metals is a zinc/iron coated steel (galveneal).
4. The method of claim 1 wherein the liquid rubber-modified epoxy resin is a liquid butadiene-acrylonitrile rubber-modified epoxy resin wherein at least a portion of the liquid rubber has a glass transition temperature especially −50° C. or lower.