Adhesive composition
An epoxy-based crash durable adhesive composition including: (I) a liquid resin system comprising: (a) at least one epoxy resin; and (b) at least one toughener; wherein the viscosity of the above liquid resin system is less than about 800 Pa s at a temperature of 15° C.; and wherein the viscosity of the above liquid resin system is greater than about 5 Pa-s at a temperature of 60° C.; (II) a solid material comprising: (c) at least one hydrophobic fumed silica, wherein the fumed silica is present in the adhesive composition at a concentration of greater than 5 weight percent; and (III) a curative material comprising: (d) at least one latent heat-activated curing agent; wherein the rheology of the epoxy-based crash durable adhesive composition is such that the adhesive composition is pumpable at a temperature of 15° C. or greater; and wherein the epoxy-based crash durable adhesive composition exhibits an increase in wash-off resistance; a process for making the above adhesive composition; and a process for bonding metal substrates together with the above adhesive composition.
1. An epoxy-based crash durable adhesive composition comprising:
(I) a liquid resin system comprising:
(a) at least one epoxy resin; and
(b) at least one polyurethane toughener capped with cashew nut shell liquid;
wherein the viscosity of the liquid resin system, component (I), is less than about 800 Pa·s at a temperature of about 15° C.; and wherein the viscosity of the liquid resin system, component (I), is greater than about 5 Pa·s at a temperature of about 60° C.;
(II) a solid material comprising:
(c) at least one hydrophobic fumed silica, wherein the at least one hydrophobic fumed silica is present in the adhesive composition at a concentration of greater than 5 weight percent; and
(III) a curative material comprising:
(d) at least one latent heat-activated curing agent;
wherein the rheology of the epoxy-based crash durable adhesive composition is such that the adhesive composition is pumpable at a temperature of about 15° C. or greater;
wherein the weight ratio of the hydrophobic fumed silica in the solid material, component (II), to the liquid resin system, component (I), is from about 0.08 to about 0.14.
2. The adhesive composition of claim 1 , wherein the at least one epoxy resin, component (a), is at least one liquid epoxy resin derived from bisphenol A or bisphenol F; and/or a blend of at least one liquid epoxy resin derived from bisphenol A or bisphenol F with at least one solid epoxy resin derived from bisphenol A or epoxy novolac resin.
3. The adhesive composition of claim 1 , wherein the at least one hydrophobic fumed silica, component (c), is a fumed silica treated with at least one grade of poly(dimethylsiloxane).
4. The adhesive composition of claim 1 , wherein the at least one curing agent, component (d), is dicyandiamide.
5. The adhesive composition of claim 1 , wherein the wash-off resistance of the adhesive composition is such that the adhesive does not flow more than about 7 millimeters on oily metal panels when exposed to spray wash-off testing conditions.
6. The adhesive composition of claim 1 , wherein the adhesive composition further comprises one or more of: (e) at least one filler; (f) at least one curing accelerator; and (g) at least one liquid resin different from component (a).
7. A pumpable and wash-off resistant epoxy paste adhesive for bonding automotive parts, comprising the epoxy-based crash durable adhesive composition of claim 1 .