Epoxy resin adhesive compositions
Disclosed are one-component epoxy resin adhesive compositions which include (a) one or more non-rubber-modified epoxy resins; (b) one or more latent epoxy curing agents; (c) one or more toughening agents; and (d) zinc oxide nanoparticles. The one-component epoxy resin adhesive compositions exhibit improved toughness of the adhesive as measured by its lap shear strength as well as improved environmental stability, i.e., corrosion protection, by addition of the zinc oxide nanoparticles when applied to metal substrates.
1. A one-component epoxy resin adhesive composition comprising:
(a) one or more non-rubber-modified epoxy resins;
(b) one or more latent epoxy curing agents, wherein the one or more latent epoxy curing agents comprises a dicyanamide and one or more urea compounds having one or more urea groups and a molecular weight per urea group of up to 250;
(c) one or more toughening agents; and
(d) 0.1 to 5 wt % zinc oxide nanoparticles, wherein the zinc oxide nanoparticles have an average particle size from 10 nm to 100 nm.
2. The one-component epoxy resin adhesive composition according to claim 1 , wherein the one or more non-rubber-modified epoxy resins comprise one or more liquid non-rubber-modified epoxy resins.
3. The one-component epoxy resin adhesive composition according to claim 2 , wherein the one or more liquid non-rubber-modified epoxy resins have an epoxy equivalent weight of from 150 to 299 g/mol.
4. The one-component epoxy resin adhesive composition according to claim 1 , wherein the one or more non-rubber-modified epoxy resins comprise at least 60% by weight of a liquid diglycidyl ether of a polyhydric phenol having an epoxy equivalent weight of from 150 to 299 g/mol.
5. The one-component epoxy resin adhesive composition according to claim 1 , wherein the one or more urea compounds comprise at least one of isophorone bis(dimethyl urea), 2,4′- and/or 4,4′-methylene bis(phenyl dimethyl urea) and 2,4- and/or 2,6-toluene bis(dimethyl urea).
6. The one-component epoxy resin adhesive composition according to claim 1 , wherein the one or more toughening agents comprise a reactive elastomeric toughener having capped isocyanate groups, wherein the reactive elastomeric toughener comprises a chain-extended and then isocyanate-capped mixture of (i) a 1000 to 10,000 number average molecular weight isocyanate-terminated polyether and (ii) a 1000 to 10,000 number average molecular weight isocyanate-terminated diene polymer.
7. The one-component epoxy resin adhesive composition according to claim 1 , comprising
(a) at least 20 weight percent, based on the total weight of the adhesive composition, of the one or more non-rubber-modified epoxy resins;
(b) the one or more latent epoxy curing agents in an amount sufficient to cure the adhesive composition;
(c) 0.5 to 40 weight percent, based on the total weight of the adhesive composition, of the one or more toughening agents; and
(d) 0.1 to 5 weight percent, based on the total weight of the adhesive composition, of the zinc oxide nanoparticles.
8. The one-component epoxy resin adhesive composition according to claim 1 , further comprising a core shell rubber.
9. A method comprising:
(a) applying a one-component epoxy resin adhesive composition to at least a portion of a one substrate, wherein the one-component epoxy resin adhesive composition comprises:
(i) one or more non-rubber-modified epoxy resins;
(ii) one or more latent epoxy curing agents, wherein the one or more latent epoxy curing agents comprises a dicyanamide and one or more urea compounds having one or more urea groups and a molecular weight per urea group of up to 250;
(iii) one or more toughening agents; and
(iv) 0.1 to 5 wt % zinc oxide nanoparticles, wherein the zinc oxide nanoparticles have an average particle size of from 10 nm to 100 nm,
(b) contacting a second substrate with the first substrate; and
(c) curing the one-component epoxy resin adhesive composition to form an adhesive bond between the first and second substrates.
10. The method according to claim 9 , wherein the one or more non-rubber-modified epoxy resins comprise one or more liquid non-rubber-modified epoxy resins.
11. The method according to claim 10 , wherein the one or more liquid non-rubber-modified epoxy resins have an epoxy equivalent weight of from 150 to 299 g/mol.
12. The method according to claim 9 , wherein the one or more toughening agents comprises a reactive elastomeric toughener having capped isocyanate groups, which reactive elastomeric toughener includes a chain-extended and then isocyanate-capped mixture of (i) a 1000 to 10,000 number average molecular weight isocyanate-terminated polyether and (ii) a 1000 to 10,000 number average molecular weight isocyanate-terminated diene polymer.
13. The method according to claim 9 , wherein the one-component epoxy resin adhesive composition comprises
(a) at least 20 weight percent, based on the total weight of the adhesive composition, of the one or more non-rubber-modified epoxy resins;
(b) the one or more latent epoxy curing agents in an amount sufficient to cure the adhesive composition;
(c) 0.5 to 40 weight percent, based on the total weight of the adhesive composition, of the one or more toughening agents; and
(d) 0.1 to 5 weight percent, based on the total weight of the adhesive composition, of the zinc oxide nanoparticles.
14. The method according to claim 9 , wherein the first substrate is a metal substrate and the second substrate is a metal substrate having a zinc-containing layer thereon.