Tie layer adhesives having graft compositions for bonding to metal substrates
Tie-layer adhesives having graft compositions for bonding to metal substrates is disclosed. The graft compositions are made up of the reaction product of a live, grafted polyolefin and an olefin elastomer. The grafted polyolefin is first made by heating a polyolefin and an unsaturated monomer. Further reaction of the live, grafted polyolefin with an olefin elastomer provides the graft composition. Grafting efficiency is boosted dramatically by the presence of the olefin elastomer and use of the additional reaction step. The graft composition, when formulated into a tie-layer adhesive provides improved bonding to metal substrates.
1. A process for preparing a multilayer structure comprising:
preparing an adhesive tie layer composition by:
(i) reacting an unsaturated monomer with a polyolefin to produce a live, grafted polyolefin,
wherein the unsaturated monomer is used in an amount between 0.1 to 15 wt. %, based on the live, grafted polyolefin produced and wherein the reacting step (i) excludes an olefin elastomer;
(ii) reacting the live, grafted polyolefin and the olefin elastomer at a temperature of 120-300° C. to produce a graft composition,
and wherein at least 90% of the unsaturated monomer is incorporated into the graft composition, and
wherein the graft composition has an adhesive strength of greater than or equal to 120 N/10 mm at a rate of 50 mm/min and a temperature of 90° C. as measured by pulling a 5″×2″×1″ tie layer adhesive strip from a metal substrate; and
bonding the graft composition to a metal substrate;
wherein the olefin elastomer is ethylene-propylene rubber (EPR) or ethylene-propylene-diene monomer rubber (EPDM) and the amount of olefin elastomer ranges from 30-40% by weight, based on the amount of graft composition produced.
2. The process of claim 1 , wherein the metal substrate is a metal, metal oxide or alloy comprising aluminum, tin, zinc, nickel, copper, platinum, gold, silver, palladium, chromium, cobalt, steel, iron, or mixtures thereof.
3. The process of claim 1 , wherein the live, grafted polyolefin is high-density polyethylene (HDPE) grafted with maleic anhydride.
4. The process of claim 1 , wherein the adhesive layer composition is also adhered to a polyolefin layer.
5. The process of claim 1 , wherein the graft composition is blended with a base resin.
6. The process of claim 1 , wherein the adhesive tie layer composition has an adhesive strength of greater than or equal to 135 N/10 mm.
7. The process of claim 1 , wherein the adhesive tie layer composition has an adhesive strength of greater than or equal to 150 N/10 mm.
8. The process of claim 1 , wherein the adhesive tie layer composition has an adhesive strength in a range of 120-185 N/10 mm.