Foamable hot melt adheisve compositions and use thereof

Abstract

The invention relates to a foamable hot melt adhesive composition, method of foaming the foamable hot melt adhesive composition, and method of using the foamed hot melt adhesive composition. The foamed hot melt adhesive provides a reliable adhesion with high heat resistance for packaging applications. The present invention provides an environmentally and economically sound adhesive that provides sufficient adhesion to the packages upon which it is being applied.

I/We claim: 
     
         1 . A method of foaming a foamable adhesive composition comprising the steps of:
 (a) preparing a foamable adhesive composition comprising a hot melt adhesive and the block copolymer;   (b) heating the foamable adhesive composition to a molten state;   (c) mechanically mixing a gas into the molten foamable adhesive composition to create foams in the matrix; and   (d) applying the foamed adhesive composition onto a substrate,
 wherein the foamable adhesive composition is prepared with
 (i) a hot melt adhesive comprising a polymer selected from the group consisting of ethylene vinyl acetate, ethylene-acrylate, polyolefin, and mixtures thereof, and optionally a wax, a tackifier, a plasticizer, and an additive; 
 (ii) from about 3 to about 10 wt % of an olefin block copolymer having a melt index of equal to or greater than 5 g/10 min measured in accordance with ASTM D1238 at 190° C. and a DSC melting point greater than 100° C.; and 
 (iii) optionally, from about 0.05 to about 10 wt % of a foam cell promoter; 
 wherein the ratio of the polymer in the hot melt adhesive to the olefin block copolymer is in the range of about 20:1 to about 2:1. 
 
   
     
     
         2 . A method of foaming a foamable adhesive composition comprising the steps of:
 (a) preparing a foamable adhesive composition comprising the hot melt adhesive, the block copolymer, and a foam cell promoter;   (b) heating the foamable adhesive composition to T1;   (c) heating the foamable adhesive composition to T2 wherein the foam cell promoter is activated at temperature greater than T1 and thereby the foamable adhesive is foamed; and   (d) applying the foamed adhesive composition onto a substrate;
 wherein the T2 is greater than T1, and 
 wherein the foamable adhesive composition is prepared with
 (i) a hot melt adhesive comprising a polymer selected from the group consisting of ethylene vinyl acetate, ethylene-acrylate, polyolefin, and mixtures thereof, and optionally a wax, a tackifier, a plasticizer, and an additive; 
 (ii) from about 3 to about 10 wt % of an olefin block copolymer having a melt index of equal to or greater than 5 g/10 min measured in accordance with ASTM D1238 at 190° C. and a DSC melting point greater than 100° C.; and 
 (iii) optionally, from about 0.05 to about 10 wt % of a foam cell promoter; 
 wherein the ratio of the polymer in the hot melt adhesive to the olefin block copolymer is in the range of about 20:1 to about 2:1. 
 
   
     
     
         3 . The method of foaming a foamable adhesive composition of  claim 2 , wherein foam cell promoter is selected form the group consisting of azodicarbonamide, oxybis(benzenesulfonylhydrazide), toulenesulfonylhydrazide, 5-phneyltetrazole, sodium bicarbonate, citric acid, acrylic copolymer and mixtures thereof. 
     
     
         4 . A method of foaming a foamable adhesive composition comprising the steps of:
 (a) preparing a foamable adhesive composition comprising the hot melt adhesive, the block copolymer, and a plurality of expandable microspheres;   (b) heating the foamable adhesive composition to T2 wherein expandable microsphere is activated at temperature greater than T1 and thereby the foamable adhesive is foamed; and   (c) applying the adhesive with expanded microsphere onto a substrate;
 wherein the T2 is greater than T1, 
 wherein the adhesive comprises essentially zero expanded microspheres at T1, and 
 wherein the foamable adhesive composition is prepared with
 (i) a hot melt adhesive comprising a polymer selected from the group consisting of ethylene vinyl acetate, ethylene-acrylate, polyolefin, and mixtures thereof, and optionally a wax, a tackifier, a plasticizer, and an additive; 
 (ii) from about 3 to about 10 wt % of an olefin block copolymer having a melt index of equal to or greater than 5 g/10 min measured in accordance with ASTM D1238 at 190° C. and a DSC melting point greater than 100° C.; and 
 (iii) optionally, from about 0.05 to about 10 wt % of a foam cell promoter;
 wherein the ratio of the polymer in the hot melt adhesive to the olefin block copolymer is in the range of about 20:1 to about 2:1.