Adhesive for bonding to low surface energy surfaces

Abstract

A novel polymodal asymmetric elastomeric block copolymer and a pressure sensitive adhesive, tape and adhesive backed article made therefrom, such as a polymer foam article having a substantially smooth surface prepared by melt-mixing a polymer composition and a plurality of microspheres, at least one of which is an expandable polymeric microsphere, under process conditions, including temperature and shear rate, selected to form an expandable extrudable composition; and extruding the composition through a die.

What is claimed is:  
     
         1 . A pressure sensitive adhesive having a rubber phase, said adhesive comprising: 
 (a) 100 parts by weight of a polymodal asymmetric elastomeric block copolymer;    (b) at least one tackifier in an amount sufficient to raise the calculated Fox T g  of the rubber phase of said adhesive to at least 245° K.;    (c) 0 to about 50 parts by weight of a crosslinking agent; and    (d) 0 to about 300 parts by weight of a plasticizer;    wherein said polymodal asymmetric elastomeric block copolymer has the formula Q n  Y and comprises from about 4 to about 40 percent by weight of a polymerized monovinyl aromatic compound and from about 96 to about 60 percent by weight of polymerized conjugated diene, wherein: 
 Q represents an individual arm of said block copolymer and has the formula S—B;  
 n represents the number of arms Q in said block copolymer and is a whole number of at least 3; and  
 Y is the residue of a multifunctional coupling agent; and further wherein: 
 (a) S is a nonelastomeric polymer segment endblock of a polymerized monovinyl aromatic homopolymer, there being at least two different molecular weight endblocks in said copolymer, a higher molecular weight endblock and a lower molecular weight endblock, wherein: 
 (i) the number average molecular weight of said higher molecular weight endblock (Mn) H  is in the range of from about 5,000 to about 50,000;  
 (ii) the number average molecular weight of said lower molecular weight endblock (Mn) L  is in the range of from about 1,000 to about 10,000; and  
 (iii) the ratio (Mn) H /(Mn) L  is at least 1.25; and  
 
 (b) B is an elastomeric polymer segment midblock which connects each arm to the residue of a multifunctional coupling agent (Y) and comprises a polymerized conjugated diene or combination of conjugated dienes, and  
 wherein said adhesive has a rubber phase exhibiting a calculated Fox T g  of at least 245° K and said adhesive forms a high strength bond to low surface energy surfaces.  
 
   
     
     
         2 . The pressure sensitive adhesive according to  claim 1 , wherein said adhesive is solvent free with only up to a 20% solvent content.  
     
     
         3 . The pressure sensitive adhesive according to  claim 1 , wherein the rubber phase of said adhesive has a calculated Fox T g  of at least 250° K.  
     
     
         4 . The pressure sensitive adhesive according to  claim 1 , wherein the rubber phase of said adhesive has a calculated Fox T g  with an upper limit of less than 300° K.  
     
     
         5 . The pressure sensitive adhesive according to  claim 1 , wherein said adhesive exhibits a 180° peel strength on a low surface energy substrate of at least about 20 N/dm.  
     
     
         6 . The pressure sensitive adhesive according to  claim 5 , wherein said adhesive exhibits a 180° peel strength on a low surface energy substrate of at least about 60 N/dm.  
     
     
         7 . The pressure sensitive adhesive according to  claim 1 , wherein said adhesive is in the form of a film.  
     
     
         8 . The pressure sensitive adhesive according to  claim 1  in combination with a backing having first and second major surfaces, and said adhesive is coated on at least a portion of at least one of the major surfaces.  
     
     
         9 . The pressure sensitive adhesive according to  claim 8 , wherein said backing is a foam core.  
     
     
         10 . The pressure sensitive adhesive according to  claim 8 , wherein said backing further comprises a release surface.  
     
     
         11 . The pressure sensitive adhesive according to  claim 8 , wherein said backing is a foam tape core made of the same or a different polymodal asymmetric elastomeric block copolymer, and said adhesive is in the form of at least one co-extruded layer on said foam tape core.  
     
     
         12 . The pressure sensitive adhesive according to  claim 8 , wherein said backing is an acrylic foam tape core, and said adhesive is in the form of at least one co-extruded layer on said foam tape core.  
     
     
         13 . The pressure sensitive adhesive according to  claim 8 , wherein said backing is in the form of a foam, at least one of the major surfaces of which is substantially smooth having an Ra value less than about 75 micrometers, as measured by laser triangulation profilometry, and said foam comprises a plurality of microspheres, at least one of which is an expandable polymeric microsphere.  
     
     
         14 . The pressure sensitive adhesive according to  claim 1 , wherein said adhesive is in the form of a foam having at least one substantially smooth major surface having an Ra value less than about 75 micrometers, as measured by laser triangulation profilometry, and said foam comprises a plurality of microspheres, at least one of which is an expandable polymeric microsphere.  
     
     
         15 . The pressure sensitive adhesive according to  claim 1 , wherein said adhesive is in the form of a foam having at least one substantially smooth major surface having an Ra value less than about 75 micrometers, as measured by laser triangulation profilometry, and said foam comprises a plurality of said expandable polymeric microspheres.  
     
     
         16 . The pressure sensitive adhesive according to  claim 15 , wherein said foam is substantially free of broken polymeric microspheres.  
     
     
         17 . The pressure sensitive adhesive according to  claim 15  in combination with at least one other polymer composition in the form of a plurality of discrete structures bonded to or embedded in said foam.  
     
     
         18 . The pressure sensitive adhesive of  claim 1 , wherein said adhesive exhibits a 90° peel strength on a low surface energy substrate of at least about 50 N/dm.  
     
     
         19 . The pressure sensitive adhesive of  claim 18 , wherein said adhesive exhibits a 90° peel strength on a low surface energy substrate of at least about 75 N/dm.  
     
     
         20 . The pressure sensitive adhesive of  claim 1 , wherein said tackifier is a low acidic or neutral tackifier.  
     
     
         21 . The pressure sensitive adhesive of  claim 1 , wherein said tackifier has a T g  in the range of from about −50° C. to about 200° C.  
     
     
         22 . The pressure sensitive adhesive of  claim 1 , wherein said tackifier has a softening point of above 80° C.  
     
     
         23 . The pressure sensitive adhesive of  claim 1 , wherein said at least one tackifier is selected from the group consisting of hydrogenated mixed aromatic tackifiers, aliphatic/aromatic hydrocarbon liquid tackifiers; napthenic oils, mineral oils, and a mixture of one or more thereof.  
     
     
         24 . The pressure sensitive adhesive of  claim 1 , wherein said adhesive comprises in the range of from about 50 parts to about 350 parts by weight of said at least one tackifier.  
     
     
         25 . The pressure sensitive adhesive of  claim 1 , wherein said adhesive comprises in the range of from about 70 parts to about 300 parts by weight of said at least one tackifier.  
     
     
         26 . The pressure sensitive adhesive according to  claim 1 , wherein the polymodal asymmetric elastomeric block copolymer is crosslinked.  
     
     
         27 . The pressure sensitive adhesive according to  claim 26 , wherein said adhesive is a radiation crosslinkable composition.  
     
     
         28 . A pressure sensitive adhesive tape, said tape comprising: 
 a foam backing having two major surfaces; and a pressure sensitive adhesive being coated on at least a portion of at least one of the major surfaces, at least one of foam backing and said adhesive comprising a blend of two or more polymers with one of said polymers comprising:    (a) 100 parts by weight of a polymodal asymmetric elastomeric block copolymer;    (b) at least one tackifier;    (c) 0 to about 50 parts by weight of a crosslinking agent; and    (d) 0 to about 300 parts by weight of a plasticizer;    wherein said polymodal asymmetric elastomeric block copolymer has the formula Q n  Y and comprises from about 4 to about 40 percent by weight of a polymerized monovinyl aromatic compound and from about 96 to about 60 percent by weight of polymerized conjugated diene, wherein: 
 Q represents an individual arm of said block copolymer and has the formula S—B;  
 n represents the number of arms Q in said block copolymer and is a whole number of at least 3; and  
 Y is the residue of a multifunctional coupling agent; and further wherein: 
 (a) S is a nonelastomeric polymer segment endblock of a polymerized monovinyl aromatic homopolymer, there being at least two different molecular weight endblocks in said copolymer, a higher molecular weight endblock and a lower molecular weight endblock, wherein: 
 (i) the number average molecular weight of said higher molecular weight endblock (Mn) H  is in the range of from about 5,000 to about 50,000;  
 (ii) the number average molecular weight of said lower molecular weight endblock (Mn) L  is in the range of from about 1,000 to about 10,000; and  
 (iii) the ratio (Mn) H /(Mn) L  is at least 1.25; and  
 
 (b) B is an elastomeric polymer segment midblock which connects each arm to the residue of a multifunctional coupling agent (Y) and comprises a polymerized conjugated diene or combination of conjugated dienes.  
 
   
     
     
         29 . The adhesive tape of  claim 28 , wherein, wherein said adhesive forms a high strength bond to low surface energy surfaces.