Low stress relaxation adhesive having high molecular weight endblock copolymer

Abstract

An adhesive formulation is provided comprising an elastomeric block copolymer having a midblock segment derived from polymerized diene monomer and at least two endblock segments derived from polymerized monovinyl substituted aromatic compound monomer, a midblock compatible tackifier, a midblock compatible oil, and endblock compatible resin and an antioxidant. The block copolymer can be either an unhydrogenated polymer having terminal endblocks with a molecular weight within the range of 13,000 to 30,000 or it can be a hydrogenated copolymer having terminal endblocks with a molecular weight of 11,000 to 20,000. The presence of roughly high molecular weight endblock segments results in an adhesive composition having superior (lower) stress relaxation and set.

What is claimed is:  
     
       1. An adhesive composition, comprising: 
       A) a base composition, comprising  
       (i) 15-35 wt % of an unhydrogenated elastomeric block copolyner having a polymerized conjugated diene midblock portion and at least two polymerized monovinyl arene endblock portions, each of said endblock portions having a molecular weight within the range of 13,000 to 30,000, wherein said endblock portions are present at a total concentration within the range of 20 to 24% wt based upon the total weight of said unhydrogenated elastomeric block copolymer; and  
       (ii) 85-65 wt % based on the total weight of (i) and (ii) of tackifying components comprising a midblock compatible resin and oil, said midblock compatible resin and said oil being present in a weight ratio within the range of 1.5:1 to 3.5:1 midblock compatible resin:oil and said midblock compatible resin and said unhydrogenated elastomeric block copolymer being present in a weight ratio of at least 120:100 midblock compatible resin:unhydrogenated elastomeric block copolymer; and  
       B) a stabilizer, said stabilizer being present in an amount within the range of 0.01 to 5 wt % based on the weight of said base composition.  
     
     
       2. The composition according to  claim 1 , wherein the ingredients of (ii) comprise in addition an endblock compatible resin in an amount within the range of 20-80 parts by weight per 100 parts by weight of said unhydrogenated elastomei block copolymer. 
     
     
       3. A pressure sensitive adhesive composition, comprising: 
       an unhydrogenated elastomeric block copolymer having a polymerized, conjugated diene midblock portion and two polymerized monovinyl arene endblock portions, each of said endblock portions having a molecular weight within the range of 13,000-30,000, wherein said endblock portions are present at a total concentration within the range of 20 to 24% wt based upon the total weight of said unhydrogenated elastomeric block copolymer;  
       120-450 parts by weight per 100 parts by weight of said unhydrogenated elastomeric block copolymer of a midblock compatible resin;  
       40-225 parts by weight per 100 parts by weight of said unhydrogenated elastomeric block copolymer of oil;  
       20-80 parts by weight per 100 parts by weight of said unhydrogenated elastomeric block copolymer of an endblock compatible resin; and  
       0.01-5 wt % based on the total weight of said unhydrogenated elastomeric block copolymer, said midblock compatible resin, said oil, and said endblock compatible resin of an antioxidant.  
     
     
       4. The composition according to  claim 3 , wherein said unhydrogenated elastomeric block copolymer is a coupled styrene/isoprene/styrene linear block copolymer and wherein said endblock portions have a molecular weight within the range of 14,000-20,000, said midblock compatible resin is present in an amount within the range of 150-300 parts by weight per 100 parts by weight of said linear block copolymer, said oil is present in an amount within the range of 45-150 parts by weight per 100 parts by weight of said linear block copolymer, and said antioxidant is present in the amount within the range of 0.5-1 weight percent based on the weight of said linear block copolymer, said midblock compatible resin, said endblock compatible resin, and said oil. 
     
     
       5. The composition according to  claim 4 , wherein said endblock portions have a molecular weight within the range of 15,000-16,000. 
     
     
       6. The composition according to  claim 3 , wherein said unhydrogenated elastomeric block copolymer has arm molecular weights of 43,000-106,000. 
     
     
       7. The composition according to  claim 6 , wherein said midblock compatible resin is an essentially completely hydrogenated polymer made from C 9  aromatics, said endblock compatible resin is a resin derived from copolymerization of aromatic monomers, said oil is an essentially completely hydrogenated naphthenic oil, and said antioxidant is a hindered phenol. 
     
     
       8. The composition according to  claim 3 , wherein said composition is essentially free of any resin which is compatible with both said midblock portion and said endblock portions. 
     
     
       9. An adhesive composition, comprising: 
       A) a base composition, comprising  
       (i) 12-33 wt % of an elastomeric block copolymer having an ethylene/propylene or ethylene/butylene midblock portion derived from hydrogenated polymerized isoprene or butadiene and at least two polymerized monovinyl arene endblock portions, each of said endblock portions having a molecular weight within the range of 11,000 to 20,000, wherein said endblock portions are present at a total concentration within the range of 20 to 24% wt based upon the total weight of said hydrogenated elastomeric block copolymer, and  
       (ii) 88-67 wt %, based on the total weight of (i) and (ii), of tackifying components comprising a midblock compatible resin and oil, said midblock compatible resin and said oil being present in a weight ratio within the range of 1.5:1 to 3.5:1 midblock compatible resin:oil and said midblock compatible resin and said hydrogenated elastomeric block copolymer being present in a weight ratio of at least 120:100 midblock compatible resin:hydrogenated elastomeric block copolymer, and  
       B) a stabilizer present in an amount within the range of 0.01-5 wt % based on the weight of said base composition.  
     
     
       10. The composition according to  claim 9 , wherein the ingredients of (i) comprise in addition an endblock compatible resin in an amount within the range of 20-80 parts by weight per 100 parts by weight of said hydrogenated elastomeric block copolymer, and said endblock compatible resin has a Tg of greater than 90° C. 
     
     
       11. An adhesive composition, comprising: 
       a hydrogenated elastomeric block copolymer having a midblock portion derived from polymerized, conjugated diene and at least two polymerized monovinylarene endblock portions, each of said endblock portions having a molecular weight within the range of 12,000-20,000, wherein said endblock portions are present at a total concentration within the range of 20 to 24% wt based upon the total weight of said hydrogenated elastomeric block copolymer;  
       140-600 parts by weight of a midblock compatible resin per 100 parts by weight of said hydrogenated elastomeric block copolymer;  
       50-300 parts by weight of oil per 100 parts by weight of said hydrogenated elastomeric block copolymer;  
       20-80 parts by weight of an endblock compatible resin per 100 parts by weight of said hydrogenated elastomeric block copolymer; and  
       0.01-5 wt % of a stabilizer based on the total weight of said hydrogenated elastomeric block copolymer, said midblock compatible resin, and said endblock compatible resin.  
     
     
       12. The composition according to  claim 11 , wherein said hydrogenated elastomeric block copolymer is derived from a sequentially polymerized styrene-isoprene-styrene or styrene-butadiene-styrene block copolymer, said endblock portions have a molecular weight within the range of 13,000-17,000, said midblock compatible resin is present in an amount within the range of 250-500 parts by weight per 100 parts by weight of said hydrogenated elastomeric block copolymer, said oil is present in an amount within the range of 50-200 parts by weight per 100 parts by weight of said hydrogenated elastomeric block copolymer, said endblock compatible resin is present in the amount from 25-40 parts by weight per 100 parts by weight of said hydrogenated elastomeric block copolymer, and said stabilizer is an antioxidant present in an amount within the range of 0.5-1 wt % based on the total weight of said hydrogenated elastomeric block copolymer, said midblock compatible resin, said oil, and said endblock compatible resin. 
     
     
       13. The composition according to  claim 11 , wherein said composition is essentially free of any resin which is compatible with both said midblock portion and said endblock portions. 
     
     
       14. The composition according to  claim 1 , wherein said hydrogenated elastomeric block copolymer has a styrene content within the range of 22 to 24 wt % based on the total weight of said hydrogenated elastomeric block copolymer. 
     
     
       15. The composition according to  claim 11 , wherein said hydrogenated elastomeric block copolymer has arm molecular weights within the range of 30,000 to 60,000. 
     
     
       16. The composition according to  claim 15 , wherein said midblock compatible resin is an essentially completely hydrogenated polymer made from copolymerizing C 9  aromatics, wherein said endblock compatible resin is a resin derived by copolymerization of aromatic monomers, said oil is an essentially completely hydrogenated napthenic oil, said antioxidant is a hindered phenol. 
     
     
       17. The composition according to  claim 16 , wherein the Tg of the aromatic endblock resin is greater than 90° C. 
     
     
       18. A process for producing an adhesive formulation, comprising: 
       selecting an elastomeric block copolymer having a midblock portion derived from polymerized diene and at least two endblocks derived from polymerized monovinyl arene, said selection being based on the molecular weight of the endblock segments;  
       selecting a first tackifying resin based on a high degree of compatibility with said midblock section and lack of compatibility with said endblock sections;  
       selecting a second tackifying resin based on a high degree of compatibility with said endblock segments and incompatibility with said midblock segment;  
       selecting an oil based on compatibility with said midblock segment and incompatibility with said endblock segments; and  
       combining said block copolymer, said first tackifying resin, said second tackifying resin, and said oil, and, in addition, an antioxidant to produce said adhesive composition, wherein said first tackifying resin and said elastomeric block copolymer are combined in a weight ratio of at least 120:100 first tackifying resin:elastomeric block copolymer.