High performance elastic composite materials made from high molecular weight thermoplastic triblock elastomers

Abstract

The present invention comprises a continuous feed spun bonded laminate having improved elastic properties measured at body temperature. The laminate comprises at least one first and second nonelastic layers between which is sandwiched at least one elastic layer, the elastic layer being comprised of a triblock polystyrene-poly(ethylene/propylene)-polystyrene (“SEPS”) copolymer having a number average molecular weight of about 81,000 g/mol. The weight percent of styrene is approximately 18% and the weight percent of ethylene/propylene is approximately 82%. The molecular weight increase in the EP block, while holding the molecular weight of the styrene block constant, increases the entanglement density, polymer chain persistence length and the relaxation time. The resulting laminate load decay rate and load loss measurements over a period of 12 hours at body temperature showed marked improvement over known CFSBL product. The laminate is particularly useful as side panel material in training pants because of the resistance to sagging at body temperature.

What is claimed is:  
     
         1 . A composite elastic material having improved elastic properties at body temperature, comprising: 
 A) a first layer of substantially parallel filaments formed of an elastomeric polymer, said polymer having a number average molecular weight of from about 65,000 g/mol to about 100,000 g/mol;    B) a second layer of elastomeric meltblown fibers, said meltblown fibers bonded to at least a portion of the first layer filaments;    C) a third layer of spunbond fibers; and, a fourth layer of spunbond fibers; wherein said first and second layers are disposed between said third and fourth layers.    
     
     
         2 . The composite elastic material of  claim 1 , wherein said elastomeric polymer of said first layer comprises an A-B-A′ triblock copolymer wherein A and A′ are the same or different thermoplastic polymer, and wherein B is an elastomeric polymer block.  
     
     
         3 . The composite elastic material of  claim 2 , wherein A is a styrene-based polymer.  
     
     
         4 . The composite elastic material of  claim 2 , wherein B is selected from the group consisting of ethylene/propylene and ethylene/butylene.  
     
     
         5 . The composite elastic material of  claim 4 , wherein said ethylene/propylene and ethylene/butylene are saturated.  
     
     
         6 . The composite elastic material of  claim 4 , wherein said ethylene/propylene and ethylene/butylene are unsaturated.  
     
     
         7 . The composite elastic material of  claim 2 , wherein said elastomeric material comprises about 18% styrene-based material and about 82% midblock material.  
     
     
         8 . The composite elastic material of  claim 1 , wherein said elastomeric polymer of said first layer is substantially free of diblock polymer.  
     
     
         9 . The composite elastic material of  claim 1 , wherein said material has a percent load loss at body temperature over a twelve hour period of less than about 40%.  
     
     
         10 . The composite elastic material of  claim 1 , wherein said material has a percent load loss at body temperature over a twelve hour period of less than about 50%.  
     
     
         11 . The composite elastic material of  claim 1 , wherein said material has a load decay slope at body temperature over a twelve hour period of about −0.08.  
     
     
         12 . The composite elastic material of  claim 1 , wherein said material has a load decay slope at body temperature over a twelve hour period of about −0.10.  
     
     
         13 . The composite elastic material of  claim 1 , wherein said polymer has a number average molecular weight of from about 65,000 g/mol to about 100,000 g/mol.  
     
     
         14 . The composite elastic material of  claim 1 , wherein said polymer has a number average molecular weight of from about 75,000 g/mol to about 90,000 g/mol.  
     
     
         15 . The composite elastic material of  claim 1 , wherein said material has a number average molecular weight of about 81,000 g/mol.  
     
     
         16 . The composite elastic material of  claim 1 , wherein said meltblown fibers comprise an elastomeric polymer selected from the group consisting of elastic polyesters, elastic polyurethanes, elastic polyamides, elastic copolymers of ethylene and at least one vinyl monomer, and elastic A-B-A′ block copolymers wherein A and A′ are the same or different thermoplastic polymers, and wherein B is an elastomeric polymer block.  
     
     
         17 . The composite elastic material of  claim 16 , wherein said elastomeric polymer is blended with a processing aid.  
     
     
         18 . The composite elastic material of  claim 16 , wherein said elastomeric polymer is blended with a tackifying resin.  
     
     
         19 . The composite elastic material of  claim 1 , further comprising a fifth layer of meltblown material.  
     
     
         20 . The composite elastic material of  claim 12 , wherein said second and said fifth layers of meltblown material are bonded to both sides of said first layer.  
     
     
         21 . A process for forming a composite elastic material having improved elastic properties at body temperature, comprising: 
 A) providing a first layer of substantially parallel filaments formed of an elastomeric polymer, said polymer having a number average molecular weight of from about 65,000 g/mol to about 100,000 g/mol;    B) a second layer of elastomeric meltblown fibers, said meltblown fibers bonded to at least a portion of the first layer filaments so that the elastic fibrous web is anisotropic;    C) adhering said first and said second layers together to form a first web;    D) stretching said first web in the machine direction;    E) providing a third layer of spunbond fibers;    F) providing a fourth layer of spunbond fibers; and,    G) adhering said third and fourth layers to both sides of said first web to form a second web.    
     
     
         22 . The process of  claim 21 , further comprising passing said second web through at least one pair of calendar rolls.  
     
     
         23 . The process of  claim 22 , further comprising relaxing said second web.  
     
     
         24 . The composite elastic material of  claim 21 , wherein said elastomeric polymer of said first layer comprises an A-B-A′ triblock copolymer wherein A and A′ are the same or different thermoplastic polymer, and wherein B is an elastomeric polymer block.  
     
     
         25 . The composite elastic material of  claim 24 , wherein A is a styrene-based polymer.  
     
     
         26 . The composite elastic material of  claim 24 , wherein B is selected from the group consisting of ethylene/propylene and ethylene/butylene.  
     
     
         27 . The composite elastic material of  claim 24 , wherein elastomeric material comprises about 18% styrene-based material and about 82% midblock material.  
     
     
         28 . The composite elastic material of  claim 21 , wherein said elastomeric polymer of said first layer is substantially free of diblock polymer.  
     
     
         29 . The composite elastic material of  claim 21 , wherein said material has a percent load loss at body temperature over a twelve hour period of about 40%.  
     
     
         30 . The composite elastic material of  claim 21 , wherein said material has a load decay slope at body temperature over a twelve hour period of about −0.08.  
     
     
         31 . The composite elastic material of  claim 21 , wherein said meltblown fibers comprise an elastomeric polymer selected from the group consisting of elastic polyesters, elastic polyurethanes, elastic polyamides, elastic copolymers of ethylene and at least one vinyl monomer, and elastic A-B-A′ block copolymers wherein A and A′ are the same or different thermoplastic polymers, and wherein B is an elastomeric polymer block.  
     
     
         32 . The composite elastic material of  claim 21 , wherein said elastomeric polymer is blended with a processing aid.  
     
     
         33 . The composite elastic material of  claim 21 , wherein said elastomeric polymer is blended with a tackifying resin.  
     
     
         34 . The composite elastic material of  claim 21 , further comprising a fifth layer of meltblown material.  
     
     
         35 . The composite elastic material of  claim 34 , wherein said second and said fifth layers of meltblown material are bonded to both sides of said first layer.  
     
     
         36 . An article of manufacture incorporating a composite elastic material made according to the process of  claim 21 .  
     
     
         37 . The article of manufacture of  claim 36 , wherein said article is selected from the group consisting of, pads, diapers, incontinence undergarments and personal care products.  
     
     
         38 . A training pants article having side panels incorporating a composite elastic material, said elastic material comprising: 
 A) a first layer of substantially parallel filaments formed of an elastomeric polymer, said polymer having a number average molecular weight of from about 65,000 g/mol to about 100,000 g/mol;    B) a second layer of elastomeric meltblown fibers, said meltblown fibers bonded to at least a portion of the first layer filaments so that the elastic fibrous web is anisotropic;    C) a third layer of spunbond fibers; and,    D) a fourth layer of spunbond fibers;    wherein said first and second layers are disposed between said third and fourth layers.    
     
     
         39 . A polymer suitable for use in an elastic material, said polymer comprising an A-B-A′ triblock copolymer wherein A and A′ are the same or different thermoplastic polymer, and wherein B is an elastomeric polymer block, said polymer having a number average molecular weight of from about 65,000 g/mol to about 100,000 g/mol; said A and A′ being a styrene-based polymer and B is selected from the group consisting of ethylene/propylene and ethylene/butylene.  
     
     
         40 . The composite elastic material of  claim 39 , wherein said elastomeric material comprises about 18% A and A′ and about 82% B.