Unidirectionally cold stretched nonwoven webs of multipolymer fibers for stretch fabrics and disposable absorbent articles containing them

Abstract

A nonwoven web of multipolymer fibers is described that is unidirectionally stretched and permanently elongated at ambient conditions and exhibits a substantial increase in tensile strength in the stretch direction. The ratio of tensile strength of the web in the direction of fiber orientation to the tensile strength in the other direction is at least about 10:1. The ratio of elongation at peak load in a direction transverse to the direction of fiber orientation is at least about 6:1. The multipolymer fibers normally are a blend of polyethylene and a polypropylene homopolymer or copolymer, one of which is a dominant phase and one of which is a dispersed phase. A third component having elastomeric properties that is at least partially miscible with one or both of the other components is included in some blends. The nonwoven webs are stretchable well beyond their initial dimensions in the direction perpendicular to the stretch direction and are especially useful in laminates with elastomeric members for use in disposable absorbent articles to impart elasticity thereto.

What is claimed is:  
     
         1 . A nonwoven web of multipolymer fibers, said fibers being substantially oriented in one direction, and said web having a plurality of discrete bond sites throughout the web bonding the fibers together, and wherein the ratio of the tensile strength of the web in the direction of orientation of the fibers to the tensile strength of the web in the other direction is at least about 10:1.  
     
     
         2 . The web of    claim 1    wherein the ratio of the tensile strength of the web in the direction of orientation of the fibers to the tensile strength of the web in the other direction is at least about 16:1.  
     
     
         3 . The web of    claim 1    wherein the ratio of the elongation at peak load of the web in the direction transverse to the direction of orientation of the fibers to the elongation at peak load in the direction of elongation is at least about 6:1.  
     
     
         4 . The web of    claim 1    wherein the ratio of the elongation at peak load of the web in the direction transverse to the direction of orientation of the fibers to the elongation at peak load in the direction of elongation is at least about 8:1.  
     
     
         5 . The web of    claim 1    wherein said discrete bond sites comprise areas where the fibers have been fusion bonded together.  
     
     
         6 . The web of    claim 5   , wherein said bond sites are embedded within the web between opposite surfaces of the web and are of a distorted, non-planar configuration extending generally in the z-axis direction of the web.  
     
     
         7 . The web of    claim 6    additionally including a plurality of bond sites that are generally planar and extend parallel to the surface of the web.  
     
     
         8 . The nonwoven web of    claim 1    wherein said multipolymer fibers comprise a blend of polypropylene and polyethylene.  
     
     
         9 . The nonwoven web of    claim 1    wherein said multipolymer fibers comprise a blend of two immiscible polymer phases and a third component which is at least partially miscible with the two immiscible polymer phases.  
     
     
         10 . The nonwoven web of    claim 1    wherein said multipolymer fibers are formed from a blend comprising: 
 a) isotactic polypropylene present in an amount of from about 65 to 80 percent by weight based upon the weight of said blend;  
 b) linear low density polyethylene present in an amount of from about 1 to 5 percent by weight based upon the weight of said blend; and  
 c) a block or grafted polyolefin copolymer or terpolymer having at least a portion of the chain thereof miscible with said isotactic polypropylene and wherein said block or grafted polyolefin copolymer or terpolymer is present in an amount of from about 15 to 30 percent by weight based upon the weight of said blend.  
 
     
     
         11 . The nonwoven web of    claim 10    wherein the multicomponent fibers are selected from the group consisting of spunbond continuous filaments, carded discontinuous staple fibers, and meltblown fibers.  
     
     
         12 . A nonwoven web of multipolymer fibers, said fibers being substantially oriented in one direction, and said multipolymer fibers comprising a blend of two immiscible polymer phases and a third component which is at least partially miscible with the two immiscible polymer phases, said web having a plurality of discrete point bond sites throughout the web bonding the fibers together, said point bond sites comprising areas where the fibers have been fusion bonded together to form bond sites, said bond sites being of a distorted, non-planar configuration extending generally in the z-axis direction of the web.  
     
     
         13 . A composite fabric comprising at least one layer of an elastomeric component bonded to at least one layer comprising the nonwoven web of    claim 1    or 12.  
     
     
         14 . The composite fabric of    claim 13    wherein said elastomeric component is selected from the group consisting of elastic strands, elastic film, and scrim comprising elastomeric strands.  
     
     
         15 . The composite fabric of    claim 14    wherein said elastic film is breathable.  
     
     
         16 . A disposable absorbent article comprising as a component thereof, the composite fabric of    claim 13   .  
     
     
         17 . A disposable absorbent article of    claim 16    wherein said composite fabric is a component of an elastic side panel for a disposable absorbent garment.  
     
     
         18 . A bonded nonwoven web of multipolymer fibers, said nonwoven web having a plurality of discrete bond sites throughout the web bonding the fibers together, said bond sites comprising areas where the fibers have been fusion bonded together, said bond sites being of a distorted, non-planar configuration extending generally in the z-axis direction of the web, and said web additionally including a plurality of bond sites that are generally planar and extend parallel to the surface of the web.  
     
     
         19 . A bonded nonwoven web comprising at least one layer of multipolymer fibers having an elongation at peak load in one or the other of the machine or cross machine directions of at least about 400% and a ratio of elongation at peak load in said one direction to the elongation at peak load in said other direction of at least about 6:1.  
     
     
         20 . The nonwoven web of    claim 19    wherein said elongation at peak load is at least about 500%.  
     
     
         21 . The nonwoven web of    claim 19    wherein said ratio of elongation at peak load in said one direction to the elongation at peak load in said other direction is at least about 8:1.  
     
     
         22 . The nonwoven web of    claim 19    wherein said ratio of elongation at peak load in said one direction to the elongation at peak load in said other direction is at least about 10:1.  
     
     
         23 . The web of    claim 19    wherein said web is a cold stretched web.  
     
     
         24 . A nonwoven web of multipolymer fibers, said web having an extensibility in one direction of at least 70 percent when a load is applied to the web in said one direction of less than or equal to 300 grams force per inch.  
     
     
         25 . The nonwoven web of    claim 24    wherein the extensibility of the web in said one direction is at least 100 percent.  
     
     
         26 . The nonwoven web of    claim 24    wherein the extensibility of the web in said one direction is at least 200 percent.  
     
     
         27 . The nonwoven web of    claim 24    wherein the extensibility of the web in said one direction is at least 350 percent.  
     
     
         28 . A nonwoven web comprising a plurality of spunbond continuous filaments formed of a blend of two immiscible polymer phases and a third component which is at least partially miscible with the two immiscible polymer phases, said web having a plurality of discrete point bond sites throughout the web bonding the continuous filaments together, said web having an extensibility in one direction of at least 70 percent when a load of less than or equal to 300 grams per inch is applied to said composite fabric in said one direction.  
     
     
         29 . The composite fabric of    claim 28    wherein said extensibility is at least 100 percent.  
     
     
         30 . The composite fabric of    claim 28    wherein said extensibility is at least 200 percent.  
     
     
         31 . The composite fabric of    claim 28    wherein said extensibility is at least 350 percent.