Fibers and fabrics prepared from blends of homopolymers and copolymers

Abstract

A fiber comprising a propylene polymer composition is disclosed. The composition comprises a resin blend of from about 75 to about 95 weight percent of a Ziegler-Natta or metallocene catalyzed isotactic polypropylene homopolymer, and from about 95 to about 75 weight percent of a metallocene catalyzed polypropylene copolymer. In this blend the copolymer component includes a comonomer in an amount from about 0.05 to about 25 weight percent, based on the copolymer. Non-woven fabrics prepared by thermally bonding the inventive fibers show improved tensile strengths, particularly machine direction, at comparable basis weights that are at least about 5 percent higher than those of fabrics prepared using identical preparation techniques but from the isotactic polypropylene homopolymer alone.

1 . A fiber, spunbond fabric, or melt blown fabric comprising a polymer composition comprising a resin blend of from about 60 to about 99 weight percent of a Ziegler-Natta or metallocene catalyzed isotactic polypropylene homopolymer, and from about 1 to about 40 weight percent of a metallocene catalyzed propylene copolymer, wherein the copolymer comprises a comonomer in an amount from about 0.05 to about 25 weight percent, based on the copolymer.  
   
   
       2 . The fiber of  claim 1  wherein the polypropylene homopolymer is Ziegler-Natta catalyzed.  
   
   
       3 . The fiber of  claim 1  wherein the metallocene used to catalyze polymerization of the propylene copolymer is a substituted isospecific CpFlu-type catalyst.  
   
   
       4 . The fiber of  claim 1  wherein the metallocene used to catalyze polymerization of the propylene copolymer is racemic Me 2 Si(2-Me-4-PhInd) 2 ZrCl 2  on 0.7/1 MAO on P10 silica, Ph is phenyl; Ind is indenyl; and MAO is methylalumoxane.  
   
   
       5 . The fiber of  claim 1  wherein the comonomer is ethylene and it is present in an amount of from about 1 to about 20 weight percent, based on the copolymer.  
   
   
       6 . An article comprising a fiber of  claim 1 .  
   
   
       7 . The article of  claim 6  wherein the article is a carpet or twine.  
   
   
       8 . The article of  claim 6  wherein the article is a staple fiber.  
   
   
       9 . The article of  claim 6  wherein the article is a spunbond fabric.  
   
   
       10 . The article of  claim 6  wherein the article is a continuous filament.  
   
   
       11 . A thermally bonded non-woven fabric comprising a fiber comprising a polymer composition comprising a resin blend of from about 75 to about 95 weight percent of a Ziegler-Natta or metallocene catalyzed isotactic polypropylene homopolymer, and from about 95 to about 75 weight percent of a metallocene catalyzed polypropylene copolymer, wherein the copolymer comprises a comonomer in an amount from about 0.05 to about 25 weight percent, based on the copolymer.  
   
   
       12 . The fabric of  claim 11  wherein the thermal bonding is carried out at a temperature of at least about 240° C.  
   
   
       13 . The fabric of  claim 12  wherein the thermal bonding is carried out at a temperature of at least about 250° C.  
   
   
       14 . The fabric of  claim 11  wherein the fabric has a machine direction tensile strength that is at least 5 percent higher than the tensile strength of a thermally bonded non-woven fabric made from a fiber that is made from the polypropylene homopolymer alone, the fabrics having basis weights of 10 gsm to 100 gsm.  
   
   
       15 . The fabric of  claim 11  wherein the fabric has a machine direction tensile strength that is at least 10 percent higher than the tensile strength of a thermally bonded non-woven made from a fiber that is made from the polypropylene homopolymer alone, the fabrics having a basis weight of 17 gsm.  
   
   
       16 . An article comprising the fabric of  claim 11 .  
   
   
       17 . The article of  claim 11  being selected from the group consisting of baby diaper coverstock, feminine hygiene coverstock, agricultural fabric, housewrap, medical gowns, drapes, and catamenial devices.  
   
   
       18 . A method for preparing a non-woven fabric comprising melt spinning a polymer composition comprising a resin blend of from about 75 to about 95 weight percent of a Ziegler-Natta or metallocene catalyzed isotactic polypropylene homopolymer, and from about 95 to about 75 weight percent of a metallocene catalyzed propylene copolymer, wherein the copolymer comprises a comonomer in an amount from about 0.05 to about 25 weight percent, based on the copolymer, to form a fiber, and thermally bonding the fiber at a temperature of at least about 240° C.  
   
   
       19 . The method of  claim 18  wherein the polypropylene homopolymer is Ziegler-Natta catalyzed.  
   
   
       20 . The method of  claim 18  wherein the metallocene used to catalyze polymerization of the propylene copolymer is a substituted isospecific CpFlu-type catalyst.  
   
   
       21 . The method of  claim 18  wherein the catalyst is racemic Me 2 Si(2Me-4-PhInd) 2 ZrCl 2  on 0.7/1 MAO on P10 silica; Ph is phenyl; Ind is indenyl; and MAO is methylalumoxane.  
   
   
       22 . The method of  claim 16  wherein the comonomer is ethylene, and it is present in an amount of from about 1 to about 10 weight percent, based on the copolymer.