Thermally stable meltblown web comprising multilayer fibers

Abstract

A thermally stable meltblown fibrous web, including a plurality of meltblown multilayer fibers, in which at least some of the meltblown multilayer fibers each include at least one primary layer that includes a primary polymer that is slow-crystallizing with a T m of at least about 200° C., and at least one secondary layer that includes a secondary polymer that is fast-crystallizing with a T m of at least about 200° C.

What is claimed is: 
     
         1 . A thermally stable meltblown fibrous web, comprising:
 a plurality of meltblown multilayer fibers, wherein at least selected meltblown multilayer fibers each comprise at least one primary layer comprised of a primary polymer that is a slow-crystallizing polymer with a T m  of at least about 200° C., and at least one secondary layer comprised of a secondary polymer that is a fast-crystallizing polymer with a T m  of at least about 200° C.,
 wherein the meltblown multilayer fibers exhibit an average weight ratio of the primary polymer to the secondary polymer of from about 45:55 to about 95:05 and wherein the thermally stable meltblown fibrous web exhibits a thermal shrink of less than about 10%. 
   
     
     
         2 . The web of  claim 1 , wherein the primary polymer exhibits a T m  of at least about 240° C. and wherein the secondary polymer exhibits a T m  of at least about 240° C. 
     
     
         3 . The web of  claim 1 , wherein the meltblown fibers exhibit an average weight ratio of primary polymer to secondary polymer of from about 60:40 to about 90:10. 
     
     
         4 . The web of  claim 1 , wherein the meltblown fibers exhibit an average weight ratio of primary polymer to secondary polymer of from about 70:30 to about 80:20. 
     
     
         5 . The web of  claim 1 , wherein the primary polymer is a polyester chosen from the group consisting poly(ethylene terephthalate), poly(ethylene naphthalate), poly(lactic acid), poly(trimethylene terephthalate), and combinations thereof. 
     
     
         6 . The web of  claim 1 , wherein the primary polymer is poly(ethylene terephthalate). 
     
     
         7 . The web of  claim 1 , wherein the primary polymer is substantially free of a non-polymeric nucleating agent. 
     
     
         8 . The web of  claim 1 , wherein the secondary polymer is chosen from the group consisting of poly(butylene terephthalate), polymethylpentene, and syndiotactic polystyrene. 
     
     
         9 . The web of  claim 1 , wherein at least selected multilayer fibers each comprise at least one pair of primary layers with a secondary layer individually sandwiched therebetween. 
     
     
         10 . The web of  claim 1 , wherein at least selected multilayer fibers each comprise at least three primary layers and at least two secondary layers, with each secondary layer being individually sandwiched between a pair of primary layers. 
     
     
         11 . The web of  claim 1 , wherein at least selected multilayer fibers each comprise at least five primary layers and at least four secondary layers, with each secondary layer being individually sandwiched between a pair of primary layers. 
     
     
         12 . The web of  claim 1 , wherein at least selected multilayer fibers each comprise at least n primary layers and at least n−1 secondary layers, at least n−2 of the secondary layers being individually sandwiched between primary layers, where n is a number between 7 and 51. 
     
     
         13 . The web of  claim 1 , wherein the primary layers are monocomponent layers and wherein the secondary layers are monocomponent layers. 
     
     
         14 . The web of  claim 1 , wherein the plurality of meltblown fibers collectively exhibit an average fiber diameter of less than about 10 micrometers. 
     
     
         15 . The web of  claim 1 , wherein the web further comprises staple fibers, the staple fibers making up from about 5 wt. % to about 50 wt. % of the total weight of the fibrous material of the web. 
     
     
         16 . The web of  claim 1 , wherein the web exhibits a thermal shrink of less than about 6%. 
     
     
         17 . The web of  claim 1 , wherein the web exhibits a thermal shrink of less than about 2%. 
     
     
         18 . The web of  claim 1 , wherein the meltblown fibers of the web comprise no more than about 5 wt. % of any polymeric material that exhibits a T m  of less than 200° C. 
     
     
         19 . The web of  claim 1 , wherein the meltblown fibers of the web are substantially free of any polymeric material with a T m  of less than 200° C. 
     
     
         20 . An article comprising the thermally stable meltblown fibrous web of  claim 1 , wherein the article is selected from the group consisting of a thermal insulation article, an acoustic insulation article, a fluid filtration article, or a combination thereof. 
     
     
         21 . The article of  claim 20 , wherein the article is an acoustic insulation article that exhibits a thermal shrink of less than about 5%. 
     
     
         22 . A method comprising:
 extruding molten multilayer flowstreams through orifices of a meltblowing die to form molten multilayer filaments;   attenuating the molten multilayer filaments with high-velocity gaseous streams to form multilayer meltblown fibers; and,   collecting the multilayer meltblown fibers as a mass of fibers,
 wherein at least selected multilayer meltblown fibers of the collected mass of fibers flowstreams each comprise at least one primary layer comprised of a molten primary polymer that is a slow-crystallizing polymer with a T m  of at least about 200° C., and at least one secondary layer comprised of a molten secondary polymer that is a fast-crystallizing polymer with a T m  of at least about 200° C. 
   
     
     
         23 . The method of  claim 22  wherein the attenuated multilayer filaments form an airborne stream of multilayer meltblown fibers, and wherein the method further includes injecting an airborne stream of staple fibers into the airborne stream of multilayer fibers and collecting the intermingled multilayer meltblown fibers and staple fibers as a mass of fibers. 
     
     
         24 . The method of  claim 22  wherein the method further includes bonding at least some of the fibers of the mass of fibers to each other to form a thermally stable meltblown fibrous web.