Dimensionally stable bonded nonwoven fibrous webs

Abstract

A dimensionally stable bonded nonwoven fibrous web formed by extruding melt blown fibers of a polymeric material, collecting the melt blown fibers as an initial nonwoven fibrous web, and annealing the initial nonwoven fibrous web with a controlled heating and cooling operation, is described. The bonded nonwoven fibrous web shrinkage is typically less than 4 percent relative to the initial nonwoven fibrous web.

What is claimed is: 
     
         1 . A bonded nonwoven fibrous web comprising melt blown fibers having a diameter in a range of 1 micrometer to 20 micrometers, wherein the melt blown fibers are substantially free of strain induced crystallization. 
     
     
         2 . The bonded nonwoven fibrous web of  claim 1 , which is dimensionally stable at a temperature in a range of 80° C. to 200° C. for at least 2 hours. 
     
     
         3 . The bonded nonwoven fibrous web of  claim 1 , exhibiting a shrinkage less than 4 percent relative to a non-bonded nonwoven fibrous web of the same composition. 
     
     
         4 . The bonded nonwoven fibrous web of  claim 1 , wherein the melt blown fibers of the bonded nonwoven fibrous web are substantially unoriented. 
     
     
         5 . The bonded nonwoven fibrous web of  claim 1 , wherein the melt blown fibers of the bonded nonwoven fibrous web are essentially discontinuous. 
     
     
         6 . The bonded nonwoven fibrous web of  claim 1 , wherein the melt blown fibers of the bonded nonwoven fibrous web are at least monocomponent. 
     
     
         7 . The bonded nonwoven fibrous web of  claim 1 , wherein the melt blown fibers of the bonded nonwoven fibrous web comprise polymeric material is selected from the group consisting of polyesters, polyamides, cyclic polyolefins and combinations thereof. 
     
     
         8 . The bonded nonwoven fibrous web of  claim 7 , wherein the polymeric material comprises poly(ethylene terephthalate). 
     
     
         9 . The bonded nonwoven fibrous web of  claim 7 , wherein the polymeric material comprises poly(lactic acid). 
     
     
         10 . The bonded nonwoven fibrous web of  claim 1 , wherein the diameter of the melt blown fibers is in a range of 1 micrometer to 10 micrometers. 
     
     
         11 . The bonded nonwoven fibrous web of  claim 1 , wherein the melt blown fibers are formed from a single thermoplastic material. 
     
     
         12 . The bonded nonwoven fibrous web of  claim 1 , wherein the melt blown fibers are formed from a blend of multiple thermoplastic materials. 
     
     
         13 . The bonded nonwoven fibrous web of  claim 1 , further comprising crimped fibers, wherein the melt-blown fibers are oriented. 
     
     
         14 . The bonded nonwoven fibrous web of  claim 1 , wherein the melt blown fibers have multiple layers of different polymeric materials. 
     
     
         15 . The bonded nonwoven fibrous web of  claim 14 , wherein the layers are arranged concentrically or longitudinally along the melt blown fiber's length. 
     
     
         16 . An insulative article comprising the bonded nonwoven fibrous web of  claim 1 , and further comprising staple fibers. 
     
     
         17 . A shaped article comprising the bonded nonwoven fibrous web of  claim 1 . 
     
     
         18 . A dimensionally stable bonded nonwoven fibrous web prepared by a method comprising the sequential steps of:
 a) extruding melt blown fibers comprising a polymeric material;   b) collecting the melt blown fibers as an initial unbonded nonwoven fibrous web, wherein the fibers are substantially free of strain induced crystallization;   c) annealing the initial unbonded nonwoven fibrous web with a controlled heating and cooling operation comprising:
 i) heating through the initial unbonded nonwoven fibrous web by forcefully passing through the initial unbonded nonwoven fibrous web a first fluid having a temperature above a cold crystallization temperature (T cc ) of the polymeric material of step a) to decrease the orientation of amorphous regions of the melt blown fibers, thereby providing a bonded nonwoven fibrous web; and 
 ii) cooling through the bonded nonwoven fibrous web by drawing a second fluid having a temperature below a glass transition temperature (T g ) of the polymeric material of step a) over and through the bonded nonwoven fibrous web to retain the amorphous regions of the melt blown fibers providing a cooled bonded nonwoven fibrous web; and 
   d) collecting the cooled bonded nonwoven fibrous web providing a dimensionally stable bonded nonwoven fibrous web;   wherein the melt blown fibers of the cooled bonded nonwoven fibrous web retain a substantial cold crystallization exotherm.   
     
     
         19 . The dimensionally stable bonded nonwoven fibrous web prepared according to  claim 18 , wherein the melt blown fibers of the bonded nonwoven fibrous web are substantially unoriented. 
     
     
         20 . The dimensionally stable bonded nonwoven fibrous web prepared according to  claim 18 , wherein the web is dimensionally stable at a temperature in a range of 80° C. to 200° C. for at least 2 hours.