Propylene Based Meltblown Nonwoven Layers and Composite Structures

Abstract

The present invention relates to propylene-based nonwoven layers made by the meltblown process, and laminates incorporating such layers. The meltblown layers of the present invention comprise propylene copolymers characterized by having less than 50 percent crystallinity. The meltblown layers of the present invention show an improved combination of extensibility and tensile strength. The laminate structures of the present invention are characterized by a combination of low bending modulus with high peel strength.

1 . A meltblown fabric which has an MD peak tensile force (F MD ) per one inch width and normalized to 20 gsm basis weight described by the following equations
 a. F MD ≧[−0.00143×elong(percent)+0.823] if elongation is between 20 to 675 percent   b. F MD ≧0.1 lb if elongation is greater than or equal to 675 percent and wherein the fabric comprises at least one copolymer with at least about 50 weight percent of units derived from propylene and at least about 5 weight percent of units derived from a comonomer other than propylene.   
     
     
         2 . The meltblown fabric of  claim 1  in which the at least one copolymer is characterized as having  13 C NMR peaks corresponding to a regio-error at about 14.6 and about 15.7 ppm, the peaks being of about equal intensity. 
     
     
         3 . The meltblown fabric of  claim 1  wherein the comonomer comprises 3 to 20 wt. percent ethylene. 
     
     
         4 . The meltblown fabric of  claim 1  wherein the comonomer comprises 9 to 20 wt. percent ethylene. 
     
     
         5 . The meltblown fabric of  claim 1  wherein the copolymer has a MFR from 25 to 5000. 
     
     
         6 . The meltblown fabric of  claim 1  wherein the copolymer has undergone chemically induced chain scission and has a MFR from 50 to 5000. 
     
     
         7 . The meltblown fabric of  claim 6  wherein the chain scission is caused by combining the composition with a free radical initiator prior to extrusion. 
     
     
         8 . The meltblown fabric of  claim 7  wherein the free radical initiator is a peroxide type. 
     
     
         9 . The meltblown fabric of  claim 7  wherein the rheology modifier is a non-peroxide type. 
     
     
         10 . The meltblown fabric of  claim 9  wherein the non-peroxide type rheology modifier is a hydroxyl amine ester. 
     
     
         11 . The meltblown fabric of  claim 6  wherein the chain scission is caused by combining the composition with at least one peroxide type and one non-peroxide type of free radical initiators. 
     
     
         12 . The meltblown fabric of  claim 1  in which the average fiber diameter is less than 10 microns. 
     
     
         13 . The meltblown fabric of  claim 1  which has immediate set of less than or equal to about 50 percent as measured by a 50 percent 1 cycle test. 
     
     
         14 . The meltblown fabric of  claim 1  which has retained load greater than or equal to about 0 percent as measured by a 75 percent 1 cycle test. 
     
     
         15 . The meltblown fabric of  claim 1  which has retained load greater than or equal to about 15 percent as measured by a 75 percent 1 cycle test. 
     
     
         16 . The meltblown fabric of  claim 1  wherein the fabric comprises less than about 10 percent by weight hPP and/or RCP. 
     
     
         17 . The meltblown fabric of  claim 1  wherein the fabric comprises less than about 8 percent by weight hPP and/or RCP. 
     
     
         18 . The meltblown fabric of  claim 1  wherein the fabric comprises less than about 6 percent by weight hPP and/or RCP. 
     
     
         19 . The meltblown fabric of  claim 1  wherein the fabric comprises less than about 4 percent by weight hPP and/or RCP. 
     
     
         20 . A nonwoven laminate comprising the meltblown nonwoven layer of any one of  claims 1 - 19  and at least one spunbond nonwoven layer. 
     
     
         21 . The nonwoven laminate of  claim 20  wherein the spunbond layer comprises fibers characterized in that a polyethylene based material comprises at least a portion of the surface of the fiber. 
     
     
         22 . The nonwoven laminate of  claim 20  wherein the spunbond layer comprises a bicomponent fiber. 
     
     
         23 . The nonwoven laminate of  claim 22  wherein the bicomponent fiber is in a sheath-core configuration. 
     
     
         24 . The nonwoven laminate of  claim 23  wherein the spunbond layer comprises a monofilament fiber. 
     
     
         25 . The nonwoven laminate of  claim 24  wherein the spunbond layer comprises a polyolefin other than polyethylene. 
     
     
         26 . A nonwoven laminate structure comprising at least two nonwoven layers, said nonwoven laminate structure being characterized by having an overall bending modulus according to ASTM D 5732-95 of 0.005 Nmm or less and a peel strength between the nonwoven layers of more than 2 N/5 cm; wherein at least one of the nonwoven layers comprises fiber comprising at least one polymer with at least about 50 weight percent of units derived from propylene. 
     
     
         27 . The nonwoven laminate structure of  claim 26  further characterized by having hydrohead behavior greater than about 200 mm H 2 O normalized to a basis weight of 25 gsm. 
     
     
         28 . The nonwoven laminate structure of  claim 26  wherein the at least two nonwoven layers include at least one meltblown layer and at least one spunbond layer 
     
     
         29 . The nonwoven laminate structure of  claim 28  further comprising at least one additional meltblown or spunbond layer. 
     
     
         30 . The nonwoven laminate structure of  claim 26  wherein at least one nonwoven layer is a meltblown nonwoven layer which comprises meltblown fibers comprising a propylene based polymer characterized by having one or more of the following traits:
 a. less than 50 percent crystallinity   b. flex modulus less than 50 kpsi   c. melting point less than about 140° C.; and/or heat of fusion less than 80 J/g   
     
     
         31 . The nonwoven laminate structure of  claim 30  wherein the meltblown fibers are further characterized as comprising copolymers of propylene and an alpha-olefin, wherein the alpha olefin is preferably ethylene. 
     
     
         32 . The meltblown nonwoven layer of  claim 31  wherein the alpha olefin is ethylene. 
     
     
         33 . The nonwoven laminate structure of  claim 30  in which the propylene based polymer is further characterized as having  13 C NMR peaks corresponding to a regio-error at about 14.6 and about 15.7 ppm, the peaks being of about equal intensity. 
     
     
         34 . The nonwoven laminate structure of  claim 30  wherein the propylene based polymer comprises 3 to 20 wt. percent ethylene. 
     
     
         35 . The nonwoven laminate structure of  claim 30  wherein the propylene based polymer comprises 9 to 20 wt. percent ethylene. 
     
     
         36 . The nonwoven laminate structure of  claim 30  wherein the propylene based polymer has an MFR from 25 to 5000. 
     
     
         37 . The nonwoven laminate structure of  claim 30  wherein the propylene based polymer has undergone chemically induced chain scission and has an MFR from 50 to 5000. 
     
     
         38 . The nonwoven laminate structure of  claim 37  wherein the chain scission is caused by combining the composition with a free radical initiator prior to extrusion. 
     
     
         39 . The nonwoven laminate structure of  claim 38  wherein the free radical initiator is a peroxide type. 
     
     
         40 . The nonwoven laminate structure of  claim 38  wherein the free radical initiator is a non-peroxide type. 
     
     
         41 . The nonwoven laminate structure of  claim 37  wherein the chain scission is caused by combining the composition with at least one peroxide type and one non-peroxide type of free radical initiators. 
     
     
         42 . The nonwoven laminate structure of  claim 30  in which the average fiber diameter of the meltblown fibers is less than about 12 microns. 
     
     
         43 . The nonwoven laminate structure of  claim 28  in which the spunbond layer comprises fibers characterized as having polyethylene based material comprising at least a portion of the surface of the fiber. 
     
     
         44 . The spunbond layer of  claim 26  comprising fibers of a bicomponent structure. 
     
     
         45 . The spunbond layer of  claim 44  in which the bicomponent fibers have a sheath-core configuration. 
     
     
         46 . A nonwoven laminate comprising at least one meltblown nonwoven layer and at least one spunbond layer wherein:
 the at least one melt blown layer comprises fibers comprising polymer having at least about 50 weight percent of units derived from propylene; and   the at least one spunbond nonwoven layer comprises fibers characterized in that a polyethylene based material comprises at least a portion of the surface of the fiber.   
     
     
         47 . The nonwoven laminate of  claim 46  wherein the at least one meltblown layer comprises fibers comprising polymer having at least about 50 weight percent of units derived from propylene and at least about 5 weight percent of units derived from a monomer other than propylene.