Nonwoven web with bimodal fiber distribution

Abstract

A nonwoven web comprising a layer of polymeric fibers, wherein, based on the total number of polymeric fibers, at least 10% the polymeric fibers in said layer are coarse fibers having a fiber diameter of 4 μm or more, and at least 10% of the polymeric fibers in said layer are fine fibers having a fiber diameter of 2 μm or less. Also described herein is a method for making the nonwoven web, comprising melt-blowing a polymer mixture comprising two immiscible or partially miscible polymers.

What is claimed is: 
     
         1 . A nonwoven web comprising a layer of polymeric fibers, wherein, based on a total number of polymeric fibers, at least 10% of the polymeric fibers in said layer are coarse fibers having a fiber diameter of 4 μm or more, and at least 10% of the polymeric fibers in said layer are fine fibers having a fiber diameter of 2 μm or less. 
     
     
         2 . The nonwoven web of  claim 1 , wherein at least 25% polymeric fibers in said layer are coarse fibers having a fiber diameter of 4 μm or more, based on the total number of polymeric fibers. 
     
     
         3 . The nonwoven web of  claim 1 , wherein at least 25% polymeric fibers in said layer are coarse fibers having a fiber diameter of 5 μm or more, based on the total number of polymeric fibers. 
     
     
         4 . The nonwoven web of  claim 1 , wherein at least 25% polymeric fibers in said layer are fine fibers having a fiber diameter of 2 μm or less, based on the total number of polymeric fibers. 
     
     
         5 . The nonwoven web of  claim 1 , wherein at least 25% polymeric fibers in said layer are fine fibers having a fiber diameter of 1 μm or less, based on the total number of polymeric fibers. 
     
     
         6 . The nonwoven web of  claim 1 , wherein the polymeric fibers in said layer have a bimodal distribution of their fiber diameters, based on the total number of polymeric fibers. 
     
     
         7 . The nonwoven web of  claim 1 , wherein the polymeric fibers in said layer have a bimodal distribution of their fiber diameters, comprising a first peak at a first fiber diameter of 2 μm or less and a second peak at a second fiber diameter of 4 μm or more. 
     
     
         8 . The nonwoven web of  claim 1 , wherein the polymeric fibers in said layer have a bimodal distribution of their fiber diameters, comprising a first peak at a first fiber diameter of 2 μm or less, a second peak at a second fiber diameter of 4 μm or more, and a trough at a third fiber diameter between the first fiber diameter and the second fiber diameter, wherein 10% or less of the polymeric fibers have a fiber diameter within ±0.5 μm of the third fiber diameter, based on the total number of polymeric fibers. 
     
     
         9 . The nonwoven web of  claim 1 , wherein the polymeric fibers in said layer have a bimodal distribution of their fiber mean, comprising a first peak at a first fiber diameter of 2 μm or less, a second peak at a second fiber diameter of 4 μm or more, and a trough at a third fiber diameter between the first fiber diameter and the second fiber diameter, wherein 5% or less of the polymeric fibers have a fiber diameter within ±0.5 μm of the third fiber diameter, based on the total number of polymeric fibers. 
     
     
         10 . The nonwoven web of  claim 1 , wherein the polymeric fibers in said layer are melt-blown fibers. 
     
     
         11 . The nonwoven web of  claim 1 , wherein the polymeric fibers in said layer comprises 0.5-10 wt. % liquid crystalline polymer. 
     
     
         12 . The nonwoven web of  claim 1 , wherein the polymeric fibers in said layer comprises polybutylene terephthalate. 
     
     
         13 . The nonwoven web of  claim 1 , wherein the nonwoven web has an air permeability of 20 cfm or more. 
     
     
         14 . The nonwoven web of  claim 1 , wherein the nonwoven web has an air permeability of 40 cfm or more. 
     
     
         15 . The nonwoven web of  claim 1 , wherein the nonwoven web has a filtration ratio of 40% or more at particle size of 10 μm. 
     
     
         16 . The nonwoven web of  claim 1 , wherein the nonwoven web has a filtration ratio of 60% or more at particle size of 10 μm. 
     
     
         17 . The nonwoven web of  claim 1 , wherein the nonwoven web has a filtration capacity of 50 mg/in 2  or more. 
     
     
         18 . The nonwoven web of  claim 1 , wherein the nonwoven web has a filtration capacity of 130 mg/in 2  or more. 
     
     
         19 . A method for making the nonwoven web of any of  claims 1 - 15 , comprising melt-blowing a polymer mixture comprising at least two immiscible or partially miscible polymers. 
     
     
         20 . The method of  claim 19 , wherein the polymer mixture is obtained by compounding the two immiscible or partially miscible polymers. 
     
     
         21 . The method of  claim 19 , wherein the polymer mixture is obtained by physically blending the two immiscible or partially miscible polymers. 
     
     
         22 . The method of  claim 19 , wherein the polymer mixture comprises (a) 0.5-30 wt. % liquid crystalline polymer and (b) polybutylene terephthalate. 
     
     
         23 . A nonwoven web comprising a layer of polymeric fibers, wherein, based on a total number of polymeric fibers, at least 10% of the polymeric fibers in said layer are coarse fibers having a fiber diameter of 3 μm or more, and at least 10% of the polymeric fibers in said layer are fine fibers having a fiber diameter of 1 μm or less. 
     
     
         24 . The nonwoven web of  claim 23 , wherein at least 25% polymeric fibers in said layer are coarse fibers having a fiber diameter of 3 μm or more, and at least 25% polymeric fibers in said layer are fine fibers having a fiber diameter of 1 μm or less, based on the total number of polymeric fibers. 
     
     
         25 . The nonwoven web of  claim 23  or  24 , wherein the polymeric fibers in said layer have a bimodal distribution of their fiber diameters, comprising a first peak at a first fiber diameter of 1 μm or less, a second peak at a second fiber diameter of 3 μm or more, and a trough at a third fiber diameter between the first fiber diameter and the second fiber diameter, wherein 10% or less of the polymeric fibers have a fiber diameter within ±0.5 μm of the third fiber diameter, based on the total number of polymeric fibers. 
     
     
         26 . A nonwoven web comprising a layer of polymeric fibers, wherein, based on the total number of polymeric fibers, at least 10% of the polymeric fibers in said layer are coarse fibers having a fiber diameter of 5 μm or more, and at least 10% of the polymeric fibers in said layer are fine fibers having a fiber diameter of 3 μm or less. 
     
     
         27 . The nonwoven web of  claim 26 , wherein at least 25% polymeric fibers in said layer are coarse fibers having a fiber diameter of 5 μm or more, and at least 25% polymeric fibers in said layer are fine fibers having a fiber diameter of 3 μm or less, based on the total number of polymeric fibers. 
     
     
         28 . The nonwoven web of  claim 26  or  27 , wherein the polymeric fibers in said layer have a bimodal distribution of their fiber diameters, comprising a first peak at a first fiber diameter of 3 μm or less, a second peak at a second fiber diameter of 5 μm or more, and a trough at a third fiber diameter between the first fiber diameter and the second fiber diameter, wherein 10% or less of the polymeric fibers have a fiber diameter within ±0.5 μm of the third fiber diameter, based on the total number of polymeric fibers. 
     
     
         29 . The nonwoven web of  claim 1 , wherein said layer of polymeric fibers is obtained by a method comprising melt-blowing a polymer mixture comprising (a) 0.5-30 wt. % liquid crystalline polymer and (b) polybutylene terephthalate.