Filter media with charge stabilizing and enhancing additives

Abstract

Electret filter media having an increased electrostatic charge that is substantially maintained in the presence of heat are provided. In one exemplary embodiment, the filter media includes a melt processable charge enhancing additive, such as a fatty acid amide, and a melt processable charge stabilizing additive, such as a fatty acid metal salt. The charge enhancing additive is particularly effective to increase or enhance the electrostatic charge of the filter media when a charge is imparted thereto, and the charge stabilizing additive is particularly effective to stabilize the charge such that, when the filter media is subjected to a heat treatment, the enhanced electrostatic charge is substantially maintained.

1 . A filter media, comprising a meltblown electret polymer fiber web having a melt processable fatty acid amide present within the web and effective to enhance the level of electrostatic charge, and a melt processable fatty acid metal salt present within the web and effective to maintain the electrostatic charge when the filter media is subjected to heat.  
   
   
       2 . The filter media of  claim 1 , wherein the melt processable fatty acid amide is present within the web at a concentration in the range of about 0.5% to 11% by weight.  
   
   
       3 . The filter media of  claim 1 , wherein the melt processable fatty acid amide is present within the web at a concentration in the range of about 1% to 8% by weight.  
   
   
       4 . The filter media of  claim 1 , wherein the melt processable fatty acid amide is present within the web at a concentration of about 1% by weight.  
   
   
       5 . The filter media of  claim 1 , wherein the melt processable fatty acid metal salt is present within the web at a concentration in the range of about 0.1% to 20% by weight.  
   
   
       6 . The filter media of  claim 1 , wherein the melt processable fatty acid metal salt is present within the web at a concentration in the range of about 0.1% to 5% by weight.  
   
   
       7 . The filter media of  claim 1 , wherein the melt processable fatty acid metal salt is present within the web at a concentration of about 0.4% by weight.  
   
   
       8 . The filter media of  claim 1 , wherein the melt processable fatty acid metal salt comprises a metal stearate.  
   
   
       9 . The filter media of  claim 8 , wherein the metal stearate comprises magnesium stearate.  
   
   
       10 . The filter media of  claim 8 , wherein the metal stearate comprises zinc stearate.  
   
   
       11 . The filter media of  claim 1 , wherein the melt processable fatty acid amide is selected from the group consisting of a stearamide, ethylene bis-stearamide, and mixtures thereof.  
   
   
       12 . The filter media of  claim 1 , wherein the meltblown electret polymer fiber web is formed from a polymer selected from the group consisting of polyethylene, polypropylene, polyamide, polyvinyl chloride, polymethylmethacrylate, polyester, and mixtures thereof.  
   
   
       13 . The filter media of  claim 1 , wherein the meltblown electret polymer fiber web is formed from fibers having a fiber diameter in the range of about 1μ to 15μ.  
   
   
       14 . The filter media of  claim 1 , wherein the meltblown electret polymer fiber web is formed from fibers having a fiber diameter of about 3μ.  
   
   
       15 . The filter media of  claim 1 , wherein the meltblown electret polymer fiber web has a basis weight that is in the range of about 10 g/m 2  to 200 g/m 2 .  
   
   
       16 . The filter media of  claim 1 , wherein the meltblown electret polymer fiber web has a basis weight that is in the range of about 20 g/m 2  to 70 g/m 2 .  
   
   
       17 . The filter media of  claim 1 , wherein the meltblown electret polymer fiber web is incorporated into a respiratory filter.  
   
   
       18 . A filter media, comprising an electret web of fibers, the fibers comprising a blend of a polymer, a fatty acid amide, and a metal stearate, the fatty acid amide being present within the web at a concentration in the range of about 0.5% to 11% by weight, and the metal stearate being present within the web at a concentration in the range of about 0.1% to 20% by weight.  
   
   
       19 . The filter media of  claim 18 , wherein the meltblown web is incorporated into a respiratory filter.  
   
   
       20 . A filter media, comprising a meltblown electret polymer fiber web having a basis weight of about 60 g/m and having a melt processable ethylene bis-stearamide present within the web at a concentration in the range of about 0.5% to 11% by weight, and a melt processable magnesium stearate present within the web at a concentration in the range of about 0.1% to 20% by weight.  
   
   
       21 . A meltblown electret web of polymer fibers, the polymers fibers comprising a polymer, about 0.5% to 11% by weight of a fatty acid amide, and about 0.1% to 20% by weight of a fatty acid metal salt, the fatty acid amide and the fatty acid metal salt being dispersed in the polymer as a melt blend additive.  
   
   
       22 . A method for forming a filter media, comprising: 
 extruding a polymer composition containing a polymer, a fatty acid amide, and a fatty acid metal salt to form a meltblown polymer fiber web; and    imparting an electric charge to the meltblown polymer fiber web to form a meltblown electret polymer fiber web.    
   
   
       23 . The method of  claim 22 , further comprising subjecting the meltblown electret polymer fiber web to a heat treatment.  
   
   
       24 . The method of  claim 23 , wherein the heat treatment comprises subjecting the meltblown electret polymer fiber web to a temperature of at least about 70° C.  
   
   
       25 . The method of  claim 22 , wherein a corona charge is used to impart the charge.  
   
   
       26 . The method of  claim 22 , wherein the polymer composition includes about 0.5% to 11% by weight of the melt processable fatty acid amide, and about 0.1% to 20% by weight of the melt processable fatty acid metal salt.  
   
   
       27 . The method of  claim 22 , wherein the polymer composition includes about 1% to 8% by weight of the melt processable fatty acid amide, and about 0.1% to 5% by weight of the melt processable fatty acid metal salt.  
   
   
       28 . The method of  claim 22 , wherein the polymer composition includes about 1% by weight of the melt processable fatty acid amide, and about 0.4% by weight of the melt processable fatty acid metal salt.  
   
   
       29 . The method of  claim 22 , wherein the melt processable metal salt comprises a metal stearate.  
   
   
       30 . The method of  claim 29 , wherein the metal stearate comprises magnesium stearate.  
   
   
       31 . The method of  claim 29 , wherein the metal stearate comprises zinc stearate.  
   
   
       32 . The method of  claim 22 , wherein the melt processable fatty acid amide is selected from the group consisting of a stearamide, ethylene bis-stearamide, and mixtures thereof.