Plasma treatment of filter media

Abstract

The present invention is drawn to an improved electrostatic filter medium comprising a web of electret fibers which have been treated with fluorine-containing plasmas at a deposition amount of about 0.03 g/m 2 to about 1.5 g/m 2 ; rinsing; and drying prior to being electrically charged. The present invention is further drawn to a method of producing non-woven webs which have been treated with a fluorine-containing plasma at a deposition amount of about 0.03 g/m 2 to about 1.5 g/m 2 ; rinsed; and dried prior to electrostatically charging the web.

I claim:  
     
         1 . A filter medium, comprising a web of electret fibers, said fibers having been formed from a material that was 
 1) treated with a fluorine-containing plasma at a deposition amount of about 0.03 g/m 2  to about 1.5 g/m 2 ;    2) electrostatically charged    3) rinsed; and    4) dried    
     
     
         2 . The filter medium according to  claim 1 , wherein said fibers are made of a polyolefin.  
     
     
         3 . The filter medium according to  claim 1 , wherein said fibers are made of polypropylene.  
     
     
         4 . The filter medium according to  claim 1 , wherein said fluorine source is trifluoromethane, tetrafluoroethane, or tetrafluorosilane.  
     
     
         5 . The filter medium according to  claim 1 , wherein said web is non-woven.  
     
     
         6 . A method of forming a non-woven web, which comprises: 
 (1) melt blowing polyolefin fibers into a non-woven web;    (2) treating said non-woven web with a fluorine-containing plasma at a deposition amount of about 0.03 g/m 2  to about 1.5 g/m 2 ;    (3) charging said treated non-woven web to form a non-woven web of electret fibers;    (4) rinsing said treated non-woven web; and    (5) drying said non-woven web.    
     
     
         7 . The method according to  claim 6 , wherein said polyolefin fibers are made of polypropylene.  
     
     
         8 . The method according to  claim 6 , wherein said plasma contains a trifluoromethane, tetrafluoroethane, or tetrafluorosilane.  
     
     
         9 . A method of forming a non-woven web, which comprises: 
 (1) treating a thin film of polymer with a fluorine-containing plasma at a deposition amount of about 0.03 g/m 2  to about 1.5 g/m 2 ;    (2) rinsing said treated non-woven web;    (3) drying said non-woven web;    (4) electrically charging said treated thin film;    (5) fibrillating said charged film to form fibers; and    (6) forming said fibers into a non-woven web of electret fibers.    
     
     
         10 . The method according to  claim 9 , wherein said polymer is polypropylene.  
     
     
         11 . The method according to  claim 9 , wherein said plasma contains a trifluoromethane, tetrafluoroethane, or tetrafluorosilane.  
     
     
         12 . In a method of forming a web of electret fibers, which comprises charging electrically charging a filter material in film or fiber form, the improvement which comprises treating the filter material with a fluorine-containing plasma at a deposition amount of about 0.03 g/m 2  to about 1.5 g/m 2 ; rinsing the filter material and drying the filter material prior to carrying out electrical charging of the filter material.  
     
     
         13 . The filter medium of  claim 1 , wherein the treatment with a fluorine-containing plasma is at a deposition amount of about 0.07 g/m 2 .  
     
     
         14 . The method of  claim 6 , wherein the treatment with a fluorine-containing plasma is at a deposition amount of about 0.07 g/m 2 .  
     
     
         15 . The method of  claim 9 , wherein the treatment with a fluorine-containing plasma is at a deposition amount of about 0.07 g/m 2 .  
     
     
         16 . The method of  claim 12 , wherein the treatment with a fluorine-containing plasma is at a deposition amount of about 0.07 g/m  2 .