Remote fluorination of fibrous filter webs

Abstract

A method of making a fluorinated fibrous web, which method includes providing a nonwoven web 22 that contains polymeric fibers, creating a plasma that contains fluorine atoms at a first location 14, and contacting the nonwoven web with products from the plasma at a second location 26 remote from the first location 14. The method avoids exposure of the web to the plasma and hence expands the manufacturing processing window. Webs so fluorinated have a different C 3 F 4 H + to C 2 F 5 + ratio when compared to locally fluorinated webs having similar levels of surface fluorination. The remote fluorinated webs can be subsequently charged electrically to provide a good performing electret filter 40 suitable for use in an air purifying respirator 30. Webs fluorinated in accordance with this invention also may exhibit good performance even after being “aged” at high temperatures.

What is claimed is: 
     
         1 . A spun-bond fibrous filtration web comprising bicomponent, fluorinated electret fibers with first and second thermoplastic organic nonconductive polymer components arranged concentrically therein in a sheath-core configuration, wherein the first and second polymer components are chosen from polypropylene and poly-4-methyl-pentene, and wherein the bicomponent, fluorinated electret fibers are hydrocharged, plasma-fluorinated fibers that comprise fluorine atoms on the surfaces of the fibers so as to exhibit greater than 40 atomic % fluorine. 
     
     
         2 . The spun-bond fibrous filtration web of  claim 1  wherein the spun-bond fibrous filtration web is at least 0.25 mm thick. 
     
     
         3 . The spun-bond fibrous filtration web of  claim 1  wherein the spun-bond fibrous filtration web exhibits a Q 9  quality factor of at least 1.8/mmH 2 O. 
     
     
         4 . The spun-bond fibrous filtration web of  claim 1  with the proviso that the spun-bond fibrous filtration web does not include any meltblown fibers. 
     
     
         5 . The spun-bond fibrous filtration web of  claim 1  with the proviso that the spun-bond fibrous filtration web does not include any staple fibers. 
     
     
         6 . The spun-bond fibrous filtration web of  claim 1  with the proviso that the bicomponent, fluorinated electret fibers do not include any charging additive. 
     
     
         7 . The spun-bond fibrous filtration web of  claim 1  wherein the spun-bond fibrous filtration web comprises sorbent particles. 
     
     
         8 . The spun-bond fibrous filtration web of  claim 6  wherein the sorbent particles include at least some activated carbon particles. 
     
     
         9 . The spun-bond fibrous filtration web of  claim 1  wherein the bicomponent, fluorinated electret fibers are quenched fibers. 
     
     
         10 . The spun-bond fibrous filtration web of  claim 1  wherein the spun-bond fibrous filtration web exhibits a basis weight from 20 to 150 grams per square meter. 
     
     
         11 . The spun-bond fibrous filtration web of  claim 1  wherein the spun-bond fibrous filtration web exhibits a solidity of from 3 to 10%. 
     
     
         12 . The spun-bond fibrous filtration web of  claim 1  wherein the bicomponent, fluorinated electret fibers exhibit a ToF-SIMS C 3 F 4 H +  to C 2 F 5   +  ratio that is greater than 0.3. 
     
     
         13 . The spun-bond fibrous filtration web of  claim 1  wherein the bicomponent, fluorinated electret fibers exhibit a fluorosaturation ratio in a range of 270 to 413. 
     
     
         14 . The spun-bond fibrous filtration web of  claim 1  wherein the bicomponent, fluorinated electret fibers do not contain heteroatoms. 
     
     
         15 . The spun-bond fibrous filtration web of  claim 1  wherein the bicomponent, fluorinated electret fibers are hydrocharged, plasma-fluorinated fibers that comprise fluorine atoms on the surfaces of the fibers so as to exhibit greater than 42 atomic % fluorine. 
     
     
         16 . The spun-bond fibrous filtration web of  claim 1  wherein the bicomponent, fluorinated electret fibers are hydrocharged, plasma-fluorinated fibers that comprise fluorine atoms on the surfaces of the fibers so as to exhibit greater than 45 atomic % fluorine. 
     
     
         17 . A filter that comprises the spun-bond fibrous filtration web of  claim 15 .