Electret filter media comprising a nonwoven web of thermoplastic nonconductive microfibers having trapped charge, said charge provided by (1) subjecting the nonwoven web to a corona treatment, followed by (2) impingement of jets of water or a stream of water droplets on the web at a pressure sufficient to provide the web with filtration enhancing electret charge and (3) drying the web. This electret filter media may be used in a respiratory mask to provide extraordinarily good filtration properties.
This application is a continuation of application Ser. No. 08/591,217 filed on Jan. 17, 1996 (now abandoned), which is a is a continuation of application Ser. No. 08,291,611 filed Aug. 17, 1994 (now U.S. Pat. No. 5,496,507), which is a continuation-in-part of application Ser. No. 08/107,517 filed Aug. 17, 1993 (now abandoned). Issued U.S. Pat. No. 6,119,691 is also related to this case.
An electret article that includes a polymeric material that has electric charge imparted thereto, that has one or more heteroatoms, that has a fluorosaturation ratio of less than 200, and that has an atomic percent fluorine of greater than about 40%. The inventive electret article is resistant to charge degradation upon exposure to high temperatures for prolonged time periods.
An electret article that includes a polymeric material that has electric charge imparted thereto, that has a CF.sub.3:CF.sub.2 ratio of at least 0.15 and that has a fluorosaturation ratio greater than about 200. The electret article may be in the form of a porous web of polymeric fibers suitable for use as a filter. The inventive electret article is resistant to charge degradation upon exposure to high temperatures for prolonged time periods.
Methods and apparatus for hydrodischarging and hydrocharging substrates and articles to produce enhanced ability to avoid attraction of contaminants or improved capability of removing contaminants from fluids are disclosed. In another form the method involves removal of electric charges or neutralization of charge on or within substrates. Also disclosed are methods of making using electret substrates and articles for removing particulates and mists from fluid streams.
