ELECTROSTATIC FIBROUS FILTER WEB AND METHOD OF MAKING SAME

摘要

The present invention provides an electret nonwoven filter medium comprising a nonwoven filter web of electrostatically charged fibrillated fibers ultrasonically joined to each other at a plurality of spots distributed acro ss said nonwoven filter web, the total surface occupied by said spots being les s than 5% of the surface of said nonwoven filter web and the number of spots p er square centimeter being at least 2. The present invention also provides a method of making the electret nonwoven filter medium.