Nonwoven fabric having a pore size gradient and method of making same

摘要

Methods and apparatus for forming a nonwoven fiber web containing a pore size gradient resulting in enhanced wicking properties. A first method utilizes a conventionally formed web having an average pore size and comprises selectively contacting the web with a heat source to shrink the fibers in selected areas. The smaller pore sizes have greater wicking ability. A second method utilizes a novel apparatus and comprises forming a nonwoven fiber web having zones of fibers, each zone having generally an average set of fiber structure and/or composition, the zones preferably overlapping. The zones of fibers are exposed to a heat source, which shrinks the fibers according to their denier and composition. The apparatus uses a conventional meltblown or spunbond system and provides a plurality of resin sources which feed resin to a plurality of meltblowing dies. Each die produces fibers of a particular denier and/or composition which forms zones in a web collected on a collecting belt. The web moves underneath a manifold which blows heated air or sprays boiling water onto the fibers. The fibers shrink according to their structure and composition to form a web having a pore gradient.