Nonwoven fabric having a pore size gradient and method and apparatus for forming same

Abstract From the Canadian patent

A method for forming a web structure having a pore size gradient which utilizes a spunbond process for producing fibers. The fibers are deposited on a contoured collection surface. Preferably the surface is shaped as an , elongated dome having the central zone at the apex and the peripheral zones along the curved sides. The fibers are deposited onto the central zone and accumulate until they flow down the sides onto the peripheral zones. Fibers deposited onto the central zone have greater average pore size and fibers deposited onto the peripheral zone have smaller average pore size and greater fiber alignment. In an alternative embodiment a plurality of dies in a row is , used each …