Patent ID: 7790641

Claim:
A nonwoven sheet material having liquid barrier properties, said sheet material having opposite sides and consisting of a spunbond nonwoven fabric including bicomponent filaments having first and second polymer components that are arranged in substantially distinct zones within the filaments, with the first polymer component formed of a relatively lower melting polyethylene polymer and the second component formed of a relatively higher melting polymer, the filaments of the nonwoven fabric being densely arranged and compacted against one another to form a substantially smooth outer surface on at least one said side of the nonwoven sheet material, and the nonwoven fabric being high pressure calendered at a nip pressure of about 1500 to 3000 pounds per lineal inch and at an elevated temperature such that the lower melting first polymer component of the filaments is fused to the contacting surface portions of adjacent filaments to impart strength and coherency to the nonwoven fabric, and the lower melting polymer component has softened and flowed to form a microporous film that permits moisture vapor to be transmitted through the sheet material while serving as a barrier to the penetration of liquids, and said sheet material having an air permeability, measured in accordance with ASTM test method D-1117, of from 0 to 5 cfm/ft 2 /min.