Abstract: This invention relates to improved sheet products and specifically to improved nonwoven sheet products made from highly oriented plexifilamentary film-fibril webs. The improved sheet products have high opacity and strength with a much wider range of porosity or Gurley Hill Porosity Values. In particular, sheet products made in accordance with the present invention have considerably higher Gurley Hill Porosity Values than similar weight sheet products subject to the same finishing treatments in accordance with prior known sheet materials. Similarly, sheet products made in accordance with the present invention can be made which have much lower Gurley Hill Porosity Values than prior sheet materials. The invention includes numerous methods and data characterizing the webs and sheets that form the improved sheet materials.

Abstract: This invention relates to improved elongation properties for flash-spun plexifilamentary film-fibrils. The technique for obtaining the improved properties is to increase the length to diameter ratio of the spin orifice and to reduce the ratio of polymer in the spin solution.

Abstract: This invention relates to a system and process for modifying the resulting properties of a flash spun plexifilamentary film-fibril web and spunbonded nonwoven sheets made from such webs. In particular, the system includes specifically designed letdown chamber arrangements wherein the solution of polymer and spin agent transitions from a single phase solution to a two phase solution in the letdown chamber prior to spinning at the spin orifice. The method comprises altering the configuration of the letdown chamber to alter the properties of the web and the sheet products made therefrom.

Abstract: A flash spin pack for a flash-spinning apparatus is provided in which the pack includes a spin mixture inlet, that communicates with a spin mixture passage, that discharges through a spinning orifice that opens into a slot defined by two opposing faces of the body of the spin pack. The slot is 0.25 mm to 7 mm wide proximate the spinning orifice outlet, 0.25 mm to 10 mm at the slot outlet, and the distance from the orifice outlet to the slot outlet is 1.5 mm to 40 mm. The spin pack may have five or more spinning orifices that each discharge into a different slot so configured.