Method of manufacturing a foam fibrillated fibrous web from an isotactic polypropylene, polystyrene and α-methylstrene blend

Claim 1

A process of producing a foam fibrillated fibrous web comprising heating a blend of from 50 to 98 weight percent as based on said blend of isotactic polypropylene and from 50 to 2 weight percent as based on said blend of polystyrene which may contain up to 10 weight percent α -methylstyrene, in an extruder to a temperature generally maintained in a range of from 175° to 260°C whereby a molten blend is formed, extruding said blend and from 0.1 to 20 percent by weight as based on said blend of a material which is gaseous under the extrusion conditions used mixed with said molten blend from a die which is generally maintained in the temperature range of from 220° to 260°C into a zone of reduced pressure to produce a foam fibrillated fibrous web extrudate, quenching said extrudate to a temperature below about 150°C while withdrawing said extrudate from said die by a first linear take-up means at a linear rate of from two to 25 times the linear rate at which said blend reaches the lips of said die whereby a foam-fibrillated web is formed, and stretching said foam fibrillated web from two to 10 times in the machine direction at a temperature of from about 90°C to about 150°C to increase the strength thereof.