Heat seal fibrous web and method of its manufacture

Claim 1

In a wet papermaking process for preparing a light weight multiphase heatsealable fibrous web material having excellent infusion characteristics comprising the steps of forming a dilute dispersion of heatsealable fibers in an aqueous dispersing medium; providing a fibrous substrate phase of non-heatsealing character; depositing said dispersion on said substrate phase while simultaneously removing a sufficient portion of said dispersing medium to form a partially dewatered heatsealable fiber phase superimposed on said substrate phase, said partially dewatered heatsealable phase having a fiber consistency of at least about one percent by weight with the remainder being substantially dispersing medium; and subsequently drying the resultant multi-phase web material to remove the dispersing medium and firmly secure the superimposed heatsealable phase to said substrate phase, the improvement wherein the heatsealable fibers are highly fibrillated synthetic thermoplastic particles and the process includes the step of disruptively dislodging and displacing portions of the heatseal particle in the partially dewatered heatseal fiber phase while superimposed on the fibrous substrate and prior to removing a major portion of the dispersing medium initially retained within said superimposed phase to provide a random array of discrete areas of reduced heatseal particle content and enhanced infusion in said multi-phase web material, the enhanced infusion areas being present throughout said heatseal phase at a concentration sufficient to occupy about 10-75 percent of the planar surface area of said heatseal fiber phase having an average diameter per area of up to 5 mm and an average planar area of at least 1×10 -3 cm 2 and being substantially invisible in the dried web material, said substrate phase being substantially unaffected by the displacement of portions of the heatseal phase and being itself substantially unmodified.