Multilayer nonwoven composite structure

A method of preparing a nonwoven composite structure having at least two melt-extruded nonwoven layers adjacent to each other in which each melt-extruded nonwoven layer comprises at least a portion of a nonwoven web and the boundary between any two adjacent melt-extruded nonwoven layers is indistinct in that fibers at or near the surfaces of such adjacent layers are significantly intermingled, which method comprises the steps of:

• (A) sequentially melt extruding one or more additional nonwoven webs directly onto a first melt-extruded nonwoven web;
• and
• (B) pattern bonding the resulting nonwoven composite by the application of heat and pressure;
• in which
• (1) the fibers of at least one melt-extruded nonwoven layer are prepared by melt extrusion through a die at a shear rate of from about 50 to about 30,000 sec.sup.-1 and a throughput of no more than about 5.4 kg/cm/hour of a mixture of an additive and a thermoplastic polymer, which additive imparts to the surfaces of said fibers, as a consequence of the preferential migration of said additive to the surfaces of said fibers as they are formed, at least one characteristic which is different from the surface characteristics of fibers prepared from said thermoplastic polymer alone, said preferential migration taking place spontaneously upon the formation of said fibers without the need for a post-formation treatment of any kind;
• (2) said thermoplastic polymer is selected from the group consisting of polyolefins, polyesters, polyetheresters, and polyamides;
• and
• (3) the additive present in any melt-extruded nonwoven layer does not migrate to an adjacent layer to a significant degree in use, so that the surface characteristics of each layer remain substantially as originally prepared.