Post-treatment of nonwoven webs

A nonwoven web made from a precursor nonwoven web, said precursor comprising a lamination of individual nonwoven webs having nonelastomeric fibers and being uniaxially drawn and heat set, wherein the uniaxial heating and drawing are carried out continuously by passing the precursor web into an oven at a first linear velocity and withdrawing the precursor web from the oven at a second linear velocity and wherein the ratio of the second velocity to the first velocity ranges from about 1.1:1 to 2:1, whereby a majority of the fibers are consolidated and aligned generally in the direction of draw and a minority of segments of fibers are disposed crosswise or transversely to the direction of draw, whereby the web is characterized by a maximum pore size of less than 80% that of the precursor web and has an elasticity in the cross direction defined by at least 70% recovery from a 50% elongation in the cross direction.

A longitudinally extending nonwoven web made from a precursor nonwoven web having nonelastomeric, thermoplastic fibers characterized in that the majority of the fibers have been consolidated in a direction transverse the length of the web and are disposed generally in the longitudinal direction of the web, wherein the consolidation is carried out by passing the precursor web into an oven at a first linear velocity and withdrawing the precursor web from the oven at a second linear velocity and wherein the ratio of the second velocity to the first velocity ranges from about 1.1:1 to 2:1, whereby the maximum pore size of the web represents less than 70% of the maximum pore size of the precursor web and, a minority of the fibers in the web extent transverse the longitudinal direction of the web and a portion of which are bonded to the longitudinal fibers, disposed said web further being characterized as having a level of elasticity defined by at least 70% recovery from a 50% elongation in a direction crosswise of the longitudinal direction of the web.

A filter comprising meltblown web having nonelastomeric thermoplastic fibers having an average diameter of 0.5 to 8 microns, the majority of which are generally aligned in one direction, wherein the fibers are aligned by passing a precursor web into an oven at a first linear velocity and withdrawing the precursor web from the oven at a second linear velocity and wherein the ratio of the second velocity to the first velocity ranges from about 1.1:1 to 2:1, said web having a mean flow pore size of 2 to 50 microns, a pore size distribution spread of 4 to 100 microns, and an elastic recovery of at least 40% from a 100% elongation in a direction normal to the direction of the aligned fibers.