Multi-layer, fluid transmissive fiber structures containing nanofibers and a method of manufacturing such structures

1. A multi-layer, fluid transmissive structure comprising:

a first fiber layer comprising a first plurality of polymeric fibers bonded to each other at spaced apart contact points, the polymeric fibers having diameters greater than one micron and collectively defining a first plurality of interconnected interstitial spaces providing tortuous fluid flow paths and a first set of flow characteristics through a first portion of the first fiber layer; and

a second fiber layer adhered to the first fiber layer, the second fiber layer comprising a second plurality of polymeric fibers bonded to each other at spaced apart contact points, the polymeric fibers having diameters greater than one micron and collectively defining a second plurality of interconnected interstitial spaces providing tortuous fluid flow paths and a second set of flow characteristics through a first portion of the second fiber layer,

wherein at least a portion of the polymeric fibers in a second portion of the first layer are bonded to at least a portion of the polymeric fibers in a second portion of the second layer to form an interface zone comprising fibers of both the first and second fiber layers, the fibers collectively defining a third plurality of interstitial spaces,

wherein a plurality of nanofibers is disposed within the third plurality of interstitial spaces in the interface zone and wherein the first portion of the first fiber layer and the first portion of the second fiber layer are free of nanofibers, and

wherein the interface zone has a third set of flow characteristics that is different from the first set of flow characteristics and the second set of flow characteristics.

2. A multi-layer, fluid transmissive structure according to claim 1 wherein the plurality of nanofibers includes nanofibers comprising at least one polymer material selected from the group consisting of polyvinylidene fluoride, polyamides, polyesters, polyolefins, polyurethanes, polycarbonates, and polystyrene.

3. A multi-layer, fluid transmissive structure according to claim 1 wherein at least one of the first and second plurality of polymeric fibers includes fibers comprising one or more of polyethylene, low density polyethylene, polypropylene, polyethylene terephthalate, polybutylene terephthalate and nylon.

4. A multi-layer, fluid transmissive structure according to claim 1 wherein the first and second fiber layers each comprise at least one of the set consisting of woven and non-woven polymeric materials.

5. A multi-layer, fluid transmissive structure according to claim 1 wherein at least one of the set consisting of the first and second fiber layers is a bonded nonwoven fiber structure comprising a plurality of sheath-core bicomponent fibers.

6. A multi-layer, fluid transmissive structure according to claim 1 wherein the first portion of the first fiber layer has a first porosity and the first portion of the second fiber layer has a second porosity that is different from the first porosity.

7. A multi-layer, fluid transmissive structure according to claim 1 wherein the nanofibers and the polymeric fibers of the first and second layers in the interface zone collectively define tortuous passages establishing pore sizes in a range of about 1 micron to about 6 microns.

8. A multi-layer, fluid transmissive structure according to claim 1 further comprising:

a third fiber layer adhered to the second fiber layer, the third fiber layer comprising a third plurality of polymeric fibers bonded to each other at spaced apart contact points, the polymeric fibers having diameters greater than one micron and collectively defining a third plurality of interconnected interstitial spaces providing tortuous fluid flow paths and a fourth set of flow characteristics through a first portion of the third fiber layer;

wherein at least a portion of the polymeric fibers in a third portion of the second layer are bonded to at least a portion of the polymeric fibers in a second portion of the third fiber layer to form a second interface zone comprising fibers of both the second and third fiber layers, the fibers collectively defining a fourth plurality of interstitial spaces,

wherein a second plurality of nanofibers is disposed within the fourth plurality of interstitial spaces in the second interface zone, and

wherein the second interface zone has a fifth set of flow characteristics that is different from the second set of flow characteristics and the fourth set of flow characteristics.

9. A multi-layer, fluid transmissive structure according to claim 1 wherein the fibers of the first plurality of polymeric fibers have different characteristics from the fibers of the second plurality of polymeric fibers.

10. A multi-layer, fluid transmissive structure according to claim 1 , wherein the interface zone, from a top-most side of the interface zone to a bottom-most side of the interface zone, comprises fibers of both the first and second fiber layers and the plurality of nanofibers.

11. A multi-layer, fluid transmissive structure comprising:

a first fiber layer comprising a first plurality of polymeric fibers bonded to each other at spaced apart contact points, the polymeric fibers having diameters greater than one micron and collectively defining a first plurality of interconnected interstitial spaces providing tortuous fluid flow paths and a first set of flow characteristics through a first portion of the first fiber layer; and

a second fiber layer adhered to the first fiber layer, the second fiber layer comprising a second plurality of polymeric fibers bonded to each other at spaced apart contact points, the polymeric fibers having diameters greater than one micron and collectively defining a second plurality of interconnected interstitial spaces providing tortuous fluid flow paths and a second set of flow characteristics through a first portion of the second fiber layer,

wherein at least a portion of the polymeric fibers in a second portion of the first layer are bonded to at least a portion of the polymeric fibers in a second portion of the second layer to form an interface zone comprising fibers of both the first and second fiber layers, the fibers collectively defining a third plurality of interstitial spaces,

wherein a plurality of nanofibers is disposed within the third plurality of interstitial spaces in the interface zone and wherein the first portion of the first fiber layer and the first portion of the second fiber layer are free of nanofibers such that the plurality of nanofibers in the interface zone is sandwiched between non-nanofiber layers,

wherein the interface zone has a third set of flow characteristics that is different from the first set of flow characteristics and the second set of flow characteristics, and

wherein the first portion of the first fiber layer has a first porosity and the first portion of the second fiber layer has a second porosity that is different from the first porosity.