Structured material having apertures and method of producing the same
View Patent ↗A method for producing an apertured structured material for accommodating passage of fluids, particularly high viscosity fluids, through the apertured structured material. In one embodiment, the apertured structured material is a composite material formed by differential shrinkage of a shrinkable second layer, for example an ethylene-propylene copolymer, which is laminated to a first layer, for example a polypropylene polymer. During the differential shrinkage process, a plurality of slits which are formed in the second layer open to form uniformly-shaped apertures. In another embodiment, an apertured structured heterogenous material is made of a heterogeneous mixture of at least two homogeneous fiber sets or components having different shrinkage extents.
1. A method for producing a structured composite material having a plurality of apertures for accommodation passage of fluids through the structured composite material, the method comprising the steps of:
forming a first layer having a first shrinkage extent, said first layer comprising a fibrous thermoplastic nonwoven web;
extruding a heat shrinkable second layer onto the first layer, the second layer comprising a thermoplastic film and having a second shrinkage extent different from the first shrinkage extent;
forming the plurality of apertures only through the second layer after extrusion; and
differentially heat shrinking the second layer relative to the first layer to increase a bulk of the composite material and produce the structured composite material;
whereby the apertures are effective in transferring particles into the structured composite material and the first layer is effective in retaining them.
2. The method of claim 1 , wherein the plurality of apertures are formed through the second layer using one of pin embossing, slitting, laser embossing and thermal embossing.
3. The method of claim 1 , wherein the apertures formed each have a diameter of about 100 microns to about 10,000 microns.
4. The method of claim 1 , wherein the first layer comprises a polypropylene polymer.
5. The method of claim 1 , wherein the second layer comprises an ethylene-propylene random copolymer.
6. The method of claim 1 , wherein an initial bulk of the composite material is increased by at least 50% during the shrinkage step.
7. The method of claim 1 , wherein an initial bulk of the composite material is increased by at least 100% during the shrinkage step.
8. The method of claim 1 , further comprising the step of heating the composite material to effect shrinkage of at least the second layer.
9. The method of claim 8 , wherein the composite material is heated using one of infrared, hot air, microwave, a cure oven and a through-air-bonder.
10. The method of claim 1 , wherein a filler is added to the film.
11. The method of claim 10 , wherein the filler is selected from the group consisting of clay, calcium carbonate, diatomaceous earth, titanium dioxide, and talc.
12. The method of claim 1 , wherein the apertures are formed by producing a plurality of slits through the second layer, and opening each slit to form a corresponding aperture.
13. The method of claim 12 , wherein the slits are formed using expanded metal plates.
14. The method of claim 12 , wherein the slits are formed in one of a machine direction, a cross machine direction and an angular direction.