Low permeability and high strength woven fabric and methods of making the same
A method for producing a woven fabric comprises weaving fibers in a warp direction and a weft direction to form a fabric having a top surface and a bottom surface, wherein the warp fibers and weft fibers each comprises one or more filaments of a synthetic polymer having substantially uniform cross-sectional composition. At least a portion of the filaments in the fibers on the top and/or bottom surface of the fabric are then fused together in the presence of a heat transfer liquid or vapor added during the fusing step or added in a prior step of the fabric production process and retained by the filaments. The fusing step produces a treated fabric having a tensile strength in both the warp and weft directions of 1000 N or greater and having, in the absence of any coating, a static air permeability (SAP) of 3 l/dm 2 /min or lower.
1. A method for producing a woven fabric, said method comprising:
(a) weaving fibers in a warp direction and a weft direction to form a fabric having a top surface and a bottom surface, wherein the warp fibers and weft fibers each comprises one or more filaments of a synthetic polymer having substantially uniform cross-sectional composition;
(b) fusing together at least a portion of the filaments in the fibers on the top surface of the fabric or at least a portion of the filaments in the fibers on the bottom surface of the fabric, wherein said filaments are fused together in the presence of a heat transfer liquid or vapor added prior to fusing and retained by the filaments, wherein the amount of heat transfer liquid or vapor added prior to fusing is in the range from about 5 to about 30 wt % based on the weight of the dry fabric and wherein the fusing step produces a treated fabric having a tensile strength in both the warp and weft directions of 1000 N/50 mm or greater and having, in the absence of any coating, a static air permeability (SAP) of 3 l/dm 2 /min or lower.
2. The method of claim 1 , wherein the fusing is performed by treating the woven fabric at a temperature and/or pressure sufficient to permanently modify a cross-sectional dimension and fuse at least a portion of the filaments in the fibers on the top surface of the fabric or at least a portion of the filaments in the fibers on the bottom surface of the fabric.
3. The method of claim 2 , wherein the temperature in step (b) is decreased as compared to a temperature required to permanently modify the cross-sectional dimension and fuse at least a portion of the filaments in the absence of a heat transfer liquid or vapor.
4. The method of claim 2 , wherein the temperature in step (b) is below the dry softening point of the synthetic polymer filaments.
5. The method of claim 2 , wherein the pressure in step (b) is decreased as compared to a pressure required to permanently modify the cross-sectional dimension and fuse at least a portion of the filaments in the absence of a heat transfer liquid or vapor.
6. The method of claim 2 , wherein the permanently modified cross-section results in at least a portion of the filaments having an aspect ratio from about 1.2:1 to about 10:1.
7. The method of claim 2 , wherein the fusing comprises hot roll calendering the woven fabric.
8. The method of claim 7 wherein the hot roll calendering is performed at a fabric speed from about 5 to about 80 m/minute.
9. The method of claim 1 , wherein the treated fabric has a root mean square surface (RMS) surface roughness in the range from about 2 to about 70 μm.
10. The method of claim 1 , wherein the treated fabric exhibits an edgecomb resistance in both the warp and weft directions of 150 N or greater when the fabric is unaged.
11. The method of claim 1 , wherein the heat transfer liquid or vapor comprises water.
12. The method of claim 1 and further comprising applying a coating to the treated fabric to further reduce the static air permeability (SAP) thereof.
13. The method of claim 1 , wherein heat transfer liquid or vapor is added to said filaments during the fusing step.