Liquid-pervious fibrous non-woven fabric
A liquid-pervious fibrous non-woven fabric includes staple fibers made of thermoplastic synthetic resin fused together which is formed on its upper surface with a plurality of ridges, and a plurality of grooves extending in parallel in a longitudinal direction. The ridges and grooves are arranged alternately in a transverse direction. On the upper surface, some of the staple fibers extend across the ridges to the adjacent grooves on each side of the ridges and are, in the respective grooves, fused to the staple fibers of a different type from the former staple fibers.
1. A liquid-pervious fibrous non-woven fabric having a longitudinal direction, a transverse direction and a thickness direction being orthogonal to one another, said liquid-pervious fibrous non-woven fabric comprising:
upper and lower surfaces opposed to each other in the thickness direction and both extending in the longitudinal direction and the transverse direction, the upper surface being formed with ridges and grooves extending in parallel in the longitudinal direction to be alternately arranged in the transverse direction, and the lower surface being substantially flat; and
staple fibers, made of thermoplastic synthetic resin, being fused together in the liquid-pervious fibrous non-woven fabric,
wherein:
a thickness t measured from the lower surface to a bottom of one of the grooves is in a range of 40 to 60% of a thickness T measured from the lower surface to an apex of one of the ridges,
the staple fibers include fibers each having a fiber length sufficiently long to extend across at least one ridge of the ridges to the grooves on both sides of the at least one ridge, and
a specific volume of one of the ridges is greater than a specific volume of one of the grooves.
2. The liquid-pervious fibrous non-woven fabric defined by claim 1 , wherein the staple fibers extending across the ridges are fused, in each of the grooves adjacent to the ridge, with staple fibers of a different type from the staple fibers extending across the ridges.
3. The liquid-pervious fibrous non-woven fabric defined by claim 1 , wherein the liquid-pervious fibrous non-woven fabric has a mass per unit square meter in a range of 15 to 35 g/m 2 .
4. The liquid-pervious fibrous non-woven fabric defined by claim 1 , wherein the specific volume of said one of the ridges is in a range of 70 to 105 cc/g and the specific volume of said one of the grooves is in a range of 40 to 60 cc/g.
5. The liquid-pervious fibrous non-woven fabric defined by claim 1 , wherein the staple fibers comprise staple fibers each having an apparent fiber length in a range of 10 to 80 mm.
6. A method of manufacturing a liquid-pervious fibrous non-woven fabric having a longitudinal direction, a transverse direction and a thickness direction being orthogonal to one another, said liquid-pervious fibrous non-woven fabric comprising:
upper and lower surfaces opposed to each other in the thickness direction and both extending in the longitudinal direction and the transverse direction, the upper surface being formed with ridges and grooves extending in parallel in the longitudinal direction to be alternately arranged in the transverse direction, and the lower surface being substantially flat; and
staple fibers, made of thermoplastic synthetic resin, being fused together in the liquid-pervious fibrous non-woven fabric,
wherein:
a thickness t measured from the lower surface to a bottom of one of the grooves is in a range of 40 to 60% of a thickness T measured from the lower surface to an apex of one of the ridges,
the staple fibers include fibers each having a fiber length sufficiently long to extend across at least one ridge of the ridges to the grooves on both sides of the at least one ridge, and
a specific volume of one of the ridges is greater than a specific volume of one of the grooves,
said method comprising:
compressing a fibrous web containing a given mass/m 2 of the staple fibers under an ejection pressure of first hot air jets until a thickness of the fibrous web is reduced to ½ to ¼ of an initial thickness of the fibrous web; and then
forming the ridges and the grooves by subjecting the fibrous web to second hot air jets ejected from second nozzles arranged in a cross direction orthogonal to a machine direction while the fibrous web is continuously transported in the machine direction so that each of the ridges is formed directly below a space defined between each pair of adjacent second nozzles and each of the grooves is formed directly below one of the second nozzles.
7. The method defined by claim 6 , wherein said first hot air jets are ejected from first nozzles to the fibrous web to compress the fibrous web.
8. The method defined by claim 7 , wherein said first nozzles are disposed upstream of said second nozzles in the machine direction.
9. The method defined by claim 7 , wherein the ejection pressure of the first hot air jets ejected from said first nozzles is different from that of the second hot air jets ejected from said second nozzles.
10. The method defined by claim 7 , wherein a temperature of the first hot air jets ejected from said first nozzles is different from that of the second hot air jets ejected from said second nozzles.
11. The method defined by claim 7 , wherein the first hot air jets ejected from said first nozzles render smooth a surface of the fibrous web facing the first nozzles, before the grooves and ridges are formed in the smooth surface of the fibrous web by the second hot air jets ejected from second nozzles.