Nonwoven fabric sheet and method for making the same

Abstract

The invention relates to a patterned spunbonded nonwoven fabric sheet comprising a plurality of spunbonded crimped fibers bonded together at a plurality of bonding points, wherein all fibers of the patterned spunbonded nonwoven fabric sheet are spunbonded crimped fibers and wherein the configuration of the fibers within the sheet is inhomogeneous and varies according to a preferably regular pattern. The invention further relates to a method for forming such patterned spunbonded nonwoven fabric sheet from a flat spunbonded nonwoven fabric sheet starting material. Still further, the invention relates to such flat spunbonded nonwoven fabric sheet starting material.

Claims

1. A patterned spunbonded nonwoven fabric sheet comprising a plurality of spunbonded crimped fibers bonded together at a plurality of bonding points, wherein all fibers of the patterned spunbonded nonwoven fabric sheet are spunbonded crimped fibers, wherein a density of fibers, or a mean orientation of the fibers, or a mean crimp radius of the fibers within the fabric sheet, or any combination thereof, are inhomogeneous and varies according to a regular pattern, wherein the regular pattern is such that the fabric sheet has a three-dimensional structure comprising a plurality of alternating elevations and depressions arranged according to the regular pattern, wherein the three-dimensional structure is such that a cross-sectional profile of the fabric sheet in a cross-machine direction thereof is windy such that when there is an elevation on one surface of the fabric sheet, there is a depression on another surface of the fabric sheet corresponding to each elevation, wherein the fabric sheet comprises high-density areas having an above average fiber density of the fabric sheet, and low-density areas having a below average fiber density of the fabric sheet, wherein the plurality of alternating elevations and depressions are the high density areas and transition zones between the plurality of alternating elevations and depressions are the low-density areas, wherein the regular pattern comprises parallel, uninterrupted, straight stripes oriented in a machine direction of the fabric sheet and said regular pattern is irrespective of the plurality of bonding points present, and wherein each of the parallel, uninterrupted, straight stripes is a continuous stripe from one end of the fabric sheet to another end of the fabric sheet.

2. The patterned spunbonded nonwoven fabric sheet according to claim 1, wherein the high-density areas account for between 50 and 80% of the overall weight of the fabric sheet.

3. The patterned spunbonded nonwoven fabric sheet according to claim 1, wherein the crimped fibers are crimped multicomponent fibers.

4. The patterned spunbonded nonwoven fabric sheet of claim 3, wherein one or all components of the crimped multicomponent fibers are polymer components.

5. The patterned spunbonded nonwoven fabric sheet of claim 3, wherein one or all components of the crimped multicomponent fibers comprise polypropylene.

6. A method for forming a patterned spunbonded nonwoven fabric sheet of claim 1, the method comprising: providing a flat spunbonded nonwoven fabric sheet starting material comprising a plurality of spunbonded crimped fibers bonded together at a plurality of bonding points, wherein all fibers of the patterned spunbonded nonwoven fabric sheet are spunbonded crimped fibers; and mechanically activating the starting material upon application of localized stretching forces to change the configuration of the fibers according to the pattern.

7. The method of claim 6, wherein the steps of providing and mechanically activating the starting material are carried out at different sites remote from one another.

8. The method of claim 6, wherein the step of mechanically activating includes rolling the flat spunbonded nonwoven fabric sheet starting material in a mill comprising a pair of interacting rolls whose surfaces comprise interlocking annular grooves and crests.

Description

(1) Further details and advantages of the invention are explained with reference to the figures and working examples described in the following. The figures show:

(2) FIG. 1: an illustration of a mill configured to carry out a method according to the invention;

(3) FIG. 2: an illustration of the mill of FIG. 1 in operation;

(4) FIG. 3: enlarged top view pictures of an activated nonwoven fabric sheet according to the invention; and

(5) FIG. 4: enlarged perspective pictures of the sheet of FIG. 3; and

(6) FIG. 5: top view pictures of the fabric of FIG. 3 and two other nonwoven fabric sheets according to the invention of different basis weights.

(7) FIG. 1 shows a mill 1 configured to carry out a method according to the invention. It comprises a pair of counter rotating rollers 2 and 3. Annular discs 4 are mounted to the surfaces of both rollers 2 and 3 to obtain a surface structure of annular grooves (between the discs) and crests (the discs). The discs 4 are mounted with an offset on rollers 2 and 3 and the discs 4 of one roller 2 or 3 interlock with the discs 4 of the other roller 3 or 2. In the working example, the width “a” of the discs 4 is 0.8 mm, the depth of engagement “b” (“DOE”) is variable and the distance “c” between the discs 4 is 1.65 mm.

(8) FIG. 2 shows the mill of FIG. 1 in operation. A flat nonwoven fabric sheet 5 comprising a plurality of crimped fibers bonded together at a plurality of bonding points is fed to the mill at a certain line speed and a corrugated pattern is worked into the nonwoven 5 by stretching in stress zones 6 while not stretching in stress-free zones 7.

(9) The starting materials, i.e., the flat nonwoven fabric sheets used in different working examples were spunbonded polypropylene nonwovens made from crimped fibers in a side-by-side configuration with a regular PP homopolymer in combination with a PP/PE random copolymer at a distribution ratio of 50/50. The denier of the fibers was 1.8. All materials were open dot bonded at 24 dots/cm.sup.2 by calender bonding at an engraving depth of 0.75 mm to obtain a bonding ratio of 12.1%. The starting materials had the characteristics as described in Table 1.

(10) TABLE-US-00001 TABLE 1 Material Basis weight Caliper.sup.1 Density # [g/m.sup.2] [mm] [g/cm.sup.3] Quotient.sup.2 A 99.9 0.75 0.133 133.2 B 50.5 0.63 0.0802 67.3 C 21.0 0.39 0.0538 28.0 Material TSMD.sup.3 TEMD.sup.4 TSCD.sup.5 TECD.sup.6 # [N/50 mm] [%] [N/50 mm] [%] A 75.8 62.5 55.2 108.0 B 65.2 93.6 37.8 117.7 C 28.2 85.6 14.6 97.7 .sup.1Caliper: Thickness of the material according to WSP.120.1 (R4) .sup.2Quotient: Quotient obtained by dividing the basis weight [g/m.sup.2] with the engraving depth of calender bonding [mm] .sup.3TSMD: Tensile strength in MD according to WSP 110.4 .sup.4TEMD: Tensile elongation in MD according to WSP 110.4 .sup.5TSCD: Tensile strength in CD according to WSP 110.4 .sup.6TECD: Tensile elongation in CD according to WSP 110.4

(11) These starting materials were activated in a mill as shown in FIG. 1 in a process as shown in FIG. 2. The settings were as shown in Table 2.

(12) TABLE-US-00002 TABLE 2 Example # Material # DOE [mm] Line speed [m/min] 1 A 3.0 20 2 B 4.0 10 3 B 4.0 20 4 B 4.0 30 5 B 2.0 20 6 C 5.0 20

(13) The resulting materials had the characteristics as described in Table 3.

(14) TABLE-US-00003 TABLE 3 Example # Basis weight [g/m.sup.2] Caliper [mm] Density [g/cm.sup.3] 1 66.6 1.37 0.0486 2 26.9 0.820 0.0328 3 25.9 0.818 0.0320 4 27.3 0.874 0.0312 5 43.9 0.602 0.0729 6 11.0 0.320 0.0344 TSMD TEMD TSCD TECD Example # [N/50 mm] [%] [N/50 mm] [%] 1 37.4 56.0 30.2 72.2 2 19.8 45.1 19.4 91.8 3 18.6 48.0 18.2 94.5 4 23.3 98.0 18.3 47.8 5 48.9 91.9 35.3 83.7 6 6.8 59.0 6.4 28.8

(15) FIG. 3a shows a top view picture of the inventive nonwoven fabric sheet of Example 3. The material has a corrugated three-dimensional structure with grooves and crests oriented in longitudinal direction (MD) and a wavelike cross-section when cut in a direction perpendicular thereto (CD). It can be seen that the fiber structure within the material has been rearranged and is inhomogeneous. It varies according to the corrugated pattern.

(16) There are longitudinal (MD) stripes 8 with a high fiber density and a mean fiber orientation in MD. These stripes appear brighter in the picture and extend longitudinally (in MD) in the top areas of the crests and the bottom areas of the valleys. The areas corresponding to these stripes 8 have not or hardly been stretched during the activation process. They correspond to the stress-free zones 7 of FIG. 2.

(17) The stripes 8 are interrupted by longitudinal (MD) stripes 9 of lower fiber density and a mean fiber orientation in CD. These stripes appear darker in the picture and extend longitudinally (in MD) in the transition zones between crests and valleys. The areas corresponding to these stripes 9 have significantly been stretched during the activation process. They correspond to the stress zones 6 of FIG. 2.

(18) To determine the fiber concentration in the high concentration areas 8 and the low concentration areas 9, the sheet of Example 3 has been sliced in longitudinal stripes as shown in FIG. 3b. The cutting lines are marked with reference numeral 10 and extend longitudinally (in MD) along the boundaries between areas 8 and 9. The cutting lines 10 where chosen such that all strips had an equal width, meaning that the width of all strips corresponding to the areas 8 was equal to the width of all strips corresponding to the areas 9. This allowed a comparative analysis by simple weighting of the materials. In one step, all strips corresponding to the areas 8 were weighed. In another step, all strips corresponding to the areas 9 were weighted. The result was that the high concentration areas 8 account for 61.7% of the overall weight of the sample and the low concentration areas 9 account for 38.3% of the overall weight of the samples.

(19) As apparent from FIGS. 4a and 4b, the activated fabric of Example 3 has a textile-like appearance, which can be desirable in certain applications, for example, hygiene applications.

(20) FIGS. 5a to 5c show top view pictures the nonwoven fabrics of Example 1 (FIG. 5a), again Example 3 (FIG. 5b) and Example 6 (FIG. 5c). As apparent from these illustrations, activation according to the invention can be observed in all examples. Different qualities of activation are observed. When using the dense starting material as in Example 1, the web does not open up as readily during activation as when using a more open fabric as in Example 3. On the other hand, when using a very open fabric as in Example 6, the high and low density areas in the activated fabric are not as emphasized.