Nonwoven fabric and the production thereof

Abstract

The present invention relates to a nonwoven fabric and the production thereof. More specifically, the invention relates to a dispersible and biodegradable nonwoven fabric comprising a web prepared using a wet lay forming process. The process involves forming a web from the aqueous suspension on a wire support, hydroentangling and drying the web. The web can be provided with a high quality hydroembossed pattern, which remains even in wet wipes prepared from the material.

Claims

1. A nonwoven fabric comprising hydroentangled fibers, the fibers comprising about 5%-45% by weight of regenerated short cut fibers and about 55%-95% by weight of natural fibers, wherein 10%-20% by weight of the short cut fibers have a length in a range of 6-12 mm and 80%-90% by weight have a length in a range of from 3 mm to less than 6 mm.

2. The nonwoven fabric according to claim 1, wherein 10%-20% by weight of the short cut fibers have a length in a range 6-8 mm and 80-90% by weight have a in a range of 4-5 mm.

3. The nonwoven fabric according to claim 1, wherein the short cut fibers have a dtex is in a range 0.7 to 2.2 dtex.

4. The nonwoven fabric according to any claim 1, wherein the regenerated short cut fibers are selected from the group consisting of, lyocell, viscose, rayon, and tencel.

5. The nonwoven fabric according to claim 1 wherein the natural fibers are formed from a material selected from the group consisting of wood pulp, hemp, flax, cotton, jute, bamboo, sisal, jute, and kapok.

6. The nonwoven fabric according to claim 1, wherein the non-woven fabric comprises a three-dimensional pattern.

7. The nonwoven fabric according to claim 6, wherein the three-dimensional pattern comprises a height equal to a difference between a minimum thickness and maximum thickness of the nonwoven fabric of at least 200 m.

8. The nonwoven fabric according to claim 6, wherein the three dimensional pattern comprises an angle of inclination between the minimum thickness to the maximum thickness in a range of 48-90.

9. The nonwoven fabric according to 6, wherein the three dimensional pattern comprises at least 10% more fibers by weight than the non-patterned area of the non-woven fabric.

10. The nonwoven fabric according to claim 1, wherein the nonwoven fabric comprises a basis weight of 50 gsm-120 gsm.

11. The nonwoven fabric according to claim 1, wherein a machine direction (MD) wet strength of the nonwoven fabric is in a range of 650 g/50 mm to 1400 g/50 mm and a cross direction (CD) wet strength is in a range 400 g/50 mm to 650 g/50 mm.

12. The nonwoven fabric according to claim 1, wherein upon wetting of the nonwoven fabric with liquid 2.5 times a weight of dry nonwoven fabric and aged for more than one week has a slosh box dispersibility according to EDANA & INDA FG502 (GD4) Guidelines of more than 94% in 5 min and 98% in 10 min.

13. The nonwoven fabric according to claim 1, which when wetted with liquid 2.5 times the weight of dry nonwoven fabric and aged for more than one week has a slosh box dispersibility according to IWSFG Test Methods of more than 95% in 30 min.

14. The nonwoven fabric according to claim 1, wherein the natural fibers have a length in a range of 1-3 mm and a dtex in a range of 1.0 to 1.4 dtex.

15. A method for producing a nonwoven fabric material, comprising: providing an aqueous suspension of fibers comprising about 5%-45% by weight of regenerated short cut fibers and about 55%-95% of natural fibers, wherein 10%-20% by weight of the regenerated short cut fibers have a length in a range of 6-12 mm and 80%-90% by weight of the regenerated short cut fibers have a length in a range of 3 to less than 6 mm: forming a web from the aqueous suspension on a wire support; hydroentangling the web; and drying the web to the produce nonwoven fabric material.

16. The method according to claim 15, wherein 10%-20% of the short cut fibers have a length in a range 6-8 mm and 80-90% by weight have a length in a range of 4-5 mm.

17. The method according to claim 15, further comprising removing the web from the wire support and transferring the web to a hydroembossing roll, wherein the hydroentangling comprises hydroembossing the web.

18. The method according to claim 15, where the hydroembossing roll forms a three-dimensional pattern on the nonwoven fabric.

19. The method according to claim 18, where the three dimensional pattern defines a machine readable code.

Description

DETAILED DESCRIPTION

[0031] Advantageously, the fiber suspension has a solids content in the range 0.5% to 5%. In an embodiment, the short cut fibers in the suspension have a dtex in the range of 0.7 to 2.2, and in a particular embodiment in the range of 0.9-1.7 dtex.

[0032] Preferably, the appropriate degree of consolidation is a consequence of using the composition set out above and the following parameters:

TABLE-US-00001 Vacuum Speed (ft/min) Nozzle psi Nozzle size m (mbar) 500-1200 1-1200 5 to 150 20-700

[0033] Following hydroentanglement and dewatering on a wire, the tensile strength of the web is in the range 80 to 120% of its final tensile strength.

[0034] Following the hydroentanglement and dewatering step, the web is transferred to a hydroembossing roll having a surface pattern which is imposed on the web, forming a high definition three-dimensional pattern. Preferably, the pattern is on a sleeve supported by the roll.

[0035] Inside the roll there will be a partial vacuum for removing excess water from the hydroembossing through provided openings. In an embodiment, 1 to 5 nozzle bars are used for hydroembossing the web.

[0036] In a high definition pattern, fibers have been moved from their initial location in the plane of the web, creating a three-dimensional structure which is more distinct than the two-dimensional patterns that can be created using belt hydroembossing or thermal calendaring.

[0037] In the following discussion, the top surface of the fabric is the surface that faces the sleeve during the hydroembossing operation; the bottom surface is the one exposed to the water jets.

[0038] For considering the three-dimensional structure of the web of the present invention, the base level is defined as the level of the bottoms of the deepest depressions in the fabric, i.e. the level of the thinnest areas in the fabric or a minimum thickness of the fabric. In an embodiment, the thickness of the fabric at its thinnest points or minimum thickness is at least 30 m.

[0039] The embossing level is a level on the top surface of the fabric which is farthest or at a maximum distance from the base level. Put another way, the embossing level comprises areas (elevated portions) with a maximum thickness of the fabric. In this context, a pattern in a nonwoven web is considered a three-dimensional high definition pattern if the embossing level or maximum thickness is at least 200 m above the base level or minimum thickness. In the present context, this dimension may also be referred to as a height of the pattern. In an embodiment, the embossing level or maximum thickness is at least 250 m; and in other embodiments is at least 300 m above the base level of the fabric. The angle of inclination in a high definition three-dimensional pattern refers to the angle of the slope of the elevated portions of the fabric relative to a plane of the base level. In a three-dimensional high definition pattern, the angle of inclination of the rise from the base level to respective elevated portion(s) is in the range 48 to 90; preferably in the range of 55-88. In certain embodiments, the 3D pattern is machine readable.

[0040] Angles and dimensions in nonwoven fabric structures may be determined using laser triangulation technology. Further, angles and dimensions of the embossing tool may be determined.

[0041] As a portion of the fibres are moved from their original location during hydroembossing using a sleeve, the grammage of the patterned portions of the fabric, i.e. the portions of the fabric receiving the displaced fiber increases at least 10% by weight, e.g., 10-30% by weight or 15-30% by weight. Thus, the patterned areas contain at least 10% by weight more fiber than the non-patterned areas.

[0042] Inside the roll there will be a partial vacuum for removing excess water from the hydroembossing. In an embodiment, there are from 1 to 5 hydroentanglement units hydroembossing the web.

[0043] The web is subsequently subjected to drying using e.g. an air dryer, a can dryer, an omega dryer or combinations of these.

[0044] In an embodiment, the basis weight of the finished nonwoven fabric according to the invention is in the range 50 to 120 gsm.

[0045] In at least one embodiment, the suspension may be laid on the wire on top of a second, previously unwound web which is of the spunlace, wetlaid or tissue type. In at least one embodiment, a third layer of unwound material of the types mentioned above may be applied on top of the first, wetlaid layer.

[0046] In at least one embodiment, the suspension may be laid on the wire in several steps. Further, layers can be added using air laying or carding technology.

[0047] The nonwoven fabric according to the invention wetted with liquid 2.5 times the weight of dry nonwoven fabric and aged for more than one week had a slosh box dispersibility of more than 94% in 5 min and 98% in 10 min, similar to dry toilet tissue. Overall, the dispersibility ranges for a fabric according to the invention are from 94% to 99% for a 5 min slosh box test. All slosh box tests were carried out according to EDANA & INDA FG502 (GD4) Guidelines.

[0048] As set forth above, aspects of the present invention provide for a material that has excellent structural integrity in use, but also desirable water dispersability properties.

[0049] In one aspect, there is provided a nonwoven fabric comprising hydroentangled fibers, the fibers comprising about 5%-45% by weight of regenerated short cut fibers and about 55%-95% by weight of natural fibers, wherein 10%-20% by weight of the short cut fibers have a length in a range of 6-12 mm and 80%-90% by weight have a length in a range of from 3 mm to less than 6 mm. In an embodiment, 10%-20% by weight of the short cut fibers have a length in a range 6-8 mm and 80-90% by weight have a in a range of 4-5 mm.

[0050] In another aspect, there is provided a method for producing a nonwoven fabric material, comprising: [0051] providing an aqueous suspension of fibers comprising about 5%-45% by weight of regenerated short cut fibers and about 55%-95% of natural fibers, wherein 10%-20% by weight of the regenerated short cut fibers have a length in a range of 6-12 mm and 80%-90% by weight of the regenerated short cut fibers have a length in a range of 3 to less than 6 mm: [0052] forming a web from the aqueous suspension on a wire support; [0053] hydroentangling the web; and [0054] drying the web to the produce nonwoven fabric material. [0055] In an embodiment of the method, 10%-20% of the short cut fibers have a length in a range 6-8 mm and 80-90% by weight have a length in a range of 4-5 mm.

Example

[0056] In the following example, the short cut fibers are viscose. A first group of short cut fiber has a length of 5 mm, and a second group of short cut fiber has a length of 8 mm. The dtex of the short cut fiber is either 0.9 or 1.7 dtex. Further, the compositions comprise softwood pulp. The results set out in Table 1 clearly show, that when only shorter regenerated short cut fibers are used (Sample A), the tensile strength values are clearly inferior to those of samples B, C and D. When only longer regenerated shortcut fibers are used (sample E), decreased dispersibility is obtained.

[0057] The weak strength and 100% slosh box (10 min) values are due to the 25% lower basis weight. When combining 5 mm and 8 mm short cut fibers, good strength values are obtained with dispersibility on par with dry toilet paper.

[0058] Table 1 shows test results of various nonwoven fabric made with different compositions compared to dry toilet tissue. Samples B, C and D are in accordance with the invention.

TABLE-US-00002 TABLE 1 Basis % of Wet Wet Slosh Slosh Weight Fiber % of MD CD Box Box Sample (gsm) Shortcut Fiber A/Fiber B A/B Pulp g/50 mm g/50 mm (5 min) (10 min) Code 80 0.9 dtex*5 mm 40% 60% 852 580 98.95 99.80 A 80 1.7 dtex*5 mm/1.7 dtex*8 mm 35%/5% 60% 1160 518 98.29 98.02 B 80 1.7 dtex*5 mm/1.7 dtex*8 mm 25%/5% 70% 1010 454 94.64 98.49 C 80 0.9 dtex*5 mm/1.7 dtex*8 mm 35%/5% 60% 1070 404 99.84 100 D 60 1.7 dtex*8 mm 30% 70% 820 530 85 100 E 80 Pulp 0% 100% 95.28 99.04 Toilet Tissue (Dry)

[0059] International Water Services Flushability Group (IWSFG) (PAS) 3: Disintegration Test Method-Slosh Box, is a modified version of the INDA/EDANA slosh box test.

[0060] In this test, sample B has a slosh box dispersibility percentage of 97.37%. Overall, the dispersibility ranges according to (IWSFG) (PAS) 3 for a fabric according to the invention are more than 95% in 30 min.