WO2004035901A1

WO2004035901A1 - Non woven textile structure incorporating stabilized filament assemblies

Info

Publication number: WO2004035901A1
Application number: PCT/GB2003/004269
Authority: WO
Inventors: Georg Martin Barth; Edmund Hugh Carus
Original assignee: Georg Martin Barth; Edmund Hugh Carus
Priority date: 2002-10-17
Filing date: 2003-10-03
Publication date: 2004-04-29
Also published as: AU2003271887A1; GB2394231A; GB0303292D0

Abstract

A method of producing a nonwoven textile structure comprises the steps of: (a) stretching a plurality of substantially parallel continuous tow filaments (1) of absorbent material, such as cellulose acetate or solvent spun rayon, to provide a filament assembly, (b) consolidating the resulting filament assembly (4) by a compacting operation (at 5) to produce a three-dimensional rod or pack while maintaining substantially uninterrupted capillary along the entire length of the filament assembly, and (c) wrapping the three-dimensional rod or pack (6) in a water porous material (7). A plurality of the resulting wrapped rods or packs (9) may then be incorporated into a composite structure, such as that used for a thin diaper. Such wrapped rods or packs exhibit excellent fluid transmission and wet strength characteristics.

Description

ON WOVEN TEXTILE STRUCTURE INCORPORATING STABILIZED FILAMENT ASSEMBLIES

The present invention relates to nonwoven textile materials and in particular to composite absorbent textile materials.

The present invention has particular application to absorbent textile structures for uses in the fields of sanitary protection, infant care and adult incontinence protection.

WO 99/27876, WO 99/27879, WO 99/30661 , WO 00/56258 and WO 01/72253 A1 , (SCA Hygiene Products AB) and US 2002/0026699A1 , US 2002/0029026A1 , US 2002/0028624A1 , US 2002/0029023A1 , US 2002/0029024A1 , US 2002/0029025A1 and US 2002/0049419A1 (Uni-Charm Corporation) all describe use of filament "tows" as a fluid acquisition material in infant diapers and the like but as only one component in the absorbent matrices specified. More particularly, these specifications disclose production of a layer or layers of continuous "tow" filaments which are bonded in various ways and which may be of cellulose acetate, or of polyethylene, polypropylene, polyamide, polyester, polyvinyl acetate, viscose or rayon, or bi-component polymers. Steps in production of said layer can include crimping or curling, then stretching and distributing the "tow" filaments in various ways, then bonding same in a pattern of lines, spots or points by any suitable technique including thermal or ultrasonic bonding, calendering, laser or print-bonding or undefined hydroentangiement. The filaments are cut to length either before or after the aforesaid bonding. In some cases, the "tow" filaments are bonded, at the same time as the pattern of bonding mentioned above, to a liquid containment layer which can be a non-woven composite material. Conventional bonding techniques are described, all of which would depress the performance of such tow assemblies by capillary blockage at points of bonding.

An object of this invention is to develop the methodology disclosed in the applicant's earlier WO00/63479 and provide an improved manner of handling continuous filaments to facilitate their incorporation into a finished product which has enhanced properties, e.g. of absorbency and/or fluid management, compared to known products.

A method of producing a non-woven textile structure is now proposed which comprises the steps of:

(a) stretching a plurality of substantially parallel continuous tow filaments of absorbent material to provide a filament assembly,

(b) consolidating said filament assembly by a compacting operation to produce a three-dimensional rod or pack while maintaining substantially uninterrupted capillarity along the entire length of said filament assembly, and

(c) wrapping the three-dimensional rod or pack in a water porous material.

In the finished product significant improvements in fluid management, notably wicking and fluid containment are apparent over currently used materials. This is because the processing of the filament assembly is such as to maintain substantially uninterrupted capillarity along its entire length.

In accordance with the present invention the processing of the filament assemblies or tows can be reduced to stretching, shaping and wrapping operations. Multifilament rods or packs of chosen size and cross-sectional shape can be produced from bales of crimped tow by stretching such tow and by subsequent consolidation of same into bundles of round or oval or oblong (rectangular) cross-section which exhibit uninterrupted capillarity along their entire length. Structural stabilization of these filament bundles, which may in practice resemble cigarette-type filter rods, is maintained by a simple fluid permeable wet-strength wrap material, for instance a highly porous nonwoven material.

The composition of such tow filament assemblies can, of course, be selected for optimum end-use performance.

The size of the consolidated filament packs or rods is dependent on the end use of the products containing same and the nature of the fluids being considered for entrapment. These consolidated filament packs or rods can be positioned in controlled spaced apart arrays across the finished composites with one or more nonwoven outer layer(s) providing the full composite finished width.

Whilst any polymer filaments which can be rendered hydrophilic can be considered applicable for production of these three-dimensional consolidated bundles or rods, either alone or with other polymers to form blended filament assemblies, the preferred polymer is cellulose acetate which achieves outstanding fluid take up and wicking properties. Staple cellulose acetate fibre has been used in non-woven fabrics in the past and reported in literature by Celanese Acetate LLC and other sources such as Kimberly-Clark but such non-woven materials have been conventional weblike structures without the use of shaped bundles or rods of filaments. Solvent spun rayons, as produced for example by Lenzing AG and Acordis Pic, are also a favourable option.

The fluid management performance of filament assemblies produced in accordance with the invention can be optimised by the careful selection of filament diameters and packing density. Mixtures of coarser and finer filaments may be advantageous since filament spacing and the presence of capillaries are required for optimum fluid management. In this regard, the use, in the assemblies of the invention, of filaments which have "Y" shaped or "stellar" shaped cross-section or the like may be advantageous since the crevices running along such shaped filaments act like fine capillary structures thus enhancing fluid wicking and full utilisation of the composite structures.

Many well known nonwoven technologies are suitable for bonding such consolidated and wrapped filament packs or rods (collectively referred to herein as "bundles") to a carrier layer of fibres, filaments or a non-woven web made from similar material to the consolidated filament assemblies themselves. These include known processes whereby pulp fibres can be blown onto and around consolidated, wrapped filament assemblies produced according to the invention. The positioning of these consolidated assemblies in absorbent composite structures can be enhanced by the use of binding agents or binding fibres. The latter may be bicomponent fibres such as sheath/core or side by side types as known in airlaid structures or they may be related melt blown fibres and used in Kimberley-Clark "COFORM" materials. In these cases previous inadequate fluid wicking is overcome due to the three- dimensional structure of the compacted multifilament rods or packs of the invention coupled with the presence of long filaments and uninterrupted capillarity.

The consolidated multi-filament bundles of the invention are advantageous when combined with other materials, for example fluff-pulp/superabsorbent airlaid fluid containment composites as currently used in hygiene applications since the filament bundles facilitate fluid transfer to all parts of the total composite. The traditional approach is to use a nonwoven layer to facilitate fluid flow to the fluff- pulp/superabsorbent layer. However, nonwoven layers used to date tend to intrinsically "lock" fluids in place and prevent effective total absorbent composite utilization, particularly on second and third fluid insults. When the consolidated filament bundles of the invention are positioned above or more preferably within a fluff-pulp/superabsorbent medium (but with one edge available to receive fluid immediately on insult) the uninterrupted capillarity of such bundles allows for effective and maximised utilization of such composites.

The invention will be exemplified by reference to the accompanying drawings, in which:

Figure 1 is a sketch illustrating apparatus used for the production of an embodiment of consolidated three-dimensional filament rods in accordance with the invention;

Figure 2 is a perspective, partial sketch of the product of the apparatus of Figure 1;

Figure 3 is a sketch illustrating a portion of one version of a completed composite containing filament rods as produced in accordance with the invention; and

Figure 4 is an end view of the composite of Figure 3.

Figure 1 illustrates a three step in-line consolidation procedure for forming multifilament rods of substantially circular cross-section form, in this case, cellulose acetate spun filaments. Spun filaments 1 are drawn from a bale 2 of crimped filamentary tow, as is commercially available, and are subjected to stretching, at least longitudinally, using textile drafting rollers 3. The parallel stretched filaments 4 are then drawn and compressed into an elongate cylindrical form in a tunnel device 5. A compacted three-dimensional structure 6 of substantially circular cross-section results. At this stage the density of the cellulose acetate filaments may be in the region of 5 denier/fil.

This multi-filament structure 6 is held in its desired compacted form by a highly porous water insoluble lightweight nonwoven fabric 7 which is wrapped around the three-dimensional structure 6 and lightly adhered to itself (at 8). An ideal material for this purpose is a wet laid "tea bag" hydroentangled material (as produced by Crompton Pic for example) containing a binder for self-adherence. Such material, at a typical weight of 20 grams per square metre, exhibits superb fluid transmission and wet strength.

Optimum capillarity for resultant wrapped filament rod 9 (Figure 2) has been obtained using 5 denier cellulose acetate filaments at a controlled packing density of 0.05 grams/cc.

Figures 3 and 4 illustrate a composite structure suitable for hygiene applications. Cellulose acetate filament rod assemblies 10 made as described with reference to Figure 1 are deposited and partially embedded in an airlaid structure 11 (formed at 12) containing pulp, superabsorbent polymer and low temperature binding fibres. The composite product is used with the rod assemblies facing the direction from which fluid is to be received. Such composite structures exhibit fluid distribution by the filament rods 10 to the entire length of the airlaid structure 11 by both longitudinal and lateral liquid spreading. This structure is ideal for incorporation into thin diaper absorbent composites.

Claims

1. A method of producing a nonwoven textile structure comprising the steps of:

(c) wrapping the three-dimensional rod or pack in a water porous material.

2. A method according to claim 1 including the further step of incorporating a plurality of the resulting wrapped rods or packs into a composite structure.

3. A method according to claim 2 wherein the wrapped rods or packs are cut at intervals and an array of longitudinally and/or transversely spaced apart wrapped rods packs are incorporated into the composite.

4. An absorbent nonwoven structure produced by the method set forth in claim 1.

5. A structure according to claim 4 wherein the filament assembly comprises cellulose acetate.

6. A structure according to claim 4 wherein the filament assembly comprises solvent spun rayon.

7. An absorbent composite nonwoven structure produced by the method set forth in claim 2 or 3.

8. A structure according to claim 7 wherein the wrapped rods or packs are bonded to a carrier layer or between respective outer layers.

9. A structure according to claim 7 wherein the rods or packs are embedded in a fluff-pulp matrix.

10. A structure according to claim 7, 8 or 9 further including one or more of a superabsorbent polymer, binding fibres and chemical binders to facilitate fluid take up and distribution.