Non woven textile structure incorporating stabilized filament assemblies

Abstract

A plurality of substantially parallel continuous filaments, e.g. of cellulose acetate or rayon, and preferably newly formed, are consolidated or partially stabilised, e.g. by application of solvent and pressure, by hydroentanglement, by embossing, or by crimping and stretching. The filament assembly or subassemblies thus produced are further stablised by folding, bundling, twisting or intertwining, e.g. to form braids (10), and are then bonded to a carrier layer or sandwiched between outer layers (12, 14), e.g. by hydroentanglement, melt blowing, spinbonding etc. The stablised filament assemblies may be arranged spaced transversely and may be cut just prior to bonding so as also to provide longitudinally spaced three dimensionally thicker regions, ready for conversion to finished products such as absorbant feminine hygiene products or medical swabs or the like.

Description

[0001] This application is a continuation-in-part of International Patent Application No. PCT/GB00/01510 filed Apr. 18, 2000.

FIELD OF THE INVENTION

[0002] The present invention relates to nonwoven textile materials and in particular to composite absorbent textile materials.

[0003] The present invention has particular application to absorbent textile materials or structures for uses in the medical field, for example in or as dressings, sponges or swabs and laparotomy sponges. There are applications also in the fields of sanitary protection, infant care and adult incontinence protection.

BACKGROUND ART

[0004] Nonwoven materials made by many different processes have been utilised as components to produce absorbent materials for use in feminine hygiene, infant diapers and incontinence products. Modern technologies utilising fluff pulp structures often combined with other non-woven materials to form multilayer composites, have been used to facilitate fluid capture, distribution and containment. Other materials such as superabsorbent polymers are often incorporated in these composites to maximise fluid containment.

[0005] 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 hydroentanglement. The filaments are cut to length either before or after the aforesaid bonding. Optionally in some cases, the “tow” filaments can be 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. In some cases, some further details are provided of the method of handling the “tow” filaments to produce a finished layer or layers. The prior art describes conventional bonding of tow filaments by various techniques, all of which depress the performance of such tow assemblies by capillary blockage at points of bonding.

OBJECT OF THE INVENTION

[0006] The present object is to 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.

SUMMARY OF THE INVENTION

[0007] A method of producing a non-woven textile structure is now proposed which comprises the steps of initially stretching a plurality of substantially parallel continuous tow filaments to provide a partially stabilized filament assembly, further constraining said filament assembly by folding, bundling or twisting operations, subjecting this constrained filament assembly to low hydroentangling pressures, and bonding the resulting filament assembly to a carrier layer or layers. An alternative to hydroentangling is light tacking.

[0008] In the finished product, where the filament material is absorbent, significant improvements in fluid management, notably wicking and fluid containment are apparent over existing materials currently utilised and known to those skilled in the art. This is because the processing of the filament assembly is such as to maintain substantially uninterrupted capillary along its entire length.

[0009] In more detail, the initial stages of the method of the invention require tow stretching followed by a carefully controlled corrugation or compaction procedure using for example, overfeed technology such as forced fluid or air injection stuffer box processes. These latter processes enhance the coherence and integrity of multifilament tow assemblies and also impart a degree of loft, bulk, airiness and/or three dimensionality to the assembly.

[0010] Other comparable techniques known to those skilled in the art and optional layering operations can also or alternatively be used at this stage.

[0011] Subsequent to these processes is a second, full consolidation operation preferably using controlled very light hydroentangling. This may mean low water pressure and/or widely spaced water injection manifolds. Alternatively, very light but highly controlled tacking using simplified thermal spot calendering or ultrasonic means can be employed. Either technique should provide sufficient strength and integrity to these tow assemblies to facilitate further processing without disrupting the inherent capillarity of such structures.

[0012] From such a multi-stage process, three-dimensional tow structures of chosen size and shape result with properties that can be selected for optimum end-use performance.

[0013] One or more of the resulting three dimensional stabilized tow assemblies can then be incorporated into simple composite structures by appropriate highly controlled light bonding means such as, but not limited to, controlled light hydroentangling. In this way one or more such stabilized tow assemblies can be bonded to a carrier layer of nonwoven fabric, or between respective outer layers of nonwoven fabric. Such bonding retains the capillary structures in these consolidated tow assemblies. Any capillary tortuosity as a result of controlled light hydroentangling can be accepted since the capillary matrices remain substantially intact and functional.

[0014] Surprisingly, it has been discovered that the presence of such nonwoven fabric outer layers serves to preserve the capillarity of the three dimensional tow assemblies by lessening the impact of resultant hydroentangling water jets on these assemblies by a shielding action. At the same time though, the nonwoven fabrics are lightly mechanically adhered to the tow assemblies to form the completed desired composite assemblies. Naturally, in specific locations where the tow assemblies are absent in the composite structures, the outer nonwoven fabric layers adhere to each other as a consequence of the controlled hydroentangling procedure.

[0015] Such composite structures can, of course, contain more than or less than three layers of material, and these layers may include, in addition to fully consolidated tow assemblies, the nonwoven fabrics already mentioned and/or other materials appropriate to the desired end-use.

[0016] The materials or structures described in this disclosure can be made into converted pieces with controlled tow assembly deposition. The simplest product envisaged is a single elongate stabilized tow assembly of the type already described and of somewhat flattened cross-sectional shape bonded to a nonwoven fabric web. This could serve as or be incorporated with other layers as a bandage. In a preferred, modified version, the tow assembly would be sandwiched between respective outer layers of nonwoven fabric and bonded thereto, by hydroentanglement or tacking, as already outlined. In either form, there may be free edge margins where no tow assembly is present and there is only a marginal strip of carrier material, or the outer layers are bonded to each other.

[0017] In a further development, favourable for mass production, several such stabilized tow assemblies are spaced apart transversely and bonded to a carrier layer or between outer layers. Again there may be free edge margins also, with no tow present. The composite formed can be cut, if required, only at the end of the procedure. That cutting can be along the strips between the presence of the tow assemblies, to provide several elongate bandages, but it could also be transversely of the composite to provide individual dressings.

[0018] Another way of obtaining smaller individual products, like dressings, is to cut the single stabilized tow assembly, mentioned above, into short sections and spaced these apart longitudinally before sandwiching between outer layers and further bonding.

[0019] In a more favourable further development, particularly for production of individual medical dressings or surgical sponges, several such filament assemblies may be spaced apart transversely and also cut and the resulting sections spaced apart longitudinally on a carrier nonwoven web and then subjected to controlled hydroentangling possibly following the addition of an upper carrier nonwoven web.

[0020] This yields areas of carrier material around each island of filament tow, and the individual pieces can be cut apart at each end of the procedure.

[0021] The fully consolidated filament assemblies can be secured during their preparation and/or prior to the final composite assembly procedure by a degree of “moistening”. This acts to secure the filaments by a combination of hydrogen bonding between these filaments possibly combined with light mechanical filament cohesion by surface tension forces imparted by the presence of this added moisture. Such a moistening procedure enhances the quality of the nonwoven composites produced by hydroentangling by retaining the shape and geometry of the filament assemblies.

[0022] Whilst any polymer filament system which can be rendered hydrophilic can be considered applicable for production of these three-dimensional stabilized filament assemblies, 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 web-like structures. Solvent spun rayons as described in the literature by Acordis plc and Lenzing AG are also a favoured option since such materials exhibit excellent fluid handling properties particularly in fully stabilized three-dimensional tow formats

[0023] 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 filaments which have a “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.

[0024] A preferred nonwoven material for use in the outer layers of such composites surrounding the fully stabilized filament assemblies is solvent spun cellulose. Such cellulose exhibits excellent hydroentangling properties yielding strong composites with excellent tactile and absorbency properties, essential in medical applications such as swabbing or laparotomy. Such hydroentangled structures also exhibit excellent fibre retention (i.e. minimal loose fibres) in both wet and dry states, again vital in medical uses.

[0025] The stabilized filament assemblies can be cut by heat, ultrasonic or laser technologies prior to their deposition onto a carrier nonwoven web to produce nonwoven composites. These forms of cutting prevent filament loss which is highly undesirable in many end use applications, such as medical swabs and the like.

[0026] All the nonwoven structures described can be laminated to suitable backing sheets either during manufacture or as an after process to provide for extra security in use by preventing fluid leakage through the thickness of the absorbent composites. Such backing sheets include polymeric films, preferably those having water vapour permeability to optimise skin wellness in use. Preferred backing sheets such as, for example, those made from cellulose or cellulose acetate exhibit environmentally responsible disposability.

[0027] The nonwoven composites disclosed in this current invention are suitable as a novel and innovative alternative to traditional gauze, as used in medical dressings, sponges, laparotomy sponges and bandages. In particular, due to their capillarity, the composites are highly absorbent. Moreover, by correct material usage in the outer nonwoven component or components they can possess a non-adherent surface for single sided or double sided dressings, respectively. Because of the high absorbency of these composites, there is no need for folding or use in multiple plies as is the case with all woven and nonwoven sponges used to date. It is also possible to produce shaped sponges which are advantageous to the end-user and which are difficult to produce when folding is involved.

[0028] The composites described can possess chosen tactile properties dependent on the ingredients used. Furthermore, it is possible to reproduce the feel and three-dimensionality of conventional woven products. The texture, absorbency performance and appearance of the finished composites are dependent on the number, size, morphology and spacing of the filament assemblies incorporated into the composites coupled with the composition of the outer nonwoven layers surrounding these filament assemblies.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The invention will be exemplified by reference to the accompanying drawings, in which:

[0030] FIG. 1 is a sketch illustrating apparatus used for the three step production of a practical embodiment of newly formed fully stabilized three-dimensional filament assembly in accordance with the present invention;

[0031] FIG. 2 is a sketch illustrating one type of apparatus for the production of composite material incorporating cut sections of the fully stabilized three-dimensional filament assembly resulting from the apparatus shown I FIG. 1; and

[0032] FIG. 3 is a sketch illustrating a version of a completed composite article or product containing a cut section of the filament assembly resulting from the apparatus of FIG. 1, as produced, for example, by the apparatus of FIG. 2.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0033] FIG. 1 illustrates a three step in-line consolidation procedure for the formation of a stabilized three dimensional multifilament assembly with substantially continuous capillarity from, in this case, cellulose acetate spun filaments. Spun filaments (1) from a bale (2) of crimped filamentary tow as is commercially available are subjected to a longitudinal stretching process using textile drafting rollers (3) coupled with a degree of lateral stretching using bowed “Mount Hope” rollers (4). Corrugation and compaction of these stretched filaments (5) is achieved using a stuffer box (6) with forced air injection (7).

[0034] The initially consolidated three-dimensional compacted filaments are then subjected to a very light and highly controlled specialist hydroentangling operation. In this respect, an extremely light, minimal water pressure, preferably in the region of only 10-15 bars, is used in the hydroentangling operation. Portions of two pairs of hydroentangling manifolds 8 are shown. Water jets issue from apertures in these manifolds 8 directed upwards and downwards onto the compacted filament assembly. This is sufficient to impart handling integrity to the resultant filament assembly (9) without interfering with the capillarity of said structure.

[0035] FIG. 2 illustrates a typical process whereby such formed fully stabilized filament assemblies 9 can be incorporated into finished absorbent nonwoven composites. Fully stabilized filament assemblies (9), production of which was described in relation to FIG. 1, are positioned onto a prepared nonwoven fabric (12). Three such assemblies 9 are shown spaced apart transversely across the width of the apparatus and of the fabric 12, with a margin at each transverse edge of the fabric 12. The assemblies 9 are cut at intervals so as also to produce a longitudinal array of filament assembly sections 10.

[0036] The fabric 12 is pre-moistened at a preliminary station 13 to facilitate positioning of the filament assemblies' sections 10 by drum-like apparatus 14 in a controlled manner and specifically to prevent movement of the assembly sections 10 on the base nonwoven material 12.

[0037] A second nonwoven fabric 15, in this case identical to the base nonwoven material 12 is placed onto the assembly of fully stabilized filament assembly sections 10 and base nonwoven 12. The total structure thus formed is subjected to light but controlled hydroentangling by further pairs of hydroentangling manifolds 16. This should be sufficient to hold the composite 17 securely together but insufficient to destroy the capillarity and three dimensionality of the fully stabilized filament assembly sections 10. Suitable hydroentangling pressures at this stage may be between 40 and 200 bars, optimally possibly between 50 and 100 bars. The completed composite 17 is then subjected to drying, in this case using through-air technology in enclosure 18.

Claims

1. A method of producing a nonwoven textile structure comprising the steps of initially stretching a plurality of substantially parallel continuous tow filaments to provide a partially stabilized filament assembly, further constraining said filament assembly by folding, bundling or twisting operations, subjecting this constrained filament assembly to low hydroentangling pressures and bonding the resulting filament assembly to a carrier layer or layers so as to maintain substantially uninterrupted capillarity along the entire length of the said resulting filament assembly.

2. A method as set forth in claim 1 wherein the resulting filament assembly is cut at intervals and deposited at spaced intervals on the carrier layer prior to bonding to the carrier layer or layers.

3. A method as set forth in claim 1 wherein a plurality of spaced apart fully stabilized filament assemblies are bonded to the carrier layer or between carrier layers.

4. A nonwoven textile structure produced by the method set forth in claim 3 and comprising a plurality of spaced apart stabilized filament assemblies bonded between respective outer layers, each assembly being composed of filaments having substantially uninterrupted capillarity.

5. A nonwoven textile structure as set forth in claim 4 wherein the filament assemblies comprise cellulose acetate.

6. A nonwoven textile structure as set forth in claim 4 wherein the filament assemblies comprise solvent spun rayon.

7. A nonwoven textile structure as set forth in claim 4 wherein the outer layers extend beyond the filament assemblies at the edges thereof and are bonded only to each other in these locations.

8. A method of producing a nonwoven textile structure comprising the steps of initially stretching a plurality of substantially parallel continuous tow filaments to provide a partially stabilized filament assembly, further constraining said filament assembly by folding, bundling or twisting operations, subjecting this constrained filament assembly to light tacking by means of thermal spot calendaring or by ultrasonic means and bonding the resulting filament assembly to a carrier layer or layers so as to maintain substantially uninterrupted capillarity along the entire length of the said resulting filament assembly.

9. A method as set forth in claim 8 wherein the resulting filament assembly is cut at intervals and deposited at spaced intervals on the carrier layer prior to bonding to the carrier layer or layers.

10. A method as set forth in claim 8 wherein a plurality of spaced apart fully stabilized filament assemblies are bonded to the carrier layer or between carrier layers.

11. A nonwoven textile structure produced by the method set forth in claim 10 and comprising a plurality of spaced apart stabilized filament assemblies bonded between respective outer layers, each assembly being composed of filaments having substantially uninterrupted capillarity.

12. A nonwoven textile structure as set forth in claim 11 wherein the filament assemblies comprise cellulose acetate.

13. A nonwoven textile structure as set forth in claim 11 wherein the filament assemblies comprise solvent spun rayon.

14. A nonwoven textile structure as set forth in claim 11 wherein the outer layers extend beyond the filament assemblies at the edges thereof and are bonded only to each other in these locations.

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

(a) drawing a bundle of crimped filaments, i.e. tow, from a bale;

(b) stretching said bundle lengthways and across its width;

(c) folding or corrugating said stretched bundle in a stuffer box process which includes air injection so as to increase its bulk and loft; and

(d) subjecting the resulting material to a hydroentangling process.

16. A method as set forth in claim 15 wherein step (d) comprises directly subjecting the corrugated and bulked material to a process of hydroentanglement employing widely spaced water injection manifolds.

17. A method as set forth in claim 15 wherein step (d) comprises directly subjecting the corrugated and bulked material to a process of hydroentanglement at lower water pressure.

18. A method as set forth in claim 17 including the further step of feeding the resulting material between upper and lower layers of nonwoven textile web and subjecting this layered structure to a process of hydroentanglement at lower water pressure and/or using widely spaced water injunction manifolds.

19. A method as set forth in claim 18 including the additional step of cutting the resulting material and feeing the cut pieces in a spaced array between the upper and lower layers of nonwoven textile web.

20. A bandage formed by the method set forth in claim 18.

21. Dressings or pads for medical and surgical purposes formed by the method set forth in claim 19.