WO2011097661A1

WO2011097661A1 - Highly absorbent reusable pads, a process for their manufacture and their use in reusable hygiene products

Info

Publication number: WO2011097661A1
Application number: PCT/AT2011/000040
Authority: WO
Inventors: Shayda Rahbaran; Alan Cottenden; Raquel Santamarta Vilele; Stephen John Russel; Mao Ningtao
Original assignee: Lenzing Ag
Priority date: 2010-02-09
Filing date: 2011-01-25
Publication date: 2011-08-18
Also published as: AT509349A1

Abstract

The present invention relates to absorbent pads for reusable incontinence and hygiene products, wherein the nonwovens fabric contains a blend of man-made cellulose fibers with multilobal cross-section and synthetic fibers, to its manufacture and to its use in a reusable incontinence and hygiene product.

Description

Highly absorbent reusable pads, a process for their manufacture and their use in reusable hygiene products

The present invention relates to the improvement of reusable nonwoven fabrics and incorporation as absorbent pads for reusable incontinence and hygiene products, among others for incontinence applications, wherein the nonwovens fabric contains a blend of man-made cellulose fibers with multilobal cross-sections and synthetic fibres. For the purpose of this invention "reusable" means that the article can be used, washed and reused again. It also relates to reusable incontinence and hygiene products, containing such an absorbent pad of 200-650 g/m², preferably 480-600 g/m² that is characterized in that it has a volume at leakage value of at least 11 ml per cm² cross-section, a fluid spread at leakage of at least 4 cm forward and 8 cm backward of the point of fluid entry and a wicked height of >9cm in 30min.

Women commonly suffer from light urinary incontinence and many use absorbent products to contain their leakage. They need effective, leak-free products to carry out their daily lives with confidence. Most women use disposable (single use) pads but another approach is to use so-called "Pantegrals", washable pants with an integral absorbent pad. The absorbent pad in existing Pantegrals is usually made from a blend of regular viscose and polyester fibers, with a topsheet (facing the user's skin) which is usually made from a knitted fabric. Extensive clinical evaluations have shown that although Pantegrals are popular for their good aesthetics (similar appearance to normal underwear) and are substantially cheaper per use than disposable pads, their poor leakage performance limits their use mainly to women with only the lightest incontinence. Although less common, Pantegrals are also available in design for men and for children and they suffer from the same poor leakage performance. The invention described in this patent seeks to address this limitation.

Viscose fibers, even with multilobal cross-section, are well-known. For the purposes of the present invention "multilobal cross-section" shall mean a cross-section with between three and eight regular lobes which is obtained intentionally by using spinning nozzles with suitably designed holes. The terms "regular" and "intentionally" are important in this context because standard viscose fibers have no clear circular cross-section like most synthetic fibers or lyocell; rather their cross-section is irregularly shaped. Man-made cellulose fibers with a multilobal cross-section show high absorbency because of their specific cross-section. Such fibres are commercially available, e.g. with trilobal cross-section from Lenzing AG, Austria, under the trade name Viscostar® with fiber titer (linear density) of 1 ,3 dtex - 6,7 dtex and mean fiber length of 30 - 60 mm. The water holding capacity of such Viscostar® fibers is in the range of 22 - 27 g/g (according to the test method in: European Pharmacopoeia 6.0, 01/2008:0034 Viscose Wadding, absorbent). The high absorbency of such fibers is already exploited in disposable products such as feminine hygiene tampons but they have yet to be used in washable (reusable) products. But these known applications are always only disposable products, which mean that they are basically not suitable for washing or other processes which are necessary for reusable products.

Manufacturing of multilobal fibers and processing of fibers in tampons are described in WO 2004/085720 and EP 0301874.

US 5,356,402 disclose a reusable absorbent pad for hygiene applications which contains a median layer of pure multilobal viscose fibres. But to make this pad washable and therefore reusable, the viscose layer has to be fixed by a special technique - stitch bonding - to a second, inner layer for contact with the skin, consisting of knitted polyester fibres. A third, outer layer consisting of waterproof polyurethane film is added, too.

Surprisingly it was found that the solution to this need is an absorbent pad for reusable incontinence and hygiene products, which is made of a nonwovens fabric, wherein the nonwovens fabric contains a blend of man-made cellulose fibers with multilobal cross-section and synthetic fibers. The focus is on washable Pantegrals but similar fabrics could be used to advantage in reusable absorbent bedpads and chairpads. By using the absorbent pads according to the invention Pantegrals with about 30% improvement in absorbency and leakage performance compared to known Pantegrals can be made. The Pantegrals according to the invention can be washed repeatedly using domestic laundry cycles without showing loss in absorbency and leakage performance and also without loosing their wear comfort.

Preferably the fiber blend in the nonwovens fabric contains at least 15 % man- made cellulose multilobal fibres. Especially preferred are blends consisting of 30-90% by weight of man-made cellulose fibers, and 10-70% by weight of synthetic fibers. The blend may contain man-made cellulose fibers, preferably standard viscose and/or Lyocell as a third component. But as a minimum 15% of the man-made cellulose multilobal fibre is required in the blend to obtain an improvement in fluid handling over blends containing standard viscose fibres. The blended synthetic fibers preferably are polyester fibers. Other suitable synthetic fibers - such as copolyester, polyamide, copolyamide, polylactic acid, polypropylene, or polyethylene fibers or bicomponent fibers containing two or more of these polymers within the cross-section - may be used. The synthetic fiber component may be composed of either a single fiber type with a circular cross-section or a blend of two fibre types with different cross- sectional shapes, for example a blend of circular and trilobal polyester fibers.

Multilobal cellulosic man-made fibers like Viscostar® can be processed into nonwoven fabrics according to the invention and also in blends with other types of man-made cellulose fibers, natural fibers and synthetic fibers. According to possible embodiments of the invention suitable and preferred man-made cellulose fibers are standard viscose fibers - sometimes also called "rayon" - and Lyocell (Tencel®); suitable natural fibers are preferably cotton and wool.

The term„nonwoven fabric" is defined in ISO 9092:1988 as: a manufactured sheet, web or batt of directionally or randomly orientated fibres, bonded by friction, and/or cohesion and/or adhesion, excluding paper and products which are woven, knitted, tufted, stitch-bonded incorporating binding yarns or filaments, or felted by wet-milling, whether or not additionally needled. The fibres may be of natural or man-made origin. Nonwoven fabrics will be manufactured by web forming and bonding a web of fibers or filaments. The present invention is concerned specifically with the forming of webs from staple fibers using the technologies of carding, airlaid, Wetlaid or combinations thereof. Bonding of the webs is achieved by the technologies of hydroentanglement, needlepunching, thermobonding, chemical bonding or combinations thereof.

The absorbent pads according to the invention demonstrate improved volume at leakage performance over existing Pantegrals pads, while showing the same suitability for repeated washing. Preferably the nonwoven fabric is a needlepunched fabric and has a mass per unit area in the range 200 - 650 g/m², preferably 480 - 600 g/m². The mass density of the fabric is preferably in the range 0,09 - 0,10 g/cm³, with a mean thickness of 5 mm to 7 mm. More preferably this needlepunched fabric was drylaid.

The fabric may be substantially uniform in density throughout or made with discrete needled "strips" of high density or reduced thickness arranged periodically or quasi-periodically across the width of the fabric and aligned in the longitudinal direction. The periodically arranged regions of high density or small thickness exhibit higher capillary pressure than in, the adjacent regions and contribute to the spreading of fluid preferentially in the longitudinal direction of the fabric.

The strips give rise to areas of different localised density across the width of the fabric and an undulating surface on at least one side.

The needlepunched fabric may be made from a blend of Viscostar fibre (in the range 30-90% by weight) and polyester fibre (in the range 10-70% by weight) but of course can be made of any of the other blends described above. The polyester fiber may be substantially circular in cross-section or more preferably, is trilobal in cross-section. Particularly recommended is the utilization of polyester with a durable hydrophilic finish whose hydrophilicity is maintained after multiple washing treatments. The simultaneous use of circular and trilobal polyester fibers in an intimate blend is possible, too. One particularly recommended fabric composition consists of an intimate blend of three fibre components as follows: 25% trilobal PET fibre (7dtex and 60mm fibre length), 25% standard PET fibre (Udtex/ 40mm) with a circular cross- section and 50% Viscostar® fibre (3.3 dtex/ 60mm).

Typically the needlepunched fabrics of this invention are made from dry-laid webs (or batts) produced by carding or by carding and lapping prior to bonding using needlepunching. Lapping may be accomplished by parallel- lapping or cross-lapping. Preferably, fibres are preferentially oriented in either the machine or cross direction to give anisotropic liquid transport behaviour in the fabric. Once installed in the Pantegral, preferably, the fabric should be aligned such that the direction of preferential fibre orientation in the fabric is parallel to the two outer (long) sides of the absorbent pad. The needlepunched fabric may be needled by successive beds of needles or multiple needlelooms to gradually increase the degree of bonding and densification in a progressive manner. At the final needlepunching stage, it is particularly advantageous to position the needles in the needleboard such that needling in the fabric is localised. This produces "strips" of dense or thin regions in the fabric that run longitudinally in the machine direction. These may be periodic or quasi-periodically arranged across the width of the fabric. This leads to an undulating surface with regions of low and high density arranged periodically across the width of the fabric. Once installed in the Pantegral (Fig. 3), the top surface of the fabric is normally arranged uppermost below the topsheet. The function of the topsheet fabric is to provide a skin-contact layer that permits rapid penetration of the fluid directly in to the absorbent pad attached below. Preferably, the top sheet should be in direct contact with the absorbent pad of the invention and preferably is comprised of a weft or warp knitted fabric composed of cotton, cotton-PET blend or any other wettable fibrous polymer composition. Furthermore the mode of attaching the topsheet to the absorbent pad should be such that there is minimal compression of the latter. This is to maintain the fluid handling properties of the absorbent pad after repeated laundering, which is influenced by its thickness and mass density. Preferably, the mode of attaching the topsheet to the absorbent pad is by stitching (or sewing) using a low yarn stitching tension. Preferably, compression of the absorbent pad as a result of stitching should be >50% of the original pad thickness. A further object of the invention is a durable, reusable incontinence and hygiene product, containing an absorbent pad, characterized therein that the absorbent pad is made of a nonwoven fabric which contains a blend of man- made cellulose fibers with multilobal cross-section and synthetic fibers. Test methods:

The fluid handling properties of the absorbent pads were measured using a range of test methods, some of them developed at University College London, England. Fabric mass per unit area

The nonwoven fabric mass per unit area was measured using a method based on ISO standards (BS EN 29073-1 :1992, ISO 9073-1 : 1989) and E DANA- IN DA standards (WSP130.1 , IST130.1 and ERT40.3-90). The mean value of the mass per unit area was calculated in grams per square metre (gsm or g/m²) based on two measurements due to the small area of the fabric sample.

Test conditions and fluid

All measurement were made in a controlled environment room (23°C and 50% RH) and all samples were conditioned for at least 24h in that controlled environment room prior to testing. Distilled water was used as test fluid and was also conditioned for at least 24h in the controlled environment room before use. For those experiments where the wet portion of a test piece needed to be made visible, a solution of 0.2 g/l of Methyl Blue in distilled water was used. It was established that at this concentration Methyl Blue has a negligible effect on the surface tension of distilled water.

Test pieces

Test pieces measuring 15x2cm were used to measure the wicking properties while test pieces for measuring absorption capacity . at leakage and fluid spreading were and 7cm wide and of various lengths, but always long enough for fluid spread not to reach the ends. All test pieces were tested without a topsheet, unless stated otherwise.

Vertical wicking

Wicking is important in redistribution of fluid, in other words moving fluid away from the lowest point of the pad (to which gravity tends to draw it) towards the ends (forwards and backwards). The experimental setup used for measuring the ability of a fabric to wick fluid against gravity is shown in Fig. 1.

Test pieces (2x15cm) were marked with horizontal lines 1 cm apart parallel to the short sides to facilitate the reading of the wicking height. The test piece was suspended vertically over a large cross section reservoir (to minimize changes in the reservoir fluid level during experiments) which was placed on the balance and filled with test fluid (a solution of 0.2 g/l of Methyl Blue in distilled water). The test piece was then immersed to a depth of 0.5 cm for 30 min. A camcorder was used to record how the height and shape of the wetted portion of the test piece developed with time. The balance reading was logged every second to calculate the wicked mass against time.

Absorption volume at leakage and fluid spreading - forced flow

This test method was developed to evaluate the ability of a fabric to promote uphill, lengthwise fluid spread rather than lateral and also to study the whole fluid distribution process up to the point of first leakage.

A curved rig (see Fig 2) was used whose geometry was designed to simulate the sagittal cross section of the diaper area of a woman. The lower portion was approximated closely by a half cylinder of radius 110 mm. The samples were placed on a transparent plastic sheet which was equipped with gndlines (1 cm apart along the length of the curve and 2 cm apart across the width) to help with measurement of fluid spread in subsequent image analysis. A peristaltic pump was used to apply dyed water (same solution as before) at a rate of 2 ml/s on to the transverse centre of the test piece at a point 1.5 cm anterior to the lowest point (test 1) or 5.5 cm anterior to the lowest point (test 2). The outflow tube was placed perpendicular to the test piece with its outlet about 0.3 cm above it. A camcorder (placed above the sample) and a timer were used to record how the shape of the wet portion changed with time at the top surface and simultaneously (using a mirror) at the bottom surface. The experiment was stopped as soon as fluid began to leak from the test piece. Finally, the volume of fluid held by the test piece at the point of leakage was calculated and normalised to the cross sectional area; and the maximum spread of fluid forward and backward of the point of fluid entry noted.

The invention will now be illustrated by examples. These examples are not limiting the scope of the invention in any way.

Examples:

Needlepunched fabrics were made with different fiber blends. Fluid handling properties of the fabrics were tested according to the mentioned test methods. Table 1 illustrates the results of the absorbency of the needlepunched felts. Wicked mass and wicked height were determined from test pieces of width 2 cm and the results for the wicked mass given in g(fluid) / cm² cross- section(test piece) and the results for the wicked height given in cm. Volume at leakage was determined from test pieces of width 7 cm and the results given in ml(fluid) / cm² cross-section (test piece). The absorbency results clearly show that the addition of 50% triloba! viscose fibers (Viscostar®) into the needlepunched fabrics according to example increases the wicked mass, wicked height and absorbency at leakage compared to those containing regular 1 ,7 and 3,3 dtex viscose and 2,4 dtex Tencel® according to examples 1 to 3. Table 1:

Legend for the drawings:

1. Camera

2. Fluid introduced

3. Perspex sheet

4. Core of pad

5. Camera

6. Mirror

7. Female

8. Male

9. Waterproof (fabric covered) gusset

10. Integral washable pad

Claims

Claims:

1. An absorbent pad for reusable incontinence and hygiene products, wherein the nonwoven fabric contains a blend of man-made cellulose fibers having a multilobal cross-section and synthetic fibers

2. Pad according to claim 1 , wherein the fiber blend contains 30-90% by weight of man-made cellulose fibers and 10-70% by weight of synthetic fibers.

3. Pad according to claim 1 , wherein the synthetic fibers are selected from polyester, copolyester, polyamide, copolyamide, polylactic acid, polypropylene, or polyethylene fibers or bicomponent fibers containing two or more of these polymers within the cross-section.

4. Pad according to claim 1 , wherein the synthetic fibers are a blend of two fibre types with different cross-section shapes, preferably a blend of circular and trilobal polyester fibers.

5. Pad according to claim 1 , wherein the blend additionally contains a second type of man-made cellulose fibers, preferably viscose and/or Lyocell.

6. Pad according to claim 1 , wherein the nonwovens fabric is a needlepunched fabric with a weight per unit area of between 200 and 650 g/m².

7. Pad according to claim 6, wherein the nonwovens fabric in the absorbent pad is aligned such that the direction of preferential fibre orientation in the fabric is parallel to the two outer (long) sides of the absorbent pad.

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8. Pad according to claim 6, wherein the needlepunched fabric has a undulating surface showing strips obtained by the needle punching process.

9. Pad according to claim 8, wherein the undulating surface is arranged in the absorbent pad uppermost below the topsheet.

10. Pad according to claim 8, wherein the strips in the needlepunched fabric are aligned in the same direction as the principal direction of fibre orientation

1 1 . Pad according to claims 1 and 2 with a weight per unit area of between 200 and 650 g/m², preferably between 200 and 650 g/m², that is characterized in that it has a volume at leakage value of at least 1 1 ml/cm² Cross-section a fluid spread at leakage of at least 4 cm forward and 8 cm backward of the point of fluid entry and a wicked height of >9 cm in 30min.

12. Use of the pad according to claim 1 in a reusable incontinence and hygiene product.

13. Use according to claim 12, wherein the reusable incontinence and hygiene product is a Pantegral or an absorbent bed pad.

14. Method for manufacturing an absorbent pad according to claim 1 , characterized in that a nonwovens fabric is aligned in the pad such that the direction of preferential fiber orientation in the fabric is parallel to the two outer (long) sides of the absorbent pad, and that the nonwoven fabric contains a blend of man-made cellulose fibers having a multilobal cross-section and synthetic fibers.

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