WO1996033680A1

WO1996033680A1 - Absorbent article

Info

Publication number: WO1996033680A1
Application number: PCT/EP1996/001718
Authority: WO
Inventors: Ian Cheyne; Ervin Dan; Curtis Cordell Buxton
Original assignee: Camelot Superabsorbents Limited; Camelot Superabsorbents B.V.
Priority date: 1995-04-27
Filing date: 1996-04-25
Publication date: 1996-10-31
Also published as: GB9508541D0; AU5761196A

Abstract

A multiple layer water-absorbent core suitable for use in an absorbent article comprises a water-absorbent layer and a non-water-absorbent spacer layer, preferably comprising a layer of loose non-water-absorbent fibers, located above the water-absorbent layer. Also provided is an absorbent article wherein the core is enclosed between a liquid pervious cover sheet and a liquid impervious back sheet.

Description

Absorbent Article

The present invention relates to absorbent articles such as sanitary napkins and pads, incontinence garments and disposable diapers. In addition, the present invention relates to a water-absorbing layer for an absorbent article.

As used herein, the term "water" when used alone or in the phrases "water- absorbing", "water-absorbent" and "water-swellable" is understood to mean not only water but also aqueous media such as, in particular, electrolyte solutions such as body fluids.

Sanitary napkins, pads, incontinence garments and disposable diapers have been known for many years and much effort has been made to improve the functional efficiency of such articles to make them more absorbent, more comfortable to wear and less obtrusive to the wearer.

In general, such products have a core which includes a water-absorbent layer. This water-absorbent layer may be formed from any suitable water-absorbent material including wood pulp, rayon, tissue or any of the water-absorbing polymer compositions known as superabsorbent polymers.

A number of absorbent compositions have been developed which exhibit the capacity to be water-absorbing. For example, U.S. Patent numbers 3,954,721 and 3,983,095 disclose preparations for derivatives of copolymers of maleic anhydride with at least one vinyl monomer in fibrous form. The fibrous copolymers are rendered hydrophillic and water-swellable by reaction with ammonia or an alkali metal hydroxide. U.S.

Patent No. 3,810,468 discloses lightly cross-linked olefin-maleic anhydride copolymers prepared as substantially linear copolymers and then reacted with a diol or a diamine to introduce cross-linking. The resultant lightly cross-linked copolymers are treated with ammonia or an aqueous or alcohol solution of an alkali metal hydroxide. U.S. Patent No. 3,980,663 describes water-swellable absorbent articles made from carboxylic polyelectrolytes via cross-linking with glycerine diglycidyl ether. These patents are incorporated herein by reference. European Published Application No. 0 268 498 (incorporated herein by reference) describes a water-absorbent composition formed by causing a substantially linear polymer of water-soluble ethylenically unsaturated monomer blends comprising carboxylic and hydroxylic monomers to cross-link internally.

Further examples of water-absorbent compositions are those produced from a copolymer of an α,β uosatuxated monomer having, at least one. f*^nf1an> " + ^pi »■ »/■ from a carboxylic acid group and derivatives thereof and a copolymerisable monomer. A proportion of the pendant units are present in the final copolymer as the free acid and a proportion as the salt of the acid. These copolymers are capable of being cross- linked, either internally or with a variety of cross-linking agents, to form the water- swellable composition. Examples of water-swellable compositions of this type can be found in U.S. Patent Nos 4,616,063, 4,705,773, 4,731,067, 4,743,244, 4,788,237, 4,813,945, 4,880,868 and 4,892533 and European Patent Nos 0 272 074 and 0 264 208 and European Published Application No. 0 436514 which are incorporated herein by reference.

Derivatives of carboxylic acid groups include carboxylic acid salt groups, carboxylic acid amide groups, carboxylic acid imide groups, carboxylic acid anhydride groups and carboxylic acid ester groups.

Other examples of water-absorbent compositions can be found in US 4798861, WO93/17066, WO93/255735, WO 93/24684, WO93/12275, European Published

Application Nos 0 401 044, 0 269 393, 0 326 382, 0227 305, 0 101 253, 0213 799, 0 232 121, 0 342 919, 0 233 014, 0 268 498 and 0 397 410, British Patent Application Nos 2 082 614, 2 022 505, 2 270 030, 2 269 602 and 2 126 591, U.S. Patent Nos 4,418,163, 4,418,163, 3,989,586, 4,332,917, 4,338,417, 4,420,588 and 4,155,957 and French Patent Application No. 2 525 121 which are all incorporated herein by reference.

Whatever material is used for the absorbent layer, the core is generally backed by a fluid-impervious backing sheet to protect clothing and the surrounding area from

RAD ORIGINAL soiling and to prevent leakage of the body fluid which would cause embarrassment to the user.

The article generally has a water-permeable non-woven type cover sheet which defines the surface of the article which will, in use, be in contact with the user. The cover sheet is intended to insulate the wearer from contact with water that has been absorbed into the water-absorbent layer of the core, thus the cover sheet should allow water to pass through it into the core but remain dry and soft to the touch. One example of a cover sheet is described in US 5257982 which is incorporated herein by reference.

As there is often a discharge of a substantial volume of water in a short time, the core may additionally include a distribution layer which is generally located above the water-absorbent layer. This distribution layer serves to wick the water away from the point of initial contact with the article and transport it to other parts of the water- absorbent layer. The use of a distribution layer of this type is advantageous in addressing the problem of pooling if a substantial volume of water is discharged in a short time and thereby gives the user a feeling of dryness. Examples of distribution layers of this type include those described in EP 0 565 606, GB 2 266 465 and GB 2 278 371 which are incorporated herein by reference.

Whilst the use of distribution layers of this type go some way to reducing the effects of pooling, they do not satisfactorily overcome the problems of rewet once the water has been absorbed into the water-absorbent layer. Rewet is a measure of how dry the articles feel to the touch after water-absorption. This is generally measured under load of approximately 3-5kPa. Rewet is of particular importance in the applications to which the absorbent articles of the present invention are directed as if the article feels damp the user will feel damp and uncomfortable. Further, where the article is, for example, a diaper, the problem of rewet may result in irritation of the babies skin.

The problem of rewet is particularly acute where the water-absorbent layer is formed from or includes the superabsorbent polymers described above, in particular from superabsorbent fibers. Although the superabsorbent polymers described above can absorb a large volume of water and absorption can take place in a short time period, the water, in some circumstances, is not held wholly in the fibers and the polymers may feel damp to the touch. Without wishing to be bound by any theory, we believe that water may be desorbed from the polymers.

We have now discovered that the aforementioned problems can be overcome if the core additionally includes a non-water-absorbent spacer layer which prevents the absorbent layer from coming into contact with the cover sheet of the end product.

Thus, according to one aspect of the present invention there is described a multiple layer water-absorbent core suitable for use in an absorbent article comprising a water- absorbent layer and a non-water-absorbent spacer layer located above the water- absorbent layer. The non-water-absorbent spacer layer is preferably thick, resilient or both thick and resilient.

Suitable materials for the production of the spacer layer include woven and non- woven materials and apertured films. Any suitable apertured film may be used. One example of an apertured film is described in WO 94/28846 which is incorporated herein by reference. Where the spacer layer includes an apertured polymeric film, the film may be corrugated.

We have also discovered that the aforementioned problems are overcome where the spacer layer comprises loose non-water-absorbent fibers between the water-absorbing layer of the core and the cover sheet.

Thus, according to a second aspect of the present invention there is described a multiple layer water-absorbent core suitable for use in an absorbent article comprising a water-absorbent layer and a layer of loose non-water-absorbent fibers located above the water-absorbent layer.

The loose fibers of the present invention are distinct from the non-woven fabrics that have been used in known distribution layers in that there is no cohesion between the fibers. The fibers may be continuous or staple.

By "non-water-absorbent" we mean that the fibers do not absorb water to an appreciable extent. Suitable materials from which these fibers may be formed include natural or synthetic fibers such as cellulose, viscose, polyester, non-water-absorbent polymers of ethylene, non-water-absorbent polymers of propylene, polyamide and ethylene-propylene copolymer fibers, and mixtures thereof and the like, with polyester, polyethylene and polypropylene fibers being particularly preferred.

The multiple layer water-absorbent core suitable for use in an absorbent article may additionally include a distribution layer. Where a distribution layer is included, it may be located above or below the layer of loose fibers. However, it is preferred that when a distribution layer is present, it is located between the loose fibers and the water-absorbent layer.

The loose fibers may be of high denier, high resilience or of both high denier and high resilience. By "high denier" we mean that the fibers have a thickness of greater than about 5 denier and preferably a thickness of greater than 10 denier. By "high resilience" we mean that when a pressure of up to 5kPa is applied, the fibers are not crushed.

The loose fibers are preferably crimped. Crimping serves to improve the ability of the loose fibers to prevent rewet.

The water-absorbent layer of the core preferably includes a superabsorbent polymeric composition which may be in the form of fibers.

According to a second aspect of the present invention there is provided an absorbent article comprising a liquid pervious cover sheet, a liquid impervious backsheet and an multiple layer water-absorbent core described in the above first aspect wherein the cover sheet is joined to the backsheet to enclose the water-absorbent core. An absorbent article in accordance with a preferred embodiment of the present invention will now be described with reference to the accompanying drawing which is a schematic representation of a cross-section through an absorbent article in accordance with the present invention.

The use of the multiple layer water-absorbent core is particularly suitable for use where the core includes water-absorbent fibers formed from a syrup comprising an α,B unsaturated monomer having at least one pendant unit selected from a carboxylic acid group and derivatives thereof and a copolymerisable monomer. A proportion of the pendant units are preferably present in the final copolymer as the free acid and a proportion as the salt of the acid. These copolymers are capable of being cross- linked, either internally or with a variety of cross-linking agents, to form the water- absorbent composition

In Figure 1, the absorbent article 1 comprises a liquid impervious backsheet 2, a liquid pervious cover sheet 3 and a multiple layer water-absorbent core 4. The core comprises a water-absorbent layer 4a, a distribution layer 4b and a layer of loose non-water-absorbent fibers 4c. This absorbent article exhibits improved rewet over conventional water absorbent articles. Although Figure 1 describes the distribution layer 4b as being located between the water-absorbent layer 4a and the layer of loose non-water-absorbent fibers 4c, it will be understood that the distribution layer 4b may be located between the layer of loose non-water-absorbent fibers 4c and the cover sheet 3.

The application will now be described with reference to the following example which is not intended to limit the scope of the application.

Example 1 A 14" x 4" core comprised consisting of polypropylene, having a core weight of 14g and including 25% by weight of superabsorbent fibers of the type commercially available from Camelot Superabsorbents Limited. 3g of loose non-water-absorbent fibers were placed on the water-absorbing layer of the core and a cover sheet was laid over the non- water-absorbing fibers. 3 x 43ml of saline were applied to the cover sheet and the rewet was measured.

One method of measuring rewet is by adding 15mls of 0.9% saline solution to the absorbent article at a rate of 2ml/sec. After 15 minutes, 10 preweighed Whatman ™ #3 filter papers (dry weight Wl) are placed on top of the composite pad and a 3kPa load is applied for 2 minutes. The filter papers are then removed and reweighed (wet weight W2). Rewet can then be calculated according to the following formula:

Rewet = Wl - W2.

The rewet was measured in accordance with this method and was found to be 0.2.

Whilst the present invention has been described with reference to sanitary napkins and pads, incontinence garments and disposable diapers it will be understood that the invention is equally applicable to other products which require high water-absorption capability such as pant liners, adult incontinence pads, bandages, patient underpads, mortuary pads, meat trays, wipes, medical tray pads, fenestration drapes, and the like.

Claims

1. A multiple layer water-absorbent core suitable for use in an absorbent article comprising a water-absorbent layer and a non-water-absorbent spacer layer located above the water-absorbent layer.

2. A multiple layer water-absorbent core according to Claim 1, wherein the spacer layer is thick, has high resilience or is both thick and has high resilience.

3. A multiple layer water-absorbent core according to Claim 1 wherein the spacer layer comprises a layer of loose non-water-absorbent fibers.

4. A multiple layer water-absorbent core according any one of Claims 1 to 3, additionally including a distribution layer.

5. A multiple layer water-absorbent core according to Claim 4, wherein the distribution layer is located between the spacer layer and the water-absorbent layer.

6. A multiple layer water-absorbent core according to any one of Claims 3 to 5, wherein the loose fibers are fibers of cellulose, viscose, polyester, non-water- absorbent polymers of ethylene, non-water-absorbent polymers of propylene, polyamide, an ethylene-propylene copolymer or mixtures thereof.

7. A multiple layer water-absorbent core according to any one of Claims 3 to 6, wherein the loose fibers are of high denier, high resilience or both high denier and high resilience.

8. A multiple layer water-absorbent core according to Claim 7, wherein the fibers have a thickness of greater than 5 denier.

9. A multiple layer water-absorbent core according to Claim 7 or 8, wherein the fibers are not crushed when subjected to a pressure of up to 5 kPa.

10. A multiple layer water-absorbent core according to any one of Claims 3 to 9, wherein the fibers are crimped.

11. A multiple layer water-absorbent core according to any one of Claims 1 to 10, wherein the water-absorbent layer of the core includes a superabsorbent polymeric composition.

12. A multiple layer water-absorbent core according to Claim 11, wherein the superabsorbent polymeric composition is in the form of fibers.

13. An absorbent article comprising a liquid pervious cover sheet, a liquid impervious backsheet and an multiple layer water-absorbent core as claimed in any one of Claims 1 to 12, wherein the cover sheet is joined to the backsheet to enclose the water-absorbent core.