WO1997015258A2

WO1997015258A2 - Absorbent articles

Info

Publication number: WO1997015258A2
Application number: PCT/EP1996/004558
Authority: WO
Inventors: Ervin Dan; Ian Cheyne; Dirk Bouman
Original assignee: Camelot Superabsorbents Limited; Camelot Superabsorbents B.V.
Priority date: 1995-10-24
Filing date: 1996-10-21
Publication date: 1997-05-01
Also published as: CA2242638A1; WO1997015258A3; EP0862401A2; AU7296496A

Abstract

An absorbent article is described in which a non-water-absorbent substrate is coated on at least one side with a second layer comprising a water-absorbent composition. The water-absorbent layer may be applied as a preformed polymeric material or as a syrup which may be cured in situ to form the water-absorbent material.

Description

ABSORBENT ARTICLES

The present invention relates to absorbent articles.

Included in the term absorbent articles are wipes, domestic wipes, industrial wipes, towels, tissues and toilet papers which will hereinafter collectively be referred to as wipes.

It has been known for many years to use pieces of textile material to clean up spillages, to wipe surfaces and to wipe the human body.

In recent years the use of textile materials has declined in favour of disposable wipes made from non- woven materials. These disposable wipes may be formed from a variety of non-woven materials, the most common being paper. As the range of uses to which such wipes are required to be put has been extended to include domestic cleaning, personal, medical and industrial use, much time has been devoted to producing wipes that have improved strength and enhanced absorbency. Wipes have also been produced which are impregnated with various agents such as detergents.

These wipes may be used to absorb a variety of liquids, including both aqueous and non-aqueous media. For ease of reference, the term "water" will be used hereinafter to refer not only to water but also to aqueous media such as, in particular electrolyte solutions such as body fluids, and non-aqueous fluids. The term "water" also includes fluids that are commonly spilled in industrial, medical or domestic environments.

Also included in the term absorbent articles are disposable diapers, sanitary napkins, tampons, pant liners, training pads, adult incontinence pads, coverstock for feminine hygiene products, surgical and dental sponges, bandages, patient underpads (for example pads of the type described in US3,814, 101, US4, 342,314 and EPO052403 which are incorporated herein by reference), medical tray pads, fenestration drapes, mortuary pads, casket liners, forensic examination pads, other medical related articles, food tray pads, soaker pads for food use, food preservation articles, seed germination pads, capillary mats; household pet litter, packaging, baby bibs, desiccant strips for anti-rust use, bath mats, sorbents, breast pads, underarm pads, wound covers, operating gowns, spill control materials, waste management materials; protective articles, filters, roofing materials, automotive trim, furniture, bedding, gasket sealants, pond liners, clothing, cable wrap, cement and soil modifiers. It will be understood that some of the articles referred to are not per se absorbent but may be rendered absorbent by means of the presence in their structure of absorbent materials.

In general, such absorbent articles are produced from fibrous materials which, whilst absorbing some water, do not absorb water to an appreciable extent. For ease of reference, the fibers from which these articles are formed will be referred to as non- water-absorbent.

In order to increase the water-absorbency of the absorbent articles, it has been proposed to include into the non- water-absorbent materials any of the water-absorbent polymeric compositions known as superabsorbent polymers. Where the non- water- absorbent materials are fibers, the water-absorbent polymer compositions are generally incorporated into a non-woven web of the non- water-absorbent fibers. These polymers may be in any suitable form including powders, particles, granules, or fibers; the fibers may be curled and/or crimped. Details of such curled/crimped fibers may be found in US4,822,453, 4,888,453, 5,462,793 and 4,898,462 which are incorporated herein by reference. In one alternative material the water-absorbent polymer may be coated on the whole or a part of the surface of other materials such as non- water-absorbent fibers. Details of one type of fiber of this type may be found in WO96/ 15307 which is incorporated herein by reference.

A number of water-absorbent compositions have been developed which exhibit the capacity to be water-absorbing. U.S. 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. 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. 3,980,663 describes water-swellable absorbent articles made from carboxylic polyelectrolytes via cross-linking with glycerine diglycidyl ether. These patents are incoφorated herein by reference.

European Published Application No. 0 268 498 (incoφorated 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 unsamrated 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 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. 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 EP 0 272 074, 0 264 208 and No. 0 436 514 which are incoφorated 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 4,798,861 , WO 93/17066, WO 93/25735, WO 93/24684, WO 93/12275 EP 0 401 044, 0 269 393, 0 326 382, 0 227 305, 0 101 253, 0 213 799, 0 232 121, 0 342 919, 0 233 014, 0 268 498 and 0 397 410, GB 2 082 614, 2 022 505, 2 270 030, 2 269 602 and 2 126 591 , U.S. 4,418, 163, 3,989,586, 4,332,917, 4,338,417, 4,420,588 and 4, 155,957 and FR 2 525 121 which are incoφorated herein by reference.

The non-water-absorbent fibers used to form the above-mentioned absorbent articles are generally formed as a non-woven web by conventional means such as by air- laying. The water-absorbent material is generally included during the formation of the non- woven web. The fibers are then bonded, for example by the action of an adhesive, including water, and/or heat.

Whilst the known absorbent articles can satisfactorily absorb small volumes of water, this absorbtion causes the water-absorbent composition to swell. As the composition swells it fills the void areas within the fibrous web. Once these void areas have been filled, the ability of the composition to expand is hindered and thus further water cannot be readily absorbed.

Further, once an absorbent article has been used to absorb a particular volume of water it may feel damp to the touch and water may even leak from the article.

Further, the effectiveness of the article to absorb water may be reduced by the phenomenon known as gel blocking.

We have now discovered that the aforementioned disadvantages and drawbacks can be overcome if an absorbent article is formed from a non-water-absorbent layer having a coating on at least one side comprising a water-absorbent composition.

Thus according to one aspect of the present invention there is provided an absorbent article comprising a first layer of a non-water-absorbent substrate having applied to at least one side thereof a second layer comprising a water-absorbent composition.

The absorbent article may comprise a first layer of a non-water-absorbent substrate having applied to both sides thereof a second layer comprising a water-absorbent composition. The second layer may be provided as a preformed water-absorbent composition which is preferably in the form of fibers. Thus, in one example, a non-woven web of, or including, water-absorbent material may be formed and then laminated to the first layer. The second layer may be attached to the first layer by means of an adhesive. In one alternative arrangement, the second layer may be attached to the first layer using water as adhesive. In a second alternative arrangement the first and second layers may be attached to the first layer by fiber entanglement caused by, for example, embossing techniques.

The water-absorbent composition may be applied to the first layer as discrete fibers or particles.

In one alternative embodiment, the second layer may be formed from a composition which on curing becomes water-absorbent. That is to say, a composition which on curing becomes water-absorbent may be coated onto the first layer by any suitable means, including spraying and dipping. The article is then treated to cause the composition to cure such that it becomes water-absorbent.

As the water-absorbent layer is provided on the surface of the non-water-absorbent layer, the water-absorbent composition is free to swell in the direction away from the non-water-absorbent substrate. Further, where the absorbent article is a flexible article such as a wipe, medical tray pads, filters, pant liners and the like and where the water-absorbent layer is located on only one side of the non-water-absorbent layer, the absorbent article having been used can be folded such that the water absorbent layer is innermost prior to disposal. This is particularly important where the absorbent article is a wipe, drape or similar article and which may have been used to absorb, for example, blood.

The non-water-absorbent substrate may be formed from any suitable material. It is preferably a non-woven web of non-water- absorbent fibers. However, a woven fabric of non- water-absorbent fibers may be used. Suitable non- water- absorbent fibers include namral materials such as wood pulp or cellulose or synthetic materials such as synthetic cellulose, viscose, polyester, non-water-absorbent polymers of ethylene, non-water-absorbent polymers of propylene, polyamide and ethylene-propylene copolymer fibers, and mixmres thereof with polyester, polyethylene and polypropylene fibers being particularly preferred. Particularly preferred fibers are those selected from the group consisting of rayon fibers, cellulose ester fibers, protein fibers, polyamide fibers, polyester fibers, polyvinyl fibers, polyolefin fibers, polyurethane fibers, aramid fibers, glass fibers and mixmres thereof. In one alternative, the non-water-absorbent fibers may be, fibers having hollow cores such as the polyester, typically polyethylene terephthalate fibers commercially available from E.I. DuPont de Nemours under the trade mark HOLLO WFILL.

Where the non-water-absorbent substrate is formed from a non-woven web of non- water-absorbent fibers it may be formed by any suitable means, such as air laying, wet laying, melt-blowing, spin-binding, carding and needling techniques. The fibers of the non-water- absorbent layer may be bonded using any conventional binder. Binding may take place before or after the or each water-absorbent layer is applied to the non- water- absorbent layer.

Where the non-water-absorbent layer is a non-woven web, a binder may be omitted. The presence of the water-absorbent layer will then serve to bind the web of the non- water- absorbent layer.

In a particularly preferred embodiment of the present invention, the water-absorbent layer is discontinuous. In a particularly preferred embodiment, the water-absorbent layer is formed of spaced nodules of a preformed water-absorbent composition or nodules of a composition which on curing becomes water-absorbent on the surface of the non- water-absorbent layer. Arranging the water-absorbent material as spaced nodules provides increased space for the water-absorbent composition to swell. In an even more preferred embodiment, the nodules are so spaced that on absoφtion of water, each swollen nodule does not impinge on any other nodule. Any suitable size and spacing of the nodules may be selected. By this means the absorbency of the article may be optimised. However in some articles it is preferred that the nodules are spaced such that an absorbtion they are caused to impinge on each other. Thus, where the absorbent article is, for example, cable wrap, the nodules may be spaced such that on swelling each nodule impinges on those surrounding it. This has particular advantages as the nodule will absorb an amount of water and will therefore swell. Once the nodules have swollen such that they impinge on each other, further water is not absorbed and effective protection for the cable is achieved. Without wishing to be bound by any particular theory, it is believed that once the nodules impinge the phenomenon of gel blocking prevents the absoφtion of any additional water.

Similarly where the absorbent article is a pond liner, the external surface of the liner, that is the surface that is removed from the water of the pond, may be coated with nodules, the nodules may be spaced such that on swelling each nodule impinges on those surrounding it. This has particular advantages as in the event that the liner is damaged and starts to leak, the nodules will absorb an amount of water and will therefore swell. Once the nodules have swollen such that they impinge on each other, further water is not absorbed and further leakage may be prevented.

The use of the gel blocking technique may be employed where the article is a gasket, such as a gasket for use as a sealant in, for example cylinder blocks and heads. At least one surface of the gasket may be coated with nodules, the nodules may be spaced such that on swelling each nodule impinges on those surrounding it. This has particular advantages as in the event that the leakage occurs, the nodules will absorb an amount of water and will therefore swell. Once the nodules have swollen such that they impinge on each other, further water is not absorbed and further leakage may be prevented.

The water-absorbent layer, whether continuous or discontinuous may be formed by any suitable means including dipping and spray coating. Where the water-absorbent layer consists of spaced nodules they may be coated onto the non-water-absorbent layer by any suitable means including printing, spraying and pressing. In a particularly preferred embodiment the non-water-absorbent layer is wet laid and, prior to drying, the pre-formed water- absorbent composition, either as a non- woven or woven layer or discrete fibers or particles, is then simply laid onto the wet layer. The water present in the non-water absorbent layer may be sufficient to bond the water-absorbent fibers and no additional adhesive between the layers may be required.

Where the non-water-absorbent layer is dry laid or has been wet laid and subsequently dried, the layer may be sprayed with water to make it damp prior to laying the water- absorbent composition onto the wet layer.

The water-absorbent article of the present invention may additionally include a further non- water-absorbent layer above the water-absorbent layer. This arrangement is particularly advantageous where the non-water-absorbent layer is discontinuous and is preferably in the form of spaced nodules.

Where the water-absorbent layer is applied to the non-water-absorbent substrate in the form of a syrup that requires curing to become water-absorbent it is not necessary to use adhesive to bond the layers together. Thus, the additional non-water-absorbent layer may be applied to the water-absorbent layer prior to curing.

Where the water-absorbent layer is applied to the non- water-absorbent substrate in the form of pre-formed water-absorbent compositions, such as water-absorbent fibers, may be applied to wet laid substrate. The additional layer may be applied in any suitable form, including in a dry form. The combined action of the water in the wet- laid substrate and the water-absorbent composition is sufficient to bind the strucmre together. Where the substrate and the additional layer are dry it is necessary to add water to at least one of the layers. In a preferred embodiment it is only necessary to add water to one layer.

In a further embodiment of the present invention the water-absorbent layer may be formed by a tow of water-absorbent fibers. These may then be laid as strands over the non- water-absorbent substrate. The spacing of the strands will be chosen depending on whether the strands are intended to improve absorbency or to form a block. Thus where it is intended that the absorbency of the article is to be increased, the strands are spaced such that as each strand swells as it absorbs it does not impinge on the adjacent strands and where it is intended that the a block is to be formed, the strands are spaced such that as each strand swells as it absorbs it impinges on the adjacent strands. Without wishing to be bound by any particular theory, it is believed that once the strands impinge the phenomenon of gel blocking prevents the absoφtion of any additional water.

In a further embodiment of the present invention there is provided water-absorbent fluff for use in absorbent cores of, for example, diapers and sanitary towels. Conventionally, the fluff used in diapers and sanitary towels is produced from cellulosic material such as wood. The cellulosic material is normally formed as a sheet and then rolled prior to being treated in a hammer mill to form the fluff. In order to improve the absorbency of the fluff, the conventional cellulosic material is coated on at least one side with water-absorbent composition. If the water-absorbent composition is a material which becomes water-absorbent on curing, the coated material may then be treated to cause the material to cure. The cellulosic material is then rolled and treated in the hammer-mill in the conventional manner. The amount of water-absorbent material may be controlled by applying the water-absorbent composition as nodules; the spacing of the nodules may be adjusted to control the amount of water-absorbent composition in the resultant fluff. The amount of water- absorbent material in the fluff is preferably 15 to 40%, more preferably 20 to 30%, most preferably 25 % of the finished fluff.

The invention of the first embodiment will now be described with reference to the following examples.

The Free Swell Index test procedure used is described in U.S. Pat No. 4454055, the teachings of which are incoφorated herein by reference. To determine the Free Swell Index at atmospheric (room) pressure, the samples to be tested were placed in an empty W-shaped tea bag. The tea bag containing the samples was immersed in brine (0.9 wt% NaCl) for 10 minutes, removed and allowed to sit on a paper towel for 30 seconds to remove surface brine. The Free Swell Index of the sample that is the units of liquid absorbed per each unit of sample, is calculated using the following formula:

Swell Index = Weight of Wet Sample -1 Weight of Dry Sample

To determine Free Swell Index under pressure (0.5 psi retention), the following modified procedure was used.

After the tea bag containing the fiber sample was immersed in brine and surface brine had been removed, it was immediately placed in a 16 cm ID Buchner funnel fitted with a 2000 ml sidearm vacuum filter flask and connected to a manometer. A piece of dental dam rubber sheeting was securely fixed over the mouth of the funnel such that the sheeting just rested on the tea bag. Next, a vacuum sufficient to create the desired pressure was drawn on the flask for a period of 5 minutes, and the Free Swell Index under pressure was calculated using the above formula.

Examples 1 to 3

A 20 gsm PET non- woven fabric of width 56cm was coated with a 30% syrup concentration of a solution of an isobutylene/maleic anhydride copolymer that has been hydrolysed and neutralised to form a sodium salt and 3 % butanediol and 2% glycerol as crosslinkers. The nodules, which had a diameter of 2 - - mm were spaced at the following densities:

Example 1 40 dots/cm² Example 2 10 dots/cm² Example 3 12 dots/cm²

The coated fabric was dried at 110°C in a 6m long air through oven (1.2 min drying time).

Crosslinking then occurred at 175°C for 15 mins in a laboratory oven. The properties of the fabrics were then examined and the results are detailed in Table 1.

Table 1

Example 1 Example 2 Example 3

SA nominal loading - 6 8 7 dried uncured g/m²

SA % measured 18 22 20

Free Swell (g/g) 23 24 22

Retention 0.5 psi 12 12 9

(g/g)

AC1 @ 0.1 kPa - 18 20 16 10 layers

AC1 @ 3.0 kPa - 12 13 11 10 layers

AC1 @ 5.0 kPa - 11 12 10 10 layers

Examples 4 to 9

A sample of a substrate of width 56 cm was coated with a syrup of a solution of an isobutylene/maleic anhydride copolymer that had been hydrolysed and neutralised to form a sodium salt and 3% butanediol and 2% glycerol as crosslinkers. The nodules, which had a diameter of 2-3 mm were spaced at a density of 12 dots/cm². The coated fabric was dried at 110°C in a 6m long air through oven (1.2 min drying time). Crosslinking then occurred at 175° C for 15 minutes in a laboratory oven.

Details of the fabrics and their properties are detailed in Table 2. Table 2

Example 4 Example 5 Example 6 Example 7 Example 8 Example 9

Substrate PET Paper Polypropyl Air Laid Viscose Pulp Tissue ene Paper Board

Substrate 44 23 50 17.5 38 - Weight g/m²

SA% 15.7 27 22.5 - 24.5 4.8 Measured

Free Swell 9.2 9.1 10.1 8.7 9.7 3.1

(g/g)

Retention 64 68 69 46 53 87 0.5 psi

Claims

1. An absorbent article comprising a first layer of a non-water-absorbent substrate having applied to at least one side thereof a second layer comprising a water-absorbent composition.

2. An absorbent article according to Claim 1 wherein the second layer is provided as a preformed water-absorbent composition.

3. An absorbent article according to Claim 2 wherein the preformed water- absorbent composition is in the form of fibers.

4. An absorbent article according to Claim 1 wherein the second layer is formed from a composition which on curing becomes water-absorbent.

5. An absorbent article according to any one of Claims 1 to 4 wherein the non- water-absorbent layer is formed from fibers selected from wood pulp, cellulose, synthetic cellulose, viscose, polyester, non-water-absorbent polymers of ethylene, non-water-absorbent polymers of propylene, polyamide and ethylene-propylene copolymer fibers, and mixmres thereof.

6. Au absorbent article according to any one of Claims 1 to 5 wherein the water- absorbent layer is discontinuous.

7. An absorbent article according to Claim 6 wherein the discontinuous layer is formed of spaced nodules of preformed water-absorbent composition or nodules of a composition which on curing becomes water-absorbent.

8. An absorbent article according to Claim 7 wherein the nodules are so spaced that on absoφtion of water, each swollen nodule does not impinge on any other nodule.

9. An absorbent article according to Claim 7 wherein the article is cable wrap and the nodules are spaced such that on swelling each nodule impinges on those surrounding it.

10. An absorbent article according to Claim 7 wherein the article is a pond liner and the nodules are spaced such that on swelling each nodule impinges on those surrounding it.