WO1991011164A1

WO1991011164A1 - An absorbent body which includes fibre wadding

Info

Publication number: WO1991011164A1
Application number: PCT/SE1991/000074
Authority: WO
Inventors: Annika Ahnell; Berith Porsö; Berit Rosseland
Original assignee: Mölnlycke AB
Priority date: 1990-02-01
Filing date: 1991-02-01
Publication date: 1991-08-08
Also published as: AU7231791A; SE9000360D0; SE465806B; SE9000360L

Abstract

The present invention relates to an absorbent body (3) for use in a disposable absorbent article, such as a diaper, an incontinence guard, a sanitary napkin, an underwear protector or like article, including fibre wadding (4). According to the invention, the fibre wadding (4) includes a mixture of coarse fibres having a size of at least 17 dtex and fine fibres having a size of at most 2 dtex.

Description

An Absorbent Body Which Includes Fibre Wadding

The present invention relates to an absorbent body for use in disposable absorbent articles, such as diapers, incontinence guards, sanitary napkins, underwear pro¬ tectors or the like and including fibre wadding.

Absorbent articles of the aforesaid kind are normally constructed from absorbent,bodies which include hydro- filic fibres, such as cellulose fibres for instance.

For the purpose of absorption, it is also known to use fibre wadding which will function as an absorbent body, with or without the addition of another absorbent material, for instance superabsorbents. By superabsor- bents is meant substances which are capable of absorb¬ ing liguid in guantities many times their own weight.

It is also known to permit fibre wadding to form a shape-stable layer between the liquid-permeable layer and the absorbent pad of such an article, with the purpose of distancing the skin of a user from the absorbent pad, so that absorbed liquid will not come into direct contact with the user.

In this case, the purpose of the fibre wadding is not to absorb liquid to any great extent, but instead to enable liquid to pass quickly through the wadding, or to be transported thereby to an underlying absorbent layer. At the same time, the wadding should not col¬ lapse when subjected to pressure, for instance when the user sits down, since liquid would then be able to penetrate up through the wadding and come into contact with the user, causing considerable discomfort. This is combined with considerable difficulties in obtaining a suitable wadding composition which will fulfil the above requirements, since these requirements require wadding properties which, to some extent, are directly opposed to one another.

Coarse heat-meltable fibres, for instance fibres of polyester, polypropylene or polypropylene, provide a shape-stable resilient and springy fibre wadding. Fibre wadding constrμcted from such fibres, however, will lack a fine capillary system which is capable of con¬ ducting liquid in a desired direction, for instance to an absorbent layer adjoining the fibre wadding. Neither is such fibre wadding particularly soft and comfortable when worn immediately next to the skin.

On the other hand, fine hydrofilic fibres, for instance viscose fibres or cellulose-based fibres, provide dense, soft fibre wadding with a fine-mesh capillary system and therewith good liquid transport properties. Such wadding, however, will also collapse readily when wet.

The present invention, however, provides a fibre wadding with which the aforesaid difficulties and drawbacks have been overcome.

An inventive absorbent body is mainly characterized in that the fibre wadding includes a mixture of coarse fibres having a size of at least 17 dtex and fine fibres having a size of at most 2 dtex.

The presence of both coarse and fine fibres in the wadding provides a wadding which is highly suitable for its intended purpose, i.e. wadding which is shape-

4

stable and Which will spring-back resiliently when in a wet state and which will transport liquid effectively. It has also been found ctf great *importance with respect to the invention that the fibres are present in a given mixture ratio. It has been found suitable to construct the wadding from 80-90% by weight coarse fibres and 10- 20% by weight fine fibres.

It has been found that a particularly suitable fibre mixture is one which comprises 85% by weight coarse fibres and 15% by weight fine fibres. The presence of coarse fibres causes the*fibre wadding to be bulky and to obtain spring-back properties, i.e. the fibre wadding will spring back subsequent to having been com- pressed, for instance by *the weight of the user. Another method of increasing the stability of the wadding is to join the fibres together, for instance by applying heat, so as to obtain a thermobonded wadding. When the coarse fibres consist of heat-meltable so- called thermoplastic fibres of the type bicomponent fibres, the fibres in their molten state function as a binder in such thermobonded wadding, without needing to use additional binder. Another advantage obtained with bonded wadding is that it- can be handled in production much more readily than non-bonded wadding.

The fine fibres are intended to fill the empty spaces between the coarse fibres, so that the fibre wadding will obtain a structure comprising many fine capil- laries, which is a prerequisite for liquid transport in the wadding. A particular advantage is afforded when the fine fibre is a hydrofilic fibre, since the wadding will therewith also be absorbent to some extent. The present invention thus provides a thermobonded wadding which is both dense, bulky, shape-stable and springy and which will both absorb and transport liquid.

An absorbent body constructed in accordance with the invention will now be described in more detail with reference to exemplifying embodiments thereof illus¬ trated in the accompanying drawings.

Figure 1 is a view from above of an absorbent article which includes an inventive absorbent body, with the side intended to face towards the user facing the viewer; Figure 2 is a sectional view of a first embodiment of the absorbent article, taken on the line II-II in Figure 1; and

Figure 3 is a sectional view of a second embodiment of the absorbent article, taken along the same line II-II in Figure 1.

Figures 1 and 2 illustrate schematically a diaper 1, which is representative of an absorbent article. The diaper 1 comprises a liquid-permeable layer 2, suitably a non-woven fabric, an absorbent pad 3 which is posi¬ tioned beneath the layer 2 and which includes a liquid- receiving layer 4 and an absorbent layer 5 positioned beneath the liquid-receiving layer. Positioned beneath the absorbent layer 5 is a liquid-impermeable layer 6 which may be made, for instance, of liquid-proof poly¬ ethylene film or a liquid-proof plastic film which is vapour and air permeable. The liquid-impermeable layer 6 and the liquid permeable layer 2 extend somewhat beyond the edges of the absorbent pad 3 and are bonded together with the aid of an adhesive, in a conventional manner. The two layers 2, 6 can also be joined to the absorbent pad 3 in a desired manner if found suitable, for instance in order to stabilize the absorbent pad.

The liquid-receiving layer 4 of the absorbent pad 3 comprises fibre wadding which includes a mixture of coarse and fine fibres. As will be evident from the following example, it i& particularly advantageous to construct the fibre wadding from a mixture of heat- meltable fibres and hydrofilic fibres. The heat- meltable fibres may comprise, for instance, polyester fibres, polyethylene fibries, bicomponent fibres or mixtures thereof. It is particularly preferred to use bicomponent fibres where the components consist of polypropylene/polyethylene, polyester/polyester, poly¬ ester/polyethylene.

It is particularly suitable to use a bicomponent fibre consisting of a polypropylene core and a polyethylene casing. Polyethylene namiiiy has a lower melting point than polypropylene and heating of the bicomponent fibre to a temperature higher than the melting point of polyethylene but lower than the melting point of poly¬ propylene will result in melting of the polyethylene component while leaving the polypropylene component unaffected. In this way, the polyethylene component will function as a binder for stabilizing the wadding, therewith obviating the iceed to add a separate binder.

The hydrofilic fibres will preferably be viscose fib¬ res. The actual mixture is preferably homogenous, although a hetrogenous ittixture is also conceivable. A preferred fibre wadding has a density of 0.05-0.07 g/cm 3 and a grammage of about 200 g/m2. The fibre wadding can be produced in any manner known to those skilled in the art, for instance by carding or air- laying.

The absorption layer 5 may include any suitable absorp- tion material, for instance cellulose fluff in which superabsorbing polymers may be dispersed. The superab- sorbents may be mixed homogenously with the cellulose fibres or arranged in layers on or within the absorp¬ tion layer 5. The superabsorbents may be used in seve- ral different forms, i.e. fibre or particle form.

Figure 3 illustrates a second embodiment of an inven¬ tive diaper which, similar to the earlier embodiment, comprises a liquid-permeable layer 2, suitably a non- woven fabric, which is intended to lie against the skin of the wearer in use.

Placed beneath the liquid-permeable layer 2 is an absorbent pad 7 which includes a liquid-receiving layer 4 of the same kind as that used in the Figure 2 embodi¬ ment, and an absorption laminate 8 which is placed beneath the liquid-receiving layer. The absorption laminate 8 includes two material layers 9, 10 and an absorption layer placed between said two material layers. The material layers 9, 10 may consist, for instance, of a tissue layer or some other compressed cellulose-fibre layer. The absorption layer 11 will preferably consist of superabsorbents. The absorption laminate 8 may also be constructed in the manner taught by Swedish Patent Application No. 8901964-0, i.e. the number of absorption layers 11 may be more than one and the superabsorbents present in the various layers may exhibit mutually different absorption properties. Finally, a liquid-impermeable layer 6 of the same kind as that used in the Figure 2 embodiment is placed on the side of the absorbent pad 7 distal from the wearer. The earlier described features of the liquid-permeable and liquid-impermeable layers 2, 6 of the Figure 2 embodiment are also applicable to corresponding layers of the Figure 3 embodiment. <

The diaper may be provided with fastening devices, elastic devices or the like in a known manner, without having any bearing on the invention, and consequently such diaper characteristics have not been shown in the drawings. When the invention is applied with incon¬ tinence guards, sanitary napkins and underwear protec¬ tors, these articles can be provided, for instance, with means for attachment of the article to underwear, although such means of attachment forms no part of the present invention.

The following examples illustrate the manner in which the properties of the fibre wadding is influenced by the mixture ratio between the wadding components.

Example 1

Fibre wadding comprising various weight percentages of 20 dtex bicomponent fibres having a polyethylene casing and a polypropylene core, and 1.7 dtex viscose fibre, were tested with respect to thickness in a dry and wet state, at low and high loads respectively. The fibre waddings had a grammage of 200 g/m 2. The thicknesses were measured by placing a plate on the dry fibre waddings and subjecting the waddings to variable loads, whereafter the thickness of the waddings was measured with the aid of a ruler. The thickness was measured at a load of 2.3 g/cm 2 and at a load of 10.5 g/cm2. The lighter load resulted in only slight compression of the fibre wadding and is intended to define a readily measurable starting thickness of the wadding.

The fibre waddings were then soaked in water and were allowed to drain until no liquid dripped from the waddings, whereafter the thickness of the waddings was measured in the same way as that used to measure the dry waddings. The values recited in Table 1 are rela¬ tive and relate to the respective thickness of a wet and a dry fibre wadding for respective viscose quan¬ tities and loads in relation to the thickness of a dry fibre wadding subjected to a low load.

Table 1

Viscose Quantity Relative Thickness

V = Wet fibre wadding

Tl = Dry fibre wadding at low loads

T = Dry fibre wadding

2 Low load = 2.3 g/cm

2 High Load = 10.5 g/cm

In order to function as a spacing layer between the liquid-permeable layer and the absorption layer, the fibre wadding shall essentially retain its thickness in a wet state when subjected to load. Table 1 shows that in the case of fibre wadding containing 10% and 15% viscose, the relationship between dry and wet wadding is essentially the same at the high load. In the case of wadding containing 20% viscose, a slightly poorer value is obtained, whereas a markedly poorer result is obtained when the wadding contains 30% viscose.

Example 2

Liquid leakage in a sloping plane was measured in respect of a sample body containing fibre wadding whose composition varied between the tests.

The test body comprised an outer layer of non-woven fabric which enclosed fibre wadding placed on top of an absorption layer which contained superabsorbents. The absorption layer comprised an upper tissue laminate in which 2.5 g of powdered Aqualic CA W-4 were dispersed, and a bottom tissue laminate in which 2.5 g of powdered Waterlock J 550 were dispersed. Aqualic CA W-4 and Waterlock J 550 are the designations of commercially available superabsorbents. The test body had an elon¬ gated rectangular shape and was placed with its lon- gitudinal axis inclined at 30° to the horizontal plane. 100 ml of 0.9% NaCl (aq) were delivered to the upper end of the body over a period of 7 seconds. The quan¬ tity of non-absorbed liquid was collected at the lower end of the body and weighed. The results are given in Table 2. Table 2

Viscose Quantity Liquid Leakage

(Weight Percent) (g)

10 24

20 16

30 1

The values in Table 2 were compared with the results of a similar test in which the viscose fibre was replaced with 15% by weight polypropylene of 2.2 dtex. Liquid leakage was 28 g in the case of this test body.

Example 3

Re-wetting was measured for a test body which contained a fibre wadding having a grammage of 150 g/m 2 and of varied composition placed on top of an absorption layer comprising a tissue laminate in which 5.1 g (± 0.1 g) of Aqualic CA W-4 were distributed.

Re-wetting is a measurement of the amount of liquid discharged from the test body when load is applied thereto.

50 ml of 0.9% NaCl (aq) were delivered to an area of

1-2 cm 2 of the fibre wadding of the test body. The test body was allowed to absorb liquid over a period of 3 minutes, whereafter five weighted filter papers, loaded with a weight of 1800 g, were placed on the body for a period of one minute. The filter papers were then weighed and their weight increase noted. The results are given in Table 3. Table 3

Viscose Quantity Re-wetting (Weight Percent) (g)

0 0.9 10 0.4 20 0.3 30 0.1

The values in Table 3 were compared with the results of a similar test in whiςh the viscose fibres were re¬ placed with 15% by weight polypropylene of 2.2 dtex. Re-wetting in the case of this test body was 0.7 g.

The conclusion can be drawn from the results shown in Examples 1-3 that when the viscose quantity is in¬ creased both re-wetting and leakage in an inclined plane will decrease. The improvement obtained with 30% viscose is particularly noticeable. However, when the viscose content is as high as 30% or higher, the fibre wadding will collapse when wet. At this mixture, the thickness of the wet fibre wadding after being sub¬ jected to load is considerably less than the corres¬ ponding thickness of the dry wadding. A weight pro¬ portion of 30% viscose in the wadding is therefore unsuitable, and the preferred range is 10-20% viscose fibres. It can also be seen that a dry fibre wadding is less resilient and has poorer spring-back when the viscose content is increased. It will also be noted that the resiliency of fibre wadding which contains no viscose is superior to fibre wadding in which viscose fibres are included. It has been found that the coarse fibres should suitab¬ ly have a size of 17 dtex in order for the wadding to be sufficiently resilient and exhibit sufficient spring-back. Although benefits are obtained with regard to resiliency and spring-back with fibre sizes much greater than 20 dtex, the resultant wadding is stiff and uncomfortable to the wearer. The fine fibres should have a size of 1.5-2 dtex, because coarse fibres do not provide a sufficiently fine capillary system in the wadding.

The invention is not restricted to the aforedescribed embodiments and several modifications are possible within the scope of the following Claims.

Claims

1. An absorbent body (3, 7) for use in disposable absorbent articles, such as diapers, incontinence guards, sanitary napkins, underwear protectors or like articles which include fibre wadding (4) , c h a r ¬ a c t e r i z e d in that the fibre wadding (4) in¬ cludes a mixture of coarse fibres having a size of at least 17 dtex and fine fibres having a size of at most 2 dtex.

2. An absorbent body according to Claim 1, c h a r ¬ a c t e r i z e d in that the coarse fibres have a size of 20 dtex and the fine fibres a size of 1.7 dtex.-

3. An absorbent body according to Claim 1 or 2, c h a r a c t e r i z e d in that the fibre wadding (4) comprises 80-90% by weight coarse fibres and 10-20% by weight fine fibres.

4. An absorbent body according to Claim 3, c h a r ¬ a c t e r i z e d in that the fibre wadding (4) com¬ prises 85% by weight coarse fibres and 15% by weight fine fibres.

5. An absorbent body according to any one of Claims 1-4, c h a r a c t e r i z e d in that the coarse fibres are hydrophobic, heat-meltable fibres; in that the fine fibres are hydrofilic fibres; and in that the fibre wadding (4) is thermobonded.

6. An absorbent body according to Claim 5, c h a r ¬ a c t e r i z e d in that the coarse fibres are poly- ethylene fibres, polypropylene fibres, polyester fibres, bicomponent fibres or mixtures thereof; and in that the fine fibres are viscose fibres.

7. An absorbent body according to Claim 6, c h a r - a c t e r i z e d in that the fibre wadding (4) in¬ cludes bicomponent fibres composed of polypropylene/ polyethylene, polyester/polyester or polyester/ polyethylene.

8. An absorbent body according to Claim 7, c h a r ¬ a c t e r i z e d in that the bicomponent fibres comprise a polypropylene core and a polyethylene casing.

9. An absorbent body according to any one of the preceding Claims, c h a r a c t e r i z e d in that the absorbent body (3, 7) includes an absorbent layer (5, 8) arranged in direct contact with the fibre wadding (4), on that side of the wadding (4) which is intended to be distal from the wearer.

10. An absorbent body according to Claim 9, c h a r ¬ a c t e r i z e d in that the absorbent layer (5, 8) presents a finer capillary system than the fibre wadding (4), thereby enabling liquid which passes through the wadding (4) to be absorbed in the absorbent layer (5, 8) .

11. An absorbent body according to Claim 9 or 10, c h a r a c t e r i z e d in that the absorbent layer (5, 8) comprises a laminate (8) of at least two liquid- transporting material layers (9, 10) and includes superabsorbent material. 15

12. An absorbent body according to Claim 11, c h a r a c t e r i z e d in that the superabsorbent material is disposed in a layer (11) between two liquid-transporting material layers (9, 10).

13. An absorbent body according to Claim 11 or 12, c h a r a c t e r i z e d in that the material layers (9, 10) comprise tissue, cellulose fibre, perforated plastic or non-woven fabric.