Layered absorbant pad material

Abstract

A layered absorbent pad material comprising an absorbent layer disposed between upper and lower surface layers, is provided, between the upper surface layer and the absorbent layer, with a layer of particulate swelling substance which swells subsequent to the material absorbing liquid, and thereafter prevents liquid being displaced back into the upper surface layer upon squeezing of the material.

Description

This invention relates to layered absorbent pad material for hygienic purposes such as absorbent, sanitary or invalid's underlays, diapers, sanitary towels and the like, and comprises an absorbent layer disposed between an upper surface layer and a lower surface layer and incorporating a swelling substance. As used herein, the term "swelling substance" means a substance which swells upon absorbing a liquid, such as water, the water being retained by adsorption.

Absorbent pads of this kind are already known. For example in German Patent Specification No. 489308 it has been proposed to incorporate into absorbent pads, which are to be used, for example, for the production of sanitary towels and for other sanitary and surgical purposes, in order to increase their absorptive capacity, adsorptive substances which are capable of combining chemically with water contained in the liquid expected to be absorbed by the pads. Organic natural products, such as potato flour, cereal starch, gelatine and the like, have been proposed as agents on this score.

Hydrophilic colloids of this kind are not, however, generally acceptable as swelling substances in hygienic or sanitary articles of the kinds mentioned. Only in recent times has it been possible to find substances having better absorptive capacities and having in addition, the property of being substantially immune to the growth of bacteria. Thus, for example in German Patent Specification No. 1,079,796 it is proposed to use, as swelling substance, carboxymethyl cellulose of which the degree of etherification is adjusted to values from 0.05 to 0.3. For the same purposes, in German Offenlegungsschrift No. 1,642,072, polyacryl amides, as well as sulphonated polystyrenes, having a specific chemical structure are recommended. Finally, it can be understood from German Offenlegungschrift No. 2,048,721 that cross-linked polymers of the polyethylene oxide type or of the polyethylene imine type are also suitable for the same purpose.

In most of these prior documents, it is proposed that the swelling substances should be in the form of powder or granulate, and that they should be accommodated either in a special bag or envelope of a material which is pervious to liquid, or to introduce the swelling substances into the absorbent pad in a mixture with cellulose wadding. In the aforesaid German Offenlegungschrift No. 1,642,072, it has also been proposed initially to coat a suitable liquid-pervious foil with a layer of adhesive and then to sprinkle the layer of adhesive with swelling-substance in powder form. The individual particles of the powder then stick fast by their undersides on the layer of adhesive and are thus retained in position. The flat product obtained in this way is then introduced into the absorbent layer at the side which lies downwards in use or is incorporated into the centre of the absorbent layer.

In comparison with the conventional absorbent hygienic pads containing cellulose wadding, absorbent pads containing a swelling substance have a considerably higher liquid absorption capacity. Whereas cellulose can, as a rule, absorb only about 20 grammes of water per gramme of cellulose, the liquid absorption capacity of the said swelling substances can amount to up to 150 grammes of water per gramme of swelling substances depending on the chemical nature of the substance. Added to this is the fact that the water is chemically completely adsorbed by the swelling substances and is retained by chemical combination e.g. by principal valencies. This means that the swelling substance, once it has taken up the water does not release it again, even under pressure loading or upon squeezing, which improves the utility of such substances. In contrast thereto, the water in paper or cellulose is largely retained by secondary valency forces or by capillary forces, which means there is much weaker retention so that such substances will readily give up the absorbed liquid under the effect of pressure, like a sponge.

Despite the considerable advantages which absorbent pads, laden with swelling substances, have in the hygienic or sanitary field, naturally the liquid absorptioin capacity of such pads is likewise limited. When the swelling substance has swollen to its maximum, it is saturated and can no longer absorb any further liquid which may be present. This excess liquid is stored in the pad in the conventional manner, like a sponge, by the cellulose wadding or crepe paper layers which are also present, and is yielded up again when the absorbent pad is subjected to pressure or squeezed. Such squeezing action cannot be avoided in the practical use of the absorbent pads and it therefore necessarily leads to expression of liquid from the pads and to the formation of pools of liquid on the surfaces of the pads.

Having regard to this state of the prior art the problem still exists of providing a faced or enveloped absorbent pad containing a swelling substance, for hygienic purposes, the liquid retention capacity of which is improved in comparison with the known pads.

In accordance with the invention, this problem is solved in that the pad material incorporates a particulate swelling substance is arranged exclusively or additionally in one of the layers, lying at the top in use, of the absorbent body or of the envelope and in that the distribution of the particles throughout the layer of swelling substance is such that the spacing between adjacent particles is no greater than half of the particle diameter increase which occurs upon swelling of said particles. With such arrangement, upon swelling the particles coalesce, after the fashion of a jelly, and form a barrier layer which is impervious to liquid.

In the practical use of absorbent pads constructed in this way, upon wetting of the pad the wetting liquid initially enters in the conventional manner into the absorbent pad and flows through the layer of swelling substance arranged at the top or largely at the top, resulting in the particles of swelling substance being moistened and slowly beginning to swell. Surplus liquid flows past the particles of swelling substance and into the absorbent layer lying therebelow, which absorbent layer consists, for example of cellulose wadding, crepe paper plies or the like.

The swelling procedure itself may last, for example, from one to five minutes depending on the fineness of grain of the swelling substance. A considerable increase in diameter of the individual particles occurs, so that these, because of their density of distribution, coalesce into a poreless liquid-impervious gel-like barrier layer. If subsequently to the swelling a fairly severe pressure loading is imposed on the pad or the pad is squeezed locally, the liquid stored like a sponge by the absorbent layer (cellulose wadding layer or crepe paper layer) is no longer able to penetrate the barrier layer and to rewet the exterior of the absorbent pad outwardly. What is advantageous in this connection is the fact that once the chemical reaction of liquid adsorption is once initiated, the swelling proceeds initially slowly and then comparatively rapidly. Towards the end of the reaction, the speed of swelling dies away, which leads to the fact that the gel layer, even though it may have coalesced to such an extent that it will not let liquid pass through outwardly from the interior of the absorbent layer, can still take up relatively small quantities of liquid still present on the outside of the absorbent pad or which may subsequently arise. An invalid or sanitary underlay, diaper, sanitary towel or the like, conforming to the invention therefore displays the advantageous property that it can initially absorb a relatively large quantity of liquid during which the swelling material layer correspondingly swells and coalesces despite considerable pressure loading, to form an effective sealing layer or skin with the result that the top surface of the pad becomes dry again.

It is advantageous if the swelling substance is arranged directly below the filter layer or one of the upper surface layers of the pad material, and that it should be in one or more layers itself. To this end, the swelling substance should preferably have a granulate form and be held fast, by way of example adhered, on a liquid-pervious carrier or support sheet. This carrier sheet or several of these sheets arranged one above the other in layers can then be introduced in the manufacture of the absorbent pad.

It is furthermore possible to confine the swelling substance between two layers of cellucotton (or artificial cotton) and to introduce it in this form into the absorbent pad during the manufacture. In this connection, the cellucotton acts as a support and filter layer which prevents the swelling substance from escaping from the absorbent pad.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is an enlarged diagrammatic sectional view of a preferred form of the absorbent pad material of the invention;

FIG. 2 is a view similar to FIG. 1, but showing the material subjected to pressure after wetting and before completion of swelling;

FIG. 3 is a view similar to FIG. 1 but showing the material after swelling has taken place;

FIG. 4 is a view similar to FIG. 3, but showing the material subjected to pressure loading; and

FIG. 5 is a diagrammatic plan illustrating the particle distribution in the swelling substance layer in the material of FIGS. 1 to 4.

The layered absorbent pad material illustrated in the drawings comprises a plurality of superimposed layers consisting of flat areal structures or sheets, and absorbent substances. Upper surface layer 1 is in the form of a plastics-bound fibre fleece or web which imparts to the entire absorbent pad material a textilelike texture which is kind to the skin. Underneath this fleece substance layer 1 there is disposed one, or several, layers 2 of cellucotton acting as a filter layer and serving to prevent swelling substances (yet to be described), in the unswollen state, from escaping from the material, e.g. as a result of rough treatment of the absorbent pad material.

Beneath the layer or layers 2 of cellucotton there is disposed one or several layers 3 of swelling substance, which are preferably prepared as has already been described above. In this connection, the powdery or granular swelling substance (which may consist for example of polyacrylamide, sulphonated polystyrene or other suitable substance) is fixed, for example adhered, to a carrier sheet of cellucotton. Underneath the layer 3 of swelling substance there is disposed a relatively thick layer 4, which consists of one or more laps of cellulose wadding. Crepe paper can, if desired, be incorporated into this layer; furthermore, intermediate layers of cellucotton can be present therein, those serving for example as carriers for disinfecting or deodorising substances.

Finally, arranged as lower layer 5 there are once more one or more surface layers which may also consist of cellucotton, plastics-bound fibre fleece or which may be of liquid-impervious foil, for example thin polyethylene foil.

Should the absorbent pad material be wetted, in other words if a liquid, for instance water, impinges in the direction of arrows 6 (FIG. 1) on the upper surface layer 1 of the pad, this liquid is absorbed instantaneously by the pad and becomes distributed in the absorbent layer 4, as is indicated in FIG. 1 by arrows 7. Also the layer 3 of swelling substance is penetrated and the particles of swelling substance are moistened.

If, before the swelling substance of the layer 3 has swollen, the pad is subjected to pressure as indicated in FIG. 2 by the arrow 8, part of the liquid stored in the pad by the absorbent layer 4 is expelled after the manner of squeezing a sponge. This expelled liquid flows partially away from the location at which the pressure is applied, as is indicated in FIG. 2 by the arrows 9. Part of this expelled liquid will, however, as indicated by the arrows 10 in FIG. 2, penetrate the still comparatively pervious layer 3 of swelling substance and the layers 2 and 1 arranged thereabove and flow back onto the upper surface of the absorbent pad. There it can form a pool 11, which, of course, is undesirable.

Contact of the liquid with the swelling substance layer 3 results in the particles of the swelling substance absorbing the liquid and beginning to swell. This swelling proceeds slowly at first. After a few minutes, however the reaction between the particles of swelling substance and the liquid will have progressed to such an extent that, as is shown in FIG. 3, the particles will have considerably increased in diameter. As a result, the swollen particles coalesce into a jellylike liquid-impervious layer 3' (FIGS. 3 and 4) which creates a barrier for the liquid which is already present in the suction layer 4. The layer 3' of swelling substance can still absorb small quantities of liquid from above which leads to the fact that the upper fleece material layer 1 as well as the cellucotton layer 2 yield their residual liquid content to the layer 3' of swelling substance and are caused to dry out. Should the pad now be squeezed or subjected to pressure loading, as indicated in FIG. 4 by the arrow 8', the layer 3' remains liquid-impervious so that no liquid can be expressed upwards out of the absorbent layer 4, and the diaper, invalid underlay, sanitary towel or the like remains dry even if subjected to violent treatment resulting in considerable surface deformation of the pad.

The embodiment shown in the drawings is given only by way of example and variations may be made thereto. For example, it is possible to arrange the layer 3 of swelling substance not as shown above the absorbent pad layer 4, but to accommodate it within this layer, but near to its upper surface. This would be the equivalent, of course, to providing a further thin absorbent layer between the swelling substance layer 3 and the cellucotton layer 2. If the layer 3 of swelling substance were, for example, accommodated in the centre of the absorbent layer or in the latter near to its lower surface, naturally the drying and barrier effect above-discussed would not be achieved. However, this does not preclude the possibility of providing additional swelling substance layers in the centre and/or near the bottom surface of absorbent layer, over and above the layer 3 at or near the top surface of the absorbent layer 3, if this is desired and is acceptable for economic reasons.

In FIG. 5, several particles 12 of the swelling substance are shown, very diagrammatically, as lying side-by-side. In fact, the particles of swelling substance naturally will not be regularly-disposed as illustrated nor will they be in the form of spheres, but will be more or less non-uniformly shaped structures; the fundamental requirement for the distribution of the particles remains however,, the same. The particles 12 of swelling substance (which are shown in their non-swollen conditions in full lines) absorb water in the swelling procedure, and combine chemically therewith; as a result they increase in volume and consequently in diameter as indicated in dotted lines at 12'. An essential feature of the absorbent pad material of this invention is that the distribution of the unswollen particles 12 of swelling substance is such that at no point throughout the layer is the spacing 13 of the particles 12 of swelling substance from one another greater than half the increase in diameter which occurs upon swelling thereof. Only with observance of this condition is it ensured that the particles of swelling substance coalesce tightly and thus form the liquid-impervious barrier layer 3'. Theoretically there could remain, between the coalesced particles 12', a free space which considered two-dimensionally is an enveloping rectangle, but considered three-dimensionally is an enveloping octahedron. Microscopic observations show, however, that this free space in fact does not remain, but becomes filled as a result of deformation of the swollen particles, and the entire layer thus coalesces into a uniform mass.

To ensure that no liquid can be expressed from the pad when subjected to all-over pressure, or pressure applied over large areas thereof, the pad or the pad material may be enveloped or faced, except at its upper surface layer, by an additional water-impervious envelope or foil.

Claims

I claim:

1. A layered absorbent hygienic pad of joined-together layers comprising:

an uppermost surface layer of plastics-bound fiber fleece, a next-adjacent carrier filter sheet of cellucotton, a next-adjacent layer of granulated particulate swelling substance formed from the group consisting of polyacrylamide or sulphonated polystyrene with spacings between adjacent particles,

an absorbent layer consisting of one or more laps of cellulose wadding and being free of any swelling substance, and a lowermost surface layer of a material formed from the group consisting of a plastics-bound fiber fleece or a liquidimpervious foil with the distribution of the particles of the layer of the swelling substance being such that the spacing between adjacent particles is no greater than half of the particle diameter increase realized upon particle swelling.