Absorption material, preferably for use in disposable articles such as diapers, sanitary napkins or wound dressings

Abstract: The invention relates to an absorption material, prefer­ ably for use in disposable articles such as diapers, sanitary napkins or wound dressings. The primarily distinguishing feature of such a material, made in accordance with the invention, is that it comprises ­ 70-95% of at least one type of absorbing fibers, 220-% of a binder activated by heat, and 2-25% of a highly absorbent material, the absorption fibers and the highly absorbent mat­ erial having been bonded into a coherent body by means of the binder.

Description: The present invention relates to an absorption material, preferably for use in disposable articles such as diapers, sanitary napkins or wound dressings, comprising 70-95% of absorption fibers, 2-25% of a super absorbent material and 2-20% of a binder in the form of bonding fibers, which are heat fused and thus bond the absorption fibers and the super absorbent material into a coherent body. The determining factor with regard to function and economy of absorbent articles such as sanitary napkins, diapers, incontinence articles, tampons, etc. is the amount of absorption material required to absorb a certain quantity of fluid in relation to the intended use of the specific absorbent article. In most cases it is further of vital importance to bind the fluid, thereby preventing it from being pressed out under the influence of the stresses placed on the article during its use. In order to overcome the problem of liquid-containing capacity in absorbent articles, efforts have been made to utilize so-called super absorbents. Because of their poor liquid-transmitting properties, however, it has proved difficult to take advantage of the otherwise high liquid-retaining potential of these super absorbents. Furthermore, the costs involved in producing absorption materials with the aid of super absorbents are considerably higher than those connected to the use of so-called cellulose fluff pulp, for example. Absorbent articles including a mixture of super absorbents and fluff pulp are previously known. With regard to the liquid-containing capacity, these articles present absorption values relating in principle to the proportion between the absorbent capacity of the incorporated components, whereas the liquid-transmitting capacity of these articles has shown itself to be insufficient. At first, the manufacturers of absorbent articles intended for single use seemed to be very optimistic when faced with the opportunities associated with super absorbents, but despite great efforts during a period of at least ten years, no one has so far succeeded in the development of commercially marketable products with regard to manufacturing costs and total absorbency. In EP-A-122 042, however, is disclosed a flexible, substantially unbonded, absorbent structure comprising 30-98% of hydrophilic fibers and 2-70% of a super absorbent material. This structure has a density of from 0.15-1 g/cm 3 and a moisture content of less than 10% by weight of the dry structure. Since this structure is substantially unbonded, the absorption possibilities of its super absorbent material might be utilized through swelling of the structure. Another absorption material comprising at least one type of absorption fiber and in addition super absorbent material is disclosed in WO 83/01965. The absorption fibers in this material are melt blown polymeric fibers and the super absorbent material is of the granular type. The super absorbent granules or particles are firmly adhered to the polymeric fibers by being brought into contact with these fibers whilst they are still in a tacky condition which implies that the melt blown polymeric fibers act as a binder for the particulate super absorbent material. DE-A-2 721 511 discloses adsorbing nonwoven webs for use as filters for adsorbing undesirable components from gases or liquids. The main idea behind these structures is to obtain a filter material that is more convenient to handle than the usual material in powder or particulate form. More specifically, the method and articles disclosed in this document are meant to eliminate the defects of known thin adsorptive sheets, such as adsoptive paper. These webs comprise a mixture of cellulose supporting fibres, short-length heatfusible fibers and an adsorptive material, e.g. active carbon. Polymers having excellent swelling (or liquid-holding) abilities can be fixed in such webs. However, the webs disclosed do not have a density gradient in their direction of thickness. Moreover, such a thin fabric web can not fullfil the object of the present invention to enable the creation of an absorption body for a diaper or a sanitary napkin having excellent liquid-retaining capacity as well as liquid-transmitting capacity in order to keep the side of the absorbent article facing the wearer as dry as possible. With the present invention, however, there has been achieved an absorption material intermixed with highly absorbent material, which composite absorption material has proved superior to previously known articles of this type. An absorption material, according to the invention is distinguished by the features of the characterizing portion of claim 1. When using the absorption material in accordance with the invention, it has most surprisingly been found that the liquid-transmitting capacity of this composite material is greater than that of the separate components forming part thereof. In view of this fact, and considering also the small amount of the comparatively expensive, highly absorbent material incorporated, it has now been possible for the first time to achieve a commercially marketable absorption material with a mixed-in, super absorbent material. The invention will be described in more detail below with reference to the accompanying drawing, in which Fig. 1 is a cross-sectional view through an absorption body made of the inventive absorption material; Fig. 2 shows the cross-section of Fig. 1 but provided with a distribution image of liquid absorbed in the absorption body; and Fig. 3 is a cross-sectional view corresponding to that of Fig. 2 through an absorption body but having another density gradient. The embodiment illustrated in Fig. 1 of an absorption body made of an absorbent material in accordance with the invention is constructed of paper-making fibers in the form of so-called fluff pulp and bonding fibers such as, for example, those marketed under the trade name PULPEX by the U.S. company Hercules, as well as highly absorbent material such as, for example, that marketed under the trade name SANWET by the Japanese company Sanyo. The bonding fibers will melt at their binding temperature and are thereby bonded together with the absorption fibers, obtaining in this way an absorption body which is comparatively shape-stable both, in its wet and its dry state, and in which the intermixed, highly absorbent powder is bonded to the voluminous network structure of the material. In Fig. 1 the side of the absorption body facing the wearer during use of the article is denoted by 1, and the opposed side by 2. The absorption fibers which are cellulose fibers in this case, are being united by means of the bonding fibers. The absorption body is designed to have a density which increases gradually in the direction from the side surface 1 facing the wearer and towards the opposed side surface 2. By appropriately balancing this density gradient and by selecting the density desired for the two outer layers 1, 2, an absorption body having the optimal absorbency properties with regard to its intended use can be obtained. The absorption body is air-laid, while adding in this connection the highly absorbent powder, the concentration of the powder in the direction of thickness of the absorption body varying so that the highest concentration is located at the side 2 facing away from the wearer using the article. Fig. 2 illustrates the distribution of liquid, and thereby the density gradient in the direction of thickness of the inventive absorption body. Liquid has been supplied here to a so-called wetting point 4 in the low-density surface layer 1 facing the wearer. The value of the density within the region closest to the surface layer 1 is so low that the liquid is substantially spread in the direction towards the opposed surface layer 2, gaining in this way the advantage that the side or surface 1 facing the wearer will not be wetted but remains essentially dry with a pleasant feel to the wearer. As liquid penetrates into the gradually densed compressed absorbent material in the absorption body, the lateral distribution of absorbed liquid accelerates; the highly absorbent intermixed powder contributing to this increased spread as well. Only after the layer closest to the side surface 2 facing away from the wearer has been saturated with liquid, the spread of liquid will be reversed in the direction from the latter layer and towards the side surface 1 facing the wearer, which side will therefore remain at least essentially dry until all other absorbent material in the absorption body has been saturated with liquid. As already mentioned, the density gradient in an absorption body made in accordance with the invention may be selected with regard to the intended use of the absorption body. The liquid distribution profile 3 shown in Fig. 2, i.e. the distribution of liquid from the side surface 1 facing the wearer towards the opposed side 2 facing away from the wearer prior to the spread returning in the direction away from already saturated zones and back to the side surface 1 facing the wearer, illustrates an essentially optimal distribution of liquid for use in e.g. sanitary napkins. Besides the selection of density gradient in the direction of thickness of the absorption body, made with regard to absorbency only, this density can also be selected with regard to the desired stability and softness of the finished product. Fig. 3 illustrates an absorption body made in accordance with the invention and having a density gradient which is extremely well suited for absorbent articles containing large amounts of liquid, such as diapers for example. In absorbent articles for diapers, a high capacity of transporting liquid away from the wetting point 4 is in fact a vital point. In an absorption body made in accordance with the invention, this requirement is fulfilled by means of the density gradient and supply of highly absorbent powder, chosen for a distribution profile 5, designed as shown in Fig. 3. The density and concentration of highly absorbent powder increases more rapidly here in the direction away from the upper side 1 of the absorption body facing the wearer and downwards in comparison with the absorption body shown in Fig. 2. The invention will also be elucidated below by means of the following example. 84% cellulose fluff pulp was air-laid together with 8% of bonding fibers and 8% of highly absorbent material. The admixture was heated to the binding temperature of the melting fibers, and was then compressed to a suitable density. The absorption body built up in this manner had a liquid-retaining capacity of 27 grams per gram of absorption material, and a liquid-transmitting capacity of no less than 18 grams of liquid per gram of absorption material. These are extremely good absorption properties, which is elucidated by the comparison with an absorption body of fluff pulp and bonded with the binder to the same density, which had a liquid-retaining capacity of 14 grams per gram of absorption material and a liquid-transmitting capacity of only 11 grams of liquid per gram of absorption material. The inventive, highly absorbent material in itself had a liquid-retaining capacity of 32 grams per gram of absorption material, and a negligible liquid-transmitting capacity. The invention is not restricted to the embodiments and the example described herein, but a plurality of modifications are possible within the scope of the following claims.

Claims: Absorption material, preferably for use in disposable articles such as diapers, sanitary napkins or wound dressings, comprising 70-95% of cellulose absorption fibers, 2-25% of a super absorbent material and 2-20% of a binder in the form of bonding fibers, which are heat fused and thus bond the absorption fibers and the super absorbent material into a coherent body, characterized in that the absorption material, by being compressed in its direction of thickness, has been given a continuous density gradient in said direction of thickness which is essentially retained in both its wet and its dry state, the absorption body formed having its lowest density in the layer facing the wearer during use of the article. Absorption material according to Claim 1, characterized in that it comprises 80-90% of the absorption fibers, 4-12% of the binder, and 6-12% of the super absorbent material. Absorption material according to any one of the preceding claims, characterized in that the amount of binder in the absorption material has been selected with regard to the swelling capacity of the super absorbent material so that upon expansion, this material is capable of breaking up the bonds in order to optimally utilize the absorbing capacity of the super absorbent material. Absorption material according to any one of the preceding claims, characterized in that the bonded absorption body, by selecting the desired degree of compression, has been given a structure such that the super absorbent material will have an expansion volume allowing for its swelling capacity to be utilized at least to a high degree within the bonded structure. Absorption material according to any one of the preceding claims, characterized by a concentration of super absorbent material which increases in the direction of thickness of the absorption body and away from the side facing the wearer during use of the article.

Inventors: HELLGREN MAUD, ZOELLER HENRY, HELLGREN, MAUD, ZOELLER, HENRY, Zöller, Henry 
Applicants: MOELNLYCKE AB
Application year: 1986
Main classification: A61F13
IPC codes: A61F13