Absorbent panel for body fluid absorptive garments

Abstract: Here is an absorbent panel for body fluid absorptive garments such as a disposable diaper formed from a mixture of at least fibrous or granular liquid-absorptive material and thermoplastic fibers being compressed to a uniform thickness wherein said thermoplastic fibers are welded to each other with a welding density of their cross points to be higher in a crotch zone than in the remaining zone and to provide a tensile strength correspondingly higher in said crotch zone than in said remaining zone.

Description: BACKGROUND OF THE INVENTION The present invention relates to an absorbent panel for body fluid absorptive garments and, more particularly, to such absorbent panel used in disposable diapers, disposable training pants and the like. A mixture of fluffy pulp, water-insoluble polymer granules of high water absorptivity and hydrophilic or hydrophobic fibers has been conventionally used to form the absorbent panel of the above-mentioned type, wherein said mixture as a whole has been compressed or embossed to improve its absorptivity/diffusibility and shape holding ability. EP-A-0 157 649 discloses an absorbent core comprising two longitudinally spaced end portions and a central portion disposed intermediate said end portions, wherein said central portion has a greater average density and a greater average basis weight than said end portions. So, the density of the material varies from one end portion over the central portion to the other end portion. Further, EP-A-0 059 498 shows an absorptive device comprising a facing element, a support element, an absorbent core and a backsheet, especially the absorbent core is described as being any convenient material which absorbs and retains body fluid. For example there is disclosed creped cellulose wadding and airlaid comminuted good pulp fibers. A thermal treatment occurs only when different layers are bonded together. It is disclosed that the facing element of this prior art device comprises a fluid permeable unbonded web of thermal plastic fibers and there are special bonding regions where this facing element is bonded to a support element. In the US-A-4 610 685 there is disclosed special bonding regions where the different layers are bonded together at marginal portions by means of thermally fusing the fibers of adjacent layers. US-A-3 886 942 discloses a sanitary napkin comprised of an inner core of absorbent material and a cover. The absorbent material can be of conventional shape and side and can be of any of those materials ordinarily used in sanitary napkin applications such as wood pulp fluff, cellulose wadding, cotton or rayon fibers etc.. The cover consists essentially of a porous web of unfinished thermoplastic fibers which web is prepared to have a loop-like arrangement of the fibers, wherein a certain amount of fibers are arranged as parallel filaments. The filaments of the webs are bonded together at a discrete number of spot bond areas distributed intermittently throughout the web. However, the absorbent panel of prior art still has a problem remaining unsolved, concerning the shape holding ability and there has often occurred so-called shape loss during use of the associated garments particularyl in the proximity of the user's crotch in which the panel is affected by a deforming force due to movement of the user. Accordingly, it is an object of the invention to provide an absorbent panel positioned in the proximity of the user's crotch but so constructed that the portion being inevitably prone to said deforming force due to the user's movement is more resistive to the shape loss than the remaining portion of the absorbent panel. SUMMARY OF THE INVENTION The object set forth above is achieved, in accordance with the present invention in an absorbent panel for body fluid absorptive garments formed from a mixture of fibrous or granular liquid-absorptive material and thermoplastic fibers this mixture being pressed substantially to a uniform thickness, said absorbent panel comprising a crotch zone and a remaining zone, by the measure that said thermoplastic fibers are welded to each other with a welding density of their cross points adjusted to be higher at least in the crotch zone in order to provide a higher tensile strength in said crotch zone. Preferably, the welding density of said thermoplastic fibers in zones extending from the both sides of the crotch zone therealong to longitudinally opposite ends also is adjusted to be higher than in the remaining zone so that said zones also have a tensile strength correspondingly higher than that in said remaining zone. The absorbent panel constructed according to the invention as has been mentioned above is well resistive to a significant shape loss particularly in the crotch zone even under a deforming force due to the user's movement and eliminates discomfort to wear as well as decrease in absorptivity due to the shape loss, since said crotch zone has a higher tensile strength. The particular zones of the absorbent panel inclusive of said crotch zone have a relatively high rigidity because these particular zones have the higher tensile strength, but the remaining zone has a relatively low tensile strength and, in average, a comfort to wear can be assured. BRIEF DESCRIPTION OF THE DRAWINGS The invention will become more readily apparent from the following description of a preferred embodiment thereof shown by way of example only, in the accompanying drawings, in which: Fig. 1 is a plan view of an absorbent panel for disposable diaper constructed as an embodiment of the invention; Fig. 2 is a plan view showing another embodiment of the absorbent panel; Fig. 3 is a plan view of the absorbent panel having top and bottom surfaces covered with tissue paper; and Fig. 4 is a sectional view taken along a line X - X in Fig. 3. PREFERRED EMBODIMENT OF THE INVENTION Referring to Fig. 1, an embodiment of the absorbent panel constructed in accordance with the invention is shown in a plan view. The absorbent panel 1 is composed of fluffy pulp, water absorptive polymer granules and thermoplastic crimped fibers mixed together, and presents so-called hourglass-shape formed along both sides of a crotch zone with notches 2. The absorbent panel 1 is formed by compressing the above-mentioned mixed material substantially to a uniform thickness wherein said thermoplastic crimped fibers are welded together at their cross points so that the absorbent panel 1 has a thickness restoring ability of 30% or higher with respect to its compressed state when its water absorption reaches a saturation point. Furthermore, in the absorbent panel 1, a welding density of cross points of said thermoplastic climped fibers is adjusted to be higher in the crotch zone 3 adapted to be positioned in the proximity of the corresponding zone of the associated garments such as disposable diaper or disposable training pants when it is put on a user's body than the other zone 4 so that the absorbent panel 1 presents a tensile strength higher in said crotch zone 3 than in the remaining zone 4. Said thermoplastic crimped fibers may be composite film of two components having different melting points such as polyethylene-polypropylene or polyethylene-polypropylene-polyethylene composite film which was treated by a scratching roller provided therearound a plurality of scratching needles to produce short fibers which were then crimped by heat treatment, or may be polyethylene-polypropylene composite fibers of side-by-side type or sheath-core type which was crimped by heat treatment. Such givers extend in three dimensional direction and entangle together, forming a three dimensional network structure among said fulffy pulp and polymer granules, wherein said fibers are welded to each other with the density of their cross points through the low m.p. component such as the polyethylene component and supported by the high m.p. component such as polypropylene serving as a framework. This network structure has a high compression elasticity and siginificantly contributes to the thickness restoring by water absorption of the absorbent panel 1. For such contribution, it is essential not only that the fibers are crimped and partially welded together to form the three dimensional network structure by also that amount and finess of these fibers are appropriate. The appropriate amount of the fibers is 10 to 70% by weight and preferably 30 to 40% by weight. So far as the ability of thickness restoring from the compressed state is concerned, the amount of the fibers should be increased. However, it is critical to assure a desired amount of said fluffy pulp and polymer granules providing a water holding function within the absorbent panel 1 and therefore the maximum amount of the fibers should be limited to 70% by weight. The appropriate finess is 3d or higher and preferably 10 to 50d. Crimping may be effected by said heat treatment or by a mechanical treatment, for example, by guiding the fibers between heating rollers having therearound relieves and grooves, respectively. The number of crimps is preferably ca 1,2 to 15,7/cm (3 to 40/inch) and the fiber length is preferably 30 to 60mm. Said fluffy pulp may be obtained by crushing or fibrillation of pulp sheet with use of a garnet or the like so as to obtain fibers having a length less than 5mm. The amount thereof to mixed is 10 to 70% by weight and preferably 20 to 55% by weight. Said polymer granules may be those commonly employed by the disposable diaper, menstrual napkin, etc. on account of their water-insolubility and significant water holding function. Useful polymer granules may be, for example, of those such as hydrolyte of bridged polyacrylate and acrylic acid-acrylic acid ester copolymer or of self-bridging polyacrylate-starch acrylonitril graft copolymer. The amount thereof to be mixed is 5 to 50% by weight and preferably 10 to 40% by weight. These polymer granules may be bonded integrally with the fibers so that the crimped fibers forming the three dimensional network structure are intermittently covered with the polymer granules in spherical or elliptical shapes or the fibers extend through spherical or elliptical polymer granules which are intermittently distributed in the panel. Such bonding is effected, for example, by spraying the fibrous assembly with liquid monomers for polymerization. The absorbent panel 1 composed of the mixed material as has been mentioned above will be preferably of 100 to 700 g/m² when it is associated with, for example, disposable diaper or disposable training pants. In addition, the absorbent panel 1 assembled from said mixed material is preferably compressed in the direction of its thickness in the presence of a small amount of water or aqueous solution of binder so that the absorbent panel 1 has a density of 0.033 to 0.7 g/cm³. To assure that the welding dendity of said thermoplastic crimped fibers is higher in the crotch zone 3 than in the remaining zone of the absorbent panel and the correspondingly higher tensile strength than in the remaining zone 4, after said mixed material has been compressed, the crotch zone 3 of the absorbent panel 1 may be, for example, subjected to hot air blasting at a predetermined temperature while the remaining zone 4 may be substantially protected against the effect of such hot air blasting. It should be understood that this heat treatment may be utilized also to achieve the same effect as the previously mentioned crimping of the fibers by heat treatment. In the embodiment shown by Fig. 2, the welding density of said thermoplastic crimped fibers in not only the crotch zone 3 but also zones 5 extending from the laterally both sides of the crotch zone 3 therealong to longitudinally opposite ends is adjusted to be higher than in the remaining zone 6 so that said zones 5 also have a tensile strength higher than in the remaining zone 6. Referring to Figs. 3 and 4, the top and bottom surfaces of the absorbent panel 1 as shown by Fig. 1 or 2 and having been subjected to said heat treatment are covered with sheets of tissue paper 7 having water absorptivity and diffusibility, and these sheets of tissue paper 7 are heat sealed along peripheries therof. This construction resulting in improving the shape hold of the absorbent panel 1 and, if desired, this assembly may be embossed from above the sheets of tissue paper at desired locations of the absorbent panel 1 for further improvement of the shape hold as well as the tensile strength. Though not shown, particularly in the crotch zone 3 required to have a high absorptivity, the content of said mixed material used in this zone 3 may be increased with respect to the remaining zone and then the absorbent panel 1 may be subjected to a substantially uniform compression in the direction of its thickness.

Claims: An absorbent panel (1) for body fluid absorptive garments formed from a mixture of fibrous or granular liquid-absorptive material and thermoplastic fibers this mixture being pressed substantially to a uniform thickness, said absorbant panel (1) comprising a crotch zone (3) and a remaining zone (4), being characterized in that said thermoplastic fibers are welded to each other with a welding density of their cross points adjusted to be higher at least in the crotch zone (3) in order to provide a higher tensile strength in said crotch zone (3). The absorbent panel as recited in claim 1, wherein said welding density of said thermoplastic fibers in zones extending laterally and longitudinally from both sides of the crotch zone (3) to the opposite ends of the absorbent panel also is adjusted to be higher in these zones than in the rest zone of the remaining zone (4). The absorbent panel as recited in claim 1 or 2, wherein said thermoplastic fibers have been crimped.

Inventors: IGAUE TAKAMITSU, NOMURA HIRONORI, SHINOHARA JUNJI, SHIROTO TSUTOMU, TANJI HIROYUKI, IGAUE, TAKAMITSU, NOMURA, HIRONORI, SHINOHARA, JUNJI, SHIROTO, TSUTOMU, TANJI, HIROYUKI
Applicants: UNI CHARM CORP, UNI-CHARM CORPORATION
Application year: 1991
Main classification: A61F13
IPC codes: A41B9, A61F13