Sanitary napkin with improved liquid retention capability

Details Sanitary napkin with improved liquid retention capability Sanitary napkin with improved liquid retention capability

2000-01-04

2003-02-04

Lewis, Aaron J. (Department: 3761)

Surgery

Means and methods for collecting body fluids or waste material

Absorbent pad for external or internal application and...

C604S383000, C604S385101

Reexamination Certificate

active

06515195

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to sanitary absorbent articles and in particular to such articles, for example sanitary napkins which are thin, yet highly absorbent.
BACKGROUND OF THE INVENTION
Sanitary absorbent articles find wide and varied use in absorbing and trapping body fluids and maintaining body surfaces in a state of dryness and comfort. The development of materials having a high liquid absorption capacity per unit volume has allowed the required overall thickness of sanitary absorbent articles to be reduced providing products which are more comfortable and less obtrusive to wear. Such articles find use, for example in feminine protection devices such as sanitary absorbent napkins. Thin sanitary napkins are generally constructed of multiple layers of material each having a particular function, as for example disclosed in U.S. Pat. No. 5,575,786 to T. W. Osborne III. The sanitary napkin disclosed in this document includes a top sheet which is placed nearest the body surface of the wearer, a first absorbent layer which may function as an acquisition or transfer sheet with a relatively open structure having a relatively high void volume for accepting fluid and transporting fluid to a second absorbent layer which serves as the main dispository for liquid absorbed by the napkin. The napkin also has a barrier sheet which is impervious to liquid absorbed into the second absorbent layer and serves as a protective barrier between the second absorbent layer material and the wearers clothing. The second absorbent layer has a high liquid absorption capacity relative to the top and first absorbent layers and can be made from materials such as wood pulp, creped cellulose wadding, absorbent foams and sponges, polymeric fibres and polymeric gelling agents. The average thickness of the napkin disclosed in U.S. Pat. No. 5,575,786 is less than 2.6 mm.
A problem which confronts designers of sanitary absorbent napkins is their ability to retain the absorbed liquid when subjected to mechanical loads as would be applied by the wearer in use. When subjected to such loading, liquid can leak from the second absorbent layer and rewet the layers above through which liquid was originally passed to the second absorbent layer. As the first absorbent layer and the cover layer are made from materials with little absorption capacity, the liquid expelled from the second absorbent layer will tend to reside next to the body surface of the wearer resulting in discomfort and possible staining of the wearers garments.
There is therefore a need for a thin sanitary absorbent article with an improved ability to retain liquids under load.
According to the present invention there is provided a sanitary napkin adapted to be worn in the crotch portion of an undergarment comprising a fibrous fluid permeable, body facing cover layer and an absorbent system adjacent said cover layer for receiving liquid therefrom, said napkin having a thickness of less than or equal to 5 mm, a capacity of at least 18 grams, a rewet potential of less than or equal to 0.8 grams, and a flexural resistance of less than 700 grams.
The “rewet potential” as used herein is a measure of the ability of the absorbent article to retain liquid when subjected to mechanical pressure and is defined and determined according to the procedure described in detail below. The “thickness”, the “capacity” and the “flexural resistance” of an absorbent article as used herein are also defined and determined in accordance with the test procedures described in detail below.
The inventors have found that a thin sanitary absorbent article can be made having surprisingly good rewet characteristics relative to its absorption capacity.
Preferably, the sanitary napkin has a rewet potential of less than 0.8 grams and more preferably a re-wet potential of less than 0.3 grams.
In a preferred embodiment, the absorbent system includes superabsorbent material, such as superabsorbent polymer. In one embodiment, the absorbent system comprises a blend of cellulosic fibers and superabsorbent material.
In a preferred embodiment, the absorbent system includes first absorbent layer underlying the cover layer for transferring liquid from the cover layer to a second absorbent layer. In a preferred embodiment, the first absorbent layer comprises a material having a structure with relatively open pores for efficiently absorbing liquid from the cover layer and transferring the liquid to the second absorbent layer. The first absorbent layer may comprise a material having a density in the range from about 0.04 to 0.05 g/cc, a basis weight of between about 80 to 110 g/m
2
and a thickness in the range of about 2 to 3 mm.
Advantageously, the absorbent system includes a second absorbent layer having a basis weight from about 100 g/m
2
to about 700 g/m
2
which has been air-laid as a bottom layer of pulp, a middle layer of pulp and superabsorbent polymer disposed in amongst the pulp, and a top layer containing at least some pulp. The second absorbent layer preferably has a density of more than about 0.25 g/cc and more preferably from about 0.3 to 0.4 g/cc.
Preferably, the second absorbent layer includes from about 5 weight percent to about 60 weight percent superabsorbent polymer, and more preferably in the range of about 30 to 40 weight percent superabsorbent polymer. The second absorbent layer preferably has a basis weight in the range from about 150 g/m
2
to about 350 g/m
2
and more preferably in the range from about 200 g/m
2
to about 300 g/m
2
.
In a preferred embodiment, the napkin has at least one and preferably a plurality of spaced-apart elongate channel formations arranged to direct liquid therealong for subsequent absorption into the first absorbent layer. The channels may be formed in the cover layer and/or the first absorbent layer and/or between the two.
The channel(s) may extend obliquely of the longitudinal axis and may be linear or arcuate.
The inventors have found that the provision of channels has a significant affect in reducing the rewet potential. The channels serve to distribute liquid over the surface or near surface portion of the napkin away from the initial deposition site so that liquid is presented for absorption to the first absorbent layer over a large proportion of its surface area. This increases the effectiveness with which the second absorbent layer is able to draw and retain liquid from the first absorbent layer.
Advantageously, the channel(s) may be formed by applying pressure to localized regions of the napkin, for example by embossing, which has the simultaneous effect of densifying the material at the floor of the channel, making it less pervious to liquid and thereby enabling liquid to flow further along the channel before being absorbed.
In a preferred embodiment, the sanitary absorbent napkin comprises a barrier layer which is substantially adjacent the second absorbent layer and impervious to liquid absorbed by the second absorbent layer.


REFERENCES:
patent: 4610678 (1986-09-01), Weisman et al.
patent: 4795455 (1989-01-01), Luceri et al.
patent: 5267992 (1993-12-01), Van Tilburg
patent: 5466513 (1995-11-01), Wanek et al.
patent: 5514104 (1996-05-01), Cole et al.
patent: 5830555 (1996-05-01), Sirinivasan
patent: 5562645 (1996-10-01), Tanzer et al.
patent: 5575786 (1996-11-01), Osborn, III
patent: 6007528 (1996-12-01), Osborn, III
patent: 5609588 (1997-03-01), DiPalma et al.
patent: 0 781 537 (1997-07-01), None

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