Absorbent articles for absorption of body fluids such as menses or blood are well known in the art, and comprise for example feminine hygiene articles such as sanitary napkins, panty liners, tampons, interlabial devices, as well as wound dressings, and the like. When considering for example sanitary napkins, these articles typically comprise a liquid-pervious topsheet as wearer-facing layer, a liquid-impervious backsheet as garment-facing layer and an absorbent core between topsheet and backsheet. The body fluids are acquired through the topsheet and subsequently stored in the absorbent core. The backsheet prevents the absorbed fluids from wetting the wearer's garment.
An absorbent core can comprise one or more fibrous absorbent material, which in turn can comprise natural fibers, such as for example cellulose fibers, typically wood pulp fibers, synthetic fibers, or combinations thereof, as known in the art, either as combination of different fibrous layers, e.g. batts or nonwovens or tissue layers, each constituted of a selected fiber type, or comprising layers made of different natural and/or synthetic fibers. Said structures can comprise different individual layers joined or combined together, or alternatively can be structures prepared by forming different layers in a continuous process, as will be defined in more detail further on.
It is also widely known in the art that it is beneficial for the absorption and retention characteristics of absorbent articles when portions of the article, typically the absorbent core, comprise superabsorbent materials, such as absorbent gelling materials (AGM), usually in finely dispersed form, e.g. typically in particulate form. Superabsorbent materials known in the art for use in absorbent articles typically comprise water-insoluble, water-swellable, hydrogel-forming crosslinked absorbent polymers which are capable of absorbing large quantities of liquids and of retaining such absorbed liquids under moderate pressure. Absorbent gelling materials can be incorporated in absorbent articles, typically in the core structure, in different known ways; for example, absorbent gelling materials in particulate form can be dispersed among the fibers of fibrous layers comprised in the core, or rather localized in a more concentrated arrangement between fibrous layers, or also in pockets, as it is known in the art.
In general, absorbent articles comprising absorbent gelling materials commonly have good absorption and retention characteristics to body fluids like urine; however, there still remains room for improvement of absorption and retention towards other body fluids. In particular, menses and blood are particularly difficult to be effectively absorbed and retained into absorbent articles containing superabsorbent materials since said materials do not show optimal absorption and retention characteristics towards said body fluids.
Such not optimal absorption and retention are mainly caused by poor permeability of superabsorbent materials towards menses and blood as such, in turn due to the viscosity and/or to the complex nature of these fluids. Menses and blood in fact are water based fluids comprising higher molecular weight and also corpuscular components, including red cells, white cells, soluble proteins, cellular debris and mucus, which slow down the absorption of these fluids by superabsorbents. Menses and blood are rather thick, hence inherently more difficult to absorb in conventional absorbent structures comprising absorbent gelling materials; moreover, corpuscular components like red cells may decrease the absorption capacity of certain superabsorbent particles. This translates into a slower initial uptake rate of the fluid into the superabsorbent material, and in turn in the absorbent structure comprising the superabsorbent material, which can result in a lower final absorption and retention capacity.
Also when considering more in general fibrous absorbent materials, it is known that different fibers and different fibrous structures as well, show different behaviors and effectiveness towards body fluids, particularly towards menses and blood. For example, cellulose fibers, such as for example wood pulp fibers, show a greater absorption and diffusion capacity towards the water fraction of menses and blood, which may be very rapidly acquired and may be transported within the fibrous structure, far from the initial acquisition area, while the corpuscular and higher molecular weight components do not diffuse equally well, and may remain closer to the initial acquisition area. Such corpuscular and higher molecular weight components tend to travel preferentially in a direction perpendicular to the plane of the absorbent structure. Also, natural and synthetic fibrous materials can be more or less suitable to provide compact, or alternatively bulkier, absorbent structures to be employed in absorbent cores.
The tendency, in the last years, has been towards thinner and more effective absorbent structures, taking advantage of the combination of typically fibrous structures with superabsorbent materials. Said thinner structures in turn provide absorbent articles combining a better comfort, discreetness and adaptability.
While a great deal of different absorbent core structures with various combinations and arrangements of fibers and absorbent gelling materials are known, there is still the need for an improved absorbent core structure for an absorbent article, particularly for absorption of menses or blood, which takes advantage of the peculiarities of the different absorbent materials in the absorption and management of these complex body fluids, achieving a better result in terms of fluid acquisition and distribution, in a structure which is stably thin, or in any case does not significantly change (for example increase) its thickness upon absorption throughout its normal use.