Surgery – Means and methods for collecting body fluids or waste material – Absorbent pad for external or internal application and...
Reexamination Certificate
1999-07-20
2003-11-04
Lo, Weilun (Department: 3761)
Surgery
Means and methods for collecting body fluids or waste material
Absorbent pad for external or internal application and...
Reexamination Certificate
active
06642431
ABSTRACT:
TECHNICAL FIELD
The invention pertains to an absorbent, porous structure, intended for use in an absorbent article, wherein the structure exhibits a first region, primarily consisting of a first material, which stands in direct connection with a second region, primarily consisting of a second material.
BACKGROUND OF THE INVENTION
A large problem, in connection with the construction of absorbent bodies for absorbent articles of the discussed type, is to achieve an optimum combination of a sufficiently large liquid acquisition ability, sufficient local and total absorption capacity and sufficient liquid distribution ability. Furthermore, it is essential that the absorbent article is able to retain absorbed body fluid so that rewetting, i.e. liquid passage back out from the article, is avoided. Another important property of, above all, diapers and incontinence protectors is that the article repeatedly should be able to receive and absorb relatively large liquid quantities, emitted during a short period of time.
One type of commonly occurring absorbent bodies for absorbent articles consists of one or several layers of cellulose fluff pulp. When such an absorbent body is wetted, the region of the absorbent body which initially is hit by the liquid will absorb essentially all liquid. Thereby, this region is saturated with liquid and, when subsequent wettings occur, the absorbent body does not have sufficient capacity in order to receive all excreted body fluid. Accordingly, the liquid will flow out over the surface of the article and leak out over the edges of the article.
In order to remedy such leakage, it has been suggested to provide the absorbent body with compression patterns of different types and thereby to increase the liquid distribution ability of the article. One example of such a compression pattern is grooves which extend in the longitudinal direction of the article. In this way, it is possible to achieve a certain drainage of the initially wetted region on the absorbent body, since the finer capillaries in the compressed portions of the absorbent body transport liquid better than the surrounding portions of the absorbent body. Such capillary transport, however, takes place slowly and the draining of the wetted region of liquid will therefore often be incomplete and insufficient.
Another problem, in connection with compressed fibre structures, is that the compressed regions swell when wetted, whereas surrounding, less compressed regions often collapse. Thereby, the initial differences in capillary size in the structure are levelled out, and the liquid distribution ability of the fibre structure is impaired.
One way of avoiding that liquid flows out onto the surface of the absorbent body is to arrange two or more absorbent layers with mutually different properties on top of each other. For example in accordance with WO 93/15702, an upper layer, intended to be facing the user during use, may thereby consist of cellulose fluff pulp with a high critical bulk and a comparatively coarse capillary network, while a lower layer consists of a layer of cellulose fluff pulp with lower critical bulk and finer capillaries. Thereby, critical bulk refers to the bulk at which the fluff pulp neither swells nor collapses when wetted.
The intention with such a construction is that the liquid rapidly should be allowed into the upper, more porous layer, and then gradually be emptied of liquid by means of the upper layer being drained by the finer capillaries in the lower layer. The expectation is that the upper layer should be sufficiently emptied of liquid in order to avoid leakage when the absorbent body once again is hit by body fluid. However, it has been found that in practice this will not work as expected. The reason for this is that the surface properties of the fibres in the two cellulose fluff layers are such that liquid drainage from the upper layer to the lower layer does not take place to the extent which might be expected from the difference in capillary size.
One type of cellulose fluff pulp with high critical bulk is chemi-thermomechanically manufactured fluff pulp, so-called CTMP. In a structure of the type which is disclosed in WO 93/15702, CTMP is combined with chemically manufactured fluff pulp, so-called CP, which has a lower critical bulk. Such pulps initially also exhibit a difference in hydrophilicity, or wettability, wherein CTMP is less hydrophillic than CP. Such a difference in hydrophilicity facilitates the liquid transport in a direction from a region consisting of CTMP to a region consisting of CP.
During wetting, however, the surface properties of the cellulose fibres change, so that also cellulose fluff pulp which in a dry state exhibits low wettability instead becomes more hydrophillic. The reason for this, amongst other things, is that the surface-chemical properties of the pulp fibres are changed because a reorientation occurs at the fibre surfaces so that hydrophillic groups are concentrated, as a result of which the fibre surfaces become more wettable. Another reason, contributing to the changed surface properties, is that a change takes place also with regard to resins and other components, for example by means of certain components dissolving, while other, more hydrophillic components migrate towards the fibre surfaces.
SUMMARY OF THE INVENTION
By means of the present invention, however, an absorbent structure of the type mentioned in the introduction has been achieved in which the problems with liquid transfer between the regions in the absorbent body, consisting of absorption materials with different surface properties, have been essentially eliminated.
An absorbent structure according to the invention is primarily characterized in that the receding wetting angle &thgr;
r
, is larger for the first material than for the second material, as a result of which liquid transport between the two regions takes place in a direction from the first region to the second region when the porous structure is wet.
According to one advantageous embodiment, also the advancing wetting angle &thgr;
a
is larger for the first material than for the second material, as a result of which liquid transport takes place from the first region to the second region, irrespectively of whether the structure is dry or wet.
It is advantageous for the liquid transfer between the regions in the absorbent structure if the average pore size in the absorbent structure is larger within the first region with the first material than within the second region with the second material. Since, for example, a porous fibre material exhibits pores, or voids with different sizes within a size interval, it is impossible to define an exact pore size. The expression “average pore size” refers to an average of the size of the pores in the absorbent structure. Thereby, it is desirable that the majority of the pores have a size which is close to the average pore size. This implies that the pore size variation is small and that the liquid transportation properties of the structure are easier to predict, based on the knowledge of the average pore size.
According to one embodiment of the invention, the first region is constituted of a first layer in the absorbent structure, and the second region is constituted of a second layer in the absorbent structure, wherein the two layers stand in direct connection with each other via surfaces of the layers bearing on each other.
Alternatively, the two regions can be constituted of parts of the one and the same material layer. Thereby, the division of the material layer into different regions may be such that the first region and the second region are arranged next to each other in the plane of the material layer. However, it is also possible to design an absorbent structure according to the invention exhibiting a material layer where the two regions of material with different surface properties are arranged next to each other in the thickness direction of the material layer.
Still another possibility, within the scope of the, invention is to arrange a number of region
Chihani Thami
Fernkvist Maria
Gellerstedt Fredrik
Lo Weilun
SCA Hygiene Products AB
Young & Thompson
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