Absorbent structure with improved absorption properties

Details Absorbent structure with improved absorption properties Absorbent structure with improved absorption properties

1999-08-10

2002-10-15

Ruhl, Dennis (Department: 3761)

Surgery

Means and methods for collecting body fluids or waste material

Absorbent pad for external or internal application and...

C604S375000, C604S378000

Reexamination Certificate

active

06465710

ABSTRACT:

TECHNICAL FIELD
The present invention pertains to an absorbent structure in an absorbent article such as a diaper, an incontinence protector, a sanitary napkin or the like, which structure exhibits two end portions and a crotch portion located therebetween, wherein the absorbent structure comprises superabsorbent material having a thermo-reversible liquid absorption capacity.
BACKGROUND OF THE INVENTION
In current absorbent articles such as diapers, sanitary napkins or the like, only approximately 60% of the total liquid absorption capacity of the absorbent body is utilized. Therefore, it has long been a wish to be able to increase the degree of utilization of the absorption capacity in the absorbent body.
An absorbent body of an absorbent article exhibits two end portions, and a crotch portion located therebetween. The crotch portion is the part of the diaper which is intended to be arranged at the narrowest region between the thighs of the user during use, and is the area of the diaper which is expected to be wetted by excreted body fluid first. Since the area which the liquid reaches first is constituted by a relatively limited area of the total absorbent structure, this implies that the area is rapidly saturated with liquid. Therefore, it is important that the liquid rapidly can be distributed from this area to the remaining parts of the absorbent structure. However, a small portion of the liquid always remains within the area around the wetting site, without being able to be distributed further to the remaining parts of the absorbent structure. Therefore, it is of great significance that the area of the absorbent structure which initially is wetted has the ability to retain the liquid which is not distributed out into the absorbent structure, so that rewetting, i.e. passage of liquid back out from the article, is avoided.
In order to obtain high absorption capacity in an absorbent body, absorbent articles of the above-mentioned sort usually contain superabsorbent materials. Superabsorbents are polymers with the ability to absorb liquid in a quantity many times their own weight. Furthermore, they have the ability to retain absorbed liquid even when they are subjected to an external pressure. The efficiency of such superabsorbents is dependent on many factors, such as where and how the superabsorbent is mixed into the absorbent body, which physical form the superabsorbent has, and physical and chemical properties such as absorption rate, gel strength, and liquid retention.
A phenomenon which is referred to as gel-blocking may negatively affect the absorption capacity of a fibre structure containing superabsorbents. Gel-blocking means that the superabsorbent forms a gel during wetting which blocks the pores in the fibre structure and thereby renders the transport of liquid from the wetting area to the remainder of the absorbent body difficult. This results in a poor utilization of the total absorption capacity of the absorbent body and, furthermore, results in an increased risk of leakage.
In order to increase the degree of utilization of the total capacity of the absorbent structure, and in order to prevent gel-blocking, the absorbent structure usually exhibits a number of layers with mutually different properties with regard to, among other things, absorption rate, liquid distribution and liquid retention.
For instance, it is previously known through EP 0,202,125 to have a lower content of superabsorbent material in an upper liquid receiving layer of an absorbent body, i.e. a layer intended to be facing a user, than in a lower part of the absorbent body. Accordingly, the liquid passes through the receiving layer without being absorbed by this and is brought further downwards in the absorbent structure. Thus, an advantage with this design is that the liquid is stored in the lower part of the absorbent body, which implies that the upper layer, closer to the user, substantially remains free from liquid. Another advantage of this previously known design is that the liquid also has time to be distributed from the wetting site out to the end portions of the article, since it takes a certain time for the liquid to reach the superabsorbent. This results in a higher utilization of the total liquid absorbing capacity of the absorbent article. However, a problem with such a design is that there is a risk that the upper absorbent structure is perceived as wet when repeated wettings occur, since it only has the ability-to retain a limited liquid quantity.
Furthermore, it is previously known through EP 0,343,941 to build up the absorbent body of three different layers, namely, a receiving layer, a liquid-distributing layer and a liquid-storing layer. The first layer, the receiving layer, consists of a hydrophillic structure with a wetting area which has a lower density than the remaining areas of the receiving layer. By means of this design of the absorbent body, with a more open structure having a lower density in the wetting area that in the remaining absorbent structure, a rapid liquid absorption of large liquid quantities is obtained within the wetting area. Thereafter, the liquid is distributed via the liquid-distributing layer and is absorbed by the liquid-storing bottom layer. With such a design of the absorbent body, it is true that a relatively rapid liquid admittance is obtained. On the other hand, the problem remains that the upper structure in the wetting area of the article has difficulty in retaining liquid when subjected to repeated wettings, something which results in increased rewetting and, accordingly, an increased risk of a wet surface closest to the user.
Still another disadvantage with the previously known absorbent structure is that it is complicated to manufacture since it consists of several different materials which have different densities in different portions.
SUMMARY OF THE INVENTION
However, by means of the present invention an absorbent structure of the sort mentioned in the introduction has been achieved, exhibiting a higher degree of utilization of the total liquid absorption capacity of the structure. By means of the invention an absorbent structure which exhibits an increased liquid-retaining ability in the wetting area of the article has also been achieved.
Furthermore, the risk of gel-blocking, with entailing impairment of the liquid distribution pattern and increased risk of leakage, is reduced by means of the invention.
According to the invention, this has been achieved by means of an absorbent structure comprising a superabsorbent material having a thermo-reversible liquid absorption capacity, located in one or several delimited areas in the absorbent structure.
According to a preferred embodiment, the superabsorbent material having a thermo-reversible liquid absorption capacity is primarily located in the crotch portion of the structure.
According to one embodiment, the thermo-reversible superabsorbent is constituted by a polymer, exhibiting a thermo-reversible liquid absorption capacity. A polymer which exhibits a thermo-reversible liquid absorption capacity is characterized in that the polymer changes geometrical configuration at a certain temperature, whereby the hydrophillic and hydrophobic groups of the polymer, respectively, take up another position, resulting in a substantial change of the liquid absorption capacity of the polymer. Accordingly, thermo-reversible polymers exhibit a cloud point at a certain temperature, C
p
, at which the liquid absorption capacity of the polymer is changed. For those polymers which have been found to be suitable for the purpose, the cloud point C
p
occurs within the temperature interval 30-37° C., preferably within the temperature interval 32-35° C.
The liquid absorbtion capacity-of the intended polymers is lower at a temperature above 32-35° C., than at a temperature below 32-35° C. Since the body fluid initially has a temperature which is approximately 37° C., this implies that the body fluid, when reaching the absorbent structure, passes the thermo-reversible superabsorbent without being absorbed by i

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