Surgery – Means and methods for collecting body fluids or waste material – Absorbent pad for external or internal application and...
Reexamination Certificate
1998-09-29
2002-05-14
Weiss, John G. (Department: 3761)
Surgery
Means and methods for collecting body fluids or waste material
Absorbent pad for external or internal application and...
C604S378000, C604S358000
Reexamination Certificate
active
06388166
ABSTRACT:
The present invention relates to disposable absorbent articles such as diapers, incontinence articles, sanitary towels, training pants and the like, and in particular to the control of their hydration effect on the human skin.
BACKGROUND OF THE INVENTION
Disposable, absorbent articles such as diapers, incontinence articles, sanitary towels, training pants and the like are well know in the art. Typically, disposable absorbent articles comprise a liquid previous topsheet that faces the wearers body, a liquid impervious backsheet that faces the wearers clothing, an absorbent core interposed between the liquid previous topsheet and the backsheet, and means to keep the core in fixed relation to the wearers body.
The absorbent core needs to be capable of acquiring, distributing, and storing discharges initially deposited on the topsheet of the absorbent article. Preferably the design of the absorbent core is such that the core acquires the discharges substantially immediately after they have been deposited on the topsheet of the absorbent article, with the intention that the discharges do not accumulate on or run off the surface of the topsheet, since this may result in inefficient fluid containment by the absorbent article which may lead to wetting of outer garments and discomfort for the wearer. After the insult, it is an essential functionality of the absorbent article to retain the discharged fluids firmly so as to avoid over-hydration of the skin of the wearer. If the absorbent article is not well functioning in this respect, liquid coming from the absorbent core back to the skin—also often called “rewet”—can have detrimental effects on the condition of the skin, which can for example be observed by skin irritations.
There, have been many attempts to improve the fluid handling properties of absorbent articles or cores, in particular when further requirements were brought up such as a desired reduction of product bulkiness or thickness.
Several patent publications deal with such improvements by adding specially treated cellulosic material. For example U.S. Pat. No. 4,898,642 of Moore et al. discloses specially twisted, chemically stiffened cellulosic fibres and absorbent structures made therefrom. EP 0 640 330 (Bewick-Sonntag) et al. discloses the use of such fibres in a specific arrangement with specific superabsorbent materials. EP 0 397 110 (Latimer) discloses an absorbent article comprising a surge management region for improved fluid handling, having specific basis weights, acquisition times and residual wetness.
EP 0 312 118 (Meyer) discloses an absorbent article with a fibrous topsheet with larger pores than the pores of the underlying transport layer, which in turn has larger pores than the underlying absorbent body. Further, the transport layer has to have a hydrophilicity which is less than the one of the absorbent core, and may generally be characterized as being substantially hydrophobic.
In EP 0 312 118 it is said that some liquid might remain in the transport layer and in the topsheet, so as to cause a wet feel on the surface. In order to overcome this problem, it is proposed in EP 0 312 118 to exploit the resilient compressibility of the transport layer, such that in use under the pressure exerted by the baby, the pores become smaller and then can dry out the topsheet and transport the fluid away into the underlying absorbent body.
In accordance with the development direction of these various approaches, the tools to assess the performance of such structures were generally aiming at measuring the liquid transfer—either from the surface of the absorbent structure into the structure itself often referred to as the acquisition, or within the absorbent structure referred to as distribution.
On the other hand the rewetting from the absorbent structure has been tested, either by using in-vivo methods or by using laboratory tests.
The in-vivo methods have in common, that they assess directly the condition of the skin of the wearer of an absorbent article either under real in-use loadings or possibly with artificially loaded articles, which are for example worn on the forearm of a test person for a certain period.
Elsner et al. provides a comprehensive overview of such methods in “Bio-engineering of the: Water and Stratum Corneum”, CRC Press, 1994. The most relevant methods are the “Transepidermal Water Loss” (often abbreviated TEWL) measuring the moisture evaporation from the skin; methods to measure the electrical properties like capacitance, impedance, or conductance of the skin, which depend strongly on the moisture content, such as with the NOVAMETER (capacitance of skin) the CORNEOMETER or other instruments. Elsner further discusses in detail the negatives of both too dry and too wet (overhydrated) skin, and the risks of higher occurrence of skin irritations or even damages, which can be most easily detected by “redmarking” of the skin, in particular, when the over-hydration occurs in combination with mechanical stress such as chafing.
However, all in-vivo methods have in also common, that the comparison of absorbent structures or articles for development purposes is cumbersome. Apart from the fact of needing test persons as such, individual parameters of the test persons—such as varying reaction to certain room conditions as temperature or relative humidity—are responsible for a large variability in the test results. In order to still get meaningful data, the number of test persons must be increased to substantial amounts.
Hence, significant effort has already been put against evaluating absorbent articles and structures under reproducible and easy to execute laboratory conditions, whereby mostly the human skin is replaced by standardized fluid pick-up filter paper. Essentially, these methods are based on the “capillary rewet” principle, whereby a test sample is loaded with a certain amount of test fluid, such as synthetic urine. After a certain time such as to allow for equilibration and preferably under a certain pressure, the pick up filter paper as “skin replacement” is placed on top of the surface of the loaded structure for a certain time, under a certain pressure. The pick-up filter paper is well defined such as by porosity, basis weight, or absorbency. Due to the capillary forces of its pores, it is sucking up readily available moisture (i.e. “free” moisture not being bound such as through superabsorbent materials or in smaller pores than the ones of the pick-up paper) from the surface of the test specimen and the weight increase is a measure for the “rewet” performance of the absorbent article.
Optionally, this test procedure can be combined with other fluid handling evaluation protocols, for example a “post-acquisition-rewet-test” indicates, that during the first part of the combined protocol the fluid acquisition behaviour of the test specimen is studied, whereas the rewet assessment is then carried out in the second part of the test.
A number of such tests have been described, such as in WO 93/02 188 (Guidotti et al.); EP-0 039 974 (Mullane); EP 0 278 601 (Kobayashi); EP 0 539 703 (Hanson).
However, these tests have significant drawback, in so far as they are only sensitive to liquid moisture, which is present in capillaries larger then the capillaries of the pick-up medium. In particular upon development of better absorbent products, it has been found that not only the small amounts of liquid in relatively small pores (i.e. smaller than the pores of the filter pick up paper) can still contribute significantly to the overhydration of the skin of the wearer, but that also the moisture released by the skin itself in the form of sweat can have significant negative effects on overhydration of the skin, such as when covered with an impermeable material. This latter situation is often referred to as “occlusion”, and of particular relevance for the non-absorbent regions in the absorbent article, often referred to as “chassis” or “peripheral” elements.
Another approach to assess the performance of such articles has been proposed by Lask et al. in EP-B-312919,
Dominguez-Staedke Jose
Herrlein Mathais Kurt
Lankhof John Peter
Olliver Ivan Jean
Robertson Muir Charles
Bogart Michael G
Cunningham Joan B.
Miller Steven W.
Patel Ken K.
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