Continuous biaxially stretchable absorbent with low tension

Details Continuous biaxially stretchable absorbent with low tension Continuous biaxially stretchable absorbent with low tension

2001-12-18

2004-01-27

Lo, Weilun (Department: 3761)

Surgery

Means and methods for collecting body fluids or waste material

Absorbent pad for external or internal application and...

C604S385220, C604S385210, C604S385270

Reexamination Certificate

active

06682512

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention is generally related to absorbent cores of absorbent articles where the absorbent core is formed from one continuous piece of material and where the absorbent core has elastic properties at low tensions.
Absorbent articles are used for a variety of applications including disposable diapers, training pants, disposable swim pants, adult incontinence garments, feminine hygiene products, wound dressings and nursing pads. The “workhorse” of an absorbent article is the absorbent core, which is the portion of the article that collects and retains a targeted exudate. This workhorse component can be thick and bulky relative to the other components of the article. Consequently, the absorbent core can reduce the flexibility and conformability of the article, thereby compromising the fit of the article on or against a wearer. “Good” fit is generally understood to correlate with good performance of the absorbent article.
The absorbent cores of the invention overcome deficiencies associated with known absorbent cores. Technical advances and the resulting improvements in the materials available for use in absorbent articles have led to better-fitting absorbent articles. For example, many years ago leg elastics were introduced to disposable diapers to improve the fit of the diaper around the legs of the wearer and to have a gasketing effect. Subsequently, extensibility and elasticity have been proposed for other components of disposable diapers and other absorbent articles. Not to be overlooked, various constructions and designs have been proposed for making the absorbent core extensible or elastic. Depending on the overall configuration or construction of an absorbent article, it can be beneficial to incorporate “stretch” into the absorbent core. Benefits include improvement of overall fit provided by virtue of the bulkiest component being more flexible and by virtue of not inhibiting any stretch or flexibility that may be possessed by other components of the absorbent article.
Generally speaking, when a material is “extensible”, it is understood that the length or another dimension of the material can be increased with application of a force. The same can be said about a material that is described as being “elastic”. The fundamental difference between “extensibility” and “elasticity” is the degree to which the material retracts once the force causing increase in length or other dimension is released. Extensible materials do not return to their original length or dimension as much as elastic materials. Extensible and elastic materials can be selected for almost every component of an absorbent article, including the absorbent core. Various considerations go into selecting such materials for a particular absorbent article design: the magnitude of elongation that the material is capable of; the force required to achieve that magnitude of elongation; the magnitude of retraction experienced by the material upon removal of the force and the speed with which the material retracts. Once the materials are selected for each component of the absorbent article, the materials must all work together to provide an article that is easy to apply, fits comfortably and performs its intended function.
The materials used to form the components of absorbent articles can be made extensible or elastic by building extension-capacity into the material (such as by necking or creping) or by incorporating an elastic material (such as LYCRA elastic strands) into the material. The actual components of an absorbent article (e.g. the outer cover, the liner, the containment flaps etc.) can also be made extensible or elastic by building extension-capacity into the component (such as by pleating or segmentation) or by incorporating an elastic material into the component. Generally speaking, materials and components are selected and designed to readily provide elongation or stretch without application of much force. Otherwise, the absorbent article would be difficult to use or uncomfortable to wear.
Attempts have been made to build extensibility or elasticity into the absorbent cores of absorbent articles. Those attempts have included both the building-in of extension capability and the incorporation of elastic materials. One way to “build-in” extension capability is to break the typical length of the absorbent core down into free-moving segments. A segmented absorbent core will typically have greater extensibility than a continuous piece or unitary absorbent core. For example, if a unitary absorbent core that is six inches in length is modified to be a segmented absorbent core having six, one inch segments, the segmented absorbent core will have more inherent extensibility that the continuous (six inch long) absorbent core. Broken down into independent-moving increments, the segmented core has increased freedom of movement over a unitary absorbent core; the segmented core can more readily respond to the relative motion of outer cover and liner components that may be extensible or elastic. Despite the advantages provided by the segmented absorbent core, the performance of the absorbent core, vis-à-vis the ability to rapidly distribute and retain fluids, may be compromised. The “breaks” or “discontinuities” between segments of the core may interrupt the wicking of fluids. Consequently, while segmentation is one approach to build-in extensibility or elasticity, segmentation has its drawbacks.
Elasticity has been built-in to absorbent cores through the incorporation of elastic materials into the traditional superabsorbent plus fluff (wood pulp) mixture. For example, elastic materials like LYCRA elastic strands, have been incorporated with superabsorbent and wood pulp to form elastic absorbent cores; the result is an absorbent structure having the ability to extend and retract. In some executions, relatively high quantities of elastic materials (e.g. greater than 30%) have been incorporated into the absorbent structure. While such absorbent cores have definitive elastic properties, it is possible that their absorptive capacity is diminished. Absorptive capacity is potentially diminished because superabsorbent and wood pulp are significantly replaced by elastic materials. A potential outcome is that the absorbent core must be oversized to have an absorptive capacity equal to a non-elastic core; the extra bulk counteracts the benefits of flexibility and conformability provided by an elastic core.
When elasticity is built-in to absorbent cores, it is known that is desirable to have the absorbent core extend at low tension. That is to say, the absorbent core extends or elongates with the application of minimal force (or tension). Typically, the absorbent core of an absorbent article forms the central portion of the article and the other components are built around the absorbent core. If the absorbent core requires the application of a relatively high force to extend it, any extensible or elastic capacity built-in to the other components will be dwarfed. Therefore, it is desirable to have the central and bulkiest component capable of elongating with the application of a relatively low force. In some applications, the absorbent core is capable of elongating under low tension and the absorbent core retracts almost completely (i.e. more than 90%) upon release of the force. While near total retraction is indicative of the elasticity of a component, near complete retraction may not be desirable. The force to elongate an absorbent article or components of an absorbent core is typically applied by the wearer or caregiver during the application of the article. It can be desirable for the article to form some “memory” of the elongation during application and to not completely or nearly completely retract. Some “set” (i.e. less than complete retraction) of the elastic components of the article can be desirable to provide customized fit of the article to an individual wearer. Less than total or near total retraction by the elastic components can also impart a more comfortable fit to the absorbent

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