Elastic absorbent structures

Details Elastic absorbent structures Elastic absorbent structures

1998-11-20

2002-03-26

Weiss, John G. (Department: 3761)

Surgery

Means and methods for collecting body fluids or waste material

Absorbent pad for external or internal application and...

C604S364000, C604S368000, C604S373000, C604S385160

Reexamination Certificate

active

06362389

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to nonwoven elastic absorbent materials having improved conformability at low levels of loading. More specifically, the invention relates to a combination of nonwoven elastomeric filaments, pulp fibers and a superabsorbent material, having greater flexibility and conformability than conventional elastomeric absorbent materials.
BACKGROUND OF THE INVENTION
Elastomeric absorbent materials have been evaluated in a variety of personal care structures including, without limitation, diapers, training pants, sanitary napkins, wipes, bibs, wound dressings, and surgical caps or drapes. U.S. Pat. No. 5,645,542 issued to Anjur et al., discloses an elastomeric absorbent structure made from a combination of thermoplastic elastomer fibers and wettable staple fibers. The reference discloses useful ranges of about 20-80% by weight staple fibers, and about 20-80% by weight elastomeric fibers, with intermediate amounts being preferred. Useful staple fibers include wood pulp fibers, modified cellulose fibers, textile fibers such as cotton or rayon, and substantially nonabsorbent synthetic polymer fibers.
The patent to Anjur et al. also discloses that a hydrogel-forming polymer can be added to increase the absorbency. The hydrogel-forming polymer may constitute about 15-60% by weight of the structure, with intermediate amounts being preferred.
Conventional elastic absorbent materials typically stretch under a fairly high tensile load, and tend to recover to an unstretched state when the load is relaxed or released. The relatively high retractive force associated with these structures is often unnecessary, and is sometimes undesirable. For instance, a high retractive force present in a personal care article may cause the article to have an uncomfortably tight fit. Also, a high retractive force may reduce the absorbency of an article by physically inhibiting the swelling of an absorbent material contained within the article.
For these reasons, there is a need or desire for an elastic nonwoven absorbent material which is more conformable and has less retractive force. There is also a need or desire for a less expensive elastic nonwoven absorbent material which requires lower amounts of the elastic filament ingredient, and relatively greater amounts of a less expensive absorbent material.
SUMMARY OF THE INVENTION
The present invention is directed to a conformable, comfortable, and highly absorbent elastic nonwoven material which addresses the foregoing concerns. The absorbent nonwoven material of the invention includes a mixture of nonwoven elastomeric polymer filaments, absorbent fibers, and superabsorbent particles or fibers. The elastomeric polymer filaments may be substantially continuous or staple in length, and preferably are substantially continuous. The nonwoven elastomeric polymer filaments constitute less than 20% by weight of the absorbent nonwoven material, and at least about 3% by weight of the absorbent nonwoven material. The absorbent fibers and superabsorbent particles or fibers each constitute about 20-77% by weight of the absorbent nonwoven material.
The absorbent nonwoven material of the invention can be stretched to at least about 110% of its original unstretched length, using a lower tensile load per basis weight than similar composite materials containing higher elastic filament levels. This low stretching force also means there is less retractive force when the absorbent nonwoven material is stretched. The low stretching force, and corresponding low retractive force, causes absorbent articles made from the material to have better comfort and better absorption. The improved absorption is attributed, in part, to the fact that there is less elastic restraint on the swelling of the superabsorbent polymer ingredient.
The absorbent nonwoven material of the invention is also relatively inexpensive to produce, because the lower amount of elastomeric polymer filaments permits inclusion of a correspondingly higher amount of the less expensive pulp fibers. Also, the absorbent nonwoven material of the invention exhibits better wicking than conventional elastomeric absorbent materials.
DEFINITIONS
The term “nonwoven fabric or web” means a web having a structure of individual fibers or filaments which are interlaid, but not in an identifiable manner as in a knitted fabric. The terms “fiber” and “filament” are used herein interchangeably. Nonwoven fabrics or webs have been formed from many processes such as, for example, meltblowing processes, spunbonding processes, air laying processes, and bonded carded web processes. The term also includes films that have been perforated or otherwise treated to allow air to pass through. The basis weight of nonwoven fabrics is usually expressed in ounces of material per square yard (osy) or grams per square meter (gsm) and the fiber diameters are usually expressed in microns. (Note that to convert from osy to gsm, multiply osy by 33.91. ) The term “microfibers” means small diameter fibers having an average diameter not greater than about 75 microns, for example, having an average diameter of from about 1 micron to about 50 microns, or more particularly, having an average diameter of from about 1 micron to about 30 microns.
The term “spunbonded fibers” refers to small diameter fibers which are formed by extruding molten thermoplastic material as filaments from a plurality of fine capillaries of a spinnerette having a circular or other configuration, with the diameter of the extruded filaments then being rapidly reduced as by, for example, in U.S. Pat. No. 4,340,563 to Appel et al., U.S. Pat. No. 3,692,618 to Dorschner et al., U.S. Pat. No. 3,802,817 to Matsuki et al., U.S. Pat. No. 3,338,992 and 3,341,394 to Kinney, U.S. Pat. No. 3,502,763 to Hartman, U.S. Pat. No. 3,502,538 to Petersen, and U.S. Pat. No. 3,542,615 to Dobo et al. Spunbond fibers are quenched and generally not tacky on the surface when they enter the draw unit, or when they are deposited onto a collecting surface. Spunbond fibers are generally continuous and may have average diameters larger than 7 microns, often between about 10 and 30 microns.
The term “meltblown fibers” means fibers formed by extruding a molten thermoplastic material through a plurality of fine, usually circular, die capillaries as molten threads or filaments into converging high velocity heated gas (e.g., air) streams which attenuate the filaments of molten thermoplastic material to reduce their diameter, which may be to microfiber diameter. Thereafter, the meltblown fibers are carried by the high velocity gas stream and are deposited on a collecting surface to form a web of randomly dispersed meltblown fibers. Such a process is disclosed for example, in U.S. Pat. No. 3,849,241 to Butin et al. Meltblown fibers are microfibers which may be continuous or discontinuous, are generally smaller than 10 microns in diameter, and are generally self bonding when deposited onto a collecting surface. Meltblown fibers used in the invention are preferably substantially continuous.
The term “polymer” generally includes but is not limited to, homopolymers, copolymers, including block, graft, random and alternating copolymers, terpolymers, etc. and blends and modifications thereof. Furthermore, unless otherwise specifically limited, the term “polymer” shall include all possible geometrical configurations of the material. These configurations include, but are not limited to isotactic, syndiotactic and atactic symmetries.
The term “substantially continuous filaments or fibers” refers to filaments or fibers prepared by extrusion from a spinnerette, including without limitation spunbonded and meltblown fibers, which are not cut from their original length prior to being formed into a nonwoven web or fabric. Substantially continuous filaments or fibers may have lengths ranging from greater than about 15 cm to more than one meter; and up to the length of the nonwoven web or fabric being formed. The definition of “substantially continuous filaments or fibers” includes those which are not cut prior t

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