Thin until wet structures for acquiring aqueous fluids

Details Thin until wet structures for acquiring aqueous fluids Thin until wet structures for acquiring aqueous fluids

2000-09-20

2004-06-08

Cole, Elizabeth M. (Department: 1771)

Fabric (woven, knitted, or nonwoven textile or cloth, etc.)

Coated or impregnated woven, knit, or nonwoven fabric which...

Coated or impregnated natural fiber fabric

C442S409000, C442S412000, C442S413000, C442S153000, C428S913000

Reexamination Certificate

active

06746976

ABSTRACT:

TECHNICAL FIELD OF THE INVENTION
This application relates to materials suitable for use in articles directed to absorbing body fluids. The application particularly relates to materials capable of rapidly acquiring aqueous fluids (e.g., urine, menses, etc.) and preferably releasing such fluids to fluid distribution and storage materials.
BACKGROUND OF THE INVENTION
The development of highly absorbent articles for use as disposable diapers, adult incontinence pads and briefs, and catamenial products such as sanitary napkins is the subject of substantial commercial interest. The ability to provide high performance absorbent articles such as diapers has been contingent on the ability to develop relatively absorbent cores or structures that can acquire, distribute and store large quantities of discharged body fluids, in particular urine where a wearer may expel a large quantity of fluid very quickly (typically called a “gush”) and, at the sane time, provide desirable fluid handling properties so as to keep the wearer's skin dry and comfortable. These three functions can be accommodated by specific portions of the absorbent articles optimized for each. An acquisition material (or layer) is designed to take in fluid rapidly during a gush. The acquisition material also has sufficient capillary pressure to pull residual fluid away from adjacent layers (e.g., a topsheet). The gush fluid is stabilized prior to being given up to the distribution material. An optional distribution material (or layer) has sufficient capillary pressure (described in more detail below) to pull fluid away from the acquisition member and distribute it toward the front and rear of the absorbent article, often against the force of gravity to a height of 10-20 cm according to the size of the core. The storage member (or layer) has the highest capillary pressure and may comprise hydrogel-forming absorbent polymers or HIPE-derived hydrophilic absorbent foams to pull the fluid away from any distribution layer that may be present and store the fluid “permanently” away from the skin of the wearer.
Significant effort has been devoted towards the development of superior fluid acquisition and storage components. For example, U.S. Pat. No. 4,898,642 (Moore et al.) issued Feb. 6, 1990, U.S. Pat. No. 4,888,093 (Dean et al.) issued Dec. 19, 1989, U.S. Pat. No. 5,137,537 (Herron et al.), U.S. Pat. No. 5,217,445 (Young et al.), issued Jun. 8, 1993, and U.S. Pat. No. 4,822,453 (Dean et al.) describe curly, stiffened fibers that, when formed into low density webs, do not collapse when wet and retain their ability to acquire fluids at high rates as is experienced in a “gush” situation during urine voiding. Certain types of polymeric foams have been used in absorbent articles for the purpose of actually imbibing, wicking and/or retaining aqueous body fluids. See, for example, U.S. Pat. No. 3,563,243 (Lindquist), issued Feb. 6, 1971 (absorbent pad for diapers and the like where the primary absorbent is a hydrophilic polyurethane foam sheet); U.S. Pat. No. 4,554,297 (Dabi), issued Nov. 19, 1985 (body fluid absorbing cellular polymers that can be used in diapers or catamenial products); U.S. Pat. No. 4,740,520 (Garvey et al.), issued Apr. 26, 1988 (absorbent composite structure such as diapers, feminine care products and the like that contain sponge absorbents made from certain types of super-wicking, crosslinked polyurethane foams). U.S. Pat. No. 5,563,179 (Stone et al.) issued Oct. 8, 1996, describes hydrophilic absorbent foams useful for acquiring and distributing aqueous fluids in, e.g., absorbent cores. Similarly, various nonwoven materials have been proposed for fluid acquisition. Of key importance is the ability of these materials to acquire fluids repeatedly in use, to survive storage in a compressed state, and to release the acquired fluid to a subsequent fluid distribution or storage material.
The desirability of reducing the bulk of an absorbent article in the crotch area thereof is also well known. For example commonly assigned U.S. Pat. No. 5,549,589, issued to Horney, et al. on Aug. 27, 1996, commonly assigned U.S. Pat. No. 5,800,416, issued to Seger, et al. on Sep. 1, 1998, and copending, commonly assigned U.S. patent application Ser. No. 08/825,072, filed Mar. 27, 1997 by G. Young et al., Ser. No. 08/825,071, filed Mar. 27, 1997 by G. LaVon et al., and Ser. No. 08/826,208, filed Mar. 27, 1997 by G. Young et al. are all directed to materials that distribute acquired body fluids from the crotch area of an absorbent article to other parts of the absorbent article which allows a reduction in crotch size.
The art has also recognized the desirability of keeping the crotch area of an absorbent article as thin as possible.
U.S. Pat. No. 5,779,860, issued to Hollenberg, et al. on Jul. 14, 1998 describes through air dried tissue structures that are said to expand substantially when wetted. The tissue structures comprise chemithermomechanical pulp and a wet strength resin and are calendered to significantly increase density and reduce caliper. While the '860 patent states that the calendered web can increase in caliper 200 to 600% when fully wetted or saturated, such increased caliper is determined by saturating the web with no confining pressure, drying the web, and measuring the caliper of the dried web. While such increases may be substantial, they are not predictive of the performance of a material useful as a component of a core in an absorbent article where any fluid insult will typically happen while the core is under pressure (e.g., due to the wearer sitting or lying down). Such wearer-applied pressure results in a need to expand against such a confining pressure.
U.S. Pat. No. 5,877,097, issued to West, et al. on Mar. 2, 1999 describes densified webs comprising cellulose fibers and a bonding agent that are formed at a low density and compressed to a higher density. The webs are said to have an absorbent capacity that is superior to prior densified and bonded webs. While such webs may have superior absorbent capacity (on a gram of fluid/gram of absorbent basis), there is no indication that the webs can acquire such fluids quickly enough for use as an acquisition member or that such webs would be able to release acquired fluids to other components for ultimate storage.
The art has also considered sponges as an expansive absorbent medium. For example, a sanitary napkin is described in U.S. Pat. No. 3,512,530, issued to Jones on May 19, 1970, where a compressed regenerated cellulose sponge layer is bonded to a larger fibrous cellulose layer to form a multi-ply absorbent core. The compressed regenerated cellulose sponge layer is positioned over the fibrous layer, and it is typically centered about it; it is intended as the primary absorbent element of the sanitary napkin, while the fibrous layer acts as a secondary or back up absorber. The sanitary napkin described therein is said to be thin prior to use, as compared to other sanitary products having the same absorbent capacity. However, because the sponge layer is intended to provide the primary absorbent capacity, fluid would only wick into the backup fibrous layer after the sponge is substantially saturated with resulting risk of rewet because the underlying layer does not absorb fluid from the sponges.
In another use of sponges, EP Patent 293 208 B1, granted to the Lion Corporation on Jul. 24, 1991, describes the use of multiple layers of compressed regenerated cellulose sponge sheets in a sanitary napkin as the sole absorbent material. Because the sponge serves as the sole absorbent material in the sanitary napkin, the focus is on providing multiple layers of sponge material for softness and there is no recognition therein of the importance of the fluid handling properties that are necessary for a material to be suitable for use as an acquisition material in an absorbent article.
There have also been several attempts to create a fluid-activated acquisition zone in absorbent articles by taking advantage of the swelling of hydrogel-forming absorbent polymers in

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