Fabric (woven – knitted – or nonwoven textile or cloth – etc.) – Nonwoven fabric – Including an additional nonwoven fabric
Reexamination Certificate
1999-01-19
2002-11-12
Cole, Elizabeth M. (Department: 1771)
Fabric (woven, knitted, or nonwoven textile or cloth, etc.)
Nonwoven fabric
Including an additional nonwoven fabric
C442S385000, C442S389000, C442S393000, C442S416000, C442S417000
Reexamination Certificate
active
06479415
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to improved fibrous absorbent structures having separate layers for fluid acquisition, distribution , and storage. The acquisition layer contains latex-bonded synthetic fibers, and is useful in providing improved disposable absorbent products, such as diapers, adult incontinence pads, and sanitary napkins.
BACKGROUND OF THE INVENTION
Absorbent articles such as disposable diapers, adult incontinence pads, sanitary napkins, and the like, are generally provided with an absorbent core, or storage layer, to receive and retain bodily liquids. The absorbent core is usually sandwiched between a liquid pervious top sheet, whose function is to allow the passage of fluid to the core, and a liquid impervious backsheet which contains the fluid and prevents it from passing through the absorbent article. An absorbent core (e.g., for diapers and adult incontinence pads) typically includes fibrous batts or webs constructed of defiberized, loose, fluffed, hydrophilic, cellulosic fibers. The core may also include superabsorbent polymer (SAP) particles, granules, flakes or fibers. In addition, an absorbent article may contain a distribution layer that aids in transporting liquid quickly from the acquisition layer to the storage layer of the core.
In recent years, market demand for thinner and more comfortable absorbent articles has increased. Such articles may be obtained by decreasing the thickness of the diaper core, by reducing the amount of fibrous material used in the core while increasing the amount of SAP particles, and by calendering or compressing the core to reduce caliper and hence, increase density. However, higher density cores do not absorb liquid as rapidly as lower density cores because densification of the core results in smaller effective pore size. Accordingly, to maintain a suitable liquid absorption rate, it is necessary to provide a lower density layer having a larger pore size above the high density absorbent core to increase the rate of uptake of liquid discharged onto the absorbent article. The low density layer is typically referred to as an acquisition layer.
The storage layer portion of a disposable diaper core for example, is generally formed in place, during the converting process, from loose, fluffed cellulose. Superabsorbent powder is blended with the fluff cellulose fibers as the absorbent core is formed on the diaper converting line. Such cellulose material is generally not available in preformed roll form because it exhibits insufficient web strength, due to the lack of interfiber bonding or entanglement.
The acquisition layer portion of a disposable diaper is generally a carded synthetic staple fiber web that is thermally bonded, latex bonded, or point bonded. Typical staple fibers for acquisition layers are crimped polyester (PET) or polypropylene fibers that have a size of 6 to 15 denier and a length of at least 40 mm. The acquisition layer is formed, bonded and slit as a homogenous rolled good on a dedicated nonwoven textile production line. The slit roll of acquisition layer material is subsequently unrolled onto the diaper converting line where it is affixed on top of the absorbent core and below the topsheet. Examples of commercial infant diapers with a bonded carded staple fiber are Huggies Diapers produced by Kimberly-Clark Corp. (Dallas, Tex.) and private label diapers produced by Paragon Trade Brands (Atlanta, Ga.).
Modern infant disposable diaper converting machines have become extremely complex as more and more features such as elastication and multiple nonwovens have been implemented to improve diaper performance. This complexity has created significant raw material handling issues and a resultant loss of converting line productivity. There is a need to replace the bulky and cumbersome fluff pulp and superabsorbent powder forming systems with a single material that can simply be fed directly into the converting line from a roll or other suitable compact package. Because the acquisition layer and absorbent core are placed together in the final product, it can maximize the efficiency of the converting operation to combine the fluid acquisition layer and the absorbent core in a single material.
Ultra-thin feminine napkins are generally produced from roll-goods based nonwoven material. Such a roll of preformed absorbent core material is unwound directly onto the absorbent article converting equipment without the defiberization step required for fluff-based products, such as diapers and incontinence pads. The nonwoven web is typically bonded or consolidated in a fashion that gives it sufficient strength to be handled in the converting process. The web may also contain SAP particles.
The web consolidation mechanisms used in the roll-goods approach to making preformed cores provide strength and dimensional stability to the web. Such mechanisms include latex bonding, bonding with thermoplastic or bicomponent fibers or thermoplastic powders, hydroentanglement, needlepunching, carding, or the like.
One embodiment of a structure having an acquisition layer and a distribution layer (an “ADL”) typically found on die-cut feminine hygiene pads is an airlaid cellulose web bonded with an aqueous binder resin that has been dried and cured. Airlaid materials typically retain up to 16 g of fluid per gram of material against gravity under negligible load. Thus, an ADL can acquire a surge of fluid within the absorbent product until the superabsorbent particles in the absorbent core can absorb the retained fluid out of the airlaid cellulose ADL and into final storage containing superabsorbent particles.
An example of a conventional airlaid cellulose material is Vicell 6002 (Buckeye Technologies Inc., Memphis Tenn.), which is a 105 gsm (grams per square meter) airlaid cellulose non-woven bonded with a vinyl acetate binder resin. Vicell 6002 is prepared by spraying an aqueous emulsion of the vinyl acetate binder resin onto the airlaid cellulose web followed by drying and curing in a hot air oven. It is used commercially in an ADL for feminine hygiene pads.
The disadvantage of certain commercially available airlaid cellulose structures is that they may collapse under normal use. This typically occurs when the structure is compressed by the weight of the wearer and particularly when the structure becomes wet. This structural collapse significantly reduces the fluid acquisition rate of the absorbent product and thus increases the chance of leakage. When a completely or partially fluid saturated airlaid cellulose structure collapses, the fluid escapes from the ADL and the product feels wet against the wearer's skin.
There is a need for thin absorbent core material which facilitates fluid transport from an acquisition zone to a storage zone, has a high absorbent capacity in use, and can be delivered in roll-goods form to simplify the manufacturing and converting processes.
Applicants have now surprisingly discovered an improved ADL containing at least two discrete layers, the top and the bottom layer, which overcomes the above-described disadvantage of commercially available products. The top layer (i.e., the layer in contact with the skin of wearer) of the ADL of the present invention is highly porous, thus preventing the collapse of the structure and minimizing the leakage problem.
SUMMARY OF THE INVENTION
The present invention provides a highly absorbent, high-bulk low density article having an absorbent structure comprising a liquid acquisition and, optionally, a distribution layer and a fibrous liquid storage layer in communication with the acquisition layer. The storage layer contains SAP particles, latex-bonded fibers, thermally bonded-fibers, or a combination thereof.
In one embodiment, the invention relates to an improved acquisition and distribution layer (ADL) having at least two layers for use in disposable absorbent products, a top (acquisition) layer in contact with the wearer of the absorbent product, and a bottom (distribution) layer between the top layer and a storage layer. Thus, according to one a
Baer Samuel Charles
Erspamer John P.
Li S. K. Laurence
BKI Holding Corporation
Cole Elizabeth M.
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