Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Composite having voids in a component
Reexamination Certificate
1998-05-22
2001-07-17
Lovering, Richard D. (Department: 1712)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Composite having voids in a component
C425S00400R, C264S045200, C264S045300, C427S244000, C428S317100, C428S317700
Reexamination Certificate
active
06261679
ABSTRACT:
BACKGROUND OF THE INVENTION
In the manufacture of absorbent articles, it is desirable to employ materials having high void volume, a hydrophilic nature, and wet resiliency, or the ability to maintain void volume when wet and when under load. Traditional fluff pulp and creped tissue offer high void volume and are hydrophilic, but they collapse when wetted, especially if a load is applied. Wet laid materials in general suffer from high density due to the largely two-dimensional, planar arrangement of fibers. Air laid materials can have high bulk, but are limited in their stability and resiliency and still have definite limits in porosity and bulk.
Many nonwoven materials made from long synthetic fibers offer high void volume and wet resiliency, but lack inherent hydrophilicity. The fibers can be treated with surfactants or other additives to increase the hydrophilicity of the structure, but such processes are expensive and do not provide the same level of affinity for water offered by cellulose or other hydrophilic polymers. Open cell plastics or plastic foams, also referred to as expanded or sponge plastics, can offer very high void volume and wet resiliency, but suffer the same problem of lacking inherent hydrophilicity and have high cost. Foams made of hydrophilic materials, such as superabsorbent foams, offer the ability to absorb and retain liquids, but can suffer from poor wet resiliency or high cost. Fiber reinforced foams are known wherein fibers are added to increase the strength of a foam matrix, but such materials are generally hydrophobic and lack the high-bulk, absorbent attributes desired of an absorbent article.
Therefore, there is a need for a fibrous structure that has many desirable attributes of a foam, particularly an open-celled foam, but wherein the structure is primarily composed of hydrophilic fibers with fibers serving at least in part as the struts between the open cells.
SUMMARY OF THE INVENTION
It has been discovered that high-bulk fibrous materials suitable for absorbent articles can be made wherein the fibers are oriented in three dimensions. The fibers can be distributed in a substantially uniform distribution or in a substantially nonuniform distribution wherein the fibers serve as struts which define boundaries between three-dimensional void spaces, similar to the solid matrix of an open-cell foam and more particularly similar to the struts in a reticulated open-cell foam. It has also been discovered that known methods and materials for producing foams can be exploited as fiber-structuring tools for the placement, arrangement and binding of hydrophilic fibers, wherein the resulting absorbent fibrous structure has good integrity and resiliency. According to such methods, the fibers are mixed with a structuring composition having a binder material or precursor binding material that can be converted into a water-insoluble binding material, and a removable phase which can be removed from the fibrous mixture to define void spaces. The resulting structure is stabilized by the binder material which serves to hold fibers in place or to establish bonds, particularly water-insoluble bonds, between fibers. In one sense, a preferred embodiment of the invention can be described as a foam-reinforced fibrous network, in contrast to previously known fiber-reinforced foams. In other words, in many embodiments of the present invention, apart from the role played by binder materials in holding fibers together, the components of the structuring composition or foam play a relatively minor structural role in the final absorbent material, once the fibers have been properly positioned and bound.
In another embodiment, the binder material is added to a foamable structuring composition after the fibers have been structured by the foam. Thus, the fibers can be mixed with a structuring composition comprising a removable phase and a non-gaseous phase, and after production of foam, the binder material can be added or, alternatively, a precursor binder material in the structuring composition can be converted to a binder material to provide water-insoluble bonds between fibers in an open, absorbent fibrous structure.
As with traditional open-celled foams, the absorbent fibrous structures of the present invention are generally “open,” meaning that the void spaces within the absorbent fibrous structure are substantially interconnected and permit gas transport, analogous to the open nature of open-cell foams. Specifically, an open structure can have at least 50% of the void space in the structure occupied by interconnected voids, and more specifically at least 80% of the void space occupied by interconnected voids. The materials of the present invention are also generally substantially gas permeable, meaning that gas can pass relatively freely through the absorbent fibrous structure in at least one direction, desirably in two orthogonal directions, more desirably in three orthogonal directions, and most specifically in substantially any direction. In one embodiment, the materials of the present invention have a Frazier permeability (hereafter defined) of at least about 50 cfm, more specifically about 100 of more, more specifically still about 200 cfm or more, and most specifically about 400 cfm or more, with an exemplary range of about 75 cfm to about 1100 cfm. In some embodiments, however, the absorbent fibrous structure may have a skin, such as a film of binder material, on one or more surfaces which is liquid or gas impervious, while the interior of the absorbent fibrous structure remains substantially open (apart from any flow restriction caused by the outer skin). For best results in absorbent articles and filters, if a skin exists, at least one portion of the outer surface of the absorbent fibrous structure should be free of either a liquid or gas impervious skin.
Possible uses of the present invention include absorbent articles for intake, distribution, and retention of human body fluids. Examples include feminine care pads, tampons, diapers, incontinence articles, training pants, bed pads, sweat absorbing pads, shoe pads, bandages, helmet liners, wipes and wipers, etc., or, in a suitably thin and flexible form, as a novel tissue or towel. A valuable benefit of many embodiments of the present invention is its ability to maintain a three-dimensional structure and maintain stability under stress and when wet. Thus, a wide variety of shaped composites can be envisioned, including tampons, shock-absorbing shoe pads, articles adapted for particular portions of garments or the body, gaskets for ostomy bags, hemostatic sponges and other medical sponges and absorbents for surgical purposes, dental absorbents such as plugs for extracted teeth or saliva absorbents to fit in portions of the mouth, and the like. Besides serving as absorbent articles, materials of the present invention can serve as components in filters, including filters for absorbing liquid droplets and other entrained materials in the air, including face masks. Filters made with the absorbent fibrous structures of the present invention can be particularly useful when they comprise activated carbon fibers or granules. Such filtration materials are capable of absorbing pollutants or odors from gases and organic pollutants from liquids, particularly water. The absorbent fibrous structures of the present invention can also be used in additional products such as shock absorbing pads, groundcover materials, erosion barriers, pads for absorbing pet waste, industrial spill and leak absorbents, floating barriers for oil spills and chemical containment, fireproofing materials, insulation, packaging materials, padding, and the like. The absorbent fibrous structures of the present invention can also be combined with other functional materials internally (as by adding material into the absorbent fibrous structure) or externally (as by joining with additional layers) such as odor absorbents, activated carbon materials, fire retardants, superabsorbent particles, nonwoven materials, plastic films or apertured films, extruded webs,
Chen Fung-Jou
Li Yong
Lindsay Jeffrey Dean
Qin Jian
Croft Gregory E.
Kimberly--Clark Worldwide, Inc.
Lovering Richard D.
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