US20060141891A1

US20060141891A1 - Absorbent structure with aggregate clusters

Info

Publication number: US20060141891A1
Application number: US11/021,043
Authority: US
Inventors: Shannon Melius; Jeffrey La Fortune; Michael Faulks; David Fell; Michael Venturino
Original assignee: Kimberly Clark Worldwide Inc
Current assignee: Kimberly Clark Worldwide Inc
Priority date: 2004-12-23
Filing date: 2004-12-23
Publication date: 2006-06-29
Also published as: MX2007007399A; WO2006071423A1; KR20070097449A

Abstract

An absorbent structure has a macro absorbent structure with a plurality of aggregate clusters intermixed therein. The aggregate clusters have a periphery, an interior, and thermoplastic binder fibers. The thermoplastic binder fibers have thermoplastic binder fiber ends. The thermoplastic binder fiber ends are located at the periphery of the aggregate clusters. The interior of the aggregate clusters are substantially free of thermoplastic binder fiber ends. The macro absorbent structure and the aggregate clusters may also include thermoplastic binder fibers, staple fibers, superabsorbent particles and the like. A method of making absorbent structures includes a first absorbent structure, dividing the first absorbent structure to create aggregate clusters, providing a stream of the aggregate clusters, providing polymeric fibers, merging the aggregate cluster stream and polymeric fiber stream into a single product stream, and making a second absorbent structure. The method may further include staple fibers, superabsorbent particles, and the like.

Description

BACKGROUND OF THE INVENTION

Disposable 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, nursing pads, bed pads, wipes, bibs, wound dressings, surgical capes or drapes, and the like. Such disposable absorbent products are generally suited to absorb many substances such as water and body exudates such as urine, menses, blood, and the like.
Some disposable absorbent articles are formed from densified cellulose intermixed with superabsorbent particles. Others are formed from high integrity absorbent structures containing high concentrations of superabsorbent particles entangled or otherwise commingled with long thermoplastic fibers and/or cellulosic fibers to improve fit, comfort, and/or performance. In general, the absorbent structures may be mechanically constrained or limited, particularly the high integrity structures, in such a way that the absorbent structure is not able to fully expand in the presence of liquids. Additionally, the high integrity absorbent structures may be expensive due to the addition of thermoplastic fibers.
Therefore, there exists a need for absorbent structures, including high integrity absorbent structures, that can expand more fully in the presence of liquids and are more cost effective to manufacture.

SUMMARY OF THE INVENTION

In response to the discussed needs, the present invention provides absorbent structures with aggregate clusters and methods of making absorbent structures with aggregate clusters.
In various embodiments, an absorbent structure includes a macro absorbent structure. The macro absorbent structure includes a plurality of aggregate clusters intermixed within the macro absorbent structure. The aggregate clusters have a periphery and an interior and include thermoplastic binder fibers having thermoplastic binder fiber ends. The thermoplastic binder fiber ends are located at the periphery of the aggregate clusters.
The interiors of the aggregate clusters are substantially free of thermoplastic binder fiber ends. The macro absorbent structure includes long thermoplastic binder fibers and superabsorbent particles constrained within the long thermoplastic binder fibers. In these embodiments, the aggregate clusters may include superabsorbent particles constrained within the thermoplastic binder fibers within the aggregate clusters, staple fibers constrained within the thermoplastic binder fibers within the aggregate clusters, or both superabsorbent particles and staple fibers constrained within the thermoplastic binder fibers within the aggregate clusters.
In various other embodiments, an absorbent structure includes a macro absorbent structure. The macro absorbent structure includes a plurality of aggregate clusters intermixed within the macro absorbent structure. The aggregate clusters have a periphery and an interior and include thermoplastic binder fibers have thermoplastic binder fiber ends. The thermoplastic binder fiber ends are located at the periphery of the aggregate clusters. The interiors of the aggregate clusters are substantially free of thermoplastic binder fiber ends. The macro absorbent structure includes long thermoplastic binder fibers and staple fibers constrained within the long thermoplastic binder fibers. In these embodiments, the aggregate clusters may include superabsorbent particles constrained within the thermoplastic binder fibers within the aggregate clusters, staple fibers constrained within the thermoplastic binder fibers within the aggregate clusters, or both superabsorbent particles and staple fibers constrained within the thermoplastic binder fibers within the aggregate clusters.
In yet other embodiments, an absorbent structure includes a macro absorbent structure. The macro absorbent structure includes a plurality of aggregate clusters intermixed within the macro absorbent structure. The aggregate clusters have a periphery and an interior and include thermoplastic binder fibers having thermoplastic binder fiber ends. The thermoplastic binder fiber ends are located at the periphery of the aggregate clusters. The interiors of the aggregate clusters are substantially free of thermoplastic binder fiber ends. The macro absorbent structure includes long thermoplastic binder fibers, superabsorbent particles constrained within the long thermoplastic binder fibers, and staple fibers constrained within the long thermoplastic binder fiber. In these embodiments, the aggregate clusters may include superabsorbent particles constrained within the thermoplastic binder fibers within the aggregate clusters, staple fibers constrained within the thermoplastic binder fibers within the aggregate clusters, or both superabsorbent particles and staple fibers constrained within the thermoplastic binder fibers within the aggregate clusters.
In yet other embodiments, an absorbent structure includes a macro absorbent structure. The macro absorbent structure includes a plurality of aggregate clusters intermixed within the macro absorbent structure. The aggregate clusters have a periphery and an interior and include thermoplastic binder fibers having thermoplastic binder fiber ends. The thermoplastic binder fiber ends are located at the periphery of the aggregate clusters. The interiors of the aggregate clusters are substantially free of thermoplastic binder fiber ends. The macro absorbent structure includes staple fibers and superabsorbent particles intermixed with the staple fibers. In these embodiments, the aggregate clusters may include superabsorbent particles constrained within the thermoplastic binder fibers within the aggregate clusters, staple fibers constrained within the thermoplastic binder fibers within the aggregate clusters, or both superabsorbent particles and staple fibers constrained within the thermoplastic binder fibers within the aggregate clusters.
In various embodiments, the aggregate clusters may have a greatest dimension of 0.5 mm to 20 mm and/or a weight percent of 20 to 50 percent. In various embodiments, the long thermoplastic binder fibers are elastic.
In one embodiment, a stabilized absorbent structure includes 5 to 50 weight percent meltblown polyolefin binder fibers having an average fiber length greater than 1 cm. The stabilized absorbent structure also has 1 to 50 weight percent cellulose fibers constrained within the polyolefin binder fibers. The stabilized absorbent structure also has 30 to 90 weight percent superabsorbent particles constrained within the polyolefin binder fibers. The stabilized absorbent structure also has 1 to 50 weight percent aggregate clusters. Each aggregate cluster has a periphery and an interior. The aggregate clusters include meltblown polyolefin binder fibers having meltblown polyolefin binder fiber ends. The aggregate clusters further include cellulose fibers constrained within the polyolefin binder fibers within the aggregate clusters. The aggregate clusters further include superabsorbent particles constrained in the polyolefin binder fibers within the aggregate clusters. The meltblown polyolefin binder fiber ends are located at the periphery of the aggregate clusters. The interiors of the aggregate clusters are substantially free of meltblown polyolefin binder fiber ends.
In another aspect, the present invention provides a method of making a stabilized absorbent structure. The method includes providing a first absorbent structure. The first absorbent structure includes long thermoplastic binder fibers. The method further includes dividing the first absorbent structure into aggregate clusters. The aggregate clusters are provided as a stream of aggregate clusters. The method includes providing a stream of extruded molten thermoplastic polymeric fibers. The aggregate clusters stream and the polymeric fiber stream are merged into a single product stream. The single product stream is collected on a forming surface to make a second stabilized absorbent structure including aggregate clusters. In various embodiments, the second stabilized absorbent structure including aggregate clusters may be used to produce a disposable absorbent article.
In various embodiments, the process further includes merging a stream of superabsorbent particles into the aggregate clusters stream, the polymeric fiber stream, or the single product stream.
In various embodiments, the process further includes merging a stream of wood pulp fibers into the aggregate cluster stream, the polymeric fiber stream, or the single product stream.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 representatively illustrates a perspective view of an exemplary absorbent article according to the present invention;
FIG. 2A representatively illustrates a cross-sectional view of a first alternative embodiment of the absorbent article of FIG. 1 taken along the line 2-2;
FIG. 2B representatively illustrates a cross-sectional view of a second alternative embodiment of the absorbent article of FIG. 1 taken along the line 2-2;
FIG. 3A is a light photomicrograph image of an exemplary macro absorbent structure containing aggregate clusters according to the present invention;
FIG. 3B is a Scanning Electron Micrograph image of a portion of the exemplary macro absorbent structure of FIG. 3A;
FIG. 4 is a Scanning Electron Micrograph image of an exemplary aggregate cluster according to the present invention;
FIG. 4A is a Scanning Electron Micrograph image of a cut thermoplastic binder fiber end;
FIG. 5 is a Scanning Electron Micrograph image of an exemplary aggregate cluster according to the present invention;
FIG. 6A representatively illustrates an embodiment of an aggregate cluster according to the present invention;
FIG. 6B representatively illustrates another embodiment of an aggregate cluster according to the present invention;
FIG. 6C representatively illustrates a further embodiment of an aggregate cluster according to the present invention; and
FIG. 7 is a partially schematic side elevation, partially in section, of a method and apparatus for producing the absorbent structure of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

In one aspect, the absorbent structures according to the present invention are suited to absorb many liquids, such as water, saline, and synthetic urine, and body liquids such as urine, menses, and blood, and are suited for use in disposable absorbent products such as diapers, adult and youth incontinent garments and pads, and bed pads; in catamenial devices such as sanitary napkins, interlabial pads, and tampons; and in other disposable absorbent products such as wipes, bibs, wound dressings, and surgical capes or drapes. For purposes of illustration, the absorbent structure of the present invention will be described as used in a disposable diaper. However, those skilled in the art will appreciate the many other uses available for this structure.
The absorbent structure of the present invention generally includes a macro structure and a micro structure. The micro structure comprises a plurality of aggregate clusters that form a component of the macro structure. The macro structure includes the aggregate clusters and may further include one or more of the following: staple fibers, long thermoplastic fibers, superabsorbent materials, and the like.
As used herein, the term “fiber” or “fibrous” is meant to refer to a particulate material wherein the length to diameter ratio of such particulate material is greater than about 10. Conversely, a “nonfiber” or “nonfibrous” material is meant to refer to a particulate material wherein the length to diameter ratio of such particulate material is about 10 or less.
As used herein, the term “virgin” refers to materials or fibers that are being introduced to the manufacturing process for the first time. The term “virgin” excludes fibers or materials that are “reclaimed” or “recycled”. As used herein, the terms “reclaim” or “recycle” refer to fibers, particles, aggregates, or materials that have previously been introduced to a manufacturing process, have been segregated because of defect or other reason, and have been reintroduced to the manufacturing process and/or a second manufacturing process. The recycled materials may be subjected to additional processing prior to reintroduction to the manufacturing process or the recycled material may be added to the manufacturing process in the condition in which it was removed.
As used herein, the term “wettable” refers to a fiber which exhibits a liquid (such as water, synthetic urine, or a 0.9 weight percent aqueous saline solution) in air contact angle of less than 90°. As used herein, the contact angle may be determined, for example, as set forth by Robert J. Good and Robert J. Stromberg, Ed., in “Surface and Colloid Science—Experimental Methods”, Vol. 11, (Plenum Press, 1979). Suitably, a wettable fiber refers to a fiber which exhibits a 0.9 weight percent aqueous saline solution in air contact angle of less than 90° at a temperature between about 0° C. and about 100° C. and suitably at ambient conditions, such as about 23° C.
As used herein, the term “staple fiber” is meant to refer to a natural fiber or a length cut from, for example, a manufactured filament. Such staple fibers are intended to act in the absorbent structure of the present invention as a temporary reservoir for liquid and also as a conduit for liquid distribution.
Suitably, the staple fibers used in the absorbent structures herein may range in length from about 0.5 millimeters (mm) to about 20 mm, and more suitably from about 1 mm to about 15 mm. In some embodiments, the staple fibers may be from 3 mm to 6 mm in length. In some embodiments, the staple fibers may be 1 to 2 mm. Staple fibers of these size characteristics help to impart desirable bulk, liquid acquisition, liquid distribution and strength characteristics, and/or desirable flexibility and resilience properties to the absorbent structures of this invention.
A wide variety of staple fiber materials can be employed in the absorbent structures described herein. Staple fibers useful in the present invention may be formed from natural or thermoplastic materials and may include cellulosic fibers such as wood pulp fibers and modified cellulose fibers, textile fibers such as cotton or rayon, and substantially nonabsorbent thermoplastic polymeric fibers.
For reasons of availability and cost, cellulosic fibers will frequently be preferred for use as the staple fiber component of the absorbent structures of this invention, for example wood pulp fibers. However, other cellulosic fiber materials, such as cotton fibers, may also be used as the staple fiber.
Another preferred type of staple fiber useful herein comprises substantially nonabsorbent, crimped thermoplastic polymeric fibers. The individual fibers of this type are in and of themselves substantially nonabsorbent. Thus, such fibers should be prepared from a thermoplastic polymer material which does not substantially swell or gel in the presence of liquids, such as urine or menses, typically encountered in disposable absorbent products. Suitable polymeric materials which may be used to prepare the staple fibers include polyesters, polyolefins, polyacrylics, polyamides, and polystyrenes. In some embodiments, the staple fibers are made of polyethylene, polypropylene, or polyethylene terephthalate.
The staple fibers used herein may also be crimped such that the resulting absorbent structure has the desired resilience and resistance to bunching during use in absorbent products. Crimped staple fibers are those which have a continuous wavy, curvy or jagged character along their length. Fiber crimping of this sort is described more fully in U.S. Pat. No. 4,118,531 issued Oct. 3, 1978 to Hauser, the entirety of which is incorporated herein by reference where not inconsistent.
Suitable wettable fibers may be formed from intrinsically wettable fibers or may be formed from intrinsically hydrophobic fibers having a surface treatment thereon which renders the fiber hydrophilic. When surface treated fibers are employed, the surface treatment is desirably nonfugitive. That is, the surface treatment desirably does not wash off the surface of the fiber with the first liquid insult or contact. For the purposes of this application, a surface treatment on a generally hydrophobic polymer will be considered to be nonfugitive when a majority of the fibers demonstrate a liquid in air contact angle of less than 90° for three consecutive contact angle measurements, with drying between each measurement. In other words, the same fiber is subjected to three separate contact angle determinations and, if all three of the contact angle determinations indicate a contact angle of liquid in air of less than 90°, the surface treatment on the fiber will be considered to be nonfugitive. If the surface treatment is fugitive, the surface treatment will tend to wash off of the fiber during the first contact angle measurement, thus, exposing the hydrophobic surface of the underlying fiber and will demonstrate subsequent contact angle measurements greater than 90°.
The wettable staple fibers are desirably present in an elastomeric absorbent structure of the present invention in an amount from 0 to about 80 weight percent, suitably from about 1 to about 50 weight percent, and more suitably from about 10 to about 40 weight percent wettable staple fiber. “Weight percent (wt %)” is based on the total weight of the materials present. For example, a 60 gram mixture consisting of 10 grams substance X, 20 grams substance Y, and 30 grams substance Z, would have 16.7 wt % X, 33.3 wt % Y, and 50 wt % Z.
It has been found that by including a thermoplastic binder fiber in an absorbent structure, the properties of the absorbent structure may be substantially improved, particularly as compared to an otherwise essentially identical absorbent structure not comprising a thermoplastic binder fiber. As used herein, the term “thermoplastic binder fiber” is meant to describe a material that softens when exposed to heat and which substantially returns to its original condition when cooled to room temperature. The thermoplastic binder fiber, when in the softened state, conforms around, entangles, constrains, or entraps those fibers or particles proximate the thermoplastic binder fiber to stabilize the absorbent structure.
As used herein, the term “constrain” refers to staple fibers and/or aggregate clusters and/or superabsorbent particles that are substantially immobilized, such that the staple fibers and/or aggregate clusters and/or superabsorbent particles, and/or other components are not free to substantially move or migrate within or without the web structure. Such constraining may be, for example, by autogeneous bonding, thermal deformation, entrapment, or by the entanglement of the thermoplastic fibers of the web structure. The thermoplastic binder fibers may be elastic or non-elastic.
The thermoplastic binder fibers may be long or short. As used herein, the term “long” means fibers that are greater than 6 mm. In some embodiments, the long fibers may be greater than 1 centimeter (cm), greater than 2.5 cm, greater than 50 cm, or greater than 100 cm in length. In some embodiments, the long thermoplastic binder fibers may be substantially continuous filaments or fibers. As used herein, the terms “substantially continuous” or “substantially continuously formed” 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 lengths greater than the length of the nonwoven web or fabric being formed. The definition of “substantially continuous filaments or fibers” includes those fibers which are not cut prior to being formed into a nonwoven web or fabric, but which are cut after the nonwoven web, article, or fabric are formed, such as when the absorbent article is cut into individual product units or divided into aggregate clusters. As used herein, the term “short” generally means less than about 6 mm.
As used herein, the terms “elastic” and “elastomeric” are used interchangeably to mean a material that is generally capable of recovering its shape after deformation when the deforming force is removed. Specifically, as used herein, elastic or elastomeric is meant to be that property of any material which, upon application of a biasing force, permits that material to be stretchable to a stretched, biased length, which is at least about 125 percent, that is about 1.25 times, its relaxed, unbiased length, and that will cause the material to recover at least 40 percent of its elongation upon release of the stretching, elongating force. A hypothetical example which would satisfy this definition of an elastomeric material would be a 10 centimeter sample of a material which is elongatable to at least 12.5 centimeters and which, upon being elongated to 12.5 centimeters and released, will recover to a length of not more than 11.5 centimeters. Many elastic materials may be stretched by much more than 25 percent of their relaxed length, and many of these will recover to substantially their original relaxed length upon release of the stretching, elongating force. This latter class of materials is generally beneficial for purposes of the present invention.
The term “recover” relates to a contraction of a stretched material upon termination of a biasing force following stretching of the material by application of the biasing force. For example, if a material having a relaxed, unbiased length of 10 centimeters were elongated 50 percent by stretching to a length of 15 centimeters, the material would have been elongated 50 percent and would have a stretched length that is 150 percent of its relaxed length. If this exemplary stretched material contracted, that is, recovered to a length of 11 centimeters after release of the biasing and stretching force, the material would have recovered 80 percent (4 centimeters) of its elongation.
Materials suitable for use in preparing thermoplastic elastomeric binder fibers include diblock, triblock, or multiblock elastomeric copolymers such as olefinic copolymers such as styrene-isoprene-styrene, styrene-butadiene-styrene, styrene-ethylene/butylene-styrene, or styrene-ethylene/propylene-styrene, such as those available from the Shell Chemical Company, under the trade designation KRATON elastomeric resin; polyurethanes, such as those available from Invista Corporation with offices in Wichita, Kans., U.S.A. under the trade name LYCRA; polyamides, such as polyether block amides available from Ato Chemical Company, under the trade name PEBAX polyether block amide; polyesters, such as those available from E. I. Du Pont de Nemours Co., under the trade name HYTREL polyester; or low molecular weight metallocene polyolefins, such as those available from ExxonMobil Chemical Company, having offices in Houston, Tex., U.S.A. under the trade name VISTAMAXX.
A number of block copolymers can be used to prepare the thermoplastic elastomeric binder fibers useful in this invention. Such block copolymers generally comprise an elastomeric midblock portion and a thermoplastic endblock portion. Suitable block copolymers and methods for synthesizing them are described in U.S. Pat. No. 5,645,542 issued Jul. 8, 1997 to Anjur et al. and U.S. Pat. No. 6,362,389 issued Mar. 26, 2002 to McDowall et al., the entireties of both are incorporated herein by reference where not contradictory.
Materials suitable for use in preparing non-elastic thermoplastic binder fibers include polyolefins such as polypropylene and polyethylene, polyamides, and polyesters such as polyethylene tetraphthalate. Other suitable thermoplastic polymers are described in U.S. Pat. No. 4,100,324 issued Jul. 11, 1978 to Anderson et al., the entirety of which is incorporated by reference where not contradictory.
The thermoplastic binder fiber may generally be formed from any thermoplastic composition capable of extrusion into fibers. A suitable thermoplastic binder fiber for the present invention comprises meltblown fibers. Such meltblown fibers are typically very fine fibers prepared by extruding liquefied, or melted, fiber-forming copolymer through orifices in a die into a high velocity gaseous stream. The fibers are attenuated by the gaseous stream and are subsequently solidified. For example, the resulting stream of solidified thermoplastic fibers can be collected as an entangled coherent fibrous mass on a screen disposed in the gaseous stream. Such an entangled fibrous mass is characterized by extreme entanglement of the fibers which results in a stabilized absorbent structure. This entanglement provides coherency and strength to the resulting web structure. For example, the dry strength of such a structure can be 6 Newtons per 50 mm or more and the wet strength can be 2 Newtons per 50 mm or more as measured by the tensile strength test disclosed in example 4 of U.S. publication 2004/0122394A1 to Fell et al. published Jun. 24, 2004, the entirety of which is incorporated herein by reference where not contradictory.
Such entanglement also adapts the web structure to constrain or entrap the wettable staple fiber, the aggregate clusters, the superabsorbent particles, or other components within the absorbent structure either during or after formation of the web structure. The thermoplastic fibers are generally entangled sufficiently that it is difficult if not impossible to remove one complete fiber from the mass of fibers or to trace one fiber from beginning to end.
The thermoplastic binder fiber used herein may be circular in cross section but may also have other cross-sectional geometries such as elliptical, rectangular, triangular, irregular or multi-lobal. The thermoplastic binder fiber is suitably wettable. The thermoplastic binder fiber may be made wettable by first preparing the thermoplastic binder fiber and then subsequently applying a hydrophilizing surface treatment to the fiber.
Alternatively, the thermoplastic binder fibers may be made wettable by adding a hydrophilic ingredient to the polymer prior to spinning. In general, any polymeric component capable of being polymerized with the thermoplastic component, capable of hydrophilizing the resultant copolymeric material to render it wettable, wherein the hydrophilizing component does not substantially affect the properties of the prepared fiber, is suitable for use in the present invention. Hydrophilizing polymeric components suitable for use in the present invention include, without limitation, polyethylene oxide or polyvinyl alcohol, as well as a wide variety of commercial hydrophilic surfactants.
The thermoplastic binder fibers are therefore desirably present in an absorbent structure of the present invention in an amount from about 1 to about 80 weight percent, from about 10 to about 50 weight percent, and from about 15 to about 30 weight percent, with all weight percents based on the total weight of the absorbent structure. The thermoplastic binder fibers are generally greater than about 1 cm in length, greater than about 10 cm in length, greater than about 50 cm, or may be substantially continuous. The thermoplastic binder fibers may be less than about 100 microns in average diameter, may be less than about 50 microns in average diameter, and may be less than about 30 microns in average diameter.
In various embodiments, the absorbent structure may include superabsorbent material, such as a hydrogel-forming polymeric material. The introduction of hydrogel-forming polymeric material into such an absorbent structure generally allows for the use of less wettable staple fiber, since the hydrogel-forming polymeric material generally has a higher liquid absorption capacity on a gram per gram basis than the wettable staple fiber. Moreover, such hydrogel-forming polymeric material is generally less pressure sensitive than wettable staple fiber. Thus, the use of the hydrogel-forming polymeric material generally allows for the production and use of a smaller, thinner disposable absorbent product. As such, the absorbent structure of the present invention may also optionally include a hydrogel-forming polymeric material either in the macro structure, micro structure, or both.
As used herein, “hydrogel-forming polymeric material” is meant to refer to a high absorbency material commonly referred to as a superabsorbent material. Such high absorbency materials are generally capable of absorbing an amount of a liquid, such as synthetic urine, a 0.9 weight percent aqueous saline solution, or bodily fluids, such as menses, urine, or blood, at least about 10, suitably about 20, and up to about 100 times the weight of the superabsorbent material at the conditions under which the superabsorbent material is being used. Typical conditions include, for example, a temperature of between about 0° C. to about 100° C. and suitably ambient conditions, such as about 23° C. and about 30 to about 60 percent relative humidity. Upon absorption of the liquid, the superabsorbent material typically swells and forms a hydrogel.
The hydrogel-forming polymeric material may be formed from an organic hydrogel material which may include natural materials, such as agar, pectin, and guar gum, as well as polyacrylate hydrogel polymers. Suitable hydrogels are taught in U.S. Pat. No. 5,645,542 issued Jul. 8, 1997 to Anjur et al., the entirety of which is incorporated herein by reference where not contradictory. Additionally, suitable hydrogel-forming materials are commercially available as FAVOR SXM-880 supplied by Degussa Superabsorbers with offices in Greensboro, N.C., U.S.A. and HYSORB 8800AD supplied by BASF with offices in Charlotte, N.C., U.S.A.
Suitably, the hydrogel-forming polymeric material is in the form of particles which, in the unswollen state, have maximum cross-sectional diameters within the range of from about 50 micrometers to about 1000 micrometers, preferably within the range of from about 100 micrometers to about 800 micrometers, as determined by sieve analysis according to American Society for Testing and Materials (ASTM) test method D-1921. It is to be understood that the particles of hydrogel-forming polymeric material falling within the ranges described above may comprise solid particles, porous particles, or may be agglomerated particles comprising many smaller particles agglomerated into particles falling within the described size ranges.
The hydrogel-forming polymeric material may additionally or alternatively comprise “coated” superabsorbent as taught in U.S. Pat. No. 6,387,749 issued May 14, 2002 to Reeves et al., the entirely of which is incorporated herein in its entirety where not contradictory.
The hydrogel-forming polymeric material is beneficially present in an absorbent structure in an amount of from about 0 to 90 weight percent, suitably in an amount of from about 20 to about 85 weight percent, and more suitably of from about 30 to about 80 weight percent, based on the total weight of the absorbent structure.
It has been found that by including aggregate clusters in an absorbent structure, the properties of the absorbent structure may be maintained or improved but at a lower overall manufacturing cost as compared to an otherwise essentially identical absorbent structure not comprising aggregate clusters. Although suitable for a wide range of absorbent articles, the absorbent structure of the present invention will be described, for purposes of illustration, in conjunction with a disposable diaper.
Referring to FIG. 1, a disposable diaper is shown generally at 26. The diaper 26 has a topsheet 28, a backsheet 30, and an absorbent structure 10 disposed between the topsheet 28 and the backsheet 30. FIGS. 2A and 2B are cross sectional views of two alternative examples of the disposable diaper of FIG. 1 taken along line 2-2. The disposable diaper 26 of FIG. 2A illustrates a macro absorbent structure 10 comprising long or substantially continuous thermoplastic binder fibers 12, staple fibers 14, superabsorbent particles 16, and aggregate clusters 18. In various embodiments, the macro absorbent structure may comprise long thermoplastic binder fibers, superabsorbent particles, and aggregate clusters, but no staple fibers outside the aggregate clusters. In various embodiments, the macro absorbent structure may include long or substantially continuous thermoplastic binder fibers, staple fibers, aggregate clusters, but no superabsorbent particles outside the aggregate clusters. In various embodiments, the macro absorbent structure may include long or substantially continuous thermoplastic binder fibers and aggregate clusters, but no superabsorbent particles, or staple fibers outside of the aggregate clusters.
The disposable diaper 26 of FIG. 2B illustrates an alternative exemplary macro absorbent structure 10 comprising staple fibers 14, superabsorbent particles 16, and aggregate clusters 18. In various embodiments, the macro absorbent structure may comprise only staple fibers and aggregate clusters in the macro absorbent structure.
As used herein, the term “aggregate clusters” refers to structures that are the collection of units into a mass; that are generally less than 2 cm in the greatest dimension; that form discrete parts of the macro absorbent structure; that have a periphery and an interior; that are held together by thermoplastic binder fibers having thermoplastic binder fiber ends at the periphery while the interior of the aggregate cluster is substantially free of thermoplastic binder fiber ends; that include superabsorbent particles, staple fibers, or both constrained within the thermoplastic binder fibers; and that require no additional bonding, cross-link polymerization, adhesive, or associating agent to maintain the structure.
In various embodiments, the aggregate clusters may additionally include cross-link polymerization, adhesive, associating agent, or the like, but such additional element is not required to maintain the physical structure of the aggregate clusters.
As used herein, the terms “end” or “ends” refer to the extreme or distal part lengthwise of a fiber. A fiber may have a natural end such as found in cellulose fibers, cotton fibers, and the like, or a fiber may have an end that is mechanically formed, for example, by cutting, crushing, breaking, pinching, nipping, and the like.
As used herein, the term “periphery” refers to the external boundary or surface of a body, such as an aggregate cluster. As used herein, the term “interior” refers to the volume defined by the periphery.
As used herein, the term “substantially free of ends” means having 5 or less thermoplastic binder fiber ends visible within the interior of the aggregate cluster. One way of determining whether the thermoplastic binder fibers in the interior of an aggregate cluster are substantially free of ends is to use a scanning electron microscope (SEM) or equivalent instrument. A suitable SEM is a model JSM-840 available from JEOL USA Inc. having offices in Peabody, Mass., USA.
FIG. 3A is a light photomicrograph produced using a NIKON brand digital camera model 8700. The image uses light transmitted through a portion of a macro absorbent structure, shown generally at 10. The image is produced at 4× magnification. The darker areas are aggregate clusters and are indicated generally by arrows. Two of the aggregate clusters are identified as 1 and 2.
FIG. 3B is an image from a SEM of a portion of the macro absorbent structure of FIG. 3A. The aggregate clusters 1 and 2 located in the macro absorbent structure 10 are generally outlined in dash line, for purposes of illustration.
FIG. 4 is an image from an SEM of one exemplary aggregate cluster according to the present invention shown generally at 18. The aggregate cluster 18 has a periphery 62 and an interior. The aggregate cluster 18 was manually removed from the absorbent structure containing the aggregate cluster 18 for inspection in such a way so as to minimize any disruption to the aggregate cluster structure. The periphery 62 can be examined at various magnifications to see the thermoplastic binder fiber ends 60. For example, at 150× magnification, a thermoplastic binder fiber end 60 can be seen in FIG. 4A.
FIG. 5 is a SEM image of one exemplary aggregate cluster shown generally at 18 according to the present invention that has been manipulated with a small probe to expose the interior 64. The interior 64 can be examined at various magnifications to confirm that the interior 64 is substantially free of thermoplastic binder fiber ends.
As an alternative to SEM imaging, a three dimensional visualization and measurement technique such as micro computerized tomography may be used to non-destructively view the structure. A suitable apparatus is a SkyScan-1072 available from SkyScan having offices in Aartselaar, Belgium. Suitable software is Voxblast™ 3D Visualization and Measurement software available from VayTek, Inc. having offices in Fairfield, Iowa, U.S.A.
Exemplary aggregate clusters 18, according to the present invention, are representatively illustrated in FIGS. 6A, 6B, and 6C. Referring to FIG. 6A, one or more thermoplastic binder fibers 20 may constrain or entrap one or more staple fibers 22 and one or more superabsorbent particles 24 to form an aggregate cluster 18. The aggregate clusters 18 have a periphery 62, generally depicted for purposes of illustration with dashed lines, and an interior 64. The thermoplastic binder fibers 20 have thermoplastic binder fiber ends 60 that are formed when the aggregate clusters 18 are divided from a stabilized absorbent structure. The thermoplastic binder fiber ends 60 are located at the periphery 62 of the aggregate clusters 18, whereas the interior 64 of the aggregate clusters 18 is substantially free of thermoplastic binder fiber ends 60. In contrast, the staple fibers 22 may also be cut, fractured, or broken during the formation of the aggregate clusters 18 thus creating staple fiber ends 66, but the interior 64 of the aggregate clusters 18 will generally include many staple fiber ends 66 unlike the thermoplastic binder fiber ends 60.
FIG. 6B representatively illustrates an alternative example of an aggregate cluster 18. In FIG. 6B, the aggregate cluster 18 includes thermoplastic binder fibers 20 and staple fibers 22 constrained or entrapped within the thermoplastic binder fibers 20. The thermoplastic binder fibers 20 have thermoplastic binder fiber ends 60 at the periphery 62 of the aggregate clusters 18. The interior 64 of the aggregate clusters 18 is substantially free of thermoplastic binder fiber ends 60. The staple fibers 22 have staple fiber ends 66 both at the periphery 62 and within the interior 64 of the aggregate clusters 18.
FIG. 6C representatively illustrates an alternative example of an aggregate cluster 18. In FIG. 6C, the aggregate cluster 18 includes thermoplastic binder fibers 20 and superabsorbent particles 24 constrained or entrapped within the thermoplastic binder fibers 20. The thermoplastic binder fibers 20 have thermoplastic binder fiber ends 60 at the periphery 62 of the aggregate clusters 18. The interior 64 of the aggregate clusters 18 is substantially free of thermoplastic binder fiber ends 60. The superabsorbent particles 24 may be at least partially located at the periphery 62 of the aggregate cluster 18, within the interior 64 of the aggregate cluster 18, or both.
Typically, the aggregate clusters are formed by dividing a stabilized absorbent structure comprising substantially continuous thermoplastic binder fibers into discrete units of various sizes. Dividing the stabilized absorbent structure can be accomplished by pulverizing, grinding, chopping, micerating, shocking, shredding or otherwise breaking apart the stabilized absorbent composite. The stabilized absorbent composite used to produce the aggregate clusters may be stabilized absorbent composites produced specifically for the purpose of creating aggregate clusters or may be waste material, trim material, or reclaimed product.
Once produced, the aggregate clusters are then introduced into an absorbent manufacturing process along with virgin materials to form macro absorbent structures of absorbent articles. The aggregate clusters described herein retain a similar structure to the macro composite structure, from which the aggregate clusters are formed, due to the inherently high integrity of the source absorbent material. The high integrity of the source absorbent material is due, at least in part, to the long or substantially continuously formed thermoplastic binder fibers constraining, entrapping, or entangling the other components. It is believed that the aggregate clusters retain most of the fluid handling performance of the original absorbent material from which they are divided. While not wishing to be bound by any single theory, it is believed that the aggregate clusters create discontinuities in the otherwise continuous fibrous structures of various macro absorbent structures, and stabilized absorbent structures in particular, which may improve the absorbent capacity of the entire absorbent assembly because of the increased interstitial space created by the aggregate clusters. This interstitial space may result in less restrictive swelling of the superabsorbent material outside and surrounding the aggregate clusters. In other words, the superabsorbent material, which may otherwise have been hindered by the macro absorbent structure, may now be able to move and expand into areas opened by the aggregate clusters. In addition, the use of aggregate clusters in absorbent structures can reduce costs when using reclaimed product or trim waste generated in the production of stabilized absorbent composites as the source material.
The aggregate clusters may be divided into discrete units of various sizes. In various embodiments, the aggregate clusters may have a greatest dimension of less than 20 mm, less than 10 mm, or less than 5 mm. In some embodiments, the aggregate clusters may have a greatest dimension of 0.5 mm to 5 mm.
The absorbent structure may be in the form of a single, integrally formed layer or of a composite comprising multiple layers. If the absorbent structure comprises multiple layers, the layers are preferably in liquid communication with one another, such that, a liquid present in one layer can flow or be transported to the other layers. For example, the layers may be separated by cellulosic tissue wrap sheets such as those known to those skilled in the art.
The absorbent structure of the present invention may also be used or combined with other absorbent structures, with the absorbent structure of the present invention being used as a separate layer or as an individual zone or area within a larger, composite absorbent structure. The absorbent structure of the present invention may be combined with other absorbent structures by methods well known to those skilled in the art, such as by using adhesives or simply by layering the different structures together and holding together the composite structures with, for example, a tissue wrap sheet.
The hydrogel-forming polymeric material may be distributed in the individual layers in a generally uniform manner or may be present in the fibrous layers as a layer or other nonuniform distribution. Likewise, the aggregate clusters may be distributed in the individual layers in a general uniform manner or may be present in the fibrous layers as a layer or other nonuniform distribution.
The absorbent structures of the present invention suitably have a basis weight of about 50 grams per square meter (g/sm) to about 2000 g/sm, or about 200 g/sm to about 1500 g/sm, or about 300 g/sm to about 1000 g/sm depending on the end use. A pantiliner, for example, would require a lower basis weight (about 100 g/sm) than a diaper (about 700 g/sm).
The absorbent structures of the present invention suitably have a density of about 0.03 gram per cubic centimeter (g/cc) to about 0.5 g/cc, or about 0.05 g/cc to about 0.45 g/cc, or about 0.08 g/cc to about 0.4 g/cc. In specific embodiments, the density may be 0.12 g/cc to 0.32 g/cc.
In some embodiments, the macro absorbent structure may include long or substantially continuously formed thermoplastic binder fibers, wettable staple fibers, superabsorbent particles, a plurality of aggregate clusters, or combinations thereof. The aggregate clusters may include thermoplastic binder fibers, staple fibers, superabsorbent particles, and combinations thereof. The thermoplastic binder fibers, within the aggregate clusters, may have thermoplastic binder fiber ends located at the periphery of the aggregate clusters, but the interior of the aggregate clusters may be substantially free of thermoplastic binder fiber ends. In various embodiments, the wettable staple fibers of the macro absorbent structure and/or the aggregate clusters may be selected from the group consisting of cellulose fibers, textile fibers, and thermoplastic polymeric fibers. In certain embodiments, the wettable staple fibers of the macro absorbent structure and/or the aggregate clusters may be wood pulp fiber.
In one embodiment, the macro absorbent structure may include 5 to 50 wt % meltblown polyolefin binder fibers having an average fiber length greater than 1 cm. The macro absorbent structure may further include 0 to 50 wt % cellulose fibers constrained or entrapped within the polyolefin binder fibers. The macro absorbent structure may further include 30 to 90 wt % superabsorbent particles constrained or entrapped within the polyolefin binder fibers. The macro absorbent structure may further include 1 to 50 wt % aggregate clusters. The aggregate clusters may include meltblown polyolefin binder fibers having meltblown binder fiber ends located at the periphery of the aggregate clusters, but the interior of the aggregate clusters may be substantially free of meltblown binder fiber ends. In other embodiments, the aggregate clusters may include meltblown polyolefin binder fibers having a fiber length greater than 5 mm.
The fiber length can be determined by well known optical imaging techniques including Scanning Electron Micrography or other methods. This may be applied to the macro absorbent structure or the aggregate cluster. Inspection of the inside of the aggregate clusters may require disruption of the structure by manipulating the aggregate cluster with a small probe. Alternatively, a three dimensional visualization and measurement technique such as micro computerized tomography may be used to non-destructively view the structure, as discussed previously.
In one embodiment, the macro absorbent structure may include 5 to 50 wt % meltblown polyolefin binder fibers having an average fiber length greater than 1 cm. The macro absorbent structure may further include 0 to 50 wt % cellulose fibers constrained or entrapped within the polyolefin binder fibers. The macro absorbent structure may further include 30 to 90 wt % superabsorbent particles constrained or entrapped within the polyolefin binder fibers. The macro absorbent structure may further include 1 to 50 wt % aggregate clusters. The aggregate clusters may include continuously formed meltblown polyolefin binder fibers. The aggregate clusters may be created by dividing a stabilized absorbent structure formed, in part, by continuous meltblown binder fibers. The process of dividing the stabilized absorbent material, the source absorbent material, results in polyolefin binder fiber ends being located at the periphery of the aggregate clusters.
In various embodiments, the aggregate clusters may also include cellulose fibers constrained or entrapped within the long meltblown polyolefin binder fibers within the aggregate clusters. The aggregate clusters may further include superabsorbent particles constrained or entrapped within the meltblown polyolefin binder fibers within the aggregate clusters.
In another embodiment, the macro absorbent structure may include 10 to 40 wt % meltblown polyolefin binder fibers having an average fiber length greater than 1 cm. The macro absorbent structure may further include 40 to 80 wt % cellulose fibers constrained or entrapped within the polyolefin binder fibers. The macro absorbent structure may further include 0 to 20 wt % superabsorbent particles constrained or entrapped within the polyolefin binder fibers. The macro absorbent structure may further include 1 to 50 wt % aggregate clusters. The aggregate clusters may include meltblown polyolefin binder fibers having a fiber length greater than 1 cm or greater than 5 mm. The meltblown polyolefin binder fibers of the aggregate clusters may have meltblown polyolefin binder fiber ends located at the periphery of the aggregate clusters. The interiors of the aggregate clusters being substantially free of meltblown polyolefin binder fiber ends. The aggregate clusters may also include cellulose fibers constrained or entrapped within the polyolefin binder fibers within the aggregate clusters. The aggregate clusters may further include superabsorbent particles constrained or entrapped within the polyolefin binder fibers within the aggregate clusters.
In another embodiment, the macro absorbent structure may include short thermoplastic binder fibers, wettable staple fibers, superabsorbent particles, and a plurality of aggregate clusters. The aggregate clusters may include thermoplastic binder fibers constraining or entrapping wettable staple fibers and superabsorbent particles. The thermoplastic binder fibers, within the aggregate clusters, have thermoplastic binder fiber ends located at the periphery of the aggregate clusters, whereas the interior of the aggregate clusters is substantially free of thermoplastic binder fiber ends.
In another embodiment, the macro absorbent structure may include wettable staple fibers, superabsorbent particles, and a plurality of aggregate clusters. The aggregate clusters may include thermoplastic binder fibers constraining or entrapping cellulose fibers and superabsorbent particles. The thermoplastic binder fibers, within the aggregate clusters, have thermoplastic binder fiber ends located at the periphery of the aggregate clusters, whereas the interior of the aggregate clusters is substantially free of thermoplastic binder fiber ends.
In another embodiment, the macro absorbent structure may include long or substantially continuous thermoplastic binder fibers, wettable staple fibers, superabsorbent particles, and a plurality of aggregate clusters. The aggregate clusters may include thermoplastic binder fibers and wettable staple fibers constrained or entrapped in the thermoplastic binder fibers. The thermoplastic binder fibers, within the aggregate clusters, have thermoplastic binder fiber ends located at the periphery of the aggregate clusters, whereas the interior of the aggregate clusters is substantially free of thermoplastic binder fiber ends.
In another embodiment, the macro absorbent structure may include substantially continuous thermoplastic binder fibers constraining or entrapping wettable staple fibers, superabsorbent particles, and a plurality of aggregate clusters. The aggregate clusters may include thermoplastic binder fibers and superabsorbent particles constrained or entrapped within the thermoplastic binder fibers. The thermoplastic binder fibers, within the aggregate clusters, have thermoplastic binder fiber ends located at the periphery of the aggregate clusters, whereas the interior of the aggregate clusters is substantially free of thermoplastic binder fiber ends.
In another embodiment, the macro absorbent structure may include wettable staple fibers, superabsorbent particles, and a plurality of aggregate clusters. The aggregate clusters may include thermoplastic binder fibers and wettable staple fibers constrained or entrapped within the thermoplastic binder fibers. The thermoplastic binder fibers, of the aggregate clusters, have thermoplastic binder fiber ends located at the periphery of the aggregate clusters but the interior of the aggregate clusters is substantially free of thermoplastic binder fiber ends.
In another embodiment, the macro absorbent structure may include short thermoplastic binder fibers, wettable staple fibers, superabsorbent particles, and a plurality of aggregate clusters. The aggregate clusters may include thermoplastic binder fibers and cellulose fibers constrained or entrapped within the thermoplastic binder fibers. The thermoplastic binder fibers, within the aggregate clusters, have thermoplastic binder fiber ends located at the periphery of the aggregate clusters but the interior of the aggregate clusters is substantially free of thermoplastic binder fiber ends.
In another embodiment, the macro absorbent structure may include wettable staple fibers, superabsorbent particles, and a plurality of aggregate clusters. The aggregate clusters may include thermoplastic binder fibers and superabsorbent particles constrained or entrapped within the thermoplastic binder fibers. The thermoplastic binder fibers, within the aggregate clusters, have thermoplastic binder fiber ends located at the periphery of the aggregate clusters but the interior of the aggregate clusters is substantially free of thermoplastic binder fiber ends.
In another embodiment, the macro absorbent structure may include short thermoplastic binder fibers, wettable staple fibers, superabsorbent particles, and a plurality of aggregate clusters. The aggregate clusters may include thermoplastic binder fibers and superabsorbent particles constrained or entrapped within the thermoplastic binder fibers. The thermoplastic binder fibers, within the aggregate clusters, have thermoplastic binder fiber ends located at the periphery of the aggregate clusters but the interior of the aggregate clusters being substantially free of thermoplastic binder fiber ends.
In another embodiment, the macro absorbent structure may include substantially continuous thermoplastic binder fibers, superabsorbent particles, and a plurality of aggregate clusters. The aggregate clusters may include thermoplastic binder fibers and superabsorbent particles constrained or entrapped within the thermoplastic binder fibers. The thermoplastic binder fibers, within the aggregate clusters, have thermoplastic binder fiber ends located at the periphery of the aggregate clusters, whereas the interior of the aggregate clusters is substantially free of thermoplastic binder fiber ends.
In another embodiment, the macro absorbent structure may include substantially continuous thermoplastic binder fibers, wettable staple fibers, and a plurality of aggregate clusters. The aggregate clusters may include thermoplastic binder fibers and wettable staple fibers constrained or entrapped within the thermoplastic binder fibers. The thermoplastic binder fibers, of the aggregate clusters, have thermoplastic binder fiber ends located at the periphery of the aggregate clusters but the interior of the aggregate clusters is substantially free of thermoplastic binder fiber ends.
In another embodiment; the macro absorbent structure may include substantially continuous thermoplastic binder fibers and a plurality of aggregate clusters. The aggregate clusters may include thermoplastic binder fibers and wettable staple fibers constrained or entrapped within the thermoplastic binder fibers. The thermoplastic binder fibers, of the aggregate clusters, have thermoplastic binder fiber ends located at the periphery of the aggregate clusters but the interior of the aggregate clusters is substantially free of thermoplastic binder fiber ends.
In another embodiment, the macro absorbent structure may include substantially continuous thermoplastic binder fibers and a plurality of aggregate clusters. The aggregate clusters may include thermoplastic binder fibers and superabsorbent particles constrained or entrapped within the thermoplastic binder fibers. The thermoplastic binder fibers, of the aggregate clusters, have thermoplastic binder fiber ends located at the periphery of the aggregate clusters but the interior of the aggregate clusters is substantially free of thermoplastic binder fiber ends.
In another embodiment, the macro absorbent structure may include substantially continuous thermoplastic binder fibers and a plurality of aggregate clusters. The aggregate clusters may include thermoplastic binder fibers, wettable staple fibers constrained or entrapped within the thermoplastic binder fibers, and superabsorbent particles constrained or entrapped within the thermoplastic binder fibers. The thermoplastic binder fibers, of the aggregate clusters, have thermoplastic binder fiber ends located at the periphery of the aggregate clusters but the interior of the aggregate clusters is substantially free of thermoplastic binder fiber ends.
In another embodiment, the macro absorbent structure includes short thermoplastic binder fibers, wettable staple fibers, and a plurality of aggregate clusters. The aggregate clusters include thermoplastic binder fibers. The aggregate clusters further include superabsorbent particles constrained or entrapped within the thermoplastic binder fibers, staple fibers constrained or entrapped within the thermoplastic binder fibers, or both. The thermoplastic binder fibers, within the aggregate clusters, have thermoplastic binder fiber ends located at the periphery of the aggregate clusters but the interior of the aggregate clusters being substantially free of thermoplastic binder fiber ends.
In another embodiment, the macro absorbent structure includes short thermoplastic binder fibers, superabsorbent particles, and a plurality of aggregate clusters. The aggregate clusters include thermoplastic binder fibers. The aggregate clusters further include superabsorbent particles constrained or entrapped within the thermoplastic binder fibers, staple fibers constrained or entrapped within the thermoplastic binder fibers, or both. The thermoplastic binder fibers, within the aggregate clusters, have thermoplastic binder fiber ends located at the periphery of the aggregate clusters but the interior of the aggregate clusters being substantially free of thermoplastic binder fiber ends.
In another embodiment, the macro absorbent structure includes short thermoplastic binder fibers and a plurality of aggregate clusters. The aggregate clusters include thermoplastic binder fibers. The aggregate clusters further include superabsorbent particles constrained or entrapped within the thermoplastic binder fibers, staple fibers constrained or entrapped within the thermoplastic binder fibers, or both. The thermoplastic binder fibers, within the aggregate clusters, have thermoplastic binder fiber ends located at the periphery of the aggregate clusters but the interior of the aggregate clusters being substantially free of thermoplastic binder fiber ends.
In another embodiment, the macro absorbent structure may include wettable staple fibers and a plurality of aggregate clusters. The aggregate clusters include thermoplastic binder fibers. The aggregate clusters further include superabsorbent particles constrained or entrapped within the thermoplastic binder fibers, staple fibers constrained or entrapped within the thermoplastic binder fibers, or both. The thermoplastic binder fibers, within the aggregate clusters, have thermoplastic binder fiber ends located at the periphery of the aggregate clusters but the interior of the aggregate clusters being substantially free of thermoplastic binder fiber ends.
In embodiments that include substantially continuous thermoplastic binder fibers in the macro absorbent structure and thermoplastic binder fibers in the aggregate clusters, the substantially continuous thermoplastic binder fibers of the macro absorbent structure, may be essentially the same composition as the thermoplastic binder fibers of the aggregate clusters. Additionally, in embodiments that include staple fibers in the macro absorbent structure and the aggregate clusters, the staple fiber of the macro absorbent structure, may have essentially the same composition as the staple fibers of the aggregate clusters. Likewise, in embodiments that include superabsorbent particles in the macro absorbent structure and the aggregate clusters, the superabsorbent particles of the macro absorbent structure, may have essentially the same composition as the superabsorbent particles of the aggregate clusters.
In embodiments that include substantially continuous thermoplastic binder fibers in the macro absorbent structure and thermoplastic binder fibers in the aggregate clusters, the substantially continuous thermoplastic binder fibers of the macro absorbent structure may have a different composition than the thermoplastic binder fibers of the aggregate clusters. Additionally, in embodiments that include staple fibers in the macro absorbent structure and the aggregate clusters, the staple fibers of the macro absorbent structure, may have a different composition than the staple fibers of the aggregate clusters. Likewise, in embodiments that include superabsorbent particles in the macro absorbent structure and the aggregate clusters, the superabsorbent particles of the macro absorbent structure, may have a different composition than the superabsorbent particles of the aggregate clusters. In some embodiments, the macro absorbent structure and/or the aggregate clusters may have one or more additional types of staple fibers.
The absorbent structure of the present invention can include other components not adversely affecting the desired absorbent of the absorbent structure. Exemplary materials which could be used as additional components would include, without limitation, pigments, antioxidants, stabilizers, surfactants, waxes, flow promoters, particulates, binder fibers, and materials added to enhance processability, liquid handling and mechanical properties or visual/tactile appearance of the absorbent of the components, and/or the various components.
Referring again to FIG. 1, a disposable diaper 26 is illustrated according to one embodiment of the present invention. Disposable diaper 26 includes a backsheet 30, a topsheet 28, and an absorbent structure 10, located between the backsheet 30 and the topsheet 28. Absorbent structure 10 is an absorbent structure according to the present invention.
Those skilled in the art will recognize various materials suitable for use as the topsheet and backsheet. Exemplary of materials suitable for use as the topsheet are liquid-permeable materials, such as spunbonded polypropylene or polyethylene having a basis weight of from about 15 to about 25 grams per square meter. Exemplary of materials suitable for use as the backsheet are liquid-impervious materials, such as polyolefin films, as well as vapor-pervious materials, such as microporous polyolefin films. Also laminates including cloth-like nonwovens are well known in the art and are suitable for use herein as a backsheet.
Those skilled in the art will also recognize that additional components may optionally be added depending upon the intended use of the diaper. For example, the diaper may include containment flaps, leg elastics, waist elastics, fasteners, lotions and treatments, surge management layers, tissue layers, spacer layers, fit panels, and the like. These components and others are described in U.S. Pat. No. 6,682,512 issued Jan. 27, 2004 to Uitenbroek et al., the entirety of which is incorporated herein by reference where not contradictory.
In another aspect, the present invention concerns a method of making an absorbent structure with aggregate clusters and one or more: wettable staple fibers, thermoplastic fibers, superabsorbent particles, and the like. The absorbent structure is in the form of a fibrous matrix. The fibrous matrix may be formed by air-laying fibers, through a spunbond or meltblown process, a carding process, a wet-laid process, or through essentially any other means, known to those skilled in the art, for forming a fibrous matrix.
Methods of incorporating the wettable staple fiber and/or a hydrogel-forming polymeric material into the fibrous matrix are known to those skilled in the art. Suitable methods include incorporating the wettable staple fiber and/or a hydrogel-forming polymeric material into the matrix during formation of the matrix, such as by air laying the fibers of the fibrous matrix and the wettable staple fiber and/or a hydrogel-forming polymeric material at the same time or wet-laying the fibers of the fibrous matrix and the wettable staple fiber and/or a hydrogel-forming polymeric material at the same time. Alternatively, it is possible to apply the wettable staple fiber and/or a hydrogel-forming polymeric material to the fibrous matrix after formation of the fibrous matrix. Other methods include sandwiching the hydrogel-forming polymeric material between two sheets of material, at least one of which is fibrous and liquid permeable. The hydrogel-forming polymeric material may be generally uniformly located between the two sheets of material or may be located in discrete pockets formed by the two sheets. It is preferable that the wettable staple fiber be generally uniformly distributed within the fibrous matrix. However, the wettable staple fiber may be non-uniformly distributed to achieve the desired liquid absorptive properties.
One method of making a stabilized absorbent structure comprises providing a stream containing substantially continuously extruded molten polymeric binder fibers, such as polyolefin; providing a stream containing individualized staple fibers, such as wood pulp fibers; and providing a stream containing a plurality of aggregate clusters. One or more of the streams may be merged into a single product stream prior to collecting the contents of the streams on a forming surface to create a stabilized absorbent structure. In various embodiments, the method may include a carrier sheet onto which the product streams are collected. In various embodiments, the stabilized absorbent structure made by this process may include an intimate mixture of the wood pulp fibers and the aggregate clusters integrated by physical entrapment and mechanical entanglement within the substantially continuous polymeric binder fibers. In various embodiments, the method may further include a stream comprising superabsorbent particles. In particular embodiments, the superabsorbent stream and the pulp fiber stream are combined into a single stream prior to combining with the stream containing the substantially continuous extruded molten polymeric binder fiber.
The stream containing aggregate clusters can be introduced into the absorbent manufacturing process, in several locations, via pneumatic conveying. Locations that are under a vacuum (negative pressure) are preferred for proper blending.
Referring to FIG. 7, one method of introducing a plurality of aggregate clusters includes pneumatically conveying the aggregate clusters 18 to a fiberizer 32 generally at an entry location 34. The fiberizer 32 is a commercially available device that separates the individual staple fibers 14 from a source sheet 36, such as a cellulose pulp sheet. Fiberizers are available from Paper Converting Machine Company located in Green Bay Wis., U.S.A.; Curt G. Joa Inc. a company having an office in Sheboygan Falls Wis., U.S.A.; and Kamas Industries AB a company having an office in Vellinge Sweden among others.
One advantage of introducing the aggregate clusters 18 stream into the fiberizer 32 at entry location 34 is the uniform mixing of the aggregate clusters 18 with the virgin staple fibers 14. This method of introduction may also provide uniform basis weight and low weight variability in the absorbent structure 10. Adding the aggregate clusters 18 to the fiberizer 32 imposes significant fiberizer impact energy upon the superabsorbent within the aggregate clusters 18. As a result, it is possible with this configuration that some degradation of the superabsorbent's fluid handling properties may occur.
Alternatively, the aggregate clusters 18 can be introduced into the forming process after the fiberizer discharge; in a conduit duct 38 that connects the fiberizer 32 to a forming surface 40, illustrated at entry location 44. Examples of such conduit ducts include forming chambers, usually constructed of polycarbonate, or ductwork of the galvanized spiral, or seamless variety.
Most forming systems utilize a fan 42 or other device to create motive energy for transporting the staple fibers 14 to a forming surface 40. Some forming systems locate this motive energy device on the side of the forming surface 40 opposite the fiberizer 32. Other forming systems locate this motive energy device between the fiberizer 32 and the forming surface 40. For those instances, the vacuum created by the motive energy device (suction side) is a preferred location for introduction of the aggregate clusters 18 to the manufacturing process. The vacuum helps integrate the flow of aggregate clusters 18, while the motive energy device helps blend the aggregate clusters 18 with the virgin staple fibers 14. Examples of motive energy devices include fans, blowers, and venturi eductors, available from New York Blower Company, having offices in LaPorte Id., U.S.A. and Fox Valve, a company having offices in Dover N.J., U.S.A.
Forming systems that pneumatically convey superabsorbent particles 16 to the forming process offer another alternative location for introducing aggregate clusters 18 to the process. A venturi eductor 50 may be used to impart a vacuum to draw superabsorbent 16 into a delivery pipe 46. This vacuum source provides an opportunity to introduce the aggregate clusters 18 into the superabsorbent delivery system at entry location 48. The venturi eductor vacuum helps to integrate the flow of the pneumatically conveyed aggregate clusters 18, while the venturi eductor 50 helps blend the aggregate clusters 18 with the virgin superabsorbent 16.
In general, to minimize any degradation of the fluid handling properties of the superabsorbent 24 within the aggregate clusters 18, the pneumatic conveying velocity of the aggregate clusters 18 to the forming process should be kept to a minimum. To prevent the aggregate clusters 18 from settling out of the air stream (salutation) a velocity above 3,500 ft/min should be maintained. Therefore, it is suitable to pneumatically convey the aggregate clusters 18 at a velocity of 3,000 to 6,000 ft/min (914.4 m/min to 1,828.8 m/min), 3,000 to 5,000 ft/min (914.4 m/min to 1,524 m/min), or 3,500 to 4,000 ft/min (1,066.8 m/min to 1,219.2 m/min). A suitable method and apparatus for delivering particulate material to an air stream is taught in U.S. Pat. No. 6,461,086, issued Oct. 8, 2002 to Milanowski et al., the entirety of which is incorporated herein by reference where not contradictory.
In another aspect, the present invention involves a method of making an absorbent structure comprising the production of a plurality of first absorbent articles on a first production line. The first absorbent articles have macro structures including substantially continuous thermoplastic binder fibers. The macro absorbent structures may further include superabsorbent particles, staple fibers, aggregate clusters or combinations thereof, constrained or entrapped within the substantially continuous thermoplastic binder fibers of the macro absorbent structure.
The first absorbent articles from the first production line may then be pulverized, ground, chopped, micerated, shocked, or otherwise worked or divided to produce aggregate clusters having a periphery and an interior. The aggregate clusters include thermoplastic binder fibers and may include superabsorbent particles, staple fibers, or both constrained or entrapped within the thermoplastic binder fibers within the aggregate clusters. The thermoplastic binder fibers within the aggregate clusters have thermoplastic binder fiber ends located at the periphery of the aggregate clusters but the interior of the aggregate clusters is substantially free of thermoplastic binder fiber ends.
The aggregate clusters are then combined with virgin materials on a second production line to produce at least one second absorbent article. The second absorbent article may further include, but is not limited to: thermoplastic fibers, long fibers, staple fibers, superabsorbent particles, and combinations thereof.
In various embodiments, the second production line may be the same as the first production line. As such, at least a portion of the first absorbent articles may be worked to form aggregate clusters and the aggregate clusters may be reintroduced into the same process to produce more of the first absorbent articles further including aggregate clusters. In other embodiments, the second production line may produce absorbent articles by means of air forming, wet laying, or other absorbent article forming processes known to those of skill in the art.
It will be appreciated that details of the absorbent cores of the invention, given for purposes of illustration, are not to be construed as limiting the scope of this invention.
Those skilled in the art will readily appreciate that many modifications are possible in the exemplary aspects without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention, which is defined in the following claims and all equivalents thereto. Further, it is recognized that many aspects may be conceived that do not achieve all of the advantages of some aspects, particularly of the preferred aspects., yet the absence of a particular advantage should not be construed to necessarily mean that such an aspect is outside the scope of the present invention.

Claims

1. An absorbent structure comprising a macro absorbent structure, the macro absorbent structure comprising a plurality of aggregate clusters intermixed within the macro absorbent structure, the aggregate clusters having a periphery and an interior and comprising thermoplastic binder fibers having thermoplastic binder fiber ends, the thermoplastic binder fiber ends being located at the periphery of the aggregate clusters, and the interior of the aggregate clusters being substantially free of thermoplastic binder fiber ends.

2. The absorbent structure of claim 1 wherein the macro absorbent structure further comprises long thermoplastic binder fibers and superabsorbent particles constrained within the thermoplastic binder fibers.

3. The absorbent structure of claim 2 wherein the aggregate clusters further comprise superabsorbent particles constrained within the thermoplastic binder fibers within the aggregate clusters.

4. The absorbent structure of claim 3 wherein the aggregate clusters further comprise staple fibers constrained within the thermoplastic binder fibers within the aggregate clusters.

5. The absorbent structure of claim 2 wherein the aggregate clusters further comprise staple fibers constrained within the thermoplastic binder fibers within the aggregate clusters.

6. The absorbent structure of claim 1 wherein the macro absorbent structure further comprises long thermoplastic binder fibers and staple fibers constrained within the long thermoplastic binder fibers.

7. The absorbent structure of claim 6 wherein the aggregate clusters further comprise superabsorbent particles constrained within the thermoplastic binder fibers within the aggregate clusters.

8. The absorbent structure of claim 7 wherein the aggregate clusters further comprise staple fibers constrained within the thermoplastic binder fibers within the aggregate clusters.

9. The absorbent structure of claim 6 wherein the aggregate clusters further comprise staple fibers constrained within the thermoplastic binder fibers within the aggregate clusters.

10. The absorbent structure of claim 1 wherein the macro absorbent structure further comprises long thermoplastic binder fibers, superabsorbent particles constrained within the long thermoplastic binder fibers, and staple fibers constrained within the long thermoplastic binder fibers.

11. The absorbent structure of claim 10 wherein the aggregate clusters further comprise superabsorbent particles constrained within the thermoplastic binder fibers within the aggregate clusters.

12. The absorbent structure of claim 11 wherein the aggregate clusters further comprise staple fibers constrained within the thermoplastic binder fibers within the aggregate clusters.

13. The absorbent structure of claim 10 wherein the aggregate clusters further comprise staple fibers constrained within the thermoplastic binder fibers within the aggregate clusters.

14. The absorbent structure of claim I wherein the macro absorbent structure further comprises staple fibers and superabsorbent particles intermixed with the staple fibers.

15. The absorbent structure of claim 1 wherein the macro absorbent structure further comprises long thermoplastic binder fibers and the aggregate clusters are constrained within the long thermoplastic binder fibers.

16. A stabilized absorbent structure comprising,

a. 5 to 50 wt % meltblown elastomeric polyolefin binder fibers having an average fiber length greater than 1 cm;

b. 1 to 50 wt % cellulose fibers constrained within the elastomeric polyolefin binder fibers;

c. 30 to 90 wt % superabsorbent particles constrained or entrapped within the polyolefin binder fibers; and

d. 1 to 50 wt % aggregate clusters each having a periphery and interior, the aggregate clusters comprising meltblown polyolefin binder fibers having meltblown polyolefin binder fiber ends, cellulose fibers constrained within the polyolefin binder fibers within the aggregate clusters, superabsorbent particles constrained or entrapped within the polyolefin binder fibers within the aggregate clusters, wherein the meltblown polyolefin binder fiber ends are located at the periphery of the aggregate clusters and the interiors of the aggregate clusters are substantially free of meltblown polyolefin binder fiber ends.

17. A method of making a stabilized absorbent structure comprising;

a. providing a first absorbent structure comprising long thermoplastic binder fibers;

b. dividing the first absorbent structure to create aggregate clusters;

c. providing a stream of the aggregate clusters;

d. providing a stream of extruded molten polymeric fibers;

e. merging the aggregate cluster stream and polymeric fiber stream into a single product stream; and

f. collecting the single product stream on a forming surface to make a second absorbent structure.

18. The method of claim 17 further comprising, merging a stream of superabsorbent particles in the aggregate cluster stream, the polymeric fiber stream, or the single product stream.

19. The method of claim 17 further comprising, merging a stream of wood pulp fibers in the aggregate cluster stream, the polymeric fiber stream, or the single product stream.

20. A disposable absorbent article produced by the method of claim 17.