Note: Descriptions are shown in the official language in which they were submitted.
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FLUTED ABSORBENT COMPOSITE
Field of the Invention
The present invention relates generally to an absorbent composite and, more
particularly, to an air-laid composite that includes absorbent material.
Background of the Invention
Cellulose fibers derived from wood pulp are used in a variety of absorbent
articles, for example, diapers, incontinence products, and feminine hygiene
products.
It is desirable for the absorbent articles to have a high absorbent capacity
for liquid,
rapid liquid acquisition, low rewet, as well as to have good dry and wet
strength
characteristics for durability in use and effective fluid management. The
absorbent
capacity of articles made from cellulose fibers is often enhanced by the
addition of
absorbent materials, such as superabsorbent polymers. Superabsorbent polymers
known in the art have the capability to absorb liquids in quantities from 5 to
100
times or more their weight. Thus, the presence of superabsorbent polymers
greatly
increases the liquid holding capacity of absorbent articles made from
cellulose.
However, absorbent composites that contain superabsorbent materials
commonly suffer from gel blocking. Upon liquid absorption, superabsorbent
materials tend to coalesce and form a gelatinous mass which prevents the
wicking of
liquid to unwetted portions of the composite. By preventing distribution of
acquired
liquid from a composite's unwetted portions, gel blocking precludes the
effective and
efficient use of superabsorbent materials in fibrous composites. The wicking
capacity of conventional fibrous composites that include relatively
homogeneous
distributions of superabsorbent material is generally significantly reduced
after initial
liquid insult. The diminished capacity of such fibrous composites results from
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narrowing of capillary acquisition and distribution channels that accompanies
superabsorbent material swelling. The diminution of absorbent capacity and
concomitant loss of capillary distribution channels for conventional absorbent
cores
that include superabsorbent material is manifested by decreased liquid
acquisition
rates and far from ideal liquid distribution on successive liquid insults.
Accordingly, there exists a need for an absorbent composite that includes
superabsorbent material and that effectively acquires and wicks liquid
throughout the
composite and distributes the acquired liquid to absorbent material where the
liquid
is efficiently absorbed and retained without gel blocking. A need also exists
for an
absorbent composite that continues to acquire and distribute liquid throughout
the
composite on successive liquid insults. In addition, there exists a need for
an
absorbent composition containing superabsorbent materials that exhibits the
advantages associated with wet-laid composites including wet strength,
absorbent
capacity and acquisition, liquid distribution, softness, and resilience. The
present
invention seeks to fulfill these needs and provides further related
advantages.
Summary of the Invention
In one aspect, the present invention provides a fibrous absorbent composite
that includes absorbent material distributed throughout the composite and in
selected
regions of the composite. The concentration of absorbent material in these
regions
can be varied to provide a composite having variable absorbent material
concentration. In one embodiment, the composite includes absorbent material
dispersed in bands across the composite's width and that extend along the
composite's length. On contact with liquid, the composite's bands enriched
with
absorbent material swell with acquired liquid and expand and rise from the
composite's wetted surface to form ridges and to provide a fluted structure.
The
wetted composite's fluted structure enhances liquid wicking, acquisition, and
distribution on subsequent liquid insult.
In another aspect of the invention, a method for forming an absorbent
composite having variable absorbent material content is provided. In one
embodiment, the method includes increasing the concentration of absorbent
material
in the composite by adding absorbent material to selective regions of the
composite.
In another embodiment, the method provides for forming regions of increased
absorbent material concentration in the composite by selectively increasing
the
composite's basis weight. In the method, the composite is formed by
selectively
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densifying a substantially homogeneous composite containing fibers and
absorbent
material.
Brief Description of the Drawings
The foregoing aspects and many of the attendant advantages of this invention
will become more readily appreciated as the same becomes better understood by
reference to the following detailed description, when taken in conjunction
with the
accompanying drawings, wherein:
FIGURE 1 is a lateral cross-sectional view of a representative fluted
absorbent composite formed in accordance with the present invention;
I 0 FIGURE 2 is a perspective view of the composite shown in FIGURE 1;
FIGURE 3 is a lateral cross-sectional view of a representative fluted
absorbent composite of the present invention in a wetted state;
FIGURE 4 is a perspective view of the wetted composite shown in
FIGURE 3;
FIGURE 5 is a lateral cross-sectional view of a representative composite that
includes a relatively homogeneous distribution of fibers and absorbent
material;
FIGURE 6 is a lateral cross-sectional view of an absorbent construct that
includes a representative fluted absorbent composite formed in accordance with
the
present invention;
FIGURE 7 is a lateral cross-sectional view of another absorbent construct that
includes a representative fluted absorbent composite formed in accordance with
the
present invention;
FIGURE 8 is a lateral cross-sectional view of the composite shown in
FIGURE 5 with an overlying acquisition layer;
FIGURE 9 is a lateral cross-sectional view of the composite shown in
FIGURE 5 with an overlying acquisition layer;
FIGURE 10 is a lateral cross-sectional view of a portion of an absorbent
article incorporating a representative fluted absorbent composite formed in
accordance with the present invention;
FIGURE 11 is a lateral cross-sectional view of a portion of another absorbent
article incorporating a representative fluted absorbent composite formed in
accordance with the present invention;
FIGURE 12 is a lateral cross-sectional view of a portion of another absorbent
article incorporating a representative fluted absorbent composite formed in
accordance with the present invention; and
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FIGURE 13 is a lateral cross-sectional view of a portion of another absorbent
article incorporating a representative fluted absorbent composite formed in
accordance with the present invention.
Detailed Description of the Preferred Embodiment
The absorbent composite of the present invention is a fibrous composite that
includes absorbent material distributed throughout the composite and in
selected
regions of the composite. The concentration of absorbent material in these
regions
can be varied to provide a composite having variable absorbent material
content. In
one embodiment, the absorbent composite includes absorbent material dispersed
in
bands across the composite's width (i.e., cross-machine direction) and that
extend
along the composite's length (i.e., machine direction). Distribution zones
that are
composed primarily of fibers lie between the composite's bands enriched with
absorbent material. The composite's fibrous distribution zones serve to
acquire liquid
contacting the composite and to distribute the acquired liquid throughout the
composite and, ultimately, to the absorbent material. The absorbent material
serves
to absorb and retain liquid acquired by the composite.
The absorbent composite can be advantageously incorporated into a variety of
absorbent articles such as diapers including disposable diapers and training
pants;
feminine care products including sanitary napkins, tampons, and pant liners;
adult
incontinence products; toweling; surgical and dental sponges; bandages; food
tray
pads; and the like. Because the composite is highly absorbent, the composite
can be
included into an absorbent article as a liquid storage core. In such a
construct, the
composite can be combined with one or more other composites or layers
including,
for example, an acquisition and/or a distribution layer. Because of the
composite's
capacity to rapidly acquire and distribute liquid, the composite can also
serve as an
liquid management layer that acquires and releases a portion of the acquired
liquid to
an underlying storage core. Thus, in another embodiment, the absorbent
composite
can be combined with a storage core to provide an absorbent construct that is
useful
in absorbent articles.
The absorbent composite of the present invention is a fluted storage
composite. As used herein, the term "fluted" refers to the nature of the
composite,
which on wetting, develops ridges and becomes a fluted structure as a result
of
absorbent material expansion. As noted above, the composite includes regions
(i.e.,
bands) enriched with absorbent material that are distributed across the
composite's
width and that extend in bands along the composite's length. On contact with
liquid
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acquired by the fibrous composite, the absorbent material swells resulting in
a wetted
composite having ridges that include swollen absorbent material. The
composite's
ridges are separated by distribution zones or channels, which are fibrous
regions of
the composite that include lesser amounts of absorbent material relative to
the
composite's absorbent material enriched regions.
The banded nature of the fluted absorbent composite of the present invention
is illustrated in FIGURES I -4. Referring to FIGURES 1 and 2, a representative
fluted absorbent composite indicated generally by reference numeral 10 formed
in
accordance with the present invention includes regions 12 (i.e., liquid
storage zones)
enriched with absorbent material and regions 14 (i.e., liquid distribution
zones) that
are generally fibrous regions and include relatively lesser amounts of
absorbent
material compared to regions 12.
Liquid is rapidly acquired by the predominantly fibrous regions of the
composite when the absorbent composite is contacted with liquid. The fibrous
1 S regions are relatively open and porous in nature and promote rapid liquid
acquisition,
wicking, and distribution. Liquid acquired by the composite generally travels
rapidly
longitudinally through the fibrous composite along the composite's length via
the
distribution zones (i.e., regions 14) and is absorbed by regions of the
composite
enriched with absorbent material (i.e., regions 12). The acquired liquid is
generally
wicked laterally into the absorbent material as the liquid is distributed
along the
composite's length.
For the fluted composite, successive liquid insults are absorbed at even
greater rate through the establishment of flutes and corresponding channels on
initial
liquid insult. On wetting, the composite of the present invention becomes on a
fluted
structure having channels for rapidly acquiring additional liquid and
distributing the
liquid to sites that are remote to insult. For the fluted composite,
acquisition times
for subsequent liquid insult are generally less than that for the initial
acquisition.
Reduced acquisition times for successive liquid insults is not generally
observed for
conventional absorbent constructs. Because conventional absorbent structures
cannot
form a fluted structure and therefore lack channels for distributing
additional liquid,
acquisition times for these structures generally increase with successive
liquid
insults. Increased acquisition time can be attributed to the fact that liquid
is only
slowly acquired and distributed through a composite's saturated regions to
more
remote regions of the composite that are capable of absorbing liquid. Thus,
the fluted
absorbent composite provides initial liquid acquisition rates that are
generally
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comparable to or greater than those for conventional absorbent structures. The
composite also has significantly increased rates of liquid acquisition for
successive
liquid acquisition relative to conventional composites.
Wet structures of the fluted absorbent composite of the present invention are
shown in FIGURES 3 and 4. These figures illustrate the fluted nature of the
composite, which results from liquid contact and swelling and expansion of
absorbent material. Referring to FIGURES 3 and 4, absorbent material enriched
regions 12 (i.e., liquid storage regions) are shown as ridges separated by
regions 14
(i.e., liquid distribution zones) that form valley floors or channels between
the ridges.
Due at least in part to the fluted structure of the wetted fibrous composite,
subsequent
liquid insults are rapidly absorbed by the composite compared to composites
that
contain absorbent material in other configurations, for example, composites in
which
absorbent material is distributed substantially uniformly throughout the
composite.
Fibers are a principal component of the fluted absorbent composite of this
invention. Fibers suitable for use in the present invention are known to those
skilled
in the art and include any fiber from which an absorbent composite can be
formed.
Suitable fibers include natural and synthetic fibers. Combinations of fibers
including
combinations of synthetic and natural fibers, and treated and untreated
fibers, can
also be suitably used in the composite. In a preferred embodiment, the
absorbent
composite of the present invention includes cellulosic fibers, hardwood
fibers,
chemithermomechanical pulp fibers (i.e., CTMP) and, more preferably,
crosslinked
cellulosic fibers.
Generally, fibers are present in the composite in an amount from about 20 to
about 90 weight percent, preferably from about 50 to about 70 weight percent,
based
on the total weight of the composite. In a preferred embodiment, the composite
includes about 60 weight percent fibers.
Cellulosic fibers can be a basic component of the fluted absorbent composite.
Although available from other sources, cellulosic fibers are derived primarily
from
wood pulp. Suitable wood pulp fibers for use with the invention can be
obtained
from well-known chemical processes such as the Kraft and sulfite processes,
with or
without subsequent bleaching. Pulp fibers can also be processed by
thermomechanical, chemithermomechanical methods, or combinations thereof. The
preferred pulp fiber is produced by chemical methods. Ground wood fibers,
recycled
or secondary wood pulp fibers, and bleached and unbleached wood pulp fibers
can be
used. Softwoods and hardwoods can be used. Details of the selection of wood
pulp
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fibers are well known to those skilled in the art. These fibers are
commercially
available from a number of companies, including Weyerhaeuser Company, the
assignee of the present invention. For example, suitable cellulose fibers
produced
from southern pine that are usable with the present invention are available
from
Weyerhaeuser Company under the designations CF416, NF405, PL416, FR516, and
NB416.
The wood pulp fibers of the present invention can also be pretreated prior to
use with the present invention. This pretreatment may include physical
treatment,
such as subjecting the fibers to steam, or chemical treatment, for example,
crosslinking the cellulose fibers using any one of a variety of crosslinking
agents.
Crosslinking increases fiber bulk and resiliency, and thereby can improve the
composite's absorbency. Generally, crosslinked fibers are twisted or crimped.
The
use of crosslinked fibers allows the composite to be more resilient, softer,
bulkier.
and to have enhanced wicking. Suitable crosslinked cellulose fibers produced
from
1 S southern pine are available from Weyerhaeuser Company under the
designation
NHB416. Crosslinked cellulose fibers and methods for their preparation are
disclosed in U.S. Patents Nos. 5,437,418 and 5,225,047 issued to Graef et al..
expressly incorporated herein by reference.
Crosslinked fibers are prepared by treating fibers with a crosslinking agent.
Suitable cellulose crosslinking agents include aldehyde and urea-based
formaldehyde
addition products. See, for example, U.S. Patents Nos.3,224,926; 3,241,533;
3,932,209; 4,035,147; 3,756,913; 4,689,118; 4,822,453; U.S. Patent No.
3,440,135,
issued to Chung; U.S. Patent No. 4,935,022, issued to Lash et al.; U.S. Patent
No. 4,889,595, issued to Herron et al.; U.S. Patent No. 3,819,470, issued to
Shaw
et al., U.S. Patent No. 3,658,613, issued to Steijer et al.; and U.S. Patent
No. 4,853,086, issued to Graef et al., all of which are expressly incorporated
herein
by reference in their entirety. Cellulose fibers have also been crosslinked by
carboxylic acid crosslinking agents including polycarboxylic acids. U.S.
Patents
Nos. 5,137,537; 5,183,707; and 5,190,563, describe the use of CZ-C9
polycarboxylic
acids that contain at least three carboxyl groups (e.g., citric acid and
oxydisuccinic
acid) as crosslinking agents.
Suitable urea-based crosslinking agents include methylolated areas,
methylolated cyclic areas, methylolated lower alkyl cyclic areas, methylolated
dihydroxy cyclic areas, dihydroxy cyclic areas, and lower alkyl substituted
cyclic
areas. Specific preferred urea-based crosslinking agents include
dimethyldihydroxy
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urea (DMDHU, 1,3-dimethyl-4.5-dihydroxy-2-imidazolidinone), dimethylol-
dihydroxyethylene urea (DMDHEU, 1,3-dihydroxymethyl-4,5-dihydroxy-2-
imidazolidinone), dimethylol urea (DMU, bis[N-hydroxymethyl]urea), dihydroxy-
ethylene urea (DHEU, 4,5-dihydroxy-2-imidazolidinone), dimethylolethylene urea
(DMEU, 1,3-dihydroxymethyl-2-imidazolidinone), and dimethyldihydroxyethylene
urea (DDI, 4,5-dihydroxy-1,3-dimethyl-2-imidazolidinone).
Suitable polycarboxylic acid crosslinking agents include citric acid, tartaric
acid, malic acid, succinic acid, glutaric acid, citraconic acid, itaconic
acid, tartrate
monosuccinic acid, and malefic acid. Other polycarboxylic acids crosslinking
agents
include polymeric polycarboxylic acids such as poly(acrylic acid),
poly(methacrylic
acid), poly(maleic acid), poly(methylvinylether-co-maleate) copolymer,
poly(methyl-
vinylether-co-itaconate) copolymer, copolymers of acrylic acid, and copolymers
of
malefic acid. The use of polymeric polycarboxylic acid crosslinking agents
such as
polyacrylic acid polymers, polymaleic acid polymers, copolymers of acrylic
acid, and
copolymers of malefic acid is described in U.S. patent application Serial
No. 08/989,697, filed December 12, 1997, and assigned to Weyerhaeuser Company.
Mixtures or blends of crosslinking agents may also be used.
The crosslinking agent can include a catalyst to accelerate the bonding
reaction between the crosslinking agent and cellulose fiber. Suitable
catalysts
include acidic salts, such as ammonium chloride, ammonium sulfate, aluminum
chloride, magnesium chloride, and alkali metal salts of phosphorous-containing
acids.
Although not to be construed as a limitation, examples of pretreating fibers
include the application of surfactants or other liquids which modify the
surface
chemistry of the fibers. Other pretreatments include incorporation of
antimicrobials,
pigments, dyes and densification or softening agents. Fibers pretreated with
other
chemicals, such as thermoplastic and thermosetting resins also may be used.
Combinations of pretreatments also may be employed. Similar treatments can
also
be applied after the composite formation in post-treatment processes.
Cellulosic fibers treated with particle binders and/or densification/softness
aids known in the art can also be employed in accordance with the present
invention.
The particle binders serve to attach other materials, such as cellulosic fiber
superabsorbent polymers, as well as others, to the cellulosic fibers.
Cellulosic fibers
treated with suitable particle binders and/or densification/softness aids and
the
process for combining them with cellulose fibers are disclosed in the
following U.S.
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patents and patent applications: (1) Patent No.5,543,215, entitled "Polymeric
Binders for Binding Particles to Fibers"; (2) Patent No. 5,538,783, entitled
"Non-
Polymeric Organic Binders for Binding Particles to Fibers"; (3) Patent
No. 5,300,192, entitled " Wet-laid Fiber Sheet Manufacturing With
Reactivatable
Binders for Binding Particles to Binders"; (4) Patent No.5,352,480, entitled
''Method for Binding Particles to Fibers Using Reactivatable Binders"; (5)
Patent
No.5,308,896, entitled "Particle Binders for High-Bulk Fibers"; (6) Serial
No. 07/931,279, filed August 17, 1992, entitled "Particle Binders that Enhance
Fiber
Densification"; (7) Serial No. 08/107,469, filed August 17, 1993, entitled
"Particle
Binders"; (8) Serial No. 08/107,219, filed August 17. 1993, entitled "Particle
Binding to Fibers"; (9) Serial No. 08/107,467. filed August 17, 1993, entitled
"Binders for Binding Water Soluble Particles to Fibers"; (10) Patent No.
5,547,745,
entitled "Particle Binders"; (11) Serial No. 08/108,218, filed August 17,
1993,
entitled "Particle Binding to Fibers" and (12) Patent No.5,308,896, entitled
"Particle Binders for High-Bulk Fibers"; all expressly incorporated herein by
reference.
In addition to natural fibers, synthetic fibers including polymeric fibers,
such
as polyolefin, polyamide, polyester, polyvinyl alcohol, and polyvinyl acetate
fibers
can also be used in the absorbent composite of the present invention. Suitable
polyolefin fibers include polyethylene and polypropylene fibers. Suitable
polyester
fibers include polyethylene terephthalate fibers. Other suitable synthetic
fibers
include, for example, nylon and rayon fibers. The absorbent composite can also
include combinations of natural and synthetic fibers.
In one preferred embodiment, the absorbent composite includes a
combination of pulp fibers (e.g., Weyerhaeuser designation NB416) and
crosslinked
cellulosic fibers (e.g., Weyerhaeuser designation NBH416). Pulp fibers
preferably
present in such a combination in an amount from about 15 to about 85 weight
percent. In another preferred embodiment, the absorbent composite includes a
combination of pulp fibers present in the composite in about 50 weight percent
and
crosslinked cellulosic fibers present in the composite in about 50 weight
percent
based on the total weight of fibers.
The fluted absorbent composite of the present invention can serve as a storage
layer for acquired liquids when incorporated into an absorbent article. To
effectively
retain acquired liquids, the composite includes absorbent material.
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As described above, absorbent material is generally located throughout the
composite and in increased concentrations in selected regions of the
composite.
These selected regions include bands incorporated into the composite. The
bands are
positioned across the composite's width and extend along the composite's
length.
The composite's bands are regions of the composite that are enriched with
absorbent
material. The bands of absorbent material can be configured in virtually any
shape,
size, and composite location. Suitable configurations of the composite's bands
include any configuration that does not significantly impede liquid
acquisition or
promote gel blocking. The composite's distribution zones also include some
absorbent material. However, the liquid absorbent capacity of the absorbent
material
in the composite's bands is significantly greater than the absorbent material
present
in the composite's distribution zones.
As use herein, the term "absorbent material'' refers to a material that
absorbs
water and that generally has an absorbent capacity greater than the cellulosic
fibrous
component of the composite. Preferably, the absorbent material is a water
swellable,
generally water insoluble material capable of absorbing at least about 5,
desirably
about 20, and preferably about 100 times or more its weight in water. The
absorbent
material can be swellable in the dispersion medium utilized in the composite
forming
method. In a preferred embodiment, the absorbent material is untreated and
swellable in the dispersion medium.
The amount of absorbent material present in the composite can vary greatly
depending on the composite's intended use. The amount of absorbent material
present in a composite incorporated into as an absorbent core for an infant's
diaper
can be from about 10 to about 80 weight percent, preferably from about 30 to
about
50 weight percent, based on the total weight of the composite.
The absorbent material may include natural materials such as agar, pectin, and
guar gum, and synthetic materials, such as synthetic hydrogel polymers.
Synthetic
hydrogel polymers include, for example, carboxymethyl cellulose, alkaline
metal
salts of polyacrylic acid, polyacrylamides, polyvinyl alcohol, ethylene
malefic
anhydride copolymers, polyvinyl ethers, hydroxypropyl cellulose, polyvinyl
morpholinone, polymers and copolymers of vinyl sulphonic acid, polyacrylates,
polyacrylamides, and polyvinyl pyridine among others. In a preferred
embodiment,
the absorbent material is a superabsorbent material. As used herein, a
"superabsorbent material" refers to a polymeric material that is capable of
absorbing
large quantities of fluid by swelling and forming a hydrated gel (i.e., a
hydrogel). In
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addition to absorbing large quantities of fluids, superabsorbent polymers can
also
retain significant amounts of bodily fluids under moderate pressure.
Superabsorbent materials generally fall into three classes: starch graft
copolymers, crosslinked carboxymethylcellulose derivatives, and modified
hydrophilic polyacrylates. Examples of such absorbent polymers include
hydrolyzed
starch-acrylonitrile graft copolymers, neutralized starch-acrylic acid graft
copolymers, saponified acrylic acid ester-vinyl acetate copolymers, hydrolyzed
acrylonitrile copolymers or acrylamide copolymers, modified crosslinked
polyvinyl
alcohol, neutralized self crosslinking polyacrylic acids, crosslinked
polyacrylate salts,
carboxylated cellulose, and neutralized crosslinked isobutylene-malefic
anhydride
copolymers.
Superabsorbent polymers are available commercially, for example,
polyacrylates from Clariant of Portsmouth, Virginia. These superabsorbent
polymers
come in a variety of sizes, morphologies and absorbent properties (available
from
Clariant under trade designations such as IM 3500 and IM 3900). Other
superabsorbent polymers are marketed under the trademarks SANWET (supplied by
Sanyo Kasei Kogyo Kabushiki Kaisha), and SXM77 and SR1001 (supplied by
Stockhausen of Greensboro, North Carolina). Other superabsorbent materials are
described in U.S. Patent No.4,160,059; U.S. Patent No.4,676,784; U.S. Patent
No. 4,673,402; U.S. Patent No. 5,002,814; U.S. Patent No. 5,057,166; U.S.
Patent
No. 4,102,340; and U.S. Patent No. 4,818,598, all expressly incorporated
herein by
reference. Products such as diapers that incorporate superabsorbent materials
are
described in U.S. Patent No. 3,699,103 and U.S. Patent No. 3,670,731.
Suitable superabsorbent materials useful in the absorbent composite of the
present invention include superabsorbent particles and superabsorbent fibers.
The fluted absorbent composite of the present invention can be formed by air-
laid methods known to those of ordinary skill in the pulp processing art.
Representative air-laid processes are generally described in U.S. Patent
Nos.4.640,810 and 4,065,832, both expressly incorporated herein by reference.
Generally, air-laid fibrous webs that include absorbent materials such as
superabsorbent materials are known in the art. In these webs, absorbent
materials are
conventionally distributed uniformly throughout the web. Conventional air-laid
webs
that contain absorbent material typically suffer gel blocking which limits the
rate of
liquid acquisition, distribution, and can adversely impact absorbent capacity.
Air-laid
webs also tend to have lower acquisition rates, absorbent capacity, and
tensile
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strength compared to wet-laid fibrous webs. Despite these limitations, the air-
laid
composites formed in accordance with the present invention have enhanced
liquid
absorbent properties, including increased acquisition rate, compared to air-
laid
composites having absorbent material uniformly distributed throughout the
entire
web.
The fluted absorbent composite of the present invention is a composite having
absorbent material concentrations that vary between adjacent regions of the
composite. The variation in absorbent material concentration provides a
composite
having differential liquid absorption and swelling characteristics.
The composite can be formed by any method that provides a fibrous
composite having variable absorbent material content. For example, the
composite
can be formed by varying the basis weight of a composite formed from a
homogeneous blend of absorbent material and fibers (e.g.. a fibrous composite
having a relatively uniform concentration of absorbent material).
Alternatively, the
1 S composite can be formed by selectively varying absorbent material
concentration in
the composite (i.e., across the composite's width to provide bands or regions
that are
enriched with absorbent material).
Variable basis weight composites can be formed by a number of methods
including methods that affect the laydown of materials (i.e., fibers and
absorbent
material) during the air-lay process. For example, a composite having variable
basis
weight can be formed by creating zones of differing porosity or air
permeability on
the foraminous support (e.g., forming wire) on which the composite is formed.
Airflows carrying fibers and absorbent material will bias to lower resistance
zones on
the support (i.e., material flows bias toward high porosity). In such a
method, higher
basis weight regions are created in the composite where flow through the
support is
least restrictive and lower basis weight regions are created where the flow is
more
restricted.
The support's backing plate can be shaped into patterns that permit drawing
forming air through areas of the support at a rate that is greater than for
other areas.
Such a method also biases the laydown of material to provide a composite
having
higher basis weight regions (i.e., regions of higher airflow) and lower basis
weight
regions (i.e., regions of lower airflow).
The methods noted above can also provide fibrous webs having absorbent
material concentration gradients. In these methods, a previously deposited
fibrous
web can be subjected to forming airflow carrying absorbent material. In such a
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method, absorbent material applied to the deposited web is distributed
throughout the
web based on airflow through the deposited web.
Alternatively, absorbent material can be added to a fibrous web by any other
method that provides for the formation of bands or other absorbent material
enriched
regions in the composite.
Composites of the present invention having variable basis weight and variable
absorbent material concentration can also be formed from composites that are
relatively homogeneous blends of fibers and absorbent material (i.e.,
composites
having a relatively uniform concentration of absorbent material). In the
method,
fibers and absorbent material are first laid on a foraminous support to
provide a
composite having a homogeneous blend of fibers and absorbent material.
Following
deposition, the homogeneous air-laid web's upper surface is scarfed (i.e.,
removed)
to provide a web having ridges and valleys. A representative homogeneous web
formed by air laying fibers and absorbent material followed by scarfing is
shown in
FIGURE 5. Referring to FIGURE 5, scarfed web 20 includes ridges 22 and valleys
24. After scarfing, the homogeneous composite is then densified to, for
example, a
relatively uniform thickness (i.e., caliper). On densification, the materials
in the
scarfed web's ridges are compacted. In a preferred embodiment, densification
provides an air-laid web having a relatively uniform in thickness. As a result
of
densification, the method provides a composite that includes regions having
increased basis weight and regions having increased absorbent material
concentration. When densification results in a web having a relatively uniform
thickness, the method provides a composite that can be represented by
composite 10
shown in FIGURE 1. Referring again to FIGURE l, composite 10 includes regions
12 that are enriched with absorbent material. In accordance with the method
noted
above, regions 12 have an absorbent material concentration that is increased
relative
to regions 14. Furthermore, regions 12 also have a basis weight that is
increased
relative to regions 14.
The fluted absorbent composite of the present invention can be incorporated
as an absorbent core or storage layer in an absorbent article including, for
example, a
diaper or feminine care product. The absorbent composite can be used alone, or
as
illustrated in FIGURES 6 and 7, can be used in combination with one or more
other
layers. FIGURE 6 illustrates absorbent construct 30 where composite 10 is
employed
as a storage layer in combination with an upper acquisition layer 32. As
illustrated in
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FIGURE 7, construct 40 includes a third layer 42 (e.g., distribution layer)
that can
also be employed, if desired, with composite 10 and acquisition layer 32.
Alternatively, construct 30 can be formed by overlying an acquisition layer on
a scarfed web followed by densification. Referring to FIGURE 8, construct 50
includes scarfed web 20 and acquisition layer 32. Depending on the amount of
contact desired between the acquisition layer and storage core, the
acquisition layer
can be formed to substantially occupy the valleys formed in the scarfed web.
Referring to FIGURE 9, construct 60 includes scarfed web 20 and acquisition
layer
32, which substantially occupies the web's valleys. Densification of
constructs 50 or
60 provides construct 30.
A variety of suitable constructs can be produced from the absorbent
composite. The most common include absorptive consumer products, such as
diapers, feminine hygiene products such as feminine napkins, and adult
incontinence
products. For example, referring to FIGURE 10, absorbent article 70 includes
absorbent composite 10 and has a liquid pervious facing sheet 52 and a liquid
impervious backing sheet 54. Referring to FIGURE 1 l, absorbent article 80
includes
absorbent composite 10 and an overlying acquisition layer 32. A liquid
pervious
facing sheet 52 overlies acquisition layer 32, and a liquid impervious backing
sheet 54 underlies absorbent composite 10. These absorbent composites will
provide
advantageous liquid absorption performance for use in, for example, diapers.
FIGURE 12 illustrates absorbent construct 90, which further includes
distribution
layer 42 interposed between acquisition layer 32 and composite 10.
One of ordinary skill will be able to make a variety of different constructs
using the concepts taught herein. For example, a typical construction of an
adult
incontinence absorbent structure is shown in FIGURE 13. Referring to FIGURE
13,
article 100 includes facing sheet 52, acquisition layer 32, absorbent
composite 10,
and backing sheet 54. Facing sheet 22 is pervious to liquid while backing
sheet 24 is
impervious to liquid. In this construct, a liquid pervious tissue 44 composed
of a
polar, fibrous material is positioned between absorbent composite 10 and
acquisition
layer 32.
The present invention provides a fibrous absorbent composite containing
absorbent material and methods for its formation. The absorbent composite is a
fibrous structure that includes absorbent material dispersed throughout the
composite
and in increased concentration in bands across the composite's width that
extend
along the composite's length. Between the bands of absorbent material, the
absorbent
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composite includes fibrous. distribution zones that prevent gel blocking in
the
composite. After initial liquid insult, the composite develops ridges that
open the
fibrous structure and increase the liquid acquisition rate for subsequent
liquid insults.
The combination of ridges enriched with absorbent material and fibrous
distribution
S zones allows for total utilization of the absorbent composite as a storage
core when
incorporated into an absorbent article such as a diaper.
While the preferred embodiment of the invention has been illustrated and
described, it will be appreciated that various changes can be made therein
without
departing from the spirit and scope of the invention.
