Note: Descriptions are shown in the official language in which they were submitted.
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ABSORBENT COMPOSITE HAVING FIBROUS BANDS
Cross-Reference to Related Application
This application claims the benefit of the priority of the filing date of
copending U.S.
application No. 60/155,464, filed September 21, 1999, which is expressly
incorporated herein
by reference in its entirety.
Field of the Invention
The present invention relates to an absorbent composite and more particularly,
to an
absorbent composite that includes superabsorbent material and fibrous bands.
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 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
superabsorbent 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.
Because superabsorbent polymers absorb liquid and swell upon contact with
liquid,
superabsorbent polymers have heretofore been incorporated primarily in
cellulose mats that
are produced by the conventional dry, air-laid methods. Wet-laid processes for
forming
cellulose mats have not been used commercially because superabsorbent polymers
tend to
absorb liquid and swell during formation of the absorbent mats, thus requiring
significant
energy for their complete drying.
Cellulose structures formed by the wet-laid process typically exhibit certain
properties
that are superior to those of an air-laid. structure. The integrity, fluid
distribution, and the
wicking characteristics of wet-laid cellulosic structures are superior to
those of air-laid
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structures. Attempts to combine the advantages of wet-laid composites with the
high
absorbent capacity of superabsorbent materials has led to the formation of
various wet-laid
absorbent composites that include superabsorbent materials. Generally, these
structures
include superabsorbent materials distributed as a layer within a multilayered
composite. In
these structures the superabsorbent polymer is relatively localized and not
uniformly
distributed throughout the absorbent structure and thus renders these
composites susceptible
to gel blocking. Upon liquid absorption, superabsorbent materials tend to
coalesce and form
a gelatinous mass that 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 diminished capacity of such fibrous composites results from
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
are
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
The present invention relates to a reticulated fibrous absorbent composite
containing
absorbent material. The absorbent composite is a fibrous matrix that includes
absorbent
material and a three-dimensional network of channels or capillaries. The
composite's
reticulated nature enhances liquid distribution, acquisition, and wicking,
while the absorbent
material provides high absorbent capacity. Wet strength agents can be
incorporated into the
composite to provide wet integrity and also to assist in securing the
absorbent material in the
composite.
The absorbent composite formed in accordance with the present invention
includes a
stable three-dimensional network of fibers and channels that afford rapid
acquisition and
wicking of liquid. The fibers and channels distribute the acquired liquid
throughout the
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composite and direct liquid to absorbent material present in the composite
where the liquid is
ultimately absorbed. The composite maintains its integrity before, during, and
after liquid is
introduced. In one embodiment, the composite is a densified composite that can
recover its
original volume on wetting.
In one aspect, the present invention provides an absorbent composite having a
fibrous
matrix that includes absorbent material. The fibrous matrix defines voids and
passages
between the voids, which are distributed throughout the composite. Absorbent
material is
located within some of the voids. The absorbent material located in these
voids is
expandable into the void.
In one embodiment, the reticulated absorbent composite includes at least one
fibrous
stratum. For such an embodiment, the composite includes a reticulated core and
a fibrous
stratum adjacent and coextensive with an outward facing surface of the core.
In another
embodiment, the composite includes strata on opposing outward facing surfaces
of the core.
The composite's strata can be composed of any suitable fiber or combination of
fibers and
can be formed from fibers that are the same as or different from the fibers
used for forming
the reticulated core.
In another embodiment, the absorbent composite includes fibrous bands.
In another aspect of the invention, absorbent articles that include the
reticulated
composite are provided. The absorbent articles include consumer absorbent
products such as
diapers, feminine care products, and adult incontinence products.
Brief Description of the Drawings
The foregoing aspects and many of the attendant advantages of this invention
will
become more readily appreciated by reference to the following detailed
description, when
taken in conjunction with the accompanying drawings, wherein:
FIGURE 1 is a cross-sectional view of a portion of a reticulated absorbent
composite
formed in accordance with the present invention;
FIGURE 2 is a photomicrograph of a cross section of a representative
reticulated
absorbent composite formed by a wet-laid method in accordance with the present
invention at
12 times magnification;
FIGURE 3 is a photomicrograph of the wet-laid composite of FIGURE 2 at 40
times
magnification;
FIGURE 4 is a photomicrograph of a cross section of a representative
reticulated
absorbent composite formed by a foam method in accordance with the present
invention at 12
times magnification;
FIGURE 5 is a photomicrograph of the foam-formed composite of FIGURE 4 at
times magnification;
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FIGURE 6 is a photomicrograph of a cross section of a representative
reticulated
absorbent composite formed by a wet-laid method in accordance with the present
invention in
a wetted state at 8 times magnification;
FIGURE 7 is a photomicrograph of the wet-laid composite of FIGURE 6 at 12
times
magnification;
FIGURE 8 is a photomicrograph of a cross section of a representative
reticulated
absorbent composite formed by a foam method in accordance with the present
invention in a
wetted state at 8 times magnification;
FIGURE 9 is a photomicrograph of the foam-formed composite of FIGURE 8 at
12 times magnification;
FIGURE 10 is a cross-sectional view of a portion of an absorbent construct
incorporating a reticulated absorbent composite formed in accordance with the
present
invention;
FIGURE 11 is a cross-sectional view of a portion of another absorbent
construct
incorporating a reticulated absorbent composite formed in accordance with the
present
invention;
FIGURE 12 is a cross-sectional view of a portion of an absorbent article
incorporating
a reticulated absorbent composite formed in accordance with the present
invention;
FIGURE 13 is a cross-sectional view of a portion of another absorbent article
incorporating a reticulated absorbent composite formed in accordance with the
present
invention;
FIGURE 14 is a cross-sectional view of a portion of another absorbent article
incorporating a reticulated absorbent composite formed in accordance with the
present
invention;
FIGURE 15 is a cross-sectional view of a portion of an absorbent construct
incorporating a reticulated absorbent composite formed in accordance with the
present
invention;
FIGURE 16 is a cross-sectional view of a portion of another absorbent
construct
incorporating a reticulated absorbent composite formed in accordance with the
present
invention;
FIGURE 17 is a cross-sectional view of a portion of another absorbent
construct
incorporating a reticulated absorbent composite formed in accordance with the
present
invention;
FIGURE 18 is a cross-sectional view of a portion of an absorbent article
incorporating
a reticulated absorbent composite formed in accordance with the present
invention;
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FIGURE 19 is a cross-sectional view of a portion of another absorbent article
incorporating a reticulated absorbent composite formed in accordance with the
present
invention;
FIGURE 20 is a cross-sectional view of a portion of another absorbent article
incorporating a reticulated absorbent composite formed in accordance with the
present
invention;
FIGURES 21A and B are cross-sectional views of portions of reticulated
absorbent
composites formed in accordance with the present invention;
FIGURE 22 is a diagrammatic view illustrating a twin-wire device and method
for
forming the composite of the present invention;
FIGURE 23 is a diagrammatic view illustrating a representative headbox
assembly
and method for forming the composite of the present invention;
FIGURE 24 is a diagrammatic view illustrating a representative headbox
assembly
and method for forming the composite of the present invention;
FIGURE 25 is a view illustrating representative conduits for introducing
absorbent
material into a fibrous web in accordance with the present invention;
FIGURES 26A-C are cross-sectional views of portions of absorbent constructs
incorporating an acquisition layer and a reticulated absorbent composite
formed in
accordance with the present invention;
FIGURES 27A-C are cross-sectional views of portions of absorbent constructs
incorporating an acquisition layer, intermediate layer, and a reticulated
absorbent composite
formed in accordance with the present invention;
FIGURES 28A-C are cross-sectional views of portions of absorbent articles
incorporating a reticulated absorbent composite formed in accordance with the
present
invention;
FIGURES 29A-C are cross-sectional views of portions of absorbent articles
incorporating an acquisition layer and a reticulated absorbent composite
formed in
accordance with the present invention;
FIGURES 30A-C are cross-sectional views of portions of absorbent articles
incorporating an acquisition layer, intermediate layer, and a reticulated
absorbent composite
formed in accordance with the present invention;
FIGURE 31 is a schematic illustration of a representative composite having
fibrous
bands formed in accordance with the present invention;
FIGURE 32 is a graph comparing the wicking height at 15 minutes, capacity at
15 cm,
and wetted zone capacity for representative composites formed in accordance
with the
present invention;
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FIGURE 33 is a graph correlating composite ring crush and tensile strength for
representative composites formed in accordance with the present invention;
FIGURE 34 is a graph correlating composite unrestrained vertical wicking
height and
saturation capacity for representative composites formed in accordance with
the present
invention;
FIGURE 35 is a graph comparing composite ring crush and tensile strength for
representative composites formed in accordance with the present invention; and
FIGURE 36 is a graph comparing composite unrestrained vertical wicking height
and
saturation capacity for representative composites formed in accordance with
the present
invention.
Detailed Description of the Preferred Embodiment
The absorbent composite formed in accordance with the present invention is a
reticulated fibrous composite that includes absorbent material. The absorbent
material is
distributed substantially throughout the fibrous composite and serves to
absorb and retain
liquid acquired by the composite. In a preferred embodiment, the absorbent
material is a
superabsorbent material. In addition to forming a matrix for the absorbent
material, the
composite's fibers provide a stable three-dimensional network of channels or
capillaries that
serve to acquire liquid contacting the composite and to distribute the
acquired liquid to the
absorbent material. The composite optionally includes a wet strength agent
that further
increases tensile strength and structural integrity to the composite.
The composite is a fibrous matrix that includes absorbent material. The
fibrous
matrix defines voids and passages between the voids, which are distributed
throughout the
composite. Absorbent material is located within some of the voids. The
absorbent material
located in these voids is expandable into the void.
The absorbent composite can be advantageously incorporated into a variety of
absorbent articles such as 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 having a high liquid storage
capacity, the
composite can be incorporated 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 distribution layer. In a
preferred embodiment,
an absorbent article, such as a diaper, includes an acquisition layer
overlying a reticulated
storage core and having a liquid pervious facing sheet and a liquid impervious
backing sheet.
Because of the composite's capacity to rapidly acquire and distribute liquid,
the composite
can serve as a liquid management layer that acquires and transfers a portion
of the acquired
liquid to an underlying storage layer. Thus, in another embodiment, the
absorbent composite
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can be combined with a storage layer to provide an absorbent core that is
useful in absorbent
articles.
The absorbent composite formed in accordance with the present invention is a
reticulated absorbent composite. As used herein, the term "reticulated" refers
to the
composite's open and porous nature characterized as having a stable three-
dimensional
network of fibers (i.e., fibrous matrix) that create channels or capillaries
that serve to rapidly
acquire and distribute liquid throughout the composite, ultimately delivering
acquired liquid
to the absorbent material that is distributed throughout the composite.
The reticulated composite is an open and stable structure. The fibrous
composite's
open and stable structure includes a network of capillaries or channels that
are effective in
acquiring and distributing liquid throughout the composite. In the composite,
fibers form
relatively dense bundles that direct fluid throughout the composite and to
absorbent material
distributed throughout the composite. The composite's wet strength agent
serves to stabilize
the fibrous structure by providing interfiber bonding. The interfiber bonding
assists in
providing a composite having a stable structure in which the composite's
capillaries or
channels remain open before, during, and after liquid insult. The composite's
stable structure
provides capillaries that remain open after initial liquid insult and that are
available for
acquiring and distributing liquid on subsequent insults.
Referring to FIGURE 1, a representative reticulated absorbent composite
indicated
generally by reference numeral 10 formed in accordance with the present
invention is a
fibrous matrix that includes fibrous regions 12 substantially composed of
fibers 16 and
defining voids 14. Some voids include absorbent material 18. Voids 14 are
distributed
throughout composite 10.
Representative reticulated composites formed in accordance with the invention
are
shown in FIGURES 2-9. These composites include 48 percent by weight matrix
fibers (i.e.,
southern pine commercially available from Weyerhaeuser Co. under the
designation NB416),
12 percent by weight resilient fibers (i.e., polymaleic acid crosslinked
fibers), 40 percent by
weight absorbent material (i.e., superabsorbent material commercially
available from
Stockhausen), and about 0.5 percent by weight wet strength agent (i.e.,
polyamide
epichlorohydrin resin commercially available from Hercules under the
designation
Kymene~). FIGURE 2 is a photomicrograph of a cross section of a representative
composite
formed by a wet-laid process at 12 x magnification. FIGURE 3 is a
photomicrograph of the
same cross section at 40 x magnification. FIGURE 4 is a photomicrograph of a
cross section
of a representative composite formed by a foam process at 12 x magnification.
FIGURE 5 is
a photomicrograph of the same cross section at 40 x magnification. The
reticulated nature of
the composites is shown in these figures. Referring to FIGURE 3, fibrous
regions extend
throughout the composite creating a network of channels. Void regions,
including those that
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include absorbent material, appear throughout the composite and are in fluid
communication
with the composite's fibrous regions. Absorbent material appears in the
composite's voids,
generally surrounded by dense fiber bundles.
Photomicrographs of the representative composites shown in FIGURES 2-5 in a
wetted state are illustrated in FIGURES 6-9, respectively. These
photomicrographs were
obtained by sectioning freeze-dried composites that had acquired synthetic
urine under free
swell conditions. FIGURES 6 and 7 are photomicrographs of the wetted wet-laid
composite
at 8 x and 12 x magnification, respectively. FIGURES 8 and 9 are
photomicrographs of the
wetted foam-formed composite at 8 x and 12 x magnification, respectively.
Referring to
FIGURE 6, absorbent material in the wetted composite has swollen and increased
in size to
more fully occupy voids that the absorbent material previously occupied in the
dry composite.
The composite's fibrous matrix is composed primarily of 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. Fibers
suitable for use in the present invention are known to those skilled in the
art and include any
fiber from which a wet composite can be formed.
The composite includes resilient fibers. As used herein, the term "resilient
fiber"
refers to a fiber present in the composite that imparts reticulation to the
composite.
Generally, resilient fibers provide the composite with bulk and resiliency.
The incorporation
of resilient fibers into the composite allows the composite to expand on
absorption of liquid
without structural integrity loss. Resilient fibers also impart softness to
the composite. In
addition, resilient fibers offer advantages in the composite's formation
processes. Because of
the porous and open structure resulting from wet composites that include
resilient fibers,
these composites drain water relatively easily and are therefore dewatered and
dried more
readily than wet composites that do not include resilient fibers. Preferably,
the composite
includes resilient fibers in an amount from about 5 to about 60 percent by
weight, more
preferably from about 10 to 40 percent by weight, based on the total weight of
the composite.
Resilient fibers include cellulosic and synthetic fibers. Preferred resilient
fibers
include chemically stiffened fibers, anfractuous fibers, chemithermomechanical
pulp
(CTMP), and prehydrolyzed kraft pulp (PHKP).
The term "chemically stiffened fiber" refers to a fiber that has been
stiffened by
chemical means to increase fiber stiffness under dry and wet conditions.
Fibers can be
stiffened by the addition of chemical stiffening agents that can coat and/or
impregnate the
fibers. Stiffening agents include the polymeric wet strength agents including
resinous agents
such as, for example, polyamide-epichlorohydrin and polyacrylamide resins
described below.
Fibers can also be stiffened by modifying fiber structure by, for example,
chemical
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crosslinking. Preferably, the chemically stiffened fibers are intrafiber
crosslinked cellulosic
fibers.
Resilient fibers can include noncellulosic fibers including, for example,
synthetic
fibers such as polyolefin, polyamide, and polyester fibers. In a preferred
embodiment, the
resilient fibers include crosslinked cellulosic fibers.
As used herein, the term "anfractuous fiber" refers to a cellulosic fiber that
has been
chemically treated. Anfractuous fibers include, for example, fibers that have
been treated
with ammonia.
In addition to resilient fibers, the composite includes matrix fibers. As used
herein,
the term "matrix fiber" refers to a fiber that is capable of forming hydrogen
bonds with other
fibers. Matrix fibers are included in the composite to impart strength to the
composite.
Matrix fibers include cellulosic fibers such as wood pulp fibers, highly
refined cellulosic
fibers, and high surface area fibers such as expanded cellulose fibers. Other
suitable
cellulosic fibers include cotton linters, cotton fibers, and hemp fibers,
among others.
Mixtures of fibers can also be used. Preferably, the composite includes matrix
fibers in an
amount from about 10 to about 60 percent by weight, more preferably from about
20 to about
50 percent by weight, based on the total weight of the composite.
The composite preferably includes a combination of resilient and matrix
fibers. In
one preferred embodiment, the composite includes resilient fibers in an amount
from about 5
to about 20 percent by weight and matrix fibers in an amount from about 20 to
about 60
percent by weight based on the total weight of the composite. In a more
preferred
embodiment, the composite includes from about 10 to about 15 percent by weight
resilient
fibers, preferably crosslinked cellulosic fibers, and from about 40 to about
50 percent by
weight matrix fibers, preferably wood pulp fibers, based on the total weight
of the composite.
Cellulosic fibers are a basic component of the 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. The pulp fibers may 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 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
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invention are available from Weyerhaeuser Company under the designations
CF416, NF405,
PL416, FR516, and NB416.
The wood pulp fibers 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 fibers' absorbency. Generally, crosslinked fibers are twisted or
crimped. The
use of crosslinked fibers allows the composite to be more resilient, softer,
bulkier, have better
wicking, and be easier to densify than a composite that does not include
crosslinked fibers.
Suitable crosslinked cellulose fibers produced from 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.
Intrafiber crosslinked cellulosic fibers are prepared by treating cellulose
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.5.
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 ureas,
methylolated
cyclic ureas, methylolated lower alkyl cyclic ureas, methylolated dihydroxy
cyclic ureas,
dihydroxy cyclic ureas, and lower alkyl substituted cyclic ureas. Specific
preferred urea-
based crosslinking agents include dimethyldihydroxyethylene urea (DMeDHEU, 1,3-
dimethyl-4,5-dihydroxy-2-imidazolidinone), dimethyloldihydroxyethylene urea
(DMDHEU,
1,3-dihydroxymethyl-4,5-dihydroxy-2-imidazolidinone), dimethylol urea (DMU,
bis[N-
hydroxymethyl]urea), dihydroxyethylene urea (DHEU, 4,5-dihydroxy-2-
imidazolidinone),
and dimethylolethylene urea (DMEU, 1,3-dihydroxymethyl-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 acid crosslinking agents include
polymeric
polycarboxylic acids such as poly(acrylic acid), poly(methacrylic acid),
poly(maleic acid),
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poly(methylvinylether-co-maleate) copolymer, poly(methylvinylether-co-
itaconate) copoly-
mer, 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 can 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 that 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. patents: (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) Patent No. 5,589,256, entitled "Particle Binders that Enhance
Fiber
Densification"; (7) Patent No.5,672,418, entitled "Particle Binders"; (8)
Patent
No.5,607,759, entitled "Particle Binding to Fibers"; (9) Patent No.5,693,411,
entitled
"Binders for Binding Water Soluble Particles to Fibers"; (10) Patent No.
5,547,745, entitled
"Particle Binders"; (11) Patent No. 5,641,561, entitled "Particle Binding to
Fibers"; (12)
Patent No.5,308,896, entitled "Particle Binders for High-Bulk Fibers"; (13)
Patent
No. 5,498,478, entitled "Polyethylene Glycol as a Binder Material for Fibers";
(14) Patent
No. 5,609,727, entitled "Fibrous Product for Binding Particles"; (15) Patent
No. 5,571,618,
entitled "Reactivatable Binders for Binding Particles to Fibers"; (16) Patent
No. 5,447,977,
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entitled "Particle Binders for High Bulk Fibers"; (17) Patent No.5,614,570,
entitled
"Absorbent Articles Containing Binder Carrying High Bulk Fibers; (18) Patent
No. 5,789,326, entitled "Binder Treated Fibers"; and (19) Patent No.
5,611,885, entitled
"Particle Binders", 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 may also be
used in the absorbent composite. Suitable polyolefm fibers include
polyethylene and
polypropylene fibers. Suitable polyester fibers include polyethylene
terephthalate fibers.
Other suitable synthetic fibers include, for example, nylon fibers. The
absorbent composite
can include combinations of natural and synthetic fibers.
In one preferred embodiment, the absorbent composite includes a combination of
wood pulp fibers (e.g., Weyerhaeuser designation NB416) and crosslinked
cellulosic fibers
(e.g., Weyerhaeuser designation NHB416). Wood pulp fibers are present in such
a
combination in an amount from about 10 to about 85 weight percent by weight
based on the
total weight of fibers.
When incorporated into an absorbent article, the reticulated absorbent
composite can
serve as a storage layer for acquired liquids. To effectively retain acquired
liquids, the
absorbent composite includes absorbent material. As used herein, the term
"absorbent
material" refers to a material that absorbs liquid 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 polymeric material
capable of
absorbing at least about 5, desirably about 20, and preferably about 100 times
or more its
weight in saline (e.g., 0.9 percent saline). The absorbent material can be
swellable in the
dispersion medium utilized in the method for forming the composite. In one
embodiment,
the absorbent material is untreated and swellable in the dispersion medium. In
another
embodiment, the absorbent material is a coated absorbent material that is
resistant to
absorbing water during the composite formation process.
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 an
absorbent article, such as an absorbent core for an infant's diaper, is
suitably present in the
composite in an amount from about 5 to about 60 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
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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 addition to
absorbing large quantities of fluids, superabsorbent materials 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 materials 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 materials are marketed
under the
trademarks SANWET (supplied by Sanyo Kasei Kogyo Kabushiki Kaisha), and SXM77
(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 include
superabsorbent particles and superabsorbent fibers.
In a preferred embodiment, the absorbent composite includes a superabsorbent
material that swells relatively slowly for the purposes of composite
manufacturing and yet
swells at an acceptable rate so as not to adversely affect the absorbent
characteristics of the
composite or any construct containing the composite. Generally, the smaller
the absorbent
material, the more rapidly the material absorbs liquid.
The absorbent composite can optionally include a wet strength agent. The wet
strength agent provides increased strength to the absorbent composite and
enhances the
composite's wet integrity. In addition to increasing the composite's wet
strength, the wet
strength agent can assist in binding the absorbent material, for example,
superabsorbent
material, in the composite's fibrous matrix.
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Suitable wet strength agents include cationic modified starch having nitrogen-
containing groups (e.g., amino groups) such as those available from National
Starch and
Chemical Corp., Bridgewater, NJ; latex; wet strength resins such as polyamide-
epichlorohydrin resin (e.g., Kymene~ 557LX, Hercules, Inc., Wilmington, DE),
polyacrylamide resin (described, for example, in U.S. Patent No.3,556,932
issued
January 19, 1971 to Coscia et al.; also, for example, the commercially
available
polyacrylamide marketed by American Cyanamid Co., Stanford, CT, under the
trade name
ParezTM 631 NC); urea formaldehyde and melamine formaldehyde resins, and
polyethylenimine resins. A general discussion on wet strength resins utilized
in the paper
field, and generally applicable in the present invention, can be found in
TAPPI monograph
series No. 29, "Wet Strength in Paper and Paperboard", Technical Association
of the Pulp
and Paper Industry (New York, 1965).
Generally, the wet strength agent is present in the composition in an amount
from
about 0.01 to about 2 weight percent, preferably from about 0.1 to about 1
weight percent,
and more preferably from about 0.3 to about 0.7 weight percent, based on the
total weight of
the composite. In a preferred embodiment, the wet strength agent useful in
forming the
composite is a polyamide-epichlorohydrin resin commercially available from
Hercules, Inc.
under the designation Kymene~. The wet and dry tensile strengths of an
absorbent
composite formed in accordance with the present invention will generally
increase with an
increasing the amount of wet strength agent. The tensile strength of a
representative
composite is described in Example 7.
The absorbent composite generally has a basis weight from about 50 to about
1000
g/m2, preferably from about 200 to about 800 g/m2. In a more preferred
embodiment, the
absorbent composite has a basis weight from about 300 to about 600 g/m2. The
absorbent
composite generally has a density from about 0.02 to about 0.7 g/cm3,
preferably from about
0.04 to about 0.3 g/cm3. In a more preferred embodiment, the absorbent
composite has a
density of about 0.15 g/cm3.
In one embodiment, the absorbent composite is a densified composite.
Densification
methods useful in producing the densified composites are well known to those
in the art.
See, for example, U.S. Patent No. 5,547,541 and patent application Serial No.
08/859,743,
filed May 21, 1997, entitled "Softened Fibers and Methods of Softening
Fibers," assigned to
Weyerhaeuser Company, both expressly incorporated herein by reference. Post-
dryer
densified absorbent reticulated storage composites generally have a density
from about 0.1 to
about 0.5 g/cm3, and preferably about 0.1 S g/cm3. Predryer densification can
also be
employed. Preferably, the absorbent composite is densified by either a heated
or room
temperature calender roll method. See, for example, U.S. Patents Nos.
5,252,275 and
5,324,575, both expressly incorporated herein by reference.
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The composition of the reticulated absorbent composite can be varied to suit
the
needs of the desired end product in which it can be incorporated. In one
preferred
embodiment, the absorbent composite includes about 60 weight percent
cellulosic fibers
(about 48 percent by weight wood pulp fibers and about 12 percent by weight
crosslinked
cellulosic fibers), about 40 percent by weight absorbent material (e.g.,
superabsorbent
particles), and about 0.5 percent by weight wet strength agent (e.g.,
polyamide-
epichlorohydrin resin, Kymene~, about 10 pounds resin per ton fiber) based on
the total
weight of the composite.
The reticulated absorbent composite can be formed by wet-laid and foam
processes
known to those of ordinary skill in the pulp processing art. A representative
example of a
wet-laid process is described in U.S. Patent No. 5,300,192, issued April 5,
1994, entitled
"Wet-laid Fiber Sheet Manufacturing with Reactivatable Binders for Binding
Particles to
Fibers", expressly incorporated herein by reference. Wet-laid processes are
also described in
standard texts, such as Casey, PULP AND PAPER, 2nd edition, 1960, Volume II,
Chapter VIII
Sheet Formation. Representative foam processes useful in forming the composite
are known
in the art and include those described in U.S. Patents Nos. 3,716,449;
3,839,142; 3,871,952;
3,937,273; 3,938,782; 3,947,315; 4,166,090; 4,257,754; and 5,215,627, assigned
to Wiggins
Teape and related to the formation of fibrous materials from foamed aqueous
fiber
suspensions, and "The Use of an Aqueous Foam as a Fiber-Suspending Medium in
Quality
Papermaking," Foams, Proceedings of a Symposium organized by the Society of
Chemical
Industry, Colloid and Surface Chemistry Group, R.J. Akers, Ed., Academic
Press, 1976,
which describes the Radfoam process, all expressly incorporated herein by
reference.
In the methods, the absorbent material is incorporated into the composite
during the
formation of the composite. Generally, the methods for forming the reticulated
absorbent
composite include combining the components of the composite in a dispersion
medium (e.g.,
an aqueous medium) to form a slurry and then depositing the slurry onto a
foraminous
support (e.g., a forming wire) and dewatering to form a wet composite. Drying
the wet
composite provides the reticulated composite.
As noted above, the reticulated composite is prepared from a combination of
fibers,
absorbent material, and optionally a wet strength agent in a dispersion
medium. In one
embodiment of the method, a slurry is formed by directly combining fibers,
absorbent
material, and wet strength agent in a dispersion medium. In another
embodiment, the slurry
is prepared by first combining fibers and the wet strength agent in a
dispersion medium to
provide a fibrous slurry to which is then added absorbent material in a second
step. In yet
another embodiment, a fibrous slurry is combined with a second slurry
containing absorbent
material, the combined slurry then being deposited onto the support.
Alternatively,
individual slurries, for example, a fibrous slurry and a slurry containing
absorbent material,
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can be deposited onto the foraminous support through the use of a divided
headbox, for
example, a twin slice headbox that deposits two slurries onto a support
simultaneously.
In one embodiment, the slurry or slurries containing the composite's
components in a
dispersion medium are deposited onto a foraminous support. Once deposited onto
the
support the dispersion medium begins to drain from the deposited fibrous
slurry. Removal of
the dispersion medium (e.g., dewatering) from the deposited fibrous slurry
continues through,
for example, the application of heat, pressure, vacuum, and combinations
thereof, and results
in the formation of a wet composite.
The reticulated absorbent composite is ultimately produced by drying the wet
composite. Drying removes the remaining dispersion medium and provides an
absorbent
composite having the desired moisture content. Generally, the composite has a
moisture
content less than about 20 percent and preferably has a moisture content in
the range from
about 6 to about 10 percent by weight based on the total weight of the
composite. Suitable
composite drying methods include, for example, the use of drying cans, air
floats, and
through air dryers. Other drying methods and apparatus known in the pulp and
paper industry
may also be used. Drying temperatures, pressures, and times are typical for
the equipment
and methods used, and are known to those of ordinary skill in the art in the
pulp and paper
industry. A representative wet-laid method for forming a reticulated absorbent
composite is
described in Example 1.
For foam methods, the fibrous slurry is a foam dispersion that further
includes a
surfactant. Suitable surfactants include ionic, nonionic, and amphoteric
surfactants known in
the art. A representative foam method for forming a reticulated absorbent
composite is
described in Example 2.
The deposition of the components of the absorbent composite onto the
foraminous
support, followed by dewatering, results in the formation of a wet composite
that includes
absorbent material that may have absorbed water and, as a result, swollen in
size. The wet
composite containing the water-swollen absorbent material is distributed onto
a support from
which water (i.e., the dispersion medium) can be withdrawn and the wet
composite dried.
Drying causes the water-swollen absorbent material to dehydrate and decrease
in size, thereby
creating voids in the composite surrounding the absorbent material.
In the methods, the absorbent material preferably absorbs less than about 20
times its
weight in the dispersion medium, more preferably less than about 10 times, and
even more
preferably less than about 5 times its weight in the dispersion medium.
Foam methods are advantageous for forming the absorbent composite for several
reasons. Generally, foam methods provide fibrous webs that possess both
relatively low
density and relatively high tensile strength. For webs composed of
substantially the same
components, foam-formed webs generally have densities greater than air-laid
webs and lower
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than wet-laid webs. Similarly, the tensile strength of foam-formed webs is
substantially
greater than for air-laid webs and approach the strength of wet-laid webs.
Also, the use of
foam forming technology allows better control of pore and void size, void size
to be
maximized, the orientation and uniform distribution of fibers, and the
incorporation of a wide
range of materials (e.g., long and synthetic fibers that cannot be readily
incorporated into wet-
laid processes) into the composite.
For fabrication, the reticulated absorbent composite can be formed by a foam
process,
preferably a process by Ahlstrom Company (Helsinki, Finland). The process
encompasses
desirable manufacturing efficiencies while producing a product with desirable
performance
characteristics.
The formation of a reticulated absorbent composite by representative wet-laid
and
foam processes is described in Examples 1 and 2, respectively. Absorbent
properties (i.e.,
rewet, acquisition time, liquid distribution, dry strength, and resilience)
for representative
reticulated absorbent composites are described in Examples 3 and 4. Wicking
and liquid
distribution for a representative absorbent composite are described in
Examples 5 and 6,
respectively. The tensile strength of representative composites formed in
accordance with the
present invention is described in Example 7. The softness (i.e., Taber
stiffness) of
representative wet-laid and foam-formed composites is described in Example 8.
One variable that affects the absorbent composite's performance
characteristics
including, for example, liquid acquisition and distribution rate and absorbent
capacity, is the
extent of swelling of the absorbent material in the composite. The methods
allow for control
and variation of absorbent material swelling. Absorbent material swelling
generally depends
on the degree of crosslinking (e.g., surface and internal crosslinking) and
the amount of water
absorbed by the absorbent material. The extent of swelling depends on a number
of factors,
including the type of absorbent material, the concentration of absorbent
material in an
aqueous environment (e.g., the dispersion medium and the wet composite), and
the period of
time that the absorbent material remains in contact with such an environment.
Generally, the
lower the concentration of the absorbent material in an aqueous medium and the
longer the
contact time, the greater the swelling of an absorbent material. Absorbent
material swelling
can be minimized by dispensing the absorbent in chilled water.
In general, the greater the initial swelling of the absorbent material, the
greater the
void volume and, consequently, the lower the density of the resulting
absorbent composite.
The greater the void volume of a composite, the greater its liquid acquisition
rate and,
generally, the greater the composite's absorbent capacity.
As noted above, the composite's voids are formed by the hydration and swelling
of
absorbent material (i.e., during wet composite formation) and the subsequent
dehydration and
decrease in size of the absorbent material (i.e., during wet composite
drying). Ultimately, the
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density of the composite depends on the extent to which the absorbent material
absorbs liquid
and swells during the formation of the wet composite, and the conditions and
extent to which
the wet composite incorporating the swollen absorbent material is dried. Water
absorbed by
the absorbent material during wet composite formation is removed from the
absorbent
material, decreasing its size, on drying the wet composite. The dehydration of
the swollen
absorbent material defines some of the voids in the fibrous composite.
The reticulated absorbent composite 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 10 and
1 l, can be
used in combination with one or more other layers. In FIGURE 10, absorbent
composite 10
is employed as a storage layer in combination with upper acquisition layer 20.
As illustrated
in FIGURE 11, a third layer 30 (e.g., distribution layer) can also be
employed, if desired, with
absorbent composite 10 and acquisition layer 20.
A variety of suitable absorbent articles 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 12, absorbent article 40 comprises absorbent
composite 10
and overlying acquisition layer 20. A liquid pervious facing sheet 22 overlies
acquisition
composite 20, and a liquid impervious backing sheet 24 underlies absorbent
composite 10.
The absorbent composite will provide advantageous liquid absorption
performance for use in,
for example, diapers. The reticulated structure of the absorbent composite
will aid in fluid
transport and absorption in multiple wettings. For absorbent articles that
incorporate the
composite and that are suitable for use as diapers or as incontinence
products, the articles can
further include leg gathers.
The construct in FIGURE 12 is shown for purposes of exemplifying a typical
absorbent article, such as a diaper or feminine napkin. One of ordinary skill
will be able to
make a variety of different constructs using the concepts taught herein. The
example, a
typical construction of an adult incontinence absorbent structure is shown in
FIGURE 13.
The article 50 comprises a facing sheet 22, acquisition layer 20, absorbent
composite 10, and
a backing sheet 24. The facing sheet 22 is pervious to liquid while the
backing sheet 24 is
impervious to liquid. In this construct, a liquid pervious tissue 26 composed
of a polar,
fibrous material is positioned between absorbent composite 10 and acquisition
layer 20.
Referring to FIGURE 14, another absorbent article includes a facing sheet 22,
an
acquisition layer 20, an intermediate layer 28, absorbent composite 10, and a
backing
sheet 24. The intermediate layer 28 contains, for example, a densified fibrous
material such
as a combination of cellulose acetate and triacetin, which are combined prior
to forming the
article. The intermediate layer 28 can thus bond to both absorbent composite
10 and
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acquisition layer 20 to form an absorbent article having significantly more
integrity than one
in which the absorbent composite and acquisition layer are not bonded to each
other. The
hydrophilicity of layer 28 can be adjusted in such a way as to create a
hydrophilicity gradient
among layers 10, 28, and 20.
The reticulated absorbent composite can also be incorporated as a liquid
management
layer in an absorbent article such as a diaper. In such an article, the
composite can be used in
combination with a storage core or layer. In the combination, the liquid
management layer
can have a top surface area that is smaller, the same size, or greater than
the top surface area
of the storage layer. Representative absorbent constructs that incorporate the
reticulated
absorbent composite in combination with a storage layer are shown in FIGURE
15.
Referring to FIGURE 15, absorbent construct 70 includes reticulated composite
10 and
storage layer 72. Storage layer 72 is preferably a fibrous layer that includes
absorbent
material. The storage layer can be formed by any method, including air-laid,
wet-laid, and
foam-forming methods. The storage layer can be a reticulated composite.
An acquisition layer can be combined with the reticulated composite and
storage
layer. FIGURE 16 illustrates absorbent construct 80 having acquisition layer
20 overlying
composite 10 and storage layer 72. Construct 80 can further include
intermediate layer 74 to
provide construct 90 shown in FIGURE 17. Intermediate layer 74 can be, for
example, a
tissue layer, a nonwoven layer, an air-laid or wet-laid pad, or a reticulated
composite.
Constructs 70, 80, and 90 can be incorporated into absorbent articles.
Generally,
absorbent articles 100, 110, and 120, shown in FIGURES 18-20, respectively,
include a
liquid pervious facing sheet 22, a liquid impervious backing sheet 24, and
constructs 70, 80,
and 90, respectively. In such absorbent articles, the facing sheet is joined
to the backing
sheet.
In another embodiment, the reticulated absorbent composite formed in
accordance
with the present invention further includes a fibrous stratum. In this
embodiment, the
composite includes a reticulated core and a fibrous stratum adjacent an
outward facing
surface of the core. The fibrous stratum is integrally formed with the
reticulated core to
provide a unitary absorbent composite. Generally, the stratum is coextensive
with an
outward facing surface (i.e., an upper and/or lower surface) of the composite.
Preferably, the
composite includes first and second strata adjacent each of the core's outward
facing surfaces
(i.e., the strata are coextensive with opposing surfaces of the core). A
representative
absorbent composite having a fibrous stratum is shown in FIGURE 21A and a
representative
composite having fibrous strata is shown in FIGURE 21B. Referring to FIGURE
21A,
absorbent composite 130 includes reticulated core 10 and stratum 132 and, as
shown in
FIGURE 21B, composite 140 includes reticulated core 10 intermediate strata 132
and 134.
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As noted above, core 10 is a fibrous matrix that includes fibrous regions 12
defining
voids 14, some of which include absorbent material 18.
The stratum or strata of the composite are fibrous and can be composed of any
suitable fiber or combination of fibers noted above. The stratum's fibrous
composition can
be widely varied. The stratum can be formed from fibers that are the same as
or different
from the fibers used for forming the reticulated core. The stratum can be
formed from
resilient fibers, matrix fibers, or combinations of resilient and matrix
fibers. The stratum can
optionally include a wet or dry strength agent. Suitable strata can be formed
from a single
fiber type, for example, a stratum composed of 100 percent wood pulp fibers
(e.g., southern
pine fibers). Alternatively, the stratum can be formed from fibrous blends,
such as an 80:20
blend of wood pulp fibers and crosslinked fibers, and synthetic blends, and
blends of
synthetic and cellulosic fibers.
The stratum composition can be varied to provide a composite having desired
characteristics. For example, to provide a stratum having high liquid wicking
capacity, the
stratum preferably has a relatively high wood pulp fiber content. Thus, for
liquid distribution,
the stratum is preferably composed of wood pulp fibers such as southern pine
fibers.
However, such a stratum has a lower liquid acquisition rate compared to a
similarly
constituted stratum containing relatively less wood pulp fiber and, for
example, greater
amounts of crosslinked fibers. Conversely, to provide a stratum having a high
liquid
acquisition rate, the stratum preferably has a relatively high crosslinked or
synthetic fiber
content. However, as a consequence of its high crosslinked fiber content, such
a stratum
provides less liquid distribution than a comparable stratum that includes
relatively less
crosslinked fiber. For liquid acquisition, the stratum is preferably a blend
of crosslinked
fibers and pulp fibers, for example, the stratum can include from about 30 to
about 50
percent by weight crosslinked fibers and from about 50 to about 70 percent by
weight pulp
fibers. Alternatively, strata having high liquid acquisition rates can also
include, in
combination with cellulosic fibers, a relatively high synthetic fiber content
(e.g., PET fibers
or a blend of PET and thermobondable fibers). Optionally, one or both strata
can include
synthetic fibers.
Because the composite's stratum is formed with the reticulated core to provide
an
integrated unitary structure, the overall characteristics of the composite can
be optimized by
appropriate selection of the individual core and stratum components. To
further optimize the
performance of the composite, the nature of first and second strata can be
selectively and
independently controlled and varied. The compositions of the first and second
strata need not
be the same. The strata can be formed from the same or different fiber
furnishes. For
compositions formed by foam methods, stratum basis weight can also be
independently
controlled and varied. Stratum basis weight can also be varied with respect to
the core's
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basis weight. In a foam method, basis weight can be varied by adjusting the
rate at which the
fibrous furnish is supplied to and deposited on the forming support. For
example, varying
pump speed for a specific furnish effectively controls the basis weight of
that portion of the
composite. Accordingly, in one embodiment, the absorbent composite includes a
reticulated
core intermediate first and second strata, each stratum having a different
basis weight.
Stratum basis weights can also be varied for absorbent composites formed by
wet-laid
methods.
The stratum can be integrally formed with the reticulated core by wet-laid and
foam
methods. Generally, the composite including the reticulated core and strata
can be formed by
substantially simultaneously depositing fibrous slurries that include the core
and stratum
components. The deposition of more than a single fibrous slurry onto a forming
support can
be accomplished by standard devices known in the art including, for example,
divided and/or
multislice headboxes.
Representative absorbent composites can be formed using conventional
papermaking
machines including, for example, Rotoformer, Fourdrinier, and twin-wire
machines.
Absorbent composites having a single stratum can be formed by Rotoformer and
Fourdrinier
machines, and composites that include two strata can be formed by twin-wire
machines. A
representative method for forming the absorbent composite using a Rotoformer
machine is
described in Example 9. The performance characteristics of representative
absorbent
composites formed by the method are described in Examples 10-15. Absorbent
composites
formed using the Rotoformer machine include a wire-side fibrous stratum. The
stratum
thickness and overall composite structure can be controlled by the position of
headbox
spargers, which deliver absorbent material to and effectively mix the
absorbent material with
the fiber stock. Generally, the deeper the sparger introduces the absorbent
material into the
fiber stock at the Rotoformer drum, the thinner the resulting stratum.
Conversely, a relatively
thicker stratum can be formed by introducing absorbent material into the fiber
stock at a
greater distance from the drum.
The absorbent composite can be formed by devices and processes that include a
twin
wire configuration (i.e., twin-forming wires). A representative twin-wire
machine for
forming composites is shown in FIGURE 22. Referring to FIGURE 22, machine 200
includes twin-forming wires 202 and 204 onto which the composite's components
are
deposited. Basically, fibrous slurry 124 is introduced into headbox 212 and
deposited onto
forming wires 202 and 204 at the headbox exit. Vacuum elements 206 and 208
dewater the
fibrous slurries deposited on wires 202 and 204, respectively, to provide
partially dewatered
webs that exit the twin-wire portion of the machine as partially dewatered web
126. Web 126
continues to travel along wire 202 and continues to be dewatered by additional
vacuum
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elements 210 to provide wet composite 120 which is then dried by drying means
216 to
provide composite 10.
Absorbent material can be introduced into the fibrous web at any one of
several
positions in the twin-wire process depending on the desired product
configuration. Referring
S to FIGURE 22, absorbent material 122 can be injected into the partially
dewatered web at
positions 2, 3, or 4, or other positions along wires 202 and 204 where the web
has been at
least partially dewatered. Absorbent material can be introduced into the
partially dewatered
web formed and traveling along wire 202 and/or 204. Absorbent material can be
injected
into the partially dewatered fibrous webs by nozzles spaced laterally across
the width of the
web. The nozzles are connected to an absorbent material supply. The nozzles
can be
positioned in various positions (e.g., positions 1, 2, or 3 in FIGURE 22) as
described above.
For example, referring to FIGURE 22, nozzles can be located at positions 2 to
inject
absorbent material into partially dewatered webs on wires 202 and 204.
Depending on the position of absorbent material introduction, the twin-wire
method
for forming the composite can provide a composite having a fibrous stratum.
The composite can include integrated phases having fibrous strata coextensive
with
the outward surfaces of the composite. These fibrous composites can be formed
from
multilayered inclined formers or twin-wire formers with sectioned headboxes.
These
methods can provide stratified or phased composites having strata or phases
having
specifically designed properties and containing components to attain
composites having
desired properties.
Basically, the position of the absorbent material in the composite's z-
direction
effectively defines the fibrous stratum covering the band. For a formation
method that
includes a single fiber furnish, the band position can be adjusted by
positioning the absorbent
material injection system (e.g., nozzle set) in relation to the forming wire.
For methods that
include multiple furnishes, the upper and lower strata can be composed of the
same or
different components and introduced into a sectioned headbox.
Referring to FIGURE 22, composite 10 having strata 11 can be formed by
machine 200. For composites in which strata 11 comprise the same components, a
single
fiber furnish 124 is introduced into headbox 212. For forming composites
having strata 11
comprising different components, headbox 212 includes one or more baffles 214
for the
introduction of fiber furnishes (e.g., 124a, 124b, and 124c) having different
compositions. In
such a method, the upper and lower strata can be formed to include different
components and
have different basis weights and properties.
Preferably, the reticulated composite is formed by a foam-forming method using
the
components described above. In the foam-forming method, fibrous webs having
multiple
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strata and including absorbent material can be formed from multiple fibrous
slurries. In a
preferred embodiment, the foam-forming method is practiced on a twin-wire
former.
The method can provide a variety of multiple strata composites including, for
example, composites having three strata. A representative composite having
three strata
includes a first stratum formed from fibers (e.g., synthetic fibers,
cellulosic, and/or binder
fibers); an intermediate stratum formed from fibers and/or other absorbent
material such as
superabsorbent material; and a third stratum formed from fibers. The method of
the
invention is versatile in that such a composite can have relatively distinct
and discrete strata
or, alternatively, have gradual transition zones from stratum-to-stratum.
A representative method for forming a fibrous web having an intermediate
stratum
generally includes the following steps:
(a) forming a first fibrous slurry comprising fibers and a surfactant in an
aqueous dispersion medium;
(b) forming a second fibrous slurry comprising fibers and a surfactant in
an aqueous dispersion medium;
(c) moving a first foraminous element (e.g., a forming wire) in a first path;
(d) moving a second foraminous element in a second path;
(e) passing the first slurry into contact with the first foraminous element
moving in a first path;
(f) passing the second slurry into contact with the second foraminous
element moving in the second path;
(g) passing a third material between the first and second slurries such that
the third material does not contact either of the first or second foraminous
elements; and
(h) forming a fibrous web from the first and second slurries and third
material by withdrawing liquid from the slurries through the first and second
foraminous
elements.
As noted above, the method is suitably carried out on a twin-wire former,
preferably a
vertical former, and more preferably, a vertical downflow twin-wire former. In
the vertical
former, the paths for the foraminous elements are substantially vertical.
A representative vertical downflow twin-wire former useful in practicing the
method
of the invention is illustrated in FIGURE 23. Referring to FIGURE 23, the
former includes a
vertical headbox assembly having a former with a closed first end (top),
closed first and
second sides and an interior volume. A second end (bottom) of the former is
defined by
moving first and second foraminous elements, 202 and 204, and forming nip 213.
The
interior volume defined by the former's closed first end, closed first and
second sides, and
first and second foraminous elements includes an interior structure 230
extending from the
former first end and toward the second end. The interior structure defines a
first volume 232
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on one side thereof and a second volume 234 on the other side thereof. The
former further
includes supply 242 and means 243 for introducing a first fiber slurry into
the first volume,
supply 244 and means 245 for introducing a second fiber slurry into the second
volume, and
supply 246 and means 247 for introducing a third material into the interior
structure. Means
for withdrawing liquid (and/or foam) (e.g., suction boxes 206 and 208) from
the first and
second slurries through the foraminous elements to form a web are also
included in the
headbox assembly.
In the method, the twin-wire former includes a means for introducing at least
a third
material through the interior structure. Preferably, the introducing means
include at least a
first plurality of conduits having a first effective length. A second
plurality of conduits
having a second effective length different from the first length may also be
used. More than
two sets of conduits can also be used.
Another representative vertical downflow twin-wire former useful in practicing
the
forming method is illustrated in FIGURE 24. Referring to FIGURE 24, the former
includes a
vertical headbox assembly having an interior volume defined by the former's
closed first end,
closed first and second sides, and first and second foraminous elements, 202
and 204, and
includes an interior structure 230 extending from the former first end and
toward the second
end. In this embodiment, interior structure 230 includes plurality of conduits
235 and 236,
and optional divider walls 214.
The interior structure defines a first volume 232 on one side thereof and a
second
volume 234 on the other side thereof. The former further includes supply 242
and means 243
for introducing a first fiber slurry into the first volume, supply 244 and
means 245 for
introducing a second fiber slurry into the second volume, supply 246 and means
247 for
introducing a third material into plurality of conduits 236, supply 248 and
means 249 for
introducing a third material into plurality of conduits 235, and supply 250
and means 251 for
introducing another material, such as a foam slurry, within the volume defined
by walls 214.
Plurality of conduits 235 can have an effective length different from
plurality of
conduits 236. The third material can be introduced through conduits 235 and
236, or,
alternatively, a third material can be introduced through conduits 235 and a
fourth material
can be introduced through conduits 236. Preferably, the ends of conduits 235
and 236
terminate at a position beyond where the suction boxes begin withdrawing foam
from the
slurries in contact with the foraminous elements (i.e., beyond the point where
web formation
begins). Plurality of conduits 235 and/or 236 are suitable for introducing
stripes or bands of
third material in fibrous webs formed in accordance with the present
invention. Plurality of
conduits 235 and 236 can be moved in a first dimension toward and away from
nip 213, and
also in a second dimension substantially perpendicular to the first, closer to
one forming wire
or the other. Representative plurality of conduits 235 and 236 are illustrated
in FIGURE 25.
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Generally, the former's interior structure (i.e., structure 230 in FIGURES 23
and 24)
is positioned with respect to the foraminous elements such that material
introduced through
the interior structure will not directly contact the first and second
foraminous elements.
Accordingly, material is introduced through the interior structure between the
first and
second slurries after the slurries have contacted the foraminous elements and
withdrawal of
foam and liquid from those slurries has commenced. Such a configuration is
particularly
advantageous for introducing superabsorbent materials and for forming
stratified structures in
which the third material is a foam/fiber slurry. Depending upon the nature of
the composite
to be formed, the first and second fiber slurries may be the same, or
different, from each other
and from the third material.
In a preferred embodiment, the method includes introducing the third material
at a
plurality of different points. The positions of at least some of the plurality
of different points
for introducing the third material into the headbox can be adjusted when it is
desired to adjust
the introduction point in a first dimension toward and away from the headbox
exit (i.e., nip
213 in FIGURES 23 and 24); and to adjust at least some of the plurality of
points in a second
dimension substantially perpendicular to the first dimension, closer to one
forming wire or
the other.
The method can also include utilizing a plurality of distinct conduits, the
conduits
being of at least two different lengths, for introducing the third material
into the headbox.
The method can also be utilized in headboxes having dividing walls that extend
part of the
length of the conduits toward the headbox exit. Such headboxes are illustrated
in
FIGURES 22 and 24.
The means for introducing first and second slurries into the first and second
volumes
can include any conventional type of conduit, nozzle, orifice, header, or the
like. Typically,
these means include a plurality of conduits are provided disposed on the first
end of the
former and facing the second end.
The means for withdrawing liquid and foam from the first and second slurries
through
the foraminous elements to form a web on the foraminous elements are also
included in the
headbox assembly. The means for withdrawing liquid and foam can include any
conventional means for that purpose, such as suction rollers, pressing
rollers, or other
conventional structures. In a preferred embodiment, first and second suction
box assemblies
are provided and mounted on the opposite sides of the interior structure from
the foraminous
elements (see boxes 206 and 208 in FIGURES 22, 23, and 24).
In another embodiment, the composite of the invention includes one or more
fibrous
bands in a fibrous base. The base includes a fibrous matrix and absorbent
material. Suitable
fibrous bases are as described above. The fibrous bands are substantially free
of absorbent
material. In one embodiment, the fibrous band or bands extend along the
machine direction
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of the composite. The number of bands in a particular composite is not
particularly critical,
and will depend upon the nature of the absorbent article into which the
composite is
incorporated. In one embodiment, the composite includes two fibrous bands, and
in other
embodiments, the composite includes more than two bands, for example, from
three to about
six bands.
A representative composite of the invention having two fibrous bands is
illustrated
schematically in FIGURE 31. Referring to FIGURE 31, composite 300 includes
base matrix
310 and fibrous bands 320. For embodiments of the composite in which the base
matrix
includes absorbent material, the fibrous bands conduct fluid along the
composite's length
distributing fluid throughout the composite and to absorbent material in the
base matrix
where the fluid is ultimately stored. In the FIGURE 31, fluid movement is
indicated by the
arrows.
Representative composites having fibrous bands and their performance
characteristics
are described in Examples 18, 19, and 21. A representative composite having
two fibrous
bands is described in Example 19. For this composite, wicking height at 15
minutes, capacity
at 15 cm, and wetted zone capacity for representative composites are presented
graphically in
FIGURE 32. Representative foam-formed composites having two fibrous bands are
described in Example 21. For these composites, ring crush and tensile strength
for are
correlated graphically in FIGURE 33; unrestrained vertical wicking height and
saturation
capacity are correlated graphically in FIGURE 34; ring crush and tensile
strength are
compared graphically in FIGURE 35; and unrestrained vertical wicking height
and saturation
capacity are compared graphically in FIGURE 36.
The fibrous bands can include any of the fibrous materials described above
including
blends of fibers. For example, the fibrous band can include matrix fibers,
resilient fibers, and
blends of matrix and resilient fibers. In certain embodiments, the fibrous
band includes
crosslinked cellulosic fibers and/or matrix fibers. The fibrous band can
include crosslinked
fibers in an amount from about 15 percent to about 90 percent by weight based
on the total
weight of fibers in the band. In one embodiment, the fibrous band includes
crosslinked fibers
in an amount from about 20 percent to about 80 percent by weight based on the
total weight
of fibers in the band. In another embodiment, the fibrous band includes
crosslinked fibers in
an amount from about 40 percent to about 60 percent by weight based on the
total weight of
fibers in the band. The fibrous band can include matrix fibers in an amount
from about 10
percent to about 85 percent by weight based on the total weight of fibers in
the band. In one
embodiment, the fibrous band includes matrix fibers in an amount from about 20
percent to
about 80 percent by weight based on the total weight of fibers in the band. In
another
embodiment, the fibrous band includes matrix fibers in an amount from about 40
percent to
about 60 percent by weight based on the total weight of fibers in the band.
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As noted above, in one embodiment, the fibrous band includes a blend of
crosslinked
and matrix fibers. In one embodiment, the weight ratio of matrix fibers to
crosslinked
cellulosic fibers is about 1:1, in another embodiment the ratio is about 1:4,
and in another
embodiment the ratio is about 4:1.
The absorbent composite having fibrous bands offers advantages over other
composites that lack fibrous bands. Among other advantages, the fibrous band
or bands act
as liquid distribution paths or channels within the composite's fibrous matrix
that includes
absorbent material. Thus, liquid acquired by the composite is rapidly
distributed along the
fibrous band and is absorbed out of these bands and into the surrounding
fibrous matrix
where the liquid is ultimately absorbed and retained by absorbent material.
The composites
including fibrous bands offer advantages associated with liquid wicking, total
liquid
absorbed, the rate of liquid uptake, and liquid flux, among other advantageous
properties.
For example, as described below, a representative absorbent composite having
fibrous bands
has an unrestrained vertical wicking height at 30 minutes of at least about 10
cm and,
preferably, at least about 12 cm. The composite also has an unrestrained
vertical wicking
total fluid absorbed value at 30 minutes of at least about 30 g and,
preferably, at least about
40 g. The composite also has an unrestrained vertical wicking uptake rate at
12 cm of at least
about 1.0 g/g/min and, preferably, at least about 2.0 g/g/min. The composite
also has an
unrestrained vertical wicking flux at 12 cm of at least about 2.0 /g/cm2/min
and, preferably, at
least about 3.0 g/cmz/min.
The composite having fibrous bands also provides strength and softness
advantages.
Fibrous bands running the length of a composite will generally increase the
softness of the
composite across its width.
Fibrous bands also offer advantages related to composite processing. For
example,
the relatively porous fibrous band increases composite drying efficiency.
Also, fibrous bands
can impart breathability to the composite when utilized in an absorbent
article.
Although the composite has been described as having bands of fibrous material,
it
will be appreciated that other configurations of fiber-only regions are within
the scope of the
invention. Representative configurations include circular, annular, ring,
star, cross, and
rectangular shapes, among others. The width of the band or other configuration
can also be
varied to suit a particular need. Wide bands have greater capacity than thin
bands. The band
or other configuration can also be tapered to facilitate, for example, fluid
movement. In
addition to having a tapered or changing length or width, the band or other
configuration can
also have a tapered or changing thickness (i.e., in direction of composite
thickness).
The fibrous band can also be located in the fibrous base in various positions
(e.g.,
variation in composite length, width, and thickness) to provide composites
having a variety of
fluid movement properties.
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The absorbent composite having fibrous bands can be formed by wetlaid and foam-
forming methods described above. The fibrous bands can be incorporated into
the fibrous
matrix to provide the composite by the methods described above. Fibrous bands
can be
formed by introducing fibers as the third (or fourth) material in the above-
described method.
Blends of fibers can also be introduced as the third material. In such forming
methods,
absorbent material can be introduced into the composite through other
conduits, for example,
as the fourth (or third) material, as described above.
The absorbent composite formed in accordance with the present invention can be
incorporated as an absorbent core or storage layer into an absorbent article
such as a diaper.
The composite can be used alone or combined with one or more other layers,
such as
acquisition and/or distribution layers, to provide useful absorbent constructs
as illustrated
herein. In the figures illustrating constructs and articles, reference numeral
10 refers to all of
the embodiments of the composites of the invention.
Representative absorbent constructs incorporating the absorbent composite
having a
reticulated core and fibrous strata are shown in FIGURES 26A-C and 27A-C.
Referring to
FIGURE 26A, construct 150 includes composite 130 (i.e., reticulated core 10
and
stratum 132) employed as a storage layer in combination with an upper
acquisition layer 20.
FIGURE 26B illustrates construct 160, which includes composite 130 and
acquisition layer
with stratum 132 adjacent acquisition layer 20. Construct 170, including
acquisition layer
20 20 and composite 140, is illustrated in FIGURE 26C.
In addition to the constructs noted above that include the combination of
absorbent
composite and acquisition layer, further constructs can include a distribution
layer
intermediate the acquisition layer and composite. FIGURE 27A illustrates
construct 180
having intermediate layer 30 (e.g., distribution layer) interposed between
acquisition layer 20
and composite 130. Similarly, FIGURES 27B and 23C illustrate constructs 190
and 200
having layer 30 intermediate acquisition layer 20 and composites 130 and 140,
respectively.
Composites 130 and 140 and constructs 150, 160, 170, 180, 190, and 200 can be
incorporated into absorbent articles. Generally, absorbent articles 210, 220,
and 230 shown
in FIGURES 28A-C, respectively; absorbent articles 240, 250, and 260 shown in
FIGURES
29A-C, respectively; and absorbent articles 270, 280, and 290 shown in FIGURES
30A-C,
respectively, include liquid pervious facing sheet 22, liquid impervious
backing sheet 24, and
composites 130, 140, and constructs 150, 160, 170, 180, 190, and 200,
respectively. In such
absorbent articles, the facing sheet is joined to the backing sheet.
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The following examples are provided for the purposes of illustration, and not
limitation.
EXAMPLES
Example 1
Reticulated Absorbent Composite Formation: Representative Wet-laid Method
This example illustrates a wet-laid method for forming a representative
absorbent
composite.
A wet-laid composite formed in accordance with the present invention is
prepared
utilizing standard wet-laid apparatus known to those in the art. A slurry of a
mixture of
standard wood pulp fibers and crosslinked pulp fibers (48 and 12 percent by
weight,
respectively, based on total weight of dried composite) in water having a
consistency of about
0.25 to 3 percent is formed. Consistency is defined as the weight percent of
fibers present in
the slurry, based on the total weight of the slurry. A wet strength agent such
as Kymene~
(0.5 percent based on total composite weight) is then added to the fibrous
mixture. Finally,
absorbent material (40 percent by weight based on total weight of dried
composite) is added
to the slurry, the slurry is thoroughly mixed, and then distributed onto a
wire mesh to form a
wet composite. The wet composite is dried to a moisture content of about 9 to
about 1 S
weight percent based on total composite weight to form a representative
reticulated absorbent
composite.
Absorbent composites having a variety of basis weights can be prepared from
the
composite formed as described above by pre- or post-drying densification
methods known to
those in the art.
Example 2
Reticulated Absorbent Composite Formation: Representative Foam Method
This example illustrates a foam method for forming a representative absorbent
composite.
A lab-size Waring blender is filled with 4L of water and pulp fibers are
added. The
mixture is blended for a short time. Crosslinked cellulose fibers are then
added to the pulp
fibers and blended for at least one minute to open the crosslinked fibers and
effect mixing of
the two fibers. The resulting mixture may contain from 0.07 to 12 percent by
weight of
solids.
The mixture is placed in a container and blended for a few seconds with an air-
entrapping blade. A surfactant (Incronan 30, Croda, Inc.) is added to the
blended mixture.
Approximately 1 g of active surfactant solids per gram of fiber is added. The
mixture is
blended while slowly raising the mixer blade height from the rising foam.
After about one
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minute, the mixing is terminated, superabsorbent is added, and the mixing is
restarted for
another one-half minute at constant mixer blade height. The resulting foam-
fiber mixture
will have a volume about three times the volume of the original mixture.
The mixture is rapidly poured into a sheet mold having an inclined diffusion
plate.
After the addition of the mixture, the plate is removed from the mold, and a
strong vacuum is
applied to reduce the foam-fiber height. After most of the visible foam
disappears, the
vacuum is discontinued and the resulting sheet removed from the mold and
passed, along
with a forming wire, over a slit couch to remove excess foam and water.
The sheet is then dried in a drying oven to remove the moisture.
Example 3
Acquisition Times for a Representative Reticulated Absorbent Composite
In this example, the acquisition time for. a representative reticulated
absorbent
composite formed in accordance with the present invention (Composite A) is
compared to a
commercially available diaper (Diaper A, Kimberly-Clark).
The tests were conducted on commercially available diapers (Kimberly-Clark)
from
which the core and surge management layer were removed and the surrounds used.
The test
diapers were prepared by inserting the absorbent composite into the diaper.
The aqueous solution used in the tests is a synthetic urine available from
National
Scientific under the trade name RICCA. The synthetic urine is a saline
solution containing
135 meq./L sodium, 8.6 meq./L calcium, 7.7 meq./L magnesium, 1.94% urea by
weight
(based on total weight), plus other ingredients.
A sample of the absorbent structure was prepared for the test by determining
the
center of the structure's core, measuring 1 inch to the front for liquid
application location,
and marking the location with an "X". Once the sample was prepared, the test
was conducted
by first placing the sample on a plastic base (4 3/4 inch x 19 1/4 inch) and
then placing a
funnel acquisition plate (4 inch x 4 inch plastic plate) on top of the sample
with the plate's
hole positioned over the "X". A donut weight (1400 g) was then placed on top
of the funnel
acquisition plate to which was then attached a funnel (4 inch diameter).
Liquid acquisition
was then determined by pouring 100 mL synthetic urine into the funnel and
measuring the
time from when liquid was first introduced into the funnel to the time that
liquid disappeared
from the bottom of the funnel into the sample. The measured time is the
acquisition time for
the first liquid insult. After waiting one minute, a second 100 mL portion was
added to the
funnel and the acquisition time for the second insult was measured. After
waiting an
additional one minute, the acquisition was repeated for a third time to
provide an acquisition
time for the third insult. The acquisition times reported in seconds for each
of the three
successive 100 mL liquid insults for Diaper A and Composite A are summarized
in Table 1.
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Table 1. Acquisition Time Comparison
Acquisition
Time
sec)
Insult Dia er A Com osite A
1 45 10
2 60 11
3 75 10
As shown in Table 1, liquid is more rapidly acquired by the absorbent
composite than
for the commercially available diaper containing an air-laid storage core. The
results show
that the air-laid core does not acquire liquid nearly as rapidly as the
reticulated composite.
The commercial diaper also exhibited characteristic diminution of acquisition
rate on
successive liquid insults. In contrast, the composite formed in accordance
with the invention
maintained a relatively constant acquisition time as the composite continued
to absorb liquid
on successive insult. Significantly, the absorbent composite exhibits an
acquisition time for
the third insult that is substantially less (about fourfold) than that of the
commercially
available diaper for initial insult. The results reflect the greater wicking
ability and capillary
network for the wet-laid composite compared to a conventional air-laid storage
core .in
general, and the enhanced performance of the reticulated absorbent composite
in particular.
Example 4
Acquisition Rate and Rewet for Representative Reticulated Absorbent Composites
In this example, the acquisition time and rewet of representative reticulated
absorbent
composites formed in accordance with the present invention (designated
Composites A1-A4)
are compared to a commercially available diaper (Diaper A, Kimberly-Clark).
Composites
Al-A4 differ by the method by which the composites were dried.
Certain properties of the tested composites, including the amount of
superabsorbent
material (weight percent SAP) in the composite and basis weight for each of
the composites,
are summarized in Table 2.
The tests were conducted on commercially available diapers (Kimberly-Clark)
from
which the cores were removed and used as surrounds. The test diapers were
prepared by
inserting the tested composites into the diapers.
The acquisition time and rewet are determined in accordance with the multiple-
dose
rewet test described below.
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Briefly, the multiple-dose rewet test measures the amount of synthetic urine
released
from an absorbent structure after each of three liquid applications, and the
time required for
each of the three liquid doses to wick into the product.
The aqueous solution used in the tests was a synthetic urine available from
National
Scientific under the trade name RICCA, and as described above in Example 1.
A preweighed sample of the absorbent structure was prepared for the test by
determining the center of the structure's core, measuring 1 inch to the front
for liquid
application location, and marking the location with an "X". A liquid
application funnel
(minimum 100 mL capacity, 5-7 mL/s flow rate) was placed 4 inches above the
surface of the
sample at the "X" . Once the sample was prepared, the test was conducted as
follows. The
sample was flattened, nonwoven side up, onto a tabletop under the liquid
application funnel.
The funnel was filled with a dose (100 mL) of synthetic urine. A dosing ring
(5/32 inch
stainless steel, 2 inch ID x 3 inch height) was placed onto the "X" marked on
the samples. A
first dose of synthetic urine was applied within the dosing ring. Using a
stopwatch, the liquid
acquisition time was recorded in seconds from the time the funnel valve was
opened until the
liquid wicked into the product from the bottom of the dosing ring. After a
twenty-minute
wait period, rewet was determined. During the twenty-minute wait period after
the first dose
was applied, a stack of filter papers ( 19-22 g, Whatman #3, 11.0 cm or
equivalent, that had
been exposed to room humidity for minimum of 2 hours before testing) was
weighed. The
stack of preweighed filter papers was placed on the center of the wetted area.
A cylindrical
weight (8.9 cm diameter, 9.8 1b.) was placed on top of these filter papers.
After two minutes
the weight was removed, the filter papers were weighed and the weight change
recorded. The
procedure was repeated two more times. A second dose of synthetic urine was
added to the
diaper, and the acquisition time was determined, filter papers were placed on
the sample for
two minutes, and the weight change determined. For the second dose, the weight
of the dry
filter papers was 29-32 g, and for the third dose, the weight of the filter
papers was 39-42 g.
The dry papers from the prior dosage were supplemented with additional dry
filter papers.
Liquid acquisition time is reported as the length of time (seconds) necessary
for the
liquid to be absorbed into the product for each of the three doses. The
results are summarized
in Table 2.
Rewet is reported as the amount of liquid (grams) absorbed back into the
filter papers
after each liquid dose (i.e., difference between the weight of wet filter
papers and the weight
of dry filter papers). The results are also summarized in Table 2.
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Table 2. Acauisition Time and Rewet Comparison
SAP Basis Acquisition Rewet
Com osite% (w/w) Weight Time ( )
( sm) sec)
InsultInsultInsultInsultInsultInsult
1 2 3 1 2 3
A 1 49.4 568 16 19 26 0.1 0.4 2.4
A2 38.3 648 17 19 22 0.1 0.7 2.5
A3 35.9 687 29 26 27 0.2 0.2 0.7
A4 38.8 672 17 18 21 0.1 0.3 0.9
Commercial40.0 625 34 35 39 0.1 4.0 12.6
air-laid
core
As indicated in Table 2, the acquisition times for representative composites
formed in
accordance with the invention (Composites Al-A4) were significantly less than
for the
commercially available core.
The rewet of the representative composites (Composites A1-A4) is significantly
less
than for the other cores. While the composites exhibited relatively low rewet
initially, after
the third insult the commercially available core showed substantial rewet. In
contrast,
Composites A continued to exhibit low rewet.
Example 5
Horizontal and Vertical Wicking for a Representative Reticulated
Absorbent Composite
In this example, the wicking characteristics of a representative reticulated
absorbent
composite (Composite A) are compared to a commercially available diaper
storage core
(Diaper B, Procter & Gamble).
The horizontal wicking test measures the time required for liquid to
horizontally wick
preselected distances. The test was performed by placing a sample composite on
a horizontal
surface with one end in contact with a liquid bath and measuring the time
required for liquid
to wick preselected distances. Briefly, a sample composite strip (40 cm x 10
cm) was cut
from a pulp sheet or other source. If the sheet has a machine direction, the
cut was made
such that the 40 cm length of the strip was parallel to the machine direction.
Starting at one
end of the 10 cm width of the strip, a first line was marked at 4.5 cm from
the strip edge and
then consecutive lines at 5 cm intervals were marked along the entire length
of the strip (i.e.,
0 cm, 5 cm, 10 cm, 15 cm, 20 cm, 25 cm, 30 cm, and 35 cm). A horizontal
wicking
apparatus having a center trough with level horizontal wings extending away
from opposing
sides of the trough was prepared. The nonsupported edge of each wing was
positioned to be
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flush with the inside edge of the trough. On each wing's end was placed a
plastic extension
to support each wing in a level and horizontal position. The trough was then
filled with
synthetic urine. The sample composite strip was then gently bent at the 4.5 cm
mark to form
an approximately 45° angle in the strip. The strip was then placed on
the wing such that the
strip lay horizontally and the bent end of the strip extended into and
contacted the liquid in
the trough. Liquid wicking was timed beginning from when the liquid reached
the first line
marked on the composite 5 cm from the 4.5 cm bend. The wicking time was then
recorded at
5 cm intervals when 50 percent of the liquid front reached the marked interval
(e.g., 5 cm,
cm). The liquid level in the trough was maintained at a relatively constant
level
10 throughout the test by replenishing with additional synthetic urine. The
horizontal wicking
results are summarized in Table 3.
Table 3. Horizontal Wicking Comparison
Wicking Time
Distance
(sec)
(cm)
Dia er B Com osite A
5 48 15
10 150 52
290 134
458 285
783 540
1703 1117
- 1425
The results tabulated above indicate that horizontal wicking is enhanced for
the
absorbent composite formed in accordance with the invention compared to a
conventional
15 air-laid core. The wicking time for Composite A is about 50 percent of that
for the
conventional diaper core. Thus, the horizontal wicking for Composite A is
about 1.5 to about
3 times that of a commercially available storage core.
The vertical wicking test measures the time required for liquid to vertically
wick
preselected distances. The test was performed by vertically suspending a
sample composite
20 with one end of the composite in contact with a liquid bath and measuring
the time required
for liquid to wick preselected distances. Prior to the test, sample composites
(~10 cm x 22 cm)
were cut and marked with consecutive lines 1 cm, 11 cm, 16 cm, and 21 cm from
one of the
strip's edges. Preferably, samples were preconditioned for 12 hours at 50
percent relative
humidity and 23°C and then stored in sample bags until testing. The
sample composite was
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oriented lengthwise vertically and clamped from its top edge at the 1 cm mark,
allowing its
bottom edge to contact a bath containing synthetic urine. Timing was commenced
once the
strip was contacted with the liquid. The time required for 5 percent of the
wicking front to
reach 5 cm, 10 cm, 15 cm, and 20 cm was then recorded. The vertical wicking
results are
summarized in Table 4.
Table 4. Vertical Wicking Comparison
Distance Wicking Time
(cm) sec
Dia er B Com osite A
5 20 6
Fell A art 54
- 513
- 3780
As for the horizontal wicking results, Composite A had significantly greater
vertical
wicking compared to the commercial core. The results also show that the
composite formed
in accordance with the invention has significantly greater wet tensile
strength compared to
10 the conventional air-laid composite.
Example 6
Liquid Distribution for a Representative Reticulated Absorbent Composite
In this example, the distribution of liquid in a reticulated absorbent
composite
(Composite A) is compared to that of two commercially available diapers
(Diapers A and B
15 above). The test measures the capacity of a diaper core to distribute
acquired liquid. Perfect
distribution would have 0% deviation from average. Ideal liquid distribution
would result in
equal distribution of the applied liquid in each of the four distribution
zones (i.e., about 25%
liquid in each zone).
Liquid distribution is determined by weighing different zones of a sample that
has
20 been subjected to the multiple-dose rewet test described above in Example
4. Basically, after
the last rewet, the wings of the diaper are removed and then cut into four
equal length
distribution zones. Each zone is then weighed to determine the weight of
liquid contained in
each zone.
The liquid distribution results for a representative reticulated absorbent
composite
approach ideality. The results indicate that while the representative
commercial storage cores
accumulate liquid near the site of insult, liquid is efficiently and
effectively distributed
throughout the reticulated absorbent storage core.
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Example 7
Wet and Dry Tensile Strength for a Reticulated Absorbent Composite
In this example, the measurement of wet and dry tensile strength of a
representative
absorbent composite is described.
A dry pad tensile integrity test is performed on a 4 inch by 4 inch square
test pad by
clamping a dry test pad along two opposing sides. About 3 inches of pad length
is left visible
between the clamps. The sample is pulled vertically in an Instron testing
machine and the
tensile strength measured is reported in N/m. The tensile strength is
converted to tensile
index, Nm/g, by dividing the tensile strength by the basis weight g/m2.
A wet tensile integrity test is performed by taking a sample composite that
has been
immersed in synthetic urine for 10 minutes and then allowed to drain for 5
minutes and
placing the sample in a horizontal jig. Opposite ends of the sample are
clamped and then
pulled horizontally on the Instron testing machine. The wet tensile strength,
N/m, is
converted to tensile index, Nm/g, by dividing the tensile strength by the
basis weight g/m2.
Typically, increasing the amount of Kymene~ from 2 to 100 pounds per ton of
fiber
may increase the dry tensile strength from about 0.15 Nm/g to 0.66 Nm/g and
the wet tensile
from about 1.5 Nm/g to about 2.4 Nm/g.
Example 8
Taber Stiffness for Representative Reticulated Absorbent Composites
The stiffness of representative reticulated absorbent composites formed in
accordance
with the present invention was determined by the Taber Stiffness method.
Representative
composites were formed by wet-laid and foam methods. These composites included
matrix
fibers (48 percent by weight, southern pine commercially available from
Weyerhaeuser Co.
under the designation NB416), resilient fibers (12 percent by weight,
polymaleic acid
crosslinked fibers), and absorbent material (40 percent by weight,
superabsorbent material
commercially available from Stockhausen). One of the wet-laid and one of the
foam-formed
composites further included a wet strength agent (about 0.5 percent by weight,
polyamide-
epichlorohydrin resin commercially available from Hercules under the
designation Kymene~.
The stiffness of the foam-formed composites was significantly lower than the
similarly constituted wet-laid composites. The results also indicate that, for
the wet-laid
composites, the inclusion of a wet strength agent increases the composite's
stiffness.
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Example 9
Reticulated Absorbent Composite Formation: Representative Wet-laid Method
This example illustrates a representative wet-laid method for forming a
reticulated
composite using a Rotoformer papermaking machine.
Briefly, slurries of absorbent material and fibers in water were introduced'
into the
Rotoformer's headbox. The fibrous slurry was introduced to the headbox in the
conventional
manner. The absorbent slurry was introduced through the use of a dispersion
unit consisting
of a set of spargers. The spargers were fed from a header fed by the absorbent
slurry supply.
The dispersion unit is mounted on the Rotoformer headbox with the spargers
inserted into the
headbox fiber stock such that the flow of the absorbent slurry is against the
fiber stock flow.
Such a reversed flow for the absorbent slurry is believed to provide more
effective mixing of
the absorbent material and the fibers than would occur for absorbent material
flow in the
same direction as the fiber stock.
Absorbent material is introduced into the Rotoformer headbox as a slurry in
water.
One method that provides suitable results for introducing absorbent material
into the headbox
is a mixing system that includes a funnel attached directly to the inlet of a
pump into which
chilled water is fed at a controlled rate. The funnel receives water and dry
absorbent material
delivered from absorbent material supply by auger metering and forms a pond
that contains
absorbent material and water. The absorbent slurry is preferably pumped from
the funnel to
the headbox at approximately the same rate as water is delivered to the
funnel. Such a system
minimizes the exposure of the absorbent to the water. In practice, the
absorbent slurry is
delivered from the mixing system to the headbox through a 10 to 50 foot
conduit in less than
about 10 seconds.
In a typical formation run, fiber stock flow to the Rotoformer headbox was
about
90 gpm (gallon/min) and absorbent slurry ( 1 - 2.6 % solids) flow was about 10
gpm. Prior to
initiation of fiber stock flow to the headbox and the introduction of
absorbent slurry to the
dispersion unit, water was flowed into the dispersion unit to the headbox to
prevent fibers
from plugging the spargers. Once the target basis weight of fiber was reached,
the absorbent
auger metering system was initiated and absorbent slurry was introduced into
the headbox.
For the runs made in accordance with the method described above, the target
fiber basis
weight was about 370 gsm (g/mz) and the production speed was about 10 fpm
(ft/min). The
relatively slow production speed was a consequence of the relatively limited
drying capability
of the machine's flatbed dryer.
The headbox contents including fibers and absorbent were deposited on a
forming
wire and dewatered to provide a wet composite. The wet composite was then
dried to a
moisture content of from about 9 to about 15 weight percent based on total
composite weight
to form a representative reticulated absorbent composite.
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Absorbent composites having a variety of basis weights can be prepared from
the
composite formed as described above by pre- or post-drying densification
methods known to
those in the art.
Examples 10-15 illustrate the formation of representative reticulated
absorbent
composites using the method described above.
Example 10
A representative composite was formed as described in Example 9. The composite
included about 60% by weight fibers and about 40% by weight absorbent material
based on
the total weight of composite. The fiber stock was a mixture of 80% by weight
standard
wood pulp fibers (once-dried southern pine commercially available from
Weyerhaeuser
Company under the designation FR416) and 20% by weight crosslinked pulp
fibers. The
absorbent material was a crosslinked polyacrylate commercially available from
Stockhausen
under the designation SXM 77, which was screened using 300 micron mesh to
eliminate
fines prior to use. The composite also included about 25 pounds wet strength
agent (a
polyacrylamide-epichlorohydrin resin commercially available from Hercules
under the
designation Kymene°' 557LX) per ton of fibers.
Target density of the absorbent composite was accomplished by calendering
using a
single nip with no applied load.
Performance data for the representative composite formed as described above
(Composite B) is presented in Tables 5 and 6 in Example 16.
Example 11
A representative composite was formed as described in Example 10 except that
the
composite was calendered at 25 fpm.
Performance data for the representative composite formed as described above
(Composite C) is presented in Tables 5 and 6 in Example 16.
Example 12
A representative composite was formed as described in Example 11 except that
the
amount of wet strength agent in the composite was reduced to 12.5 pounds per
ton fiber and
the standard wood pulp fibers were never-dried FR416 fibers.
Performance data for the representative composite formed as described above
(Composite D) is presented in Tables 5 and 6 in Example 16.
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Example 13
A representative composite was formed as described in Example 12 except that
the
composite was not densified.
Performance data for the representative composite formed as described above
(Composite E) is presented in Tables 5 and 6 in Example 16.
Example 14
A representative composite was formed as described in Example 12 except that
the
wood pulp fibers were once-dried FR416 fibers.
Performance data for the representative composite formed as described above
(Composite F) is presented in Tables 5 and 6 in Example 16.
Example 15
A representative composite was formed as described in Example 12 except that
the
amount of fibers in the composite was increased to about 80% by weight and the
amount of
absorbent present in the composite was decreased to about 20% by weight of the
total
composite.
Performance data for the representative composite formed as described above
(Composite G) is presented in Tables 5 and 6 in Example 16.
Example 16
The performance of representative composites (Composites B-D) prepared as
described in Examples 10-15 is summarized in Tables S and 6. The liquid
wicking,
absorbent capacity, wet and dry tensile strength, and wet strength of the
representative
composites are compared to a conventional handsheet in Table 5. The
conventional
handsheet had a basis weight and density comparable to the representative
composites and
included 60 percent by weight fibers (25 percent crosslinked fibers and 75
percent standard
wood pulp fibers), 40 percent by weight superabsorbent material, and 12.5
pounds Kymene
per ton fibers. The results presented in Table 5 are the average of three
measurements except
for the tensile values, which average four measurements. In the table, "MD"
refers to the
composites' machine direction and "CD" refers to the cross-machine direction.
The wicking
values were obtained by the methods described in Example 5 and the wet and dry
tensile
values were obtained by the method described in Example 7. The wet strength
value was
calculated and is defined as the ratio of wet tensile to dry tensile values.
The mass flow rate
value (g/min/g) was determined by measuring the -weight gain of a portion of a
composite
(22 cm x S cm) divided by the lesser of the time required for the liquid to
wick 15 cm or
1 S minutes, divided by the weight of the original sample.
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The absorbent capacity of several of the representative composites is
summarized in
Table 6. In this capacity test, portions of the representative composites
(i.e., 10 cm squares)
were immersed in a 1% saline solution. The samples were allowed to absorb
liquid and swell
for 10 minutes. The difference in the weight of the composite before and after
the 10 minute
swell is the capacity that is reported as cc/g.
Table 6. Absorbent capacity
Com osite Ca achy cc/
B 16.9
C 16.9
D 20.4
E 21.5
Example 17
Method for Determining Fluid Wickin fg~or Representative Composites
The absorbent properties of representative composites can be determined by
measuring unrestrained vertical wicking height, which is indicative of the
composite's ability
to wick and distribute fluid.
Unrestrained vertical wicking height at 15 minutes was measured for
representative
composites as described below.
Material:
Synthetic urine for wicking - "Blood Bank" 0.9% Saline Solution
Samples:
Size: 6.5 cm(CD) x 25 cm(MD), marked with both permanent and water permeable
lines at l, 11, 16, and 21 cm along MD.
Method:
1 ) Perform % Solids on sample material
and record.
2) Cut Sample and record (as is) weight
and dry caliper.
3) Clamp sample at 1 cm from top.
4) Dip into liquid up to the 1 cm line.
5) Immediately start timing.
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6) At the end of 5, 10, and 15 minutes, record the Wicking Height by measuring
down from the next highest line. Report the wicking height to the nearest
0.5 cm.
7) At 15 minutes raise sample out of fluid and while still clamped, cut sample
at
the 1 cm and 15 cm height lines. Discard the 1 cm section.
8) Weigh wet 15 cm long sample and record.
9) Unclamp remaining sample and add to balance in order to record entire pad
wet weight.
10) Report Total Wick Height at 15 minutes.
11) Report As-is and O.D. basis Entire Pad Capacity(g/g) by calculating:
Entire Pad Ca acit / __ Wet Wt.-(As Is or O.D. Wt.)
p y(g g) As - Is or O. D. Wt.
*Pad weight(-lcm section)=(Total sample weight x 0.96)
15) Calculate the Wicked Pad Capacity if needed:
Wicked Pad Capacity = Entire Pad Capacity x 24
Wicking Ht at 15 min
Unrestrained vertical wicking height for representative composites is
described in the
following examples.
Example 18
Performance Characteristics of Representative Composites Having Fibrous Bands
The performance characteristics of representative composites prepared as
described
above are summarized in Table 7. The unrestrained vertical wicking height and
total fluid
absorbed at 30 minutes and the uptake rate and flux at 12 cm are compared for
composites
formed in accordance with the present invention and for commercially available
air-laid
cores. In Table 7, Composite I is a reticulated absorbent composite formed in
accordance
with the present invention having a composition that includes about 58% by
weight absorbent
material, 32% by weight crosslinked fibers, and 8% by weight matrix fibers
based on the total
weight of the composition. Composites J and K are composites that include two
fibrous
bands. For these composites, the fibrous matrix included 69% by weight
absorbent material,
24% by weight crosslinked fibers, and 6% by weight matrix fibers based on the
total weight
of the matrix. Composite J had fibrous bands composed of crosslinked and
matrix fibers in
which the ratio of crosslinked to matrix fibers was 1:4. Composite K had a
crosslinked to
matrix fiber ratio of 1:1.
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TahlP 7 RPnrPCPntatlVP C'nmnncitP TTnreetrainPrT VPrtieal Wiekina Parameter
Unrestrained
Composite Vertical
Wicking
Total Fluid Uptake Rate Flux
Height (cm) Absorbed (g/g/min) (g/cmz/min)
( )
I 12.3 47.2 1.0 2.2
J 15.5 49.0 2.5 5.7
K 15.6 52.0 3.0 5.8
Airlaid core7.5* 27.5* -- --
* integrity loss after 6 min.
As shown in Table 7, composites formed in accordance with the present
invention
vastly outperformed the commercially available airlaid core. Composites J and
K, which
included fibrous bands, had liquid wicking and distribution characteristics
that were
enhanced compared to Composite I, a composite lacking the fibrous bands.
Example 19
Performance Characteristics of a Representative Composite Having Two Fibrous
Bands
The performance characteristics for a representative composite having two
fibrous
bands (Composite L) were compared to a similarly constituted composite lacking
fibrous
bands (Control). The control composite had a basis weight of 700 gsm and
included 50
percent by weight superabsorbent material; 25 percent by weight crosslinked
cellulosic fibers;
25 percent by weight fluff pulp fibers (refined southern pine) based on the
total weight of the
composite. The composite having fibrous bands was constructed from the control
composite
and fibrous strips. The components were adhered together to provide the
composite (see, for
example, FIGURE 31). The composite had a length of 25 cm, width 5 cm, and
included two
fibrous strips having a width of 0.75 cm.
Wicking height at 15 minutes, capacity at 15 cm, and wetted zone capacity for
the
composites are compared graphically in FIGURE 32. As shown in FIGURE 32,
wicking
height and capacity at 15 minutes for the Composite L were increased relative
to the control
composite.
The properties and characteristics of Composite L and the control are
summarized in
Table 8.
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Table 8. Unrestrained Vertical Wicking Performance.
CompositeBasis DensityBulk Total Wet 15 cm Height
Weight(g/cm3)(cm3/g)Fluid Zone g/g at 15
(gsm) Wicked (g/g) cap min.
OD
(g) cap
OD
Control 700 0.144 6.93 80.90 17.16 11.80 10.4
L 810 0.165 6.05 120.37 16.63 14.58 13.8
Example 20
Method for Determining Flexibility and Softness for Representative Composites
Composite flexibility and softness are factors for determining the suitability
of
composites for incorporation into personal care absorbent products. Composite
flexibility
can be indicated by composite edgewise ring crush, which is a measure of the
force required
to compress the composite as described below. For a composite to be
incorporated into a
personal care absorbent product, suitable ring crush values range from about
400 to about
1600 gram/inch. Composite softness can be indicated by a variety of parameters
including
composite edgewise compression. Edgewise compression (EC) is the force
required to
compress the composite corrected by the composite's basis weight as described
below. For a
composite to be suitably incorporated into a personal care absorbent product,
the composite
has a ring crush value in the range from about 400-1600 g and a basis weight
in the range
from about 250 to about 650 gsm.
The flexibility and softness of representative reticulated absorbent
composites formed
by wetlaid and foam-forming methods in accordance with the present invention
were
determined by measuring composite edgewise ring crush and edgewise
compression.
The flexibility and softness of representative composites was determined by an
edgewise ring crush method. In the method, a length of the composite
(typically about
12 inches) is formed into a cylinder and its ends stapled together to provide
cylinder having a
height equal to the composite's width (typically about 2.5 inches). Edgewise
ring crush is
measured by adding mass to the top of the composite ring sufficient to reduce
the composite
cylinder's height by one-half. The more flexible the composite, the less
weight required to
reduce the height in the measurement. The edgewise ring crush is measured and
reported as a
mass (g). Edgewise compression (EC) is the ring crush reported in units of
g/gsm in the
tables below.
The following is a description of the ring crush method.
Samples: 6.35 cm (2.5 in) X 30.5 cm (12 in)
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Triplicate analysis (A, B, C)
Method:
1 ) Cut triplicate of sample size, lengthwise in the composite machine
direction
(MD).
2) Condition samples for 2 hours at 50% relative humidity or ambient
conditions.
3) With the wire side on the outside, form the individual samples into loops
so
the two narrow ends meet without any overlap. Using four staples, attached
the ends together at the top, bottom, and twice in the middle. The top and
bottom staples should be 0.3-0.5 cm from the edge and the middle staples
should be less than 2 cm from each other and the respective top or bottom
staple. Finally, ensure that each staple penetrates fiber only areas.
4) Set the bottom platen on a smooth, level surface.
5) Place the sample, edgewise and in the center, between the top and bottom
platens.
6) Gently place a 100-g weight on the center of the top platen (or 500-weight)
and wait 3 seconds.
7) Then, gently stack 3 more 100-g weights at 3-second intervals.
8) If the ring collapses 50% or more of it's original height within a 3-second
interval, then record the total amount of weight necessary to do so, i.e., add
the
weight of the top platen and the other combined weights.
9) If the combined weight doesn't crush the sample, then carefully remove the
four 100-g weights.
10) Gently add another) 500-g weight and weight 3 seconds.
11) If the ring collapses 50% or more of it's original height within a 3-
second
interval, then record the total amount of weight necessary to do so, i.e., add
the
weight of the top platen and weight(s).
12) Repeat step 6 through 1 l, increasing the number of 500-g weights by one
for
each cycle.
13) Repeat steps 5 through 11 for the other replicates.
14) Record the average weight for the replicates in g~f rounded to the nearest
10 g.
Calculations:
Average ring crush weight = (Weight A + Weight B + Weight C)/3
The ring crush values determined as described above for representative
composites
formed in accordance with the present invention are summarized in Example 21.
The softness of representative reticulated absorbent composites formed in
accordance
with the present invention can be indicated by edgewise compression. Edgewise
compression is discussed in The Handbook of Physical and Mechanical Testingyof
Paper and
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Paperboard, Richard E. Mark, Dekker 1983 (Vol. 1). Edgewise compression was
determined
by correcting edgewise ring crush, determined as described above, for
composite basis
weight. The edgewise compression (EC) values for representative composites
formed in
accordance with the present invention are summarized in Example 21.
Example 21
Performance Characteristics of Representative Foam-Formed Composites Having
Fibrous
Bands
The performance characteristics of representative foam-formed composites
having
fibrous bands (Composites M, N, O) were compared to similarly constituted foam-
formed
composites lacking fibrous bands (Control A and B). The composites were
prepared on a
twin-wire former as described above.
Fluff pulp fibers for the composites were unrefined softwood fibers (southern
pine,
745 CSF), and refined fibers were refined softwood (southern pine, 200 CSF).
The
superabsorbent polymer was a lightly crosslinked polyacrylate (SR1001). All
composites
included a wet strength agent (KYMENE), 0.45 percent by weight based on the
total weight
of the composite.
Control A included 58 percent by weight superabsorbent material and 42 percent
by
weight fibrous material based on the total weight of the composite. The
fibrous material
included 67 percent by weight crosslinked fibers and 33 percent by weight
fluff pulp fibers
based on the total weight of fibers.
Control B included 50 percent by weight superabsorbent material and 50 percent
by
weight fibrous material based on the total weight of the composite. The
fibrous material
included 67 percent by weight crosslinked fibers and 33 percent by weight
fluff pulp fibers
based on the total weight of fibers. Control B further included the fibrous
material making
up the fibrous bands in Composites M, N, and O.
Composites M-O included two fibrous bands (50 gsm) in a fibrous base. The
fibrous
base included 50 percent by weight superabsorbent material and 50 percent by
weight fibrous
material based on the total weight of the composite. The fibrous material
include 67 percent
by weight crosslinked fibers and 33 percent by weight fluff pulp fibers based
on the total
weight of fibers.
For Composite M, the fibrous bands included 50 percent by weight crosslinked
fibers
and 50 percent by weight refined fibers based on the total weight of fibers in
the bands.
For Composite N, the fibrous bands included 80 percent by weight crosslinked
fibers
and 20 percent by weight refined fibers based on the total weight of fibers in
the bands.
For Composite O, the fibrous bands included 50 percent by weight crosslinked
fibers
and 50 percent by weight fluff pulp fibers based on the total weight of fibers
in the bands.
CA 02384376 2002-03-08
WO 01/21873 PCT/US00/25955
-47-
The saturation capacity (Sat Cap), unrestrained vertical wicking (URVW)
height, ring
crush, and tensile of Controls A and B and Composites M, N, and O are
summarized in
Table 9.
Table 9. Representative Composite Characteristics.
Composite Sat Cap URVW Height Ring Crush Tensile
(g/ ) OD at 15 min. g/inch)
Control A 19.65 9.75 350.00 258.50
Control B 19.25 10.00 500.00 310.20
M 17.36 14.50 900.00 1008.15
N _20.87 14.00 _600.00 1861.20
O I 19.20 14.50 I 675.00 878.90
As shown in Table 9, wicking for the composites having fibrous bands is
increased
compared to the control composites. The fibrous bands also enhance composite
tensile
significantly.
Ring crush and tensile strength for control and representative composites are
correlated graphically in FIGURE 33. As shown in FIGURE 33, ring crush
increases
dramatically with increasing tensile strength for the control composite. In
contrast, ring crush
remains substantially constant with increasing tensile strength for the
representative
composite having fibrous bands. This correlation demonstrates that higher
tensile strengths
can be achieved in these composites without significantly increasing ring
crush (i.e.,
decreasing softness).
Unrestrained vertical wicking height and saturation capacity for control and
representative composites are correlated graphically in FIGURE 34. As shown in
FIGURE
34, wicking decreases dramatically with increasing saturation capacity for the
control
composite. In contrast, wicking remains substantially constant with increasing
saturation
capacity for the representative composite having fibrous bands. This
correlation
demonstrates that greater wicking and fluid distribution can be achieved for
these composites
without decreasing saturation capacity.
Ring crush and tensile strength for control and representative composites are
compared graphically in FIGURE 35. Composites M, N, and O all show increased
tensile
compared to the controls.
Unrestrained vertical wicking height and saturation capacity for control and
representative composites are compared graphically in FIGURE 36. Composites M,
N, and
O all show increased wicking compared to the controls.
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 this invention.
