Note: Descriptions are shown in the official language in which they were submitted.
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RETICULATED ABSORBENT COMPOSITE
Field of the Invention
The present invention relates to an absorbent composite and more particularly,
to a reticulated absorbent composite that includes superabsorbent material in
a fibrous
matrix.
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.
1 S 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.
Wetlaid
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 wetlaid process typically exhibit certain
properties that are superior to those of an air-laid structure. The integrity,
fluid
2S distribution, and the wicking characteristics of wetlaid cellulosic
structures are
superior to those of air-laid structures. Attempts to combine the advantages
of
wetlaid composites with the high absorbent capacity of superabsorbent
materials has
led to the formation of various wetlaid 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
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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
S 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 wetlaid composites including wet strength,
absorbent
capacity and acquisition, liquid distribution, softness, and resilience. The
present
invention seeks to fulfill these needs and provides fi~rther 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 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.
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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 other aspects of the invention, methods for forming the composite and
absorbent articles that include the composite are provided. The absorbent
articles
include consumer absorbent products such as diapers, feminine care products,
and
adult incontinence products.
Brief Description of the Drawin_Qs
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 wetlaid method in accordance with
the
present invention at 12 times magnification;
FIGURE 3 is a photomicrograph of the wetlaid 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 40 times magnification;
FIGURE 6 is a photomicrograph of a cross section of a representative
reticulated absorbent composite formed by a wetlaid method in accordance with
the
present invention in a wetted state at 8 times magnification;
FIGURE 7 is a photomicrograph of the wetlaid 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
3 5 present invention in a wetted state at 8 times magnification;
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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;
FIGURES 12A and 12B are cross-sectional views of portions 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;
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;
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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 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;
FIGURE 2$ 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;
FIGURE 26 are cross-sectional views of portions of absorbent articles
incorporating a reticulated absorbent composite formed in accordance with the
1$ present invention;
FIGURE 27 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;
FIGURE 28 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 29 is a graph illustrating the correlation between composite edgewise
compression and percentage matrix fiber in the composite; and
FIGURE 30 is a graph illustrating the correlation between composite dry
2$ tensile strength and edgewise compression.
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
3 $ includes a wet strength agent that further increases tensile strength and
structural
integrity to the composite.
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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
can
be combined with a storage layer to provide an absorbent core that is usefixl
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
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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 photonucrograph of a
cross section of a representative composite formed by a wetlaid 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 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
wetlaid 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 filly occupy voids that
the
absorbent material previously occupied in the dry composite.
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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. In one embodiment, the
composite
includes resilient fibers in an amount from about 5 to about 60 percent by
weight,
preferably from about 10 to 40 percent by weight, based on the total weight of
the
composite.
Resilient fibers include cellulosic and synthetic fibers. 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 crosslinking. In one embodiment, 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 one
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.
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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. In one embodiment,
the
composite includes matrix fibers in an amount from about 10 to about 60
percent by
weight, preferably from about 20 to about 50 percent by weight, based on the
total
weight of the composite.
The composite can include a combination of resilient and matrix fibers. In one
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 another
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 invention are available from Weyerhaeuser Company
under the
designations CF416, NF405, PL416, FRS 16, 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
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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.S. Patents Nos. 5,137,537; 5,183,707; and 5,190,563, describe the use of Cz-
C9
polycarboxylic acids that contain at least three carboxyl groups (e.g., citric
acid and
oxydisuccinic acid) as crosslinking agents.
Suitable urea-based crosslinking agents include methylolated 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-imidazoIidinone), 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), poly(methylvinylether-co-maleate) copolymer,
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poly(methylvinylether-co-itaconate) copolymer, copolymers of acrylic acid, and
copolymers of malefic acid. The use of polymeric polycarboxylic acid
crosslinking
agents such as polyacrylic acid polymers, polymaleic acid polymers, copolymers
of
acrylic acid, and copolymers of malefic acid is described in U.S. patent
application
Serial No. 08/989,697, filed December 12, 1997, and assigned to Weyerhaeuser
Company. Mixtures or blends of crosslinking agents 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"; (S) 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
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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, 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 polyolefin 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 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 ZO 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
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percent, preferably from about 30 to about 50 weight percent, based on the
total
weight of the composite.
The absorbent material may include natural materials such as agar, pectin, and
guar gum, and synthetic materials, such as synthetic hydrogel polymers.
Synthetic
hydrogel polymers include, for example, carboxymethyl cellulose, alkaline
metal salts
of polyacrylic acid, polyacrylamides, polyvinyl alcohol, ethylene malefic
anhydride
copolymers, polyvinyl ethers, hydroxypropyl cellulose, polyvinyl morpholinone,
polymers and copolymers of vinyl sulphonic acid, polyacrylates,
polyacrylamides, and
polyvinyl pyridine among others. In one 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.
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Suitable superabsorbent materials useful in the absorbent composite include
superabsorbent particles and superabsorbent fibers.
In one 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.
Suitable wet strength agents include cationic modified starch having nitrogen
containing groups (e.g., amino groups) such as those available from National
Starch
IS 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
3 S 1000 g/m2, preferably from about 200 to about 800 g/mz. In one embodiment,
the
absorbent composite has a- basis weight from about 300 to about 600. g/m2. The
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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 one 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 glcm3, and preferably
about 0.15
g/cm3. Predryer densification can also be employed. In one embodiment, 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.
1 S 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
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 wetlaid and foam
processes known to those of ordinary skill in the pulp processing art. A
representative example of a wetlaid process is described in U. S. Patent No.
5,300,192,
issued April 5, 1994, entitled "Wetlaid Fiber Sheet Manufacturing with
Reactivatable
Binders for Binding Particles to Fibers", expressly incorporated herein by
reference.
Wetlaid processes are also described in standard texts, such as Casey, PULP
~1D
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.,
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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, 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 can be 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, in one embodiment, 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
3 5 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.
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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 wetlaid 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 than wetlaid webs. Similarly, the tensile
strength of
foam-formed webs is substantially greater than for air-laid webs and approach
the
strength of wetlaid 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 wetlaid
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 wetlaid
and foam processes is described in Examples 1 and 2, respectively. Absorbent
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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
wetlaid
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 its
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 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.
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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 11, 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, refernng to FIGURE 12A, absorbent article 38 comprises
composite 10, liquid pervious facing sheet 22 and liquid impervious backing
sheet 24.
Refernng to FIGURE 12B, 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 constructs in FIGURES 12A and 12B are 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 acquisition layer 20 to form an absorbent article
having
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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 airlaid, wetlaid, 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
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 airlaid or
wetlaid
20 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 fi~rther 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. As used herein,
the
term "integrally formed" refers to a composite having more than one strata
produced
in a formation process that provides the composite as a unitary structure.
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
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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. As noted above, core 10 is a fibrous matrix that includes fibrous regions
12
defining voids 14, some of which include absorbent material 18.
In this embodiment, the present invention provides an absorbent composite
that is a unitary structure that includes two or more strata. The term
"unitary" refers
to the composite's structure in which adjacent strata are integrally connected
through
a transition zone to provide a structure with adjacent strata in intimate
fluid
communication. Referring to FIGURE 21A, surface stratum 132 is integrally
connected to core stratum 10 through a transition zone. Similarly, referring
to
FIGURE Z1B, strata 132 and 134 are each integrally connected to core stratum
10
through a transition zone.
In the composite, transition zones separate the composite's strata. The nature
of the transition zone can vary from composite-to-composite and from stratum-
to-
stratum within a composite. The transition zone can be designed to satisfy the
performance requirements of a particular composite. In general, the transition
zone
integrally connects adjacent strata and provides for intimate liquid
communication
between strata. The transition zone includes fibers from one stratum extending
into
the adjacent stratum. For adjacent strata, the transition zone includes fibers
from the
first stratum extending into the second stratum and fibers from the second
stratum
extending into the first stratum.
Transition zone thickness within a composite can be widely varied depending
on the composite. Absorbent composites of the present invention can include a
transition zone that is relatively thin. Absorbent composites that include
such thin
transition zones have fairly abrupt transitions in material composition
between strata.
Alternatively, the composite can include a transition zone that is gradual
such that the
transition from one zone to the next occurs over a relatively greater
thickness of the
composite. In such a composite, the material compositions of each zone are
intermixed to a significant extent resulting in rather extended composition
gradients.
Unitary composites having multiple strata and methods for their formation are
described in international patent application Serial No. PCT/US97/22342,
Unitary
Stratified Composite, and U.S. patent application Serial No. 09/326,213,
Unitary
Absorbent System, each incorporated herein by reference in its entirety.
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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
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methods, stratum basis weight can also be independently controlled and varied.
Stratum basis weight can also be varied with respect to the core's 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 wetlaid methods.
The stratum can be integrally formed with the reticulated core by wetlaid 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 anto 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.
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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 elements 210
to
S 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 to FIGURE 22, absorbent material can be introduced
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 wire. The nozzles are
connected to an absorbent material supply. The nozzles can be positioned in
various
positions (e.g., positions 2, 3, or 4 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 fibrous
stratum.
The composite can include 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 composites having strata having specifically designed properties
and
containing components to attain composites having desired properties.
For example, composite 130 having stratum 132 and composite 140 having
strata 132 and 134 can be formed by machine 200. For composites in which
strata 132 and 134 comprise the same components, a single fiber furnish 124 is
introduced into headbox 212. For forming composites having strata 132 and 134
comprising different components, headbox 212 includes one or more bales 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.
In one embodiment, the reticulated composite is formed by a foam-forming
method using the components described above. In the foam-forming method,
fibrous
webs having multiple strata and including absorbent material can be formed
from
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multiple fibrous slurries. The foam-forming method can be 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 ca.n
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 foam fibrous slurry comprising fibers and a
surfactant in an aqueous dispersion medium;
(b) forming a second foam 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 foam slurry into contact with the first
foraminous element moving in a first path;
passing the second foam slurry into contact with the second
foranvnous element moving in the second path;
(g) passing a third material between the first and second foam
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 foam slurries
and third material by withdrawing foam and 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 downtlow twin-wire former useful in practicing the
3 5 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
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(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
S interior structure 230 extending from the former first end and toward the
second end.
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/foam slurry into the first volume,
supply 244
and means 245 for introducing a second fiber/foam slurry into the second
volume, and
supply 246 and means 247 for introducing a third material into the interior
structure.
Means for withdrawing 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.
Generally, the former's interior structure (i.e., structure 230 in FIGURE 23)
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
superabsorbent
material-containing slurry. Depending upon the nature of the composite to be
formed,
the first and second fiber/foam slurries may be the same, or different, from
each other
and from the third material.
The means for withdrawing 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 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 and 23).
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
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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
300 to about 600 gsm.
The composites achieve the desired flexibility and softness by adjusting
composite composition. Composite flexibility and softness can be adjusted,
controlled, and optimized by adjusting the amount and ratio of the composite's
components. The composites include three basic components: (1) absorbent
material;
(2) crosslinked cellulosic fibers; and (3) matrix fibers. Generally,
increasing the
amount and/or proportion of absorbent material (e.g., superabsorbent material)
and/or
crosslinked fiber in the composite increases composite flexibility and
softness.
Conversely, increasing the amount of matrix fiber (e.g., pulp fiber) in the
composite
generally decreases composite flexibility and softness.
Representative composites of the invention having suitable flexibility and
softness include from about 30 to about 80 percent by weight absorbent
material,
from about 10 to about 50 percent by weight crosslinked fiber, and from about
5 to
about 30 percent by weight matrix fiber.
In one embodiment, the composite includes from about 40 to about 70 percent
and, preferably, about 60 percent by weight superabsorbent material based on
the total
weight of the composite; from about 20 to about 50 percent and, preferably,
about 30
percent by weight crosslinked fiber; and from about 5 to about 20 percent and,
preferably, about 10 percent by weight matrix fiber based on the total weight
of the
composite. For composites including less than about 50 percent by weight
superabsorbent material, the ratio of crosslinked fibers:matrix fibers can be
at least 1:1
and, preferably, about 2:1.
In another embodiment, the composite includes about 70 percent by weight
superabsorbent material and about 30 percent by weight fibers. In one
embodiment,
the fibers include a blend of matrix fibers (e.g., southern pine) and
crosslinked fibers
having a ratio of crosslinked fibers:matrix fibers of at least 1:1 and,
preferably, at least
about 2:1.
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In a further preferred embodiment, the composite includes superabsorbent
polymeric particles having an average particle diameter in the range from
about
0.50 mm to about 1.0 mm.
Examples 17-19 describe the composition and flexibility and softness of
representative absorbent composites formed in accordance with the invention.
The
composites described in Example 17 were formed as handsheets and the
composites
described in Example 18 were formed by a foam-forming process on a twin-wire
former. The effect of superabsorbent polymer particle size on composite
flexibility
and softness is described in Example 20.
In addition to having flexibility and softness suitable for incorporation into
personal care absorbent products, the composites of the invention exhibit
advantageous structural integrity. Composite structural integrity can be
indicated by
tensile strength. Suitable composites for use in a personal-care absorbent
product
have a wet tensile strength of at least about 50 g/in. For machine processing,
suitable
1 S composites have a dry tensile strength of at least about 450 g/in.
Generally, as tensile strength increases, composite ring crush increases. The
correlation between composite edgewise ring crush and dry tensile is presented
graphically in FIGURE 30, which shows that edgewise ring crush increases
dramatically as dry tensile increases. Although there appears to be no
correlation
between composite basis weight and dry tensile, some correlation exists
between
composite density and dry tensile.
The tensile strength and edgewise compression of representative composites
of the invention are provided in Example 21.
The composites of the invention exhibit advantageous fluidic properties. The
properties can be indicated by various measures including liquid acquisition
rate,
wicking, and rewet. Acquisition rate and rewet, unrestrained vertical wicking
height,
and saddle acquisition rate, distribution, and wicking height for
representative
composites is described in Example 22.
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.
Representative absorbent constructs incorporating the absorbent composite
having a reticulated core and fibrous strata are shown in FIGURES 24 and 25.
Referring to FIGURE 24A, construct 150 includes composite 130 (i.e.,
reticulated
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core 10 and stratum 132) employed as a storage layer in combination with an
upper
acquisition layer 20. FIGURE 24B illustrates construct 160, which includes
composite 130 and acquisition layer 20 with stratum 132 adjacent acquisition
layer 20.
Construct 170, including acquisition layer 20 and composite 140, is
illustrated in
S FIGURE 24C.
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
25A
illustrates construct 180 having intermediate layer 30 (e.g., distribution
layer)
interposed between acquisition layer 20 and composite 130. Similarly, FIGURES
25B and 25C 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, I90, and 200 can
be incorporated into absorbent articles. Generally, absorbent articles 210,
220, and
230 shown in FIGURES 26A 26C, respectively; absorbent articles 240, 250, and
260
shown in FIGURE 27A 27C, respectively; and absorbent articles 270, 280, and
290
shown in FIGURE 28A-28C, 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.
The following examples are provided for the purposes of illustration, and not
limitation.
EXAMPLES
Example 1
Reticulated Absorbent Composite Formation' Representative Wetlaid Method
This example illustrates a wetlaid method for forming a representative
absorbent composite.
A wetlaid composite formed in accordance with the present invention is
prepared utilizing standard wetlaid apparatus known to those in the art. A
slurry of a
mixture of standard wood puip 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
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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 15 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 Com osite Formation: Re resentative 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 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.
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The sheet is then dried in a drying oven to remove the moisture.
Example 3
Acauisition Times for a Representative Reticulated Absorbent Composite
Tn 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. Acauisition Time Comparison
Acquisition
Time
sec
Insult Dia er A Com osite A
1 45 10
2 60 11
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
S 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
fozzned 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 wetlaid composite compared to a conventional air-laid storage core in
general, and
the enhanced performance of the reticulated absorbent composite in particular.
Example 4
Acguisition 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 Al-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.
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The acquisition time and rewet are determined in accordance with the
multiple-dose rewet test described below.
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 I 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 (S/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 lb.) 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.
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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.
Table 2. Acauisition Time and Rewet Comparison
S
SAP Basis Acquisition Rewet
Com site % w/w Weight Time
sm
InsultInsultInsultInsultInsultInsult
1 2 3 1 2 3
A1 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 I8 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 Al-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 S
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
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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,
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 flush with the inside edge of the trough. On each wing's end
was
10 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
1 S 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 SO percent of the liquid front reached the marked interval (e.g., 5 cm,
10 cm).
The liquid level in the trough was maintained at a relatively constant level
throughout
the test by replenishing with additional synthetic urine. The horizontal
wicking results
are summarized in Table 3.
Table 3. Horizontal Wicking Comparison
Distance Wicking Time
(cm) sec
Dia er B Com osite A
48 15
10 150 52
15 290 134
20 458 285
783 540
1703 1117
- 1425
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The results tabulated above indicate that horizontal wicking is enhanced for
the absorbent composite formed in accordance with the invention compared to a
conventional 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. S 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 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 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
10 Fell A art 54
15 - 513
20 - 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 the conventional air-laid composite.
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Example 6
Liauid Distribution for a Reuresentative 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 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 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.
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. The wet tensile strength is
determined as described below using a 2.5 x 4 inch strip wetted with 0.9%
saline at a
10:1 weight ratio of salineaample. The dry tensile strength is performed as
described
by TAPPI Method T 494 om-96-T.
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
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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.
Wet tensile is determined by the following procedure:
Sample:
6.35 cm (2.5 in.) CD x 10.2 cm (4 in.) MD*
Equipment:
Horizontal Instron
10 Newton Load Cell
Clamp Pressure 20 psi, minimize compromising sample integrity
60 mL syringe
0.9% Blood Bank Saline Solution
Procedure:
1) Weigh sample to the nearest 0.1 gram.
2) Using a syringe, uniformly add 10 times the sample weight of
Saline Solution to the topside of the sample.
3) Control the solution delivery so the sample is not damaged.
4) When all the solution has been delivered, start a timer for 5
minutes.
5) After the 5 minutes, clamp the sample in the Instron and test
for tensile.
6) Repeat three times for each sample type.
7) Record the average value in b/in.
*Note: Sample size may be shorter than 10.2 cm as long as the sample is
securely held by the end clamps.
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 wetlaid 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
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(12 percent by weight, polymaleic acid crosslinked fibers), and absorbent
material
(40 percent by weight, superabsorbent material commercially available from
Stockhausen). One of the wetlaid 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 wetlaid composites. The results also indicate that, for
the wetlaid
composites, the inclusion of a wet strength agent increases the composite's
stii~ness.
Example 9
Reticulated Absorbent Composite Formation' Representative Wetlaid Method
This example illustrates a representative wetlaid 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 fimnel 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 fiznnel 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 (gallonlmin) and absorbent slurry (1 - 2.6 % solids) flow was
about 10
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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 flat-bed 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.
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
3 0 of fibers.
Target density of the absorbent composite was accomplished by calendering
using a single rup 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.
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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.
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.
Exam~Ie 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.
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Example 16
The performance of representative composites (Composites B-D) prepared as
described in Examples 10-15 is summarized in Tables 5 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. S 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, "117" 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 5 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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-43-
o ~ ~ O O N N
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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 os'ite Ca acit cc/
B 16.9
C 16.9
20.4
E 21.5
Example 17
The Flexibility and Softness of Representative Reticulated Absorbent
Composites:
Wetlaid Handsheets
The flexibility and softness of representative reticulated absorbent
composites
formed in accordance with the present invention 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)
Triplicate analysis (A, B, C)
Method:
1) Cut triplicate of sample size, lengthwise in the composite machine
direction (MD).
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2) Condition samples for 2 hours at SO% 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-O.S 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.
ZO 4) Set the bottom platen on a smooth, level surface.
S) 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
S00-weight} and wait 3 seconds.
1 S 7) Then, gently stack 3 more 100-g weights at 3-second intervals.
8) If the ring collapses SO% 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.
20 9) If the combined weight doesn't crush the sample, then carefully remove
the four 100-g weights.
10) Gently add another) S00-g weight and weight 3 seconds.
11) If the ring collapses SO% or more of it's original height within a
3-second interval, then record the total amount of weight necessary to
2S do so, i.e., add the weight of the top platen and weight(s).
12) Repeat step 6 through 11, increasing the number of S00-g weights by
one for each cycle.
13) Repeat steps S through 11 for the other replicates.
14) Record the average weight for the replicates in g~f rounded to the
30 nearest 10 g.
Calculations:
Average ring crush weight = (Weight A + Weight B + Weight C)/3
Representative composites were formed by wetlaid and foam methods. The
representative composites were formed as handsheets using a 20 inch X 20 inch
3S handsheet mold. The target basis weight for the composites was 400 g/m2. To
increase post-forming consistency to about 20 to 3 S percent, five blotters
and a
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vacuum couch were utilized. To reduce swelling of the absorbent material, ice
water
was used as the dispersion medium. The composites were dried a 150°C.
Unless
otherwise noted each composite included a wet strength agent (polyamide-
epichlorohydrin resin commercially available from Hercules under the
designation
S Kymene~, 10 lb/ton fiber) and absorbent material (superabsorbent material
obtained
from Stockhausen, 40 percent by weight based on the total weight of the
composite).
The composites included various amounts of matrix fibers (southern pine
commercially available from Weyerhaeuser Co. under the designation NB416),
resilient fibers (crosslinked fibers), synthetic fibers, and other materials
as indicated.
The compositions of the representative composites that were evaluated for
softness by the edgewise ring crush are described below.
Control Composite. A wetlaid composite composed of 40 percent by weight
superabsorbent material and 60 percent by weight matrix fibers.
Composite 1. A foam-formed composite composed of 40 percent by weight
superabsorbent material, 30 percent by weight matrix fibers, and 30 percent by
weight
crosslinked fibers.
Composite 2. A wetlaid composite composed of 40 percent by weight
superabsorbent material, 30 percent by weight matrix fibers, and 30 percent by
weight
crosslinked fibers.
Composite 3. A wetlaid composite composed of 40 percent by weight
superabsorbent material, 15 percent by weight matrix fibers, and 45 percent by
weight
crosslinked fibers.
Composite 4. A wetlaid composite composed of 40 percent by weight
superabsorbent material, 30 percent by weight matrix fibers, and 30 percent by
weight
chemithermomechanical pulp (CTMP). (Svenska Cellulosa Aktiebolaget, Sweden).
Composite 5. A wetlaid composite composed of 40 percent by weight
superabsorbent material, 30 percent by weight matrix fibers, and 30 percent by
weight
high porosity fibers (HPZ). (Buckeye Corp., Memphis, TIC.
Composite 6. A wetlaid composite composed of 60 percent by weight
superabsorbent material and. 40 percent by weight matrix fibers.
Composite 7. A wetlaid composite composed of 60 percent by weight
superabsorbent material, 20 percent by weight matrix fibers, and 20 percent by
weight
crosslinked fibers.
Composite 8-1. A wetIaid composite composed of 40 percent by weight
superabsorbent material (large screened SXM-77, 0.05-1.00 mm, SXM-77 available
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from Stockhausen), 30 percent by weight matrix fibers, and 30 percent by
weight
crosslinked fibers.
Composite 8-2. A wetlaid composite composed of 40 percent by weight
superabsorbent material (small screened SXM-77, 0.208-0.355), 30 percent by
weight
matrix fibers, and 30 percent by weight crosslinked fibers.
Composite 8-3. A wetlaid composite composed of 40 percent by weight
superabsorbent material (unscreened SXM-77), 3 0 percent by weight matrix f
tiers,
and 30 percent by weight crosslinked fibers.
Composite 8-4. A wetlaid composite composed of 40 percent by weight
superabsorbent material (large screened superabsorbent, 0.50-1.00 mm}, 30
percent
by weight matrix fibers, and 30 percent by weight crosslinked fibers.
Composite 9. A wetlaid composite composed of 40 percent by weight
superabsorbent material, 60 percent by weight matrix fibers (NB416) that had
been
coated with clay (25 percent by weight) (made by Weyerhaeuser and designated T
757).
Composite 10. A wetlaid composite composed of 40 percent by weight
superabsorbent material, 30 percent by weight matrix fibers (T-757), and 30
percent
by weight crosslinked fibers.
Composite 11. A wetlaid composite composed of 40 percent by weight
superabsorbent material, 30 percent by weight crosslinked fibers, and 30
percent by
weight matrix fibers (NB416) that had been coated with precipitated calcium
carbonate (10 percent by weight) (made by Weyerhaeuser and designated MT-10).
Composite 12. A wetlaid composite composed of 40 percent by weight
superabsorbent material, 30 percent by weight matrix fibers, and 30 percent by
weight
synthetic fibers (PET fibers, straight T-224). (Hoechst Celanese Corp.,
Charlotte,
NC).
Composite 13. A wetlaid composite composed of 40 percent by weight
superabsorbent material, 30 percent by weight matrix fibers, and 30 percent by
weight
synthetic fibers (PET fibers, curly T-224).
Composite 14. A wetlaid composite composed of 40 percent by weight
superabsorbent material, 30 percent by weight matrix fibers, and 30 percent by
weight
cellulose acetate.
Composite 15. A wetlaid composite composed of 40 percent by weight
superabsorbent material, 30 percent by weight matrix fibers, and 30 percent by
weight
crosslinked fibers. Surfactant RW-150 (Union Carbide Corporation} was included
in
the formation process.
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Composite 16. A wetlaid composite composed of 40 percent by weight
superabsorbent material, 30 percent by weight matrix fibers, and 30 percent by
weight
crosslinked fibers. Surfactant QS-15 (Union Carbide Corporation) was included
in
the formation process.
Composite 17. A wetlaid composite composed of 40 percent by weight
superabsorbent material and 60 percent by weight matrix fibers. A debonding
agent,
Quaker 224C (Quaker Chemical Corp., Conshohken, PA), was included in the
formation process.
Composite 18. A wetlaid composite composed of 40 percent by weight
superabsorbent material, 30~percent by weight matrix fibers, and 30 percent by
weight
crosslinked fibers. A debonding agent, Quaker 224C, was included in the
formation
process.
Composite 19. A wetlaid composite composed of 40 percent by weight
superabsorbent material, 30 percent by weight matrix fibers, and 30 percent by
weight
crosslinked fibers. The composite was formed by partially drying the web to
about 70
percent consistency, conveying the web through an "S" configuration around two
narrow diameter (1 inch) rolls followed by complete drying.
Composite 20. A wetlaid composite composed of 40 percent by weight
superabsorbent material, 30 percent by weight matrix fibers, and 30 percent by
weight
crosslinked fibers. The composite was treated with ethanol prior to drying to
displace
water in the composite.
A summary of the compositions of the representative composites is
summarized in Table 7.
Table 7. Representative Absorbent Composite Composition
SuperabsorbentMatrix Crosslinked Other
Material Fiber Fiber Material
Control40 60
1 40 30 30 Foam formed
2 40 30 30
3 40 15 45
4 40 30 30 CTMP
40 30 30 HPZ
6 60 40
7 60 2 20
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SuperabsorbentMatrix Crosslinked Other
Material Fiber Fiber Material
8-1 40 30 30 Lar a SXM-77
8-2 40 30 30 Small SXM-77
8-3 40 30 30 SXM-77
8-4 40 30 30 Large screened
superabsorbent
material
40 60 T-757
40 30 30 T-757
11 40 30 30 PCC-10
12 40 30 30 T-224-strai
t
13 40 30 30 T-224-curl
14 40 30 30 Cellulose acetate
40 30 30 Am hoteric
16 40 30 30 Sul hated
17 40 60 Debonder
18 40 30 30 Debonder
19 40 30 30 Mechanical
40 30 30 Ethanol
Edgewise ring crush values {g) and edgewise compression values (g/gsm) of
representative composites are summarized in Table 8. The values in Table 8
represent
the average of three measurements. The ring crush values were determined for
30.5
cm X 6.35 cm composite sheets.
Table 8. Representative Composite Edgewise Ring Crush and Edgewise Compression
Edgewise Edgewise
CompositeWeight Caliper Basis DensityRing CrushCompression
(g) (mm) Weight (g/cm3)(g) (g/gsm)
mz
CONTROL 9.42 3.92 487 0.12 6300 12.9
1 7.98 3.75 412 0.11 2400 5.8
2 9.63 4.84 498 0.10 2333 4.7
3 8.61 5.43 445 0.08 850 1,9
4 .9.51 3.68 492 0.13 3900 7.9
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Edgewise Edgewise
CompositeWeight Caliper Basis Density Ring CrushCompression
(g) (mm) Weight (gkm3) (g) (g/gsm)
mz
7.05 3.61 364 0.10 3300 9.1
6 10.30 2.74 532 0.19 3667 6.9
7 9.42 3.92 487 0.12 1133 2.3
8-1 8.81 4.35 455 0.10 2867 6.3
8-2 8.41 4.42 43 5 0.10 2967 6. 8
8-3 7.61 4.28 393 0.09 2267 5.8
8-4 9.40 5.14 486 0.09 2467 5.1
9 8.40 2.47 434 0.18 12833 29.6
8.70 3.91 449 0.12 6100 13.6
11 8.74 5.11 452 0.09 1600 3.5
12 9.35 4.43 483 0.11 1700 3.5
13 9.15 7.09 473 0.07 1800 3.8
14 6.65 3.23 343 0.11 1733 5.0
10.01 4.72 517 0.11 2167 4.2
16 8.55 3.95 442 0.11 2367 5.4
17 8.3 3 2.3 6 431 0.18 2767 6.4
18 8.75 4.19 452 0.11 1367 3.0
19 9.43 5.09 487 0.10 1933 4.0
9.07 5.49 468 0.09 1400 3.0
The results demonstrate that composite flexibility and softness, as measured
by
the edgewise ring crush and edgewise compression, can be adjusted and
controlled by
optimizing the composite's components and their amounts. Generally, increasing
the
percentage of matrix fiber in a composite decreases its softness, and
conversely,
5 increasing the percentage of either crosslinked fiber or superabsorbent
material in a
composite results in increased softness.
The presence of crosslinked fiber in a composite increases its flexibility and
softness. For example, Control Composite includes no crosslinked fiber and has
a
edgewise compression value of 12.9 g/gsm. Composite 2, in which SO percent of
its
10 fibrous content is crosslinked fiber, has a edgewise compression value of
5.8 g/gsm.
Increasing the amount of crosslinked fiber relative to matrix fiber further
increases
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flexibility and softness. Composite 3, in which 67 percent of its fibrous
content is
crosslinked fiber, has an edgewise compression value of 1.9 g/gsm.
Replacing the crosslinked fiber in the composite with other materials such as
CTMP (Composite 4) or HPZ (Composite S) results in increased ring crush values
and reduced flexibility and softness. Replacing the composite's crosslinked
fiber with
additional superabsorbent material (Composite 6) also decreases flexibility
and
softness. However, increasing the amount of superabsorbent material and
maintaining
a relatively high proportion (about 50 percent by weight based on total weight
of
fibers) of crosslinked fiber. provides a composite (Composite 7) having
increased
flexibility and softness compared a representative wetlaid composite
(Composite 2).
Substituting cellulose acetate for crosslinked fiber (Composite 14) also
resulted in a
composite having increased flexibility and softness compared a representative
wetlaid
composite (Composite 2).
Replacing the matrix fiber in the composite with other fibers such as calcium
carbonate coated fiber (Composite 11) and synthetic (PET) fiber (Composites 12
and
13) resulted in composites having increased flexibility and softness. The
addition of a
debonding agent also increased the composite's flexibility and softness.
Mechanical and chemical treatments of composites also increased composite
flexibility and softness. These effects are shown by comparing the ring crush
values of
Composite 2 to Composites 19 and 21, respectively.
No relationship appears to exist between either ring crush and basis weight or
ring crush and density for the composites evaluated.
The flexibility and softness of the composites of the invention can be
dramatically increased by -increasing the amount of superabsorbent material
and
crosslinked fiber in the composite. The flexibility and softness of
representative
composites composed of superabsorbent (40, 50 and 60 percent by weight),
crosslinked fiber (10, 15, 25, 30, and 45 percent by weight), and matrix fiber
(10, 15,
25, 30, and 45 percent by weight) is summarized in Table 9. In Table 9,
superabsorbent A refers to a superabsorbent obtained from Stockhausen and
superabsorbent B refers to a superabsorbent obtained from Stockhausen under
the
designation SXM-77.
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Table 9. Representative Composite Edgewise Ring Crush and Compression'
Effect of Superabsorbent and Crosslinked Fiber
MatrixBasis
SuperabsorbentSuperabsorbentCrosslinlcedFiber Wt. EdgewiseEdgewise
Com (%) TargetRing Compression
site Material Material Fiber m2 Crush sm
T % %
21 A 40 45 15 500 1430 2.9
22 A 40 15 45 500 8220 16.4
23 A 60 30 10 400 430 1.1
24 A 60 10 30 400 2000 5.0
25 B 40 45 15 500 1500 3.0
26 B 40 15 45 500 8220 16.4
27 B 60 30 10 400 570 1.4
28 B 60 10 30 400 2100 5.3
29 A 50 25 25 450 2070 4.6
30 B 50 25 25 450 2270 5.0
Referring to Table 9, at constant superabsorbent material percentage (40
percent by weight), decreasing the amount of crosslinked fiber from 45 percent
to 15
percent and increasing the matrix fiber from 15 percent to 45 percent
dramatically
reduces flexibility and softness. Comparing Composites 21 and 25 to Composites
22
and 26, respectively, the edgewise compression increases more than about 5-
fold
(from 2.9 to 16.4 g/gsm and from 3.0 to 16.4 g/gsm). Maintaining the
proportion of
crosslinked to matrix fibers at 3:1 and increasing the amount of
superabsorbent
material to 60 percent by weight further significantly increases flexibility
and softness.
Comparing Composites 21 and 25 to Composites 23 and 27, respectively, the
edgewise compression value decreases more than about 2-fold (from 2.9 to 1.1
g/gsm
and from 3.0 to 1.4 g/gsm). Increasing the amount of superabsorbent material
to 60
percent from 40 percent provides for increased flexibility and softness even
for
composites in which the proportion of crosslinked to matrix fiber is 1:3.
Comparing
Composites 24 and 28 to Composites 22 and 26, respectively, the edgewise
compression value decreases about 3-fold (from 16.4 to 5.0 g/gsm and from 16.4
to
5.3 g/gsm).
The results demonstrate that for these representative composites replacing
matrix fibers with either crosslinked fiber or superabsorbent material
decreases ring
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crush and edgewise compression and improves flexibility and softness. The
correlation between ring crush and percentage matrix fiber is presented
graphically in
FIGURE 29. Refernng to FIGURE 29, ring crush increases dramatically as the
percentage of matrix fiber increases.
Example 18
The Flexibility and Softness of Representative Reticulated Absorbent
Composites
Foam-Formed Sheets
The flexibility and softness of representative reticulated absorbent
composites
formed by a foam-forming method in accordance with the present invention was
determined by the an edgewise ring crush and edgewise compression methods.
Representative composites were formed as described in above using a twin-wire
former and included 70 percent by weight superabsorbent material and 30
percent by
weight fibers. The first composites included 50 percent by weight matrix
fibers
(NB416) and 50 percent by weight crosslinked fibers based on the total weight
of
fibers. The second composites included 30 percent by weight matrix fibers
(NB416)
and 70 percent by weight crosslinked fibers based on the total weight of
fibers. Both
composites included a wet strength agent (polyamide-epichlorohydrin resin, 10
lb/ton
fiber) and had surface strata composed of matrix fibers (NB416, 40 percent by
weight) and crosslinked fibers (60 percent by weight). The first composites
had an
average edgewise compression value of about 2.9 g/gsm and the second
composites
had an average edgewise compression value of about 1.1 g/gsm. The results
demonstrate that for these high superabsorbent-containing composites
increasing the
amount of crosslinked fibers significantly reduces edgewise compression and
improves
flexibility and softness. For these composites containing 70 percent by weight
superabsorbent, increasing the percentage of crosslinked fiber in the fibrous
component from 50 percent to 70 percent decrease ring crush and compression
and
increased flexibility and softness by about 2.5-fold.
Example 19
The Softness and Wet Inte~aritv of Representative Reticulated Absorbent
Composites
Edgewise Compression
The softness and wet integrity of representative reticulated absorbent
composites formed by wetlaid and foam-forming methods in accordance with the
present invention was determined by the edgewise compression. Edgewise
compression is discussed in The Handbook of Physical and Mechanical Testiest
of
Parser and Paperboard, Richard E. Mark, Dekker 1983 (Vol. I). As noted above,
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edgewise compression (EC) is an indication of the softness of a dried
absorbent
composite.
Representative composites were formed as described above using a twin-wire
former and included 40 percent by weight superabsorbent material and 60
percent by
weight fibers. The first composites included 80 percent by weight matrix
fibers
(NB416) and 20 percent by weight crosslinked fibers based on the total weight
of
fibers. The second composites included 40 or 60 percent by weight matrix
fibers
(NB416) and 60 or 40 percent by weight crosslinked fibers based on the total
weight
of fibers. Certain of the composites included a wet strength agent (polyamide-
epichlorohydrin resin). Referring to Table 10, Composites 31-34 are wetlaid
composites and Composites 35-39 are foam-formed composites. Several of the
composites were further treated by, for example, calendering, after formation.
The EC values for the representative composites is summarized in Table 10.
The values presented in the table represent the average value of three
repetitions.
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~ M ...-yn M 00 v~ ~Yl~ M - '~T~D
W 'r ~ ~t "~M ~1C cV oocV N cV
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The results demonstrate that the foam-formed composites are generally more
flexible and softer than comparably constituted wetlaid composites. Referring
to
Table 10, wetIaid Composites 31 and 33 had EC values of 10.8 and 11 g/gsm,
respectively, while foam-formed Composite 38 had an EC value of 8.4 g/gsm.
The effect of crosslinked fiber content on composite flexibility and softness
is
demonstrated by comparing the ring crush and EC values for Composites 37 and
38.
Composite 38 (40:12:48) includes about 20 percent by weight crosslinked fiber
based
on the total weight of fibers and has an EC value of 8.4. Composite 37
(40:36:24)
includes about 60 percent by weight crosslinked fiber based on the total
weight of
fibers and has an EC value of 2.8. As noted above, increasing the amount of
crosslinked fiber significantly increases composite flexibility and softness.
In this
example, increasing the crosslinked fiber:matrix fiber ratio from 1:4 to 3:2,
resulted in
a 3-fold increase in flexibility softness.
Post-formation mechanical treatment (e.g., channeling or caiendering) of the
composites increased the composites' flexibility and softness by more than 2-
fold,
reducing the EC value from 10.8 to 4.3 for Composites 31 and 32, from 11 to
3.5 for
Composites 32 and 33, and from 8.4 to 2.7 for Composites 38 and 39. For these
composites, post-formation treatment did not significantly adversely affect
the
composites' wet integrity.
Composites 40 - 43 are foam-formed composites in which the matrix fiber
(i.e., southern pine) is replaced with a synthetic fiber blend consisting of
20% by
weight polyethylene terephthalate fibers (PET 224) and 10% by weight synthetic
thermobondable binder fiber (Celbond~ T-105).
Example 20
The Effect of Su erabsorbent Pol er Particle Size on Com osite Flexibilit and
Softness
The effect of superabsorbent polymer particle size on the flexibility and
softness of representative composites of the invention is described.
Representative
composites were formed as described above using a foam-forming twin-wire
method.
The composites included 60% by weight superabsorbent particles, 20% by weight
matrix fibers (southern pine, NB416), and 20% crosslinked fiber. The
composites
also included a wet strength agent (polyamide-epichlorohydrin resin, 10 lb/ton
fiber).
The superabsorbent polymer particles incorporated into the representative
composites
included lightly crosslinked polyacrylates: (1) superabsorbent A obtained from
Stockhausen; (2) SXM77; and (3) screened SXM77 having particle diameter in the
range of from about 0.5 to about 1.0 mm.
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The measured ring crush, saturation capacity (oven dried), tensile strength,
wicking, and basis weights for the representative composites 43-4$ are
summarized in
Table 11. Composite 43-4$ included the components described above and
superabsorbent polymer particles A, SXM77, and screened SXM77, respectively.
CA 02348648 2001-04-20
WO 00/27625 PCT/US99/26560
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N ~OO
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Referring to Table 11, the results demonstrate that the composite
incorporating screened superabsorbent polymer particles having a diameter in
the
range of from about 0.5 to about 1.0 mm had an edgewise compression value of
3.2 g/gsm compared to 5.2 g/gsm for the similarly formed composite including
the
corresponding unscreened superabsorbent polymer particles. The edgewise
compression value for the composite incorporating the screened superabsorbent
polymer particles was about 1.6-fold less than for the corresponding composite
indicating its increased flexibility and softness.
The composite incorporating the screened superabsorbent particles also had an
increase in saturation capacity of about 10% compared to the composite
incorporating
unscreened superabsorbent particles.
Example 21
The Tensile Strength of Rearesentative Reticulated Absorbent Composites
Wetlaid
Handsheets
The tensile strength of representative reticulated absorbent composites formed
in accordance with the present invention was determined by the dry tensile
strength
method described in TAPPI Method T 494 om-96-T.
Representative composites were formed as described above in Example 17.
Edgewise compression and dry tensile strength of representative composites are
summarized in Table 12. In the table, the control composite is composed of
superabsorbent particles (40% by weight) and matrix fibers (60% by weight,
southern
pine), and Composite 2 is composed of superabsorbent particles (40% by
weight),
matrix fibers (30% by weight, southern pine), and crosslinked fibers (30% by
weight).
Table 12. Representative Composite Dry Tensile
Composite EC Value Dry Tensile
sm in
Control 12.9 3206
1 5.8 919
2 4.7 744
3 1.9 235
4 7.9 1366
9~1 1310
6 6.9 1837
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Composite EC Value Dry Tensile
sm in
7 2.3 386
8-1 6.3 870
8-2 6.8 837
8-3 5.8 740
8-4 5.1 793
9 29.6 4769
13.6 1873
11 3.5 600
12 3.5 692
13 3.8 761
14 5.0 1200
4.2 686
16 5.4 548
17 6.4 1090
18 3.0 293
19 4.0 689
3.0 496
The correlation between composite edgewise compression and dry tensile is
presented graphically in FIGURE 30. Referring to FIGURE 30, edgewise
compression increases dramatically as dry tensile increases. Generally, as
tensile
5 strength increases, composite flexibility and softness decreases. Although
there
appears to be no correlation between composite basis weight and dry tensile,
there is
some correlation between composite density and dry tensile.
Example 22
Absorbent Properties ofRepresentative Reticulated Absorbent Comnosites~ Foam_
10 Formed Composites
Representative composites were prepared by foam-forming methods in
accordance with the methods described above. The composites included absorbent
material (from about 35 to about 45 percent by weight superabsorbent particles
based
on the total weight of the composite), crosslinked cellulosic fiber, and
matrix fibers
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(weight ratio of crosslinked fibers to matrix fibers, 1:1). The compositions
and
physical properties of representative composites (Composites 46-48) are
summarized
in Table 13.
Table 13. Representative Reticulated Absorbent Composites
CompositeOD As OD Crotch SAP Total StrataStrata
is XL XL
BW DensityCapacitySoftnessContentContent BW Content
m2 cm3 cmz ~ % % Fiber mz % Fiber
46 411.2 0.14 0.72 427 35 50 50 50
47 508.5 0.19 0.97 536 45 50 50 50
48 498.3 0.20 0.96 563 45 50 50 50
The absorbent properties of these representative composites were determined
by measuring ( 1 ) unrestrained vertical wicking height; (2) acquisition rate
and rewet;
{3) saddle acquisition rate; (4) saddle acquisition wicking distribution; and
(5) saddle
acquisition wicking height.
Unrestrained Vertical Wickin~Heittht. The unrestrained vertical wicking
height at 15 minutes was measured for the above-identified composites (i.e.,
unsoftened Composites 43-45) and the corresponding calendered composites as
described below.
Material:
Synthetic urine for wicking - "Blood Bank" 0.9% Saline Solution
Samples:
Size: 6.Scm(CD) x 25cm(MD), marked with both permanent and water
permeable lines at 1, 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 Capacity(g / g) = Wet Wt.-(As Is or O.D. Wt.)
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
The results are summarized in Table 14.
Table 14. Unrestrained Vertical Wickins~Height
Composite Calendered Uncalendered
Hei ht cm Densit cm3 Hei t cm Densit cm3
46 10.7 0.15 15.2 0.18
47 11.5 0.19 14.7 0.23
48 11.3 0.2 14 0.20
The results indicate that wicking height is reduced by calendering. The result
also suggests that calendering disrupts the fibrous network leading to
effective
wicking throughout the composite.
AcQUisition Rate and Rewet. The acquisition rate and rewet of the
representative composites was determined by the methods described above in
Example 4. In addition to measuring the acquisition rate for three liquid
insults and
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rewet for Composite 48, the acquisition rate and rewet for Composites 47 and
48
combined with a pledget was also determined. For these constructs, the pledget
acts
as an acquisition/distribution layer. The results are summarized in Table 15.
Table 15. Ac4uisition Rate and Rewet (ml/sec)
Com osite 1st Insult 2nd Insult 3rd Insult Final Rewet
47/ led et 2.73 2.53 2.26 15.81
48 2.60 2.12 1.92 18.71
48/ led et 2.65 2.39 2.15 14.65
n he results show that the acquisition rate decreases slightly in subsequent
insults and that the addition of a pledget slightly decreases acquisition
rate. However,
the rewet measured for constructs that include a pledget is less than the
rewet for
constructs that do not include the pledget.
Saddle Acauisition Rate Distribution and Wickinrz Height. Saddle wicking,
including acquisition rate, distribution, and wicking height, was determined
by the
method described below.
Procedure:
1 ) Run in triplicate.
2) Perform % solids on material. Cut sample to 43cm
x (6.Scm-llcm
(will vary with sample)).
3) Measure (as is) weight and caliper of sample.
Calculate Basis weight
and density.
4) Draw and label the 12 cells using a template and
a permanent marker.
5) Construct Diaper via instructions on Service Request.
(This may
result in replacing certain diaper components
(i.e., Core) with the
sample)).
6) Position diaper in Saddle Device so that the "X"
is squarely at the
bottom of the apparatus and then position the
funnel approximately 1
cm directly above the "X."
7) Measure out 75m1 of Synthetic Urine (Blood Bank
0.9% Saline) and
pour into funnel.
8) Open the funnel and start the timer. Measure the
time at which aU of
the fluid has left the funnel to the point where
the fluid is absorbed into
the sample. Record as SWAT.
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9) At the end of 20 min, 40 min, and 60 min, repeat steps 7 and 8.
10) When the timer has reached 80 min, pull out diaper and cut sample
into designated cells.
11) Pull apart and weigh each cell and record the weight.
12) If requested perform wet calipers.
The saddle acquisition rate results for Composite 45 combined with a pledget
are compared to a control composite (removed from Supreme Diaper, commercially
available from Kimberly-Clark, Neenah, WI) and are summarized in Table 16.
Table 16. Saddle Acquisition Rate (mUsec,~
Com osite 1st Insult 2nd Insult 3rd Insult
48/ led et 28.05 28.01 31.50
Control 37.77 52.30 53.06
nne results indicate that the acquisition rate generally increased with
subsequent insults and that the acquisition rate for the construct including
Composite
48 and a pledget was less than the rate for the commercially available core.
The saddle acquisition distribution results for Composite 48 combined with a
pledget are compared to a control composite and are summarized in Table 17.
Table 17. Saddle Acquisition Distribution tttl~t)
Zone 45/pledget . Control
1 0 0
2 3.73 2.06
3 11.88 9.28
4 13.01 12.40
12.16 10.66
6 10.62 9.44
7 3.73 3.91
8 0 0
~ ne resuns show that the representative composite has relatively effective
distribution of acquired liquid throughout the composite.
The saddle acquisition wicking height results for Composite 48 combined with
a pledget are compared to a control composite and are summarized in Table 18.
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Table 18. Saddle Acquisition Wicking Height~cm)
Com osite 10 min 1S 20 min 30 min 40 min SO 60 min
min min
48/ led et 8.3 8.3 8.3 9.2 9. 7 13.2 13.
S
Control 8.S 8.S S.S 9.3 9.S 12.9 13.4
The results indicate that the construct including Composite 4S and pledget
have wicking heights comparable to the control composite (removed from Supreme
S Core, commercially available from Kimberly-Clark, Neenah, WI).
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.
