Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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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.
I O 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 fox durability in
use and
effective fluid management. The absorbent capacity of articles made from
cellulose
fibers is often enhanced by the addition of superabsorbent materials, such as
superabsorbent polymers. Superabsorbent polymers known in the art have the
capability to absorb liquids in quantities from 5 to 100 times or more their
weight.
Thus, the presence of superabsorbent polymers greatly increases the liquid
holding
capacity of absorbent articles made from cellulose.
Because superabsorbent polymers absorb liquid and swell upon contact with
liquid, superabsorbent polymers have heretofore been incorporated primarily in
cellulose mats that are produced by the conventional dry, air-laid methods.
Wetlaid
processes for forming cellulose mats have not been used commercially because
superabsoxbent polymers tend to absorb liquid and swell during formation of
the
absorbent mats, thus requixing 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
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
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a layer within a multilayered composite. In these structures the
superabsorbent
polymer is relatively localized and not uniformly distributed throughout the
absorbent
structure and thus renders these composites susceptible to gel blocking. Upon
liquid
absorption, superabsorbent materials tend to coalesce and form a gelatinous
mass that
prevents the wicking of liquid to unwetted portions of the composite. By
preventing
distribution of acquired liquid from a composite's unwetted portions, gel
blocking
precludes the effective and efficient use of superabsorbent materials in
fibrous
composites. The diminished capacity of such fibrous composites results from
narrowing of capillary acquisition and distribution channels that accompanies
superabsorbent material swelling. The diminution of absorbent capacity and
concomitant loss of capillary distribution channels for conventional absorbent
cores
that include superabsorbent material are manifested by decreased liquid
acquisition
rates and far from ideal liquid distribution on successive liquid insults.
Accordingly, there exists a need for an absorbent composite that includes
superabsorbent material and that effectively acquires and wicks liquid
throughout the
composite and distributes the acquired liquid to absorbent material where the
liquid is
efficiently absorbed and retained without gel blocking. A need also exists for
an
absorbent composite that continues to acquire and distribute liquid throughout
the
composite on successive liquid insults. In addition, there exists a need for
an
absorbent composition containing superabsorbent materials that exhibits the
advantages associated with wetlaid composites including wet strength,
absorbent
capacity and acquisition, liquid distribution, softness, and resilience. The
present
invention seeks to fulfill these needs and provides further related
advantages.
SUMMARY OF THE INVENTION
The present invention relates to a reticulated fibrous absorbent composite
containing absorbent material. The absorbent composite is a fibrous matrix
that
includes absorbent material and a three-dimensional network of channels or
capillaries. The composite's reticulated nature enhances liquid distribution,
acquisition, and wicking, while the absorbent material provides high absorbent
capacity. Wet strength agents can be incorporated into the composite to
provide wet
integrity and also to assist in securing the absorbent material in the
composite.
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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.
In one embodiment, the reticulated absorbent composite includes at least one
fibrous stratum. For such an embodiment, the composite includes a core and a
fibrous
stratum adjacent and coextensive with a surface of the core. In another
embodiment,
the composite includes strata on opposing 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 fibexs 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 DRAWINGS
The foregoing aspects and many of the attendant advantages of this invention
will become more readily appreciated by reference to the following detailed
description, when taken in conjunction with the accompanying drawings,
wherein:
FIGURE 1 is a cross-sectional view of a portion of a reticulated absorbent
composite formed in accordance with the present invention;
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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
present invention in a wetted state at 8 times magnification;
FIGURE 9 is a photomicrograph of the foam-formed composite of FIGURE 8
at 12 times magnification;
FIGURE 10 is a cross-sectional view of a portion of an absorbent construct
incorporating a reticulated absorbent composite formed in accordance with the
present
invention;
FIGURE 11 is a cross-sectional view of a portion of another absorbent
construct incorporating a reticulated absorbent composite formed in accordance
with
the present invention;
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;
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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
S incorporating a reticulated absorbent composite formed in accordance with
the present
invention;
FIGURE 1 S 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
1 S 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;
2S 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;
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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 25 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
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 presentinvention;
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 dry
tensile strength and edgewise compression; and
FIGURE 30 is a graph illustrating the correlation between composite edgewise
compression and percentage matrix fiber in the composite.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The absorbent composite formed in accordance with the present invention is a
reticulated fibrous composite that includes absorbent material. The absorbent
material is distributed substantially throughout the fibrous composite and
serves to
absorb and retain liquid acquired by the composite. In a preferred embodiment,
the
absorbent material is a superabsorbent material. In addition to forming a
matrix for
the absorbent material, the composite's fibers provide a stable three-
dimensional
network of channels or capillaries that serve to acquire liquid contacting the
composite and to distribute the acquired liquid to the absorbent material. The
composite optionally includes a wet strength agent that further increases
tensile
strength and structural integrity to the composite.
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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 useful
in
absorbent articles.
The absorbent composite formed in accordance with the present invention is a
reticulated absorbent composite. As used herein, the term "reticulated" refers
to the
composite's open and porous nature characterized as having a stable three-
dimensional network of fibers (i.e., fibrous matrix) that create channels or
capillaries
that serve to rapidly acquire and distribute liquid throughout the composite;
ultimately
delivering acquired liquid to the absorbent material that is distributed
throughout the
composite.
The reticulated composite is an open and stable structure. The fibrous
composite's open and stable structure includes a network of capillaries or
channels
that are effective in acquiring and distributing liquid throughout the
composite. In the
composite, fibers form relatively dense bundles that direct fluid throughout
the
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composite and to absorbent material distributed throughout the composite. The
composite's wet strength agent serves to stabilize the fibrous structure by
providing
interfiber bonding. The interfiber bonding assists in providing a composite
having a
stable structure in which the composite's capillaries or channels remain open
before,
during, and after liquid insult. The composite's stable structure provides
capillaries
that remain open after initial liquid insult and that are available for
acquiring and
distributing liquid on subsequent insults.
Referring to FIGURE 1, a representative reticulated absorbent composite
indicated generally by reference numeral 10 formed in accordance with the
present
invention is a fibrous matrix that includes fibrous regions 12 substantially
composed
of fibers 16 and defining voids 14. Some voids include absorbent material 18.
Voids 14 are distributed throughout composite 10.
Representative reticulated composites formed in accordance with the invention
are shown in FIGURES 2-9. These composites include 48 percent by weight matrix
fibers (i.e., southern pine commercially available from Weyerhaeuser Co. under
the
designation NB416), 12 percent by weight resilient fibers (i.e., polymaleic
acid
crosslinked fibers), 40 percent by weight absorbent material (i.e.,
superabsorbent
material commercially available from Stockhausen), and about 0.5 percent by
weight
wet strength agent (i.e., polyamide-epichlorohydrin resin commercially
available from
Hercules under the designation I~YMENE). FIGURE 2 is a photomicrograph 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.
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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 fully occupy voids that
the
absorbent material previously occupied in the dry composite.
The composite's fibrous matrix is composed primarily of fibers. Generally,
fibers are present in the composite in an amount from about 20 to about 90
weight
percent, preferably from about 50 to about 70 weight percent, based on the
total
weight of the composite. Fibers suitable for use in the present invention are
known to
those skilled in the art and include any fiber from which a wet composite can
be
formed.
The composite includes resilient fibers. As used herein, the term "resilient
fiber" refers to a fiber present in the composite that imparts reticulation to
the
composite. Generally, resilient fibers provide the composite with bulk and
resiliency.
The incorporation of resilient fibers into the composite allows the composite
to
expand on absorption of liquid without structural integrity loss. Resilient
fibers also
impart softness to the composite. In addition, resilient fibers offer
advantages in the
composite's formation processes. Because of the porous and open structure
resulting
from wet composites that include resilient fibers, these composites drain
water
relatively easily and are therefore dewatered and dried more readily than wet
composites that do not include resilient fibers. 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).
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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.
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
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50 percent by weight matrix fibers, preferably wood pulp fibers, based on the
total
weight of the composite.
Cellulosic f bers 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, FR516, and NB416.
The wood pulp fibers can also be pretreated prior to use with the present
invention. This pretreatment may include physical treatment, such as
subjecting the
fibers to steam, or chemical treatment, for example, crosslinking the
cellulose fibers
using any one of a variety of crosslinking agents. Crosslinking increases
fiber bulk
and resiliency, and thereby can improve the fibers' absorbency. Generally,
crosslinked fibers are twisted or crimped. The use of crosslinked fibers
allows the
composite to be more resilient, softer, bulkier, have better wicking, and be
easier to
densify than a composite that does not include crosslinked fibers. Suitable
crosslinked cellulose fibers produced from southern pine are available from
Weyerhaeuser Company under the designation NHB416. Crosslinked cellulose
fibers
and methods for their preparation are disclosed in U.S. Patents Nos. 5,437,418
and
5,225,047 issued to Graef et al., expressly incorporated herein by reference.
Intrafiber crosslinked cellulosic fibers are prepared by treating cellulose
fibers
with a crosslinking agent. Suitable cellulose crosslinking agents include
aldehyde and
urea-based formaldehyde addition products. See, for example, U.S. Patents
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Nos.3,224,926; 3,241,533; 3,932,209; 4,035,147; 3,756,913; 4,689,118;
4,822,453;
U.S. Patent No. 3,440,135, issued to Chung; U.S. Patent No. 4,935,022, issued
to
Lash et al.; U.S. Patent No. 4,889,595, issued to Herron et al.; U.S. Patent
No. 3,819,470, issued to Shaw et al.; U.S. Patent No. 3,658,613, issued to
Steijer
et al.; and U.S. Patent No. 4,853,086, issued to Graef et al., all of which
are expressly
incorporated herein by reference in their entirety. Cellulose fibers have also
been
crosslinked by carboxylic acid crosslinking agents including polycarboxylic
acids.
U.5. Patents Nos. 5,137,537; 5,183,707; and 5,190,563, describe the use of C2-
C9
polycarboxylic acids that contain at least three carboxyl groups (e.g., citric
acid and
oxydisuccinic acid) as crosslinking agents.
Suitable urea-based crosslinking agents include methylolated areas,
methylolated cyclic areas, methylolated lower alkyl cyclic areas, methylolated
dihydroxy cyclic areas, dihydroxy cyclic areas, and Lower alkyl substituted
cyclic
areas. Specific preferred urea-based crosslinking agents include
dimethyldihydroxyethylene urea (DMeDHEU, 1,3-dimethyl-4,5-dihydroxy-2
imidazolidinone), dimethyloldihydroxyethylene urea (DMDHEU, 1,3
dihydroxymethyl-4,5-dihydroxy-2-imidazolidinone), dimethylol urea (DMU, bis[N
hydroxymethyl]urea), dihydroxyethylene urea (DHEU, 4,5-dihydroxy-2
imidazolidinone), and dimethylolethylene urea (DMEU, 1,3-dihydroxymethyl-2
imidazolidinone).
Suitable polycarboxylic acid crosslinking agents include citric acid, tartaric
acid, malic acid, succinic acid, glutaric acid, citTaconic 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,
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.
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The crosslinking agent can include a catalyst to accelerate the bonding
reaction between the crosslinking agent and cellulose fiber. Suitable
catalysts include
acidic salts, such as ammonium chloride, ammonium sulfate, aluminum chloride,
magnesium chloride, and alkali metal salts of phosphorous-containing acids.
Although not to be construed as a limitation, examples of pretreating fibers
include the application of surfactants or other liquids that modify the
surface
chemistry of the fibers. Other pretreatments include incorporation of
antimicrobials,
pigments, dyes and densification or softening agents. Fibers pretreated with
other
chemicals, such as thermoplastic and thermosetting resins, also may be used.
Combinations of pretreatments also may be employed. Similar treatments can
also be
applied after the composite formation in post-treatment processes.
Cellulosic fibers treated with particle binders and/or densification/softness
aids
known in the art can also be employed in accordance with the present
invention. The
particle binders serve to attach other materials, such as cellulosic fiber
superabsorbent
polymers, as well as others, to the cellulosic fibers. Cellulosic fibers
treated with
suitable particle binders and/or densification/softness aids and the process
for
combining them with cellulose fibers are disclosed in the following U.S.
patents:
(1) Patent No. 5,543,215, entitled "Polymeric Binders for Binding Particles to
Fibers";
(2) Patent No. 5,538,783, entitled "Non-Polymeric Organic Binders for Binding
Particles to Fibers"; (3) Patent No. 5,300,192, entitled "Wet Laid Fiber Sheet
Manufacturing With Reactivatable Binders for Binding Particles to Binders";
(4) Patent No. 5,352,480, entitled "Method for Binding Particles to Fibers
Using
Reactivatable Binders"; (5) Patent No. 5,308,896, entitled "Particle Binders
for High-
Bulk Fibers"; (6) Patent No. 5,589,256, entitled "Particle Binders that
Enhance Fiber
Densification"; (7) Patent No. 5,672,418, entitled "Particle Binders"; (8)
Patent
No. 5,607,759, entitled "Particle Binding to Fibers"; (9) Patent No.
5,693,411, entitled
"Binders for Binding Water Soluble Particles to Fibers"; (10) Patent No.
5,547,745,
entitled "Particle Binders"; (11) Patent No. 5,641,561, entitled "Particle
Binding to
Fibers"; (12) Patent No. 5,308,896, entitled "Particle Binders for High-Bulk
Fibers";
(13) Patent No. 5,498,478, entitled "Polyethylene Glycol as a Binder Material
for
Fibers"; (14) Patent No. 5,609,727, entitled "Fibrous Product for Binding
Particles";
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(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 10 to about 85 weight percent by weight
based
on the total weight of fibers.
When incorporated into an absorbent article, the reticulated absorbent
composite can serve as a storage layer for acquired liquids. To effectively
retain
acquired liquids, the absorbent composite includes absorbent material. As used
herein, the term "absorbent material" refers to a material that absorbs liquid
and that
generally has an absorbent capacity greater than the cellulosic fibrous
component of
the composite. Preferably, the absorbent material is a water-swellable,
generally
water-insoluble polymeric material capable of absorbing at least about 5,
desirably
about 20, and preferably about 100 times or more its weight in saline (e.g.,
0.9 percent
saline). The absorbent material can be swellable in the dispersion medium
utilized in
the method for forming the composite. In one embodiment, the absorbent
material is
untreated and swellable in the dispersion medium. In another embodiment, the
absorbent material is a coated absorbent material that is resistant to
absorbing water
during the composite formation process.
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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 2 to about 80 weight percent,
preferably from about 30 to about 60 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 staxch-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, crosslinleed polyacrylate
salts,
caxboxylated 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
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superabsorbent materials are marketed under the trademarks SANWET (supplied by
Sanyo Kasei Kogyo Kabushiki Kaisha), and SXM77 (supplied by Stockhausen of
Greensboro, North Carolina). Other superabsorbent materials are described in
U.S.
Patent No. 4,160,059; U.S. Patent No. 4,676,784; U.S. Patent No. 4,673,402;
U.S.
Patent No. 5,002,814; U.S. Patent No. 5,057,166; U.S. Patent No. 4,102,340;
and U.S.
Patent No. 4,818,598, all expressly incorporated herein by reference. Products
such
as diapers that incorporate superabsorbent materials are described in U.S.
Patent
No. 3,699,103 and U.S. Patent No. 3,670,731.
Suitable superabsorbent materials useful in the absorbent composite include
superabsorbent particles and superabsorbent fibers.
In 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
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 PAREZ 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
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monograph series No.29, "Wet Strength in Paper and Paperboard", Technical
Association of the Pulp and Paper Industry (New York, 1965).
Generally, the wet strength agent is present in the composition in an amount
from about 0.01 to about 2 weight percent, preferably from about 0.1 to about
1 weight percent, and more preferably from about 0.3 to about 0.7 weight
percent,
based on the total weight of the composite. In a preferred embodiment, the wet
strength agent useful in forming the composite is a polyamide-epichlorohydrin
resin
commercially available from Hercules, Inc. under the designation KYMENE. The
wet and dry tensile strengths of an absorbent composite formed in accordance
with
the present invention will generally increase with an increasing the amount of
wet
strength agent. The tensile strength of a representative composite is
described in
Example 7.
The absorbent composite generally has a basis weight from about 50 to about
1000 g/m2, preferably from about 200 to about 800 g/m2. In one embodiment, the
absorbent composite has a basis weight from about 300 to about 600 g/m2. The
absorbent composite generally has a density from about 0.02 to about 0.7
g/cm3,
preferably from about 0.04 to about 0.3 g/cm3. In 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 g/cm3, 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.
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
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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 s, 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
and
Paper, 2nd edition, 1960, Volume II, Chapter VIII - Sheet Formation.
Representative
foam processes useful in forming the composite are known in the art and
include
those described in U.S. Patents Nos. 3,716,449; 3,839,142; 3,871,952;
3,937,273;
3,938,782; 3,947,315; 4,166,090; 4,257,754; and 5,215,627, assigned to Wiggins
Teape and related to the formation of fibrous materials from foamed aqueous
fiber
suspensions, and "The Use of an Aqueous Foam as a Fiber-Suspending Medium in
Quality Papermaking," Foams, Proceedings of a Symposium organized by the
Society
of Chemical Industry, Colloid and Surface Chemistry Group, R.J. Akers, Ed.,
Academic Press, 1976, which describes the Radfoam process, all expressly
incorporated herein by reference.
In the methods, the absorbent material is incorporated into the composite
during the formation of the composite. Generally, the methods for forming the
reticulated absorbent composite include combining the components of the
composite
in a dispersion medium (e.g., an aqueous medium) to form a slurry and then
depositing the slurry onto a foraminous support (e.g., a forming wire) and
dewatering
to form a wet composite. Drying the wet composite provides the reticulated
composite.
As noted above, the reticulated composite is prepared from a combination of
fibers, absorbent material, and optionally a wet strength agent in a
dispersion medium.
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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
example, the use of drying cans, air floats, and through air dryers. Other
drying
methods and apparatus known in the pulp and paper industry may also be used.
Drying temperatures, pressures, and times are typical for the equipment and
methods
used, and are known to those of ordinary skill in the art in the pulp and
paper industry.
A representative 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
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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
times its weight in the dispersion medium, more preferably less than about
10 times, and even more preferably less than about S times its weight in the
dispersion
medium.
15 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
20 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 (e.g.,
34-
40°F). The residence time (i.e., time from absorbent material addition
to dispersion
medium to wet composite introduction to dryer) for absorbent material in the
forming
process is preferably less than about 30 seconds.
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
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which the absorbent material absorbs liquid and swells during the formation of
the
wet composite, and the conditions and extent to which the wet composite
incorporating the swollen absorbent material is dried. Water absorbed by the
absorbent material during wet composite formation is removed from the
absorbent
material, decreasing its size, on drying the wet composite. The dehydration of
the
swollen absorbent material defines some of the voids in the fibrous composite.
The reticulated absorbent composite can be incorporated as an absorbent core
or storage layer in an absorbent article including, for example, a diaper or
feminine
care product. The absorbent composite can be used alone or, as illustrated in
FIGURES 10 and 1 l, can be used in combination with one or more other layers.
In
FIGURE 10, absorbent composite 10 is employed as a storage layer in
combination
with upper acquisition layer 20. As illustrated in FIGURE 11, a third layer 30
(e.g.,
distribution layer) can also be employed, if desired, with absorbent composite
10 and
acquisition layer 20.
A variety of suitable absorbent articles can be produced from the absorbent
composite. The most common include absorptive consumer products, such as
diapers,
feminine hygiene products such as feminine napkins, and adult incontinence
products.
For example, referring to FIGURE 12A, absorbent article 38 comprises composite
10,
liquid pervious facing sheet 22 and liquid impervious backing sheet 24.
Referring 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
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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
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 20 overlying composite 10 and storage layer 72. Construct 80 can further
include intermediate layer 74 to provide construct 90 shown in FIGURE 17.
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Intermediate layer 74 can be, for example, a tissue layer, a nonwoven layer,
an airlaid
or wetlaid 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 j oined to the backing sheet.
In one embodiment, the reticulated absorbent composite formed in accordance
with the present invention further includes a fibrous stratum. In this
embodiment, the
composite includes a reticulated core and a fibrous stratum adjacent an
outward facing
surface of the core. The fibrous stratum is integrally formed with the
reticulated core
to provide a unitary absorbent composite. 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. In another embodiment, the composite includes first and second
strata
adjacent each of the core's outward facing surfaces (i.e., the strata are
coextensive
with opposing surfaces of the core). A representative absorbent composite
having a
fibrous stratum is shown in FIGURE 21A and a representative composite having
fibrous strata is shown in FIGURE 21B. Referring to FIGURE 21A, absorbent
composite 130 includes reticulated core 10 and stratum 132 and, as shown in
FIGURE 21B, composite 140 includes reticulated core 10 intermediate strata 132
and
134. As noted above, core 10 is a fibrous matrix that includes fibrous regions
12 .
defining voids 14, some of which include absorbent material I 8.
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
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FIGURE 21B, 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. PCT1LTS97l22342,
Unitary
Stratified Composite, and U.S. patent application Serial No. 09/326,213,.
Unitary
Absorbent System, each incorporated herein by reference in its entirety.
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 vaxied. 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,
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the stratum can be formed from fibrous blends, such as an 80:20 blend of wood
pulp
fibers and crosslinked fibers, and synthetic blends, and blends of synthetic
and
cellulosic fibers.
The stratum composition can be varied to provide a composite having desired
characteristics. For example, to provide a stratum having high liquid wicking
capacity, the stratum preferably has a relatively high wood pulp fiber
content. Thus,
for liquid distribution, the stratum is preferably composed of wood pulp
fibers such as
southern pine fibers. However, such a stratum has a lower liquid acquisition
rate
compared to a similarly constituted stratum containing relatively less wood
pulp fiber
and, for example, greater amounts of crosslinked fibers. Conversely, to
provide a
stratum having a high liquid acquisition rate, the stratum preferably has a
relatively
high crosslinked or synthetic fiber content. However, as a consequence of its
high
crosslinked fiber content, such a stratum provides less liquid distribution
than a
comparable stratum that includes relatively less crosslinked fiber. For liquid
acquisition, the stratum is preferably a blend of crosslinked fibers and pulp
fibers, for
example, the stratum can include from about 30 to about 50 percent by weight
crosslinked fibers and from about 50 to about 70 percent by weight pulp
fibers.
Alternatively, strata having high liquid acquisition rates can also include,
in
combination with cellulosic fibers, a relatively high synthetic fiber content
(e.g., PET
fibers or a blend of PET and thermobondable fibers). Optionally, one or both
strata
can include synthetic fibers.
Because the composite's stratum is formed with the reticulated core to,
provide
an integrated unitary structure, the overall characteristics of the composite
can be
optimized by appropriate selection of the individual core and stratum
components. To
further optimize the performance of the composite, the nature of first and
second
strata can be selectively and independently controlled and varied. The
compositions
of the first and second strata need not be the same. The strata can be formed
from the
same or different fiber furnishes. For compositions formed by foam methods,
stratum
basis weight can also be independently controlled and varied. Stratum basis
weight
can also be varied with respect to the core's basis weight. In a foam method,
basis
weight can be varied by adjusting the rate at which the fibrous furnish is
supplied to
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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.
Strata 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
axe
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 spaxgers,
which
deliver absorbent material to and effectively mix the absorbent material with
the fiber
stock. Generally, the deeper the sparger introduces the absorbent material
into the
fiber stock at the Rotoformer drum, the thinner the resulting stratum.
Conversely, a
relatively thicker stratum can be formed by introducing absorbent material
into the
fiber stock at a greater distance from the drum.
The absorbent composite can be formed by devices and processes that include
a twin-wire configuration (i.e., twin-forming wires). A representative twin-
wire
machine for forming composites is shown in FIGURE 22. Referring to FIGURE 22,
machine 200 includes twin-forming wires 202 and 204 onto which the composite's
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components are deposited. Basically, fibrous slurry 124 is introduced into
headbox 212 and deposited onto forming wires 202 and 204 at the headbox exit.
Vacuum elements 206 and 208 dewater the fibrous slurries deposited on wires
202
and 204, respectively, to provide partially dewatered webs that exit the twin-
wire
portion of the machine as partially dewatered web 126. Web 126 continues to
travel
along wire 202 and continues to be dewatered by additional vacuum elements 210
to
provide wet composite 120 which is then dried by drying means 216 to provide
composite 10.
Absorbent material can be introduced into the fibrous web at any one of
several positions in the twin-wire process depending on the desired product
configuration. Referring 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
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comprising different components, headbox 212 includes one or more baffles 214
for
the introduction of fiber furnishes (e.g., 124a, 124b, and 124c) having
different
compositions. In such a method, the upper and louver strata can be formed to
include
different components and have different basis weights and properties.
In one embodiment, the composite can be formed by a wetlaid process using
the components described above. In another embodiment, is formed by a foam-
forming method using the components described above. In these methods, fibrous
webs having multiple strata and including absorbent material can be formed
from
multiple fibrous slurries. These methods 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 can
have the
composite 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 (e.g., core) generally includes the following steps:
(a) forming a first fibrous slurry comprising fibers in an aqueous
dispersion medium;
(b) forming a second fibrous slurry comprising fibers in an
aqueous dispersion medium;
for a foam method, the slurries are foams that include, in addition to fibers,
a
surfactant;
(c) moving a first foraminous element (e.g., a forming wire) in a
first path;
(d) moving a second foraminous element in a second path;
(e) passing the first slurry into contact with the first foraminous
element moving in a first path;
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(f) passing the second slurry into contact with the second
foraminous element moving in the second path;
(g) passing a third material between the first and second slurries
such that the third material does not contact either of the first or
second foraminous elements; and
(h) forming a fibrous web from the first and second slurries and
third material by withdrawing liquid from the slurries through
the first and second foraminous elements.
As noted above, the method is suitably carried out on a twin-wire former,
preferably a vertical former, and more preferably, a vertical downflow twin-
wire
former. In the vertical former, the paths for the foraminous elements are
substantially
vertical.
A representative vertical downflow twin-wire former useful in practicing the
method of the invention is illustrated in FIGURE 23. Referring to FIGURE 23,
the
former includes a vertical headbox assembly having a former with a closed
first end
(top), closed first and second sides and an interior volume. A second end
(bottom) of
the former is defined by moving first and second foraminous elements, 202 and
204,
and forming nip 213. The interior volume defined by the former's closed first
end,
closed first and second sides, and first and second foraminous elements
includes an
interior structure 230 extending from the former first end and toward the
second end.
The interior structure defines a first volume 232 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 liquidlfoam (e.g., suction boxes 206 and 20~) 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.
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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 liquidlfoam 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/foam. Depending upon the nature of the composite to
be
formed, the first and second fiberlfoam slurries may be the same, or
different, from
each other and from the third material.
The means for withdrawing liquid/foam from the first and second slurries
through the foraminous elements to form a web on the foraminous elements are
also
included in the headbox assembly. The means for withdrawing liquid/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
the force required to compress the composite as described below. For a
composite to
be incorporated into a personal care absorbent product, suitable ring -crush
values
range from about 400 to about 1600 gram/inch. Composite softness can be
indicated
by a variety of parameters including composite edgewise compression. Edgewise
compression (EC) is the force required to compress the composite corrected by
the
composite's basis weight as described below. For a composite to be suitably
incorporated into a personal care absorbent product, the composite has a ring
crush
value in the range from about 400-1600 g and a basis weight in the range from
about
250 to about 650 gsm.
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The composites can 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, in another
embodiment at least about 2:1, and in another embodiment at least about 3:1.
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
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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.
The composites of the invention advantageously exhibit strength (e.g.,
structural integrity) and softness. 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 dry tensile strength. Suitable composites have a dry tensile
strength in
the range from about 100 to about 800 g/inch as measured by the dry tensile
strength
method described in Example 21. In one embodiment, the composites have a dry
tensile strength of at least about 200 g/inch; in another embodiment, at least
about
400 g/inch; and in a further embodiment, at least about 700 glinch. Composites
having dry tensile strengths in excess of about 800 g/inch can be insufficient
for direct
incorporation into personal care products. For machine processing, a minimum
dry
tensile strength of about 450 g/inch is preferred. Composites having wet
tensile
strengths below about 50 g/inch tend to lack structural integrity and
compromise the
effectiveness of absorbent products into which such composites are
incorporated.
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 Examples 20, 21, and 25.
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 Examples 22 and 25.
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By virtue of the composites' components, composition, and formation
methods, the composites of the invention exhibit advantageous fluidic
properties
including high liquid absorbent capacity and high liquid wicking. Liquid
absorbent
capacity can be indicated by an absorbency under load measure (e.g.,
Gravimetric
Absorbency Test, or Demand Absorbency as described in U.S. Patent No.
4,357,827).
The composite exhibits a demand absorbency of from about 15 to about 35 mL/g.
In
one embodiment, the composite exhibits a demand absorbency of at least about
18 mL/g. In another embodiment, the composite exhibits a demand absorbency of
at
least about 20 mL/g; and in a further embodiment, the composite exhibits a
demand
absorbency of at least about 22 ml/g. Liquid wicking can be indicated by
unrestrained
vertical wicking height measurement (see Example 22). The composite exhibits
an
unrestrained vertical wicking height of from about 5 to about 30 cm. In one
embodiment, the composite exhibits an unrestrained vertical wicking height of
at least
about 8 cm. In another embodiment, the composite exhibits an unrestrained
vertical
15, wicking height of at least about 12 cm. In a further embodiment, the
composite
exhibits an unrestrained vertical wicking height of at least about 18 cm. In
another
embodiment, the composite exhibits an unrestrained vertical wicking height of
at least
about 20 cm.
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
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 FIGURE 24C.
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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, 190, 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 pulp fibers and crosslinked pulp fibers (48 and 12
percent
by weight, respectively, based on total weight of dried composite) in water
having a
consistency of about 0.25 to 3 percent is formed. Consistency is defined as
the weight
percent of fibers present in the slurry, based on the total weight of the
slurry. A wet
strength agent such as KYMENE (0.5 percent based on total composite weight) is
then added to the fibrous mixture. Finally, absorbent material (40 percent by
weight
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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 Composite Formation: Representative Foam Method
This example illustrates a foam method for forming a representative absorbent
composite.
A lab-size blaring 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 fox 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
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mold and passed, along with a forming wire, over a slit couch to remove excess
foam
and water.
The sheet is then dried in a drying oven to remove the moisture.
Example 3
Acquisition Times for a Representative Reticulated Absorbent Composite
In this example, the acquisition time for a representative reticulated
absorbent
composite formed in accordance with the present invention (Composite A) is
compared to a commercially available diaper (Diaper A, Kimberly-Clark).
The tests were conducted on commercially available diapers (Kimberly-Claxk)
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 ftumel 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
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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.
Table 1. Acquisition Time Comparison
Acquisition
Time
(sec)
Insult Diaper A Composite A
1 45 10
2 60 11
3 75 10
As shown in Table 1, liquid is more rapidly acquired by the absorbent
composite than for the commercially available diaper containing an air-laid
storage
core. The results show that the air-laid core does not acquire liquid nearly
as rapidly
as the reticulated composite. The commercial diaper also exhibited
characteristic
diminution of acquisition rate on successive liquid insults. In contrast, the
composite
formed in accordance with the invention maintained a relatively constant
acquisition
time as the composite continued to absorb liquid on successive insult.
Significantly,
the absorbent composite exhibits an acquisition time for the third insult that
is
substantially less (about fourfold) than that of the commercially available
diaper for
initial insult. The results reflect the greater wicking ability and capillary
network for
the 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
Acquisition Rate and Rewet for Representative Reticulated Absorbent Composites
In this example, the acquisition time and rewet of representative reticulated
absorbent composites formed in accordance with the present invention
(designated
Composites Al-A4) are compared to a commercially available diaper (Diaper A,
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Kimberly-Clark). Composites Al-A4 differ by the method by which the composites
were dried.
Certain properties of the tested composites, including the amount of
superabsorbent material (weight percent SAP) in the composite and basis weight
for
each of the composites, are summarized in Table 2.
The tests were conducted on commercially available diapers (Kimberly-Clark)
from which the cores were removed and used as surrounds. The test diapers were
prepared by inserting the tested composites into the diapers.
The acquisition time and rewet are determined in accordance with the
multiple-dose rewet test described below.
Briefly, the multiple-dose rewet test measures the amount of synthetic urine
released from an absorbent structure after each of three liquid applications,
and the
time required for each of the three liquid doses to wick into the product.
The aqueous solution used in the tests was a synthetic urine available from
National Scientific under the trade name RICCA, and as described above in
Example 1.
A preweighed sample of the absorbent structure was prepared for the test by
determining the center of the structure's core, measuring 1 inch to the front
for liquid
application location, and marking the location with an "X". A liquid
application
funnel (minimum 100 mL capacity, 5-7 mL/s flow rate) was placed 4 inches above
the surface of the sample at the "X". Once the sample was prepared, the test
was
conducted as follows. The sample was flattened, nonwoven side up, onto a
tabletop
under the liquid application funnel. The funnel was filled with a dose (100
mL) of
synthetic urine. A dosing ring (5/32 inch stainless steel, 2 inch ID x 3 inch
height)
was placed onto the "X" marked on the samples. A first dose of synthetic urine
was
applied within the dosing ring. Using a stopwatch, the liquid acquisition time
was
recorded in seconds from the time the funnel valve was opened until the liquid
wicked
into the product from the bottom of the dosing ring. After a twenty-minute
wait
period, rewet was determined. During the twenty-minute wait period after the
first
dose was applied, a stack of filter papers (19-22 g, Whatman #3, 11.0 cm or
equivalent, that had been exposed to room humidity for minimum of 2 hours
before
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testing) was weighed. The stack of preweighed filter papers was placed on the
center
of the wetted area. A cylindrical weight (8.9 cm diameter, 9.8 1b.) was placed
on top
of these filter papers. After two minutes the weight was removed, the filter
papers
were weighed and the weight change recorded. The procedure was repeated two
more
times. A second dose of synthetic urine was added to the diaper, and the
acquisition
time was determined, filter papers were placed on the sample for two minutes,
and the
weight change determined. For the second dose, the weight of the dry filter
papers
was 29-32 g, and for the third dose, the weight of the filter papers was 39-42
g. The
dry papers from the prior dosage were supplemented with additional dry filter
papers.
Liquid acquisition time is reported as the length of time (seconds) necessary
for the liquid to be absorbed into the product for each of the three doses.
The results
are summarized in Table 2.
Rewet is reported as the amount of liquid (grams) absorbed back into the
filter
papers after each liquid dose (i.e., difference between the weight of wet
filter papers
and the weight of dry filter papers). The results are also summarized in Table
2.
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M
-~''~d; ~n I~ a1
ranN N O O ,N-,,
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O O O O d~
.-a ,~ N ~ .-,
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r~
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_~ _
N N N M
N
N
O ~' 01 O~ ~O o0 v7
U ~
~' ,-, r.,N ,~ M
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by
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..
p.., d; cn c, oo O
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-42-
As indicated in Table 2, the acquisition times for representative composites
formed in accordance with the invention (Composites AI-A4) were significantly
less
than for the commercially available core.
The rewet of the representative composites (Composites A1-A4) is
significantly less than for the other cores. While the composites exhibited
relatively
low rewet initially, after the third insult the commercially available core
showed
substantial rewet. In contrast, Composites A continued to exhibit low rewet.
Example 5
Horizontal and Vertical Wicking for a Representative
Reticulated Absorbent Composite
In this example, the wicking characteristics of a representative reticulated
absorbent composite (Composite A) are compared to a commercially available
diaper
storage core (Diaper B, Procter & Gamble).
The horizontal wicking test measures the time required for liquid to
horizontally wick preselected distances. The test was performed by placing a
sample
composite on a horizontal surface with one end in contact with a liquid bath
and
measuring the time required for liquid to wick preselected distances. Briefly,
a
sample composite strip (40 cm x 10 cm) was cut from a pulp sheet or other
source. If
the sheet has a machine direction, the cut was made such that the 40 cm length
of the
strip was parallel to the machine direction. Starting at one end of the 10 cm
width of
the strip, a first line was marked at 4.5 cm from the strip edge and then
consecutive
lines at 5 cm intervals were marked along the entire length of the strip
(i.e., 0 cm,
5 cm, 10 cm, 15 cm, 20 cm, 25 cm, 30 cm, and 35 cm). A horizontal wicking
apparatus having a center trough with level horizontal wings extending away
from
opposing sides of the trough was prepared. The nonsupported edge of each wing
was
positioned to be flush with the inside edge of the trough. On each wing's end
was
placed a plastic extension to support each wing in a level and horizontal
position. The
trough was then filled with synthetic urine. The sample composite strip was
then
gently bent at the 4.5 cm mark to form an approximately 45° angle in
the strip. The
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strip was then placed on the wing such that the strip lay horizontally and the
bent end
of the strip extended into and contacted the liquid in the trough. Liquid
wicking was
timed beginning from when the liquid reached the first line marked on the
composite
cm from the 4.5 cm bend. The wicking time was then recorded at centimeter
5 intervals when 50 percent of the liquid front reached the marked interval
(e.g., 5 cm,
cm). The liquid level in the trough was maintained at a relatively constant
level
throughout the test by replenishing with additional synthetic urine. The
horizontal
wicking results are summarized in Table 3.
Table 3. Horizontal Wickine~~Comparison
Distance Wicking Time
(cm) (sec)
Diaper B Composite A
5 48 15
10 150 52
290 134
458 285
783 540
1703 1117
- 1425
10 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 1.5 to about 3 times that of a commercially available storage core.
15 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
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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 Com arp ison
Distance Wicking Time
(cm) (sec)
Diaper B Composite A
5 20 6
10 Fell Apart 54
- 513
- 3780
As for the horizontal wicking results, Composite A had significantly greater
vertical wicking compared to the commercial core. The results also show that
the
composite formed in accordance with the invention has significantly greater
wet
tensile strength compared to the conventional air-laid composite.
15 Example 6
Liquid Distribution for a Representative Reticulated Absorbent Composite
In this example, the distribution of liquid in a reticulated absorbent
composite
(Composite A) is compared to that of two commercially available diapers
(Diapers A
and B above). The test measures the capacity of a diaper core to distribute
acquired
20 liquid. Perfect distribution would have 0% deviation from average. Ideal
liquid
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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 net 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
strength, N/m, is converted to tensile index, Nm/g, by dividing the tensile
strength by
the basis weight g/m2.
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Typically, increasing the amount of I~YMENE from 2 to 100 pounds per ton
of fiber rnay 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
Newton Load Cell
10 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
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composites included matrix fibers (48 percent by weight, southern pine
commercially
available from Weyerhaeuser Co. under the designation NB416), resilient fibers
(12 percent by weight, polymaleic acid crosslinked fibers), and absorbent
material
(40 percent by weight, superabsorbent material commercially available from
Stockhausen). One of the 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
stiffness.
Example 9
Reticulated Absorbent Composite Formation: R~resentative 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 funnel attached directly
to the
inlet of a pump into which chilled water is fed at a controlled rate. The
funnel
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receives water and dry absorbent material delivered from absorbent material
supply
by auger metering and forms a pond that contains absorbent material and water.
The
absorbent slurry is preferably pumped from the funnel to the headbox at
approximately the same rate as water is delivered to the funnel. Such a system
minimizes the exposure of the absorbent to the water. In practice, the
absorbent slurry
is delivered from the mixing system to the headbox through a 10 to 50 foot
conduit in
less than about 10 seconds.
In a typical formation run, fiber stock flow to the Rotoformer headbox was
about 90 gpm (gallon/min) and absorbent slurry (1 - 2.6% solids) flow was
about
10 gpm. Prior to initiation of fiber stock flow to the headbox and the
introduction of
absorbent slurry to the dispersion unit, water was flowed into the dispersion
unit to
the headbox to prevent fibers from plugging the spargers. Once the target
basis
weight of fiber was reached, the absorbent auger metering system was initiated
and
absorbent slurry was introduced into the headbox. For the runs made in
accordance
with the method described above, the target fiber basis weight was about 370
gsm
(g/m2) 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.
Exam 1p a 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
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80% by weight standard wood pulp fibers (once-dried southern pine commercially
available from Weyerhaeuser Company under the designation FR416) and 20% by
weight crosslinked pulp fibers. The absorbent material was a crosslinked
polyacrylate
commercially available from Stockhausen under the designation SXM 77, which
was
screened using 300 micron mesh to eliminate fines prior to use. The composite
also
included about 25 pounds wet strength agent (a polyacrylamide-epichlorohydrin
resin
commercially available from Hercules under the designation KYMENE 557LX) per
ton of fibers.
Target density of the absorbent composite was accomplished by calendering
using a single nip with no applied load.
Performance data for the representative composite formed as described above
(Composite B) is presented in Tables 5 and 6 in Example 16.
Example 11
A representative composite was formed as described in Example 10 except
that the composite was calendered at 25 fpm.
Performance data for the representative composite formed as described above
(Composite C) is presented in Tables 5 and 6 in Example 16.
Example 12
A representative composite was formed as described in Example 11 except
that the amount of wet strength agent in the composite was reduced to 12.5
pounds
per ton fiber and the standard wood pulp fibers were never-dried FR416 fibers.
Performance data for the representative composite formed as described above
(Composite D) is presented in Tables 5 and 6 in Example 16.
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.
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Example 14
A representative composite was formed as described in Example 12 except
that the wood pulp fibers were once-dried FR416 fibers.
Performance data for the representative composite formed as described above
(Composite F) is presented in Tables 5 and 6 in Example 16.
Example 15
A representative composite was formed as described in Example 12 except
that the amount of fibers in the composite was increased to about 80% by
weight and
the amount of absorbent present in the composite was decreased to about 20% by
weight of the total composite.
Performance data for the representative composite formed as described above
(Composite G) is presented in Tables 5 and 6 in Example 16.
Example 16
The performance of representative composites (Composites B-D) prepared as
described in Examples 10-15 is summarized in Tables 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
12.5 pounds I~YMENE per ton fibers. The results presented in Table 5 are the
average of three measurements except for the tensile values, which average
four
measurements. In the table, "MD" refers to the composites' machine direction
and
"CD" refers to the cross-machine direction. The wicking values were obtained
by the
methods described in Example 5 and the wet and dry tensile values were
obtained by
the method described in Example 7. The wet strength value was calculated and
is
defined as the ratio of wet tensile to dry tensile values. The mass flow rate
value
(g/min/g) was determined by measuring the weight gain of a portion of a
composite
(22 cm x 5 cm) divided by the lesser of the time required for the liquid to
wick 15 cm
or 15 minutes, divided by the weight of the original sample.
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0 00 01 O O N N
N N N N V V
N
V V N V V V
'r'
t~ o ~ ~ ~ o o
o
O M ~ N M '
d ~ d
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0 0 0 0 0
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G~ ~~ N ~h ~ ~ ~ 0
p o
U o~ ~ ~ p ~ ~ o
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~ ~ .--i ~ .--i.-i
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tin
O ~ ~ ~ ~ ~'~?~ ~; N ~ N
N V V M cV
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~j~c t~ oo o; 4i ~ oo
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.~5~'. U M d' 00 ~ ~ N l0
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~r N N ~ ~ N N
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O a> V7 ~ O O O
V ~ N N ~ ~ ~ N
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O U d' d' v7 r",,M
~
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~1 U Ca W w c7
E~ o
U
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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
Composite Capacity (cclg)
B 16.9
C 16.9
D 20.4
E 21.5
Example 17
The Flexibility and Softness of Representative Reticulated Absorbent
Composites:
Wetlaid Handsheets
Composite flexibility and softness are factors for determining the suitability
of
composites for incorporation into personal care absorbent products. Composite
flexibility can be indicated by composite edgewise ring crush, which is a
measure of
the force required to compress the composite as described below. For a
composite to
be incorporated into a personal care absorbent product, suitable ring crush
values
range from about 400 to about 1600 gram/inch. Composite softness can be
indicated
by a variety of parameters including composite edgewise compression. Edgewise
compression (EC) is the force required to compress the composite corrected by
the
composite's basis weight as described below. For a composite to be suitably
incorporated into a personal care absorbent product, the composite has a ring
crush
value in the range from about 400-1600 g and a basis weight in the range from
about
250 to about 650 gsm.
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The flexibility and softness of representative reticulated absorbent
composites
formed by wetlaid and foam-forming methods in accordance with the present
invention were determined by measuring composite edgewise ring crush and
edgewise compression.
The flexibility and softness of representative composites was determined by an
edgewise ring crush method. In the method, a length of the composite
(typically
about 12 inches) is formed into a cylinder and its ends stapled together to
provide
cylinder having a height equal to the composite's width (typically about 2.5
inches).
Edgewise ring crush is measured by adding mass to the top of the composite
ring
sufficient to reduce the composite cylinder's height by one-half. The more
flexible the
composite, the less weight required to reduce the height in the measurement.
The
edgewise ring crush is measured and reported as a mass (g). Edgewise
compression
(EC) is the ring crush reported in units of g/gsm in the tables below.
The following is a description of the ring crush method.
Samples: 6.35 cm (2.5 in) X 30.5 cm (12 in)
Triplicate analysis (A, B, C)
Method:
1 ) Cut triplicate of sample size, lengthwise in the composite
machine direction (MD).
2) Condition samples for 2 hours at 50% relative humidity or
ambient conditions.
3) With the wire side on the outside, form the individual samples
into loops so the two narrow ends meet without any overlap.
Using four staples, attached the ends together at the top,
bottom, and twice in the middle. The top and bottom staples
should be 0.3-0.5 cm from the edge and the middle staples
should be less than 2 cm from each other and the respective top
or bottom staple. Finally, ensure that each staple penetrates
fiber only areas.
4) Set the bottom platen on a smooth, level surface.
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5) Place the sample, edgewise and in the center, between the top
and bottom platens.
6) Gently place a 100-g weight on the center of the top platen (or
500-weight) and wait 3 seconds.
7) Then, gently stack 3 more 100-g weights at 3-second intervals.
8) If the ring collapses 50% or more of it's original height within a
3-second interval, then record the total amount of weight
necessary to do so, i.e., add the weight of the top platen and the
other combined weights.
9) If the combined weight doesn't crush the sample, then carefully
remove the four 100-g weights.
10) Gently add another) 500-g weight and weight 3 seconds.
11) If the ring collapses 50% or more of it's original height within a
3-second interval, then record the total amount of weight
necessary to do so, i.e., add the weight of the top platen and
weight(s).
12) Repeat step 6 through 11, increasing the number of 500-g
weights by one for each cycle.
13) Repeat steps 5 through 11 for the other replicates.
14) Record the average weight for the replicates in g~f rounded to
the neaxest 10 g.
Calculations:
Average ring crush weight = (Weight A + Weight B + Weight C)/3
The ring crush values determined as described above for representative
composites formed in accordance with the present invention are summarized in
Table 10 below.
The softness of 'representative reticulated absorbent composites formed in
accordance with the present invention can be indicated by edgewise
compression.
Edgewise compression is discussed in The Handbook of Physical and Mechanical
Testing of Paper and Paperboard, Richaxd E. Mark, Dekker 1983 (Vol. 1).
Edgewise
compression was determined by correcting edgewise ring crush, determined as
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described above, for composite basis weight. The edgewise compression (EC)
values
for representative composites formed in accordance with the present invention
are
summarized in Table 10 below.
Representative composites were formed by wetlaid and foam methods. The
representative composites were formed as handsheets using a 20 inch X 20 inch
handsheet mold. The target basis weight for the composites was 400 g/m2. To
increase post-forming consistency to about 20 to 35 percent, five blotters and
a
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
I~YMENE, 10 lb.lton 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.
Com osp ite 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.
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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).
Com osp ite 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, TN).
Com osite 6. A wetlaid composite composed of 60 percent by weight
superabsorbent material and 40 percent by weight matrix fibers.
Com osp ite 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 wetlaid composite composed of 40 percent by weight
superabsorbent material (large screened SXM-77, 0.05-1.00 mm, SXM-77 available
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), 30 percent by weight matrix
fibers,
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.
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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.
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 2240 (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.
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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
CompositeSuperabsorbentMatrix Crosslinked Other
Material Fiber Fiber Material
(%) (%) (%)
Control 40 60
1 40 30 30 Foam formed
2 40 30 30
3 40 15 45
4 40 30 30 CTMP
5 40 30 30 HPZ
6 60 40
7 60 20 20
8-1 40 30 30 Large SXM-
77
8-2 40 30 30 Small SXM-
77
8-3 40 30 30 SXM-77
8-4 40 30 30 Large
screened
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CompositeSuperabsorbentMatrix Crosslinked Other
Material Fiber Fiber Material
(%) (%) (%)
superabsorbent
material
9 40 60 T-757
40 30 30 T-757
11 40 30 30 PCC-10
12 40 30 30 T-224-straight
13 40 30 30 T-224-curly
14 40 30 30 Cellulose
acetate
40 3 0 3 0 Amphoteric
16 40 30 30 Sulphated
17 40 60 Debonder
18 40 3 0 3 0 Debonder
19 40 30 30 Mechanical
40 3 0 3 0 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.
CA 02406501 2002-10-25
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0
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CA 02406501 2002-10-25
WO 01/85083 PCT/USO1/15271
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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,
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 50 percent of
its
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
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 5) 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.
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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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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
crush and edgewise compression and improves flexibility and softness. The
correlation between ring crush and percentage matrix fiber is presented
graphically in
FIGURE 30. Referring to FIGURE 30, ring crush increases dramatically as the
percentage of matrix fiber increases.
Exam 1p a 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
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(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 Intearitv of Representative Reticulated Absorbent
Composites:
Edgewise Compression and Wet Modified Circular Bend Values
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 and wet modified
circular bend methods. Edgewise compression is discussed in The Handbook of
Physical and Mechanical Testing of Paper and Paperboard, Richard E. Mark,
Dekker
1983 (Vol. 1). Modified circular bend can be determined by ASTM D4032-82
Circular Bend Procedure. As noted above, edgewise compression (EC) is an
indication of the softness of a dried absorbent composite. Modified circular
bend
(MCB) is a measure of the composite's wet integrity. Suitably, the composite
has a
wet MCB value greater than about 0.3 g/gsm, preferably greater than about 0.4
g/gsm,
and more preferably greater than about 0.5 g/gsm.
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
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(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. Composites 40-43
are foam-formed composites in which the matrix fiber (i.e., southern pine) was
replaced with a synthetic fiber blend consisting of 20% by weight polyethylene
terephthalate fibers (PET T-224) and 10% by weight synthetic thermobondable
binder
fiber (CELBOND T-105). As indicated in the table, several of the composites
were
further treated by, for example, calendering, after formation.
The EC and wet MCB values for the representative composites is summarized
in Table 10. The values presented in the table represent the average value of
three
repetitions. The wet MCB values were generated as described in ASTM D4032-82
using an Instron Model 1130 with a crosshead speed of 500 mm/min and a gauge
length of 25.4 mm.
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N O ~t O ~ ~ pp op
C O O ' '
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as
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bn
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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, wetlaid Composites 31 and 33 had ring crush values of 4300 and 4200
g
and EC values of 10.8 and 11 g/gsm, respectively, while foam-formed Composite
38
had a ring crush value of 3100 g and 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 (superabsorbent:crosslinked fiber:matrix fiber, 40:12:48)
includes
about 20 percent by weight crosslinked fiber based on the total weight of
fibers and
has a ring crush value of 790 g and an EC value of 8.4 g/gsm. Composite 37
(superabsorbent:crosslinked fiber:matrix fiber, 40:36:24) includes about 60
percent by
weight crosslinked fiber based on the total weight of fibers and has a ring
crush value
of 790 g and an EC value of 2.5 g/gsm. 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 calendering) of the
composites increased the composites' flexibility and softness by more than 2-
fold,
reducing the ring crush from 4300 to 1800 g and the EC value from 10.8 to 4.3
for
Composites 31 and 32, from 4200 to 1200 g and from 11 to 3.5 g/gsm for
Composites 32 and 33, and from 3100 to 900 g and from 8.4 to 2.7 g/gsm 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 fiber (CELBOND T-105).
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Example 20
The EfFect of Superabsorbent Polymer Particle Size on
Composite Flexibility 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.
The measured ring crush, saturation capacity (measured by immersing a
weighed portion of a composite in saline for a period of time, placing the
wetted
composite on a screen and covering the composite with a rubber dam, applying a
specified vacuum to the assembly, and then reweighing the composite) tensile
strength, wicking, and basis weights for the representative composites 44-46
are
summarized in Table 11. Composite 44-46 included the components described
above
and superabsorbent polymer particles A, SXM77, and screened SXM77,
respectively.
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~~ N ~O O
~ oo ~ a;
U
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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 glgsm
compared
to 5.2 g/gsrn 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 Representative 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 Edgewise Compression and Dry Tensile
EC Value Dry Tensile
Composite (g/gsm) (g/in)
Control 12.9 3206
1 5.8 919
2 4.7 744
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EC Value Dry Tensile
Composite (g/gsm) (g/in)
3 1.9 235
4 7.9 1366
9.1 1310
6 6.9 1837
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 29. Referring to FIGURE 29, edgewise
compression increases dramatically as dry tensile increases. Generally, as
tensile
strength increases, composite flexibility and softness decreases. Although
there
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appears to be no correlation between composite basis weight and dry tensile,
there is
some correlation between composite density and dry tensile.
Exam 1p a 22
Absorbent Properties of Representative Reticulated Absorbent Composites: Foam-
s Formed Composites
Representative composites were prepared by foam-forming methods in
accordance with the methods described above. The composites included absorbent
material (SAP, from about 35 to about 45 percent by weight superabsorbent
particles
based on the total weight of the composite), crosslinked cellulosic fiber
(XL), and
matrix fibers (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
CompositeBW As CapacityEdgewiseSAP Total StrataStrata
g/m2 is g/cm2 Ring ContentXL BW XL
Density Crush % Contentg/m2 Content
g/cm3 gf % fiber % fiber
46 411.20.14 0.72 427 35 50 50 50
47 508.50.19 0.97 536 45 50 50 50
48 498.30.20 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 Wicking Height. 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:
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Synthetic urine for wicking - "Blood Bank" 0.9% Saline Solution
Samples:
Size: 6.5 cm(CD) x 25 cm(MD), marked with both permanent and water
permeable lines at 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.
6) At the end of 5, 10, and 15 minutes, record the Wicking Height
by measuring down from the next highest line. Report. the
wicking height to the nearest 0.5 cm.
7) At 15 minutes raise sample out of fluid and while still clamped,
cut sample at the 1 cm and 15 cm height lines. Discard the
1 cm section.
8) Weigh wet 15 cm long sample and record.
9) Unclamp remaining sample and add to balance in order to
record entire pad wet weight.
10) Report Total Wick Height at 15 minutes.
11) Report As-is and O.D. basis Entire Pad Capacity(g/g) by
calculating:
Entire Pad Ca acit / __ Wet Wt.-(As Ts or O.D. Wt.)
p y(g g) As - Is or O. D. Wt.
*Pad weight(-1 cm section)=(Total sample weight x 0.96)
12) Calculate the Wicked Pad Capacity if needed:
Wicked Pad Capacity = Entire Pad Capacity x 24
Wicking Ht at 15 min
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The results are summarized in Table 14.
Table 14. Unrestrained Vertical Wicking Height
Composite Calendered Density UncalenderedDensity
Height (cm) (g/cm3) Height (cm)(g/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
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. Acquisition Rate and Rewet (ml/sec~
Composite1st Insult2nd Insult 3rd InsultFinal Rewet
(g)
47/pledget2.73 2.53 2.26 15.81
48 2.60 2.12 1.92 18.71
48/pledget2.65 2.39 2.15 14.65
The 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.
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Saddle Acquisition Rate, Distribution, and Wicking 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 43 cm x (6.5 cm-
11 cm (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.
S) 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 75 ml of Synthetic Urine (Blood Bank 0.9%
Saline) and pour into furniel.
8) Open the fumlel and start the timer. Measure the time at which
all of the fluid has left the funnel to the point where the fluid is
absorbed into the sample. Record as SWAT.
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 I~immberly-Clark, Neenah, WI) and are summarized in Table 16.
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Table 16. Saddle Acguisition Rate (ml/sec~,
Composite 1st Insult 2nd Insult 3rd Insult
48/pledget 28.05 28.01 31.50
Control 37.77 52.30 53.06
The 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 (~/~1
Zone 45/pledget Control
1 0 0
2 3.73 2.06
3 11.88 9.28
4 13.01 12.40
5 12.16 10.66
6 10.62 9.44
7 3.73 3.91
8 0 0
The results 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)
Composite 10 min 15 20 min 30 40 min SO 60 min
min min min
48/pledget8.3 8.3 8.3 9.2 9.7 13.2 13.5
Control 8.5 8.5 8.5 9.3 9.5 12.9 13.4
The results indicate that the construct including Composite 45 and pledget
have wicking heights comparable to the control composite (removed from Supreme
Core, commercially available from Kimberly-Clark, Neenah, WI).
Example 23
The Composition of Representative Reticulated Absorbent Com op sites
The compositions of representative composites of the invention are
summarized in Table 19 below. In the table, the amount of matrix fibers (e.g.,
southern pine), crosslinked cellulosic fibers, and superabsorbent material is
given in
percent by weight based on the total weight of the composite. The amount of
optional
wet strength agent (e.g., polyamide-epichlorohydrin adduct) is given in pounds
per
ton fiber. The representative compositions have basis weights ranging from
about
161 to about 900 g/m2. The representative composites include composites having
matrix fibers in an amount from about 8 to about 72 percent by weight,
crosslinked
fibers in an amount from about 5 to about 64 percent by weight, and
superabsorbent
material in an amount from about 10 to about 60 percent by weight based on the
total
weight of the composite. The optional wet strength agent can be present in an
amount
up to about 25 pounds per ton fiber.
Table 19. Representative Composite Composition
Basis WeightMatrix Crosslinked SuperabsorbentWet Strength
Fiber Fiber
(g/m2) (weight (weight percent)Material Agent
percent) (weight percent)(lb/ton
fiber)
161 16 24 60 10
200 40 20 40 25
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Basis WeightMatrix Crosslinked SuperabsorbentWet Strength
(g/m2) Fiber Fiber Material Agent
(weight (weight percent)(weight percent)(lb/ton
percent) fiber)
200 70 20 10 25
200 48 12 40 5.5
201 48 12 40 10
210 24 36 40 10
220 17.6 26.4 56 12.5
232 32 48 20 10
232 24 36 40 10
243 20 30 50 10
250 48 12 40 10
270 36 24 40 10
285 24 16 60 10
290 26 39 35 12.5
297 28 42 30 10
300 48 12 40 5.5
300 24 36 40 10
300 36 24 40 10
300 12 48 40 10
300 48 12 40 0
300 24 36 40 0
300 36 24 40 0
300 16 24 60 0
302 20 30 50 10
305 48 12 40 10
305 20 30 50 10
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Basis WeightMatrix Crosslinked SuperabsorbentWet Strength
(g/m2) Fiber Fiber Material Agent
(weight (weight percent)(weight percent)(lb/ton
percent) fiber)
312 16 24 60 10
313 24 36 40 10
316 36 24 40 10
320 32 48 20 10
329 25.2 37.8 37 10
331 26 39 35 10
332 48 32 20 10
336 16 24 60 10
336 8 32 60 10
340 16 24 60 0
348 30 30 40 10
355 33 22 45 10
356 28 12 60 12.5
360 24 16 60 10
360 16 24 60 10
362 42 18 40 25
362 48 32 20 0
367 24 16 60 10
367 16 24 60 10
368 40 20 40 25
368 40 20 40 15
368 40 20 40 10
368 72 8 20 25
368 56 24 20 25
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Basis WeightMatrix Crosslinked SuperabsorbentWet Strength
(g/m2) Fiber Fiber Material Agent
(weight (weight percent)(weight percent)(lblton
percent) fiber)
368 40 40 20 25
368 54 13.5 32.5 25
368 40.5 27 32.5 25
368 47.2 5.3 47.5 25
368 36.7 15.8 47.5 25
368 26.2 26.3 47.5 25
368 32 8 60 25
368 24 16 60 25
368 72 8 20 25
368 40 20 40 13
368 60 0 40 13
368 48 12 40 10
368 48 12 40 25
368 32 48 20 10
368 24 36 40 10
368 16 24 60 10
370 36 24 40 0
370 48 12 40 0
370 24 36 40 0
373 48 12 40 10
380 42 28 30 10
387 16 24 60 10
387 48 32 20 10
387 32 48 20 10
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Basis WeightMatrix Crosslinked SuperabsorbentWet Strength
(g/m2) Fiber Fiber Material Agent
(weight (weight percent)(weight percent)(lb/ton
percent) fiber)
387 16 64 20 10
387 0 80 20 10
388 24 36 40 10
389 48 32 20 0
390 36 24 40 0
393 40 20 40 25
397 42 28 30 0
400 32 48 20 10
400 16 24 60 10
400 24 36 40 10
400 48 9 40 10
400 20 20 60 10
402 42 28 30 10
403 32.5 32.5 35 10
407 48 12 40 25
407 42 18 40 25
408 28 12 60 10
418 32 48 20 10
420 48 32 20 10
421 48 12 40 0
421 24 36 40 0
421 36 24 40 0
426 24 36 40 10
430 40 20 40 25
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Basis WeightMatrix Crosslinked SuperabsorbentWet Strength
(g/m2) Fiber Fiber Material Agent
(weight (weight percent)(weight percent)(lb/ton
percent) fiber)
432 24 36 40 10
444 48 12 40 10
444 48 12 40 10
457 36 24 40 10
457 24 36 40 10
457 38.5 16.5 45 12.5
467 3 8.5 16.5 45 10
481 36 24 40 0
498 27.5 27.5 45 10
500 40 20 40 25
509 27.5 27.5 45 10
529 30 30 40 10
550 32.5 32.5 35 10
691 25 25 50 10
Example 24
Flexibility of Representative Reticulated Absorbent Composites
The compositions and flexibility of representative composites formed by
foam-forming methods in accordance with the present invention are summarized
in
Table 20 below. In the table, the amount of matrix fibers (e.g., southern
pine),
crosslinked cellulosic fibers, and superabsorbent material is given in percent
by
weight based on the total weight of the composite. The amount of optional wet
strength agent (e.g., polyamide-epichlorohydrin adduct) is given in pounds per
ton
fiber. The flexibility of representative reticulated absorbent composites was
determined by measuring composite edgewise ring crush as described in Example
17
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above. As indicated in the table, several of the composites were treated after
formation by, for example, calendering.
Table 20. Representative Composite Composition and Edgewise Ring Crush
Basis Matrix CrosslinkedSuperabsorbentWet StrengthEdgewise
Weight Fiber Fiber Material Agent Ring Crush
(g/m2) (weight (weight (weight percent)(lb/ton (g)
percent)percent) fiber)
243 20 30 50 10 513
297 28 42 30 10 1496
302 20 30 50 IO 325*
305 20 30 50 10 401*
329 25.2 37.8 37 10 389*
331 26 39 35 10 406*
332 48 32 20 10 299/270*
355 33 22 45 10 1925
362 48 32 20 0 562*
380 42 28 30 IO 826
389 48 32 20 0 866
400 20 20 60 10 730
402 42 28 30 10 1487/140*
403 32.5 32.5 35 10 518
420 48 32 20 10 1460
481 36 24 40 0 267*
498 27.5 27.5 45 10 563*
509 27.5 27.5 45 IO 536
529 30 30 40 10 3458
550 32.5 32.5 35 10 2200
691 25 25 50 10 1877
*Composite softened post-formation by, for example, calendering.
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Example 25
Representative Composite Wickin,~ Height
In this example, the several performance characteristics for representative
foam-formed composites is described. These performance characteristics include
unrestrained vertical wicking height, edgewise ring crush, tensile strength,
and
acquisition rate for third insult. Unrestrained vertical wicking height was
measured as
described in Example 22, edgewise ring crush was measured as described in
Example 17, tensile was measured as described in Example 21, and acquisition
rate
was measured as described in Example 4. The compositions' compositions and
performance characteristics are summarized in Table 21.
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U
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t~ O ~n O ~n ~ N
p ~ O 01 M N N pp O
., ~ N ,~
O
O
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U
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U
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p
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a
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N
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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.
