Note: Descriptions are shown in the official language in which they were submitted.
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ABSORBENT COMPOSITES COMPRISING
SUPERABSORBENT MATERIALS
1 o FIELD OF THE INVENTION
The present invention is directed to absorbent articles
containing superabsorbent materials. The present invention is
also directed to a method of making absorbent articles containing
superabsorbent materials. The present invention is further
1 s directed to fiber-containing fabrics and webs comprising
superabsorbent materials and their applicability in disposable
personal care products.
BACKGROUND OF THE INVENTION
2o In the manufacture of disposable diapers, there is
continual effort to improve the performance characteristics of the
diaper. Although the structure of a diaper has many components,
in many instances the in-use performance of the diaper is directly
related to the characteristics of the absorbent composite contained
2s within the diaper. Accordingly, diaper manufacturers strive to
find ways of improving the properties of the absorbent composite,
including in-use absorbency, in order to reduce the tendency of
the diaper to leak.
One means of reducing the leakage of a diaper has
3o been the extensive use of superabsorbent materials. Recent trends
in commercial diaper designs have been to use more
superabsorbent materials and less fiber in order to make the
diaper thinner. However, notwithstanding the increase in total
absorbent capacity contributed by the addition of larger amounts
3s of superabsorbent material, such diapers often still suffer from
excessive leaking during use.
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One reason that diapers with a high content of
superabsorbent materials still leak is that many superabsorbent
materials are unable to absorb liquid at the rate at which the
liquid is applied to the absorbent composite during use. The
s addition of fibrous material to the absorbent composite improves
the leakage of an absorbent composite by temporarily holding the
liquid until the superabsorbent material absorbs it. Fibers also
serve to separate the particles of superabsorbent material so that
gel-blocking does not occur. As used herein, the term "gel-
1 o blocking" refers to the situation wherein particles of
superabsorbent material deform during swelling and block the
interstitial spaces between the particles, or between the particles
and the fibers, thus preventing the flow of liquid through the
interstitial spaces. Even when fibrous material is incorporated
15 into an absorbent composite, a poor choice of a superabsorbent
material, especially one which exhibits gel-blocking behavior
within the absorbent composite, results in poor liquid handling
properties initially and later in the life cycle of the absorbent
composite. Consequently, the choice of a particular
2o superabsorbent material greatly affects the in-use absorbency and
leakage of the absorbent product.
Another problem with commercially available
diapers is the tendency of diapers to leak after multiple insults.
As used herein, the term "insults" refers to a single introduction
25 of liquid into the absorbent composite or diaper. During use, a
diaper is typically exposed to multiple insults during the life cycle
of the diaper. To reduce diaper leakage during the life cycle of
the diaper, it is desirable to maintain the level of intake
performance of the absorbent composite throughout the life of the
3o product.
A number of U.S. patents address different problems
associated with absorbent composites. For example, U.S. Patent
No. 5,147,343 issued to Kellenberger teaches the importance of
having a superabsorbent with high Absorbency Under Load
3s values in an absorbent product. U.S. Patent No. 5,149,335 issued
to Kellenberger et al. teaches the importance of superabsorbent
rate and capacity in a composite. U.S. Patent No. 5,415,643 issued
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to Kolb teaches a method of increasing the flushability of an
absorbent composite by incorporating superabsorbent materials
having a high Absorbency Under Load (AUL) to Centrifuge
Retention Capacity (CRC) ratio with AUL evaluated in 90 minutes
s under 0.6 psi (41,370 dynes/cm2) into the composite. U.S. Patent
No. 5,415,643 issued to Melius et al. teaches the importance of
AUL values under different pressures. U.S. Patent No. 5,599,335
issued to Goldman emphasizes the benefits of the combination of
high Saline Flow Conductivity and high Performance Under
to Pressure. U.S. Patent No. 5,728,082 issued to Gustafsson et al
describes an absorbent body consisting of two layers containing
superabsorbent, wherein the superabsorbent in the first layer has
a high degree of cross-linking while the superabsorbent in the
second layer has a higher absorbent capacity than the
~5 superabsorbent in the first layer.
The aforementioned patents disclose specific
superabsorbent properties, which result in improved composite
performance. In general, the aforementioned patents teach that
superabsorbent materials exhibiting high capacity under load
2o result in improved gel stiffness and permeability behavior for
enhanced composite performance. However, the aforementioned
patents do not specifically address the problems mentioned above,
namely, improving leakage/intake over the life cycle of the
absorbent composite.
2s What is needed in the art is a method of determining
which superabsorbent materials lead to optimum composite
properties. What is also needed in the art is an absorbent
composite containing superabsorbent materials, which exhibits
improved fluid intake rate, and superior fluid intake of multiple
3o insults over the life of the composite, without the problems
associated with known absorbent composites.
SUMMARY OF THE INVENTION
The present invention is directed to absorbent
3s composites containing superabsorbent materials, which have been
developed to address the above-described problems associated
with currently available, absorbent composites and other
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absorbent composites described in literature. The absorbent
composites contain superabsorbent materials, which have a Gel
Bed Permeability (GBP) value of greater than about 70 x10-9 cm2
and an Absorbency Under Load (AUL) value of less than about
s 25 g/g at 0.6 psi (41,370 dynes/cm2). This combination of
properties for superabsorbent materials enables an absorbent
composite to have improved fluid intake rate and superior fluid
intake of multiple insults over the life of the composite. Unlike
known absorbent composites, which lose their fluid intake
to performance over the life of the composite, the absorbent
composites of the present invention perform exceptionally well,
exhibiting superior fluid intake after multiple insults to the
composite.
The present invention is also directed to a method of
~ 5 making absorbent articles containing superabsorbent materials
having a Gel Bed Permeability (GBP) value of greater than about
70 x10-9cmz and an Absorbency Under Load (AUL) value of less
than about 25 g/g at 0.6 psi (41,370 dynes/cm2). The
superabsorbent materials may be incorporated into a fibrous
2o substrate by a variety of processes. The superabsorbent material
may be incorporated into a fibrous substrate as solid particulate
material or as a solution. The superabsorbent materials may be in
any form suitable for use in absorbent composites including
particles, fibers, flakes, spheres, and the like.
25 The present invention is further directed to absorbent
composites comprising superabsorbent materials and fibrous
material, and their applicability in disposable personal care
products. The absorbent composites of the present invention are
particularly useful as absorbent components in personal care
3o products such as diapers, feminine pads, panty liners, incontinence
products, and training pants.
BRIEF DESCRIPTION OF THE FIGURES
Fig. 1 is an illustration of equipment for
35 determining the Gel Bed Permeability (GBP) value of a
superabsorbent material.
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Fig. 2 is an cross-sectional view of the piston head
taken along line 2-2 of Figure 1.
Fig. 3 is an illustration of equipment for
determining the Absorbency Under Load (AUL) value of a
superabsorbent material.
Fig. 4 is an cross-sectional view of the porous plate
taken along line 4-4 of Figure 3.
Figs. Sa-c are an illustration of equipment for
determining the Composite Permeability value of an absorbent
to composite.
Fig. 6 is an illustration of equipment for
determining the Fluid Intake Flowback Evaluation (FIFE) value
of an absorbent composite.
Fig. 7 is an illustration of equipment for determining
I5 the Intake/Desorption value of an absorbent composite.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention is directed to absorbent
composites containing superabsorbent materials, wherein the
2o absorbent composites possess the ability to maintain exceptional
intake performance even after multiple insults to the composite.
The present invention achieves these results by approaching the
problems of intake performance and leakage in an unconventional
manner. Traditionally, the approach taken to address fluid intake
2s has been to incorporate superabsorbents having a high capacity
under load into an absorbent composite. The goal was to produce
an absorbent composite having increased capacity and
permeability behavior, and ultimately provide to the composite
improved intake performance over multiple insults. However, it
3o has been determined that the pursuit of higher superabsorbent
capacity inevitably leads to limited performance improvement.
Instead, the present invention achieves high composite
permeability and other desirable composite properties using lower
capacity superabsorbents.
35 As used herein, the term "superabsorbent material"
refers to a water-swellable, water-insoluble organic or inorganic
material capable, under the most favorable conditions, of
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absorbing more than 15 times its weight in an aqueous solution
containing 0.9 weight percent sodium chloride. Organic materials
suitable for use as a superabsorbent material of the present
invention may include natural materials such as agar, pectin, guar
gum, and the like; as well as synthetic materials, such as synthetic
hydrogel polymers. Such hydrogel polymers include, but are not
limited to, alkali metal salts of polyacrylic acids, polyacrylamides,
polyvinyl alcohol, ethylene malefic anhydride copolymers,
polyvinyl ethers, hydroxypropylcellulose,
polyvinylmorpholinone; and polymers and copolymers of vinyl
sulfonic acid, polyacrylates, polyacrylamides, polyvinylpyrridine,
and the like. Other suitable polymers include hydrolyzed
acrylonitrile grafted starch, acrylic acid grafted starch, and
isobutylene malefic anhydride copolymers and mixtures thereof.
is The hydrogel polymers are desirably lightly crosslinked to render
the material substantially water insoluble. Crosslinking may, for
example, be by irradiation or by covalent, ionic, van der Waals,
or hydrogen bonding. The superabsorbent materials may be in
any form suitable for use in absorbent composites including
2o particles, fibers, flakes, spheres, and the like.
While a wide variety of superabsorbent materials are
known, the present invention relates, in one aspect, to the proper
selection of superabsorbent materials to allow formation of
improved absorbent composites and disposable absorbent
25 garments. The present invention is directed to a method of
achieving optimum performance in an absorbent composite due to
the discovery that superabsorbent materials having a high Gel Bed
Permeability (GBP) value and a low Absorbency Under Load
(AUL) value at 0.6 psi (41,370 dynes/cm2) provide unexpected
3o intake performance improvement over known superabsorbent
materials. More specifically, superabsorbent materials having, in
combination, a Gel Bed Permeability (GBP) value of greater than
about 70 x10-~ cm2 and an Absorbency Under Load (AUL) value
of less than about 25 g/g at 0.6 psi (41,370 dynes/cm2), provide
3s desirable properties and performance to absorbent composites.
These lower capacity superabsorbent materials have the capability
of delivering improved intake performance as described below.
CA 02293864 1999-12-30
The present invention has determined that lower
capacity superabsorbent materials provide much more room for
improvement in absorbent composite performance. Not only do
the low capacity superabsorbent materials enhance the ability of
the absorbent composite to rapidly take in liquid, the low capacity
superabsorbent materials also enable constant or even improved
fluid intake performance over the life of the absorbent composite.
The present invention discloses that superabsorbent
materials may be divided into two categories: those having a ( 1 )
Gel Bed Permeability (GBP) value of greater than about 70 x10-~
cm2 and an Absorbency Under Load (AUL) value of less than
about 25 g/g at 0.6 psi (41,370 dynes/cm2) (Class-I
superabsorbents), and the rest (Class-II superabsorbents). Use of
Class I superabsorbents having relatively low AUL behavior and
~ 5 high GBP provides the unexpectedly improved intake behavior
described below.
Superabsorbent materials suitable for the present
invention may include any superabsorbent material, which has a
Gel Bed Permeability (GBP) value of greater than about 70 x10-9
2o cm2 and an Absorbency Under Load (AUL) value of less than
about 25 g/g at 0.6 psi (41,370 dynes/cm2). Desirably, the
superabsorbent material has a GBP value of greater than about
150 x 10-~ cm2 and an AUL value of less than about 25 g/g at 0.6
psi. More desirably, the superabsorbent material has a GBP value
2s of greater than about 180 x 10-~ cm2 and an AUL value of less than
about 25 g/g at 0.6 psi. More desirably, the superabsorbent
material has a GBP value of greater than about 210 x10-~ cm2 and
an AUL value of less than about 25 g/g at 0.6 psi. More desirably,
the superabsorbent material has a GBP value of greater than about
30 250 x10-9 cm2 and an AUL value of less than about 25 g/g at 0.6
psi. Even more desirably, the superabsorbent material has a GBP
value of greater than about 300 x10-9 cm2 and an AUL value of
less than about 25 g/g at 0.6 psi.
In another desired embodiment of the present
3s invention, the superabsorbent material has a GBP value of greater
than about 70 x10-9 cm2 and an AUL value of less than about 24
g/g at 0.6 psi. More desirably, the superabsorbent material has a
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_g_
GBP value of greater than about 150 x10-9 cm2 and an AUL value
of less than about 24 g/g at 0.6 psi. More desirably, the
superabsorbent material has a GBP value of greater than about
180 x 10-9 cm2 and an AUL value of less than about 24 g/g at 0.6
s psi. More desirably, the superabsorbent material has a GBP value
of greater than about 210 x 10-9 cm2 and an AUL value of less than
about 24 g/g at 0.6 psi. More desirably, the superabsorbent
material has a GBP value of greater than about 250 x 10 9 cm2 and
an AUL value of less than about 24 g/g at 0.6 psi. Even more
desirably, the superabsorbent material has a GBP value of greater
than about 300 x10-9 cm2 and an AUL value of less than about 24
g/g at 0.6 psi.
In a further desired embodiment of the present
invention, the superabsorbent material has a GBP value of greater
1 s than about 70 x 10-9 cm2 and an AUL value of less than about 23
g/g at 0.6 psi. More desirably, the superabsorbent material has a
GBP value of greater than about 150 x10-9 cm2 and an AUL value
of less than about 23 g/g at 0.6 psi. More desirably, the
superabsorbent material has a GBP value of greater than about
20 180 x 10-9 cm2 and an AUL value of less than about 23 g/g at 0.6
psi. More desirably, the superabsorbent material has a GBP value
of greater than about 210 x 10-9 cm2 and an AUL value of less than
about 23 g/g at 0.6 psi. More desirably, the superabsorbent
material has a GBP value of greater than about 250 x10-9 cm2 and
2s an AUL value of less than about 23 g/g at 0.6 psi. Even more
desirably, the superabsorbent material has a GBP value of greater
than about 300 x10-9 cm2 and an AUL value of less than about 23
g/g at 0.6 psi.
In yet a further desired embodiment of the present
3o invention, the superabsorbent material has a GBP value of greater
than about 70 x 10-9 cm2 and an AUL value of less than about 21
g/g at 0.6 psi. More desirably, the superabsorbent material has a
GBP value of greater than about 150 x10-9 cm2 and an AUL value
of less than about 21 g/g at 0.6 psi. More desirably, the
35 superabsorbent material has a GBP value of greater than about
180 x10-9 cm2 and an AUL value of less than about 21 g/g at 0.6
psi. More desirably, the superabsorbent material has a GBP value
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of greater than about 210 x10-9 cm2 and an AUL value of less than
about 21 g/g at 0.6 psi. More desirably, the superabsorbent
material has a GBP value of greater than about 250 x10-~ cm2 and
an AUL value of less than about 21 g/g at 0.6 psi. Most desirably,
the superabsorbent material has a GBP value of greater than about
300 x10-~ cm2 and an AUL value of less than about 21 g/g at 0.6
psl.
In addition to having a GBP value of greater than
about 70 x10- cmz and an AUL value of less than about 25 g/g at
l0 0.6 psi, desirably the superabsorbent material used in the present
invention has a pH in a range such that no skin irritation can
occur when the superabsorbent material is present in an absorbent
composite. Desirably, the superabsorbent material used in the
present invention has a pH of from about 3 to about 8, as
~ s measured by the pH test method described below. More
desirably, the superabsorbent material used in the present
invention has a pH of from about 4 to about 7. Most desirably,
the superabsorbent material used in the present invention has a pH
of from about 5.2 to about 6.5.
2o In one embodiment of the present invention, the
superabsorbent material comprises a sodium salt of a cross-linked
polyacrylic acid. Suitable superabsorbent materials include, but
are not limited to, Stockhausen W-65431 (available from
Stockhausen Chemical Company, Inc., Greensboro, NC); Dow
2s AFA-173-60A, Dow AFA-173-60B, Dow XU 40671.00, Dow
XUS 40665.07, Dow XZ-91060.02/91080.20 (hereinafter, "Dow
XZ"), and Dow XUS 40667.01 (all available from The Dow
Chemical Company, Midland, MI).
The present invention is further directed to absorbent
3o composites containing one or more Class I superabsorbent
materials described above. The Class I superabsorbent materials
may be used alone or in combination with one or more Class II
superabsorbent materials. In addition to the superabsorbent
materials described above, the absorbent composites of the present
35 invention may comprise means to contain the superabsorbent
material. Any means capable of containing the above-described
superabsorbent materials, which means is further capable of being
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located in a disposable absorbent garment, is suitable for use in
the present invention. Many such containment means are known
to those skilled in the art. For example, the containment means
may comprise a fibrous matrix such as an air-laid or wet-laid web
s of cellulosic fibers, a meltblown web of synthetic polymeric
fibers, a spunbonded web of synthetic polymeric fibers, a
coformed matrix comprising cellulosic fibers and fibers formed
from a synthetic polymeric material, air-laid heat-fused webs of
synthetic polymeric material, open-celled foams, and the like.
1 o Alternatively, the containment means may comprise
two layers of material which are joined together to form a pocket
or compartment, more particularly a plurality of pockets, which
pocket contains the superabsorbent material. In such a case, at
least one of the layers of material should be water-pervious. The
15 second layer of material may be water-pervious or water-
impervious. The layers of material may be cloth-like wovens and
nonwoven, closed or open-celled foams, perforated films,
elastomeric materials, or may be fibrous webs of material. When
the containment means comprises layers of material, the material
2o should have a pore structure small enough or tortuous enough to
contain the majority of the superabsorbent material. The
containment means may also comprise a laminate of two layers of
material between which the superabsorbent material is located and
contained. Further, the containment means may comprise a
25 support structure, such as a polymeric film, on which the
superabsorbent material is affixed. The superabsorbent material
may be affixed to one or both sides of the support structure,
which may be water-pervious or water-impervious.
Desirably, the absorbent composites of the present
3o invention comprise superabsorbent material in combination with a
fibrous matrix containing one or more types of fibrous materials.
The fibrous material forming the absorbent composites of the
present invention may be selected from a variety of materials
including natural fibers, synthetic fibers, and combinations
3s thereof. A number of suitable fiber types are disclosed in U.S.
Patent No. 5,601,542, assigned to Kimberly-Clark Corporation,
the entirety of which is incorporated herein by reference. The
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choice of fibers depends upon, for example, the intended end use
of the finished absorbent composite. For instance, suitable
fibrous materials may include, but are not limited to, natural
fibers such as cotton, linen, jute, hemp, wool, wood pulp, etc.
s Similarly, regenerated cellulosic fibers such as viscose rayon and
cuprammonium rayon, modified cellulosic fibers, such as
cellulose acetate, or synthetic fibers such as those derived from
polyesters, polyamides, polyacrylics, etc., alone or in combination
with one another, may likewise be used. Blends of one or more
of the above fibers may also be used if so desired.
In one embodiment, the relative amount of
superabsorbent material and fibrous material used to produce the
absorbent composites of the present invention may vary
depending on the desired properties of the resulting product, and
1 s the application of the resulting product. Desirably, the amount of
Class I superabsorbent material in the absorbent composite is
from about 20 wt% to about 100 wt% and the amount of fibrous
material is from about 80 wt% to about 0 wt%, based on the total
weight of the absorbent composite. More desirably, the amount
20 of Class I superabsorbent material in the absorbent composite is
from about 30 wt% to about 90 wt% and the amount of fibrous
material is from about 70 wt% to about 10 wt%, based on the
total weight of the absorbent composite. Most desirably, the
amount of Class I superabsorbent material in the absorbent
25 composite is from about 40 wt% to about 80 wt% and the amount
of fibrous material is from about 60 wt% to about 20 wt%, based
on the total weight of the absorbent composite.
In another embodiment, the basis weight of Class I
superabsorbent material used to produce the absorbent composites
30 of the present invention may vary depending on the desired
properties, such as total composite thickness and basis weight, in
the resulting product, and the application of the resulting product.
For example, absorbent composites for use in infant diapers may
have a lower basis weight and thickness compared to an absorbent
35 composite for an incontinence device. Desirably, the basis weight
of Class I superabsorbent material in the absorbent composite is
greater than about 80 grams per square meter (gsm). More
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desirably, the basis weight of Class I superabsorbent material in
the absorbent composite is from about 80 gsm to about 800 gsm.
More desirably, the basis weight of Class I superabsorbent
material in the absorbent composite is from about 120 gsm to
s about 700 gsm. Most desirably, the basis weight of Class I
superabsorbent material in the absorbent composite is from about
150 gsm to about 600 gsm.
The absorbent composites of the present invention
may be made by any process known to those of ordinary skill in
1o the art. In one embodiment of the present invention,
superabsorbent particles are incorporated into an existing fibrous
substrate. Suitable fibrous substrates include, but are not limited
to, nonwoven and woven fabrics. In many embodiments,
particularly personal care products, preferred substrates are
15 nonwoven fabrics. As used herein, the term "nonwoven fabric"
refers to a fabric that has a structure of individual fibers or
filaments randomly arranged in a mat-like fashion. Nonwoven
fabrics may be made from a variety of processes including, but
not limited to, air-laid processes, wet-laid processes,
2o hydroentangling processes, staple fiber carding and bonding, and
solution spinning. The superabsorbent material may be
incorporated into the fibrous substrate as a solid particulate
material or formed in situ from a solution applied to the
substrate. The superabsorbent materials may be in any form
25 suitable for use in absorbent composites including particles,
fibers, flakes, spheres, and the like.
In a further embodiment of the present invention, the
superabsorbent material and fibrous material are simultaneously
mixed to form an absorbent composite. Desirably, the composite
3o materials are mixed by an air-forming process known to those of
ordinary skill in the art. Air-forming the mixture of fibers and
superabsorbent material is intended to encompass both the
situation wherein preformed fibers are air-laid with the
superabsorbent material, as well as, the situation in which the
35 superabsorbent material is mixed with the fibers as the fibers are
being formed, such as through a meltblowing process.
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In should be noted that the superabsorbent material
may be distributed uniformly within the absorbent composite or
may be non-uniformly distributed within the absorbent
composite. The superabsorbent material may be distributed
s throughout the entire absorbent composite or may be distributed
within a small, localized area of the absorbent composite.
The absorbent composites of the present invention
may be formed from a single layer of absorbent material or
multiple layers of absorbent material. In the case of multiple
layers, the layers may be positioned in a side-by-side o r
surface-to-surface relationship and all or a portion of the layers
may be bound to adjacent layers. In those instances where the
absorbent composite includes multiple layers, the entire thickness
of the absorbent composite may contain one or more
superabsorbent materials or each individual layer may separately
contain some or no superabsorbent materials. Each individual
layer may also contain different superabsorbent materials from an
adjacent layer.
The absorbent composites of the present invention
2o desirably possess constant or improved fluid intake over the life
of the composite. The fundamental absorbent property of
composite permeability of an absorbent material is a key to fast
intake. One method of measuring composite permeability is with
the Composite Permeability test, which is described in detail
below. This test measures the time required for a fixed volume
of liquid to flow through a pre-saturated composite in the z-
direction. As shown in Table 1, the majority of Class-I
superabsorbent materials enable about twice as much composite
permeability for an absorbent composite containing 50 wt%
3o superabsorbent material and 50 wt% fibers as compared to
control superabsorbent materials, Favor 880 (available from
Stockhausen Inc., Greensboro, NC) and Dow DryTech 2035
(available from Dow Chemical Company, Midland, MI).
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Table 1. Composite Permeability for 50 wt% SAM Absorbent
Composites
Class SAP SuperabsorbentComposite
Designation Material Permeability
(x 10-8 cm2)
I S 1 W-65431 ~ 191
I Dl AFA-173-60A 100
I D2 AFA-173-60B 177
I D3 XUS 40665.07 202
I D4 XU 40671.00 ~ 192
I DS XZ ~ 115
I D6 XUS 40667.01 ~ 168
I I - Favor 8 80 ~ 112
II - Dr Tech 2035 ~61
Another important measure of intake performance is
measured by the Fluid Intake Flowback Evaluation (FIFE) test,
which is described in detail below. The FIFE test measures how
fast liquid can flow into a material. Table 2 shows the 3'd insult
FIFE intake rates for a variety of absorbent composites containing
50 wt% superabsorbent material and 50 wt% fibers. It can be
seen that absorbent composites containing different
superabsorbents exhibit different FIFE intake rates. As shown in
Table 2, most of the Class-I superabsorbents exhibited fast intake
rates (>2.75 ml/sec).
is
2s
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Table 2. 3rd Insult FIFE Rate for 50 wt% SAM Absorbent
Composites
Class SAP Superabsorbent Composite
Designation Material Permeability
(x 10-8 cm2)
I S1 W-65431 ~3.2
I D1 AFA-173-60A ~2.5
I D2 AFA-173-60B ~3.1
I D3 XUS 40665.07 ~3.1
I D4 XU 40671.00 ~3.4
I DS XZ ~2.1
I D6 XUS 40667.01 ~3.0
II - Favor 880 ~2.1
II - Dr Tech 2035 ~1.6
s
The improved intake behavior as seen by the 3rd
Insult FIFE Intake Rate may be controlled by the type and amount
of superabsorbent material present in the absorbent composite.
1o Table 3 shows the 3'd Insult FIFE Intake Rate for two sets of
composites containing either a conventional superabsorbent
material (identified as Favor 880) or a Class I superabsorbent
material, exhibiting the desirable properties of a GBP value
greater than about 70 x 109 cm2 and an AUL value of less than
is about 25 g/g at 0.6 psi (identified as D3 and XUS 40665.07).
Additionally, for each type of superabsorbent material,
composites containing either 30, 40, 50, or 60 wt%
superabsorbent material were prepared and evaluated. All
composites had a total basis weight of 400 gsm. This results in
2o composites having a superabsorbent basis weight of 120, 160,
200, or 240 gsm.
CA 02293864 1999-12-30
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Table 3. 3rd Insult FIFE Rate for SAM Absorbent Composites
with Variable SAM Weight Percent
3'd Insult
FIFE
Rate
(ml/sec)
SuperabsorbentSuperabsorbent Favor XUS 40665.07
wt% Basis Wei ht 880 (D3)
( sm)
30 120 6.6 6.6
40 160 4 5.7
50 200 2.2 3.1
60 240 2 3
s
As can be seen in Table 3, as the amount of
superabsorbent material in the composite changes, the 3'd Insult
FIFE Intake Rate of the composite changes. In addition, at 40,
50, and 60 wt % superabsorbent levels, a composite comprising
Class I superabsorbent material (XUS 40665.07) exhibits a faster,
more desirable, 3rd Insult FIFE Intake Rate compared to a
composite comprising a superabsorbent that is not Class I (Favor
880).
To further demonstrate the impact of the type and
~ 5 amount of superabsorbent material present in the composite on
the composite intake behavior, Table 4 shows the 3'd Insult FIFE
Intake Rate for two sets of composites containing either a
conventional superabsorbent (identified as Favor 880) or a Class I
superabsorbent material, exhibiting the desirable properties of a
2o GBP value greater than about 70 x 10-9 cm2 and an AUL value of
less than about 25 g/g at 0.6 psi (identified as D3 and XUS
40665.07). However, in these two sets, for each type of
superabsorbent material, composites having a total composite
basis weight of either 200, 300, 400, or 500 gsm were prepared
2s and evaluated. All composites had 50 wt % superabsorbent
material. This results in composites having a superabsorbent basis
weight of 100, 150, 200, or 250 gsm.
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Table 4. 3rd Insult FIFE Rate for 50 wt% SAM Absorbent
Composites with Variable Composite Basis Weight
3rd FIFE
Rate
(ml/sec)
Composite Basis Superabsorbent Favor XUS 40665.07
Wei ht ( sm) Basis Wei ht ( 880 (D3)
sm)
200 100 4.4 4.4
300 150 3.3 5.5
400 200 2.2 3.3
500 250 2.5 3.5
s
As can be seen in Table 4, as the composite basis
weight (and superabsorbent basis weight) changes, the 3'd Insult
FIFE Intake Rate of the composite changes. In addition, at
superabsorbent basis weights of 150, 200, or 250 gsm, a
Io composite comprising Class I superabsorbent material (XUS
40665.07) exhibits a faster, more desirable, 3rd Insult FIFE Intake
Rate compared to a composite comprising a superabsorbent that is
not Class I (Favor 880).
The absorbent composites according to the present
1 s invention are suited to absorb many fluids including body fluids
such as urine, menses, and blood, and are suited for use in
absorbent garments such as diapers, adult incontinence products,
bed pads, and the like; in catamenial devices such as sanitary
napkins, tampons, and the like; and in other absorbent products
2o such as wipes, bibs, wound dressings, food packaging, and the
like. Accordingly, in another aspect, the present invention relates
to a disposable absorbent garment comprising an absorbent
composite as described above. A wide variety of absorbent
garments are known to those skilled in the art. The absorbent
2s composites of the present invention can be incorporated into such
known absorbent garments. Exemplary absorbent garments are
generally described in U.S. Pat. Nos. 4,710,187 issued Dec. 1,
1987, to Boland et al.; 4,762,521 issued Aug. 9, 1988, to Roessler
et al.; 4,770,656 issued Sep. 13, 1988, to Proxmire et al.;
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4,798,603 issued Jan. 17, 1989; to Meyer et al.; which references
are incorporated herein by reference.
As a general rule, the absorbent disposable garments
according to the present invention comprise a body-side liner
s adapted to contact the skin of a wearer, an outer cover superposed
in facing relation with the liner, and an absorbent composite, such
as those described above, superposed on said outer cover and
located between the body-side liner and the outer cover.
Those skilled in the art will readily understand that
to the superabsorbent materials and absorbent composites of the
present invention may be advantageously employed in the
preparation of a wide variety of products, including but not
limited to, absorbent personal care products designed to be
contacted with body fluids. Such products may only comprise a
15 single layer of the absorbent composite or may comprise a
combination of elements as described above. Although the
superabsorbent materials and absorbent composites of the present
invention are particularly suited for personal care products, the
superabsorbent materials and absorbent composites may be
2o advantageously employed in a wide variety of consumer products.
TEST METHODS
For Testing Superabsorbent Materials:
The methods for performing the Gel Bed
25 Permeability (GBP) test and the Absorbency Under Load (AUL)
test, used to distinguish Class I superabsorbent materials from
Class II superabsorbent materials, are described below. Further,
the pH test method is described below.
3o Gel Bed Permeability (GBP)
A suitable piston/cylinder apparatus for performing
the GBP test is shown in Figs. 1 and 2. Referring to Fig. 1,
apparatus 128 consists of a cylinder 134 and a piston generally
indicated as 136. As shown in Fig. 1, piston 136 consists of a
35 cylindrical LEXAN~ shaft 138 having a concentric cylindrical
hole 140 bored down the longitudinal axis of the shaft. Both ends
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of shaft 138 are machined to provide ends 142 and 146. A weight,
indicated as 148, rests on end 142 and has a cylindrical hole 148a
bored through the center thereof. Inserted on the other end 146 is
a circular piston head 150. Piston head 150 is sized so as to
vertically move inside cylinder 134. As shown in Fig. 2, piston
head 150 is provided with inner and outer concentric rings
containing seven and fourteen approximately 0.375 inch (0.95
cm) cylindrical holes, respectively, indicated generally by arrows
160 and 154. The holes in each of these concentric rings are
bored from the top to bottom of piston head 150. Piston head 150
also has cylindrical hole 162 bored in the center thereof to receive
end 146 of shaft 138.
Attached to the bottom end of cylinder 134 is a No.
400 mesh stainless steel cloth screen 166 that is biaxially stretched
~ s to tautness prior to attachment. Attached to the bottom end of
piston head 150 is a No. 400 mesh stainless steel cloth screen 164
that is biaxially stretched to tautness prior to attachment. A
sample of superabsorbent material indicated as 168 is supported
on screen 166.
2o Cylinder 134 is bored from a transparent LEXAN°
rod or equivalent and has an inner diameter of 6.00 cm (area =
28.27 cm2), a wall thickness of approximately 0.5 cm, and a
height of approximately 5.0 cm. Piston head 150 is machined
from a LEXAN° rod. It has a height of approximately 0.625
2s inches (1.59 cm) and a diameter sized such that it fits within
cylinder 134 with minimum wall clearances, but still slides freely.
Hole 162 in the center of the piston head 150 has a threaded 0.625
inch ( 1.59 cm) opening ( 18 threads/inch) for end 146 of shaft
138. Shaft 138 is machined from a LEXAN° rod and has an outer
3o diameter of 0.875 inches (2.22 cm) and an inner diameter of
0.250 inches (0.64 cm). End 146 is approximately 0.5 inches
( 1.27 cm) long and is threaded to match hole 162 in piston head
150. End 142 is approximately 1 inch (2.54 cm) long and 0.623
inches (1.58 cm) in diameter, forming an annular shoulder to
35 support the stainless steel weight 148. The annular stainless steel
weight 148 has an inner diameter of 0.625 inches ( 1.59 cm), so
that it slips onto end 142 of shaft 138 and rests on the annular
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shoulder formed therein. The combined weight of piston 136 and
weight 148 equals approximately 596 g, which corresponds to a
pressure of 0.30 psi (20,685 dynes/cm2) for an area of 28.27 cm2.
When solutions flow through the piston/cylinder
apparatus, the cylinder 134 generally rests on a 16 mesh rigid
stainless steel support screen (not shown) or equivalent.
The piston and weight are placed in an empty
cylinder to obtain a measurement from the bottom of the weight
to the top of the cylinder. This measurement is taken using a
to caliper readable to 0.01 mm. This measurement will later be used
to calculate the height of the gel bed. It is important to measure
each cylinder empty and keep track of which piston and weight
were used. The same piston and weight should be used for
measurement when gel is swollen.
The superabsorbent layer used for GBP
measurements is formed by swelling approximately 0.9 g of a
superabsorbent material in the GBP cylinder apparatus (dry
polymer should be spread evenly over the screen of the cylinder
prior to swelling) with 0.9% (w/v) aqueous NaCl for a time
2o period of about 60 minutes. The sample is taken from
superabsorbent material which is prescreened through U.S.
standard #30 mesh and retained on U.S. standard #50 mesh. The
superabsorbent material, therefore, has a particle size of between
300 and 600 microns. The particles may be pre-screened by hand
or automatically pre-screened with, for example, a Ro-Tap
Mechanical Sieve Shaker Model B available from W. S. Tyler,
Inc., Mentor, Ohio.
At the end of this period, the cylinder is removed
from the fluid and the piston weight assembly is placed on the gel
layer. The thickness of the swollen superabsorbent layer is
determined by measuring from the bottom of the weight to the
top of the cylinder with a micrometer. The value obtained when
taking this measurement with the empty cylinder is subtracted
from the value obtained after swelling the gel. The resulting
value is the height of the gel bed H.
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The GBP measurement is initiated by adding the
NaCI solution to cylinder 134 until the solution attains a height of
4.0 cm above the bottom of superabsorbent layer 168. This
solution height is maintained throughout the test. The quantity of
fluid passing through superabsorbent layer 168 versus time is
measured gravimetrically. Data points are collected every second
for the first two minutes of the test and every two seconds for the
remainder. When the data are plotted as quantity of fluid passing
through the bed versus time, it becomes clear to one skilled in the
1 o art when a steady flow rate has been attained. Only data collected
once the flow rate has become steady is used in the flow rate
calculation. The flow rate, Q, through the superabsorbent layer
168, is determined in units of gm/sec by a linear least-square fit
of fluid passing through the superabsorbent layer 168 (in grams)
versus time (in seconds).
Permeability in cm2 is obtained by the following
equation:
K = [Q*H*Mu)]/[A*Rho*P]
2o where K = Gel Bed Permeability (cm2); Q = flow rate (g/sec);
H = height of gel bed (cm); Mu = liquid viscosity (poise);
A = cross-sectional area for liquid flow (cm2); Rho = liquid
density (g/cm3); and P - hydrostatic pressure (dynes/cmz)
[normally 3923 dynes/cm2].
2s
Absorbency Under Load (A UL) test
The Absorbency Under Load (AUL) test is a measure
of the ability of a superabsorbent material to absorb a liquid while
3o the superabsorbent material is under a restraining load. The test
may best be understood by reference to Figs. 3 and 4. Referring
to Fig. 3, a demand absorbency tester (DAT) 300 is used, which is
similar to a GATS (gravimetric absorbency test system), available
from M/K Systems, banners, Mass., as well as a system described
3s by Lichstein in pages 129-142 of the INDA Technological
Symposium Proceedings, March 1974.
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A porous plate 302 is used having ports 304 confined
within the 2.5 centimeter diameter covered, in use, by the
Absorbency Under Load apparatus 306. Fig. 4 shows a cross-
sectional view of porous plate 302. The porous plate 302 has a
s diameter of 3.2 centimeters with 7 ports (holes) 304 each with
diameter of 0.30 centimeters. The porous plate 302 has one hole
304 in the center and the holes are spaced such that the distance
from the center of one hole to another adjacent to it is 1.0
centimeter. An electrobalance 308 is used to measure the flow of
to the test fluid (an aqueous solution containing 0.9% w/v NaCI) into
the superabsorbent material 310.
The AUL apparatus 306 used to contain the
superabsorbent material may be made from 1 inch (2.54
centimeter), inside diameter, thermoplastic tubing 312 machined-
1 s out slightly to be sure of concentricity. One hundred mesh
stainless steel wire cloth 314 is adhesively attached to the bottom
of tubing 312. Alternatively, the steel wire cloth 314 may be
heated in a flame until red hot, after which the tubing 312 is held
onto the cloth until cooled. Care should be taken to maintain a
2o flat, smooth bottom and not distort the inside of the tubing 312.
A 4.4 gram piston 316 may be made from 1 inch (2.54 cm) solid
material (e.g., Plexiglas) and machined to closely fit, without
binding, in the tubing 312. A 200 gram weight 318 (outer
diameter 0.98 inch (2.49 cm)) is used to provide 39,500 dynes per
25 square centimeter (about 0.57 psi) restraining load on the
superabsorbent material. For the purpose of the present
invention, the pressure applied during the AUL test is referred to
as 0.6 psi.
Desirably, about 0.160 grams of superabsorbent is
3o used. The sample is taken from superabsorbent material, which is
pre-screened through U.S. standard #30 mesh and retained on
U.S. standard #50 mesh. The superabsorbent material, therefore,
has a particle size of between 300 and 600 microns. The particles
may be pre-screened by hand or automatically pre-screened with,
35 for example, a Ro-Tap Mechanical Sieve Shaker Model B
available from W. S. Tyler, Inc., Mentor, Ohio.
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The desired amount of superabsorbent material 310
(0.160 grams) is weighed onto weigh paper and placed on the
wire cloth 314 at the bottom of the tubing 312. The tubing 312 is
shaken to level the superabsorbent material on the wire cloth 314.
Care is taken to be sure no superabsorbent material is clinging to
the wall of the tubing 312. The piston 316 and weight 318 are
carefully placed on the superabsorbent material to be tested. The
test is initiated by placing a 3 centimeter diameter glass filter
paper 320 (Whatman filter paper Grade GF/A, available from
to Whatman International Ltd., Maidstone, England) onto the plate
302 (the paper is sized to be larger than the internal diameter and
smaller than the outside diameter of the tubing 312) to ensure
good contact, while eliminating evaporation over the ports 304 of
the demand absorbency tester 300 and then allowing saturation to
~ 5 occur. The device is started by placing the apparatus 306 on the
glass filter paper 320 and allowing saturation to occur. The
amount of fluid picked up is monitored as a function of time
either directly by hand, with a strip chart recorder, or directly
into a data acquisition or personal computer system.
2o The amount of fluid pick-up measured after 60
minutes is the AUL value and is reported in grams of test liquid
absorbed per gram of superabsorbent material as determined
before starting the test procedure. A check can be made to ensure
the accuracy of the test. The apparatus 306 can be weighed before
2s and after the test with a difference in weight equaling the fluid
pick-up.
pH Test Method
The pH test method used to determine the pH of
3o superabsorbent materials of the present invention is performed as
follows in a room having a room temperature of 23 +/- 1 °C (73.4
+/- 1.8°F) and a relative humidity of 50 +/- 2%. Into a 250 ml
beaker with magnetic stirrer is added 150 g of a 0.9 wt% NaCl
solution. The NaCI solution is stirred to create a vortex of about
3s 2 inches. A 1.0 g sample of superabsorbent material, having a
particle size of 300 to 600 microns, is weighed onto a weighing
paper. The particles may be pre-screened by hand or
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automatically pre-screened with, for example, a Ro-Tap
Mechanical Sieve Shaker Model B available from W. S. Tyler,
Inc., Mentor, Ohio. The 300-600 micron particles are placed in a
sealed container immediately to maintain its moisture content.
The superabsorbent material is slowly poured into
the NaCI solution. The solution is allowed to stir for three
minutes. After three minutes, the stirring is stopped and the
magnetic stirrer is removed from the solution using clean
tweezers. The beaker is then covered with a moisture barrier
to film (e.g., Parafilm~, available from Fischer-Scientific
Company, Pittsburg, PA) and allowed to sit undisturbed for
twenty minutes. As the superabsorbent material gels, it settles to
the bottom of the beaker.
The electrodes of a pH meter (e.g., pH Meter Model
1 s 140, available from Corning, Corning, NY) are rinsed with
distilled water. The electrodes are inserted into the salt solution,
making sure that the electrodes are not inserted into the sediment
at the bottom of the beaker. The pH value is allowed to stabilize.
The pH value is recorded, rounding the number to one decimal
2o place.
For Testing Absorbent Composites:
The test methods for the Composite Permeability
Test, the Fluid Intake Flowback Evaluation test, and the
2s Intake/Desorption test are described below:
Composite Permeability Test
The Composite Permeability test determines the
permeability of a composite in cmz by calculating the time for a
3o fluid to flow through a composite. As shown in Figs. 5a and 5b,
the permeability tester consists of two Plexiglas or polycarbonate
concentric cylinders, wherein one fits inside the other with very
little clearance, but still slides freely. The inner cylinder 510 has
an outer diameter of 6.9 cm and an inner diameter of 5.10 cm.
3s The outer cylinder/base & stopper assembly 515 has a metal
screen 512, on which the test material is placed for testing. This
screen is desirably a type 504 stainless steel screen with a hole
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diameter of 0.156 inches (0.40 cm) and 63% open area, 20 gauge,
and 3/16 inch (0.48 cm) center to center spacing. The outer
cylinder 511 of the base and stopper assembly has an inner
diameter of 7.0 cm and an outer diameter of 7.5 cm. A ruler 513
s is on the outside of the outer cylinder 511 with height markings 3
5/8 inch (9.21 cm) and 1 1/8 inch (2.86 cm) from the bottom of
the screen 512.
An absorbent composite of superabsorbent material
and fluff, or fluff alone, is air-formed on tissue to a desired basis
weight and density. This composite 500 is die cut to a desired
size, desirably, a 6.83 cm (2.69 inch) diameter circle is used. As
shown in Fig. Sc, the composite is placed in a dish 501 of
approximately the same size (diameter) as the composite 500.
This prevents swelling in the radial direction. The sample is
~s saturated using a 0.9% (w/v) aqueous NaCI solution. A cover 502
is placed over the dish and allowed to sit 30 minutes to
equilibrate. More solution may be added, if necessary, to fully
saturate the sample. One will generally know when the composite
is fully saturated when an excess of liquid exists within the dish
20 501. After a total of 30 minutes, the composite 500 and dish 501
are placed upside down on an absorbent medium such as paper
toweling to remove the interstitial liquid. This is done by placing
the paper toweling over the dish and composite, and while holding
the dish and toweling, flipping it over. This puts the composite in
2s direct contact with the toweling. No pressure is applied during
this process.
After the blotting process, a wet bulk of the sample is
taken by placing the sample under a thickness gauge with an
acrylic platen or the like, which applies approximately 0.05 psi
30 (3,448 dynes/cm2) pressure. The composite is then placed on the
inner cylinder 510 and the outer cylinder (permeability tester)
515 is turned upside down over the inner cylinder with the
composite. The entire apparatus, which now contains the test
composite and the inner cylinder, is flipped back over for the test.
3s This ensures that the composite rests neatly (with least amount of
handling) on screen 512 at the bottom of test apparatus 515. The
test fluid is poured in the inner cylinder on top of the composite.
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The fluid should be above the top mark on the ruler (at least 1
inch (2.54 cm)). before starting the test. To initiate the test, the
stopper 514 is removed from the bottom of the permeability
apparatus 515 and the timer is started when the fluid front reaches
the top mark on the ruler (3 5/8 inch (9.21 cm) above the screen)
and the timer is stopped when the fluid front reaches the bottom
mark on the ruler (1 1/8 inch (2.86 cm) above the screen). Time
in seconds is recorded.
Permeability (K) in cmz is calculated as follows:
to
K = { [(ln (h,/h2) * Mu)/(g * Rho)] * WB/t}
where K = composite permeability (cm2); h, = height of upper
marker (cm) [normally 9.21 cm]; h2 = height of lower marker
(cm) [normally 2.86 cm]; Mu = liquid viscosity (poise) [normally
0.01 poise]; g = acceleration due to gravity (cm/sec2) [normally
980 cm/sec2]; Rho - liquid density (gm/cm3) [normally 1.0
gm/cm3]; WB = wet bulk of composite (cm); t = time for liquid to
move from h, to hz while flowing through composite (sec).
Fluid Intake Flowback Evaluation test
The Fluid Intake Flowback Evaluation (FIFE) test
determines the amount of time required for an absorbent
composite to intake a preset amount of fluid. A suitable apparatus
for performing the FIFE test is shown in Fig. 6.
A composite of superabsorbent and fluff, or fluff
only, is air-formed on tissue to a desired basis weight and density.
The composite is cut to the desired size, in this case, the composite
600 is cut to a 5 inch ( 12.70 cm) square. The composite 600 is
3o placed under the FIFE test pad 601. The test pad is a flexible
conformable silicon bed that is 10 inches (25.4 cm) by 20 inches
(50.8 cm). The silicon pad is constructed using Dow Corning 527
primerless silicon dielectric gel and wrapping it in shrinkable
plastic wrapping. This pad is made with a sufficient thickness to
3s produce a pressure of approximately 0.03 psi (2,069 dynes/cm2).
The pad contains a Plexiglas cylinder 602 with an inner diameter
of 5.1 cm and an outer diameter of 6.4 cm and the bottom of the
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cylinder has a cap 603 with a 1 inch (2.54 cm) circle bore in the
center where the test fluid comes in direct contact with the
composite 600. The center of the cylinder is located 6.75 inches
( 17.15 cm) down from the top edge of the silicon pad 601 and is
s centered from side to side (5 inches ( 12.70 cm) from the edge).
An automated controller 605 can be connected to electrodes 606
and 607 that auto-initiate the test upon the entry of the test fluid.
This can eliminate tester variability. The test fluid is desirably a
0.9% (w/v) NaCl solution.
The test is run by placing the composite 600 under
the silicon test pad 601. The desired amount of fluid is dispensed
from a positive displacement pump. The fluid amount in this case
is calculated according to the composition of the composite. For
example, the fluid amount for a 400 gsm composite of size 5 inch
1 s ( 12.70 cm) square consisting of 50% superabsorbent and 50%
fluff is calculated by assuming the superabsorbent capacity is 30
g/g and the fluff capacity is 6 g/g. The total amount of capacity
of the composite in grams is calculated and 25% of this amount is
one insult. The fluid is dispensed at a rate of approximately 10
2o ml/sec. The time in seconds for fluid to drain from the cylinder
602 is recorded.
After a 15 minute wait, a second insult is done and
after another 15 minute wait, the third and final insult is done.
The FIFE Intake Rate for each insult is determined by dividing
2s the insult fluid amount in milliliters by the time necessary for the
fluid to drain from the cylinder 602 in seconds.
If during the test, leakage of fluid occurs from the
top, bottom, or sides of the composite, the amount of leaked fluid
should be measured. In this case, the FIFE Intake Rate for each
3o insult is determined by subtracting the leaked fluid amount from
the insult fluid amount and then dividing this quantity by the time
for the fluid to drain from the cylinder 602 in seconds.
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IntakelDesorption Test
The Intake/Desorption test measures the intake and
desorption capability of a material or composite. A suitable
apparatus for performing the Intake/Desorption test is shown in
s Fig. 7.
A composite may consist of superabsorbent material
and fluff, or fluff only. In this case, composites consisting of
superabsorbent material and fluff were air-formed on tissue to a
desired basis weight and density. The composite is then cut to the
desired size, in this case, the composite is cut to 2.5 inches (6.35
cm) by 6 inches ( 15.24 cm). The dry weight of the composite
701 to be tested is recorded. The test composite 701 is placed on
a piece of polyethylene film 702 that is the exact size of the test
composite 701 and centered in a Plexiglas cradle 703 such that the
15 length of the composite ( 15.24 cm) is perpendicular to the slot
704 in the bottom of the cradle 703. The cradle 703 has a width
of 33 cm. The ends 705 of the cradle 703 are blocked off at a
height of 19 cm to form an inner distance of 30.5 cm and an angle
between the upper arms of 60 degrees between upper arms 706 of
2o cradle 703. The cradle 703 has a 6.5 mm wide slot 704 at the
lowest point running the length of the cradle 703. The slot 704
allows run-off from the test composite 701 to enter tray 707. The
amount of run-off is recorded by a balance 708 readable to the
nearest 0.01 g. A pre-set amount of liquid is delivered in the
25 center of the test composite 701 at a desired rate. In this case the
amount is 100 ml at a rate of 15 ml/sec and 1/2 inch (1.27 cm)
above the sample. The amount of run-off is recorded.
The test composite 701 is immediately removed from
the cradle 703 and placed on a 2.5 inches (6.35 cm) by 6 inches
30 (15.24 cm) pre-weighed dry pulp/superabsorbent desorption pad
having a total basis weight of 500 gsm and a density of about 0.20
g/cc and a superabsorbent material wt % of 60 in a horizontal
position under 0.05 psi pressure for 15 minutes. The
superabsorbent material is desirably Favor 880, available from
35 Stockhausen, Inc. (Greensboro, NC). The pulp is desirably Coosa
1654, available from Alliance Forest Products (Coosa Pines, AL).
This pressure is applied by using a Plexiglas plate. After the 15
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minutes, the desorption pad weight is recorded and the test
composite 701 is placed back in the cradle 703 and a second insult
of 100 ml is done. After the amount of run-off is recorded, the
test composite 701 is once again placed on a pre-weighed dry
desorption pad under 0.05 psi (dynes/cm') load for 15 minutes.
After 15 minutes, a weight of the desorption pad is recorded.
The composite 701 is placed back in the cradle 703 for a third
insult. The amount of run-off is recorded and the test composite
701 is placed on a dry pre-weighed desorption pad under 0.05 psi
to pressure for 15 minutes. The amount of fluid picked up in g/g
for each insult is calculated by subtracting the run-off from 100
ml and dividing by the dry weight of the test composite 701. A
particularly useful measure of the ability of a composite to exhibit
superior fluid intake of multiple insults over the life of the
composite is to divide the 3"' insult pickup value by the ls' insult
pickup value.
The present invention is further illustrated by the
following examples, which are not to be construed in any way as
2o imposing limitations upon the scope thereof. On the contrary, it
is to be clearly understood that resort may be had to various other
embodiments, modifications, and equivalents thereof which, after
reading the description herein, may suggest themselves to those
skilled in the art without departing from the spirit of the present
invention and/or the scope of the appended claims.
EXAMPLE 1
Testing of Superabsorbents for Gel Bed Permeability (GBP) and
Absorbency Under Load (A UL)
3o Using the above-described procedure for measuring
Gel Bed Permeability (GBP) and Absorbency Under Load
(AUL), GBP and AUL values of various superabsorbent materials
(SAM) were determined. The results of the testing are given
below in Table 5.
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Table 5. GBP and AUL Values for Superabsorbent Materials
SAM SAM SAM Identification Gel Bed AUL
Design- Permeability0.6 psi
anon (x 10-~ cm2)( / )
A Sl Stockhausen W-65431 302 23.4
B D2 Dow AFA-173-60B 194 21
C D4 Dow XU 40671.00 1552 19.5
D D3 Dow XUS 40665.07 925 19.6
E D5 Dow XZ 630 23.7
F D6 Dow XUS 40667.01 967 22.2
G D7 Dow XU40669 26 16
H - Stockhausen 880 110 27.9
(600-850 micron)
I D1 Dow AFA-173-60A 150 16.9
J S2 Stockhausen W-65406 175 26.8
K S3 Stockhausen W-77553 962 28
L - Stockhausen Favor 79 28.4
880
M - Dow Dr Tech 2035 58 23.9
As shown in Table 5, superabsorbents A through F
s and I exhibit a GBP value greater than 70 x 10-9 cmz and an AUL
value of less than 25 g/g. Superabsorbents G and H and J through
M exhibit a GBP value less than 70 x 10-~ cm2 and/or an AUL
value of greater than 25 g/g.
i o EXAMPLE 2
Testing of Superabsorbents for pH
Using the above-described procedure for measuring
pH, pH values of various superabsorbent materials (SAM) were
determined. The results of the testing are given below in Table 6.
Is
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Table 6. pH Values for Superabsorbent Materials
SAP Superabsorbent MaterialpH
Desi nation
S1 Stockhausen W-65431 5.8
D2 Dow AFA-173-60B 5.6
D3 Dow XUS 40665.07 5.3
D4 Dow XU 40671.00 5.7
DS Dow XZ 6.0
D6 Dow XUS 40667.01 6.7
D1 Dow AFA-173-60A 6.1
- Stockhausen Favor 880 6.8
- Dow Dr Tech 2035 6.3
s EXAMPLE 3
Testing of Absorbent Composites for Composite Permeability, 3rd
FIFE Intake Rate, and IntakelDesorption 3rdll St pickup
The superabsorbents tested in Example 1 were
combined with fluffed pulp fibers (Coosa River CR-1654;
to available from Alliance Forest Products (Coosa Pines, AL) and
formed into webs using conventional air-forming equipment. The
weight percent of superabsorbent material and the basis weight of
superabsorbent material was varied as shown in Table 7.
is
25
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Table 7. Nonwoven Webs of Superabsorbent Material and Pulp
Fibers
Sample SAM SAM ConcentrationSAM Basis Weight
Number (mass %) ( sm)
1 A 50 200
2 B 50 200
3 C 50 200
4 D 50 200
E 50 200
6 F 50 200
C-1 G 50 200
C-2 H 50 200
11 I 50 200
C-4 J 50 200
C-5 K 50 200
C-6 L 50 200
C-7 M 50 200
7 D 50 250
8 D 50 150
C-8 D 50 100
9 D 60 240
D 40 160
C-9 D 30 120
C-10 L 50 250
C-11 L 50 150
C-12 L 50 100
C-13 L 60 240
C-14 L 40 160
C-15 L 30 120
s
The composites identified as samples 1 to 11 and
comparative examples C-1 to C-2 and C-4 to C-15 were evaluated
for one or more of the following: composite permeability, 3ra
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FIFE Intake Rate, and Intake/Desorption 3~d/ls' pickup as
described above. The results of these tests are shown in Table 8.
Table 8. Testing for Composite Permeability, 3'd FIFE Intake
Rate, and Intake/Desorption 3'~d/ls' Pickup
Sample Composite 3rd FIFE Intake Intake/Desorption
PermeabilityRate 3rd/15
(x 10-g (ml/sec) Pickup
cm2)
1 191 3.2 1
2 177 3.1 1.18
3 192 3.4 1.35
4 202 3.1 1.52
5 115 2.1 1.18
6 168 3.0 1.22
7 - 3.5 -
8 - 5.5 -
9 159 3.0 -
255 5.7 -
C-1 163 2.7 0.92
C-2 110 2.5 0.99
11 100 2.5 1.30
C-4 198 2.0 0.86
C-5 152 1.7 0.98
C-6 112 2.2 0.90
C-7 61 1.6 0.92
C-8 - 4.4 -
C-9 226 6.6 -
C-10 - 2.5 -
C-11 - 3.3 -
C-12 - 4.4 -
C-13 63 2.0 -
C-14 172 4.0 -
C-15 161 6.6 ~ -
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As can be seen when examining the above data, the
Class I superabsorbent materials provided improved intake
performance.
The above disclosed examples are preferred
embodiments and are not intended to limit the scope of the present
invention in any way. Various modifications and other
embodiments and uses of the disclosed superabsorbent polymers,
apparent to those of ordinary skill in the art, are also considered
to be within the scope of the present invention.
