Note: Descriptions are shown in the official language in which they were submitted.
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ABSORBENT ARTICLES WITH IMPROVED ABSORPTION PROPERTIES
FIELD OF THE INVENTION
The present invention is directed to absorbent articles such as disposable
diapers,
training pants and adult incontinence undergarments comprising superabsorbent
polymer
particles.
BACKGROUND OF THE INVENTION
Absorbent articles, such as disposable diapers, training pants, and adult
incontinence
undergarments, absorb and contain body exudates. Many absorbent articles, like
diapers,
contain superabsorbent polymer material. Superabsorbent polymers are typically
present in
the core of the absorbent articles in the form of particles. Superabsorbent
polymer particles
are able to absorb liquid and swell when entering into contact with liquid
exudates. However,
it has been shown in the past that not all categories of superabsorbent
polymer particles are
equally suitable for use in an absorbent article.
It is known that in order to have absorbent articles comprising superabsorbent
polymer particles which exhibit good absorbing and containing functions,
specific technical
requirements need to be fulfilled by the superabsorbent polymer particles.
The superabsorbent polymer particles need first to be able to absorb the
liquid exudates fast.
The absorption speed of superabsorbent polymer particles has generally been
characterized in
the prior art by measuring the Free Swell Rate (FSR) of the particles.
In addition to having a high absorption speed, the superabsorbent polymer
particles
present in the core need to be also highly permeable to liquid. A poor
permeability of the
superabsorbent polymer particles may induce leakage of the absorbent article
due to gel
blocking. Gel blocking can occur in the absorbent core when swelling
superabsorbent
polymer particles block the void spaces between the particles. In such a case,
the liquid
exudates can not or only slowly reach underneath layers of superabsorbent
polymer particles
disposed in the core. The liquid exudates remain on the surface of the
absorbent core and
may therefore leak from the diaper.
The permeability of the superabsorbent polymer particles has typically been
characterized in the prior art by measuring the SFC (Saline Flow Conductivity)
of the
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particles. This parameter is measured at equilibrium, i.e. the measure is
performed on a fully
preswollen gel bed of superabsorbent polymer particles.
However, the inventors have now surprisingly found that absorbent cores
comprising
superabsorbent polymer particles having high FSR and high SFC values do not
automatically
conduct to fast acquisition times of liquid exudates into the absorbent
article, especially at the
first gush, i.e. when the absorbent cores first come into contact with liquid.
The present invention therefore provides an absorbent article having improved
absorption properties and therefore reduced leakage, especially at the first
gush, i.e. when the
article starts to be wetted.
SUMMARY OF THE INVENTION
The present invention relates to an absorbent article comprising an absorbent
structure. The absorbent article is divided into three portions: a front
portion, a back portion
and a crotch portion disposed between the front portion and the back portion.
The absorbent
structure comprises an absorbent core. The absorbent core has a dry thickness
at the crotch
point of the article of from 0.2 to 5 mm. One or more portion(s) of the
absorbent structure
comprise(s) at least 90% by weight of superabsorbent polymer particles and
require(s) a time
to reach an uptake of 20 g/g (T20) of less than 440 s as measured according to
the K(t) test
method.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a plan view of a diaper in accordance with an embodiment of the
present
invention.
Fig. 2 is a cross sectional view of the diaper shown in Fig. 1 taken along the
sectional
line 2-2 of Fig. 1.
Fig. 3 is a partial cross sectional view of an absorbent core layer in
accordance with
an embodiment of this invention.
Fig. 4 is a partial cross sectional view of an absorbent core layer in
accordance with
another embodiment of this invention.
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Fig. 5a is a partial sectional view of an absorbent core comprising a
combination of
the first and second absorbent core layers illustrated in Figs. 3 and 4.
Fig. 5b is a partial sectional view of an absorbent core comprising a
combination of
the first and second absorbent core layers illustrated in Figs. 3 and 4.
Fig. 6 is a schematic representation of a rheometer.
Fig. 7 is a partial cross-sectional side view of a suitable permeability
measurement
system for conducting the Dynamic Effective Permeability and Uptake Kinetics
Measurement Test.
Fig. 8 is a cross-sectional side view of a piston/cylinder assembly for use in
conducting the Dynamic Effective Permeability and Uptake Kinetics Measurement
Test
Fig. 9 is a top view of a piston head suitable for use in the piston/cylinder
assembly
shown in Fig. 8.
Fig. 10 is a partial cross-sectional side view of a suitable permeability
measurement
system for conducting the Urine Permeability Measurement Test.
Fig. 11 is a cross-sectional side view of a piston/cylinder assembly for use
in
conducting the Urine Permeability Measurement Test.
Fig. 12 is a top view of a piston head suitable for use in the piston/cylinder
assembly
shown in Fig. 11.
Fig. 13 is a cross-sectional side view of the piston/cylinder assembly of Fig.
11 placed
on fritted disc for the swelling phase.
Fig. 14 is a cross-sectional view of a suitable Flat Acquisition measurement
system
for conducting the Flat Acquisition Test
Fig. 15 is a cross-sectional view of an absorbent structure to be tested
according to the
K(t) Test Method wherein a layer of material which is not part of the
absorbent structure is
removed from the absorbent structure with the aid of a Cold Spray
Fig. 16 is a cross-sectional view of an absorbent structure to be tested
according to the
K(t) Test Method wherein the upper layer of the absorbent structure is
perforated using a
perforating tip.
Fig. 17 is a top view of the perforation pattern according to which the upper
or lower
layer of an absorbent structure can be perforated.
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Fig. 18A is a graphic representing the uptake in g/g as a function of time for
the
absorbent structures of the comparative examples 1 and 2 and of Example 1 as
measured
according to the K(t) Test Method.
Fig. 18B is a graphic representing the uptake in g/g as a function of time for
the
absorbent structures of the comparative examples 1 and 2 and of Example 2 as
measured
according to the K(t) Test Method.
DETAILED DESCRIPTION OF THE INVENTION
Absorbent article" is used herein to refer to devices that absorb and contain
body
exudates, and, more specifically, refers to devices that are placed against or
in proximity to
the body of the wearer to absorb and contain the various exudates discharged
from the body.
Absorbent articles include diapers, training pants, adult incontinence
undergarments,
feminine hygiene products and the like. As used herein, the term "body fluids"
or "body
exudates" includes, but is not limited to, urine, blood, vaginal discharges,
breast milk, sweat
and fecal matter. In some embodiments of the present invention, the absorbent
article is a
diaper or training pant.
"Absorbent core" is used herein to refer to a structure disposed between a
topsheet
and a backsheet of an absorbent article for absorbing and containing liquid
received by the
absorbent article. The core comprises superabsorbent polymer particles. The
core may
comprise one or more substrate layer(s), superabsorbent polymer particles
disposed on the
one or more substrate layer(s), and a thermoplastic composition typically
disposed on the
superabsorbent polymer particles. Typically the thermoplastic composition is a
thermoplastic
adhesive material. The thermoplastic adhesive material may form a fibrous
layer which is at
least partially in contact with the superabsorbent polymer particles on the
one or more
substrate layers and partially in contact with the one or more substrate
layers. Auxiliary
adhesive may be deposited on the one or more substrate layers before
application of the
superabsorbent polymer particles for enhancing adhesion of the superabsorbent
polymer
particles and/or of the thermoplastic adhesive material to the respective
substrate layer(s).
The absorbent core may also include one or more cover layer(s) such that the
superabsorbent
polymer particles are disposed between the one or more substrate layer(s) and
the one or
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more cover layer(s). The one or more substrate layer(s) or cover layer(s) may
comprise or
consist of a nonwoven, a tissue or a film or combinations thereof. The
absorbent core may
further comprise odor control compounds.
The absorbent core may consist essentially of the one or more substrate
layer(s), the
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superabsorbent polymer particles, the thermoplastic composition, optionally
the auxiliary
adhesive, optionally the cover layer(s), and optionally odor control
compounds.
The absorbent core may comprise superabsorbent polymer particles which are
sandwiched between two layers namely an upper layer and a lower layer with no
superabsorbent polymer particles above the upper layer and below the lower
layer. The upper
layer corresponds to the substrate layer or cover layer of the absorbent core
which is closest
to the topsheet of the article and the lower layer corresponds to the
substrate layer or cover
layer of the absorbent core which is closest to the backsheet of the absorbent
article.
Alternatively, in the absence of an upper layer, the absorbent core may
correspond to the
structure which is disposed between the topsheet and the lower layer or in the
absence of a
lower layer, the absorbent core may correspond to the structure which is
disposed between
the upper layer and the backsheet. In the absence an upper layer and a lower
layer, the
absorbent core may correspond to the whole structure which is disposed between
the topsheet
and the backsheet of the absorbent article. The substrate layer(s) or cover
layer(s) may
comprise or consist of a nonwoven, a tissue or a film or combinations thereof.
"Absorbent structure" is used herein to refer to one of the following
structures:
a. the absorbent core of the absorbent article in case the absorbent core
comprises superabsorbent polymer particles which are sandwiched between
two layers namely an upper layer and a lower layer with no superabsorbent
polymer particles above the upper layer and below the lower layer. The upper
layer corresponds to the substrate layer or cover layer of the absorbent core
being closest to the topsheet of the article and the lower layer corresponds
to
the substrate layer or cover layer of the absorbent core being closest to the
backsheet of the absorbent article
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b. the absorbent core of the absorbent article in combination with the
topsheet of
the absorbent article in case the absorbent core does not comprise an upper
layer as defined hereinbefore
c. the absorbent core of the absorbent article in combination with the
backsheet
of the absorbent article in case the absorbent core does not comprise a lower
layer as defined hereinbefore
"Portion of the absorbent structure" is used herein to refer to a portion of
the
absorbent structure through the thickness of the absorbent structure, i.e. a
portion of the
absorbent structure comprising all the different layers the absorbent
structure is made of in
the respective portion.
"Front portion" and "back portion" is used herein to refer to the front and
back waist
regions of the absorbent article. The length of both the front portion and the
back portion is
one third of the overall length of the article starting at the respective
front and back waist
edges. For embodiments, wherein the front and/or back waist edge is/are not
configured as a
straight line extending in parallel to the transverse centerline of the
absorbent article, the
length of the absorbent article is determined on or parallel to the
longitudinal centerline by
starting from the point of the front waist edge which is closest to the
transverse centerline and
terminating at the point of back waist edge which is closest to the transverse
centerline.
"Crotch portion" is used herein to refer to the region of the article
positioned in the
center of the article between the front and the back portion of the article.
The length of the
crotch portion is one third of the overall length of the article.
"Crotch point" is used herein to refer to the point of the article which is
positioned in
the center of the absorbent article at the intersection of the longitudinal
centerline and the
transverse centerline of the article. It should be understood for the purpose
of the invention
that the crotch point of the article is not necessarily positioned in the
center of the absorbent
core, namely at the intersection of the longitudinal centerline and the
transverse centerline of
the absorbent core, especially in case the absorbent core is not centered on
the transverse
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centerline of the article, i.e. in case the absorbent core is shifted to the
front and/or the back
of the article.
"Center of the front portion" is used herein to refer to the point of the
absorbent
article which is positioned at the intersection of the longitudinal centerline
of the article and
the line which is parallel to the transverse centerline of the article and
positioned at a distance
from the transverse centerline of one third of the overall length of the
absorbent article. For
embodiments, wherein the front and/or back waist edge is/are not configured as
a straight
line extending in parallel to the transverse centerline of the absorbent
article, the length of the
absorbent article is determined on or parallel to the longitudinal centerline
by starting from
the point of the front waist edge which is closest to the transverse
centerline and terminating
at the point of back waist edge which is closest to the transverse centerline.
"Comprise," "comprising," and "comprises" are open ended terms which also
encompass the terms "consist of', "consisting of' or "consists of' which are
closed ended
terms.
"Airfelt" is used herein to refer to comminuted wood pulp, which is a form of
cellulosic fiber.
"Superabsorbent polymer particle" is used herein to refer to cross linked
polymeric
materials that can absorb at least 10 times their weight of an aqueous 0.9%
saline solution as
measured using the Centrifuge Retention Capacity test (EDANA WSP 241.2-05).
The
superabsorbent polymer particles are in particulate form so as to be flowable
in the dry state.
Preferred superabsorbent polymer particles of the present invention are made
of
poly(meth)acrylic acid polymers. However, e.g. starch-based superabsorbent
polymer
particles are also within the scope of the present invention
"Thermoplastic adhesive material" is used herein to refer to a polymer
composition
from which fibers may be formed and applied to the superabsorbent polymer
particles with
the intent to immobilize the superabsorbent polymer particles in both the dry
and wet state.
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The thermoplastic adhesive material of the present invention preferably forms
a fibrous
network over the superabsorbent polymer particles.
A "nonwoven" is used herein to refer to a manufactured sheet, web or batt of
directionally or randomly orientated fibers, bonded by friction, and/or
cohesion and/or
adhesion, excluding paper and products which are woven, knitted, tufted,
stitch-bonded
incorporating binding yarns or filaments, or felted by wet-milling, whether or
not
additionally needled. The fibers may be of natural or man-made origin and may
be staple or
continuous filaments or be formed in situ. Commercially available fibers have
diameters
ranging from less than about 0.001 mm to more than about 0.2 mm and they come
in several
different forms: short fibers (known as staple, or chopped), continuous single
fibers
(filaments or monofilaments), untwisted bundles of continuous filaments (tow),
and twisted
bundles of continuous filaments (yarn). Nonwoven fabrics can be formed by many
processes
such as meltblowing, spunbonding, solvent spinning, electrospinning, and
carding. The basis
weight of nonwoven fabrics is usually expressed in grams per square meter
(gsm).
"Attached" is used herein to refer to configurations whereby a first element
is directly
secured to another element by affixing the first element directly to a second
element or
whereby a first element is indirectly secured to a second element by affixing
the first element
to a third, intermediate member(s), which in turn are affixed to the second
element. The
attachment means may comprise adhesive bonds, heat bonds, pressure bonds,
ultrasonic
bonds, dynamic mechanical bonds, or any other suitable attachment means or
combinations
of these attachment means as are known in the art.
Fig. 1 is a plan view of an absorbent article 10 according to some embodiments
of the
present invention. The absorbent article 10 is shown in its flat out,
uncontracted state (i.e.,
without elastic induced contraction) and portions of the absorbent article 10
are cut away to
more clearly show the underlying structure of the diaper 10. A portion of the
absorbent
article 10 that contacts a wearer is facing the viewer in Fig. 1. The
absorbent article 10
generally comprises a chassis 12 and an absorbent core 14 disposed in the
chassis 12.
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The chassis 12 of the absorbent article 10 in Fig. 1 may comprise the main
body of
the absorbent article 10. The chassis 12 may comprise an outer covering 16
including a
topsheet 18, which may be liquid pervious, and/or a backsheet 20, which may be
liquid
impervious. The absorbent core 14 may be encased between the topsheet 18 and
the
backsheet 20. The chassis 12 may also include side panels 22, elasticized leg
cuffs 24, and
an elastic waist feature 26.
The leg cuffs 24 and the elastic waist feature 26 may each typically comprise
elastic
members 28. One end portion of the absorbent article 10 is configured as the
front portion 30
and the other end portion is configured as the back portion 32 of the
absorbent article 10.
The intermediate portion of the absorbent article 10 is configured as the
crotch portion 34,
which extends longitudinally between the front and the back portions 30 and
32.
The absorbent article 10 is depicted in Fig. 1 with its longitudinal
centerline 36 and its
transverse centerline 38. The periphery 40 of the absorbent article 10 is
defined by the outer
edges of the absorbent article 10 in which the longitudinal edges 42 run
generally parallel to
the longitudinal centerline 36 of the absorbent article 10 and the front and
back waist edges
43 and 44 run between the longitudinal edges 42 generally parallel to the
transverse
centerline 38 of the absorbent article 10. The chassis 12 may also comprise a
fastening
system, which may include at least one fastening member 46 and at least one
landing zone
48.
The absorbent article 10 may also include such other features as are known in
the art
including front and rear ear panels, waist cap features, elastics and the like
to provide better
fit, containment and aesthetic characteristics. Such additional features are
well known in the
art and are e.g., described in U.S. Pat. No. 3,860,003 and U.S. Pat. No.
5,151,092.
In order to keep the absorbent article 10 in place about the wearer, at least
a portion of
the front portion 30 may be attached by the fastening member 46 to at least a
portion of the
back portion 32 to form leg opening(s) and an article waist. When fastened,
the fastening
system carries a tensile load around the article waist. The fastening system
may allow an
article user to hold one element of the fastening system, such as the
fastening member 46,
and connect the front portion 30 to the back portion 32 in at least two
places. This may be
achieved through manipulation of bond strengths between the fastening device
elements.
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According to certain embodiments, the absorbent article 10 may be provided
with a
re-closable fastening system or may alternatively be provided in the form of a
pant-type
diaper. When the absorbent article is a diaper, it may comprise a re-closable
fastening
system joined to the chassis for securing the diaper to a wearer. When the
absorbent article is
5 a pant-type diaper, the article may comprise at least two side panels
joined to each other to
form a pant.
The absorbent structure
The absorbent structure comprises superabsorbent polymer particles.
10 One or more portion(s) of the absorbent structure comprises at least 90%
by weight of
superabsorbent polymer particles based on the weight of the portion of the
absorbent
structure, excluding the weight of any substrate layer and/or cover layer
and/or topsheet
and/or backsheet that might be included in the portion of the absorbent
structure. The one or
more substrate layer(s) or cover layer(s) may comprise or consist of a
nonwoven, a tissue or a
film, or combinations thereof.
One of the one or more portion(s) of the absorbent structure may be centered
on the
center of the front portion of the article and/or one of the one or more
portion(s) of the
absorbent structure may be centered on the crotch point of the article.
At least one of the one or more portion(s) of the absorbent structure may have
a
surface area of 30 cm2 or more. Alternatively, each of the one or more
portion(s) may have a
surface area of 30 cm2 or more.
At least one of the one or more portion(s) of the absorbent structure having a
surface
area of 30 cm2 or more may encompass a circular area. Alternatively, each of
the one or more
portion(s) of the absorbent structure having a surface area of 30 cm2 or more
may encompass
a circular area.
The one or more portion(s) of the absorbent structure may comprise at least
95% by
weight of superabsorbent polymer particles.
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The one or more portion(s) of the absorbent structure may comprise at least
98% by
weight of superabsorbent polymer particles.
The one or more portion(s) of the absorbent structure may comprise at least
99% by
weight of superabsorbent polymer particles.
The whole absorbent structure may comprise at least 90% by weight, preferably
at
least 95% by weight, more preferably at least 98% by weight, even more
preferably at least
99% by weight of superabsorbent polymer particles.
These embodiments are particularly preferred since absorbent articles
comprising a
high percentage of superabsorbent polymer particles typically have a reduced
thickness when
dry in comparison with the thickness of conventional absorbent articles having
a higher
amount of conventional absorbent materials, such as airfelt and the like in
addition to the
superabsorbent polymer particles. The reduced thickness helps to improve the
fit and the
comfort when the article is positioned on the wearer.
The one or more portion(s) of the absorbent structure require a time to reach
an
uptake of 20 g/g (T20) of less than 440 s, or less than 400 s, or less than
350 s, or less than
300 s, or less than 250 s as measured according to the K(t) test method set
out below.
The time to reach an uptake of 20 g/g (T20) may be of 50 s to 440 s, or 100 s
to 350 s,
or 150 s to 300 s, as measured according to the K(t) test method set out
below.
The one or more portion(s) of the absorbent structure may have an effective
permeability at 20 minutes (K20) of at least 2.9.10-8 cm2
as measured according to the K(t)
test method.
The one or more portion(s) of the absorbent structure may have an effective
permeability at 20 minutes (K20) of at least 2.95.10-8 cm2, or at least 3.10-8
cm2, or of
2.95.10-8 cm2 to 1Ø10-6 cm2, or of 2.95.10-8 cm2 to 1Ø10-7 cm2, or of
3Ø10-8 to 1Ø10-7
cm2 as measured according to the K(t) test method set out below.
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The one or more portion(s) of the absorbent structure may have a ratio between
the
minimum effective permeability and the permeability at 20 minutes (Kmin/K20
ratio) of
more than 0.75, or more than 0.8 or more than 0.9 as measured according to the
K(t) test
method set out below. In such embodiments the transient gel blocking is
minimum and the
liquid exudates are able to travel fast through the void spaces present
between the particles
throughout all the swelling process and especially in the initial part of the
swelling phase
which is the most critical for the first gush.
The uptake of the one or more portion(s) of the absorbent structure at 20 min
(U20) is
of at least 24 g/g or at least 24.5 g/g, or of 24 g/g to 60 g/g, or of 24.5
g/g to 50 g/g, or of
24.5 g/g to 40 g/g as measured according to the K(t) test method set out
below.
In some embodiments, the whole absorbent structure meets the T20, K20 and U20
values mentioned hereinbefore.
Absorbent articles comprising such an absorbent structure have improved
absorption
properties and therefore exhibit reduced leakage in comparison with absorbent
articles of the
prior art, especially at the first gush. Such absorbent structures are
particularly suitable for
use in absorbent articles.
The absorbent core
In some embodiments, the absorbent core comprises an average amount of
superabsorbent polymer particles per area of from 50 to 2200 g/m2 or 100 to
1500 g/m2 or
200 to 1000 g/m2.
In some embodiments, the absorbent core comprises an average amount of
superabsorbent polymer particles per area of from 100 to 1500 g/m2, or 150 to
1000 g/m2, or
200 to 900 g/m2, or 400 to 700 g/m2 in the crotch portion of the article. The
absorbent article
comprises enough amount of superabsorbent polymer particles to have good
absorption
properties as well as to be sufficient thin to provide fit and comfort to the
wearer. However,
superabsorbent polymer particles are also present in the front and back
portions, though
especially in back portion amount may be low (or even zero). In some
embodiments, the
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absorbent core comprises an average amount of superabsorbent polymer particles
per surface
area of less than 300 g/m2, or less than 200 g/m2, alternatively from 25 to
300 g/m2, or 50 to
200 g/m2 or 50 to 100 g/m2 in the back portion of the article.
In some embodiments, the absorbent core may further comprise minor amounts of
an
absorbent material other than superabsorbent polymer particles, e.g. airfelt.
In some embodiments, the absorbent core typically comprises less than 5% by
weight of
airfelt, preferably less than 2% and more preferably is airfelt free. In some
embodiments, the
absorbent structure can also be airfelt free.
The absorbent core has a dry thickness at the crotch point of the article of
less than 10
mm, preferably less than 5 mm, more preferably less than 3 mm, even more
preferably less
than 1.5 mm, alternatively from 0.1 to 10 mm, preferably from 0.2 to 5 mm,
more preferably
from 0.3 to 3 mm, even more preferably from 0.5 to 1.5 mm, as measured
according to the
test method set out below. The absorbent core is thus sufficiently thin
compared to
conventional airfelt containing absorbent cores. Thereby, fit and comfort is
substantially
improved.
The superabsorbent polymer particles
The superabsorbent polymer particles useful for the present invention may be
of
numerous shapes. The term "particles" refers to granules, fibers, flakes,
spheres, powders,
platelets and other shapes and forms known to persons skilled in the art of
superabsorbent
polymer particles. In some embodiments, the superabsorbent polymer particles
can be in the
shape of fibers, i.e. elongated, acicular superabsorbent polymer particles. In
those
embodiments, the superabsorbent polymer particles fibers have a minor
dimension (i.e.
diameter of the fiber) of less than about 1 mm, usually less than about 500
[tm, and
preferably less than 250 [tm down to 50 [t.m. The length of the fibers is
preferably about 3
mm to about 100 mm. The fibers can also be in the form of a long filament that
can be
woven.
Alternatively, in some preferred embodiments, superabsorbent polymer particles
of
the present invention are spherical-like particles. According to the present
invention and in
contrast to fibers, "spherical-like particles" have a longest and a smallest
dimension with a
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particulate ratio of longest to smallest particle dimension in the range of 1-
5, where a value
of 1 would equate a perfectly spherical particle and 5 would allow for some
deviation from
such a spherical particle. In such embodiments, the superabsorbent polymer
particles may
have a particle size of less than 850 i.tm, or from 50 to 850 i.tm, preferably
from 100 to 500
,tm, more preferably from 150 to 300 ,tm, as measured according to EDANA
method WSP
220.2-05. Superabsorbent polymer particles having a relatively low particle
size help to
increase the surface area of the absorbent material which is in contact with
liquid exudates
and therefore support fast absorption of liquid exudates.
The superabsorbent polymer particles useful in the present invention include a
variety
of water-insoluble, but water-swellable polymers capable of absorbing large
quantities of
fluids. Such polymers materials are generally known in the art.
Suitable superabsorbent polymer particles may for example be obtained from
inverse
phase suspension polymerizations as described in U.S. Pat. No. 4,340,706 and
U.S. Pat. No.
5,849,816 or from spray- or other gas-phase dispersion polymerizations as
described in U.S.
Patent Applications No. 2009/0192035, 2009/0258994 and 2010/0068520. In some
embodiments, suitable superabsorbent polymer particles may be obtained by
current state of
the art production processes as is more particularly described from page 12,
line 23 to page
20, line 27 of WO 2006/083584.
In some embodiments, the surface of the superabsorbent polymer particles may
be
coated. In such embodiments, the coating makes surface sticky so that
superabsorbent
polymer particles cannot rearrange (so they cannot block voids) easily upon
wetting.
In some embodiments, the superabsorbent polymer particles may be coated with a
cationic polymer. Preferred cationic polymers can include polyamine or
polyimine materials
which are reactive with at least one component included in body fluids,
especially in urine.
Preferred polyamine materials are selected from the group consisting of (1)
polymers having
primary amine groups (e.g., polyvinylamine, polyallyl amine); (2) polymers
having
secondary amine groups (e.g., polyethyleneimine); and (3) polymers having
tertiary amine
groups (e.g., poly N, N-dimethylalkyl
amine).
Practical examples of the cationic polymer are, for example,
polyethyleneimine, a modified
polyethyleneimine which is crosslinked by epihalohydrine in a range soluble in
water,
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polyamine, a modified polyamidoamine by graft of ethyleneimine,
polyetheramine,
polyvinylamine, polyalkylamine, polyamidopolyamine, and polyallylamine.
In preferred embodiments, a cationic polymer has a weight-average molecular
weight of at least 500, more preferably 5,000, most preferably 10,000 or more.
Cationic
5 polymers having a weight-average molecular weight of more than 500 or
more are not
limited to polymers showing a single maximum value (a peak) in a molecular
weight analysis
by gel permeation chromatography, and polymers having a weight-average
molecular weight
of 500 or more may be used even if it exhibits a plural maximum value (peaks).
A preferable amount of the cationic polymer is in a range of from about 0.05
to 20
10 parts by weight against 100 parts by weight of the superabsorbent
polymer particle, more
preferably from about 0.3 to 10 parts by weight, and most preferably from
about 0.5 to 5
parts by weight.
In some embodiments, the superabsorbent polymer particles may be coated with
15 chitosan materials such as the one disclosed in US 7 537 832 B2.
In some other embodiments, the superabsorbent polymer particles may comprise
mixed-bed Ion-Exchange absorbent polymers such as the one disclosed in WO
99/34841 and
WO 99/34842.
As already mentioned above, absorbent structures comprising superabsorbent
polymer particles having high SFC and FSR values do not automatically lead to
fast
acquisition times of liquid exudates, especially at the first gush, i.e. when
the dry absorbent
structures come into contact with liquid. Without being bound by theory it is
thought that dry
superabsorbent polymer particles are typically more reluctant to absorb water
than wetted
superabsorbent polymer particles since the diffusivity of water into dry
superabsorbent
polymer particles is lower than the diffusivity of water into wetted
superabsorbent polymer
particles.
Hitherto, absorption properties of dry absorbent structures comprising
superabsorbent
polymer particles related to the initial uptake has not been investigated.
Rather, the focus has
been on Saline Flow Conductivity (SFC) of the superabsorbent polymer
particles, which is
determined at equilibrium and thus at a stage remote from initial liquid
uptake. For absorbent
structures containing a significant amount of airfelt in addition to
superabsorbent polymer
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16
particles, temporary storage of liquid entering the absorbent core is provided
by the airfelt
allowing the superabsorbent polymer particles to absorb liquid from the
surrounding airfelt
with a certain delay. But even for airfelt free absorbent articles disclosed
in the prior art,
permeability of the superabsorbent polymer particles has always been measured
at
equilibrium, thus not taking into account the behaviour of dry superabsorbent
polymer
particles upon initial exposure to liquid. The inventors of the present
invention have carefully
investigated the behaviour of absorbent structures comprising superabsorbent
polymer
particles upon initial exposure to liquid. They have found that certain, not
yet publicly
available absorbent structures comprising superabsorbent polymer particles and
no or very
low amounts of airfelt exhibit superior performance. The superior performance
has lead to
improved liquid acquisition, thus reducing the risk of leakage. It has been
found that superior
absorbent structures comprising superabsorbent polymer particles can be
described in terms
of the time it takes for dry absorbent structures comprising superabsorbent
polymer particles
to reach a certain liquid uptake when absorbing against a confining pressure.
Thereby, it is
now possible to purposefully and easily select these newly developed absorbent
structures,
without the need for additional extensive investigation and testing.
In some embodiments, the absorbent structure comprises superabsorbent polymer
particles having a permeability at equilibrium expressed as UPM (Urine
Permeability
Measurement) value of more than 50, preferably more than 60, or of 50 to 500,
or of 55 to
200, or of 60 to 150 UPM units, where 1 UPM unit is 1 x 10-7 (cm3.$) /g.
The UPM value is measured according to the UPM Test method set out below. This
method is closely related to the SFC test method of the prior art. The UPM
Test method
typically measures the flow resistance of a preswollen layer of superabsorbent
polymer
particles, i.e. the flow resistance is measured at equilibrium. Therefore,
such superabsorbent
polymer particles having a high UPM value exhibit a high permeability when a
significant
volume of the absorbent article is already wetted by the liquid exudates.
Absorbent structures
comprising such superabsorbent polymer particles exhibit good absorption
properties not
only at the first gush but also at the subsequent gushes.
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In some embodiments, the absorbent structure may comprise superabsorbent
polymer
particles having a FSR (Free Swell Rate) of more than 0.1 g/g/s, or of from
0.1 to 2 g/g/s, or
0.3 to 1 g/g/s, or 0.3 to 0.6 g/g/s, or 0.4 to 0.6 g/g/s.
The Free Swell Rate of the superabsorbent polymer particles is measured
according to
the FSR test method set out below. Absorbent structures comprising
superabsorbent polymer
particles having high free swell rate values will be able to absorb liquid
quickly under no
confining pressure. Contrary to the K(t) test method, no external pressure is
applied to the gel
bed in order to measure the free swell rate. Absorbent structures comprising
superabsorbent
polymer particles having a too low FSR value may not require less than 440s to
reach an
uptake of 20 g/g as measured according to the K(t) test method of the present
invention and
will consequently not be able to absorb the liquid exudates as fast as
necessary. However, as
stated above, absorbent structures comprising superabsorbent polymer particles
having a high
FSR value do not automatically lead to high uptake values as measured
according to the K(t)
test method.
In some embodiments, the absorbent structure may comprise superabsorbent
polymer
particles having a CRC (centrifuge retention capacity) value of more than 20
g/g, or more
than 24 g/g, or of from 20 to 50 g/g, or 20 to 40 g/g, or 24 to 30 g/g, as
measured according
to EDANA method WSP 241.2-05. The CRC measures the liquid absorbed by the
superabsorbent polymer particles for free swelling in excess liquid.
Absorbent structures comprising superabsorbent polymer particles having a high
CRC value
are preferred since less superabsorbent polymer particles are needed to
facilitate a required
overall capacity for liquid absorption.
In some embodiments, the absorbent article may have an acquisition time for
the first
gush of less than 30 s, preferably less than 27 s, as measured according to
the Flat
Acquisition test method set out below. This acquisition time is measured on a
baby diaper
which is designated for wearers having a weight in the range of 8 to 13 kg
20% (such as
Pampers Active Fit size 4 or other Pampers baby diapers size 4, Huggies baby
diapers size 4
or baby diapers size 4 of most other tradenames). An absorbent article
comprising an
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absorbent structure which comprises superabsorbent polymer particles and
requires less than
440 s to reach an uptake of 20 g/g as measured according to the K(t) test
method can provide
faster acquisition times, especially at the first gush and thus reduced
leakage, in comparison
with the absorbent articles of the prior art, as shown in the Examples section
of the
application.
Structure of the absorbent core
In the following, an example for an absorbent core of the present invention is
given.
The present invention is however not limited to such absorbent cores.
In some embodiments, the absorbent core 14 comprises an absorbent layer 60, as
illustrated in Fig. 3 and 4. The substrate layer 64 of the absorbent layer 60
may be referred to
as a dusting layer and has a first surface 78 which faces the backsheet 20 of
the diaper 10 and
a second surface 80 which faces the superabsorbent polymer particles 66.
According to some
embodiments, the substrate layer 64 is a non-woven material such as a multi-
layered
nonwoven material having spunbonded layers as outer layers and one or more
meltblown
layers inbetween the spunbond layers, including but not limited to SMS
material, comprising
a spunbonded, a melt-blown and a further spunbonded layer. The absorbent layer
60 may
include a cover layer 70 as illustrated in Fig. 4. The cover layer 70 may be a
non-woven
material such as a multi-layered nonwoven material having spunbonded layers as
outer layers
and one or more meltblown layers inbetween the spunbond layers, including but
not limited
to SMS material, comprising a spunbonded, a melt-blown and a further
spunbonded layer. In
some embodiments, the substrate layer 64 and the cover layer 70 are made of
the same
material.
As illustrated in Fig. 3 and 4, the superabsorbent polymer particles 66 can be
deposited on the substrate layer 64 in clusters 90 of particles comprising
land areas 94 and
junction areas 96 between the land areas 94. As defined herein, land areas 94
are areas where
the thermoplastic adhesive material does not contact the nonwoven substrate or
the auxiliary
adhesive directly; junction areas 96 are areas where the thermoplastic
adhesive material does
contact the nonwoven substrate or the auxiliary adhesive directly. The
junction areas 96
contain little or no superabsorbent polymer particles 66. The land areas 94
and junction areas
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96 can have a variety of shapes including, but not limited to, circular, oval,
square,
rectangular, triangular, and the like.
Thereby, the thermoplastic adhesive material 68 provides cavities to hold the
superabsorbent polymer particles 66, and thereby immobilizes this material. In
a further
aspect, the thermoplastic adhesive material 68 bonds to the substrate layer 64
and thus affixes
the superabsorbent polymer particles 66 to the substrate layer 64. In some
other
embodiments, the thermoplastic adhesive material 68 will also penetrate at
least partly into
both the superabsorbent polymer particles 66 and the substrate layer 64, thus
providing for
further immobilization and affixation.
In some other embodiments, the absorbent core 14 may comprise two absorbent
layers, a first
absorbent layer 60 and a second absorbent layer 62. As best illustrated in
Fig. 5A and 5B,
the first absorbent layer 60 of the absorbent core 14 comprises a substrate
layer 64,
superabsorbent polymer particles 66 on the substrate layer 64, and a
thermoplastic adhesive
material 68 on the superabsorbent polymer particles 66. Although not
illustrated, the first
absorbent layer 60 may also include a cover layer such as the cover layer 70
illustrated in
Fig. 4.
Likewise, as best illustrated in Fig. 5A and 5B, the second absorbent layer 62
of the
absorbent core 14 may also include a substrate layer 72, superabsorbent
polymer particles 74
on the second substrate layer 72, and a thermoplastic adhesive material 76 on
the
superabsorbent polymer particles 74. Although not illustrated, the second
absorbent layer 62
may also include a cover layer such as the cover layer 70 illustrated in Fig.
4. As mentioned
above, the substrate layer 64 of the first absorbent layer 60 may be referred
to as a dusting
layer and has a first surface 78 which faces the backsheet 20 of the diaper 10
and a second
surface 80 which faces the superabsorbent polymer particles 66. Likewise, the
substrate
layer 72 of the second absorbent layer 62 may be referred to as a core cover
and has a first
surface 82 facing the topsheet 18 of the diaper 10 and a second surface 84
facing the
superabsorbent polymer particles 74. The first and second substrate layers 64
and 72 may be
adhered to one another with adhesive about the periphery to form an envelope
about the
superabsorbent polymer particles 66 and 74 to hold the superabsorbent polymer
particles 66
and 74 within the absorbent core 14.
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The area of the absorbent core 14 which comprises superabsorbent polymer
particles
may vary depending on the desired application of the absorbent core 14 and the
particular
absorbent article 10 in which it may be incorporated. In some embodiments,
however, the
superabsorbent polymer particles area extends substantially entirely across
the absorbent core
5 14. In some alternative embodiments, the superabsorbent polymer particles
area extends
entirely across the absorbent core 14 in the crotch portion 34 of the
absorbent article 10 while
the superabsorbent polymer particles area does not extend entirely across the
absorbent core
14 in the front and in the back portions of the absorbent article 10.
The first and second absorbent layers 60 and 62 may be combined together to
form
10 the absorbent core 14 such that the layers may be offset such that the
superabsorbent polymer
particles 66 on the substrate layer 64 and the superabsorbent polymer
particles 74 on the
substrate layer 72 are substantially continuously distributed across the
superabsorbent
polymer particles area, as illustrated in Fig. 5A and 5B. In some embodiments,
superabsorbent polymer particles 66 and 74 are substantially continuously
distributed across
15 the superabsorbent polymer particles area despite superabsorbent polymer
particles 66 and 74
discontinuously distributed across the first and second substrate layers 64
and 72 in clusters
90. In some embodiments, the absorbent layers may be offset such that the land
areas 94 of
the first absorbent layer 60 face the junction areas 96 of the second
absorbent layer 62 and
the land areas of the second absorbent layer 62 face the junction areas 96 of
the first
20 absorbent layer 60, as illustrated in Fig. 5A and 5B. When the land
areas 94 and junction
areas 96 are appropriately sized and arranged, the resulting combination of
superabsorbent
polymer particles 66 and 74 is a substantially continuous layer of
superabsorbent polymer
particles across the superabsorbent polymer particles area of the absorbent
core 14 (i.e. first
and second substrate layers 64 and 72 do not form a plurality of pockets, each
containing a
cluster 90 of superabsorbent polymer particles 66 and 74 therebetween), as
shown on Figure
5A.
The amount of superabsorbent polymer particles may or not vary along the
length of
the core, typically the core being profiled in its longitudinal direction. It
has been found that,
for most absorbent articles such as diapers, the liquid discharge occurs
predominately in the
front half of the diaper. The front half of the absorbent core 14 should
therefore comprise
most of the absorbent capacity of the core. Thus, according to certain
embodiments, the front
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21
half of said absorbent core 14 may comprise more than about 60% of the
superabsorbent
polymer particles, or more than about 65%, 70%, 75%, 80%, 85%, or 90% of the
superabsorbent polymer particles.
Typically the thermoplastic adhesive material may serve to at least partially
immobilize the superabsorbent polymer particles both in dry and wet state. The
thermoplastic
adhesive material can be disposed essentially uniformly between the
superabsorbent polymer
particles. However, typically the thermoplastic adhesive material may be
provided as a
fibrous layer which is at least partially in contact with the superabsorbent
polymer particles
and partially in contact with the substrate layer(s). Typically, the
thermoplastic adhesive
material of the present invention forms a fibrous network over the
superabsorbent polymer
particles. Typically as for example illustrated in Figures 5A and 5B, the
superabsorbent
polymer particles 66 and 74 are provided as a discontinuous layer, and a layer
of fibrous
thermoplastic adhesive material 68 and 76 is laid down onto the layer of
superabsorbent
polymer particles 66 and 74, such that the thermoplastic adhesive material 68
and 76 is in
direct contact with the superabsorbent polymer particles 66 and 74, but also
in direct contact
with the second surfaces 80 and 84 of the substrate layers 64 and 72, where
the substrate
layers are not covered by the superabsorbent polymer particles 66 and 74. This
imparts an
essentially three-dimensional structure to the fibrous layer of thermoplastic
adhesive material
68 and 76, which in itself is essentially a two-dimensional structure of
relatively small
thickness, as compared to the dimension in length and width directions. In
other words, the
thermoplastic adhesive material 68 and 76 undulates between the superabsorbent
polymer
particles 68 and 76 and the second surfaces of the substrate layers 64 and 72.
The thermoplastic adhesive material may provide cavities to enlace the
superabsorbent polymer particles, and thereby immobilizes these particles. In
a further
aspect, the thermoplastic adhesive material bonds to the substrate layer(s)
and thus affixes the
superabsorbent polymer particles to the substrate layer(s). Some thermoplastic
adhesive
materials will also penetrate into both the superabsorbent polymer particles
and the substrate
layer(s), thus providing for further immobilization and affixation. Of course,
while the
thermoplastic adhesive materials disclosed herein provide an improved wet
immobilization
(i.e., immobilization of absorbent material when the article is at least
partially loaded), these
thermoplastic adhesive materials may also provide a very good immobilization
of absorbent
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22
material when the absorbent core is dry. The thermoplastic adhesive material
may also be
referred to as a hot melt adhesive.
Without wishing to be bound by theory, it has been found that those
thermoplastic
adhesive materials which are most useful for immobilizing the superabsorbent
polymer
particles combine good cohesion and good adhesion behavior. Good adhesion may
promote
good contact between the thermoplastic adhesive material and the
superabsorbent polymer
particles and the substrate layer(s). Good cohesion reduces the likelihood
that the adhesive
breaks, in particular in response to external forces, and namely in response
to strain. When
the absorbent core absorbs liquid, the superabsorbent polymer particles swell
and subject the
thermoplastic adhesive material to external forces. The thermoplastic adhesive
material may
allow for such swelling, without breaking and without imparting too many
compressive
forces, which would restrain the superabsorbent polymer particles from
swelling.
The thermoplastic adhesive material may comprise, in its entirety, a single
thermoplastic polymer or a blend of thermoplastic polymers, having a softening
point, as
determined by the ASTM Method D-36-95 "Ring and Ball", in the range between 50
C and
300 C, or alternatively the thermoplastic adhesive material may be a hot melt
adhesive
comprising at least one thermoplastic polymer in combination with other
thermoplastic
diluents such as tackifying resins, plasticizers and additives such as
antioxidants. In some
embodiments, the thermoplastic polymer has typically a molecular weight (Mw)
of more
than 10,000 and a glass transition temperature (Tg) usually below room
temperature or -6 C
< Tg < 16 C. In some embodiments, typical concentrations of the polymer in a
hot melt are
in the range of about 20 to about 40% by weight. In some embodiments,
thermoplastic
polymers may be water insensitive. Exemplary polymers are (styrenic) block
copolymers
including A-B-A triblock structures, A-B diblock structures and (A-B)n radial
block
copolymer structures wherein the A blocks are non-elastomeric polymer blocks,
typically
comprising polystyrene, and the B blocks are unsaturated conjugated diene or
(partly)
hydrogenated versions of such. The B block is typically isoprene, butadiene,
ethylene/butylene (hydrogenated butadiene), ethylene/propylene (hydrogenated
isoprene), or
a mixture thereof.
Other suitable thermoplastic polymers that may be employed are metallocene
polyolefins, which are ethylene polymers prepared using single-site or
metallocene catalysts.
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Therein, at least one comonomer can be polymerized with ethylene to make a
copolymer,
terpolymer or higher order polymer. Also applicable are amorphous polyolefins
or
amorphous polyalphaolefins (APAO) which are homopolymers, copolymers or
terpolymers
of C2 to C8 alpha olefins.
In some embodiments, the thermoplastic adhesive material is present in the
form of
fibers. In some of these embodiments, the fibers will have an average
thickness of about 1 to
about 50 micrometers or about 1 to about 35 micrometers and an average length
of about 5
mm to about 50 mm or about 5mm to about 30 mm. To improve the adhesion of the
thermoplastic adhesive material to the substrate layer(s) or to any other
layer, in particular
any other non-woven layer, such layers may be pre-treated with an auxiliary
adhesive.
In certain embodiments the thermoplastic adhesive material is applied on the
substrate layer at an amount of between 0.5 and 30 g/m2, between 1 to 15 g/m2,
between 1
and 10 g/m2 or even between 1.5 and 5 g/m2 per substrate layer.
An exemplary thermoplastic adhesive material 68 and 76 may have a storage
modulus
G' measured at 20 C of at least 30,000 Pa and less than 300,000 Pa, or less
than 200,000 Pa,
or between 140,000 Pa and 200,000 Pa, or less than 100,000 Pa. In a further
aspect, the
storage modulus G' measured at 35 C may be greater than 80,000 Pa. In a
further aspect, the
storage modulus G' measured at 60 C may be less than 300,000 Pa and more than
18,000 Pa,
or more than 24,000 Pa, or more than 30,000Pa, or more than 90,000 Pa. In a
further aspect,
the storage modulus G' measured at 90 C may be less than 200,000 Pa and more
than 10,000
Pa, or more than 20,000 Pa, or more then 30,000Pa. The storage modulus
measured at 60 C
and 90 C may be a measure for the form stability of the thermoplastic adhesive
material at
elevated ambient temperatures. This value is particularly important if the
absorbent product
is used in a hot climate where the thermoplastic adhesive material would lose
its integrity if
the storage modulus G' at 60 C and 90 C is not sufficiently high.
G' is measured using a rheometer as schematically illustrated in Fig. 6 for
the purpose
of general illustration only. The rheometer 627 is capable of applying a shear
stress to the
adhesive and measuring the resulting strain (shear deformation) response at
constant
temperature. The adhesive is placed between a Peltier-element acting as lower,
fixed plate
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628 and an upper plate 629 with a radius R of 10 mm, which is connected to the
drive shaft
of a motor to generate the shear stress. The gap between both plates has a
height H of 1500
micron. The Peltier-element enables temperature control of the material (+0.5
C). The strain
amplitude is set at 0.05%, the strain frequency at 1Hz and the cooling rate at
2 C/min (with
start temperature at 150 C or higher and end temperature at -5 C). .
The absorbent core may also comprise an auxiliary adhesive which is not
illustrated
in the figures. The auxiliary adhesive may be deposited on the substrate
layer(s) before
application of the superabsorbent polymer particles on the substrate layer(s)
for enhancing
adhesion of the superabsorbent polymer particles and the thermoplastic
adhesive material to
the respective substrate layer. The auxiliary adhesive may also aid in
immobilizing the
superabsorbent polymer particles and may comprise the same thermoplastic
adhesive
material as described hereinabove or may also comprise other adhesives
including but not
limited to sprayable hot melt adhesives. An example of commercially available
auxiliary
adhesive is H.B. Fuller Co. (St. Paul, MN) Product No. HL-1620-B. The
auxiliary adhesive
may be applied to the substrate layer(s) by any suitable means, but according
to some
embodiments, may be applied in about 0.5 to about lmm wide slots spaced about
0.5 to
about 2 mm apart.
The topsheet
The absorbent article 10 may comprise a topsheet 18 which may be liquid
pervious.
The topsheet 18 may be manufactured from a wide range of materials such as
woven and
nonwoven materials; polymeric materials such as apertured formed thermoplastic
films,
apertured plastic films, and hydroformed thermoplastic films; porous foams;
reticulated
foams; reticulated thermoplastic films; and thermoplastic scrims. Suitable
woven and
nonwoven materials can be included of natural fibers (e.g., wood or cotton
fibers), synthetic
fibers (e.g., polymeric fibers such as polyester, polypropylene, or
polyethylene fibers) or
from a combination of natural and synthetic fibers.
In some embodiments, the topsheet 18 may be made of a hydrophobic material to
isolate the wearer's skin from liquids which have passed through the topsheet
18. In such
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embodiments, at least a part of the upper surface of the topsheet 18 is
treated to be
hydrophilic so that liquids will transfer through the topsheet 18 more
rapidly. This diminishes
the likelihood that body exudates will flow off the topsheet 18 rather than
being drawn
through the topsheet 18 and being absorbed by the absorbent core. The topsheet
18 can be
5 rendered hydrophilic by treating it with a surfactant. Suitable methods
for treating the
topsheet 18 with a surfactant include spraying the topsheet material with the
surfactant and
immersing the material into the surfactant.
In some embodiments, the topsheet includes an apertured formed film. Apertured
10 formed films are are pervious to body exudates and yet non-absorbent and
have a reduced
tendency to allow liquids to pass back through and rewet the wearer's skin.
Thus, the surface
of the formed film which is in contact with the body remains dry, thereby
reducing body
soiling and creating a more comfortable feel for the wearer. Suitable formed
films are
described in U.S. Pat. No. 3,929,135, entitled "Absorptive Structures Having
Tapered
15 Capillaries", issued to Thompson on Dec. 30, 1975; U.S. Pat. No.
4,324,246 entitled
"Disposable Absorbent Article Having A Stain Resistant Topsheet", issued to
Mullane, et al.
on Apr. 13, 1982; U.S. Pat. No. 4,342,314 entitled "Resilient Plastic Web
Exhibiting Fiber-
Like Properties", issued to Radel, et al. on Aug. 3, 1982; U.S. Pat. No.
4,463,045 entitled
"Macroscopically Expanded Three-Dimensional Plastic Web Exhibiting Non-Glossy
Visible
20 Surface and Cloth-Like Tactile Impression", issued to Ahr, et al. on
Jul. 31, 1984; and U.S.
Pat. No. 5,006,394 "Multilayer Polymeric Film" issued to Baird on Apr. 9,
1991.
Alternatively, the topsheet includes apertured nonwoven materials. Suitable
apertured
nonwoven materials are described in U.S. Pat. No. 5,342,338 and in PCT
Application No.
WO 93/19715.
The backsheet
The absorbent article may comprise a backsheet 20 which may be attached to the
topsheet. The backsheet may prevent the exudates absorbed by the absorbent
core and
contained within the diaper from soiling other external articles that may
contact the diaper,
such as bed sheets and undergarments. In some embodiments, the backsheet may
be
substantially impervious to liquids (e.g., urine) and comprise a laminate of a
nonwoven and a
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thin plastic film such as a thermoplastic film having a thickness of about
0.012 mm (0.5 mil)
to about 0.051 mm (2.0 mils). Suitable backsheet films include those
manufactured by
Tredegar Industries Inc. of Terre Haute, Ind. and sold under the trade names
X15306,
X10962, and X10964. Other suitable backsheet materials may include breathable
materials
that permit vapors to escape from the diaper while still preventing liquid
exudates from
passing through the backsheet. Exemplary breathable materials may include
materials such as
woven webs, nonwoven webs, composite materials such as film-coated nonwoven
webs, and
microporous films such as manufactured by Mitsui Toatsu Co., of Japan under
the
designation ESPOIR NO and by EXXON Chemical Co., of Bay City, Tex., under the
designation EXXAIRE. Suitable breathable composite materials comprising
polymer blends
are available from Clopay Corporation, Cincinnati, Ohio under the name HYTREL
blend
P18-3097. Such breathable composite materials are described in greater detail
in PCT
Application No. WO 95/16746, published on Jun. 22, 1995 in the name of E. I.
DuPont.
Other breathable backsheets including nonwoven webs and apertured formed films
are
described in U.S. Pat. No. 5,571,096 issued to Dobrin et al. on Nov. 5, 1996.
TEST METHODS
= K(t) Test Method (Dynamic Effective Permeability and Uptake Kinetics
Measurement Test method)
This method determines the time dependent effective permeability (K(t)) and
the uptake
kinetics of an absorbent structure containing superabsorbent polymer particles
under a
confining pressure. The objective of this method is to assess the ability of
the absorbent
structure containing superabsorbent polymer particles to acquire and
distribute body fluids
when the polymer is present at high concentrations in an absorbent article and
exposed to
mechanical pressures as they typically occur during use of the absorbent
article. Darcy's law
and steady-state flow methods are used to calculate effective permeability
(see below). (See
also for example, "Absorbency," ed. by P.K. Chatterjee, Elsevier, 1982, Pages
42-43 and
"Chemical Engineering Vol. II, Third Edition, J.M. Coulson and J.F.
Richardson, Pergamon
Press, 1978, Pages 122-127.)
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In contrast to previously published methods, the sample is not preswollen
therefore the
hydrogel is not formed by preswelling hydrogel-forming superabsorbent polymer
particles in
synthetic urine, but the measurement is started with a dry structure.
The equipment used for this method is called `Zeitabhangiger
Durchlassigkeitspriifstand' or
'Time Dependent Permeability Tester', Equipment No. 03-080578 and is
commercially
available at BRAUN GmbH, Frankfurter Str. 145, 61476 Kronberg, Germany and is
described below. Upon request, operating instructions, wiring diagrams and
detailed
technical drawings are also available.
Dynamic Effective Permeability and Uptake Kinetic Measurement System
Fig. 7 shows the dynamic effective permeability and uptake kinetic measurement
system, called 'Time Dependent Permeability Tester' herein.
The equipment consists of the following main parts:
- M11 Digital Laser Sensor for caliper measurement 701 (MEL Mikroelektronik
GmbH, 85386 Eching, Germany
- Fiber for Liquid Level Detection 702 (FU95, Keyence Corp., Japan)
- Digital Fiber Sensor 703 (FS-N10, Keyence Corp., Japan)
- Precision Balance 704 (XP6002MDR, Mettler Toledo AG, 8606 Greifensee,
Switzerland)
- Power Unit Logo!Power (C98130-A7560-A1-5-7519, Siemens AG)
- Labview Software License 706 (National Instruments, Austin, Tx, USA)
- Receiving Vessel 707 (5L Glass Beaker, Roth)
- Reservoir 708 (5L Glass bottle, VWR) with joint 709 and open-end tube for
air
admittance 723
- Operating unit and console 705(Conrad Electronics)
- Computerized data acquisition system 710
- A piston/cylinder assembly 713 as described herein
- A controlled valve 714 (Biirkert)
Fig. 8 shows the piston/cylinder assembly 713 comprising piston guiding lid
801, piston 802
and cylinder 803. The cylinder 803 is made of transparent polycarbonate (e.g.,
Lexani0) and
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has an inner diameter p of 6.00 cm (area=28.27 cm2). The inner cylinder walls
850 are
smooth; the height of the cylinder r is about 7.50 cm. The bottom 804 of the
cylinder 803 is
faced with a US. Standard 400 mesh stainless-steel screen cloth (not shown)
(e.g. from
Weisse and Eschrich) that is bi-axially stretched to tautness prior to
attachment to the bottom
804 of the cylinder 803. The piston 802 is composed of a stainless steel
piston body 805 and
a stainless steel head 806. The piston head 806 diameter q is slightly less
than 6 cm so as to
slide freely into the cylinder 803 without leaving any gap for the hydrogel-
forming particle to
pass trough. The piston body 805 is firmly attached perpendicularly at the
center of the piston
head 806. The piston body diameter t is about 2.2 cm. The piston body 805 is
then inserted
into a piston guiding lid 801. The guiding lid 801 has a POM
(Polyoxymethylene) ring 809
with a diameter allowing a free sliding of the piston 802 yet keeping the
piston body 805
perfectly vertical and parallel to the cylinder walls 850 once the piston 802
with the guiding
lid 801 are positioned on top of the cylinder 803. The top view of the piston
head 806 is
shown in Fig. 9. The piston head 806 is meant to apply the pressure
homogeneously to the
sample 718. It is also highly permeable to the hydrophilic liquid so as to not
limit the liquid
flow during measurement. The piston head 806 is composed of a US. standard 400
mesh
stainless steel screen cloth 903 (e.g. from Weisse and Eschrich) that is bi-
axially stretched to
tautness and secured at the piston head stainless steel outer ring 901. The
entire bottom
surface of the piston is flat. Structural integrity and resistance to bending
of the mesh screen
is then ensured by the stainless steel radial spokes 902. The height of the
piston body 805 is
selected such that the weight of the piston 802 composed of the piston body
805 and the
piston head 806 is 596 g ( 6g), this corresponds to 0.30 psi over the area of
the cylinder 803.
The piston guiding lid 801 is a flat circle of stainless steel with a diameter
s of about 7.5 cm
held perpendicular to the piston body 805 by the POM ring 809 in its center.
There are two
inlets in the guiding lid (810 and 812).
The first inlet 812, allows the Fiber for Liquid Level Detection 702 to be
positioned exactly 5
cm above the top surface of the screen (not shown) attached to the bottom
(804) of the
cylinder 803 once the piston 802 is assembled with the cylinder 803 for the
measurement.
The second inlet 810 allows connecting a liquid tube 721 providing the liquid
to the
experiment.
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To make sure that the assembly of the piston 802 with the cylinder 803 is done
consistently a
slit 814 is made on the cylinder 803 matching a position marker 813 in the
guiding lid 801. In
this way the rotation angle of the cylinder and the guiding lid is always the
same.
Prior to every use, the stainless steel screen cloth 903 of the piston head
806 and cylinder 803
should be inspected for clogging, holes or over-stretching and replaced when
necessary. A
K(t) apparatus with damaged screen can deliver erroneous K(t) and uptake
kinetic results,
and must not be used until the screen has been replaced.
A 5 cm mark 808 is scribed on the cylinder at a height k of 5.00 cm ( 0.02 cm)
above the top
surface of the screen attached to the bottom 804 of the cylinder 803. This
marks the fluid
level to be maintained during the analysis. The Fiber for Liquid Level
Detection 702 is
positioned exactly at the 5 cm mark 808. Maintenance of correct and constant
fluid level
(hydrostatic pressure) is critical for measurement accuracy
A reservoir 708 connected via tubing to the piston/cylinder assembly 713
holding the sample
and a controller valve 714 are used to deliver salt solution to the cylinder
803 and to maintain
the level of salt solution at a height k of 5.00 cm above the top surface of
screen attached to
the bottom of the cylinder 804. The valve 714, the Fiber for Liquid Level
Detection 702 and
the Digital Fiber Sensor 703 are connected to the computerized acquisition
system 710
trough the operating unit 705. This allows the Dynamic Effective Permeability
and Uptake
Kinetic Measurement System to use the information from the Fiber for Liquid
Level
Detection 702 and the Digital Fiber Sensor 703 to control the valve 714 and
ultimately
maintain the level of the liquid at the 5 cm mark 808.
The reservoir 708 is placed above the piston/cylinder assembly 713 in such a
manner as to
allow a 5 cm hydrohead to be formed within 15 seconds of initiating the test,
and to be
maintained in the cylinder throughout the test procedure. The piston/cylinder
assembly 713 is
positioned on the support ring 717 of the cover plate 716 and the first inlet
812 is held in
place with the docking support 719. This allows only one position of the
guiding lid 801.
Furthermore, due to the position marker 813, there is also only one position
for the cylinder
803. The screen attached to the bottom of the cylinder 804 must be perfectly
level and
horizontal. The supporting ring 717 needs to have an internal diameter small
enough, so to
firmly support cylinder 803 but larger than 6.0 cm so to lay outside of the
internal diameter
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of the cylinder once the cylinder is positioned on the supporting ring 717.
This is important
so to avoid any interference of the supporting ring 717 with the liquid flow.
The salt solution, applied to the sample 718 with a constant hydrohead of 5 cm
can now
freely flow from the piston/cylinder assembly 713 into a receiving vessel 707
positioned on
5 the balance 704 which is accurate within 0.01 g. The digital output of
the balance is
connected to a computerized data acquisition system.
The caliper (thickness) of the sample is constantly measured with a Digital
Laser
Sensor for caliper measurement 701. The laser beam 720 of the digital laser
sensor 701 is
directed at the center of the POM cover plate 811 of the piston body. The
accurate
10 positioning of all the parts of the piston/cylinder assembly 713 allows
the piston body 805 to
be perfectly parallel to the laser beam 720 and as a result an accurate
measure of the
thickness is obtained.
Test Preparation
15 The reservoir 708 is filled with test solution. The test solution is an
aqueous solution
containing 9.00 grams of sodium chloride and 1.00 grams of surfactant per
liter of solution.
The preparation of the test solution is described below. The receiving vessel
707 is placed on
the balance 704 which is connected to a computerized data acquisition system
710. Before
the start of the measurement the balance is reset to zero.
Preparation of test liquid:
Chemicals needed:
- Sodium Chloride (CAS#7647-14-5, eg: Merck, cat# 1.06404.1000)
- Linear C12-C14 alcohol ethoxylate (CAS#68439-50-9, eg. Lorodac , Sasol,
Italy)
- Deionized H20
Ten liters of a solution containing 9.00 grams per litre of NaC1 and 1.00
grams per liter linear
C12-C14 alcohol ethoxalate in distilled water is prepared and equilibrated at
23 C 1 C for
1 hour. The surface tension is measured on 3 individual aliquots and should be
28 0.5
mN/m. If the surface tension of the solution is different from 28 0.5 mN/m,
the solution is
discarded and a new test solution is prepared. The test solution has to be
used within 36 hours
from its preparation and is considered expired afterwards.
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K(t) Sample preparation
A representative, circular portion of the absorbent structure of 6.00 cm
diameter is
obtained. The portion of the absorbent article can be obtained with a suitable
circular die and
a hydraulic press cutter (like e.g. Electro-Hydraulic Alfa Cutter 240-10
available at Thwing-
Albert instrument company, 14 W. Collings Ave.West Berlin, NJ 08091).
The circular sample 118 is carefully positioned flat on the screen (not shown)
attached to the bottom 204 of the cylinder 203 occupying all the available
surface on the
screen. It is important to position the circular sample 118 in a way that the
side in direct
contact with the screen is the one that in use is usually more distant from
the liquid source so
as to reproduce the common flow direction in use. For example for samples
related to
absorbent articles such as diapers, the side usually facing the wearer should
be positioned on
top while the side facing the garments should be positioned in contact with
the screen at the
bottom of the cylinder. A careful positioning of the sample is critical for
the measurement's
accuracy. In case the dimension of the absorbent structure is small and a 6.0
cm diameter
sample cannot be obtained from it, it is possible to join two absorbent
structures of equal size
so to obtain the minimum sample size necessary. The two samples need to be
taken in the
same position from two identical absorbent structures. The two absorbent
structures should
be joined through a straight edge and if necessary cut to obtain such a
straight edge. The
intent is that the joined edges recreate a flat homogeneous layer with no or
only a minimal
gap. This joint layer is then handled according to the standard sample
preparation described
above with the additional precaution to center the join line in the cutting
die so to obtain two
half circles of identical shape. It is important that both the half circles
are carefully positioned
inside the sample holder so to recreate a full circle and occupying the entire
available surface
on the screen with no or only a minimal gap. Both the halves have to be
positioned with the
side facing the screen as explained above. However, in most embodiments, the
sample will
consist of a unitary circular portion of the absorbent structure.
Method for Extracting an absorbent structure from an absorbent article
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The absorbent article is positioned on a flat surface. In case the product
contains features
that prevent it to lay flat (such as the cuff elastics) they are cut at
suitable intervals to allow
the product to lay flat.
Portion(s) of the absorbent structure comprising at least 90% by weight of
superabsorbent
polymer particles to be tested according to the K(t) Test Method are first
identified and
should be isolated as explained hereinbelow.
All materials which are not part of the absorbent structure are removed from
the
absorbent structure paying attention to not unduly damage the absorbent
structure.
If the materials to be removed are attached to the absorbent structure for
example by
adhesive material such as thermoplastic adhesive material, to avoid damages to
the structure,
they could be removed with the aid of Cold sprays with a cooling temperature
from -50 to -
60 C (such as "IT Icer"or "PRF 101 cold spray" available at Taerosol,
Kangasala Finland)
as shown for example in Fig. 15.
Fig. 15 shows an absorbent structure 151 comprising superabsorbent polymer
polymer
particles 152 which are sandwiched between two substrate layers 153, 154. A
layer of
material 156 is attached to one of the substrate layers 153, 154 and is
therefore not part of the
absorbent structure 151. This layer needs to be removed from the absorbent
structure 151. To
avoid undue damage to the absorbent structure 151 the layer of material 156 to
be removed
from the absorbent structure 151 is pulled off the absorbent structure 151 in
a 180 peel
geometry while the adhesive material 155 is cooled with the Cold spray 157.
The spraying
should last at least 1 seconds but no more than 5 seconds for each single
portion of the layer
of material 156.
After removal of each material, the remaining part of the absorbent structure
is kept
under 0.3 psi pressure until the temperature is back to the initial value
(TAPPI lab condition).
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The upper layer and/or the lower layer of the absorbent structure may be
properly
perforated to allow liquid flow through as shown for example in Fig. 16
representing an
absorbent structure 161 comprising superabsorbent polymer particles 162 which
are
sandwiched between two substrate layers 163, 164. The perforation is performed
using a hot
metal tip also called perforating tip 165 which comprises a steel rod 166 with
a diameter H of
0.7 0.2 mm. A standard paper clip, bend around a solder tip 167 such as CT
60/621
available at ERSA GmbH, Wertheim, Germany can be used for the purpose. The
perforating
tip 165 should be set at the temperature of 310 20 C. The perforating tip
165 is positioned
in contact with the layers to be perforated for a short period of time with
low pressure so to
perforate the layers, for example by melting without affecting any of the
other materials of
the absorbent structure 161. The holes are created with the same procedure in
a regular
square perforation pattern with a hole edge to edge distance D of 1 0.2 mm,
as shown for
example in Fig. 17.
Each absorbent structure is visually checked for integrity and discarded if
damaged with
the help of a back light. Examples of damages are for examples: cuts, holes,
wrinkles which
were not present before removing the absorbent structure from the absorbent
article. The
perforations in the layers done with the perforating tip, are not considered
damages unless
they affect other layers. The substantial migration of superabsorbent polymer
particles and
fibers within the absorbent structure is also considered damage.
The absorbent structures prepared as such are then cut according the K(t) test
method
K(t) Procedure
The measurement is carried out at Tappi lab conditions: 23 C 1 C/50% RH 2%.
The empty piston/cylinder assembly 713 is mounted in the circular opening in
the cover
plate 716 and is supported around its lower perimeter by the supporting ring
717. The
piston/cylinder assembly 713 is held in place with the docking support 719
with the cylinder
803 and piston 802 aligned at the proper angle. The reference caliper reading
(r,) is
measured by Digital Laser sensor. After this, the empty piston/cylinder
assembly 713 is
removed from the cover plate 716 and supporting ring 717 and the piston 802 is
removed
from the cylinder 803.
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The sample 718 is positioned (absorbent structure) on the cylinder screen as
explained
above. After this, the piston 802 assembled with the guiding lid 801 is
carefully set into the
cylinder 803 by matching the position marker 813 of the guiding lid 801 with
the slit 814
made in the cylinder 803
The piston/cylinder assembly is held in place with the docking support 719
with the
cylinder and piston aligned at the proper angle
This can be only done in one way. The liquid tube 721 connected to the
reservoir 708 and
the Digital Fiber Sensor 703 are inserted into the piston/cylinder assembly
713 via the two
inlets 810 and 812 in the guiding lid 801.
The computerized data acquisition system 710 is connected to the balance 704
and to the
digital laser sensor for caliper measurement 701. Fluid flow from the
reservoir 708 to the
cylinder 803 is initiated by the computer program by opening valve 714. The
cylinder is
filled until the 5 cm mark 808 is reached in 5 to 15 seconds, after which the
computer
program regulates the flow rate to maintain a constant 5 cm hydrohead. The
quantity of
solution passing through the sample 718 is measured by the balance 704 and the
caliper
increase is measured by the laser caliper gauge. Data acquisition is started
when the fluid
flow is initiated specifically when the valve 714 is opened for the first
time, and continues for
21 minutes or until the reservoir runs dry so that the 5 cm hyrdrohead is no
longer
maintained. The duration of one measurement is 21 min, laser caliper and
balance readings
are recorded regularly with an interval that may vary according to the
measurement scope
from 2 to lOsec, and 3 replicates are measured.
After 21 min, the measurement of the 1st replicate is successfully completed
and the
controlled valve 714 closes automatically. The piston/cylinder assembly 713 is
removed and
the measurements of the 2nd and 3rd replicates are done accordingly, always
following the
same procedure. At the end of the measurement of the 3rd replicate, the
controlled valve 714
stops the flow of liquid and stopcock 722 of the reservoir 708 is closed. The
collected raw
data is stored in the form of a simple data table, which then can be imported
easily to a
program for further analysis e.g. Excel 2003, SP3.
In the data table the following relevant information is reported for each
reading:
= Time from the beginning of the experiment
= Weight of the liquid collected by the receiving vessel 707 on the balance
704
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= Caliper of the sample 718
The data from 30 seconds to the end of the experiment are used in the K(t) and
uptake
kinetics calculation. The data collected in the first 30 seconds are not
included in the
calculation. The effective permeability K(t) and the uptake kinetics of the
absorbent structure
5 are then determined using the equation sets below.
Used equations:
The table below describes the notation used in the equations.
A x-section of the absorbent structure sample which corresponds to the
cylinder inner radius: 28.27 cm2
height of water column, 5.0 cm
Ap driving pressure applied by the 5.00cm hydrohead (h) : 4929.31 g / (cm
s2)
gravity constant: 981 cm/ s2 _______________________________________________
11 Temperature dependent effective viscosity of the liquid in g/(cm s)
Temperature in C
density of the liquid: 1.0053 g/cm3
A ________________________________________________________________
ps Apparent sample density of the porous medium or powder in g/cm3
Ps Average density of the solid part of the dry sample in g/cm3
Ps k Density of the component k of the dry sample in g/cm3
dry mass of the sample in g: 2.00 g if measuring superabsorbent particles
mk Mass of the component k of the dry sample in g
Vs Dry sample volume in cm3
time at step i of N discrete points in s
caliper of the absorbent structure sample at time t1 in cm
reading of caliper instrument at time tin cm
r, reference reading of caliper instrument (reading of the
piston/cylinder
assembly without sample) in cm
mouti balance reading at time ti; mass of the liquid that left the sample
at time t1 in
Sample uptake at time Lin g
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T20 time required to reach an uptake of 20 g/g, starting at 0 s
(to) in s
U20 Sample uptake after 20 minutes in g/g
T80% Time required to reach an uptake of 80% of U20 starting at 0 s
(to) in s
K20 Sample permeability at 20 minutes in m2
Kmin the minimum value of the permeability during the experiment in
m2
Kmin/K20 the ratio of Kmin and K20
The driving pressure is calculated from the hydro head as follows:
Ap = h = G = p = 4929.31 g/(cm = s 2 )
The caliper at each time t, is calculated as the difference of the caliper
sensor reading at
time t, and the reference reading without sample:
d1 = ¨ r, [cm]
For superabsorbent particles samples the caliper of the sample at time t,=0
(do) is used to
evaluate the quality of the particle sprinkling.
An apparent sample density inside the cylinder can be in fact calculated as:
A ______________________________________
Ps = d= A [g/cm31
o
If this apparent density inside the cylinder differs from the apparent density
of the powder
by more than 40% the measurement has to be considered invalid and
eliminated.
The apparent density can be measured according EDANA method 406.2 ¨ 02
("Superabsorbent materials - Polyacrylate superabsorbent powders - GRAVIMETRIC
DETERMINATION OF DENSITY")
The rate of change with time of the balance reading at time t, is calculated
as follows:
dmout (ti ) 'flout ¨ 'flout ,-1
[g/sec]
dt t1+1 ¨t1_1
The rate of change with time of the caliper reading at time t, is calculated
as follows:
dd(ti ) = d1+1 ¨
______________________________________________ [cm/sec]
dt t1+1 ¨ ti 1
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The uptake Kinetics is calculated as follows:
(A = di ¨ Vs ) = p
U(ti ) = _________________________________________ [gigi
na
By dry sample volume (V,) is intended the skeletal volume of the sample
therefore V, is
the actual volume occupied by the solid material in the dry sample excluding
pores and
interstitials that might be present.
V, can be calculated or measured by different methods known by the skilled
person for
example, knowing the exact composition and the skeletal density of the
components it can be
determined as follows:
Vs = E Vk = E (tri [cm3]
k PS k
Alternatively for an unknown material composition V, can be easily calculated
as follow:
[cm3]
PS
The average density p, can be determined by pycnometry with a suitable non-
swelling
liquid of known density. This technique cannot be performed on the same
samples
subsequently used for the K(t) measure therefore a suitable additional
representative set of
samples should be prepared for this experiment measurement.
From U(t) at the different time steps calculated as explained above, one can
determine
the uptake at any specific time by linear interpolation. For example one of
the important
outputs is the uptake at 20 minutes also called U20 (in g/g).
From U(t) at the different time steps one can also determine the time required
to reach a
certain uptake by linear interpolation. The time where the uptake of 20 g/g is
first reached is
called T20. Similarly the time to reach any other uptakes can be calculated
accordingly (e,g
T5 or T10). Knowing U20 it is possible to determine from U(t) at the different
time steps
also the time to reach 80% of U20, this property is called T80%.
The Effective Permeability is calculated as follows from the rates of mass
change and
caliper change:
K(t i) = d1 r 1 dm out (t )+ dd (t
1 [CM2]
Ap p.A dt dt
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The effective viscosity of the liquid depends on the temperature and in the
interval of
the experiment (23 C 1 C) is calculated according the following empirical
equation:
= A + B = T [g/(cm.$)]
wherein A = 1,479.10-2 [g/(cm.$)] and B = -2.36.104 [g/(cm.s. C)]
From K(t) one can determine the effective permeability at a certain time by
linear
interpolation. For example one of the important outputs is the uptake at 20
minutes or K20
(m2). Similarly the Permeability at any other time can be calculated
accordingly (e.g. K5 or
K10).
Another parameter to be derived from the data is Kmin, which is the minimum
K(t)
value measured over the whole curve in the interval from t,= 30s to t,= 1200s.
This value is
useful to calculate Kmin/K20 which is the ratio between the minimum effective
permeability
and the permeability at 20 minutes. This parameter express the temporary gel
blocking that
might occur in some of the samples. If the value is close to 1 there is no
temporary gel
blocking if the value is close to 0 it is an indication that the material goes
through a strong
effective permeability drop when initially loaded with liquid.
The average values for T20, T80%, K20, U20 and Kmin/K20 are reported from 3
replicates according to the accuracy required as known by the skilled man.
= Caliper measurement Test method,
The intent of this method is to provide a procedure to determine the thickness
of
the absorbent core at the crotch point of an absorbent article. The test can
be executed
with a conventional caliper gauge, such as Type EG-225 available from ONO
SOKKI
Technology Inc., 2171 Executive Drive, Suite 400, Addison, IL 60101, USA, with
an
appropriate gauge stand, having an aluminium circular sample foot of 41 mm
diameter, having a force exerted by the foot of 10 gf. An additional weight is
added
to achieve a total of 160 gf to adjust the pressure to 1.18 kPa (0.173 psi).
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The thickness of the absorbent core is determined prior to assembly of the
absorbent core in the absorbent article after the exact position which the
absorbent
core will have in the absorbent article upon assembly has been decided on.
However,
the thickness may also be determined after removing of the absorbent core from
a
finished product by any suitable method known by the person skilled in the
art.
The crotch point of an absorbent article is determined at the intersection of
the
longitudinal centerline and the transverse centerline of the article.
Basic Protocol
1. All testing is conducted at 23 1 C and 50 2% relative humidity.
2. The absorbent core is allowed to equilibrate at 23 1 C and 50 2%
relative
humidity for 8 hours.
3. The crotch point is determined as decribed above and marked on the wearer
surface of the absorbent core.
4. The absorbent core is positioned under the caliper gauge with the wearer
surface toward the sample contact foot and with the crotch point centered
under the foot.
5. The sample contact foot is gently lowered into contact with the surface of
the
absorbent core.
6. The caliper reading is taken 5 seconds after the foot comes into contact
with
the absorbent core.
= Urine Permeability Measurement (UPM) Test method
Urine Permeability Measurement System
This method determined the permeability of a swollen hydrogel layer 1318. The
equipment used for this method is described below. This method is closely
related to the SFC
(Saline Flow Conductivity) test method of the prior art.
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Fig. 10 shows permeability measurement system 1000 set-up with the constant
hydrostatic head reservoir 1014, open-ended tube for air admittance 1010,
stoppered vent for
refilling 1012, laboratory jack 1016, delivery tube 1018, stopcock 1020, ring
stand support
1022, receiving vessel 1024, balance 1026 and piston/cylinder assembly 1028.
5 Fig. 11 shows the piston/cylinder assembly 1028 comprising a metal weight
1112, piston
shaft 1114, piston head 1118, lid 1116, and cylinder 1120. The cylinder 1120
is made of
transparent polycarbonate (e.g., Lexan ) and has an inner diameter p of 6.00
cm (area =
28.27 cm2) with inner cylinder walls 1150 which are smooth. The bottom 1148 of
the
cylinder 1120 is faced with a US. Standard 400 mesh stainless-steel screen
cloth (not shown)
10 that is bi-axially stretched to tautness prior to attachment to the
bottom 1148 of the cylinder
1120. The piston shaft 1114 is made of transparent polycarbonate (e.g., Lexan
) and has an
overall length q of approximately 127 mm. A middle portion 1126 of the piston
shaft 1114
has a diameter r of 21.15 mm. An upper portion 1128 of the piston shaft 1114
has a diameter
s of 15.8 mm, forming a shoulder 1124. A lower portion 1146 of the piston
shaft 1114 has a
15 diameter t of approximately 5/8 inch and is threaded to screw firmly
into the center hole 1218
(see Fig. 12) of the piston head 1118. The piston head 1118 is perforated,
made of
transparent polycarbonate (e.g., Lexanc)), and is also screened with a
stretched US. Standard
400 mesh stainless-steel screen cloth (not shown). The weight 1112 is
stainless steel, has a
center bore 1130, slides onto the upper portion 1128 of piston shaft 1114 and
rests on the
20 shoulder 1124. The combined weight of the piston head 1118, piston shaft
1114 and weight
1112 is 596 g ( 6g), which corresponds to 0.30 psi over the area of the
cylinder 1120. The
combined weight may be adjusted by drilling a blind hole down a central axis
1132 of the
piston shaft 1114 to remove material and/or provide a cavity to add weight.
The cylinder lid
1116 has a first lid opening 1134 in its center for vertically aligning the
piston shaft 1114 and
25 a second lid opening 1136 near the edge 1138 for introducing fluid from
the constant
hydrostatic head reservoir 1014 into the cylinder 1120.
A first linear index mark (not shown) is scribed radially along the upper
surface 1152
of the weight 1112, the first linear index mark being transverse to the
central axis 1132 of the
piston shaft 1114. A corresponding second linear index mark (not shown) is
scribed radially
30 along the top surface 1160 of the piston shaft 1114, the second linear
index mark being
transverse to the central axis 1132 of the piston shaft 1114. A corresponding
third linear
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index mark (not shown) is scribed along the middle portion 1126 of the piston
shaft 1114, the
third linear index mark being parallel with the central axis 1132 of the
piston shaft 1114. A
corresponding fourth linear index mark (not shown) is scribed radially along
the upper
surface 1140 of the cylinder lid 1116, the fourth linear index mark being
transverse to the
central axis 1132 of the piston shaft 1114. Further, a corresponding fifth
linear index mark
(not shown) is scribed along a lip 1154 of the cylinder lid 1116, the fifth
linear index mark
being parallel with the central axis 1132 of the piston shaft 1114. A
corresponding sixth
linear index mark (not shown) is scribed along the outer cylinder wall 1142,
the sixth linear
index mark being parallel with the central axis 1132 of the piston shaft 1114.
Alignment of
the first, second, third, fourth, fifth, and sixth linear index marks allows
for the weight 1112,
piston shaft 1114, cylinder lid 1116, and cylinder 1120 to be re-positioned
with the same
orientation relative to one another for each measurement.
The cylinder 1120 specification details are:
Outer diameter u of the Cylinder 1120: 70.35 mm
Inner diameter p of the Cylinder 1120: 60.0 mm
Height v of the Cylinder 1120: 60.5 mm
The cylinder lid 1116 specification details are:
Outer diameter w of cylinder lid 1116: 76.05 mm
Inner diameter x of cylinder lid 1116: 70.5 mm
Thickness y of cylinder lid 1116 including lip 1154: 12.7 mm
Thickness z of cylinder lid 1116 without lip 1154: 6.35 mm
Diameter a of first lid opening 1134: 22.25 mm
Diameter b of second lid opening 1136: 12.7 mm
Distance between centers of first and second lid openings 1134 and 1136: 23.5
mm
The weight 1112 specification details are:
Outer diameter c: 50.0 mm
Diameter d of center bore 1130: 16.0 mm
Height e: 39.0 mm
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The piston head 1118 specification details are
Diameter f: 59.7 mm
Height g: 16.5 mm
Outer holes 1214 (14 total) with a 9.65 mm diameter h, outer holes 1214
equally spaced with centers being 47.8 mm from the center of center hole
1218
Inner holes 1216 (7 total) with a 9.65 mm diameter i, inner holes 1216 equally
spaced with centers being 26.7 mm from the center of center hole 1218
Center hole 1218 has a diameter j of 5/8 inches and is threaded to accept a
lower portion 1146 of piston shaft 1114.
Prior to use, the stainless steel screens (not shown) of the piston head 1118
and
cylinder 1120 should be inspected for clogging, holes or over-stretching and
replaced when
necessary. A urine permeability measurement apparatus with damaged screen can
deliver
erroneous UPM results, and must not be used until the screen has been
replaced.
A 5.00 cm mark 1156 is scribed on the cylinder 1120 at a height k of 5.00 cm (
0.05
cm) above the screen (not shown) attached to the bottom 1148 of the cylinder
1120. This
marks the fluid level to be maintained during the analysis. Maintenance of
correct and
constant fluid level (hydrostatic pressure) is critical for measurement
accuracy.
A constant hydrostatic head reservoir 1014 is used to deliver salt solution
1032 to the
cylinder 1120 and to maintain the level of salt solution 1032 at a height k of
5.00 cm above
the screen (not shown) attached to the bottom 1148 of the cylinder 1120. The
bottom 1034
of the air-intake tube 1010 is positioned so as to maintain the salt solution
1032 level in the
cylinder 1120 at the required 5.00 cm height k during the measurement, i.e.,
bottom 1034 of
the air tube 1010 is in approximately same plane 1038 as the 5.00 cm mark 1156
on the
cylinder 1120 as it sits on the support screen (not shown) on the ring stand
1040 above the
receiving vessel 1024. Proper height alignment of the air-intake tube 1010 and
the 5.00 cm
mark 1156 on the cylinder 1120 is critical to the analysis. A suitable
reservoir 1014 consists
of a jar 1030 containing: a horizontally oriented L-shaped delivery tube 1018
for fluid
delivery, a vertically oriented open-ended tube 1010 for admitting air at a
fixed height within
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the constant hydrostatic head reservoir 1014, and a stoppered vent 1012 for re-
filling the
constant hydrostatic head reservoir 1014. Tube 1010 has an internal diameter
of 12.5 mm
0.5 mm. The delivery tube 1018, positioned near the bottom 1042 of the
constant hydrostatic
head reservoir 1014, contains a stopcock 1020 for starting/stopping the
delivery of salt
solution 1032. The outlet 1044 of the delivery tube 1018 is dimensioned to be
inserted
through the second lid opening 1136 in the cylinder lid 1116, with its end
positioned below
the surface of the salt solution 1032 in the cylinder 1120 (after the 5.00 cm
height of the salt
solution 1032 is attained in the cylinder 1120). The air-intake tube 1010 is
held in place with
an o-ring collar (not shown). The constant hydrostatic head reservoir 1014 can
be positioned
on a laboratory jack 1016 in order to adjust its height relative to that of
the cylinder 1120.
The components of the constant hydrostatic head reservoir 1014 are sized so as
to rapidly fill
the cylinder 1120 to the required height (i.e., hydrostatic head) and maintain
this height for
the duration of the measurement. The constant hydrostatic head reservoir 1014
must be
capable of delivering salt solution 1032 at a flow rate of at least 3 g/sec
for at least 10
minutes.
The piston/cylinder assembly 1028 is positioned on a 16 mesh rigid stainless
steel
support screen (not shown) (or equivalent) which is supported on a ring stand
1040 or
suitable alternative rigid stand. This support screen (not shown) is
sufficiently permeable so
as to not impede salt solution 1032 flow and rigid enough to support the
stainless steel mesh
cloth (not shown) preventing stretching. The support screen (not shown) should
be flat and
level to avoid tilting the piston/cylinder assembly 1028 during the test. The
salt solution 1032
passing through the support screen (not shown) is collected in a receiving
vessel 1024,
positioned below (but not supporting) the support screen (not shown). The
receiving vessel
1024 is positioned on the balance 1026 which is accurate to at least 0.01 g.
The digital output
of the balance 1026 is connected to a computerized data acquisition system
(not shown).
Preparation of Reagents (not illustrated)
Jayco Synthetic Urine (JSU) 1312 (see Fig. 13) is used for a swelling phase
(see UPM
Procedure below) and 0.118 M Sodium Chloride (NaC1) Solution is used for a
flow phase
(see UPM Procedure below). The following preparations are referred to a
standard 1 liter
volume. For preparation of volumes other than 1 liter, all quantities are
scaled accordingly.
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JSU: A 1L volumetric flask is filled with distilled water to 80% of its
volume, and a
magnetic stir bar is placed in the flask. Separately, using a weighing paper
or beaker the
following amounts of dry ingredients are weighed to within 0.01 g using an
analytical
balance and are added quantitatively to the volumetric flask in the same order
as listed below.
The solution is stirred on a suitable stir plate until all the solids are
dissolved, the stir bar is
removed, and the solution diluted to 1L volume with distilled water. A stir
bar is again
inserted, and the solution stirred on a stirring plate for a few minutes more.
Quantities of salts to make 1 liter of Jayco Synthetic Urine:
Potassium Chloride (KC1) 2.00 g
Sodium Sulfate (Na2504) 2.00 g
Ammonium dihydrogen phosphate (NH4H2PO4) 0.85 g
Ammonium phosphate, dibasic ((NH4)2HPO4) 0.15 g
Calcium Chloride (CaC12) 0.19 g ¨ [ or hydrated calcium chloride (CaC12=2H20)
0.25 gl
Magnesium chloride (MgC12) 0.23 g ¨ [or hydrated magnesium chloride
(MgC12=6H20) 0.50 gl
To make the preparation faster, each salt is completely dissolved before
adding the
next one. Jayco synthetic urine may be stored in a clean glass container for 2
weeks. The
solution should not be used if it becomes cloudy. Shelf life in a clean
plastic container is 10
days.
0.118 M Sodium Chloride (NaC1) Solution: 0.118 M Sodium Chloride is used as
salt
solution 1032. Using a weighing paper or beaker 6.90 g ( 0.01 g) of sodium
chloride is
weighed and quantitatively transferred into a 1L volumetric flask; and the
flask is filled to
volume with distilled water. A stir bar is added and the solution is mixed on
a stirring plate
until all the solids are dissolved.
Test Preparation
Using a solid reference cylinder weight (not shown) (40 mm diameter; 140 mm
height), a caliper gauge (not shown) (e.g., Mitotoyo Digimatic Height Gage) is
set to read
zero. This operation is conveniently performed on a smooth and level bench top
1046. The
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piston/cylinder assembly 1028 without superabsorbent polymer particles is
positioned under
the caliper gauge (not shown) and a reading, L1, is recorded to the nearest
0.01 mm.
The constant hydrostatic head reservoir 1014 is filled with salt solution
1032. The
bottom 1034 of the air-intake tube 1010 is positioned so as to maintain the
top part (not
5 shown) of the liquid meniscus (not shown) in the cylinder 1120 at the
5.00 cm mark 1156
during the measurement. Proper height alignment of the air-intake tube 1010 at
the 5.00 cm
mark 1156 on the cylinder 1120 is critical to the analysis.
The receiving vessel 1024 is placed on the balance 1026 and the digital output
of the
balance 1026 is connected to a computerized data acquisition system (not
shown). The ring
10 stand 1040 with a 16 mesh rigid stainless steel support screen (not
shown) is positioned
above the receiving vessel 1024. The 16 mesh screen (not shown) should be
sufficiently
rigid to support the piston/cylinder assembly 1028 during the measurement. The
support
screen (not shown) must be flat and level.
15 UPM Procedure
1.5 g ( 0.05g) of superabsorbent polymer particles is weighed onto a suitable
weighing paper or weighing aid using an analytical balance. The moisture
content of the
superabsorbent polymer particles is measured according to the Edana Moisture
Content Test
Method 430.1-99 ("Superabsorbent materials ¨ Polyacrylate superabsorbent
powders ¨
20 Moisture Content ¨ weight loss upon heating" (February 99)). If the
moisture content of the
superabsorbent polymer particles is greater than 5%, then the superabsorbent
polymer
particles weight should be corrected for moisture (i.e., in that particular
case the added
superabsorbent polymer particles should be 1.5 g on a dry-weight basis).
The empty cylinder 1120 is placed on a level benchtop 1046 and the
superabsorbent
25 polymer particles are quantitatively transferred into the cylinder 1120.
The superabsorbent
polymer particles are evenly dispersed on the screen (not shown) attached to
the bottom 1148
of the cylinder 1120 by gently shaking, rotating, and/or tapping the cylinder
1120. It is
important to have an even distribution of particles on the screen (not shown)
attached to the
bottom 1148 of the cylinder 1120 to obtain the highest precision result. After
the
30 superabsorbent polymer particles have been evenly distributed on the
screen (not shown)
attached to the bottom 1148 of the cylinder 1120 particles must not adhere to
the inner
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cylinder walls 1150. The piston shaft 1114 is inserted through the first lid
opening 1134, with
the lip 1154 of the lid 1116 facing towards the piston head 1118. The piston
head 1118 is
carefully inserted into the cylinder 1120 to a depth of a few centimeters. The
lid 1116 is then
placed onto the upper rim 1144 of the cylinder 1120 while taking care to keep
the piston head
1118 away from the superabsorbent polymer particles. The lid 1116 and piston
shaft 1126
are then carefully rotated so as to align the third, fourth, fifth, and sixth
linear index marks
are then aligned. The piston head 1118 (via the piston shaft 1114) is then
gently lowered to
rest on the dry superabsorbent polymer particles. The weight 1112 is
positioned on the upper
portion 1128 of the piston shaft 1114 so that it rests on the shoulder 1124
such that the first
and second linear index marks are aligned. Proper seating of the lid 1116
prevents binding
and assures an even distribution of the weight on the hydrogel layer 1318.
Swelling Phase: An 8 cm diameter fritted disc (7 mm thick; e.g. Chemglass Inc.
#
CG 201- 51, coarse porosity) 1310 is saturated by adding excess JSU 1312 to
the fritted disc
1310 until the fritted disc 1310 is saturated. The saturated fritted disc 1310
is placed in a
wide flat-bottomed Petri dish 1314 and JSU 1312 is added until it reaches the
top surface
1316 of the fritted disc 1310. The JSU height must not exceed the height of
the fitted disc
1310.
The screen (not shown) attached to the bottom 1148 of the cylinder 1120 is
easily
stretched. To prevent stretching, a sideways pressure is applied on the piston
shaft 1114, just
above the lid 1116, with the index finger while grasping the cylinder 1120 of
the
piston/cylinder assembly 1028. This "locks" the piston shaft 1114 in place
against the lid
1116 so that the piston/cylinder assembly 1028 can be lifted without undue
force being
exerted on the screen (not shown).
The entire piston/cylinder assembly 1028 is lifted in this fashion and placed
on the
fritted disc 1310 in the Petri dish 1314. JSU 1312 from the Petri dish 1314
passes through
the fritted disc 1310 and is absorbed by the superabsorbent polymer particles
(not shown) to
form a hydrogel layer 1318. The JSU 1312 available in the Petri dish 1314
should be enough
for all the swelling phase. If needed, more JSU 1312 may be added to the Petri
dish 1314
during the hydration period to keep the JSU 1312 level at the top surface 1316
of the fritted
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disc 1310. After a period of 60 minutes, the piston/cylinder assembly 1028 is
removed from
the fritted disc 1310, taking care to lock the piston shaft 1114 against the
lid 1116 as
described above and ensure the hydrogel layer 1318 does not lose JSU 1312 or
take in air
during this procedure. The piston/cylinder assembly 1028 is placed under the
caliper gauge
(not shown) and a reading, L2, is recorded to the nearest 0.01 mm. If the
reading changes
with time, only the initial value is recorded. The thickness of the hydrogel
layer 1318, Lo is
determined from L2 ¨ L1 to the nearest 0.1 mm.
The piston/cylinder assembly 1028 is transferred to the support screen (not
shown)
attached to the ring support stand 1040 taking care to lock the piston shaft
1114 in place
against the lid 1116. The constant hydrostatic head reservoir 1014 is
positioned such that the
delivery tube 1018 is placed through the second lid opening 1136. The
measurement is
initiated in the following sequence:
a) The stopcock 1020 of the constant hydrostatic head reservoir 1014 is
opened to permit
the salt solution 1032 to reach the 5.00 cm mark 1156 on the cylinder 1120.
This salt
solution 1032 level should be obtained within 10 seconds of opening the
stopcock
1020.
b) Once 5.00 cm of salt solution 1032 is attained, the data collection
program is initiated.
With the aid of a computer (not shown) attached to the balance 1026, the
quantity of
salt solution 1032 passing through the hydrogel layer 1318 is recorded at
intervals of 20
seconds for a time period of 10 minutes. At the end of 10 minutes, the
stopcock 1020 on the
constant hydrostatic head reservoir 1014 is closed.
The data from 60 seconds to the end of the experiment are used in the UPM
calculation. The data collected prior to 60 seconds are not included in the
calculation. The
flow rate Fs (in g/s) is the slope of a linear least-squares fit to a graph of
the weight of salt
solution 1032 collected (in grams) as a function of time (in seconds) from 60
seconds to 600
seconds.
The Urine Permeability Measurement (Q) of the hydrogel layer 1318 is
calculated
using the following equation:
Q=1Fgx Lo 1 /1p x A x AP1,
where Fg is the flow rate in g/sec determined from regression analysis of the
flow rate results,
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Lo is the initial thickness of the hydrogel layer 1318 in cm, p is the density
of the salt solution
1032 in gm/cm3. A (from the equation above) is the area of the hydrogel layer
1318 in cm2,
AP is the hydrostatic pressure in dyne/cm2, and the Urine Permeability
Measurement, Q, is in
units of cm3 sec/gm. The average of three determinations should be reported.
= FSR Test method
This method determines the speed of superabsorbent polymer particles,
especially
polymeric hydrogelling particles, such as cross-linked poly-acrylates to swell
in 0.9% Saline
(aqueous 0.9 mass % NaC1 solution). The measurement principle is to allow
superabsorbent
polymer particles to absorb a known amount of fluid, and the time taken to
absorb the fluid is
measured. The result is then expressed in grams of absorbed fluid per gram of
material per
second. All testing is conducted at 23 2 C.
Four grams of a representative sample of the superabsorbent polymer particles
is dried in
an uncovered 5 cm diameter Petri dish in a vacuum chamber at 23 2 C and 0.01
ton or
lower for 48 hours prior to measurement.
About 1 g (+/- 0.1g) of the test specimen is removed from the vacuum chamber
and
immediately weighed to an accuracy of 0.001 g into a 25 ml beaker, which has
32 to 34 mm
inside diameter, and 50 mm height. The material is evenly spread over the
bottom. 20 g of
0.9% Saline are weighed to an accuracy of +/- 0.01 g in a 50 ml beaker, and
are then poured
carefully but quickly into the beaker containing the test material. A timer is
started
immediately upon the liquid contacting the material. The beaker is not moved
or agitated
during swelling.
The timer is stopped, and the time recorded to the nearest second (or more
accurately if
appropriate), when the last part of undisturbed fluid is reached by the
swelling particles. In
order to increase the reproducibility of the determination of the end point,
the liquid surface
can be illuminated by a small lamp without heating the surface by that lamp.
The beaker is
re-weighed to determine the actually picked up liquid to within 0.1g.
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The free-swell rate is calculated by dividing the weight of superabsorbent
polymer
particles by the amount of actually picked up liquid, and dividing the result
by the time
required for this pick up, and is expressed in "g/g/s". Three measurements are
performed and
the results averaged to obtain the FSR value in g/g/s, reported to 3
significant figures.
= Flat Acquisition Test Method
This method determines the acquisition times of a baby diaper typically
designated for
wearers having a weight in the range of 8 to 13 kg 20% (such as Pampers
Active Fit size 4
or other Pampers baby diapers size 4, Huggies baby diapers size 4 or baby
diapers size 4 of
most other tradenames).
Apparatus
The test apparatus is shown in Figure 14 and comprises a trough 1411 made of
polycarbonate (e.g. LexanCi) nominally 12.5 mm (0.5 inch) in thickness. The
trough 1411
comprises a rectilinear horizontal base 1412 having a length of 508 mm (20.0
inches), and a
width of 152 mm (6.0 inches). Two rectilinear vertical sides 1413 64 mm (2.5
inches) tall x
508 mm (20 inches) in length are affixed to the long edges of the base 1412to
form a U-
shaped trough 1411 having a length of 508 mm (20.0 inches), an internal width
of 152 mm
(6.0 inches), and an internal depth of 51 mm (2.0 inches). The front and back
ends of the
trough 1411 are not enclosed.
A slab of open-cell polyurethane foam 1414 with dimensions 508 x 152 x 25 mm
is wrapped
in polyethylene film and placed in the bottom of the trough 1411 in such a way
that the edges
of the foam 1414 and the trough 1411 are aligned, and the upper surface of the
polyethylene
film is smooth and free of seams, wrinkles or imperfections. The polyurethane
foam 1414
has a compressive modulus of 0.48 psi. A reference line is drawn across the
width of the
upper surface of the polyethylene cover 152 mm (6.0 inches) from one end (the
front edge)
parallel to the transverse centerline using an indelible marker.
A rectilinear polycarbonate top plate 1415 has a nominal thickness of 12.5 mm
(0.5
inch), a length of 508 mm (20.0 inches), and a width of 146 mm (5.75 inches).
A 51 mm
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(2.0 inch) diameter hole is bored in the center of the top plate 1415 (i.e.
the center of the hole
is located at the intersection of the longitudinal and transverse axes of the
upper surface of
the top plate 1415). A polycarbonate cylinder 1416 with an outside diameter of
51 mm (2.0
inches), an internal diameter of 37.5 mm (1.5 inches) and a height of 102 mm
(4.0 inches) is
5
glued into the hole in the top plate 1415 so that the bottom edge of the
cylinder 1416 is flush
with the lower surface of the top plate 1415 and the cylinder 1416 protrudes
vertically 89 mm
(3.5 inches) above the upper surface of the top plate 1415, and the seam
between the cylinder
1416 and the top plate 1415 is watertight. An annular recess 1417 with a
height of 2 mm and
a diameter of 44.5 mm (1.75 inches) is machined into the bottom internal edge
of the cylinder
10
1416. Two 1 mm diameter holes are drilled at a 45 angle to the upper surface
of the top
plate 1415 so that the holes intersect the inner surface of the cylinder 1416
immediately
above the recess 1417 and are at opposite sides of the cylinder 1416 (i.e. 180
apart). Two
stainless steel wires 1418 having a diameter of 1 mm are glued into the holes
in a watertight
fashion so that one end of each wire is flush with the inner cylinder wall and
the other end
15
protrudes from the upper surface of the top plate 1415. These wires are
referred to as
electrodes hereinbelow. A reference line is scribed across the width of the
top plate 1415
152 mm (6.0 inches) from the front edge parallel to the transverse centerline.
The top plate
1415/cylinder 1416 assembly has a weight of approximately 1180 grams.
20 Two
steel weights each weighing 9.0 Kg and measuring 146 mm (5.75 inches) wide,
76 mm (3.0 inches) deep, and approximately 100 mm (4 inches tall) are also
required.
Procedure:
All testing is carried out at 23 2 C and 35 15% relative humidity.
25 The
polycarbonate trough 1411 containing the wrapped foam slab 1414 is placed on a
suitable flat horizontal surface. A disposable absorbent product is removed
from its
packaging and the cuff elastics are cut at suitable intervals to allow the
product to lay flat.
The product is weighed to within 0.1 grams on a suitable top-loading balance
then placed
on the covered foam slab 1414 in the acquisition apparatus with the front
waist edge of the
30
product aligned with the reference mark on the polyethylene cover. The product
is centered
along the longitudinal centerline of the apparatus with the topsheet (body-
side) of the product
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facing upwards and the rear waist edge toward the rear end of the foam slab
1414. The top
plate 1415 is placed on top of the product with the protruding cylinder facing
upwards. The
scribed reference line is aligned with the front waist edge of the product and
the rear end of
the top plate 1415 is aligned with the rear edge of the foam slab 1414. The
two 9.0 Kg
weights are then gently placed onto the top plate 1415 so that the width of
each weight is
parallel to the tranverse centerline of the top plate, and each weight is 83
mm (3.25 inches)
from the front or rear edge of the top plate 1415.
A suitable electrical circuit is connected to the two electrodes to detect the
presence
of an electrically conductive fluid between them.
A suitable pump; e.g. Model 7520-00 supplied by Cole Parmer Instruments,
Chicago,
USA, or equivalent; is set up to discharge a 0.9 mass % aqueous solution of
sodium chloride
through a flexible plastic tube having an internal diameter of 4.8 mm (3/16
inch), e.g
Tygon R-3603 or equivalent. The end portion of the tube is clamped vertically
so that it is
centered within the cylinder 1416 attached to the top plate 1415 with the
discharge end of the
tube facing downwards and located 50 mm (2 inches) below the upper edge of the
cylinder
1416. The pump is operated via a timer and is pre-calibrated to discharge a
gush of 75.0 ml
of the 0.9% saline solution at a rate of 15 ml/sec.
The pump is activated and a timer started immediately upon activation. The
pump
delivers 75 mL of 0,9% NaC1 solution to the cylinder 1416 at a rate of 15
ml/sec, then stops.
As test fluid is introduced to the cylinder 1416, it typically builds up on
top of the absorbent
structure to some extent. This fluid completes an electrical circuit between
the two
electrodes in the cylinder. After the gush has been delivered, the meniscus of
the solution
drops as the fluid is absorbed into the structure. When the electrical circuit
is broken due to
the absence of free fluid between the electrodes in the cylinder, the time is
noted.
The acquisition time for a particular gush is the time interval between
activation of
the pump for that gush, and the point at which the electrical circuit is
broken.
Four gushes are delivered to the product in this fashion; each gush is 75 ml
and is
delivered at 15 ml/sec. The time interval between the beginning of each gush
is 300 seconds.
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The acquisition time for four gushes is recorded. Three products are tested in
this
fashion and the average gush time for each of the respective gushes (first
through fourth) is
calculated.
EXAMPLES
Absorbent structures according to the present disclosure have been prepared to
compare
their properties with the properties of absorbent structures of the prior art.
All the tested
absorbent structures comprise superabsorbent polymer particles which are
sandwiched
between two substrate layers made of nonwoven material. For the data given in
Table 1, all
the samples have been taken from an absorbent core. The samples correspond to
the portion
of the absorbent core of an absorbent article (size 4) which is centered on
the longitudinal
centerline of the article, at a distance of 152 mm from the front waist edge
of the article. In
the portion of the absorbent core where the samples are taken, the absorbent
structures of
examples 1 and 2 and comparative examples 1 and 2 have the same structure.
They only
differ with regard to the superabsorbent polymer particles which have been
used. For the data
given in Table 2, the whole absorbent structures of Example 2 and Comparative
Examples 1
and 2 have the same structure and only differ with regard to the
superabsorbent polymer
particles which have been used.
= Comparative Example 1
An absorbent structure comprising the same superabsorbent polymer particles as
the ones
which are used in Pampers Active Fit diapers commercially available in the UK
in August
2010 has been prepared. These superabsorbent polymer particles are generally
made
according to US 2009/0275470A1. It should be noted that the superabsorbent
polymer
particles may be isolated from the commercially available Pampers Active Fit
diapers as
described in European patent application n 10154618.2 entitled "Method of
separating
superabsorbent polymer particles from a solidified thermoplastic composition
comprising
polymers".
The Standard particle size distribution of the superabsorbent polymer
particles is of 45 to 710
p.m with a maximum of 1% below 45 p.m and a maximum of 1% above 710 p.m.
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53
= Comparative Example 2
300 g of superabsorbent polymer particles have been prepared according to
comparative
example 11 disclosed in the PCT patent application WO 2010/095427 Al entitled
"Polyacrylic acid-based water-absorbing resin powder and method for producing
the same".
An absorbent structure comprising such superabsorbent polymer particles has
been prepared.
= Example 1
4000 kg of superabsorbent polymer particles of comparative example 1 have been
sieved
over a AISI 304 standard 300 p.m stainless steel wire mesh in a riddle sieve
equipment with a
capacity of about 100-150 kg per hours yielding to 750 kg of superabsorbent
polymer
particles with a medium diameter (D50) of about 180-200 p.m and a particle
size distribution
of 45 to 300 p.m with a maximum of 3% below 45 p.m and a maximum of 3% above
300p.m.
An absorbent structure comprising such superabsorbent polymer particles has
been prepared
= Example 2
300 g of superabsorbent polymer particles have been prepared according to
example 9
disclosed in the PCT patent application WO 2010/095427 Al entitled
"Polyacrylic acid-
based water-absorbing resin powder and method for producing the same". An
absorbent
structure comprising such superabsorbent polymer particles has been prepared.
Several parameters of the absorbent structures of examples 1 and 2 and of the
comparative examples 1 and 2 have been measured: the time to reach an uptake
of 20 g/g
(T20), the uptake at 20 min (U20), the time to reach an uptake of 80% of U20
(T80%), the
effective permeability at 20 minutes (K20) and the transient gel blocking
index (Kmin/K20)
have been measured according to K(t) Test Method set out above. The UPM (Urine
Permeability Measurement) of the superabsorbent polymer particles of the
absorbent
structures of Examples 1 and 2 and of the comparative examples 1 and 2 has
been measured
according to the UPM Test method set out above. The CRC (Centrifuge Retention
Capacity)
of the superabsorbent polymer particles has been measured according to EDANA
method
WSP 241.2-05.
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Fig. 18A and 18B represent the uptake in g/g as a function of time for the
absorbent
structures of the comparative examples 1 and 2 vs. examples 1 and 2 as
measured according
to the K(t) Test Method set out above.
The different values for the measured parameters are summarized in Table 1
below.
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Table 1
U20 T80% UPM (1x10-7 CRC
Examples T20(s) (g/g) (g/g) K20 (cm2) Kmin/K20
(cm3.$)/g) (g/g )
Comparative
Example 1 495 23.8 414 3.43.10-8 0.92 98 26.5
Comparative
Example 2 477 24.1 410 4.75.10-8 0.96 110 27.3
Example 1 200 23.9 177 2.8 .10-8 0.72 66 24.1
Example 2 344 25.0 343 3.13.108 0.86 100 27.7
As can be seen from Fig. 18A and 18B and from Table 1, the times to reach an
uptake
5 of 20g/g (T20) as measured according to the K(t) test method for the
absorbent structures
made according to examples 1 and 2 are significantly lower than for the
absorbent structures
made according to the comparative examples 1 and 2. Therefore, these absorbent
structures
are able to rapidly absorb liquid even in the dry stage, i.e. upon initial
exposure to liquid.
As can also be seen from Table 1 is that superabsorbent polymer particles
having a
10 high permeability at equilibrium (high UPM value) such as the
superabsorbent polymer
particles of the absorbent structures of comparative examples 1 and 2 do not
automatically
lead to a high T20 value for the absorbent structure comprising such
superabsorbent polymer
particles which means that the permeability at equilibrium of the
superabsorbent polymer
particles is not a reliable criterion in order to select the absorbent
structures which are able to
15 rapidly absorb liquid upon initial exposure to liquid.
= Acquisition times of diapers comprising an absorbent structure which
comprises the
superabsorbent polymer particles of comparative examples 1 or 2 vs. diapers
comprising an absorbent structure which comprises the superabsorbent polymer
20 particles according to the present disclosure.
Acquisition times of Pampers Active Fit size 4 diapers commercially available
in the UK
in August 2010 have been measured according to the Flat Acquisition Test
Method set out
above. These diapers comprise an absorbent core which comprises the
superabsorbent
polymer particles of the comparative example 1. Acquisition times of the same
diapers
25 wherein the absorbent core has been replaced by an absorbent core with
the same structure
but wherein the superabsorbent polymer particles have been replaced by the
superabsorbent
polymer particles of comparative example 2 or example 2 have been measured
according to
the Flat acquisition test method set out above. The absorbent cores of all the
diapers have a
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56
dry thickness at the crotch point of the diaper of 1.7 mm as measured
according to the
Caliper Measurement Test Method set out above. The values obtained for the
acquisition
times of all samples are summarized in Table 2 below.
Table 2
Comparative Comparative
Samples Example 2
Example 1 Example 2
Acquisition time of 1st gush (75 mL) in s 30 28 26
As can be seen from Table 2 above, the acquisition times of the first gush for
diapers
comprising an absorbent core which comprises superabsorbent polymer particles
according
to comparative examples 1 or 2 are higher than the acquisition time of the
first gush for the
same diaper wherein the superabsorbent polymer particles have been replaced by
the
superabsorbent polymer particles of Example 2.
Hence, absorbent articles according to the present invention, namely absorbent
articles comprising an absorbent structure wherein one or more portion(s) of
the absorbent
structure comprise(s) at least 90% of superabsorbent polymer particles and
require(s) a time
to reach an uptake of 20 g/g (T20) of less than 440 s as measured according to
the K(t) test
method have improved absorption properties, especially at the first gush, i.e.
when the article
starts to be wetted.
The dimensions and values disclosed herein are not to be understood as being
strictly
limited to the exact numerical values recited. Instead, unless otherwise
specified, each such
dimension is intended to mean both the recited value and a functionally
equivalent range
surrounding that value. For example, a dimension disclosed as "40 mm" is
intended to mean
"about 40 mm."
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