Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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ABSORBENT CORES WITH Y-DENSITY GRADIENT
Related Applications
This application claims the benefit of U.S. Provisional Patent Application
No. 60/166,489 filed November 19, 1999; U.S. Provisional Patent Application
No.
60/211,090 filed June 12, 2000 and U.S. Provisional Patent Application No.
60/211,091
filed June 12, 2000, all of which are hereby incorporated by reference.
Field of the Invention
This invention is directed to the field of unitary absorbent structures for
use
in absorbent articles, in which one or more of the strata of the absorbent
structure is
profiled in the y-direction, in one or more of the properties of basis weight,
functional
particle content, or density, and processes for the production of the
structure.
Background of the Invention
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Absorbent structures are used in a wide range of disposable absorbent
articles, including baby diapers, adult incontinence products, sanitary
napkins and the like.
These and other absorbent articles are generally provided with an absorbent
structure
which is disposed as a core, to receive and retain body liquids. The absorbent
core is
usually sandwiched between a liquid pervious topsheet, whose function is to
allow the
passage of fluid to the core, and a liquid impervious backsheet, whose
function is to
contain the fluid and to prevent it from passing through the absorbent article
to the
garment of the wearer of the absorbent article.
An absorbent structure which is used as a core for diapers and adult
incontinence pads frequently includes fibrous batts or webs constructed of
defiberized,
loose, fluffed, hydrophilic, cellulosic fibers. The core may also include
functional
particles, such as superabsorbent polymer ("SAP") particles, granules, flakes
or fibers
(collectively "particles")
In recent years, market demand for an increasingly thinner and more
comfortable absorbent article has increased. Such an article may be obtained
by
decreasing the thickness of the structure used as the diaper core, by
increasing the amount
of functional particles, and by calendaring or pressing the core to reduce
caliper and hence,
increase density.
However, higher density articles used as cores do not absorb liquid as
rapidly as lower density cores, because densification of the core results in a
smaller
effective pore size. Accordingly, to maintain suitable liquid absorption, it
is necessary to
provide a low-density strata having a larger pore size above the high-density
absorbent
core to increase the rate of uptake of liquid discharged onto the absorbent
article. The
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low-density ply is typically referred to as an acquisition strata: Multiple
strata absorbent
core designs involve a more complicated manufacturing process.
The storage ply portion of a disposable diaper, for example, is generally
formed in place, during the converting process, from loose, fluffed cellulose.
Such
cellulose material is generally not available in preformed sheet form because
it exhibits
insufficient web strength, owing to its lack of interfiber bonding or
entanglement, to be
unwound or unfestooned directly onto and handled in absorbent pad-making
equipment.
Some absorbent articles such as ultra-thin feminine napkins are generally
produced from
roll-goods based nonwoven material. Such a roll of preformed absorbent core
material is
unwound directly as feedstock into the absorbent article converting equipment
without the
defiberization step normally required for fluff based products, such as
diapers and
incontinence pads. The nonwoven web is typically bonded or consolidated in a
fashion
that gives it sufficient strength to be handled during the converting process.
Absorbent
structures made from such nonwoven webs may also contain SAP particles.
However,
these absorbent structures are often inefficient in cases where a demand is
for acquisition
and absorption of high amounts or a surge of body fluids. In these cases, a
single ply
absorbent material often is not sufficient to serve as the absorbent core
because the liquid
is not distributed in the structure along the length of the absorbent core. As
a result,
regions of the absorbent core remain unused. The web consolidation
mechanism used in the roll-goods approach to making preformed cores provides
strength
and dimensional stability to the web. Such mechanisms include latex bonding,
bonding
with thermoplastic or bicomponent fibers or thermoplastic powders,
hydroentanglement,
needlepunching, carding or the like. However, such bonded materials provide a
relatively
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stiff core which often does not conform well to the shape of the human body,
especially in
those situations where there is a demand for good fit to acquire and contain
high volumes
of body fluids.
Pliability and softness of the absorbent core are necessary to ensure that the
absorbent core can easily conform itself to the shape of the human body or to
the shape of
a component, for example, another absorbent strata, of the absorbent article
adjacent to it.
This in turn prevents the formation of gaps and channels between the absorbent
article and
the human body or between various parts of the absorbent article, which might
otherwise
cause undesired leaks in the absorbent article.
Integrity of the absorbent structure used as a core is necessary to ensure
that
the absorbent core does not deform and exhibit discontinuities during its use
by a
consumer. Such deformations and discontinuities can lead to a decrease in
overall
absorbency and capacity, and an increase in undesired.leakage. Prior absorbent
structures
have been deficient in one or more of pliability, integrity, profiled
absorbency and
capacity. For example, a conventional fluff pulp core has good conformability
because of
its high pliability and softness but at the same time it may disintegrate
easily during use,
due to its poor integrity. As another example, certain bonded cores, such as
sirlaid cores
made from cellulose fluff pulp densified to a density greater than 0.35 g/cc
have dry
integrity, but have no wet integrity and poor conformability.
Absorbent structures having improved softness and pliability have been
described in International Patent Application WO 00/41882, published July 20,
2000.
However, there is still a need to enhance even more the capacity of such
structures by
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incorporating high amounts of SAP particles and, at the same time, with
maintaining high
fluid acquisition efficiency of such structures.
Absorbent structures made from nonwoven webs may contain SAP
particles to obtain sufficient absorbent capacity. However, there are
practical limits to
increasing the proportion of SAP particles in currently available commercial
absorbent
structure. If the concentration of SAP particles in an absorbent structure
used as a core is
too high, gel blocking can result and the rate of acquiring and redistributing
the liquid
within the core will become too slow for satisfactory performance of the
absorbent core.
As adjacent SAP particles swell, they form a barrier to free liquid not
immediately
absorbed by the SAP particles. As a result, access by the liquid to unexposed
SAP
particles may be blocked by the swollen, gelled SAP particles. When gel
blocking occurs,
liquid pooling, as opposed to absorption, takes place in the core. As a
result, large
portions of the core remain unused, and failure (leaking) of the absorbent
core can occur.
Gel blocking caused by high concentrations of SAP particles results in reduced
core
permeability, or fluid flow, particularly under pressures encountered during
use of the
absorbent product.
One way to minimize gel blocking and maintain core permeability for
efficient fluid intake and redistribution is to limit the proportion of SAP
particles to matrix
fibers in the absorbent structure used as the core. In this way, there is
sufficient separation
between particles, such that even after the particles have been swollen by
exposure to
liquid they do not contact adjacent particles and free liquid can migrate to
unexposed SAP
particles. Unfortunately, limiting the concentration of SAP particles in the
absorbent core
also limits the extent to which the core can be made thinner and more
comfortable. To
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avoid gel blocking, commercial absorbent cores are presently limited to SAP
particle
concentrations of 20 percent to 50 percent by weight of the core. However,
even with this
limit of SAP particle concentration, these absorbent cores have poor fluid
acquisition rates.
The absorbent structures used as cores in current commercial disposable,
absorbent articles are constructed by combining several plies of material at
the converting
line. Typically, these mufti-ply absorbent.cores contain one or more plies of
varying
width, wherein at least one of the ply in the absorbent core is narrower than
the full width
of the core. The narrow ply are present in these commercial absorbent cores to
improve
performance and reduce raw-material costs by targeting absorbent material
where it is
most needed, and removing material where it is not needed. The existing art
for the
manufacture of absorbent cores which are profiled in basis weight involves
merging
several plies or structures of absorbent material at the converting line to
manufacture
layered absorbent cores.
Typical airlaid forming units for the manufacture of absorbent structures to
be used as cores contain mechanical equipment on one side of the full width
forming wire
designed to accept air-suspended absorbent material and uniformly distribute
the absorbent
material onto the forming wire. Typically, located on the other side of the
forming wire,
and working in concert with the distributing equipment, is a vacuum system
that is present
to collect the air-suspended absorbent material onto the forming wire.
Summary of the Invention
It would be highly desirable to provide an absorbent structure to be used as
a core, which is capable of bearing a SAP particle concentration of about 10
percent to 80
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percent by weight, preferably about 30 percent to 80 percent by weight, while
maintaining
fast fluid acquisition rate and stability of the core. It would also be
desirable to provide a
wet-stable absorbent core, which exhibits improved fluid acquisition and
storage
efficiency for a given SAP concentration.
The present invention provides for an increase in converting efficiencies by
using unitary absorbent structures comprising several strata of absorbent
material.
Applicants have now discovered a method of simplifying the manufacture of
absorbent
products containing profiled absorbent cores. In a first embodiment, a
profiled core can be
obtained by use of a forming surface which can be blocked physically with a
mask to
prevent absorbent material from being deposited in specific zones, resulting
in the
formation of an absorbent structure with profiled strata. In an alternative
embodiment, a
profiled structure can be obtained by controlling the vacuum system by use of
a block for
the vacuum system. The block can be placed in the airlaid forming unit
operation between
the vacuum system and the forming wire.
One object of the invention is to provide a unitary absorbent core
comprising one or more strata of absorbent material, in which one or more of
the
properties of basis weight, functional particle content, or density of at
least one of the
strata is profiled in the y-direction.
Another object of the invention is to provide a process for manufacturing
unitary absorbent cores comprising one or more strata in which one or more of
the basis
weight, functional particle content, or density of at least one of the strata
is profiled in the
y-direction.
It is a further object of the invention to increase converting efficiencies by
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producing unitary absorbent cores via the airlaid process versus producing
mufti-ply
absorbent cores at the converting line by merging several absorbent materials.
Another object of the invention is to introduce y-direction density gradients
into unitary absorbent cores.
An additional object of the invention is to provide for greater control over
the attributes of unitary absorbent cores, thus providing product developers
with greater
flexibility.
Further objects of the invention are to improve product performance by
placing absorbent material in unitary absorbent cores where it is most
effective, or
removing absorbent material in unitary absorbent cores where it is not
effective.
Another object of the invention is to form absorbent cores having improved
fluid acquisition and containment, as well as reduced leak potential.
It is a further object of the invention to simplify the final product
converting
processes by reducing the number of plies in the absorbent structure.
In a first embodiment, the present invention is directed to absorbent
structures having a y-directional, profile comprising one stratum or a
plurality of strata, at
least one stratum of which is produced by a continuous series of unit
operations and which
contains functional particles and has a y-directional profile. The stratum
produced by a
continuous series of unit operations comprises first and second zones disposed
in contact
with each other, wherein the first zone has one or more of a higher density, a
higher
content of functional particles and a higher basis weight than the second
zone.
In a second embodiment, the present invention is directed to absorbent
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structures comprising functional particles and having a fluid storage and
acquisition
efficiency(FASE), as defined herein, of higher than about 50. In this
embodiment, the
structure has a y-directional profile, and comprises one stratum or a
plurality of strata,
wherein at least one stratum comprises first and second zones disposed in
contact with
each other, wherein the first zone has one or more of a higher density, a
higher content of
functional particles and a higher basis weight than the second zone.
In further embodiments of the first and second embodiments, the invention
is directed to structures having a first zone having a higher density and a
higher basis
weight than the second zone, or structures having a higher density and
functional particle
content than the second zone. In certain embodiments, the first zone is
disposed at the side
edge of the absorbent structure. In additional embodiments, the structures
comprise third
and fourth zones, wherein the third zone has a higher density and higher
content of
functional particles then the second and the fourth zones.
In particular embodiments of the structures described above, the structure
comprises a plurality of strata, wherein at least one stratum has a major
surface area which
is less than 80 per cent of the surface area of a corresponding major surface
of another
stratum.
In certain embodiments, the y-directional profile of the structures of the
invention may be the result of a single strata having a y-directional profile,
or the y-
directional profile may be the result of a plurality of strata having a y-
directional profile.
Further, at least one of the stratum may be of substantially uniform density
or basis weight.
In particular embodiments, the structure may also have a z-directional
profile.
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In the embodiments described above, the structures may comprise fibers,
both natural and/or synthetic fibers. Suitable fibers include fibers having a
water retention
value of at least 80 per cent, and fibers having a curl of at least 25 per
cent.
In the embodiments described above, the structures may comprise a binder,
including a liquid binder (such as a latex binder), thermoplastic powders,
thermoplastic
fibers, bicomponent fibers and mixtures thereof. The binder may, for example,
be present
in the amount of about 0.1 percent to about 10 per cent of the structure.
The invention is also directed to the above embodiments, further
comprising an acquisition stratum in fluid communication with the first zone,
the second
10 zone, or with both the first zone and the second zone. The acquisition
stratum may
comprise synthetic matrix fibers bonded with a binder, wherein the matrix
fibers may have
a length of from about 2 to about 15 mm.
In any of the above embodiments, the basis weight of the first zone is from
about 50 gsm to about 1000 gsm. The basis weight of the second zone may be
from about
0.1 gsm to about 800 gsm.
In certain aspects of the invention, the density of the first zone may be
from about 0.15 g/cm3 to about 0.25 g/cm3.
Additionally, in certain aspects of the invention the functional particle
content in the first zone may be about 10 per cent to about 90 per cent by
weight, and/or
the functional particle content in the second zone may be about 0 per cent to
about 70 per
cent by weight.
In particular embodiments of the structures described above, the FASE
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value is higher than about 80. The structure may also have a wet integrity
higher than
about 4.0 mN/gm, a softness higher than about 8.0/J, or a pliability higher
than about
70/N.
In particular embodiments of the structures described above, the structure is
produced by a continuous series of unit operations, wherein each stratum is
formed in one
unit operation from one or more materials selected from fibers, functional
particles,
binders, carrier tissue and additives.
The present invention is also directed to disposable absorbent articles
comprising:
(A) a liquid pervious topsheet,
(B) a liquid impervious backsheet,
(C) between the topsheet and the backsheet and in fluid communication with the
topsheet an absorbent structure as described above, the structure comprising
one stratum or
a plurality of strata, at least one stratum containing functional particles,
the absorbent
structure having a y-directional profile comprising first and second zones
disposed in
contact with each other, wherein the first zone has one or more of a higher
density, a
higher content of functional particles and a higher basis weight than the
second zone, and,
optionally,
(D) between (C) and (B),and in fluid communication with (C) a storage stratum
comprising fibers and functional particles where a major surface of (C) in
fluid
communication with a major surface of (D) has a surface area which is less
than 80 percent
of the surface area of a corresponding major surface of (D).
In particular embodiments, the absorbent structure (C) may comprise
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(1) a y-directionally profiled acquisition stratum; and
(2) a y-directionally profiled acquisition and storage stratum having a higher
content of
functional particles than that of the acquisition stratum.
The articles described above may be infant diapers, training pants, adult
incontinence devices, or feminine hygiene pads. In particular embodiments, the
articles of
the invention may have a FASE of 50 or higher, preferably 80 or higher, more
preferably
100 or higher.
In certain aspects, the structures of the present invention can be
manufactured by suspending absorbent material in a fluid and depositing the
material on a
porous forming surface, or forming wire. The suspending fluid for the
absorbent material
can be water or air, but preferably is air. Placing several forming unit
operations in series
provides for the formation of unitary absorbent structures comprising several
strata of
absorbent material.
Typical airlaid forming unit operations contain mechanical equipment on
one side of the forming wire designed to accept air-suspended absorbent
material and
uniformly distribute the absorbent material onto the forming wire. Typically
located on
the other side of the forming wire, and working in concert with the
distributing equipment,
is a vacuum system that is present to collect the air-suspended absorbent
material onto the
forming wire. The present invention provides for reducing the vacuum in
specific zones in
the y-direction, such that one or more of the properties of basis weight,
density or SAP
content of the absorbent material collected on the forming wire is profiled.
In a preferred embodiment of the invention, the vacuum used to collect air-
suspended absorbent material is blocked, essentially reducing the vacuum to
zero in
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specific zones in the CD. When the vacuum is blocked in specific zones, the
striped strata
of the present invention can be formed.
In another preferred embodiment of the invention, the distribution of air-
suspended absorbent material is physically blocked in certain areas, so as to
cause
deposition on the forming wire which is profiled in the cross-machine
direction and the
striped strata of the present invention can be formed.
This invention provides a process for the production of an absorbent
structure comprising a plurality of strata, at least one stratum of which is
produced by a
series of unit operations and which contains functional particles and has a y-
directional
profile comprising first and second zones disposed in contact with each other,
wherein the
first zone has one or more of a higher density, higher content of functional
particles or
higher basis weight than the second zone, the process comprising:
( 1 ) forming a first stratum A comprising fibers and, optionally, functional
particles;
(2a) forming a second stratum B comprising fibers and functional particles
such
that a major surface of B is in fluid communicating contact with a major
surface of A and
the y-directional length of B is less than the y-directional length of A; or
(2b) forming a second stratum B comprising fibers and functional particles
such
that first and second zones disposed in contact with each other are formed,
wherein the
first zone has a higher density and a higher content of functional particles
than the second
zone.
In particular embodiments of the process described above, strata are formed
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on a forming wire of an airlaid process from fibers and functional particles
distributed
from a forming head and the first and second zones of stratum B are formed by
partially
blocking distribution into the second zone but not the first zone.
In an alternative embodiment of the process of the invention, strata are
formed on a forming wire of an airlaid process from fibers and functional
particles
distributed from a forming head and the first and second zones of stratum B
are formed by
partially blocking distribution into the second zone but not the first zone.
The invention is also directed to absorbent structures made by the process
described above.
Brief Description of the Drawings
Fig. 1 depicts a unitary absorbent structure on a forming wire, and depicts
the x-direction, y-direction and z-direction in relation to the structure;
Fig. 2a depicts a prior art unitary absorbent structure;
Fig. 2b depicts a unitary absorbent structure of the invention;
Fig. 2c depicts a unitary absorbent structure of the invention;
Fig. 3 depicts an absorbent structure of the invention having y-directional
structural profile of density and SAP content;
Figs. 4a-4i depict unitary absorbent structures of the invention with three
strata, including striped strata;
Fig. Sa-Sd depict additional embodiments of unitary absorbent structures of
the invention;
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Fig. 6 depicts an absorbent structure of the invention composed of two
strata, wherein the upper strata has y-directional structural profile of
density and SAP
content;
Fig. 7 depicts an absorbent structure of the invention composed of two strata,
5 wherein the lower strata has a y-directional structural profile of density
and SAP content;
Fig. 8 depicts a process of making an absorbent structure according to the
present invention;
Fig. 9 depicts a closeup view of the forming wire of Fig. 8;
Fig. 10 is a view along the direction A to B of the forming wire of Fig. 9;
10 Figs. 11A and 11B depict a tester used to test absorbency properties of
absorbent structures of the present invention;
Fig. 12 depicts a Gurley Stiffness Tester used to measure the pliability of
absorbent structures of the invention;
Figs. 13A and 13B depicts a clamp used to measure the pliability of absorbent
15 structures of the invention;
Figs. 14A-14C depict basis weight profiles of Samples A through C;
Fig. 15 depicts y-direction basis weight profiles for Samples A through C.;
Fig. 16 depicts y-direction density profiles for Samples A through C;
Figs. 17A and 17B depict schematic drawings for Samples D and E;
Figs. 18A and 18B depict schematic drawings for Samples F and G; and
Fig. 19 graphs the rewet properties as a function of the bottom stratum basis
weight and width for Samples H and J.
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Detailed Description of the Invention
All patents and patent applications cited in this specification are hereby
incorporated by reference into this specification. In case of conflict in
terminology, the
present disclosure controls.
Definitions
As used herein, the term "stratum" and in the plural "strata" means the output
of a unit operation designed to place absorbent material on the forming
surface, which may
employ a carrier tissue, or wire of a forming process. The process can be
wetlaid or airlaid,
but preferably is airlaid. Materials deposited on the forming surface by the
unit operation
include fibers, powders including additives and functional particles, such as
SAP and binders.
The totality of materials deposited on the forming surface may be referred to
as a "web" which
grows during the forming process as a successive unit operations add to the
web.
As used herein, the term "profiled stratum" means a stratum in which one or
more of the basis weight, density or content of functional particles (such as
super absorbent
polymer particles) of the stratum varies (is profiled) in the y-direction
and/or the z-direction.
As used herein, the term "striped stratum" means a special case of a profiled
stratum in which one or more of the absorbent material basis weight, density
or content of
functional particles in the stratum drop to very low levels or zero for a
finite length in the y-
direction. This finite length of zero basis weight, density or content of
functional particles
can be continuous or it can be parceled in discontinuous segments. The
parceled segments
can be distributed in a uniform pattern in the y-direction or there can be no
uniform pattern.
The finite length of very low levels or zero basis weight, density or content
of functional
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particles can be distributed symmetrically about the longitudinal axis of the
structure or it can
be distributed asymmetrically about the longitudinal axis of the structure.
As used herein, the term "ply" refers to a fibrous material which may be used
as a component in an absorbent article. A unitary absorbent core is an example
of a ply.
Other exemplary plies include a storage and acquisition layer, a liquid
pervious topsheet and
a liquid impervious backsheet. A series of plies may be assembled into an
absorbent article
in a converting process, in which plies are attached by glue or other
adhesive, by thermal
bonding, or by pressing or densifying the plies to produce entanglement.
As used herein, the term "content" means percentage by weight. Thus, the
content of functional particles in a given stratum is the percent by weight of
functional
particles in that stratum.
As used herein, the term "x-direction" refers to the direction along the
length
of the absorbent article 1, as illustrated in Figure 1. When the web is formed
so that the
absorbent article is disposed on a horizontal or flat forming wire 2, the x-
direction is the
machine direction (MD).
As used herein, the term "y-direction" refers to the direction along the width
of the absorbent article (see Figure 1). Referring to Figure 1, when the web
is formed so that
the fibrous material is disposed on a horizontal or flat forming wire 5, the y-
direction is the
cross-machine direction (CD).
As used herein, the term "z-direction" refers to the direction into the plane
of
the absorbent article (see Figure 1 ).
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As used herein, the term "width" of a stratum is the distance from one side of
the stratum to the other, measured in the y-direction normal to the
longitudinal axis of the
structure.
As used herein, the term "basis weight" is the weight of a web per unit area.
It is usually expressed as grams per square meter (g/m2 or gsm). Basis weight
is an intensive
property of a web, in that it is independent of the amount of web that is
present.
As used herein, the term "density" is expressed in grams per cubic centimeter
(g/cc), and is defined according to the following equation:
Density (g/cc) = Basis weight (glmZ) / [10,000 cm2 / m2 x Thiclmess (cm)]
As used herein, the term "unitary absorbent structure" or "absorbent
structure"
mean a structure or core of the invention containing one or more strata. When
the unitary
absorbent core contains a plurality of strata there is no interface between
the strata, i.e. once
the strata are disposed on each other they cannot be separated. Unitary
absorbent structures
which are formed from more than one straxa are formed without glue or other
adhesive
between the layers. A unitary structure may be formed, far example, in a
single
manufacturing line, for example in a single airlaid line. Typically, airlaid
absorbent cores
contain a combination of cellulosic fibers, mixed with various functional
synthetic fibers,
functional particles or granulates and additives.
Absorbent Structures
The present invention includes an absorbent structure which may be used as
a core, having a profile of basis weight, density or SAP content in its y-
direction, the direction
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perpendicular to the longitudinal axis of a finished product. In particular
embodiments, the
structure may be profiled in both the y- and z- directions.
Prior art absorbent cores typically comprise strata that run the full width of
the
core. As shown in Figure 2a, in the existing art, all of the strata are of the
same width. The
present invention can be used to improve on the existing art by providing a
method for
selectively placing absorbent material where it can be used most efficiently.
For example, as
shown in Figure 2b , the present invention contemplates placement of absorbent
material in
a selective manner in the center of the unitary absorbent core, at the point
of fluid insult,
instead of uniformly distributing the absorbent material across the full width
of the pad.
While 2b illustrates the use of strata having differing widths, in fact the
structure of the
invention will appear as Figure 2c, in which the strata having greater width
will meet at the
area where the stratum having lesser width is absent. The resulting structure
is profiled in
the y- and z-directions to form a zone containing greater basis weight,
density or functional
particle content.
Analogous to placing absorbent material in a unitary absorbent core where it
can be used most efficiently, the present invention contemplates removal of
material from the
unitary absorbent core where it is not being used efficiently. Stratum
profiling can be used
to reduce raw-material costs by removing absorbent material form the unitary
absorbent core
where it is not effective.
With reference to Figure 3, wherein the y-direction and z-direction are
indicated by arrows, the structure of the invention comprises at least one
zone A, having one
or more of higher basis weight, density or functional particle (such as SAP)
content, and
preferably at least two such zones A having one or more of higher basis
weight, density or
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functional particle (such as SAP) content, as well as at least one zone B
having lower basis
weight, density or functional particle content, or no functional particles. In
one of the
preferred embodiments the zones A have higher basis weight than the zones B.
One, and
more preferably two of the zones A, may be located at the edges on the sides
of the absorbent
5 structure.
For example, a y-directional and/or z-directional profile may be achieved by
placing higher amount of SAP particles along with natural or synthetic fibers
in narrow lanes
creating zones A along the absorbent structure. Such zones are then separated
by lower
density lanes of natural or synthetic fibers with lower amount of SAP or no
SAP, thus
10 creating zones B. Such a controlled placement of SAP particles allows for
better containment
of the particles within the absorbent structure and allows for easier flow and
wicking of the
fluid along the length of the core (x-direction). The pliability of such a
material can thus also
be improved, particularly across the width of the core.
Further, the structures of the invention may have unexpectedly high fluid
15 acquisition rate even at high SAP content, that is at SAP content higher
than 30 percent. The
absorbent structures known so far could not achieve such high acquisition
rates at high SAP
content because of the drastic loss in the permeability of these structures
when they become
saturated. This effect is associated with so called gel blocking of the SAP as
the SAP particles
swell and close the pores in the absorbent core. Without being bound to
theory, it is believed
20 that high acquisition rates of the structures of the invention, containing
high amount of SAP,
are due to the ability of these structures to maintain their high void volume
and acquire more
liquid in zones B (having one or more of lower basis weight, density or SAP
content) even
at high degree of saturation of the absorbent structure. It is also believed
that the high void
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21
volume in zones B can be maintained because the liquid is withdrawn from them
by capillary
forces to denser zones A, where it is retained by SAP particles in higher
concentration. As
a consequence of this, the structures of the invention have at the same time
exceptionally high
fluid acquisition and storage efficiency. This in turn allows for improved
performance of the
finished absorbent product, for example, a personal hygiene product, by
reducing leakage
during its use and for better utilization of the absorbent core. Increased
amount of SAP in the
absorbent core also enable manufacturers to produce thinner, more absorbent,
and more
comfortable absorbent articles.
One measurement used to evaluate the absorbent properties of a structure is
fluid acquisition and storage efficiency ("FASE"). FASE is a dimensionless
number, which
is obtained by multiplying the fluid acquisition rate and the content of SAP
particles in an
absorbent structure. The higher the fluid acquisition rate and the higher the
SAP particle
content are, the higher is the FASE. However, so far, it has been difficult to
achieve both high
acquisition rate and high SAP particle content at the same time because any
increase in the
SAP particle content led in general to more gel blocking, less permeability
and, consequently,
to lower fluid acquisition rate. Desirably, the absorbent structures of this
invention have a
FASE of SO or higher, more desirably 80 or higher, preferably 100 or higher
and more
preferably 180 or higher.
Referring to Figure 3, the fluid acquisition rate can be enhanced even
further if the structure of the invention comprises a porous upper stratum C
having
essentially no x,y-wicking properties and capable of maintaining substantial
dryness of the
surface. Such a stratum may be made for example with a matrix of synthetic
fibers bonded
with a binder.
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22
In some embodiments of the invention, stratum C is a low density
acquisition stratum including from between 50 to 99 percent by weight of
wettable
synthetic fibers, preferably from 75 to 90 percent synthetic fibers, the
balance of the
stratum being binder material. Due to its relatively low density, large pore
size, and lower
wettability than that of the other strata below, the stratum C has essentially
no x,y-aqueous
liquid wicking capability. Fluid is easily wicked from it downward to the more
wettable
and smaller-pore, higher density strata below. In the preferred case, the
stratum C would
include synthetic fibers having a thickness of from 2 to 35 dtex, preferably
of from 6 to 17
dtex. In this embodiment the synthetic fibers have a length of from 2 to 15
mm, preferably
of from 4 to 12 mm. Optionally, the fibers may be crimped and may have a
variety of
cross-sectional shapes. Examples of suitable synthetic matrix fibers include
polyethylene,
polypropylene, polyester, including polyester terephthalate (PET), polyamide,
polyacetates, cellulose acetate and rayon fibers. Certain hydrophobic
synthetic fiber, such
as polyolefins, should be surface treated with surfactant to improve
wettability.
Preferred embodiments of the unitary absorbent structures of the invention
contain at least one striped stratum. A striped stratum is a stratum in which
one or more of
the basis weight, density or functional particle (such as SAP) content drops
to very low
levels or zero for a finite length in the y-direction. This finite length of
very low levels or
zero basis weight, density or functional particle content can be continuous or
can be
parceled in discontinuous segments. The parceled segments can be distributed
in a
uniform pattern in the y-direction or there can be no uniform pattern. The
finite length of
very low levels or zero basis weight can be distributed symmetrically about
the
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23
longitudinal axis of the structure, or can be distributed asymmetrically about
the
longitudinal axis of the structure.
Figures 4a-4i depict representative, three-strata absorbent structure designs
containing at least one striped stratum. Figures 4c, 4e, 4f and 4g depict
absorbent
structures with more than one striped stratum. As shown by Figure 4g, the
striped strata
do not necessarily have the same width. As shown by Figure 4, the invention
contemplates absorbent structures with more than one stripe per stratum. As
shown by
Figure 4i, the invention also contemplates striped strata that are not
centered with respect
to the longitudinal axis of the structure. Figures 4a-i depict the absorbent
structures in a
theoretical manner. In fact, as explained in the discussion of Figures 2b and
2c, the strata
having greater width will meet in the area where the stratum or strata having
lesser width
is absent.
Figures Sa-Sd depict still additional embodiments of the absorbent
structures of the present invention. Figures Sa-Sd demonstrate how structures
may be
constructed stratum-by-stratum. In fact, in the structures of Figures Sa-Sd
the strata having
greater width will meet in the area where the stratum or strata having lesser
width is
absent.
These additional embodiments can be produced by vacuum segmentation,
i.e. by segmenting the vacuum system under the forming wire of the airlaid
process. The
vacuum system can be segmented into regions of relatively high vacuum and
regions of
relatively low vacuum. According to one method of the invention, the vacuum
may be
physically blocked in certain zones, in order to achieve zones of one or more
of higher
basis weight, density or functional particle (such as SAP) content. In
alternative methods
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24
of the invention, a block or mask may be used to shield the vacuum in desired
zones, in
order to achieve zones of one or more of higher basis weight, density or
functional particle
(such as SAP) content.
In an additional method of the invention, the distribution of air- bonded
absorbent material is physically blocked in certain areas, so as to prevent
deposition on the
forming wire. Thus, a flow divider or other block may be disposed between the
outlet of
the forming head or particle applicator and the forming wire, to block the
deposition of
particles or fibers. This results in an absorbent structure which is profiled
in the y-
direction.
Figure Sa is an example of an absorbent structure having more than one
strata, in which the bottom stratum is formed by blocking the deposition or
particles or
fibers at the edges of the forming wire, or by segmenting the vacuum system
into a region
of relatively high vacuum at the center of the forming wire and regions of
relatively low
vacuum at the edges of the forming wire. Thus, regions of high basis weight
are formed
by relatively high vacuum and regions of low basis weight are formed by
relatively low
vacuum or by blocking the deposition of fibers of particles. Figure Sb depicts
an
embodiment of the invention containing multiple regions of relatively high and
relatively
low basis weight in the y-direction. Figure Sc depicts an embodiment of the
invention in
which the center of mass of the unitary absorbent structure need not
correspond to the
longitudinal axis.
Figures 4 and 5 show examples of how the unitary absorbent structures of
the present invention may be constructed, stratum by stratum on a typical
airlaid line
modified as described by the present invention. Once the strata have been
formed, the
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present invention provides for uniformly compacting or densifying the
absorbent material.
The compaction may also provide for unitary absorbent structures to be used as
cores,
having density variation in the CD.
The absorbent structure may also be used as cores in absorbent articles.
In one embodiment of an absorbent article of the invention, depicted in
Figure 6, the structure of the invention comprises two separate absorbent
structures (or
plies), wherein the structures are in fluid communication with each other. The
structure
includes a shorter, upper structure 3, and a longer, lower absorbent structure
4. In general,
the surface area of the bottom surface of upper structure 3 is less than 80
percent of the
10 surface area of the upper surface of lower structure 4. This arrangement
has an advantage
over single-stratum structures by allowing for better containment and usage of
the
absorbent material during use of the absorbent article by the user. In Figure
6, the upper
structure of this embodiment is a y-profiled absorbent structure comprising
zones A and B
(wherein zones A have one or more of higher basis weight, density or
functional particle )
15 content than zones B), of the type exemplified in Figure 3.
In another embodiment of an absorbent article, depicted in Figure 7,
the lower structure 5 of the two-structure system is a profiled absorbent
structure of the
invention comprising zones A and B. The surface area of the bottom surface of
upper
structure 6 is less than 80 percent of the surface area of the upper surface
of lower
20 structure 5. Yet another example of the two-strata embodiment is a system,
in which both
the upper stratum and the bottom stratum are y-profiled structures of the
invention
comprising zones A and B.
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26
Referring to Figure 6, the advantage obtained by providing a two structure
system as described above, is that the fluid discharge from the human body
occurs mainly
over the frontal region 7 and central region 8 of the absorbent core. This
embodiment
places more of the absorbent capacity in the region where the liquid discharge
insults the
core.
Fibers
The structures of this invention can include natural fibers, synthetic fibers
or mixtures of both natural and synthetic fibers. Examples of the types of
natural fibers
which can be used in the present invention include fluffed cellulose fibers
prepared from
cotton, softwood and/or hardwood pulps, straw, keaf fibers, cellulose fibers
modified by
chemical, mechanical and/or thermal treatments, keratin fibers such as fibers
obtained
from feathers, bagasse, hemp, and flax, as well as man-made staple fibers made
with
natural polymers such as cellulose, chitin, and keratin. Cellulosic fibers
include
chemically modified cellulose such as chemically stiffened cellulosic fibers
by
crosslinking agents, fibers treated with mercerizing agents and cellulose
acetate.
Examples of suitable synthetic matrix fibers include polyethylene,
polypropylene,
polyester, including polyester terephthalate (PET), polyamide, polyacetates,
cellulose
acetate and rayon fibers. Certain hydrophobic synthetic fibers, such as
polyolefins, should
be surface treated with surfactant to improve wettability.
The final purity of the preferred cellulose fiber of the present invention
may range from at least 80 percent alpha to 98 percent alpha cellulose,
although purity of
greater than 95 percent alpha is preferred, and purity of 96.5 percent alpha
cellulose, is
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27
most preferred. As used herein, the term " purity" is measured by the
percentage of alpha
cellulose present. This is a conventional measurement in the dissolving pulp
industry.
Methods for the production of cellulose fiber of various purities typically
used in the pulp
and paper industry are known in the art.
Preferred fibers used in zones having higher levels of basis weight, density
or functional particle content (such as Zones B in Figure 3) are those which
have lower
water retention value (WRV). Water retention value (WRV) of cellulosic fibers
is an
indication of a fiber's ability to retain water under a given amount of
pressure. Cellulose
fibers that are soaked in water swell moderately, and physically retain water
in the swollen
fiber walls. When an aqueous fiber slurry is centrifuged, the majority of the
water is
removed from the fibers. However, a quantity of water is retained by the fiber
even after
centrifugation, and this quantity of water is expressed as a percentage based
on the dry
weight of the fiber.
The fibers having lower WRV value are in general stiffer than
conventional fluff fibers and thus contribute to improved structure
permeability. The
preferred water retention value (WRV) of the cellulose fibers of the present
invention is
less than 85 percent, more preferably between 30 percent and 80 percent, most
preferably
40 percent. The WRV refers to the amount of water calculated on a dry fiber
basis, that
remains absorbed by a sample of fibers that has been soaked and then
centrifuged to
remove interfiber water. The amount of water a fiber can absorb is dependent
upon its
ability to swell on saturation. A lower number indicates internal cross-
linking has taken
place. U.S. Patent No. 5,190,563 describes a method for measuring WRV.
30-08-2001 US003162 i
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28
Preferred fibers used in zones having lower levels of basis weight, density
or functional particle content (such as Zones B in Figure 3) are those which
have higher
curl. Curl is defined as a fractional shortening of the fiber due to kinks,
twists and/or
blends in the fiber. The per cent curl of the cellulose fibers of the present
invention is
preferably from 25 percent to 80 percent, and is more preferably from 40
percent to 75
percent. For the purpose of this disclosure, fiber curl may be measured in
terms of a two
dimensional field.
Curl is defined as a fractional shortening of the fiber due to kinks, twists
and/or bends in the fiber. The percent curl of the cellulose fibers of the
present invention
is preferably from 25 percent to 80 percent, and is more preferably 75
percent. For the
purpose of this disclosure, fiber curl may be measured in terms of a two
dimensional field.
The fiber curl is determined by viewing the fiber in a two dimensional plane,
measuring
the projected length of the fiber as the longest dimension of a rectangle
encompassing the
fiber, L (rectangle), and the actual length of the fiber L (actual), and then
calculating the
fiber curl factor from the following equation:
Curl Factor = L. (actual) / L (rectangle) - 1
A fiber curl index image analysis method is used to make this measurement
and is described in U.S. Patent No. 5,190,563. Fiber curl may be imparted by
mercerization.
Methods for the mercerization of cellulose typically used in the pulp and
paper industry are
24 known in the art.
Another source of cellulosic fibers for use in the present invention,
especially
for use in zones having lower basis weight, density or functional particle
content (zones B),
is chemically stiffened cellulose fibers. As used herein, the term "chemically
stiffened
.a_ - rt
_ r:
AMENDED SHEET -
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29
cellulose fibers" means cellulose fibers that have been treated to increase
the stiffness of the
fibers under both dry and wet aqueous conditions. In the most preferred
stiffened fibers,
chemical processing includes intrafiber crosslinking with crosslinking agents
while such fibers
are in a relatively dehydrated, defibrated (i.e., individualized), twisted,
curled condition.
These fibers are reported to have curl values greater than 70 percent and WRV
values less
than 60 percent. Fibers stiffened by crosslink bonds in individualized form
are disclosed, for
example, in U.S. Patent No. 5,217,445 issued June 8, 1993, and U.S. Pat. No.
3,224,946
issued Dec. 21, 1965.
Another source of cellulosic fibers for use in the present invention,
especially
for use in zones having lower basis weight, density or functional particle
content, are fibers
obtained from high-yield pulp, that is cellulose pulp containing lignin.
Typical examples of
such fibers are chemical thermo-mechanical pulp (CTMP) or bleached chemical
thermo-
mechanical pulp (BCTM). These fibers are stiffer both in dry and wet state
than cellulose
fibers with low or no lignin content.
Functional Particles
Functional particles for use in the absorbent cores of the invention include
particles, flakes, powders, granules or the like which serve as absorbents,
odor control
agents, e.g. zeolites or calcium carbonates, fragrances, detergents,
antimicrobial agents and
the like. The particles may include any functional powder or other particle
having a
particle diameter up to 3,000 (microns). In preferred embodiments, the
particles are
super absorbent polymer particles ("SAP")
U.S. PatentNos. 5,147,343; 5,378,528; 5,795,439; 5,807,916; and
5,849,211, which describe various superabsorbent polymers and methods of
manufacture,
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are hereby incorporated by reference. Examples of the types of SAP particles
which may
be used in this invention, include superabsorbent polymers in their
particulate form such as
irregular granules, spherical particles, staple fibers and other elongated
particles. The term
"superabsorbent polymer" or "SAP" refers to a normally water-soluble polymer,
which has
been cross-linked. There are known methods of making water-soluble polymers
such as
carboxylic polyelectrolytes to create hydrogel-forming materials, now commonly
referred
to as superabsorbents or SAPs, and it is well known to use such materials to
enhance the
absorbency of disposable absorbent articles. There are also known methods of
crosslinking carboxylated polyelectrolytes to obtain superabsorbent polymers.
SAP
10 particles useful in the practice of this invention are commercially
available from a number
of manufacturers, including Dow Chemical (Midland, Michigan), Stockhausen
(Greensboro, North Carolina), and Chemdal (Arlington Heights, Illinois). One
conventional granular superabsorbent polymer is based on poly(acrylic acid)
which has
been crosslinked during polymerization with any of a number of multi-
functional co-
15 monomer crosslinking agents, as is well known in the art. Examples of
multifunctional
crosslinking agents are set forth in U.S. Patent Nos. 2,929,154; 3,224,986;
3,332,909; and
4,076,673. Other water-soluble polyelectrolyte polymers are known to be useful
for the
preparation of superabsorbents by crosslinking, these polymers include
carboxymethyl
starch, carboxymethyl cellulose, chitosan salts, gelatin salts, etc. They are
not, however,
20 commonly used on a commercial scale to enhance absorbency of disposable
absorbent
articles, primarily due to lower absorbent efficiency or higher cost.
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31
Superabsorbent polymers are well-known and are commercially available.
Superabsorbent particulate polymers are also described in detail in U.S.
Patents 4,102,340
and Re 32, 649.
Suitable SAPS yield high gel volumes or high gel strength as measured by
the shear modulus of the hydrogel. Such preferred SAPS contain relatively low
levels of
polymeric materials that can be extracted by contact with synthetic urine (so-
called
"extractables"). SAPS are well known and are commercially available from
several
sources. One example is a starch graft polyacrylate hydrogel marketed under
the name
IM1000 (Hoechst-Celanese; Portsmouth, VA). Other commercially available
superabsorbers are marketed under the trademark SANWET (Sanyo Kasei Kogyo;
Kabushiki, Japan), SUMIKA GEL (Sumitomo Kagaku Kabushiki; Haishi, Japan),
FAVOR
(Stockhausen; Garyville, LA) and the ASAP series (Chemdal; Aberdeen, MS). Most
preferred for use with the present invention are polyacrylate-based SAPS. As
used in the
present invention, SAP particles of any size or shape suitable for use in an
absorbent core
may be employed.
Binders
If the use of binders is preferred, examples of binders useful in the
absorbent structure of the present invention include polymeric binders in a
solid or liquid
form. The term "polymeric binder" refers to any compound capable of creating
interfiber
bonds between matrix fibers to increase the integrity of the stratum. At the
same time, the
binder may optionally bind fibers and SAP particles to each other.
For example, a dispersion of natural or synthetic elastomeric latex may be
used as a binder. Thermoplastic fibers or powder, which are well known in the
art, are
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32
also commonly used to provide bonding upon heating of the absorbent structure
to the
melting point of the thermoplastic fiber or powder. Other binders, which can
be used for
stabilizing the absorbent structure of the present invention, include bonding
agents used to
bond cellulose fibers. These agents include polymers dispersed in water, which
are cured
after application to the fibrous web and create bonds between fibers or
between fibers and
SAP particles. Examples of such agents include various cationic starch
derivatives and
synthetic cationic polymers containing crosslinkable functional groups such as
polyamide-
polyamine epichlorohydrin adducts, cationic starch, dialdehyde starch and the
like. Any
combination of the above-described polymeric binders may be used for
stabilizing the
structure of the present invention.
Suitable binders for use in the structures of the invention include binders in
liquid form or-having a liquid carrier, including latex binders. Useful latex
binders include
vinyl acetate and acrylic ester copolymers, ethylene vinyl acetate copolymers,
styrene
butadiene carboxylate copolymers, and polyacrylonitriles, and sold, for
example, under the
trade names of Airbond, Airflex and Vinac of Air Products, Inc., Hycar and
Geon of
Goodrich Chemical Co., and Fulatex of H. B. Fuller Company. Alternatively, the
binder
may be a non-latex binder, such as binding agents applied in aqueous solutions
(for
example kymene, dialdehyde starch, chitosan or PVA), or epichlorohydrin and
the like.
For bonding the fibers specifically, and for structural integrity of the
unitary
absorbent structure generally, water-based latex binders may be used.
Alternatively, or in
combination with a latex binder, thermoplastic binding material (fibers or
powders) may be
used for bonding upon heating to the melting point of the thermoplastic
binding material.
Suitable thermoplastic binding material includes thermoplastic fibers, such as
bicomponent
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33
thermoplastic fibers ("bico"). Preferred thermoplastic binding fibers provide
enhanced
adhesion for a wide range of materials, including synthetic and natural
fibers, particles, and
synthetic and natural carrier sheets. An exemplary thermoplastic bico fiber is
Celbond Type
255 Bico fiber from Hoechst Celanese.
Other suitable thermoplastic fibers include polypropylenes, polyesters, nylons
and other olefins, or modifications thereof. A preferred thermoplastic fiber
is FiberVisions
type AL-Adhesion-C Bicomponent Fiber, which contains a polypropylene core and
an
activated copolyolefin sheath.
In certain embodiments, the binder in the invention is a binding fiber, which
comprises less than about 10 percent by weight of the SAP particles. In other
embodiments
of the invention, the binder fibers comprise less than about 7 percent by
weight of the
absorbent structure.
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Airlaid Manufacture of a Structure of the Invention
An absorbent structure having improved particle containment may be delivered
in roll-goods form, or in other packaging formats such as festooning, and is
particularly useful
as an absorbent core for disposable absorbent articles such as diapers, adult
incontinence pads
and briefs, and feminine sanitary napkins.
Preferably, the structure of the present invention is prepared as an airlaid
web.
The airlaid web is typically prepared by disintegrating or defiberizing a
cellulose pulp sheet
or sheets, typically by hammermill, to provide individualized fibers. The
individualized fibers
are optionally mixed with functional particles, and are then air conveyed to
one or more
forming heads on the airlaid web forming machine. The forming head then
deposes a stratum
in the forming wire. A stratum may contain, for example, cellulose fibers, SAP
and other
functional particles, and bicomponent fibers.
In some embodiments, the structures of the invention contain a carrier tissue.
The use of a compaction roll prior to the introduction of the particle areas
eliminates the need
1 S for the tissue.
Through the use of flow dividers or vacuum blocks, each of the forming heads
are adapted to provide a stratum having zones of one or more of higher basis
weight, density
or functional particle, e.g., SAP, content. Unit operations involve the use of
multiple
forming heads, for example, up to four, five, six or seven forming heads may
be used to
provide additional strata to the web. Any one or more than one of the strata
may comprise
zones of one or more of higher basis weight, density or functional particle,
e.g., SAP, content.
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According to the method of the invention, the zones may be obtained by
physical blocking with a mask, preventing absorbent material from being
deposited in specific
zones, thereby resulting in an absorbent product with profiled strata.
Alternatively, the zones
may be obtained by vacuum segmentation, controlling the vacuum properties,
after deposit
5 of the stratum from the forming head. Vacuum segmentation may be used to
control the width
of the stratum. For example, the vacuum segmentation may be achieved by the
use of a
forming screen.
Several manufacturers make airlaid web forming machines, including M&J
Fibretech of Denmark and Dan-Web, also of Denmark. The forming heads include
rotating
10 drums, or agitators generally in a racetrack configuration, which serve to
maintain fiber
separation until the fibers are pulled by vacuum onto a foraminous condensing
drum or
foraminous forming conveyor, or forming wire. For example, in machines
manufactured by
M&J Fibretech, the forming head includes a rotary agitator above a screen.
Other fibers, such
as a synthetic thermoplastic fiber, may also be introduced to the forming head
through a fiber
15 dosing system, which includes a fiber opener, a dosing unit and an air
conveyor.
The airlaid web is transferred from the forming wire to a calender or other
densification stage to densify the web, increase its strength and control web
thickness. The
fibers of the web may alternatively, or additionally, be bonded by application
of a binder or
foam addition system, followed by drying or curing. As a result, heat seals
between the
20 thermoplastic material and the fibers of the various strata are formed. The
finished web is
then rolled for future use.
Figure 8 depicts a process of making a fibrous web according to the present
invention. Optionally, a carrier tissue 20 may be unwound from the supply roll
21. The tissue
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36
20 is rolled on to forming wire 18. The tissue may alternatively be used as a
carrier or as the
lower stratum of the absorbent structure. As contemplated for the present
invention, a forming
head 24 of the airlaid web-forming machine distributes the desired fiber to
form the lower
stratum 23 of the absorbent structure. The strata may comprise further fibers,
such as
cellulosic fiber, thermoplastic fibers, and functional particles.
As contemplated by the present invention, one or more forming heads of the
airlaid web forming machine distributes the desired fiber for the various
strata of the
absorbent core or structure. For example, a first forming head may be used to
provide a first
fibrous stratum, for example a stratum comprising a cellulose fiber,
bicomponent fiber, and
optionally a carrier tissue. The first stratum may be a wicking stratum.
Functional particles may optionally (or additionally) be applied to the lower
strata by particle applicator 28. Thus, SAP particles or other functional
particles are thus
applied to stratum 23 deposited by forming head 24.
The deposition of fibers and particles in each strata is controlled in order
to
create zones of one or more of higher basis weight, density or functional
particle content. As
further described in Figure 9, forming wire 40 has flow dividers above or
blocks 41, which
are disposed over the forming wire, and below the outlet of the forming head.
For example,
the flow dividers 41 may be attached to a carriage or other device which is
located above the
forming wire. Fibers or particles which are deposited from the forming head
are blocked from
the forming wire. As a result, the stratum contains zones of one or more of
higher basis
weight, density or functional particle content. The zones can be varied by
manipulation of the
location or size of the flow dividers, or by variation of the types and
amounts of fibers and
functional particles in each stratum.
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37
Figure 10 depicts the flow dividers 41 located above forming wire 40, along
the direction A ~ B of Figure 9. In preferred embodiments, the flow dividers
are tapered so
that fibers or particles do not accumulate on the top of the divider. Also
depicted in Figure
are vacuum blocks 42, which may be located below the forming wire in order to
block the
5 vacuum.
Returning to Figure 8, optionally the strata is compacted or densified in a
nip
formed by a pair of calender rolls 26. The fibers may be compressed to the
desired thickness
and density. The lower stratum 23 may be compacted at this point in the
manufacturing
process to close the pores of the web if the particles are fine, and to
prevent spillage on to the
10 forming wire.
Additional strata 27 and 28 can then be formed on top of lower strata 23 in
the
same manner the first stratum is formed, by use of forming heads 30 and 31,
optionally
particle applicators 33 and 34, and optionally nips formed by calender rolls
at 35 and 36.
The airlaid web is transferred from the forming wire 18 and is compacted or
densified, for example, by use of a calender 37 or to increase its strength
and control web
thickness. Preferred ranges of densification are from about 0.035 to about
0.50 g/cc, more
preferably about 0.050 to about 0.50 g/cc, even more preferably about 0.20
g/cc. The web is
then subjected to further treatment including pressure, heat and/or the
application of a binder.
For example, a binder (such as a spray or foam binder), may be applied at
binder applicators,
which may be disposed after the calendar 37. A series of ovens also may be
used in processes
of the invention, after application of the binder, for drying, curing or
thermal bonding. The
airlaid structure may be heated to a temperature in the range of from 125 to
180 °C. A further
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overall binder may then be applied to the structure. This binder can be
applied by spray, foam
or mist, and is applied to reduce dust-off on the surface of the structure.
The air laid structure may be heated in additional ovens at a temperature in
the
range of from 125 to 180 ' C. The airlaid structure may be treated at pressure
in the range
S of from 0.1 psi (0.7 kPa) to 10 psi (70 kPa), preferafily 1.5 psi (10 kPa).
The finished web is then rolled at roll 50 for future use. This continuous
band of fibrous web can be slit or cut to form individual absorbent articles
in a cutting
unit, which has not been depicted in this figure.
Optionally, the finished web may be slit or perforated at the heat seal to
yield
narrow slit core material having a heat seal along both edges. The heat seals
to be slit must
be of sufficient width to provide two egective seals after slitting.
In other embodiments, various other strata containing other types and amounts
of fibers may be applied above or below the upper and lower strata of the
structure of the
present invention. For example, the absorbent article may contain also a fluid
previous top
sheet and a fluid impervious backsheet. Exemplary absorbent articles which can
be formed
from absorbent cores of the invention include diapers, feminine sanitary
napkins, and adult
incontinence products.
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Test methods
1. Fluid Acquisition Time and Rate
The Acquisition Time, the time for a given volume of saline solution to be
absorbed by an absorbent structure (until any free liquid disappears from the
surface of the
absorbent) was measured.
The following method was used to measure the Acquisition Time:
1. Condition sample in lab at 21° C and 50 percent relative humidity
for 2
hours prior to testing.
2. Prepare standard saline solution (0.9 percent NaCI in deionized water by
weight). Add dye if desired.
3. Determine insult volume and load to be used. Medium capacity samples
(most diapers of medium size (size #3)) use 3 x 75m1 insults and 2.7 kPa load.
4. If sample is formed in lab or on pilot machine (airlaid), cut to 10 cm x
35.6 cm for samples made on the lab pad former, 10 cm x 40.6 cm for samples
made on the
pilot machine. If sample is a commercial diaper, simply cut elastic legbands
so that diaper
will lay flat. Take weight/thicirness measurements of each sample.
5. Prepare airlaid samples by placing on plastic backsheet, Exxon EMB-685
polyethylene film, and adding coverstock material, 15 g/m2 Avgol spunbond
polypropylene.
Ensure that plastic backsheet material edges fold up toward top of sample to
protect against
leakage while testing.
6. Place sample in acquisition apparatus by placing sample on bottom plate,
positioning foam piece on top of sample, placing insult ring into hole in
foam, and then
positioning weighted top plates over foam~piece.
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7. Set timer for 20 minutes and place beside test apparatus.
8. With stopwatch in one hand and graduate cylinder containing insult volume
in other hand, prepare to insult sample. Pour fluid into insult ring. Start
stopwatch at moment
the fluid strikes the sample. Empty fluid from cylinder as quickly as
possible. Stop stopwatch
5 when fluid is absorbed by sample.
9. Note time taken by sample to absorb fluid. Start 20 minute timer as soon
as fluid is absorbed by sample.
10. After 20 minutes, repeat steps 7-9.
11. After another 20 minutes, repeat steps 7-9. Note: If no other tests are to
10 be done after the Acquisition test, the 20-minute interval following the
third insult can be
omitted. However, if another test is to be done following the Acquisition test
(Rewet and
Retention or Distribution), the 20-minute interval must be used and then the
other test may
be started.
The following formula is used to calculate the Acquisition Rate:
15 Insult Volume (ml)
Acquisition Rate (ml/s) - -----------------------------------
Acquisition Time (s)
2. Rewet Retention
The Rewet and Retention Test is designed to be performed immediately
20 following the Acquisition Test. The Acquisition Test procedure must be
followed before
starting this test. If no acquisition information is needed, acquisition times
do not have to be
recorded, however the pattern of 3 insults separated by 20-minute intervals
must be followed.
It is imperative that the 20 minute interval has elapsed before starting this
test.
Sample/solution preparation is the same as in the Fluid Acquisition test.
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1. Sample is now assumed to have been through the Acquisition Test and left
undisturbed for the final 20-minute time interval. Set a timer for 5 minutes
and place beside
test apparatus.
2. Weigh stack of 10 Buckeye S-22 Blotter papers cut to same dimension as
sample.
3. Remove weight over sample, foam piece, and insult ring.
4. Place stack of papers on sample.
5. Replace foam piece and weights over sample. Start 5-minute timer.
6. At end of 5 minutes, remove weight and weigh stack of papers.
Note weight differences between wet and dried papers. The rewet is calculated
according to the formula:
Rewet (g) = Weight of wet papers (g) - weight of dry papers (g)
The following formula is used to calculate the Rewet Retention after the third
insult:
1 S Vol. of All Insults (ml)-(Rewet (g) x 1 ml/g) x 100
Rewet Retention (percent) _
________________________________________________________________
Volume of ALL insults (ml)
3. Fluid Acquisition and Storage Efficiency
Fluid Acquisition and Storage Efficiency, FASE, is understood herein as a
property of an absorbent structure combining its fluid acquisition performance
with its fluid
storage function, the latter being determined by the content of SAP particles.
Fluid
Acquisition and Storage Efficiency is defined here by the following formula:
FASE = (Third Acquisition Rate, ml/s) x (percent SAP),
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where Third Acquisition Rate is the rate of acquisition of the third insult
measured according
to the method described in the Section "Measurement of Fluid Acquisition Time
and Rate",
and percent SAP is weight per cent content of SAP particles in an absorbent
structure or in
a an acquisition component of an absorbent structure. Fluid Acquisition
Efficiency is
presented as a dimensionless number although it- is~ a product of
multiplication of the
acquisition rate expressed in milliliters per second and ofthe SAP content
expressed in weight
per cent. According to this definition, a structure exhibiting high fluid
acquisition rate but
containing no SAP particles will have Fluid Acquisition and Storage Efficiency
equal to zero.
The structures of this invention have FASE higher than 80, preferably higher
than 120 and
most preferably higher than 160.
4. Absorbent Capaci
This method is used to test diapers and adult incontinence structures that
typically consist of an absorbent core containing superabsorbent polymer
(SAP). All samples
should be conditioned at 70°F (21°C) and 50 percent relative
humidity prior to testing.
1 S This test is used to evaluate an absorbent structure's ability to absorb
and retain
fluid after being submerged in a pool of saline solution. It is performed
under load in order
to simulate actual use of the product. From a performance standpoint, it is
important that a
structure be able to absorb as much fluid as possible. Even more importantly,
the structure
should be able to retain the fluid. Otherwise, the user will have a wet
sensation and the
product may leak. Absorbency and retention capacity are both reported in units
of grams per
gram.
The following procedure is used to measure Absorbent capacity:
.~u.
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A. For commercial, finished product samples:
1. Remove leg cuffs, waistbands, etc. before cutting.
2. Measure the length of the core to be evaluated.
3. If the length of the core is < 35.6 cm, e.g. all newborn diapers, use the
10 cm x
35.6 cm test apparatus.
4. If the length of the core is > 35.6 cm, use the 10 cm x 40.6 cm test
apparatus.
5. Most of the time, the core cannot be cut to measure exactly 35.6 cm or 40.6
cm in
length. When this is the case, it is necessary to "make-up" for the smaller
length
to insure that the desired load is applied to the core. Therefore, cut a
section out
of another core in order to make the total sample length either 35.6 cm or
40.6 cm.
(This piece should be 10 cm in width and taken from either the front or back
section of the core.) Wrap this section of diaper in plastic in order to
prevent any
insult fluid from wicking or absorbing into it. Some adult incontinence
products
are larger than 40.6 cm. If this is the case, do not cut the product. Instead,
fold to
form a 10 cm x 40.6 cm sample.
6. Determine the weight and thickness of the sample only. (Record as "Dry
Weight.") Before weighing the sample, remove the backsheet and coverstock. It
is usually difficult to remove the coverstock without tearing it into pieces.
However, it is important to remove the coverstock as best as possible. Instead
of
getting the coverstock's actual weight, assume it weighs 18 grams and subtract
this amount from the sample weight.
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B. For pad-former or machine-made (pilot or plant) samples: ,
1. Using a cutting board, cut samples to the required dimensions: 10 cm x 35.6
cm
for samples made on the pad-former or 10 cm x 40.6 cm for samples made either
on the pilot or plant lines.
2. Determine the weight and thiclaiess of the sample. (Record as "Dry
Weight.").
For all samples: .
3. Condition the sample in the lab at 70°F (21°C) and 50 percent
relative humidity
for 2 hours prior to testing. Samples that have akeady been tested do not need
additional conditioning time since they were already tested in a conditioned
lab
space.
4. Prepare 0.9 percent saline solution. For better visibility, add food grade
dye, if
desired.
S. Determine what load (via weight plates) will be used for evaluation. Choose
the
load depending on the type of the finished product, for example for small-size
diapers - 0.7 kPa (low capacity); medium size diapers - 2.7 kPa (medium
capacity); Adult Incontinence, high capacity products - 2.7 kPa or 6.8 kPa
(large
capacity).
6. Place the sample on the screen of the Absorbency Tester (Figure 11A). Place
the
foam on top of the sample, followed by the required number of weight plates.
For
commercial cores, the coversheet should be in contact with the screen while
the
backsheet should be facing up. The same applies to pad-former and machine-
made cores: the side of the sample that will be closest to the user should
face the
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screen while the bottom of the core should face up.
7. Set the timer for 20 minutes.
8. Open the valve to allow fluid (0.9 percent NaCI solution, by weight, in
deionized
water) to flow from the zero head aspirator bottle. This will help to keep the
fluid
5 level constant.
9. Start the timer as soon as the sample is submerged into the saline solution
container.
10. At least 2 minutes before the 20 minute time period expires, close the
aspirator
valve and open the air ejector aspirator pump valve in order to allow a vacuum
to
10 pull fluid from the base of the screen. In addition, turn on the water
faucet in
order to provide maximum vacuum. All of the liquid does not need to be
removed; however, there should be no fluid on the screen of apparatus B
(Figure
11 B).
11. When the appropriate time has elapsed, turn off the water faucet.
15 12. Remove the basket containing the sample and weight plates out of the
container
and drain on a flat plastic board that has been covered with blotter paper.
13. Drain for 5 minutes.
14. Remove the weight plates, foam, and weigh the wet sample. Record the
weight as
"Wet Weight Post Drainage."
20 15. Place a sheet of blotter paper on a flat surface. Place the sample on
top of the
blotter paper. Add the foam and weight plates.
16. Allow the sample to sit for 5 minutes.
17. Weigh the sample only. Record the weight as "Wet Weight Post Blotting."
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The following formula is used to calculate Absorbent Capacity:
Absorbent Capacity (g) = Wet Weight Post Blotting (g) - Dry Weight (g)
The apparatus used to measure absorbency and retention is depicted in Figures
11A and 11B. The Absorbency Tester consists of two parts. Part A (Figure 1 1A)
is a
container to hold saline solution. A drain nozzle, which is located in the
bottom of the
container, should be about 2.5 cm long, and about 1 cm in diameter. A support
cylinder
with 1 cm gap is used to support drain nozzle. Part B (Figure 11B)has a fine
screen (for
example, 200 mesh (0.07 mm nominal sieve opening and 0.05 mm inside wire
diameter)
screen bed). The screen is designed to hold a weight of up to 11.35 kg. The
sample and
weight plates are placed on top of this screen. Part B is placed inside of
Part A.
The foam is used during the test for placing between the absorbent core and
the
weight plates. This foam is covered with plastic film (at least 4 mm
thickness) and sealed
in any appropriate way (heat seal, seal tape, etc.) such that a waterproof
barrier is created
around the foam.
5. Wet Integrity
As used herein, "integrity" is a measure of the tensile strength of a fibrous
sheet, normalized for unit basis weight and is expressed in units
(milliNewtons, mN) of x-
directional force required to break a 2.5 cm wide sample of the sheet per
normalized basis
weight of 1 gsm. In order to measure Wet Integrity (wet tensile strength) of
an absorbent
core or a commercial absorbent product, the following procedure is used:
1. 2.5 cm x 10 cm samples are prepared.
:~;.: ..~..
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2. Remove any removable plastic backsheet, coverstock or synthetic
acquisition material, leaving only the core.
3. Weigh sample. Apply 0.9 percent saline solution, in an amount equal
to twice the sample weight, to the center of the sample using pipette or spray
bottle
(Example: sample weighs l .00g. Apply 2.00g saline solution for total of
3.00g).
4. insert sample into Tensile Tester (for example a Thwing-Albert LT-150
Universal Materials Tester, default software settings used for test) by
placing in
pressurized clamps.
5. Start test.
6. When test is finished, record results displayed. These results include
Force at Peak, Elongation at Peak, Maximum Elongation, Energy at Peak, and
Energy at
Maximum.
The Wet Integrity as used herein is defined as the Force at Peak as
measured by using the above procedure. The Wet Integrity of the absorbent
structures of
the present invention are higher than 4.0 mNIg/m2, and preferably higher than
6Ø
mN/g/mz.
6. Softness
The softness of the absorbent structure is an important factor contributing
to the overall conformability of the structure. As used herein, "softness" is
the inverse of
the amount of energy necessary to compress a sheet, in this case the sheet
being the
absorbent structure. The greater the amount of energy necessary to compress a
sheet, the
less soft it is.
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with obvious machine direction and cross direction, cut 20 cm dimension in
machine
direction.
2. Allow plastic backsheet and coverstock material to remain on sample
(applies to commercial diaper samples). If testing prototype core samples,
apply plastic
backsheet, Exxon EMB-685 polyethylene film, to bottom of sample and
coverstock, 15
gsm Avgol spunbond polypropylene, to top of sample (same size as sample,
adhered with
a small amount of spray adhesive).
3. Program modified compression test (for example, a Thwing-Albert LT-
150 Universal Materials Tester): Compression test using following non-default
settings:
Break Detection Method = % Drop/Displacement, Break Value = % Drop = 50,
Distance
Traps = 0.8cm/1.3cm/1.8 cm, Units: Distance/Displacement = cm; Force = grams,
Test
speed = 2.5 cm/min. All other settings left at defaults.
4. Insert sample into Tensile Tester using custom clamps as depicted in
Figure 12. The clamp may be formed of .16 cm thick aluminum, and is 2.5 cm
wide x 20
cm long. The U-shape simulates the shape a diaper will take when placed on a
baby. The
function of the clamp is two fold. First, it facilitates the testing of a full
width core.
Second, it maintains the U-shape during the softness test, simulating the
force required by
the baby to compress the diaper between its legs, thus conforming to diaper of
its body.
The sample is inserted on its edge, such that it will be compressed in the y-
direction (10
cm direction), having 2.5 cm on both edges within the custom clamps, thus
leaving a 5 cm
gap.
5. Start test.
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cm direction), having 2.5 cm on both edges within the custom clamps, thus
leaving a 5 cm
gap.
5. Start test.
6. When deflection exceeds 1.8 cm, push down on top pressurized clamp
to simulate a sample break and stop the test (does not affect test results).
Record results
displayed. These results include Force at Peak, Deflection at Peak, Maximum
Deflection,
Energy at Peak, and Energy at Maximum Deflection, and Force at Distance Traps.
The value, which is used to calculate the softness, is Energy at Maximum
Deflection, which is expressed in Joules. Energy of Maximum Deflection, Ed
""x, is
calculated according to the following formula:
d max
' Ed ""x = j F dd
d min
where Ed ""x is Energy at Maximum Deflection, F is force at given deflection,
d , and d min
and d max are the deflections at the start of the test and at the end of the
test, respectively.
Softness, S, is defined here according to the following formula:
S =1/(Energy at Maximum Deflection).
The result, S, is expressed here in 1 per Joule, 1/J.
In general, Softness of the overall absorbent structure of the present
invention
should be higher than 8.0/J, preferably higher than 15.0/J.
;;y;: v..
. ,
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7. Pliabili
The pliability of the absorbent structure is also an important factor
contributing to the overall conformability of the sheet. As used herein,
"pliability" is the
inverse of the amount of force necessary to bend a sheet, in this case the
sheet being the
5 absorbent structure of the invention. The greater the force necessary to
bend the sheet, the
less pliable the sheet is.
Pliability can be measured by the following procedure, using a Gurley tester
(Model 4171, Gurley Precision Instruments, Trey, NY). A sample Gurley
Stiffness Tester is
depicted at Figure 12.
10 1. Cut sample to 2.5 cm x 8.3 cm as accurately as possible. If there is a
definite
machine direction and cross direction, cut one sample in each direction and
test each.
2. Fit custom clamp as shown in Fig. 12, over the original clamp provided
with the Gurley tester, and tighten smaller, upper thumbscrews to secure (see
Figure 12
illustrating the custom clamp for higher basis weight, lofty sheets). The
custom clamp was
15 designed in such a way that it does not change the thickness of the tested
material, where the
material is inserted into the clamp. If the thickness is changed as a result
of clamping then the
properties of the structure are changed and the results obtained by using the
Gurley tester are
affected. In the present method, the clamp of Figure 12 is used to eliminate
such undesired
effects.
20 3. The purpose of this custom clamp is to allow for the testing of samples
that
are too thick to be tested using the existing Gurley clamp without being
compressed. The
existing Gurley clamp allows for testing of samples having a maximum thickness
of about
0.63 cm. Examples of structures tested using the custom clamp are commercial
and prototype
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diapers and diaper cores, and commercial and prototype adult incontinence
structures. This
custom clamp allows the sample to be tested without any z-directional
structural compression,
such as would be present if the existing clamp were used. This, therefore,
removes the
densification during testing issue, which can have a significant adverse
effect on the test
results.
4. Open the custom clamp adjustable plate by loosening longer, lower
thumbscrews. Place sample in clamp by sliding sample up until it just contacts
original
clamp. There should be 5 cm of sample contained in the custom clamp.
5. Adjust height of custom clamp by loosening height adjustment screw on
original clamp. Adjust height so that a gap of 2.5 cm exists between the point
where the
sample exits the custom clamp and the point where the sample will contact the
lever arm.
6. Ensure that the remaining 0.6 cm of sample extends below the top of the
lever arm. Ensure that lever arm is not moving. Press motor button to move
sample towards
lever arm. Continue pressing motor button until sample clears lever arm. While
doing this,
observe and note the highest number reached on the scale. Repeat this in the
opposite
direction.
7. Average the two values obtained. In the conversion chart on the apparatus,
find the factor for a 2.5 cm wide x 3.8 cm long sample depending on the weight
used and the
distance the weight was placed from the center on the lever arm. A 2.5 cm x
8.3 cm sample
tested using the custom clamp corresponds to a 2.5 cm x 8.3 cm sample tested
without using
the custom clamp. Without the custom clamp, 0.6 cm of sample is in the
original clamp, 0.6
cm extends below the top of the lever arm, and 2.5 cm is the gap between.
Using the custom
clamp, the same 0.6 cm in the custom clamp is used; the other 4.4 cm in the
custom clamp
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secures the thicker sample in place. The same 0.6 cm extends below the top of
the lever arm
and the same 2.5 cm gap is in between.
8. Multiply the average reading on the scale by the appropriate conversion
factor found on the chart.
The result is Stiffness, which is expressed in milligrams force, mg.
Pliability,
P, is defined here according to the following formula:
P = 106/9.81 * Stiffness.
The result, P, is expressed here in 1 per Newton, 1/N. In general, Pliability
of the entire
absorbent structure of the present invention is higher than 60/N, preferably
higher than 80/N.
In the present invention, high levels of softness, pliability and wet
integrity
may be achieved by applying one or a combination of the following features in
the preparation
of an absorbent structure: by using soft fibers, curled or crimped fibers, by
applying soft
binder systems, such as for example fine or crimped binding fibers, elastic
latex binders or
water-soluble bonding agents, by minimizing the amounts of binder, applying
relatively low
pressure during compaction before curing, and using relatively low pressure
during the
calendaring of the sheet after it has been cured. In general, the density of
the sheet after
compaction and/or calendaring in the absorbent structures of the invention
should be lower
than 0.35 g/cc, and preferably lower than 0.3 g/cc.
8. Thickness
Thickness is measured using an analog thickness gauge (B.C. Ames Co.;
Waltham, MA). The gauge has a 4.1-cm diameter foot and is equipped with a 150-
gram
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weight so that the pressure applied to the sample is 11.4 g/cmz. Thickness is
measured in
inches and is converted to centimeters as needed for calculations.
9. Combination Acquisition and Rewet Test
Equipment involved in this test includes the following materials:
Electronic balance (t 0.01 g precision)
Fluid intake tester (FIT, Buckeye "B144-97" design)
Grade S22 blotter paper, 10.16 cm x 24.13 cm (4 in. x 9.5 in.)
Weight, 8408.5 8,10.16 cm x 24.13 cm (4 in. x 9.5 in.)
Latex foam, 10.16 cm x 24.13 cm x 3.81 cm (4 in. x 9.5 in. x 1.5 in.)
Synthetic menstrual fluid
Topsheet, spunbond polypropylene, 22 8/m2, 25.4 cm x 10.16 cm (10 in. x 4
in.)
Latex foam can be obtained from Scott Fabrics; Memphis, TN. Blotter paper
can be obtained from Buckeye Technologies; Memphis, TN. The topsheet material
can be
obtained from Avgol Nonwoven Industries; Holon, Israel. The fluid intake
tester (FITS, of
Buckeye design, consists of a top plate and a bottom plate. The top plate is a
29.7 cm x I9.0
cm x 1.3 cm plate of polycarbonate plastic. The plate has a hole cut out of
its center and a
hollow intake cylinder is mounted in the hole. The inner diameter of the
intake cylinder is 2.5
cm and the complete top plate weighs 872 grams. The bottom plate of the FIT is
essentially
a 29.7 cm x 19.0 cm x 1.3 cm monolithic plate of polycarbonate plastic.
The synthetic menstrual fluid used in the combination acquisition and rewet
test contains the following ingredients in the designated amounts:
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Deionized water 903.3 g
Sodium chloride 9.0 g
Polyvinylpyrrolidone 122.0 g
Biebrich Scarlet 4.0 g
Total solution volume 1 liter '
Biebrich Scarlet (red dye) can be obtained from Sigma Chemical Co.; St. Louis,
MO.
Polyvinylpyrrolidone (PVP, weight-average molecular weight approximately
55,000) can be
obtained from Aldrich; Milwaukee, WI. Sodium chloride (ACS grade) can be
obtained from
J.T. Baker; Phillipsburg, NJ. The dry ingredients are mixed in water for at
least two hours to
ensure complete dissolution. The solution temperature is adjusted to
22°C exactly. 26 ml of
solution is pipetted into the UL adapter chamber of a Brookfield Model DV-II+
viscometer
(Brookfield Engineering Laboratories, Inc., Stoughton, MA). The UL spindle is
placed into
the chamber and the viscometer speed is set to 30 rpm. The target viscosity is
between 9 and
10 centipoise (32 and 36 kg/m hour). Viscosity can be adjusted with additional
water or PVP.
The sample is cut to 7 cm x 20 cm with the longer dimension in the machine
direction. The sample weight and thickness are measured and recorded. An "X"
is placed at
the center of the top of the sample with a marking pen. The sample is centered
on the FIT
bottom plate. The topsheet is centered vn the sample and the FIT top plate is
lowered on top
of the topsheet. The top plate is centered on the sample so that the intake
cylinder is centered
on the "X" marked on the sample. A 10-ml insult of the synthetic menstrual
fluid is poured
into the intake cylinder and the amount of time taken for the sample to
acquire the fluid is
measured and recorded. This time, reported in seconds (s), is the acquisition
time for the
_,.
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sample. Simultaneous with the end of the acquisition time, a 20-minute waiting
period
begins. At the end of the waiting period, rewet is measured by removing the
top FIT plate,
then placing a pre-weighed stack of eight S22 blotter papers on the topsheet
of the sample.
The foam is placed on the paper and the weight is placed on top of the foam
(the foam and the
5 paper constitute a 3.4 kPa pressure on the sample) for two minutes. The
rewet, reported in
grams (g), is calculated by subtracting the initial weight of the stack of
papers from the final
weight of the stack of papers. This combination test is usually performed in
triplicate and the
results are averaged.
The structures of the present invention having y-directional profile in basis
10 weight, density and SAP content may be employed in any disposable absorbent
article
intended to absorb and contain body exudates, and which are generally placed
or retained in
proximity with the body of the wearer. Disposable absorbent articles include
infant diapers,
adult incontinence products, training pants, sanitary napkins and other
feminine hygiene
products.
15 Exemplary Embodiments of the Invention
The invention is illustrated here by performing a series of experiments in
which
unitary absorbent structures are produced and tested.
Example 1 i(Samples A through C)
Samples A through C are three-strata, unitary absorbent cores that were
20 manufactured on an airlaid pilot line containing three forming heads. For
this group of
samples, the second forming head of the pilot line was modified to form the
striped strata of
the present invention. In Samples A through C, the first or bottom wicking
stratum comprised
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70 gsm of Grade ND-416 pulp (Weyerhaeuser Co.; Tacoma WA), 7 gsm of
bicomponent
binder fiber (Grade AL-Adhesion-C, 1.7 dtex x 4 mm, FiberVisions; Covington,
GA) and
carrier tissue (absorbent core wrap, 18 gsm, Cellu Tissue Corporation; East
Hartford, CT).
In Samples A through C, the third or top acquisition stratum comprised 35 gsm
of polyester staple fiber (15 dpf x 6 mm, Grade 376X2, Wellman, Inc.;
Johnsonville, SC) to
which was applied an emulsion binder (6 gsm, Airflex 192, Air Products
Polymers;
Allentown, PA).
Sample A serves as the control for this group because it was not produced by
practicing the present invention. In Sample A, the middle storage stratum
comprised 50 gsm
of Grade HPF pulp (Buckeye Technologies, Memphis, TN), 50 gsm of Favor SXM 70
superabsorbent powder (Stockhausen, Inc.; Greensboro, NC) and 7 gsm of Grade
AL-
Adhesion-C bicomponent binder fiber (1.7 dtex x 4 mm).
The present invention was used to construct the second or middle storage
strata
for Samples B and C. The objective was to keep the second strata weight the
same as found
in Sample A, but to increase the basis weight of the second stratum by
concentrating
absorbent material in a zone located in the center of Samples B and C. This
was done by
reducing the width of the second stratum and, concomitantly, fixing the total
amount of
absorbent material present in the stratum. Reducing the area over which the
absorbent
material was distributed increased the stratum basis weight. The standard
product footprint
for these examples was 70 mm by 200 mm. While keeping the overall weight of
the stratum
constant, the width of the middle stratum was reduced from 70 mm (full width,
Sample A)
to 55 mm (Sample B) to 40 mm (Sample C).
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For Sample A (control), the target basis weight was 243 g/m2 and the target
caliper was 2.85 mm, resulting in a target density of 0.085 g/cc. Samples B
and C were also
uniformly compacted to a target caliper of 2.85 mm.
Figure 14 is a schematic drawing indicating how samples A through C were
formed, stratum by stratum. Figure 14 indicates that the basis weight and
density of sample
A should be constant across its width. However, Figure 14 also indicates that,
compared to
sample A, samples B and C should have regions of higher basis weight and
density at their
centers and regions of lower basis weight and density at their edges.
Figure 15 shows the y-direction basis weight profiles that were measure for
samples A through C. The basis weight for sample A is uniform. The basis
weight of the
edges for samples B and C are the same, indicating the absence of a
contribution to the overall
basis weight from the second or middle storage stratum. As indicated by the
schematic
drawings of Figure 14, the basis weight is the center of the unitary absorbent
cores increased
from sample A to sample B to Sample C.
Samples A through C were compacted to the same thickness on the airlaid pilot
line. Figure 16 shows y-direction density profiles for Samples A through C.
Figure 14 shows
the increase in density in the center as the basis weight increased in the
center at fixed
thickness. Figure 16 shows the decrease in density in the edges as the basis
weight decreased
in the edges at fixed thickness.
Example 2 lSamnles D through G)
Samples D to G show how the present invention can be used to improve
product performance over the conventional technology.
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Samples D and E are three-strata, unitary absorbent cores that were
manufactured on an airlaid pilot line containing three forming heads. The
first or bottom
wicking stratum for these examples comprised 101.8 g/m2 of Grade ND-416 pulp
(Weyerhaeuser Co; Tacoma WA), 8.9 g/m2 of bicomponent binder fiber (Grade AL-
Adhesion-
C, 1.7 dtex x 4 mm, FiberVisions; Covington, GA)~and carrier tissue (absorbent
core wrap,
18 gsm, Cellu Tissue Corporation; East Hartford, CT).
The second or middle storage stratum comprised SO g/m2 of Grade HPF pulp
(Buckeye Technologies; Memphis, Tip, 50 g/m2 of Favor SXM 70 superabsorbent
powder
(Stockhausen, Inc.; Greensboro, NC) and 7 g/m2 of Grade AL-Adhesion-C
bicomponent
binder fiber (1.7 dtex x 4 mm). The third or top acquisition stratum comprised
35 gsm of
polyester staple fiber (17 dtex x 6 mm, Grade 376X2, Wellman, Inc.;
Johnsonville, SC) to
which was applied an emulsion binder (6 g/m2, Airflex 192, Air Products
Polymers;
Allentown, PA).
For Sample D, the first forming head of the pilot line was modified to form
the
striped strata of the present invention. The standard product footprint is 70
mm by 200 mm.
For Sample D, the first strata was formed in two 22.3-mm stripes with a 25.4-
mm gap
between the stripes. Sample E was constructed in the conventional way to serve
as a control.
Note that the basis weight and density in the center of sample D was lower
than the basis
weight and density of sample E. Both samples were compacted to a thickness of
2.97 mm.
Figure 17A is a schematic drawing indicating how sample was formed,
stratum-by-stratum, and Figure 17B is a schematic drawing indicating how
Sample E was
formed, stratum-by-stratum. In Figures 17A and 17B, the longitudinal axis of
the product is
normal to the plane of the drawing. Figures 17A and 17B do not indicate the
end-view
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59
profiles of the actual finished products after they were uniformly compacted
to target
thickness.
Table 1 shows acquisition and rewet data for samples D and E. Acquisition
was faster and rewet was lower for sample D compared to control, sample E. It
is well known
to those skilled in the art that acquisition time cau be a strong function of
absorbent-core
density. The lower density in the central portion of sample D accounts for its
shorter
acquisition time.
Table 1. Acquisition and rewet data for Samples D and E
Sample ConfigurationAcquisition times)Rewet
(g)
D Profiled 9.9 1.32
E Control 16.8 1.73
Samples F and G are two-strata, unitary absorbent cores that were
manufactured using a laboratory pad former of Buckeye design (Buckeye
Technologies;
Memphis, TN). For these samples, the fowling screen of the laboratory pad
former was
modified to form the striped strata of the present invention. These cores were
formed upside
down in the laboratory pad former (the top strata of the cores were formed
first and the bottom
strata of the cores were formed second).
Sample G serves as the control for this pair of samples. A top stratum was
formed on topsheet material that also functioned as a carrier (polypropylene
spunbond with
durable hydrophilic finish, 22 g/mz, Avgol Nonwoven Industries; Holon,
Israel). This stratum
comprised 92 glm2 of fluff pulp (Foley Fluffs, Buckeye Technologies; Memphis,
TN) and 10
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g/m2 of bicomponent binder fiber (Grade AL-Adhesion-C, 1.7 dtex x 4 mm,
FiberVisions;
Covington, GA).
The present invention was used to construct the top stratum for sample F. The
objective was to keep the top stratum weight the same as found in sample G,
but to increase
5 the basis weight of the top stratum by concentrating absorbent material in
the center of F.
This was done by reducing the width of the top stratum and, concomitantly,
fixing the total
amount of absorbent material present in the stratum. Reducing the area over
which the
absorbent material was distributed increased the stratum basis weight. The
standard product
footprint for these samples was 70 mm by 200 mm. While keeping the overall
weight of the
10 stratum constant, the width of the top stratum was reduced from 70 mm (full
width, sample
G) to 44 mm (sample F).
In samples F and G, the bottom stratum comprised 59 g/mz of fluff pulp (Foley
Fluffs, Buckeye Technologies; Memphis, TIC, 7 g/m2 of bicomponent binder fiber
(Grade
AL-Adhesion-C,1.7 dtex x 4 mm, FiberVisions; Covington, GA), 50 g/m~ of Favor
SXM 70
15 superabsorbent powder (Stockhausen, Inc.; Greensboro, NC).
For sample G (control), the target basis weight was 240 g/m2 and the target
caliper was 2.67 mm, resulting in a target density of 0.090 g/cc. Sample F was
also uniformly
compacted to a target caliper of 2.67 mm.
Figure 18 is a schematic drawing indicating how samples F and G were
20 formed, stratum-by-stratum. Samples F and G were formed upside down in the
laboratory
former, but their profiles are depicted right side up in Figures 18A and 18B,
respectively. In
Figure 18, the longitudinal axis of the product is normal to the plane of the
drawing.
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Table 2 shows acquisition and rewet data for samples F and G. Product
dryness, as measured by the rewet test, was better for sample F over the
control (Sample G).
Absorbent material was concentrated in the central portion of sample F,
resulting in improved
rewet over control.
Acquisition was slower in sample F compared to control, sample G. It is well
known to those skilled in the art that acquisition time can be a strong
function of absorbent-
core density. The higher density in the central portion of sample F accounts
for the longer
acquisition time.
Table 2. Acquisition and rewet data for Samples F and G
Sample ConfigurationAcquisition times)Rewet(g)
F Profiled S 1.28 4.42
G Control 37.7 4.93
Example 3 (Samples H and J):
The next several samples show how the present invention can be used to
maintain performance while reducing raw material costs.
Samples H and J are three-strata, unitary absorbent cores that were
manufactured on an airlaid pilot line containing three forming heads. The
first or bottom
wicking stratum for these samples comprised specified amounts of Grade ND-416
pulp
(Weyerhaeuser Co.; Tacoma WA). The first stratum for samples H and J contained
60 gsm
of ND-416 pulp. See Table 4. The first stratum for these examples also
contained 7 gsm of
bicomponent binder fiber (Grade AL-Adhesion-C,1.7 dtex x 4 mm, FiberVisions,
Covington;
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62
GA) and carrier tissue (absorbent core wrap, 18 g/m2, Cellu Tissue
Corporation; East
Hartford, CT).
Table 3. Product parameters and rewet data for Samples H through K
Sample Bottom Bottom stratum Rewet(g)
stratum basis
width (mm)weight (g/m=)
H SS 60 1.97
J 40 60 1.69
The second or middle storage stratum comprised 50 g/m2 of Grade HPF pulp
(Buckeye Technologies; Memphis, TN), SO g/mz of Favor SXM 70 superabsorbent
powder
(Stockhausen, Inc.; Greensboro, NC) and 7 g/m2 of Grade AL-Adhesion-C
bicomponent
binder fiber (1.7 dtex x 4 mm).
The third ortop acquisition stratum comprised 35 g/m2 ofpolyester staple fiber
(17 dtex pf x 6 mm, Grade 376X2, Wellman, Inc.; Johnsonville, SC) to which was
applied an
emulsion binder (6 g/m2, Airflex 192, Air Products Polymers; Allentown, PA).
For this group of samples, the first forming head of the pilot line was
modified
to form the striped strata of the present invention. The standard product
footprint is 70 mm
by 200 mm. For sample H, the first stratum was formed in one 55-mm wide stripe
centered
about the longitudinal axis of the product. For sample J, the first stratum
was formed in one
40-mm wide stripe centered about the longitudinal axis of the product. Table 3
shows the
basis weights and widths for the bottom strata for samples H and J.
._..~
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Samples H and J were uniformly compacted to a target density of 0.085 g/cc.
The target basis weight in the central portions of samples H and J was 233
g/m2.
Figure 19 shows rewet data for Samples H and J as a function of the basis
weight and width of the bottom wicking stratum. Figure 19 shows that rewet is
essentially
flat with respect to stratum width. Assuming that the rewet performance shown
here is
acceptable, the examples with the narrower width would be favored based on raw
material
costs.
Example 4
Seven commercially available brand diaperproducts (products 1-'~ were tested
for SAP % content in the absorbent core, absorbency, rewet retention and third
acquisition
time. The results are summarized in Table 4.
Table 4
OverallOverall AbsorbentRewetRewet Third FASE
Avg. SAP Capacity (ga RetentionAcquisition
roduct Basis Content (g) (Percent)Rste
Wt (~'t
Percent)
1 710 40.1 443 0.4 . 99.8 0.55 22.1
2 600 30.5 422 5.3 97.7 0.71 21.7
3 658 36.8 321 162 92.8 124 45.6
4 719 39.9 251 3.4 98.5 0.83 33.1
5 680 37.7 551 0.6 99.7 025 9.4
6 820 42.6 537 0.7 99.7 0.33 14.1
7 750 14.7 422 15.8 93.0 0.21 3.1
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Comparison of the data in Table 4 with the data in Tables 5 and 6 reveals that
the absorbent
systems comprising y-directionally profiled absorbent structures have
considerably higher
FASE values than any of the tested commercial absorbent articles.
Example 5
The absorbent samples tested in Example 4 were used for reference to compare
the performance of systems without y-directionally profiled structures
(Example 4) to the
systems containing y-directionally profiled structures (Examples 5 and 6).
The following raw materials were used as structural components ofthe samples
described in Example 5 and 6:
a) Foley Fluff (FF)- bleached southern softwood Kraft (BSSK) fibers from
Buckeye
Technologies; Memphis, Tennessee;
b) ND 416 compressible pulp available from Weyerhaeuser Company; Tacoma,
Washington;
c) Chemically crosslinked fibers (CS) such as those described in U.S. Pat. No.
5,190,563 by
treating Southern Softwood Kraft pulp with citric acid and sodium
hypophosphite. The fibers
had WRV of about 40% and Curl Factor of about 0.5;
d) Polyethylene terephthalate (PET) fibers having the name of Fillwell 093TM ,
Wellman PET
376X2, having thickness of 16.7 dtex per fiber (dtexpfJ and length of 6 mm,
available from
Wellman International Limited; Mullagh, Kells, County Meath, Ireland;
e) Superabsorbent polymers:
- FAVORTM SXM 3950, obtained from Stockhausen GmbH & CoKG.; Krefeld
Germany
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- FAVOR'~'M SXM 9100 obtained from Stockhausen GmbH & CoKG.; Krefeld
Germany
- K - SANITM MG-2600 obtained from Kolon Chemical Co., LTD.; Kwacheon-
City Kyunggi-Do, Korea; .
5 - K - SAMTM MG-3 500 obtained from Kolon Chemical Co., LTD.; Kwacheon-
City Kyunggi-Do, Korea;
f) LicontrolTM nonwoven acquisition stratum having basis weight of 48 g/m2,
reference
number 381002-0000 from Jacob Holm Industries; Alsace, France SAS;
g) AirFlexTM 124 latex emulsion available from Air Products Polymers, L. P.;
Allentown,
10 Pennsylvania;
h) T255TM bicomponent, crimped binder fiber having thickness of 2.3 dtexpf and
length of
6mm available from Kosa; Houston, Texas;
i) Fiber Vision bicomponent binder fiber having thickness of 1.7 dtexpf and
length of 6 mm,
available from FiberVisions; Varde, Denmark.
15 The absorbent samples used in Example 5 consisted each of an upper stratum
and a lower stratum, both strata having rectangular shape. Each upper stratum
was 10 cm
wide and 20 cm long, whereas each lower stratum was 10 cm wide and 40.6 cm
long. For
testing the acquisition time and rewet of each absorbent sample, the upper
stratum was placed
on the top of the lower stratum so that the front edges of both plies were on
the same line.
20 For the absorbent sample "L" and "M" the same lower ply material X612 was
used. The
sample "N" consisted of higher basis weight upper (DXI19) and bottom (DX122)
plies
described in this Example.
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The lower stratum material, X612, basis weight of 330 g/m2, and used in
Example 6, was produced on an M&J commercial air laid machine by forming an
absorbent
on Cellutissue 3024, an 18 g/m2 carrier tissue. The absorbent was formed in
four steps. First
a homogeneous stratum comprised of 37 g/m2 ND416 pulp fibers, 92.3 glm2
ofFavorTM SXM
3950, and 4.0 glm2 T-255TM (2.3dtexpfj bicomponent staple fiber. A second
homogeneous
stratum comprised of 37 g/m2 ND416 pulp fibers, 92.3 g/mz of FavorTM SXM 3950,
and 4.0
gsm T-255 (2.3dtexpf) staple fiber. A third homogeneous stratum comprised of
38.5 g/m2
ND416 pulp fibers and 6.9 g/m2 T-255 (2.3dtexpfj staple fiber. Water in an
amount of 49.1
g/m2 was sprayed on top of the third stratum before the drying and curing
stage.
Sample L was made using an upper stratum material produced on a Danweb
pilot air laid machine in the following manner: The nonwoven acquisition
stratum type
LicontrolTM 48 g/m2 was used as a forming sheet. The absorbent structure was
formed on the
spunbond side of the two-strata nonwoven. The raw materials were homogeneously
mixed
consisting of 144 g/m2 FF pulp fibers,150 g/mz FavorTM SXM 9100 and 6.0 g/m2
FiberVision
(1.7 dtex). Total basis weight was 348 g/m2.
Sample M was made using an upper stratum material produced on a Danweb
pilot air laid machine. The nonwoven acquisition stratum type LicontrolTM 48
g/m2 was used
as a forming sheet. The absorbent structure was formed on the spunbond side of
the two-strata
nonwoven. The raw materials, consisting of 144 g/m2 CS fibers, 150 g/m2
FavorTM SXM
9100 and 6.0 g/m2 FiberVision (1.7 dtexpfj, were homogeneously mixed. Total
basis weight
was 348 g/m2.
Sample N consisted of DXl 19 material as an upper ply and DX122 material
as a lower ply.
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DX119 material was made in the following manner:
A cellulose based tissue, Cellutissue 3024 18 g/m', was first applied and used
as a
transfer/carrier medium for the subsequent material. The next stratum
consisted of a uniform
blend of 130 g/m2 Southern Softwood pulp fibers (Foley Flub, 103.5 g/m2
superabsorbent
Kolon MG 2600, and 7.5 g/m2 self adhesion bicomponent fiber with a
polypropylene core and
polyethylene sheath (Fiber Visions 1.7 dtexpf/ 4mm cut). The next stratum
consisted of a
uniform blend of 130 glmz of Foley Fluff, 103.5 g/m2 of Kolon MG 2600, and 7.5
glmz of
Fiber Vision bicomponent fiber,1.7 dtexpf/ 4mm cut. The last or top stratum
was 42 g/m2
poly (ethylene terephthalate) fibers Wellman'i'M PET 376 x 2, 16.7 dtexpf and
8 g/mZ binder
Air Products AF 124 latex binder used at 10 percent solids. The web was
densified to 0.07
g/cc before curing. The total basis weight of the material was 547 g/mz.
DX122 material was made in the following manner:
A cellulose based tissue, Cellutissue 3024 18 g/m2, was first applied and used
as a
transfer/carrier medium for the subsequent material. The next stratum
consisted of a uniform
blend of 117 g/m2 highly compressible softened pulp fibers (ND416) , 85 g/m2
high permeable
superabsorbent (Kolon MG 2600), and 11 g/m2 self adhesion bicomponent fiber
with a
polypropylene core and polyethylene sheath (Fiber Visions 1.7 dtexpf/ 4mm
cut). The next
stratum consisted of a uniform blend of 117 g/m2 of ND416, 201 g/m2 of Kolon
MG 2600,
and 4 g/m2 of Fiber Vision bicomponent fiber 1.7 dtexpf/ 4mm cut. The last or
top stratum
was 5 g/m2 binder add on of-Air Products AF 124 latex binder at 14 percent
solids. The web
was densified to 0.15 g/cc before curing. The total basis weight of the
material was 5 SO g/m2.
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6s
Table S. Properties of Samples L to nT
OverallOverall Tbird
Avg. SAP Absorben Rewet Acquisition
Basis Content t Capacity RetentionRaxe
wt -
Sample (g/mZ) (%) (g) Rewet (%) (mLlsec) FASE
(g)
L 504 54.2 373 9.4 96.0 0.88 47.7
M 504 54.2 398 6.5 97.1 i.50 81.3
S N 824 42.9 550 2.9 98.7 1.36 58.3
The data in Tables 4, S, 7 and 10 clearly demonstrate the superiority of
absorbent
systems comprising y-directionally profiled structures over the absorbent
systems without
such profiled structures.
Example b
The absorbent samples tested in Example 6 consisted each of an upper stratum
and a lower stratum, both strata having rectangular shape. Each upper stratum
had a y-
directional profile described in Table 5 and was 10 cm wide and 20 cm long
whereas each
lower ply was 10 cm wide and 40.6 cm long. For testing the acquisition time
and rewet of
each sample, the upper ply was placed on the top of the lower ply so that the
front edges of
both plies were on the same line.
The lower stratum material, named as X612, was the same as described in
Example 5.
Sample O was made using an upper stratum material produced on a Danweb
pilot air laid machine in the following manner: The LicontrolTM nonwoven
acquisition
stratum was used as a forming sheet. The first stratum was formed on the
spunbond side of
the two-strata nonwoven. The first stratum formed was the high-density zone A
region as 5.1
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69
cm, spaced 5.1 cm stripes running in the 1VLD direction. The stripes were
composed of 175
gsm ND416 pulp fibers, 281 g/m2 FavorTM SXM 9100, and 14.0 g/m2 FiberVision
(1.7
dtexpf) bico staple fibers. These materials were homogcneously mixed. The
second stratum
filled zone B. It consisted of 62 g/m2 FF pulp Sbers, 66 g/m2 FavorTM SXM 9100
and 4.0 g/m2
FiberVision ( 1.7 dtexpf] biro staple fibers. These materials were
homogeneously mixed filling
the areas .between the high-density zone A region. Total basis weight was 348
g/m2.
Sample P was made using an upper stratum material produced on a Danweb
pilot air laid machine in the following manner: The LicontrolTM nonwoven
acquisition stratum
was used as a forming shCet. The first stratum was formed on the spunbond side
of the two-
strata nonwoven. The first stratum formed was the high-density zone A region
as 5.1 cm,
spaced 5.1 cm stripes running in the MD direction. The stripes were composed
of 175 g/m2
ND4 i 6 pulp fibers, 281 g/m2 FavorTM SXM 9100, and 14.0 g/m2 FiberVision (
1.7 dtexpfj bico
staple fibers. These materials were homogeneously mixed. The second stratum
filled zone B.
It consisted of 62 g/m2 CS pulp fibers, 66 glm2 FavorTM SXM 9100 and 4.0 g/m2
FiberVision ( 1.7 dtexp~ bico staple fibers. These materials were
homogeneously mixed filling
the areas between the high-density zone A region. Total basis weight was 348
g/mZ.
Sample Q was made using an upper stratum material produced on a
Danweb pilot air laid machine in the following manner: The LicontrolTM
nonwoven
acquisition stratum was used as a forming sheet. The first stratum was formed
on the
spunbond side of the two-strata nonwoven. The first stratum formed was the
high-density
zone A region as S.1 cm, spaced S.l cm stripes running in the MD direction.
The stripes
were composed of 175 glmz ND 416 pulp fibers, 281 g/m2 FavorTM SXM 9100, and
14.0
g/m2 FiberVision (1.7 dtexpf) bico staple fibers. These materials were
homogeneously
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mixed. The second stratum filled zone B. It consisted of 62 glm2 Fillwell
093TM
Wellman PET 376X2 16.7 dtexpf 6 mm synthetic staple fibers, 66 g/m2 FavorTM
SXM
9100 and 4.0 g/m2 FiberVision (1.7 dtexpf) bico staple fibers. These materials
were
homogeneously mixed filling the areas between the high-density zone A region.
Total
5 basis weight was 348 g/m2.
Tab a 6
Zone
A
Y-ProfiledBasisDensitySAP Zone Basis densitySAP Zone
Structurewt g/cm' ContentWidth wt glcm' contentWidtb
in Sample(glm~) (Percent)(cm) (~/n~2) (Percent)(cm)
IO O 551 0.305 60 2.5 273 0.203 50 5.1
P 562 0.214 60 2.5 282 O.I36 50 5.1
Q , 749 0.27? 60 I 2.5 303 0.140 SO l 5.1
~ , I , I
Zones A and B, basis weights and densities for each zone were calculated
values from total weight and bulk measurements.
15 Tabe7
Tbird
~'e~u Rewet Acquisition
SAP Absorbent RetentionRate
Sample Content CapacityRewet (Percent)(mlJsec)FASE
(g)
(%) (g)
O 54.2 390 4.29 98.1 1.94 105.1
P 542 408 1.35 99.4 3.73 202.2
Q 54.2 437 2.49 98.9 3.41 184.8
20 Analysis of the data in Tables 4, 5, 6 and 7 reveals that the absorbent
samples comprising y-directionally profiled absorbent structures have
considerably higher
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FASE values than any of the commercially available and tested absorbent
articles, as well
as absorbent samples without y-directional profile. The highest FASE values
were
obtained with the y-profiled structures, in which zones B comprised either
crosslinked
cellulose fibers (CS) or PET fibers (WellmanTM PET 376X2 16.7 dtexpfj.
The y-profiled upper ply components of the samples P and Q were
tested for wet integrity, softness and pliability. The results are shown in
Table 8.
ab a
Wet Wet Softness, Pliability,Pliability,
integrity,integrity UJ 1lN 1/N
Sample mN/g/mz, mN/g/m=, complete high low density
high low sample density area
density density area
area area
P 39.2 93.1 73.9 470 278
Q 28.8 74.6 97.3 371 230
Examgle 7
The absorbent samples tested in Example 7 consisted each of an upper
stratum and a lower stratum, both plies having rectangular shape. The upper
stratum was
Unicore 8902 material which is commercially available from Buckeye
Technologies Inc.
It was 9 cm wide and 20 cm long. The lower ply was 10 cm wide and 35.6 cm
long. For
testing the acquisition time and rewet of each absorbent system, the upper
stratum was
placed on the top of the lower stratum so that the front edges of both strata
were on the
same line.
,:.._
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Sample R contained a lower stratum made in a laboratory pad former in the
following
manner:
1. A carrier tissue (Cellutissue 3024, an 18 g/m2 cellulosic tissue), was laid
down.
2. The first set of material lanes were deposited. This was accomplished using
a
variant grid. The variant grid consisted of alternating l Omm open and lOmm
blocked lanes. The first set of lanes deposited material consisted of Aracruz
Eucalyptus fiber at a weight of 86 g/m2 and FiberVisions 1.7dtexpf/4mm
bicomponent fiber at a weight of 12 g/m2. These weights represent material
weights in the first l Omm wide lanes only. The overall average gsm for the
pad is
therefore half of these in-lane-only g/m2 's.
3. The variant grid was then shifted l0mm in the cross direction such that the
open
areas of the grid were then over the empty lanes of the pad. The second set of
material lanes were then deposited. The deposited material consisted of
Weyerhauser ND416 fiber at a weight of 86 g/m2, FiberVisions 1.7dtexpf/4mm
bicomponent fiber at a weight of 12 g/m2, and Stockhausen SXM70 superabsorbent
polymer at a weight of 368 gJm2. These weights represent material weights in
the
second set of l Omm wide lanes only. The overall average g/mZ for the pad is
therefore half of these in-lane-only g/m2's.
4. The resulting structure was then densified using a laboratory roller press.
Resultant
density for the first set of material lanes was 0.06g/cc. Resultant density
for the
second set of material lanes was 0.28g/cc.
5. A latex spray was then applied to the structure above stratum 2. Latex used
was
Air Products Airflex 124. Latex spray was a 10 percent solids mixture. This
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mixture also contained Aerosol OT (75 percent) surfactant added at a 0.1
percent level.
The mixture sprayed resulted in a 2 g/m2 latex solids add-on to the sample.
6. The sample was then dried/cured in an oven (LindbergBlue IVl7 for 25
minutes at
150°C.
Table 9
Tone A Zone
B
Y-profiled
structure
in
sample density (glcm')zone width density (g/cm')zone width
(cm) (cm)
R 0.28 1.0 0.06 1.0
Table 10
Overall Rewet Third
target SAP Absorbent Retention Acquisition
Sample content Capacity (%) Time (see)FASE
(%) (g)
R 50 290 91.9 2.19 109.5
S 50 298 97.8 t.22 61.0
Sample S contained a lower stratum made in a laboratory pad former in the
following
manner:
1. A carriertissue was laid down. This material was Celludssue 3024, an 18
g/m2 cellulosic
tissue.
2. Stratum 1 was deposited. This stratum consisted of a uniform mixture of
Weyerhauser
ND416 fiber at a weight of 86 g/m2, FiberVisions l.SSdpf/4mm bicomponent fiber
at a
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weight of 12 g/m2, and Stockhausen SXM70 superabsorbent polymer at a weight of
184
g/mz.
3. The resulting structure was then densified using a laboratory roller press.
Resultant
density for the structure was then 0.23g/cc.
4. A latex spray was then applied to the structure above stratum 1. Latex used
was Air
Products Airflex 124. Latex spray was a 10 percent solids mixture. This
mixture also
contained Aemsol OT (75 percent) surfactant added at a 0.1 percent level. The
mixture
sprayed resulted in a 2 g/m2 latex solids add-on to the sample.
5. The sample was then dried/cured in an oven (LindbergBlue lv~ for 25 minutes
at 150°C.
As seen from the data in Table 9 the sample R with y-directionally
profiled lower ply has significantly higher FASE valuc than the control sample
"S".
While the invention has been described in detail with specific reference to
preferred embodiments thereof, the invention is capable of other and different
embodiments, and its details are capable of modifications in various obvious
respects. As
would be readily apparent to those skilled in the art, variations and
modifications can be
affected while remaining within the spirit and scope of the invention.
Accordingly, the
foregoing disclosure, description and Figures are for illustrative purposes
only, and do not
in any way limit the invention, which is defined only by the claims.
AMENDED SHEET
