Note: Descriptions are shown in the official language in which they were submitted.
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ABSORBENT BARRIER STRUCTURES HAVING A HIGH CONVECTIVE AIR FLOW RATE
AND ARTICLES MADE THEREFROM
10
FIELD OF INVENTION
The present invention relates to absorbent articles which provide superior
protection against wet
through under impact or sustained pressure, and high convective air flow
therethrough for skin health and
comfort benefits. In particular, the present invention relates to an absorbent
barrier structure for such
articles.
BACKGROLTND OF THE INVENTION
Many known absorbent articles such a's diapers, incontinence articles,
feminine hygiene products,
training pants, typically comprise absorbent core materials located between a
liquid pervious body-side
liner or topsheet and a vapor permeable, liquid impermeable outer cover or
backsheet. The bodyside liner
allows bodily liquids to flow through easily and towards the absorbent core.
The absorbent core takes up the
liquids quickly. Thus, no excessive pooling of liquids occurs on the body-
facing surface of the absorbent
article. The outer cover is typically liquid impermeable such that there would
be no leakage from the
absorbent article. However, because the disposable absorbent article may be
worn for hours, sometimes
after the absorbent article has taken up liquids, perspiration from the
wearer's body, and liquid vapors
escaped from the absorbent core, can get entrapped in the space between the
absorbent ardcle and the
wearer's skin, resulting in an increased relative humidity in the occluded
area. As is known in the art, the
increased relative humidity leads to discomfort and overhydrated skin, which
is prone to skin health
problems, especially rashes and other contact dermatitis.
Such backsheets are well suited to prevent the leakage of bodily fluids (such
as urine, menses or
fecal matters) from the absorbent material to the outer garment of a wearer.
Unfortunately, the use of such
an impermeable backsheet can result in a high degree of humidity in the
absorbent- article when the
absorbent article is in use such that a relatively elevated skin hydration
levels may result.
The problem of high relative humidity near the skin in an absorbent article
has been addressed in
the art through a number of means. For example, U.S. Pat. No. 5,137,525 uses
mechanical means to
increase airflow in the article. Altematively, breathable outer covers
comprising, for example, microporous
or monolithic films, allow air and water vapor diffusion and have been
disclosed previously. PCT
Publication WO 98/58609 discloses absorbent article with good liquid retention
in the absorbent core
combined with water vapor permeability, liquid impermeable barrier materials
for backsheet.
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PCT Publication WO 00/10497, WO 00/10498, WO 00/10499, WO 00/10500, WO
00/10501 relate to
breathable absorbent articles including the diffusion properties of the wet
articles. These publications
disclose absorbent articles having high permeability zones within the
absorbent core, such as by aperturing
the absorbent core or by creating portions in the core containing
substantially less high absorbency
materials than in other portions of the core. These publications disclose gas
or vapor transfer mechanism
through the absorbent article by diffusion mechanism such as diffusion through
the use of a microporous
film. Since diffusion mechanism is not very effective, the absorbent articles
disclosed therein can lead to
relatively good humidity conditions while being worn so long as the article is
not substantially loaded with
a large amount of liquids such as urine. However, these absorbent articles
will still exhibit significantly
increased relative humidity between the skin of the wearer and the article
when the article is loaded.
Another performance parameter of interest for the loaded/wet absorbent article
is its ability to hold
the liquid and prevent leakage especially when the article is subjected to
pressure or iinpact force due to the
wearer's motion, such as sitting, walking, bending, and falling. Prior art
also failed to provide satisfactory
absorbent article which can hold liquids when its loaded to its absorbent
capacity especially when the
loaded absorbent article is under pressure or impact due to wearer's motion.
Consequently there is a need
for absorbent articles which have a balance of property - on one hand it is
able to keep the relative humidity
within the diaper in the range that's generally accepted as being comfortable,
typically between about 30%
to about 70% and more typically between about 30% to about 50% relative
humidity. Such an absorbent
article should also have the ability to hold liquids without leakage,
especially when the article is loaded with
bodily fluids. There is further a need to provide an absorbent article which
manages the relative humidity
within the absorbent article by a convective transport mechanisin. There is
further a need for absorbent
articles wherein good microclimate conditions are achieved by carefully
designing the chassis elements.
Typically to reduce the humidity level within the space between the absorbent
article and the
wearer's skin, breathable polymer films have been used as the outer cover for
the absorbent article. The
breathable films are typically constructed with micropores to provide
substantial liquid impermeability and
some level of diffusive air/vapor permeability, which is not as effective as
the convective air/vapor
permeability.
Other disposable absorbent articles have been designed to provide breathable
regions in the form
of breathable panels or perforated openings in the backsheet or in the core to
help ventilate the garment.
Articles using perforated components or breathable panels often exhibit
excessive leakage or wet through of
liquids from the article. Moreover, wearer's movements (e.g., sitting,
falling, walking, lying) may subject
the absorbent article to physical exertions, such as impact, compression,
bending and the like, which may
lead to increased leakage and wet through. The leakage/wet tlirough problem
becomes more severe under
higher impact or pressure, heavy discharges and/or extended wear time.
Alternatively, multi-layered backsheets or outer covers have been used to
address the wet through
problem. For example, breathable materials such as a fibrous textile or a
nonwoven web have been used in
the outer cover, either alone or in laminates with the microporous film. The
relatively open structures of
such materials allow air or vapor to diffuse through easily. The laminates may
provide improved liquid
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impermeability and diffusive air/vapor permeability. The materials may be
treated to furflier improve the
liquid impermeability. However, the laminates still do not provide
satisfactory protection against wet
through under impact and/or sustained pressure. Further, the transport of air
or vapor through the laminates
via a diffusive mechanism is not as effective as the transport via a
convective mechanism.
An alternative approach to the wet through problem is to improve the absorbent
material such that
little or no liquid comes into contact with the backsheet, thereby preventing
wet through. This is typically
achieved by increasing the amount of absorbent material in the article.
However, this approach may lead to
an increase in thickness of the article and a decrease in comfort as well as a
decrease in vapor/air
permeability through the article.
Another approach to the wet through problem is to place formed films between
the core and the
backsheet. Formed films having apertures in the shape of slanted cones are
disclosed in PCT publications
WO 99/39672, WO 99/39673 and WO 99/39674. However, after compaction or
sustained pressure, these
formed films fail to maintain its formed shape, consequently, they fail to
provide the desired balance of
properties. Thus, while these formed films may appear to have material
properties to provide air
permeability and adequate leakage protection, they are not useful as a
component within an absorbent
article, which typically is subjected to a series of processes that compacts
the article (including packaging,
shipping and storage) before consumer use, and may be subjected to sustained
pressure (e.g., being sat on
by the wearer) during use.
Therefore, there is a need to have absorbent articles that provide consumer
comfort, in terms of
reduced relative humidity within the absorbent article at a desirable overall
thickness, and still achieve
satisfactory wet through protection.
There is also a need to provide absorbent articles which manage the relative
humidity within the
space between the article and the wearer's skin to maintain good skin health.
Further, there is a need to
manage the relative humidity within the absorbent article by an effective
convective transport mechanism,
and, optionally some degree of diffusive transport mechanism may be
incorporated as well.
Additionally, there is a need for absorbent articles wherein the optimal
microclimate condition
within the space between the article and the wearer's skin is achieved by
careful designs of components of
the article. Specifically, there is a need for an absorbent barrier structure
which provides the desired wet
through protection and air/vapor permeability. Further, such an absorbent
barrier structure has a desirable
thickness for wearer comfort.
There is a further need to provide absorbent articles comprising a barrier
absorbent structure that
can be exposed to compact and/or sustained pressure conditions for at least 24
hours without substantially
degrading its performance, such as air permeability, liquid impermeability and
resistance to leakage under
impact or sustained pressure.
SUMMARY OF THE INVENTION
The present invention relates to absorbent articles with improved protection
and comfort by use of
an absorbent barrier structure. This is achieved by the selection of
individual components meeting specific
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requirements such that the combination thereof provides the absorbent articles
having desired performance.
A typical absorbent article comprises an air/vapor permeable, liquid
impermeable outer cover, a
liquid permeable bodyside liner or topsheet, an absorbent body between the
outer cover and the bodyside
liner and an absorbent barrier structure positioned between the outer cover
and the absorbent body.
The absorbent barrier structure of the present invention has a balanced
property between
convective air flow and absorptive barrier property. The convective air flow
property is effective to reduce
the relative humidity within the space between the absorbent article and the
wearer's skin. The
combination of liquid absorption and liquid barrier property provides
protection against the wet througli
problem, and is especially beneficial when the absorbent article is under
impact and/or sustained pressured
conditions.
The absorbent barrier structure is a composite structure having at least one
barrier zone and at least
one reservoir zone. The barrier zone is resistant to liquid penetration so
that the outflow of liquids from the
absorbent core is substantially slowed or retarded to allow additional time
for the absorbent core to acquire,
distribute and retain the liquids to its full capacity. Suitable materials for
the barrier zone should have a
hydrohead value of at least about 10 mBars. The reservoir zone absorbs and
retains any errant liquids that
escape both the core and the barrier zone, thus, provides added protection
against wet through.
Cooperatively, the zones of the absorbent barrier structure effectively
protect against wet through problem
even under extreme conditions, such as impact or sustained pressure.
The absorbent barrier structure typically has a hydrohead value of at least
about 10 mBars, a
convective air permeability of at least about 10 Darcy/mm, a dynamic liquid
impact (LIT) value of less than
about 10 grams per square meters and an absorbency of at least about 1 g/g.
In one embodiment, the absorbent barrier structure comprises one barrier layer
disposed adjacent
to the garinent-facing surface of the absorbent core, and one reservoir layer
disposed adjacent to the
garment-facing surface of the barrier layer. An additional barrier layer may
be disposed on the opposite
surface of the reservoir layer. In another embodiment, the absorbent article
may further include a dampness
management layer.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is partially broken top plan view of an absorbent article containing
the absorbent barrier
structure of the present invention;
Figure 2A is a cross sectional view of an absorbent barrier structure of the
present invention which
has a barrier layer and a reservoir layer;
Figure 2B is a cross sectional view of an absorbent barrier structure of the
present invention which
has a reservoir layer disposed between two barrier layers;
Figures 3A-3D are cross sectional views of alternative embodiments of the
absorbent barrier
structure of Figure 2A;
Figure 4A is a top plan view of the absorbent barrier structure of the present
invention which has a
barrier zone and a reservoir zone in a side-by-side arrangement;
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Figure 4B is a top plan view of the absorbent barrier structure of the present
invention in an
alternative arrangement;
Figure 5 is a schematic illustration of the Dynamic Liquid Impact Tester.
DETAILED DESCRIPTION OF THE INVENTION
DEFINITIONS
As used herein, the term "absorbent articles" refers to devices which absorb
and contain body
exudates, and, more specifically, refers to devices which are placed against
or in proximity to the body of
the wearer to absorb and contain the various exudates discharged from the
body. Absorbent articles may
include diapers, training pants, adult incontinence undergarments, feminine
hygiene products, breast pads,
and the like. As used herein, the term "body fluids" or "body exudates"
includes, but is not limited to, urine,
blood, vaginal discharges, sweat and fecal matters.
The term "disposable" is used herein to describe absorbent articles which are
not intended to be
laundered or otherwise restored or reused as an absorbent article (i.e., they
are intended to be discarded after
use and, preferably, to be recycled, composted or otherwise disposed of in an
environmentally compatible
manner).
As used herein, the term "zone" refers to a region or an area comprising a
material being
physically, chemically, or visually distinguishable from surrounding or
adjoining materials. Various zones
of materials may include transitional zones in between. The zones may be
positioned in the z-dimension or
in the xy-dimension. As used herein, the term "z-dimension" refers to the
dimension orthogonal to the
length and width of the structure or article. The z-dimension usually
corresponds to the thickness of the
structure or article. As used herein, the term "xy-dimension" refers to the
plane orthogonal to the thickness
of the member, core or article when the member, core or article is in a flat-
out state. The xy-dimension
usually corresponds to the length and width, respectively, of the structure or
article,in a flat-out state.
As used herein, the term "unitary structure" refers to a structure comprising
materials having
different characteristics joined together to form an integral entity such that
the materials are substantially
inseparable physically, and the unitary structure exhibits properties
resulting from the combination of the
materials therein. The materials may be arranged in a face-to-face
relationship in the z-dimension, or in a
side-by-side relationship in the xy-dimension.
As used herein, the term "operatively associated" refers to a structure
comprising different
materials positioned at least in partial contact with each other in use. The
materials are physically separable
and each exhibits properties that can be measured individually. The materials
may be arranged in a face-to-
face relationship in the z-dimension, or in a side-by-side relationship in the
xy-dimension.
As used herein, the term "bonded" refers to different materials being attached
(cohesively or
adhesively) in at least a portion thereof. The attached portions may be random
or may have a pattern such as
stripes, spirals, dots, and the like. The attached portions may be located at
the peripheries, throughout the
surface area, or both. Suitable attachment means known in the art may be
used,.including but not limited to
adhesives, heat, pressure, crimping, ultrasonic, chemical (via hydrogen bonds
or other cohesive forces),
mechanical (e.g., fasteners, entanglements), hydraulic, vacuum and
combinations thereof.
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As used herein, the term "composite structure" refers to a multi-zoned
structure wherein the
materials comprising the zones may be operatively associated or bonded. The
zones may even be in
intimate contact such that the composite has a unitary structure. Further, the
zones may be positioned in a
layered (face-to-face) arrangement, or a side-by-side arrangement
As used herein, the term "absorbent core" refers to the component of the
absorbent article that is
primarily responsible for fluid handling properties of the article, including
acquiring, transporting,
distributing and storing body fluids. As such, the absorbent core typically
does not include the topsheet,
backsheet or outer cover of the absorbent article.
As used herein, the term "pulp" or "cellulosic fibers" include those natural
fiber derived from trees
or vegetations (e.g., hardwood fibers, softwood fibers, hemp, cotton, flax,
esparto grass, milkweed, straw,
bagasse and the like), their processed/regenerated fibers (e.g., Rayon ) or
chemically derivatized fibers
(e.g., cellulose esters), and combinations thereof. Suitable hardwood fibers
include eucalyptus fibers.
Suitable hardwood fibers may be prepared by kraft or other chemical pulping
methods. Suitable softwood
fibers include southern softwood (SS) fibers and northern softwood (NS)
fibers. Softwood fibers for use
herein can be chemically (e.g., without limitation, kraft pulp) or
mechanically pulped (e.g., without
limitation, chemithermal mechanical pulp (CTMP) and thermal mechanical pulp
(TMP)).
As used herein, the term "nonwoven web" refers to a web that has a structure
of individual fibers
which are interlaid forming a matrix, but not in an identifiable repeating
manner. Nonwoven webs may be
formed by a variety of processes known to those skilled in the art, for
example, meltblowing, spunbonding,
wet-laying, air-laying, and various bonding-carding processes.
As used herein, the term "spunbonded web" refers to a web having fibers formed
by extruding a
molten thermoplastic material as filaments from a plurality of fine
capillaries of a spinnerette having a
circular or other configuration, then rapidly reducing the diameter of the
extruded filaments by fluid
drawing or other well known spunbonding mechanisms. Spunbond fibers are
quenched and generally not
tacky when they are deposited onto a collecting surface. Spunbond fibers are
generally continuous and often
have average between 20 to 30 microns.
As used herein, the term "meltblown web" refers to a web having fibers formed
by extruding a
molten thermoplastic material through a plurality of fine, usually circular,
die capillaries as molten threads
or filaments into converging high velocity heated gas/air streams which
attenuate the molten filaments to
reduce their diameter. The reduction in fiber diameter is substantial greater
then the reduction of fiber
diameter in the spunbonding process, resulting in microfibers having average
fiber diameter larger than 0.2
microns and typically in the range of 0.6 to 10 microns. Thereafter, the
meltblown fibers are carried by the
high velocity gas stream and are deposited on a collecting surface to form a
web of randomly disbursed
fibers. Various melt blown processes are known in the art.
The following detailed description of the absorbent barrier structure of the
present invention is in
the context of a disposable diaper. However, it is readily apparent that the
absorbent barrier structure of the
present invention is also suitable for use in other absorbent articles such as
feminine hygiene products,
training pants, incontinence articles, and the like. It is also apparent that
the absorbent barrier structure of
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the present invention is suitable for use in other hygiene or health care
products, such as bandages,
dressings, wipes, bibs, surgical drapes, surgical gowns, and the like.
The Barrier Structure or The Absorbent Barrier Structure
The present invention provides a barrier structure which allows convective air
or water vapor
transport though this structure. Particularly, the structure of the present
invention achieves the desirable
convective air flow capacity without sacrificing the barrier protection
against wet through. When the barrier
structure is included in an absorbent article, the resulting absorbent article
shows effective reduction of the
relative humidity in the space between the absorbent article and the wearer,
thus, improves and/or maintains
skin health and wearer comfort.
Convective transport capacity is different from the diffusive transport
capacity. The convective
transport is driven by a gas or air pressure differential and is typically at
a much higher transport rate than
the diffusive transport, which is driven by random molecular movements.
Typical example of the diffusive
transport includes the moisture migration through the pores of a microporous
films such as those known in
the art as the backsheet materials, or through the molecular structure of a
nonporous monolithic film such as
that made from Hytrel (available from DuPont, Wilmington, DE). Convective
transport, on the other
hand, is directed by the air pressure differential between the inside and the
outside of the article. Though
the local pressure (i.e., the local pressure within the space between the
article and the wearer) and the
pressure of the environment (i.e., outside the article) are substantially the
same, small changes in the local
pressure may cause convective air flow, typically through the gaps between the
wearer and the article.
Factors that may lead to convective transport include, but are not limited to,
movements by the wearer,
small pressure and/or temperature differential between the local and the
outside environment, and the like.
With the advances made to the absorbent articles, using elastic materials and
elastic components,
the absorbent articles now provide a tighter seal (i.e., less gaps) against
the wearer's body to minimize fluid
leakage to the outside. Consequently, the convective air flow through the gaps
are substantially reduced,
leading to a humid and hot local environment in the space between the article
and the wearer. While
absorbent cores are typically air permeable; the air permeability typically is
reduced when the cores absorb
liquid (i.e., become loaded). The loaded cores can be vented (i.e., made air
permeable) relatively easily,
typically by venting means. Alternatively, openness of the core structures can
be achieved by selecting
particular arrangements of permeable materials.
These vented or open-structured cores generally require a leakage protection
component, which is
typically a microporous film backsheet or a relatively thick nonwoven fabric
that provides liquid
impermeability and leakage protection. However, these liquid impermeable
components will reduce the air
permeability of the article. In contrast, the barrier structure of the present
invention allows the convective
air flow through the structure itself.
The barrier structure of the present invention also provides liquid absorbency
and good liquid
retention capability. Thus, it is also an absorbent barrier structure. The
liquid retention capability is
especially beneficial when wearer's motions, such as sitting, falling, lying,
bending, walking, may apply
pressure/forces on the loaded (i.e., wetted with bodily fluids) absorbent body
and/or the adjacent
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absorbent barrier structure and may lead to leakage. Thus, when the absorbent
barrier structure is included
in an absorbent article, the resulting absorbent article not only provides
effective conveative air flow
capacity, it also provides effective protection against wet through, even when
the article is subjected to
impact forces.
Typically, the absorbent barrier structure is positioned between the absorbent
core and the outer
cover, preferably adjacent to the garment-facing side of the absorbent core.
The absorbent barrier structure
is a composite structure, which comprises a plurality of individual zones of
materials that are joined, or
operatively associated together. Alternatively, the plurality of zones may be
combined into a unitary
structure such that the individual zones become physically inseparable. The
individual zones of the
absorbent barrier structure may be coextensive or non-coextensive, depending
on the requirements of the
absorbent article. The individual zones may be joined by attachment means such
as those well known in the
art.
As used herein, the term "joined" encompasses configuration whereby a member
is directly
secured to the other member by affixing the member directly to the other
member; and configurations
whereby a member is indirectly secured to the other member by affixing one
member to intermediate
member(s), which in turn are affixed to the other member. For example, the
zones may be secured together
by a uniform continuous layer of adhesive, or an array of separate lines,
spirals, or droplets or beads of
adhesive. The adhesive may be applied continuously or intermittently. For
example, each application of the
adhesive spans the length of the absorbent barrier structure and is separated
from one another by a selected
distance. The adhesive is applied to tack the zones together for handling the
webs in the assembly process.
Preferably, the adhesive is applied to portions of the surface of the
absorbent barrier strucbm, leaving
sufficient open (i.e., free of adhesives) surface areas for air/vapor
permeability. Alt:eraatively, the adhesive
may be applied to modify the liquid impenneability. Typically, the open or
adhesive-free surface area is no
less than about 50%, preferably no less than about 70%, more preferably no
less than about 80%, and most
preferably no less than about 90% of the total surface area of the absorbent
barrier structure. Suitable
adhesives are manufactured by H.B. Fuller Company of St. Paul, Minnesota and
marketed as HL-1258TM and
by Ato-Findley Inc. of Milwaukee, Wisconsin, under the trade designation H2031
FTM;
In one embodiment, the adhesive is applied in a stripe along the peripheries
of the zones. In
another embodiment, the adhesive is applied in spaced-apart stripes aligned
with the longitudinalcenterline
of the diaper when it is used in a diaper. In another embodiment, the adhesive
is applied to the-web in three
stripes along the longitudinal centerline of the diaper. Each stripe is 22mm
wide (in the lateral direction of
the diaper) and the two outer stripes are disposed at or near (about 4 mm
from) the longitudinal peripheries.
The adhesive is typically applied from its softened or melt state to the
surface of at least one of the
webs comprising the absorbent barrier structure. The adhesive is heated to at
least above its softening
temperature prior to being applied to a substrate surface. Once applied, the
adhesive is allowed to cool and
harden/solidify. Various methods for softened or melt state application are
known. Methods particularly
suitable for use herein include, but are not limited to, spraying, dipping,
gravure printing, and extrusion.
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Alternatively, the attachment means may comprise heat bonds, pressure bonds,
ultrasonic bonds,
mechanical bonds (via, for example, entanglements, cohesive forces, electric
or static charges) or any other
suitable attachment means or combinations of these attachment means as are
known in the art.
The individual zones may be arranged in layers, wherein individual zones are
in an operable,
intimate contact with at least a portion of the adjacent layer. Such contacts
may be random, or may have a
regular pattern, such as dots, stripes, and the like. Preferably, each layer
is connected to at least a portion of
an adjacent layer of the absorbent barrier structure by a suitable bondiiig
and/or attachment means, such as
ultrasonic bonding, adhesive bonding, mechanical bonding, or hydraulic
needling. In another embodiment,
the individual zones may be arranged in an operable, intimate contact along at
least a portion of its
boundary with the adjacent layer of the absorbent barrier structure.
The absorbent barrier structure of the present invention may be constructed to
have a convective
air permeability of at least about 1 Darcy/mm, preferably at least about 10
Darcy/mm, more preferably at
least about 30 Darcy/mm, and most preferably at least about 50 Darcy/mm.
Convective air permeability is
especially effective in removing moisture vapor from inside the absorbent
article, resulting in a lower
humidity in the local environment next to the skin. Thus, the absorbent
barrier structure reduces incidences
of skin irritation or rash, promotes skin health and provides better comfort.
Though the liquids are mainly absorbed by the absorbent core, the absorbent
barrier structure
provides additional leakage protection against errant liquids that are not
absorbed by or are released from
the absorbent core. Thus, the absorbent barrier structure of the present
invention should have a minimal
liquid absorbency.
Liquid absorbency may vary, depending on the materials used in the absorbent
structure, the
surface tension of the liquid being tested for absorbency, and the contact
angle between the test liquid and
the material. The absorbent barrier structure suitable for use herein
typically has an absorbency (as
measured by Test Method G using a 0.2 wt % Triton solution) of at least about
1 g/g, typically from about
1 to about 100 g/g, preferably from about 5 to about 50 g/g, more preferably
from about 10 to about 30 g/g.
Further, in order to provide the additional leakage protection, the absorbent
barrier structure of
should also have a liquid retention capability, especially under impact and/or
sustained pressure conditions.
This property is especially beneficial in the absorbent article applications.
When an absorbent article is wet,
wearer motions, such as sitting, falling, lying, rolling, may squeeze the
absorbed liquids out of the
absorbent core, resulting in leakage through the article. Thus, the absorbent
barrier structure of the present
invention preferably has a liquid impact value (as measured by Test Method C)
of less than about 30 g/m2,
more preferably less than about 20 g/mz, more preferably less than about 15
g/m2, more preferably less
than about 10 g/m2, and most preferably less than about 6.5 g/m2.
Also related to the leakage protection performance, the absorbent barrier
structure should have a
certain degree of resistance to liquid penetration. Thus, the absorbent
barrier structure of the present
invention has a hydrohead value (as measured by Test Method B) of at least
about 10 mBars, preferably at
least about 30 mBars, more preferably at least about 50 mBars, and most
preferably at least about 75
mBars. In some embodiments, the absorbent barrier structure has a hydrohead
value in the range from
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about 30 to about 100 mBars.
The absorbent barrier structure of the present invention also has desired
leakage protection in
terms of a static liquid transmission value (measured according to Test Method
D). In this respect, the
absorbent barrier structure of the present invention has a static liquid
transmission value of less than about
45 g/m2, preferably less than about 30 g/m2, more preferably less than about
20 g/m2, and most preferably
less than 13 g/m2, at 15 minutes after impact. Further, the absorbent barrier
structure of the present
invention has a static liquid transmission value of no more than about 50
g/m2, preferably no more than
about 35 g/mz, more preferably no more than about 20 g/m2, at 60 minutes after
impact.
In another aspect, after the absorbent barrier structure has been subjected to
the compaction
condition such as that described below in the Test Method F, it does not
suffer substantial changes in
barrier properties. The structural integrity during compaction and recovery
after compaction are important
for practical purposes. The absorbent articles are typically packaged into a
compacted condition for
shipping and storage. When the articles are eventually removed from the
compaction for the intended use,
the material or structure that fail to recover to its pre-compaction state may
fail to provide the properties it
was originally designed for. The absorbent barrier structure of the present
invention should typically have a
post-compaction air permeability decrease of no more than 35 %, preferably no
more than 25 % decrease
and most preferably no more than 15 % decrease, compared to its pre-compaction
air permeability. In a
preferred embodiinent, the absorbent barrier structure has the post-compaction
air perineability as disclosed
above, after 7 days, preferably after 30 days, more preferably after 90 days.
The thickness and basis weight of the absorbent barrier structure may vary,
depending on the
materials used, the properties desired, the intended use, the construction,
and the like. For example,
thickness and/or basis weight may affect the diffusive breathability and/or
the convective air permeability
between the interior of an article and the outside, the absorbency and/or
leakage protection of the article, the
fit of the article to the wearer's body, the wearer's comfort, and like
effects that typically relate to thickness
of a structure. Typically, the absorbent barrier structure of the present
invention intended for use in an
absorbent article has a thickness of less than about 1.5 mm, preferably less
than about 1.2 mm, and more
preferably less than about 1.0 mm. The thickness of the absorbent barrier
structure suitable for use in an
absorbent article should also have a minimal thickness greater than about 0.1
mm, preferably greater than
about 0.2 mm. Further, the absorbent barrier structure of the present
invention suitable for use in an
absorbent article typically has a basis weight in the range of from about 20
gsm (g/m2) to about 200 gsm
(g/m2), preferably from about 30 gsm (g/m2) to about 150 gsm (g/m2), more
preferably from about 40 gsm
(g/hn) to about 120 gsm (g/m2), and most preferably from about 50 gsm (g/mz)
to about 100 gsm (g/mz).
The absorbent barrier structure typically comprises two zones: a barrier zone
and a reservoir zone.
The barrier zone is "substantially impermeable" to liquids, including water,
urine, menses, and other bodily
fluids. The term "substantially impermeable" means that the barrier zone
exhibits a resistance to liquid
penetration but does not necessarily eliminate liquid wet through. In other
words, it is possible for liquid to
penetrate and flow through the barrier zone under certain conditions, such as
under impact force, high
applied pressure, or under sustained (i.e., continuously applied) pressure for
a period of time. The
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reservoir zone is liquid absorbent. When the reservoir zone is positioned
adjacent to the barrier zone, any
wet-through and/or leakage from the barrier zone is absorbed by the reservoir
zone. In addition, the
reservoir zone will also absorb errant liquids from the absorbent core. Thus,
the combination of the barrier
zone and the reservoir zone achieves the unique balance of properties that
when exposed to liquids, the
barrier zone provides a resistance to liquid wet through, and the reservoir
zone absorbs any errant liquids
that break through the resistance of the barrier zone. That is, the absorbent
zone provides the added
protection against liquid wet through problem. When the absorbent barrier
structure of the present invention
is positioned adjacent to a loaded absorbent core, it provides the additional
protection against wet through,
particularly when the liquid loading level is high and/or the loaded absorbent
core is under a sudden, high
impact force or a sustained forces/pressure.
This added wet through protection is especially beneficial in diapers,
training pants, pull-on
diapers, or adult incontinence products, for which the liquid loading level
can be fairly high (in comparison
to feminine hygiene products) and the probability of sudden impact or
sustained pressure (e.g., when babies
or incontinent adults fall, sit down, roll, sleep) is also high. The absorbent
barrier structure of the present
invention is also beneficial when the absorbent core is subjected to gushes of
liquids. The resistance to
liquid wet through provides by the barrier zone serves to temporarily slow
down the gushes of liquids,
possibly pooling the liquids at the interface between the absorbent core and
the barrier zone. The slowed
flow and pooling provide the additional time for the absorbent core to acquire
and distribute the liquids to
other regions of the core beyond the point of insult. Consequently, the
absorbent core may achieve its full
absorbent capacity.
The absorbent barrier structure of the present invention can be more clearly
understood by
referring to the following illustrative figures. FIG. 2A is a cross sectional
view of an embodiment of the
absorbent barrier structure of this invention. The absorbent barrier structure
10 comprises a barrier layer 12
and a reservoir layer 14. Optionally, an additional barrier layer 16, as shown
in FIG. 2B, may be disposed
on the other side of the reservoir layer 14 such that the reservoir layer 14
is sandwiched between the barrier
layers 12 and 16. The first and the second barrier layers may be made of
identical or different (in terms of
construction of the web, basis weight, thickness, porosity, fiber denier,
material, and the like) fibrous webs.
Various arrangements of the barrier zone and the reservoir zone are shown in
FIG. 3A-3D. In FIG.
3A, multiple barrier zones 12 and reservoir zones 14 are arranged in a side-by-
side relation, wherein the
barrier zones 12 and the reservoir zones 14 are preferable stripes. In FIG.
3B, the barrier zone 12 is a
continuous web and the reservoir zone 14 is disposed adjacent thereto in a
discontinuous pattern, such as
stripes, circles, ellipses, squares, and the like. In FIG. 3C, the reservoir
zone 14 is a continuous web and the
barrier zone 12 is disposed adjacent thereto in a discontinuous pattern, such
as stripes, circles, ellipses,
squares and the like. In FIG. 3D, the discontinuous barrier zones 12 overlap
at least partially with the
discontinuous reservoir zones 14, each may have the shape of stripes, circles,
ellipses, squares, and the like.
In all of the einbodiments illustrated in FIG. 2A-3D, at least a portion of
the barrier zone is
positioned adjacent to the garment-facing side of the absorbent core. In one
embodiment, the absorbent
barrier structure may extend through substantially the entire portion of the
absorbent core or the
I1
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absorbent barrier structure may be stripes or patches that extend to portions
of the absorbent core. In
another embodiment, the absorbent barrier structure may extend beyond the
outer edges of the absorbent
core or only through the length and width of the central portion of the
absorbent core. In a preferred
embodiment, the barrier zone and the reservoir zone are arranged in a layered
relation, wherein the barrier
layer is disposed immediately adjacent to the garment-facing side of the
absorbent core. Configurations in
which the barrier zone has at least the same length and width of the absorbent
core are highly preferred.
Furthermore, the reservoir zone needs not have the same dimensions as the
barrier zone.
The Reservoir Zone
The reservoir zone should be capable of absorbing, spreading and retaining
liquids such as urine,
blood and other body exudates. The reservoir zone has a garment-facing
surface, a body-facing surface,
front and rear edges, and side edges. The reservoir zone absorbs and retains
the errant liquids that escape
from other components such as the absorbent core and the barrier zone. Thus,
the reservoir zone provides
additional protection against wet through.
The thickness and basis weight of the reservoir zozie may vary, depending on
the materials used,
the properties desired, the intended use, the openness of the construction,
and the like. Specifically, the
thickness of the reservoir zone may affect the air/gas permeability, the
absorbency and/or leakage protection
of the barrier absorbent structure, as well as the comfort and fit of the
absorbent article, and like effects
typically related to the thickness of a structure. Thus, the reservoir zone
typically has a thickness of less
than about 1.5 mm, preferably less than about 1.0 mm, and more preferably less
than about 0.8 mm. The
reservoir zone should also have a minimal thickness to provide for adequate
absorbency and structural
integrity. The minimal thickness of the reservoir zone is typically no less
than about 0.2 mm, preferably no
less than about 0.1 mm, more preferably no less than 0.05 min, and most
preferably no less than 0.02 mm.
Further, the basis weight of the reservoir zone is typically in the range from
about 5 gsm (g/m2) to about
120 gsm (g/mz), preferably from abut 10 gsm (g/m2) to about 100 gsm (g/m2),
and more preferably from
about 30 gsm (g/m2) to about 80 gsm (g/m).
When compared to the absorbent core, the reservoir zone absorbs fluids more
readily (i.e., a faster
fluid uptake) and releases fluids more readily. The reservoir zone typically
has an absorbency of at least
about 1 g/g, preferably at least about 5 g/g, more preferably at least about
10 g/g, based on Test Method G
and using 0.2 wt% Triton as the test fluid. The absorbency of the reservoir
zone is preferably less .than
about 30 g/g, and more preferably less than about 20 g/g. Further, the
reservoir should have an absorbency
that is less than that of the absorbent core by at least about 20%, preferably
by about 30%.
The reservoir zone may be of any fonn having an open structure such that its
air or gas
permeability is at least equal to that of the resulting absorbent barrier
structure. The convective air/vapor
permeability of the reservoir zone is typically at least about 1 Darcy/mm,
preferably at least about 10
Darcy/mm, more preferably at least about 30 Darcy/mm, and most preferably at
least about 50 Darcy/mm.
Further, the openness of the structure may enhance absorbency by holding or
absorbing the fluids
in the interstitial spaces in the open structure. Suitable open structures may
include fibrous webs (e.g.,
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woven or nonwoven webs); absorbent foams (e.g., porous or reticulated foams);
fibrous wads; and the like.
In one embodiment, the reservoir zone is made of fibrous webs. The fibrous
webs constituting the
reservoir zone need not necessarily comprise absorbent fibers, so long as the
webs are absorbent. Thus, the
constituent fibers may simply be hydrophilic fibers and have no absorptive
capacity by themselves.
The reservoir zone may be made from a wide variety of hydrophilic fibers, such
as cellulosic
fibers; natural wood pulp; synthetic fibers made from hydrophilic polymers
such as polyesters and
polyamides (such as Nylon); hydrophobic fibers, such as polyolefins surface-
treated to improve its
hydrophilicity; or any combinations of materials such as bi-component fibers,
sheathed fibers. In one
embodiment, the reservoir zone is made of primarily cellulosic fibers which
are primarily hydrogen bonded
to one another. Cellulosic fibers may be natural or processed, and may be
chemically stiffened, modified or
cross-linked. Processed cellulosic fibers may include commercially available
fibers made of regenerated
cellulose or derivatized cellulosic, such as Rayon. In a preferred
einbodiment, the reservoir zone can be
composed of at least about 70 wt% of cellulosic fibers, preferably at least
about 80 wt% and more
preferably at least about 90 wt%. Alternatively, the reservoir zone can be
composed of from about 95 to
100 wt% cellulosic fibers.
In another embodiment, the reservoir zone may be in the fonn of single or
multi-ply tissue; creped
tissue; tissue wadding; and airfelt mat. High wet strength tissue may also be
used as the reservoir zone. In
another embodiment, the reservoir zone may be of any form having an open
structure whereby the bodily
fluids are held or absorbed in the fine interstitial spaces in the open
structure. Further, inter-ply spaces and
surface textures may provide additional interstitial, liquid holding spaces,
which enhance the absorbency of
the reservoir zone.
The reservoir zone may include supplemental chemical bonding agents that are
well known in the
art. For example, the reservoir zone may include a chemical bonding agent such
as vinyl acrylic
copolymers, polyvinyl acetate, crosslinkable polyamides, polyvinyl alcohol and
the like. Additionally, wet
strength resins and/or resin binders may be added to improve the strength of
the cellulosic web. Useful
binders and wet strength resins include commercially available resins, for
example, Kymene0, available
from Hercules Chemical Company and Parez available from American Cyanamid,
Inc. Crosslinking
agents and/or hydrating agents may also be added to the pulp mixture to reduce
the degree of hydrogen
bonding if an open or loose fibrous web is desired. An exemplary debonding
agent is available from
Quaker Chemical Company, Conshohocken, Pennsylvania, under the trade name
Quaker 2008. The
reservoir zone may contain no more than 5 weight percent and optionally may
contain no more than about 2
weight percent of the chemical bonding agent to provide desired benefits. The
reservoir zone typically
comprises a high wet strength tissue. Alternatively, the reservoir zone may
comprise a synthetic fibrous
web. The reservoir zone can be bonded, such as with adhesives, to the barrier
zone or other components of
the diaper construction.
Suitable materials for the reservoir zone may comprise a primarily cellulosic
fibrous web, such as
commercially available consumer paper towels Bounty , manufactured by The
Procter & Gamble
Company, Cincinnati, Ohio, or Hi-Dry , manufactured by The Kimberly-Clark
Corporation.
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Suitable fibrous webs may have a single-ply or a multi-ply construction. As
used herein, the term
"ply" means individual webs being disposed in a substantially contiguous, face-
to-face relationship,
forming a multiple layered web. Further, a single web may form two plies, for
example, by folding on itself.
In a multi-ply construction, the individual webs are at least partially
joined, typically via point bonding,
with or without adhesives.
It is found that the multi-ply construction provides higher resistance to
liquid breakthrough than a
single-ply construction on a unit weight basis. Further, the absorbency of a
two-ply fibrous web is at least
double that of the single-ply fibrous web, on a unit weight basis. Without
being bound by theory, it is
believed that the interstitial spaces (i.e., structural voids) between the
plies provide additional liquid holding
space, consequently, a higher absorptive capacity. Furthermore, post-
treatments of the cellulosic web,
including, but not limited to, aperturing, creping, embossing, or otherwise
texturizing, increases the
absorbency of the web. Fibrous webs having apertured or texturized surfaces
show higher absorptive
capacity, possibly due to the microvoids and/or interstitial spaces created by
the treatments. In a preferred
embodiment, the reservoir zone is made from a fibrous web having a
construction of at least two plies and a
texturized surface. Additionally, certain additives, such as debonding agents,
may also increase the
absorbency of the web by reducing the inter-fiber bondings (e.g., hydrogen
bonds between cellulosic
fibers), thus, loosening the compacted fibrous network in the webs. The
openness of the resulting web
provides more interstitial spaces to hold liquids, which enhances the
absorbency of the web.
In an alternative embodiment, other types of wettable and/or hydrophilic
fibrous materials may be
used to form the reservoir zone of the absorbent barrier structure. Exemplary
fibers include naturally
occurring organic fibers made from intrinsically wettable inaterial, such as
cellulose or processed cellulose
fibers, including regenerated or derivatized cellulose fibers commercially
available as Rayon fiber,
Viscose fibers; synthetic fibers made from inherently wettable thermoplastic
polymers, such as polyesters,
polyamides, their copolymers, polyvinyl alcohols, polyalkylene oxides, and
mixtures of these polymers; and
synthetic fibers made from a nonwettable thermoplastic polymers, such as
polyethylene, polypropylene,
polybutylene and other polyolefins, which may be hydrophilized by appropriate
means. These nonwettable
fibers may be hydrophilized by treatments with surfactants or surface active
agents having suitable
hydrophilic functionalities, or by sheathing. These nonwettable fibers may
also become of more wettable by
grafting hydrophilic functionalities onto the polymer chains. Suitable
hydrophilic functionalities include,
but are not limited to, acrylic, methacrylic, ester, amide, and mixtures
thereof.
The reservoir zone may contain additives such as chemical bonding agents,
crosslinking agents,
wet strength resins, debonding agents, liquid or moisture absorbing agents,
odor absorbing agents,
antimicrobials, coloring agents, stiffening agents, and mixtures thereof. The
liquid or moisture absorbing
agents, include, but are not limited to, clays, silicas, talc, diatomaceous
earth, perlite, vermiculite, carbon,
kaolin, mica, barium sulfate, aluminum silicates, sodium carbonate, calcium
carbonate, other carbonates,
superabsorbent polymers or other osmotic liquid holding agents, and mixtures
thereof.
In one embodiment, the reservoir zone additionally contains superabsorbent
polymers, which are
coated onto the fibers, blended into the fibers in-situ, or are made into
fibers or particles.
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The Barrier Zone
The barrier zone preferably has a "barrier-like" property, which provides
resistance to liquid wet through.
The barrier property is typically measured by the Test Method B (Hydrohead
Pressure Test) described
below. The hydrohead value of the barrier zone should be higher than that of
the absorbent core and of the
reservoir zone. The barrier zone material suitable for use herein should
exhibit a hydrohead value of at least
about 10 mBars, preferably at least about 30 mBars, more preferably at least
about 50 mBars, and most
preferably at least about 75 mBars. In some embodiments, the suitable barrier
zone has a hydrohead value
in the range from about 30 to about 100 mBars.
In addition, the barrier zone should not substantially reduce the air/vapor
permeability of the
absorbent article. In that respect, the barrier zone should have a convective
air permeability of at least about
10 Darcy/mm and preferably at least about 30 Darcy/mm.
The hydrohead value of a fibrous web increases with finer fiber diameter,
higher fiber density,
higher basis weight, or combinations thereof. Suitable fibrous web for the
barrier zone typically has a basis
weight of at least about 2 gsm, preferably from about 5 to about 100 gsm, more
preferably from about 10 to
about 75 gsm, and most preferably from about 15 to about 55 gsm.
The thickness of the barrier zone may vary, depending on the materials used,
the properties
desired, the intended use, the construction, and the like. Specifically, the
thickness of the barrier zone may
affect the air/gas permeability, the absorbency and/or leakage protection of
the barrier absorbent structure,
as well as the comfort and fit of the absorbent article, and like effects
typically related to the thickness of a
structure. Thus, the barrier zone typically has a thickness of less than about
1.5 mm, preferably less than
about 1.0 mm, more preferably less than about 0.8 mm, and most preferably less
than about 0.5 mm.
It has been found that some materials which do not appreciably limit the air
permeability of the
absorbent article in the dry state, will significantly decrease the air
permeability of the article when the
absorbent core becomes loaded with liquids. Thus, suitable materials for use
in the barrier zone should
allow sufficient water vapor transmission, when the absorbent article is in a
dry state, such that the air/
water vapor permeability of the diaper does not change substantially from that
of an equivalent diaper
without the barrier zone material. When the absorbent core becomes loaded from
absorbing liquids
discharged from the body, the barrier zone may lower the air/vapor
permeability of the absorbent article
(relative to an equivalent article without a barrier zone), thereby reducing
or eliminating the dampness
which may develop on the garment side of the outer cover.
In order to provide the desired hydrohead value or the "barrier-like"
property, suitable materials
are preferably hydrophobic, though this is not a required characteristic.
Exemplary hydrophobic polymeric
materials are typically polyolefins, such as polyethylene, polypropylene,
polybutylene and copolymers
thereof. Materials that are not hydrophobic, such as polyamides, polyesters,
polyalkylene oxides, polyvinyl
alcohols, may be treated by suitable hydrophobic agents to achieve the desired
hydrophobicity.
Additionally, the reservoir layer may also be treated on at least one surface
to improve its hydrophobicity,
hence, barrier property.
CA 02411868 2006-05-29
Treatments for improved hydrophobicity may include chemical, radiation, plasma
or combinations
thereof. Further, the surface treatment to modify the surface characteristics
may be accomplished by a
coating on the surface, by pre-blending with a hydrophobic agent or by
incorporating a hydrophobic agent
in-sita, which blooms to the surface by further processing.
In one embodiment, fluorocarbon treatments of the web material provides the
desired
hydrophobicity such that the web exhibits the desired water resistance
characteristics, measured, for
example, by the hydrohead test. In another embodiment, fluorocarbon treatment
using plasma or like
technology provides a very thin, hydrophobic coating such that the air
permeability of the treated web is
substantially unchanged. If desired, the treatment may be applies to only
portions of the substrate surface.
These treatments may be applied to materials that are suitable for use herein
as the barrier zone, the
reservoir zone, the outer cover, or other diaper components. Siiitable
substrate materials for this treatment
include, but are not limited to, nonwoven webs, cellulosic webs, thermoplastic
films, modified/processed
films (e.g.; formed, apertured) and the like. Exemplary surface treatments
using fluorocarbons are described
in U.S. Patent 5,876,753, issued to Timmons et al. on March 2, 1999; U.S.
Patent 5,888,591 issued to
Gleason et al. on March 30, 1999; U.S. Patent 6,045,877 issued to Gleason et
al. on April 4, 2000;
PCT Publication 00/14296
by D'Agostino et al., published on March 16, 2000.
Other surface coating methods using silicones or fluoro chemicals are known in
the art and may be
used herein. The conventional coating or surface treatment methods typically
fill the voids within the web,
thus, lowers its air permeability. Coating methods to provide hydrophobicity
to the substrate without the
decrease in air permeability can be found in U.S. Patent 5,322,729 and PCT
Publication WO 96/03501.
The barrier zone may comprise fibrous web materials such as nonwoven webs
including, but not
limited to, meltblown (MB) webs; spunbond (SB) webs, particularly fine fiber
spunbond webs sucb as those
having fiber deniers of about 2 or less; composite webs having layers of
ineltblown and spunbonded fibers,
commonly known as MS nonwovens, and SMS nonwovens; bonded and carded webs; air
laid webs; hydro-
entangled webs; knitted webs; and woven webs. Fine denier fibrous webs are
particularly suitable for use
herein, for example, meltblown webs comprising nanofibers.
The melt blowing process is well suited to make fine, low denier fibers,
particularly low denier
microfiber nonwoven webs. Suitable meltblown nonwoven webs preferably comprise
fine fibers having as
small a diameter as possible and dispersed in the web as uniformly as
possible. Such nonwoven webs
provide the desired combination of high liquid resistance and high air
permeability.
In one embodiment, the barrier zone comprises a meltblown web of polypropylene
fibers having a
basis weight of from about 4 to about 80 g/m2, preferably from about 6 to
about 70 g/m2, more preferably
from about 8 g/m2 to about 50 g/m2, and most preferably froni about 10 to
about 30 g/m2.
The meltblown fibers typically have an average diameter in the range of less
than about 20
microns, preferably less than about 10 microns. Most typically, the meltblown
fibers have an average
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fiber diameter in the 5 to 10 microns range. Particularly suitable for use
herein are nanofibers having an
average fiber diameter in the range of less than about 500 nanometers,
preferably less than about 300
nanometers, and more preferably less than about 150 nanometers. Exemplary
nonwoven webs made from
nanofibers (having average fiber diameters from about 10 to about 100
nanometers) are available from E-
Spin Technologies (Chattanooga, TN).
While the strength of the meltblown nonwoven web generally decreases with
decreasing fiber
fineness, the strength can be improved by lamination with a reinforcing scrim
or another web such as
tissues, paper towels, or spunbonded nonwoven webs. Any conventional
lamination process may be used,
including adhesive bonding, thermal boning, ultrasonic bonding, calendaring,
needling, and combinations
thereof. However, the lamination process should be carefully exercised to
minimize adverse effects on the
air permeability of the resulting laminate. In one embodiment, the microfiber
nonwoven web may be
integrally laminated during the manufacture by direct melt blowing onto
another web or a reinforcing scrim.
The fibrous barrier zone may comprise a single web or multiple layers of webs
which collectively
have the desired characteristics. However, when using multiple layers of webs,
it is desirable that they are
juxtaposed without being point bonded across a substantial surface area of the
zones or otherwise bonded in
a manner which would substantially limit the breathability of the zones. In
one embodiment, the barrier
zone is not thermally point bonded or otherwise laminated to the absorbent
core and/or the reservoir zone in
a manner which destroys the breathability of the article. In this regard, it
may be desirable that the barrier
zone be attached to other components the absorbent article (such as the
absorbent core, the reservoir zone)
primarily at the peripheries of the barrier zone. The multiple zones can be
bonded by heat, pressure,
ultrasonic, adhesive or by other means known in the art.
The barrier zone may contain additives such as chemical bonding agents,
crosslinking agents,
liquid or moisture absorbing agents, odor absorbing agents, antimicrobials,
coloring agents, stiffening
agents, and mixtures thereof. The liquid or moisture absorbing agents,
including, but not limited to, clays,
silicas, talc, diatomaceous earth, perlite, vermiculite, carbon, kaolin, mica,
barium sulfate, aluminum
silicates, sodium carbonate, calciuin carbonate, other carbonates,
superabsorbent polymers or other osmotic
liquid holding agents, and mixtures thereof.
Absorbent Article Components
FIG. 1 is a partially broken top plan view of a diaper 20 containing the
absorbent barrier structure
10 of the present invention. The diaper 20 is in a flat-out state with
portions of the structure cut away to
more clearly show the construction of the diaper 20. The garment-facing
surface of the diaper 20 is oriented
away from the viewer.
A "unitary" absorbent article refers to absorbent articles which are formed of
separate parts united
together to form a coordinated entity so that they do not require separate
manipulative parts like a separate
holder and/or liner. As used herein, the term "diaper" refers to an absorbent
article generally worn by
infants and incontinent persons about the lower torso. A "unitary" absorbent
article refers to absorbent
articles which are formed of separate parts united together to form a
coordinated entity so that they do not
require separate manipulative parts. The term "disposable" is used herein to
describe absorbent
17
CA 02411868 2006-05-29
= ~
articles which generally are not intended to be laundered or otherwise
restored or reused as: absorbent
articles (i.e., they are intended to be discarded after a single use and,
preferably, to be recycled, composted
or otherwise discarded in an environmentally compatible manner).
As shown in FIG. 1, the diaper 20 comprises a liquid pervious topsheet 24; a
dampness
management means 26; an absorbent core 28, which is positioned between at
least a portion of the topsheet
24 and the outer cover 22; an absorbent barrier structure 10 positioned
between the absorbent core 28 and
the outer cover 22; side panels 30; elasticized leg cuffs 32; elastic waist
features 34; and a festening system
40. An absorbent barrier structure 10 of the present invention is disposed
adjacent to the absorbent core 28
on the garment facing surface 45 of the absorbent core 28.
Diaper 20 is shown in FIG. 1 to have a front waist region 36, a rear waist
region 38 opposed to the
front waist region 36 and a crotch region 37 located between the front and the
rear waist regions. The
peripheries of the diaper 20 are defined by the outer edges of the diaper 20
in which the longitudinal edges
50 run generally parallel to the longitudinal centerline 100 of the diaper 20
and end edges 52 run between
the longitudinal edges 50 generally parallel to the lateral centerline 110 of
the diaper 20:
The main body of the diaper 20 comprises at least the absorbent core 28, the
topsheet 24, and
preferably, though not necessarily the dampness management means 26. An outer
cover 22 fornns the
chassis, onto which other components of the diaper 20 are added to form the
unitary structure of the diaper.
FIG. I shows an embodiment of the diaper 20 in which the topsheet 24 and tite
dampness
management means 26 have length and width dimensions generally no smaller than
those of the absorbent
core 28 and the absorbent barrier structure 10. The topsheet 24 and the
dampness management means 26
may extend to the peripheries of the diaper 20. In another embodiment, the
absorbent barrier sttucturae 10
may extend beyond the edges of the absorbent core 28 to the peripheries of the
diaper 20.
While the components of the diaper 20 may be assembled in various well lmown
configurations,
preferred diaper configurations are described generally in U.S. Pat. No.
3,860,003 entitled "Contractible
Side Portions for Disposable Diaper" issued to Kenneth B. Buell on January 14,
1975; U.S. Pat. No.
5,151,092 issued to Buell on September 9, 1992; and U.S. Pat. No. 5,221,274
issued to Buell on
June 22, 1993; and U.S. Pat. No. 5,554,145 entitled "Absorbent Article With
Multiple Zone Structural
Elastic-Like Film Web Extensible Waist Feature" issued to Roe et al. on
September 10, 1996; U.S. Pat. No.
5,569,234 entitled "Disposable Pull-On Pant" issued to Buell et al. on October
29, 1996; U.S. Pat. No.
5,580,411 entitled "Zero Scrap Method For Manufacturing Side Panels For
Absorbent Articles" issued to
Nease et al. on December 3, 1996; and U.S. Patent No. 6,004,306 entitled
"Absorbent Article With Multi-
Directional Extensible Side Panels" issued to Robles et al. on December 21,
1999;
'Topsheet or Body-side Liner
The topsheet is compliant, soft feeling, and non-irritating to the wearer's
skin. The topsheet
material can also be elastically stretchable in one or two directions.
Further, the topsheet is fluid pervious,
perniitting fluids (e.g., urine, menses, other bodily fluids) to readily
penetrate through its thickness. A
suitable topsheet can be manufactured from a wide range of materials such as
woven and nonwoven
1S
CA 02411868 2006-05-29
materials; apertured or hydroformed thermoplastic films; porous foams;
reticulated foams; reticulated
thermoplastic films; and thermoplastic scrims. Suitable woven and nonwoven
materials may comprise of
natural fibers such as wood or cotton fibers; synthetic fibers such as
polyester, polypropylene, or
polyethylene fibers; or combinations thereof.
Preferred topsheet for use in the present invention are selected from high
loft nonwoven topsheets
and apertured film topsheet. Apertured fihn topsheet typically are pervious to
bodily exudates, yet non-
absorbent, and have a reduced tendency to allow ftuids to pass back through
and rewet the wearer's skin.
Suitable apertured films include those described in U. S. Patent 5.628,097,
U.S. Patent 5,916,661,
EP 1,051,958, EP 1,076,539,
Nonwoven materials, such as described in bY 774,242 (Palumbo), which is
incorporated herein by
reference, generally exhibit high gas permeability, thus, do not exhibit a
significant resistance to air flow.
Further, suitable tospheet materials for depositing solid excretions thereon
may include nonwovens
baving apertures, which are at least in the portions that are aligned with the
feces deposition region of the
article. Suitable apertured nonwovens are described in more detail in EP
714,272 or EP 702,543.
In another embodiment of feces handling articles, such
topsheets can be combined with feces handling members e.g. underlying such
topsheets, and further
descnbed in these applications.
The material forming the topsheet may be hydrophilic so as to facilitate fluid
transport through the
topsheet. Surfactants may be incorporated into the polyrheric materials to
improved the hydrophilicity of
the topsheet, such as is disclosed in EP-A-166,056
Alternatively, the topsneet may ne
treated with a surfactant to render the body-facing surface hydrophilic, such
as is disclosed in U.S. Patent
4,950,254.
Absorbent Core
The absorbent core may includes the following components: (a) optionally, a
primary fluid
distribution layer; (b) optionally, a secondary fluid distribution layer; (c)
a fluid storage layer; (d) other
optional components, such as a fibrous "dusting" layer.
The optionally primary fluid distribution layer is typically disposed under
the topsheet and is in
fluid communication with the topsheet. The topsheet transfer the acquired
bodily fluids to the primary
distribution layer to ultimate distribution to the storage layer. This
transfer of fluid through the primary
distribution layer occurs not only in the thickness, but also along the length
and width directions of the
absorbent core, The optionally secondary fluid distribution layer is typically
disposed under the primary
fluid distribution layer and is in fluid communication therewith. The
secondary fluid distribution layer
readily acquires fluid from the primary distribution layer and transfers it
rapidly to the underlying storage
layer. Thus, the fluid capacity of the underlying storage layer may be fully
utilized, especially when gushes
of bodily discharge occur.
The fluid storage layer typically comprises absorbent materials including
absorbent gelling
materials, which are usually referred to as "hydrogels", "superabsorbent"
"bydrocolloid" materials.
19
CA 02411868 2006-05-29
Absorbent gelling materials are those materials that, upon contact with
aqueous fluids, such as bodily fluids,
imbibes such fluids and form hydrogels. These absorbent gelling materials are
typioally capable of
absorbing large quantities of aqueous bodily fluids, and further capable of
retaining such absorbed fluids
under moderate pressures. These absorbent gelling materials are typically in
the form of discrete,
nonfibrous particles. Other forms, such are fibers, foams, sheets, strips, or
other maerostruohit+es, are also
suitable for use herein. Suitable absorbent gelling matemals in the form of
open cell foams may include
those disclosed in U.S. Patent 3,563,243 (Lindquist), U.S. Patent 4,554,297
(Dabi), U.S. Patent 4,740,520
(Garvey), U.S. Patent 5,260,345 (DesMarais et al.).
Improvements of these foams can be found in WO 96/21679, WO 96/21680, WO
96/21681, WO 96/21682,
WO 97/07832 and WO 98/00085.
The absorbent gelling materials suitable for use herein may comprise a
substantially water-
insoluble, slightly crosslinked, partially neutralized, polymeric gelling
material. This material forms a
hydrogel upon contact with water. Suitable absorbent gelling= materials
include.thosa disclosed in U.S.
Patent 4,654,039, U.S. Patent 5,562,646, U.S. Patent 5,599,335, U.S. Patent
5,669,894,
it has been found, that superabsorbent materials are particularly suited to be
used in articles
according to the present invention, if they exhibit high Saline Flow
Conductivity performance (SFC),
preferably of more than 30 * 1C cm3 sec/g, when evaluated according to the
disclosure. of U.S. Patent
5,599,335.
Such materials can be arranged in a homogeneous mixing with fluff pulp, or can
be layered
between suitably open and penneable layers of porous materials, such as
tissues, especially if these are air-
laid, or nonwoven materials.
Particularly suitable materials are superabsorbent materials as described in
the above refecenced
U.S. Patent 5,599,335, when arranged in a homogeneous blend with conventional_
fluff pulp, at a
concentration of 50% superabsorbent, preferably 80% and even more preferably
more than 90%
concentration based on the weight of the superabsorbent/fluff mixture.
Suitable mixtures can fiuther exhibit
densities of between 0.1 g/ cm3 and 0.3 cm3, preferably between 0.15 cm3 and
0.2 cm3 .
In particular embodiments, such mixtures can comprise means which enhance the
integri.ty of the
mixture, especially in the dry state. Thus, low amounts of adhesive may be
added to the mixture, or other
binders, such a thermobondable synthetic fibers.
In addition to the liquid storage elements in the core, the core may comprise
other liquid handling
members, such as for enhancing fluid acquisition, or distribution.
The fluid storage layer may comprise of absorbent gelling materials alone or
dispersed in a suitable
carrier, homogeneously or inhomogenously, or may comprise of absorbent carrier
materials alone. The
storage layer may also include filler materials, such as perlite, diatomaceous
earth, vermiculite, and the like,
which absorb and retain the fluid, thus, reduces the rewet through the
topsheet.
Suitable carrier materials include cellulose fibers, in the fonn of fluff,
tissues or paper. Modified
cellulose fibers (e.g., stiffened, cliemically treated, crosslinked) may also
be used. Synthetic fibers
CA 02411868 2006-05-29
may also be used. Suitable synthetic fibers may be made of cellulose acetate,
polyvinyl fluoride,
polyvinylidene chloride, acrylics (such as Orlon ), polyvinyl ~ acetate, non-
soluble polyvinyl alcohol,
polyethylene, polypropylene, polyamides (such as Nylon ), polyesters, bi- or
tri- component fibers thereof,
and mixtures of these materials. Preferably, the fiber surfaces are
hydrophilic or are treated to be
hydrophilic.
Typically, the storage layer comprises from about 15 to 100 wt% of the
absorbent gelling mat.erial
dispersed in a carrier material. Preferably the storage layer comprises from
about 30 to about 95 wt%, more
preferably from about 60 to about 90 wt% of the absorbent gelling material.
The carrier material typically
comprises from about 0 to about 85vvt%, preferably from about 5 toabout 70
wt%, and more preferably
from about 10 to about 40 wt% of the storage layer.
An optional component for inclusion in the absorbent core is a fibrous layer
adjacent to, and
typically underlying the storage layer. This underlying fibrous layer is
typically referred to as a "dusting"
layer since' it provides a substrate on which to deposit absorbent gelling
material in the storage layer during
manufacture of the absorbent core. Further, the "dusting" layer provides some
additional fluid handling
capability such as rapid wicking of fluid along the length of the absorbent
core.
The absorbent core may include other optional components. For example, a
reinforcing scrim may
be positioned within the respective zones, or between the respective zones, of
the absorbent core.
Optionally, odor control agents may be included in the absorbent core.
Suitable odor control agents include
active carbons, zeolites, clays, silicas, and mixtures tliereof. The
configuration and construction of the
absorbent core may also be varied (e.g., the absorbent core may have varying
caliper zones, a hydrophilicity
gradient, a pore size gradient, a superabsorbent gradient, or lower average
density and lower average basis
weight acquisition zones; or may comprise one or more zones or structures).
The total absorbent capacity
of the absorbent core should, however, be compatible with the design loading
and the intended use of the
diaper. Further, the size and absorbent capacity of the absorbent core may be
varied to accommodate
wearers ranging from infants through adults. Suitable absorbent cores include
those disclosed in EP
1,051,958, EP 797,968 and EP 774,242.
Outer Cover
The term "outer cover" as used herein means a structural element positioned on
the garment-facing
surface of the absorbent article. The outer cover typically forms the chassis
onto which other components of
the diaper are added. However, the outer cover may just be a coating layer on
the garment side of the
absorbent article.
Suitable material for the outer cover should provide a barrier function with
respect to liquids (i.e.,
liquid impervious) while allowing air or vapor to flow through (i.e., vapor
permeable). The outer cover
should not be the rate limiting element to gas or vapor transport through the
absorbent article. Preferably,
the outer cover has a structure that is relatively open to allow for
convective air or gas permeability. The
suitable outer cover typically has a moisture vapor transmission rate (MVTR)
of at least about 500
g/24hrs/m2, more preferably of at least about 1500 g/24hrs/m2, and most
preferably at least about 3000
g/24hrs/m2. Additionally, the outer cover provides a soft, pleasant feel to
the skin, either by the material
21
CA 02411868 2006-05-29
property, or by texturizing or embossing its surface, or both.
The outer cover may be a single layer of homogeneous or multi-component
material, or a
composite of various layers of materials. The outer cover suitable for use
herein comprises pomus materials
such as an apertured film (e.g., baving a plurality of shaped openings or
angled capillaries), a knitted web, a
porous woven or nonwoven web, a foam, or combinations or laminates thereof. In
one embodiment, the
outer cover comprises nonwoven webs or multi-layered nonwovens such,as
spunbond/meltblown (SB)
nonwoven, spunbond/meltblown/spunbond (SBS) nonwoven.
The outer cover, or any portion thereof, may be elastically extensible in one
or more directions. In
one embodiment, the outer cover may comprise a structural elastic-like film
("SELF") web. A SELF web is
an extensible material that exhibits an elastic-like behavior in the direction
of elongation without the use-of
added elastic materials and is described in more detail in U.S. Patent No.
5,518.801 entitled "Web Materials
Exhibiting Elastic-Like Behavior" issued to Chappell, et al. on May 21, 1996,,
In alternate embodiments, the outer cover may Fombine elastomeric components -
(such as
films, foams, strands, or combinations thereof) with nonwovens or synthetic
films.
In another embodiment, the outer cover may be a nonwoven web constructed to
provide the
required level of liquid impermeability. For example, a nonwoven web of
spunbonded or meltblown
polymer fibers may be treated, at least partially, with a hydrophobic coating.
Exemplary treatments using
fluorocarbons are described in U.S. Patent 5,876,753, issued to Timmons et al.
on March 2, 1999; U.S
Patent 5,888,591 issued to Gleason et al. on March 30, 1999; U.S. Patent
6,045,877 issued to Gleason et al.
on April 4, 2000.
Optionally, the outer cover matenal may comprise the absorbent ana swellable
materials described
in U.S. Patent 5,955,187 issued to McCormack et al. on September 21, 1999;
or the absorbent and differential strainable materials described in PCT
Publication WO
00/68003 by Dawson et al.
The absorbent article may comprise an outer cover which is separated from the
absorbent core at
least partially by the absorbent barrier structure of the present invention
and is preferably joined to the
absorbent barrier structure andlor the absorbent core by attachment means such
as those well known in the
art. As used herein, the term "joined" encompasses configurations wherein an
element is directly secured to
the other element by affixing the element directly to the other element, and
configurations wherein the
element is indirectly secured to the other element by affixing the element to
intennediate member(s), which
in turn are affixed to the other element.
The outer cover may be secured to the absorbent barrier structure and/or the
absorbent core by a
unifomi continuous layer of adhesive, an open pattem network of filaments of
adhesive, or an array of
separate lines, spirals, or spots of adhesive, as disclosed in U.S. Patent
4,573,986 issued to Minetola et al.
on March 4, 1986; U.S. Patent 3,911,173 issued to Sprague, Jr. on October 7,
1975; U.S. Patent 4,785,996
issued to Ziecker, et al. on November 22, 1978; and U.S. Patent 4,842,666
issued to Werenicz on June
22
CA 02411868 2006-05-29
27, 1989. Adhesives which have been found to
be satisfactory are manufactured by H.B. Fuller Company of St. Paul, Minnesota
and marketed as HL-1258.
Alternatively, the attachment means may comprise heat bonds, pressure bonds,
ultrasonic bonds, dynamic
mechanical bonds, or any other suitable attachment means dr combinations of
these attachment means as
are known in the art
The outer cover material sliould not significantly lower the convective air
permeability of the
absorbent article. More importantly, the combination of the absorbent barrier
structure and the outer cover
(hereinafter, referred to as the "combined structure" or "combination")
provide the desired balance of
properties,'including, but not limited to, absorbency, barrier property and
convective air permeability.
The combined structure of the present invention may be constructed to have a
convective air
permeability of at least about 10 Darcy/mm, preferably at least about 20
Darcy/mm, more preferably at least
about 30 Darcy/mm, and most preferably at least about 50 Darcy/mm. Convective
air permeability is
especially -effective in removing moisture vapor from inside the absorbent
article, resulting in a lower
humidity in the local environment next to the skin, which reduces incidences
of skin irritation or rash and
promotes skin health.
Further, the combined structure of the present invention preferably has a
dynamic liquid impact
value (as measured by Test Method C) of no more than about 10 glm2; rimore
preferably no more than about
8 g/m2, and most preferably no more than about 5 g/m2.
Moreover, the combined structure should exhibit a hydrohead value of at least
about 20 mBars,
preferably at least about 35 mBars, more preferably at least about 50 mBars,
and most preferably at least
about 75 mBars.
' In a preferred embodiment, the combined structure of the present invention
exhibits desired
leakage protection or barrier properties at least equal to that of the
absorbent barrier structure.
Dampness Management Means
Optionally, as shown in FIG. 3, a dampness management means 26 may be included
in the
absorbent article of the present invention. The dampness management means 26
may provide further
leakage protection. Suitable dampness management means materials are
breathable materials which permit
vapors to escape from the diaper 20 while still preventing exudates from
passing through the dampness
management means 26. Exemplary materials may include apertured films;
monolithic or microporous films,
preferably with apertures; modified (with respect to pore structures and
distributions) nonwovens or
composite materials such as film/nonwoven laminates.
Suitable apertured films typically has open surface area at least about 1%,
preferably at least about
5% more preferably at least about 10%. In another embodiment, the open surface
area may be 0.1% or
more, provided there are sufficient amount of relatively large pores present.
Further, suitable apertured
films should have an open surface area less than about 20% such that it would
have insubstantial effect on
the leakage protection properties of the article. Apertured films may be
vacuum formed or hydro-formed to
provide macro and/or micro apertures. More detailed descriptions of suitable
apertured films can be found
in U.S. Patent 4.629,643, U.S. Patent 4,609,518 and IJ.S. Patent 4,695,422,
U.S. Patent 4,342,314 and
23
CA 02411868 2006-05-29
U.S. 4,463,045f
In anotner embodiment, the dampness management means may include zones of:
different
breathability and/or liquid permeability. For example, the dampness management
means may be higher in
breathability and/or liquid permeability in zones which do not coincide with
the absorbent core. As vsed
herein, the term "breathability" refers to the diffusive transport of water
vapor through the material. The
dampness management means may be assembled of one or more layers and
preferably includes at least one
layer which is liquid impermeable, the liquid impenneable layer preferably
located adjacent the absorbent
core and preferably covers an area at least as large as the absorbent core.
Further, moisture condensation on the outer surface (i.e., the garment side)
of the absorbent atticlo
leads to dampness to the touch, which reduces .wearer comfort and is often
perceived as a perfoimance
problem with the article. The convective transport of moisture vapor through
the absorbent article of the
present invention is very effective such that it may lead to moisture
condensation on the outer surfaee of the
article and the perceived dampness problem. Thus, it may be beneficial to
incorporate a relatively low
breathability dampness management means into the article of the present
inverttion. Suitabld low
breathability dampness management means should have a MVTR of no more than
about 4500 g/m2/24hrs,
preferably of no more than about 3500 g/m2/24hrs, more preferably no more than
about 3000 g/mZ/24hrs,
and most preferably no more than about 2500 g/m2/24hrs.
The dampness management means may be disposed between the outer cover and the
absorbent
barrier structure of the present invention. Altematively, the dampness
management means may be disposed
within the absorbent barrier structure between the absorbent layer and one or
both of the barrier layers.
Other Components
In addition, the diaper, as represented in FIG. 3, may further include a pair
of fasteners 40 which
are employed to secure the diaper about the waist of the wearer. Suitable
fasteners include book and-loop
type fasteners, adhesive tape fasteners, buttons, snaps, mushroom-and-loop
fasteners and the like. The
diaper of the present invention may also include elasticized leg bands which
help securing the diaper to the
wearer and, thus, help reduce leakage from the diaper. Similarly, it is also
known to include a pair of
elasticized, longitudinally extending containment flaps which are configured
to maintain a substantially
upright, perpendicular arrangement along the central portion of the diaper to
serve as an additional barrier to
the lateral flow of body exudates.
It is also common to include a surge management layer positioned between the
topsheet and the
absorbent core in order to help prevent pooling of fluids on the portion of
the diaper adjacent the wearer's
skin.
The articles of the present invention may also include waste management
features, such as pockets
for receiving and containing waste, spacers which provide voids for waste,
barriers for liniiting the
movement of waste in the article, compartments or voids which accept and
contain waste materials
deposited in the diaper 20, and any combinations thereof.
Optionally, the absorbent articles of the present invention may include a
sk.in care composition,
preferably on the skin-contacting surfaces of the article. The skin care
composition useful herein is
24
CA 02411868 2006-05-29
directed to maintain and/or improve the skin condition of the skin under an
absorbent article or skin that is
subjected to chronic or acute exposures to body exudates, moisture, irritants,
etc. It is preferred that the skin
care composition provides a protective, and preferably non-occlusive function
(e.g., a relatively liquid
impervious but vapor pervious barrier) to avoid skin overhydration 9nd skin
exposure to materials contained
in body exudates (e.g., urine, feces, menstrual fluids). It is also preferable
that the skin care composition
provides an abrasion minimizing function to reduce skin irritation in the
areas where the absorbent article is
in contact with the wearer's skin. Additionally, the skin care composition may
contain skin care ingredients,
which directly or indirectly, deGver skin care benefits, such as reduction of
overhydration, reduction of
redness, skin conditioning, and removal or reduction of skin irritants (n body
exudates. It is also preferred
that the sldn care composition contains emollients that protect or improve the
sldn against chaffing,
roughness, wrinkled appearance or itchiness. The skin care composition may
also contain skin soothing
agents, such as aloe vera, chamomile.
Skin care compositions suitable for use.in the present invention are described
in co-pending U.S.
Patent Nos. 6,803,496 and 6,710,223, each filed on September 10, 1997; U.S.
Patent Application No.
6,570,054, filed on May 2, 2000; U.S. Patent No. 5,607,760 issued March 4,
1997; U.S. Patent No.
6.716,441, filed on December 17, 1999; U.S. Patent No. 5,609,587 issued
March 11, 1997; U.S. Patent No. 5,635,191 issued June 3, 1997; U.S. Patent No.
5,643,588 issued
July 1, 1997; and U.S. Patent No. 6,153,209 issued November 28, 2000,
L .
Making The Absorbent Barrier Structure
In one embodiment, the nonwoven web and the cellulosic web forming the
absorbent barrier
structure are adhesively bonded together using Ato-Findley adhesive H2031F.
The nonwoven web is
unwound from a supply roll and advances to the spray station where the
adhesive is pre-heated to its melt
state and sprayed (using a Dynatec spray head) onto the web substrate before
the nonwoven web is
assembled with the cellulosic web to form the absorbent barrier structure. The
adhesive forms three
continuous stripes along the longitudinal direction of the advancing web. The
stripes are substantially
parallel. Each stripe is 22 mm in widtli and the outer stripes are about 4 mm
from the peripheries of the
web.
In another embodiment, the 'first nonwoven web and the cellulosic web may be
adhesively joined
together according to the method described above. A second nonwoven web is
unwound from a supply roll,
spray-coated with adhesives, then joined to the free surface of the cellulosic
web. In another three-layered
absorbent barrier structure, the two nonwoven webs may be unwound from
separate supply rolls and spray-
coated with adhesives, then simultaneously joined to the opposed surfaces of
the cellulosic web.
The absorbent barrier structure may be incorporated into a disposable diaper
having the general
construction as the diaper shown in FIG. 1 following well-known assembly
processes_ Typically, the
absorbent barrier structure is disposed between the absorbent core and the
outer cover. In a two-layered
constnietion, the barrier layer is disposed adjacent to the garment-facing
side of the absorbent core and
CA 02411868 2002-12-12
WO 01/97731 PCT/US01/19817
the absorbent layer is disposed adjacent to the outer cover. In a three-
layered construction, the first barrier
layer is disposed adjacent to the garment-facing side of the absorbent core
and the second barrier layer is
disposed adjacent to the outer cover. Other well known components may be
incorporated within the diaper
without departing from the spirit of the present invention. Further, the
manner and method of using these
well known components in connection with the absorbent article of the present
invention will likewise be
readily appreciated by those skilled in the art.
TEST METHODS
A. Air Permeability
The air permeability is determined by measuring the time in which a standard
volume of air is
drawn through the test specimen at a constant pressure and temperature. This
test is particularly suited to
materials having relatively high permeability to gases, such as nonwovens,
apertured films and the like.
A TexTest FX3300 instrument is used. The Test Method conforms to ASTM D737.
The test is operated in a
laborotory environment typically about 22 2 C and about 35% 15 % relative
humidity. The test
specimen has to be conditioned for at least 2 hrs. The test pressure is 125
Pascals and the test area is 38 cm2.
In this test, the instrument creates a constant differential pressure across
the sample which draws air through
the sample. The rate of air flow through the sample is measured in ft3/min/ftz
and converted to permeance
(in Darcy/mm) according to the Darcy's Law:
K/d (Darcy/mm) = (V . ) / (t . A .Ap)
wherein k is the permeability per unit area of the specimen; V/t is the
volumetric flow rate in cm3/sec; is
the viscosity of air (1.86 . 10"5 Pa sec); d is the test material thickness in
mm; A is the cross sectional area
of the specimen in cm2; Op is the pressure differential in Pascal or Pa; and 1
Darcy = 9.869 . 10"9 cm2.
For each sample, three replicates should be run, and the averaged result is
reported.
B. Hydrostatic Head (Hydrohead) Pressure Test
This property determined by this test is a measure of the liquid barrier
property (or liquid
impermeability) of a material. Specifically, this test measures the
hydrostatic pressure the material will
support when a controlled level of water penetration occurs.
A rising water column tester, TexTest Hydrostatic Head Tester FX3000
(available from Advanced
Testing Instruments, Corp., Spartanburg, SC) is used. The test method conforms
to Edana 120.1-18. For this
test, pressure is applied to a defined sample portion gradually increases
until water penetrates through the
sample.
The test is conducted in a labotory environment typically about 73 F 2.0 F
(22.8 C 0.6 C)
and a relative humidity of about 50 :L 2%. The sample is clamped over the top
of the column fixture, using
an appropriate gasketing material (o-ring style) to prevent side leakage
during testing. When an absorbent
barrier structure having a layer of a barrier material and a layer of a
reservoir material is the sample being
tested, the sample is oriented such that the layer of the barrier material
faces the water column during the
test. The area of water contact with the sample is equal to the cross
sectional area of the water column,
which equals 28 cm2.
26
CA 02411868 2002-12-12
WO 01/97731 PCT/US01/19817
Water is pumped into the water column at a rate of 3 mBar/min. Thus, the
sample is subjected to a
steadily increasing water pressure on one surface. When water penetration
appears on three locations on the
other surface of the sample, the pressure at which the third penetration
occurs is recorded. If water
immediately penetrates the sample (i.e., the sample provided no resistance), a
zero reading is recorded. For
each material, three specimens are tested and the results are averaged.
C. Dynamic Liquid Impact Test
The properties determined by this method correlates with the fluid resistance
capability under
sudden impact, which relates to leakage protection, provided by the absorbent
structure of the present
invention. In this test, a sample of the absorbent structure is positioned
adjacent to a loaded absorbent core
simulant, and the combination is subjected to an impact force. The properties
determined by this method is
relevant to the actual use condition where the wearer (especially a baby)
falling from a standing position,
thus, applying an impact force on a loaded diaper.
Dynamic liquid impact test is measured with the apparatus 9100 shown in Figure
1. According to
this test, an absorbent core simulant 9104 is placed directly on top of the
energy absorbing impact pad 9103.
The absorption core simulant comprises four layers of No. 4 filter paper
available from Whatman
Laboratory Division, Distributed by VWR Scientific of Cleveland, OH. The
absorbent core simulant is
loaded with 2 grams of simulated urine. The simulated urine is an aqueous 0.9%
by weight saline solution,
exhibiting a surface energy value as conventionally determined of 72.5 mN/m.
The energy absorbing impact pad 9103 is a carbon black filled crosslinked
rubber foam. The impact pad
9103 is 12.7 cm by 12.7 cm (5 inch by 5 inch) and has a density of 0.1132
g/cm3 and a thickness of 0.79 cm
(0.3125 inches). The impact pad 9103 has a Durometer Value of A/30/15
according to ASTM 2240-91.
A sample 9105 of the absorbent structure of the present invention, including a
barrier zone and a
reservoir zone arranged in layered relation, is placed over the absorbent core
simulant 9104, with the barrier
layer facing down (i.e., the barrier layer is placed directly over the
absorbent core simulant). The
sample/core simulant assembly is positioned in the center of the pad 9103.
An absorbent material 9102 weighted to the nearest 0.0001 gram is placed on
top of the sample
9105 to be tested. The absorbent material 9102 comprises a No. 4 filter paper
available from Whatman
Laboratory Division. The absorbent material 9102 should be able to absorb and
retain simulated urine
which passes through the test sample 9105. The absorbent core simulant 9104
and the sample 9105 should
have an area slightly larger than that of the impact area of'the surface 9110.
The impact arm 9108 is raised to a desired impact angle (about 30 ) to provide
the desired impact energy.
The impact arm 9108 is dropped and the impact arm 9108 is then allowed to rest
on the sample for two
minutes after impact. The arm is then raised and the filter paper 9102 is
removed and placed on a digital
scale. The mass of the wet filter paper is then recorded at the three minute
mark. The liquid impact
transmission (LIT) value is calculated and expressed in g/m2 using the
following formula:
LIT =[mass of the wet filter paper (grams) - mass of the dry filter paper
(grams)] / [impact area (m)]
The impact area, expressed in m2, is the area of the absorbent core simulant
9104. The impact area
is 0.003848 mZ. For each material, three specimens are tested and the averaged
result is reported.
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D. Static Liquid Transmission Test
The property determined by this test correlates with the fluid retaining
ability (or leakage
protection) provided by the absorbent barrier structure of the present
invention under an impact and
sustained pressure condition. The property determined by this test is relevant
to the actual use condition
where the wearer suddenly moves from a standing position to a second position
(e.g., sitting), and maintains
the second position for an extended time period.
The equipment and sample set-up are the same as those descnbed above in the
Dynamic Liquid
Impact Test~ except in this test, the iunpact arin 9108 is dropped and=is
allowed to rest on the sample for a
controlled period of time after impact. Arm 9108 is then raised, the filter
paper 9102 is removed and
weighed, and the cbange in weight is reported as described above. The hold
times at the resting position are
2, 5, 8, 15, 30 and 60 minutes.
E. Moisture Vapor Transmission Rate
The Moisture Vapor Transmission Rate (MVTR) deterniines the amount of moisture
adsorbed by
calcium chloride in a "cup" like container that is covered by a test specimen
where the moisture source is a
controlled temperatute/humidity environment (40f3 C / 75f3 % relative
humidity) separated from the
calcium chloride by the test specimen. This method is applicable to thin
films, multi layer laminates and the
like.
The sample holding a cup is a cylinder with an inner diameter of 30 mm and an
inside height from
bottom to top flange of 49 mm. A flange having a circular opening to match the
opening of the cylinder can
be fixed by screws, and a silicone rubber sealing ring with an opening
matching the inner diameter of the
cup, fits between the top flange and the cylinder. The test specimen is
positioned such that it covers the
cylinder opening. The specimen is tightly fixed between the silicone rubber
sealing and the upper flange of
the cylinder so it acts as a barrier to moisture transport.
The equipment as well as the test specimen should be equilibrated to the
temperature of the
controlled environment prior to testing.
The absorbent desiccant material is CaCl2, such as can be purchased from Wako
Pure Chemical
Industries Ltd., Riclunond, VA under the product designation 030-00525. If
kept in a sealed bottle, it can be
used directly. It also can be sieved to remove lumps, or excessive amounts of
fines, if existing. It also can
be dried at 200 C for about 4 hours.
The CaC12 is weighed (15.0f0.02 g) into the cup, and tapped lightly so as to
level it out, such that
the surface is about 1 em from the top of the cup.
A test sample, cut to about 3.2 cm by 6.25 cm, is placed flat and overlapping
with the seal over the
opening, and the seal and the top flange are affixed by the screws without
over tightening. The total weight
of the cup assembly is accurately recorded to four decimal places, and the
assembly is placed into the
constant temperature/humidity chamber.
After 5 hours exposure to the test humidity (without opening of chamber), the
sample is renioved
and immediately covered tightly with a non-vapor permeable plastic film such
as SARAN WRAPT"'. After
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cooling about 30 minutes to allow for temperature equilibration, the plastic
film is removed and the
assembly is reweighed.
The MVTR value is then calculated by determining the moisture increase over 5
hours due to
transport through the 3 cm circular opening and converting the result to units
of "g/m2/24 hr". For each
sample, three replicates should be run, the resulting values will be averaged,
and the result rounded to the
nearest 100 value.
F. Post-Compression Air Permeability
When a material, especially one with a relatively flexible or open structure,
is subjected to
compaction or sustained pressure, the material may experience structural
changes. After the applied forces
are removed, the material may not return to its original state completely.
This residual structure changes
often result changes in properties, such as air permeability. This test method
is a measure of the resilience)
of the sample material after it has been subjected to compaction or a
sustained pressure for a pre-determined
period of time.
When an absorbent barrier structure of the present invention is incorporated
into absorbent articles,
such as diapers, the articles are often packaged in a highly compact
condition, and stored under such
condition for an extended period of time. Moreover, while the absorbent
article is worn, the wearer may
subject the article to sudden impact force (e.g., the wearer moves from a
standing to a sitting position
abruptly), which may be followed by a sustained pressure (e.g., the wearer
maintains the sitting position).
Certain materials or structures are susceptible to change under such
conditions, and does not recover to its
original state even after the compaction or pressure has been removed. Thus, a
material or structure may
have high air permeability when made but may not be able to deliver such
performance after it has been
compacted and stored in a package or when it suffers sustained pressure
applied by a wearer.
Sample sheets or laminates are cut to 40 mm by 165 mm in size. The sample
sheets are stacked
and placed between two Plexiglas plates. Pressure is applied over the glass
plates to reduce the overall
caliper of the stack of sample sheets to a controlled value. The level of
compression is calculated according
to the following:
H=kxnxd
wherein H is the overall caliper after pressure is applied to compress the
sample stack;
d is the initial caliper of the sample stack;
ra is the number of layers of sample sheets; and
k is compression level.
The compressed sample stacks are placed inside a climate-controlled chamber at
60 C, 50%RH,
for a pre-determined time period. Typically, the test is done with five sample
sheets or laminates in each
stack and at 50% compression. The test may be adapted to any number of layers
of the sample sheets or at
different compression levels.
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Air permeability of the sample is determined before compression and after 24
hours in
compression. The post compression air permeability is measured after a waiting
period, which is sufficient
to allow the sample to recover (taking into consideration that the sample may
exhibit permanent
deformation and will not recover to its original, pre-compression state). For
this test, the air permeability is
determined by measuring the time in which a standard volume of air is drawn
through the test specimen at a
constant pressure and temperature.
The test is operated in a temperature and liumidity controlled environment, at
22 12 C and 35%
~ 15 % relative humidity. The test specimen has to be conditioned for at least
2 hrs.
The test equipment as manufactured by Hoppe & Schneider GmbH, Heidelberg,
Germany, under
the designation "Textiluhr nach Kretschmar", is essentially a bellows in a
vertical arrangement, with its
upper end being mounted in a fixed position, and the lower end being
releasably hold at its upper position,
which can be loosened by means of a release handle to slide under controlled
conditions to the lower
position, thereby increasing the volume inside the bellows by pulling air
through the test specimen which is
covering the air entering opening at the upper end of the bellows. The test
specimen is firmly hold to cover
the air entering opening by means of a fastening ring of 5 cm2 or 10 cm2 to
allow for different samples sizes
and/or different permeability ranges. If the 10 em2 ring is used, the sample
should be at least 55 mm wide,
for the 5 cm2 ring at least 35 mm. For both, the samples should have a length
of about 150 mm.
In case of very high permeability materials, the opening can be further
reduced, with appropriate
adjustments to the equipment and calculation.
The equipment comprises a stopwatch (1/100 sec) which automatically measures
the time between
the operation of the release handle thus starting the sliding of the bellows,
and the bottom of the bellows
reaching its lower end position.
The air permeability k of the material is calculated by the Darcy law as
described above, wherein
different parameters are used (due to the differences in equipment set-up).
Specifically for the test
equipment used here, V is 1900 cm3, A is 4.155 cm2 and Ap is 160 Pa.
The test is repeated once for each test specimen (either sheets made of single
material or laminates
of different materials), and should be repeated on five specimens. For each
sample material or laminate, the
average of at least three satisfactory runs is reported. The averaged value is
reported in Darcy/mm, taking
into account the unit thickness of the material.
G. Absorption Test
This test measures the high suction capillary absorption of absorbent
materials. Capillary sorption
is a fundamental property of any absorbent that governs how fluid would be
absorbed by the absorbent
structure. High suction capillary sorption characterizes the ability of a
material to partition fluid from
competing materials.
A porous glass frit is connected via an uninterrupted colunm of fluid to a
fluid reservoir whose
fluid level is located at the same height as the horizontal center of the frit
porous structure. The sample
absorbs fluid upon demand and its weight at equilibrium is recorded. The fixed
height capsorption
experiment thus gives information about the liquid uptake (g/g) in the
horizontal direction.
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Experimental Setup
The test liquid used herein is 0.2 wt% Triton X-100 (available from Sigma-
Aldrich Inc.) aqueous
solution having a surface tension of about 33 dyne/cm). This test method may
be adapted to use other test
liquids such as water or synthetic urine (having a surface tension of about 75
dyne/cm and about 55
dyne/cm, respectively).
A porous glass fritted funnel is filled with the test liquid. The fritted
funnel (available from VWR
Scientific Products, Cleveland, OH) has a 350 ml volume and 10-15 micron
pores; its bottom outlet is
modified by glass blower to accommodate tubing. A 1.40 m long piece of Tygon
tubing (Part No. R3603,
available from VWR Scientific Products) is attached to the funnel bottom and
filled with test liquid. The
fritted funnel is clamped onto a stand. The Tygon tubing end is aitached to
the fritted funnel with the tubing
end raised several centimeters above the fritted disk.
The funnel is filled with 100 ml of test liquid (the raised tubing end
prevents the liquid from draining
through the frit) and covered with plastic wrap. The frit is then stored for 5-
12 hours to allow any air
trapped in the frit pores to escape. Any observable air bubbles should also be
removed from the frit or the
tubing. The Tygon tubing is placed in the glass fluid reservoir (20-25 cm
diameter) filled with test liquid.
The center of the frit and the fluid level in the reservoir are set to the
same height. A level is used to ensure
that the frit surface is horizontal.
In between experiments the fritted funnel is covered with plastic wrap to
prevent evaporation and
drying of the test liquid in the frit pores; however, during an experiment the
fritted funnel is not covered.
If frits are not used for several hours, they should be stored as follows: the
Tygon tubing is removed
from the fluid reservoir and attached to the fritted funnel with the tubing
end raised several cm above the
fritted disk. The funnel is filled with 100 ml of test liquid (the raised
tubing end prevents the liquid from
draining through the frit) and covered with plastic wrap.
Experiinental Procedure
Ensure that no observable air bubbles are trapped below the frit or in the
tubing. Cut a 5.40 cm
diameter sample using an arch punch. Weigh the sample. Clamp off tubing below
fritted funnel. Evenly
spread the sample over the central area of the frit surface. Place a ring
weight on the sample. Remove clamp
and allow the samples to absorb for 2.5 minutes. Remove the ring weight, then
the sample from frit. If it is
necessary to lower the fritted funnel or tilt it for sample removal, the
fritted funnel tubing has to be clamped
off below the fritted funnel prior to removing the sample from the frit (to
ensure that no additional fluid is
absorbed by the sample during removal). Weigh the samples. Repeat procedure
with the next sample.
Perform two replicates for each sample and report the net uptake obtained for
each frit as well as the
average net uptake. Report which frits were used (frit # or other id). If
results of the two tests differ by
more than 10% (based on the higher value), check frits and sample preparation
and repeat the experiment.
The liquid absorption (or uptake) by the sample is calculated according to the
following:
Net uptake, g/g = (sample wet weight, g - sample dry weight, g) / sample dry
weight, g
EXAMPLES
Example 1
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In this example, the absorbent barrier structure of the present invention is a
two-layered laminate
comprising an absorbent zone and a barrier zone substantially superimposed
over the barrier zone. FIG. 2A
illustrates this embodiment schematically, wherein the absorbent barrier
structure 10 includes a barrier layer
12 and an absorbent layer 14. The absorbent layer is a natural fiber
cellulosic web commercially available
as BOUNTY paper towel (manufactures by the Procter and Gamble Company,
Cincinnati, OH). The web
has a two-ply construction. The total basis weight is about 43 gsm, and the
total thickness is about 0.686
mm. The barrier layer is a polypropylene spunbond/meltblown nonwoven web
(manufactured by BBA
Nonwovens, Simpsonville, SC under the designation MD2005) which has a basis
weight of about 27 gsm
and a thickness of about 0.305 mm.
Example 2
In this example, the absorbent barrier structure has a three-layered
structure, which includes a first
and a second barrier zones are disposed on the opposed sides of the absorbent
zone. FIG. 2B illustrates this
embodiment schematically, wherein the absorbent barrier structure 10 includes
two barrier layers 12 and 16
and an absorbent layer 14 between the two barrier layers. The absorbent layer
is a two-ply BOUNTY
paper towel. The first and the second barrier layers are meltblown
polypropylene nonwoven webs
(manufactured by Jentex Corporation, Buford, GA with the designation PP-015-F-
N). Each of the MB
nonwoven web has a basis weight of about 15 gsm.
Example 3
In this example, the absorbent barrier structure having substantially the same
construction as
described in Example 2, except that the first barrier layer is a MB
polypropylene nonwoven web from
Jentex with a basis weight of about 10 gsm, the second barrier layer is a
spunbond/spunbond polypropylene
nonwoven web made of microdenier fibers with a basis weight of about 17 gsm
(available from First
Quality Fibers Nonwovens, Hazelton, PA under the designation GCAS 16002184).
Example 4
In this example, the absorbent barrier structure having substantially the same
construction as
described in Example 2, except that the first barrier layer is a MB nonwoven
web from Jentex with a basis
weight of about 5 gsm and the second barrier layer is a MB nonwoven web from
Jentex with a basis weight
of about 10 gsm.
Example 5
In this example, the absorbent barrier structure having substantially the same
construction as
described in Example 3, except that the first barrier layer is a MB nonwoven
web from Jentex with a basis
weight of about 10 gsm and the second barrier layer is a MB nonwoven web from
Jentex with a basis
weight of about 5 gsm.
Example 2b
In this example, the absorbent barrier structure having substantially the same
construction as
described in Example 2, except that the absorbent layer is a single-ply BOUNTY
.
ExamQle 3b
In this example, the absorbent barrier structure having substantially the same
construction as described in
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Example 3, except that the absorbent layer is a single-ply BOUNTY .
Example 2c
In this example, the absorbent barrier structure having substantially the same
construction as
described in Example 2, except that the absorbent layer comprises two
superimposed layers of single-ply
BOUNTY&
Comparative Examples
Comparative Example 1 is a two-ply BOUNTY towel available from the Procter &
Gamble
Company, Cincinnati, OH.
Comparative example 2 is a formed film having angled capillaries on its
surface such as those
described in EP 934,735 and EP 934,736. The formed film is made of
polyethylene and is available from
Tredegar Film Products Corporation, Terre Haute, IN.
Comparative example 3 is a microporous film. The microporous is made of
polyethylene having
40-45 wt% CaCO3 fillers. The microporous film is available from Clopay Plastic
Products Company,
Cincinnati, OH.
Comparative example 4 is a polypropylene SS nonwoven web available from First
Quality Fibers
Nonwovens, Hazelton, PA under the designation GCAS 16002184.
Comparative Example 5 is a polypropylene MB nonwoven web available from Jentex
Corporation,
Buford, GA) with the designation PP-015-F-N.
Example 6
The properties of the above examples are tested according to the Test Methods
disclosed herein.
For the three-layered structure, the first barrier layer is disposed adjacent
to the absorbent core during the
tests. The test results are summarized in Table la and Table lb.
Table 1a
EXAMPLE AIR HYDROHEAD LIQUID IMPACT BASIS
PERMEABILITY PRESSURE VALUE (gsm) WEIGHT (gsm)
Darc /mm (mBars)
1 57 41.3 7.2 70
2 24 49.3 6.8 73
3 51 45.3 8.3 69.3
4 47 23.5 7.4 57.1
5 46 39.3 8.5 57.1
2b 24 55.5 10.5 54
3b 40 38.3 9.6 42.5
2c 21.4 81.5 7.1 78
Table lb
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COMPARATIVE AIR HYDROHEAD LIQUID BASIS
EXAMPLE PERMEABILITY PRESSURE (mBars) IMPACT WEIGHT
Darc /mm VALUE (gsm) (gsm)
1 143 <0.5 57 43
2 133 3 5 42
3 0.05 >100 0.2 52
4 407 10.8 37 17
53 68.5 25 15
The test results in Table la indicate that the present invention provides a
unique structure having
the desirable balance of properties.
The test results in Table lb indicate that the comparative examples fail to
provide the desirable
5 balance of properties. BOUNTY paper towel (Comparative example 1) has
excellent air permeability but
poor liquid impermeability. Microporous film (Comparative example 2) has
excellent liquid impermeability
but is substantially air impermeable. The nonwoven webs (Comparative examples
3-5) are air permeable
and liquid impermeable under general conditions. However, the nonwoven webs
become liquid permeable
under impact and/or pressure conditions.
Example 7
In this example, the absorbent barrier structure having a three-layered
construction as described in
Example 2 is combined with an outer cover material, which is a polypropylene
SM nonwoven web having a
16gsm SB layer and a 11.5 gsm MB layer. The combination structure is tested
according to the Test
Methods described herein. The test results are summarized in Table 2.
Table 2
EXAMPLE AIR HYDROHEAD LIQUID IMPACT
PERMEABILITY PRESSURE (mBars) VALUE (gsm)
(Darc /mm
7 13 71.7 5.1
2 24 49.3 6.8
When compared to the absorbent barrier structure of Example 2, the combined
structure enhances
the liquid impermeability and resistance to wet through under impact but
decreases the air permeability.
Overall, the combined structure also provides the desired balance of
properties.
Example 8
In this example, the absorbent barrier structure of Example 2 is combined with
an outer cover
material according to Example 7. Further, an apertured film is disposed
between the second barrier layer of
Example 2 and the outer cover of Example 7. The apertured film is made of
polyethylene having 11.7%
open area. The apertures are hexagonal-shaped openings. The apertured film
used herein is manufactured
by BP Chemicals, Wassergurg, Germany under the trade designation (HEX-B Type
45109). Apertured
films manufactured by Tredegar Film Products Corporation, Terre Haute, IN,
under the
34
CA 02411868 2006-05-29
designation HEX-B, are equally suitable for use herein.
The overall structure, including the absorbent barrier structure, the
apertured film and the outer
cover, are tested according to the Test Methods described herein, and are
compare with Example 7, which
does not include the apertured film. The results are summarized in Table 3
below.
Table 3
EXAMPLE AIR HYDROHEAD LIQUID IMPACT MVTR
PERMEABILITY PRESSURE VALUE (gJm2/24hrs)
(Darcy/mm) (mBars) (gsm)
7 13 71.7 5.1 3972
8 13 66.2 (f 10) 2.5 3434
The open stracture of the apertured film has insubstantial effect on the
convective air permeability
overall. The apertured film reduces the liquid impermeability of the overall
structure, especially under
impact condition. The results show that the overall structure including the
addition of the apertured film,
still achieves the desired balance of properties. More importantly, the
apertured film reduces the diffusive
MVTR of the overall structure. Thus, the unique combination of permeabilities
provides a structure that
desirably exhibits reduced dampness or condensation on the outer surface of
the structure.
Example 9
In this example, the absorbent layer is a cellulosic web (namely, a two-ply
BOUNTY towel)
which has been surface-treated with a hydrophobic agent on both sides. The
surface treatment method is
described in PCT publication WO 00/14296 (D'Agostino et al.).
The hydrophobic agent used is a fluorocarbon, namely,
perfluoromettrylcyclohexane.
The treated cellulosic web is disposed between two barrier layers to form a
three-layered absorbent barrier
structure. Example 9a has substantially the same structure as Example 2 except
that the treated BOUNTY
is used in place of the untreated BOUNTY as the absorbent layer. Table 4
below shows the properties of
this example in comparison to the example using the untreated web.
Table 4
EXAMPLE AIR HYDROHEAD LIQUID IMPACT
PERMEABILITY PRESSURE VALUE (gsm)
(Darcy/mm) (mBars)
9a 27 74.3 4.7
3 24 49.3 6.8
The results show that the hydrophobic treatment significantly enhances the
liquid impermeability
while maintaining the air permeability.
Example 10
In this example, example 3 and Comparative example 2 are tested according to
Test Method G
(Post-Compaction Air Permeability). The results are summarized below in Table
5.
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Table 5
EXAMPLE PRE-COMPACTION POST-COMPACTION
AIR PERMEABILITY AIR PERMEABILITY
Darc /mm Darc /mm
Comp. 2 109 10 66 16
3 115 7 94 8
As the test results show that compaction results in insubstantial change in
air permeability of
example 3 of the absorbent barrier structure of the present invention. In
contrast, a material, such as
Comparative example 2, suffers significant loss in air permeability, which is
attributable to its structural
changes under compaction and its inability to recover its original structure.
While particular embodiments of the present invention have been described, it
would be obvious to
those skilled in the art that various other changes and modifications can be
made without departing from the
spirit and scope of the invention.
36
