Note: Descriptions are shown in the official language in which they were submitted.
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FLEXIBLE ABSORBENT ARTICLE WITH IMPROVED BODY FIT
FIELD OF THE INVENTION
The present invention concerns an absorbent article, preferably a disposable
absorbent article, such as a diaper. The present invention specifically
relates to an
absorbent core for such an absorbent article that provides the article with
improved
softness and conformity to a wearer's body. This absorbent core is also useful
for
providing an absorbent article having increased wearing comfort.
BACKGROUND OF THE INVENTION
Absorbent articles, such as diapers and adult incontinence products, are well
known
articles of commerce. Multiple attempts have been made to provide them with an
overall
good fit and with a high absorbent capacity. Modern diapers make use of
superabsorbent
materials which allow for storage of significant amounts of aqueous liquids
such as urine
(e.g., on the order 300 ml for a typical baby diaper).
While such an absorbent article is generally a disposable product, it is
frequently
worn over many hours and worn in a dry state as well as in a urine loaded
state. As a
result, providing good wearing comfort is very important both when the article
is dry and
when the article is fully or partially loaded with urine (or other bodily
liquids).
One way the art has approached wearing comfort is to provide thinner absorbent
articles. For example, US Pat. 4,673,402 describes an absorbent article with a
dual layer
core where the lower core component has a relatively high concentration of
superabsorbent material and a relatively high density. US Pat. 4,950,264
describes sanitary
napkins with fiber/superabsorbent material blends where the superabsorbent is
at a
relatively high concentration. US Pat. 5,102,597 describes absorbent polymeric
macrostructures that comprise an interparticle crosslinked aggregate where
individual
superabsorbent particles are reacted with an interparticle crosslinking agent
to form an
aggregate which may take a sheet form. US Pat. 5,411,497 discloses an
absorbent article
which includes superabsorbent material located in discrete pockets formed
between a first
and a second carrier layer and water-sensitive attaching means for securing
the carrier
layers together to form the pockets. US Pat. Publication No. 2004/0167486
discusses
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absorbent articles with a discontinuous layer of superabsorbent material. The
layer may
contain up to 20% of an absorbent fibrous material.
The art has also considered increasing density as a means to achieve thinness.
For
example, published US Pat. Application 2005/0119632 discloses absorbent
structures said
to feature a relatively high concentration of superabsorbent material, a
relatively high
density and a relatively high level of flexibility.
However, there is a continuing need for absorbent articles having improved
thinness
and flexibility that maintain the capability to acquire and store enough of
the fluid
deposited thereon so as to continue to provide desirable wearer skin dryness
and
satisfactory leakage performance. Caregivers and adult wearers of such
absorbent articles
desire improved discretion in order that a diaper is less visible under
clothes or, in the
case of an infant diaper, looks more like underwear. More conformable cores
are also
desired in order to reduce the amount of material placed between a wearer's
legs.
SUMMARY OF THE INVENTION
The present invention is directed to an absorbent article, preferably a
disposable
absorbent article, such as a diaper. The diaper has a thin, conformable
absorbent core
where the core structure provides the diaper with improved flexibility as
measured using
a circular bend test. Suitably, the diaper has a core region with a circular
bend flexibility
of less than about 15 N and an acquisition rate on the third gush of less than
about 170
seconds and/or less than about 190 seconds.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view of a diaper as a preferred embodiment of an absorbent
article
according to the present invention.
FIG. 2 is a cross-sectional view of the diaper shown in FIG. 1 taken along the
sectional line 2-2 of FIG. 1.
FIG. 3 is a schematic view of an apparatus for production of one preferred
embodiment of the cores of the present invention.
DETAILED DESCRIPTION
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The present invention is directed to an absorbent article, preferably a
disposable
absorbent article, such as an infant diaper or adult incontinence product.
As used herein, the following terms have the following meanings:
The terms "superabsorbent material"; "superabsorbent polymer"; "SAP";
"absorbent gelling material" and "AGM" all refer to a polymeric material that
is capable
of absorbing at least about 5 times its weight of an aqueous fluid such as
0.9% saline as
measured using the Centrifuge Retention Capacity test as is known to those of
skill in the
art.
"Absorbent article" refers to devices that absorb and contain liquid, and more
specifically, refers to devices that are placed against or in proximity to the
body of the
wearer to absorb and contain the various exudates discharged from the body.
Absorbent
articles include but are not limited to diapers, adult incontinence briefs,
training pants,
diaper holders and liners, sanitary napkins and the like.
"Diaper" refers to an absorbent article generally worn by infants and
incontinent
persons about the lower torso.
"Disposable" is used herein to describe articles that are generally not
intended to be
laundered or otherwise restored or reused (i.e., they are intended to be
discarded after a
single use and, preferably, to be recycled, composted or otherwise disposed of
in an
environmentally compatible manner).
The terms "comprise," "comprising," and "comprises" specify the presence of
what
follows (e.g., a component) but do not preclude the presence of other
features, elements,
steps or components known to the art or disclosed herein.
A structure (e.g. layer) that is "substantially cellulose free" means that the
structure
comprises at least 90% by weight of superabsorbent material and less than 10%
(by
weight of the structure) cellulose fibres, typically less than 5% cellulose
fibres or less
than 1% cellulose fibres, or optionally no cellulose fibres, and typically it
means that the
structure comprises at least about 90% superabsorbent material. Preferably,
such
substantially cellulose free structures comprise at least about 95%
superabsorbent
material, or in certain embodiments at least about 99% superabsorbent
material.
FIG. 1 is a plan view of a preferred embodiment of an absorbent article
according to
the present invention diaper 20. The diaper is shown in its flat out,
uncontracted state (i.e.,
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without elastic induced contraction). Portions of the structure are cut away
to more clearly
show the underlying structure of the diaper 20. The portion of the diaper 20
that contacts a
wearer is facing the viewer. The chassis 22 of the diaper 20 in FIG. I
comprises the main
body of the diaper 20 and does not include core 28 thereof. The chassis 22
comprises an
outer covering including a liquid pervious topsheet 24 and backsheet 26. The
chassis
preferably further includes side panels 30, elasticized leg cuffs 32, and
elastic waist feature
34, the leg cuffs 32 and the elastic waist feature each typically comprise
elastic members
33. One end portion of the diaper 20 is configured as a first waist region 36
of the diaper
20. The opposite end portion is configured as a second waist region 38 of the
diaper 20.
An intermediate portion of the diaper 20 is configured as a crotch region 37,
which
extends longitudinally between the first and second waist regions 36 and 38.
The waist
regions 36 and 38 may include elastic elements such that they gather about the
waist of the
wearer to provide improved fit and containment (e.g., elastic waist feature
34). The crotch
region 37 is that portion of the diaper 20 which, when the diaper 20 is worn,
is generally
positioned between the wearer's legs. The diaper 20 is depicted with its
longitudinal axis
and its transverse axis 12. The periphery of the diaper 20 is defined by the
outer edges
of the diaper 20 in which the longitudinal edges 44 run generally parallel to
the
longitudinal axis 10 of the diaper 20 and the end edges 46 run between the
longitudinal
edges 44 generally parallel to the transverse axis 12 of the diaper 20.
For unitary absorbent articles, the chassis 22 comprises the main structure of
the
diaper with other features added to form the composite diaper structure. While
diaper 20
may be assembled in a variety of well-known configurations, preferred diaper
configurations are described generally in US Pats. 4,940,464, 5,554,145;
5,569,234;
6,004,306, U.S. Pat. Application Publication No. 2003/0233082 and in U.S. Pat.
Application Publication No. 2005/0234410.
The absorbent core 28 in FIG. 1 generally is disposed between the topsheet 24
and
the backsheet 26. The absorbent core. 28 may comprise any absorbent material
that is
generally compressible, conformable, non-irritating to the wearer's skin, and
capable of
absorbing and retaining liquids such as urine and other certain body exudates.
Exemplary
absorbent structures for use as the absorbent assemblies are described in US
Pats.
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4,610,678; 4,834,735; 5,260,345; 5,387,207; 5,397,316; and 5,625,222.
As can be seen more clearly in FIG. 2, absorbent core 28 comprises at least
two
layers: acquisition system 50 which comprises at least acquisition/storage
layer 54 that
provides acquisition along with temporary distribution and storage of acquired
fluids and
permanent storage of a portion thereof and storage system 60 which provides
the majority
of the storage capacity of diaper 20.
The topsheet 24 is compliant, soft feeling, and non-irritating to the wearer's
skin.
Further, the topsheet 24 is liquid pervious permitting liquids to readily
penetrate through
its thickness. A suitable topsheet 24 can be manufactured from a wide range of
materials
such as porous foams, reticulated foams, apertured plastic films, natural
fibers (e.g., wood
or cotton fibers), synthetic fibers (e.g., polyester or polypropylene fibers)
or from a
combination of natural and synthetic fibers. In one embodiment, the topsheet
24 is made
of a hydrophobic material to isolate the wearer's skin from liquids in the
absorbent core
10. Preferably the topsheet comprises a means to adjust hydrophilicity of the
material.
A preferred topsheet 24 comprises a nonwoven material made using means well
known to those skilled in the fabrics art. Preferably, the topsheet 24 has a
basis weight
from about 10 to about 25 g/m2, a minimum dry tensile strength of at least
about 150
g/cm in the machine direction and a strikethrough of less than about 3 seconds
according
to European Disposables and Nonwovens Association standard method 150.4-99.
One
suitable topsheet 24 comprises a polypropylene spunbonded nonwoven comprises
fibers
of less than 3 denier having a basis weight of about 18 g/m2 as is available
from BBA
Fiberweb of Simpsonville, SC.
The backsheet 26 is preferably joined to the topsheet 24 at least about a
portion of
the periphery thereof. The backsheet 26 prevents exudates absorbed by the
absorbent core
28 and contained within diaper 20 from soiling other external articles that
may contact the
diaper 20, such as bed sheets and clothing. The backsheet 26 is preferably
manufactured
from a thin polymer film. In one preferred embodiment the film comprising
backsheet 26
is impervious to liquids. Typically, the backsheet 26 comprises a layer of
polyethylene
film having a basis weight between about 10 g/m2 and about 30 g/m2, although
other
flexible, liquid impervious materials can be used. Preferably, the film is
breathable (e.g.,
via micropores) so as to permit vapors to escape from the diaper 20 while
still preventing
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exudates from passing through the backsheet 26. Particularly preferred
backsheet
materials have a nonwoven laminated to the film layer so as to make backsheet
26 more
"cloth-like". Such a nonwoven layer may comprise a nonwoven material (e.g.,
one having
a spunbonded or other suitable structure) with a basis weight between about 15
g/m2 and
about 25 g/m2. Suitable materials for use as backsheet 26 are available form
Clopay
Plastic Products Company of Mason, OR
The diaper 20 may also include such other features (not shown) as are known in
the
art including front and rear ear panels, waist cap features, elastics and the
like to provide
better fit, containment and aesthetic characteristics. Such additional
features are well
known in the art and are e.g., described in US Pat. 3,860,003 and US Pat.
5,151,092.
In order to keep the diaper 20 in place about the wearer, at least a portion
of the first
waist region 36 is attached by the fastening member 42 to at least a portion
of the second
waist region 38, so as to form leg opening(s) and a waist opening. The
fastening system is
designed to allow an article user to hold one element of the fastening system
such as the
fastening member 42, and connect the first waist region 36 to the second waist
region 38
in at least two places. This is achieved through manipulation of bond
strengths between
the fastening device elements.
FIG. 2 shows a cross section of FIG. 1 taken along section line 2-2 of FIG. 1.
Starting from the body facing side, the diaper comprises the topsheet 24, the
components
of the absorbent core 28, and the backsheet 26. Absorbent core 28 preferably
comprises
an acquisition system 50, which preferably comprises an acquisition layer 52
underlying
topsheet 24 and acquisition/storage layer 54 disposed between acquisition
layer 52 and
the remaining component of core 28, storage system 60.
In particularly preferred embodiments, core 28 is narrower in crotch region 37
than
it is in either of waist regions 36, 38. Preferably, the ratio of the width of
core 28 at
transverse axis 12 to the widest lateral width thereof in either of first
waist region 36 or
second waist region 38 is less than 1Ø More preferably the ratio is less
than about 0.8,
most preferably less than about 0.7.
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In one preferred embodiment acquisition layer 52 comprises a non-woven.
Alternatively acquisition layer 52 may comprise a chemically stiffened,
twisted and
curled fibers, foams or other materials suitable for acquiring aqueous fluids
as are known
to the art. As will be discussed in below, acquisition/storage layer 54 is
substantially free
of cellulosic fibers and comprises a highly permeable superabsorbent material.
Preferably, acquisition/storage layer 54 is in direct contact with storage
system 60.
Alternatively, storage system 60 may be wrapped by a core wrap material so as
to dispose
a layer between storage system 60 and acquisition/storage layer 54. In one
preferred
embodiment the core wrap material comprises an upper wrap layer 56 and a lower
wrap
layer 58. No matter what the relationship between acquisition/storage layer
54, storage
system 60 and various arrangements of wrap materials, acquisition/storage
layer 54 and
storage system 60 must be in fluid communication. The material comprising wrap
layers
56, 58 preferably is a nonwoven material. One preferred material comprises a
spunbonded, a melt-blown and a further spunbonded layer (i.e., a SMS
material). The
non-woven materials are suitably made using synthetic fibers, such as
polyethylene,
polyester and, most preferably, polypropylene. Highly preferred are
permanently
hydrophilic non-wovens, and in particular nonwovens with durably hydrophilic
coatings.
Such hydrophilicity may be provided by surfactant treatment of the nonwoven.
An
alternative material comprises an SMMS-structure or a cellulosic tissue
structure.
Similarly, but not shown, acquisition/storage layer 54 may be provided with a
wrap
material so as to enclose the layer. Materials suitable for upper and lower
wrap layers 56,
58 are also suitable for use as a wrap material in designs for core 28 where
it is desired to
wrap acquisition/storage layer 54.
In a third alternative, wrap materials 56, 58 enclose both acquisition/storage
layer
54 and storage system 60. In this embodiment acquisition/storage layer 54 and
storage
system 60 are in direct facing contact.
Suitably, acquisition/storage layer 54 has the same area as storage system 60
or
smaller. Preferably, acquisition/storage layer 54 is laterally centered on
storage system 60
with the same lateral width but a shorter longitudinal length than storage
system 60.
Acquisition/storage layer 54 may also be narrower than storage system 60 while
remaining centered thereon. Said another way, acquisition/storage layer 54
suitably has
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an area ratio with respect to storage system 60 of 1Ø Preferably, the area
ratio is less than
1.0 (e.g., less than about 0.75), more preferably less than about 0.50.
When the acquisition/storage layer 54 is longitudinally shorter than the
storage
system 60, it is positioned such that more than 50% of its longitudinal length
is forward
of transverse axis 12. This positioning is desirable so as to place
acquisition/storage layer
under the point where urine is most likely to first contact diaper 20
(Sometimes called the
"pee point"). Such positioning will facilitate acquisition of liquids absorbed
by
acquisition/storage layer 54.
Also, both acquisition/storage layer 54 and storage system 60 may comprise an
uneven distribution of superabsorbent material basis weight in one or both of
the machine
and cross directions. Such uneven basis weight distribution may be
advantageously
applied in order to provide extra, predetermined, localized absorbent capacity
to diaper
20. For example, the basis weight of superabsorbent material in one or both of
acquisition/storage layer 54 and storage system 60 could be increased in the
region of
core 28 adjacent the "pee point". This "profiled" distribution can also be
sued to provide
diaper 20 with a desirable configuration to core 28 for improved body fit. For
example,
predetermined regions of low superabsorbent basis weight could be provided to
create
preferential fold zones in the core to help insure that core 28 flexes in a
predetermined
manner.
In alternative embodiments (not shown), the article may be preformed by the
manufacturer by joining opposing portions of the longitudinal edges 44 that
lie adjacent
to the end edges 46 to create a pant. The term "pant", as used herein, refers
to disposable
garments having a waist opening and leg openings designed for infant or adult
wearers. A
pant may be placed in position on the wearer by inserting the wearer's legs
into the leg
openings and sliding the pant into position about the wearer's lower torso. A
pant may be
preformed by any suitable technique including, but not limited to, joining
together
portions of the article using refastenable and/or non-refastenable bonds
(e.g., seam, weld,
adhesive, cohesive bond, fastener, etc.). A pant may be preformed anywhere
along the
circumference of the article (e.g., side fastened, front waist fastened).
While the term
"pant" is used herein, pants are also commonly referred to as "closed
diapers",
"prefastened diapers", "pull-on diapers", "training pants" and "diaper-pants".
Suitable
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pants are disclosed in US Pats. 5,246,433; 5,569,234; 6,120,487; 6,120,489;
4,940,464;
5,092,861; 5,897,545; 5,957,908 and in Published US Pat. Application
2003/0233082A1.
In additional alternative embodiments (also not shown) acquisition/storage
layer 54
and storage system 60 can comprise a removable/replaceable component of an
absorbent
article. Such removable/replaceable components allow the absorbent article to
be
"refreshed" without the necessity of changing the entire article. The
acquisition/storage
layer 54 and storage system 60 are disposed beneath at least one fluid
permeable layer
similar to topsheet 24. Such embodiments having removable/replaceable
components are
described more fully in one or more of the following: US Patent No. 6,989,005,
filed in
the name of Lavon, et al. on March 27, 1997 and US Pat. Publication No.
2006/0229582
filed in the name of Lavon, et al. on April 4, 2005 and in published US Pat.
Applications
2004/0039361, 2002/0091368, 2003/0199844, 2004/0024379, 2004/0030314.
A particularly preferred storage system 60 is described in aforementioned US
Pat.
Publication No. 2004/0167486. In summary, the layer comprises a superabsorbent
material
that is stabilized by a fibrous layer of thermoplastic material, preferably a
thermoplastic
adhesive to provide dry and wet immobilization of the superabsorbent material.
As can be
seen, such a structure is substantially free of cellulosic fibers. A
particularly preferred
superabsorbent material has an Absorption Against Pressure (AAP) of at least
about 20 g/g
and a Saline Flow Conductivity (SFC) that is greater than about 30 x 10"7 (cm3
seconds)/g.
Preferably, AAP is greater than about 23 g/g, more preferably greater than
about 25 g/g.
AAP is measured according to the method described in the TEST METHODS section
below and SFC is measured according to the method described in US Pat.
5,599,335.
These superabsorbent materials are used at a basis weight of at least about
200 g/m2,
preferably at least about 400 g/m2, more preferably at least about 600 g/m2,
to produce
storage system 60. In order to maintain satisfactory flexibility, the basis
weight is also less
than about 2000 g/m2.
Because storage system 60 is substantially free of cellulosic fibers, it has a
higher
density than components of an absorbent core used by the prior art for similar
purposes.
Suitably, a storage system 60 according to the present invention has a density
greater than
about 0.4 g/cm3. Preferably, the density is greater than about 0.5 g/cm3, more
preferably
3
greater than about 0.6 g/cm.
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Acquisition/storage layer 54 cooperates with storage system 60 to make more
efficient use of the capacity thereof by providing temporary capillary storage
of acquired
fluids to allow time for fluid distribution into storage system 60. In
addition, because
acquisition/storage layer 54 comprises a superabsorbent material, it provides
at least -a
portion of the ultimate storage capacity of absorbent core 28.
Importantly, because acquisition/storage layer 54 is intended to provide at
least
some temporary capillary storage and distribution of acquired fluid, it has a
more open
structure when wet than storage system 60 (i.e., the wet porosity is greater).
The art has
typically used fibrous structures (e.g., blends of cellulose fluff and
superabsorbent material
or crosslmked cellulose fibers for this purpose). However, such fibrous
structures have
considerable dry bulk compared to the substantially cellulosic fiber free
acquisition/storage layers 54 of the present invention. Suitable
superabsorbent materials
for use in acquisition/storage layer 54 are described in US Pat. Publication
No. No.
2005/0101928, in US Pat. Application Publication No. 2005/0070867, US Pat.
Application
Publication No. 2005/0222547 and in JP 2004-105118, entitled "An Aqueous-
Liquid-
Absorbing Agent and Its Production Process", filed in the name of Nippon
Shokubai Co.
Ltd. On March 31, 2004. The superabsorbent material is used at a basis weight
of at least
about 100 g/ni2, preferably at least about 150 g/m2, more preferably at least
about 200
g/m2, to produce acquisition/storage layer 54.
Because an acquisition/storage layer 54 according to the present invention is
substantially free of cellulosic fibers, it has a higher density than
components of an
absorbent core used by the prior art for similar purposes. Suitably, an
acquisition/storage
layer 54 according to the present invention has a density greater than about
0.4 g/em3.
Preferably, the density is greater than about 0.5 g/cm3, more preferably
greater than about
0.6 g/cm3.
Acquisition/storage layer 54 and storage system 60 also cooperate to provide
diaper 20 with improved wearer fit and comfort. Specifically a diaper 20 that
comprises a
core 28 where the acquisition system 50 includes at least an
acquisition/storage layer 54
according to the present invention has desirable low caliper and crotch
flexibility. As will
be recognized, a low caliper and a flexible material result in a flexible core
that can more
closely conform to a wearer's body throughout the full range of wearer motion.
Such
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thin/flexible diapers are also less visible under a wearer's clothing and can
have a very
underwear-like appearance.
As noted above, cores 28 according to the present invention have a desirable
low
caliper. Desirably, the acquisition system 50 of the present invention
comprises both an
acquisition layer 52 and an acquisition/storage layer 54. For a core 28 of
this construction
dry core caliper is less than about 5 mm when measured at the center of
acquisition layer
52. Preferably, the caliper of core 28 is less than about 4.5 mm, more
preferably less than
about 4 mm when measured at the center of acquisition layer 52. Structures
that do not
incorporate the acquisition layer 52 are even thinner.
It should be noted that, when many of the absorbent structures of the art
discuss
caliper, the caliper of the absorbent structure is discussed in terms of only
a single layer,
rather than the assembled layers necessary to form a complete core 28 for a
diaper 20.
Thus it is believed the low caliper of a core 28 of the present invention is
particularly
advantageous. Said another way, the low caliper of core 28 provides diaper 20
with a
desirable low caliper. That is, the thickness of all diaper components between
the body
surface of the topsheet and the garment surface of the backsheet is
meaningfully less than
the thickness of prior art diapers. For example, in one embodiment, a diaper
20 that
comprises a core 28 according to the present invention has a dry caliper
(measured 10 cm
from the front edge 29 of core 28) that is less than about 5 mm. Preferably,
the dry caliper
of diaper 20 is less than about 4.5 mm, more preferably less than about 4 mm.
Core 28 according to the present invention is also desirably flexible so as to
facilitate reduced bulk and improved conformity of diaper 20. Without being
bound by
theory, it is believed that the combination of a thin construction as
discussed above (as is
known, stiffness increases with thickness) and flexible joinder of the
absorbent polymer
particles by the thermoplastic material (see, for example, published US Pat
Application
2004/0162536) cooperate to provide the desirable flexibility. As a result,
core 28 can
more readily conform to varying wearer body shapes and respond to wearer
motion. As
can be seen in Example 1, diaper products of the prior art vary widely in
flexibility (from
4.0 N to 70.5 N when evaluated according to the Circular Bend Flexibility
test). It will be
recognized that such flexibility is a result of many factors coming together
in a finished
diaper product. For example the Circular Bend Flexibility of Comparative
Diapers A and
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B is markedly different although the diapers have very similar storage
systems. Without
being bound by theory, it is believed that the difference in Circular Bend
Flexibility can
be attributed to the difference in the acquisition systems. Specifically, the
dual layer
acquisition system used in Comparative Diaper A has desirable fluid handling
properties
(e.g., the dual layer acquisition system provides substantial temporary
storage for urine
"gushes" with resulting rapid acquisition). These benefits come at the price
of
substantially less flexibility than Comparative Diaper B. Reference to Example
2 shows
that the core designs of the present invention maintain much of the improved
flexibility of
Comparative Core B (-12N for a core according to the present invention vs. -
44N for
Comparative Core A) while also providing the desirable fluid handling
properties of
Comparative Core A (third gush acquisition rate of -100 seconds for a core
according to
the present invention vs. -200 seconds for Comparative Core B). Specifically,
replacing
the dual layer acquisition system of Comparative Diaper A with a
storage/distribution
system according to the present invention provides much of the rapid
acquisition of the
dual layer system while remaining thin and flexible when dry so as to provide
much of
the dry flexibility of Comparative Diaper B.
Suitably an absorbent core 28 according to the present invention has a
Circular
Bend flexibility of less than about 13 N, preferably less than about 12 N, and
more
preferably less than about 10 N. Similarly, an absorbent article according to
the present
invention has a Circular Bend Flexibility substantially lower than that of
commercially
available and prior art diapers. Suitably, an absorbent article according to
the present
invention has a Circular Bend Flexibility less than about 15 N in a specimen
taken from
crotch region 37, forward of the lateral centerline of absorbent core 28
thereof.
Preferably, the Circular Bend Flexibility in crotch region 37 is less than
about 13.5 N,
more preferably less than about 11 N. A method for measuring Circular Bend
Flexibility
is given in the Test Methods section below.
The absorbent cores 28 of the present invention not only have the low caliper
and
improved flexibility discussed above they also provide a wearer with desirable
fluid
handling properties. With respect to absorbent articles at least two types of
fluid handling
properties need to be considered: fluid acquisition and fluid storage
capacity.
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An absorbent article should have good fluid acquisition properties in order to
rapidly transfer aqueous fluids from the body surface of the absorbent article
to minimize
free fluid that can bypass cuffs and waistbands with a resulting leak. In the
case of the
present invention, acquisition/storage layer 54 cooperates with acquisition
layer 52 (when
such an acquisition layer is present) to provide void volume for containing
"gushes" of
aqueous liquids so as to allow time for storage system 60 to acquire and
permanently
store such fluids. Because acquisition/storage layer 54 comprises a highly
permeable
superabsorbent material, such void volume is maintained even after the
superabsorbent
material comprising acquisition/storage layer 54 begins to swell after
exposure to an
aqueous fluid. Fluid acquisition properties can be conveniently measured using
the Fluid
Acquisition test described in the TEST METHODS section below. This test
measures the
time required for an absorbent article to acquire a predefined volume of fluid
that is
delivered in a series of "gushes". The volume and delivery rate are intended
to represent
typical conditions for a specific size absorbent article. Depending on the
size of the
article, the time required to acquire the third or fourth gush of fluid can be
an important
measure of acquisition performance. Suitably, an absorbent article according
to the
present invention has a third gush acquisition rate of less than about 170
seconds,
preferably less than about 150 seconds, more preferably less than about 130
seconds.
Particularly preferred embodiments have a third gush acquisition rate of less
than about
100 seconds. For larger sizes, acquisition rate for a fourth gush is also
important.
Suitably, an absorbent article according to the present invention has a fourth
gush
acquisition rate of less than about 190 seconds, preferably less than about
180 seconds,
more preferably less than about 170 seconds.
Specifically, a core 28 of the present invention must provide sufficient
storage
capacity to function while simultaneously providing substantially reduced dry
caliper and
improved flexibility. As is also known, the required absorbent capacity for an
absorbent
article is basically defined by the intended use thereof. That is, an
absorbent article
intended for adult incontinence uses will have a larger design capacity than
and absorbent
article intended for an infant. Importantly, an absorbent core 28 according to
the present
invention does not give up the capacity to store an appropriate quantity of
aqueous fluid
in order to provide a reduction in core caliper. One way of considering
capacity is as
normalized capacity, that is capacity per unit area. This approach takes into
account that
CA 02616904 2010-01-06
14
absorbent articles designed for larger wearers will have both a larger design
capacity and a
larger core area to absorb fluids deposited thereon. A method for normalized
capacity is
given in US Pat. Application Publication No. 2005/0222547. Suitably, a core 28
according
to the present invention will have a normalized capacity in the portion
thereof that
comprises acquisition storage layer 54 of greater than about 0.3 g/cm2.
Preferably, the
normalized capacity in the portion thereof that comprises acquisition storage
layer 54 is
greater than about 1.0 g/cm2, more preferably greater than about 2.0 g/cm2. In
those
portions of core 28 that do not comprise acquisition/storage layer 54 the
normalized
capacity may be lower. For designs where the bulk of the capacity for aqueous
liquids is
within or adjacent to the crotch region 37, suitably, the normalized capacity
in such areas
is less than about 0.9 g/cm2, preferably less than about 0.5 g/cm2, more
preferably less
than about 0.2 g/cm2.
In an alternative embodiment core 28 is designed to provide a substantial
portion
of the ultimate storage in one or both of waist regions 36, 38. For this
embodiment the
normalized core capacity in one or both of waist regions 36, 38 may be equal
to or higher
than the normalized core capacity in crotch region 37. For example such waist
region
normalized core capacity may be greater than about 1.0 g/cm2, even greater
than about 2.0
g/cm2. For this embodiment, the area of crotch region 37 is less than the area
of the
embodiment discussed above where the bulk of the capacity for aqueous liquids
is within
or adjacent to the crotch region 37 and acquisition/storage layer 54 may
extend into waist
regions 36, 38.
As will be recognized, if it is desired to calculate the total capacity of a
core 28, the
respective areas of a core 28 with and without acquisition layer 54 can be
determined
using means known to the art (e.g., image analysis) and those areas multiplied
by the
normalized capacity for the area to determine the total capacity of a core 28
having a
particular size.
Storage system 60 can suitably be produced using the method described in the
aforementioned US Pat Application Publication No. 2004/0167486.
Acquisition/storage layer 54 can be produced using a method that is
substantially
the same as that used to produce storage system 60. The main difference is
that, rather
than being provided with an uneven surface so as to provide areas of junction
where an
CA 02616904 2010-01-06
adhesive directly contacts a substrate layer as described in US Pat.
Application Publication
No. 2004/0167486, a laydown drum is provided with a series of "pockets" having
a shape
and volume substantially defined by the desired shape and volume of
acquisition/storage
layer 54. As will be recognized, the shape and volume of these pockets may be
used to
provide a predefined superabsorbent material profile to one or both of
acquisition/storage
layer 54 and storage system 60. This laydown drum is provided with vacuum
means as
described in the aforementioned US Pat. Application Publication No.
2004/0167486 that is
suitable for drawing a substrate into the pocket. Any nonwoven suitable for
use as a
substrate for storage system 60 is also suitable for use to produce
acquisition/storage layer
54.
In one preferred embodiment, storage system 60 and acquisition/storage layer
54
are produced so as to provide a core 28 with no upper wrap layer 56
therebetween. One
suitable process for producing this structure is shown in Fig. 3 and discussed
in the
following paragraphs.
As can be seen in Fig. 3, a storage layer precursor 160 can be produced by
depositing a first superabsorbent material (not shown) that is contained in
hopper 105 onto
substrate 100. As described in US Pat. Application Publication No.
2004/0167486, first
substrate 100 is caused to conform to depressions (not shown) in first laydown
drum 110
by a vacuum in first vacuum portion 115 so as to enable filling the
depressions with the
first superabsorbent material as the depression passes under first hopper 105.
After the
depression passes under first hopper 105 the first superabsorbent material is
stabilized
with a thermoplastic polymer applied at first spray station 120 so as to form
storage layer
precursor 160.
Acquisition/storage layer precursor 154 can be produced in essentially the
same
manner. Second substrate 130 is caused to conform to a depression in second
laydown
drum 140 prior to filling with a second absorbent polymer (not shown)
delivered from
second hopper 135. The second superabsorbent material in the filled
depressions is
stabilized by thermoplastic polymer delivered from second spray station 150.
To form core precursors 128, the substrate webs carrying storage layer
precursor 160 and
acquisition/storage layer precursor 154 are phased for proper alignment using
methods
known to the art and combined at nip 180. As will be recognized, the rolls
comprising nip
180 can be provided with pockets to receive precursors 160, 154 to enable
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16
the first and second substrates 100, 130 to be sealed about the periphery of
storage layer
precursor 160 effectively enclosing core precursor 128 in a wrap material. If
necessary,
one or both of the rolls comprising nip 180 could be heated to soften the
thermoplastic
material to facilitate the enclosure step.
As will also be recognized separate nips (not shown) essentially the same as
nip 180
and a web of a suitable nonwoven material (not shown) could be provided
between the
spray stations 120, 150 and nip 180 if it was desired to enclose either or
both of
precursors 160, 154.
TEST METHODS
Fluid Acquisition
The fluid acquisition test provides a measure of the ability of an absorbent
structure
to rapidly acquire aqueous fluids under simulated use conditions. The sample
is loaded
with a gush of 0.9% saline solution at a predetermined volume and rate using a
pump
(The Model 7520-00 available from Cole Parmer Instruments Co. of Chicago, IL
is
suitable). The time to absorb saline solution is recorded by a timer. The gush
is repeated
at 5 minute gush intervals for 4 gushes. The detailed description below is
directed to
infant diapers, for other types of absorbent articles the gush volume and
confining
pressure may be adjusted as described herein.
The test sample, which comprises a core and includes a topsheet and a
backsheet, is
arranged to lie flat on a foam platform within a polymethyl methacrylate
(e.g.,
PERSPEX) box (see the detail assembly of the test apparatus in US Pat.
6,083,210) and a
weight representative of a typical confining pressure is placed on a PERSPEX
cover as
discussed below. The following provides suitable setup parameters for various
sizes of
infant diapers. If a diaper product to be tested does not list a size, the
product size is
defined by determining the weight range with the greatest overlap with the
weight ranges
listed below.
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17
Size Approx.
Infant Wt Loading Vol. Loading Rate Confining Pressure Weight
(kg) (ml) (ml/sec) (kg)
Newborn <4 16 5.33 0.9 at each end of plate= 1.8 total
1 4-6 24 8 2.3 at each end of plate= 4.6 total
2 5-8 40 8 2.9 at each end of plate= 5.8 total
3 7-13 50 10 4.5 at each end of plate= 9.0 total
4 10-17 75 15 9.1 at each end of plate= 18.2 total
and larger >12 75 15 9.1 at each end of plate= 18.2 total
If products with significantly different capacities from those listed in the
table above are
evaluated (such as can be envisaged for adult incontinence products or diapers
for
premature infants), the fluid volume per gush should be adjusted to 20% of the
total
article design capacity and the weight for the confining pressure should be
adjusted to be
representative of the pressure exerted a wearer on the product when the wearer
is sitting.
Design capacity can be determined by summing the capacity of superabsorbent
material
(defined as the Centrifuge Retention Capacity) and any contribution from
fibrous material
in the core (e.g., 4 g/g for cellulosic fibers). Any deviation from the
standard test protocol
should be recorded.
The outer surface of the backsheet faces the foam platform. A PERSPEX plate
with
a 5 cm diameter opening substantially in its middle is placed on top of the
sample. The
sample is oriented such that the topsheet is directly below the opening of the
PERSPEX
plate. The opening in the plate (i.e., the loading point for the saline
solution) is placed
about 10 cm from the front edge of the complete core and about in the halfway
between
the lateral sides of the core. Saline solution is introduced to the sample
through the
cylinder fitted and glued into the opening. Electrodes are about 1 mm to 2 mm
above the
surface of the absorbent structure and also connected to the timer. Loads are
placed on top
of the plate to simulate, for example a baby's weight. Two weights with an
area of 744.6
cm2 (51 cm x 14.6 cm) appropriate for the particular size (see table above)
are placed on
top of the plate.
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As saline solution is introduced into the cylinder, it builds up on top of the
absorbent structure thereby completing an electrical circuit between the
electrodes. This
starts the timer. The timer is stopped and recorded when the absorbent
structure has
absorbed the gush, and the electrical contact between the electrodes is
broken.
Acquisition rate is defined as the time in seconds required to absorb the gush
volume that is delivered. The acquisition rate is calculated for each gush
introduced into
the sample.
Basis Weight
European Disposables and Nonwovens Association (EDANA) standard method for
Mass per Unit Area (40.3-90) is suitable
Caliper
European Disposables and Nonwovens Association (EDANA) standard method for
Thickness (No 30.5-99) is suitable. A suitable apparatus is described in
paragraph 4.1.
The specified pressure is 2.1 kPa.
Density
Divide the basis weight determined using the Basis Weight method by the
caliper
determined by the Caliper method.
Circular Bend Flexibility
Sample Preparation
This method is suitable for measuring the flexibility of absorbent articles or
absorbent article components having a core with sufficient area to cut a 2.5
inch X 6.5
inch (6.4 cm X 6.4 cm) sample therefrom. Samples should equilibrate at 23 C
2 C and
50% 2% relative humidity for at least 2 hours before testing. Open the side
seals if the
absorbent article is a pants type diaper. Remove all elastics (leg cuffs,
waist bands, etc.)
from the absorbent article. Gently stretch the absorbent article on a flat
surface, with the
backsheet toward that surface, to eliminate any folds therein. Mark the
intersection of the
longitudinal and transverse axes of the absorbent core. Measure 62 mm along
the
longitudinal axis toward the front waist edge of the absorbent article, and
make a second
mark. Using a hydraulic press (suitable presses are available from Carver,
Inc. of
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Wabash, IN) with a 2.5 inch square die (6.4 cm), cut a sample centered at the
second
mark.
Apparatus and Method
The circular bend method is performed on a constant rate of extension tensile
tester
with computer interface (a suitable instrument is the MTS Q-tester using
Testworks 4
Software; as is available from MTS Systems Corp, Eden Prairie, MN) and a 100 N
load
cell. The instrument is set up for a standard compression test using the
platform and
plunger fixtures described in ASTM D4032-94 (Standard Test Method for
Stiffness of
Fabric by the Circular Bend Procedure). The sample is centered on the platform
over the
aperture. The piston is rigidly connected to the crosshead of the tensile
tester, centered on
the aperture and positioned 20 mm above the top plane of the platform at the
start of the
test. Upon test initiation, crosshead motion causes the plunger to descend at
a rate of 100
mm/min to a depth of 15 mm below the top plane of the platform.
Replicates and Calculations
At least 5 replicates for each sample are evaluated.
The circular bend flexibility is reported as the maximum peak force in Newtons
(N).
Each set of five identical replicates (or n replicates if n is greater than 5)
is tested and the
five values measured for that set are averaged as the value for the sample.
EXAMPLES
Example 1
This example is intended to show the flexibility of the core region of machine
made
diaper products of the prior art. In this example, commercially available
diapers, and
other diapers according to the prior art were evaluated for Circular Bend
Flexibility in
two sections of the crotch region (before and after the lateral centerline of
the core) using
the method described herein. The results of this evaluation can be found in
Table 1.
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Table 1
Circular Bend Flexibility
Diaper Type Crotch Front
(N)
Pampers Easy Ups ' 3T/4T 51.3
Pampers Feel n Learn ' 24.4
Huggies Pull Ups Girl
Size 2T/3T
18.4
Size 3T/4T
24.7
Size 4T/5T
15.6
Huggies Pull Ups 2 Boy Size 4
49.3
Pampers Cruisers el Size 4
43.9
Huggies Supreme 2 Size 4
70.5
Huggies Baby Shape 2 Size 4
38.2
Comparative Diaper A3
50.1
Comparative Diaper B4
4.0
Cloth Underwear5
0.2
1. Available from Procter & Gamble of Cincinnati, OH
2. Available from Kimberly Clark of Neenah, WI
3. Storage system according to published US Pat Application 2004/0162536 with
dual layer acquisition system comprising crosslinked cellulose fibers
(250g/m2)
and carded/resin bonded polyester nonwoven (60 g/m2)
4. Storage system according to published US Pat Application 2004/0162536 with
nonwoven acquisition layer comprising carded/resin bonded polyester
nonwoven (43 g/m2)
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21
5. Hanes Her Way cotton briefs Size 4 available from Hanes Company, Inc. of
Winston-Salem, NC, two plies of fabric in crotch area. A 10 N load cell was
used in the force measurement instead of a 100 N load cell due to the high
flexibility.
As can be seen, there is a wide variation in flexibility among the diapers
tested and
underwear is the most flexible of all products tested.
Example 2
This example is intended to compare the flexibility and acquisition rate of
absorbent
cores according to the present invention with two cores from the prior art. In
this example
the core samples are disposed on a backsheet comprising a laminate of a18 g/m2
spunbonded polypropylene from BBA Fiberweb of Simpsonville, SC and a 28 g/m2
polyethylene film from Clopay Plastic Products Company of Mason, OH.with a
topsheet
(18 g/m2 spunbonded polypropylene from BBA Fiberweb of Simpsonville, SC)
disposed
thereon and are evaluated for Circular Bend Flexibility in the front portion
of the crotch
region (before the lateral centerline of the core) and Third Gush Acquisition
Rate.
Table 2
Average Circular Bend
Digger Type Flexibility Crotch Front Arc uisition Rate 3d Gush
(N) (seconds)
Comparative Core A' 44 90
Comparative Core B2 2 198
Core According to Present Invention 12 97
1. Storage system according to published US Pat Application 2004/0162536
(800 g/m2) with dual layer acquisition system comprising crosslinked cellulose
fibers (250 g/m2) and carded/resin bonded polyester nonwoven (60 g/m2)
2. Storage system according to published US Pat Application 2004/0162536
(400 g/m2) nonwoven acquisition layer comprising carded/resin bonded
polyester nonwoven (43 g/m2)
3. Storage system according to published US Pat Application 2004/0162536
(680 g/m2), acquisition/storage layer according to the present invention
(superabsorbent material according to US Pat. Application Publication
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22
No. 200510222547 with a basis weight of 200 g/m2) and carded/resin bonded
polyester nonwoven (60 g/m2)
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23
Example 3
This example is intended to compare the dry caliper of diapers according to
the
present invention with commercially available diapers and a diaper made
according to
published US Pat Application 2004/0162536. This comparison is shown in Table
3.
Table 3
Product Dry Caliper
(mm)
Pampers* Active Fit (size 4)1 7.1
Huggies Super-Flex (size 4)' 7.2
HuggiesmPull-UpsOGirlm3 3.2
Huggies Pull-UpseBoyO3 4.0
Diaper According to published US Pat
Application 2004/01625364 5.9
Present Inventions 3.9
1. Available from Procter & Gamble GMBH. of Schwalbach am Tanus, Germany
2. Available from Kimberly Clark of Reigate, United Kingdom
3. Available from Kimberly Clark of Neenah, WI
4. Dual layer acquisition system: consists of curly cellulosic fiber (200g/m2)
and
carded/resin bonded polyester nonwoven (60 g/m2)
5. Acquisition/storage layer according to the present invention
All documents cited in the Detailed Description of the Invention are,
not to be construed
as an admission that it is prior art with respect to the present invention.
While particular embodiments of the present invention have been illustrated
and
described, it would be obvious to those skilled in the art that various other
changes and
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24
modifications can be made without departing from the spirit and scope of the
invention.
As will be also be apparent to the skilled practitioner, all combinations of
the embodiments and
features taught in the foregoing disclosure are possible and can result in
preferred executions of
the invention. It is therefore intended to cover in the appended claims all
such changes and
modifications that are within the scope of this invention.
