Note: Descriptions are shown in the official language in which they were submitted.
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ABSORBENT ARTICLE HAVING A BREATHABILITY GRADIENT
Backqround of the Invention
Field of the Invention
The present invention relates to an absorbent articie for absorbing body fluids and
lC exudates, such as urine. More particularly, the present invention relates to absorbent
garments, such as disposable diapers and adult incontinence garments, which are
configured to absorb body exudates while also helping to provide reduced skin hydration.
DescriPtion of the Related Art
Many known diaper configurations employ absorbent materials located between a liquid
pervious topsheet and a vapor and liquid impermeable backsheet. Such backsheets are
well suited to prevent the migration of liquid waste from the absorbent materials to the
outer garments of a wearer. Unfortunately, the use of liquid and vapor impermeable
backsheets can result in a relatively high degree of humidity within the diaper when in use.
This may result in relatively high skin hydration levels and may lead to the onset of diaper
rash.
In order to reduce the humidity level within diapers, breathable polymer fllms have been
employed as outer covers for absorbent garments, such as disposable diapers. Thebreathable films are typically constructed with micropores to provide desired levels of
liquid impermeability and vapor permeability. Other disposable diaper designs have been
arranged to provide some level of breathability at the leg cuff regions of the diaper. Still
other disposable diaper designs have been arranged to provide humidity transfer regions
in the form of breathable panels in otherwise vapor-impermeable backsheets or to employ
perforated regions to help ventilate the garment.
Conventional absorbent articles, such as those described above, have not been
completely satisfactory. For example, articles which employ a microporous outer cover
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can exhibit a cold and clammy feeling when the garment is wetted and moisture isevaporating through the microporous film. The articles which employ perforated films or
breathable panels can exhibit excessive leakage of liquids from the article and can
excessively soil the wearer's outer garments. In addition, when the absorbent material of
the article becomes loaded with liquid, the wet absorbent can bloc~ the escape of
moisture from the wearer's s,cin. Such absorbent garment designs have not been able to
sufficiently reduce the hydration of the wearer's skin. As a result, the wearer's skin has
remained susceptible to rashes, abrasion and irritation.
10 Summarv of the Invention
In response to the difficulties and problems discussed above, a new disposable absorbent
article which has a breathability gradient has been discovered.
As used herein, reference to "humidity transfer" refers to the transfer of water vapor from
15 the interior of a diaper, when in use on a wearer, to the exterior of the diaper (ambient
atmosphere).
As used herein, a substantially liquid impermeable material is constructed to provide a
hydrohead of at least about 60 cm (centimeters), desirably at least about 80 cm, and
more desirably at least about 100 cm. A suitable technique for determining the hydrohead
value is the Hydrostatic Pressure Test which is described in further detail herein below.
As used herein, a substantially vapor permeable material is constructed to provide a water
vapor transmission rate (WVTR3 of at least about 100 glsq.m/24 hr, desirably at least
about 250 g/sq.m/24 hr, and more desirably at least about 500 g/sq.ml24 hr. A suitable
technique for determining the WVTR value is the WVTR Test which is described in further
detail herein below.
In one aspect, the present invention relates to an absorbent article which defines a
garment facing surface, a body facing surface, a front waistband section, a rear waistband
section and an intermediate section which interconnects the front and rear waistband d
sections. The absorbent article comprises a first zone of vapor permeability which is
located on the garment facing surface and which defines a water vapor transmission rate
of from about 100 to about 2500 glsq.ml24 hr. The absorbent article further co",prises a
second zone of vapor permeability which is located on the garment facing surface and
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which defines a water vapor transmission rate of at least about 3000 glsq.ml24 hr. The
first zone of vapor permeability may define an area which is at teast about 75 percent of
the garment facing surface of the absorbent article. The first zone of vapor permeability
may further define a width which is less than a width of the absorbent article and the
second zone of vapor permeability may extend beyond the first zone of vapor permeability
thereby providing a breathability gradient across the width of the absorbent article.
In another aspect, the present invention relates to an absorbent article which conl~lises a
vapor permeable backsheet which includes a first zone of vapor permeability which
lO defines a water vapor transmission rate of at least about 100 glsq.ml24 hr and a second
zone of vapor permeability which defines a water vapor transmission rate of at least about
3000 glsq.ml24 hr. The absorbent article further comprises a liquid permeable topsheet
which is positioned in facing relation with the backsheet and an absorbent body located
between the backsheet and the topsheet. In a particular aspect, the first zone of vapor
permeability covers at least about 75 percent of a garment side of the absorbent body.
In still another aspect, the present invention relates to an absorbent article which
comprises a substantially liquid impermeable, vapor permeable backsheet which defines a
water vapor transmission rate of at least about 1500 glsq.ml24 hr, a liquid permeable
topsheet which is positioned in facing relation with the backsheet, and an absorbent body
which is located between the backsheet and the topsheet. The absorbent article further
comprises a vapor permeable barrier layer which is smaller in size than the backsheet and
which is located between the absorbent body and the backsheet. The combination of the
vapor permeable barrier layer and the vapor permeable backsheet defines a water vapor
transmission rate of from about 100 to about 2500 glsq.ml24 hr. In a particular aspect,
the substantially liquid impermeable, vapor permeable backsheet is constructed to provide
a hydrohead of at least 60 cm. The vapor permeable barrier layer may define a water
vapor transmission rate of from about 100 to about 5000 glsq.ml24 hr.
The present invention advantageously provides an improved absorbent article which
substantially reduces the hydration of the wearer's skin when compared to conventional
absorbent articles. Thus, wearer's of absorbent articles made according to the present
invention should have a reduced incidence of skin irritation or rash.
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BrieF DescriDtion of the Drawinqs
The invention will be more fuily understood and further advantages will become apparent
when reference is made to the following detailed description of the invention and the
accompanying drawings, in which:
5 =
Fig. 1 representatively shows a partially cutaway, top plan view of an absorbent articie
according to one embodiment of the invention; and
Fig. 2 representatively shows a partially cutaway, top plan view of an absorbent article
10 according to a second embodiment of the invention.
C)etailed Description of the Invention
The following detailed description will be made in the context of a disposable diaper article
which is adapted to be worn by infants about the lower torso. It is readily apparent,
however, that the absorbent article of the present invention would also be suitable for use
8s other types of absorbent articles, such as feminine care pads, incontinence garments,
training pants, and the like.
With reference to Figs. 1 and 2, an integral absorbent garment article, such as the
disposable diaper 10, generally defines a front waistband section 12, a rear waistband
section 14, and an intermediate section 16 which interconnects the front and rear
waistband sections. The front and rear waistband sections include the general portions of
the article which are constructed to extend substantially over the wearer's front and rear
abdominal regions, respectively, during use. The intermediate section of the article
includes the generat portion of the article which is constructed to extend through the
wearer's crotch region between the legs. The absorbent article also includes a garment
facing surface 18 and a body facing surface 19.
The absorbent article includes a substantially liquid impermeable, vapor permeable
backsheet 20, a liquid permeable topsheet 22 positioned in facing relation with the
backsheet 20, and an absorbent body 24, such as an absorbent pad, which is located
between the backsheet and the topsheet. The absorbent body 24 overlays at least a
portion of the backsheet 20. The backsheet 20 has a length 26 and a width 28 which, in
the illustrated embodiment. coincides with the length and width of the diaper 10 . The
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absorbent body 24 generally has a length 30 and width 32 which are less than the length
26 and width 28 of the backsheet 20, respectively. Marginal portions of the diaper 10,
such as marginai sections of the backsheet 20, may extend past the terminal edges of the
absorbent body 24. In the illustrated embodiments, for example, the backsheet 20extends outwardly beyond the terminal marginal edges of the absorbent body 24 to form
side margins 34 and 36 and end margins 38 and 40 of the diaper 10. The topsheet 22 is
generally coextensive with the backsheet 20 but may optionally cover an area which is
larger or smaller than the area of the backsheet 20, as desired.
lO The absorbent article further includes a zone of low vapor permeability 60 and a zone of
high vapor permeability 62. In the illustrated embodiments, for example, the absorbent
article may include a zone of low vapor permeability 60 which extends along a longitudinal
centerline 58 of the article and has a length 64 and width 66 which are less than the
length 26 and width 28 of the backsheet 20. In such a configuration, the zone of high
vapor permeability 62 generally extends beyond the edges of the zone of low vapor
permeability 60 to the outermost edges of the backsheet 20 of the absorbent article
providing a breathability gradient across the length 26 and width 28 of the diaper. The
zones of vapor permeability are configured to enhance the breathability of the absorbent
article to reduce the hydration of the wearer's skin during use without allowing excessive
condensation of vapor, such as urine, on the garment facing surface of the backsheet 20
which can undesirably dampen the wearer's clothes.
To provide improved fit and to help reduce leakage of body exudates from the diaper 10,
the diaper side margins and end margins may be elasticized with suitable elasticmembers, such as single or multiple strands of elastic. The elastic strands may be
composed of natural or synthetic rubber and may optionally be heat shrinkable or heat
elasLi~ able. Elastic members 42 and 44 are constructed to operably gather and shirr the
side margins 34 and 36 of the diaper 10 to provide elasticized leg bands which can closely
fit around the legs of the wearer to reduce leakage and provide improved comfort and
appearance. Similarly, waist elastic members 46 and 48 can be employed to elasticize
the end margins 38 and 40 of the diaper 10 to provide elasticized waistbands. The waist
elastics are configured to operably gather and shirr the waistband sections to provide a
resilient, comfortably close fit around the waist of the wearer. In Figures 1 and 2, the
elastic members are illustrated in their uncontracted, stretched condition for the purpose
of clarity.
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Fastening means, such as adhesive tapes 50, are employed to secure the diaper on a
wearer. Alternatively, other fastening means, such as buttons, pins, snaps, hook-
and-loop fasteners, mushroom-and-loop fasteners, or the like, may be employed.
The illustrated embodiment of the diaper 10 includes ear portions 52 which extend
laterally along the diaper cross-direction 54 and are positioned at least at the rear
waistband section 14 of the diaper 10. Ear portions 52 may also be located at the front
waistband section 12 of the diaper. The ear portions may be integral with the backsheet
l0 20 or may comprise separate sections which are composed of the same or different
material than the backsheet 20 and are suitably assembled and attached to the backsheet
20. The ear portions 52 typicaily provide extensions of the diaper waistband suitable for
completely encircling the waist of the wearer during use.
The diaper 10 may be of various suitable shapes. For example, the diaper may have an
overall rectangular shape, T-shape or an approximately hour-glass shape. In the shown
embodiment, the diaper 10 has a generally l-shape. Other suitable diaper components
which may be incorporated on absorbent articles of the present invention includecontainment flaps, waist flaps, elastomeric side panels, and the like.
Examples of diaper configurations suitable for use in connection with the instant
application and other diaper components suitable for use on diapers are described in U.S.
Patent 4.798,603 issued January 17, 1989, to Meyer et al.; U.S. 5,176,668 issuedJanuary 5, 1993, to Bernardin; U.S. 5,176,672 issued January 5, 1993, to Bruemmer
et al.; U.S. 5,192,606 issued March 9, 1993, to Proxmire et al., and U.S. Patent
Application Serial No. 08/096,654 filed July 22, 1993, in the name of Hanson et al., the
disclosures of which are herein incorporated by reference to the extent they are consistent
herewith.
The various components of the diaper 10 are integrally assembled together employing
various types of suitable attachment means, such as adhesive, sonic bonds, thermal
bonds or combinations thereof. In the shown embodiment, for example, the topsheet 22
_ and backsheet 20 are assembled to each other and to the absorbent body 24 with lines of
adhesive, such as a hot melt, pressure-sensitive adhesive. Similarly, other diaper
components, such as the elastic members 42, 44, 46 and 48, and the fastening members
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.
50, may be assembled into the diaper article by employing the above-identified
attachment mechanisms.
The topsheet 22, as representatively illustrated in Figs. 1 and 2, suitably presents a
bodyfacing surface which is compliant, soft feeling, and nonirritating to the wearer's skin.
Further, the topsheet 22 may be less hydrophilic than the absorbent body 24, to present a
relatively dry surface to the wearer, and may be suffficiently porous to be liquid permeabte,
permitting tiquid to readity penetrate through its thickness. A suitable topsheet 22 may be
manufactured from a wide setection of web materiats, such as porous foams, reticutated
lO foams, apertured plastic films, natural fibers (for example, wood or cotton fibers),
synthetic fibers (for exampte, polyester or polypropylene fibers), or a combination of
natural and synthetic fibers. The topsheet 22 is suitably employed to help isolate the
wearer's skin from liquids held in the absorbent body 24.
Various woven and nonwoven fabrics can be used for the topsheet 22. For example, the
topsheet may be composed of a meltblown or spunbonded web of polyolefin fibers. The
topsheet may also be a bonded-carded web composed of naturat andtor synthetic fibers.
The topsheet may be composed of a substantially hydrophobic materiat, and the
hydrophobic materiat may, optionally, be treated with a surfactant or otherwise processed
to impart a desired tevet of wettabitity and hydrophiticity. tn a particutar embodiment of the
present invention, the topsheet 22 comprises a nonwoven, spunbond, potypropylenefabric composed of about 2.8-3.2 denier fibers formed into a web having a basis weight of
about 22 grams per square meter and a density of about 0.06 gram per cubic centimeter.
The fabric is surface treated with about 0.28 weight percent of a surfactant commerciatty
availabte from Rohm and Haas Co. under the trade designation
Triton X-102.
The absorbent body 24 of the diaper 10, as representatively illustrated in Figs. 1 and 2,
may suitably comprise a matrix of hydrophitic fibers, such as a web of cettulosic fluff,
mixed with particles of a high-absorbency material commonly known as superabsorbent
material. In a particular embodiment, the absorbent body 24 comprises a matrix of
cellulosic ftuff, such as wood pulp fluff, and superabsorbent hydrogel-forming particles.
_ The wood pulp fluff may be exchanged with synthetic, polymeric, meltblown fibers or with
a combination of meltblown fibers and natural fibers. The superabsorbent particles may
be substantially homogeneously mixed with the hydrophilic fibers or may be nonuniformiy
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mixed. Alternativeiy, the absorbent body 24 may comprise a laminate of fibrous webs and
superabsorbent material or other suitable means of maintaining a superabsorbent
material in a localized area.
The absorbent body 24 may have any of a number of shapes. For example, the
absorbent core may be rectangular, I-shaped, or T-shaped. It is generally preferred that
the absorbent body 24 be narrower in the intermediate section than in the front or rear
waistband sections of the diaper 10.
10 The high-absorbency material can be selected from natural, synthetic, and modified
natural polymers and materials. The high-absorbency materials can be inorganic
materiais, such as silica gels, or organic compounds, such as crosslinked poiymers. The
term "crosslinked" refers to any means for effectively rendering normally water-soluble
materials substantially water insoluble but swellable. Such means can include, for
example, physical entanglement, crystalline domains, covalent bonds, ionic complexes
and associations, hydrophilic associations such as hydrogen bonding, and hydrophobic
associations or Van der Waals forces.
Examples of synthetic, polymeric, high-absorbency materials include the alkali metal and
ammonium salts of poly(acrylic acid) and poly(methacrylic acid), poly(acrylamides),
poly(vinyl ethers), maleic anhydride copolymers with vinyl ethers and alpha-olefins,
poly(vinyl pyrolidone), poly(vinyl morpholinone), poly(vinyl alcohol), and mixtures and
copolymers thereof. Further polymers suitable for use in the absorbent core include
natural and modified natural polymers, such as hydrolyzed acrylonitrile-grafted starch,
acrylic acid grafted starch, methyl cellulose, carboxymethyl cellulose, hydroxypropyl
cellulose, and the natural gums, such as alginates, xanthum gum, locust bean gum, and
the like. Mixtures of natural and wholly or partially synthetic absorbent polymers can also
be useful in the present invention.
The high absorbency material may be in any of a wide variety of geometric forms. As a
general rule, it is preferred that the high absorbency material be in the form of discrete
particles. However, the high absorbency material may also be in the form of fibers, flakes,
rods, spheres, needles, or the like. As a general rule, the high absorbency material is
present in the absorbent body in an amount of from about 5 to about 90 weight percent
based on total weight of the absorbent body 24.
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Optionally, a substantially hydrophilic tissue wrapsheet (not illustrated) may be employed
to help maintain the integrity of the airlaid fibrous structure of the absorbent body 24. The
tissue wrap sheet is typically placed about the absorbent body over at least the two maior
facing surfaces thereof and composed of an absorbent cellulosic material, such as creped
wadding or a high wet-strength tissue. In one aspect of the invention, the tissue wrap can
be configured to provide a wicking layer which helps to rapidly distribute liquid over the
mass of absorbent fibers comprising the absorbent body.
10 The backsheet 20 of the diaper 10, as representatively illustrated in Figs. 1 and 2, is
composed of a substantially liquid impermeable material which is also substantially vapor
permeable. In particular, the backsheet 20 is constructed to provide a hydrohead value of
at least about 60 cm, desirably at least about 80 cm, and more desirably at least about
100 cm when subjected to the Hydrostatic Pressure Test. Materials which have
hydrohead values less than those above undesirably result in the strike through of liquids,
such as urine, during use. Such fluid strike through can undesirably result in a damp,
ciammy feeling on the backsheet 20 during use. The backsheet 20 is further constructed
to be substantially permeable to at least water vapor and has a water vapor l~dnsl"ission
rate of at least about 3000 glsq.ml24 hr. and desirably at least about 5000 glsq.m/24 hr.
Materials which have a water vapor transmission rate less than those above do not allow
a sufficient amount of humidity transfer and undesirably result in increased levels of skin
hydration.
The backsheet 20 may be composed any suitable materials which either directly provide
the above desired levels of liquid impermeability and vapor permeability or, in the
alternative, materials which can be modified or treated in some manner to provide such
levels. In one embodiment, the backsheet 20 may be a nonwoven fibrous web
constructed to provide the required level of iiquid impermeability. For example, a
nonwoven web composed of spunbonded or meltblown polymer fibers may be selectively
treated with a water repellent coating or laminated with a liquid impermeable polymer film
to provide the backsheet 20. In a particular embodiment of the invention, the backsheet
20 may comprise a nonwoven web composed of a plurality of randomly deposited
hydrophobic thermoplastic meltblown fibers which are sufficiently bonded or otherwise
connected to one another to provide a substantially vapor permeable and substantially
liquid impermeable web. The backsheet 20 may also comprise a vapor permeable
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nonwoven layer which has been partially coated or otherwise configured to provide liquid
impermeability in selected areas.
An example of a suitable material for the backsheet 20 is described in COI l ll l ~only owned,
5 copending U.S. Patent Application Serial No. 08/223,210 filed April 5, 1994, in the name
of Bradley et al. Other suitable materials for the backsheet 20 inctude those described in
U.S. Patent 4,713,068 issued December 15, 1987, to Wang et al.; U.S. 4,758,239 issued
July 19, 1988, to Yeo et al.; U.S. 4,818,600 issued April 4, 1989, to Braun et al.; and
U.S. 4,828,556 issued May 9, 1989, to Braun et al., the disclosures of which are herein
l0 incorporated by reference to the extent they are consistent herewith.
The zones of low vapor permeability 60 and high vapor permeability 62 of the absorbent
article, as representatively illustrated in Fig. 1, are configured to enhance the breathability
of the article to reduce the hydration of the wearer's skin during use without allowing
15 excessive condensation of vapor, such as urine, on the garment facing surface of the
backsheet 20 which can dampen the wearer's clothes. The zone of high vapor
permeability 62 is designed to provide the maximum humidity transfer from the absorbent
article while the zone of low vapor permeability 60 is designed to reduce the risk of
excessive condensation of vapor on the garment facing surface of the backsheet while
still providing at least some level of humidity transfer. Accordingly, the zone of low vapor
permeability 60 is generally positioned in the area of the absorbent article which is
intended to receive and hold the majority of the body exudates while the zone of high
vapor permeability 62 is generally positioned in the side and end margins of the absorbent
article.
~
The zone of high vapor permeability 62 is generally that area of the diaper in which water
vapor can transfer from the inside of the diaper, when in position on a wearer, to the
outside of the diaper with relative ease. That is, it is the area over which humidity can
l, dnsr~r from the topsheet 22, through any intervening layer of material, and out the vapor
permeable backsheet 20. For example, the zone of high vapor permeability 62 may
include the entire area in which the topsheet 22 is in direct face-to-face overlapping
relationship with the vapor permeable backsheet 20. The zone of low vapor permeabillty
effectively prevents the transfer of liquids and excessive vapor from the interior of the
diaper, when in use, through the vapor permeable backsheet in those areas of the diaper
where at least a portion of the absorbent body 24 overlays the backsheet, such as in the
-- 10
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intermediate section 16 of the diaper 10. The zone of low vapor permeability 60 may also
prevent the transfer of a high level of humidity from the interior of the diaper. In many
instances this is desirable since a high degree of transfer of humidity across the entire
surface of the diaper has been found to produce a clammy feeling on the outer surface of
the diaper which many co~sumers perceive in a negative manner. Thus, the humidity
transfer from the interior of the diaper to the ambient atmosphere (exterior of the diaper)
occurs generally in the zone of relatively high vapor permeability 62 but can also occur in
the zone of relatively low vapor permeability 60 to a limited degree.
10 The zones of low and high vapor permeability are located on the absorbent article to
provide the desired humidity transfer. The zones of low and high vapor permeability may
have any desired configuration including rectangular, hourglass, oval, and the like, and
may also include selected strips or multiple zones which may be intermittently located.
For example, in the illustrated embodiments, the absorbent article includes a zone of low
vapor permeability 60 having a generally rectangular configuration. As representatively
illustrated, the zone of low vapor permeability extends along a longitudinal centerline 58 of
the article and has a length 64 and width 66 which are less than the length 26 and width
28 of the backsheet 20. In such a configuration, the zone of high vapor permeability 62
generally extends beyond the edges of the zone of low vapor permeability 60 to the
outermost edges of the backsheet 20 of the absorbent article thereby providing abreathability gradient across the length 26 and width 28 of the diaper. The zones of low
and high vapor permeability 60 and 62 may cover the entire backsheet 20 or only a
portion thereof. In the illustrated embodiments, the zones of low and high vaporpermeability cover the entire exposed or body facing surface of the backsheet 20.
The zones of low and high vapor permeability may have any desired dimensions which
effectively provides improved humidity l,dn:jrer whiie preventing excessive condensation
of vapor from the absorbent body 24 through and onto the garment facing surface of the
backsheet 20. In the embodiment illustrated in Fig. 1, the length 64 of the zone of low
vapor permeability 60 is substantially the same as the length 30 of the absorbent body 24
to reduce the risk of excessive condensation on the backsheet 20 in this area. Whereas,
in the embodiment illustrated in Fig. 2, the length 64 of the zone of low vapor permeability
r, 60 is somewhat less than the length of the absorbent body 24. In such a configuration, it
is desirable that the zone of low vapor permeability 60 cover at least a substantial portion
of the absorbent body 24 in the front section 12 of the absorbent article for improved
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performance. In both of the illustrated embodiments, the width 66 of the zone of low
vapor permeabiiity 60 is somewhat less than the width of the absorbent body 24 in the
intermediate section 16 of the absorbent article. However, the zone of low vaporpermeability 60 may extend completely across the absorbent body 24 or the absorbent
article in the intermediate section 16 if desired. In a particular embodiment. it is desirable
that the zone of low vapor permeability 60 have a length 64 which is at least about 75
percent of the length 30 of the absorbent body 24 and a width 66 which is at least about
100 percent of the width of the absorbent body 24 as measured at the narrowest portion
of the intermediate section 16 of the article.
The zone of relatively low vapor permeability 60 generally has an area which corresponds
to at least a portion of the area of the garment side of the absorbent body 24 to effectively
prevent excessive conder~sation of vapor on the garment facing surface of the backsheet
20. For example, on a medium-sized diaper adapted to fit an infant weighing from 22-35
pounds, the zone of relatively low vapor permeability 6Q generally has an area of at least
about 200 square centimeters and desirably at least about 300 square centimeters.
Desirably, the zone of low vapor permeability 60 has an area of at least about 75 percent,
desirably at least about 90 percent, and more desirably at least about 100 percent of the
garment side of the absorbent body 24 of the diaper 10. Moreover, the zone of low vapor
permeability 60 desirably has an area of at least about 30 percent and more desirably at
1east about 50 percent of the total exposed area of the backsheet 20 of the diaper 10. For
example, the zone of relatively low vapor permeability 60 may have an area of from about
30 to about 85 percent of the total exposed area of the backsheet 20 of the diaper 10.
When the area of the zone of low vapor permeability 60 is too small, the diaper 10 may
exhibit an undesirable amount of condensation of vapor on the exposed, garment facing
surface of the backsheet 20 resulting in a clammy feeling on the outer surface of the
diaper which many consumers perceive in a negative manner. Whereas, when the area
of the zone of low vapor permeability 60 is too large, the diaper 10 may exhlbit a low level
of humidity transfer resulting in high levels of skin hydration, skin irritation and rash.
The zone of relatively high vapor permeability 62 generally has an area which
corresponds to at least the side margins 34 and 36 and end margins 38 and 40 of the
diaper 10 to effectively allow the humidity transfer from the interior of the diaper to the
ambient atmosphere. For example, on a medium-sized diaper adapted to fit an infant
weighing from 22-35 pounds, the zone of high vapor permeability 62 generally has an
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area of at least about 100 square centimeters, desirably at least about 200 square
centimeters, and more desirably from about 200 to about 800 square centimeters for
improved performance. Desirably, the zone of high vapor permeability 62 has an area of
at least about 15 percent and more desirably at least about 30 percent of the total
exposed area of the backsheet 20 of the diaper 10. For example, the zone of relatively
high vapor permeability 62 may have an area of from about 15 to about 70 percent of the
total exposed area of the backsheet 20 of the diaper 10. When the area of the zone of
high vapor permeability 62 is too small, the diaper 10 may exhibit a low level of humidity
transfer resulting in skin irritation and rash. Whereas, when the area of the zone of high
10 vapor permeability 62 is too high, the diaper 10 may exhibit an undesirable amount of
vapor condensation.
The zone of low vapor permeability 60 of the diaper 10, as representatively illustrated in
Figs. 1 and 2, is constructed to provide a hydrohead value of at least about 60 cm,
desirably at least about 80 cm, and more desirably at least about 100 cm when subjected
to the Hydrostatic Pressure Test. Hydrohead values less than those above undesirably
result in the strike through of liquids, such as urine, during use. The zone of low vapor
permeability 60 is further constructed to be substantially permeable to at least water vapor
and has a water vapor transmission rate of at least about 100 glsq.m/24 hr., suitably from
about 100 to about 2500 glsq.m/24 hr, and desirably from about 1500 to about
2000 glsq.ml24 hr. Applicants have discovered that when the zone of low vapor
permeability has water vapor transmission rates greater than those above, excessive
condensation of vapor appears on the garment facing sur~ace of the backsheet which
undesirably results in a damp feeling.
The zone of high vapor permeability 62 of the diaper 10, as representatively illustrated in
Figs. 1 and 2, is constructed to provide a hydrohead value of at least about 60 cm,
desirably at least about 80 cm, and more desirably at least about 100 cm when subjected
to the Hydrostatic Pressure Test. Hydrohead values less than those above undesirably
result in the strike through of liquids, such as urine, during use. The zone of high vapor
permeability 62 is further constructed to be substantially permeable to at least water vapor
and has a water vapor ~l~nsnlission rate of at least about 3000 glsq.ml24 hr., suitably at
least about 4000 glsq.ml24 hr, and desirably at least about 5000 glsq.ml24 hr. Water
vapor transmission rates less than those above for the zone of high vapor permeability do
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not allow a suf~icient amount of humidity transfer and undesirably resu!t in increased
levels of skin hydration.
The ratio of the water vapor transmission rates of the zone of high vapor permeability to
the zone of low vapor permeability can be seiectively controlled to provide the desired
humidity transfer while still preventing excessive vapor condensation. Applicants have
discovered that absorbent articles according to the present invention having a ratio of the
water vapor transmission rates of the zone of high vapor permeability 62 to the zone of
low vapor permeability 60 of at least about 1.1 and desirably from about 2.0 to about 2.5
10 have provided a breathability gradient across the article which has resulted in reduced
levels of skin hydration during use.
The zones of low and high vapor permeability of the absorbent article of the present
invention may be provided in a variety of ways. For example, the zones of low and high
vapor permeability may be an integral portion of the backsheet 20 of the absorbent article
or may be a separate component which may or may not be laminated to the backsheet
20. For example, a portion of a backsheet 20 having a high level of vapor permeability
may be treated or coated with an adhesive or latex spray to provide the zone of low vapor
permeability 60 in selected areas. Alternatively, a nonwoven material or polymeric film
may be laminated to a portion of such a backsheet 20 to provide a two layer composite
which provides the zones of low and high vapor permeabiiity 60 and 62. For exampie, a
nonwoven material such as those described above for use as the backsheet 20 or apolymeric film may be laminated to selected portions of the backsheet 20 to provide the
zones of low and high vapor permeability 60 and 62. Such film materials are well known
to those skilled in the art. The polymeric film may inherently possess the desired level of
vapor permeability or may include perforations to provide the desired level of vapor
permeability while preventing liquid strikethrough. The nonwoven material or polymeric
film may be positioned between the absorbent body 24 and backsheet 20 while not being
directly adhered to the backsheet 20 in any manner. Alternatively, the nonwoven material
or polymeric film material may be adhered to the garment side of the absorbent body.
In the embodiments illustrated in Figs. 1 and 2, the zones of low and high vapor_ permeability are provided by applying an adhesive in the desired pattern on the backsheet
20. Suitable adhesives include pressure sensitive hot melt adhesives which are known to
those skilled in the art. A particularly suitable adhesive is an adhesive which is
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commercially available from the National Starch Company under the trade designation 34-
5563. The adhesive is applied to the backsheet 20 by slot-coating. The amount ofadhesive add-on may vary depending upon the type of adhesive and the desired level of
liquid impermeability and vapor permeability of the low zone of vapor permeability 60.
Adhesive add-on levels of from about 10 to about 30 gsm (grams per square
meter) and desirably from about 15 to about 25 gsm have been found to provide the
desired levels of vapor permeability and liquid impermeability for the zone of low vapor
permeability 60.
lO The absorbent article of the present invention may optionally include a humidity transfer
material (not shown) located between the topsheet 22 and the absorbent body 24 or
between the backsheet 20 and the absorbent body 24. The humidity transfer material
serves to facilitate the movement of air within the diaper. Specifically, it is hypothesized
that the humidity transfer material serves as a conduit through which water vapor can
move from the intermediate section of the interior of the diaper (when in use) to the side
margins 34 and 36 and end margins 38 and 40 wherein the water vapor can be
transferred out of the interior of the diaper through the zone of high vapor permeability
and the vapor permeable backsheet 20. The humidity transfer material may suitably be
formed from a nonwoven, (e.g., spunbond, meltblown or carded), woven, or knitted fibrous
webs composed of natural fibers and/or synthetic poiymeric fibers. Suitabie fibers
include, for example, acrylic fibers, polyolefln fibers, polyester fibers, or blends thereof.
The humidity transfer material may also be formed from a porous foam material such as
an open-celled polyolefin foam, a reticulated polyurethane foam, and the like. In a further
aspect of the invention, the humidity transfer material includes a plurality of two or more
individual layers positioned in facing adjacent relationship. For example, 2-5 individual
iayers may be located between the topsheet and the absorbent body and together
collectively comprise the humidity transfer material. Examples of materials particularly
well suited for use as a humidity transfer material are described in U.S. Patent Application
Serial No. 08/344,429 filed November 23, 1994, in the name of Menard et al., thedisclosure of which is hereby incorporated by reference to the extent it is consistent
herewith.
r The humidity transfer material may extend completely or partially over the zone of iow
vapor permeability 60. It is generally desired that the entire zone of low vaporpermeability 60 be overlaid with the humidity transfer material. This allows for the
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maximum degree of humidity transfer. Further, the humidity transfer material may extend
completely or partially over the adiacent surface of the absorbent body 24. The humidity
transfer material is suitably located over the intermediate section 16 of the diaper and is
substantially centered side-to-side with respect to the longitudinal centerline 58 of the
diaper. The humidity transfer material suitably extends over about 35 to about 100
percent of the total length 26 of the backsheet 20. The humidity transfer material may
extend over about 50 to about 100 percent of the width of the diaper as measured at the
narrowest portion of the diaper intermediate section 16. It is generally preferred that the
humidity transfer material extend at least partially into the zone of high vapor permeability
62~
TEST PROCEDURi-S
Hvdrostatic Pressure Test
The Hydrostatic Pressure Test is a measure of the liquid barrier properties of a material.
In general, the Hydrostatic Pressure Test determines the height of water (in centimeters)
in a column which the material will support before a predetemmined amount of water
passes through. A material with a higher hydrohead value indicates it is a greater barrier
to liquid penetration than a material having a lower hydrohead value. The Hydrostatic
Pressure Test is performed according to Method ~514 - Federal Test Methods Standard
No. 191A.
Water Vacor Transmission Rate
A suitable technique for determining the WVTR (water vapor transmission rate) value of a
material is as follows. For the purposes of the present invention, 3-inch diameter (76
millimeter) circular samples are cut from the test material and from a control material,
CelguardD 2500 (Hoechst Celanese Corporation). Two or three samples are prepared for
each material. Test cups used for testing are cast aluminum, flanged, 2 inches deep and
come with a mechanical seal and necprene gasket. The cups are distributed by
Thwing-Albert Instrument Company, Pi iladelphia, Pennsylvania, under the designation
Vapometer cup ;Y681. One hundred milliiiters of distilled water are poured into each
Vapometer cup, and each of the individual samples of the test materiais and control
material are placed across the open top area of an individual cup. Screw-on flanges are
tightened to form a seal aiong the edges of the cups leaving the associated test material
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or control materiai exposed to the ambient atmosphere over a 62 millimeter diameter
circular area (an open, exposed area of about 30 cm2). The cups are then weighed,
placed on a tray, and set in a forced air oven set at 100~F (38~C). The oven is a constant
temperature oven with external air circulating through it to prevent water vaporaccumulation inside. A suitable forced air oven is, for example, a Blue M Power-O-Matic
60 oven distributed by Blue M Electric Co of Blue Island, lllinois. After 24 hours, the cups
are removed from the oven and weighed. The preliminary, test WVTR value is calculated
as follows:
Test WVTF~ = r(qrams wei~ht loss over 24 hours) x 75711 (g/m2/24hours)
24
The relative humidity within the oven is not specifically controlled. Under predetermined
set conditions of 100~F and ambient relative humidity, the WVTR for Celguard 2500 has
been determined to be 5000 glm2124 hours. Accordingly, Celguard 2500 is run as acontrol sample with each test. Celguard 2500 is a 0.0025 cm thick film composed of a
microporous polypropylene.
The following example is presented to provide a more detailed understanding of the
invention. The specific materials and parameters are exemplary and are not intended to
specifically limit the scope of the invention.
ExamDle 1
Material which could be used as the backsheet on absorbent articles such as diapers was
produced. The liquid impermeable and vapor permeable backsheet comprised a
spunbondfmeltblown/spunbond (SMS) laminate material having a basis weight of about
50 grams per square meter (gsm). The SMS was formed from a meltblown polypropylene
layer which has a basis weight of about 17 gsm and which was positioned between two
spunbond polyethylene/polypropylene layers, each of which had a basis weight of about
17 gsm. The meltblown and spunbond layers were manufactured by Kimberly-Clark. The
meltblown layer was composed of up to 5 weight percent polybutylene which was
commercially available from Shell under the trade designation DP 8911 and the remainder
polypropylene which was commercially available from Exxon under the trade designation
3546G. The spunbond layers were composed of up to 4 weight percent of a 50
percent concentration of titanium dioxide pigment which was commercially available from
Ampacet under the trade designation Ampacet 41438. The remainder of the spunbondlayers was composed of a 3 weight percent polyethylene/ 97 weight percent
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polypropylene copolymer which is commercially available from Shell under the trade
designation 6D43. The meltblown layer provided from about 25 to about 35 weight
percent of the SMS laminate material. The SMS material had a WVTR of about 5000
glm2124 hours and was constructed to provide a hydrohead value of about 80 cm.
The material was configured to define a zone of low vapor permeability and a zone of high
vapor permeability. The zone of low vapor permeability was formed by slot-coating an
adhesive in a substantially uniform pattern on a surface of the material. The adhesive
was commercially available from the National Starch Company under the trade
10 designation 34-5563 and was applied at different levels of adhesive add-on from about 0
to about 25 gsm. The combination of the SMS material and the adhesive coating which
provided the zone of low vapor permeability had a WVTR of about 4500 glm2124 hours at
an adhesive add-on of about 5 gsm, a WVTR of about 3100 glm2124 hours at an adhesive
add-on of about 10 gsm, a WVTR of about 2200 glm2/24 hours at an adhesive add-on of
about 15 gsm, and a WVTR of about 1100 glm2124 hours at an adhesive add-on of
about 20 gsm.
Having thus described the invention in rather full detail, it will be readily apparent to a
person of ordinary skill that various changes and modifications can be made without
departing from the spirit of the invention. All of such changes and modifications are
contemplated as being within the scope of the present invention as defined by the
subjoined claims.
