Note: Descriptions are shown in the official language in which they were submitted.
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Breathable disposable absorbent article for topical adhesive attachment to the
skin of a wearer
Field of the invention
IS
The present invention relates to breathable absorbent articles particularly
sanitary napkins, pantiliners, adult incontinence products or sweat pads. In
particular the present invention relates to such breathable absorbent articles
which are wom by direct attachment to the skin of the wearer in the area were
absorption of bodily liquids is desired.
Background of the invention
The prior art in the field of disposable absorbent articles for topical
application to
the skin of a wearer is particularly developed in the field of band-aids,
plasters
and bandages. These articles are often breathable, but typically applied in an
emergency situation where for example a cut into the skin of the wearer has
occurred and absorption of the body liquids emanating from a wound is desired.
tn this context performance aspects of the absorbent article such as
comfortable
and easy use and application, painless removal, discreteness are subordinate
to
criteria such as sterility, healing support, mechanical protection of the
wound.
Also such wound covering absorbent articles are mostly used in skin areas
where prior to application of the absorbent article body hair can be removed
or
where little or no hair grows.
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The present invention does not relate to wound covering absorbent articles but
relates to breathable absorbent articles for absorption of body liquids which
naturally emanate from a body without a wound. For example breathable
sanitary napkins or pantiliners for use in the genital region are such
articles. Also
breathable incontinence devices which are worn e.g. in the genital region or
breathable sweat pads which are worn in the arm pit region of a person are the
subject of the present invention.
If such articles are applied to the skin of a wearer in a region were
typically a
considerable amount of hair grows then the criteria of easy and painless
removal
of the article is of key importance. Such articles have generally been
disclosed in
US statutory invention registration H1602 or WO 96/33683. Some more details of
such articles have been considered for example in PCT application WO
95/16424. In this document sanitary articles having a body adhesive which is
applied on the wearer facing side of a sanitary napkin along the entire
periphery
are disclosed. The problem underlying this document is primarily the safe
attachment to the skin but mentions also the problems of detachment of such
articles after use without causing undue pain to a wearer.
The disclosure of WO 95116424 includes a detailed analysis of the criteria for
the
body adhesive in respect to rheological criteria. However, this document has
little
regard to the problem of painless removal of such articles since the
rheological
criteria taught include epilatory, i.e. hair removal, compositions which are
commercially available such as STREP MIELE (TM) sold in Italy by Laboratori
Vaj S.p.A. The adhesives for topical attachment mentioned in WO 95116424
include also today's pressure sensitive adhesives which are used to attach
sanitary napkins to undergarments. Further, this document only identifies
static
rheological characteristics but is silent as to the dynamic rheological
behaviour of
a body adhesive.
In WO 96/13238 a frequency dependent body adhesive modes is disclosed.
However, all measurements disclosed, e.g. on page 9, were made at
temperatures between -60°C and +120°C and at actual frequencies
of 0.1 to 100
rad/s. In order to obtain the necessary data at application temperature (about
20°C, typical bath room, i.e. storage temperature) the Williams-Landel-
Ferry
(hereinafter WLF) equation was used.
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This WLF equation is empirical and only valid within certain limits e.g. it
cannot
be used to extrapolate to temperatures below the glass transition temperature
of
a polymeric adhesive also the WLF cannot be used on the basis of values
obtained below the glass transition temperature. Details about the WLF
equation
and its applicability can be found in "Principles of Polymer processing" by Z.
Tadmor and C.G. Gogos, published by John Wiley 8~ Sons or in "Viscoelastic
Properties of Polymers" by J.D. Ferry also published by John Wiley & Son.
Since
this is already missing from WO 96/13238 the applicability of the disclosed
data
cannot be assessed. Further this disclosure does not relate to self adhesive
articles which are breathable.
European Patent Application EP-638 303 discloses the use of a body adhesive
on side cuffs of sanitary napkins in order to keep the cuffs in an upright
position.
Swiss publication CH-643730 discloses the use of a very long sanitary napkin
having chamfered outer edges with a body adhesive at the four corners of the
outer edges in order to provide a body adhesive area well outside the region
of
public hair growth.
Further improvements in the definition and formulation of body adhesive now
allow an improved direct attachment of absorbent articles to the skin.
However,
such close wearing conditions also cause a problem since the absorbent
articles
have an impermeable plastic film on their outer surface. This causes sweating
and a temperature raise inside the article, usually described as stuffiness,
which
is unacceptable at least to sensitive users of such articles. This problem is
substantially more pertinent for articles attached to the skin of a wearer
than for
articles attached to a garment because these articles allow breathability
through
their wearer facing surface.
Based on the above state of the art it is an objective of the present
invention to
provide disposable absorbent articles for absorption of natural emanating
liquids
from the body of a wearer which are attached to the skin of a wearer, allow
painless removal of the absorbent article and do not suffer from stuffiness.
It is
another objective of the present invention to ensure upon removal of the
absorbent article that no residual adhesive remains .on the skin or on the
hair of
the wearer. It is yet another objective of the present invention to provide
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disposable absorbent articles which are worn in such close proximity to the
liquid
emanating area of the wearer that liquid losses to the outside of the
absorbent
article is minimised or eliminated, without stuffiness resulting from the
close
proximity. For disposable absorbent articles worn in the crotch region of a
wearer
this will translate into an improved security against soiling of the
surrounding skin
tissue and clothing.
In addition to the above objectives of the present invention it is also
desirable for
sanitary napkins, pantiliners and catamenial devices to reduce or even
eliminate
odour emanating from the product since its application to the skin of the
wearer
provides an odour seal which prevents odours of the absorbed liquid or forming
from the absorbed liquid to reach beyond the absorbent article.
Brief description of the invention
The present invention relates to breathable disposable absorbent articles for
topical adhesive attachment to a wearer of such articles. The breathable
article
typically has a wearer facing surface and an outside surface also called
garment
facing surface in the context of articles worn underneath clothing. The
garment
facing side of usual sanitary napkins and of sanitary napkins employing body
adhesive are usually impermeable to liquid, air and water vapour. In contrast
the
articles of the present invention provide breathability by at least being
water
vapour permeable since the highest effect on heat dissipation (and hence
preventing a sweaty, sticky feeling) is achieved from water vapour
permeability.
Preferably, however, the garment facing side of the article is also air
permeable,
however) without compromising the liquid impermeability which is essential for
the leakage.
In a particularly preferred embodiment according to the present invention the
backsheet comprises an apertured formed film wherein the apertures are funnel
shaped and have a base opening at the funnel entrance and a peak opening at
the funnel exist. This apertured formed film is oriented in the backsheet of
the
breathable absorbent article such that the peak openings are closer to the
absorbent core than the base opening.
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In another preferred embodiment according to the present invention the wearer
facing surface is provided by a breathable backsheet which has at least a
first
and a second layer. The layers are oriented such that the first layer is
closer to
the absorbent core than the second layer and preferably the first layer is an
air
5 permeable apertured formed flm as described above and the second layer is a
microporous film or meltblown non-woven substrate.
The breathable article comprises an absorbent core structure between the
wearer facing surface and the garment facing surface for absorbing liquids
naturally emanating from a wearer. The breathable disposable absorbent article
according to the present invention comprises on at least part of the wearer
facing
surface an adhesive for topical adhesive attachment of the article to the skin
of
the wearer. .
In a preferred embodiment the adhesive is particularly characterised by having
an elastic modules at a temperature of 37°C (100° Fahrenheit)
abbreviated G'37
and having a viscous modules at a temperature of 37°C (100°
Fahrenheit) of
G"37. The adhesive is selected to have a dynamic elastic behaviour such that
the difference _ G'37 of G'37 at a frequency of 100 rad/sec and G'37 at a
frequency of 1 rad/sec is not greater than 150 %, preferably 80 %) of G'37 at
1
rad/sec or preferably less than 10000 Pa. The adhesive further is selected to
have a dynamic viscous behaviour such that the difference _ G"37 of G"37 at a
frequency of 100 rad/sec and G"37 at a frequency of 1 rad/sec is not greater
than 10000 Pa, preferably not greater than 5000 Pa, most preferably not
greater
than 1000 Pa.
It is particularly preferred that the articles according to the present
invention have
a value of the ratio G'37 over G"37 in the whole frequency range from 1 to 100
rad/sec of greater or equal to 1, preferably greater or equal to 1.6 and most
preferably greater or equal to 3.3.
The value of the ratio G'37 over G"37 at least for the frequency range 1 to
100
rad/sec can change with increasing frequency, while not necessarily being
proportional to the frequency change. This ratio of G'37 over G"37 should not
change within the frequency range by a factor of more than 3, preferably more
than 2, and most preferably should stay constant.
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At 1 rad the preferred value of G'37 is below 20000 Pa, preferably below 15000
Pa and most preferably even less than 10000 Pa. On the other hand the value of
G" 37 at a frequency of 1 rad/sec should not exceed 15000 Pa, it should
preferably be less than 10000 Pa and most preferably even less than 5000 Pa.
The above rheological criteria can be satisfied by adhesive compositions where
the composition comprises from 51 % to 99.5 % of a plasticising compound or
composition which is liquid at 20°C) from 0.5 to 20 %, preferably 5 %
to 15 %) of
a polymeric compound or composition which is soluble or swellable in the
plasticising compound or composition and with a tackifying resin in an amount
in
the range from 0 % to 600 % by weight of the polymeric compound. The
plasticising compound or composition is preferably selected from the group
consisting of water, alcohols, preferably glycerol, glycols, polyglycols,
liquid
polybutenes, oil or combinations thereof while the polymeric compound or
I S composition is preferably selected from the group consisting of block-
copolymer-
thermoplastic-elastomers, styrene-block-copolymers and hydrogenated styrene-
block-copolymers.
Quite generally the preferred body adhesive is at least partially hydrophobic,
preferably 60 %) more preferably 80 %) by weight of the adhesive consist of
hydrophobic components and most preferably none of the materials in the
adhesive are hydrophilic, i.e. it is made totally from hydrophobic components.
In a particularly preferred embodiments according to the present invention the
adhesive covers less than 20 % or even more preferably less than 10 % of the
wearer facing surface of the absorbent article. The present invention is most
beneficially applied in the field of sanitary napkins or pantiliners.
Detailed description of the invention
This invention relates to breathable disposable absorbent articles which are
applied directly to the skin of a user. The article exhibits absorbency for
bodily
fluids, the protection of the user's garments from soiling) improved physical
comfort to the user, due to breathability and the application mode and is easy
to
produce and to package. The breathable disposable absorbent article is
described below by reference to a sanitary napkin or catamenial, however
_____M.~~_T ______.
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especially panty liners, adult incontinence articles or sweat pads are also
included under the term disposable absorbent articles. The term "sanitary
napkin", as used herein, refers to an article which is worn by females
adjacent to
the pudendal region and which is intended to absorb and contain the various
body fluids which are discharged from the body (e.g., vaginal discharges,
menses, and/or urine) and which is intended to be discarded after a single
use.
The disposable absorbent article is preferably thin, more preferably between 1
and 5 mm thick and either substantially flat prior to use or in a preshaped
form.
The terms "joined" or "affixed", as used herein, encompasses configurations
whereby a first member is directly connected to a second member and
configurations whereby a first member is indirectly connected to a second
member by connecting the first member to intermediate members which in turn
are connected to the second member.
in a preferred embodiment a sanitary napkin of the present invention comprises
a liquid pervious topsheet, a liquid impervious but breathable backsheet
joined
to the topsheet, and an absorbent core intermediate the topsheet and the
breathable backsheet. The sanitary napkin has two main surfaces, a body
contacting or wearer facing surface, and a garment facing or contacting
surface.
The topsheet is compliant, soft feeling, and non-irritating to the wearer's
skin.
The topsheet also can have elastic characteristics allowing it to be stretched
in
one or two directions in portions of the topsheet or throughout its extension.
Further) the topsheet is fluid pervious permitting fluids (e.g., menses and/or
urine) to readily penetrate through its thickness. A suitable topsheet can be
manufactured from a wide range of materials such as woven and non woven
materials; polymeric materials such as apertured formed thermoplastic films,
apertured plastic films, and hydroformed thermoplastic films; and
thermoplastic
scrims. Suitable woven and non woven materials can be comprised of natural
fibers (e.g., wood or cotton fibers), synthetic fibers (e.g., polymeric fibers
such as
polyester, polypropylene, or polyethylene fibers) or from a combination of
natural and synthetic fibers or bi-/multi-component fibers.
Preferred topsheets for use in the present invention are typically selected
from
high loft nonwoven topsheets and apertured formed film topsheets. Apertured
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formed films are especially preferred for the topsheets because they are
pervious to body exudates and yet non absorbent and have a reduced tendency
to allow fluids to pass back through and rewet the wearer's skin. Thus, the
surface of the formed film that is in contact with the wearer remains dry,
thereby
reducing body soiling and creating a more comfortable feel for the wearer.
Suitable formed films are described in U.S. Patent 3,929,135; U.S. Patent
4,324,246; U.S. Patent 4,342,314; U.S. Patent 4,463,045; and U.S. Patent
5,006,394. Particularly preferred micro apertured formed film topsheets are
disclosed in U.S. patent 4,609,518 and U.S. patent 4,629,643. A preferred
topsheet for the present invention comprises the formed film described in one
or
more of the above patents and marketed on sanitary napkins by The Procter &
Gamble Company of Cincinnati, Ohio as "DRI-WEAVE".
Topsheets having not a homogeneous distribution of liquid passage ways but
only a portion of the topsheet comprising liquid passage ways are also
contemplated by the present invention. Typically such topsheets would have the
liquid passage ways oriented such that they result in a centrally permeable
and
peripherally impermeable topsheet for liquids.
The wearer facing surface of the formed film topsheet can be hydrophilic so as
to
help liquid to transfer though the topsheet faster than if the body surface
was not
hydrophilic. In a preferred embodiment, surfactant is incorporated into the
polymeric materials of the formed film topsheet such as is described in PCT-
publication WO 93/09741. Alternatively, the wearer facing surface of the
topsheet can be made hydrophilic by treating it with a surfactant such as is
described in U.S. 4,950,254.
Another alternative are so called hybrid topsheets which incorporate fibrous
and
film like structures particularly useful embodiments of such hybrid topsheets
are
disclosed in PCT publications WO 93/09744; WO 93/11725 or WO 93111726.
When referring to the topsheet a mufti layer structure or a mono layer
structure is
contemplated. The hybrid topsheet mentioned above is such a mufti layer design
but other mufti layer topsheets such as primary and secondary topsheet designs
are also considered.
__._ r.. ......._ .._,...._.-..T.-o.~.._..._. _ ......... .... ____~
.~.r...~~_..._.
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The absorbent structure or absorbent core can include the following
components: (a) optionally a primary fluid distribution layer preferably
together
with a secondary optional fluid distribution layer; (b) a fluid storage layer;
(c)
optionally a fibrous ("dusting") layer underlying the storage layer; and (d)
other
optional components.
a Primary/Secondary Fluid Distribution Layer
One optional component of the absorbent structure according to the present
invention is a primary fluid distribution layer and a secondary fluid
distribution
layer. The primary distribution layer typically underlies the topsheet and is
in fluid
communication therewith. The topsheet transfers the acquired fluid to this
primary distribution layer for ultimate distribution to the storage layer.
This
transfer of fluid through the primary distribution layer occurs not only in
the
thickness, but also along the length and width directions of the absorbent
product. The also optional but preferred secondary distribution layer
typically
underlies the primary distribution layer and is in fluid communication
therewith.
The purpose of this secondary distribution layer is to readily acquire fluid
from
the primary distribution layer and transfer it rapidly to the underlying
storage
layer. This helps the fluid capacity of the underlying storage layer to be
fully
utilised. The fluid distribution layers can be comprised of any material
typical for
such distribution layers. In particular fibrous layers which maintain the
capillaries
between fibers even when wet are useful as distribution layers.
b Fluid Storagie Layer
Positioned in fluid communication with, and typically underlying the primary
or
secondary distribution layers, is a fluid storage layer. The fluid storage
layer can
comprise any usual absorbent material or combinations thereof. It preferably
comprises absorbent gelling materials usually referred to as "hydrogel",
"superabsorbent", hydrocolloid" materials in combination with suitable
carriers.
The absorbent gelling materials are capable of absorbing large quantities of
aqueous body fluids, and are further capable of retaining such absorbed fluids
under moderate pressures. The absorbent gelling materials can be dispersed
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homogeneously or non-homogeneously in a suitable carrier. The suitable
carriers) provided they are absorbent as such, can also be used alone.
Suitable absorbent gelling materials for use herein will most often comprise a
5 substantially water-insoluble, slightly cross-linked, partially neutralised)
polymeric
gelling material. This material forms a hydrogel upon contact with water Such
polymer materials can be prepared form poiymerizable, unsaturated, acid-
containing monomers which are well known in the art.
10 Suitable carriers include materials which are conventionally utilised in
absorbent
structures such as natural, modified or synthetic fibers, particularly
modified or
non-modified cellulose fibers, in the form of fluff and/or tissues. Suitable
carriers
can be used together with the absorbent gelling material, however, they can
also
be used alone or in combinations. Most preferred are tissue or tissue
laminates
in the context of sanitary napkins/panty liners.
An embodiment of the absorbent structure made according to the present
invention comprises a double layer tissue laminate formed by folding the
tissue
onto itself. These layers can be joined to each other. Absorbent gelling
material
or other optional material can be comprised between the layers.
Modified cellulose fibers such as the stiffened cellulose fibers can also be
used.
Synthetic fibers can also be used and include those made of cellulose acetate,
polyvinyl fluoride, polyvinylidene chloride, acrylics (such as Orlon),
polyvinyl
acetate, non-soluble polyvinyl alcohol, polyethylene, polypropylene)
polyamides
(such as nylon), polyesters, bicomponent fibers, tricomponent fibers, mixtures
thereof and the like. Preferably, the fiber surfaces are hydrophilic or are
treated
to be hydrophilic. The storage layer can also include filler materials, such
as
Perlite, diatomaceous earth, Vermiculite, etc., to improve liquid retention.
If the absorbent gelling material is dispersed non-homogeneously in a carrier,
the
storage layer can nevertheless be locally homogenous, i.e. have a distribution
gradient in one or several directions within the dimensions of the storage
layer.
Non-homogeneous distribution can also refer to laminates of carriers enclosing
absorbent gelling materials partially or fully.
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c Optional Fibrous ("Dustinq'~ Layer
An optional component for inclusion in the absorbent structure according to
the
present invention is a fibrous layer adjacent to) and typically underlying the
storage layer. This underlying fibrous layer is typically referred to as a
"dusting"
layer since it provides a substrate on which to deposit absorbent gelling
material
in the storage layer during manufacture of the absorbent structure. Indeed, in
those instances where the absorbent gelling material is in the form of macro
structures such as fibers, sheets or strips, this fibrous "dusting" layer need
not be
included. However, this "dusting" layer provides some additional fluid-
handling
capabilities such as rapid wicking of fluid along the length of the pad.
d Other Optional Components of the absorbent structure
I S The absorbent structure according to the present invention can include
other
optional components normally present in absorbent webs. For example, a
reinforcing scrim can be positioned within the respective layers, or between
the
respective layers) of the absorbent structure. Such reinforcing scrims should
be
of such configuration as to not form interfacial barriers to fluid transfer.
Given the
structural integrity that usually occurs as a result of thermal bonding,
reinforcing
scrims are usually not required for thermally bonded absorbent structures.
Another component which can be included in the absorbent structure according
to the invention and preferably is provided close to or as part off the
primary or
secondary fluid distribution layer are odor control agents. Active carbon
coated
with or in addition to other odor control agents, in particular suitable
zeolite or
clay materials, are optionally incorporated in the absorbent structure. These
components can be incorporated in any desired form but often are included as
discrete particles.
Breathable Backsheet
According to the present invention, the absorbent articles comprise as an
essential component a breathable backsheet. The primary role of the breathable
backsheet is to prevent the extrudes absorbed and contained in the absorbent
article from wetting articles that contact the absorbent article such as
pyjamas
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and undergarments. In order to achieve this the backsheet typically extends
across the whole of the absorbent structure and can extend onto and form part
of the topsheet by folding around the absorbent structure. Thereby a topsheet
configuration as disclosed in US 4,342,314, column 16, lines 47 - 62 can be
achieved without the requirement to selectively aperture the topsheet.
In addition to the prevention of liquid transport through the backsheet
however,
the breathable backsheet also permits the transfer of water vapour and
preferably both water vapour and air through it and thus allows the
circulation of
air into and out of the backsheet and the absorbent article itself.
Suitable breathable backsheets for use herein can be chosen from all
breathable
backsheets known in the art. In principle there are two types of breathable
backsheets, single layer breathable backsheets which are breathable and
impervious to liquids and backsheets having at least two layers, which in
combination provide both breathability and liquid imperviousness. The term
"liquid impervious" as used herein for the breathable backsheet relates only
to
the barrier against liquid loss from the article. In principle liquid entering
the
article through the breathable backsheet is not intended to be excluded by
this
term.
Suitable single layer breathable backsheets for use herein include those
described for example in GB A 2184 389, GB A 2184 390, GB A 2184 391, US
4 591 523, US 3 989 867 US 3 156 242 and European Patent Application
number 95120653.1.
Suitable dual or multi layer breathable backsheets for use herein include
those
exemplified in US 3 881 489, US 4 341 216, US 4 713 068, US 4 818 600, EPO
203 821, EPO 710 471, EPO 710 472, European Patent Application numbers
95120647.3, 95120652.3, 95120653.1 and 96830097Ø
Particularly preferred are backsheets meeting the requirements as defined in
European Patent Application number 96830343.8 and more preferably wherein
the absorbent article in general also meets the requirements as described
therein.
_...____. _ .. _._.... . __. ,...__.~-...._~._.._~._.___.__.._ . _. _._._..~.~
_.
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According to the present invention the breathable backsheet comprises at least
one, preferably at least two water vapour permeable layers. Suitable water
vapour permeable layers include 2 dimensional, planar micro and macro-porous
films, monolithic films, macroscopically expanded films and formed apertured
films. According to the present invention the apertures in the layer may be of
any
configuration, but are preferably spherical or oblong. The apertures may also
be
of varying dimensions. In a preferred embodiment the apertures are preferably
evenly distributed across the entire surface of the layer, however layers
having
only certain regions of the surface apertured are also envisioned.
2 dimensional planar films as used herein have apertures having an average
diameter of from 5 micrometers to 200 micrometers. Typically, 2-dimensional
planar micro porous films suitable for use herein have apertures having
average
diameters of from 150 micrometers to 5 micrometers, preferably from 120
micrometers to 10 micrometers, most preferably from 90 micrometers to 15
micrometers. Typical 2 dimensional planar macroporous films have apertures
having average diameters of from 200 micrometers to 90 micrometers.
Macroscopically expanded films and formed apertured films (3-dimensional
films)
suitable for use herein typically have apertures having diameters from 100
micrometers to 500 micrometers. Embodiments according to the present
invention wherein the backsheet comprises a macroscopically expanded film or
an apertured formed film, the backsheet will typically have an open area of
more
than 5%, preferably from 10% to 35% of the total backsheet surface area.
Suitable 2 dimensional planar layers of the backsheet may be made of any
material known in the art, but are preferably manufactured from commonly
available polymeric materials. Suitable materials are for example GORE-TEX
(TM) or Sympatex (TM) type materials well known in the art for their
application
in so-called breathable clothing. Other suitable materials include XMP-1001 of
Minnesota Mining and Manufacturing Company, St. Paul, Minnesota, USA. As
used herein the term 2 dimensional planar layer refers to layers having a
depth
of less than 1 mm, preferably less than 0.5mm, wherein the apertures have an
average uniform diameter along their length and which do not protrude out of
the
plane of the layer. The apertured materials for use as a backsheet in the
present
invention may be produced using any of the methods known in the art such as
described in EPO 293 482 and the references therein. In addition) the
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dimensions of the apertures produced by this method may be increased by
applying a force across the plane of the backsheet layer (i.e. mono- or bi-
axial
stretching the layer).
Suitable apertured formed films include films which have discrete apertures
which extend beyond the horizontal plane of the garment facing surface of the
layer towards the core thereby forming protuberances (3-dimensional films).
The
protuberances have an orifice located at their terminating ends. Preferably
said
protuberances are of a funnel shape, similar to those described in US 3,
929,135. The apertures located within the plane and the orifices located at
the
terminating end of protuberance themselves maybe circular or non circular,
provided the cross sectional dimension or area of the orifice at the
termination of
the protuberance is smaller than the cross sectional dimension or area of the
aperture located within the garment facing surface of the layer. Preferably
such
apertured formed films are uni directional such that they have at least
substantially, if not complete one directional liquid transport abilities in a
direction
towards the core. Suitable macroscopically expanded films for use herein
include
films as described for example in US 4 637 819 and US 4 591 523.
Suitable monolithic films include Hytrel_, available from DuPont Corporation)
USA, and other such materials as described in Index 93 Congress, Session 7A
"Adding value to Nonwovens", J-C. Cardinal and Y. Trouilhet, DuPont de
Nemours International S.A., Switzerland.
According to the present invention the backsheet may comprise in addition to
said water vapour permeable layer additional backsheet layers. Said additional
layers may be located on either side of said water vapour permeable layer of
the
backsheet. The additional layers may be of any material, such as fibrous non-
woven layers, particularly of hydrophobic fibers and preferably of meltblown
fibers, or additional water vapour permeable layers as described herein above
so
long as they maintain the basic breathability of the article and preferably
improve
the liquid transport resistance of the backsheet.
Adhesive for topical attachment
r _.. .. _ . _ ..._. _ .. ...._ ~.___. . .. T~._.___~ r ~~ _ .. _..__.._ _ .
__..___________~.
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The articles according to the present invention as said above is applied
directly
to the skin of the user. In particular, sanitary napkins are applied in the
genital
region of a typically female user around the area of liquid discharge. The
word
"skin" according to the present invention does not only relate to the specific
5 derma of the user but include the mucous tissue as well as the hair which is
typically found in the genital region of users of sanitary napkins.
In order to provide fixation of the article according to the present invention
to the
skin of the user it is necessary to provide a certain area on the topsheet
side of
10 the article which is facing the wearer with the adhesive for topical
attachment
also referred to as body adhesive.
Various designs in this respect are contemplated but preferably the body
adhesive is provided along the peripheral edge of the topsheet such that a
15 central area of the article is left without adhesive. This will most
appropriately
facilitate placing the article such that the liquid permeable topsheet without
adhesive on it is placed adjacent the bodily liquid emanating orifice such
that
emanating liquid is immediately transported into the absorbent structure of
the
absorbent article without the possibility of leakage or spillage.
It is, however, not necessary that the body adhesive is provided in a closed
circle
around the periphery of the topsheet but it can be provided in incremental
areas
such as dots or discrete lines such that decoupling between the different
places
of attachment is providing additional comfort to the wearer of such articles.
In order to satisfy the objectives according to the present invention the
following
should be considered.
Physical, Rheoloaical and Adhesive Characteristics of a Bob Adhesive
Even so body adhesives are used like pressure sensitive adhesives on human
skin hair and mucous tissues, it is understood that the body adhesive
compositions could only with difficulty be considered typical pressure
sensitive
adhesives (referred to as PSA hereinafter) on the basis of the most
characteristic
rheological behaviours identifying such materials.
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In fact as the person skilled in the art of adhesives knows, the most
characteristic
feature that distinguish a PSA from other substances that can temporarily
stick
things (as e.g. water could) is the fact that their Theological parameters and
especially the Elastic Modulus G' vary greatly with the frequency of applied
stresses. More in particular, G' of PSA can increase over some orders of
magnitude while the frequency of applied stresses varies from typical bonding
frequency to typical debonding frequency, i.e. 1 rad/s to 100 rad/s as
indicated
below.
As a first consequence, it derives that it is inadmissible to define materials
intended for use as "adhesives" by giving values of Theological parameters and
especially of G' at a fixed value of frequency. This can be misleading because
in
the absence of other characteristics it may lead to include materials which
have
no practical value. It is hence believed that Theological characterisation
must be
i 5 on the base of dynamic considerations.
This not only applies to the Elastic Moduius G' but also to the viscous
moduius
G" and hence also for tan (s) = G" I G'. It is well known that typical PSA
have not
only a high variation of G' across the considered frequencies but also there
is an
even higher variation of G" which can get close or become even higher than the
value of G', i.e. tan (8) becomes about or even greater than 1, in particular
at the
frequencies that are typical of the debonding.
Without wishing to be bound by theory this can be interpreted as meaning that
a
high fraction of the energy applied for the debonding is dissipated in
internal
frictions (so it is not effective in causing the debonding) while this fact
causes
macroscopically the recording of a very high level of adhesive force.
In order to provide good conditions of bonding, i.e. at a frequency of about 1
rad/sec, the absolute values of the elastic modulus should not be too high,
otherwise the adhesive is too hard and it is not able to intimately join or
mold to
the surface to which it is expected to adhere. It is also important to have a
low
absolute value of G" in order to have good cohesion which is particularly
valuable for a direct application on the human body while the material remains
soft and capable of gently adhering to the skin.
... r ....... . .. ........_~._~__ _
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Finally the person skilled in the art will also recognise that the Glass
Transition
Temperature Tg of the PSA is a parameter which is useful to more fully define
completely the group of useful PSA materials.
As indicated above materials useful as body adhesives according to the present
invention have rheological characteristics which are measured at a reference
temperature of 37°C as body temperature and in a range of frequencies.
It has
been found that upon application of an article with a body adhesive the
adhesive
contact is formed at a low frequency, while debonding happens at the speed of
removing the article. This speed is expressed as a frequency of 100 rad/s
while
the low frequency of forming the adhesive bond has been found to be on the
order of 1 rad/s. Therefore, the frequency range for use according to the
present
invention is between 1 and 100 rad/s. The following set of characteristics
should
be satisfied:
- in the range of frequencies the percent variation of the elastic modulus
G'37 is
lower or equal to 150 %, preferably lower than 100 % and more preferably lower
than 80 %, of G'37 at 1 rad/s, preferably the variation is less than 10000 Pa
in
absolute terms. This is met by the body adhesive exemplified below while e.g.
Promeon RG-63B, quoted in the prior art, shows in the same range of
frequencies a variation of G'37 of 331 % which is not acceptable according to
the
present invention.
- in the range of frequencies the percent variation of the viscous modulus
G"37 is
not greater than 10000 Pa, preferably not greater than 5000 Pa, most
preferably
not greater than 1000 Pa.
- the value of the ratio G'37/G"37 at least for the frequency range 1 rad/s to
100
rad/s should preferably be unity or above, more preferably 1.6 or above and
most preferably 3.3 or above, while preferably not exceeding about 50.
It should be noted that G' and G" at the application frequency of 1 rad/s are
taken at a temperature of 37°C. In practical use of articles according
to the
present invention the actual storage temperature of the article and hence the
temperature of the body adhesive upon application varies widely. E.g. storage
in
a hot bathroom near a radiator could reach up to about 37°C, while
storage in a
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storage room or in a bathroom without heating but with an open window during
winter could be close to 0°C. However, since the article according to
the present
invention is used directly on skin and the wearer typically would not want to
apply
a too cold article the actual temperature of the body adhesive will reach
37°C
very quickly or even be warmed up by the wearer prior to application. Hence it
is
believed that the adhesive bonding characteristics are selected most
appropriately at body temperature.
As indicated above the rheological behaviour can also be related to the values
of
the Glass Transition Temperature Tg. For body adhesives according to the
present invention Tg should preferably be less than -15°C, more
preferably less
than -20°C and most preferably less than -25°C.
Chemical and compositional characteristics of a Body Adhesive
In order to satisfy the requirements of the above rheological and physics!
characteristics of a body adhesive the following formulation criteria can be
used
in addition. It should be noted that the most of the compositions useful as
body
adhesive have a substantially gel-like structure and are preferably gels. This
derives from the fact that:
- the prevailing component is a material liquid at room temperature
- a macromolecufar or polymeric component is present in minor quantities vs
the
plasticiser. It forms, in the preferred embodiments, a three dimensional
network
caused by physical or chemical links between the molecules. Particularly
useful
physical links are the ones present in systems containing Block Thermoplastic
Elastomers.
More specifically, the compositions comprise:
- from 0.5 to 20 %, preferably 5 % to 15 %, by weight of a macromolecular
polymeric substance or a mixture of such substances soluble or swellable in
the
below mentioned plasticiser(s). As not limiting examples such macromolecular
or
polymeric substances can be natural and/or synthetic such as natural gums or
derivatives such as natural gums and gelatines, their derivatives and
alginates;
T__.__.__ .__.. _ _._. __ __~.~_____ _ . _ ....__....~~.~.~ _ __ .
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polyacrilics; polyvinyl alcohol; polyethylene oxide; polyvinylpyrrolidon (PVP)
or
polyvinylethers, their copolymers and derivatives; cellulose derivatives;
Block
Copolymer Thermoplastic Elastomers and preferably Styrenic Block Copolymers
and more preferably the hydrogenated grades StyroI/Ethylene-Butylene/Styrol
(SEBS)) Styrene/lsoprene/Styrene (SIS), and Styro!/Ethylene-Propylene/Styrol
(SEPS).
- from 51 to 99.5 % by weight of a plasticising substance or a mixture of
plasticising substances) which are liquid at room temperature. As non-limiting
examples the plasticiser can be water, various alcohols (like in particular
glycerol), glycols, polyglycols, liquid polybutenes, natural or synthetic oils
such
as vegetable oils, mineral oils, or combinations thereof.
- from 0 to 600 % by weight of the macromoiecular polymeric substance of a
tackifying resin whose main scope is to tailor the Tg especially in systems
based
on synthetic polymers.
- from 0 to 10 % and more preferably form 0 to 5 % by weight of substances for
facilitating and stabilising the gelation both of hydrophilic or hydrophobic
liquid
plasticisers. These may be for oily systems, e.g. the fatty acids of CS to
C22, their
metallic salts and their polyoxo-derivatives; lanolin derivatives; silica;
bentonite,
montmorillonite and their derivatives; polyamides, waxes or mixtures thereof.
Common additives known in the art as preservatives, antioxidants, anti UV,
pigments, mineral fillers, rheology modifiers etc. can also be comprised in
quantities up to 10 % each.
When chemical crossfinks are formed in the system, a crosslinking agent can be
present preferably in quantities up to ~5 % by weight. Chemical crosslinking
can
be formed also by mutual neutralisation of polymers having different
functionalities as in the reaction between acid polyacrylics and
polysaccharides.
The resulting compositions for body adhesives can be divided into three
families
according to the nature of the main component, i.e. the liquid plasticiser(s):
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1 ) Hydrophobic compositions in which the plasticiser is typically an oil or
blend of oils of vegetable or mineral origin and the polymer is usually a
synthetic
polymer) preferably an elastomer, soluble or swellable in oil(s).
2) Mixed phase compositions in which both hydrophobic and hydrophilic
5 components, possibly in both plasticisers and polymers, form two or more
separate phases. In such cases an emulsifierlsurfactant is preferably present
at
a suitable level to form stable emulsions between the incompatible phases. For
body adhesives according to the present invention it is preferably that the
hydrophobic components are prevailing vs. the hydrophilic ones.
10 3) Hydrophilic compositions in which typically the plasticiser is
water/glycerol/glycols and the like andlor mixtures thereof and the polymeric
phase is of synthetic (e.g. polyacrilics) or natural (e.g. natural gums)
origin or
mixtures thereof.
15 It is to stress that, differently from what is already known in the medical
field and
from the cited prior art, the hydrophilic compositions are not preferred while
the
hydrophobic and mixed phases compositions 1 ) and 2) are preferred in the
applications of the present invention.
20 This depends partially on technical reasons in the sense that many
hydrophilic
compositions used in the medical field show too low elastic character and
cohesion for being useful in the present application. The other reason to
prefer
hydrophobic or mixed phase compositions is that the application of the present
invention in particular in the sanitary napkin field will include a
probability of
contacting the body adhesive with the liquid to be absorbed. Since the liquid
to
be absorbed are all of a general aqueous kind contact with a hydrophilic body
adhesive would result in a certain absorption of the bodily liquids into the
body
adhesives.
This would then have the result of changing the rheological characteristics
and
therefore the functionality of the body adhesive, causing a non-hygienic
appearance but also would cause the bodily liquids to remain in direct skin
contact over an extended period which is typically not desired by any of the
disposable absorbent articles according to the present invention. In addition
this
may also constitute a potential drawback for the user, since some hydrophilic
,. .. _. .._ ....._._..T_..........._....,~__._ .... ........._ . ...
._...._._~.~..._ ... _. .
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compositions are potentially good culture media for the growth of many micro-
organisms including even pathogens.
Further hydrophilic body adhesive also tend to be perceived as cold and wet
which upon application of a fresh sanitary napkin or an underarm sweat pad is
not in line with typical consumer expectation. Additional problems result from
the
fact that in particular body adhesives comprising water as the plasticiser
have a
tendency to dry out unless they are sealed into an impermeable package.
Absorbent articles according to the present invention can be made by any of
the
ways usual in the art. The application of the adhesive to the topsheet side of
the
absorbent article should not cause major problems to those skilled in the art
since it can be provided by similar techniques as is commonly used for a panty
fastening adhesive. The total area of the wearer facing surface of the
absorbent
1 S article which is covered by body adhesive should be not more than 20 %,
preferably not more than 10 %. Preferably, the adhesive is close to the
periphery
of the absorbent article and in the case of film topsheets (or when the
backsheet
is folded onto the topsheet) the adhesive is preferably on a portion of the
film
which is not permeable to liquids.
The body adhesive on the article (as is common with panty fastening adhesives)
needs to be protected prior to use. This protection can be provided by a
release
liner such as a siliconised or surfactant treated paper, provided this paper
is a
good release surface for the particularly selected body adhesive.
In principle the absorbent article according to the present invention is
supported
on the wearer by the body adhesive and does not require additional support to
remain in place. However, it is possible to provide for example a sanitary
napkin
with a skid resistant coating on the backsheet side in order to prevent the
sanitary napkin form gradually migrating out of position. Also even though
panty
fastening adhesives are not desired and hence not preferred according to the
present invention they are not strictly speaking excluded in the context of
the
present invention.
EXAMPLE 9
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An oil based composition useful in the present invention was compounded using
9.9 % by weight of Kraton G-1651, a Styrene/Ethylene-Butylene/Styrene block
copolymer containing 33% by weight styrene and available from Shell Co, and
59.3 % by weight of Kaydol, a paraffinic mineral oil available from Witco Co.
Moreover the composition contained 301 parts of tackifying resin per 100 parts
of
Kraton polymer. The tackifying resin was Escorez 5300, a hydrogenated resin
available from Exxon Co.
Magnesium Stearate, available from Carlo Erba S.p.A., was used a a co-
gelifying
agent for oil at a level of 0.7 % by weight.
Irganox 1010) an antioxidant available from Ciba-Geigy, was added at a level
of
0.3 % by weight.
So finally the formulation had the following percent composition:
Kraton G-1651 9.9 % by weight
Kaydol 59.3 % by weight
Escorez 5300 29.8 % by weight
Magnesium Stearate 0.7 % by weight
Irganox 1010 0.3 % by weight
The composition showed the following rheological properties at 37°C.
a) Elastic Modulus at 1 radls, G'37 = 6876 Pa
b) - Ratio between Elastic and Viscous Modulus at 1 rad/s) G'37 I G"37 = 12.49
- Ratio between Elastic and Viscous Modulus at 100 rad/s, G'37 I G"g7 = 7.01
c) The ratio G'37 at 100 rad/s over G'37 at 1 radls was 1.308.
The above formulation was judged as comfortable for application on sensitive,
hairy skin.
...._ T. _.._.~.....T_.~___.___~.~~....__..._
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COMPARATIVE EXAMPLE
A componotine oil based composition was compounded using 7.1 % by weight of
Kraton G-1651, a Styrene/Ethylene-Butylene/Styrene block copolymer containing
33% by weight styrene and available from Shell Co, and 41.9 % by weight of
Kaydol, a paraffinic mineral oil available from Witco Co.
Moreover the composition contained 704 parts of tackifying resin per 100 parts
of
Kraton polymer. The tackifying resin was Regalrez 3102, a hydrocarbon resin
available from Hercules Co.
Magnesium Stearate, available from Carlo Erba S.p.A., was used a a co-
gelifying
agent for oil at a level of 0.7 % by weight.
Irganox 1010) an antioxidant available from Ciba-Geigy, was added at a level
of
1 S 0.3 % by weight.
So finally the formulation had the following percent composition:
Kraton G-1651 7.1 % by weight
Kaydol 41.9 % by weight
Regalrez 3102 50.0 % by weight
Magnesium Stearate 0.7 % by weight
Irganox 1010 0.3 % by weight
The composition showed the following rheological properties at
37°C.
a) Elastic Modulus at 1 rad/s, G'37 = 3059 Pa
b) - Ratio between Elastic and Viscous Modulus at 1 rad/s, G'37 / G"37 = 2.53
- Ratio between Elastic and Viscous Modulus at 100 rad/s, G'37 I G"37 = 0.74
c) The ratio G'37 at 100 rad/s over G'37 at 1 rad/s was 4.944
The above formulation was judged as highly uncomfortable for application on
fore-arm skin. Application to sensitive hairy skin was unacceptable.
