Note: Descriptions are shown in the official language in which they were submitted.
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Extensible and/or flexible disposable absorbent article for topical adhesive
attachment to the skin of a wearer
Field of the invention
The present invention relates to disposable absorbent articles particularly
sanitary napkins, pantiliners, adult incontinence products or sweat pads. In
particular the present invention relates to such disposable absorbent articles
which are worn by direct attachment to the skin of the wearer in the area were
absorption of bodily liquids is desired. In order to provide the articles
according to
the present invention with additional comfort they are adaptable) preferably
elastically adaptable.
Background of the invention
The general 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, however, 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.
In 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 absorbent articles for absorption of body liquids which naturally
emanate from a body without a wound. For example sanitary napkins or
pantiliners for use in the genital region are such articles. Also incontinence
devices which are worn e.g. in the genital region or sweat pads which are worn
in the arm pit region of a person are the subject of the present invention.
Such articles are applied to the skin of a wearer in a region were typically a
considerable amount of hair grows such that 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 H 1602 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 95/16424 includes a detailed analysis of the criteria for
the
body adhesive in respect to theological criteria. However, this document has
little
regard to the problem of painless removal of such articles since the
theological
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 95/16424
include also today's pressure sensitive adhesives which are used to attach
sanitary napkins to undergarments. Further) this document only identifies
static
theological characteristics but is silent as to the dynamic theological
behaviour of
a body adhesive.
In WO 96/13238 a frequency dependent body adhesive model 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 absorbent
articles
provided with adaptability.
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.
None of the prior art documents relates to the problem that absorbent articles
which are attached to the skin of the wearer have to follow the expansion and
contraction or generally the relative movement in the area on the skin which
they
cover. It is well known in the art of wound coverings that e.g. a common
plaster
applied over a joint on the hand is either limiting movement of that joint or
not
providing acceptable coverage. The same is true for absorbent articles
according
to the present invention which are attached in the genital area or the arm pit
of a
wearer. For absorbent articles the problem is) however, compounded since an
article not capable of following the relative movement can easily detach and
then
causes leakage of liquids intend for absorption.
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 while
providing adaptability to follow the relative movement in the area of skin of
a
wearer which they cover. Another objective of the present invention is the
painless removal of the absorbent article.
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It is yet 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
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. 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 descriation of the invention
The present invention relates to disposable absorbent articles for topical
adhesive attachment to a wearer of such articles. The 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 article has a
longitudinal
axis separating the article as it is worn into right and left side. The
article also
has a transverse axis which is perpendicular to the longitudinal axis. The
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 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. According to the present
invention the article is adaptable in at lest one direction, preferably two
directions, parallel to the longitudinal and/or the transverse axis.
In one embodiment according to the present invention the adaptability is
provided in that the article is corrugated or pleated. This can be provided
either
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parallel to the longitudinal axis or parallel to the transverse axis or in a
combination of both. Also corrugating or pleating parallel to both axis can be
considered which results in articles being adaptable in both directions.
5 In an alternative embodiment according to the present invention the article
is
contractible which will allow adaptability when some part of the skin surface
covered by the absorbent article is reduced in size and be elastically
extensible
in which case the article extends together with an extending surface (e.g, in
the
arm pit region when the arm is lifted) while it has the ability to return at
least to
IO some extend to the original size. This elasticity can be provided by
rendering the
various components of the absorbent article elastic or rendering some portions
of
the components of the absorbent article elastic.
In general any body adhesive acceptable to the wearer of an article according
to
the present invention can be used. It is, however, particularly preferred that
the
adhesive has the following characteristics. The adhesive is particularly
characterised by having an elastic modulus at a temperature of 37°C
(100°
Fahrenheit) abbreviated G'37 and having a viscous modulus 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
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change within the frequency range by a factor of more than 3, preferably more
than 2, and most preferably should stay constant.
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 radlsec 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 sweilable 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
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 disposable absorbent articles which are adaptable
and
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, and is easy to produce and to package. The disposable
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absorbent article is described below by reference to a sanitary napkin or
catamenial, however 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 pudenda! 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) most preferably between 1
mm and 5 mm thick and can either be substantially flat prior to use or in a
preshaped condition.
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 backsheet joined to the
topsheet,
and an absorbent core intermediate the topsheet and the backsheet. The
sanitary napkin has two main surfaces, a body contacting or wearer facing
surface, and a garment facing or contacting surface.
In one aspect the present invention is concerned with the adaptability of the
product. The degree of adaptability is determined by the selection of the
materials for the components of the product as mentioned above, their
respective quantity and to which extend they have been treated to provide
adaptability. It will be apparent to those skilled in the art that, in order
to achieve
the adaptability according to the present invention, the selection of kind,
quantity
and treatment of raw materials has to be balanced with other desired
characteristics of the absorbent product such as for example absorbent
capacity)
absorption speed and surface dryness on the outside of the topsheet during
use,
and so on.
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Therefore the following description of typical materials of the main
components
of the absorbent product will allow to provide a large number of product
variants
which satisfy the requirements according to the present invention.
In addition to adaptability the absorbent articles according to a preferred
embodiment of the present invention are elastically stretchable. The term
'elastically stretchable') as used herein, means that when the stretching
forces
are removed, the article will tend to return toward its unextended or
unstretched
(or 'original' dimensions). It need not return all the way to its unstretched
dimensions, however. If the absorbent article is elastically stretchable it
may be
stretchable in one or two directions (which are not-parallel) within the plane
of
the product i.e. topographically parallel to the wearer facing surface.
Materials for contractible and elastically stretchable articles can be
elastically
stretchable per se or be treated so as to provide elastic stretchablility. f n
particular elastic backsheet material, elastic topsheet material) filamentary
materials combined with elastic strands, threads or webs as well as shirring)
pleating or ring rolling of the materials may be employed in this context.
Suitable
material and methods are known in the art and e.g. disclosed in detail in US
application 08/192240 of February 4, 1994 specifically referred to in order to
facilitate selection of materials if elastically stretchable absorbent
articles
according to the present invention are made.
In the following, non-limiting embodiments of the main elements of the
absorbent
product are described which can be employed in contractible and preferably
also
elastically stretchable or non-stretchable designs.
The absorbent core typically includes the following components: (a} optionally
a
primary fluid distribution layer; (b) optionally) but preferably, a secondary
fluid
distribution layer; (c) a fluid storage layer; (d) optionally a fibrous
("dusting") layer
underlying the storage layer; and (e} other optional components.
a. Primary Fluid Distribution Layer
One optional component of the absorbent cores according to the present
invention is the primary fluid distribution layer. This primary distribution
layer
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typically underlies the topsheet and is in fluid communication therewith. The
topsheet transfers the acquired menstrual 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.
b. Optional Secondary Fluid Distribution Layer
Also optional but a preferred component of the absorbent cores according to
the
present invention is a secondary fluid distribution layer. This 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 utilized.
c. Fluid Stora a Layer
Positioned in fluid communication with, and typically underlying the primary
or
secondary distribution layers) is a fluid storage layer comprising certain
absorbent gelling materials and/or other absorbent materials, which can form
the
carrier matrix for the absorbent gelling materials. Absorbent gelling
materials are
usually referred to as "hydrogels," "superabsorbent" "hydrocolloid" materials.
Absorbent gelling materials are those materials that, upon contact with
aqueous
fluids, especially aqueous body fluids, imbibes such fluids and thus form
hydrogels. These absorbent gelling materials are typically capable of
absorbing
large quantities of aqueous body fluids, and are further capable of retaining
such
absorbed fluids under moderate pressures. These absorbent gelling materials
are typically in the form of discrete) nonfibrous particles.
The fluid storage layer can comprise solely absorbent gelling materials, or
these
absorbent gelling materials can be dispersed homogeneously or non
homogeneously in a suitable carrier or it can comprise solely an absorbent
carrier material.
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Suitable carriers include cellulose fibers, in the form of fluff, tissues or
paper
such as is conventionally utilized in absorbent cores. 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,
5 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. Preferred synthetic fibers have a denier of from about 3 denier per
friament
to about 25 denier per filament, more preferably from about 5 denier per
filament
10 to about 16 denier per filament. Also 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., that
tower
rewet problems.
If dispersed non-homogeneously in a carrier, the storage layer can be locally
homogeneous, 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. If laminates are used they can be formed with or without absorbent
gelling
particles. in particular thermally bonded air laid fibrous sheets or laminates
and/or thermally bonded wet laid sheets or laminates have been found useful,
especially in the context of panty liners when no absorbent gelling material
is
used.
Preferably, the storage layer comprises from about 15 to 100% absorbent
gelling
materials and from 0 to about 85% carrier. More preferably, the storage layer
comprises from about 30 to 100 %, most preferably from about 60 to 100%
absorbent gelling materials and from 0 to about 70 %, most preferably from 0
to
about 40 %, carrier.
Suitable absorbent gelling materials for use herein will most often comprise a
substantially water-insoluble, slightly crosslinked, partially neutralized,
polymeric
gelling material. This material forms a hydrogel upon contact with water. Such
polymer materials can be prepared from polymerizable) unsaturated, acid-
containing monomers. Suitable unsaturated acidic monomers for use in
preparing the polymeric absorbent gelling material used in this invention
include
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those listed in U.S. Patent 4,654,039 and reissued as RE 32,649. Preferred
monomers include acrylic acid, methacrylic acid, and 2-acrylamido-2-methyl
propane sulfonic acid. Acrylic acid itself is especially preferred for
preparation of
the polymeric gelling material. The polymeric component formed from the
unsaturated, acid-containing monomers can be grafted onto other types of
polymer moieties such as starch or cellulose. Polyacrylate grafted starch
materials of this type are especially preferred. Preferred polymeric absorbent
gelling materials that can be prepared from conventional types of monomers
include hydrolyzed acrylonitriie grafted starch, polyacrylate grafted starch,
poiyacrylates, malefic anhydride-based copolymers and combinations thereof.
Especially preferred are the polyacrylates and polyacrylate grafted starch.
While these absorbent gelling materials are typically in particle form, it is
also
contemplated that the absorbent gelling material can be in the form of
macrostructures such as fibers, sheets or strips.
d. Optional Fibrous ("Dusting") Leer
An optional component for inclusion in the absorbent cores 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 core. Indeed, in
those
instances where the absorbent gelling material is in the form of laminates or
of
macrostructures such as fibers, sheets or strips, this fibrous "dusting" layer
need
not be included. However, because this "dusting" layer provides some
additional
fluid-handling capabilities such as rapid wicking of fluid along the length of
the
pad, its inclusion is typically preferred in absorbent cores according to the
present invention.
e. Other Optional Components
The absorbent cores 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 cores. Such reinforcing scrims should be
of
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such confrguration as to not form interfacial barriers to fluid transfer,
especially if
positioned between the respective layers of the absorbent core. Given the
structural integrity that usually occurs as a result of thermal bonding,
reinforcing
scrims are usually not required for the absorbent structures according to the
present invention. If used however they have to allow the desired
contractability.
Another component which can be included in the absorbent core according to
the invention and preferably is provided close to or as part of the primary or
secondary fluid distribution layer are odor control agents. These can be
selected
from active carbon or coated active carbon to conceal the color, suitable
zeolite
or clay materials, are optionally incorporated in the absorbent core also
absorbent gelling material in combination with certain zeolites have been
found
useful. These components can be incorporated in any desired form but often are
included as discrete, non-fibrous particles.
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-Imulti-component fibers.
Preferred topsheets for use in the present invention are typically selected
from
high loft nonwoven topsheets and apertured formed film topsheets. Apertured
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
surtace 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
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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 8
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 frlm 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 93/11726.
When referring to the topsheet a multi layer structure or a mono layer
structure is
contemplated. The hybrid topsheet mentioned above is such a multi layer design
but other multi layer topsheets such as primary and secondary topsheet designs
are also considered.
The backsheet primarily prevents the exudates absorbed and contained in the
absorbent structure from wetting articles that contact the absorbent product
such
as underpants, pants, pyjamas and undergarments. The backsheet is preferably
impervious to liquids (e.g. menses and/or urine) and is preferably
manufactured
from a thin plastic film, although other flexible liquid impervious materials
can
also be used. As used herein, the term "flexible" refers to materials that are
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14
compliant and will readily conform to the general shape and contours of the
human body. The backsheet also can have elastic characteristics allowing it to
stretch in one or two directions.
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, fines 47 - 62 can be achieved without the requirement to
selectively
aperture the topsheet.
The backsheet can comprise a woven or nonwoven material, polymeric films
such as thermoplastic films of polyethylene or polypropylene, laminates of
such
materials or composite materials such as a film-coated nonwoven material.
Preferably) the backsheet is a polyethylene film having a thickness of from
about
0.012 mm (0.5 mil) to about 0.051 mm (2.0 mils).
Exemplary polyethylene films are manufactured by Clopay Corporation of
Cincinnati, Ohio, under the designation P18-1401 and by Ethyl Corporation,
Visqueen Division, of Terre Haute, Indiana, under the designation XP-39385.
The backsheet is preferably embossed and/or matte finished to provide a more
clothlike appearance.
Preferably, the backsheet also provides breathability to the absorbent article
by
being at least water vapour permeable, preferably air permeable, however,
without compromising the main function of the backsheet. The backsheet can be
a laminate material e.g. of a combination of microporous film, non-woven
material, and/or apertured formed film. Breathability if desired can be
limited to
the periphery of the backsheet or it can be across the whole backsheet.
Adaptability of the article
The term "adaptability", as used herein) incompasses the characteristics of
contractability, extensibility) and combinations thereof. Adaptability usually
refers
to the ability to adapt in the size in one or both directions of a sanitary
napkin.
Adaptability according to the present invention can be provided by creating a
series of corrugations or pleats in the direction perpendicular to the
direction in
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which the product is desired to be adaptable. For example a thin sanitary
article
having corrugations or pleats in longitudinal direction will provide the
ability to be
. stretched in transverse direction in order to accommodate a crotch width
change
of the article upon application of the article or during use. These
corrugations or
5 pleats can also provide the ability to enlarge or reduce the width of the
article in
order to result in the usual wearing position for wearers of differing crotch
width.
The ability to adapt to the desired extend can be provided in longitudinal or
transverse direction. It can be employed to provide synergistic effects
together
10 . with elastically extensible materials in the construction of the
absorbent article. It
is of course also possible to use inherent material adaptability with the
structural
adaptability provided by corrugations or pleats.
The term "corrugated or corrugations" as used herein designates the existence
15 of a series of continuous changes of the normal direction of a plain of a
sheet.
The "normal direction" of a plain is the direction perpendicular to that
plain. While
corrugations are a continuous change of the normal direction in the plain of a
sheet the term "pleats" or pleated" as used herein refers to foldings along a
specific line or) in other words) an uprupt change in the normal direction of
a
plain of a sheet. A series of pleats can also be used to simulate
corrugations.
In particular for thin articles a process termed ring-rolling can be employed
upon
the whole product to provide structural corrugations allowing for adaptability
of
the product as desired. Such ring-rolling at least in a high speed
manufacturing
operation does require the materials to be carefully selected by a man skilled
in
the art which however is no problem given the above material choices and a
desired adaptability in mind. Ring-rolling of individual materials prior to
combination can also be useful in order to provide products in addition to
their
adaptability having a flexibility and softness improvement over usual
products.
Ring-rolling is described in more detail in US 4, 107, 364, US 4, 834, 741, US
5)
156) 793, US 5, 143) 679, US 5, 167, 897 and US 5, 354, 400 which gives a
detailed explanation how to provide differential extensibility as well.
Also corrugating is well-known and will be easily usable for those skilled in
the
art. Corrugations may be present in both longitudinal and transverse direction
of
the absorbent article, however, corrugation techniques have been developed to
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16
provide corrugations which are transverse to the direction of material
transport
during manufacturing of an article. Hence a ring-rolling operation can be
considered to provide corrugation in the direction of transport of a material
during
manufacturing while a corrugation process would typically provide only
corrugation in the perpendicular direction.
However, the term corrugations or pleats as used herein does refer to the
result
of ring-rolling or corrugating irrespective of whether the process was used in
the
direction of transport of a material during manufacturing or perpendicular
thereto.
The required extend of corrugation or pleats (defined by amplitude and
frequency) can easily be defined by simple trial and error to accommodate the
required adaptability. It will depend on the combined thickness and
flexibility of
the article. Those skilled in the art will also realize that the same
corrugation or
pleats can be provided such that they allow different extends of adaptability
depending on whether they have been partially flatened out again.
tn order to provide the wearer with an article having a high degree of
adaptability
it is necessary to maintain the corrugations formed upon manufacturing during
the remainder of the manufacturing process as well as the packaging operation,
transport to the product supply locations and personal handling of the article
prior to attaching it to the skin. This can be achieved for example by
stabilising or
freezing the product in its corrugated or pleated state by affixing it in that
state to
a rigid substrate such as for example a release paper or adhesive protection
means for the body adhesive.
Adhesive for topical attachment
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
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.
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17
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
. 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
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.
Even though any body adhesive which is acceptable to the wearer of an article
according to the present invention can be used it is particularly preferable
that
the following considerations are followed.
Phvsicai, Rheolo4ical and Adhesive Characteristics of a Body 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.
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 rheological 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
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18
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 rheological 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 rheological characterisation
must be
on the base of dynamic considerations.
This not only applies to the Elastic Modulus G' but also to the viscous
modulus
G" and hence also for tan (8) = G" / 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.
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
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19
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. fn 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, white
storage in a
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
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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
5 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.
Preferred Chemical and compositional characteristics of a Body Adhesive
In order to satisfy the requirements of the above preferred rheological and
physical 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.
i5 This derives from the fact that:
- the prevailing component is a material liquid at room temperature
- a macromolecular 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 finks 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 swellabte 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;
polyacrilics; polyvinyl alcohol; polyethylene oxide; polyvinylpyrrolidon (PVP)
or
polyvinylethers, their copolymers and derivatives; cellulose derivatives;
Block
Copolymer Thermoplastic Elastomers and preferably Styrentc Block Copolymers
and more preferably the hydrogenated grades Styrol/Ethylene-Butytene/Styrol
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(SEBS), Styrene/Isoprene/Styrene (SIS), and Styro!/Ethylene-Propylene/Styrol
(SEPS).
- frorn 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 plasticises 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 macromolecular 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 C8 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 crosslinks 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):
1 ) Hydrophobic compositions in which the plasticises 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
components, possibly in both plasticisers and polymers, form two or more
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22
separate phases. In such cases an emulsifier/surfactant 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.
3) Hydrophilic compositions in which typically the plasticiser is
water/glycerol/glycols and the like and/or mixtures thereof and the polymeric
phase is of synthetic (e.g. polyacrilics) or natural (e.g. natural gums)
origin or
mixtures thereof.
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.
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 theological 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
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
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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
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 1
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.
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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 rad/s, G'g7 = 687.6 Pa
b) - Ratio between Elastic and Viscous Modulus at 1 rad/s) G'37 / G"37 = 12.49
- Ratio between Elastic and Viscous Modulus at 100 rad/s, G'37 I G"37 = 7.01
c) The ratio G'37 at 100 rad/s over G'37 at 1 rad/s was 1.308.
The above formulation was judged as comfortable for application on sensitive,
hairy skin.
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.
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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.
5
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
10 ~ 0.3 % by weight.
So finally the formulation had the following percent composition:
Kraton G-1651 7.1 % by weight
15 Kaydol 41.9 % by weight
Regalrez 3102 50.0 % by weight
Magnesium Stearate 0.7 % by weight
Irganox 1010 0.3 % by weight
20 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 I G"37 = 2.53
25 - 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. .
