Note: Descriptions are shown in the official language in which they were submitted.
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Flexible and breathable absorbent articles and their fixation to
undergarments
Field of the invention
The present invention relates to breathable absorbent articles
such as sanitary napkins, pantyliners, and incontinence pads
which are adhered to an undergarment during use. More
particularly the present invention relates to articles which are air
permeable or breathable and which have a flexibility in a
longitudinal direction which provides improved comfort to the
wearer of the article.
Background of the invention:
Disposable absorbent articles such as baby diapers, adult
incontinence articles, sanitary napkins and panty liners are well
known in the art. These articles have a wearer facing side
through which they typically absorb liquids discharged by the
wearer. The liquid is stored in an absorbent structure. Liquid
leakage from the article through the surface opposite the
wearer facing side is usually prevented by incorporating a liquid
impermeable backsheet on that side.
It is also well established in the art that a backsheet allowing
gaseous fluid (air) communication with the environment, usually
referred to as breathability, is highly desirable. Breathability
improves with the amount of air permeating through a
' backsheet. This amount is proportional to the open area (the
sum of the area of all apertures) in the backsheet. Obviously
' too many and particularly too large apertures in the backsheet
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lead to compromising the liquid leakage prevention, which is the
primary function of a backsheet.
Many suggestions how to provide breathable backsheets have
been recorded in the art. Numeral attempts of combining the
mutual contradicting features of gas permeability and liquid
impermeability have been documented in patents and patent
applications. However the lack of commercially available
breathable disposable absorbent articles indicates that the
technology so far suggested has not provided an all around
satisfactory result for the desired technical requirements at
commercially acceptable conditions. More often than not
satisfaction of one desired feature went to such an extreme
that the respective other feature was not properly satisfied any
longer.
For example sanitary napkins with very high breathability at the
cost of frequent liquid leakage (leading to soiling of the
undergarments of a wearer) cannot be considered satisfactory.
On the other hand satisfying the liquid leakage problem properly
usually resulted in almost impermeable, that is non-breathable,
backsheets.
Combinations of breathable and liquid permeable sheets in order
to provide a certain liquid impermeability while satisfying the
desire for breathable backsheets have already been suggested
for example in US 3,881,489. In this disclosure a breathable
backsheet is provided by confining an outer layer of formed film
material having surface aberrations with apertures therein and
an inner layer of a paper tissue having a high void volume and
having been made hydrophobic by impregnating it with a
paraffin wax. This document does not disclose the desire for
using a directional liquid transport type polymeric film structure
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with a hydrophobic fibrous fabric layer made of polymeric
material.
Other prior art attempts to provide breathable backsheet
assemblies comprising more than one layer are e. g.
documented in US 4,341,216, EP-A-109 126 or EP-A-203 821.
Neither of these disclosures provides constructions of
breathable backsheets similar to the present invention.
Single layer breathable backsheets are known for example from
GB-A-2184391, GB-A-2184390, GB-A-2184389, US
4,591,523, US 4,839,216 or EP 156471. None of the
mentioned disclosures attempts however to address the
comfort problems associated with stiff or not sufficiently
flexible absorbent articles.
Another solution to the problem of conflict between leakage
and breathability is of course to provide so much absorbent
material that leakage is prevented by liquid retention rather than
impermeability of the backsheet. This leads to early designs of
catamenial articles having a very thick absorbent core with a
fully permeable non-woven or gauze wrapping. However these
articles are not used any longer due to being extremely
uncomfortable. Also they are too costly due the high material
consumption required in order to provide the end user with
peace of mind regarding the leakage performance of these
articles.
Also this solution, as did other alternatives which increased
material consumption, causes the absorbent article to become
less flexible. Flexibility in particular the ability to bend and twist
easily in longitudinal and preferably in all directions has
however become of key importance especially for everyday
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usage absorbent articles such as panty liners, sanitary napkins
and incontinence pads.
Such sanitary napkins, pantyliners, and incontinence pads are
typically worn in the crotch region of an undergarment and
attached to the undergarment by a so called panty-fastening-
adhesive. In order to be comfortable to the wearer these articles
need to be flexible. It is believed that the more flexible an
absorbent article is the less will it be noticeable to the wearer.
Hence this provides comfort by more closely resembling the
situation when no such absorbent article is worn.
Flexibility can easily be achieved by reducing the amount of
material in an absorbent article or replacing stiff or inflexible
components by more flexible ones. However it has long been
recognised that extreme flexibility can reduce the absorbent
performance of these articles, for example by an insufficient
amount of absorbent material or by bunching or densifying of
the absorbent material during use. Also a too flexible article
may be difficult to handle for the wearer when attaching it to
the undergarment.
The problem of too much flexibility in an article due to a low
amount of inflexible material has been addressed for example in
U.S. 4,217,901 where particularly the stiffness of an absorbent
article is increased in order to provide satisfactory performance.
This prior art reference accepts the comfort implications caused
by its stiffness requirement. Also breathability is not even
considered in this document. Therefore flexibility and leakage
prevention (as well as breathability and leakage prevention) are
mutually apposite characteristics of absorbent articles. Hence
flexibility and breathability combined are working in synergy
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against leakage prevention while all three features are highly desirable.
It now has been found that the comfort of breathable absorbent articles can
be drastically improved when providing a high flexibility in longitudinal
direction in combination with a particular panty-fastening-adhesive
configuration so as to maintain the breathable article flat relative to the
undergarment of the wearer. The flexibility then becomes limited only by
material requirements (e.g. to provide sufficient absorbent performance) and
by handling requirements of the absorbent article.
It is therefore an objective of an aspect of the present invention to provide
sanitary napkins with an improved flexibility without the previously
experienced drawbacks. In particular a high degree of flexibility and
breathability in the absence of bunching problems without major handling
difficulties is achieved by the selected ranges of design parameters of the
articles according to the present invention.
It is another objective of an aspect of the present invention to provide
highly
flexible absorbent articles in particular sanitary napkins or panty liners
having
a superior breathability of the backsheet while simultaneously retarding
liquid
leakage through the backsheet to such an extend that the user of such
articles does not experience a recognisable difference between a liquid
impermeable backsheet and the breathable backsheet according to the
present invention.
These and other objectives of aspects of the present invention will be more
readily apparent when considered in reference to the following description.
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Summary of the invention
The present invention provides a breathable absorbent article
such as a sanitary napkin, an incontinence pad and particularly
a panty liner for use in an undergarment. The absorbent article
has a breathable backsheet which comprises a garment facing
surface. On the garment facing surface is an adhesive to adhere
the article to the undergarment. The article may optionally
comprise protective side-flaps which during use are folded
around the side edges in the crotch region of the undergarment
so as to improve soiling protection for the undergarment. The
absorbent article also comprises the other typical components
of such articles namely an absorbent core and a liquid pervious
wearer facing surface which is preferably provided by a liquid
pervious topsheet. The absorbent article comprises a breathable
backsheet which usually provides the garment facing surface of
the absorbent article. If topsheet and backsheet are present the
absorbent core is enclosed by them on the wearer and on the
garment side respectively.
The adhesive can be provided across the whole, pan or several
distinct parts of the garment facing surface. The adhesive is
provided so as not to clog the full surface area. If it covers the
whole garment facing surface it can be in a filamentary fashion
which is random or in a defined design like spirals. The total
area of all adhesive on the garment facing surface of the
absorbent article defines the actual adhesive surface. In
addition a theoretical adhesion surface is given by the periphery
of an endless line which is the shortest encircling line of the
adhesive without extending beyond the periphery of the
garment facing surface itself.
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The absorbent article according to the present invention has a
surface ratio of theoretical adhesion surface to the garment
facing surface in a range of 0.6 to 1, preferably 0.85 to 1 for
articles without the protective side flaps and in a range of 0.5
to 1, preferably from 0.7 to 0.9 for articles with protective side
flaps. In a preferred embodiment the theoretical adhesion
surface is substantially coextensive to the actual surface
covered by the adhesive.
In order to realise the benefits of the present invention the
absorbent article as a whole needs to provide exceptional
flexibility. The flexibility is measured by the modified ASTM
method D1388 as described herein below in longitudinal
direction. The expression "flexibility" is also referred to as
"drapability" due to the particular method. It should be
understood that stiffness is characteristic of the opposite
behaviour of a material. The flexibility should be in the range of
1300 to 5000, preferably from 2000 to 3500, most preferably
2000 to 3000, mg x cm.
These flexibility values in combination with the surface ratio
indicated above provide exceptional wearer comfort without
soiling and/or absorbent performance problems due to bunching
or densification of the absorbent material and still allows the
wearer to attach the article to the undergarment without undue
effort. According to the present invention flexibility is measured
in longitudinal direction because this is the value more readily
measurable and important. In principle the transverse flexibility
also could be used, possibly at different values. Due to the
small extension of articles in the transverse direction it is
however usually not possible to properly measure flexibility in
this direction.
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The thickness of a preferred embodiment of the present
invention especially for pantyliners is less than 3 mm and even
more preferably in the range of 0.5 to 1.5 mrn according to the
thickness measurement method described herein below.
The combination of appropriate panty-fastening adhesive
coverage and flexibility is particularly useful in the context of
stretchable absorbent articles. Absorbent articles being
stretchable in one direction and more so absorbent articles
being stretchable in two for all! directions are inherently flexible.
Stretchability in itself already provides an improvement for
comfort such that the absorbent articles combining
stretchability with the present invention are particularly
desirable.
The second key aspect according to the present invention is the
breathability of the backsheet of the absorbent articles. The
articles according to the present invention have a breathable
backsheet comprising an inner layer and an outer layer where
the inner layer is closer to the absorbent core than the outer
layer. The outer layer comprises a hydrophobic, gas permeable
fibrous fabric layer composed of polymeric fibres such as
polymeric non-wovens well known in the art of absorbent
articles.
The inner layer comprises a hydrophobic gas-permeable (air-
permeablel polymeric film such as a microporous film having
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micro-apertures or a macroscopically expanded, polymeric film having macro-
apertures.
If the inner layer comprises a hydrophobic gas-permeable micro-or macro-
apertured, polymeric film, it preferably has a directional liquid transport
phenomena. The film has a first and a second liquid transport direction which
are opposite to each other. The first liquid transport direction is from the
outer
layer towards the absorbent core. Liquid transport in the first direction is
larger
than liquid transport in the second direction when measured under an
identical pressure drop across the apertured film.
This directional liquid transport phenomena is preferably provided by funnel
shaped apertures with the direction from larger funnel opening towards
smaller funnel opening being parallel to the first liquid transport direction.
In accordance with one embodiment of the present invention, a flexible and
breathable absorbent article for use in an undergarment, the article
optionally
comprising protective side flaps, the article comprises a breathable backsheet
having a garment facing surface and the article comprising an absorbent core;
the garment facing surface comprising an adhesive to adhere the article to the
undergarment, the adhesive having an actual adhesive surface and the
adhesive defining a theoretical adhesion surface inside of an endless line
which is the shortest encircling line of the adhesive without extending beyond
the periphery of the garment facing surface;
the backsheet comprising an inner layer and an outer layer, the inner layer
being closer to the absorbent core than the outer layer;
the article being characterised in that
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-the outer layer comprises a hydrophobic, gas-permeable fibrous fabric layer
composed of polymeric fibres;
-the inner layer comprises a hydrophobic, gas-permeable polymeric film;
-the surface ratio of the actual adhesive surface to the garment facing
surface
is in the range of 0.2 to 0.8;
-the surface ratio of the theoretical adhesion surface to the garment facing
surface is
in the range of 0.6 to 1.0 for articles without the protective side flaps, and
in the range of 0.5 to 1.0 for articles with the protective side flaps;
and
-the article has a flexibility of 1300 mg x cm to 5000 mg x cm measured
according to modify ASTM D1388.
Brief description of the drawings
Figure 1 shows a plan view of the garment facing surface of a pantyliner
without protective side flaps according to the present invention.
Figure 2 shows the garment facing surface of a sanitary napkin having
protective side flaps according to an alternative embodiment of the present
invention.
Detailed description of the present invention
The present invention will be described by reference to pantyliners. It is
however equally well applicable to sanitary napkins or adult incontinence
articles which are worn in an
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undergarment and are joint to the undergarment during wearing
of the absorbent article .
Absorbent articles according to the present invention comprise
typically three main components: a liquid pervious topsheet, a
breathable backsheet and an absorbent core. The absorbent
core is enclosed by the backsheet and the topsheet and the
article is worn such that the exposed surface of the topsheet
faces the wearer of the absorbent article while the exposed
surface of the backsheet faces the undergarment to which the
article is joint by a panty-fastening attachment means. Typically
this is an adhesive but could also be a mechanical attachment.
The present invention is concerned with the flexibility of the
article and its breathability. The degree of flexibility is
determined by the selection of the materials for the components
of the article as mentioned above and their respective quantity.
It will be apparent to those skilled in the art that, in order to
achieve the flexibility according to the present invention, the
selection of kind and quantity of raw materials has to be
balanced with other desired characteristics of the absorbent
article such as for example absorbent capacity, absorption
speed and surface dryness on the outside of the topsheet
during use.
Therefore the following description of typical materials of the
main components of the absorbent article will allow to provide
an almost infinite number of article variants inside and outside
the flexibility limitations according to the present invention.
Whether or not an absorbent article meets the requirements of
flexibility of the present invention can then be confirmed by
simple measurements according to the method described below.
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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 article i.e. parallel to the garment facing
surface.
Materials for elastically stretchable articles can be elastically
stretchable per se or be treated so as to provide elastic
stretchablility. In 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.
In the following, non-limiting embodiments of the main elements
of the absorbent article are described which can be employed in
elastically stretchable or non-stretchable designs.
The absorbent core typically includes the following
components: la) optionally a primary fluid distribution layer; Ib)
optionally, but preferably. a secondary fluid distribution layer;
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(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 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 article .
b. Qotional 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 menstrual 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 Storage Layrer
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
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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
hydrogsls. 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 'tt
can comprise solely an absorbent carrier material. 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, polyvir~ fluoride,
polyvinylidene chloride, acrylics (such as Orlonl, 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 thickness of from
about 3 denier per filament to about 25 denier per filament.
more preferably from about 5 denier per filament 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 T I~lsr materials, such as Perlite diatomaceous
earth, Vermiculite, etc., that lower rewet problems.
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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 absorbent gelling materials are present, preferably the storage
layer comprises from about 15 to 100% absorbent gelling
materials and from 0 to about 85% carrier. Preferably, the
storage layer comprises from about 30 to 100 °~b, 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 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
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hydrolyzed acrylonitrile grafted starch, polyacrylate grafted
starch, polyacrylates, 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. These macrostructures are typically prepared by forming
the particulate absorbent gelling material into an aggregate,
treating the aggregated material with a suitable crosslinking
agent, compacting the treated aggregate to density it and form
a coherent mass, and then curing the compacted aggregate to
cause the crosslinking agent to react with the particulate
absorbent gelling material to form a composite, porous
absorbent. Such porous, absorbent macro structures are
disclosed, for example, in U.S. Patent 5,102,597.
d. Optional Fibrous ("Dusting"1 Laver
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. This layer can comprise all those materials
disclosed above as carrier materials for the storage layer.
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, because this "dusting" layer provides some additional
fluid-handling capabilities such as rapid wicking of fluid along
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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 such configuration 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 and indeed may
cause the desired flexibility to be unachievable.
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. Typically 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 core. These components can be incorporated in any
desired form but often are included as discrete, non-fibrous
particles.
Toosheet
The topsheet is compliant, soft feeling, and non-irritating to the
wearer's skin. As indicated above the topsheet also can be
elastically stretchable in one or two directions. Further, the
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topsheet is fluid pervious permitting fluids le.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 nonwoven materials; polymeric materials
such as apertured formed thermoplastic films, apertured plastic
films, and hydroformed thermoplastic films; porous foams;
reticulated foams; reticulated thermoplastic films; and
- thermoplastic scrims. Suitable woven and nonwoven 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.
Preferred topsheets for use in the present are selected from
high loft nonwoven topsheets and aperture formed film
topsheets. Apertured formed films are especially preferred for
the topsheet 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 body
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.
5,006,394. Particularly preferred microapetured formed film
topsheets are disclosed in U.S. patent 4,609,518 and U.S.
patent 4,629,643. The preferred topsheet for the present
invention is the formed film described in one or more of the
above patents and marketed on sanitary napkins by T~ 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
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liquid passage ways are also useful for 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 body surface of the formed film topsheet can be
hydrophilic so as to help liquid to transfer through 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 application number US 92/09227.
Alternatively, the body surface of the topsheet can be made
hydrophilic by treating it with a surfactant such as is described
in the above referenced U.S. 4,950,254.
Breathable backsheet
The breathable backsheet prevents the exudates absorbed and
contained in the absorbent core from wetting articles that
contact the sanitary napkin such as pants, pyjamas and
undergarments. The inner layer of the backsheet is a polymeric
film having apertures and the outer layer is a fibrous fabric
layer. Both layers are hydrophobic improving their liquid
retention characteristics without effecting their breathability.
The fibrous fabric layer of the outer layer preferably has a basis
weight of 10 to 100 g/m2- more preferably 15 to 30 g/m2. The
fibres can be made of any hydrophobic polymeric material usual
in the art of making fibrous fabric layers. Depending on the
circumstances of the ultimate use and manufacturing of the
breathable absorbent article fibres of polyethylene,
polypropylene, polyester, polyacetat or combinations thereof
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(infra- and inter-fibres combinations) have been found useful.
The fibres are preferably spunbonded, carded or melt blown.
The polymeric film can be provided with "micro-porous"
apertures or with larger apertures also referred to as "macro-
apertures" and is then typically a macroscopically expanded
apertured film. The distinction is the visible discernability of the
apertures and their ability to retain liquid.
Although the pattern as a whole of micro-apertured surface
aberrations of the apertured film in the backsheet of the articles
according to the present invention may be visible to the normal
naked eye i.e., a normal eye having 20/20 vision unaided by
any instrument that changes the apparent size or distance of an
object or otherwise alters the visual powers of the eye, when
the perpendicular distance between the viewer's eye and the
plane of the web is about 300 mm, the micro-apertured surface
aberrations comprising the pattern are not individually
discernible to the normal naked eye when the perpendicular
distance between the viewer's eye and the plane of the web is
about 300 mm.
In this regard, the individual micro-apertured surface aberrations
of the present invention preferably have a maximum cross-
sectional dimension of 500 micro meters or less, more
preferably 0.2 micro meters or less, most preferably 0.1 micro
meters or less, to satisfy the foregoing individual discernibility
criteria.
Typically the apertures in the macroscopically expanded
apertured film of the inner layer are larger than about 0.5 mm.
It is also possible to have combinations of micro-apertures and
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macro-apertures. For leakage prevention reasons it is however
preferred to have more micro-apertures than macro-apertures.
The apertured film according to the present invention can be
any of those well known in the art. This includes in particular,
but is not limited to those films disclosed in U.S. 3,929,135,
U.S. 4,151,240, U.S. 4,319,868, U.S. 4,324,426, U.S.
4,342,314, U.S. 4,591,523, and U.S. 4,609,518, U.S.
4,629,643, U.S. 5,158,819, U.S. 4,772,444.
A preferred apertured film comprised in the inner layer of the
breathable backsheet has funnel shaped apertures similar to
those described e. g. in US 3,929,135 for large apertures or
U.S. 4,629,643 for micro-apertures. The apertures maybe
circular or non-circular but have a cross sectional dimension at
one end of the funnel which is wider than the opening at the
other end of the funnel. The direction from the larger funnel
opening towards the smaller opening is of course parallel to the
first liquid transport direction. The apertured films can be made
of any material typical in the art but preferably is made of a
polymer similar to those used for the fibrous fabric layer.
The minimum hydraulic diameter of the apertures in the film
should be as small as possible while still providing sufficient gas
permeability without hydraulic blockage of the apertures. A
hydraulic diameter of as little as 2 to 5 micro meter for micro-
apertures and up to 700 micro meters for larger apertures has
been found possible in the context of the present invention.
Hydraulic diameter for non circular apertures is the diameter
that a circular aperture with the same cross section would
have. Diameter is always determined in the plane of smallest
cross section of an aperture.
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In particularly preferred embodiments of the present invention
the layers of the breathable backsheet are not joined to each
other in the area coextensive with the absorbent core.
Particularly inner and outer layers can be thermally laminated or
soldered to each other in only some spots for integrity reasons
but remain unattached across at least 50% of the area
coextensive with the absorbent core.
The novel multilayer breathable backsheets suggested in
simultaneously filed applications entitled "Breathable backsheet
design for disposable absorbent articles" and "Breathable dual
layer backsheet design .for disposable absorbent articles" both
assigned to The Procter and Gamble Company and designating
M.Depner and M. Divo as coinventors disclose particularly
useful backsheet embodiments which are also useful in the
context of the present invention. However it should be
understood that these multi layer backsheet designs are in
particular useful to improve flexibility if the addition of layers
does not increase stiffness. This can be achieved e.g. by
maintaining the amount of material while increasing the number
of layers i.e. several lighter/thinrier layers replacing a thicker
layer.
The ~antv-fastening-adhesive
The backsheet typically forms the garment facing surface on
which the panty fastening adhesive is placed.
According to the present invention it is important that the ratio
of theoretical adhesion surface to actual garment facing surface
is within the range according to the claims of the present
invention. The theoretical adhesion surface is defined by the
surface area inside the shortest possible endless line encircling
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the panty-fastening adhesive however without extending
beyond the periphery of the garment facing surface.
In addition the ratio of actual adhesive surface to garment
facing surface is in the range of 0.2 to 0.8. If there is for
example one rectangular adhesive area on the garment facing
surface then the theoretical adhesion surface and the actual
adhesive surface are identical, this can be seen in Figure 1
where the adhesive 22 is indicated by hatching. The encircling
line 26 results in a theoretical adhesion surface 24 identical to
the surface covered by the adhesive 22. For absorbent articles
having protective side flaps Figure 2 shows that the three
adhesive areas 22 are smaller in surface area than the
theoretical adhesion surface 24 encircled by line 26. If the
backsheet is elastically stretchable the adhesive surfaces are
measured on the unstretched backsheet prior to initial
stretching thereof.
Panty-fastening-adhesives can comprise any adhesive or glue
used in the art for such purposes with pressure-sensitive
adhesives being preferred. Suitable non-extensible adhesives
are Century A-305-IV manufactured by the Century Adhesives
Corporation, Instant Lock 34-2823 manufactured by the
National Starch Company , 3 Sigma 3153 manufactured by 3
Sigma, and Fuller H-2238ZP manufactured by the H.B. Fuller
Co. Suitable adhesive fasteners are also described in U.S.
Patent 4, 917, 697.
In order to maintain to breathability provided by the backsheet
according to the present invention it is important that the panty
fastening adhesive does not close or clog the apertures in the
garment facing side of the backsheet. For this purpose it is
possible to use an adhesive in such a pattern to only seal off a
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fraction of the apertures such that no more than 80% of the
actual garment facing surface is covered by adhesive. On the
other hand 20°~ adhesive coverage has been found necessary
to provide the benefit of proper attachment to the
undergarment of the breathable absorbent article.
Therefore, preferably the panty fastening adhesive is applied in
intermittent patterns such as for example intermittent dots,
intermittent strips, random or designed filamentary patternslike
spirals to permit the sanitary napkin to remain breathable.
In addition, other types of fasteners can be used instead of , or
in addition to adhesives. These other types of fasteners are
arranged in patterns similar to those of the adhesive. Such
fasteners include, but are not limited to conventional VELCRO
hook material or similar fasteners.
The protective side flaps can have optional fasteners thereon
for additional security. The optional protective side flap
fasteners can be any of the types of fastening materials herein
above. The fasteners assist the protective side flaps in staying
in position after they are wrapped around the edges of the
_ crotch surface of the protective side flaps.
Prior to use of the absorbent article the panty fastening
adhesive is typically protected from contamination and from
sticking to any surface where this is not desired by a protective
cover means such as a silicone coated release paper, a plastic
film or any other easily removable cover. The protective
covermeans can be provided as a single piece or in a multitude
of pieces e.g. to cover the individual adhesive areas.
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The procedure for measuring the flexibility/drapability of the
absorbent article is as follows:
REFERENCE
ASTM Method D1388-64: Standard Methods for Test for
Stiffness of Fabrics (modified as described herein).
PRINCIPLE
This test is based on the cantilever beam principle. The distance
a strip of sample can be extended beyond a flat platform before
it bends through a 41.5° angle is measured. The inter-action
between sample weight and sample stiffness measured as the
sample bends or drapes under its own weight through the given
angle under specified test conditions is used to calculate the
Flexibility/Drapability.
GENERAL COMMENTS
The flexibility test is only one way of measuring a sample's
flexibility and is believed to be one of the components which
users of absorbent articles often refer to as softness. This
measurement method should be followed as closely as possible
and should not be confused with the multidirectional flexibility
described in US 5,009,653. Even so testing of samples in only
the longitudinal direction is described and necessary for the
present invention it is also possible for very wide or
exceptionally flexible articles to measure flexibility in the
transverse direction.
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In general, a single sample strip should be tested only ne time.
The two sides of the sample should be tested on different
sample strips. Likewise, sample strips for use in this test must
be very carefully handled to prevent folds, wrinkles, bends, etc.
This test is intended to be used on articles before they have
been folded or bent for packaging by the manufacturer. If the
sample is placed by the manufacturer in a folded configuration,
it should be gently unfolded for the test. If only folded articles
are available, the Flexibility/Drapability can be approximated by
measuring a sample taken from between the fold lines. The test
should be used on complete samples, i.e. with all layers
having the same shape extending to the complete sample
surface and fully glued together. For each sample four different
strips with topsheet up and four different strips with topsheet
down should be measured. Samples should be measured in
longitudinal direction.
To note for relative stiff absorbent articles measurements even
in longitudinal direction may not be obtainable due to the
sample length being insufficient for bending through 41.5°.
APPARATUS
Cantilever Drape Stiffness-Tester Type SDL 0038 SDL
International
Obtain form Carl von GehIen/Germany
(Tel.:
02168/2910; Fax 02168/24570)
1-inch Wide Cutter Double edge cutter, 25.4 mm wide ( 1
inch)
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Conditioned Room A room conditioned to 21.7°C - 23.9°C,
50 % ~ 2 % Relative Humidity
Talcum Powder
Zerostat Anti-Static To eliminate static charge on the
drape Pistol (optional) tester and/or tissue. Distributed
in the
USA by Discwasher, Inc., Columbia,
MO 65201. May be obtained from
Morgan Instruments, Inc., P.O. Box
46442, 113 Circle Freeway Dr.,
Cincinnati, OH 45246. Morgan
Catalog No. 70-35-00. Also available
from record shops and photographic
supply stores. Use of this pistol is an
approved way to remove-static
charges for this test. Never use fabric
softener to remove static charge from
a drape test. Operate the Anti-Static
Pistol according to the manufacturer's
instructions.
SAMPLE PREPARATION
The samples should be placed in an area of the room permitting
maximum recirculation of air and maximising equilibration with
the humidity and temperature conditions.
1. Cut 8 samples using a 1-inch wide cutter. The sample
strip has to be cut lengthwise from the center of the
absorbent article to be rectangular without crimp. Usual
sample dimensions for measurements are 2.54 cm x 14.0
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cm = 35.56 cm2. The samples may be shorter but must
comprise
absorbent material throughout.
2. Remove the release paper and weight the sample (mg).
Round the weight to the nearest 1 mg.
3. Carefully powder the PFA with the minimum amount of
talcum sufficient to avoid sticking. Blow out the
remaining talcum from the sample.
4. Weight the sample strip with talcum (mg). Round the
weight to the nearest 1 mg.
5. For each sample calculate the basis weight of the sample
based on weight measurement with and without talcum
and the actual surface area of the sample.
Discard the sample if its weight increased more than 2.0
mg/cm2 after adding the talcum.
INSTRUMENT OPERATION
Drape-tester should be placed on a bench directly in front of the
operator. It is important that the bench is relatively free of
vibration, that there is no air flow during the measurement and
that the bench is free of draft.
The operator may either sit or stand in front of the tester while
it is being used. Then the operator has to chose his position so
that looking in the mirror of the tester he sees the front
reference line covering the back reference line. If he sees only
one line he has the right position for the measurement.
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The tester shall:
1. Remove the sample slide bar from the sample slot on the
top platform of the drape tester.
2. Place the sample trip on the sample slot so that one end
of the strip is exactly even with the vertical edge of the
tester. The strip should be placed as close as possible to
the side rail of the sample slot but not touching it.
3. Place the sample slide bar on top of the sample strip so
that its front edge is aligned with the edge of the sample strip
in the tester and so that it touches the side rail. The sample
slide bar must be carefully placed so that the sample is
not wrinkled or moved forward.
4. Pulling from its free edge and using very light, gentle
pressure, move the slide bar slowly and steadily forward
with a speed of about 1 cm/s. As the slide bar moves
forward, the sample should move at an equal slow
rate. As the slide bar and the sample strip project
over the edge of the tester, the sample strip will begin to
bend or drape downward. Stop moving the slide bar the
instant when the leading edge of the sample strip falls level
with the 41.5 ° reference lines.
If the sample has a tendency to twist, take the reference
point at the center of its leading edge. Samples which
twist more than 45° cannot be measured. Samples can only be
measured if the sample length is at least 0.5 cm longer
than the overhang length. For non measurable samples, the
overhang length can be measured only if a long enough
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strip can be obtained which is at least 0.5 cm longer than
the overhang length.
5. Mark the overhang length on top of the sample
(Overhang length:distance from the start point of movement
until the point where the sample bends through 41.5°?.
6. Measure the overhang length in cm with a ruler. Read the
overhang length to the nearest 1 mm.
CALCULATION
The equation used to express Flexibility/Drapability according to
the present invention is as follows:
G = WL3
Where G equals the Flexibility/Drapability, W is the sample basis
weight including talcum in milligrams/cm2, and L is the length
of the overhang in cm. Results are expressed in milligrams x cm
or grams x cm.
Thickness measurement
The thickness should always be measured at the thickest
possible place, usually in the center of the absorbent article. For
convenience the measurement is conducted on the absorbent
article inclusive any protective cover means present. The article
should be reconditioned at 50 % humidity and 23° C for two
hours within its usual package and be removed not more than
five minutes prior to the measurement.
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The thickness is measured with a micrometer gauge having a
range of 0 to 30 mm and capable of plus minus 0.5 mm
tolerance. The gauge must not be spring loaded and should
have a foot moving downwards under gravity. The micrometer
foot has a diameter of 40 mm and is loaded with a 80 gram
weight. The measurement is taken between 5 and 10 seconds
after the foot has been lowed to come into contact with the
absorbent article. Measurements should be taken often enough
to allow statistical analysis to determine average thickness
within a sigma of plus minus 0.1 mm. A detailed description of
the thickness measurement can also be found in US-Patent 5,
009, 653.
