Note: Descriptions are shown in the official language in which they were submitted.
2133299
-- 1 --
TITLE: TRI-DIMENSIONAL NON-WOVEN FABRIC FOR U8E AS A
SRIN-CONTACTING COVER LAYER OF A SANITARY
ABSORBENT ARTICLE, A NETHOD FOR MANUFACTURING
THE NON-WOVEN FABRIC AND A SANITARY ARTICLE
UTILIZING SANE
FIELD OF THE lNv~..lON
The present invention relates to a non-woven fabric
particularly well-suited for use as a skin-contacting
cover layer of a sanitary absorbent article such as a
sanitary napkin, a diaper, a urinary pad, an adult brief,
a wound dressing or a nursing pad, among others. In a
most preferred embodiment, the non-woven fabric has the
ability of guiding a discharge of body exudate to disperse
longitudinally on the absorbent article surface to reduce
the potential risk of failure as a result of overflow
leakage at the sides. In addition, the non-woven fabric
is capable of dynamically inducing body exudate to migrate
therethrough in order to reduce the residence time of the
liquid discharge on the cover layer of the absorbent
article. The invention also extends to a method for
manufacturing the non-woven fabric and to a sanitary
absorbent article utilizing same. Furthermore, the
invention extends to a sanitary absorbent article
utilizing a skin-contacting cover layer united in an
2133299
-- 2
intimate liquid-communicative relationship with the
absorbent core substantially without any adhesive.
BACRGROUND OF THE lNv~.,lON
s
The ability of a sanitary absorbent article to
efficiently capture and retain a discharge of body exudate
is the result of a cooperative relationship between a
plurality of superposed layers of porous material having
different liquid-absorbency characteristics. In its
simplest form, a laminated absorbent article comprises an
absorbent core whose function is to permanently trap the
liquid discharge, which is overlaid by a liquid-permeable
cover layer that in use contacts the skin of the wearer.
Ideally, a cover layer should be able to manifest a very
high liquid take-up rate in order to capture on contact a
liquid discharge. This feature is desirable for two
reasons. Firstly, a high liquid take-up rate reduces the
potential risk of failure due to liquid leaking past the
edges of the sanitary article and staining the wearer's
clothes. Secondly, the unpleasant sensation of wetness,
due to extended contact between free body exudate in the
process of being acquired by the cover layer and the skin,
is diminished.
In addition to the criteria expressed above, the
cover layer of a sanitary absorbent article should reduce
21332~9
as much as possible the undesirable wet-back phenomenon
which occurs when liquid captured in the absorbent core
migrates back to the skin-contacting surface of the cover
layer. The wet-back phenomenon is most likely to occur
when the sanitary absorbent article is saturated with
liquid and it is subjected to compression, such as when
the wearer adopts a seating posture.
In an attempt to reduce the possibility of wet-back,
attempts have been made in the past to design a cover
exhibiting unidirectional flow characteristics. More
particularly, such cover layer is capable of efficiently
transferring liquid toward the absorbent core, however it
manifests a higher resistance to liquid migration in the
opposite direction. Those principles have been embodied
in a sanitary napkin commercialized by Johnson & Johnson
under the trademark STAYFREE.
Another area of interest which greatly influences the
functionality of a cover layer is the quality of the
interface between the cover layer and the absorbent core.
To achieve the objective of an intimate liquid-
communicative relationship between these components, the
prior art suggest to use an adhesive to bond the cover
layer to the absorbent core at a multitude of pin-point
sites dispersed over the entire interface cover/core.
Although this solution has some merits, it raises the
21332~9
production costs of the sanitary absorbent article.
Furthermore, the adhesive sites, however small, may create
localized barriers to the migration of liquid toward the
absorbent core.
s
As a result of technology shortcomings and cost
considerations the materials currently available for cover
layer usage rarely combine all the desirable attributes
discussed above. However, the technology in this field is
far from having reached a state of maturity. Hence,
significant developments are expected that could lead to
materials that are better performers while being
inexpensive to produce.
OBJECTS OF THE lNV~. ~ lON
A general object of this invention is a non-woven
fabric having enhanced liquid-absorbency characteristics
(hereinafter the term "liquid-absorbent" and "liquid-
absorbency" shall only refer to the ability of a porousbody to take-up liquid, irrespective of how liquid-
retentive the body is. For example, the cover layer of a
sanitary absorbent article will be considered liquid-
absorbent although the liquid merely transits through it
before being trapped by the absorbent core of the sanitary
article) particularly well-suited for use as a skin-
contacting cover layer of a sanitary absorbent article.
21332~
A more specific object of the invention is a non-
woven fabric capable of dynamically inducing body exudate
discharged thereon to migrate through the non-woven fabric
when its fibrous network is subjected to repeated, non-
destructive deformations.
Another object of the invention is a method for
manufacturing the aforesaid non-woven fabric.
A further object of the invention is a novel sanitary
absorbent article having a skin-contracting cover layer
which is capable of directing a discharge of body exudate
to disperse longitudinally over the absorbent article.
Another object of the invention is a novel sanitary
absorbing article in which the cover layer and the
absorbent core are united substantially without adhesive,
yet being in an intimate-liquid communicative
relationship.
gUMMARY OF THE lNV ~ lON
As embodied and broadly described herein, the
invention provides a tri-dimensional non-woven fabric
comprising fibers in mechanical engagement forming a
unitary foraminous network, said network including:
21332~9
-- 6 --
- a multitude of discrete protuberant fiber packings
protruding out of a plane of said unitary foraminous
network, fibers in said packings being bonded to one
another to consolidate said network;
- a plurality of high fiber density areas in said
plane;
- a plurality of low fiber density areas (herein the
expressions "high fiber density area" and "low fiber
density area" are relative terms with no reference to any
absolute fiber density values, used to indicate that in
the former case a greater number of fibers per unit volume
are present than in the latter case) in said plane, fibers
in said low fiber density areas being capable of moving
one relative to the other when said non-woven fabric is
deformed in order to dynamically induce liquid discharged
on said fabric to migrate through said low fiber density
areas.
This non-woven fabric is particularly well-suited for
use as a skin-contacting cover layer of a sanitary
absorbent article.
In a preferred embodiment, the fiber distribution
profile in the plane of the non-woven fabric is such as to
provide a pattern of elongated and alternating high and
low fiber density areas. Such fiber distribution profile
has the ability of directing liquid discharged on the non-
213329~
-- 7
woven fabric to flow along a preferential direction, the
longitudinal axis of the sanitary article, for instance.
This feature reduces the risks of failure of the sanitary
article as a result of liquid leaking past its sides.
The ability of the fibers in the low fiber density
areas to move one relative to the other disrupts the
integrity of the surface tension developed between the
liquid and the fibrous network. Accordingly, the
residence time of a liquid discharge on the non-woven
fabric can be reduced. This is particularly true for
highly viscous body exudate. In practice, the inter-
fiber motion observed to facilitate the liquid migration
through the fabric is obtained when the fibrous network is
locally distorted either in the machine or in the cross-
directions. This deformation occurs when bending or
twisting movements are imposed on the sanitary article by
the wearer performing some sort of physical activity, such
as walking or otherwise shifting the position of the legs.
The protuberant fiber packings which engage the
absorbent core of the sanitary absorbent product, act to
some degree as small spacers which in use reduce the
possibility of wet-back.
In a most preferred embodiment, the tri-dimensional
non-woven fabric in accordance with the invention includes
2133~93
-- 8
rectilinear low fiber density areas alternating with high
fiber density areas which are also rectilinear. The
protuberant fiber packings originate solely from the high
density areas and are located only on one side of the
fabric in order to maintain the other side which forms the
skin-contacting surface of the sanitary absorbent article,
smooth, soft and comfortable to the wearer. To increase
the resistance of the fibrous network to a loss of
integrity in use, the non-woven fabric is treated with
binder. Advantageously, the binder substance is applied
at selected areas of the fibrous network, such as to the
protuberant fiber packings, in order to preserve the
inter-fiber movement ability in the low fiber density
areas. The selective binder treatment also allows to
preserve the softness of the skin-contacting surface of
the non-woven fabric by preventing substantial amounts of
binder to reach that surface and form a hard crust
thereon.
To enhance the hydrophilicity of the non-woven
fabric, it may be treated with wetting agent. Most
preferably, the wetting agent is applied concurrently with
the binder and it is also concentrated in the protuberant
fiber packings.
The non-woven fabric in accordance with the invention
can be manufacturing from a plurality of different fibers,
2133299
such as polyester, acrylic, polypropylene, rayon and
mixtures thereof, among others. Preferably the fibers
have a denier in the range from about 1 to about 5. The
density of the non-woven fabric is preferably in the range
S from about O.OlS grams per cubic centimeter (g/cc) to
about O.OS5 g/cc, and most preferably of about 0.035
g/cc.
As embodied and broadly described herein, the
invention also provides a method for manufacturing a tri-
dimensional non-woven fabric comprising fibers in
mechanical engagement forming a generally planar unitary
foraminous network, said network including:
- a multitude of discrete protuberant fiber packings
lS protruding out of a plane of said unitary foraminous
network;
- a plurality of high fiber density areas in said
plane;
- a plurality of low fiber density areas in said
plane, said method including the steps of:
a) jetting fluid against a web of loosely
associated fibers which are capable of moving one relative
to the other under the influence of applied fluid forces
to mechanically entangle said loosely associated fibers
2S and form said unitary foraminous network; and
b) bonding fibers in said packings to one
another to consolidate said network, said method being
2133293
-- 10 --
completed substantially without bonding fibers in said low
fiber density areas to one another for allowing fibers in
said low fiber density areas to move relative to one
another when said fabric is deformed in order to
dynamically induce liquid discharged on said fabric to
migrate through said low fiber density areas.
In a most preferred embodiment, the non-woven fabric
in accordance with the invention is manufactured by the
well-known ROSEBUD hydro-entanglement process which
consists of confining the fibrous starting material
between an apertured rotating drum and a foraminous
screen-belt, and directing water jets at the fibrous
material from the outside of the drum. The resulting
lS fluid forces entangle the fibers into a pattern of
alternating elongated high and low density areas lying in
a common plane from which project the protuberant fiber
packings. The packings distribution profile is determined
by the pattern of apertures on the drum.
Downstream of the fiber entangling station, the non-
woven fabric is treated with binder and wetting agent.
Most preferably, the binder and the wetting agent are in
physical admixture and are applied to the non-woven fabric
with a binder applicator roll contacting only the fiber
packings in order to achieve the selective binder
deposition discussed above.
213329~
-- 11 --
As embodied and broadly described herein, the
invention also provides a sanitary absorbent article,
comprising:
- an absorbent core;
- a skin-contacting cover layer in liquid-
communicative relationship with said absorbent core, said
skin-contacting cover layer comprising a non-woven fabric
having adjoining high and low fiber density areas, said
low density areas being elongated and extending generally
along a longitudinal axis of said absorbent article,
whereby liquid discharged on said skin-contacting cover
layer is guided to flow in said low fiber density areas
longitudinally on said absorbent article.
As embodied and broadly described herein, the
invention further provides a sanitary absorbent article,
comprising:
- an absorbent layer made of soft particulate (for
the purpose of this specification "particle" means a
small amount of material without limitation of shape. A
fiber that is characterised by a geometrical extension
along a preferential direction will be considered a
particle. Hence, "particulate material" covers a material
made of fibers, particles having non-fibrous identity or
a combination of both) material;
- a skin-contacting, liquid-permeable cover layer
including a plurality of downwardly projecting fiber
2133299
- 12 -
packings, said fiber packings mechanically engaging said
absorbent layer and constituting means for mechanically
bonding said skin-contacting cover layer and said
absorbent layer in a liquid-communicative relationship.
s
The ability of a non-woven, skin-contacting cover
layer to bond to the absorbent layer solely due to the
mechanical engagement of the protuberant fiber packings
with the particles of the absorbent layer is particularly
advantageous over the traditional approach which utilizes
adhesives because it allows to simplify the manufacturing
process of the sanitary absorbent product. Furthermore,
this method avoids the undesirable formation of localized
pin-point liquid barriers at the interface between the
cover/absorbent layer, due to the presence of adhesive.
This method requires soft absorbent layers i.e.
layers of material which is sufficiently compressible such
that when the non-woven fabric described earlier is
applied against the absorbent layer under a pressure of
0.5 pounds per square inch (psi) the protuberant fiber
packings that face the absorbent layer are substantially
embedded in the particulate material. An example of
"soft" absorbent layer as per the above definition is pulp
fluff. This material provides at its surface a relatively
large number of loosely entangled fibers which can
mechanically interlock with the protuberant fiber packings
~1332~9
of the cover in order to create a comparatively strong
bond. On the other hand, materials such as compacted
sphagnum moss may not work because the protuberant fiber
packings cannot easily penetrate the dense sphagnum moss
structure.
BRIEF DESCRIPTION OF THE DRAWINGS
- Figure 1 is a highly enlarged perspective view of
a non-woven fabric in accordance with the present
invention;
- Figure 2 is a top plan view of the non-woven fabric
shown in Figure 1;
- Figure 3 is a highly enlarged cross-sectional view
of a sanitary absorbent article which utilizes the non-
woven fabric shown in Figures 1 and 2 as a skin-contacting
cover layer;
- Figure 4 is a perspective schematical view of a
fiber-entangling station for manufacturing the non-woven
fabric in accordance with the invention;
- Figure 5 is a fragmentary, enlarged cross-sectional
view of the fiber entangling station shown in Figure 4;
2133299
- 14 -
- Figure 6 is a fragmentary, yet further enlarged
perspective view of the fiber entangling station shown in
Figures 4 and 5, illustrating the mechanism of fabric
formation;;
- Figure 7 is a schematical view of a binder
applicator station for treating selected areas of the non-
woven fabric with binder;
- Figure 8 is an elevational view of a binder
applicator roll of the binder applicator station shown in
Figure 7; and
- Figure 9 is a photomicrograph of the non-woven
fabric in accordance with the invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
Figures 1, 2 and 9 of the annexed drawings illustrate
in detail the structure of a three-dimensional non-woven
fabric in accordance with the invention which is
comprehensively designated by the reference numeral 10.
The non-woven fabric 10 has highly desirable liquid-
absorption properties making the fabric particularly well-
suited for use as a skin-contacting cover layer of a
sanitary absorbent article such as a sanitary napkin, a
- 15 _ 2133299
diaper, a urinary pad, an adult brief a wound dressing and
a nursing pad, among others.
The fibrous network of the non-woven fabric 10
displays randomly oriented and mechanically interlocked
fibers which are grouped in band-shaped, high fiber
density areas 12 which are generally parallel with one
another and extend in the machine direction of the non-
woven fabric 10. The high-fiber density areas 12 are
transversely spaced apart from one another defining
therebetween narrow strip-like, low fiber density areas
14. The resulting pattern of alternating high and low
fiber density areas 12 and 14 provides a planar multi-
channel structure capable of directing a liquid discharge
on the non-woven fabric 10 to disperse on the fabric
surface in a preferential direction, as it will be
subsequently discussed in detail.
From the high fiber density areas 12 project
equidistant fiber packings 16 which are individually
constituted by an aggregate of randomly oriented and
mechanically interlocked fibers. Collectively, the fiber
packings 16 form a staggered pattern and provide the
three-dimensional character of the non-woven fabric 10.
In order to increase the resistance of the non-woven
fabric 10, it is treated with binder which consolidates
213329~
- 16 -
the fibrous network. The binder substance, when cured,
establishes bonds between adjacent fibers and prevents
them from moving one relative to the other. Accordingly,
the tenacity of the non-woven fabric 10 increases by
virtue of a reduction in the inter-fiber displacement when
destructive forces act on the non-woven fabric.
An important aspect of the invention resides in that
the binder is applied only at selected areas of the non-
woven fabric 10, namely on the fiber packings 16 for thepurpose of allowing a limited inter-fiber displacement in
the low fiber density areas 16 when the non-woven fabric
10 is folded, stretched or otherwise distorted, in a non-
destructive fashion. In contrast, the binder precludes
any inter-fiber displacement in the fiber packings 16.
The limited freedom of movement that the fibers in
the low fiber density area 16 acquire as a result of the
selective binder deposition is another important
characteristic of the invention. This feature increases
the liquid take-up rate of the non-woven fabric by
dynamically inducing the liquid to penetrate in the
fibrous network when the latter is subjected to repeated
deformations by the action of external forces. This
characteristic will be discussed in detail during the
description of possible applications of the non-woven
213~23g
- 17 -
fabric 10 as a cover layer for a sanitary napkin, which is
found later in this specification.
Figures 4, 5 and 6 of the annexed drawings illustrate
with an increasing level of detail a fiber-entangling
station which generates the fibrous network depicted in
Figures 1 and 2. The fiber-entangling station, identified
comprehensively by the reference numeral 18, comprises a
hollow metallic drum 20 mounted for rotation about its
longitudinal axis into a suitable cradle (not shown). A
drive mechanism (not shown) is provided to rotate the drum
20 in the counter-clockwise direction, as shown by the
arrows 22 at a controlled speed. The drive mechanism is
of a well-known construction and does not form part of
this invention. The shell of the drum 20 is provided on
its entire surface with circular apertures 24 arranged
according to a staggered pattern. The apertures 24 are
separated from one another by solid land areas 26
corresponding to closed or impermeable zones of the drum
20.
The fiber-entangling station 18 also comprises an
endless screen belt 28 which is set in a partially
overlapping relationship with the drum 20 by means of
guide rollers 30. Support rollers 32 are positioned at
the corners of an imaginary rectangle and act, in
conjunction with guide rollers 30, to tension and
21~329~
- 18 -
establish a path of travel for the screen belt 28. One or
more of the rollers 30 or 32 are drive rollers for
advancing the belt 28 in unison with the drum 20.
A manifolds 34 is mounted outside the structure
formed by the screen belt 28 and the hollow perforated
drum 20 to create liquid streams for rearranging loosely
associated fibers confined between the drum 20 and the
screen belt 28 into the unitary fibrous network 10. The
manifold 34 includes a metallic casing 38 with a concave
wall 40 which faces the screen belt/drum and has a
curvature corresponding to the curvature of the drum
shell. On the concave wall 40 are mounted a series of
nozzles 42 in liquid communication with the casing 38 so
as to create a plurality of fluid streams impinging on the
screen belt 28. The concave shape of the wall 40 permits
the orientation of each nozzle 42 into a radial direction
relative to the screen belt/drum and also to position the
extremity of each nozzle at exactly the same distance from
the screen belt 28.
The nozzles 42 are grouped into four parallel rows,
each row extending along the longitudinal axis of the drum
20. The nozzles 42 produce fluid streams, preferably
water under the form of flat cones lying in respective
imaginary horizontal planes which contain the drum
longitudinal axis, the nozzles in the same row being
213329~
-- 19 --
spaced apart from one another by a distance so that a
certain overlap occurs between streams from adjacent
nozzles immediately in front of the screen belt 28. The
gap between successive nozzle rows is relatively small so
that for all practical purposes, the individual fluid
streams produced by the nozzles 42 are united into a
common fluid front acting on the screen belt 28 and the
drum 20.
The operation of the fiber entangling station 18 is
as follows. A web 44 of starting material, containing
loosely associated fibers, thus capable of movement one
relative to the other, is supplied in a continuous sheet
form from a supply station (not shown) that will also card
the fibers in the machine direction, and is deposited over
the horizontally extending forward run of the screen belt
28 preceding the section of the screen belt which loops
the hollow drum 20. Fibers of material in the group
comprising polyester, acrylic, polypropylene, rayon and
mixtures thereof have been found satisfactory. The web 44
is pulled between the hollow drum 20 and the screen belt
28, which form in combination a fluid permeable, web
confining and supporting structure guiding and advancing
the web 44 through the water streams from the manifold 34
applying fluid forces to the web fibers to entangle them
and form a unitary network.
2133299
- 20 -
When the web 44 passes through the fluid treatment
zone the fibers in the area of the web 44 on which the
fluid front generated by the manifolds acts, are subjected
to the influence of fluid forces which cause the fibers to
migrate toward preferential positions, overcoming inter-
fiber friction, fiber to screen belt friction and fiber to
drum friction. The fibers leaving the treatment zone are
reoriented into a reticular network whose basic
configuration is dependent upon the drum/screen belt
combination.
Further details on the principle for
manufacturing a non-woven fabric by fluid entanglement can
be found in the prior art. At this end, the reader may
consider the following Canadian patents granted to Johnson
~ Johnson, USA which constitute references of interest to
the present subject. The subject matter of these patents
is incorporated herein by reference.
20 CANADIAN PATENT8 ISSUE DATES
915,398 November 28, 1972
915,397 November 28, 1972
915,398 November 28, 1972
915,399 November 28, 1972
- 21 _213 329 9
915,400 November 28, 1972
915,401 November 28, 1972
915,402 November 28, 1972
915,403 November 28, 1972
915,408 November 28, 1972
1,143,929 April 5, 1983
The non-woven fabric generated by the fiber
entangling station 18 is processed at a binder applicator
station, shown in Figures 7 and 8, which applies a
solution of binder to the non-woven fabric. The binder,
when cured, solidifies and consolidates the non-woven
fabric, increasing its resistance. Binders are
commercially available compounds and the selection of a
particular binder depends upon the desired characteristics
of the final product. The following binders have been
found satisfactory: vinyl ethylene, vinyl chloride, vinyl
acetate, vinyl acrylate, polyvinyl alcohol, polyvinyl
acetate, carboxylated polystyrene, polyacrylonitrile,
rubber polyethylene and mixtures thereof.
The binder applicator station, denoted
comprehensively by the reference numeral 46 comprises a
coating roll 48 having a lower end immersed in a binder
21~293
bath. A back-up roll 50 is provided above the roll 48 to
define therewith a nip through which the non-woven fabric
10 passes. As the roll 48 rotates, a thin film of binder
adheres thereto which is deposited on the non-woven fabric
10 through rolling contact therewith. A scraper blade 56
is provided to control the thickness of the binder film
adhering to the surface of the coating roll 48. A smooth-
surfaced coating roll 48 which achieve a uniform binder
deposition, which is acceptable for some applications.
However, it is preferred to apply the binder according to
a pattern of co-extensive lines which has the advantage of
sufficiently consolidating the non-woven fabric without
stiffening the fibrous network to the point where it
becomes uncomfortable to wear. To achieve the desired
binder deposition pattern, a coating roll having a relief
surface is required, the recessed areas of the relief
surface constituting the binder transfer surfaces. An
example of such roll is shown in Figure 8. The
circumferential surface of the roll is machined to form a
multitude of axially extending zig-zag grooves 52 which
are parallel to one another.
An important aspect of the binder treatment resides
in that the binder is applied on the surface of the non-
woven fabric which contains the protuberant fiber packings16. This is achieved by setting the orientation of the
non-woven fabric through the binder application station
21~32~9
- 23 -
46, whereby solely the fiber packings 16 engage the
coating roll 48.
In a most preferred embodiment, the binder applicator
station is also used as an agency for treating the non-
woven fabric with wetting agent in order to enhance its
hydrophilicity. The wetting agent is applied to the non-
woven fabric in physical admixture with the binder
solution. At this end, the solution containing the
selected binder and wetting agent is prepared and it is
supplied to the binder applicator station 46.
In a specific example, a fabric according to the
invention has been produced under the following process
conditions.
~luid-entangling station Parameters
starting material polye~ter fibers 3 denier
apertures 24 on drum Staggered patterD -
46 apertures per inch both ;D ~he ~;.. ' ' aDd the axial
directions - 30% open area
20Screen belt 28 24 ~trands per inch both ;D the machine and the transver~e
direction - 55 % open area
Manifold 34 four rows of Do~es 15-10-0~
fluid supply pressure ~30 pouDds per ~uare inch gage (p~ig)
2~33~99
- 24 -
The first numeral in the nozzle size refers to the
spread angle of the spray produced by the nozzle while the
second numeral is ten times the flow rate of the nozzle
expressed in U.S. gallons per minute at a pressure of 40
psig. The third numeral refers to tilt angle of the spray
relative a horizontal plane. Accordingly, a 15-10-00 size
means that the angle of the spray is 150, the nozzle flows
1.0 U.S. gallons per minute at 40 psig and the spray is
horizontally oriented.
Binder applicator station Parameters
Acrylic binder and Triton GR-5M surfact~mt as wetting
agent~ooth ~ ' ' by Union Carbide). The solution
Binder solution
hAs a surfact~mt contents (solids) which is less than 1%.
width - 0.46 rmn
depth - 0.46 rnrn
15Binder transfer grooves on
6 grooves per inch ( ~ . ' . ' direction)
roll 48
Direction of rotation of Opposite to direction of ~ _ of the non-woven f~bric
roll 48
The non-woven fabric generated by the fiber
entangling station 18 under the above process conditions
is characterized by a basis weight of about 28 g/m2, a
thickness of 0.74 mm measured at a pressure of 3.45 Kpa
and a density of 0.035 g/cc. The protuberances 16 project
- 25 _ 2133~9
from the plane of the non-woven fabric to a height of
approximately 1.575 mm and the number of protuberances per
square inch is of 43. The approximate transverse
dimensions of the high and low fiber density areas 12 and
14 is of 2 mm.
This non-woven fabric is particularly suitable for
manufacturing cover layers of disposable sanitary
articles, such as sanitary napkins. Figure 3 of the
annexed drawings illustrates a sanitary napkin
construction 58 comprising an absorbent core 60 made of
pulp fluff and a body-contacting cover layer 62 made from
the non-woven fabric 10. Note that the protuberances 16
face the pulp fluff material and they are embedded therein
to an appreciable degree, by virtue of the high
compressibility of the absorbent core. Yet, the main body
of the cover 62 that contains the high and low fiber
density areas 12 and 14 is only in gentle contact with the
absorbent core 60 since the protuberances 16 act as
spacers to some degree. This arrangement manifests a
significant reduction in wet-back, particulary for highly
viscous menses.
Without the intent of being bound by a specific
theory, the present inventor explains the observed wet
back reduction by the ability of the protuberances 16 to
act as spacers and reduce the incidence of firm contact
213329~
- 26 -
between the main body of the cover 62 and the absorbent
core 60. As a consequence, a path of higher resistance is
developed preventing liquid in the absorbent core 60 from
freely migrating back onto the skin-contacting surface of
the cover 62. At the same time the protuberances 16
constitute individual pathways, allowing liquid discharged
on the cover 62 to quickly migrate within the absorbent
core 60. The surfactant contained in the protuberances 16
enhances this lead-in action. In short, the cover 62
behaves as a non-linear liquid path, allowing
significantly more liquid to flow toward the absorbent
core 60 than in the opposite direction.
The ability of the cover 62 to quickly acquire a
liquid discharge is enhanced by the relative mobility of
the fibers in the low fiber density areas 14. For,
instance, by imparting a bending or twisting movement on
the sanitary napkin 10 (this deformation occurs when the
wearer is performing some sort of physical activity, such
as walking or otherwise shifting the position of the legs)
the fibers in the areas 14 are caused to shift position
and as a consequence, they disrupt the surface tension
developed between the menstrual liquid and the cover 62.
Hence, the liquid is dynamically induced to penetrate the
cover 62.
21~3299
- 27 -
Another interesting advantage of the cover 62 is the
high frictional resistance developed by the protuberances
16 against the absorbent core 60 that enables to assemble
the sanitary napkin 58 free of adhesive at the interface
cover/absorbent core. The capability of the cover 62 to
grip the absorbent core 60, or any other absorbent layer,
such as a transfer layer that may be used between the
cover 62 and the core 60, is observable when the absorbent
network engaging the cover 60 is soft and compressible.
Most preferably, the absorbent network contains a
significant amount of fibers capable of mechanically
entangling themselves around the protuberances 16. Pulp
fluff is an example of material that works well.
The advantage of eliminating or at least
substantially reducing the adhesive at the interface
cover/absorbent layer is two fold. First the
manufacturing cost of the product is reduced. Second, the
pin-point adhesive zones that constitute individual liquid
barriers are eliminated to further enhance the liquid
take-up rate of the sanitary napkin 58.
The improvement in terms of adherence of the non-
woven fabric 10 against a pulp fluff absorbent layer is
demonstrated by a test that consists of measuring the
horizontal force required to cause a displacement of the
non-woven fabric sample over the absorbent core of a
2133299
- 28 -
sanitary napkin commercialized by Johnson & Johnson under
the name STAYFREE MAXI. The test procedure consists of
urging the sample against the absorbent core under
different pressures and observing the force required to
displace the sample for each pressure level. The sample
is co-extensive with the absorbent core and the pressure
is applied uniformly thereon. The test data is summarized
in the following table.
Horizontal pulling force (grams)
SamplePres ure 0.05PressurePressure 0.51
p5i 0. 125 psi psi
Invention 310 478 1575
Control* 293 460 1357
Difference(%) 5.8 3.9 16.1
~ The control is the cover layer of a sanitary napk_n commercialize~
by Johnson & Johnson under the name STAYFREE MAXI.
It is apparent that the non-woven fabric in
accordance with the invention exhibits a significant
improvement in terms of adherence with the pulp fluff
absorbent core.
The process for assembling the sanitary napkin 58
differs from the prior art by the omission of the adhesive
application step between the cover and the absorbent core.
In the present case, the cover 62 is retained to the
21332~9
- 29 -
napkin structure by thermally or adhesively bonding the
marginal portions of the cover to adjoining marginal
portions of the barrier layer so as to totally enclose the
absorbent system which may be a single or a multi-layered
structure. It is preferable to complete the manufacturing
process by tightly compressing the cover 62 against the
underlying absorbent layer to cause the protuberances 16
to penetrate that layer for better mechanical engagement.
Applications of the product and methods of the
present invention for sanitary and other health-care uses
can be accomplished by any sanitary protection,
incontinence, medical and absorbent methods and techniques
as are presently or prospectively known to those skilled
in the art. Thus, it is intended that the present
application covers the modifications and variations of
this invention provided that they come within the scope of
the appended claims and their equivalents.
