Note: Descriptions are shown in the official language in which they were submitted.
WO 94/02092 PCT/US93/06179
'~ ~ ~ ~ ~ ...
SANITARY NAPKIN HAVING A CENTRAL ACQUISITION ZONE
Field of the invention
The invention relates to sanitary napkin comprising a
liquid pervious topsheet, a liquid impervious backsheet and
an absorbent core interposed between the topsheet and the
backsheet, the core comprising two longitudinal sides, a
centeral acquisition zone, two side zones that are located
between the acquisition zone and the longitudinal sides,
WO 94/02092 ~ ~ ~ ~ ~ ~ PCT/US93/06179
w 2
the core further comprising a layer containing absorbent
gelling material, the concentration of absorbent gelling
material in the acquisition zone of the core being lower
than the concentration of absorbent gelling material in the
side zones.
Background of the invention
Such an absorbent article is known from US-A-4,988,345.
In this patent an absorbent article is described in which
the absorbent core comprises a lower liquid handling layer
of relatively low density and an upper liquid storage layer
comprising absorbent gelling materials. The upper liquid
storage layer has a basis weight of between 0.01 and 0.1
g/cm2 and can contain up to 60~ by weight of absorbent
gelling material. The liquid storage layer is provided with
acquisition apertures for transmission of liquids to the
underlying liquid handling layer, in which layer transport
of fluids can take place in a longitudinal and lateral
direction of the absorbent article. The liquid handling
layer has a void volume of over 80~, a basis weight of
between 15 to 75 g/sq yard, and can comprise synthetic foam
materials or synthetic fibers. The fluids that are
transmitted through an acquisition aperture in the liquid
storage layer, are transported in the liquid handling layer
to portions of the liquid storage layer remote from the
WO 94/02092 ~ ~ ~ ~ ~ ~ ~ 3 PCT/US93/06179
acquisition apertures. Due to the difference in capillary
size between the storage layer and the liquid handling
layer, the liquid is drawn out of the latter which is
thereby emptied and can transport subsequent gushes of body
fluids .
Since the liquid handling layer is relatively broad,
lateral spread of liquids towards the sides of the
absorbent article can relatively easily take place. The
purpose of the known liquid handling layer is to improve
the distribution of large quantities of liquid away from
the acquisition apertures and to increase the absorption
speed without gel blocking of the absorbent material taking
place. Especially in narrow absorbent articles, too large a
lateral spread of liquids can however lead to undesired
side soiling.
From the American patent US-A-5,009,653 a sanitary napkin
is known having an absorbent core that is formed of a layer
of hydrogel material interposed between two layers of air-
laid tissue sheets. The core is covered by a wet-laid
tissue which serves to improve wicking of the discharged
body fluids over the core, so that a more efficient use of
the hydrogel material is made. However, next to improving
liquid migration in the longitudinal direction of the
sanitary napkin, liquid migration in the lateral direction
also takes place, so that side soiling remains possible.
It is an object of an aspect of the invention to provide an absorbent
article of relatively small caliper that has a good liquid distribution
capacity
and is of a relatively simple structure.
It is an object of an aspect of the invention to provide for an absorbent
article having low side soiling and a relatively high effective absorption
capacity.
It is an object of an aspect of the invention to provide an absorbent
article having a relatively high acquisition speed and is of relatively low
cost.
Summary of the Invention
Various aspects of the invention are as follows:
Sanitary napkin comprising a liquid pervious topsheet, a liquid
impervious backsheet and an absorbent core interposed between said
topsheet and said backsheet, said core comprising two longitudinal sides, a
central acquisition zone, two side zones that are located between said
acquisition zone and said longitudinal sides, said core further comprising a
layer containing absorbent gelling material, the concentration of absorbent
gelling material in said acquisition zone of said core being lower than the
concentration of absorbent gelling material in said side zones,
wherein said absorbent gelling material is comprised between an
upper and a lower fibrous layer of said layer containing absorbent gelling
material, the amount of absorbent gelling material per unit area of fibrous
layer in said acquisition zone being lower than the amount of absorbent
gelling material per unit area in said side zones, the width of said
acquisition
zone and the concentration of absorbent gelling material in said side zones
being adapted for transport of liquids in a predominantly longitudinal
direction of said core.
Sanitary napkin comprising a liquid pervious topsheet, a liquid
impervious backsheet and an absorbent core interposed between said
topsheet and said backsheet, said core comprising two longitudinal sides, a
central acquisition zone, two side zones that are located between said
acquisition zone and said longitudinal sides, said core further comprising a
layer containing absorbent gelling material, the concentration of absorbent
gelling material in said acquisition zone of said core being lower than the
concentration of absorbent gelling material in said side zones, wherein
said absorbent gelling material is comprised between an upper and a
lower fibrous layer of said layer containing absorbent gelling material, said
4
4a
side zones comprising at least one more layer of absorbent gelling material
than said acquisition zone, the width of said acquisition zone being adapted
for transport of liquids in a predominantly longitudinal direction of said
core.
Sanitary napkin comprising a liquid pervious topsheet, a liquid
impervious backsheet and an absorbent core interposed between said
topsheet and said backsheet, said core comprising two longitudinal sides, a
central acquisition zone, two side zones that are located between said
acquisition zone and said longitudinal sides, said core further comprising a
layer wherein an absorbent gelling material is mixed with an absorbent bulk
material,
wherein said layer is continuous, said side zones and said acquisition
zone being located within said layer, the width of said acquisition zone and
the concentration of absorbent gelling material in said side zones being
adapted for transport of liquids in a predominantly longitudinal direction of
the core.
By way of added explanation, an absorbent article according to an
aspect of the invention is characterized in that the absorbent gelling
material
is comprised between an upper and a lower fibrous layer, the amount of
absorbent gelling material per unit area of fibrous layer in the acquisition
zone being lower than the amount of absorbent gelling material per unit area
in the side zones, the width of the acquisition zone and the concentration of
absorbent gelling material in the side zones being adapted for transport of
liquids in a predominantly longitudinal direction of the core.
,,' ~ ~ ~'
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WO 94/02092 ~ '~ ~ Q ~ ~ PGT/US93/06179
By reducing the amount of absorbent gelling material in the
centeral part of the core of the sanitary napkin, an
acquisition zone is obtained having a relatively large
fluid-acquisition and -transport capacity compared to the
side areas which contain a higher level of absorbent
gelling material and hence have a relatively high fluid
retention capacity. Surprisingly it was found that by
selective reduction of the concentration of absorbent
gelling material in the centeral acquisition area, a higher
effective capacity (capacity before occurrence of side
soiling) of the sanitary napkin can be achieved. This is
especially important for sanitary napkins having a
relatively small caliper, for instance smaller that 3 mm.
The capacity of such sanitary napkins in the vertical
direction is low so that optimum use of the absorbent
surface of the sanitary napkin need be made. To achieve a
sufficient absorption capacity of the small caliper
sanitary napkin, the concentration of absorbent galling
material in the core is relatively high compared to the
concentration of absorbent gelling materials in cores
wherein the absorbent gelling material is mixed with the
cores fibers. The absorbent gelling material
concentration in the wide zones of the small caliper
sanitary napkin can not be increased at will due to ~~gel
blocking~~, so that the capacity of such sanitary napkins is
,determined by the maximum possible absorbent gelling
material concentration without gel blocking occurring.
WO 94/02092 PCT/US93/06179
6
According~to the invention it was found that by using less
than the maximum absorbent gelling material concentration
in the acquisition zone, a higher effective capacity was
obtained.
Since the amount of absorbent galling material of the
sanitary napkin according to the invention, is lower than
the amount used in sanitary napkins in which the absorbent
gelling material is evenly applied across the whole surface
o! the fibrous layers that retain the absorbent galling
material, or is evenly mixed with the core s absorbent bulk
material, the sanitary napkin can be manufactured at a
reduced price.
The increased concentration of absorbent gelling material
in the side zones can also be obtained by folding over of
the core onto itself in the side zones, or by superimposing
on the core an extra pair of fibrous layers enclosing
absorbent gelling material in the side zones.
Frog European patent application EP-A-0 Z17 666, a diaper
is known in which two or more strips of super absorbent
material are placed between the core and the topshaet. The
area between the absorbent strips can quickly acquire large
quantities of body fluids, in particular urine. However,
lateral spread of liquids can still take place in a
significant amount in the core, which is located underneath
r
WO 94/02092 PCT/US93/06179
7
the superabsorbent strips. The relatively large width of
the acquisition zone also allows significant lateral
transport of liquids.
An embodiment of a sanitary napkin according to the
invention is characterized in that the width of the
acquisition zone is between 5 and 28 mm, preferably~about
15 mm.
By providing a relatively narrow centeral acquisition zone
in the sanitary napkin, the transport of body liquids, in
particular menses, in a predominantly longitudinal
direction is increased. Upon wetting of the absorbent
galling materials, these materials swell and show a
decreased rats of fluid absorption, a phenomenon which is
called "gal blocking". The relatively low amounts of
absorbent gelling materials in the acquisition zone cause
little gel blocking and pose a low resistance to flow. At
the borders o! the acquisition zone, the lateral spread of
liquids is reduced, due to the gel blocking of the wetted
absorbent gelling material. Hence longitudinal spread of
the fluids discharged into the acquisition zone is
improved. Next to the reduction of the amount of absorbent
gelling material in the acquisition zone, the relatively
narrow dimension of the centeral acquisition zone forces
the fluid which is discharged into this zone in the
longitudinal direction of the absorbent article.
WO 94/02092 a PCT/US93/06179
An embodiment of an absorbent article according to tha
invention, in particular a sanitary napkin, is
characterized in that the concentration of absorbent
gelling material in the acquisition zone is between 0 and
3.59 g/sq foot and the concentration of absorbent gelling
material in the side zones is between 2 and
7.5 g/sq foot for absorbent gelling material having a gel
strength less than about 1.2 kPa after exposure to
synthetic urine in a modified AGEP test and between 2 and
15 g/sq foot for absorbent gelling material having a gel
strength higher than about 1.2 kPa after exposure to
synthetic urine solution in a modified AGED test.
Concentrations of low gel strength absorbent galling
materials in the side zones, such as, for instance under
the brandname Aqualon C from Hercules Inc of Wilmington
Del, higher than 7.5 g/sq foot were found to give rise to
undesired gel blocking which causes liquids discharged into
the acquisition zone to flow laterally across the gel
blocked parts of the side zones. Concentrations of
absorbent galling material in the side zones of below 2
g/sq foot were found to reduce the overall capacity of the
sanitary napkin to an undesirable low level. For high gel
strength absorbent gelling materials, such as for instance
Aquakeep 13 SHPS, a sodium polyacrylate supplied by
Autochem S.A., Cours Michelet, La Defense, Paris, France
and Sanwet IM 5600-S, a cross linked starch grafted sodium
WO 94/02092 PCT/US93/06179
~". '~ ~ 9
polyacrylate supplied by Farbwerke Hoechst AG of Frankfurt,
Germany, concentrations above 15 g/sq foot ware found to
lead to undesirable gel blocking.
Another embodiment of an absorbent article according to the
invention is characterized in that the acquisition zone the
upper fibrous layer is depressed to form a channel.
When in the side zones~of a laminate core (a core wherein
the absorbent gelling material is comprised between two
tissue sheets) the absorbent gelling material, which
preferably is of granular nature, is applied as a uniform
layer, the omission of absorbent gelling material in the
acquisition zone will leave an open space between the upper
and the lower tissue between which the absorbent gelling
material is comprised. Hy depression of the upper tissue
into the open space of the acquisition zone, a channel is
formed in the core which aids in collecting and
distributing body fluids.
Instead of depressing the upper tissue into the acquisition
zone, the absorbent gelling material in the acquisition
zone can be replaced by a wicking material, such as a web
of low density and high resiliency, for instance comprising
synthetic fibers such as polyester fibers, or crimped or
.coiled PET fibers. A better wetting can be achieved by
WO 94/02092 ~° ~ '~ ~ ~ ~ PCT/US93/06179
treating the acquisition zone with a wetting agent such as
a surfactant.
It is noted that in order to promote liquid transport in
the longitudinal direction of an absorbent article it is
known from the European patent EP-A-0 173 068, to provide a
sanitary napkin with a longitudinal channel. No mention is
made however about the presence of absorbent gelling
material in the core material flanking the channel and the
concentration of absorbent gelling material in the area of
the absorbent article wherein the channel is located.
Again another embodiment of a sanitary napkin according to
the invention is characterized in that the upper and the
lower fibrous sheet are formed by a single tissue, the
tissue having two mutually opposed longitudinal edges which
are superimposed in the acquisition zone.
Hy enveloping the absorbent gelling material in a single
tissue, the edges of which overlap in the acquisition zone,
an extra layer of tissue is present in the acquisition area
for quick absorption of gushes of liquids and improved
wicking.
WO 94/02092 PCT/US93/06179
11
Brief deSCZ'i nt i r", of he ,~,."~,;
Some embodiments of an absorbent article according to the
present invention will be described in detail with
reference to the accompanying drawings. In the drawings:
Fig. 1 shows a top plan view of a sanitary napkin wherein a
part of the overlying layers have been cut away to expose
underlying structures, the sanitary napkin having a
generally straight core,
Fig. 2 shows a top plan view of a sanitary napkin having a
shaped core,
Fig. 3 shows a cross sectional view of the sanitary napkin
of fig 1 along the transverse center line 16,
Fig. 4 shows the sanitary napkin of figure 3, no absorbent
gelling material being provided in the acquisition zone,
Fig. 5 shows the sanitary napkin of Fig 4, the upper tissue
being dapreessd into the acquisition zone,
Fig. 6 shows the sanitary napkin of figure 5 , the topsheet
being provided with a channel,
Figs. 7 and 8 show the sanitary napkin of Fig. 3, a single
tissue enveloping the absorbent gelling material, the
tissue's longitudinal edges overlapping,
Fig. 9a and 9b shpw an alternative embodiment of an
absorbent core of a sanitary napkin according to the
invention,
12
Fig. 10 shows a graph of liquid distributions at various loadings for a
sanitary napkin according to the invention. Fig. 11 shows another
embodiment of an absorbent core of a sanitary napkin according to the
invention.
Detailed description of the Invention
The embodiments of the absorbent article as illustrated in the
drawings refer to a disposable sanitary napkin, i.e. an article which is worn
by females adjacent to the pudendal region and which is intended to absorb
and contain the various exudates which are discharged from the body (e.g.
blood, menses and urine) and which are intended to be discarded after a
single use. The invention is however not limited to sanitary napkins only,
but also covers other absorbent articles such as pantiliners, which generally
have a lower capacity than sanitary napkins. Although the embodiment
described in detail in the drawings has a so called "laminate" core wherein
the absorbent gelling material is present as a layer between two sheets, the
invention is not limited thereto and also applies to Cores wherein the
absorbent gelling material is mixed with fibers, such as described in
Canadian patent application No. 2,124,798, filed on November 6, 1992 in the
name of The Procter & Gamble Company.
~;<' ''~;~°.
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WO 94/02092 ~~ ,~, ~ ~ ~~ ~ 13 PCT/US93/06179
Figure 1 shows a sanitary napkin 1 comprising a liquid
pervious topsheet 3, an absorbent core 5 underlying the
topsheet and a liquid impervious backsheet 7. The core 5
has two longitudinal sides 9 and 11, which extend in a
generally longitudinal direction of a longitudinal center
line 13 of the core 5. The longitudinal sides 9,11 need
not be straight but can also ba curved towards the
longitudinal center line) to provide a shaped core, as
shown in figure 2. The absorbent core 5 can bs covered by
one or more acquisition layers for distributing fluids
which have penetrated through the topsheet 3, across the
absorbent core 5. The acquisition sheets have for reasons
of clarity been omitted from the schematic drawings of Figs
4 to 8. The absorbent core 5 comprises a lancinata wherein
the absorbent gelling material is interposed between an
upper tissue 24 and a lower tissue 25, as shown in figures
3-6. The tissues 24, 25 can be part of a single sheet
enveloping the absorbent galling material 29 as is shown in
Figs. 7, 8 and 9.
The core 5 is provided with a centeral acquisition zone 15
that is flanked by two side zones 17 and 19. Tha centeral
acquisition zone 15 comprises a lower concentration of
absorbent gelling materials than the side zones, the
concentration in the side zones 17,19 being between 2 and
7.5 g./sq. foot, preferably about 5.5 g/sq foot, for a
relatively low gel strength absorbent gelling material and
WO 94/02092 " ~ ~ ~ ~ °~ ~ PCT/US93/06179
between 2-and 15 g/sq foot, preferably about 10 g/sq foot
for relatively high gel strength absorbing gelling
materials, and in the acquisition zone 15 being preferably
about 0 g/sq. foot.
The concentration of absorbent gelling material need not
change abruptly when going from side zones to the
acquisition zone, but can for instance decrease linearly
from high to low, or according to any other desired
profile.
The width, W, of the acquisition zone preferably is narrow
compared to the narrowest width, L, of the absorbent core 5
and amounts to between 5 and 28 mm. For sanitary napkins
having a shaped core 5, as is shown in figure 2, the
narrowest lateral dimension L of the sanitary napkin is
located along the transverse center line 16 thereof and
measures preferably about 70 mm. The sanitary napkin 1 is
at its longitudinal perimeter provided with two lateral
tlapa or wings, which can during use be folded around the
edgy o! the user's garment to position the sanitary napkin
width respect to the garment and to reduce side soiling.
Looking at some of the elements of the sanitary napkin more
specifically, the,absorbent core 5 may be any means which
,is generally compressible, conformable, non-irritating to
the wearer's skin and capable of absorbing and containing
WO 94/02092 '~ ~ PCT/US93/06179
body exudates. The absorbent core 5 may be manufactured in
a wide variety of sizes and shapes (e. g. rectangular, hour-
glass, etc.). A preferred shape of the absorbent core 5 is
the dogbone shape shown in FIG 2. This preferred absorbent
core 5 is about 22.0 centimeters long (longitudinal
dimension along the longitudinal centerline 13)) about 7.0
centimeters wide across its midportion (lateral dimension)
along the traverse center line 16. Ths absorbent core 5 is
symmetrically-configured for ease of manufacture and so
that no conscious effort is required by the wearer to
properly place the napkin 1 in the direction it should be
worn. Ths midportion is configured to basically conform to
the wearer's thighs and to the thinner crotch portion of
the wearer's panties so as to prevent excessive bunching.
The size of the absorbent core 5 may be varied to
accommodate wearers ranging in size and also ranging in the
expected amount of exudats fluid volume. The absorbent
core 5 may bs attached over the core's major top and bottom
surfaces respectively, to adjacent members such as the
topahsst 3 and back sheet 7 by any of the means well known
in the art, such as by spray-gluing or lines or spots of
adhesive. Such attachment facilitates integrity and
recoverability of the absorbent materials in use so as to
maintain an optimum degree of absorbency. Preferably, the
absorbent core 5 has a wet-tensile strength in the cross-
direction of at least about 100.0 grams per centimeter.
WO 94/02092 ~ ~ ~ ~ PCT/US93/06179
16
Wet tensile strength is detenainable by ASTM Standard D
829-49. v
The absorbent core 5 may be manufactured from a wide
variety of liquid absorbent materials commonly used in
disposable sanitary napkins, diapers, and other absorbent
articles. Examples of suitable absorbent materials include
comminuted wood pulp which is generally referred to as
airfelt, creped cellulose wadding, absorbent foams,
absorbent sponges, synthetic staple fibers, polymeric
fibers, hydrogel-forming polymer gelling agents, or any
equivalent materials or combinations of materials. A
particularly preferred absorbent material are absorbent
gelling materials or polymeric gelling agents. Polymeric
gelling agents are those materials which, upon contact with
fluids (i.e., liquids) such as water or body fluids, imbibe
such fluids and thereby form hydrogels. In this manner,
fluid discharged into the absorbent core 5 can be acquired
and held by the polymeric galling agent, thereby providing
tha articles herein with enhanced absorbent capacity and/or
improved fluid retention performance.
The polymeric gelling agent which is employed in the
absorbent core 5 will generally comprise particles of a
substantially water-insoluble, slightly cross-lined,
partially neutralized, hydrogel-forming polymer material.
Such polymer materials can be prepared from polymerizable,
WO 94/02092 PCT/US93/06179
m
unsaturated, acid-containing monomers. Suitable
unsaturated acidic monomers for use in preparing the
polymeric gelling agents used in this invention include
those listed in US-A-4,654,039, entitled "Fiydrogel-Forming
Polymer Compositions for Use in Absorbent Structures°,
which is:ued to Hrandt, Goldman and Inglin on March 31,
1987, and which patent is incorporated herein by reference.
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 agent material.
In the hydrogel-forming polymeric gelling agent the
polymeric component formed from unsaturated, acid-
containing monomers may be grafted onto other types of
polymer moieties such as starch or cellulose. Polyacrylate
grafted starch materials of this type are especially
preferred for use herein.
Preferred polymer gelling agents which can ba prepared from
conventional types of monomers include hydrolyzed
acrylonitrila grafted starch, polyacrylate grafted starch,
polyacrylates, malefic anhydride-based copolymers and
combinations thereof. Especially preferred are the
polyacrylates and polyacrylate grafted starch.
i8
Whatever the nature of the basic polymer components of the hydrogel-
forming polymeric gelling agents used in the absorbent core 5 herein, such
materials will in general be slightly cross-linked. Cross-linking serves to
render the hydrogel-forming polymer gelling agents used in this invention
substantially water-insoluble, and cross-linking thus in part determines the
gel volume and extractable polymer characteristics of the hydrogels formed
from the polymeric gelling agents employed. Suitable cross-linking agents
are well known in the art and include, for example, those described in greater
detail in US-A-4,076,663, which patent issued to Masuda et al on February 28,
1978. Preferred cross-linking agents are the di- or polyesters of unsaturated
mono- or polycarboxylic acids with polyols, the bisacrylamides and the di- or
triallyl amines. Especially preferred cross-linking agents are N,N'-
methylenebisacrylamide, trimethylol propane triacrylate and triallyl amine.
The cross-linking agent can generally comprise from about 0.001 mole
percent to 5.0 mole percent of the resulting hydrogel-forming polymer
material. More preferably, the cross-linking agent will comprise from about
0.01 mole percent to 3.0 mole percent of the hydrogel-forming polymeric
gelling agent used herein.
The slightly cross-linked, hydrogel-forming polymeric gelling agents
which may be used in the articles of the
t.
WO 94/02092 PCT/US93/06179
19
present invention are generally employed in their partially
neutralized form. For purposes of this invention, such
materials are considered partially neutralized when at
least 25.0 mole percent and preferably at least 50.0 mole
percent of monomers used to form the polymer are acid
group-containing monomers which have been neutralized with
a salt-forming cation. Suitable salt-forming cations
include alkali metal, ammonium, substituted ammonium, and
amines. This~percentage of the total monomer utilized
which are neutralized acid group-containing monomers is
referred to herein as the "degree of neutralization".
The polymeric gelling agent materials used in the absorbent
articles as shown in Figs 3 and 8 must have a relatively
high capacity for imbibing fluids encountered in such
articles. The absorbent capacity of these materials can be
quantified by referencing the "gel volume" of the polymeric
gelling agents which are to be selected for use in the
present invention.
For purposes of this invention, gel volume can be defined
in terms of the amount of synthetic urine absorbed by any
given polymeric gelling agent and is specified as grams of
synthetic urine per gram of polymeric gelling agent. Gel
volume in synthetic urine can be determined for forming a
suspension of about 0.1-0.2 parts of dried polymeric
gelling agent to be tested with about 20 parts of synthetic
WO 94/02092 ~~~ ~ ~ ~ ~ PCT/US93/06179
.'
urine. This suspension is maintained at ambient
temperature under gentle stirring for a time sufficient,
e.g., about 1 hour, for swelling equilibrium to ba
attained. The gel volume of the polymeric gelling agent is
then calculated from the weight fraction of the polymeric
gelling agent in grams of synthetic urine per gram of
polymeric gelling agent is then calculated from the weight
fraction of the polymeric gelling agent in the suspension
and the ratio-of the liquid volume excluded from the formed
hydrogel to the total volume of the suspension.
The gel volume of the gelling agents used in the absorbent
core 5 herein will generally be at least about 20.0 grams
of synthetic urine per gram of polymeric gelling agent.
More preferably, the gel volume of the materials employed
will range from about 20.0 to about 60.0, most preferably
from about 22.0 to about 35.0 grams of synthetic urine per
gram o! polymeric gelling agent.
In a preferred embodiment, the sanitary napkin has a
minimum core width measured along the transverse center
line 16, of 70 mm, the centeral acquisition zone 15
comprising between 0 and 3.5 gram per square foot,
preferably about 0 gram/square foot polymeric absorbent
gelling material of the type. The width w of the
acquisition zone 15 is between 10 and 20 mm, preferably
about 15 mm. The concentration of polymeric absorbent
21
gelling material in the side zones 17 and 19 is preferably an even
distribution,
i.e. constant in the direction, of the transverse center line of about 4
gram/square foot for an acquisition zone of width w of 15 mm, and 5.5
gram/square foot for an acquisition zone of a width of about 20 mm, the
overall concentration of absorbent gelling material of the core being about
3.1
gram/ square foot. The preferred dimensions of the sanitary napkin, the
width of the acquisition zone and the concentration of absorbent gelling
material relate to the absorbent article as shown in Figs 2-8, i.e. a sanitary
napkin having a shaped core 5, and comprising a laminate of air laid sheets
24 and 25. The absorbent gelling material 29 used in the preferred
embodiment has a gel strength of less than 1.2 kPa. However a central
acquisition zone 15 having a low concentration of absorbent gelling material
can also advantageously be used in combination with high gel strength
absorbent gelling materials, which can be applied in higher concentrations
without gel blocking occurring.
The concentrations of absorbent gelling materials in the side zones and
the width of the centeral acquisition zone will have to be varied according to
the gel strength, the different absorbent gelling materials used, the caliper
of
the core and the minimum lateral dimension, L, of the core.
,,
WO 94/02092 , '~'~ ~ ~ ~ PCT/US93/06179
22
The gel strength of absorbent gelling materials can be
measured according to the modified Absorbent Gel Expansion
Pressure test (aGEP). The modified AGEP test measures the
force exerted by the gel as it,,expands following exposure
absorption to a synthetic urine solution. The force is
measured by a circular pressure foot that fits closely
within a 2 cm diameter sample cell of an Ametek Precision
Stage Model C1395X available from Ametek Corporation,
Mansfield & Brown Division, 8600 Somerset Drive, Largo,
Florida 36543, USA. The Force guage is an 'Accuforce'
device available from Brown Tool & Supply Co, Solon, Ohio,
USA.
The following procedure is used:
1. Weigh out 0.1798 +/- O.OOlg polymeric gelling agent
material into the absorption cell.
2. Place the cell containing the sample in the sample
alignment bracket on the precision stage of the
Ametak, and line up the sample holder so that the
pressure foot will be centered when in the tube.
3. Add a 56 x load (10 ml) of Jayco synurine (see note 1)
to the sample.
4. Using the level on the Ametek stand, raise the sample
until the foot is almost touching the fluid.
'5. Zero and clear the Ametek Force Guage and if using a
chart recorder start it with the speed set to icm/min.
PCT/US93/06179
WO 94/02092 ~ '~ ~, ~ ~ ~ ~ 2 3
6. Turn~the illuminator off.
7. Using the coarse and fine adjustments on the precision
stage, raise the sample until the level of the fluid
is even with the top of the foot. This is achieved by
sighting across the foot. The fluid that is on the
wall of the absorption call due to tha surface tension
' will appear as a white band. As this band moves up
the cell it will block the silver colour of the foot.
When the-white band is above the top of the foot a
silver band will reappear. At this point lower the
sample using the fine adjuster until the silver band
disappears.
e. Turn off the illuminator immediately.
9. When the gel reaches the foot, set the timer for 30
minutes and start it.
10. At the end of 5, 10, 15, 20 and 30 minutes record the
farce in grams.
Pressure = Reading of machine (g) /area of foot (cm2) x
98.1 (kPa)
WO 94/02092 ~~.. ~ ~ ~ ~ ~ ~ PCT/US93/06179
24
1. Jayco Svnurine
The Jayco Synurine is made up with the following
quantities of compounds per litre of solution.
Na2S04 2.Og/1
KC1 2.Og/1
~~4 ~ 2HP04 0 .15g/ 1
~~4~ H2P04 0.85g/1
MgC12:6H20 0.5g/14
CaC12:2H20 0.25g/1
2. Testing should be conducted with the equipment and
sample at a stable temperature of 25°C.
3. The tube internal diameter is 2 cm so that the surface
area of the foot is 3.14 cm2.
The absorbent gelling materials having an absorbent gel
strength of more that 1.2 kPa after 5 minutes are
classified as high gel strength absorbent gelling materials
and can be used in higher concentrations in the side zones.
Preferred absorbent gelling materials show a generally
regular increase in gel strength from the value after 5
minutes exposure to the value after 30 minutes exposure.
25
In the preferred embodiments shown in Figs. 3-8, the absorbent core 5
is a laminate comprised of a layer of absorbent gelling material disposed
between two air-laid tissues 24 and 25. A suitable laminate is the absorbent
laminate WATER-LOCK L-535 available from the Grain Processing
Corporation of Muscatin, Iowa (WATER-LOCK registered TM by Grain
Processing Corporation). Such superabsorbent laminates are disclosed in US-
A-4,467,012, entitled "Composition for Absorbent Film and Method of
Preparation ', which patent issued to Pedersen et al. on August 21, 1984, and
US-A-4,260,443, entitled "Laminated Absorbent Process", which patent
issued to Lindsay et al. on April 7, 1981. The WATER-LOCK L535 has a
hydrogel polymer loading of 0.005 grams per square centimeter, however,
loadings of 0.001-0.009 grams per square centimeter have been found
acceptable. The first and second tissue layers 24 and 25 provide containment
of the absorbent polymer material, improve lateral wicking of the absorbed
exudates throughout the absorbent core 5 and provide a degree of
absorbency. In the case of non-particulate hydrogel-forming polymer gelling
agents which can be formed into fibrous sheets, foams or films, the non-
particulate gelling agent may comprise from about 15% to about 100% by
weight of the absorbent core 5, more preferably of from about 40% to about
100%, and most preferably of from about 60% to
~.~.~r ..
.1
WO 94/02092 ',~ ~~ ~r ~ ~ ~ PCT/US93/06179
26
about 100. Two suitable and commercially available non-
particulate absorbent materials of relatively low gel
strength for use in the absorbent core 5 are a double layer
.:
acrylic fibrous material available under the tradename
Lanseal F from the Chol,i'Company, LTD., of Higashi, Osaka,
Japan and a carboxymethylcellulose fibrous material
available under the tradename Aqualon C from Hercules, Inc.
of Wilmington, Del.
The total absorbent capacity of the absorbent core 5 should
be compatible with the design exudate loading for the
intended use of the sanitary napkin 1. Further, the
absorbent capacity of the absorbent core 5 may be varied to
accommodate wearers ranging in the expected amount of
exudate fluid volume. For instance, a different absorbent
capacity may be utilized for sanitary napkins intended for
daytime use as compared with those intended for night-time
use, or for sanitary napkins intended for use by teenage
famalea as compared with those intended for use by more
mature women.
Superimposed over the absorbent core 5 and extending 3.0
millimeters beyond the edges 9 and 11 of the absorbent core
can be placed wet-laid tissue 31. The wet-laid tissue 31
is liquid permeable. A satisfactory wet-laid tissue 31 has
a basic weight of about 15.8 grams per square meter and an
air permeability of about 30.5 cubic meters per minute per
27
square meter at a pressure differential of about 12.08 millimeters of water.
Preferably, the wet-laid tissue 31 maintains integrity when wetted, in
use. The wet-laid tissue 31 preferably has a wet tensile strength in the cross-
direction of at least about 15.0 grams per centimeter. Suitable tissues 31 and
their manufacture are disclosed in U.S. Patent No. 3,301,746, entitled
"Process
for Forming Absorbent Paper by Imprinting a Fabric Knuckle Pattern thereon
prior to Drying and Paper thereof", which patent issued to Sanford and
Sisson on January 31, 1967. In a preferred embodiment, those parts of the
wet-laid tissue 31 which extend beyond the longitudinal sides 9 and 11 of the
absorbent core 5 are associated with the back sheet 7. The wet-laid tissue 31
may be associated with the back sheet 7 by attachment means as are well
known in the art such as by spray-gluing on lines or spots of adhesive. The
wet-laid tissue 31 serves a number of purposes. The tissue 31 serves to
confine any loose superabsorbent material 37 between the tissue 31 and the
back sheet 7 thereby preventing the superabsorbent material 27 from coming
in contact with the wearer s skin. Also, the tissue 31 improves lateral
wicking
of the absorbed exudates over the absorbent core 5 thereby providing a more
even distribution of the exudates throughout the absorbent core 5. Further,
1 ;_. ,
3:.
WO 94/02092 ~ ~ ~ ~ ~ '~ ~ PCT/US93/06179
28
the tissue 31 provides some degree of absorbency and
further inhibits exudates which~have reached and been
absorbed by the absorbent core 5 from rewetting the
wearer's skin.
Superimposed over the wet-laid tissue 31 can be a~liquid
permeable wipe acquisition sheet 33. In a preferred
embodiment, the wipe acquisition sheet 33 is a nonwoven
sheet, such as a spunlaced 70%/30% rayon/polyester fiber
sheet. Spunlaced fabrics of this type are manufactured by
E.I. DuPont Nemours and Company of Wilmington, Delaware,
and are made available under the tradename "SONTARA"
(SONTARA registered TM by E.Z. DuPont Nemours P Company))
These-fabrics are available in a number of suitable styles,
however, Style 8407 in its apertured form, having a basis
weight of 0.005 grams per square centimeter and a thickness
of about 0.04 millimeters, is preferred. The wipe
acquisition sheet 33 extends beyond the edges of the wet-
laid tissue 31 where it too is associated with back sheet
7. The wipe acquisition sheet 33 greatly improves lateral
wicking of exudates over the absorbent core 5 thereby, in
combination with the centeral acquisition zone 15,
providing a more even distribution of the exudates
throughout the absorbent core 5. The lateral wicking of
the wipe acquisition sheet 33, in combination with the
longitudinal spread of liquids in the centeral acquisition
zone 15, is important for the following reason. Many bulky
WO 94/02092 PGT/US93/06179
29
prior art sanitary napkins rely on a high degree of
vertical absorption at the point where exudates are
initially deposited. In other words, because the absorbent
cores of these napkins are fairly thick, they can absorb a
high degree of exudates throughout their thickness while
utilizing only a small degree of their surface area or
lateral absorption capability. However, the relatively
thin napkins 10 of the present invention have a
comparatively small degree of vertical absorption.
Therefore, for a relatively large amount of exudates to be
absorbed, a wipe acquisition sheet 33, and a centeral
acquisition zone 15, which can transversely and
longitudinally, disperse the exudates over a large surface
area of the absorbent core 5 where the exudates can better
and faster be vertically absorbed is highly desirable.
Superimposed over the wipe acquisition sheet 33 is the
liquid permeable topsheet 3. in a preferred embodiment,
the topsheet 3 is associated with the wipe acquisition
sheet 33 by spray-gluing the topsheet 3 to the surface of
the wipo acquisition sheet 33. The topsheet 3 is
compliant, soft feeling, and non-irritating to the wearer s
skin. Further, the topsheet 3 is liquid pervious,
permitting liquid to readily transfer through its
thickness. A suitable topsheet 3 may be manufactured from
a wide range of materials such as polymeric materials,
formed thermoplastic films, apertured plastic films, porous
30 ~~0 ~~
foams, reticulated foams, natural fibers (e.g., wood or cotton fibers),
synthetic
fibers (e.g., polyester or polypropylene fibers) or from a combination of
natural and synthetic fibers, with apertured formed films being preferred.
Formed films are preferred for the topsheet 3 because they are pervious to
liquids and yet non-absorbent. Thus, the surface of the formed film which 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 US-A-3,929,135, entitled "Absorptive Structure having Tapered
Capillaries", which patent issued to Thompson on December 30, 1975, US-A-
4,324,246, entitled "Disposable Absorbent Article having a Stain Resistant
Topsheet", which patent issued to Mullane and Smith on April 13, 1982, US-
A-4,342,314, entitled "Resilient Plastic Web Exhibiting Fiber-like
Properties",
which patent issued to Radel and Thompson on August 3, 1982, and US-A-
4,463,045, entitled "Macroscopically Expanded Three-Dimensional Plastic
Web Exhibiting Non-Glossy Visible Surface and Cloth-like Tactile
Impression', which patent issued to Ahr, Louis, Mullane, and Ouellette on
July 31, 1984.
In a preferred embodiment of the present invention, the body surface
of the topsheet 3 is hydrophilic. The hydrophilic body surface helps liquid to
transfer through
~~ ~'f,:
WO 94/02092 ~ ~ p ~ PGT/US93/06179
31
the topsheet 3 faster than if the body surface was not
hydrophilic. This diminishes the likelihood that menstrual
fluid will flow off the topsheet 3 rather than being
absorbed by the absorbent core 5. In a preferred
embodiment, the body surface of the topsheet 3 is made
hydrophilic by treating the body surface with a surfactant.
It is preferred that the surfactant be substantially evenly
and completely distributed throughout the body surface of
the topsheet 3. This can be accomplished by any of the
common techniques well know to those skilled in the art.
For example, the surfactant can be applied to the topsheet
3 by spraying, by padding, or by the use of transfer rolls.
Further, the surfactant can be incorporated into the
polymeric materials of a formed film topsheet or between or
within the fibers of a nonwoven topsheet.
The back sheet 7 is adjacent the absorbent core 5. In a
preferred embodiment, the absorbent core may be affixed to
the back sheet 7. Any of the common techniques well known
in the art, such as spray-gluing or lines or spots of
adhesive may be used for this purpose. The back sheet 7
generally defines the garment surface of the sanitary
napkin. The back sheet 7 may be any means which is
impervious to liquids and which prevents exudates absorbed
and contained in the absorbent core 5 from soiling
.articles, such as panties, which come in contact with
garment surface of the sanitary napkin 1. In the preferred
r
WO 94/02092 ~ ~ ~~ ~ ~ ~ PCT/US93/06179
32
s
embodiment of the sanitary napkin 1 illustrated in Figs. 1
and 6, the back sheet 7 is a barrier sheet manufactured
from a thin plastic film. other flexible liquid impervious
materials may also be used. Preferably, the back sheet 7
is a polyethylene film having a thickness of from about
0.012 millimeter to about 0.051 millimeter. As used
herein, the terra "flexible" refers to materials which are
compliant and which will readily conform to the general
shape and contours of the human body.
A suitable polyethylene film is manufactured by Monsanto
Chemical Corporation and marketed in the trade as Film No.
8020. The back sheet 7 is preferably embossed and/or matte
finished to provide a more clothlike appearance. Further,
the back sheet 7 may permit vapors to escape from the
absorbent core 5 which still preventing exudates from
passing through the back sheet 7.
Preferably, the topsheet 3 and the back sheet 7 have length
and width dimensions generally larger than the absorbent
core 5 so that they extend beyond the longitudinal edges 9
and 11 of the absorbent core 5 where they are associated
together in a suitable manner. As used herein, the term
"associated" encompasses configurations whereby a first
member is directly joined to a second member and
configurations whereby a first member is indirectly joined
to a second member by affixing the first member to
WO 94/02092 PCT/US93/06179
33
intermediate members which in turn are affixed to the
second member. In an embodiment, the back sheet 7 and the
topsheet 3 have an elliptical shape and extend beyond the
absorbent core 5 a distance of at least about 1.0
centimeter where they are joined directly to each other by
attachment means as are well known in the art. The
attachment means may be, for example, a uniform continuous
layer of adhesive, patterned layer of adhesive, or an array
of separate lines or spots of adhesive.
In Fig. 4 the acquisition zone 5 comprises no absorbent
gelling material so that the upper sheet 24 can be pressed
into the acquisition zone 5 to form a channel 30, as is
shown in Fig. 5. The topsheet 3 can also be pressed into
the channel 30 to provide a longitudinal groove on the body
facing side of the sanitary napkin, thus assisting in
increasing the longitudinal spread of liquids along the
topsheet 3. As is shown in Fig 7 and 8, the upper and
lower sheet 24 and 25 can be parts of a single sheet which
sides overlap in the acquisition zone 5, so that an extra
layer of tissue is present in the acquisition zone to
assist in wicking liquids in the longitudinal direction.
Figs. 9a and 9b show how an absorbent core can be produced
from a single sheet 35, wherein a strip 37 having a low
concentration of absorbent gelling material is
symmetrically located. After e-folding of the sheet 35,
the strip 37 of low concentration of absorbent galling
WO 94/02092 ~ ~, ~ ~ ~~ ~ PCT/US93/06179
34
material is centerally located in the acquisition zone 15
as shown in figure 9b.
In the embodiment as shown in Fi,g. li, the layers 24 and 25
of the absorbent core 5 are folded over, so that in the
side zones 17 and 19, the core comprises two layers of
absorbent gelling material, whereas in the central
acquisition zone 15 a single layer of absorbent gelling
material is present. A layer of wicking material 30, which
may comprise a hydrophilic tissue or non-woven material, or
a hydrophilic coating, can extend across the bottom of the
acquisition zone 15 and between the layers of absorbent
gelling material 29 in the side zones 17 and 19.
Instead of folding over of the core to obtain a double
layer of absorbent gelling material in the side zones 17
and 19, a separate pair of fibrous layers enclosing
absorbent gelling material may be superimposed in the side
zones on a lower pair of fibrous layers enclosing absorbent
gelling material. The open sides of the fibrous layers can
be sealed off by for instance a hot malt adhesive 26.
It is noted that the acquisition zone 15 does not
necessarily extend along the whole length of the absorbent
core 5, but can be located in the central region of the
'core only to prevent leakage of liquids from the core s
ends.
WO 94/02092 ~ ,~ ~ ~ ~ ~ ~ . 3 5 PCT/US93/06179
To demonstrate the increased product performance of the
sanitary napkin according to the invention versus a similar
sanitary napkin having a uniform distribution of absorbent
gelling across the surface of the absorbent core, the
sanitary napkins were wetted by a step-wise increasing
load. The test conditions and the products under test will
be set out herebelow. The test results are summarized in
tables I, II, III and Fig 9.
The reference product comprised a shaped laminate core,
having a length of 207 mm and a width along the transverse
center line 16 of 70 mm. The concentration of absorbent
gelling material commercially available from Shokubai under
type number L-074 was 5.5 g/sq foot.
The tested sanitary napkins according to the invention
comprised a first type having a centeral acquisition zone
of 15 mm in width containing no absorbent gelling material
(type A) and a second type having a centeral acquisition
zone of 20 mm in width not containing absorbent gelling
material (type B), the concentration of absorbent gelling
material in the side zones being 5.5 g/sq feet for both
~pes A and B. The dimensions and materials of the sanitary
::apkins according to the invention were identical to those
of the reference product.
WO 94/02092 '~, ~! c, ~ ' PCT/US93/06179
36
Load to width distribution
To measure the ratio of transverse liquid spread to
longitudinal liquid spread under various loading
conditions, the sanitary napkins were wetted with Paper
Industrial Fluid, having a viscosity of 16.5 cps and
containing:
Glycerol 80 g/1
NaCl 10 g/1
NaIiC03 4 g/ 1
Carboxymethylcellulose 18 g/1
The pads were flattened out on a flat surface and the
center of the absorbent core 5 was marked on the topsheet
of each pad. The center of the core 5 corresponds to the
point of interaction of the longitudinal center line 13 and
the transverse center line 16, as shown in Fig. 2. 2 ml of
fluid were discharged onto the center of the pad within 4s,
using a peristaltic pump of type PA-SF 5, marketed by IKA.
minutes after completion of the discharge, the farthest
points reached by the fluid in the direction of the
longitudinal center line l3 and the transverse centerline
16 were measured. Table I gives the results of width of the
fluid for respective loadings for the reference product,
and the sanitary napkin having a 20 mm wide acquisition
zone without absorbent gelling material (type B).
WO 94/02092 PCT/US93/06179
37
Loading versus width distribution
loading (ml) Distribution width
(cm)
reference roduct
t a B
2 4.1 4.0
6 6.6 5.8
7 6.5
12 7 6.8
14 7 7
From table I it appears that for the sanitary napkin having
the centeral acquisition zone, the liquid reaches the
longitudinal sides 9,11 of the core 5 after absorption of
14 ml for which loading the distribution width equals the
narrowest width of the core, which is 70 mm. This means
that the effective capacity of the sanitary napkin with the
acquisition zone is larger than the effective capacity of
the reference product, for which at a load of 10 ml the
fluid reached the longitudinal sides 9,11 of the product.
Lencth versus width d~sltribut »n
From the measurements on the length and the width of the
fluid distribution as made in the above described test, the
ratio of length and width (1/w) of the fluid distribution
was calculated for the sanitary napkin of type A (width of
WO 94/02092 3 8 PCT/US93/06179
acquisition zone of 15 mm) and for a sanitary napkin having
an acquisitions zone free of absorbent gelling material and
measuring 25 mm in width, the concentration of absorbent
gelling material in the side zones being 5.5 g/sq foot
(type C). Another sanitary napkin, similar to type A, but
having a concentration of absorbent gelling material in the
acquisition zone of between 1-2 g/sq foot (type D)' was also
tested. Of each type of sanitary napkin (type A, type C and
the reference product), three samples were wetted with
stepwise increasing loads of fluid. The results of the
average length to width ratio and the standard deviation
(av and st. dev) for 3 samples each time, are summarized in
table II for type A, type C and the reference product. For
the sanitary napkin of type D, only one sample was wetted
with increasing loads, so that no standard deviation is
available for this type of sanitary napkin.
As appears from table II, and more clearly from Fig. 10,
the length-to-width distribution of the sanitary napkins
having an acquisition zone not containing any absorbent
gelling material, increases with respect to the reference
product, for loads larger than 6 ml. It also can be seen by
comparing the results of type A and type D product, that a
total absence of absorbent gelling material from the
acquisition zone results in the larger length-to-width
distribution, and that too high a concentration of
absorbent gelling material in the acquisition zone results
WO 94/02092 ~ '~ ~, ~ Q ~ ~ PGT/US93/06179
39
in a reduced length-to-width ratio compared to the
reference product. For an acquisition zone of a width of 15
mm, the length-to-width distribution is better than for an
acquisition zone of a width of 25 mm.
Table ~,
Length versus width distribution
loading type A type C reference
ml
1 w av at. dev 1 w av at. dev 1 w av st. dev
2 1.29 0.02 1.20 0.07 1.18 0.04
4 1.26 0.03 1.26 0.07 1.23 0.11
6 1.40 0.03 1.32 0.02 1.25 0.04
8 1.62 0.02 1.50 0.02 1.34 0.05
1.77 0.03 1.68 0.05 1.49 0.09
12 1.93 0.05 1.86 0.06 1.63 0.10
14 2.12 0.04 ~ 2.05 0.04 1.75 0.06
_R_enetitive strike-throucrh test
For type A and type C sanitary napkins, the strikethrough
time was tested versus the reference product for stepwise
increasing loads. The napkins were placed on a flat
surface, and the center of the core was marked on the
topsheet. The hole of an electronic strike-through plate
was centered on the center of the core, and 2 ml of liquid
was discharged via a funnel through the hole of the strike-
WO 94/02092 PCT/US93/06179
~,~r ~ ~ ~ ~ 4 0
through plate. A strike-through timer which is connected
to the strike through plate and which stops counting if all
fluid has cleared the plate, was se't to ~~record~~.
Subsequently the liquid was released through the strike-
through plate and the time was recorded from the strike-
through timer. After 60 seconds, the following load of 2 ml
was discharged from the funnel onto the pad, the procedure
being repeated until 14 ml was discharged. For each load,
three samples~of the product of type A,C and the reference
product were loaded, and the strike-through time was
averaged over these products. The results are summarized in
table III. From table III appears that for type C product,
having the larger width of the acquisition zone (25 mm),
the strike through times are shortest. The difference in
strike-through time with respect to the reference product
becomes more pronounced for higher loadings (higher than
6 ml).
WO 94/02092 ~, ~, ~ ~ ~ ~ PCT/US93/06179
41
Strike through time
loading time time time
(s) (s) (s)referenee
type type
A C
ml
av. st. dev av. st. dw av. at. dev
2 4.40 0.17 4.03 0.06 4.13 0.25
4 1777 2.35 15.30 1.40 21.60 1.32
6 26.27 0.98 23.77 1.50 39.20 1.47
8 39.23 0.12 32.43 1.37 55.43 4.73
56.77 4.04 47.23 2.65 77.10 12.87
12 74.60 0.17 61.47 4.56 95.00 11.82
14 86.17 1.62 74.67 2.65 115.03 23.49
