Note: Descriptions are shown in the official language in which they were submitted.
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FIELD OF THE INVENTIO~
The invention relates to a sanitary napkin
and particularly a napkin having layers of different
absorptive materials.
BACKGROUND OF THE INVENTION
There are several features which are desir-
able in a sanitary napkin. The sanitary napkin must
be comfortable, it must be highly absorbent, it must
rapidly remove fluid from the surface adjacent the
wearer and must be relatively inexpensive to produce.
Wood pulp fibers or other similar natural
cellulosic fiber systems have long been used as the
primary absorptive component of these napkins. Wood
pulp fluff is soft, resilient, absorptive and
inexpensive.
One of the dif~iculties in using wood pulp
solely as an absorbent for menstrual fluid is that
there is no preferential directional transfer so that -
higher exudate concentration exists in regions closest
to immediate con~act. The result is a wet pad surface
which is conducive to early leakage. These transfer
problems are accentuated as the pad becomes wetter.
Prior art has recognized these problems and
has attempted to provide suitable composite absorptive
systems utilizing wood pulp or the like as one of the
absorptive layers. The other absorptive layer which is
usually placed on the top has been chosen based upon the
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theory that it is desirable to pass fluid as quickly
through the surface of the top absorptive layer as
possible. In some instances this is done by rendering
the upper surface of the top absorptive layer "hydro-
phobic" and/or by selective absorption of the more
viscous parts of menstrual fluid in the top layer
with, at least hypothetically, preventing the aqueous
portion of the menstrual fluid from passing through to
the fluff layer. It has also been theorized that
absorptive systems utilizing two highly absorptive
entities on successive layers would be particularly
valuable.
An Example of composite absorbent systems,
U. S. patent 3,371,667 discloses a highly porous
resilient element designed to "entrap highly viscous
mucoid and gelatinous constituents of the body fluids".
This patent teaches that the top layer so described
would pass through the less viscous components,
Suitable fibers contemplated are rayon which has been
rendered rela,tively hydrophobic at the surface but
treated with hydrophilic agents for the inner portion
of the fibrous web.
Another representative composite napkin is
described in U. S. patent 4,047,531 which has an outer
fluff layer prepared from a thermomechanical pulp used
in conjunction with a traditional fluff layer as an
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absorbent system. Again, the concept set foxth in
this patent is the use of a "hydrophobic" fiber ln
the uppermost layer.
There are other prior art composite absorptlve
systems but they all seem to, in effect~ describe the
use of a top layer which is at best less absorptive
than the bottom layer and, may in fact, have little
actual absorptive capabilities particularly as related
to the aqueous components of the m~ënstrual fluid.
SUMMARY OF THE INVENTION
This invention provides an absorptive system
for a sanitary napkin or the like having two layers
with the layer closest to the body of the user passing
fluid rapidly through the upper surface and still
retaining overall absorptive capabilities while also
wetting the bottom surface of a conventional cellulosic
fi~rous matt.
It has been found that the composite absorp-
tive systems can be substantially improved by utilizing
a top layer which may function as an absorbent for all
of the components of menstrual fluid by combining a
high capacity with good fluid transfer properties.
Menstrual fluid, as it contacts the top absorp-
tive layer of the composite sanitary napkin of this
invention rapidly passes through the upper surface of
the_layer and d perses rapidly radially as it passes
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through the thickness of the first layer. During this
passage a portion of all of the components of the fluid
is retained.
The upper layer mus~ possess relatively large
interfiber spaces for the upper layer to allow rapid
fluid transfer. If extremely high fluid retention for
the top layer is present, after the top layer is satu-
rated, there will be fluid runoff between the top layer
and the cellulosic fibrous layer abutting it with the
resulting problems of side leakage. Also, there may
be, in the case of a highly absorbent top layer,
blockage of the capillaries in this layer as a result
of the high level of absorption which would prevent
at least a part of the flow from contacting the second
absorptive layer.
It has now been found that a top layer having
a capillary absorption composite value not greater than
0.5 and an equilibrium capacity not greater than 4.6
grams absorbed per grams of absorbent, in combination
with a conventional cellulosic layer such as a wood
pulp fiber, provides a highly effective absorptive
system utilizing the absorptive capabilities of both
layers with a high degree of efficiency without side
leakage or surface puddling on the top of either absorp-
tive layer.
This invention will be more readily understood
with reference to the drawings in which FIG. 1 is a
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perspective view and partial cross section of a typical
sanitary napkin construction and FIGS. 2 and 3 are
diagramatic representations of the tests utilized to
characterize the top absorptive layer in the pad of the
subject invention.
With reference to FIG. 1, a sanitary napkin
N is depicted as having a fluid permeable outer wrap
completely enclosing the remaining constituents of the
napkin. A top absorptive layer 2~is located directly
below the bottom upper face of the surrounding wrap.
The conventional wood pulp or similar absorbent layer
3 is located directly below the top absorptive layer
and is disposed on top of a fluicl impermeable baffle 4.
The fluid impermeable baffle actually surrounds the
sides of the bottom absorptive layer and may extend to
cover part of the sides of the top absorptive layer.
This construction has the advantage of minimizing
leakage from the sides of the pad. The pad is sealed
at the forward and rearward edges 5 and 6 in any conven-
tional manner such as adhesive sealing. Th~ sealing isindicated by the closely spaced line set inward from
the edges at their respective ends. This particular
pad is of the tabless variety and as shown partially
in phantom lines, there is an adhesive peel strip which
exposes bottom adhesive surface for attachment to
undergarments.
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The pad illustrated in FIG. 1 in its cur-
rently preferred embodiment, utilizes an outer fluid
permeable wrapper of spunbonded polypropylene as
described in U. S. Patent No. 3,886,942 and a presently
preferred baffle material is 0.6 mil polypropylene.
The bottom absorbent layer presently preferred is wood
pulp fluff and the upper absorbent l~yer is chosen
based upon an evaluation set ~orth in the table below
and cost factors.
It is to be understood that the embodiment
depicted in ~IG. 1 is merely representative of a
particular configuration which may be chosen and
the inventive concept is not to be limited to that
configuration. For example, a sandwich type of napkin
can be made in which the fluid permeable top layer
only extends to the edge of the pad and the fluid
impermeable bottom sheet or baffle is affixed directly
to the fluid pervious top layer completely around the
periphery of the pad.
The capillary absorption composite value is
obtained by the capillary absorption composite test.
This test is performed as follows: first, the material
to be tested is produced on web forming equipment which
for purposes of comparison is set to form a web having
a basis weight of 34 grams per square foot. The material
is die cut to produce a three inch diameter circle. A
similar die cut wood pulp fluff three inch diameter disc
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is also cut by the same means and placed under -the
experimental absorbent material for testing. The
testing apparatus is depicted in FIG. 2.
The testing apparatus consists of a variable
rate syringe pump and means for maintaining constant
temperature and pressure on the sample. The fluid
utilized for testing is bovine blood-which has its
hematocrit i.e. red blood cell level adjusted to a
level of 20 percent of weight of t~e solution. The
blood is fed by the pump 11 past a magnetic stirrer
12 through a syringe ejector 13 and into intake tube 14.
Intake tube 14 leads into a hollow walled heat exchanger
15 which, as shown in partial cross section, rests upon
a supporting block B which in turn rests upon the sample
pads 19. A colostomy bag 10 is located beneath the
samples and sits upon a support 1~3. The colostomy bag is
fluidly connected with a constant temperature bath 23
through colostomy intake tube 21 via pump P. As shown
in the drawings, pump P also provides the heat exchanger
15 with a temperature control water flow through water
intake tube 20. Stand pipe 22 is also connected to
the colostomy bag by pressure tube 24. The stand pipe
in conjunction with the constant temperature bath 23
controls both temperature and pressure. The sample is
maintained at a constant temperature of 37 C. which is
body temperature by means of the constant temperature
bath-generated fluid flow into the heat exchanger 15
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through line tube 20 (with the fluid exiting from the
heat exchanger jacket through exit conduit 16) and also
through the flow through tube 21 into the colostomy
bag 17. The pressure is maintained at 75 centimeters
of water and the flow of the modified bovine blood is
maintained for 90 minutes at a flow rate of 2 milli-
llters per hour. The capillary absorption composite
value is calculated after the test is completed. The
value is a ratio of the surface area of the stain from
the bovine blood of the upper surface of the absorbent
top layer with the stain area on the lower surface of
the bottom layer absorbent. The lower the value the
greater the amount of Z-direction passage of the fluid
and spread of the fluid along the bottom surface of
the absorbent material. It should be stressed that
the value calculated is not one reflective solely of
capillarity or the size of the capillaries. If this
was to be the desired test then there would be only a
measure of the time it took to pass the bulk of the
fluid through from one surface to the other. By
measuring the actual radial spread or dispersal of
the fluid along the bottom surface and by comparing
this value with the spread on the top, an indication
of capillarity in conjunction with absorption is
obtained.
The second method utilized for characterizing
the upper absorptive layer in the pad of the subject
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invention is controlled capacity. By the term con-
trolled capacity is meant that the absorptive layer
has some absorptlve capacity but of a limited amount.
As mentioned previously, it is desired that the second
absorptive layer contributes substantially to the
absorption process and in order to accomplish this
desideratum, it is necessary to carefully control the
absorptive capacity of the uppermost layer. The value
of absorptive capacity is determined by the capillary
sorption apparatus depicted at FIG. 3. The test will
be explained with reference to the component parts of
the apparatus described therein. Generally this par-
ticular test can be summed up as an analysis which
determines the relationship between pore volume and
capillary pressure during absorpti.on of a particular
system. The apparatus utilized fc>r conducting this
test includes a filter funnel 35 including a flat
ground PYREX filter disk 40 of medium porosity. The
filter disk is three inches in diameter and the sample
prepared is described for the previous test and cut
to the three inch diameter configuration is placed
upon the filter disk. Tubing 33 connects the funnel
to a length of capillary glass tubing which lies in a
fixed horizontal position. The fluid reservoir 30 is
connected to the capillary tube 31 by a three-way
stopcock 32. Interposed between the capillary tube
and the stopcock is a drain 36. The capillary tube
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is calibrated either internally or by utilization of a
meter stick so that the volume fluid per centimeter of
tubing can be calculated. The reservoir 30 is filled
with a commercially available research fluid called
Isoton~. This fluid has a pH of 7.4 and the surface
tension was adjusted to 54 dynes. After filling the
reservoir, an uninterrupted column of liquid extends
from the lower face of the filter plate into the capil-
lary tube. A porous Teflon weight~of approximately 210
grams is placed on top of the sample as it rests on the
sample plate and a cover is placed over the filter funnel
to prevent fluid loss. The filter funnel 35 is mounted
on a graduated meter stick 34 and the funnel is raised
to a position of 60 centimeters with the stopcock closed.
; The stopcock is then opened to allow the free flow of
fluid from the specimen tested to the capillary tube.
The system is then allowed to equilibrate with equili-
bration depending upon the particular choice of
absorptive pad tested. The cell is then lowered at
predetermined intervals allowing equilibrium at each
until the total void volume of the sample has been
filled i.e. at 0 cm. At this point the sample has gone
from a state of dryness to one of complete satu~ation.
For purposes of the particular test, the absorptive
value chosen is the amount of fluid retained per gram
of absorbent at 30 centimeters height on the desorption
cycle.
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A series of absorbent materials were tested
according to the test procedures described above and
the results set out in Table I.
Table I
MATERIALS CHARACTERIZATION
Capacity
Top/Bottom Capillary
Basis Wt.StainTension
Material g/ft~2Ratio~g/g@30cm)
Body Wadding 34g/ft21.07 1.54
(20 plys)
Wood Pulp Fluff 32g/ft2 .77 4.6
Polyester 3.0 32g/ft2 .06 .6
Denier
ABSORBIT 3.3 33~7g/ft2.13 2.8
Denier
ABSORBIT 1.5 33g/ft2 .78 3.0
Denier
Rayon 1.5 Denier 32g/ft2 1.14 1.4
Rayon 3.0 Denier 32g/ft .28 1.5
Polyester/Rayon 32g/ft2 .05 4
80/20 Blend
3.0 Denier
BUCKEYE CLD 34g/ft2 .12 7.58
AQUALON 34g/ft2 .10 7.79
Thermo Mechanical 34g/ft2 1.39 3.40
(Australian TMP)
(Pinus Radiata)
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The pulp referred to as thermo-mechanical on
the table is an example of the material described in
U. S. patent 4,047,531 set forth previously in the
disclosure as prior art.
AQUALON is a trademark of Hercules Incorporated
and is a material noted for its highly absorbent or
so-called superabsorbent characteristics. The composi-
tion is of carboxymethylated cotton linters.
BUCKEYE CLD is a trademark of Procter & Gamble
and is also a so-called superabsorbent material and con~
sists of carboxymethylated wood pulp fibers.
ABSORBIT is a trademark of American Enka,
Division of Akzona and is an alloyed cellulose fiber
containing an alkali metal salt or ammonium salt of a
copolymer or terpolymer of acrylic acid and/or meth-
acrylic acid.
It should be noted that denier seems to have
a substantial effect on performance of the particular
material chosen. Note that the higher denier ABSORBIT
and the higher denier rayon samples meet the criteria
for the test but the lower denier ABSORBIT and rayon
samples do not. It is apparent, therefore, that in
order to satisfy the particular test parameters which
definè the subject inventionj factors other than the
choice of absorbent material play a role.
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