U.S. patent number 3,888,255 [Application Number 05/511,979] was granted by the patent office on 1975-06-10 for sanitary napkin having improved attachment system.
This patent grant is currently assigned to Personal Products Company. Invention is credited to Praful H. Shah, Subramania Srinivasan.
United States Patent |
3,888,255 |
Shah , et al. |
June 10, 1975 |
Sanitary napkin having improved attachment system
Abstract
A sanitary napkin is provided to be worn in the crotch portion
of an undergarment and comprises a garment contacting surface, a
body contacting surface and an absorbent element therebetween. A
garment contacting surface is provided with a layer of material
thereon having a high co-efficient of friction. Applied to a
portion of this layer is a second layer comprising a pressure
sensitive adhesive. This system provides great resistance to
repositioning when the napkin is worn.
Inventors: |
Shah; Praful H. (Kendall Park,
NJ), Srinivasan; Subramania (East Brunswick, NJ) |
Assignee: |
Personal Products Company
(Milltown, NJ)
|
Family
ID: |
24037197 |
Appl.
No.: |
05/511,979 |
Filed: |
October 4, 1974 |
Current U.S.
Class: |
604/369; 604/366;
604/375; 604/373; 604/379 |
Current CPC
Class: |
A61F
13/5611 (20130101) |
Current International
Class: |
A61F
13/56 (20060101); A61f 013/16 () |
Field of
Search: |
;128/288,29R,29H,29W,291 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Medbery; Aldrich F.
Attorney, Agent or Firm: Lipow; Jason
Claims
What is claimed is:
1. A sanitary napkin to be adhered to the crotch portion of a
garment comprising a garment contacting surface, a body contacting
surface and an absorbent element therebetween, said garment
contacting surface having a first layer of material therein having
a high co-efficient of friction, said first layer having over at
least a portion thereof a second layer comprising a pressure
sensitive adhesive.
2. The sanitary napkin of claim 1 wherein said first layer has a
co-efficient of friction greater than about 2.0.
3. The sanitary napkin of claim 1 wherein said first layer has a
co-efficient of friction greater than about 2.5.
4. The sanitary napkin of claim 1 wherein said first layer is a
flexible, compressible, polymeric foam.
5. A sanitary napkin to be adhered to the crotch portion of a
garment comprising an absorbent body enveloped in a fluid pervious
sheet, said enveloped body having a garment contacting surface and
a body contacting surface, said garment contacting surface having a
first layer of material thereon having a high co-efficient of
friction, said first layer having a second layer thereon of an area
smaller than said first layer comprising a pressure sensitive
adhesive.
6. The sanitary napkin of claim 5 wherein said first layer has a
co-efficient of friction greater than about 2.0.
7. The sanitary napkin of claim 6 wherein said first layer has a
co-efficient of friction greater than about 2.5.
8. The sanitary napkin of claim 1 wherein said first layer is a
flexible, compressible, polymeric foam.
9. A sanitary napkin comprising an absorbent body sandwiched
between a fluid impervious sheet and a fluid pervious layer, said
fluid impervious sheet having a first layer of material thereon
having a high co-efficient of friction, said first layer having
over at least a portion thereof a second layer comprising a
pressure sensitive adhesive.
Description
BACKGROUND OF THE INVENTION
This invention concerns an attachment system for sanitary napkins
and is specifically directed toward such a system for the so called
"beltless" sanitary napkins which are worn without the use of
belts, pins, or the like.
The art has recognized the great inconvenience associated with
conventional napkins which are generally provided with longitudally
extending tabs for attaching to a sanitary belt or for pinning to
an undergarment to hold the napkin in place. Substitutes have been
sought and so napkins are now on the market having pressure
sensitive adhesive means for attaching the napkin to the crotch
portion of an undergarment. It has also been suggested that a
napkin may be held in place in the crotch of an undergarment by the
frictional restraining forces between the material of the garment
and the bottom of the napkin and to this end, napkins have been
provided with layers of polymeric cellular foam on their
garment-contacting surface to enhance this frictional
resistance.
While both the adhesively attached systems and the frictional
systems have been accepted by the consumer to a degree, they have
failed to supplant the use of the conventional napkin in many
instances in that they do not provide satisfactory assurance to the
wearer that they will remain in place and so improvements have been
sought.
Naturally, with respect to an adhesive system, sufficient
quantities of adhesive having a sufficiently substantial tackiness
can be applied to a napkin to insure its maintenance in the proper
position when worn. Such a system, however, has great disadvantages
in that the adhesive will then cling too tenaceously to the
undergarment and therefor be deposited thereon or the adhesive may
create so strong a bond as to cause the napkin or the undergarment
to tear when the napkin is being discarded, after use.
The frictional securement systems, on the other hand, does not
suffer from any of these drawbacks. It should be understood however
that, as is implicit in a frictional mechanism, the system is only
effective when forces are exerted in a direction normal to the
direction in which motion is to be restrained. While such forces
are, in fact, exerted on a napkin being worn in the crotch of an
undergarment, these forces are sporadic and vary with the positions
of the wearer and with her movements. Frequently, at some point in
time, no forces sufficient to create any frictional resistance to
movement are exerted and accordingly, the napkin is free to, and
does, move out of position.
Because of these drawbacks no attachment designed to provide
securement for sanitary napkins without the use of belts has been
completely satisfactory.
SUMMARY OF THE INVENTION
It has been discovered that these drawbacks found in prior beltless
attachment systems can be obviated and a superior system provided
which does not depend on an aggressively tenacious adhesive, yet
does not completely eliminate the ability of an attachment system
to be independent of externally applied pressure, as is the case
with a frictional system.
In accordance with this invention, there is provided a sanitary
napkin to be worn in the crotch portion of an undergarment. The
napkin comprises a garment contacting surface, a body contacting
surface and an absorbent element therebetween. The garment
contacting surface has a layer of material thereon having a high
co-efficient of friction such as, for example, a layer of cellular
foam. Applied onto at least a portion of this layer, is a second
layer comprising a pressure sensitive adhesive.
It has been discovered that this combination, for reasons not yet
clearly understood, has the completely unexpected effect of
rendering the napkin, to a surprisingly high degree, resistant to
repositioning once it is emplaced in the crotch of an undergarment.
It would be expected that, upon the application of a repositioning
force, to such an applied napkin, either the adhesive mechanism or
the frictional mechanism would be controlling, depending upon such
factors as the tenacity of the adhesive layer or the magnitude of
forces normal to the repositioning forces. It would, therefore, be
expected that the resistance to repositioning for the attachment
system of this invention would assume a value equal to either the
value for a frictional system alone or for an adhesive system
alone.
Even if one were to suspect that the frictional and the adhesive
layers in some way were each contributing to the resistance to
repositioning, the maximum total resistance to reposition that
could possibly be expected would be the sum of the resistance of
each of the systems operating alone.
Not withstanding these possible expectations, it has been
discovered that an attachment system provided in accordance with
the teachings of this invention, exhibits a resistance far greater
than the combined sum of a frictional system and an adhesive system
each taken alone. In fact, by applying to a frictional substrate
substantially less adhesive than has been heretofore used in
adhesive attachment systems, a resistance to displacement results
which exceeds the sum of the measured resistances for the
frictional system and the prior adhesive attachment system when
each is operating alone.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
FIG. 1 is a perspective view of a full sized sanitary napkin
embodying the teachings of this invention and illustrated with its
protective cover partially peeled off;
FIG. 2 is a cross sectional view of the napkin illustrated in FIG.
1 and taken through line 2--2 of FIG. 1;
FIG. 3 is a perspective view of a minipad also embodying the
teachings of this invention; and
FIG. 4 is a cross sectional view of the minipad of FIG. 3 taken
through line 4--4.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to FIGS. 1 and 2 of the drawings, illustrated therein
in perspective and cross sectional views, respectively, is a full
size sanitary napkin 10 embodying the teachings of this invention
and shown with the surface normally worn away from the body facing
upwardly. The napkin consists of an absorbent element 12 which is
shown in the form of a generally rectangular pad and may consist of
loosely associated absorbent material such as; cellulosic fibers,
for example, wood pulp, regenerated cellulose or cotton fibers;
other chemically or physically modified cellulose fibers; other
polymeric absorbent materials, both natural and synthetic, such as
hydrophilic foams (e.g. hydrophilic polyurethane foam); or may be
such commonly used absorbent material as wadded tissue paper or the
like. Alternatively, the absorbent element 12 may be a shaped form
such as molded hydrophilic polymer (e.g. a molded hydrophilic
polyurethane foam or a molded cellulosic form), or any combination
of these absorbent materials. The absorbent element 12 is wrapped
in a fluid pervious sheet material 14 which overlies the garment
contacting surface of the napkin (i.e. that surface normally worn
away from the body) and the body contacting surface of the napkin
(i.e. that surface normally worn against the body) as well as the
sides of the napkin. The sheet material may be of rectangular shape
and somewhat wider and longer than the absorbent element so that it
can be sealed by overlapping the longitudinal edges 16 and 18 of
the sheet on the garment contacting surface and sealing them
together in the area of overlap with a suitable adhesive 20. The
ends 22, 24 of the sheet may also be sealed or crimped together
thereby fully enclosing the absorbent element. The sheet material
may be any woven or nonwoven material pervious to fluid striking
its surface, such sheets being well known in the art in connection
with sanitary napkins.
In accordance with the teachings of this invention, a frictional
layer 26 of material having a high co-efficient of friction is
provided on the garment contacting surface of the napkin and as
shown in FIGS. 1 and 2, overlies a portion of the sheet material
14. Preferably, the frictional layer overlies the major portion of
the sheet on the garment contacting surface. The frictional layer
may be secured to the garment contacting layer by any of the
methods known in the art, such as with a suitable adhesive, with
heat sealing, or may be extruded thereon.
Further, in accordance with the invention, at least a portion of
the frictional layer is overlaid with a pressure sensitive adhesive
layer 28 which may be arranged in a wide variety of patterns onto
the frictional layer 26. As shown in this specific embodiment, the
pressure sensitive adhesive layer is in the form of an elongated
rectangular strip longitudinally extending on the friction layer
26. To protect this pressure sensitive layer 28, a peelable
protective cover 30 is provided which may be removed just prior to
use, and is shown partially peeled from the napkin.
In use, the protective cover 30 is peeled from the napkin exposing
the pressure sensitive adhesive. The napkin is then pressed into
position in the crotch of an undergarment and, because of the
unique combination of frictional and adhesive layers taught herein,
the napkin will resist repositioning to a remarkable and totally
unexpected extent. Notwithstanding the strong tendency to remain in
place when worn, the napkin easily peels from the crotch portion of
the undergarment when the user is disposing of the same. In fact,
because of the greater resistance to repositioning, far less
adhesive may be used in the napkin of this invention, as contrasted
with that used in the prior adhesively supported napkins, and
accordingly, the napkin of the invention peels with no more effort
than these prior napkins and with less tendency to leave
undesirable adhesive residue deposited on the undergarment and less
tendency to tear the napkin upon separation from the garment.
Referring to FIGS. 3 and 4 of the drawings illustrated there in
perspective and cross-sectional views, respectively, is a minipad
32 embodying the teachings of this invention, the minipad being
shown with the garment contacting surface facing upwardly. The
minipad 32, a smaller, thinner version of the full size sanitary
napkin, consists of a relatively thin, flat, generally rectangular,
absorbent element 34 which may be comprised of the same kind of
absorbent materials as described above in connection with the full
size napkin of FIGS. 1 and 2. A fluid pervious sheet 36 envelopes
the body contacting surface, the sides and a portion of both
longitudinal margins of the garment contacting surface of the
absorbent element. Again this sheet may be of the same type as that
used in connection with the above described full size napkin.
Overlying the garment contacting surface of the element 34 and
marginal portion of the sheet 36, is a fluid impervious layer 38
provided to preclude fluid from passing onto an undergarment and
which may be any thin flexible impervious layer, for example a
polymeric film such as polyethylene or polypropylene film,
cellophane, or a generally fluid pervious material that has been
treated to be impervious such as impregnated, fluid repellent
paper.
Adhesive may be applied to the surface of the impervious layer 38
which faces the absorbent element 34 and will permeate through the
portions of the pervious layer 36 on the garment contacting surface
of the element 34, securing both the pervious and impervious layers
to the element 34. Likewise, the ends of the minipad may be secured
by adhering the pervious and impervious layers together where they
extend beyond the ends of the absorbent element 34.
In accordance with the teachings of this invention, a frictional
layer 40 is provided overlying the major portion of the fluid
impervious layer on the garment contacting surface of the minipad,
this frictional layer 40 having a high coefficient of friction and
adhered to the minipad by the means described above, e.g., with
heat sealing adhesives, or extrusion. Overlying a portion of the
frictional layer 40 are, in this specific embodiment, two generally
square-shaped pressure sensitive adhesive layers 42 protected by
peelable protective covers 44.
Again, as was the case for the full sized napkin above described,
the protective covers 44 may be peeled off to expose the adhesive
layer 42. The minipad may be pressed into the crotch of an
undergarment where it will remain firmly in place yet be easily
peeled off after use and discarded without the tearing of the
napkin or the undergarment and without the deposition of adhesive
residue.
It will be appreciated by one skilled in the art that many
variations are possible in the two above described embodiments,
both with respect to the securement systems and with respect to the
general structure of the napkin and minipad. For example, the full
size napkin may be provided with a fluid impervious sheet, either
as an outer cover as is shown for the minipad, or as a barrier
sheet disposed between the absorbent element and the pervious layer
or even within the absorbent element. Similarly, many variations in
the configuration of the frictional layer is possible and in fact,
the fricational layer may be discontinuous, e.g., a plurality of
patches, spots, or the like distributed on the garment contacting
surface of the napkin all without sacrificing any of the advantages
taught herein. Likewise, the pressure sensitive adhesive may be
disposed in various configurations on the frictional layer. For
example, the longitudinally extending strip of pressure sensitive
adhesive shown in FIGS. 1 and 2 are to an extent interchangeable
with the square patches of adhesive shown in FIGS. 3 and 4.
The frictional layer of this invention may be one or a combination
of several available materials which meet the requirements
necessary for their use herein in that they are flexible, readily
available in the form of sheets and exhibit a high co-efficient of
friction which should be greater than 2.0 and preferably greater
than about 2.5. As used herein, the co-efficient of friction is
defined by the Instron Frictional Test as will be described in
greater detail below but may be generally stated as the force
necessary to slidably displace, on a standard surface, the surface
being tested divided by a force applied normal to the direction of
displacement. Examples of such usable frictional layer materials
are those woven and nonwoven fabrics, films and sheets which meet
the co-efficient of friction requirements set forth above and are
not incompatible with the desired use. The surface of otherwise
unsuitable materials may be treated to increase their co-efficient
of friction by mechanical means such as by embossing, micropleting
or creping or coating or impregnating with binders, adhesives, or
chemicals such as vinyl polymers e.g., ethyl vinyl acetate polymer,
polystyrene; rubbers e.g., butadiene rubber, nitrile rubber, latex
rubber or the like.
Of particular interest for use as the frictional layer are a wide
variety of flexible compressible polymeric foams. Examples are the
polyurethane foams (both ester and ether type), cellulosic foams,
polyethylene foams, both natural and synthetic latex foams,
silicone foams, and various polyvinyl foams such as
polyvinylchloride, polyvinylchloride-vinyl acetate copolymer and
copolymers of vinyl chloride and vinylidene chloride although the
latter two are not yet commercially available.
The foams may be used either alone or bonded or otherwise attached
to substrates such as films or nonwoven fabrics to add to the foam
strength during handling. Such attachment methods as flame
lamination, wet adhesive lamination, needling, fusion bonding with
hot melt, extrusion coating or transfer coating may be
employed.
The pressure sensitive adhesive element may comprise any of a large
number of pressure sensitive adhesives available on the market
including, for example, both the so-called cold pressure sensitive
adhesives, generally applied in the form of a liquid dispersion and
then dried to a tacky mass or alternatively, the rapid setting
thermoplastic (hot melt) adhesives, generally applied by heating to
a temperature above their melting point and extruding the heated
mass onto the substrate. Cold pressure sensitive adhesives are
generally based on an elastomer selected from natural or synthetic
rubbers, e.g., pale crepe rubber, smoked sheets, reclaimed rubber,
Buna-S and Buna-N type rubbers, polyisoprene, polyisobutylene, and
synthetic elastomers such as polyvinyl ethers, polyacrylates or the
like. The adhesive may be especially compounded or interpolymerized
to provide the desired characteristics of pressure sensitive
adhesives. Any of the conventional tackifiers such as rosin,
polyterpenes, coumaroneindene resins, polyalkyl styrene and the
like, may be used in proportions well known in the art. Other
ingredients such as fillers, antioxidants and pigments may also be
included. The hot melt adhesives generally comprise such block
copolymers such as styrene and butadiene styrene copolymers and are
also known in the art.
While the specific dry weight of adhesive disposed on a napkin may
vary depending on such factors as the specific adhesive used and
the specific geometric arrangement of the adhesive in general, less
adhesive is required to obtain a satisfactory resistance to
frictional forces when following the teachings of this invention
than has heretofor been found necessary. A quantity as low as 0.05
grams of adhesive per napkin has been found to be satisfactory
although it is preferred that at least 0.1 gram be used, e.g., 0.15
grams produces a superior product.
The invention, and the surprising advantages which accrue therefrom
may be better understood by consideration of the following
examples. In each of these examples and wherever else referred to
herein, quantitative valves for resistance to friction are obtained
by using the Instron Frictional Tester (Model Number TM-S). The
surface to be tested is places surface down, onto a standard
substrate which has been mounted on the movable carriage of the
Tester. One end of the sample being tested is held by a clip which
in turn is attached by means of a nylon monofilament thread to the
measuring and recording instrument of the Tester which measures and
records the force, in ounces, applied to the thread. The movable
carriage is moved in a direction away from the attached thread at a
fixed constant rate and the resistance to such movement is measured
and recorded by the instrument. For the tests used herein, the
standard substrate is a sheet of 80 .times. 80 count, bleached,
cotton print cloth obtained from Testfabrics Incorporated of
Middlesex, New Jersey and designated by them as Style 400. This
substrate is affixed to the cleaned, stainless steel surface of the
carriage by using double faced adhesive tape. The surface of the
sample to be tested is pressed down upon the standard substrate and
a four pound weight is rolled over the sample. When testing a
sample for frictional resistance under the influence of a force
acting normal to the frictional force, a weight, equal to the
desired normal force is placed upon the sample. In all cases, the
carriage is moved at a constant speed of 12 inches per minute. The
frictional force referred to herein is the maximum force recorded
by the instrument during the test and represents the force required
to dislodge the sample from the substrate. As repeated herein, the
co-efficient of friction is defined as the recorded value in grams
for the frictional resistance of the sample under normal load of
100 grams divided by 100. When testing samples as described herein,
in all cases the sample is tested, is attached to a sanitary napkin
and generally the napkin is cut transversely in half to accommodate
the size restrictions of the testing equipment.
EXMAPLE 1
A full size sanitary napkin is prepared having the general
construction of that illustrated in FIGS. 1 and 2. The napkin has
the overall dimensions of 9.72 inches long and 2.68 inches wide and
comprises a pad of comminuted wood pulp weighing 13.1 grams and
having the dimension of 7.66 inches long, 2.68 inches wide and 0.7
inch thick. The napkin is identical in all respects to the product
now being sold by the Personal Products Company of Milltown, New
Jersey as their Stayfree, (Registered trademark), Maxipad feminine
napkins with the exception that a frictional layer having the
planar dimensions of 9.72 inches long and 2 inches wide is
adhesively attached to the bottom of the napkin (the face worn
against the garment) and an elongated pressure sensitive adhesive
strip is applied centrally onto the surface of the frictional
layer.
The frictional layer is comprised of a cellular polyurethane foam
of the ether type and is obtained from the Tenneco Chemicals
Corporation, Plastic and Foam Division of East Rutherford, N.J. and
designated by them as code number 3845.
This foam has an average density of 1.38 lbs./cu. ft., a tensile
strength of at least 11 lbs./sq. in., an elongation at break of
about 150%, a tear strength of about 0.1 lb./in., and an open
cellular area of 90%. The foam has a thickness of about 0.06
inches. A sample of this foam as attached to a napkin but without
adhesive, is tested on the Instron Frictional Tester and exhibits a
co-efficient of friction of 3.9.
The pressure sensitive adhesive layer applied to the surface of the
foam is in the form of a rectangular strip having the dimensions of
7.66 inches long by 3/8 inch wide and is centrally located on the
friction layer. The adhesive is one of the rapid-setting,
thermoplastic hot melt adhesives and is obtained from the Essex
Chemical Corporation, BFC Division of Sayreville, New Jersey and
designated by them as 52-J. A total weight of 0.15 grams of
adhesive is used on the napkin. The adhesive has a viscosity of
6,800 .+-. 700 cps when measured at 350.degree.F, a specific
gravity of 0.98 at 78.degree.F, a melting range of 168.degree. .+-.
8.degree.F. The adhesive is heated to a temperature of 325.degree.F
and then extruded onto the frictional layer through a nozzle.
The napkin, when pressed into the crotch portion of an undergarment
and worn, exhibits a great resistance to repositioning and when
being discarded after use, easily peels from the undergarment.
EXAMPLE 2
A full size napkin is prepared identical to that of Example 1 with
the exception of the frictional layer and the pressure sensitive
adhesive. In this case, the frictional layer is a polyurethane foam
of the ester type obtained from the same Tenneco Chemical
Corporation and designated by them as F-4100. This foam has an
average density of 1.75 lbs/sq. in., a tensile strength of 35
lbs./sq. in., an elongation at break of 300%, a tear of 4 lbs./in.
and an average open cellular area of 45%. The foam layer is 0.035
inch thick and when a sample as attached to a napkin, but without
adhesive, is tested on the Instron Frictional Tester, it exhibits a
co-efficient of friction of 3.4.
Centrally applied to the surface of this frictional layer is a
rectangular layer of pressure sensitive adhesive measuring 7.66
inches by 3/8 inch and comprising 0.2 grams of a pressure sensitive
adhesive obtained from the Bostik Division of U.S.M. Corporation of
Middleton, Mass. and designated by them with the code number 8760.
The adhesive is a 48% solids, water-based emulsion of acrylic
polymer having a viscosity range of 2,100 -2,400 cps at 76.degree.F
and a specific gravity of 1.13. This emulsion is extruded onto the
surface of the frictonal layer and allowed to dry into a tacky
pressure sensitive layer.
The napkin, when pressed into the crotch portion of an undergarment
and worn, again exhibits a great resistance to repositioning
although somewhat less than that of the prior example. Again, upon
being discarded, the napkin easily peels from the undergarment.
EXAMPLE 3
A series of napkins having the identical configuration and
dimensions of the napkins of Example 2 are prepared, with the
exception that the quantity of Bostik adhesive is varied, as is
shown in Table 1 below. A second series of napkins are also
prepared identical to that of Example 2 with the exception that
various quantities of the Essex hot melt adhesive described in
Example 1 are applied to the ester polyurethane frictional layer as
the pressure sensitive element.
These napkins are tested on the Instron Frictional Tester under
condition of essentially zero normal force, by cutting each of the
napkins transversely in haalf to accomodate the size restrictions
of the testing equipment. As a control, a sample of the product
currently being sold by Personal Products Company as Stayfree, Maxi
Pad feminine napkins is also cut in half and identically tested.
This control sample is identical in all respects to the other
samples being tested with the exception that the frictional layer
is omitted and instead, the rectangular, pressure sensitive
adhesive, comprised of the aforementioned Bostik adhesive, is
applied directly to the nonwoven cover on the bottom of the napkin.
The control sample has 0.225 grams of this adhesive applied
thereon. The results of these tests are reported in Table 1.
TABLE 1 ______________________________________ Frictional Force at
Zero Normal Force Sample Tested (Ozs.)
______________________________________ 1. Control samples without
foam and with Bostik cold adhesive Weight of Adhesive 0.225 gm.
70.9 2. Samples with Polyurethane ester and Bostik cold adhesive
Weight of Adhesive 0.08 108.6 0.10 110.0 0.15 136.9 0.18 123.3 0.25
89.6 3. Samples with Polyurethane ester and Essex Hot Melt Weight
of Adhesive .10 83.2 .15 99.3 .20 106.4 .25 94.8 .30 88.6 .35 135.8
.40 125.4 ______________________________________
As Table 1 indicates, the frictional forces required to dislodge
the samples which, in accordance with the teachings of this
invention, include a frictional layer between the nonwoven cover
and the pressure sensitive adhesive are far greater than the forces
required to dislodge the conventional napkin sample. This is
totally unexpected in view of the fact that these tests are run
under conditions of zero normal force, i.e., when the frictional
layer should be contributing nothing to the resistance to
dislodgement. It should be noted that an advantageous enhancement
in the resistance to dislodgement is evidenced even when a quantity
of adhesive substantially less than that applied to the
conventional napkin is used.
EXAMPLE 4
A first series of napkins are prepared identical to that of Example
1 in all respects (including the ether type polyurethane frictional
layer and the 0.15 gram of Essex hot melt adhesive as the pressure
sensitive element.) A second series of napkins are prepared,
identical with the first series with the exception that the
polyurethane foam of the ester type as described in Example 2 is
used as the frictional layer. For comparative purposes, a third
series of samples are prepared identical in all respects with the
the first series with the exception that the pressure sensitive
adhesive is eliminated. Also, for comparative purposes, a fourth
series of samples are prepared identical to the conventional
Stayfree, Maxi Pad feminine Napkin, described above. Each of the
series of napkins are tested on the Instron Frictional Tester,
again by cutting the napkin transversely in half, under conditions
of varying normal loads as shown in Table 2 below. The results of
these tests are reported in that Table.
TABLE 2
__________________________________________________________________________
SAMPLE FRICTIONAL FORCE (Ozs.) Normal Force (Gm) No Load 100 gm 200
gm 500 gm 1000 gm
__________________________________________________________________________
Product with ether type Polyurethane Foam and 0.15 gm. hot melt
adhesive 144.0 160.0 163.2 174.4 208.0 Product with ester type
Polyurethane Foam and 0.15 gm. hot melt adhesive 103.4 122.7 143.7
165.4 197.4 Product with ether type Polyurethane Foam and no
adhesive 2.7 14.8 22.7 45.9 88.8 Conventional Product 74.6 81.3
86.6 97.0 110.9 Total of 3. and 4. 77.3 96.1 109.3 142.9 199.7
__________________________________________________________________________
As can be noted from an examination of Table 2, the products of
this invention, as embodied in the first and second series of
samples tested, far exceed both the conventional adhesive
attachment system and one utilizing only a frictional layer in
their abilities to resist dislodgement. Not surprisingly, the
system using only the frictional layer does not exhibit any
significant resistance to dislodgement until a substantial normal
force is applied. In view of this, it is completely surprising that
the products embodying this invention show such a marked
improvement at zero normal force conditions.
Still more surprisingly, is the fact that the sum of the
resistances of the frictional layer and that of the adhesive layer
when taken alone, are still less than the combination of these two
operating together, as in accordance with this invention.
Although the present invention has been described with reference to
several examples and embodiments showing specific products in
specific arrangements and configurations, such is not to be
considered limitative of the invention but merely illustrative
thereof.
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