Note: Descriptions are shown in the official language in which they were submitted.
~73~
The present invention relates to heat-shrinkable elastomers,
and in its more specific aspect to heat-shrinkable elastomers
especially useful for elastic shirring in garments, such as
disposable diapers or like incontinence products.
Elastic shirring of the garments in selected reglons is
desirable or essential in order that the garment will conform to
the body of the wearer such as at the waist or wrist. This
feature is especially true with respect to disposable garments,
including plastic garments such as disposable diapers. Hence,
the invention, its background and several embodiments, will be
described with particular reference to disposable diapers or
incontinence garments, but it is understood that the invention is
applicable to other garments such as gowns, masks, shoe covers,
etc.
Disposable diapers typically have an "hour glass" or general
"I-shaped" configuration. The diapers are produced from a
continuous web of inner and outer facing sheets and an absorbent
batt wherein each waistband area of a diaper module is integrally
connected to the waistband area of immediately ad~acent diaper
modules, as described in more detail below. The web is cut at
the waistband area transverse to the web travel direction to
thereby form individual diapers. Thus, the waistband is cut in a
cross-machine direction.
Application of elastomeric material to the legbands of
disposable diapers has been commercially achieved. However, when
elastomeric material is attempted to be applied to waistbands on
the same diaper having the legband attached, significant produc-
tion problems arise. For example, if tension is maintained in
the legband
-- 1 --
~7~
direction, the elastomer attached to the waistband tends to buneh the
diaper and thus interfere with folding, packaging or other production
sequences. We know of no commercial solution to the production
problems described above.
Recently, certain proposals have been made regarding
heat-set, heat-shrinkable elastomeric materials for use in effecting
shirring of disposable garments suGh as disposable diapers or hospital
gowns as evidenced by U.S. Patent Nos. 3,912,565; 3,819,401; and
3,639,917.
U.S. 37912,565 to Koch et al and U.S. 3,819,~01 to
Massengale et al disclose that flexible polyurethane and plastici7ed
vinyl chloride sheet materials, respectively, are heated, stretched, and
cooled to prevent premature shrinkage. In order to prevent premature
shrinkage, the elastomeric sheet materials are again heated to permit
limited relaxation and cooled to heat set the sheet materials. The heat
set sheet materials are then applied to articles and upon application of
heat, they shrillk to their original lengths thus shirring the articles. As
more fully explained with reference to Figure 1 in Koch et al and
Massengale et al, the sheet material is stretched between heated roll
25 and nip rolls 31, 33, then cooled, partially relaxed in heated liquid
bath 45 and collected in roll 49. What should be noted in Koch et al
and Massengale et al is that stretching is accomplished by application
of external heat, cooled at the stretched condition, then again heated
by application of external heat to effect controlled heat shrinkage.
U.S. 3,639,917 to Althouse discloses an elastomer
comprising block copolymers that are heat-shrinkable. According to
Althouse, the block copolymers are expanded or deformed from an
original length at elevated temperatures to achieve a new length and
then cooled to maintain the copolymers at the new length in the
expanded state. The copolymers of Althouse therefore retain the new
length when cooled until again heated at which time shrinkage to the
original length occurs. The copolymers of Althouse therefore are
expanded from their original length to a new length, maintained at the
new length by cooling, and subsequently returned to the original length
upon application of heat.
According to one aspect of the present invention there is
provided a method of producing a heat shrinkable elastomer which
includes the steps of uniaxially orienting ~n elastomer of a
first length consisting essentially of a copolymer of alternating
polyamide and polyether repeat block polymer segments, the
orientating being conducted with the application of external heat
to uniaxially orient the elastomer to a second length substan-
tially greater than a third length at which permanent deformation
of said elastomer occurs, and releasing the uniaxial tensioning
applied according to the above step to allow the elastomer to
naturally relax to the third length which is substantiall
greater than the first length, thereby providing a heat
shrinkability of at least about 20%.
The present invention also relates to a heat shrinkable
elastomer produced according to the above method.
According to yet another aspect of the present invention
there is provided an article which is produced by fixing the
elastomer which has been produced in accordance with the above
method to a portion of the article and subjecting the article ~o
heat so as to heat shrink the elastomer and thus shirr the
portion to which the elastomer is affixed.
More specifically, the elastomer of the present invention
which exhlbits potential elastic energy recoverable upon heat-
shrinking is oriented as by stretching or rolling ln one direc-
tion without the application of external heat to a length so that
when the applied tension is removed, the elastomer relaxes to a
permanent deformation length greater than the original length yet
less than the stretched length. More significantly, the he~t-
shrinkable elastomer having an original or first length is
stretched in one direction to a substantially greater or second
length wlthout the application of external heat as, for example,
to at least about 200%. When relaxed, the elastomer assumes a
permanent deformation at a third length somewhere between or
somewaht intermediate to the first and second lengths. This
third length or intermediate state is somet~mes known as a
-- 3 --
31~
preform. The tensioned elastomer including the preform exhibits
reduced elastic properties while in the deformed state. Upon the
subsequent application of heat, the elastomer shrinks and
recovers or assumes its elastic properties. The elastomer, when
tensioned at practical or preferred values, exhibits an increase
in permanent deformation length with increased tension whereas
the conventional elastomers exhibit minimal permanent deforma-
tion.
It is significant that heat-setting and cooling of the
elastomeric preform is obviated. Tensioning and relaxing the
elastomer, which apparently results in uniaxial orien~ation of
the polymer, is preformed without the application of external
heat, that is at room temperature or ambient conditions (e.g. 70-
75~F) althouyh an internal rise in temperature occurs. However,
the elastomer retains its heat shrinkable characteristics. Thus,
certain processing steps and associated equipment are eliminated
in the commercial application of the elastomer to a garment.
In accordance with one embodiment of the invention, the
elastomer is coextruded or laminated with a nonelastic. The
elastomer and the nonelastic may be coextruded as a composite
sheet according to known techniques. More desirably, the com-
posite
- 3a -
7~
comprises three layers - an intermediate elastomeric layer and two
outer layers. The elastomer may exhibit tackiness and on standing as
in roll form may block. The skin layer of inelastic is selected to
provide non-blocking or release when the material is unrolled, Nhich
5 facilitates processing, such as, guiding, cutting and placement.
Further, the elastomer may exhibit poor or no adhesion to many
garment materials. Therefore, the oppositely disposed outer layer of
the composite which ~aces the garment is affixed to the garment as
with a pressure sensitive or heat-sensitive adhesive. Thus, the
10 composite has these advantages not possessed by the single layer
composite.
BRIE~F DESCRIPTION OF
T~ ACS~OMPANYING DRAWINGS
Reference will hereinafter be made to the accompanying
15 drawings wherein like reference numerals throughout the various
Figures denote like elements and wherein:
FIGURE 1 is a block diagram representing the processing
steps of the present invention;
F~GURE Z is a schematic plan view of a portion of a
continuous diaper web during manu~acture having ribbons o~ the P;lm oP
the present invention attached to the waistband area thereof and shown
prior to being heat-shrunk; and
FIGURE 3 is a schematic view of a means to coe~trude the
multilayer film embodiment of this invention.
DETAILED D~SCRIPTION OF THE
PREFERRED EX M LARY E BODIMENTS
1. Slnale Layer Film Embodiment
Referring to FIGURE 1, it is seen that the process of the
present invention begins with the extrusion of the polymer which
may be in pellet form by conventional extrusion means 10 to form
a film 12 which is preferably subsequently stored in rolls 14 and
transported to the next processing station e.g. film stetching
16. Advantageously, the extruded film has a thickness of between
about 2 mils to about 4 mils, although other thicknesses are
possible in dependence upon the amount of stretching that is
needed to achieve the desired degree of article shirring, the
specific polymer that is u~ed, the economiss of production or the
like.
While the term "film" has been used above, the elastomers of
the present invention can be produced in other structural ~orms
such as ribbon, thread, tape or the like. For convenience of
re~erence, however, the term "film" will be used hereinafter.
As briefly mentioned above, the polymer used to produce the
film in accordance with the present invention is preferably a
block copolymer having alternating segments of polyamide and
polyether block polymers according to the general formula:
l' ]
wherein Rl represents the polyamide polymer block exemplified by
nylon 6, nylon 6,6, nylon 10, nylon 11, and nylon 12 and R~
represents the polyether polymer block exemplified by
polyethylene glycol, polypropylene glycol and polytetramethylene
glycol and wherein n is an integer. The copolymers in accordance
with the above description are commercially available from the
Rilsan Corporation of Glen Rock, New Jersey under the trade mark
PEBAX. Particularly preferred for the
-- 5 --
films of the present invention are the PEB~X extrusion grades 2533
and 3533.
The film 12 formed as described previously is then
subjected to uniaxial stretching without application of external heat by
any conventional film stretching means 16 such as by the differential
speed roll process. A particularly preferred differential speed roll
suitable for use as film stretching means 16 to stretch films of the
present invention is a Marshall and Williams Model D7700 machine
direction stretching apparatus. According to well-known principles of
differential roll stretching, the film 12 is uniaxially stretched due to
the differential speed of low- and high-speed rolls. Another method of
orientation to induce heat shrinking is by "cold rolling" on multi-stack
rolling mills under external pressure similar to that used in rolling thin
metal sheet such as aluminum foil. Regardless of the orientation
method, however, the common phenomenon accomplished is an increase
of the dimension in the direction of orientation by a corresponding
decrease in thickness.
Conventional, uniaxially stretched polymeric films are
typically preheated to a temperature at or above the second order
phase transition temperature. The conventional film is then stretched
while at such elevated temperatures and subsequently cooled while
being maintained in its stretched condition. Such preheating is
important to conventional films so as to ensure proper stretching and
orientation thereof.
Preheating is completely unnecessary with the present
invention, however. Some heat may be generated during the unia~ial
stretching of the film 12 due to erictional forces or the like
particularly if differential speed rolls are utilized to effect eilm
stretching, but it has been surprisingly found that such temperature is
significantly below (e.g. substantially less than 175F) the temperature
at which deformation relaxation of the copolymer film begins to occur.
That is, even though some heat may be frictionally generated during
film stretching, the temperature at which the eilm of the present
invention reaches is substantially below the temperature at which
35 relaxation of the deformation occurs. Heat setting, oE course,
contemplates that the temperature must be at or above the tempera-
ture at which deformation relaxation begins to occur. (See, U.S.
3,912,565 at column 3, lines 28-38.) Thus, no heat-setting of the
oriented film of the present invention is required in direct contrast to
5 what was conventionally thought to be essential in this art.
The amount of uniaxial stretching of the elastomer films
of this invention is important to achieve adequate shrinkage and thus
shirring of an article utilizing the film. In accordance with the present
invention, uniaxial tensioning is accomplished so that the film is
10 stretched to an elongated length significantly greater than that length
at which permanent deformation occurs. Upon removal of the applied
tension, the film will naturally rela2~ (e.g. wi thout being induced to
relax by the application of heat) to a length greater than the original
length, corresponding to the amount of permanent deformation which
15 has been imparted thereto. Thus, the differential length between the
permanent deformation length and the original, pre-stretched length is
available for heat shrinkage. Upon application of heat therefore (e.g.
at or above 175F) the stretched film will further be induced to relax
and shrink. That is, a large portion Oe the differential length of the
2 0 stretched film between the original length and the permanent
deformation length is present as permanent deformation which is
capable of recovery upon application of heat.
The film of the present invention is uniaxially stretched to
achieve between about 200% to about 100% elongation per unit length
25 of the film. It has been discovered that when the film of the present
invention is uniaxially stretched within the ranges noted above, it will
exhibit some natural relaxation upon removal of the stretching force
but such relaxation will not proceed below the respective p~rmanent
deformation length. The length of the film corresponding to the
30 amount of permanent deformation imparted thereto is therefore
dependent upon the amount of uniaxial tensioning to which the film is
subjected. However, for uniaxial stretching in the range of about 200%
to 700%, the permanent deformation length will be between about 20~6
and 60% of the film's elongated length. That is, the amount of
35 permanent deformation available for heat shrinkage will be about 20?6
3~9
to about 60% of the stretched length of the film when stretched
between about 200% to about 700% (e.g. when stretched 3x to 8x of
the orlginal length).
The amount of permanent deformation which is imparted to the
film of the present invention will therefore determine the degree
of heat shrinkage which is available to adequately shirr that
portion cf an article with which it i5 associated. It has been
found that a permanent deformation o~ between about 20-60% of the
elongated length (termed the "unrestricted shrinkage") will
advantageously translate into between about 30-45% shrinkage
(termed the "restricted shrinkage") when the uniaxially stretched
film i5 attached to a portion of a flexible garment such as the
waistband of a disposable diaper. That is, since the flexible
article will interfere or restrict the shrinkage of the film
somewhat, complete return to the original, pre-stretched film
length does not occur upon heat shrinkage. Nevertheless, when
the film of the present invention is uniaxially stretched as
described above (e.g. between about 20-60% permanent deformation
or elongation based upon the final elongation to which the film
is subjected), desirable article shirring occurs.
Subsequent to stretching, the film of the present invention
is advantageously slit by conventional film slitting means 40
along the direction of permanent deformation (that is, parallel
to the uniaxial stretching direction) to form ribbons which are
advantageously 3/8" to 1~2" wide but other widths are, of course,
possible depending upon the intended application. The ribbons
can then be level wound according to known techniques into spools
for use in diaper production equipment 42.
The ribbons are preferably cut to desired lengths (ad-
vantageously about 6") while still in their heat-shrinkable
elongated condition and adhesively secured to waistband portions
50, 52 of diapers 54, 56 as the connected web 60 travels in the
machine direction (arrow 57 in FIGURE 2). Adhesives suitable for
binding ribbons of the films of this invention to the waistband
areas of the diapers are commercially available from the H.B.
-- 8
4~
Fuller Co. under the designation HL-130~-33-1 and the Findley Co,
under the de~ignation X807-378-01.
It is presently contemplated that a stack of folded diapers
(advantageously eight to ten diapers per stack) having ribbons of
the heat-shrinkable elastomeric film of the present invention
will be collectively subjected to heat by suitable heat shrinking
means 44 so as to cause heat shrinkage of the ribbons to thus
shirr the waistband portions of the diapers. Preferably, heat
shrinkage of the ribbons in the diaper stack is accompllshed
according to copending and commonly owned Canadian Patent
Application Serial No. 4~9,482, filed April 18, 19~5, and
entitled "FORMATION OF ELA5TICIZ~D PORTIONS OF DISPOSABL~
GARMENTS AND OTHER ARTICLES". In such a mann~r no interference
with diaper folding equipment due to premature cross-machine
ga~hering or shirring of the waistbands will occur.
2. Multilayer Film Embodiment
A further embodiment of the present invention resides in the
coextrusion of the polyether/polyamide copolymer described
hereinabove with nonelastic polymers such as ethylene vinyl
acetate (EVA), EVA ionomers such as, Plexar 3, Plexar 102, and
Surlyn 17021, and polyethylene or the like to advantageously
produce a film which is heat-shrinkable but yet exhibits a
pleasing hand. Skin compatability of ealstic waistbands is
desirable when the films of the present invPntion are used as
waistbands for disposable diapers. According to this embodiment
of the present invention, the polyether~polyamide copolymer is
coextruded as the core or intermediate layer with surface exposed
layers or outer layers of nonelastic polymers. Although the
_ g
1PleY.ar 3 and Plexar 102 are trade marks for commercially
available materials of the Chemplex Corporation while
Surlyn 1~02 is a trade mark for a commercially available
material from DuPont.
outer layers may not be heat-shrinkable~ they will not significantly
affect the heat shrinkage of the core of such an extent that adequate
shirring of the garment will not occur owing to the superior heat-
shrinking capabilities Oe the core layer film.
The coextrusion of layers of diverse polymers or
thermoplastic materials is, in and of itself, well known in the art as
generally exemplified by U.S. Patent Nos. 3,557,Z65 to Chisholm et al
and 3,479,425 to Lefevre et al. Coextrusion of diverse polymer
materials is typically accomplished utilizing a multi-manifold
coextrusion die or a single manieold die with combining adaptors which
permit the melt lamination of multiple layers of dissimilar polymer
materials. One particularly preferred combining adaptor which can be
advantageously employed to achieve coextruded films of this invention
is described in U.S. Patent No. 4,152,387 to Cloeren.
A conventional means of producing coextruded multilayer
films of this invention is schematically depicted in accompanying
FIGURE 3. As shown therein the outer nonelastic layers ~0, 72 are
formed by melt extruding the nonelastic polymers 74 by means of
extruder 76. Similarly, the elastic core layer 80 is formed by melt
extrusion of the elastic polymer 82 (e.g. preferably PEBAX extrusion
grades 2533 or 3533) by means of extruder 84. The melt extruded
polymers 74, 82 are then passed to combining adaptor 90 via conduits
78, 8~, respectively. As schematically shown, the elastic polymer 82
melt laminates with the nonelastic polymer 74 to form a core layer 80
of the elastic polymer 82 which is sandwiched between outer layers 70,
72 of the nonelastic polymer 74.
Although the temperature of the combining adaptor 90 is
dependent upon the polymers utilized, it is preferable to maintain the
temperature thereof between about 360F to about 500F (preferably
about 400F) to advantageously form the coextruded films of this
invention. Additionally, it is preferable that the total thickness of the
coextruded film be between about 2 to about 5 mils with between about
2 to about 4 mils being particularly preferred, although other film
thicknesses could be utilized in dependence upon the Einal stretched
thickness that is desired. The coextruded film contacts chill rolls 92,
94 so as to cool it to substantially maintain the extruded thickness
thereof. A~other means for forming the multila~Jers is by blown
coextrusion using a circular die with coaxial flow channels
corresponding to the individual layers of the composite. The
coextruded film can then be oriented by conventional stretching means
16, slit into ribbons by slitting means 40, applied to diapers in diaper
production means 42 and heat shrunk by heat shrinking means 44 as
described above with reference to FIGURE 1.
The core layer of elastic polyether/polyamide block
polymer is preferably the major constituent (based on percent of
coextruded eilm by weight) present in the resulting coextruded eilm.
The core layer therefore preferably is present in the coextruded film in
an amount between about 70% to about 90% by weight, with the
balance being substantially evenly distributed between each of the
outer layers.
The behavior of the coe2ctruded composite or laminate of
this invention is similar to the behavior of the single layer films
described above. That is, when the composite is uniaxially oriented to
a length between about 200% to about 700% of the original length,
permanent deformation will be imparted thereto at a length generally
between about 20% to about 60% of the elongated length. Upon
removal of the tension force, the coextruded film will likewise
naturally (e.g. without application of heat) relax to the length
indicative of the permanent deformation imparted thereto (e.g. the
permanent deformation length). Thus, the differential in length
between the elongated length and the permanent deformation length is
available as a shrinkage length so that when heat is applied thereto
(generally at temperatures near 1~5F) the film substantially relaxes
and shrinks to recover its elastic properties.
As briefly noted above, the outer layers or skins of the
composite tend to interfere somewhat with heat shrinkage of the
overall film due to the nonelastic nature of the skins. However, such
interference is not of a degree which masks the heat shrinkability of
the composite. Since the outer layers are nonelastic, uniaxial
tensioning of the coextruded film also permanently deforms such outer
.3~9
layers. However, the overall coextruded film will stlll natural-
ly relax to between about 20%-60% of the elongated length upon
removal of the tensioning force owing to the presence of the
elastic core layer.
The intralaminar bonding strength between the outer
layers and core layer is preferably at least 1200 grams~in to
ensure that the layers remain laminated to one another when
subjected to uniaxial orientation of up to about 700% elongation.
The use of microwave energy as the means to heat shrink
both the single layer and multilayer film embodiments of the
invention is also possible. It has been discovered that when the
elastomers of the 1nvention are exposed to microwave energy of
24~Q MHz and between 3-6 kilowatts for about 5-10 seconds,
adequate heat shrinkage occurs. That is, when exposed to
microwave energy the elastomers shrink between about 20% to about
60% of the stretched length. For example, a particular heat-
shrinkable elastomeric ribbon of this invention formed of a core
layer of PEBAX extrusion grade 3533 coextruded with outer layers
of Plexar 102 and uniaxially stretched to 4x the or~ginal length
(e.g. 300% stretch) to achieve a ribbon thickness of 1.5 mils,
exhibited at least 20~ heat shrinkage when affixed to the inside
waistband area of a diaper when the ribbon-affixed diaper was
exposed to microwave energy of 2450 MHz and between 3-6 kilowatts
for about 5-10 seconds.
The following nonlimit~ng examples further illustrate
the invention.
EXAMPLE 1
Single layer films were prepared from various commer-
cially available polymers by the chill roll cast method using a
36" extrusion die at die temperatures of 400-425F and at line
speeds of 120 fpm for 2 mll and 60 ~pm for 4 mil film. Heat
shrinkabillty of film samples was examined by preparing 1" x 10"
~trips of film cut in the machine direction. The film samples
were then marked at initial lengths of 4" (101.6 mm) and were
conditioned at 72F, 55% relative humidity for 24 hours.
Subsequent to conditioning, individual samples were stretched on
an Instron Tensile Tester at ~2F and 55% relative
- 12 -
humidity to 100%, 300% and 500% elongation (e.g. 2X, 4X and 6X
stretch). The initial jaw span o~ the instron Tensile Tester ~,7as
4.5 inches which translated into film sample lengths of 9 inches
at 100% elongation; 18 inches at 300% elongation and 2~ inches at
500% elongation, respectively. In each instance, the rate of
stretching was 1000 mm/min, The stretched samples were again
conditioned at 72F and 55% relative humidity for 24 hours.
Permanent deformation was then measured as a percentage of
the original 4 inch film length according to the formula:
% Permanent Deformation = L~ - Lo x 100
Lo
wherein Lo represents the original film length and L~ represents
the final length to which the film relaxes without applica~ion o~
heat after the applied tension is removed.
To determine the amount of heat shrinkability which is
imparted to the films, the stretched film samples were then heat
shrunk by subjecting the samples to 175F for 5 seconds. The
length of each film sample subsequent to heat shrinkage ~Lf1) was
measured and the percent heat shrinkability was calculated by the
formula:
% Heat Shrinkability = L~ - L~1 x 100
L~
wherein L~ is the length of the film as defined above with
respect to percent permanent deformation.
In order to determine the elastic nature of the heat shrink
materials, the hysterisis ratio of each sample was calculated
using an Instron Tensile Tester equipped with an integrator unit.
In each instance, the stretched and heat shrunk samples were
secured between the jaws of the Instron Tensile Tester to
establish a 4" initial length regardless o~ the sample size
subsequent to heat shrinkage. ~ach sample was then stretched to
100% elongation at 500 mm/min stretching rate. Thus all samples
were elongated to 8 inches. During the elongation, the in-
tegrator unit measured the area under the stretch curve and the
resulting data was noted. When 100% elor.gation occurred, the
integrator unit was reset and relaxation of the instron
- 13 -
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jaws was initiated until the initial 4 inch separation length was
achieved. During relaxation, the integrator unit measured the area
under the relaxation curve. The hysterisis ratio (HR) was therefore
calculated as follows:
HR Area under stretching curve
~ Area under relsxation curve
Since a true elastomer (e.g. rubber) will exhibit a hysteresis ratio of
about 1.0, measurement of the hysterisis ratios of the tested films
provided an indication of their elasticity subsequent to heat shrinkage.
Thus, single layer films which exhibited heat shrinkage of between
about 40% to about 60% or more while yet having a hysterisis ratio of
less than 2.0 were suitable for use as elastic waistbands for disposable
diapers. The results are tabulated below in Table 1.
~ 2~73~.9
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E~AAIPLE II
Coextruded multilayer films having an elastomeric film
core layer and nonelastomeric film outer layers were prepared using a
conventional combining adaptor commercially obtained from the
Cloeren Co. and was the type described in U.S. 4,152,387. Testing for
percent permanent deformation, percent heat shrinkage and hysterisis
ratio were conducted as in Example I, above7 and the results are
tabulated in Table II below.
V
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E~AMPLE III
Example ll was repeated with the exceptions that Plexar
102 (commercially available from the Chemplex Corp.) and Surlyn-1702
(commercially obtained from DuPont) were utilized as outer layers in
10%/80%/10% relative volume compositions (e.g. outer layer/core
layer/outer layer) with a core layer of PEBAX 2533 and 3533. Testing
for percent heat shrinkage and hysteresis ratio were conducted as in
Example I and the results thereof are tabulated in Table 111 below.
~2a~3~
21
o
v
o r~o ~ tn u7 ~ o ~ ~ ~ o ,~ o o
~7 r~ o ~ ~ o N N ~ O 0
~ _N ~1 ~ N _~ N N N N N ~ 1 N _1 N
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O O
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3~
From the above examples, it is readily apparent that both
the single layer and coextruded PEBAX films exhibit satisfactorJ
results in percent heat shrinkability (e.g. between about 30-70%) when
stretched to elongation values of between about 200% to about 500% so
5 that, when applied to the waistbands of disposable diapers, for
example, adequate shirring is achievedO For most of the tested films,
the percent heat shrinkability decreased as the percent film stretch
increased from 300% to 500%, while in direct contrast, the films of
this invention increased in percent heat shrinkage as the film stretch
increased from 300% to 500% (e.g. compare sample nos. 4-5 to 1-2; 8-
10 to 11-19). Sample Nos. 3 and 6, although increasin~ somewhat in
percent heat shrinkability did not exhibit the requisite heat
shrinkability useful eor elastically shirred articles. Thus, the films of
the present invention now mske it economically feasible to produce
15 disposable diapers having elastic waistbands which exhibit the
necessary amount of heat shrinkability to achieve suPficient shirring.
Moreover, the films of the present invention overcome many of the
commercial and production disadvantages of conventional heat-
shrinkable elastomers since no heat setting is required in order to
20 achieve the above-described advantages.
