CA1247319A

CA1247319A - Heat shrinkable elastomer, method of producing the elastomer and articles utilizing the elastomer

Info

Publication number: CA1247319A
Application number: CA000479349A
Authority: CA
Inventors: Attila Matray; William S. Pomplun
Original assignee: Kimberly Clark Corp
Current assignee: Kimberly Clark Worldwide Inc
Priority date: 1984-05-01
Filing date: 1985-04-17
Publication date: 1988-12-28
Also published as: DE3515804A1; ZA852583B; AU572286B2; FR2563769A1; KR850008131A; AU4129185A; KR920007728B1; BR8502101A; GB2160473A; GB8511013D0; JPS60250935A; GB2160473B

Abstract

ABSTRACT

A heat-shrinkable elastomer having a first length is produced by uniaxially orienting a copolymer having alternating polyamide and polyether block polymer segments to a second length substantially greater than a third length at which partial permanent deformation occurs. Upon removal of the tensioning force, the stretched elastomer naturally relaxes to the third length which is substantially greater than the first length but less than the second length. Upon application of heat, the elastomer shrinks and recovers its elastic properties. The heat-shrinkable elastomer can be coextruded by conventional techniques as a core layer disposed between nonelastic outer layers or skins, and the resulting coextruded elastomer can be uniaxially tensioned as above. Articles or garments such as disposable diapers advantageously use the heat-shrinkable elastomer of the present invention as a means to shirr portions thereof, such as waistbands.

Description

~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 ~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 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 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.

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.

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 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 ,i 7~

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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.

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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.

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e z ~ ~ u7 1~ ~ _ _1 cn I u-~7~

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~

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
U~
3:

~:r 3J C~ lo ~'1 ~I N ~ N N 0~ ~r r- N ~'1 ~`7 Cl~
:1 d~ r U~

JJ C
O
~:: V~D _/ N N ~ N a~ 111 N CO tl~ O N U~
O O
a ~
x ro O O O o o o o o o o o o o o O O O O F

U~ _I N ~'1 ~r 111 _i N 1~ ~ U- .-1 N rl ~r 117 1-l N ~) er 1~ o dP ,a E la a U~
~ ~ e F e E fl~
3 ~ (" r~l ~ N ~.) ~

h ~ ~ O
11~ N 1/'1 Il') ~ ~
~ I X I I L~h L~ ~J ~ 1 XX L~ O O
O I~ ~ * ~ ~O ~ :~

11 o t~ O ~ N ~ N .
JJ O ~ 1 0 ~ O ~1 ~1 ~ ~~ ~ _~ ~ ~1 O ~ a 0 ~ ~0 4 (a 0 ~ o X ~~_~ ~ X ~ o X ~ O , O a~~ ~ N C~
_ _~~ ~ U~ ~ D. ~ ~ ~ ~ ~ O
L~~

E~ Z~ ~ ~ ~
o ~a 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.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of producing a heat-shrinkable elastomer comprising the steps of:

(a) uniaxially orienting an elastomer of a first length consisting essentially of a copolymer of alternating polyamide and polyether repeat block polymer segments, said orienting conducted without the application of external heat to uniaxially orient said elastomer to a second length substantially greater than a third length at which permanent deformation of said elastomer occurs; and (b) releasing the uniaxial orientation applied according to step (a) to allow said elastomer to naturally relax to said third length, which is substantially greater than said first length, thereby providing a heat shrinkability of at least about 20%.

2. A method as in claim 1 wherein said elastomer is uniaxially oriented above about 200% elongation to achieve said second length and produce a heat shrinkability of at least about 40%.

3. A method as in claim 1 wherein said elastomer is uniaxially oriented between about 200% to about 700% elongation to achieve said second length.

4. A method as in claim 1 wherein said third length is between about 40% to about 60% of the said second length.

5. A method as in claim 1, which further comprises the step of (c) heat shrinking said elastomer.

6. A method as in claim 2, which further comprises the step of (c) heat shrinking said elastomer.

7. A method as in claim 3, which further comprises the step of (c) heat shrinking said elastomer.

8. A method as in claim 5 wherein step (c) is conducted by exposing said elastomer to microwave energy.

9. A heat shrinkable elastomer produced as in claim 1, 2 or 3.

10. A heat-shrinkable elastomer produced as in claim 1, 2 or 3 wherein said copolymer has the formula:

wherein R1 is a polyamide selected from the group consisting of nylon 6, nylon 10, nylon 11, nylon 12, and nylon 6,6; R2 is a polyether selected from the group consisting of polyethylene glycol, polypropylene glycol and polytetramethylene glycol; and n is an integer.

11. An article having a portion which is elastically shirred, comprising a heat shrunk elastomer attached to the article and produced according to claim 5, 6 or 7.

12. A method of manufacturing an article having a portion which is elastically shirred, said method comprising the steps of:
(a) forming a heat-shrinkable elastomer by uniaxially orienting an elastomer of a first length consisting essentially of a copolymer of alternating polyamide and polyether repeat block polymer segments, said orienting being conducted without the application of external heat to uniaxially orient said elastomer to a second length substantially greater than a third length at which permanent deformation of said elastomer occurs, and releasing the uniaxial orientation to allow the elastomer to naturally relax to said third length which is substantially greater than said first length, thereby providing a heat shrinkability of at least about 20%;
(b) affixing the elastomer formed according to step (a) to said portion of the article in a direction generally parallel to the desired direction of shirr; and (c) heat shrinking said affixed elastomer to thereby elastically shirr said portion of the article whereby said elastomer upon heat shrinkage becomes substantially elastomeric.

13. A method of manufacturing an article comprising the steps of:
(a) forming a heat-shrinkable elastomer by uniaxially orienting an elastomer of a first length consisting essentially of a copolymer of alternating polyamide and polyether repeat block polymer segments, said orienting being conducted without the application of external heat to uniaxially orient said elastomer to a second length substantially greater than a third length at which permanent deformation of said elastomer occurs, and releasing the uniaxial orientation to allow the elastomer to naturally relax to said third length which is substantially greater than said first length, thereby providing a heat shrinkability of at least about 40%; and (b) affixing the elastomer formed according to step (a) to said article.

14. A method as in claim 13 further comprising the step of:
(c) heat shrinking the affixed elastomer to cause shirring of said article.

15. A method as in claim 14 wherein step (c) is conducted by means of microwave energy.

16. An article manufactured according to the method of claim 12, 13 or 14.

17. A method of producing a heat-shrinkable elastomer comprising the steps of:
(a) uniaxially orienting an elastomer having a first length and including outer layers of a nonelastomer and a core layer disposed between the outer layers, said core layer composed of an elastomer consisting essentially of alternating polyamide and polyether repeat block polymer segments, and said orienting being conducted without the application of external heat to uniaxially orient said elastomer above about 200% elongation to achieve a second length substantially greater than a third length at which permanent deformation of said elastomer occurs; and (b) releasing the uniaxial orientation applied according to step (a) to allow said elastomer to naturally relax to said third length which is substantially greater than said first length, thereby providing a heat shrinkability of at least about 20%.

18. A method as in claim 17 wherein prior to step (a) there is practiced the step of forming said elastomer by melt laminating said core and outer layers.

19. A method as in claim 17 wherein said core layer is between about 70% to about 90% by weight of said elastomer.

20. A method as in claim 17 wherein said third length is between about 20% to about 60% of said second length.

21. A method as in claim 17 wherein step (a) is conducted so as to uniaxially orient said elastomer to a second length which is between about 200% to about 700% of said first length.

22. A method of claim 17 wherein said core layer is a copolymer having the formula:

wherein R1 is a polyamide selected from the group consisting of nylon 6, nylon 10, nylon 11, nylon 12 and nylon 6,6; R2 is a polyether selected from the group consisting of polyethylene glycol, polypropylene glycol and polytetramethylene glycol; and n is an integer.

23. A heat shrinkable elastomer produced according to claim 17, 18 or 19.

24. A heat shrinkable elastomer produced according to claim 20, 21 or 22.

25. An article produced by affixing an elastomer produced according to claim 17, 18 or 19 to a portion of the article and subjecting the article to heat so as to heat shrink said elastomer and thus shirr said portion to which said film is affixed.

26. An article produced by affixing an elastomer produced according to claim 20, 21 or 22 to a portion of the article and subjecting the article to heat so as to heat shrink said elastomer and thus shirr said portion to which said film is affixed.