CA1299331C - Method and apparatus for line-stretching an elastomer film - Google Patents

Abstract

ABSTRACT

The present invention provides an improved method and apparatus for uniaxially orienting an elastomer. A
supplying mechanism provides a strip of elastomer material, which is capable of being deformed from an initial length to a retained, activatable elongated length. A restricting mechanism limits a movement of the elastomer material from the supplying mechanism, and a traction mechanism applies a selected amount of uniaxial tension to an intermediate portion of the elastomer material, which is located between the restricting mechanism and the traction mechanism. The traction mechanism is spaced from the the restricting means by a selected distance, is constructed to receive the elastomer material from the supplying mechanism, and is arranged to cooperate with the restricting mechanism to stretch the intermediate portion of the elastomer material by a selected amount. A regulating mechanism controls a movement of the elastomer material from the traction mechanism to allow a selected amount of contraction of the elastomer material, thereby imparting a selected elongated length thereto. A take-up mechanism then accumulates the elongated elastomer material.

Description

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METHOD AND APPARATUS FOR LINE-STRETCHING AN ELASTOMER FILM
_ Description Field of the Invention The present invention relates to a method and apparatus for stretching a film material. More particularly, the invention relates to a method and apparatus for line stretching an elastomer film material to impart heat shrink characteristics thereto.

Background of the Invention The technique of stretching and drawing a plastic film to increase its length and decrease its thickness has been well known. In particular, U. S. Patent 3,619,460 describes a multi-stage process ~or uniaxially orienting a stereoregular polypropylene film between rolls to ultimate draw ratios in the range of 6:1 up to fibrillation. The orientation of the film is performed in two or more successive integral orientation stages.
U. S. Patent 2,854,697 issued October 7, 1958 to W.
Ryan describes a device for controllably stretching continuous sheet material bv the controlled application of opposed tensional forces and heat. The tensional forces and heat are applied to the material such that the material is restrained from narrowing substantially. U. S. Patent 2,804,652 issued September 3, 1957 to S. Balkan describes a device for processing continuous sheets of extensible organic plastic material. The material is longitudinally stretched under conditions whereby the width of the stretched sheet is substantially the same as the width of the unstretched sheet. U. S. Patent 3,201,826 issued August 2~, 1965 to G. Bruckner describes another device for stretching flexible strips of organic plastic materials.
The device presses the lateral edge portions of the plastic sheet material upon a preferably rotatable support during ~ .

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z the stretching operation and thus maintains the original width of the plastic sheet.
In conventional stretching operations, the stretched, plastic film is ~reated to "set" the plasticized film after it has been stretched. This "set" can be produced by heating or cooling the stretched film to a selected temperature, as discussed in U. S. Patent 3,208,100 issued September 28, 1965 to J. Nash; and U. S. Patent 3,243,844 issued April 5, 1966 to J. Nash.
Various devices and techniques have been employed to change the dimensions of a stretched thermoplastic film.
For example, U. S. Patent 2,812,550 issued November 12, 1957 to M. Chavannes describes a technique for reducing the thickness o~ a thermal plastic film. The technique employs multiple stretching steps and multiple annealing steps. U.
S. Patent 2,838,800 issued June 17, 1958 to D. Hertz describes a technique for improving the appearance of a thermoplastic sheet material. The sheet material is subjected to pressure and heat by immersing the sheet material in a bath of molten metal. U. S. Patent ~,310,485 issued January 12, 1982 to R. Dauber descrih,es a process for improving the flatness of plastic film that has been sub~ected to compression rolling. The flatness of the compression-rolled plastic film is improved by passing the film under tension over heated rolls, stretching the heated film, setting the stretched film by passing it over a tempering roll and then cooling the set film by passing it over a cooling roll.
Conventional stretching devices, such as those described above, have not been adequate for stretching and uniaxially Grienting an elastomeric strip material. The conventional devices have caused excessive breakage of the stretched elastomer strip and have induced undesired nonuniformlties therein. In addition, the conventional techniques and devices have not reliably produced a selected amount of stretch within the elastomer sheet, and ,, I ~ ~_,.. .

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have not been able to accumulate the oriented, stretched elastomer sheet on a storage reel without developing excessive forces, which can undesirably collapse the cores on the take-up reel.
According to one aspect of the present invention there is providPd an apparatus for uniaxially orienting an elastomer, the apparatus having supply means for providing a strip of elastomer material which is capable of being deformed from an initial length to a retained, elongated length. The apparatus has restricting means, which contacts a restricted portion of the elastomer material, for moving the elastomer from the supplying means at a limited, supply speed. Traction means is provided for contacting the elastomer material received from the restricting means and for moving the elastomer at a selected traction speed that is greater than the supply speed. The traction means is spaced from the restricted means by an effective distance of at least about 2 meters and constructed to apply a selected amount of uniaxial tension and stretch to an intermediate portion of the elastomer material which is located between the restricting means and the traction means. The tension applied producPs a stretch rate of at least about 20 in/min/in. Means are provided for holding a temperature of the tensioned elastomer during the stretching to less than about 38~C. The apparatus has regulating means for contacting the elastomer material received from the traction means and for moving a contacted portion of the elastomer at a selected relaxation speed that is not more than about 40% of the traction spaed to allow a selected amount of natural contraction of the elastomer, thereby imparting a retained, elongated length thereto and providing an oriented elastomer capable of being heat-activated to contract from the elongated length to a length substantially equal to tha initial length. Take-up means is provided for accumulating the heat activatable elastomer material.

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Another aspect of the invention resides in a method for uniaxially orienting an elastomer, the method including the steps of providing a strip of elastomer material which is capable of being deformed from an initial length to a retained elongated length and moving a restricted portion of the elastomer at a limited, supply speed. The method further includes the step of moving a traction portion of the elastomer at a selected traction speed that is greater than the supply speed to apply a selected amount of uniaxial tension and stretch to an intermediate portion of the elastomer material which is located over an effective distance of at least about 2 meters between the restricted portion and the traction portion thereof, the applied tension th~reby producing a a stretching rate of at least about 20 in/min/in. Additionally, the method includes the steps of holding a temperature of the tension elastomer during the stretching to less than about 38C and moving a regulated portion of the elastomer at a selected relaxation speed that is not more than about 40~ of the traction speed to allow a selected amount of natural contraction of the elastomer so as to impart a selected elongated length thereto to provide an oriented elastomer capable of being heat activated to contract from the elongated length to a length substantially equal to the initial length. Finally the heat activatable, elastomer material is accumulated.

Brief Description of the Drawings The present invention will be more fully understood and further advantages will become apparent when reference is made to the following detailed description of the invention and to the drawings in which:
Fig~ 1 shows a representative schematic of the apparatus of the invention;
Fig. 2 representatively shows a perspective view of the apparatus of the invention;

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Figs. 3 and 3A representatively show an embossment roll which can be employed to produce a selected embossment pattern on the stretched elastomer strip material.

Detailed Description of the Invention For the purposes of the present invention, the term "strip" refers to a continuous member, the lengthwise dimension of which is much greater than its transverse width and thickness dimensions. Thus, the term strip includes films, filaments, ribbons, sheets and the like having regular or irregular cross section.
The method and apparatus of the present invention are particularly useful for uniaxially orienting and deforming an elastomer into an activatable configuration. More particularly, the elastomer material is capable of being stretched from a first initial length to a second elongated length. The elastomer material is then capable of naturally relaxing and contracting from the second length to a third length, which is less than the second length but greater than the first length. The elastomer material can maintain this third deformed length until it is activated by a suitable initiating means. When activated, the elastomer material then contracts to a length which is substantially equal to its initial first length. In a particular aspect of the invention, the deformed oriented elastomer strip is heat activatable. That is, the elastomer strip contracts from the third deformed length back to essentially the first length when the temperature of the elastomer material is raised above a particular activation temperature. A suitable elastomer material is one consisting essentially of a block copolymer having alternating segments of polyamide and polyether block polymers. Copolymers of this type are commercially available from the ATOCHE~ Polymers of Glen Rock, New Jersey under the trademark PEBAX. Other suitable -.

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elastomeric materials include polyurethanes and EPDM
(ethylene propylene diene monomer) copolymers.
Referring to Figures 1 and 2, a representative apparatus for uniaxially orienting an elastomer includes a supplying means, such as supply reel 14, for providing a strip of elastomer material 12. This elastomer is capable of being deformed from an initial length to a retained, activatable, elongated length. Restricting means, such as unwind roller 10, limits a movement cf elastomer material 12 from supply reel 14. Traction means, such as a pair of counterrotating nip rollers 16 and 18, apply a selected amount of uniaxial tension to an intermediate traction portion 20 of the elastomer material, which is located between the contacting nip region 15 of unwind roller 10 and the nipping region 17 of traction nip rollers 16 and 18. The traction rollers are spaced from the unwind roller 10 by a selected distance 22 and are constructed to receive the elastomer delivered from the supply reel. The traction rollers are also arranged to cooperate with unwind roller 10 to stretch the intermediate portion of the elastomer material by a selected amount. Regulating means, such as rewind roller 26, controls a movement of the elastomer material from the traction rollers to allow a seIected amount of contraction of the elastomer material and thereby impart a selected, elongated length theretoO Take-up means, such as rewind reel 24, accumulates the elongated elastomer material. In this manner, the method and apparatus of the invention can advantageously stretch, relax, and selectively orient an elastomer strip in a continuous, inline operation.
Supply reel 14 is rotatable about an axle 38 which is mounted on a pivotable support frame 32. Pivot frame 32 is configured to pivotably rotate about a frame pivot 34. ~n actuating means, such as pneumatic actuator 36, operably connects to pivot frame 32 and is configured to rotate pivot frame 32 about frame pivot 34, thereby moving a ~Z9~33~

portion of the wound elastomer strip 12 located on supply reel 14 into a contacting, frictional engagement with unwind roller 10. Typically, supply reel 14 is removeably mounted upon axle 38 to allow a ready replenishment of the supply of the elastomer strip.
Unwind roller 10 rotates about a roller axle 28 which is suitably journalled and mounted on a support frame 30.
The unwind roller is operably driven by a suitable drive means, such as an electric motor 31, energized by a variable frequency/variable voltage power supply 33. The power supply is adjusted to drive unwind roller at a selected, substantially constant angular velocity which, in turn, provides a selected, substantially constant peripheral speed at the outer surface of the unwind roller.
A suitable power supply is a variable speed drive manufactured by FMC Corporation located at Chicago, Illinois Actuator 36 is suitably pressurized with a gas and operably rotates pivot frame 32 to move an outer surface of the elastomer strip 12 located on supply reel 14 into a resilient, contacting engagement with unwind roller 10. In a particular aspect of the invention, actuator 36 provides a selected, resilient contacting force between unwind roller 10 and the elastomer strip to produce a frictional, substantially nonslip engagement therebetween at nip region 15. As a result, the constant rotational speed of unwind roller 10 produces a selected movement of the elastomer from the supply reel at a limited, supply speed, and the resiiient force provided by actuator 36 continuously maintains a contacting engagement between unwind roller 10 and the elastomer strip on the supply reel while the diameter of the wound strip gradually decreases. The controlled rotation of unwind roller 10 also provides a braking or retarding effect that maintains a selected, substantially constant supply speed movement when a . ~
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tensile, stretching force is applied to the elastomer strip.
The elastomer strip from supply reel 14 is received in nip region 17 between counterrotating traction rollers 16 5 and 18, which rotate about axles 46 and 48, respectively.
Axles 46 and 48 are mounted on a traction roller support frame 44, and a suitable driving means such as traction drive motor 42 moves traction rollers 16 and 18 in a counterrotating relationship. A suitable traction power 10 supply, such as a variable frequency/variable voltage power supply energiæes traction drive motor ~2 to produce a selected traction speed at the nip between the peripheral outer surfaces of the traction rollers. This traction speed is greater than the supply speed provided by unwind roller 10. Traction rollers 16 and 18 are spaced away from the restricting means ~e.g. unwind roller 14) by a selected distance, and are constructed to apply a selected amount of uniaxial tension and stretch to an intermediate elastomer strip portion 20, which is located between unwind roller 14 20 and the traction rollers. To impart the desired traction speed to the elastomer strip, the traction rollers are constructed and arranged to contact the elastomer strip in a substantially nonslip engagement therewith. Since the traction speed is greater than the supply speed, the 25 traction rollers operablv stretch the elastomer strip by an amount which is partly determined by the relative difference between the traction speed and the supply speed.
In a particular aspect of the invention, the traction speed is at least about 150% of the supply speed. Preferably, 30 the traction speed is within about 150 - 375% of the supply speed, and more preferably, is within about 225 - 275% of the supply speed to impart desired physical properties to the stretched elastomer strip. ~or example, when the elastomer material is PEBAX, the traction speed is about 35 250% of the supply speed.

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Conventional film stretching devices have typically minimized the distance between the members employed to stretch the film. For example, see U. ~. Patent 3,619,460.
It has been discovered, however, that increasing the effective distance between the restricting means and the traction means can advantageously improve the reliability when the system is employed to stretch elastomeric strips~
More particularly, the effective distance between unwind roller 14 and the traction rollers 16 and 18 is at least about 2.0 meters. Preferably, this distance is within the range of 2.0 - 3.5 meters, and more preferably, is within the range of about 3.0 - 3.5 meters to provide improved performance. These effective separation distances are determined by measuring the actual lengths of the curvilinear travel paths around the respective rollers and between the regions at which the uniaxial tensioning force is applied to the elastomeric material. In the shown embodiment, the effective separation distance is the curvilinear path length around and between unwind roller 14 and traction roller 16, and represents the travel path length between nip regions 15 and 17.
The relatively large distance between the unwind roller and the traction rollers helps to minimize the breakage of the elastomer strip that can occur during the stretching operation. While not intending to be bound by any particular theory, it is believed that this reduced breakage results from a reduction in the cross-directional forces induced across the width of the stretched elastomer strip portion 20. The greater distance between unwind 3~ roller 14 and traction rollers 16 and 18 creates a greater degree of "neck-down" or reduction in the width of the stretched elastomer strip. With the method and apparatus of the present invention, however, these neck-down forces are more gradually applied over a greater distance and over a greater period of time. As-a result, it is believed that the cross-directional forces induced by the stretching 12~9~3~
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operation are less suddenly applied to the elastomer strip.
ConsequentLy, there is a lower probability that any small imperfections in the elastomer strip would initiate a break in the strip.
It has also been discovered that the rate a~ which the uniaxial stretching is applied to the elastomer can significantly affect the heat shrinkage value of the oriented elastomer. To improve the amount of heat shrinkage, apparatus is constructed and arranged to stretch the elastomer at a rate of at least about 9in/min/in, preferably is configured to stretch the elastomer at a rate of at least about 20in/min/in, and more preferably, is configured to stretch the elastomer at a rate of at least about 40in/min/in to improve the efficiency of the orienting process In a particular aspect of the invention, a heating means can optionally be employed to slightly increase the temperature of the elastomer strip material. This increased temperature can increase the tackiness of the elastomer strip and thereby assist the movement of the elastomer strip at the selected traction speed. In the shown embodiment, the heating means is comprised of a pair of spaced apart, counterrotating rollers 70 and 72. These rollers rotate about axles 74 and 76, respectively, and direct elastomer strip 12 in a S-shaped, serpentine path therebetween. A suitable mounting frame 78 supports the heat rollers thereon, and a conventional roller heatin~
means is employed to raise the temperature of the peripheral surfaces of roller 70 up to a selected value.
- 30 For example, in a particular configuration, roller 72 is composed of hard rubber and roller 70 is composed of a heated metal roll. The selected increased temperature imparted to strip 12 should be sufficient to increase the tackiness of the elastomer strip. For example, when the elastomer strip is composed of a polyether block amide copolymer, the selected increased temperature ranges from ~Z9~3;~

about 38 - 46C. If the temperature of the elastomer strip is raised too high, however, the heat shrinkage value of the oriented strip may be decreased.
After the elastomer has been stretched, lt is allowed to contract back to a generally untensioned and stable, deformed length. The apparatus of the invention advantageously empl.oys a regulating means to control the movement of the elastomer strip and allow the desired amount of contraction during a continuous inline process.
Only a low amount of residual tension remains in the elastomer to maintain the integrity of the wound spool.
In the shown embodiment, the regulating means comprises take-up reel 24 and rewind roller 26. The rewind roller is rotatable about a rewind roller axle 66, which is mounted on support frame 68. A suitable driving means, such as an electric motor, operably rotates rewind roller 26 at a selected rotation velocity which, in turn, provides a selected relaxation speed at an outer peripheral surface 64 thereof. A rewind power supply 62 is suitably adjusted to energize rewind drive motor 60 to provide the desired relaxation speed at the surface of rewind roller 26. As a result, the rewind roller operably moves the contacting portion of elastomer strip 12 in nip region 23 at a selected relaxation speed that is less than the traction speed. In particular aspects of the invention, the relaxation speed is not more than about 40% of the traction speed. Preferably, the relaxation speed is within about 10 - ~0% of the traction speed, and more preferably, is within about 25 - 30% of the traction speed to impart selected physical properties to the sequentially stretched and then contracted elastomer strip.
The take-up reel illustrated in the shown embodiment is rotatable about a winding axle 52 which, in turn, is operably mounted on a rewind frame 54. This rewind frame is pivotable about pivot 56, and an actuating means t such as pneumatic actuator 58, operatably connects to the ~.
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moveable frame 54 to rotate the assembly comprised of frame 54 and take-up reel 24 about the pivot point. This rotation urges a selected portion of the wound spool of elastomer strip 12, which is located at nip region 23 on take-up reel 24, into a contacting, generally nonslip engagement with rewind roller 26. Actuator 58 is suitably pressurized to provide a selected, resilient contact force between rewind roller 26 and elastomer strip 12. In addition, take-up reel 24 is releasably mounted on winding axle 52 to facilitate the removal and replacement of the reel. For example, axle 52 may be comprised of a pneumatically expandable shaft which can be selectively pressurized to allow the installation and removal of take~up reel 24.
As the wound diameter of the spool of elastomer stxip on take-up reel 24 increases, the take-up reel translates away from rewind roller 26 and moves against the resilient force provided by actuator 58. Rewind roller 26 can thereby re~ain in a substantially nonslip engagement with the outermost layer of elastomer strip on the take-up reel.
As a result, the rewind roller 26 can maintain a substantially constant relaxation speed at the peripheral surface portion of strip 12 which contacts the rewind roller even though the diameter of the wound elastomer strip on take-up reel 24 is continuously increasing.
In a further aspect of the invention lllustrated in Figs. 1, 3 and 3A, an embossing means is employed to form a selected pattern of embossments on the elastomer strip to reduce the tensile modulus thereof. To provide improved effectiveness, the embossments are formed on the elastomer material while the elastomer is being stretched under tension. In particular, the illustrated embossing means is comprised of a pair of counterrotating embossment rollers 84 and 86. These embossment rollers are supported on a mounting frame 88, and are configured to rotate about axles 84 and 86, respectively. The elastomer strip 12 moves over ~Z9~3331;

the embossment rollers and throuyh the nip therebetween along a S-shaped, serpentine path. With reference to Figure 3, embossment roller ~0 includes a plurality of protrusions 90 located on an outer peripheral surface of the roller. These protrusions are arranged in a selected embossment pattern, and in the illustrated embodiment, protrusions 90 are arranged in a random pattern.
As elastomer strip 12 moves through the nip between embossment rollers 80 and 82, the protrusions 90 on roller 80 press the elastomer strip against the peripheral surface of embossment roller 82. As a result, protrusions 90 press into and deform the elastomer material at selected embossment locations. The size, number and locations of the emboss~ents can be adjusted to reduce or otherwise change the tensile modulus of the elastomer strip to a selected value.
For the purposes of the present invention, the tensile modulus of the elastomer strips is the tensile stress in the elastomer strip when it is subjected to a 90%
elongation. In particular aspects of the invention, the oriented elastomer strip has a tensile modulus within the range of about 2.12MPa - 7.43MPa. Preferably, the tensile modulus of the elastomer strip ranges from about 3.19MPa -6.37MPa, and more preferabiy, ranges from about 3.72MPa -5.31MPa.
In yet another configuration of the invention, theembossing means can comprise a textured embossing surface located on the surface of traction roller 16. Traction roller 18 i5 the driven roller; and the textured embossing surface on roller 16 is similar to the embosslng surface of roller 82 in Fig. 3. With this configuration, rollers 80 and 82 may be replaced by rollers which do not produce an embossment on the elastomer strip. .In such case, the rollers serve as guiding means to direct the elastomer strip along a path toward traction rollers 16 and 18.

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Similarly, rollers 70 and 72 may also be employed solely as guide rollers The following examples are provided to give a more detailed understanding of the invention. The particular materials, compositions, proportions and parameters are exemplary and are not intended to specifically limit the scope of the invention.

EXAMPLES
Samples of elastomeric strip material were processed employing the method and apparatus of the invention. The effec`tive separation distance between the unwind roller 10 and the traction rollers 16 and 18 was 3.4m, and the effective separation distance 29 between the traction rollers and rewind roller 26 was 1.2m. These effective separation distances were determined by measuring the travel path lengths between the respective nip regions 15, 17 and 23. The stretching parameters, the amounts of allowed relaxation and the heat shrinkage performances of the processed samples are set forth in Table 1 below.

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Having thus described the invention in rather full detail, it will be appreciated that various changes and modifications can be made, all of which are contemplated as being within the scope of the invention as defined by the subjoined claims.

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Claims (16)

1. An apparatus for uniaxially orienting an elastomer, comprising:
a. supplying means for providing a strip of elastomer material which is capable of being deformed from an initial length to a retained, elongated length;
b. restricting means, which contacts a restricted portion of said elastomer material, for moving said elastomer from said supplying means at a limited, supply speed;
c. traction means for contacting elastomer material received from said restricting means and for moving said elastomer at a selected traction speed that is greater than said supply speed, said traction means spaced from said restricting means by an effective distance of at least about 2 meters and constructed to apply a selected amount of uniaxial tension and stretch to an intermediate portion of said elastomer material which is located between said restricting means and said traction means, and said tension applied to produce a stretching rate of at least about 20 in/min/in;
d. means for holding a temperature of said tensioned elastomer during said stretching to less than about 38° C;
e. regulating means for contacting elastomer material received from said traction means and for moving a contacted portion of said elastomer at a selected relaxation speed that is not more than about 40% of said traction speed to allow a selected amount of natural contraction of said elastomer, thereby imparting a retained, elongated length thereto and providing an oriented elastomer capable of being heat-activated to contract from said elongated length to a length substantially equal to said initial length; and f. take-up means for accumulating said heat activatable, elastomer material.

2. An apparatus as recited in claim 1, wherein said traction means provides a stretching rate of at least about 40 in/min/in.

3. An apparatus as recited in claim 2, wherein said relaxation speed is within about 10-40% of said traction speed.

4. An apparatus as recited in claim 2, wherein said relaxation speed is within about 25-30% of said traction speed.

5. An apparatus as recited in claim 4, further comprising embossing means for forming a selected pattern of embossments on said elastomer material to reduce the tensile modulus thereof.

6. An apparatus as recited in claim 5, wherein said embossing means is constructed to form said embossments on said elastomer material while the elastomer is under tension.

7. An apparatus as recited in claim 2, wherein said traction means is spaced from said restricting means by an effective distance within the range of about 2 - 3.5 meters.

8. An apparatus as recited in claim 2, wherein said traction means is spaced from said restricting means by an effective distance within the range of about 3.0 - 3.5 meters.

9. A method for uniaxially orienting an elastomer, comprising the steps of:
a. providing a strip of elastomer material which is capable of being deformed from an initial length to a retained elongated length;
b. moving a restricted portion of said elastomer at a limited, supply speed;
c. moving a traction portion of said elastomer at a selected traction speed that is greater than said supply speed to apply a selected amount of uniaxial tension and stretch to an intermediate portion of said elastomer material which is located over an effective distance of at least about 2 meters between said restricted portion and said traction portion thereof, said applied tension thereby producing a stretching rate of at least about 20 in/min/in;
d. holding a temperature of said tensioned elastomer during said stretching to less than about 38° C.
e. moving a regulated portion of said elastomer at a selected relaxation speed that is not more than about 40% of said traction speed to allow a selected amount of natural contraction of said elastomer, thereby imparting a selected elongated length thereto and providing an oriented elastomer capable of being heat-activated to contract from said elongated length to a length substantially equal to said initial length; and f. accumulating said heat activatable, elastomer material.

10. A method as recited in claim 9, wherein said step (c) of applying uniaxial tension stretches said intermediate portion of the elastomer material at a stretching rate of at least about 40 in/min/in.

11. A method as recited in claim 10, wherein said relaxation speed is within about 10-40% of said traction speed.

12. A method as recited in claim 10, wherein said relaxation speed is within about 25-30% of said traction speed.

13. A method as recited in claim 12, wherein said intermediate portion of said elastomer material is located over an effective distance within the range of about 2.0 - 3.5 meters.

14. A method as recited in claim 127 wherein said intermediate portion of said elastomer material is located over an effective distance within the range of about 3.0 - 3.5 meters.

15. A method as recited in claim 9, further comprising the step of forming a selected pattern of embossments on said elastomer material to reduce the tensile modulus thereof.

16. A method as recited in claim 15, wherein said embossing step is performed on the elastomer while the elastomer is under tension.

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