U.S. patent number 3,819,401 [Application Number 05/089,304] was granted by the patent office on 1974-06-25 for method of preparing shirred, elastic, flexible articles.
This patent grant is currently assigned to FMC Corporation. Invention is credited to Walter T. Koch, John T. Massengale.
United States Patent |
3,819,401 |
Massengale , et al. |
June 25, 1974 |
**Please see images for:
( Certificate of Correction ) ** |
METHOD OF PREPARING SHIRRED, ELASTIC, FLEXIBLE ARTICLES
Abstract
Method of preparing a shirred elastic, flexible article by
attaching to a sheet material a thin layer of flexible, plasticized
vinyl chloride polymer material which is heat shrinkable in only
one direction thereof, and thereafter heating the layer of vinyl
chloride material to effect shrinkage thereof and shirring of the
sheet material which is attached thereto.
Inventors: |
Massengale; John T. (West
Chester, PA), Koch; Walter T. (Havertown, PA) |
Assignee: |
FMC Corporation (Philadelphia,
PA)
|
Family
ID: |
22216885 |
Appl.
No.: |
05/089,304 |
Filed: |
November 13, 1970 |
Current U.S.
Class: |
156/85; 2/406;
156/73.1; 156/244.25; 264/342R; 2/402; 112/413; 156/229;
223/28 |
Current CPC
Class: |
B32B
27/00 (20130101); B29C 61/02 (20130101); A41D
27/245 (20130101); B29K 2027/06 (20130101); B29L
2031/4878 (20130101) |
Current International
Class: |
A41D
27/24 (20060101); A41D 27/00 (20060101); B29C
61/02 (20060101); B29C 61/00 (20060101); B32B
27/00 (20060101); B29c 027/20 (); B32b
031/26 () |
Field of
Search: |
;156/84,85,229,244,73
;161/410,76,256,249 ;264/342R ;223/28 ;2/224A ;112/413 ;117/7 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Martin; William D.
Assistant Examiner: Trenor; William R.
Claims
I claim:
1. A method of preparing a shirred, elastic, flexible article which
is capable of rapidly assuming a relaxed condition after being
tensioned including the steps of disposing in direct contact with
at least one side of a flexible sheet material a thin layer of
flexible, plasticized vinyl chloride polymer material which is
heat-shrinkable in the desired direction of article shirring,
attaching the sheet material and layer of vinyl chloride polymer
material together without shrinking of such layer, and thereafter
heating the layer of vinyl chloride polymer material to cause
shrinkage thereof and shirring of the sheet material attached
thereto.
2. A method as defined in claim 1 wherein the layer of vinyl
chloride polymer material is attached to the sheet material at only
spaced portions thereof.
3. A method as defined in claim 2 wherein the layer of vinyl
chloride polymer material and sheet material are attached together
along lines spaced from each other and extending substantially
perpendicular to the direction of shrinkage of the layer of vinyl
chloride polymer material.
4. A method as defined in claim 1 wherein the layer of vinyl
chloride polymer material is shrinkable from 30 percent to 50
percent of its length when attached to the sheet material and is
substantially completely relaxed following the heating thereof.
5. A method as defined in claim 4 wherein the layer of vinyl
chloride polymer material is shrinkable from 40 percent to 45
percent of its length when attached to the sheet material.
6. A method as defined in claim 1 wherein the layer of vinyl
chloride polymer material is heated to a temperature of about
100.degree.C. to effect shrinkage thereof.
7. A method as defined in claim 1 wherein the layer of
heat-shrinkable vinyl chloride polymer material is formed by
shaping a plastisol of vinyl chloride polymer material into a web
form and setting the same, uniaxially stretching the web of vinyl
chloride polymer material while the web is heated to an orientation
temperature between its second order phase transition temperature
and below a temperature at which relaxation of the orientation
effect achieved by stretching occurs so rapidly that the web
retains no significant orientation once stretching is ceased, and
thereafter cooling the web while it is in a stretched
condition.
8. A method as defined in claim 7 further including the step of
heating the stretched web of vinyl chloride polymer material to a
heat-setting temperature which is less than the temperature to
which the layer of vinyl chloride polymer material is to be heated
subsequent to its attachment to the sheet material, permitting the
web to shrink while at such heat-setting temperature and thereafter
cooling the heat-set web.
9. A method as defined in claim 8 wherein the web of vinyl chloride
polymer material is heat-set at about 65.degree.C.
10. A method as defined in claim 1 wherein the layer is formed of
foamed, plasticized vinyl chloride polymer material.
Description
The present invention is directed to an improved method of
preparing a shirred, elastic flexible article.
Flexible articles having shirred, elastic portions, as for example,
along openings in wearing apparel, protective covers and the like,
are conventionally produced by stretching a layer of rubber or
other elastic material and, while being held in such stretched
condition, sewing the same to a sheet material. Once attached and
permitted to relax, the contracting elastic layer, which may be in
the form of a strip, sheet or filament, causes the sheet material
attached thereto to shirr or gather. In such conventional process,
attachment of the elastic layer by sewing is slow, tedious and
costly. More important, difficulties are encountered in maintaining
a uniform tension on the elastic layer during its attachment to the
sheet material and, also in handling of the shirred article once
such elastic layer is relaxed. Accordingly, a primary object of
this invention is to provide an improved method for preparing
shirred, elastic, flexible articles.
Another object is the provision of an improved method for preparing
shirred, elastic articles which involves no stretching of any
components of such articles during the actual assembly thereof.
Still another object is to provide an improved method for making
shirred, elastic articles in which the assembly of the components
thereof and the actual shirring may be effected in independent
stages which are separated as to time and location.
A further object is to provide an improved method for preparing
shirred, elastic articles in which conventional slow and costly
sewing procedures are not required.
A still further object is the provision of an improved method for
making shirred, elastic, flexible articles which is rapid,
economical, simple, and which can be tailored to provide different
degrees of article shirring.
The above and other objects of the invention are achieved by a
method in which a thin layer of flexible, plasticized vinyl
chloride polymer material, which is heat shrinkable in the desired
direction of article shirring, is disposed in direct contact with
at least one side of a flexible sheet material and attached thereto
without any significant shrinkage or other distortion of such
layer. Subsequently, the layer of vinyl chloride polymer material
is heated to cause shrinkage thereof whereby the sheet material
attached thereto is shirred.
Assembly of the layer of vinyl chloride polymer material and sheet
material as described above may be achieved, as for example, by the
use of adhesives, heat sealing, ultrasonic horns, or sewing.
Preferably, but not necessarily, the layer of heat-shrinkable vinyl
chloride polymer material and sheet material are attached to each
other at only spaced locations thereof and desirably along lines or
areas which are spaced from each other and extend substantially
perpendicular to the direction in which such layer is capable of
shrinking.
It is important in the method of the present invention that the
heat-shrinkable layers which are employed be formed of vinyl
chloride polymer materials. Layers of vinyl chloride polymer
materials, which are often described as psuedo-crystalline, may be
stretched while at an elevated temperature and, if held under
tension during the cooling thereof, will retain substantially their
stretched lengths, yet may be shrunk to their original lengths by
heat. It is known that structures formed of materials other than
vinyl chloride ploymer materials, as for example polypropylene, may
be subjected to treatment as described above and that such
structures will also retain their stretched lengths and are
heat-shrinkable.
Distinguishing the heat-shrinkable layers of vinyl chloride polymer
materials from such other structures, however, is that once shrunk
these layers exhibit the elasticity and recovery rate
characteristics which are essential in shirred articles and which
are not offered by structures formed of other materials. More
particularly, a heat-shrinkable layer formed of vinyl chloride
polymer materials, after initial heat shrinkage, may be repeatedly
elongated to its stretched length at the temperature of the ambient
atmosphere and, in each instance, returns to substantially its
shrunken length when relaxed after elongation. Equally important is
that such layer recovers rapidly to its shrunken length after being
elongated. With these characteristics of the layer of vinyl
chloride polymer material, shirred articles formed in accordance
with the method of the present invention are capable of being
repeatedly tensioned and relaxed without any apparent sacrifice in
the shirring experienced by such article and without any
significant delay in article shirring as it is relaxed from a
tensioned condition.
The amount of shrinkage experienced by the layer of vinyl chloride
polymer material, and thus the degree of shirring of the resulting
article, may be varied within a wide range. In effect the shrinkage
of the layer of vinyl chloride polymer material may be tailored to
suit specific article applications, with a shrinkage of from 40 to
45 percent being preferred in making shirred articles having
elastic properties similar to those made by conventional processes
using a rubber strip as a shirring means.
The flexible, heat shrinkable vinyl chloride polymer material layer
employed in the method of the present invention is formed by
shaping, as by extrusion, plasticized vinyl chloride polymer
materials into the form of a tape, ribbon, sheet, film or tube or
like structure followed by uniaxial stretching of such structure to
orient the molecules thereof. The elastic and recovery rate
characteristics of heat-shrinkable vinyl chloride layers formed by
known dry-blend extrusion techniques are unsatisfactory and
certainly do not approach those of elastic rubber layers employed
in conventional shirred article manufacture. The necessary high
degree of plasticization can be achieved, however, by employing
vinyl chloride plastisols; that is, colloidal dispersions of vinyl
polymers or copolymers in plasticizers, without the use of volatile
solvents, which may be shaped and then oriented by known
procedures.
Conventional vinyl polymers capable of plasticization to a
flexible, extensible condition may be employed in the plastisols
formulations, including such materials as polyvinyl chloride, as
well as copolymers of a predominate proportion of vinyl chloride
with minor proportions of vinyl acetate, vinylidene chloride or
other copolymerizable materials. Suitable plasticizers for such
vinyl chloride compositions are well known in the art and include,
for example, dibutyl phthalate, dioctyl phthalate, didecyl
phthalate, didecyl adipate, tricresyl phosphate, etc., which may be
used alone or in combination with each other or in admixture with
resin-type plasticizers, such as glycol adipate. The amount of
plasticizers employed will depend upon the elasticity and recovery
characteristics desired in the shirred article. Extenders,
processing aids, stabilizers, blowing agents, pigments, colorants,
etc. may also be incorporated into such plastisols if desired.
As heretofore mentioned vinyl chloride plastisols may be shaped
into a desired layer by conventional procedures, as for example by
extruding in a molten condition as a continuous stream, followed by
rapid quenching of such stream as on a chill roll or in a bath of
cool water or other liquid. The layer of vinyl chloride polymer
material thus formed may be collected for subsequent processing at
a later stage or, in continuous operations, may be uniaxially
stretched directly after its formation. This is conveniently
achieved by known techniques, as by stretching such layer of vinyl
chloride polymer material longitudinally between spaced pairs of
differential speed rolls; that is, with one such pair of rolls
being rotated at a more rapid speed than the other of such pair of
rolls. For reasons as hereafter described, the layer of vinyl
chloride material is stretched to an extent greater than the
elasticity desired in the finished shirred article.
During stretching, the layer of vinyl chloride polymer material is
heated to within an orientation temperature range which extends
from a temperature above the second order phase transition
temperature of the vinyl chloride polymer material and below the
temperature at which relaxation of the orientation effect, produced
by stretching, occurs so rapidly that the layer retains no
significant orientation once stretching is ceased. This orientation
temperature range for vinyl chloride polymer materials will vary
with the amount of plasticizers incorporated into such materials
and will range generally from about 50.degree. to 149.degree.C.
While in its stretched condition, the layer of vinyl chloride
polymer material is cooled to the temperature of the ambient
atmosphere.
This stretched layer of vinyl chloride polymer material will retain
substantially its stretched length and when maintained at a
constant temperature well below its orientation temperature it
exhibits fair dimensional stability. Prior to its use, however, the
stretched layer of vinyl chloride polymer material is often exposed
to varying temperatures, as during storage and transit, and thus
may experience at least some premature shrinkage. Such shrinkage
may be non-uniform along the layer and thus impart varying shirring
properties in resulting articles, and even if uniform, may be
unsuitable for use in shirred article manufacture.
Accordingly, in the method of the present invention the uniaxially
oriented layer of vinyl chloride polymer material is heat set by
being brought to a temperature slightly above its second order
phase transition temperature, permitted a limited relaxation, and
then cooled to the temperature of the ambient atmosphere. Shrinkage
of the layer at this stage may range up to 35 percent or more and
preferably from about 10 percent to 30 percent. Once cooled the
layer is dimensionally stable; that is, undergoes no significant
shrinkage, until heated at least to the temperature employed during
the heat-setting thereof.
As employed in the description and claims of the present invention,
the terminology, "sheet material" may consist of textile materials
formed of natural or synthetic fibers which are in a woven,
non-woven, knitted, or other construction, or may be in the form of
films or sheets capable of withstanding the elevated temperatures
to which the elastic layer is subjected to during its attachment
and shrinking.
Articles formed by the method of the present invention have at
least portions thereof which are shirred or gathered, as in the
case of shirred openings in wearing apparel, shower caps, dish
covers and the like. Included also are articles which are
completely shirred to facilitate compact storage thereof. Such
articles may be employed, for example, as awnings, swimming pool
covers, wrapping material and etc. Thus, the layer of vinyl
chloride polymer material may be in the form of a narrow strip tape
or ribbon or may be a relatively wide film or web.
An elastic layer of vinyl chloride polymer material may be attached
to one or opposite sides of the sheet material which is to be
shirred. Any suitable means may be employed to effect such
attachment, as for example, impulse heat sealing or ultrasonic
apparatus, adhesives, sewing or metal fasteners. Once attached
shrinkage of the layer of vinyl chloride polymer material can be
accomplished by merely heating the same, as with a hot gas or
liquid, to a temperature above that at which such layer was heat
set. As this layer of vinyl chloride polymer material shrinks, the
sheet material attached thereto, of course, assumes a shirred or
gathered condition along the areas of attachment.
In the drawing,
FIG. 1 is a diagrammatic illustration of the method employed in
making the layer of heat shrinkable vinyl chloride polymer material
which is used in the method of the present invention;
FIG. 2 is a diagrammatic view illustrating one stage in the
manufacture of an article of wearing apparel by the method of the
present invention;
FIG. 3 illustrates the article of FIG. 2 in its finished, shirred
condition; and
FIG. 4 illustrates another shirred article formed by the method of
the present invention.
With reference to the drawing, FIG. 1 illustrates the manufacture
of a layer, and particularly a narrow tape, of uniaxially
heat-shrinkable vinyl chloride polymer material for use in the
method of the present invention. More specifically, a plastisol of
chloride polymer material is rendered molten in a conventional
screw extruder, shown in part at 15, and is discharged through a
die orifice as a continuous stream 17 which is received on the
periphery of the rotating chill roll 19. The peripheral surface of
the roll 19 is maintained cool, as by circulating cold water
therethrough, to rapidly quench the stream 17 and provide a solid
flat tape 21. A pair of driven rolls 23 and 25, assisted by a
stripping roll 27, effect removal of the tape 21 from the roll 19
without stretching the same, afterwhich the tape 21 may be
collected and perhaps stored before further processing.
Preferably, and as illustrated, the tape 21 is uniaxially oriented
by longitudinal stretching immediately after its formation. To
facilitate such stretching, the nip roll 23 is provided with a
rubber covering 29, while the nip roll 25 of bare metal
construction. Steam or other hot fluid is circulated through the
nip roll 25 to effect heating of the tape 21 to within the
orientation temperature range during its contact with such roll. If
necessary, additional rolls may be provided to increase the arc of
contact which the tape 21 makes with the surface of the nip roll
25.
Spaced from the rolls 23 and 25 is a like pair of driven nip rolls
31 and 33, in which the roll 31 is formed with a rubber covering 35
while the roll 33 is of bare metal construction. The nip roll 33
differs from the corresponding nip roll 25, however, in that no
heated fluid is circulated therethrough. Suitable means, not shown,
are provided for rotating the pair of rolls 31 and 33 at a faster
speed than the rolls 23 and 25 so as to longitudinally stretch and
thus uniaxially orient the heated tape 21 during its passage
between such pairs of rolls.
The longitudinally stretched tape 21 is at a temperature
substantially below its orientation temperature range as it issues
from between the nip rolls 31 and 33 and is passed directly, by
guide rolls 37 and 39 and nip rolls 41 and 43, through a heated
liquid bath 45 contained in a tank 47. The bath 45, which may be
water, is heated to a temperature slightly above the second order
phase transition temperature of the vinyl chloride material from
which the tape 21 is formed and the nip rolls 41 and 43 are driven
at such speed as to permit a predetermined, partial shrinkage of
the tape 21 during its passage through such bath. The heat
shrinkable and now heat-set, tape 21 rapidly assumes the
temperature of the ambient atmosphere as it leaves the bath 45 and
is transported to a suitable core for winding in roll form as shown
at 49.
In the practice of the method of the present invention, a length of
tape 21 from the roll 49 is placed in direct contact with one or
both sides of a sheet material along the area of such sheet
material which is to be shirred and is attached thereto. Other than
smoothing out the sheet material and/or tape 21, no tension is
necessary on either of such components. The tape 21 is then heated,
as by hot air, to a temperature above its heatsetting temperature
to effect shrinkage thereof to substantially its length prior to
its longitudinal stretching. In view of the attachment between the
tape 21 and sheet material, the sheet material will, of course,
shirr or be gathered along the length of the tape as it is
shrunk.
Illustrated in FIG. 2 is an application of the method of the
present invention in the manufacture of a garment which includes a
body 51 formed, for example, of non-woven textile materials, and
having openings 53, 55 and 57. Lengths of the heat-shrinkable,
heat-set tape 21 are removed from the roll 49 and, as indicated at
59, 61 and 63, are placed in direct contact with the garment body,
adjacent to the opening 53, 55 and 57 therein. These lengths 59, 61
and 63 are then bonded to the garment body 51, as by an impulse
heat-sealing apparatus, along lines 65 which are spaced from each
other and extend substantially transverse to the direction in which
such tape lengths are capable of shrinking. The attached tape
lengths are then heated, as heretofore described, to shrink the
same and cause the portions of the body 51 which is attached
thereto to shirr or gather, as shown in FIG. 3.
The method of the present invention is adapted for making a variety
of shirred articles. Shown in FIG. 4 is a drape having a fabric
body 67 which has been gathered or ruffled at 69 by the method of
the present invention. While the above description makes reference
to a solid tape 21 of vinyl chloride polymer material, blowing
agents may be incorporated into the plastisol to provide
heat-shrinkable, heat-set tapes having a foamed or cellular
structure. Such foamed tape is, of course, of light weight and has
a pleasant feel and is thus well suited for making shirred articles
of wearing apparel.
For a better understanding of the method of the present invention,
reference is made to the following examples.
EXAMPLE I
A plastisol paste was prepared by blending in a Hobart mixer
materials, as follows:
Parts Polyvinyl chloride dispersion grade resin 100. Dibutyl
phthalate, primary plasticizer 60. Epoxy-type secondary plasticizer
5. Barium-cadmium, zinc stabilizer 3.
This plastisol paste was spread to a thickness of one-eighth inch
on a glass tray and gelled by oven heating at 125.degree.C. for ten
minutes. After cooling the gel was broken into a loose crumb and
fed to a conventional 3/4 inch screw extruder.
Within the extrusion barrel this plasticized polyvinyl chloride
composition was rendered molten and was passed through two 80 mesh
screen packs before being discharged through a 1 inch flattype die.
The feed section of the extruder barrel was maintained at a
temperature of 132.degree.C. while its discharge section was kept
at about 177.degree.C. The temperature of the extrusion die itself
was maintained at about 205.degree.C. Some variation in the
specific temperatures could be tolerated without degradation of the
polyvinyl chloride composition. For example, extrusion die
temperatures of from 177.degree.C. to 218.degree.C. could be
employed without appreciable differences in the characteristics in
the resulting extruded product.
The extrudate was rapidly quenched on the surface of a 6 inch
diameter chill roll, which was cooled by water at a temperature of
25.degree.C. circulated therethrough, and was collected as a
continuous tape without being tensioned.
Subsequently this unoriented, plasticized polyvinyl chloride tape
was longitudinally stretched during advancement thereof between
spaced pairs of nip rolls. Each pair of nip rolls included a metal
roll and a cooperating rubber covered roll, with only the metal
roll of the trailing of such pair of rolls being heated internally
by steam. The rolls of both pairs of rolls were positively driven,
with the leading pair of rolls having a speed five times greater
than that of the trailing pair of rolls.
Upon leaving the leading pair of such nip rolls, the now
longitudinally oriented polyvinyl chloride tape was at about the
temperature of the ambient atmosphere and was heat-set by passage
through a water bath heated to a temperature of 65.degree.C. A pair
of nip rolls served to advance the tape through this heated bath
and were driven as to permit such tape to shrink 30 percent during
this heat-setting stage. After removal from this water bath, the
tape assumed the temperature of the ambient atmosphere and was
collected without being tensioned.
Sections of tape exhibited a shrinkage of 43 percent when immersed
in boiling water and tensile properties of such sections, measured
after the shrinkage thereof, were similar to those of a
corresponding strip of rubber.
Another section of such heat-shrinkable, heat-set polyvinyl
chloride tape was bonded at spaced intervals to a cellulosic
non-woven fabric by means of a conventional impulse heat-sealing
apparatus. These locations of bonding were spaced one-fourth inch
from each other and extended generaly perpendicular to the
direction in which the tape sections were capable of shrinking. No
shrinkage or other distortion of the polyvinyl chloride tape was
apparent during the bonding thereof to the non-woven fabric.
The non-woven fabric together with the attached tape was heated to
100.degree.C. causing the tape to shrink and the non-woven fabric
to shirr or gather. Once at room temperature the shirred non-woven
fabric was repeatedly tensioned to stretch the tape to
approximately its length prior to shrinking and to remove the folds
or pleats from such fabric. The fabric was permitted to relax after
each tensioning thereof and during each such relaxation the tape
returned to its shrunken length and again shirred the fabric
attached thereto.
Another section of the above-described heat-shrinkable, heat-set
polyvinyl chloride tape was attached at spaced intervals thereof to
a non-woven ceelulosic fabric by means of an ultrasonically
activated horn placed on the fabric side of the overlying
components. Still other sections of such tape were sewn onto
non-woven cellulosic fabrics using a variety of stitch patterns.
All such assemblies were heated as described above to effect
shrinkage of the tapes and shirring of the non-woven fabrics
attached thereto. The resulting shirred articles exhibitd stretch
and shrink properties similar to that initially described in this
example.
Set forth below is a tabulation of characteristics of a braided
elastic (rubber) tape, as conventionally employed in the
manufacture of shirred articles, a heat-shrinkable, heat-set
polyvinyl chloride tape produced as described above and employed in
the method of the present invention and a heat shrinkable polyvinyl
chloride tape, having 35 parts of plasticizer per 100 parts of
resin, formed by conventional dry-blend techniques. These materials
are designated below as Sample A, B and C, respectively.
______________________________________ Recovery Yield Force to
Behavior (Sq. Thick- Elongate 3/8" Time for 90% inch/ ness wide
sample (gms) recovery after Sample pound) (mils) to 50 % to 100 %
100% stretch ______________________________________ A 1050 35 400
710 almost instan- taneous B 1800 13 990 2130 15 seconds C 1690 14
1530 2580 >5* minutes ______________________________________ *
90% recovery not achieved within 5 minutes measurement period.
EXAMPLE II
A polyvinyl chloride plastisol formulation was prepared as
described in Example I with the exception that 4 parts of
azodicarbonamide was added as a blowing agent and a conventional
blowing agent activator-stabilizer was substituted for the
stabilizier heretofore mentioned. This plastisol was fused at
125.degree.C. for a period of 8 minutes without foaming thereof,
cooled and broken into a loose crumb.
This crumb was fed into the extruder described in Example I in
which the feed and discharge sections were heated to 155.degree.C.
and 185.degree.C., respectively. The 1 inch flat die of such
extruder was maintained at 200.degree.C. whereupon the polyvinyl
chloride plastisol, rendered molten within the extruder, issued
from the die as a continuous foamed stream. This extruded stream
was rapidly quenched in a water bath to provide a tape having a
foamed or cellular structure.
Using the procedure described in Example I the foamed polyvinyl
chloride tape was stretched longitudinally and heat-set. The
resulting heat-shrinkable, heat-set tape was white in color,
lighter and more pleasing to the touch than the solid
heat-shrinkable tape employed in Example I and, when heated to
100.degree.C., exhibited a shrinkage of 41 percent.
In a manner as described in Example I, sections of this foamed,
heat-shrinkable, polyvinyl chloride tape were attached to
cellulosic non-woven fabrics, shrunk, and tested for their elastic
properties which were found to be similar to those of elastic
members employed in the manufacture of shirred articles.
Set forth below is a tabulation of the characteristics of a braided
elastic (rubber) tape and a foamed, heat-shrinkable, heat-set
polyvinyl chloride tape as described above. These materials are
designated below as Samples A and B, respectively.
______________________________________ Recovery Yield Force to
Behavior (Sq. Thick- Elongate 3/8" Time for 90% inch/ ness wide
sample (gms) recovery after Sample pound) (mils) to 50% to 100%
100% stretch ______________________________________ A 1050 35 400
710 Almost instan- taneous B 3200 11 440 960 4 seconds
______________________________________
It is to be understood that changes and variations may be made
without departing from the spirit and scope of the invention as
defined in the appended claims.
* * * * *