Note: Descriptions are shown in the official language in which they were submitted.
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INTRODUCTION
This application relates to spindraw processes for the
preparation of synthetic organic filamentary structures, and
particularly yarns for textile use. More specifically, it in-
volves high speed takeup operations employing fiber forming
polymers capable of developing substantial tensile properties
through the application of extensional stresses. Particularly,
polymers having lower rates of crystallization such as polyethylene
terephthalate are subjected to high speed stress-anneal processes
under conditions to control tensile property development on a
continous basis adapted to commercial application.
Most specifically, this invention provides a novel poly-
ester yarn characterized by a low tensile factor, as low as
14-22 in the case of the preferred polyethylene terephthalate;
and a process for its production in high speed stress-anneal
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operations.
~ BACKGROUND OF THE INVENTION
- Yarns of low tensile factor adapted particularly for useas fleece yarns have not been prepared heretofore by a straight-
forward spinning process from ordinary polymer in a manner con-
sistent with co~mercial production techniques~ Rather, it had
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~ ~` been necessary to deliberately degrade the intrinsic viscosity
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of the polymer ~see U.S. Patent 3,396~,446 issued Augus~ 13, 196~)
or to disrupt the crystalline structure by the addition of
modifying monomer ingredients such as pentaerythritol (see ; ~;
Canadian Patent 901,716 issued May 30, 1972~ to achieve yarn
structures of such tensile properties: typically tenacity of
~; l about 3.0 gpd and an elongation of about 30% (TE = 16).
It is of course known that by utilization of various
~3a spinning techniques in conventional systems, a 'trade-off' as ;~
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between tensile strength and elongation may be achieved at -
relatively constant tensile factor. However, even in these `
; systems it is difficult to secure balanced tensile character-
istics in the low tensile factor range e.g. 14 to 22, with
tenacities of 2.S to 4.0 gpd, preferably about 3~0 gpd and
elongations of 25 to 40% preferably about 30.
In the course of development, it has been determined that
intermediate and high tensile fibers having properties like
those prepared in a conventional lagged drawing operation can
be produced directly from the spinning step by utilizing high
speed takeup techni~ues. An improvement in such processing is
effected by introducing a stress annealing step post-quench.
In this approach disclosed in U.S. 3,946,100, the yarn is
i
~ passed under tension through a heat treatment zone prior to
"!, initial windup in a high speed spin-draw sequence. The fibers
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~l so produced exhibit significant tensile development at low
;~ shrinkage and a novel morphological structure.
GENERAL DESCRIPTION OF THE INVENTION
It has now been discovered that a post-quench
~20 stress anneal process can be utilized to successfully spin-
draw polymer of low rate of crystalliza~ion at high speed
~, to products of balanced low tensile characteristics by
selective control of operating parameters.
It was anticipated from conventional teachings that
maximization of spin line stress would enhance tensile proper-
ties in such systems, and increasing takeup speed is correla-
table with increased tensile development at spinning. Increased
~, spin line stre~s is al~o ~nown ~n this art to be conventionally
afforded by lowering ~pin temperature or increa~ing intrinslc `
viscosityt wh~ch tend toward an increa~e in melt viscoslty and
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concomitant enhancement of tensile development. Accordingly,
were products of low tensile characteristics to be pxedict-
ably produced under controlled process conditions by a system of
conventional spinning, the expected correlation would be to
higher spin temperatures of decreased intrinsic viscosity i.e.
lower melt viscosities.
Surprisingly, it has now been discovered that balanced low ;
tensile yarns can be produced directly from ordinary polymer in
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a selected process regime utilizing high speed spin-draw stress
anneal spinning. Specifically, balanced and controlled lcw
tensile charact~ristics are developed in high speed spin-draw
operations by utilization of controlled high melt viscosity: -
ordinarily, with given polymer viscosity and static system para- ;
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meters by reducing spinning temperature. Such an approach as -
practised according to this specification is inconsistent with `~
conventional techniques. ~ -
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In particular, the present invention provides~a process
I for the production of filamentary yarn structures of low tensile
`~~ factor (TEl/2) characterized by controlled and balanced tensile
characteristics and low tensile factor comprising
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spinning polyethylene terephthalate polymer having an in-
trinsic viscosity of at least 0.55 through a multifilament
.:
spinning pack maintained at a spinning temperature in the ~
range of 280 to 295 degrees centigrade; ~ -
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coordinating ~aid intrinsic viscosity and said spinning
'f temperature to maximize the polymer melt viscosity, extrud-
ing said polymer into a plurality of filaments of 1 to 8
deniers per filament;
~uenching the fllament~ to below the glass tran3ition temp-
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erature; passing said filament~ under the stress of high
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speed winding through an annealing zone to 1 to ~ feet in
length commencing 3 to 6 feet from the spinning pack, said
annealing zone being maintained at a temperature of 150
degrees centigrade up to the melting temperature; simultane-
ously gathering together and forwarding said filaments as
a yarn by taking up said filaments at a windup speed of 10,000
to 15,000 feet per minute;
and recovering a yarn having a tensile factor of between
about 14 and 22, a tenacity of between about 2.5 and 4.0
grams per denier and an elongation of between about 25 and -
about 40 percent.
According to another aspect of the present invention there
is provided filamentary yarn of low tensile factor and balanced
tensile characteristics comprising filaments formed of a linear
terephthalate polyester exhibiting a tenacity of ~.5 to ~.0 grams
per denier, an elongation of 25 to 40 percent and a tensile factor
(TE 1/2) of between about 14 and 22.
Yarns can be produced which when composed wholly of
ethylene terephthalate units exhibit tensile factors (TEl/2)
in the range o~ e.~. 14-22, preferably about 15-17 and retain
intrinsic viscosities on the order of 0.6. Employing the pre-
cepts of this invention, the spinning temperature is controlled
to lie in a somewhat reduced value range e.g. 280 up to about
295C., preferably at least 285C. for a 0.55-0.70 e.g. 0.65
intrinsic viscosity polymer. Here the increase in melt viscosity
afforded together with the high speed takeup stress anneal
treatment generates directly a fiber structure characterized by
low tensile factor, yielding all other attributes of a con-
ventionally spun yarn from ordinary polymer, all with perser-
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vation of maximum productivity.
While not wishlng to be bound by an eQ~entially hypothetical
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explanation, it is believed that the production of useable
low tensile yarn in accordance with this disclosure may be
the result of the dynamic interaction of stress anneal process-
ing with actual or incipient melt fracture induced under the
high speed spinning conditions imposed upon a high melt
viscosity system. Consistently, it has been suggested that
stress anneal processing is associated with an effective in-
crease in the number of 'tie' molecules with relaxed amorphous
chains between the crystalline regions.
Thus, it is surmised that microfissures developed in the
course of low temperature, high melt viscosity spinning are
modified and possibly at least partially cured by subsequent
stress anneal treatment, providing useable fiber structures of
low tensile factor in direct spinning.
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The yarns of this invention are produced, as stated above,
under conditions to maximize melt viscosity utilizing ordinary
I undegraded virgin polymer on standard high speed equipment.
;¦ Most sensibly, the process regime required is achieved under ;~
constant operating parameters in other respects by reducing
spinning temperature. It will be understood by one skillPd in -
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this art that reduction of temperature ultimately generates an
unworkable condition. Further, it is appreciated that absolute
l ,
j temperature monitoring is not available in plant equipment with-
' out excessive calibration, hence a stepwise reduction of 1-2
~, degrees may be most readily employed to achieve the desired
critical range.
The necessary condition in the ~tress anneal zone i& the
maintenance of temperature and residence time at levels such
that modification in crystal~ine morphology i8 completed in
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that zone, minimizing the fluctuation in yarn properties which
would otherwise result. Thus, the rate characteristic of the
polymer for development of tenacity and elongation is taken into
account in determining the length of the stress anneal zone and
the temperature at which it is operated at a given takeup speed.
If this rate is not separately considered, a simple monitoring
step will permit the necessary regulation. Under normal con- ;~
ditions with static system parameters in other respects, fluctu-
ation in yarn properties reflecting incomple~e modification of
crystalline structure is avoided, and tensile properties optimized,
at maximum stress anneal zone temperature. Polymer of lower
intrinsic viscosity exhibiting a higher rate of crystalli-
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zation will permit lower temperatures or a reduced length of
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zone.
In practical terms, the takeup speed is maximized to
exceed 10000 fpm, preferably to lie in the range of 12000-
15000 fpm or higher, and zone length is fixed to conform to
plant requirements ordinarily less than 10 feet. Accordingly,
the necessary process control is achieved by interrelating
polymer viscosity, spinning temperature, and stress anneal
temperature. Thus, in ~pinning a given polymer a selective
spinning temperature i~ correlated with stress anneal tempera-
ture by reference to crystallization and tensile development
rates.
SPECIFIC DESCRIPTION OF THE INVENTION
:
Typically, polyethylene terephthalate having an intrinsic
viscosity o 0~60 to 0.70 is spun through a conventional melt
~` spinning pack employing a spinnerette of the u~ual design adapted
to produce a multiplicity of filaments, normally 15 or more,
' 30 usually of 1-8 denier per filament~
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The filaments are expressed directly into a stable
quench zone adapted to reduce the material temperature below
glass transition or second order transition temperature,
; suitably by the use of relatively cooler and often ambient
air. In high speed takeup operations extensional stresses
induced will ordinarily extend into the quench zone and act
directly upon filament forming from the bulge at the exit
from the spinnerette face. In the ordinary course, the
quench zone will be on the order of 2 to 3 feet in length and
may employ an air flow in the range of 40 to 100 cfm. Cross ~ -
flow quench systems are particularly preferred for the pro~
`, vision of superior yarn uniformity.
The filaments are sequentially passed to a stress anneal
zone providing an elavated temperature post quench, ordinarily
in the form of a heater tube as of the type represented by a
standard nylon steam conditioning tube.
The rather high speed at which the thread line is passed
through these treatment zones requires consideration of residence
times relative to the rates at which the morphological develop-
20 ment in that phase can occur. It is found that the stress -
anneal zone should in the ordinary system be removed at least
3 feet-and up to 6 feet from the spinnerette face and therefore
need not be contiguous with the termination of the quench zone.
The conditioning tube itself may be of any length although plant
requirements will ordinarily dictate a length of less than 10
feet, often as little as 1 up to 9 feet. Usually the structure
is that of a jacketed chamber heated with steam or Dowtherm
vapor to in excess of 100C. up to 2~0C. or more. One suitable
device i8 constituted by a 5/16 inch diameter cylindrical tube.
Temperatures and residence time then are selected for a tube of
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given length such that as discussed above, the region of
temperature induced stress crystallization is exceeded. The
filaments are gathered as yarn which is passed from the tube
to a takeup and may, of course, in its traverse through this
zone, be treated in other respects as by application of finish,
introduction of compaction or interlacing by the action of air
jets and the like, if desired.
While the cylindrical tube can vary in length and internal
diameter, it is clear that such dimensions are mere~y chosen
so as to provide sufficient heat into the filament at the high -
speed throughput to raise the filament temperature above the
second order transition temperature without the filament con- -
tacting the interior walls of the tube. At the noted required
high speed throughput, strong air currents are generated by
the frictional drag of the filament in the air such that these air
currents tend to follow the filament through the tube, thereby
; insulating the filament from the heated walls of the tube. These
~ insulating effects can be mitigated by reducing the interior tube
:` t, diameter to the minimum as well as by tube length and operating ``~
temperatures. Modifications of tube structure to reduce such
air currents are also known such that the particular tube size
becomes a matter of convenience based on the requirements of
heat input into the filament. In general, interior tube diameters
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ranging from about 1/4 inch to 4.0 inches, depending on the noted
factors and total yarn denier, have been found to be satisfactory
~ at tu~e lengths of 1 to 9 feet. Shorter tubes with more efficient
- I heat transfer capabilities and countercurrent heat flows are
also envisioned.
The most significant operating parameter for the control
30 of tensile properties i spinning temperature, as the most
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practical means of effecting the desired melt viscosity.
A reduction in spinning temperature from the norm for a
polymer of given viscosity grade is employed to secure yarn
of low tensile pxoperties directly. A reduction in temperature
of 3 to 8 degrees is ordinarily adequate for this purpose.
Accordingly, values of 285-295 are preferably employed with
polyethylene terephthalate of intrinsic viscosity 0.55-0.70,
preferably 0.60-0.65, particularly at higher wind-up speeds.
Excessively cool operations are detectable by poor stringup ~ -
and runnability and will therefore be readily avoided.
At these spinning temperatures and a 2-5 filament denier
; the conditioning tube is maintained at a temperature of at
least 200C. preferably 220C. to 260C. for a conditioning -
tube of 1-4 feet in length and operations in the range of
10-15 thousand feet per minute.
Fibrous structures having low tensile properties may there-
fore be recovered directly i.e. without further processing such
as drawing, and employed in the form of continuous filament,
~20 or staple; yarn, tow or roving; or processed into non-woven
structures having utility in e.g. interlining.
A particularly valuable property of the yarns produced by
this invention is that the tensile characteristics are develop-
ed in a balanced manner for a given tensile factor. Thus it
has always been possible to produce yarn of low tensile factor
~` ~ at insignificant tenacity but the product i~ of virtually no
use. In contradistinction, the yarns of this invention exhibit
interrelated tensile characteristics balanced in their development,
where each element contributes significantly to the calculation of
tensile factor. For tensile factors of 14 to 22, tenacity may
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; range from 2.5 to 4.0 g/denier and elongation may be 25 to 40%.
The polymers employed are prepared in a manner usual for
fiber forming operations, and typically exhibit intrinsic vis-
cosities in the region 0.50 to 1.0 or more. The preferred poly-
mers are the linear polyesters,particularly the terephthalate
type most preferably containing at least 85 mol percent of
recurring ethylene terephthalate units. These polyesters may be
modified for dye receptivity by the inclusion of dye openers
such as adipic acid or dye sites such as 5-sulfoisophthalate
units. Polymer blends may of course be employed, and certain
mixtures employing a minor amount of polymer of higher rate of
crystallinity such as polybutylene terephthalate or a crystal-
line nucleation agent is seen to offer advantages.
Although the invention has been described hereinabove with
particular reference to polymers like polyethylene terephthalate
having lower rates of crystallization, it is understood that an
appreciation of the principles underlying these disclosures will
` permit application to other polymers.
EXAMPLE I
' . 20 To illustrate the invention, 70/36 yarn was spun from poly-
ethylene terephthalate polymer through a 72 hole pack with
.009 x .012" orifices to a cross flow quench zone 3 ft in length
and thence to a 2 meter nylon steam conditioner tube at 80 psig.
positioned 6 ft. from the spinnerette under the conditions and
with the results indicated in the following table.
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EXAMPLE II
Low tensile 70/36 yarn was produced from .675 I.V.
polyethylene terephthalate under controlled conditions at
a threadline (spin-draw) speed of 13000 fpm, wherein the
spun and quenched yarn was passed through a 2 ft. zone of
controlled elevated temperature (185C. at the bottom and
105C.ak the top) removed 6 ft. from the spinnerette.
, As polymer temperature (pack inlet, Dowbox reading)
was lowered from 291 to 287~C. the yarn of this invention
was produced:
Polymer Temp.;
C. Ten. Elong. TE BWS
.
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291 4.14 41.8 26.82 5.2
290 4.02 42.1 26.04 5.7
287 3.55 30.5 19.77 5.0
, The abrupt property change as a function of polymer i
temperature is evident, suggesting the criticality in the
process regime for provision of the novel fiber structures
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of the present invention.
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