Note: Descriptions are shown in the official language in which they were submitted.
PROCESS FOR DIMENSTUNALLY STABLE POLYESTER YARN
1. Field of the Invention
This invention relates to a process for production
of polyester multi-filament drawn yarn of 2.5 denier per
filament or greater, whereby high birefringence (p"n)
yarns are prepared at lower spinning speeds and lower
intrinsic viscosity than prior art processes.
2. Description of the Prior Art
Polyethylene terephthalate filaments of high
strength are well known in the art and are commonly
utilized in industrial applications including tire cord
for rubber reinforcement, conveyor belts, seat belts,
V-belts and hosing.
Dimensionally stable polyester (DSP) industrial
yarns are desired to minimize sidewall indentations (SWI)
in the bodies of radial tires and to achieve good tire
handling characteristics. An additional objective is to
make advanced DSP's having the strength and modulus
equivalent to rayon at elevated tire service temperatures,
while using up to 30 percent less material. While the
current polyester tire cords have sufficient strength,
their elevated temperature modulus is too low. , U.S.
Patent 4,101,525 to Davis et al. provides a high
strongth multifilament polyester yarn with low shrinkage
and work-loss characteristics. While yarns exhibiting the
features taught by Davis are classified as DSP's, they do
not meet the modulus requirements for rayon replacement.
Additionally, low denier per filament (dpf or 2 or less)
and rapid cooling of the filament immediately after
emerging from the spinneret can result in excessive
filament breakage and thus yield yarn with poor mechanical
quality. U.S. Patent 4,491,657 to Saito et al. discloses
high modulus, low shrinkage polyester yarn, but requires a
low terminal modulus to achieve good yarn to treated cord
conversion efficiency for such dimensionally stable yarns.
The low terminal modulus is translated into the treated
cord and results in a lower tenacity than the high
terminal modulus cords made by present invention. The
process of Saito et al. requires high spinning speeds,
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which makes it difficult to incorporate the Saito process
into a continuous spin-draw process, whereas the present
invention permits the use of lower spinning speeds whereby
more readily available and/or less costly equipment can be
used.
U.S. 4,690,866 to Kumakowa et al. describes a
means of making yarns which yield highly dimensionally
stable treated cords using ultra high viscosity polymer.
On a comparative experimental basis, i.e. utilizing our
solvent system, the Kumakowa intrinsic viscosity (IV)
values would be 5o higher than indicated in their patent,
i.e. they require a minimum of 0.95 IV polymer by our
measurements. Also, these cords have low terminal modulus
and hence do not achieve the full tenacity benefit of a
given polymer viscosity.
It is known, shown by the prior art cited above,
that undrawn birefringence can be increased by increasing
the spinning speed or yarn IV.
An important need exists for a process to
produce high undrawn birefringence ( ~,nu) yarns at lower
spinning speeds and lower intrinsic viscosity (IV), than
previously. Processing at lower speeds is important
because of the speed limitations of commercial equipment,
particularly winders. The ability to use lowor IV means
that costly processing steps such as solid state
polymerization or costly/environmentally hazardous '
additives can be eliminated.
Summary of the Invention
A process for production of a dimensionally
stable drawn polyethylene terephthalate multifilament yarn
having filaments of at least 2.5 denier per filament
comprising the steps of:
a) extruding a polyethylene terephthalate
polymer melt through a spinnerette having a plurality of
extrusion orifices to form filaments;
b) advancing the extruded multifilament yarn
first through a delay zone then through a quenching zone
to solidify the filaments in a controlled manner;
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c) withdrawing the solidified multifilament yarn
from the quenching zone at a desired spinning speed V;
whereby steps a) through c) are performed
under conditions to form a partially--oriented
multifilament yarn having a undrawn birefringence (~nu)
of at least 0.020 and wherein ~,nu = Rf V2~0 IV2~4 where
IV is the intrinsic viscosity of the undrawn yarn and is
at least 0.80 and Rf is at least 9.0 x 10-3; then
d) hot drawing the partially-oriented
multifilament yarn. The process permits production of high
undrawn birefringence yarns at lower speeds and lower IV's
than previously demonstrated in the prior art.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The dimensionally stable polyester multifilament
yarns made by the process of the present invention
provide dimensionally stable treated cords when
incorporated as fibrous reinforcement into rubber
composites such as tires.
Dimensional stability is defined as high modulus
at a given shrinkage and directly relates to tire
sidewall indentations (SWI) and tire handling. While the
modulus of the cord in the tire is the primary variable
governing both SWI and handling, shrinkage is important in
two ways. First, excessive cord shrinkage during tire
curing can significantly reduce the modulus from that of
the starting treated cord. Second, cord shrinkage is a
potential source of tire non-uniformity. Thus, comparison
of modulus and tenacity at a given shrinkage is a
meaningful comparison for tire cords. Since tire cords
experience deformations of a few percent during service, a
good practical maasure of modulus is LASE-5 (load at 5
percent elongation). Alternatively, E4,5 (elongation at
4.5 g/d load) can be used as a practical measure of
compliance.
For both tire SWI and handling, modulus at
elevated temperature (up to 110°C) is the important
parameter governing performance. Due to the highly
crystalline nature of treated cords based on conventional
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or dimensionally stable tire yarns, the modulus retention
(in percent) at elevated tire temperatures is essentially
similar for all current commercial treated cords and for
those of this invention when loss modulus peaks occur at
110°C or greater. Thus, room temperature measurement of
LASS-5 is sufficient to establish meaningful differences
in polyester cord dimensional stability.
The polyester yarn contains at least 90 mol
percent polyethylene terephthalate (PET). In a preferred
embodiment, the polyester is substantially all
polyethylene terephthalate. Alternatively, the polyester
may incorporate as copolymer units minor amounts of units
derived from one or more ester-forming ingredients other
than ethylene glycol and terephthalic acid or its
derivatives. Illustrative examples of other esterforming
ingredients which may be copolymerized with the
polyethylene terephthalate units include glycols such as
diethylene glycol, trimethylene glycol, tetramethylene
glycol, hexamethylene glycol, etc., and dicarboxylic acids
such as isophthalic acid, hexahydroterephthalic acid,
bibenzoic acid, adipic acid, sebacic acid, azehaic acid,
The polymer may be polymerized in a separate
operation or polymerized in a directly coupled continuous
polymerization and direct melt spinning process.
An important aspect of this invention permits
obtaining high undrawn birefringence yarn without the need
' to utilize molecular weight enhancing additives such as
multifunctional coupling agents exemplified by
2,2'-bis(2-oxazoline). Catalysts for the polymerization
reaction are not considered to be included in the
definition of molecular weight enhancing additive.
The multifilament yarn of the present invention
commonly possesses a denier per filament of about 2.5 to
20 (e. g. about 3 to 10), and commonly consists of about
6 to 600 continuous filaments (e.g. about 20 to 400
continuous filaments). The denier per filament and the
number of continuous filaments present in the yarn may
be varied widely within the ranges of this invention as
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will be apparent to those skilled in the art.
The multifilament yarn made by the process is
particularly suited for use in industrial applications
including rubber composites, ropes, cordage and tarps.
The fibers are particularly suited for use in environments
where elevated temperatures (e.g. 80°C to 110°C) are
encountered.
The yarn characterization parameters referred to
herein rnay conveniently be determined by testing the
multifilament yarn which consists of substantially
parallel filaments.
Undrawn bi ref ringence ( f~,nu ) was determined
using a polarizing light microscope equipped with a
Berek compensator.
Intrinsic viscosity (IV) of the polymer and yarn
is a convenient measure of the degree of polymerization
and molecular weight. IV is determined by measurement of
relative solution viscosity ('~'~r) of PET sample in a
mixture of phenol and tetrachloroethane (60/40 by weight)
solvents. The relative solution viscosity (~ r) is the
ratio of the flow time of a PET/solvent solution to the
flow time of pure solvent through a standard capillary.
Billrneyer approximation (J. Polym. Sci. 4, 83-86 (1949))
is used to calculate IV according to
IV = 1/4 ( ~r-1 ) + 3/4 l.n 7~r
C C
where C is concentration in gm/100 ml. In this study, the
concentration was 1.3 gms/100 ml. It will be understood
that IV is expressed in units of deciliters per gram
(dl/g), even when such units are not indicated.
Comparison to IV measurements in other solvents is given
in an article by C. J. Nelson and N. L. Hergenrother, J.
Poly. Sci., 12 2905 (1974). The invention makes possible
obtaining high modulus drawn yarn without the need to
utilize exceptionally high IV polymer. Satisfactory drawn
yarns with high ~ nu with IV of at least 0.8U, for example
0.85 to 0.95 can be obtained by this invention.
The tensile properties referred to herein
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were determined on yarns conditioned for two hours through
the utilization of an Instron tensile tester (Model TM)
using a 10-inch gauge length and a strain rate of 120
percent per minute in accordance with ASTM D885. All
tensile measurements were made at room temperature.
Elongation at the specified load of 4.5 g/d (E4,5)
is inversely related to modulus. It is particularly
useful in that the sum E4,5 + FS is a good indicator of
dimensional stability for yarns processed under different
relaxation levels. Lower sums (E4,5 + FS) indicate better
dimensional stability. Drawn yarn of the present
invention is produced with ~ nu greater yarn than 0.020 and
possess a dimensional stability defined by E4.5 + FS <
16~. Free shrinkage (FS) values were determined in
accordance with ASTM D885 with the exception that the
testing load was 0.009 g/d. Such improved dimensional
stability is of particular importance if the product
serves as fibrous reinforcement in a radial tire.
Identified hereafter is a description of the
continuous spin-draw process which has been found to be
capable of forming the desired improved yarns. Figures 1
and 2 illustrate apparatus which~may be utilized to
practice the process of this invention, though it will be
recognized by those of skill 'in the art that the apparatus
illustrated may be modified in known ways.
Referring to Figs. 1 and 2, like numbers indicate
like apparatus. Molten polymer is fed by extruder 11 to
spin pump 12 which feeds spin block 13 containing a
spinnerette and a spinning filter disposed between the
spin pump and spinnerette. The spinnerette is designed
for the extrusion of one or more ends of filaments, each
end containing a plurality of filaments. Fig. 1
illustrates the simultaneous extrusion of two ends 14 and
15 of multifilament, continuous filament yarn from one
spinnerette. Ends 14 and 15 are extruded from the
spinnerette at a spinning temperature in the range of 285
to 320°C and at a desired polymer volumetic flowrate (Q,
cm3/min/capillary), and are passed downwardly from the
spinnerette into a delay zone, chamber 16, which
preferably is a quiescent delay zone or a heated sleeve
of a desired delay length preferably 1 to 40 inches,
maintained at a desired heated sleeve temperature
preferably 100 to 450°C. Yarn leaving chamber 16 is
passed directly into the top of the quenching zone,
apparatus 17, preferably a radial inflow quench. The
quench chamber is an elongated chimney of conventional
length for example 1 to 40 inches. Ends 14 and 15 of yarn
are lubricated by finish applicator 18. A spinning finish
composition is used to lubricate the filaments. For the
examples in this application, finish applicator 18 was a
lube roll which is rotated with the direction of the yarn
movement. Other means of applying finish could also be
used.
To achieve desired properties in the final drawn
yarn, it is necessary to hot draw the partially-oriented
multifilament yarn withdrawn from the quenching zone, for
example to at least 85 percent of the maximum draw ratio.
This can be accomplished either in an off-line drawing
process or preferably in a continuous spin-draw. process.
The drawing may be multiple steps and include high
temperature annealing with or without relaxation. In this
illustration, ends 14 and 15 are then transported to spin
draw panel 21. A typical configuration is shown in Fig.
2. In Fig. 2, ends 14 and 15, are all processed on the
same single set of forwarding (first roll 1), drawing
(rolls 2-3 and rolls 5-6) and relaxing rolls (rolls 7-8).
From draw roll 2, the ends are passed through a steam
impinging draw point localizing steam jet 4. From
relaxing rolls 7 and 8, the yarn ends are forwarded to
winder 22. For the discussion following V is taken as the
linear speed of roll 1.
With respect to conditions for operating the
apparatus to achieve the process of this invention, it is
generally known that undrawn birefringence ((~,nu) can be
increased by increasing the spinning speed (V given in
km/min) or the IV of the yarn (dl/g). By experimental
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work accomplished during the course of this invention,
this can now be quantified by the following experimentally
determined relationship:
nu = Rf V 2.0 IV 2.4
V is the spinning speed given in
kilometers/minute. IV is the intrinsic viscosity of the
undrawn yarn given in dl/g. Rf is a value characteristic
of the additional processing variables other than V and
IV.
For conventional and prior art processes, Rf is
typically _< 8 x 10'3, whereas for the process of this
invention Rf is _> 9.0 x 10'3. Of course, the higher the
Rf value, the higher the undrawn birefringence for a given
IV and V. Apparently, the combination of high molecular
weight (IV > 0.80) and inherent stiffness of the PET
molecule results in a sufficiently slow relaxation rate
in the molten state to achieve high Rf values. High
Rf values, for example Rf > 15 x 10'3, are readily
attainable by this invention and are of prime commercial
interest.
Rf can be broken down into two more basic terms:
Rf ~ RrRe
Rr is related to the retention in orientation after
thermally induced polymer relaxation. This parameter .
increases with increasing severity of the quenching and
decreases with increasing extruded polymer temperature and
heated sleeve length and temperature. One skilled in the
art can adjust these parameters to maximize ~ nu and still
maintain good spinnability.
The core of the invention is in the Re term
which is related to the effective polymer extension from
flow orientation in the spinnnerette and draw-down in the
spin column. The net result is substantial orientation even at
moderate spinning speeds. The experimentally determined
relationship is D0.5
Re =
q0.7
where D is the spinnerette capillary diameter (inches) and
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Q is the polymer flow rate through the capillary expressed
in cm3/min/capillary. Q is calculated using a polymer
density of 1.2 gm/cm3. This invention also teaches the
proper combination of D and ~ to achieve Re of at least
10.5 x 10'2. More preferred, Re is at least 13 x 10'2.
If one looks only at the IV range 0.80-0.95, a
simplified expression may be obtained which shows the
advantage of this invention over prior art, with ~,nu
of at least 7.0 x 10'3 V2. It may be preferred to achieve
even higher birefringence for a given V, with ~ nu of at
least 11.5 X 10'3 V2. Thus, for this viscosity range, the
invention can also be defined solely in terms of V.
The particular examples which follow show how
proper selection of process variables results in Rf _>
9.0 x 10'3 and the desired improved yarns which exhibit
improved dimensional stability. The comparative examples
are taken from the patents previously cited and are
summarized in Table I. This table contains all examples
in which (a) the drawn yarn had a dpf of at least 2.5, (b)
nu was at least 0.020, and (c) the yarn IV was between
0.85 and 0.96. The latter IV range was chosen 'since it is
close to the 0.88 - 0.92 range in our examples.
EXAMPLE 1
PET polymer was pumped at 296°C to a spinnerette
containing multiple orifices, each orifice of 0.030 inch
diameter (D=0.030 inch). The extension rate per hole (Q)
was 0.88 cm3/min. The filaments were passed through a 1
inch heated sleeve and then quenced in a radial quench
stack. The spun yarn was subsequently drawn on a panel
similar to figure 2, with roll 1 maintained at 90°C, the
yarn drawn 1.5/1 to unheated rolls 2, 3 with a normal
ambient temperature of 40-50°C, then drawn 1.6/1 from
rolls 2, 3 to rolls 5, 6 maintained at 200°C, the yarn was
then relaxed to rolls 7, 8 at 1 to 1.5 percent. Rolls 7
and 8 had an operating temperature of 150°C. The drawn
yarn was taken up at 2.98 km/min. Polymer thruput for the
two ends was 85 lbs./hour. The drawn yarn was 1004
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denier, 3.3 dpf, 17.5 lbs, breaking strength, 7.9 g/d
tenacity, 10.6 percent ultimate elongation, 3.9 g/d
LASS-5, 5.5% E4.5 and 9.2 percent FS. The sum E4,5 + FS
is 14 percent. The undrawn yarn birefringence (~ nu) was
0.026 and IV was 0.92 dl/g. Rf was 24 x 10-3. The yarn
produced in this example, while produced at a moderate
spinning take-up speed usually associated with standard
yarn products, is then shown to have that enhanced
dimensional stability associated with substaintially
higher spinning speeds in the prior art. Rf and Re were
24 x 10-3 and 19 x 10-2, respectively.
L~YTMDT L' 7
An ultradimensionally stabilized PET was
produced in the following manner. PET polymer was pumped
into a spinnerette containing multiple orifices, each
orifice of 0.027 inch diameter (D = 0.027 inch). Q was
1.3 cm3/min/cap. The filaments were then passed through a
heated sleeve (HST = 220-300°C, residence time 0.02-0.03
sec) and quenched in a radial quench stack. The spun yarn
was first drawn 1.4/1 between rolls at 90°C and unheated
rolls, then drawn 1.15/1 between these and rolls
maintained at 220°C. The drawn yarn was then relaxed at
3~ to rolls maintained at 135°C. The yarn was taken up by
a high speed winder at 4.6U km/min. The drawn yarn was
924 denier, 3.3~dpf, 5.8 g/d tenacity, 4.1 g/d LASE-5, 6.5
percent E4,5, 10.3 percent ultimate elongation, 4.3
percent free shrinkage. The sum E4,5, + FS was 1U.8
percent. The undrawn yarn birefringence was O.U82 and IV
was 0.92 dl/g. Rf was 11 x 10'3 and Re was 14 x 10-2.
EXAMPLE 3
Yarn (IV = 0.92) was produced in a similar
manner to that in Example 1, only (a) a 2-inch sleeve was
heated to 220-300°C (b) the spinnerette orifice was 0.018
inch, and (c) Q was 1.0 cm3/min/cap. The drawn yarn was
taken-up at 4.72 km/mins after experiencing a 2.46/1 hot
draw ratio. This yarn had similar properties to Example
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I: 3.3 dpf, tenacity of 8.1 g/d, ultimate elongation of
10.00, LASE-5 of 3.9 g/d, E4y5 of 5.5~, and free shrinkage
of 10Ø The 0.028 undrawn birefringence corresponded to
a Rf of 11 x 10-3. Re was 13 x 10'2.
EXAMPLE 4
A high viscosity yarn (IV = 0.88) was prepared
similar to Example 2 only D = 0.018 inches and V = 3.5
km/min. The undrawn yarn had a birefringence of 0.088
which corresponds to Rf = 9.8 x 10'3. Drawn dpf was 2.7
and Re was 11 x 10-2.
TABLE I
Prior Art
Examples*
n IV(dl/g)@V(km/min) Rf(10-3)Re(10-2)Ref.
0.021 0.96 2.0 5.9 7.7 U.S. Patent
4,491,657
0.039 0.96 3.05 4.7 6.9 "
0.052 0.96 3.5 4.7 6.7 "
0.072 0.95 4.0 5.2 6.4 "
0.088 0.95 4.5 4.8 6.4 "
0.097 0.95 5.0 4.4 6.2 "
0.073 0.90 3.5 7.5 8.9 U.S. Patent
4,690,866
* Includes drawn dpf at least2.5 IV between
only of and
0.85 and 0.96.
60:40 Phenol/TQtrachloroethylene vent.
sol
