Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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IMPROVED PARTIALLY ORIENTED NYLON YARN AND PROCESS
SPECIFICATION
As used in the specification and claims, the term "nylon
66" shall mean those synthetic linear polyamides containing in the
polymer molecule at least 85% by weight of recurring structural
units of the formula
r--O O H H
¦ C -(CH2)4 - C ~ h (CH2)6 N
Historically, certain nylon 66 apparel yarns were spun
at low speeds of up to about l400 meters per minute and packaged.
The spun yarns were then drawn on a second machine and packaged
again. The drawn yarn was then false-twist textured at slow
speeds of the order of 55-230 meters per minute by the pin-twist
method, yielding a very high quality stretch yarn suitable for
stretch garments such as leotards. An exemplary false-twisting
element for the pin-twist texturing process is disclosed in
Racshle U.S. 3,475,895.
More recently, various other types of false twisting
apparatus have come into commercial use, and are collectively
referred to as "friction-twist". Some of the most widely used of
these include a disc aggregate of the general type illustrated in
Yu U.S. 3,973,383, Fishback U.S. 4,012,896 or Schuster U.S.
3,885,378. Friction-twisting permits considerably higher
texturing speeds than pin-twisting, with yarn speeds currently at
about 700-900 mpm. Such high texturing speeds are more economical
than those attained by the pin-twist process.
; Along with the shift to friction-twisting has come a
shift to partially-oriented nylon 66 (PON) yarns as the feeder
yarns for the friction-twist process. In the conventional PON
spinning process, the winding speed is merely increased from the
previous standard of about 9QO-l50Q meters per minute to speeds
generally in the 2750-4QOQ meters per minute range, resulting in a
PON yarn. PON yarn performs better in the high speed
friction-twist texturing process than either the earlier drawn
yarn or the low-speed spun yarn mentioned above. However,
heretofore yarns textured by the friction-twist process were of
distinctly lower quality in terms of crimp development than yarns
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textured by the pin-twist process. The apparel nylon 66
false-twist textured yarn market is accordingly in essentially two
distinct segments: the older, expensive, high quality pin-twist
yarns, and the newer, less costly, lower quality friction-twist
yarns
PON feeder yarns for false~twist texturing have had RV's
~` in the range from the middle or upper thirties to the low forties,
~, as indicated by U.S. 3,994,121. Such yarns have more than
adequate tenacity for conventional apparel end uses. With
conventional nylon 66 polymerization techniques, increasing the
polymer RV is expensive and leads to increased rates of gel
formation, with consequent shortening of spinning pack (filter)
` life. High RV polymer is therefore ordinarily not used unlessrequired for some special purpose, such as when high yarn tenacity
is required.
It has recently been discovered that high RV PON feeder
yarns permit manufacture of friction-twist yarns having increased
crimp development, in some cases comparable to that of pin-twist
yarns. This increased crimp development provides a substantial
` 20 increase in fabric covering power as compared to fabrics made from
friction-twist yarns made from PON feeder yarns as disclosed by
Adams U.S. 3,994,121. Accordingly, less textured yarn is required
to provide a fabric of equivalent covering power. Increased
productivity in spinning and texturing is also provided by high RV
PON yarns.
According to the present invention, a further and
substantial improvement in the art is provided by a novel PON
feeder yarn, permitting formation of a friction-twist textured
yarn having in some cases markedly higher crimp development than
even pin-twist yarns. This permits either or both of increased
stretching capability in a fabric or use of even less yarn to
provide a fabric of equivalent covering power, even as compared to
pin-twist yarns.
The yarns of the invention are, broadly, false-twist
texturing feed yarns spun at high speeds and characterized by a
sheath-core conjugate structure, with the sheaths formed from
nylon 66 polymer having a higher melt viscosity at 284C. than the
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polymer forming the cores. The mechanism or precise reason for
the improved results of the present invention are not entirely
understood
;~ According to a first principal aspect of the invention,
there is provided a sheath-core filament spun at a spinning speed
of at least 2200 MPM, the filament having a nylon 66 sheath
component surrounding a polymeric core component, the sheath
component having a higher melt viscosity at 284C. than that of
the core component.
According to a second principal aspect of the invention
there is provided a process for spinning a sheath-core filament,
comprising generating a molten stream comprising a nylon 66 sheath
component having a higher melt viscosity at 284C. than that of
the core component, extruding the stream through a spinneret
capillary, quenching the stream into a filament, and withdrawing
i the filament at a spinning speed of at least 2200 MPM.
According to a third principal aspect of the invention
there is provided a process for producing a textured yarn,
comprising simultaneously drawing and friction-twist texturing a
sheath-core filament spun at a spinning speed of at least 2200
MPM, the filament having a nylon 66 shealth component surrounding
a polymeric core component, the sheath component having a higher
melt viscosity at 284C. than the core component.
In accordance with each of the above principal aspects,
the core component is preferably nylon 66. Preferably the RV of
the sheath component is at least lO RV units higher than the RV of
the core component, and optimally the RV of the sheath component
is at least 20 units higher than the RV of the core component. It
is preferred that the RV of the sheath component be at least 50,
with a sheath component RV of at least 60 being most desirable.
Preferably the shealth-core volumetric ratio optimally being about
3 to 7. For best results the spinning speed is selected such that
.
`~ the filament has an elongation lower than l50/O, with the range
~ between 50% to 120% being particularly advantageous.
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Other aspects of the invention will in part appear
hereinafter and will in part be obvious from the following
detailed description taken together with the accompanying drawing,
wherein:
FIGURE 1 is a schematic front elevation of an examplary
apparatus for spinning the yarns of the invention; and
FIGURE 2 is a cross-section of an exemplary filament
according to the invention.
As shown in FIGURE 1, molten polymer streams 20 are
extruded through capillaries in spinneret 22 downwardly into
quench zone 24 supplied with transversely directed quenching air
at room temperature. Streams 20 solidify into filaments 26 at
; some distance below the spinneret within the quench zone.
Filaments 26 are converged to form yarn 28 and pass through
interfloor conditioner tube 30. A conventional spin-finish is
applied to yarn 28 by finish roll 32. Yarn 28 next passes in
partial wraps about godets 34 and 36 and is wound on package 38.
The filaments may be entangled if desired, as by pneumatic tangle
chamber 40.
Ordinarily, godets 34 and 36 perform the functions of
withdrawing filaments 26 from streams 20 at a spinning speed
determined by the peripheral speed of godet 34, and of reducing
the tension in yarn 28 from the rather high level just prior to
godet 34 to an acceptable level for winding onto package 38.
Winding tensions within the range oF 0.03 to 0.25 grams per denier
are preferred, with tensions of about 0.1 grams per denier being
particularly preferred. Godets 34 and 36 may be dispensed with if
the yarn winding tension immediately prior to the winder in the
absence of the godets is within the yarn tension ranges indicated
in this paragraph. "Winding tension" as used herein means the
yarn tension as measured just prior to the yarn traversing and
winding mechanism. Some commercially available winders include an
auxiliary roll designed to both assist in yarn traversing and to
permit reducing the yarn tension as the yarn is wound onto the
bobbin or package. Such winders may be of assistance when using
the upper portions of the yarn tension ranges indicated in this
paragraph.
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Description of the Prior Art
Example 1
This is an example within the range of present
conventional practice. Nylon 66 polymer having an RV of 39 is
extruded through a conventional spinning pack and spinneret at a
melt temperature of 285C. Spinneret 22 contains 34 capillaries
having lengths of 0.012" (0.3 mm.) and diameters of 0.009" (0.229
mm.) Quench zone 24 is 35 inches (60.96 to 88.9 cm) in height,
and is supplied with 20C. quench air having an average horizontal
10 velocity of l foot (30.5 cm.) per second. Filaments 26 are
converged into yarn 28 approximately 36 inches (91.4 cm.) below
the spinneret. Conditioner tube 30 is 72 inches (183 cm.) long
and is o-f the type disclosed in Koschinek U.S. 4,181,697, i.e., a
steamless tube heated to 120C. through which yarn 28 passes. The
15 speed of godets 34 and 36 are 4100 meters per minute and 4140
meters per minutes, respectively, to prevent the yarn from
wrapping on godet 36. The polymer metering rate is selected such
that the yarn wound has a denier of 89. The winder used is the
Toray 601, and the winder speed is adjusted to provide a winding
tension of 0.1 grams per denier. The yarn has an
elongation-to-break of 65-68% and an RV of 41 (about 700 poise
calculated zero shear rate viscosity at 284C).
; The spun yarn is then simultaneously drawn and
friction-twist textured on a Barmag~FK6-L900 texturing machine
using a 2-1/2 meter primary heater and a Barmag disc-aggregate
with Kyocera ceramic discs in a draw zone between a feed and draw
~ or mid roll. The heater temperature is 225C.j and the ratio of
; the peripheral speed of the discs to draw roll speed (the D/Y
ratio) is 1.95. The draw roll speed is set at 750 meters per
minute, and the feed roll speed is adjusted to some lower speed to
control the draw ratio and hence the draw-texturing tension (the
yarn tension between the exit of the heater and the aggregate).
In order to maximize the crimp development, the draw ratio is
changed by adjustment of the feed roll speed so that the
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draw-texturing tension is high enough for stability in the false
twist zone and yet low enough that the filaments are not broken,
this being the operable texturing tension range. Within the
operable tension range, the "maximum texturing tension" is defined
as the tension producing the maximum initial crimp development
without an unacceptable level of broken filaments (frays). More
than 10 broken filaments per kilogram are unacceptable in
commercial use.
With the Example 1 yarn, the operable texturing tension
range is quite narow when draw-texturing at 750 meters per minute.
The maximu~ texturing tension is found to be about 0.43 grams per
draw roll denier, and the aged crimp development (yarn stored on
the bobbin two weeks after texturing) is about 13-15%. The draw
roll denier is defined as the spun yarn denier divided by the
mechanical draw ratio provided by the different surface speeds of
the feed roll feeding the yarn to the heater and of the draw or
mid roll just downstream of the false-twist device. When the
texturing tension is more than 0.45 grams per draw roll denier, an
unacceptable level of broken filaments is produced. An attempt to
increase initial crimp development by increase in heater
temperature much above 225C. also leads to an unacceptable level
of broken filaments. The textured yarn denier is about 70.
Example 2
This is an example of high RV PON yarn. The spinning
process of the first paragraph of Example 1 is repeated, except
the polymer is selected and dried so that the yarn RV is about 70
(about 2200 poise calculated zero shear rate viscosity at 284C).
The PON yarn denier is 98, and the yarn has an elongation-to-break
of 88%. When the spun yarn of this paragraph is draw-textured
(245C. heater), its maximum texturing tension is found to be 0.54
grams per draw roll denier and the operable range of yarn tensions
in the false-twist zone is broader than in the case of Example 1
above. The textured yarn has a denier of 70 and an aged crimp
development of about 18%. Finished fabrics formed from the
textured yarn of this example have greater covering power and
stretch than similar fabrics formed from the textured yarn of
Example 1, and are comparable to those made from pin-twist yarns.
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Further increases in texturing tension do no appreciably
affect the crimp development, but merely result in broken
filaments or yarn breaks.
THE INVENTION
FIGURE 2 illustrates the preferred sheath-core filament
according to the invention, with sheath 40 surrounding core 42.
Spinneret pack designs for forming such sheath-core filaments are
well known in the art. According to the invention, sheath 40 is
nylon 66 spun at a lower temperature than core 42 and the spinning
speed is at least 2200 MPM.
Example 3
This is an example according to the invention. The
apparatus described in Example 1 is used except the spinneret pack
used in Examples 1 and 2 above is replaced by a spinneret pack
designed to produce 34 sheath-core filaments. A batch of nylon 66
polymer is dried to produce nominal 75 yarn RV (about 2570 poise
calculated zero shear rate viscosity at 284C.), and a second
batch of nylon 66 polymer is dried to produce nominal 41 yarn RV
(about 700 poise calculated ~ero shear rate viscosity at 284C.).
The polymers are spun under the conditions set forth in Example 1
above as sheath-core filaments with the high RV polymer forming
the sheaths and the low polymer forming the cores, the sheath-core
volumetric ratio being 2 to 3. That is, 40% by volume of the
filament is formed by the sheath component, with the remaining 60%
being formed by the core. The PON yarn denier is 108 and the
elongation is 79%.
When the PON yarn is drawtextured by the friction-twist
method at its maximum texturing tension, the resulting textured
yarn has a denier of 70 and an aged crimp development of about
23%. This is substantially greater than the crimp development
levels achieved by friction-twist texturing of any other known
yarn, and even exceeds levels achieved by various applications of
the pin-twist method. The increased crimp development provides
for greater stretch and covering power in fabrics made from the
textured yarn of the invention as compared to all known prior art
yarns textured by the friction-twist method.
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Example 4
It has been discovered that a small amount of draw
(between 1.05 and 2.0 draw ratio) prior to winding gives improved
results in some instances. Example 3 is repeated, except godet 34
is run at 3154 MPM, to provide a draw ratio of about 1.3. The PON
has a denier of 1nO and an elongation of 64, and the aged crimp
development of the resulting 70 denier textured yarn is 24%.
Example 5
The experiment in Example 3 is repeated except that the
spinneret is replaced with a similar spinneret designed to produce
68 rather than 34 filaments. The sheath polymer is nylon 66
having an RV of 70 (about 2200 poise calculated zero shear rate
viscosity at 284C.), while the core is nylon 66 having an RV of
39 (about 610 poise calculated zero shear rate viscosity at
384C.). The sheath-core volumetric ratio is 2 to 3. The PON has
a denier of 1~8 and an elongation of 76%, and the aged crimp
development of the resulting 70 denier textured yarn is about 14%.
This is comparable to the Example 1 yarn even though the denier
per filament is half that of that in Example 1. Fabrics made from
the textured yarn of this example have useful stretch properties
comparable to similar fabrics made from the textured yarn in
Example 1, and have greatly increased covering power and softness.
Fabrics made from friction-twisted 40 RV yarns having 70 denier
and 68 filaments, while having improved covering power as compared
to fabrics formed from friction-twisted yarns having 70 denier and
34 filaments, do not have such useful stretch properties since
they have aged crimp developments of about 8-10%.
Example 6
The experiment in Example 5 is repeated except that the
spinning and winding speeds are reduced to 2000 MPM and the
polymer metering rates are reduced to provide a yarn denier of 132
and an elongation of 132%. Aged crimp development of the
resulting 70 denier textured yarn is 9-10%, illustrating that the
major improvement in crimp development provided by the invention
is available only at spinning speeds above about 2200 MPM.
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Example 7
The preferred sheath-core volumetric ratio is less than
1 to 1, with a ratio of about 3 to 7 being especially preferred.
Example 3 is modified to provide a sheath-core volumetric ratio of
3 to 7 (30% of the filament by volume being formed by the sheath
polymer, and 70% by volume being formed by the core polymer). The
PON has a denier of 114 and an elongation of 76%, and the aged
crimp development of the resulting 70 denier textured yarn is
about 23.4%, somewhat higher than that of Example 3 wherein the
ratio is 2 to 3.
Test Methods
All yarn packages to be tested are conditioned at 21
degrees C. and 65% relative humidity for one day prior to testing.
The yarn elongation-to-break (commonly referred to as
"elongation") is measured one week after spinning. Fifty yards of
yarn are stripped from the bobbin and discarded. Elongation-to-
break is determined using an Instron tensile testing instrument.
The gage length (initial length) of yarn sample between clamps on
the instrument) is 25 cm., and the crosshead speed is 30 cm. per
minute. The yarn is extended until it breaks.
Elongation-to-break
is defined as the increase in sample length at the time of maximum
load or force (stress) applied, expressed as a precentage of the
original gage length (25 cm.).
Crimp development is measured as follows. Yarn is wound
at a positive tension less than 2 grams on a Suter denier reel or
equivalent to provide a 1 1/8 meter circumference skein. The
number of reel revolutions is determined by 2840/yarn denier, to
the nearest revolution. This provides a skein of approximately
5680 skein denier and an initial skein length of 9/16 meter. A
14.2 gram weight or load is suspended from the skein, and the
loaded skein is placed in a forced-air oven maintained at 180C.
for 5 minutes. The skein is then removed from the oven and
conditioned for 1 minute at room temperature with the 14 2 gram
weight still suspended from the skein, at which time the skein
lenght L2 is measured to the nearest 0.1 cm. The 14.2 gram weight
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is then replaced with a 650 gram weight. Thirty seconds after the
650 gram weight is applied to the skein, the skein length L3 is
measured to the nearest 0.1 cm. Percentage crimp development is
defined as L3-L~/L3 x 100. Crimp development decreases with time
as the textured yarn ages on the bobbin, rapidly for the first
hours and days, then more slowly. When "aged crimp development"
is specified herein, the textured yarn is stored on its bobbin at
; room temperature, and measurement is made two weeks after
texturing.
Relative viscosity (RV) is determined by ASTM D789-81,
using 90% formic acid. ~
Broken filaments are determined visually, by counting
the number of broken filaments on the exposed surfaces of the
package.
