Note: Descriptions are shown in the official language in which they were submitted.
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The invention relates to improving the drawing perfor-
mance of a permanently conjugated yarn formed by melt spinning
Together a segmented elastomeric polyurethane with a hard (non-
elastomeric) fiber. More partlcularly, the invention relates
to certain crltical parameters in the polyurethane, which lead to
less breaks and wraps when the conjugate yarn is subsequently
drawn.
There have been recent suggestions in the art relating
to conjugating an elastomeric segmented polyurethane with a non-
elastomeric or hard fiber, the resulting melt-spun conjugate
yarn being drawn before it is suitable for its ultimate and
intended utility. It has heretobefore not been known how to
reproduceably make such a yarn which could be drawn at commer-
cially practical speeds with an acceptably low level of yarn
breaks and wraps per pound of yarn.
It has now been found that this and other difficulties
wlth the prior art practice are avoided by stoichiometric adjust-
ment such that the finished polyurethane polymer when used for
melt spinning contains between 1 and 45, and preferably between
1 and 27, microequivalents or unreacted isocyanate groups per `
gram of polymer, as more fully set forth below.
In a preferred embodiment of the present invention
there is provided a process for preparing a conjugate filament
comprising
(a~ preparing an elastomeric polyurethane polymer having
between 1 and 30 microequivalents of free isocyanate
per gram of said polyurethane polymer at the time of
spinning;
(b) melt spinning said polyurethane polymer conjugately
with a hard polymer to form a conjugate filament; and
(c) drawing said fllament at a draw ratio of at least 2.0
to 1.
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In a further embodiment of the present invention there
is provided a process -for preparing a conjugate filament com-
prising: :
(a) preparlng an elastomeric polyurethane polymer having
between 1 and 27 microequivalents of free isocyanateper gram of said polyurethane polymer at the time of
~. . . . .
spinning;
(b) melt spinning said polyurethane polymer conjugately
with a hard polymer to form a conjugate filament; and
(c) drawing said filament at a draw ratio of at least 2.0
to 1.
In a further embodiment of the present invention there
i~ provided a process for preparing a drawn conjugate filament
from a hard polymer and an elastomeric polyurethane polymer,
said process comprising:
(a) measuring the free isccyanate group concentration
NCOm at a time Tm after said polyurethane polymer
was formed;
(b) melt-spinning said polyurethane polymer conjugately
with a hard polymer at a time
~ NCO ~
T ~ T ~ m J 5,75
to form a conjugate filament; and
(c) drawing said conjugate filament at a draw ratio of ~:
at least 2 to 1.
In a still further embodiment of the present invention
there is provided a process for preparing a drawn conjugate fila-
ment from a hard polymer and an elastomeric polyurethane polymer,
said process comprising:
(a) measuring the free isocyanate group concentration
NCOm at a time Tm after said polyurethane polymer
was formed;
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(b) melt-spinning said polyurethane polymer conjugately
with a hard polymer at a time
~ NCO ~
; T ~ Tm ~ m ~ 5 75
'A ,
to form a conjugate filament; and
(c) drawing said conjugate filament at a draw ratio of
at least 2 to 1.
The invention will be readily understood from the
-' following detailed description taken in connection with the
accompanying drawing, wherein the FIGURE is a block diagram of
; the process for making the desired drawn conjugate yarn.
As shown generally in the FIGURE, the conjugate yarn
is prepared by a sequence of operations, most of which are
known per se. A polyurethane polymer as prepared according to
the invention is indicated in block 20, as more fully disclosed
below. The finished polyurethane polymer is melted, as by
screw extruder 22, and fed to conjugate spinning unit 24. A
hard polymer is provided in block 26, melted as by screw ex-
truder 28, and also fed to conjugate spinning unit 2~. The
two molten polymers are brought together in spinning unit 24
and spun as a molten bicomponent filament stream 30. Filament
30 is quenched (cooled until solidified) in block 32 as by a
cool air stream to form a solidified spun conjugate filament 34.
Spun conjugate filament 34 is then subjected to optional other
processes in block 36, these optional other processes including
such conventional steps as applying to the filament a spin
finish composition, winding the spun filament onto an initial
temporary package, etc.
Bicomponent filament 34, after being subjected to such
processes in block 36 as are desirable, is fed to draw zone 38
wherein it is drawn by a draw ratio of at least 2.0 to 1.
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Ordinarily the draw ratio will be between about 3 and 5 to 1,
depending largely on the properties of the hard polymer.
The resulting drawn filament 40 is fed to further
operations represented by block 42, wherein it is wound, twisted
and wound, heated under controlled tension, or the like. The
processes as thus far described, except for the preparation and
composition o~ the polyurethane as set forth in block 20, are
known in the art.
The polyurethanes useful in the practice of this inven-
tion are formed by reacting together (1) a high molecular weight
hydroxy terminated polymeric diol having a molecular weight be-
tween 800 and 3000 ~preferably between 1800 and 2200), (2) a low
molecular weight polyol, and (3) a diisocyanate. Minor
amounts of additives can also be present if desired. Typical
additives are stabilizers against light, heat or oxidation, such
as hindered phenols; materials for reducing the tackiness of the
freshly extruded polyurethane polymer, typified by alkylene bis-
amides; pigments or fillers, such as titanium dioxide; or
catalysts.
The high molecular weight diol may be a polyether or a
polyester. Suitable polyethers include poly(oxyethylene)glycol;
poly(oxypropylene)glycol; poly(l,4-oxybutylene)glycol; poly(oxy- -
propylene)-poly(oxethylene)glycol; etc. Suitable polyesters are
obtained by the condensation reaction between a dicarboxylic acid
and a glycol, or from a polymerizable lactone. Preferred poly-
esters are derived Erom adipic, glutaric or sebacic acid, one or
more of which is reacted with a moderate excess of such glycols
as ethylene glycol; 1,4-butylene glycol; propylene glycol; di-
ethylene glycol; dipropylene glycol; 2,3 butanediol; 1,3-butane-
diol; 2,5-hexanediol; 1,3-dihydroxy-2,4,4-trimethylpentane; or
mixtures of such diols. Useful polyesters may also be made by
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the reaction of a polymerizable lactone such as caprolactone
- with an initiator such as a glycol.
Many different common glycols can be used as the low
molecular weight polyol or chain extender; typical examples are
1,4-butanedioli ethylene glycol; propylene glycol; and 1,4~
hydroxyethoxy benzene. The combination of low molecular weight
polyol and diisocyanate, as to type and amount, preferably is
chosen so as to provide a polyurethane polymer having a melting
point by differential thermal analysis (DTA) in the range of
10 200-235C. The polyol should be primarily composed of one or
more diols having a molecular weight below 500, although as ex-
plained below, it may be desirable to include as part of the
polyol a small molar amount of a multifunctional compound con-
taining three or more hydroxyl groups per molecule. In such a
case, the latter compound can have a molecular weight up to
1,500. Amounts up to 0.3 mols of the multifunctional compound
per mol of the high molecular weight diol can be used, although
ordinarily only about 1/10 or less o~ this amount need be added
for viscosity control. Typical multifunctional polyhydric com-
pounds are glycerine, trimethylol propane, hexantriol and the
like. Suitable diisocyanates may be selected from a variety
of classes, including alicyclic, aromatic, aryl-aliphatic, and
aliphatic diisocyanates. Particularly useful diisocya~tes are
2,4-tolylene diisocyanate; 4,4'-dicyclohexylmethane diisocyanate;
4,4'-diphenylmethane diisocyanate; xylylene diisocyanate (either
meta- or para-); 1,4-cyclohexane diisocyanate; 1,6-hexamethylene
diisocyanate; and l,4-tetramethylene diisocyanate.
It has been discovered that improved drawing perfor-
mance of the conjugate yarn is achieved if the polyurethane poly-
mer has between 1 and 45 microequivalents of unreacted isocyanategroups per gram of polymer, as measured just prior to spinning.
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Preferably such a polyurethane polymer is made by reacting to-
gether, for each mol of the high molecular weight diol, between
2.2 and 8.5 mols of the low molecular weight polyol, and a small
excess of diisocyanate sufficient to provide between 1 and 45
microequivalents of free isocyanate in the resulting substanti-
; ally completely reacted polyurethane polymer measured just prior
to spinning. Preferably there are between 3.0 and 6.5 mols of
the polyol or chain extender for each mol of the high molecular
weight diol, since polymers with less than 3.0 mols polyol tend
to be excessively tacky, while those with more than 6.5 molstend to have poorer elastomeric properties. These reagents are
preferably combined by first heating a premixture of the hydroxyl
compounds and then blending the diisocyanate into the premixture.
Temperatures of the reagents at blending should he above the
melt point of all the reagents and below about 180C. Tempera-
tures of 90-110C.are preferred. After mixing the reagents, the
resulting molten mixture exotherms and is maintained within the
temperature range between 100C.and 180C,(preferably between
120-170C.) until the molten mixture solidifies at which point
polymeri~ation is not yet complete. Polymèrization is contin-
ued to substantial completion in the solid state at a temperature
or temperatures between room temperature and 1~0C. When the un-
reacted isocyanate group content reaches a level between 1 and
45 Cpreferably between 1 and 30 or less) microequivalents of iso-
cyanate groups per gram of the finished polyurethane polymer, the
polymer is ready to be melt spun.
Example
One mol of poly(butylene adipate), acid number 1.5,
hydroxyl number 55, is mixed at a temperature of 100C.with 5.34
mols of 1,4-butanediol. The resulting premixture is thoroughly
blended with 6.4 mols of 4,4'-diphenylmethane diisocyanate by
-
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rapid stirring for one minute. The blended reaction mixture is
then cast on a heated tray in an oven heated to 130C. The re-
action mixture solidifies to a low molecular weight polymer in
two or three minutes. The oven temperature is then increased
to 150C.for 6 minutes to increase the molecular weight. The
polymer is then removed from the oven, chopped into flake of the
desired size and stored at temperatures below 50C.in sealed cans.
The process of the example is repeated, adjusting the
amount of diisocyanate so that the content of unreacted isocya-
nate groups in the polyurethane polymer at the time of spinning
several days later is as indicated in Table ~O The polyure-
thane polymer is melt spun conjugately side-by-side with nvlon 6
- (a representative hard polymer) at a temperature of 226C, air
quenched, coated with a spin finish, and collected at a speed of
300 yards (274.3 meters) per minute. The resulting conjugate
filament contains between 20% and 80~ polyurethane, for example,
50%. The filament is conventionally drawn at a draw ratio of
4.0 to 1 at a speed of 400 yards (365.7 meters) per minute to
yield a crimped side-by-side conjugate yarn with a drawn denier
of about 26. Drawtwist performance is set forth in Table I.
TABLE I
Unreacted NCO at Average Drawing Breaks/Lb.
Spinning, M eg/gm (0-453 ~g? of filament
a. 60 0 95
b. 50 0.45
c. 45 0.32
d. 40 0.22
e. 30 0.09
f. 27 0.06
. .
At lower unreacted isocyanate concentrations, the breaks
per unit weight are still further reduced somewhat. More than
about 0.32 breaks per pound (0.453 kg) of yarn is not acceptable
from a commercial standpoint, while a break level of less than
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0.09 per pound (0.453 kg) and preferably less than 0.06 per
pound (0.453 ~g) is highly desirable in a commercial operation.
According to one major aspect of the invention, these increas-
ingly desirable levels of performance are achieved by using a
polyurethane with between 1 and 45) and preferably no more
than 30 microequivalents of unreacted isocyanate groups per gram
of polymer at the time of spinning. Optimum resul-ts are
- obtained when not more than 27 microequivalents of un~eacted
isocyanate groups per gram of polymer are present at the time
1~ of spinning,
According to a second major aspect of the invention,
it is possible to control the stoichiometry of the polyurethane
reagents so that the desired content of unreacted isocyanate --
groups are achieved within a reasonable time after the polymer
is first formed. This is done by adjusting the stoichiometry so
that th~ content of unreacted isocyanate groups (as measured 4.8
hours after the reagents are blended) is between 10 and 120
(preferably between 50 and 85) microequivalents per gram of poly-
mer. The content of unreacted isocyanate groups is then decrea-
sed if necessary (as by storing the polymer at room temperature)
to a final level at the time of spinning between 1 and 45 micro-
equivalents per gram. Higher initial levels than 120 microequ-
ivalents per gram of polymer would require excessive storage time
before acceptable drawing performance would be achieved, while
lower initial levels than 10 microequivalents per gram of polymer
would provide a polyurethane polymer having a melt viscosity too
low for acceptable spinning performance. The viscosity can be
increased, if necessary, by addition of small amounts of amulti-
functional compound having three or more hydroxyl groups as part
of the low molecular weight polyol. Ordinarily, a satisfactory
viscosity increase can be achieved with the addition of very
small amounts of the multifunctional compound, such as about 0.01
~ g
... . . . .
-
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or 0.02 mols of triol per mol of the high molecular weight diol.
Since such small molar quantities of the multifunctional com-
pound are used, advantageously the rnolecular weight of this com-
ponent is relatively high to minimize the effect of small errors
in metering; molecular weights up to 1500 are suitable. Such
high molecular weight multifunctional compounds may be made by
polyethoxylating a triol, or by other conventional techniques.
Unreacted isocyanate groups within the narrower pre-
ferred range of 50 to 85 microequivalents per gram of polymer are
indicative of polymers which will have the desired viscosity and
which can be spun after a reasonable period of storage at room
temperature to yield a conjugate yarn with good drawing perfor-
mance.
According to a third major aspect of the invention, it
is possible to determine when a given polyurethane polymer should
be conjugately spun if a desired level of drawing performance is
to be achieved. It has been discovered that the unreacted iso-
cyanate level NCOm in microequivalents per gram of polymer meas-
ured at any number of hours Tm after the polymer reagents are
blended can be related to the minimum polymer age in hours Tm at
room temperature prior to spinning to achieve the desired unre-
acted content of isocyanate groups by the following relationship:
T = Tm ( NCm ) 5.75 , ~;
where X represents the desired unreacted isocyanate content at
the time of spinning. X accordingly can range from 1 to 45
microequivalents per gram polymer according to the broader as-
pects of the invention, with markedly superior drawing perfor-
mance being obtained when X is less than 30. Optimum results
are achieved when X is less than 27.
Determination of Unreacted Isocyanate Groups
.
The content of unreacted isocyanate groups can be
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;- determined ~y various methods. The following is an exemplary
technique for their determination, and is based on the addition
of an excess of dibutylamine in ary toluene to the polymer
sample, followed by titration of the excess dibutylamine with a
standard hydrochloric acid solution to a bromphenol blue end
point
Dibutylamine reagent is prepared by dissolving approx-
imately 0.65 gram dibutylamine (Fisher Scientific Co., Catalog
No. 1260 or equivalent) in one liter of dry reagent grade toluene.
-~ 10 Bromphenol blue indicator solution is prepared by dissolving
- 0.04% by weight of bromphenol blue indicator in dry reagent grade
isopropyl alcohol. Thoroughly dried N,N' dimethylacetamide (Du-
Pont solvent grade or equivalent) is provided.
Four grams of a representative sample of the polyure-
thane polymer are frozen to the temperature of liquid nitrogen at
atmospheric pressure and finely pulverized, as by use of a Spex
Freezer Mill, Catalog 6700 or equivalent.
About 1.0 gram of the powdered polymer weighed to the
nearest 0.0001 gram, is transferred to a clean dry 125 mllliliter
(ml~ flask. 20 ml of dibutylamine reagent and 15 ml.of dry N,N'
dimethylacetamide are transferred by microburet to the flask. A
magnetic stirrer bar, coated with an inert material such as poly-
tetrafluoroethylene, is placed in the flask, and the flask is
stoppered. The flask is then placed on a magnetic stirrer and
gently stirred for 30 minutes. A blank is also prepared as
described in this paragraph, except the powdered polymer is
omitted.
50 ml of anhydrous isopropyl alcohol is then added to
each flask, the stopper being rinsed during this addition. 2 ml.
of bromphenol blue indicator solution is next added to each flask,
and while vigorously stirring, the materials in both flasks are
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titrated to a yello~ end point stab:le for 15 seconds using 0.01
normal hydrochloric acid. The unreacted isocyanate CNCO) then
equals
(A-B)x N x 1000
sample weight, grams,
~here A equals the milliliters of the hydrochloric acid required
by the blank, B equals the milliliters of the hydrochloric acid
; required by the sample, and N is the normality of the hydro-
` chloric acid solution.
~s used in the specification and claims, the term
"hard polymer" means those melt-spinnable polymers which in spun
fiber form can be permanently extended in length at least 100%
by drawing at a temperature between room temperature and 150C,
and ~hich in substantially fully dra~n form has a maximum fur-
ther elongation of 80% before breaking, this further elongation
; being substantially fully recoverable after release of tension.
By way of contrast, the elastomeric polyurethanes, even after
being subjected to a stretching in excess of 100% of their
..
original length and relaxed, can be stretched or elongated at
least 100% before breaking. Typical common hard polymers in-
clude the various nylons or polyamides; the polyesters such as
polyethylene terephthalate; and the polyolefins, such as poly-
ethylene and polypropylene.
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