CA1051626A

CA1051626A - Polyurethane hard fiber

Info

Publication number: CA1051626A
Application number: CA197,866A
Authority: CA
Inventors: Donald H. Martin
Original assignee: Monsanto Co
Current assignee: Monsanto Co
Priority date: 1973-04-20
Filing date: 1974-04-19
Publication date: 1979-04-03
Also published as: IL44674A; FR2226485A1; AR200600A1; IT1007971B; IL44674A0; ZA742503B; DE2418948B2; GB1427889A; AU6807274A; LU69897A1; JPS559093B2; BE813950A; FR2226485B1; NL7405184A; JPS5012323A; BR7403185D0; DE2418948A1; DE2418948C3

Abstract

POLYURETHANE HARD FIBER
Abstract of the Disclosure Drawing performance of a conjugated elastomeric poly-urethane-hard fiber yarn is improved by critical stoichiometry in preparation of the polyurethane polymer, which is made by reacting together a high molecular weight diol, a low molecular weight diol, and a diisocyanate so that the resulting poly-urethane contains between 1 and 45 (preferably between 1 and 27) microequivalents of unreacted isocyanate groups per gram of polymer at the time of melt spinning.

Description

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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 ~5~L~;2~;
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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~5~26 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 -": `
~ 5~ 6 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 _ ~ _ ' ' ~ ' ': . ' ~5~ 6 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 ... . . . .

-113tS~L~Z~i 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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3L~516~:6 ;- 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 -- 1]. --. ,. .. , ' , ~

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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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Claims

The embodiments of the invention in which an exclu-sive property or privilege is claimed are defined as follows:

1. A process for preparing a conjugate filament com-prising:
(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 con-jugately 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.

2. A process for preparing a conjugate filament com-prising:
(a) preparing an elastomeric polyurethane polymer having between 1 and 27 microequivalents of free isocyanate per gram of said polyurethane polymer at the time of spinning;
(b) melt spinning said polyurethane polymer con-jugately 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.

3. A process for preparing a drawn conjugate filament from a hard polymer and an elastomeric polyurethane polymer, said process comprising:
(a) measuring the free isocyanate group concentra-tion NCOm at a time Tm after said polyurethane polymer was formed;

(b) melt-spinning said polyurethane polymer con-jugately with a hard polymer at a time to form a conjugate filament; and (c) drawing said conjugate filament at a draw ratio of at least 2 to 1.

4. A process for preparing a drawn conjugate filament from a hard polymer and an elastomeric polyurethane polymer, said process comprising:
(a) measuring the free isocyanate group concentra-tion NCOm at a time Tm after said polyurethane polymer was formed;
(b) melt-spinning said polyurethane polymer con-jugately with a hard polymer at a time to form a conjugate filament, and (c) drawing said conjugate filament at a draw ratio of at least 2 to 1.