US3048465A - Polyolefin wet spinning process - Google Patents

Description

Aug. 7, 1962 w. JURGELEIT 3,048,465

POLYOLEFIN WET SPINNING PROCESS Filed Sept. '7, 1960 2 Sheets-Sheet 1 FIG! 22"PUMP INVENTOR. WOL EGANG JURGELEIT ATT'Y S Aug. 7, 1962 w. JURGELEIT POLYOLEFIN WET SPINNING PROCESS 2 Sheets-Sheet 2 Filed Sept. 7, 1960 ATT'YS United States Patent 3,048,465 POLYOLEFIN WET SPINNING PROCESS Wolfgang Jurgeieit, Coraopolis, Pa., assignor to Vereinigte Glanzstofi-Fahriken A.G., Wuppertal-Elberfeld, Germany Filed Sept. 7, 1960, Ser. No. 54,406 Claims priority, application Germany June 16, 1956 15 Claims. (CI. 18-54) This invention relates to spinning solutions and to processes or methods for spinning and further processing polyolefin filaments so as to increase the rate of filament production and to improve in other ways processes for producing fine denier polyolefin filaments. In particular, the invention is concerned with the so-called wet-spinning process for the production of polyolefin filaments in which the polyolefin is first dissolved in an organic solvent, the filaments then spun from the hot spinning solution and solidified, after which the solvent is extracted from the filaments in a liquid bath and the filaments stretched for molecular orientation and/or diameter reduction.

This application is a continuation-in-part of my copending applications Serial No. 76,688, filed September 23, 1958, and now abandoned, and Serial No. 664,289, filed June 7, 1957, and now abandoned.

In a known wet-spinning process for the manufacture of high-pressure polyolefin filaments, the polymer is spun as a solution in a suitable organic solvent, e.g., as described in US. Patent No. 2,210,771, and the extruded or spun filament emerges from a spinneret into a socalled precipitation bath in which the filament solidifies because of extraction of the solvent with a liquid which is inert to the polymer but miscible with the solvent. Suitable precipitation bath liquids include many alcohols and ethers, and various ketones and esters have also been used. The function of the precipitation bath is to withdraw at least part of the solvent from the extruded polymer spinning solution such that the spun filaments will have sutficient strength to undergo subsequent operations, e.g., those in which the filaments are drawn or stretched for molecular orientation. An inadequate removal or extraction of the solvent, either during precipitation or in subsequent steps prior to stretching the filament for molecular orientation, as in conventional wet-spinning processes, yields filaments which are still semi-liquid and which tend to stick together and are very easily deformed.

Certain wet-spinning processes have been developed to overcome some of these disadvantages byremoving a major portion of the solvent in the precipitation bath. However, in order to avoid poor fiber properties, this more complete extraction of the solvent must be carried out very slowly, thereby requiring additional space for the bath and/or a relatively inadequate production capacity. 7

It is particularly difficult 'in these prior processes to obtain a fine denier filament together with a high production capacity. The wet-spinning process is desirable because it is usually possible toproduce finer deniers and higher tensile strengths than when merely spinning the polymer in its molten form and in the absence of any solvents. However, wet-spinning is not only slower than melt-spinning, but many of the solvents and precipitating 3,048,465 Patented Aug. 7, 1962 ice liquids are difiicult to work with and in some cases present a serious explosion hazard.

An object of the present invention is to provide new and improved processes for the production of polyolefin filaments so as to overcome the disadvantages of prior wet-spinning and melt-spinning processes.

A specific object of the invention is to provide simplified processes for producing fine denier polyolefin filaments of high tensile strength at a more rapid rate, i.e., a higher production capacity.

Another particular object of the invention is to produce polyolefin filaments from spinning solutions in processes wherein the polymer solvent can be very rapidly and substantially completely extracted from the spun filaments without damage to fiber properties. In a preferred form of the invention, a specific extraction liquid is provided for this purpose.

Yet another object of the invention is to provide improved processes in which the low pressure, high-molecular weight polyolefins can be advantageously spun to provide excellent fibers for textile uses.

These and other objects and advantages of the invention are more clearly brought forth in the following detailed description of the invention.

In the drawings:

FIG. 1 is a diagrammatic side elevation of equipment for preparing and spinning hot solutions of polyolefins into a solidification bath; and

FIG. 2 is a diagrammatic illustration of a preferred process of the invention.

Briefly, I have found that high molecular weight polyolefin filaments can be spun rapidly and processed into excellent filaments if a hot polyolefin-containing spinning solution is extruded and first introduced .into a solidifying bath which contains a liquid medium inert to and substantially immiscible with both the polyolefin and its solvent.

The filaments are solidified in this first bath by reducing their temperature, the bath being maintained at a temperature below about 30 C., and preferably between about 0 C. and 30 C. This cooled and solidified filament is easily processed even though substantially no solvent has been extracted therefrom and even can be drawn or stretched mildly, if desired; Exemplary liquids for the solidifying bath are water and lower alkanols, e.g., propanol and butanol.

The solvent is not extracted until after the solidifying bath, and such extraction is accomplished before the first stretching of the filaments. I

It is especially advantageous to rapidlyand as completely as possible extract the solvent from the cooled and solidified filament with a liquid media which is inert to the polyolefin but miscible with the solvent such as petroleum ether, diethyl ether or, more preferably, with liquid methylene chloride which gives a surprisingly good extraction of the solvent. In this respect, methylene chloride is particularly advantageous as compared to such liquids as petroleum ether with which there is a danger of an explosion. The extraction and stretching steps may be repeated once or twice more. 7 l t More particularly, the polyolefins spun in accordance with this invention are polymers of mono-olefins having from 2 to 5 carbon atoms, inclusive, such as those produced by the recently developed low pressure polymerization process to provide a polymer molecular weight of at least 60,000 and preferably above 70,000. Polyethylene and polypropylene are the preferred polymers for filaments. Poly-butylene, polyisobutylene and polymerized pentene or isopentene can also be spun into filaments by the practice of this invention.

The polyolefin spinning solution is prepared by dissolving the polyolefin in a hydrocarbon solvent selected from the group consisting of paraffins and cycloparafiins to form a spinning solution containing about 10 to 18% by weight of the polyolefin. The hot spinning or extrusion of the filaments is then carried out at a temperature of about 150 C. and 250 C., and preferably about 180 C. to 220 C., the parafiin or cycloparaffin hydrocarbon being in its liquid state at this spinning temperature. 'It will be recognized that the hydrocarbon solvent should not boil at the spinning temperature and should therefore be selected from those compounds having an initial boiling point in the range of between about 150 C. and 380 0., preferably above 150 C. to about 300 C. These solvents are ordinarily obtained as the intermediate to heavy distillates in the fractionation of petroleum and consist essentially of parafiins, naph-thenes, or mixtures of paraffin and naphthene (i.e., cycloparatfin) hydrocarbons. They are known under such commercial or familiar names as mineral oil, gas oil, paraffin oil,

spindle oil, White oil and the like.

The spinning head is spaced above the surface of the solidifying bath at a distance so that the freshly spun filaments pass through an air space of at least 5 centimeters. The air space is ordinarily in the range of 510 cm. 'The production of the spinning solution and the subsequent spinning process can be carried out in the tity. The polymer is dispersed in the oil by vigorous stirring. The tank is kept at a temperature of to 20 C. by means of a cooling jacket 12. The valve in conduit 16 is opened, and the dispersion flows into the heated worm '18, which again stirs the mixture. This stirring worm is heatedto about l80-220 C. by a heating jacket 20; The dispersion of the polyolefin powder in the corresponding oil' is converted, in the course of the passage through the worm, into a clear viscous solution. This solution is pumped by the action of the worm 18 into the spinning pump 22, heated to about the same temperature as the solution. The solution is pumped to the spinning head 24, and the fine filaments emerging from the nozzle 28 first traverse an air space of at least 5 cm. in length and then pass into the cool solidifying bath 26.

It is an essential "feature of the present invention that the hot, freshly spun filaments of polyolefin solution at a diameter of 100-300 containing at least about 82% solvent are introduced through an air space of at least 5 cm. into a cool solidifying liquid bath which is inert to both the polyolefin and its solvent. By inert it is meant that the liquid in the solidifying bath is not miscible with and is substantially a non-solvent for either the polymer or its solvent. Of course, this liquid should not react chemically with the polymer or otherwise be damaging to the highly linear fiber-forming structure of the polymer.

Water isby far the most useful inert liquid for the solidifying bath since it .is. the cheapest and most easily inert impurity or anti-freeze agent is added to the water to form an aqueous solution. No additional substances w carbons, preferably n-propanol, n buta'nol, or sec-butanol.

The function of the solidifying bath'required by the present process is distinct from that which is required in the usual wet-spinning process. Accordingly, the term solidifying bath is employed herein to distinguish from the usual so-called precipitation bath in which the primary purpose is to solidify the filament by extracting solvent rather than'by a simple cooling effect. Surprisingly, a mere cooling of the filaments in water according to the present invention was found to provide a solidified filament of polyolefin solution having sufficient strength to be easily handled in a spinning procedure with conventional drawing or filament conveying apparatus.

It is a particularly preferred embodiment of the invention to follow the solidification bath with an extraction bath of methylene chloride because methylene chloride gives very excellent and rapid extraction of the polymer solvent from the filaments. If the polyolefin spinning solution is spun directly into methylene chloride, the excessive and rapid extraction of the solvent will prevent proper filament formation and cause the filaments to become crumbly. For this reason, it is especially surprising that such good results could be obtained with methylene chloride subsequent to the solidifying treatment with water in the present invention.

Following the first solvent extraction, the filaments are stretched by an amount of 1.5 to 3 fold of the original length of the spun filaments at a temperature between about C. and C. It is done expeditiously in a water bath heated to a temperature of 90-l00 C., preferably about 95 C. If more extraction of solvent from the filaments is necessary, the extraction step above-described is repeated. The filaments are then, again, stretched by 2 to 6 fold of the filament length just prior to the second stage stretching at elevated temperature, preferably at least C., but not higher than the softening point of the filaments. The second stretching is done conveniently by running the filaments over a heated surface just prior to or during the stretching stage of the process.

Although it is feasible to use a single extraction bath with the present process, it is diflicult to achieve a rapid and complete extraction in this manner, and an optimum productioncapacity cannot be realized. The reason for this is that the solvent is first extracted near the surface of the filament and the time required to remove the solvent increases disproportionately as it becomes more difiicult to remove solvent nearer to the central portion or axis of the filament. By using more than one extraction step, a minor portion or surface portion of the solvent can first be extracted quite rapidly, after which the filament can be stretched so that the solvent is again more uniformly distributed throughout the filament. The solvent is actually believed to be exuded or distributed toward the surface of the filament by the reduction in diameter during such stretching. The content of solvent is thus preferably reduced from about 80% or more down to not more than 70% in this first extraction in order tjo prevent filament breakage, and usually down to around With methylene chloride, one additional extracting step is sufficient to substantially remove the solvent, e.g., to a content of not more than 5% by weight of the filament, and preferably so that the filament has a residual solvent content of not more than about 1%, usually about 0.5 to 1%. Such a two-step procedure requires considerably less time for extraction and permits a much higher production capacity. Liquids other than methylene chloride such as diethyl ether or petroleum ether ordinarily require more than two extraction steps or much longer extraction baths so as to lose the advantages of small space requirements and optimum production capacity. The importance of solvent extraction according to the present invention resides in the fact that a rapid and almost complete removal of solvent can be accomplished even though such procedure is not always required. 801* vent extraction is done at any suitable temperature below the boiling point of the solvent. Room temperature or ambient temperature ordinarily is adequate.

The first stretching step will most ordinarily require a drawing out of the fiber of up to about 2 to 2 /2 or even 3 times its original length. The final stretching after the second stage solvent extraction is completed most ordinarily is an additional three to six-fold elongation, such that the total stretching or elongation ratio with relation to the original filament length is usually not more than about 1:9 or 1:10. A high degree of stretching or drawing is possible in this process so that very fine denier filaments can be obtained. Both stretching steps can be accomplished in heated liquid baths. Conventional heated bars, plates, godets or the like can also be used for the second stretching stage. Prestretching after a first extraction bath is carried out at about 90 C. to 105 C., preferably in a hot water bath, while the final stretching is best carried out at a temperature above about 110 C. but below the softening point of the polymer.

Various techniques in stretching are possible depending upon the properties desired in the filament, and the amount of stretching at any particular point in the process can be easily determined by those skilled in the art. In this connection, the present invention is not concerned with such subsequent steps as crimping, finishing, dyeing, twisting or preparation of staple fibers, but such steps are not to be excluded.

A diagrammatic illustration of a preferred embodiment is shown in FIG. 2 of the drawing. The heated polyolefin solution in parafiin and/ or cycloparafiin solvent is spun from spinneret 30 as filaments 32 of said solution pass through an air space into a solidification bath 34 containing water at -30 C. The filaments are drawn from the solidification bath without significant stretching into a solvent extraction bath 36 of methylene chloride. The extracted filaments are drawn into a stretching bath 38 of water at 9598 C., in which they are stretched by the desired amount.

The stretched filaments are drawn through a second solvent extraction bath 40 of methylene chloride in which substantially all of the remaining solvent is extracted from the filaments. The extracted filaments are stretched further by the desired amount between roller pairs 42, 44 while in contact with a heated, arcuate plate 46 at a temperature of at least 110 C. The filaments are spooled on spool 48.

The invention is further illustrated by the following examples. The invention is not to be limited to these examples, however.

Example I A low pressure polyethylene having a molecular weight of about 150,000 is dissolved in parafiin oil (a mineral oil which is practically free of aromatic compounds and has a boiling point of 220-225 C.) in a concentration of 15% by weight. The solution is heated to a temperature of 180 C. and extruded from a conventional spining head or spinneret having orifices with an individual size of ZOO/1. in diameter. The extruded or spun filaments first pass through a short air space of about 10 cm. in which about 2 to of the solvent (by weight of the filament) is given off by evaporation. The filaments are next introduced into a cold water bath maintained at a temperature of about 20 C. in which the polyethylene-containing filaments harden or solidify to form filaments capable of being withdrawn from the bath by a conventional draw roll or conveying roll. In this water bath, the paraflin oil content of the filaments remains practically constant, i.e., about to by weight of the filament.

The solidified filaments are then passed or conveyed into a first methylene chloride bath at the same temperature as the water bath, the extraction bath being arranged as a Washing tube through which the methylene chloride can be continuously passed. The paraffin oil content falls to about 55% by weight of the filament in this first extraction bath. 7

The filaments are next stretched in hot water (98 C.) to about twice their original length and this stretching causes a slight solvent loss down to about 48-50% by weight of the filament. The remaining solvent is then removed in a second washing tube, again with methylene chloride, to a residual content of 0.5l% by weight of the filament. Once again the filament is subsequently stretched four times its length for an over-all elongation of eight times its original spun length.

The resulting filaments have excellent textile properties of tensile strength and a fine denier.

Example [I Polyethylene of the molecular weight 150,000 is dissolved in paraifin oil (boiling point 260 to 280 C. 6.5 mm.) at 200 C. to form a 14% strength spinning solution and spun through a 30-hole spinning head with openings of 200 diameter each. The filaments emerging from the nozzle pass through a 10 cm. air space and enter a solidification bath of propanol maintained at 20 C. The filaments run approximately 2 /2 meters in this bath, are then conducted into an extraction bath, 4 meters long, of petroleum ether, a petroleum fraction consisting primarily of C H and C H hydrocarbons, B.P. 40-60 C., at room temperature and are thereupon immediately subjected to preliminary stretching to about three times their original length. After the preliminary stretching, the filaments are extracted again in a petroleum ether bath and afterwards again stretched to three times their length for a total stretch of 9 times their original lengh.

Example III Polypropylene of the molecular weight 150,000 is dissolved to form a 12% spinning solution in commercial paraffin oil at 180 C. This spinning solution is extruded through a l2-h0le spinning head, as described in the preceding example, and conducted through a 6 cm. air space into a solidification bath of propanol at 10 C. About 8.2 cc. per minute of the spinning solution emerge through the 12 openings of the spinning head, each of 200 diameter. The filaments emerging from the solidification bath traverse a petroleum ether extraction bath and then pass through a stretching device in which they are stretched to 2 /2 times their original length. The filament rate into the stretching device amounts to 20 m./ min., the filament rate out of the device 50 m./min. After passing through the stretching device the threads are washed in ether and spooled.

The threads obtained in this manner can be further stretched above C., and twisted on stretch-twist machines, such as are used, for example, in the processing of polyamides or linear polyesters. After completion of the final stage, the stretching amounts, altogther, to about 9 times the original length. The threads obtained have a strength of 70 Reiss kilometer (7.8 g./ denier) at 15% extension and an individual titer of about 3 den.

Example IV 60 g. of polyethylene powder of average molecular weight 500,000 are dissolved by heating to C. in 400 g. of a colorless mineral oil with a boiling point of 204 to 227 C. This spinning solution is spun through a 30-hole spinning head, as described in the preceding examples, into a cold solidification bath of propanol at 20 C. Between the nozzle opening and the surface of the solidification bath there is an air space of about 8 cm. in length. The filaments run for about 2 /2 meters through the solidification bath and then enter a petroleum ether extraction bath of about 6 meters in length. They are then stretched to 2.4 times their original length in a hot water bath at 95 C., which is 4 meters long. Thereupon, the filaments again run through a petroleum ether extraction bath of about 6 meters in length, and are then spooled in the usual manner.

The spooled filaments are stretched later to 3.3 times their spooled length on a hot plate (112) in a stretchtw-ist machine, as described in Example 111.

The extraction bath can be made elfectively in the form of 3%. meter tubes, into which the filaments are introduced from above, are conducted over a guide roller at the bottom and are finally led out at the upper end. In order to avoid a larger concentration of the polyolefin solvent in the extracting liquid, it is continuously drawn off underneath and, in distilled form, returned above.

Example V 150 g. of polyethylene powder of the molecular weight of 150,000 are dissolved in 1 kg. of white oil, corresponding to a 15% spinning solution. The further processing of the spun filaments corresponds exactly with Example IV. The filaments obtained have a final stretch of 9 times their original length, and a strength of 125 Reiss kilometer (13.9 g./denier) at 3.8% extension. The titer of the individual filaments amounts to 1.8 den.

The present invention avoids most if not all of the many disadvantages previously encountered with a wet-spinning of polyethylene or other polyolefins. The bath liquids employed are relatively inexpensive and much easier to handle than those required in prior processes. There are no explosion hazards in the present process. While polyethylene is a very inexpensive raw material and has very valuable fiber properties, particularly with the low pressure polymer, polypropylene is more desirable from the standpoint of fiber properties even if more expensive. The present invention permits both to be produced in a highly convenient and practical commercial process with a high production capacity.

The essential features of my invention are outlined as follows. A l-l8% solution of a polyolefin of at least 60,000 molecular weight in a solvent of parafiin and/or naphthene hydrocarbons is spun through an air space of at least cm. into a solidification bath maintained at about 0-30 C. The function of this bath is to cool the spun filaments of polyolefin solution without substantial extraction of the solvent or the polyolefin.

The solidified filamentary solution is then extracted to remove a substantial part of the polyolefin solvent. The extracted filaments are stretched at 90-105" C. They are extracted again to remove more polyolefin solvent so that the solvent content of the filaments is certainly less than 10%, preferably less than 5%, and most optimally less than one percent on a weight basis. Though not essentialin all cases, the filaments thereafter can be stretched again up to a total amount of stretch not exceeding 9 or 10 times the original length of the spun filaments.

The invention is hereby claimed as follows:

1. In a process for the production of a polyolefin filament in which the polyolefin has a molecular weight of at least 60,000 and is spun from an organic solvent spinning solution, the solvent extracted from the filament and the filament stretched for fiber orientation, the steps which comprise: extruding the polyolefin spinning solution conrtaining from about 10 to not more than 18% by Weight of said polyolefin through an air space of at least five centimeters into a solidifying bath containing a liquid medium inert to both the polyolefin and its solvent; cooling and solidifying the spun filament substantially without solvent extraction in'said liquid medium which is maintained at a temperature of about 0 C. to 30 C.; extracting the solvent from the filament in a second bath containing a liquid which is inert to the polyolefin but which is miscible with the organic solvent; and stretching the solventextracted filament.

2. In a process for the production of a polyolefin filament in which the polyolefin has a molecular weight of at least 60,000 and is spun from an organic hydrocarbon solvent spinning solution, said hydrocarbon solvent being selected from the group consisting of parafiins and cycloparafiins the solvent is extracted from the filament and the filament is stretched for fiber orientation, the steps which comprise: extruding the polyolefin spinning solution containing from about 10 to not more than 18% by weight of said polyolefin through an air space of at least five centimeters into an inert aqueous solidifying bath; cooling and solidifying the spun filament in said aqueous bath which is maintained at a temperature of about 0 C. to 30 C.; extracting said solvent from the filament in a second bath comprising methylene chloride; and stretching the solvent-extracted filament.

3. A process as claimed in claim 2 wherein the polyolefin is a low pressure, high-molecular weight polymer of a mono-olefin having from 2 to 5 carbon atoms, inclusive.

4. A-process for the production of a fine denier polyolefin filament which comprises: dissolving a low pressure polymer of a mono-olefin having from 2 to 5 carbon atoms, inclusive, and a molecular weight of at least 60,000 in a hot organic hydrocarbon solvent for said polymer, said solvent being selected from the group consisting of paraflins and cycloparalfins; extruding the resulting spinning solution as a filament through an air space of at least five centimeters into an inert aqueous solidifying bath; cooling and solidifying the spun filament in said aqueous bath which is maintained at a temperature of about 0 C. to 30 C.; subsequently extracting a part of the solvent from the filament in a methylene chloride bath and stretching the solidified filament; and repeating said extracting and stretching steps at least once.

5. A process as claimed in claim 4 wherein the polyolefin is polyethylene.

6. A process as claimed in claim 4 wherein a minor portion of the solvent is extracted in a first methylene chloride bath followed by stretching in a hot water bath; and the solvent is then further extracted to not more than 5% by weight of the filament in a second methylene chloride bath followed by additional stretching to obtain a highly oriented fine denier filament.

7. A process as claimed in claim 6 wherein the residual amount of solvent in the filament amounts to less than about 1% by weight after leaving the second methylene chloride bath.

8. A process for the production of a fine denier polyethylene filament which comprises: dissolving a low pressure polymer of polyethylene having a molecular weight of at least 60,000 in a hot hydrocarbon solvent selected from the group consisting of paraffins and cycloparafiins and in a quantity of about 10 to not more than 18% by weight of the resulting spinning solution; extruding said spinning solution at a temperature of between about 150 C. and 250 C. into an inert aqueous solidifying bath; cooling and solidifying the spun filament in said aqueous bath which is maintained at a temperature of about 0 C. to 30 C.; subsequently extracting the solvent from the solidified filament in a methylene chloride bath; stretching the solidified filament; and

repeating extracting and stretching steps at least once.

9. A process as claimed in claim 8 wherein a minor portion of the solvent is extracted in a first methylene chloride bath followed by stretching at a temperature of about C. to C., and the solvent is then further extracted to not more than about 5% by weight of the filament in a second methylene chloride bath followed by additional stretching at a temperature of above about C. but below the softening point of the polymer.

10. A process as claimed in claim 9 wherein the residual amount of solvent in the filament amounts to less spawns 9 10 than about 1% by weight after leaving the second 15. A process as claimed in claim 1 wherein said methylene chloride bath. liquid in said second bath is diethyl ether. 11. A process as claimed in claim 1 wherein said liquid medium is a lower alkanol containing not more References Cited In the file of thls Patent than four carbons. 5 UNITED STATES PATENTS 12. A process as claimed in claim 1 wherein said 2,210,771 Myles Aug. 6, 1940 hqmd medlum PYOPaHPI' 2 354 745 Dreyfus Aug 1 1944 13. A process as claimed 1n claim 1 wherein said 2706674 Rothrock 1955 hquid medlum 1S butano1 22 237 Iwamae in F b 4 195 14. A process as claimed in claim 1 wherein said 10 2825721 Hogan 1958 liquid in said second bath is petroleum ether.

I corrected below.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,048,465 August 71 I962 Wolfgang .Iurgeleit ed that error appears in the above numbered patters Patent should read as It is hereby certifi nd that the said Let ent requiring correction a Column I line 24, for "T6 688" read 762,688

nd sealed this 22nd day of January 1963 Signed a (SEAL) Attest: ERNEST w. SWIDER DAVID L DD Commissioner of Patents Attesting Officer

Claims (1)

1. IN A PROCESS FOR THE PRODUCTION OF POLYOLEFIN FILAMENT IN WHICH THE POLYOLEFIN HAS A MOLECULAR WEIGHT OF AT LEAST 60,000 AND IS SPUN FROM AN ORGANIC SOLVENT SPINNING SOLUTION, THE SOLVENT EXTRACTED FROM THE FILAMENT AND THE FILAMENT STRETCHED FOR FIBER ORIENTATION, THE STEPS WHICH COMPRISE: EXTRUDING THE POLYOLEFIN SPINNING SOLUTION CONTAINING FROM ABOUT 10 TO NOT MORE THAN 18% BY WEIGHT OF SAID POLYOLEFIN THROUGH AN AIR SPACE OF AT LEAST FIVE CENTIMETERS INTO A SOLIDIFYING BATH CONTAINING A LIQUID MEDIUM INERT TO BOTH THE POLYOLEFIN AND ITS SOLVENT; COOLING AND SOLIDIFYING THE SPUN FILAMENT SUBSTANTIALLY WITHOUT SOLVENT EXTRACTION IN SAID LIQUID MEDIUM WHICH IS MAINTAINED AT A TEMPERATURE OF ABOUT 0* C. TO 30* C.; EXTRACTING THE SOLVENT FROM THE FILAMENT IN A SECOND BATH CONTAINING A LIQUID WHICH IS INERT TO THE POLYOLEFIN BUT WHICH IS MISCIBLE WITH THE ORGANIC SOLVENT; AND STRETCHING THE SOLVENTEXTRACTED FILAMENT.

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