US3134833A - Production of asymmetrically birefringent, crystallizable, thermoplastic polymer filaments - Google Patents

Description

y 26, 1964 L. CIPORIN ETAL 3,134,333

PRODUCTION OF ASYMMETRICALLY BIREFRINGENT, CRYSTALLIZABLE, THERMOPLASTIC POLYMER FILAMENTS Filed Dec. 26, 1961 2 Sheets-Sheet 1 FIG.!

T FIG. 4 3

2.8 O O O E 2.7 l E a: l u l I 3 2.6 w 2 l 3 l TEMPERATURE (c) INVENTORS LEON ClPORIN PIERR E R. LATOUR y 1964 L. CIPORIN ETA'L 3,134,833

- PRODUCTION OF ASYMMETRICALLY BIREFRINGENT,

CRYSTALLIZABLE, THERMOPLASTIC POLYMER FILAMENTS 2 Sheets-Sheet 2 Filed Dec. 26, 1961 INVENTORS LEON CIPORIN PIERRE R. LATOUR United States Patent PRGDUCTEUN 0F ASYlVHi EETRECALLY Em- IFRRNGENT, CRYSTALLIZABLE, THERMO- PLASTEC POLYMER FHLAMENTS Leon Ciporin and Pierre R. Latour, Kinston, N.C., as-

signors to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Filed Dec. 26, 1961, Ser. No. 162,019 8 Claims. (Cl. 264-210) This invention relates to filaments and fibers of synthetic polymers which crimp spontaneously after they have been drawn. More particularly, it relates to an improved process and apparatus for producing the filaments and fibers whereby an enhanced degree of crimp is obtained.

It has been previously recognized that crimpecl filaments can be prepared from certain thermoplastic polymers by extruding the molten polymers in the form of filaments, quenching the extruded filaments in an asymmetric manner so that one side of each filament is solidified before the other side, and orienting the extruded filament. Asymmetric cooling of the filament may be achieved, for example, by employing as the quenching medium a jet of air or other gas directed upon one side of the extruded filament a short distance from the spinneret rather than by cooling the filament over a considerable distance with a current of air, as in conventional melt spinning. Although the as-spun filaments are straight and indistinguishable by sight from ordinary asspun filaments, they show different optical properties; i.e., an asymmetrically quenched filament exhibits an asymmetric birefringence differential across the diameter of the filament as contrasted with a symmetric differential, or lack of any differential, associated with ordinary filaments. When the asymmetrically spun filaments are drawn several times their extruded length and tension is released, they exhibit crimp of a three-dimensional nature unobtainable by conventional mechanical crimping methods. The crimped filaments are highly valuable, especially when converted to staple fibers, for many important uses including the preparation of bulky fabrics and as stutfing materials for pillows and the like.

Unfortunately, in preparing the crimped filaments on a commercial scale, it has been found that the filaments frequently have far less crimp than expected on the basis of preliminary laboratory experiments. The lack of crimp development is especially pronounced when large quantities of the asymmetrically quenched filaments are oriented in the form of tow by conventional methods involving the use of hot water or steam to heat the tow in the draw zone. A practical method for preparing the novel crimped filaments and fibers in commercially significant quantities has therefore been greatly desired.

It is an object of this invention to provide a method for drawing asymmetrically quenched filaments of thermoplastic polymers to provide oriented filaments characterized by a lfigh degree of three-dimensional crimp. Another object is to provide a process adaptable for orienting such filaments in large numbers, in the form of a tow. A further object is to provide apparatus for orienting asymmetrically quenched filaments of thermoplastic polymers for maximum development of three-dimensional crimp in the oriented filaments. Other objects will appear as the description of the invention proceeds.

These objects are achieved by the present invention which, briefly described, comprises orienting filaments composed of a crystallizable, thermoplastic polymer and exhibiting an asymmetric birefringence differential across the diameter of the filaments by drawing the filaments at a temperature above the second order transition temperature, T of the polymer; and substantially imme- 3,134,833 Patented May 26, 1964 ice diately after the filaments have been drawn, contacting the filaments with a liquid maintained below T to cool the filaments below T Preferably, the filaments are drawn in the presence of a liquid maintained above T and are then cooled by contacting them with a liquid maintained below T at a point just after the draw point. In a particularly preferred embodiment of the invention, the process is employed to draw a tow comprising a multiplicity of crystallizable linear condensation polyester filaments which have been jet quenched to produce an asymmetric birefringence diiferential across the diameter of the filaments.

Surprisingly, when the filaments are drawn and then immediately cooled in the manner described, they possess a degree of crimp which is highly superior to the crimp obtained upon drawing in the same manner without immediately subsequent application of cooling means to the filaments. The superior crimp level is characterized by a greatly enhanced ability of a quantity of the crimped fibers to resist compression. In other words, the crimped fibers produced in accordance with the present invention have a greater bulk under a given load than do fibers produced by the same process with the omission of the positive cooling step after drawing.

' The expression second order transition temperature, designated herein by the symbol T is defined as the temperature at which a discontinuity occurs in the curve of a first derivative thermodynamic quantity with temperature. It is correlated with yield temperature and polymer fluidity and can be observed from a plot of density, specific volume, specific heat, sonic modulus or index of refraction against temperature. T is sometimes also known as the glass transition temperature because it is the temperature below which the polymer exhibits glasslike behavior; above T the polymer is somewhat more rubberlike. A convenient method for determining T for a given sample of polymer is given by Pace in his US. Patent 2,556,295 (col. 3, line 24- to col. 4, line 19). The crystallinity of the polymer sample selected for measurement of T should be comparable with the crystallinity of the drawn filaments of the polymer.

The term tow, as used herein, refers to a large number of continuous, substantially parallel, synthetic filaments without definite twist collected in a loose, rope-like form. Generally speaking, the minimum number of filaments to which the term tow is considered applicable is on the order of about 10 and normally there are 10 or more. While there is no fixed maximum number, tows containing on the order of 10 filaments are frequently encountered, and there may be occasions to employ tows of 10 filaments or even more.

The nature of the invention will be more readily understood by reference to the following description taken in conjunction with the accompanying drawings, in which FIGURE 1 is a sectional elevation taken through a spinneret assembly and quenching apparatus which may be employed to produce filaments to be drawn in accordance with the present invention,

FIGURE 2 is a schematic drawing illustrating the proce'ss of the invention and apparatus which may be used in carrying out the process of the invention,

FEGURE 3 is a cross sectional side view of a liquidcooled draw roll which may be used in the apparatus shown in FIGURE 2, and

FIGURE 4 is a graph illustrating the relationship between the bulk of the ultimate product, as measured by the card sliver index defined hereinafter, and the temperature of the filaments measured immediately after the draw point. The data employed to plot the graph are given in Example 1 below.

Referring now to FIGURE 1, molten polymer is introduced into a conventional spinneret pack 1, the lower part of which is shown in the figure. The polymer flows through channels 2 into annular polymer distribution space 3 and thence through orifices 4- in spinneret plate 5. The resulting filaments 6 are immediately quenched by a strong flow of gas from annular nozzle 7. The gas enters the annular nozzle through conduit 8 and flows through foraminous members 9 from vertical annular opening it) across the filament bundle as indicated by the arrows. The spinneret is held by bolts 11 to the spinneret pack 1. An insulating disc 12 is provided in the central portion of the spinneret, held against the spinneret face by screw 13, to help keep the temperature of the spinneret uniform even when the quenching gas is introduced at high velocity. Insulating ring 14 around the spinneret pack and spinneret also helps to keep the temperature uniform; its depth is determined such that the annular nozzle 7 is spaced at the exact distance desired from the spinneret face, the annular nozzle being placed flush under the insulating ring. The upper edge of the nozzle is preferably positioned quite close to the face of the spinneret. Conventional winding means, not shown in the figure, are employed to wind the jet quenched filaments.

FIGURE 2 illustrates the process of the invention and apparatus useful in accomplishing the process. The tow 2G to be oriented, comprising large numbers of the filaments 6 jet quenched in accordance with the description above the reference to FIGURE 1, is drawn by being passed from feed rolls 21 through 28, respectively, maintained at a given uniform peripheral speed and then around draw rolls 31 through 33, respectively, having a uniform peripheral speed considerably higher than that of the feed rolls. Between rolls 24 and 25 the tow passes through prewetting vessel 29, which contains an aqueous bath which may be at room temperature or may be heated to a temperature in the range 4-O70 C. Additional quantities of the aqueous bath used in prewetting bath 29, and at the same temperature, are usually sprayed onto or otherwise applied to rolls 25, 26, 27, and 28.

Between rolls 28 and 31 the tow passes through spray zone 39. From nozzles 39 hot liquid spray is directed upon the moving tow, whereupon the tow is drawn to a length several times its original length in response to the tension imposed by the draw rolls. The entire drawing process occurs while the tow is in contact with hot spray from nozzles 39, which usually occupy the greater part of the spray zone. Preferably, the hot spray supplied to the tow is at a temperature equal to or higher than the second order transition temperature, T of the polymer of which the filaments are made. At the end of the spray zone 30, a spray of cool liquid is directed upon the moving tow from nozzles 49. The liquid, preferably aqueous, should be maintained considerably below the second order transition point of the polymer, T when room temperature water is suitable, this is conveniently used, although a liquid maintained below room temperature may be employed if desired. A baffle 41 is usually placed between the hot spray nozzles 39 and the cool spray nozzles 40. Shield 42 serves to protect the feed rolls from contact with the hot spray and shield 43 similarly may be used to prevent further contact of the tow and the spray after the tow reaches the draw rolls. A temperature measuring device 44 is conveniently employed in the draw roll section, usually between the first two draw rolls, to monitor the temperature of the tow so that T is not inadvertently exceeded when processing conditions are changed.

After leaving the draw section, the tow is passed around puller rolls 45 and between a pair of rolls 46 so spaced that excess liquid remaining is squeezed from the tow. The tow is then passed through air jet 47 to open the tow, after which it is laid down on conveyor 48 and passed through drying chamber 49. The dried tow may then be cut to staple and relaxed (not shown).

Some or all of the draw rolls may be liquid cooled to facilitate cooling of the tow after drawing. As shown in FIGURE 3, draw roll 31 is hollow and cooling liquid is introduced and removed through its hollow shaft 59. Centrally positioned inlet tube 51 leads to the far end of the hollow roll, and the cooling liquid then circulates through perforated plates 52 until it reaches outlet 53, where it is forced out.

Instead of being drawn in the manner described above, the tow may be drawn through a medium of steam or other hot vapor, or it may be drawn in other ways. It is frequently desired to have a liquid, especially water, present at some stage of the drawing process; since this aids uniform heating of the filaments and also appears to facilitate drawing in other ways. The presence of the liquid at the end of the drawing step also tends to make cooling of the filaments below T more difficult, which magnifies the loss of bulk in the ultimate product. In the preferred embodiment of the invention, this difiiculty is solved by applying a liquid below T (preferably at room temperature or below) substantially immediately after the tow has been drawn, thus preserving the full amount of bulk developed in the drawing step. The process is usually carried out in such a manner that a part of the cooling liquid is entrained by the moving tow and carried along in contact with it, aiding in completion of the cooling step. If desired, the draw rolls may be internally cooled to help maintain the cooling liquid in contact with the tow below T with perhaps some direct cooling of the tow itself. If the surrounding atmosphere is quite humid and the rolls are suificiently chilled, cooling liquid may be supplied at least in part by condensation of the water from the air.

The cooling liquid employed in the process is preferably water, which may contain other material in solution or dispersion such as textile finishes, antistatic agents, or the like. However, other inert liquids may be employed as cooling liquids, such as kerosene, mineral oil, propanol, etc. The expression inert liquid, as used herein, refers to any liquid which is a non-solvent for the drawn polymeric fiber. It is usually desired also that the liquid be chemically and physically inert with respect to the drawn polymeric filaments; however, in special instances it may be desired to employ a liquid which not only cools the filaments below T but also exerts an incidental chemical effect or physical effect, e.g., crystallization of the fiber.

In general, the invention is applicable to any crystallizable, thermoplastic polymer, especially those having a second order transition temperature, T substantially above ordinary room temperature. The preferred class of polymers is the class consisting of crystallizable, linear condensation polyesters. These comprise linear polymers containing in the polymer chain carbonyloxy linking radicals,

Polymers containing oxycarbonyloxy radicals are comprehended within this group. The polymers should be of fiber forming molecular weight; usually, this implies a relative viscosity of about 10 or higher as measured in solution in a solvent for the polymers. A good solvent for most of the linear condensation polyesters is a mixture of 58.8 parts of phenol and 41.2 parts of trichlorophenol. Copolyesters, terpolyesters, and the like are intended to be comprehended within the term polyesters.

Examples of crystallizable, linear condensation polyesters include polyethylene terephthalate, polyethylene terephthalate/isophthalate (35/15), polyethylene terephthalate/S-(sodium sulfo)isophthalate (97/3), poly(phexahydroxylene terephthalate), poly(diphenylolpropane isophthalate), poly(diphenylolpropane carbonate), the polyethylene naphthalenedicarboxylates (especially those derived from the 2,6- and 2,7-isomers), and poly(mphenylene isophthalate) as well as many others.

The following examples will serve to illustrate the invention, although they are not intended to be limitative.

:2 EXAMPLE 1 Spontaneously crimped staple fibers are produced in a series of experiments for which the results are summarized in Table 1. The polymer employed is polyethylene terephthalate containing 0.3% TiO and having a relative viscosity of 27; T for this polymer is 79 C. The polymer is extruded from a spinning block maintained at 300 C. through a spinneret containing 210 orifices, each 0.009 inch in diameter and 0.012 inch in length, arranged on three concentric circles having diameters of 3", 2.8", and 2.6", respectively, with 0.125" spacing between orifices in each circle. The extruded filaments are quenched with high velocity air from a concentric nozzle jet as shown in FIGURE 1. The spinning speed is 457 yards per minute and the quenched filaments, which are found to have a spun denier per filament of 10.6, are wound on bobbins. The individual as-spun filaments, when examined under a polarizing microscope, exhibit an asymmetric birefringence difterential across the filament diameter.

Filaments from 878 bobbins are combined to form a tow comprising 184,380 filaments. The tow is drawn as shown in FIGURE 2 from a feed section comprising 8 feed rolls and a prewetting bath (30 C.) through a spray draw zone to a draw section comprising 8 draw rolls. The speed of the tow in the draw section is 100 yards .per minute, and the draw ratio is 3.26. Hot aqueous spray, maintained at the temperature indicated in Table 1, is passed down upon the moving tow throughout most of the spray draw zone; while at the draw roll end of the draw zone aqueous spray maintained at 30 C. is passed down upon the tow, the hot and cool spray sections being separated by a bafiie as shown in FIGURE 2. Except where indicated, shield 43 is employed also to prevent the aqueous spray from contacting the tow as it passes around the draw rolls. In two control experiments, as indicated in the table, no 30 C. aqueous spray is applied at the end of the draw zone. The prewetting bath, hot aqueous spray, and 30 C. aqueous spray each comprise a 1% aqueous solution of a textile finish agent comprised primarily of diethanolamine and triethanolamine salts. The draw rolls are hollow and water having the temperature indicated in hte table is circulated through the hollow rolls at the rate of gallons per minute per roll. The temperature of the tow is measured between the first and second draw rolls by means of a lubricated thermocouple point pressed lightly against the center of a small rotating roll in contact with the wet tow.

After leaving the draw roll section, the tow is passed between two rolls to squeeze excess moisture from the tow, after which it is laid down on a conveyer by means of a large air jet and passed through a drier in which it is exposed to circulating room temperature air for a residence time of 3 minutes.

Upon release of the tension of drawing, it is observed that the filaments exhibit a high level of three-dimensional crimp. The oriented crimped filaments are cut to 2.5- inch lengths and relaxed for 1.1 minutes in a hot air oven maintained at 160 C. When examined under a polarizing microscope, the individual filaments again exhibit an asymmetric birefringence differential across the filament dameter.

To measure the degree of crimp of the fibers prepared as described above, the relative compressibility of quantities of each sample of fibers is determined. This measurement of bulk is designated herein as the card sliver index)? In determining this parameter, samples are prepared by processing quantities of the staple yarn through a worsted card which is equipped with a 4" by A doffing trumpet. The fiat sliver so produced is cut into 6-inch squares. The same worsted card is used to prepare all samples tested, and the settings of the card are maintained rigidly constant, in order to produce sliver having a constant degree of openness. Since the absolute values of card sliver index are dependent on the openness of the sliver, maintenance of constant worsted card settings thus permits correlation of sample values obtained at different times.

A stack of the squares of card sliver weighing 20 grams :1 gram is prepared by piling the squares crisscross. The weight of the stack is determined to the nearest 0.1 gram, after which the stack is placed on the compression cell platform of a tensile tester equipped with a 4" diameter plunger (commercially available from Instron Engineering Corporation, Quincy, Mass.) to determine the relationship of pressure applied to the height of the card sliver stack. The compression plates of the tensile tester are 8.0 inches apart. The stack is compressed at the rate of 20 inches per minute to a maximum pressure of 2 pounds, allowed to recover, and subjected to another compression and recovery cycle. The relationship of pressure applied versus stack height is continuously recorded by the machine, and the resulting curve is used to calculate the card sliver index. In making the calculation, the point on the second compression curve corresponding to a card sliver height of exactly 4.5 inches is used as a base point (nominal zero load); from this point, the height of the card sliver at an added load of 1.04 pounds is determined. It the weight of the card sliver stack was not exactly 20.0 grams, the value obtained for the height under the added load is corrected to that of a standard 20.0 gram stack, using a calibration curve plotted by using data from a number of stacks of a uniform sample of card sliver weighing from 19 to 21 grams. The height of the standard card sliver under the added load is taken as the card sliver index, which accordingly has the dimensions of inches per pound of load.

Table 1.-Drawing Jet Quenced Polyethylene Terephthalate Tow at 100 Y.P.M.

Temp. of Temp. of Inlet Temp, Tow Bulk Hot Spray, Cool Spray, Draw Roll Temp, (Card 0. 0. Water, 0. C. Sliver Index) 30 9 65 2. 8 92 1 30 18 75 2.8 30 9 77 2. 8 95 30 9 78 2. 9 92 (None) 18 83 2. 5 6 92 (None) 18 83. 5 2. 5

! Shield 43 in Figure 2 was omitted in this experiment.

Card sliver index values are reported for each of the runs recorded in Table l as a measure of the bulk of the resulting fibers, which in turn is dependent upon the degree of crimp of the fibers.

FIGURE 4 is a graph in which the tow temperature and bulk data of Table 1 are plotted. Each circle represents one determination. As illustrated by the graph, there is a sharp drop in bulk at the temperature T (ca. 79 C.).

EXAMPLE 2 Polyethylene terephthalate filaments having a denier of 10.6 are spun with jet quenching as described in Example 1. Filaments from 660 bobbins are combined to form a tow comprising 138,600 filaments and the tow is drawn 3.13 X at a draw speed of 300 yards per minute in accordance with the general procedure described in Example 1. The feed bath temperature is 30 C. Hot aqueous spray at 95 C. is applied throughout the major part of the draw zone, and a bafiie is employed near the end of the draw zone to separate the hot aqueous spray from cool aqueous spray applied at 30 C. The draw rolls are cooled by circulating through them water at 10 C.; the etfluent water from the second draw roll has a temperature of 30 C. and efiluent water from the other draw rolls have temperatures in the range 16-22 C. The measured temperature of the tow between the first and second draw roll is 63 C. (T =79 C.). A shield is employed to prevent the aqueous spray from contacting the tow as it passes around the draw rolls.

The tow is de-watered, opened, dried, and cut to 2.5- inch staple fibers as in Example 1; after which the fibers are relaxed for one minute at 160 C. The resulting fibers have a card sliver index of 2.8, a denier per filament of 3.8, a tenacity of 2.7 g.p.d., an elongation of 29%, an initial modulus of 26.8 g.p.d., a yield point of 1.3 g.p.d., and a boil-01f shrinkage of 0.8%. When examined under a polarizing microscope, the individual filaments exhibit as asymmetric birefringence differential across the filament diameter. The number of crimps per inch is 7.4 and the crimp index is 29.7. In the measurement of the crimp index, the required data are obtained by measuring the length of the fibers hanging under an added load of 0.1 g.p.d. for a period of two seconds (length A), under which condition they are held straight, and measuring the length of the same fibers hanging under no added weight after they have relaxed for 15 seconds from the first extension (length B). The crimp index is calculated in accordance with the formula:

EXAMPLE 3 A tow of polyethylene terephthalate filaments is formed and drawn as described in Example 2, except that a draw speed of 125 yards per minute is employed. The crimp index of the filaments so obtained is 57.4. When the cool spray is turned off, the temperature of the tow between the first and second draw rolls rises above 80 C. and the crimp index of the filaments obtained under these conditions drops to 46.7.

EXAMPLE 4 Polyethylene terephthalate filaments are spun with jet quenching as described in Example 1. A bundle of 61 of the jet quenched filaments is wound on a bobbin as a yarn package. The package is then placed on a draw winding apparatus in which the yarn is taken off the package, passed around a block maintained at 90 C. (5 wraps), thence around a snub pin (one-quarter wrap), thence around a draw roll (five and three-quarters wraps), after which it is finally wound up at 302 yards per minute. The draw ratio is 3.113, and the actual point at which the yarn is drawn is the snub pin as would be expected. The crimp index of the drawn yarn is measured and found to be 54.4. The experiment is then repeated, except that as the yarn leaves the snub pin it is caused to pass over a sponge wetted with water at C. The crimp index of this yarn cooled with the wetted sponge is 72.0.

The above experiments are repeated at a windup speed of 149 yards per minute. The crimp index of the yarn cooled with a wetted sponge after the snub pin is 54.6, while the crimp index of the yarn which is not cooled after the snub pin is only 41.5.

The experiment employing the windup speed of 302 yards per minute is repeated as described above, without employing the wetted sponge; except that as the yarn leaves the snub pin, it is cooled by blowing room air C.) upon it from a sucker gun of the type disclosed by Miller in his United States Patent 2,667,964, the direction of air flow in the gun being reversed to provide a Crimp Index X 100% Cit stream of air rather than suction. A stream of about 10 cubic feet of air per minute, delivered from a As-inch I.D. nozzle, is employed. Surprisingly, the crimp index of the yarn cooled with the stream of air immediately subsequent to drawing is only 36.2, as contrasted with a crimp index of 54.4 for the control yarn with no cooling means employed. At a windup speed of 149 yards per minute the crimp index is only 32.6 with air cooling as contrasted to a crimp index of 41.5 with no cooling.

In this example the crimp index is determined according to the general method outlined in Example 2, except that the added load is 0.02 g.p.d. and it is employed for a period of 30 seconds, after which the fibers are allowed to hang under no added weight for 60 seconds before the final length of the fibers is measured.

It will be apparent that many widely different embodiments of this invention may be made without departing from the spirit and scope thereof, and therefore it is not intended to be limited except as indicated in the appended claims.

We claim:

1. In the process of orienting filaments composed of a crystallizable, thermoplastic polymer which have an asymmetric birefringence dilferential across their diameter by drawing the filaments at a temperature above the second order transition temperature, T of the polymer; the improvement which comprises cooling the filaments to a temperature below T by contacting them, substantially immediately after they have been drawn, with a liquid maintained below T 2. The process of claim 1, in which the filaments are drawn in the presence of a liquid maintained above T and are then cooled by contacting them with a liquid maintained below T at a point just after the draw point.

3. The process of claim 1, in which the cooling liquid is Water.

4. The process of claim 1, in which the polymer of which the filaments are composed is a linear condensation polyester.

5. The process of claim 4, in which the polyester of which the filaments are composed is polyethylene terephthalate.

6. The process of claim 4, in which a multiplicity of polyester filaments are drawn in the form of a tow.

7. In the process of melt spinning a crystallizable, thermoplastic linear condensation polyester to form filaments, in which the filaments are jet quenched to produce an asymmetric birefringence differential across the diameter of the filaments, after which the filaments are drawn in the presence of water maintained at a temperature above the second order transition temperature, T of the polyester; the improvement which comprises cooling the filaments to a temperature below T by contacting them substantially immediately after they have been drawn, with water at a temperature below T 8. The process of claim 7, in which the polyester of which the filaments are composed is polyethylene terephthalate.

References Cited in the file of this patent UNITED STATES PATENTS 824,577 Great Britain Dec. 2, 1959

Claims (1)

1. IN THE PROCESS OF ORIENTING FILAMENTS COMPOSED OF A CRYSTALLIZABLE, THERMOPLASTIC POLYNER WHICH HAVE AN ASYMMETRIC BIREFRINGENCE DIFFERENTIAL ACROSS THEIR DIAMETER BY DRAWING THE FILAMENTS AT A TEMPERATURE ABOVE THE SECOND ORDER TRANSITION TEMPERATURE, TG, OF THE POLYMER; THE IMPROVEMENT WHICH COMPRISES COOLING THE FILAMENTS TO A TEMPERATURE BELOW TG BY CONTACTING THEM, SUBSTANTIALLY IMMEDIATELY AFTER THEY HAVE BEEN DRAWN, WITH A LIQUID MAINTAINED BELOW TG.

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