US2556295A - Process of drawing formed structures of synthetic linear polyesters - Google Patents

Description

June 12, 1951 A. PACE.,J'R 2,556,295

PROCESS OF DRAWING FORMED STRUCTURES OF.

' SYNTHETIC LINEAR POLYESTERS 2 Sheets-Sheet 1 Filed July 25, 1947 -Tg Determination for 0r stolline Polyjthylene T reph1halarte(?) 0. 6|

m E E= H 310 E 0.7l80 0.7IO0 o 40 8O I20 DEGREES CENTIGRADE F G INVENTOR.

v I ANDERSON PA GE, JR.

ATTORNEY.

Julie 12, 1951 A. PACE..JR PROCESS OF DRAWING FORMED STRUCTURES OF SYNTHETIC LINEAR POLYESTERS Filed July 23, 1947 2 Sheets-Sheet 2 Polyet Determination for Amorphous 'aylene Teraphfrholofe SPECIFIC VOLUME ml/ rn.

DEGREES CENTIGRADE FIG. 2

I I I1V1 ENToR. A NDERSON PA CE, JR.

ATTORNEY Patented June 12, 1951 2,556,295 PROCESS OF DRAWING FORMED STRUC- TURES F SYNTHETIC ESTERS LINEAR- POLY- Anderson Pace, Jr., Buffalo, N. Y., assignor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware Application July 23, 1947, Serial No. 763,088

11 Claims.

This invention relates to the manufacture of shaped structures comprised of linear superpolymers. More particularly it relates to a new and improved method for drawing filaments, yarns, threads, ribbons, films and like shaped structures comprised of synthetic linear polyesters.

In the drawing of nylon yarn to enhance tenacity, i. e., tensile strength, it is customary to draw in a single stage, and at an expedient temperature, utilizing a draw pin to localize the drawing. Drawing of nylon yarn in two stages has been suggested but since no advantage is realized over a single-stage draw, and since there are obvious economic draw-backs in-the operation of the two-stage draw the latter has never been practiced commercially. The experience of the nylon art therefore, is that the drawing of yarn synthetic linear polymers is most advantageously accomplished in one stage. However, when the conventional singled raw procedure for nylon was used for drawing the newly discovered synthetic linear polyester yarns considerable difiiculty in obtaining uniform yarn properties and satisfactory operability was encountered. Drawing at room temperature and somewhat above resulted in an unaccountable number of broken filaments and imperfectly stretched yarn, while drawing at substantially elevated temperatures proved erratic in the extreme in that the properties of the drawn yarn varied to a considerable degree, and results could not be duplicated from run to run.

This invention has as its principal objective therefore, the provision of a satisfactory method for drawing filaments, yarn, thread, ribbon, film, and like shaped structures of synthetic linear polyester.

Another object is to provide a simple, economical method for uniformly stretching synthetic linear polyester shaped structures to achieve maximum tensile strength without sacrifice in quality.

Another object is to produce stretched filaments, yarn, thread, ribbon and film of synthetic linear polyester which structures are characterized by uniform optimum physical properties including high tenacity.

A further object is to draw filaments and yarns of synthetic linear polyesters so as to achieve maximum tenacity and improved physical and chemical properties with a high degree of uniformity.

,A still further object is to produce filaments and yarns of synthetic linear polyesters having enhanced tenacities, improved transverse properties, improved resistance to acids and alkalis, im-

Briefly stated the present invention comprises first drawing a formed yarn of synthetic linear polyester at a temperature between the second order transition temperature (represented herein by the symbol T3) and the apparent minimum crystallization temperature (represented herein by the symbol T1) and thereafter further drawing the yarn at a temperature above, and preferably at least 50 C. above, the apparent minimum crystalization temperature (T1) to give a yarn of maximum tenacity. If desired, the drawing operation may be followed by a hot relaxing step to secure an increased elongation in the finished yarn.

In the annexed drawings Figs. 1 and 2 are graphical illustrations of representative determinations of the value of the second order transition temperature (Tg) for a representative synthetic linear polyester, viz., polyethylene terephthalate.

To facilitate an understanding of the invention reference should be had to the following definitions and explanations of terms, it being understood that these terms whenever employed in the following description and claims are to be construed in accordance with such definitions and explanations.

By the expression synthetic linear poly-.-

ester(s) is meant a linear polyester having an intrinsic viscosity of at least 0.3, a low degree of solubility in organic solvents and having the further characteristic property when formed into filaments of-being capable of being cold-drawn to the extent of at least two times the original filament length to form useful textile fibersof strength and pliability.

critical great I 3 The expression intrinsic viscosity, denoted by the symbol no, is used herein as a measure of the degree of polymerization of the polyester and may be defined as:

limit 6+ as O approaches zero wherein m is the viscosity of a dilute phenoltetrachloroethane (60:40) solution of the poly-- is the concentration in grams of the-polyester per 100 cc. of solution.

The expression second order transition temperature, (Tg), is defined as -the temperature atwhich a discontinuity occurs in the-curve of a first derivative thermodynamic -quan'tity:withtemperature. It is correlated with yield temperature and polymer fluidity and can be ob-- served from a plot of density, specific volume, specific heat, sonic modulus or index of refraction against temperature.

For the purpose of this invention, a satisfactory method for measuring the second order transition temperature is as follows:

A plug of the polymer to be tested is formed. The plug should preferably be formed from the melt and rapidly cooled so that it is obtained in the amorphous form. It is then weighed in air and fitted for hanging from a balance. The plug is so suspended from the balance that it hangs centrally in a bath of silicone oil and l below the surface. The temperature of the bath is thermostatically controlled. A silicone oil is especially desirable because of the excellent stability and low probability of attack on polymer specimens. A thermometer calibrated in 0.l C. is placed in the bath with the polymer plug to measure thetemperature. The bath is held at a given temperature until the polymer plug in the silicone oil has reached a constant weight. The plug normally reaches the value within 15 minutes. After the balance reading-is made, the temperature is raised 10 C. and the process repeated. Usually a temperature range of approximately 0-160 0. gives enough points to allow calculation of Tg. This-range is obviously determined by polymer type.

From-the weight of the polymer plug in air and in silicone oil, it is possible 'tocalculate density and specific volume at a given-tempera ture. Corrections are made for the buoyant efiect of air on the polymer plug. The equation used in calculation is:

where Vp=specific volume of polymer, p=density of polymer ps=density of'silicone oil, Wv=weight of polymer in vacuo, Ws=weight of polymer in silicone oil.

The portions of the curveof specific volume vs. temperature above and below Tg are linear as shown in Figs. 1 and 2. The coefiic'ient's of expansion are calculated from the slopes of the curve.

tensions of the twolinear portio'nsof the curve intersect. Figures 1 and 2 show graphically how Tg for a representative polyester is determined. Figure 1 refers to crystalline polyethylene terephthalate while Figure 2 refers to the amorphous form of the same polymer.

For an accurate determination of operating draw temperatures, it is preferred to measure Tg for amorphous polymer since polyesters, asspun or cast, are quenched so rapidly that little or no crystallization takes place. Since Tg increases as the degree of crystallization of the polymer increases, the true draw temperature range of as-spun yarn or film is better delineated if the determination is run using amorphous polymer. Of course if a crystalline or partially crystalline polyester is normally obtained in the-as-spun state a Tg determination should be run, using as-spun polymer. This will give a more accurate lower limit for the actual primary draw temperature.

The expression apparent minimum crystal lization temperature, (Ti), is defined as the lowest temperature at which a marked rate of density change, which is known to occur simultaneously with crystallization, takes place within six hours. apparent minimum crystallization temperature a sample of polyester maintained constant at said temperature below T1 will not vary substan tially in density over a long period e. g., six hours.

However, as soon as the polyester is subjected to the temperature T1 there occurs a rapid changev in density. Acutally the rate changes quite abruptly from no change in six hours to a change within minutes for only a few degrees temperature difference. The value of T1 is conveniently assigned from density determinations done in airor silicone oil and is based on crystallization by heat only.

Since a change in density accompanies the mechanism of crystallization, it is only necessary to determine the temperature at which a significant change in density occurs. Thus, the temperature at which the density of the polymeric material starts to rapidly increase may be takenas the apparent minimum crystallization temperature. A suitable apparatus with which to measure the density of polymeric materials is that of a density gradient tube. Briefly, one

embodiment-may consist of a long tube filledwith' partially mixed carbon tetrachloride and toluene, so that a density gradient of 0.86-1.59 grams: per

milliliter is maintained-from top to bottom of the tube. After proper calibration of density vs. position, the tube can be used to measure densities of polymeric materials by determining the position of smallsamp'les in the tube. The method is especially applicable to heavy denier monofils, since with multi-filament yarns, there'is always the possibility of small bubbles of air-being entrapped, which will tend to give inaccurate density readings.

To measure T1 several small pieces of monofil- (appro'xim'ately 10 grams) of the amorphous synping a piece of the 'monofil into the density gradient tube andallowing it to reach an equilibrium height.- This occurs-within about 15 min.

For every temperature below the utes and does not allow enough time for swelling by the 0014- toluene mixture. At various time intervals up to 6 hours, density measurements are made and the density is plotted against time to show the rate of crystallization. Below the apparent minimum crystallization temperature, this graph will normally show a straight line with no apparent increase in density of the polymeric material over this period of time. Simultaneously, other samples may be run at increasing temperatures say in steps of 2, 5, or .The plot of density vs. time, will in nearly all cases, be substantially a straight line until the apparent minim-um crystallization temperature is exceeded, at which time the density will increase over a period of time until a maximum order of crystallinity is reached and the curve will again flatten out. This procedure will give a temperature range as an approximation of T1. Further density determinations are carried. out in the vicinity of this approximate temperature using smaller temperature increments of the order of 0.5-l.0 to determine accurately the apparent minimum crystallization temperature. Depending upon the accuracy of the apparatus used and the care with which the procedure is followed, T1 is ordinarily reliable to within 1 or 2.

The type of synthetic linear polyester hereinabove defined which responds to treatment in accordance with the principles of this invention may be formed by any of the general processes described in United States Patent Nos. 2,071,250 and 2,071,251 (Carothers), e. g., by the action of dihydric alcohol, such as glycol, on a suitable bibasic acid, such as terephthalic acid, or dibasic acid derivative such as dimethyl terephthalate. As specific examples of synthetic linear polyesters contemplated for purposes of this invention. there may be mentioned high molecular weight linear polymers of ethylene terephthalate, of trimethylene terephthalate, of tetramethylene terephathalate, of hexamethylene terephthalate, etc.; the linear polymers of polymethylene diphenoxy-n-alkane-4 :4 -dicarboxylates disclosed in Dickson application Serial No. 638,485, filed December 29, 1945, now U. S. No. 2,465,150; the

in Cook,

I-Iuggill, and Lowe application Serial No. 708,440,

filed November 7, 1946, now abandoned; the linear polyesters derived from p-(hydroxymethyl) -benzoic acid and similar hydroxy carboxylic acids disclosed in Cook, Dickson, Lowe, and Whinfield application Serial No. 711,470, filed November 21, 1946, now U. S. Patent No. 2,471,023, and the linear polyesters polymethylene-diphenylthioether 4:4 dicarboxylates and the like disclosed in Lowe application Serial No. 708,442, filed November 7, 1946, now abandoned. A preferred polyester, particularly suited to yarn manufacture, is polyethylene terephthalate and the invention will be further described with specific reference to said polyester. It is to be understood however, that my invention contemplates the two-stage drawing in like fashion of any member of the class of synthetic ,esters previously defined.

linear poly- Fiber-forming synthetic linear polyesters should possess an intrinsic viscosity of at least 0.3 and preferably should have an intrinsic viscosity of from 0.3 to 1.5. Polymers having an intrinsic viscosity less than 0.3 do not form commercially-acceptable fibers. Both the transition temperatures and the degradation temperatures are too low to be useful. The intrinsic viscosity of the polyester is one of the main determining factors with regard to Tg and T1. Generally, as the intrinsic viscosity increases Tg increases until a maximum value is reached. Any increase in the intrinsic viscosity above a certain value will not appreciably increase Tg. The following table shows the relation of Tg to intrinsic viscosity for a representative crystalline polyester, i. e. polyethylene terephthalate:

Table I 51. 0 0. 24 57. 0 0. 2s 70. 5 0. 4o 81. 0 o. 51 80.0 0. 61 so. 0 o. 81. o o. 76

Synthetic linear polyesters in the amorphous form exhibit a similar change of Tg with respect to increasing intrinsic viscosity. It is important to remember, however, that for a given intrinsic viscosity, Tg for, an amorphous polyester is not the same as Tg of a crystalline one. Actually, Tg increases as the crystalline-amorphous ratio increases. For example, polyethylene terephthalate with an intrinsic viscosity in the vicinity of 0.70 has a Tg in the amorphous state of 67 C. while the same polymer exhibits a Tg of 80 C when crystalline.

It is generally true that when a synthetic linear polyester is spun or cast and rapidly quenched from the molten state that the formed structure is almost totally amorphous. Quite conceivably a spun or cast structure could be cooled slowly and would, therefore, be in the temperature range inducing crystallization (above T1) for a considerable length of time. Therefore, in such a case the polymer would be predominantly crystalline and exhibit a Tg considerably higher than that of the amorphous form.

This latter possibility, however, will not generally be met in commercial operations since the as-spun yarn is cooled so quickly that it has little or no chance to crystallize. In any event it is not desirable to start with a partially crystalline yarn or film since it is difficult to secure the alignment desired in orientation when the free movement of the molecules in the polymeric structure is restricted by crystal formation. However, even if the as-spun yarn is partially crystalline it can be drawn by this two-stage process by paying strict attention to its Tg criterion.

Continuous filaments and yarns of the highly polymeric linear esters of this invention are best prepared by melt spinning the polyesters, e. g. melting chips'of synthetic linear polyesters on a heated grid, passing the melt through a filter bed made up of a number of small particles, such as sand, forcing it through a spinneret and cooling the filaments so formed. When melt spinning these polymeric esters, it is necessary for the esters to be substantially water free if hydrolysis of the polyesters during thisprocess is to be avoided. Filamentsmay alsobe formed from solutions of these polymeric esters using any of the solution spinning processes known.

in the art; suitable solventsfor these: polymeric esters are cresol, nitrobenzone andchlorinated compounds, such as tetrachloroethane, etc;

Films of these synthetic linear polyesters are best prepared by extrusion of the molten polymer through a suitable shaped orifice and then quenching the molten material. Inthis'process the film may be quenched on extrusion by jets of cold inert gas, e. g. air, immersion in a liquid, e. g. water or by contact with one or more metal surfaces, which surfaces. may themselves be cooled by jets of gas or immersion inliquidsu The filmmay. also be extruded, if desired,'as a large diameter tube having thin. walls, which tube may be flattened and on cutting provide one or more films. In the latter method of working, the cooling is carried out very satisfactorily by jets of inert gas. It is preferred that these films are stretched after extrusion while they are being quenched, in order that unduly, narrow orifices are not required for the extrusion of thin films. Films may also be prepared from solution of the polymeric esters by evaporating the solvents from thin layers of solution at temperatures below the boiling point of the. solvent. Solvents for the solution spinning process described herein before may be used.

As stated previously the synthetic linear polyester structure is given a first or primary draw while the structure is at a temperature between Tg and Ti, and preferably in the vicinity of Tg. Maximum orientation should be obtained by the primary draw. The final, or secondary draw is given while the polymer structure is at a temperature above Tl. For the sake of efiiciency and to secure maximum crystallinity with contact times commensurate with present day high speed drawing operations e. g., m of a second or less for yarn, it is necessary to raise the temperature of the polymer structure to a value at least 50 higher than its apparent minimum crystallization temperature for the secondary draw. If maximum crystallinity is not desired the secondary draw may be imposed at lower temperatures above the apparent minimum crystallization temperature.

It is preferable, but not essential, to secure. maximum orientation of amorphous yarn in the vicinity of the primary draw temperature if optimum yarn properties are desired. The higher the degree of orientation in the yarn, the higher the crystallization temperature which can be used to secure a high degree of crystallinity at economical speeds of operation. Conceivably, of course, a non-oriented amorphous yarn may be heated to a point where crystallization. takes place without seriously degrading the yarn, e. g. in the vicinity of 108 C. a fairly high degree of crystallinity may be achieved by this process but the yarn tenacity and elongation will generally not be in a range useful for textile purposes eX- cept, perhaps, for very special applications.

The drawing of synthetic linear polyester yarns is preferably done so that the combination of initial and final draw ratios, depending upon the individual polymer, imposes a stretch of from 310 and more times the original length of the yarn and preferably from 5-8 times-the original length of the yarn. As mentioned previously,

the drawing is preferably accomplished so that total orientation of the amorphous structure is achieved during the primary draw followed by complete or nearly complete crystallization during .the. secondary draw:

cosityin: thevicinityofOfi, thisv can be accoma.

plishedby-adraw ratio of about-4:1 at the pri.-..v mary draw: temperature, .as. hereinbefore defined,;

followed-bye 1.5:]. drawratio at a temperature in excess-.of 50 above Ti.

maybeused to increase the tenacity of the yarn. The preferred ratios will be dependent to a large; extent onthe ultimate use of the yarns so processedz;v By hot relaxingtheyarn various amounts.

aftendrawing, physical properties, such as tenace.

ity, elongation, and work recovery, maybe fur.-

thenchanged through wide limits.

The drawing tension for the primary draw may; Thelsecondary draw, although carried out at. a higher. temperature; requires. more force: and.-.is.in.the range of 0.1 g./denier. to. the breaking tensions be in the range of 0.05-1.5 g./denier.

The exact tension .to be used depends on the amount of draw being accomplished in each;

stage.

The drawing of synthetic linear. polyester yarns; may be carried: out by the use of hot rolls, heated; These. various:

draw pins, or heated.v chambers. methods are well-known and only need the coordinating of details by one skilled in the artto work successfully. The yarn may be packaged,

between the primary. and secondary draw or pref-.-

erably it may be run in a continuous, manner,

from the primary draw to the secondary. It may: alsobe. desired to hot relax the yarn 0011-,

tinuously after the secondary drawand in this.

manner. a completelycontinuous process may be obtained.

A convenient method for the orientation of. film is by the extrusion. ofa large diameter tube of synthetic linear polyester from a disk which.

od is to. extrude the film from a slot orifice:

Then'the film is drawn longitudinally by means of a pinch'roll system and at the same time is drawn; laterally by means of clamps which are fastened at both edges of the film and move apartas the film is drawn longitudinally by the action of the pinch roll. This film, during the two-dimensional drawing, may be heated by pass.- ing over heated rolls during drawing or by means of hot, inert gases or liquids or by induction.

heating. While it is preferred that. two-dimensional orientation of the films of this invention takes place in two directions at once, this is not essential. A film may be drawn, for example, between two sets of rolls, first in one direction and then in another.

This invention is further illustrated by the fol-. lowing examples wherein are set forth preferred modes for practicing the principles of the invene tion and the many advantages derived therefrom.

EXAMPLE I Polyethylene terephthalate yarn is passed through suitable guides to a heated roll (79 C. to C'.) which has a peripheral speed of 60 feet per minute and several wraps are made about it to prevent slippage. The yarn then passes to a :second cold roll (35 C. to 50 C.)

which acts as the initial drawroll. The second In. the caseofipolw; ethylene. terephthalate. having, .an intrinsic.-

Of course, it will be. realizedthat other-combinations. of draw ratios.

9 roll has a surface speed of 4.4 to 6.2 times that of the first roll depending on the initial draw ratio desired as shown in the table below. Several wraps are made around the second roll to prevent slippage and the yarn passes over a hot curved plate (160 C. to' 180 C'.) to a third roll which acts as the secondary draw roll. The third roll is cold and has a peripheral speed of 1.36 times that of the second roll. Several wraps are made around the third roll and the yarn then passes around a cork faced driven roll to prevent slippage and the yarn is then taken up on a down-twister. In the following table various Another type of double-drawing apparatus that may be used to obtain the improvement of the process of this invention demonstrated by the following examples: I

A 1200 denier, 70 filament polyethylene terephthalate yarn (T =80 C.; Ti=99 0.) prepared from polymer having an intrinsic viscosity of 0.61 is passed over a snubber feed roll to a hot pin (100 C.) --Two wraps'are made about this pin and then "the yarn passes immediately over a 3 hot plate (180 C.) and then t the draw roll which has a peripheral speed (corresponding to the desired draw ratio) faster than the feed roll. Three .or more wraps are made about the draw roll to prevent slippage and then the yarnpasses to an appropriate yarn takeup device. The table below shows the exact conditions at each step in the process for this apparatus as well asi'the'icomparative properties:

' Copolymers of polyesters also may be spun into fibers, yarns, etc. and these structures may also be double-drawn under the conditions outlined herein to give improved structures. For example, a mixed polyester prepared by reacting terephthalic acid, ethylene glycol and diethylene glycol *under polymerizing conditions may be spun using conventional melt-spinning techniques to give a drawable yarn. The following table shows the improved properties obtained by double-drawing a yarn prepared from a representative copolymer of terephthalic acid, as compared to single-stage drawing of the same copolymer.

Table II [Control] Yam 1 2 1 3 4 Intrinsic Viscosity (no) 1st Stage Draw and Temp 0 0.6 0. 7

1st Stage Draw and Temp 6 0 1 (85) 5. 44: (85) 4. :1 (85) 4. 85:1 (85) 2nd Stage Draw and Temp 1.36:1 (180) 1. 36:1 (180) 1. 36:1 (130).

Total Draw 6. 0:1 7.421 6.021 6.6:1 -Relaxation (75) Temp. (C.)

Dty Tenacity (g. p. d.) 6.8 8.1 8. 1 8- 7 "Dry Elongation, Per Cent 9.3 8.2 8.2 y 7.8

; From the above examples, it is obvious that Table IV the double-drawing process results in improved yarn. While the increase in tenacity is important, Yamm 1 2' the improved operability, which accompanies this I process, is also very desirable. This is rather 40 gem Temp. at pin draw point o. 9 so raw ratio at pin 5.6 6. 2: surprising s nce the prior art has taught gen Yam mm at plate (00% g 180 180 .erally that smgle-stage drawmg exhibits the best g raii w mo at pi e... 1.1:1 1.1:: ota raw Ratio 6.25:1 6.85: operability. g t z fi 3 6118.01 y .p. nu. EXAMPLE II Elongation (Per Cent) 9.2 6.0

The above table demonstrates that as the draw ratios increase, the tenacity increases also with a slight reduction in elongation. .Draw ratios much in excess of 6:1 (for polyethylene terephthalate) are not possible when the singlestage pin drawing procedure, as described in the work of Carothers, is used. For this reason, 'single-stagefdrawing"does not'devlop maximum tenacities. Furthermore, yarn drawn by hot tandem hot pin-hot plate proces's to the same draw-ratio as yarn drawn by the single stage pin drawing processexhibits a higher tenacity.

The increased draw ratio possible by doubledrawing for optimum quality of yarn is shown in the' following table' The unstretched yarns were identical and made from polyethylene terephthalate having an intrinsic viscosity of 0.7, a T of 80 and a T1 of 99.2. The single-stage drawing and the initial draw of the double-drawing were both made at 85 C. The second stage of the double-draw was carried out at 180 C.

Table V Yarn .A. B

Optimum Single Draw Ratio 5. 9:1 6.0:1 Optimum Double Draw Ratio- 6.6:1 '6. 6:1 Single Drawn Dry Tenacity (g. p. 6.6 6. 8 Double Drawn Dry Tenacity (g. p. d.) & 7 2

1:1 Yarn B shows thatin the-zcase of polyethylene terephthalate, single-stage drawing, at a draw ratio "of Gi l/which is about maximum for the "single-stage 'drawingof *thispolyester does not develop maximumwarn properties. From this it can be seen that by double-drawing the draw "ratio for 'optimum' quality of yarn can be increased about 10%. Furthermore, this increase is accompanied -'bya very appreciable tenacity increase.

Theimprovement to be realized by this inven- -tion-a's demonstrated by b'reaks per pound of yarn drawn issho'wn by a-comparison of a hot pin single-stage draw vs. the hot pin, hot plate tandem double-draw previously described in EX- -ample III. The following-table shows comparatively the improvement in the case of polyethylene terephthalate aswell as the improved 'yarn properties:

:rTable VI Draw Breaks, Tenacity, Elongation, Drawmg Method Ratio per lb. g./d. Per Cent Hot pin 5. 56:1 71.7 7.8 --6.-50 8.1 Hot pin-Hot plate tandem 5. 56:1 72. 6 1. 6 7. 02 ll. 4

KEY

' Yarn Identity l r '2 3 4 Polymer Intrinsic Viscosity -0. 7 -O. 7 0. 7 0.7 1st Stage Draw 813-80 C. Y 6.05:1 6.05:1 4. 92:1 4.92:1

2nd Stage Draw at 180 C 1.36:1 1.36:1 'TotalDraW 5.05:1 6 05:1 6.621 6.6:1 Relaxation (Per- Dent) and Temperature. 10.0 (155) 0 (180) Drawn Denier 78 75 71 62 Dry Tenacityig. p..d.)- 6.4 6. 6 6. 7 7. 6

' Table VII Dry Teifierence nacity at From f Yarn Test fionditions eudoi' 1 Starting test ,(gIIlS Tenacity denier) (Per Cent) {2-8131 }'Immersed in 2% H61 for 6 6.0 8,0 4DD weeks at room ateniperature. 7. 6 ,0. O {2SD Immersed-in 10% NaOHior l5 .2. 7 -59.0 4-DD days at room temperature. 7. 2 -5. O 1SD V 6.2 -4.0 0 Z-SD Exposed to room air at 90? C. 6.2 -.6.0 3DD for 4 weeks. 7 7.2 +8.0 4-1311. 7. 6 +1.0

The double-drawnryarns pf this invention have improved shrinkage properties, The shrinkage, when double drawn yarns are heated to temperaturessuchas thosenormally experienced in washing and ironing fabrics, is to less than the shrinkage of single-drawn yarns- In the fol- :lowing. table thepreviouslymentibhed test yarns were tested for shrinkage:

Table -.VIII

1 Three min 1 i'iglne'half u es in our in yam boiling dry oven :water air- C.

The drawing process of'this 'invention'also greatly increases the modulus of theyarn'i 'This is a very important factor whereyarnsof high strength and 'high elasticity under heavy==loads are desired. Thefollowing is a'comparison of Youngsmodulus for two of the yarns previously mentioned:

Table IX Young's Modulus Yarn (grams per denier) 2-SD 73 4-LDD Water absorption of polyesterzfibers is.=very low so-that moisture causes no appreciable change in dimensions; When the yarn is wetted, it dries ver quickly without shrinking.- The'yarns are not affected by customary organic solvents, nor b oxidizing agents or acids except in extremely high concentrations. Ultra-violet light has little "effect upon these yarns.'andinseets-=or microorganisms do not-attack it. The'yarns* exhibit a'highmodulus: and high impact strength.

.gives the fiber-forming polymer.

Becaus of the superior properties hereinabove disclosed, the yarns composed of synthetic linear polyesters and produced in accordance with. this invention areespecially adapted for use-as sewing .thread, particularly where high strength andrevsistance to chemicals, moisture, bacteria,.mil-

dew, etc., is desired. The yarn may be-made-into cords suitable for use in parachute shrouds and Webbing, cordage for use in the electroplating industry and for conversioninto rope which can be used for halyards, binding rope, glider tow rope, landing nets, fishing nets, or nets for sports such as tennis, badminton-or the like. Yarns may be woven or knitted intofabrics of allkinds and are-especially useful for a variety ofpurposes including fabrics for. window shades, Window curtains, balloon fabrics, parachute cloth, deck cloth for boats, airplane fabrics and canoe covers, sleeping bags, hunting coats, lifepreserver covers,

"War: map fabrics and bolting or screening cloths.

Because of its dimensional stability and dye resistance, fabrics for use inthe fabrication of jungle boots, jungle hammocks, automobile-tops, harvester aprons, mine blankets,.conveyorbelts,

especially where resistance to acid, insects, mil-p 4 dew, and bacteria in connection with high strength is desirable. Other industrial uses for which this yarn is suited are as filter cloths, separators and liners of storage batteries and insulating tapes. This fiber is also useful in the preparation of fabrics used in underground mining works, for example, in tubing for conveying air and other gases where high resistance to acid waters is required. Fabrics composed of these yarns find use in the manufacture of fire hose because of their strength and resistance to abrasion. Since the yarns exhibit high resistance to stain and are unaffected by ultra-violet light, they are especially useful as table linens, aprons and the like where stainproofness is desirable, and for use as zipper tapes, Venetian blind tapes, draperies and the like where ultra-violet resistance is important, Fabrics formed of these yarns and, if desired, .calendered and/or treated with a waterrepellent agent have a special utility in raincoats and shower curtains; or, if the weave is made coarser, as mosquito netting and window screens. Since these fibers are, among other things, highly resistant to chemicals, they can be used as mechanical packing, particularly in the form of a multifilament tow or rope which is braided into a structure of the kind customarily used for packing joints surrounding moving shafts. Diaphragm fabrics for fuel pumps can also be prepared from the polyethylene terephthalate fibers described herein.

Fabrics made from these yarns are extremely useful in the fabrication of laminated structures. Excellent adhesive bonds are obtained between these ethylene terephthalate polymers and various resins, synthetic rubbers and natural rubber. Fabrics of these yarns impregnated with urea formaldehyde, phenol formaldehyde, melamine formaldehyde resins and the like may be formed into laminated structures which have extraordinary properties of dimensional stability, resistance to moisture, high dielectric properties, etc., which make them useful for electrical insulating purposes, instrument panels, parts for electrical devices or mechanical equipment and the like. Panels for structural purposes, wall board, side wall material and bottom material for small boats, pontoons and containers of various kinds can also be made from these laminated materials.

Similarly, molded structures can be made by mixing staple or cut flock prepared from these ethylene terephthalate polymers with suitable bonding resins such as the urea formaldehyde type which can be molded by extrusion or pressure. Cable conduits, tubing, piping and numerous other structures can be made.

While yarns made from these polymers are capable of use wherever yarns have previously been used with more or less advantage, there are certain fields where the properties of the polymer especially commend themselves. For example, the high tenacity, flexibility and resilience of the yarns of this invention make them suitable for use in the manufacture of hosiery and other articles of clothing, while the resistance to soiling and ease of cleaning (common cleaning agents may be used on them without danger) make them desirable for use in flat fabrics and either as multifilament or monofilament yarns in the manufacture of pile fabrics including velvets, plushes, upholstery, or carpeting. The yarns can be advantageously used as either the pile and/or backing of such fabrics.

14 At theysame'time their low .Water absorption, high resistance-to mold and bacteria growth and pronounced resistance to ultra-violet light make the yarns highly suited for use in outdoor fab-- rics such as tents, awnings, tarpaulin, fla s, sails and the like. These same factors also permit the yarns to be manufactured into clothing and. other articles for use in tropical climates where light-weight flexible fabrics that resist the action ever the light-weight, low water absorption and high resistance of the polymer to ultra-violet light, sulphur fumes and salt air are important attributes.

As many widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is understood that said invention is to be in no way delimited or restricted except as defined in the appended claims. a

I claim:

1. The process of drawing shaped structures of synthetic linear polyesters which comprises first drawing the shaped structure of a substantially amorphous synthetic linear polyester at a temperature between the second order transition temperature for said polyester and the apparent minimum crystallization temperature for said polyester discontinuing the draw while the polyester is in the amorphous state, heating the structure so drawn to a temperature above said apparent minimum crystallization temperature and further drawing said structure at said temperature above said apparent minimum crystallization temperature.

2. The process of drawing'yarn of synthetic linear polyesters which comprises first drawing yarn of a substantially amorphous synthetic linear polyester at a yarn temperature between the second order transition temperature for said polyester and the apparent minimum crystallization temperature for said polyester discontinuing the draw while the polyester is in the amorphous state, heating the yarn so drawn to a temperature above said apparent minimum crystallization temperature and further drawing said yarn at said temperature above said apparent minimum crystallization temperature.

3. The process of claim 2 wherein the synthetic linear polyester is polyethylene terephthalate.

4. The process of drawing yarn of synthetic linear polyester which comprises first drawing yarn of a substantially amorphous synthetic linear polyester at a yarn temperature between the second order transition temperature for said polyester and the apparent minimum crystallization temperature for said polyester discontinu ing the draw while the polyester is in the amorphous state, heating the yarn so drawn at a yarn temperature at least 50 C. higher than said apparent minimum crystallization temperature and further drawingthe yarn at said yarn tempera- 15= ture at least- 50 'CI' higherlthan' said apparent minimum ciystallization: tempeiature.

5. The process of claim: 4 wherein: the syn-v theti'c 'linear 'polyester' is polyethylene terephthalatel 6. The process of drawing yarn ofsynthetic linear polyester which comprises first drawing a yarn of a substantially amphorous synthetic: linea polyester having an intrinsicviscosity of at least-0.3 at a yarn temperature between the second order -"transition temperature for said polyesten and the apparent minimum crystallization temperature for said polyeste discontinuing the draw while the polyester-is inthe amorphous state; heating the yarn sodrawn to a temperature above said-apparent minimum crystallization temperatureand further drawing said yarn'at said: temperature above said :apparent' minimum"- crystallization temperature.

'7. Theproce'ss' of claim 6 wherein the syn;

thetic linear polyester is polyethylene terephthalate.

8. The process-of drawing yarn" of synthetic linear polyester which comprises'first drawing a yarn of a substantially amorphous synthetic 1 linear polyester having an intrinsic Viscosity of fromO.3 to 1.5, at a yarn temperature between the secondorder-transition temperature for said polyester and the apparent minimum crystallization temperature for said polyester discontinuing the draw while the polyester isin'the amorphous state, heating the yarn so drawn at a yarn temperature at least 50 C. higher than said apparent'minimum .crystallizationetemperature and": *1 further. drawing the yarnat-said yarn'temperaa? ture' at" least 50 C. higherthanrsaid. apparent-* minimum crystallization temperaturethe first drawing constitutingthe major proportion of the total draw.

9. The process of claim 8 wherein 'tl'ie yarn" is drawn a total of from3' to 10 times its original length;

10. The process'of claim 8" wherein the yarn is drawn a totalof from5-to'8 times its original-- length.

11. The process ofmlaim '10 wherein the syn-" thetic linear polyester: is" polyethylene terephthala'tep ANDERSON PACE, JR.

REFERENCES CITED The following'references are of record in the 1 file oi -this patent:

UNITED STATES PATENTS? i OTHER REFERENCES Wiley, Transition Temperature andCubical Expansion of Plastic'Materialsf" Ind;"'& Eng;

CheniL, Sept. 1942;pages 1052-6.

Claims (1)

1. THE PROCESS OF DRAWING SHAPED STRUCTURES OF SYNTHETIC LINEAR POLYESTERS WHICH COMPRISES FIRST DRAWING THE SHAPED STRUCTURE OF A SUBSTANTIALLY AMORPHOUS SYNTHETIC LINEAR POLYESTER AT A TEMPERATURE BETWEEN THE SECOND ORDER TRANSITION TEMPERATURE FOR SAID POLYESTER AND THE APPARENT MINIMUM CRYSTALLIZATION TEMPERATURE FOR SAID POLYESTER DISCONTINUING THE DRAW WHILE THE POLYESTER IS IN THE AMORPHOUS STATE, HEATING THE STRUCTURE SO DRAWN TO A TEMPERATURE ABOVE SAID APPARENT MINIMUM CRYSTALIZATION TEMPERATURE AND FURTHER DRAWING SAID STRUCTURE AT SAID TEMPERATURE ABOVE SAID APPARETN MINIMUM CRYSTALLIZATION TEMPERATURE.

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