US3213171A - Process of producing spontaneously crimpable filaments from asymmetrically quenched and drawn fiber-forming polymers - Google Patents

Description

Oct. 19, 1965 J. J. KILIAN 3,213,171

PROCESS OF PRODUCING SPONTANEOUSLY CRIMPABLE FILAMENTS FROM ASYMMETRICALLY QUENCHED AND DRAWN FIBER-FORMING POLYMERS Filed Nov. 12, 1963 3 Sheets-Sheet l FIGZ INVENTOR JOSEPH JOHN KILIAN ATTORNEY Oct. 19, 1965 Filed NOV. 12, 1963 J. J. KlLlAN 3 Sheets-Sheet 2 1N VENTOR JOSEPH JOHN KILIAN ATTORNEY Oct. 19, 1965 J. J. KILIAN 3,213,171

PROC OF DUCING SPONTANEOUSLY CRIMPA FILA TS R M ASYMMETRIGAL QUENCHED A DRAWN FIBER-FORMING YMERS Filed Nov. 12, 1963 3 Sheets-Sheet 3 ENTOR JOSEPH JOH ILIAN ATTORNEY United States Patent Office 3,213,171 Patented Oct. 19, 1965 PROCESS OF PRODUCING SPONTANEOUSLY CRIMPABLE FILAMENTS FROM ASYMMETRI- CALLY QUENCHED AND DRAWN FIBER-FORM- ING POLYMERS Joseph John Kilian, Covingtou, Va., 'assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Filed Nov. 12, 1963, Ser. No. 322,738 4 Claims. (Cl. 264168) This application is a continuation-in-part of my copending application Serial No. 182,990 filed March 8, 1962 and now U.S. Patent No. 3,118,012 which is a continuation-in-part of my application Serial No. 810,362 filed May 1, 1959 and now abandoned. This invention relates to the melt spinning of filaments from synthetic polymers. More particularly it relates to the production of spontaneously crimpable filaments by a high-productivity method of spinning, drawing, and relaxing the filaments.

In the preparation of fibers from fusible polymers it is customary to force the molten polymer through the orifices of a spinneret into a region where the temperature is lower than the temperature of the molten polymer. In the cooler region, the molten polymer sets up into filaments sufiiciently firm to be drawn away continuously by a yarn forwarding device. Conventionally, the molten polymer is spun through a spinneret having orifices spaced from each other by relatively large distances in order to keep newly formed filaments separated until they have congealed sufficiently to prevent their sticking together or coalescing. Productivity of yarn per spinneret under these conditions is low even at the highest practicable speeds of windup.

The large hole-to-hole spacing in conventional meltspinning spinnerets contrasts sharply with that used in spinning viscose, where the holes are spaced so closely together that a tow of several thousand filaments can be spun at a single position. Owing to smaller plant space, smaller investment in equipment, and lower expense of labor and up-keep, this high density of spinneret holes permits preparation of fibers at a much lower cost than is possible with conventional melt spinning.

A second disadvantage of known melt-spinning practices concerns the difficulty of coupling the steps in yarn preparation. After a yarn is spun, drawing is generally necessary in order to raise the mechanical properties of the yarn to an acceptable level. However, yarn input to the drawing step usually proceeds at a rate necessarily different from the rate of yarn output from the spinning step. For example, it may be necessary to draw the yarn at a much lower rate than it is desirable to spin the yarn. Under such conditions it is most efficient to interrupt the process of the yarn preparation, that is, to package the yarn temporarily after the spinning step for subsequent use in the drawing step. Even when it is possible to draw the yarn at a sufficiently rapid rate to allow its being used directly from the spinning step, the rate of yarn travel at the output from the drawing step often exceeds the capacity of currently available yarn handling equipment.

This difficulty could be avoided by extruding the yarn slowly enough to allow the drawn yarn to be collected at a reasonable rate. But such an expedient would reduce the productivity of current spinning processes and would, therefore, be economically undesirable.

Accordingly, it is an object of this invention to provide a melt-spinning process for preparing yarns at high productivity. It is also an object to provide a melt-spinning process for preparing filaments having cross-sections which conform closely to the shape of the spinneret holes. Still anothed object is to spin yarns at high productivity at relatively low threadline velocity. The production of spontaneously crimpable filaments with maximum crimp development is an additional object of this invention. Other objects will become apparent from the following specification and claims.

According to illustrative embodiments of this invention, a molten synthetic organic polymer is extruded through to 2000 orifices arranged to form a pattern in which the centers of the orifices are positioned at the corners of contiguous quadrilaterals formed by lines connecting the centers of adjacent orifices, with each side of each quadrilateral being between about 0.005 and about 0.125 inch in length, and all inside angles in each quadrilateral being at least 30. The polymer is extruded at a weight rate W of 4 to 40 g./min./cm. and preferably from 10 to 30 g./min./cm. of effective spinneret face area within the quadrilaterals. Effective spinning under these conditons, although impossible under previously known procedures, is readily accomplished in accordance with the present invention by directing a stream of gaseous quenching medium against each filament at a velocity of at least 0.6W feet per minute within 1 inch of the spinneret face at an angle between 45 below and 45 above the horizontal, to cool the extruded filaments at least about 15 C. and preferably at least 25 C. below the melting point of the polymer prior to a point 2 inches below the spinneret, while maintaining the extruded filaments being under a tension of at least 0.003 gram per denier immediately below the spinneret.

By the expression effective spinneret face area is meant the area within a quadrilateral defined by four straight lines between the centers of four adjacent orifices. Thus, if the orifices are arranged in a square pattern, the effective spinneret area is the square of the center-tocenter spacing of the orifices. When the orifices are arranged in staggered rows, the effective area is a parallelogram with sides corresponding to center-to-center distances in a row and center-to-center spacings between orifices in different rows. The manner of determining this value for other arrangements will be obvious.

It has been found that the minimum velocity of gaseous quenching medium necessary at the threadline within 1 inch of the spinneret face may be calculated from the expression:

where V is the linear velocity in feet per minute of the gas impinging on the filaments and W is the weight extrusion rate of throughput of polymer in grams/minute/cm. of effective spinneret face area. This expression is valid for a quenching medium having a temperature of about 20 C. Since W has a value of at least 4 g./min./cm. the minimum velocity of the quench medium useful in the present invention is 0.6(4) +150, or approximately feet/minute.

The quench velocity (V which is satisfactory at a given extrusion rate and quench medium temperature (T in degrees Kelvin) may be corrected to the required velocity (V at a different temperature of the quenching medium (T in degrees Kelvin) by the expression:

The temperature correction is so slight that the process can be operated within a range of 20i7 with a variation of no more than i2.5% in the quenching medium velocity.

Preferably, the temperature of the quenching medium will be between about 15 and 40 C. The use of a cooler medium adds undue cost to the process. The use of 'hot mediums, e.g., 170 C. and above is undesirable because the velocity of quench must be increased to an extent which makes good spinning diificult, as the filaments may be blown together or the threadline broken. The quenching medium is preferably a gas or vapor of a liquid having a boiling point at atmospheric pressure below about C. Vapors of higher boiling liquids can cause process difficulties due to partial condensation of the vapor, which can interfere with the quenching system and cause non-uniformities in the yarn. The preferred class of quenching medium is illustrated by air, nitrogen, helium, Or carbon dioxide.

It is found that the as-spun denier of the filaments prior to drawing has no practical effect on the minimum quench velocities required at a given extrusion rate. In general, filaments having as-spun deniers in the range of /2 to 100 can be spun by the process of this invention using the previously stated quenching conditions.

Other spinning process variables, such as orifice diameter and spinning speed, do not affect the minimum quench velocity needed at a specified extrusion rate.

The amount of quenching used in accordance with this invention is unlike anything known to the prior art. A typical prior art disclosure is that of US. Patent No. 2,821,749, issued February 4, 1958, to J. E. Spohn et al., 'which relates to the use of a very gentle fiow of air at a die face, during extrusion of filaments, in order to avoid clogging of the spinneret holes. Although the air is supplied at a jet velocity of 100 feet per minute through a small jet located about 2.8 inches from the die, nevertheless, due to the expansion of the air past the jet, the linear velocity of the air decreases to less than 10 feet/minute by the time it reaches the filaments at the die face. The patient also specifically discloses operation with air pressures as high as 7 and as low as 0.5 pound per square inch gauge and jet clearances of between 0.005 inch and 0.030 inch. The maximum velocity would be obtained from the higher pressure and larger jet clearance. I have determined that the maximum'velocity of the air at the die face under these conditions is less than 35 feet per minute. Y The rapid quenching which is achieved in the present invention leads to filaments having high as-spun properties. Molecular orientation is induced both during flow of the molten polymer through the channel leading to the spinneret hole and by stretching as the filament is drawn away under relatively high tension. By suificiently rapid quenching, this orientation may be frozen into the polymer structure, and a stronger, stiffer fiber results. When the quenching is carried out asymmetrically, the orientation is preserved to a greater extent on the quenched than on the unquenched side of the filament. Upon drawing the asymmetrically quenched filaments to increase their orientation, spontaneous crimping of the filaments is observed upon release of the tension of drawmg.

In accordance with a preferred embodiment of the present invention, the crimped filaments are maintained free of tension at a temperature below their second order transition temperature, Tg, for at least about two minutes subsequent to the release of tension in the drawing step and the filaments are then set in their crimped form by heating them still free of tension, at a temperature at least about 20 higher than T g and below the softening temperature of the polymer. Surprisingly, the degree of crimp in the filaments so prepared is markedly enhanced as compared with filaments which are passed into the relaxing chamber and heated above Tg immediately after the release of tension in the drawing step.

The preferred embodiment of the invention is particularly adapted for use with filaments of crystallizable linear condensation polyesters, since the polyesters of commercial importance for fiber production generally have second order transition temperatures substantially above room temperature, and processing temperatures with respect to Tg are readily controlled. Drawing of the filaments is greatly facilitated by beating them above Tg. In commercial practice, the polyester filaments are drawn above T g at a draw ratio of about 2 to 5, preferably in steam or in a bath or spray of hot water. The filaments are cooled on the draw rolls or as the tension of drawing is released. The filaments may be dried while the crimp is developing so long as they are not heated above Tg.

More specifically, the preferred embodiment of the present invention is an improvement in the process of melt-spinning a crystallizable linear condensation polyester to form filaments, rapidly and asymmetrically quenching the filaments, drawing the filaments at a draw ratio of about 2 to 5 times to orient them, and subse quently heating them free of tension at a temperature at least about 20 C. above the second order transition temperature, Tg, of the polyester;-the improvement comprising maintaining the oriented filaments free of tension at a temperature below Tg for at least about two minutes subsequent to the release of tension in the drawing step and prior to the heating step (at least 20 C. above Tg).

In the drawings, which illustrate specific embodiments of the invention,

FIGURE 1 illustrates schematically the process of the invention.

FIGURE 2 shows a spinneret hole pattern suitable for use in the process.

FIGURES 3 and 4 illustrate a particular apparatus embodiment of the process.

FIGURE 5 illustrates apparatus suitable for drawing and relaxing spontaneously crimpable filaments in accordance with a preferred embodiment of the invention.

In FIGURE 1, the invention is shown in its simplest form. Molten polymer is extruded through orifices 1 in spinneret 2, the orifices being arranged in a plurality of parallel straight rows 3 forming a pattern 4 bounded by perimeter 5. A strong current of quenching gas from nozzle 6 impinges upon the newly formed filaments 7 as they emerge from the spinneret. The bundle of quenched filaments is removed from the quenching region under tension by yarn-forwarding roll 8, which may be a windup or a guide roll for conveying the yarn to the next processing step, which may be a drawing step. The pattern 4 consists of closely spaced multiple rows of holes 1. The position of the quenching nozzle 6 may be specified by d and h which are, respectively, the vertical and horizontal distances of the nozzle from the center of the pattern. The orientation of the nozzle: is specified by the angle 0, measured from the hori-- zontal, which is the angle the quenching stream makes with the horizontal. Ordinarily, it is advantageous if the quenching stream is imposed perpendicular to the rows of holes 3 in the pattern 4. However, the quenching stream may be imposed at an angle to the rows of holes. The angle is used to designate this angle. The invention is intended to include such a quenching arrangement, so long as the major component of the quenching stream is perpendicular to the rows of holes,

that is, so long as 4) is less than 45. The distance s between the rows of holes 3 is no more than about 0.125 inch. The pattern 4 need not be rectangular, but may, for example, consist of rows of holes arranged on the circumferences of a plurality of closely spaced concentric circles as shown in FIGURE 2. For this arrangement of the holes, the quenching stream is preferably radially inward as at S, or radially outward as at B, and the spacing s between circumferences 22 and 23 is less than about 0.125 inch.

FIGURE 3 shows one embodiment of the apparatus in greater detail. Molten polymer is forced through sand pack 12 and then through channels 13 leading to holes 14 on the face of the spinneret 15. Band heater 16 may be used to control the temperature of the spinneret independently of the flow of polymer, which heats the spinneret, and quenching gas, which cools it. The filaments 17 emerging from the holes are immediately quenched by a strong flow of gas from primary nozzles 18, directed across the bundle of filaments and parallel to the face of the spinneret. In this embodiment, after passing through the initial quenching zone, the filaments enter a secondary cooling zone in which they are subjected to a flow of gas from nozzles 19. This flow of gas further cools the filaments, and also is so imposed as to counteract the deflection due to the action of gas from nozzles 18. Thereafter the filaments pass to a windup or yarn-forwarding device.

Gas supplied to nozzles 18 and 19 passes over flow chopper vanes 20, which serve to distribute the gas evenly. The nozzles may also be covered by screens 21 in order to make the flow of gas more homogeneous.

FIGURE 4 shows in plan the face of one type of spinneret suitable for use with a circular 5" pack. The working area ABCDEFGH is divided into two parts for more effective quenching. The two areas ABGH and CDEF each contain 810 holes arranged in rows with a center-to-center spacing of 0.060 inch between rows and between holes. In each area there are 14 rows of holes perpendicular to the direction of the quenching gas. The position of the quenching nozzles is shown as 18 and 19. Example 2 below describes in detail the operation of this embodiment under a particular set of conditions.

FIGURE 5 illustrates apparatus suitable for drawing and relaxing a tow of filaments composed of polymer having Tg above room temperature, e.g., polyethylene terephthalate or other polyesters having a high Tg. Tow 29 comprises a large number of polyester filaments which have been melt-extruded and rapidly and asymmetrically quenched in apparatus such as that shown in FIGURE 3. The tow is drawn by being passed from feed rolls 31 through 38, respectively, maintained at a given uniform peripheral speed and then around draw rolls 41 through 48, respectively, having a uniform peripheral speed considerably higher than that of the feed rolls. Between rolls 34 and 35 the tow passes through a pre-wetting vessel 40, which contains an aqueous bath which may be at room temperature or which may be heated to a temperature somewhat below Tg. Additional quantities of the aqueous bath used in pre-wetting bath 40 are usually sprayed onto or otherwise supplied to rolls 35, 36, 37, and 38. Between rolls 38 and 41 the tow passes under spray nozzles 49, from which 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.

After leaving the draw section, the tow is passed around puller rolls 50 and through an air jet traversing funnel 51 which lays the tow down on a conveyor 52, upon which the tow is carried to and through relaxing chamber 53. The three-dimensional or reversing helical crimp becomes apparent in the filaments as they are released from tension upon passing out of the air jet traversing funnel 51. In accordance with a preferred 6 embodiment of the invention, the rate of travel of the conveyor 52 should be such that there is at least a twominute interval between the passage of the filaments from the air jet traversing funnel 51 and their entrance into the relaxing chamber 53. At the end of the relaxing chamber, the tow is deposited in container 54, preferably with a traversing means (not shown).

The term tow, as used herein, refers to a large number of continuous, substantially parallel, synthetic filaments without definite twist collected in a loose, ribbon-like or rope-like form. Generally speaking, the minimum number of filaments to which the term tow is considered applicable is on the order of about one thousand, and normally there are 10,000 or more filaments. While there is no fixed maximum number, tows containing on the order of 1,000,000 filaments are frequently encountered, and there may be occasions to em ploy tows of 10,000,000 filaments or even more. The filaments may be of round cross section or of trilobal or other non-round cross section.

The expression second-order transition temperature, designated herein by the symbol Tg, 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. Tg is sometimes also known as the glass transition temperature because it is the temperature below which the polymer exhibits glass-like behavior; above Tg the polymer is somewhat more rubber-like. A convenient method for determining Tg for a given sample of polymer is given by Pace in his U.S. Patent 2,556,295 (col. 3, line 24, to col. 4, line 19). The crystallinity of the polymer sample selected for measurement of Tg should be comparable with the crystallinity of the drawn filaments of the polymer.

It is a surprising fact, unrecognized by the art, that multiple rows of holes at close spacing may be employed in conjunction with a strong current of quenching gas, imposed at the spinneret, in the melt spinning of synthetic polymers.

In conventional spinning practice it is not possible to spin a large number of holes at one position. In the case of S-denier-per-filament polyethylene terephthalate a maximum of about 250 holes can be spun from a 5-inch pack, while in the case of nylon only about holes can be spun. One 'diificulty which arises when it is attempted to spin more holes is that a stronger current of air must blow across the chimney. This causes a more severe deflection of the newly formed filaments and leads to yarn which is less uniform. It also causes filaments to move about more, leading to stuck filaments. The fact that the filaments are closer together aggravates the situation and increases the number of stuck filaments still further. Consequently, conventional spinning is very limited in the number of holes which can be spun per position. With the present invention at least 20003 denier per filament polyethylene terephthalate or nylon filaments may be spun from a 5-inch pack.

It is a feature of the present invention that the number of holes in the spinneret and the amount of quenching air are simultaneously increased without resulting in stuck filaments. This is achieved by imposing the quenching stream at, or very near, the face of the spinneret. The benefit derived from this mode of operation is that the filaments are quickly cooled to a temperature at which their viscosity is sufficiently great to support a much greater tension. Owing to the tension which is imposed upon the threadline at the windup, large deflections of the filament do not occur. In addition, the 'length of the critical region where the filaments are tacky is drastically reduced. In fact, when the temperature of the threadline at a point two inches below the spinneret is reduced to below about 15 C. and preferably below 25 C. below the melting temperature, no stuck filaments result.

Thus, in comparison with conventional melt spinning, the present process allows a much larger number of filaments to be spun per spinneret, or alternatively, it allows the same number of filaments to be spun from a much smaller spinneret. Under suitable conditions, its allows a yarn to be spun at a speed which is low enough to allow it to be drawn directly in a coupled process. Alternatively, it allows a yarn to be spun with sufiiciently highas-spun properties to render a drawing step unnecessary. In either case the product may be made spontaneously crimpable if desired, by imposing a strong asymmetric quenching stream having a velocity strong enough to impart a tension of at least about 19 rug/denier to the threadline. This spontaneously crimpable product has an unusual spiral crimp, and leads to fabrics having greatly improved cover, when compared with fabrics prepared from stuifer-box crimped fiber.

Example 1 shows that for polyethylene terephthalate, the invention may be operated under a wide range of conditions, provided the filaments are quenched enough to bring the threadline within two inches of the spinneret to a temperature below 15 C. below and preferably below 25 C. below the melting point of the polymer. Relative viscosities are determined at 25 C.

EXAMPLE 1 Polyethylene terephthalate chip having a relative viscosity of 35 in trichlorophenol/phenol and a melting point of 245 C. is vacuum dried for 16 hours at 105 C. The polymer is charged into the hopper of a grid melt spinning unit and blanketed with nitrogen. The temperature of the grid melt unit is maintained at 285 C. The molten polymer is then pumped through a sand pack filter and extruded vertically downward through a spinneret containing 8 holes in a 4 x 12 rectangular array. The diameter of each hole is 0.009 inch, and the center-to-center spacing is 0.050 inch. Thus, the eifective spinneret face area is 0.016 cm The capillary leading to each hole is 0.030 inch long, and it in turn is fed through a larger capillary having a diameter of 0.040 inch and a length of 0.35 inch. The spinneret temperature is 275 C.

The newly formed filaments are uniformly quenched with air directed slightly upward toward the center of the spinneret pattern from a A3" x 2" slot situated 7" ihorizontally distant and vertically downward from the face of the spinneret. The long dimension of the slot is parallel to the ground and to the long dimension of the spinneret pattern. Quench air is controlled by means of a Fischer and Porter Flowrator (Type B- 27-250/70) with a pressure reducer and pressure gauge upstream of the Flowrator. Air velocity is measured at the spinneret by means of a Weston or Alnor anemometer.

The temperature of the quenched filament is measured at a point 2 below the face of the spinneret. This measurement is made by a comparison technique, using an infrared vacuum thermocouple as a detector. A strip heater is covered with polyethyelene terephthalate film and placed /2" from the filament bundle as a background. A concave mirror placed on the opposite side of the bundle focuses infrared radiation on the detector. As the temperature of the background is raised, the mirror 'is focused alternately on the background and on the background and filament bundle together. When the temperature of the background is the same as the temperature of the filament bundle, there will be no change in the output from the detector when the focus is changed. At this point the temperature of the background is determined by thermocouple.

The temperature of the filaments is measured for various throughputs, quench velocities, and windup speeds. The data are presented in Table 1. The temperature is observed to vary with the logarithm of the quench velocity.

The tension of the threadline as measured with a tensiometer 5 feet below the spinneret for the following spins varied from 3 to 40 milligram (mg.) per denier at y.p.m. Higher tensions accompanied higher quenching rates. Conventional spinning affords tensions of 1 to 3 mg/denier at similar windup speeds.

Table 1.Filament temperature measurement of jet quench spun polyethylene terephthalate filaments Through- Denier Air Windup Filament Run put (g./ per velocity speed mp.,

min/0111.2) filament (ft/min.) y.p.m. C.

The above polymer was also extruded from spinnerets having 300 holes spaced 0.018 inch apart on centers, and from spinnerets having 96 holes spaced .030 inch apart using a similar quench.

Operating the above procedure without a quenching fluid at a throughput of from 8.7 to 24 g./min./cm. produced filament temperatures greater than 250 C. and in all cases the filaments were fused together.

EXAMPLE 2 Polyethylene terephthalate chip having a relative viscosity of 21.7 in a mixture of terachloroethane/phenol 91 is spun from the apparatus shown in FIGURES 3 and 4. The spinneret holes are 0.007 inch in diameter and have capillaries 0.012 inch in length. Individual counterbores 0.040 inch in diameter and 0.30 inch in length feed the capillaries. The effective spinneret face area is 0.0232 cm. The polymer temperature is maintained at 290 C. The volume of room temperature air delivered from each primary quench nozzle is 60 standard cubic feet per minute (s.c.f.m.) flowing at an average velocity of 1525 feet per minute. The volume of air delivered from each of the secondary nozzles is 18 s.c.f.m., flowing at an average velocity of 450 feet per minute. Polymer is extruded at a rate of 0.45 gram per minute per hole (19.4 g./min./cm. and is wound up as a 17.7 denier per filament undrawn yarn at 250 yards per minute. Since there are 1620 holes in the spinneret, this corresponds to a productivity of 96 pounds per hour of 28,700 denier yarn for the entire spinneret. The as-spun yarn has a tenacity of 0.76 g.p.d. and an elongation to break of 406%. The yarn is drawn to 4.6 times its original length (4.6X). Boiling the yarn in water to relax it causes the development of 8 helical crimps per inch. The drawn and relaxed product (4.6 d.p.f.) has a tenacity of 2.9 grams per denier, an elongation of 33%, and an initial modulus of 26.4 grams per denier.

An advantage of the present process is that polymers which would ordinarily be considered unspinnable because of their relatively low melt viscosities can be spun without difiiculty. This comes about because the temperature of the extruded polymer is quickly reduced and its viscosity thereby raised to a value at which the filament resists threadline breakage due to the force of surface tension. This circumstance can be put to use in avoiding filtration difficulties. Thus, at the high throughputs achieved in the present invention sufficiently rapid filtration of the polymer melt sometimes presents a problem For polymers whose fiber properties are not highly sensitive to changes in molecular weight, the problem may be avoided by lowering the molecular weight of the polymer, with a consequent reduction in viscosity and more rapid filtration.

The expression relative viscosity as used herein signifies a ratio of the flow time in a viscosimeter of a polymer solution containing 8.2% i0.2% by weight of polymer in a solvent relative to the flow time of the solvent by itself.

Poly(ethylene terephthtlate) of relative viscosity 22 or greater must be used in conventional procedures for commercial spinning and drawing but relative viscosities of 25-33 are currently used in commerce to avoid denier non-uniformities, spinning and drawing breaks that are prevalent when using the lower molecular weight. Using the process of this invention, such polyesters with a viscosity of 9 or higher can readily be spun at commercially feasible rates.

EXAMPLE 3 This example illustrates a preferred process of this invention.

Polyethylene terephthalate chip having a relative viscosity of 31.2. as measured in a mixture of tetrachloromethane/phenol is melted and the melt (at about 290 C.) is extruded (49-51 pounds of polymer per hour) through a spinneret maintained at 278 C.-300 C. by an auxiliary electric heater around the circumference of the spinneret. The spinneret comprises 900 holes (each 0.007" in diameter) arranged on six concentric circles whose radii differ by 0.052 inch each, the smallest circle of which has a radius of 1.437 inches. The holes are located on radii of the circle. Adjacent radii are spaced 112 apart and contain holes spaced on alternate circles so that a staggered pattern is obtained. Thus, the center-to-center spacings in a row (circle) vary from about 0.060 inch in the inner circle to about 0.071 inch in the outer circle. The average effective spinneret face area per hole (taken between rows 3 and 4) is 2.2 cm? to give a throughput of 18.7-19.5 g./min./cm. The extruded filaments are quenched with room temperature air from a quenching nozzle surrounding the circle of filaments comprising a slot 1 inch high located on the inside surface of a cylinder chamber having an inside diameter of 4% inches. The top of the slot is spaced inch below the spinneret face by a ring of aluminum foil and heavy asbestos cloth. The filaments are wound up at various speeds and the as-spun filaments are combined to a tow of convenient size and drawn 10 threadline for the five items are 2200, 440, 1770, 1770, and 2600 feet/minute, respectively. Item a has 11 crimps per inch of crimped length.

Item 2 is spun from polyethylene terephthalate having a relative viscosity of 14. Tg for polyethylene terephthalate is 79 C. The tow for item e is drawn through an aqueous spray at 85 C. followed by an aqueous spray at room temperature at the end of the draw zone. The 85 C. spray zone and the room temperature spray zone are separated by a baffie, and in moving from the hot zone to the cool zone the tow is passed between a pair of wiper bars to remove entrained hot water. From the draw roll section the tow is passed as shown in FIGURE 5 around puller rolls and down through an air jet traversing funnel which lays the tow on a moving conveyor. Upon release of tension as the tow leaves the air jet traversing funnel, the filaments in the tow spontaneously develop crimp. Two minutes after the tow leaves the air jet traversing funnel it is passed into a relaxing chamber wherein it is heated at 140 C. for 5 minutes. As shown in Table 2, the relaxed tow exhibits a crimp index of 35 When entrance of the tow into the relaxing chamber is delayed for 30 minutes after lay-down from the air jet traversing funnel, the crimp index of the relaxed tow remains 35%. In contrast, tow passed into the relaxing chamber only 20 seconds after lay-down on the conveyor has a crimp index of only 25%. Tow relaxed 60 seconds after lay-down has a crimp index of only 29%.

The crimp index is used as a measure of the extent of crimp and is determined from the length of a sample of crimped tow hanging under an added load of 0.1 g.p.d. for a period of 2 seconds (length A) and the length of that tow hanging under no added weight after it has relaxed for 15 seconds from the first extension (length B) where crimp index= Table 2 Quenching conditions Relaxed fiber properties It Windgp em s cc yi pm. spinneret Cu. it. air/ Draw Crimp Tenacity, Initial temp., 0. lb. polymer ratio index g.p.d modulus D.p.f.

elongatlon, percent through a hot water bath or spray (about C.) to an extent so as to give about 10% elongation at the break of the as-drawn yarn. The as-drawn filaments develop a high degree of helical crimp immediately upon release of the drawing tension. The amount of crimp is increased by allowing the fibers to stand at room temperature for several minutes (at least two minutes) and then relaxing the fibers at -200 C. (preferably C.) for 2 to 20 minutes. The effect of different amounts of quench is shown in Table 2. The velocities of the quench at the 75 higher viscosities do lead to a higher frequency of crimps.

I draw ratio.

Spinneret block temperature (temperature of the polyrner melt before passage through the spinneret).For purposes of making crimped filaments, a higher temperature of the melt is usually required in the case of copolyesters than is normally used in conventional spinning.

Spinneret temperature-The crimp index is reduced as the spinneret temperature is raised.

Hole spacings.The hole spacings of this invention, i.e., where the centers of adjacent orifices are less than 0.125 inch apart are satisfactory.

Hole size or orifice size-In general, larger holes give a higher crimp index level at the crimp index levels of 30 and higher. Thus, a 0.014 inch diameter orifice is preferred in the preparation of products such as shown in Table 2.

Air quench.-As the air quench is increased, the crimp index is increased. A radially directed inward quenching stream at to horizontal is preferred as producing substantially more uniform products.

Polymer throughput-As the amount of polymer going through an orifice in a given time increases, the crimp index of the final yarn decreases.

Draw rati0.This should be considered as the total orientation obtained in combination by spinning and drawing as the spinning conditions will control the absolute However, as the draw ratio is decreased, below that required to give a break elongation (on unrelaxed drawn yarn) of less than about 17%, the crimp index decreases rapidly. Preferably, to gain maximum crimp index, the yarn should be drawn to give a 10% elongation at the break of the unrelaxed drawn yarn.

Drawing c0nditions.Drawing in a bath or spray of hot water is preferred. Drawing over a hot pin (e.g., 8090 C.) lowers the crimp index.

Filament denier.As the denier is increased, the crimp index is reduced.

Crystallizable linear condensation polyesters which may be employed for the production of spontaneously crimpable filaments in accordance with the preferred embodiment of the invention include poly(isopropylidene- 4,4-diphenylene isophthalate), poly(isopropylidene-4,4'- diphenylene carbonate), poly(ethylene-2,=6naphthalen dicarboxylate), poly(decahydronaphthalene 2,6 dimethylene-4,4-bibenzoate, and poly(bicyclohexyl-4,4'- dimethylene-4,4-bibenzoate). The preferred polyesters are the linear terephthalate polyesters, i.e., polyesters of a glycol containing from 2 to 20 carbon atoms and a dicarboxylic acid component containing at least about 75% terephthalic acid. The remainder, if any, of the dicarboxylic acid component may be any suitable dicarboxylic acid such as sebacic acid, adipic acid, isophthalic acid, sulfonyl-4,4' dibenzoic acid, or 2,8-dibenzofurandicarboxylic acid. The glycols may contain more than two carbons in the chain, e.g., diethylene glycol, butylene glycol, decamethylene glycol, and bis- 1,4-(hydroxymethyl)cyclohexane. Examples of linear terephthalate polyesters which may be employed include poly(ethylene terephthalater), poly(ethylene terephthalate/S-chloroisophthalate) (85/15), poly(ethylene terephthalate/5-.[sodium sulfo]is-ophthalate) (97/3), poly- (cyclohexane-1,4-dimethylene terephthalate), and poly- (cyclohexane 1,4-dimethylene terephthalate/hexahydroterephthalate) (75/25).

The spinneret may have a flat face or a face so Sculptured as to facilitate cooling of the vicinity of the orifices, either symmetrically or asymmetrically. For instance, the face of the spinneret may have flanges or grooves in the direction of quenching in order to conduct th flow of gas in a more uniform fashion. If desired, the holes may also be placed on individual nipples in order to facilitate rapid cooling.

The spinneret orifices may be round, to produce filaments having circular cross sections, or may be non- -round to produce filaments having arbitrary cross sections.

Since many different embodiments of the invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited by the specific illustrations except to the extent defined in the following claims.

What is claimed is:

1. A process comprising extruding a synthetic molten fiber-forming polymer through a plurality of orifices, said orifices forming a pattern in which the centers of the orifices are positioned at the corners of contiguous quadrilaterals formed by lines connecting the centers of adjacent orifices, each side of each quadrilateral being between about 0.005 and about 0.125 inch in length, all inside angles in each quadrilateral being at least 30, said polymer being extruded at the rate of at least 4 g./ min/cm. of spinneret face area within the quadrilaterals, directing a stream of a quenching fluid against each filament at a velocity of at least 0.6W feet per minute, wherein W is the rate of extrusion of the polymer in g./min./cm. of effective spinneret face, within 1 inch of the spinneret face at an angle between 45 below and 45 above the horizontal to cool the extruded filament to a temperature below about 15 C. below the melting point of the polymer prior to a point 2 inches below the spinneret, the extruded filaments being under a tension of at least 0.003 gram per denier immediately below the spinneret, drawing the filaments at a draw ratio of about 2 to 5 times to orient them, maintaining the oriented filaments free of tension at a temperature below the second order transition temperature of the polymer for at least about 2 minutes subsequent to the release of tension in the drawing step, and heating the filaments free of tension at a temperature at least about 20 C. above the second order transition temperature.

2. The process of claim 1 wherein the fiber-forming polymer is a crystallizable, linear condensation polyester.

3. The process of claim 1 wherein the fiber-forming polymer i polyethylene terephthalate.

4. In a process wherein a crystallizable, linear condensation polyester is melt-spun to form filaments, and the filaments are rapidly and asymmetrically quenched and drawn at a draw ratio of about 2 to 5 times and subsequently heated free of tension at a temperature at least about 20 C. above the second order transition temperature of the polyester, the improvement comprising maintaining the oriented filaments free of tension at a temperature below the second order transition temperature for at least about two minutes subsequent to the releasing of tension in the drawing step and prior to the heating step.

References Cited by the Examiner UNITED STATES PATENTS 2,957,747 10/60 Bowling 264l68 3,024,517 3/62 Bromley et al. -2 254168 3,115,385 12/63 Beck 264-l78 3,134,833 5/64 Ciporin et a1. 264-210 FOREIGN PATENTS 572,083 3/59 Canada.

ALEXANDER BRODMERKEL, Primary Examiner.

Claims (1)

1. A PROCESS COMPRISING EXTRUDING A SYNTHETIC MOLTEN FIBER-FORMING POLYMER THROUGH A PLURALITY OF ORIFICES, SAID ORIFICES FORMING A PATTERN IN WHICH THE CENTERS OF THE ORIFICES ARE POSITIONED AT THE CORNERS OF CONTIGUOUS QUADRILATERALS FORMED BY LINES CONNECTING THE CENTERS OF ADJACENT ORIFICES, EACH SIDE OF EACH QUARDRILATERAL BEING BE TWEEN ABOUT 0.005 AND ABOUT 0.125 INCH IN LENGTH, ALL INSIDE ANGLES IN EACH QUADRILATERAL BEING AT LEAST 30*, SAID POLYMER BEING EXTRUDED AT THE RATE OF AT LEAST 4 G./ MIN./CM.2 OF SPINNERET FACE AREA WITHIN THE QUADRILATERALS, DIRECTING A STREAM OF A QUENCHING FLUID AGAINST EACH FILAMENT AT A VELOCITY OF AT LEAST 0.6W2+150 FEET PER MINUTE, WHEREIN W IS THE RATE OF EXTRUSION OF THE POLYMER IN G./MIN./CM.2 OF EFFECTIVE SPINNERET FACE, WITHIN 1 INCH OF THE SPINNERET FACE AT AN ANGLE BETWEEN 45* BELOW AND 45* ABOVE THE HORIZONTAL TO COOL THE EXTRUDED FILAMENT TO A TEMPERATURE BELOW ABOUT 15*C. BELOW THE MELTING POINT OF THE POLYMER PRIOR TO A POINT 2 INCHES BELOW THE SPINNERET, THE EXTRUDED FILAMENTS BEING UNDER A TENSION OF AT LEAST 0.003 GRAM PER DINER IMMEDIATELY BELOW THE SPINNERET, DRAWING THE FILAMENTS AT A DRAW RATIO OF ABOUT 2 TO 5 TIMES TO ROIENT THEM, MAINTAINING THE ORIENTED FILAMENTS FREE OF TENSION AT A TEMPERATURE BELOW THE SEOND ORDER TRANSITION TEMPERATURE OF THE POLYMER FOR AT LEAST ABOUT 2 MINUTES SUBSEQUENT TO THE RELEAST OF TENSION IN THE DRAWING STEP, AND HEATING THE FILAMENTS FREE OF TENSION AT A TEMPERATURE AT LEAST ABOUT 20*C. ABOVE THE SECOND ORDER TRANSITION TEMPERATURE.

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