US3414646A - Coupled process for the production of polycarbonamide filaments - Google Patents

Description

G. PITZL Dec. 3, 1968 COUPLED PROCESS FOR THE PRODUCTION OF POLYCARBONAMIDE FILAMENTS 5 Sheets-Sheet 1 Filed April 29, 1965 F/G. 2A

F/G. Ml

GILBERT PITZL ATTORNEY Dec. 3, 1968 G. PITZI. 3,414,645

COUPLED PROCESS FOR THE PRODUCTION OF POLYCARBONAMIDE FILAMENTS Filed Apri} 29, 1965 5 Sheets-Sheet 2 FIG. 3

INVENTOR GILBERT PITZL BY @M ATTORNEY Dec. 3, 1968 PlTZL 3,414,646

COUPLED PROCESS FOR THE PRODUCTION OF POLYCARBONAMIDE FILAMENTS Filed April 29, 1965 3 Sheets-Sheet 3 GI so 40 so so 10 80 STEAM FILAHENT SURFACE TEHP.. c

INVENTOR GILBERT PITZ L BY @M 4% ATTORNEY United States Patent 3,414,646 COUPLED PROCESS FOR THE PRODUCTION OF POLYCARBONAMIDE FILAMENTS Gilbert Pitzl, Chattanooga, Tenn., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Filed Apr. 29, 1965, Ser. No. 451,822 Claims. (Cl. 264-210) ABSTRACT OF THE DISCLOSURE A coupled process for the production of polycarbonamide filaments which includes extruding, quenching in a gaseous non-aqueous atmosphere, treating with steam while the temperature of the filaments is in the range of T to T +60 C., then drawing. T is the force-todraw transition temperature of the filaments.

This invention relates to improved nylon yarn and a process for its production.

Commercially available nylon yarn is usually produced by melt-spinning polyamide filaments, winding the undrawn yarn into a package, and subsequently unwinding and drawing the yarn. Due to the separation of the spinning and drawing steps, this practice may be termed a split process. Split process yarns are usually subjected to a steam treatment as taught by Babcock in US. 2,289,- 860 to provide satisfactory package formation on winding the undrawn yarn.

The need for increased yarn production at decreased cost has led to the development of processes wherein the spinning and drawing steps are operated continuously, i.e., are not separated by an intermediate packaging step. Such an operation is termed a coupled process. In addition to operating economics, the coupled process, under optimum conditions, produces yarn which is superior in some respects to split-process yarns, particularly in strength, modulus and rate and depth of dyeing.

It has been found, however, that coupled-process filaments tend to have a very smooth surface which, in turn, leads to high yarn-to-guide friction in processing the yarn into fabrics. This high level of friction results in higher and more variable tension which in turn causes undesirable non-uniformities such as streaks in the fabric. This diificulty is avoided with split process yarns by aging the undrawn yarn for several hours before drawing. The surface roughness of the filaments is appreciably increased by this procedure.

In accordance with one embodiment of the invention, there is provided in a coupled-process for the continuous production of drawn synthetic polymer filaments from a melt of a polycarbonamide by the sequential steps of extruding said melt in the form of filaments, at least partially quenching the melt in a gaseous, non-aqueous cooling medium to solidify the filaments and then drawing the filaments to at least twice their as-spun length; the improvement comprising intermediate said quenching and drawing steps treating the filaments with steam while their surface temperature is in the range of T to T +60 C.,'wherein T is the force-to-draw transition temperature of the filaments.

The term sequential used in describing the steps of the above process is intended to connote that the operations of extruding, quenching, steaming and drawing occur in that order prior to windup of the filaments. It will be understood that intermediate operations in the continuous process, especially between steaming and drawing or between drawing and windup, are not meant to be excluded from the scope of this invention. A typical inter- Patented Dec. 3, 1968 "ice mediate operation of this nature would be the application of a lubricant or finish to the filaments. In any case there is no intermediate packaging or other appreciable delay, e.g. aging, prior to the drawing step.

The novel product of the invention is a low friction yarn comprising synthetic polymer filaments of a polycarbonamide, said filaments being characterized by a rough texture on their surface and, as viewed in electron micrographs of shadowed cross-sections, as having a smooth central portion surrounded by a rough, grainy peripheral area. This structure will be best understood by reference to the photomicrographs to be described hereinafter.

The steaming of yarns in accordance with the process of the present invention will be seen to resemble, in certain respects, a steaming procedure described in my US. application Ser. No. 420,654, filed Dec. 23, 1964, now US. Patent No. 3,291,880. The latter, however, is directed to the production of undrawn yarns of low birefringence and these, even following aging and drawing steps, do not contain filaments which in cross-section exhibit the pronounced variation in texture from center to periphery.

The invention will be more readily understood by reference to the drawings wherein:

FIGURE 1 shows photomicrographs of filament crosssections, that of A being a product of the invention and B and C being prior art products;

FIGURE 2 shows photomicrographs of filament surfaces, that of A being a product of the invention and B and C being prior art products;

FIGURE 3 is a schematic drawing showing the various steps of the process of the present invention;

FIGURE 4 is a graph, to be explained in connection with Example 2, showing the effect upon tension when the filament surface temperature is varied in the steaming step.

As shown in FIGURE 3, filaments 1 freshly extruded from spinneret 2, pass into cooling chimney 3 where they are contacted by cross flow air 4. Convergence guide 5, adjustable in position to assist control of filament temperature, leads the yarn at the desired temperature out of chimney 3 and into steamer 6 where a cross flow of steam 7 contacts the still hot filaments. After passing out of steamer 6, the yarn passes over finish roller 8 to apply a lubricating finish and then around a pair of rolls 10. The yarn is continuously drawn by wraps around a pair of heated rolls 12 moving at higher speed. The yarn then passes over driven roll 13 and finally advances through guide 15 to a package 20 where it is wound on cylindrical core 21 which is surface driven by drive roll 22.

The process of this invention, in particular the application of steam to the filaments at a critical period in the consolidation of their structure, promotes crystal growth at and near the filament surface and as a result a very rough, bumpy surface, as illustrated in FIGURE 2-A, is formed when the yarn is drawn. Unlike splitprocess yarns, however, this effect does not extend throughout the filament cross-section and, as a consequence, the improved properties of the yarn relativeto split-process yarn are retained.

When a nucleating agent, such as the kaolinite particles exemplified hereinafter or other finely divided particulate material, is added to the polymer before extrusion, spherulites are formed near the filament surface when the yarn is steamed in accordance with this invention and this leads to a somewhat rougher surface than obtained with steaming alone. As is well known to those expert in the polymer art, spherulites are crystalline aggregates of more or less spherical shape which form when certain polymer melts are cooled. Excessive spherulitic growth, i.e., throughout the filament cross-section, is undesirable from the standpoint of obtaining optimum fiber properties and is usually avoided by rapid cooling of the extruded filaments to a temperature below the glassor second-order transition temperature which is referred to herein as the force-todraw transition temperature.

If the temperature of the filaments entering the steaming zone is allowed to drop below the force-to-draw transition temperature, which is about 59 C. for 6-6 nylon yarn prepared as described herein, the desired filamentsurface roughening is not achieved.

The initial modulus of the yarn is indicative of the rate at which the yarn elongates with increasing load in the early stages of elongation. Practically, it is determined from the stress-strain curve by multiplying the load in grams at 1% elongation on the loading curve by 100 and dividing by the denier of the yarn.

Measurements of yarn friction as reported herein are made by passing the yarn at 250 y.p.m. (228.5) meters/ min.) over 21% inch (9.5 mm.) diameter polished chrome pin. The yarn contacts the pin over an angle of 164 C. The yarn is passed from a supply package over a magnetic brake to apply the desired tension, then downwardly to and around a small pulley attached to a Statham strain gauge. From the pulley, the yarn is passed up and over the chrome pin and then down to a second pulley attached to another strain gauge. From the second pulley, the yarn is passed upwardly to a powerdriven roller and an associated idler roller where it is given several passes around these rollers to avoid slippage. The yarn is passed from the power-driven roller to an aspirator which carries the yarn to a waste container. The input tension, T is adjusted to 10 grams as measured on the first strain gauge. The output tension, T is measured by the second strain gauge, the strain gauges being connected to suitable recorders for this purpose. For comparative purposes, the output tension developed may be compared when the input tension is constant. The coefiicient of friction 1 may be calculated from the equation wherein T is the input tension, T the output tension, 12 is the angle of yarn contact in radians and e is the base of the natural log.

The values for force-to-draw transition temperatures, as reported herein, are determined by measurin the force-to-draw at different yarn temperatures and plotting a curve of force-to-draw vs. yarn temperature. The lowest temperature above room temperature at which a definite break in the curve is observed is taken as the transition temperature for the particular yarn. Since the force-todraw transition temperature for nylon varies with the degree of crystallinity, orientation and moisture content, the force-to-draw is determined by passing yarn directly after quenching to a heated feed roll of 6.72 inches (17 cm.) diameter, passing the yarn around the feed roll for 16 turns to insure temperature equilibration, then passing the yarn to a draw roll and drawing to a 2.2 draw ratio. The force-to-draw transition temperature of the 66 nylon yarns referred to herein is about 59 C in all cases.

The surface temperature of the filaments is determined with a compensating thermocouple arrangement in which one of a pair of thermocouples is placed in contact with the running filament and the other thermocouple is heated electronically until the two are in balance. A commercially available instrument of this type and manufactured by the Hastings-Radist Company was used in measuring the filament temperatures reported herein.

The rate and depth of dyeing of yarns, as reported herein, are determined using an aqueous solution of anthraquinone blue SWF at a concentration of 1% based on the weight of the yarn to be immersed in the dye bath and a temperature of C. The depth of dyeing is reported in terms of the number of shades difference in depth of one sample relative to another. Plus signs indicate deeper dyeing, while minus signs indicate slighter dyeing. The rate of dyeing is calculated on a basis of the percent dye, based on the weight of the yarn, taken up in a unit of time.

Examination of shadowed filament-cross-sections in the electron microscope is carried out as follows: the filament is embedded in a copolymer of methyl and butyl methacrylate. Cross sections of 0.3-0.5 micron thickness are then cut using a microtome with a glass knife. Knives other than glass, particularly diamond, should be avoided. The embedded filament cross-section is then placed on a metal grid or screen and placed under a bell jar where a high vacuum is created. A mixture of gold and palladium is then deposited on the cross section from a heated goldpalladium filament mounted at an angle with respect to the surface of the filament cross-section. If the surface of the cross-section is completely smooth, an even coating of the metal results. However, if the cross-section is rough or irregular, then more metal is deposited on the side adjacent the heated metal filament and an irregular coating results. The cross-section is then examined in the electron microscope and an electron micrograph prepared using conventional techniques with the electron beam perpendicular to the surface of the filament.

Surface replicas of filaments are prepared as follows: the filament is mounted on a microscope slide, placed in vacuum and exposed to metal vaporization at an angle to the surface of the filament following the procedure described above for shadowed cross sections. The filament is then dipped in polyacrylic acid to embed one side. After the polyacrylic acid hardens, the slide is removed, leaving the metal-coated filament with one side (the metalcoated side) embedded in the hardened polyacrylic acid. The filament is then peeled out of the metal coating which remains adhered to the polyacrylic acid. The polyacrylic acid is then dissolved with water and an electron micrograph made of the metal surface replica.

In the following examples all parts and percentages are by weight unless otherwise stated.

EXAMPLE I Polyhexamethylene adipamide having a relative viscosity of 36.5 is melt extruded in the conventional manner to form 34 filaments. By an arrangement silim'ar to that illustrated in FIGURE 3, the filaments are passed downwardly through a quenching chimney where they are cooled by transverse air flow. When the filaments reach an external temperature of -85" C., they are converged by passing over a convergence guide and then immediately through a 12-inch length steamer where steam at essentially atmospheric pressure is passed across the yarn. The yarn is then passed over a finish roller where a lubricating finish is applied, then around a feed roller and its associated idler roller, then around a draw roller having a sufficiently higher peripheral speed than the feed roller to draw the yarn to a ratio of 3.2. The draw roller is located in a heated compartment having an air temperature of C. and the peripheral speed of the draw roller is 3,500 y.p.m. From the draw roller, the yarn is passed around a second roller in the heated compartment and then back around the draw roller, the second roller having the same peripheral speed as the draw roller so that the yarn is subjected to a constant-length heat treatment. The yarn then passes from the heated compartment directly to and around a roller having a lower peripheral speed to permit the yarn to retract slightly and thereby reduce the winding tension. The yarn is then passed to a rotating bobbin where it is Wound into a package in the conventional manner.

When electron micrographs of shadowed across sections, prepared as previously described, are examined, the area in the center is found to be relatively smooth while the area near the skin is rough and grainy as illustrated in FIGURE lA. An electron micrograph of a replica of the filament surface shows it to be rough and bumpy as illustrated in FIGURE 2-A.

For comparison, electron micrographs of shadowed cross sections and skin replicas of a filament from a yarn prepared as above except for omission of the steaming 4. As can be seen, the output tension drops sharply as the temperature exceeds 50 C., but becomes constant again at temperatures of -60-65 C. and higher. At temperatures above about 120 C. the process becomes inoperable due to the filaments becoming sticky and fusing together. Conditions employed in preparing the yarns of FIGURE 4 are given in Table II below.

TAB LE II Denier Quenching Air Flow Spinning speed Yarn Draw/ratio Yarn Filament C.f.m. Liters/min. Y.p.m. Meters/min.

so 2. 0 50 1, 416 1,175 1, 074 3. 0 so 3. 1 50 1, 416 1, 175 1, 074 3. 0 s0 4. 0 65 1, 841 900 823 3. 2 100 5. 0 70 1, 982 700 640 3. 4

are illustrated, respectively, in FIGURES 1-B and 2-B. Here the entire cross section is smooth and the surface EX MP E II of the filament is smooth relative to the steamed filament.

Two hundred parts of a commercially avallable Al 0 o a 1 ar 1s re ared b the s ht so f 6 mp rson a y n p p y p kaolinite powder (Al O -2S1O -2H O), purified by an process, the yarn being steamed after quenching using an 82 inch (208 cm.) steamer in the usual manner. The filament temperature at steaming is 50 C. After steaming, the undrawn yarn is wound into a package in the conventional manner. The undrawn yarn is then drawn immediately using the drawing stage of the coupledprocess machine as described above so that drawing conditions are identical with those of the coupled-process yarn. Electron micrographs of a shadowed cross section and a filament surface replica are prepared and illustrated in FIGURES 1-C and 2C. As can be seen from these figures, the rough, grainy structure appears throughout the shadowed cross section and the surface, although rough and striated, appears smoother than that of the yarn of this invention. Shadowed cross sections and surface replicas are also prepared from split process yarns which have been aged for more than 8 hours before drawing and are found to be identical with those of FIGURES l-C and 2-C.

Properties of the above three yarns are shown for comparison in Table I below. As can be seen therefrom, the yarn of this invention, i.e., the coupled-process steamed yarn, retains the high tenacity, initial modulus and good dyeability of the unsteamed coupled-process yarn and is superior in this respect to the split-process steamed yarn. On the other hand, the co-efiicient of friction of the yarn of this invention is substantially lower than either of the other two.

When the yarn of this invention is used as a filling in a fabric having a conventional 70-denier nylon warp, the quilling tension being 20 grams, the quill barr is judged to be at an acceptable level. Under the same conditions, the unsteamed coupled-process yarn produces 35 grams quilling tension and an unacceptable level of quill barr.

TABLE I Tenacity, Yarn Draw ratio Denier Elongation, g.p.d.

percent Yarn A=coupled process-steamed. Yarn B coupled processunstea1ned. Yarn C =split processsteamed.

N 0. shades difierence in depth.

EXAMPLE II coupled-process yarns of various filament deniers are prepared as in Example I except that the temperature of the yarn at the point of steaming, i.e., as the yarn enters the steamer, is varied in the range 45-90 C., by changing the location of the steamer or the convergence guide. When these yarns are subjected to friction tests as previously described with a constant input tension of 10 grams, the output tension varies with the temperature of the yarn at steaming as shown by the curve in FIGURE ultra flotation process (US. Patent No. 2,990,958) to substantially eliminate metal oxides other than aluminum and silicon oxide and classified by centrifugation to provide an average maximum dimension of 0.55 micron, are mixed with 300 parts water and 1.2 parts tetrasodiumpyrophosphate decahydrate in a high-shear mixing mill. After milling for 1 hour, the mixture is diluted with 300 parts water, transferred to a tank and stirred for 24 hours. The slurry is allowed to settle for 20 hours, then decanted from the settled materials and diluted with water to a concentration of 20% solids. The diluted slurry is then passed through a standard commercial filter having an average pore size of 5 microns and continuously stirred until used.

Several 450 pound. batches of polyhexamethylene adipamide having a relative viscosity of about 37 are prepared in an autoclave in the conventional manner except that to certainbatches sufiicient amounts of the kaolinite slurry are added during the polymerization cycle to give the concentrations indicated in Table III below. The kaolinite slurry is added to the autoclave when the temperature reaches 200 C. The polymer is extruded from the autoclave and cut into flake in the conventional manner.

The various batches of polymer are melt extruded and processed into 70-denier, 34-filament yarn by the coupled process following the procedure described in Example I. As indicated in Table III below, yarns I and I were steamed as described in Example I whilethe other yarns were not steamed. When friction measurements are made as previously described at a constant input tension of 10 grams, the output tension varies for the different yarns as shown in Table III. As can be seen, yarn I which combines the use of 0.5% kaolinite with steaming gives the lowest friction.

TABLE III Yarn Steamed Kaolinite, Output tension,

percent g.

None None 94 0. 5 78 0. 5 102 1. 0 84 2. 0 89 As illustrated by the foregoing examples, the product of this invention has a structure such that when examined microscopically at a magnification of at least 1600 the outer surface of the filament is rough to provide low yarn to guide friction which is needed in textile processing operations, while the internal or core structure is apparently unchanged so that advantages in strength and modulus are retained. Also, even though the outer portion of the filament cross section is changed, the enhanced dyeability of the coupled filament is retained. This desirable structure is obtained by steaming the filaments at a temperature above the force-to draw transition temperature. Preferably, the temperature of the filaments as they enter the steaming zone is at least C. above the force-to-draw transition temperature in order to insure the maximum reduction in friction as well as uniformity in this respect. The temperature should not exceed the softening temperature of the filaments. For best results, the temperature of the filaments should be in the range of 540 C. above the force-to-draw transition temperature. The preferred temperature range for 66 nylon is 65-1 00" C. The temperature referred to is, in all cases, the surface temperature of the filaments, since this is the only temperature which can be measured practically.

The yarns of this invention may be prepared from any polyamide which crystallizes readily in the presence of heat and moisture. The preferred polyamides are 66 and 6 nylon; that is, poly(hexamethylene adipamide) and poly(epsiloncaproamide), respectively. Other suitable polyamides for this purpose are those disclosed in US. Patents 2,071,253, 2,130,523 and 2,130,948.

The duration of steaming is not highly critical; however, for reasons of economy and operability, steaming times in the range of 0.0040.02 second are preferred. Particularly with the shorter steaming periods, the steam should be applied uniformly and with minimum turbulence in order to prevent non-uniformities in the resulting filaments. For this purpose, a steamer of the type disclosed and claimed in co-pending U.Sv application Ser. No. 420,547 filed Dec. 23, 1964, now US. Patent No. 3,316,741, is preferred. The particular temperature and degree of saturation of the steam do not alfect the results obtained.

Intermediate packaging of the yarn, or other appreciable delay, between steaming and drawing must be avoided in order to obtain the product of this invention. Thus, the split process is not suitable for this purpose regardless of the method of steaming employed.

As many widely dififerent embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that this invention is not to be limited to the specific embodiments thereof except as defined in the appended claims.

What is claimed is:

1. In a coupled process for the continuous production of drawn synthetic polymer filaments from a melt of a polycarbonamide by the sequential steps of extruding said melt in the form of filaments, at least partially quenching the melt in a gaseous, non-aqueous cooling medium to solidify the filaments and then drawing the filaments to at least twice their as-spun length; the improvement comprising intermediate said quenching and drawing steps treating the filaments with steam while their surface temperature is in the range of T to T C., wherein T is the force-to-draw transition temperature of the filaments.

2. Process according to claim 1 wherein the said polycarbonamide melt contains .a nucleating agent.

3. Process according to claim 1 wherein the filaments are treated with steam while their surface temperature is in the range of 540 C. above T 4. Process according to claim 1 wherein the filaments are treated with steam for 0.004 to 0.02 second.

5. Process according to claim 1 wherein the said polycarbonamide is poly(hexamethylene adipamide) and the steaming temperature is in the range of to C.

References Cited UNITED STATES PATENTS 2,289,860 7/1942 Babcock 264176 3,039,171 6/1962 Hume et al. 264176 3,291,880 12/1966 Pitzl 264-176 DONALD J ARNOLD, Primary Examiner.

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