US 3907957 A
Oxidative deposits on a spinneret in a melt spinning process can be reduced by introducing a small amount of a noncondensible inert gas, such as nitrogen, below the steam blanketed zone, but above the point at which quenching air is first directed toward the extruded filaments.
Description (OCR text may contain errors)
United States Patent [1 1 Inventor: Donald Edward Shaffer,
Assignee: E. I. Du Pont de Nemours and Company, Wilmington, Del. Filed: Apr. 18, 1914 App]. No.: 462,036
Related U.S. Application Data Continuation-impart of Ser. No. 370,678, June 18, 1973, abandoned.
References Cited UNITED STATES PATENTS 9/1962 Griehl 264/176 Z Shaffer Sept. 23, 1975  QUENCHING PROCESS FOR MELT 3,129,272 4/l968 Ferrier et al. 264/176 Z EXTRUDED L NT 3,553,305 l/l97l Au 264/176 Z FOREIGNPATENTS OR APPLICATIONS 44-2l169 9/l969 Japan... 264/176 Z Primary ExaminerJay l-l. W00
 ABSTRACT Oxidative deposits on a spinneret in a melt spinning process can be reduced by introducing a small amount of a noncondensible inert gas, such as nitrogen, below the steam blanketed zone, but above the point at which quenching air is first directed toward the extruded filaments.
9 Claims, 3 Drawing Figures US Patent Sept. 23,1975 Sheet 10f2 3,907,957
US Patent Sept. 23,1975 Sheet 2 of2 3,907,957
QUENCHING PROCESS FOR MELT EXTRUDED FILAMENTS CROSS REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of myco- 1973 and now abandoned.
BACKGROUND OF THE INVENTION This invention relates to melt spinning synthetic polymer filaments. More specifically, this invention provides an improvement in melt spinning processes whereby better continuity of operation is obtained.
The problem of polymer oxidation at the spinneret has long created difficulties when melt spinning synthetic polymers. It is known to provide a blanket of inert gas around the spinneret, to decrease the tendency for oxidized polymer to form around the-spinneret orifices. Such deposits must be removed, by the technique termed wiping (described hereinafter) else they will interrupt the spinning. Steam has been used for the inert gas, to minimize formation of oxidized polymer.
The molten filaments, after extrusion, are normally cooled by a current of cross flow air or by air which is supplied radially of the filament bundle, and which then flows longitudinally, cocurrent with the filaments motion. Extreme care is required to minimize exposure of the filaments to turbulent quenching air, since'while molten, they are very sensitive to erratic air currents, which may produce denier variations and even cause contact between and fusing of filaments. In some cases, a combination of radially directed and cross flow cooling air has been employed.
Efforts to combine the inert gas blanket and the cooling feature led to the use of cooling with 100 percent inert gas, to quench filaments at a controlled rate, or to processes that combined steam blanketing with carefully controlled cooling air.
In spite of continual efforts to decrease polymer oxidation at the spinneret, it was found impractical to completely eliminate oxygen at the spinneret face; even a very low concentration was enough to cause spinneret deposits with polymers spun at high temperatures, or with those polymers which were easily oxidized.
SUMMARY OF THE INVENTION It has been found that oxidative deposits on the spinneret in a melt-spinning process can be reduced below levels heretofore attained, by a process for quenching a melt extruded filament issuing from a spinning pack which comprises introducing immediately below the spinning pack in successive first, second and third zones steam, noncondensible inert gas, and air respectively; and passing the melt extruded filament through said zones toquench the filament.
An additional advantage may be obtained when the inert gas is preheated prior to introduction into said second .zone.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 represents schematically the apparatus elements employed in the process ofthe invention.
FIG. 2 shows a quench box arrangement which is adapted to processing four threadlines simultaneously.
FIG. 3 shows an enlarged partial scale-up of the cross section as illustrated in FIG. 1 showing the steam blanketer arrangement in more detail.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS The process of the invention can be best understood by reference to the drawings. FIG. 1 shows schematically a melt spinning apparatus in which filaments l are extruded from a spinneret filter pack 2 from a source of molten polymer, not shown. Filter pack 2 is surrounded by a heated spinning block 3. The filaments are extruded into a steam-blanketed first zone indicated by the numeral 4, supplied with steam from conduit 5. The filaments l are cooled as they pass through quench box 6, which is supplied with room temperature air passing through a duct 7 from a source, not shown. The cooling air reaches the filaments by passing through perforations of screen tubes 8, 15 which surround the filament bundle. Tube 8 is formed of perforated metal, and a tube 15 is'a double tube consisting of one layer of 20 and two layers of mesh screen. Air is supplied at a rate just equal to the rate at which quiescent air would be aspirated by the moving filaments.
The upper portion of quench box 6 has a partition or baffle plate 12 dividing it into two zones, i.e., second and third zones designated 9 and 10, respectively. Plate 12 is connected to the top flange 14 of the quench box by a seal, which may be flexible as shown at 17 of FIG. 2. Noncondensible inert gas is delivered to zone 9, through conduit 11 and air is delivered to zone 10 through duct 7.
FIG. 2 is a perspective drawing of quench box 6, adapted to furnish quenching air and inert gas to four quench tubes simultaneously. Like numbers denote like parts.
FIG. 3 shows in greater detail the steam blanketed spinneret arrangement in cross section. Again, like' numbers denote like parts. In FIG. 3, 2 denotes the filter pack and 2" the spinneret through which filaments l are extruded. Steam is injected through steam conduit 5, into annular slot l9,providing a blanket of steam extending downwardly from the face of spinneret 2". Annular slot 19 is formed in its lower part by steam blanketer insert 13. Flange 14 of quench box 6 is in sealing contact with blanketer l3. Quench box 6 contains quench tubes 8 and 15, positioned as shown more clearly in FIG. 1.
The maximum amount of cooling air which can be used in any melt spinning process is restricted by the need to protect the filaments from turbulent air currents which may cause filament breaks, fusing and denier variations, as mentionedpreviously. For the pre ferred cocurrent quench process disclosed herein, it is desirable that this amount of air correspond to that which is aspirated by the running threadline. This volume of air will vary with number of filaments, size of yarn bundle, and spinning speed. It may be determined empirically, from a study of the relation between yarn defects and air flow rate, or a mathematical model may be devised. The benefits of the instant invention are obtained when a portion of this air is replaced by an inert gas, preferably nitrogen. As will be shown in the examples, optimum improvement in spinning continuity is obtained when from 5 to 20 percent of the quench air is replaced by nitrogen. Surprisingly, replacing larger amounts of the air with nitrogen appears to provide poorer results, in addition to being more expensive.
It might be hypothesized that a similar improvement could be obtained by increasing the steam flow by an amount'corresponding to the volume of nitrogen. This approach is not practical, since the maximum tolerable steam flow is limited by the effect of gas velocity on the freshly extruded filaments; increasing the steam flow next to the spinneret reduces denier uniformity. Introducing additional steam at 11 (FIG. 1) rather than nitrogen when the filaments are cooler, would cause excessive moisture condensation in the quench tube, and, because of condensation, might not reduce oxygen at the spinneret. In addition, cooling with a condensing gas often leads to nonuniformly quenched yarn.
In an attempt to determine the mechanism which produces the benefits of the instant invention, the steam in the blanketer was replaced by an equal volume .of (a) heated nitrogen and (b) heated helium, to determine whether a density difference between blanketer and cooling medium was necessary. In both cases, (a) and (b), polymer oxidation at the spinneret was not reduced, indicating that the density difference was not a factor.
In order to achieve the benefits of the invention, baffle 12 should be placed at the optimum position in quench box 6, which position may be empirically determined. However, it is believed that the optimum position for the baffle is controlled by the theoretical considerations described below.
When air is used to cool filaments spun from a steam blanketed spinneret, as in FIG. 1, but without provision for adding inert gas (i.e., partition 12 removed and inlet 11 closed), most of the air introduced radially through screen tubes 8, 15, is immediately carried downward by the moving filaments. In the upper section of the screen tube, however, some of the air eddies upward, mixing with the steam in zone 4, and producing a small oxygen concentration at the spinneret, which causes polymer oxidation around the spinneret orifices. The best location for baffle 12 is believed to be sufficiently far from the spinneret so that none of the air admitted below the baffle will be carried up to the spinneret. This point is believed to lie just below the zone where the upward eddies begin to form.
When using partial inert gas quenching, it will often happen that the lower part (zone of quench box 6 can be dispensed with; the filaments may be cooled by air aspirated through screen tubes 8, 15, or by cross flow air furnished in conventional manner. It is apparent, of course, that when cross flow air is used to cool the filaments, the inert gas should be introduced above the point where the air is first directed toward the filaments.
The process of the instant invention may also be adapted to the various known methods used to delay the cooling of the filaments, for example, by heating the inert gas supplied to zone 9.
Although nitrogen is the preferred inert gas for use in the process of the invention, any nonoxidizing (and, preferably, nontoxic) gas may be used, such as helium, combustion gas and the like.
The principal objective of the invention is to decrease the need to remove oxidized polymer deposits from the face of the spinneret by the technique known as wiping which involves carefully scraping the exposed surface of a spinneret with a brass chisel-like tool. Ob-
viously, this is a costly operation, since it requires hand operation by skilled operators and involves an interruption in production during wiping.
If preventive wiping is not scheduled sufficiently frequently, spinning interruptions will occur; these are of the following types:
a. a molten filament may spin discontinuously, by dripping from the spinneret orifice;
b. an occasional thick section of filament is produced;
c. yarn may break and wrap on the feed roll at the draw zone;
(I. filaments may start to break and wrap on any of the other rolls.
v A careful statistical study of the coupled spinning drawing operation is made, and a schedule of preventa tive wiping is developed to decrease the probability of all interruptions a-d to some specified level. The time interval between the preventative wipes determined by this schedule is termed wipe cycle herein; it is taken as a measure of the effectiveness of the gas blanketing system, while all other variables are held constant. Obviously, it is important to increase the wipe cycle as much as possible.
In some tests, the total hours of spinning before an actual interruption by any of (a) to (d) is determined; this period is identified as drip life herein.
The process of the instant invention will be exemplified by a coupled spinning drawing process described by R. H. Knospe in U.S. Pat. No. 3,416,302, which process'is used for preparing mixed shrinkage yarns from polymer compositions based on polyamides from bis(4- aminocyclohexyl) methane(abbreviated PACM) and dodecanedioic acid (-12 acid)..lt is apparent, of course, that the invention may also beadvantageously used in the melt spinning of PACM-l 2 homopolymer alone, or, indeed, for melt spinning any polymer where spinning temperatures are so high (or oxidation resistance so low) that spinning into a steam blanket is used.
EXAMPLE I PACM-l2 tt isomer) homopolymer and PACM-lZ-PACM-I copolymer (70% tt, also) are prepared essentially as described in Example I of the Knospe patent, U.S. Pat. No. 3,416,302. The polymer and copolymer are then extruded as filaments through separate orifices of a single spinneret, using a quenching chimney as shown in FIG. 1. In this instance, there is only one quench tube assembly 8 within quench box 6, instead of the four tubes shown in FIG. 2. One hundred forty-four filaments (72 of each composition) are extruded into steam blanket zone 4. The filaments are cooled as they pass through nitrogen quench zone 9 and air quench zone 10, after which they are converged into yarn bundles and drawn to a 240 denier yarn, essentially as described in Example I of Knospe, ata yarn windup speed of 2,700 yd./min. (2,550 m./min.). The spinning block temperature is 337C. The steam blanketer zone 4 is supplied with 0.2 to 0.3-cfm (5.7 to 8.5 l./min.) of steam at 270C. Nitrogen is supplied at 11 to zone 9 and air at 7 to zone 10.
In two series of tests, various positions of baffle 12 are evaluated, as well as varying amounts of air and nitrogen. The oxygenconcentration at the spinneret face is determined, aswell as the average drip life under each condition. In all tests, the steam flow is 0.2 to 0.3
cfm (5.7 to 8.5 l./min.) at 'a temperature of 270C. The results are listed in Table I. i i
In Tests 1 and 3, baffle 12 is not in place and air c001- ing only is employed. In Test 4, air is injected at 11 inlowing conditions: the spinning block temperature is 332C; 1.85 lb/hr (0.87 Kg/hr) steam at 270C. is supplied to e'achspinnert blanketer, yarn is spun from eac'h spinnert and after drawing, the yarn is wound up at stead of nitrogen. It should be noted that steam flow is 5 3,100 yd./min; (2,830 m./min.). The quenching condireported as cu. ft./min. measured at 1 atm. and 270C., tions, air and nitrogen flows, (control employs no inert TABLE I Baffle Position, N Flow, Air Flow Air 7 Cone! Avg. Drip Life Test No. Test in. (cm.). scfm(l/min) scfm(l/min) Repl. Wt. Hrs.
Test Series I 1 Control, None None 63.6( l800) None 2.0 4.5
air i I i 2 Part,N. 3.25(8.25) 27.0(764) 36.6(1004) -42 0.8 9.5
Test Series II 3 Control. None None 63.6( 1800) 'None 3.0' 4.3
air 4 Air-air l.75(4.44) 7.5 Air 56.l( 1-585 None ND 4,2
212) A 5 Part N 3.45(8.75) (424) 48.6( 1375) 23 0.7 12.0 6 Part N. l.75(4.44) 7.5(212) 56.](1585) 12 0.6 14.9
'"Baffle position: distance between bufl'le l2 and top of quench box 6, inches (and Cm.
*Oxygen concentration at the spinneret face. wt. '12. "ND indicates values not determined. ""71 of normal quenching air, replaced l' N It is observed that oxygen concentration at the spinphysical properties and denier uniformity.
gas), wipe cycle and drip life are listed in Table II (test runs 9, l0, and ll) which shows that excellent improvement in drip life is obtained when 6 or 1 l percent of the quenching air is replaced with nitrogen.
EXAMPLE II The test of Example I is repeated on a large scale, EXAMPLE IV using the four-tube quench box of FIG. 2. The spinning block temperature is 337C; 0.8 to 1.0 cfm (21.7 to A 28.3 l-lmin.) steam at 270C. is supplied to each spin- It may be advantageous to heat the inert gas used to neret blanketer. Various filament counts are spun from replace a portion of the quenching air, as shown in this each spinneret; after drawing, the yarn is wound up at example. 2,700 yd./min. (2,550 m./min.). In separate runs, poly- The procedure of Example III is repeated with the mer with various amounts of kaolinite delusterant (see following conditions: the spinning block temperature is ller US. Pat. No. 3,397,171) is employed. 40 335C; 1.75 lbs/hr (0.78 Kg/hr) steam at 280C. is sup- The quenching conditions, air and nitrogen flows, oxplied to each spinneret blanketer; yarn is spun from ygen concentration and wipe cycle are listed in Table each spinneret and after drawing, the yarn is wound up [1, (t runs 1-8), at 3,500 yd./min. (3,200 m.lmin.). The quenching con- It is observed that the addition ofnitrogen in the zone dmons. air and nitrogen flows r l employs no above the quench air input reduces oxygen concentra- Inert gas) wipe cycle and drip life are listed in Table II tion at the spinneret, and increases the wipe cycle. (test 12 and The g n added in Test run However, as in Example I, it is seen that excessive 13 is preheated to 200C., before injection at 11 into amounts of nitrogen are frequently less advantageous. nd quench zone 9. Increased wipe cycle is ob- EXAMPLE m served when 5 percent of the quench air is replaced by heated nitrogen, and in addition, yarn properties are The procedure of Example I] is repeated with the folimproved.
TABLE II Drawn Kao- Test Yarn linite Baffle N Flow, Air Flow, 7: Air 0 Cone. Avg. Wipe Avg. Drip No. Test Count "/1 Posn.,in.(cm) scfm(l/m) scfn1(I/min) Rep]. Cycle. hrs. Life hrs.
1 Control l20-72 3.3 None None 5()( I780) None 0.35 15.5 2 Test 120-72 3.3 226.61 10(280) (1780) 16 0.2 26.5 3 Control 250-72 l.5 None None 160(4520) None 0.7 3.4 4 Test 250-72 15 1.44 20 500 (4520) 11 0.14 8.2 5 Test 250-72 1.5 1.75 4.44 30 x40) 160(4520) 161 0.21 6.3 6 Control 90-30 2.0 None None l l()(3l 10) None N.D. 7.0 7 Test 90-30 2.0 l.25(3.l8) 17.0 110(3110) 13.4 0.22 8.0 8 Test 90-30 2.0 1.25(3.|s) 17.01470 80(2260) 17.4 0.28 14.0 9 Control 250-72 3.3 None None 160(4520) None N.D. 3.3 3.9 10 Test 250-72 3.3 2.5(03) 10(280) 160(4520) 59* N.D. 8.7 10.8 11 Test 250-72 3.3 2.5 03) 20(560) 160(4520) 11.0* N.D. 6.6 9.2 12 Control l80-l08 3.3 None None 200(5660) None N.D. 2.5 4.0 13 Test lBO-IOX 3.3 2.5(6.3) 10(283) 5370 5.0 N.D. 9.0 14.0
nitrogen as :1 ercent of total quench gas What is claimed is:
l. A process for quenching a melt extruded filament issuing from a spinning pack which comprises introducing immediately below the spinning pack in successive first, second and third zones steam, noncondensible inert gas, and air respectively; and passing the melt extruded filament through said zones to quench the filament.
2. The process as defined in claim 1, wherein said noncondensible inert gas is nitrogen and amounts to from about to about percent of the volume of air being introduced.
3. The process as defined in claim 1, said process being a radial cocurrent quenching process.
4. The process as defined in claim 1, said inert gas being preheated prior to introduction into said second zone.
5. In a process for quenching a melt extruded filament issuing from a spinning pack that includes the v steps of. introducing immediately below the spinning pack in successive zones steam and air and passing the filament through the zones to quench the filament, the improvement comprising: replacing a portion of said air being introduced with noncondensible inert gas; and introducing said noncondensible inert gas into a zone between the zones for introducing steam and air.
6. The process as defined in claim 5, about 5 to about 20 percent of said air being replaced by said noncondensible inert gas.
7. The process as defined in claim 6, said noncondensible inert gas being nitrogen.
8. The process as defined in claim 5, said quenching process being a radial cocurrent quenching process.
9. The process as defined in claim 5, said inert gas being preheated prior to introducing said inert gas into said zone between the zones for introducing steam and all.