US 3109195 A
Description (OCR text may contain errors)
Nov. 5, 1963 J. COMBS ETAL 3,109,195
SPINNERET PLATE Filed Feb. 15, 1961 2 Sheets-Sheet 1 FIG. I FIG. 2
1 f8 MSECTIONAL CONTROL EXERTED.
CE TENSION AND F I 5 C-SURFA FLUID FORCES ACTIVE.
1r luv D-FINAL FORM OF I I l I I I l FILAMENTSSET.
INVENTORS JACK LEE COMBS DONALD RITTLER STRACHAN ATTORNEY NOV. 5, 1953 J. 1.. COMBS ETAL 3,109,195
SPINNERET PLATE Filed Feb. 13, 1961 2 Sheets-Sheet 2 FIG.7' F|G.8 F|G.9
FIG. I! FIG-I2 .ZNVENTORS JACK LEE coMBs DONALD RITTLER STRACHAN BY K/M ATTORNEY United States Patent 3,109,195 SPINNERET PLATE Jack Lee Combs and Donald Rittler Strachan, Martinsville, Va., assignors to E. I. du Pont de Nemours and Company, Wilmington, Del, a corporation of Delaware Filed Feb. 13, 1961, Ser. No. 88,894 8 Claims. ((11. 18-3) This invention relates generally to the field of extrusion of viscous organic materials, and more particularly to a new and improved apparatus used in the spinning of synthetic filaments having multi-lobed transverse crosssections.
The spinning of organic materials by extrusion through an orifice is a generally accepted and well-known practice in textile manufacture. Such practice in the past has been, to a large degree, concerned with the production of filaments which possess a round or nearly round transverse cross-section. In many instances, the production of very fine filaments, i.e., filaments of low denier, is necessary in order to take advantage of some desirable physical characteristics which such filaments exhibit when a part of a given fabric product. Fabric products having certain other physical characteristics are obtained many times through the use of filaments with larger deniers. It has been found that among the physical properties which can be modified in such a manner, i.e., by variation of denier, are the optical properties such as dullness, sparkle, brightness. Other properties important to a particular desired use of the end product and also the adaptability of certain filaments or yarns to particular end products can be affected in this manner.
It has also been disclosed in the prior art that certain important desired physical properties can be obtained by producing filaments having modified transverse crosssections, other than circular.
U.S. Patents 2,939,201 and 2,939,202 to Holland indicate that filaments of certain trilobal and shield crossseotions exhibit particular physical properties which are very desirable in certain end uses of the filaments. As dis cussed in these patents, it is believed that the physical properties are related to and controlled by the particular transverse cross-section of the filament. A detailed system for identifying the cross-sectional features of such filaments by means of modification ratio, tip radius ratio, and arm angle is given in this patent and referred to in the present disclosure. In addition, other patents such as Shaw U.S. Patent 2,637,893 and Terry et al. U.S. 2,746,839 disclose the use of filaments having other specific cross-sections in order to obtain certain desired physical characteristics.
In producing filaments with particular transverse crosssections by melt extrusion there are many problems involving the tendency of the cross-section of a newly spun filament to return toward the circular shape due to the action of surface tension and fluid forces before the material of the filament finally solidifies. This observed tendency is affected by the viscosity of the material of which the filament is formed and also by the quenching or cooling conditions to which the newly formed filament is subjected. It can be seen that if the quenching conditions vary widely from orifice to orifice in the same spinneret plate or from spinneret plate to spinneret plate, the final shape of the solidified filament cross-section will likewise vary. This will result in the filaments exhibiting variable properties which is undesirable generally. Also, it has been found that certain exaggerated filament cross-sections can only be obtained under extreme costly quenching conditions or by use of very high viscosity material or both.
a providing enlargements at the extremities of the slots so that a disproportionate amount of polymer passes through the extremities of the slots, thus placing as much of the polymer as possible at considerable distance from the center of the spinneret orifice. Similarly, Pamm et al.
U.S. 2,816,349 describes abrupt expansions placed every 10 to 20 mils along the slot.
It is one object of this invention to provide a new and improved process for producing synthetic filaments having a multi-lobal transverse cross-section in which a wide range of multi-lobal cross-section filaments can be produced with great cross-sectional uniformity from orifice to orifice and from spinneret plate to spinneret plate without the need for extreme costly quenching conditions or reliance upon more costly, high viscosity materials.
It is a further object of this invention to provide a novel and improved apparatus for the efiicient, precisely controlled, and rapid production of synthetic filaments having multi-lobal cross-sections and properties of great uniformity.
Another object of this invention is to provide a process for spinning filaments from orifices with odd cross-sectional configurations without substantial losses in the perimeter-to-area ratio of the cross-section during solidification.
Still another object is to provide spinneret orifices suitable for preparing filaments with unusual multi-lobal cross-sectional configurations having low modification ratio and low tip radius ratio, or low modification ratio and low arm angle.
The objects of this invention generally are achieved by an arrangement of novel process steps and novel apparatus in which the molten polymer passing through a spinneret plate is forced into a multi-armed cross-sectional configuration with the material in the outer portion of the arms being forced into contours which provide a high surface area-to-volurne ratio such that quenching occurs .before the forces of cohesion and surface tension can distort the material appreciably, and a high viscosity is thereby provided in the arms of the threadline, thereby preventing drifting of the filament cross-sectional configuration toward the circular form.
These and other objects and advantages will be apparent from a consideration of the following specification, claims and drawings in which:
FIGURE 1 is a diagram illustrating the dimensional parameters characteristic of spinneret orifice exits of the present invention,
FIGURE 2 is a partial end view of a' spinneret plate embodying features of the present invention showing a form of orifice exit for spinning fibers with trilobal crosssection,
FIGURE 3 is'a partial end view of a spinneret plate embodying features of the present invention illustrating yet another form of orifice exit for spinning fibers with tetralobal cross-section,
FIGURE 4 is a partial schematic view of a spinneret assembly with parts broken away showing the pressurized starting material moving through the orifices and the zone in which the improved action of this invention occurs,
FIGURE 5 is a partial end view of a spinneret plate showing another form of orifice exit,
FIGURES 6-13 illustrate a number of examples of various spinneret plate orifice exit configurations to achieve the desired surface area-to-volume relationship for the molten extruded material,
FIGURE 9 additionally illustrates three various ways to utilize distinct separate small orifices at the extremities of the main elongated openings to achieve the desired filament configuration.
This invention is most directly concerned with an improved process and apparatus for the melt'extrusion of synthetic filaments of multi-lobal cross-sections. However, the principles ot the invention can be applied with beneficial results to other processes of extruding filaments.
Generally, in the melt extrusion of synthetic filaments, the starting material 34 is subjected to heat and pressure in a zone A (FIGURE 4) suifioient to maintain it in a molten condition in which it may be forced through the orifices 33 in a spinneret plate =32 to form a plurality of filamentary structures, The extruded filamentary structures are subjected to controlled conditions in a zone C which bring them to the desired solidified condition in the form of solid filaments 35.
In the past, the production of certain exaggerated multilobal cross-section filaments, such as those identified in the above-named Holland patent as having negative lobe angles and low modification ratios, has been very difficult since the transverse cross-section of the molten material flowing from the multi-armed cross-section ocrifices in the spinneret plate would return very quickly under surface tension and other fluid forces toward a centralized form before solidification. Some of the solidified filaments consequently had positive lobe angles instead of negative lobe angles. Also, variations in the quenching zone con ditions from orifice to orifice would result in filaments with diiferent cross-section being produced from identical orifices. In order to avoidsuch non-uniformities, or to prevent drifting of the fiber shape away from the orifice configuration, it has been the practice to increase the velocity of the cooling air surrounding the threadline. Unfortunately, this procedure is unsatisfactory for it blows the filaments about the spinning chimney causing them to stick together or to stick to the sides of the chimney and raise other problems.
It has also been difficult in the past to spin uniform filaments with low modification ratio and low tip radius. This type of filament cross-section is described in commonly assigned, copending U.S. patent application Serial No. 58,342, filed September 26, 1960. Similarly commonly assigned, U.S. Serial No. 742, filed January 6, 1960, describes other fiber cross-sections which are spun with improved control by the process of the present invention.
Applicants have solved this problem of uniformity and control of the final multi-lobal filament cross-section by manipulating the cross-section of the flowing molten material in a particular manner as it passes through the spinneret plate (zone B). The cross-section of the flowing material is formed, during passage through the plate 32, so as to have two or more arm-like portions radiating from a central point or central slot and the material flowing in each of the arm-like portions of the stream crosssection is forced to take a configuration having high surface area-to-volume ratio whereby the material flowing in the arm-like portions of the stream is substantially cooled and solidified (zone C) before the material can move to a more centralized cross-sectional form under the force of surface tension or other fluid forces. Stating the preferred action in another way, a plurality of thin fins are formed on the arms of the flowing material cross section to give the rapid cooling action described above. This novel and beneficial action is produced by spinning from the improved spinneret plate orifice exit cross-sections as shown in the drawings While carefully controlling the quenching condition within reasonable limits. The orifice cross-sections produce a stream of flowing material having a greatly distorted cross-section with respect to the final filament cross-section, which distorted cross section for given quench conditions will be acted upon by surface tension and other fluid forces during quenching in such a way as to produce the desired final cross-section by increasing the flow rate of quenching air in the spinning column or by introducing the cooling air at a point nearer the spinneret. Further control is effected by changing spinneret plates to introduce molten multi-armed threadlines with larger cooling fins. For each configuration of molten threadline there is a corresponding set of quenching conditions. The ranges of cross-sectional configuration which are available for a series of spinnerets overlap, so that it is possible to obtain a given fiber cross section from a number of spinnerets having orifices with fins of various placement, shapes, and lengths.
Another method for controlling the ztorm of the flowing material comprises passing the molten polymer through an adjustable spinneret orifice having movable slots. The position of the fins in the flowing threadline is then adjusted by adjusting the position of the cross arms during the spinning operation. Alternatively the length of the cross arms in the orifice could be adjusted during spinning to give greater or lesser perimeter area ratio as required.
The preferred process is achieved by using the orifice exit cross-sections shown in FIGURES 2, 3, or 5 and quenching with a cooling gas having a temperature of 50 to F. flowing at a linear speed of 30 to fiL/min. The polymer is extruded at a rate preferably exceeding 0.7 gram per minute per hole, and the cross section of the solidified polymer has a modification ratio less than 2.6 and has either a tip radius ratio less than 0.3 or lobe angle less than 10, or both. FIGURES 6l2 illustrate other exit cross-sections and distorted stream cross-sections which will achieve the desired results when coupled with proper quenching according to this invention.
The various forms of orifice cross-section which are suitable for the practice of this invention are characterized by certain dimensional measurements as illustrated in FZGURE l. The cross-section comprises a plurality of elongated openings or main arms 0 which intersect the central point j. The main arms are in turn provided with narrow transverse enlargements or fins b positioned along the length of the arms. There are at least two fins at each such position on the arm. The narrowest width of the main arm is W and the length is L The length L, is measured from the intersection of the longitudinal axes of two main arms to the tip of the arm, and falls within the limits 2W to ZOW The fins positioned along the arms are preferably oblong in cross-section with a width W: at the point of attachment and a length L; measured from the intersection k of the axis of the fin and the axis of the main arm to the tip of the fin. The fins are located on the arm at a distance D from the center of the intersection of the arms. This distance D is preferably less than 0.8L and greater than 0.2L However, useful application of this invention may be made in which D is greater than 0.8L The longer dimension of the fin is positioned generally transversely to the direction of the slot. The width of the fin is at least 0.5W The longer dimension L; of the fins is at least 1.5W and is never greater than the length of the main arm L The length of the fin is also limited by the length which would cause the flowing molten material passing through a fin on one arm of the orifice to join with or contact similar material flowing in an adjacent arm or fin. The limit on this dimension L varies with the number of main arms and with the radial position along the arm at which the fins are found. In an orifice having radially equi-spaced arms the maximum fin length L; is
0.8D tangent where n is the number of main arms.
The elongated openings or main arms may be of different length. The angles between the axes of the various arms may be unequal, and the fins 17 need not be positioned at similar positions along each slot, depending on the final filament cross-section desired. Furthermore, not all of the main slots need have fins.
The orifice may consist of a central slot with fins extending from either side as in FIGURE 5. In order to simplify the description, the orifice of FIGURE is interpreted as having four arms radiating from a central point. Two of the arms have fins.
Orifice cross-sections having two arms such as in FIGURE 12 are also useful.
The cross-section of the fins or transverse enlargements need not be rectangular. Furthermore, it has been noted that provision of a plurality of separate small orifices adjacent the outer end of the main arms will provide a suificient perimeter-to-area ratio P/ Q for the material flowing in a given arm to give satisfactory improved results according to the invention. However, the separate orifices must be sufiiciently close so that the separate streams of material will quickly and permanently fuse together to form a single lobe of the extruded filamentary structure. An example of various arrangements of this type orifice is shown in FIGURE 9. Generally, there will not be any practical advantage in positioning the transverse enlargements closer than about 0.2 of the slot length from the central portion of the orifice, since the general objective is to hold more of the material in the outer arm portions of the stream and solid filament.
In order to obtain the advantages offered by this invention the surface area-to-volume ratio in the arms of the molten threadline should be high enough to promote rapid cooling. Considering the perimeter P and the area Q of the cross-section of each arm of the spinneret independently, and as representative of the surface area and volume of the molten material passing through such an arm at a given instant, it has been determined that the ratio of perimeter P and the area Q, expressed in thousandths of an inch units, should not fall below a particular value in order to effectively compensate for the tendency of the stream of flowing material to return toa centralized transverse cross-section under surface tension and other fluid forces. This minimum value for P/ Q has been found to be about 0.5 in order to achieve significant benefits from the practice of this invention. The preferred P/ Q ratio however is 0.9 or higher.
It is believed clear that this invention with regard to both process and apparatus will be of great value and benefit to the art of producing synthetic filaments of the various non-circular forms, particularly where there have been problems as to uniformity of filament cross-section or in obtaining suitable cross-sections from low viscosity material. In addition, this improved process will allow maintenance of the specified cross-section without extreme quenching which would disrupt the flow of filaments or cause them to blow about or stick together, since the velocity of quenching air can be kept at a minimum by the methods of the present invention.
The spinneret orifices and process of this invention, furthermore, will permit fibers with odd cross-sections to be manufactured without the losses in productivity which ordinarily occur when extrusion rate is reduced to promote better quenching. This invention will permit lower viscosity polymers to be used in the manufacture of specific odd fiber cross-sections. Because these lower viscosity polymers may be drawn to much higher draw ratios, higher deniers may be spun, which in turn gives higher spin- 6 ning productivity in pounds per 'hour than for high viscosity polymers.
For the practice of this invention any melt spinnable polymer is satisfactory. The following polymers are illustrative of the types which may be used to spin fibers with uniform odd cross-sectional shapes: polyamides, such as polyhexamethylerreadipamide and polyepsiloncaprolactam; polyesters, such as polyethylene terephthalate; or copolymers derived from ethylene glycol, terephthalic acid, and up to 2% sulfoisophthalic acid, cellulose triaeetate and other meltable cellulose derivatives. In addition plasticized melt-spinnable fibers such as acrylonitrile or copolymers containing at least 85% acrylonitrile may be utilized. Other polymers which can be spun into filaments with odd-cross-section by the use of this invention are poly(ethylene 2,6 naphthalate); poly(tetrachloro diphenylol propane isopbthalate); the polyester reaction product of ethylene glycol, terephthalic acid and dibenzoic acid; the polyam-ide from bis(p-aminocycloheXyDmethane and azelaic acid; the block copolymer from poly(hexarnethylene adipamide) and poly(hexamethylene isophthalamide); poly(hexamethylene adipamide) containing a phenol formaldehyde resin; and poly(m-xylylene adipamide) to name a few. In addition, odd cross-section fibers may be spun from the polyamides listed in U.S. Patent Nos. 2,071,250, 2,071,251, 2,465,150,
2,465,319, 2,071,253, 2,130,523, 2,130,948, 2,190,770, 2,252,555, 2,252,557, and 2,374,137.
EXAMPLE I Polyhexamethylene adipamide containing 0.3% by weight of TiO delusterant was spun using apparatus similar to that of Waltz disclosed in US. Patent 2,571,- 975. The grid and melt pool temperature was maintained at 291 C., and the molten polymer was blanketed with steam. The polymer was spun through a spinneret having 34 holes, each hole in the spinneret having identical cross-sectional configuration. A number of different spinnerets were used successively with this apparatus. The orifices had a three-armed cross-section with an angle of between any two adjacent arms. The dimensions of the orifices in each spinneret are described in Tablel, the dimensions being in thousandths of inches. Each of the main arms had a pair of fins placed perpendicularly to the main arm in the form of a cross-arm. During each spin the severity of quenching was changed from time to time and samples were taken of yarn under each of the quenching conditions. In Table I maximum quenching is indicated by the rating of 1 in the column describing sevenity of quench. Decreasing degrees of quench are indicated by increasing numbers, the mildest quench being rated as 6. Q 3
The severity of quench was adjusted in these experiments by increasing the air flow from about 30 c.f.m. to 70 c.f.m. or by closing the chimney more completely around the molten threadlines to promote countercurrent flow of the cooling air around the filaments or both. In Table I, flake RV is the relative viscosity of the polymer before spinning. Relative viscosity was determined by the method described in U.S. 2,3 85,890. The windup speed indicated in the table was the speed of the undrawn yarn as it was wound on the spinning bobbin. The ratio of the linear extrusion speed to windup speed in spinning was approximately constant in these experiments.
After spinning in the above fashion the yarn was drawn at sufiicient draw ratio to give yarn with a break elongation of about 27%. The spun denier before drawing was in the range of 174 to 262 and the final drawn denier was about 70'. In the drawing operation the yarn was passed around a inch ceramic pin at room temperature.
The average measurements of a large number of in dividual filament cross-sections taken from yarns produced at each operating condition are shown in the Table I filaments or causing them to waver. In addition, the threadlines were almost completely enclosed to get countercurrent flow of the cooling air. Four spinnerets, each having 34 orifices with a specific orifice cross-sectional configuration were used successively on the spinning equipment described in Example I. The fibers were drawn about 3.5 X. Each of the spinnerets had three main arms radiating from a central point, there being a 120 angle EFFECT OF SPINNERET ORIFIOE DESIGN AND QUENOHING ON FILAMENT GROSS-SECTION Orifice dimensions, mils Filament;
cross-section Spinneret Type Flake Wind- No. Main arms Cross arms of RV up quench speed, y.p.m. Lu W! Li D M n/R A Key Severity of quench: (1) Maximum quench, air flow 70 e.1.rn., eountercurrent flow of air, closed chimney; (2) Next to maximum quench, air flow 50 c.i.m., countercnrrent In addition, these data show that fibers with the combination of low modification ratio (2. 6 or lower), and low lobe angle (10 or lower) may easily be obtained by spinning from orifices having cross arms on the main arms. In addition, the data show that it was easy to obtain filaments with tip radius ratio less than 0.3 and modification ratio less than 2.6. These fibers when prepared with good quenching conditions (1 to 3 rating) had exceptionally uni-form cross-section configuration from filament to filament.
EXAMPLE II Polyhexarnethylene adipamide having a relative viscosity of about 40 was spun by the procedures described in Example I. Maximum quenching was utilized, the air flow being as high as'could be applied without en-tangling the 75 ments for (3) Moderate quench. air flow 70 c.f.m., open chimney; (4) flow 50 c.i.m., open chimney; (5) Very poor quench, air flow 30 c.i.m., (6) Poorest quench, air flow- 3O c.f.m., open chimney.
between each of the adjacent arms. The dimensions of the main arms are given in Table I1. Spinneret No. 11 had a round hole in the end of each of the three arms, the hole being 5' mils in diameter. The total arm length given in Table 11 includes the 5 mil hole. Spinneret No. 12 had a 9 mil diameter hole in the end of each of the three arms. Spinneret No. 13 had a cross slot in the end of each of the arms. The cross slot was perpendicular to the main arm. The dimensions of the cross slot were 2 mils by 10 mils; hence the fin length L was 5 mils. Spinneret No. 14 had a similar cross slot which was 2 mils wide and 20 mils long. Thus the fins in spinneret No. 14 were 10 mils in length.
Table 11 gives the perimeter-to-area ratio for the various orifice cross-sections and gives the cross-section measurethe fibers which were obtained. The two spinnerets 11 and 12 having round holes in the ends of the orifice arms were of a type described by Lehmicke in U.S. 2,945,739. It is obvious from the table that by using a high perimeter-to area ratio in the spinneret orifice the ability to spin fibers with lobe angles less than 30 is greatly improved. It is further obvious that the techniques outlined by Lehmicke are inadequate for obtaining the desired low lobe angles in the fiber cross-sections with low modification ratio. In fact the data show that the larger one makes the round hole diameter, the further one comes from the desired fiber cross-section. The Lehmicke spinneret is, of course, satisfactory for manufacturing other types of fiber cross-section having different properties from those with low lobe angle.
Table II which are suitable for invention will depend on the I polymer type, upon concentration of the polymer in the solvent used to test viscosity, upon the type of solvent, and other well-known factors. In general, the minimum relative viscosity of the polymers which can be spun advantageously by the present invention will be the lowest relative viscosity which can he spun by the prior art meth- EFFECT OF SHAPE OF ENLARGEMENT ON FIBER CROSS-SECTION Main arm dimen- Fiber cross-section Spinneret sions Spmneret N 0. Type of enlargement arm, P/Q
W Lu M Tr/R A 3 15 Round hole, 5 mil dia 72 1. 6 32 37 3 Round hole, 9 mil dia 49 1. 3 50 61 2 15 Cross arm, 2 x 10 mil 1. 04 1. 9 37 27 2 Cross arm, 2 x 20 mil 1.02 2.0 41 5 EXAMPLE HI ods under the most extreme quenching conditions with Polyhexamethylene adipamide was spun using an apparatus similar to that described in U.S. Patent 2,571,975. Two different spinnerets (Nos. 15 and 16) were tested on the same spinning equipment, each spinneret having 34 orifices. The orifices in both spinnerets had a three-armed cross-section with the arms radiating from a central point. There was an angle of 120 between adjacent arms.
The orifices of the No. 15 spinneret had three arms consisting of rectangular slots each 3 mils wide and 15 mils long. At the end of each arm was a round hole 5 mils in diameter. The measured length of each main arm included this 5 mil hole.
Spinneret No. 16 was similar to No. 15 but had a rectangular cross arm on each of the three main arms and did not have the round holes described for No. 15. The main aims were 2 mils wide and mils long. The crossarms were 2 mils wide and 30 mils long (two fins each 15 mils long). The cross slot was positioned with its center 3 mils from the end of the main slot.
Yarns were spun from each of the above spinnerets at the maximum extrusion rates consistent with obtaining fibers having cross-sectional measurements within the following specific limits after drawing: modification ratio M, 1.90 to 1.95; tip radius ratio r /R, 0.41 to 0.43; arm angle A, -8 to 14. At the same time the linear air velocity around the molten filaments was the maximum that could be maintained without disrupting the uniform nature of the molten threadlines. In addition to maintaining the cross-sectional measurements within the prescnibed limits, the yarns were drawn sufiiciently to obtain a final yarn denier of 70. In each case the drawn yarns had tenacities of 4.5 to 5.0 grams per denier and break elongations of 24% to 30%.
Because of the necessity of maintaining the cross-sectional measurements within the prescribed ranges, the maximum extrusion rate for spinneret No. 15 (round holes at tip) was 0.48 gram per minute per orifice and the maximum windup speed before drawing was 700 yards per minute. On the other hand the extrusion rate for spinneret No. 16 (having cross-arms) was 0.70 gram per minute per orifice and the w'indup speed was 1206 yards per minute.
It should be noted that the relative viscosity of the polymer flake used in spinneret No. 15 (round holes at tip) was 45 and in spinneret No. 16 was 42. Despite the very slow extrusion and wind-up speed.
It will be apparent that modifications of this invention will occur to persons skilled in the art, and all such are considered to fall within the spirit and scope of the invention as defined in the following claims.
1. An improved spinneret plate for use in spinning synthetic filaments having a multilobal transverse cross section comprising: a solid plate having at least one patterned orifice therethrough, said orifice having at least two straight arms extending outwardly and in an angular direction from a central portion with the smallest angle between adjacent arms being less than said arms intersecting said central portion thereby providing communication from arm to arm, at least two of said arms each being traversed by slots, said slots intersecting each of the said arms at a position remote from said central portion and spaced from the extremity thereof, each of said arms having a perimeter-to-area ratio P/Q of at least 0.5.
2. The spinneret plate of claim 1 wherein said arms have a length L, and said slots intersect said arms at a distance D between 0.2L and 0.8L from the intersection of said arms and said central position.
3. The spinneret plate of claim 2 wherein said slots are comprised of two fins having a length Lg which is at least one and one-half times the width W of said arms.
4. The spinneret plate of claim 2 wherein said slots are comprised of two fins having a length L: which is at least one and one-half times the width W: of said fins.
5. The spinneret plate of claim 2 wherein said arms are substantially equispaced about a central point and said slots are comprised of two fins having a length Lg which is less than 0.8D tangent (180/n) where n is equal to the total number of arms.
6. The spinneret plate of claim 5 wherein n is 3.
7. The spinneret plate of claim 2 wherein said orifice has four arms substantially equispaced about a central point, two of said arms opposite each other being traversed by slots.
8. The spinneret plate of claim 2 wherein the perimeter-to-area ratio P/ Q of each of said arms is at least 0.9.
(References on following page) References Cited in fl ie file of this patent 843,179 GreatBritair i Aug. 4, 1960 UNITED STATES PATENTS 853,062 Great Britain Nov. 12, 1960 2,816,349 Pamm et' a1; Dec. 17, 1957 OTHER REFERENCES 2945739 Lehmicke July 1960 5 Faserforschung and Textiltechm'k 6 (1955), Heft. 5
FOREIGN PATENTS (German), 199-203 relied upom 837,285 Great Britain June 9, 1960