US3457341A - Process for spinning mixed filaments - Google Patents

Description

y 22, 1969 w. J. DUNCAN ET AL 3,457,341

PROCESS FOR SPINNING MIXED FILAMENTS Filed May 26, 1967 puz/vaw/ve NA'D/l/M YMIU? (DIP/96' ilnited States Patent 3,457,341 PROCESS FOR SPINNING MIXED FILAMENTS William Joseph Duncan, Chattanooga, Charles Frank Fisher and Frank Houston Moye, Signal Mountain, and Samuel Allen Piercy, Chattanooga, Tenn., assignors to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Filed May 26, 1967, Ser. No. 641,524 Int. Cl. D01d 5/10 US. Cl. 264-177 4 Claims ABSTRACT OF THE DISCLOSURE A process for producing multilobal mixed filament yarns which increases operability of spinning and yields improved mixed shrinkage yarns. The copolymer is extruded through larger orifices in the same spinneret than the homopolymer while maintaining the relative viscosity of the copolymer at a value at least as high as the homopolymer.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to the production of synthetic yarns and more particularly to an improved process for multilobal mixed filament synthetic polycarbonamide yarns.

Description of the prior art Mixed filament synthetic yarns are well known in the art. United States Patent 3,225,534, discloses and claims differential shrinkage yarns containing filaments of different polymer compositions which shrink differently when heat treated. Such yarns produce fabrics with enhanced bulk, covering power, and desirable aesthetic quality. As disclosed by United States Patent 3,225,534, it is desirable to employ non-round filament shapes such as multilobal filaments in the production of such yarns. Particularly desirable are the trilobal shapes disclosed and claimed in United States Patents 2,939,201 and 2,939,202.

When diflerent polymer compositions such as a copolymer and a homopolymer are extruded from ditferent orifices in the same spinneret to produce multilobal filaments, the copolymer is usually extruded at the same melt viscosity and consequently at a lower relative viscosity than that of the homopolymer in order to obtain substantially the same cross-sectional shape for the two sets of filaments. However, under these conditions, the various process elements must be controlled within narrow limits to achieve the desired product characteristics and level of operability.

SUMMARY OF THE INVENTION The invention disclosed herein provides an improvement in the process for producing a mixed filament yarn by extruding multilobal filaments from a homopolymer and a copolymer, comprising the steps of (a) maintaining the relative viscosity of the copolymer at least as high as the relative viscosity of the homopolymer; (b) extruding the homopolymer and copolymer through separate orifices in the same spinneret. The orifices through which the copolymer is extruded must be sufliciently larger than the orifices through which the homopolymer is extruded to provide filaments of each which have substantially the same cross-sectional configuration. A further improvement in the process comprises quenching the extruded filaments by directing the flow of quench medium to first impinge upon the copolymer filaments and thereafter to impinge upon the homopolymer.

BRIEF DESCRIPTION OF THE DRAWING FIGURE I is a schematic diagram of the face of a spinneret 1 showing rows of orifices 2 and 3.

FIGURE II. is an enlarged schematic cross-sectional view of one of the orifices of row 2.

FIGURE III is an enlarged schematic cross-sectional view of one of the orifices of row 3.

EXAMPLE The following example is intended to be illustrative of a preferred embodiment of the invention.

A 48% aqueous solution of hexamethylenediammonium adipate (66 nylon salt) is charged into an evaporator. A 40% aqueous solution of hexamethylenediammonium isophthalate (6-I nylon salt), prepared by combining equimolar portions of hexamethylenediamine and isophthalic acid, is added to the evaporator in suflicient amount to provide 8% by weight of hexamethylenediammonium isophthalate based on the total weight of dry salt present. The salt solution is then evaporated to a concentration level, at which point the temperature is about 138 C. The 75 salt solution is then charged to an autoclave and heated to a temperature of about 242 C. and 17 atmospheres pressure, about to minutes being required for this operation. The pressure is then reduced over a period of 85 minutes to atmospheric pressure and the temperature increased to 270-275" C. The polymer is then held 40 minutes at this temperature and extruded in the form of a ribbon which is quenched on a water-cooled casting wheel and cut into /2 inch flake in the conventional manner. The polymer flake has a relative viscosity of 40. The polyhexamethylene adipamide-polyhexamethylene isophthalamide copolymer (66/ 6-1) flake and the polyhexamethylene adipamide (66) flake, the latter prepared in the conventional manner and having a relative viscosity of 43, are melted separately in screw melters. The relative viscosity of the 66/ 6-1 polymer increases to 45 during processing while the 66 polymer remains at a level of about 43. The two molten polymers are fed separately to separate sand filters of a common spinneret assembly. After filtration the 66 polymer is fed to one row of 7 orifices in the spinneret and the 66/6-I copolymer to an adjacent row of 7 orifices. A meter plate of the type described in United States Patent 3,095,607, is situated above the spinneret to insure denier uniformity among the filaments. The spinneret orifices are Y-shaped and are oriented relative to the quenching air as illustrated in the drawing. Each arm of the Y-shaped orifices through which the 66 polymer is extruded is 3 mils wide and 15 mils long while the copolymer orifices are larger, each arm eing 4 mils wide and 15 mils long.

After extrusion, the filaments are quenched in a conventional quenching chamber with cross flow air and converged into a yarn at a guide below the chimney. The yarn is then passed 3 /2 times around a feed roller with its associated separator roll and then 2 /2 times around a draw roll and separator roll, the draw roll having a higher peripheral speed whereby the yarn is drawn to a ratio of 2.5. The yarn is then passed to a second draw roll located in a heated compartment having an air temperature of C. where the yarn is drawn sufliciently to give a total draw ratio of 3.2. From the draw roll the yarn is passed around a second roll in the heated compartment and then back around the draw roll for 7 /2 turns, the second roll having the same peripheral speed as the draw roll so that the yarn is subjected to a constant length heat treatment. The yarn then passes from the heat compartment directly to and around a roll having a lower peripheral speed whereby the yarn is permitted to retract about 2.5% in length. The yarn is then passed through an interlacing jet of the type described in United States Patent 3,069,836. The yarn is then wound into a package in the conventional manner. The denier of the final yarn is 40. Examination of the yarn reveals that the filaments have an average modification ratio of 2.1 and that the 66 filaments do not vary substantially from the 66/ 6-I filaments in this respect. The filaments have a tip radius ratio of 0.25 and a lobe angle of 32 degrees on the average. Properties of the yarn, designated as yarn A, are shown in the table below together with other pertinent data. For comparison, the properties of a yarn spun in a similar fashion, designated as yarn B, except that the spinneret orifices are all the same size and the viscosity is varied to give matching modification ratios are also shown in the table. In regard to the yarn properties, the higher shrinkage differential and slightly higher modulus of yarn A more than offsets the slight reduction in tenacity as compared to yarn B. The processability of the yarn as indicated by filament breaks is far superior for yarn A.

TABLE GENERAL DESCRIPTION Definitions and standards In a multilobal filament, the shape of the filament cross section may be defined as disclosed in United States Patent 2,939,201 by the modification ratio, the tip ratio, and arm angle. For the purposes of this invention, the modification ratio is the most important parameter and it is a primary objective to provide yarn in which the filaments have substantially the same modification ratio.

The expression relative viscosity as used herein signifies the ratio of flow time in a viscometer of a polymer solution containing 8.2% by Weight of polymer relative to the flow time of the solvent by itself. Measurements of relative viscosity are made with 5.5 grams of polyamide in 50 ml. of formic acid (90%) at 25 C.

For determination of initial modulus and shrinkage the yarn is first conditioned in an atmosphere of 72% relative humidity at 75 for at least 24 hours. Yarn shrinkage is determined using a loop of approximately 70 centimeters in length prepared by carefully tying two ends together so as not to stretch the yarn. The range of the loop is accurately measured as it hangs under a load of 0.1 g.p.d., based on the original denier of the yarn. The measurement is made as quickly as possible after removal of the sample from the yarn package. The loop is then carefully folded in cheese cloth and placed in vigorously boiling water for minutes. It is then dried under relaxed conditions for 20 minutes to 4 hours before the final length measurement. The final length is then determined under a load of 0.1 g.p.d. as previously described. The shrinkage is calculated as the percentage decrease in length based on the original yarn length.

Initial modulus is determined with an Instron Tensile tester at an elongation of 60% per minute. The load in grams at 1% yarn elongation is multiplied by 100 and divided by the yarn denier to give the modulus in grams per denier,

The definition of tenacity and methods by which it can be determined are given in the following references: Handbook of Textile Testing and Quality Control, Cleaver, E. B., and Hanby, D. S., Textile Book Publishers, New York (1960), at page 39; Artificial Fibers, Moncrieif, I. E., J. Wiley & Sons, New York (1950), at page 8.

Process The process of this invention surprisingly produces yarns having the desired characteristics, i.e., the desired shrinkage difference between the filaments, strength, etc. at a lower draw ratio than previously achieved. This leads to a marked improvement in process operability, i.e., reduction in broken filaments and increased yield of firstgrade yarn. In addition, however, this process yields yarns With improved characteristics such as higher differential shrinkage and higher modulus, both of which contribute to improved fabric aesthetics, Yarns produced by the process of this invention also have the advantage that the higher shrinkage, load bearing, component has the higher modulus so that the yarn tends to retain its bulk to a greater degree under the stresses imposed in the fabric. To obtain the most highly desired yarn characteristics, it is preferable to maintain the relative viscosity of the polymer at a higher level than the relative viscosity of the homopolymer.

In the spinning of homopolymers and copolymers from different orifices of the same spineret, where the copolymer has a relative viscosity at least equal to that of the homopolymer, the orifices through which the copolymer is extruded must be somewhat larger than the homopolymer orifices. While the relationship between orifice size and modification ratio is somewhat em i ical, an increase in orifice size of about 30-35% will be required Where the viscosity of the copolymer is about the same or slightly higher than that of the homopolymer A further increase in orifice size is required if the copolymer viscosity is increased beyond this point. Where a Y-shaped orifice is used to extrude trilobal filaments or a cruciform shape is used to extrude tetralobal filaments, the increase in size is preferably made by increasing the width of the arms and maintaining the length constant.

Preferably, the spinneret orifices are arranged relative to the flow of quenching medium so that the quenching gas impinges first on the copolymer filaments and then on the homopolymer filaments. This leads to improved threadline stability and improved operability. The reverse arrangement leads to filaments contacting one another occasionally and sticking together.

After extrusion and quenching, the filaments may be wound into a package and subsequently drawn on a drawtwister. Optionally, the filaments may be passed directly to the drawing stage without intermediate winding into a package. Preferably, the filaments are subjected to heat treatment after drawing to equalize the retraction of the filaments and prevent loopiness when the filaments are removed from the package for processing into fabric.

Homopolyamides suitable for use in the process of this invention include those derivable from polymerizable monoaminocarboxylic acids or their amide-forming derivatives, e.g., polycaproamide and those derived from the reaction of diamines with dicarboxylic acids or their amide-forming derivatives, e.g., polyhexamethylene adipamide. In addition to those set forth in the example, other suitable polyamides are those prepared from the polymers disclosed in United States Patents 2,071,253, 2,130,523, and 2,130,948. The copolymers may be prepared from mixtures of diamines, dibasic acids, and amino acids such as those disclosed in the above patents.

Apparatus The apparatus used to produce the fibers of the invention is of the type disclosed in United States Patent 3,- 095,607. The figures are schematic representations of a spinneret face and orifices therein. The spinneret face has at least two rows of orifices through which molten polymer is extruded to form fibers. The orifices are of a Y configuration having equal angles between each arm of the Y. Row 2 represents copolymer orifices and the orifices from which the homopolymer is extruded are represented by row 3. More than one row of orifices for each of the polymers can be employed without affecting the final product if the arrangement segregates the orifices into two groups, i.e., the copolymer orifices should not be intermingled with the homopolymer orifices.

FIGURE II and FIGURE III are enlarged cross-sectional views of a copolymer orifice from row 2 and a homopolymer orifice from row 3, respectively. As set out previously, when the relative viscosity of the copolyamide is maintained at a level equal to or higher than the relative viscosity of the homopolyamide, variance in cross section of filaments is encountered if orifices of equal size are used. Therefore, to obtain filaments of substantially equal size and modification ratio, a larger orifice must be used to extrude the copolymer. Preferabl the change in dimension of the orifice is only in the Width of the arm and not in length. FIGURES II and III are representative of the orifices used in the example, a 4 x mil copolymer orifice and a 3 x 15 mil homopolymer orifice.

FIGURE I also shows the desired direction of fiow of the quenching medium to obtain optimum operability of the process. If the quenching flow were to impinge first upon the newly spun homopolymer filament, some blowing of the homopolymer stream into the adjacent c0- polymer stream would be encountered. This cannot be tolerated in an efificient operation, thus the fiow of quenching medium is directed first to impinge upon the co olymer stream and then upon the homopolymer stream.

Although a unitary preferred embodiment of the instant invention has been illustrated and described in the foregoing portion of the specification, it is manifest that equivalent substitution may be effected without deviating from the spirit of the invention or the scope of the annexed claims.

What is claimed is:

1. In a process for producing a mixed filament yarn by extruding multilobal filaments from a homopolyamide and a copolymer of said homopolyamide, the improvement comprising the steps of (a) maintaining the relative viscosity of said copolymer at least as high as the relative viscosity of said homopolyamide, (b) extruding said homopolyamide and said copolymer through a plurality of separate orifices in the same spinneret, said orifices through which said copolymer is extruded being sufficiently larger than said orifices through which said homopolyamide is extruded to provide filaments of said copolymer and homopolyamide having substantially the same cross section.

2. In the process of claim 1 the additional step of quenching the extruded filaments by directing the flow of quenching medium to first impinge upon the said copolyamide filaments and thereafter to impinge upon the said homopolyamide filaments.

3. In the process of claim 1 the said homopolyamide composed of polyhexamethylene adipamide, the said copolyamide composed of the copolymer reaction product of hexamethylenediammonium adipate and hexamethylenediammonium isophthalate.

4. In the process of claim 1, the relative viscosities of the said polyamides being at least 40.

References Cited UNITED STATES PATENTS 3,161,914 12/1964 Bloomfeld et al. 264168 X 3,225,534 12/1965 Knospe.

3,244,785 4/ 1966 HollandsWorth.

3,271,837 9/1966 Au et al.

3,297,807 1/ 1967 Setbele.

3,320,633 5/1967 Carcio et al.

3,341,891 9/1967 Shrimzu et al.

3,365,873 1/1968 Matsumoto et al.

JULIUS FROME, Primary Examiner J. H. WOO, Assistant Examiner US. Cl. X.R.

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