US3115437A - Nubby yarns - Google Patents

Description

Dec. 24, 1963 D, s. ADAMS M NUBBY YARNS Filed May 1, 1959 INVENTOR DUSTIN STE'TSON ADAMS ATTORNEY Iii (5.4

: DROP SIZE United States Patent 3,115,437 NUBBY YARNS Dustin Stetson Adams, Wilmington, DeL, assignor to E. I. du Pont de Nemours and Company, Wilmington, DeL, a corporation of Delaware Filed May 1, 1959, Ser. No. 810,377 1 Claim. (Cl. 161179) This invention relates to yarns of nubby filaments from melt spinnable synthetic polymers.

In general, synthetic fibers, and particularly melt spun fibers, exhibit remarkable uniformity in denier and cross section owing to the manner in which they are prepared. This uniformity is desirable from the point of view of processing, in that identical fibers respond to any given operation in exactly the same fashion, resulting in good processing continuity. Uniformity is also desirable when it is important that the fibers have optimum physical properties, as in tire cord and other industrial uses. However, the use of filament yarns in textiles sometimes encounters unexpected difficulties, since the uniformity, while good, is not perfect, and the eye readily detects luster or dye streaks due to subtle differences in the filaments which arise during spinning. Regularity of structure has also been partly responsible for the plastic appearance and slippery handle of certain types of fabrics made from synthetic filament yarns. Staple yarns, especially those prepared from natural fibers, do not suffer from these afilictions owing to their being inherently non-uniform, in a random way, such that the irregularities blend with one another and produce in a fabric a homogeneous and aesthetically pleasing effect.

It is an object of this invention to provide a yarn comprising filaments having along their lengths a high and random frequency of denier irregularities. It is also an object to provide a filament yarn which can be woven or knitted into fabrics having improved appearance and handle. Another object is to provide a method for preparing such a yarn.

These and other objects are accomplished by continuously directing a spray, having a uniform distribution of fine liquid droplets throughout, against freshly spun filaments which are still in a plastic condition owing to their being at an elevated temperature, while simultaneously exerting tension on the said filaments suflicient to reduce substantially the diameter of all sections along the length of the said filaments except those sections which have been contacted by said droplets. The attenuated nubby filaments may then be packaged or drawn or otherwise treated according to conventional procedures. The ratio of the average diameter of the liquid droplets to the diameter of the unquenched, unextended filaments preferably lies between about 1:1 and 4: 1. The tension which must be applied to the filaments in order to produce the nubs in the filaments is shown by the spin-stretch factor which is This factor must be 5 or more to afford proper tension and proper nub formation.

By a uniform distribution of liquid droplets is meant a spray which contains, throughout the region in which it impinges upon the filament bundle, that is, the area immediately adjacent to the yarn bundle where it is contacted by droplets, a constant average density of droplets whose diameters lie in a restricted range.

One embodiment of the invention employs a novel method for obtaining a fine homogeneous liquid spray, wherein a liquid is forced out of small orifices situated on a circumference of a rapidly rotating axially symmetric chamber, liquid being supplied to the said chamber through the hollow axis thereof.

The novel product of this invention is a yarn bundle comprising a plurality of filaments, the said filaments being characterized by the presence of nubs at random intervals along the individual filaments and from filament to filament across the yarn bundle. The nubs are present on an individual filament at a frequency of greater than one nub per inch of filament.

By the expression a nub is meant a lump or nodule on a filament, which is integral with and chemically identical with the filaments, the nub having a length of from 1 to 10 times the maximum diameter of the nub and preferably l to 5 times the maximum diameter of the nub. The nubs have a maximum diameter of 1.1 to 20 times the smallest diameter of the filament. This latter ratio is hereafter referred to as contrast ratio. By the expression randomly situated is meant that no two filaments have the same patter-n of nubs along their length and there is no cycle of patterns of thin sections and nubs repeated along the length of any one filament. Hereafter, the phrase nub frequency will be used to denote the average number of nubs per inch per filament.

FIGURE 1 is a schematic illustration of one embodiment of the apparatus and process of this invention.

FIGURE 2 shows a spray generator useful in carrying out the process of this invention.

FIGURE 3 is a detail drawing of the spray generator of FIGURE 2.

FIGURE 4 illustrates the distribution of droplet size for the spray of FIGURE 2.

FIGURE 5 shows some filamentary products of this invention.

FIGURE 1 illustrates schematically one embodiment of the process and apparatus of the present invention. Molten polymer is extruded through orifices in spinneret 1, the molten filaments thus formed emerging from the spinneret as a conical bundle 2. Thereafter the molten filaments pass through quenching zone 3, where they are subjected to a spray generated by quenching device 4, which in this embodiment is the rotary jet spray generator of FIGURES 2 and 3 described more particularly hereafter.

Droplets from the spray generator intercept each filament frequently and at random intervals thereby providing localized quenching of the filaments at these sites to a temperature at which they do not attenuate, or attenuate only very little when compared to the unquenched portions of the threadline. After passing through the quenching zone 3, the filaments are collected on wind-up 5. In the region between the quenching zone 3 and the wind-up 5, those elements of the filaments which have not been directly quenched by an encounter with a liquid droplet are attenuated to a greater or lesser extent depending upon the speed of the wind-up 5. In a coupled process the wind-up may be replaced by a yarn forwarding device which assists in conducting the filament bundle to the draw rolls.

FIGURES 2 and 3 illustrate one type of spray generating device which is useful in carrying out the process of this invention. This device, term-ed a rotary jet, comprises a cylindrical drum 11, sealed at one end 12, and having on the opposite end a shaft 13 coaxial with the cylindrical chamber, by which the drum may be rotated and through which liquid may be introduced into the drum. Around the periphery of the drum are a multiplicity of small orifices 14-, situated on a single circumference. The drum may be rotated by any convenient means, as, for example, by a flexible shaft. Water may be introduced into the spray head through a rotary shaft seal of the bellows type. A spray of droplets is generated when the assembly is thus set in rotation and liquid is supplied to the orifices. The size of the droplets, and the volume in which they are delivered, is determined by the size and number of these orifices, together with the diameter of the circle on which they lie, the angular velocity of the drum, and the hydrostatic pressure with which the liquid is suppliedto. the orifices. A drum having a diameter of L'Arinches and holes of .003 inch diameter, when rotated at 1500 rpm. generates droplets to 13 mils in diameter and 3 to Smils in diameter. At 600 rpm. the larger droplets are 25 to 30 mils in diameter. A l-inch drum having holes .003 inch in diameter delivers at 2000 rpm. larger droplets of 5 to 6 milsin diameter. In each case the water is supplied at a line pressure of 70* p.s.i.g. In order to'minimize hole contamination the water is filtered, as by means of a candle type filter in the water line and glass wool packing inside the spray head.

The rotary jet does not generate objectionable air currents when used in the current process, and in this it enjoys an advantage over some types of spray generators. For success in the present process the molten filaments should not be unduly deflected or blown about, since they tend to fuse with one another on contact, resulting. in an unacceptable product. It is an advantage of the rotary jetthat it may be placed at the center of a bundle of filaments so that a large number or filaments are situated equidistant from the spray source, and when struck by droplets, these filaments tend to be deflected away from one another (i.e., radially outward). The absence of protuberances on the drum of the rotary jet is important in minimizing windage.

Another type of. spray generator which may be used in some embodiments of the invention is a pressure nozzle, which is well known to the art and is described, for example, on page 13 of Atomizationand Spray Drying, by W. R. Marshall, Jr., published by the American Institute of Chemical Engineers (Chemical Engineering Progress Series, No. 2, Vol.50, 1954). An elliptical orifice. giving a flat spray, is preferred for accurate definition of the quench position.

Distribution of particle size for the pressure jetmay be narrowed and the particle size reduced by increasing the pressure. An important advantage of a rotary jet in the present invention is that it develops a very narrow distribution of water droplets in very large quantities. FIG- URE 4 shows a typical droplet distribution curve for the rotaryjet spray. It will be noted that there are two peaks in the distribution curve. In terms of weight, most of the liquid is contained in droplets having the diameter "2. droplets, comprise only a minor fraction of the total liquid rdelivered. This sharp distribution of droplet sizes is not observed unless the jet is actually rotating. The combination of sharp particle size distribution and high Weight of droplets delivered per unit time is an exceptional feature of the apparatus. In addition to theseadvantages, the rotary jet spray delivers substantially all of its droplets in a single plane, the plane of the orifices. This is highly advantageous in that it allows one to quench precisely at the desired distance below the spinneret and assures that for each quenching event the quenchedelements are in the same condition of plasticity.

The following examples will serve to illustrate the invention. In all examples the spin-stretch factor is greater than 5 unless otherwise indicated.

EXAMPLE I Polyhexamethylene adipamide is extruded from a melt through a spinneret containing 13 holes of 0.010 inch diameter arranged in a circle of one inch diameter. A four Droplets having the diameter r called satellite.

cated 4 inches from the center of the threadline and A of an inch below the face of the spinneret. The tangent to the droplet trajectory at the point of droplet formation is in the plane of the disk and the average velocity of the droplets during their time of flight to impact with the filament is such that the impact occurs nearly in the plane of the. disk. The yarn is wound up at 100 yards per minute and'is found to have 3 nubs per inch per filament randomly located along the length of each filament. The yarn can be drawn 4x Similar resultsare obtained when the polyamide is replacedwith polyethylene terephthalate.

EXAMPLE II Semi-dull polyhexamethylene adipamide having a relative viscosity of 35 at a concentration of 8.4% in formic. acid, is spun from a melt at a temperature of 290 C. through a spinneret having a temperature of 288 C. The spinneret comprises 26 holes of 0.009 inch diameter situated'on 2 concentric semicircular arcs. The yarn is quenchedand wound up at a speed of 1000 y.p.m. The quenching spray is supplied by the rotary jet of FIGURE 3. The rotor is 1 inch in diameter and has 200 holes 0.003 inch in diameter situated on a single circumference. It is rotated at 4000 r.p.m., being so situated that the spray strikes the filaments at a point 3% inches vertically downward from the face of'the spinneret. The droplets comprising a majority of the weight of the'spray are 3-4 mils in diameter. Water is supplied to the jet at a pressure of 70 p.s.i.g. The yarn is wound up at 1000 y.p.m. and

drawn subsequently at room temperature 2;2 The product then has a denier of 4.3, and shows a nub fre-- showed good liveliness, drape and texture and a nonsynthetic fiber appearance and dry handle.

EXAMPLE III Polyethylene terephthalate, with a relative viscosity of 35 at a concentration of 2.15 grams per cc. of solvent in a mixture of 2,4,fi-trichlorophenol/phenol (70/100), is spun from a melt at a temperature of 288 C. through a spinneret at a temperature of 285 C. The spinneret contains 34 holes, each 0.009 inch in diameter, situated on a single semicircular arc whose radius is 1 /2 inches. The filamentsare quenched at points 4% and 5 inches below the spinneret by the rotary jet spray of Example I, the speed of rotation being 875 rpm. The droplets comprising a major weight of the spray were about 1015 mils in diameter. The spray is situated coaxially with the semicircle of filaments. The following table shows the effect of distance of the spray from the spinneret on nub characteristics.

Item a has an as-spun denier per filament of 6.8 (1.1 mils in diameter).

5. EXAMPLE IV Polyhexamethylene adipamide having a relative viscosity of 35 is extruded from a melt at a temperature of 290 C. through a spinneret having 10 holes, each 0.009 inch in diameter, situated in a straight line at a center-tcenter spacing of 42 inch. Filaments emerging from the spinneret are subjected to a spray generated by a pressure nozzle (made by Spraying Systems Company, Bellwood, Illinois: /4 T-250017) and are wound up at a point 18 feet below the face of the spinneret at a speed of 1000 y.p.m. The pressure nozzle is situated 4% inches vertically downward from the face of the spinneret and 3% inches horizontally distant from the threadline' and is directed substantially perpendicularly to the row of spinneret holes. Water is supplied to the nozzle at a pressure of 70 p.s.i.g. The droplets comprising the major weight of the spray are 8-10 mils in diameter. The yarn (as-spun denier of 8.1 d.p.f. or a diameter of 1.2 mils) produced is drawn to 2.7 times its original length (2.7x) and then has a denier per filament of 3 and shows nubs with a contrast ratio up to about 5. Nub frequencies of 710 per inch per filament were observed.

EXAMPLE V Polyhexamethylene adipamide having a relative viscosity of 34 is spun from a melt at a temperature of 288 C. through a spinneret at a temperature of 282 C. The spinneret contains one hole 0.010 inch in diameter.

The extruded monofilament is quenched by the pressure nozzle of Example IV, the droplets furnishing the major weight of the spray being 8-10 mils in diameter. The following table shows the effect of varying the distance below the spinneret at which the spray is imposed.

Table 11 Distance below spinneret (inches) 15 20 26 Nub contrast ratio 2 1% 1+ Nub frequency 1. 7 1. 4 1 Physical properties:

Tensile strength (g.p.d.) 3. 3.6 4. 3

Elongation. 24 37 52 Modulus 2O 19 23 Denier 14 15 Draw ratio 4. 2X 4. 2X 4. 2X Draw method pin pin pin Draw temperature C.) 50 50 50 Diameter of as-spun filaments (mi1s) 3. 5 3. 4 3. 5

The preferred range of droplet sizes is dependent upon the diameter of the filaments being spun, the contrast ratio desired, and the distance from the spinneret that the droplets strike the filaments. At distances from 0 to 3 inches, droplets having diameters of between 1 and 4 times the diameter of the filament are preferred. As the quenching zone is removed to 4 inches and greater below the spinneret, the size of the droplets can be increased without harming the spinning performance. For best results, droplet diameter should be between about 1 and 4 times the diameter of the filament immediately prior to quenching.

Very fine droplets have the effect of quenching filaments without creating a nub, resulting in non-uniform orientation and crystallinity of the yarn, so that drawability is substantially reduced. Too large a droplet causes an excessive deflection of the threadline which results in stuck filaments. Large droplets may also develop too long a nub for acceptable drawing.

Droplets must be supplied in adequate volume in order to produce the desired nub frequency. The number of encounters between droplets and filaments is 'based on the law of probabilities and may be calculated by statistioal analysis. tI has been calculated that in order to prepare a 40 denier, 13 filament yarn (a popular count for nylon tricot) with 10 nubs per inch per filament at 1000 yds./ min. and an after-draw of 2.5 times, about 200,000 collisions per second between nub-producing droplets and spinning filaments are necessary. The vertical distance below the spinneret at which the quenching spray is imposed is important in determining contrast ratio. The quenching effect of a water droplet will be less on a cooler filament than a hotter one. In practice, this effect must be balanced against another consideration: a relatively low spinneret temperature gives an increase in the melt viscosity of the jetting polymer, which results in decreased deflection of the filaments upon being struck by a water droplet. Lower spinneret temperatures also lead to higher orientations in the as-spun yarn. Preferable regions for quenching filaments depend upon denier to some extent, normal textile deniers being preferably quenched within 3 or 4 inches of the spinneret, and heavier filaments such as hosiery monofi-lament being processed most effectively between 10 and 25 inches below the spinneret. Moving the spray plane closer to the spinneret causes a larger average nub diameter in the final yarn. The quenching spray may be any liquid which does not interact chemically with the filaments. Since the bulk of the heat removed from the filament at the quenched site is dissipated through evaporation of the liquid, it is desirable that the liquid be volatile at the spinning temperature and that it have a high heat of vaporization. Since water generally fuifills all of these requirements and is inexpensive, non-flammable, and non-toxic, it is the preferred quenching liquid.

For maximum nub contrast ratio, drawing is carried out at a temperature such that the yield value for the nubby sections of the yarn exceeds the drawing tension of the section of the yarn between nubs. Consequently, the nubs are not drawn out. Yarns prepared in accordance with the invention are characterized by the permanence of the nubs in subsequent use.

For low nub contrast ratio, the as-spun yarn should be drawn over a surface heated to 50 C. or higher C. to C. for a polyester).

Any fiber-forming melt-spinnable synthetic organic polymer may be processed in accordance with the invention. Because of their commercial availability, ease of processing and excellent properties, the condensation polymers and copolymers, e.g., polyamides, polysulfonamides and polyesters, and particularly those that can be readily :me'lt spun are preferred for application in this method. Suitable polymers can be found, for instance, among the fiber-forming polyamides and polyesters which are described, e.g., in US. Patents 2,071,250; 2,071,253; 2,130,523; 2,130,948; 2,190,770; and 2,465,319. The preferred group of polyamides comprises such poly-mers as poly(hexamethylene adipamide), poly(hexamethylene sebacamide), poly(epsilon-caproamide), and the copolymers thereof. Among the polyesters that may be mentioned, besides poly(ethylene terephthalate), are the corresponding copolyrners containing sebacic acid, adipic acid, isophthalic acid, as well as the polyesters containing recurring units derived from glycols with more than two carbons in the chain, e.g., diethylene glycol, butylene glycol, deoamethylene glycol and trans-bis-l,4-(i1ydr0xy methyl) -cyclohexane.

Other suitable polymers include polyhydrocarbons such as polyethylene and polypropylene; polyurethanes; polyureas; vinyl polymers such as polyvinyl chloride, polyvinylidene chloride, and copolymers thereof; acrylic polymers such as polyacrylonitri-le when sufficiently plasticized to render it fusible, copolymers of acrylonitrile; halogenated hydrocarbons such as polychlorotnifiuoroethylene, polyacetals, polyanhydrides, polyoxymethylenes, polycarbonates, polyformals, polyethers, polythioethers, polysulfides, polythioesters, polys-ulfones, polythioureas, polythioamides, polysulfonamides, polyimides, and polytriazoles. Copolymers of all sorts are usable. Yarns prepared from polymers which tend to be brittle in the highly crystalline, unoriented state exhibit preferential breaking at the nub sites. For this reason yarns prepared from polyamides, which have good toughness even when unoriented, are an especially preferred species of the present invenment of at least 1.

tion. However, yarns spun from polymers exhibiting brittleness in the crystalline state, such as poly(ethylene terephthalate) yarns, are also of interest in that when a filament yarn prepared from such a polymer is passed through a texturing jet such as that described in US. 2,783,609, it tends to break at some of the nub sites, producing a staple-like teXtllred yarn.

It has been found that the handle, appearance, and other aesthetic properties of a fabric knitted or woven from a nubby yarn depends upon the size, frequency, and distribution of nubs. In general, large and frequent nubs lead to a fabric of desirable texture. The present process brings the production of nubby yarns within economical reach, and is the. first process to provide yarns characterized by nubs of the size and random frequency necessary for showing't-he desired improvement in aesthetics of the final fabric. The random distribution of the nubs, both from point to point along an individual filament and from filament to filament within the yarn bundle is an important feature of the process and product. For while it is possible to modify the present process in such a way as to produce periodic fluctuations in the average density of nubs along the filaments, the desirable features inherent in the fabrics prepared from these yarns are owing to the completerandomness of the nub distribution. Apparently, in a fabric the random short range non-uniformities produced by the nubs tend to mask the longer range nonuniformities which are generally present in synthetic filainent. yarns and which lead to optical blemishes such as luster and dye streaks.

Although fabric aestheticsare difficult to characterize in terms of numbers, it has been found in the present.

work that in order to produce in a knitted or woven fabric a substantial improvement in handle and appearance'over prior art fabrics, it is necessary for multifilament yarns in the denier range 1 to 5 to have a contrast ratio of between about 1 /z and 10, and a frequency of nubs/in/fila- The case is somewhat different in the case of monofilament yarns such as are used in the knitting of Womens hosiery. Such monofilaments are usually in the denier range 7to 15 and the desirable contrast ratio has been found to lie in the range 1.3 to 2.0 and the frequency of nubs/inch in the range of about 1.0 to 1.5. Yarns so characterized confer upon the fabric a desirable heather or crepe-like appearance.

While the principal utility for the nubby yarns of this invention is in the form of continuous filament yarns,

1. provide bulk and fulling characteristics.

The term freshly spun, as used in the. specification.

and claims, refers to a filament or yarn issuing from a spinneret and still in a plastic. state due to. its elevated.

temperature. The term as-spun refersto afilament or yarn of this invention as packaged prior. to drawing. A nub is an enlarged portion of a filament extending be! tween adjacent minimum diameter portions of the filament.

I claim:

Ayarn bundle consisting essentially of a plurality of continuous filaments, of fiber-forming melt-spinnable synthetic organic polymer, characterized by the presence of nubs at random intervals along the individual'filaments and from filament to filament across the yarn bundle integral with and chemically identical with the filaments, randomly situated along the. filaments at a frequency greater than one nub per inch per filament, the nubs being nodules of random size each of which has a maximum diameter within the range of about 1.1 to 20 times the smallest diameter of the filament and a length of about 1 to -10 times the maximum diameter of the nub.

References Cited in the file of this patent UNITED STATES PATENTS 1,617,544 Rosenthal Feb. 15, 1927' 2,034,008 Taylor Mar. 17, 1936 2,064,279 Taylor et a1; Dec. 15, 1936 2,264,415 Taylor et a1. Dec. 2, 1941 2,278,888 Lewis Apr. 7, 1942 2,296,394 Meloon Sept. 22, 1942 2,377,810 Robbins June 5, 1945 2,612,679 Ladisch Oct. 7, 1952' 2,674,025 Ladisch Apr. 6, 1954 2,729,539 Lulay Jan. 3, 1956 2,820,986 Seney Jan. 28, 1958 2,836,850; Lindemann June 3, 19.58 2,953,427 Egger Sept. 20, 1960 2,976,105 Rose et a1. Mar. 21, 1961 FOREIGN PATENTS 116,133 Sweden Apr. 2, 1946

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