US3439491A - Process for making core spun yarns - Google Patents

Description

- April 22, 1969 J. G. .SCRUGGS PROCESS FOR MAKING CORE SPUN YARNS Filed Aug. 9, 1965 FIG.4.

INVENTOR. JACK e. SCRUGGS g TToRflEY United States Patent 3,439,491 PROCESS FOR MAKING CORE SPUN YARNS Jack G. Scruggs, Cary, N.C., assignor to Monsanto Company, St. Louis, Mo., a corporation of Delaware Filed Aug. 9, 1965, Ser. No. 478,217 Int. Cl. D02g 3/36, 3/38, 3/02 U.S. Cl. 57-160 6 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to sheath-core yarns. More particularly, this invention relates to composite yarn structures comprised of core yarn having a sheath of microfibers deposited thereon and a method for producing said structures.

Various methods have been developed in recent years to produce microfiber yarns. Because of the unique properties exhibited by the microfibers they have been found to be very useful for special purposes. The term microfibers as used herein refers to fibers having diameters which range from about 0.1 micron to about 15.0 microns with the average diameter being between 2.0 and 5.0 microns. These fibers are generally spun by feeding a synthetic organic polymer, in liquid state, to a rotating surface where the polymer is discharged as elongated droplets from the rotating surface by centrifugal force and the droplets become entrained in a stream of gas flowing parallel to the axis of the rotating surface to form fibers which are transported to a collection screen. Regardless of the particular method used to prepare the fibers, the collection thereof employed has been similar in that the fibers are deposited on a screen in the form of a web or batting. For textile processes such as knitting and weaving which employ yarn, the webs of microfibers must be removed from the collection screens and roved into yarn prior to being fashioned into fabrics. Because of the large roving formed in this manner, extensive drafting is necessitated to provide the small denier yarns required for most fabricating operations. Furthermore, the low deniers that are preferred for some applications cannot be easily prepared by the known processes.

Another disadvantage which has been experienced with the known methods for producing microfiber yarns is the high production cost of yarns composed entirely of microfibers. Also, these yarns are limited by the physical properties and characteristics common to the material from which the single component of microfibers are spun.

With the foregoing in mind, a primary object of the present invention is to provide composite yarns composed of a core yarn having a microfiber sheath spun from a material other than the core yarn.

Another object of the invention is to provide composite yarns having a combination of unique properties.

Another object of the invention is to provide a method for depositing a sheath of microfibers on a yarn to produce a composite yarn having the combined characteristics and properties of the core yarn and the sheath fibers.

Another object of the invention is to provide a method for producing low denier yarns having the unique properties exhibited by microfiber yarns.

Another object of the invention is to provide an improved method of producing sheath-core yarns.

Another object of the invention is to provide a method for mechanically entwinging microfibers around a core yarn to produce a novel composite yarn.

Other objects and advantages of the invention will be apparent from a consideration of the description and claims which follow.

In general, the objects of this invention are accomplished by passing a core yarn essentially transversely through the fiber stream of microfiber spinning operations such as described in copending application Ser. No. 464,477 of T. E. Crompton filed June 16, 1965, whereupon the microfibers are deposited and mechanically entwined on the core yarn in the form of parallel helixes to produce a composite structure. Ssytems for preparing microfibers other than by cone spinning may also be employed to carry out the present invention. The ratio in weight per unit length between the core yarn and the sheath fibers is predetermined by the denier of the core yarn, the rate at which the core is advanced through the fiber stream and the rate of microfiber formation. The spnning rate of the microfibers may be regulated within certain limits to vary the sheath portion. Preferably, a false twist is imposed on the core yarn while passing through the path of the microfibers to impart a wrapping action to the core which causes the sheath fibers to twist around the core and anchor thereon firmly to provide the core with a uniform concentric sheath. Either a spindle type or an air type false-twist device may be employed to cause the core yarn to rotate about its axis in the region of the microfiber stream. If false twist is not imposed on the core yarn, a greater portion of the microfibers tend to collect on one side thereof to form an eccentric sheath around the core. Whether false twist is employed or not, the microfibers are securely entwined around the core yarn without the aid of an adhesive and remain compact throughout subsequent processes.

The materials satisfactory for the preparation of the composite yarn in accordance with the present invention are comprised a wide selection. For example, material for the core yarn may include any of the organic polymers and copolymers that can be solution or melt spun; materials such as metal, glass, ceramic, and inorganic compositions; natural fibers such as cotton, wool, hemp, cellulose and bast fibers; elastomeric materials such as spandex or rubber, either natural or synthetic; and any combination of the above materials which may be blended or spun as conjugates. The core may exist in the form of a monofilament, staple, continuous filament, ribbons of slit film, or textured yarns, all of which may be fully drawn, partially drawn, or undrawn. Although a Wide range of materials may be utilized the polyamides are preferred.

The sheath fibers may be compirsed of any of the so called airborne-type microdenier fibers. Such fibers are generated in a forced-fluid medium and are generally called airborne fibers. While the polyacrylonitriles and copolymers of acrylonitrile and other monomers copolymerizable therewith are preferred, all other compositions of materials that can be generated into fine denier fibers may be employed.

Prefrably, the core yarn and the sheath of microfibers are prepared from different materials so that the desirable qualities and advantages of each may be utilized. For example, the core yarn may be made from a polyamide to obtain strength and the sheath fibers made from polyacrylonitrile which has a good hand, good ultraviolet light stability, and good dyeing qualities. Thus, the two materials can be combined economically to produce a yarn which exhibits the good qualities of both. Another example of an improved yarn prepared in accordance with the present invention is a high bulk elastomeric yarn which is composed of an elastic core having a sheath of microfibers prepared from a selected material to provide certain desired properties.

A better understanding of the invention will be possible by reference to the drawing in which:

FIGURE 1 is a diagrammatical arrangement of apparatus suitable for practicing the invention;

FIGURE 2 is a section of the composite yarn, enlarged, to show the helical arrangement of the sheath of microfibers;

FIGURE 3 illustrates a cross-sectional view, greatly magnified, of yarn produced in accordance with the arrangement of apparatus shown in FIGURE 1; and,

FIGURE 4 is a cross-section, greatly magnified, illustrating the eccentric core of yarn produced when false twist is not imparted to the core yarn.

Referring specifically to FIGURE 1, there is shown a threadline or core yarn being advanced essentially transversely through a stream of microfibers 12. The microfibers may be prepared by any method capable of producing fibers suitable for the invention, but preferably a cone spinning system 14, as shown, and being of the type disclosed in the copending application Ser. No.

464,477 of T. E. Crompton filed June 16, 1965, is employed.

The core yarn 10 is withdrawn from a supply bobbin 16 by a pair of feed rolls 18 and advancing through an enclosure 20 wherein the microfibers .12 are collected on the moving threadline. As the threadline traverses the path of the microfiber stream, more than 95 percent of them become entwined around the moving core to cover the surface thereof with a multiplicity of axially spaced helixes. A false twist is imparted to the core yarn by a pneumatic false-twist device 22 to facilitate a more uniform deposition of the microfibers on the core yarn and thereby produce a c one-corespun yarn 24 having a concentrically located core as shown in FIGURE 3. The cone-corespun yarn 24 is then passed through a wash bath 26 and taken up on a bobbin 28.

The threadline or core yarn 10 must be spaced far enough away from the cone 30 to permit the removal of solvent and tackiness from the microfibers prior to their engagement with the core. If the solvent is not removed from the microfibers, an undesirable sheet or mass of material is found on the core yarn. It has been found that for most operating conditions the distance may range from 1.0 to 5.0 feet, but distances from 1.25 to 2.0 feet are preferred. Since the microfibers are discontinuous and entrained in a gas stream moving at high velocity, they become firmly entwined around the threadline upon contact therewith to form an excellent mechanical bond.

As illustrated in FIGURE 1, the threadline 10 is directed slightly at an angle with the face of the cone. The oblique movement of the threadline 10 with respect to the fiber stream 12 causes the microfibers to advance axially along and around the threadline to deposit the fibers thereon in the shape of parallel helixes as shown in FIG- URE 2. It will be apparent however that the angle must be very small so that a proper amount of wrapping or entwinement will occur to mechanically retain the sheath of imicrofibers in place on the core yarn.

An outstanding and unusual aspect of the present invention is displayed by the fact that almost 100 percent of the microfibers are collected on the core yarn regardless of the denier. The sheath fibers are discontinuous and may range in lengths from about 4; inch to several inches. If the fibers are permitted to travel to a screen for collection, they are deposited in a wide sheet. Quite unexpectedly however, when a yarn having a denier which may range from about 15 to several hundred is drawn through the flow path of the microfibers, the relatively widely scattered fibers are attracted to the single small threadline. The core yarn may be of any size preferred, the only requirement being that the strength thereof is suificient to withstand the collecting process.

The relative proportions of the components combined to produce the composite yarn of this invention are practically unlimited. By varying the linear speed of the collecting threadline 10 and the rate of microfiber output, a Wide range of core to sheath ratios can be obtained. For example, the core component could ultimately be totally removed by a selective eluting technique. This removal could be accomplished either before or after the yarn has been formed into a product. Thus, all intermediate proportions between all core and no sheath or vice versa may be attained.

Composite yarns prepared in accordance with the present invention can be drawn, twisted, plied, annealed, etc. within the usual limits for conventional yarns. These processing operations may be carried out using conventional equipment.

The following examples illustrate specific embodiments of the invention. All parts and percentages are by weight unless otherwise specified. Test procedures employed were as follows:

The abrasion resistance was determined as described in ASTM D11751.1.2; the air permeability was measured using the procedure described in ASTM D737; the water absorption was determined by placing 3 inch diameter discs of the woven fabrics in contact with a fritted glass funnel surface. The surface of the disc not in contact with the funnel was previously attached, by the use of an adhesive tape having adhesive on both sides and sold under the trademark Scotch brand tape, to a 3 inch diameter cotton bag containing approximately 50 g. of fine lead shot. The applied weight held the fabric in intimate contact with the funnel surface. The funnel contained water beneath the fritted glass surface and was directly connected to a meniscus which was calibrated to read directly weight of water, in grams absorbed. After allowing the sample to come to equilibrium, the percent weight gain due to water absorbed was calculated; and the insulation tests were carried out using an apparatus which consisted of two layers of 1 inch x 8 inches x 8 inches Marinite, an insulating material containing asbestos fiber, diatomaceous silica, and an inorganic binder, with a inch x 8 inches X 8 inches aluminum plate sandwiched between the Marinite. The upper Marinite layer contained a square 4 inch hole to allow exposure of the fabric. A thermocouple was connected to the bottom of the aluminum plate. The test was carried out by placing the fabric on top of the aluminum plate, fitting the top Marinite layer in place and exposing the sample to either a 250 watt infrared heat lamp or a 150 watt lamp at a distance of 6 inches. The temperature after 40 minutes exposure was selected for comparing the insulating properties of the fabric.

EXAMPLE 1 A 19 percent solution of a copolymer of approximately 93 percent acrylonitrile and 7 percent vinylacetate in dimethylacetamide was pumped through the hollow drive shaft of a cone rotating at approximately 4500 r.p.m. into an attenuating air stream in the manner taught by T. E. Crompton in copending application Ser. No. 464,477 filed June 16, 1965. Instead of collecting the fibers on a screen as described in Ser. No. 464,477, the fibers were collected by passing a denier nylon 66 yarn having a tenacity of 4.86 grams per denier and an elongation of 36 percent through the path of the cone-formed microfibers. The nylon yarn was introduced and withdrawn at approximately f.p.m. at a distance of approximately 2 feet from the rotating cone. The nylon core, now containing a sheath of microfibers, was next passed through a pneumatic twister, such as described by E. P. Carter et al. in Ser. No. 466,159 filed June 23, 1965, now US. Patent No. 3,303,639, set at 20 p.s.i.g. air pressure. The twisting device imparted false twist to the yarn which produced a wrapping action that wound the microfiber sheath around the nylon core. After the winding step, the composite yarn was then passed through a boiling water wash bath and taken up with a conventional take up unit. The bobbin of washed yarn was dried in a vacuum oven and then drawn 1.38 times over a hot shoe device at C. The

EXAMPLE 2 The procedure described in Example 1 was repeated with the exceptions that the drying step was omitted and the moist fiber drawn using a steam drawing tube at a temperature of 126 C. The walls of the drawing tube were electrically heated to 200 C. to prevent the accumulation of condensate on the interior walls of the drawing tube. The composite yarn had essentially the same properties as the hot shoe drawn fiber in Example 1 with the exceptions that the modulus of the yarn was increased from 7.0 grams per denier to 15.0 grams per denier by steam drawing, but the hot shoe drawn product was more lustrous in appearance than the steam tube drawn yarn.

EXAMPLE 3 The procedure described in Example 1 was repeated with the exceptions that a 204 denier, 34 filament, undrawn nylon 66 yarn was used, the core drawn 1.5 time during the sheath collecting step, and the hot shoe draw ratio increased to 2.6 times. The yarn obtained had a denier of 154, a tenacity of 1.9 grams per denier and an elongation of 19.6 percent. The composite yarn contained 65.0 percent acrylic microfiber.

EXAMPLE 4 The procedure followed in Example 1 was repeated with the exceptions that the undrawn nylon core used in Example 2 was drawn 2 times prior to the microfiber collection step and was not drawn during the collection step. The final drawing of the composite fiber after collection of the microfiber sheath and drying was carried out on a hot shoe at a draw ratio of 2.4 times to give a product having a denier of 164, a tenacity of 2.74 grams per denier, and an elonagtion of 20.7 percent. The composite yarn contained 74.0 percent acrylic microfibers as a sheath.

EXAMPLE 5 The procedure followed in Example 1 was repeated with the exceptions that a 2-ply, 70 denier, 34 filament, textured nylon 66 core sold under the trademark Superloft Was employed for collecting the acrylic microfiber sheath and a draw ratio of 1.21 times was employed in the hot shoe drawing. The bulky yarn obtained had a denier of 538, a tenacity of 1.43 grams per denier, an elongation of 20.3 percent and contained 79.5 percent microfiber sheath. The composite was converted to a very highly bulked condition by exposure to hot, humid conditions in a relaxed state.

EXAMPLE 6 The procedure described in Example 1 was repeated with the exceptions that a 350 denier spun cotton yarn having a tenacity of 1.8 grams per denier and an elongation of 8.1 percent was employed as the core yarn, and no drawing was carried out, either during the collection step or after washing and drying. The composite yarn had a denier of 658, a tenacity of 1.4 grams per denier and an elongation of 11.8 percent. The yarn contained 47.0 percent acrylic micrmofibers as a protective sheath. When the fiber obtained in this example and the uncoated cotton yarn employed as the core were submitted to a garden soil burial test for three months at room temperature the core sheath fiber properties were yarn was attacked by parasitic fungi and rendered unessentially unchanged while the unprotected cotton suitable for further use.

EXAMPLE 7 The procedure followed in Example 1 was repeated with the exception that a 420 denier spandex fiber core was used to collect the microdenier acrylic fibers.

The core fiber was introduced at 54 f.p.m. and withdrawn at f.p.m. The washed fiber was drawn an additional 2.0 times in the steam tube device employed in Example 2. The spandex core-acrylic micrmofiber sheath fiber had a denier of 586, an elongation of 280 percent and a tenacity of 0.43 gram per denier. 'Fabric made from these fibers had a soft, wool-like hand which was an improvement over the clammy feeling imparted to fabrics fashioned from uncoated spandex yarns.

EXAMPLE 8 The procedure described in Example 2 was repeated with the exception that a bicomponent, self-crimping fiber was employed as the microfiber collecting core. The bicomponent fiber contained polyethylene terephthalate as one component and a mixture of 90 percent polyethylene terephthalate and 10 percent polycarbonate as the other component. The bicomponent fiber containing an acrylic microfiber sheath was drawn 1.5 times in a steam tube at 153 C. to give a bulky fiber with a woollike hand. The bulky nature of the fiber was further developed by exposure to steam in a relaxed state.

EXAMPLE 9 The procedure described in Example 2 was repeated with the exceptions that a 308 denier-10 filament polypropylene core was employed to collect the microdenier fiber sheath, the twisting and washing steps were omitted. The composite was simultaneously drawn 20 times and stripped of residual solvent in a steam tube at 194 C. The composite yarn obtained had a denier of 487, a tenacity of 1.1 grams per denier, and elongation of 6.0 percent and contained 80 percent acrylic microfibers as a sheath.

EXAMPLE 10 The procedure followed in Example 1 was followed with the exception that drawing steps were omitted and the speed at which the core yarn was introduced was varied to demonstrate a simple process available for controlling the core-sheath ratio. The commercial drawn nylon 66 core yarn and the core-sheath fibers were spun at speeds and had properties shown in the following table.

TAB LE I Core speed Core-sheath Tenacity Elongation Acrylic (f.p.m.) yarn denier (gJdenier) (percent) microfiber (percent) EXAMPLE 11 Composite yarn prepared as described in Example 1, was woven as filling into a crowfoot-weave fabric with 84 picks per inch using commercial nylon 66 as the warp yarn. An identical fabric sample was prepared with the exception that a commercial acrylic, 3 denier per filament, total denier yarn was used as filling instead of the composite yarn obtained in Example 1. The fabrics were tested for abrasion resistance, air permeability, water absorption and insulation properties. The test results are tabulated below in Table II.

TABLE II Abrasion Air perrne- Filling resistance ability (cu. Water Insulation Test yarn (strokes to ftJmin. at absorption infrared white failure) 0.5 in. press (percent) 0.) 0.)

drop) Control.-- 76 199 130 74. 8 47. 5 From Ex. 1- 310 52 195 68.5 43. 3

EXAMPLE 12 The procedure followed in Example 1 was employed with the exception that a 861 denier nylon 66 core containing a conventional ultraviolet stabilizer was passed through the microfiber stream at a speed of 140 f.p.m. The resulting composite yarn was not drawn further and had a denier of 991, a tenacity of 7.16 grams per denier, an elongation of 20.2 percent and contained 13 percent microfibers as a sheath. The microfiber sheath-containing yarn produced in this example was compared with a coreyarn without a sheath coating by exposing both in a Fade- O-Meter for 60 standard Fade-O-Meter hours and then measuring the percent loss in strength. The sheath containing yarn lost 251 percent of its strength while the unprotected fiber lost 5.60 percent of its strength. Therefore, a sheath protected yarn will retain about 70 percent of its original strength after exposure to 100 standard Fade-O- Meter hours whereas the unprotected yarn will retain only about 30 to 40 percent of its original strength.

From the data of the foregoing examples it is apparent that the yarns contemplated by the present invention and products made therefrom have several unique and useful properties. Heretofore, it has not been possible to so easily and economically combine the various fibers to promote the unusual properties of each and also compensate for the deficiencies which exist in particular applications. One example of how the outstanding properties of two materials are combined so that a weakness of each is overcome by the other will be recognized in the use of nylon cord covered with acrylic fibers for flood control purposes. A material having the strength of nylon is re quired for sand bags but because of poor ultraviolet stability the bags are useful for only a short duration. On the other hand acrylic fibers are not strong like nylon, but are quite stable for extended periods of outdoor usage. Consequently, when nylon cord is coated with acrylic fibers in accordance with the present invention an excellent yarn is produced for use in flood control projects which will Withstand adverse weather conditions for extended periods. Other important advantages and products resulting from the invention are properties such as increased bulk, good hand, improved dyeability, flame retardance and fiber covered electrical conducting wires which may be woven into blankets, heating pads, carpets and the like.

The foregoing detailed description has been given for clearness of understanding only, and unnecessary limitations are not to be construed therefrom. The invention is not to be limited to the exact details shown and described since obvious modifications will occur to those skilled in the art.

What is claimed is:

1. A method of producing composite yarns composed of a core strand and a sheath of fibers mechanically entwined around said strand, comprising:

(a) generating a multiplicity of fine denier fibers in a high velocity gaseous medium,

(b) directing the fibers toward a collecting zone by the gaseous medium,

(c) advancing a threadline through the collecting zone at an oblique angle with the path of the fibers,

(d) depositing the fibers on the moving threadline,

(e) causing the threadline to rotate about its natural axis to wrap the fibers uniformly around said threadline and mechanically entwine said fibers thereon to form a composite yarn, and

(f) collecting the composite yarn in an orderly manner.

2. A method of producing composite yarns composed of a core strand and a sheath of microdenier fibers mechanicaly entwined around said strand to provide the composite yarn with a uniform cover sheath having improved ultraviolet light stability, comprising:

(a) generating a multiplicity of microdenier fibers in a confined area,

(b) directing the fibers under the force of a gaseous medium along a predetermined path in the confined area,

15 (c) advancing a strand through said confined area generally transversely across the path of said fibers,

(d) causing the strand to rotate about its natural axis whereupon the fibers wrap uniformly around the strand to form a concentric sheath thereon, and

00 (e) withdrawing the strand from said confined area.

3. A method for mechanically entwining microfibers around a continuous strand, which comprises:

(a) advancing a fiber-forming material onto a rotating surface to form a multiplicity of microdenier fibers in a confined area,

(b) advancing a continuous threadline through the confined area approximately 1.0 to 5.0 feet from the rotating surface,

(c) entraining the microfibers in a stream of gas moving at a high velocity sufficient to direct said fibers against said threadline with suflicient force to tightly entwine the said fibers around said threadline to form a composite yarn, and

(d) collecting the composite yarn.

4. The method of claim 3 in which the threadline traverses the confined area at an oblique angle with the path of the fibers whereby helical wrapping of the fibers is accomplished.

5. The method of claim 4 in which the threadline is caused to rotate about its natural axis to increase the entwinement of said fibers.

6. The method of claim 5 in which the composite yarn is drawn at least 1.5 times to improve yarn properties.

References Cited UNITED STATES PATENTS 1,990,337 2/1935 Lewis et al 575 X 2,131,598 9/1938 Obermaier 57-5 2,208,897 7/1940 Dockerty et a1. 57-5 2,241,405 5/1941 Hyde et a1. 57-5 2,411,559 11/1946 Sonin et a1 117-33 2,902,820 9/1959 Bronson et a1. 57163 2,997,837 8/1961 Breen et al 57139 3,009,309 11/1961 Breen et a1. 57139 JOHN PETRAKES, Primary Examiner.

US. Cl. X.R.

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