US3386871A - Method of splicing polyamide yarn and bonding composition therefor - Google Patents

Description

United States Patent 3,386,871 METHOD OF SPLICING POLYAMIDE YARN AND BONDING COMPOSITION THEREFOR Grady N. Dulin, J12, and John I. Scott, Chester, Va., as-

signors to Allied Chemical Corporation, New York,

N.Y., a corporation of New York No Drawing. Filed May 10, 1963, Ser. No. 279,615

5 Claims. (Cl. 156-158) ABSTRACT OF THE DISCLOSURE The invention provides a bonding composition useful for uniting multifilament polyamide yarns, wherein a polyamide of formic acid relative viscosity at least about 50 is dissolved at 8%-17% concentration in a solvent of boiling point between 90 C. and 115 C. to form a solution of viscosity at room temperature between 2500 and 6000 cps. Such composition can be applied with no more than slight warming whereby it can be applied by hand. It forms a permanent bond in a few seconds which sets 1n a few hours to a strength such as 70% of the breaking strength of the yarn and which is flexible allowing a textured effect at the bond and withstands elevated temperatures and moisture.

This inventionrelates to the uniting of ends of multifilament polyamide yarns with bonding compositron s, to novel bonding compositions useful therefor contalning dissolved polyamide, and to uniform yarns thereby obtained made up of smaller yarn segments cohesively united by said bonding compositions.

In the utilization of continuous multifilament yarns in various textile applications, specialized packages of yarn are generally employed in accommodating the various specific requirements of textile processes and machinery. During the formation of specialized yarn packages discontinuities due to yarn breakage or the run-out of feed sources may occur prior to completion of the pack age. In yarn packages such as convolutely wound cones, beams, tubes, pirns, spools, bobbins, and the like designed for use in texturizing, weaving, knitting, t-ufting, or other textile operations, the uniting of ends by knotting is generally found unsatisfactory. The presence of such knots in the yarn causes difficu-lties in subsequent textile operations; and, when present in the finished textile article, detracts from the desired aesthetic qualities of the product.

In utilizing continuous multifilament synthetic yarns in the production of textile articles, it is frequently necessary to increase the bulk or covering power of the yarn to a degree approximating that of spun cotton and woolen yarns. The bulking or texturizing processes are generally accomplished by methods such as crimping, heat curling, and analogous techniques wherein the yarn is generally subjected to physical forces capable of deforming the individual filaments under conditions of elevated temperature, and usually in the presence of steam or other plasticizing agents. For example, in stufiier-box crimping operations carried out on multifilament polycaprolactam yarn, the crimp setting conditions quite frequently employed require steam at temperatures between about 120 and 140 C., for periods up to 10 seconds acting on the highly compressed yarn structure. In such stuffer-box crimping operations, the presence of knots is found undesirable in view of the nonmniformities and entanglements they produce. Although it is known that yarn ends can be spliced or united without knotting by application of adhesives, it is generally found that an adhesive bond is easily weakened or broken under the hot, wet conditions generally experienced by yarns during texturing operations or during subsequent hot stretching operations. In order to se cure adequate dry strengths with adhesive agents it has generally been found necessary to extend the length of the spliced section to over /2 inch; and such spliced sections are generally found too stiff or bulky to be textured, and will not pass through the fine guides and needles utilized in textile manufacturing operations. 7

Suitable splicing methods, to be satisfactory in operation must be capable of rapid execution with minimum disruption of the continuous operations of the synthetic fiber manufacturing operation. An acceptable bonding composition must therefore be capable of quickly effecting an acceptable strength splice in a non-tacky condition without materially altering the over-all yarn path.

It is an object of this invention to provide a method for rapidly forming a strong splice between ends of a continuous multifilament polyamide yarn. It is another object of this invention to provide bonding compositions capable of rapidly effecting a strong non-tacky short splice between two ends of a multifilament polyamide yarn, said spliced portion being crimpable. It is a still further object of this invention to provide a method of making uniform knotless textured multifilament polyamide yarn consisting of two or more segments united by a short splice resistant to breaking under hot, wet crimping conditions. Other objects and advantages will become apparent hereinafter.

The objects of this invention are accomplished in general by applying to portions of polyamide multifilament yarns a practically saturated solution of 8%-l7% of a polyamide of formic acid relative viscosity in the high range, suitably the ultrahigh range, at least about 50 and desirably l00250. 'Formic acid relative viscosity, hereinafter designated V. Rel., is determined in aqueous formic acid solution of 11 grams of polymer per ml. of solvent, at 25 C., by ASTM method No. D-789-53T, using polymer which has been leached with hot water to remove the low molecular weight constituents. The solvent used must have a boiling point between 90 C. and C., and the solution must have viscosity at room temperature between 2500 and 6000 centipoises. The impregnated filaments to be bonded are brought into intimate contact over a length suitably about A inch-V2 inch, and the solvent is then allowed to evaporate.

Typically the polyamide composing the filaments bonded in this invention will have V. Rel. in the range from about 30 to about 80. Dissolved polyamide materials useful in the practice of this invention are characterized by recurring carbonamide groups in the backbone chain of the polymer, and include polymers of lactams such as caprolactam and lactams of smaller or larger ring size; polymers of diacid-diamine combinations such as poly(hexamethylene adipamide) and aromatic analogs thereof; and polyamide compounds which have been submitted to chemical modification, such as methoxymethylated polyamides. In order to secure adequate strength, flexibility, and bonding characteristics, the polyamide should have, as above stated, V. Rel. of at least about 50. Higher viscosity materials, up to V. Rel. of 350 and greater, can be used as long as the concentration remains in the specified 8%17% range and the solution viscosity remains in the 25006000 poise range. The V. Rel. can be correlated with polymer number average molecular Weights. V. Rel. of 50 corresponds approximately to number average molecular weight of 15,000; V. Rel. of 65 corresponds approximately to number average molecular weight of 20,000; V. Rel. of 100 corresponds approximately to number average molecular weight of 25,000; and V. Rel. of 350 corresponds approximately to number average molecular weight of 40,000.

The solvents useful in the practice of this invention must have an afiinity for the yarn such that the solvent is capable Patented June 4, 1968 of dissolving the yarn at room temperature. It has been found that the volatility of the solvent should be such that its boiling point is between about 90 C. and 115 C. Solvents having a lower boiling point generally lead to difiiculties in the application of the bonding composition to the yarn, and yield inferior quality splices. Solvents having a boiling point above 115 C. evaporate too slowly to yield a non-tacky splice in reasonably short time. The solvent should be capable of forming saturated solutions of the dissolved or bonding polyamide containing between 8% and 17% of the dissolved polymer at room temperatures, and solutions having viscosities between about 2500 and 6000 centipoises. Viscosity values outside of the herein-prescribed range lead to splices of inadequate quality. It is generally preferred to employ solvents which are relatively non-toxic, non-inflammable and non-corrosive. Mixtures of pure solvents may be employed to secure a composite solvent having the characteristics required in the practice of this invention, in which case minor amounts of solvents having a boiling point within about 25 C. outside the preferred range may be employed, and especially solvent mixtures which form azeotropic combinations. Preferred solvents useful singly or in combinations include: tetrafiuoropropanol, chlorodifiuoroethanol, and other species analogous thereto, e.g., trifiuoroethanol.

The bonding composition may be applied to the yarn ends by hand, as taught in U.S. Patent 1,986,974, or may be applied mechanically by means of rollers, extruders, troughs, belts, or analogous devices. Similarly, the yarn ends containing the viscous solution of polymer may be brought into intimate contact by hand or mechanical devices, and supported mechanically or by hand under no tension until the solvent has partially evaporated. Solvent evaporation may be effected at room or elevated temperatures under static air conditions or by contact with a stream of air. The overlapped portion of the two yarn ends which constitute the splice should be not over /2 inch in length.

Yarns containing splices prepared in accordance with this invention can be subjected, without breaking, to crimping operations employing a stuffer-box as described in U.S. Patents 3,037,260 and 3,031,734. For effective crimping and setting of a polyamide yarn by stuifer-box methods, temperatures in the range of about 110 C. to 140 C. are employed, generally in the presence of moisture which facilitates the crimping and setting operations. Under such conditions, ordinary adhesive-based splices are unreliable, exhibiting failure probabilities in excess of about 1%. It has been found that the reliability of splices under stuffer-box conditions may be determined in advance by measuring the percentage retention of breaking strength of a spliced portion of the yarn after submergence in boiling water for one hour. The maximum permissible loss of splice strength determined by this method, which will still afford reliable stufier-box treatment, is a loss of 5%. Splices prepared in accordance with this invention generally lose less than 3% of their original strength when tested by this method, and exhibit less than 0.1% failures during stuffer-box operations. It is found moreover, that the spliced portion of yarn becomes crimped, thereby maintaining the uniformity of the continuous textured yarn structure.

In the texturing of polyamide yarns by false-twist heat setting methods, as described in U.S. Patents 3,041,814, and 2,987,869, the yarn is subjected to dry heating means which elevate the yarn temperature to the range of 170 C. to 230 C. Under these conditions, ordinary splices exhibit a high failure rate. It has been found that, as a general criterion of satisfactory operation under falsetwist heat setting conditions, the spilced portion should have a breaking strength at least 70% as high as an unspliced portion of the same yarn. Splices prepared in accordance with this invention will generally have breaking strengths in excess of 70% of the yarn tensile strength, frequently having strengths above 80% and 90% of the original yarn, and are found eminently suited for falsetwist heat setting texturing operations.

Although the exact bonding mechanism of the splicing method of this invention is not completely understood, it is quite likely that the bonding composition penetrates and spreads practically throughout the yarn bundle, forming the bundle into a tough, flexible, cohesive mass by wetting, tackifying, and slightly dissolving adjacent filaments, without causing filament weakening or complete inter-filament coalescence. Use of nearly saturated solution is important to avoid any extensive dissolving up of the filaments, which would tend to distort and/ or weaken the joint. The cohesive mass is characterized by the absence of inter-facial areas adhesively attracted by Van der Waals forces of attraction. It is generally well recognized that adhesive bonds, characterized by Van der Waals forces of surface attraction, exhibit depreciated bond strengths when intimately contacted by water, since the water molecules tend to satisfy the attractive surface forces. Cohesive bonds characterized by a continuum of molecules similar or identical to those of the bonded members intermingled at interatomic distances and molecularly blended with both bonded members, are unaffected by water or other chemical or physical entities except those which affect the cohesive state of the bonded members. The critically selected bonding compositions of this invention appear to accomplish the unexpected function of effecting strong cohesive bonding without appreciably attacking or weakening individual filaments. The resulting joint is smooth and only slightly bulging. Upon passage through the feed rolls of a crimping apparatus the joint is flattened out, and in this flattened form it takes a crimp under the same conditions which crimp the filaments composing the spliced yarn of this invention.

The following specific examples are given to illustrate preferred methods of carrying out the present invention. It is to be understood however that these examples are not to be considered as limitative of the scope of the invention. All parts and percentages are by weight unless otherwise indicated.

EXAMPLE 1 A polycaproamide polymer having a molecular weight of 20,000 as determined by viscosity measurement was dissolved in 2,2,3,3-tetrafiuoropropanol (B.P. C.) to the point of saturation. The saturated solution, at room temperature (24 C.), was found to have a viscosity of 3500 centipoises, and a poylmer content of 12%. The bonding composition thus prepared was applied by hand to the ends of a 1200 denier 70 filament polycaproamide yarn having been prepared in conventional manner by melt spinning followed by application of a lubricating oil finish, and drawing. The two yarn ends containing the bonding composition were then rolled together between the fingers and held for about two seconds in the ambient air without applying tension to the freshly formed splice. A non-tacky splice, inch long, was thereby obtained having a breaking strength of 85% of the yarn breaking strength. After immersion of the spliced portion in boiling water for one hour, followed by re-drying prior to testing, the splice was found to lose only 1.5% of its original breaking strength.

Yarn containing splices prepared in accordance with this example was subjected to a continuous stutfer-box crimping operation employing apparatus essentially as described in U.S. Patent 3,037,260, and process conditions essentially as described in U.S. Patent 3,031,734. The yarn was fed as a 60 end flat ribbon to the crimper at a speed of about 750 feet per minute, With a rate of removal from the crimper of about 560 feet per minute, an exit gate weight of 1 1b., and a moist yarn temperature of about C. in the crimping zone. The yarn emerging from the stutfer-box had a crimp frequency of about 12 crirnps per inch, and was crimped in the spliced portions. This yarn was then subjected to a continuous stretching operation at 175 C. under 750 grams tension; the purpose of said stretching operation being to impart latent recovery properties to the crimped yarn so that textile articles prepared therefrom would develop improved bulk by exposure of the article to elevated temperatures. The yarn thus textured was convolutely wound onto 1b., at profile spools.

The packaged yarn thus prepared was employed in twoply form in the manufacture of a tufted carpet having six tufts per inch and 20 ounces of fiber per square yard of carpet. The tufting needle had an oval shaped eye inch high and inch wide, and operated at a rate of 520 tufts per minute.

In the over-all operation of yarn texturing, stretching and tufting, no splice failures occurred during the passage of 25-6 splices through the entire operation in the manufacture of a carpet. After dyeing and finishing, the carpet was of highly uniform quality with none of the splices being visibly detectable.

By way of contrast, a bonding composition outside the purview of this invention was prepared employing the same bonding polymer and solvent as in this example, except that the solution was prepared as an unsaturated solution containing only 7% of dissolved polymer and having a viscosity of about 2000 centipoise. When applied in the same manner to the yarn of this example, a splice was obtained having only about 55% of the yarn breaking strength, and was found unsatisfactory in the yarn texturing, stretching and tufting process described above.

By way of further comparison, yarn was spliced employing the bonding composition of this invention described in this example, employing conditions identical to those employed above in this example except that the length of the spliced portion was made to he /s inch, thereby outside the scope of this invention. This yarn was then subjected to the texturing, stretching and tufting operation described above. It was found however a failure frequency of approximately 2.5% occurred during passage of the spliced portions through the tufting needle.

EXAMPLE 2 TABLE I Polymer Viscosity of Bonding Breaking Strength of Molecular Weight Composition 1 Splice, Percent 2 1 In centipoises. 2 As percent of breaking strength of the yarn.

As the data of Table I indicate, molecular weights of the bonding polymer below about 15,000 (V. Rel. below about 50) provide splices having unsatisfactory breaking strength. Polymers having formic acid relative viscosity much above about 350 generally provide, at the desired concentrations, solution viscosities above 6000 centipoise which results in excessive tackiness leading to stringing of the composition during application, whereby protruding short filaments are formed.

EXAMPLE 3 A polycaproarnide polymer having a molecular weight of 20,000 was dissolved to the point of saturation in a mixture of 45 parts of 2,2,2 trifiuoroethanol (B.P. 74 C.) and 55 parts of 2,2,'3,3 tetrafluoropropanol (B.P. 110 C.). The bonding composition thus prepared was applied in amounts less than about /2 gram to the ends of a 1200 denier 70 filament polycaproarnide yarn. The two yarn ends containing the bonding composition were rolled together and held under a stream of warm air for about two seconds without applying tension to the freshly formed splice. A non-tacky splice, inch long, is thereby obtained having a breaking strength of of the yarn breaking strength. After immersion of the spliced portion in boiling water for one hour followed by re-drying prior to testing, the splice was found to lose only 1.5% of its original breaking strength.

In applying the bonding composition of this example in similar fashion to yarns of poly(hexamethylene adipamide), splices are obtained having breaking strengths about 82% of yarn strength; said yarns performing satis factorily in stutfer-box and false-twist heat setting opera tions to give textured yarns wherein the spliced portion receives an angular or helical crimp analogous to unspliced yarn portions.

EXAMPLE 4 A poly (hexamethylene adipamide) polymer of molecular weight 30,000 having been methoxymethylated by treatment with methanol and formaldehyde, was dissolved to the point of saturation in a mixture of 60 parts 2,2,3,3 tetrafiuoropropanol and 40 parts methanol. The bonding composition thus prepared, having a viscosity of 4500 centipoise, was applied to the ends of a 2400 denier filament polycaproarnide yarn. The two yarn ends containing the bonding composition were splayed, placed in /2 inch abutting contact, and held under a stream of cool air for about three seconds without applying tension to the freshly formed splice. A non-tacky splice was thereby obtain having a breaking strength of 90% of the yarn breaking strength.

By way of contrast, a non-polyamide polymer, polymethyl methacrylate, outside the purview of this invention but nevertheless well known as an adhesive ingredient, was employed as the bonding polymer in the practice of this invention. It was found that, regardless of specific sol-vent, solution concentration, or solution viscosity, splices could not be produced having breaking strengths higher than 52% of yarn strength. It was also found that such splices exhibited adhesive rather than cohesive bonding in view of their excessive strength losses of 10%- 50% in boiling water.

By employing bonding compositions containing less than 17% dissolved polymer, and dissolved polymers having molecular weights below about 40,000, the bonding compositions of this invention can successfully be employed without stringing, i.e., the formation of bridging filaments from the dissolved polymer. The stringing effect, characteristic of previous compositions of dissolved polymer employed in gluing or coating operations is especially undesirable in the course of the splicing process of this invention since the presence of protruding filamentary material near the splice leads to snagging during weaving operations, and the stringing effect would create problems in the handling of the bonding composition during the splicing operation.

The bonding compositions of this invention may also be employed to consolidate untwisted yarns so that they will secure the runability characteristics of twisted yarns. This may be accomplished by applying small amounts of the bonding composition to a running zero twist yarn at points thereon spaced about 1 inch apart. The flexible nature of the inter-filament bonding causes essentially no adverse change in the physical or aesthetic qualities of the yarn. The bonding compositions are also useful in the bonding of films, multi-yarn cords, and woven and nonwoven polyamide textile articles; and are generally unaffected by the presence of lubricating oils, dyes, antistatic agents, water repellants, or other chemical auxiliaries commonly employed with polyamide fibers. The bonding compositions may contain indicating agents such '7 as fluorescent materials to locate the splices or to distinguish one type of splice from another under ultraviolet light.

As many apparently widely diiferent embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that this invention is not limited to the specific embodiments thereof except as defined in the appended claims.

We claim:

1. A bonding composition comprising a practically saturated solution of a polyamide having formic acid relative viscosity of at least about 50, in a solvent having a boiling point between 90 C. and 115 C., said solution containing between 8% and 17% of said polyamide and having a viscosity between 2500 and 6000 centipoises at room temperature.

2. The bonding composition of claim 1 wherein said solvent comprises an organic alcohol.

3. The bonding composition of claim 1 wherein said solvent consists essentially of 2,2,3,3-tetrafiuoropropanol and wherein the polyamide is poly-e-caproamide having formic acid relative viscosity by ASTM Method D7 89- 53T of 50350.

4. A process for uniting filaments of multifilament polyamide yarns comprising applying to said yarns the bonding composition of claim 1, bringing said filaments into intimate contact, and evaporating the solvent of said bonding composition while said filaments are maintained in supported contact.

5. The process of claim 4 wherein yarn ends are rolled together priror to completion of the splicing process, over a length of about fit- /z inch.

References Cited UNITED STATES PATENTS 1/1935 Kellogg 15615=8 4/1964 Castle 893 FOREIGN PATENTS 961,763 11/ 1962 Great Britain.