US3088792A - Thermoplastic yarns - Google Patents

Description

y 1963, w. c. MATHIS, JR 3,088,792

THERMOPLASTIC YARNS Filed June 29. 1959 INVENTOR. WILLIAM C. MATHIS JR.

j/LM AJ- BY A TO EY atet 3,088,792 Patented May 7, 1963 3,088,792 THERMOPLASTIC YARNS William C. Mathis, J12, Asheville, N.C., assignor to American Enka Corporation, Enka, NC, a corporation of Delaware I 7 Filed June 29, 1959, Ser. No. 823,718 1 Claim. (Cl. 8-1301) This invention relates in general to the treatment of thermoplastic yarns and more particularly to a process for producing thermoplastic yarns having improved shrinkage characteristics and which upon being woven into a fabric is substantially free of the phenomenon known as pirn barr.

This invention is applicable to thermoplastic yarns formed from polyamides such as polycaprolactam, polymetaxyleneadipate and diamine-dicarboxylic acid condensation polymers such as polyhexamethylene adip-ate, from polyesters such as polyethylene terephthalate, and from polyolefins such as polypropylene. These thermoplastic yarns may be produced by grid and extruder spinning, or other melt spinning processes wherein heat and pressure are combined to transfer starting materials into elongated filaments or fibers. These yarns usually are drawn after extrusion, that is, permanently elongated under stress in the solid state, in order to yield a product of improved strength and to provide molecular orientation in a longitudinal direction. Yarns produced in this manner exhibit an inherent capacity to shrink, or residual shrinkage, when subjected to hot water or other liquids, in the neighborhood of 100 C. In other Words, a given sample of this yarn will contact lengthwise when exposed to 'hot water in a relaxed condition. Such shrinkage greatly reduces the yarn tensile strength and results in a highly non-uniform molecular orientation.

It can be seen from the foregoing that fabrics woven from what will be termed herein high shrink yarn will be substantially distorted if subjected to washing, for example, at elevated temperatures. For this reason, ways and means have been suggested not only for raising the shrinkage temperature of this type yarn, but also for preshrinking the same prior to release on the commercial market. For further discussion of these systems, attention is invited to Us. Patent No. 2,325,060, issued on July 27, 1943, to H. G. Ingersoll, which teaches that heat setting drawn yarn while permitting relaxationof the same improves the shrinkage characteristics thereof.

Thermoplastic yarns, particularly polyamide yarns, are collected on packages known as pirns. This collection normally takes place after drawing and twisting. The package is fashioned in a manner so that there is more yarn collected in the middle than on the ends. A typical package is shown in the drawing as part of the collec tion means 15. Yarn may be taken from this package and processed in a conventional manner. Such yarn when used as a filling in woven fabrics produces a phenomenon known as pirn barr, which is an undesirable streakiness in the fabric.

Surprisingly enough, it has now been found that heat setting the drawn yarn while maintaining the same at constant length produces a yarn having even lower shrinkage characteristics than that described in the aforesaid patent and also permits use of this yarn in a fabric without the production of barr. As a result of this newly discovered phenomenon, it is possible not only to combine the drawing and treating stages in a practical man- .ner, but to accomplish this with no substantial change in existing drawing machinery. Although patentee Ingersoll suggests a continuous drawing-treating procedure, the same cannot be performed on commercially available drawing apparatus because his system requires the use of 2 relaxing rollers which must have a surface speed lower than that of the draw or feed rollers.

A primary object of the invention, therefore, is to provide a process for reducing shrinkage of thermoplastic yarns which does not have the disadvantage of known systems.

Another object of the present invention is to provide a commercially feasible process for drawing and reducing the shrink-age characteristics of thermoplastic yarns.

Still another object of this invention is to provide an improved process for drawing and reducing the residual shrinkage of thermoplastic yarns which can be accomplished on substantially unmodified drawing or drawtwisting apparatus.

A further object of the present invention is to provide a process for producing low shrinkage yarn which requires no additional major machinery and no additional training of operating personnel.

A further object of this invention is to provide a process for substantially eliminating pirn barr.

Still another object of this invention is to provide a thermoplastic yarn of reduced residual shrinkage and which when woven into a fabric is substantially free of pirn barr.

A more specific object of this invention is .to provide a system for threading up slightly modified but conventional yarn drawing equipment in order that the same will simultaneously and continuously orient the molecules and reduce the residual shrinkage of thermoplastic yarns.

These and other objects may be accomplished in accordance with the present invention .by the addition of a heated pin or roller at each processing station'of a drawing machine, and by passing yarn from the draw roller or godet over this heated pin and thereafter passing the heat treated yarn a plurality of turns about the draw roller and existing separator roller. Inasmuch as the yarn passes from the draw roller to the heat treating pin and then back to the draw roller, it can be seen that there is neither yarn elongation nor yarn relaxation during the heat treating stage, and the yarn is permitted to cool by contact with the unheated draw roller while its length is maintained constant.

Other objects and advantages willv become apparent upon study of the following detailed explanation taken in conjunction with the accompanying drawing, wherein:

The FIGURE is a perspective elevational view of a known yarn drawing machine modified in the manner described herein, and showing the thread-up scheme between the draw roller-separator roller and heated auxiliary pin. Only one treating station is shown, it being understood that others should be identical in construction to that described hereinbelow.

The framework of the machine illustrated in the figure is immaterial to this discussion and, consequently, has been omitted for the sake of clarity. Moreover, although a conventional drawtwisting machine has been selected to illustrate the principles of this invention, it should be understood that the twister take-up is not essential and could be of the winder or flat take-up type.

The usual drawtwisting machine, indicated. generally by reference numeral 10, is provided with feed roller 11, pressure roller 12, cylindrical draw roller or godet l3, cylindrical separator roller '14-, and twister collection means 15, all disposed in a "generally vertical alignment, and all supported from a conventional machine frame, not shown. The surface speed of draw roller 13 of course is greater than that of feed roller 11, usually having a ratio of at least three to one, and the same is unheated.

Mounted in the path of yarn travel between feed roller 11 and draw roller 13 is a twin pin arrangement 16, 17, which functions to confine, at least to some extent, the point of drawing. These pins may be heated either electrically or otherwise, if necessary or desired. Further, other draw pin arrangements could be utilized equally effectively as the pins shown, insofar as concerns this invention. It is not necessary that yarn 18 be wrapped completely around, or snubbed at, either pin 16 or 17. Consequently, these pins may and usually do extend normal to the machine face or front.

- The twister take-up or collection means comprises a spindle 20 mounted for rotation about a vertical axis, a drive sheave or pulley 21, a drive belt 22, and a vertically reciprocating ring mechanism 23, as is known in the art. A suitable thread guide 30 is provided for confining the apex of yarn ballooning around the take-up package, also as known.

An auxiliary heat treating pin 24 is secured to the machine frame immediately adjacent to, but slightly offset from, separator roller 14. Although a heated roller should operate as well as pin 24, use of such would require a bearing-type mounting bracket and of course would produce complications with regard to heating means and heat transfer or thermal efliciency. In order to modify existing drawtwisting machinery to practice this invention, 'it is necessary only to provide a stationary pin 24, a suitable mounting bracket 25, and heating means 26 at each yarn processing station to be converted. It is desirable, of course, also to provide means such as 27 for controlling the temperature of pin 24. This could be either a thermostatic or manually operable rheostatic control in case electrical heating means such as that illustrated is utilized. Suitable heating elements per se, and controls therefor, not only are well known but are commercially available at low cost, and will not be discussed in detail here. The surface of pin 24 may be smooth or rough as is obtainable by means known to the art such as by sand-blasting. Although either surface may be used, slightly improved results are obtainable with a rough surface.

Thermoplastic yarn 18 processed in a conventional manner on the apparatus described above is fed at a controlled linear speed vby feed roller 11 into the drawing zone, or pins 16, 17. These pins may or may not be heated, depending on the type of yarn processed and the desired end product. In other words, yarn 18 may be cold drawn, warm drawn, or hot drawn, as desired.

From the drawing zone, yarn 13 passes alternately around draw roller 13 and separator roller 14, as indicated by arrows. At least three wraps as shown are required to provide the frictional force necessary for drawing. From the draw roller, yarn 18 usually passes directly to the twister take-up 15 through the thread guides 30. The drawing or longitudinal molecular orientation resulting from this process produces a high strength yarn, but does not alleviate the residual yarn shrinkage or pirn barr problems discussed supra.

As previously explained, it was thought heretofore that added heat treatment, or heat treating subsequent to molecular orientation, coupled with controlled yarn relaxation produced the most desirable yarn shrinkage characteristics. Although some improvement results from the known system, an even better result can be obtained if the yarn is maintained fixed at the original drawn length during subsequent heat and cooling treatments.

Accordingly, in the practice of this invention, yarn 18 is fed directly from the first, or draw, stage of draw roller 13 to and over heated pin 24, and then to a second, or cooling stage of the draw roller 13 around which the yarn passes at least three turns. From the second stage of said roller the yarn is passed to the collection means 15. Although the yarn as shown is wrapped three times around the treating stage of roller 13, a greater number of turns might be necessary, this of course being dependent upon surface characteristics of the particular yarn processed. The surfaces of draw roller 13 and separator roller 14 may be smooth or rough as is obtainable by means known to the art such as sand-blasting. Either surface may be used without significant differences in results.

From the foregoing it can be seen that undrawn yarn 18 entering drawtwisting machine 10 not only is continu ously stretched in the usual manner but also is heat treated and cooled while maintaining fixed its drawn length to overcome the inherent residual shrinkage, or tendency to shrink when subjected to elevated temperatures in relaxed condition. In addition, it was unexpectedly found that when this yarn was woven into a fabric it did not produce pirn barr.

The following are specific examples of the application of this invention and are to be considered merely as illustrative of this invention.

Example I A 40 denier, 8 filament polycaprolactam yarn was fed into the drawtwisting machine shown in the figure, and drawn at a linear speed of 1250 feet per minute. This drawn yarn was passed one turn over a 1 /2 inch pin 24 heated to a temperature of 180 C. and then passed back onto the draw roller and separator roller for three wraps, after which the drawn and treated yarn was collected by take-up device 15.

A predetermined length of the yarn described above next was submerged in boiling water for a period of about minutes, removed, and measured. It was found that this yarn had shrunk only about 7%. The normal residual shrinkage for this particular yarn is about 13%. It is evident, therefore, that the residual shrinkage was reduced by 46%. Other tests indicate that this shrinkage can be reduced from 50 to depending on the temperature of pin 24 and the type of yarn treated.

Some of this yarn was collected on pirns and stored for up to three months. The yarn was then processed in a conventional manner and used as a filling in a woven fabric. This fabric was examined for pirn barr and none was found to exist.

Example 11 A 70 denier, 34 filament Vitel yarn was fed into the drawtwisting machine shown in the figure, and drawn at a linear speed of 860 feet per minute. Vitel is the trademark of Goodyear Tire and Rubber Company for a copolyester obtained from the polymerization of ethylene glycol, terephthalic acid and isophthalic acid. This drawn yarn was passed one turn over a 1 /2 inch pin 24, heated to a temperature of 140 C., and then passed back onto the draw roller and separator roller for three wraps, after which the drawn and treated yarn was collected by takeup device 15.

This yarn was subjected to the same test as in Example I and it was found to have a residual shrinkage of 10.4%, whereas the normal residual shrinkage for this type yarn is about 16 This represents a reduction in residual shrinkage of 35%.

Example 111 A denier, 16 filament polypropylene yarn was processed as in Example 1, except that the speed of drawing was 650 feet per minute, a single draw pin was used and heated to 100 C., and the pin 24 was heated to a temperature of C. It was found that this yarn had a residual shrinkage of about 40-45%, whereas similar yarn not processed according to this invention had a residual shrinkage of about 7.5-8.0*%. This represents a reduction in residual shrinkage of 40-50%.

Example IV A 70 denier, 32 filament polymetaxyleneadipate yarn was processed as in Example III, except that the draw pin was heated to 70 C. and pin 24 was heated to about C. This yarn had a residual shrinkage of about 10.6%, Whereas similar yarn not treated according to this invention had a shrinkage of about 21%. This represents about a 50% reduction in residual shrinkage.

The improved products described above were obtained without additional handling of yarn, with no increase in processing time, and at the expense of only a slight modification to the drawtwisting apparatus. The foregoing examples illustrate that this novel process is equally applicable to thermoplastic yarns formed from polyamides such as polycaprolactam, polymetaxyleneadipate, and diamine-dicarboxylic acid condensation polymers such as polyhexamethylene adipate, from polyesters such as polyethylene terephthalate, and from polyolefins such as polypropylene.

Inasmuch as other modifications and end uses will become apparent to those skilled in this art, it is intended that the scope of the present invention be limited only to the extent set forth in the following claim.

What is claimed is:

A process for simultaneously producing both drawn and heat treated yarn comprising the steps of feeding successive lengths of thermoplastic yarn having substantially unoriented molecules into a drawing zone at a first rate of speed, passing said yarn from said drawing zone directly to a cylindrical draw roller having a peripheral speed about three times the said first rate of speed, wrapping the yarn at least three times about said draw roller whereby drawing of the yarn to a substantially oriented molecular condition will occur, deflecting the yarn from said draw roller and subjecting the yarn to a dry heat treatment at a temperature of about to C. and returning the thus heat treated yarn to the surface of said draw roller while maintaining the drawn length thereof fixed during said deflecting, heating and returning stages, rewrapping the yarn at least three times about said roller in order to maintain the drawn length thereof fixed during cooling, and collecting said drawn and heat treated yarn in package form.

References Cited in the file of this patent UNITED STATES PATENTS 2,197,896 Miles Apr. 23, 1940 2,199,411 Lewis May 7, 1940 2,289,232 Babcock July 7, 1942 2,298,868 Catlin Oct. 13, 1942 2,307,846 Miles Jan. 12, 1943 2,325,060 Ingersoll July 27, 1943 2,346,208 Conaway Apr. 11, 1944 2,509,741 Miles May 30, 1950

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