US3111364A - Process for drawing a continuous, unwashed, undrawn polycapolactam filament - Google Patents

Description

3,111,364 PROCESS FOR DRAWING A CONTINUOUS, UNWASHED, UNDRAWN Nov. 19, 1963 A. F. G. MEERDINK POLYCAPROLACTAM FILAMENT Flled Aprll 2a, 1960 ANTON F. 6. MEERDINK BYWfM ATTORNEY United States Patent PRQCESS FGR DRAWING A CQNTINUOUS, UN-

WASEED, UNDRAWN PQLYCAERSLACTAM FEAMENT Anton Frederik George Meerdinh, Velp, Netherlands, as-

signor to American Erika Corporation, Erika, Nil, a corporation of Delaware Filed Apr. 28, 1960, Ser. No. 25,257 Claims priority, appiication Netherlands May 13, 1959 5 Claims. (Ci. 1848) This invention relates generally to synthetic linear polycaprolactam yarns and threads and more particularly to synthetic linear polycaprolactam for use in knitted articles and to a process for producing the same.

In the prior art, polycaprolactam threads and yarns which have been cold drawn and then twisted are used in knitted articles. The stitches in these articles are long and narrow with the result that the article is narrower than those produced from polyhexamethylene adipamide. More yarn is thus required to produce the same size article with the attendant increase in cost.

In addition, the snag resistance of the articles knitted from polycaprolactam yarn is very poor. Snag resistance is the ability or" the knitted article to resist the pulling out of the stitches. A stitch that has been pulled out or snagged will project outwardly from the article in the form of a small loop.

It has been proposed that these difficulties of polycaprolactam yarns be overcome by washing the drawn and twisted yarns in hot water. This is undesirable in that it requires an additional processing step in the manufacture of these yarns.

it is, therefore, an object of the present invention to provide a synthetic linear polycaprolactam yarn that is free of the CililiClllikS of the prior art.

it is a further object of this invention to provide a process for producing polycaprolactarn yarns for use in knitted articles.

An additional object of this invention is to provide a polycaprolactam yarn that when used in knitted articles produces an article of greater width and improved snag resistance.

A further object of this invention is to provide a process for manufacturing polycaprolactam yarn for use in knitted articles whereby snag resistance and width of the articles are improved.

These and other objects or" this invention will become apparent from a reading of the following detailed description taken in conjunction with the drawing.

it has been found that the objects of this invention can be accomplished by providing a synthetic linear polycaprolactam yarn of a denier of less than 50. The yarn must also have a boiling water shrinkage of at least 9% and a permanent birefringence when subjected to a 20% elongation. Yarn of these characteristics may be obtained by drawing undrawn polycaprolactam yarn in a single drawing operation and during the drawing operation, heating the yarn to an internal temperature of 140 to 160 C.

The undrawn polycaprolactarn yarn may be obtained by conventional processes well know to those skilled in the art. For instance, caprolactam may be polymerized by known methods and extruded into filaments which are collected in undrawn form. The packages of undrawn yarn are then subjected to a drawing and twisting operation which operation may be performed on a conventional drawtwister.

To insure that the boiling water shrinkage is at least 9%, the drawn and twisted yarn should not be washed in hot water. Such a washing operation is undesirable and it also reduces the boiling water shrinkage to less than 6%.

The birefringence of the yarn of this invention is permanent after a 20% elongation. This is, if at any time in the future, the yarn is subjected to a temporary elongation of 20%, the birefringence both before and after the elongation will be the same. This is contrary to ordinary cold drawn polycaprolactam yarn. There is no decrease in birefringence of the cold drawn polycaprolactam yarn if immediately after drawing and twisting it is subjected to a temporary elongation. However, if the yarn is elongated at some time in the future after, for instance, about four weeks, there will be a substantial reduction in birefrin ence of this cold-drawn yarn. Such a decrease does not occur at this time for the yarn according to this invention.

It is believed that the desired wide and round loop formation in knitting is the result of the birefringence, remaining the same after a lapse of time and an elongation. This becomes important because the yarn will be subjected to elongation in the knitting process. Thus, it can be seen that this elongation will result in a decrease in the birefringence of cold-drawn polycaprolactarn with an attendant undesirable stitch formation. However, if yarn according to this invention is used, there will be no decrease in birefringence after this elongation with the result that this yarn produces the desired stitch formation. it is, therefore, important that the birefringence remain the same even after long periods of storage because in normal processing several weeks and even months elapse between the production of the yarn and its processing into knitted article It should be understood that this above is a theory and is not to be construed as limiting this invention.

The stitch formation obtained by using freshly drawn and twisted polycaprolactarn yarn is slightly better than that which had been drawn and twisted several weeks before. However, this stitch formation is inferior to that of the polycaprolactam yarn of this invention.

The elongation used in measuring the decrease in birefringence of polycaprolactam yarn according to this invention is 20%. The yarns are subjected to this elongation for a short period or" time, usually about five seconds.

As indicated above, the polycaprolactam yarns of this invention are obtained by drawing undrawn synthetic linear polycaprolactarn yarn and heating said yarns during at least a portion of said drawing to an internal temperature of to C. Even in drawing yarns by the cold-drawing method, the yarns are heated. This heat is produced by friction during the passage of the yarn over the cold drawn pin. However, the temperature of the yarn of less than 50 denier is less than 100 C. and even lower for yarn of the preferred denier of less than 32. Yarns produced by this method which are heated during drawing, but to less than the required internal temperature do not produce the desired wide and 3 round stitch upon knitting. In addition, the birefringence of these yarns decreases upon being subjected temporarily to a 20% elongation.

If yarn of a denier of less than 50 is heated during a portion of the drawing to a temperature of 140 to 160 C., the polycaprolactarn yarn thus obtained will produce, upon knitting, a wide and round stitch. In addition, the birefringence of this yarn will not decrease when subjected to a 20% temporary elongation. This elongation may occur at any time subsequent to the drawing and heating operation.

The internal temperature of these yarns may be raised to the required 140 to 160 level by several met. ods. For instance, the draw pin or pins may be heated to a temperature of 100 to 110 C., preferably 105 C. This heat plus that generated by friction of the yarn as it passes over the draw pin, raises the internal temperature of the yarn to 140 to 160 C.

The use of draw pins to localize the drawing of synthetic linear polycaprolactam is well known. The yarn is passed one or more times around a pin which is positioned between the feed roller and draw roller of a conventional draw-twisting machine. The wraps around the pin are to localize yarn drawing to an area immediately adjacent the pin.

In normal operations, no heat is supplied to the draw pins from any external source other than the yarn. The only heat that is generated is that caused by friction of the yarn as it passes over the pin. When processing yam of less than 50 denier, the yarn will, by radiation and conduction, have an internal temperature of less than 100 C.

When yarn of less than 50 denier is passed over the draw pins to which heat from another source is applied to raise the temperature of the pin to 100 to 110 C., the yarn will have an internal temperature of 140 to 160 C. This temperature can be obtained at the 531.3 or higher, if desired, speeds as that used in the cold-drawing operation.

The draw pins may be heated by any conventional means, such as by electric heating elements. In addition, a heated liquid or vapor may also be used without departing from this invention.

It should be understood that successful operation of this invention does not require that the yarn be heated to the requisite internal temperature throughout the drawing operation. It is only required that the yarn be heated to this temperature during at least a portion of the drawing operation. Thus, it is possible to use heated plates or tubes between the draw pin and the draw roller to accomplish the required internal temperature. This is because a portion of the drawing will occur when the yarn is passed over the heated plate or through the heated tube;

The temperature of the plate or tube should be higher than that of the above-mentioned raw pins because even though some drawing occurs after the yarn leaves the draw pin, it will not be as much as that which occurs at, the draw pin; thus, little additional heat will be developed by friction. The temperature of the plate or tube should be adjusted to the time during which the yarn passes over the plate or through the tube. Thus adjustment is by means known to those skilled in the art. It should be understood that the adjustment should be sufilcient to insure that the yarn is heated to 140 to 160 C. during this latter drawing stage.

For example, if a single filament polycaprolactam yarn of a denier suflicient to yield after drawing a yarn of 15 denier is to be drawn at a speed of 400 meters per minute, the heated plate or tube should have a yarn passageway of 5 centimeters and a temperature of 170 C. This will insure that the yarn is heated to an internal temperature of 140 to 160 C.

It is also possible to practice this invention by heating the draw roller. This, is of course, the least preferred method of operation because of the small amount of drawing that occurs on the draw roller.

This invention will now be described with reference to the annexed drawing. It should be understood that this drawing illustrates but one apparatus capable of performing this invention.

Referring now to the drawing, reference numeral 10 denotes a synthetic linear polycaprolactam yarn package obtained from a conventional extrusion and winding operation. Package 10 is placed on supply point 11 of a conventional draw twister indicated generally at 12. Yarn or thread 13 is withdrawn from package 10 by feed roller 1 and thence around draw pin 16, which is heated to C. to C. by electrical current supplied from a source (not shown) through wires 15. Yarn 13 is substantially drawn at pin 16 by the pulling action or" draw roller 17, around which the yarn is passed. Yarn 13 is heated to an internal temperature of to C. by the combination of the friction generated by its passing around pin 16 and the additional heat supplied to pin 16. The difference in speed of draw roller 17 and feed roller 14 determines the draw ratio to which yarn 13 is subjected.

After leaving draw roller 17, yarn 13 is twisted and collected on pirn 18 by conventional twister take-up device All of the equipment discussed above is supported in a conventional manner and the supports have not been shown for purposes of clarity.

The following specific examples are offered merely for the purpose of illustration and are not to be considered as limiting the scope of this invention.

EXAMPLE I An unwashed and undrawn synthetic linear polycaprolactam yarn of a denier of 133 and having four filaments was withdrawn from a yarn package on a conventional draw twister by a feed roller. From this roller, the yarn was passed over a draw roller operating at a suflicient speed greater than the feed roller to draw the yarn 3.4 times its length between the two rollers thereby obtaining a yarn of a denier of 39. The speed of the draw roller was 375 meters per minute.

The yarn encircles, two draw pins which were positioned between the feed and draw rollers over an arc of 360. These pins had a diameter of 12 mm. and were heated to a temperature of 105 to 110 C. The yarn from the draw roller was twisted an collected by a conventional ring twister takeup.

A further sample of this yarn was processed over the same machine, except that the draw pins were not heated by an external supply of heat. The following Table I illustrates properties of these yarns. The flat width of the stocking is measured by laying flat a stocking that has been stabilized on a form in a stream chest in a conventional manner. The flat width of the stocking is proportional to the width of the stitch.

EXAMPLE H An unwashed and undrawn, mono-filament, polycaprolactam yarn was withdrawn from a yarn package of a conventional draw twister by a feed roller. The yarn was passed from the feed roller 360 around an unheated draw pin to and around a draw roller. The yarn was passed over a slighlty curved plate heated to C. The plate Was positioned between the draw pin and draw roller and had a yarn-contacting surface of cm. in length. The yarn was stretched between the feed roller and draw roller to a denier of and the yarn had an internal temperature or" 143 C. as it left the heated plate.

A similar yarn was processed in the same manner as above, except that the yarn was not passed over a heated plate, The following Table 11 illustrates the properties of these two yarns.

Table H Heated Without plate heated plate Tensile strength/grams per denier 7. 0 6.7 Elongation at rupture, percent 28 30 Boiling water shrinkage, percent. 13.3 13. 4 Specific birefringence 552 10- 535 10- Specific birefringence after elongat. 11 (determined 6 weeks later) 552x10 518X10-4 Flat width of thigh of stocking (cotton machine, 66 gauge), cm 18.0 17.3

EXAMPLE 111 An unwashed and undrawn, mono-filament, 64 denier, polycaprolactarn yarn was processed in a manner similar to that of Example 1, except that the yarn was drawn by passing it 360 around a single draw pin, having a diameter of 12 cm. The draw pin was heated to a temperature of 105 to 110 C. The yarn was drawn 4.3 times its length to a denier of 15.

A similar yarn was processed in an identical manner, except the draw pin was not heated. The following Table III illustrates the properties of these two samples:

It can be seen from the foregoing examples that this invention produces a yarn that when used in knitted articles has an improved Width and one whose specific birefringence does not decrease when the yarn is subjected to a 20% elongation. Such yarn has improved snag resistance.

It should be understood that various modifications may be made in this invention without departing from the spirit and scope of this invention which is to be limited only by the following claims.

What is claimed is:

1. A process for drawing a continuous, unwashed, undrawn polycaprolactam filament to produce a fine denier yarn comprising passing said undrawn, unwashed filament through a drawing zone wherein said filament is heated in at least a portion of said drawing zone to an internal temperature of from about C. to about C., drawing said filament a multiple of its original length in one drawing operation in said drawing zone, to provide a drawn yarn having a denier of less than about 50, a boiling water shrinkage of at least 9%, and a permanent birefringence when subjected to 20% elongation, and thereafter collecting said drawn yarn without subjecting it to a further drawing operation.

2. The process according to claim 1 wherein the drawing of said filament in said drawing zone is carried out by passing said filament around at least one unheated drawing pin and said heating of said filament is carried out by means separate from said drawing pin.

3. The process according to claim 2 wherein said heating is carried out by passing said filament over the surface of a hot plate.

4. The process according to claim 2 wherein said heating is carried out by passing said filament through a heated tube.

5. A process for drawing a continuous, undrawn, unwashed polycaprolactam filament to produce a fine denier yarn comprising passing said undrawn, unwashed filament through a drawing Zone, wherein said filament is heated to an internal temperature of from about 140 C. to about 160 C. by passing around at least one heated drawing pin,

rawing said filament a multiple of its original length in one drawing operation in said drawing zone to provide a drawn yarn having a denier of less than about 50, a boiling water shrinkage of at least 9%, and a permanent birefringence when subjected to 20% elongation, and thereafter collecting said drawn yarn from said drawing zone without subjecting it to a further drawing operation.

References Cited in the file of this patent UNITED STATES PATENTS 2,577,915 Piller et a1 Dec. 11, 1951 2,686,955 Luther Aug. 24, 1954 2,719,776 Kummel Oct. 4, 1955 2,733,122 Herele et al Jan. 31, 1956 2,735,840 Lynch Feb. 21, 1956 2,750,653 White June 19, 1956 2,768,057 Friederich Oct. 23, 1956 2,794,700 Cheney June 4, 1957 2,869,972 Head et al. Jan. 20, 1959 FOREIGN PATENTS 811,349 Great Britain Apr. 2, 1959

Claims (1)

1. A PROCESS FOR DRAWING A CONTINUOUS, UNWASHED, UNDRAWN POLYCAPROLACTAM FILAMENT TO PRIDUCE A FINE DENIER YARN COMPRISING PASSING SAID UNDRAWN, UNWASHED FILAMENT THROUGH A DRAWING ZONE WHEREIN SAID FILAMENT IS HEATED IN AT LEAST A PORTION OF SAID DRAWING ZONE TO AN INTERNAL TEMPERATURE OF FROM ABOUT 140*C. TO ABOUT 160*C., DRAWING SAID FILAMENT A MULTIPLE OF ITS ORIGNAL LENGTH IN ONE DRAWING OPERATION IN SAID DRAWING ZONE, TO PROVIDE A DRAWN YARN HAVING A DENIER OF LESS THAN ABOUT 50, A BOILING WATER SHRINKAGE OF AT LEAST 9%, AND A PERMANENT BIREFRINGENCE WHEN SUBJECTED TO 20% ELONGATION, AND THEREAFTER COLLECTING SAID DRAWN YARN WITHOUT SUBJECTING IT TO A FURTHER DRAWING OPERATION.

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