US2325060A - Nonshrinking yarn - Google Patents

Description

July 27 W43 H. G. INGERsoLL 2325,06@

NON- SHRINKING YARN Filed Feb. 25, 1942 2 Sheezls-Sheel 2 INVENTOR HEHIIE. @51151311 ATTORNEY Watented July 27, 1943 NONSHRINKIN G YARN Henry G. Ingersoll, Wilmington, Del., assgnor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware Application February 25, 1942, Serial No. 432,369

3 Claims. (Cl. 8-11 5.5)

This invention relates to iilaments from normally solid ethylene polymers and more particularly to the manufacture of filaments of this kind having improved shrinking characteristics.

Fibers and laments useful in textiles and for other purposes can be obtained by melt extrusion or by other methods from the high molecular weight, normally solid ethylene polymers prepared by polymerizing ethylene under pressure. The nlaments thus obtained can be cold drawn, that is permanently elongated under stress in the solid state to yield products oi improved strength, which by X-ray diffraction analysis exhibit molecular orientation along the ber axis. Completely oriented ethylene polymer filaments begin to shrink at 45-50 C. This shrinkage greatly reduces their tensile strength and leaves them in a highly non-uniform condition. Such shrinkage, for example, warps and distorts fabrics made from such filaments so completely as to materially reduce their utility. Similar shrinknge eliects are encountered in the case of filaments obtained from other high molecular weight polymers, such as nylon, vinylidene chloride polymers, and from the vinyl chloride-vinyl acetate interpolymer known as Vinyon. Various stretch-setting processes designed to avoid this difficulty are described in the prior art. Certain of these processes improve to some extent the shrinkage resistance of normally solid ethylene polymer laments, but none produces the result desired. The previously used method of preshrinking, in which relaxed iilaments are shrunk by heat treatment, is ineffective in the case of ethylene polymer nlaments.

This invention has as an object the manufacture of improved ethylene polymer filaments. A further object is to provide a method for raising the shrinking temperature of these filaments without materially reducing their tenacity and other desirable properties. Further objects will appear hereinafter.

The above objects, generally speaking, are accomplished by maintaining the oriented ethylene polymer filaments at a temperature higher than the desired initial shrinkage temperature, and below the melting point, while allowing no retraction in the direction of orientation, that is in the direction of the length of the laments, until there is no further reduction in tension, and then heating the filaments in the relaxed condition at a temperature at least as high as the desired initial shrinkage temperature until substantially no further shrinkage occurs.

The thermal conditioning of ethylene polymer filaments in accordance with the present process consists of two distinct steps or processes: (1) heat-setting, that is maintaining the laments at constant length during the iirst heating above the desired initial shrinkage temperature until there is no further reduction in tension, and (2) allowing equilibrium shrinkage, that is relaxing under zero tension during the second heating. The temperature selected for the conditioning depends upon the combination of shrinkage and tensile properties desired in the finished product. Higher temperatures cause a greater reduction in iilament strength but also proportionally raise their initial shrinkage temperature. Thus, the initial shrinkage temperature of oriented ethylene polymer filaments can be raised to a temperature not lower than about 40 C. to about 5 C. below the melting point of the polymer by maintaining the filament in the iirst step at a temperature of from 30 C. to 2 C. below the melting point of the polymer. During this first step the filament is not allowed to retract in the direction of its length and is thus maintained until there is no further reduction in tension. For the second step the filament is heated in a relaxed condition at a temperature above about 40 C. below the melting point of the polymer but not higher than the temperature of the preceding treatment until substantially no further shrinkage occurs.

To obtain the optimum combination of shrinkage and tensile properties the rst stage of the thermal conditioning is conducted at the maximum temperature that will not cause lament injury, that is slightly below the melting point of the polymer and is continued until there is no further reduction in the residual shrinkage of the relaxed lament. Usually this temperature is 2 to 5 C. below the melting point of the polymer. During the second stage the temperature employed is usually 10 to 20 C. below the melting point of the polymer.

The exact time and temperature limits for both stages of the conditioning treatment can be determined by simple test in any particular instance. That is, stage (1) of the conditioning is completed when the residual shrinkage, that is the tension on the laments held against retraction, is at a minimum, and stage (2) is completed when the relaxed filaments show no more shrinkage. The time and temperature limits are interdependent and are influenced also by the grade and orientation of the laments, the heating means used, and the type of conditioning process, that is whether batch or continuous.

At temperatures of 95 to 103 C. contact times of the order oi one second suillce for both stages. In the batch process it is best to use immersion times of 5 minutes or thereabouts because of the additional heat capacity of the bobbin and cake.

By residual shrinkage is meant the loss of length upon exposure of the relaxed filament to elevated temperatures.

The requirement of minimum filament tension in the first stage of the process corresponds to minimum residual shrinkage. For example, when the change in tension during heating at constant length is measured by a dynamic method wherein the oriented filaments traveling between rolls positively driven at the same speed are heated by a copper block to 100 C. and tensions for various heating times at this temperature are determined by varying the speed, it is found that the tension increases rapidly to a maximum, then decreases asymptotically to a constant minimum value after the filaments have been heated for about 0.64 second. This asymptotic tension value is the ilnal minimum value, as evidenced by the fact that it is substantially maihtained continuously when the illaments are held at 100 C. for minutes. This value also corresponds to the minimum residual shrinkage desired since minimum shrinkage properties are attained when short samples of the laments are held at constant length at 100 C. for about 1 second.

Various heating means are applicable.' Any type of uid bath may be used provided that the fluid does not soften the filaments or injure them mechanically or chemically. For the rst stage in batch process conditioning, it is convenient to hold the laments at constant length on a bobbln. In the second stage it is suspended in the heating medium in skein form. The filaments can be conditioned continuously by running them over three consecutive separator rolls. The first two run at exactly the same speed, corresponding to the iirst stage in the conditioning process. The second stage is accomplishedby running the third roll slowly enough to allow equilibrium relaxation between the last two rolls. Heated rolls, a heated pin, a hot metal surface or a hot powder or uid bath placed between the rolls provide satisfactory heating.

The filaments or bers of yethylene polymer to which this process is applied can be prepared by extrusion of the polymer in a fluid condition. Illustrative processes are described in United States patents, 2,210,774 and 2,219,700. Before conditioning treatment, the filaments or bers must be completely oriented, as by drawing to the greatest extent possible without breakage.

The ethylene polymers useful in the practice lof this invention must be capable of remaining in an oriented condition when allowed to relax freely at room temperature and in addition the oriented polymer should show marked shrinkage when relaxed at elevated temperatures. These polymers can be obtained by heating ethylene alone or in admixture with another polymerizable unsaturated compound under a pressure above 500 atmospheres and preferably above 1000 atmospheres and at temperatures of from 100 to 400 C., and preferably from 150 to 250 C. as described in United States patents, 2,153,553, 2,188,465, and 2,200,429, or in contact with water and a per-compound catalyst at temperatures in the range of 40 to 350 C. and at superatmospheric pressures in excess of 3 atmospheres. The polymers of ethylene alone are normally solid, correspond in composition substantially to (CH2M, and show a crystalline pattern by X-ray diilraction analysis. The physical properties of the polymers of ethylene with other polymerizable organic compounds vary depending upon the composition of the polymer and the nature of the organic compound polymer-ized with the ethylene.

The melting point of the ethylene polymer, as dened herein, is the temperature of zero tensile strength and can be accurately and conveniently determined by measuring the tensile strength at several temperatures near the melting point. The temperature of zero tensile strength is particularly signiiicant to thermal conditioning since it is closely associated with the highest permissible setting temperatures. Usually fairly s imilarv results are obtained by other melting point determinations such as by the ball and ring method described in United States Patent 2,210,771 or by the temperature of sticking to a heated copper block.

This invention will `be better understood in connection with the accompanying drawings in which: Y-

Fig. lis an elevational view of apparatus' that can be used inthe -batch treatment of the yarn during the irst stage ci the process;

Fig. 2 is asimilar view of apparatus for treating the yam in the second stage lor the process;

Fig. 31s a diagrammatic view in perspective oi mechanism suitable for carrying out the invention in a. continuous manner;

llg. 4 is a similar view of a. modied apparatus; an

Figs. 5 to 7 are perspective views of heating means for the yarn which can replace that used in Figs. 3 and 4.

In carrying out the invention as a batch process the yarn I, secured at constant length on the bobbin 2, is immersed in the hot iluid bath 3 contained in the vessel 4. The bobbin is then withdrawn from the iluid bath, the yarn cooled, and after being formed into the skein 5 it is suspended in a second hot fluid bath 6 contained in the vessel l. The baths 3 and 6 can be heated by any suitable means, for example, electrically or by the ame 8.

In the apparatus shown in Figs. 3 and 4 for continuously conditioning the yarn, the yarn passes over draw roll-separator roll combinations referred to herein as separator rolls composed of the rolls 9, I0 and I I with the spaced guide rolls I2, I3 and I4. The rolls 9 and I 0 run at exactly the same speed and the yarn thereby held at; constant length while heat is applied by means of a hot block I5, the treatment of the yarn between these ilrst two rolls being that of stage 1. The separator roll II is driven at less speed and runs slowly enough to allow equilibrium relaxation during the heating of the yarn by the hot block I6 which is the heating at the second stage of the process.

Alternatively, several wraps of the yarn are passed over a heated separator roll I1. which completes the rst stage of the process. The roll I8 then takes up the yarn at a rate which is slow enough to allow the equilibrium relaxation which is produced at the temperature of the heating block I9.

In Figs. 5 to 7 are shown differentI means for heating the yarn which can replace the hot blocks of Figs. 3 and 4. In Fig. 5 the yarn 20 passes into a hot fluid bath contained in a vessel 2I provided with grooved wheels 22, 23 and 24 for guiding the yarn into and out of the bath. In Fig. 6

the numeral 25 indicates a trough containing heated sand 26 through which the yarn passes. In Fig. 7vthe yarn passes a few turns over a heated pin 21.

The examples which follow are illustrative of the practice of this invention.

EXAMPLE I Fully oriented fllament yarn having a denier of 90 made from an ethylene polymer having a molecular weight 'of 20,000 and a melting point of 110 C. is wound upon a metal bobbin. Both yarn ends are tied securely and the bcbbin is immersed for 5 minutes in a sodium chloride-water bath held at 108 C. (stage 1). The bobbin is then cooled and the yarn removed and skeined. The skein is suspended in a 90 C. water bath for 5 minutes and allowed to relax completely (stage 2) This treatment remarkably improves the shrinkage characteristics of the yarn Without substantial decrease in its tenacity, as summarized in Table I. Tenacities here are given in grams per denier based upon the original dimensions of the yarn (o. d.).

Fully oriented yarn having a denier of 92 and a filament count of 5 made from an ethylene polymer having a molecular weight of 9,000 and a melting point of approximately 100 C. is wound upon a metal bobbin. Both yarn ends are tied to prevent contraction and the bobbin immersed for 5 minutes in a water bath held at 95 C. (stage 1). The bobbin is cooled and the yarn rewound in skein form. This skein is then placed in a water bath held at 90 C. to allow equilibrium relaxation, and removed after 5 minutes. This procedure raises the initial shrinkage temperature of the yarn about 52 C. without unduly reduclng the tenacity. The results obtained are shown in the following table.

Table II Initial shrinkage shrinks Tenacity Elongage at 90 C. at about (g /d.-o.d.) tion Per cent C. 1 7 Per cez Ori inal 34 40 16 70 1.6 30 Stages l and 2 0 92 1.1 57

produces a setting action which in this instance must still necessarily occur after the filament has been oriented. It is also possible to combine both steps of the process into one step procedurally but the actual physical changes must be stepwise. For example, passing several wraps of nated, laminated, or composite fabrics.

the filament around a heated separator roll would accomplish stage 1 of the process. The lament can then be taken over a hot surface for the second stage heating and allowed to relax completely before being wound up Crimped bers can be obtained by combining a crimping operation with the first step of the present process, for example, by using a mandrel of suitable shape. The crimped fibers have a high degree of crimp and are valuable as artiilcial wool since they are highly elastic and are unaffected by moisture. Degree of' crimp refers to the ratio of straightened length to crimped length.

The ethylene polymers mentioned herein are intended to include any of the polymers which are solid at ordinary temperatures, which contain the ethylene constituent in substantial proportions, and which are obtained by polymerizing ethylene alone or in admixture with at least one other' polymerizable unsaturated organic compound such as other mono-oleilns (propylene or butylene); dichloroethylenes such as 1,2-dichloroethylene, 2-chloropropene; tetrafiuoroethylene; vinyl ethers, ketones and ester, and other vinyl compounds such as methyl vinyl ether, methyl and ethyl vinyl ketones, vinyl chloroacetate, vinyl propionate, N-vinyl phthalimide, vinyl thiolacetate; stilbene; styrene; acrylic and methacrylic acids, their esters, amides, and imides; esters of maleic and fumarie acids; and esters of itaconic acid.

The ethylene polymers used in the practice of this invention can, if desired, be blended with such modifiers as dyes, plasticizers, fillers and the like.

The usefulness of ethylene polymer laments is markedly increased by the present process since shrinkage does not occur at temperatures lower than 15 or 20 C. below the melting point. Thus, the fibers and filaments obtained in accordance with this invention are useful for tapered or cylindrical bristles which are used, for example, in rotary brushes for cleaning filter screens, and in brushes for use in plating and pickling baths. Likewise, the filaments are useful as surgical sutures which can be readily sterilized by chemical means and are inert to water, and to body uids and tissues. The laments are also useful as fishing leaders and their property of floating on water makes them of special value as dry-ily leaders. Many types of useful screen which are highly durable can be fabricated from these filaments. The filaments are also useful in the fabrication of such articles as fish nets, hair nets, and dental oss. They can also be used as fibers in currency paper, as corrosion resistant packing, as elastic bers, as wrappings for heat and electrical insulation, as windings for baseballs and golf balls, and as cords for reenforced rubber articles.

'I'he ethylene polymer laments are also valuable in the manufacture of yarns, metallized yarns, braided cords, ropes, and coated, impreg- The filaments or yarns can be used alone or in admixture with other textiles such as cotton, silk, rayon, or Wool and the composite material fabricated into textile fabrics such as by knitting, weaving or felting.

In making felted fabrics or artificial felt, heat is applied to the oriented ber and the resulting shrinkage produces a felting or interlocking action. An articial leather may be made by felting and fusing the fabric.

Fabrics comprising the ethylene polymer laments of this invention, because of their water resistance, durability, and elasticity, nd many industrial applications, for example, in making awnings, tents, sail cloth, Holland cloth, lamp shades, flags, parachutes, gloves, camera bellows, aeroplane fabrics, iilter cloths, corrosion resistant packings and gaskets, aprons for trade, laboratory and surgical uses, diaphragms for gas meters and the like, balloon fabrics, blankets, garters, foundation garments, belting, hosiery, helmets, Suspenders, brassires, jackets, artificial fur, composite fabrics, carpets, rugs, and the like.

As many apparently widely diilerent embodiments of this invention may be made Without departing from the spirit and scope thereof, it is to be understood that I do not limit myself to the specific embodiments thereof except as dened in the appended claims.

I claim:

1. A process for raising the shrinking temperature of oriented ethylene polymer filaments selected from the class oi iibers, yarns, and the like which comprises maintaining the filaments at a temperature of from 30 C. to 2 C. below the melting point of the polymer while preventing retraction in the direction of the length of the filaments and then heating the maments in relaxed condition at a temperature above about 40 C. below the melting point of the polymer,

vbut not higher than the temperature of the pre- -retraction in the direction of the length of the iilaments and then heating the laments in relaxed condition at a temperature at least as high as the temperature of said rst mentioned shrinking. but not higher than the temperature of the preceding treatment.

3. An ethylene polymer lament which does not shrink when heated to temperatures lower than 40 C. to 5 C. below the melting point of the polymer, and which is obtained by the process dened in claim 2.

HENRY G. INGERSOLL.

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