US2385403A - Method for stretching cellulose ester yarn - Google Patents

Description

Patented Sept. 25, 1945 METHOD FOR STBETCHING CELLULOSE ESTER YARN Rollin F. Conaway,

E. I. du Pont de Nemour Wilmington, DeL, assignmto s & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application April 8, 1941, Serial No. 387,550

9 Claims.

This invention relates to the treatment of preformed filaments, yarns, threads, and ribbons of artificial thermoplastic material. More particularly it relates to a method for the thermal stretching of filaments, yarns, threads, and ribbons of thermoplastic cellulose derivatives, whereby to increase the tenacity or tensile strength thereof.

In the stretching of preformed fibers, one of the important prerequisites and most difficult objectives to accomplish is rendering the article uniformly plastic prior to stretching, since small differences in plasticity produce large differences in the chemical and physical characteristics of the stretched article. The general procedures employed for stretching preformed fibers may be classified as follows: (1) solvent swelling methods; (2) combined solvent swelling and thermal procedures; and (3) thermal processes. The thermal stretching procedure has many inherent advantages over the other processes, but in all of the variations of this procedure heretofore disclosed, heating and stretching has taken place in air, with the result that the filaments, etc. are not plasticized uniformly and the quality of the stretched product suffers accordingly.

An object of this invention therefore is to uniformly plasticize a preformed filament, yarn, thread or ribbon of. artificial thermoplastic material, by heat treatment alone, and to stretch the same while it is undergoing the heat treatment. A further object is to provide a method for uniformly heat-plasticizing and stretching preformed filaments, yarns, threads, or ribbons of thermoplastic cellulose derivatives, in the substantial absence of air and media which would exert an appreciable swelling or solvent action on the cellulose derivative. These and other objects will more clearly appear hereinafter.

These objects are accomplished by the followme invention which, broadly stated, comprises softening and stretching filaments, yarns, threads and ribbons of artificial thermoplastic materials in a liquid medium maintained at a temperature above the softening point of the thermoplastic materials, which medium is relatively nonvolatile, stable, and substantially inert toward the artificial materials at the temperature of treatment, i. e. which does not appreciably swell or dissolve them or react chemically with them.

In its preferred form the process consists essentially in passing yarn consisting of continuous thermoplastic filaments of a cellulose derivative at a uniform rate into a liquid bath maintained at a temperature sufiiciently high to render the sufilcient tension to the to stretch it to the deyarn plastic and applying thermally softened yarn sired extent, Preferably the yarn is wet or moistened with water prior to its passage through the bath, for I have found yarns so treated yield stretched yarns of superior tensile strength. The process is carried out by passing the yarn under tension over a positively-driven feed roll and either horizontally or vertically through the hot liquid bath and onto a positively-driven wind-up bobbin. The extent of stretching is determined by the relative speeds of the feed and wind-up rolls. The baths can be heated by any of the standard procedures that are subject to accurate control, such as electrical units, steam, or vapors of boiling liquids. An antisticking finish, such as that described in copending application Serial No. 387,551 filed April 8, 1941, can be applied to the yarn in a separate operation or by inserting a size roll or other suitable sizing equipment in the process before the yarn reaches the hot liquid bath.

The substances employed as the heating media may consist of any substance which is liquid and substantially nonvolatile at the temperature required to soften the yarn, and which is substantially inert toward the yarn, i. e. does not swell, dissolve, or react chemically with the yarn. They may be classified broadly into two types, namely those that wet the yarn and those that do not wet or adhere to the yarn. Potassium thiocyanate, which melts at 172 C. to form a clear,

stable liquid, is an example of a suitable liquid heating medium that wets the yarn, whereas fusible metals, such as Wood's metal and ordinary solder (50:50 lead-tin), are examples of liquid heating media that do not wet the yarn.

The temperature of the liquid heating medium depends on the composition of the yarn, the effective length of the bath, the denier of the yarn, and the extent and rate of stretching. In the stretching of the cellulose acetate textile yarns, at speeds of -500 ft./min., bath temperatures in the order of 220-260 C. are required.

The methods for processing the stretched yarns depend to an appreciable extent on the type of heating medium employed. When the stretched yarn is coated with the heating medium, such as with potassium thiocyanate, the yarns are usually washed and dried prior to twisting and coning, whereas with the molten metal media that do not adhere to the yarn, the yarn can be processed in regular textile equipment without washing and the various finishes removed from the yarn in the regular boil-off operations prior to dyeing.

The following examples further illustrate the process.

Example I This example illustrates the stretching of cellulose acetate yarn with a potassium thiocyanate bath.

A dry 300 denier-100 filament cellulose acetate yarn was stretched 500% by passing the yarn 20 ft./min. and a wind-up speed of 100 ft./min. 'I'he'yarn was passed through the molten bath maintained at a temperature of 238 C. in which the contact length of the yarn with the bath was approximately 6 inches. The yarn passed through the bath in a horizontal manner by means of suitable guide rolls. The resulting purified 60 denier-100 filament yarn possessed 2.

Example II This example illustrates the stretching of water-wet cellulose acetate yarn in molten potassium thiocyanate.

A 300 denier-100 filament cellulose acetate yarn was wet with stretching the passed into a molten potassium thiocyanate bath under a tenture of the bath' was 238 length of the yarn with the bath was 10 inches. The resulting purified 60 denier-100 filament yarn possessed a tenacity of 3.5 g./den. and an elongation of 6%. The maximum variation in C. and the contact ing media is not obtained ing units.

melting alloy (61 C.) containing 12.5% tin, 25% lead, 12.5% cadmium, and 50% bismuth.

A 300 denier-100 filament cellulose acetate yarn. The

C., at a speed of 5.5 ft./mm., and a wind-up speed of 33 the yarn with The resulting 50 denierfilament stretched yarn was f from stuck filaments and possessed a tenacity 3.4 g./den., an elongation of 4%, and unifo physical and chemical properties.

Example IV This example illustrates the stretching of 01 lulose acetate yarn in a molten solder (50: tin-lead) bath.

A 300 denier-100 filament cellulose aceta with an aqueous solution of l possessed a tenacity of 3.3 g./den. and an elonga tion of 5.5%.

In contrast, the same type of cellulose acetate yam was sized under the same conditions witl parts of sodium chloride, by passing the yarn over ./min. One

and 86 parts of water a size roll at a linear namely, a bath length of 14 inches, a bath tem- C., a feed speed of 20 It./min., a wind-up speed 01 ft./min., and a stretching tension of 7 grams. The 76 denier-66 filament stretched yarn obtained by stretching the moist, sized yarn possessed of 3.1 g./den. and an elongation This shows as the heating media, the tenacity of the stretched yarn is improved if the original yarn is moist or waterwet when passed into the hot liquid medium.

Example VI This example illustrates the stretching of cellulose acetate yarn possessing high yarn and filament deniers in molten metal baths.

"-A 2400 denier-120 filament cellulose acetate yarn sized with an aqueous solution, described in copending application Serial No. 3 7,551, containing 2 parts of saponin, 10 parts of sodium chloride, and 88 parts of water was stretched 1600% by passing the moist yarn into a solder bath at a temperature of 240 C., under a stretching tension of 20 grams, a feed speed of 8 ft./min., a wind-up speed of 128 ft. /min. and a bath length of 21 inches. The resulting 150 denier-120 filament stretched yarn possessed a tenacity of 2.4 g./den., an elongation of 4%, a soft hand indicating the absence of stuck filaments, and uniform chemical and physical properties. The original 2400 denier yarn possessed a tenacity of 1.2 g. /den. and an elongation of 50%.

Example VII This example illustrates the stretching of cellulose acetate yarn in molten tin as the heating medium.

A 660 denier-66 filament cellulose acetate yarn sized with an aqueous antisticking finish, described in copending application Serial No. 387,551, containing 2 parts of saponin, 10 parts of sodium chloride, and 88 parts of water, was stretched 1025% in a vertical bath of molten tin. The heating bath was 2 inches in diameter and 8 inches in depth so that the contact length 01 the yarn with the molten tin was approximately 15 inches, since the yarn passed over a metal roller guide in the bottom of the bath. This bath was surrounded'by a metal jacket and was heated uniformly by Dowtherm vapor. The moist, sized yarn was stretched in the molten tin at a feed speed of 20 ft./min., a wind-up speed of 205 ft./ min., a stretching tension of 10 grams, and a bath temperature of 242 C. The resulting 65 denier-66 filament stretched yarn possessed a tenacity of 3.0 g./den. and an elongation of 4%.

Example VIII stretching of celin a molten solder A 150 denier-38 filament mixed ester yarn prepared from cellulose acetate propionate containing approximately 2.5% of combined propionic acid and 52% of combined acetic acid was sized with an aqueous solution, described in copending application Serial No. 387,551, containing 2 part of saponin, 10 parts of sodium chloride, and 88 parts of water. The wet, sized yarn was passed into a molten solder bath maintained at a temperature of 240 C., at a feed speed of 22 ft./min. and a wind-up speed of 132 ft./min. The heat-softened yarn was stretched 600% in the solder bath under a stretching tension of 8 grams. The resulting stretched yarn possessed a tenacity of 3.0 g./den., an elongation of a soft pleasant hand indicating the absence of stuck filaments, and uniform denier characteristics.

Example IX This example illustrates the stretching of delustered cellulose acetate yarn in a molten metal bath.

A 300 denier-100'filament cellulose acetate yarn delustered with titanium dioxide pigment was sized with an aqueous solution, described in copending application Serial No. 387,551, constaining 2 parts of saponin, 10 parts of sodium chloride, and 88 parts of water, by passing the yarn over a size roll at a linear speed of 22 ft./min. The resulting moist, sized yarn was stretched 600% by passing the yarn into a hot molten solder bath maintained at a temperature of 240 C. Th stretching tension on the yarn was 8 grams, the wind-up speed was 132 ft./min., and the contact length of the yarn with the bath was 12 inches. The resulting delustered denier stretched yarn possessed a tenacity of 3.0 g./den. and an elongation of 4%- The invention has been illustrated with particular reference to thermoplastic organic derivatives of cellulose, such as cellulose acetate, nitrate, propionate, butyrate, acetate propionate, acetate benzoate, ethyl cellulose, benzyl cellulose, ethyl lauryl cellulose, and ethyl celluose acetate; it is to be understood, however, that the process is applicable to thermoplastic artificial filamentforming material in general, including vinyl resins, polyamides, polyesters, polyalcohols, etc.

The invention is further susceptible to a wide variation in materials and conditions not specifically delineated in the examples. Thus the yarn may either be dry (0% to 5% moisture) or contain a substantial quantity of water (waterwet). Stretched yarns with improved physical properties are obtained when the original yarn contains between 5% and of water. The preferred amount of water associated with the yarns is between 5% and 50% based on the dry weight of the yarn. The yarn may contain small amounts of additional materials such as delusterants, resins, or sizes ordinarily employed to improve the quality or facilitate handling of the yarn.

Any of the commercial methods, such as by positively-driven rolls and bobbins for passing yarn continuously'from one point to another, may be employed for passing the yarn continuously and uniformly through the heated liquid baths. The temperature of the heating bath should be uniform and be controlled very accurately, such as to within :1" C. of the desired temperature. The baths may be heated by any of the standard methods, such as by steam, electrical units, or heated vapors.

The heating medium may be any substance that is a mobile, stable, and relatively nonvolatile liquid at the desired stretching temperature and does not have a solvent or swelling action on the yarn at this temperature. In reference to each of these limitations, it is desirable that the liquid be mobile at the stretching temperature so that the yarn can be passed through the bath easily. The liquid bath should be relatively stable to decomposition by prolonged thermal treatment at high temperatures and to the action of steam or any of the components in the finishes that may be applied to the yarn. The bath should be neutral in order that the cellulos derivative will not be degraded or decomposed by the stretching treatment and should be relatively nonvolatile at temperatures up to 275 C. so that the bath can be operated at atmospheric pressure without an appreciable loss of the heating medium by evaporation. A most important requisite of the liquid bath is that the liquid heating medium should not have an appreciable swelling or solvent action on the yarn.

The substances comprising the heating medium may differ widely in other characteristics, such as general solubility, melting points, and specific gravity. Many of the substances fulfilling the requirements are solids at room temperature, such as potassium thiocyanate which melts at 172 C., Wood's metal at 61 0., ordinary solder at 180 C., and tin at 232 C. At stretching temperatures above 200 C. the low melting inorganic salts, such as potassium thiocyanate and eutectic mixtures of sodium nitrate with other inorganic nitrates and the fusible metals or alloys are the most satisfactory media.

The stretching conditions may. vary widely and are determined largely by the composition and denie'r of the original yarn or article, the length of the heatlng bath, the stretching tension, and the rate and extent of stretching. In general, the longer the bath length the higher is the stretching tension that can be obtained, and the slower the rate of stretching the lower is the temperature at which the bath can be operated. The bath length can vary from a few inches to several feet in length and one yarn or a number of yarns can be stretched simultaneously in the same bath. In the case of cellulose acetate yarn, the bath temperature can vary from approximately 200 C. with long baths, small yarn, and slow rates of stretching to 300 C. or more for short baths, large yarn, and high rates of stretching. The stretching tensions can vary rather widely, such as from 1 gram to 50 grams depending on the yarn, stretching temperature, etc. Likewise, the extent and rate of stretching can vary widely. In general, it is ciable improvement in tenacity, and higher extents of stretching, such as in the order of 500400095, are preferable. The extent of stretching is determined primarily by the char a continuous or step-wise manner and special finishes may be applied to the yarn prior to stretching or to the stretched yarn.

The stretched yarn may be processed in a number of ways. It is generally necessary to in the regular boil-off operation prior to dyeing. In general, the stretched yarns can be processed in the same manner as regular textile yarns.

yarns of a physical and chemical uniformity not heretofore obtainable.

I claim:

silestrength thereof.

2. The process which comprises passing preformed water-wet filaments, yarns, threads and state whereby thereof.

the softened state.

acetate containing from about 5% to about 100% by weight of water based on the weight of dry cellulose acetate into a bath consisting of 50% lead and 50% tin maintained at a. temperature 5 sufliciently high to soften the filaments, and

stretching said filaments to the desired degree while in the softened state.

ROILIN F. CONAWAY.