US2636217A - Dry spinning apparatus - Google Patents

Description

April 28, 1953 w. H. HAMMOND ET AL DRY SPINNING APPARATUS Filed July 20, 1949 flOGiH L. QGHAIFER VAL-run. HAMMOND IN VEN TOR.

, ATTORNEY Patented Apr. 28, 1953 DRY SPINNING APPARATUS Walter H. Hammond, Miamisburg, and Laurence C. Holt, Dayton, Ohio, and Rodger L. Schaefer, Decatur, Ala., assignors, by mesne assignments, to The Chemstrand Corporation, a corporation of Delaware Application July 20, 1949, Serial No. 105,790

6 Claims.

This invention relates to an apparatus and procedure for preparing synthetic resinous structures. More specifically the invention relates to an improved method of spinning fibers by extruding solutions of synthetic resins into a co agulative medium.

The preparation of linear structures, such as films, fibers, rods, and other shapes, by forcing solutions of resins through a suitable die into a gaseous medium which removes the solvent and precipitates the resin in a continuous form, is well known. Many methods and types of apparatus for practicing the dry spinning technique have been described in the published literature. These publications show various methods of circulating the coagulation medium and structures for manipulation of the extruded fiber. In general there are two methods described for the movement of the gaseous medium with respect to the fiber, countercurrent and concurrent, each of which has inherent undesirable attributes as well as beneficial aspects. The countercurrent fiow of the spinning medium is effective in reducing the residual solvent in the fiber to a minimum, because the solvent free gas is in contact with the fiber nearly exhausted of solvent. This method, however, provides the initial coagulation in the presence of gas containing substantial solvent content which retards the evaporation of solvent from the freshly spun fiber. The concurrent fiow of the gaseous spinning medium provides a solvent free gas at the spinneret to accelerate the rate of coagulation, but the solvent laden gas in contact with the fiber at the exit end prevents or retards the adequate removal of solvent from the fiber. In each of these conventional procedures one object is achieved at the expense of other desirable objectives.

The primary purpose of the present invention is to provide a method of obtaining rapid coagulation and simultaneously highly eificient solvent removal. A further objective is to provide a novel and useful dry-spinning method by which fibers may be spun efiectively and economically.

It has been found that if a dry-spinning operation, conducted in a vertical tower with a downwardly moving fiber, is modified by introducing the solvent free gaseous medium at a point immediately below the spinneret at a temperature substantially that of the boiling point of the solvent, withdrawing the solvent laden gas above the spinneret, and contacting the fiber during its downward course in the tower with a stream of gas at a substantially lower temperature, the

beneficial effects of both countercurrent and concurrent fiber spinning maybe achieved. By this practice a small amount of the relatively cold gaseous medium is introduced at the bottom of the tower, said amount being from two to 20 percent of the volume of the efliuent gas. The relatively cold gas stream passes upward and is heated to a moderately high temperature by the heating elements in the tower walls. At the top of the tower the small amount of gas containing the solvent removed from the fiber is diluted with a large volume of hot gas which provides an atmosphere relatively free of solvent and at a temperature substantially that of the boiling point of the solvent.

The new apparatus and spinning method may be effectively used in the preparation of fibers of the acrylonitrile polymers, such as polyacrylonitrile and copolymers of over percent acrylonitrile and up to 20 percent of other copolymerizable olefinic monomers, for example vinyl acetate, vinyl pyridine, methacrylonitrile, vinylidene chloride, and the esters of acrylic and methacrylic acids.

Conventional dry-spinning practice, involving the use of high boiling solvents, for example N,N-dimethylformamide, ethylene carbonate, N,N-dimethylacetamide and butyrolactone, is often harassed with the development of a yellow or brown discoloration in the fiber. The difliculty is believed to be due to the high spinning temperatures required to efiectively remove the solvent. Through the use of the novel method and apparatus described herein fibers free of discoloration may be prepared. The use of high boiling solvents is usually necessary in the prepa ration of fibers of polyacrylonitrile and copolymers of substantial proportions of acrylonitrile and minor proportions of other monomers, because of the inherent difiiculties of preparing suitable spinning solutions. Accordingly, a further purpose of this invention is to provide an efiective method of eliminating the color in acrylonitrile fibers.

The essential features of the new method are the extrusion of the resin solution into a countercurrently flowing stream of gas at a high temperature and with a very low solvent vapor content. Shortly after spinning the fiber passes into a zone of countercurrent fiow at a lower temperature and usually lower velocity. This lower temperature zone is fed with fresh solvent free air at a point from which the finished fiber is withdrawn. The stream of cold air, as it passes countercurrently with respect to the fiber, carries alon with it the solvent which has evaporated from the surface of the fiber and is gradually increased in temperature by the heating means provided in that zone. As the stream of air approaches the spinneret it is mixed with a substantially-largerstream of solvent free gas at a muchshigher temperature and the, increased volume of hotter gas passes rapidly over the freshly extruded fiber in the vicinity of the spinneret, past the spinneret and is exhausted through a suitable solvent recovery apparatus. The gaseous medium may be movedthroughthe tower by the positive pressureof the hotj'arid cold gas streams entering ,the apparatua orgit may be withdrawn by means of a suitable exhaust fan.

To be eifective the new method should involve the use of suitable baiiiing means to prevent fiber injury by the force of the gas streamsywith in the tower. The substantial velocity of the .hot;.g as stream; entering near the spinneret. may gdamageor even break the fre hly spun fiber.

Accordingly, Lthe bevis pref y inclosed in asheath which. fleets the gas stream and dicots it in the desired countercurrentdirection in close prozsiniityito the freshly spun fiber. If desiredlthe ,baii Qmaybe tapered in the directionofi the fspinneret so as to insurethemaxi- ."f-m urn contactpi the low solvent containing gas -.-with.;the{freshlyispun. fiber at the spinneret. It 1is oiten-desirable to have a deflecting means ,oyerthe gas ei'citftofprevent a non-uniiorm gas withdrawa lfand'.to assure a more nearly uniform.distribution'of gasilow around the periphery of the 'spinneret.

'lfhe new rnethod :isfconducted in a spinning .to,w,er comprisedoftwo parts, the tower proper oldwh ch theforrned'fiber is contactedwith a countercurrent .gasj'strea n at a moderate temperature,.-and ,.-the, .spinning head or operating aonezin which. the bunker the air is introduced ;at highertemperature and in which the'fiber ;;i s aetuallyspunin.'contact with the stream of gas at the higher temperature. The "tower proper is provided with suitable heating 'elements whichf rnayfbe electrically heated coils of a st eam heated means for maintaining Iv the de ired temperature-{at which the solvent has a ,substantial vapor pressure. For reasons of yeconorny thetower is preferably coated with a.

.substantial layer 01" aTsuit'able insulation inal i-i ,{Ihe-operatingheadl of the tower is provided with gas inletand outlet ports, a suitable aperture at the top for; the introduction of the spin- 7 neret, .bafiles; of suitable. size and shapeito prevent damage to thegfiber and to intimate contact oft-hefiber with the as streanrand a suitable port or window through which the'operator may inspect theoperation, and ii necessary, to manipulate the fiber in initiating theoperation or for cleaning the Spinneret. I

.The attached, drawing is the cross-sectional view of a spinning tower assembly in :which'the spinning tower! is anelonga edtube of any desir ed cross=section which is heated by a suitableheating element 2 and enclosed by a suit -ableinsulation;material 3. The spinninghead .oraoperatingarcane is superposed on the tower .aandis providedvwitha hinged door ii for ob- .servation andsnanipulation of the ::dur-ing ..the-f spinning operation. The spinneret he. isrprovided: with} resin solu i n hrough cenadult L.pas'sing.-1t-hrot 1ghv vthev cover ,plzo'sev 8 V at the ;top Qof i the tower. -The aextrudedfiber -9 r oomare not critical.

4 prised of numerous minute filaments passes downwardly through the tower and out at the bottom through an enclosure l0 which is provided with hinged doors ll having an aperture 52 for the normal passage of the fiber, which leaves the tower andis conveyed to subsequent operations by ineans oi thread; guide iii.

A small amount of the necessary gaseous atmosphere is introduced at room temperature through port i land is passed up the tower counter'currently with respect to the fiber direction. As it passes intothe spinning head or operating "tone it is mixed with a larger stream of air at "fiber and into the funnel shaped baflie l'i' which directs the stream in close proximity to the freshly spun fiber at the spinneret. A suitable bailielbpi'ovides ior'a uniform withdrawal of gasfrom the spinningheadfrozn'which it passes out through passage lil to a suitablesolvent recovery system notshown.

The size and shape of theparts of the tower The tower may be any con venient width, but preierablyfrom'iour to twelve "inches, so as to provide an adequate volume of gasin laniellar now for the removal= of-thc normal solvent content'olj" the; fiber withoutrequiring an excessive velocity, and avoiding turbulence eliects. Thelength of the tower will depend upon the desired extent oi-solvent removal. Ii completafor'substantially complete solvent removal is desired a tower of ten to I00 times the length oitheoperating head may be required. The length ofthe operatinghead,

or the distance between the "hot airiniet'and the spinneretwill also depend upon the size of the fiber, the number of fila' nents; the volume of hot gas passedintofithe' tower, the temperature of the gas, thetype of resin and solvent, Q the sensitivity oi the fiber with respect to discoloration, and the spinning speed. The manipulation of the size and shape or the spinning head to produce the optimum'fiber may be practiced by one'skilled' in the'art. in general, the

, tower length maybe from fiveto ZOtimes the 7 length of thespinning' head, and-iisolvent recovery is not a seriousjproblem it rnay-be as 'short as two tiznes'the length of the spinning head. l

The new method andapparatus are =particuother allryl'esters o'facrylic acid,-especially those 'Whereinthe allrylgroup has up to six carbon atoms, methyl methaorylate and other alkyl methacrylates wherein-the alkyl group has up 'to six carbon atoms, styrene, and other vinyl Qsubstituted aromatic hydrocarbons, 'methacry'lonitrile and vinyl pyridine. In-the preparation of fibersirom the acrylonitrile polymers the spinning 1nethod"utiliz es solutionscof the desired resin in a solvent, such as dimethyliormamide, butyrolactone or" ethylene carbonate.

Under such circumstances the temperature at the'spinneret will bebetween 14;) and 169 (3., 'the countercurrentflowthrough thetower is initiated. with air at room" temperatureand is f gradually heated up to@8 0"to;10 0?" C: by means or the heating elements -in'fthetower. At the top of the tower the countercurrent stream of air is diluted with a much larger volume of a hot gas, for example at a temperature of 150 to 170 C. By the use of this spinning method acrylonitrile fibers of excellent color may be spun efiiciently.

The invention is described by the following claims.

1. A method of preparing fiber, which comprises extruding a solution of a polymer of at least 80 per cent acrylonitrile in a volatile solvent into a countercurrent gas stream, which stream is solvent free gas at room temperature in contact with the finished fiber, is heated to a temperature intermediate to the boiling point of the solvent and room temperature, is mixed with at least five volumes of solvent free gas heated to the approximate boiling point of the solvent at a point close to the fiber source, is passed countercurrent to the freshly spun fiber at the spinneret, and is directed away from the fiber.

2. A method of preparing fibers of acrylonitrile polymers, which comprises extruding a solution of a polymer into a countercurrent stream of air which was introduced at room temperature in contact with the finished fiber, which stream is passed over heating elements in countercurrent contact with the fiber at a temperature below 100 C., which stream is then mixed with at least five volumes of a solvent free gas at a temperature above 140 C., said mixed gas stream being passed countercurrently with respect to the freshly spun fiber at the fiber source.

3. An apparatus for dry-spinning thermoplastic synthetic fibers comprising, a vertical tower, an enclosure attached to the top of the tower, a hinged closure attached to the bottom of the tower having a fiber-exit opening therein, a spinneret mounted in the enclosure and pointed downward toward the tower, conduit means attached adjacent the bottom of the tower for introducing cold gas into the tower, a second conduit means attached to the enclosure adjacent the upper portion thereof for removing gas therefrom, a bafiie mounted in the enclosure intermediate the second conduit means and spinneret, a third conduit means attached to the enclosure adjacent the lower portion thereof for introducing hot gas therein, a funnel-shaped member mounted in the enclosure below the spinneret for leading all of the gas stream in parallel countercurrent relationship to the fibers in intimate contact therewith at their source, said funnel-shaped member having its sides diverging away from the spinneret and attached to the wall of the enclosure, a cylindrical bafiie means positioned opposite the third conduit means, said cylindrical bailie means extending upwardly into the space formed by said funnel-shaped member, the axes of the cylindrical bafiie means and spinneret being coincident, and heating means attached to the wall of the tower.

4. An apparatus as defined in claim 3 wherein the lower end of the tower is spaced from the hinged closure, and wherein the hinged closure has side-walls spaced from the walls of the tower, whereby a passage is formed around the bottom end of the tower, and wherein the first conduit means communicates with said passage.

5. A method of spinning acrylonitrile polymer fiber, which comprises extruding a solution of the acrylonitrile polymer into a countercurrent atmosphere between 140 and 160 C., said atmosphere being comprised of two components, the first component comprising from two to 20 volumes of a gas passing countercurrently with respect to the fiber at a temperature below C., said gas being introduced into the path of the fiber at a point removed from the fiber source, and the second component comprising from 80 to 98 volumes of solvent-free gas at a temperature above C., said gas being introduced into the path of the fiber at a point between the fiber source and the point of introduction of the first gas.

6. A method for spinning fibers from fiberforming acrylonitrile polymers, which comprises extruding a solution of a polymer of at least 80% acrylonitrile and up to 20% of another monoolefinic polymerizable substance into a gaseous medium flowing countercurrent to the direction of extrusion, directing the entire stream of gaseous medium into contact with and immediately adjacent to the freshly formed fibers at the fiber source, said stream being heated to a temperature between 140 C. and 0., and passing the fibers in countercurrent relationship to a smaller volume of the said gaseous medium at a temperature below 100 0., said smaller volume being from two to 20% of the said larger volume.

WALTER H. HAMMOND. LAURENCE C. HOLT. RODGER L. SCHAEFER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,959,443 Payne et a1 May 22, 1934 2,002,066 Taylor May 21, 1935 2,404,714 Latham July 23, 1946 2,404,722 I-Ioutz July 23, 1946

Images