Wet spinning synthetic fibers

Oct. 30, 1962

J. H. SANDERS

WET SPINNING SYNTHETIC FIBERS Filed Nov. 15, I960

3,061,402

Mere ring

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INVENTOR.

John H. ’SoncJerts

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United States Patent Office

3,061,402

Patented Oct. 30, 1962

3,061,402

WET SPINNING SYNTHETIC FIBERS

John H. Sanders, Newport News, Va., assignor to The Dow Chemical Company, Midland, Mich., a corporation of Delaware

Filed Nov. 15, 1960, Ser. No. 69,315

Claims. (Cl. 18—54)

The present invention resides in the field of synthetic textile fibers and contributes to the art of their manufacture. More precisely, it relates to a useful and advantageous process for the continuous wet spinning of manmade fibers that are prepared by being coagulated from suitable spinning solutions or equivalent compositions (such as spinnable dispersions) in aqueous coagulating spin baths. The invention has particular reference to· the manufacture of acrylonitrile polymer fibers which are fabricated from fiber-forming acrylonitrile polymers that contain in the polymer molecule at least about 80 weight percent of polymerized acrylonitrile, especially polyacrylonitrile, which are wet spun in and with systems that are adapted to utilize aqueous coagulating liquids for the spinning operation, such as systems wherein ethylene glycol, dimethyl formamide, dimethyl sulfoxide, butyrolactone and the like or the various aqueous saline polyacrylonitrile-dissolving solvents are employed as spinning solution solvents for the polymer and are also present in non-polymer-dissolving quantities in the aqueous coagulating liquid used in the spin bath.

The utile, known aqueous saline solvents for the various fiber-forming acrylonitrile polymers and polyacrylonitrile include zinc chloride, the various thiocyanates such as calcium, lithium bromide, salt mixtures of the so-called “lyotropic” series, and others recognized by the art, as has been disclosed, among other places, in United States Letters Patents Nos. 2,140,921; 2,425,192; 2,648,592; 2,648,593; 2,648,646; 2,648,648; 2,648,649; and 2,949,435. Advantageously, aqueous zinc chloride solutions are used for the purpose.

The known methods of fiber-forming may generally be classified in three categories; melt spinning, dry or evaporative spinning, and wet spinning. Briefly, melt spinning entails extruding a molten polymer and coagulating the extruded filament by cooling with an inert gaseous medium. In dry spinning, the fiber-forming material or polymer is dissolved in a suitable volatile solvent, and the resulting solution is extruded into a heated atmosphere wherein the solvent is evaporated leaving a coagulated filament. In wet spinning, like dry spinning, the fiberforming polymer is dissolved in a suitable solvent (which is not necessarily volatile) and the solution is extruded or spun into a liquid coagulating or spinning bath which is a solvent for or miscible with the polymer solvent but a non-soivent for the extruded polymer. Thus, the polymer solvent is dissolved or leached out of the polymer leaving a coagulated polymeric filament.

In the prior known methods of wet spinning, the spinnerette is usually immersed in a coagulating bath or placed just immediately preceding a bath so that the extruded solution is contacted immediately with coagulant upon emergence from the spinnerette face. In any event, an actual “bath” has always been employed for coagulating, that is, the solution has been extruded into a confined volume of liquid. The shape of the bath container has not been limited, taking on numerous geometrical configurations from cube-like to cylindrical. Ordinarily, rectangular trough-like baths are employed with the upper surface of the bath exposed to the atmosphere. However, totally enclosed baths are frequently encountered as in cylindrical chambers oftentimes used in tube spinning. The direction of spinning has been vertically upward or downward, horizontal or oblique so long as in the path of the spinning was a confined coagulating bath.

The necessity to maintain a coagulating bath presents many processing and economic difficulties among which δ are: considerable floor space is required to accommodate the baths; the spinnerettes are usually inaccessible for observation and maintenance; means are required to move the spinnerettes into and out of the baths such as having the spinnerette assemblies pivotally mounted, 10 which in itself is costly construction and presents leak sources; threading-up or start-up is particularly difficult; large inventories of coagulating liquids are often necessary; and, problems of adequate mixing and prevention of stratification in the bath are prevalent due to concentra15 tion gradients that develop during spinning.

It is the chief aim and concern of this invention to provide a wet-spinning process that will eliminate or minimize the above and other difficulties and at the same time provide a process that will assure production of 20 fibers of consistently high quality. A particular object of the invention is to provide a process of the indicated type and nature that would be peculiarly well adapted for utilization for and in the prepartion of acrylonitrile polymer fibers, yarn, threads, tow bundles and the like 25 and related filamentary products using the highly advantageous salt spinning techniques with aqueous systems, such as those that employ aqueous solutions of zinc chloride or its saline equivalents for dissolution of the polymer into a spinning solution and for constitution, in 30 non-polymer-dissolving quantities, of the coagulating liquid.

These objects and cognate benefits and advantages may be achieved readily in the practice of the present invention whose process, in continuous and uninterrupted se35 quence, comprises and entails extruding or spinning into filamentary or the like form a spinning solution of a synthetic fiber-forming polymer dissolved in a watermiscible solvent for said polymer, said spinning solution being adapted to be coagulated in an aqueous solution ⁴⁰ of said solvent of non-polymer-dissolving concentration, said spinning solution being extruded through a suitable spinnerette or other extruding device vertically upward while applying to the so-formed filaments at some point above the spinnerette face an aqueous coagulant, and ⁴⁵ allowing said coagulant to run down the filaments counter-current to the run of the filaments to the spinnerette face, from which said non-polymer-dissolving solvent is withdrawn. Thus, this invention is based on the surprising discovery that a filament bundle can be made to ⁵⁰ serve as its own coagulating bath.

Further features and advantages of the invention will be manifest in the following description and specification, taken in connection with the accompanying drawing, _gg which schematically illustrates the invention.

Referring to the drawing, a spinning solution, a solution or dispersion of a polymeric fiber-forming material, is delivered from a pumping means (not shown) to a spinnerette which is positioned to spin or extrude essen₆θ tially vertically upward. Upon emerging from the spinnerette face the freshly formed filaments are formed into a filament bundle and drawn over a godet serving to draw the filaments away from the spinnerette. The filaments may then be subjected to any number of subse65 quent processing treatments common to a wet spinning process, such as are illustrated, washing, stretching, and finally drying. The coagulation of the freshly extruded filament is provided by metering onto the filament bundle a suitable coagulant at some point above the spinnerette 70 face.

The composition of the coagulating liquid is preferably substantially pure water or an aqueous solution compris3,061,402 ing the same constituents as the spinning solution solvents, but in non-polymer dissolving concentrations.

After application of the coagulant to the fiber bundle, the coagulant is allowed to travel down the filament bundle by gravity flow, counter-current to the direction of travel of the fiber bundle, to the spinnerette face and then to a suitable collecting pan positioned below the spinnerette. The spent or effluent coagulant can then be withdrawn for further treatment.

The spinning solution may be a solution or spinnable dispersion of a fiber-forming polymeric material that is capable of being coagulated in an aqueous coagulating spin bath. As has been indicated, when acrylonitrile polymer, particularly polyacrylonitrile, fibers are being manufactured, zinc chloride may most advantageously be utilized as the sole, or at least the principal, saline solute in the spinning solvent employed for the polymer. In such instances, the aqueous solution of zinc chloride in the spinning solution may advantageously be in a concentration of from 55 to 65, preferably about 60 percent by weight, based on the weight of the aqueous solution.

The quantity and concentration of the coagulant applied and passed countercurrent to the filaments should be sufficient, when such aqueous zinc chloride solvent spinning solutions are employed, so as to maintain the concentration of zinc chloride in the zone immediately adjacent the spinnerette face at a non-polymer-dissolving coagulating concentration of at least about 25 percent by weight; advantageously from about 30 to 50 percent by weight, and preferably between about 40 and 45 percent by weight. In such aqueous zinc chloride systems for acrylonitrile polymers, wherein the freshly wet spun polymer is generally obtained in an aquagel form, it is generally desirable for the spinning solution that is extruded to contain between about 4 and 20 percent by weight of dissolved polymer; more advantageously from about 6 to 15 percent by weight of dissolved polymer; and preferably, particlularly when polyacrylonitrile fibers are being manufactured, from about 8.5 to 11.5 percent by weight of fiber-forming polymeric solids in the spinning solution.

As the coagulant travels down the fiber bundle it will become enriched with the spinning solvent as the fibers are leached or washed free of the solvent. It is thus apparent that the concentration and point of application of the coagulant must be gaged so that polymer-dissolving concentrations in the coagulant are nto attained during the down-flow contact of the coagulant with the filaments.

Aqueous zinc chloride spinning solutions of fiber-forming acrylonitrile polymers are beneficially extruded at a spinning temperature of from 0 to 50° C.; preferably from about 10 to 30° C., into an aqueous zinc chloride coagulating liquid that is maintained at a coagulating temperature of from 0 to 30° C.; preferably from about 10 to 20° C. Under the indicated conditions, the amount and concentration of coagulant that is required to effect a suitable coagulation in the area of the spinnerette face can be determined by simple material balance, taking into account the quantity per unit time of spinning solution being extruded and the amount of water being withdrawn from the liquid by entrapment and entrainment in the freshly wet spun and washed aquagel filaments. Similarly, a desirable point of application can be determined. Thoroughly washed acrylonitrile polymer aquagel fibers, incidentally, are usually found to contain not more than 5½ parts by weight of water (including residual extrinsic or exterior water associated therewith) for each part by weight of dry polymer therein. More frequently, washed acrylonitrile polymer aquagel fibers are found to contain from about 2 and usually from about 3 to 4 parts by weight of water for each part by weight of polymer.

When practicing the present invention, it is usually advantageous to position the take-away godet over the spinnerette so that the travel of the filament bundle is vertically upward. This allows the coagulant to flow down around and within the filament bundle without any inordinate channeling due to one side of the bundle being lower than another. However, travel at slight inclinations from the vertical may in some instances be satisfactory. Ordinarily, the coagulant flows down into a shallow pool which is inherently maintained on the face of the spinnerette and then over the side to a collecting receptacle. Incidentally, no inventory of spent coagulant need be maintained below the spinnerette. Instead, the coagulant may be withdrawn at the same rate it overflows the spinnerette face.

The size of the spinnerette and the number of individual orifices in the spinnerette are not critical. For instance, spinnerettes of round, rectangular, square, etc. shapes having face areas up to 25 square inches or so and from a few hundred to several thousand orifices may be employed. Of course, a plurality of spinnerettes may be operated simultaneously but when so doing it is preferable to individually apply coagulant to each filament bundle. A common header system can be employed so that the feed rate of coagulant is the same to all bundles, or the coagulant can be individually metered to each bundle. A common take-away godet may serve several filament bundles simultaneously.

Several means of administering the coagulant to the fiber bundle are possible. It may be administered by a running stream, drop-wise, spraying, padding, etc. Advantageously, the coagulant is applied to the filaments at the point at which they make contact with the takeaway godet or immediately below the godet. The bundle at this point occupies the least volume and problems of distribution of the coagulant on the bundle are minimized. If application is desired nearer the spinnerette a suitable distributor may need to be employed, such as a tube encircling the tow and perforated so that coagulant is sprayed inwardly on the bundle.

The height of the take-away godet above the spinnerette is beneficially from about two to five feet, but the exact height is best determined for each particular set of spinning conditions being practiced. For instance the height will be somewhat dependent on filament composition and denier. The speed of the godet is preferably set to coincide with the spinning speed or slightly higher so that a slight stretch is imparted to the filaments; for example, a stretch of 1:1.4 may be beneficially given the freshly formed filaments between the spinnerette and the godet.

Starting-up the spinning operation according to the invention is a relatively simple procedure. Usual operation is to start the spinning pump and extrude a mass of spinning solution through the spinnerette which is then coagulated by pouring water on the exuding mass. The coagulated mass is then used as a leader and is drawn away by hand as the filaments are formed behind it, laced over the godet and through subsequent treating operations.

As another modification of the invention, saturated steam may be sprayed on the filament bundle and caused to condense serving as the coagulant. Certain conditioning effects can be obtained by such treatment. Additionally, the coagulant may be metered onto the filament bundle at more than one elevation, and differing concentrations may be employed at each elevation. The application of water to the filaments may be so adapted, such as at the upper extremity of vertical climb of the filaments, that filaments essentially free of residual spinning solvent are obtained.

After spinning and coagulating, the freshly wet spun filaments may be subsequently handled and treated in any desired or necessary manner for purposes of converting them to a finished fiber product. Thus, they may be stretched or otherwise treated for purpose of heat treating or relaxing the fibers in any desired way

3,061,402 or they may be subjected to additional treatments of any appropriate nature, including application of finishes, lubricants and the like or imposition of crimp prior to being dried and finally collected as completely manufactured products.

The invention will be further illustrated with the following example in which all parts and percentages are by weight unless otherwise specified.

Example 1

A spinning solution was prepared comprised of polyacrylonitrile with an average molecular weight between about 30 and 35 thousand dissolved in an aqueous 60 percent by weight solution of zinc chloride. The total polymer solids in the spinning solution were about 10 percent by weight, based on the weight of the solution.

The solution was pumped through a spinnerette (500 hole, 8 mils per hole), positioned to spin in a vertically upward direction, at about 40 grams per minute at 20° C. At the start of the run, the spinning solution was coagulated at the spinnerette face by running water at the face so that a bulky mass of coagulated solution was obtained. This mass was used as a leader for threading up the filament bundle. As the mass was drawn upward from the spinnerette, an open stream of water was applied beneath the mass so that individual filaments were formed at the spinnerette face and extended up to the bulky coagulated mass.

After the filament bundle was laced over a take-away godet, room temperature water was metered onto the filaments adjacent their initial point of contact with the godet, and the water was allowed to run down the fiber bundle, without any additional confining or controlling means, to the spinnerette face and into a collecting pan beneath the spinnerette. The distance from the spinnerette face to the godet was about 34 inches. The effluent coagulant from the collecting pan had a concentration of about 26 percent ZnCl₂.

Continuous spinning of fibers was maintained from a feed rate of 40 grams per minute of spinning solution and from metering substantially pure water to the fiber bundle as above at about 80 grams per minute. The takeup godet was driven at 5 r.p.m. which corresponds to about 4.7 ft./min. After passing over the take-up godet the fibers were washed and hot-stretched about 8:1, and finally dried at about 140° C. for 7 minutes.

The resulting fibers were surprisingly uniform, had an excellent white coloring and had the following physical properties:

Denier_____________________________________ 6.9

Tenacity ______________________________g./d 1.2

Elongation__________________________percent 39

Yield ________________________________0.42 ⁶ .

Since certain other modifications and ramifications of this invention can be entered into without departing from its intended spirit and scope, the invention is intended to be definitive in the hereto appended claims without unnecessary limitation to or by the foregoing specification and description.