US3410940A - Mist spinning process - Google Patents

Description

1968 w. B. HENDERSON ETAL 3,

MIST SPINNING PROCESS Filed 001:. 12, 1964 INVENTORS WILLIAM B; HENDERSON GERD R. BAUR ATTOR United States Patent 3,410,940 MIST SPINNING PROCESS William E. Henderson and Gert! R. Baur, Decatur, Ala.,

assignors to Monsanto Company, St. Louis, Mo., a corporation of Delaware Filed Oct. 12, 1964, Ser. No. 403,190 6 Claims. (Cl. 264-182) ABSTRACT OF THE DISCLOSURE A process, which substantially increases dye receptivity, tenacity and elongation of acrylic filaments, pro- The present invention relates to the preparation of acrylonitrile filaments. More particularly, this invention relates to an improved dry-jet wet Spinning process for producing acrylonitrile continuous filaments having valuable properties as are hereinafter described.

In the production of continuous filaments by the standard dry-jet wet spinning process, a solution of acrylonitrile polymers and copolyme-rs dissolved in a suitable organic solvent is extruded through a spinneret posltioned in close proximity to a coagulating bath which the extrusions enter to form filaments. Once the extrusions are immersed in the bath, coagulation occurs almost immediately to form filaments that are removed from the bath and subjected to various stretch ratios on several pairs of heated rolls operated at different rates of speed to establish draft ratios for orienting the molecular structure of the filaments.

The dry-jet wet spinning technique is utilized to facilitate preliminary drawing and reduce the porosity of the fiber structure whereby the jet stretch is increased to produce a" faster spinning rate. By spacing the spinneret above the coagulating bath, a semi-coagulation zone is established wherein the cmbroyic filaments are exposed to the atmosphere for a fraction of a second. During this short interval a membrane-like skin is formed as an outer coat for the extrusions which strengthens them and r of desired physical characteristics. The dry-jet wet spinning process is limited however, for the reason that the exposure time cannot be increased because the extrusions tend to coalesce and adhere to each other if the face of the spinneret is more than one-half inch from the surface of the bath. Thus, the filaments produced by a standard dry-jet wet spinning process do not meet the necessary requirements for such properties as abrasion, dyeing, elongation, and tenacity.

With the foregoing in mindjit is an object of the present invention to provide an improved dry-jet wet spinning process which accelerates initial coagulation of extruded filament-forming material to strengthen the filaments whereby increased drawing may be imposed prior to immersion in a coagulating bath to impart desirable physical characteristics to the filaments.

Another object of the present invention is to provide an improved process for increasing the spinning rate of aorylonitrile polymers and copolymers to produce continuous filaments having improved dye receptivity, abrasiveness, tenacity, and elongation properties.

A further object of the invention is to provide an im proved spinning process wherein the extruded filaments are exposed to an annealing medium prior to complete coagulation thereof to achieve desirable physical properties.

Still another object of the present invention is to provide a process for increasing the amount of jet stretch of filaments to reduce the surface area thereof before they come into contact with the coagulating bath and thereby reduce frictional drag between the filaments and the liquid bath.

Other objects and advantages will become apparent from the following detailed explanation of the invention.

These and other objects of the invention have been accomplished by positioning the face of a spinneret or jet from one-half to four and one-half inches from the surface of a coagulating bath comprised of a mixture of Water and dimethylacetamide and enclosing the spinneret in a chamber having a pair of spray nozzles connected thereto for producing a mist or annealing medium which promotes initial coagulation of filament-forming solution of acrylonitrile polymers and copolymers being extruded thrugh the spinneret into the coagulating bath. The fog atmosphere is comprised of either water or dimethylacetamide or a mixture of both atomized by an air supply and is introduced into the chamber through conventional spray nozzles.

In accordance with the present invention, the chamber is filled with the fog atmosphere by a pair of spray nozzles positioned at a level between the coagulating bath and the spinneret and directed toward each other. The emerging filaments are exposed to the semi-coagulating atmosphere immediately and a skin-like membrane is formed on the outer surface thereof to strengthen the filaments while the central portions remain in a gel-like state until entering the coagulating bath. The extra strength imparted to the filaments by he fog amosphere makes possible the imposition of more drawing force on the filaments to achieve a higher jet stretch which results in faster spinning rates and improves particular physical characteristics such as dye receptivity, resistance to abrasion, tenacity, and elongation. Heretofore, these properties have been obtained by annealing the filaments in a stretched condition during a subsequent operation. The faster spinning rate is made possible by the fact that the spinneret can be positioned farther away from the coagulating bath since the fog accelerate initial coagulation which strengthens the filaments and makes them capable of withstanding more drawing to maintain enough tension on the filaments to prevent coalescence with one another unless the distance exceeds four and one-half inches. Thus, there are two important aspects present which aid each other to accomplish the principal objects of this invention. For example, as more initial coagulation occurs the filaments are strengthened to permit spacing of the spinneret face farther from the coagulating bath which extends exposure time and causes further coagulation.

Another important feature of the present invention which makes faster spinning speeds possible is the drawing down of the filaments as they are extruded from the spinneret face before they come into contact with the liquid coagulating bath where frictional drag normally reduces the maximum speed on unstretched filaments. The attenuating forces imposed on the semicoagulated filaments reduces the porosity of them and promotes better homogenity. The reduction in diameter of the filaments is facilitated by the increased jet stretch which is made possible by this invention. By jet stretch is meant the ratio of the linear rate of withdrawal of fibers from the spin bath to the linear rate of extrusion of spinning solution into the spin bath.

The present invention will be more clearly understood by reference to the drawing which illustrates a side elevation, partly in cross-section, of a dry-jet wet spinning apparatus modified in accordance with the requirements necessary for carrying out the invention.

Referring specifically to the single figure of the drawing, there is shown a spinneret or jet positioned above a suitable liquid coagulating bath 12 with the face thereof directed toward the bath. The spinneret may be of any well known type and may be spaced one-half to four and one-half inches from the liquid depending on the results desired. The spinneret is enclosed in a cylindrical casing 14 having a closure provided with an opening 18 to receive a rounder arm 20 which supplies the spinning solution from a source, not shown, and the other is open but extends substantially to the liquid bath 12 to form a fogging chamber 22. The spinning solution is extruded through the orifices in the spinneret 10 and into the liquid coagulating bath 12 to form a ribbon of filaments 24. At an elevation intermediate the spinneret and liquid bath, a pair of conventional spray nozzles 26 are positioned inside chamber 22 on each side of the filaments for injecting a mist or fog into the chamber to establish a fog-like atmosphere which functions as a semi-coagulation zone. The mist or fog is comprised of Water or dimenthylacetamide or a mixture of both and is atomized by pressurized air, the sources not being shown. The filament ribbon is guided through the liquid bath 12 by a pair of bars 28 and withdrawn through a stripper bar 30 before passing over take-up rolls 32.

A clearance is provided around rounder arm 20 at opening 18 and between cylinder 14 and the liquid bath 12 to permit the exhausting of air from chamber 22. The chamber remains completely saturated with the atomized liquid at all times to insure that all surface areas of the filaments are exposed to the fog atmosphere so that maximum desired results are obtained.

The invention will be further illustrated but is not to be limited by the following examples. All parts are given by weight unless otherwise specified.

EXAMPLE I A spinning dope was prepared by dissolving 24 parts of a copolymer comprised of 94% acrylonitrile and 6% vinyl acetate in 76 parts of N,N-dimethylacetamide solvent. The dope was heated to 85 C., filtered, and delivered to the spinning apparatus. The dope was extruded through a spinning jet containing 68 holes 0.010 inch in diameter. The spinning jet was positioned 3.5 inches above a spin bath comprised of water and N,N-dimethylacetamide solvent at 42 C., and was enclosed by a mist chamber which extended from above the spinning jet to within A inch of the surface of the spinbath. A mist of N,N-dimethylacetamide solvent in air was continuously introduced into the chamber by means of two opposing spray nozzles. The filaments extruded from the spinning jet passed through the mist and into the spin bath while undergoing a jet stretch of 6.5x. The coagulated filaments proceeding from the spin bath were washed with hot water to remove residual solvent, given an additional stretch of 2.0x to provide molecular orientation, and dried to reduce the moisture content to less than 1.0 percent.

The resulting fiber product was evaluated for physical properties and basic dyeability. The fiber tenacity was 2.7 grams per denier, and elongation was 49%, as determined by a single filament tests on the Instron tester. The fiber dye acceptance (BDA) was 1.6% dye uptake based on the weight of fiber.

4. EXAMPLE II The process of Example I was repeated except that the mist chamber was removed and the spinning jet was lowered so that a /2 inch air space existed between the surface of the spin bath and the face of the jet. The maxi mum stretch which could be imposed upon the filaments extruded from the jet and passing into the spin bath was 3.0x. An additional stretch of 4.0x was taken during the subsequent washing step to provide a total filament stretch of 12.0

After the filaments were washed and dried, the tenacity was determined to be 2.2 grams per denier, and elongation was 24%. The BDA of the fiber was only 0.6%.

EXAMPLE III The process of Example I was repeated except that a mist of water and air was sprayed into the mist chamber. The face of the spinning jet was positioned 2% inches above the surface of the spin bath, and a stretch of 3.1x was imparted to the extruded filaments passing through the mist chamber and into the spin bath. An additional stretch of 6.2x was taken during the washing step providing a total fiber stretch of 19 After the fiber was dried, the tenacity was determined to be 2.9 grams per denier and the elongation 30%.

EXAMPLE IV A spinning solution was prepared by dissolving 16.7 parts of a first copolymer comprising 94% acrylonitrile and 6% vinyl acetate and 2.3 parts of a second copolymer comprising 50% acrylonitrile and 50% methyl vinyl pyridine in 81 parts of N,N-dimethylacetamide solvent. The solution was heated to 85 C., filtered, and transferred to the spinning apparatus, where it was extruded through a spinning jet containing 68 holes 0.010 inch in diameter. The face of the spinning jet was positioned 2 inches above the surface of the spin bath, which was comprised of 45% Water and 55% N,N-dimethylacetamide at 42 C. A vertical tube mist chamber enclosed the spinning jet and extended to within inch of the surface of the spin bath. A mist of N,N-dimethylacetamide solvent and air was introduced into the chamber by means of two opposing spray nozzles located approximately midway between the spinning jet and the surface of the spin bath. A stretch of 3.0x was imparted to the extruded filaments while passing through the mist chamber and into the spin bath. An additional stretch of 1.6-X was taken during subsequent washing of the coagulated filaments.

After drying, the filamentary tow bundles were texturized according to conventional techniques. The resulting textured yarn was evaluated on an IP-4 tester, and found to have a tenacity of 1.15 grams per denier, and an elongation of 13%. The basic dye acceptance of the yarn was 1.6 grams of dye per grams of yarn.

EXAMPLE V The process of Example IV was repeated except that a 50/50 mixture of N,N-dimethylacetamide solvent and water were sprayed into the mist chamber. The texturized yarn product had a tenacity of 1.12 grams per denier and an elongation of 14%. The basic dye acceptance of the yarn was 1.5 grams of dye per 100 grams of yarn.

EXAMPLE VI The spinning solution of Example IV was extruded through an identical jet positioned /2 inch above the surface of the spin bath, and not enclosed by the mist chamber. A first stretch of 1.7 was taken as the extruded filaments passed from the jet through the air space and into the spin bath. A second stretch of 2.2 was taken while the filaments were washed after proceeding from the spin bath.

The dried, filamentary tow bundles were texturized according to conventional techniques. The resulting textured yarn was evaluated on the IP-4 tester, and found to have a tenacity of 1.14 grams per denier and an elongation of 7.0%. The basic dye acceptance of the yarn was 0.62 gram of dye per 100 grams of yarn.

It is obvious by comparing the yarn data of this example with that of Example IV that the incorporation of the mist chamber device produces yarn with improved physical properties and considerably greater aifiinity for basic dyestuffs.

EXAMPLE VII The process of Example IV was repeated except that the jet enclosed by the mist chamber was lowered so that the jet face was /2 inch above the surface of the spin bath, and a water-air mist was sprayed into the chamber. The fiber passing from the jet to the spin bath was stretched 3.0x, and a second stretch of 1.5 X was taken during the subsequent washing operation.

The dried filamentary tow bundles were texturized according to conventional procedures, and the resulting yarn evaluated for physical properties on the IP-4 tester. The yarn was found to have a tenacity of 1.2 grams per denier, and an elongation of 11%. The basic dye acceptance of the yarn was 1.1 grams of dye per 100 grams of fiber.

It will be understood that various modifications may be made in the embodiment and practice of the invention illustrated and described herein without departing from the scope thereof except as defined by the following claims.

We claim:

1. A wet spinning process for forming continuous synthetic filaments from a solution comprised of a copolymer of acrylonitrile and a volatile solvent comprising the steps of:

(a) forming continuous filament lengths by extruding said solution from a spinneret substantially vertically downwardly toward a coagulating bath and into an enclosed chamber;

(b) coagulating the exterior surfaces of said filamer lengths to form filaments having a skin comprise essentially of said filament forming material and core gel comprised of said solution by injecting int said chamber an atomized coagulating liquid, sai atomized liquid contacting and removing said vola tile solvent from the exterior filament surfaces t form said skin while said filament lengths pass th distance from said spinneret to said coagulating bath (0) stretching said filaments while in contact with sail atomized coagulating liquid to a final length of a least three times their orginal lengths; and

(d) coagulating said filament core by advancing sai fiber through said coagulation bath.

2. The process of claim 1 wherein the atomized fillit is water.

3. The process of claim 1 wherein the atomized fluid i dimethylacetamide.

4. The process of claim 1 wherein the atomized fillit is a mixture of water and dimethylacetamide.

5. The process of claim 1 wherein said filaments wen stretched at least six times their original length.

6. The process of claim 1 wherein said distance be tween said spinneret and said coagulating bath is fron one to four and one-half inches.

References Cited UNITED STATES PATENTS 2,354,744 8/ 1944 Dreyfus 264-175 2,688,010 8/1954 Chaney 264-203 )4 2,425,782 8/1947 Bludworth et a1. 264-203 2,437,263 3/1948 Manning 264-176 2,542,973 2/1951 Abernethy 264-178 2,948,584 8/1960 Euler et al. 264-206 3,097,415 7/1963 Davis 264-206 JULIUS FROME, Primary Examiner.

J. H. WOO, Assistant Examiner.

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