US 3372218 A
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United States Patent Ufiice 3,372,218 Patented Mar. 5, 1968 3,372,218 MELT-SPINNING POLYESTER FELAMENTS David George Bennie, Kinston, and Thurman Ralston Jones, .lr., Greenville, N.C., assignors to E. i. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Filed Sept. 30, 1964, Ser. No. 400,556
1 Claim. (Cl. 264-160) This invention relates to an improvement in melt-spinning artificial fibers. More specifically, it relates to a process for treating the outer face of a spinneret used in the preparation of artificial fibers by the melt-spinning process and to the treated spinneret produced thereby.
The general procedure of forming thermoplastic resins into shapes by forcing them under heat and pressure through an opening generally referred to as an extrusion die is well known. This procedure of extruding includes a forcing of a thermoplastic resin through a specially designed extrusion die known as a spinneret, which is usually referred to as melt-spinning.
In conventional melt-spinning processes, the spinneret is suspended so as to permit the hot, extruded liquid to fall downward, the extruded streams being cooled and solidified into the filament form during this descent. Among the problems encountered in this process have been flicking, bending, and dripping. Flicking is an obvious and repeated deviation of the liquid stream in the face of the spinneret from the normal path of descent. This phenomenon may occur at regular or irregular intervals. At times, an oscillating effect is observed. When the liquid stream is permanently deflected from its normal path of descent, it is said to have undergone bending. Where the liquid stream has flicked or bent to such an extent that it touches and wets the spinneret face, fouling occurs, the continuous liquid stream is broken, and the liquid thereafter drips from the orifice. This is known as dripping. It has been the practice to wipe the outer face of such spinnerets with a brass rod on a scheduled basis to avoid these problems insofar as is practical.
Several methods have been suggested for treating the face of the spinneret in order to reduce the flicking, bending, or dripping tendencies. Berry and Downing U.S. Patent No. 2,403,476, dated July 9, 1946, discloses the use of tetrafiuoroethylene polymer as a coating on the face of a spinneret. This coating was found to be effective for a short period of time but eventually degraded, at the high temperature necessary for melt-spinning of polyesters, and the spinneret then required an even greater amount of wiping until removed from service. An alternate procedure suggested by U.S. Patent No. 2,403,476, consisting of manufacturing the entire extrusion die from a block of tetrafiuoroethylene polymer, has not been found practical for melt-spinning because of inability to machine the small orifices to critical dimensions, particularly non-round orifices. Other treatments of spinnerets, including those of Cresswell U.S. Patent No. 2,475,128, Polak U.S. Patent No. 2,483,783, Cresswell U.S. Patent No. 2,515,697, and Olson U.S. Patent No. 2,719,073, have all been found unsuitable at the high temperatures required for spinning polyesters, because of poor durability of the coating materials or their inadequate abrasion resistance at those temperatures.
It is an object of the present invention to provide an improved process for the production of artificial filaments and fibers and, particularly, for the melt-spinning of fusable, filament-forming polymers. A further object is to provide a process for melt-spinning which lessens the tendency for bending, flicking, and dripping of the extruded liquid. A still further object is to provide a novel and improved spinneret particularly for use in the meltspinning of synthetic fibers. These and other objects will become apparent in the course of the following specification and claims.
In accordance with the present invention, the outer face of a spinneret is coated With a film of an unusually high molecular weight fluorocarbon polymer, by applying a dispersion of the polymer and fusing the coating at considerably higher temperatures than will be encountered in the melt-spinning process. A film of fluorocarbon polymer having a molecular weight of about 25,000 to 35,000 is particularly effective for overcoming the difficulties mentioned. As a result, the number of spinning discontinuities have been reduced by as smuch as 70% of the number of discontinuities which result when using one of the techniques of the prior art. In addition, there is no longer any need to wipe spinnerets routinely to remove accumulated deposits.
Tetrafiuoroethylene telomers of the type described by Brady in U.S. Patent No. 3,067,262, and dated Dec. 4, 1962, have been found particularly useful in the present invention. These materials are normally solid, essentially non-distillable, open-chain, highly crystalline reaction products of tetrafluoroethylene and an active telogen. One compound that has been found to be particularly effective as a coating for spinnerets is prepared, by suitable changes in the procedure of Example V of U.S. Patent No. 3,067,262, as follows:
A 1.03 liter stainless-steel autoclave equipped with an efiicient agitator unit was filled with a solution of 1,1,2- trichloro-1,2,2-trifiuoroethane containing 0.3% by weight di-tert-butyl peroxide. The reactor was closed and heated to 150 C. Gaseous tetrafiuoroethylene compressed to 600 p.s.i. ('42 kgm. per sq. cm.) was introduced into the agitated solution at a rate of 1.7 kgm. of tetrafiuoroethylene per hour in a continuous manner, while the liquid feed solution was continuously passed into the reactor at a rate of 20 kgm. per hour of a 0.03% solution the di-tert-butyl peroxide in trichlorotrifiuoroethane with the reactor being kept liquid full at all times. The pressure was maintained at 600 p.s.i. by gradual release of the product as it was formed. After the reacting mixture was at essentially equilibrium conditions and the reaction was at essentially steady state, the product was formed at a conversion of of the tetrafiuoroethylene. The product was discharged from the reactor as a dispersion of the white wax-like solid in 1,l,2-trichloro-l,2,2-trifluoroethane with the dispersion containing 25% by weight of the solid. The solid wax-like product obtained by evaporation of the liquid medium has a crystalline melting point of 323327 C. The number average molecular weight of the product was 30,000.
The method of applying the fluorocarbon polymer dispersion to the outer face of the spinneret is not critical. It may be accomplished by wiping, spraying, wicking, or dipping. However, it is necessary that the face of the spinneret be thoroughly cleaned before applying the dispersion, and that the polymer dispersion be dried after application and then be fused at a temperature above 325 C., for a sufiicient period of time to allow the spinneret to reach an equilibrium temperature. A time of 30 minutes has been found satisfactory.
A preferred method of cleaning a spinneret prior to the application of the fluorocarbon polymer dispersion includes a heat treatment of the spinneret in an electric furnace after any polishing treatments given to the spinneret. A clean spinneret is placed in an electric furnace heated to a temperature of about 500 C. for at least 30 minutes. The spinneret is removed from the furnace and cooled to room temperature. This is believed to remove any oily accumulations from the face of the spinneret and to provide an oxidized surface on the spinneret which improves the adhesion of the subsequently applied fluorocarbon polymer film on the face of the spinneret.
The amount of fluorocarbon polymer employed is not important as long as sufficient is present to provide a continuous film upon the spinneret outer face. About 0.2 milligram of tetrafluoroethylene polymer per square centimeter of spinneret surface has been found useful, although more or less may be used.
While such spinnerets coated with fluorocarbon polymers have been found particularly effective in the melt-spinning of polyester filaments such as polyethylene terephthalate, they oifer considerable advantage in the spinning of other synthetic polymers which are subjected to similar difficulties and which are extruded at temperatures ranging from about 175 C. to 350 C.
The telomer-coated spinneret of the present invention is particularly adapted to continuous processes since it is not necessary to take it out of operation over long periods of time to treat it, and discontinuities are avoided during the spinning time. The efficiency of the spinning operation has reached as high as 99.98% on tests conducted as long as 9 days over 16 positions.
The following example illustrates one method of carrying out the invention, but it is given merely by way of illustration and not by way of limitation.
Example I A spinneret of the design shown in US. Patent No. 2,341,555, fabricated from a nickel-free steel containing 18% chromium as taught in U.S. Patent No. 2,362,277, having a 4.25-inch diameter outer face and 600 extrusion orifices, each of 0.015-inch diameter, is prepared by burning away any organic matter in an electrically heated furnace to remove any previous polymer accumulations. The spinneret is washed with a detergent in water and then dried, inspected, and repaired if necessary. The cleaned spinneret is coated with about 20 milligrams of the fluorocarbon polymer described above, having a number average molecular weight of about 30,000. The coating is applied by spraying with the described dispersion reduced to half strength with perchloroethylene solvent, using a De Vilbiss spray gun (Model MBC-SlO-SOE) with pressure cup under 25 pounds per square inch (1.8 kgm. per sq. cm.) air pressure. The spray adjustments on the gun are set to give a fine mist about the same size as the spinneret diameter. The coated spinneret is placed in a Lindberg Electric Cyclone furnace and held at 370 C.i10 C. for minutes. The coated spinneret is then cooled and assembled in conventional melt-spinning assembly. Molten polyethylene terephthalate is then fed to the spinneret assembly at a temperature of 290 C. and under pressure of about 2500 psi. The extruded melt is spun at a rate of at least 1500 yards per minute into a 4.35-denier per filament, 600-filament yarn, which provides a typical 1.5-denier per filament yarn after drawing. In a test continuing over a 9-day period using 16 spinning positions, the number of drips per pound of yarn spun is 0.019.
Example 11 In another test under identical conditions, the fluorocarbon polymer coating is replaced with a coating consisting of a tetrafluoroethylene telomer having a crystalline melting point of 300 C. and a number average molecular weight of about 3700. The number of drips per pound of yarn spun is 0.176.
Example III In still another test, spinnerets of the same description are coated with a silicone compound as described in Olson US. Patent No. 2,719,073, and compared to the results of the above examples. The results are tabulated in Table 1.
Example IV A control test is run under identical conditions but without a coating on the spinneret. The results are tabulated below in Table 1.
TABLE 1 Coating on Molecular Dripsdper Example N0. spinneret Weight poun of Spun Yarn 1. None 0.18
While the invention has been described with respect to melt-spinning, the coated spinnerets are also useful in dry-spinning processes and other forms of spinning in which the benefits of the invention can be realized. While particular mention has been made of nickel-free chromium steel as the spinneret material, the invention is applicable to other chromium steels, including those which contain nickel, and also to spinnerets made of other metals and even non-metals to which the invention can be applied with benefit. Many other modifications will be apparent to those skilled in the art without a departure from the inventive concept.
What is claimed is:
1. In a melt-spinning process wherein molten polyethylene terephthalate is spun at a temperature of about 290 C. through a spinneret of chromium steel to form a multifilament yarn, and wherein wetting of the outer face of said spinneret by the molten polyethylene terephthalate has caused spinning discontinuities; the improvement for greatly reducing the frequency of said spinning discontinuities over an extended period of time which comprises conducting said melt-spinning process with a coating on said spinneret face of a continuous film of Wax-like tetrafluoroethylene telomer having a number average molecular weight of about 25,000 to 35,000; said coating being produced by heating said spinneret in an electric furnace at a sufficiently high temperature to provide an oxidized surface and cleaning said spinneret, then applying said tetrafiuoroethylene telomer as a dispersion, drying the applied dispersion to form a coating, and fusing the coating at a temperature above 325 C.
References Cited UNITED STATES PATENTS 2,403,476 7/1946 Berry et al 18-8 2,923,640 2/1960 Buckingham 1l7l32 3,067,262 12/1962 Brady 260-653.1 3,071,856 1/1963 Fischbein 117132 3,170,972 2/1965 Knipp et a1. 264169 X 3,223,739 12/1965 Teumac 260-653.1
ALEXANDER H. BRODh/IERKEL, Primary Examiner.
J. H. WOO, Assistant Examiner,