Apparatus and a process for the production of elastane filaments

#This invention relates to an apparatus and a process for the production of elastane filaments by the wet spinning method, with improved titer uniformity of the elastane filaments and an increased service life of the spinning nozzles.

#Elastane filaments are currently mainly produced by two methods which are fundamentally different, namely the dry spinning method and the wet spinning method. In the dry spinning method, the spinning solvent of a solution of a polyurethane, typically in dimethylacetamide, is removed from the filaments which are spun in the spinning shaft, by hot gas in the spinning shaft and by heating the spinning shaft. In the wet spinning method for the production of elastane filaments, the elastane solution to be spun is generally pre-filtered after a degassing step and is transferred into a spinning vessel. The polymer solution is subsequently filtered, and after the optional further addition of additives the spinning solution is fed to spinning nozzles by means of metering pumps. This procedure is described, for example, by F. Fourne in Chemiefasern/Textilindustrie 44/96th Volume Year, page 365, and in U.S. Pat. No. 3 526 689.

#Elastane solutions are understood to be solutions of polyurethanes or polyurethane-ureas, which are usually structured in a segmented manner from hard and soft segments, in suitable solvents such as dimethylacetamide or dimethylformamide. Depending on the area of application, polyester or polyether chains are usually incorporated in the polyurethane(-ureas) as the soft segments.

#The invention is explained in more detail below with reference to the Figures, where:

#FIG. 1 is a cross-section through one embodiment of the spinning nozzle apparatus according to the invention; and

#FIG. 2 is a diagram which illustrates the arrangement of the spinning nozzle apparatus shown in FIG. 1 in a precipitation bath 11.

#The nozzle apparatus which is constructed as a "nozzle package" is shown in FIG. 1. It consists of a shaped cylindrical body 1 which contains stainless steel, and which contains a static mixer (Type SMK, Sulzer) and a filtration element 3, which is joined to the spinning nozzle 5 via the passageway 9 of a connection piece 8, with the aid of a quick-change bayonet coupling 4. The connection piece 8 and the shaped body 1 can be detachably joined at the bores 17 by means of threaded screws. At its outlet in the direction of the spinning nozzle 5 the shaped body 1 has recesses 6 which are employed for its rapid suspension in the pegs of a holding device 10 on the precipitation bath 11 and for adjusting the nozzle package in the precipitation bath 11 (see FIG. 2). Via a flexible hose connection 7, the entire apparatus is fashioned for feeding the spinning solution so that the entire nozzle package 1, 8, 5, including the spinning nozzle 5, can be replaced without problems within one minute if it is necessary to change the spinning nozzle. As a rule, there is a plurality of nozzle packages of this type which are disposed side by side or one above another in a precipitation bath 11 for the production of wet-spun elastane filaments. A fine cloth filter 16 with a mesh aperture of less than 10 .mu.m is mounted just in front of the nozzle aperture 5.

#A 30% elastane spinning solution, prepared according to Example 7 of DE-OS 4 222 772, which had been pre-treated for about 10 minutes with 0.8% diethylamine at 130.degree. C. and which had a spinning viscosity of 18 Pa.s at 70.degree. C., was spun via the nozzle package, as described above, from a 40-orifice nozzle 5 into an aqueous precipitation bath solution 12 containing 15% by weight dimethylacetamide (DMAC) in the precipitation bath 11. A so-called "SMX mixer" supplied by Sulzer, Switzerland, was used as the static mixer 2 in the nozzle package. A cylindrical metal filter candle supplied by the Fuji Filter Manufacturing Co., Tokyo/Japan, which had a mesh aperture of 10 .mu.m, was used as the filter 3. The precipitation bath temperature was 80.degree. C. As described in DE-OS 4 446 340, Example 1, the filaments were pulled off via a deflection roller 13 and pull-off rollers 15, and moreover were subsequently treated as described in DE-OS 4 446 340. The take-up rate was 80 m/minute. The elastane filaments had a titer of 318 dtex for 40 individual filaments. The coefficient of variation of the titer was 0.89, as determined from 250 separate measurements. The nozzle 5 operated for 9 days overall. After a spinning period of 5 days, the nozzle 5 could be used again for spinning without problems after a 2-day interruption, after briefly washing it down with DMAC.

#A 30% elastane spinning solution was prepared and spun as described in Example 1. A conventional spinning apparatus (corresponding to an arrangement from US 35 26 689) was used instead of the nozzle package. The elastane filaments obtained had a titer of 316 dtex for 40 individual filaments. The coefficient of variation of the titer, which was again determined from 250 separate measurements, was 3.91. The nozzle 5 operated for 3.5 days overall. Individual torn-off filament portions in the form of so-called "smears" subsequently occurred in front of the nozzle. Coil formation and the formation of wound-on deposits occurred on the deflection roller 13 in the precipitation bath 11. Production had to be interrupted.