Patent GB-973085-A (GB)
Title: Production of polypropylene filamentary materials
IPC: B29C48/38
Filed: 1960-11-29
Abstract: 973,085. Polypropylene filaments. FMC CORPORATION. Nov. 29, 1960 [June 10, 1960], No. 41023/60. Heading B5B. Filamentary materials are made from a polymer consisting essentially of isotactic polypropylene having an intrinsic viscosity of 1.3 to 4.5 measured in decahydronaphthalene at 135 C. by a process including the steps of rendering the polymer molten and homogenizing the same, maintaining the molten polymer at a temperature at least equal to the tempature at which the polymer is homogenized and below the temperature at which thermal degradation of the polymer occurs while extruding uniform streams thereof through orifices of a spinneret, said spinneret orifices being alike with each having a diameter ranging up to 125 mils. and a length-to-diameter ratio of from 1.5/1.0 to 7.0/1.0, passing the shaped streams of molten polymer through a heated atmosphere immediately after extrusion thereof to maintain the same in a molten condition, solidifying the shaped polymer streams into filaments as they leave the heated atmosphere, and collecting the solidified filaments at a rate of speed greater than that at which the molten polymer is extruded, whereby the shaped streams of molten polymer are elongated immediately after being extruded and during passage through said heated atmosphere and wherein the polymer molecules are oriented during cooling of the shaped streams thereof into solid filaments. Desirably, the polymer is heated from 225 to 250 C. during homogenizing of the same and is subsequently heated to a temperature of not greater than 325 C. during the extrusion thereof. Preferably, the spinneret orifices each have a diameter of 11 to 125 mils., and the shaped polymer streams are solidified by a uniform flow of cool gas directed substantially perpendicularly across the parts thereof, air velocities of about 16-65 metres per minute being satisfactory. The solidified filaments are desirably heated to a temperature of from 75 C. to a temperature less than that at which the filaments are molten (suitably 75 to 225 C.) and stretched, suitably 3 to 6 times, to induce further orientation, cooled and collected. Apparatus as shown comprises a screw type extrusion apparatus 15 which melts, degasses, compresses and homogenizes the polymer, which then passes through pump 17 to the extrusion assembly 19, comprising a filter 21 and spinneret 23 mounted in a block 24 and encased by a heater 25, which serves to maintain the molten polymer at a desired uniform temperature just prior to extrusion and extends well beyond the spinneret face, to provide a heated zone 27 within which the extruded polymer streams are elongated as a result of the jet stretch applied by a conventional take-up means 29. Heated zone 27 preferably has a maximum length not exceeding 75 mm. As the filaments travel to the take-up means 29 they are solidified or quenched with a minimum or turbulence by a continuous cross-flow of air supplied by a blower 31 through a screened duct 33. In examples, filaments spun and stretched as above show tenacities of 6.3-11.87 g.p.den., with elongations of 21.0-52% and uniformities of 8.8-10%.