Patent GB-1121871-A (GB)
Title: Treatment of oriented crystalline polyester filaments
Inventor: CHAPMAN ROY
IPC: D02J13/00
Filed: 1965-08-23
Abstract: 1,121,871. Polyethylene terephthalate filaments. IMPERIAL CHEMICAL INDUSTRIES Ltd. 12 Aug., 1966, No. 36025/65. Heading B5B. High tenacity filaments are made from polyethylene terephthalate in which the intrinsic viscosity of the polymer is 0.85 to 1.00 dl. per gram and which have uniform properties throughout their length with a tenacity of at least 8 grams per denier in the form of a yarn of up to 10,000 denier and not more than 1 turn per inch twist, an extension of at least 10% and a shrinkage of less than 8% and a 2 % modulus of at least 80 g.p.d. and a shrinkage force at 150‹ C. of less than 0.35 g.p.d. Such filaments may be made by positively passing filament yarns of up to 10,000 denier with not more than one turn per inch twist between feed means to take-up or winding means rotating at predetermined relative speeds, which may be the same, greater or slower, wherein the filaments are passed through a heating zone for a time between 1 and 12 seconds, the heating zone being equipped with positive heat exchange means comprising a multitude of solid particles maintained precisely at a temperature Œ3‹ C. in the range 240 to 264‹ C., that is to say 25 to 1‹ C. below the melting temperature of the filaments. In a preferred method, the filaments are relaxed 3 to 4% whilst passing through the heating zone at a speed of at least 300m. per minute using treating times of the order of 2 to 5 seconds in which the tension is controlled by suitable means. Alternatively the filaments may be heat set at constant length while passing through the heating zone at speeds of at least 300m. per minute using treating times of the order to 2 to 5 seconds. In both these methods speeds of 1,000m. per minute are preferred. Dwell times, depending on denier, may vary preferably between 1 and 12 seconds. Thus for 1,000 denier yarn, a dwell time of 1 to 5 seconds, preferably 2.5 to 3.5 seconds, is suitable. Path lengths through the hot zone may be varied by adjusting the number of passes, i.e. numbers of wraps round a presystem in a single bed, or by using a number of beds in series. Suitably, the filaments are preheated before being brought into contact with the solid particles. The solid particles are suitably of cross-section between 1 mm. and 50 microns and may be heated by means of heating coils immersed in a bed of such particles, by circulating heating fluids through a suitable jacket around a container in which the particles are situated, by heating the particles electrically by heated elements which are immersed in the particles, or by using heated elements which form a wall of the container. The gas stream itself may be heated during or before passage through the bed of particles. The solid particles are suitably maintained in a fluidized condition by a gas stream which is heated and maintained at the required temperature within Œ1‹ C. The particles may be brought to the required temperature in a suitable bed and metered by gravity downwards on to the filaments followed by bringing the particles back into the bed by suitable means. The heat relaxation process is preferred if low shrinkage properties are more important than yarn modulus, but if yarn modulus is more important, heat setting at constant length is preferable. In both cases heat setting at the stated highest possible setting temperature gives the best result. Oriented crystalline filaments so made are useful in the form of rubber reinforcements including V-belts, conveyor belts, tyres, hose and fabrics, including fabrics coated with polyvinyl chloride and neoprene.