GB860827A - Apparatus and method for forming pellets of organic thermoplastic material - Google Patents

Abstract

860,827. Extruding pellets. EASTMAN KODAK CO. Feb. 22, 1957 [Feb. 23, 1956], No. 5983/57. Class 87(2). A method of forming pellets from a semimolten organic thermoplastic composition containing a gas under a disruptive pressure, e.g. polyethylene containing unpolymerised ethylene comprises extruding the composition directly into a column of inert liquid, e.g. water, having a hydrostatic pressure at the point of extrusion greater than the pressure of the gas and at a temperature less than that of the material, cutting the material at the point of extrusion whilst immersed in the liquid, permitting the pellets to rise in the column of liquid, maintaining the hydrostatic pressure on the cut pellets during the rise in the liquid until the pellets cool to a non-deformable state, conducting the pellets out of the liquid and then drying the pellets. An apparatus is claimed which comprises an extrusion head 10, with heaters 11, 12, a screen 14 and an annular discharge passage 16 in communication with a series of circularly-spaced die orifices 18 in a die plate 17. A cutter plate 22, with heating passages 26, and a similar series of die orifices 29, is bolted to the extrusion head 10 and is insulated from the die plate 17 by a gasket 20. The cutter plate 22 is part of the side of a liquid container 45, with liquid inlets 40, 50 having a horizontal top portion 48 with a weir 49 discharging on to a mesh conveyer 51 having a drain trough 53. A rotatable cutting head 31, with a liquid discharge opening 38, has spring loaded cutting blades in contact with the exit face of the cutter plate 72. In operation, plastic material passes through the screen 14 into the annular passage 16, separates into rods in the die orifices 18, 29, is cut into pellets by the rotating blades where the flow of liquid through the opening 38 sweeps the pellets clear of the blades and separates them, they are then carried upwards by the flow of liquid from the inlets 40, 50 to discharge over the weir 49 to the belt 51 where the liquid passes to the trough 53 from whence it may be recycled. Thermoplastic materials pelleted may be vinyl chloride, methyl methacrylate, styrene, cellulosics and polyethylene. The pressure of the column of liquid in the container 45 is such as to be greater than the internal pressure of the ethylene gas contained in the pellets so that the gas does not rupture the pellets but diffuses out when the pellets are at least partly solidified. The temperatures of the liquids and thermoplastics are such that on reaching the belt 51 the pellets have sufficient latent heat to be self drying but other drying means such as hot air jets, infra-red lamps, steam coils or electric heaters may be used. A further apparatus may be used (not illustrated) wherein the rods of thermoplastic material are discharged radially from the cutter plate to be cut by blades moving around its circumference.