GB631945A - Improvements relating to the making of thermoplastic moulding pellets - Google Patents

Abstract

Moulding-pellets of cellulose derivatives are prepared by mixing granular cellulose acetate, ethyl cellulose &c. with a plasticizer which is not a solvent therefor in such a way as to retain its granular character, drying the mix, still retaining its granular character, to remove all aqueous moisture in excess of 0.5 per cent, and feeding the material to a hot extrusion machine to form rods which are subsequently cut into pellets. The granular material is mixed with plasticizer in batches in a tumbling mill, each bath being delivered to a reservoir from which the mixture is fed by a chute 18 to a drier. The mixture falls in a thin stream on to inclined vibrating plates 20, 21 where it is exposed to radiant heat from lamps 22 and gradually moves towards the closed passage 25 leading to the hot extrusion machine in which it is plasticized by heat and homogerized by a screen 40, finally issuing as plastic rods 53. The rods are guided down on to a conveyer 54, cooled by air blasts 58 and <PICT:0631945/IV (a)/1> <PICT:0631945/IV (a)/2> finally cut into pellets by a rotary cutter 62. In an example a composition containing 72 per cent of acetylated cellulose (acetyl content 56 per cent) 14 per cent dimethyl phthalate, 14 per cent diethyl phthalate with pigment, if required, added up to 1.5 per cent of the batch, is mixed for 20-30 minutes (for a batch of 320 lb.), dried at 260 DEG F. and extruded &c. In another example a composition of 89.6 per cent ethyl cellulose, 4.9 per cent butyl oleate, 4 per cent dibutyl phthalate, 1 per cent opal wax and 0.5 per cent diphenylamine with pigment, if required, is mixed and dried at 260 DEG F. and extruded.