GB1218438A - Improvements in or relating to the manufacture of foamed articles of thermoplastic materials - Google Patents

Abstract

1,218,438. Extruding foamed resins. JAPAN STYRENE PAPER CORP. 23 Feb., 1968, No. 9008/68. Heading B5A. [Also in Divisions B1 and C3] In the production by extrusion of foamed thermoplastic resins, the resin with additives, e.g. cell size control additives, pigments, flame retardants, static preventing agents, is fed to a space 7 in barrel 2 where it is plasticized, the compressive forces on the resin increasing from the hopper in the downstream direction to a maximum at or downstream of a feed port 6 where a liquid foaming agent is injected into the plasticized resin, the pressure of the resin at the point of injection being greater than the critical pressure of the foaming agent. As shown, the compressive forces are increased by increasing the diameter of the core of screw 3. Alternatively, the core diameter may be kept constant and the screw pitch decreased, Fig. 2, or both the core diameter and the screw pitch may be varied. Further configurations are described in Figs. 3 and 4 (not reproduced). In three examples, to a mixture of polystyrene with citric acid and sodium bicarbonate are added respectively 6% by weight of isopentane, 5% by weight of normal pentane and 7% by weight of propane, and in a fourth example 7À5% of normal pentane is added to a mixture of polyethylene, citric acid and sodium bicarbonate. Further specific polymers are mentioned as well as the use of cellulose.