GB1345975A - Production of open cell ethylene copolymer foams - Google Patents

Abstract

1345975 Extruding cross-linked foam BADISCHE ANILIN- & SODA-FABRIK AG 2 July 1971 [3 July 1970] 31064/71 Heading B5A [Also in Division C3] A process for the production of an open-cell ethylene copolymer foam comprises forming a homogeneous mixture of a cross-linked copolymer of ethylene and one or more vinyl esters and/or esters of unsaturated carboxylic acids and a low boiling blowing agent at a temperature above the crystallite melting point of the copolymer and a pressure above the vapour pressure of the blowing agent at the mixing temperature, the copolymer being cross-linked to such an extent that the elongation at break of the cross-linked copolymer is 20-60% lower than that of the uncrosslinked copolymer, cooling the homogeneous mixture to a temperature of from 15‹ C. above the crystallite melting point of the copolymer to 20‹ C. below said crystallite melting point, keeping the cooled homogeneous mixture in a zone for a period of at least 10 minutes at a temperature of from 15‹ C. above the crystallite melting point of the copolymer to 20‹ C. below said melting point, the pressure in said zone being such as to prevent expansion of the mixture, and extruding the homogeneous mixture into a zone of lower pressure. The crosslinking is usually carried out in the presence of a low-boiling agent at pressures which prevent foaming of the mixture. Alternatively an already crosalinked copolymer may be mixed with the blowing agent. In one embodiment of carrying out the process the polymer and crosslinking agent are fed through a hopper 3 to an extruder 1 equipped with a rotatable screw 2 where the polymer is melted and partially crosslinked. Blowing agent is passed through inlet 4 under pressure and the melt is cooled to a temperature in the range specified above, before being extruded through the nozzle 5 to a cylinder 6 surrounded by a heat exchanger 7. The cylinder 6 is filled with the melt which is kept at a temperature in the specified range and in which the pressure is such that expansion of the mixture is prevented. After the required period of time the outlet nozzle 9, which is initially closed, is opened and nozzle 5 is closed, and the homogeneous mixture is extruded by plunger 8 whereby the continuous extrudate forms. Alternatively the cylinder 6 may be replaced by a second extruder or a number of cylinders may be connected in parallel so that the melt may be fed to one of the cylinders from the extruder while the homogeneous mixture is being discharged to another cylinder and further melt being allowed to reside in a third cylinder. Specific examples also refer to the use of a simple twin-screw extruder.