Verfahren und Vorrichtung zur Herstellung von Polyaethylenschaum und zellfoermigen Gegenstaenden

A process for making polyethylene foam comprises forming under pressure a flowable composition comprising essentially molten polyethylene having a volatile organic fluid as a foaming agent uniformly dispersed throughout, feeding the composition to a treating zone and subjecting the composition under pressure to ionizing radiations in amount sufficient to bring about an increase in resistance to flow of the polyethylene at a temperature of 100 DEG C. and insufficient to prevent appreciable flow of the polyethylene at said temperature and thereafter extruding the composition into a zone of lower pressure sufficient to cause expansion of the extruded material with resultant formation of a cellular body. As ionizing radiation beta-rays, gamma-rays, X-rays, neutrons or accelerated electrons are mentioned. The polyethylene preferably has a molecular weight of 4000 or above. As foaming agents tetramethylmethane, monochlorodifluoromethane, monochlorotrifluoromethane, dichlorodifluoromethane or dichlorochlorotetrafluoroethane or mixtures of these are suitable. Finely divided inert materials such as calcium silicate, barium sulphate or silica are also advantageously incorporated with the polyethylene to initiate the formation of cells. The extrusion can be effected at 90 DEG to 220 DEG C. In one method, polythene of molecular weight 30,000 is placed in cylinder 2 (Fig. 1) with frangible disc 5. The volatile fluid is added and plunger 6 is inserted followed by cover-plate 7. The jackets 3 and 10 are supplied with heated heat transfer material and then a liquid such as glycol or glycerine or a gas such as nitrogen is pumped into inlet 8 whereby disc 5 is ruptured, and the gel is forced through the constricted passage of head 9 past window 12 from a source of ionising radiation 13 and into the atmosphere, forming a cellular product. A continuous process is also described.