To the stratified of foam of polyethylene having a porous structure anisotropic

摘要

1527162 Anisotropic porous cross-linked polyethylenes BAYER AG 19 Feb 1976 [20 Feb 1975] 06562/76 Heading C3C [Also in Division B5] A laminate of cross-linked polyethylene layers which have an anisotropic pore structure in which the cells which are elongated in a direction perpendicular to the plane of the layer in at least one internal layer is produced by arranging as a multilayer structure at least three polyethylene sheets which contain equal quantities of a peroxide as cross-linking agent and differing quantities of a chemical blowing agent with the two external layers containing no or a smaller proportion of blowing agent than the inner layer or layers, heating the structure, e.g. at a temperature of at least 160‹ C. in a continuous heating furnace, so that the individual sheets are cross-linked and at the same time welded together and subsequently foamed by increasing the temperature, e.g. to between 190‹ and 250‹ C. The polyethylene sheets may be extruded from a multiple sheet extruder. Low or high pressure polyethylene may be used. Suitable peroxides which may be used in quantities of 0À3-1À5% by weight are dicumyl peroxide, 2,5 dimethyl - 2,5 - di- (tert. - butylperoxy) - hexane, 2,5 - dimethyl- 2,5 - di - (tert. - butylperoxy) - 3 - hexine, tert. butyl hydroperoxide, cumyl - tert. butylperoxide, di - tert. - butylperoxide and bis - (tert. - butylperoxy - isopropyl) - benzene. The blowing agent may be azodicarbonamide, disulpho hydrazide or N,NSP1/SP-dinitrocopentamethylene tetramine. The laminates may be used for the manufacture of roof covers or wall linings in cars or caravans.