GB1041704A - Improvements in and relating to synthetic plastic leaf or film - Google Patents

Abstract

A leaf or film of synthetic organic plastic material comprising a cellular layer having a continuous smooth surface skin of the same material integrated with the cellular layer is prepared by fabricating a starting leaf or film with a smooth surface skin from a mixture based on a synthetic thermoplastic material and a blowing agent which decomposes with the evolution of a gas at a temperature between the softening temperature of the mixture and the melting point of the mixture, immersing the starting leaf in an inert liquid which is less dense than the unexpanded leaf at a temperature at least equal to the decomposition temperature of the blowing agent, removing from the liquid a leaf or film of the synthetic plastic material comprising a cellular layer covered by at least one surface layer and washing the leaf or film with a solvent for the inert liquid. A suitable thermoplastic material is polyvinyl chloride and among suitable blowing agents is azodicarbonamide. The inert liquid may be a polyethylene glycol or an emulsifiable silicone oil. To produce a leaf which is capable of "breathing" a filler which is soluble in the liquid in which the washing is later effected may be incorporated in the mixture before expansion. A suitable filler is pentaerythritol. Alternatively a hygroscopic filler such as cellulose powder may be incorporated in the mixture before expansion so as to render the leaf more or less absorbent with regard to moisture. Plasticizers, stabilizing agents and lubricants may also be added to the mixture.