Patent GB-706632-A (GB)
Title: A process for the production of seamless hollow structures
IPC: C08J7/02
Filed: 1951-05-28
Abstract: A seamless hollow article is obtained by treating a solid blank of swellable plastic material and of appropriate shape with a liquid capable of penetrating into and swelling the blank, continuing the swelling treatment for a period of time insufficient to allow complete diffusion of the swelling liquid, thereby retaining inside the blank a substantially unswollen core layer surrounded by an outer swollen layer, and subjecting the swollen blank to a heat treatment at a temperature causing a rapid evaporation of the swelling liquid in the surface of the blank, whereby the surface layer becomes strengthened and solidified and the core layer becomes swollen, and whereby the vapour generated inside the blank splits it in the core layer and distends it with formation of the desired hollow article. The swelling agent is preferably a low boiling point liquid with no strong solvent action at room temperature.  At the temperature of the heat treatment, the swelling liquid may be capable of both swelling and dissolving the previously unaffected core layer.  The swelling liquid may be a single liquid or a mixture, e.g. a mixture of a solvent and a non-solvent liquid.  The blank may be in the form of a foil, sheet, or film of cellulosic, cellulose derivative, rubber, thermoplastic synthetic resin, protein, or protein-like composition. The blank is cut to a shape corresponding to the desired hollow article, e.g. a strip or band is used for the production of a cylindrical hollow article, e.g. a tube.  The blank may be of rectangular, circular, or other cross-section. The heat treatment of the swollen blank may be effected by placing it in or passing it through a heating chamber or a bath containing a heated liquid such as paraffin oil.  Such a liquid may contain softeners, e.g. phthalic esters, or vulcanization accelerators. Heating may be effected by means of infra-red or high frequency radiation.  After the hollow article has been produced it may be submitted to treatment to remove residual swelling agent, e.g. in the case of cylindrical articles, by passing gases or liquids through the interior.  Such treatment may be combined with treatments with softeners, vulcanizing agents, and vulcanizing accelerators.  In general the blanks split at the centre so as to produce hollow bodies of uniform wall thickness, but if desired one surface of a blank may be exposed for a shorter time to the action of the swelling agent so that splitting takes place nearer to that surface, thus producing walls of different thickness.  In an example, cellulose triacetate film strip is immersed for 30 seconds in a mixture of methylene chloride and methyl or ethyl alcohol.  The strip is then placed in a drying oven at 120 DEG C. so that the strip splits internally and becomes distended to form a seamless hollow structure.  An uncured rubber film is placed for 2 minutes in a mixture of benzine, benzene and methanol.  It is then placed in an oven at 150 DEG C.  A hollow body is formed.  Other examples describe the production of hollow bodies of polyvinyl chloride and gelatine.