PROCESS FOR MANUFACTURE OF TWO-OR MULTILAYER ARTICLES, MADE OF A THERMOPLASTIC MATERIAL IMPERMEABLE TO GASES, VAPOURS OR ODOURS, BY MEANS OF CO-EXTRUSION OF AT LEAST TWO DIFFERENT THERMOPLASTIC POLYERS ONE OF WHICH IS POLYVINYL ALCOHOL

摘要

There is disclosed a new process for preparing coupled and coextruded multilayer articles (consisting of two or more layers) made of thermoplastic materials, and closed-surface bodies comprising the same. The process comprises (a) feeding, to an extruder connected with a coextrusion head, a polyvinyl alcohol having a high degree of hydrolysis mixed with an aqueous mixture of plasticizing compounds and heated under pressure to bring it to the plastisol state; (b) subjecting the plastisol polyvinyl alcohol to rapid decompression with simultaneous venting of the evolved vapors, before it enters the coextrusion head and while it is at a temperature at least equal to, and preferably higher than, the temperature of the coextrusion head; (c) separately feeding at least one other thermoplastic polymer to the same coextrusion head; (d) adjusting the temperature of the polymers, after contact thereof, so that the temperature of the polyvinyl alcohol is at least equal to, and preferably higher than, the temperature of the other coextruded polymer or polymers; (e) adjusting the flow rate of the polymers so that the outflow linear velocities thereof are equal or differ no more than +/-10%; and (f) molding the coextruded article leaving the coextrusion head into a manufactured article.