PRODUCING ARTICLES BY COEXTRUDING POLYVINYL ALCOHOL AND ANOTHER THERMOPLASTIC MATERIAL

摘要

ABSTRACT OF THE DISCLOSUREThere is disclosed a new process for preparing coupledand coextruded multilayer articles (consisting of two or morelayers) made of thermoplastic materials, and closed-surfacebodies comprising the same.The process comprises(a) feeding, to an extruder connected with a coextru-sion head, a polyvinyl alcohol having a highdegree of hydrolysis mixed with an aqueous mixtureof plasticizing compounds and heated under pres-sure to bring it to the plastisol state;(b) subjecting the plastisol polyvinyl alcohol to rapiddecompression with simultaneous venting of theevolved vapors, before it enters the coextrusionhead and while it is at a temperature at leastequal to, and preferably higher than, thetemperature of the coextrusion head;(c) separately feeding at least one other thermo-plastic polymer to the same coextrusion head;(d) adjusting the temperature of the polymers, aftercontact thereof, so that the temperature of thepolyvinyl alcohol is at least equal to, and pre-ferably higher than, the temperature of the othercoextruded polymer or polymers;(e) adjusting the flow rate of the polymers so thatthe outflow linear velocities thereof are equalor differ no more than + 10%; and(f) molding the coextruded article leaving the coextru-sion head into a manufactured article.