Methods for injection molding and blow-molding multi-layer plastic

Abstract

Methods for injection molding and injection blow-molding multi-layer plastic articles, including containers and parisons for forming containers, which comprise providing a plurality of co-injection nozzle means for injecting plastic materials into associated injection cavities to form each article, providing streams of polymeric materials to form corresponding layers of the articles, moving each stream separately to plural nozzle means, separately receiving the streams in the plural nozzle means, and injecting the streams to form the multi-layer plastic articles. Preferably, each stream of material which is to form a corresponding layer of the articles is provided with substantially the same polymer flow, preferably from where each stream is split and moved to each nozzle means. Valve means can be employed in each nozzle means for positively controlling preferably substantially simultaneously the flow and nonflow of respective materials into the central channel of the nozzle means. Preferably, injection is effected to provide uniform onset flow of one or more internal layer materials into the central channel, cause foldover of one or more of the internal layers and provide in the parison or container sidewall one or more internal layers whose leading edge is substantially unbiased relative to the terminal end of the sidewall.