Injection Blow Molding of Multi-Component Parisons
New Possibilities for Designing Bottles and Flacons
A patent recently granted to Inotech GmbH, Nabburg, Germany, describes a novel process technology for injection blow molding of plastic containers from multi-component parisons. The parison consists of at least two thermoplastic layers. The process starts with application of the first layer to an injection blow molding core. The cavity has protrusions or indentations that give rise to areas of different layer thickness. A further thermoplastic layer is then applied to the parison. This second layer covers only certain areas of the first layer. Finally, the multi-component parison is inserted into a stretch blow molding machine, where it is expanded.
According to the patent, no voids are formed in the parison during the expansion process and the individual layers bond firmly together. The polymer compound of the first layer is cooled to a defined temperature before the second component is applied. Thus, the two polymer components can meld without bleeding into each other.
The thickness of the material layers can be continuously changed in certain areas of the parison by designing the cavity and the injection molding process appropriately. This affords a way of achieving a smooth transition from one color to another when two different-colored materials are used.
The patent also discloses the possibility of simultaneously injecting several thermoplastic components into a cavity during manufacture of the parison. The flow rate of the polymer components in the cavity is regulated by means of the injection pressure and the injection speed. The outcome is a parison with a defined color design.
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