Media-Tight Polymer-Polymer Assemblies By Means of Sintered Powder Layer in Assembly Injection Moulding

Abstract

The demand for media-tight assemblies has increased continuously in recent years. The explanation for this is the increasing automation, which not only is the reason for more electronics and sensors, but also for the application in increasingly exposed areas. Components must be efficiently protected from these new stresses, such as those caused by contact with aggressive and corrosive media. Assembly injection moulding is a process suitable for large series production that can be used to achieve a protective effect by overmoulding. The focus in this article is a novel and innovative approach that exploits local additive structuring to generate increased media-tightness due to a labyrinth sealing effect. Using an IR spot, the surface of the insert made of polyamide 12 (PA12) is melted and a powder layer made of PA12 is applied, thus creating a structure made of identical material. The inserts prepared in this way are overmolded with polypropylene (PP). The properties of this adhesion-incompatible polymer combination were then examined with regard to their bond quality in the pull-out test and their media-tightness by differential pressure method. It was shown that the additive structuring clearly increased both the bond quality and the media-tightness. This showed the functionality of the pre-treatment. In addition to the feasibility, various application variants were investigated in order to be able to define an initial process window. Overall, it was shown that, depending on the powder application, very good local tightness increases can be achieved.