Structure size effect on polymer infiltration in injection molded direct joining

Abstract

Polymer infiltration into metal surface structures during injection molding results in a direct and tight metal–polymer joint. Sizes of metal surface structures were maintained within the 50–500 nm range by anodization, and the infiltration depth into several sizes of the structures under various injection speed conditions were investigated in this study. Replicated structures were evaluated using atomic force microscopy after dissolving the metal parts of the joint specimens. The experimental results revealed that the structure size caused a transition of the infiltration dependence on the injection speed. In the case of polybutylene terephthalate–aluminum alloy joining, the infiltration depth increased with the low injection speed the pores equal to or smaller than 300 nm, while the high injection speed led to deep infiltration for the large pores. In structures of the order of tens of nanometers, the viscoelasticity of flowing polymer and molecular orientation could affect the polymer deformation and infiltration much more than the solidification process. The findings in this study provide insights into the anchoring mechanism of injection molded direct joining and could improve the micro/nano replication in the injection molding process.