New aspects of process induced properties of microinjection moulded parts

The microinjection moulding process is subject to microspecific phenomena, such as rapid cooling or high shear rates, which greatly affect part properties. While the correlations between morphology, crystallinity and the mechanical properties are well known for parts of usual macroscopic dimensions, there is less information available for microparts. In this paper, these correlations are discussed, related to the dimensions of semicrystalline thermoplastic parts. Results indicate that, if submitted to rapid cooling, microparts exhibit a fine structure, with low crystallinity, low yield strength and low elastic modulus. Experimental investigations have shown the influence of process parameters to be negligible. More important are the material's rate and ability to crystallise, which allow for properties to be significantly enhanced. Another possibility to considerably improve the performance of microparts independent of the used polymer is processing with slow cooling in thermally conductive moulds.