Advanced coating systems towards the analysis of polymer flow within microcavities

Abstract

It is known that the production of polymeric micro components by injection moulding presents technology challenges that differ from the ones of conventional macro parts. High shear heating is known to occur in microcavity flows and may significantly contribute to increase wear within the microimpression compromising both tool life service and overall quality of the moulded parts. Advanced coating systems, detaining high hardness, high thermal conductivity, high thermal shock capacity and low friction coefficient may help to reduce the aforementioned problems. In this paper, a micromoulding insert is coated with a nanocrystalline diamond film on one side and a chromium nitride film on the opposite one. The coatings have been characterized as deposited and after the moulding runs. The coated micromoulding block was then used to produce polypropylene parts and specific quality signatures (i.e. weld line relative position) were established in order to assess the coating performance on semicrystalline polymer flow behaviour. It was found that polymeric flow at lower melt temperature may benefit from a diamond coating, which seems to be related with the thermal shock resistance capacity of diamond. The latter may act as a temperature buffer, fading the high influence of the polymer/mould interface heat transfer mechanism.