Evaluation of non-stick properties of magnetron-sputtered coatings for moulds used for the processing of polymers

The use of magnetron-sputtered coatings to address the adhesion of low-density polyethylene (LDPE) to moulds during processing has been investigated. Eight different coatings were deposited on stainless steel substrates using a closed-field unbalanced magnetron sputtering process. The adhesion of LDPE to non-coated and coated surfaces was evaluated by measuring the tensile force required to separate the polymer which had been compression moulded on the surface. Surface composition, surface energy and roughness affected the adhesion of LDPE to the surface. Alumina, NiCr(N) and Dymon-iC coatings showed the smallest release forces. Study of the effect of surface roughness showed that in the case of coatings that showed near zero release forces, surface roughness did not affect the LDPE adhesion. For coatings that showed significant adhesion to LDPE, however, the release force increased with increasing surface roughness. This suggests that surface composition controls the adhesion behaviour to a greater extent than other factors.