Multilayer coatings based on the combination of perfluorinated organosilanes and nickel films for injection moulding tools

Different multilayer coatings consisting of NiO and Ni layers supporting a 1H,1H,2H,2H-perfluorooctyltriethoxysilane/1,8-bis(triethoxysilyl) octane (PFOS) layer have been studied as possible alternatives for typical injection moulding tools. The NiO layer has been obtained by thermal annealing of an electroless Ni layer, whereas the PFOS layer was deposited by dip-coating. The physical and chemical properties of the ascoated steel have been studied by FIB-SEM-EDX, AFM, contact angle, Raman spectroscopy, X-ray photoelectron spectroscopy and PM-IRRAS. Furthermore, cyclic voltammetry, linear-sweep voltammetry, EIS and MottSchottky analyses were performed to determine the electrochemical properties of the coatings. Thermally grown NiO leads to a nanoporous surface layer with n-semiconducting properties, whereas the addition of the PFOS induced a decrease in the roughness of the studied samples. The corrosion resistance of the thermally grown NiO is strongly improved in comparison to the non-oxidised Ni-coating. Contact angles showed an effective reduction in surface energy on adsorbed PFOS-film. Injection-moulding tests using polyamide (PA6) and polyamide with 30% glass fibre content (PA6-GF30) were performed on a tool coated with PFOS/Ni to assess the anti-adhesive properties of this coating. After 150 cycles, the PFOS/Ni coating displayed remarkable stability, improved wear resistance and anti-adhesion properties to the studied polymers compared with the uncoated and TiN-coated tool.