Corrosion protection on texturized steel moulds for polymeric products by sol-gel anti-adherent coatings

During the moulding of polymeric pieces, the important temperatures involved, and the gases produced by decomposition of components from the polymer can induce corrosion on the working surface of the steel mould. Polymers can also stick to the mould surface, being their separation (demoulding) one of the critical aspects in their processing. Demoulding agents typically used in this process are expected to contribute in some extend to protect the mould against corrosion. In this work, hybrid sol-gel technology for anti-adherent coatings presented in previous papers is extended to formulations doped with different metallic precursors of proven chemical and wear resistance such as Zn, Ti, and Zr, with the aim to increase the corrosion resistant at the same time that keep good demoulding properties. Different synthetic routes one-pot or two components were followed depending on the doped agent. Sol-gel formulations were applied onto steel substrates by controlled dip coating technique, resulted in ultra-thin films of similar to 0.15 mu m, being capable to protect micro texturized steel moulds. Hardness of these films was superior (10H) to those formulations with fluorosilane and PDMS used as reference. Corrosion protection was evaluated obtaining good results in both polarization resistance and corrosion rate for Zn (5232 omega x cm(2), 0.08 mm/year), protecting the bare steel up to 6.5 times more in terms of annual corrosion, followed by Zr and Ti. Their behaviour as anti-adherent coating was also discussed and compared with fluorosilane and PDMS-based coatings.