Chrome plating is still one of the best solutions to coat martensitic steel used in the molding of plastics and rubbers. However, current stringent regulations on environmental impact call for more sustainable processes. In the present work, some physical vapor deposition (PVD) nitride coatings were produced on X155CrMoV12 steel and characterized in terms of both corrosion behavior and surface properties. Results indicated that titanium-based PVD coatings could be a valuable alternative to chromium-based coatings as they exhibited a good compromise between corrosion and surface properties. AlTiN and TiN PVD coatings exhibited adequate hardness for plastic mold applications, with AlTiN reaching hardness as high as 2000 HV. Moreover, the critical loads and adhesion properties were found to be definitely better than those of chromium-based coatings. From a corrosion point of view, the presence of multilayers in AlTiN did not seem to be beneficial as the breakdown potential for TiN (single layer) was ca. 1.1 V vs. saturated calomel electrode (SCE) compared to 0.85 V vs. SCE for AlTiN in aggressive media (NaCl).

In polymer processing, the formation of undesired fouling hinders the plastic manufacturing processes. Hence, the use of emulsions as releasing agents is mandatory and their affinity to the mold substrates plays a crucial role. Therefore, this research work has been focused on the wetting properties of commercial water-based release agents (namely Marbocote ® W2140, EP, EV-333) towards different Physical Vapor Deposition (PVD) nitride coatings (AlTiN, NbN, ZrN and TiN), usually adopted in the industrial manufacture of Hydrogenated Nitrile Butadiene Rubber (HNBR). The investigated solid substrates were characterized by means of profilometry, SEM/EDX and Surface Free Energy (SFE) analyses, whereas, tensiometric determinations were acquired on the commercial pure and diluted emulsions. The release agents/mold substrates wettability features were studied by means of the work of adhesion and the spreading coefficient. Finally, nitride-coated mold seals were directly tested in an industrial plant with the most performing release agent in terms of adhesive features; for the first time, a deep correlation between the service life, in terms of number of molded seals, and surface (contact angles, work of adhesion and spreading coefficient)/electrochemical (OCP) features was drawn. IntroductionPolymer processing technology, including injection and compression molding [1-3], entails a prolonged polymer/metal tool contact. Hence their adhesion [4][5][6], depending on the process conditions, the solid tool surface features (type, roughness and surface free energy) and the polymer chemistry, plays a pivotal role in affecting the quality of the final plastic product.However, when the affinity between the polymers and the mold substrates is relatively low, the formation of mold fouling [7] occurs, causing the interruption of the plastic manufacturing process. Specifically, mold fouling is a layer of material, which forms on the surface of metal molds during the rubber vulcanization. Indeed, it is the result of thermochemical changes in components of rubber compounds during high temperature molding condition, impeding the heat transfer from the mold to the polymer. Thus, in order to obtain defect-free rubber articles, mold fouling must be removed from the metal surface tools by means of regular cleanings, therefore representing an onerous step for the industry (i.e. the production line shutdown, the use of expensive chemical products).Hence, two approaches can be followed to limit the mold fouling phenomena. The first one consists in the modification of the rubber formulation, for example by choosing the right plasticizing agents, such as extender oils [8,9]. The second approach involves the use of release agents [10,11] (typically emulsion-based compounds [12,13]), which are applied to the mold surfaces to ensure the total removal of the undesired products from the surfaces themselves. Regarding the former, the plasticizer is fundamental for the vulcanizing process, because this component allows the phase transitions. However, ba...