Comparative Study of Anti-Sticking Properties of Coatings for Tire Molds

To improve the anti-sticking performance of tire molds, six types of coatings (i.e., nano-ceramic coating, bilayer waterborne polytetrafluoroethylene (PTFE) coating, fluorinated ethylene propylene (FEP)-based Whitford coating, PTFE, FEP, and perfluoroalkoxy (PFA) aqueous dispersions) were selected to modify type-45 steel specimens by air spraying. Their wettability, microstructure, demolding force, and anti-fouling properties in rubber vulcanization tests were studied. The results show that the demolding forces of the coatings were at least 24% lower than that of uncoated surface. Whitford coating, PFA, and FEP coatings had zero demolding force and no pollutant residue. PTFE coating had no pollutant residue but had high demolding force. The other two coatings had poor anti-sticking property. Upon combining the surface morphology and chemical composition analysis results, the coating demolding force was related to the surface micro-morphology: smoother surfaces led to lower demolding forces, while the surface chemical composition had a direct influence on the rubber contaminant residual. The C–F bonds on the surfaces resulted in less rubber residual due to intrinsic low surface energy. X-ray photoelectron spectrometry (XPS) analysis showed that ZnS was one of the main pollutants after rubber vulcanization test.