Extrusion Dies Industries, LLC (EDI) unveiled a new surface coating on flat dies at NPE 2009 which it says withstands attacks from the corrosive hydrochloric acid (HCl) generated in the course of extruding PVC. The surface coating called DuraCoat™, is inert when exposed to harsh chemicals, according to Gary D. Oliver, vice president of technology. While EDI is exploring possible uses with a range of other corrosive plastics, it is recommending DuraCoat for dies used to produce PVC foam, film, and sheet. The thermal degradation of PVC caused by heat and shear during extrusion generates HCl byproduct that can inflict extensive damage to dies with conventional surfaces.
"This new coating forms an extremely thin film on the steel surface of the die that has no effect on even the most intricate features machined into flow surfaces," said Oliver. "The low friction coefficient of the coating provides improved slip release in comparison with that of standard chrome plating." DuraCoat™ exhibits exceptional hardness, very high melting and oxidation temperatures, and insolubility in most acids and bases, Oliver added. The coating has been successfully applied to tooling in the injection molding industry and has already been used by EDI customers producing vinyl residential siding (post-formed from sheet) and foams, according to Oliver.