Extrusion-free fabrication of zinc-rich powder coatings: Press bonding

Abstract

Given their environmental benefits, zinc-rich powder coatings (ZRPCs) have been used to replace their solvent-based counterparts. However, current ZRPCs can load only 70 wt% zinc, and therefore cannot meet higher anti-corrosive requirements where the zinc concentration is usually over 80 wt%. Above 70 wt% zinc, powder coatings manufacturers encounter problems with powder homogeneity and extruder screw wear. Here, we demonstrate for the first time an extrusion-free method to fabricate ZRPCs by employing a press to avoid using the extruder. The binder and zinc particles formed a raspberry-like zinc-on-binder structure after press bonding. The zinc dust content can reach about 90 wt% in the coating powders. In addition, the press-bonded zinc-rich coating films with 80 wt% zinc showed slightly lower barrier effects, but a more uniform dispersion of zinc particles and a higher zinc utilization and in turn, longer cathodic protection (110 days), narrower corrosion creepage and fewer localized corrosion sites than the extruded coating films (101 days) with the same zinc content.