Designing self-stratify coatings based on epoxy-PU systems containing three pigments

摘要

A self-stratifying coating contains at least two resins of different natures, which spontaneously stratify after application on a substrate. Various self-stratifying systems have been reported in the literature, but self-stratifying coatings containing three pigments have rarely been discussed. In this paper, a series of self-stratifying coatings based on an epoxy-PU system and containing three pigments, i.e. zinc dust, micaceous iron oxide (MIO) and titanium dioxide (TiO2) were prepared and applied on glass plates. Stratification was studied and evaluated by Fourier Transform Infrared Spectroscopy using Attenuated Total Reflectance (FTIR-ATR) on both sides of the films. Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM-EDX) analyses and mappings with line scans from cross-sections of the films were carried out to characterise the degree of stratification and the location of the pigments. The aim of this research is to study the factors that affect stratification and the location of the pigments in self-stratifying coatings containing three pigments, and leading to the design of a three-layered self-stratifying epoxy-PU anti-corrosive coating system. It was found that a higher solid percent of epoxy resin has a positive effect on stratification and pigment location. It was also found that better stratification was obtained by replacing some of the xylene in a formulation with a solvent with a higher evaporation rate (butyl acetate).