A new approach to design self stratifying coatings containing nano and micro pigments

Abstract

A self-stratifying coating contains at least two resins of different natures which spontaneously stratify after application onto a substrate. Various self-stratifying systems are reported in the literature, but the incorporation of nano pigments in such coatings and impact of the pigment size on stratification phenomenon are rarely discussed. In this paper, a self-stratifying coating based on epoxy and chlorinated rubber resins was formulated, and two pigments, i.e. nano titanium dioxide and micro red iron oxide were incorporated in the formulation, separately or together. The formulations were then applied on glass substrates. Various formulas of different viscosities and with different ratios of epoxy and chlorinated rubber were made to find the best formulas with acceptable stratification and pigment migration. SEM–EDX cross section analyses and mappings were carried out to characterize stratification and pigment location. It was found that, in clear coat, a very neat stratification is observed, with the chlorinated rubber resin above the epoxy layer. When iron oxide is added in the epoxy resin, it migrates during curing to the chlorinated rubber, without affecting the self-stratification. When both pigments are incorporated, stratification is not observed anymore. However, by changing the viscosity of the formulation (by modifying the epoxy ratio), an acceptable degree of stratification was obtained, and both pigments were obtained in the desired location. These pigments being used for anticorrosive and antibacterial applications, so this formulation could lead to the design of multifunctional coatings.

Graphical Abstract

Keywords:

• Stratification
• phase separation
• pigment migration
• pigment dispersion
• nano sized pigments