Making Paint from Alkyd Emulsions

Abstract

Every producer and user of paints is familiar with binders that are dissolved in organic solvents. When changing from those 'conventional' systems towards water based alkyd emulsions and/or physically drying acrylic dispersions, certain difficulties concerning paint-formulation, application, open-time, and film formation can arise. The properties of coatings strongly depend on film formation. It turns out that in this respect, paints based on binder dispersions are more critical than solvent-based paints. This is because coalescence of the binder particles is a critical and property-detemining step in the case of dispersions. Film formation, and hence protective properties, are mainly governed by viscosity and miscibility of the resins that constitute the binder particles. By means of a comparison of these two parameters for acrylic and alkyd resins, the differences in film formation between acrylic dispersions and alkyd emulsions are highlighted. It is shown that during film formation an alkyd can spread completely because it inverts from an o/w emulsion to a w/o emulsion. The particles that form a physically drying acrylic dispersion, on the contrary, only coalesce to a certain degree during film formation, even when coalescing agents are used. Complete spreading of the alkyd is very favourable in obtaining high gloss, barrier properties, adhesion/penetration etc. Favourable properties of both acrylic dispersions and alkyd emulsions can be combined to obtain solvent-free paints with good properties.