Zinc Oxide in Water-based Paint ~ Archie Paint

Does the use of zinc oxide pigments in water-based paints cause an improvement in the water and solvent resistance of the paint film?

The fungicidal effects of zinc oxide (ZnO) pigments in organic coatings are well known and are also being utilised. The presence of zinc oxide in the pigments used also improves corrosion resistance. Indeed, this is an excellent way of preventing sub-surfacde rusting and bubbling of the film, especially if it is in a very damp environment. There is, however, the risk in waterbased paints of zinc oxide reacting with the binder (as well as with other constituents), resulting in a distinct increase in viscosity. In such cases the paint can be stabilised by adding amines such as morpholine or ethanolamine.

Water-based paints containing zinc oxide have been used with great success in many applications and have been on the market for some considerable time. As far as quantities are concerned, formulations containing 1 part of zinc oxide to 4 or 5 parts total pigment and extender can serve as a starting point. lt is difficult to predict whether zinc oxide pigments will markedly improve the water and solvent resistance of any given water—based paint.

The viscosity increase mentioned above indicates that chemical reactions are taking place and it is probable that free carboxyl groups of the binder molecules react with ZnO or Zn(OH)2. Investigations of styrene-acrylate and other copolymer emulsions containing additions of zirconium compounds have shown that these cause hardly any changes in the rheological properties of such systems in the dry state.
On the other hand, there is a distinct improvement in the water and solvent resistance of the films. One can assume that this is a surface effect rather than one due to crosslinkage.