The barrier properties of paint coatings

There are many applications where the barrier properties of paint coatings are key factors determining performance: for example, in protection against the corrosion of metals, carbonation of concrete and rotting of wood. The paint technologist therefore needs an understanding of the important parameters controlling permeability in order to design an appropriate product. The aim of this article is to outline the theory of diffusion of small molecules through polymer films and to describe some techniques for the measurement of water vapour, oxygen and carbon dioxide permeation through paint coatings. The effect of polymer type and pigmentation on permeability will be discussed, together with some practical applications where permeability is an important factor governing performance.