Highlights in substrate protection

Abstract

After a few introductory remarks on the composition, formulation and application of organic coatings, this paper reviews some special subjects with respect to substrate protection by organic coatings. The substrates discussed are wood, steel, concrete, galvanised steel and paint, each characterised by specific degradation processes. The degradation of wood is caused mainly by moisture, UV radiation and fungi. Substrate protection can be supplied either by transparent coatings or by opaque paints. The protective function of transparent coatings is improved by the incorporation of UV absorbing compounds, and by the use of transparent iron oxides with very small particle sizes. Recent developments in the field of opaque paints include water-borne and highsolids formulations. In the latter case, research is focused on the problems associated with the use of resins with low molecular weights and narrow molecular weight distributions. The effectiveness of protective coatings on steel depends to a large extent on the pretreatment of the surface and the conditions during application. A tendency is seen towards high-solids and solvent-free protective coatings. A point of special interest is the widening of the application window, i.e. the development of materials and processes which allow application under adverse conditions. Two examples are discussed, viz. a recently developed primer curing at low temperatures, and a technique for simultaneous blasting and priming. As an example of concrete protection, a new lining material capable of bridging cracks is discussed. The progressive acidification of the environment necessitates the protection of galvanised steel surfaces by an organic coating. A study has been made of the surface of galvanised steel by means of modern surface-analytical techniques. In many cases paints are applied on existing paint systems. Paint, as a substrate for a new paint system, has its problems, especially with respect to adhesion. Modern techniques are available to study the performance of paint as a substrate.