Developments in raw materials part 5: Convertible media

The binder or media component of surface coatings can be subdivided into two broad groups, non‐convertible and convertible, which differ in their mode of film formation. Binders of the non‐convertible type do not undergo chemical conversion reactions whenthey cure, and film formation here involves loss or evaporation of a volatile solvent and concomitant deposition of the solid binder. Important members of this group are the rubber derivatives and the many examples of vinyl copolymers; some recent developments in the technology of these polymers were described in the previous article in this series. This article will consider the convertible media used in coatings, where film formation involves some form of chemical reaction. Commencement of this reaction is dependent upon either the presence of a suitable initiator, or by exposure to some form of radiant energy, which causes the binder (in the form of a monomer or partially‐polymerised component) to rapidly polymerise. This polymerisation reaction can take one of several forms though the result is the same; the binder and hence the liquid paint is converted into a solid material which is substantially insoluble in the original carrier solvent. This review will consider some of the recent literature concerned with three important members of the convertible group of media; alkyd, epoxy and polyurethane resins.