Coatings, Antifoulings

AbstractAntifouling coatings are used to combat the growth of marine fouling on the underwater areas of ships, boats, and offshore structures. The problems caused by marine fouling and the main types of marine fouling species encountered are described, followed by the history of the development of antifouling coatings. There are four main antifouling technology types in use at present, three of which use biocides to control fouling.The first of these biocidal types uses rosin, or rosin derivatives, to control the release of biocides. There is a buildup of “spent” film, exhausted of biocide, in these systems, which means that the path length for diffusion of the biocides from within the bulk film to the surface, through the spent film (leached layer) increases with time. Biocide leaching thus reduces with time, and so does the efficacy of the coating.The second is the self‐polishing copolymer (SPC) type, where there is continual removal of the paint surface by polymer hydrolysis or ion exchange ensuring that the spent film is completely removed. In this case, there is steady and controlled release of the biocides, which is much more efficient than in rosin‐based systems. The first SPC antifoulings were based on tributyltin (TBT) copolymers, and these dominated the antifouling market for the last two decades of the twentieth century. However, these are now being replaced by TBT‐free SPC systems. The environmental pressure on TBT, leading to a ban on the application of TBT antifoulings in an increasing number of countries from January 2003, has bought about this change.The third type of biocidal antifouling is a relatively new “hybrid” SPC/rosin system, combining the two previously described technologies, to give products with price and performance midway between both.The fourth antifouling type does not use biocides for fouling control. It is based on foul release technology, and coatings of this type rely solely on having a “nonstick” surface to minimize or prevent fouling adhesion. Silicones are the most common type of foul release coating in use at present, and since foul release coatings are environmentally benign they are likely to become increasingly important in future years.