Читать книгу Additives for Water-borne Coatings - Wernfried Heilen - Страница 91

The structure of foam is not homogeneous. Depending on the air content and composition of the liquid phase it can have very different properties. Moreover, many foams change their structure over time. There is no universal defoamer for combating all types of foam. Experiments on different model systems have demonstrated various defoaming mechanisms, some of which interact synergistically while others do not interact at all. The complexity of coating formulations does not allow defoaming mechanisms to be investigated directly in real systems. Even today the search for the best defoamer for a particular water-borne coating is largely dependent on empirical knowledge. Important selection criteria are the chemistry of the binder system, the application system, the pigment volume concentration, the application method and the incorporation conditions for the defoamer. Recommendations by suppliers of defoamers provide helpful advice for selecting the right product. However, in the end, testing under conditions close to practice is the only way of proving if the choice is correct.