APPLICATIONS OF MICHAEL ADDITION CHEMISTRY IN COATINGS TECHNOLOGY

Since the first filings of patent applications on the use of the Micha el addition as crosslinking reaction for coatings around 1984, a lot o f research work has been carried out on its application in practical s ystems. Initial work on the development of coatings for aircraft, car refinishing and timber showed that, especially with urethane acrylate/ malonate polyester combinations, the expected high level of durability could be achieved. Further developments in the field of high solids c oatings revealed inhibition problems however. They were caused by the interaction of the strong bases, used as the catalysts for the Michael reaction, with acidic ingredients from the substrate and with carbon dioxide from the atmosphere. In principle the problem can be solved by using higher doses of catalyst, but the potlife is too short for gene ral use then. Temporary blocking of the catalysts with an alcohol or w ith carboxylic acids was investigated as a way to achieve an acceptabl e potlife. The use of catalysts blocked with carboxylic acids, deblock able with heat or UV light, is a good solution for industrial coatings . Blocking with an alcohol helps to solve the problem of inhibition by carbon dioxide but not the problem of inhibition by the acidic sites in the substrate. (C) 1997 Elsevier Science S.A.