Metal Finishing Guide Book

2012 Organic Finishing Guidebook Issue

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Page 97 of 331

domination of polyurethane-based coatings. Similar to other applications, au- tomotive refinish coating formulators also face the challenges of reducing haz- ardous emissions. To comply with increasingly stringent environmental regu- lations, automotive refinish formulators are moving toward higher-solid sys- tems. Because the surface appearance will always be the most important re- quirement for automotive refinish applications, new high-solid polyurethanes must reduce VOC without significantly increasing the viscosity of the resulting coatings. The development of low-viscosity polyisocyanates will allow polyurethane coatings to continue to dominate the automotive refinish market in the future. With the improvements in VOC recovery systems, the coil coating industry is able to compete with powder coatings for many metal finishing applica- tions. The benefits of precoated metal have been recognized by many large users, including manufacturers of appliances, automotive under-the-hood parts, and prefinished building panels.Currently, polyurethanes have only a mi- nor presence in these applications; however, in order for the coil coating industry to be competitive in these important applications, it must provide coatings with better flexibility in combination with better chemical and solvent resis- tance. To address these demanding challenges, formulators are developing new technologies that combine urethane with other traditional epoxy or poly- ester formulations. These emerging technologies provide coatings with desir- able performance and good performance/cost balance. Because of the high-performance requirements in durability, flexibility, and corrosion protection, aerospace and military camouflage coatings have tradi- tionally used two-component polyurethane systems. As in other coating appli- cations, the need to reduce VOC emissions is leading to new developments. In ad- dition to the one- or two-component waterborne polyurethane systems, high-sol- id solvent-based coatings were also developed for many applications. Some of these high-solid systems are also being developed as a two-component self-priming top- coat. With the ability to eliminate use of a separate primer, the one-coat polyurethane systems can further reduce their VOC levels. In architectural and industrial maintenance applications, the labor cost has increased rapidly in recent years. For maintaining outdoor metal structures that are exposed to harsh environments, the cost of the paint represents a much smaller portion of the total cost than the time-consuming, labor-intensive re- painting process. Polyurethane coatings offer the best weathering and chem- ical resistance under these environments. The ability to extend repaint cycle times gives urethane protective coatings significant competitive benefits in these applications. Furthermore, longer repainting cycles have the additional benefit of also reducing emissions to the environment. To meet the challenge of air quality regulations, today's high-solid maintenance polyurethane coatings have already achieved 2.8 to 3.5 pounds per gallon VOC levels. In the future, combining the developments in low-viscosity polyisocyanates, lower molecular weight resins, reactive diluents, and waterborne urethane coat- ings, these emissions will be reduced further without compromising the coating performance. SUMMARY Polyurethane coatings offer many advantages for metal substrate applications. Polyurethanes have excellent appearance ("wet look"), mechanical performance, UV resistance, and chemical resistance compared with other coatings. 96

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