Polyurea spray coatings technology is one of the new developments of the last 20 years. This technology combines fast curing, even at very low temperatures, and water insensitivity with exceptional mechanical properties, chemical resistance and durability.
The development of new raw materials and improved spray equipment has made it possible to overcome the initial problems of this technology such as substrate wetting, intercoat adhesion and surface finish quality.
The latest development programs are focussing on the extension of the application fields through the introduction of MDI-prepolymers combining low viscosity with low NCOcontent, resulting in slower reactivity and/or higher flexibility. Alternatively, prepolymers with higher NCO-content produce coatings with superior hardness. This paper details the technology, eradicates the misconceptions and provides an update on the latest developments in the field of raw materials, formulation and application performance for polyurea spray.
Polyurea spray coatings technology is a recent development in the polyurethane coatings industry. The polyurethane chemistry is about 60 years old. Since the 1970s elastomeric urethane coatings have been available. The polyurea elastomer technology was introduced some 10 years later.
Two main application areas are Reaction Injection Moulding (RIM) and sprayable coatings. Polyurea coatings combine extreme application properties such as rapid cure, even at temperatures well below 0°C, and insensitivity to humidity, to exceptional physical properties such as high hardness, flexibility, tear strength, tensile strength, chemical and water resistance. The result is good weathering and abrasion resistance. The systems are 100 percent-solids, making them compliant with the strictest VOC regulations. Due to its specific curing profile and exceptional film properties, the polyurea spray coating technique developed into various areas, including corrosion protection, containment, membranes, linings and caulks.
The choice between the different polyurethane (PU) technologies is based upon different parameters (Figure 2). Polyurethane presents the best compromise between cost and quality, but is limited by the application performance. The polyurethane system is susceptible to blistering when the substrate contains more than 5% humidity. This is due to the competition between hydroxyl-polyols and water for the reaction with an isocyanate group. Humidity content of the environment and the application temperature are limiting factors for polyurethanes and other chemically reacting systems. Hybrid systems already have a larger scope of application conditions, but the presence of catalysts in hybrids makes them more sensitive to humidity than “pure” polyurea systems. Moreover, because the catalysed polyol/isocyanate reaction behaves differently from the amine/isocyanate reaction to changing application temperatures, the system becomes less robust. Polyurea can be used in extreme conditions. When it is used on substrates almost saturated with water, polyurea will not provoke blistering nor will blistering occur when the air contains high amounts of humidity. Even at very low temperatures (as low as minus 20°C) the polyurea coating will still cure. Polyurea coatings combine high flexibility with hardness. They are the most suitable coatings when the following is required:
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