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Powder coatings have gained a lot of attention since the 1960s and the 1970s (implementation of polyurethanes into the market) because of the environmental and ecological concerns. Over the decades, there have been several publications relating the manufacturing and development of powder coatings as an alternative for liquid/solvent or water-based organic coatings. In general, powder coatings can be divided into two main groups based on the properties of the resin being used, thermoplastic and thermoset powder coating systems. Among thermoset powder coatings, polyurethane powder coatings have outstanding properties such as weather stability and are the best choice for exterior applications comparing overall properties. This paper reviews the most recent advances in the field of powder coating by focusing on polyurethane powder coating as a group of thermoset powder coatings. It also considers the industrial problems engaged in this field, such as emission of the blocking agents, the low reactivity of uretdione systems, and high curing temperature and their solutions. Finally, it also suggests the future potential investigation of polyurethane powder coating compositions and improvements.

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The effect of a thermal treatment, i.e. annealing, on the adhesion of a thermoplastic polyurethane overmolded on a precoated steel substrate was evaluated. The hybrid part was subjected to three different annealing temperatures after the overmolding process. Adhesion of the thermoplastic elastomer was achieved by using an in-house-developed, two-step curable organic powder coating, which was selectively crosslinked to a polyallophanate state. The powder material was applied to the steel substrate by electrostatic charging followed by molecular crosslinking in an oven. The influence of the metal surface pretreatment was also evaluated regarding adhesion. The effects of the postthermal treatment were assessed through mechanical peel test, differential scanning calorimetry, atomic force microscopy, and scanning electron microscopy. Interesting results were obtained regarding strong adhesion between the precoated metal sheets and thermoplastic polyurethane after injection molding, especially in hybrids that were annealed at higher temperatures with the in-house adhesive coating.