Tailor-Made Polyurethane Powders for High-Quality Coatings
This obstacle has been overcome with the market launch of PU hardeners such as Crelan VP LS 2147, which are based on blocking-agent-free polyuretdiones. Uretdione crosslinkers result in no emissions and release no other molecules during the crosslinking reaction (see Figure 1). Like blocked PU hardeners, they require no labeling. The high quality of traditional polyurethane coatings — namely their outstanding film properties, excellent lightfastness and weather stability, and good mechanical and chemical resistance — was always matched by PU powder coatings. Uretdione hardeners have the additional benefit that the required property profile can be achieved using emission-free powder coatings. This class of products, their advantages and a number of examples are presented in this article.
With the increasing hydroxyl number of the polyester, there are more reaction centers in the molecule. As a result, the viscosity minimum shifts to lower temperatures. The gel time is reduced and curing is faster. The shift of the viscosity minimum to higher values caused by using polyesters with a higher hydroxyl number results in slightly poorer leveling.