For special applications like coil coatings or clear coats it is common to use glycidylesters as hardener component, their cross-linking is based on the carboxy-epoxy chemistry too. A different chemical reaction is used in so-called polyurethane powders, where the binder resin carries hydroxyl functional groups that react with isocyanate groups of the hardener component. The isocyanate group is usually introduced into the powder in blocked form where the isocyanate functionality is pre-reacted with ε-caprolactame as blocking agent or in form of uretdiones, at elevated temperatures (deblocking temperature) the free isocyanate groups are released and available for the cross-linking reaction with hydroxyl functionality.