Polyurethane paints offer some of the best performance available. Given their high performance, they are widely used in the automotive and industrial sectors, as well as in metalwork where good protection for ferrous materials exposed to the elements is required.

As the name suggests, these paints produce multiple urethanes. The chemical base is always formed by the reaction of isocyanates/isocyanurates (known as catalysts or hardeners) with hydroxyl (OH) groups added to the base, which can vary in composition (such as alkyd, polyester, or acrylic). Simply using the term “polyurethane” is therefore quite reductive; the number of bonds created and, especially, the quality of those bonds (aromatic, aliphatic, or mixed, and rigid or flexible) are critical for performance.

This explains the price differences among various products labeled as polyurethane. Isocyanates are essentially aromatic or aliphatic; the former are generally more reactive but are vulnerable to intense solar exposure, leading to noticeable yellowing, fading, and dulling of the applied film. The latter don’t suffer from these issues but are considerably more expensive and less reactive, requiring suitable reaction accelerators. Another factor that affects the durability of the paint film is the quantity of bonds created—the more bonds, the greater the resistance. The drawbacks are the high cost and the toxicity of isocyanates, which is why recent European directives require users to have a valid “license” to use them. Spraying isocyanates also requires the use of approved respiratory protection, such as fully-sealed facial masks with external oxygen supply through tubes. Other types of respiratory protection (still widely used) are considered non-compliant, potentially exposing employers to legal consequences in case of later health issues.

Article by: Ind. Exp. Massimo Rubbi – A.I.T.I.V.A. member, Emilia Romagna Region – CTU n. 48, Piacenza Court.