Urethane coating components pigments

One-component urethane coatings are usually based on MDI, TDI or HDI terminated prepolymers containing free isocyanate groups. Pigmenting such systems is delicate due to moisture in the pigment, which can cause premature gelation. Therefore, these systems must contain additives for moisture removal such as zeolites (alumosilicates). Since the chain extension in such systems is carried out with water from air, one of the products of the reaction is CO2, which diffuses from the film without foaming. 

Acrylic urethanes are used widely in the coating of plastic components, primarily as a clear or pigmented topcoat for basecoated or primed plastics. Clearcoats are formulated with aliphatic polyisocyanates. The addition of a UV absorber and a hindered amine light stabiliser further improve the photostability. Catalysts for the reaction fall into two categories, namely metallic salts and tertiary amines. 

---