The benefits of blocked isocyanates are well-known in various industries including coatings and adhesives. Blocked isocyanate and blocked polyurethane prepolymer technology enable 1K polyurethane systems with reduced free isocyanates and extended storage stability by minimizing moisture sensitivity of the system. Coating applications such as electro-deposition, electro-static spraying, powder coating, insulating wire coating, and coil coatings have extensively explored this technology because this approach provides a solution to minimize health concerns from free isocyanate exposure while allowing coatings to cure by heat. In the case of blocked prepolymers, they are used in 1K and 2K epoxy-amine adhesives, 1K polyurethane hotmelts, pressure sensitive adhesives, and sealants.
Commonly used isocyanate blocking agents include Phenol, Nonyl phenol, Methylethylketoxime (MEKO), Alcohols, ɛ-caprolactam, Amides, Imidazoles, and Pyrazoles. The chemical structure of the blocking group has a major impact on the deblocking temperature and cure rate of the coating or adhesive, and also impact volatile content and final properties. Phenols and Nonyl phenols have been employed as isocyanate capping agents for many years, but recent health concerns over toxicity of these molecules motivated consumers to look for safer and affordable alternatives.
NX-2026, which is a very high purity, renewable phenolic material derived from cashew nutshell liquid, has been introduced as the most suitable alternative to various phenols based on its favorable deblocking conditions, low viscosity, and better labeling.