Polyurethane adhesive are reactive adhesives. This means that these products are applied on substrates as mixture of low molecular weight entities and use a chemical curing reaction to create a polymer, often cross-linked. Polyurethane are formed by polyaddition polymerisation.
Among the reactive adhesives, polyurethane are by far the most diverse group: water-based, solvent-based or solvent free two-component adhesives.
Polyurethane adhesives show very good adhesion to substrates, high mechanical strength, as well as good flexibility and chemical resistance. Due to these properties, polyurethane adhesives are used in a wide range of applications.
For the production of urethane adhesives, either aromatic or aliphatic diisocyanates for PU adhesive are used, most commonly the following types: the use of aromatic iscyanates might promote the formation of primary aromatic amines if the reactive adhesive is not fully cured. As these amines are considered to be carcinogenic, the substances have to be monitored. Aromatic isocyanates are more reactive than aliphatic types, while aliphatic isocyanates possess better UV stability and heat stability. Aliphatic diisocyanates with less reactivity are mainly used in water-based urethane systems and high performance adhesives, either solvent-based or solvent-free.
