Reactive Hot Melt Adhesives (PUR, POR)
Reactive polyurethane-based hot melt adhesives (PUR) are becoming increasingly significant. These can be used to realize high-strength structural bonds. Once the reactive PUR hot melt has been applied, it initially sets physically, followed by a chemical reaction with the humidity resulting into highly molecular polymers with a very high cohesion. This enables extraordinarily high adhesion values, high degrees of temperature resistance, high flexibility at cold temperatures and solvent resistance.
It is important to bear in mind that it may take a while for the adhesive bond to reach its final strength, depending on the moisture content available for chemical cross-linking. To prevent undesirable reactions while the PUR adhesive is in storage, reactive hot melt adhesives are packaged in moisture-proof containers.
Another group in the reactive hot melt adhesives segment are silane-modified polyolefin-based formulas (POR). Compared with PUR hot melts, these are characterised in particular by the fact that they stick much better to untreated substrates such as polyethylene (PE) and polypropylene (PP). Furthermore, they also contain no isocyanates and therefore do not have to be labelled as hazardous goods. In contrast, their cohesion properties are far below those of polyurethane-based adhesives.