Stringing of Hot-Melt Adhesives at Bead Application

Stringing (synonym angel hair, cob webbing) is a recurring, undesirable phenomenon in hot-melt adhesives that are applied by bead application. The stringing of eight different hot-melt adhesives for packaging relevant applications was analysed at different temperatures, different distances between nozzle head and substrate, and different nozzle types. Larger gaps resulted in longer strings in most cases. No clear correlations were found for the influence of temperature and viscosity. The use of needle seat valves resulted in less stringing than the use of ball seat valves. The nozzle size had no effect. For all adhesives, a combination of measurement conditions could be found where no or hardly any stringing occurred. Experience shows that these are often not optimal for the application and the properties of the adhesive.