Understanding the Sprayability of Hot-Melt Adhesives, 1998 Hot Melt Symposium Proceedings

High productivity spraying processes, such as melt-blown or Controlled FiberizationÒ, are expanding at a rapid pace in the Hot-Melt Adhesives industry. Yet, the materials parameters governing these processes are still unknown, and improving sprayability often resumes to tedious trials-and-error methods. In this work, we first carry out a dimension analysis of the spraying process, and demonstrate that the processing problems occur during the strong and fast extensional flow encountered by the stretched filament. Then, we describe a gram-scale rheological experiment providing a quantitative criterion that correlates with spraying behavior. We show that the spraying process is limited by the cohesive break of the HMA filament, which indicates that low melt elasticity is needed for optimum sprayability. As an important consequence, polymers having narrow molecular weight distribution, such as metallocene catalyzed ExactÒ plastomers (Mw/Mn ~ 2) or VectorÒ styrenic block copolymers (Mw/Mn ~ 1) offer optimum sprayability.