Heat-Stress Resistance of Hot Melt Adhesives, 1993 Hot Melt Symposium Proceedings

Michael J. Ambrosini

Elevated-temperature stress resistance can be an important consideration when selecting and troubleshooting adhesives. This is particularly true when packaging flaps have high spring-back forces and when goods are stored under warm conditions or shipped in warm climates.

Peel strength, shear strength and softening point are often used as indicators of heat-stress resistance, but they can be very misleading. This is particularly true in packaging applications where bond stresses tend to be more complex than a simple peel or shear stress. Also, typical storage temperatures tend to be much lower than the softening point of the adhesives and adhesive properties can differ greatly between these temperatures.

In this paper, an overview is presented of a test method developed by the Adhesion Committee of the INSTITUTE of PACKAGING PROFESSIONALS (IoPP) which compares heat-stress properties of hot-melt adhesives. Also included is a discussion on how selected variables, such as type and amount of adhesive, stress force and substrate type, affect the elevated-temperature stress resistance of hot-melt adhesives. In addition, examples are given to show how adhesive viscosity and softening point can be misleading indicators of elevated-temperature bond strength.