Dynamic Mechanical Properties of Pressure-Sensitive Adhesives

Abstract

The performance of pressure-sensitive adhesives (PSA) is related to the viscoelastic response of the bulk adhesives as well as to the surface energies of the adhesives and adherend. Testing the performance of a pressure-sensitive adhesive involves both the formation and destruction of a bond. For the typical tack, peel strength, and shear strength tests, the bonding conditions, such as the applied stress and dwell time, are specified, as are the debonding conditions of strain rate for tack and peel, and stress for time to failure in the shear test. To perform satisfactorily as a pressure-sensitive adhesive, the material must respond to a deforming force in a prescribed manner during both bonding and debonding. It must adhere to the substrate during bonding and exhibit a measurable resistance to separation at debonding conditions. In each of these steps, both the rate and extent of deformation are important. Bonding is a low rate process at low deformation, when the adhesive is brought into contact with a surface, while debonding in the tack or peel tests is a high rate process at high deformation relative to the thickness of the adhesive. The shear strength test is essentially a creep test carried to high deformation. Thus, the viscoelastic behavior of the adhesive controls its response in adhesive testing and is a major factor in its performance.