Testing the rolling tack of pressure-sensitive adhesive materials. Part I. Novel method and apparatus

Tack is an essential property of pressure-sensitive adhesive (PSA) materials. A novel method and custom-made apparatus for testing the tack of PSA and related materials were developed to simplify the measurement of bonding and debonding processes. A modified rolling cylinder tack test was employed using a custom-made device attached to an Instron Universal Testing Machine. By predetermining the angle (position) of a cylindrical probe-roller hanging down from the Instron's cross-head and lying parallel to a rotary drum covered with a tacky substance, the pressure of the tacky probe and its rolling velocity could be controlled independently. Using this method, it is shown that the bonding and debonding processes have a remarkable influence on the shape of the tack vs. velocity curves. At high velocities (∼0.12-2.12 m/s), debonding occurred before efficient contact between the PSA and substrate was formed and the measured tack force tended to decrease. A statistical procedure was used to differentiate between the 'initial' and 'complete' processes of bond formation. As the longitudinal load increased from 0.2 to 22.0 g/cm, the dwell time (period of bond formation) decreased from 3.6 × 10^-3 to 0.9 × 10^-3 s and from 0.3 × 10^-3 to 0.1 × 10^-3 s, to form 'complete' and 'initial' bonds, respectively. In general, additional longitudinal load compensated for short-term bonding, in which bond formation could not proceed to completion. The experimentally observed features of the rolling tack vs. velocity of the rotary drum for a typical commercial PSA material validated the usefulness of this novel methodology and apparatus to serve as an important tool for studying time-dependent bonding and debonding processes simultaneously. The ease of execution and the high reproducibility enable it to be used to study the experimental tack of adhesive materials.