A modified apparatus for testing the probe tack of pressure-sensitive adhesive materials

A modified probe-tack test is described in which a special device is capable of detecting the first contact between the probe and a pressure-sensitive adhesive (PSA) and to determine this contact as the initial dwell time. In tests using viscoelastic PSA materials (hydrogels), this modified device gives results which differ significantly from those obtained with conventional probe-tack testers. In particular, when tack values are plotted against dwell time, the modified tester reveals a regime of sigmoid low-energy tack and then a transition to the normal power-law high-energy tack. This transition behavior was studied as a function of crosshead velocity, compression pressure, adhesive rheology and adherend surface roughness. The practical implication is that far more information can be obtained from this modified device than from conventional probe-tack testers. The modified machine and methodology should prove particularly valuable as an experimental tool and for quality-control tests in the manufacture of PSA products, particularly soft and tacky viscoelastic substances.