According to PSTC’s definition, tack is the property of a pressure sensitive adhesive that allows it to adhere to a surface under very slight pressure. It is determined by the ability of the adhesive to wet quickly the surface it contacts (Ref 1). Commonly there are three methods adopted to test the initial tack for PSAs: probe tack, loop tack, and rolling ball tack.
Probe Tack
The benefits of the probe tack test is that the effect of the tape backing is eliminated because the tape is either rigidly affixed to a steel plate or mounted on an annular ring of known weight. However it might be challenging to accurately control the testing parameters, e.g. probe material and surface properties, adhesive softness, real rate of debonding of probe form adhesive, et al.
Loop Tack
The rigidity of carriers play very important role in compression and debonding stage. Therefore the effects of carrier should be considered in evaluating the tack of a PSA. the good things include loop tack test can evaluate different adherends, well-controlled bonding/debpnding rates, and relatively consistent results.
Rolling Ball Initial Tack
Rolling ball method is very easy and quick; it is also a broadly adopted method. It might works fine with rubber based PSA but may not present reasonable results for other type PSAs, e.g. Acrylic. Strictly specking rolling ball methods are not measuring initial tack but a property remotely related to tack.