Peeling Shear and Cleavage Failure Due to Tape Prestrain

In 1960 Kaelble published data for the peeling of several tapes secured by pressure-sensitive adhesives at a range of peeling angles. Several of the cellophane tapes showed a small dropoff or “jog” in the value of the peeling force of approximately 0.1–0.2 lbf when the peel angle was in the range of 20–40 degrees. The jog was associated with a relatively rapid change in decohesion mechanism from one of cleavage to one in which shear played a much larger role, and a similar but much larger effect was noted with metal foil tapes. These observations were in contrast to data presented some months earlier in which no such “jog” had been seen using a similar cellophane tape tested in much the same way. The setup for all of these tests consisted of a stripping wheel to which the tape had been roll-bonded by a wheel of 1/2 inch diameter loaded at an intensity of 6 lbf/inch. Although there have been several attempts to explain the dropoff in peel force, none have been entirely successful so far. An analysis of this effect is presented based on the magnitude of the prestrain in the tape introduced by the roller bonding method of attaching the tape to the stripping wheel. This is consistent both with these observations and some further tests we have ourselves conducted at lower than usual peeling angles.