Changes were investigated on the release torque of a pilferproof metal closure as affected by hot end surface treatment of the glass container finish. It was found that the torque required for closure slip was not affected, but the presence of a treated glass surface was linked with an increased torque required to break the metal bridge on the closure. The results were explained in terms of the effect of surface treatment on the coefficient of friction at high loading between glass and lacquered metal, particularly on the upper part of the glass thread. Other factors could also affect the coefficient of friction in this region, and the results suggested that the quality of the lacquer on the inner surface of the metal closure could be an important factor.
