The ‘loop’ tack value of a pressure sensitive material is expressed as the force required to separate, at a specified speed, a loop of material (adhesive outermost) which has been brought into contact with a specified area of a standard surface (usually glass or metal).
An adhesive strip is formed into a loop and held within the jaws of a tensile tester. It is then compressed onto the standard surface until it makes full contact over a specified area (typically 25mm x 25mm). It is then pulled off the surface at a fixed speed to establish the tackiness. The result is the average tension force after ignoring the initial peak and is expressed in Newtons.
Loop tack testing allows the comparison of the "initial grab" or "application tack" of different laminates and can be extremely useful to those working with automatic labelling equipment where this property is of particular importance.