Q: Why does a roll of sticky tape telescope itself into a cone shape after it has been left unused for a long period? This is most annoying when you return to use the roll in, say, a year's time.
A: A roll of sticky tape telescopes as a result of the level of tension at which the tape was wound and the presence of the adhesive which acts as a lubricant between the different layers of wound tape. The core is then forced out sideways just like an orange pip is propelled when it is squeezed between the fingers.
This same telescoping phenomenon occurs when clingfilm is wound onto large rolls in the factory. Since the clinginess of the film is produced by a highly viscous additive and the accumulated rolling tension in large rolls is very high, the cores can telescope easily.
This causes problems - particularly in hot weather - when rolls that are stacked high up on pallets in a warehouse can come tumbling down. Fortunately, the effect can be negated by using specially shaped cores and these are the subject of numerous patents.
In sticky tape, the viscosity of the adhesive is high but not so high that with time it is not squeezed out - which also explains why the sides of old rolls of tape are often sticky and covered with dust. The telescoping problem is most easily "solved" by careful control of the winding tension. Unfortunately, many tapes can also shrink with age and this can lead to increased tension - and more telescoping.