How does the “shrinking principles” after heating the heat-shrinkable film apply?
For the average plastic film, the macromolecule chain of the chemical structure is naturally curved and generally does not shrink under heating.
The shrinkable film is different because its finished film undergoes the following process:
the raw material is melted under specified temperature and the thin film is “stretched” under external force, so that the macromolecules could not slide while the unnatural state gets frozen. At room temperature, macromolecule in the plastic film shows poor activity and could not eliminate such an unnatural state by relying on molecular motion, and this is the reason that heat-shrinkable film not shrinking at room temperature.