How the stretch film is cooled and shaped

The stretch wrap film is blow-molded by the process of rapid cooling and shaping. This quenching production process is designed according to the principle of polymer orientation. After the PVC powder is completely plasticized and extruded into an embryonic film, the polymer will proceed in both vertical and horizontal directions between the glass transition temperature and the viscous flow temperature. Forced stretching causes the molecular chains of the polymer to be oriented along the stretching direction.

At this time, the film is rapidly cooled to "freeze" the strain generated by the stretching orientation. When the film is reheated/thawed to 0 temperature (90~110°C), stress relaxation will occur, that is, the oriented molecular chain will be de-oriented, and at this time, the stretched chain that is forced to be in a state of tension will return to the orientation. The folded chains in the pre-relaxed state, thus imparting good shrinkage properties to the shrink film.