Popular science of shrink film

Shrink film for product sales and transportation, its main role is to stabilize, cover and protect the product.  The heat-shrinkable film must have high puncture resistance, good shrinkage and certain shrinkage stress.  

The macromolecules of ordinary plastic film are in a natural state of curling and generally do not shrink when heated.  Shrinkage film is different, its film formation has gone through two steps, raw material melting at a specified temperature and under the action of external forces to stretch the film, macromolecules can not slip between each other, unnatural state is frozen.  At room temperature, plastic macromolecules are not active enough to eliminate this unnatural state by molecular motion, which is why heat-shrinkable films do not shrink at room temperature.  However, this is only a superficial phenomenon, this seemingly stable thermal shrinkage film has hidden instability factors.  When the film is reheated to a certain temperature, its frozen macromolecules start to move again, trying to return to their natural state from an unnatural state. The result is contraction.