There Are Two Major Reasons For Excessive Shrinkage Of Stretch Film

1. The stretch film is too retracted during the stretching process and cannot reach the width required by the product;

2. The stretch film is too retracted by heat during the secondary compounding process, which exceeds the standard requirements and cannot reach the width required by the product.

The raw material of stretch film is an amorphous polymer, and when it is subjected to a tensile force greater than the yield strength within a certain temperature range, it will produce plastic extension deformation, and the polymer structural units (chain segments, macromolecules and microcrystals) begin to orient due to stretching during the deformation process. With the increase of orientation, the force between macromolecules increases, causing the polymer viscosity to increase and harden tendency, and the deformation tends to stabilize and no longer develop, this phenomenon is called "stress hardening".

Appropriately increase the temperature, the ductility of the stretch film is further improved, the tensile ratio can be increased, and even some polymers with poor ductility can be stretched. Generally, the deformation around Tg (minimum processing temperature) at room temperature is called "cold drawing", and after the polymer is stressed during the stretching process, the flow of polymer molecules is restricted, thereby preventing the further increase of the tensile ratio. The stretch film that has undergone "cold stretching" returns to its original shape when the tensile force is lifted, resulting in a large retraction.