Introduction to related knowledge of stretch film

Stretch film, also known as stretch film and heat shrink film, is the first in China to produce PVC stretch film with PVC as base material and DOA as plasticizer and self-adhesive function. Due to environmental protection issues, high cost (relative to PE aluminum-plastic vacuum bags with high specific gravity, less unit packaging area), poor stretchability, etc., it was gradually eliminated when domestic production of PE stretch films was started from 1994 to 1995. The PE stretch film first used EVA as the self-adhesive material, but its cost was high and it had a taste. Later, PIB and VLDPE were used as self-adhesive materials. The base material is now mainly LLDPE, including C4, C6, C8 and metallocene PE (MPE).

In the early days, LLDPE stretched films were mostly blown films, from single-layer to two-layer and three-layer; LLDPE stretched films were mainly produced by the casting method. The process is shown in the figure below. This is because the production of the casting line has uniform thickness , High transparency and other advantages, suitable for high-magnification pre-stretching requirements. Because single-layer casting cannot achieve single-sided adhesion, the application field is limited. Single-layer and double-layer casting are not as wide as three-layer casting in terms of material selection, and the formulation cost is also high, so it is better to use a three-layer co-extrusion structure. A high-quality stretch film should have the characteristics of high transparency, high longitudinal elongation, high yield point, high transverse tear strength, and good puncture performance.