Stretch film, also known as stretch film, heat shrink film, is the earliest domestic use of PVC as a substrate, DOA as a plasticizer and self-adhesive role in the production of PVC stretch film. Due to environmental issues, high cost (relatively large PE ratio, small unit packaging area), poor stretchability, etc., it was gradually phased out when domestic production of PE stretched films began in 1994-1995. PE stretch film first uses EVA as a self-adhesive material, but it has high cost and taste. Later, PIB and VLDPE were used as self-adhesive materials. The base material was mainly LLDPE, including C4, C6, C8 and metallocene PE ( MPE).
2.The control of viscosity
Good adhesion makes the packaging film layer and layer on the outside of the goods stick together to make the goods firm. There are two main ways to obtain the viscosity: one is to add PIB or its masterbatch to the polymer; the other is to blend VLDPE . PIB is a semi-transparent viscous liquid. Direct addition requires special equipment or transformation of equipment. Generally, PIB masterbatch is used. There is a process of PIB emigration, which usually takes three days. In addition, it is also affected by temperature. When the temperature is high, the viscosity is strong; when the temperature is low, it is not sticky, and the viscosity is greatly reduced after stretching. Therefore, it is better to store the finished film in a certain temperature range (recommended storage temperature is 15 ℃ ~ 25 ℃). Blending VLDPE, the viscosity is slightly worse, but there is no special requirement for the equipment, the viscosity is relatively stable, not controlled by time, but it is also affected by the temperature. When the temperature is higher than 30℃, it is relatively viscous, and when it is lower than 15℃, the viscosity is slightly worse. By adjusting the amount of sticky layer LLDPE to achieve the desired viscosity. Three-layer co-extrusion uses this method.
Stretch film utilizes the film's strong winding force and retractability to bundle the product compactly and fixedly into a unit. Even in an unfavorable environment, the product does not have any looseness and separation, and has no sharp edges and stickiness, so as not to Cause damage.
Stretch film can be divided into: PE stretch film, PE stretch stretch film, LLDPE stretch stretch film, PE slit stretch film, etc.