- Material selection and performance
Stretch film must have high toughness, puncture resistance, and good self adhesiveness, so the selection of raw materials is crucial. The molecular structure of linear low-density polyethylene (LLDPE) resin is chain like, with relative molecular weight
The quantity distribution is narrow, with short and few branches. The structural characteristics make it have excellent physical properties, such as impact strength, puncture resistance, and good low-temperature impact resistance. If processed properly, it also has good self adhesiveness. Due to these characteristics meeting the performance requirements of the wrapping film, LLDPE was chosen as the raw material. In addition, the melt flow rate (MR) and density of LLDPE are closely related to the film properties. If the MFR value of the resin is too high, it will decrease the puncture resistance of the film and reduce its self adhesiveness; On the contrary, thin films are difficult to form and can easily cause serious shrinkage, affecting production efficiency. After repeated experiments, the optimal MFR value for IDPE is around 2g/1min. - Product structure design
Stretch film is divided into two types: double-sided adhesive stretch film and single-sided adhesive stretch film. Double sided stretch film has excellent self-adhesive properties on both sides, suitable for wrapping and packaging angular items. The film is not affected by the edges of the items, and the strapping operator can freely adjust the stretching force to keep the goods together; One side of the single-sided adhesive stretch film has excellent self-adhesive properties, while the other side is smooth and suitable for packaging without pallets, carpets, and silage. The multi-layer co extrusion casting method can be used to produce the above two types of winding films, which have three structures: A1/A2/A3, A1/BA2, and A/B/C (A, B, and C are three materials). Usually, the structure of thin films is designed according to the requirements of the application. For example, the structure of double-sided adhesive stretch film is AB/A. The main consideration is that the outer layer resin (layer A) must have viscosity and toughness, and the middle layer resin (layer B) must have load retention and compatibility, etc. This structural design can fully meet the requirements of double-sided adhesive wrapping film. In short, the biggest advantage of co extrusion casting method is to integrate the excellent characteristics of various materials together, thereby meeting the requirements of packaging various items and making the application field more extensive.
