In the process of laminating the composite packaging film, the laminated film will curl due to various reasons such as machine, temperature, etc.The following are several important reasons:
Due to the effect of unwinding tension and heating temperature, when they are combined together, the shrinkage rate is different, resulting in internal stress in the composite rolled film. The distribution and equilibrium state of these internal stresses determine the final curling degree and state of the composite rolled film.
Curling of the composite rolled film will affect the flatness of the sheet film and cause inward curling of the material at the opening edge of the packaging bag, thus affecting the sealing operation.
The basic law of curling of composite rolled film is as follows:
1. The greater the shrinkage of the inner layer material and the worse the stiffness of the outer layer material, the more obvious the curl of the composite film will be.For example, the curl phenomenon of ONY/PE composite membrane is obvious, while the curl phenomenon of ONY/CPP composite membrane is less.
2. The longitudinal crimp degree of the composite roll film is greater than the transverse crimp degree, and the longer the opening length, the more obvious the crimp.The longitudinal internal stress of the composite membrane is obvious due to tension during processing.Therefore, when making bags with the same structure, the effect of material curling at the opening of the transverse composite packaging bag is smaller than that of the longitudinal packaging bag.
3. For composite products under normal conditions, dry composite products have less warpage than extruded composite products.The dry compound product does not need to set high temperature in the compound process part, and the compound product has good stiffness and less warpage.
4. Improper control of the following factors will also affect the crimp degree of the composite roll film.
1) Composite tension control does not match.
2) Shrinkage of rolled film caused by too high drying temperature or pressing temperature.
3) Excessive rolling contact pressure causes crimping deformation.
4) Heat shrinkage caused by over curing (too long time, too high temperature).