What are the reasons for the curling of composite film?

The curling of the composite film will affect the flatness of the film and cause the material of the opening edge of the packaging bag to curl inward and affect the sealing operation.　　The basic law of the curling of the composite 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 curling of the composite film. For example, the curling phenomenon of ONY//PE structure composite film is obvious, while the curling phenomenon of ONY//CPP structure composite film is less.　　2. The longitudinal curl of the composite film is greater than the transverse curl, and the longer the opening length, the more obvious the curl. Because of the tension of the composite membrane during processing, the longitudinal internal stress is more obvious. Therefore, the impact of material curling at the opening of the composite packaging bag with the same structure is less than that of the longitudinal packaging bag 　　. 3. Under normal conditions, the composite product of the dry composite product has less warpage than the extruded product. The dry compound product does not need to set high temperature in the compounding process, and the compounded product has good stiffness and less warpage.　　4. Improper control of the following factors will also affect the degree of curling of the composite film.　　1) The composite tension control does not match.　　 2) The film shrinkage caused by the drying temperature or the pressing temperature is too high.　　3), the winding contact pressure is too strong, causing curling deformation.　　4) Heat shrinkage caused by excessive maturation (excessive time, excessive temperature).　　 Label: Machine roll film