Process composite film during the film composite machine due to various reasons, temperature and the like will lead to good composite film curling. The following is our analysis of several reasons.
Due to the unwinding tension and heating temperature of the composite film substrate, when they are combined together, the shrinkage rate of each other is different, which causes the internal stress of the composite film. The distribution and equilibrium state of these internal stresses determine the final curl of the composite film. And status.
The curling of the composite film will affect the flatness of the film and cause the material at the opening edge of the packaging bag to curl inward, which will 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 pronounced the curling of the composite film. For example , the phenomenon of curling of the composite film of ONY // PE structure is obvious, and the phenomenon of curling of the composite film of ONY // CPP structure is less.
2. The longitudinal curl degree of the composite film is greater than the lateral curl degree, and the longer the opening length, the more obvious the curl. Because of the effect of tension during the processing of the composite film, the internal stress in the longitudinal direction is more obvious. Thus the influence of the transverse structure of the bag when the same composite material of the bag opening is smaller than the longitudinal curl of the bag.
3. For compound products under normal conditions, dry-compound products have less warpage than squeeze-compound products. There is no need to set a high temperature in the compounding part of the dry compound product, and the product has good stiffness and less warpage after compounding.
4. Improper control of the following factors will also affect the degree of curling of the composite film.
1 ) The compound tension control does not match.
2 ) Film shrinkage caused by excessively high drying temperature or pressing temperature.
3 ) The curling deformation is caused by the excessive pressure of winding.
4 ) Thermal shrinkage caused by excessive aging (too long time, too high temperature).
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