Effected by unwinding tension and heating temperature, different shrink rate of different platic makes internal stress in laminated film, the distribution and equilibrium state of these internal stresses determine the final degree of curl and state of the laminated film. The curl will effect the sesaling effect in packing machine. The basic law of the curl is as follows.

1. Inner layer material shrinkage is great, and fitness of outer material is poor, curl will be obvious.

2. The longitudina curl of the laminated film is greater than the horizontal curl.

3. Dry lamination is better than other lamination way, cos dry lamination product does not need to set a high temperature in the pre-process part, and product has good stiffness and less warpage after lamination.

Improper control of following factors will also affect the degree of curling of the composite film:

  - lamination tension control does not match.

  - film shrinkage caused by excessive drying temperature or high pressing temperature.

  - excessive pressure on the winding cause deormation of the coil.

  - heat shrinkage caused by too long aging time and excessive tempearture.