‍In solvent free composite processes, tension control is extremely important and must be very precise. Tension control includes main unwinding tension, film tension after coating, secondary unwinding tension, winding tension, and winding taper.
Key points for solvent-free composite tension control
1. Generally speaking, the unwinding tension is based on the secondary unwinding tension, increasing the main unwinding tension to match the secondary unwinding tension, so that the composite film ultimately reaches a straight state. Under this premise, the unwinding tension is the minimum tension without longitudinal or transverse wrinkles.
2. The tension after coating the film is slightly greater than the unwinding tension, which is used to pull the coated film, so that the corresponding coating steel roller does not require a large driving current.
3. The winding tension is slightly greater than the unwinding tension. The winding tension needs to withstand the initial adhesion force of the composite film, which is generally only about 0.2N/15mm. It is better to control the winding taper within 20%. As the coil diameter increases, the degree of tension decrease is slower than that of dry composite.
4. For different materials of thin films, the tension of each part during the composite process also varies, and even the tension of the same material of thin films varies greatly depending on the composite structure. In the PET/PE structure, because PE is easy to stretch, its tension is approximately 3-5 N, while PET needs to resist the shrinkage stress of PE, and its tension is relatively large, approximately 20 N; Similarly, in the composite structure of PET/paper, PET film only requires a minimum tension of around 5N due to its good tensile properties.
Method for checking the suitability of tension
During the composite process, stop the machine and use a blade to make a cross cut on the composite film at the winding point. The ideal state is that the composite film remains flat after the cut. If the composite film curls in a certain direction, it indicates that the tension of that layer of film is too high. The tension of that layer of film should be appropriately reduced or the tension of another layer of film should be increased.
Tips for checking whether the tension matches
During the composite process, stop the machine and apply force to make a cross cut on the composite film at the winding point. The ideal state is that the composite film remains flat after the cut. If the composite film curls in a certain direction, it indicates that the tension of that layer of film is too high. The tension of that layer of film should be appropriately reduced or the tension of another layer of film should be increased.