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#744
Author: Tim Walker,
Email:
Subject: The source of the core impression is high interlayer pressures that can develop...
What you describe is common in film winding, especially if you are winding films using winding process settings normally used with paper products.
The source of the core impression is high interlayer pressures than can develop at the core due to winding tension and the torniquet effect. If you wrap a rubberband around your finger you will feel the torniquet effect; every wrap will increase the pressure on your finger. However, if you wrap a strip of paper around your finger, you will see less pressure buildup with additional wraps. The pressure buildup is dependent on winding conditions (tension, diameter, buildup), but more important, on web and stack properties (tensile modulus, stack compressibility). Lastly, the pressure buildup is also dependent on the core (material, diameter, wall thickness).
Soft cores, high modulus, high radially compressible, low tension, more taper tension, and smaller buildup ratios will all reduce the pressure at the core.
Next, think about the step shape at the core attachment. Thicker tape or wrinkled starts will create a larger stress concentration point. Consider thinner tape or a spray-on or transfer adhesive. If the product is thicker than your attaching tape, then tape changes will have little effect.
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