Suppress Static Sparks When Unwinding Release Liners Or Laminated Webs

Suppress Static Sparks When Unwinding Release Liners Or Laminated Webs

Kelly Robinson
Electrostatic Answers

The goal is to unwind with no sparking and for the web exiting the unwinding roll to be charge-free. High static on unwinding rolls may be caused by charge separation at the unwinding nip where the web peels from roll. Release liners and laminated web are prone to charge separation because the two web surfaces are chemically different. And, release liners are particularly prone to damage from sparks because the release coating is very thin. Even low energy static discharges can damage the thin release coating. Using a static dissipative or conductive lay-on roller together with two active static bar achieves the goal of unwinding release liners and laminated webs with no static sparks and for the web exiting the unwinding roll to be nearly charge-free. Tribocharging at the unwinding nip deposits static on the outside surface of the unwinding roll and an equal amount of opposite charge on the inside surface of the web exiting the unwinding roll. Two static dissipators may be used to effectively neutralize these charges. However, charge separated by the two chemically different surfaces of release liners and laminated web can be so high that damaging sparks may occur at the unwinding nip before we have an opportunity to neutralize the static. A “static blanket” or “static curtain” draped on the unwinding nip may suppress these damaging sparks. However, using a “static blanket” or a “static curtain” in this way deposits high static on the web exiting the unwinding roll and causes subsequent static problems at the winding roll. A better alternative is to suppress these damaging sparks using a conducting or static dissipative lay-on roller.