October 28, 2008
by Charlie Acquista
Converters of non-conductive web surfaces, such as pressure-sensitive adhesive (PSA) tapes, need to be constantly vigilant in controlling static electricity. High levels of electrostatic charges can be dangerous, and even moderate levels can permanently destroy an adhesive system—causing fouling and jamming of production processes and significant damage to the finished products.
Moreover, many new technologies designed to enable faster production speeds can also exacerbate static-related problems—often forcing operators to slow down production process for no other reason than simply to reduce static.
In simplest terms, static electricity is an accumulation of electrical charges on a surface, whereby the polarity of the charge can be the result of an excess of electrons, aka negative charge, or a deficiency of electrons, resulting in a positive charge. Both of these types of charges can accumulate on the surface of non-conductive material, such as paper or plastic film, and they can also accumulate on ungrounded conductive materials—including machine parts and the human body.
When surfaces come in contact with each other, a transfer of electrons occurs—with friction, pressure and web speed all important variables in accelerating this transfer. When separated, the surface which has gained electrons becomes negatively charged, and the mating surface giving up the electrons becomes positively charged.
Because the build-up of electrostatic charges is a cumulative process—increasing each time the web contacts another surface—the PSA tape can accumulate a high charge as it passes through transport systems, especially where it comes in contact with several idlers.
On non-conductive materials, such as the papers and films used for PSA tapes, charges do not build up uniformly across the surface, and a single contiguous surface may accumulate a positive charge in some regions and a negative charge, or no charge, in other regions.
Most of us are all very familiar with the shock or spark caused by so-called electrostatic discharge (ESD) events.
On a small scale, you may feel an ESD in the form of a spark when you touch a door-knob after walking across a carpet. On a much larger scale, you observe an ESD when lightning storms light up the sky.
In basic terms, an ESD occurs when a static electrical field exceeds a certain threshold value—causing an ionized conductive channel to form in the air as Mother’s Nature’s desire for balance plays out.