Friction, pressure and separation are the major causes of static electricity. This process is called the Triboelectric Effect ("tribo" means rubbing).
The magnitude of the static charge is determined by material composition, applied forces, separation rate, and relative humidity. These factors conspire to cause conveying mechanisms, and other systems, to act as static generators. Even slow-moving conveying mechanisms are capable of generating ample static charge to cause an ESD ( Electrostatic Discharge ) event. An uncontrolled ESD event can generate enough EMI to damage electronic components.
Environmental variables like relative humidity influence the level of electrostatic charges. When humidity is low, higher static charges are generated (see Table I). Static becomes more noticeable in the winter months, in dry climates, and in air conditioned environments. Increasing humidity to 60% limits static build-up because surface moisture on materials makes a good conductor. Unfortunately, 60% relative humidity is extremely uncomfortable, can cause equipment problems and introduce contaminants into your system.
Fortunately, static control devices can be located at critical points to control the ESD event by reducing the static charge to low levels. Static Control devices allow smoother operation of conveying mechanisms and eliminate electronic component damage caused by ESD events.
Static Control Devices
EST static control devices, such as brushes, work by induction, much like a lightning rod. Physical contact between the static eliminator and the target material is not necessary. The electric field created by the static charge is focused on sharp points. If the charge on the material is high enough, the energy concentrated on the points will induce ionization. The static charge must exceed several thousand volts for ionization to be created using a static control device.
With brushes, the ionizing effect is uncontrolled. Static control devices can be used in contact with the material to provide a path to ground, neutralizing static on isolated conductors.