Monroe Electronics Electrostatic Fieldmeter - Static Monitor - model 177A - Manual (Page 55)

APNE-0015 54
II. How Electrostatic Charge Builds-Up on a Moving Web
Electrostatic Charging On A Web Converting Machine
Electrostatic charging can occur in several different ways, but for the purposes of this
document, we will limit our discussion to contact and separation (triboelectric) charging
between two surfaces. Triboelectric charging is a surface event that occurs when two
surfaces are brought together and then separated or rubbed against each other (friction).
Different materials have different abilities to hold onto their free electrons (work function).
During contact and separation of materials, one material will give up free electrons to the
other, resulting in a net positive charge on one material and a net negative charge on the
other material. Of the two materials, the material with the lower work function gives up
electrons to the other material and becomes positively charged. The material with the
higher work function takes electrons from the other material and becomes negatively
charged.
Theoretically, if two surfaces are chemically and mechanically identical in structure and
surface finish on an atomic or molecular level, then their work functions will be identical.
When they are separated or rubbed together, no charge transfer will take place.
Unfortunately, real materials are seldom completely pure, and they often have surface
finishes and/or contamination that strongly influence their charging characteristics.
Unwinding a roll of plastic sheeting can demonstrate this by sparking where the sheet
separates from the roll, and by static attraction of contaminants to the sheet after
separation. See Figure IV-1.
Figure IV-1
Unwinding Roll of Plastic Sheeting
Separation of charge