Monroe Electronics Electrostatic Fieldmeter - Static Monitor - model 177A - Manual (Page 60)

APNE-0015 59
Techniques To Minimize Web Charge And How They Work
As much as possible, control the factors that govern charge transfer from objects (e.g.
rollers, web laps) to the web. Usually, not all factors are known and/or controllable. Some
general guidelines for reducing web charge transfer can be given, but they may be product
and process dependent.
 Electrically ground all conductive machine parts including rollers (use conductive
bearings and conductive bearing lubricants) to eliminate dangerous sparking from
capacitive discharges to another conductor such as a person or metal. Please note
that grounded conductive rollers cannot reduce charges of insulating web surfaces
that pass over them! The purpose of grounding the rollers is to prevent the rollers
from becoming highly charged.
 Maintain web-converting machines in excellent condition, making sure rollers are in
alignment and turning freely.
 Use web substrates and coating materials that are conductive or dissipative, or can
be made so before converting begins with the addition of antistatic agents.
 Use web substrates that were manufactured, wound, and packaged in environments
with 50% or higher relative humidity (RH).
 Control RH in the web converting machine environment to 50-55%. Higher levels can
cause iron and steel parts to rust, and may be uncomfortable to operators working in
the area. In building areas with uncontrolled humidity, increased static charging is
usually very dramatic during the winter when RH in heated buildings can frequently
drop to less than 10%.
 If possible, avoid using pinch drive rollers. If they must be used, minimize the pinch
roller pressure and tackiness.
 Reduce machine speed and web tension as much as practical.
 Increase web and roller surface roughness as much as practical.
 Clean machine rollers frequently. Web/roller electrification can be affected by
previous products because of web material transfer to the rollers.
 Control drying conditions of web coatings to as low a temperature, and as high a
relative humidity, as practical.
 Cover conductive rollers only with sleeves made of conductive or dissipative material.
Large amounts of charge can be stored at the interface of resistive sleeve material
and a conductor, which can be released in very hazardous sparks either
spontaneously or when approached by a person (conductor).
Use passive and/or active ionization devices to reduce web charge density. If properly
installed in the correct locations, it may be possible to initially control all static problems on
the web-converting machine using ionization. Over time, though, the effectiveness of all
these devices will degrade, and they will have to be cleaned, maintained, or replaced to
return their effectiveness to original condition. The proper operation and effectiveness of
ionization systems can be verified by continuous downstream monitoring using permanent
installations of Monroe Electronics Model 177A fieldmeters with Monroe 1036 fieldmeter
probes.
The application note, ANPE-0015 Electric Fields and Fieldmeters, deals with the practical
issues of measuring and interpreting electric fields with the Monroe Electronics Models
265A and 282 handheld fieldmeters to determine where continuous monitoring is
necessary.