The failure of the most widely used static eliminators is due to a problem known as voltage suppression.
The day-to-day effects of static charge that most people are familiar with include cling, drag, dust attraction, and shocks to operators. These common effects carry over to the printing industry, where they cause problems in print quality and consistency.
Dust attraction has long affected the printing industry because high static levels on substrates attract particles. Many of the rigid and eco-friendly materials come with high levels of static electric charge. That static charge is multiplied when press operators handle substrates. A particle of dust that lands on a screen can create a repeatable defect. This printing defect has the potential to ruin all prints until its source is discovered and eliminated. A high level of static charge can also cause ink particles to move on the substrate, leading to a variety of other printing defects: fogging, ghost tracks, and overspray (Figure 1).
Some static charge is acceptable. As long as the charge on the surface of a substrate is below 3000 v, for example, there will be no problems. However, the majority of static eliminators used by industrial printers actually fail to keep the static charge below 3000 v. Many printers complain that the static-control systems they use do not work in all applications. The failure of the most widely used static eliminators is due to a problem known as voltage suppression.
Hidden voltage
Dust attraction and other common printing defects are difficult to prevent with conventional static eliminators. This is because static is difficult to remove when a sheet is lying flat. The electric charge is hidden between the sheet and the stack, or between the sheet and the machine, in a space where most static eliminators cannot reach.
The press operator can also become charged with static while handling plastic sheets. The static charge is stored on the operator’s body until it discharges to any metal surface near that person’s skin. This type of static discharge is quite common and is very painful for the operator.
In one example, an operator received electric shocks when he attempted to remove a substrate from a printing press. The plastic sheets charged up the operator’s skin, and the metal machine components caused a painful discharge of static electricity. To prevent this problem, the operator now uses a grounded ionizing wand to keep him grounded and to neutralize the substrates as he removes them from the printer.
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