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Substrate Static and Surface Energy Demystified

(December 2013) posted on Wed Nov 06, 2013

Many screen-printed products are insulators, so completely eliminating static through grounding isn’t really possible.

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By Screen Printing's Solution Sourcebook

Static is the excess or deficit of electrons on a material. Static in screen printing is most often caused by friction, separation, heat change, and improper grounding. Screen-printed products normally experience all of these during handling. Potential results of untreated static energy include ink spidering, sheets sticking together, delivery/stacking difficulty, accumulation of dirt and dust, electric shocks, damage and interference in electronic components, and even fires and explosions.

Friction: Static is most often caused by friction, the rubbing of two materials together during the printing or converting process. Rubbing a plastic substrate over a metal feedboard creates a charge. The plastic picks up the negative charge, while the metal feedboard carries the positive charge. Metal is a good conductor, so its acquired charge is short-lived. Plastic is a poor conductor, so it retains its charge for a long time.

Separation: Static can be generated when two materials are separated―for example, pulling the barrier film off of a substrate. Generally, the barrier film holds a charge that is opposite of the product it protects. Media that holds a charge generated by separation can attract airborne dust and debris from several feet away.

Heat change: Products that are subjected to continuous heat changes can build a static charge. Dryers are a major source of this phenomenon. Charges and temperatures constantly change when a printed product is in the drying phase. In extreme conditions, dust and particulates can be drawn onto the product’s surface and adhere to the product.

Improper grounding: Even the greatest efforts to ground machinery can be thwarted by greased bearings and poor metal-to-metal connections, both of which can actually interrupt the ground. Furthermore, some charges may be too high to ground properly. Many screen-printed products are insulators, so completely eliminating static through grounding isn’t really possible.

Static control
Active static-elimination systems include active electrical ionizers, static bars, air ionizers, ionizing nozzles, steady-state DC generators, and pulsed DC controllers. They create ionization by forcing high voltage to ground and breaking down the air molecules in between into low levels of ozone. Passive static control uses grounding and conductive metals. Carbon fiber, stainless steel, phosphor bronze, and copper tinsel are commonly used in screen printing.


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