1. How to handle electrostatic paper
charges
Problem
Electrostatically charged paper can cause any number of problems during print runs, from poor performance
in general to blocking and misfeeding. With some basic understanding of the phenomenon, however, and of
the circumstances under which electrostatic charging is likely to occur, most of the common issues become
fairly manageable.
Definition – What is static electricity ?
• Identical charges reject, opposite charges attract.
Paper and press infeed have different charges.
• Static electricity is the result of charge separation. When the air, or the paper itself, is too dry, the
discharging rate of the paper is diminished, causing sheets to misfeed.
• Paper is an insulator, which makes it a non-conducting material (a condensator). A natural paper's
surface resistance is around 1010 Ohm.
• At sheet separation, charges are separated as well, resulting in high field strength charging.
• There are essentialy different types of charges – parallel or opposite. What to do in a specific case,
in other words, the choice of remedies, depends very much on the type of charge.
• How and to what extent paper becomes charged, is influenced by a number of variables – paper
moisture, climate conditions and run speed for instance. Each paper also has specific electric
characteristics, which play a part as well.
• The dryer the paper, the better it insulates. What this means, is that the surface resistance is
increased and that, as a result, the paper's ability to discharge is decreased.
• Statically charged paper has a better chance to discharge at modest running speeds. It doesn't
additionally charge as fast as it would at high speed, so the existing charge has more time to
dissipate.
• Another important factor is the paper's smoothness, in combination with its stiffness. Smoothness
determines the number of contact points with other materials, in the infeed, or with the following
sheet. In general, a relatively smooth paper will have more contact points.
• The other thing is stiffness. Papers of relatively low grammages are less stiff than "heavy" papers,
which means that they are also less resistant to electrostatic forces. In general, higher grammages
mean more stiffness.
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05/03/13 ● www.sappi.com/houston

2. Charge or no charge?
When the paper is cut into sheets, vertical pressure of 2 to 3 tons is applied to the stack in order to remove
air. This also causes the sheets to slightly stick together, which is often, but mistakenly, attributed to static
charge. The only reason the sheets stick together, in this case, is the absence of buffering air layers.
Solutions, remedies and precautions
1. Always carefully measure and manage moisture levels. The moisture percentage of all papers
should be in the range of 48 to 55%.
2. Infrared drying is used as part of many printing procedures. IR heat however, though drying
is obviously the purpose of its use, can cause excessive loss of moisture in an extremely
short period of time.
3. Temperature in the print room should be at approx. 23 °C, with a relative humidity of around
50% to 55%.
4. In case of very dry air in the print room, atomizers can be used for moisturization.
5. Powder can be appled to the paperstack in order to keep the sheets from sticking. This
powder, which is blown between the sheets by the front blowers of the feeder, acts as a
separation layer.
6. Before use, always allow the paper time to adapt to the conditions in the print room. It should
be left in its packaging for at least 24 hours.
7. To increase the air humidity in the direct environment of the press, water can be applied to
the floor around it.
The digital universe of paper and printing knowledge
05/03/13 ● www.sappi.com/houston