Causes and elimination of printed static electricity

In the printing production process, sometimes paper or printing products attract each other to stick together and it is difficult to separate. This phenomenon is the phenomenon of electrostatic printing. In the dry climate in winter, the phenomenon of static electricity on printed paper is particularly prominent. Lightness causes obstacles to normal paper feeding, paper delivery, and paper sizing, but it is impossible to start printing. Therefore, understanding printing static electricity and mastering coping methods have positive significance for promoting production.

Paper has such a property that, when its moisture content is high, its electrical conductivity increases; conversely, when its water content is very low, the insulating property increases. In this case, the paper tends to be electrostatically charged.

The papermaking process is not easy to statically charge the paper. During the papermaking process, due to the low content of electrolytes (such as alum, sodium chloride, etc.), excessive content of sizing materials, and low content of certain fillers (such as kaolin, etc.), the paper is subjected to high temperatures in the drying and calendering process. And the role of pressure makes the paper electrostatic with high voltage. Improper storage of paper can also generate static electricity. When there is a great disparity between the temperature of the paper warehouse and the temperature of the printing shop, the variation of the moisture content of the paper will not only cause retraction but also affect the registration, and it will also easily cause static electricity. In addition, the paper placement time before printing is too short, the paper and the printing environment lacks an effective balance of temperature and humidity, and the stack pressure is too high and heavy, which can also cause the paper to be electrostatically charged.

Friction in printing causes static electricity. When the moisture content of the paper is too low, the paper is very dry. The paper is subjected to friction and pressure in the process of feeding and imprinting to cause the paper to be electrostatically charged.

Paper is charged with static electricity for one reason, some are caused by several situations, and the situation is not the same. The amount of static electricity carried by various paper or batches of paper is not necessarily the same. Another feature is that the polarity of the charge on the two sides of the paper is reversed when the paper is charged. The papers that are in contact with each other on the front and back sides are firmly attached to each other and cannot easily be separated. Therefore, it has brought obstacles to printing, paper feeding, conveying, and papermaking, which not only affects the production efficiency and product quality (such as easily causing under-imprinting, misalignment, and misalignment, etc.), but also increases the loss of printed products.

In order to prevent the occurrence of printing static electricity, first of all, it is necessary to control it from the source. First, the paper with static electricity can be put on hold, the time of inventory is properly extended, and the temperature and humidity of the paper storehouse must be controlled. The temperature in the storehouse is directly controlled between 18°C ​​and 20°C, and the relative humidity in the air is controlled at 60-65. Between these two conditions, it is beneficial to reduce or eliminate static electricity on paper. Secondly, the paper can be used to remove paper static electricity. When the paper needs urgent use, paper dryers can be used to suspend electrostatically charged paper. Hanging should pay attention to speed and air humidity coordination, that is, when the speed is faster, the relative humidity of the ambient air is controlled at 80-85%. On the contrary, in the case of slow speed, the humidity is maintained at 70-80% and the hanging effect is better. It is worth noting that the thickness of each stack of paper should be kept within 10mm when hanging, and the paper should be loosened as much as possible when paper is clamped so that the moisture in the air can evenly enter the paper. Third, the emergency paper removes static electricity. If static electricity cannot be properly printed on the cut paper, the paper can be quickly “steamed” to reduce the static electricity of the paper and complete printing as soon as possible. The author in a machine production practice, with a speed of 3500 speeds when printing 30 grams of glossy paper, paper static due to more severe, so that the paper transport, transfer difficulties, overprint inaccurate. Therefore, it was necessary to stop the emergency paper-hanging on the charged paper, that is, put each stack of paper about 15 mm thick on each layer of the paper holder, and then sprinkled with hot water around the paper holder to increase the paper quickly. Moisture content in order to achieve static reduction to maintain normal printing.

Eliminating paper static electricity can also be a comprehensive approach, combining paper temperature increase, moisture content increase, and the use of static eliminators. This is better. Its main measures are:

1. Install air-conditioning equipment in the printing shop, adjust and maintain a certain constant temperature and humidity in the printing shop according to the strength of paper electrostatics. Under normal circumstances, the workshop temperature is adjusted between 18°C ​​and 20°C, and the relative air humidity is maintained between 60-65%. If the paper is charged more severely, the relative humidity of the air can be adjusted to between 80-85%.

2. Install a static eliminator on the printing press to eliminate paper static electricity. The static eliminator is adjustable and eliminates sheet static by adjusting the voltage and frequency. High voltage and high frequency are used when the static electricity of the paper is large, and the voltage and frequency are lowered when the static electricity of the paper is not large.

3. The use of isotope emitters eliminates the printing of static electricity. The principle of the elimination of static electricity by isotopes and static eliminators is basically the same. They ionize parts of air molecules into ions. Because the ions have different charges, when the paper passes through the ion space, part of the charged electrostatic charge is neutralized, thus achieving the purpose of eliminating static electricity.

In summary, the static electricity has a bad influence on printing efficiency and quality, and also increases paper loss. Therefore, the correct understanding and understanding of printed static electricity, and to take appropriate measures to overcome and eliminate in order to ensure the smooth progress of the printing, to improve production efficiency and quality.

Lu Qingxiang The First Light Industry School in Anhui Province
Reprinted from: Guangdong Printing

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