Causes and elimination of printing static electricity
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In the printing production process, sometimes paper or prints are attracted to each other and stick together, which is difficult to separate. This phenomenon is the phenomenon of printing static electricity. In the dry climate of winter, the phenomenon of static electricity on printed paper is particularly prominent. Lightly, it can cause obstacles to normal paper feeding, paper delivery and paper-cutting. Therefore, understanding the printing static and mastering the coping methods have positive significance for promoting production.
Paper has such an attribute that when its water content is high, the electrical conductivity is increased; conversely, when the water content is low, the insulating property is increased, and in this case, the paper is more prone to static electricity.
The papermaking process is not easy to bring the paper to static electricity. In the process of papermaking, due to the low content of electrolytes (such as alum, sodium chloride, etc.), the content of sizing substances is too much, the content of some fillers (such as kaolin) is too small, and the paper is subjected to high temperature during drying and calendering. And the role of pressure to make paper with high voltage static electricity. Improper storage of paper can also generate static electricity. When there is a large disparity between the temperature of the paper library and the temperature of the printing workshop, the variation of the moisture content of the paper not only causes the expansion and contraction to affect the registration, but also easily causes static electricity. In addition, the paper placement time before printing is too short, the paper and the printing environment lack an effective balance between temperature and humidity, and the paper stack pressure is too high and too heavy, which may cause the paper to be electrostatically charged.
Friction in printing causes static electricity. When the water content of the paper is too small, the paper is very dry, and the paper is subjected to friction and pressure during the paper feeding and imprinting process to cause the paper to be electrostatically charged.
There is a cause of static electricity on paper, and some cases are caused by several situations, and the situation is different. The amount of static electricity carried by various papers or batches of paper is not necessarily the same. Another feature is that after the paper is charged, the opposite sides of the charge are opposite in polarity, and the papers that are in contact with each other are firmly attached to each other and are not easily separated. Therefore, it brings obstacles to printing paper feeding, conveying and aligning paper, which not only affects production efficiency and product quality (such as tying faults such as over-blotting and misregistration), but also increases printing loss.
In order to prevent the occurrence of printing static electricity, first of all, to control from the source. First, the paper with static electricity can be suspended, the stock time should be extended appropriately, and the temperature and humidity of the paper library should be controlled. The temperature inside the warehouse is directly controlled between 18 °C and 20 °C, and the relative humidity of the air is controlled at 60-65. Between %, under these conditions, it is beneficial to reduce or eliminate static electricity on the paper. Secondly, the paper can be used to remove static electricity from the paper. When the paper needs to be used urgently, use a paper machine to hang the paper with static electricity. When hanging and drying, pay attention to the coordination between machine speed and air humidity. When the machine speed is faster, the relative humidity of the ambient air is controlled at 80-85%. On the contrary, in the case of a slower machine speed, the humidity is kept at 70-80% and the hanging effect is better. It is worth noting that the thickness of each stack of paper should be within 10mm when hanging, and the paper should be looser and better between paper and paper, so that the moisture in the air can enter the paper evenly. Third, emergency air-paper removes static electricity. If the static electricity of the cut paper cannot be printed normally, the “steam method” can be used to quickly dry the paper to reduce the static electricity of the paper and complete the printing as soon as possible. In the practice of a temporary machine production, the author used 30 g of speed paper to print 30 g of glossy paper at a speed of 3,500 mph, which made the paper feeding and paper transfer difficult and the overprinting was inaccurate. Therefore, it is necessary to stop the emergency paper drying of the charged paper, that is, put each stack of paper with a thickness of about 15 mm on each layer of the paper towel rack, and then sprinkle the hot water around the paper towel rack to make the paper increase rapidly. Water content to achieve a reduction in static electricity to maintain normal printing.
Eliminating static electricity from paper can also be a combination of improved paper temperature, increased water content, and the use of static eliminators. The main measures are:
1. Install air conditioning equipment in the printing workshop to adjust and maintain the printing workshop at a constant temperature and humidity according to the static electricity of the paper. Under normal circumstances, the workshop temperature is adjusted between 18 ° C and 20 ° C, and the relative humidity of the air is maintained between 60 and 65%. If the paper is charged more strongly, adjust the relative humidity of the air to between 80-85%.
2. Install a static eliminator on the printing press to eliminate static electricity on the paper. The static eliminator is adjustable to eliminate static electricity from the paper by adjusting the voltage and frequency. Use high voltage and high frequency when the paper is static. When the paper is not static, turn down the voltage and frequency.
3. The isotope emitter is used to eliminate the printing static electricity. The principle of the isotope emitter and the static eliminator to eliminate static electricity is basically the same, and some of the air molecules are ionized into ions. Because the ions have different charges, when the paper passes through the ion space, part of the electrostatic charge will be neutralized, thus achieving the purpose of eliminating static electricity.
In summary, static electricity adversely affects printing efficiency and quality, and also increases paper loss. Therefore, correctly understand and recognize the printing static electricity, and take corresponding measures to overcome and eliminate, in order to ensure the smooth progress of printing, to achieve the purpose of improving production efficiency and quality.