Printing is performed on the surface of the object, and the phenomenon of static electricity is mainly manifested on the surface of the object. During the printing process, all substances involved in printing generate static electricity due to friction, impact and contact between different substances.
1. Affect the quality of product printing
The surface of the substrate is charged, such as paper, polyethylene, polypropylene, cellophane, etc., which will absorb paper dust or dust, impurities, etc. floating in the air, affecting the transfer of ink, making the printed matter, etc., resulting in a decline in the quality of the printed matter. Secondly, if the ink is charged, it will discharge during the movement, and "electrostatic ink spots" will appear on the printed matter, which is often the case in the layered printing. In solid printing, if charged ink is discharged on the edge of the print, it is easy to have "ink whiskers" on the edges.
2. Affect safety production
In the printing process, due to high-speed friction, the peeling generates static electricity, and when static electricity accumulates, it is easy to cause air discharge, causing electric shock or fire. When the voltage is high, the charged ink will cause the ink and solvent to catch fire, which directly threatens the safety of the operator.
Static elimination method in printing
1. Chemical elimination method
Apply an antistatic agent to the surface of the substrate to make the substrate conductive and become a slightly conductive insulator. The application of chemical elimination is very limited in practice. For example, when chemical components are added to printed paper, the quality of the paper is adversely affected, such as reducing the strength, adhesion, tightness, and tensile strength of the paper. Therefore, the chemical method is not Too widely used.
2. Physical elimination method
Eliminating the nature of materials without the use of static properties is the most common method available.
(1) The grounding elimination method uses a metal conductor to connect the substance to be electrostatically removed to the earth and to the same potential as the earth, but this method has no effect on the insulator.
(2) Humidity control elimination method
The surface resistance of the printed material decreases as the humidity of the air increases, so increasing the relative humidity of the air can increase the conductivity of the surface of the paper. The suitable environmental conditions for the printing shop are: the temperature is about 20 degrees, and the ambient humidity of the charged body is more than 70%.
(3) Principles for selection of static elimination equipment
The static elimination equipment commonly used in printing plants is inductive, high-voltage corona discharge, ion current static eliminator and radioisotope. Among them, the first two are cheap, easy to install and use, and no atomic radiation is widely used:Inductive static eliminator bar: Inductive static elimination brush, the principle is that when the tip of the eliminator is close to the charged body, the polarity opposite to the electrostatic polarity on the charged body is induced, thereby neutralizing the static electricity.
High-voltage discharge static eliminator: divided into electronic and high-voltage transformer type, divided into unipolar and bipolar according to discharge polarity, unipolar static eliminator only acts on one kind of charge, bipolar can eliminate any An electric charge. In the printing process, static electricity brush and high-pressure discharge can be used to eliminate static electricity. The principle of the installation position of the static eliminator: easy to operate, next to the subsequent part of the solvent.