Printing is carried out on the surface of the object, electrostatic phenomena are also mainly manifested on the surface of the object. The printing process due to friction between different substances, impact and contact, so that all the substances involved in the printing of static electricity.
The harm of static electricity
1. affect the quality of product printing
The surface of the substrate charged, such as paper, polyethylene, polypropylene, cellophane, etc., will adsorb paper dust or floating in the air, dust, impurities, etc., affecting the transfer of ink, so that the print blossom, etc., resulting in a decline in the quality of printed products. Secondly, such as ink with an electric charge, in the movement of the discharge, the print will appear on the “electrostatic ink spot”, in the level of thin printing often appear in this situation. In the field of printing, such as charged ink discharge on the edge of the print, it is easy to appear in the edge of the “ink whiskers”.
2. Affect the safety of production
In the printing process due to high-speed friction, stripping will generate static electricity, when static electricity accumulates to easily lead to air discharge, resulting in electric shock or fire. When the voltage is very high, the charged ink will cause the ink, solvent fire, a direct threat to the safety of the operator.
The test of static electricity
1. The main purpose of static electricity testing in packaging and printing plants is to analyze the degree of harm; study preventive measures; judge the effectiveness of static electricity elimination. Must designate a person responsible for anti-static shoes, conductive shoes, anti-static work clothes and each post regular static electricity detection, the results will be collated and reported to the relevant departments.
2. classification of electrostatic detection project: the use of new raw materials when the object with static performance prediction; actual production process charged condition detection; electrostatic security measures to judge the effectiveness of the use of detection.
(1) object with static electricity performance prediction projects are as follows: object surface resistivity. The use of high resistance meter or ultra-high resistance meter measurement, the range to 1.0-10 ohms.
(2) the actual production of charged body with static electricity detection projects are as follows: charged body electrostatic potential measurement, electrostatic potential measurement instrument with a maximum range of 100KV is appropriate, the accuracy of 5.0 level; surrounding space temperature and relative humidity measurement; charged body running speed measurement; combustible gas concentration determination; conductive ground to ground resistance value determination; Deray company’s ACL-350 is the current volume The smallest non-contact digital electrostatic measurement meter.
Static electricity elimination methods in printing
1. Chemical elimination method
In the substrate surface coated with a layer of antistatic agent, so that the substrate conductive, become slightly conductive insulator. Chemical elimination of the application in practice there are great limitations, such as the addition of chemical components in the printing paper, the paper quality of adverse effects, such as reducing the strength of the paper, adhesion, tightness, tensile strength, etc., so the chemical method is less widely used.
2. Physical elimination method
Do not change the nature of the material using the electrostatic properties to eliminate, is the most commonly used method.
(1) grounding elimination method: the use of metal conductors to eliminate static electricity and earth connection, and earth isotropic, but this way no effect on the insulator.
(2) humidity control elimination method
Printing material surface resistance with the air humidity increases and decreases, so increase the relative humidity of the air, you can improve the conductivity of the paper surface. Print shop suitable for environmental conditions are: temperature of about 20 degrees, charged body environment humidity of 70% or more.
(3) electrostatic elimination equipment selection principles
Printing plant commonly used electrostatic elimination equipment induction, high-voltage corona discharge type, ion flow electrostatic eliminator and radioisotope type several. The first two of them are cheap, easy to install and use and there is no atomic radiation and other advantages are widely used:.
Induction type electrostatic eliminator bar: that is, induction type electrostatic elimination brush, the principle is that the tip of the eliminator close to the charged body, induction of polarity and charged body on the electrostatic polarity of the opposite charge, thus making the electrostatic neutralization.
High-voltage discharge electrostatic eliminator: divided into electronic and high-voltage transformer type, according to the discharge polarity is divided into unipolar and bipolar, unipolar electrostatic eliminator only has an effect on a charge, bipolar can eliminate any kind of charge. In the printing process can be used in the elimination of static electricity brush and high voltage discharge type two combination of ways to eliminate static electricity. The principle of static electricity eliminator installation location: easy to operate, immediately after the subsequent part of the coating solvent.
3. measures to prevent static electricity
Where there are electrostatic hazards process equipment and places, must be in the surrounding areas where explosive gases may occur, strengthen ventilation measures, so that the concentration is controlled below the explosive range; to prevent electrostatic insulators on the occasion of electric shock to the operator, the insulator electrostatic potential control below 10KV. Where there is an explosion and fire hazard area, operators must wear anti-static shoes and anti-static overalls. The operation area is paved with conductive ground, conductive ground resistance to the ground is less than 10 ohms, to maintain the conductive properties, operators are strictly prohibited to wear synthetic fiber clothes (except for clothes that have been regularly treated with anti-static solution) into the above area, and it is strictly prohibited to undress in the above area.
Post time: Dec-12-2022