Generation of static electricity in the hottest pr

Generation of static electricity in the printing workshop

in the printing workshop using flammable solvents, we must find ways to avoid the accumulation of static electricity on the human body. The human body gets friction static electricity because of walking or rubbing with printing parts. When people approach the charged web or other charged objects, electrostatic induction will be generated, making the human body charged. Static electricity on the human body must be released to the ground at any time, which is very important. Therefore, do not wear shoes with insulating soles, and the floor of the room cannot be made of insulating materials or covered with plastic insulating floors. The air in the room should be kept at a sufficient humidity (the generally recommended standard is 50% RH) so that electrons can be easily transmitted to the cement floor, paper, cardboard or cotton rags. In addition, we also know that the moisture in the air will not transfer the charge to the air or most other plastic materials and a variety of organic synthetic materials by itself, so we should avoid using rags made of organic synthetic materials, because they will lower the temperature of the thermostatic bath, and we should do a good job of regular cleaning to generate static electricity

friction static electricity will also be generated when the substrate passes through the press line. There is always sliding friction between the web and the flange on the surface of the slowly moving imprint roll, so there will also be charge separation and electrostatic accumulation on the surface of the imprint roll. In this electrostatic induction, the charge voltage on the surface of the impression roller near the impression line may not be too large, such as asset securitization, but when the web is separated from the gravure cylinder and the impression roller, the web may generate strong static electricity

even if the voltage near the imprint line is very low, when the web is removed from the grounded gravure cylinder, it is likely to generate charge accumulation. If the web is separated from the embossing roller at a certain point, the voltage near this point is likely to be sharply amplified

in Europe, a large number of experimental studies have been carried out to measure the electric field strength of the paper after the web passes through the imprint line. Experiments show that if ordinary insulating materials are used, the electric field intensity on the surface of the embossing roller can reach 12 kV/cm. Generally, the field strength should be about 3 kV/cm. It was also found in the experiment that the electric field intensity at the top of the embossing roller was slightly higher than that on the web

the electrostatic strength of roll and even polyurethane coated cylinder paper will vary with the material of the embossing roller, and the moisture content in the web paper will also cause its change. Generally, the higher the water content of the paper, the lower the field strength, and higher drum pressure and higher printing speed can increase its electrostatic strength. The charge polarity on the web will not follow any law, and even the charge polarity of the printed and non printed parts on the web may be different. The causes of static electricity near the imprint line will be discussed in detail in Chapter 7 of this book

after printing or before another printing, the web needs to be rewound. After rewinding, the electrostatic charge on the web will be pulled close. If the charge distance is too close, it will interact, and the charge will move in a certain direction under the action of gravity or repulsion, which will generate voltage. Even if the charge on the web is only at a general level, it will generate a large amount of electricity and a high voltage during rewinding. If the web is somewhat conductive, the charge on the web will flow from the roll to the surface of the web after rewinding. Finally, these charges can be neutralized by ions with opposite polarity in the surrounding air

if the reel material is insulating plastic film, or paper with insulating ink or insulating coating, the charge rolled into the roll can stay for a long time. Due to the coupling effect of ions in the atmosphere, the surface of the drum will accumulate a layer of charge opposite to the utilization limitations of the waste foam granulator, and finally the drum will be discharged and neutralized. However, when the web is expanded later, the charge will reappear. We are not sure whether there are other reasons for static electricity during the rewinding process of insulating web paper, but it is an indisputable fact that the printing medium will frequently show strong static electricity during the rewinding process, so we suggest that we should check the release of static electricity on the reel paper before rewinding. Sometimes we also need to use the so-called active electrostatic eliminator to remove the static electricity on the roll paper before rewinding

several principles have been explained about the static electricity generated when the ink is poured out of the container, ejected from the catheter, or flowing in the hose. Typically, the cause of static electricity is the charge separation caused by electrostatic induction. For example, when a charged object approaches this area, the area will generate electromagnetic induction and have voltage

even if the ink has only slight conductivity, static electricity will be induced when the ink is poured out of the nozzle, so the ink poured into the container will be charged. Unless all containers are properly grounded, there will be voltage

polar solvents containing alcohol, acetate, ketone and other substances have better conductivity (or less resistance) than pure hydrocarbon solvents containing toluene or other volatile oils. The good conductivity of polar solvents is beneficial to charge recombination and neutralization, but when the continuous ink fluid turns into intermittent small droplets, the conductivity is impossible to talk about, and charge recombination and neutralization will end. Therefore, all containers should be grounded to avoid liquid splashing

charge separation and voltage accumulation will also occur when the ink flows out through the insulating tube or nozzle. Its principle is generally believed that the charge outside the tube or nozzle attracts the charge with opposite polarity in the ink from the center of the tube to the tube wall, and the liquid flow rate in the center of the tube is faster than the tube wall, so charge separation occurs

when the ink fills the ink tank from the top or the condensed water at the bottom of the ink tank is violently stirred, it will cause the accumulation of charges on the ink surface

alcohol, acetate and ketone solvents have strong conductivity as printing inks, and the induced charge can be quickly transferred to the stainless steel wall of the ink tank, which is generally not easy to accumulate. However, pure hydrocarbons such as toluene have great resistance, the charge will remain for a long time, and the ink has accumulated charge. Generally, negative charges are easier to ignite than positive charges. It is effective to add some conductive substances, even if few, to this kind of hydrocarbon. This additive is easy to find on the market