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Paper is an insulator and has poor conductivity.
In the dry winter, the paper is subject to friction and pressure. After losing the electrons, it is difficult to replenish the lost electrons. When the charge is stable in the formation area, static electricity is generated.
1. Static electricity is generated during printing 1. Static electricity is generated by friction and squeezing During the paper feeding process, the paper is rubbed by brushes, rollers, and belts; during the printing process, the paper is pressed by the impression cylinder and blanket cylinder. Because the paper is in close contact, squeezed by gravity, and intense friction, the temperature of the surface is increased, and the thermal motion of the molecules is intensified, causing charge migration. Some objects lose positively charged electrons, while others get negatively charged electrons, so that the paper is produced. Static electricity.
2. The influence of temperature and humidity The static paper generated is stored in the paper library and the workshop. Because the difference in temperature and humidity is too large, the change in paper moisture content is also very obvious. Once the relative humidity of the air drops to a certain level (below 40%), static electricity is easily generated.
When the ambient temperature rises, the paper is rubbed, and the movement of the charge is accelerated, which causes the generation and accumulation of static electricity. Second, temperature and humidity are interrelated. When the temperature rises, the air dries and the relative humidity decreases, exacerbating the generation of static electricity. When the temperature drops, the air is dry again, there will be no water film condensation on the surface of the insulators such as paper and plastic accessories on the printing press, and the static electricity generated during printing cannot be eliminated in time, but it will aggravate the accumulation of static electricity.
3. After printing, the electrostatic paper is peeled off and quickly peeled from the impression cylinder and blanket cylinder to send the static electricity to the printing fault and eliminate Zhang Butang. Editor's note: During the printing process, between the printing plant and the paper mill often due to the printing quality There is a dispute over the failure. In order to reduce the contradiction between each other, narrow the technical gap between the printing plant and the paper mill, further improve the printing plant's operation process problems and improve the paper mill's papermaking quality, and manufacture high-quality paper that meets the printing suitability, this journal opens "Paper "Troubleshooting and troubleshooting" series of lectures for readers' reference.
Paper printing faults and troubleshooting series of lectures 60 printing process to the delivery chain. When the paper is peeled off, charge migration occurs between the paper and the roller. The size of the peeling force is determined by the adhesion of the blanket and the viscosity of the ink. The greater the peeling, the more the charge transfer and the greater the amount of static electricity generated.
4. Ink produced by static ink In the process of high-speed operation of ink fountain, ink roller and printing plate, due to separation and friction, it is drawn into filaments and broken into ink droplets. The ink droplets are electrically charged, repel each other, generate static electricity, and form a misty "flying ink", which scatters in the workshop, pollutes semi-finished products and equipment, and damages human health.
2. Cutting and folding produce static electricity 1. Single sheet of paper generates static sheet paper needs to be cut before and after printing. The cut paper is stacked too high. Under the action of the dragging force, static electricity is generated. Once the paper scraps adsorbed on the edge of the paper enter the printing machine, a similar fluff failure will occur. In order to keep the paper clean, some stack turning systems should have a ventilation function. In addition, a non-ionic "air flow" device to eliminate static electricity should be used on the paper striker and the booster roller.
2. Roll paper produces a resistance on the surface of the electrostatic paper, usually about 10 10 ~ 10 11 Ω, with the increase and decrease of moisture will have greater changes. In offset rotary printing, when the paper is dried and the moisture is reduced to 1% to 2%, its electrical conductivity is greatly reduced, and the resistance will be increased to more than 10 18Ω. The greater the resistance, the greater the static electricity generated by friction. After the paper comes out of the drying device, it passes through the friction of several rollers and reaches the paper cutter or folding machine, which generates a relatively high static electricity, so that the paper cannot be output normally. Therefore, the static elimination device should generally be arranged after the drying device.
3. Static electricity is produced in the papermaking process. The ratio of paper chemical raw materials is inappropriate. In the papermaking process, after drying and calendering, static electricity is generated under specific circumstances. Static electricity stays on the paper sheet at the end of the dryer section of the paper machine, and may reach a high voltage during super calendering. Due to friction in the papermaking process, electric charges will also occur on the paper sheet, thus forming a printing static phenomenon.
This batch and that batch of various papers or similar papers have different static electricity levels and different voltage levels. It has been determined that after the paper is charged with static electricity, sometimes the voltage is as high as 15,000 to 20,000 V.
In addition, the stacking time and stacking environment of the paper will also prevent the moisture of the paper from reaching the equilibrium state and may also cause static electricity failure.
Fourth, the method of eliminating static electricity 1. It is very necessary to install a temperature and humidity adjustment device to control the temperature and humidity of the workshop environment, so that the moisture content of the paper reaches a balanced state. Some enterprises have no conditions to install constant humidity equipment, and can spray some water or install simple sprayers on the floor of the printing workshop. This method can solve the static electricity fault, but if not handled properly, it will cause the relative humidity to be too high, causing paper shrinkage, bow wrinkles and other disadvantages.
2. Printed parts grounding device The printed parts and the ground are contacted with metal conductors to maintain a good potential for each other, so that the static electricity of the paper is quickly discharged when it contacts the ground, which can reduce the accumulation of static electricity and eliminate static electricity.
3. Eliminate the static electricity of the ink Add antistatic agent to the ink. This chemical method is mainly to increase the moisture absorption and conductivity of the paper. Generally, about 1.8% of antistatic agent is added to the ink to eliminate static electricity.
4. Install a static eliminator. Install a static eliminator on the printing machine. According to the amount of static electricity on the paper, adjust the voltage or high frequency to eliminate the static electricity of the paper.
5. Install the same position mercury emitter The same position mercury emitter is basically the same as the principle of the static eliminator to eliminate static electricity, which is to ionize various molecules in the air into ions. Because the ions have different electrodes, the air becomes an ionic layer and becomes a good conductive conductor. When the paper passes through the ion space, the electrostatic charge will be neutralized.
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