According to statistics, in the plastic gravure printing industry, there are equipment damages or casualties caused by static electricity almost every year. Static electricity has become a potentially important source of harm in the plastic gravure printing industry. Experiments have shown that static electricity can be generated not only when rubbed, but when two substances are in close contact and then separated. During the printing process, static electricity will be generated due to the contact separation ink, solvent transfer, and flow during the winding and unwinding of the friction film between the plastic film and the guide roller, impression roller, and plate roller.
In the process of printing and composite production, static electricity is easily produced. Plastic printing, friction printing with rollers and rubber pressure rollers during compounding. Friction ink between the friction drive belt and the pulley when the film roll is peeled off and taken up during unwinding or winding. Or friction caused by the flow of solvent in the ink pipeline. Compressed gas flowing in the pipeline or friction caused by the nozzle orifice. The friction generated by the operator when pulling the film roll to transport the ink. Factors affecting the degree of static electricity generation â‘ The generation and accumulation of static electricity are affected by Wen Yin Xiaodong's materials. The surface resistivity of the material has a great influence on electrostatic leakage. Only materials that are prone to gain and lose electrons and have a high resistivity can easily generate and accumulate static electricity. Among the materials commonly used in gravure printing, the accumulation of static electricity is relatively easy to produce toluene, tear tear, nylon film, etc. â‘¡ The generation of static electricity is affected by the production process equipment.
Because the static electricity is mainly generated by friction, the larger the frictional contact area between the objects, the rougher the contact surface, the greater the pressure between the contact surfaces, the faster the contact surface sliding or the faster the fluid flow rate, the greater the friction, and the generated static electricity. The more. In the printing and compounding process, the contact pressure between the printing or compounding platen roller and the printing plate is large and the wrap angle between the printed film is large, and the contact surface is many. It is the most prone to generate static electricity under the condition of high-speed printing.
If the static electricity can not be eliminated in time, it will form static electricity accumulation until the static spark discharge electrode is easy to cause the ink or solvent to burn or explode. The surface resistivity of the material decreases with increasing air humidity. The higher the relative humidity, the lower the charge density on the surface of the material. However, when the relative humidity is below, the density of the electrostatic charge on the surface of the material is almost unaffected by the relative humidity and remains at a certain maximum value. In the winter in the middle of the winter, the relative humidity of the north of China is relatively low, so the plastic gravure printing industry should strengthen the management of technology and systems to prevent and eliminate static electricity to prevent the occurrence of fire or explosion accidents caused by electrostatic discharge. In the process of plastic gravure printing and compounding, the generation of static electricity must be strictly controlled because the generation of static electricity will cause a decline in the quality of printing and compounding, and sometimes cause electric shock to the human body, and even cause fires and explosions. Affecting the printing quality of the product Under the effect of static electricity, the printing film will absorb the dust and impurities suspended in the air and affect the transfer of the ink, which will cause the printing quality to deteriorate. If the ink is charged and discharged during the transfer process, "hairs" on the printed version or the edge of the printed product will be formed on the printed matter. Static electricity can also cause malfunctions of electronic control components or automated instruments, which can cause the device to operate or Control procedures are confusing and result in product failure. Electrostatic shock When the human body is close to the electrostatic body or the electrostatic body is close to the grounding body, it may be shocked. However, due to the small electrostatic energy, the electric shock itself does not cause significant harm to the human body, but it is very easy to cause a fall when working at height. Injury accident.
Fire and explosion During the printing process, static electricity will be generated due to high-speed friction and peeling. Although the static energy is not large, when the static electricity accumulates to a certain high voltage, it is easy to cause air discharge and electric sparks. In the presence of explosive gases, explosive dust, or flammability When the substance and concentration reach the explosion or combustion limit, it is very likely to cause explosion and fire.
The impression roller of gravure printing and compound equipment is the most prone to generate static electricity, and this part is on the upper part of the printing and compounding ink plate. It is easy to cause fire or explosion accidents near the ink and solvent, which directly threatens the safety of the operator. Due to the widespread existence of friction, the elimination of static electricity is relative, so strengthening the protection of static electricity to prevent electric shocks caused by static electricity and explosions and fire accidents. Reducing the adverse effects of static electricity on product quality is an important working environment for plastic gravure printing companies. Control â‘ Humidity system. The electrical resistance of the surface of the printed plastic material decreases as the humidity of the air increases. Therefore, increasing the relative humidity of the air can improve the conductivity of the film surface.
But humidification is mainly to enhance the leakage of static electricity along the surface of the insulator rather than to increase the leakage through the air. Although humidification is very effective in removing static electricity from plastic films, at the same time, because the water film is easily formed on the plastic surface, it also has a negative impact on the printing effect. Therefore, from the perspective of eliminating static electricity and ensuring the printing process, the suitable temperature for the printing workshop is an environmental relative humidity Good inside. There are many methods for air humidification, but due to the need for plastic gravure printing to ensure the solvent concentration of the workshop and the production process, the amount of air exchange is very large.
Therefore, there are two types of humidification methods suitable for printing workshops: dry steam humidification and high-pressure spray humidification. These two types of methods have their own characteristics and can complement each other. The dry steam humidifier is generally installed between the air filtration section and the air supply section of the central air-conditioning room of the workshop. There is no need for additional pipelines in the workshop. The initial investment is low and the humidity control is uniform. Dry steam humidification will increase the temperature of the workshop at the same time as the humidity of the workshop increases, so it is particularly suitable for winter and autumn and winter, winter and spring seasons. It can reduce the heating time of the workshop. The working principle of the high-pressure spray humidification method is through the high-pressure spray host The plunger pump pressurizes the purified water to the nozzle through a high-pressure water pipe. After being atomized, it is sprayed into the entire space with a fine mist of water. The water mist absorbs heat in the air and changes from liquid to gas to make the space humidity Increased and achieved the purpose of reducing the air temperature. Therefore, high-pressure spray humidification is suitable for use in summer and spring, summer, summer and autumn, and can reduce the cooling time of the workshop.
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