Paper with static electricity on printing
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Once the paper is electrostatically charged, it will cause a lot of trouble for printing. The first is that the paper can't be hit. Under the action of static electricity, the paper and the paper are firmly sucked and jagged, and the air is difficult to enter between the papers. If you want to hit them, sometimes you have to pull them one by one, which is a waste of time. During the printing process, due to the electrostatic attraction, the sheets are firmly adhered together, sometimes two, sometimes several, sometimes a sheet of paper can not be separated, resulting in the paper nozzle can not absorb the paper. When the brush is pressed heavily, it often produces broken sheets and empty sheets; the brush is lightly pressed, and double sheets and sheets are produced. A plurality of sheets of paper enter between the blanket cylinder and the impression cylinder, which can cause boring and crushing the blanket and the liner. Paper with static electricity is not smooth when it is transported forward on the paper feeding table. If the front gauge is not skewed and the positioning is not accurate, the second overprinting cannot be registered, and the quality of the product is inferior and wasteful. Even after passing through the embossed part, the delivery is very uneven, which brings great trouble to the second whole paper and seriously affects the production speed.
Paper with static electricity has a certain relationship with papermaking. Under normal circumstances, the base paper is less charged at the factory, and the probability of the coated paper being charged is not large. Since printing paper (white paper, cardboard, etc.) and coated paper are reworked on the basis of the base paper, even if the base paper is charged, it is eliminated during the processing. Generally, paper with a basis weight of 80g/m2 has more static electricity, but the paper is electrostatically charged before printing on the machine or the static electricity before printing is not obvious, and the static electricity is often increased after imprinting. In the offset printing process, due to the presence of water, it is rare to carry static electricity after printing. For offset printing, static electricity is mainly generated before printing.
Cause Analysis:
The main cause of static electricity on paper is frictional electricity generation. Many objects are charged by friction. The friction between the paper and the calender during papermaking, the friction between the paper and the blanket cylinder and the impression cylinder during printing are all important factors for generating static electricity.
The nucleus of various substances has different binding forces to electrons, or has different affinity characteristics for electrons. When two different substances are in close contact, the electron-eliminating side is weak due to the binding force to the electrons, and some electrons are attached to the surface of the electrophilic side through the interface. As a result of this electron transfer, an electric double layer is formed at the interface. At this time, if the two substances are rapidly separated, the electron-eliminating side is positively charged due to the loss of some electrons, and the pro-electron side is negatively charged by obtaining some electrons. This is the essence of frictional electricity generation.
Paper, blankets, inks, printing plates, etc. in printed materials have different characteristics of electrons. The pressure in the printing process makes them close to each other, and they have a high speed to separate them quickly. Electrical conditions. Therefore, it is understandable that thousands of volts of static electricity appear in printing, especially that some papers are electrostatically charged before printing. The paper has generated static electricity during the manufacturing process. When it is not ready to be packaged and sent to the printing house, some static electricity is still retained. This is also the reason why the paper is charged before printing. When using these papers, it is necessary to take different measures to eliminate the static electricity they carry in combination with the actual production conditions.
Solution
1. Stock method
After the paper enters the printing factory, the storage time should be longer. The storage location can be better connected with the printing workshop. The temperature is 18~25°C and the relative humidity is 60%~70%. Make the temperature and humidity of the printing workshop consistent with the paper library, which is beneficial to change the water content of the paper. The change in paper moisture is a process of releasing static electricity.
2. Drying method (humidification method)
Mainly to eliminate the static electricity by adjusting the main humidity. When the relative humidity in the workshop is less than 50%, high static electricity is easily generated during printing or plate making, and the relative humidity of the workshop and the water content of the paper are increased. Especially when the paper is dried, it is effective to eliminate static electricity. The humidity control equipment can be used to increase the relative humidity of the room. When there is no humidity control equipment, enough water can be sprinkled on the ground. The humidity control equipment is mainly a humidifier, and a centrifugal automatic humidifier can be installed on the ceiling or wall of the workshop. When the indoor relative humidity does not meet the requirements, the humidifier can automatically spray the misty water vapor to increase the relative humidity in the room. After the relative humidity in the room reaches the requirement, the spray is automatically stopped.
3. Static Eliminator Method
The ions generated by the static eliminator are used to neutralize the charge on the charged body to achieve the purpose of eliminating static electricity. There are three types of static eliminators: one is a voltage-type static eliminator, which applies a high voltage to the needle-shaped or thin-line electrode, and corona discharge generates ions. Generally, the transistor static eliminator used on the printing machine belongs to this category. The second is a self-discharge static eliminator, which is made of a conductive needle, a conductive rubber or a conductive metal material into a needle-like or thin-line electrode and grounded well. The electric field of the charged body is used to generate corona discharge to generate ions. And the charge on the charged body; the third is the radioactive element destaticizer, which uses the ionization of the radioactive isotope to ionize the air to generate ions, neutralizing the static electricity on the charged body.
4. Antistatic agent method
Antistatic agents are also known as static elimination agents or static elimination agents. The principle is to give hygroscopic ions on the surface of a charged body such as paper or film to make it hydrophilic, absorb moisture in the air, reduce electric resistance, increase conductivity, and make static charge less likely to accumulate. The antistatic agent is mainly a surfactant having a hydrophilic group and a hydrophobic group, or a polar group and a non-polar group. The hydrophilic group has a strong affinity for a substance having a relatively high polarity such as water, and the hydrophobic group has a strong affinity for a relatively small object such as an oil. Antistatic agents are widely used in printing, such as antistatic agents to make soft rubber rollers that prevent static electricity.
5. Process operation method
In the printing process, a wet towel can be added to the delivery part, and the water-repellent towel is fixed on the tie rod, so that the paper is in contact with the moist towel to eliminate static electricity, which is a temporary but effective method for eliminating static electricity, and the disadvantage is that Always wet the towel.