Printing is performed on the surface of the object, and the electrostatic phenomenon is also mainly manifested on the surface of the object. The relationship between the two is naturally very close. The effect of static electricity on printing has a dual nature. It has a side that is harmful to normal printing and a side that can be used. The printing process involves frequent impact, friction, and contact-separation processes. As a result, almost all objects involved in the printing process are electrostatically charged.
The harm of static electricity to the printing industry:
1. Affect the printing quality of the product: First, the surface of the substrate is charged, such as paper, polyethylene, polypropylene, cellophane, etc. They will absorb paper scraps or a large amount of dust and impurities diffused in the air, which will affect the ink transfer and reduce Ink transfer rate, "flowers. Dots" appear on printed products, or rewinding slippage and uneven rewinding due to mutual exclusion. In addition, the ink will be fogged due to electrification, causing serious pollution to printed matter and printing environment.
2. Affect production safety: When the printed substrate is severe, the air may even be discharged due to ultra-high potential, resulting in electric shock or fire. Charged ink may cause the ink, solvent to catch fire, or shock workers with ink.
3. During the printing process, the paper on the paper pile is separated and conveyed forward under the friction of the paper conveying belt and the pressure roller. There is always friction between paper and paper, and between paper and machine, and friction generates electric charges. When the charges accumulate, the paper has a charge. When the papers have the same polarity charge, the papers repel each other, causing overprinting and inconsistency when printing. When the paper has a different charge, it causes There are problems such as empty sheets, double sheets, multiple sheets, and overprinting during paper feeding. The paper surface with static electricity is also prone to absorb some paper hair and dust, which will cause the printed image to have flowers or spots. Therefore, when printing, It is important to eliminate static electricity from the paper.
Elimination of static electricity 1. Grounding is the simplest way to eliminate static electricity. That is, the metal conductor is connected to the earth, so that it has the same potential as the earth, and the charges leak through the earth, but this method has almost no effect on the insulator.
2. Ion neutralization method, which is to ionize the air so that it generates positive and negative ions to neutralize the static electricity on the paper. It can be eliminated by static eliminator. Generally, static eliminators used on printing presses include inductive static eliminators, high-frequency high-voltage static eliminators, and high-frequency high-voltage static eliminators. They should be placed near the rollers during installation. ,
3. Control the relative humidity. This is a simple and effective method. Surface resistance decreases with increasing air relative humidity. Therefore, increasing the relative humidity of the air can increase the electrical conductivity of the paper surface and accelerate the leakage of charge. Therefore, sprinkle some water in the surrounding environment of printing, and use an air humidifier if possible, which can effectively eliminate static electricity.
4. Adjust the viscosity of the ink and increase the viscosity of the ink. It can also effectively reduce (eliminate) the static electricity in the ink and improve the printing quality.
5. Add antistatic agent or isopropyl alcohol to the ink, it is best to use antistatic agent, because adding more isopropyl alcohol will cause ink "anti-slag". Many books introduce that the amount of isopropyl alcohol is not more than 2 %, However, according to practice, it must be far beyond this amount to be effective.
6. When the water content of the paper is low, the paper is prone to static electricity. When the paper has serious static electricity, it is necessary to hang the paper or pile it in a relatively humid environment for a period of time, but pay attention to prevent the lotus leaf edge phenomenon of the paper.