The application of static electricity in printing

Static electricity is a factor that plagued printing. This static electricity is the static electricity generated by the paper or film surface during the printing process of the paper or film material, friction with the roller or ionization of the air on the surface of the paper or film. It has a slight impact on the printing quality, and the static electricity involved in this article. It is produced by specialized equipment and plays an auxiliary processing role in printing and post-printing processes.

The application of static electricity in the printing industry:

Gravure is the process of transferring traces of ink from gravure roll pockets to the surface of the substrate. Due to the surface tension of the gravure printing ink, the capillary effect of the paper, and the factors such as the cell wall and the rough surface of the paper, it is difficult to transfer the ink and easily form white spots. In order to solve such problems, the German ELTEX company developed an electrostatic ink-absorption system. The structure is: a high voltage generator, an electrostatic discharge rod, two static elimination rods, the principle of which is the principle of electrophoresis, the voltage is applied through the electrostatic discharge rod -27KV, one-way direct current through the air ionization makes the surface of the embossing cylinder charged, An electrostatic action zone is formed between the embossing roller and the plate roller, and the ink is pulled to change the surface morphology, so that part of the surface of the roller is higher than the surface of the printing roller, and it is easy to come into contact with the substrate. This contact occurs and the ink can be transferred. Improve the transfer rate of ink and avoid the loss of dots, thus improving the printing quality of the product. Electrostatic ink-absorption systems can be used for gravure printing of decorative materials, gravure printing for books and magazines, and gravure printing for tobacco packaging. In this printing process, solvents are present. Electrostatic ink-absorbing systems use high voltage to generate sparks, which may cause fire hazards, but ELTEX's The electrostatic ink-absorbing system adopts a reasonable structure, which can reduce the current to μA and the short-circuit current of 33μA. During the use, there is no spark, which can ensure the safety of use.

With China's accession to the WTO, commercial printing will not only increase in quantity, but will also have higher and higher requirements for printing quality. As a commercial rotary printing company, it is necessary to improve the quality of its own printing products, reduce production costs, and increase production efficiency.

From the perspective of China's existing paper and ink, the use of thermosetting inks not only improves printing efficiency, but also reduces costs. Due to equipment configuration problems, there are problems such as severe water dispersion, easy paper breakage, severe paper and folding, and low cooling efficiency in the printing process, which results in the equipment being unable to produce at normal speed and reducing the production efficiency. ETEX Corporation of Germany has developed a static air humidification system and electrostatic compounding as well as a gap eliminator for improving the cooling efficiency.

In commercial rotary printing, the moisture content of the web is generally 5% to 4%. After offset printing, the paper absorbs ink and the moisture absorption reaches 6.5%, while the use of thermoset ink requires high temperature drying, and the temperature is generally 100. °C ~ 120 °C, at this time the paper moisture has dropped to less than 1%, paper fibers lose more moisture, loose fibers will appear paper lint, paper dust more, and the paper is easily broken. Edge breaks occur during hemming. Due to the uneven moisture absorption of the paper, a depression or a booklet may be formed at the binding band, resulting in wrinkles or short and long pages. In order to avoid this phenomenon, domestic commercial rotary press manufacturers will reduce the machine speed but increase the production cost.

Foreign commercial rotary printing presses are generally equipped with electrostatic devices that electrostatically humidify and increase the cooling efficiency of the roller gap. Japan's ToPPan PrinTing ComPanY Komori commercial rotary printing press is equipped with Eltex's LG50 electrostatic humidification system, USA's RRDonnEllY PrinTing ComPang, and its Heidelberg M600 commercial rotary press is equipped with ELTEX's WE.B.rEmoisTEn electrostatic humidification system.

The structure is: pressure generator, electrostatic discharge stick, water mist spray device, electrostatic humidification system use process; high voltage electricity generated by the voltage generator, and then electrostatic discharge stick (electrostatic discharge stick placed on the roller, with the ground Associated with the formation of electric field) 3kV high pressure, the surface of the paper charged through the mist spray device, due to the role of electrostatic field, water mist will spread evenly along the direction of the electrostatic field on the paper, so that the paper moisture rose to 3% ~ 4 %, the problem of water loss without this system can be avoided. At the same time, the electrostatic application device is used on the first cooling roller. Since the paper is output from the high-temperature drying device, the surface temperature is high, and it comes into contact with the cooling roller, and the air between the high-temperature paper and the cooling roller is heated. As the air rises, the paper is lifted so that the paper cannot contact the cooling roller well (the angle of the paper and the cooling roller is reduced), and the static electricity application device uses static electricity on the surface of the paper because the cooling roller is grounded through the bracket. The paper with static electricity contacts the cooling roller better, so that the wrap angle of the paper and the cooling roller is increased, so that the cooling efficiency of the first cooling roller is improved, which can increase the speed of the printing machine and reduce the number of cooling rollers. , Reduce the cost of printing.

There are two kinds of folding methods on the commercial rotary printing press. One is to fold the paper into a book by a forming machine, and the other is to use a first dividing and re-clutching and then folding into a book. In the former method, the thickness of the inner crease of the folded edge is significantly thicker than that of the second type, because the smallest rounded corner of the former is determined, and there is a minimum roundedness at the first fold, and when the second fold, the first The rounded arc length of the two fold outer fold line is longer than the rounded arc length at the second fold inner fold line. On the one hand, there is waste of paper, and on the other hand, it is not conducive to folding. The second method is to eliminate the problem of fold angle at the edge of the fold first, so it is easy to fold and can save printing materials (paper is the highest cost factor in web printing). Electrostatic clutch device. There are two electrostatic discharge sticks on the two sides of several paper strips, so that the paper is charged with static electricity, due to the role of static electricity, the paper firmly "glued" together. It can prevent the paper from sliding so that it can be folded correctly in the subsequent process.