Application of static electricity in printing
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Static electricity is a factor that plagues printing. This kind of static electricity is the static electricity generated by paper or film material during the printing process, with roller friction or air ionization on the surface of paper or film. It has a little influence on the printing quality, and the static electricity involved in this paper. It is produced by special equipment and plays an auxiliary role in the printing and printing process.
The application of static electricity in the printing industry:
Gravure is the process of transferring a trace amount of ink from a gravure roll to the surface of a substrate. Due to the surface tension of the gravure ink and the capillary effect of the paper, factors such as the wall of the grid and the roughness of the surface of the paper make the ink transfer difficult, and white spots are easily formed. In order to solve such problems, ELTEX Germany developed an electrostatic ink absorption system. The structure is: a high voltage generator, an electrostatic discharge rod, and two static elimination rods. The principle is electrophoresis principle. The voltage is applied by electrostatic application rod -27KV, and the unidirectional direct current is charged by air ionization to charge the surface of the impression roller. An electrostatic interaction zone is formed between the embossing roller and the plate roller, and the ink is pulled to change the surface morphology, so that a part of the surface is higher than the surface of the plate roller, and is easy to contact with the substrate, and when the contact occurs, the ink can be transferred. Improve the transfer rate of the ink, avoid the phenomenon of dot loss, and improve the printing quality of the product. The electrostatic ink absorption system can be applied to decorative material gravure, book gravure and tobacco packaging gravure. In the printing process, there are solvents, while the electrostatic ink absorption system uses high voltage to generate sparks, which may cause fire hazards, but ELTEX The electrostatic ink absorption system adopts a reasonable structure to reduce the current to μA, the short-circuit current is 33μA, and no sparks appear during use, which ensures safe use.
With China's accession to the WTO, commercial printing will not only increase in quantity, but also in the demand for printing quality. As a commercial rotary printing enterprise, it is necessary to improve the quality of its own printing products, reduce production costs, and improve production efficiency.
From the perspective of China's existing paper and ink, the use of thermosetting inks can not only improve printing efficiency, but also reduce costs. Due to the problem of equipment configuration, there are problems such as water dispersion in the printing process, paper breakage, paper wool and folding fracture, and low cooling efficiency, which results in equipment not being produced at normal speed and reducing production efficiency. Germany's ETEX has developed an electrostatic humidification system and electrostatic recombination as well as a gap eliminator to improve cooling efficiency.
In commercial rotary printing, the moisture content of the general web is 5% to 4%. After offset printing, the paper absorbs ink and absorbs water to 6.5%. While using thermosetting ink, it needs high temperature drying. The temperature is generally 100. °C ~ 120 ° C, at this time the paper moisture has dropped below 1%, the paper fiber loses more water, the loose fibers will appear paper fluff, paper dust is more, and the paper is easy to be broken. During the hemming process, paper edge breakage occurs. Due to the unevenness of the ink absorption and resurgence of the paper, wrinkles or long and short pages may occur after the depression or the book is formed at the binding tape. In order to avoid this phenomenon, domestic manufacturers of commercial rotary printing presses will reduce the speed of the machine but increase the production cost.
Foreign commercial rotary presses generally have electrostatic devices that are equipped with electrostatic humidification and roller gaps that increase cooling efficiency. Japan's ToPPan PrinTing ComPanY Komori commercial rotary press, equipped with ElTEX's LG50 electrostatic humidification system, the United States R.R.DonnEllY PrinTing ComPang, its Heidelberg M600 commercial rotary press equipped with German ELTEX WE.B.rEmoisTEn electrostatic humidification system.
The structure is: pressure generator, electrostatic application rod, water mist spraying device, electrostatic humidification system use process; high voltage electricity is generated by a voltage generator, and then electrostatically applied to the rod (electrostatic application rod is placed on the over roller, ground) Connected to form an electric field) with a high voltage of 3kV, the surface of the paper is charged through the water mist spraying device. Due to the action of the electrostatic field, the water mist will spread evenly along the direction of the electrostatic field to the paper, so that the paper moisture rises to 3%~4 %, the problem of water dispersion caused by 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 the cooling roller is in contact with the air between the high-temperature paper and the cooling roller due to heat. As the air rises, the paper is lifted so that the paper does not come into good contact with the cooling roller (the angle between the paper and the cooling roller is reduced), and the electrostatic 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 is better contacted with the cooling roller, 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 increased, thereby increasing the speed of the printing machine and reducing the number of cooling rollers. To reduce printing costs.
There are two types of folding on a commercial rotary press. One is to fold the paper into a book by a former, and the other is to use a strip to re-separate and then fold into a book. In the former way, the thickness of the inner crease of the folded edge is significantly thicker than the second one, because the minimum fillet of the former is determined, and there is a minimum rounded curvature at the first fold, and the second fold, The rounded arc length of the two-folded 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 suitable for folding. The second way is to first divide the strip without the problem of the wrap angle of the folding edge, so it is easy to fold and can save the printing material (paper is the most expensive factor in the web printing operation). Electrostatic clutch device. There are two electrostatic application rods on both sides of several paper strips to make the paper electrostatic. Due to the action of static electricity, the paper is firmly "bonded" together. It prevents the paper from slipping in order to facilitate the correct folding of the post-process.