Selection guide for electrostatic ink transfer device of gravure printing machine
The electrostatic ink removal device consists of an electrostatic pressure roller. Conductive aluminum roller (or conductive brush), control cabinet (including high-voltage electrostatic generator) and other parts, as shown in Figure 1.
Its working principle is shown in Figure 2. It generates high voltage and low current through the control cabinet, and transmits the current to the electrostatic pressure roller through the conductive aluminum roller or conductive brush, so that the electrostatic pressure roller is charged with a positive (or negative) charge, so that the electrostatic pressure roller is in contact with the paper A high voltage electrostatic area is established between a conductive surface, paper and gravure plate. Under the action of static electricity, the ink in the gravure printing plate is sucked out and transferred evenly to the surface of the paper, so that the transfer rate of the ink reaches or approaches 100%.
In the process of electrostatic loading, the positive or negative charge should be selected according to the color of the ink, the composition of the ink, and the positive and negative charges on the surface of the paper.
Matters needing attention when selecting electrostatic ink transfer device
1. The first is the choice of electrostatic ink transfer device manufacturers. If the company has a certain strength, it should choose imported products, mainly from manufacturers in Germany and Japan. The price of each electrostatic pressure roller is about 0.8 million and 15,000 yuan. Each color group needs 200,000 yuan (excluding static electricity) (Pressure roller), each gravure production line is equipped with at least 3-4 groups, which requires hundreds of thousands of yuan of funds, but this is also a long-term investment in gravure screen mesh adjustment products. If you choose a domestic device, it is understood that there are only two companies in Beijing and Tianjin that are currently more successful. The price of each color group is about 35,000 to 40,000 yuan (including electrostatic pressure rollers). Only 150,000 yuan is needed, which is equivalent to the price of one color group of similar products abroad.
2. After the manufacturer selects, it is necessary to determine some parameters and auxiliary facilities of the device, such as the way of electrostatic loading, electrostatic pressure roller, the width of the printing machine, the width of the printed product, etc.
(1) There are two main ways of electrostatic loading, namely aluminum roller and electrostatic brush. These two methods have disadvantages, such as: there is a gap between the aluminum roller and the electrostatic pressure roller when the aluminum roller is loaded; the brush is easy to wear and deform when the brush is loaded, which will cause uneven electrostatic loading.
(2) When selecting the electrostatic pressure roller, distinguish it from the pressure roller. The surface of the electrostatic pressure roller must be conductive, and the hardness should be different from that of the pressure roller. The hardness of the general pressure roller should reach HS90, and the hardness of the electrostatic pressure roller should be controlled at HS80-85 according to the different equipment. , Durability is poor; too hard and easy to cause incomplete ink transfer, static effect is not obvious.
(3) The width of the printing machine and the width of the printed product should be considered together to solve the production of the electrostatic pressure roller and the length of the conductive part. In the past, the length of the electrostatic pressure roller was the length of the conductive part, which easily caused the paper to break, or the edge of the paper was damaged, and could not be used on the machine. The electrostatic pressure roller is now divided into a conductive part and an insulating part in the longitudinal direction, just like the pressure roller.
Matters needing attention in the use of electrostatic ink transfer device
Since the electrostatic ink removal device is mainly used when printing mesh-adjusted products, an electrostatic pressure roller must be installed every time it is used, and the pressure is readjusted, which takes a long time to prepare. In addition, in order to ensure a good ink transfer effect and safety in printing, the following must be noted.
1. Check the installation position of the electrostatic pressure roller. Pressure of the pressure roller and pressure at both ends of the pressure roller.
2. Check the installation location of the conductive aluminum roller and electrostatic brush and the wires connected to the electrostatic control cabinet.
3. Check the working status of the pressure switch or speed controller.
4. The loading of electrostatic voltage should be carried out when the speed of the gravure printing machine reaches more than 30 meters / minute. According to the improvement of the printing effect, the voltage is gradually increased from zero. If the increase of the voltage has no obvious effect, the voltage should be stopped and changed Load the polarity of the voltage or check the existing problems in time.
5. If the screen printing effect is not improved after using the electrostatic ink transfer device, you should also check the surface smoothness of the paper used and the engraving quality of the printing plate.
Shortcomings of electrostatic ink transfer device
Due to the relatively narrow range of use of electrostatic ink transfer devices in China, the research on this technology has just begun. There are still some deficiencies in the domestic devices that are currently used more. I hope that colleagues can use this as a mirror.
1. The number of engraved lines of the gravure screen mesh-adjusted product can be up to 175 lines / inch, which makes the fineness of the gravure mesh hole greatly restricted, so only the electrostatic ink removal device is used to improve the level of the product. The level of sophistication is still difficult to meet the requirements.
2. Adding static electricity to the paper through the electrostatic pressure roller will cause a strong static area to be formed within 300mm of the paper just after leaving the intaglio, so a static elimination device must be installed in this part, otherwise the electrostatic strength of the chimney may be high and cause the ink tank to catch fire . Although this fire phenomenon will not cause great losses, it has hidden hidden dangers.
3. The current electrostatic ink transfer device still has major deficiencies in printing gold and coated paper, and the printing quality has not been significantly improved.
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