Selection and use of gravure printing machine electrostatic ink transfer device
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Gravure is a relatively simple process with less variable factors, so quality control is simple and repeatability is high. With the wide application of gravure printing in the field of printing, people have put forward higher requirements for the adaptability of gravure printing process.
For different products or substrates, we often use different processes, especially for the printing of paper substrates, especially for the printing of fine products, gravure printing is increasingly using electrostatically assisted ink transfer systems ( ESA).
Why use an electrostatic ink transfer device?
We all know that the printing method such as gravure and embossing has the advantage that the gravure can not only control the tone of the printed matter through the area ratio of the dot, but also the level of the image on the printed matter through the thickness of the ink layer. It is precisely because of this gravure that it can express some rich patterns, and it is more advantageous for the performance of some special requirements. Similarly, our use of gravure is actually due to the stability of its print quality.
However, in the printing process of paper, we often have problems because we can't completely release the ink in the cell. Sometimes it can only reach 70%, so it often causes our gravure products not to reach gravure printing. Requirements, so a process came into being, is the ESA system (electrostatic ink transfer device) we mentioned earlier. Through such a device, we can solve the problem of residual ink in the cell.
How the electrostatic ink transfer device works
The electrostatic ink transfer device is composed of an electrostatic pressure roller, a conductive aluminum roller (or a conductive brush), a control cabinet (including a high voltage electrostatic generator), and the like.
Its working principle is shown as in Fig. 2. It generates high voltage and low current through the control cabinet, and the current is transmitted to the electrostatic pressure roller through the conductive aluminum roller or the 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 region is created between a conductive surface, paper, and gravure plate. Under the action of static electricity, the ink in the gravure plate is uniformly transferred to the surface of the paper, so that the transfer rate of the ink reaches or approaches 100%.
In the electrostatic loading process, it is necessary to select a positive or negative charge depending on the color of the ink, the composition of the ink, and the positive and negative of the electrostatic charge on the surface of the paper.
Experience in assembling electrostatic removal devices
A. It is important to choose the right product for your company. Sometimes such a choice is really a headache, but you have to choose between price and quality. Imported products from Germany and Japan, the price of each electrostatic pressure roller is about 0.8 million to 15,000 yuan, and each color group needs 200,000 yuan (excluding electrostatic pressure roller), and each gravure production line is equipped with at least 3~4 groups, which requires hundreds of thousands of dollars, but the overall quality can be said to be quite good. Domestically produced devices, it is understood that the current successful companies are only two companies in Beijing and Tianjin, the price of each color group is about 35,000 ~ 40,000 yuan (including electrostatic pressure roller), so a production line is only 15 Ten thousand yuan can be equivalent to the price of a color group of similar foreign products, but both the quality of use and the life of the product are obviously different from those of foreign products.
B. After the product is selected, some parameters and auxiliary facilities of the device, such as the way of electrostatic loading, the electrostatic pressure roller, the width of the printing machine, the width of the printed product, etc., are determined.
(1) There are two main types of electrostatic loading: there is a gap between the aluminum roller and the electrostatic pressure roller; the brush is easy to wear and deform when the brush is loaded, which causes uneven electrostatic loading.
(2) When selecting an electrostatic pressure roller, it must be distinguished from the pressure roller. The surface of the electrostatic pressure roller must be electrically conductive. The hardness and pressure roller should also be different. 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 equipment. It is too soft and easy to cause wear. , poor durability; too hard and easy to cause ink transfer is not complete, the static effect is not obvious.
(3) The width of the printing press and the width of the printed product should be considered together to solve the fabrication of the electrostatic pressure roller and the length of the conductive portion. In the past, the length of the electrostatic pressure roller was the length of the conductive portion, which easily caused the paper to break, or the paper edge was broken and could not be used on the machine. The length direction of the electrostatic pressure roller is now divided into a conductive portion and an insulating portion, just as with a pressure roller.
Problems that should be paid attention to when using electrostatic ink moving device
Since the electrostatic ink transfer device is mainly used in the printing mesh adjustment product, the electrostatic pressure roller should be installed every time the product is used, and the pressure is re-adjusted, and the capital accumulation time is long. In addition, in order to ensure better ink transfer and safety during printing, the following items must be observed.
1 Check the mounting position of the electrostatic pressure roller, the pressure of the pressure roller, and the pressure at both ends of the pressure roller.
2 Check the mounting position of the conductive aluminum roller and the electrostatic brush and the wires connected to the static control cabinet.
3 Check the working status of the pressure switch or speed controller.
4 The loading of the electrostatic voltage should be carried out when the speed of the gravure printing machine reaches 30 m/min or more. The voltage is gradually increased from zero according to the improvement of the printing effect. If the voltage is not increased, the voltage should be stopped. Change the polarity of the load voltage and check for problems in time.
5 If the screen printing effect is not improved after using the electrostatic ink shifting device, you should also check the surface flatness of the paper used and the engraving quality of the plate hole.
Insufficient presence of electrostatic ink transfer devices
Since the range of electrostatic ink transfer devices used in China is relatively narrow, the research on this technology has just started. There are still some shortcomings in the domestically used devices, and it is hoped that the peers can learn from this.
1 The number of engraving lines of gravure mesh products can be up to 175 lines/inch, which makes the degree of fineness of gravure meshes greatly restricted. Therefore, it is difficult to improve the level and fineness of products by electrostatic ink transfer device alone. Claim.
2 Adding static electricity to the paper by the electrostatic pressure roller will cause a strong electrostatic area to form in the range of about 300mm from the gravure. Therefore, the static elimination device must be installed in this part, otherwise it will easily cause the ink tank to ignite due to the high electrostatic strength. . Although the fire phenomenon will not cause great losses, it will pose a safety hazard.
3 The current electrostatic ink transfer device still has a large deficiency in the printing of gold and coated paper, and the printing quality has not been significantly improved.