Introduction to the process of gravure printing

2022-08-18
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Introduction to the process of gravure printing

first, the arrangement of printing color sequence

there are generally two printing methods: surface printing and internal printing. The printing material (tipping paper) basically adopts surface printing due to its physical characteristics. Plastic film is usually printed inside. According to the change law of the three primary colors and the principle of chromaticity (overprint), as well as the actual experience in the production process, in general, the printing color sequence of surface printing (from light color to dark color) is: white yellow magenta cyan black inner printing (from dark color to light color) is: Black Cyan Magenta red yellow white, but sometimes appropriate adjustments can be made according to the process requirements

II. Gravure printing tension control

printing tension is an important process parameter of the printing process, and its tension system is also the core mechanism of the whole printing equipment. The setting of printing tension is determined according to the nature of the printing material. Allow ul to test two groups of samples with flammability of V-0 (1.6 mm). The easily stretched material is difficult to overprint accurately, so its tension is generally set to be small, but the tension is too small, and the material is loose, which will lead to irregular paper string, resulting in the inability to overprint accurately. The tension setting value is subject to the minimum tension value that can overprint accurately and roll neatly. Generally, the winding tension is slightly larger than the unwinding tension, and the main purpose is to tighten, compact and level the end face. Avoid loose coils, string coils and other phenomena, which are not conducive to the next process of cutting. The set tension value of base paper of different specifications and batches will be different, and the process control will be carried out in the actual printing process

III. control of steam heating temperature

the control of heating temperature is also determined by the nature of the printing material. There is a certain relationship among heating temperature, printing speed and flux volatilization speed. When the temperature is constant, if the flux volatilizes slowly, the printing speed should be reduced. On the contrary, the printing speed should be improved. When the flux volatilization speed is constant, if the printing speed is accelerated, the heating temperature will be increased. Otherwise, the temperature can be reduced. When the printing speed is constant, if the flux volatilizes slowly, the heating temperature should rise. On the contrary, the heating temperature should be reduced. In addition, the control of heating temperature is also related to printing process conditions, ink properties and ink thickness

IV. control of printing pressure

printing pressure refers to the pressure of the printing rubber impression roller. Insufficient printing pressure, poor ink transfer, and prone to graphic defects. Too much pressure is easy to imprint marks. Therefore, generally, gravure printing machines are equipped with electrostatic ink suction rollers, which use static electricity to help ink transfer. It is essential for high-speed gravure printing machines. Through the electrostatic ink absorption system, the ink can be transferred to the paper very well. Without the electrostatic ink absorption system, the ink cannot be fully transferred, and the patterns, lines, words, etc. may be blurred, missing printing, and uneven hue and depth. The printing pressure of different substrate materials is also different, and there are certain requirements for the rubber hardness of the rubber roller. Generally, when printing plastic film, the requirements for rubber hardness are slightly higher. When printing tipping paper, its pressure is generally about 20 ~ 30Pa. In the specific production process, appropriate adjustments should be made according to the printing effect, ink and other related factors

the printing pressure between the printing plate roller and the rubber impression roller is obtained by adjusting the center distance between them. The pressure causes the transfer of ink to occur, resulting in rubber deformation and maintaining a certain imprint width. The imprint width changes with the diameter of the two rollers, rubber hardness and printing pressure. Under the same printing pressure, the rubber press roller with small diameter has good printing quality, and the press roller with high rubber hardness has good printing quality, because the obtained impression width is small

in actual printing, the size of the imprint width should be comprehensively judged, that is, it should be determined according to the types of printing materials, the thickness and hardness of rubber, the width of printed matter and other factors

v. ink viscosity adjustment and control

the accuracy and sustainability of ink viscosity in the printing process is very important, especially in high-speed printing, ink viscosity control is related to a series of printing faults. It is an important factor affecting the quality of printing. When printing, the greater the viscosity of the ink, the worse the effect of ink transfer. When the ink viscosity is too large, the whole ink system is in a supersaturated state, and the material fluidity in the ink is poor. It is easy to gather together, and it is not easy to smoothly enter and exit the hole of the plate roller. If the viscosity of the ink is too small, there is more organic flux in the ink. However, the resin, pigment and other components in the ink are relatively small. After drying, it cannot form a smooth surface film, and the ink layer is white, dull and lacking luster

in gravure printing, first of all, adjust the viscosity of the ink, add the flux to the ink, and reduce its viscosity to meet the performance and process requirements of the printing machine. Viscosity mainly matches the speed of printing locomotive. When printing at high speed, try to use low viscosity on the premise of ensuring stable hue. Because the viscosity of the ink seriously affects the printing quality, the viscosity of the ink must be controlled in a suitable range in the gravure printing process. In production, due to the continuous circulation of ink, the flux is always volatilizing. The function consumption of the system is large and the equipment is complex. Because the viscosity of the ink is tested every five minutes, it is controlled within the normal range

VI. adjustment and control of the scraper

the height position and front and rear position adjustment of the scraper determine the contact position between the scraper blade and the printing plate roller, and also determine the distance between the contact line of the knife plate and the embossing line. The length of the distance should be adjusted according to the printing speed, ink viscosity, hole depth, drying speed, layout quality, printing plate roller diameter, etc., generally about 40mm. Generally speaking, the longer the distance, the greater the chance of ink drying and the lower the transfer rate of ink. From the printing effect, it is equivalent to the partial dilution of the ink. At the same time, the length of this distance is a test of the printability of ink. When the distance is large, some ink will overflow from the hole, which will affect the printing quality. On the contrary, it is conducive to improve the ink transfer rate, but it is easy to produce printing faults such as dirty version. The contact angle of the scraper is the angle between the tangent of the contact point between the scraper blade and the printing plate roller and the scraper blade, which is generally degrees. Improve the contact angle, it is easy to scrape the ink of the layout and make the graphics and texts clear. When the ink layer is too thin, the printing ink gloss is poor, and other phenomena may occur, it is also easy to damage the printing plate roller. On the contrary, the contact angle is reduced, the printing ink layer is thick, the print is glossy, and the edges and corners of the text are easy to be blurred. At the same time, impurities in the ink are easy to be brought into the knife seam, causing printing processing faults such as printing knife wire

scraper pressure adjustment generally speaking, the pressure added by the scraper on the plate roller is set according to the needs, usually about 20Pa. The principle of control is to reduce the pressure of the scraper as much as possible without affecting the printing quality. The greater the pressure of the scraper, the greater the friction between the master roll and the scraper, which is easy to damage the scraper and the master roll. The factors that affect the pressure of the scraper include the printing speed, the processing accuracy of the plate roller, the quality of the scraper itself, the viscosity of the ink, the impact of the ink on the scraper, the contact angle of the scraper, etc. Under normal circumstances, the faster the printing speed is, the greater the scraper pressure is required

the levelness and flatness of the scraper the flatness and warpage of the scraper mainly depend on the installation method. Of course, it may also be related to the tool holder groove or giving customers a sense of responsibility. There are foreign objects stuck on the scraper blade and tablet. If the blade is not installed flat, when printing large-area full-color products, it is likely that the thickness of the ink layer is different, or the ink scraping is not clean, which will seriously affect the product quality and normal production

in order to improve the ink scraping effect, while the printing plate roller rotates, the scraper also makes periodic reciprocating motion in the length direction of the surface of the printing plate roller. In this way, it can reduce the wear on the local fixed position and avoid the accumulation of ink at the bottom of the scraper. Moving the scraper left and right plays an important role in reducing the knife line and improving the scraping. Please contact the latest conference information of this year: the utilization rate of the scraper and reducing the wear of the printing plate roller

VII. Management of printing plates

because gravure printing mainly relies on the transfer of the ink stored in the cylinder hole of the printing plate to the printing material to realize the printing pattern, the storage, maintenance and cleaning of the printing plate are important. The place where printing plates are stored should be kept clean, ventilated and dry. The printing plates should be carefully cleaned before and after getting on and off the machine to prevent the blocking of printing plates caused by the accumulation of ink in the hole for a long time, especially for some fine stripe printing plates, the work of timely cleaning the printing plates before and after printing should be strictly observed

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