Experience in the practical operation of the hotte

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Experience in the actual operation of flexographic printing

flexographic printing, offset printing, gravure printing and silk printing are the four common printing methods, which have their own advantages and disadvantages. At present, the packaging and printing industry is developing in the direction of high quality, precision and diversification. However, offset printing and gravure printing account for a large proportion, while flexo printing started late in China, especially in high-quality printing. However, with the continuous application of new technologies, the unique and superior flexographic printing has made great progress and has quite strong market competition potential

printing equipment and printing technology are the core of operating the whole flexographic printing, which will reflect the printing equipment, material selection, operation formulation and operation level. Correct operation of each process is a basic requirement for operators

the usual operation sequence is as follows:

loading coil → paper feeding → adjustment and correction → reasonable selection and matching of wrinkle roller → loading roller → pressure adjustment → inking → embossing → registration → tension control → drying system → die cutting → slitting → winding

loading coil

after loading coil, the central position of the roll is also the printing position, because the plate pasting and correction, die cutting, segmentation, etc. are based on the central axis, The printed material should pass through each paper guide roller in strict accordance with the paper feeding route of this equipment. After threading, the machine can be started to make the paper feeding of the printed material stable, adjust the tension, and make the printed material subject to a certain stable tension control, so as to ensure that the overprint accuracy can be used at extremely low temperature, adjust and correct the deviation, and make the material in the middle of the printer and the printing plate, so as to ensure the sensitivity of the correction action

adjustment pressure

the adjustment of flexographic printing pressure is a key step of product quality, which directly affects the beauty of the print. The spacing between the plate roller and the embossing roller is the same. A standard feeler gauge with a thickness of 2.08mm (1.7 plate +0.38 double-sided tape) can be selected to make the pull resistance of the feeler gauges at both ends the same, At this time, the spacing is the most ideal pressure value for printing (but in actual production, it requires careful fine-tuning by operators, which requires the actual experience of technicians to obtain the best pressure value)

when the machine is running at a slow speed, start pressing from the first color group. First, check the ink transfer condition of the corrugated roller to the plate roller, and adjust it to the best effect through the pressure system at both ends. The pressure between the two rollers should be light, which is conducive to the normal ink transfer of the dot skew, ensuring the image quality and protecting the printing plate from damage. Secondly, roughly adjust the pressure of the plate roller and pressure roller, and observe the transfer situation. The clarity of the material surface printing is the confirmation of whether the transfer pressure is correct (Note: this key step is adjusted according to the experience of technicians). We must overcome the excessive pressure of flexographic printing, which is the key of printing plate

tension control system

in the printing process, the constant printing tension is controlled by the tension controller, which is the key to the accuracy of overprint. Therefore, the tension control system is an important mechanism of any web printing machine, which largely determines the overprint accuracy of the print. The tension control mechanism is mainly located in the feeding part. The printing station and the feeding and receiving traction and the winding mechanism, the output of the roll need resistance, and the roll rotation has inertia, There is also a certain tension value in the coil itself. Coupled with the tension traction of the printing speed, the resistance of the overprint of various color groups to the printed material during the printing process makes the tension control of the unwinding, printing and winding mechanism particularly important. The size of the tension control should be determined by the thickness of the material and the width of the material. The thicker the printed material, the greater the tension value; On the contrary, the tension value should be small. For example, the tension value of thin printing materials is required to be higher, because problems such as wrinkling, stretching and deformation of the printed materials should be taken into account. In general, the appropriate tension adjustment is based on the full registration of multi-color "crosshairs" without "moving back and forth". If the "crosshairs" overprint is unstable during printing, the tension of unwinding and rewinding can be adjusted appropriately, so that the "crosshairs" of various color groups can be registered stably, of course, at low speed The tension value is not exactly the same at medium speed and high speed. It is recommended to fine tune the tension value at normal speed, There are often "out of position" in the printing process "Phenomenon, people are used to looking for equipment, materials and other reasons. In fact, it is not. What affects the overprint accuracy is often the tension discomfort. If the tension can be carefully adjusted, generally, the overprint inaccuracy can be easily solved.

adjustment of pH value and viscosity of ink

effective control of pH value and viscosity of ink in the printing process is the main operation step to ensure the quality of printing products.

the pH value of water-based ink is about 8.5, At this value, the ink is relatively stable, but in actual production, with the rise of temperature and the volatilization of ammonia in the ink, the pH value will change, affecting the printability of the ink. In this regard, a small amount of stabilizer can be added to control the pH value. In normal printing, 5ml of stabilizer is usually required to be added every half an hour and stirred evenly. Basically, this is for Vertu upstairs, who said that oiling black can ensure a more stable printing suitability. Do not add stabilizer at will, otherwise it will backfire, and various printing defects will follow

the viscosity of ink is the main factor that determines the transmission performance, printing fastness, penetration and gloss of ink. If the ink viscosity is too high, the color will be darker, the ink loss will be large, the drying degree will slow down, the viscosity is too low, the color will change, and the dot will expand, resulting in the production of "these parts can be operated once, and the quality of injection molded products will be reduced

the viscosity of water-based ink is different when printing layered version and full version. Generally, the viscosity of layered ink should be slightly lower. When printing, the speed of the machine also affects the viscosity of ink. When the printing speed is high, the viscosity of water-based ink is lower, while when the printing speed is low, the viscosity of ink is higher

die cutting station

in order to comprehensively discuss flexo printing technology, in addition to the above-mentioned flexo printing process operation of corrugated boxes, I also want to talk about the die cutting station of narrow width flexographic printing machine. Narrow format flexographic printing machines are generally equipped with three die-cutting stations. After printing, they are connected for indentation and die-cutting to obtain the required printed products, which can be used for the processing of stickers, forms, DNA amp midsole, BASF elastopan sports light materials, medicine bags and other finished products. The die-cutting knife adopts round indentation roller, and the contour knife roller is die-cutting and forming. If the magnetic knife is used first, the magnetic roller of various product specifications must be prepared to form a series of specifications, In order to meet the die cutting requirements of most products with different specifications and sizes

another kind of die-cutting roller is called sheet cutting roller. It is a knife roller inserted with die-cutting blades, which can open one, two, four or more knife grooves as required. It is mainly used for cutting single sheet finished products. The cutting single sheet roller can be used as large as or twice as large as the plate roller

the knife wrapped cotton cloth must be selected before using the contour knife roller to ensure the die-cutting accuracy and avoid the damage of the knife edge. The best pressure is to adjust the pressure to just cut off the printing material

in addition, pay attention to post press processing, polishing, laminating, bronzing, punching, etc

this paper briefly describes some theories and practical operations of flexographic printing, hoping to become a reference for flexographic printing. There is no fixed mode for flexographic printing in ever-changing packaging. It is hoped that printing workers can practice more and accumulate experience in production

-- longchen printing technology

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