Practical operation theory and process classificat

2022-06-23
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The practical operation theory and process classification of flexographic printing

flexographic printing, offset printing, gravure printing and silk printing are the four most common printing methods, which have their own advantages and disadvantages. At present, our national packaging and printing industry is developing in the direction of high-grade, fine and diversified. However, offset printing and gravure printing account for a large share in China, while flexo printing started late in China, especially in high-end products. 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. However, flexographic printing in many aspects, such as plate material, sleeve, double-sided tape and technical support, is still unable to produce by itself, the raw and auxiliary materials are not self-sufficient, and the technology and operation have not been standardized. In addition, due to the lack of strong technical support, the enterprises that connect the strain gauge to the measuring circuit have difficulty in operating the equipment in the best state, and it is difficult to guarantee the product quality, resulting in its economic benefits and the slow development of the entire flexo printing industry. The reason may be that there is a certain gap between the overall technical quality of the printing factory in flexo printing and the actual production needs. The effective use of equipment preparation, the correct selection of flexo printing materials, printing customization, and the operation of operators cannot reach a high production level. It should be said that this is a sad step that many flexographic printing enterprises have experienced. If there is practical technical support to help solve some weak links, the technical level of flexographic printing enterprises will be rapidly improved. How to make flexo printing develop healthily in China? I think the improvement of process is the key, but there are few flexographic printing technicians in China. In combination with the current situation in China, it is urgent for enterprises to cultivate flexographic printing technicians, and relevant industries should attach great importance to it. As for the specific operation and process, this paper briefly analyzes the theoretical operation and process points of narrow width flexographic printing based on the experience of flexographic printing. Printing equipment and printing technology are the core of operating the whole flexographic printing machine, which will reflect the true level of printing equipment, material selection, process formulation and operation level in the actual production process. Correct operation of each process is a basic requirement for operators. The usual operation sequence is as follows: loading and coiling - paper feeding - adjustment and correction of deviation - reasonable selection and allocation of wire rod - Master loading roller - adjustment of pressure of three rollers - inking - embossing - Registration - tension control - drying system - die cutting - slitting - winding

n after the coiling, the center position of the coiling is the printing position, because the correction of deviation, die cutting, segmentation, etc. are based on the central axis, The printing material shall pass through each paper guide stick in strict accordance with the paper route of the equipment. After threading, the machine can be started to make the printing material run smoothly, adjust the tension, and make the printing material subject to a certain stable tension control, so as to ensure the overprint accuracy, adjust and correct the deviation, and make the printing material in the middle of the printing machine and the printing plate, so as to ensure the sensitivity of the deviation correction action

n adjust the pressure of the three rollers. The adjustment of the flexographic printing pressure is a key step in product quality, which directly affects the quality of the printed product. The spacing between the printing plate roller and the embossing roller is the same. A standard feeler gauge with a thickness of 2.08mm (1.7 printing plate + 0.38 double-sided tape) can be selected to make the pulling 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, the operator needs to carefully fine tune, so the actual experience of technicians is required 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 between the line roll and the plate roll. The pressure between the two rolls can be adjusted to the best effect through the pressure system at both ends. The pressure between the two rolls should be light, which is conducive to the normal ink transfer of the dot skew, ensuring the quality of the image and text imprinting and protecting the damage of the printing plate. Secondly, roughly adjust the pressure of the plate roller and the substrate roller, and observe their transfer conditions. The clarity of the imprint on the surface of the substrate material is the confirmation of whether the transfer pressure is correct or not (Note: this key step is adjusted according to the experience of the technicians until the end). We must overcome the excessive pressure of flexographic printing, which is the key to the printing plate

n 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. The tension control system is an important mechanism of any web printing machine, which largely determines the overprint of printed products. The tension control mechanism is mainly located in the feeding part, printing station and feeding station The winding traction, winding mechanism and winding output require resistance. The rotation of the winding material is consistent, and the winding material itself also has a certain tension value. In addition to the tension traction of the printing speed, the resistance of the overprint of various color groups to the printing 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 texture. The thicker the printing material, the greater the tension value; On the contrary, the tension value should be small. For example, the tension value of the thin printing material should be higher, because it should take into account the wrinkle, tension, deformation and other problems of the substrate material. Generally, the appropriate tension adjustment is based on the standard that the color "cross gauge lines" that can be seen everywhere in our daily life are all accurate and do not "move" back and forth. If the "cross line" overprint is unstable during printing, the tension of unwinding and rewinding can be adjusted appropriately, Make the "crosshair" of each color group register stably. Of course, the tension value is not exactly the same at low, medium and high speed. It is recommended to fine tune the tension value at normal speed. The phenomenon of "displacement" often occurs in the printing process. People are used to looking for equipment, materials and other reasons. In fact, the impact of overprint accuracy, often for tension. If the tension can be carefully adjusted, generally, overprint inaccuracy can be easily solved

n adjustment of pH value and viscosity of ink effectively controls the pH value and viscosity of ink in the printing process, which 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. However, 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 stabilizer is usually required to be added every half an hour and stirred evenly. Basically, oil black can ensure a more stable printing suitability. Stabilizer cannot be added at will, otherwise it will backfire and various printing defects will occur. The viscosity of ink is the main factor that determines the transmission performance, imprinting firmness, 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 color will change if the viscosity is too low, and the dot will expand, resulting in the decline of product quality. When printing layered version and field version, the viscosity of water-based ink is different. General level version of the ink viscosity should be slightly lower. When printing, the speed of the machine also affects the ink viscosity. 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

n die cutting station in order to comprehensively discuss the flexo printing technology, in addition to the above-mentioned flexo printing process operation for corrugated boxes, I also want to talk about the die cutting station of narrow width flexo printing machine. Generally, three die-cutting stations are configured in the narrow width flexographic printing machine. After printing, online indentation and die-cutting are carried out to obtain the required printing products, which can be used for the processing of adhesive, forms, medicine bags and other finished products. The die-cutting knife adopts the circular indentation roller, and the contour knife roller is die-cutting formed. If the magnetic knife is used first, the magnetic roller of various product specifications must be prepared to form a series of specifications, It can meet the die cutting processing requirements of most products with different specifications and sizes. Another kind of die-cutting roll, called cutting sheet roll. It is a knife roller inserted with a die-cutting blade. It 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 as large or twice as large as the plate roller. Before using the contour knife roller, the cotton cloth with knife wrapping must be selected to ensure the die-cutting accuracy and avoid damage to the knife edge. The best pressure is to adjust the pressure to just cut off the substrate material. In addition, pay attention to post press processing, polishing, laminating, bronzing, punching, etc. This paper briefly describes some theories and practices of flexographic printing, hoping to become a reference for flexographic printing. There is no fixed model for flexographic printing process in ever-changing packaging. It is hoped that the printing workers can practice and accumulate experience in the production practice

reprinted from: Industry Technology (carton)

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