Flexo printing, offset printing, gravure printing and screen printing are the most common four printing methods. They have their own merits. At present, our country's packaging and printing industry is moving toward high-grade, refined and diversified directions. However, the proportion of offset printing and gravure printing in China is relatively large, while flexo printing has started relatively late in China, especially in high-end products. However, with the continuous application of new technologies, unique and superior flexo printing has made great progress and has a very strong potential for market competition. However, flexographic printing is still unable to produce on its own in many aspects such as plate, sleeve, double-sided tape, and technical support. The original materials cannot be self-sufficient, and technologies and operations have not been standardized. In addition, due to the lack of strong technical support for more companies, equipment is difficult to operate in the best condition, product quality is difficult to guarantee, resulting in its economic benefits and the slow development of the entire flexo industry. Analysis of the reasons may be mainly due to the fact that there is a certain gap between the overall technical quality of the printing plant in terms of flexo printing and the actual production needs, effective use of equipment preparation, correct selection of flexo printing materials, printing customization, operation of operators, etc. Unable to reach higher production levels. It should be said that this is a period of sadness that many flexographic printing companies have experienced. If there is effective technical support to help solve some weak points, the technical level of flexographic printing companies will be improved quickly. . How can we make flexo printing healthy development in our country? I think that the improvement of the process is the key, but there are few flexographic printing technicians in China. Combining with the current situation in China, it is imperative for companies to cultivate flexo technology people. The relevant industries should pay close attention to. As for specific operations and processes, the theoretical operation and process points of narrow-width flexographic printing are briefly analyzed based on the flexographic printing experience. Printing equipment and printing technology are the core of the operation of the entire flexographic printing press. It 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 an essential requirement for operators. The usual sequence of operations is as follows: Feeding coils - Feeding - Adjusting rectification - Reasonably matching reel - Printing roll - Adjusting the pressure of three rolls - Inking - Imprinting - Registering - Tension control - Drying system - Die cutting - slitting - winding

n After rewinding, the center position of the reel material is the printing position. Since the offset correction, die-cutting, and sub-sections are based on the central axis, the printing material should pass through the paper path of the equipment. After each paper guide stick and paper is put through, the machine can be started to allow the printing material to run smoothly and the tension is adjusted so that the printing material is subjected to a certain level of steady tension control. This can ensure overprint accuracy, adjust the deviation, and make the printing material between the printer and the printing plate. Location to ensure the correctness of corrective action.

n Adjusting the pressure of the three-roller flexo printing pressure adjustment is a key step in product quality and directly affects the fineness of the printed product. The spacing between the plate roller and the embossing roller is the same, and 2.08 mm (1.7) can be selected. Plate + 0.38 double-sided tape) The thickness of the standard feeler gauge, so that the pull resistance of the feeler at both ends is the same. The spacing at this time is the ideal pressure value for printing (but in the actual production, the fine adjustment of the operator needs to be performed. , then it needs the actual experience of the technicians to get the best pressure value). When the machine is running at a slow speed, starting from the first color group to start pressing, first check the ink transfer condition of the roller of the screen roller. The pressure can be adjusted to the best effect by the pressure system at both ends. The pressure between the two rollers is light. Well, it is conducive to the normal transmission of ink in the dot network, ensuring the quality of the imprinting and protecting the printing plate. Followed by the rough adjustment pressure of the plate roller and the printing roller, observe the transfer condition, the clearness of the surface of the sample bearing material is the correctness of the transfer pressure (Note: This key step is adjusted according to the experience of the technicians. , point to the end). We must overcome the pressure of flexographic printing, which is the key to the printing plate.

n tension control system in the printing process by the tension controller to control the constant print tension, is the key to accurate overlay, tension control system is an important mechanism for any web press, it to a large extent determine the print In India, the tension control mechanism is mainly located in the discharge section, printing station and place. The receiving traction and winding mechanism, the output of the coil needs resistance, the rotation of the coil is consistent, and the coil itself has a certain tension value. In combination with the pulling speed of the printing speed, the resistance of the various sets of overprinting to the printing materials in the printing process makes the tension control of the unwinding, printing, and winding mechanisms particularly important. The size of the tension control should be determined by the thickness and the texture of the material. The thicker the printing material, the greater the tension value; conversely, the tension value should be small, such as the tension value of the printing material is more demanding, because he should take into account the printing material wrinkling tension, deformation and other issues, under normal circumstances the appropriate tension adjustment is Multi-color "cross-line" standard, not "move" back and forth as a standard, if the "crosshair" overprinting is not stable, can be adjusted to adjust the unwinding and winding tension, so that the colored group "crosshair" register Until stable, of course, the tension values ​​at the low, medium, and high speeds are not exactly the same at the time of printing. It is recommended that the tension value be fine at normal speed, and the “walking” phenomenon often occurs during the printing process. People are accustomed to finding equipment. , materials and other reasons. In actual fact, affecting the accuracy of overprinting is often tension discomfort. If you can carefully adjust the tension, under normal circumstances, overprinting can be solved.

n Adjusting the PH value and viscosity of the ink The effective control of the ink's pH and viscosity during the printing process is the main operation step to ensure the quality of the print. Water-based ink PH value of about 8.5, at this value, the ink is relatively stable, but in actual production with the temperature rise and the volatilization of ammonia in the ink, PH value will change, affect the printability of the ink. A small amount of stabilizing agent can be added to control the PH value. In normal printing, it is usually required to add 5 ml of stabilizer every half hour, and stir it evenly. Basically oil black can ensure more stable printability. Add stabilizers, otherwise it will be counterproductive and various printing defects will follow. The viscosity of the ink is a major factor in determining the ink transfer properties, print fastness, penetration, and gloss. The viscosity of the ink is too high, the darker the color, the greater the loss of the ink, the slower the drying, the lower the viscosity, the more the color changes, and the larger the dots, which leads to a drop in product quality. Water-based inks have different viscosities when printing gradation and field editions. General grade ink viscosity should be slightly lower. When printing, the speed of the machine also has an effect on the viscosity of the ink. When the printing speed is high, the viscosity of the water-based ink is lower, and the viscosity of the ink is higher when the printing speed is low.

n Die-cutting station In order to discuss the flexo printing technology in a more comprehensive way, besides the above-mentioned operation of the corrugated carton flexo printing process, I would like to talk about the die-cutting station of a narrow-width flexographic printing press here. In a narrow-width flexo printing press, three die-cutting stations are generally prepared. After printing, indentation and die-cutting are performed to obtain the desired printed products. The products can be used for processing of stickers, forms, and packages, and die-cutting. The knife adopts circular pressure indentation roller and the external knife roller is used for die cutting. If you use a magnetic tool, you must prepare a variety of product specifications of the magnetic roller to form a series of specifications to meet the requirements of most products of different sizes and sizes. Cut processing requirements. Another type of die-cutting roll is a single-cut roll. It is a knife roller set into a die-cutting blade. It can open one, two, four or more sipes as required. It is mainly used for cutting single-finished products. The cut-off single-roller can be used with the size of the plate roller. Or double use. The knife roller must be used before the use of the knife roller to ensure the cutting accuracy and avoid the damage of the knife edge. The pressure is adjusted to just cut off the printing material to be the best pressure. In addition, we must pay attention to post-printing, glazing, lamination, bronzing, and punching. This article briefly describes some of the theoretical and practical operations of flexo printing. Hopefully it can become a reference for flexographic printing. The ever-changing packaging and flexo printing process do not have a fixed pattern for reference. It is hoped that the printing workers will practice more and accumulate experience in production practice.

Reprinted from: Industry Technology (Carton)