Viewing printing problems from the use of equipment and consumables
At present, the printing of packaging cartons is booming, and customers have increasingly higher requirements for product quality. How to avoid production problems and improve product quality have become the pursuit of enterprises. Printing is a systematic project and a dynamic process. Equipment conditions, technical personnel level, ink and printing materials are all factors that affect product quality. There are three main ways of carton printing: offset printing before mounting, flexographic direct printing, pre-printing and offset printing. With the improvement of printing technology, flexographic printing has been adopted by carton companies with its high quality and high efficiency. This requires companies to start small and improve printing problems. Printing equipment Printing equipment is one of the five major elements of printing. Good equipment is the prerequisite for producing high-quality products. The use status of the equipment, precision adjustment, and good maintenance directly affect product quality. Pay attention to the pressure adjustment. The ink transmission and printing parts of the flexographic printing machine have four cylinders, an inking roller, an anilox roller, a plate cylinder, and an impression cylinder. The following figure shows the schematic diagram of the ink transfer part of the flexographic printing machine. The appropriateness of the pressure between the four directly affects the ink transmission, which in turn affects the product quality.
The printing pressure is the pressure between the plate cylinder and the impression cylinder. Its main function is to evenly transfer the ink on the plate to the substrate. Many problems in the printing process are caused by improper pressure adjustment, such as too large or too small ink. If the printing pressure is too heavy, on the one hand, it is easy to make the lines thicker on the printing material, the dots are expanded, and the accuracy of the graphics and text is reduced. In addition, excessive embossing force will also deform the ribs and reduce the strength of the cardboard. If the pressure is too light, the appropriate amount of ink cannot be transferred on the substrate, the ability to reproduce graphics and text is poor, the lines are prone to broken lines, and the defects of imprinting are prone to occur on the ground, which directly affects the printing effect. In serious cases, the printing cannot be performed . The adjustment of the printing pressure is suitable for the ink to be uniform and moderate, the ink trace is clear, the ridge surface of the tile is not depressed, flat and not deformed. Once the pressure is determined, do not adjust it casually. n Printing inking pressure Printing inking pressure is the pressure between the anilox roller and the printing plate. Its main function is to evenly transfer the ink from the anilox roller to the printing plate. In actual operation, the influence of the printing plate inking pressure on the printing quality is very important. If the inking pressure is too heavy, the printing plate is easy to insert ink, which affects the quality of the product and also affects the printing durability of the printing plate. , The printing plate can not be printed without ink. Therefore, attention should be paid to the adjustment in the printing process to ensure that the printing can be carried out smoothly.
This pressure is the pressure between the inking roller and the anilox roller, which controls the thickness of the ink, that is, the amount of ink, and evenly transfers the ink. The pressure is inversely proportional to the thickness of the ink layer. Will make the ink layer too thin, otherwise it will make the ink layer too thick. If the amount of ink changes during the printing process, you should first check whether the pressure has changed and adjust it carefully. These three pressures are related to the entire ink transfer process from the ink tank to the cardboard, and are the key to the amount of ink on the cardboard and whether the printing is uniform. Pay attention to the adjustment of equipment accuracy. In the printing process, the printing plate cylinder, impression cylinder, anilox roller, inking roller and various transmission gears, etc., due to various factors, may have their own accuracy and adjustment accuracy Changes occur, which affect the accuracy and quality of printed images. In the printing process, you should check carefully to find the problem and solve it in time.
The precision adjustment between the rollers mainly has the problems of concentricity and parallelism. The concentricity mainly includes the concentricity between the roller body and the supporting journal and between the rollers. These two concentricity must be adjusted. When the printing machine is in normal operation, the vibration error cannot exceed 0.01mm, otherwise there will be failures in ink transmission and dot printing. The idea is to expand the idea, but the image dots are not clear or not printed. Gear accuracy is the basis to ensure the concentricity of the rollers. The change of the transmission gear accuracy will cause mechanical defects such as micro-vibration, which will bring certain difficulties to screen printing and make it impossible to obtain an ideal pressure for the entire printing. Mechanical vibration will also damage the anilox roller and the printing plate, affecting the service life and product quality. Parallelism mainly means that the relative positions of the axes between the two rollers are parallel. If the axes of the two rollers are not parallel, the gap between the two ends will be different, resulting in a difference in pressure between the rollers and affecting the amount of ink transfer. Taking the impression cylinder and the plate cylinder as an example, the end with a small gap has a high pressure and sufficient ink for the printed matter; the end with a large gap has a small printing pressure and a small amount of ink transfer, making the printing ink light.
In the same printing surface, there is a fault that the ink is thick at one end and the ink is light at the other end. In the same way, the unevenness of the gap will also cause inconsistent ink transmission between the inking roller and the anilox roller, and the anilox roller and the plate cylinder. In addition, pay attention to the surface conditions of the inking roller and anilox roller. If there are grinded lines or scratches on the surface of the roller, when printing dot products, uneven ink transmission will make the color uneven. Yinping network cable is more obvious. If it finds ground silk or scratches, it should be replaced in time. In the daily production process, in addition to overhaul, attention should also be paid to the cleanliness of the workshop environment. If the surface of the transmission gear is not clean and dirty, it will also affect its transmission accuracy. Note the choice of anilox roller Anilox roller can be regarded as the core of the flexo printing machine ink transfer system, the level of the anilox roller line, the quality of the quality directly affects the ink transfer effect. In addition, the depth, shape, and surface finish of the anilox also have an effect on the ink transfer performance of the anilox roller.
The line number of the anilox roller is not as high as possible. It needs to be comprehensively considered according to the type of printing press, the printed text, the substrate and economic factors. Generally speaking, the higher the number of lines of the anilox roller, the smaller the amount of ink transfer. On the contrary, the lower the number of lines, the larger the amount of ink transfer. In actual operation, the slower the printing speed, the larger the ink transfer amount, and the greater the viscosity, the greater the ink transfer amount. It can be seen that in the field printing or block printing, the anilox roller with a lower line number can be considered, and the ink with higher viscosity can be used in combination with a slightly slower printing speed. On the contrary, when printing high screen lines and color gradation dots. Anilox rollers with higher thread counts can be selected, lower viscosity inks are used, and faster printing speeds are used. Of course, this can be used in combination with the actual situation. The accuracy of the printed graphics on corrugated cardboard boxes is generally not very high. Factors such as the rough surface of corrugated cardboard also determine that it is not necessary to use expensive ceramic anilox rollers but general metal anilox rollers to meet the needs. watt
The number of corrugated box printing lines is generally 55-65 lines / in, and some up to 85 lines / in. According to the 4: 1 relationship between the optional anilox roller and the printing plate screen line, 200 lines / in, 300 lines / in If there is a coated or large-scale printed product, the anilox roll can be equipped with an anilox roll of 150 lines / in. Therefore, you can consider using 150 lines / in anilox roller for large-scale printing, 200 lines / in for daily general corrugated box printing, and 300 lines / in for high-precision color overprinting. If the number of screen lines of the anilox roller does not match the quality requirements of the printed product during the printing process, it should be replaced in time. When the anilox roller is engraved deep in the mesh hole, the amount of ink output is large, and the ink layer of the printed product is thick and dark, and the color is bright. But if the amount of ink is too much, pay attention to the drying of the ink layer to prevent the product from sticking to the ink and getting dirty. Conversely, if the screen engraving is shallow, the amount of ink transferred to the printing plate on the anilox roller is small. The printed product lacks a certain amount of ink and has poor color. At present, the depth of general anilox roller cell carving is between 22μ and 30μ. According to the substrates of different natures, the ink and the products should adopt the corresponding network depth in production. The anilox roller engraving has a good finish, the ink transfer is uniform and delicate, and the dot pattern formed is good.
Especially in flat screen printing, it is more obvious, otherwise it will make the ink uneven, and the dot gradation formed after the dot printing is not ideal, and the definition will be damaged. Pay attention to the maintenance of the anilox roller in production, and pay attention to the filtration of the ink to prevent scratches caused by particles. In flexographic printing, in addition to the improper relationship between the screen angles of the various printing plates, which can cause moire, improper relationship between the angle of the anilox roller and the screen line and the number of lines can also cause moire. Avoid this phenomenon during the plate making process. In actual production, the turtle collision phenomenon occurs from time to time. The mesh holes on the anilox roller are generally engraved at a 45-degree angle to the axis. Therefore, during the printing process, it is necessary to avoid the use of a 45-degree net line angle.
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