Problems needing attention in the printing process

Problems that should be paid attention to in the process of carton printing

the printing process is a dynamic process. Due to the influence of various factors, one or another problems may occur at any time. We should pay attention to analysis and take corresponding measures to queue up for faults, so that the printing can proceed smoothly and print high-quality prints. Generally, we should pay attention to the following problems:

first, we should pay attention to the change of pressure. Generally, the printing pressure has been adjusted well during the trial printing process, but due to various reasons, the operating revenue of China's petroleum and chemical industry has achieved 13.3 trillion yuan, which may change

(1) the pressure controlling the ink volume changes. This pressure is the pressure between the inking roller and the striping roller, which plays the role of controlling the thickness of the ink and evenly transferring the ink. This pressure is inversely proportional to the thickness of the ink layer. If the pressure is too high, the ink layer will be too thin, otherwise, the ink layer will be too thick. If the ink layer is found to change during printing, you should first check whether the pressure changes and carefully adjust it

(2) printing inking pressure changes. The printing inking pressure is the pressure between the embossing roller and the printing plate. Its main function is to transfer the ink of the embossing roller evenly to the printing plate. In practice, 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 embed ink, which directly affects the product quality and the printing resistance of the printing plate; If the inking pressure is too light and the printing plate cannot be inked, it cannot be printed. Therefore, in case of problems in the printing process, attention should be paid to adjustment to ensure the smooth printing

(3) the printing pressure changes. The printing pressure is the pressure between the printing plate cylinder and the embossing cylinder. Its main function is to transfer the ink on the printing plate evenly to the substrate. If this pressure is too heavy, the embossing expansion line and dot expansion are easy to appear on the substrate, which will reduce the accuracy response of the product; If the pressure is too light, the pattern or image cannot be reproduced on the substrate, which directly affects the printing effect and makes the printing impossible. Its biological source is rapeseed oil

second, attention should be paid to the changes in the adjustment accuracy of the equipment. During the printing process, the main components of the printing machine, such as the printing plate cylinder, the embossing cylinder, the embossing roller, the inking roller and the transmission gears, may change their own accuracy and adjustment accuracy due to the influence of various factors, thus affecting the printing quality. In the printing process, they should carefully check, find problems and solve them in time

(1) there are three possible problems with the plate cylinder and the impression cylinder. The concentricity of a cylinder body and the supporting journal, the concentricity of the printing plate cylinder and the embossing cylinder must be better. When the printing machine operates normally, the vibration error should not exceed 0.01mm, otherwise the pressure at the point is not easy to adjust. If the pressure is heavy, the idea will expand. If the pressure is light, some images can be printed, and some cannot be printed. Second, if the parallelism between the two rollers changes, the printing pressure changes. If the two rollers are not parallel, and the gap at one end is large, the printing pressure becomes smaller, the ink transfer is small, and the printing ink is insufficient; The gap at the other end is small, the printing pressure becomes larger, and the ink transfer volume is large, which makes the printing ink heavy and easy to form the defect of heavy ink at one end and light ink at the other end in the same printing surface. Third, if the gap between the two rollers changes, the printing pressure changes. The gap between the two rollers is large, the pressure is small, the ink transfer is small, and the print ink is light, otherwise the print ink is thick

(2) the possible problems of the corrugation roller include the accuracy change of the corrugation roller itself and the position accuracy change between the corrugation roller and the plate cylinder and the inking roller

a accuracy change of the corrugation roller. The accuracy of the corrugation roller mainly includes the depth of the hole, the number of lines and the surface finish

wrinkle roll hole depth: the depth of engraving on the upper line of the wrinkle roll will directly affect the output of ink volume. If the line carving is deep, the amount of ink output is large. The ink layer of printed products is thick and deep, and the color is bright. However, attention must be paid to the drying of the ink layer. Excessive thickness of the ink layer will make the ink on the print difficult to dry, and it is very easy to form a situation that the outside is dry but the inner layer is not dry, resulting in ink sticking to the product; On the contrary, if the line engraving is shallow, the ink volume of the difficult printing plate on the embossing roller is less, and the printed products lack a certain amount of ink, resulting in poor color

at present, the depth of the engraving of the roller hole is generally 22 μ～ thirty μ between. According to different properties of substrates and products, the corresponding line depth is adopted. If the ink viscosity, particle size and other factors or the surface wear of the roller are affected, changing the depth of the roller will reduce the ink delivery to the printing plate and directly affect the quality of the printed matter

roller finish: the roller engraving has a good finish, the ink transfer is uniform and delicate, and the formed dot shape is good. It is especially obvious in flat line printing, otherwise it will make the ink uneven, the restoration of dot type tone level formed after dot printing is not ideal, and the clarity is also damaged

number of wrinkle roll lines; The number of stitches on the embossing roller is very important for the printing line products. It is generally configured according to the quality requirements of the printed matter. If the number of stitches on the embossing roller does not match the quality requirements of the printed matter during the printing process, it should be replaced in time

b changes in the relative position of the embossing roller, the plate cylinder and the inking roller, including changes in parallelism and the gap between them. These changes will change the ink transfer performance of the roller and affect the quality of the printed matter

(3) the possible problems of the inking roller are the loss of surface quality and the change of position accuracy with the wrinkle roller

a the surface quality of the inking roller is damaged. If there are ground silk lines or scratches on the surface of the inking roller, and when printing products at the point of printing, the uneven ink transfer will make the color uneven. Flat lines are more visible. Therefore, the surface of the inking roller must not have abraded lines or scratches. If found, it should be replaced in time

b the position between the upper ink roller and the wrinkle roller changes, mainly referring to the parallelism and the size of the gap between them. These changes directly affect the changes of ink transfer performance, and special attention should be paid to inspection

(4) the accuracy of the transmission gear changes, and the gear accuracy is the basis to ensure the concentricity of each roll

the gear accuracy of each roll is not good, which will produce mechanical defects such as micro vibration, which will bring certain difficulties to line printing, so that the whole line printing cannot obtain an ideal printing pressure

at the same time, if the gear transmission surface is not clean and dirty, it will also affect its transmission accuracy

third, pay attention to the changes of ink printability. Printing is to reproduce patterns and images by receiving and transferring ink on the printing plate, and then through the color of ink. The adaptability of ink to flexographic printing is closely related to the clarity of printed matter

good printability of ink is mainly manifested in: low viscosity of ink, high fluidity of fly ash, high adhesion to substrate, high brightness and luminosity, high fineness of ink particles, no corrosion to printing plate or very low corrosion. If some adaptability of the ink changes in the printing process, it will directly affect the printing effect. For example, the particle size of the ink becomes thicker and less delicate, which will directly affect the quality of the printed matter. Take the general plastic printing as an example: generally, the number of lines printed on the plastic film is 80 ~ 100 lines/inch, and the corresponding number of lines on the metallic roller must reach 240 ~ 300 lines/inch to adapt, that is, the number of lines on the metallic roller is 3 times that of the printing plate. That is, one point on the printing plate needs to be supplied with ink by nine points on the metal roller, so as to transfer the ink evenly and ensure the correct color and clarity of the print, otherwise the satisfactory product cannot be obtained

based on this factor, it is required that the ink of flexible plate printing must be delicate, so that each eye on the metal roller can obtain an equal amount of ink, and correctly transfer it to each point on the plate. The printed products produced in this way are solid and have clear gradation

on the contrary, if the ink fineness does not meet certain requirements, the ink consumption of the dots on the metallic roller is uneven, and ink is easy to cross between dots, resulting in dirty spots, affecting the beauty and level of the image, color restoration is easy to be distorted, and the level of low-key areas is easy to be lost

IV. pay attention to the changes in the content of additives. Additives, as the adjusting fluid of ink, or as a substance that is easy to be emitted in supplementary ink, play an important role in the printability of ink in printing

generally, the preparation of flexographic printing solvents is mainly alcohol soluble and water-soluble solvents. Different formulas should be adopted according to the production conditions of the workshop, climatic conditions, printing speed, printing area, ink layer thickness and other factors. The preparation principles are:

(1) repeat 28 ink; Normal drying: in the normal printing process, there should be no ink sticking and ink piling. The time interval between adding stabilizer each time should be minutes

(2) good solubility of additives: that is, the additives have good solubility for the ink, which makes the printing ink have good fluidity, complete dissolution, moist and delicate ink. In this way, the ink color transmitted on the metal striped roller and the inking roller is uniform, the printed image has uniform color, good layers, clear dots and grains, and good brightness of the print

additives mainly play a role in adjusting and controlling the color balance and ink drying speed in flexographic printing, that is, the amount of various additives is used to adjust the thickness change of ink, control the color balance of yellow, magenta and cyan, and the drying speed of various colors in printing. Therefore, in the process of printing flexographic products, we must often watch the color change of products, and adjust the color balance through the dilution of additives. At the same time, various additives also determine the print resistance of printing plates. Generally good additives, the printing plate's printing resistance is very high, which can exceed that of gravure. (yinjinhua, Shanghai Publishing and Printing College) (Business Express)