Failure Analysis of Printing Blocking of Plastic Film Label

Failure analysis of blocking of plastic film label printing Release time: 2020-12-17 Failure analysis of blocking of gravure printing 　　 The transfer rate of ink in gravure printing is usually 50% to 70%, and the remaining ink remains in the cells. If the residual rate of the ink always remains at a certain value, no problem will occur. However, in the actual printing process, the residual rate of the ink in the cells is often increased due to several reasons, resulting in blockage. After the blockage occurs, the printed graphics will be blurred, the small print will not be printed, the color of the printed product will change, and the printing cannot continue when it is severe.　　Causes of blockage failure　　Generally, shallow mesh parts are most likely to block up. Blocking is mainly caused by insoluble materials such as solidified materials, high-viscosity materials or foreign materials in the ink blocking the cells, including the following reasons. 1. The ink is dried on the plate. The ink remaining in the cell will be partially dried due to some factors (such as solvent volatilization too fast). When the printing plate cylinder enters the ink tank again, the solidified ink in the cell is difficult to completely Dissolve, the ink transfer rate also decreases, and the cumulative effect is that the cells are blocked more and more shallowly until the blockage failure occurs. This kind of blocking failure is related to factors such as ink type, viscosity, drying speed, solvent type, printing speed, and printing press structure, among which the following two reasons are the most common.　　 (1) Ink drying speed. When the ink dries too fast, a part of the ink will produce a film before it is transferred to the printing substrate. Poor resolubility of the ink film will inevitably lead to poor ink transfer. After a period of accumulation, the printing plate will block. The temperature and humidity of the printing workshop will affect the drying speed of the ink. Too high temperature or low humidity will speed up the drying speed of the ink. If coupled with the poor ink circulation, the ink in the ink tank will easily produce a film and cause blockage.　　 (2) Problems with gravure printing equipment. If there are some problems in the design of the various mechanisms of the gravure printing equipment, such as the cylinder diameter is too large, the printing plate cylinder is immersed very shallowly in the ink tank, etc., the hot air leaking from the drying box will blow directly on the printing plate surface, causing the ink to be on the screen. The hole is dry and solid.　　2, impurities in the ink 　　 (1) impurities mixed into the ink from the external environment. The gravure printing speed is relatively fast, and the printing substrate is prone to static electricity during high-speed operation. Under the action of electrostatic adsorption, the dust in the surrounding environment and impurities such as debris falling off the printing substrate may be carried into the ink. These impurities are caused An important reason for blockage of printing plate cells. In order to prevent this kind of accident, a filter should be used at the suction nozzle of the circulating pump to remove insoluble impurities in the ink.　　 (2) Impurities contained in the ink itself. When the number of screen lines of the gravure printing plate is high, the larger particles, insoluble substances, and precipitates in the ink will cause blockage of the printing plate cells. When the ink itself undergoes changes such as separation, precipitation, and re-agglomeration of the pigment, substances that are not easy to re-dissolve will be produced, resulting in blockage.　　3. The quality of plate making is not high. 　　 Gravure plate making must go through multiple processing procedures such as corrosion or engraving, chrome plating, and grinding. Unsmooth inner walls of the cells due to corrosion or inadequate engraving processing technology and burrs generated during grinding will have a certain impact on the transfer rate of the ink, and will cause blockage in severe cases.　　4. Poor ink dissolution 　　 Poor ink dissolution will reduce the transfer rate and cause blockage. The following conditions will affect the solubility of the ink.　　Ink deterioration, changes in solvent balance, mixing of moisture, etc., will cause changes in the ink itself such as separation, precipitation, and re-agglomeration of pigments.　　 (2) When replacing the ink, if the printing machine is not cleaned thoroughly, different types of ink are mixed in the new ink, and inappropriate solvents are misused or accidentally mixed.　　(3) When adding solvents to ink tanks and ink tanks during printing (especially when adding more solvents), if the addition speed is too fast, the solubility of the ink may deteriorate due to solvent impact.　　5. Chemical reaction of the ink. 　　 Two-liquid ink or reactive ink will gradually undergo chemical reactions such as cross-linking during the printing process, which will make the fluidity of the ink worse, increase the viscosity, and reduce the transfer rate, which will cause blockage.　　The solution to the blockage failure　　 Through the analysis of the cause of the gravure blockage, the author summed up the following solutions.　　 (1) The temperature and humidity of the printing workshop must be appropriate, and the drying speed of the solvent must be compatible with the printing speed and printing environment.　　 (2) The distance between the scraper and the impression cylinder should be as short as possible, and prevent the hot air from the drying oven from blowing directly on the printing plate.　　 (3) Use slow-drying solvents to increase the printing speed appropriately.　　 (4) When the printing plate is blocked due to ink performance defects, the ink should be replaced. When replacing the ink, first thoroughly clean the ink tank and circulation pump, and then pour in new ink and try to avoid mixing inks with significant density differences.　　 (5) Always stir the ink in the ink tank to keep the ink in all parts in a fluid state. New ink should be added or replaced in time to avoid the ink film.　　 (6) Before or just after starting the machine, wipe the plate cylinder with solvent. During the printing process, it is necessary to avoid stopping in the middle of the journey. For a long time, the printing plate must be cleaned or the printing plate cylinder must be immersed in the ink tank and kept idling continuously. (7) When using a new ink, due to temperature differences and other reasons, the additives and wax substances in the ink will crystallize out. Therefore, the new ink should be heated to 40-50°C and wait until the crystallized matter is dissolved. use.　　 (8) Use regular special dilution solvent. Previous: Quality control of plastic film label printing