[Packaging bag printing] About the problem of dry version, that is, the solution to blocking version that we often talk about. Composite packaging bags, aluminum foil bags, plastic packaging bags Since we want to talk about solutions, we must first analyze the reasons for this situation. The reason for the blockage failure is generally that the shallow screen part is the most likely to block the version. Blocking is mainly caused by insoluble substances such as solidified substances, high-viscosity substances or foreign substances in the ink blocking the cells, including the following reasons. 1. The ink that is left in the cells when the ink dries and solidifies on the plate will be partially dried and solidified by some factors (such as the solvent volatilizes too quickly). When the printing plate cylinder enters the ink tank again, the ink solidified in the cells is difficult to be completely cu. Dissolving, the ink transfer rate will also decrease, 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 the structure of the printing machine, 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 form a film before it is transfer to the printing substrate, and the poor resolubility of the ink film will inevitably lead to poor ink transfer, and after a period of accumulation, the printing plate will be blocked. The temperature and humidity of the printing workshop will affect the drying speed of the ink. If the temperature is too high or the humidity is too low, the drying speed of the ink will be accelerated. If the ink circulation is poor, the ink in the ink tank will easily form a film, which will lead to 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 large diameter of the cylinder and the shallow immersion of the printing plate cylinder in the ink tank, etc., the hot air leaking from the drying box will blow directly on the printing plate layout, which will cause the ink on the screen. Dry inside the hole. 2. Impurities in the ink (1) Impurities mixed into the ink from the external environment. Gravure printing is fast, and the printing substrate is prone to static electricity during high-speed operation. Under the action of electrostatic adsorption, impurities such as dust in the surrounding environment and debris falling off the printing substrate may be brought into the ink. An important reason for the blockage of the printing plate cells. In order to prevent this kind of accident, the filter screen should be used to remove the insoluble impurities in the ink at the suction nozzle of the circulating pump. (2) Impurities contained in the ink itself. When the number of screen lines in gravure printing 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 easily re-dissolved will be produced, resulting in blockage. 3. The quality of plate making is not high. Gravure plate making has to undergo multiple processing procedures such as corrosion or engraving, chrome plating, and grinding. The inner wall of the cell is not smooth due to corrosion or insufficient engraving process, and the burrs generated during grinding will have a certain impact on the transfer rate of ink, and in severe cases, it will lead to blockage. 4. Poor ink dissolution Poor ink dissolution will uce the transfer rate and cause blockage. The following conditions will affect the solubility of the ink. (1) The ink deteriorates, the solvent balance changes, and water is mixed, which will cause the ink itself to separate, precipitate, and re-agglomerate the pigment. (2) When replacing the ink, if the printing machine is not cleaned thoroughly, different kinds of inks are mixed into the new ink, and inappropriate solvents are misused or accidentally mixed. (3) When adding solvent (especially if a lot of solvent is added) to the ink tank and ink tank during printing, if the addition speed is too fast, the solubility of the ink may be deteriorated due to the impact of the solvent. 5. Ink chemical reaction Two-liquid ink or reactive ink will gradually undergo chemical reactions such as cross-linking during the printing process, which will make the ink flow worse, the viscosity will increase, and the transfer rate will decrease, resulting in blockage. The solution to the blockage fault Through the analysis of the reasons for the gravure blockage, the author summarizes the following solutions. (1) The temperature and humidity of the printing workshop should be suitable, and the drying speed of the solvent must be adapted to 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 leaking from the drying box from blowing the printing plate directly. (3) Mix and use slow-drying solvents to appropriately increase the printing speed. (4) When the printing plate is blocked due to the defect of ink performance, consider replacing the ink. When replacing ink, thoroughly clean the ink tank and circulation pump before pouring in new ink and try to avoid mixing inks with significant density differences. (5) Always stir the ink in the ink tank so that the ink in each part is in a flowing state. New ink should also be added or replaced in time to avoid the ink from producing a film. (6) Before or just starting the machine, the plate cylinder should be wiped with solvent. During the printing process, it is necessary to avoid stopping in the middle as far as possible. If you stop for a long time, you must first clean the printing plate or immerse the printing plate cylinder in the ink tank and keep it running continuously. (7) When using new ink, due to the temperature difference and other reasons, the phenomenon of crystal precipitation of additives and wax substances in the ink will occur. Therefore, the new ink should be heated to 40 ~ 50 ℃, and then the crystalline precipitates are dissolved. use. (8) Use a regular special dilution solvent.
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