Blocking the cause of the failure
The shallowest part of the net is most likely to block. Blocked plates are caused mainly by the infiltration of the cells with insoluble substances such as cured substances, high-viscosity substances, or foreign substances in the ink, including the following reasons.
1. The ink is dried on the plate
The ink remaining in the cell is partially dried due to certain factors (such as too rapid solvent evaporation). When the plate cylinder enters the ink tank again, the cured ink in the cell cavity is difficult to completely dissolve, and the ink transfer rate also varies. The cumulative effect of the reduction is that the mesh is blocked more and more shallow until a blockage failure occurs. This type of blocking failure is related to factors such as ink type, viscosity, drying speed, solvent type, printing speed, and the structure of the printing press, among which the following two factors are the most common.
(1) The ink drying speed. When the ink is dried too quickly, a portion of the ink will have a film before being transferred to the printing substrate. The poor re-dissolvability of the ink film will inevitably result in poor ink transfer, and accumulation of the printing plate will occur after a period of time. The temperature and humidity of the printing shop will affect the drying speed of the ink. If the temperature is too high or the humidity is too low, the ink will dry faster. If the ink circulation is poor, the ink in the ink tank is prone to filming, resulting in blockage.
(2) Problems with gravure printing equipment. If there are some problems in the design of each mechanism of the gravure printing apparatus, such as a large drum diameter and a very shallow immersion of the printing plate cylinder in the ink tank, the hot air leaked from the drying box will directly blow the plate layout, thereby causing the ink on the net. Dry inside the hole.
2. Impurities in the ink
(1) The impurities in the ink are mixed from the outside environment. The gravure printing speed is faster, and the printed substrate is prone to generate static electricity during high-speed operation. Under the effect of electrostatic adsorption, impurities such as debris coming off the dust and printing substrate in the surrounding environment may be brought into the ink, and these impurities are caused. An important reason for the blockage of the printing plate network. In order to prevent such accidents, a filter should be used to remove insoluble impurities from the ink at the suction nozzle of the circulation pump.
(2) Impurities contained in the ink itself. When the gravure printing plate has a higher number of screens, the larger particles, insoluble materials, and precipitates in the ink will cause clogging of the printing plate. When the ink itself undergoes changes such as separation, precipitation, and re-agglomeration of the pigment, substances that are not easily re-dissolved are generated, resulting in blockage.
3. The quality of plate making is not high
The gravure printing plate must go through many processes such as etching or engraving, chrome plating, and grinding. Due to the corrosion or engraving process, the inner wall of the cell wall is not smooth and the burrs generated during polishing will have a certain influence on the ink transfer rate. In severe cases, it will result in blockage.
4. Poor ink dissolution
Poorly dissolved ink will reduce its transfer rate, resulting in blockage. The following conditions will affect the ink solubility.
Hey. ?) The deterioration of the ink, the change of the solvent balance, and the mixing of moisture, etc., will cause the ink itself to undergo changes such as separation, precipitation, and re-agglomeration of the pigment.
(2) When replacing the ink, if the printer is not thoroughly cleaned, the new ink is mixed with different types of ink, and misuse or inadvertent mixing with inappropriate solvents.
(3) When adding a solvent (especially many solvents) to the ink tank and the ink tank during printing, if the addition speed is too high, the solubility of the ink may be deteriorated due to the impact of the solvent.
5. Ink reaction
Two-component inks or reactive inks will gradually undergo cross-linking and other chemical reactions during the printing process, which will result in deterioration of the ink's fluidity, increase of viscosity, and decrease of transfer rate, resulting in blockage.
Blocking fault solution
Through the analysis of the cause of gravure blocking, the author summarized the following solutions.
(1) The temperature and humidity of the printing shop should be appropriate, and the drying speed of the solvent must be compatible with the printing speed and the printing environment.
(2) Keep the distance between the doctor blade and the impression cylinder as short as possible, and prevent the hot air from the dryer box from directly blowing the plate layout.
(3) Use a slow-drying solvent in combination to appropriately increase the printing speed.
(4) Replace the ink when it is blocked due to defects in ink properties. When replacing the ink, first wash the ink tank and the circulation pump thoroughly, then pour in new ink and try to avoid mixing the ink with a significant difference in density.
(5) Always mix the ink in the ink tank so that the ink in each part is in a flowing state. New inks should also be added or replaced in time to avoid ink filming.
(6) Wipe the plate cylinder with solvent before or just after starting the machine. During the printing process, midway parking should be avoided as much as possible. For long-term parking, it is necessary to first clean the plate or immerse the plate cylinder in the ink tank and keep it idle continuously.
(7) When using a new ink, due to temperature differences and other reasons, the phenomenon of crystal precipitation of additives, waxes, etc. in the ink may occur. Therefore, the new ink should be heated to 40 to 50Â°C until the crystals are dissolved. use.
(8) Use a regular special dilution solvent.
The transfer rate of ink in gravure printing is usually between 50% and 70%, and the remaining ink remains in the cells. If the residual rate of the ink is always maintained at a certain value, there will be no problem, but in the actual printing process, the residual rate of ink in the cell site is often increased due to several reasons, resulting in blockage. After the blockage phenomenon occurs, the printed images will be blurred, the small prints will not be printed, and the colors of the printed products will change. In severe cases, printing cannot continue.