The transfer rate of ink in gravure printing is usually 50% to 70%, and the remaining ink remains in the mesh. If the residual rate of ink is always maintained at a certain value, there will be no problems, but in the actual printing process, the residual rate of ink in the mesh is often increased for several reasons, resulting in blockage. After the blocking phenomenon occurs, the printed graphics will be blurred, the small print will not be printed out, and the color of the printed product will change. In severe cases, the printing cannot continue.

Causes of blockage failure

Generally, the shallow mesh part is most likely to block the plate. Blocking is mainly caused by insoluble substances such as cured products, high-viscosity substances or foreign substances in the ink clogging the holes, including the following reasons.

1. The ink is dry on the plate

The ink remaining in the cell will be partially dried by the influence of certain factors (such as the solvent volatilizes too quickly). When the plate cylinder enters the ink tank again, the cured ink in the cell is difficult to completely dissolve, and the ink transfer rate also varies with the The reduction, the cumulative effect is that the net hole is blocked more and more shallow, until the blocking failure occurs. This blockage failure is related to factors such as ink type, viscosity, drying speed, solvent type, printing speed, and the structure of the printing machine. 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 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 become clogged. 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 is likely to produce a film, resulting in blockage.

(2) Problems with gravure printing equipment. If there are some problems in the design of the mechanisms of the gravure printing equipment, such as the diameter of the cylinder is too large, the plate cylinder is immersed in the ink tank very shallow, etc., the hot air leaking from the drying box will directly blow the plate surface, which causes the ink Dry inside.

2. Impurities in the ink

(1) Impurities mixed into the ink from the external environment. The gravure printing speed is fast, and the printing substrate easily generates static electricity during high-speed operation. Under the action of electrostatic adsorption, impurities such as debris that fall off the printing substrate in the surrounding environment and the printing substrate may be brought into the ink. These impurities are caused by An important cause of clogging of the printing plate network. In order to prevent such accidents, the filter screen should be used to remove insoluble impurities in the ink at the suction nozzle of the circulation pump.

(2) Impurities contained in the ink itself. When the number of screen lines of the gravure printing plate is high, large particles, insoluble substances, and precipitates in the ink can cause clogging of the printing plate mesh. When the ink itself undergoes changes such as separation, precipitation, and re-agglomeration of pigments, it will produce substances that are not easily re-dissolved, causing blockage.

3. The quality of plate making is not high

Gravure plate-making has to go through multiple processing procedures such as corrosion or engraving, chrome plating, and grinding. Unsmooth inner walls of the cavity and burrs generated during grinding due to corrosion or inadequate engraving process will have a certain effect on the transfer rate of ink. In severe cases, it will cause blockage.

4. Poor ink dissolution

Poor ink dissolution will reduce its transfer rate and cause blockage. The following conditions will affect the solubility of the ink.

Ink deterioration, solvent balance changes, mixing with water, etc. will cause the ink itself to separate, precipitate, and re-agglomerate.

(2) When replacing the ink, if the printing machine is not cleaned thoroughly, the new ink is mixed with different types of ink, and the inappropriate solvent is misused or accidentally mixed.

(3) When adding a solvent to the ink tank or ink tank during printing (especially when a large amount of solvent is added), if the addition speed is too fast, the solubility of the ink may deteriorate due to the impact of the solvent.

5. Chemical reaction of ink

Double-liquid inks or reactive inks will gradually undergo chemical reactions such as cross-linking during the printing process, resulting in poor fluidity, increased viscosity, and reduced transfer rate, resulting in blockage.

Solutions to blockage faults

Through the analysis of the reasons for gravure blocking, 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 compatible with the printing speed and printing environment.

(2) The distance between the doctor blade and the impression cylinder should be as short as possible, and the hot air leaking from the drying box should be prevented from directly blowing on the plate layout.

(3) Mix slow-drying solvents to increase printing speed appropriately.

(4) When the plate blocking failure is caused by the defect of ink performance, the replacement of ink should be considered. When changing the ink, first clean the ink tank and circulation pump thoroughly, then pour in new ink and try to avoid mixing inks with significant density differences together.

(5) Always stir the ink in the ink tank to keep the ink in all parts flowing. New ink should also be added or replaced in time to avoid ink film.

(6) Before or immediately after starting up, wipe the plate cylinder with solvent. During the printing process, it is necessary to avoid stopping halfway. 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 continuous idling.

(7) When using new ink, due to temperature difference and other reasons, crystal precipitation of additives, waxes and other substances in the ink will occur, so the new ink should be heated to 40 to 50 ℃, after the crystal precipitate is dissolved use.

(8) Use regular special dilution solvents.

School Tote Bag

Mianyang Crossing Cross-Border E-Commerce Co., Ltd. , https://www.wycybag.com