Four aspects are not done well, the knife line will be repeatedly banned
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First, the ink factor
1, the effect of ink viscosity
The viscosity of the ink should match the printing speed. The viscosity of the ink is too high, and the adhesion to the plate cylinder is too strong. It is not conducive to scraping the excess ink of the plate by the squeegee, and the probability of printing the line is high. During the printing process, the viscosity of the ink should be measured and controlled regularly, usually measured every 20 minutes to 30 minutes.
2, the effect of ink drying
The ink dries too fast and is prone to crusting. If the crust is not dissolved during the ink circulation, it will adhere to the edge of the knife or the bottom of the knife once it comes into contact with the doctor blade, resulting in a printed cut line. If the ink circulation system uses an open ink tank, ink crusts and agglomeration are more likely to occur. In order to reduce the occurrence of such cutter line failure, the ink in the ink tank should be stirred frequently; an appropriate amount of slow drying agent should be added as needed; if necessary, a sealing cover can be added to effectively control and reduce the printing cutter line failure.
3, the influence of ink fineness
The fineness of the pigment particles has a direct influence on the frequency of occurrence of the cut line. For example, the pigment particles used in the blue ink have high hardness, and it is difficult to achieve very fine particle size even after sufficient grinding, and it is easy to damage the scratching during the printing process. The knife or the effect of the ink scraping often causes a knife line failure when printing blue ink.
4, the impact of ink activity
In the ink production process, a certain amount of active agent is generally added. The plate cylinder has a certain activity after chrome plating. If the activity of the ink and the plate cylinder is too high, the active material will adhere firmly to the roller during printing, and the squeegee is difficult to scrape it to form a knife. line. At this time, the plate cylinder is first cleaned to remove the active material on the surface, and an activity slowing agent is added to the ink to eliminate the cut line.
5, the impact of ink quality
When the ink is stored for too long, the solvent balance changes, causing the ink to dissolve, or the ink is improperly formulated or used, causing a chemical reaction, which causes the ink to precipitate. During the printing process, the precipitate in the ink tends to accumulate at the doctor blade to cause the knife line, and the ink needs to be replaced.
Second, the printing factor
1. Influence of layout finish
If the gravure plate fails to polish the burr during polishing, the ink on the burr part of the plate is not easy to be scraped during the printing process, and the squeegee is damaged in serious cases to form the knives. For printing knives caused by rough surface of the printing plate, the printing plate can be lightly polished with 1200 mesh fine sandpaper, but it is generally best not to polish the printing plate to avoid damage to the printing plate.
2, the impact of the hardness of the chromium layer
At the time of plate making, if the chrome plating is too long, the hardness of the chrome layer on the surface of the printing plate is too high, and it is easy to damage the squeegee, and the stencil will be changed on the printing. On the contrary, if the chrome plating is too short, the chrome layer on the surface of the printing plate is too soft, and the squeegee is likely to damage the printing plate, and a fixed cutting line appears on the printing.
3, the impact of layout cleanliness
The chips generated by the plate grinding process are not completely removed and adhere to the printing plate, which may damage the printing plate and the doctor blade during the printing process, thereby producing the cutting line. Before printing on the plate, it is best to clean it thoroughly with solvent to remove oil and impurities to reduce the failure of the printed knife line.
4, the impact of machining accuracy
The poor machining accuracy of the plate cylinder can also cause the printing knife line to be faulty, and it is difficult to detect or difficult to check, so it is easy to be neglected. In actual operation, it can be checked on the machine. In addition, the installation accuracy of the printing plate should be strictly controlled so as to avoid the occurrence of a printing knife line failure due to excessive impact on the squeegee during high-speed printing due to the concentricity error exceeding the standard.
Third, the impact of the squeegee
1, the hardness of the doctor blade
The hardness of the squeegee is lower than the hardness of the chrome layer on the surface of the plate. If the hardness of the squeegee is too high, it will accelerate the wear of the printing plate and cause scratches: if the squeegee is of poor quality, it will wear out in a short period of time, which will cause the ink of the printing plate to fail to be cleaned and the knives appear. At this time, it is necessary to frequently adjust the knife and change the knife.
2, there is a gap in the squeegee
When the squeegee blade is damaged and a gap is formed, a regular knife line moving left and right will appear on the printing, and the knive line is relatively easy to recognize. If the gap on the squeegee is relatively small, it can be polished to smooth and smooth with oil stone or fine sandpaper. If the gap is large, a replacement squeegee is required. When replacing the knife, the ink accumulated in the pressure blade and the sipe must be completely removed first, so as not to affect the flatness of the squeegee installation, and the length of the squeegee exposed to the pressure blade portion should be consistent, about 5 mm. In the printing process, some squeegees need to be combined with the printing plate for a long time to achieve a good squeegee effect. At this time, the edge of the squeegee can be smoothed with metallographic sandpaper to make the squeegee reach Better ink scraping effect and is beneficial to the improvement of raw efficiency.
3, the flatness of the doctor blade installation
The flatness of the squeegee installation also causes the print line to be printed. Therefore, when installing the squeegee, make sure that the flatness is good and the squeegee is evenly stressed.
4, the pressure and angle of the scraper
The pressure and angle of the doctor blade also have a large effect on the print line. At the time of printing, the angle and pressure of the squeegee should be properly adjusted according to the degree of squeegee printing and the printing of the printing, so as to achieve a good squeegee effect, thereby reducing the failure of the printing knives.
Fourth, the impact of solvents
In the printing process, if the solvent is used improperly, the ink is not dissolved sufficiently and sticks together, and once adhered to the doctor blade, a knife line is formed. This cut line is generally a dark line, sometimes not. It is more common to use gold ink to print solid color blocks. Since gold ink is prepared by using gold powder, gold oil and solvent, the metal particles are relatively heavy and easy to precipitate. If the solvent used is poor in solubility, plus stirring. Sufficient, metal particles will accumulate due to uneven distribution. If it is stuck at the edge of the doctor blade, a thicker dark line is formed. The characteristic of this dark line is that it disappears automatically after a period of time, and then forms again, which seriously affects the printing quality. Such cut lines are difficult to eliminate in printing, and it is necessary to start from the root cause to prepare for the work before printing. When the ink is prepared, a suitable solvent is used, and the mixture is fully stirred to fully dissolve, and the ink is kept well in circulation.