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 liable 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.