1. The influence of ink viscosity
The viscosity of ink in Jinan printing plant should match the printing speed. When printing at high speed, the viscosity of the ink should be controlled between 12 and 15 seconds (3 × chaen cup); in medium speed printing, the viscosity of ink should be controlled between 16 and 18 seconds (3 × chaen cup). The viscosity of the ink is too high, and the adhesion to the printing plate cylinder is too strong, which is not conducive to the scraping knife to clean the redundant ink in the layout, and the probability of knife line in printed matter is high. During the printing process, the ink viscosity should be measured and controlled regularly, usually every 20-30 minutes.
2. The influence of ink dryness
If the ink dries too fast, it is easy to skin. If the crust is not dissolved in the process of ink circulation, once it contacts the doctor blade, it will adhere to the edge or the bottom of the knife, resulting in printed product knife line. If the ink circulation system is open ink tank, it is more likely to occur ink crust, caking phenomenon. In order to reduce the occurrence of such knife line failure, the ink in the ink tank should be stirred frequently; appropriate amount of slow drying agent should be added as required; if possible, a sealing cover can be added to effectively control and reduce the knife line fault of printed matter.
3. The influence of ink fineness
Gravure ink is mainly composed of pigments, binders and additives. If the pigment is not fully grinded, the particles are coarse and insoluble in the binder and solvent, and stay at the edge of the squeegee during printing, it will lead to small and irregular knife lines. The fineness of pigment particles has a direct impact on the frequency of knife line. For example, the pigment particles used in blue ink have high hardness, and it is difficult to achieve a very fine particle size even after full grinding. In the printing process, it is easy to damage the doctor blade or affect the scraping effect. When printing blue ink, knife line failure often occurs.
4. The influence of ink activity
In the ink production process, generally add a certain amount of active agent. The plate cylinder also has a certain activity after chromium plating. If the activity of the ink and plate cylinder is too high, the active substance will adhere firmly to the cylinder during printing, and it is difficult for the scraper to clean it, thus forming a knife line. At this time, the plate cylinder is cleaned to remove the active substances on its surface, and the active retarder is added to the ink to eliminate the knife line.
5. The influence of ink quality
Ink storage time is too long, solvent balance changes, resulting in ink solubility reduction; or ink deployment, improper use, causing chemical reactions, will make ink precipitation. In the printing process, the deposit in the ink is easy to accumulate on the blade edge, causing knife line, so the ink needs to be replaced.
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